Patent Publication Number: US-2022234326-A1

Title: Pressure sensitive adhesive particle, cartridge, apparatus for producing printed material, method for producing printed material, printed material, sheet for producing printed material, and method for producing sheet for producing printed material

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-006586 filed Jan. 19, 2021. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a pressure sensitive adhesive particle, a cartridge, an apparatus for producing a printed material, a method for producing a printed material, a printed material, a sheet for producing a printed material, and a method for producing a sheet for producing a printed material. 
     (ii) Related Art 
     Japanese Unexamined Patent Application Publication No. 2012-188512 describes a water-dispersed pressure-sensitive adhesive composition that contains two acrylic polymers in an aqueous solvent. 
     Japanese Unexamined Patent Application Publication No. 2018-002889 describes an adhesive material that satisfies the formula: “20° C.≤T (1 MPa)−T (10 MPa)” (where T (1 MPa) represents a temperature at which the viscosity is 10 4  Pa·s at an applied pressure of 1 MPa, and T (10 MPa) represents a temperature at which the viscosity is 10 4  Pa·s at an applied pressure of 10 MPa). 
     Japanese Unexamined Patent Application Publication No. 2018-163198 describes a pressure-fixing toner that contains a styrene resin and a (meth)acrylate resin having a glass transition temperature at least 30° C. lower than the glass transition temperature of the styrene resin, that has a sea-island structure having a sea containing the styrene resin and islands containing the (meth)acrylate resin, and that includes a core that includes islands having a long diameter of 200 nm or more and 500 nm or less and a shell layer that covers the core and contains a resin having a glass transition temperature of 50° C. or higher. 
     Japanese Patent No. 6468727 discloses a water-dispersed pressure-sensitive adhesive composition that contains an acrylic polymer (A) which is a polymer of a monomer material (A) and an acrylic polymer (B) which is a polymer of a monomer material (B), in which the acrylic polymer (B) has a glass transition temperature of 0° C. or higher and has a weight average molecular weight of more than 0.3×10 4  but not more than 5×10 4 , the acrylic polymer (A) has a weight average molecular weight of 40×10 4  or more, the difference between the glass transition temperatures of the acrylic polymer (B) and the acrylic polymer (A) is 70° C. or more, and the monomer material (B) contains 3 wt % or more and 20 wt % or less of a carboxyl group-containing monomer. 
     Japanese Unexamined Patent Application Publication No. 2007-229993 describes a pressure-bonding postcard paper sheet that includes an adhesive layer containing an acrylic acid alkyl methacrylate copolymer. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a pressure sensitive adhesive particle that has a sea phase containing a styrene resin and island phases that contain a (meth)acrylate resin and that has adhesiveness that releasably bonds surfaces of a recording medium to each other is excellent compared to a pressure sensitive adhesive particle that has a sea phase containing a styrene resin and island phases that contain a (meth)acrylate resin in which the area of the island phases in a cross section of the pressure sensitive adhesive particle is less than 30%. 
     Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above. 
     According to an aspect of the present disclosure, there is provided a pressure sensitive adhesive particle including a styrene resin that contains, as polymerization components, styrene and a vinyl monomer other than styrene; and a (meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components of the (meth)acrylate resin, in which the pressure sensitive adhesive particle has a sea phase that contains the styrene resin, and island phases that are dispersed in the sea phase and contain the (meth)acrylate resin, the pressure sensitive adhesive particle has at least two glass transition temperatures, and a difference between the lowest glass transition temperature and the highest glass transition temperature is 30° C. or more, and in a cross section of the pressure sensitive adhesive particle, an area ratio of the island phases is 30% or more and 85% or less. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram illustrating one example of an apparatus for producing a printed material according to an exemplary embodiment; 
         FIG. 2  is a schematic diagram illustrating an ink jet recording apparatus, which is one example of a color image forming unit; 
         FIG. 3  is a schematic diagram illustrating another example of the apparatus for producing a printed material according to an exemplary embodiment; 
         FIG. 4  is a schematic diagram illustrating another example of the apparatus for producing a printed material according to an exemplary embodiment; and 
         FIG. 5  is a schematic cross-sectional view illustrating a first region, a second region, and a third region of a pressure sensitive adhesive particle. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will now be described. These descriptions and examples are merely illustrative exemplary embodiments and do not limit the scope of the exemplary embodiments. 
     In the present disclosure, a numerical range that uses “to” indicates a range that includes a figure that precedes “to” and a figure that follows “to” as the minimum value and the maximum value, respectively. 
     In numerical ranges described stepwise, the upper limit or the lower limit of one numerical range may be substituted with an upper limit or a lower limit of a different numerical range also described stepwise. In addition, in any numerical range described in the present disclosure, the upper limit or the lower limit of the numerical range may be substituted with a value indicated in Examples. 
     In the present disclosure, the term “step” indicates not only an independent step but also any feature that achieves the intended purpose of a certain step although such a feature may not be clearly distinguishable from other steps. 
     When exemplary embodiments of the present disclosure are described by referring to the drawings, the features of the exemplary embodiments are not limited to those illustrated in the drawings. Furthermore, the size of components illustrated in the drawings is schematic, and the relative size relationship between the components it not limited to what is illustrated in the drawings. 
     In the present disclosure, each component may contain more than one corresponding substances. In the present disclosure, when the amount of a component in a composition is referred and when there are two or more substances that correspond to that component in the composition, the amount is the total amount of the two or more substances in the composition unless otherwise noted. 
     In the present disclosure, particles corresponding to each component may contain more than one types of particles. 
     When there are more than one types of particles corresponding to one component in the composition, the particle diameter of each component is a particle diameter of a mixture of the more than one types of particles present in the composition unless otherwise noted. 
     In the present disclosure, the notation “(meth)acryl” means “acryl” or “methacryl”. 
     In the present disclosure, a printed material formed by folding a recording medium and bonding the opposing surfaces thereof or a printed material formed by stacking two or more recording media on top of each other and bonding the opposing surfaces thereof is referred to as a “pressure-bonded printed material”. 
     Pressure Sensitive Adhesive Particle 
     A pressure sensitive adhesive particle according to an exemplary embodiment includes a styrene resin that contains, as polymerization components, styrene and a vinyl monomer other than styrene; and a (meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components of the (meth)acrylate resin, in which: the pressure sensitive adhesive particle has a sea phase that contains the styrene resin, and island phases that are dispersed in the sea phase and contain the (meth)acrylate resin; the pressure sensitive adhesive particle has at least two glass transition temperatures, and a difference between the lowest glass transition temperature and the highest glass transition temperature is 30° C. or more; and in a cross section of the pressure sensitive adhesive particle, an area ratio of the island phases is 30% or more and 85% or less. 
     The pressure sensitive adhesive particle of the exemplary embodiment softens under pressure and releasably bonds surfaces of recording media. 
     The pressure sensitive adhesive particle of this exemplary embodiment undergoes pressure-induced phase transition due to its thermal properties, namely, the pressure sensitive adhesive particle “has at least two glass transition temperatures, and the difference between the highest glass transition temperature and the lowest glass transition temperature is 30° C. or more”. In the present disclosure, a pressure sensitive adhesive particle that undergoes pressure-induced phase transition refers to a pressure sensitive adhesive particle that satisfies formula 1 below: 
       10° C.≤ T 1− T 2  Formula 1:
 
     In formula 1, T1 represents a temperature at which the viscosity is 10000 Pa·s at a pressure of 1 MPa, and T2 represents a temperature at which the viscosity is 10000 Pa·s at a pressure of 10 MPa. The method for determining the temperature T1 and the temperature T2 is described below. 
     The pressure sensitive adhesive particle of this exemplary embodiment readily undergoes pressure-induced phase transition and exhibits excellent adhesiveness since the pressure sensitive adhesive particle contains “a styrene resin that contains, as polymerization components, styrene and a vinyl monomer other than styrene” and “a (meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components of the (meth)acrylate resin”. The mechanism behind this is presumably as follows. 
     In general, a styrene resin and a (meth)acrylate resin have low compatibility to each other, and thus it is considered that a pressure sensitive adhesive base particle contains these resins in a phase separated state. Moreover, it is considered that when a pressure sensitive adhesive base particle is pressurized, the (meth)acrylate resin having a relatively low glass transition temperature is fluidized first, and this fluidization affects the styrene resin, resulting in fluidization of both resins. It is also considered that when the two resins in the pressure sensitive adhesive base particle solidify and form a resin layer as the pressure is decreased after the two resins have fluidized under pressure, a phase separated state is again formed due to their low compatibility. 
     It is assumed that a (meth)acrylate resin that contains at least two (meth)acrylates as polymerization components is easily fluidizable under pressure because there are at least two types of ester groups bonded to the main chain and thus the degree of molecular alignment in a solid state is low compared to a homopolymer of a (meth)acrylate. Moreover, it is assumed that when the (meth)acrylates account for 90 mass % or more of all polymerization components, at least two types of ester groups are present at a high density; thus, the degree of molecular alignment in a solid state decreases further, and thus the resin becomes more easily fluidizable under pressure. Thus, it is assumed that the pressure sensitive adhesive particle of this exemplary embodiment more readily fluidizes under pressure, in other words, undergoes pressure-induced phase transition, compared to a pressure sensitive adhesive particle that contains a homopolymer of a (meth)acrylate as the (meth)acrylate resin. 
     In addition, it is assumed that a (meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components has a low degree of molecular alignment during re-solidification also, and, thus, a microphase separation occurs with the styrene resin. The finer the state of phase separation between the styrene resin and the (meth)acrylate resin, the higher the uniformity of the state of the adhesive surface to an adherend, and the more excellent the adhesiveness. Thus, it is assumed that the pressure sensitive adhesive particle of this exemplary embodiment has excellent adhesiveness compared to a pressure sensitive adhesive particle that contains a homopolymer of a (meth)acrylate as the (meth)acrylate resin. 
     In the pressure sensitive adhesive particle of this exemplary embodiment, a styrene resin and a (meth)acrylate resin co-exist in a phase separated state. In the pressure sensitive adhesive particle of this exemplary embodiment, the styrene resin is contained in a relatively continuous state, and the (meth)acrylate resin is contained in a relatively discontinuous state. The continuous phase containing the styrene resin is the “sea phase”, and the dispersed phases that contain the (meth)acrylate resin are the “island phases”. In this exemplary embodiment, a structure that has a sea phase, which is a continuous phase, and island phases, which are dispersed phases, is referred to as a sea-island structure. 
     The pressure sensitive adhesive particle according to this exemplary embodiment has a sea phase that contains a styrene resin and island phases that are dispersed in the sea phase and contain the (meth)acrylate resin, and the area ratio of the island phases in a cross section of the pressure sensitive adhesive particle is 30% or more and 85% or less. When the area ratio of the island phases is 30% or more, the pressure sensitive adhesive particle easily undergoes pressure-induced phase transition, and thus exhibits excellent adhesiveness that enables releasable bonding between the surfaces of the recording medium. When the area ratio of the island phases is 85% or less, excellent mechanical strength suitable for the pressure sensitive adhesive particle (for example, the strength that withstands deformation during stirring in a developing device) is exhibited. From these viewpoints, the area ratio of the island phases in a cross section of the pressure sensitive adhesive particle is preferably 35% or more and 80% or less and more preferably 40% or more and 75% or less. 
     The average diameter of the island phases contained in the pressure sensitive adhesive particle may be 200 nm or more and 500 nm or less. When the average diameter of the island phases is 500 nm or less, the pressure sensitive adhesive particle easily undergoes pressure-induced phase transition, and thus exhibits excellent adhesiveness that enables releasable bonding between the surfaces of the recording medium. When the average diameter of the island phases is 200 nm or more, excellent mechanical strength suitable for the pressure sensitive adhesive particle (for example, the strength that withstands deformation during stirring in a developing device) is exhibited. From these viewpoints, the average diameter of the island phases is more preferably 220 nm or more and 450 nm or less and yet more preferably 250 nm or more and 400 nm or less. 
     The average number of island phases per pressure sensitive adhesive particle in a cross section of the pressure sensitive adhesive particle may be 20 or more and 4000 or less. When the average number of island phases is 20 or more, the pressure sensitive adhesive particle easily undergoes pressure-induced phase transition, and thus exhibits excellent adhesiveness that enables releasable bonding between the surfaces of the recording medium. When the average number of island phases is 4000 or less, excellent mechanical strength suitable for the pressure sensitive adhesive particle (for example, the strength that withstands deformation during stirring in a developing device) is exhibited. From these viewpoints, the average number of island phases per pressure sensitive adhesive particle is preferably 35 or more and 2000 or less and more preferably 50 or more and 1000 or less. 
     In a cross section of the pressure sensitive adhesive particle, the island phases may satisfy the following requirements (1) and (2). 
     Requirement (1): The area ratio As1(%) of the island phases in a first region and the area ratio As2(%) of the island phases in a second region have a relationship of 0.70≤As2/As1≤1.20. 
     Requirement (2): The area ratio As1(%) of the island phases in the first region and the area ratio As3(%) of the island phases in a third region have a relationship of 0.70≤As3/As1≤1.20. 
     The first region, the second region, and the third region are regions in a cross section of the pressure sensitive adhesive particle and are formed by dividing a portion that spans from a position 550 nm deep from a surface to a center of gravity equally into three parts that respectively correspond to the first region, the second region, and the third region in order of proximity to the center of gravity. 
     The first region, the second region, and the third region will now be described with reference to  FIG. 5 .  FIG. 5  is a schematic cross-sectional view of a pressure sensitive adhesive particle. The first region, the second region, and the third region are determined by using image analyzing software as follows. 
     A curve In is drawn at a position 550 nm deep from a surface Sf of the pressure sensitive adhesive particle. 
     The center of gravity C of the cross section of the pressure sensitive adhesive particle is determined. When the number of pixels within the contour of the pressure sensitive adhesive particle is represented by n and the xy coordinates of the pixels are represented by (x i , y i ) (i=1, 2, . . . , n), the x coordinate of the center of gravity C=(x 1 +x 2 + . . . +x n )/n and the y coordinate of the center of gravity C=(y 1 +y 2 + . . . +y n )/n. 
     The distance between the center of gravity C and the curve In is trisected, a curve L1 is drawn one third of that distance from the center of gravity C, and a curve L2 is drawn one third of that distance from the curve In. 
     The region surrounded by the curve L1 is a first region A1, the region surrounded by the curve L1 and the curve L2 is a second region A2, and the region surrounded by the curve L2 and the curve In is a third region A3. 
     The area ratio of the island phases in the first region A1 is As1(%), the area ratio of the island phases in the second region A2 is As2(%), and the area ratio of the island phases in the third region A3 is As3(%). 
     As2/As1 and As3/As1 are indices that indicate the dispersed state of the island phases, and the closer the index is to 1, the more evenly dispersed are the island phases. From the viewpoints of facilitating pressure-induced phase transfer of the pressure sensitive adhesive particle and improving the adhesiveness that enables releasable bonding between the surfaces of the recording medium, As2/As1 and As3/As1 may each be close to 1 and are ideally each 1. 
     In a cross section of the pressure sensitive adhesive particle, the island phases may satisfy the following requirements (1′) and (2′). 
     Requirement (1′): The area ratio As1(%) of the island phases in the first region and the area ratio As2(%) of the island phases in the second region have a relationship of 0.85≤As2/As1≤1.15. 
     Requirement (2′): The area ratio As1(%) of the island phases in the first region and the area ratio As3(%) of the island phases in the third region have a relationship of 0.85≤As3/As1≤1.15. 
     In a cross section of the pressure sensitive adhesive particle, the island phases may satisfy the following requirements (1″) and (2″). 
     Requirement (1″): The area ratio As1(%) of the island phases in the first region and the area ratio As2(%) of the island phases in the second region have a relationship of 0.90≤As2/As1≤1.10. 
     Requirement (2″): The area ratio As1(%) of the island phases in the first region and the area ratio As3(%) of the island phases in the third region have a relationship of 0.90≤As3/As1≤1.10. 
     Examples of the method for controlling the area ratio, average diameter, average number, and dispersed state of the island phases to be within the respective ranges described above through the method of producing the pressure sensitive adhesive base particles described below include increasing or decreasing the amount of the (meth)acrylate resin relative to the amount of the styrene resin, increasing or decreasing the rate of elevating the temperature of the resin particle dispersion, and increasing or decreasing the time of maintaining a high temperature in the step of fusing and coalescing aggregated resin particles. 
     Method for Measuring Form of Island Phases 
     Identifying the sea-island structure and measuring the dimensions and area of the island phases are conducted as follows. 
     (1) Capturing Images of Cross Sections of Pressure Sensitive Adhesive Particles 
     Pressure sensitive adhesive particles are embedded in an epoxy resin, a cross section is prepared by using a diamond knife or the like, and the prepared cross section is stained with osmium tetroxide or ruthenium tetroxide in a desiccator. The stained cross section is imaged with a scanning electron microscope (SEM). 
     While the SEM image contains particle cross sections of various sizes, those particle cross sections which have a long diameter equal to or larger than 85% of the volume-average particle diameter are extracted, and, from among the extracted particle cross sections, one hundred particle cross sections are selected at random. In the present disclosure, the long diameter refers to the length of the longest straight line among all straight lines that connect two points on the contour line. 
     The reason for extracting the particle cross sections having a long diameter equal to or larger than 85% of the volume-average particle diameter is that the particle sections having a long diameter less than 85% of the volume-average particle diameter are highly possibly the sections of end portions of the particles that do not satisfactorily reflect the dispersed state of the island phases in the pressure sensitive adhesive particles. 
     (2) Distinguishing Between Sea Phase and Island Phases 
     The sea phase and the island phases of the sea-island structure are distinguished by the shade created by the degree of staining with osmium tetroxide or ruthenium tetroxide, and the presence or absence of the sea-island structure as well as the presence or absence of the sea phase and the island phases is identified by the shade. 
     (3) Average Number of Island Phases Per Pressure Sensitive Adhesive Particle 
     The total number of island phases included in the aforementioned one hundred particle sections is counted and divided by 100 to obtain the average number of island phases per pressure sensitive adhesive particle. 
     (4) Average Diameter of Island Phases 
     The long diameters of all island phases included in the aforementioned one hundred particle sections are measured, and the arithmetic average thereof is assumed to be the average diameter (nm) of the island phases. 
     (5) Area Ratio of Island Phases 
     In the aforementioned one hundred particle sections, the total area of the one hundred particles and the total area of the island phases included in the one hundred particles are determined, the ratio of the total area of the island phases to the total area of the particles is calculated, and the result is assumed to be the area ratio (%) of the island phases. 
     (6) As1, As2, and As3 
     In the aforementioned one hundred particle sections, the total area of the first regions in the one hundred particles and the total area of the island phases included in the first regions are determined, the ratio of the total area of the island phases included in the first regions to the total area of the first regions is calculated, and the result is assumed to be the area ratio As1(%). 
     Similarly, in the aforementioned one hundred particle sections, the total area of the second regions in the one hundred particles and the total area of the island phases included in the second regions are determined, the ratio of the total area of the island phases included in the second regions to the total area of the second regions is calculated, and the result is assumed to be the area ratio As2(%). 
     Similarly, in the aforementioned one hundred particle sections, the total area of the third regions in the one hundred particles and the total area of the island phases included in the third regions are determined, the ratio of the total area of the island phases included in the third regions to the total area of the third regions is calculated, and the result is assumed to be the area ratio As3(%). 
     The total concentration of Al, Mg, and Ca contained in the pressure sensitive adhesive particle of the exemplary embodiment may satisfy the following requirement (3), more preferably satisfies the following requirement (3′), and yet more preferably satisfies the following requirement (3″). 
     Requirement (3): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the total concentration Mes (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6×D+0.9 (kV) and the total concentration Met (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.15≤Mes/Met&lt;0.60. 
     Requirement (3′): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the total concentration Mes (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6× D+0.9 (kV) and the total concentration Met (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.20≤Mes/Met&lt;0.60. 
     Requirement (3″): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the total concentration Mes (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6× D+0.9 (kV) and the total concentration Met (%) of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.25≤Mes/Met&lt;0.60. 
     The concentration Mes is the total concentration of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at a low acceleration voltage of 0.6× D+0.9 (kV), and is the total concentration (mass basis) of Al, Mg, and Ca in the particle surface layer (for example, a region from the particle surface irradiated with the electron beam to a depth of D×15%). 
     The concentration Met is the total concentration of Al, Mg, and Ca as measured by energy-dispersive X-ray spectroscopy at a high acceleration voltage of 1.8× D++4.9 (kV), and is the total concentration (mass basis) of Al, Mg, and Ca in the entirety of the particle (the entire region from the particle surface irradiated with the electron beam to a particle surface on the opposite side). 
     Satisfying the requirement (3), (3′), or (3″) indicates that the Al, Mg, and Ca in the pressure sensitive adhesive particle are unevenly distributed in the particle surface layer. 
     Among Al, Mg, and Ca, Al, which can form trivalent ions, is a metal that can be easily ion-crosslinked; thus, the Al concentration in the pressure sensitive adhesive particle of the exemplary embodiment preferably satisfies the following requirement (4), more preferably satisfies the following requirement (4′), and yet more preferably satisfies the following requirement (4″). 
     Requirement (4): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the Al concentration Als (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6× D+0.9 (kV) and the Al concentration Alt (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.15≤Als/Alt&lt;0.60. 
     Requirement (4′): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the Al concentration Als (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6× D+0.9 (kV) and the Al concentration Alt (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.20≤Als/Alt&lt;0.60. 
     Requirement (4″): When the volume-average particle diameter of the pressure sensitive adhesive particle is represented by D (μm), the Al concentration Als (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 0.6× D+0.9 (kV) and the Al concentration Alt (%) as measured by energy-dispersive X-ray spectroscopy at an acceleration voltage of 1.8× D+4.9 (kV) have a relationship of 0.25≤Als/Alt&lt;0.60. 
     The concentration Als is the Al concentration as measured by energy-dispersive X-ray spectroscopy at a low acceleration voltage of 0.6× D+0.9 (kV), and is the Al concentration (mass basis) in the particle surface layer (for example, a region from the particle surface irradiated with the electron beam to a depth of D×15%). 
     The concentration Alt is the Al concentration as measured by energy-dispersive X-ray spectroscopy at a high acceleration voltage of 1.8× D+4.9 (kV), and is the Al concentration (mass basis) in the entirety of the particle (the entire region from the particle surface irradiated with the electron beam to a particle surface on the opposite side). 
     Satisfying the requirement (4), (4′), or (4″) indicates that Al in the pressure sensitive adhesive particle is unevenly distributed in the particle surface layer. 
     The pressure sensitive adhesive particle may be made to satisfy the requirement (3) or (4) by, for example, the choice of the type of the aggregating agent and increasing or decreasing the amount of the aggregating agent added in the method for producing a pressure sensitive adhesive base particle described below. 
     The Al, Mg, and Ca concentrations are measured by the energy-dispersive X-ray spectroscopy as follows. 
     By using a tablet former, 120 mg of pressure sensitive adhesive particles are formed into a disk having a diameter of 13 mm, and this disk is used as a measurement sample. By using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (X-MAX produced by Horiba Ltd.), the acceleration voltage is set to 0.6× D+0.9 (kV) or 1.8×D+4.9 (kV), and the types and quantities of elements in the measurement sample within the range obtained at an observation factor of 1000 are analyzed. 
     When the pressure sensitive adhesive particle contains an external additive, the external additive is removed from the surface of the pressure sensitive adhesive particle, and then a measurement sample is prepared by using a tablet former. The external additive is removed from the surface of the pressure sensitive adhesive particle by repeating ultrasonic washing in water (at a water temperature of 20° C. and an amplitude of 180 μm for 30 minutes) and drying. 
     From the viewpoint of handling ease of the pressure sensitive adhesive particle, the volume-average particle diameter (D50v) of the pressure sensitive adhesive particle is preferably 4 μm or more, more preferably 5 μm or more, and yet more preferably 6 μm or more, and from the viewpoint of facilitating the pressure-induced phase transition of the entire pressure sensitive adhesive particle, the volume-average particle diameter (D50v) is preferably 12 μm or less, more preferably 10 μm or less, and yet more preferably 9 μm or less. 
     The volume-average particle diameter (D50v) of the pressure sensitive adhesive particle is determined by using Coulter MULTISIZER II (produced by Beckman Coulter Inc.) with an aperture having a diameter of 100 μm. Into 2 mL of a 5 mass % aqueous sodium alkyl benzenesulfonate solution, 0.5 mg or more and 50 mg or less of the pressure sensitive adhesive particles are added and dispersed, and then the resulting dispersion is mixed with 100 mL or more and 150 mL or less of an electrolyte (ISOTON-II produced by Beckman Coulter Inc.). The resulting mixture is dispersed for 1 minute in an ultrasonic disperser, and the obtained dispersion is used as a sample. The particle diameters of 50000 particles having a particle diameter of 2 μm or more and 60 μm or less in the sample are measured. The particle diameter at 50% accumulation in a volume-based particle size distribution calculated from the small diameter side is used as the volume-average particle diameter (D50v). 
     The components, structure, and properties of the pressure sensitive adhesive particle according to this exemplary embodiment will now be described in detail. In the description below, unless otherwise noted, a “styrene resin” refers to a “styrene resin that contains, as polymerization components, styrene and a vinyl monomer other than styrene”, and a “(meth)acrylate resin” refers to a “(meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components”. 
     The pressure sensitive adhesive particle of the exemplary embodiment contains at least a pressure sensitive adhesive base particle and, if needed, an external additive. 
     Pressure Sensitive Adhesive Base Particle 
     The pressure sensitive adhesive base particle contains at least a styrene resin and a (meth)acrylate resin. The pressure sensitive adhesive base particle may further contain a coloring agent, a releasing agent, and other additives. 
     From the viewpoint of maintaining adhesiveness, the pressure sensitive adhesive base particle may contain a larger amount of the styrene resin than the (meth)acrylate resin. The styrene resin content relative to the total content of the styrene resin and the (meth)acrylate resin is preferably 55 mass % or more and 80 mass % or less, is more preferably 60 mass % or more and 75 mass % or less, and is yet more preferably 65 mass % or more and 70 mass % or less. 
     Styrene Resin 
     The pressure sensitive adhesive base particle that constitutes the pressure sensitive adhesive particle of this exemplary embodiment contains a styrene resin that contains, as polymerization components, styrene and a vinyl monomer other than styrene. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the mass ratio of styrene relative to the total of the polymerization components of the styrene resin is preferably 60 mass % or more, more preferably 70 mass % or more, and yet more preferably 75 mass % or more. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the mass ratio is preferably 95 mass % or less, more preferably 90 mass % or less, and yet more preferably 85 mass % or less. 
     Examples of the vinyl monomer other than styrene constituting the styrene resin include styrene monomers other than styrene and acryl monomers. 
     Examples of the styrene monomers other than styrene include vinyl naphthalene; alkyl-substituted styrenes such as α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, and p-n-dodecylstyrene; aryl-substituted styrenes such as p-phenylstyrene; alkoxy-substituted styrenes such as p-methoxystyrene; halogen-substituted styrenes such as p-chlorostyrene, 3,4-dichlorostyrene, p-fluorostyrene, and 2,5-difluorostyrene; and nitro-substituted styrenes such as m-nitrostyrene, o-nitrostyrene, and p-nitrostyrene. These styrene monomers may be used alone or in combination. 
     The acryl monomer may be at least one acryl monomer selected from the group consisting of (meth)acrylic acid and (meth)acrylates. Examples of the (meth)acrylates include alkyl (meth)acrylates, carboxy-substituted alkyl (meth)acrylates, hydroxy-substituted alkyl (meth)acrylates, alkoxy-substituted alkyl (meth)acrylates, and di(meth)acrylates. These acryl monomers may be used alone or in combination. 
     Examples of the alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate. 
     An example of the carboxy-substituted alkyl (meth)acrylates is 2-carboxylethyl (meth)acrylate. 
     Examples of the hydroxy-substituted alkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. 
     An example of the alkoxy-substituted alkyl (meth)acrylates is 2-methoxyethyl (meth)acrylate. 
     Examples of the di(meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, pentanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, and decanediol di(meth)acrylate. 
     Examples of the (meth)acrylates also include 2-(diethylamino)ethyl (meth)acrylate, benzyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate. 
     Examples of other vinyl monomer constituting the styrene resin include, in addition to the styrene monomers and acryl monomers, (meth)acrylonitrile; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and vinyl isopropenyl ketone; and olefines such as isoprene, butene, and butadiene. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the styrene resin preferably contains, as a polymerization component, a (meth)acrylate, more preferably an alkyl (meth)acrylate, yet more preferably an alkyl (meth)acrylate in which the alkyl group contains 2 to 10 carbon atoms, still more preferably an alkyl (meth)acrylate in which the alkyl group contains 4 to 8 carbon atoms, and particularly preferably at least one of n-butyl acrylate and 2-ethylhexyl acrylate. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the styrene resin and the (meth)acrylate resin may contain the same (meth)acrylate as a polymerization component. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the mass ratio of the (meth)acrylate relative to the total of the polymerization components of the styrene resin is preferably 40 mass % or less, more preferably 30 mass % or less, and yet more preferably 25 mass % or less. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the mass ratio is preferably 5 mass % or more, more preferably 10 mass % or more, and yet more preferably 15 mass % or more. The (meth)acrylate here is preferably an alkyl (meth)acrylate, yet more preferably an alkyl (meth)acrylate in which the alkyl group contains 2 to 10 carbon atoms, and still more preferably an alkyl (meth)acrylate in which the alkyl group contains 4 to 8 carbon atoms. 
     The styrene resin particularly preferably contains, as a polymerization component, at least one of n-butyl acrylate and 2-ethylhexyl acrylate, and the total amount of n-butyl acrylate and 2-ethylhexyl acrylate relative to the total of polymerization components of the styrene resin is preferably 40 mass % or less, more preferably 30 mass % or less, and yet more preferably 25 mass % or less from the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the total amount is preferably 5 mass % or more, more preferably 10 mass % or more, and yet more preferably 15 mass % or more. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the weight-average molecular weight of the styrene resin is preferably 3000 or more, more preferably 4000 or more, and yet more preferably 5000 or more. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the weight-average molecular weight is preferably 60000 or less, more preferably 55000 or less, and yet more preferably 50000 or less. 
     In the present disclosure, the weight-average molecular weight of a resin is measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is conducted by using HLC-8120GPC produced by TOSOH CORPORATION as a GPC instrument with columns, TSKgel Super HM-M (15 cm) produced by TOSOH CORPORATION, and tetrahydrofuran as a solvent. The weight-average molecular weight of a resin is calculated by using a molecular weight calibration curve prepared by using monodisperse polystyrene standard samples. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the glass transition temperature of the styrene resin is preferably 30° C. or more, more preferably 40° C. or more, and yet more preferably 50° C. or more. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the glass transition temperature is preferably 110° C. or less, more preferably 100° C. or less, and yet more preferably 90° C. or less. 
     In the present disclosure, the glass transition temperature of a resin is determined from a differential scanning calorimetry curve (DSC curve) obtained by performing differential scanning calorimetry (DSC). More specifically, the glass transition temperature is determined from the “extrapolated glass transition onset temperature” described in the method for determining the glass transition temperature in JIS K 7121:1987 “Testing Methods for Transition Temperatures of Plastics”. 
     The glass transition temperature of a resin can be controlled by the types of polymerizable components and the polymerization ratios. The glass transition temperature has a tendency to decrease as the density of flexible units, such as a methylene group, an ethylene group, and an oxyethylene group, contained in the main chain increases, and has a tendency to increase as the density of rigid units, such as aromatic rings and cyclohexane rings, contained in the main chain increases. Moreover, the glass transition temperature has a tendency to decrease as the density of aliphatic groups in side chains increases. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the mass ratio of the styrene resin relative to the entire pressure sensitive adhesive base particle in this exemplary embodiment is preferably 55 mass % or more, more preferably 60 mass % or more, and yet more preferably 65 mass % or more. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the mass ratio is preferably 80 mass % or less, more preferably 75 mass % or less, and yet more preferably 70 mass % or less. 
     (Meth)Acrylate Resin 
     The pressure sensitive adhesive base particle constituting the pressure sensitive adhesive particle of this exemplary embodiment contains a (meth)acrylate resin that contains, as polymerization components, at least two (meth)acrylates that account for 90 mass % or more of all polymerization components. 
     The (meth)acrylates preferably account for 90 mass % or more, preferably 95 mass % or more, more preferably 98 mass % or more, and yet more preferably 100 mass % of all polymerization components of the methacrylate resin. 
     Examples of the (meth)acrylates include alkyl (meth)acrylates, carboxy-substituted alkyl (meth)acrylates, hydroxy-substituted alkyl (meth)acrylates, alkoxy-substituted alkyl (meth)acrylates, and di(meth)acrylates. 
     Examples of the alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate. 
     An example of the carboxy-substituted alkyl (meth)acrylates is 2-carboxylethyl (meth)acrylate. 
     Examples of the hydroxy-substituted alkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. 
     An example of the alkoxy-substituted alkyl (meth)acrylates is 2-methoxyethyl (meth)acrylate. 
     Examples of the di(meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, pentanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, and decanediol di(meth)acrylate. 
     Examples of the (meth)acrylates also include 2-(diethylamino)ethyl (meth)acrylate, benzyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate. 
     These (meth)acrylates may be used alone or in combination. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition and has excellent adhesiveness, the (meth)acrylates are preferably alkyl (meth)acrylates, yet more preferably alkyl (meth)acrylates in which the alkyl group contains 2 to 10 carbon atoms, still more preferably alkyl (meth)acrylates in which the alkyl group contains 4 to 8 carbon atoms, and particularly preferably n-butyl acrylate and 2-ethylhexyl acrylate. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the styrene resin and the (meth)acrylate resin may contain the same (meth)acrylate as a polymerization component. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition and has excellent adhesiveness, the alkyl (meth)acrylates preferably account for 90 mass % or more, more preferably 95 mass % or more, yet more preferably 98 mass % or more, and still more preferably 100 mass % of all polymerization components of the (meth)acrylate resin. The alkyl (meth)acrylates here preferably each have an alkyl group having 2 to 10 carbon atoms and more preferably each have an alkyl group containing 4 to 8 carbon atoms. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition and has excellent adhesiveness, the mass ratio between two (meth)acrylates having the largest and second-largest mass ratios among the at least two (meth)acrylates contained as the polymerization components in the (meth)acrylate resin is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and yet more preferably 60:40 to 40:60. 
     The two (meth)acrylates having the largest and second-largest mass ratios among the at least two (meth)acrylates contained as the polymerization components in the (meth)acrylate resin are preferably alkyl (meth)acrylates. The alkyl (meth)acrylates here preferably each have an alkyl group having 2 to 10 carbon atoms and more preferably each have an alkyl group containing 4 to 8 carbon atoms. 
     When the two (meth)acrylates having the largest and second-largest mass ratios among the at least two (meth)acrylates contained as polymerization components in the (meth)acrylate resin are alkyl (meth)acrylates, from the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition and has excellent adhesiveness, the difference in the number of carbon atoms in the alkyl group between the two alkyl (meth)acrylates is preferably 1 to 4, more preferably 2 to 4, and yet more preferably 3 or 4. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition and has excellent adhesiveness, the (meth)acrylate resin preferably contains, as polymerization components, n-butyl acrylate and 2-ethylhexyl acrylate. In particular, the two (meth)acrylates having the largest and second-largest mass ratios among the at least two (meth)acrylates contained as polymerization components in the (meth)acrylate resin are preferably n-butyl acrylate and 2-ethylhexyl acrylate. The total amount of n-butyl acrylate and 2-ethylhexyl acrylate relative to all polymerization components of the (meth)acrylate resin is preferably 90 mass % or more, more preferably 95 mass % or more, yet more preferably 98 mass % or more, and still more preferably 100 mass %. 
     The (meth)acrylate resin may further contain, as polymerizable components, vinyl monomers other than (meth)acrylates. Examples of the vinyl monomers other than the (meth)acrylates include (meth)acrylic acid; styrene; styrene monomers other than styrene; (meth)acrylonitrile; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and vinyl isopropenyl ketone; and olefines such as isoprene, butene, and butadiene. These vinyl monomers may be used alone or in combination. 
     When the (meth)acrylate resin contains a vinyl monomer other than (meth)acrylates as polymerization components, the vinyl monomer other than the (meth)acrylates is preferably at least one of acrylic acid and methacrylic acid and is more preferably acrylic acid. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the weight-average molecular weight of the (meth)acrylate resin is preferably 50,000 or more, more preferably 100,000 or more, yet more preferably 120,000 or more, and still more preferably 150,000 or more. From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the weight-average molecular weight is preferably 250,000 or less, more preferably 220,000 or less, and yet more preferably 200,000 or less. 
     From the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the glass transition temperature of the (meth)acrylate resin is preferably 10° C. or less, more preferably 0° C. or less, and yet more preferably −10° C. or less. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the glass transition temperature is preferably −90° C. or more, more preferably −80° C. or more, and yet more preferably −70° C. or more. 
     In this exemplary embodiment, from the viewpoint of forming a pressure sensitive adhesive particle that easily undergoes pressure-induced phase transition, the mass ratio of the (meth)acrylate resin relative to the entire pressure sensitive adhesive base particle is preferably 20 mass % or more, more preferably 25 mass % or more, and yet more preferably 30 mass % or more. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the mass ratio is preferably 45 mass % or less, more preferably 40 mass % or less, and yet more preferably 35 mass % or less. 
     In this exemplary embodiment, the total amount of the styrene resin and the (meth)acrylate resin contained in the pressure sensitive adhesive base particle relative to the entire pressure sensitive adhesive base particle is preferably 70 mass % or more, more preferably 80 mass % or more, yet more preferably 90 mass % or more, still preferably 95 mass % or more, and most preferably 100 mass %. 
     Other resins The pressure sensitive adhesive base particle may contain, for example, polystyrene, and a non-vinyl resin such as an epoxy resin, a polyester resin, a polyurethane resin, a polyamide resin, a cellulose resin, a polyether resin, or modified rosin. These resins may be used alone or in combination. 
     Various Additives 
     The pressure sensitive adhesive base particle may contain, if needed, a coloring agent (for example, a pigment or a dye), a releasing agent (for example, hydrocarbon wax, natural wax such as carnauba wax, rice wax, or candelilla wax, a synthetic or mineral or petroleum wax such as montan wax; or ester wax such as fatty acid ester or montanic acid ester), a charge controlling agent, and the like. 
     When the pressure sensitive adhesive particle of this exemplary embodiment is transparent, the amount of the coloring agent in the pressure sensitive adhesive base particle relative to the entire pressure sensitive base particle may be 1.0 mass % or less, and, from the viewpoint of increasing the transparency of the pressure sensitive adhesive particle, is preferably as small as possible. 
     Structure of Pressure Sensitive Adhesive Base Particle 
     The inner structure of the pressure sensitive adhesive base particle is a sea-island structure. The sea-island structure has a sea phase that contains the styrene resin, and island phases that are dispersed in the sea phase and contain the (meth)acrylate resin. Specific examples of the styrene resin contained in the sea phase are as described above. Specific examples of the (meth)acrylate resin contained in the island phases are as described above. Alternatively, island phases not containing a (meth)acrylate resin may be dispersed in the sea phase. 
     In the sea-island structure of the pressure sensitive adhesive base particle, the average diameter of the island phases may be 200 nm or more and 500 nm or less. When the average diameter of the island phases is 500 nm or less, the pressure sensitive adhesive base particle easily undergoes pressure-induced phase transition. When the average diameter of the island phases is 200 nm or more, excellent mechanical strength suitable for the pressure sensitive adhesive base particle (for example, the strength that withstands deformation during stirring in a developing device) is exhibited. From these viewpoints, the average diameter of the island phases is more preferably 220 nm or more and 450 nm or less and yet more preferably 250 nm or more and 400 nm or less. 
     Examples of the method for controlling the average diameter of the island phases in the sea-island structure to be within the aforementioned range include increasing or decreasing the amount of the (meth)acrylate resin relative to the amount of the styrene resin and increasing or decreasing the length of time of maintaining a high temperature in the step of fusing and coalescing aggregated particles in the method for producing pressure sensitive adhesive base particles described below. 
     The pressure sensitive adhesive base particle may have a single layer structure or may have a core-shell structure including a core and a shell layer that covers the core. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the pressure sensitive adhesive base particle may have a core-shell structure. 
     From the viewpoint of facilitating the pressure-induced phase transition, when the pressure sensitive adhesive base particle has a core-shell structure, the core may contain a styrene resin and a (meth)acrylate resin. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the shell layer may contain a styrene resin. The specific examples of the styrene resin are as described above. The specific examples of the (meth)acrylate resin are as described above. 
     When the pressure sensitive adhesive base particle has a core-shell structure, the core may have a sea phase that contains a styrene resin, and island phases that are dispersed in the sea phase and contain a (meth)acrylate resin. The average diameter of the island phases may be within the aforementioned range. In addition to the core having the above-described structure, the shell layer may contain a styrene resin. In such a case, the sea phase of the core and the shell layer form a continuous structure, and the pressure sensitive adhesive base particle easily undergoes pressure-induced phase transition. The specific examples of the styrene resin contained in the sea phase of the core and the shell layer are as described above. The specific examples of the (meth)acrylate resin contained in the island phases of the core are as described above. 
     Examples of the resin contained in the shell layer also include polystyrene, and non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins polyether resins, and modified rosin. These resins may be used alone or in combination. 
     From the viewpoint of suppressing deformation of the pressure sensitive adhesive base particle, the average thickness of the shell layer is preferably 120 nm or more, more preferably 130 nm or more, and yet more preferably 140 nm or more. From the viewpoint of facilitating the pressure-induced phase transition of the pressure sensitive adhesive base particle, the average thickness is preferably 550 nm or less, more preferably 500 nm or less, and yet more preferably 400 nm or less. 
     The average thickness of the shell layer is measured by the following method. 
     The pressure sensitive adhesive particles are embedded in an epoxy resin, a section is prepared by using a diamond knife or the like, and the prepared section is stained with osmium tetroxide or ruthenium tetroxide in a desiccator. The stained section is observed with a scanning electron microscope (SEM). From an SEM image, sections of ten pressure sensitive adhesive base particles are selected at random, the thickness of the shell layer is measured at twenty positions for each of the pressure sensitive adhesive base particles, and the average thickness is calculated. The average value of ten pressure sensitive adhesive base particles is used as the average thickness. 
     From the viewpoint of handling ease of the pressure sensitive adhesive base particle, the volume-average particle diameter (D50v) of the pressure sensitive adhesive base particle is preferably 4 μm or more, more preferably 5 μm or more, and yet more preferably 6 μm or more, and from the viewpoint of facilitating the pressure-induced phase transition of the entire pressure sensitive adhesive base particle, the volume-average particle diameter (D50v) is preferably 12 μm or less, more preferably 10 μm or less, and yet more preferably 9 μm or less. 
     The volume-average particle diameter (D50v) of the pressure sensitive adhesive base particle is determined by using Coulter MULTISIZER II (produced by Beckman Coulter Inc.) with an aperture having a diameter of 100 μm. Into 2 mL of a 5 mass % aqueous sodium alkyl benzenesulfonate solution, 0.5 mg or more and 50 mg or less of the pressure sensitive adhesive base particles are added and dispersed, and then the resulting dispersion is mixed with 100 mL or more and 150 mL or less of an electrolyte (ISOTON-II produced by Beckman Coulter Inc.). The resulting mixture is dispersed for 1 minute in an ultrasonic disperser, and the obtained dispersion is used as a sample. The particle diameters of 50000 particles having a particle diameter of 2 μm or more and 60 μm or less in the sample are measured. The particle diameter at 50% accumulation in a volume-based particle size distribution calculated from the small diameter side is used as the volume-average particle diameter (D50v). 
     External Additive 
     An example of the external additive is inorganic particles. Examples of the inorganic particles include SiO 2 , TiO 2 , Al 2 O 3 , CuO, ZnO, SnO 2 , CeO 2 , Fe 2 O 3 , MgO, BaO, CaO, K 2 O, Na 2 O, ZrO 2 , CaO.SiO 2 , K 2 O (TiO 2 ) n, Al 2 O 3 .2SiO 2 , CaCO 3 , MgCO 3 , BaSO 4 , and MgSO 4 . 
     The surfaces of the inorganic particles serving as an external additive may be hydrophobized. Hydrophobizing involves, for example, immersing inorganic particles in a hydrophobizing agent. The hydrophobizing agent may be any, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination. The amount of the hydrophobizing agent is, for example, 1 part by mass or more and 10 parts by mass or less relative to 100 parts by mass of the inorganic particles. 
     Other examples of the external additive include resin particles (resin particles of polystyrene, polymethyl methacrylate, melamine resin, etc.), and cleaning activating agents (for example, particles of metal salts of higher aliphatic acids such as zinc stearate and fluorine high-molecular-weight materials). 
     The externally added amount of the external additive relative to the pressure sensitive adhesive base particle is preferably 0.01 mass % or more and 5 mass % or less and is more preferably 0.01 mass % or more and 2.0 mass % or less. 
     Properties of Pressure Sensitive Adhesive Particle 
     The pressure sensitive adhesive particle of the exemplary embodiment has at least two glass transition temperatures, one of which is presumed to be that of the styrene resin and the other one of which is presumed to be that of the (meth)acrylate resin. 
     The pressure sensitive adhesive particle of the exemplary embodiment may have three or more glass transition temperatures; however, the number of glass transition temperatures is preferably two. Examples of the case in which there are two glass transition temperatures include the case in which a styrene resin and a (meth)acrylate resin are the only resins contained in the pressure sensitive adhesive particle, and the case in which the amount of resins other than the styrene resin and the (meth)acrylate resin is small (for example, the amount of other resins is 5 mass % or less relative to the entire pressure sensitive adhesive particle). 
     The pressure sensitive adhesive particle of this exemplary embodiment has at least two glass transition temperatures, and the difference between the lowest glass transition temperature and the highest glass transition temperature is 30° C. or more. From the viewpoint of facilitating the pressure-induced phase transition of the pressure sensitive adhesive particle, the difference between the lowest glass transition temperature and the highest glass transition temperature is preferably 40° C. or more, yet more preferably 50° C. or more, and still more preferably 60° C. or more. The upper limit of the difference between the highest glass transition temperature and the lowest glass transition temperature is, for example, 140° C. or less, and may be 130° C. or less or 120° C. or less. 
     From the viewpoint of facilitating the pressure-induced phase transition of the pressure sensitive adhesive particle, the lowest glass transition temperature of the pressure sensitive adhesive particle of this exemplary embodiment is preferably 10° C. or less, more preferably 0° C. or less, and yet more preferably −10° C. or less. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the lowest glass transition temperature is preferably −90° C. or more, more preferably −80° C. or more, and yet more preferably −70° C. or more. 
     From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the highest glass transition temperature of the pressure sensitive adhesive particle of this exemplary embodiment is preferably 30° C. or more, more preferably 40° C. or more, and yet more preferably 50° C. or more. From the viewpoint of facilitating the pressure-induced phase transition of the pressure sensitive adhesive particle, the highest glass transition temperature is preferably 70° C. or less, more preferably 65° C. or less, and yet more preferably 60° C. or less. 
     In the present disclosure, the glass transition temperature of the pressure sensitive adhesive particle is determined from a differential scanning calorimetry curve (DSC curve) obtained by performing differential scanning calorimetry (DSC). More specifically, the glass transition temperature is determined from the “extrapolated glass transition onset temperature” described in the method for determining the glass transition temperature in JIS K 7121:1987 “Testing Methods for Transition Temperatures of Plastics”. 
     The pressure sensitive adhesive particle of the exemplary embodiment undergoes pressure-induced phase transition, and satisfies formula 1 below: 
       10° C.≤ T 1− T 2  Formula 1:
 
     In formula 1, T1 represents a temperature at which the viscosity is 10000 Pa·s at a pressure of 1 MPa, and T2 represents a temperature at which the viscosity is 10000 Pa·s at a pressure of 10 MPa. 
     From the viewpoint of facilitating the pressure-induced phase transition of the pressure sensitive adhesive particle, the temperature difference (T1−T2) is preferably 10° C. or more, more preferably 15° C. or more, and yet more preferably 20° C. or more. From the viewpoint of suppressing fluidization of the pressure sensitive adhesive particle in an unpressured state, the temperature difference (T1−T2) is preferably 120° C. or less, more preferably 100° C. or less, and yet more preferably 80° C. or less. 
     The value of the temperature T1 is preferably 140° C. or less, more preferably 130° C. or less, yet more preferably 120° C. or less, and still more preferably 115° C. or less. The lower limit of the temperature T1 is preferably 80° C. or more and more preferably 85° C. or more. 
     The value of the temperature T2 is preferably 40° C. or more, more preferably 50° C. or more, and yet more preferably 60° C. or more. The upper limit of the temperature T2 may be 85° C. or less. 
     One indicator of how easily the pressure sensitive adhesive particle undergoes pressure-induced phase transition is the temperature difference (T1−T3) between the temperature T1 at which the viscosity is 10000 Pa·s at a pressure of 1 MPa and the temperature T3 at which the viscosity is 10000 Pa·s at a pressure of 4 MPa. The temperature difference (T1−T3) may be 5° C. or more. From the viewpoint of facilitating the pressure-induced phase transition, the temperature difference (T1−T3) of the pressure sensitive adhesive particle is preferably 5° C. or more and more preferably 10° C. or more. 
     The temperature difference (T1−T3) is typically 25° C. or less. 
     From the viewpoint of adjusting the temperature difference (T1−T3) to 5° C. or more, the temperature T3 of the pressure sensitive adhesive particle of the exemplary embodiment at which the viscosity is 10000 Pa·s at a pressure of 4 MPa is preferably 90° C. or less, more preferably 85° C. or less, and yet more preferably 80° C. or less. The lower limit of the temperature T3 may be 60° C. or more. 
     The method for determining the temperature T1, the temperature T2, and the temperature T3 is as follows. 
     Pressure sensitive adhesive particles are compressed into a pellet-shaped sample. The pellet-shaped sample is placed in a Flowtester (CFT-500 produced by Shimadzu Corporation), the applied pressure is fixed at 1 MPa, and the viscosity at 1 MPa relative to the temperature is measured. From the obtained viscosity graph, the temperature T1 at which the viscosity is 10 4  Pa·s at an applied pressure of 1 MPa is determined. The temperature T2 is determined by the same method for determining the temperature T1 except that the applied pressure is changed from 1 MPa to 10 MPa. The temperature T3 is determined by the same method for determining the temperature T1 except that the applied pressure is changed from 1 MPa to 4 MPa. The temperature difference (T1−T2) is calculated from the temperature T1 and the temperature T2. The temperature difference (T1−T3) is calculated from the temperature T1 and the temperature T3. 
     Method for producing pressure sensitive adhesive particle The pressure sensitive adhesive particle of the exemplary embodiment is obtained by first producing a pressure sensitive adhesive base particle and then externally adding an external additive to the pressure sensitive adhesive base particle. 
     The pressure sensitive adhesive base particle may be produced by a dry method (for example, a kneading and pulverizing method) or a wet method (for example, an aggregation and coalescence method, a suspension polymerization method, or a dissolution suspension method). There is no limitation on these methods, and any known method may be employed. Among these methods, the aggregation and coalescence method may be employed to produce the pressure sensitive adhesive base particle. 
     When the pressure sensitive adhesive base particle is to be produced by the aggregation and coalescence method, the pressure sensitive adhesive base particle is produced through, for example, the following steps: 
     a step of preparing a styrene resin particle dispersion in which styrene resin particles containing a styrene resin are dispersed (styrene resin particle dispersion preparation step); 
     a step of polymerizing a (meth)acrylate resin in the styrene resin particle dispersion so as to form composite resin particles containing the styrene resin and the (meth)acrylate resin (composite resin particle forming step); 
     a step aggregating the composite resin particles in the composite resin particle dispersion in which the composite resin particles are dispersed so as to form aggregated particles (aggregated particle forming step); and 
     a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed so as to fuse and coalesce the aggregated particles and thereby form pressure sensitive adhesive base particles (fusing and coalescing step). 
     These steps will now be described in detail. 
     In the description below, a method for obtaining a pressure sensitive adhesive base particle not containing a coloring agent or a releasing agent is described. A coloring agent, a releasing agent, and other additives may be used as needed. When the pressure sensitive adhesive base particle is to contain a coloring agent and a releasing agent, the fusing and coalescing step is performed after the composite resin particle dispersion, a coloring agent particle dispersion, and a releasing agent particle dispersion are mixed. The coloring agent particle dispersion and the releasing agent particle dispersion can be, for example, prepared by mixing raw materials and then dispersing the particles in a known disperser machine. 
     Styrene Resin Particle Dispersion Preparation Step 
     The styrene resin particle dispersion is, for example, prepared by dispersing styrene resin particles in a dispersion medium by using a surfactant. 
     Examples of the dispersion medium include aqueous media such as water and alcohols. These may be used alone or in combination. 
     Examples of the surfactant include anionic surfactants such as sulfate esters, sulfonates, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycol, alkyl phenol-ethylene oxide adducts, and polyhydric alcohols. A nonionic surfactant may be used in combination with an anionic surfactant or a cationic surfactant. Among these, an anionic surfactant may be used. The surfactants may be used alone or in combination. 
     Examples of the method for dispersing the styrene resin particles in a dispersion medium include methods that involve mixing a styrene resin and a dispersion medium and then dispersing the resin by stirring in a rotational shear-type homogenizer, or a mill that uses media such as a ball mill, a sand mill, or a dyno mill. 
     Another example of the method for dispersing styrene resin particles in a dispersion medium is an emulsion polymerization method. Specifically, after polymerization components of a styrene resin, and a chain transfer agent or a polymerization initiator are mixed, an aqueous medium containing a surfactant is added to the resulting mixture, the resulting mixture is stirred to prepare an emulsion, and the styrene resin is polymerized in the emulsion. Here, the chain transfer agent may be dodecanethiol. 
     The volume-average particle diameter of the styrene resin particles dispersed in the styrene resin particle dispersion is preferably 100 nm or more and 250 nm or less, more preferably 120 nm or more and 220 nm or less, and yet more preferably 150 nm or more and 200 nm or less. 
     The volume-average particle diameter (D50v) of the resin particles contained in the resin particle dispersion is determined by measuring the particle diameter with a laser diffraction scattering particle size distribution meter (for example, LA-700 produced by Horiba Ltd.) and determining the particle diameter at 50% accumulation in a volume-base particle size distribution calculated from the small diameter side. 
     The styrene resin particle content in the styrene resin particle dispersion is preferably 30 mass % or more and 60 mass % or less and is more preferably 40 mass % or more and 50 mass % or less. 
     Composite Resin Particle Forming Step 
     The styrene resin particle dispersion and the polymerization components of a (meth)acrylate resin are mixed, and the (meth)acrylate resin is polymerized in the styrene resin particle dispersion so as to form composite resin particles containing the styrene resin and the (meth)acrylate resin. 
     The composite resin particles may be resin particles containing a styrene resin and a (meth)acrylate resin that are in a microphase-separated state. Such resin particles can be produced by, for example, the following method. 
     To a styrene resin particle dispersion, polymerization components (a group of monomers including at least two (meth)acrylates) of the (meth)acrylate resin are added, and, if needed, an aqueous medium is added thereto. Next, while slowly stirring the dispersion, the temperature of the dispersion is elevated to a temperature higher than or equal to the glass transition temperature of the styrene resin (for example, a temperature 10° C. to 30° C. higher than the glass transition temperature of the styrene resin). Next, while maintaining the temperature, an aqueous medium containing a polymerization initiator is slowly added dropwise, and then stirring is continued for a long time within the range of 1 to 15 hours. Here, the polymerization initiator may be ammonium persulfate. 
     The detailed mechanism is not clear; however, it is presumed that when the aforementioned method is employed, the monomers and the polymerization initiator penetrate into the styrene resin particles, and the (meth)acrylates become polymerized inside the styrene resin particles. It is presumed that because of this mechanism, composite resin particles in which the (meth)acrylate resin is contained inside the styrene resin particles and in which the styrene resin and the (meth)acrylate resin are in a microphase-separated state inside the particles are obtained. 
     During or after production of the composite resin particles described above, polymerization components (in other words, styrene and a vinyl monomer other than styrene) of the styrene resin may be added to the dispersion containing the dispersed composite resin particles, and the polymerization reaction may be continued. Presumably as a result, composite resin particles in which the styrene resin and the (meth)acrylate resin form a microphase-separated state inside the particles and in which the styrene resin is attached to the particle surfaces are obtained. A pressure sensitive adhesive particle produced by using a composite resin particle having a styrene resin attached to a particle surface thereof generates relatively fewer coarse particles. 
     The vinyl monomer, which is a polymerization component of the styrene resin to be attached to the surface of the composite resin particle, may contain the same monomer as at least one of the monomers constituting the styrene resin or the (meth)acrylate resin inside the composite resin particle, and, specifically, may contain at least one of n-butyl acrylate and 2-ethylhexyl acrylate. 
     The volume-average particle diameter of the composite resin particles dispersed in the composite resin particle dispersion is preferably 140 nm or more and 300 nm or less, more preferably 150 nm or more and 280 nm or less, and yet more preferably 160 nm or more and 250 nm or less. 
     The composite resin particle content in the composite resin particle dispersion is preferably 20 mass % or more and 50 mass % or less and is more preferably 30 mass % or more and 40 mass % or less. 
     Aggregated Particle Forming Step 
     The composite resin particles are aggregated in the composite resin particle dispersion so as to form aggregated particles having diameters close to the target diameter of the pressure sensitive adhesive base particle. 
     Specifically, for example, an aggregating agent is added to the composite resin particle dispersion while the pH of the composite resin particle dispersion is adjusted to acidic (for example, a pH of 2 or more and 5 or less), and after a dispersion stabilizer is added as needed, the dispersion is heated to a temperature close to the glass transition temperature of the styrene resin (specifically, for example, a temperature 10° C. to 30° C. lower than the glass transition temperature of the styrene resin) so as to aggregate the composite resin particles and form aggregated particles. 
     In the aggregated particle forming step, heating may be performed after an aggregating agent is added to the composite resin particle dispersion being stirred in a rotational shear-type homogenizer at room temperature (for example, 25° C.), the pH of the composite resin particle dispersion is adjusted to acidic (for example, a pH2 or more and 5 or less), and a dispersion stabilizer is added as needed. 
     Examples of the aggregating agent include a surfactant having an opposite polarity to the surfactant contained in the composite resin particle dispersion, an inorganic metal salt, and a divalent or higher valent metal complex. When a metal complex is used as the aggregating agent, the amount of the surfactant used is reduced, and the charge properties are improved. 
     An additive that forms a complex with a metal ion in the aggregating agent or that forms a similar bond therewith may be used in combination with the aggregating agent as needed. An example of such an additive is a chelating agent. 
     Examples of the inorganic metal salt include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. 
     A water-soluble chelating agent may be used as the chelating agent. Examples of the chelating agent include oxycarboxylic acids such as tartaric acid, citric acid, and gluconic acid; and aminocarboxylic acids such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA). 
     The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass relative to 100 parts by mass of the resin particles. 
     Fusing and Coalescing Step 
     Next, the aggregated particle dispersion containing dispersed aggregated particles is heated to, for example, a temperature equal to or higher than the glass transition temperature of the styrene resin (for example, a temperature 10° C. to 30° C. higher than the glass transition temperature of the styrene resin) to fuse and coalesce the aggregated particles and form pressure sensitive adhesive base particles. 
     The pressure sensitive adhesive base particle obtained through the above-described steps usually has a sea-island structure that has a sea phase containing a styrene resin and island phases containing a (meth)acrylate resin and being dispersed in the sea phase. It is presumed that although the styrene resin and the (meth)acrylate resin are in a microphase-separated state in the composite resin particles, the styrene resin has gathered to form a sea phase, and the (meth)acrylate resin has gathered to form island phases in the fusing and coalescence step. 
     The average diameter of the island phases of the sea-island structure can be controlled by, for example, increasing or decreasing the amount of the styrene resin particle dispersion or the amount of the at least two (meth)acrylates used in the composite resin particle forming step, or by increasing or decreasing the length of time of maintaining a high temperature in the fusing and coalescing step. 
     The pressure sensitive adhesive base particles having a core-shell structure are produced through the following steps, for example: 
     after an aggregated particle dispersion is obtained, a step of mixing the aggregated particle dispersion and a styrene resin particle dispersion so that the styrene resin particles further attach to the surfaces of the aggregated particles and form second aggregated particles; and 
     a step of heating the second aggregated particle dispersion in which the second aggregated particles are dispersed so as to fuse and coalesce the second aggregated particles and thereby form pressure sensitive adhesive base particles having a core-shell structure. 
     The pressure sensitive adhesive base particle having a core-shell structure obtained through the aforementioned steps has a shell layer containing a styrene resin. Instead of the styrene resin particle dispersion, a resin particle dispersion in which a different type of resin particles are dispersed may be used to form a shell layer that contains the different type of resin. 
     After completion of the fusing and coalescing step, the pressure sensitive adhesive base particles formed in the solution are subjected to a washing step, a solid-liquid separation step, and a drying step known in the art so as to obtain dry pressure sensitive adhesive base particles. From the viewpoint of chargeability, the washing step may involve thorough displacement washing with ion exchange water. From the viewpoint of productivity, the solid-liquid separation step may involve suction filtration, pressure filtration, or the like. From the viewpoint of productivity, the drying step may involve freeze-drying, flash-drying, fluid-drying, vibration-type fluid-drying, or the like. 
     The pressure sensitive adhesive particle of this exemplary embodiment is formed by, for example, adding an external additive to the obtained dry pressure sensitive adhesive base particle, and mixing the resulting mixture. Mixing may be performed by using a V blender, a HENSCHEL mixer, a Lodige mixer, or the like. Furthermore, if needed, a vibrating screen, an air screen, or the like may be used to remove coarse particles of the pressure sensitive adhesive particle. 
     Cartridge 
     A cartridge according to an exemplary embodiment stores the pressure sensitive adhesive particle of the exemplary embodiment and is detachably attachable to a printed material producing apparatus. When the cartridge is attached to a printed material producing apparatus, the cartridge connects, via a supply pipe, to an applying unit that constitutes a part of the printed material producing apparatus and that applies the pressure sensitive adhesive particle to a recording medium. 
     When the pressure sensitive adhesive particle is supplied from the cartridge to the applying unit and the pressure sensitive adhesive particle level in the cartridge has run low, the cartridge is replaced. 
     Apparatus and Method for Producing Printed Material, and Printed Material 
     An apparatus for producing a printed material according to an exemplary embodiment includes an applying unit that stores the pressure sensitive adhesive particle of the exemplary embodiment and applies the pressure sensitive adhesive particle to a recording medium; and a pressure bonding unit that folds and pressure-bonds the recording medium or pressure-bonds the recording medium and another recording medium placed on top of each other. 
     The applying unit is equipped with, for example, a placing device that places the pressure sensitive adhesive particle on a recording medium, and a fixing device that fixes the pressure sensitive adhesive particle placed on the recording medium onto the recording medium. 
     For example, the pressure bonding unit is equipped with: a folding device that folds a recording medium having the pressure sensitive adhesive particle applied thereto or a stacking device that stacks another recording medium on top of the recording medium having the pressure sensitive adhesive particle applied thereto; and a pressurizing device that pressurizes the folded recording medium or the recording media stacked on top of each other. 
     The pressurizing device in the pressure bonding unit applies a pressure to a recording medium having pressure sensitive adhesive particle applied thereto. In this manner, the pressure sensitive adhesive particle is fluidized and exhibits adhesiveness on the recording medium. 
     A method for producing a printed material of this exemplary embodiment is performed by using the apparatus for producing a printed material of this exemplary embodiment. The method for producing a printed material according to the exemplary embodiment includes an applying step of using the pressure sensitive adhesive particle of the exemplary embodiment and applying the pressure sensitive adhesive particle to a recording medium; and a pressure bonding step of folding the recording medium and pressure-bonding the folded recording medium, or pressure-bonding the recording medium with another recording medium stacked on top thereof. 
     The applying step includes, for example, a step of placing a pressure sensitive adhesive particle onto a recording medium, and may further include a step of fixing the pressure sensitive adhesive particle placed on the recording medium onto the recording medium. 
     The pressure bonding step includes, for example, a folding step of folding the recording medium or a stacking step of stacking another recording medium on the recording medium; and a pressurizing step of pressurizing the folded recording medium or the stacked recording media. 
     The pressure sensitive adhesive particle may be applied to the entire surface of the recording medium or one part of the recording medium. One layer or two or more layers of the pressure sensitive adhesive particle are applied to the recording medium. The layer of the pressure sensitive adhesive particle may be a layer continuous in the surface direction of the recording medium or a layer discontinuous in the surface direction of the recording medium. The layer of the pressure sensitive adhesive particle may be a layer in which the pressure sensitive adhesive particles are aligned as particles or a layer in which adjacent pressure sensitive adhesive particles are fused and aligned with each other. 
     The amount of the pressure sensitive adhesive particles (preferably, transparent pressure sensitive adhesive particles) on the recording medium and applied in the region is, for example, 0.5 g/m 2  or more and 50 g/m 2  or less, 1 g/m 2  or more and 40 g/m 2  or less, or 1.5 g/m 2  or more and 30 g/m 2  or less. The thickness of the layer of the pressure sensitive adhesive particles (preferably, transparent pressure sensitive adhesive particles) on the recording medium is, for example, 0.2 μm or more and 25 μm or less, 0.4 μm or more and 20 μm or less, or 0.6 μm or more and 15 μm or less. 
     Examples of the recording medium used in the apparatus for producing a printed material according to this exemplary embodiment include paper, coated paper obtained by coating the surface of paper with a resin or the like, cloths, nonwoven cloths, resin films, and resin sheets. The recording medium may have an image on one surface or both surfaces. 
     Although some examples of the apparatus for producing a printed material according to the exemplary embodiment are described below, the exemplary embodiments are not limited to these. 
       FIG. 1  is a schematic diagram of an example of an apparatus for producing a printed material according to this exemplary embodiment. The apparatus for producing a printed material illustrated in  FIG. 1  is equipped with an applying unit  100  and a pressure bonding unit  200  downstream of the applying unit  100 . The arrow indicates the direction in which the recording medium is conveyed. 
     The applying unit  100  is a device that applies the pressure sensitive adhesive particles of the exemplary embodiment to a recording medium P. The recording medium P has an image formed on one or both surfaces in advance. 
     The applying unit  100  is equipped with a placing device  110  and a fixing device  120  disposed downstream of the placing device  110 . 
     The placing device  110  places pressure sensitive adhesive particles M onto a recording medium P. Examples of the placing method employed by the placing device  110  include a spraying method, a bar coating method, a die coating method, a knife coating method, a roll coating method, a reverse roll coating method, a gravure coating method, a screen printing method, an ink jet method, a lamination method, and an electrophotographic method. Depending on the placing method, the pressure sensitive adhesive particles M may be dispersed in a dispersion medium to prepare a liquid composition, and this liquid composition may be used by the placing device  110 . 
     The recording medium P having the pressure sensitive adhesive particles M placed thereon by the placing device  110  is conveyed to the fixing device  120 . 
     Examples of the fixing device  120  include a heating device that has a heating source and heats the pressure sensitive adhesive particles M on the recording medium P passing therethrough to fix the pressure sensitive adhesive particles M onto the recording medium P; a pressurizing device that has a pair of pressurizing members (roll/roll or belt/roll) and pressurizes the recording medium P passing therethrough to fix the pressure sensitive adhesive particles M onto the recording medium P; and a pressurizing and heating device that has a pair of pressurizing members (roll/roll or belt/roll) equipped with heating sources inside and pressurizes and heats the recording medium P passing therethrough to fix the pressure sensitive adhesive particles M onto the recording medium P. 
     When the fixing device  120  has a heating source, the surface temperature of the recording medium P heated by the fixing device  120  is preferably 10° C. or more and 80° C. or less, more preferably 20° C. or more and 60° C. or less, and yet more preferably 30° C. or more and 50° C. or less. 
     When the fixing device  120  has a pressurizing member, the pressure applied to the recording medium P from the pressurizing member may be lower than the pressure applied to the recording medium P2 from the pressurizing device  230 . 
     The recording medium P that has passed the applying unit  100  turns into a recording medium P1 having pressure sensitive adhesive particles M applied on the image. The recording medium P1 is conveyed toward the pressure bonding unit  200 . 
     In the apparatus for producing a printed material according to this exemplary embodiment, the applying unit  100  and the pressure bonding unit  200  may be close to each other or distant from each other. When the applying unit  100  and the pressure bonding unit  200  are distant from each other, the applying unit  100  and the pressure bonding unit  200  are, for example, linked via a conveying unit (for example, a belt conveyor) that conveys the recording medium P1. 
     The pressure bonding unit  200  is equipped with a folding device  220  and a pressurizing device  230 , and folds and pressure-bonds the recording medium P1. 
     The folding device  220  folds the recording medium P1 passing therethrough to prepare a folded recording medium P2. The recording medium P2 may be folded in two, in three, or in four, and may be folded only partly. The pressure sensitive adhesive particles M are applied to at least part of at least one of the opposing surface of the recording medium P2. 
     The folding device  220  may have a pair of pressurizing members (for example, roll/roll or belt/roll) that apply a pressure to the recording medium P2. The pressure which the pressurizing members of the folding device  220  apply to the recording medium P2 may be lower than the pressure which the pressurizing device  230  applies to the recording medium P2. 
     The pressure bonding unit  200  may be equipped with a stacking device that stacks another recording medium on top of the recording medium P1 instead of the folding device  220 . Examples of the way in which the recording medium P1 and the additional recording medium are stacked on top of each other include stacking one recording medium on the recording medium P1, and stacking one recording medium on each of multiple regions in the recording medium P1. This additional recording medium may have an image formed on one or both surfaces in advance, may be free of any image, or may be a pressure-bonded printed material prepared in advance. 
     The recording medium P2 exits the folding device  220  (or stacking device) and is conveyed toward the pressurizing device  230 . 
     The pressurizing device  230  is equipped with a pair of pressurizing members (in other words, pressurizing rolls  231  and  232 ). The pressurizing roll  231  and the pressurizing roll  232  contact and push each other at their outer peripheral surfaces to apply a pressure onto the passing recording medium P2. The pair of pressurizing members in the pressurizing device  230  is not limited to the combination of pressurizing rolls, and may be a combination of a pressurizing roll and a pressurizing belt or a combination of a pressurizing belt and a pressurizing belt. 
     When a pressure is applied to the recording medium P2 passing the pressurizing device  230 , the pressure sensitive adhesive particles M on the recording medium P2 are fluidized under pressure and exhibit adhesiveness. 
     The pressurizing device  230  may have a heating source (for example, a halogen heater) inside for heating the recording medium P2, but this is optional. The pressurizing device  230  may have no heating source inside, and this does not exclude that the temperature inside the pressurizing device  230  increases to a temperature equal to or more than the environment temperature due to heat from a motor in the pressurizing device  230  or the like. 
     As the recording medium P2 passes the pressurizing device  230 , the opposing folded surfaces bond with each other with the fluidized pressure sensitive adhesive particles M, and a pressure-bonded printed material P3 is obtained. Two opposing surfaces of the pressure-bonded printed material P3 are bonded to each other partly or entirely. 
     The finished pressure-bonded printed material P3 is discharged from the pressurizing device  230 . 
     A first form of the pressure-bonded printed material P3 is formed of a folded recording medium having opposing surfaces bonded with the pressure sensitive adhesive particles M. The pressure-bonded printed material P3 of this form is produced by the apparatus for producing a printed material equipped with a folding device  220 . 
     A second form of the pressure-bonded printed material P3 is formed of multiple recording media stacked on top of each other and having opposing surfaces bonded with the pressure sensitive adhesive particles M. The pressure-bonded printed material P3 of this form is produced by the pressure-bonded printed material producing apparatus equipped with a stacking device. 
     The apparatus for producing a printed material according to this exemplary embodiment is not limited to a type that continuously conveys the recording medium P2 from the folding device  220  (or stacking device) to the pressurizing device  230 . The apparatus for producing a printed material according to this exemplary embodiment may be of a type that stocks the recording media P2 discharged from the folding device  220  (or stacking device) and conveys the recording media P2 to the pressurizing device  230  after a predetermined amount of the recording media P2 are stored. 
     In the apparatus for producing a printed material according to this exemplary embodiment, the folding device  220  (or stacking device) and the pressurizing device  230  may be close to each other or distant from each other. When the folding device  220  (or stacking device) and the pressurizing device  230  are distant from each other, the folding device  220  (or stacking device) and the pressurizing device  230  are, for example, linked via a conveying unit (for example, a belt conveyor) that conveys the recording medium P2. 
     The apparatus for producing a printed material according to this exemplary embodiment may be equipped with a cutting unit that cuts the recording medium into a predetermined size. Examples of the cutting unit include a cutting unit that is disposed between the applying unit  100  and the pressure bonding unit  200  and cuts off a part of the recording medium P1, the part being a region where no pressure sensitive adhesive particles M are applied; a cutting unit that is disposed between the folding device  220  and the pressurizing device  230  and cuts off a part of the recording medium P2, the part being a region where no pressure sensitive adhesive particles M are applied; and a cutting unit that is disposed downstream of the pressure bonding unit  200  and cuts off a part of the pressure-bonded printed material P3, the part being a region not bonded with the pressure sensitive adhesive particles M. 
     The apparatus for producing a printed material according to this exemplary embodiment is not limited to a single-sheet type. The apparatus for producing a printed material according to this exemplary embodiment may be of a type that performs an applying step and a pressure bonding step on a long recording medium to form a long pressure-bonded printed material, and then cuts the long pressure-bonded printed material into a predetermined size. 
     The apparatus for producing a printed material (image forming apparatus) according to this exemplary embodiment may further include a color image forming unit that forms a color image on a recording medium by using a coloring material. Examples of the color image forming unit include a unit that forms a color ink image on a recording medium by an inkjet method using a color ink as a coloring material, and a unit that electrophotographically forms a color image on a recording medium by using a color electrostatic charge image developer. 
     The above-described production apparatus is used to implement the method for producing a printed material of the exemplary embodiment, the method further including a color image forming step of forming a color image on the recording medium by using a coloring material. Examples of the color image forming step include a step of forming a color ink image on a recording medium by an inkjet method using a color ink as a coloring material, and a step of electrophotographically forming a color image on a recording medium by using a color electrostatic charge image developer. 
     An inkjet-type color image forming unit that serves as the color image forming unit will now be described with reference to the drawings.  FIG. 2  illustrates an inkjet recording apparatus  400 , which is an inkjet-type exemplary embodiment. The inkjet recording apparatus  400  is, for example, installed upstream of the applying unit  100  of the printed material production apparatus illustrated in  FIG. 1 . 
     The inkjet recording apparatus  400  includes, in a casing  40 , a container  42  that stores recording media P before image recording, a endless conveying belt  50  stretched across a driving roll  52  and a driven roll  54 , ink ejection heads  30 Y,  30 M,  30 C, and  30 K (these may be collectively referred to as ink ejection heads  30 ), drying units  34 Y,  34 M,  34 C, and  34 K (these may be collectively referred to as drying units  34 ), and a container  66  that stores recording media P after image recording. 
     A conveying path  44  through which the recording medium P before image recording is conveyed is disposed between the container  42  and the conveying belt  50 , and a take-up roll  46  that takes one recording medium P at a time from the container  42 , and multiple pairs of rolls  48  that convey the recording medium P are disposed along the conveying path  44 . A charging roll  56  is disposed upstream of the conveying belt  50 . The charging roll  56  is driven as it holds the recording medium P and the conveying belt  50  placed between the charging roll  56  and the driven roll  54 , generates a potential difference with respect to the grounded driven roll  54 , and provides charges to the recording medium P so that the recording medium P is electrostatically attracted to the conveying belt  50 . 
     The ink ejection heads  30  are disposed above the conveying belt  50  and oppose the flat portion of the conveying belt  50 . The regions where the ink ejection heads  30  and the conveying belt  50  oppose each other are the regions where ink droplets are ejected from the ink ejection heads  30 . 
     The ink ejection heads  30 Y,  30 M,  30 C, and  30 K are, respectively, a head that records a yellow (Y) image, a head that records a magenta (M) image, a head that records a cyan (C) image, and a head that records a black (K) image. The ink ejection heads  30 Y,  30 M,  30 C, and  30 K are, for example, arranged in this order from the upstream side to the downstream side of the conveying belt  50 . The ink ejection heads  30 Y,  30 M,  30 C, and  30 K are respectively linked, via supply tubes (not illustrated), to ink cartridges  32 Y,  32 M,  32 C, and  32 K of respective colors detachably attachable to the inkjet recording apparatus  400 , and the inks of respective colors are supplied to the ink ejection heads from the ink cartridges. 
     Examples of the ink ejection heads  30  include long heads that have an effective recording region (region where nozzles ejecting inks are disposed) having a length equal to or larger than the width (the length in a direction orthogonal to the conveying direction of the recording medium P) of the recording medium P; and short heads that have an effective recording region having a length smaller than the width of the recording medium P and that move in the width direction of the recording medium P as they eject the inks. 
     Examples of the inkjet method employed by the ink ejection heads  30  include a piezoelectric system that utilizes the oscillating pressure from piezoelectric elements; a charge controlling system that ejects the ink by utilizing the electrostatic force of attraction; an acoustic inkjet system that transforms electrical signal into acoustic beams and radiates the acoustic beams to the ink to eject ink by utilizing the radiation pressure; and a thermal inkjet system that heats the ink to form bubbles and utilizes the pressure generated as a result. 
     The ink ejection heads  30  are, for example, low-resolution recording heads that eject ink droplets in the ink droplet amount range of 10 pL or more and 15 pL or less (for example, 600 dpi recording heads) or high-resolution recording heads that eject ink droplets in the ink droplet amount range of less than 10 pL (for example, 1200 dpi recording heads). Here, dpi means “dots per inch”. 
     The inkjet recording apparatus  400  is not limited to a structure equipped with four ink ejection heads. The inkjet recording apparatus  400  may be equipped with more than four ink ejection heads to eject inks of Y, M, C, K, and additional intermediate colors, or may be equipped with one ink ejection head that forms a one-color image. 
     Drying units  34 Y,  34 M,  34 C, and  34 K that respectively correspond to the ink ejection heads of the respective colors are disposed downstream of the ink ejection heads  30  and above the conveying belt  50 . Examples of the drying units  34  include contact-type heating units and hot air blowing units. The structure of the inkjet recording apparatus  400  is not limited to the structure in which one drying unit is provided for each ink ejection head of each color, and may be equipped with only one drying unit downstream of the most downstream ink ejection head. 
     A releasing plate  58  that opposes the driving roll  52  is disposed downstream of the drying units  34 . The releasing plate  58  releases the recording medium P from the conveying belt  50 . 
     A conveying path  62  through which the recording medium P after image recording is conveyed is disposed between the conveying belt  50  and the container  66 , and multiple pairs of rolls  64  that convey the recording medium P are disposed along the conveying path  62 . 
     The operation of the inkjet recording apparatus  400  will now be described. 
     The recording medium P before image recording is taken up by the roll  46  one by one from the container  42 , and is conveyed to the conveying belt  50  by the multiple roll pairs  48 . Next, the recording medium P is electrostatically attached to the conveying belt  50  by the charging roll  56 , and conveyed to the underside of the ink ejection heads  30  by the rotation of the conveying belt  50 . Next, the ink is ejected from the ink ejection heads  30  onto the recording medium P to record an image. Next, the ink on the recording medium P is dried by the drying units  34 . Next, the recording medium P having a dried ink thereon and an image fixed thereon is released from the conveying belt  50  by the releasing plate  58 , and is conveyed to the container  66  by the multiple roll pairs  64 . 
     Sheet for producing printed material and method for producing sheet for producing printed material A sheet for producing a printed material according to an exemplary embodiment includes a substrate and pressure sensitive adhesive particles applied to the substrate. The sheet for producing a printed material according to this exemplary embodiment is produced by using the pressure sensitive adhesive particles of the exemplary embodiment. The pressure sensitive adhesive particles on the substrate may or may not keep the particle shape from before being applied to the substrate. 
     The sheet for producing a printed material according to this exemplary embodiment serves as, for example, a masking sheet to be placed on and bonded to a recording medium to conceal information recorded on the recording medium, or as a releasing sheet used to form an adhesive layer on a recording medium when recording media placed on top of each other are to be bonded. 
     Examples of the substrate that serves as the sheet for producing a printed material according to the exemplary embodiment include paper, coated paper obtained by coating the surface of paper with a resin or the like, cloths, nonwoven cloths, resin films, and resin sheets. The substrate may have an image formed on one or both surfaces. 
     In the sheet for producing a printed material according to this exemplary embodiment, the pressure sensitive adhesive particles may be applied to the entire surface of or one part of the substrate. One layer or two or more layers of the pressure sensitive adhesive particles are applied to the substrate. The layer of the pressure sensitive adhesive particles may be a layer continuous in the surface direction of the substrate or a layer discontinuous in the surface direction of the substrate. The layer of the pressure sensitive adhesive particles may be a layer in which the pressure sensitive adhesive particles are aligned as particles or a layer in which adjacent pressure sensitive adhesive particles are fused and aligned with each other. 
     The amount of the pressure sensitive adhesive particles on the substrate applied in the region is, for example, 0.5 g/m 2  or more and 50 g/m 2  or less, 1 g/m 2  or more and 40 g/m 2  or less, or 1.5 g/m 2  or more and 30 g/m 2  or less. The thickness of the layer of the pressure sensitive adhesive particles on the substrate is, for example, 0.2 μm or more and 25 μm or less, 0.4 μm or more and 20 μm or less, or 0.6 μm or more and 15 μm or less. 
     The sheet for producing a printed material according to the exemplary embodiment is produced by, for example, a production method that includes an applying step of using the pressure sensitive adhesive particles of the exemplary embodiment and applying the pressure sensitive adhesive particles to a substrate. 
     The applying step includes, for example, a placing step of placing the pressure sensitive adhesive particles onto a substrate and, furthermore, a fixing step of fixing the pressure sensitive adhesive particles on the substrate onto the substrate. 
     The placing step is performed by a placing method such as a spraying method, a bar coating method, a die coating method, a knife coating method, a roll coating method, a reverse roll coating method, a gravure coating method, a screen printing method, an ink jet method, a lamination method, or an electrophotographic method, for example. 
     Depending on the placing method employed in the placing step, the pressure sensitive adhesive particles may be dispersed in a dispersion medium to prepare a liquid composition, and the liquid composition may be used the placing step. 
     The fixing step is, for example, a heating step of heating pressure sensitive adhesive particles on the substrate with a heating source to fix the pressure sensitive adhesive particles onto the substrate; a pressurizing step of pressurizing the substrate having the pressure sensitive adhesive particles placed thereon with a pair of pressurizing members (roll/roll or belt/roll) to fix the pressure sensitive adhesive particles onto the substrate; or a pressurizing and heating step of pressurizing and heating a substrate having the pressure sensitive adhesive particles placed thereon with a pair of pressurizing members (roll/roll or belt/roll) equipped with heating sources inside to fix the pressure sensitive adhesive particles onto the substrate. 
     Producing printed material by electrophotographic method An exemplary embodiment in which the pressure sensitive adhesive particles of the exemplary embodiment are used in the electrophotographic method will now be described. In the electrophotographic method, the pressure sensitive adhesive particles are used as a toner for developing an electrostatic charge image (may also be referred simply to as a “toner”). 
     Electrostatic Charge Image Developer 
     An electrostatic charge image developer (may also be referred to as simply the “developer”) of this exemplary embodiment contains at least the pressure sensitive adhesive particles of the exemplary embodiment. The electrostatic charge image developer of the exemplary embodiment may be a one-component developer that contains only the pressure sensitive adhesive particles of the exemplary embodiment or a two-component developer that is a mixture of the pressure sensitive adhesive particles of the exemplary embodiment and a carrier. 
     The carrier is not particularly limited and may be any known carrier. Examples of the carrier include a coated carrier prepared by covering the surface of a magnetic powder core with a resin, a magnetic powder-dispersed carrier prepared by dispersing and blending magnetic powder in a matrix resin, and a resin-impregnated carrier prepared by impregnating porous magnetic powder with a resin. The magnetic powder-dispersed carrier and the resin-impregnated carrier may each be a carrier that has a core being composed of the particles constituting the carrier and having a resin-coated surface. 
     Examples of the magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite. 
     Examples of the resin for coating and the matrix resin include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, a vinyl chloride-vinyl acetate copolymer, a styrene-acrylate copolymer, a straight silicone resin containing an organosiloxane bond and modified products thereof, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. The resin for coating and the matrix resin may contain other additives, such as conductive particles. 
     Examples of the conductive particles include particles of metals such as gold, silver, and copper, and particles of carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate. 
     An example of the method for covering the surface of the core with the resin is a method that involves coating the surface of the core with a coating layer-forming solution prepared by dissolving the resin for coating and various additives (used as needed) in an appropriate solvent. The solvent is not particularly limited and may be selected by considering the type of the resin to be used, suitability of application, etc. 
     Specific examples of the resin coating method include a dipping method involving dipping cores in the coating-layer-forming solution, a spraying method involving spraying the coating-layer-forming solution onto core surfaces, a fluid bed method involving spraying a coating-layer-forming solution while having the cores float on a bed of air, and a kneader coater method involving mixing cores serving as carriers and a coating-layer-forming solution in a kneader coater and then removing the solvent. 
     In a two-component developer, the pressure sensitive adhesive particle-to-carrier mixing ratio (mass ratio) is preferably 1:100 to 30:100 and is more preferably 3:100 to 20:100. 
     Apparatus and method for producing printed material An apparatus for producing a printed material according to an exemplary embodiment that employs an electrophotographic method includes an applying unit that stores a developer that contains the pressure sensitive adhesive particles of the exemplary embodiment and electrophotographically applies the pressure sensitive adhesive particles to a recording medium; and a pressure bonding unit that folds and pressure-bonds the recording medium or pressure-bonds the recording medium and another recording medium stacked on top of each other. 
     The method for producing a printed material of this exemplary embodiment by an electrophotographic method is performed by using the apparatus for producing a printed material of this exemplary embodiment. The method for producing a printed material according to an exemplary embodiment includes an applying step of electrophotographically applying pressure sensitive adhesive particles of the exemplary embodiment to a recording medium by using a developer that contains the pressure sensitive adhesive particles; and a pressure bonding step of folding and pressure-bonding the recording medium or pressure-bonding the recording medium and another recording medium stacked on top of each other. 
     The applying unit included in the apparatus for producing a printed material according to this exemplary embodiment includes, for example, a photoreceptor, a charging unit that charges a surface of the photoreceptor, an electrostatic charge image forming unit that forms an electrostatic charge image on the charged surface of the photoreceptor, a developing unit that stores the electrostatic charge image developer of the exemplary embodiment and develops the electrostatic charge image on the surface of the photoreceptor into a pressure sensitive adhesive particle portion by using the electrostatic charge image developer, and a transfer unit that transfers the pressure sensitive adhesive particle portion on the surface of the photoreceptor onto a surface of a recording medium. 
     The applying unit may further include a fixing unit that fixes the pressure sensitive adhesive particle portion which has been transferred onto the surface of the recording medium. 
     The applying step included in the method for producing a printed material according to this exemplary embodiment includes, for example, a charging step of charging a surface of the photoreceptor, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the photoreceptor, a developing step of developing the electrostatic charge image on the surface of the photoreceptor into a pressure sensitive adhesive particle portion by using the electrostatic charge image developer of the exemplary embodiment, and a transfer step of transferring the pressure sensitive adhesive particle portion on the surface of the photoreceptor onto a surface of a recording medium. The applying step may further include a fixing step of fixing the pressure sensitive adhesive particle portion on the surface of the recording medium. 
     The applying unit is, for example, a direct transfer type device with which a pressure sensitive adhesive particle portion on the surface of the photoreceptor is directly transferred onto a recording medium; an intermediate transfer type device with which a pressure sensitive adhesive particle portion on the surface of the photoreceptor is first transferred onto a surface of an intermediate transfer body and then the pressure sensitive adhesive particle portion on the intermediate transfer body is transferred onto a surface of a recording medium; a device equipped with a cleaning unit that cleans the surface of the photoreceptor before charging and after the transfer of the pressure sensitive adhesive particle portion; and a device equipped with a charge erasing unit that erases charges on the surface of the photoreceptor by applying charge erasing light after the transfer of the pressure sensitive adhesive particle portion and before charging. When the applying unit is of an intermediate transfer type, the transfer unit includes, for example, an intermediate transfer body having a surface onto which a pressure sensitive adhesive particle portion is transferred, a first transfer unit that transfers the pressure sensitive adhesive particle portion on the surface of the photoreceptor onto the surface of the intermediate transfer body, and a second transfer unit that transfers the pressure sensitive adhesive particle portion on the surface of the intermediate transfer body onto a surface of a recording medium. 
     A portion of the applying unit that includes the developing unit may be configurated as a cartridge structure (process cartridge) that is detachably attachable to the applying unit. A process cartridge that stores the electrostatic charge image developer of the exemplary embodiment and is equipped with a developing unit, for example, is suitable as this process cartridge. 
     The pressure bonding unit included in the apparatus for producing a printed material according to this exemplary embodiment applies a pressure to a recording medium to which the pressure sensitive adhesive particles of the exemplary embodiment have been applied. In this manner, the pressure sensitive adhesive particles of the exemplary embodiment become fluidized and exhibit adhesiveness on the recording medium. The pressure that the pressure bonding unit applies to the recording medium to fluidize the pressure sensitive adhesive particles of the exemplary embodiment is preferably 3 MPa or more and 300 MPa or less, more preferably 10 MPa or more and 200 MPa or less, and yet more preferably 30 MPa or more and 150 MPa or less. 
     The pressure sensitive adhesive particles of the exemplary embodiment may be applied to the entire surface of the recording medium or one part of the recording medium. One layer or two or more layers of the pressure sensitive adhesive particles of the exemplary embodiment are applied to the recording medium. The layer of the pressure sensitive adhesive particles of the exemplary embodiment may be a layer continuous in the surface direction of the recording medium or a layer discontinuous in the surface direction of the recording medium. The layer of the pressure sensitive adhesive particles according to the exemplary embodiment may be a layer in which the pressure sensitive adhesive particles are aligned as particles or a layer in which adjacent pressure sensitive adhesive particles are fused and aligned with each other. 
     The amount of the pressure sensitive adhesive particles (preferably, transparent pressure sensitive adhesive particles) of the exemplary embodiment on the recording medium and applied in the region is, for example, 0.5 g/m 2  or more and 50 g/m 2  or less, 1 g/m 2  or more and 40 g/m 2  or less, or 1.5 g/m 2  or more and 30 g/m 2  or less. The thickness of the layer of the pressure sensitive adhesive particles (preferably, transparent pressure sensitive adhesive particles) of the exemplary embodiment on the recording medium is, for example, 0.2 μm or more and 25 μm or less, 0.4 μm or more and 20 μm or less, or 0.6 μm or more and 15 μm or less. 
     Examples of the recording medium used in the apparatus for producing a printed material according to this exemplary embodiment include paper, coated paper obtained by coating the surface of paper with a resin or the like, cloths, nonwoven cloths, resin films, and resin sheets. The recording medium may have an image on one surface or both surfaces. 
     Although some examples of the apparatus for producing a printed material according to the exemplary embodiment employing an electrophotographic system are described below, the exemplary embodiments are not limited to these. 
       FIG. 3  is a schematic diagram of an example of an apparatus for producing a printed material according to this exemplary embodiment. The apparatus for producing a printed material illustrated in  FIG. 3  is equipped with an applying unit  100  and a pressure bonding unit  200  downstream of the applying unit  100 . The arrow indicates the direction in which the photoreceptor rotates or the recording medium is conveyed. 
     The applying unit  100  is of a direct transfer type and uses a developer containing the pressure sensitive adhesive particles of the exemplary embodiment to electrophotographically apply the pressure sensitive adhesive particles of the exemplary embodiment to a recording medium P. The recording medium P has an image formed on one or both surfaces in advance. 
     The applying unit  100  includes a photoreceptor  101 . A charging roll (one example of the charging unit)  102  that charges the surface of the photoreceptor  101 , an exposing device (one example of the electrostatic charge image forming unit)  103  that forms an electrostatic charge image by exposing the charged surface of the photoreceptor  101  with a laser beam, a developing device (one example of the developing unit)  104  that develops the electrostatic charge image by supplying pressure sensitive adhesive particles to the electrostatic charge image, a transfer roll (one example of the transfer unit)  105  that transfers the developed pressure sensitive adhesive particle portion onto the recording medium P, and a photoreceptor cleaning device (one example of the cleaning unit)  106  that removes the pressure sensitive adhesive particles remaining on the surface of the photoreceptor  101  after the transfer are disposed around the photoreceptor  101 . 
     The operation of the applying unit  100  applying the pressure sensitive adhesive particles of the exemplary embodiment to the recording medium P will now be described. 
     First, the surface of the photoreceptor  101  is charged by the charging roll  102 . The exposing device  103  applies a laser beam onto the charged surface of the photoreceptor  101  in accordance to image data sent from a controller (not illustrated). As a result, an electrostatic charge image of an application pattern of the pressure sensitive adhesive particles of this exemplary embodiment is formed on the surface of the photoreceptor  101 . 
     The electrostatic charge image formed on the photoreceptor  101  is rotated to a developing position as the photoreceptor  101  is run. The electrostatic charge image on the photoreceptor  101  is developed by the developing device  104  at this developing position so as to form a pressure sensitive adhesive particle portion. 
     A developer that contains at least the pressure sensitive adhesive particles of this exemplary embodiment and a carrier is stored in the developing device  104 . The pressure sensitive adhesive particles of this exemplary embodiment are frictionally charged as they are stirred with the carrier in the developing device  104 , and are carried on the developer roll. As the surface of the photoreceptor  101  passes the developing device  104 , the pressure sensitive adhesive particles electrostatically adhere to the electrostatic charge image on the surface of the photoreceptor  101 , and the electrostatic charge image is thereby developed with the pressure sensitive adhesive particles. The photoreceptor  101  on which the pressure sensitive adhesive particle portion has been formed is continuously run, and the pressure sensitive adhesive particle portion on the photoreceptor  101  is conveyed to a transfer position. 
     After the pressure sensitive adhesive particle portion on the photoreceptor  101  is conveyed to the transfer position, a transfer bias is applied to the transfer roll  105 . An electrostatic force working from the photoreceptor  101  toward the transfer roll  105  also acts on the pressure sensitive adhesive particle portion, and, thus, the pressure sensitive adhesive particle portion on the photoreceptor  101  is transferred onto the recording medium P. 
     The pressure sensitive adhesive particles remaining on the photoreceptor  101  are removed by the photoreceptor cleaning device  106  and recovered. The photoreceptor cleaning device  106  is, for example, a cleaning blade or a cleaning brush. From the viewpoint of suppressing the phenomenon in which the pressure sensitive adhesive particles of the exemplary embodiment remaining on the surface of the photoreceptor fluidize under a pressure and attach to the surface of the photoreceptor while forming a film, the photoreceptor cleaning device  106  may be a cleaning brush. 
     The recording medium P onto which the pressure sensitive adhesive particle portion has been transferred is conveyed to a fixing device (one example of the fixing unit)  107 . The fixing device  107  is, for example, a pair of fixing members (roll/roll or belt/roll). The applying unit  100  need not be equipped with a fixing device  107 ; however, from the viewpoint of suppressing detachment of the pressure sensitive adhesive particles of the exemplary embodiment from the recording medium P, the applying unit  100  is preferably equipped with a fixing device  107 . The pressure which the fixing device  107  applies to the recording medium P may be lower than the pressure which the pressurizing device  230  applies to the recording medium P2, and may specifically be 0.2 MPa or more and 1 MPa or less. 
     The fixing device  107  may have a heating source (for example, a halogen heater) for heating the recording medium P inside, but this is optional. When the fixing device  107  has a heating source inside, the surface temperature of the recording medium P heated by the heating source is preferably 150° C. or more and 220° C. or less, more preferably 155° C. or more and 210° C. or less, and yet more preferably 160° C. or more and 200° C. or less. The fixing device  107  may have no heating source inside, and this does not exclude that the temperature inside the fixing device  107  increases to a temperature equal to or more than the environment temperature due to heat from a motor in the applying unit  100  or the like. 
     The recording medium P that has passed the applying unit  100  turns into a recording medium P1 having pressure sensitive adhesive particles of the exemplary embodiment applied on the image. The recording medium P1 is conveyed toward the pressure bonding unit  200 . 
     In the apparatus for producing a printed material according to this exemplary embodiment, the applying unit  100  and the pressure bonding unit  200  may be close to each other or distant from each other. When the applying unit  100  and the pressure bonding unit  200  are distant from each other, the applying unit  100  and the pressure bonding unit  200  are, for example, linked via a conveying unit (for example, a belt conveyor) that conveys the recording medium P1. 
     The pressure bonding unit  200  is equipped with a folding device  220  and a pressurizing device  230 , and folds and pressure-bonds the recording medium P1. 
     The folding device  220  folds the recording medium P1 passing therethrough to prepare a folded recording medium P2. The recording medium P2 may be folded in two, in three, or in four, and may be folded only partly. The pressure sensitive adhesive particles of the exemplary embodiment are applied to at least part of at least one of the opposing surfaces of the recording medium P2. 
     The folding device  220  may have a pair of pressurizing members (for example, roll/roll or belt/roll) that apply a pressure to the recording medium P2. The pressure which the pressurizing members of the folding device  220  apply to the recording medium P may be lower than the pressure which the pressurizing device  230  applies to the recording medium P2, and may specifically be 1 MPa or more and 10 MPa or less. 
     The pressure bonding unit  200  may be equipped with a stacking device that stacks another recording medium on top of the recording medium P1 instead of the folding device  220 . Examples of the way in which the recording medium P1 and the additional recording medium are stacked on top of each other include stacking one recording medium on the recording medium P1, and stacking one recording medium on each of multiple regions in the recording medium P1. This additional recording medium may have an image formed on one or both surfaces in advance, may be free of any image, or may be a pressure-bonded printed material prepared in advance. 
     The recording medium P2 exits the folding device  220  (or stacking device) and is conveyed toward the pressurizing device  230 . 
     The pressurizing device  230  is equipped with a pair of pressurizing members (in other words, pressurizing rolls  231  and  232 ). The pressurizing roll  231  and the pressurizing roll  232  contact and push each other at their outer peripheral surfaces to apply a pressure onto the passing recording medium P2. The pair of pressurizing members in the pressurizing device  230  is not limited to the combination of pressurizing rolls, and may be a combination of a pressurizing roll and a pressurizing belt or a combination of a pressurizing belt and a pressurizing belt. 
     When a pressure is applied to the recording medium P2 passing the pressurizing device  230 , the pressure sensitive adhesive particles of the exemplary embodiment on the recording medium P2 are fluidized under pressure and exhibit adhesiveness. The pressure that the pressurizing device  230  applies to the recording medium P2 is preferably 3 MPa or more and 300 MPa or less, more preferably 10 MPa or more and 200 MPa or less, and yet more preferably 30 MPa or more and 150 MPa or less. 
     The pressurizing device  230  may have a heating source (for example, a halogen heater) inside for heating the recording medium P2, but this is optional. When the pressurizing device  230  has a heating source inside, the surface temperature of the recording medium P2 heated by the heating source is preferably 30° C. or more and 120° C. or less, more preferably 40° C. or more and 100° C. or less, and yet more preferably 50° C. or more and 90° C. or less. The pressurizing device  230  may have no heating source inside, and this does not exclude that the temperature inside the pressurizing device  230  increases to a temperature equal to or more than the environment temperature due to heat from a motor in the pressurizing device  230  or the like. 
     As the recording medium P2 passes the pressurizing device  230 , the opposing folded surfaces bond with each other with the fluidized pressure sensitive adhesive particles of the exemplary embodiment, and a pressure-bonded printed material P3 is obtained. The opposing surfaces of the pressure-bonded printed material P3 are partly or entirely bonded to each other. 
     The finished pressure-bonded printed material P3 is discharged from the pressurizing device  230 . 
     A first form of the pressure-bonded printed material P3 is formed of a folded recording medium having opposing surfaces bonded with the pressure sensitive adhesive particles of the exemplary embodiment. The pressure-bonded printed material P3 of this form is produced by the apparatus for producing a printed material equipped with a folding device  220 . 
     A second form of the pressure-bonded printed material P3 is formed of multiple recording media stacked on top of each other and having opposing surfaces bonded with the pressure sensitive adhesive particles of the exemplary embodiment. The pressure-bonded printed material P3 of this form is produced by the pressure-bonded printed material producing apparatus equipped with a stacking device. 
     The apparatus for producing a printed material according to this exemplary embodiment is not limited to a type that continuously conveys the recording medium P2 from the folding device  220  (or stacking device) to the pressurizing device  230 . The apparatus for producing a printed material according to this exemplary embodiment may be of a type that stocks the recording media P2 discharged from the folding device  220  (or stacking device) and conveys the recording media P2 to the pressurizing device  230  after a predetermined amount of the recording media P2 are stored. 
     In the apparatus for producing a printed material according to this exemplary embodiment, the folding device  220  (or stacking device) and the pressurizing device  230  may be close to each other or distant from each other. When the folding device  220  (or stacking device) and the pressurizing device  230  are distant from each other, the folding device  220  (or stacking device) and the pressurizing device  230  are, for example, linked via a conveying unit (for example, a belt conveyor) that conveys the recording medium P2. 
     The apparatus for producing a printed material according to this exemplary embodiment may be equipped with a cutting unit that cuts the recording medium into a predetermined size. Examples of the cutting unit include a cutting unit that is disposed between the applying unit  100  and the pressure bonding unit  200  and cuts off a part of the recording medium P1, the part being a region where no pressure sensitive adhesive particles of the exemplary embodiment are applied; a cutting unit that is disposed between the folding device  220  and the pressurizing device  230  and cuts off a part of the recording medium P2, the part being a region where no pressure sensitive adhesive particles of the exemplary embodiment are applied; and a cutting unit that is disposed downstream of the pressure bonding unit  200  and cuts off a part of the pressure-bonded printed material P3, the part being a region not bonded with the pressure sensitive adhesive particles of the exemplary embodiment. 
     The apparatus for producing a printed material according to this exemplary embodiment is not limited to a single-sheet type. The apparatus for producing a printed material according to this exemplary embodiment may be of a type that performs an applying step and a pressure bonding step on a long recording medium to form a long pressure-bonded printed material, and then cuts the long pressure-bonded printed material into a predetermined size. 
     The apparatus for producing a printed material according to this exemplary embodiment may further include a color image forming unit that forms a color image on a recording medium by an electrophotographic method by using a color electrostatic charge image developer. The color image forming unit is equipped with, for example, a photoreceptor, a charging unit that charges a surface of the photoreceptor, an electrostatic charge image forming unit that forms an electrostatic charge image on the charged surface of the photoreceptor, a developing unit that stores a color electrostatic charge image developer and develops the electrostatic charge image on the surface of the photoreceptor into a color toner image by using the color electrostatic charge image developer, a transfer unit that transfers the color toner image on the surface of the photoreceptor onto a surface of a recording medium, and a thermal fixing unit that thermally fixes the color toner image transferred onto the surface of the recording medium. 
     The above-described production apparatus is used to implement the method for producing a printed material of the exemplary embodiment, the method further including a color image forming step of forming a color image on the recording medium by an electrophotographic method using a color electrostatic charge image developer. The color image forming step includes, specifically, a charging step of charging a surface of a photoreceptor, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the photoreceptor, a developing step of developing the electrostatic charge image on the surface of the photoreceptor into a color toner image by using a color electrostatic charge image developer, a transfer step of transferring the color toner image on the surface of the photoreceptor onto a surface of a recording medium, and a thermal fixing step of thermally fixing the color toner image transferred onto the surface of the recording medium. 
     Examples of the color image forming unit included in the apparatus for producing a printed material according to the exemplary embodiment include: a direct transfer type device with which a color toner image on the surface of the photoreceptor is directly transferred onto a recording medium; an intermediate transfer type device with which a color toner image on the surface of the photoreceptor is first transferred onto a surface of an intermediate transfer body and then the color toner image on the intermediate transfer body is transferred onto a surface of a recording medium; a device equipped with a cleaning unit that cleans the surface of the photoreceptor before charging and after the transfer of the color toner image; and a device equipped with a charge erasing unit that erases charges on the surface of the photoreceptor by applying charge erasing light after the transfer of the color toner image and before charging. When the color image forming unit is an intermediate transfer type device, the transfer unit has, for example, an intermediate transfer body having a surface to which a color toner image is transferred, a first transfer unit that transfers (first transfer) the color toner image on the surface of the photoreceptor onto a surface of the intermediate transfer body, and a second transfer unit that transfers (second transfer) the color toner image on the surface of the intermediate transfer body onto a surface of a recording medium. 
     In the apparatus for producing a printed material according to this exemplary embodiment, when the applying unit for applying a developer containing the pressure sensitive adhesive particles of the exemplary embodiment and a color image forming unit both employ an intermediate transfer method, the applying unit and the color image forming unit may share the intermediate transfer body and the second transfer unit. 
     In the apparatus for producing a printed material according to this exemplary embodiment, the applying unit that applies an image developer containing the pressure sensitive adhesive particles of the exemplary embodiment and the color image forming unit may share the thermal fixing unit. 
     Other examples of the apparatus for producing a printed material according to the exemplary embodiment equipped with a color image forming unit are described below, but these examples are not limiting. Only relevant parts illustrated in the drawing are described in the description below, and descriptions of other parts are omitted. 
       FIG. 4  is a schematic diagram of an example of an apparatus for producing a printed material according to this exemplary embodiment employing an electrophotographic system. The apparatus for producing a printed material illustrated in  FIG. 4  is equipped with a printing unit  300  that applies the pressure sensitive adhesive particles of the exemplary embodiment to a recording medium and forms a color image on the recording medium, and a pressure bonding unit  200  disposed downstream of the printing unit  300 . 
     The printing unit  300  is a five-stand-tandem intermediate transfer-type printing unit. The printing unit  300  is equipped with a unit  10 T that applies the pressure sensitive adhesive particles (T) of the exemplary embodiment, and units  10 Y,  10 M,  10 C, and  10 K that respectively form yellow (Y), magenta (M), cyan (C) black (K) images. The unit  10 T is the applying unit that applies the pressure sensitive adhesive particles of the exemplary embodiment to the recording medium P by using a developer that contains the pressure sensitive adhesive particles of the exemplary embodiment. Each of the units  10 Y,  10 M,  10 C, and  10 K is a unit that forms a color image on the recording medium P by using a developer that contains a color toner. 
     The units  10 T,  10 Y,  10 M,  10 C, and  10 K employ an electrophotographic system. 
     The units  10 T,  10 Y,  10 M,  10 C, and  10 K are disposed side by side with spaces therebetween in the horizontal direction. The units  10 T,  10 Y,  10 M,  10 C, and  10 K may each be a process cartridge detachably attachable to the printing unit  300 . 
     An intermediate transfer belt (one example of the intermediate transfer body)  20  extends below and throughout the units  10 T,  10 Y,  10 M,  10 C, and  10 K. The intermediate transfer belt  20  is wound around a driving roll  22 , a supporting roll  23 , and a counter roll  24  that are in contact with the inner surface of the intermediate transfer belt  20 , and runs in a direction from the unit  10 T to the unit  10 K. An intermediate transfer body cleaning device  21  is installed on the image carrying surface side of the intermediate transfer belt  20  so as to face the driving roll  22 . 
     The units  10 T,  10 Y,  10 M,  10 C, and  10 K are respectively equipped with developing devices (examples of the developing units)  4 T,  4 Y,  4 M,  4 C, and  4 K. The pressure sensitive adhesive particles of the exemplary embodiment stored in the pressure sensitive adhesive particle cartridge  8 T, and, a yellow toner, a magenta toner, a cyan toner, and a black toner stored in the cartridges  8 Y,  8 M,  8 C, and  8 K are respectively supplied to the developing devices  4 T,  4 Y,  4 M,  4 C, and  4 K. 
     Since the units  10 T,  10 Y,  10 M,  10 C and  10 K are identical in structure and in operation, the unit  10 T that applies the pressure sensitive adhesive particles of this exemplary embodiment to the recording medium is described as a representative example. 
     The unit  10 T has a photoreceptor  1 T. A charging roll (one example of the charging unit)  2 T that charges the surface of the photoreceptor  1 T, an exposing device (one example of the electrostatic charge image forming unit)  3 T that forms an electrostatic charge image by exposing the charged surface of the photoreceptor  1 T with a laser beam, a developing device (one example of the developing unit)  4 T that develops the electrostatic charge image by supplying pressure sensitive adhesive particles to the electrostatic charge image, a first transfer roll (one example of the first transfer unit)  5 T that transfers the developed pressure sensitive adhesive particle portion onto the intermediate transfer belt  20 , and a photoreceptor cleaning device (one example of the cleaning unit)  6 T that removes the pressure sensitive adhesive particles remaining on the surface of the photoreceptor  1 T after the first transfer are provided in that order around the photoreceptor  1 T. The first transfer roll  5 T is disposed on the inner side of the intermediate transfer belt  20  and is positioned to face the photoreceptor  1 T. 
     In the description below, operation of applying the pressure sensitive adhesive particles of the exemplary embodiment and formation of a color image on the recording medium P is described by using the operation of the unit  10 T as an example. 
     First, the surface of the photoreceptor  1 T is charged by the charging roll  2 T. The developing device  3 T applies a laser beam onto the charged surface of the photoreceptor  1 T in accordance to image data sent from a controller (not illustrated). As a result, an electrostatic charge image of an application pattern of the pressure sensitive adhesive particles of this exemplary embodiment is formed on the surface of the photoreceptor  1 T. 
     The electrostatic charge image formed on the photoreceptor  1 T is rotated to a developing position as the photoreceptor  1 T is run. The electrostatic charge image on the photoreceptor  1 T is developed by the developing device  4 T at this developing position so as to form a pressure sensitive adhesive particle portion. 
     A developer that contains at least the pressure sensitive adhesive particles of this exemplary embodiment and a carrier is stored in the developing device  4 T. The pressure sensitive adhesive particles of this exemplary embodiment are frictionally charged as they are stirred with the carrier in the developing device  4 T, and are carried on the developer roll. As the surface of the photoreceptor  1 T passes the developing device  4 T, the pressure sensitive adhesive particles electrostatically adhere to the electrostatic charge image on the surface of the photoreceptor  1 T, and the electrostatic charge image is thereby developed with the pressure sensitive adhesive particles. The photoreceptor  1 T on which the pressure sensitive adhesive particle portion has been formed is continuously run, and the pressure sensitive adhesive particle portion on the photoreceptor  1 T is conveyed to a first transfer position. 
     After the pressure sensitive adhesive particle portion on the photoreceptor  1 T is conveyed to the first transfer position, a first transfer bias is applied to the first transfer roll  5 T. An electrostatic force working from the photoreceptor  1 T toward the first transfer roll  5 T also acts on the pressure sensitive adhesive particle portion, and, thus, the pressure sensitive adhesive particle portion on the photoreceptor  1 T is transferred onto the intermediate transfer belt  20 . The pressure sensitive adhesive particles remaining on the photoreceptor  1 T are removed by the photoreceptor cleaning device  6 T and recovered. The photoreceptor cleaning device  6 T is, for example, a cleaning blade or a cleaning brush, and is preferably a cleaning brush. 
     An operation similar to that performed in the unit  10 T is also performed in the units  10 Y,  10 M,  10 C, and  10 K by using developers that contain color toners. The intermediate transfer belt  20  onto which the pressure sensitive adhesive particle portion has been transferred in the unit  10 T sequentially passes the units  10 Y,  10 M,  10 C, and  10 K, and toner images of respective colors are transferred (multi-layer transfer) onto the intermediate transfer belt  20 . 
     The intermediate transfer belt  20  onto which the pressure sensitive adhesive particle portion and the toner images are transferred and superposed as the intermediate transfer belt  20  passes the units  10 T,  10 Y,  10 M,  10 C, and  10 K reaches a second transfer portion constituted by the intermediate transfer belt  20 , the counter roll  24  in contact with the inner surface of the intermediate transfer belt  20 , and a second transfer roll (one example of the second transfer unit)  26  disposed on the image carrying surface side of the intermediate transfer belt  20 . 
     Meanwhile, a recording medium P is supplied to a gap where the second transfer roll  26  and the intermediate transfer belt  20  contact each other via a supplying mechanism, and a second transfer bias is applied to the counter roll  24 . During this process, an electrostatic force working from the intermediate transfer belt  20  toward the recording medium P and the toner images acts on the pressure sensitive adhesive particle portion, and the pressure sensitive adhesive particle portion and the toner images on the intermediate transfer belt  20  are transferred onto the recording medium P. 
     The recording medium P onto which the pressure sensitive adhesive particle portion and the toner images have been transferred is conveyed to a thermal fixing device (one example of the thermal fixing unit)  28 . The thermal fixing device  28  is equipped with a heating source such as a halogen heater, and heats the recording medium P. The surface temperature of the recording medium P when heated by the thermal fixing device  28  is preferably 150° C. or more and 220° C. or less, more preferably 155° C. or more and 210° C. or less, and yet more preferably 160° C. or more and 200° C. or less. As the recording medium P passes the thermal fixing device  28 , the color toner images are thermally fixed to the recording medium P. 
     From the viewpoints of suppressing detachment of the pressure sensitive adhesive particles of the exemplary embodiment from the recording medium P and improving the fixability of the color image to the recording medium P, the thermal fixing device  28  may be a device that applies heat and pressure, for example, a pair of fixing members (roll/roll or belt/roll) equipped with heating sources inside. When the thermal fixing device  28  is to apply pressure, the pressure which the thermal fixing device  28  applies to the recording medium P may be lower than the pressure which the pressurizing device  230  applies to the recording medium P2, and may specifically be 0.2 MPa or more and 1 MPa or less. 
     The recording medium P passes the printing unit  300  and turns into a recording medium P1 on which color images and the pressure sensitive adhesive particles of the exemplary embodiment are placed. The recording medium P1 is conveyed toward the pressure bonding unit  200 . 
     The structure of the pressure bonding unit  200  illustrated in  FIG. 4  may be the same as that of the pressure bonding unit  200  illustrated in  FIG. 3 , and the detailed descriptions of the structure and the operation of the pressure bonding unit  200  are omitted. 
     In the apparatus for producing a printed material according to this exemplary embodiment, the printing unit  300  and the pressure bonding unit  200  may be close to each other or distant from each other. When the printing unit  300  and the pressure bonding unit  200  are distant from each other, the printing unit  300  and the pressure bonding unit  200  are, for example, linked via a conveying unit (for example, a belt conveyor) that conveys the recording medium P1. 
     The apparatus for producing a printed material according to this exemplary embodiment may be equipped with a cutting unit that cuts the recording medium into a predetermined size. Examples of the cutting unit include a cutting unit that is disposed between the printing unit  300  and the pressure bonding unit  200  and cuts off a part of the recording medium P1, the part being a region where no pressure sensitive adhesive particles of the exemplary embodiment are applied; a cutting unit that is disposed between the folding device  220  and the pressurizing device  230  and cuts off a part of the recording medium P2, the part being a region where no pressure sensitive adhesive particles of the exemplary embodiment are applied; and a cutting unit that is disposed downstream of the pressure bonding unit  200  and cuts off a part of the pressure-bonded printed material P3, the part being a region not bonded with the pressure sensitive adhesive particles of the exemplary embodiment. 
     The apparatus for producing a printed material according to this exemplary embodiment is not limited to a single-sheet type. The apparatus for producing a printed material according to this exemplary embodiment may be of a type that performs a color image forming step, an applying step, and a pressure bonding step on a long recording medium to form a long pressure-bonded printed material, and then cuts the long pressure-bonded printed material into a predetermined size. 
     Process Cartridge 
     A process cartridge used in an apparatus for producing a printed material by an electrophotographic method will now be described. 
     A process cartridge according to an exemplary embodiment is equipped with a developing unit that stores the electrostatic charge image developer of the exemplary embodiment and develops an electrostatic charge image on the surface of a photoreceptor into a pressure sensitive adhesive particle portion by using the electrostatic charge image developer, and is detachably attached to the apparatus for producing a printed material. 
     The process cartridge of this exemplary embodiment may be configured to include a developing unit and, if needed, at least one selected from a photoreceptor, a charging unit, an electrostatic charge image forming unit, a transfer unit, and other units. 
     An example of the process cartridge is a cartridge in which a photoreceptor, and a charging roll (one example of the charging unit), a developing device (one example of the developing unit), and a photoreceptor cleaning device (one example of the cleaning unit) disposed around the photoreceptor are integrated by a casing. The casing has an opening to allow exposure. The casing has an installation rail, and the process cartridge is installed to the apparatus for producing a printed material by using the installation rail. 
     EXAMPLES 
     The exemplary embodiments of the present disclosure will now be described in detail through examples, but the present disclosure is not limited by these examples. In the description below, “parts” and “%” are on a mass basis unless otherwise noted. 
     Preparation of Dispersion Containing Styrene Resin Particles 
     Preparation of Styrene Resin Particle Dispersion (St1) 
     Styrene: 390 parts 
     n-Butyl acrylate: 100 parts Acrylic acid: 10 parts 
     Dodecanethiol: 7.5 parts 
     The above-described materials are mixed and dissolved to prepare a monomer solution. 
     In 205 parts of ion exchange water, 8 parts of an anionic surfactant (DOWFAX 2A1 produced by The Dow Chemical Company) is dissolved, and is dispersed and emulsified by adding the aforementioned monomer solution to obtain an emulsion. 
     In 462 parts of ion exchange water, 2.2 part of an anionic surfactant (DOWFAX 2A1 produced by The Dow Chemical Company) is dissolved. The resulting solution is charged into a polymerization flask equipped with a stirrer, a thermometer, a reflux cooling tube, and a nitrogen inlet tube and is heated to 73° C. under stirring, and the temperature is retained thereat. 
     In 21 parts of ion exchange water, 3 parts of ammonium persulfate is dissolved, and the resulting solution is added dropwise to the aforementioned polymerization flask over a period of 15 minutes via a metering pump. Then, the aforementioned emulsion is added dropwise thereto over a period of 160 minutes via a metering pump. 
     Subsequently, while slow stirring is continued, the polymerization flask is retained at 75° C. for 3 hours, and then the temperature is returned to room temperature. 
     As a result, a styrene resin particle dispersion (St1) that contains styrene resin particles having a volume-average particle diameter (D50v) of 174 nm, a weight-average molecular weight of 49000 as determined by GPC (UV detection), and a glass transition temperature of 54° C., and that has a solid content of 42% is obtained. 
     The styrene resin particle dispersion (St1) is dried to obtain styrene resin particles, and the thermal behavior in the temperature range of −100° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). One glass transition temperature is observed. Table 1 indicates the glass transition temperatures. 
     Preparation of Styrene Resin Particle Dispersions (St2) to (St13) 
     Styrene resin particle dispersions (St2) to (St13) are prepared as with the preparation of the styrene resin particle dispersion (St1) except that the monomers are changed as indicated in Table 1. 
     The compositions and the physical properties of the styrene resin particle dispersion (St1) etc., are indicated in Table 1. In Table 1, the monomers are abbreviated as follows. 
     Styrene: St, n-butyl acrylate: BA, 2-ethylhexyl acrylate: 2EHA, ethyl acrylate: EA, 4-hydroxybutyl acrylate: 4HBA, acrylic acid: AA, methacrylic acid: MAA, 2-carboxyethyl acrylate: CEA 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Styrene resin particle dispersion 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 D50v of 
                   
                   
               
               
                   
                   
                 resin 
                 Mw 
               
               
                   
                 Polymerization components (mass ratio) 
                 particles 
                 (k) 
                 Tg 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 St 
                 BA 
                 2EHA 
                 EA 
                 4HBA 
                 AA 
                 MAA 
                 CEA 
                 nm 
                 — 
                 ° C. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 St1 
                 78 
                 20 
                 0 
                 0 
                 0 
                 2 
                 0 
                 0 
                 174 
                 49 
                 54 
               
               
                 St2 
                 88 
                 10 
                 0 
                 0 
                 0 
                 2 
                 0 
                 0 
                 170 
                 50 
                 76 
               
               
                 St3 
                 83 
                 15 
                 0 
                 0 
                 0 
                 2 
                 0 
                 0 
                 172 
                 52 
                 65 
               
               
                 St4 
                 78 
                 20 
                 0 
                 0 
                 0 
                 0 
                 2 
                 0 
                 177 
                 48 
                 57 
               
               
                 St5 
                 80 
                 15 
                 0 
                 0 
                 5 
                 0 
                 0 
                 0 
                 172 
                 46 
                 55 
               
               
                 St6 
                 80 
                 15 
                 5 
                 0 
                 0 
                 0 
                 0 
                 0 
                 174 
                 51 
                 54 
               
               
                 St7 
                 80 
                 20 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 169 
                 50 
                 54 
               
               
                 St8 
                 77 
                 20 
                 0 
                 0 
                 0 
                 0 
                 0 
                 3 
                 168 
                 48 
                 54 
               
               
                 St9 
                 72 
                 26 
                 0 
                 0 
                 0 
                 2 
                 0 
                 0 
                 172 
                 55 
                 43 
               
               
                 St10 
                 68 
                 30 
                 0 
                 0 
                 0 
                 2 
                 0 
                 0 
                 173 
                 53 
                 35 
               
               
                 St11 
                 80 
                 0 
                 20 
                 0 
                 0 
                 0 
                 0 
                 0 
                 171 
                 52 
                 56 
               
               
                 St12 
                 78 
                 0 
                 20 
                 0 
                 0 
                 2 
                 0 
                 0 
                 167 
                 49 
                 56 
               
               
                 St13 
                 63 
                 0 
                 0 
                 35 
                 0 
                 2 
                 0 
                 0 
                 169 
                 51 
                 54 
               
               
                   
               
            
           
         
       
     
     Preparation of Dispersion Containing Composite Resin Particles 
     Preparation of Composite Resin Particle Dispersion (M1) 
     Styrene resin particle dispersion (St1): 1190 parts (solid content: 500 parts) 
     2-Ethylhexyl acrylate: 250 parts 
     n-Butyl acrylate: 250 parts 
     Ion exchange water: 982 parts 
     The above-described materials are charged into a polymerization flask, stirred at 25° C. for 1 hour, and heated to 70° C. 
     In 75 parts of ion exchange water, 2.5 parts of ammonium persulfate is dissolved, and the resulting solution is added dropwise to the aforementioned polymerization flask over a period of 60 minutes via a metering pump. 
     Subsequently, while slow stirring is continued, the polymerization flask is retained at 70° C. for 3 hours, and then the temperature is returned to room temperature. 
     As a result, a composite resin particle dispersion (M1) that contains composite resin particles having a volume-average particle diameter (D50v) of 219 nm and a weight-average molecular weight of 219000 as determined by GPC (UV detection) and that has a solid content of 32% is obtained. 
     The composite resin particle dispersion (M1) is dried to obtain composite resin particles, and the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed. Table 2 indicates the glass transition temperatures. 
     Preparation of Composite Resin Particle Dispersions (M2) to (M21) and (cM1) to (cM3) 
     Composite resin particle dispersions (M2) to (M21) and (cM1) to (cM3) are prepared as with the preparation of the composite resin particle dispersion (M1) except that the styrene resin particle dispersion (St1) is changed as described in Table 2 or that the polymerization components of the (meth)acrylate resin are changed as described in Table 2. 
     The compositions and the physical properties of the composite resin particle dispersion (M1) etc., are indicated in Table 2. In Table 2, the monomers are abbreviated as follows. 
     Styrene: St, n-butyl acrylate: BA, 2-ethylhexyl acrylate: 2EHA, ethyl acrylate: EA, 4-hydroxybutyl acrylate: 4HBA, acrylic acid: AA, methacrylic acid: MAA, 2-carboxyethyl acrylate: CEA, hexyl acrylate: HA, propyl acrylate: PA 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Composite resin particle dispersion 
               
            
           
           
               
               
            
               
                   
                 Composite resin particles (or 
               
               
                   
                 comparative resin particles) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 St resin 
                   
                 St resin-to- 
                 D50v of 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 St resin 
                 Ac resin 
                 Ac resin 
                 resin 
                 Mw 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 particle 
                 Polymerization 
                 Tg 
                 Polymerization 
                 mass ratio 
                 particles 
                 (k) 
                 Tg 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 dispersion 
                 components 
                 ° C. 
                 components 
                 (St:Ac) 
                 nm 
                 — 
                 ° C. 
                 ° C. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 cM1 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA = 100 
                 50:50 
                 222 
                 230 
                 −50 
                 54 
               
               
                 cM2 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 BA = 100 
                 50:50 
                 225 
                 220 
                 −53 
                 54 
               
               
                 cM3 
                 St12 
                 St/2EHA/AA = 78/20/2 
                 56 
                 BA = 100 
                 50:50 
                 224 
                 212 
                 −53 
                 56 
               
               
                 M1 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 219 
                 219 
                 −52 
                 54 
               
               
                 M2 
                 St2 
                 St/BA/AA = 88/10/2 
                 76 
                 2EHA/BA = 50/50 
                 50:50 
                 218 
                 240 
                 −52 
                 76 
               
               
                 M3 
                 St3 
                 St/BA/AA = 83/15/2 
                 65 
                 2EHA/BA = 50/50 
                 50:50 
                 220 
                 231 
                 −52 
                 65 
               
               
                 M4 
                 St4 
                 St/BA/MAA = 78/20/2 
                 57 
                 2EHA/BA = 50/50 
                 50:50 
                 221 
                 250 
                 −52 
                 57 
               
               
                 M5 
                 St5 
                 St/BA/4HBA = 80/15/5 
                 55 
                 2EHA/BA = 50/50 
                 50:50 
                 224 
                 242 
                 −52 
                 55 
               
               
                 M6 
                 St6 
                 St/BA/2EHA = 80/15/5 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 225 
                 233 
                 −52 
                 54 
               
               
                 M7 
                 St7 
                 St/BA = 80/20 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 224 
                 243 
                 −52 
                 54 
               
               
                 M8 
                 St8 
                 St/BA/CEA = 77/20/3 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 222 
                 260 
                 −52 
                 54 
               
               
                 M9 
                 St9 
                 St/BA/AA = 72/26/2 
                 43 
                 2EHA/BA = 50/50 
                 50:50 
                 223 
                 251 
                 −52 
                 43 
               
               
                 M10 
                 St10 
                 St/BA/AA = 68/30/2 
                 35 
                 2EHA/BA = 50/50 
                 50:50 
                 220 
                 243 
                 −52 
                 35 
               
               
                 M11 
                 St11 
                 St/2EHA = 80/20 
                 56 
                 2EHA/BA = 50/50 
                 50:50 
                 221 
                 249 
                 −52 
                 56 
               
               
                 M12 
                 St12 
                 St/2EHA/AA = 78/20/2 
                 56 
                 2EHA/BA = 50/50 
                 50:50 
                 227 
                 237 
                 −52 
                 56 
               
               
                 M13 
                 St12 
                 St/2EHA/AA = 78/20/2 
                 56 
                 2EHA/HA = 50/50 
                 50:50 
                 224 
                 226 
                 −55 
                 56 
               
               
                 M14 
                 St13 
                 St/EA/AA = 63/35/2 
                 54 
                 2EHA/PA = 50/50 
                 50:50 
                 224 
                 243 
                 −45 
                 54 
               
               
                 M15 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/HA = 50/50 
                 50:50 
                 226 
                 270 
                 −54 
                 54 
               
               
                 M16 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 90/10 
                 50:50 
                 224 
                 264 
                 −51 
                 54 
               
               
                 M17 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 80/20 
                 50:50 
                 226 
                 248 
                 −52 
                 54 
               
               
                 M18 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 70/30 
                 50:50 
                 226 
                 260 
                 −52 
                 54 
               
               
                 M19 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 30/70 
                 50:50 
                 225 
                 273 
                 −52 
                 54 
               
               
                 M20 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 20/80 
                 50:50 
                 224 
                 233 
                 −52 
                 54 
               
               
                 M21 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 10/90 
                 50:50 
                 223 
                 243 
                 −53 
                 54 
               
               
                   
               
            
           
         
       
     
     Preparation of Composite Resin Particle Dispersions (M28) to (M30) 
     Composite resin particle dispersions (M28) to (M30) containing composite resin particles having different weight average molecular weights are prepared as with the preparation of the composite resin particle dispersion (M1) except that the amount of ammonium persulfate is changed as indicated in Table 3. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Ammonium persulfate 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 M28 
                 3.0 parts 
               
               
                   
                 M29 
                 5.0 parts 
               
               
                   
                 M30 
                 7.5 parts 
               
               
                   
                   
               
            
           
         
       
     
     The compositions and the physical properties of the composite resin particle dispersion (M28) etc., are indicated in Table 4. In Table 4, the monomers are abbreviated as follows. 
     Styrene: St, n-butyl acrylate: BA, acrylic acid: AA, 2-ethyhexyl acrylate: 2EHA 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Composite resin particle dispersion 
               
            
           
           
               
               
            
               
                   
                 Composite resin particles 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 St resin 
                   
                 St resin-to- 
                 D50v of 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 St resin 
                 Ac resin 
                 Ac resin 
                 resin 
                 Mw 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 particle 
                 Polymerization 
                 Tg 
                 Polymerization 
                 mass ratio 
                 particles 
                 (k) 
                 Tg 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 dispersion 
                 components 
                 ° C. 
                 components 
                 (St:Ac) 
                 nm 
                 — 
                 ° C. 
                 ° C. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 M28 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 219 
                 150 
                 −52 
                 54 
               
               
                 M29 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 219 
                 100 
                 −52 
                 54 
               
               
                 M30 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 219 
                 60 
                 −52 
                 54 
               
               
                   
               
            
           
         
       
     
     Preparation of Pressure Sensitive Adhesive Particle 
     Preparation of Pressure Sensitive Adhesive Particle (1) 
     Composite resin particle dispersion (M1): 504 parts 
     Ion exchange water: 710 parts 
     Anionic surfactant (DOWFAX 2A1 produced by The Dow Chemical Company): 1 part 
     The above-described materials are placed in a reactor equipped with a thermometer and a pH meter, and the pH is adjusted to 3.0 by adding a 1.0% aqueous nitric acid solution at a temperature of 25° C. Then, while the resulting mixture is dispersed in a homogenizer (ULTRA-TURRAX T50 produced by IKA Japan) at a rotation rate of 5000 rpm, 23 parts of a 2.0% aqueous aluminum sulfate solution is added. Subsequently, a stirrer and a heating mantle are attached to the reactor. The temperature is elevated at a temperature elevation rate of 0.2° C./minute up to a temperature of 40° C. and then at 0.05° C./minute beyond 40° C. The particle diameter is measured every 10 minutes with MULTISIZER II (aperture diameter: 50 μm, produced by Beckman Coulter Inc.). The temperature is retained when the volume-average particle diameter reached 5.0 μm, and 170 parts of the styrene resin particle dispersion (St1) is added thereto over a period of 5 minutes. After completion of addition, a temperature of 50° C. is held for 30 minutes, a 1.0% aqueous sodium hydroxide solution is added thereto, and the pH of the slurry is adjusted to 6.0. Subsequently, while the pH is adjusted to 6.0 every 5° C., the temperature is elevated at a temperature elevation rate of 1° C./minute up to 90° C., and the temperature is retained at 90° C. The particle shape and the surface property are observed with an optical microscope and a field emission-type scanning electron microscope (FE-SEM), and coalescence of particles is confirmed at the 10th hour. The reactor is then cooled with cooling water over a period of 5 minutes to 30° C. 
     The cooled slurry is passed through a nylon mesh having 15 μm opening to remove coarse particles, and the slurry that has passed through the mesh is filtered at a reduced pressure by using an aspirator. The solid matter remaining on the paper filter is manually pulverized as finely as possible and is added to ion exchange water (temperature: 30° C.) in an amount ten times the amount of the solid matter. The resulting mixture is stirred for 30 minutes. Subsequently, the solid matter remaining on the paper filter after filtration at a reduced pressure in an aspirator is pulverized manually as finely as possible and is added to ion exchange water (temperature: 30° C.) in an amount ten times the amount of the solid matter. The resulting mixture is stirred for 30 minutes and is again filtered at a reduced pressure with an aspirator. The electrical conductivity of the filtrate is measured. This operation is repeated until the electrical conductivity of the filtrate is 10 μS/cm or less so as to wash the solid matter. 
     The washed solid matter is finely pulverized in a wet-dry-type particle sizer (Comil) and then vacuum-dried in an oven at 25° C. for 36 hours. As a result, pressure sensitive adhesive base particles (1) is obtained. The volume-average particle diameter of the pressure sensitive adhesive base particles (1) is 8.0 μm. 
     One hundred parts of the pressure sensitive adhesive base particles (1) and 1.5 parts of hydrophobic silica (RY50 produced by Nippon Aerosil Co., Ltd.) are mixed, and the resulting mixture is mixed in a sample mill at 13000 rpm for 30 seconds. The mixture is then screened through a vibrating screen having 45 μm openings. As a result, pressure sensitive adhesive particles (1) are obtained. 
     Using the pressure sensitive adhesive particle (1) as a sample, the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed. Table 5 indicates the glass transition temperatures. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (1) are measured by the aforementioned measuring method, and the pressure sensitive adhesive particles (1) satisfy formula 1, “10° C. T1−T2”. 
     A cross section of the pressure sensitive adhesive particle (1) is observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particle (1) has a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases is indicated in Table 5. 
     The area ratio of the island phases in a cross section of the pressure sensitive adhesive particle (1) is in the range of 30% or more and 85% or less. 
     Preparation of Pressure Sensitive Adhesive Particles (2) to (21) 
     The pressure sensitive adhesive particles (2) to (21) are prepared as with the preparation of the pressure sensitive adhesive particle (1) except that the composite resin particle dispersion and the styrene resin particle dispersion are changed as indicated in Table 5. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (2) to (21) are measured by the aforementioned measuring method, and all of the pressure sensitive adhesive particles (2) to (21) satisfy formula 1, “10° C.≤T1−T2”. 
     Cross sections of the pressure sensitive adhesive particles (2) to (21) are observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particles (2) to (21) have a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases is indicated in Table 5. 
     In the cross sections of the pressure sensitive adhesive particles (2) to (21), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Preparation of Pressure Sensitive Adhesive Particles (28) to (30) 
     The pressure sensitive adhesive particles (28) to (30) are prepared as with the preparation of the pressure sensitive adhesive particle (1) except that the composite resin particle dispersion is changed as indicated in Table 6. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (28) to (30) are measured by the aforementioned measuring method, and all of the pressure sensitive adhesive particles (28) to (30) satisfy formula 1, “10° C.≤T1−T2”. 
     Cross sections of the pressure sensitive adhesive particles (28) to (30) are observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particles (28) to (30) have a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases is indicated in Table 6. 
     In the cross sections of the pressure sensitive adhesive particles (28) to (30), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Preparation of Pressure Sensitive Adhesive Particle (31) 
     Pressure sensitive adhesive base particles are prepared by the following crushing method. 
     The composite resin particle dispersion (M1) is dried to obtain composite resin particles (M31). The composite resin particles (M31) are heat-kneaded in an extruder at a set temperature of 100° C., cooled, and then crushed and classified to obtain pressure sensitive adhesive base particles (31) having a volume-average particle diameter of 8.0 μm. 
     One hundred parts of the pressure sensitive adhesive base particles (31) and 1.5 parts of hydrophobic silica (RY50 produced by Nippon Aerosil Co., Ltd.) are mixed, and the resulting mixture is mixed in a sample mill at 13000 rpm for 30 seconds. The mixture is then screened through a vibrating screen having 45 μm openings. As a result, pressure sensitive adhesive particles (31) are obtained. 
     Using the pressure sensitive adhesive particle (31) as a sample, the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed. Table 6 indicates the glass transition temperatures. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (31) are measured by the aforementioned measuring method, and the pressure sensitive adhesive particles (31) satisfy formula 1, “10° C.≤T1−T2”. 
     A cross section of the pressure sensitive adhesive particle (31) is observed with a scanning electron microscope (SEM). A sea-island structure is observed. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases is indicated in Table 6. 
     The area ratio of the island phases in a cross section of the pressure sensitive adhesive particle (31) is in the range of 30% or more and 85% or less. 
     Preparation of Pressure Sensitive Adhesive Particles (c1) to (c3) for Comparison 
     The pressure sensitive adhesive particles (c1) to (c3) are prepared as with the preparation of the pressure sensitive adhesive particle (1) except that the composite resin particle dispersion and the styrene resin particle dispersion are changed as indicated in Table 5. 
     Evaluation of Pressure-Induced Phase Transition 
     The temperature difference (T1−T3), which is the indicator of how easily the pressure sensitive adhesive particles undergo pressure-induced phase transition, is determined. For each pressure sensitive adhesive particle sample, the temperature T1 and the temperature T3 are measured with a Flowtester (CFT-500 produced by Shimadzu Corporation), and the temperature difference (T1−T3) is calculated. Tables 5 and 6 indicate the temperature difference (T1−T3). 
     Evaluation of Adhesiveness 
     Postcard paper V424 produced by Fuji Xerox Co., Ltd., is prepared as a recording medium. By using an image forming apparatus DocuCentre C7550I produced by Fuji Xerox Co., Ltd., and commercially available yellow toner, magenta toner, cyan toner, and black toner products available from Fuji Xerox Co., Ltd., an image having an area density of 30% and including both black characters and a full-color photographic image is formed on one surface of a postcard sheet and is fixed. 
     Next, the pressure sensitive adhesive particles are sprayed onto the entire image-formed surface of the postcard sheet so that the amount of the pressure sensitive adhesive particles applied is 3 g/m 2 , and the postcard sheet is passed through a belt roll-type fixing machine so as to fix the pressure sensitive adhesive particles onto the image-formed surface of the postcard sheet and form a layer of the pressure sensitive adhesive particles. 
     The postcard sheet having a layer of the pressure sensitive adhesive particles on the image-formed surface is folded in two with the image-formed surface facing inward by using a sealer, PRESSLE multi II produced by Toppan Forms Co., Ltd., and a pressure is applied to the bi-folded recording medium so as to bond the inner image-formed surfaces to each other at a pressure of 90 MPa. 
     Ten postcards are continuously formed by using the above-described apparatus under the above-described conditions by folding a postcard sheet in two with the image-formed surfaces facing inward and then bonding the image-formed surfaces of the postcard sheet. 
     The tenth postcard is cut in the long side direction at a width of 15 mm to prepare a rectangular test piece, and the test piece is subjected to the 90 degrees peel test. The peeling speed of the 90 degrees peel test is set to 20 mm/min, the load (N) from 10 mm to 50 mm is sampled at 0.4 mm intervals after start of the measurement, the average of the results is calculated, and the loads (N) observed from three test pieces are averaged. The load (N) required for peeling is categorized as follows. The results are indicated in Tables 5 and 6. 
     A: 0.8 N or more
 
B: 0.6 N or more but less than 0.8 N
 
C: 0.4 N or more but less than 0.6 N
 
D: 0.2 N or more but less than 0.4 N
 
E: Less than 0.2 N
 
     
       
         
           
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
             
            
               
                   
                   
                   
                 Pressure sensitive 
               
               
                   
                   
                   
                 adhesive particles 
               
            
           
           
               
               
               
               
            
               
                   
                 Core 
                   
                 Average 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Pressure 
                 Composite 
                   
                   
                 St resin-to- 
                 Shell layer 
                   
                 diameter 
               
               
                 sensitive 
                 resin 
                 Polymerization 
                 Polymerization 
                 Ac resin 
                 St resin 
                   
                 of island 
               
               
                 adhesive 
                 particle 
                 components of 
                 components of 
                 mass ratio 
                 particle 
                 D50v 
                 phases 
               
               
                 particles 
                 dispersion 
                 St resin 
                 Ac resin 
                 (St:Ac) 
                 dispersion 
                 μm 
                 nm 
               
               
                   
               
               
                 c1 
                 cM1 
                 St/BA/AA = 78/20/2 
                 2EHA = 100 
                 50:50 
                 St1 
                 8.0 
                 600 
               
               
                 c2 
                 cM2 
                 St/BA/AA = 78/20/2 
                 BA = 100 
                 50:50 
                 St1 
                 8.0 
                 550 
               
               
                 c3 
                 cM3 
                 St/2EHA/AA = 78/20/2 
                 BA = 100 
                 50:50 
                 St12 
                 11.0 
                 570 
               
               
                 1 
                 M1 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St1 
                 8.0 
                 200 
               
               
                 2 
                 M2 
                 St/BA/AA = 88/10/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St2 
                 11.0 
                 250 
               
               
                 3 
                 M3 
                 St/BA/AA = 83/15/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St3 
                 11.0 
                 280 
               
               
                 4 
                 M4 
                 St/BA/MAA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St4 
                 11.0 
                 240 
               
               
                 5 
                 M5 
                 St/BA/4HBA = 80/15/5 
                 2EHA/BA = 50/50 
                 50:50 
                 St5 
                 11.0 
                 240 
               
               
                 6 
                 M6 
                 St/BA/2EHA = 80/15/5 
                 2EHA/BA = 50/50 
                 50:50 
                 St6 
                 11.0 
                 250 
               
               
                 7 
                 M7 
                 St/BA = 80/20 
                 2EHA/BA = 50/50 
                 50:50 
                 St7 
                 9.5 
                 250 
               
               
                 8 
                 M8 
                 St/BA/CEA = 77/20/3 
                 2EHA/BA = 50/50 
                 50:50 
                 St8 
                 9.5 
                 250 
               
               
                 9 
                 M9 
                 St/BA/AA = 72/26/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St9 
                 9.5 
                 220 
               
               
                 10 
                 M10 
                 St/BA/AA = 68/30/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St10 
                 9.5 
                 230 
               
               
                 11 
                 M11 
                 St/2EHA = 80/20 
                 2EHA/BA = 50/50 
                 50:50 
                 St11 
                 9.5 
                 220 
               
               
                 12 
                 M12 
                 St/2EHA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St12 
                 9.5 
                 230 
               
               
                 13 
                 M13 
                 St/2EHA/AA = 78/20/2 
                 2EHA/HA = 50/50 
                 50:50 
                 St12 
                 5.8 
                 250 
               
               
                 14 
                 M14 
                 St/EA/AA = 63/35/2 
                 2EHA/PA = 50/50 
                 50:50 
                 St13 
                 5.8 
                 350 
               
               
                 15 
                 M15 
                 St/BA/AA = 78/20/2 
                 2EHA/HA = 50/50 
                 50:50 
                 St1 
                 5.8 
                 400 
               
               
                 16 
                 M16 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 90/10 
                 50:50 
                 St1 
                 8.0 
                 400 
               
               
                 17 
                 M17 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 80/20 
                 50:50 
                 St1 
                 8.0 
                 300 
               
               
                 18 
                 M18 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 70/30 
                 50:50 
                 St1 
                 8.0 
                 250 
               
               
                 19 
                 M19 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 30/70 
                 50:50 
                 St1 
                 8.0 
                 250 
               
               
                 20 
                 M20 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 20/80 
                 50:50 
                 St1 
                 8.0 
                 300 
               
               
                 21 
                 M21 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 10/90 
                 50:50 
                 St1 
                 8.0 
                 400 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Pressure sensitive adhesive particles 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Pressure- 
                   
                   
               
               
                   
                 Pressure 
                   
                   
                   
                   
                 induced phase 
               
               
                   
                 sensitive 
                   
                   
                 Difference 
                   
                 transition 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 adhesive 
                 Tg 
                 in Tg 
                 T3 
                 (T1-T3) 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 particles 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 Adhesiveness 
                 Remarks 
               
               
                   
                   
               
               
                   
                 c1 
                 −50 
                 54 
                 104 
                 95 
                 3 
                 D 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                   
                 c2 
                 −53 
                 54 
                 107 
                 93 
                 4 
                 D 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                   
                 c3 
                 −53 
                 56 
                 109 
                 93 
                 4 
                 D 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                   
                 1 
                 −52 
                 54 
                 106 
                 75 
                 15 
                 A 
                 Example 
               
               
                   
                 2 
                 −52 
                 76 
                 128 
                 70 
                 13 
                 A 
                 Example 
               
               
                   
                 3 
                 −52 
                 65 
                 117 
                 78 
                 15 
                 A 
                 Example 
               
               
                   
                 4 
                 −52 
                 57 
                 109 
                 70 
                 10 
                 A 
                 Example 
               
               
                   
                 5 
                 −52 
                 55 
                 107 
                 74 
                 16 
                 A 
                 Example 
               
               
                   
                 6 
                 −52 
                 54 
                 106 
                 73 
                 14 
                 A 
                 Example 
               
               
                   
                 7 
                 −52 
                 54 
                 106 
                 73 
                 13 
                 A 
                 Example 
               
               
                   
                 8 
                 −52 
                 54 
                 106 
                 75 
                 10 
                 A 
                 Example 
               
               
                   
                 9 
                 −52 
                 43 
                 95 
                 75 
                 15 
                 A 
                 Example 
               
               
                   
                 10 
                 −52 
                 35 
                 87 
                 73 
                 15 
                 A 
                 Example 
               
               
                   
                 11 
                 −52 
                 56 
                 108 
                 72 
                 15 
                 A 
                 Example 
               
               
                   
                 12 
                 −52 
                 56 
                 108 
                 75 
                 20 
                 A 
                 Example 
               
               
                   
                 13 
                 −55 
                 56 
                 111 
                 70 
                 15 
                 A 
                 Example 
               
               
                   
                 14 
                 −45 
                 54 
                 99 
                 80 
                 5 
                 B 
                 Example 
               
               
                   
                 15 
                 −54 
                 54 
                 108 
                 81 
                 7 
                 B 
                 Example 
               
               
                   
                 16 
                 −51 
                 54 
                 105 
                 80 
                 10 
                 B 
                 Example 
               
               
                   
                 17 
                 −52 
                 54 
                 106 
                 70 
                 20 
                 A 
                 Example 
               
               
                   
                 18 
                 −52 
                 54 
                 106 
                 75 
                 15 
                 A 
                 Example 
               
               
                   
                 19 
                 −52 
                 54 
                 106 
                 73 
                 15 
                 A 
                 Example 
               
               
                   
                 20 
                 −52 
                 54 
                 106 
                 75 
                 20 
                 A 
                 Example 
               
               
                   
                 21 
                 −53 
                 54 
                 107 
                 80 
                 9 
                 B 
                 Example 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
             
            
               
                   
                   
                   
                 Pressure sensitive 
               
               
                   
                   
                   
                 adhesive particles 
               
            
           
           
               
               
               
               
            
               
                   
                 Core 
                   
                 Average 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Pressure 
                 Composite 
                   
                   
                 St resin-to- 
                 Shell layer 
                   
                 diameter 
               
               
                 sensitive 
                 resin 
                 Polymerization 
                 Polymerization 
                 Ac resin 
                 St resin 
                   
                 of island 
               
               
                 adhesive 
                 particle 
                 components St 
                 components 
                 mass ratio 
                 particle 
                 D50v 
                 phases 
               
               
                 particles 
                 dispersion 
                 of resin 
                 of Ac resin 
                 (St:Ac) 
                 dispersion 
                 μm 
                 nm 
               
               
                   
               
               
                 28 
                 M28 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St1 
                 8.0 
                 200 
               
               
                 29 
                 M29 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St1 
                 8.0 
                 200 
               
               
                 30 
                 M30 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 St1 
                 8.0 
                 200 
               
               
                 31 
                 M31 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 50:50 
                 — 
                 8.0 
                 400 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Pressure sensitive adhesive particles 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 Pressure- 
                   
                   
               
               
                   
                 Pressure 
                   
                   
                   
                   
                 induced phase 
               
               
                   
                 sensitive 
                   
                   
                 Difference 
                   
                 transition 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 adhesive 
                 Tg 
                 in Tg 
                 T3 
                 (T1-T3) 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 particles 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 Adhesiveness 
                 Remarks 
               
               
                   
                   
               
               
                   
                 28 
                 −52 
                 54 
                 106 
                 75 
                 15 
                 A 
                 Example 
               
               
                   
                 29 
                 −52 
                 54 
                 106 
                 75 
                 15 
                 A 
                 Example 
               
               
                   
                 30 
                 −52 
                 54 
                 106 
                 75 
                 15 
                 B 
                 Example 
               
               
                   
                 31 
                 −52 
                 54 
                 106 
                 75 
                 7 
                 B 
                 Example 
               
               
                   
                   
               
               
                   
                 *Pressure sensitive adhesive particles (31) are produced by a crushing method by using, as a raw material, composite resin particles (M31) obtained by drying a composite resin particle dispersion (M1). 
               
            
           
         
       
     
     In the cross sections of the pressure sensitive adhesive particles (1) to (21) and (28) to (31), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Preparation of Dispersion Containing Composite Resin Particles 
     Preparation of Composite Resin Particle Dispersion (M50) 
     Styrene resin particle dispersion (St1): 1190 parts (solid content: 500 parts) 
     2-Ethylhexyl acrylate: 200 parts 
     n-Butyl acrylate: 200 parts 
     Ion exchange water: 1360 parts 
     The above-described materials are charged into a polymerization flask, stirred at 25° C. for 1 hour, and heated to 70° C. 
     In 75 parts of ion exchange water, 2.5 parts of ammonium persulfate is dissolved, and the resulting solution is added dropwise to the aforementioned polymerization flask over a period of 60 minutes via a metering pump. 
     Subsequently, while slow stirring is continued, the polymerization flask is retained at 70° C. for 2 hours, and then a mixture of 85 parts of styrene and 15 parts of n-butyl acrylate is added dropwise over a period of 60 minutes. After dropwise addition, the mixture is retained at 75° C. for 3 hours and then returned to room temperature. 
     As a result, a composite resin particle dispersion (M50) that contains composite resin particles having a volume-average particle diameter (D50v) of 223 nm and a weight-average molecular weight of 220000 as determined by GPC (UV detection) and that has a solid content of 32% is obtained. 
     The composite resin particle dispersion (M50) is dried to obtain composite resin particles, and the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed. Table 7 indicates the glass transition temperatures. 
     Preparation of Composite Resin Particle Dispersions (M51) to (M55) 
     Composite resin particle dispersions (M51) to (M55) are prepared as with the preparation of the composite resin particle dispersion (M50) except that the raw materials are changed as indicated in Table 7. 
     The compositions and the physical properties of the composite resin particle dispersion (M50) etc., are indicated in Table 7. In Table 7, the monomers are abbreviated as follows. 
     Styrene: St, n-butyl acrylate: BA, acrylic acid: AA, 2-ethyhexyl acrylate: 2EHA 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Composite resin particle dispersion 
               
            
           
           
               
               
            
               
                   
                 Composite resin particles 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 St resin (1) 
                   
                 St resin-to- 
                 D50v of 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 St resin 
                 Ac resin 
                 St resin (2) 
                 Ac resin 
                 resin 
                 Mw 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 particle 
                 Polymerization 
                 Tg 
                 Polymerization 
                 Polymerization 
                 mass ratio 
                 particles 
                 (k) 
                 Tg 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 dispersion 
                 components 
                 ° C. 
                 components 
                 components 
                 (St:Ac) 
                 nm 
                 — 
                 ° C. 
                 ° C. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 M50 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 St/BA = 85/15 
                 60:40 
                 223 
                 220 
                 −52 
                 55 
               
               
                 M51 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 St/BA = 90/10 
                 60:40 
                 224 
                 215 
                 −52 
                 55 
               
               
                 M52 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 70/30 
                 St/BA = 70/30 
                 60:40 
                 223 
                 212 
                 −54 
                 53 
               
               
                 M53 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 30/70 
                 St/BA = 90/10 
                 60:40 
                 223 
                 200 
                 −52 
                 54 
               
               
                 M54 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 60/40 
                 St/BA = 85/15 
                 50:50 
                 230 
                 220 
                 −52 
                 54 
               
               
                 M55 
                 St3 
                 St/BA/AA = 83/15/2 
                 65 
                 2EHA/BA = 60/40 
                 St/BA = 85/15 
                 50:50 
                 228 
                 223 
                 −52 
                 65 
               
               
                   
               
            
           
         
       
     
     Preparation of Pressure Sensitive Adhesive Particle 
     Preparation of Pressure Sensitive Adhesive Particles (50) to (55) 
     The pressure sensitive adhesive particles (50) to (55) are prepared as with the preparation of the pressure sensitive adhesive particle (1) except that the raw materials are changed as indicated in Table 8. 
     Using the pressure sensitive adhesive particles (50) to (55) as samples, the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed. Table 8 indicates the glass transition temperatures. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (50) to (55) are measured by the aforementioned measuring method, and all of the pressure sensitive adhesive particles (50) to (55) satisfy formula 1, “10° C.≤T1−T2”. 
     Cross sections of the pressure sensitive adhesive particles (50) to (55) are observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particles (50) to (55) have a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases is indicated in Table 8. 
     In the cross sections of the pressure sensitive adhesive particles (50) to (55), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Evaluation of Pressure-Induced Phase Transition 
     For each pressure sensitive adhesive particle sample, the temperature T1 and the temperature T3 are measured with a Flowtester (CFT-500 produced by Shimadzu Corporation), and the temperature difference (T1−T3) is calculated. Table 8 indicates the temperature difference (T1−T3). 
     Evaluation of Adhesiveness 
     The adhesiveness is evaluated as with the pressure sensitive adhesive particles (1) etc., by the evaluation method described in “Evaluation of adhesiveness” described above. The results are indicated in Table 8. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
             
            
               
                   
                 Core 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Pressure 
                   
                   
                   
                   
                 St resin-to- 
                 Shell layer 
               
               
                 sensitive 
                 Composite 
                 Polymerization 
                 Polymerization 
                 Polymerization 
                 Ac resin 
                 St resin 
               
               
                 adhesive 
                 resin particle 
                 components of St 
                 components of 
                 components of 
                 mass ratio 
                 particle 
               
               
                 particles 
                 dispersion 
                 resin (1) 
                 Ac resin 
                 St resin (2) 
                 (St:Ac) 
                 dispersion 
               
               
                   
               
               
                 50 
                 M50 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 St/BA = 85/15 
                 60:40 
                 St1 
               
               
                 51 
                 M51 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 50/50 
                 St/BA = 90/10 
                 60:40 
                 St1 
               
               
                 52 
                 M52 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 70/30 
                 St/BA = 70/30 
                 60:40 
                 St1 
               
               
                 53 
                 M53 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 30/70 
                 St/BA = 90/10 
                 60:40 
                 St1 
               
               
                 54 
                 M54 
                 St/BA/AA = 78/20/2 
                 2EHA/BA = 60/40 
                 St/BA = 85/15 
                 50:50 
                 St1 
               
               
                 55 
                 M55 
                 St/BA/AA = 83/15/2 
                 2EHA/BA = 60/40 
                 St/BA = 85/15 
                 50:50 
                 St1 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Pressure sensitive adhesive particles 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Pressure- 
                   
                   
               
               
                   
                   
                   
                 Average 
                   
                   
                   
                   
                 induced 
               
               
                   
                 Pressure 
                   
                 diameter 
                   
                   
                   
                   
                 phase 
               
               
                   
                 sensitive 
                   
                 of island 
                   
                   
                 Difference 
                   
                 transition 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 adhesive 
                 D50v 
                 phases 
                 Tg 
                 in Tg 
                 T3 
                 (T1-T3) 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 particles 
                 μm 
                 nm 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 ° C. 
                 Adhesiveness 
                 Remarks 
               
               
                   
                   
               
               
                   
                 50 
                 8.0 
                 250 
                 −52 
                 55 
                 107 
                 75 
                 10 
                 A 
                 Example 
               
               
                   
                 51 
                 8.0 
                 250 
                 −52 
                 55 
                 107 
                 75 
                 10 
                 A 
                 Example 
               
               
                   
                 52 
                 8.0 
                 250 
                 −54 
                 53 
                 107 
                 74 
                 13 
                 A 
                 Example 
               
               
                   
                 53 
                 8.0 
                 250 
                 −52 
                 54 
                 106 
                 73 
                 13 
                 A 
                 Example 
               
               
                   
                 54 
                 8.0 
                 270 
                 −52 
                 54 
                 106 
                 78 
                 15 
                 A 
                 Example 
               
               
                   
                 55 
                 8.0 
                 270 
                 −52 
                 65 
                 117 
                 74 
                 15 
                 A 
                 Example 
               
               
                   
                   
               
            
           
         
       
     
     In the cross sections of the pressure sensitive adhesive particles and (50) to (55), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Producing Printed Material by Electrophotographic Method 
     Into a V-type blender, 10 parts of any one of the pressure sensitive adhesive particles (1) to (21), (28) to (31), (c1) to (c3), and (50) to (55) and 100 parts of the following resin-coated carrier (1) are placed, and the resulting mixture is stirred for 20 minutes. Then the mixture is screened through a vibrating screen having 212 μm openings to obtain a developers (1) to (21), (28) to (31), (c1) to (c3), and (50) to (55). 
     Resin-Coated Carrier (1) 
     Mn—Mg—Sr ferrite particles (average particle diameter: 40 μm): 100 parts 
     Toluene: 14 parts 
     Polymethyl methacrylate: 2 parts 
     Carbon black (VXC72 produced by Cabot Corporation): 0.12 parts 
     Glass beads (diameter: 1 mm, in an amount equal to the amount of toluene) and the above-described materials other than the ferrite particles are mixed, and the resulting mixture is stirred in a sand mill produced by KANSAI PAINT CO., LTD., at a rotation rate of 1200 rpm for 30 minutes. As a result, a dispersion is obtained. This dispersion and the ferrite particles are placed in a vacuum deaerator-type kneader, and the resulting mixture is dried at a reduced pressure under stirring to obtain a resin-coated carrier (1). 
     An apparatus of a type illustrated in  FIG. 4  is prepared as the apparatus for producing a printed material. In other words, an apparatus for producing a printed material, the apparatus being equipped with a five-stand-tandem intermediate transfer-type printing unit that performs application of the pressure sensitive adhesive particles of the exemplary embodiment and formation of color images on a recording medium, and a pressure bonding unit that has a folding device and a pressurizing device is prepared. 
     The developer (or comparative developer) of this exemplary embodiment, a yellow developer, a magenta developer, a cyan developer, and a black developer are respectively placed in five developing devices in the printing unit. Commercially available products produced by Fuji Xerox Co., Ltd., are used as the developers of respective colors such as yellow. 
     Postcard paper V424 produced by Fuji Xerox Co., Ltd. is prepared as a recording medium. 
     The image to be formed on the postcard paper is an image having an area density of 30% and including both black characters and a full-color photographic image. The image is formed on one surface of the postcard sheet. 
     The amount of the pressure sensitive adhesive particles of the exemplary embodiment (or comparative pressure sensitive adhesive particles) applied is 3 g/m 2  in an image-formed region of an image-formed surface of the postcard sheet. 
     The folding device is a device that folds the postcard sheet in two such that the surface on which the image is formed is arranged on the inner side. 
     The pressurizing device is to apply a pressure of 90 MPa. 
     Ten postcards are continuously formed by using the above-described apparatus under the above-described conditions by folding a postcard sheet in two with the image-formed surface facing inward and then bonding the image-formed surfaces of the flaps of the postcard sheet. 
     The tenth postcard is cut in the long side direction at a width of 15 mm to prepare a rectangular test piece, and the test piece is subjected to the 90 degrees peel test. The peeling speed of the 90 degrees peel test is set to 20 mm/min, the load (N) from 10 mm to 50 mm is sampled at 0.4 mm intervals after start of the measurement, the average of the results is calculated, and the loads (N) observed from three test pieces are averaged. The load (N) required for peeling is categorized as follows. The results are indicated in Tables 9, 10, and 11. 
     A: 0.8 N or more
 
B: 0.6 N or more but less than 0.8 N
 
C: 0.4 N or more but less than 0.6 N
 
D: 0.2 N or more but less than 0.4 N
 
E: Less than 0.2 N
 
     
       
         
           
               
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                 Pressure sensitive 
                   
                   
               
               
                 Developer 
                 adhesive particles 
                 Adhesiveness 
                 Remarks 
               
               
                   
               
             
            
               
                 c1 
                 c1 
                 D 
                 Comparative Example 
               
               
                 c2 
                 c2 
                 D 
                 Comparative Example 
               
               
                 c3 
                 c3 
                 D 
                 Comparative Example 
               
               
                 1 
                 1 
                 A 
                 Example 
               
               
                 2 
                 2 
                 A 
                 Example 
               
               
                 3 
                 3 
                 A 
                 Example 
               
               
                 4 
                 4 
                 A 
                 Example 
               
               
                 5 
                 5 
                 A 
                 Example 
               
               
                 6 
                 6 
                 A 
                 Example 
               
               
                 7 
                 7 
                 A 
                 Example 
               
               
                 8 
                 8 
                 A 
                 Example 
               
               
                 9 
                 9 
                 A 
                 Example 
               
               
                 10 
                 10 
                 A 
                 Example 
               
               
                 11 
                 11 
                 A 
                 Example 
               
               
                 12 
                 12 
                 A 
                 Example 
               
               
                 13 
                 13 
                 A 
                 Example 
               
               
                 14 
                 14 
                 B 
                 Example 
               
               
                 15 
                 15 
                 B 
                 Example 
               
               
                 16 
                 16 
                 B 
                 Example 
               
               
                 17 
                 17 
                 A 
                 Example 
               
               
                 18 
                 18 
                 A 
                 Example 
               
               
                 19 
                 19 
                 A 
                 Example 
               
               
                 20 
                 20 
                 A 
                 Example 
               
               
                 21 
                 21 
                 B 
                 Example 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                   
                 Pressure sensitive 
                   
                   
               
               
                 Developer 
                 adhesive particles 
                 Adhesiveness 
                 Remarks 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 28 
                 28 
                 A 
                 Example 
               
               
                 29 
                 29 
                 A 
                 Example 
               
               
                 30 
                 30 
                 B 
                 Example 
               
               
                 31 
                 31 
                 B 
                 Example 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                 TABLE 11 
               
               
                   
               
               
                   
                 Pressure sensitive 
                   
                   
               
               
                 Developer 
                 adhesive particles 
                 Adhesiveness 
                 Remarks 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 50 
                 50 
                 A 
                 Example 
               
               
                 51 
                 51 
                 A 
                 Example 
               
               
                 52 
                 52 
                 A 
                 Example 
               
               
                 53 
                 53 
                 A 
                 Example 
               
               
                 54 
                 54 
                 A 
                 Example 
               
               
                 55 
                 55 
                 A 
                 Example 
               
               
                   
               
            
           
         
       
     
     Examination on Features of Island Phases 
     Preparation of Dispersion Containing Composite Resin Particles 
     Composite resin particle dispersions (M60) to (M69) are prepared as with the preparation of the composite resin particle dispersion (M1) except that the amounts of 2-ethylhexyl acrylate and n-butyl acrylate used are adjusted. 
     The compositions and the physical properties of the composite resin particle dispersion (M60) etc., are indicated in Table 12. In Table 12, the monomers are abbreviated as follows. 
     Styrene: St, n-butyl acrylate: BA, acrylic acid: AA, 2-ethyhexyl acrylate: 2EHA 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Composite resin particle dispersion 
               
            
           
           
               
               
            
               
                   
                 Composite resin particles 
               
            
           
           
               
               
               
               
               
            
               
                   
                 St resin 
                   
                 St resin-to- 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 St resin 
                 Ac resin 
                 Ac resin 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 particle 
                 Polymerization 
                 Tg 
                 Polymerization 
                 mass ratio 
                 Tg 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 No. 
                 dispersion 
                 components 
                 ° C. 
                 components 
                 (St:Ac) 
                 ° C. 
                 ° C. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 M1 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 50:50 
                 −52 
                 54 
               
               
                 M60 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 95:5  
                 −52 
                 54 
               
               
                 M61 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 90:10 
                 −52 
                 54 
               
               
                 M62 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 85:15 
                 −52 
                 54 
               
               
                 M63 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 80:20 
                 −52 
                 54 
               
               
                 M64 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 70:30 
                 −52 
                 54 
               
               
                 M65 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 60:40 
                 −52 
                 54 
               
               
                 M66 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 39:61 
                 −52 
                 54 
               
               
                 M67 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 33:67 
                 −52 
                 54 
               
               
                 M68 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 30:70 
                 −52 
                 54 
               
               
                 M69 
                 St1 
                 St/BA/AA = 78/20/2 
                 54 
                 2EHA/BA = 50/50 
                 26:74 
                 −52 
                 54 
               
               
                   
               
            
           
         
       
     
     Preparation of Pressure Sensitive Adhesive Particles (60) to (74) and (c4) to (c7) 
     The pressure sensitive adhesive base particles are prepared as with the preparation of the pressure sensitive adhesive base particle (1) except that the production process is changed as indicated in Table 13. 
     One hundred parts of the pressure sensitive adhesive base particles and 1.5 parts of hydrophobic silica (RY50 produced by Nippon Aerosil Co., Ltd.) are mixed, and the resulting mixture is mixed in a sample mill at 13000 rpm for 30 seconds. The mixture is then screened through a vibrating screen having 45 μm openings. As a result, pressure sensitive adhesive particles are obtained. 
     Using the pressure sensitive adhesive particles (60) to (74) as samples, the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed from each of the samples. The two glass transition temperatures are, respectively, −52° C. and 54° C. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (60) to (74) are measured by the aforementioned measuring method, and all of the pressure sensitive adhesive particles (60) to (74) satisfy formula 1, “10° C.≤T1−T2”. 
     Cross sections of the pressure sensitive adhesive particles (60) to (74) are observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particles (60) to (74) have a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. The average diameter of the island phases is determined by the aforementioned measuring method. The average diameter of the island phases and the like are indicated in Table 14. 
     Evaluation of Adhesiveness 
     Postcard paper V424 produced by Fuji Xerox Co., Ltd. is prepared as a recording medium. By using an image forming apparatus DocuCentre C7550I produced by Fuji Xerox Co., Ltd., and commercially available yellow toner, magenta toner, cyan toner, and black toner products available from Fuji Xerox Co., Ltd., an image having an area density of 30% and including both black characters and a full-color photographic image is formed on one surface of a postcard sheet and is fixed. 
     Next, the pressure sensitive adhesive particles are sprayed onto the entire image-formed surface of the postcard sheet so that the amount of the pressure sensitive adhesive particles applied is 3 g/m 2 , and the postcard sheet is passed through a belt roll-type fixing machine so as to fix the pressure sensitive adhesive particles onto the image-formed surface of the postcard sheet and form a layer of the pressure sensitive adhesive particles. 
     The postcard sheet having a layer of the pressure sensitive adhesive particles on the image-formed surface is folded in two with the image-formed surface facing inward by using a sealer, PRESSLE multi II produced by Toppan Forms Co., Ltd., and a pressure is applied to the bi-folded recording medium so as to bond the inner image-formed surfaces to each other at a pressure of 90 MPa. 
     Ten postcards are continuously formed by using the above-described apparatus under the above-described conditions by folding a postcard sheet in two with the image-formed surfaces facing inward and then bonding the image-formed surfaces of the postcard sheet. 
     The tenth postcard is cut in the long side direction at a width of 15 mm to prepare a rectangular test piece, and the test piece is subjected to the 90 degrees peel test. The peeling speed of the 90 degrees peel test is set to 20 mm/min, the load (N) from 10 mm to 50 mm is sampled at 0.4 mm intervals after start of the measurement, the average of the results is calculated, and the loads (N) observed from three test pieces are averaged. The load (N) required for peeling is categorized as follows. The results are indicated in Table 14. 
     A: 0.8 N or more
 
B: 0.6 N or more but less than 0.8 N
 
C: 0.4 N or more but less than 0.6 N
 
D: 0.2 N or more but less than 0.4 N
 
E: Less than 0.2 N
 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 13 
               
             
            
               
                   
                   
               
               
                   
                 Base particle production process 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Core 
                 Aggregated particle 
                 Fusing and coalescing 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Pressure 
                 Shell 
                 Composite 
                 St resin-to- 
                 forming step 
                 step 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Pressure 
                 sensitive 
                 St resin 
                 resin 
                 Ac resin 
                 Temperature 
                 Temperature 
                 Temperature 
                 Retention 
                   
               
               
                 sensitive 
                 adhesive 
                 particle 
                 particle 
                 mass ratio 
                 elevation rate 
                 elevation rate 
                 elevation rate 
                 time at 
               
               
                 adhesive 
                 base 
                 dispersion 
                 dispersion 
                 (St:Ac) 
                 up to 40° C. 
                 beyond 40° C. 
                 up to 90° C. 
                 90° C. 
               
               
                 particles 
                 particles 
                 — 
                 — 
                 — 
                 ° C./min 
                 ° C./min 
                 ° C./min 
                 min 
                 Remarks 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 c4 
                 c4 
                 St1 
                 M60 
                 95:5  
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 c5 
                 c5 
                 St1 
                 M61 
                 90:10 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 60 
                 60 
                 St1 
                 M62 
                 85:15 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 61 
                 61 
                 St1 
                 M62 
                 85:15 
                 0.05 
                 0.01 
                 0.1 
                 1200 
                 Example 
               
               
                 62 
                 62 
                 St1 
                 M63 
                 80:20 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 63 
                 63 
                 St1 
                 M64 
                 70:30 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 64 
                 64 
                 St1 
                 M65 
                 60:40 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 65 
                 65 
                 St1 
                 M1 
                 50:50 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 66 
                 66 
                 St1 
                 M66 
                 39:61 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 67 
                 67 
                 St1 
                 M67 
                 33:67 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 68 
                 68 
                 St1 
                 M67 
                 33:67 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 69 
                 69 
                 St1 
                 M67 
                 33:67 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Example 
               
               
                 70 
                 70 
                 St1 
                 M67 
                 33:67 
                 0.40 
                 0.10 
                 1.0 
                 300 
                 Example 
               
               
                 c6 
                 c6 
                 St1 
                 M68 
                 30:70 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 c7 
                 c7 
                 St1 
                 M69 
                 26:74 
                 0.20 
                 0.05 
                 1.0 
                 600 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 71 
                 71 
                 St1 
                 M1 
                 50:50 
                 0.20 
                 0.01 
                 1.0 
                 600 
                 Example 
               
               
                 72 
                 72 
                 St1 
                 M1 
                 50:50 
                 0.20 
                 0.05 
                 0.1 
                 600 
                 Example 
               
               
                 73 
                 73 
                 St1 
                 M1 
                 50:50 
                 0.05 
                 0.01 
                 0.1 
                 1200 
                 Example 
               
               
                 74 
                 74 
                 St1 
                 M1 
                 50:50 
                 0.40 
                 0.10 
                 1.0 
                 300 
                 Example 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 14 
               
             
            
               
                   
                   
               
               
                   
                 Island phases 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                 First 
                 Second 
                 Third 
                   
                   
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                 region 
                 region 
                 region 
               
               
                   
                 Pressure 
                   
                   
                 Average 
                 Average 
                 Island 
                 Island 
                 Island 
               
               
                 Pressure 
                 sensitive 
                   
                 Island 
                 diameter 
                 number 
                 phase 
                 phase 
                 phase 
                   
                   
                 Performance 
               
               
                 sensitive 
                 adhesive 
                   
                 phase 
                 of island 
                 of island 
                 area ratio 
                 area ratio 
                 area ratio 
                 As2/ 
                 As3/ 
                 evaluation 
               
               
                 adhesive 
                 base 
                 D50v 
                 area ratio 
                 phases 
                 phases 
                 As1 
                 As2 
                 As3 
                 As1 
                 As1 
                 Adhesiveness 
               
               
                 particles 
                 particles 
                 μm 
                 % 
                 nm 
                 — 
                 % 
                 % 
                 % 
                 — 
                 — 
                 — 
                 Remarks 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 c4 
                 c4 
                 9.5 
                 15 
                 250 
                 173 
                 18 
                 15 
                 12 
                 0.83 
                 0.67 
                 E 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 c5 
                 c5 
                 9.5 
                 24 
                 300 
                 193 
                 24 
                 29 
                 19 
                 1.20 
                 0.80 
                 D 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 60 
                 60 
                 9.5 
                 31 
                 300 
                 249 
                 28 
                 33 
                 33 
                 1.17 
                 1.17 
                 B 
                 Example 
               
               
                 61 
                 61 
                 5.5 
                 31 
                 500 
                 25 
                 29 
                 33 
                 31 
                 1.16 
                 1.06 
                 C 
                 Example 
               
               
                 62 
                 62 
                 9.5 
                 38 
                 300 
                 305 
                 42 
                 32 
                 40 
                 0.77 
                 0.95 
                 A 
                 Example 
               
               
                 63 
                 63 
                 9.5 
                 50 
                 300 
                 401 
                 50 
                 53 
                 48 
                 1.05 
                 0.95 
                 A 
                 Example 
               
               
                 64 
                 64 
                 9.5 
                 60 
                 280 
                 553 
                 69 
                 51 
                 60 
                 0.74 
                 0.87 
                 A 
                 Example 
               
               
                 65 
                 65 
                 9.5 
                 70 
                 270 
                 694 
                 67 
                 70 
                 74 
                 1.05 
                 1.11 
                 A 
                 Example 
               
               
                 66 
                 66 
                 9.5 
                 80 
                 270 
                 793 
                 74 
                 86 
                 80 
                 1.15 
                 1.08 
                 A 
                 Example 
               
               
                 67 
                 67 
                 9.5 
                 85 
                 250 
                 983 
                 81 
                 94 
                 81 
                 1.16 
                 1.00 
                 A 
                 Example 
               
               
                 68 
                 68 
                 5.5 
                 85 
                 250 
                 275 
                 78 
                 83 
                 94 
                 1.07 
                 1.20 
                 A 
                 Example 
               
               
                 69 
                 69 
                 8.0 
                 85 
                 250 
                 666 
                 85 
                 77 
                 94 
                 0.90 
                 1.10 
                 A 
                 Example 
               
               
                 70 
                 70 
                 14.7 
                 85 
                 200 
                 3994 
                 87 
                 82 
                 86 
                 0.95 
                 0.99 
                 B 
                 Example 
               
               
                 c6 
                 c6 
                 9.5 
                 87 
                 260 
                 930 
                 87 
                 96 
                 78 
                 1.10 
                 0.90 
                 Breaking 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 c7 
                 c7 
                 9.5 
                 91 
                 200 
                 1644 
                 86 
                 96 
                 91 
                 1.11 
                 1.05 
                 Breaking 
                 Comparative 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Example 
               
               
                 71 
                 71 
                 9.5 
                 71 
                 320 
                 501 
                 67 
                 67 
                 78 
                 1.00 
                 1.16 
                 A 
                 Example 
               
               
                 72 
                 72 
                 9.5 
                 69 
                 400 
                 312 
                 76 
                 66 
                 66 
                 0.86 
                 0.86 
                 A 
                 Example 
               
               
                 73 
                 73 
                 9.5 
                 70 
                 500 
                 202 
                 70 
                 74 
                 67 
                 1.05 
                 0.95 
                 A 
                 Example 
               
               
                 74 
                 74 
                 9.5 
                 71 
                 200 
                 1282 
                 70 
                 70 
                 73 
                 1.01 
                 1.05 
                 A 
                 Example 
               
               
                   
               
            
           
         
       
     
     Examination of Divalent Metal Concentration 
     Preparation of Pressure Sensitive Adhesive Particles (80) to (87) 
     The pressure sensitive adhesive base particles are prepared as with the preparation of the pressure sensitive adhesive base particle (1) except that the aggregating agent is further added as indicated in Table 15 in the fusing and coalescing step. 
     One hundred parts of the pressure sensitive adhesive base particles and 1.5 parts of hydrophobic silica (RY50 produced by Nippon Aerosil Co., Ltd.) are mixed, and the resulting mixture is mixed in a sample mill at 13000 rpm for 30 seconds. The mixture is then screened through a vibrating screen having 45 μm openings. As a result, pressure sensitive adhesive particles are obtained. 
     Using the pressure sensitive adhesive particles (80) to (87) as samples, the thermal behavior in the temperature range of −150° C. to 100° C. is analyzed with a differential scanning calorimeter (DSC-60A produced by Shimadzu Corporation). Two glass transition temperatures are observed from each of the samples. The two glass transition temperatures are, respectively, −52° C. and 54° C. 
     The temperature T1 and the temperature T2 of the pressure sensitive adhesive particles (80) to (87) are measured by the aforementioned measuring method, and all of the pressure sensitive adhesive particles (80) to (87) satisfy formula 1, “10° C.≤T1−T2”. 
     Cross sections of the pressure sensitive adhesive particles (80) to (87) are observed with a scanning electron microscope (SEM). A sea-island structure is observed. The pressure sensitive adhesive particles (80) to (87) have a core in which island phases are present, and a shell layer in which no island phases are present. The sea phase contains a styrene resin, and the island phases contain a (meth)acrylate resin. In the cross sections of the pressure sensitive adhesive particles (80) to (87), the area ratio of the island phases is in the range of 30% or more and 85% or less. 
     Evaluation of Adhesiveness 
     The adhesiveness is evaluated by the evaluation method described in “Evaluation of adhesiveness” described above. The results are indicated in Table 15. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 15 
               
               
                   
               
             
            
               
                   
                   
                   
                   
                 Metal concentration in 
                   
                   
               
               
                   
                   
                   
                   
                 particle surface layer 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pressure 
                 Aggregating agent 
                   
                 Total 
                 Metal concentration 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Pressure 
                 sensitive 
                   
                 Amount 
                   
                 of three 
                 in entire particle 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 sensitive 
                 adhesive 
                   
                 added 
                 Al 
                   
                   
                 elements 
                 Al 
                   
               
               
                 adhesive 
                 base 
                 Type 
                 Parts 
                 (Als) 
                 Mg 
                 Ca 
                 (Mes) 
                 (Alt) 
                 Mg 
               
               
                 particles 
                 particles 
                 — 
                 by mass 
                 % 
                 % 
                 % 
                 % 
                 % 
                 % 
               
               
                   
               
               
                 80 
                 80 
                 Aluminum 
                 23.0 
                 0.28 
                 0.01 
                 0.01 
                 0.30 
                 0.48 
                 0.01 
               
               
                   
                   
                 sulfate 
               
               
                 81 
                 81 
                 Aluminum 
                 11.5 
                 0.11 
                 0.00 
                 0.00 
                 0.11 
                 0.36 
                 0.00 
               
               
                   
                   
                 sulfate 
               
               
                 82 
                 82 
                 Aluminum 
                 0.0 
                 0.04 
                 0.01 
                 0.00 
                 0.05 
                 0.24 
                 0.01 
               
               
                   
                   
                 sulfate 
               
               
                 83 
                 83 
                 Aluminum 
                 23.0 
                 0.27 
                 0.01 
                 0.00 
                 0.28 
                 0.48 
                 0.01 
               
               
                   
                   
                 chloride 
               
               
                 84 
                 84 
                 Polyaluminum 
                 23.0 
                 0.29 
                 0.00 
                 0.01 
                 0.30 
                 0.49 
                 0.00 
               
               
                   
                   
                 chloride 
               
               
                 85 
                 85 
                 Polyaluminum 
                 23.0 
                 0.26 
                 0.00 
                 0.01 
                 0.27 
                 0.48 
                 0.00 
               
               
                   
                   
                 hydroxide 
               
               
                 86 
                 86 
                 Magnesium 
                 23.0 
                 0.04 
                 0.25 
                 0.00 
                 0.29 
                 0.23 
                 0.28 
               
               
                   
                   
                 chloride 
               
               
                 87 
                 87 
                 Calcium 
                 23.0 
                 0.04 
                 0.00 
                 0.27 
                 0.31 
                 0.23 
                 0.00 
               
               
                   
                   
                 chloride 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Metal concentration 
                   
                   
               
               
                   
                   
                 in entire particle 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Total 
                 Uneven 
                   
                   
               
               
                   
                 Pressure 
                   
                 of three 
                 distribution 
                 Performance 
               
               
                   
                 sensitive 
                   
                 elements 
                 of metal 
                 evaluation 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 adhesive 
                 Ca 
                 (Met) 
                 Mes/Met 
                 Als/Alt 
                 Adhesiveness 
                   
               
               
                   
                 particles 
                 % 
                 % 
                 — 
                 — 
                 — 
                 Remarks 
               
               
                   
                   
               
               
                   
                 80 
                 0.01 
                 0.50 
                 0.60 
                 0.58 
                 A 
                 Example 
               
               
                   
                 81 
                 0.01 
                 0.37 
                 0.30 
                 0.31 
                 A 
                 Example 
               
               
                   
                 82 
                 0.00 
                 0.25 
                 0.20 
                 0.17 
                 B 
                 Example 
               
               
                   
                 83 
                 0.00 
                 0.49 
                 0.57 
                 0.56 
                 A 
                 Example 
               
               
                   
                 84 
                 0.01 
                 0.50 
                 0.60 
                 0.59 
                 A 
                 Example 
               
               
                   
                 85 
                 0.01 
                 0.49 
                 0.55 
                 0.54 
                 A 
                 Example 
               
               
                   
                 86 
                 0.00 
                 0.51 
                 0.57 
                 0.17 
                 A 
                 Example 
               
               
                   
                 87 
                 0.29 
                 0.52 
                 0.60 
                 0.17 
                 A 
                 Example 
               
               
                   
                   
               
            
           
         
       
     
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.