Patent Description:
<CIT> discloses an electrostatic charge image developing toner having a surface property index value of <NUM> or more to <NUM> or less.

<CIT> discloses an electrostatic charge image developing carrier including a carrier body having a core material and a coating resin layer, and spherical silica particles having a volume average particle diameter of <NUM> or more and <NUM> or less and adhering to a surface of the carrier body at a ratio of <NUM> parts by mass or more and <NUM> parts by mass or less with respect to <NUM> parts by mass of the carrier body.

<CIT> discloses an electrostatic charge image developer containing a carrier having a resin coating layer on a core material and a toner. The carrier contains <NUM> to <NUM> mass% of silica or carbon black in the resin coating layer. A weight average molecular weight of a resin to be coated is <NUM>,<NUM> to <NUM>,<NUM>. The toner contains external additive fine particles having a number average particle diameter of <NUM> to <NUM>.

An object of the present disclosure is to provide an electrostatic charge image developer including a toner containing toner particles and an external additive, and a carrier having magnetic particles and a resin layer. The electrostatic charge image developer prevents occurrence of fogging as compared with an electrostatic charge image developer in which a surface property index value of the toner particles is <NUM> or more, or an electrostatic charge image developer in which a ratio B/A of a surface area B of the carrier to a planar view area A of the carrier which are obtained by three-dimensional analysis of a surface of the carrier is less than <NUM> or more than <NUM>.

According to the aspect of <<NUM>>, the electrostatic charge image developer prevents occurrence of fogging as compared with the electrostatic charge image developer in which the surface property index value of the toner particles is <NUM> or more, or an electrostatic charge image developer in which the ratio B/A of the surface area B to the planar view area A which are obtained by three-dimensionally analysis of the surface of the carrier is less than <NUM> or more than <NUM>.

According to the embodiment of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the surface property index value of the toner particles is less than <NUM> or more than <NUM>.

According to the embodiment of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the ratio B/A of the surface area B to the planar view area A is less than <NUM> or more than <NUM> in which the planar view area A and the surface area B are obtained by three-dimensional analysis of the surface of the carrier.

According to the embodiment of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the average particle diameter of the inorganic particles contained in the resin layer of the carrier is less than <NUM> or more than <NUM>.

According to the aspect of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the average thickness of the resin layer of the carrier is less than <NUM> or more than <NUM>.

According to the embodiment of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the average thickness of the resin layer of the carrier is less than <NUM> or more than <NUM>.

According to the embodiment of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the storage elastic modulus G' of the toner is less than <NUM> × <NUM><NUM> Pa or more than <NUM> × <NUM><NUM> Pa.

According to the aspect of <<NUM>>, the electrostatic charge image developer prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the silicon element concentration on the carrier surface is <NUM> atomic% or less or <NUM> atomic% or more.

According to the embodiment of <<NUM>>, there is provided an electrostatic charge image developer that prevents the occurrence of fogging as compared with the electrostatic charge image developer in which the weight average molecular weight of the resin contained in the resin layer of the carrier is <NUM>,<NUM> or more.

According to the aspect of <<NUM>>, the process cartridge prevents occurrence of fogging as compared with a process cartridge that accommodates the electrostatic charge image developer in which the surface property index value of the toner particles is <NUM> or more, or an electrostatic charge image developer in which the ratio B/A of the surface area B to the planar view area A which are obtained by three-dimensional analysis of the surface of the carrier is less than <NUM> or more than <NUM>.

According to the aspect of <<NUM>>, the image forming apparatus prevents occurrence of fogging as compared with an image forming apparatus that accommodates the electrostatic charge image developer in which the surface property index value of toner particles is <NUM> or more, or the electrostatic charge image developer in which the ratio B/A of the surface area B to the planar view area A which are obtained by three-dimensional analysis of the surface of the carrier is less than <NUM> or more than <NUM>.

According to the aspect of <<NUM>>, the image forming method prevents occurrence of fogging as compared with an image forming method of accommodating the electrostatic charge image developer in which the surface property index value of toner particles is <NUM> or more, or the electrostatic charge image developer in which the ratio B/A of the surface area B to the planar view area A which are obtained by three-dimensional analysis of the surface of the carrier is less than <NUM> or more than <NUM>.

Hereinafter, an exemplary embodiment according to the present disclosure will be described. These descriptions and Examples illustrate the exemplary embodiment, and do not limit the scope of the exemplary embodiment.

In the present disclosure, a numerical range indicated by "to" indicates a range including numerical values before and after "to" as a minimum value and a maximum value, respectively.

In numerical ranges described in stages in the present disclosure, an upper limit or a lower limit described in one numerical range may be replaced with an upper limit or a lower limit of a numerical range described in other stages. In the numerical ranges described in the present disclosure, the upper limit or the lower limit of the numerical range may be replaced with values illustrated in Examples.

In the present disclosure, the term "step" indicates not only an independent step, and even when a step cannot be clearly distinguished from other steps, this step is included in the term "step" as long as an intended purpose of the step is achieved.

When an exemplary embodiment is described in the present disclosure with reference to the drawings, a configuration of the exemplary embodiment is not limited to a configuration illustrated in the drawings. Sizes of members in each drawing are conceptual, and a relative size relation between the members is not limited thereto.

In the present disclosure, each component may include plural corresponding substances. In the present disclosure, in a case of referring to an amount of each component in a composition, when there are plural substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in a composition refers to a total amount of the plural substances present in the composition.

In the present disclosure, plural kinds of particles corresponding to each component may be selected. When there are plural kinds of particles corresponding to each component in the composition, unless otherwise specified, a particle diameter of each component means a value for a mixture of the plural kinds of particles present in the composition.

In the present disclosure, the term "(meth)acryl" means at least one of acryl and methacryl, and the term "(meth)acrylate" means at least one of acrylate and methacrylate.

In the present disclosure, the term "electrostatic charge image developing toner" is also referred to as a "toner". The term "electrostatic charge image developing carrier" is also referred to as a "carrier". The term "electrostatic charge image developer" is also referred to as a "developer".

A developer according to the present exemplary embodiment is a two-component developer including a toner and a carrier.

In the present exemplary embodiment, a mixing ratio (mass ratio) of the toner and the carrier is preferably toner: carrier = <NUM>: <NUM> to <NUM>: <NUM>, more preferably <NUM>: <NUM> to <NUM>: <NUM>, and still more preferably <NUM>: <NUM> to <NUM>: <NUM>.

The toner according to the present exemplary embodiment includes a toner particle and an external additive, and the surface property index value of the toner particle is <NUM> or more and less than <NUM>.

In the present exemplary embodiment, the surface property index value of the toner particle is an index for evaluating ruggedness of a toner particle surface. As the surface property index value approaches <NUM>, the toner particle surface tends to be smooth. As the surface property index value moves away from <NUM>, the toner particle surface tends to be rough. The surface property index value of the toner particle is calculated from the following Equations <NUM> and <NUM>.

The specific surface area measured value of the toner particle is obtained from a nitrogen adsorption amount by BET one-point method (equilibrium relative pressure: <NUM>).

A flow particle image analysis apparatus FPIA-<NUM> manufactured by Sysmex Corporation is used for the flow particle image analysis performed to determine the specific surface area calculation value of the toner particle. The FPIA-<NUM> captures the toner particle, performs two-dimensional image processing, and calculates the equivalent circle diameter from a projection area. Assuming that the toner particle is a true sphere, a surface area and a volume of the true sphere are calculated from the equivalent circle diameter. A sum of the surface areas and a sum of the volumes are calculated from equivalent circle diameters of <NUM>,<NUM> toner particles.

Density of the toner particle is measured by measuring true density in accordance with <NUM>. <NUM> of JIS K0061: <NUM> using a Gulysack type specific gravity bottle.

The toner particle to be subjected to the measurement is the particle obtained by removing the external additive from the toner. Removal of the external additive from a surface of the toner is performed by repeating ultrasonic treatment in water containing a surfactant and washing with water.

The carrier in the present exemplary embodiment is a resin-coated carrier including magnetic particle and a resin layer covering the magnetic particle. In the carrier according to the present exemplary embodiment, a ratio B/A of the surface area B of the carrier to the planar view area A of the carrier is <NUM> or more and <NUM> or less. The planar view area A and the surface area B are obtained by three-dimensional analysis of the surface of the carrier.

In the present exemplary embodiment, the ratio B/A is an index for evaluating ruggedness of the carrier surface. The ratio B/A is determined by the following method.

As an apparatus for three-dimensional analysis of the carrier surface, a scanning electron microscope including four secondary electron detectors (for example, electron beam three-dimensional roughness analysis apparatus ERA-8900FE, manufactured by Elionix Inc. ) is used, and analysis is performed as follows.

The surface of one carrier particle is enlarged <NUM>,<NUM> times. A distance between two measurement points is set to <NUM>. The measurement point is set to <NUM> points in a long side direction and <NUM> points in a short side direction. A region of <NUM> × <NUM> is measured to obtain three-dimensional image data.

For the three-dimensional image data, a limit wavelength of a spline filter (a frequency selection filter using a spline function) is set to <NUM> to remove wavelengths having a period of <NUM> or more. Accordingly, a waviness component of the carrier surface is removed and a roughness component is extracted to obtain a roughness curve.

Furthermore, a cutoff value of a Gaussian high-pass filter (a frequency selection filter using a Gaussian function) is set to <NUM> to remove wavelengths having a period of <NUM> or more. Accordingly, wavelengths corresponding to convex portions of the magnetic particle exposed on the carrier surface are removed from the roughness curve after the spline filtering to obtain a roughness curve from which a wavelength component having a period of <NUM> or more is removed.

From three-dimensional roughness curve data after the filtering, the surface area B (µm<NUM>) of a region, which is a central portion of <NUM> × <NUM>, (the plan view area A = <NUM><NUM>) is obtained, so as to obtain the ratio B/A. The ratio B/A is calculated for each of <NUM> carriers and arithmetically averaged.

The electrostatic charge image developer according to the present exemplary embodiment prevents occurrence of fogging. The "fogging" is a phenomenon in which toner scatters and an unintended minute dot-like image appears on an image forming surface of a recording medium. The following is presumed as a mechanism for preventing the occurrence of fogging in the present exemplary embodiment.

The toner is triboelectrically charged by being stirred together with the carrier in a developing device. When a charge amount of the toner is insufficient, the toner does not adhere to an image carrier during development and scatters. As a result, the fogging occurs. One of ways for preventing the occurrence of the fogging is to prevent toner aggregation in the developing device to allow the individual toner to be stirred and sufficiently triboelectrically charge the individual toner.

In the developer according to the present exemplary embodiment, the surface property index value of the toner particle is less than <NUM>, and the ratio B/A of the carrier surface is <NUM> or more. That is, in the developer according to the present exemplary embodiment, a height difference of the ruggedness of a toner particle surface is relatively small, and the number of the ruggedness of the carrier surface is relatively large or the height difference of the ruggedness of the carrier surface is relatively large. When the developer according to the present exemplary embodiment having such surface characteristics is stirred in the developing device, it is presumed that a distribution of the external additive is less biased at the toner particle surface, and the external additive easily moves between the toner particle surface and the convex portion of the carrier surface. Accordingly, a sufficient amount of the external additive is uniformly distributed at the toner particle surface. Therefore, the toner aggregation is unlikely to occur in the developing device, and it is presumed that the individual toners are well stirred.

When the surface property index value of the toner particle is <NUM> or more, it is presumed that the height difference of the ruggedness of the toner particle surface is excessively large, the external additive is easily biased to the concave portion of the toner particle surface, and the amount of the external additive of the convex portion of the toner particle surface is reduced. Then, it is presumed that the toner is aggregated via the convex portion at the toner particle surface having a small amount of the external additive, the individual toners are not stirred, the toner having an insufficient charge amount is generated, and the fogging is generated.

When the ratio B/A of the carrier surface is less than <NUM>, it is presumed that the carrier surface is excessively flat, a contact surface of the carrier with the toner becomes large, and as a result, a transfer amount of the external additive from the toner to the carrier becomes large. Then, it is presumed that the toner in which the amount of the external additive is reduced aggregates, the individual toners are not stirred, the toner having the insufficient charge amount is generated, and the fogging occurs.

On the other hand, when the ratio B/A of the carrier surface is more than <NUM>, it is presumed that the number of ruggedness at the carrier surface is excessively large or the height difference of the ruggedness at the carrier surface is too large, the amount of the external additive entering the concave portion at the carrier surface increases, and the amount of the external additive returning from the carrier to the toner decreases. Then, it is presumed that the toner in which the amount of the external additive is reduced aggregates, the individual toners are not stirred, the toner having the insufficient charge amount is generated, and the fogging occurs.

From the viewpoint of preventing the above-described phenomenon, in the developer according to the present exemplary embodiment, the surface property index value of the toner particle is less than <NUM>, and the ratio B/A of the carrier surface is <NUM> or more and <NUM> or less.

For the above reasons, the ratio B/A of the carrier surface is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and still more preferably <NUM> or more and <NUM> or less.

For the above reasons, the surface property index value of the toner particle is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less.

Since it is difficult to manufacture the toner particle having the surface property index value of less than <NUM>, from a viewpoint of ease of manufacture, the surface property index value of the toner particle is <NUM> or more, preferably <NUM> or more, more preferably <NUM> or more, and still more preferably <NUM> or more.

The surface property index value of the toner particle can be controlled, for example, by adjusting a temperature or pH at the time of fusing and coalescing aggregated particles including the resin particles when the toner particle are produced by an aggregation and coalescence method.

The ratio B/A of the carrier surface can be controlled by manufacturing conditions for forming the resin layer. Details will be described later.

The toner and the carrier according to the present exemplary embodiment will be described in detail.

The toner preferably has a storage elastic modulus G' of <NUM> × <NUM><NUM> Pa or more and <NUM> × <NUM><NUM> Pa or less at a temperature of <NUM> in dynamic viscoelasticity measurement.

The storage elastic modulus G' means an elastic response component of an elastic modulus in a relationship a stress generated with respect to strain when deformed. The toner tends to be harder as a value of the storage elastic modulus G' is larger.

The temperature of <NUM> is a temperature at which phase separation between an amorphous polyester resin and a crystalline polyester resin is maintained when the crystalline polyester resin is used. The temperature at which the hardness of the toner is evaluated in the present exemplary embodiment is specified to be <NUM>.

When the storage elastic modulus G' of the toner at the temperature of <NUM> is <NUM> × <NUM><NUM> Pa or more, the external additive is less likely to be embedded in the toner particle, and aggregation of the toner in which the external additive is reduced can be prevented. Therefore, the individual toners are not stirred, and toner having the insufficient charge amount is less likely to be generated, and the fogging is less likely to occur.

When the storage elastic modulus G' of the toner at the temperature of <NUM> is <NUM> × <NUM><NUM> Pa or less, the external additive is less likely to be detached from the toner particle and the external additive is held at the toner particle surface, so that the aggregation of the toner in which the external additive is reduced can be prevented. Therefore, the individual toners are not stirred, and toner having the insufficient charge amount is less likely to be generated, and the fogging is less likely to occur.

From the above viewpoint, the storage elastic modulus G' of the toner at the temperature of <NUM> is more preferably <NUM> × <NUM><NUM> Pa or more and <NUM> × <NUM><NUM> Pa or less, and still more preferably <NUM> × <NUM><NUM> Pa or more and <NUM> × <NUM><NUM> Pa or less.

The storage elastic modulus G' of the toner can be controlled by an amount ratio between the amorphous resin and the crystalline resin contained in the toner. The storage elastic modulus G' of the toner tends to decrease as the amount of the crystalline resin increases.

The storage elastic modulus G' of the toner is determined by performing the dynamic viscoelasticity measurement as follows.

Sample: Using a press molding machine, <NUM> of toner is tablet-molded into a disk having a diameter of <NUM> and a thickness of <NUM> in an environment of <NUM> ± <NUM>.

The toner particle contains, for example, a binder resin, and if necessary, a colorant, a mold releasing agent, and other additives.

The binder resin is a polyester resin including a crystalline polyester resin in combination with an amorphous polyester resin. The crystalline polyester resin is used in a range in which a content thereof is <NUM> mass% or more and <NUM> mass% or less (preferably <NUM> mass% or more and <NUM> mass% or less) with respect to a total amount of the binder resin.

"Crystalline" of a resin means that the resin has a clear endothermic peak rather than a stepwise endothermic amount change in differential scanning calorimetry (DSC), and specifically means that a half width of the endothermic peak when measured at a heating rate of <NUM> (°C/min) is within <NUM>.

On the other hand, "amorphous" of a resin means that a half width exceeds <NUM>, a stepwise change in an endothermic amount is exhibited, or a clear endothermic peak is not observed.

Examples of the amorphous polyester resin include a condensed polymer of polycarboxylic acid and polyhydric alcohol. As the amorphous polyester resin, a commercially available product may be used, or a synthetic resin may be used.

Examples of the polycarboxylic acid include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenyl succinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower (for example, having <NUM> or more and <NUM> or less carbon atoms) alkyl esters thereof. Among these, the polycarboxylic acid is preferably, for example, an aromatic dicarboxylic acid.

As the polycarboxylic acid, a trivalent or higher carboxylic acid having a crosslinked structure or a branched structure may be used in combination with the dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower (for example, having <NUM> or more and <NUM> or less carbon atoms) alkyl esters thereof.

The polycarboxylic acid may be used alone or in combination of two or more kinds thereof.

Examples of the polyhydric alcohol include aliphatic diols (such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, and neopentyl glycol), alicyclic diols (such as cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A), and aromatic diols (such as an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of bisphenol A). Among these, the polyhydric alcohol is preferably, for example, an aromatic diol or an alicyclic diol, and more preferably an aromatic diol.

As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked structure or a branched structure may be used in combination with the diol. Examples of the trihydric or higher polyhydric alcohol include glycerin, trimethylolpropane, and pentaerythritol.

The polyhydric alcohol may be used alone or in combination of two or more kinds thereof.

A glass transition temperature (Tg) of the amorphous polyester resin is preferably <NUM> or higher and <NUM> or lower, and more preferably <NUM> or higher and <NUM> or lower.

The glass transition temperature is obtained from a DSC curve obtained by the differential scanning calorimetry (DSC), and is more specifically obtained by an "extrapolated glass transition onset temperature" described in a method for obtaining the glass transition temperature of <NPL>".

A weight average molecular weight (Mw) of the amorphous polyester resin is preferably <NUM>,<NUM> or more and <NUM>,<NUM>,<NUM> or less, and more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less.

A number average molecular weight (Mn) of the amorphous polyester resin is preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less.

A molecular weight distribution Mw/Mn of the amorphous polyester resin is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

The weight average molecular weight and the number average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurement by GPC is performed by using a GPC·HLC-8120GPC manufactured by Tosoh Corporation as a measurement apparatus, using a column TSKgel SuperHM-M (<NUM>) manufactured by Tosoh Corporation, and using a THF solvent. The weight average molecular weight and the number average molecular weight are calculated from measurement results using a molecular weight calibration curve prepared using a monodispersed polystyrene standard sample.

The amorphous polyester resin is obtained by a known production method. Specifically, for example, the amorphous polyester resin is obtained by a method in which a polymerization temperature is set to <NUM> or higher and <NUM> or lower, the pressure inside a reaction system is reduced as necessary, and reaction is performed while removing water or alcohols generated during condensation.

When a raw material monomer is not dissolved or compatible at a reaction temperature, a solvent having a high boiling point may be added as a dissolution aid to dissolve the monomer. In this case, a polycondensation reaction is carried out while distilling off the dissolution aid. When there is a monomer having poor compatibility in a copolymerization reaction, the monomer having the poor compatibility may be previously condensed with an acid or alcohol to be polycondensed with the monomer, and then the obtained product may be polycondensed with a main component.

Examples of the crystalline polyester resin include a polycondensate of a polycarboxylic acid and a polyhydric alcohol. As the crystalline polyester resin, a commercially available product may be used, or a synthetic resin may be used.

Here, in order to easily form a crystal structure, the crystalline polyester resin is preferably a polycondensate using a linear aliphatic polymerizable monomer rather than a polymerizable monomer having an aromatic ring.

Examples of the polycarboxylic acid include aliphatic dicarboxylic acids (such as oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, <NUM>,<NUM>-nonandicarboxylic acid, <NUM>,<NUM>-decandicarboxylic acid, <NUM>,<NUM>-dodecanediocarboxylic acid, <NUM>,<NUM>-tetradecanedicarboxylic acid, and <NUM>,<NUM>-octadecanedicarboxylic acid), aromatic dicarboxylic acids (such as dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalene-<NUM>,<NUM>-dicarboxylic acid), anhydrides thereof, and lower (for example, having <NUM> or more and <NUM> or less carbon atoms) alkyl esters thereof.

As the polycarboxylic acid, a trivalent or higher carboxylic acid having a crosslinked structure or a branched structure may be used in combination with the dicarboxylic acid. Examples of the trivalent carboxylic acid include aromatic carboxylic acids (such as <NUM>,<NUM>,<NUM>-benzenetricarboxylic acid, <NUM>,<NUM>,<NUM>-benzenetricarboxylic acid, and <NUM>,<NUM>,<NUM>-naphthalenetricarboxylic acid), anhydrides thereof, and lower (for example, having <NUM> or more and <NUM> or less carbon atoms) alkyl esters thereof.

As the polycarboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids.

Examples of the polyhydric alcohol include aliphatic diols (such as linear aliphatic diols having <NUM> or more and <NUM> or less carbon atoms in the main chain part). Examples of the aliphatic diol include ethylene glycol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-pentanediol, <NUM>,<NUM>-hexanediol, <NUM>,<NUM>-heptanediol, <NUM>,<NUM>-octanediol, <NUM>,<NUM>-nonanediol, <NUM>,<NUM>-decanediol, <NUM>,<NUM>-undecanediol, <NUM>,<NUM>-dodecanediol, <NUM>,<NUM>-tridecandiol, <NUM>,<NUM>-tetradecanediol, <NUM>,<NUM>-octadecanediol, and <NUM>,<NUM>-eicosanediol. Among these, the aliphatic diol is preferably <NUM>,<NUM>-octanediol, <NUM>,<NUM>-nonanediol, or <NUM>,<NUM>-decanediol.

As the polyhydric alcohol, a trihydric or higher alcohol having a crosslinked structure or a branched structure may be used in combination with the diol. Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol.

Here, the polyhydric alcohol preferably has an aliphatic diol content of <NUM> mol% or more, and preferably <NUM> mol% or more.

A melting temperature of the crystalline polyester resin is preferably <NUM> or higher and <NUM> or lower, more preferably <NUM> or higher and <NUM> or lower, and still more preferably <NUM> or higher and <NUM> or lower.

The melting temperature is obtained from a DSC curve obtained by the differential scanning calorimetry (DSC) according to the "melting peak temperature" described in a method for obtaining the melting temperature of JIS K7121: <NUM> "Method for measuring transition temperature of plastics".

A weight average molecular weight (Mw) of the crystalline polyester resin is preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less.

The crystalline polyester resin can be obtained by, for example, a known production method same as the amorphous polyester resin.

A content of the binder resin is preferably <NUM> mass% or more and <NUM> mass% or less, more preferably <NUM> mass% or more and <NUM> mass% or less, and still more preferably <NUM> mass% or more and <NUM> mass% or less with respect to a total amount of the toner particle.

Examples of the colorant include pigments such as Carbon Black, Chrome Yellow, Hansa Yellow, Benzidine Yellow, Threne Yellow, Quinoline Yellow, Pigment Yellow, Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Watchung Red, Permanent Red, Brilliant Carmine 3B, Brilliant Carmine 6B, DuPont Oil Red, Pyrazolone Red, Lithol Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, and Malachite Green Oxalate; and acridine dyes, xanthene dyes, azo dyes, benzoquinone dyes, azine dyes, anthraquinone dyes, thioindigo dyes, dioxazine dyes, thiazine dyes, azomethine dyes, indigo dyes, phthalocyanine dyes, aniline black dyes, polymethine dyes, triphenylmethane dyes, diphenylmethane dyes, and thiazole dyes.

The colorant may be used alone or in combination of two or more kinds thereof.

As the colorant, a surface-treated colorant may be used as necessary, or the colorant may be used in combination with a dispersant. Plural kinds of colorants may be used in combination.

A content of the colorant is preferably <NUM> mass% or more and <NUM> mass% or less, and more preferably <NUM> mass% or more and <NUM> mass% or less, with respect to the total amount of the toner particle.

Examples of the mold releasing agent include hydrocarbon wax, natural wax such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral/petroleum wax such as montan wax, and ester wax such as fatty acid ester and montanic acid ester. The mold releasing agent is not limited thereto.

The melting temperature of the mold releasing agent is preferably <NUM> or higher and <NUM> or lower, and more preferably <NUM> or higher and <NUM> or lower.

The melting temperature is obtained from a DSC curve obtained by the differential scanning calorimetry (DSC) according to the "melting peak temperature" described in a method for obtaining the melting temperature of <NPL>".

A content of the mold releasing agent is preferably <NUM> mass% or more and <NUM> mass% or less, and more preferably <NUM> mass% or more and <NUM> mass% or less, with respect to the total amount of the toner particle.

Examples of the other additives include known additives such as a magnetic body, an electrostatic charge control agent, and an inorganic powder. These additives are contained in the toner particle as internal additives.

The toner particle may be toner particle having a single layer structure, or may be toner particle having a so-called core-shell structure made of a core portion (core particles) and a coating layer (shell layer) coating the core portion.

The toner particle having a core-shell structure may be made of, for example, a core portion made of a binder resin and, if necessary, other additives such as a colorant and a mold releasing agent, and a coating layer made of a binder resin.

A volume average particle diameter (D50v) of the toner particle is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

The volume average particle diameter (D50v) of the toner particle is measured using Coulter Multisizer II (manufactured by Beckman Coulter, Inc. ) and the electrolytic solution is ISOTON-II (manufactured by Beckman Coulter, Inc.

During measurement, <NUM> or more and <NUM> or less of a measurement sample is added to <NUM> of a <NUM> mass% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as the dispersant. The obtained mixture is added to <NUM> or more and <NUM> or less of the electrolytic solution.

The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for <NUM> minute with an ultrasonic disperser, and the Coulter Multisizer II is used to measure a particle size distribution of particles having a particle diameter within the range of <NUM> or more and <NUM> or less using an aperture having an aperture diameter of <NUM>. The number of the particles sampled is <NUM>,<NUM>. A divided particle size range (channel) is set and a volume-based particle size distribution is obtained. Then, a cumulative distribution is drawn from a small particle diameter side and a particle diameter corresponding to the cumulative percentage of <NUM>% with respect to all the particles is the volume average particle diameter D50v.

An average circularity of the toner particle is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

The average circularity of the toner particle is obtained by (circle equivalent perimeter)/(perimeter)[(perimeter of a circle having the same projection area as a particle image)/(perimeter of the projected particle image)]. Specifically, the average circularity is a value measured by the following method.

First, the toner particles to be measured are sucked and collected to form a flat flow, and flash light is emitted instantly to capture a particle image as a still image. The average circularity is obtained by the flow-type particle image analysis apparatus (FPIA-<NUM> manufactured by Sysmex Corporation) that analyzes the particle image. The number of samples for obtaining the average circularity is <NUM>,<NUM>.

When the toner contains the external additive, the toner to be measured is dispersed in water containing the surfactant, and then an ultrasonic treatment is performed to obtain toner particle from which the external additive is removed.

Examples of the external additive include inorganic particles. Examples of the inorganic particles include SiO<NUM>, TiO<NUM>, Al<NUM>O<NUM>, CuO, ZnO, SnO<NUM>, CeO<NUM>, Fe<NUM>O<NUM>, MgO, BaO, CaO, K<NUM>O, Na<NUM>O, ZrO<NUM>, CaO·SiO<NUM>, K<NUM>O·(TiO<NUM>)n, Al<NUM>O<NUM>·2SiO<NUM>, CaCO<NUM>, MgCO<NUM>, BaSO<NUM>, and MgSO<NUM>.

The surfaces of the inorganic particles as the external additive are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is performed by, for example, immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited. Examples thereof include a silane coupling agent, a silicone oil, a titanate coupling agent, and an aluminum coupling agent. The hydrophobic treatment agent may be used alone or in combination of two or more kinds thereof.

An amount of the hydrophobic treatment agent is generally, for example, <NUM> part by mass or more and <NUM> parts by mass or less with respect to <NUM> parts by mass of the inorganic particles.

Examples of the external additive also include resin particles (resin particles such as polystyrene, polymethylmethacrylate, and melamine resin), and cleaning activators (for example, metal salts of higher fatty acids represented by zinc stearate, and particles of a fluoropolymer).

An amount of the external additive externally added is, for example, preferably <NUM> mass% or more and <NUM> mass% or less, and more preferably <NUM> mass% or more and <NUM> mass% or less, with respect to the toner particle.

The toner is obtained by preparing toner particle and then externally adding an external additive to the toner particle.

The toner particles may be produced by either a dry production method (for example, a kneading pulverization method) or a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, and a dissolution suspension method). These production methods are not particularly limited, and known production methods are adopted. Among these, it is preferable to obtain the toner particles by the aggregation and coalescence method.

Specifically, for example, when the toner particles are produced by an aggregation and coalescence method,
the toner particles are produced through a step of preparing a resin particle dispersion liquid in which resin particles to be a binder resin are dispersed (resin particle dispersion liquid preparation step), a step of aggregating the resin particles (other particles if necessary) in the resin particle dispersion liquid (in a dispersion liquid after mixing with another particle dispersion liquid if necessary) to form aggregated particles (aggregated particle forming step), and a step of heating an aggregated particle dispersion liquid in which the aggregated particles are dispersed and fusing and coalescing the aggregated particles to form the toner particles (fusion and coalescence step).

Details of each step will be described below.

In the following description, a method for obtaining toner particles containing a colorant and a mold releasing agent will be described, but the colorant and the mold releasing agent are used as necessary. Of course, other additives other than the colorant and the mold releasing agent may be used.

Along with the resin particle dispersion liquid in which the resin particles to be the binder resin are dispersed, for example, a colorant particle dispersion liquid in which colorant particles are dispersed and a mold releasing agent particle dispersion liquid in which mold releasing agent particles are dispersed are prepared.

The resin particle dispersion liquid is prepared by, for example, dispersing the resin particles in a dispersion medium with a surfactant.

Examples of the dispersion medium used in the resin particle dispersion liquid include an aqueous medium. Examples of the aqueous medium include water such as distilled water and ion-exchanged water, and alcohols. These media may be used alone or in combination of two or more kinds thereof.

Examples of the surfactant include a sulfate-based, sulfonate-based, phosphate-based, soap-based or other anionic surfactant, an amine salt type or quaternary ammonium salt type cationic surfactant, and a polyethylene glycol-based, alkylphenol ethylene oxide adduct-based, or polyhydric alcohol-based nonionic surfactant. Among these, the anionic surfactant and the cationic surfactant are particularly mentioned. The nonionic surfactant may be used in combination with the anionic surfactant or the cationic surfactant.

The surfactant may be used alone or in combination of two or more kinds thereof.

Examples of a method for dispersing the resin particles in the dispersion medium in the resin particle dispersion liquid include general dispersion methods such as a rotary shear homogenizer, a ball mill having a medium, a sand mill, and a dyno mill. Depending on a kind of the resin particles, the resin particles may be dispersed in the dispersion medium by a phase inversion emulsification method. In the phase inversion emulsification method, a resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, and a base is added to an organic continuous phase (O phase) to neutralize the resin, and then an aqueous medium (W phase) is charged to perform phase inversion from W/O to O/W, and the resin is dispersed in the aqueous medium in the form of particles.

A volume average particle diameter of the resin particles dispersed in the resin particle dispersion liquid is, for example, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and still more preferably <NUM> or more and <NUM> or less.

The volume average particle diameter D50v of the resin particles is calculated measured by the volume-based particle size distribution obtained by measurement with a laser diffraction type particle size distribution measuring device (for example, LA-<NUM> manufactured by HORIBA, Ltd. A divided particle size range is set and the volume-based particle size distribution is obtained. Then, a cumulative distribution is drawn from a small particle diameter side and as a volume average particle diameter D50v, which is a particle diameter corresponding to the cumulative percentage of <NUM>% with respect to all the particles is the volume average particle diameter D50v. The volume average particle diameters of the particles in other dispersion liquid are measured in the same manner.

A content of the resin particles contained in the resin particle dispersion liquid is preferably <NUM> mass% or more and <NUM> mass% or less, and more preferably <NUM> mass% or more and <NUM> mass% or less.

Similar to the resin particle dispersion liquid, for example, the colorant particle dispersion liquid and the mold releasing agent particle dispersion liquid are also prepared. That is, the volume average particle diameter, dispersion medium, dispersion method, and content of particles of the particles in the resin particle dispersion liquid are the same for the colorant particles dispersed in the colorant particle dispersion liquid and the mold releasing agent particles dispersed in the mold releasing agent particle dispersion liquid.

Next, the resin particle dispersion liquid, the colorant particle dispersion liquid, and the mold releasing agent particle dispersion liquid are mixed. Then, the aggregated particles containing the resin particles, the colorant particles, and the mold releasing agent particles having a diameter close to the diameter of the target toner particle is formed by hetero-aggregating the resin particles, the colorant particles, and the release agent particles in the mixed dispersion liquid.

Specifically, for example, the aggregated particles are formed by adding an aggregating agent to the mixed dispersion liquid, adjusting the pH of the mixed dispersion liquid to acidic (for example, a pH of <NUM> or more and <NUM> or less), adding a dispersion stabilizer as necessary, then heating the mixed dispersion liquid to a temperature close to the glass transition temperature (specifically, for example, the glass transition temperature of the resin particles -<NUM> or higher and the glass transition temperature -<NUM> or lower) of the resin particles, and aggregating the particles dispersed in the mixed dispersion liquid.

In the aggregated particle forming step, for example, the aggregating agent may be added at room temperature (for example, <NUM>) while stirring the mixed dispersion liquid with a rotary shearing homogenizer, the pH of the mixed dispersion may be adjusted to be acidic (for example, pH <NUM> or more and <NUM> or less), a dispersion stabilizer may be added as necessary, and then heating may be performed.

Examples of the aggregating agent include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion liquid, an inorganic metal salt, and a divalent or higher metal complex. When the metal complex is used as the aggregating agent, an amount of the surfactant used is reduced and chargeability is improved.

If necessary, an additive that forms a complex or a similar bond with metal ions of the aggregating agent may be used together with the aggregating agent. The additive is preferably 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.

As the chelating agent, a water-soluble chelating agent may be used. 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).

An addition amount of the chelating agent is preferably <NUM> parts by mass or more and <NUM> parts by mass or less, and more preferably <NUM> parts by mass or more and less than <NUM> parts by mass, with respect to <NUM> parts by mass of the resin particles.

Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated to, for example, a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature higher than the glass transition temperature of the resin particles by <NUM> to <NUM>), so that the aggregated particles are fused and coalesced to form the toner particles.

The toner particles are obtained through the above steps.

The toner particles may be produced through a step of obtaining the aggregated particle dispersion liquid in which the aggregated particles are dispersed, then further mixing the aggregated particle dispersion liquid and the resin particle dispersion liquid in which the resin particles are dispersed, and performing aggregation to further adhere and aggregate the resin particles to surfaces of the aggregated particles to form second aggregated particles, and a step of heating a second agglomerated particle dispersion liquid in which the second aggregated particles are dispersed to fuse and coalesce the second aggregated particles to form the toner particles having a core-shell structure.

After the fusion and coalescence step is completed, the toner particles formed in the solution are subjected to a washing step, a solid-liquid separation step, and a drying step, which are known, to obtain dried toner particles. In the washing step, from the viewpoint of chargeability, displacement washing with ion-exchanged water may be sufficiently performed. In the solid-liquid separation step, from the viewpoint of productivity, suction filtration, pressure filtration, and the like may be performed. In the drying step, from the viewpoint of productivity, freeze-drying, air-flow drying, fluid-drying, vibration-type fluid-drying, and the like may be performed.

The toner is produced by adding the external additive to the toner particles in a dry state and mixing the materials. The mixing may be carried out by, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Further, if necessary, coarse particles in the toner may be removed by using a vibration sieving machine, a wind sieving machine, or the like.

The carrier includes magnetic particle and a resin layer covering the magnetic particle.

The magnetic particle is a particle of a magnetic oxide selected from ferrite and magnetite. Other magnetic particles include a resin-impregnated magnetic particle obtained by impregnating a porous magnetic powder with a resin; and a magnetic powder-dispersed resin particle in which a magnetic powder is dispersed and blended in a resin. A ferrite particle is preferred as the magnetic particle in the present exemplary embodiment.

A volume average particle diameter of the magnetic particle is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and still more preferably <NUM> or more and <NUM> or less.

Here, the volume average particle diameter means a particle diameter D50v corresponding to the cumulative percentage of <NUM>% in a volume-based particle size distribution from the side of the small diameter.

The arithmetic average height Ra (JIS B0601: <NUM>) of the roughness curve of the magnetic particle is obtained by observing the magnetic particle at an appropriate magnification (for example, a magnification of <NUM> times) using a surface shape measurement apparatus (for example, "Ultra Depth Color 3D shape measurement microscope VK-<NUM>" manufactured by KEYENCE CORPORATION), obtaining a roughness curve at a cutoff value of <NUM>, and extracting a reference length of <NUM> from the roughness curve in a direction of an average line thereof. The arithmetic average value of Ra of <NUM> magnetic particles is preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

As for a magnetic force of the magnetic particle, saturation magnetization in a magnetic field of <NUM>,<NUM> Oersted is preferably <NUM> emu/g or more, and more preferably <NUM> emu/g or more. The saturation magnetization is measured using a vibration sample type magnetic measurement apparatus VSMP10-<NUM> (manufactured by Toei Industry Co. A measurement sample is packed in a cell having an inner diameter of <NUM> and a height of <NUM> and set in the apparatus. The measurement is performed by applying an applied magnetic field and sweeping up to <NUM> Oersted. Next, the applied magnetic field is reduced to create a hysteresis curve on recording paper. The saturation magnetization, residual magnetization, and a holding force are obtained from data of the curve.

A volume resistivity of the magnetic particle is preferably <NUM> × <NUM><NUM> Ω·cm or more and <NUM> × <NUM><NUM> Ω·cm or less, and more preferably <NUM> × <NUM><NUM> Ω·cm or more and <NUM> × <NUM><NUM> Ω·cm or less.

The volume resistivity (Ω·cm) of the magnetic particle is measured as follows. A layer is formed by flatly placing an object to be measured on a surface of a circular jig on which a <NUM><NUM> electrode plate is arranged so as to have a thickness of <NUM> or more and <NUM> or less. Another <NUM><NUM> electrode plate is placed thereon to sandwich the layer. In order to eliminate voids between the object to be measured, the thickness (cm) of the layer is measured after applying a load of <NUM> on the electrode plate arranged on the layer. Both electrodes above and below the layer are connected to an electrometer and a high voltage power generator. A high voltage is applied to both electrodes so that an electric field is <NUM> V/cm, and a current value (A) flowing at this time is read. A measurement environment is under a temperature of <NUM> and a relative humidity of <NUM>%. An equation for calculating the volume resistivity (Ω·cm) of the object to be measured is as illustrated in the equation below.

In the above equation, R represents the volume resistivity (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I<NUM> represents a current value (A) under an applied voltage of <NUM> V, and L represents the thickness (cm) of the layer. The coefficient <NUM> represents the area (cm<NUM>) of the electrode plate.

Examples of a resin include: a styrene-acrylic acid copolymer; polyolefin-based resins such as polyethylene and polypropylene; polyvinyl-based or polyvinylidene-based resins such as polystyrene, an acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinylcarbazole, polyvinyl ether, and polyvinylketone; a vinyl chloride-vinyl acetate copolymer; straight silicone resins consisting of an organosiloxane bond or a modified product thereof; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester, polyurethane; polycarbonate; amino resins such as urea and formaldehyde resins; and epoxy resins.

The resin layer contains an acrylic resin having an alicyclic. A polymerization component of the acrylic resin having the alicyclic is preferably a lower alkyl ester of (meth)acrylic acid (for example, (meth)acrylic acid alkyl ester having an alkyl group having <NUM> or more and <NUM> or less carbon atoms), and specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, and <NUM>-ethylhexyl (meth)acrylate. These monomers may be used alone or in combination of two or more kinds thereof.

The acrylic resin having the alicyclic preferably contains cyclohexyl (meth)acrylate as the polymerization component. A content of a monomer unit derived from the cyclohexyl (meth)acrylate contained in the acrylic resin having the alicyclic is preferably <NUM> mass% or more and <NUM> mass% or less, more preferably <NUM> mass% or more and <NUM> mass% or less, and still more preferably <NUM> mass% or more and <NUM> mass% or less, with respect to a total mass of the acrylic resin having the alicyclic.

The weight average molecular weight of the resin contained in the resin layer is preferably less than <NUM>,<NUM>. When the weight average molecular weight of the resin contained in the resin layer is less than <NUM>,<NUM>, a strength of the resin layer is higher than that when the weight average molecular weight of the resin is <NUM>,<NUM> or more, and the resin layer is less likely to be peeled off when image formation is repeated. As a result, it is presumed that the stirring of the toner in the developing device is improved, the toner is sufficiently triboelectrically charged, and the occurrence of fogging is prevented.

From a viewpoint of increasing the strength of the resin layer and preventing the resin layer from peeling off, the weight average molecular weight of the resin contained in the resin layer is preferably <NUM>,<NUM> or more and less than <NUM>,<NUM>, more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less, and still more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less.

From the viewpoint described above, the weight average molecular weight of the acrylic resin having the alicyclic contained in the resin layer is preferably <NUM>,<NUM> or more and less than <NUM>,<NUM>, more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less, and still more preferably <NUM>,<NUM> or more and <NUM>,<NUM> or less.

When the resin layer contains plural kinds of resins, the weight average molecular weight of the resin contained in the resin layer is a weighted average obtained by weighting the weight average molecular weight of each resin by a content ratio (on a mass basis) of each resin.

The weight average molecular weight of the resin contained in the resin layer is measured by gel permeation chromatography (GPC). In the molecular weight measurement by the GPC, GPC·HLC-8120GPC manufactured by Tosoh Corporation is used as a measurement apparatus, column TSKgel Super HM-M (<NUM>) manufactured by Tosoh Corporation is used, and tetrahydrofuran is used as a solvent. The weight average molecular weight is calculated from a measurement result using a molecular weight calibration curve prepared using a monodispersed polystyrene standard sample.

The resin layer contains silica particles as inorganic particles. In the present exemplary embodiment, the carbon black is not treated as an inorganic particle in the resin layer of the carrier.

When the inorganic particles are contained in the resin layer, a form in which fine ruggedness is appropriately present in the carrier surface is formed. Most of the ruggedness are covered with the resin, but some inorganic particles may be exposed. Since the exposed inorganic particles are not charged by contact with the toner unlike the resin, excessive charging of the carrier surface can be reduced. Further, when the resin layer of the carrier is abraded by repeating the image formation, the ruggedness is selectively abraded, and a part of the inorganic particles in the resin layer is newly exposed. When a part of the inorganic particles continues to be appropriately exposed at the carrier surface, the chargeability of the carrier surface is lowered, and an increase in the toner charging is prevented. As a result, transferability of a toner image is likely to be satisfactorily maintained.

Examples of inorganic particles include metal oxide particles such as silica, titanium oxide, zinc oxide, and tin oxide, metal compound particles such as barium sulfate, aluminum borate, and potassium titanate, and metal particles such as gold, silver, and copper. In accordance with claim <NUM>, the inorganic particles are silica particles.

Surfaces of the inorganic particles may be subjected to the hydrophobic treatment. Examples of the hydrophobic treatment agent include known organic silicon compounds having an alkyl group (for example, a methyl group, an ethyl group, a propyl group, and a butyl group), and specific examples thereof include an alkoxysilane compound, a siloxane compound, and a silazane compound. Among these, the hydrophobic treatment agent is preferably a silazane compound, and preferably hexamethyldisilazane. The hydrophobic treatment agent may be used alone or in combination of two or more kinds thereof.

Examples of a method for hydrophobizing the inorganic particles with the hydrophobic treatment agent include a method in which supercritical carbon dioxide is used and the hydrophobic treatment agent is dissolved in the supercritical carbon dioxide to be attached to the surfaces of the inorganic particles, a method in which a solution containing a hydrophobic treatment agent and a solvent for dissolving the hydrophobic treatment agent is applied (for example, sprayed or coated) to the surfaces of the inorganic particles in the atmosphere to attach the hydrophobic treatment agent to the surfaces of the inorganic particles, and a method in which a solution containing a hydrophobic treatment agent and a solvent for dissolving the hydrophobic treatment agent is added to and held in an inorganic particle dispersion liquid in the air, and then a mixed solution of the inorganic particle dispersion liquid and the solution is dried.

An average particle diameter of the inorganic particles contained in the resin layer is preferably <NUM> or more and <NUM> or less. When the average particle diameter of the inorganic particles in the resin layer is <NUM> or more, a filler effect to increase the strength of the resin layer is easily obtained, and the resin layer is less likely to be peeled off when the image formation is repeated. When the average particle diameter of the inorganic particles in the resin layer is <NUM> or less, the inorganic particles are less likely to be detached from the convex portion of the resin layer, and the resin layer is less likely to be peeled off when the image formation is repeated. In either case, as a result, it is presumed that the stirring of the toner in the developing device is improved, the toner is sufficiently triboelectrically charged, and the occurrence of fogging is prevented.

From the viewpoint described above, the average particle diameter of the inorganic particles in the resin layer is more preferably <NUM> or more and <NUM> or less, still more preferably <NUM> or more and <NUM> or less, and yet still more preferably <NUM> or more and <NUM> or less.

The average particle diameter of the inorganic particles contained in the resin layer can be controlled by a size of the inorganic particles used for forming the resin layer.

An average thickness of the resin layer is <NUM> or more and <NUM> or less.

When the average thickness of the resin layer is <NUM> or more, the resin layer is less likely to be peeled off when the image formation is repeated. When the average thickness of the resin layer is <NUM> or less, the toner external additive is less likely to adhere to or be embedded in the resin layer after the toner external additive is transferred to the resin layer, and the transfer amount of the external additive from the toner to the carrier does not become excessive. In either case, as a result, it is presumed that the stirring of the toner in the developing device is improved, the toner is sufficiently triboelectrically charged, and the occurrence of fogging is prevented.

From the viewpoint described above, the average thickness of the resin layer is more preferably <NUM> or more and <NUM> or less, and still more preferably <NUM> or more and <NUM> or less.

The average thickness of the resin layer can be controlled by an amount of the resin used for forming the resin layer, and the average thickness of the resin layer increases as the amount of the resin with respect to the amount of the magnetic particle increases.

In the present exemplary embodiment, the average particle diameter of the inorganic particles contained in the resin layer and the average thickness of the resin layer are determined by the following methods.

The carrier is embedded in an epoxy resin and cut with a microtome to prepare a carrier cross section. A scanning electron microscope (SEM) image obtained by capturing the carrier cross section with the SEM is taken into an image processing analysis apparatus for image analysis. <NUM> inorganic particles (primary particles) in the resin layer are randomly selected, and an equivalent circular diameter (nm) of each particle is calculated and arithmetically averaged to obtain the average particle diameter (nm) of the inorganic particles. The thickness (µm) of the resin layer is measured by randomly selecting <NUM> points per particle of the carrier, and <NUM> particles of the carrier are further selected to measure thicknesses thereof, and all the thicknesses are arithmetically averaged to obtain the average thickness (µm) of the resin layer.

The resin layer of the carrier contains the silica particles, and a silicon element concentration at the carrier surface determined by an X-ray photoelectron spectroscopy is more than <NUM> atomic% and less than <NUM> atomic%.

When the silicon element concentration is more than <NUM> atomic%, it means that the silica particles are appropriately distributed at the resin layer surface. Therefore, the chargeability of the carrier surface is appropriately lowered.

When the silicon element concentration is less than <NUM> atomic%, it means that an amount of silica particles distributed at the resin layer surface is not too large. Therefore, the chargeability of the carrier surface is not excessively lowered.

In either case, as a result, it is presumed that the toner is appropriately triboelectrically charged and the occurrence of fogging is prevented.

From the viewpoint described above, the silicon element concentration is more preferably more than <NUM> atomic% and less than <NUM> atomic%, and still more preferably more than <NUM> atomic% and less than <NUM> atomic%.

The silicon element concentration at the carrier surface can be controlled by the amount of the silica particles used for forming the resin layer, and the silicon element concentration at the carrier surface increases as the amount of the silica particles with respect to the amount of the resin increases.

The silicon element concentration (atomic%) of the carrier surface is determined based on a peak intensity of each element by analyzing the carrier as a sample by the X-ray photoelectron spectroscopy (XPS) under the following conditions.

A content of the inorganic particles contained in the resin layer is preferably <NUM> mass% or more and <NUM> mass% or less, more preferably <NUM> mass% or more and <NUM> mass% or less, and still more preferably <NUM> mass% or more and <NUM> mass% or less with respect to a total mass of the resin layer.

A content of the silica particles contained in the resin layer is preferably <NUM> mass% or more and <NUM> mass% or less, more preferably <NUM> mass% or more and <NUM> mass% or less, and still more preferably <NUM> mass% or more and <NUM> mass% or less with respect to a total mass of the resin layer.

The resin layer may contain conductive particles for a purpose of controlling charging and resistance. Examples of the conductive particles include carbon black and conductive particles among the above-mentioned inorganic particles.

Examples of a method for forming the resin layer on surfaces of the magnetic particle include a wet production method and a dry production method. The wet production method is a production method using a solvent that dissolves or disperses the resin constituting the resin layer. On the other hand, the dry production method is a production method that does not use the above solvent.

Examples of the wet production method include an immersion method in which the magnetic particles are immersed in a resin liquid for forming the resin layer to be coated, a spray method in which a resin liquid for forming the resin layer is sprayed on the surfaces of the magnetic particles, a fluidized bed method in which a resin liquid for forming the resin layer is sprayed while the magnetic particles are in a state of being fluidized in a fluidized bed, and a kneader coater method in which the magnetic particles and a resin liquid for forming the resin layer are mixed in a kneader coater to remove a solvent. These production methods may be repeated or combined.

The resin liquid for forming the resin layer used in the wet production method is prepared by dissolving or dispersing a resin, inorganic particles, and other components in a solvent. The solvent is not particularly limited. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane may be used.

Examples of the dry production method include a method of forming the resin layer by heating a mixture of the magnetic particles and a resin for forming the resin layer in a dry state. Specifically, for example, the magnetic particles and the resin for forming the resin layer are mixed in a gas phase and heated and melted to form the resin layer.

The ratio B/A can be controlled by production conditions.

For example, in a production method in which the kneader coater method is repeated plural times (for example, twice) to form the resin layer stepwise, in a final kneader coater step, the ratio B/A is controlled by adjusting a mixing time between particles to be coated and a resin liquid for forming the resin layer. The longer the mixing time in the final kneader coater step, the smaller the ratio B/A tends to be.

Alternatively, for example, in a production method in which a liquid composition containing inorganic particles (a resin may or may not be contained) is applied, by a spray method, to the resin-coated carrier surface manufactured by the kneader coater method, the ratio B/A is controlled by adjusting the particle diameter and the content of the inorganic particles contained in the liquid composition or an amount of the liquid composition applied to the resin-coated carrier.

An exposed area ratio of the magnetic particle at the carrier surface is preferably <NUM>% or more and <NUM>% or less, more preferably <NUM>% or more and <NUM>% or less, and still more preferably <NUM>% or more and <NUM>% or less. The exposed area ratio of the magnetic particle in the carrier can be controlled by the amount of the resin used for forming the resin layer, and the exposed area ratio becomes smaller as the amount of the resin relative to the amount of the magnetic particle increases.

The exposed area ratio of the magnetic particle at the carrier surface is a value obtained by the following method.

A target carrier and magnetic particle obtained by removing the resin layer from the target carrier are prepared. Examples of a method for removing the resin layer from the carrier include a method of dissolving a resin component with an organic solvent to remove the resin layer and a method of removing the resin component by heating at about <NUM> to remove the resin layer. The carrier and the magnetic particle are used as measurement samples, and Fe concentrations (atomic%) at surfaces of the samples are quantified by XPS, and (Fe concentration of the carrier)/(Fe concentration of the magnetic particle) × <NUM> is calculated and used as the exposed area ratio (%) of the magnetic particle.

A volume average particle diameter of the carrier is preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and still more preferably <NUM> or more and <NUM> or less.

An image forming apparatus according to the present exemplary embodiment includes: an image carrier; a charging unit that charges a surface of the image carrier; an electrostatic charge image forming unit that forms an electrostatic charge image on the surface of the charged image carrier; a developing unit that accommodates an electrostatic charge image developer and develops, by the electrostatic charge image developer, an electrostatic charge image formed on the surface of the image carrier as a toner image; a transfer unit that transfers the toner image formed on the surface of the image carrier to a surface of a recording medium; and a fixing unit that fixes the toner image transferred to the surface of the recording medium. As the electrostatic charge image developer, the electrostatic charge image developer according to the present exemplary embodiment is applied.

In the image forming apparatus according to the present exemplary embodiment, an image forming method (image forming method according to the present exemplary embodiment) including a charging step of charging a surface of an image carrier, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the image carrier, a developing step of developing, by the electrostatic charge image developer according to the present exemplary embodiment, the electrostatic charge image formed on the surface of the image carrier as a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to a surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium is performed.

A known image forming apparatus such as a direct transfer type apparatus that directly transfers the toner image formed on the surface of the image carrier to the recording medium, an intermediate transfer type apparatus that primarily transfers the toner image formed on the surface of the image carrier to a surface of an intermediate transfer member, and secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of the recording medium, an apparatus provided with a cleaning unit that cleans the surface of the image carrier after the transfer of the toner image and before charging, and an apparatus provided with a discharging unit that discharges the surface of the image carrier by irradiation with discharging light after the transfer of the toner image and before the charging, is applied to the image forming apparatus according to the present exemplary embodiment.

When the image forming apparatus according to the present exemplary embodiment is an intermediate transfer type apparatus, the transfer unit includes, for example, an intermediate transfer member on which a toner image is transferred onto a surface thereof, a primary transfer unit that primarily transfers the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer member, and a secondary transfer unit that secondarily transfers the toner image transferred on the surface of the intermediate transfer member onto the surface of the recording medium.

In the image forming apparatus according to the present exemplary embodiment, for example, a part including the developing unit may have a cartridge structure (process cartridge) attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge that accommodates the electrostatic charge image developer according to the present exemplary embodiment and provided with a developing unit is preferably used.

Hereinafter, an example of the image forming apparatus according to the present exemplary embodiment will be described, whereas the image forming apparatus is not limited thereto. In the following description, main parts illustrated in the drawings will be described, and description of other parts will be omitted.

<FIG> is a schematic configuration diagram illustrating the image forming apparatus according to the present exemplary embodiment.

The image forming apparatus illustrated in <FIG> includes first to fourth electrophotographic image forming units 10Y, <NUM>, 10C, and <NUM> (image forming units) that output images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) based on image data subjected to color separation. The image forming units (hereinafter may be simply referred to as "unit") 10Y, <NUM>, 10C, and <NUM> are arranged side by side at a predetermined distance from each other in a horizontal direction. The units 10Y, <NUM>, 10C, and <NUM> may be process cartridges that are attached to and detached from the image forming apparatus.

Above the units 10Y, <NUM>, 10C, and <NUM>, an intermediate transfer belt (an example of the intermediate transfer member) <NUM> extends through respective units. The intermediate transfer belt <NUM> is provided by being wound around a drive roller <NUM> and a support roller <NUM>, and travels in a direction from the first unit 10Y to the fourth unit <NUM>. A force is applied to the support roller <NUM> in a direction away from the drive roller <NUM> by a spring or the like (not shown). Tension is applied to the intermediate transfer belt <NUM> wound around the drive roller <NUM> and the support roller <NUM>. An intermediate transfer member cleaning device <NUM> is provided on a side surface of an image carrier of the intermediate transfer belt <NUM> so as to face the drive roller <NUM>.

Yellow, magenta, cyan, and black toners contained in toner cartridges 8Y, <NUM>, 8C, and <NUM> are supplied to developing devices 4Y, <NUM>, 4C, and <NUM> (an example of the developing unit) of the units 10Y, <NUM>, 10C, and <NUM>, respectively.

Since the first to fourth units 10Y, <NUM>, 10C, and <NUM> have the same configuration and operation, here, the first unit 10Y, which is arranged on an upstream side in a travelling direction of the intermediate transfer belt and forms a yellow image, will be described as a representative. <NUM>, 1C, and <NUM> in the second to fourth units <NUM>, 10C, and <NUM> are photoconductors corresponding to a photoconductor 1Y in the first unit 10Y. <NUM>, 2C and <NUM> are charging rollers corresponding to a charging roller 2Y. <NUM>, 3C, and <NUM> are laser beams corresponding to a laser beam 3Y. <NUM>, 6C, and <NUM> are photoconductor cleaning devices corresponding to a photoconductor cleaning device 6Y.

The first unit 10Y includes the photoconductor 1Y that acts as an image carrier. Around the photoconductor 1Y, the following members are arranged in order: the charging roller (an example of the charging unit) 2Y that charges a surface of the photoconductor 1Y to a predetermined potential; an exposure device (an example of the electrostatic charge image forming unit) <NUM> that exposes the charged surface with the laser beam 3Y based on a color-separated image signal to form an electrostatic charge image; the developing device (an example of the developing unit) 4Y that supplies a charged toner to the electrostatic charge image to develop the electrostatic charge image; a primary transfer roller 5Y (an example of the primary transfer unit) that transfers the developed toner image onto the intermediate transfer belt <NUM>; and the photoconductor cleaning device (an example of the cleaning unit) 6Y that removes the toner remaining on the surface of the photoconductor 1Y after the primary transfer.

The primary transfer roller 5Y is arranged on an inner side of the intermediate transfer belt <NUM> and is provided at a position facing the photoconductor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to each of the primary transfer rollers 5Y, <NUM>, 5C, and <NUM> of respective units. Each bias power supply changes a value of the transfer bias applied to each primary transfer roller under the control of a controller (not shown).

Hereinafter, an operation of forming a yellow image in the first unit 10Y will be described.

First, prior to the operation, the surface of the photoconductor 1Y is charged to a potential of -<NUM> V to -<NUM> V by using the charging roller 2Y.

The photoconductor 1Y is formed by laminating a photoconductive layer on a conductive substrate (for example, having a volume resistivity of <NUM> × <NUM>-<NUM> Ω·cm or less at <NUM>). The photoconductive layer usually has high resistance (resistance of general resin), but has a property that when irradiated with a laser beam, a specific resistance of the portion irradiated with the laser beam changes. Therefore, the charged surface of the photoconductor 1Y is irradiated with the laser beam 3Y from the exposure device <NUM> in accordance with yellow image data sent from the controller (not shown). Accordingly, an electrostatic charge image having a yellow image pattern is formed on the surface of the photoconductor 1Y.

The electrostatic charge image is an image formed on the surface of the photoconductor 1Y by charging, and is a so-called negative latent image formed by lowering the specific resistance of the portion of the photoconductive layer irradiated with the laser beam 3Y to flow charges charged on the surface of the photoconductor 1Y and by, on the other hand, leaving charges of a portion not irradiated with the laser beam 3Y.

The electrostatic charge image formed on the photoreceptor 1Y rotates to a predetermined developing position as the photoreceptor 1Y travels. Then, at the developing position, the electrostatic charge image on the photoconductor 1Y is developed and visualized as a toner image by the developing device 4Y.

In the developing device 4Y, for example, an electrostatic charge image developer containing at least a yellow toner and a carrier is accommodated. The yellow toner is triboelectrically charged by being stirred inside the developing device 4Y, and has charges of the same polarity (negative polarity) as the charges charged on the photoconductor 1Y and is held on a developer roller (an example of a developer holder). Then, when the surface of the photoconductor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to a discharged latent image portion on the surface of the photoconductor 1Y, and the latent image is developed by the yellow toner. The photoreceptor 1Y on which the yellow toner image is formed continuously travels at a predetermined speed, and the toner image developed on the photoconductor 1Y is conveyed to a predetermined primary transfer position.

When the yellow toner image on the photoconductor 1Y is conveyed to the primary transfer position, a primary transfer bias is applied to the primary transfer roller 5Y, an electrostatic force from the photoconductor 1Y to the primary transfer roller 5Y acts on the toner image, and the toner image on the photoconductor 1Y is transferred onto the intermediate transfer belt <NUM>. The transfer bias applied at this time has a polarity (+) opposite to the polarity (-) of the toner, and is controlled to, for example, +<NUM>µA by the controller (not shown) in the first unit 10Y.

On the other hand, the toner remaining on the photoconductor 1Y is removed and collected by the photoconductor cleaning device 6Y.

The primary transfer biases applied to the primary transfer rollers <NUM>, 5C, and <NUM> of the second unit <NUM> and the subsequent units are also controlled in the same manner as in the first unit.

In this way, the intermediate transfer belt <NUM> to which the yellow toner image is transferred by the first unit 10Y is sequentially conveyed through the second to fourth units <NUM>, 10C, and <NUM>, and toner images of the respective colors are superimposed and transferred in a multiple manner.

The intermediate transfer belt <NUM> onto which the toner images of four colors are transferred in a multiple manner through the first to fourth units arrives at a secondary transfer unit including the intermediate transfer belt <NUM>, the support roller <NUM> in contact with an inner surface of the intermediate transfer belt, and a secondary transfer roller (an example of a secondary transfer unit) <NUM> arranged on an image holding surface side of the intermediate transfer belt <NUM>. On the other hand, a recording paper (an example of the recording medium) P is fed through a supply mechanism into a gap where the secondary transfer roller <NUM> and the intermediate transfer belt <NUM> are in contact with each other at a predetermined timing, and a secondary transfer bias is applied to the support roller <NUM>. The transfer bias applied at this time has the same polarity (-) as the polarity (-) of the toner. An electrostatic force from the intermediate transfer belt <NUM> to the recording paper P acts on the toner image, and the toner image on the intermediate transfer belt <NUM> is transferred onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection unit (not shown) that detects the resistance of the secondary transfer unit, and is subjected to voltage control.

Thereafter, the recording paper P is sent to a pressure contact portion (nip portion) of a pair of fixing rollers in a fixing device <NUM> (an example of the fixing unit), and the toner image is fixed onto the recording paper P, thereby forming a fixed image.

Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers and printers. As the recording medium, in addition to the recording paper P, an OHP sheet or the like may be used.

In order to further improve the smoothness of the image surface after fixing, the surface of the recording paper P is also preferably smooth. For example, coated paper obtained by coating the surface of the plain paper with a resin or the like, or art paper for printing is preferably used.

The recording paper P, on which the fixing of the color image is completed, is conveyed out toward a discharge unit, and a series of color image forming operations is completed.

The process cartridge according to the present exemplary embodiment includes a developing unit that accommodates the electrostatic charge image developer according to the present exemplary embodiment and develops, by the electrostatic charge image developer, the electrostatic charge image formed on the surface of the image carrier as the toner image, and is attached to and detached from the image forming apparatus.

The process cartridge according to the present exemplary embodiment is not limited to the above configuration and may be configured to include a developing unit and, if necessary, at least one selected from other units such as an image carrier, a charging unit, an electrostatic charge image forming unit, and a transfer unit.

Hereinafter, an example of the process cartridge according to the present exemplary embodiment will be illustrated, whereas the process cartridge is not limited thereto. In the following description, main parts illustrated in the drawings will be described, and description of other parts will be omitted.

<FIG> is a schematic configuration diagram illustrating the process cartridge according to the present exemplary embodiment.

A process cartridge <NUM> illustrated in <FIG> is formed as a cartridge by, for example, integrally combining and holding a photoconductor <NUM> (an example of the image carrier), a charging roller <NUM> (an example of the charging unit), an image developing device <NUM> (an example of the developing unit), and a photoconductor cleaning device <NUM> (an example of a cleaning unit) provided around the photoconductor <NUM> by a housing <NUM> provided with a mounting rail <NUM> and an opening <NUM> for exposure.

In <FIG>, <NUM> denotes an exposure device (an example of the electrostatic charge image forming unit), <NUM> denotes a transfer device (an example of the transfer unit), <NUM> denotes a fixing device (an example of the fixing unit), and <NUM> denotes recording paper (an example of the recording medium).

Hereinafter, the exemplary embodiment according to the invention will be described in detail with reference to Examples, whereas the exemplary embodiment according to the invention is not limited to these Examples.

In the following description, all "parts" and "%" are based on mass unless otherwise specified.

Synthesis, treatment, production, and the like are performed at a room temperature (<NUM> ± <NUM>), unless otherwise specified.

The above materials are charged into a flask and raised to a temperature of <NUM> over <NUM> hour, and after confirming that the inside of the reaction system is uniformly stirred, <NUM> parts of dibutyltin oxide is added. The temperature is raised to <NUM> over <NUM> hours while water to be produced is distilled off, and stirring is continued at <NUM> for <NUM> hours to obtain an amorphous polyester resin (<NUM>) (weight average molecular weight <NUM>,<NUM>, glass transition temperature <NUM>).

The amorphous polyester resin (<NUM>) is transferred to an emulsification disperser (CAVITRON CD1010 manufactured by Eurotech Co. ) at a rate of <NUM> per minute while the amorphous polyester resin is in a molten state. Separately, dilute ammonia water having a concentration of <NUM>% obtained by diluting reagent ammonia water with ion exchange water is put into a tank and transferred to the emulsification disperser at the same time as the amorphous polyester resin at a rate of <NUM> liter per minute while being heated to <NUM> in a heat exchanger. The emulsification disperser is operated under conditions of a rotation speed of <NUM> and a pressure of <NUM>/cm<NUM> of a rotor to obtain an amorphous polyester resin dispersion liquid (<NUM>) having a volume average particle diameter of <NUM> and a solid content of <NUM>%.

The above materials are put into a heated and dried three-necked flask, air in the three-necked flask is replaced with nitrogen gas to make an inert atmosphere, and stirring and refluxing are performed at <NUM> for <NUM> hours by mechanical stirring. Subsequently, the temperature is gradually increased to <NUM> under reduced pressure, the mixture is stirred for <NUM> hours, and when the mixture is in a viscous state, the mixture is air-cooled to stop the reaction, thereby obtaining a crystalline polyester resin (<NUM>) (weight average molecular weight: <NUM>, melting temperature: <NUM>).

<NUM> parts of the crystalline polyester resin (<NUM>), <NUM> parts of an anionic surfactant (NEOGEN RK, manufactured by Dai-ichi Kogyo Seiyaku Co. ), and <NUM> parts of ion exchange water are mixed, heated to <NUM>, dispersed using a homogenizer (ULTRA-TURRAX T50, manufactured by IKA), and then subjected to a dispersion treatment for <NUM> hour using a pressure discharge type Gaulin homogenizer to obtain a resin particle dispersion liquid in which resin particles having a volume average particle diameter of <NUM> are dispersed. Ion exchange water is added to the resin particle dispersion liquid to adjust a solid content to <NUM>%, thereby obtaining the crystalline polyester resin dispersion (<NUM>).

The above materials are mixed and subjected to a dispersion treatment for <NUM> minutes using a high-pressure impact type disperser (ULTIMAIZER HJP30006 manufactured by Sugino Machine Limited) to obtain a colorant dispersion liquid (C1) having a solid content of <NUM>%.

The above materials are mixed and heated to <NUM>, dispersed using the homogenizer (ULTRA-TURRAX T50 manufactured by IKA Co. ), and then subjected to a dispersion treatment with a pressure discharge type Gaulin homogenizer to obtain a mold releasing agent dispersion liquid in which mold releasing agent particles having a volume average particle diameter of <NUM> are dispersed. The ion-exchange water is added to the mold releasing agent dispersion liquid to prepare a solid content of <NUM>%, thereby obtaining a mold releasing agent dispersion liquid (W1).

The above materials are put into a round stainless steel flask, <NUM>. 1N nitric acid is added to adjust pH to <NUM>, and then an aqueous solution of polyaluminum chloride in which <NUM> parts of polyaluminum chloride (<NUM>% powdery product manufactured by Oji Paper Co. ) is dissolved in <NUM> parts of ion-exchange water is added. The mixture is dispersed at <NUM> using the homogenizer (ULTRA-TURRAX T50 manufactured by IKA Co. ), the heated to <NUM> in an oil bath for heating, and held until the volume average particle diameter becomes <NUM>.

Next, <NUM> parts of the amorphous polyester resin dispersion liquid (<NUM>) are added and held for <NUM> minutes. Next, when the volume average particle diameter is <NUM>, <NUM> parts of the amorphous polyester resin dispersion liquid (<NUM>) are added and held for <NUM> minutes.

Next, <NUM> parts of <NUM>% nitrilotriacetic acid (NTA) metal salt aqueous solution (CHELEST <NUM> manufactured by Chelest Corporation) is added, and a 1N sodium hydroxide aqueous solution is added to adjust the pH to <NUM>. Next, <NUM> part of anionic surfactant (Tayca Power) is charged and heated to <NUM> while stirring is continued, and held for <NUM> hours. Next, the mixture is cooled to <NUM> at a rate of <NUM>/min. Next, the solution is filtered, sufficiently washed with the ion-exchanged water, and dried to obtain cyan toner particles (<NUM>) having a volume average particle diameter of <NUM>.

Cyan toner particles (<NUM>) to (<NUM>) are prepared in the same manner as in the preparation of the cyan toner particles (<NUM>), except that a pH and a temperature in a fusion and coalescence step or a usage amount of the crystalline polyester resin dispersion liquid (<NUM>) is changed as illustrated in Table <NUM>.

<NUM> parts of any of the cyan toner particles (<NUM>) to (<NUM>) and <NUM> parts of hydrophobic silica particles (RY50 manufactured by Nippon Aerosil Co. ) are charged into a sample mill and mixed at a rotation speed of <NUM>,<NUM> rpm for <NUM> seconds. Next, the mixture is sieved with a vibrating sieve having an opening of <NUM> to obtain cyan toners (<NUM>) to (<NUM>).

<NUM> parts of Fe<NUM>O<NUM>, <NUM> parts of Mn(OH)<NUM>, and <NUM> parts of Mg(OH)<NUM> are mixed and calcined at a temperature of <NUM> for <NUM> hours. A calcined product, <NUM> parts of polyvinyl alcohol, <NUM> parts of polycarboxylic acid as a dispersant, and zirconia beads having a medium diameter of <NUM> are charged into water, pulverized, and mixed in a sand mill to obtain a dispersion liquid. A volume average particle diameter of particles in the dispersion liquid is <NUM>.

The dispersion liquid is used as a raw material and granulated and dried with a spray dryer to obtain granules having a volume average particle diameter of <NUM>. Next, under an oxygen-nitrogen mixed atmosphere having an oxygen partial pressure of <NUM>%, main firing is performed using an electric furnace at a temperature of <NUM> for <NUM> hours, and then heating is performed in air at a temperature of <NUM> for <NUM> hours to obtain fired particles. The fired particles are crushed and classified to obtain ferrite particles (<NUM>) having a volume average particle diameter of <NUM>. An arithmetic average height Ra (JIS B0601: <NUM>) of a roughness curve of the ferrite particles (<NUM>) is <NUM>.

Commercially available hydrophilic silica particles (fumed silica particles, without surface treatment, volume average particle diameter: <NUM>) are prepared as silica particles (<NUM>).

<NUM> parts of methanol and <NUM> parts of <NUM>% ammonia water are charged into a <NUM> glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer and mixed to obtain an alkaline catalyst solution. After the alkaline catalyst solution is adjusted to <NUM>, <NUM> parts of tetramethoxysilane and <NUM> parts of <NUM>% ammonia water are simultaneously added dropwise over <NUM> minutes while stirring to obtain a silica particle dispersion liquid (A). The silica particles in the silica particle dispersion liquid (A) have a volume average particle diameter of <NUM> and a volume particle size distribution index of <NUM> (volume particle size distribution index is (D84v/D16v)<NUM>/<NUM> which is square root of a ratio of a particle diameter D84v at <NUM>% accumulation to a particle diameter D16v at <NUM>% accumulation from the small diameter side in the volume-based particle size distribution).

<NUM> parts of the silica particle dispersion liquid (A) are charged into an autoclave equipped with a stirrer, and the stirrer is rotated at a rotation speed of <NUM> rpm. While the stirrer is continuously rotated, liquefied carbon dioxide is injected into the autoclave from a carbon dioxide cylinder via a pump, a pressure inside the autoclave is raised by the pump while the temperature is raised by a heater, and the inside of the autoclave is brought into a supercritical state of <NUM> and <NUM> MPa. A pressure valve is operated to circulate supercritical carbon dioxide while keeping the inside of the autoclave at <NUM> MPa, and methanol and water are removed from the silica particle dispersion liquid (A). When an amount of carbon dioxide supplied into the autoclave reaches <NUM> parts, supply of carbon dioxide is stopped to obtain a powder of silica particles.

In a state in which the inside of the autoclave is maintained at <NUM> and <NUM> MPa by the heater and the pump to maintain the supercritical state of carbon dioxide, <NUM> parts of hexamethyldisilazane with respect to <NUM> parts of silica particles is injected into the autoclave by an entrainer pump while the stirrer of the autoclave is continuously rotated, the temperature inside the autoclave is raised to <NUM>, and a reaction is carried out for <NUM> minutes. Next, the supercritical carbon dioxide is circulated again in the autoclave, and excess hexamethyldisilazane is removed. Next, stirring is stopped, the pressure valve is opened to release the pressure in the autoclave to atmospheric pressure, and the temperature is lowered to room temperature (<NUM>). In this way, silica particles (<NUM>) surface-treated with the hexamethyldisilazane are obtained. The silica particles (<NUM>) have a volume average particle diameter of <NUM>.

In the same manner as the preparation of the silica particles (<NUM>), amounts of the tetramethoxysilane and the <NUM>% ammonia water dropped when the silica particle dispersion liquid (A) is prepared are increased to change the volume average particle diameter of the silica particles in the silica particle dispersion liquid to <NUM>, thereby obtaining silica particles (<NUM>) surface-treated with the hexamethyldisilazane. The silica particles (<NUM>) have a volume average particle diameter of <NUM>.

Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle diameter: <NUM>) are prepared as silica particles (<NUM>).

Commercially available calcium carbonate particles (volume average particle diameter: <NUM>) are prepared as inorganic particles (<NUM>).

Commercially available barium carbonate particles (volume average particle diameter: <NUM>) are prepared as inorganic particles (<NUM>).

Commercially available barium sulfate particles (BARIFINE BF-<NUM>, volume average particle diameter: <NUM>) are prepared as inorganic particles (<NUM>).

The above materials and glass beads (diameter: <NUM>, the same amount as toluene) are charged into a sand mill and stirred at a rotation speed of <NUM> rpm for <NUM> minutes, to obtain a coating agent (<NUM>) having a solid content of <NUM>%. The weight average molecular weight of the resin constituting the coating agent (<NUM>) is <NUM>,<NUM>.

Coating agents (<NUM>) to (<NUM>) are obtained in the same manner as in preparation of the coating agent (<NUM>), except that the silica particles (<NUM>) are changed to any of the silica particles (<NUM>) to (<NUM>).

Coating agents (<NUM>) to (<NUM>) are obtained in the same manner as in the preparation of the coating agent (<NUM>), except that the addition amount of the silica particles (<NUM>) is changed as follows.

The above materials and glass beads (diameter: <NUM>, the same amount as toluene) are charged into a sand mill and stirred at a rotation speed of <NUM>,<NUM> rpm for <NUM> minutes to obtain a coating agent (<NUM>-<NUM>) having a solid content of <NUM>%.

The above materials and glass beads (diameter: <NUM>, the same amount as toluene) are charged into a sand mill and stirred at a rotation speed of <NUM> rpm for <NUM> minutes, to obtain a coating agent (<NUM>) having a solid content of <NUM>%.

<NUM> parts of the ferrite particles (<NUM>) and <NUM> parts of the coating agent (<NUM>) are charged into a kneader and mixed at a room temperature (<NUM>) for <NUM> minutes. Then, the mixture is heated to <NUM> and reduced in pressure to be dried.

A dried product is cooled to the room temperature (<NUM>), <NUM> parts of the coating agent (<NUM>) are additionally charged, and the mixture is mixed at the room temperature (<NUM>) for <NUM> minutes. Then, the mixture is heated to <NUM> and reduced in pressure to be dried.

Next, a dried product is taken out from the kneader, and coarse powder is sieved with a mesh having an opening of <NUM> and removed to obtain the carrier (<NUM>).

Carriers (<NUM>) to (<NUM>) are obtained in the same manner as in the preparation of the carrier (<NUM>), except that the mixing time after the additional coating agent (<NUM>) is charged is changed as illustrated in Table <NUM>.

Carriers (<NUM>) to (<NUM>) are obtained in the same manner as in the preparation of the carrier (<NUM>), except that the coating agent (<NUM>) is changed to any one of the coating agents (<NUM>) to (<NUM>).

Carriers (<NUM>) to (<NUM>) are obtained in the same manner as in the preparation of the carrier (<NUM>), except that the amount of the additionally charged coating agent (<NUM>) is changed as illustrated in Table <NUM>.

<NUM> parts of the ferrite particles (<NUM>) and <NUM> parts of the coating agent (<NUM>-<NUM>) are placed in a vacuum degassing kneader, heating and decompression are conducted with stirring, and the mixture is stirred and dried in an atmosphere of <NUM>/-<NUM> mmHg for <NUM> minutes. <NUM> parts of the coating agent (<NUM>-<NUM>) are applied to the taken-out carrier by a spray method, dried, and then allowed to stand at <NUM> for <NUM> hour in an electric furnace to be fired. The coarse powder is removed by sieving with a mesh having an opening of <NUM> to obtain the carrier (<NUM>).

As illustrated in Tables <NUM> and <NUM>, any one of the cyan toners (<NUM>) to (<NUM>) and any one of the carriers (<NUM>) to (<NUM>) are combined, put into a V blender at a mixing ratio of toner: carrier = <NUM>: <NUM> (mass ratio), and stirred for <NUM> minutes to obtain a cyan developer.

The specific surface area measured value of the toner particles is obtained from a nitrogen adsorption amount by BET one-point method (equilibrium relative pressure: <NUM>).

The toner particles are taken into the flow particle image analysis apparatus (FPIA-<NUM> manufactured by Sysmex Corporation), the toner particles are captured, subjected to the two-dimensional image processing, and the equivalent circle diameter is calculated from the projection area. A sum of the surface areas and a sum of the volumes are calculated from equivalent circle diameters of <NUM>,<NUM> toner particles.

Density of the toner particles is measured by measuring true density in accordance with <NUM>. <NUM> of JIS K0061: <NUM> using a Gulysack type specific gravity bottle.

Using a press molding machine, <NUM> of toner is tablet-molded into a disk having a diameter of <NUM> and a thickness of <NUM> in an environment of <NUM> ± <NUM>. The disk-shaped sample is placed on a parallel plate of a rheometer ("ARES" manufactured by TA Instruments Inc. The sample is adhered to a parallel plate at a temperature of <NUM>, cooled to a temperature of <NUM> at a cooling rate of <NUM>/min, held at a temperature of <NUM> for <NUM> minutes, and then measured at the temperature of <NUM>. Measurement conditions include a frequency of <NUM>, an angular frequency of <NUM> rad/sec, and a strain of <NUM> to <NUM>% (automatic control).

As an apparatus for three-dimensional analysis of the surface of the carrier, an electron beam three-dimensional roughness analysis apparatus ERA-8900FE manufactured by Elionix Co. The surface analysis of the carrier by ERA-8900FE is specifically performed as follows.

The surface of one carrier particle is magnified <NUM>,<NUM> times, and three-dimensional measurement is performed by taking <NUM> measurement points in a long side direction and <NUM> points in a short side direction to obtain three-dimensional image data in a region of <NUM> × <NUM>. For the three-dimensional image data, the limit wavelength of the spline filter is set to <NUM> to remove wavelengths having a period of <NUM> or more, and the cutoff value of the Gaussian high-pass filter is set to <NUM> to remove wavelengths having a period of <NUM> or more, so as to obtain three-dimensional roughness curve data. From three-dimensional roughness curve data, the surface area B (µm<NUM>) of a central portion <NUM> × <NUM> region (the plan view area A = <NUM><NUM>) is obtained, so as to obtain the ratio B/A. The ratio B/A is calculated for each of <NUM> carriers and the arithmetic average value is obtained.

The carrier is embedded in an epoxy resin and cut with a microtome to prepare a carrier cross section. An SEM image obtained by capturing the carrier cross section with a scanning transmission electron microscope (S-<NUM>, manufactured by Hitachi, Ltd. ) is taken into an image processing analysis apparatus (Nireco, Luzex AP), and image analysis is performed. <NUM> silica particles (primary particles) in the resin layer are randomly selected, and an equivalent circular diameter (nm) of each particle is calculated and arithmetically averaged to obtain the average particle diameter (nm) of the silica particles.

The SEM image is taken into the image processing analysis apparatus (Nireco, Luzex AP) to perform the image analysis. The thickness (µm) of the resin layer is measured by randomly selecting <NUM> points per particle of the carrier, and <NUM> particles of the carrier are further selected to measure thicknesses thereof, and all the thicknesses are arithmetically averaged to obtain the average thickness (µm) of the resin layer.

The carrier is used as a sample and analyzed by X-ray photoelectron spectroscopy (XPS) under the following conditions, and the silicon element concentration (atomic%) is obtained from a peak intensity of each element.

A modified machine of an image forming apparatus DocuPrint Color <NUM> (manufactured by Fuji Xerox Co. ) is prepared, and a developer is put into a developing device. A toner of the same kind as the toner used for preparing the developer is put into the toner cartridge (for example, when the developer in the developing device is a developer in which the cyan toner (<NUM>) and the carrier (<NUM>) are combined, the cyan toner (<NUM>) is put into the toner cartridge).

The image forming apparatus is left in an environment at a temperature of <NUM> and a relative humidity of <NUM>% for <NUM> hours. Under an environment of the temperature of <NUM> and the relative humidity of <NUM>%, <NUM>,<NUM> sheets of cyan test images having an image density of <NUM>% are output on A3 size paper. Next, <NUM> cyan test images with the image density of <NUM>% are output on the entire surface of the A3 size paper, and the presence or absence of fogging is observed with naked eyes and a loupe with a magnification of <NUM> times, and classified as follows.

A: Fogging is not observed in all <NUM> sheets. B: Fogging is slightly observed in one sheet by a loupe, but does not cause a problem. C: Fogging is slightly observed in plural sheets by a loupe, but is slight, which is practically acceptable. D: Fogging is observed in plural sheets by the naked eyes, but is slight, and is practically acceptable. E: Fogging is observed in all <NUM> sheets by the naked eyes, which is not suitable for practical use.

Claim 1:
An electrostatic charge image developer comprising:
a toner containing a toner particle and an external additive; and
a carrier containing a magnetic particle which is a particle of a magnetic oxide wherein the particle of a magnetic oxide is selected from ferrite and magnetite, and a resin layer covering the magnetic particle and the resin layer has an average thickness of <NUM> or more and <NUM> or less as determined in accordance with the description, wherein
the toner particle has a surface property index value of <NUM> or more and less than <NUM> and is measured in accordance with the description; and
the toner contains a binder resin and the binder resin is a polyester resin including a crystalline polyester resin in combination with an amorphous polyester resin and the crystalline polyester resin is used in a range in which a content thereof is <NUM> mass% or more and <NUM> mass% or less with respect to a total amount of the binder resin;
the carrier has a surface having a ratio B/A of a surface area B to a plane view area A of <NUM> or more and <NUM> or less, the plane view area A and the surface area B being obtained by three-dimensional analysis of the surface of the carrier and in accordance with the description;
the resin layer contains an acrylic resin having an alicyclic;
and the resin layer comprises silica particles, and has a silicon element concentration of more than <NUM> atomic% and less than <NUM> atomic% at the surface of the carrier, the silicon element concentration being determined by X-ray photoelectron spectroscopy and in accordance with the description.