# Patent

## Title
Liquid toner comprising encapsulated pigment, methods and uses

## Abstract

Liquid electrographic toner compositions are provided that comprise at least one visual enhancement additive encapsulated within an amphipathic copolymer. The amphipathic copolymer comprises one or more S portions and one or more D portions. Methods of making and methods of using these toner compositions are also provided. The liquid carrier of the toner has a Kauri-Butanol number less than about 30 mL

## Background
FIELD OF THE INVENTION
The present invention relates to liquid toner particles having utility in electrography, particularly electrophotography. More specifically, the present invention relates to amphipathic copolymeric binder particles that are chemically grown to encapsulate a pigment as a component of an organosol and provided in a liquid toner composition.
BACKGROUND OF THE INVENTION
In electrophotographic and electrostatic printing processes (collectively electrographic processes), an electrostatic image is formed on the surface of a photoreceptive element or dielectric element, respectively. The photoreceptive element or dielectric element may be an intermediate transfer drum or belt or the substrate for the final toned image itself, as described by Schmidt, S. P. and Larson, J. R. in Handbook of Imaging Materials Diamond, A. S., Ed: Marcel Dekker: New York; Chapter 6, pp 227–252, and U.S. Pat. Nos. 4,728,983, 4,321,404, and 4,268,598.
In electrostatic printing, a latent image is typically formed by (1) placing a charge image onto a dielectric element (typically the receiving substrate) in selected areas of the element with an electrostatic writing stylus or its equivalent to form a charge image, (2) applying toner to the charge image, and (3) fixing the toned image. An example of this type of process is described in U.S. Pat. No. 5,262,259.
In electrophotographic printing, also referred to as xerography, electrophotographic technology is used to produce images on a final image receptor, such as paper, film, or the like. Electrophotographic technology is incorporated into a wide range of equipment including photocopiers, laser printers, facsimile machines, and the like.
Electrophotography typically involves the use of a reusable, light sensitive, temporary image receptor, known as a photoreceptor, in the process of producing an electrophotographic image on a final, permanent image receptor. A representative electrophotographic process involves a series of steps to produce an image on a receptor, including charging, exposure, development, transfer, fusing, and cleaning, and erasure.
In the charging step, a photoreceptor is covered with charge of a desired polarity, either negative or positive, typically with a corona or charging roller. In the exposure step, an optical system, typically a laser scanner or diode array, forms a latent image by selectively discharging the charged surface of the photoreceptor in an imagewise manner corresponding to the desired image to be formed on the final image receptor. In the development step, toner particles of the appropriate polarity are generally brought into contact with the latent image on the photoreceptor, typically using a developer electrically-biased to a potential opposite in polarity to the toner polarity. The toner particles migrate to the photoreceptor and selectively adhere to the latent image via electrostatic forces, forming a toned image on the photoreceptor.
In the transfer step, the toned image is transferred from the photoreceptor to the desired final image receptor; an intermediate transfer element is sometimes used to effect transfer of the toned image from the photoreceptor with subsequent transfer of the toned image to a final image receptor. In the fusing step, the toned image on the final image receptor is heated to soften or melt the toner particles, thereby fusing the toned image to the final receptor. An alternative fusing method involves fixing the toner to the final receptor under high pressure with or without heat. In the cleaning step, residual toner remaining on the photoreceptor is removed.
Finally, in the erasing step, the photoreceptor charge is reduced to a substantially uniformly low value by exposure to light of a particular wavelength band, thereby removing remnants of the original latent image and preparing the photoreceptor for the next imaging cycle.
Two types of toner are in widespread, commercial use: liquid toner and dry toner. The term “dry” does not mean that the dry toner is totally free of any liquid constituents, but connotes that the toner particles do not contain any significant amount of solvent, e.g., typically less than 10 weight percent solvent (generally, dry toner is as dry as is reasonably practical in terms of solvent content), and are capable of carrying a triboelectric charge.
A typical liquid toner composition generally includes toner particles suspended or dispersed in a liquid carrier. The liquid carrier is typically nonconductive dispersant, to avoid discharging the latent electrostatic image. Liquid toner particles are generally solvated to some degree in the liquid carrier (or carrier liquid), typically in more than 50 weight percent of a low polarity, low dielectric constant, substantially nonaqueous carrier solvent. Liquid toner particles are generally chemically charged using polar groups that dissociate in the carrier solvent, but do not carry a triboelectric charge while solvated and/or dispersed in the liquid carrier. Liquid toner particles are also typically smaller than dry toner particles. Because of their small particle size, ranging from about 5 microns to sub-micron, liquid toners are capable of producing very high-resolution toned images.
A typical toner particle for a liquid toner composition generally comprises a visual enhancement additive (for example, a colored pigment particle) and a polymeric binder. The polymeric binder fulfills functions both during and after the electrophotographic process. With respect to processability, the character of the binder impacts charging and charge stability, flow, and fusing characteristics of the toner particles. These characteristics are important to achieve good performance during development, transfer, and fusing. After an image is formed on the final receptor, the nature of the binder (e.g. glass transition temperature, melt viscosity, molecular weight) and the fusing conditions (e.g. temperature, pressure and fuser configuration) impact durability (e.g. blocking and erasure resistance), adhesion to the receptor, gloss, and the like.
Polymeric binder materials suitable for use in liquid toner particles typically exhibit glass transition temperatures of about −24° C. to 55° C., which is lower than the range of glass transition temperatures (50–100° C.) typical for polymeric binders used in dry toner particles. In particular, some liquid toners are known to incorporate polymeric binders exhibiting glass transition temperatures (Tg) below room temperature (25° C.) in order to rapidly self fix, e.g., by film formation, in the liquid electrophotographic imaging process; see e.g. U.S. Pat. No. 6,255,363. However, such liquid toners are also known to exhibit inferior image durability resulting from the low Tg (e.g. poor blocking and erasure resistance) after fusing the toned image to a final image receptor.
In other printing processes using liquid toners, self-fixing is not required. In such a system, the image developed on the photoconductive surface is transferred to an intermediate transfer belt (“ITB”) or intermediate transfer member (“ITM”) or directly to a print medium without film formation at this stage. See, for example, U.S. Pat. No. 5,410,392 to Landa, issued on Apr. 25, 1995; and U.S. Pat. No. 5,115,277 to Camis, issued on May 19, 1992. In such a system, this transfer of discrete toner particles in image form is carried out using a combination of mechanical forces, electrostatic forces, and thermal energy. In the system particularly described in the '277 patent, DC bias voltage is connected to an inner sleeve member to develop electrostatic forces at the surface of the print medium for assisting in the efficient transfer of color images.
The toner particles used in such a system have been previously prepared using conventional polymeric binder materials, and not polymers made using an organosol process. Thus, for example the '392 patent states that the liquid developer to be used in the disclosed system is described in U.S. Pat. No. 4,794,651 to Landa, issued on Dec. 27, 1988. This patent discloses liquid toners made by heating a preformed high Tg polymer resin in a carrier liquid to an elevated temperature sufficiently high for the carrier liquid to soften or plasticize the resin, adding a pigment, and exposing the resulting high temperature dispersion to a high energy mixing or milling process.
Although such non self-fixing liquid toners using higher Tg (Tg generally greater than or equal to about 60° C.) polymeric binders should have good image durability, such toners are known to exhibit other problems related to the choice of polymeric binder, including image defects due to the inability of the liquid toner to rapidly self fix in the imaging process, poor charging and charge stability, poor stability with respect to agglomeration or aggregation in storage, poor sedimentation stability in storage, and the requirement that high fusing temperatures of about 200–250° C. be used in order to soften or melt the toner particles and thereby adequately fuse the toner to the final image receptor.
To overcome the durability deficiencies, polymeric materials selected for use in both nonfilm-forming liquid toners and dry toners more typically exhibit a range of Tg of at least about 55–65° C. in order to obtain good blocking resistance after fusing, yet typically require high fusing temperatures of about 200–250° C. in order to soften or melt the toner particles and thereby adequately fuse the toner to the final image receptor. High fusing temperatures are a disadvantage for dry toners because of the long warm-up time and higher energy consumption associated with high temperature fusing and because of the risk of fire associated with fusing toner to paper at temperatures approaching the autoignition temperature of paper (233° C.).
In addition, some liquid and dry toners using high Tg polymeric binders are known to exhibit undesirable partial transfer (offset) of the toned image from the final image receptor to the fuser surface at temperatures above or below the optimal fusing temperature, requiring the use of low surface energy materials in the fuser surface or the application of fuser oils to prevent offset. Alternatively, various lubricants or waxes have been physically blended into the dry toner particles during fabrication to act as release or slip agents; however, because these waxes are not chemically bonded to the polymeric binder, they may adversely affect triboelectric charging of the toner particle or may migrate from the toner particle and contaminate the photoreceptor, an intermediate transfer element, the fuser element, or other surfaces critical to the electrophotographic process.
In addition to the polymeric binder and the visual enhancement additive, liquid toner compositions can optionally include other additives. For example, charge control agents can be added to impart an electrostatic charge on the toner particles. Dispersing agents can be added to provide colloidal stability, aid fixing of the image, and provide charged or charging sites for the particle surface. Dispersing agents are commonly added to liquid toner compositions because toner particle concentrations are high (inter-particle distances are small) and electrical double-layer effects alone will not adequately stabilize the dispersion with respect to aggregation or agglomeration. Release agents can also be used to help prevent the toner from sticking to fuser rolls when those are used. Other additives include antioxidants, ultraviolet stabilizers, fungicides, bactericides, flow control agents, and the like.
One fabrication technique involves synthesizing an amphipathic copolymeric binder dispersed in a liquid carrier to form an organosol, then mixing the formed organosol with other ingredients to form a liquid toner composition. Typically, organosols are synthesized by nonaqueous dispersion polymerization of polymerizable compounds (e.g. monomers) to form copolymeric binder particles that are dispersed in a low dielectric hydrocarbon solvent (carrier liquid). These dispersed copolymer particles are sterically-stabilized with respect to aggregation by chemical bonding of a steric stabilizer (e.g. graft stabilizer), solvated by the carrier liquid, to the dispersed core particles as they are formed in the polymerization. Details of the mechanism of such steric stabilization are described in Napper, D. H., “Polymeric Stabilization of Colloidal Dispersions,” Academic Press, New York, N.Y., 1983. Procedures for synthesizing self-stable organosols are described in “Dispersion Polymerization in Organic Media,” K. E. J. Barrett, ed., John Wiley: New York, N.Y., 1975.
Liquid toner compositions have been manufactured using dispersion polymerization in low polarity, low dielectric constant carrier solvents for use in making relatively low glass transition temperature (Tg≦30° C.) film-forming liquid toners that undergo rapid self-fixing in the electrophotographic imaging process. See, e.g., U.S. Pat. Nos. 5,886,067 and 6,103,781. Organosols have also been prepared for use in making intermediate glass transition temperature (Tg between 30–55° C.) liquid electrostatic toners for use in electrostatic stylus printers. See e.g. U.S. Pat. No. 6,255,363 B1. A representative non-aqueous dispersion polymerization method for forming an organosol is a free radical polymerization carried out when one or more ethylenically-unsaturated monomers, soluble in a hydrocarbon medium, are polymerized in the presence of a preformed, polymerizable solution polymer (e.g. a graft stabilizer or “living” polymer). See U.S. Pat. No. 6,255,363.
Once the organosol has been formed, one or more additives can be incorporated, as desired. For example, one or more visual enhancement additives and/or charge control agents can be incorporated. The composition can then subjected to one or more mixing processes, such as homogenization, microfluidization, ball-milling, attritor milling, high energy bead (sand) milling, basket milling or other techniques known in the art to reduce particle size in a dispersion. The mixing process acts to break down aggregated visual enhancement additive particles, when present, into primary particles (having a diameter in the range of 0.05 to 1.0 microns) and may also partially shred the dispersed copolymeric binder into fragments that can associate with the surface of the visual enhancement additive.
According to this embodiment, the dispersed copolymer or fragments derived from the copolymer then associate with the visual enhancement additive, for example, by adsorbing to or adhering to the surface of the visual enhancement additive, thereby forming toner particles. The result is a sterically-stabilized, nonaqueous dispersion of toner particles having a size in the range of about 0.1 to 2.0 microns, with typical toner particle diameters in the range 0.1 to 0.5 microns. In some embodiments, one or more charge control agents can be added after mixing, if desired.
SUMMARY OF THE INVENTION
In addition to the above concerns, it has been noted that toner particles derived from an organosol wherein the visual enhancement additive is added after organosol formation may result in toner particles having some or most of the surface of the visual enhancement additive exposed relative to the amphipathic copolymer It has been found that advantages may be obtained by providing toner particles having visual enhancement additives that are encapsulated within an amphipathic copolymer. For purposes of the present invention, a visual enhancement additive is considered to be encapsulated if it is substantially uniformly distributed throughout the polymer matrix. Such uniform distribution indicates that the polymer substantially or completely surrounds the visual enhancement additive, as compared to visual enhancement additives that are associated with the polymer by a media milling (e.g. ball milling) or other dispersion or mixing process. Previous dispersion processes, such as media milling processes, tend to generate toners having visual enhancement additives having substantial portions of their surfaces exposed to both visual observation and adverse physical and electrical environments.
Encapsulation of the visual enhancement additive within an amphipathic copolymer may provide a specific benefit in preventing undesired electrical interaction of the visual enhancement additive during storage or use. Specifically, certain visual enhancement additives are electrically conductive in nature. Encapsulation of such visual enhancement additives provides an electrically insulative layer that prevents undesired discharge of the toner during storage or use.
Additionally, encapsulation of the visual enhancement additive within an amphipathic copolymer may provide a specific benefit in protection of visual enhancement additives that are sensitive to heat and/or certain light wavelengths. Encapsulation of such visual enhancement additives provides a protective and/or insulative layer that prevents premature and uncontrolled exposure of the visual enhancement additives to harmful heat or light for a period of undesired discharge of the toner during storage or use.
Also, certain visual enhancement additives are sensitive to mechanical disruption. Encapsulation of such visual enhancement additives provides an physically protective layer that prevents mechanical disruption due to forces such as shear forces that may fracture of otherwise damage fragile visual enhancement additives during manufacture, transportation, image processing or on the final imaged product.
Additionally, encapsulation of the visual enhancement additive within an amphipathic copolymer may provide a specific benefit in protection of visual enhancement additives that are sensitive to various substances in the environment, such as water, solvents, atmospheric oxygen or other gasses, and the like. Encapsulation of such visual enhancement additives provides a continuous protective layer that prevents undesired chemical interaction of the visual enhancement additives.
Finally, encapsulation of the visual enhancement additive within an amphipathic copolymer may provide a specific benefit in providing a uniform appearance of the color of the toner. In toners where the visual enhancement additive is not encapsulated, certain portions of the visual enhancement additive are directly observable without modification by an overcoat of polymer. In certain embodiments, one may observe different color intensities or even different apparent colors, depending on the degree of encapsulation of the visual enhancement additive. This potential non-uniformity of the color may be undesirable, particularly when one is striving to provide uniform and reproducible images.
The present invention relates to toner particles derived from an organosol comprising copolymeric binder particles that have been chemically grown with at least one dispersed visual enhancement additive in a substantially nonaqueous liquid carrier, e.g. an organic solvent. The resultant organosol having an encapsulated visual enhancement additive is easily combined with other desired ingredients.
As used herein, the term “amphipathic” is well known and refers to a copolymer having a combination of portions having distinct solubility and dispersibility characteristics, respectively, in a desired liquid carrier that is used to make the copolymer and/or used in the course of incorporating the copolymer into the dry toner particles. Preferably, the liquid carrier is selected such that at least one portion (also referred to herein as S material or portion(s)) of the copolymer is more solvated by the carrier while at least one other portion (also referred to herein as D material or portion(s)) of the copolymer constitutes more of a dispersed phase in the carrier.
In order to provide the unique encapsulation of the visual enhancement additive, the amphipathic copolymer is polymerized in situ in a composition comprising the visual enhancement additive in a manner to encapsulate the visual enhancement additive. Such polymerization is preferably carried out in the desired substantially nonaqueous liquid carrier as this yields monodisperse copolymeric particles suitable for use in toner with little, if any, need for subsequent comminuting or classifying. The resulting pigmented organosol is optionally mixed with one or more other desired ingredients.
In one aspect, the present invention relates to a liquid electrophotographic toner composition comprising a liquid carrier having a Kauri-Butanol number less than about 30 mL and a plurality of toner particles dispersed in the liquid carrier. The toner particles comprise at least one visual enhancement additive encapsulated within an amphipathic copolymer, wherein the amphipathic copolymer comprises one or more S portions and one or more D portions. In certain preferred embodiments, the liquid electrophotographic toner further comprises a charge control additive. In one preferred embodiment, the toner is a liquid electrophotographic toner.
In another aspect, the present invention relates to a method of making a liquid electrographic toner composition. This process includes the steps of:

    1) dispersing the visual enhancement additive in a composition comprising solvent and graft stabilizer (i.e. S portion) prepolymer; and
    2) conducting a dispersion polymerization by reacting D materials with the graft stabilizer prepolymer, thereby encapsulating the visual enhancement additive within a layer of amphipathic polymer to form encapsulated pigmented organosol particles.


Optionally the encapsulated pigmented organosol particles can be further blended with toner additives, such as charge control agents, surface flow agents, and the like. Alternatively, such toner additives may be provided in the initial dispersion of the visual enhancement additive in a composition comprising solvent and graft stabilizer prepolymers, and incorporated in the encapsulated pigmented organosol particles in the polymerization process.
In a preferred aspect of the present invention, the graft stabilizer prepolymer is prepared by providing a plurality of free radically polymerizable monomers, wherein at least one of the monomers comprises hydroxyl functionality. The monomers are free radically polymerized in a solvent to form a hydroxyl functional polymer, wherein the monomers and the hydroxyl functional polymer are soluble in the solvent. A compound having NCO functionality and free radically polymerizable functionality is reacted with the hydroxyl functional polymer under conditions such that at least a portion of the NCO functionality of the compound reacts with at least a portion of the hydroxyl functionality of the polymer to form one or more urethane linkages by which the compound is linked to the polymer, thereby providing a polymer with pendant free radically polymerizable functionality. This reaction step may or may not occur in the same solvent as subsequent toner processing steps.
In another aspect, the present invention relates to a method of electrophotographically forming an image on a substrate surface. In this method, a liquid toner composition is provided comprising a plurality of toner particles that comprise at least one visual enhancement additive encapsulated within an amphipathic copolymer. An image comprising the toner particles is formed on the substrate surface.
In another aspect, the present invention relates to a method of electrographically forming an image on a substrate surface. A liquid toner composition is provided comprising a plurality of toner particles that comprise at least one visual enhancement additive encapsulated within an amphipathic copolymer is provided. An image comprising the toner particles is formed on a charged surface. The image from the charged surface is transferred to the substrate surface. This process may be either an electrostatic process or an electrophotographic process.
The toners of the present invention comprising encapsulated visual enhancement additive have a markedly reduced tendency to produce dried, fused toner films on the final image receptor that exhibit visual or surface defects, including e.g. “mud cracking.” This ability to produce uniform and defect free high resolution images is of great advantage, particularly when the particle size of the dispersed particles is greater than about one micron and the fusing temperature is below the temperature at which complete coalescence of the toner particles into a contiguous film can occur. Toners of the present invention additionally advantageously exhibit more uniform charging and more predictable charge retention as compared to toners that do not have encapsulated visual enhancement additives. This is of particular advantage when the toner is used in electrophotographic imaging processes making use of an electrostatic transfer assist to effect image transfer.


DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
Preferably, the nonaqueous reaction solvent for formation of the organosol (also referred to herein as the “liquid carrier”) is selected such that at least one portion (also referred to herein as the S material or portion) of the amphipathic copolymer is more solvated by the carrier while at least one other portion (also referred to herein as the D material or portion) of the copolymer constitutes more of a dispersed phase in the carrier. Preferred copolymers of the present invention comprise S and D material having respective solubilities in the desired liquid carrier that are sufficiently different from each other such that the S blocks tend to be more solvated by the carrier while the D blocks tend to be more dispersed in the carrier. More preferably, the S blocks are soluble in the liquid carrier while the D blocks are insoluble. In particularly preferred embodiments, the D material phase separates from the liquid carrier, forming dispersed particles.
From one perspective, the polymer particles when dispersed in the liquid carrier may be viewed as having a core/shell structure in which the D material tends to be in the core, while the S material tends to be in the shell. The S material thus functions as a dispersing aid, steric stabilizer or graft copolymer stabilizer, to help stabilize dispersions of the copolymer particles in the liquid carrier. Consequently, the S material may also be referred to herein as a “graft stabilizer.”
While not being bound by theory, it is believed that the D portion of the copolymer will tend to physically and/or chemically interact with the surface of the visual enhancement additive, while the S portion helps promote dispersion in the reaction solvent without use of a separate surfactant or dispersant.
The solubility of a material, or a portion of a material such as a copolymeric portion, may be qualitatively and quantitatively characterized in terms of its Hildebrand solubility parameter. The Hildebrand solubility parameter refers to a solubility parameter represented by the square root of the cohesive energy density of a material, having units of (pressure)1/2, and being equal to (ΔH/RT)1/2/V1/2, where ΔH is the molar vaporiz enthalpy of the material, R is the universal gas constant, T is the absolute temperature, and V is the molar volume of the solvent. Hildebrand solubility parameters are tabulated for solvents in Barton, A. F. M., Handbook of Solubility and Other Cohesion Parameters, 2d Ed. CRC Press, Boca Raton, Fla., (1991), for monomers and representative polymers in Polymer Handbook, 3rd Ed., J. Brandrup & E. H. Immergut, Eds. John Wiley, N.Y., pp 519–557 (1989), and for many commercially available polymers in Barton, A. F. M., Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters, CRC Press, Boca Raton, Fla., (1990).
The degree of solubility of a material, or portion thereof, in a liquid carrier may be predicted from the absolute difference in Hildebrand solubility parameters between the material, or portion thereof, and the liquid carrier. A material, or portion thereof, will be fully soluble or at least in a highly solvated state when the absolute difference in Hildebrand solubility parameter between the material, or portion thereof, and the liquid carrier is less than approximately 1.5 MPa1/2. On the other hand, when the absolute difference between the Hildebrand solubility parameters exceeds approximately 3.0 MPa1/2, the material, or portion thereof, will tend to phase separate from the liquid carrier, forming a dispersion. When the absolute difference in Hildebrand solubility parameters is between 1.5 MPa1/2 and 3.0 MPa1/2, the material, or portion thereof, is considered to be weakly solvatable or marginally insoluble in the liquid carrier.
Consequently, in preferred embodiments, the absolute difference between the respective Hildebrand solubility parameters of the S portion(s) of the copolymer and the liquid carrier is less than 3.0 MPa1/2, preferably less than about 2.0 MPa1/2, more preferably less than about 1.5 MPa1/2. In a particularly preferred embodiment of the present invention, the absolute difference between the respective Hildebrand solubility parameters of the S portion(s) of the copolymer and the liquid carrier is from about 2 to about 3.0 MPa1/2. Additionally, it is also preferred that the absolute difference between the respective Hildebrand solubility parameters of the D portion(s) of the copolymer and the liquid carrier is greater than 2.3 MPa1/2, preferably greater than about 2.5 MPa1/2 more preferably greater than about 3.0 MPa1/2, with the proviso that the difference between the respective Hildebrand solubility parameters of the S and D portion(s) is at least about 0.4 MPa1/2, more preferably at least about 1.0 MPa1/2. Because the Hildebrand solubility of a material may vary with changes in temperature, such solubility parameters are preferably determined at a desired reference temperature such as at 25° C.
Those skilled in the art understand that the Hildebrand solubility parameter for a copolymer, or portion thereof, may be calculated using a volume fraction weighting of the individual Hildebrand solubility parameters for each monomer comprising the copolymer, or portion thereof, as described for binary copolymers in Barton A. F. M., Handbook of Solubility Parameters and Other Cohesion Parameters, CRC Press, Boca Raton, p 12 (1990). The magnitude of the Hildebrand solubility parameter for polymeric materials is also known to be weakly dependent upon the weight average molecular weight of the polymer, as noted in Barton, pp 446–448. Thus, there will be a preferred molecular weight range for a given polymer or portion thereof in order to achieve desired solvating or dispersing characteristics. Similarly, the Hildebrand solubility parameter for a mixture may be calculated using a volume fraction weighting of the individual Hildebrand solubility parameters for each component of the mixture.
In addition, we have defined our invention in terms of the calculated solubility parameters of the monomers and solvents obtained using the group contribution method developed by Small, P. A., J. Appl. Chem., 3, 71 (1953) using Small's group contribution values listed in Table 2.2 on page VII/525 in the Polymer Handbook, 3rd Ed., J. Brandrup & E. H. Immergut, Eds. John Wiley, New York, (1989). We have chosen this method for defining our invention to avoid ambiguities which could result from using solubility parameter values obtained with different experimental methods. In addition, Small's group contribution values will generate solubility parameters that are consistent with data derived from measurements of the enthalpy of vaporization, and therefore are completely consistent with the defining expression for the Hildebrand solubility parameter. Since it is not practical to measure the heat of vaporization for polymers, monomers are a reasonable substitution.
For purposes of illustration, Table I lists Hildebrand solubility parameters for some common solvents used in an electrophotographic toner and the Hildebrand solubility parameters and glass transition temperatures (based on their high molecular weight homopolymers) for some common monomers used in synthesizing organosols.







TABLE I





Hildebrand Solubility Parameters


Solvent Values at 25° C.


















Kauri-Butanol




Number by
Hildebrand



ASTM Method
Solubility


Solvent Name
D1133-54T (ml)
Parameter (MPa1/2)





Norpar TM 15
18
13.99


Norpar TM 13
22
14.24


Norpar TM 12
23
14.30


Isopar TM V
25
14.42


Isopar TM G
28
14.60


Exxsol TM D80
28
14.60










Source: Calculated from equation #31 of Polymer Handbook, 3rd Ed.,


J. Brandrup E. H. Immergut, Eds. John Wiley, NY, p. VII/522 (1989).







Monomer Values at 25° C.










Hildebrand Solubility
Glass Transition


Monomer Name
Parameter (MPa1/2)
Temperature (° C.)*





3,3,5-Trimethyl Cyclohexyl
16.73
125


Methacrylate


Isobornyl Methacrylate
16.90
110


Isobornyl Acrylate
16.01
94


n-Behenyl acrylate
16.74
 <−55 (58 m.p.)**


n-Octadecyl Methacrylate
16.77
  −100 (45 m.p.)**


n-Octadecyl Acrylate
16.82
−55


Lauryl Methacrylate
16.84
−65


Lauryl Acrylate
16.95
−30


2-Ethylhexyl Methacrylate
16.97
−10


2-Ethylhexyl Acrylate
17.03
−55


n-Hexyl Methacrylate
17.13
−5


t-Butyl Methacrylate
17.16
107


n-Butyl Methacrylate
17.22
20


n-Hexyl Acrylate
17.30
−60


n-Butyl Acrylate
17.45
−55


Ethyl Methacrylate
17.62
65


Ethyl Acrylate
18.04
−24


Methyl Methacrylate
18.17
105


Styrene
18.05
100










Calculated using Small's Group Contribution Method, Small, P.A. Journal


of Applied Chemistry 3 p. 71 (1953). Using Group Contributions from


Polymer Handbook, 3rd Ed., J. Brandrup E. H. Immergut, Eds.,


John Wiley, NY, p. VII/525 (1989).


*Polymer Handbook, 3rd Ed., J. Brandrup E. H. Immergut, Eds.,


John Wiley, NY, pp. VII/209–277 (1989). The Tg listed is for the


homopolymer of the respective monomer.


**m.p. refers to melting point for selected Polymerizable Crystallizable


Compounds.






The liquid carrier is a substantially nonaqueous solvent or solvent blend. In other words, only a minor component (generally less than 25 weight percent) of the liquid carrier comprises water. Preferably, the substantially nonaqueous liquid carrier comprises less than 20 weight percent water, more preferably less than 10 weight percent water, even more preferably less than 3 weight percent water, most preferably less than one weight percent water.
The substantially nonaqueous carrier liquid may be selected from a wide variety of materials, or combination of materials, which are known in the art, but preferably has a Kauri-butanol number less than 30 ml. The liquid is preferably oleophilic, chemically stable under a variety of conditions, and electrically insulating. Electrically insulating refers to a dispersant liquid having a low dielectric constant and a high electrical resistivity. Preferably, the liquid dispersant has a dielectric constant of less than 5; more preferably less than 3. Electrical resistivities of carrier liquids are typically greater than 109 Ohm-cm; more preferably greater than 1010 Ohm-cm. In addition, the liquid carrier desirably is chemically inert in most embodiments with respect to the ingredients used to formulate the toner particles.
Examples of suitable liquid carriers include aliphatic hydrocarbons (n-pentane, hexane, heptane and the like), cycloaliphatic hydrocarbons (cyclopentane, cyclohexane and the like), aromatic hydrocarbons (benzene, toluene, xylene and the like), halogenated hydrocarbon solvents (chlorinated alkanes, fluorinated alkanes, chlorofluorocarbons and the like) silicone oils and blends of these solvents. Preferred carrier liquids include branched paraffinic solvent blends such as IsoparTM G, IsoparTM H, IsoparTM K, IsoparTM L, IsoparTM M and IsoparTM V (available from Exxon Corporation, NJ), and most preferred carriers are the aliphatic hydrocarbon solvent blends such as NorparTM 12, NorparTM 13 and NorparTM 15 (available from Exxon Corporation, NJ). Particularly preferred carrier liquids have a Hildebrand solubility parameter of from about 13 to about 15 MPa1/2.
As used herein, the term “copolymer” encompasses both oligomeric and polymeric materials, and encompasses polymers incorporating two or more monomers. As used herein, the term “monomer” means a relatively low molecular weight material (i.e., generally having a molecular weight less than about 500 Daltons) having one or more polymerizable groups. “Oligomer” means a relatively intermediate sized molecule incorporating two or more monomers and generally having a molecular weight of from about 500 up to about 10,000 Daltons. “Polymer” means a relatively large material comprising a substructure formed two or more monomeric, oligomeric, and/or polymeric constituents and generally having a molecular weight greater than about 10,000 Daltons.
The term “macromer” or “macromonomer” refers to an oligomer or polymer having a terminal polymerizable moiety. “Polymerizable crystallizable compound” or “PCC” refers to compounds capable of undergoing polymerization to produce a polymer portion capable of undergoing reversible crystallization over a reproducible and well-defined temperature range (e.g. the copolymer exhibits a melting and freezing point as determined, for example, by differential scanning calorimetry). PCC's may include monomers, functional oligomers, functional pre-polymers, macromers or other compounds able to undergo polymerization to form a polymer portion copolymer. The term “molecular weight” as used throughout this specification means weight average molecular weight unless expressly noted otherwise.
The weight average molecular weight of the amphipathic copolymer of the present invention may vary over a wide range, and may impact imaging performance. The polydispersity of the copolymer also may impact imaging and transfer performance of the resultant dry toner material. The particle size of the pigmented organosol may instead be correlated to imaging and transfer performance of the resultant toner material. Generally, the volume mean particle diameter (Dv) of the dispersed graft copolymer particles, determined by laser diffraction particle size measurement, should be in the range 0.1–100 microns, more preferably 0.5–50 microns, even more preferably 1.0–20 microns, and most preferably 3–10 microns.
In addition, a correlation exists between the molecular weight of the solvatable or soluble S portion of the graft copolymer, and the imaging and transfer performance of the resultant toner. Generally, the S portion of the copolymer has a weight average molecular weight in the range of 1000 to about 1,000,000 Daltons, preferably 5000 to 400,000 Daltons, more preferably 50,000 to 300,000 Daltons. It is also generally desirable to maintain the polydispersity (the ratio of the weight-average molecular weight to the number average molecular weight) of the S portion of the copolymer below 15, more preferably below 5, most preferably below 2.5. It is a distinct advantage of the present invention that copolymer particles with such lower polydispersity characteristics for the S portion are easily made in accordance with the practices described herein, particularly those embodiments in which the copolymer is formed in the liquid carrier in situ.
The relative amounts of S and D portions in a copolymer can impact the solvating and dispersability characteristics of these portions. For instance, if too little of the S portion(s) are present, the copolymer may have too little stabilizing effect to sterically-stabilize the organosol with respect to aggregation as might be desired. If too little of the D portion(s) are present, the small amount of D material may be too soluble in the liquid carrier such that there may be insufficient driving force to form a distinct, dispersed phase in the liquid carrier. The presence of both a solvated and dispersed phase helps the ingredients of particles self assemble in situ with exceptional uniformity among separate particles. Balancing these concerns, the preferred weight ratio of D material to S material is in the range of 1:20 to 20:1, preferably 2:1 to 18:1, more preferably 4:1 to 14:1, and most preferably 8:1 to 12:1.
Glass transition temperature, Tg, refers to the temperature at which a (co)polymer, or portion thereof, changes from a hard, glassy material to a rubbery, or viscous, material, corresponding to a dramatic increase in free volume as the (co)polymer is heated. The Tg can be calculated for a (co)polymer, or portion thereof, using known Tg values for the high molecular weight homopolymers (see, e.g., Table I herein) and the Fox equation expressed below:

1/Tg=w1/Tg1+w2/Tg2+. . . wi/Tgi

wherein each wn is the weight fraction of monomer “n” and each Tgn is the absolute glass transition temperature (in degrees Kelvin) of the high molecular weight homopolymer of monomer “n” as described in Wicks, A. W., F. N. Jones & S. P. Pappas, Organic Coatings 1, John Wiley, NY, pp 54–55 (1992).

In the practice of the present invention, values of Tg for the D or S portion of the copolymer were determined using the Fox equation above, although the Tg of the copolymer as a whole may be determined experimentally using e.g. differential scanning calorimetry. The glass transition temperatures (Tg's) of the S and D portions may vary over a wide range and may be independently selected to enhance manufacturability and/or performance of the resulting dry toner particles. The Tg's of the S and D portions will depend to a large degree upon the type of monomers constituting such portions. Consequently, to provide a copolymer material with higher Tg, one can select one or more higher Tg monomers with the appropriate solubility characteristics for the type of copolymer portion (D or S) in which the monomer(s) will be used. Conversely, to provide a copolymer material with lower Tg, one can select one or more lower Tg monomers with the appropriate solubility characteristics for the type of portion in which the monomer(s) will be used.
For copolymers useful in dry toner applications, the copolymer Tg preferably should not be too low or else receptors printed with the toner may experience undue blocking. Conversely, the minimum fusing temperature required to soften or melt the toner particles sufficient for them to adhere to the final image receptor will increase as the copolymer Tg increases. Consequently, it is preferred that the Tg of the copolymer be far enough above the expected maximum storage temperature of a printed receptor so as to avoid blocking issues, yet not so high as to require fusing temperatures approaching the temperatures at which the final image receptor may be damaged, e.g. approaching the autoignition temperature of paper used as the final image receptor. In this regard, incorporation of a polymerizable crystallizable compound (PCC) in the copolymer will generally permit use of a lower copolymer Tg and therefore lower fusing temperatures without the risk of the image blocking at storage temperatures below the melting temperature of the PCC. Desirably, therefore, the copolymer has a Tg calculated using the Fox equation of about 0° to about 100° C., more preferably about 20° to about 80° C., most preferably about 45° to about 75° C. The advantages of incorporating PCC's into the copolymer are further described in assignee's co-pending U.S. Patent Application titled ORGANOSOL LIQUID TONER INCLUDING AMPHIPATHIC COPOLYMERIC BINDER HAVING CHEMICALLY-BONDED CRYSTALLIZABLE COMPONENT, which is Ser. No. 10/612,534, filed on Jun. 30, 2003 in the names of Julie Y. Qian et al., said co-pending patent application being incorporated herein by reference in its entirety.
For copolymers in which the D portion comprises a major portion of the copolymer, the Tg of the D portion will dominate the Tg of the copolymer as a whole. For such copolymers useful in dry toner applications, it is preferred that the Tg calculated using the Fox equation of the D portion fall in the range of about 20° to about 125° C., more preferably about 30°to about 85° C., most preferably about 50° to about 75° C. In this regard, incorporation of a polymerizable crystallizable compound (PCC) in the D portion of the copolymer will generally permit use of a lower D portion Tg and therefore lower fusing temperatures with reduced risk of image blocking at storage temperatures below the melting temperature of the PCC.
Blocking with respect to the S portion material is not as significant an issue inasmuch as preferred copolymers comprise a majority of the D portion material. Consequently, the Tg of the D portion material will dominate the effective Tg of the copolymer as a whole. Further, surprisingly because of the dispersion polymerization process as described herein, the orientation of the polymer in the ultimate toner particle is unique, in that the visual enhancement additive is primarily associated with the S portion of the copolymer rather than the D portion. This unique orientation surprisingly substantially reduces concern of having a Tg of the S portion that is too low, causing the particles to aggregate and/or agglomerate during drying.
Thus, in a preferred embodiment of the present invention, the S portion of the copolymer may have a Tg that is lower than the Tg of the D portion of the copolymer. This unique configuration provides significant advantages in expanding the material choices available for use in preparation of amphipathic copolymers for use in toner compositions. The expanded monomer choices and lower Tg organosol components that may be used thus facilitate lower fusing temperatures and may assist in better fixing of the toner to the final image receptor and/or formation of more uniform and contiguous toner films during fusing, resulting in more durable and defect free final images.
On the other hand, it is noted that if the Tg is too high, then the requisite fusing temperature may be too high. Balancing these concerns, the S portion material is preferably formulated to have a Tg of from about −70 to about 125° C., preferably from about 0 to about 100° C., and more preferably from about 25 to about 75° C. In this regard, incorporation of a polymerizable crystallizable compound (PCC) in the S portion of the copolymer will generally permit use of a lower S portion Tg.
A wide variety of one or more different monomeric, oligomeric and/or polymeric materials may be independently incorporated into the S and D portions, as desired. Representative examples of suitable materials include free radically polymerized material (also referred to as vinyl copolymers or (meth) acrylic copolymers in some embodiments), polyurethanes, polyester, epoxy, polyamide, polyimide, polysiloxane, fluoropolymer, polysulfone, combinations of these, and the like. Preferred S and D portions are derived from free radically polymerizable material. In the practice of the present invention, “free radically polymerizable” refers to monomers, oligomers, and/or polymers having functionality directly or indirectly pendant from a monomer, oligomer, or polymer backbone (as the case may be) that participate in polymerization reactions via a free radical mechanism. Representative examples of such functionality includes (meth)acrylate groups, olefinic carbon-carbon double bonds, allyloxy groups, alpha-methyl styrene groups, (meth)acrylamide groups, cyanate ester groups, vinyl ether groups, combinations of these, and the like. The term “(meth)acryl”, as used herein, encompasses acryl and/or methacryl.
Free radically polymerizable monomers, oligomers, and/or polymers are advantageously used to form the copolymer in that so many different types are commercially available and may be selected with a wide variety of desired characteristics that help provide one or more desired performance characteristics. Free radically polymerizable monomers, oligomers, and/or monomers suitable in the practice of the present invention may include one or more free radically polymerizable moieties.
Representative examples of monofunctional, free radically polymerizable monomers include styrene, alpha-methylstyrene, substituted styrene, vinyl esters, vinyl ethers, N-vinyl-2-pyrrolidone, (meth)acrylamide, vinyl naphthalene, alkylated vinyl naphthalenes, alkoxy vinyl naphthalenes, N-substituted (meth)acrylamide, octyl (meth)acrylate, nonylphenol ethoxylate (meth)acrylate, N-vinyl pyrrolidone, isononyl (meth)acrylate, isobornyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, beta-carboxyethyl (meth)acrylate, isobutyl (meth)acrylate, cycloaliphatic epoxide, alpha-epoxide, 2-hydroxyethyl (meth)acrylate, (meth)acrylonitrile, maleic anhydride, itaconic acid, isodecyl (meth)acrylate, lauryl (dodecyl) (meth)acrylate, stearyl (octadecyl) (meth)acrylate, behenyl (meth)acrylate, n-butyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylic acid, N-vinylcaprolactam, stearyl (meth)acrylate, hydroxy functional caprolactone ester (meth)acrylate, isooctyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyisopropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyisobutyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate vinyl acetate, combinations of these, and the like.
Preferred copolymers of the present invention may be formulated with one or more radiation curable monomers or combinations thereof that help the free radically polymerizable compositions and/or resultant cured compositions to satisfy one or more desirable performance criteria. For example, in order to promote hardness and abrasion resistance, a formulator may incorporate one or more free radically polymerizable monomer(s) (hereinafter “high Tg component”) whose presence causes the polymerized material, or a portion thereof, to have a higher glass transition temperature, Tg, as compared to an otherwise identical material lacking such high Tg component. Preferred monomeric constituents of the high Tg component generally include monomers whose homopolymers have a Tg of at least about 50° C., preferably at least about 60° C., and more preferably at least about 75° C. in the cured state.
An exemplary class of radiation curable monomers that tend to have relatively high Tg characteristics suitable for incorporation into the high Tg component generally comprise at least one radiation curable (meth)acrylate moiety and at least one nonaromatic, alicyclic and/or nonaromatic heterocyclic moiety. Isobornyl (meth)acrylate is a specific example of one such monomer. A cured, homopolymer film formed from isobornyl acrylate, for instance, has a Tg of 110° C. The monomer itself has a molecular weight of 222 g/mole, exists as a clear liquid at room temperature, has a viscosity of 9 centipoise at 25° C., and has a surface tension of 31.7 dynes/cm at 25° C. Additionally, 1,6-Hexanediol di(meth)acrylate is another example of a monomer with high Tg characteristics.
Trimethyl cyclohexyl methacrylate (TCHMA) is another example of a high Tg monomer useful in the practice of the present invention. TCHMA has a Tg of 125° C. and tends to be soluble in oleophilic solvents. Consequently, TCHMA is easily incorporated into S material. However, if used in limited amounts so as not to unduly impair the insolubility characteristics of D material, some TCHMA may also be incorporated into D the material.
In one particularly preferred embodiment of the present invention, the S portion of the copolymer has a glass transition temperature calculated using the Fox equation (excluding grafting site components) of at least about 90° C., and more preferably has a glass transition temperature calculated using the Fox equation (excluding grafting site components) of from about 100° C. to about 130° C. Preferably, at least about 75%, and more preferably at least about 90%, of the S portion (excluding grafting site components) is derived from ingredients selected from the group consisting of trimethyl cyclohexyl methacrylate; t-butyl methacrylate; n-butyl methacrylate; isobornyl (meth)acrylate; 1,6-Hexanediol di(meth)acrylate and combinations thereof. Toners using copolymers having the above described S portion characteristics exhibit particularly superior performance properties in image quality and transfer as described herein.
In another particularly preferred embodiment of the present invention, the S portion of the copolymer has a glass transition temperature calculated using the Fox equation (excluding grafting site components) less than about 0° C. Preferably, at least about 75%, and more preferably at least about 90%, of the S portion (excluding grafting site components) of this embodiment is derived from ingredients selected from the group consisting of C1 to C24 (meth)acrylates. More preferably, the S portion is derived from ingredients selected from C12–C18 (meth)acrylates, e.g. lauryl methacrylate.
Nitrile functionality may be advantageously incorporated into the copolymer for a variety of reasons, including improved durability, enhanced compatibility with visual enhancement additive(s), e.g., colorant particles, and the like. In order to provide a copolymer having pendant nitrile groups, one or more nitrile functional monomers can be used. Representative examples of such monomers include (meth)acrylonitrile, β-cyanoethyl-(meth)acrylate, 2-cyanoethoxyethyl (meth)acrylate, p-cyanostyrene, p-(cyanomethyl)styrene, N-vinylpyrrolidinone, and the like.
In order to provide a copolymer having pendant hydroxyl groups, one or more hydroxyl functional monomers can be used. Pendant hydroxyl groups of the copolymer not only facilitate dispersion and interaction with the pigments in the formulation, but also promote solubility, cure, reactivity with other reactants, and compatibility with other reactants. The hydroxyl groups can be primary, secondary, or tertiary, although primary and secondary hydroxyl groups are preferred. When used, hydroxy functional monomers constitute from about 0.5 to 30, more preferably 1 to about 25 weight percent of the monomers used to formulate the copolymer, subject to preferred weight ranges for graft copolymers noted below.
Representative examples of suitable hydroxyl functional monomers include an ester of an α, β-unsaturated carboxylic acid with a diol, e.g., 2-hydroxyethyl (meth)acrylate, or 2-hydroxypropyl (meth)acrylate; 1,3-dihydroxypropyl-2-(meth)acrylate; 2,3-dihydroxypropyl-1-(meth)acrylate; an adduct of an α, β-unsaturated carboxylic acid with caprolactone; an alkanol vinyl ether such as 2-hydroxyethyl vinyl ether; 4-vinylbenzyl alcohol; allyl alcohol; p-methylol styrene; or the like.
Polymerizable crystallizable compound(s) (PCC's), e.g. crystalline monomer(s), also may be advantageously incorporated into the copolymer in order to improve blocking resistance between printed receptors and to reduce offset during fusing. Polymerizable crystallizable compounds are incorporated into the copolymer by chemical incorporation, e.g., polymerization or copolymerization. The term “crystalline monomer” refers to a monomer whose homopolymeric analog is capable of independently and reversibly crystallizing at or above room temperature (e.g., 22° C.).
In these embodiments, the resulting toner particles can exhibit improved blocking resistance between printed receptors and reduced offset during fusing. If used, one or more of these crystalline monomers may be incorporated into the S and/or D material, but preferably is incorporated into the D material. Suitable crystalline monomers include alkyl(meth)acrylates where the alkyl chain contains more than 13 carbon atoms (e.g. tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, octadecyl(meth)acrylate, etc). Other suitable crystalline monomers whose homopolymers have melting points above 22° C. include aryl acrylates and methacrylates; high molecular weight alpha olefins; linear or branched long chain alkyl vinyl ethers or vinyl esters; long chain alkyl isocyanates; unsaturated long chain polyesters, polysiloxanes and polysilanes; polymerizable natural waxes with melting points above 22° C.; polymerizable synthetic waxes with melting points above 22° C.; and other similar type materials known to those skilled in the art. As described herein, incorporation of crystalline monomers in the copolymer provides surprising benefits to the resulting dry toner particles.
It will be understood by those skilled in the art that blocking resistance can be observed at temperatures above room temperature but below the crystallization temperature of the polymer or copolymer portion incorporating the crystalline monomers or other polymerizable crystallizable compound. Improved blocking resistance is observed when the crystalline monomer is a major component of the S material, preferably greater than or equal to 45%, more preferably greater than or equal to 75%, most preferably greater than or equal to 90% of the S material incorporated into the copolymer.
Many crystalline monomers tend to be soluble in oleophilic solvents commonly used as liquid carrier material(s) in an organosol. Thus, crystalline monomer is relatively easily incorporated into S material without impacting desired solubility characteristics. However, if too much of such crystalline monomer were to be incorporated into D material, the resultant D material may tend to be too soluble in the organosol. Yet, so long as the amount of soluble, crystalline monomer in the D material is limited, some amount of crystalline monomer may be advantageously incorporated into the D material without unduly impacting the desired insolubility characteristics. Thus, when present in the D material, the crystalline monomer is preferably provided in an amount of up to about 30%, more preferably up to about 20%, most preferably up to about 5% to 10% of the total D material incorporated into the copolymer.
When crystalline monomers or PCC's are chemically incorporated into the S material, suitable co-polymerizable compounds that can be used in combination with the PCC include monomers such as other PCC's, 2-ethylhexyl acrylate, 2-ethylhexyl (methacrylate), lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl(methacrylate), isobornyl acrylate, isobornyl (methacrylate), hydroxy(ethylmethacrylate), other acrylates and methacrylates, combinations of these and the like.
It is also advantageous to incorporate monomers into the copolymer that provide polymerized portions that are inherently triboelectrically charged. When used, it is preferred to incorporate such materials into the S material, as this material tends to be more solvated by the liquid carrier and is therefore located towards the outside surface or shell of the resultant triboelectrically charged toner particles. Monomers that provide polymer portions with positive and/or negative triboelectric charges may be used in amounts effective to produce the desired inherent triboelectric charge characteristics. For instance, butyl methacrylate generally tends to provide a more positive (less negative) triboelectric charge while styrene tends to provide a more negative (less positive) triboelectric charge, particularly when used in combination with other monomers.
Multifunctional free radically reactive materials may also used to enhance one or more properties of the resultant toner particles, including crosslink density, hardness, tackiness, mar resistance, or the like. Examples of such higher functional, monomers include ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and neopentyl glycol di(meth)acrylate, divinyl benzene, combinations of these, and the like.
Suitable free radically reactive oligomer and/or polymeric materials for use in the present invention include, but are not limited to, (meth)acrylated urethanes (i.e., urethane (meth)acrylates), (meth)acrylated epoxies (i.e., epoxy (meth)acrylates), (meth)acrylated polyesters (i.e., polyester (meth)acrylates), (meth)acrylated (meth)acrylics, (meth)acrylated silicones, (meth)acrylated polyethers (i.e., polyether (meth)acrylates), vinyl (meth)acrylates, and (meth)acrylated oils.
Copolymers of the present invention can be prepared by free-radical polymerization methods known in the art, including but not limited to bulk, solution, and dispersion polymerization methods. While a number of amphipathic copolymers would be suitable, preferred copolymers are graft copolymers. A preferred embodiment is a graft copolymer comprising one or more oligomeric and/or polymeric arms attached to an oligomeric or polymeric backbone. In graft copolymer embodiments, the S portion or D portion materials, as the case may be, may be incorporated into the arms and/or the backbone.
Any number of reactions known to those skilled in the art may be used to prepare a free radically polymerized copolymer having a graft structure. Common grafting methods include random grafting of polyfunctional free radicals; copolymerization of monomers with macromonomers; ring-opening polymerizations of cyclic ethers, esters, amides or acetals; epoxidations; reactions of hydroxyl or amino chain transfer agents with terminally-unsaturated end groups; esterification reactions (i.e., glycidyl methacrylate undergoes tertiary-amine catalyzed esterification with methacrylic acid); and condensation polymerization.
Representative methods of forming graft copolymers are described in U.S. Pat. Nos. 6,255,363; 6,136,490; and 5,384,226; and Japanese Published Patent Document No. 05-119529, incorporated herein by reference. Representative examples of grafting methods are also described in sections 3.7 and 3.8 of Dispersion Polymerization in Organic Media, K. E. J. Barrett, ed., (John Wiley; New York, 1975) pp. 79–106, also incorporated herein by reference.
Representative examples of grafting methods also may use an anchoring group to facilitate anchoring. The function of the anchoring group is to provide a covalently bonded link between the core part of the copolymer (the D material) and the soluble shell component (the S material). Suitable monomers containing anchoring groups include: adducts of alkenylazlactone comonomers with an unsaturated nucleophile containing hydroxy, amino, or mercaptan groups, such as 2-hydroxyethylmethacrylate, 3-hydroxypropylmethacrylate, 2-hydroxyethylacrylate, pentaerythritol triacrylate, 4-hydroxybutylvinylether, 9-octadecen-1-ol, cinnamyl alcohol, allyl mercaptan, methallylamine; and azlactones, such as 2-alkenyl-4,4-dialkylazlactone.
The preferred methodology described below accomplishes grafting via attaching an ethylenically-unsaturated isocyanate (e.g. dimethyl-m-isopropenyl benzylisocyanate, TMI, available from CYTEC Industries, West Paterson, N.J.; or isocyanatoethyl methacrylate, also known as IEM) to hydroxyl groups in order to provide free radically reactive anchoring groups.
A preferred method of forming a graft copolymer of the present invention involves three reaction steps that are carried out in a suitable substantially nonaqueous liquid carrier in which resultant S material is soluble while D material is dispersed or insoluble. In a first preferred step, a hydroxyl functional, free radically polymerized oligomer or polymer is formed from one or more monomers, wherein at least one of the monomers has pendant hydroxyl functionality. Preferably, the hydroxyl functional monomer constitutes about 1 to about 30, preferably about 2 to about 10 percent, most preferably 3 to about 5 percent by weight of the monomers used to form the oligomer or polymer of this first step. This first step is preferably carried out via solution polymerization in a substantially nonaqueous solvent in which the monomers and the resultant polymer are soluble. For instance, using the Hildebrand solubility data in Table 1, monomers such as octadecyl methacrylate, octadecyl acrylate, lauryl acrylate, and lauryl methacrylate are suitable for this first reaction step when using an oleophilic solvent such as heptane or the like.
In a second reaction step, all or a portion of the hydroxyl groups of the soluble polymer are catalytically reacted with an ethylenically unsaturated aliphatic isocyanate (e.g. meta-isopropenyldimethylbenzyl isocyanate commonly known as TMI or isocyanatoethyl methacrylate, commonly known as IEM) to form pendant free radically polymerizable functionality which is attached to the oligomer or polymer via a polyurethane linkage. This reaction can be carried out in the same solvent, and hence the same reaction vessel, as the first step. The resultant double-bond functionalized polymer generally remains soluble in the reaction solvent and constitutes the S portion material of the resultant copolymer (also referred to herein as the “S portion prepolymer”), which ultimately will constitute at least a portion of the solvatable portion of the resultant triboelectrically charged particles. The resultant free radically reactive functionality provides grafting sites for attaching D material and optionally additional S material to the polymer.
In a third step, a visual enhancement additive is dispersed in the composition comprising solvent and S portion prepolymer.
As a fourth step, the grafting site(s) of the S portion prepolymer are used to create an amphipathic polymer via reaction with “D materials” through a dispersion polymerization reaction. The formation of this polymer in this composition encapsulates the visual enhancement additive within a layer of amphipathic polymer to form encapsulated pigmented organosol particles.
“D materials” are one or more free radically reactive monomers, oligomers, and or polymers that are initially soluble in the solvent, but then become insoluble as the molecular weight of the graft copolymer increases. For instance, using the Hildebrand solubility parameters in Table 1, monomers such as e.g. methyl (meth)acrylate, ethyl (meth)acrylate, t-butyl methacrylate and styrene are suitable for this third reaction step when using an oleophilic solvent such as heptane or the like.
The product of the fourth reaction step is generally an organosol comprising the resultant copolymer, which encapsulates the visual enhancement additive, dispersed in the reaction solvent. The reaction solvent constitutes a substantially nonaqueous liquid carrier for the organosol. At this stage, it is believed that the copolymer tends to exist in the liquid carrier as discrete, monodisperse particles having dispersed (e.g., substantially insoluble, phase separated) portion(s) and solvated (e.g., substantially soluble) portion(s). As such, the solvated portion(s) help to sterically-stabilize the dispersion of the particles in the liquid carrier. It can be appreciated that the copolymer is thus advantageously formed in the liquid carrier in situ.
Before further processing, the copolymer particles may remain in the reaction solvent. Alternatively, the particles may be transferred in any suitable way into fresh solvent that is the same or different so long as the copolymer has solvated and dispersed phases in the fresh solvent.
Optionally, one or more other desired toner additives also can be mixed into the organosol. Depending on the conditions of addition of these toner additives, the additives may be associated at the surface of the copolymer particles or may be internally incorporated in the particles. Particularly with energetic mixing, toner additives may be internally incorporated in such a process. During such combination, it is believed that ingredients comprising the additional additives and the copolymer will tend to self-assemble into composite particles having a structure wherein the dispersible phase portions generally tend to associate with the additional additives (for example, by physically and/or chemically interacting with the surface of additive particles), while the solvatable phase portions help promote dispersion in the carrier.
The visual enhancement additive(s) generally may include any one or more fluid and/or particulate materials that provide a desired visual effect when toner particles incorporating such materials are printed onto a receptor. Examples include one or more colorants, fluorescent materials, pearlescent materials, iridescent materials, metallic materials, flip-flop pigments, silica, polymeric beads, reflective and non-reflective glass beads, mica, combinations of these, and the like. The amount of visual enhancement additive incorporated into the toner particles may vary over a wide range. In preferred embodiments, a suitable weight ratio of copolymer to visual enhancement additive is from about 1:1 to about 20:1, more preferably from about 2:1 to about 10:1 and most preferably from about 3:1 to about 6:1.
Useful colorants are well known in the art and include materials listed in the Colour Index, as published by the Society of Dyers and Colourists (Bradford, England), including dyes, stains, and pigments. Preferred colorants are pigments which may be combined with ingredients comprising the copolymer to interact with the amphipathic copolymer to form dry toner particles with structure as described herein, are at least nominally insoluble in and nonreactive with the carrier liquid, and are useful and effective in making visible the latent electrostatic image. It is understood that the visual enhancement additive(s) may also interact with each other physically and/or chemically, forming aggregations and/or agglomerates of visual enhancement additives that also interact with the copolymer, particularly with the D portion thereof. Examples of suitable colorants include: phthalocyanine blue (C.I. Pigment Blue 15:1, 15:2, 15:3 and 15:4), monoarylide yellow (C.I. Pigment Yellow 1, 3, 65, 73 and 74), diarylide yellow (C.I. Pigment Yellow 12, 13, 14, 17 and 83), arylamide (Hansa) yellow (C.I. Pigment Yellow 10, 97, 105 and 111), isoindoline yellow (C.I. Pigment Yellow 138), azo red (C.I. Pigment Red 3, 17, 22, 23, 38, 48:1, 48:2, 52:1, and 52:179), quinacridone magenta (C.I. Pigment Red 122, 202 and 209), laked rhodamine magenta (C.I. Pigment Red 81:1, 81:2, 81:3, and 81:4), and black pigments such as finely divided carbon (Cabot Monarch 120, Cabot Regal 300R, Cabot Regal 350R, Vulcan X72, and Aztech EK 8200), and the like.
In addition to the visual enhancement additive, other toner additives optionally may be formulated into the triboelectrically charged particle formulation. A particularly preferred toner additive comprises at least one charge control additive (charge control agent, CCA). The charge control additive, also known as a charge director, helps to provide uniform charge polarity of the toner particles. The charge director may be incorporated into the toner particles using a variety of methods such as, copolymerizing a suitable monomer with the other monomers used to form the copolymer, chemically reacting the charge director with the toner particle, chemically or physically adsorbing the charge director onto the toner particle (resin or pigment), or chelating the charge director to a functional group incorporated into the toner particle. A preferred method is via a functional group built into the S material of the copolymer.
The charge control agent acts to impart an electrical charge of selected polarity onto the toner particles. Any number of charge control agents described in the art can be used. For example, the charge control agent can be provided it the form of metal salts consisting of polyvalent metal ions and organic anions as the counterion. Suitable metal ions include, but are not limited to, Ba(II), Ca(II), Mn(II), Zn(II), Zr(IV), Cu(II), Al(III), Cr(III), Fe(II), Fe(III), Sb(III), Bi(III), Co(II), La(III), Pb(II), Mg(II), Mo(III), Ni(II), Ag(I), Sr(II), Sn(IV), V(V), Y(III), and Ti(IV). Suitable organic anions include carboxylates or sulfonates derived from aliphatic or aromatic carboxylic or sulfonic acids, preferably aliphatic fatty acids such as stearic acid, behenic acid, neodecanoic acid, diisopropylsalicylic acid, octanoic acid, abietic acid, naphthenic acid, lauric acid, tallic acid, and the like.
Preferred negative charge control agents are lecithin and basic barium petronate. Preferred positive charge control agents include metallic carboxylates (soaps), for example, as described in U.S. Pat. No. 3,411,936 (incorporated herein by reference). A particularly preferred positive charge control agent is zirconium tetraoctoate (available as Zirconium HEX-CEM from OMG Chemical Company, Cleveland, Ohio).
The preferred charge control agent levels for a given toner formulation will depend upon a number of factors, including the composition of the S portion and the organosol, the molecular weight of the organosol, the particle size of the organosol, the D:S ratio of the polymeric binder, the pigment used in making the toner composition, and the ratio of organosol to pigment. In addition, preferred charge control agent levels will depend upon the nature of the electrophotographic imaging process. The level of charge control agent can be adjusted based upon the parameters listed herein, as known in the art. The amount of the charge control agent, based on 100 parts by weight of the toner solids, is generally in the range of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight.
The conductivity of a liquid toner composition can be used to describe the effectiveness of the toner in developing electrophotographic images. A range of values from 1×10−11 mho/cm to 3×10−10 mho/cm is considered advantageous to those of skill in the art. High conductivities generally indicate inefficient association of the charges on the toner particles and is seen in the low relationship between current density and toner deposited during development. Low conductivities indicate little or no charging of the toner particles and lead to very low development rates. The use of charge control agents matched to adsorption sites on the toner particles is a common practice to ensure sufficient charge associates with each toner particle.
Other toner additives may also be added to the formulation in accordance with conventional practices. These include one or more of UV stabilizers, mold inhibitors, bactericides, fungicides, antistatic agents, gloss modifying agents, other polymer or oligomer material, antioxidants, anticaking agents such as silane or silicone-modified silica particles (typically 5 to 50 nm particle size), combinations of these, and the like.
The particle size of the resultant triboelectrically charged toner particles may impact the imaging, fusing, resolution, and transfer characteristics of the toner incorporating such particles. Preferably, the volume mean particle diameter (determined by laser diffraction light scattering) of the toner particles is in the range of about 0.5 to about 30.0 microns, more preferably in the range of about 1 to about 15 microns, most preferably in the range of about 3 to about 10 microns.
In electrophotographic and electrographic processes, an electrostatic image is formed on the surface of a photoreceptive element or dielectric element, respectively. The photoreceptive element or dielectric element may be an intermediate transfer drum or belt or the substrate for the final toned image itself, as described by Schmidt, S. P. and Larson, J. R. in Handbook of Imaging Materials Diamond, A. S., Ed: Marcel Dekker: New York; Chapter 6, pp 227–252, and U.S. Pat. Nos. 4,728,983; 4,321,404; and 4,268,598.
In electrography, a latent image is typically formed by (1) placing a charge image onto the dielectric element (typically the receiving substrate) in selected areas of the element with an electrostatic writing stylus or its equivalent to form a charge image, (2) applying toner to the charge image, and (3) fixing the toned image. An example of this type of process is described in U.S. Pat. No. 5,262,259. Images formed by the present invention may be of a single color or a plurality of colors. Multicolor images can be prepared by repetition of the charging and toner application steps.
In electrophotography, the electrostatic image is typically formed on a drum or belt coated with a photoreceptive element by (1) uniformly charging the photoreceptive element with an applied voltage, (2) exposing and discharging portions of the photoreceptive element with a radiation source to form a latent image, (3) applying a toner to the latent image to form a toned image, and (4) transferring the toned image through one or more steps to a final receptor sheet. In some applications, it is sometimes desirable to fix the toned image using a heated pressure roller or other fixing methods known in the art.
While the electrostatic charge of either the toner particles or photoreceptive element may be either positive or negative, electrophotography as employed in the present invention is preferably carried out by dissipating charge on a positively charged photoreceptive element. A positively-charged toner is then applied to the regions in which the positive charge was dissipated using a dry toner development technique.
The substrate for receiving the image from the photoreceptive element can be any commonly used receptor material, such as paper, coated paper, polymeric films and primed or coated polymeric films. Polymeric films include polyesters and coated polyesters, polyolefins such as polyethylene or polypropylene, plasticized and compounded polyvinyl chloride (PVC), acrylics, polyurethanes, polyethylene/acrylic acid copolymer, and polyvinyl butyrals. The polymer film may be coated or primed, e.g. to promote toner adhesion.
These and other aspects of the present invention are demonstrated in the illustrative examples that follow.
EXAMPLES
Test Methods and Apparatus
In the following examples, percent solids of the copolymer solutions and the organosol and ink dispersions were determined gravimetrically using the Halogen Lamp Drying Method using a halogen lamp drying oven attachment to a precision analytical balance (Mettler Instruments, Inc., Highstown, N.J.). Approximately two grams of sample were used in each determination of percent solids using this sample dry down method.
In the practice of the invention, molecular weight is normally expressed in terms of the weight average molecular weight, while molecular weight polydispersity is given by the ratio of the weight average molecular weight to the number average molecular weight. Molecular weight parameters were determined with gel permeation chromatography (GPC) using tetrahydrofuran as the carrier solvent. Absolute weight average molecular weight were determined using a Dawn DSP-F light scattering detector (Wyatt Technology Corp., Santa Barbara, Calif.), while polydispersity was evaluated by ratioing the measured weight average molecular weight to a value of number average molecular weight determined with an Optilab 903 differential refractometer detector (Wyatt Technology Corp., Santa Barbara, Calif.).
Organosol and toner particle size distributions were determined by a Laser Diffraction Method using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.). Samples were diluted approximately 1/500 by volume and sonicated for one minute at 150 watts and 20 kHz prior to measurement. Particle size was expressed as both a number mean diameter (Dn) and a volume mean diameter (Dv) and in order to provide an indication of both the fundamental (primary) particle size and the presence of aggregates or agglomerates.
One important characteristic of xerographic toners is the toner's electrostatic charging performance (or specific charge), given in units of Coulombs per gram. The specific charge of each toner was established in the examples below using a blow-off tribo-tester instrument (Toshiba Model TB200, Toshiba Chemical Co., Tokyo, Japan). To use this device, the toner is first electrostatically charged by combining it with a carrier powder. The latter usually is a ferrite powder coated with a polymeric shell. The toner and the coated carrier particles are brought together to form the developer. When the developer is gently agitated, tribocharging results in both of the component powders acquiring an equal and opposite electrostatic charge, the magnitude of which is determined by the properties of the toner, along with any compounds deliberately added to the toner to affect the charging (e.g., charge control agents).
Once charged, the developer mixture is placed in a small holder inside the blow-off tribo-tester. The holder acts a charge-measuring Faraday cup, attached to a sensitive capacitance meter. The cup has a connection to a compressed nitrogen line and a fine screen at its base, sized to retain the larger carrier particles while allowing the smaller toner particles to pass. When the gas line is pressurized, gas flows thought the cup and forces the toner particles out of the cup through the fine screen. The carrier particles remain in the Faraday cup. The capacitance meter in the tester measures the charge of the carrier; the charge on the toner that was removed is equal in magnitude and opposite in sign. A measurement of the amount of toner mass lost yields the toner specific charge, in microCoulombs per gram.
For the present measurements, a silicon coated ferrite carrier (Vertex Image Systems Type 2) with a mean particle size of about 80–100 microns was used. Toner was added to the carrier powder to obtain a 3 weight percent toner content in the developer. This developer was gently agitated on a roller table for at least 45 minutes before blow-off testing. Specific charge measurements were repeated at least five times for each toner to obtain a mean value and a standard deviation. Tests were considered valid if the amount of toner mass lost during the blow-off was between 50 and 100% of the total toner content expected in each sample. Tests with mass losses outside of these values were rejected.
Materials
The following abbreviations are used in the examples:

    EMA: Ethyl methacrylate (available from Aldrich Chemical Co., Milwaukee, Wis.)
    HEMA: 2-Hydroxyethyl methacrylate (available from Aldrich Chemical Co., Milwaukee, Wis.)
    LMA: Lauryl methacrylate (available from Aldrich Chemical Co., Milwaukee, Wis.)
    TCHMA: Trimethyl cyclohexyl methacrylate (available from Ciba Specialty Chemical Co., Suffolk, Va.)
    TMI: Dimethyl-m-isopropenyl benzyl isocyanate (available from CYTEC Industries, West Paterson, N.J.)
    AIBN: Azobisisobutyronitrile (an initiator available as VAZO-64 from DuPont Chemical Co., Wilmington, Del.)
    V-601: Dimethyl 2,2′-azobisisobutyrate (an initiator available as V-601 from WAKO Chemicals U.S.A., Richmond, Va.)
    DBTDL: Dibutyl tin dilaurate (a catalyst available from Aldrich Chemical Co., Milwaukee, Wis.)
    DAAM: diacetone acrylamide (available from Aldrich Chemical Co., Milwaukee, Wis.)
    EA: ethyl acrylate (available from Aldrich Chemical Co., Milwaukee, Wis.)

Nomenclature



In the following examples, the compositional details of each copolymer will be summarized by ratioing the weight percentages of monomers used to create the copolymer. The grafting site composition is expressed as a weight percentage of the monomers comprising the copolymer or copolymer precursor, as the case may be. For example, a graft stabilizer (precursor to the S portion of the copolymer) is designated TCHMA/HEMA-TMI (97/3-4.7) is made by copolymerizing, on a relative basis, 97 parts by weight TCHMA and 3 parts by weight HEMA, and this hydroxy functional polymer was reacted with 4.7 parts by weight of TMI.
Similarly, a graft copolymer organosol designated TCHMA/HEMA-TMI//EMA (97-3-4.7//100) is made by copolymerizing the designated graft stabilizer (TCHMA/HEMA-TMI (97/3-4.7)) (S portion or shell) with the designated core monomer EMA (D portion or core) at a specified ratio of D/S (core/shell) determined by the relative weights reported in the examples.
EXAMPLES
1. Preparation of Graft Polymeric Dispersants













Example
Graft Polymeric Dispersant
Solids
Molecular Weight











Number
Composition (% w/w)
(%)
Mw
Mw/Mn





1
LMA/HEMA-TMI (97/3–4.7)
25.28
261,550
2.4


2
TCHMA/HEMA-TMI
28.88
301,000
3.3



(97/3–4.7)


3
LMA/DAAM-TMI (90/10–4.7)
25.43
141,400
2.1


4
TCHMA/DAAM-TMI
27.78
225,050
2.6



(90/10–4.7)









Example 1
A 5000 ml 3-neck round flask equipped with a condenser, a thermocouple connected to a digital temperature controller, a nitrogen inlet tube connected to a source of dry nitrogen and a magnetic stirrer, was charged with a mixture of 2561 g of NorparTM 12, 849 g of LMA, 26.7 g of 98% HEMA and 8.31 g of AIBN. While stirring the mixture, the reaction flask was purged with dry nitrogen for 30 minutes at flow rate of approximately 2 liters/minute. A hollow glass stopper was then inserted into the open end of the condenser and the nitrogen flow rate was reduced to approximately 0.5 liters/min. The mixture was heated to 70° C. for 16 hours. The conversion was quantitative.
The mixture was heated to 90° C. and held at that temperature for 1 hour to destroy any residual AIBN, and then was cooled back to 70° C. The nitrogen inlet tube was then removed, and 13.6 g of 95% DBTDL were added to the mixture, followed by 41.1 g of TMI. The TMI was added drop wise over the course of approximately 5 minutes while stirring the reaction mixture. The nitrogen inlet tube was replaced, the hollow glass stopper in the condenser was removed, and the reaction flask was purged with dry nitrogen for 30 minutes at a flow rate of approximately 2 liters/minute. The hollow glass stopper was reinserted into the open end of the condenser and the nitrogen flow rate was reduced to approximately 0.5 liters/min. The mixture was allowed to react at 70° C. for 6 hours, at which time the conversion was quantitative.
The mixture was then cooled to room temperature. The cooled mixture was a viscous, transparent liquid containing no visible insoluble mater. The percent solids of the liquid mixture was determined to be 25.28% using the Halogen Drying Method described above. Subsequent determination of molecular weight was made using the GPC method described above; the copolymer had a Mw of 261,550 and Mw/Mn of 2.4 based on two independent measurements. The product is a copolymer of LMA and HEMA containing random side chains of TMI and is designed herein as LMA/HEMA-TMI (97/3-4.7% w/w) and can be used as a dispersant for pigments.
Example 2
Using the method and apparatus of Example 1, 2561 g of NorparTM 12, 849 g of TCHMA, 26.8 g of 98% HEMA and 8.31 g of AIBN were combined and resulting mixture reacted at 70° C. for 16 hours. The mixture was then heated to 90° C. for 1 hour to destroy any residual AIBN, and then was cooled back to 70° C. To the cooled mixture was then added 13.6 g of 95% DBTDL and 41.1 g of TMI. The TMI was added drop wise over the course of approximately 5 minutes while stirring the reaction mixture. Following the procedure of Example 1, the mixture was reacted at 70° C. for approximately 6 hours at which time the reaction was quantitative. The mixture was then cooled to room temperature. The cooled mixture was viscous, transparent solution, containing no visible insoluble mater.
The percent solids of the liquid mixture was determined to be 28.88% using the Halogen Drying Method described above. Subsequent determination of molecular 301,000 Da and Mw/Mn of 3.3 based upon two independent measurements. The product is a copolymer of TCHMA and HEMA containing random side chains of TMI and is designed herein as TCHMA/HEMA-TMI (97/3-4.7% w/w) and can be used as a dispersant for pigments.
Example 3
Using the method and apparatus of Example 1, 2557 g of NorparTM 12, 788 g of LMA, 88 g of DAAM and 13.13 g of V-601 were combined and resulting mixture reacted at 70° C. for 16 hours. The mixture was then heated to 90° C. for 1 hour to destroy any residual V-601, and then was cooled back to 70° C. To the cooled mixture was then added 13.6 g of 95% DBTDL and 41.1 g of TMI. The TMI was added drop wise over the course of approximately 5 minutes while stirring the reaction mixture. Following the procedure of Example 1, the mixture was reacted at 70° C. for approximately 6 hours at which time the reaction was quantitative. The mixture was then cooled to room temperature. The cooled mixture was viscous, transparent solution, containing no visible insoluble mater.
The percent solids of the liquid mixture was determined to be 25.43% using the Halogen Drying Method described above. Subsequent determination of molecular 141,400 Da and Mw/Mn of 2.1 based upon two independent measurements. The product is a copolymer of LMA and DAAM containing random side chains of TMI and is designed herein as LMA/DAAM-TMI (90/10-4.7% w/w) and can be used as a dispersant for pigments.
Example 4
Using the method and apparatus of Example 1, 2557 g of NorparTM12, 788 g of TCHMA, 88 g of DAAM and 13.13 g of V-601were combined and resulting mixture reacted at 70° C. for 16 hours. The mixture was then heated to 90° C. for 1 hour to destroy any residual V-601, and then was cooled back to 70° C. To the cooled mixture was then added 13.6 g of 95% DBTDL and 41.1 g of TMI. The TMI was added drop wise over the course of approximately 5 minutes while stirring the reaction mixture. Following the procedure of Example 1, the mixture was reacted at 70° C. for approximately 6 hours at which time the reaction was quantitative. The mixture was then cooled to room temperature. The cooled mixture was viscous, transparent solution, containing no visible insoluble mater.
The percent solids of the liquid mixture was determined to be 27.78% using the Halogen Drying Method described above. Subsequent determination of molecular 225,050 Da and Mw/Mn of 2.6 based upon two independent measurements. The product is a copolymer of TCHMA and DAAM containing random side chains of TMI and is designed herein as TCHMA/DAAM-TMI (90/10-4.7% w/w) and can be used as a dispersant for pigments.
2. Preparation of Pigment Dispersion














Example
Pigmented Organosol
Solids




Number
Composition (% w/w)
(%)
Dv
Dn







5
LMA/HEMA-TMI//EK8200
12.19
1.69
0.41


6
TCHMA/HEMA-TMI//EK8200
11.19
1.78
0.68


7
LMA/HEMA-TMI//Solsperse13940//
12.99
1.19
0.28



EK8200


8
LMA/DAAM-TMI//EK8200
19.27
0.74
0.26


9
LMA/HEMA-TMI//PR81:4
19.85
1.18
0.56









Example 5
This is an example of preparing a black pigment dispersion using the dispersant prepared in Example 1.57 g of the graft polymeric dispersant @ 25.28%(w/w) solids in NorparTM 12 were combined with 221 g of NorparTM 12 and 22 g of pigment black EK-8200 (Aztech Company, Tucson, Ariz.) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1⁄4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
The percent solids of the pigment dispersion was determined to be 12.19% using the Halogen Drying Method described above. The particle size of the dispersed pigments was determined using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.), as described above. The dispersed pigments had a volume mean particle diameter of 1.69 μm and number mean particle diameter of 0.41 μm.
Example 6
This is an example of preparing a black pigment dispersion using the dispersant prepared in Example 2.50 g of the graft polymeric dispersant @ 28.88%(w/w) solids in NorparTM 12 were combined with 229 g of NorparTM 12, and 22 g of pigment black EK-8200 (Aztech Company, Tucson, Ariz.) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1/4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
The percent solids of the pigment dispersion was determined to be 11.19% using the Halogen Drying Method described above. The particle size of the dispersed pigments was determined using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.), as described above. The dispersed pigments had a volume mean particle diameter of 1.78 μm and number mean particle diameter of 0.68 μm.
Example 7
This is an example of preparing a black pigment dispersion using the dispersant prepared in Example 1 and a commercial polymeric dispersant. 57 g of the graft polymeric dispersant @ 25.28%(w/w) solids in NorparTM 12 and 5.40 g of Solsperse 13940 @ 40% active ingredient (Avecia Inc., Charlotte, N.C.) were combined with 216 g of NorparTM 12, and 22 g of pigment black EK-8200 (Aztech Company, Tucson, Ariz.) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1/4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
The percent solids of the pigment dispersion was determined to be 12.99% using the Halogen Drying Method described above. The particle size of the dispersed pigments was determined using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.), as described above. The dispersed pigments had a volume mean particle diameter of 1.19 μm and number mean particle diameter of 0.28 μm.
Example 8
This is an example of preparing a black dispersion using the dispersant prepared in Example 3.94 g of the graft polymeric dispersant @ 25.43%(w/w) solids in NorparTM 12 were combined with 170 g of NorparTM 12, and 36 g of pigment black EK-8200 (Aztech Company, Tucson, Ariz.) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1/4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
The percent solids of the pigment dispersion was determined to be 19.27% using the Halogen Drying Method described above. The particle size of the dispersed pigments was determined using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.), as described above. The dispersed pigments had a volume mean particle diameter of 0.74 μm and number mean particle diameter of 0.27 μm.
Example 9
This is an example of preparing a magenta pigment dispersion using the dispersant prepared in Example 1.95 g of the graft polymeric dispersant @ 25.28 %(w/w) solids in NorparTM 12 were combined with 169 g of NorparTM 12, and 36 g of Pigment Red 81:4 (“PR81:4” Magruder Color Company, Tucson, Ariz.) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1⁄4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
The percent solids of the pigment dispersion was determined to be 19.85% using the Halogen Drying Method described above. The particle size of the dispersed pigments was determined using a Horiba LA-900 laser diffraction particle size analyzer (Horiba Instruments, Inc., Irvine, Calif.), as described above. The dispersed pigments had a volume mean particle diameter of 1.18 μm and number mean particle diameter of 0.56 μm.
3. Encapsulating Pigment by Dispersion Polymerization














Example
Pigmented Organosol
Solids




Number
Composition (% w/w)
(%)
Dv
Dn







10
LMA-EK8200//EA-EMA
14.21
2.3
0.6


11
LMA-Solsperse-EK8200//EA-EMA
15.85
3.2
1.0


12
LMA-PR81:4//EA-EMA
12.05
2.4
1.0









Example 10
This is an example using the pigment dispersion in Example 5 to prepare an encapsulated black liquid toner by dispersion polymerization. A 5000 ml 3-neck round flask equipped with a condenser, a thermocouple connected to a digital temperature controller, a nitrogen inlet tube connected to a source of dry nitrogen and a magnetic stirrer, was charged with a mixture of 2148 g of NorparTM 12, 48.5 g of EA, 324.8 g of EMA, 972.2 g of the pigment dispersion in Example 5 @ 12.19% solids, and 6.30 g of V-601. While stirring the mixture, the reaction flask was purged with dry nitrogen for 30 minutes at flow rate of approximately 2 liters/minute. A hollow glass stopper was then inserted into the open end of the condenser and the nitrogen flow rate was reduced to approximately 0.5 liters/min. The mixture was heated to 70° C. for 16 hours. The conversion was quantitative.
Approximately 350 g of n-heptane were added to the cooled pigment dispersion, and the resulting mixture was stripped of residual monomer using a rotary evaporator equipped with a dry ice/acetone condenser and operating at a temperature of 90° C. and a vacuum of approximately 15 mm Hg.
This encapsulated pigmented organosol liquid toner was designed LMA-EK8200//EA-EMA, and the percent solids of the toner dispersion after stripping was determined to be 14.21% using Halogen Drying Method described above.
To the 750 g of the above encapsulated pigment dispersion, 1.37 g of 5.91% Zirconium HEX-CEM solution (OMG Chemical Company, Cleveland, Ohio) was added, and the resulting liquid toner was placed on the shaker for 24 hours before testing.
A 14% (w/w) solids liquid toner concentrate exhibited the following properties as determined using the test methods described above:
Volume Mean Particle Size: 2.3 micron
Q/M: 230 μC/g
Bulk Conductivity: 436 picoMhos/cm
Percent Free Phase Conductivity: 25%
Dynamic Mobility: 4.08E-11 (m2/Vsec)
This toner was tested on printing apparatus described previously. The reflection optical density (OD) was 1.2 at plating voltages greater than 450 volts.
Example 11
This is an example using the pigment dispersion in Example 7 to prepare an encapsulated black liquid toner by dispersion polymerization. Using the method and apparatus of Example 10, 2129 g of NorparTM 12, 48.5 g of EA, 324.8 g of EMA, 972.2 g of the graft stabilizer mixture from Example 7 @ 12.99% solids, and 6.30 g of AIBN were combined. The mixture was heated to 70° C. for 16 hours. The conversion was quantitative. The mixture then was cooled to room temperature. After stripping the encapsulated pigment dispersion using the method of Example 10 to remove residual monomer, the stripped mixture was cooled to room temperature.
This encapsulated pigmented organosol liquid toner was designed LMA-solsperse-EK8200//EA-EMA, and the percent solids of the toner dispersion after stripping was determined to be 15.85% using Halogen Drying Method described above.
To the 750 g of the above encapsulated pigment dispersion, 2.01 g of 5.91% Zirconium HEX-CEM solution (OMG Chemical Company, Cleveland, Ohio) was added, and the resulting liquid toner was placed on the shaker for 24 hours before testing.
A 15% (w/w) solids liquid toner concentrate exhibited the following properties as determined using the test methods described above:
Volume Mean Particle Size: 3.2 micron
Q/M: 192 μC/g
Bulk Conductivity: 344 picoMhos/cm
Percent Free Phase Conductivity: 37%
Dynamic Mobility: 5.28 E-11 (m2/Vsec)
This toner was tested on printing apparatus described previously. The reflection optical density (OD) was 0.94 at plating voltages greater than 450 volts.
Example 12
This is an example using the pigment dispersion in Example 9 to prepare an encapsulated magenta liquid toner by dispersion polymerization. Using the method and apparatus of Example 10, 2196 g of NorparTM 12, 63.0 g of EA, 421.7 g of EMA, 814.2 g of the pigment dispersion from Example 9 @ 19.85% solids, and 5.25 g of V-601 were combined. The mixture was heated to 70° C. for 16 hours. The conversion was quantitative. The mixture then was cooled to room temperature. After stripping the encapsulated pigment dispersion using the method of Example 10 to remove residual monomer, the stripped mixture was cooled to room temperature.
This encapsulated pigmented organosol liquid toner was designed LMA-PR81:4//EA-EMA, and the percent solids of the toner dispersion after stripping was determined to be 12.05% using Halogen Drying Method described above.
To the 750 g of the above encapsulated pigment dispersion, 3.82 g of 5.91% Zirconium HEX-CEM solution (OMG Chemical Company, Cleveland, Ohio) was added, and the resulting liquid toner was placed on the shaker for 24 hours before testing.
A 12% (w/w) solids liquid toner concentrate exhibited the following properties as determined using the test methods described above:
Volume Mean Particle Size: 2.4 micron
Q/M: 192 μC/g
Bulk Conductivity: 66 picoMhos/cm
Percent Free Phase Conductivity: 8.5%
Dynamic Mobility: 1.92 E-11 (m2/Vsec)
This toner was tested on printing apparatus described previously. The reflection optical density (OD) was 1.1 at plating voltages greater than 450 volts.
Comparative Example
This is a comparative example to prepare the liquid toner without using the encapsulated pigmented organosol.
1) Organosol Preparation
This example illustrates the use of the graft stabilizer in Example 1 to prepare an organosol using the dispersion polymerization without the pigments. Using the method and apparatus of Example 10, 2936 g of NorparTM12, 373 g of EMA, 185 g of the graft stabilizer mixture from Example 1 @ 25.28% polymer solids, and 6.3 g of V-601 were combined. The mixture was heated to 70° C. for 16 hours. The conversion was quantitative. The mixture then was cooled to room temperature. After stripping the organosol using the method of Example 5 to remove residual monomer, the stripped organosol was cooled to room temperature, yielding an opaque white dispersion. This organosol is designed LMA/HEMA-TMI//EMA (97/3-4.7//100%w/w) and can be used to prepare ink formulations. The percent solid of the gel organosol dispersion after stripping was determined as 14.83% using Halogen Drying Method described above. Subsequent determination of average particles size was made using the light scattering method described above; the organosol had a volume average diameter of 24.3 μm.
2) Liquid Toner Preparation
This is an example of preparing a black liquid toner using the above organosol. 208 g of the organosol @ 14.83% (w/w) solids in NorparTM 12 were combined with 86 g of NorparTM 12, 5 g of Pigment Black EK8200 (Aztech Company, Tucson, Ariz.) and 1.04 g of 5.91% Zirconium HEX-CEM solution (OMG Chemical Company, Cleveland, Ohio) in an 8 ounce glass jar. This mixture was then milled in a 0.5 liter vertical bead mill (Model 6TSG-1/4, Amex Co., Ltd., Tokyo, Japan) charged with 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, N.J.). The mill was operated at 2,000 RPM for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.
A 12% (w/w) solids toner concentrate exhibited the following properties as determined using the test methods described above:
Volume Mean Particle Size: 4.2 micron
Q/M: 163 μC/g
Bulk Conductivity: 364 picoMhos/cm
Percent Free Phase Conductivity: 1.1%
Dynamic Mobility: 7.63E-1 1 (m2/Vsec)
This toner was tested on printing apparatus described previously. The reflection optical density (OD) was 1.4 at plating voltages greater than 450 volts.










Charging Retention Time (CRT) of Liquid Toners









Examples
Q/M (μC/g)
CRT (sec)












10
230
113


11
192
39


Comparative
163
2.7


Example









Other embodiments of this invention will be apparent to those skilled in the art upon consideration of this specification or from practice of the invention disclosed herein. Various omissions, modifications, and changes to the principles and embodiments described herein may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.

## Claims

1. A liquid electrophotographic toner composition comprising:
a) a liquid carrier having a Kauri-Butanol number less than about 30 mL; and
b) a plurality of toner particles dispersed in the liquid carrier, wherein the toner particles comprise at least one visual enhancement additive dispersed and encapsulated within an amphipathic copolymer, wherein the amphipathic copolymer comprises one or more S portions and one or more D portions, wherein the S material portions and the D material portions have respective solubilities in the liquid carrier that are sufficiently different from each other such that the S material portions tend to be more solvated by the liquid carrier while the D material portions tend to be more dispersed in the liquid carrier.

2. The liquid electrophotographic toner composition according to claim 1, wherein said at least one visual enhancement additive is a pigment.

3. The liquid electrophotographic toner composition according to claim 1, wherein said amphipathic copolymer is a graft copolymer.

4. The liquid electrophotographic toner composition according to claim 1, wherein said particle has a volume mean particle diameter of about 1 μm to about 9 μm, and a number mean particle diameter of about 0.1 μm to about 4 μm.

5. The liquid electrographic toner composition according to claim 1, wherein said particle has a volume mean particle diameter of about 2 μm to about 7 μm, and a number mean particle diameter of about 0.5 μm to about 3 μm.

6. The liquid electrographic toner composition according to claim 1, wherein the weight ratio of amphipathic copolymer to visual enhancement additive is from about 2:1 to about 18:1.

7. The liquid electrographic toner composition according to claim 1, wherein the weight ratio of amphipathic copolymer to visual enhancement additive is from about 4:1 to about 14:1.

8. The liquid electrographic toner composition according to claim 1, wherein the weight ratio of amphipathic copolymer to visual enhancement additive is from about 8:1 to about 12:1.

9. The liquid electrographic toner composition according to claim 1, wherein the copolymer has a Tg calculated using the Fox equation of about 0°–100° C.

10. The liquid electrographic toner composition according to claim 1, wherein the copolymer has a Tg calculated using the Fox equation of about 20°–80° C.

11. The liquid electrographic toner composition according to claim 1, wherein the copolymer has a Tg calculated using the Fox equation of about 45°–75° C.

12. The liquid electrographic toner composition according to claim 1, wherein the S portion has a glass transition temperature calculated using the Fox equation of from about −70 to about 125° C.

13. The liquid electrographic toner composition according to claim 1, wherein the S portion has a glass transition temperature calculated using the Fox equation of from about 0 to about 100° C.

14. The liquid electrographic toner composition according to claim 1, wherein the S portion has a glass transition temperature calculated using the Fox equation of from about 25 to about 75° C.

15. The liquid electrographic toner composition according to claim 1, wherein the S portion of the copolymer has a Tg that is lower than the Tg of the D portion of the copolymer.

16. The liquid electrographic toner composition according to claim 1, wherein said D portion has a glass transition temperature calculated using the Fox equation of about 20° to about 125° C.

17. The liquid electrographic toner composition according to claim 1, wherein said D portion has a glass transition temperature calculated using the Fox equation of about 30° to about 85° C.

18. The liquid electrographic toner composition according to claim 1, wherein said D portion has a glass transition temperature calculated using the Fox equation of about 50° to about 75° C.

19. The liquid electrographic toner composition according to claim 1, wherein at least about 75% of the S portion (excluding grafting site components) is derived from ingredients selected from the group consisting of C1 to C24 (meth)acrylates, trimethyl cyclohexyl methacrylate, t-butyl methacrylate, isobornyl (meth)acrylate, and combinations thereof.

20. A method of making a liquid electrographic toner composition, comprising the steps of:
a) dispersing a visual enhancement additive in a composition comprising S portion prepolymer and a solvent; and
b) conducting a dispersion polymerization by reacting D portion materials with the S portion prepolymer to form an amphipathic copolymer, thereby encapsulating the visual enhancement additive within a layer of amphipathic copolymer to form encapsulated pigmented organosol particles.

21. The method of claim 20, further comprising blending the encapsulated pigmented organosol particles with a toner additive.

22. The method of claim 20, further comprising dispersing a toner additive in the visual enhancement additive/S portion prepolymer/solvent composition.

23. The method of claim 21, wherein the toner additive comprises at least one charge control agent.

24. The method of claim 20, wherein the S portion prepolymer is provided by a method comprising the steps of:
a) providing a plurality of free radically polymerizable monomers, wherein at least one of the monomers comprises hydroxyl functionality;
b) free radically polymerizing the monomers in a solvent to form a hydroxyl functional polymer, wherein the monomers and the hydroxyl functional polymer are soluble in the solvent; and
c) reacting a compound having NCO functionality and free radically polymerizable functionality with the hydroxyl functional polymer under conditions such that at least a portion of the NCO functionality of the compound reacts with at least a portion of the hydroxyl functionality of the polymer to form one or more urethane linkages by which the compound is linked to the polymer, thereby providing a polymer with pendant free radically polymerizable functionality.

25. The method of claim 20, wherein the solvent is a nonaqueous liquid having a Kauri-butanol number less than 30 ml.

26. The method of claim 20, wherein the solvent is not a nonaqueous liquid having a Kauri-butanol number less than 30 ml, and the solvent is exchanged with a solvent that is a nonaqueous liquid having a Kauri-butanol number less than 30 ml after formation of the encapsulated pigmented organosol particles.

27. The method of claim 20, wherein the D materials comprise one or more free radically polymerizable monomers wherein the polymeric material derived from ingredients comprising the one or more free radically polymerizable monomers is insoluble in the solvent.

28. The method of claim 20, wherein the weight ratio of amphipathic copolymer to visual enhancement additive is from about 2:1 to about 18:1.

29. The method of claim 20, wherein said S portion has a glass transition temperature calculated using the Fox equation of from about −70 to about 125° C.

30. A method of electrographically forming an image on a substrate surface, comprising the steps of:
a) providing a liquid toner composition of claim 1;
b) providing a chargeable substrate;
c) placing a charge onto the chargeable substrate in selected areas of the substrate to form a charge image;
d) applying the liquid toner to the charge image to provide a toned image; and
e) fixing the toned image.

31. A method of electrographically forming an image on a substrate surface, comprising the steps of:
a) providing a liquid toner composition of claim 1;
b) providing a chargeable substrate;
c) placing a charge onto the chargeable substrate in selected areas of the chargeable substrate to form a charge image;
d) applying the liquid toner to the charge image to provide a toned image; and
e) transferring the toned image from the chargeable surface to the substrate surface.

32. The method of claim 31, wherein the method is an electrostatic imaging method.

33. The method of claim 31, wherein the method is an electrophotographic imaging method.