Process for the preparation of coated carrier particles

Abstract: A carrier particle composition comprised of a core and thereover a mixture of a first and second polymer, and wherein said first polymer contains a conductive component, and said second polymer contains copper iodide. The carrier particle composition is suitable for use as a component of developer compositions for use in electrophotographic printing processes.

Description: This invention relates to a process for the preparation of coated carrier particles for use in electrostatographic imaging processes. The electrostatographic process, and particularly the xerographic process, is well known. This process involves the formation of an electrostatic latent image on a photoreceptor, followed by development, and subsequent transfer of the image to a suitable substrate. Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive toner compositions are selected depending on the development systems used. Moreover, of importance with respect to the aforementioned developer compositions is the appropriate triboelectric charging values associated therewith as it is these values that enable continued constant developed images of high quality and excellent resolution. Prior art carrier particles obtained by applying insulating resinous coatings to porous metallic carrier cores using solution coating techniques are undesirable from many viewpoints. For example, the coating material will usually reside in the pores of the carrier cores, rather than at the surfaces thereof; and, therefore, is not available for triboelectric charging when the coated carrier particles are mixed with finely divided toner particles. Attempts to resolve this problem by increasing the carrier coating weights, for example, to as much as 3 percent or greater to provide an effective triboelectric coating to the carrier particles necessarily involves handling excessive quantities of solvents, and further, usually these processes result in low product yields. Also, solution coated carrier particles, when combined and mixed with finely divided toner particles, provide in some instances triboelectric charging values which are too low for many uses. The powder coating processes of the present invention overcome these disadvantages; and further enable developers that are capable of generating high and useful triboelectric charging values with finely divided toner particles; and also wherein the carrier particles are of substantially constant conductivity. Further, when resin coated carrier particles are prepared by the powder coating process of the present invention, the majority of the coating materials are fused to the carrier surface thereby reducing the number of toner impaction sites on the carrier material. Additionally, there can be achieved with the process of the present invention and the carriers thereof, independent of one another, desirable triboelectric charging characteristics and conductivity values; that is, for example the triboelectric charging parameter is not dependent on the carrier coating weight as is believed to be the situation with the process of U.S. Patent 4,233,387 wherein an increase in coating weight on the carrier particles may function to also permit an increase in the triboelectric charging characteristics. Specifically, therefore, with the. carrier compositions and process of the present invention there can be formulated developers with selected triboelectric charging characteristics andlor conductivity values in a number of different combinations. Thus, for example, there can be formulated in accordance with the invention of the present application developers with conductivities of from 10 -6 ohm-cm to 10 -17 ohm-cm, preferably from 10 -8 ohm-cm to 10 -6 ohm-cm, determined in a magnetic brush conducting cell, and a wide carrier triboelectric charging value of from -30 to +40, and in embodiments of from -15 to +20 microcoulombs per gram on the carrier particles as determined by the known Faraday Cage technique. Thus, the developers can be formulated with constant conductivity values with different triboelectric charging characteristics by, for example, maintaining the same total coating weight on the carrier particles and changing the amount of cuprous iodide and conductive component ratio. Similarly, there can be formulated developer compositions wherein constant triboelectric charging values are achieved and the conductivities are altered by retaining the same total coating weight on the carrier particles. U.S. Patent 5,595,851 being of the same patent family as JP 09006058 discloses a conductive carrier composition comprising a core with a coating thereover comprising a mixture of a first polymer and a second polymer, wherein the first polymer contains a conductive component and the second polymer contains a metal oxide. U.S. Patent 4,810,611 discloses a conductive carrier composition comprising a core with a coating thereover, said coating comprising a colorless conductive metal halide such as copper iodide. The metal halide is added in an amount of from 25% by weight to 75% by weight. It is an object of the present invention to provide dry coating processes for generating carrier particles of substantially constant conductivity parameters. It is another object of the present invention to provide dry coating processes for generating carrier particles with a wide range of preselected triboelectric charging values. The present invention provides a process for the preparation of coated carrier particles for use in electrostatographic imaging processes, said process comprising (1) mixing carrier core particles with a mixture of a first and second polymer, wherein said first polymer contains a conductive component, and said second polymer contains cuprous iodide in an amount of at least 77 weight percent based on the amount of said second polymer and said iodide; (2) dry mixing the mixture of carrier core particles and polymers for a sufficient period of time enabling the polymers to adhere to the carrier core particles; (3) subsequently heating the mixture of carrier core particles and polymers to.a temperature of between 93°C (200°F) and 288°C (550°F), whereby the polymers melt and fuse to the carrier core particles; and (4) thereafter cooling the resulting coated carrier particles. Preferred embodiments of the present invention are set forth in the sub-claims. The carrier particles are comprised of a core with a certain coatings thereover. More specifically, the carrier particles selected can be prepared by mixing low density porous magnetic, or magnetically attractable metal core carrier particles with from, for example, between 0.05 percent and 3 percent by weight, based on the weight of the coated carrier particles, of a first polymer especially polymethacrylate, and which polymer has dispersed therein carbon black or similar conductive component, and a second polymer containing cuprous iodide in certain important amounts, until adherence thereof to the carrier core by mechanical impaction or electrostatic attraction; heating the resulting mixture of carrier core particles and polymer to a temperature of from 93°C to 288°C (200°F to 550°F) for an effective period of, for example, from 10 minutes to 60 minutes enabling the polymer to melt and fuse to the carrier core particles; cooling the coated carrier particles; and thereafter, classifying the obtained carrier particles to a desired particle size of, for example, from 50 to 200 micrometers in diameter. The copper iodide may be cuprous iodide present in an amount of up to 95 weight percent based on the amount of the second polymer and the iodide. The conductive component for the first polymer may be a metal oxide, or preferably carbon black, and when the conductive component for said first polymer is carbon black it is preferably selected in an amount of from 15 to 50 weight percent. The first polymer may be a polyester, or a styrene based polymer, and the second polymer may be polymethylmethacrylate, wherein the first polymer is selected in an amount of from 1 to 99 weight percent and the second polymer is selected in an amount of from 99 to 1 weight percent. The carrier core may be a metal, a ferrite, a metal oxide, and the like such as known carrier cores. Various suitable solid core carrier materials can be selected for the developers. Characteristic core properties of importance include those that will enable the toner particles to acquire a positive charge or a negative charge, and carrier cores that will permit desirable flow properties in the developer reservoir present in the xerographic imaging apparatus. Also of value with regard to the carrier core properties are, for example, suitable magnetic characteristics that will permit magnetic brush formation in magnetic brush development processes; and also wherein the carrier cores possess desirable mechanical aging characteristics. Examples of carrier cores that can be selected include iron, steel, ferrites such as Sr (strontium)-ferrite, Ba-ferrite, Cu/Zn-ferrite, and Ni/Zn-ferrite, magnetites, nickel, mixtures thereof, and the like. Preferred carrier cores include ferrites, and sponge iron, or steel grit with an average particle size diameter of from 30 micrometers to 200 micrometers. The first polymer coating has dispersed therein conductive components, such as metal oxides like tin oxide, conductive carbon blacks, and the like, in effective amounts of, for example, from 1 to 70 and preferably from 15 to 60 weight percent. Specific examples of conductive components include the conductive carbon black SC Ultra manufactured by Conductex, Inc., and antimony-doped tin oxide Zelec ECP3005-XC (tradename) manufactured by DuPont. Of importance with respect to the present invention is the presence of cuprous iodide in at least one. polymer coating, and more specifically, in a second polymer that contains no other conductive component, which iodide is present in an amount of at least 77 percent by weight, and specifically, up to 95 weight percent. With the combination of two polymers, conductive component and iodide containing component, there are enabled the advantages of the present invention, including the wide ranges of carrier tribo and carrier conductivity as indicated herein. For example, a polymer coating comprised of a combination of powders of (1) 19 percent by weight of Conductex SC Ultra conductive carbon black incorporated into poly(methylmethacrylate) polymer, and (2) 80 percent by weight of cuprous iodide incorporated into a reactive extruded polyester will provide carrier triboelectric values of from -10 microcoulombs per gram to +10 microcoulombs per gram depending on the relative ratios of the two polymers used, at conductivities greater than 5 x 10 -10 mhos per centimeter. The process for incorporating these polymers onto a carrier core can be sequential, a process in which one of the two polymers is fused to the surface in a first step and the second polymer is fused to the surface in a subsequent fusing step. Alternatively, the process for incorporation can comprise a single fusing step in which the two polymers, which are mixed with each other prior to the fusing process, are incorporated onto the core in a single fusing step. Also, the carrier coating can have incorporated therein various charge enhancing additives, such as quaternary ammonium salts, and more specifically, distearyl dimethyl ammonium methyl sulfate (DDAMS), bis[1-[(3,5-disubstituted-2-hydroxyphenyl)azo]-3-(mono-substituted)-2-naphthalenolato(2-)] chromate(1-), ammonium sodium and hydrogen (TRH), cetyl pyridinium chloride (CPC), FANAL PINK® D4830, including those as specifically illustrated herein, and other effective known charge agents or additives. The charge additives are selected in various effective amounts, such as from 0.05 to 15 weight percent. Examples of first and second polymers selected include polymethacrylate, polyvinylidenefluoride, polyvinylfluoride, polypentafluorostyrene, polyethylene, polymethylmethacrylate, copolyethylenevinylacetate, copolyvinylidenefluoride tetrafluoroethylene, and polyethylene; polymethylmethacrylate, polyurethane and copolyethylene, and preferably wherein the first and second polymers are dissimilar. Other known related polymers not specifically mentioned herein may also be selected, such as those illustrated in US-A-4,937,166 and US-A-4,935,326. Various processes can be selected to apply the polymer, or mixture of polymer coatings to the surface of the carrier particles. Examples of typical processes for this purpose include combining the carrier core material, and the polymers with cuprous iodide and conductive component by cascade roll mixing, or tumbling, milling, shaking, electrostatic powder cloud spraying, fluidized bed, electrostatic disc processing, and an electrostatic curtain. Following application of the polymers, heating is initiated to permit flowout of the coating material over the surface of the carrier core. The concentration of the coating material powder particles, and the parameters of the heating step, may be selected to enable the formation of a continuous film of the coating polymers on the surface of the carrier core, or permit only selected areas of the carrier core to be coated. When selected areas of the metal carrier core remain uncoated or exposed, the carrier particles will possess electrically conductive properties when the core material comprises a metal. The aforementioned conductivities can include various suitable values. Generally, however, this conductivity is from 10 -9 to 10 -17 mho-cm -1 as measured, for example, across a 2.54 mm (0.1 inch) magnetic brush at an applied potential of 10 volts; and wherein the coating coverage encompasses from 10 percent to 100 percent of the carrier core. Illustrative examples of toner resins selected for the toner which when admixed with carrier generates developer compositions includes a number of thermoplastics, such as polyamides, epoxies, polyurethanes, diolefins, vinyl resins, polyesters, such as those obtained by the polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Specific vinyl monomers that can be used are styrene, p-chlorostyrene vinyl naphthalene, unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; vinyl esters like the esters of monocarboxylic acids including methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methylalphachloracrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate; acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers, inclusive of vinyl methyl ether, vinyl isobutyl ether, and vinyl ethyl ether; vinyl ketones inclusive of vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; vinylidene halides such as vinylidene chloride, and vinylidene chlorofluoride; N-vinyl indole, N-vinyl pyrrolidene; styrene butadiene copolymers; and mixtures thereof. As one preferred toner resin there can be selected the esterification products of a dicarboxylic acid and a diol comprising a diphenol, reference U.S. Patent 3,590,000. Other preferred toner resins include styrene/methacrylate copolymers; styrene/butadiene copolymers; polyester resins obtained from the reaction of bisphenol A and propylene oxide; and branched polyester resins resulting from the reaction of dimethyl terephthalate, 1,3-butanediol, 1,2-propanediol and pentaerythritol. Generally, from 1 part to 5 parts by weight of toner particles are mixed with from 10 to 300 parts by weight of the carrier particles. Numerous well known suitable pigments or dyes, and preferably pigments can be selected as the colorant for the toner particles including, for example, carbon black, nigrosine dye, lamp black, iron oxides, magnetites, and mixtures thereof. The pigment, which is preferably carbon black, should be present in a sufficient amount to render the toner composition highly colored. Thus, the pigment is present in amounts of from 1 percent by weight to 20, and preferably from 5 to 12 percent by weight, based on the total weight of the toner composition, however, lesser or greater amounts of pigment may be selected. When the pigment particles are comprised of magnetites, which are a mixture of iron oxides (FeO•Fe 2 O 3 ) including those commercially available as MAPICO BLACK®, they are present in the toner composition in an amount of from 10 percent by weight to 70 percent by weight, and preferably in an amount of from 20 percent by weight to 50 percent by weight. The resin particles are present in a sufficient, but effective amount, thus when 10 percent by weight of pigment, or colorant, such as carbon black like REGAL 330®, is contained therein about 90 percent by weight of resin material is selected. Generally, however, the toner composition is comprised of from 85 percent to 97 percent by weight of toner resin particles, and from 3 percent by weight to 15 percent by weight of pigment particles such as carbon black. Also, there may be selected colored toner compositions comprised of toner resin particles, carrier particles and as pigments or colorants, magenta, cyan and/or yellow particles; as well as mixtures thereof. These pigments are generally present in the toner composition in an amount of from 1 weight percent to 15 weight percent based on the weight of the toner resin particles. For further enhancing the positive charging characteristics of the developer compositions described herein, and as optional components there can be incorporated therein with respect to the toner charge enhancing additives inclusive of alkyl pyridinium halides, reference U.S. Patent 4,298,672; organic sulfate or sulfonate compositions, reference U.S. Patent 4,338,390; distearyl dimethyl ammonium sulfate, reference U.S. Patent 4,560,635; and other similar known charge enhancing additives. These additives are usually incorporated into the toner in an amount of from 0.1 percent by weight to 20 percent by weight. These charge additives can also be dispersed in the carrier polymer coating as indicated herein. The toner composition can be prepared by a number of known methods including melt blending the toner resin particles, and pigment particles or colorants followed by mechanical attrition, or emulsion/aggregation. The toner and developer compositions may be selected for use in electrostatographic imaging processes containing therein conventional photoreceptors, including inorganic and organic photoreceptor imaging members. Examples of imaging members are selenium, selenium alloys, and selenium or selenium alloys containing therein additives or dopants such as halogens. Furthermore, there may be selected organic photoreceptors, illustrative examples of which include layered photoresponsive devices comprised of transport layers and photogenerating layers, reference U.S. Patent 4,265,990. Images obtained with this developer composition had acceptable solids, excellent halftones, and desirable line resolution with acceptable or substantially no background deposits. In the following Examples parts and percentages are by weight unless otherwise indicated. EXAMPLE I 1,091 Grams of copper iodide and 273 grams of a 30 percent (by weight) gel content partially crosslinked polyester resin, obtained by the reactive extrusion of a linear polyester, which linear polyester was obtained from the polymeric esterification of the dicarboxylic acid fumaric acid, and propoxylated bisphenol A, reference U.S. Patents 5,376,494 and 5,227,460, were combined and processed in an extruder (APV) with the following process parameters: 127°C (260°F) barrel temperature, 127°C (260°F) die head temperature, 57 percent load, a feed rate of 11.4 grams per minute, and a tool speed of 150 rotations per minute. The resulting extrudate comprised of 80 percent copper iodide by weight dispersed in the polyester polymer resin was size reduced by mechanical attrition in an 0202 Jet-O-Mizer (Fluid Energy Aljet) with the following process parameters: feed pressure of 6.9 x 10 5 Pa (100 pounds per square inch), grinding pressure of 6.9 x 10 5 Pa (100 pounds per square inch), and a feed rate of 146 grams per minute. The volume median particle size after mechanical attrition was 5.2 micrometers. In the first step of the two step carrier coating process, 4.55 kilograms of 100 micrometer spherical steel shot (Nuclear Metals, Inc.) was mixed with 68 grams of a carbon black-loaded poly(methylmethacrylate) with about 20 weight percent of Conductex SC Ultra conductive carbon black produced with a volume median particle size of 2 micrometers in a chemical process prior to mixing. The mixing was accomplished in a Munson M5R Minimixer (tradename) blender with the following process conditions: blender speed 50 rotations per minute and a blend time of 30 minutes. There resulted uniformly distributed and electrostatically attached, as determined by visual observation, on the carrier core the polymer with carbon black therein. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 30 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymer with carbon black to melt and fuse to the core. The second step of the two step carrier coating process comprised mixing the output of the above first step of the process, that is polymer with carbon black, with the above prepared 80 percent copper iodide dispersed in the 30 percent gel polyester resin at a concentration of 0.5 percent by weight. This mixing was accomplished in a Munson M5R Minimixer (tradename) blender with the following process conditions: blender speed 50 rotations per minute and a blend time of 30 minutes. There resulted uniformly distributed and electrostatically attached, as determined by visual observation, on the powder resulting from the first step of the process the copper iodide/polymer material. The resulting mixture with two polymer coatings was then placed in a rotating kiln furnace for 30 minutes to reach a peak temperature of 204°C (400°F). This functions to primarily fuse the cuprous iodide loaded polyester onto the surface of the carbon black loaded poly(methylmethacrylate). The final product was comprised of a carrier core with a total of 2 percent polymer mixture by weight on the surface with the polymer being a combination of 75 percent by weight of the carbon black loaded poly(methylmethacrylate) and 25 percent by weight of the copper iodide loaded polyester. A developer composition was then prepared by mixing 194 grams of the above prepared carrier with 6 grams of a toner composition comprised of 87 percent by weight of a 30 percent (by weight) gel content partially crosslinked polyester resin, obtained by the reactive extrusion of a linear polyester, reference the same polyester selected for the polymer coating above, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of 8.5 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 2.9 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. In all the Examples, the triboelectric charging values and the conductivity numbers were obtained in accordance with the aforementioned procedure. EXAMPLE II The process of Example I was repeated, except that the second step of the carrier coating process comprised the mixing of the output of the first step of the process, that is polymer with carbon black, with the 80 percent copper iodide dispersed in polyester resin particles at a concentration of 1.0 percent by weight. The final product was comprised of a carrier core with a total of 2.5 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 60 percent by weight of carbon black loaded poly(methylmethacrylate) first polymer, and 40 percent by weight of copper iodide loaded polyester second polymer. A developer composition was then prepared by mixing 194 grams of the above prepared carrier particles with 6 grams of a toner composition comprised of 87 percent by weight of a crosslinked polyester resin, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of -3.8 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 2.6 x 10 -10 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE III The procedure of Example I was repeated, except that the second step of the carrier coating process involved mixing the output of the first step of the process with the 80 percent copper iodide dispersed in polyester resin particles at a concentration of 1.5 percent by weight. The final product was a carrier core with a total of 3 percent polymers by weight on the surface with the polymer mixture being a combination of 50 percent by weight carbon black loaded poly(methylmethacrylate) and 50 percent by weight copper iodide loaded polyester. A developer composition was then prepared by mixing 194 grams of the above prepared carrier particles with 6 grams of a toner composition comprised of 87 percent by weight of a crosslinked polyester resin, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of -7.9 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 8.5 x 10 -10 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE IV 1,091 Grams of copper iodide and 273 grams of a poly(styrene-butadiene) resin, 91/9 styrene/butadiene, were combined and processed in an extruder (APV) with the following process parameters: 204°C (400°F) barrel temperature, 177°C (350°F) die head temperature, 26 percent load, a feed rate of 23 grams per minute, and a tool speed of 150 rotations per minute. The resulting extrudate of 80 percent copper iodide by weight dispersed uniformly in the styrenelbutadiene polymer resin was size reduced by mechanical attrition in a 38.1 cm (15 inch) Sturtevant Fluid Energy Mill with the following process parameters: feed pressure of 6.9 x 10 5 Pa (100 pounds per square inch), grinding pressure of 6.9 x 10 5 Pa (100 pounds per square inch), and a feed rate of 146 grams per minute. The volume median particle size after mechanical attrition was 5.2 micrometers. In the carrier coating process, 85 grams of the above prepared 80 percent by weight copper iodide powder was mixed with 28 grams of a carbon black-loaded poly(methylmethacrylate) with a volume median particle size of 2 micrometers in a chemical process prior to admixing the two polymers. This powder mixture was then combined with 4.55 kilograms of 100 micrometer spherical steel shot (Nuclear Metals, Inc.) in a Munson M5R Minimixer blender with the following process conditions: blender speed of 50 rotations per minute and a blend time of 30 minutes. There resulted uniformly distributed and electrostatically attached, as determined by visual observation, on the carrier core the two polymer mixture. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 30 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymer to melt and fuse to the core. A developer composition was then prepared by mixing 194 grams of the above prepared carrier particles with 6 grams of a toner composition comprised of 87 percent by weight of the crosslinked polyester resin, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of -4.7 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 7.6 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE V The procedure of Example I was repeated, except that the carrier coating process involved mixing 45 grams of the 80 percent by weight copper iodide powder with 45 grams of the carbon black-loaded poly(methylmethacrylate) with a volume median particle size of 2 micrometers, and generated in a chemical process prior to mixing. A developer composition was then prepared by mixing 194 grams of the above prepared carrier particles with 6 grams of a toner composition comprised of 87 percent by weight of a crosslinked polyester resin, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of 4.5 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 5.5 x 10 -7 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE VI The procedure of Example IV was repeated, except that the carrier coating process involved mixing 16 grams of this 80 percent by weight copper iodide powder with 48 grams of a carbon black-loaded poly(methylmethacrylate) produced with a volume median particle size of 2 micrometers in a chemical process prior to mixing the two polymers. Thereafter, the remainder of the process is identical to that of Example IV. A developer composition was then prepared by mixing 194 grams of the above prepared carrier particles with 6 grams of a toner composition comprised of 87 percent by weight of a crosslinked polyester resin, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, and 4 percent by weight of a compatibilizing agent comprised of KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process, and there was measured on the carrier a charge of 7.9 microcoulombs per gram. Further, the conductivity of the carrier as determined by forming a 2.5 mm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 1.1 x 10 -6 mho-cm -1 . Therefore, these carrier particles are conducting. The toner carbon black selected for the above Examples was, unless otherwise indicated, REGAL 330®; the polypropylene was of a low molecular weight, about 7,000 it is believed, and was obtained from Sanyo Chemicals of Japan, or VISCOL 660P®; and the KRATON™ compatibilizer was a styrene-ethylene-butylene styrene block copolymer (Shell KRATON G 1726X®), reference U.S. Patent 5,229,242

Claims: A process for the preparation of coated carrier particles for use in electrostatographic imaging processes, said process comprising (1) mixing carrier core particles with a mixture of a first and second polymer, wherein said first polymer contains a conductive component, and said second polymer contains cuprous iodide in an amount of at least 77 weight percent based on the amount of said second polymer and said iodide; (2) dry mixing the mixture of carrier core particles and polymers for a sufficient period of time enabling the polymers to adhere to the carrier core particles; (3) subsequently heating the mixture of carrier core particles and polymers to a temperature of between 93°C (200°F) and 288°C (550°F), whereby the polymers melt and fuse to the carrier core particles; and (4) thereafter cooling the resulting coated carrier particles. The process of claim 1 wherein said carrier cores are selected from the group consisting of iron, steel, ferrites, magnetites, and nickel. The process of claim 1 or 2 wherein said conductive component for said first polymer is selected from the group consisting of metal oxides and carbon black. The process of claim 3 wherein said conductive component for said first polymer is carbon black present in an amount of from 15 to 60 weight percent. The process of any of claims 1 to 4 wherein said first polymer is a polyester, or a styrene based polymer, and said second polymer is polymethylmethacrylate. The process of any of claims 1 to 5 wherein the cuprous iodide in said second polymer is present in an amount of from 80 to 95 weight percent. The process of claim 1 wherein the conductive component is a conductive carbon black present in an amount of from 15 to 50 weight percent, the cuprous iodide is present in an amount of from 80 to 95 weight percent, the carried conductivity is from 10 -6 to 10 -15 (ohm-cm) -1 , and the carrier triboelectric charge is from -30 to +40 microcoulombs per gram.

Inventors: CREATURA JOHN A, ELLIS RICHARD W, HSIEH BING R, SILENCE SCOTT M, ZIOLO RONALD F, CREATURA, JOHN A., ELLIS, RICHARD W., HSIEH, BING R., SILENCE, SCOTT M., ZIOLO, RONALD F.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: G03G9
IPC codes: G03G9