Coated carrier particles

Abstract: A 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 is a poly(urethane).

Description: This invention relates to developer compositions with coated carrier particles that can be prepared by dry powder processes. The carrier particles are comprised of a core with polymeric mixture coating thereover, and more specifically, a mixture of two polymers, and dispersed in one polymer conductive components, such as carbon black, and wherein one of the polymers is a thermosetting polymer of a poly(urethane), thereby enabling carriers with increased developer riboelectric response at relative humidities of from 20 to 90 percent, improved image quality performance, excellent high conductivity ranges of from 10 -10 to 10 -7 (ohm-cm) -1 , and a carrier tribo range of from +5 to +50 µC/g, preferably from a plus 15 to a plus 40 µC/g, and most preferably from +25 to +35 µC/g. The carrier particles prepared in accordance with the processes of the present invention contain in certain important amounts a polyurethane, for example from 0.05 to 3 and preferably from 0.1 to 0.3 weight percent to enable in combination with the polymer/conductive coating a large carrier conductivity range, and a wide carrier triboelectric range, and wherein the carriers generated can be selected for a number of different xerographic copiers and printers wherein carriers with certain specific conductivity and certain tribo charge are required. Developer compositions comprised of the carrier particles illustrated herein and prepared by a dry coating process are useful in electrostatographic or electrophotographic imaging systems, especially xerographic imaging and printing processes, and digital processes. Additionally, the invention developer compositions comprised of substantially conductive carrier particles are useful in imaging methods wherein relatively constant conductivity parameters are desired. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected depending on the polymer composition and dispersant component applied to the carrier core and the type and amount of the conductive component selected. 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. Additionally, carrier particles for use in the development of electrostatic latent images are described in many patents including, for example, U.S. Patent 3,590,000. These carrier particles contain various cores, including steel, with a coating thereover of fluoropolymers, and terpolymers of styrene, methacrylate, and silane compounds. Past efforts have focused on the attainment of coatings for carrier particles for the purpose of improving development quality, and also to permit particles that can be recycled, and that do not adversely effect the imaging member in any substantial manner. A number of coatings can deteriorate rapidly, especially when selected for a continuous xerographic process where the entire coating may separate from the carrier core in the form of chips or flakes; and fail upon impact, or abrasive contact with machine parts and other carrier particles. These flakes or chips, which cannot generally be reclaimed from the developer mixture, have an adverse effect on the triboelectric charging characteristics of the carrier particles thereby providing images with lower resolution in comparison to those compositions wherein the carrier coatings are retained on the surface of the core substrate. Further, another problem encountered with some prior art carrier coatings resides in fluctuating triboelectric charging characteristics, particularly with changes in relative humidity. The aforementioned modification in triboelectric charging characteristics provides developed images of lower quality, and with background deposits. US-A-5 595 851 discloses a carrier composition comprising a cone with a coating thereof comprised of a mixture of a first and second polymer such as polymethyl methacrylate the first polymer containing a conductive component. GB-A-2124792 and US-A-4067293 disclose a carrier composition comprising a core and a core coating of a polyurethane and an other polymer. There are illustrated in U.S. Patent 4,233,387, the disclosure of which is totally incorporated herein by reference, coated carrier components for electrostatographic developer mixtures comprised of finely divided toner particles clinging to the surface of the carrier particles. Specifically, there is disclosed in this patent coated carrier particles obtained by mixing carrier core particles of an average diameter of from between about 30 µm to about 1,000 µm with from about 0.05 percent to about 3.0 percent by weight, based on the weight of the coated carrier particles, of thermoplastic resin particles. The resulting mixture is then dry blended until the thermoplastic resin particles adhere to the carrier core by mechanical impaction, and/or electrostatic attraction. Thereafter, the mixture is heated to a temperature of from about 320°F to about 650°F for a period of 20 minutes to about 120 minutes, enabling the thermoplastic resin particles to melt and fuse on the carrier core. While the developer and carrier particles prepared in accordance with the process of this patent are suitable for their intended purposes, the conductivity values of the resulting particles are not constant in all instances, for example, when a change in carrier coating weight is accomplished to achieve a modification of the triboelectric charging characteristics; and further with regard to the '387 patent, in many situations carrier and developer mixtures with only specific triboelectric charging values can be generated when certain conductivity values or characteristics are contemplated. With the invention of the present application, the conductivity of the resulting carrier particles can be substantially constant, and moreover, the triboelectric values can be selected to vary significantly, for example, from less than 30 microcoulombs per gram to +40 microcoulombs per gram. There is illustrated in United States Patents 4,937,166 and 4,935,326, the disclosures of which are totally incorporated herein by reference, carrier containing a mixture of polymers, such as two polymers, not in close proximity in the triboelectric series. Moreover, in U.S. Patent 4,810,611, the disclosure of which is totally incorporated herein by reference, there is disclosed that there can be added to carrier coatings colorless conductive metal halides in an amount of from about 25 to about 75 weight percent, such halides including copper iodide, copper fluoride, and mixtures thereof. With further reference to the prior art, carriers 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. 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 and/or 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) -1 to 10 -17 (ohm-cm) -1 , preferably from 10 -10 (ohm-cm) -1 to 10 -6 (ohm-cm) -1 , and most preferably from 10 -8 (ohm-cm) -1 to 10 -6 (ohm-cm) -1 , determined in a magnetic brush conducting cell, and a wide carrier triboelectric charging value of from +5 to +50, and in embodiments of from +10 to +40 µC/g on the carrier particles as determined by the known Faraday Cage technique. Thus, the developers of the present invention can be formulated with conductivity values in the preferred range with different triboelectric charging characteristics by, for example, maintaining the same total coating weight on the carrier particles and changing ratio of the amount of a first polymer which contains a conductive component and a second polymer. The advantages of the carriers of the present invention compared to some of the aforementioned prior art carriers include a decreased sensitivity of the carrier triboelectric value to the relative humidity of the environment. For example, a carrier comprised of a steel core onto which is coated 1 percent by weight of a carbon black containing polymethylmethacrylate has a triboelectric value of 10.4 µC/g as measured against a standard reference toner at an environmental relative humidity of 80 percent; the same carrier has a triboelectric value of 18.9 µC/g at an environmental relative humidity of 20 percent, providing a triboelectric ratio of 1.8, that is the ratio of the triboelectric value at 20 percent relative humidity to that of 80 percent relative humidity. A carrier with a steel core onto which is coated 0.8 percent by weight of a carbon black containing polymethylmethacrylate and 0.2 percent by weight of a polyurethane polymer (Envirocron, obtained from PPG Inc.) has a triboelectric value of 18.4 µC/g as measured against a standard reference toner at an environmental relative humidity of 80 percent and a triboelectric value of 22.6 µC/g at an environmental relative humidity of 20 percent. This provides a substantially improved triboelectric ratio of 1.2. It is the object of the present invention to provide toner and developer compositions with carrier particles containing polymer coatings, to provide dry coating processes for generating carrier particles of substantially constant conductivity parameters, to provide dry coating processes for generating carrier particles of substantially constant conductivity parameters, and a wide range of preselected triboelectric charging values, to provide carrier particles with a coating of two polymers of polymethylmethacrylate and a thermosetting polymer of a poly(urethane), and wherein the first polymer of polymethylmethacrylate contains therein a conductive component of for example, carbon black. This object is achieved by the subject matter of claims 1 to 12. In embodiments of the present invention, there are provided developer compositions comprised of toner particles, and carrier particles prepared by a powder coating process, and wherein the carrier particles are comprised of a core with 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 polymethylmethacrylate, and which polymer has dispersed therein carbon black or a similar conductive component, and a second thermosetting polymer 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, for example, of between from 93.3 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 µm (microns) in diameter. Embodiments of the present invention include a composition comprised of a core, and thereover a mixture of a first and second polymer, and wherein the first polymer contains a conductive component, and the second polymer is a thermosetting poly(urethane), such as Envirocron obtained from PPG Industries; a carrier composition wherein the polyurethane is present in an amount of from 1 to 99 weight percent, and preferably from 5 to 40 percent, based on the amount of the second polymer, and wherein the first polymer contains a conducting component; a carrier with two polymers thereover and wherein the conductive component for the first polymer is a metal oxide, or a pigment, like preferably carbon black, wherein the conductive component for said first polymer is carbon black selected in an amount of from 15 to 50 weight percent; wherein the second polymer is as illustrated herein, that is a thermosetting polymer, a polyester, or a styrene based polymer, and the first polymer is polymethylmethacrylate, wherein the first polymer is selected in an amount of from1 to 99, or from 5 to 50 weight percent, and the second polymer is selected in an amount of from 99 to 1, or from 5 to 50 weight percent; or wherein the carrier core is a metal, a ferrite, a metal oxide, and the like such as known carrier cores. Embodiments include a composition wherein the crosslinking temperature is from 340 to 380°F., and the carbon black is present in an amount of from 15 to 30 weight percent; and a composition wherein the carbon black is present in an amount of from 17 to 25 weight percent. Embodiments include also a process for the preparation of carrier which comprises (1) mixing carrier core with a mixture of a first and second polymer, and wherein said first polymer is polymethylmethacrylate and contains a conductive component, and said second polymer is a poly(urethane); (2) dry mixing the resulting carrier core for a sufficient period of time to enable the polymers to adhere to the carrier core; (3) subsequently heating the mixture of carrier core particles and polymers to a temperature of between 93.3 and 288°C (200°F and 550°F), whereby the polymers melt and fuse to the carrier core; and (4) thereafter cooling the resulting coated carrier particles; a process wherein the poly(urethane) possesses a melt temperature of greater than 93.3°C (200°F) and a crosslinking temperature of greater than 166°C (330°F); a process wherein the carbon black is present in an amount of from 15 to 40 weight percent; a process wherein the conductive component is carbon black present in an amount of from 16 to 20 weight percent; and a process wherein the conductive component is a conductive carbon black present in an amount of from 15 to 25 weight percent, the carrier conductivity is from 10 -7 to 10 -8 (ohm-cm) -1 , and the carrier triboelectric charge is from +5 to +50 µC/g. Embodiments include further an improved process for the preparation of carrier particles as defined above with an extended triboelectric charging range at relative humidities of from 20 to 80 percent, and with an extended conductivity range, wherein said conductive component is present in an amount of from 18 to 50 weight percent. Various suitable solid core carrier materials can be selected for the developers of the present invention. 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 between 30 to 200 µm (microns). The polymethylmethacrylate coating has dispersed therein conductive components, such as metal oxides like tin oxide, conductive carbon blacks, 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 available from Conductex, Inc., and antimony-doped tin oxide Zelec ECP3005-XC manufactured by DuPont. Also, the carrier coating can have incorporated therein various known 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. The second polymer is comprised of a thermosetting polymer, more specifically a poly(urethane) thermosetting resin which contains, for example, 20 percent by weight of a polyester polymer, which functions primarily as a crosslinking agent for the polyurethane. An example of a polyurethane is poly(urethane)/polyester polymer or Envirocron (product number PCU10101, obtained from PPG Industries, Inc.). This polymer has a melt temperature of between 99 and 130°C (210°F and 266°F), and a crosslinking temperature of 174°C (345°F). This second polymer is mixed together with the first polymer, generally prior to mixing with the core, which when fused forms a uniform coating of the first and second polymers on the carrier surface. The second polymer is present in an amount of from 1 percent to 99 percent by weight, based on the total weight of the first and second polymers and the conductive component in the first polymer, and preferably from 5 percent to 40 percent. The advantages of the carriers of the present invention include in embodiments a decreased sensitivity of the carrier triboelectric value to the relative humidity of the environment. For example, a carrier with a steel core onto which is coated 1 percent by weight of a carbon black containing polymethylmethacrylate has a triboelectric value of 10.4 µC/g as measured against a standard reference toner, such as the Xerox Corporation 5090 toner, at an environmental relative humidity of 80 percent; the same carrier has a triboelectric value of 18.9 µC/g at an environmental relative humidity of 20 percent, providing a triboelectric ratio of 1.8, that is the ratio of the triboelectric value at 20 percent relative humidity to that of 80 percent relative humidity. A carrier with a steel core onto which is coated 0.8 percent by weight of a carbon black containing polymethylmethacrylate and 0.2 percent by weight of a polyurethane polymer (Envirocron, obtained from PPG Industries, Inc.) has a triboelectric value of 18.4 µC/g as measured against a standard reference toner, such as the Xerox Corporation 5090 toner, at an environmental relative humidity of 80 percent and a triboelectric value of 22.6 µC/g at an environmental relative humidity of 20 percent. This gives a substantially improved triboelectric ratio of 1.2. Various effective suitable 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 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 flow out 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 0.25 cm (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, include 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 mono-olefins 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; mixtures thereof; and other similar known resins. As one 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 specific 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 from10 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, 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. 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; 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 of the present invention can be prepared by a number of known methods including melt blending the toner resin particles, and pigment particles or colorants of the present invention followed by mechanical attrition, emulsion/aggregation. Other methods include those well known in the art such as spray drying, melt dispersion, dispersion polymerization and suspension polymerization. In one dispersion polymerization method, a solvent dispersion of the resin particles and the pigment particles are spray dried under controlled conditions to result in the desired product. 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. The following Examples are being supplied to further define the present invention. Parts and percentages are by weight unless otherwise indicated. EXAMPLE I In the following carrier coating process, 54.5 grams of polyurethane polymer (Envirocron by PPG Industries, Inc.) with a particle size of between 4 and 7 µm (microns) were mixed in a high intensity blender with 490.5 grams of carbon black-loaded poly(methylmethacrylate) with 20 weight percent of Conductex SC Ultra conductive carbon black produced with a volume median particle size of 2 microns in a chemical process prior to mixing. These 545 grams of premixed polymer were mixed with 68.0 kilograms of 90 µm (micron) atomized steel shot (Hoeganaes, Inc.). The mixing was accomplished in a Munson Minimixer blender with the following process conditions: blender speed of 17 rotations per minute, a blend time of 20 minutes, and a humidity of 3 millimeters Hg. There resulted uniformly distributed and electrostatically attached, as determined by visual observation, on the carrier core the premixed polymers. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 194°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer being a combination of 10 percent by weight of the polyurethane and 90 percent by weight of the carbon black-loaded poly(methylmethacrylate). 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, reference U.S. Patent 5,376,494, obtained by the reactive extrusion of a linear polyester, 5 percent by weight of carbon black, 4 percent by weight of a polypropylene wax, 660P low molecular weight wax available from Sanyo Chemicals, and 4 percent by weight of a compatibilizing agent comprised of the grafted copolymer KRATON™ obtained from Shell Chemicals. Thereafter, the triboelectric charge on the carrier particles was determined by the known Faraday Cage process after churning/mixing on a magnetic roll for 60 minutes in an 27°C (80°F)/80 percent relative humidity environment and a 21°C (70°F)/20 percent relative humidity environment. There was measured on the carrier a charge of 14.6 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 22.6 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier as determined by forming a 0.25 cm (0.1 inch) long magnetic brush of the carrier particles, and measuring the conductivity by imposing a 10 volt potential across the brush was 1.9 x 10 -7 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 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 10 percent by weight of the polyurethane and 90 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 15.7 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 22. µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 6.7 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE III The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 40 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 10 percent by weight of the polyurethane and 90 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 13.4 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 19.3 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 3.7 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE IV The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 32 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 15 percent by weight of the polyurethane and 85 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 18.7 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 25.4 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 4.7 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE V The process of Example I was repeated, except that 0.8 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 17 revolutions per minute for 40 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 34 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 15 percent by weight of the polyurethane and 85 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared by repeating the process of Example I, and the developer was characterized as described in Example I. There was measured on the carrier a charge of 16.2 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 21.5 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 8.1 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE VI The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 20 minutes with a humidity of 3 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 37 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 15 percent by weight of the polyurethane and 85 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 15.9 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 21.9 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 2.3 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE VII The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 40 minutes with a humidity of 3 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 32 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 20 percent by weight of the polyurethane and 80 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as illustrated in Example I. There was measured on the carrier a charge of 18.4 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 25.9 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 2.6 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE VIII The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 17 revolutions per minute for 20 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 34 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 20 percent by weight of the polyurethane and 80 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 21.5 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 28.2 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 2.3 x 10 -8 mho-cm 1 . Therefore, these carrier particles were conducting. EXAMPLE IX The process of Example I was repeated, except that 0.8 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 20 percent by weight of the polyurethane and 80 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 15.3 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 24.3 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.4 x 10 -8 mho-cm -1 . Therefore, these carrier particles were conducting. EXAMPLE X The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 17 revolutions per minute for 30 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 33 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 25 percent by weight of the polyurethane and 75 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 23.0 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 30.5 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.1 x 10 -8 mho-cm -1 . Therefore, the carrier particles were conducting. EXAMPLE XI The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 40 minutes with a humidity of 3 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 36 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 25 percent by weight of the polyurethane and 75 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 19.1 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 26.0 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 3.8 x 10 -9 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XII The process of Example I was repeated, except that 0.8 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 20 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 33 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 25 percent by weight of the polyurethane and 75 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 16.4 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 21.7 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 8.1 x 10 -9 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XIII The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 20 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 31 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 30 percent by weight of the polyurethane and 70 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 24.8 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 31.7 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 3.9 x 10 -9 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XIV The process of Example I was repeated, except that 0.8 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 30 minutes with a humidity of 3 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 36 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 30 percent by weight of the polyurethane and 70 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 20.0 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 25.6 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 6.4 x 10 -11 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XV The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 17 revolutions per minute for 40 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 30 percent by weight of the polyurethane and 70 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 17.1 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 24.5 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 9.6 x 10 -10 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XVI The process of Example I was repeated, except that 0.8 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 40 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 34 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 0.8 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 35 percent by weight of the polyurethane and 65 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 21.2 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 31.9 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 4.0 x 10 -11 mho-cm -1 . Therefore, these carrier particles were semiconducting. EXAMPLE XVII The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 37 revolutions per minute for 20 minutes with a humidity of 12 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 35 percent by weight of the polyurethane and 65 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 20.6 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 28.8 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.8 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulating. EXAMPLE XVIII The process of Example I was repeated, except that 1.2 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 17 revolutions per minute for 30 minutes with a humidity of 3 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.2 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 35 percent by weight of the polyurethane and 65 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 21.9 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 26.9 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 9.2 x 10 -12 mho-cm -1 . Therefore, these carrier particles were insulating. EXAMPLE XIX The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 41 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 25 percent by weight of the polyurethane and 75 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 20.7 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 26.7 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.1 x 10 -9 mho-cm -1 . Therefore, these carrier particles were semiconductive. EXAMPLE XX The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 42 minutes. This furnace was maintained at a temperature of 182°C (360°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 20 percent by weight of the polyurethane and 80 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 21.1 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 24.5 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.5 x 10 -7 mho-cm -1 . Therefore, these carrier particles were conductive. EXAMPLE XXI The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 27 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 20 percent by weight of the polyurethane and 80 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 15.7 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 20.7 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 1.4 x 10 -7 mho-cm -1 . Therefore, these carrier particles were conductive. EXAMPLE XXII The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 44 minutes. This furnace was maintained at a temperature of 216°C (420°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 80 percent by weight of the polyurethane and 20 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 25.3 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 30.7 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 2.1 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXIII The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 28 minutes. This furnace was maintained at a temperature of 182°C (360°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 80 percent by weight of the polyurethane and 20 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared and characterized as described in Example I. There was measured on the carrier a charge of 26.3 µC/g in the 27°C (80°F)/80 percent relative humidity environment, and a charge of 31.2 µC/g in the 21°C (70°F)/20 percent relative humidity environment. Further, the conductivity of the carrier was 3.0 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXIV The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 28 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 40 percent by weight of the polyurethane and 60 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared as described in Example I. 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 33.7 µC/g in the 21°C (70°F)/50 percent relative humidity environment. Further, the conductivity of the carrier was 1.3 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXV The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 42 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 40 percent by weight of the polyurethane and 60 percent by weight of the carbon black loaded poly(methylmethacrylate). A developer composition was then prepared as described in Example I. 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 34 µC/g in the 21°C (70°F)/50 percent relative humidity environment. Further, the conductivity of the carrier was 2.0 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXVI The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 35 minutes. This furnace was maintained at a temperature of 204°C (400°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 60 percent by weight of the polyurethane and 40 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared as described in Example I. 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 33.5 µC/g in the 21°C (70°F)/50 percent relative humidity environment. Further, the conductivity of the carrier was 1.0 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXVII The process of Example I was repeated, except that 1.0 percent by weight of the carrier was comprised of the polymer mixture and it was mixed in the Munson at 27 revolutions per minute for 30 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 43 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 60 percent by weight of the polyurethane and 40 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared as described in Example I. 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 35.5 µC/g in the 21oC (70°F)/50 percent relative humidity environment. Further, the conductivity of the carrier was 1.6 x 10 -11 mho-cm -1 . Therefore, these carrier particles were insulative. EXAMPLE XXVIII The process of Example I was repeated, but without premixing the two polymers. Instead the polymers were added directly to the Munson mixer with the core. This mixture was mixed in the Munson at 27 revolutions per minute for 60 minutes with a humidity of 7 millimeters Hg. Thereafter, the resulting carrier particles were inserted into a rotating tube furnace for a period of 41 minutes. This furnace was maintained at a temperature of 193°C (380°F) thereby causing the polymers to melt and fuse to the core. The final product was comprised of a carrier core with a total of 1.0 percent polymer mixture by weight on the surface with the polymer mixture being a combination of 25 percent by weight of the polyurethane and 75 percent by weight of the carbon black-loaded poly(methylmethacrylate). A developer composition was then prepared as described in Example I. 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 23.0 µC/g in the 21°C (70°F)/50 percent relative humidity environment. Further, the conductivity of the carrier was 7.4 x 10 -9 mho-cm -1 . Therefore, these carrier particles were semiconductive. The toner carbon black selected for the above Examples was, unless otherwise indicated, REGAL 330®; the polypropylene was of a low molecular weight, 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: Carrier particle composition comprising a core and thereover a mixture of polymethylmethacrylate and a poly(urethane), wherein said polymethylmethacrylate contains a conductive component. Carrier particle composition in accordance with claim 1 wherein the poly(urethane) possesses a melt temperature of from 93.3 to 127°C (200 to 260°F) and a crosslinking temperature of from 166 to 216°C (330 to 420°F). Carrier particle composition in accordance with claim 1 or 2 wherein said conductive component for polymethylmethacrylate is a metal oxide. Carrier particle composition in accordance with any of claims 1 or 2 wherein said conductive component for polymethylmethacrylate is carbon black selected in an amount of from 10 to 60 weight percent. Carrier particle composition in accordance with any of claims 1 to 4 wherein said core is a metal. Carrier particle composition in accordance with any of claims 1 to 4 wherein said core is a ferrite. A process for the preparation of carrier particles which comprises (1) mixing carrier core particles with a mixture of polymethylmethacrylate and a poly(urethane), wherein said polymethylmethacrylate contains a conductive component; (2) dry mixing the resulting carrier core particles for a sufficient period of time to enable 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 93.3 to 288°C (200 to 550°F), whereby the polymers melt and fuse to the carrier core; and (4) thereafter cooling the resulting coated carrier particles. The process in accordance with claim 7 wherein the poly(urethane) polymer is uncrosslinked, and is comprised of a combination of a polyester resin and a blocked polyisocyanate resin, wherein the polyester resin contains a blocked caprolactam functionality and the blocked polyisocyanate resin contains 5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethyl-cyclohexane. The process in accordance with claims 7 or 8 wherein the conductive component is a conductive carbon black present in an amount of from about 15 to about 50 weight percent, the carrier conductivity is from 10 -6 to 10 -15 (ohm-cm) -1 , and the carrier triboelectric charge is from +5 to +50 µC/g. A developer comprised of toner particles and carrier particles having the composition of any of claims 1 to 6. The developer in accordance with claim 10 with from 0.1 to 3.0 percent of carrier coating polymer mixture by weight and containing said conductive component present in an amount of from 5 to 60 weight percent, and which carrier possesses a conductivity of from 1 x 10 -8 mho/cm to 1 x 10 -15 mho/cm, and a triboelectric value of from +5 to +50 µC/g.

Inventors: DOMBROSKI THOMAS C, DUGGAN MICHAEL J, SILENCE SCOTT M, DOMBROSKI, THOMAS C., DUGGAN, MICHAEL J., SILENCE, SCOTT M.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: G03G9
IPC codes: G03G9