Toner process with metal oxides

Abstract: A process for avoiding, or minimizing toner contamination of electrodes in a scavengeless electrophotographic imaging apparatus which comprises adding to the donor roll present in said apparatus a toner comprised of resin, pigment, charge additive, and a metal oxide, or a mixture of metal oxides.

Description: This invention relates to scavengeless development in electrophotographic, especially xerographic, imaging apparatus. Scavengeless development systems are described in, for example, U.S. Patent 4,868,600; EP-A-0 414 455 and EP-A-0 426 420. In such systems, a donor structure, for example a donor roll, transports toner to a development nip situated between an imaging member and the donor structure. An electrode structure, for example a plurality of electrode wires, is present at the development nip to generate a toner cloud, and latent images present on the imaging member are developed by the attraction of toner particles to the images. If toner particles are deposited on, or stick to, the electrode structure, the development of the images can fail through the formation of large agglomerates of toner particles. These in turn can cause imperfections and vacancies in the toner cloud, leading to insufficient development on the imaging member. This shows up as undesirable streaks on the final developed copies. The present invention is concerned with the problem of reducing toner deposition on the electrode structure of scavengeless development systems. The following United States Patents are noted: 4,837,100, which discloses a positively charged developer with toner particles containing fine particles of hydrophobic alumina and fine particles of, for example, tin oxide or titanium dioxide, reference the Abstract; apparently the developer "hardly" undergoes toner cloud or toner dropping during development, and this developer produces a high quality image, see column 1 for example; 4,873,185, which discloses a toner which is capable of eliminating tailing, see column 2; the toner contains a certain metal complex compound, and a metal complex salt-type monazo dye having a hydrophilic group; 4,871,616, which discloses a surface treated poly methyl silsesquioxane powder characterized by surface treatment with an agent comprising a compound which has at least two radicals attached to a metal atom, or a silicon atom, see the Abstract for example; examples of metal atoms in the surface treating agent include titanium, and tin, see columns 3 and 4; 4,933,251, which discloses a developer with a toner containing, for example, a layer of external additives of fine metal oxides, fine silica particles, and cleaning aid particles, see the Abstract; also see columns 1 and 2, wherein in column 2 it is indicated that there is a greatly decreased tendency for the toner to become attached to non-image areas; 4,973,540, which discloses a toner with an inorganic fine particle with at least both a negatively and positively chargeable polar group on the surface of the inorganic fine particles, see the Abstract; examples of inorganic fine particles include titanium dioxide, see column 3; and 3,888,678, which discloses treating the surface of toners with a charge control agent. It is an object of the present invention to enable the sticking of toner particles to electrode structures in scavengeless development systems to be avoided or minimized. The invention is especially, but not exclusively, applicable to hybrid scavengeless development systems as illustrated in EP-A-0426420 and EP-A-0414455 to which reference may be made for further information on scavengeless development, if required. There is disclosed, in EP-A-0426420, apparatus for developing a latent image recorded on a movable surface, including a reservoir for storing developer material comprising at least carrier and toner; a plurality of donor members spaced apart from each other in the direction of movement of the surface, and a common transport member arranged to transport developer material from said reservoir and to supply toner therefrom to at least said plurality of donor members for delivery to the surface to develop the latent image recorded thereon. In a described embodiment, wherein the transport member is a magnetic brush roll and each donor member is a donor roll, each one of said plurality of donor rolls forms, with said magnetic brush roll, a respective loading nip at which toner can be loaded onto each one of said plurality of donor rolls from the magnetic brush roll. In EP-A-0414455, there is disclosed an apparatus for developing a latent image recorded on a surface, including: a housing defining a chamber storing a supply of developer material comprising at least carrier and toner; a donor member spaced from the surface and being adapted to transport toner to a region opposed from the surface; means for advancing developer material in the chamber of said housing, said advancing means and said donor member cooperating with one another to define a region wherein a substantially constant quantity of toner having a substantially constant triboelectric charge is deposited on said donor member; and an electrode member positioned in the space between the surface and said donor member, said electrode member being closely spaced from said donor member and being electrically biased to detach toner from said donor member so as to form a toner cloud in the space between said electrode member and the surface with detached toner from the toner cloud developing the latent image. The present invention provides a process which comprises the utilization of toners with metal oxides in scavengeless development apparatus. More specifically, the present invention provides a process for avoiding, or minimizing toner contamination of electrodes in a scavengeless electrophotographic imaging apparatus, which comprises adding to the donor structure present in said apparatus a toner comprised of resin, pigment, charge additive, and a metal oxide or mixture of metal oxides. The metal oxide, which may be present as a toner surface additive, may be tin oxide, titanium oxide, or mixtures thereof. The charge additive of the toner may be a positive or negative charge control agent. The charge additive may be a metal salt of tetraphenyl borate, a metal salt of salicylic acid, dimethyl distearyl ammonium methyl sulfate, or cetyl pyridinium chloride. The resin of the toner may be a styrene acrylate, a styrene methacrylate, a styrene butadiene or a polyester. The pigment of the toner may be carbon black or a color pigment other than carbon black, for example cyan, magenta, yellow, or mixtures thereof. Preferably, the amount of metal oxide surface additive is from about 0.2 to about 5 weight percent, the amount of charge control additive is from about 0.1 to about 5 weight percent, the amount of resin is from about 75 to about 99 weight percent, and the amount of pigment is from about 1 to about 15 weight percent. In a process in accordance with the present invention, the toner supply may be comprised of toner particles or it may be comprised of toner particles and carrier particles. The process of the present invention is performed in an apparatus for developing a latent electrostatic image on a charge retentive surface, the apparatus comprising a supply of toner/developer material; a donor structure for conveying toner from the supply to an area adjacent the charge retentive surface; and an electrode structure positioned between the donor structure and the charge retentive surface for generating an electrostatic field enabling the detachment of toner from the donor structure and the attraction of toner to the latent image; wherein the toner comprises resin, pigment, charge additive, and a metal oxide or mixture of metal oxides. The electrodes structure may comprise electrode wires. The donor structure may comprise at least one donor member (which may be in the form of a roll) arranged to convey toner to the said area adjacent the charge retentive surface, and a transport member arranged to transport material from the supply to the donor member(s). In one form, the donor structure comprises a plurality of donor members spaced apart from each other in the direction of movement of the charge retentive surface. The transport member may include means for attracting magnetic material from the supply to the exterior surface of the transport member: for example, the transport member may include a non-magnetic tubular member rotatably mounted to advance material from the supply to the donor member(s); and an elongated magnetic member disposed within the tubular member for attracting magnetic material from the supply to the surface of the tubular member. The apparatus for developing latent electrostatic images on a charge retentive surface with toner comprised of resin particles, pigment particles, charge additive particles and metal oxide particles may comprise a toner supply, a donor structure spaced from the charge retentive surface for conveying toner from the supply to an area opposite the retentive surface; an electrode structure; means for establishing an alternating electrostatic field between the donor and electrode structures; the electrode structure being positioned in a space between the charge retentive surface and the donor structure and in sufficiently close proximity to the donor to permit the detachment of toner therefrom with high alternating electrostatic fields; and the attraction of toner to the latent image by, for example, creating an electrostatic field between the retentive surface and the electrode structure, whereby toner sticking and toner contamination of the wires is avoided or minimized. The electrode structure may be comprised of wires. More specifically, the electrode structure may be comprised of two tungsten wires, which may be separated by about 1 millimeter. In another embodiment, the present invention provides a process for avoiding or minimizing toner contamination of electrodes in a scavengeless electrophotographic imaging apparatus which comprises adding to the donor roll present in said apparatus a toner comprised of resin, pigment, charge additive, and a metal oxide, or a mixture of metal oxides, and wherein said apparatus is an apparatus for developing a latent image recorded on a movable surface including a reseroir for storing developer material comprising at least carrier and toner; a plurality of donor members spaced apart from each other in the direction of movememt of the surface, and a common transport member arranged to transport developer material from said reservoir and to supply toner therefrom to at least said plurality of donor members for delivery to the surface to develop the latent image recorded thereon, and wherein each one of said plurality of donor rolls forms, with said magnetic brush roll, a respective loading nip at which toner can be loaded onto each one of said plurality of donor rolls from the magnetic brush roll. In yet another embodiment, the present invention provides a process for avoiding or minimizing toner contamination of electrodes in a scavengeless electrophotographic imaging apparatus which comprises adding to the donor roll present in said apparatus a toner comprised of resin, pigment, charge additive, and a metal oxide, or a mixture of metal oxides, and wherein said apparatus is an apparatus for developing a latent image recorded on a surface, including: a housing defining a chamber storing a supply of developer material comprising at least carrier and toner; a donor member spaced from the surface and being adapted to transport toner to a region opposed from the surface; means for advancing developer material in the chamber of said housing, said advancing means and said donor member cooperating with one another to define a region wherein a substantially constant quantity of toner having a substantially constant triboelectric charge is deposited on said donor member; and an electrode member positioned in the space between the surface and said donor member, said electrode member being closely spaced from said donor member and being electrically biased to detach toner from said donor member so as to form a toner cloud in the space between said electrode member and the surface with detached toner from the toner cloud developing the latent image. In this embodiment of the invention, the advancing means may include means for attracting magnetically developer material from the supply thereof in the chamber of said housing to the exterior surface thereof. The advancing means may, for example, include: a nonmagnetic tubular member mounted rotatably so as to advance developer material from the chamber of said housing to said donor member; and an elongated magnetic member disposed interiorly of said tubular member for attracting developer material to the surface of said tubular member. In this embodiment, the donor member may include a roll. The electrode member may include a plurality of small diameter wires. Illustrative examples of suitable toner resins selected for the present invention, which resins may be present in various effective amounts such as, for example, from about 70 percent by weight to about 95 percent by weight, include polyesters, polyamides, epoxy resins, polyurethanes, polyolefins, styrene acrylates, styrene methacrylates, styrene butadienes, vinyl resins and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Homopolymers or copolymers of two or more vinyl monomers may be used. Specific examples of toner resins include styrene butadiene copolymers, especially styrene butadiene copolymers prepared by a suspension polymerization process (reference U.S. Patent 4,558,108); PLIOLITES®, PLIOTONES® available from Goodyear Chemical Company; and mixtures thereof. Numerous well known suitable pigments can be selected as the colorant for the toner particles including, for example, carbon black, such as REGAL 330® available from Cabot Corporation, nigrosine dye, aniline blue, phthalocyanine derivatives, magnetites and mixtures thereof. The pigment should be present in a sufficient amount to render the toner composition colored thereby permitting the formation of a clearly visible image. Generally, the pigment particles are present in effective amounts of, for example, from about 2 percent by weight to about 20, and preferably about 10 percent by weight, based on the total weight of the toner composition, however, lesser or greater amounts of pigment particles may be selected. When the pigment particles are comprised of magnetites, including those commercially available as MAPICO BLACK®, they are present in the toner composition in an amount of from about 10 percent by weight to about 70 percent by weight, and preferably in an amount of from about 10 percent by weight to about 30 percent by weight. Conductive metal oxides usually present as surface additives in effective amounts of, for example, from between about 0.1 to about 10 weight percent, and preferably from between about 0.2 to 2 weight percent, include tin oxides, such as S-1 available from Mitsubishi Chemical with an average size between 0.1 and 0.5 micron and a typical conductivity of 2.4 x 10 -6 (ohm-cm) -1 or tin oxide available from the Tioxide Corporation with an average size between 10 and 30 millimicrons and a conductivity of 10 -7 (ohm-cm) -1 . Conductive titanium oxides suitable for embodiments of the present invention include P-25 available from Degussa Corporation with an average particle size between 20 and 40 microns and a conductivity of 1.3 x 10 -6 (ohm-cm) -1 , T805, P25 treated with trimethoxyoctylsilane with the same particle size as P25 but a conductivity of 3.6 x 10 -4 (ohm-cm) -1 , and the like. Pigment grade zinc oxides with typical sizes of about 80 millimicrons and conductivities of 2.7 x 10 -3 (ohm-cm) -1 are also suitable. Aluminum oxides such as Aluminum Oxide C with a typical particle size of 20 millimicrons and a conductivity of 2.9 x 10 -7 (ohm-cm) -1 available from Degussa Corporation are also suitable. In general, any conductive metal oxide with a particle size below 1 micron and a conductivity greater than 10 -10 (ohm-cm) -1 may be suitable for embodiments of the present invention. Also suitable for the process of the present invention are colored toner compositions containing 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 about 2 weight percent to about 15 weight percent based on the weight of the toner resin particles. Illustrative examples of charge enhancing additives present in various effective amounts, such as for example from about 0.1 to about 20, and preferably from about 0.1 to about 3 percent by weight, include alkyl pyridinium halides, such as cetyl pyridinium chlorides, reference U.S. Patent 4,298,672; cetyl pyridinium tetrafluoroborates, quaternary ammonium sulfate, and sulfonate charge control agents as illustrated in U.S. Patent 4,338,390; stearyl phenethyl dimethyl ammonium tosylates, reference U.S. Patent 4,338,390; distearyl dimethyl ammonium methyl sulfate, reference U.S. Patent 4,560,635; stearyl dimethyl hydrogen ammonium tosylate; potassium tetraphenylborate and other tetraphenylborate salts; metal salts of salicylic acid and their derivatives, BONTRON E-84™, and BONTRON E-88™, available from Hodagaya Chemicals of Japan, and other known similar charge enhancing additives. With further respect to the toner compositions selected for the processes of the present invention, there can be added thereto a linear polymeric alcohol comprised of a fully saturated hydrocarbon backbone with at least about 80 percent of the polymeric chains terminated at one chain end with a hydroxyl group, which alcohol is represented by the following formula: CH 3 (CH 2 ) n CH 2 OH wherein n is a number of from about 30 to about 300, and preferably of from about 30 to about 100, which alcohols are available from Petrolite Corporation. Illustrative examples of carrier particles that can be selected for mixing with the toner compositions in the toner supply means include those particles that are capable of triboelectrically obtaining a charge of opposite polarity to that of the toner particles. Accordingly, the carrier particles can be selected so as to be of a negative polarity thereby enabling the toner particles which are positively charged to adhere to and surround the carrier particles. Alternatively, there can be selected carrier particles with a positive polarity enabling toner compositions with a negative polarity. Illustrative examples of carrier particles that may be selected include granular zircon, granular silicon, glass, steel, nickel, iron, ferrites, such as copper zinc manganese, silicon dioxide, and the like. Coatings for the carrier particles include fluoropolymers, such as polyvinylidene fluoride resins, polymethylmethacrylate poly(chlorotrifluoroethylene), fluorinated ethylene and propylene copolymers, terpolymers of styrene, methylmethacrylate, and a silane, such as triethoxy silane, reference U.S. Patents 3,467,634 and 3,526,533; polytetrafluoroethylene, fluorine containing polyacrylates, and polymethacrylates; copolymers of vinyl chloride; and trichlorofluoroethylene; and other known coatings. There can also be selected as carriers components comprised of a core with a polymer coating mixture thereover, reference United States Patents 4,937,166, and 4,935,326. The toner compositions for the process of the present invention can be prepared by a number of known methods, including mechanical blending and melt blending the toner resin particles, pigment particles or colorants, and charge additives followed by mechanical attrition, including classification to enable toner particles with an average diameter of from about 10 to about 20 microns. Thereafter, the metal oxides can be added to the toner as surface additives in a known blending apparatus. More specifically, the metal oxides can be added by blending in apparatus such as the Lightnin' Labmaster blender, the Lodige blender, or a Henschel blender. Another blending method is accomplished mixing the toner and metal oxides with steel, glass, ceramic or other suitable beads, mixing on a roll mill and subsequently screening out the beads. Other methods include those well known in the art such as spray drying, mechanical dispersion, extrusion, melt dispersion, dispersion polymerization, and suspension polymerization. The following examples illustrate various embodiments of the present invention. Parts and percentages are by weight unless otherwise indicated. Comparative Examples are also presented. COMPARATIVE EXAMPLE I A toner comprised of 10 percent of REGAL 330® carbon black, 1 percent of tetraphenyl borate charge control additive, and 89 percent of styrene butadiene (89/11) was blended with 0.5 percent of AEROSIL R812® fumed silica, which had been treated with 10 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS). The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The charge level of the resultant toner on the donor roll of scavengeless imaging apparatus of the type illustrated in EP-A-0426420 was measured by vacuuming the toner into a filter device capable of capturing the toner enclosed in a conductive holder. The holder was connected to ground through an electrometer, which reads the charge on the toner deposited in the filter device. The mass of the captured toner can be determined by weighing the filter device before and after the capture of the toner. By dividing the captured charge by the captured mass, the charge to mass ratio of the captured toner originally on the donor roll can be determined. Initially, this was -25 µc/gram which later stabilized at -20 µc/gram. After 50 prints (developed images) with a layered imaging member with an aluminum substrate, a photogenerating layer of trigonal selenium in contact therewith, and a hole transport layer comprised of about 55 percent of an aryl amine, and 45 percent by weight of MAKROLON® polycarbonate (reference for example U.S. Patent 4,265,990), 15 streaks per centimeter were observed on each of the prints. This was regarded as a highly undesirable level of streaking. EXAMPLE I The base toner of Comparative Example I was again blended with the same treated silica in the Labmaster for 15 minutes, but in addition 0.8 percent of S-1 tin oxide obtained from Mitsubishi Chemical was added to the mixture at the same time. The resultant toner initially provided a charge level on the donor roll of -22 µc/gram when measured by the method described in Comparative Example I. This charge level later stabilized at -21 µc/gram. After 50 prints, no streaks were observed on the developed copies generated. EXAMPLE II The base toner of Comparative Example I was again blended with the same treated silica in the Labmaster for 15 minutes, but in addition 0.8 percent of P-25 titanium dioxide obtained from Degussa Corporation was added to the mixture at the same time. The resultant toner initially provided a charge level on the donor roll of -21 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -20 µc/gram. No streaks were initially observed on the developed copy; about 2 streaks per centimeter were observed on the copies after 50 prints. This is regarded as a moderate level of steaking and is a considerable improvement over the very high level of streaking of Comparative Example I. COMPARATIVE EXAMPLE II The base toner of Comparative Example I was blended with 0.5 percent of AEROSIL R812® fumed silica, which had been treated with 15 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS). The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner initially provided a charge level on the donor roll of -24 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -16 µc/gram. No streaks were initially observed on the developed copy, but after 50 prints a moderate level of streaking (∼2/centimeter) was observed. EXAMPLE III The base toner of Comparative Example II was again blended with the same treated silica in the Labmaster for 15 minutes, but in addition 0.2 percent of P-25 titanium dioxide obtained from the Degussa Corporation was added to the mixture at the same time. The resultant toner initially provided a charge level on the donor roll of -20 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -16 µc/gram. About 1 streak per centimeter was observed after 50 prints. This is regarded as a low level of streaking. Thus 0.2 percent of P-25 provided an improvement over Comparative Example II. EXAMPLE IV The base toner of Comparative Example II was again blended with the same treated silica in the Labmaster for 15 minutes, but in addition 0.8 percent of P-25 titanium dioxide obtained from the Degussa Corporation was added to the mixture at the same time. The resultant toner initially provided a charge level on the donor roll of -15 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -13 µc/gram. No streaks were observed for any of 50 prints. COMPARATIVE EXAMPLE III The base toner of Comparative Example I was blended with 0.5 percent of AEROSIL R812® fumed silica, which had been treated with 20 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS). The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner initially provided a charge level on the donor roll of -19 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -20 µc/gram. The level of streaking for the developed images was about 4/centimeter, which is regarded as medium. EXAMPLE V The base toner of Comparative Example III was again blended with the same treated silica in the Labmaster for 15 minutes, but in addition 0.8 percent of P-25 titanium dioxide obtained from the Degussa Corporation was added to the mixture at the same time. The resultant toner initially provided a charge level on the donor roll of -19 µc/gram when measured by the method described in Comparative Example I. The charge level later stabilized at -15 µc/gram. No streaks were observed in any of 50 prints. EXAMPLE VI A base toner comprised of 0.3 percent of copper phthalocyanine, SUMIKAPRINT® Cyanine Blue GN-O obtained from Sumika, and listed in the Color Index as CI 74160, 1 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica, which had been treated with 10 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS) and 1 percent of P-25 titanium dioxide obtained from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner provided a charge level on the donor roll of -20 µc/gram when measured by the method described in Comparative Example I. No streaks were observed in any of 50 prints. EXAMPLE VII A base toner consisting of 3 percent of magenta, SUMIKAPRINT® Carmine 6BC listed in the Color Index as CI 15850-1, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica, which had been treated with 5 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS) and 1 percent of P-25 titanium dioxide obtained from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner provided a charge level on the donor roll of -24 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 50 prints. EXAMPLE VIII A base toner comprised of 3 percent of yellow, SUMIKAPRINT® Yellow ST-O listed in the Color Index as CI 21090, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica, which had been treated with 10 percent of dimethyl distearyl ammonium methyl sulfate (DDAMS) and 1 percent of P-25 titanium dioxide from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner provided a charge level on the donor roll of -9 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 50 prints. EXAMPLE IX A base toner comprised of 3 percent of copper phthalocyanine, SUMIKAPRINT® Cyanine Blue GN-O from Sumika listed in the Color Index as CI 74160, 1 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 0.2 percent of P-25 titanium dioxide obtained from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Lab master II blender. The resultant toner had a charge level on the donor roll of -25 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 50 prints. EXAMPLE X A toner comprised of 3 percent of magenta, SUMIKAPRINT® Carmine 6BC listed in the Color Index as CI 15850-1, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 2 percent of P-25 titanium dioxide from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner had a charge level on the donor roll of -27 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 1,000 prints. EXAMPLE XI A toner of 3 percent of yellow, SUMIKAPRINT® Yellow ST-O listed in the Color Index as CI 21090, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 96.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 2 percent of P-25 titanium dioxide from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner had a charge level on the donor roll of -33 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 100 prints. EXAMPLE XII A toner comprised of 5 percent of copper phthalocyanine, SUMIKAPRINT® Cyanine Blue GN-O from Sumika listed in the Color Index as CI 74160, 1 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 94 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 2 percent of P-25 titanium dioxide from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner had a charge level on the donor roll of -33 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 1,000 prints. EXAMPLE XIII A toner comprised of 5 percent of magenta, SUMIKAPRINT® Carmine 6BC listed in the Color Index as CI 15850-1, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 94.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 2 percent of P-25 titanium dioxide obtained from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. The resultant toner provided a charge level on the donor roll of -30 µc/gram when measured by the method described in Comparative Example I. No streaking was observed in 1,000 prints. EXAMPLE XIV A toner of 5 percent of yellow, SUMIKAPRINT® Yellow ST-O listed in the Color Index as CI 21090, 0.5 percent of potassium tetraphenyl borate (KTPB) charge control additive, and 94.5 percent of styrene n-butyl methacrylate was blended with 0.6 percent of AEROSIL R812® fumed silica and 2 percent of P-25 titanium dioxide from the Degussa Corporation. The blending was performed for 15 minutes in a Lightnin' Labmaster II blender. No streaking was observed in 1,000 prints.

Claims: A process for avoiding or minimizing toner contamination of an electrode structure in a scavengeless development apparatus of an electrophotographic imaging machine having a charge retentive surface, the development apparatus further comprising a toner supply, a donor structure for conveying toner from the toner supply to an area opposite the charge retentive surface, wherein said electrode structure is positioned between the charge retentive surface and the donor structure and has at least one electrode for generating an electrostatic field which enables the detachment of toner from the donor structure, so that a latent image on the charge retentive surface attracts the toner thereto, the process being characterized by: providing a toner having particles comprised of resin, pigment, charge additive, and a metal oxide or mixture of metal oxides. A process in accordance with claim 1, wherein the metal oxide is present as a toner surface additive. A process in accordance with claim 1 or claim 2, wherein the metal oxide is tin oxide, titanium oxide, or mixtures thereof. A process in accordance with claim 2, wherein the amount of metal oxide surface additive is from about 0.2 to about 5 weight percent, the amount of charge control additive is from about 0.1 to about 5 weight percent, the amount of resin is from about 75 to about 99 weight percent, and the amount of pigment is from about 1 to about 15 weight percent. A process in accordance with any one of the preceding claims, wherein the charge additive is a positive or negative charge control agent. A process in accordance with any one of the preceding claims, wherein the charge additive is a metal salt of tetraphenyl borate, a metal salt of salicylic acid, dimethyl distearyl ammonium methyl sulfate, or cetyl pyndinium chloride. A process in accordance with any one of the preceding claims, wherein the resin is a styrene acrylate, a styrene methacrylate, a styrene butadiene, or a polyester. A process in accordance with any one of the preceding claims, wherein the pigment is carbon black or a color pigment other than carbon black.

Inventors: BREWINGTON GRACE T, JULIEN PAUL C, KOCH RONALD J, BREWINGTON, GRACE T., JULIEN, PAUL C., KOCH, RONALD J.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1992
Main classification: G03G15
IPC codes: G03G9, G03G15, G03G13