Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
  • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
  • G03G15/0803—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer in a powder cloud
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
  • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
  • G03G15/0806—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer on a donor element, e.g. belt, roller
  • G03G15/0818—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer on a donor element, e.g. belt, roller characterised by the structure of the donor member, e.g. surface properties
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G2215/00—Apparatus for electrophotographic processes
  • G03G2215/06—Developing structures, details
  • G03G2215/0634—Developing device
  • G03G2215/0636—Specific type of dry developer device
  • G03G2215/0643—Electrodes in developing area, e.g. wires, not belonging to the main donor part

Definitions

• This invention relates to electroded donor development systems and more particularly to improved overcoatings for electroded donor devices and methods of making the same.
• Electroded donor development systems are used in electrostatographic processors for development of latent electrostatic images carried by an electrically insulative imaging surface as the imaging surface moves through a development zone (i.e., region where toner particles are transferred from a donor device to an imaging surface).
• the imaging surface can be a photoconductive layer which is coated on an electrically conductive imaging member which, in turn, is held at a predetermined reference potential, such as ground.
• the electroded donor development system has a housing for supporting at least one donor device adjacent the development zone.
• the donor device is spaced a predetermined, short distance from the imaging surface and is driven to bring toner near the imaging surface as it moves through the development zone.
• the toner on the electroded donor device is supplied by a magnetic brush development system.
• the developer may be a mixture of triboelectrically charged toner and carrier particles.
• suitable toner particles which can be employed in a magnetic brush development system is described in US-A-3,977,871.
• One of the main purposes of the magnetic brush development device is to transport developer into and through a toner loading zone under the influence of a magnetic field which is shaped to cause developer to form into bristle-like streamers which brush against the donor device surface.
• Those bristles or streamers are pronounced only in a relatively narrow region (hereinafter referred to as the "loading nip" region) which is more or less centered on the line along which the donor device makes its closest approach to the magnetic brush development device.
• the magnetic brush development device carries magnetically entrained developer from a pick-up point located upstream of the nip region to a discharge point located downstream of the nip region.
• Electroded donor developer devices are known for xerographic development systems. Such devices are disclosed in US-A-5,172,170 and patent application Serial No. 07/724,242, attorney docket No. D/86305Q, filed July 1, 1991. Electroded donor devices also are described in US-A-3,996,892 and US-A-4,568,955. These electroded devices contain electrically isolated conductors embedded in an insulating layer. A conductive contact brush or roll at one end of the donor is used to apply AC/DC voltages to activate the electrodes. In the device disclosed in US-A-4,568,755, applying a voltage to the conductive brush causes a toner cloud to form above the surface of the activated electrode zone for toner development to occur on a charged image receiver.
• US-A-3,996,892 discloses an insulating layer of conductive rubber between 0.025 mm to 0.635 mm (1-25 mils) thick doped with carbon black to coat electrodes on a development roll. This coating reportedly produces a resistivity of 10 7- 10 9 ohm-cm. Overcoats on electroded rolls provide a resistive layer to protect the electrodes from wear Overcoats also prevent shorting and breakdown of the device when contacted by, for example, a conductive magnetic brush carrier bead during the toner loading step. Breakdown also can occur during toner charging, metering and development when other AC/DC voltages are applied. Overcoats used for donor devices have been based on conductive particles such as carbon black dispersed in a binder.
• Desired resistivity is achieved by controlling loading of conductive material.
• very small changes in loading of conductive materials near the percolation threshold cause dramatic changes in resistivity.
• these coatings are often not durable enough and in many cases resistive heating has been observed when electrodes are activated, causing burnout through the coating, shorting and device failure.
• an electroded donor device comprising an overcoat comprising charge injection enabling particles and charge transport molecules which can be dispersed in a binder resin.
• the dielectric overcoat protects the electrodes of the electroded donor device from wear and prevents shorting and breakdown of the donor development system.
• the present invention is directed to improved overcoatings for electroded donor devices.
• the resistive overcoatings on these devices are comprised of charge transport molecules and charge injection enabling particles, which can be dispersed in a binder resin. These resistive overcoatings do not depend on particle to particle contact for charge transport through the overcoat layer, thus reducing the percentage volume of charge injection enabling particles in the overcoat which would otherwise reduce the mechanical strength of the binder.
• an electric field is generated in the overcoat layer during, for example, an electrode activating step
• the charge injection enabling particles are polarized and charges are injected into the transport medium. Injected charges are driven through the overcoat by charging fields where they are eventually neutralized. Space charge in the bulk of the overcoat is thus relaxed by charge emission. Development fields generated during toner loading or image development steps are not sufficiently strong to cause charge redistribution and breakdown in the electroded donor overcoat.
• Toner jumping thresholds in the overcoat range from about 200 to about 1,000 V AC depending on toner loading. These thresholds are the lowest values of AC amplitude which cause toner to be released from the surface of the donor device. The lower the electric field amplitude the more desirable it is as the likelihood of electrical breakdown of the overcoating is reduced. Preferably the toner jumping thresholds range from about 500-800 V AC . Electrical resistivity of the overcoat layer ranges from about 10 10 ohm-cm to about 10 18 ohm-cm, preferably from about 1012ohm-cm to about 1 0 16 0 hm-cm.
• the dielectric strength of the overcoat is high enough such t hat a conductive magnetic brush with about 500 V can be used to load toner on the overcoat layerwithout breakdown occurring.
• the dielectric constant ranges from about 3 to about 12, preferably from about 3 to about 8.
• the binder material can be any material capable of holding charge transport molecules in solid solution or as a molecular dispersion.
• a solid solution is defined as a composition in which at least one component is dissolved in another component and which exists as a homogeneous solid phase.
• a molecular dispersion is defined as a composition in which particles of at least one component are dispersed in another component, the dispersion of particles being on a molecular scale.
• Typical film forming binder materials (which are not charge transporting materials) suitable for practicing this invention include, but are not limited to, thermoplastic and thermosetting resins such as polycarbonates, polyesters, polyamides, polyurethanes, polystyrenes, polyaryl ethers, polyaryl sulfones, polybutadienes, polysulfones, polyether sulfones, polyethylenes, polypropylenes, polymethyl pentenes, polyphenylene sulfides, polyvinyl acetate, polysiloxanes, polyacrylates, polyvinylacetals, polyimides, amino resins, phenylene oxide resins, terephthalic acid resins, epoxy resins, phenolic resins, polystyrene and acrylonitrile copolymers, polyvinyl chloride, vinyl chloride and vinyl acetate copolymers, acrylate copolymers, alkyd resins, cellulosic film formers, poly(amide-
• Any suitable film forming polymer having charge transport capabilities may be used as a binder in the continuous phase of the overcoat of this invention.
• the charge transport binder may be a hole transport film forming polymer or an electron transport film forming polymer.
• Suitable charge transporting film forming polymers include, but are not limited to the following materials and mixtures thereof:
• Vinyl-aromatic polymers such as polyvinyl anthracene, polyacenaphthylene; formaldehyde condensation products with various aromatics such as condensates of formaldehyde and 3-bromopyrene; 2,4,7-trinitro-fluorene, and 3,6-dinitro-N-t-butylnaphthalimide as described in US-A-3,972,717, the entire disclosure of which is hereby incorporated herein by reference.
• transport materials such as poly-1-vinylpyrene, poly-9-vinylanthracene; poly-9-(4-pentenyl)-carbazole; poly-9-(5-hexyl)-carbazole; polymethylene pyrene; poly-1-(pyrenyl)-butadiene; polymers such as alkyl, nitro, amino, halogen and hydroxy substituted polymers such as poly-3-amino carbazole; 1,3-dibromo-poly-N-vinyl carbazole and 3,6-dibromo-poly-N-vinyl carbazole and numerous other organic polymeric transport materials as described in US-A-3,870,516, the entire disclosure of which is hereby incorporated herein by reference.
• Any suitable charge transport molecule capable of acting as a film forming binder or which is soluble or dispersible on a molecular scale in a film forming binder may be utilized in the overcoat of this invention.
• the charge transport molecule should be capable of transporting charge carriers injected by charge injection enabling particles in an applied electric field.
• the charge transport molecules may be hole transport molecules or electron transport molecules.
• the charge transport molecule is capable of acting as a film forming binder as indicated above, it may if desired be employed to function as both an insulating binder for the charge injection enabling particles and as the continuous charge transporting phase without the necessity of incorporating a different charge transport molecule in solid solution or as a molecular dispersion therein.
• non-film forming charge transporting materials include, but are not limited to, the following:
• Pyrazoline transport molecules include, but are not limited to, I-[lepidyl-(2)]-3-(p-diethylaminophenyl)-5-(p-diethylaminophenyl)pyrazoline, 1-[quinolyl-(2)]-3-(p-diethylaminophenyl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[6-methoxypyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-pyrazoline, 1-phenyl-3-[p-dimethylaminostyryl]-5- (p-dime- thylaminostyryl)pyrazoline, 1-phenyl-3-[p-diethylaminostyryl]-5-(p-
• Typical fluorene charge transport molecules include, but are not limited to, 9-(4'-dimethylaminobenzylidene)fluorene, 9-(4'-methoxybenzylidene)fluorene, 9-(2',4'-dimethoxybenzylidene)fluorene, 2-nitro-9-benzylidene-fluorene, 2-nitro-9-(4'-diethylaminobenzylidene)fluorene and the like as described in US-A-4,515,882, the entire disclosure of which is hereby incorporated by reference.
• Oxadiazole transport molecules include, but are not limited to, 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, pyrazoline, imidazole, triazole and the like as disclosed in US-A-4,5 15,882, the entire disclosure of which is hereby incorporated herein by reference.
• hydrazone transport molecules encompassed by this formula include p-diethylaminoben- zaldehyde-(diphenylhydrazone), o-ethoxy-p-diethylaminobenzaldehyde-(diphenylhydrazone), o-methyl-p-diethylaminobenzaldehyde-(diphenylhydrazone), o-methyl-p-dimethylaminobenzaldehyde-(diphenylhydrazone), p-dipropylaminobenzaldehyde-(diphenylhydrazone), p-diethylaminobenzaldehyde-(benzylphenylhy- drazone), p-dibutylaminobenzaldehyde-(diphenylhydrazone),p-dimethylaminobenzaldehyde-(diphenylhydrazone) and the like described,for example in US-A-4,150
• hydrazone transport molecules include compounds such as 1-naphthalenecarbaldehyde 1-methyl-1-phenylhydrazone, 1-naphthalenecarbaldehyde 1,1-phenylhydrazone, 4-methoxynaphthlene-1-carbaldehyde 1-methyl-1-phenylhydrazone and other hydrazone transport molecules described, for example, in US-A-4,385,106; 4,338,388; 4,387,147; 4,399,208; 4,339,207, the entire disclosures of which are hereby incorporated herein by reference.
• Another preferred charge transport molecule is a carbazole phenyl hydrazone having the general formula: wherein R1 represents methyl, ethyl, 2-hydroxyethyl, or 2-chloroethyl group and R2 represents methyl, ethyl, benzyl or phenyl group.
• transport molecules encompassed by this formula include 9-methylcarbazole-3-carbaldehyde-1,1-diphenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-methyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-ethyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1-ethyl-1-benzyl-1-phenylhydrazone, 9-ethylcarbazole-3-carbaldehyde-1,1-diphenyldrazone, and other suitable carbazole phenyl hydrazone transport molecules described, for example, in U.S. Patent No. 4,256,821, the entire disclosure of which is hereby incorporated herein by reference. Similar hydrazone transport molecules are described, for example, in US-A-34,297,426, the entire disclosure of which is hereby incorporated herein by reference
• typical transport materials include numerous organic non-polymeric transport materials described in US-A-3,870,516 and non-ionic compounds described in US-A-4,346,157, the entire disclosures of which are hereby incorporated herein by reference.
• suitable transport materials include, but are not limited to, poly-1-vinylpyrene, poly-9- vinylanthracene, poly-9-(4-pentenyl)-carbazole, poly-9-(5-hexyl)-carbazole, polymethylene pyrene, poly-1-(pyrenyl)-butadiene, polymers such as alkyl, nitro, amino, halogen, and hydroxy substituted polymers such as poly-3-amino carbazole, 1,3-dibromo-poly-N-vinyl carbazole and 3,6-dibromo-poly-N-vinyl carbazole and numerous other transparent organic polymeric or non-polymeric transport materials as described in US-A-3,870,516, the entire disclosure of which is hereby incorporated by reference.
• Charge transport molecules are combined with an insulating film forming binder, using ratios of insulating film forming binder:charge transport molecules of about 10 to about 90 parts by weight, preferably from about 25 to about 75 parts by weight.
• Charge transport molecules comprise from about 10% by weight to about 90% by weight of the overcoat layer, preferably from about 25% to about 75% by weight.
• any suitable organic or inorganic charge injection enabling particles may be utilized in the overcoat layer of this invention.
• the particles may comprise phthalocyanine, tetracyanoquinadomethane, polypyrrole, polyacetylene, polyanaline, carbon, graphite, fullerene carbon or mixtures thereof.
• the particles may comprise of tin oxide, antimony oxide, titanium oxide, iron oxide, zinc oxide, aluminum oxide, silicon dioxide and mixtures thereof.
• Charge injection enabling particles can be hole injection enabling particles or electron injection enabling particles. Any particle can function as a charge injection enabling particle as long as the concentration of the particles and the entire electric field are sufficient to cause the charge injection enabling particles to rapidly polarize and inject charge carriers into the continuous phase of the overcoating layer. Generally, charge injection enabling particles having an electrical resistivity of about 10 12 ohm-cm or less are suitable.
• Typical inorganic charge injection enabling particles include, but are not limited to, molybdenum disulfide, silicone, carbon black, graphite, tin oxide, antimony oxide, chromium dioxide, zinc oxide, titanium dioxide, magnesium oxide, manganese dioxide, aluminum oxides, other metal oxides, colloidal silica, colloidal silica treated with silanes, tin, aluminum, nickel, steel, silver, gold, other metals, their oxides, sulfides, halides and othersaitforms, and the like, such as disclosed in US-A-5,063,128, 5,063,125 and 4,515,882, the entire disclosures of which are hereby incorporated herein by reference.
• organic charge injection enabling particles include, but are not limited to, fluorinated carbon particles; phthalocyanine pigment particles; quinacridone pigment particles; conductive complexes of tetracyanoquinodimethane (TCNQ) with polymeric quaternary ammonium salts, poly(2-vinylpyridene), poly(4-vinylpyridene), poly(N-vinyl imidazole), poly(4-dimethylaminostyrene), and ionene polymers; black brominated poly(cyclopentadiene); polymeric reaction product of poly(alkyl vinyl ketones) with phosphoryl chloride; metal polyphthalocyanines; a tetranitrile formed from tetracyanoethylene solution phase deposited on metal surfaces at about 200°C; the trans isomer of polyacetylene prepared by exposure of acetylene to films of concentrated solutions of a Ziegler-Natta catalyst [Ti(OC 4 Hg-n) 4 -AI(C 2
• Suitable charge injection enabling species include copper (I) compounds such as cuprous iodide disclosed in US-A-5,120,628 the entire disclosure of which is hereby incorporated herein by reference.
• the particle size (volume average particle diameter) of the charge injection enabling particles should be less than about 45 micrometers. A particle size between about 100 Angstroms and about 5000 Angstroms has been found suitable.
• the overcoating layer should contain at least about 0.1 percent by weight of the charge injection enabling particles based on the total weight of the overcoating layer. At lower concentrations, a noticeable residual charge tends to form.
• the upper limit for the amount of the charge injection enabling particles to be used depends upon the relative quantity of charge flow desired through the overcoating layer, the efficiency of the charge injection enabling particles to inject charge and the electric field applied to the overcoating.
• the overcoating layer becomes undesirably electrically conductive in an applied field when the silica particles are replaced by a concentration of 50 percent by weight carbon black charge injection enabling particles based on the total weight of the overcoating layer dispersed in polycarbonate resin containing dissolved N,N'-diphenyl-N,N'-bis(3-methylphenyl)) 1,1'-biphenyl-4,4'-diamine.
• the components of the overcoat can be mixed together by any suitable means.
• Typical mixing means include, for example, stirring rods, ultrasonic vibrators, magnetic stirrers, paint shakers, sandmills, roll pebble mills, sonic mixers, melt mixing devices and the like. It is important, however, that if the insulating film forming binder is a different material from the charge transport molecules, the charge transport molecules must either dissolve in the insulating film forming binder or be capable of being molecularly dispersed in the insulating film forming binder.
• a solvent or solvent mixture for the film forming binder and charge transport molecules may be utilized if desired. Preferably, the solvent or solvent mixture should dissolve both the insulating film forming binder and the charge transport molecules.
• suitable solvents include, but are not limited to, methylene chloride, 1,1,2-trichloroethane methylethylketone, toluene, xylene, tetrahydrofuran, and the like.
• the overcoating of the present invention can be coated on any suitable electroded donor device.
• These electroded donor devices may be in the form of a roll, belt, a drum, a pipe, a rod, a scroll or a sheet. Examples of suitable electroded donor devices which can be employed to practice this invention are described in US-A-3,996,892 and US-A-4,568,955, the entire disclosures of which are hereby incorporated herein by reference.
• the overcoating of the present invention can be applied to the electroded donor device by any suitable means.
• Typical techniques for applying an overcoat to a donor device include, for example, spray coating, dip coating, wire wound rod coating, powder coating, electrostatic spraying, sonic spraying, blade coating, web coating, flow extrusion, and the like. If the overcoat is applied by spraying, such spraying may be effected with or without the aid of a gas. Spraying may be assisted by mechanical and/or electrical aids such as in electrostatic spraying.
• the overcoat should be uniform, smooth and free from blemishes such as entrapped gas bubbles dirt, lint and the like.
• drying or curing conditions should be selected to avoid damage to the underlying donor device.
• Typical drying temperatures range from about 20°C to about 150°C, preferably between about 30°C to about 130°C.
• the thickness of the overcoat layer after drying or curing may preferably be from about 1 f..lm to about 50 ⁇ m. Generally, overcoat thicknesses of less than about 1 f..lm fail to provide sufficient protection for the underlying electroded donor device. Greater protection is provided by an overcoat thickness of at least about 3 ⁇ m. An overcoat thickness of from about 3 ⁇ m to about 15 ⁇ m is preferred for optimum protection of the electroded donor device.
• An overcoat layer is prepared by mixing 0.6 grams of Merlon M39 polycarbonate (available from Miles, Inc., Pittsburg, PA) 0.39 grams of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine prepared as described in U.S. Patent No. 4,265,990 the entire disclosure of which is hereby incorporated herein by reference and 0.01 grams of Black Pearls 2000 carbon black (available from Cabot Corporation, Billerica, MA). The components of the overcoat composition are mixed in methylene chloride in a paint shaker, Red Devil Model No. 5100X, available from Red Devil Inc., Union, N.J., U.S.A.
• the overcoat composition is applied to axially oriented electrodes on a sheet of polyimide film 0.025 mm (1 mil) thick by means of a Gardner draw bar coater (available from Pacific Scientific) equipped with a coating bar with a 0.050 mm (0.002 inch) gap for depositing a wet film thickness which upon drying yields a coating thickness of about 5 ⁇ m.
• the overcoat is dried at room temperature overnight.
• the overcoated electroded film is laminated onto an aluminum roll to form the donor roll.
• the applicator donor roll is assembled into a mag netic brush development system for an electrostatographic processor for developing latent electrostatic images.
• the imaging surface is a conventional drum-type xerographic photoreceptor well known in the art.
• the overcoating prevents electrical shorting between the electrodes on the donor roll and the conductive magnetic brush used for loading toner on the donor roll.
• the maximum developed toner M/A (the mass density of toner developed from the donor onto the latent image) is about 0 45 mg/cm 2 for donor roll loading of about 0.50 mg/cm 2 This yields a development efficiency of about 0.9, i.e., about 90%.
• An overcoat layer is prepared as described in Example 1 above except that 0.6 grams of Lexan 4701 polyphthalate carbonate resin (available from General Electric Co., Pittsfield, MA) is used in place of Merlon M39 polycarbonate.
• the overcoat is applied to axially oriented electroded material as described in Example 1 to yield a dried overcoating thickness of about 6 ⁇ m.
• the applicator donor roll is assembled into a magnetic brush development system as in Example 1 for developing latent electrostatic images.
• the overcoating prevents electrical shorting between the electrodes on the donor roll and the conductive magnetic brush used for loading toner on the donor roll for a 0.25 mm (10 mil) gap between the photoreceptor and donor roll and AC bias of about 600 volts peak at 1.5 Khz.
• Uniform solid areas are obtained with a red toner at a synchronous speed between the donor roll and photoreceptor of about 10.2 cm/sec.
• the maximum developed mass density of toner from the donor roll onto the latent image is about 0.42 mg/cm 2 and corresponds to a development efficiency of about 70%.
• the difference in development efficiency between the overcoating layer of Example 1 and Example 2 is attributed to increased toner adhesion to the polyphthalate carbonate binder of the overcoating layer in Example 2.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Magnetic Brush Developing In Electrophotography (AREA)
• Dry Development In Electrophotography (AREA)
• Photoreceptors In Electrophotography (AREA)

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Cited By (4)

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• 1993
  • 1993-06-22 JP JP5149682A patent/JPH06149071A/ja not_active Withdrawn
  • 1993-10-15 EP EP93308225A patent/EP0594366A3/en not_active Withdrawn

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