Patent Application
20080032219
Aspects of the present disclosure relate to a photoconductive member or device comprising a substrate, an undercoat layer thereover, and wherein the undercoat layer comprises, for example, a polyol resin, an aminoplast resin, an adhesion component, and a metal oxide dispersed therein; and at least one imaging layer, such as a photogenerating layer and a charge transport layer or layers, formed on the undercoat layer; a photoconductor comprising a substrate, an undercoat layer thereover comprising a polyol resin, an aminoplast resin, a polyester or a silicone or urethane or epoxy modified polyester adhesion component, and a metal oxide, and a photogenerating layer, and at least one charge transport layer; a photoconductor comprising a supporting substrate, a hole blocking layer thereover comprising a polyol resin, an aminoplast resin, an adhesion component, and a metal oxide; a photogenerating layer and a charge transport layer; a photoconductor wherein the photogenerating layer is situated between the charge transport layer and the substrate, and which layer contains a resin binder; and wherein the adhesion component is a polyester or polyacrylate present in an amount of from about 1 to about 25 weight percent; an electrophotographic imaging member which generally comprises at least a substrate layer, an undercoat layer, and an imaging layer, and where the undercoat layer is generally located between the substrate and the imaging layer although additional layers may be present and located between these layers, and deposited on the undercoat layer in sequence a charge generating layer and a charge transport layer. This imaging member can be employed in the imaging process of electrophotography where the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Examples of adhesion additives, components, promoters selected in various suitable amounts, such as for example, from about 0.1 to about 40, from about 0.1 to about 20, or from 1 to about 10 weight percent include polyesters, such as MOR-ESTER™ 49,000; silicone modified polyesters, such as DC5000 SP™, available from Dura Coat Products, which is a 50 percent silicone modified polyester resin and offers excellent scratch and chemical resistance; a siloxane polyester copolymer; glycol modified polyesters such as PETG; acrylic modified polyester, such as AROPLAZ 4097™, available from Reichhold, which can directly crosslink with aminoplast resins, and offers hardness, excellent flexibility, and chemical stability; epoxy modified polyesters, such as EPOTUF™ 404-xx-60, available from Reichhold, which polyester is a high acid value epoxy modified (containing) polyester, and offers adhesion and chemical compatibility; urethane modified polyesters, such as PELLETHANE™ 2101-85A resin, available from Dow Chemical, and HYTREL™ G4074 resin, available from DuPont, where both resins provide excellent adhesion; polyacrylates, such as poly-4,4′-isopropylidenediphenylene terephthalate/isophthalate copolymer, and optionally mixtures thereof, and the like.
Specific examples of a silicone free or substantially silicone free polyester resins include BORCHI GEN™ HMP, available from Borchers GmbH, comprised in one variant of 80 percent by weight of solids dispersed in 1-propanol and N-methyl-2-pyrrolidinone, WORLEEADD™ 486, a polyester resin available at 75 weight percent solids in xylene/n-butanol/N-methyl-2-pyrrolidinone by Worlee-Chemie G.m.b.H, CN704™, an acrylated polyester resin, available from Sartomer, and ADHESION RESIN™ LTW, a special purpose polyester resin available at 60 weight percent solids in xylene from Degussa Corporation. The adhesion promoter can be incorporated in the undercoat layer by (1) directly adding into the already prepared undercoat layer dispersion comprised of metal oxide, polymeric resins and solvents; or (2) ball milling together with metal oxide, polymeric resins, solvents to generate the undercoat layer dispersion. The polyol resin selected for the UCL is, for example, an acrylic polyol resin, a polyglycol, a polyglycerol, and mixtures thereof. The aminoplast resin may be selected from, but is not limited to, the group comprised of urea, melamine and mixtures thereof. In embodiments, a metal oxide is included in the UCL in combination with resins to form the undercoat layer formulation. For example, the metal oxide is dispersed in the resins and the dispersion is subjected to heat. In embodiments, the metal oxide has a size diameter of from about 5 to about 300 nanometers, a powder resistance of from about 1×103 to about 6×105 ohm/cm when applied at a pressure of from about 50 to about 650 kilograms/cm2. In one embodiment, titanium dioxide TiO2 is selected as the metal oxide in the undercoat layer formulation.
Suitable polyester additives that function primarily as adhesion promoters generally comprise, for example, the reaction product of (a) at least one difunctional carboxylic acid; (b) at least one trifunctional polyol; (c) at least one chain stopper, and (d) a phosphoric acid. Examples of suitable difunctional carboxylic acids of (a) include adipic acid, azelaic acid, fumaric acid, phthalic acid, sebacic acid, maleic acid, succinic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, dimer fatty acids, itaconic acid, glutaric acid, cyclohexanedicarboxylic acid, and mixtures thereof. Specific difunctional carboxylic acids of value are adipic acid and azelaic acid.
The at least one, such as for example, from 1 to about 8, 1 to about 4, or 1, trifunctional polyol (a) may be branched or unbranched. Examples of suitable trifunctional polyols (b) are trimethylolpropane, trimethylol ethane, glycerin, 1,2,4-butanetriol, and mixtures thereof. The at least one chain stopper can be a carboxylic acid that is different from the at least one difunctional carboxylic acid (a), and more specifically, the chain stopper can be comprised of monocarboxylic acids. Suitable carboxylic acids (c) can contain one or more aromatic structures and also can contain a number of branched alkyl groups. Specific examples of suitable carboxylic acids (c) include para-t-butyl benzoic acid, benzoic acid, salicylic acid, 2-ethylhexanoic acid, pelargonic acid, isononanoic acid, C18 fatty acids, stearic acid, lauric acid, palmitic acid, and mixtures thereof. At least one refers, for example, to 1 to about 10, from 1 to about 5, from 1 to about 3, and 1. The phosphoric acid component (d) should be present in amounts of from about 0.03 to about 0.20, from about 0.05 to about 0.15, or from about 0.07 to about 0.10 weight percent. Phosphate esters, such as butyl or phenyl acid phosphate and the like, including a number of known phosphate esters, are suitable for use as component (d).
The at least one trifunctional polyol (b) may be branched or unbranched. Examples of suitable trifunctional polyols (b) are trimethyolpropane, trimethylol ethane, glycerin, 1,2,4-butanetriol, and mixtures thereof. Specific trifunctional polyols of value are (b) trimethylolpropane and trimethylolethane, with trimethylolpropane being selected in a number of embodiments.
The at least one chain stopper, which is a material added during the polymerization process to terminate or control the degree of the reaction, will generally be a carboxylic acid that is different from the at least one difunctional carboxylic acid (a). Suitable carboxylic acids (c) usually contain one or more aromatic structures, and can contain a suitable number of branched alkyl groups. Examples of suitable carboxylic acids (c) include para-t-butyl benzoic acid, benzoic acid, salicylic acid, 2-ethylhexanoic acid, pelargonic acid, isononanoic acid, C18 fatty acids, stearic acid, lauric acid, palmitic acid, and mixtures thereof. Specific carboxylic acids (c) include para-t-butyl benzoic acid, benzoic acid, and 2-ethylhexanoic acid, with para-t-butyl benzoic acid being selected in a number of embodiments. A phosphoric acid component (d) can be present in various effective suitable amounts, such as from about 0.03 to about 0.20, from about 0.05 to about 0.15, and from about 0.07 to about 0.10 weight percent. Also, phosphate esters, such as butyl or phenyl acid phosphate and the like, are suitable for use as component (d).
Polymerization of the reactants (a), (b), (c), and (d) may occur at typical esterification conditions, such as for example, from about 200° C. to about 230° C. reaction temperature while continuously removing water as a reaction byproduct. Solvents that facilitate the removal of water from the reaction system (those that form an azeotrope, such as xylenes) may be used.
Examples of polyol resins include PARALOID™ AT-400 with a Mw of 15,000, a hydroxyl equivalent weight of 652 and an acid number of 25; PARALOID™ AT-410 with a Mw of 9,000, a hydroxyl equivalent weight of 877 and an acid number of 25; RU-1100-1k™ with a Mn of 1,000 and 112 hydroxyl value, and RU-1550-k5™ with a Mn of 5,000 and 22.5 hydroxyl value, both available from Procachem Corp.; G-CURE™ 108A70, available from Fitzchem Corp.; NEOL® based polyester polyol, available from BASF; TONE™ 0201 polyol with a Mn of 530, a hydroxyl number of 117, and acid number of <0.25, available from Dow Chemical Company. Examples of aminoplast resins include SUMIMAL™ M40S, SUMIMAL™ M50S, both available from Sumitomo Chemical, CYMEL™ 323, CYMEL™ 327, CYMEL™ 303, all available from CYTEC Corporation, and GP 401W51™, available from Georgia-Pacific.
In embodiments, the undercoat layer metal oxide like TiO2 can be either surface treated or untreated. Surface treatments include, but are not limited to, mixing the metal oxide with aluminum laurate, alumina, zirconia, silica, silane, methicone, dimethicone, sodium metaphosphate, and the like, and mixtures thereof. Examples of TiO2 include MT-150W™ (surface treatment with sodium metaphosphate, available from Tayca Corporation), STR-60N™ (no surface treatment, available from Sakai Chemical Industry Co., Ltd.), FTL-100™ (no surface treatment, available from Ishihara Sangyo Laisha, Ltd.), STR-60™ (surface treatment with Al2O3, available from Sakai Chemical Industry Co., Ltd.), TTO-55N™ (no surface treatment, available from Ishihara Sangyo Laisha, Ltd.), TTO-55A™ (surface treatment with Al2O3, available from Ishihara Sangyo Laisha, Ltd.), MT-150AW™ (no surface treatment, available from Tayca Corporation), MT-150A™ (no surface treatment, available from Tayca Corporation), MT-100S™ (surface treatment with aluminum laurate and alumina, available from Tayca Corporation), MT-100HD™ (surface treatment with zirconia and alumina, available from Tayca Corporation), MT-100SA™ (surface treatment with silica and alumina, available from Tayca Corporation), and the like.
Examples of the hole blocking layer components include TiO2/VARCUM® resin mixture in a 1:1 mixture of n-butanol:xylene containing from about 2 to about 50 weight percent of an added electron transport material based on the total solid concentration in solution, and wherein the aforementioned main component mixture amount is, for example, from about 80 to about 100, and more specifically, from about 90 to about 99 weight percent, and yet more specifically, wherein the titanium oxide possesses a primary particle size diameter of from about 10 to about 25 nanometers, and more specifically, from about 12 to about 17, and yet more specifically, about 15 nanometers with an estimated aspect ratio of from about 4 to about 5, and is optionally surface treated with, for example, a component containing, for example, from about 1 to about 3 percent by weight of alkali metal, such as a sodium metaphosphate, a powder resistance of from about 1×104 to about 6×104 ohm/cm when applied at a pressure of from about 650 to about 50 kilograms/cm2; MT-150W™, and which titanium oxide is available from Tayca Corporation, and wherein the hole blocking layer is of a suitable thickness thereby avoiding or minimizing charge leakage. Metal oxide examples in addition to titanium are chromium, zinc, tin, and the like, and more specifically, zinc oxide, tin oxide, aluminum oxide, silicone oxide, zirconium oxide, indium oxide, molybdenum oxide, and mixtures thereof.
The hole blocking layer can in embodiments be prepared by a number of known methods; the process parameters being dependent, for example, on the photoconductor member desired. The hole blocking layer can be coated as solution or a dispersion onto a substrate by the use of a spray coater, dip coater, extrusion coater, roller coater, wire-bar coater, slot coater, doctor blade coater, gravure coater, and the like, and dried at from about 40° C. to about 200° C. for a suitable period of time, such as from about 10 minutes to about 10 hours, under stationary conditions or in an air flow. The coating can be accomplished to provide a final coating thickness of from about 1 to about 15 microns after drying.
The weight/weight ratio of the polyol and aminoplast resins in the undercoat layer formulation is, for example, from about 5/95 to about 95/5, or from about 25/75 to about 75/25. The weight/weight ratio of the polyol and aminoplast resins to the metal oxide like titanium oxide in the undercoat layer formulation is from about 10/90 to about 90/10, or from about 30/70 to about 70/30. In embodiments, the aminoplast resin is present in an amount of from about 5 percent to about 80 percent, or from about 5 percent to about 75 percent, or from about 20 percent to about 80 percent by weight of the total weight of the undercoat layer components. In embodiments, the polyol resin is present in an amount of from about 5 percent to about 80 percent, from about 5 percent to about 75 percent, or from about 20 percent to about 80 percent by weight of the total weight of the undercoat layer. In embodiments, the metal oxide like TiO2 is present in an amount of from about 10 percent to about 90 percent, or from about 20 percent to about 80 percent by weight of the total weight of the undercoat layer.
Optionally, the undercoat layer further contains a light scattering particle or particles with, for example, a refractive index different from the resin mixture binder, and which particles possess a number average particle size greater than about 0.8 μm. The light scattering particles, which can be an amorphous silica or a silicone ball, are present in an amount of, for example, from about 0 percent to about 10 percent by weight of the total weight of the undercoat layer.
The undercoat layer has a suitable thickness of, for example, from about 0.1 μm to about 40 μm, from about 2 μm to about 25 μm, or from about 10 μm to about 20 μm. In further embodiments, the resins/metal oxide combination is present in an amount of from about 20 percent to about 80 percent, or from about 40 percent to about 70 percent, based on the total weight of the undercoat layer. The undercoat layer may be applied or coated onto a substrate by any suitable known technique, such as spraying, dip coating, draw bar coating, gravure coating, silk screening, air knife coating, reverse roll coating, vacuum deposition, chemical treatment, and the like. Additional vacuuming, heating, drying and the like may be used to remove any solvent remaining after the application or coating to form the undercoat layer.
Alternative optional hole blocking or undercoat layer components for the imaging members of the present disclosure can contain a number of components in addition to the resins, and polyester or polyacrylate adhesion component, including for example, known hole blocking components, such as amino silanes, doped metal oxides, TiSi, a metal oxide like chromium, zinc, tin and the like; a mixture of phenolic compounds and a phenolic resin, or a mixture of two phenolic resins, and optionally a dopant such as SiO2. The phenolic compounds usually contain at least two phenol groups, such as bisphenol A (4,4′-isopropylidenediphenol), E (4,4′-ethylidenebisphenol), F (bis(4-hydroxyphenyl)methane), M (4,4′-(1,3-phenylenediisopropylidene)bisphenol), P (4,4′-(1,4-phenylenediisopropylidene)bisphenol), S (4,4′-sulfonyldiphenol), and Z (4,4′-cyclohexylidenebisphenol); hexafluorobisphenol A (4,4′-(hexafluoro isopropylidene)diphenol), resorcinol, hydroxyquinone, catechin, and the like.
Thus, the hole blocking layer can be, for example, comprised of from about 20 weight percent to about 80 weight percent, and more specifically, from about 55 weight percent to about 65 weight percent of a suitable component like a metal oxide, such as TiO2, from about 20 weight percent to about 70 weight percent, and more specifically, from about 25 weight percent to about 50 weight percent of a phenolic resin; from about 2 weight percent to about 20 weight percent, and more specifically, from about 5 weight percent to about 15 weight percent of a phenolic compound containing at least two phenolic groups, such as bisphenol S, and from about 2 weight percent to about 15 weight percent, and more specifically, from about 4 weight percent to about 10 weight percent of a plywood suppression dopant, such as SiO2. The hole blocking layer coating dispersion can, for example, be prepared as follows. The metal oxide/phenolic resin dispersion is first prepared by ball milling or dynomilling until the median particle size of the metal oxide in the dispersion is less than about 10 nanometers, for example from about 5 to about 9 nanometers. To the above dispersion are added a phenolic compound and dopant followed by mixing. The hole blocking layer coating dispersion can be applied by dip coating or web coating, and the layer can be thermally cured after coating. The hole blocking layer resulting is, for example, of a thickness of from about 0.01 micron to about 30 microns, and more specifically, from about 0.1 micron to about 8 microns. Examples of phenolic resins include formaldehyde polymers with phenol, p-tert-butylphenol, cresol, such as VARCUM™ 29159 and 29101 (available from OxyChem Company), and DURITE™ 97 (available from Borden Chemical); formaldehyde polymers with ammonia, cresol and phenol, such as VARCUM™ 29112 (available from OxyChem Company); formaldehyde polymers with 4,4′-(1-methylethylidene)bisphenol, such as VARCUM™ 29108 and 29116 (available from OxyChem Company); formaldehyde polymers with cresol and phenol, such as VARCUM™ 29457 (available from OxyChem Company), DURITE™ SD-423A, SD-422A (available from Borden Chemical); or formaldehyde polymers with phenol and p-tert-butylphenol, such as DURITE™ ESD 556C (available from Borden Chemical).
The thickness of the photoconductive substrate layer depends on many factors including economical considerations, electrical characteristics, and the like; thus, this layer may be of substantial thickness, for example over 3,000 microns, such as from about 300 to about 700 microns, or of a minimum thickness. In embodiments, the thickness of this layer is from about 75 microns to about 300 microns, or from about 100 to about 150 microns.
The substrate may be opaque or substantially transparent, and may comprise any suitable material having the required mechanical properties. Accordingly, the substrate may comprise a layer of an electrically nonconductive or conductive material such as an inorganic or an organic composition. As electrically nonconducting materials, there may be employed various resins known for this purpose including polyesters, polycarbonates, polyamides, polyurethanes, and the like, which are flexible as thin webs. An electrically conducting substrate may be any suitable metal of, for example, aluminum, nickel, steel, copper, and the like, or a polymeric material, as described above, filled with an electrically conducting substance, such as carbon, metallic powder, and the like, or an organic electrically conducting material. The electrically insulating or conductive substrate may be in the form of an endless flexible belt, a web, a rigid cylinder, a sheet, and the like. The thickness of the substrate layer depends on numerous factors including strength desired and economical considerations. For a drum, as disclosed in a copending application referenced herein, this layer may be of substantial thickness of, for example, up to many centimeters or of a minimum thickness of less than a millimeter. Similarly, a flexible belt may be of substantial thickness of, for example, about 250 micrometers, or of minimum thickness of less than about 50 micrometers, provided there are no adverse effects on the final electrophotographic device. In embodiments where the substrate layer is not conductive, the surface thereof may be rendered electrically conductive by an electrically conductive coating. The conductive coating may vary in thickness over substantially wide ranges depending upon the optical transparency, degree of flexibility desired, and economic factors.
Illustrative examples of substrates are as illustrated herein, and more specifically, substrates selected for the imaging members of the present disclosure, and which substrates can be opaque or substantially transparent comprise a layer of insulating material including inorganic or organic polymeric materials, such as MYLAR® a commercially available polymer, MYLAR® containing titanium, a layer of an organic or inorganic material having a semiconductive surface layer, such as indium tin oxide, or aluminum arranged thereon, or a conductive material inclusive of aluminum, chromium, nickel, brass, or the like. The substrate may be flexible, seamless, or rigid, and may have a number of many different configurations, such as for example, a plate, a cylindrical drum, a scroll, an endless flexible belt, and the like. In embodiments, the substrate is in the form of a seamless flexible belt. In some situations, it may be desirable to coat on the back of the substrate, particularly when the substrate is a flexible organic polymeric material, an anticurl layer, such as for example polycarbonate materials commercially available as MAKROLON®.
The photogenerating layer in embodiments is comprised of, for example, a number of know photogenerating pigments including, for example, Type V hydroxygallium phthalocyanine or chlorogallium phthalocyanine, and a resin binder like poly(vinyl chloride-co-vinyl acetate) copolymer, such as VMCH (available from Dow Chemical). Generally, the photogenerating layer can contain known photogenerating pigments, such as metal phthalocyanines, metal free phthalocyanines, alkylhydroxyl gallium phthalocyanines, hydroxygallium phthalocyanines, chlorogallium phthalocyanines, perylenes, especially bis(benzimidazo)perylene, titanyl phthalocyanines, and the like, and more specifically, vanadyl phthalocyanines, Type V hydroxygallium phthalocyanines, and inorganic components such as selenium, selenium alloys, and trigonal selenium. The photogenerating pigment can be dispersed in a resin binder similar to the resin binders selected for the charge transport layer, or alternatively no resin binder need be present. Generally, the thickness of the photogenerating layer depends on a number of factors, including the thicknesses of the other layers and the amount of photogenerating material contained in the photogenerating layer. Accordingly, this layer can be of a thickness of, for example, from about 0.05 micron to about 10 microns, and more specifically, from about 0.25 micron to about 2 microns when, for example, the photogenerating compositions are present in an amount of from about 30 to about 75 percent by volume. The maximum thickness of this layer in embodiments is dependent primarily upon factors, such as photosensitivity, electrical properties and mechanical considerations. The photogenerating layer binder resin is present in various suitable amounts of, for example from about 1 to about 50, and more specifically, from about 1 to about 10 weight percent, and which resin may be selected from a number of known polymers, such as poly(vinyl butyral), poly(vinyl carbazole), polyesters, polycarbonates, poly(vinyl chloride), polyacrylates and methacrylates, copolymers of vinyl chloride and vinyl acetate, phenolic resins, polyurethanes, poly(vinyl alcohol), polyacrylonitrile, polystyrene, and the like. It is desirable to select a coating solvent that does not substantially disturb or adversely affect the other previously coated layers of the device. Generally, however, from about 5 percent by volume to about 90 percent by volume of the photogenerating pigment is dispersed in about 10 percent by volume to about 95 percent by volume of the resinous binder, or from about 20 percent by volume to about 30 percent by volume of the photogenerating pigment is dispersed in about 70 percent by volume to about 80 percent by volume of the resinous binder composition. In one embodiment, about 8 percent by volume of the photogenerating pigment is dispersed in about 92 percent by volume of the resinous binder composition. Examples of coating solvents for the photogenerating layer are ketones, alcohols, aromatic hydrocarbons, halogenated aliphatic hydrocarbons, ethers, amines, amides, esters, and the like. Specific solvent examples are cyclohexanone, acetone, methyl ethyl ketone, methanol, ethanol, butanol, amyl alcohol, toluene, xylene, chlorobenzene, carbon tetrachloride, chloroform, methylene chloride, trichloroethylene, tetrahydrofuran, dioxane, diethyl ether, dimethyl formamide, dimethyl acetamide, butyl acetate, ethyl acetate, methoxyethyl acetate, and the like.
The photogenerating layer may comprise amorphous films of selenium and alloys of selenium and arsenic, tellurium, germanium, and the like, hydrogenated amorphous silicone and compounds of silicone and germanium, carbon, oxygen, nitrogen, and the like fabricated by vacuum evaporation or deposition. The photogenerating layer may also comprise inorganic pigments of crystalline selenium and its alloys; Group II to VI compounds; and organic pigments such as quinacridones, polycyclic pigments such as dibromo anthanthrone pigments, perylene and perinone diamines, polynuclear aromatic quinones, azo pigments including bis-, tris- and tetrakis-azos, and the like dispersed in a film forming polymeric binder and fabricated by solvent coating techniques.
Since infrared sensitivity is usually desired for photoreceptors exposed to low-cost semiconductor laser diode light exposure devices, a number of phthalocyanines can be selected for the photogenerating layer, and where, for example, the absorption spectrum and photosensitivity of the phthalocyanines depends on the central metal atom of the compound, such as oxyvanadium phthalocyanine, chloroaluminum phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine, magnesium phthalocyanine, and metal free phthalocyanine. The phthalocyanines exist in many crystal forms, and have a strong influence on photogeneration.
Examples of polymeric binder materials that can be selected as the matrix for the photogenerating layer components are illustrated in. U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference. Examples of binders are thermoplastic and thermosetting resins, such as polycarbonates, polyesters, polyamides, polyurethanes, polystyrenes, polyarylethers, polyarylsulfones, polybutadienes, polysulfones, polyethersulfones, polyethylenes, polypropylenes, polyimides, polymethylpentenes, poly(phenylene sulfides), poly(vinyl acetate), polysiloxanes, polyacrylates, polyvinyl acetals, polyamides, polyimides, amino resins, phenylene oxide resins, terephthalic acid resins, phenoxy resins, epoxy resins, phenolic resins, polystyrene and acrylonitrile copolymers, poly(vinyl chloride), vinyl chloride and vinyl acetate copolymers, acrylate copolymers, alkyd resins, cellulosic film formers, poly(amideimide), styrenebutadiene copolymers, vinylidene chloride-vinyl chloride copolymers, vinyl acetate-vinylidene chloride copolymers, styrene-alkyd resins, poly(vinyl carbazole), and the like. These polymers may be block, random or alternating copolymers.
Various suitable and conventional known processes may be used to mix, and thereafter apply the photogenerating layer coating mixture like spraying, dip coating, roll coating, wire wound rod coating, vacuum sublimation, and the like. For some applications, the photogenerating layer may be fabricated in a dot or line pattern. Removal of the solvent of a solvent-coated layer may be effected by any known conventional techniques such as oven drying, infrared radiation drying, air drying, and the like. The coating of the photogenerating layer on the UCL in embodiments of the present disclosure can be accomplished with spray, dip or wire-bar methods such that the final dry thickness of the photogenerating layer is as illustrated herein, and can be, for example, from about 0.01 to about 30 microns after being dried at, for example, about 40° C. to about 150° C. for about 1 to about 90 minutes. More specifically, a photogenerating layer of a thickness, for example, of from about 0.1 to about 30, or from about 0.5 to about 2 microns can be applied to or deposited on the substrate, on other surfaces in between the substrate and the charge transport layer, and the like. The hole blocking layer or UCL may be applied to the electrically conductive supporting substrate surface prior to the application of a photogenerating layer.
A suitable known adhesive layer can be included in the photoconductor. Typical adhesive layer materials include, for example, polyesters, polyurethanes, and the like. The adhesive layer thickness can vary, and in embodiments is, for example, from about 0.05 micrometer (500 Angstroms) to about 0.3 micrometer (3,000 Angstroms). The adhesive layer can be deposited on the hole blocking layer by spraying, dip coating, roll coating, wire wound rod coating, gravure coating, Bird applicator coating, and the like. Drying of the deposited coating may be effected by, for example, oven drying, infrared radiation drying, air drying, and the like. As optional adhesive layers usually in contact with or situated between the hole blocking layer and the photogenerating layer, there can be selected various known substances inclusive of copolyesters, polyamides, poly(vinyl butyral), poly(vinyl alcohol), polyurethane, and polyacrylonitrile. This layer is, for example, of a thickness of from about 0.001 micron to about 1 micron, or from about 0.1 to about 0.5 micron. Optionally, this layer may contain effective suitable amounts, for example from about 1 to about 10 weight percent, of conductive and nonconductive particles, such as zinc oxide, titanium dioxide, silicone nitride, carbon black, and the like, to provide, for example, in embodiments of the present disclosure, further desirable electrical and optical properties.
A number of charge transport materials, especially known hole transport molecules, may be selected for the charge transport layer, examples of which are aryl amines of the formula/structure, and which layer is generally of a thickness of from about 5 microns to about 75 microns, and more specifically, of a thickness of from about 10 microns to about 40 microns
wherein X is a suitable hydrocarbon like alkyl, alkoxy, and aryl; a halogen, or mixtures thereof, and especially those substituents selected from the group consisting of Cl and CH3; and molecules of the following formula
wherein X and Y are a suitable substituent like a hydrocarbon, such as independently alkyl, alkoxy, or aryl; a halogen, or mixtures thereof. Alkyl and alkoxy contain, for example, from 1 to about 25 carbon atoms, and more specifically, from 1 to about 12 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, and the corresponding alkoxides. Aryl can contain from 6 to about 36 carbon atoms, such as phenyl, and the like. Halogen includes chloride, bromide, iodide, and fluoride. Substituted alkyls, alkoxys, and aryls can also be selected in embodiments. At least one charge transport refers, for example, to 1, from 1 to about 7, from 1 to about 4, and from 1 to about 2.
Examples of specific aryl amines include N,N′-diphenyl-N,N′-bis(alkylphenyl)-1,1-biphenyl-4,4′-diamine wherein alkyl is selected from the group consisting of methyl, ethyl, propyl, butyl, hexyl, and the like; N,N′-diphenyl-N,N′-bis(halophenyl)-1,1′-biphenyl-4,4′-diamine wherein the halo substituent is a chloro substituent; N,N′-bis(4-butylphenyl)-N,N′-di-p-tolyl-[p-terphenyl]-4,4“-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-m-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-o-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(4-isopropylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2-ethyl-6-methylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2,5-dimethylphenyl)-[p-terphenyl]-4,4′-diamine, N,N′-diphenyl-N,N′-bis(3-chlorophenyl)-[p-terphenyl]-4,4″-diamine, and the like. Other known charge transport layer molecules can be selected, reference for example, U.S. Pat. Nos. 4,921,773 and 4,464,450, the disclosures of which are totally incorporated herein by reference.
Examples of the binder materials selected for the charge transport layer or layers include components, such as those described in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference. Specific examples of polymer binder materials include polycarbonates, polyarylates, acrylate polymers, vinyl polymers, cellulose polymers, polyesters, polysiloxanes, polyamides, polyurethanes, poly(cyclo olefins), epoxies, and random or alternating copolymers thereof; and more specifically, polycarbonates such as poly(4,4′-isopropylidene-diphenylene)carbonate (also referred to as bisphenol-A-polycarbonate), poly(4,4′-cyclohexylidinediphenylene)carbonate (also referred to as bisphenol-Z-polycarbonate), poly(4,4′-isopropylidene-3,3′-dimethyl-diphenyl) carbonate (also referred to as bisphenol-C-polycarbonate), and the like. In embodiments, electrically inactive binders are comprised of polycarbonate resins with a molecular weight of from about 20,000 to about 100,000, or with a molecular weight Mw of from about 50,000 to about 100,000 preferred. Generally, the transport layer contains from about 10 to about 75 percent by weight of the charge transport material, and more specifically, from about 35 percent to about 50 percent of this material.
The charge transport layer or layers, and more specifically, a first charge transport in contact with the photogenerating layer, and thereover a top or second charge transport overcoating layer may comprise charge transporting small molecules dissolved or molecularly dispersed in a film forming electrically inert polymer such as a polycarbonate. In embodiments, “dissolved” refers, for example, to forming a solution in which the small molecule is dissolved in the polymer to form a homogeneous phase; and “molecularly dispersed in embodiments” refers, for example, to charge transporting molecules dispersed in the polymer, the small molecules being dispersed in the polymer on a molecular scale. Various charge transporting or electrically active small molecules may be selected for the charge transport layer or layers. In embodiments, charge transport refers, for example, to charge transporting molecules as a monomer that allows the free charge generated in the photogenerating layer to be transported across the transport layer.
Examples of hole transporting molecules include, for example, pyrazolines such as 1-phenyl-3-(4′-diethylamino styryl)-5-(4″-diethylamino phenyl)pyrazoline; aryl amines such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-p-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-m-tolyl-[p-terphenyl]-4,4“-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-o-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(4-isopropylphenyl)-[p-terphenyl]-4,4′-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2-ethyl-6-methylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2,5-dimethylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-diphenyl-N,N′-bis(3-chlorophenyl)-[p-terphenyl]-4,4″-diamine; hydrazones such as N-phenyl-N-methyl-3-(9-ethyl)carbazyl hydrazone, and 4-diethyl amino benzaldehyde-1,2-diphenyl hydrazone; and oxadiazoles such as 2,5-bis(4-N,N′-diethylaminophenyl)-1,2,4-oxadiazole, stilbenes, and the like. In embodiments, to minimize cycle-up in printers with high throughput, the charge transport layer should be substantially free (less than about two percent) of di or triamino-triphenyl methane. A small molecule charge transporting compound that permits injection of holes into the photogenerating layer with high efficiency and transports them across the charge transport layer with short transit times includes N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-p-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-m-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-o-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(4-isopropylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2-ethyl-6-methylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2,5-dimethylphenyl)-[p-terphenyl]-4,4″-diamine, and N,N′-diphenyl-N,N′-bis(3-chlorophenyl)-[p-terphenyl]-4,4″-diamine, or mixtures thereof. If desired, the charge transport material in the charge transport layer may comprise a polymeric charge transport material or a combination of a small molecule charge transport material and a polymeric charge transport material.
A number of processes may be used to mix and thereafter apply the charge transport layer or layers coating mixture to the photogenerating layer. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, and the like. Drying of the charge transport deposited coating may be effected by any suitable conventional technique such as oven drying, infrared radiation drying, air drying, and the like.
The thickness of each of the charge transport layers in embodiments is, for example, from about 10 to about 75, from about 15 to about 50 micrometers, but thicknesses outside these ranges may in embodiments also be selected. The charge transport layer should be an insulator to the extent that an electrostatic charge placed on the hole transport layer is not conducted in the absence of illumination at a rate sufficient to prevent formation and retention of an electrostatic latent image thereon. In general, the ratio of the thickness of the charge transport layer to the photogenerating layer can be from about 2:1 to about 200:1, and in some instances 400:1. The charge transport layer is substantially nonabsorbing to visible light or radiation in the region of intended use, but is electrically “active” in that it allows the injection of photogenerated holes from the photoconductive layer or photogenerating layer, and allows these holes to be transported through itself to selectively discharge a surface charge on the surface of the active layer.
The thickness of the continuous charge transport overcoat layer selected depends upon the abrasiveness of the charging (bias charging roll), cleaning (blade or web), development (brush), transfer (bias transfer roll), and the like in the system employed, and can be up to about 10 micrometers. In embodiments, this thickness for each layer can be, for example, from about 1 micrometer to about 5 micrometers. Various suitable and conventional methods may be used to mix, and thereafter apply the overcoat layer coating mixture to the photoconductor. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, and the like. Drying of the deposited coating may be effected by any suitable conventional technique, such as oven drying, infrared radiation drying, air drying, and the like. The dried overcoating layer of this disclosure should transport holes during imaging and should not have too high a free carrier concentration. Free carrier concentration in the overcoat increases the dark decay.
The following Examples are provided. All proportions are by weight unless otherwise indicated.
A conventional undercoat layer dispersion, UC79, was prepared as follows: in a 4 ounce glass bottle, 16.7 grams of TiO2 (MT-150W™, Tayca Company, Japan), 5.2 grams of a phenolic resin (VARCUM™ 29159, Oxychem Company), and 5.3 grams of a melamine resin (CYMEL™ 323, CYTEC Company) were mixed with 15 grams of xylene and 15 grams of n-butanol. After mixing, 120 grams of 0.4 to 0.6 millimeter diameter zirconium oxide beads were added to the mixture resulting, and which mixture was roll milled overnight, about 18 hours. A photoconductor was prepared by coating the undercoat layer dispersion on an aluminum substrate at 5 μm thickness at a curing condition of 140° C./30 minutes. Subsequently, a 0.2 to 0.5 μm charge generating layer comprised of chlorophthalocyanine and a 29 μm charge transport layer comprised of N,N′-bis(methylphenyl)-1,1-biphenyl-4,4′-diamine, a polycarbonate, and polytetrafluoroethylene (PTFE) particles were coated on the undercoat layer.
The above undercoat layer dispersion was selected for a photoconductor device with the undercoat layer at 5 μm in thickness at a curing condition of 140° C./30 minutes. Subsequently, a 0.2 to 0.5 μm charge generating layer comprised of chlorophthalocyanine and a 29 μm charge transport layer comprised of N,N′-bis(methylphenyl)-1,1-biphenyl-4,4′-diamine, a polycarbonate (PCZ, a LUPILON 200™ (PCZ-200) or POLYCARBONATE Z™, weight average molecular weight of about 20,000, available from Mitsubishi Gas Chemical Corporation), and PTFE particles were coated on the UCL.
An undercoat layer dispersion can be prepared as follows: there is mixed 18.5 grams of titanium oxide (MT-150W™, Tayca Company, Japan), 6.25 grams of CYMEL™ 323 melamine resin (CYTEC Company), 6 grams of PARALOID™ AT-400 acrylic polyol resin (Rohm Haas), 0.3 gram) of MOR-ESTER™ 49,000, available from Morton International, and 32 grams of methylethyl ketone (MEK) in a 4 ounce glass bottle. After mixing, 140 grams of 0.4 to 0.6 millimeter ZrO2 beads were added, and the mixture resulting was roll milled for two days. The final dispersion was collected through a 20 μm nylon filter, and the solids percentage was measured to be 42.5 percent. An experimental device was prepared by coating this undercoat layer at a 5 μm thickness at a curing condition of 140° C./30 minutes onto an aluminum substrate. Subsequently, a 0.2 to 0.5 μm thick charge generating layer comprised of chlorogallium phthalocyanine, and a vinyl resin (VMCH™ available from Union Carbide) at a weight ratio of about 54 to about 46, and a 29 μm charge transport layer comprised of N,N′-bis(methylphenyl)-1,1-biphenyl-4,4′-diamine, a PCZ polycarbonate, and PTFE particles at a weight ratio of about 37/57/6 were coated onto the undercoat layer.
The above prepared photoreceptor devices were tested in a scanner set to obtain photoinduced discharge characteristic (PIDC) curves, sequenced at one charge-erase cycle followed by one charge-expose-erase cycle, wherein the light intensity was incrementally increased with cycling to produce a series of PIDC curves from which the photosensitivity and surface potentials at various exposure intensities were measured. Additional electrical characteristics were obtained by a series of charge-erase cycles with incrementing surface potential to generate several voltages versus charge density curves. The scanner was equipped with a scorotron set to a constant voltage charging at various surface potentials. The devices were tested at surface potentials of about 500 and about 700 volts with the exposure light intensity incrementally increased by means of regulating a series of neutral density filters. The exposure light source was a 780 nanometer light emitting diode. The aluminum drum was rotated at a speed of about 61 revolutions per minute to produce a surface speed of about 122 millimeters per second. The xerographic simulation was completed in an environmentally controlled light tight chamber at ambient conditions (about 50 percent relative humidity and about 22° C.).
Very similar PIDC curves were observed for all the above prepared photoreceptor devices, thus the undercoat layer containing the polyol, melamine, and polyester resins performs very similarly to a conventional undercoat layer comprised, for example, of organozirconium, and to an undercoat layer with only a polyol and melamine resin from the point of view of PIDC. The experimental device showed normal electrical properties with similar residual voltage and charge acceptance to that of the Comparative Example devices. The Vdep, Vlow, dV/dX, Verase, and dark decay all suggest that the polyester containing undercoat layer is functioning properly.
The above photoreceptor drums were then acclimated for 24 hours before further testing at (70° F./10 percent RH) in a Xerox Corporation Copeland Work Centre Pro 3545 machine using K station at t=0 and t=500 print count. Runups from t=0 to t=500 prints for all devices were completed in one of the CYM color stations. Ghosting levels were measured against TSIDU, an internal visual scale, wherein the rating is scaled from G0 to G5.
The ghosting tests revealed that the photoconductors with the polyester containing undercoat layer has ghosting levels of G2 at t=1 and G3.5 at t=500, which are improved as compared to the levels typically observed from devices comprised of the organozirconium based undercoat layer where ghosting is usually G6, even at t=0, and similar to that of the undercoating layer without the polyester resin. The ghosting tests also revealed that the polyester containing undercoat layers performed better than the above conventional undercoat layer UC79, which is typically G3 at t=0 and G4-4.5 at t=500, under the same stress conditions. Therefore, incorporation of a polyol, melamine resin, and the above polyester adhesion promoter in combination with a metal oxide, such as titanium oxide, in the undercoat layer improved print quality, such as ghosting in that the ghosting levels were minimal or nonexistent. The testing results show that the polyester containing undercoat layer formulation exhibits essentially zero or low ghosting images even at severe testing condition.
By incorporating the polyester in the photoconductor undercoat layer, the adhesion improved from G3 to G2, based on a crosshatch peel test, compared to that of the control Comparative Examples, without the presence of the polyester adhesion promoter.
The crosshatch peel test involved the use of a utility knife cutting a crosshatch pattern of about 4 to 6 millimeter grid spacing on the photoconductor device, and adhering a piece of 1 inch Scotch tape to the pattern, then peeling off the tape. The grading is based on the amount of residuals left on the tape, with G1 almost no residue to G5 almost everything is removed.
Adhesion promoters can be selected from the following classes of materials: silicone modified polyesters, such as DC5000™ SP, available from Dura Coat Products, which is a 50 percent silicone modified polyester resin, and offers excellent scratch and chemical resistance; a siloxane polyester copolymer; glycol modified polyester such as PETG; an acrylic modified polyester, such as AROPLAZ™ 4097, available from Reichhold, which can directly crosslink with the aminoplast resin and offers excellent hardness characteristics, excellent flexibility, and chemical stability; epoxy modified polyesters, such as EPOTUF™ 404-xx-60, available from Reichhold, which is a high acid value epoxy modified polyester and offers excellent adhesion and chemical compatibility; urethane modified polyesters, such as PELLETHANE™ 2101-85A resin, available from Dow Chemical, and HYTREL™ G4074 resin, available from DuPont; polyacrylates, such as poly 4,4′-isopropylidenediphenylene terephthalate/isophthalate copolymer, and optionally mixtures thereof, and the like.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.
U.S. application No. (not yet assigned) (Attorney Docket No. 20060305-US-NP), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, on Polyarylate Containing Member, by Liang-Bih Lin et al. U.S. application No. (not yet assigned) (Attorney Docket No. 20060428-US-NP), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, on Silanol Containing Photoconductor, by Jin Wu et al. U.S. application No. (not yet assigned) (Attorney Docket No. 20060444-US-NP), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, on Phosphate Ester Containing Photoconductors, by Daniel V. Levy et al. U.S. application No. (not yet assigned) (Attorney Docket No. 20060445-US-NP), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, on Silicone Free Polyester Containing Member, by Daniel V. Levy et al. U.S. application No. (not yet assigned) (Attorney Docket No. 20060454-US-NP), filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, on Phosphoric Acid Ester Containing Photoconductors, by Jin Wu et al.
