GB2258737A - Photoreceptor. - Google Patents

Abstract

A photoreceptor comprising a charge generating layer and a charge transport layer in which both layers comprise the same binder to improve adhesion and decrease generator-transport interface reflection. A process for making such a photoreceptor preferably uses solvents having boiling points between 20 DEG C and 50 DEG C such as methylene chloride. The preferred binder is a polycarbonate and the preferred photoconductor is vanadyl phthalocyanine. A charge blocking layer such as siloxane, and a polyester layer may be applied to the support before the charge generating layer is applied.

Description

INFRA RED PHOTORECEPTOR This invention relates to photoreceptors of the type comprising a plurality of layers including a charge generator layer and a charge transport layer, and to a process for preparing such multilayered photoreceptors.

In the art of xerography, a xerographic plate comprising a photoconductive insulating layer is imaged by first uniformly depositing an electrostatic charge on the imaging surface of the xerographic plate and then exposing the plate to a pattern of activating electromagnetic radiation such as light which selectively dissipates the charge in the illuminated areas of the plate while leaving behind an electrostatic latent image in the nonilluminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the imaging surface.

A photoconductive layer for use in xerography may be a homogeneous layer of a single material such as vitreous selenium or it may be of a composite layer containing a photoconductor and another material. One type of composite photoconductive layer used in electrophotography is illustrated in U.S. Pat. No. 4,265,990. A photosensitive member is described in this patent having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer.Generally, where the two electrically operative layers are positioned on an electrically conductive layer with the photoconductive layer sandwiched between a contiguous charge transport layer and the conductive layer, the outer surface of the charge transport layer is normally charged with uniform electrostatic charge and the conductive layer is utilized as an electrode. In flexible electrophotographic imaging members, the electrode is normally a thin conductive coating supported on a thermoplastic resin web. Obviously the conductive layer may also function as an electrode when the charge transport layer is sandwiched between the conductive layer and a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.The charge transport layer in this embodiment, of course, must be capable of supporting the injection of photogenerated charges from the photoconductive layer and transporting the charges through the charge transport layer.

Various combinations of materials for charge generating layers and charge transport layers have been investigated. For example, the photosensitive member described in U.S. Pat.

NO. 4,265,990 utilizes a charge generating layer in contiguous contact with a charge transport layer comprising a polycarbonate resin and one or more of certain aromatic amine compounds.

Various generating layers comprising photoconductive layers exhibiting the capability of photogeneration of holes and injection of the holes into a charge transport layer have also been investigated. Typical photoconductive materials utilized in the generating layer include amorphous selenium, trigonal selenium, and selenium alloys such as selenium-tellurium, selenium-tellurium-arsenic, selenium-arsenic, and mixtures thereof. The charge generation layer may comprise a homogeneous photoconductive material or particular photoconductive material dispersed in a binder. Other examples of homogeneous and binder charge generation layer are disclosed in U.S. Pat. No. 4,265,990. Additional examples of binder materials such as poly(hydroxyether) resins are taught in U.S. Pat. No. 4,439,507.Photosensitive members having at least two electrically operative layers as disclosed above in, for example, U.S. Pat. No.

4,265,990, provide excellent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely developed electroscopic marking particles.

When -one or more photoconductive layers are applied to a flexible supporting substrate, it has been found that the resulting photoconductive member may delaminate during flexing, particularly when the charge generator layer is formed from a vacuum deposited or sublimated material. Delamination can be especially acute when the photoreceptor is led around small diameter support rods or drive roller. For example, photoreceptor delamination can sometimes be encountered in as few as 1,000 imaging cycles under the stressful conditions of being led around rollers having a diameter of about 2 cm. The use of adhesive interface layers containing an adhesive such as a phenoxy resin or certain polyesters causes the surface potential to decline during cycling because the flow of charges is impeded.

Further, it has been found that during cycling of photoconductive imaging members containing a vacuum deposited As2Se3 charge generator layer, charge injection dark decay can reach unacceptable levels and render the photoconductive imaging member unsuitable for forming quality images.

It has also been found that coating defects in the binder-generator layer in standard photoreceptors can account for manufacturing losses of 10% to 20%. These defects are the result of microscopic particle or fiber contamination on the substrate. Dispersed particles, such as dispersed pigment particles, can agglomerate around the foreign microscopic particle or fiber which can give rise to a binder generator layer dark spot. In addition, the binder generator solution can dewet in the area around the foreign particle creating a resist spot called a binder generator layer light spot. In both situations, particles on the order to 10 to 20 micrometers can result in coating defects on the order of 100 to 500 micrometers.

It is an object of this invention to provide an electrophotographic imaging member, and a fabricating process, which enable the above-noted disadvantages to be overcome.

The present invention by provides an electrophotographic imaging member comprising a substrate having an electrically conductive surface, a charge generator layer and a charge transport layer, both layers comprising the same binder material. In addition, the charge generator layer (which also comprises a light sensitive pigment, such as vanadyl phthalocyanine), may be formed from a solution comprising a low boiling point solvent.

Accordingly, in accordance with another aspect of the invention, there is provided an electrophotographic imaging member in which the charge generating layer (comprising a photoconductive material and a binder) is formed from a solution comprising a low boiling point solvent, more particularly a solvent having a boiling point between approximately 20"C and 50"C.

In accordance with yet another aspect of the present invention, the binder of the charge generating layer of an electrophotographic imaging member (and also the binder of the charge transport member of the imaging member) are polycarbonate resins.

Although the supporting substrate layer having an electrically conductive surface may be a conventional rigid substrate, maximum benefit is derived from an increased resistance to delamination for flexible supporting substrate layers having an electrically conductive surface. The flexible supporting substrate layer having an electrically conductive surface may be opaque or substantially transparent and may comprise any of a number of suitable materials having the required mechanical properties. For example, it may comprise an underlying flexible insulating support layer coated with a flexible electrically conductive layer, or merely a flexible conductive layer having sufficient internal strength to support the electrophotoconductive layer.The flexible electrically conductive layer, which may comprise the entire supporting substrate or merely be present as a coating on an underlying flexible web member, may comprise any suitable electrically conductive material including, for example, aluminium, titanium, nickel, chromium, brass, gold, stainless steel, carbon black, graphite, zirconium and the like. The flexible conductive layer may vary in thickness over substantially wide ranges depending on the desired use of the electrophotoconductive member.

Accordingly, the conductive layer can generally range in thicknesses of from about 50 Angstrom units to many centimeters. When a highly flexible photoresponsive imaging device is desired, the thickness of the conductive layer may be between about 100 Angstrom units to about 750 Angstrom units. Any underlying flexible support layer may be of any suitable material. Typical underlying flexible support layers of film forming polymers include insulating non-conducting materials comprising various resins such as polycarbonate resins, polyethylene terephthalate resin, polyimide resins, polyamide resin, and the like. The coated or uncoated flexible supporting substrate layer may have any number of different configurations such as, for example, a sheet, a scroll, an endless flexible belt, and the like. Preferably, the insulating web is in the form of an endless flexible belt and comprises a commerciaily available polyethylene terephthalate resin (Mylar, available from E.I. du Pont de Nemours & Co.).

Preferably, a suitable charge blocking layer may be interposed between the conductive layer and the electrophotographic imaging layer. Some materials can form a layer which functions as both an adhesive layer and charge blocking layer. Any suitable blocking layer material capable of trapping charge carriers may be utilized. Typical blocking layers include polyvinylbutyral, organosilanes, epoxy resins, polyesters, polyamides, polyurethanes, silicones and the like. If a resin is employed in the blocking layer, it should preferably have a molecular weight of between about 600 and about 200,000 and glass transition temperature of at least about 5 C. The polyvinylbutyral, epoxy resins, polyesters, polyamides, and polyurethanes can also serve as an adhesive layer.Charge blocking layers preferably have a dry thickness between about 0.005 micrometer and about 0.2 micrometers. Adhesive layers preferably have a dry thickness between about 0.01 micrometer and about 2 micrometers.

It has been found that when charge generator layers are formed from vacuum deposited or sublimated photoconductive materials such as As2Se3, amorphous selenium containing tellurium, perylene, phthalocyanine, bisazo pigments, and the like, charge injection dark decay can reach unacceptable levels and render the photoconductive imaging member unsuitable for forming quality images. Such charge injection dark decay can be markedly reduced by the use of a blocking layer comprising an amino silane reaction product, a polyvinyl butyral.or polyvinyl pyrrolidone and the like.

The silane reaction product described in U.S. Pat. No. 4,464,450 is particularly preferred as a blocking layer material because cyclic stability is extended. In other words, the blocking layer may comprise silanes having the following structural formula:

wherein R1 is an alkylidene group containing 1 to 20 carbon atoms, R2 and R3 are independently selected from the group consisting of H, a lower alkyl group containing 1 to 3 carbon atoms, a phenyl group and a poly(ethylene-amino) group, and R4, R5, and R6 are independently selected from a lower alkyl group containing 1 to 4 carbon atoms.Typical hydrolyzable silanes include 3-aminopropyltriethoxysilane, N-amino-ethyl-3aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2aminoethyl-3- aminopropyltris(ethylethoxy) silane, p-aminophenyl tri methoxysilane, 3aminopropyldiethylmethylsilane, (N,N'- dimethyl 3-amino) propyltriethoxysilane, 3aminopropylmethyldiethoxysilane, 3-aminopropyl trimethoxysilane, N methylaminopropyltriethoxysilane, methyl [2-(3-tri methoxy- silyl propylami no) ethylam ino]-3- propanoate, (N,N'-dimethyl 3-amino) propyl triethoxysilane, N,N-dimethylaminophenyltriethoxy Si lane, tri methoxysilyl propyldiethylenetri amine and mixture thereof.The blocking layer forming hydrolyzed silane solution may be prepared by adding sufficient water to hydrolyze the alkoxy groups attached to the silicon atom to form a solution. Insufficient water will normally cause the hydrolyzed silane to form an undesirable gel. Generally, dilute solutions are preferred for achieving thin coatings. Satisfactory reaction product layers may be achieved with solutions containing from about 0.1 percent by weight to about 1 percent by weight of silane based on the total weight of solution. A solution containing from about 0.01 percent by weight to about 2.5 percent by weight silane based on the total weight of solution are preferred for stable solutions which form uniform reaction product layers. The pH of the solution of hydrolyzed silane is carefully controlled to obtain optimum electrical stability.A solution pH between about4 and about 10 is preferred. Optimum blocking layers are achieved with hydrolyzed silane solutions having a pH between about 7 and about 8, because inhibition of cycling-up and cycling-down characteristics of the resulting treated photoreceptor is maximized. Control of the pH of the hydrolyzed Si lane solution may be effected with any suitable organic or inorganic acid or acidic salt. Typical organic and inorganic acids and acidic salts include acetic acid, citric acid, formic acid, hydrogen iodide, phosphoric acid, ammonium chloride, hydrofluorosilicic acid, Bromocresol Green, Bromophenol Blue, p-toluene sulphonic acid and the like.

Any suitable technique may be utilized to apply the hydrolyzed silane solution to the conductive layer. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, and the like. Generally, satisfactory results may be achieved when the reaction product of the hydrolyzed silane forms a blocking layer having a thickness between about 20 Angstroms and about 2,000 Angstroms. This siloxane coating is described in U.S. Pat.

No. 4,464,450, issued Aug. 7, 1984 to Leon A. Teuscher.

Other preferred blocking layers materials are polyvinyl butyral and polyvinyl pyrrolidone. These film forming polymers preferably have a weight average molecular weight of between about 2,000 and about 200,000.

In some cases, intermediate layers between the blocking layer and the adjacent charge generating or photogenerating material may be desired to improve adhesion or to act as an electrical barrier layer. If such layers are utilized, they preferably have a dry thickness between about 0.01 micrometer to about 2 micrometer. Typical adhesive layers include filmforming polymers such as polyester, polyvinylbutyral, polyvinyl-pyrrolidone, polyurethane, polymethyl methacrylate and the like.

The charge generating layer may contain homogeneous, heterogeneous, inorganic or organic photoconductive compositions. One example of photoconductive compositions containing a heterogeneous composition is described in U.S. Patent No. 3,121,006 wherein finely divided particles of a photoconductive inorganic compound are dispersed in an electrically insulating organic resin binder. Other well known photoconductive compositions include amorphous selenium, halogen doped amorphous selenium, amorphous selenium alloys including selenium arsenic, selenium tellurium, selenium arsenic antimony, and halogen doped selenium alloys, cadmium sulfide and the like. Often, the inorganic selenium based photoconductive materials are deposited as a relatively homogeneous layer.Moreover, many of these inorganic materials may be deposited by vacuum deposition techniques, particularly the selenium, selenium alloy and arsenic triseienide materials.

Other typical charge generating materials include metal free phthalocyanine described in U.S. Pat. No. 3,357,989, metal phthalocyanines such as copper phthalocyanine, titanyl phthalocyanine and vanadyl phthalocyanine, perylene, quinacridones available from DuPont under the tradename Monastral Red, Monastral Violet and Monastral Red Y, substituted 2,4-diamino-triazines disclosed in U.S. Pat. No. 3,442,781, polynuclear aromatic quinones available from Allied Chemical Corporation under the tradename Indofast Double Scarlet, Indofast Violet Lake B, Indofast Brilliant Scarlet and Indofast Orange; chlorodiane blue; dibromoanthanthrone; thiapyrilium, diazo compounds; triazo compounds; squaraines; and the like. Some organic charge generating materials such as phthalocyanine, peryienes and the like can be deposited by sublimation.

Any suitable inactive resin binder material, which is also suitable for use in the charge transport layer, may be employed in the charge generator layer of photoreceptors having generator layers comprising a mixture of a resin binder and photoconductive material. When using an electrically inactive or insulating resin, it is essential that there be particle-to-particle contact between the photoconductive particles. This necessitates that the photoconductive material be present in an amount of at least about 15 percent by volume of the binder layer with no limits on the maximum amount of photoconductor in the binder layer. If the matrix or binder comprises an active material, e.g. poly-N-vinylcarbazole, a photoconductive material need only to comprise about 1 percent or less by volume of the binder layer with no limitation on the maximum amount of photoconductor in the binder layer. Generally from about 5 percent by volume to about 60 percent by volume of the photogenerating pigment is dispersed in about 40 percent by volume to about 95 percent by volume of binder, and preferably from about 7 percent to about 30 percent by volume of the photogenerating pigment is dispersed in from about 70 percent by volume to about 93 percent by volume of the binder. The specific proportions selected also depend to some extent on the thickness of the generator layer. If desired, the charge generating layer may contain between about 0.5 percent by weight to about 5 percent by weight of phenoxy epoxy resin or a polyester, based on the total weight by layer.

The thickness of the photogenerating binder layer is not particularly critical. Layer thicknesses from about 0.05 micrometer to about 40.0 micrometers have been found to be satisfactory. The photogenerating binder layer containing photoconductive compositions and/or pigments, and the resinous binder material preferably ranges in thickness of from about 0.1 micrometer to about 5.0 micrometers, and has an optimum thickness of from about 0.3 micrometer to about 3 micrometers for best light absorption and improved dark decay stability and mechanical properties. A layer thickness of between about 0.1 micrometer and about 1 micrometer is preferred for homogeneous vacuum deposited or sublimated photogenerator materials because almost complete absorption of incident radiation is achieved in these thicknesses.

Other typical photoconductive layers include amorphous or alloys of selenium such as arsenic triselenide, selenium-arsenic, selenium-tellurium-arsenic, selenium-tellurium, trigonal selenium and the like dispersed in a film forming binder.

The active charge transport layer should be capable of supporting the injection of photo-generated holes and electrons from the charge generator layer and allowing the transport of these holes or electrons through the charge transport layer to selectively discharge the surface charge. The active charge transport layer not only serves to transport holes or electrons, but also protects the photoconductive layer from abrasion or chemical attack and therefore extends the operating life of the photoreceptor imaging member. The charge transport layer should exhibit negligibie, if any, discharge when exposed to a wavelength of light useful in xerography, e.g. 4000 Angstroms to 8000 Angstroms. Therefore, the charge transport layer is substantially transparent to radiation in a region in which the photoconductor is to be used.Thus, the active charge transport layer is substantially nonphotoconductive material which supports the injection of photogenerated holes from the generation layer. The active transport layer is normally transparent when exposure is effected through the active layer to ensure that most of the incident radiation is utilized by the underlying charge carrier generator layer for efficient photogeneration. When used with a transparent substrate, imagewise exposure may be accomplished through the substrate with all light passing through the substrate. In this case, the active transport material need not be transparent in the wavelength region of use.The charge transport layer in conjunction with the generation layer is material which is an insulator to the extent that an electrostatic charge placed on the transport layer is not conductive in the absence of illumination, i.e. a rate sufficient to prevent the formation and retention of an electrostatic latent image thereon.

The active charge transport layer may comprise an activating compound useful as an additive dispersed in electrically inactive polymeric film forming binder materials, making these materials electrically active. These charge transporting small molecule compounds are added to polymeric film forming binder components which are incapable of supporting the injection of photogenerated holes from the generation material and incapable of allowing the transport of these holes therethrough. This will convert the electrically inactive polymeric material to a material capable of supporting the injection of photogenerated holes from the generation material and capable of allowing the transport of these holes through the active layer in order to discharge the surface charge on the active layer.

Preferred electrically active layers comprise an electrically inactive resin material, e.g.

a polycarbonate made electrically active by the addition of one or more of the following compounds: N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1 , 1 '-biphenyl-4,4'-diamine; poly-N vinyl carbazole; poly-1 -vinyl pyrene; poly-9-vi nylanthracene; polyacenaphthalene; poly-9-(4pentenyl)-carbazole; poly-9- (S-hexyl)-carbazole; polyl methylene pyrene; poly- 1 - (pyrenyl)butadiene; N-substituted polymeric acrylic acid amides of pyrene; chlorodiane blue; N,N'diphenyl-N,N'- bis(phenylmethyl)-[1 ,1 '-biphenylj-4,4'-diamine; N,N'- diphenyl-N,N'-bis(3 methylphenyl)2,2'-dimethyl-1 ,1 '- biphenyl-4,4'-diamine and the like.

Non-film forming charge transporting small molecule materials include: Diamine transport molecules of the types described in U.S. Pat. Nos. 4,306,008, 4,304,829, 4,233,384, 4,115,116, 4,299,897, 4,265,990 and 4,081,274. Typical diamine transport molecules include N,N'-diphenyl-N,N'-bis(alkylphenyl)-[1,1'-biphenyl]-4,4'- diamine wherein the alkyl is, for example, methyl, ethyl, propyl, n-butyl, etc. such as N,N'-diphenyl-N,N'-bis(3"- methyl-phenyl) [ 1,1 '-bi phenyl]4,4'-diami ne, N,N'-diphenyl- N,N'-bis(4-methylphenyl)-!1,1'-biphenyli-4,4'- diamine, N,N'-diphenyl-N,N'-bis(2-methylphenyl)-[1,1'-biphenyl]- 4,4'-diamine, N,N'-diphenyl N,N'-bis(3-ethylphenyi)-[1,1'- biphenyll-4,4'-diamine, N,N'diphenyl-N,N'-bis(4- chlorophenyl) [1,1'-biphenyl]-4,4'-diamine, N,N'-diphenyl- N,N'-bis(phenyl-methyl)-[1,1'-biphenyll-4,4'diamine, N,N,N',N'-tetra-phenyl-[2,2'-dimethyl-1,1'-biphenyl]-4,4'- diamine, N,N,N',N'-tetra(4- methylphenyl)-[2,2'-dimethyl- 1,1 '-biphenyl]-4,4'-diamine, N,N'-diphenyl-N,N'-bis(4methyl phenyl)-[2,2'-di methyl-1,1'-biphenyl]-4,4'-diamine, N,N'-diphenyl-N,N'-bis(2methylphenyl)-[2,2'-dimethyl- 1,1'-biphenyl]-4,4'-diamine, N,N'-diphenyl-N,N'-bis(3 methylphenyl)-[2,2'-dimethyl-1 ,1 '-biphenyl]-4,4'-diamine, N,N'-diphenyl-N,N'-bis(3- methylphenyl)-pyrenyl-1,6-diamine, and the like. Pyrazoline transport molecules as disclosed in U.S. Pat. Nos. 4,315,9892, 4,278,746, and 3,837,851.Typical pyrazoline transport molecules include 1 -[lepidyl-(2)1-3-(p-diethylaminophenyl)-5-(p-diethyl- aminophenyl)pyrazoline, 1 [quinolyl-(2)]-3-(p- diethylaminophenyl)-5-(p-diethylamino-phenyl)pyrazoline, 1 -[pyridyl-(2)]-3 (p-diethylaminostyryl)-5-(p-diethyl- aminophenyl)pyrazoline, 1-[6-methoxypyridyl-(2)]-3-(p- diethylaminostyryl)-5-(p-diethylaminophenyl) pyrazoline, 1-phenyl-3-[p-dimethylaminostyryl]- 5-(p- dimethylaminostyryl)pyrazoline, 1-phenyl-3-[p- diethylaminostyryi]-5-(p- diethylaminostyryl)pyrazoline, and the like. Substituted fluorene charge transport molecules as described in U.S. Pat. No. 4,245,021. Typical fluorene charge transport molecules include 9 (4'- diemethylaminobenzylidene)fluorene, 9-(4'- methoxybenzylidene)fl uorene, 9-(2',4' dimethoxy-benzylidene) fluorene, 2-nitro-9-benzyiidenefluorene, 2-nitro-9- (4' diethylaminobenzylidene)fluorene and the like. Oxadiazole transport molecules such as 2,5bis(4-diethyl- aminophenyl)-1,3,4-oxadiazole, pyrazoline, imidazole, triazole, and others described in German Pat. Nos. 1,058,836, 1,060,260 and 1,120,875 and U.S. Pat.No. 3,895,944.

Hydrazone transport molecules including p-diethylami nobenzaldehyde(di phenylhydrazone), o-ethoxy-p-diethylaminobenzaldehyde (diphenylhydrazone), o-methyl-p diethylaminobenzaldehyde(diphenylhydrazone), o-methyl-pdimethylaminobenzaldehyde(diphenylhydrazone), p-dipropyl-aminobenzaldehyde (diphenylhydrazone), p-diethylamino-benzaldehyde-(benzylphenylhydrazone), pdibutylamino-benzaldehyde-(diphenylhydrazone), p-dimethylamino-benzaldehyde (diphenylhydrazone) and the like described, for example in U.S. Pat. No. 4,150,987.Other hydrazone transport molecules include compounds such as 1-naphthalenecarbaldehyde 1methyl-1-phenylhydrazone, 1 -naphthalenecarbaldehyde 1,1 -phenylhydrazone, 4-methoxynaphthalene-1-carbaldehyde 1 -methyl-i -phenylhydrazone and other hydrazone transport molecules described, for example in U.S. Pat. Nos. 4,385,106, 4,338,388, 4,387,147, 4,399,208 and 4,399,207.Another charge transport molecule is carbazole phenyl hydrazone such as 9methyl carbazole-3- carbaldehyde- 1,1 -di phenyl hydrazone, 9-ethylcarbazole-3- carbaldehyde-1 methyl-i -phenyl hydrazone, 9-ethylcarbazole- 3-carbaldehyde- 1-ethyl- 1 -phenyl hyd razone, 9 ethylcarbazole-3-carbaldehyde- -ethyl-i -benzyl-1 -phenylhydrazone, 9-ethylcarbazole-3- carbaldehyde-i,1-diphenylhydrazone, and other suitable carbazole phenyl hydrazone transport molecules described, for example, in U.S. Pat. No. 4,256,821. Similar hydrazone transport molecules are described, for example, in U.S. Pat. No. 4,297,426.Tri- substituted methanes such as alkyl-bis(N,N-dialkyl-aminoaryl)methane, cycloalkyl-bis(N,N-dialkylaminoaryl)methane, and cycloalkenyl-bis(N,N-dialkylaminoaryl)methane as described, for example, in U.S. Pat. No. 3,820,989. 9- fluorenylidene methane derivatives including (4-nbutoxycarbonyl-9-fluorenylidene)malonontrile, (4-phenethoxycarbonyl-9- fluorenylidene)malonontrile, (4-carbitoxy-9- fluorenylidene)malonontrile, (4-nbutoxycarbonyl-2,7- dinitro-9-fluorenylidene)malonate, and the like. Other typical transport materials include the numerous transparent organic non-polymeric transport materials described in U.S. Pat. No. 3,870,516 and the nonionic compounds described in U.S. Pat. No.

4,346,157.

Any suitable inactive polycarbonate resin binder soluble in a suitable solvent may be employed in the charge generator and charge transport layers. Generally, the polycarbonate film forming binders may be represented by the formula

wherein R is a divalent group selected from the group consisting of alkylidene, phenylidene, or cycloalkylidene and n is a number from 10 to 1,000. Typical R groups include, for example, isopropylidene, cyclohexylidene, ethylidene, isobutylidene, phenylethylidene, decahydronapthylidene, and the like. Typical inactive polycarbonate resin binders include poly(4,4'-isopropylidenediphenyl carbonate), poly[1 , 1 -cyclohexylidenebis(4- phenyl)carbonate], poly(phenolphthalein carbonate), poly(diphenylmethane bis-4-phenyl carbonate), poly[2,2-(4- methyipentane)bis-4-phenyl carbonate], and the like.Molecular weights can vary from about 20,000 to about 250,000. Other specific examples of polycarbonate resins are described, for example, in U.S. Pat. No. 4,637,971.

The preferred electrically inactive resin materials are polycarbonate resins having a molecular weight from about 20,000 to about 250,000, more preferably from about 50,000 to about 100,000. The materials most preferred as the electrically inactive resin material are a) poly(4,4'-dipropylidene-diphenylene carbonate) with a molecular weight of from about 35,000 to about 40,000, available as Lexan 145 from General Electric Company; b) poly(4,4'isopropylidene-diphenylene carbonate) with a molecular weight of from about 40,000 to about 45,000 (available as Lexan 141 from the General Electric Company); from about 50,000 to about 100,000 (available as Makrolon from Farbenafbricken Bayer A.G.); and from about 20,000 to about 50,000 (available as Merlon from Mobay Chemical Company); and c) poly(1,1cyclohexylidenebis(4- phenyl)carbonate).In place of polycarbonates could be used other organic resinous binders such as acrylate polymers, vinyl polymers, and the like. The organic resinous binders may be block, random or aiternating copolymers.

In all of the above charge transport layers, the activating compound which renders the electrically inactive polymeric material electrically active should be present in amounts of from about 15 to about 75 percent by weight. The activating compound is preferably present in the range of between about 30 percent and about 60 percent because the presence of excessive transport material causes adversely affects the mechanical properties of the layers.

The charge transport layer should be an insulator to the extent that the electrostatic charge placed on the charge transport layer is not conducted in the absence of illumination of 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 charge generator layer is preferably maintained from about 2:1 to 200:1 and in some instances as great as 400:1.

Optionally, an overcoat layer may also be utilized to improve resistance to abrasion.

These overcoating layers may comprise organic polymers or inorganic polymers that are electrically insulating or slightly semi-conductive.

Electrophotographic imaging members of this invention and as described above have improved resistance to delamination and significantly lower defects in the binder-generator layer.

A number of benefits result from utilizing the same binder material in both the charge generating and change transport layers. A significant improvement in adhesion is experienced when the same binder is used in both layers. In addition, optical problems are greatly reduced when using the same binder, as problems with reflection and refraction at the interface between the two layers are eliminated. In addition, piywood problems are also eliminated (with coherent illumination).

It has also been found that using an organic pigment at a low volume loading helps to reduce the effective index of refraction difference. In addition, no fast component of dark decay was observed.

The spectral response of the photoreceptor is from 600 to 850 nm when vanadyl phthalocyanine is incorporated into the charge generating layer. The photoreceptor is thus usabie with helium neon, LED's at 660 nm and 720 nm, visible laser diodes at 660 and 670 nm, infrared laser diodes from 780 to 850 nm, and white light.

In the prior art, different binders have been used in the charge generating and charge transport layers. The use of the same binder in adjacent layers has been considered undesirable because the solvent used for the application of the second layer would thus easily attack the binder in the first layer. It has been found that the use of low boiling point solvents decreases the time required for the solvent to evaporate and thus the time during which the solvent can attack the binder in the first layer.

Common solvents used for the application of the charge generating layer are tetrahydrofuran and toluene and mixtures thereof. In general, slow drying solvent systems, such as a tetrahydrofuran and toluene mixture, allow for good coating quality from extrusion dyes. However, such slower drying solvents allow for the binder generator layer to be wet for a longer period of time, and thus allow the binder generator layer to be susceptible to microscopic irregularities such as dirt and lint particles. A particulate pigment such as dispersed trigonal selenium particles will agglomerate around a microscopic foreign particle. This agglomeration results in a binder generator layer dark spot. In addition, the binder generator layer solution can de-wet in the area around the microscopic foreign particle which can result in a resist spot (a binder generator layer light spot). In either case, microscopic particles of only 10 to 20 micrometers can result in coating defects in the binder generator layer of the order of 100 to 500 micrometers.

It has been found that the use of faster drying solvents (i.e., solvents having lower boiling points) as a sole or major component in the binder generator layer solvent system helps to greatly reduce coating defects. Microscopic examination of photoreceptor layers coated using low boiling point solvents reveals that foreign particles are present in the binder generator layer even if low boiling point solvents are used. However, due to the use of a low boiling point solvent, the binder generator layer is able to dry before any agglomeration can occur around the microscopic foreign particles. Due to the elimination of agglomeration and dewetting, the number of unusable defective layered photoreceptors is greatly reduced in the manufacturing process.

In a preferred embodiment, the solvent should have a boiling point between approximately 200C and approximately 50"C. Methylene chloride is an example of such a solvent.

EXAMPLE 1 A polyester film was vacuum coated with a titanium layer having a thickness of about 100 Angstroms by sputtering in a vacuum in the absence of oxygen, and without breaking, vacuum sputtering an additional zirconium layer of about 100 Angstroms thickness. The exposed surface of the zirconium layer was oxidized by exposure to oxygen in the ambient atmosphere. A siloxane hole blocking layer was prepared by applying a 0.22 percent (0.001 mole) solution of 3-aminopropyl triethoxysilane to the oxidized surface of the zirconium layer with a gravure applicator. The deposited coating was dried at 135 C in a forced air oven to form a layer having a thickness of 120 Angstroms. A coating of polyester resin, Goodyear PE 100 (available from the Goodyear Tire and Rubber Co.) was applied with a gravure applicator to the siloxane coated base.The polyester resin coating was dried to form a film having a thickness of about 0.05 micrometer. A slurry coating solution of 3 percent by weight sodium doped trigonal selenium having a particle size of about 0.05 micrometer to 0.2 micrometer and about 6.8 percent by weight polyvinylcarbazole and 2.4 percent by weight N,N'-diphenyl-N,N'-bis(3 methyl phenyl-)[1,1'-biphenyl]-4,4' diamine in a 1:1 by volume mixture of tetrahydrofuran and toluene was extrusion coated onto the polyester coating to form a layer having a wet thickness of 26 micrometers. The coated member was dried at 135 C in a forced air oven to form a layer having a thickness of 2.5 micrometers.A charge transport layer was formed on this charge generator by applying a mixture of 60-40 by weight solution of Makrolon, a polycarbonate resin having a molecular weight of about 50,000 to 100,000 available from Farbenfabriken Bayer A. G., and N,N'- diphenyl-N,N'-bis(3 methyl phenyl-)[1,1'-biphenyl]-4,4' diamine dissolved in methylene chloride to give a 15 percent by weight solution. The components were extrusion coated on top of the generator layer and dried at a temperature of about 135"C to form a 24 micrometer thick dry layer of hole transporting material. A ground strip coating and an anticurl backing coating were also applied. This photoreceptor was then cut and welded to form a continuous two pitch belt.

When evaluated for resist spots and agglomerations, the yield of good belts was less than 70%. When subjected to a reverse peel adhesion test by delaminating the coating from one end of a 1 centimeter wide strip of material and pulling the delaminated coating in a direction 180 degrees from the substrate, the coated layers delaminated under a tension of about 13 grams per centimeter.

EXAMPLE 2 The procedures of example 1 were repeated except that the trigonal selenium/polyvinylcarbazole generator layer was replaced by a slurry coating solution of 0.47 percent by weight vanadyl phthalocyanine and about 2.6 percent by weight Makrolon, a polycarbonate resin having a molecular weight of about 50,000 to 100,000 available from Farbenfabriken Bayer A. G., in 96.9 percent by weight of methylene chloride that was extrusion coated onto the polyester coating to form a layer having a wet thickness of 26 micrometers.

The coated member was dried at 135 C in a forced air oven to form a layer having a thickness of 1.8 micrometers. The photoreceptor was then cut and welded to form a continuous two pitch belt.

When evaluated for resist spots and agglomerations, the yield of good belts was greater than 90%. When subjected to the reverse peel adhesion test of example 1, all attempts to initiate a delamination failed as the adhesion of the coated layers to the substrate was too greatto permit delamination.

Claims (22)

CLAIMS:

1. A process for fabricating an electrophotographic imaging member comprising the steps of: providing a supporting substrate for said imaging member; applying onto said substrate a charge generating layer solution comprising a photoconductive material, a binder and a first solvent; applying onto said charge generating layer a charge transport layer solution comprising a charge transport material, the said binder and a second solvent.

2. A process as claimed in claim 1, wherein said first solvent has a boiling point between approximately 20"C and 50 .

3. A process for fabricating an electrophotographic imaging member comprising the steps of: providing a supporting substrate for said imaging member; applying onto said substrate a charge generating layer solution comprising a photoconductive material, a first binder and a first solvent; applying onto said charge generating layer a charge transport layer solution comprising a charge transport material, a second binder and a second solvent; wherein said first solvent has a boiling point between approximately 20"C and 50 C.

4. A process as claimed in any one of the preceding claims, wherein said second solvent has a boiling point between approximately 20"C and 50"C.

5. A process as claimed in any one of the preceeding claims, wherein said first and second solvents are the same.

6. A process as claimed in any one of the preceeding claims, wherein at least one of said solvents is methylene chloride.

7. A process as claimed in any one of the preceding claims, wherein the/each binder is a polycarbonate resin.

8. A process as claimed in claim 7, wherein the molecular weight of said polycarbonate resin is from about 20,000 to about 250,000.

9. A process as claimed in claim 8, wherein the molecular weight of said polycarbonate resin is from about 50,000 to about 100,000.

10. A process as claimed in any one of claims 7 to 9, wherein said polycarbonate resin is selected from the group consisting of poly(4,4'-isopropylidene-diphenylene carbonate), poly(4,4'-dipropylidene-diphenylene carbonate), and poly(1,1-cyclohexylidene-bis(4-phenyl carbonate).

11. A process as claimed in any one of the preceding claims, wherein the photoconductive material comprises vanadyl phthalocyanine particles.

12. An electrophotographic imaging member comprising: a supporting substrate; a charge generating layer on said substrate comprising a photoconductive material and a binder; a charge transport layer on said charge generating layer comprising a charge transport material and the said binder.

13. An imaging member as claimed in claim 12, wherein said binder is an acrylate polymer or a vinyl polymer.

14. An imaging member as claimed in claim 12, wherein said binder is a polycarbonate resin.

15. An electrophotographic imaging member comprising: a supporting substrate; a charge generating layer on said substrate comprising a photoconductive material and a first binder; a charge transport layer on said charge generating layer comprising a charge transport material and a second binder; wherein said first and second binders are polycarbonate resins.

16. An imaging member as claimed in claim 14 or claim 15, wherein the molecular weight of the/each polycarbonate resin is from about 20,000 to about 250,000.

17. An imaging member as claimed in claim 16, wherein the molecular weight is from about 50,000 to about 100,000.

18. An imaging member as claimed in any one of claims 14 to 17, wherein the / each polycarbonate resin is selected from the group consisting of poly(4,4'-isopropylidenediphenylene carbonate), poly(4,4'-dipropylidene-diphenylene carbonate), and poly( 1,1 - cyclohexylidene-bis(4-phenyl carbonate).

19. An imaging member as claimed in any one of claims 12 to 18, further comprising an adhesive layer.

20. An imaging member as claimed in any one of claims 12 to 19, further comprising a blocking layer.

21. An imaging member as claimed in any of one of claims 12 to 20, substantially as described herein.

22. A process as claimed in any one of claims 1 to 11, substantially as described herein.