EP0435630A2

EP0435630A2 - Composition for imaging member layers and method for its production

Info

Publication number: EP0435630A2
Application number: EP90314186A
Authority: EP
Inventors: Stuart B. Berger; Marion H. Quinlan; Douglas J. Weatherall
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1989-12-29
Filing date: 1990-12-21
Publication date: 1991-07-03
Also published as: EP0435630A3; JPH03204653A

Abstract

An electrically conductive, semi-transparent, imaging member layer includes a polymer having carbon black particles contained therein. The polymer is obtained by dispersing carbon black particles in polymer reactants prior to and/or during polymerization of the polymer. The carbon black particles become intimately connected with other carbon black particles through polymeric chains formed when the polymer forming reactants are reacted through free radical polymerization in the presence of carbon particles. The layer can have comparable conductivity with that of dispersed carbon particles in a polymer matrix, with between 10 and 50 times less carbon black particle loading.

Description

The present invention relates to electrophotography, and more specifically, to material for a photoreceptor or electroreceptor device which provides conductivity and/or partial transparency.
In electrophotography, an electrophotographic member containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The member is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated area of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided toner particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic member to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material or may be a composite layer containing a photoconductor and another material. A multilayered photoreceptor, for example, may comprise a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer and a charge transport layer. Examples of photosensitive members having at least two electrically operative layers include the charge generator layer and diamine containing transport layer members disclosed in US-A-4,265,990; 4,233,384; 4,306,008; 4,299,897; and 4,439,507.
The operation of a photoreceptor or electroreceptor device requires the incorporation of a member which has adequate conductivity to function as a counterelectrode during use. Often this function is performed by material which is opaque to electromagnetic radiation. However, there exist machine designs which require electromagnetic radiation to be at least partially transmitted through the supporting and conducting member of the photoreceptor device, especially in the visible, infrared and/or ultraviolet regions of the electromagnetic spectrum. For example, some machine designs require illumination from behind the photoreceptor to "erase" an image from its surface to prepare it for the next use or to assist toner transfer.
Methods for providing conductivity in an imaging member have been proposed which involve dispersing carbon black particles in polymeric material. For example, US-A-4,251,612. discloses a charge injecting electrode layer comprising carbon black or graphite dispersed in a polymer in a ratio of polymer to carbon black or graphite from about 0.5 to 1 to 2 to 1.
The use of carbon black for providing electrical properties is also disclosed in US-A-4,522,906. In that patent, an electrophotographic plate-making material is provided comprising a paper support comprised of a polyolefin resin layer containing between 10 and 50% by weight electrically conductive carbon black. The dispersability of the carbon black may be improved by the addition of dispersants.
US-A-4,657,835 discloses an intermediate layer, between a substrate and a photosensitive layer, formed from a liquid dispersion comprising an electroconductive powder and a composition containing either a resin or an oligomer and a crosslinking agent, which is liquid at ordinary temperature in the absence of a solvent. A weight ratio of conductive powder to resin or oligomer ranges from about 5:1 to about 1:5. the electro-conductive powder may be carbon powder.
Japanese Published Unexamined Patent Application No. 58-93063A discloses a photoreceptor comprising a layer wherein carbon black is dispersed in a photosetting resin such as epoxy, urethane, polyester or acrylic resin. The carbon black is dispersed in the resin in an amount of between 10 and 60% of the layer by weight.
German Offenlegungsschrift No. DT 2433853 discloses an electrophotographic material comprising an interlayer of polyacrylic or polyvinyl acetate pigmented with carbon black or graphite. The layer is formed from an aqueous dispersion of polyacrylate pigmented with graphite.
Japanese Published Unexamined Patent Application No. 59-022054A discloses a photoconductor comprising a conductive layer containing conductive pigment such as carbon black and an insulating resin such as acrylic, polyester or urethane resin. The conductive layer is hardened by electrolytic dissociation radiation.
In the aforementioned disclosures incorporating carbon black into various layers of the photoreceptor, the carbon black is dispersed in a polymeric material. Quantities of carbon black large enough to provide interparticle contact (10%-60% by wt) are necessary to obtain the desired electrical effects. At such high carbon black loadings, the transparency required for some electrophotographic needs cannot be obtained unless the layer is very thin, in which case it would be inappropriate for some applications. If the dispersion of carbon black particles is decreased to obtain the required transparency, then the materials fails to provide the necessary conductivity.
A further problem with dispersions of conductive materials is that conductivity is very temperature dependent. Variations in temperature on the dispersions result in changes in the electrical properties of the dispersions which are undesirable in electrophotographic applications.
Yet a further problem of dispersions is related to conductivity at the percolation threshold of the material. At the percolation threshold, large changes in resistivity/conductivity are seen with small increases in volume loading of the conductive material. Thus, any small local changes in volume loading of the conductive material may lead to undesirable changes in conductivity locally.
A further problem is that high loadings of carbon black are difficult to incorporate and disperse into polymer. High loadings also tend to have adverse effects on mechanical and surface properties of the material. For example, addition of 15 weight percent carbon black often leads to brittleness and lowering of other physical properties.
It is therefore an object of the invention to provide an electrically conductive, substantially transparent material for electrophotographic imaging members which overcomes the shortcomings of the prior art.
According to the invention, there is provided an imaging member, characterised by: a conductive layer comprising a polymer in corporating carbon black nucleating particles. Preferably, the said polymer is obtained by reacting polymer forming reactants in the presence of carbon black nucleating particles.
The invention also provides a method for producing a conductive semitransparent layer for an imaging member, comprising:
mixing polymer forming reactants with carbon black particles to obtain a mixture;
and
performing either the step of:

(a) radically polymerizing said mixture such that said carbon black particles act as nucleating centers, and forming said polymerized mixture into a layer of said imaging member;
or the step of:
(b) forming said mixture into a layer, and radically polymerizing said mixture layer such that said carbon black particles act as nucleating centers.

The invention thus provides an electrically conductive material for an electrophotographic imaging member which may have low light absorptivity. It has uniform conductivity, and is generally electrically homogeneous.
The material of the invention provides conductive plastics material suitable for xerographic and ionographic substrates, or for anti-static components, such as business machine housings, or which can be used in electrostatic spray applications.
The resulting polymer matrix requires 10-50 times less carbon black particle loading than is required for the same conductivity if carbon black particles are merely dispersed in the polymeric material. The invention effectively increases the transparency of the material by a corresponding amount. The material may be used as a conductive material in various layers of an electrophotographic imaging member.
A more complete understanding of the present invention can be obtained by reference to the accompanying Figure, which is a cross-sectional view of a multilayer photoreceptor which may incorporate the invention.
The present invention utilizes a material, for example, as a hole injecting electrode layer, ground plane layer, ground strip layer, or other conductive layer in an electrophotographic imaging member which may comprise a substrate having a ground plane overcoated with at least one photoconductive layer. The material may be semi- transparent while maintaining electrical properties necessary for an electrophotographic imaging member.
The material of the present invention generally comprises a polymer incorporating carbon black particles. The carbon black particles of the present invention become intimately connected with other black carbon particles through polymeric chains formed when polymer forming reactants are reacted in the presence of carbon particles.
During polymerization, the carbon black particles are believed to become incorporated into the resulting polymer matrix because the carbon particles act as centers of reaction nucleation. The polymer matrix having carbon black particles intimately contained therein can provide the conductivity needed for electrophotographic applications because the carbon particles are "connected" through the polymer chain. The connections act as charge path conduits which greatly enhance conductivity. The result is that less carbon black is required to achieve a given conductivity, which in turn allows for a substantially transparent material, if desired.
Jachym, Conduction in Carbon Black-Doped Polymers, Carbon Black-Polymer Composites: The Physics of Electrically Conducting Composites, edited by Enid Keil Sichel, pp. 103-135, 1982, examined polymer-based composites containing aliphatic elements, such as polyester resins, which were modified with a small amount of acetylene carbon black. After carbon is introduced to a liquid polyester resin, a physical mixture is obtained which is then subjected to free radical polymerization. The presence of free radicals in the form of unpaired spins on the carbon black surface leads to the formation of chemical bonds between polymer chains and carbon black particles. Consequently, a low concentration of carbon black is required to render the polymer conductive. In such a system, the carbon black particles are a source of charge carriers which may move freely through the polymer chains, thus giving the desired electrical properties. Comparable conductivity in corresponding materials where the carbon black particles are not involved in the polymerization but merely dispersed in the polymer matrix, requires between 10 and 50 times as much carbon black particle loading.
The transparency of the materials of the present invention is high since less carbon black is required to achieve the requisite conductivity. The transparency corresponds approximately to an inverse function of the carbon content through the Lambert-Beers law. A substantial transparency is possible with the material of the invention. Comparable transparency in corresponding materials where carbon black particles are not involved in the polymerization, but merely dispersed in the polymer matrix, requires a comparable reduction of between 10 and 50 times the carbon black loading. At such loadings, the requisite conductivity is not obtained. For layers of the intimate carbon black-polymer system of the invention, both the requisite conductivity and transparency are provided.
Carbon black in an amount greater than about 0.5% by weight is needed for obtaining a highly conductive material. Preferably, about 0.5% to about 5% by weight of carbon black is added and contained in the polymer matrix in order to achieve the requisite conductivity and transparency for electrophotographic applications. Amounts greater the 5% can be added if a substantially transparent material is not required. The concentration of carbon black particles may be selected to be sufficiently low to avoid excessive light absorption in films and sufficiently high to give the requisite conductivity. A surface resistivity between about 102 and 109 ohms/sq is possible with the material of the invention, and is desirable in the disclosed and equivalent applications.
The carbon black can be in any of numerous available forms. The particular carbon black used may have an effect on the electrical conductivity of the polymerized composition. It is believed that these effects may depend on the electrical conductivity, particle diameter, spin concentrations, and other characteristics of the carbon blacks, which characteristics may influence the resulting polymer structure during free radical polymerization.
In fabricating the material of the present invention, carbon black particles are dispersed in polymer forming reactants prior to and/or during free radical polymerization. The polymer forming reactants can be any of those used in formulating a polymer suited for a particular purpose in an imaging member. For example,
Jachym, supra, discloses as suitable polymer forming reactants solutions of unsaturated polyesters in monomers capable of free radical polymerization. The monomers may include styrene and methyl methacrylate. Polyesters that are able to copolymerize with styrene (or methyl methacrylate) are formed as a result of polycondensation of unsaturated dicarboxylic acids or their anhydrides with glycols and with saturated dicarboxylic acids. Depending on the nature of the components and the conditions of polycondensation, resins with various physical-chemical properties are obtained. The most frequently used components of unsaturated polyesters are maleic and phthalic anhydride, adipic and succinic acid, and bifunctional alcohols such as ethylene, diethylene, propylene, or butylene glycols. Similar to this example are the thermoset polymer forming reactant solutions of vinyl esters in styrene capable of free radical polymerization.
Thermoplastic polymer forming reactants may be used in the present invention. Examples of thermoplastic polymer forming reactants include styrene, methyl methacrylate, vinyl acetate and vinyl chloride which polymerize to form thermoplastics polystyrene, polymethyl methacrylate (PMMA), polyvinyl acetate and polyvinyl chloride (PVC), respectively. Other monomers which can be polymerized through free radical polymerization include fluoropolymers, for example tetrafluoroethylene and polyvinyl fluoride.
Hardening of the above mentioned resins may occur by cross-linking of unsaturated polyester or vinyl ester chains with styrene (or methyl methacrylate) in the presence of free radical initiators. Suitable initiators may be, for example, methylethyl ketone peroxide, benzoyl peroxide, ultraviolet radiation, and the like. Application of accelerators enhances the process of hardening at room temperature. Accelerators include, for example, cobalt naphthenate, dimethylaniline, diethylaniline, and the like. The use of accelerators is not necessary, but tends to provide compositions which have higher conductivities than compositions polymerized without accelerators. Jachym, et al, Electric Conduction in Polyester Resin- Acetylene Carbon Black System, Phys Stat. Sol. (a), vol 34, pp. 657-664, 1976, noted that these differences in conductivity may result from the adsorption of accelerator on the surface of carbon black, thereby increasing the probability that the carbon black particles will become centers initiating the growth of the polymer macromolecules. There is also a probability of increasing the number of carbon black particles bonding with polymer macromolecules. The presence of accelerator also increases the cross-linking density of polyester polymer.
Similarly, thermoplastic macromolecules are formed from their reactant monomers in the presence of free radical initiators. Suitable initiators, for example, include benzoyl peroxide, 2,2'-azo-bis[2,4-dimethyl-valeronitrile] available as Vazo52 from du Pont, and the like. The carbon black loaded reactants polymerize to form a conductive thermoplastic.
The materials of the present invention can be applied to or used to form an electrophotographic imaging member by any of several techniques compatible with spray technology used for forming the layers. A conductive belt or drum substrate can be formed by centrifugal casting, extrusion or molding. A conductive layer may be applied to a substrate with suitable properties by several layer forming techniques such as spray coating, dip coating, blade coating, extrusion coating and the like. The materials may be processed as an unpolymerized mixture (as in the case of, for example, casting for a complete substrate or spray coating for a conductive layer) or after polymerization is complete, as in the case, for example, of thermoplastic molding of a complete substrate.
Typically, the carbon black/polymer coatings of the invention are applied as films having a thickness of about 1 to about 10 micrometers. However, thicknesses outside this range, for example, from submicron thicknesses to a thickness of hundreds of micrometers, may be used depending on the particular application. The mixtures may be used in electrostatic spray applications since the mixture starts out non-conductive, and becomes conductive during polymerization.
In particular, the material may be applied, for example, as a substrate/ground plane layer, a ground plane layer over a substrate layer, a ground strip layer, or any other conductive layer in an electrophotographic imaging member. The material may also be used as a conductive layer or substrate in ionographic imaging members, or as anti-static components, for example, toner rolls in imaging devices, business machine housings, and the like.
A representative structure of an electrophotographic imaging member is shown in the Figure. This imaging member is provided with an optional anti-curl layer 1, a supporting substrate 2, and electrically conductive ground plane 3, a hole blocking layer 4, an optional adhesive layer 5, a charge generating layer 6, and a charge transport layer 7. An optional overcoating layer 8 is also shown in the figure. In this device, the substrate 2 and ground plane 3 may be replaced with a conductive supporting substrate.
In the above described device, a ground strip 9 may be provided adjacent the charge transport layer at an outer edge of the imaging member. See, e.g., US-A-4,664,995. The ground strip 9 may be coated adjacent to the charge transport layer so as to provide grounding contact with a grounding device (not shown) during electrophotographic processes.
A description of the layers of the electrophotographic imaging member shown in the Figure follows.

The Supporting Substrate

The supporting substrate 2 may be opaque or substantially transparent and may comprise any of numerous suitable materials having the required mechanical properties. The substrate may further be provided with an electrically conductive surface comprising the material of the present invention. As electrically non-conducting materials, there may be employed various resins known for this purpose including polyesters, polycarbonates, polyamides, polyurethanes, and the like. The substrate may be flexible or rigid and may have any number of different configurations such as, for example, a sheet, a scroll, an endless flexible belt, a drum, and the like. Preferably, the substrate is in the form of an endless flexible belt and comprises a commercially available biaxially oriented polyester known as Mylar, available from E.I. du Pont deNemours & Co., or Melinex, available from ICI Americas Inc.
Alternatively, the substrate may comprise the material of the present invention, without the need for a separate, electrically conducting ground plane layer.
The thickness of the substrate layer depends on numerous factors, including economic considerations. If the substrate is to be coated with a conducting ground plane layer comprising the material of the present invention, the thickness of the substrate layer may range from abut 65 micrometers to about 150 micrometers, and preferably from about 75 micrometers to about 125 micrometers for optimum flexibility and minimum induced surface bending stress when cycled around small diameter rollers, e.g., 19 millimeter diameter rollers. The substrate for a flexible belt or rigid drum may be of substantial thickness, for example, over 200 micrometers, or of minimum thickness, for example less than 50 micrometers, provided there are no adverse effects on the final photoconductive device.

The Electrically Conductive Ground Plane

The electrically conductive ground plane layer 3 (conductive layer) may comprise the material of the invention coated on a non-conducting substrate or conducting substrate. The layer may be formed on the substrate 2 by any suitable coating technique. The conductive layer may vary in thickness over substantially wide ranges depending on the optical transparency and flexibility desire for the electrophotoconductive member. Accordingly, for a flexible photoresponsive imaging device, the thickness of the conductive layer may be any thickness which will provide the required conductivity. Preferably, the ground plane layer has a surface resistivity less than about 10⁵ ohms/sq.

The Charge Blocking Layer

After deposition of the electrically conductive ground plane layer, the charge blocking layer 4 may be applied thereto. A charge blocking layer for a positively charged photoreceptor allows holes from the imaging surface of the photoreceptor to migrate toward the conductive layer. For negatively charged photoreceptors, any suitable hole blocking layer capable of forming a barrier to prevent hole injection from the conductive layer to the opposite photoconductive layer may be utilized. The charge blocking layer may include polymers such as polyvinylbutyral, epoxy resins, polyesters, polysiloxanes, polyamides polyurethanes and the like, or may be nitrogen containing siloxanes or nitrogen containing titanium compounds such as trimethoxysilyl propylene diamine, hydrolyzed trimethoxysilyl propyl ethylene diamine, N- beta-(aminoethyl) gamma-amino-propyl trimethoxy silane, isopropyl 4-aminobenzene sulfonyl, di(dodecylbenzene sulfonyl) titanate, isopropyl di(4-aminobenzoyl)isostearoyl titanate, isopropyl tri(N-ethylamino-ethylamino)titanate, isopropyl trianthranil titanate, isopropyl tri(N,N-dimethylethylamino)titanate, titanium-4-amino benzene sulfonate oxyacetate, titanium 4-aminobenzoate isostearate oxyacetate, [H₂N(CH₂)₄]CH₃Si(OCH₃)₂ (gamma-aminobutyl) methyl diethoxysilane, and [H₂N(CH₂)₃]CH₃Si(OCH₃)₂ (gamma- aminopropyl) methyl diethoxysilane, as disclosed in US-A-4,291,110, 4,338,387 and 4,286,033.
The charge blocking layer should be continuous and have a thickness of less than about 0.5 micrometers because greater thicknesses may lead to undesirably high residual voltage. A charge blocking layer of between about 0.005 micrometer and about 1 micrometer is preferred because charge neutralization after the exposure step is facilitated and optimum electrical performance is typically achieved. The blocking layer may be applied by any suitable 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. For convenience in obtaining thin layers, the blocking layer is preferably applied in the form of a dilute solution, with the solvent being removed after deposition of the coating by techniques such as by vacuum, heating and the like. Generally, a weight ratio of hole blocking layer material and solvent of between about 0.05:100 to about 0.5:100 is satisfactory for spray coating.

The Adhesive Layer

In most cases, intermediate layers between the injection blocking layer and the adjacent charge generating or photogenerating layer may be desired to promote adhesion. For example, the adhesive layer 5 may be employed. If such layers are utilized, they preferably have a dry thickness between about 0.001 micrometer to about 0.2 micrometer. Typical adhesive layers include film- forming polymers such as polyester, du Pont 49,000 resin (available from E.I. du Pont de Nemours & Co.), Vitel- PE100 (available from Goodyear Rubber & Tire Co.), polyvinylbutyral, polyvinylpyrrolidone, polyurethane, polymethyl methacrylate, and the like.

The Charge Generating Layer

Any suitable charge generating (photogenerating) layer 6 may be applied to the adhesive layer 5. Examples of materials for photogenerating layers include inorganic photoconductive particles such as amorphous selenium, trigonal selenium, and selenium alloys selected form the group consisting of selenium-tellurium, selenium-tellurium-arsenic, selenium arsenide and phthalocyanine pigment such as the X-form of metal free phthalocyanine described in US-A-3,357,989, metal phthalocyanines such as vanadyl phthalocyanine, titanyl phthalocyanine and copper phthalocyanine, dibromoanthanthrone, squarylium, quinacridones available from du Pont under the tradename Monastral Red, Monastral Violet and Monastral Red Y, Vat orange 1 and Vat orange 3 (trade names for dibromo anthanthrone pigments), benzimidazole perylene, substituted 2,4- diamino-triazines disclosed in US-A-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, and the like, dispersed in a film forming polymeric binder. Other suitable photogenerating materials known in the art may also be utilized, if desired. Charge generating layers comprising a photoconductive material such as amorphous silicon, microcrystalline silica, vanadyl phthalocyanine, metal free phthalocyanine, benzimidazole perylene, amorphous selenium, trigonal selenium, selenium alloys such as selenium-tellurium, selenium-tellurium-arsenic, selenium arsenide, and the like and mixtures thereof, are especially preferred because of their sensitivity to white light. Vanadyl phthalocyanine, metal free phthalocyanine and tellurium alloys are also preferred because these materials provide the additional benefit of being sensitive to infra-red light.
Any suitable polymeric film forming binder material may be employed as the matrix in the photogenerating binder layer. Typical polymeric film forming materials include those described, for example, in US-A-3,121,006. The binder polymer should adhere well to the adhesive layer, dissolve in a solvent which also dissolves the upper surface of the adhesive layer and be miscible with the copolyester of the adhesive layer to form a polymer blend zone. Typical solvents include monochlorobenzene, tetrahydrofuran, cyclohexanone, methylene chloride, 1,1,1-trichloromethane, 1,1,2-trichloromethane, dichloroethylene, toluene, and the like, and mixtures thereof. Mixtures of solvents may be utilized to control evaporation range. For example, satisfactory results may be achieved with a tetrahydrofuran to toluene ratio of between about 90:10 and about 10:90 by weight. Generally, the combination of the photogenerating pigment, binder polymer and solvent should form uniform dispersions of the photogenerating pigment in the charge generating layer coating composition. Typical combinations include polyvinylcarbazole, trigonal selenium and tetrahydrofuran; phenoxy resin, trigonal selenium and toluene; and polycarbonate resin, vanadyl phthalocyanine and methylene chloride. The solvent for the charge generating layer binder polymer should dissolve the polymer binder utilized in the charge generating layer and be capable of dispersing the photogenerating pigment particles present in the charge generating layer.
The photogenerating composition or pigment is present in the resinous binder composition in various amounts. 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 90 percent by volume of the resinous binder. 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. In another embodiment about 90% of the photogenerating pigment is dispersed in about 10% binder.
The photogenerating layer containing photoconductive compositions and/or pigments and the resinous binder material generally ranges in thickness of from about 0.1 micrometer to about 5.0 micrometers, and preferably has a thickness of from about 0.3 micrometer to about 3 micrometers. The photogenerating layer thickness is related to pigment content. Higher binder content compositions generally require thicker layers for photogeneration. Thicknesses outside these ranges can be selected providing the objectives of the present invention are achieved. Any suitable and conventional technique may be utilized to mix and thereafter apply the photogenerating layer coating mixture to the previously dried adhesive layer. 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, to remove substantially all of the solvents utilized in applying the coating.

The Charge Transport Layer

The active charge transport layer 7 may comprise any suitable transparent organic polymer of non-polymeric material capable of supporting the injection of photo- generated holes and/or electrons from the charge generating layer 6 and allowing the transport of these holes of electrons through the organic 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 negligible, if any, discharge when exposed to a wavelength of light useful in xerography, e.g. 400 nm to 900 nm. 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 a material which supports the injection of photogenerated holes or electrons from the charge generating layer. The active charge transport layer is normally transparent when exposure is effected therethrough to ensure that most of the incident radiation is utilized by the underlying charge generating layer for efficient photogeneration. When used with a transparent substrate, imagewise exposure or erase may be accomplished through the substrate with all light passing through the substrate. In this case, the active transport material need not be transmitting in the wavelength region of use. The charge transport layer in conjunction with the charge generating layer is insulative to the extent that an electrostatic charge placed on the charge transport layer is not conducted in the absence of illumination.
The active charge transport layer may comprise an activating compound useful as an additive dispersed in electrically inactive polymeric materials, making these materials electrically active. These compounds may be added to polymeric materials which are incapable of supporting the injection of photogenerated holes from the charge generating layer and incapable of allowing the transport of these holes. This will convert the electrically inactive polymeric material to a material capable of supporting the injection of photogenerated holes from the charge generating layer and capable of allowing the transport of these holes through the active charge transport layer in order to discharge the surface charge on the active charge transport layer. An especially preferred charge transport layer employed in multilayer photoconductors comprises from about 25 percent to about 75 percent by weight of at least one charge transporting aromatic amine compound, and about 75 percent to about 25 percent by weight of a polymeric film forming resin in which the aromatic amine is soluble.
The charge transport layer forming mixture may comprise an aromatic amine compound of one or more compounds having the formula:

wherein R₁ and R₂ are each an aromatic group selected from the group consisting of a substituted or unsubstituted phenyl group, naphthyl group, and polyphenyl group and R₃ is selected from the group consisting of a substituted or unsubstituted aryl group, alkyl groups having from 1 to 18 carbon atoms and cycloaliphatic groups having from 3 to 18 carbon atoms. The substituents should be free from electron withdrawing groups such as NO₂ groups, CN groups, and the like.
Typical aromatic amine compounds that are
represented by this structural formula include:

wherein R₁ and R₂ are as defined above, and R₄ is selected from the group consisting of a substituted or unsubstituted biphenyl group, diphenyl ether group, alkyl group having from 1 to 18 carbon atoms, and cycloaliphatic group having from 3 to 12 carbon atoms. The substituents should be free from electron withdrawing groups such as NO₂ groups, CN groups, and the like.
Examples of charge transporting aromatic amines represented by the structural formulae above for charge transport layers capable of supporting the injection of photogenerated holes of a charge generating layer and transporting the holes through the charge transport layer include triphenylmethane, bis(4-diethylamine-2-methylphenyl)phenylmethane; 4'-4"-bis(diethylamino)-2',2"-dimethyltriphenylmethane; N',N"-bis(alkylphenyl)-(1,1'-biphenyl)-4,4'-diamine wherein the alkyl is, for example, methyl, ethyl, propyl, n-butyl, etc., N,N'-diphenyl-N,N'-bis(3"methylphenyl)-(1,1'biphenyl)-4,4'-diamine, and the like, dispersed in an inactive resin binder.
Any suitable inactive resin binder soluble in methylene chloride or other suitable solvent may be employed. Typical inactive resin binders soluble in methylene chloride include polycarbonate resin, polyvinylcarbazole, polyester, polyarylate, polyacrylate, polyether, polysulfone, and the like. Molecular weights can vary from about 20,000 to about 1,500,000. Other solvents that may dissolve these binders include monochlorobenzene, tetrahydrofuran, toluene, dichloroethylene, 1,1,2-trichloroethane, 1,1,1-trichloroethane, and the like.
The preferred electrically inactive resin materials are polycarbonate resins having a molecular weight from about 20,000 to about 120,000, more preferably from about 50,000 to about 100,000. The materials most preferred as the electrically inactive resin material are 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; poly(4,4'-isopropylidene-diphenylene carbonate) with a molecular weight of from about 40,000 to about 45,000, available as Lexan 141 from General Electric Company; a polycarbonate resin having a molecular weight of from about 50,000 to about 100,000, available as Makrolon from Farben Fabricken Bayer A.G.; a polycarbonate resin having a molecular weight of from about 20,000 to about 50,000 available as Merlon from Mobay Chemical Company; polyether carbonates; and 4,4'-cyclohexylidene diphenyl polycarbonate. Methylene chloride solvent is a desirable component of the charge transport layer coating mixture for adequate dissolving of all the components and for its low boiling point.
An especially preferred multilayered photoconductor comprises a charge generating layer comprising a binder layer of photoconductive material and a contiguous hole transport layer of a polycarbonate resin material having a molecular weight of from about 20,000 to about 120,000 having dispersed therein from about 25 to about 75 percent by weight of one or more compounds having the formula:

wherein X is selected from the group consisting of an alkyl group having from 1 to about 4 carbon atoms and chlorine, the photoconductive layer exhibiting the capability of photogeneration of holes and injection of the holes, the hole transport layer being substantially non- absorbing in the spectral region at which the photoconductive layer generates and injects photogenerated holes but being capable of supporting the injection of photogenerated holes from the photoconductive layer and transporting the holes through the hole transport layer.

The Ground Strip

The material of the present invention may also be used as an electrically conductive ground strip layer 9. The ground strip 9 may be coated in a thickness sufficient to provide the requisite conductivity and durability.

The Anti-Curl Layer

The anti-curl layer 1 may comprise organic polymers or inorganic polymers that are electrically insulating or slightly semi-conductive. The anti-curl layer provides flatness and/or abrasion resistance.
Anticurl layer 1 may be formed at the back side of the substrate 2, opposite to the imaging layers. The anticurl layer may comprise a film forming resin and an adhesion promoter polyester additive. Examples of film forming resins include polyacrylate, polystyrene, poly(4,4'-isopropylidene diphenyl carbonate), 4,4'-cyclohexylidene diphenyl polycarbonate, and the like. Typical adhesion promoters used as additives include 49,000 (du Pont), Vitel PE-100, Vitel PE-200, Vitel PE-307 (Goodyear), and the like. Usually from about 1 to about 5 weight percent adhesion promoter is selected for film forming resin addition. The thickness of the anticurl layer is from about 3 microns to about 35 microns, and preferably about 14 microns.

The Overcoating Layer

The optional overcoating layer 8 may be provided as a protective layer. The overcoating layer 8 may comprise organic or inorganic polymers that are electrically insulating or slightly semiconductive.
The invention will be further illustrated with respect to specific embodiments thereof, it being understood that these examples are intended to be illustrative only, and that the invention is not intended to be limited to the materials, conditions, process parameters and the like recited therein.

Examples

Experiments are performed to demonstrate the feasibility of the invention.
Two parts carbon black per hundred parts resin are mixed with vinyl ester resin (Ashland Hetron 980). The mixture is promoted and cured. The resulting composite has a resistance in the kilo-ohm level (as measured by a multi-meter).
Three parts carbon black per hundred parts resin are mixed with vinyl ester resin (Ashland D-1222). The mixture is promoted and cured. The resulting composite has a resistance in the hundreds of ohms level (as measured by a multi-meter).
2.5 parts carbon black per hundred parts monomer are mixed with styrene monomer. The mixture is initiated and bulk polymerized. The resulting polymer has a resistance in the hundreds of ohms level (as measured by a multi-meter). TGA analysis (in case of monomer evaporation) shows 2.56 weight percent carbon black in the sample.
Three parts carbon black per hundred parts monomer are mixed with methylacrylate monomer. The mixture is initiated and bulk polymerized. The resulting polymer has a resistance in the kilo-ohm range (as measure by a multi-meter). TGA analysis shows 3.75 weight percent carbon black in the sample.
While the present invention has been described with reference to particular preferred embodiments, the invention is not limited to the specific examples given, and other embodiments and modifications can be made by those skilled in the art without departing from the scope of the invention.

Claims

An imaging member, characterised by:
a conductive layer comprising a polymer incorporating carbon black nucleating particles.
The imaging member of claim 1, wherein said polymer is obtained by reacting polymer forming reactants in the presence of carbon black nucleating particles.
The imaging member of claim 2, wherein said carbon black nucleating particles are present in an amount of 0.5% to 5% by weight.
The imaging member of claim 2 or claim 3, wherein said polymer forming reactants are unsaturated esters or vinyl esters in monomers or oligomers capable of free radical polymerization.
The imaging member of claim 2 or claim 3, wherein said polymer forming reactants are selected from styrene, methyl methacrylate, vinyl acetate and vinyl chloride.
The imaging member of any one of claims 2 to 5, wherein said polymer forming reactants form a thermoset or thermoplastic polymer through free radical polymerization.
The imaging member of any one of claims 1 to 6, wherein said layer has a surface resistivity less than about 10⁵ ohm/sq.
The imaging member of any one of claims 1 to 7, wherein said layer is substantially transparent.
A method for producing a conductive semitransparent layer for an imaging member, comprising:
mixing polymer forming reactants with carbon black particles to obtain a mixture;
and
performing either the step of:
(a) radically polymerizing said mixture such that said carbon black particles act as nucleating centers, and forming said polymerized mixture into a layer of said imaging member;
or the step of:

(b) forming said mixture into a layer, and radically polymerizing said mixture layer such that said carbon black particles act as nucleating centers.