GB1577237A

GB1577237A - Electrophotographic imaging member

Info

Publication number: GB1577237A
Application number: GB34705/77A
Authority: GB
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1976-08-23
Filing date: 1977-08-18
Publication date: 1980-10-22
Also published as: JPS599049B2; NL186474C; CA1104866A; DE2734990C2; BR7705593A; JPS5327033A; SU1378794A3; MX148708A; MX171443B; NL7709279A; DE2734990A1; FR2363134A1; FR2363134B1

Description

(54) ELECTROPHOTOGRAPHIC IMAGING MEMBER (71) We, XEROX CORPORATION of Rochester, New York State, United States of America, a Body Corporate organized under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates in general to xerography and, more specifically, to an electrophotographic imaging member and method of use.

In the art of xerography, a xerographic plate containing a photoconductive insulating layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulator while leaving behind a latent electrostatic image in the non-illuminated areas. This latent electrostatic image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer.

A photoconductive layer for use in xerography may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite photoconductive layer used in xerography is illustrated by U.S.

Patent 3,121,006 to Middleton and Reynolds which describes a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In its present commercial form, the binder layer contains particles of zinc oxide uniformly dispersed in a resin binder and coated on a paper backing.

In the particular examples described in Middleton et al, the binder comprises a material which is incapable of transporting injected charge carriers generated by the photoconductor particles for any significant distance. As a result, with the particular material disclosed in Middleton et at patent, the photoconductor particles must be, in substantially continuous particle-to-particle contact throughout the layer in order to permit the charge dissipation required for cyclic operation. Therefore, with the uniform dispersion of photoconductor particles described in Middleton et al, a relatively high volume concentration of photoconductor, about 50 percent by volume. is usually necessary in order to obtain sufficient photoconductor particleto-particle contact for rapid discharge.

However, it has been found that high photoconductor loadings in the binder result in the physical continuity of the resin being destroyed, thereby significantly impairing the mechanical properties of the binder layer. Systems with high photoconductor loadings are often characterized as having little or no flexibility. On the other hand, when the photoconductor concentration is reduced appreciably below about 50 percent by volume, the photo-induced discharge rate is reduced, making high speed cyclic or repeated imaging difficult or impossible.

U.S. Patent 3,037,861 to Hoegl et al teaches that poly(N - vinylcarbazole) exhibits some long-wave length U.V.

sensitivity and suggests that its spectral sensitivity can be extended into the visible spectrum by the addition of dye sensitizers.

The Hoegl et al patent further suggests that other additives such as zinc oxide or titanium dioxide may also be used in coniunction with poly(N - vinylcarbazole).

In the Hoegl et al patent, the poly(N - vinylcarbazole) is intended to be used as a photoconductor, with or without additive materials which extend its spectral sensitivity.

In addition to the above, certain specialized layered structures particularly designed for reflex imaging have been proposed. For example, U.S. Patent 3,165,405 to Hoesterey utilizes a twolayered zinc oxide binder structure for reflex imaging. The Hoesterey patent utilizes two separate contiguous photoconductive layers having different spectral sensitivities in order to carry out a particular reflex imaging sequence. The Hoesterey device utilizes the properties of multiple photoconductive layers in order to obtain the combined advantages of the separate photoresponse of the respective photoconductive layers.

It can be seen from a review of the conventional composite photoconductive layers cited above, that upon exposure to light, photoconductivity in the layered structure is accomplished by charge transport through the bulk of the photoconductive layer, as in the case of vitreous selenium (and other homogeneous layered modifications). In devices employing photoconductive binder structures which include inactive electrically insulating resins such as those described in the Middleton et al, U.S.

Patent 3,121,006, conductivity or charge transport is accomplished through high loadings of the photoconductive pigment and allowing particle-to-particle contact of the photoconductive particles. In the case of photoconductive particles dispersed in a photoconductive matrix, such as illustrated by U.S. Patent 3,121,007, photoconductivity occurs through the generation and transport of charge carriers in both the photoconductive matrix and the photoconductor pigment particles.

Although the above patents rely upon distinct mechanisms of discharge throughout the photoconductive layer, they generally suffer from common deficiencies in that the photoconductive surface during operation is exposed to the surrounding environment, and particularly in the case of repetitive xerographic cycling where these photoconductive layers are susceptible to abrasion, chemical attack, heat and multiple exposure to light. These effects are characterized by a gradual deterioration in the electrical characteristics of the photoconductive layer resulting in the printing out of surface defects and scratches, localized areas of persistent conductivity which fail to retain an electrostatic charge, and high dark discharge.

In addition to the problems noted above, these photo-receptors require that the photoconductor comprise either a hundred percent of the layer, as in the case of the vitreous selenium layer, or that they preferably contain a high proportion of photoconductive material in the binder configuration. The requirements of a photoconductive layer containing all or a major proportion of a photoconductive material further restricts the physical characteristics of the final plate, drum or belt in that the physical characteristics such as flexibility and adhesion of the photoconductor to a supporting substrate are primarily dictated by the physical properties of the photoconductor, and not by the resin or matrix material which is preferably present in a minor amount.

Another form of a composite photosensitive layer which has also been considered by the prior art includes a layer of photoconductive material which is covered with a relatively thick plastic layer and coated on a supporting substrate.

U.S. Patent 3,041,166 to Bardeen describes such a configuration in which a transparent plastic material overlies a layer of vitreous selenium which is contained on a supporting substrate, In operation, the free surface of the transparent plastic is electrostatically charged to a given polarity.

The device is then exposed to activating radiation which generates a hole-electron pair in the photoconductive layer. The electrons move through the plastic layer and neutralize positive charges on the free surface of the plastic layer thereby creating an electrostatic image. Bardeen, however, does not teach any specific plastic materials which will function in this manner, and confines his examples to structures which use a photoconductor material for the top layer.

U.S. Patent 3,598,582 to Herrick et al describes a special purpose composite photosensitive device adapted for reflex exposure by polarized light. One embodiment which employs a layer of dichroic organic photoconductive particles arrayed in oriented fashion on a supporting substrate and a layer of poly(N - vinylcarbazole) formed over the oriented layer of dichroic material. When charged and exposed to light polarized perpendicular to the orientation of the dichroic layer, the oriented dichroic layer and poly(N - vinylcarbazole) layer are both substantially transparent to the initial exposure light.

When the polarized light hits the white background of the document being copied, the light is depolarized, reflected back through the device and absorbed by the dichroic photoconductive material. In another embodiment, the dichroic photoconductor is dispersed in oriented fashion throughout the layer of poly(N vinylcarbazole).

Belgian Patent 763,540, issued August 26, 1971 discloses an electrophotographic member having at least two electrically operative layers. The first layer comprises a photoconductive layer which is capable of photogenerating charge carriers and injecting the photogenerated holes into a contiguous active layer. The active layer comprises a transparent organic material which is substantially non-absorbing in the spectral region of intended use, but which is "active" in that it allows injection of photogenerated holes from the photoconductive layer, and allows these holes to be transported to the active layer.

The active polymers may be mixed with inactive polymers or non-polymeric material.

Gilman, U.S. Defensive Publication of Serial Number 93,449, filed November 27, 1970, published in 888 O.G. 707 on July 20, 1970, Defensive Publication No P888.013, U.S. Cl. 96/1.5, discloses that the speed of an inorganic photoconductor such as amorphous selenium can be improved by including an organic photoconductor in the electrophotographic element. For example, an insulating resin binder may have TiO2 dispersed therein or it may be a layer of amorphous selenium. This layer is overcoated with a layer of electrically insulating binder resin having an organic photoconductor such as 4,4' - diethylamino - 2,2' - dimethyltriphenyl - methane dispersed therein.

"Multi-Active Photoconductive Element", Martin A. Berwick, Charles J.

Fox and William A. Light, Research Disclosure, Vol. 133; pages 38-43, May 1975, was published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, England. This disclosure relates to a photoconductive element having at least two layers comprising an organic photoconductor containing a chargetransport layer in electrical contact with an aggregate charge-generation layer. Both the charge-generation layer and the chargetransport layer are essentially organic compositions. The charge-generation layer contains a continuous, electrically insulating polymer phase and a discontinuous phase comprising a finelydivided, particulate co-crystalline complex of (1) at least one polymer having an alkylidene diarylene group in a recurring unit and (2) at least one pyrylium-type dye salt.The charge-transport layer is an organic material which is capable of accepting and transporting injected charge carriers from the charge-generation layer.

This layer may comprise ait insulating resinous material having 4,4' - bis(diethylamino) - 2,2' - dimethyl-triphenylmethane dispersed therein.

Fox, U.S. Patent 3,265,496, discloses that N,N,N',N' - tetraphenylbenzidine may be used as photoconductive material in electrophotographic elements. This compound is not sufficiently soluble in the resin binders used in the present invention to permit a sufficient rate of photo-induced discharge.

Straughan, U.S. Patent 3,312,548, in pertinent part, discloses a xerographic plate having a photoconductive insulating layer comprising a composition of selenium, arsenic and a halogen. The halogen may be present in amounts from 10 to 10,000 parts per million. This patent further discloses a xerographic plate having a support, a layer of selenium and an overlayer of a photoconductive material comprising a mixture of vitreous selenium, arsenic and a halogen.

According to the present invention, there is provided an electrophotographic imaging member comprising a charge generation layer, and a contiguous charge transport layer of electrically inactive (as herein defined) organic resinous material having dispersed therein one or more compounds having the general formula:

wherein each X independently is CH3 or Cl, said charge generation layer exhibiting the capability of photogeneration of holes and injection of said holes, and said charge transport layer being capable of supporting the injection of photogenerated holes from said charge generation layer and transporting said holes through said charge transport layer.

Most organic charge transporting layers using active materials dispersed in organic binder materials have been found to trap charge carriers causing an unacceptable build-up of residual potential when used in a cyclic mode in electrophotography. Also, most known organic charge transporting materials when used in a layered configuration contiguous to an amorphous selenium charge generating layer have been found to trap charge at the interface between the two layers. This results in lowering the potential differences between the illuminated and non-illuminated regions when these structures are exposed to an image. This in turn, lowers the print density of the end product, i.e., the electrophotographic copy.

Another consideration which is necessary in the system is the glass transition temperature (Tg). The (T ) of the transport layer has to be substantially higher than the normal operating temperatures. Many organic charge transporting layers using active materials dispersed in organic binder material have unacceptably low (T,) at loadings of the active material in the organic binder material which is required for efficient charge transport. This results in the softening of the matrix of the layer which, in turn, becomes susceptible to impaction of dry developers and toners. Another unacceptable feature of a low (Tg) is the case of leaching or exudation of the active materials from the organic binder material resulting in degradation of charge transport properties from the charge transport layer.

It has now been found, in accordance with the invention, that

as defined above, dispersed in an organic binder, can transport charge very efficiently substantially without any trapping when this layer is used contiguous with a generation layer and subjected to charge/light discharge cycles in an electrophotographic mode, there being substantially no buildup of the residual potential over many thousands of cycles.

The above described small molecules due to the presence of solubilizing groups, such as, methyl (CH3) or chlorine (Cl) are substantially more soluble in resin binders described herein whereas unsubstituted tetra phenyl benzidine, is not sufficiently soluble in the resin binders.

Furthermore, when the diamines used in the present invention dispersed in a binder are used as transport layers contiguous a charge generation layer, there is substantially no interfacial trapping of the charge photogenerated in and injected from the generating layer. When subjected to ultra-violet radiation as encountered in a normal xerographic machine environment, substantially no deterioration in charge transport was observed in these transport layers containing the diamines used in the present invention, the diamines remaining stable and maintaining their electrical properties. Also, the diamines, do not crystallise and become insoluble in the resin material in which they are dispersed.

Furthermore, such diamines dispersed in a binder have been found to have sufficiently high (Tg) even at high loadings, thereby eliminating the problems associated with low (T,) as discussed above.

None of the above-mentioned prior art overcomes the above-mentioned problems.

Furthermore, none of the above-mentioned prior art discloses specific charge generating material in a separate layer which is overcoated with a charge-transport layer comprising an electrically insulating resinous matrix material comprising an electrically inactive resinous material having dispersed therein the diamines used in the present invention. The charge transport material generally should be substantially non-absorbing in the spectral region of intended use, but is "active" in that it allows injection of photogenerated holes from the charge generation layer and allows these holes to be transported therethrough. The charge-generating layer is a photoconductive layer which is capable of photo-generating and injecting photogenerated holes into the contiguous charge-transport layer.

It has also been found that when an alloy of selenium and arsenic containing a halogen is used as a charge carrier generation layer in a multilayered device which contains a contiguous charge carrier transport layer, the member, as a result of using this particular charge generation layer, has unexpectedly high contrast potentials as compared to similar multilayered members employing cther generating layers. Contrast potentials are important characteristics which determine print density.

In accordance with a preferred embodiment, the charge generation layer comprises a mixture of amorphous selenium, arsenic and a halogen. Arsenic is present in amounts from 0.5 percent to 50 percent by weight and the halogen is present in amounts from 10 to 10,000 parts per million with the balance being amorphous selenium. This layer is capable of photogenerating and injecting photogenerated holes into the contiguous or adjacent charge transport layer. In accordance with this preferred embodiment, the charge transport layer consists essentially of an electrically inactive resinous material having dispersed therein from 10 to 75 percent by weight of the aforementioned diamines.

The charge transport layer of imaging members of the invention is electrically active, i.e. the material of the charge transport layer is capable of supporting the injection of photogenerated holes from the charge generating material and capable of allowing the transport of these holes through the electrically active layer in order to discharge a surface charge on the electrically active layer.

"Electrically inactive" when used to describe the organic material which does not contain any diamine of the kind used in the present invention means that the material is not capable of supporting the injection of photogenerated holes from the generating material and is not capable of allowing the transport of these holes through the material.

It should be understood that the electrically inactive resinous material which becomes electrically active when it contains from about 10 to about 75 percent by weight of the aforementioned diamine generally does not function as a photoconductor in the wavelength region of intended use. As stated above, hole-electron pairs are photogenerated in the photoconductive layer and the holes are then injected into the active layer and hole transport occurs through this active layer.

A typical application of the present invention involves the use of a layered configuration member which in one embodiment consists of a supporting substrate such as a conductor containing a photoconductive layer thereon. For example, the photo-conductive layer may be in the form of amorphous, vitreous or trigonal selenium or alloys of selenium such as selenium-arsenic, selenium-telluriumarsenic and selenium-tellurium. The charge transport .layer is coated over the selenium photoconductive layer. Generally, a thin interfacial barrier or blocking layer is sandwiched between the photoconductive layer and the substrate. The barrier layer may comprise any suitably electrically insulating material such as metallic oxide or organic resin.The use of the electrically inactive resinous material such as a polycarbonate containing the diamine allows one to take advantage of placing a photoconductive layer adjacent to a supporting substrate and protecting the photoconductive layer with a top surface which will allow for the transport of photogenerated holes from the photoconductor.

This structure can then be imaged in the conventional xerographic manner which usually includes charging, optical projection exposure and development.

As mentioned, when an alloy of selenium and arsenic containing a halogen is used as a charge carrier generation layer in a multilayered device which contains a contiguous charge carrier transport layer, the member, as a result of using this particular charge generation layer has unexpectedly high contrast potentials as compared with similar multilayered members using different generator layer materials.

In general, the advantages of the improved structure and method of imaging will become apparent upon consideration of the following disclosure of the invention especially when taken in conjunction with the accompanying drawings wherein: Fig. 1 is a schematic illustration of one .embodiment of a device of the present invention.

Fig. 2 illustrates a second embodiment of the device for the present invention.

Fig. 3 illustrates a third embodiment of the device of the present invention.

Fig. 4 illustrates a fourth embodiment of the device of the present invention.

In the drawings, Figs. 1--4 represent several variations of imaging members in accordance with the invention. They are all basically similar in that they comprise a substrate, a charge generation layer thereon and a charge transport layer over the generation layer.

In Fig. 1, photoreceptor 10 consists of a substrate ll; a charge generator layer 12 comprising photoconductive particles 13 dispersed randomly in an electrically insulating organic resin 14; and a charge transport layer 15 comprising a transparent electrically inactive resin having dissolved therein one or more of the diamines defined above.

In Fig. 2, photoreceptor 20 differs from Fig. 1 in the charge generator layer 12. Here the photoconductive particles are in the form of continuous chains through the thickness of the binder material 14. The chains constitute a multiplicity of interlocking photoconductive continuous paths through the binder material. The photoconductive path are present in a volume concentration of from about I to 25 percent based on the volume of said layer.

A further alternative for layer 14 of Fig. 2 comprises photoconductive material in substantial particle-to-particle contact in the layer in a multiplicity of interlocking photoconductive paths through the thickness of said member, the photoconductive paths being present in a volume concentration, based on the volume of the layer, of from about I to 25 percent.

In Fig. 3, photoreceptor 30 differs from Figs. 1 and 2 in that charge generator layer 16 comprises a homogeneous photoconductive layer 16.

In Fig. 4, photoreceptor 40 differs from Fig. 3 in that a blocking layer 17 is employed at the substrate-photoreceptor interface.

The blocking layer functions to prevent the injection of charge carriers from the substrate into the photoconductive layer.

Any suitable material may be used, e.g.

Nylon, epoxy and aluminum oxide.

In the devices of the present invention the substrate 11 may be of any suitable conductive material, e.g.

aluminum, steel, brass, graphite, dispersed conductive salts or conductive polymers.

The substrate may be rigid or flexible and of any conventional thickness. Typical substrates include flexible belts or sleeves, sheets, webs, plates, cylinders and drums.

The substrate may also comprise a composite structure such as a thin conductive layer such as aluminum or copper iodide, or glass coated with a thin conductive coating of chromium or tin oxide. Particularly preferred are substrates of metalized polyesters such as Mylar (Registered Trade Mark).

In addition, an electrically insulating substrate may be used. In this instance, the charge may be placed upon the insulating member by double corona charging techniques well known and disclosed in the art. Other modifications using an insulating substrate or no substrate at all include placing the imaging. member on a conductive backing member or plate and charging the surface while in contact with said backing member. Subsequent to imaging, the imaging member may then be stripped from the conductive backing.

The photoconductive material which may be the particles 13 of Figs. 1 and 2 or the homogeneous layer 16 of Figs. 3 and 4 may consist of any suitable inorganic or organic photoconductor and mixtures thereof.

Inorganic materials include inorganic crystalline photoconductive compounds and inorganic photoconductive glasses.

Typical inorganic crystalline compounds include cadmium sulfoselenide, cadmium selenide, cadmium sulfide and mixtures thereof. Typical inorganic photoconductive glasses include amorphous selenium and selenium alloys such as seleniumtellurium, selenium-tellurium-arsenic and selenium-arsenic and mixtures thereof.

Selenium may also be used in a crystalline form known as trigonal selenium.

Typical organic photoconductive material which may be used as charge generators include phthalocyanine pigment such as the X-form of metal-free phthalocyanine described in U.S. Patent 3,357,989 to Byrne et al; metal phthalocyanines such as copper phthalocyanine; quinacridones available from DuPont under the tradename Monastral Red, Monastral Violet and Mown astral Red Y; substituted 2,4 diamino - triazines disclosed by Weinberger in U.S. Patent 3,445,227; triphenodioxazines disclosed by Weinberger in U.S. Patent 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.

Intermolecular charge transfer complexes such as a mixture of poly(Nvinylcarbazole) (PVK) and trinitrofluorenone (TNF) may be used as charge generating materials. These materials are capable of injecting photogenerated holes into the transport material.

Additionally, intramolecular charge transfer complexes may be used as charge generation materials capable of injecting photogenerated holes into the transport materials.

A preferred generator material is trigonal selenium. A method of making a photosensitive imaging device utilizing trigonal selenium comprises vacuum evaporating a thin layer of vitreous selenium, onto a substrate, forming a relatively thicker layer of electrically active organic material over said selenium layer, followed by heating the device to an elevated temperature, e.g., 1250C to 2100C, for a sufficient time. e.g. 1 to 24 hours, sufficient to convert the vitreous selenium to the crystalline trigonal form. Another method of making a photosensitive member which utilizes trigonal selenium comprises forming a dispersion of finely divided vitreous selenium particles in a liquid organic resin solution and then coating the solution onto a supporting substrate and drying to form a binder layer comprising vitreous selenium particles contained in an organic resin matrix. Then the member is heated to an elevated temperature, e.g., 1000C to 1400C for a sufficient time, e.g., 8 to 24 hours, which converts the vitreous selenium to the crystalline trigonal form.

Another preferred embodiment is a 0.2 micron thick charge generation layer of 35.5 percent by weight arsenic, 64.5 percent by weight amorphous selenium and 850 parts per million iodine. This charge generation layer may be overcoated with a 30 micron thick charge transport layer of Makrolon (Registered Trade Mark), a polycarbonate resin, which has dispersed therein 40 percent by weight of the diamine of the kind used in the present invention.

The above list of photoconductors should in no way be taken as limiting, but merely illustrative as suitable materials. The size of the photoconductive particles is not particularly critical; but particles in a size range of 0.01 to 5.0 microns generally yield particularly satisfactory results.

Binder material 14 may comprise any electrically insulating resin such as those described in the above-mentioned Middleton et al, U.S. Patent 3,121,006.

When using an electrically inactive or insulating resin, it is essential that there be particle-to-particle contact between the photoconductive particles. This generally necessitates that the photoconductive material be present in an amount of at least 10 percent by volume of the binder layer with no limitation on the maximum amount of photoconductor in the binder layer. If the matrix or binder comprises an active material, the photoconductive material generally need only to comprise 1 percent or less by volume of the binder layer with no limitation on the maximum amount of the photoconductor in the binder layer. The thickness of the photoconductive layer is not critical. Layer thicknesses from 0.05 to 20.0 microns have been found generally satisfactory, with a preferred thickness of 0.2 to 5.0 microns generally yielding good results.

Another embodiment is where the photoconductive material may be particles of amorphous selenium-arsenic-halogen as shown as particles 13 which may comprise from 0.5 percent to 50 percent by weight arsenic and the halogen may be present in amounts from 10 to 10,000 parts per million with the balance being amorphous selenium. The arsenic preferably may be present from 20 percent to 40 percent by weight with 35.5 percent by weight being the most preferred. The halogen preferably may be iodine, chlorine or bromine. The most preferred halogen is iodine. The remainder of the alloy or mixture is preferably selenium.

Active layer 15 comprises a transparent electrically inactive organic resinous material having dispersed therein (preferably from 10 to 75 percent by weight) of one or more of the diamines defined above. Preferred diamines are N,N' - diphenyl - N,N' - bis(2 - methylphenyl) [1,1' - biphenyl] - 4,4' - diamine; N,N' - di- phenyl - N,N' - bis(3 - methylphenyl) [1,1' - biphenyll - 4,4' - diamine; N,N' - diphenyl - N,N' - bis(4 - methylphenyl) [1,1' -biphenyl] -4,4' -diamine;N,N' -diphenyl - N,N' - bis(2 - chlorophenyl) [1,1' -biphenyl] -4,4' -diamine;;N,N' -di- phenyl - N,N' - bis(3 - chlorophenyl) [1,1' - biphenyl] - 4,4' - diamine and N,N' - diphenyl - N,N' - bis(4 - chlorophenyl) - [1,1' - biphenyl] - 4,4' - diamine.

In general, the thickness of active layer 15 should be from 5 to 100 microns, but thicknesses outside this range can also be used.

Active layer 15 may comprise any transport electrically inactive resinous material such as those described in the above-mentioned Middleton et al, U.S.

Patent 3,121,006, to which the reader is referred. The amount of the above-defined diamine in the electrically inactive organic material may be from 10 percent (and preferably at least 15 percent) to 75 percent by weight.

The preferred electrically inactive resinous material are polycarbonate resins.

The preferred polycarbonate resins have a molecular weight from 20,000 to 120,000 (the preferred upper limit generally being 100,000); more preferably from 50,000 to 120,000 (the preferred upper limit generally being (100,000), although the range from 20,000 to 50,000 can also be used.

The materials most preferred as the electrically inactive resinous material are poly(4,4' - isopropylidene - diphenylene carbonate) with a molecular weight of from 25,000 to 40,000, available as Lexan (registered Trade Mark) 145, and from 40,000 to 45,000, available as Lexan (registered Trade Mark) 141, both from the General Electric Company; and from 50,000 to 120,000 available as Makrolon (registered Trade Mark) from Farbenfabricken Bayer A.G.; and from 20,000 to 50,000, available as Merlon (registered Trade Mark), from Mobay Chemical Company.

Active layer 15, as described above is non-absorbing to light in the preferred wavelength region used to generate carriers in the photoconductive layer. This preferred range for xerographic utility is generally from 4,000 to 8,000 angstrom units. In addition, the photoconductor should be responsive to all wavelengths from 4,000 to 8.000 angstrom units if panchromatic responses are required. All photoconductor-active material combinations to be used in the present invention result in the injection and subsequent transport of holes across the physical interface between the photoconductor and the active material.

The reason for the requirement that active layer 15, i.e., charge transport layer, should be transparent is that most of the .incident radiation is utilized by the charge carrier generator layer for efficient photogeneration. However, this requirement is not essential in cases where the imagewise exposure of the charge carrier generator layer is not to be through the charge transport layer. The charge transport material is further characterized by the ability to transport the carrier even at the lowest electrical fields developed in electrophotography.

The active transport layer which is employed in conjunction with the photo conductive layer in the present invention is a material which is an insulator to the extent that the electrostatic charge placed on said active transport layer is not conducted in the absence of illumination, i.e., with a rate sufficient to prevent the formation and retention of an electrostatic latent image thereon.

In general, the thickness of the active layer preferably is from 5 to 100 microns, but thicknesses outside this range can also be used. The ratio of the thickness of the active layer, i.e., charge transport layer, to the photoconductive layer, i.e., charge generator layer, preferably should be maintained from 2:1 to 200:1 and in some instances as great as 400:1.

The Examples below are intended to illustrate various preferred embodiments of the present invention. The percentages are by weight unless otherwise indicated.

EXAMPLE I Preparation of N,N' - diphenyl - N,N' bis(3 - methylphenyl) - [1,1' - bi phenyl] - 4,4' - diamine: In a 5000 milliliter, round bottom, 3 necked flask fitted with a mechanical stirrer and blanketed with argon, is placed 336 grams ( I mole) of N,N' - diphenylbenzidine, 550 grams (2.5 moles) of miodotoluene, 550 grams (4 moles) potassium carbonate (anhydrous) and 50 grams of copper bronze catalyst and 1500 ml dimethylsulfoxide (anhydrous). The heterogeneous mixture is refluxed for 6 days. The mixture is allowed to cool. 2000 ml of benzene is added. The dark slurry is then filtered. The filtrate is extracted 4 times with water. Then the filtrate is dried with magnesium sulfate and filtered. The benzene is taken off under reduced pressure. The black product is column chromatographed using Woelm neutral alumina.Colorless crystals of the product are obtained by recrystallizating the product from n-octane. The melting point is 167 169"C. The yield is 360 grams (650/n).

A photosensitive layer structure similar to that illustrated in Fig. 3 is prepared by the following technique: A 1 micron layer of vitreous selenium is formed over an aluminized Mylar (registered Trade Mark) substrate by conventional vacuum deposition technique such as those disclosed by Bixby in U.S. Patent 2,753,278 and U.S. Patent 2,970,906.

A charge transport layer is prepared by dissolving in 135 grams of methylene chloride, 3.34 grams of the N,N' - diphenyl - N,N' - bis(3 - methylphenyl) [1,1' - biphenyl] - 4,4' - diamine and 10 grams of bisphenol-A-polycarbonate (Lexan 145, obtained from General Electric Company); "Lexan" is a registered Trade Mark. A layer of the above mixture is formed on the vitreous selenium layer using a Bird Film Applicator. The coating is then vacuum dryed at 400C. for 18 hours to form a 22 micron thin dry layer of charge transport material.

The above member is then heated to about 125"C. for 16 hours which is sufficient to convert the vitreous selenium to the crystalline trigonal form.

The plate is tested electrically by negatively charging the plate to a field of 60 volts/micron and discharging it at a wavelength of 4,200 angstrom units at 2x 1012 photons/cm2 seconds. The plate exhibits satisfactory discharge at the above fields and is capable of use in forming visible images.

EXAMPLE II A photosensitive layer structure similar to that illustrated in Fig. 4 is prepared by the following technique: A 1 micron layer of amorphous selenium is vacuum evaporated on a 3 mil aluminum substrate by conventional vacuum deposition technique such as those disclosed by Bixby in U.S. Patents 2,753,278 and 2,970,906. Prior to evaporating the amorphous selenium onto the substrate, a 0.5 micron layer of an epoxy-phenolic barrier layer is formed over the aluminum by dip coating. Vacuum deposition is carried out at a vacuum of 10-8 Torr while the substrate is maintained at a temperature of about 500 C. during the vacuum deposition.A 22 micron thick layer of charge transport material comprising 50 percent by weight of N,N' - diphenyl N,N' - bis(3 - methylphenyl) - [1,1' - biphenyl] - 4,4' - diamine and 50 percent by weight of poly(4,4' - isopropylidenediphenylene carbonate) available as Lexan (registered Trade Mark) 141 from General Electric Company is coated over the amorphous selenium layer.

The charge transport layer is prepared by dissolving in 135 grams of methylene chloride, 10 grams of N,N' - diphenyl N,N' - bis(3 - methylphenyl) - [1,1' - biphenyl] - 4,4' - diamine and 10 grams of the Lexan (registered Trade Mark) 141. A layer of this solution is formed on the amorphous selenium layer by using a Bird Film Applicator. The coating is then dried at 400C. for 18 hours to form a 22 micron thick dry layer of charge transport material. The amorphous selenium layer is then converted to the crystalline trigonal form by heating the entire device to 1250C. and maintaining this temperature for about 16 hours. At the end of 16 hours, the device is cooled to room temperature.The plate is tested electrically by negatively charging the plate to fields of 60 volts/micron and discharging them at a wavelength of 4,200 angstroms at 2x 1012 photons/cm2 seconds. The plate exhibits satisfactory discharge at the above fields, and is capable of use in forming excellent visible images.

EXAMPLE III A photosensitive layer structure similar to that illustrated in Fig. 3 is prepared by the following technique: A mixture of about 35.5 percent by weight of arsenic and about 64.5 percent by weight of selenium and about 850 parts per million (ppm) of iodine are sealed in a Pyrex (registered Trade Mark) vial and reacted at about 525 C. for about 3 hours in a rocking furnace. The mixture is then cooled to about room temperature, removed from the Pyrex (registered Trade Mark) vial and placed in a quartz crucible within a bell jar.

An aluminum plate is supported about 12 inches above the crucible and maintained at a temperature of about 70"C. The bell jar is then evacuated to a pressure of about 5x10-5 torr and the quartz crucible is heated to a temperature of about 380"C. to evaporate the mixture onto the aluminum plate. The crucible is kept at the evaporation temperature for approximately 30 minutes. At the end of this time the crucible is permitted to cool and the finished plate is removed from the bell jar.

A 0.2 micron layer of vitreous seleniumarsenic-iodine is formed on the aluminum plate.

A charge transport layer is prepared by dissolving in 135 grams of methylene chloride, 3.34 grams of N,N' - diphenyl N,N' - bis(3 - methylphenyl) - [1,1' - biphenyl] - 4,4' - diamine as prepared in Example I and 10 grams of Lexan (registered Trade Mark) 145. A layer of the above mixture is formed on the vitreous selenium-arsenic-iodine layer using a Bird Film Applicator. The coating is then vaccum dried at 800C. for 18 hours to form a 30 micron thin dry layer of charge transport material.

WHAT WE CLAIM IS: 1. An electrophotographic imaging member comprising a charge generation layer, and a contiguous charge transport layer of electrically inactive (as herein defined) organic resinous material having dispersed therein one or more compounds having the general formula:

wherein each X independently is CH3 or Cl, said charge generation layer exhibiting the capability of photo-generation of holes and injection of said holes, and said charge transport layer being capable of supporting the injection of photo-generated holes from said charge generation layer and transporting said holes through said charge transport layer.

2. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N.N' - bis(2 - methylphenyl) - (1,1' - biphenyl) - 4,4' - diamine.

3. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N,N' - bis(3 methylphenyl) - (1,1' - biphenyl) - 4,4' diamine.

4. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N,N' - bis(4 - methylphenyl) - (1,1' - biphenyl) - 4,4' - diamine.

5. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N,N' - bis(2 - chlorophenyl) - (1,1' - biphenyl) - 4,4' - diamine.

6. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N,N' - bis(3 - chlorophenyl) - (1,1' - biphenyl) - 4,4' - diamine.

7. An imaging member according to claim 1, wherein said electrically inactive organic resinous material has dispersed therein N,N' - diphenyl - N,N' - bis(4 - chlorophenyl) - (1,1' - biphenyl) - 4,4' - diamine.

8. An imaging member according to any one of claims 1 to 7, wherein the amount of said one or more compounds dispersed in said charge transport layer is from 10 to 75 percent by weight.

9. An imaging member according to claim 8, wherein the amount of said one or more compounds dispersed in said charge transport layer is at least 15 percent by weight.

10. An imaging member according to any one of claims 1 to 9, wherein said charge transport layer is substantially nonabsorbing in at least one spectral region at which the charge generation layer generates and injects photogenerated holes.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 2x 1012 photons/cm2 seconds. The plate exhibits satisfactory discharge at the above fields, and is capable of use in forming excellent visible images. EXAMPLE III A photosensitive layer structure similar to that illustrated in Fig. 3 is prepared by the following technique: A mixture of about 35.5 percent by weight of arsenic and about 64.5 percent by weight of selenium and about 850 parts per million (ppm) of iodine are sealed in a Pyrex (registered Trade Mark) vial and reacted at about 525 C. for about 3 hours in a rocking furnace. The mixture is then cooled to about room temperature, removed from the Pyrex (registered Trade Mark) vial and placed in a quartz crucible within a bell jar. An aluminum plate is supported about 12 inches above the crucible and maintained at a temperature of about 70"C. The bell jar is then evacuated to a pressure of about 5x10-5 torr and the quartz crucible is heated to a temperature of about 380"C. to evaporate the mixture onto the aluminum plate. The crucible is kept at the evaporation temperature for approximately 30 minutes. At the end of this time the crucible is permitted to cool and the finished plate is removed from the bell jar. A 0.2 micron layer of vitreous seleniumarsenic-iodine is formed on the aluminum plate. A charge transport layer is prepared by dissolving in 135 grams of methylene chloride, 3.34 grams of N,N' - diphenyl N,N' - bis(3 - methylphenyl) - [1,1' - biphenyl] - 4,4' - diamine as prepared in Example I and 10 grams of Lexan (registered Trade Mark) 145. A layer of the above mixture is formed on the vitreous selenium-arsenic-iodine layer using a Bird Film Applicator. The coating is then vaccum dried at 800C. for 18 hours to form a 30 micron thin dry layer of charge transport material. The plate is tested electrically by negatively charging the plate to a field of 60 volts/micron and discharging it at a wavelength of 4,200 angstrom units at 2x 1012 photons/cm2 seconds. The plate exhibits satisfactory discharge at the above fields and is capable of use in forming visible images. WHAT WE CLAIM IS:

1. An electrophotographic imaging member comprising a charge generation layer, and a contiguous charge transport layer of electrically inactive (as herein defined) organic resinous material having dispersed therein one or more compounds having the general formula:

11. An imaging member according to any

one of claims I to 10, wherein said charge generation layer comprises a layer of photoconductive material.

12. An imaging member according to any one of claims 1 to 10, wherein said charge generation layer comprises photoconductive material dispersed in a resinous binder.

13. An imaging member according to any one of claims 1 to 10, wherein said charge generation layer comprises an insulating organic resin matrix and a photoconductive material with substantially all of the photoconductive material in said layer in a multiplicity of interlocking photoconductive continuous paths through the thickness of said layer.

14. An imaging member according to claim 13, wherein said photoconductive paths are present in a volume concentration, based on the volume of said layer, of from I to 25 percent.

15. An imaging member according to any one of claims 1 to 10, wherein said charge generation layer comprises an insulating organic resin matrix containing therein photoconductive particles, with substantially all of the photoconductive particles being in substantial particle-toparticle contact in said layer in a multiplicity of interlocking photoconductive paths through the thickness of said layer.

16. An imaging member according to claim 15, wherein said photoconductive paths are present in a volume concentration, based on the volume of said layer, of from 1 to 25 percent.

17. An imaging member according to any one of claims 11 to 16, wherein the photoconductive material is selected from the group consisting of amorphous selenium, and selenium alloys selected from the group consisting of selenium-tellurium; selenium-tellurium-arsenic and seleniumarsenic and mixtures thereof.

18. An imaging member according to any one of claims 11 to 16, wherein the photoconductive material is trigonal selenium.

19. An imaging member according to any one of claims 1 to 18, wherein said electrically inactive organic resinous material comprises a polycarbonate resin.

20. An imaging member according to claim 19, wherein the polycarbonate resin has a molecular weight of from 20,000 to 100,000.

21. An imaging member according to claim 19, or claim 20, wherein the polycarbonate resin has a molecular weight of from 20,000 to 50,000.

22. An imaging member according to claim 19 or claim 20, wherein the polycarbonate resin has a molecular weight of from 50,000 to 100,000.

23. An imaging member according to claim 19, wherein said polycarbonate resin is poly(4,4' - isopropylidene - diphenylene carbonate).

24. An imaging member according to claim 23, wherein the poly(4,4' - isopropylidene - diphenylene carbonate) has a molecular weight of from 35,000 to 40,000.

25. An imaging member according to claim 23, wherein the poly(4,4' - isopropylidene - diphenylene carbonate) has a molecular weight of from 40,000 and 45,000.

26. An imaging member according to claim 11 or any one of claims 21, 23, 24 and 25 as dependent on claim 11, wherein the photoconductive material of said layer of photoconductive material substantially consists of an amorphous mixture of selenium, arsenic and a halogen, the arsenic being present in an amount from 0.5 percent to 50 percent by weight, and the halogen being present in an amount from 10 to 10,000 parts per million parts by weight, with the balance being selenium.

27. An imaging member according to claim 26, wherein the arsenic is present in an amount from 20 percent to 40 percent by weight.

28. An imaging member according to claim 26 or claim 27, wherein the halogen is iodine.

29. An imaging member according to any one of claims 26 to 28, wherein the photoconductive material of said layer of photoconductive material substantially consists of 64.5 percent by weight selenium, 35.5 percent by weight arsenic and 850 parts per million parts by weight iodine.

30. An imaging member according to claim 12 or any one of claims 21, 23, 24 and 25 as dependent on claim 12, wherein said charge generation layer comprises particulate amorphous material substantially consisting of selenium, arsenic and a halogen, the arsenic being present in an amount from 0.5 percent to 50 percent by weight, and the halogen being present in an amount from 10 to 10,000 parts per million parts by weight, with the balance being amorphous selenium, said particulate material being dispersed in a resinous binder.

31. An imaging member according to claim 30, wherein the arsenic is present in an amount from 20 percent to 40 percent by weight.

32. An imaging member according to claim 30 or claim 31, wherein the halogen is iodine.

33. An imaging member according to any one of claims 30 to 32, wherein said particulate amorphous material substantially consists of 64.5 percent by weight selenium, 35.5 percent by weight arsenic and 850 parts per million parts by weight iodine.

34. An imaging member according to claim 19 or any one of claims 26 to 33 as dependent on claim 19, wherein the polycarbonate resin has a molecular weight of from 20,000 to 120,000.

35. An imaging member according to claim 19 or any one of claims 26 to 33 as dependent on claim 19, wherein the polycarbonate resin has a molecular weight of from 50,000 to 120,000.

36. Imaging members substantially as described with reference to, and as schematically illustrated in, the accompanying drawings.

37. An imaging member substantially as described in either of the foregoing Examples I and II.

38. An imaging member substantially as described in the foregoing Example III.

39. A method of forming an electrostatic latent image, the method comprising uniformly electrostatically charging an imaging member in accordance with any one of claims 1 to 25 and 36 and 37, and imagewise exposing the charge generation layer of said charged member to a source of activating radiation to which the photo conductive material is absorbing so that the photogenerated holes generated by said photoconductive material are injected into and are transported through said charge transport layer to form an electrostatic latent image on the surface of said member.

40. A method of forming an electrostatic latent image, the method comprising uniformly electrostatically charging an imaging member in accordance with any one of claims 26 to 35 and 38, and imagewise exposing the charge generation layer of said charged member to a source of activating radiation to which the photo conductive material is absorbing so that the photogenerated holes generated by said photoconductive material are injected into and are transported through said charge transport layer to form an electrostatic latent image on the surface of said member.