US 3894868 A
A photosensitive member having a photoreceptor binder layer comprising photoconductive particles dispersed in an electronically active matrix material. The photoconductor comprises a material which is capable of photogenerating and injecting electrons into the surrounding active binder which comprises a material capable of supporting electron injection and transport. The active matrix material has the additional property of being substantially transparent to radiation in the particular wavelength region of xerographic use thereby enabling use of a relatively small amount of photoconductor material in the binder layer. The structure may be imaged in the conventional xerographic mode which usually includes charging, exposure to light and development.
Description (OCR text may contain errors)
United States Patent Regensburger ELECTRON TRANSPORT BINDER STRUCTURE  Inventor: Paul J. Regensburger, Webster,
 Assignee: Xerox Corporation, Stamford,
 Filed: Mar. 16, 1973  Appl. No.: 341,813
Related US. Application Data  Continuation-impart of Ser. No. 93,975, Decv 1, 1970, which is a continuation-in-part of S81, No. 14,460, Feb. 26, 1970, abandoned,
 US. Cl. 96/l.5; 96/17; 96/18  Int. Cl G03g 5/02  Field of Search 96/1, 1.5, 1.6, 1.7, 1.8; 252/501  References Cited UNITED STATES PATENTS 3,113,022 12/1963 Cassiers et a1 96/1 3,159,483 12/1964 Behmenburg et a1.... 96/] 3,162,532 12/1964 Hoegl et a1. H 96/1 1 July 15, 1975 3,594,163 7/1971 Radler 96/1.5
Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. Goodrow Attorney, Agent, or Firm-James J. Ralabate; James P.
O'Sullivan; Donald M. MacKay  ABSTRACT A photosensitive member having a photoreceptor binder layer comprising photoconductive particles dispersed in an electronically active matrix material. The photoconductor comprises a material which is capable of photogenerating and injecting electrons into the surrounding active binder which comprises a material capable of supporting electron injection and transport. The'active matrix material has the additional property of being substantially transparent to radiation in the particular wavelength region of xerographic use thereby enabling use of a relatively small amount of photoconductor material in the binder layer. The structure may be imaged in the conventional xerographie mode which usually includes charging, exposure to light and development.
17 Claims, 4 Drawing Figures FIG.
FIG 3 B O O A O ABI Q Q 0 l3 ELECTRON TRANSPORT BINDER STRUCTURE BACKGROUND OF THE INVENTION This application is a continuation in part of my previous application, Ser. No. 93,975, filed Dec. 1, 1970, which is a continuation in part of Ser. No. 14,460, filed Feb. 26, 1970, now abandoned.
This invention relates in general to xerography and more specifically to a novel photosensitive device 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 ofa 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. Pat. No. 3,121,006 to Middleton and Reynolds which describes a number of binder 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 is coated on a paper backing.
In the particular examples of binder systems 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 materials disclosed in the Middleton et al. 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. With the uniform dispersion of photoconductor particles described in Middleton et al., therefore, a relatively high volume concentration of photoconductor, up to about 50 percent or more by volume, is usually necessary in order to obtain sufficient photoconductor particle-to-particle contact for rapid discharge. [t has been found, however, that high photoconductor loadings in the binder layers of the resin type result in the physical continuity of the resin being destroyed, thereby sufficiently reducing the mechanical properties of the binder layer. Layers with high photoconductor loadings are often characterized by a brittle binder layer having little or no flexibility. On the other hand, when the photoconductor concentration is reduced appreciably below about 50 percent by volume, the discharge rate is reduced, making high speed cyclic or repeated imaging difficult or impossi ble.
U.S. Pat. No. 3,l2l,007 to Middleton et al. teaches another type of photoconductor which includes a two phase photoconductive binder layer comprising photoconductive insulating particles dispersed in a homogeneous photoconductive insulating matrix. The photoconductor is in the form of a particulate photoconductive inorganic crystalline pigment broadly disclosed as being present in an amount from about 5 to percent by weight. Photodischarge is said to be caused by the combination of charge carriers generated in the photoconductive insulating matrix material and charge carriers injected from the photoconductive crystalline pigment into the photoconductive insulating matrix.
U.S. Pat. No. 3,037,861 to Hoegl et al. teaches that polyvinyl carbazole exhibits some long-wave U. V. sensitivity and suggests that its spectral sensitivity be extended into the visible spectrum by the addition of dye sensitizers. Hoegl et al. further suggests that other additives such as zinc oxide or titanium dioxide may also be used in conjunction with polyvinyl carbazole. ln Hoegl et al., it is clear that the polyvinyl carbazole is intended to be used as a photoconductor, with or without additives materials which extend its spectral sensitivity.
In addition, certain specialized layer structures particularly designed for reflex imaging have been proposed. For example, U.S. Pat. No. 3,165,405 to Hoesterey utilizes a two layered zinc oxide binder structure for reflex imaging. The l-loesterey patent utilizes two separate contiguous photoconductive layers having different spectral sensitivities in order to carry out a particular reflex imaging sequence. The l-loesterey 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 layer structure is accomplished by charge transport through the bulk of the photoconductive layer, as in the case of vitreous selenium (and other homogeneous layer modifications). ln devices employing photoconductive binder structures, which include inactive electrically insulating resins such as those described in the Middleton et al., U.S. Pat. No. 3,121,006, conductivity or charge transport is accomplished through high loadings of the photoconductive pigment allowing particle-to-particle contact of the photoconductive particles. In the case of photoconductive particles dispersed in a photoconductive matrix, such as illustrated by the Middleton et al., U.S. Pat. No. 3,l2l,007, photoconductivity occurs through the generation of charge carriers in both the photoconductive matrix and the photoconductor pigment particles.
Although the above patents rely upon distinct mechanisms of dicharge 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 cycling xerography, susceptible to abrasion, chemical attack, heat, and multiple exposures to light during cycling. 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 photoconductive layers 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 the 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 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.
US. Pat. No. 3,041,166 to Bardeen describes such a configuration in which a transparent plastic material overlays a layer of vitreous selenium which is contained on a supporting substrate. The plastic material is described as one having a long range for charge carriers of the desired polarity. 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 electron moves through the plastic layer and neutralizes a positive charge 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.
French Pat. No. l,577,855 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 polyvinyl carbazole formed over the oriented layer of dichroic material. When charged and exposed to light polarized perpendicularly to the orientation of the dichroic layer, the oriented dichroic layer and polyvinyl carbazole 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 polyvinyl carbazole.
In view of the state of the art, it can readily be seen that there is a need for a general purpose photoreceptor exhibiting acceptable photoconductive characteristics and which additionally provides the capability of exhibiting outstanding physical strength and flexibility to be reused under rapid cyclic conditions without the progressive deterioration of the xerographic properties due to wear, chemical attack, and light fatigue.
OBJECTS OF THE lNVENTlON It is therefore an object of the present invention to provide an electrophotographic plate adaptable for cyclic imaging devoid of the above noted disadvantages.
Another object of this invention is to provide a novel photosensitive binder structure.
it is yet another object of this invention to provide a novel imaging system.
It is yet another object of the instant invention to provide an electrophotographic plate having a material which exhibit facile electron transport properties.
It is still another object of this invention to provide a photoconductive insulating layer for an electrophotographic plate which is both relatively easy to make and inexpensive.
SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with the present invention by providing an electrophotographic plate having a photoreceptor layer comprising photoconductive particles dispersed throughout an electronically active matrix material. The photoconductor particles must be capable of photogenerating hole-electron pairs and injecting the photogenerated electrons into the surrounding electronically active matrix binder which comprises an electron acceptor material which is substantially nonabsorbing in the particular wavelength region of xerographic use but which is active in that it is capable of supporting electron injection and transport.
As defined herein, a photoconductor is a material which is electrically photoresponsive to light in the wavelength region in which it is to be used. More specifically, it is a material whose electrical conductivity increases significantly in response to the absorption of electromagnetic radiation in a wavelength region in which it is to be used. This definition is necessitated by the fact that a vast number of aromatic organic compounds are known or expected to be photoconductive when irradiated with strongly absorbed ultraviolet, xray, or gamma-radiation. Photoconductivity in organic materials is a common phenomenon. Practically all highly conjugated organic compounds exhibit some degree of photoconductivity under appropriate conditions. Most of these organic materials have their prime wavelength response in the ultraviolet. However, little commercial utility has been found for ultraviolet responsive materials, and their short wavelength response is not particularly suitable for document copying or color reproduction. in view of the general prevelance of photoconductivity in organic compounds following short wavelength excitation, it is therefore necessary that for the instant invention, the term photoconductor and photoc0nductive" be understood to include only those materials which are in fact substantially photoresponsive in the wavelength region in which they are to be used.
In accordance with the present invention it has been found that a xerographic or electrophotographic sensitive member can be prepared with an electrostatically active matrix material of an electron acceptor type which will facilitate the transport of photogenerated electrons from photosensitive material under the influence of an electric field. The active matrix materials to be described herein, are to be distinguished from those matrix binders or the prior art, described above, in that the present materials have the combined properties of being substantially transparent, hence, nonphotoconductive and non-absorbing, in at least some significant portion of a particular wavelength region of use corresponding to a range of photosensitivity of the photoconductor particles and are capable of supporting the injection and transport of electrons which are photogenerated in the photoconductor particles. Because of their unique combination of substantial transparency in a wavelength region of particular xerographic use and electron transport capability, the active transport materials of the present invention can be used effectively as a relatively small quantity of photoconductor to be used in the instant invention.
It should be understood that the active transport material does not function as a photoconductor in the wavelength region of use. As stated above, holeelectron pairs are photo-generated in the photoconductive layer and the photogenerated electrons are then injected across a field modulated barrier into the active matrix transport material and electron transport occurs through the transport material.
It is to be further noted that most materials which are useful for active layers of the instant invention are incidentally also photoconductive when radiation of wavelengths suitable for electronic excitation is absorbed by them. However, photoresponse in the short wavelength region, which falls outside the spectral region for which the present photoconductors are to be used, is irrelevant to the performance of the device. It is well known that radiation must be absorbed in order to excite photoconductive response, and the transparency criterion, stated above, for the active transport materials implies that these materials do not contribute significantly to the photoresponse of the photoreceptor in the wavelength region of use.
A typical application of the instant invention consists of a supporting substrate such as a conductor containing an active binder matrix layer thereon. For example, the active matrix binder layer may comprise particles of hexagonal selenium dispersed in a film of substantially transparent electron acceptor material, which is capable of supporting electron injection and transport as well as being substantially transparent in the particular wavelength region in which selenium is photoresponsive. The transparent active matrix material enables use of the extremely low photoconductor loading not previously available to the art. In addition, the structure functions effectively for repetitive use or cycling. This structure can be imaged in the conventional xerographic manner which usually includes charging, exposure and development.
The use of the active matrix concept of the present invention enables one to use particular regions of the electromagnetic spectrum for selective xerographic copying. A typical application would be the use of active matrices in color xerography to copy particular color sequentially and thereby obtain a complete color print.
DESCRIPTION OF THE DRAWINGS Further objects of the invention, together with additional features contributing thereto will be apparent from the following description of one embodiment of the invention when read in conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic sectionaly view of one embodiment of a xerographic plate contemplated by the instant invention.
FIG. 2 illustrates a discharge mechanism of the active matrix binder layer.
FIG. 3 illustrates the discharge mechanism of one binder system of the prior art.
FIG. 4 illustrates the discharge mechanism of another binder system of the prior art.
DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates one embodiment in improved xerographic plate 10 according to this invention. Reference character 11 designates a substrate or mechanical support. The substrate may comprise a metal such as brass, aluminum, gold, platinum, steel or the like. It may be of any convenient thickness, rigid or flexible, in the form of j sheet, web, cylinder, or the like, and may be coated with a thin layer of plastic. It may also comprise such other materials as metallized paper, plastic sheets covered with a thin coating of aluminum or copper iodide, or glass coated with a thin layer of chromium or tin oxide. It is usually preferred that the support member be somewhat electrically conductive or have a somewhat conductive surface and that it be strong enough to permit a certain amount of handling. In certain instances, however, support 11 need not be conductive or may even be dispensed with entirely.
Photoconductive binder layer 10 contains photoconductive particles 12 contained in an electronically active matrix or binder material 13. The photoconductive particles may consist of any suitable inorganic or organic photoconductor which photogenerates holeelectron pairs. Typical inorganic materials include inorganic crystalline compounds and inorganic photoconductive glasses. Typical inorganic materials include cadmium sulfide, cadmium sulfoselenide, cadmium selenide, zinc sulfide, zinc oxide, and mixtures thereof. The typical inorganic photoconductive glasses include amorphous selenium and selenium alloys such as selenium-tellurium, and selenium-arsenic. Selenium may also be used in its hexagonal crystalline form commonly referred to as trigonal selenium. Typical organic photoconductors include phthalocyanine pigments such as the X-form of metal free phthalocyanine described in US. Pat. No. 3,357,989 to Byrne et al., and metal phthalocyanine pigments, such as copper phthalocyanine. Other typical organic photoinjecting pigments such as Bis-benzimidazole pigments, perylene pigments, quinacridone pigments, indigoid pigments and polynuclear quinones, disclosed in copending applications Ser. Nos. 93,974, 94,066, 94,040, 94,067, 94,068, all filed on Dec. l, 1970 now abandoned.
The above list of photoconductors should in no way be taken as limiting, but is merely illustrative ofsuitable materials.
The photoconductive particles are present in a volume concentration or occupancy governed by various factors: Notably (l) the stage at which the physical properties of the matrix are seriously impaired; (2) the stage at which there is significant transport through particle-to-particle contacts; and (3) the stage at which, with conductive pigments such as trigonal selenium there is sufficient internal charge as to militate against simple condenser charging. The latter two factors frequently lead to a lack of cycling ability. In general, to attain the best combination of physical and electrical properties, the upper limit for the photoconductive pigment or particles must be about 5 percent by volume of the electron transport binder layer. A lower limit for the photoconductive particles of about 0.] percent by volume of the binder layer is required to insure that the light absorption coefficient is sufficient to give appreciable carrier generation.
The thickness of the binder layer is not particularly critical. Layer thicknesses from about 2 to I00 microns have been found satisfactory, with a preferred thickntxz of about to 50 yielding particularly good results.
i he size of the photoconductive particles is not particularly critical in the binder structure, but particles in a size range of about 0.01 to 1.0 microns yield particularly satisfactory results.
Reference character 13 designates the active matrix material which acts as a binder for the photoconductor particles 12. The active matrix layer comprises an aromatic or heterocyclic electron acceptor material which is capable of both supporting electron injection from the photoconductor particles and transporting said photogenerating electrons under the influence of an applied field. in order to function in the manner outlined above, the active matrix material should be substantially transparent to the particular wavelength region used for xerographic copying. In particular, the active matrix material should be substantially nonabsorbing in at least a significant portion of that part of the electromagnetic spectrum which ranges from about 4,200 to 8,000 Angstroms because most xerographically useful photoconductors have photoresponse to wavelengths in this region.
As mentioned above, the active transport material 13 comprises aromatic or heterocyclic electron acceptor materials which have been found to exhibit negative charge carrier transport properties as well as requisite transparency characteristics. Typical electron acceptor materials within the purview of the instant invention include phthalic anhydride, tetrachlorophthalic anhydride, benzil, mellitic anhydride, S-tricyanobenzene, picryl chloride, 2,4-dinitrochlorobenzene, 2,4-dinitrobromobenzene, 4-nitrobiphenyl, 4,4-dinitrobiphenyl, 2,4,6-trinitroanisole, trichlorotrinitrobenzene, trinitro- O-toluene, 4,6-dichloro-l ,3-dinitrobenzene, 4,6- dibromo-l ,3-dinitrobenzene, P-dinitrobenzene, chloranil, bromanil, and mixtures thereof. It is further intended to include within the scope of these materials suitable for the active transport layer other reasonable structural or chemical modifications of the above described compounds provided that the noted modified compound exhibits the desired charge carrier transport characteristics.
While any and all aromatic or heterocyclic electron acceptors having the requisite transparency characteristics are within the purview of the instant invention particularly good electron transport properties are found with aromatic or heterocyclic compounds having more than one substituent of the strong electron withdrawing substituents such as nitro-(NO sulfonate ion (SO carboxyl-(COOH) and cyano- (-CN) groupings. From this class of materials, 2,4,7-trinitro-9-fluorenone (TNF), 2,4,S,7-tetranitrofluorenone, trinitroanthracene, dinitroacridene, tetracyanopyrene, and dinitroanthraquinone are preferred materials because of their availability and superior electron transport properties.
It will be obvious to those skilled in the art that the use of any polymer having the described aromatic or heterocylic electron acceptor moiety as an integral portion of the polymer structure will function as an active matrix material. It is not the intent of the invention to restrict the type of polymer which can be employed as the transport material provided that it has an active electron acceptor moiety to provide the polymer with electron transport characteristics. Polyesters, polysiloxanes, polyamides, polyurethanes, and epoxies, as
well as block random to graft copolymers, all containing the aromatic moiety are therefore exemplary the various types of polymers which could be employed. In addition, electronically inactive polymers in which the active electron acceptor moiety is dispersed at high concentration can be employed as the active matrix material. Typically the active material will be dispersed in the inactive polymer in an amount of at least about 20 percent by weight of the polymer to provide an active transport material.
The substantial or significant transparency of the active transport material within the context of the instant invention, as exemplified by FIG. 1, means that a sufficient amount of radiation from a source must pass through the active transport layer 13 in order that the photoconductive layer 12 can function in its capacity as a photogenerator and injector of electrons. More specifically, substantial transparency is present in the active transport materials of the present invention when the active transport materials is nonphotoconductive and non-absorbing in at least some significant portion of the wavelength region of from about 4,200 to 8,000 Angstrom Units. This property of substantial transparency enables enough activating radiation to impinge the photoconductor layer so as to cause discharge of the charged active transport photoreceptor of the present invention.
The active matrix electron transport material which is employed as the binder in conjunction with the photoconductive particles in the instant invention is a material which is an insulator to the extent that an electrostatic charge placed on said active binder matrix material is not conducted in the absence of illumination at a rate to prevent the formation and retention of an electrostatic latent image thereof. In general, this means that the specific resistivity of the active matrix material should be at least 10" ohms-cm. and preferably will be several orders higher. For optimum results, however, it is preferred that this specific resistivity of the active binder material be such that the overall resistivity of the active binder layer in the absence of activating illumination or charge injection from an adjacent layer be above l0 ohms-cm.
Another variation of the binder configuration described in FIG. 1 consists of the use of a blocking layer at the substrate-photoconductor interface. This blocking layer aids in sustaining an electric field across the photoconductor-active organic layer after the charging step. Any suitable blocking material may be used. Typical materials include nylon, epoxy, aluminum oxide, and insulating resins of various types including polystyrene, butadiene polymers and copolymers, acrylic and methacrylic polymers, vinyl resins, alkyd resins and cellulose base resin.
It can therefore be seen that the photo-insulatin g portion of the xerographic members of the instant invention represented in FIG. 1 comprises a bi-functional binder layer:
l. A photoconductive material which photogenerates holes and electrons upon excitation by radiation and injects said photogenerated electrons into the surrounding active matrix binder, and,
2. A surrounding substantially transparent active matrix material which allows transmission of radiation to the photoconductor particles, accepts the subsequently photogenerated electron from the photoconductor material, and actively transports said conductive electron to a positively charged surface or substrate thereby neutralizing said charge.
This is more dramatically illustrated in FIG. 2 where the xerographic member of the present invention has been negatively charged by means of corona charging. While FIG. 2 is drawn without a substrate, as shown by numeral 11 in FIG. 1, it is to be understood that a substrate is ordinarily used with such a binder structure and the mechanism will be described with respect to a substrate. The light, represented by the arrow I4, passes through the transparent active matrix material 13 and impinges the photoconductor particles 12 thereby created a hole-electron pair. The electron and hole are then separated by the force of the applied field, the hole jumping to the surface thereby dissipating the negative charge and the electron injected into the active matrix binder material 13 where it is then transported by force of the electrostatic attraction through the active matrix binder system to the positively charged substrate. Since only photogenerated electrons can move in the electron transport active matrix binder material, large changes in surface potential result only when the electric field in the layer is such as to move the photogenerated electrons from the photoconductor particles where they are generated, through the active matrix layer, and then to an oppositely charged surface. Generally for maximum utility the active matrix layer is charged negatively. The preference as to negatively charging the binders structure is due to the fact that the proximity of the photoconductor particles to the surface of the xerographic structure enables positive charge carriers to easily dissipate a negatively charged surface while the negative charge carriers transported through the transport material to the positively charged surface.
Referring now to FIG. 3, there is illustrated an electrophotographic plate of the prior art in which a sensitizing pigment 12 has been dispersed in a photoconductor binder material 13 for the purpose of increasing the sensitivity of said photoconductor material. The light impinges the electrophotographic member and creates photogenerated holes and electrons in either the photoconductor binder material or the pigment materials depending on which the radiation falls. Since most of the carriers are created at or near the surface of the photoinsulating member charge transport presents no serious problem. Therefore, at point A light 14 has caused the photogeneration of an electron and a hole in the photoconductor and at point B photogeneration takes place in the pigment. As can be seen from the illustration, in order for the pigment to have its effect in increasing the sensitivity of the electrophotographic member it has to be present in a relatively large concentration and be at or near the surface of the photoreceptor. This is to be contrasted with FIG. 1 where photogeneration takes place exclusively in the photoconductor particles, the active matrix binder being transparent to the incident radiation. The photoconductor particles are well protected by said active matrix binder there being no requirement that they be right at the surface of the photoreceptor member in order to function as photoconductors in the structure. However, it can be seen in FIG. 3, that in order for the pigment in this type of structure to function as a sensitizer in the member, a significant amount must be kept on or at the surface where it is prone to inevitable abrasion and exposure to the atmosphere.
FIG. 4 offers by further contrast an illustration of a photoreceptor in which photosensitive pigment 12 is dispersed in an inert resin material 13. Because there is no photogeneration in the resin binder it is necessary that the photoconductive pigment or dye be in sufficient concentration or be geometrically proximate to support charge injection throughout the binder system. Hence, as can be seen, where there is a large concentration of pigment impinging light 14 creates a photogenerated hole and electron pair which is then transported through the pigments to the positively charged surface while at B where the concentration of the pigment is insufficient to effect particle-to-particle contact impinging, light creates the electron and hole pair which remains trapped because of failure of the binder system to transport the photo-generated charges either to other pigment particles or to the charged surface. Again this Figure is to be contrasted with FIG. 2 where particle-to-particle contact of the photoconductor is unnecessary in the active matrix structure. In addition, because particle-to-particle contact is necessary in the inert binder structure of FIG. 4 resolution problems occur because the geometry of the particle may not correspond to the direction of the impinging light thereby resulting in irregular dissipation of the charge.
When the binder layer of photoconductor and active matrix has sufficient strength to form a self supporting member (termed pellicle), it is possible to eliminate the physical base or support member and substitute therefore any of the various arrangements well known in the art in place of the ground plane previously supplied by the base layer. A ground plane, in effect, provides a source of mobile charges of both polarities. The deposition on the insulating two layered structure of the present invention of sensitizing charges of the desired polarity cause those charges in the ground plane of opposite polarity to migrate to the interface of the photoconductive insulating layer. Without this the capacity of the insulating member by itself would be such that it could not accept enough charge to sensitize the layer to a xerographically useful potential. It is the electrostatic field between the deposited charges on one side of the xerographic two layered member and the induced charges (from the ground plane) on the other side that stresses the xerographic member so that when an electron is excited (in the photoconductive layer) to the conduction band by a photon thereby creating a hole-electron pair, the charges migrate under the influence of this field thereby creating the latent electrostatic image. Therefore, it is obvious that if the physical ground plane is omitted a substitute therefore may be provided by depositing on opposite sides of the two layered xerographic insulating pellicle, simultaneously, electrostatic charges are placed on one side of the pellicle as by corona charging as described in U.S. Pat. No. 2,777,957 to L. E. Walkup, the simultaneous deposition of negative charges on the other side of the pellicle also by corona charging will create an induced, that is, a virtual, ground plane within the body of the pellicle just as if the charges of opposite polarity has been supplied to the interface by being induced from an actual ground plane. Such an artificial ground plane permits the acceptance of a usable sensitizing charge and at the same time permits migration of charges under the applied field when exposed to activating radiation. As used hereinafter in the specification and claims the term conductive base" includes both a physical base and an artificial one as described herein.
The physical shape of the xerographic active binder plate may be in the form whatsoever as desired by the formulator such as a flat, spherical, cylindrical plate, etc. The plate may be flexible or rigid as desired.
DESCRIPTION OF THE PREFERRED EMBODIMENT For purpose of affording those skilled in the art a better understanding of the invention, the following illustrative examples are given:
EXAMPLE I A photosensitive binder plate similar to that shown in FIG. 1 and containing photoconductive particles of copper phthalocyanine in a 2,4,7-trinitro-9-fluorenone (TNF) binder in a ratio of about 40 parts TNF by weight (50 to l by volume) is prepared by the following technique: 50 grams of a 20 weight percent TNF stock solution is formed by dissolving the appropriate amount of TNF, manufactured by the Eastman Kodak Company of Rochester, New York, in 150 grams of toluene and 30 grams of cyclohexanone. This solution is added to a solution of 0.5 grams of copper phthalocyanine and 20 grams of toluene. This mixture is milled with steel milling shot for up to an hour until a well dispersed suspension is formed. A coating is then formed on an aluminum substrate utilizing a Gardner Laboratory Bird Applicator. The final thickness after air drying at l 10C for 12 hours is about 12 microns.
The photosensitive binder plate is then placed in a Xerox Model D Machine where a copy is made by the following technique: The sample is charged by negative corona charging to a value of 800 volts. The charge plate is then exposed to a projected pattern using a tungsten light source which exposes in the wavelength region of from about 4,200 to 8,000 Angstroms. Development is then carried out by conventional cascade development using Xerox 914 toner and reversal carrier. The copy is of excellent quality being comparable to copies made on a conventional amorphous selenium electrophotographic plate.
EXAMPLE II A plate is made by the method of Example I except that trigonal selenium is used as the photoconductor with the ratio of TNF to trigonal selenium being 20/1 by weight (78/1 by volume). The binder layer has a thickness of about 12 microns. In addition, a 0.2 micron blocking layer is formed on the surface of the substrate by dip coating the substrate in a solution of nylon dissolved in methyl alcohol.
An original is copied on a Model D Xerographic Machine in the same manner as Example 1 with the resulting copy having excellent quality in that it was comparable to copies made on a conventional amorphous selenium electrophotographic plate.
EXAMPLE III A binder plate is made in the same manner as Examples l and II except that a 20/1 by weight (60/1 by volume) ratio of dinitroacridene to B form metal free phthalocyanine active matrix plate is prepared. A copy is made on a Model D Xerox Machine in the same manner as Examples 1 and II with the same excellent reproduction quality.
EXAMPLE IV A photosensitive binder plate similar to that shown in FIG. 1 is prepared by the following technique: a stock solution of 3.32 grams of duPont 49,000 polyester adhesive and 11.25g of 2,4,7trinitro-9-fluorenone is prepared by dissolving these quantities of materials in 58 g of tetrahydrofuran. After this, 24 parts by weight of solids of the stock solution is slurried with 1 part of X- form metal free phthalocyanine. The slurry is milled for one hour with steel shot, and then coated onto an aluminum substrate and dried under vacuum at 50C for 16 hours. The resulting binder plate is 23 microns thick and contains 4.5 percent by volume of phthalocyanine, with the active transport binder having a percentage of percent of 2,4,7 trinitro-9-fluorenone by weight.
Another plate is then prepared as generally described in the disclosure of US. Pat. No. 3,287,120 by dissolving:
6.5 g polyvinyl chloride 6.5 g pyrene 0.243 tetrachlorophthalic anhydride in 30 ml of butanone and ml of toluene. The solution is used to coat an aluminum sheet to form a 22 micron thick coating of the mixture after drying at 50C.
Both plates are charged both positively and negatively, and following this are exposed to a tungsten light source while the surface potential of the plates is being continuously monitored. From this monitoring the exposure times for 50 percent discharge of the surface voltage for both plates are measured. These times are expressed below in Table I as t/2 (50 percent), this being a recognized measure of the xerographic sensitivity of the noted plate.
It may be seen from of the above listed data and in view of the much faster discharge of the plate of the instant invention as compared to that of the prior art, that the plate of the instant invention is much more sensitive for xerography. Even at the highest fields, and for both positive and negative charging, the plate pursuant to US. Pat. No. 3,287,120 is at least 1,000 times slower than the plate produced pursuant to the instant invention.
The present invention has been described with reference to certain specific embodiments which have been presented in illustration of the invention. It is to be understood however the numerous variations of the invention may be made and that it is intended to encompass such variation with the scope and spirit of the invention as described by the following claims.
What is claimed is:
1. An electrophotographic plate having a photoreceptor binder layer comprising photosensitive particles dispersed in an unoriented fashion in an electronically active organic matrix binder in an amount of from about 0.1 to percent by volume of said binder, said photosensitive particles exhibiting the capability of photo-excited electron generation and injection into the surrounding active matrix binder, said active organic matrix binder being capable of supporting the injection of photo-excited electrons from said photoconductive particles and transporting said electrons through said active matrix material, wherein said active matrix comprises at least one material selected from the group consisting of phthalic anhydride, tetrachlorophthalic anhydride, benzil, mellitic anhydride, S-
tricyanobenzene, picryl chloride, 2,4-dinitrochlorobenzene, 2,4-dinitrobromobenzene, 4-nitrobiphenyl, 4,4-dinitrobiphenyl, 2,4,5 trinitroanisole, trichlorotrinitrobenzene, trinitro-O-toulene, 4,6 dichloro,-1,2 dinitrobenzene, 4,6-dibromo, -l,3 dinitrobenzene, p-dinitrobenzene, chloranil, bromoanil, 2,4,7 trinitro-9-fluorenone, 2,4,5,7 tetranitrofluorenone, trinitroanthracene, dinitroacridene, tetracyanopyrene and dinitroanthraquinone.
2. The electrophotographic plate of claim 1 in which the photosensitive particles comprise an inorganic crystalline material.
3. The electrophotographic plate of claim 1 in which the photosensitive particles comprise phthalocyanine pigments.
4. The electrophotographic plate of claim 3 in which the phthalocyanine pigment is selected from the group consisting of the X and B forms of metal-free phthalocyanine and metal phthalocyanines.
S. An electrophotographic plate having a photoreceptor binder layer comprising photosensitive particles dispersed in an electronically active organic matrix binder in an unoriented fashion in an amount of from about O.l to 5 percent by volume of said binder, said photosensitive particles exhibiting the capability of photo-excited electron generation and injection in the surrounding active matrix binder, said active organic matrix binder being capable of supporting the injection of photo-excited electrons from said photoconductive particles and transporting said electrons through said active matrix binder wherein said active matrix comprises at least one material selected from the group consisting of 2,4,7 trinitro-9-fluorenone, 2,4,5,7 tetranitrofluorenone, trinitroanthracene, dinitroacridene, tetracyanopyrene, and dinitroanthraquinone, said material being substantially transparent in the wavelength region of from about 4,200 to 8,000 Angstrom Units.
6. The electrophotographic plate of claim 5 in which the photosensitive particles comprises an inorganic crstalline material.
7. The electrophotographic plate of claim 5 in which the photosensitive particles comprise phthalocyanine pigments.
8. The electrophotographic plate of claim 7 in which the phthalocyanine pigment is selected from the group consisting of the X and B forms of metal-free phthalo cyanine and metal phthalocyanines.
9. The electrophotographic plate in claim 5 in which the photoreceptor layer is supported on an electrically conductive substrate.
10. A method of imaging which comprises:
a. providing an electrophotographic plate having a photoreceptor binder layer photoconductive particles dispersed in an electronically active organic matrix binder in an unoriented fashion and in an amount of between about 0.1 and 5 percent by volume of said binder, said photoconductive particles being capable of photogenerating electrons and injecting them into the surrounding active matrix material, said active matrix material being capable of supporting the injection of photo-excited electrons and transporting said electrons through said active material, wherein said active matrix comprises at least one material selected from the group consisting of phthalic anhydride, tetrachlorophthalic anhydride, benzil, mellitic anhydride, stricyanobenzene, picryl chloride, 2,4-dinitrochlorobenzene, 2,4-dinitrobromobenzene, 4- nitrobiphenyl, 4,4-dinitrobiphenyl, 2,4,6- trinitroanisole, trichlorotrinitrobenzene, trinitro-O- toulene, 4,6 dichloro, l,3 dinitrobenzene, 4,6 dibromo, 1,3 dinitrobenzene, p-dinitrobenzene, chloranil, bromoanil, 2,4,7 trinitro-9-fluorenone,
2,4,5,7 tetranitrofluorenone, trinitroanthracene, dinitroanidene, tetracyanopyrene, and dinitroanthraquinone,
. uniforming charging said plate, and
exposing said plate to a source of radiation to which the active layer is substantially transparent and non-absorbing whereby injection and transport of photogenerated electrons from said photosensitive particles occurs through said active transport binder to form a latent electrostatic image on the surface of said plate.
11. The method of claim 10 which further includes developing said latent image to make it visible.
12. The method of claim 10 in which the substrate is substantially transparent and exposure is carried out through said substrate.
13. The electrophotographic plate of claim 1 in which the photosensitive particles comprise a phthalocyanine pigment in a 2,4,7-trinitro-9-fluorenone binder.
14. The plate of claim 13 wherein the phthalocyanine pigment is copper phthalocyanine.
15. The electrophotographic plate of claim 1 in which the photosensitive particles comprise trigonal selenium in a 2,4,7-trinitro-9-fluorenone binder.
16. The electrophotographic plate of claim 1 in which the photosensitive particles comprise dinitroacridine and beta-form metal-free phthalocyanine in a 2,4,7-trinitro-9-fluorenone binder.
17. The electrophotographic plate of claim 1 in which the photosensitive particles comprise X-form metal-free phthalocyanine in a 2,4,7-trinitro-9- fluorenone binder.