US3486889A - Cellulosic photoconductive imaging member containing carboxyl reactive groups - Google Patents

Description

United States Patent 3,486,889 CELLULOSIC PHOTOCONDUCTIVE IMAGING MEMBER CONTAINING CARBOXYL REAC- TIVE GROUPS Edward G. Bobalek and John R. Hart, Orono, Maine, and Donald L. Fauser, Cleveland, Ohio, assignors to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware No Drawing. Filed Feb. 7, 1966, Ser. No. 525,294 Int. Cl. G03g 7/00 US. Cl. 96--1.8 23 Claims ABSTRACT OF THE DISCLOSURE A photconductive imaging member is composed of matted and intertwined fibers containing carboxyl reactive groups which are capable of chemically associating therewith a metal ion containing photoconductor, the resulting member being in the form of a flexible self-supporting sheet. The imaging member is free of mobile ionic charge carriers thus providing a surface portion of high electrical resistance in the dark. The fibers may be cellulosic containing materials such as wood pulp, cotton or other naturally occurring cellulose containing fiber materials. The content of reactive carboxyl groups in the fiber may be increased over that occurring naturally by (1) bleaching chemically pure pulp, (2) an ion exchange reaction in which ferrous ions are exchanged with carboxyl groups followed by reacting acrylic acid near the site of the exchange reaction, and (3) admixing a latex of a carboxylated polymer with the fibrous furnish.

This invention relates to an improved photoconductive imaging member comprised of a photoconductive material and a multiplicity of fibers, the fibers containing reactive groups capable of chemically associating a photoconductor material thereto, the fibers being formed into a self-supporting sheet containing a sufficient amount of substantially permanently associated photoconductor material to provide a photoconductive imaging member.

Imaging members for electrostatic photography are known which include a base having a surface coating thereon which includes photoconductive material dispersed in a binder which acts to bind the particles to each other and to the base. These binders are usually synthetic or natural resins or polymers which provide an electrically insulating medium holding the photconductor in place on the base. A variety of bases have been utilized including metal or metal foils, paper and electrically conductive plastic sheet material. In each case, the photoconductive surface layer is formed on the base by a coating operation performed after formation of the base.

In the case of an imaging member comprising a coating on a paper base, the paper base is formed by conventional paper making techniques and as is usual, the paper base itself includes what is referred to as a wire side and a felt side. The two different sides of the sheet have different characteristics, the felt side being much smoother, and the usual practice is to coat the photoconductivebinder layer on the felt side of the sheet. Sometimes, the practice includes the use of a size coating over either the wire side or felt side of the sheet in order to provide a smooth base surface upon which the photoconductive layer is deposited, and in some instances, this intermediate layer is used to provide an electrically conductive layer intermediate the paper base and the photoconductive coating. This intermediate layer may also function as a barrier layer to prevent cross-migration of components from the paper to the photoconductive layer.

The ratio by weight of photoconductor to binder in 3,486,889 Patented Dec. 30, 1969 ice imaging members of the type above described varies from 1:1 to 25:1, and the photoconductor commonly used is photoconductive zinc oxide prepared by the French process, a process will known in electrophotography. The resultant coated paper sheet usually has a relatively high basis weight as compared to ordinary coated papers and has a significant portion of the weight in the photoconductive layer. Another characteristic of coated paper imaging members utilizing a relatively high proportion of photoconductive zinc oxide pigment in the coating is the somewhat abrasive nature of the coated sheet. Other photoconductor pigments used in a coated sheet, such as photoconductive titanium dioxide and zinc sulphide, also exhibit similar abrasive characteristics.

The resin component and dispersed photoconductor of the coated imaging member may be deposited from an organic solvent, from an aqueous medium, or by hot melt technique. The usual procedure is to prepare a coating mixture which is deposited on a web of the base material by conventional paper converting equipment such as an air knife coater, reverse roll coater, trailing blade coater and the like.

In the event that a photoconductive layer is desired on each side of the base, two coating operations are required and care must be taken in the second coating operation not to affect adversely the coating previously formed on the reverse side of the base.

In accordance with the present invention the use of a binder or adhesive containing dispersed photoconductor to form a separate layer on a base is eliminated. Instead, a sufficient amount of photoconductive material is substantially permanently chemically associated with the fibrous material of a self-supporting sheet to provide a photoconductive imaging member. The chemical association in accordance with the present invention is believed to be in the nature of an ionic bond between a reactive site on or bonded to the fiber and the surface of the particulate photoconductor, or by chemi-sorption, or a combination of both types of bonding, and is to be distinguished from mere mechanical trapping of the photoconductor by the matted fibrous material.

Formation of an image member of the type in accordance with the present invention offers several advantages, the first of which is that in the case of cellulose containing fiber materials such as wood fiber, the sheet may be formed by adding the photoconductor to the aqueous pulp slurry, and forming the resultant imaging member during the felting of the fibers which takes place on the paper making machine. A non-two-sided paper, that is, a sheet having surfaces of substantially the same physical characteristics on each side, may be provided by use of a vertical paper forming machine such as a Verti-Forma machine, details of which are shown in US. Patents 2,969,- 114 and Re. 25,333.

Accordingly, it is a primary object of the present invention to provide a self-supporting imaging member having high electrical resistance in the dark and including photoconductive material and a multiplicity of fibers, at least a portion of the photoconductive material being substantially permanently chemically associated with the fibers of the member.

Another obiect of the present invention is the provision of a light-weight electrophotoconductive fiber-containing sheet including a particulate photoconductor at least a portion of which is substantially permanently chemically associated directly to the fibers of the sheet.

Another object of the present invention is the provision of an imaging member as described above wherein the fibrous material contains cellulose.

Another object of the present invention is the provision of electrophotographic imaging members comprised of fibrous material containing reactive groups wherein these groups are naturally present or chemically reacted into or on the fiber structure and wherein the fibers are formed into a self-supporting sheet, the reactive groups of the fiber operating to provide substantially permanent chemical association of a photoconductor into the sheet structure.

Another object of the present invention is the provision of an imaging member as above described wherein the reactive groups are carboxyl groups.

Another object of the present invention is the provision of an electrophotographic imaging member comprised of photoconductive material, fibrous material and a polymer, each of the latter containing reactive groups, the photoconductor being capable of chemically associating with the respective reactive groups, and the reactive groups preferably being carboxyl groups.

Another object of the present invention is the provision of an electrophotographic imaging member at least one outer surface portion of which comprises a photoconductor substantially permanently chemically associated to a network of cellulose fibers by reactive groups associated with the fibers.

Another object is the provision of an electrophotographic imaging member including a particulate photo conductor wherein the performance of the imaging member in uses other than for electrophotography is similar to conventional uncoated paper, and which may be manufactured using conventional paper making machinery.

A further object of the present invention is the provision of methods for forming electrophotographic imaging members of the types above described.

Other objects and advantages of the invention will be apparent from the following description and the ap pended claims.

In one form, the electrophotographic imaging member of the present invention is a self-supporting flexible sheet made up of a multiplicity of fiber members formed together, the fiber members including reactive groups occurring naturally, or added thereto as will be described hereinafter. Substantially uniformly dispersed throughout the sheet and permanently associated therewith is a photo conductor material which is maintained in substantially fixed position in the sheet by chemical association with the reactive groups of the fibers. The fibers preferably are those containing cellulose such as the fibers of wood pulp, cotton and other naturally occurring cellulose containing fiber materials. For the purposes of description, however, reference will be made to fibrous material available from wood.

Natural fibers, such as in wood, cotton, etc., are ordered bundles of fibrils, and cellulose constitutes a major part of the fibrils. The exact dimensions of the fibrils varies depending on the source, and while the precise dimensions of the fibrils are not clearly defined, it is known that they are larger than one molecule long and one molecule thick. In general, fibrils have a length to diameter ratio exceeding 5 to 1, and the diameter is a small fraction of a micron. In unpurified native cellulose, such as that occurring in wood, lignin and polyglucuronic acids are present, the latter having a structure similar to chemically pure cellulose but including carboxyl groups in the place of the methyl alcohol groups of each ring of the molecular chain.

In the chemical processing or pulping of wood chips, a considerable amount of the lignin is removed, leaving cellulose and polyglucuronic acid present in the individual fiber structure. Some carboxyl containing materials of the fiber have been generally classified as hemicellulose materials including polyglucuronic acid.

The processing of cellulose-containing fiber materials for the manufacture of paper usually includes the use of additives which alter the Zeta potential of cellulose, leaving residues or contaminants in the finished sheet which are detrimental for electrophotography. These additives which res lt in the presence of mobile ionic charge carriers, broadly are characterized as materials providing ionic charge carriers or materials which solubilize other compounds to produce ionic charge carriers. In either case they act to increase the electrical conductivity of the sheet to a point where it is no longer useful in electrophotography. Typical such materials are low molecular weight alkali metal salts, non-volatile amines and amides, organic non-ionic materials which are hygroscopic, such as polar non-ionic surface active agents including their non-volatile residues, nitrogenous materials, and alcohols. The non-ionic organic contaminants are also characterized by a low molecular weight and a high dipole moment compared to that of cellulose.

Some of these additives adversely affect the electrophotographic characteristics of the sheet by ionization through interaction with water (absorbed by the sheet from the air) to form ionic charge carriers. These additives include, for example, acidic paper makers alum, internal sizing additives such as metallo-organic salts, and fillers such as some clays and chrysotile asbestos fiber which increase the electrical conductivity of the sheet. While the detrimental effect of the presence of some of these materials may be overcome by effectively reducing the water contained in the sheet, for example, to a bone dry state, before carrying out the electrophotographic process, it is preferred in accordance with the present invention that the presence of these materials be eliminated. An effective Way of removing some of the materials is by washing the pulp in single or multiple stages before introducing the furnish on the drainage wire of the paper making machine. In other instances, the nature of the additive is such that it is removed only with difliculty by conventional washing procedures, and in such cases, the procedures of stock furnish preparation should be such that the use of these additives is eliminated entirely.

In some instances, the nature of the low molecular charge carrier is such that it is volatile, and while a portion of it may be removed by washing, the remainder or a substantial portion of the additive may be removed during the sheet drying operation.

Conventionally prepared stock using one or more of the additives described above was used in an attempt to form an electrophotographic imaging member in which French process zinc oxide was mixed with the stock and formed into a sheet. The zinc oxide was present in the final sheet between 50% to 400% based on the bone dry Weight of the stock. The results indicated that no image could be produced, and furthermore, electrometer tests indicated that the sheet could not be printed because of the absence of any measurable light decay characteristic. By extracting the pulp as described above, to remove these contaminants, a chemically cleaned pulp was provided and was used to form a sheet in accordance with the present invention by the addition of a particulate photoconductor, for example, zinc oxide. The sheet was charged, exposed and developed and provided an image.

For example, several sheets were made using between one and three grams of chemically cleaned wood pulp which was diluted to a consistency of 0.3%. An aqueous slurry of photoconductive zinc oxide was added to the aqueous slurry of fiber while mixing. The amount of zinc oxide in the slurry was varied from between one to four parts by weight that of the fiber (bone dry weight), and the resulting mixtures were formed into hand sheets of about eight inches by eight inches with a retention in each case of sufiicient amount of zinc oxide to provide between 50% and 400% in the finished sheet. The sheets were drum dried at between 200 to 230 F. for five minutes, and subsequently calendered. Before printing, the sheets were allowed to reach a relative humidity of less than about 45%, and printed by charging and exposing them to an original for two to four seconds using a 250 watt photoflood lamp. In exposing the sheets, a high contrast positive transparency was used and was placed in o ely spaced relation to the sheet being exposed.

Subsequently the sheets were developed with a liquid developer and a print was observed. By varying the amount of chemically cleaned fibers for a given sheet size, the basis weight of the paper or its weight per unit area could be varied.

The above procedure was followed using batches of thirty grams of fiber with between 50% and 400% of photoconductive zinc oxide present in the finished sheets based on the bone dry fiber weight, and similar results were observed. By increasing the amount of fiber, the basis weight of the sheet was increased.

Hand sheets formed as above described were made with varying percentage of air, for example, loose fiuffs containing approximately 85% air. Upon charging, exposing and developing an image was formed. By calendering, the quality of the image, particularly image density and continuity were improved'by as much as five times.

The results obtained utilizing chemically cleaned pulp tended to indicate the presence of reactive groups in the wood fiber, either along the surface thereof or in the interior of the fiber member, and that such groups cooperated to maintain the zinc oxide, or other photoconductor, such as titanium dioxide or zinc sulphide, substantially permanently chemically bound to the fiber. It is believed that the zinc oxide particles deposit on or form an array along the outer surface of each of the fibers of the pulp mass as controlled by the distribution of carboxyl reactive groups along the length of the fiber. As a sheet is formed, the matting and intertwining of the fibers into a network forms a self-supporting structure.

The fibers used to prepare the sheets in the above identified examples were approximately 2,500 to 5,000 microns long and approximately to 30 microns in diameter while the particulate photoconductor varies from about 0.2 to about 0.4 micron in diameter.

A significant feature of the present invention is to increase the content of the reactive groups of the fiber over that occurring naturally to increase the retention of photoconductor in the finished sheet. One method of increasing the amount of reactive groups in the fiber was to bleach the chemically pure pulp, the bleaching operation increasing the carboxyl content by oxidation. The pulp was thereafter washed to remove residual bleach and other contaminants, and formed into imaging members.

Another method utilized to increase the reactive groups on the fibers was to disperse the pulp in an aqueous medium, and add ferrous ions to the aqueous slurry so that the ferrous ions entered into an ion exchange reaction with the carboxyl groups. Thereafter, a carboxyl containing ethylenically unsaturated monomer such as acrylic acid was added to the mixture along with hydrogen peroxide catalyst so that the monomer was chemically reacted to the fiber near the points where the carboxyl group of the fiber had entered into an ion exchange reaction with the ferrous ion. For further information as to this process, reference is made to U.S. Patent No. 3,083,118. With this mechanism, additional carboxyl groups were added to the fiber thus increasing the retention of particulate photoconductive material along the length of the fiber to increase the quality of the electrophotographic print.

Approximately 3 grams of chemically cleaned paper fiber was pretreated as above described to polymerize methacrylic acid monomer onto the fiber such that there was a one percent increase in the weight of the paper fiber. To an aqueous slurry of the treated fiber at a pH 7 or above (by use of ammonia or acetic acid, as required), approximately 100 to 300 percent by weight (bone dry fiber weight) of photoconductive zinc oxide was added, and hand sheets formed as above described. Upon charging, exposing and developing using a high contrast positive transparency, images were visible. Other materials which may be used in grafting carboxyl groups onto the fiber include alpha or beta methacrylic acid (including crotonic acid), itaconic acid, acrylic acid and maleic acid, these acids being included on the fiber either as a homopolymer or a copolymer with non-acidic vinyl monomers, and mixtures thereof. These materials may be generically identified as ethylenically unsaturated monomeric acids including one or more carboxyl groups. Preferable acidic materials are also characterized by the fact that they are water soluble.

Another procedure for increasing the carboxyl content of the fibrous furnish includes admixture therewith of a latex of carboxylated polymers such as a copolymer of crotonic acid and vinyl acetate having a relatively low percentage of carboxyl groups or a carboxylated styrenebutadiene latex. The percentage of carboxylation of these latices is relatively small, the carboxyl groups being utilized in the latex structure to promote a mechanism for stabilizing the latex particle suspension against aggregation and flocculation as opposed to the use of soaps or anionic or cationic dispersing agents. Thus, these particular latex materials do not include the usual dispersing agents in quantities sufiicient to operate as contaminants in electrophotographic techniques.

Other latex polymers which may be used include terpolymers of styrene, butadiene, and one or more ethylenically unsaturated acidic monomers, for example, acrylic acid, fumaric acid, or crotoni-c acid. The styrene content of the polymer is at least 30% while the acidic monomer content is between 1% to 10%, the latex particle size being between 700 and 50000 Angstrom units. The terpolymer possesses a glass transition temperature of less than C. and preferably in the range of 25 to 35 C., and possesses a viscosity average molecular weight exceeding 200,000. For the purpose of the present invention, carboxylated latex materials having a glass transition temperature as described above may be used to increase the carboxyl content of the fibrous material.

A series of sheets were made by diluting three grams of paper fiber to 0.3% solids consistency with water. The latex of the type previously described was added dropwise with agitation while the dispersion was maintained at a pH of about 7. Latex was added in varying amounts of between 1% to 25% solids weight based on bone dry fiber weight. An aqueous slurry of zinc oxide was added while the mixture was agitated. The amount of zinc oxide being added was varied from 3 to 12 grams. The resultant aqueous slurries of latex, fiber and zinc oxide were placed into the headbox of a hand sheet forming machine and sheets formed of approximately 8 inches by 8 inches in size. The resultant sheets were drum dried at between 200 and 230 F. for about five minutes and then calendered. After calendering the sheets in some cases were printed immediately and in other cases Were allowed to come to an equilibrium condition in an atmosphere of less than about 50% relative humidity and then printed.

The use of a latex operates to increase the dry and wet strength of the finished sheet while retaining an increased quantity of zinc oxide, and to this end, the latex is preferably of uniform size having a particle size less than about 1000 Angstrom units and an average particle size of approximately 750 Angstrom units. This smallness of size in the latex is desirable because the latex appears to plate out on the fiber, adheres thereto by chemical cohesive forces, e.g. secondary valence forces, and helps the fiber to pick up zinc oxide more efiiciently. It is believed that the latex, being attracted to the fiber, comes close to those areas which are active carboxyl sites. It is desirable that the latex be present in an amount not greater than about 25 by weight (bone dry weight of paper fiber), and it has been observed that when present in an amount of approximately l%, the latex operates satisfactorily.

In another form of the present invention, wood fiber which has had the carboxyl content increased by a polymer deposition procedure previously described may be used as a starting material to which a carboxylated latex is added, using the procedures generally described previously. By varying the percentage of carboxyl content by polymer deposition through polymerization, or addition of a carboxylated latex, the hydrophobic-hydrophilic balance of the fibrous material may be varied. For example, a sheet to which latex has been added and wherein the carboxyl content of the fiber has been increased is more hydrophobic than one in which the latex has been omitted. A sheet including a carboxylated latex exhibits increased wet strength properties because of the increased hydrophobic nature of the sheet.

Other modifications and procedures which have been used include the addition of small amounts of ammonium lignin sulfonate, or a mixture of ammonium lignosulfonate plus wood sugars commercially available under the trademark Orzan. Approximately 0.01% by weight (bone dry fiber weight) aids in forming the aqueous slurry of zinc oxide and at the same time helps to increase the ability of the sheet to retain an electrostatic charge.

In chemically carboxylating the fiber it is preferred that a substantial portion of the fibers be carboxylated so that the increase of fiber weight due to carboxyl groups is less than 10% although the total weight increase of the fiber may be as high as 300% because most of the total weight gain is contributed by the non-carboxyl components of the carboxylated macromolecules associated with the fiber. While the total weight gain may be increased by 400% or more, increases above 100% reduce the ability of the modified fibers to form a strong sheet at a low temperature. Non-woven fabric techniques, using a supplementary adhesive, tacky at low temperatures, or use of high temperatures to melt-flow the carboxyl containing fiber adduct may be used to form a sheet from fibers which have been carboxylated to a level of 0.1 to 10% by weight but with a total weight gain in excess of 100%.

A significant practical advantage of the present invention is that thin sheets having a low basis weight can be formed into satisfactory electrophotographic sheets. However, it is to be noted that thick sheets of low basis weights, that is, sheets of low density are possible in accordance with the present invention and may be printed electrophotographically to provide good images. Thick sheets have the disadvantages that they tend to hold a residual charge and to discharge somewhat heterogenously rather than homogeneously.

Other additives which may be used include inorganic titanium gels or non-photoconductive gels, optical pigments for changing the color of the sheet construction, and sensitizers customarily used with photoconductors to extend the spectral response thereof or increase sensitivity thereof.

In the formation of the sheet and during the handling of the paper stock, it was observed that the use of relatively low pH range, for example, in the range of 3.5 to 4.5 resulted in sheets which gave poor quality prints, and accordingly it is desired that the pH be kept near neutral or slightly basic during processing of the chemically clean pulp and formation of the sheet. The preferred range of photoconductor is between 0.5 and 5 times the bone dry weight of the fiber. In the case of fibers whose carboxyl content has been increased by chemical reaction or admixture, increased amounts of photoconductor above 5 times the bone dry weight of the fiber may be used.

Bleached kraft pulp appears to give better results than bleached sulfite pulp. Further, pulp having a low Canadian freeness appears to give a slightly better image than pulp having a relatively high Canadian freeness.

In accordance with the present invention the furnish containing the photoconductor as previously described may be associated with a member providing conductivity, for example wet laminated onto a layer of partially dewatered paper base stock of another type, previously deposited onto a drainage wire as from a separate headbox. For example, any of the previously described photoconductive paper stocks may be utilized as a top portion of a sheet while the underlying portion of the sheet is formed of paper stock which may consist of between one to two grams of paper fiber and electrically conductive pigment such as a conductive non-photoconductive zinc oxide present in an amount of between to 300% based on oven dry fiber weight. Alternate underlying conductive paper stocks includes those made in the proportions of one to two grams of paper fiber to which has been added between 0.1 to 0.3 grams chrysotile asbestos fiber, or, one to two grams of paper stock to which has been added two to twenty percent based on oven dry paper fiber weight of an alkylketene dimer available under the trademark Aquapel. In this manner a sheet may be provided which has both an electrophotographic portion and an electrically conductive portion for facilitating the formation and development of images. It is also within the scope of this invention to treat the fibers of such base stock in accordance with any of the procedures of the invention outlined above so the reactive groups are provided thereon, and the conductive pigment is chemically associated with the fibers. Mobile ionic charge carriers may be substantially eliminated as noted previously if their presence interferes with the photoconductive portion of the sheet.

It is also possible in accordance with the present invention to wet laminate both sides of the base stock with photoconductive paper of the type previously described. In this case, the paper base includes paper fiber and asbestos fiber, supra, or alkylketene dimer with a high conductivity zinc oxide or combinations thereof, with each surface of the paper base member having wet laminated thereon and integrally associated therewith a photoconductive paper of the type previously described.

The advantages of the improved photoconductive imaging member of the present invention includes the fact that there is no continuous binder phase as is utilized in the conventional imaging members which incorporate a particulate photoconductor. This substantially reduces curl problems due to changes in relative humidity and/ or combinations of relative humidity and temperature because of the fact that the sheet construction in accordance with the present invention is symmetrical. Additionally, the imaging member of the present invention may be handled much in the same manner as an uncoated paper sheet in that basis weight, burst, and tear strength and various other characteristics may be varied to produce varying physical characteristics in the sheet depending on the desired use thereof. For example, the sheet may be made as thin as tissue paper or as thick as blotter paper and is still printable electrophotographically. Further, the sheet is printable on each side, that is a latent image may be formed on one side and developed while preventing deposition of developer on the other side. After formation of the first image, the sheet or web may be printed on the reverse side, with the same precaution being taken to prevent developing the previously printed side of the sheet.

Since additives may be included in the sheet, particularly resinous type materials and preferably carboxylated materials such as the latices previously mentioned, the sheet may be formulated to provide substantially wet strength characteristics thereby permitting formation of a sheet which maintains its physical integrity when in contact with an aqueous medium.

In accordance with the present invention, the photoconductive pigment is present in an amount sufficient to provide a stable electrostatic latent image upon exposure of a charged image member to a light pattern. It has been observed in accordance with the present invention that the ratio of zinc oxide to fiber may be as low as 0.5 :1 and the paper will operate satisfactorily to produce an image electrophotographically. This is significantly less than the ratio of photo conductor to resinous adhesive binders used in conventional coated electrophotographic imaging members. The result is that in the case of pigments such as photoconductive titanium dioxide, zinc oxide, zinc sulfide or mixtures thereof and the like, a reduced amount of such pigments distributed through the sheet likewise reduces substantially the abrasive character of the sheet. Also, the overall weight of the sheet is far less than the weight of a corresponding imaging member in which the photoconductor is uniformly dispersed in a continuous binder as a coating on paper or other substrates.

While the article and method herein described constitutes a preferred embodiment of the invention, it is to be understood that this invention is not limited to this precise article and method and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. An electrophotographic imaging member comprising a surface portion containing intertwined and matted fibrous cellulosic material and a finely divided metal ion containing photoconductor material dispersed in said fibrous material, said fibrous material being substantially free of mobile ionic charge carriers for providing said surface portion with a high electrical resistance in the dark for holding an electrostatic charge applied thereto, said fibrous material having carboxyl groups chemically associated therewith, said photoconductor being substantially permanently chemically associated with said carboxyl groups, and said chemically associated photoconductor material being present in said surface portion in an amount suflicient to permit formation of an electrostatic latent image thereon upon exposure to a light pattern.

2. An electrophotographic imaging member as set forth in claim 1 wherein said fibrous material contains cellulose fibers in major proportion.

3. An electrophotographic imaging member as set forth in claim 1 wherein said photoconductor is present in an amount between 0.5 and 5 times the dry weight of said fibrous material.

4. An electrophotographic imaging member as set forth in claim 1 wherein said matted fibrous material includes a carboxylated latex polymer.

5. An electrophotographic imaging member comprising a self-supporting and flexible sheet of intertwined and matted fibrous material, said fibrous material being a naturally occurring wood fiber modified, while preserving its fibrous form, to have a reactive carboxyl group content greater than that naturally occurring in said wood fiber, a finely divided metal ion containing photoconductor material admixed with said fibrous material, said fibrous material being substantially free of mobile ionic charge carriers for providing said sheet with a high electrical resistance in the dark for holding an electrostatic charge applied to a surface thereof, said reactive carboxyl groups chemically associated said photoconductor to said fibrous material, and said photoconductor material being present in an amount suflicient to permit formation of an electrostatic latent image thereon upon exposure to a light pattern.

6. An electrophotographic imaging member including a conductive base portion and at least one surface portion, said surface portion comprising a layer containing intertwined and matted fibrous cellulosic material, said fibrous material including carboxyl groups, a finely divided metal ion containing photoconductor material being substantially permanently chemically associated with said carboxyl groups, said matted fibrous material being substantially free of mobile ionic charge carriers for providing said surface portion with a high electrical resistance in the absence of light for holding an electrostatic charge applied thereto, and said photoconductor material being present in an amount suflicient to permit formation of 10 an electrostatic latent image on said surface upon exposure to a light pattern.

7. An electrophotographic imaging member according to claim 6 wherein the conductive base portion comprises intertwined and matted fibrous cellulosic material having carboxyl groups chemically associated therewith and a finely divided electrically conductive pigment chemically associated with said carboxyl groups.

8. An electrophotographic imaging member according to claim 6 and including a further surface portion on the opposite side of said base portion to provide an imaging member having photoconductive surface portions on opposite sides of said conductive base portion.

9. An electrophotographic imaging member comprising a self-supporting flexible sheet including a surface containing intertwined and matted chemically modified fibrous cellulosic material, said modified material containing reactive carboxyl groups and being the polymeriz'ation reaction product of a fibrous cellulosic material and a carboxyl containing monomer and having a high electrical resistance in the absence of light, said carboxyl containing monomer being present by weight in an amount not greater than 10% based on the dry weight of said fibrous material, and a metal ion containing photoconductor pigment chemically associated with said modified fibrous material in an amount sufficient to permit formation of an electrostatic latent image on said surface upon exposure to a light pattern.

10. An electrophotographic imaging member as set forth in claim 9 wherein said fibrous material is cellulose.

11. An electrophotographic imaging member asset forth in claim 9 wherein said member includes between 1% and 25% by weight of said fibrous material of a carboxyl containing latex polymer having a glass transition temperature less than about C.

12. An electrophotographic imaging member as set forth in claim 9 wherein said fibrous material is the reaction product of naturally occurring wood fiber and at least one organic carboxyl containing monomer.

13. An electrophotographic imaging member as set forth in claim 12 wherein said member is free of mobile ionic charge carriers.

14. An electrophotographic imaging member as set forth in claim 11 wherein said photoconductor is zinc oxide.

15. An electrophotographic imaging member as set forth in claim 14 wherein said zinc oxide is present in a ratio by weight of from 1:05 to 1:5 of fibrous material to photoconductor.

16. An electrophotographic imaging member as set forth in claim 11 wherein said carboxyl containing latex polymer has a particle size in the range of 700 A. to 5,000 A.

17. The method of producing an electrophotographic imaging member comprising the steps of providing a material containing fibrous cellulose having reactive carboxyl groups thereon, said fibrous material being free of mobile ionic charge carriers and capable of forming a self-supporting flexible sheet, admixing an aqueous slurry of said fibrous material with a finely divided metal ion containing photoconductor capable of chemically associating with said carboxyl groups, and dewatering said mixture of photoconductor and fiber to form a sheet including a surface portion having a high electrical resistance in the absence of light and having a sufiicient amount of said photoconductor to form an electrostatic latent image upon exposure to a light pattern.

18. The method as set forth in claim 17 wherein said fibrous material comprises in major proportion cellulose fibers and wherein said mobile ionic charge carriers are removed by washing.

19. The method as set forth in claim 17 wherein said fibrous material is a naturally occurring cellulose material, and wherein said fibrous material is reacted with an organic carboXylic acid to increase the active carboxyl groups on said fiber above the amount occurring natural- 20. The method as set forth in claim 17 including the step of adding to said slurry sufficient carboxyl containing latex polymer to provide between 1% and 25% by dry weight of said fibrous material of said latex polymer prior to the addition of the photoconductor.

21. The method as set forth in claim 19 wherein said organic carboxylic acid is a carboxyl containing ethylenically unsaturated monomer, and wherein said monomer increases the dry weight of fiber not more than 10%.

22. The method as set forth in claim 17 including the step of calendering the sheet after formation thereof.

23. The method as set forth in claim 21 including the step of adding to the slurry sufiicient carboxyl containing latex polymer to provide between 1% and 25% by dry weight of said fibrous material of said latex polymer prior to the addition of the photoconductor.

References Cited UNITED STATES PATENTS G'EORG'E F. LESMES, Primary Examiner M, B. WlTTENBERG, Assistant Examiner US. Cl. X.R.