US3152895A

US3152895A - Coating composition for the production of electrophotographic recording members

Info

Publication number: US3152895A
Application number: US179600A
Authority: US
Inventors: George H Tinker; Mai Shu Huai David; Roger E Burke
Original assignee: T F WASHBURN Co
Current assignee: T F WASHBURN Co
Priority date: 1962-03-14
Filing date: 1962-03-14
Publication date: 1964-10-13
Anticipated expiration: 1981-10-13

Description

Oct. 13, 1964 G, H. TINKER ETAL 3,152,895

comme COMPOSITION FOR THE PRonucTroN oF ELECTROPHOTOGRAPHIC RECORDING MEMBERS I Filed March 14, 1962 ooo; wzO-.ZOas-Oo United States Patent O This invention relates to the field of electrophotography, and more particularly refers to novel coating compositions for the production of electrophotographic recording elements, and to the products produced therefrom.

As developed in the prior art, the electrostatic printing process generally comprises placing a uniform electrostatic charge on a recording element by any one of several disclosed methods, subjecting the recording element to light from an optical image t dissipate the charge selectively in such a manner as to produce an electrostatic image, and converting the electrostatic image into a permanent visual image.

Inthe particular form of electrostatic photography with which the present invention is concerned, the recording element comprises a multi-layer sheet. The first layer is a base layer generally having highelectrical conductivity. Over the base layer is coated a second layer comprised of a resinous binder exhibiting high electrical resistivity in which are embedded particles of a photoconductive material. During processing, the base layer is normally maintained at ground potential and serves as an electron reservo1r.

In utilizing the recording member for forming an electrophotographic image, an electrostatic charge is first applied to the photosensitive or photoconductive layer, in

`the absence of actinic illumination, by means of a charging device as, for example, a corona. The charge is vretained -even after the charging device is `turned olf as long as the charged surface is not exposed to light. The charged surface is then subjected to an actinic image of the object which is to be reproduced, forming a pattern of light and shadow on the surface of the photosensitive layer. Wherever it is illuminated by actinic radiation, the conductivity of the photoconductive layer increases in proportion to the intensity of the radiation. As a result, the electrostatic charge is dissipated selectively in proportion to the magnitude of the actinic radiation to which it is exposed in each area. An electrostatic latent image is thereby formed, the greatest surface charge density remaining in unexposed areas, and the least charge density remaining in the areas which receive the strongest actinic illumination.

The latent image is then rendered visible by development with toners containing electrostatically charged pigment particles. The toners may be applied to the image as air-borne clouds, as suspensions in insulating liquids of low dielectric constant, or as dry particles adhering to oppositely charged carrier particles of substantially vlarger size such as iron powder or glass beads. Dependent upon the relative polarity of the electrostatic latent image and the developing pigments, the pigment will adhere differentially to the charged and discharge areas, thereby rendering them differentially visible. The pigment image may be then transferred by contact to a receiving sheet and aflixed thereto, or alternatively, may be directly afiixed to the photoconductive layer by dry- 3,l52,895 Patented Oct. 13, 1964 ing, thermofusion, or by the action of solvent vapor. The methods of development are well vknown in the art and do not constitute a part of the present invention.

The base layer should preferably be of a material which is more conductive than the photoconductive layer. The base layer is normally connected to ground potential during processing. Examples of base layers of this type are aluminum sheet and carbon filled paper. A nonconductive base materialV may be used if a relatively conductive interlayer is provided between the insulating base and the photoconductive layer. Examples of this type of base layer include glass plates treated with semi-conductive tin oxide, and dry paper overcoated with a vacuum-deposited aluminum film or a layer of a semiconductive pigment in a suitable binder resin. If conductive interlayers of this type are used, they are normally connected to ground potential during processing.

The photoconductive layer is comprised of a photoconductive material embedded in a resinous binder. Although numerous photoconductive materials are known in the art such as cadmium sulfide, sulfur, anthracene, anthraquinone, lead iodide, cadmium selenide, and many others, zinc oxide is generally used commercially, since it is relatively inexpensive and exhibits excellent photoconductive properties.

The resinous binder must have certain properties in order to be suitable for use in the production of electrophotographic recording members. It must not be sensitive-to normal air Yhumidity or normal temperature ranges. It must be compatible with the photoconductive pigment employed. It must havel theV ability to accept a high initial electrostatic charge, and to retain the charge over a substantial period, in the absence of actinic illumination, after the charging device is turned oli?. It must exhibit good electrical conductivity in conjunction with the photoconductive pigment when subjected to actinic illumination. It must also exhibit flexibility and the ability to offer satisfactory adhesive properties with respect to a variety of substrates. Finally, the coating composition inwhich it is applied must have a sufficiently high drying speed to permit it to be used in high speed commercial paper coating technique.

A number of resinous materials have been disclosed which may be used as binders. Among them are the silicone resins, cellulose esters such as cellulose acetate, cellulose acetate butyrate, cellulose nitrate, cellulose ethers such as ethyl cellulose, and methyl cellulose. Other suitable materials are polyvinyl acetate, polystyrene, acrylics, and various waxes.

Coating compositions for producing electrostatic recording members are generally prepared .by dissolving the resin binder in a suitable organic solvent, and then dispersing the photoconductive pigment such as zinc oxide into the solution. Coatings prepared from organic solvent coating compositions have been satisfactory with respect to electrical properties of the finished coating. However, the use of organic solvents ladds materially to the cost ofthe coating composition. Additionally, various safety hazards such as fire hazards and health hazards are encountered as a result of the inflammability and toxicity of many of the organic solvents. More recently, coating compositions have been developed which may be applied in the form of aqueous emulsions. Aqueous coating compositions have the advantages that they are nontoxic, they are explosion-proof, they permit more rapid coating and drying speeds, and they are more economical with regard to both material cost and cost of application.

Certain problems have been encountered in utilizing aqueous coating systems which somewhat offset their otherwise desirable properties. The greatest problem lies in the sensitivity of most emulsion-type or water-soluble resins to humidity. Since a good electrophotographic binder must be capable of high dark resistivity under all humidity extremes, one which tends to lose this property at higher humidity is unacceptable even though its other properties may .be good.

It is an object of the invention to provide a coating composition suitable for use in the production of electrophotographic recording elements by high speed commerical coating methods.

It is a further object to provide a coating composition which may be applied in the form of an aqueous emulsion.

It is still further an object to provide a coating composition in the form of an aqueous emulsion which may be used to produce electrophotographic recording media having excellent properties, especially with regard to electrostatic charge acceptance and dark electrostatic charge retention.

l the copolymer solution to form a stable emulsion. Various photoconductive pigments may be added to the emulsion to form a coating composition suitable for use in the production of electrophotographic coating members.

In the drawing:

FIG. 1 is a graph based on data obtained in tests of Y electrophotographic recording members.

The incorporation of hydrophobic resins and especiallyA epoxy resins into latex and emulsion paints has been accomplished in the past only with great diiiculty. The prior methods generally require the pre-emulsiiication of the resin followed by the blending of the emulsication product with the aqueous component. This process requires a complex system of adducts such as emulsiers,

wetting agents and protective colloids if a stable end product is to be produced. vSince most of these adducts are humidity-sensitive, the electrical properties of the coating are impaired.

In preparing av coating composition according to the invention, two separate components are rst formed.

` The first component is a hydrophobic component and comprises a solution of hydrophobic resin in an organic solvent, preferably an aromatic solvent. The second component is a hydrophilic component and comprises an aqueous solution of the ammonium salt of a copolymer of vinyl acetate and crotonic acid. The hydrophilic component serves in the nature of an emulsifying agent for the hydrophobic component. Additionally, the hydrophilic copolymer has a synergistic function in that it imparts certain desirable properties to the nal coating not exhibited by the hydrophobic resin alone, so that the end coating exhibits properties superior to those of both of the two individual components. The hydrophobic component is prepared by dissolving the hydrophobic resin in the organic solvent. The solution is then blended directly with the hydrophilic component. An oil-n-Water emulsion is thereby directly formed which may be brought to the proper consistency by the addition of water. The photoconductive pigment or filler may then be added together with other desired modifying agents such as various sensitizing dyes and pigments.

beads may be collected, washed, and dried before the 4 The preparation of the various components and the method of combining them are described in detail in the examples which follow.

HYDROPHILIC RESINOUS COMPONENT Example I PREPARATION OF 94%-6% VINYL ACETATE-CROTONIC ACID COPOLYMER AND ITS AMMONIUM SALT SOLUTION Y A formulation was prepared from the following ingredients in the listed proportions:

Parts by weight 1E1vano1 50-42 is a polyvinyl alcohol type of protective colloid.

The water was rst placed in a container and the Elvanol added thereto. While maintaining agitation, the vinyl acetate, crotonic acid, and benzoyl peroxide were added in that order. The mixture was heated to reflux temperature (152l56 F.), and held under reiiux until the temperature reached 190 F. The mixture was finally heated to 200 F. in order to drive off any remaining monomer. It was then cooled to F., the aqueous ammonia added, and the contents agitated until solution was complete. Hydrogen peroxide was then added and the solution cooled to room temperature. The resulting solution exhibited the following properties:

Solids 20-21%.

pH 8.5 to 9.0. Viscosity (#3, 4 r.p.m.) approx.

10,000 c.p.s. Appearance Slightly cloudy,

light color.

During the rst portion of the process described above, beads of polymer are formed when the catalyst is introduced, the polymer being insoluble in the continuous phase. Consequently, as a variation of the above procedure, when'polymerization is complete, the polymer ammonia solution is added. This avoids the necessity for driving off the unreacted monomer. However, if the ammonia is added to the reaction mixture, the monomer must be rst distilled olf before the aqueous ammonia is added.-

The formulation prepared above is freeze-thaw stable j for at least four cycles. Aging at room temperature or higher temperatures may cause a gradual yellowing of the solution, resultingfrom the break down of the residual free monomer. Yellowing can be retarded by removing as much free monomer as possible before adding the aqueous ammonia, and by the addition of hydrogen peroxide after the solution is formed.

Loss of ammonia through evaporation may cause a lowering in viscosity, as well as clouding of the solution, and even, in extreme cases, a precipitation of the copolymer. Further addition of ammonia corrects these conditions. To insure complete solution, a pH above 7 should be maintained.

The percentage by weight of crotonic acid based on the copolymer may vary from about 2% to about 12%. If the percentage of crotonic acid falls below 2%, the copolymer becomes insoluble in aqueous ammonia. When an amount greater than about 12% crotonic acid is utilized, the copolymerization does not proceed readily.

polymerization catalysts such as benzoyl peroxide and potassium persulfate. Catalyst proportions of from about 1.4% to about 3.4% based on total monomer are satisfactory. At the higher catalyst proportions, there is a tendency for the reaction mixture to coagulate upon the addition of ammonium hydroxide.

HY DROPHOBIC RESINOUS COMPONENT According to the invention, the materials which have been found to have the properties'which make them especially suitable for use in the coating compositions for the production of electrophoto'graphic record members are the resin-esters formed by reacting a polymer containing esteriable hydroxy groups With a higher fatty acid containing rosin. Among the suitable esteriiiable resins are the epoxy resins, alkyd resins, melamineformaldehyde resins, urea-formaldehyde resins, phenolformaldehyde resins, and polyurethanes. The preferred epoxy resin is the polyglycidyl polyether of Bisphenol A, 4,4"-isopropylidylidenediphenol. The preferred alkyd resin'is the reaction product of phthalic acid with glycerol.

The preferred rosin-containing higher fatty acid is tall .oil, and preferably tall oil containing from about 4% to about either of rosin itself or of the various rosin acids comprising the isomeric forms of abietic acid and other tricyclic diterpenes to be found in numerous grades and sources of naturally occurring rosin. The rosin acids occurring in unreiined tall oil are believed to comprise isomeric mixtures of tricyclic diterpenes such as 1,2,3,4tetrahydro 6 isopropyl-l-dimethyl-propyl-Z- naphthaleneacetic acid. Tall oil containing about 28% rosin is the preferred material.

Other higher fatty acids such as oleic acid, linoleic acid, and acids derived from soy-bean oil and linseed-oil may be used in conjunction with Wood or gum rosins.

The following examples illustrate `thepreparation of a hydrophobic resin component according to the invention.

Example 2 The. followingthree separate reactant groups lwere iirst prepared:

Parts Ingredients by Weight Group A Epon 1007 1 `1, 153. 4 Group B Shueo 300 2 809.8 Triphenyl phosphite..- 1. 6

Zinc naphtheuate. 10. 1

Group C Vinyl toluene 202. 5 Ditertiarybutyl pero 2. 0

1 Polyglycidyl polyether of Bisphenol A having a molecular weight of LOGO-5,000.

2 Tall oil containing 28% rosin.

` 475 F., and held until the reaction was complete. The

reaction product exhibited the following properties:

Acid number 7 9.

Total solids in `xylene 60-65.

Viscosity Z4-Z6 Holdt-Gardner. Color H-G.

The presence of the vinyl toluene in the formulation above contributes to -the drying speed of the coating composition. It may be eliminated if suitable drying agents known to the art are added as-a substitute.

5 Example 3 The following three separate reactant groups were first prepared:

The A group was heated in a container to 460 F., and held at that temperature for 30 minutes. The phthalic anhydride was then added and heated for from 2 to 3 hours at a temperature of 465 F. until an acid number of 30-40 had been attained. Throughout the reaction xylene was added as needed in order to maintain proper reflux conditions. The temperature was then lowered to 320 F., and the group consisting of vinyl toluene and ditertiarybutyl peroxide was added over a 1 hour period. The temperature was then slowly increased to 460 F., and held until the reaction had proceeded to the point Where the final desired characteristics were obtained. The reaction product had the following properties:

Acid number 15-20. Viscosity Q (Gardner-Holdt tube method). Color 5 (Gardner-Holdt tube method). Solids content 65% solids in xylene.

PREPARATION OF EMULSION Example 4 EPOXY-E STER TYPE Two separate solution components were first prepared. The first comprised an aqueous solution of the hydrophilic component formed in Example 1 containing 20% solids of the ammonium salt of a copolymer of vinyl acetate and crotonic acid, the polymer containing 6% crotonic acid by weight.

The second solution component comprised a solution of the epoxy-ester resin produced above in Example 2 containing 60-65% solids dissolved in xylol.

`While grams of the rst component were maintained under constant stirring, 21 grams of the second component were added. Only mild mixing of the two solutions was required, in contrast to the extreme agitation generally required in prior art emulsiiication processes. After complete emulsication of the epoxy-resin solution had taken place, additional water was added to obtain the desired emulsion consistency.

Example 5 A solution `of the alkyd-ester resin prepared above in Example 3 and a portion of the aqueous component prepared in Example 1 were mixed together using the proportions and method as described above in Example 4. The resulting emulsion was used to prepare a recording member by mixing with zinc oxide and subsequently coating on a base material, and drying the coating, as described in detail in Example 6 below. The recording member exhibited good electrophotographic properties.

In order to provide a satisfactory emulsion, the ratio of the copolymer of vinyl acetate and crotonic acid to the hydrophobic resin should be at least 1:6 on a dry weight basis. The preferred ratio Yis 1:1. Ratios greater than 2:1 may be used, although the electrical properties beginto deteriorate appreciably beyond that point.

Example 6 PREPARATION OF ELECTROPHOTOGRAPHIC RECORDING MEMBER Zinc oxide `pigment was blended into the emulsion as prepared above in Example 4, utilizing a pigment to dry resin ratio by weight of 3: 1. The resin and pigment mixture was premilled with a standard agitator for 20-30 minutes, suicient water being added where necessary to reduce the viscosity and maintain the mixture at about 55% solids. The material was then put through a roller mill and reduced to 45% solids by the further addition of water.

The pigment-containing emulsion thus prepared was drawn down with a standard No. 20 rod over an aluminum coated paper. The coating was dried for from two to four minutes with heated forced air (180 F., 1200 LF/ M).

The zinc oxide pigment may be dispersed in the emulsion formed in Examples 4 and 5 by any suitable means known to the art. An amount of resinous binder must be used which is suflicient to cause the particles of the pigment to adhere to each other and to the base, without unduly insulating the particles from each other. The suspension of pigment and binder is coated and dried on the base as a lm having a thickness of the order of one- -thousandth of an inch. It has been found that a minimum ratio of pigment to resin by weight of 1:1 is required. The upper limit of the pigment to resin ratio is determined by the ability of the resin to bind the pigment to the base and to itself sufficiently so that it does not ilake olf. A practical upper limit of pigment to resin ratio appears to be about 20:1 by weight. A preferred ratio range is from 2:1 to 10:1, with an optimum ratio of about 6: 1.

Evaluation of the various coating compositions, the results of which appear in the graph shown in the drawing, was made by means of an instrument termed a Spinner Electrometer. This is a device which was designed to yield quantitative data with regard to the electrical properties of electrophotographic recording media. Particularly, the following properties are measurable by the instrument.

(l) Initial charge acceptance. (2) Charge retention in darkness. (3) Charge decay upon illumination.

' scanned in rapid alternation through three windows in a nearly coplanar grounded metal plate by a probe. As each window rotates over the probe, the electrostatic field from the charge on the paper induces a voltage on the probe. As the window rotates further, the probe faces the grounded metal plate and returns to ground potential. Due to the symmetry of the windows which are cut in the turntable, the voltage appearing on the probe, rather than being in the form of a series of sharp pulses, appears in an approximately sinusoidal wave form. The signal may either be viewed directly on an oscilloscope, or may be amplified and rectied to produce a D.C. current which in turn actuates a recorder.

In carrying out the testing procedure, the recording member to be tested is rst subjected to a corona discharge of about seven thousand volts. Referring to the drawing, A represents the point at which the charge is applied. As can be seen, the charge on the recording member rises rapidly and approaches a more or less constant maximum at point B. A charging period of from 16 to 24 seconds is generally utilized. The value of the charge reached at the point B is a measure of the charge acceptance. At

point B the corona discharge is removed and the charged member permitted to remain in darkness until point C. The degree of discharge between point B and point C is an indication of the property of dark resistivity or charge retention. Dark resistivity is determined by the rate at which the charge tends to drop towards ground potential. The faster the charge drops, the poorer the resistivity. Conversely, higher dark resistivity is indicated by a slow discharge.

The corona is turned on again at C to re-establish a full charge on the recording member, and then turned olf 8 at point D. At point E, actinic illumination is applied to the recording member and the charge is dissipated to zero. The rate at which dissipation takes place is a measure of the illuminated conductivity.

A recording member which looses its charge rapidly under illumination is saidrto be highly photoconductive or have high illuminated conductivity. Conversely, a recording member which looses its charge slowly is considered to have poorV photoconductivity or illuminated conductivity. i

In order to be suitable for use in the electrophotographic recording process, a recording member should have high charge acceptance, high dark resistivity and charge retention, and high conductivity when illuminated.

The graph of FIG. 1 shows the results of electrometer tests, carried out as described above, of recording members prepared from three different coating compositions.

The rst coating composition was formulated by dissolving the epoxy ester resin product above in Example 2 in xylene, and blending zinc oxide pigment into the solution in a manner similar to that in Example 6 above. This composition is disclosed and claimed in application of George H. Tinker and Roger E. Burke entitled Coating Composition for the Production of Electrophotographic Recording Members, filed concurrently with the present application, and is considered to be an excellent coating composition of the organic solvent type for producing electrophotographic recording members. The results from the test of the recording member prepared with this composition are indicated by the curve in FIG. l labeled I.

The second coating composition was an emulsion composition prepared according to the invention by mixing equal proportions, on a dry resin weight basis, of t-he aqueous solution prepared in Example 1 with an organic solution comprised of the epoxy-ester resin prepared in Example 2, dissolved in xylene. 'Ilhe emulsion was prepared as described in Example 4, and the recording member prepared as described in Example 6. The results of the test of the recording member prepared from this coating composition are indicated by the curve labeled II.

The third coating composition was prepared by blending zinc oxide pigment into the aqueous solution of the sodium salt of a copolymer of vinyl acetate and crotonic acid, as prepared in Example 1. The results obtained from testing a recording member produced from this composition are indicated by the curve labeled III.

All three coating compositions contained a ratio of zinc oxide to resin of 3.1 on a dry weight basis. The coatings were applied on an aluminum-coated sheet of paper and dried as described above. T'hercoating in each case, when idry, had a thickness of about one-thousandth of an inch. Y

By comparing the three curves, it can be seen that the coating corresponding to the curve I attained a moderately high initial charge of about 520 volts. When the corona was removed, theY charge dropped to about 440 volts after one minute at point C.

The coating prepared according to the invention, as indicated by curve II, reached a much higher initial charge of about 670 volts at point B, and, after one minute, still had a charge of about 520 volts at point III.

The recording member prepared from the aqueous solution, as indicated by curve III, reached an initial charge of about 720 volts, and still retained a charge of about 610 volts after one minute.

Comparing the three recording members from the standpoint of initial charge and charge retention, the recording member of the invention shows a much higher initial charge and charge retention than the recording member prepared from thesame resin, but in the form of an organic solution. The recording member prepared from the aqueous solution shown by curve III had even higher initial charge and charge retention than that of as indicated by the time required to dissipate the charge from point E onward, it ,can be `seen that. the charge as indicated by both ,curvesland'II'dropped to zero within ,7..5 secondsupon the application of actinic radiation.

:Howevenfthe chargeon the recording member of curve III, even. after seconds, still remained `at almost 500 volts.

`In .evaluating .the results ofthe tests, it must be borne Min mind that a good electrophotographic recording .mem-

.ber must .have all three properties, .high initial charge,

.goodcharge retention, and high illuminatedconductivity.

higherinitialcharge Fandlcharge retention than curve II. Howeven the `recording memberof curveIII failed. badly with regard to illuminated conductivity, since the,A portion of the curve following point E slopes .olfonly ,gradually `and-thecharge is not :dissipated during the measured period. Consequently theY .recording member of curve III, although its other properties areexcellent, is unacceptable for use in electrophotography.

In summary, although the composition-of the invention (curve II) is-composed of -a combinaion of the other two compositions curve I and curve IILit unexpectedly retains all the good properties of -its -two `components and yet none of *their disadvantages, with the` result that it is superior to either-of them-individually.

Because of its 'high charge acceptance, high Iretention and high illuminated conductivity, the recording member of the invention, as characterized by curve II, is capable of producing final fixed images having higher contrast and better definition than that of the other two.

In addition to their excellent electrical properties, the coatings produced according to the invention are less suscepible to moisture and temperature effects, and have excellent flexibility and adhesive properties. The coating compositions are less susceptible to foaming, have better leveling properties and dry rapidly. When the enhanced electrical properties of recording members produced according to the invention are considered together with the greatly improved ease of preparing, handling, and applying the coating compositions in the form of emulsions, it can readily be seen that the invention constitutes a significant advance in the electrophotographic art.

We claim:

1. A coating composition in the form of an aqueous emulsion for use in the production of electrophotographic recording members, said composition being comprised of:

(A) an organic solution comprising (l) the esterification product of (a) a hydrophobic resin containing esteriable hydroxy groups, and (b) a higher fatty acid containing rosin, and (2) an organic solvent for acid esteriiication product;

(B) an aqueous solution of the ammonium salt of a copolymer of vinyl acetate and crotonic acid; and

(C) a photoconductive pigment.

2. A coating composition according to claim 1 wherein said pigment is zinc oxide.

3. A coating composition according to claim 1 wherein the proportion of crotonic acid in said copolymer is from about 2% to about 12% by Weight.

4. A coating composition in the form of an aqueous emulsion for use in the production of electrophotographic recording members, said composition being comprised of:

(A) an organic solution comprising (1) the esterification product of (a) a hydrophobic resin containing esteriable hydroxy groups, and

l@ (b) a higher fatty acid containing rosin, and (c) a vinyl ethylenically-unsaturated polymerizable monomer, and

(2) an organic solvent for said esterification product;

(B) an aqueous solution of the ammonium -salt of a copolymer of vinyl acetate and crotonic acid; and

(C) a photoconductive pigment.

5. A coating composition according to claim 4 wherein said monomer is vinyl toluene.

6. A coating composition in the form of an aqueous emulsion for use in the production of electrophotographic `recording members, said composition being comprised of:

(A) an organic solution comprising (l) the esterication product of (a) a `polyglycidyl polyether of Bisphenol A, (b) tall oil containing from about 2% to about 35% rosin byweight, and (c) vinyl toluene, and (2) an organic solvent for said esterification product;

(B) an aqueous solution of the ammonium salt of a copolymer of vinyl 'acetate and crotonic acid wherein the proportion of crotonic acid in said copolymer is from-about 2% to about 12% by weight; and

(C) zinc oxide.

`7. A coating composition in the form 4of ran aqueous emulsion for-use in the production of electrophotographic recording members, said composition beingcomprised of:

(A) an organic solution comprising (1) the esterification product of (a) an alkyd resin having esterifiable hydroxy groups comprising the reaction product of a polyhydric acid and a polyhydroxy alcohol, and (b) a higher fatty acid containing rosin, and (2) an organic solvent for said esterification product;

(B) an emulsifying agent comprising an aqueous solution of the ammonium salt of a copolymer of vinyl acetate and crotonic acid; and

(C) a photoconductive pigment.

8. A coating composition in the form of an aqueous emulsion for use in the production of electrophotographic recording members, said composition being comprised of:

(A) an organic solution comprising (1) the esterification product of (a) an alkyd resin having esteriable hydroxy groups comprising the reaction product of al Iolyhydric acid and a polyhydroxy alcoi o l (b) a higher fatty acid containing rosin, and (c) a vinyl ethylenically-unsaturated polymerizable monomer, and (2) an organic solvent for said esterification product;

(B) 'an aqueous solution of the ammonium salt of a copolymer of vinyl acetate and crotonic acid; and

(C) a photoconductive pigment.

9. An electrophotographic recording member comprising a base and having a photoconductive coating on said base comprised of:

(A) the esterification product of (l) a hydrophobic resin containing esteriable hydroxy groups, and (2) a higher fatty acid containing rosin, and

(B) a copolymer of vinyl acetate and crotonic acid,

and

(C) a photoconductive pigment.

10. An electrophotographic recording member comprising a base and having a photoconductive coating on Said base comprised of:

(A) the esterication product of (1) a polyglycidyl polyether of Bisphenol A, and

11 Y (2) tall oil containing from about 2% to about 35 rosin, and (3) vinyl toluene, and (B) a copolymer of vinyl acetate and crotonic acid 12 (B) a copolymer of vinyl acetate and .crotonic acid;

and (C) a photoconductive pigment. 13. A mehod for forming a visual image on an electrocontaining from about 2% to about 12% crotonic 5 Photographie recording member Which COmPlSeS PTO" acid by weight of said polymer, and

(C) zinc oxide.

11. An electrophotographic recording member comprising a base and having a photoconductive coating on said base'comprised of (A) the esterication product of (1) a polyglycidy polyether of Bisphenol A,

(2) tall oil containing from about 2% to about 35% rosin, and (3) vinyl toluene, and (B) a copolymer of vinyl acetate and crotonic acid wherein the proportion of crotonic acid in said copolymer is from about 2% to about 12% by Weight; and

(C) zinc oxide.

12. A method for forming a visual image on an electrophotographic recording member which comprises producing an electrostatic charge on the surface of said recording member, exposing the charged surface to a light image, and applying to the electrostatic image thus formed a toner containing charged pigment particles, said recording member comprising a base having a coating thereon comprised of:

(A) the esterication product of (1) a hydrophobic resin containing esteriable hydroxy groups, and (2) a higher fatty acid containing rosin;

ducing an electrostatic charge on the the surface of said recording member, exposing 'the charged surface to a light image, applying to the electrostatic image thus formed a toner containing charged pigment particles, and permanently xing the electrostatically-retained pigment image to the surface of said recording member said recording member comprising a base having a coating thereon comprised of (A) the esterication product of (l) a polyglycidyl polyether of Bisphenol A, (2) tall oil containing from about 2% to about rosin by Weight, and (3) vinyl toluene; and (B) a copolymer of vinyl acetate and crotonic acid wherein the proportion of crotonic acid in said copolymer is from about 2% to about 12% by weight; and (C) zinc oxide. 14. A method according to claim 13 wherein the proportion by weight `of zinc oxide to total weight of said coating is from about 1: 1 to 20:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,959,481 Kucera Nov. 8, 1960 2,990,383 Glaser June 27, 1961 3,025,160 Bunge et al Mar. 13, 1962 3,057,809 Newey Oct. 9, 1962 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,152,895 October 13, 1964 George H. Tinker et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below line 35, for "soy-bean" read soya-bean line 68,

for "6G-65." read 6065%. column 9, line 59, for "acid" read said column ll, line l2, for "polyglycidy" read polyglycidyl v; column l2, line 4, for "mehod" read method line Il, after "member" insert a comma.,

Signed and sealed this 9th day -of February 1965.

(SEAL) Attest:

` ERNEST WQ SWIDER Y EDWARD J. BRENNER Altcsting Officer Commissioner of Patents

Claims

1. A COATING COMPOSITION IN THE FORM OF AN AQUEOUS EMULSION FOR USE IN THE PRODUCTION OF ELECTROPHOTOGRAPHIC RECORDING MEMBERS, SAID COMPOSITION BEING COMPRISED OF: (A) AN ORGANIC SOLUTION COMPRISING (1) THE ESTERIFICATION PRODUCT OF (A) A HYDROPHOBIC RESIN CONTAINING ESTERIFIABLE HYDROXY GROUPS, AND (B) A HIGHER FATTY ACID CONTAINING ROSIN, AND (2) AN ORGANIC SOLVENT FOR ACID ESTERIFICATION PRODUCT; (B) AN AQUEOUS SOLUTION OF THE AMMONIUM SALT OF A COPOLYMER OF VINYL ACETATE AND CROTONIC ACID; AND (C) A PHOTOCONDUCTIVE PIGMENT.