US3547627A

US3547627A - Lithographic printing master and method employing a crystalline photoconductive imaging layer

Info

Publication number: US3547627A
Application number: US546844A
Authority: US
Inventors: Alan B Amidon; Joseph Mammino; Richard W Radler
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1966-05-02
Filing date: 1966-05-02
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15
Also published as: US3607261A

Description

Dec. 15, 1970 A. B. AMIDON ETAL LITHOGRAPHIC PRINTING MASTER AND METHOD EMPLOYING A CRYSTALLINE PHOTOCONDUCTIVE IMAGING LAYER Filed May 2, 1966 FIG. 2

INVENTORS. ALAN B. AMIDON JOSEPH MAMMINO RICHARD W. RADLER ATTORNEY United States Patent 3,547,627 LITHOGRAPHIC PRINTING MASTER AND METH- OD EMPLOYING A CRYSTALLINE PHOTOCON- DUCTIVE IMAGING LAYER Alan B. Amidon, Joseph Mammino, and Richard W. Radler, Penfieltl, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York "tFiled May 2, 1966, Ser. No. 546,844

. Int. Cl. G03g 13/22 US. Cl. 961 27 Claims ABSTRACT OF THE DISCLOSURE A lithographic printing master is disclosed prepared from a crystalline photoconductive binder plate. Due to the nature of the bond between the crystalline binder material and the underlying substrate the binder may be easily removed from the support member in those areas not protected by a fixed developed image thereby providing the necessary differential between the image and nonimage areas to satisfy the requirement of lithography.

This invention relates to an imaging system, and more specifically to lithography.

Lithographic printing is a well known and established art. In general, the process involves printing from a flat plate, depending upon different properties of the image with the nonimage areas for printability. In conventional lithography, the nonimage area is hydrophilic while the image area is hydrophobic. In the lithographic printing process, a fountain solution is applied to the plate surface which wets all portions of the surface not covered by the hydrophobic image. This solution keeps the plate moist and prevents it from scumming up. An oil based printing ink is applied to the image surface depositing the lithographic ink only on the image area, the hydrophilic non-image area repelling the ink. The ink image may then be transferred directly to a paper sheet or other receptive surface, but generally it is transferred to a rubber offset blanket which in turn transfers the print to the final paper sheet. Hence, for each print made during a run, a lithographic plate is first dampened with an aqueous fountain solution and then inked with a lithographic ink and finally printed.

It has been known that lithographic plates can be made in a photoconductive system by utilizing the conventional developed xerographic plate as a lithographic printing plate. In these systems, usually a zinc oxide type plate is charged by conventional means, exposed to the image to be reproduced and developed with conventional Xerographic toner. The toner is generally hydrophobic in nature as is the background of the conventional binder type xerographic plate. In order that the developed xerographic plate be useful as a lithographic master, a differential must be established between the toner image and the background of the plate. Since both are hydrophobic in nature, it has heretofore been required that the background photoconductive component of the xerographic plate be treated either by the use of a conversion solution or by complete removal such as with a selective solvent, to make the background surface hydrophilic in nature. After the alteration of the nonimage, background area, the plate is then wetted with a nonaqueous or oil based ink whereby the toner will accept the ink and the now hydrophilic background will repel the ink.

While basically these systems have been found useful for lithographic purposes, there are inherent disadvantages to their use. One disadvantage, for example, is the fact that it is required in one instance that a conversion solution be used to convert the initially hydrophobic back- 3,547,627 Patented Dec. 15, 1970 ground to one which is hydrophilic so that it will not accept the oil based ink in the inking step. A second disadvantage is that in the approach wherein a solvent is used to remove the hydrophobic background, not only is an additional time consuming step required as with the use of the conversion solution, but such a treatment leads to a degradation of the quality of the image that is subsequently produced from the plate. A further disadvantage to the present existing techniques is that generally they require the application of wet processes which inherently make the procedures undesirable.

It is, therefore, an object of this invention to provide a lithographic imaging system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a novel method for the preparation of a lithographic master.

Another object of this invention is to provide an imaging system utilizing a novel lithographic master prepared from a xerographic plate,

Still a further object of this invention is to provide an imaging system wherein the novel lithographic plate can be prepared without utilizing image degrading treatments.

An additional object of this invention is to provide a process of using a novel lithographic printing master.

Yet, still a further object of this invention is to provide a completely dry process for preparing of lithographic master.

The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a lithographic master prepared by loosely fixing to the surface of a hydrophilic receiving substrate a photoconductive crystalline-like binder insulating layer. The photoconductive layer of the present invention is prepared by dispersing a particulate photoconductive material such as zinc oxide in a crystalline-like binder material such as tetrachlorophthalic anhydride (TCPA). It has been found that blending the two in equal proportions will produce optimum results. The photoconductive layer can then be electrostatically charged and imaged in accordance with the conventional xerographic imaging process more fully described in US. Pat. 2,297,691. The electrostatic latent image is developed with a hydrophobic developer and the resulting developed image fixed. As a result of the physical structure of the binder material, it has been observed that the developer material penetrates the interstices of the binder particles and is alfixed to the surface of the substrate thereby forming a network of binder particles dispersed or trapped within the bounds of the impinging developer material, The plate is then subjected to a gentle nonstatic surface treatment which removes from the background areas the photoconductive insulating material not protected by the fixed toner image. There is thus produced a lithographic master having hydrophobic image areas and hydrophilic background areas. The lithographic master can then be used to continuously make prints whereby a lithographic ink is applied to the master, the ink adhering selectively to the surface of the hydrophobic or oleophilic toner image, and the master subsequently contacted with a copy sheet to transfer the image. Alternatively, the ink image may initially be transferred to the surface of an offset blanket from which it is in turn transferred to the final copy sheet. It is to be understood that if it is desired to develop the electrostatic latent image of the present invention with a hydrophilic developer, the background, nonimaged area of the hydrophilic plate may be treated in such a manner such as by spraying with an isoparaffinic aliphatic hydrocarbon, so as to exhibit oleophilic properties or by initially using a substrate having hydrophobic properties thereby producing a reverse lithographic plate.

Furthermore, the process of the present invention may be used if desired, to prepare a xeroprinting master. In this instance, the material which is to serve as the base of the printing plate is such that when the imaged plate is exposed to an electrical charge, the image areas of the plate will retain the charge while the nonimage areas, i.e., those areas from which the loosely bound photoconductive insulating material has been removed, no longer being insulated, will not retain a charge. A printing master prepared in this manner need only be charged and developed to reproduce copies of the original image, thereby eliminating the necessity of reimaging the printing plate. On uniformly charging the plate, the electrostatic charge would be retained only on the light insensitive image areas, the electrically conductive background area serving as a sink, thereby permitting the charge to leak off.

It has been found that when a particulate photoconductive material is dispersed in the crystalline-like binder material of the present invention and the resulting photoconductive composition fixed to the surface of a suitable hydrophilic substrate, the bond which exists between the resulting photoconductive binder material and the substrate is such that the photoconductive layer may easily be removed by a gentle nonstatic surface treatment which will neither affect the developed image nor the quality of the print produced therefrom. It is hypothesized that the bonding effect realized between the binder material of the present invention and the underlying substrate is due to the structural nature of the binder composition. It is generally considered that the materials suitable for use exhibit properties typical of crystalline substances but although they exhibit these properties, need not have a definite crystalline structure and may be amorphous in nature. Therefore, the phase crystalline-like is used in the course of the present invention to define a binder material which will yield the necessary bonding efiFect described above so as to satisfy the system requirements. The removal from the non-imaged or background area of the crystalline-like photoconductive insulating material exposes the hydrophilic surface of the underlying substrate. The plate thus produced comprises a hydrophilic substrate with an oleophilic toner image fused thereon. As a result of having started with a substrate possessing hydrophilic properties, it is no longer necessary to treat the surface of the imaged plate in order to establish the differential needed for lithographic printing as is generally required by the conventional lithographic plates as taught in US. Pats. 3,107,169, 3,001,872 and 3,158,476.

In accordance with the present invention, a photoconductive material is blended with a crystalline or crystallinelike binder composition in proportions of about 25 to 1.5 parts photoconductor to about 7 to 0.5 parts crystalline binder. It has been found that about 1 part photoconductive material to about 1 part of the binder composition will give optimum results. The finely divided photoconductive particles and the crystalline binder material are desirably mixed in a liquid such as acetone by any suitable means such as in a paint shaker. The solvent is added in the proportions suflicient to thin the mixture to a desirable coating consistency. Alternatively, the binder composition may be intially dissolved in a solvent therefor, and subsequently dispersed with the photoconductor particles. The resulting photoconductive composition is then applied to the desired surface by flow coating, dipping, spraying, electrostatically, with a doctor blade, or by any other suitable coating operation. The coating is dried at the necessary temperature to loosely affix the particular photoconductive composition to the substrate thereby producing a uniform layer of the photoconductive pigment dispersed in the crystalline-like binder composition. The drying temperature and time will vary depending upon the particular binder composition in use. For example, if the crystalline binder material is Eugenol (4- allyl-2-methoxy phenol) an applicable temperature range will be from about 30 to 80 C. for approximately 10 to 20 minutes.

The resulting photoconductive plate is electrostatically charged in the dark and the charged surface selectively exposed to a light source to produce a latent image. The imaged surface is then developed with hydrophobic electroscopic marking particles or toner, the developer adhering to the areas corresponding to the latent image. The developed image is then heat fused. Any suitable means may be used to fix the developed image to the surface of the hydrophilic substrate. In addition to the heating approach, the fusing procedure may be carried out by exposure to solvent vapors, a process more fully described in US. Pat. No. 3,140,160. It is also possible when the image is fused by the application of heat to develop the electrostatically charged image with a liquid developer containing charged hydrophobic particles suspended in a carrier liquid which is vaporized during the fixing of the image. A light pressure is then applied to the surface of the photoconductive plate by any suitable means such as by brushing or by directing a draft of air from a blower onto the surface of the plate, thereby disengaging the loosely bound photoconductive composition and exposing the hydrophilic underlayer. The duplicating plate is then fastened to a press cylinder of a lithographic press. The printing operation is carried out utilizing commercially available fountain solutions and lithographic inks. The electroscopic particles used to develop the electrostatic latent image comprise a resin which is hydrophobic in nature and which may be readily wetted by a lithographic ink.

When in the fixed condition, the image on the printing surface of the crystalline binder photoconductive plate of the present invention is tenaciously held to the surface of the substrate and shall neither be pulled away by printing ink nor washed away by the wet-out or fountain solutions, Furthermore, the nonimage hydrophilic background areas of the plate are readily wetted by the fountain solutions and hold a film thereof on the surface of the nonimage areas and do not permit the aqueous film to be displaced therefrom by the lithographic printing ink.

Any suitble insulating composition which has a softening point temperature somewhat greater than the toner material used to develop the electrostatic latent image, and is crystalline in nature or capable of being formed into particulate crystalline-like matter so as to produce the necessary adhesive properties as discussed above may be used in the course of the present invention. For example, when a developer composition comprising polystyrene is used to develop the electrostatic latent image, the particulate or crystalline binder composition should generally have a meltng temperature substantially greater than that of the toner, i.e., the polystyrene composition, so as not to destroy the porous nature and loosely adhering properties of the binder composition. Typical nonpolymeric organic crystalline binder compositions are: 4-allyl-2- methoxyphenol, tetrachlorophthalic anhydride, phthalic anyhdride, acetophenetidin, acetyl phenyl hydrazine, aconitic acid, adipic acid, agaric acid, para-amino azo benzene, azo benzene, benzoic acid, n-tert-butyl acrylamide, cetyl alcohol, 3,4-dichlorobenzaldehyde, di-cyclopentadiene dioxide, di-methyl-terephthalate, di-phenylguanidine, furoic acid, hexachloroethane, hydroquinone, isophthalic acid, lauric acid, maleic acid, maleic anhydride, melamine, myristic acid, beta-naphthyl-methyl ether, palmitic acid, phenazine, phenol-phthalein, orthophenyl-phenol, para-phenyl-phenol, phenyl salicylate, pirnelic acid, salicylic acid, sebacic acid, sulfo-salicylic acid, and mixtures thereof. Typical inorganic crystalline binders are the phosphonitrilic compounds as more fully described in Chemical Reviews, 62, 247 (1962). Exemplary of these compounds are the cyclophosphazenes including cyclotetraphosphazene and cyclotriphosphazene, and halogencyclophosphazene, including hexachlorocyclotriphosphazene, among others. Preferred among the crystalline binder materials are the organic nonpolymcric compositions which due to the nature of their crystalline structure more readily satisfy the requirements of the present invention as to the degree of bonding desired between the binder and the underlying substrate. Other typical binder insulating materials are silicone resins such as DC-801, DC 804, and DC-996 commercially available from the Dow Corning Corporation; acrylic and methacrylic ester polymers such as Acryloid A and Acryloid B72, polymerized ester derivatives of acrylic and alpha-acrylic acids both commercially available from Rohm & Haas Company, and Lucite 44, Lucite 45 and Lucite 46, polymerized butylmethacrylates commercially available from E. I. du Pont de Nemours & Company; chlorinated rubber such as Parlon, commercially available from the Hercules Powder Company; vinyl polymers and copolymers such as polyvinyl chloride and polyvinyl acetate, including Vinylite VYNH and VMCH, commercially available from the Bakelite Corporation; cellulose esters and ethers such as ethyl cellulose and nitrocellulose, and alkyd resins such as Glyptal 246 9, commercialy available from the General Electric Company.

Any suitable photoconductive material may be used in the course of this invention. Typical inorganic photoconductive materials are sulfur, selenium, zinc sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide, calcium-strontium sulfide, cadmium sulfide, mercuric iodide, mercuric oxide, mercuric sulfide, indium trisulfide, gallium triselenide, arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, doped chalcogenides of zinc and cadmium, bismuth oxide, molybdenum oxide, lead oxide, molybdenum iodide, molybdenum selenide, molybdenum sulfide, molybdenum telluride, aluminum selenide, aluminum sulfide, aluminum telluride, bismuth iodide, bismuth selenide, bismuth sulfide, bismuth telluride, cadmium telluride, mercuric selenide, mercuric telluride, lead oxide, lead selenide, lead sulfide, lead telluride, cadmium arsenide, lead chromate, gallium sulfide, gallium telluride, indium sulfide, indium selenide, indium telluride, red lead and mixtures thereof. Typical organic photoconductors include triphenyl amine phthalocyanine, Monastrol Red B, a quinacridone commercially available from E. I. du Pont de Nemours & Company, calcium lake of 1- (2-azonaphthalene-1-sulfonic acid) -2-naphthol; 8,13-dioxodinaphtho (1,2 2',3)-furan-6-carbox-4"-methoxyanilide; 3,3 methoxy 4,4 diphe'nyl-bis(1"-azo-2-hydroxy -3"-naphthanilide); 2,4 bis (4,4'-diethyl-amin0- phenyl)-1,3,4-oxadiazol; 4,S-diphenyl-imidazolidinone; 4, 5-diphenyl-imidazolidinethione; 4,5-bis-(4 amino-phenyl)-imidazolidinone; 1,5-cyanonaphthalene; 1,4-dicyanonaphthalene; amino-phthalodinitrile; nitrophthalidinitrile; 1,2,5,6-tetraazacyclooctatetraene-(2,4,6,8); 3,4-di-(4-methoxy phenyl) 7,8 diphenyl-1,2,5,6-tetraazacyclooctatetraene-2,4,6,8) 3,4-di-(4-phenoxy-phenyl) 7,8-diphenyl- 1,2,5,d-tetraza-cyclooctatetraene- 2,4,6,8 3 ,4,7,8-tetramethoxy 1,2,5,6 tetraazacyclooctatetraene-(2,4,-6,8); 2- mercapto-benzthiazole; 2-phenyl-4-alpha-naphthylideneoxazolone; 2-phenyl-4-diphenylide-oxazolone; 2-phenyl-4- p methoxy-benzylideneoxazolone; 6-hydroxy-2-phenyl-3- (p-dimethylamino phenyl)-benzofuran; 6-hydroxy-2,3-di- (p-methoxyphenyl) benzofurane; 2,3,'5,6-tetra-(p-methoxyphenyl furo(3,2' benzofurane; 4-dimethylaminobenzylidene benzhydrazide; 4-dimethylaminobenzylideneisonicotinic acid hydrazide furfurylidene-(Z)-4-dimethylaminobenzhydrazide; 5-benzylidene-aniino-acenaphthene; 3 benzylidene-amino-carbazole; (4-N,N-dimethyl aminobenzylidene)-p-N,N-dimethylaminoaniline; (2-nitro-benzylidene -p-bromo-aniline; N,N-dimethyl-N-(2-nitro-4- cyano benzylidene)-p-phenylene-diamine; 2,3-diphenylquinazoline; 2-(4-amino-phenyl)-phenyl-quinazoline; 2- phenyl 4-(4-di-methyl-amino-phenyl)-7-methoxy-quinazoline; 1,3-diphenyl-tetrahydroimidazole; 1,3-di-(4-chlorophenyl)-tetrahydroimiadzole; 1,3-diphenyl-2,4-dimethylamino phenyl)-tetrahydroimidazole; 1,3-di-(p-tolyl -2- quinolyl- 2 tetrahydroimidazole 3- 4'-dimethylaminophenyl) 5 (4-methoxy-phenyl)-6-phenyl-1,2,4-triazine;

3 pyridyl (4')-5-(4"-dimethyl-amino-phenyl)-6-phenyl- 1,2,4-triazine; 3-(4'-amino-phenyl)-5,6-di-phenyl-l,2,4-triazine; 2,5 -bis- [4-aminophenyl-( 1) -1,3,4-triazole; 2,5- bis [4' N-ethyl-N-acetylamino)-phenyl-(1)]-1,3,4-triazole; S-diphenyl-3-methyl-pyrazoline; 1,3,4,5-tetraphenylpyrazoline; 1-phenyl-3-(p-methoxy styryl)-5-(p-methoxy phenyl)pyrazoline; 1-methyl-2-(3',4-dihydroxymethylene phenyl)-benzimidazole; 2-(4-dimethylamino phenyl -benzoxazole; 2- (4-methoxyphenyl) -benzthiazole; 2,5-bis-[p-aminophenyl-(1)]-1,3,4-oxadiazole; 4,5 -diphenyl-imidazole; 3'aminocarbazole; mixtures thereof. In addition, other typical photoconductors are charge-transfer type photoconductors such as disclosed in copending applications, Ser. Nos. 426,409, 426,423, 426,431, 426,428 and 426,396, filed in US. Patent Ofiice on Jan. 18, 1965. It was found in the case of the organic photoconductor pigments that best results were obtained when the photoconductive pigment was encapsulated with a resinous composition. Therefore, when it was desired to use the organic photoconductor pigments, the latter were spray dried in the presence of an organic synthetic resinous material such as polyvinyl carbazole, prior to dispersion in the crystalline-like binder composition. It was felt that this latter treatment enhanced the charge retention properties of the photoconductive binder layer, thereby increasing its usefulness for the present invention. Any suitable encapsulating resinous material may be used when the photoconductive material of the present invention is organic in nature. Typical such resinous materials are polyethylene terephthalate, polystyrene, polyvinylcarbazole, and thermosetting resins such as urea formaldehyde and epoxy resins. Any conventional and/or suitable encapsulating technique known to the prior art such as disclosed in US. Pat. No. 2,800,457 may be utilized. Preferably, in the selection of the photoconductive pigment of the present invention, it was desired to utilize the inorganic pigments inasmuch as optimum properties could be obtained while avoiding the necessity of an encapsulating step generally preferred when using the organic photoconductive pigments.

The thickness of the photoconductive insulating layer of the present invention may vary from about 2 microns to about microns. It is preferred that the layers be from about 6 to about 25 microns thick in order to achieve optimum results, thereby providing maximum electrostatic contrast. The desired thickness may be built up by multiple coatings, if necessary.

Any suitable material may be used as the substrate for the lithographic master of this invention. The base or substrate used in preparing lithographic binder plates according to the present invention provides physical support for the photoconductive insulating layer and also should have an electrical resistance somewhat less than the photoconductive layer so that it will act as a ground when the electrostatically charged coating is exposed to light. The base should also be hydrophilic in nature or be so treated so as to possess hydrophilic properties in order to provide the necessary surface differential. Typical materials are aluminum, brass, conductive glass, steel, e.g., stainless and low carbon, copper, nickel, zinc alloys and mixtures thereof. If reverse lithography is practiced, as discussed above, then a hydrophobic substrate would be used. Other materials having electrical resistances and surface properties similar to the aforementioned can also be used as the base material to receive the photoconductive layer thereon. Other nonconductive materials such as thermoplastics may be used as the backing for the lithographic plate. When used, however, it is necessary to charge both sides of the plate during the imaging phase of the preparation of the plate according to the process set out in US. Pat. 2,922,883. When a conventional lithographic plate is the desired product then it is preferred to employ a hydrophilic substrate.

Any suitable wet-out or fountain solution may be used in the course of this invention. Typical such fountain solutions are 1% solutions by volume of gum cellulose and water, gum arabic and water, glycerol and water and isopropyl alcohol and water. Distilled water may also be used as the wet-out solution. Other suitable fountain solutions are disclosed in U.S. Pat. 3,107,169. The fountain solutions may contain other constituents, such as, for example, formaldehyde and if glycerin is not present, it may be added primarily to take advantage of its hygroscopic nature and hence by absorption of water, prolong the period during which the hydrophilic surface of the lithographic plate retains its hydrophilic properties. The formaldehyde additives will also achieve this effect. Therefore, the fountain solutions containing the glycerin, formaldehyde additives or mixtures thereof are preferred inasmuch as the resulting lithographic plates can be kept before use for relatively long periods of time as compared to those plates treated with a fountain solution not containing the respective additive. Solutions containing gum arabic are also found to be very effective inasmuch as a lithographic plate treated with such a solution is found to retain its hydrophilic properties in the non-imaged areas for relatively long periods of time following removal from the press. As a result, the resulting printing plate can be reused without subjecting it to an additional treatment with a fountain solution.

Any suitable toner or developer may be used in the course of this invention such as those disclosed in U.S. Pats. 2,788,288, 3,079,342 and Re. 25,136. The toner is generally a resinous material which when fixed has hydrophobic properties and will accept oily inks. Typical such developer powders are styrene polymers, polymers of substituted styrenes for example, Piccolastics, commercially available from the Pennsylvania Industrial Chemical Corporation, phenol formaldehyde resins, as well as other resins having hydrophobic properties. The developer powder may be applied directly to the latent image or admixed with a carrier such as glass beads. The toner may be applied in the form of a mixture with magnetic particles such as magnetic iron to impart a charge to the developer powder particles triboelectrically. The developer or toner particle is so chosen that it is attracted electrostatically to the charged image or repelled from the background area to the charged image and held thereon by electrostatic attraction. If a negative charge is applied to the photoconductive insulating material, a positive toner is used which adheres to the negatively charged image. If the charge applied is such that the latent image retains a positive charge, then a negative toner will be applied.

As mentioned above, liquid developers may also be used in the course of this invention. Such developers are disclosed in U.S. Pats. 2,890,174 and 2,899,335. Generally, the developer comprises a liquid combination of mutually compatible ingredients, which when brought into contact with an electrostatic latent image, will deposit upon the surface of the image in an image-wise configuration. In its simplest form, the composition comprises a finely divided opaque powder, a high resistance liquid and an ingredient to prevent agglomeration. Liquids which have been found suitable include such organic high resistance liquids as carbon tetrachloride, kerosene, benzene, tetrachloroethylene and any substituted hydrocarbon having a boiling point between about 70 and 200 C. Any of the finely divided opaque solid materials known in the art such as carbon black, talcum powder, or other pigments may be used in the liquid developer. Silica aerogel, commercially available from Monsanto Chemical Company, is a deagglomeration ingredient generally used. However, any conventional and/or suitable ingredient known to be useful by the prior art in a liquid development system may be utilized.

Any suitable development means may be used in the course of this invention, such as cascade development more fully described in U.S. Pats. 2,618,551 and 2,618,- 552, powder cloud development more fully described in U.S. Pats. 2,725,304 and 2,918,910, and magnetic brush development, as more fully described in U.S. Pats. 2,791,949 and 3,015,305. As a result of the nature of the bond which exists between the photoconductive crystalline-like binder layer and the underlying substrate, as is more fully described above, the powder cloud development technique is preferred, so as to minimize the possibility of disturbing the loosely held photoconductive binder layer.

Any suitable lithographic link may be used in the course of this invention. Typical such lithographic inks and their properties are disclosed in Printing Ink Technology by E. A. Apps, chapter 1, Chemical Publishing Co., Inc., New York, N.Y., 1959. The inks are of the same fundamental style as good quality letterpress inks, and the simplest type consist of a pigment mixture dispersed in a lithographic varnish. The lithographic or oil-based ink being oleophilic in nature adheres to the hydrophobic toner image, and is repelled by the hydrophilic nonimage areas.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 represents a magnified cross-section through a photoconductive crystalline binder plate of the present invention prior to surface treatment;

FIG. 2 represents a magnified cross-section through a lithographic printing plate of the present invention following removal of the loosely held photoconductive insulating material.

In the present process for preparing a lithographic plate 1 as illustrated in FIG. 1, a suitable substrate 2 is coated with a photoconductive insulating composition 3 comprising a photoconductive pigment 4 dispersed in a crystallinelike binder composition 5. On the surface of the photoconductive layer is superimposed a toner image 6 which is affixed to the surface of the substrate between the interstitial spaces of the photoconductive composition. The selection of the supporting substrate 2 is based upon the desired use of the lithographic plate such as to give the plate additional strength or to provide added flexibility in situations requiring it. FIG. 2 illustrates the lithographic plate 1 following removal of the photoconductive insulating material from the surface of the plate unprotected by the toner image 6, thereby exposing the hydrophilic surface 7 of the substrate 2.

To further define the specifics of the present invention, the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated. The examples are intended to illustrate various preferred embodiments of the present invention.

EXAMPLE I Equal parts of an organic binder composition, 4-allyl- 2-methoxyphenol (Eugenol) commercially available from Eastman Kodak Company, and a zinc oxide photoconductive material commercially available from New Jersey Zinc Co., are thoroughly mixed in a paint shaker for approximately 30 minutes. Acetone, containing about 002 part of zinc acetate is added to the photoconductivebinder blend, and the mixing procedure repeated until the desired coating consistency of the composition is obtained. The resulting slurry is coated on a 7 mil grained Harris Alum-o-Lith Redi-Cote aluminum master base with a No. 14 wire wound bar to a thickness of about 10 microns. The resulting coated aluminum base is dried for approximately 13 minutes at a temperature of about C. Following drying of the plate, the photoconductive coating is charged in the dark to a potential of about 200 volts with a 3-wire corotron at a potential of about 7,500 volts, and the charged plate exposed to a test pattern with about 25 foot-candle-seconds of white light. The resulting electrostatic latent image produced is then developed by magnetic brush development with a positively charged hydrophobic toner comprising a styrene terpolymer. The

toner image is then fused to the surface of the plate by the application of heat at a temperature of about 250 F. for about seconds. Following cooling of the plate, the surface is rubbed with a dry cotton swab which removes the photoconductive binder material from the areas not protected by the fused toner image. The plate is then wrapped on the cylinder of a lthographic printing press and operated in the conventional manner using an Elfo densensitizer, and acidic gum solution available from Azoplate Corporation, as the fountain solution. A lithographic ink is then applied to the printing surface of the plate and the ink image transferred in imagewise configuration upon contact to the surface of a paper copy sheet. High quality prints are obtained.

EXAMPLE II The process of Example I is repeated excepting following the inking step the plate is first contacted with a rubber offset blanket and then transferred upon contact to the surface of a paper copy sheet. With the use of a rubber offset blanket, longer runs producing prints of higher quality are obtained.

EXAMPLE III The process of Example I is repeated excepting the organic binder material used is tetrachlorophthalic anhydride in place of the Eugenol. Prints comparable to those of Example I are obtained.

EXAMPLE IV The process of Example III is repeated excepting following the inking step the plate is first contacted With a rubber offset blanket and then transferred upon contact to the surface of a paper copy sheet. Copies of enhanced quality over those made without the offset blanket are obtained.

EXAMPLE V Monolite Fast Blue GS, a metal-free phthalocyanine (oz-fOIIIl) available from Arnold Hoffman Company is spray dried in the presence of polyvinyl carbazole and the resulting encapsulated photoconductive pigment dispersed in equal parts of tetrachlorophthalic anhydride crystalline binder composition. The remainder of the process is similar to that as described in Example I with comparable results obtained.

EXAMPLE VI Monolite Fast Blue GS is spray dried in the presence of polyvinyl carbazole and the resulting encapsulated photoconductive pigment dispersed in equal parts of Eugenol. The remainder of the process is similar to that as described in Example I excepting following the inking step the imaged plate is first contacted with a rubber offset blanket and then the ink image transferred upon contact to the surface of a paper copy sheet. The use of the rubber offset blanket increases the quality of the resulting prints.

EXAMPLE VII The process of Example V is repeated excepting Monastral Red B (fi-form), a quinacridone commercially available from E. I. du Pont de Nemours & Co., is substituted for the phthalocyanine pigment and conductively treated paper is substituted for the aluminum master base. In addition, the image is tranferred intermediately to an offset blanket and from there transferred to the final copy sheet. The images obtained are similar to those produced by the plates utilizing the offset blanket as an intermediate step in the printing process as in Examples II and IV.

EXAMPLE VIII About 6 parts of trimeric phosphonitrilic chloride are heated to about 50 C. and the temperature maintained until all of the trimer is melted. About 1 part of X-form metal-free phthalocyanine, prepared as described in copending U.S. Patent Application, Ser. No. 505,723, filed Oct. 29, 1965, now U.S. Pat. No. 3,357,989, is added to the melted phosphonitrilic chloride trimer and the mixture stirred. The resulting dispersion is coated on a 7 mil grain aluminum master base as in Example I with a Number 14 wire Wound bar at a thickness of about 8 microns. The coated plate is cooled to a temperature of about 23 C. yielding a bluish crystalline coating. The photoconductive coating is charged in the dark to a potential of about 200 volts with a laboratory corotron unit powered by high voltage power supply. The charging current is about 0.1 of a milliamp at about 7,500 volts. The charged plate is exposed to a test pattern with about 25 foot-candle-seconds of white light. The resulting electrostatic latent image produced is then developed by powder cloud development with a positively chargely hydrophobic developer toner comprising a styrene terpolymer. The toner image is then fused to the surface of the plate by the application of heat at a temperature of about 250 F. for about 5 seconds. Following cooling of the plate, the surface is rubbed with a dry cotton swab which removes the photoconductive binder material from the areas not protected by the fused toner image. The plate is Wrapped on the cylinder of a lithographic printing press and operated in a conventional manner using a fountain solution consisting of an Elfo desensitizer. A lithographic ink is then applied to the surface of the plate and the ink image transferred upon contact to the surface of a paper copy sheet. The plate produces high quality images.

EXAMPLE IX The process of Example VIII is repeated excepting the ink developed image is first transferred to a rubber offset blanket and then transferred upon contact to the surface of a paper copy sheet. Higher quality images are obtained when the offset blanket is used.

EXAMPLE X The process of Example VIII is repeated excepting cadmium sulfoselenide commercially available from Ferro Corp., Cleveland, Ohio is substituted for the organic photoconductor pigment. The ink developed image is first transferred to a rubber offset blanket and then transferred upon contact to the surface of a paper copy sheet. Images of a quality similar to those obtained in IX are realized.

EXAMPLE XI A printing plate is prepared according to the process of Example I up to and including the step of fusing the toner image to the surface of the plate. At this stage of the process, the plate is cooled, the photoconductive binder material brushed from the surface of the nonimaged areas, and the resulting plate recharged in the presence of light to a potential of about 200 volts with a 3 wire corotron at a potential of about 7,5 00 volts so as to reestablish the latent image in those areas of the plate on which the electrically insulating image has been developed. The image is then contacted with electroscopic marking particles comprising a styrene terpolymer, with the particles adhering to the recharged surface of the originally developed image. The charged marking particles are then electrostatically transferred from the printing plate to the surface of a Harris Alum-o-Lith aluminum substrate according to the process described in U.S. Pat. No. 3,004,860. The transferred image is then fused to the surface of the aluminum substrate by the application of heat at a temperature of about 250 F. for about 5 seconds. The resulting plate is then Wrapped on the cylinder of a lithographic printing press and operated in the conventional manner as described in Example I. The ink image produced is first transferred to the surface of a rubber offset printing blanket from where it is transferred upon contact to the surface of the final paper copy sheet. Acceptable prints were obtained.

Although the present examples are specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to prepare the lithographic plate of the present invention, other steps or modifications may be used, if desirable. For example, the fountain solution and lithographic ink may be applied in a single step to the surface of the plate. In addition, other materials may be incorporated in the developer, ink, fountain solution, photoconductive material or xerographic plate which will enhance, synergize, or otherwise desirably effect the properties of these materials for the present use. For example, spectral sensitivity of the plates prepared in accordance With the present invention may be modified by incorporating photosensitizing dyes therein.

Anyone skilled in the art will have other modifications occur to him based on the teaching of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A process of preparing a lithographic master which comprises forming an electrostatic latent image on the surface of an electrophotographic plate, said plate comprising a base substrate having fixed to the surface thereof an insulating layer of photoconductive material dispersed in a nonpolymeric crystalline binder, developing said latent image with electroscopic marking particles, fixing said marking particles to said base substrate through the interstices of said insulating layer and removing from the surface of said plate by nonstatic, dry surface treatment in those areas not protected by the developed image said insulating layer to produce said lithographic master.

2. The process as defined in claim -1 wherein said substrate is hydrophilic and said marking particles are hydrophobic.

3. The process as defined in claim 1 wherein said insulating layer comprises an organic photoconductive pigment dispersed in a nonpolymeric crystalline binder insulating composition.

4. The process as defined in claim 1 wherein said insulating layer comprises an inorganic photoconductive pigment dispersed in a nonpolymeric crystalline binder insulating composition.

5. The process as defined in claim 3 wherein said organic photoconductive pigment comprises a phthalocyan'ine composition.

6. The process as defined in claim 3 wherein said binder composition comprises an organic crystalline material.

7. The process as defined in claim 6 wherein said organic crystalline material comprises tetrachlorophthalic anhydride.

8. The process as defined in claim 6 wherein said organic crystalline material comprises 4-allyl-2-methoxyphenol.

9. The process as defined in claim 3 wherein said binder composition comprises an inorganic crystalline material.

10. The process as defined in claim 9 wherein said inorganic crystalline material comprises trimeric phosphonitrilic chloride.

11. The process of preparing a lithographic master which comprises forming an electrostatic latent image on the surface of a photoconductive plate, said plate comprising a base substrate having fixed to the surface thereof a layer of a nonpolymeric crystalline photoconductive insulating material, said photoconductive insulating material comprising an inorganic photoconductive pigment selected from the group consisting of zinc oxide, zinc sulfide, zinc cadmium sulfide, cadmium selenide, cadmium sulfoselenide, cadmium sulfide, zinc cadmium selenide, zinc sulfoselenide and mixtures thereof dispersed in a nonpolymeric crystalline binder insulating composition, developing said latent image with electroscopic marking particles, fixing said marking particles to said base substrate through the interstices of said photoconductive insulating material, and removing from the surface of said plate in those areas not protected by the developed image by a nonstatic, dry

12 surface treatment said photoconductive insulating material to form said lithographic master.

12. The process as defined in claim 11 wherein said binder composition comprises an organic crystalline material.

13. The process as defined in claim 12 wherein said organic crystalline material comprises tetrachlorophthalic anhydride.

14. The process as defined in claim 12 wherein said organic crystalline material comprises 4-allyl-2-methoxyphenol.

15. The process as defined in claim 11 wherein said binder composition comprises an inorganic crystalline material.

16. The process as defined in claim 15 wherein said inorganic crystalline material comprises trimeric phosphonitrilic chloride.

17. A process of preparing a lithographic master which comprises bonding to the surface of a base substrate a layer of an insulating layer of photoconductive material dispersed in a nonpolymeric crystalline binder, forming on the surface of said layer an electrostatic latent image, developing said latent image with electroscopic marking particles, fixing said marking particles to said base substrate through the interstices of said insulating layer and removing from the surface of said substrate by a nonstatic dry surface treatment that portion of the insulating layer unprotected by the developed image to form said lithographic master.

18. A process of preparing a lithographic master which comprises bonding to the surface of a base substrate a layer of a nonpolymeric crystalline photoconductive insulating material, said material comprising an inorganic photoconductive pigment selected from the group consisting of zinc oxide, zinc sulfide, zinc cadmium sulfide, cadmium selenide, cadmium sulfoselenide, cadmium sulfide, zinc cadmium selenide, zinc sulfoselenide and mixtures thereof dispersed in a nonpolymeric crystalline binder insulating composition, forming on the surface of said photoconductive material an electrostatic latent image, developing said latent image with electroscopic marking particles, fixing said marking particles to said base substrate through the interstices of said photoconductive insulating material and removing from the surface of said substrate by a nonstatie dry surface treatment that portion of the photoconductive insulating material unprotected by the developed image to form said lithographic master.

19. A process for preparing a lithographic master which comprises mixing in the presence of a solvent equal parts of nonpolymeric crystalline tetrachlorophthalic anhydride and zinc oxide photoconductor for a time sufficient to cause the dispersion of said photoconductor and said crystalline composition, applying said mixture to the surface of a hydrophilic substrate so as to form a crystalline photoconductive insulating layer on the surface of said substrate, said photoconductive insulating layer being about 6 to about 25 microns in thickness, and said substrate being selected from at least one member of the group consisting of aluminum, brass, steel, copper, nickel and zinc, heating said substrate bearing said crystalline photoconductive layer at a temperature and for a time sufficient to fix said layer to the surface of said substrate, said temperature ranging from about to C. and said time being from about 12 to 15 minutes, charging the surface of said photoconductive layer, exposing said charged surface to light in an imagewise pattern so as to form an electrostatic latent image on the surface of said layer, developing said electrostatic latent image with a hydrophobic toner in such a manner that the toner adheres to the latent image in imagewise configuration, fixing said toner image to said substrate through the interstices of said photoconductor layer, dusting from the surface of the receiving substrate that portion of the crystalline binder photoconductive layer not protected by the developed image so as to expose the hydrophilic surface of the underlying substrate to produce said lithographic master.

20. The process as defined in claim 19 wherein said substrate is aluminum. I

21. A lithographic printing plate comprising an image support member having positioned thereon in imagewise configuration an image transfer means, said image transfer means comprising two distinct layers superimposed one upon the other, the lower layer comprising an insulating layer of photoconductive material dispersed in a nonpolymeric crystalline binder and the upper layerfa developer material having hygroscopic properties different from that of said support member, said developer material being fixed to said support member through the interstices of said insulating layer.

22. A lithographic plate as described in claim 21 wherein said insulating layer comprises an organic photoconductive pigment dispersed in a crystalline binder insulating composition;

23. The lithographic plate as described in claim 21 wherein said insulating layer comprises an inorganic photoconductive pigment dispersed in a crystalline binder insulating composition. I

24. A method of making multiple copies from a lithographic master which comprises forming an electrostatic latent image on the surface of a crystalline photoconductive plate, said plate comprising a hydrophilic substrate having fixed to the surface thereof an insulating layer of photoconductive material dispersed in a nonpolymeric crystalline binder, developing said latent image with a hydrophobic developer, fixing said developer to said substrate through the interstices of said insulating layer, removing from the surface of said substrate by a nonstatic dry surface treatment that portion of the insulatinglayer not protected by the developed image, applying 'to the surface of said plate a lithographic ink, said ink being distributed thereon conforming to said developed image in an imagewise configuration, contacting said inked surface with a copy sheet to thereby effect the transfer of an image to said copy sheet and repeating the inking and contacting steps at least more than onetime.

25. A method of making multiple copies from a xerographic image which comprises:

(a) forming an electrostatic latent image on the sur face ofa crystalline photocondcutive plate, said plate comprising a hydrophilic substrate having fixed to the surface thereof a crystalline photoconductive insulating layer, said photoconductive layer comprising a photoconductive pigment dispersed in a nonpolymeric crystalline binder insulating compositidjn;

'(b) developing said latent image with a hydrophobic developer;

() fixing said developer to said substrate through the interstices of said photoconductive layer;

(d) removing from the surface of said substrate that said developed image in an imagewise configuration;

(g) contacting said inked surface with an offset blanket to thereby effect the transfer of an image to said blanket;

(h) contacting said inked offset blanket with a transfer sheet; and

(i) repeating steps (e)(h) until the desired copies are produced.

26. A method of making multiple copies from a xerographic image which comprises:

(a) forming an electrostatic latent image on the surface of a crystalline photoconductive plate, said plate comprising a conductive substrate having fixed to the surface thereof a crystalline photoconductive insulating layer, said layer comprising a photoconductive pigment dispersed in a nonpolymeric crystalline binder insulating composition;

(b) developing said latent image with insulating electroscopic marking particles;

(0) fixing said marking particles to said substrate through the interstices of said photoconductive layer;

'(d) removing from the surface of said substrate by a nonstatic dry surface treatment that portion of the crystalline photoconductive layer which is unprotected by the developed image;

(e) charging the surface of said plate thereby reestablishing a latent image in those areas of the plate bearing the developed electrically insulating image;

(f) developing said recharged image with electroscopic marking particles;

(g) transferring" said marking particles to an image support member in an imagewise configuration; and

(h) repeating steps (e), (f) and (g) in their given sequence to form a multiplicity of identical images on respective image support members.

27. A xeroprinting plate comprising a conductive image support member having positioned thereon in imagewise configuration an image transfer means, said image transfer means comprising two distinct layers superimposed one upon the other, the lower layer comprising a photoconductive material dispersed on an insulating nonpoly-' meric crystalline binder composition and the upper layer an insulating developer material, said developer material being fixed to said support member through the interstices of said insulating layer.

References Cited UNITED STATES PATENTS 2,955,531 10/1960 Bogdonoff 10112 8.2 3,104,169 9/1963 Metcalfe et al 961 3,121,009 2/19 64 GiaimO 96-l 3,236,640 2/1966 Tomanek et al 96--l 3,305,359 2/1967 DelmOnt 961 GEORGE F. LESME S, Primary Examiner JOHN C. COOPER III, Assistant Examiner US. Cl. X.R.