US3793024A

US3793024A - Photoconductor containing printing plates

Info

Publication number: US3793024A
Application number: US00196445A
Authority: US
Inventors: R Gracia
Original assignee: Itek Corp
Current assignee: Northrop Grumman Guidance and Electronics Co Inc; EIDP Inc
Priority date: 1968-07-10
Filing date: 1971-11-08
Publication date: 1974-02-19
Anticipated expiration: 1991-02-19

Abstract

A planographic printing plate is prepared by exposing imagewise a copy medium comprising a physically developable photosensitive material such as a photoconductor and contacting the copy medium with image-forming materials which remain chemically reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and contacting the thus treated copy medium with a compound having an oleophilic grouping and a grouping reactive with the chemically reactive image-forming materials of the non-exposed areas of the copy medium, thereby producing a positive oleophilic image of the original. The image-forming materials and/or oleophilic compound having a reactive grouping may be incorporated in the copy medium prior, during, or subsequent to exposure. This printing plate containing the oleophilic image is suitable for contacting with ink to produce multiple copies. When a greasy printing ink is used a positive of the original (positive to positive) is produced.

Description

United States, Patent [1 1 Gracia 451 Feb. 19, 1974 PHOTOCONDUCTOR CONTAINING PRINTING PLATES [75] Inventor: Robert F. Gracia, Scituate, Mass. [73] Assignee: Itek Corporation, Lexington, Mass.

[22] Filed: NOV. 8, 1971 21 Appl. No.: 196,445

Related US. Application Data [63] Continuation-impart of Ser. No. 743,738, July 10,

1968, abandoned.

[52] US. Cl. 96/33, 96/48 PD, 101/456,

. 101/458 [51] Int. Cl. G03f 7/02, G030 5/24 [58] Field of Search..-.. 96/33, 48 PD; 101/456, 458, 101/466 [56] References Cited UNITED STATES PATENTS 3,083,097 3/1963 Lassig eta]. 96/33 3,161,508 12/1964 Hepher et al. 96/33 3,490,906 l/l970 Blake 96/33 FOREIGN PATENTS OR APPLICATIONS 1,043,250 9/1966 Great Britain 9 6/27 R Primary Examiner-David Klein Attorney, Agent, or Firm-Homer 0. Blair; Robert L. Nathans; W. Gary Goodson s71 ABSTRACT A planographic printing plate is prepared by exposing imagewise a copy medium comprising a physically developable photosensitive material such as a photoconductor and contacting the copy medium with imageforming materials which remain chemically reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and contacting the thus treated copy medium with a compound having an oleophilic grouping and a grouping reactive with the chemically reactive image-forming materials of the non-exposed areas of the copy medium, thereby producing a positive oleophilic image of the original. The image-forming materials and/or oleophilic compound having a reactive grouping may be incorporated in the copy medium prior, during, or subsequent to exposure. This printing plate containing the oleophilic image is suitable for contacting with ink to produce multiple copies. When a greasy printing ink is used a positive of the original (positive to positive) is produced.

10 Claims, 3 Drawing Figures PAIENTEOFEBI w 3,793.024

EXPOSURE DEVELOPED NEGATIVE PRINTING PLATE ROBE/i 7' F. 6R4 6/4 INVENTOR.

ATTORNEY.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to processes for the production of photographic images especially useful as printing plates and to products obtained thereby.

2. Description of the Prior Art Data or image storage media comprising a-p'hotoconductor such as TiO are described in detail in U.S.?Pat. Nos. 3,152,903; 3,052,541; 3,380,823; and British Pat. specification No. 1,043,250. In the aforementioned British patent specification, a radiation sensitive material, such as TiO functions as aphotosensitive component of the media and exposure of these media to activating radiation results in the storage of reversible latent images therein. The reversible latent image pattern may be converted to an irreversible form by contacting with suitable image-forming materials prior to, during, or subsequent to exposure.

SUMMARY OF THE INVENTION It has been discovered according to this invention that a planographic printing plate suitable for producing multiple copies of an original maybe produced by contacting a copy medium comprising a physically developable material such as a photoconductor which has been imagewise exposed and contacted with chemically reactive image-forming materials and with a coma metallic image and in the non-metallic areas a solution of metal ions, is contacted with an oleophilic compound of the type described herein to form a reaction product between the metal ions and the oleophilic compound which is more oleophilic than any intereaction of the oleophilic compound with the metallic image. Therefore, when the copy medium thus formed is used as aprinting plate, greasy ink will adhere preferentially to those areas "which originally contained the metal ion rather than those areas containing the metallic image areas. Thus, the metallic image containing area "becomes a non-printing area in distinction from the prior art wherein the metallic image becomes a "printing image when contacted with these same oleoiphilic compounds and when used with a greasy printing ink.

pound having an oleophilic grouping and a grouping reactive with the chemically reactive image-forming materials remaining in the non-exposed areas of the copy medium and non-reactive with the images in the exposed areas of the copy medium, thereby "producing a positive oleophilic imageof the original image. Some or all of the image forming materials and oleophilic compound having a reactive grouping may be applied to the copy medium prior to exposure. The planographic printing plate is preferably produced by first imagewise exposing the copy medium and then contacting the exposed copy medium with a physical developer preferably comprising separatesolutions of a solution of metal ions and a solution of a reducing agent for the metal ions, and then contacting the thus developed copy medium with a heterocyclic mercaptan compound or the salt of such compound. If desired this invention may be practiced non-photographically by typing or writing on a support 'to form an image pattern of chemically reactive image'forming materials. Thus, a

solvent permeable support may be written on with a so-' tive image-forming materials and the oleophilic compound produces a more oleophilic area than the reaction product, if any, of areas which do not contain these chemically reactive image-forming materials. Thus, in the preferred embodiment 'a copy medium comprising DRAWINGS FIG. 1 is a diagrammatic view of the exposure step of one embodiment of this invention.

FIG. 2 is a diagrammatic view of the exposed photosensitive copy medium of FIG. 1 which has been developed.

- FIG. 3 is a diagrammatic view of the developed copy medium of FIG. 2 which has been made ink receptive in the non-image areas.

In general FIG. 1 describes the exposure of a photosensitive copy medium comprising a support 11 and a photosensitive coating 12 which is preferably a photoconductor or other physically developable photosensitive material through a transparency 20.

Physical development of the exposed copy medium of FIG. 1 produces a developed negative of the original transparency having metal images 13 and non-image 14 having metal ions which are chemically reactive.

FIG. 3 shows a printing plate having oleophilic areas which correspond to the darkened portions of the original transparency 20. The printing plate of FIG. 3 can then "be inked and used as a printing plate for producing multiple copies.

DESCRIPTION OF PREFERRED EMBODIMENT( S) The compounds having an oleophilic grouping and a grouping reactive with thechemically-reactive imageforming materials of the non-exposed areas of the copy medium sometimes referred to as the oleophilic compound of this invention) are preferably polar solvent soluble organic compounds such as the polar solvent soluble salts "of compounds disclosed in U.S. Pat. No. 3,083,097, incorporated herein by reference. The preferred compounds are metal salts which are soluble in a polar solvent and which will readily undergo a metathetica] reaction with a solution of metal ions. A metathetical reaction is defined herein as a chemical reaction wherein an exchange of ions takes place. For example, a solution of a sodium mercaptide will react with a solution of silver nitrate to form sodium nitrate and a silver mercaptide. The sodium and potassium salts of the oleophilic compounds of this invention are especially preferred. The preferred oleophilic compound of this invention is the polar solvent soluble metal salts of RX wherein X is at least one reactive grouping capable of reacting with the chemicallyreactive' image-forming materials of the non-exposed areas of a copy medium which have been exposed and contacted with image-forming materials, according to 3 the teachings of this invention. X preferably includes the following groups:

2. SR where R is a group which can easily be hydrolyzed leaving -SH, such as acoyl, aroyl, amidinium or NHR wherein R is alkyl, aryl, aralkyl, cycloalkyl, heterocyclyl,

3. Thio-acid groups,

4. Thio-amide groups,

5. Thione groups,

6. Selenium analogues of the foregoing groups (I),

( and 7. Isothiocyanate group.

R is at least one oleophilic group. The oleophilic group may be a fatty chain or substituent containing at least four carbon atoms and preferably 6-20 carbon atoms. R can also be an aryl, alkaryl, or aralkyl group. The oleophilic grouping R is preferably a hetero grouping of the following general formula:

wherein R represents aryl (phenyl, tolyl), aralkyl (benzyl), cycloalkyl (cyclohexyl), alkyl, preferably a long-chained straight or branched chain, saturated or unsaturated hydrocarbon radical with at least 10, preferably 10 to carbon atoms, and a heterocyclic radical (furfuryl, thiazolyl), which substituents are either linked to one of the two A atoms, and A represents one or more of the hetero atoms 0, N, S, and Se, which are present either in'an open arrangement or as ring elements of a heterocyclic ring, such as for example, l,3,4-triazole, 1,3,4-thiodiazole, thiazole, selenazole or oxazole, and R representsaryl, aralkyl, cycloalkyl, alkyl, and a heterocyclic radical which substituents are either linked to one of the two A groups directly or by means of other linking groups, or linked to one of the ring elements of the heterocyclic ring.

The alkali and alkaline earth metal salts of the compounds having the formula R X are particularly useful in this invention.

Compounds especially preferred for this invention are the alkali and alkaline earth metal salts of the following heterocyclic mercaptans:

5-mercapto-3-phenyll ,3 ,4-thiadiazole-2-thione 2-mercaptobenzimidazole 10 .......A.......A.. H W V l 2-mercaptobenzothiazole Compounds of this class can be prepared by the method of or analogous to the method described by Burke, J.A.C.S., 69, 236-7 (1947).

A simple test to determine whether a preferred class of oleophilic compounds is suitable for this invention is to contact this compound with an aqueous solution of 0.01 N AgNO If a cloudy precipitate forms the oleophilic compound is suitable for use.

Polar solvent suitable for dissolving the oleophilic compound of this invention are materials which will allow ionization of this oleophilic compound and reaction with the chemically reactive image-forming materials of this invention. Water and simple alcohols are especially preferred.

The physically developable photosensitive material useful in this invention is preferably a photoconductor or photocatalyst and is not limited to any group of compounds but may include bothorganic and inorganic photosensitive materials. Preferred photoconductors useful in this invention are metal containing photoconductors. A preferred group of such photosensitive materials are the inorganic materials such as silver halide and compounds of a metal and a non-metallic element of group VIA of the periodic table*(*Periodic table from Langes HANDBOOK OF CHEMISTRY, 9th Edition, pp. 56-57, 1956.) such as metal oxides, such as zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide, tin oxide, and barium titanate; metal sulfides such as cadmium sulfide, zinc sulfide and tin disulfide; metal selenides such as cadmium selenide. Metal oxides are especially preferred photoconductors of this group. Titanium dioxide is a preferred metal oxide because of its unexpectedly good results. Titanium dioxide having an average particle size less than about 250 millimicrons and'which has been heat treated in an oxidizing or a reducing atmosphere is especially preferred.

Organic photoconductors suitable for use in this invention are, for example, the heteropolyacids such as phosphotungstic acid, phosphosilicic acid, and phosphomolyidic acid.

When a reversibly activatable photoconductor such as titanium dioxide is used, it should be conditioned before exposure by such methods as heating or storage in the dark from one to twenty-four hours. After conditioning, the photoconductor is not exposed to light prior to its exposure to activating radiation for recording an image pattern.

Physically developable materials such as the vdiazosulphonates and like materials disclosed in US. Pat. No. 2,738,272, incorporated herein by reference are also useful in this invention.

While the exact mechanism of the present process is 'not known it is believed that the presensitization, i.e.,

exposure to activating light, e.g., ultraviolet light,

cordingly, a simple test to determine whether materials have a photoconductor effect is to mix the material in question with aqueous silver nitrate. In the absence of light, little, if any, reduction of silver ions should occur. At the same time as exposing the same mixture to light, a control sample of an aqueous silver nitrate solution alone is similarly exposed and if the mixture darkens faster than the control sample, the test material is a ,photoconductor.

The period of exposure will depend upon the intensity of the light source, particular photoconductor, the type and amount of catalyst, if any, and like factors known to the art. In general, however, the exposure may vary from about 0.001 seconds to several minutes.

Image-forming materials which are useful in this invention are those such as described in U.S. Pat. Nos. 2,738,272 and 3,152,903 and in British Pat. specification No. 1,043,250. These image-forming materials include preferably an oxidizing agent and a reducing agent. Such image-forming materials are often referred to in the art as physical developers. The oxidizing agent is generally the image-forming component of the image-forming material. However, this is not necessarily true. Either organic or inorganic oxidizing agents may be employed as the oxidizing component of the imageforming material. Preferred oxidizing agents comprise the reducible metal ions having at least the oxidizing power of cupric ion and include such metal ions as Ag", n +a p 2 +z s +2 +2 Cu, and Cu".

The reducing agent component of the image-forming materials of this invention are inorganic compounds such as the oxalates, formates, and ethylenediaminetetraacetate complexes of metals having variable valence; and organic compounds such as dihydroxybenzenes, aminophenols, and aminoanilines. Also, polyvinylpyrrolidone, hydrazine, and ascorbic acid may be used as reducing agents in this invention. Suitable specific reducing compounds include hydroquinone or derivatives thereof, ov and paminophenol, pmethylaminophenol sulfate, p-hydroxyphenyl glycine, oand p-phenylenediamine, l-phenyl-3-pyrazolidone, alkali and alkaline earth metal oxalates and formates and ferrous-ferric couple solutions.

Additionally, the image-forming materials or physical developers may contain organic acids or alkali metal salts thereof, which can react with metal ions to form complex metal anions. Further, the developers may contain other complexing agents and the like to improve image formation and other properties found to be desirable in this art.

A preferred physical developer is that stabilized physical developer comprising silver ion, the ferrousferric couple reducing agent, a complexing agent and an ionic surfactant as a stabilizing agent. Such a developer is described in U.S. Pat. No. 3,157,502 and PS and .6 B. Vol. I3, 1969, pp. 41-42, both incorporated by refernce.

The image-forming materials of this invention may be applied after exposure of the copy medium to an image, or the image-forming materials can, in the alternative, be incorporated along with the photoconductor in the copy medium prior to exposure. For example, both the reducing agent and oxidizing agent may be present in the copy medium as described in U.S. Pat. No. 3,152,903, herein incorporated by reference. Or, in the alternative, only part of the image-forming materials may be present in the copy medium at the time of exposure as, for example, when the copy medium is coated with silver nitrate prior to exposure and then subsequent to exposure is developed by contacting with reducing agent.

The image-forming materials may be applied by any of the methods known to the art as, for example, by dipping, coating, brushing, etc. In addition, the imageforrning materials may be applied in an electrolytic process such as described in U.S. Pat. No. 3,010,883.

Spectral sensitivity of the photosensitive copy me dium of this invention may be increased by means known to the art such as by dye sensitization, doping with foreign ions, exposure to ultraviolet radiation, and the like.

The planographic master of this invention may be utilized to produce positive or negative prints of an original, depending upon how the master is used. For example, the type of ink that is used on the planographic master to produce the print may be varied. When a polar solvent-based ink is utilized, such as a water or alcohol-based ink, such as disclosed in U.S. Pat. No. 3,209,683, incorporated herein by reference, then the ink adheres to the hydrophilic portions of the master and a negative print is produced. However, when an oil base ink is utilized, the ink adheres to the oleophilic portions of the master and a positive print of an original is produced. The preferred multiple copy system of this invention utilizes an oil-based or greasy printing ink.

Additionally, the planographic master produced by this invention can be utilized as a direct printing system or an offset printing system. Also the plate may be used in lithographic or driographic printing. See U.S. Pat. No. 3,51 1,178, incorporated by reference, for a definition of driography.

Binder agents are preferably used with the photosensitive materials to bind these materials to the carrier substrate. In general, these binders are translucent or transparent so as not to interfere with transmission of light to the photosensitive materials. Preferred binder materials are hydrophilic or hydrophobic organic materials such as polymers. Examples of suitable polymers are synthetic polymers'such as butadienestyrene copolymer, 'poly(alkyl acrylates) such as poly-(methyl methacrylate) polyamides, polyvinyl acetate, polyvinyl alcohol and polyvinylpyrrolidone or natural polymers such as gelatin.

The exposure step of this invention is generally carried out by means of activating electromagnetic radiation. Thus actinic light, x-rays, or gamma rays are effective in exciting the photocatalyst. Beams of electrons and other like elemental particles may also be used in the place of the ordinary forms of electromagnetic radiation for forming an image according to this invention.

These various activating means are designated by the term activating radiation.

- lows:

- sodium sulfite 7 The inert substrate upon which the photoconductor of this invention is deposited comprises any suitable backing of sufficient strength and durability to satisfactorily serve as a reproduction carrier. The carrier substrate may be in any form such as, for example, sheets, ribbons rolls, etc. This sheet may be made of any suitable material such as'wood, metal, rag content paper, wood pulp paper, plastics such as, for example, polyethylene terephthalate .(Mylar), and cellulose-acetate, cloth, metallic foil and glass. Polyethylene coated paper having a gelatin subbing is an especially preferred support. The type of carrier substrate will depend upon the number of copies desired from the planographic master produced. Generally, if a very high number of copies is desired, it is desirable to have a more durable carrier sheet.

The invention above described is exemplified as fol- EXAMPLE 1 A photosensitive copy medium comprising a paper support coated with a finely-divided titanium dioxide dispersed in a gelatin binder which has been dyesensitized with Z-p-dimethylaminostyryl-4-methyl thiazole methochloride is exposed to an image pattern from a tungsten light source for 1-2 seconds duration, thereby giving an exposureof 400 meter candle seconds.

The thus-exposed copy medium is then immersed in an aqueous solution of 0.2 normal silver nitrate, then immersed in a Metol-sodium sulfite bath, and then contacted for a'few seconds with a pre-printing solution of the potassium salt of 2-mercaptobenzothiazole. This processing is done by machine at the rate of 4% inches per second. The processing rate is varied from about 2-10 inches/sec with satisfactory results.

The thus prepared printing plate is now placed on an offset lithographic press and used to print 500 copies which are positives of the. original because the oil base ink adheres to the non-exposed portions of the plate.

The potassium salts of 5-mercapto-3-phenyl-1,3,4- t-hiadiazole-2-thione, 2-mercaptobenzimidazole, 6- amino-2-mercaptobenzothiazole, the selenium analogue of Z-niercaptobenzothiazole are substituted for the potassium salt of 2-mercaptobenzothiazole in the above procedure to obtain'similar results. EXAMPLE 2 A copy medium comprising a finely divided titanium dioxide immersed in a high molecular weight polyvinylalcohol binder in the absence of activating radiation is dipped in an aqueous solution of silver nitrate, dried, then contacted with an aqueous solution of the potassium salt of Z-mercaptobenzimidazole and dried. This substrate is then exposed to a source of ultraviolet light and then contacted with a solution of the following composition:

2 .0 Metol 2 0 2-lmidazole .1 N,N-dimethyl- O paraphenylenedidiamine sulfate Non-ionic surfactant 1.0 Water to 1 liter.

A printing plate is produced which is useful for making multiple copies.

EXAMPLE 3.

A polyethylene coated paper having a gelatinnitrocellulose subbing layer is coated with the following formulation:

TiO Slurry surfactant TiO, H,O

Coating Formulation TiO,-H,O Slurry (20% TiO,)

but

LANG

R Ekaline F (poly(ethylene oxide) nonionic surfactant) (10%) Photographic gelatin glycerin (50%) formaldehyde (3.7%)

w O06 0&0 we e em Bath 1 Bath 11 0.4 N AgNC),

20.0 g. Sodium Sulfite 20.0 g. Metolv 0.1 g. Z-imidazole 1.0 g. N-N-dimethyl-paraphenylenediamine sulfate 1.0 ml. Nonic 218 (non-ionic surfactant) The potassium salt of 5,5 Diphenyl-Z-thiohydantoin Dimethylformamide Bath Ill WWW The thus prepared printing plate is used on an offset press with an oil base ink to print 500 copies which are positives of the original. The metallic areas of the plate are the non-printing areas.

A silver halide copy medium, exposed and processed as described above produces a printing plate which is used for making copies on a conventional lithographic offset press using a greasy ink.

EXAMPLE 4 A polyethylene coated paper support having a gelatin subbing layer is immersed in an aqueous solution of silver nitrate. This support is then written on with a hydrophilic wax crayon which writing covers up portions of the support. The support is then contacted for a few seconds with a pre-printingsolution of the sodium salt of 6-amino-2mercapto-benzothiazole, inked with a greasy printing ink and used on an offset press to produce copies which are negatives of crayon writing.

In an alternative to writing with a wax crayon on the support which has been contacted with silver nitrate is then written on by selectively contacting with a strong reducing agent for the silver nitrate as disclosed in U.S. Pat. No. 3,108,932, incorporated herein by reference, which causes a silver image to form. This support is then contacted with the above-mentioned pre-printing solution and the thus-prepared-printing plate is used to make multiple copies on an offset press.

EXAMPLE A porous anodized aluminum support is written on with a silver nitrate solutionand contacted with a preprinting solution of the sodium salt of mercaptobenzothiazole which forms a printing plate having oleophilic areas useful for use on a press for making multiple copies.

What is claimed is:

l. A process of making a planographic printing plate comprising (1) exposing a copy medium comprising a photoconductor which after exposure can be physically developed and contacting the copy medium with chemically reactive image-forming materials comprising a solution of a silver salt having reducible silver ions to form silver metal in the exposed areas and silver ions in the non-exposed areas, which image-forming materials remain chemically. reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and (2) contacting the thus-treated copy medium with a compound having an oleophilic grouping and a grouping which enters into a chemical bond with the chemicallyreactive, image-forming materials of the non-exposed areas of the copy medium thereby producing in these non-exposed silver ion containing areas oleophilic areas capable of being used as a printing plate and wherein the compound having an oleophilic grouping and a grouping reactive with a chemically-reactive, image-forming material is'a polar solvent soluble compound of the general formula and (5); (7) an isothiocyanate group; and wherein R is at least one oleophilic group selected from alkyl groups, aryl groups, alkaryl groups, aralkyl groups, and a hetero grouping of the following general formula wherein R is selected from the group consisting of aryl, aralkyl, cycloalkyl and alkyl groups and which R is linked to at least one of the two A atoms, and A is selected from at least one of the atoms 0, N, S, and Se, and wherein the hetero grouping may be present either in an open arrangement or as a ring element of a heterocyclic ring.

2. A process as in claim 1 wherein the compound 10 having an oleophilic grouping and a grouping reactive with a chemically-reactive image forming material is an alkali or alkaline earth metal salt of a heterocyclic mercaptan compound.

3. A process as in claim.2 wherein the mercaptan compound is at least one of the group consisting of 5- mercapto-B-phenyll ,3,4,-thiadiazole-2-thione, 2- mercaptobenzimidazole, 6-amino-2-mercaptobenzothiazole, and Z-mercaptobenzothiazole.

4. A process as in claim 1 wherein the photoconductor comprises silver halide or a metal containing photoconductor which becomes reversibly activated upon exposure to activating radiation.

5. A process as in claim 4 wherein the image-forming materials additionally comprise a reducing agent for said reducible silver ions.

6. A process as in claim.1 wherein the compound having an oleophilic grouping is the alkali or alkaline earth metal salt of at least one compound selected from the group consisting of l-phenyl-Z-thiourea, allylthiourea, l-acetyl-2-thiourea, Z-mercaptobenzoxazole, lphenyl-S-mercaptotetrazole, 2-mercapto thiazoline, l-dodecane thiol, 4-6-diamino Z-mercaptopyrimidine',

phenyl isothiocyanate, thiourea, 2-mercapto-4-phenyl thiazole, Z-mercapto-benzothiozole, 6-amino-2- mercaptobenzo thiazole, Z-mercapto-benzimidazole, of 5-mercapto3-phenyl- 1 ,3 ,4-thiadiazole-2-thione, and 5,5 diphenyl-Z-thiohydantoine.

7. A process as in claim 6 wherein the compound having an oleophilic grouping is the potassium or sodium salt of 5 ,5 diphenyl-Z-thiohydantoine.

8. A process of making a planographic printing plate comprising (1) exposing a photosensitive copy medium comprising a photoconductor and contacting the copy medium with chemically reactive image-forming materials comprising a solution of a silver salt having reducible silver ions to form silver metal in the exposed areas and silver ions in the non-exposed areas, which imageforming materials remain chemically reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and (2) contacting the thus-treated copy medium with a compound having an oleophilic grouping and a grouping which enters into a chemical bond with said chemically-reactive, image-forming materials and which compound is the polar solvent soluble metal salt of the compound which is at least one member selected from the group of dodecyl mercaptan; 5-mercapto-3- phenyl-l 3 4-thiadiazole-2-thione; 2- mercaptobenzimidazole; 6-amino-2-mercaptobenzothiazole; 2-mercaptobenzothiazole; and 5 ,5 diphenyl-Z- thiohydantoin.

9. A process as in claim 8 wherein said copy medium photoconductor comprises silver halide, titanium dioxide or zinc oxide.

10. A process as in claim 9 wherein the imageforming materials comprise a reducing agent for said reducible silver ions.

Claims

2. A process as in claim 1 wherein the compound having an oleophilic grouping and a grouping reactive with a chemically-reactive image forming material is an alkali or alkaline earth metal salt of a heterocyclic mercaptan compound.
3. A process as in claim 2 wherein the mercaptan compound is at least one of the group consisting of 5-mercapto-3-phenyl-1,3,4,-thiadiazole-2-thione, 2-mercaptobenzimidazole, 6-amino-2-mercaptobenzothiazole, and 2-mercaptobenzothiazole.
4. A process as in claim 1 wherein the photoconductor comprises silver halide or a metal containing photoconductor which becomes reversibly activated upon exposure to activating radiation.
5. A process as in claim 4 wherein the image-forming materials additionally comprise a reducing agent for said reducible silver ions.
6. A process as in claim 1 wherein the compound having an oleophilic grouping is the alkali or alkaline earth metal salt of at least one compound selected from the group consisting of 1-phenyl-2-thiourea, allylthiourea, 1-acetyl-2-thiourea, 2-mercaptobenzoxazole, 1-phenyl-5-mercaptotetrazole, 2-mercapto thiazoline, 1-dodecane thiol, 4-6-diamino 2-mercaptopyrimidine, phenyl isothiocyanate, thiourea, 2-mercapto-4-phenyl thiazole, 2-mercapto-benzothiozole, 6-amino-2-mercaptobenzo thiazole, 2-mercapto-benzimidazole, of 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione, and 5,5 diphenyl-2-thiohydantoine.
7. A process as in claim 6 wherein the compound having an oleophilic grouping is the potassium or sodium salt of 5,5 diphenyl-2-thiohydantoine.
8. A process of making a planographic printing plate comprising (1) exposing a photosensitive copy medium comprising a photoconductor and contacting the copy medium with chemically reactive image-forming materials comprising a solution of a silver salt having reducible silver ions to form silver metal in the exposed areas and silver ions in the non-exposed areas, which image-forming materials remain chemically reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and (2) contacting the thus-treated copy medium with a compound having an oleophilic grouping and a grouping which enters into a chemical bond with said chemically-reactive, image-forming materials and which compound is the polar solvent soluble metal salt of the compound which is at least one member selected from the group of dodecyl mercaptan; 5-mercapto-3-phenyl-1, 3, 4-thiadiazole-2-thione; 2-mercaptobenzimidazole; 6-amino-2-mercaptobenzothiazole; 2-mercaptobenzothiazole; and 5,5 diphenyl-2-thiohydantoin.
9. A process as in claim 8 wherein said copy medium photoconductor comprises silver halidE, titanium dioxide or zinc oxide.
10. A process as in claim 9 wherein the image-forming materials comprise a reducing agent for said reducible silver ions.