05/287196

06/25/1974

09/07/1972

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Eastman Kodak Company (Rochester, NY)

430/12

430/204, 101/466, 430/432

G03F7/06; G03F7/02; G03F7/06

96/33,29L 101/466

Smith, Ronald H.

Schilling, Richard L.

Byers, Henry E.

I claim

1. A composition for improving the oleophilic character of a silver image, comprising an acidic aqueous solution containing:

2. A composition of claim 1 wherein said long chain alkyl cationic compound is a quaternary ammonium compound having the formula ##SPC10##

3. A composition of claim 1 wherein said long chain alkyl cationic compound is a ternary sulfonium compound containing an alkyl chain of from 12 to 20 carbon atoms.

4. A composition of claim 2 wherein said compound is cetyl trimethyl ammonium bromide.

5. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC11##

6. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC12##

7. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC13##

8. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC14##

9. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus is 1-cetyl pyridinium bromide.

10. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC15##

11. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus has the formula ##SPC16##

12. A composition of claim 1 wherein said compound comprising a heterocyclic nucleus is 1-(2',4'-dinitrophenyl) pyridinium chloride.

13. A lithographic element comprising a support having thereon a hydrophilic surface and having thereon a silver image having been treated with the acidic aqueous solution of claim 1.

14. An element of claim 13 in which said long chain alkyl cationic compound is cetyl trimethyl ammonium bromide.

15. An element of claim 13 in which said compound comprising a heterocyclic nucleus is 1-(2',4'-dinitrophenyl) pyridinium chloride.

16. An element of claim 13 in which said silver image is formed by a photographic silver diffusion process.

17. A process of improving the oleophilic character of a silver image comprising contacting said image with the acidic aqueous solution of claim 1.

18. A process of improving the oleophilic character of a silver image comprising contacting said image with the acidic aqueous solution of claim 2.

19. A process of claim 17 in which said long chain alkyl cationic compound is a ternary sulfonium compound containing an alkyl chain having 12 to 20 carbon atoms.

20. A process of claim 17 in which said long chain alkyl cationic compound is cetyl trimethyl ammonium bromide.

21. A process of claim 20 in which said compound comprising a heterocyclic nucleus is 1-(2', 4'-dinitrophenyl) pyridinium chloride.

22. A process of claim 17 in whcih said silver image is formed by a photographic silver diffusion process.

BACKGROUND OF THE INVENTION

The present invention relates to lithographic processes and to lithographic printing plates made photographically. More particularly, this invention relates to a method of rendering oleophilic a silver image which has been produced by the photographic silver salt diffusion transfer process at a water accepting surface, such as the surface of a hydrophilic colloid layer or the surface of a hydrophilic pigment in a binder, so that the silver image accepts greasy printing ink. This invention also relates to the composition for treating the image and to the treated printing plates.

In lithography, a greasy ink is employed and the printing plate usually comprises a layer which, when wet with water, is hydrophilic and carries a line or dot image which is oleophilic.

Accordingly, a lithographic printing plate blank comprises a layer, the nature of whose surface is such that when wetted with water it will not accept greasy ink, although, if the ink is applied when the surface is dry, the ink so applied is not removed by subsequent wetting.

The practice of making a photolightographic printing plate is to produce an image at the surface of the hydrophilic layer which is sufficiently strongly oleophilic to accept ink in the presence of water.

Where only a few hundreds of copies are required, or even up to about a thousand copies, it is quite common to use a paper printing plate, but where many thousands of copies are required, it is necessary to use a more substantial printing plate, and the ones commonly used are made of aluminum sheet or zinc sheet. From these metal sheets, it is a common practice in the art to take as many as 20,000 copies. Aluminum sheet employed in the art is provided with an inert hydrophilic surface. This is often done by treating the aluminum to produce thereon an aluminum compound which is hydrophilic, for instance, aluminum oxide, as in the case of anodized aluminum, aluminum silicate and chromatized aluminum.

Various methods of obtaining a silver image on a lithographic printing plate blank can be used in a preferred process involving the photographic silver salt diffusion transfer process, in which diffusing silver halide complex contacts silver precipitating nuclei on the surface of a lightographic plate to deposit a sliver image. This silver image is then treated with a fix solution containing an olephilic compound which is adsorbed to the silver image to improve its affinity for a greasy printing ink.

DESCRIPTION OF THE PRIOR ART

Hepher et al, U.S. Pat. No. 3,161,508, issued Dec. 15, 1964, discloses organic compounds which may be used to treat the silver image to make it oleophilic. Suitable compounds include those containing a thiol group, oleophilic organic compounds generating a thiol group, and selenium analog organic compounds.

DeHaes et al, U.S. Pat. No. 3,186,842, issued June 1, 1965, indicates that the silver image can be treated with a lithographic preparation containing a quaternary ammonium compound; such as, cetyl trimethylammonium bromide or the like, and a compound containing a mercapto group; such as, 2-mercapto-benzthiazole or the like.

There has been a continuing search for treating compositions which would render the silver image more oleophilic with regard to greasy printing inks or to improve ink-up time in which the image accepts ink. Accordingly, it is one object of this inveniton to provide a composition for improving the oleophilic character of the silver image. An additional object of this invention is to provide a process for improving the affinity of silver images for greasy ink.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method of rendering oleophilic a silver image, particularly one which has been produced by the photographic silver salt diffusion transfer process, on a water-accepting surface. This method comprises contacting the silver image with an acidic aqueous fix solution containing:

a. a long chain (alkyl having 12-20 carbon atoms) non-aromatic organic cationic compound,

b. iodide ions, and

c. a heterocyclic organic compound with a nitro group bonded to an aromatic nucleus or an aromatic cationic compound with no nitro group.

In one embodiment of the invention, a composition is provided for treating the silver image, which composition contains:

a. a long chain organic quaternary ammonium compound or a long chain sulphonium compound,

b. iodide ions, and

c. a heterocyclic organic compound with a nitro group bonded to an aromatic nucleus or an aromatic cationic compound with no nitro group.

In preferred embodiments, the acidic aqueous solution contains a water-miscible alcohol having one or more hydroxy groups; e.g., methanol, and/or isopropanol and/or isobutanol so as to increase the solubility of the solutes to the desired level. The long chain organic cationic compound is preferably cetyl trimethylammonium bromide; the iodide ions are supplied by potassium iodide, and the organic compound having a nitro group bonded to an aromatic nucleus is 1-(2',4'-dinitrophenyl) pyrdinium chloride or 8-nitroquinoline.

A heterocyclic organic compound having a nitro group bonded to an aromatic nucleus is preferably employed as the component (c) when the silver image requires more oxidation as a step in the process of rendering the silver oleophilic. Whether or not more oxidation is required depends in part on the structure of the silver. If the silver is very porous the compound having a nitro group is likely to oxidize the silver too much.

By the process of this invention, a printing plate is provided comprising a silver image on a hydrophilic surface, which has been treated with the above acidic aqueous fix solution in order to improve the affinity for greasy printing ink.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By the process of this invention, a printing plate is provided comprising a silver image on a hydrophilic surface, which image has been treated with the above acidic aqueous fix solution in order to improve the affinity for greasy printing ink.

Long Chain Cationic Compound

In the present invention there may be used as the long chain organic cationic compound any of the cationic surfactants described in chapters 2 and 3 of "Cationic Surfactants", edited by E. Jungermann and published by Marcel Dekker Inc., New York, 1970.

Broad classes of long chain organic cationic compounds which may be used are represented by the following formulae: ##SPC1##

wherein R represents a long alkyl chain of 12 to 20 carbon atoms, each of R', R" and R'" may be either a long alkyl chain or a smaller alkyl group of 1-20 carbon atoms and X represents an anion. Y represents a moiety containing an anion such as Z-CH ₂ COO, or Z-CH ₂ CH ₂ OSO ₃ in which Z is a halide ion. The compounds employed may contain additional groups in the long chain such as -CONH- and may contain more than one cationic N atom.

Preferred long chain cationic compounds for use in this invention may be represented by formula I. ##SPC2##

wherein R, R', R" and R'" are each an alkyl group of 1-20 carbon atoms, at least one of R, R', R" and R'" being an alkyl group containing at least 12 carbon atoms and X is a halogen ion other than iodide or a sulphate ion.

Long chain non-aromatic cationic compounds which can be used include, preferably, those with 12 to 20 carbon atoms in the long chain; for example, cationic compounds having an aliphatic group such as lauryl, tridecyl, myristyl, cetyl, stearyl, arachidyl, etc. Quaternary salts of organic nitrogen bases are especially suitable, such as e.g., quaternary ammonium compounds, etc. Also appropriate are polyonium salts having a quaternary ammonium-, a phosphonium- or a ternary sulfonium group which is linked to the onium-atom by an organic bivalent radical also linked to another onium group. Compounds having a long chain aliphatic group such as cetyltrimethylammonium bromide are particularly useful. The preferred compounds are long chain organic quaternary ammonium compounds or long chain sulfonium compounds. The following compounds are included in the definition of long chain cationic compounds which can be used, for example:

dodecyl trimethyl ammonium chloride

trimethylsulfonium iodide

hexamethylene-S,S'-bis-dimethyl-1,6-disulfonium iodide

trimethylazonium iodide

trimethyloxy-ethylammonium iodide

tetramethylammonium iodide

diethylamino-ethyloleylamide-methyl sulfate

lauryl dimethyl amine oxide

hexadecyl trimethyl ammonium bromide

etc.

Iodide Ions

The iodide ions are preferably supplied from alkali metal salts; such as, for example, potassium, sodium, and the like, preferably potassium iodide; however, other iodide salts can be used as well as any compounds which provide iodide ions including organic materials which disassociate in aqueous solution.

Heterocyclic Organic Compound

The heterocyclic organic compounds which are useful in this invention include those having one or two rings. The heterocyclic rings may contain 5-12 atoms in the rings and preferably contain at least one nitrogen atom, such as, for example, pyridine, quinoline, quinoxaline, pyridopyridine, quinazoline, pyridazine, pyrimidine, pyrazine, pyrrole, pyrazole, isoindole, indole, pyrindine, indazole, pyridinium salts, etc.

Preferred heterocyclic organic compounds having a nitro group bonded to an aromatic nucleus may be represented by formulas II, III, IV and V. ##SPC3##

wherein each of R ₁ , R ₂ , R ₃ , R ₄ , R ₅ is H, alkyl (1-20 carbon atoms), NO ₂ , COOH, COOR' (R' is alkyl 1-20 carbon atoms) at least one of R ₁ , R ₃ and R ₅ being NO ₂ . ##SPC4##

wherein R is CH ₂ I R ₃ and R ₄ or R ₄ and R ₅ complete a nitro-substituted aromatic carbocyclic ring fused onto the cyclic ammonium ring and each of R ₁ and R ₂ is an alkyl group (1-20 carbon atoms) or a halogen-substituted alkyl group (1-20 carbon atoms). ##SPC5##

wherein R ₁ or R ₂ is NO ₂ . Compounds of this formula IV may have additional substituents. ##SPC6##

where R is alkyl having 1-20 carbon atoms or aralkyl having 1-20 carbon atoms and X is an anion.

A preferred heterocyclic organic compound is 1-(2',4'-dinitrophenyl) pyridinium chloride but other organic compounds which can be used, for example, include:

1-(2',4',6'-trinitrophenyl) picolinium chloride

1-(4'-formyl-2'-nitrophenyl) pyridinium chloride

1-(2',4', 6'-trinitrophenyl) pyrdinium chloride

1-(2',4',6'-trinitrophenyl) β-picolinium chloride

1-(2'-nitro-4'-carboxy phenyl) pyridinium chloride

8-nitro-2-tribromomethyl quinoline

8-nitroquinolinium methiodide

1-(3'-cyano-5'-nitro-pyrid-2-l) pyridinium

8-nitroquinoline

5 -nitroquinoline

p-nitrobenzyl trimethyl ammonium bromide

Cationic Compounds

Cationic heterocyclic compounds without the nitro group include all of the cationic heterocyclic rings mentioned above in connection with the nitro-substituted compounds but are not nitro substituted. Preferred compounds contain at least 10 carbon atoms. They are typically substituted with a group selected from the class consisting of alkyl, cyano, phenyl, halide, etc. Preferred organic cationic compounds having an aromatic group but no nitro group may be represented by formulas V and VI. ##SPC7##

wherein R is alkyl, e.g., methyl, ethyl or cetyl (1-20 carbon atoms); R ₁ is H or a lower alkyl group, e.g. methyl, etc. having 1-5 carbon atoms; R ₂ is H or substituent such as cyano, alkoxycarbonyl (e.g., ethoxy carbonyl) or R and R ₁ have the values given above and either R ₂ and R ₃ or R ₃ and R ₄ complete a benzene ring fused onto the cyclic ammonium ring. ##SPC8##

wherein R is a long chain alkyl group containing 12-20 carbon atoms and R ₁ is a substituent such as acyl, e.g., aceto.

The cationic heterocyclic compounds which can be used include, for example:

1-ethyl-4-cyanoquinolinium iodide

1-ethyl-4-ethoxycarbonyl quinolinium iodide

2-methyl-isoquinolinium iodide

1-ethyl-2-methyl-quinolinium iodide

4-cyano-1-ethyl quinolinium iodide

1-ethyl-4-ethylcarboxylatequinolinium iodide

2-methyl isoquinolinium iodide

1-cetyl pyridinium bromide

1-ethyl quinolinium iodide

1-methyl quinolinium iodide

2:3:5-triphenyl-tetrazolinium chloride

5-chloro-1-ethyl-2-methyl benzothiazolinium iodide

1-ethyl-2-β-(2-pyridylaminovinyl) pyridinium iodide

Solvents

An aqueous medium is employed but the medium can contain a water-miscible alcohol with one or more hydroxy groups, for example, methanol and/or isopropanol and/or isobutanol so as to increase the solubility of any of the solutes to the desired level. However, it is preferred to keep the concentration of the solvents to a minimum, in order to keep the flash point of the medium as high as possible.

The long chain organic cationic compound can be used in a concentration of about 0.01 to about 10 grams per liter, preferably about 0.05 to about 7 grams per liter.

The iodide can be used in an amount within the range of about 4 to about 50 grams per liter, preferably about 6 to about 16 grams per liter.

The organic heterocyclic compound which has a nitro group bonded to an aromatic nucleus or the aromatic cationic compound can be used in an amount within the range of about 0.5 to about 20, preferably about 4 to about 10 grams per liter.

The pH of the aqueous solution should be such that strongly colored dyes are not formed, i.e., the solution should be acid but the pH is between about 1.5 to about 7, preferably between about 1.7 to about 6. The solution can be buffered at the desired pH and an organic acid; such as, for example, citric acid, lactic acid, acetic acid, etc. can be used for this purpose. Amounts of organic acid between 5 and 150 grams per liter are useful. In a preferred embodiment, about 5 to about 40 grams per liter of an organic acid are used. A buffering capacity is desired on account of the residual alkali that is usually present on the water-accepting surface when the silver image has been formed thereon by the photographic silver salt diffusion transfer process. The pH of the acid aqueous solution should not be raised by such residual alkali which could have the result that strongly colored dyes are formed by the nitro compounds, if present. In addition, an advantage of the present invention in neutralizing any such residual alkali is that formation of soaps by reaction of such alkali with the free fatty acids present in printing inks is thus avoided. Such soaps can cause emulsification of the ink and water used in printing.

Various other components may be added to the fix solution include thickness such as 2-methyl-2,4-pentanediol, hydroxyethylcellulose, carboxymethylcellulose, etc. The keeping or storage stability of the solution is good, but with some fix solutions after 2 to 4 weeks at room temperature, dark crystals begin to form on the bottom of the walls of the container holding the fix solution. These reddish-brown crystals do not dissolve on heating, nor do they interfere with the efficiency of performance of the solution. Crystal formation can be inhibited by raising the pH of the solution to a pH of 4.5 or higher or by adding an antioxidant to the solution or by adding extra solvent. Particularly good antioxidants which may be used in an amount of about 0.1 gram per liter at a pH level below 4.5 include hydroquinone, ascorbic acid, n-propyl gallate, butylated hydroxy toluene, etc., preferably hydroquinone or ascorbic acid.

As indicated above, the water-accepting surface may be the surface of a hydrophilic colloid layer or the surface of a layer of binder containing a hydrophilic pigment. Examples of such hydrophilic colloids are gelatin, polyvinyl alcohol, alginates, carboxymethyl cellulose, etc. Examples of binder layers containing hydrophilic pigments are synthetic hydrophobic polymer layers containing hydrophilic silica particles. Such layers are described, for example in Ormsbee, U.S. Pat. No. 3,344,741, issued Oct. 3, 1967.

The degree of hydrophilicity is conveniently determined with respect to a drop of a liquid placed on the surface of the material. This can be measured by the contact angle obtained when a drop of distilled water is placed on a level sample of the coating. By projecting an image of the drop on a suitable screen, and measuring the angle of a line tangent to the dropped image at the point where the drop touches the surface, a contact angle is obtained which can be measured and utilized to determine the degree of hydrophilicity. For instance, generally a hydrophobic surface has a contact angle of 90° or greater. The contact angle of preferably from about 40° to about 75° indicates the hydrophilicity suitable for adhesion of a hydrophilic coating and is highly desirable for coatings such as gelatin coatings or the like. In connection with silver images on a hydrophilic support, it is generally desirable to have a hydrophilic support which exhibits a contact angle of less than 75° measured with distilled water.

Metal surfaces may also be used for the preparation of lithographic printing plates, including aluminum, zinc, etc. Particularly useful aluminum printing plates are those in which the aluminum surface has been treated to provide an inert hydrophilic surface. For example, the surface can be anodized by employing acids; such as, sulfuric, oxalic, phosphoric, and the like. In a particularly useful embodiment, the surface is anodized as described in Rauner et al, U.S. Pat. No. 3,511,661, issued May 12, 1970. However, when hydrophilic metal surfaces are employed to receive the silver image, it is preferable to use an aromatic heterocyclic compound without a nitro group instead of the nitro-substituted compound since the nitro-substituted compound tends to oxidize too strongly for silver images on metal plates.

Any suitable support may be used for the hydrophilic surface including polymeric materials; such as, cellulose esters, polyesters; such as, polyethylene terephthalate, polyamides, etc.

Precipitating agents which are particularly useful for use in the hydrophilic layer for formation of the silver image by a black and white diffusion transfer process include nuclei which are useful as precipitating agents with a silver halide complex, including all of those which are commonly useful in the diffusion transfer process. Nuclei which can be employed include silver precipitating agents known in the art such as sulfides, selenides, polysulfides, polyselenides, heavy metals, thiourea, stannous halides, heavy metal salts, fogged silver halide, Carey Lea silver, and complex salts of heavy metals with a compound such as thioacetamide, dithiooxamide and dithiobiuret. As examples of suitable silver precipitating agents, reference may be made to U.S. Pat. Nos. 2,698,237, 2,698,238, and 2,698,245 issued to Edwin H. Land on Dec. 28, 1954, U.S. Pat. No. 2,774,667 issued to Edwin H. Land and Meroe M. Morse on Dec. 18, 1956, U.S. Pat. No. 2,823,122 issued to Edwin H. Land on Feb. 11, 1958, U.S. Pat. No. 3,396,018 issued to Beavers et al Aug. 6, 1968 also U.S. Pat. No. 3,369,901 issued to Fogg et al Feb. 20, 1968 and U.S. Pat. No. 3,532,497 issued to Goffe Oct. 6, 1970. The noble metals, silver, gold, platinum, palladium, etc., in the colloidal form are particularly useful.

Noble metal nuclei are particularly active and useful when formed by reducing a noble metal salt using a borohydride or hypophosphite in the presence of a colloid. The metal nuclei can be prepared in the presence of a proteinaceous colloid such as gelatin and coated on the receiving sheet. The same or a different colloid may be added if desired. It will be appreciated that the coating composition generally contains not only nuclei, but also reaction products which are obtained from reducing the metal salt.

It will also be appreciated that the nuclei or silver precipitating agent may be incorporated in the lithographic layer itself by adding a suitable silver precipitant to the coating composition including the silica, titanium dioxide, polymeric material, etc. By incorporating the silver precipitating agent in the coating composition itself, a lithographic layer and silver precipitating material can be coated in one operation.

Inasmuch as the preferred image obtained by the diffusion transfer process is a silver image at the surface of the receiving sheet, a minimum of binder or dispersing agent is employed to contain the nuclei or silver precipitating agent. However, various colloids can be used as dispersing agents or as binders for the precipitating agents in the receiving layer. Any suitable colloids can be used. Particularly useful colloids are hydrophilic colloids which are used for binders in silver halide emulsions. Advantageously, they are coated in a range of about 5-5,000 mg/ft ² . Included among suitable colloids are gelatin, preferably coated at a level in the range of about 7-100 mg/ft ² , polymeric latices such as copoly(2-chloroethyl-methacrylate-acrylic acid) preferably coated in the range of 15-350 mg/ft ² in a polymeric vehicle containing two components (1) polyvinyl alcohol, and (2) inter-polymer of n-butylacrylate, 3-acryloyloxypropane-1-sulfonic acid, sodium salt and 2-aceto-acetoxyethyl methacrylate, in a preferred range of about 10-300 mg/ft ² .

It will also be appreciated that the precipitating agents can be formed in situ or can be applied by precipitating or evaporating a suitable precipitating agent on the surface.

The hydrophilic layers in the lithographic plate blanks of our invention may also have therein particles, such as silica, bentonite, diatomaceous earth such as kieselguhr, powdered glass, micro crystalline asbestos and fuller's earth. In addition, colloidal particles of metal oxides such as titanium dioxide, colloidal alumina, coarse aluminum oxide, zirconium oxide and the like may be used with the nuclei in the receiving layers.

In carrying out the diffusion transfer process, conventionally a silver halide emulsion is exposed to a light image after which it is contacted with a silver halide developing agent containing a silver halide complexing agent. The exposed emulsion is developed in the light struck areas and the unexposed silver halide is complexed with the silver halide complexing agent after which the emulsion is contacted against a receiving sheet and the silver halide complex diffuses imagewise to the receiving sheet containing a silver precipitant.

It will be appreciated that in one embodiment of the diffusion transfer process, an integral element is employed in which an unhardened silver halide emulsion is located over the nucleated layer. After the element has been exposed, the silver halide emulsion is developed employing a silver halide solvent to form a silver image in the nucleated layer. The unhardened silver halide emulsion is then removed, typically by using hot water. The silver image is then treated according to my invention to improve the oleophilic nature of the silver image.

The following examples are included for a further understanding of the invention.

Example 1

A sheet of negative material is prepared as follows:

Paper base weighing 135 grams per square meter is first made developer resistant by applying to one side a coating of pigmented polyethylene at the rate of 15 grams per square meter and on the other side a coating of unpigmented polyethylene at the rate of 10 grams per square meter. This coated base is given a hydrophilic surface by subjecting the pigmented coating to a high voltage discharge. The hydrophilic surface is then coated with an orthosensitized high contrast silver chloride emulsion at a rate equivalent to 1.5 grams per square meter of silver nitrate, the gelatin content of the emulsion being 0.5 gram per square meter. The emulsion contains formaldehyde as a hardening agent. This sensitive element is exposed to a light image and passed in contact with a polyethylene coated paper receiver having thereon a hydrophilic lithographic coating over which has been coated a layer of silver precipitating nuclei through a solution composed of:

Hydroquinone 15.00 g 1-phenyl-3-pyrazolidone 1.00 g Sodium Hydroxide 13.00 g Sodium Sulfite (anhyd.) 75.00 g Sodium Thiosulphate pentahydrate 8.00 g Potassium Bromide 0.35 g Carboxymethyl hydroxyethyl cellulose 5.00 g

The sheets are squeegeed together and separated after about 20 seconds. The imaged receiver is then treated with the following fix solution of the invention, which is applied evenly with a cotton wool pad.

______________________________________ (a) 1-(2',4' dinitrophenyl)pyridinium chloride 2.0 g (b) Cetyl Trimethyl Ammonium Bromide 1.0 g Potassium Iodide 2.0 g Citric Acid 30.0 g Isopropanol 60.0 ml Water 155.0 ml ______________________________________

The treated polyethylene based receiver is then placed on a lithographic printing press, and wet with water. The forme rollers are dropped and after allowing 10 revolutions of the press (five on inking, five on imaging) clean charp copies are immediately obtained.

The phrase "five on inking five on imaging" means that the roller bearing the plate is rotated five times in contact with the wetting and inking rollers only and then is rotated a further five times in contact with the offset roller and the wetting and inking rollers and only after these 10 rotations is the paper brought into contact with the printing roller.

Examples 2-7

As Example 1 except 1-(2',4'dinitrophenyl)pyridinium chloride is replaced by one of the following:

(2) 1(2',4',6'trinitrophenyl) picolinium chloride 2 g (3) 1(2',4',6'trinitrophenyl) pyridinium chloride 2 g (4) 1(2'nitro-4'-carboxy phenyl) pyridinium chloride 2 g (5) 8-nitroquinolinium methiodide 2 g (6) 8-nitroquinoline 2 g (7) p-nitrobenzyl trimethyl ammonium chloride 2 g

Examples 8-13

As Example 1 except that 1-(2',4'dinitrophenyl) pyridinium chloride is replaced by one of the following:

(8) 1-ethyl-4-cyanoquinolinium iodide 2 g (9) 1-ethyl-4-ethoxycarbonyl quinolinium iodide 2 g (10) 2-methyl-isoquinolinium iodide 2 g (11) cetyl pyridinium bromide 2 g (12) 1-ethyl-quinolinium iodide 2 g (13) 1-ethyl-2-methyl-quinolinium iodide 2 g

Examples 14-18

As Example 1 except cetyl trimethyl ammonium bromide is replaced by one of the following:

(14) Cetyl dimethyl ammonium chloride (15) Dodecyl trimethyl ammonium chloride (16) Lauryl dimethyl amine oxide (17) Trimethylsulfonium iodide (18) Hexadecyl trimethyl ammonium bromide

Example 19

As Example 1 except the negative after exposure is passed through the developer in contact with a paperbased receiver having an image-receciving layer composed of propylene gylcol alginate and gelatin and having the silver precepitating agent distributed on the surface of the layer. Also the imaged receiver is left exposed to the air for half an hour before fixing.

In the above Examples 2-6, clean, sharp copies are obtained using each of compounds (2), (3), (4), (5and (6) in turn as component (a). Using compound (7) the copy obtained is not as clean and sharp. Clean, sharp copies are also obtained using each of compounds 8 to 13 in turn as component (a). Very good, clean and sharp copies are obtained using each of compounds 14 -18 in turn in place of component (b).

A good clean, sharp copy is obtained also in Example 19.

Photographic silver halide emulsions, preparations, addenda, processing and systems which may be used in connection with preparing the image treated according to this invention are disclosed in Product Licensing Index, Volume 92, December, 1971, Publication 9232, pages 107-110, paragraphs, I-XII, IV-XVIII, and XXIII.

The invention has been described with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.