US3904412A

US3904412A - Method for the preparation of planographic printing plates from silver images

Info

Publication number: US3904412A
Application number: US402883A
Authority: US
Inventors: Frans Philomena Serrien; Bernard Hippoliet Tavernier; Robert Joseph Pollet; Francis Jeanne Sels
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1972-10-04
Filing date: 1973-10-03
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09
Also published as: DE2349527A1; GB1435900A; BE805519A

Abstract

A method for the preparation of a planographic printing plate wherein a sheet material comprising an outer hardenable hydrophilic colloid layer on the surface of which is concentrated a silver image which has been formed at that surface from complexed silver halide by silver complex diffusion transfer process, is treated with an aqueous lithographic fixer having a pH-value in the range from about 4.5 to about 7.2 and containing : 1. AN IRON(III) ammonium salt of an aliphatic dicarboxylic acid which at least superficially oxidizes said silver image 2. A PRECIPITATING AGENT FOR SILVER IONS, AND 3. AN ORGANIC NITROGEN-CONTAINING COMPOUND, WHICH REACTS WITH SAID OXIDIZED SILVER AT THE SURFACE OF THE SILVER IMAGE TO RENDER SAID IMAGE HYDROPHOBIC AND CONTAINS A STRUCTURAL PART CORRESPONDING TO THE FOLLOWING TAUTOMERIC STRUCTURE :

D R A W I N G

Description

United States Patent 11 1 Serrien et al.

[451 Sept. 9, 1975 METHOD FOR THE PREPARATION OF PLANOGRAPHIC PRINTING PLATES FROM SILVER IMAGES [73] Assignee: Agfa-Gevaert N.V., Mortsel,

Belgium [22] Filed: Oct. 3, 1973 [21] Appl. No.: 402,883

[30] Foreign Application Priority Data Oct. 4. l972 United Kingdom 45792/72 [52] U.S. Cl 96/29 L; 96/33; 101/466 [51] Int. Cl.'-.. G03C 5/54; G03F 7/02; B41M 5/00; B4lN 3/00 [58] Field of Search 96/29 L, 33, 60 B, 60 F; l0l/466 [56] References Cited UNITED STATES PATENTS 3 0s3 097 3/1963 Lassig ct al. 96/29 1. 3,490,906 ]/]970 Blake 96/29 L 3,615,507 l0/l97l Bard 96/60 BF 3,676.125 7/[972 dcHaas.. 96/29 L 3 700 450 10/1972 Cooley 96/60 BF 3,721,559 3/l973 DeI-Iaas et al. 96/29 L Primary Examiner-Norman G. Torchin Assistant Examiner-Richard L. Schilling Attorney, Agent, or FirmWilliam J. Daniel ABSTRACT A method for the preparation of a planographic printing plate wherein a sheet material comprising an outer hardenable hydrophilic colloid layer on the surface of which is concentrated a silver image which has been formed at that surface from complexed silver halide by silver complex diffusion transfer process, is treated with an aqueous lithographic fixer having a pH-value in the range from about 4.5 to about 7.2 and containing 1. an 1ron(IlI) ammonium salt of an aliphatic dicarboxylic acid which at least superficially oxidizes said silver image 2. a precipitating agent for silver ions, and

3. an organic nitrogen-containing compound, which reacts with said oxidized silver at the surface of the silver image to render said image hydrophobic and contains a structural part corresponding to the following tautomeric structure Hsi N 10 Claims, No Drawings METHOD FOR THE PREPARATION OF PLANOGRAPI-IIC PRINTING PLATES FROM SILVER IMAGES The present invention relates to a method for the preparation of planographic printing plates by converting silver images into hydrophobic ink-receptive images and to liquid compositions for improving the ink receptivity of the silver images.

It is known to produce planographic printing plates of improved quality by the use of a sheet material comprising an outer hydrophilic colloid layer, on the surface of which there is concentrated a silver image that has been formed on this surface from complexed silver halide by a silver complex diffusion transfer process.

According to the method for the preparation of planographic printing plates described in the United Kingdom Patent Specification 1,241,661 the thus prepared silver image is rendered hydrophobic with an aqueous liquid. called lithographic fixer, which liquid has a pH-value between 7 and 12 and contains (1 hexacyanoferrateflll) ions. by means of which said silver image is at least superficially oxidized, and (2) an organic compound that is at least in part dissolved in said liquid and which reacts with said oxidized silver to ren der said image hydrophobic.

Although the lithographic fixer described in the above-mentioned Patent Specification has particularly favourable hydrophobizing properties some disadvantages are associated therewith. For example the cyanoferrateflll) ion under the defined condition of a relatively high pH is not inert with respect to the mercaptocompounds, which are the preferred compounds for the purpose cited under the above item (2). Indeed, as a consequence of the presence of the mercapto compound some of the hexacyanoferrate( III) ions become reduced and the thus formed cyanoferratefll) ions form a blue precipitate with the excess cyanoferrate(lIl) ions. Further, also during the preparation of the printing plate by the oxidation of the silver image hexacyanoferrateUl) ions are formed, causing the formation of a blue precipitate and as a result thereof a more or less pronounced staining of the image background.

A further disadvantage associated with the use of a lithographic fixer containing hexacyanoferrate(lll) ions resides in the fact that these ions have to be kept carefully out of contact of acids, for acids set free the highly toxic hydrogen cyanide.

With reference to the relatively high pH (1 ll2) of the lithographic fixer special precautionary measures have to be taken for the operating personnel and only highly alkali-resistant machine parts can be used.

It is an object of the present invention to provide a lithographic fixer of improved stability and presenting a good ink-receptivity to silver images.

It has been found that said object can be attained by means of an aqueous lithographic fixer having a pH- value in the range of about 4.5 to about 7.2 and containing:

1. an iron(lll) ammonium salt of an aliphatic dicarhoxylie acid as oxidizing agent for the silver image,

2. a precipitating agent for silver ions and 3. an organic nitrogen-containing compound having a thiol group or in its tautomeric structure a thione group as represented in the following tautomerie structural parts:

capable of reacting with silver ions present at the surface of a silver image and hydrophobizing the silver image.

In order to avoid that during the oxidation of the silver image with the organic iron(III) ammonium salt, silver ions are accepted by the fixer solution and removed from the silver image portions so that they are lost for the hydrophobizing process, a compound is present in the fixer solution that keeps the silver ions formed at the place where they have been formed. For this purpose use is made of a substance that precipitates silver ions in the form of a poorly water-soluble silver salt.

A preferred precipitating agent is therefor a substance yielding iodide ions e.g. potassium iodide, forming the very poorly soluble silver iodide.

A preferred lithographic fixer combination of the present invention contains in admixture with the above-cited compounds (1) to (3) an aliphatic amino compound comprising at least 4 unbranched carbon atoms, preference being given to n-octylamine. The pH of the fixer is kept within the above-cited range and preferably at 6 to 6.2 by means of the dicarboxylic acid used for preparing the iron(IlI) ammonium salt thus preventing the precipitation of Fe(OH) A suitable amount of aliphatic amino compound is in the range of 10 to ml per litre.

A preferred iron(IlI) salt for use according to the present invention is iron(III) ammonium malonate. A preferred lithographic fixer contains from 20 to g of iron(IlI) ions present in the form of iron(lll)ammonium malonate.

Other suitable iron(lIl) ammonium salts are derived from the aliphatic dicarboxylic acids: oxalic acid, maleic acid and fumaric acid.

Preferred thione compounds correspond to the following structural formulae:

l. Compound 1 is prepared as described in DTOS 1,946.263

nos

2. Compound 2 is prepared as described in BE-P 523,1 15

COOH

3. Compound 3 is prepared as described in BE-P 719,338

and comprise a sulphonic acid salt group for improving the water-solubility of the tiol or thione compound.

The thione compound No. 4 which is the most preferred one can be prepared according to the following reaction scheme:

Preparation of compound 4 98 g of Z-hydrazino-6-sulfobenzothiazole are dissolved in 1.5 l of pyridine and 450 ml of water. 24 ml of carbon disulphide are added thereto and the resulting solution is refluxed for 12 h. Subsequently, it is cooled to room temperature. The reaction mixture is poured out in 2 litres of water and acidified with concentrated hydrochloric acid. The precipitate formed is sucked off and added to 250 ml of water and 125 ml of N sodium hydroxide, so that the precipitate is dissolved again. The resulting solution is concentrated by evaporation. The residue is added again to 1 litre of water and the solution obtained is acidified again with concentrated hydrochloric acid. The precipitate is sucked off. washed until neutral, and dried in vacuo at 110C. Yield: 57 g.

Other suitable thione-thiol compounds for use ac cording to the present invention belong to the class of imidazoline-Z-thiones and imidazolidine2-thiones and are e.g.

Preparation of compound 5 105 g of carbon disulphide are added dropwise to a solution of 69.3 g of N-allylethylenediamine in 1200 ml of ethanol at a temperature of 50C. A white precipitate forms. Subsequently, the mixture is refluxed for 20 h. During the reaction hydrogen sulphide is formed and a complete solution is obtained. The solution is concentrated by evaporation to a volume of 400 ml and then cooled down. The precipitate is sucked off and dried. Melting point: C. Yield: 46 g.

Preparation of compound 6 20.6 g of a-amino-isobutyric acid are suspended in ml of ethanol. 12 g of potassium hydroxide in 12 ml of water are added thereto, whereupon 20 g of allylisothiocyanate dissolved in 100 ml of ethanol are added also. The reaction mixture is refluxed for 2 hours and then concentrated by evaporation. The residue is boiled up with 900 ml of 2N hydrochloric acid, filtered while hot, and cooled. The crystals are sucked off and recrystallized from a mixture of methanol and water over animal chorcoal. Melting point: 77C. Yield: 13 g.

Preparation of compound 7 g of 85% purity potassium hydroxide, 66 g of carbon disulphide, 770 ml of ethanol, and l 15 ml of water are added to 149 g of N-methyl-o-phenylenediaminedihydrochloride. The reaction mixture is stirred and refluxed for 3 hours while hydrogen sulphide escapes. Subsequently, the mixture is cooled down. The precipitate formed in the reaction mixture is dissolved again by the addition of 750 ml of water. The solution is boiled with animal charcoal, filtered and admixed at 70C with 64 ml of acetic acid and 120 ml of water. The reaction mixture is cooled down and the resulting precipitate is sucked off and recrystallized from ethanol. Melting point: C. Yield: 45 g.

Preparation of compound 8 91 g of thiosemicarbazide and 158 g of caprylic acid methyl ester are added to 23 g of sodium in 1 l of anhydrous methanol. The reaction mixture is refluxed for 16 h and concentrated by evaporation. The residue is dis- Solved in 200 ml of water by heating and cooled afterwards. The solid product is sucked off and the filtrate is acidified with 70 ml of acetic acid. During the cool ing crystallization occurs. The crystals are sucked off, recrystallized from 40% ethanol and washed with dichloroethane. Melting point: 190C. Yield: 92 g.

Preparation of compound 9 is described in FR-P Application 2,001,068.

Compound 10 is prepared as described in J.Gen.Chem.

Preparation of compound 1 1 50 ml of 40% t'ormol are added dropwise to a mixture of 25.3 g of thiourea and 43 g of octylamine in 200 ml of water with stirring and cooling. 150 ml of ethanol are added as well and the stirring is continued for 16 h. Subsequently, the reaction mixture is concentrated completely by evaporation, so that a white amorphous product is formed, which is recrystallized from ethanol and benzene respectively. Melting point: 159C. Yield: 30 g.

Compound 12 is prepared as described in Can. l.Chem. 32, 59 (1954).

Preparation of compound 13 45.6 g of carbon disulphide are added dropwise to a solution of 50 g of N-propylethylenediamine in 275 ml of methylglycol at a temperature of 40C. A white pre- 5 cipitate forms. Subsequently, the mixture is heated for 1 hour at 90C, so that hydrogen sulphide is formed. The methylglycol is then evaporated partially in vacuo and 500 ml of water are added to the residue. After 10 having been cooled the precipitate is sucked off and recrystallized from a mixture of benzene and hexane. Melting point: 90C. Yield: 54 g.

15 14. Hooc Preparation of compound 14 see DOS 1,931 ,056.

These compounds and the compounds 1 to 3 are pre pared according to techniques known to those skilled in the art.

A relatively high amount of thione or thiol com- 5 pounds can be incorporated in the aqueous fixer when it contains water-miscible solvents e.g. n-propanol or ethylene glycol monoacetate.

A suitable amount of organic thiol or thione com pound is in the range of 0.5 to 15 g per litre.

so I A preferred lithographic fixer according to the present invention is composed as follows:

ir0n(|l|) salt 20 g to 120 g ss 5 N potassium iodide 5 40 g organic solvenNs) npropanol 0 ml 200 ml ethylene glycol monoacetate 0 ml 150 ml water to make 1 1 pH adjusted to 6-6.2 by means of malonic acid and ammonium hydroxide.

The iron(lll) salt is present in the form of iron(lll) ammonium malonate.

Optimum results were obtained by using a fixer solution prepared by the following procedure: into 780 ml of an iron(lll)ammonium malonate solution containing 10.4% by weight of iron(lll)ions 39 ml of n-octylamine were dissolved whilst stirring. Subsequently after adding 1 ml of n-propanol and ml of ethylene glycol monoacetate, 39 ml of a 10% by weight solution of the thione compound N0. 4 in highly concentrated aqueous ammonium hydroxide were added. The pH was adjusted to 5.0 by means of additional aqueous ammonium hydroxide whereupon 23 g of potassium iodide were dissolved in the obtained composition. Additional aqueous ammonium hydroxide was added so as to reach a total liquid volume of 1 litre and a pH of 6.1. The iron(lll)ammonium malonate solution was prepared by dissolving 570 ml of iron(lll)chloride in water in an amount sufficient to obtain a volume of 3 1. To the obtained solution 480 ml of ammonium hydroxide were added. The obtained precipitate was stirred for 2 h at room temperature and separated by suction whereafter it was freed from chloride ions by washing with water. Then the precipitate was redispersed in 3 l of water whereupon 750 ml of malonic acid dissolved in 1500 ml of water were added. Stirring was continued for l h. The precipitate dissolved gradually in about 24 h.

The green solution obtained was filtered and further diluted with water up to a final volume of 7 l. The con centration of iron(lll) ions was 104 g per litre.

The preparation of a planographic printing plate by using a fixer according to the present invention may be effected with a sheet material comprising a silver image obtained by any of the silver complex diffusion transfer processes hereinafter described by way of example.

A first type of silver complex diffusion transfer process utilizes a light-sensitive material and a separate image-receiving material constituting the said sheet material and containing on an outer surface thereof substance(s) for promoting the deposition of silver in the said silver complex diffusion transfer process.

In an embodiment of such a process the lightsensitive material comprises a water-permeable hydrophilic colloid layer on top of the said silver halide emulsion layer. Such a feature is described in the United Kingdom Patent Specifications 869,190 998,955 and 998,956. Alternatively a special type of imagereceiving material can be used as described in United Kingdom Patent Specifications 1,013,344 and 1,054,252. In such materials there may be incorporated in the image-receiving material and/or light-sensitive materials substances that are essential or useful for carrying out the diffusion transfer image formation, e.g. developing agents, preservatives for these developing agents, complexing agents, stabilizers, alkaline substances, black-toning agents, hardeners and softening agents, so that the aqueous processing liquid need only be an aqueous solution of alkaline substances, or merely water, the latter technique being described in United Kingdom Patent Specification 1,013,343. The incorporation of developing agents and preservatives thereof into the light-sensitive and/or image-receiving material for diffusion transfer processes is described in United Kingdom Patent Specifications 1,093,177 1,000,115 1,012,476 l.()42,477 1,054,253 and 1,057,273. Embodiments in which hardening agents and more particularly latent hardening agents are incorporated into the light-sensitive and/or image'- receiving material for such processes are described in United Kingdom Patent specification 962,483 and German Patent Specification 1,203,604.

A second type of silver complex diffusion transfer process utilizes a single material. Such a single material comprises a silver halide emulsion layer and may comprise a hardenable hydrophilic colloid layer, either beneath or above such silver halide layer. Substances for bringing about the appearance of the diffusion transfer image (development nuclei) from the diffusing complexed silver halide may be present at an outer surface of the material or at an interface of the said layer(s). In the latter arrangement the silver image obtained by diffusion transfer is obtained on top of hardenable hydrophilic colloid layer and preferably is hydrophobized thereon.

According to a special embodiment the colloid layer with the silver image obtained by diffusion transfer is transferred to another sheet material, which may then be converted to a planographic printing plate for instance as described in the United Kingdom Patent Specification l ,001 ,55 8.

The development nuclei may be supplied in a liquid medium to the hardenable hydrophilic colloid layer on top of the light-sensitive silver halide emulsion layer. The development nuclei depositing at the outer surface of the said layer make that the diffusion transfer silver deposition thus occurs at this outer surface. The silver image areas are converted into ink-receptive printing areas to form a planographic printing plate with the lithographic fixer of the present invention.

If desired, the development nuclei may be applied to the surface of the light-sensitive recording material in the alkaline processing liquid for carrying out the diffusion transfer image formation or from a separate liquid composition containing such nuclei which constitutes a step after the exposure of the light-sensitive material and before wetting with the alkaline processing liquid for forming the diffusion transfer image.

Substances for promoting the silver deposition from the diffusing complexed silver halide are sulphides of heavy metals such as the sulphides of antimony, bismuth, cadmium, cobalt, lead, nickel, silver and zinc. Other suitable salts are the selenides, polysulphides, polyselenides, mercaptans and tin(ll) halides. Heavy metals or their salts and fogged silver halides are suitable too. The complexed salts of lead and zinc sulphides are active both alone and when mixed with thioacetamide, dithiobiuret, and dithiooxamide. Heavy metals, preferably silver, gold, platinum, palladium, and mercury may be used in their colloidal form. The support of the photographic material comprising the silver halide emulsion layer may be any conventional flexible support sheet e.g. a paper sheet or a transparent hydrophobic film support, such as a support of cellulose triacetate or of a polyester e.g. polyethylene terephthalate.

The image sharpness of the silver pattern and, as a consequence thereof, the sharpness of the final result of printing can be improved by applying antihalation dyes or pigments. These dyes or pigments may be present in the silver halide emulsion layer or in the support, but preferably are incorporated into a layer situated between the silver halide emulsion layer and the support. If a transparent support is used, the antihalation dyes or pigments, may be applied to the rear side of the material or on top of the emulsion layer dependent on the manner in which the exposure is carried out, viz. at the front side or through the support. Preferably a red or black antihalation dye or pigment is used. Any silver halide emulsion of the negative or direct-positive type may be used depending on the nature of the original to be reproduced. Preferably emulsions of the negative type are used, having a somewhat high sensitivity suitable for use in a camera. As a matter of fact, although the exposure of the silver halide emulsion layer may be carried out according to any usual technique e.g. by contact, by back reflection, by transmission or episcopically. Usually an episcopic exposure in a camera is carried out, particularly when the development nuclei are provided on top of the silver halide emulsion layer as detailedly described hereinafter. The silver halide emulsion layer generally comprises an amount of silver halide equivalent to from 0.5 g.sq. metre to 1.5 g sq. metre of silver nitrate and preferably amounting only to the equivalent of about 1 g sq. metre of silver nitrate. This means a considerable economy of silver halide with respect to the silver halide content of emulsion layers commonly used in the production of diffusion transfer copies. If necessary a suitable subbing layer is provided for strongly adhering the hydrophilic colloid layer(s) to the support sheet. The data in this paragraph also apply to any embodiment for the production of silver pattern substantially at the surface of a hydrophilic colloid layer according to the silver complex diffusion transfer process described hereinafter.

The sheet materials suited for use with the fixer solution of the invention are generally of simple composition. and may comprise a suitable support such as transparent hydrophobic film support or a paper sheet, either in direct contact or indirectly, e.g., by means of a suitable subbing layer, with a hydrophilic colloid outer layer having at its surface a pattern of finely divided silver particles. A silver halide emulsion layer may be present between the colloid outer layer and the support and also antihalation dyes or pigments are provided. The silver pattern obtained by the complex diffusion transfer process may be intensified by chemical or physio-chemical after-treatment for intensifying the silver pattern in or at the surface of the outer colloid layer.

According to a preferred embodiment, a photographic material is used which comprises successively a support layer (preferably a paper support), an antihalation layer, a silver halide emulsion layer and develop ment nuclei on top thereof.

In order to obtain a diffusion transfer silver deposition that will be sufficiently dense, the said photographic material has to be kept for a period of time, e.g. for about l seconds, in the dark after it has been wetted with the alkaline processing liquid for carrying out the diffusion transfer image formation. The application of the lithographic fixer composition may take place during the period the multi-layer material is kept in the dark. However. this application of lithographic fixer may also occur thereafter.

For the production of the diffusion transfer silver image a photographic material comprising development nuclei on top of the silver halide emulsion layer may be provided in roll-form. After image-wise exposure, e.g. an episcopic exposure in a camera or an exposure through a transparent original in contact with the photographic material, the latter may be guided automatically through a usual processing unit containing the alkaline processing liquid and comprising guiding and driving means as generally known in the art.

For the preparation of the hydrophilic colloid outer layer any hardenable hydrophilic colloid is suitable. Although gelatin is favoured, other hardenable hydrophilic colloids such as polyvinyl, alcohol, casein, carboxymethylcellulose and sodium alginate can be used too, the nature of the hardener used being dependent on the type of hydrophilic colloid to be hardened. lf gelatin is used for forming the hydrophilic colloid outer layer, it may be submitted to a treatment as described in the United Kingdom Patent Specification 883,843 in order to improve the printing characteristics of the planographic printing plate.

Hardening of the hydrophilic colloid layer may occur before, during or after the treatment with the lithographic fixer composition and must occur at least to such an extent that no substantial amount of colloid is transferred on printing either to the rollers for applying water and ink to the printing plate or to the material to be printed. In other words hardening (i.e. insolubilizing in water and strengthening against mechanical damage) must occur at least to such an extent that the material obtained can be used as planographic printing plate.

The said hardening mostly occurs before the treatment with lithographic fixer. In that case the said hardening may be effected by addition of the generally known hardening agents for gelatin and similar col loids, such as formaldehyde, glyoxal, mucochloric acid and chrome alum, to the coating composition of the outer layer, at the surface of which the silver pattern will be produced, and/or to the coating composition of another layer, with which the said outer layer is in water-permeable relationship whereby hardening of the said outer layer takes place by diffusion of hardener from said other layer to said outer layer. When, as hereinbefore described a coating composition comprising development nuclei, possibly together with a minor amount of a hydrophilic colloid to keep the development nuclei in dispersion but insufficient to form a continuous binder layer with the nuclei enclosed is applied on top of the said outer layer, the hardeners can also be incorporated into said coating composition. Hardening of the hydrophilic colloid binder of the outer layer may also occur during the production of the silver pattern. The said hardening may be effected by incorporating a latent hardeners in one or more layers of the sheet material, whereby a hardener is released at the stage of the application of an alkaline processing liquid for carrying out the complex silver diffusion transfer process. These latent hardeners are active only in a well defined pH-range, mostly the pH-range of the usual developing liquids. Finally, hardening of the outer hydrophilic colloid layer can also occur after the production of the silver pattern namely by treatment with a hard ening liquid. This liquid may be an aqueous hardening composition applied before the treatment with the lithographic fixer, the fixer composition itself, or an aqueous hardening composition applied after the treatment with the said fixer. At least one compound for improving the hydrophilic properties of the non-printing areas may be applied during the preparation of the printing plate.

Thus the presence of certain hydrophilic colloid binders e.g. carboxymethylcellulose, gum arabic, sodium alginate, propyleneglycol ester of alginic acid, hy-

droxyethyl starch, dextrine, hydroxyethylcellulose, polyvinylpyrrolidone, polystyrene sulphonic acid and polyvinyl alcohol in the outer hydrophilic colloid layer carrying at its surface the pattern of silver particles often improves the hydrophilic, ink-repellent proper ties of the non-printing areas of the printing plate finally obtained. Also hygroscopic substances e.g. sorbitol, glycerol, tri(hydroxyethyl)ether of glycerol and turkey red oil, and certain wetting agents, may be present.

The hydrophilic colloid layer also may advantageously comprise a pigment particles homogeneously dispersed therein to prevent the so-called scumming (i.e. ink-acceptance that arises in the non-printing areas of the printing plate after a certain number of copies has been printed). The usual inorganic pigments e.g. barium sulphate, titanium dioxide, china clay and silica applied from a colloidal solution, have proved to be particularly suitable for this purpose. The pigment particles are generally homogeneously applied in such an amount that about 520 g sq.cm of the hydrophilic colloid outer layer are present. A similar antiscumming effect may also be obtained by adding at least one member selected from colloidal silica, an inorganic acid eg o-phosphoric acid, a hygroscopic substance hereinbefore described and a suitable wetting agent to the fountain solution used during the printing process. Suitable wetting agents include:

sodium dodecylsulphate sodium tetradecylsulphate R-CH SO;,l\la wherein R represents an alkyl group comprising from 14 to 18 carbon atoms The lithographic fixer of the present invention is very stable to airial oxidation and to temperature fluctuations and it is suited for the production of planographic printing plates having non-staining image background parts.

At the moment the treatment with the aqueous lithographic fixer starts the outer colloid layer showing the silver pattern may be in a dry or wet condition. A superficial oxidation of the silver pattern suffices, al-

though complete oxidation is advantageous. Generally the treatment with the lithographic fixer does not last long, mostly not longer than about 20 seconds and can be accelerated by increasing the concentration of the components in the said fixer. The plate may be stored for a long time before being fixed and even thereafter it may be stored for a long time before being used in the printing process. Preferably, however, the lithographic fixing step is carried out just before printing.

The lithographic fixer as well as the development or activating liquid for the production of the diffusion transfer image can be applied in different ways, eg by spraying, by rubbing with a roller, or by dipping the material to be treated in the liquid composition. The lithographic fixing step of the printing plate may proceed automatically by conducting the plate through a device having a narrow channel filled with the fixer composition and conveying the printing plate at the end of the channel between two squeezing rollers removing the excess of liquid.

The production of a silver image on top of the outer hydrophilic colloid layer and the treatment with the fixed may occur in a compact processing unit comprising both the processing stations.

After the application of the lithographic fixer the sheet material is ready for inking and use as a printing plate. Treatment of the material with a lacquer composition for strengthening the printing parts is not necessary. Nevertheless, in some cases the hydropobic character of the ink-receptive parts and their mechanical strength may be improved by applying a lacquer thereon. Suitable lacquer compositions are solutions of oils, waxes and resins in organic solvents. Suitable organic solvents are cyclohexanone, acetone, butanol, monomethyl ether of ethylene glycol, monoethyl ether of diethylene glycol, tetrahydrothiophenel,1-dioxide, diacetone alcohol, dioxane, 1,2-dichloroethane, ethyl acetate, trichloroethylene, butyl butyl-ate. diethanolamine and dimethylformamide. Mixtures of such organic solutions with an aqueous phase or dispersions of such organic solutions in an aqueous phase are also suitable. In that case the aqueous phase may contain thickeners or other compounds for improving the hydrophilic character of the non-printing areas of the lithographic printing plate as described above. Suitable lacquers are described in the United Kingdom Patent Specifications 967,598 968,706 1,004,342 1,071,163 and 1,071,164. Resins that have proved to be especially suitable for improving the ink-receptive character of the printing areas and strengthening them are phenol-formaldehyde resins e.g. phenolformaldehyde resins, a-eresol formaldehyde resins, and p-tert.-butylphenol formaldehyde resins, alkyd resins e.g. rosin maleic acid esters, epoxy resins. condensation productsof a poly( aryl ethylene oxide) with an acid anhydride, an amine or another suitable compound and epoxidized polyesters.

The resin, wax or oil is usually used in a concentration of from about to about 500 g per litre of liquid lacquer composition. The liquid lacquer composition may be applied after the aqueous composition containing the oxidizing agent has been applied and while the printing plate is still wet. When an emulsion lacquer is used the plate needs not necessarily be wet at the stage the lacquer is applied. The lacquer may be applied by dipping. spraying, spreading or by means of a material soaked therewith. The lacquer is rubbed e.g. with a plugof wadding. The hydrophobic solid substances settle on the image areas and improve the hydrophobic ink-receptive character thereof. At the same time the mechanical strength of the printing areas is improved. The adherence of the lacquer to the printing areas may further be improved by heating the plate.

Instead of being applied by means of a separate aftertreatment of the printing plate, the liquid lacquer composition may also be incorporated with the aqueous composition containing the iron(lIl) ammonium salt of an aliphatic dicarboxylic acid and the organic compounds for converting the silver image in a hydrophobicink-receptive pattern. The ratio of the organic phase that contains the hydrophobic solid substances to the aqueous phase is generally between 1:] and 1:10.

The printing plate has to be wet at the stage the greasy printing ink is applied. This is generally known in the art and it is usual to apply an aqueous liquid before applying the printing ink. This may occur by means of a wet sponge or by means of the fountain arrangements (damping system) of the printing machine.

The following examples illustrate the use of the lithographic fixer according to the present invention. All percentages are by weight unless otherwise stated.

EXAMPLE 1 water 890 ml 12.5 aqueous solution of saponin l() ml aqueous dispersion of colloidal nickel sulphidc comprising per H1O ces 0.2 g of nickel sulphide and l() g of gelatin as protective colloid l()() ml The material obtained was exposed to an original and treated for 30 sec. in the following processing composition:

sodium hydroxide l() g anhidrous sodium sulphite 75 g potassium bromide l g h \dr'oquinone 16 g lphenyl-3pyrazolidinone l g water up to 1000 ml anhydrous sodium thiosulphate l() g The material was then rubbed for some 20 seconds with a plug of wadding saturated with the following 8 lithographic fixer composition:

iron( lll )salt 74 g n-octylamine 39 ml n-propanol ll5 ml ethylene gl \col monoacetate 20 ml S Nii( TH NC% 4 g potassium iodide 23 g aqueous solution of ammonium hydroxide to reach a final volume of l litre of Composition having a 'pH of (1.00

The iron(lll) salt is present in the form of iron( 111) ammonium malonate.

The material thus obtained was a positive planographic printing plate with very good printing characteristics and with which more than 1000 copies of high quality could be printed. Applying a lithographic lacquer in order to strengthen the printing parts was not necessary and could be omitted. The fountain solution used on printing could be water or liquid having the following composition:

water ml glycerol 10 ml colloidal silica l ml phosphoric acid 2 ml EXAMPLE 2 To a paper support of weight 250 g per sq.m a highsensitive negative silver ehlorobromide gelatin emulsion layer, hardened by means of formaldehyde and comprising hydroquinone and 1-phenyl-3- pyrazolidinone, was applied so that per sq.m were present: an amount of silver halide equivalent to l g of silver nitrate, 0.5 g of hydroquinone and 0.25 g of l-phenyl-3-pyrazolidinone.

The light-sensitive material obtained was image-wise exposed and then dipped for 10 sec. in the following processing liquid:

water 1000 ml sodium phosphatel2-water 75 g anhydrous sodium sulphite 40 g potassium bromide 0.5 g anhydrous sodium thiosulphatc 10 g aqueous dispersion of colloidal nickel sulphide of example 1 20 ml In this way a positive diffusion transfer silver image was produced at the surface of the silver halide emulsion layer.

The material was then rubbed for some 15 seconds with a plug of wadding saturated with the lithographic fixer described in Example 1, wherein, however, thione compound 4 had been replaced by a same amount of mercapto compound I. The printing plate thus prepared could be used for printing in the same manner as described in Example 1 and about the same good results were obtained.

EXAMPLE 3 To a paper support of weight 135 g per sq.m; a highsensitive silver chlorobromide gelatin emulsion layer comprising hydroquinone and l-phenyl-3- pyrazolidinone was applied so that per sq.m are present, an amount of silver halide equivalent to l g of silver nitrate, l g of hydroquinone and 0.5 g of l-phenyl- Il-pyrazolidinone.

After drying the silver halide gelatin emulsion layer the latter was overcoated in a proportion of g per sq.m with the following composition:

water 926 ml gelatin lo g l2.5 '71 aqueous solution of saponin 8 ml 20 /r aqueous solution of formaldehyde 56 ml A Then the following liquid is applied in a proportion of 22 g per sq.m:

water 890 ml 12.5 aqueous solution of saponin ml aqueous dispersion of colloidal nickel sulphide of Example 1 100 ml The light-sensitive material obtained was exposed image-wise and then guided through an automatic twobath processing device, the baths of which had the following compositions respectively:

I. (Activating liquid) water 1000 ml sodium phosphate-l2-water 75 g anhydrous sodium sulphite 40 g potassium bromide 0.5 g anhydrous sodium thiosulphate 10 g I]. The lithographic fixer described in Example 1, with the modification that thione compound 4 had been replaced by a same amount of the thiol compound listed herein.

The material obtained after this treatment was readly for use as planographic printing plate with positive image values compared to the original. More than 1000 copies could be printed therewith. The fountain solution might be mere water or the specific fountain com position of Example 1.

EXAMPLE 4 To a strong paper support of weight 135 g per sq.m a thin gray antihalation was applied by pouring a dispersion of 3 g of lamp black in 1 litre ofa 4% aqueous solution of gelatin at a rate of 1 litre per 40 sq.m.

To this antihalation layer a high-sensitive silver chlorobromide gelatin emulsion layer comprising hydroquinone and 1-phenyl-3-pyrazolidinone was applied in such a way that per sq.m. were present: an amount of silver halide equivalent to l g of silver nitrate, l g of hydroquinone and 0.5 g of l-phenyl-3-pyrazolidinone.

After drying. the silver halide gelatin emulsion layer was overcoated at a rate of 100 g per sq.m with the following composition:

water 926 ml gelatin 10 g 12.5% aqueous solution of saponin 8 ml )2 aqueous solution of fomialdehyde 56 ml Then the following liquid was applied at a rate of 22 g per sq.m:

water 890 ml 12.5 71 aqueous solution of saponin 10 ml aqueous dispersion of colloidal nickel sulphide comprising per 100 ml of 0.2 g of nickel sulphide and 10 g of gelatin 100 ml The light-sensitive multilayer thus obtained was image-wise exposed to an original.

This exposure might be an episcopic exposure in a camera or an exposure through an intermediate original having a sufficiently transparent background and being pressed with its rcarside against the nuclei side of the multilayer material.

The multilayer material can be used in roller form and after the image-wise exposure be cut off as desired.

After the image-wise exposure the multilayer material was guided through a processing unit containing the following alkaline liquid:

water 1000 ml sodium phosphate-l2-water g anhydrous sodium sulphite 40 g potassium bromide 05 g anhydrous sodium thiosulphatc 10 g Thereafter the multilayer material was kept for some 10 seconds in the dark in order to permit an intense diffusion transfer silver deposition to take place. A sharp bronzed legible diffusion transfer image became visible on a gray background.

The plate was then moistened (e.g. by means of a plug of wadding) for some 20 seconds with the following lithographic fixer composition:

iron(lll) salt 60 g noctylamine 42 g n-propanol 100 ml ethylene glycol monoacetate 100 ml S N NaO S Cl 1TH 6 g NC=S potassium iodide 30 g aqueous ammonium hydroxide solution of to reach a final volume of l litre of composition having a pH of 6.1.

The iron(lll) salt is present in the form of iron(lll) ammonium malonate.

The said fixer composition was very stable to aerial oxidation and to temperature fluctuations. With 1 litre thereof about 100 printing plates (21 cm X 29.7 cm size) could be prepared.

The preparation of the printing plate proceeded automatically in a compact processing unit comprising the successive treating stations and wherein the plate was transported automatically from one unit to the other.

The printing plate thus obtained was ready for use as a planographic printing plate with positive image values based on the original. It was mounted on an offset apparatus and after having been wetted with water or other fountain solution (e.g. a liquid composed of ml of water, 10 ml of glycerol, 2 ml of colloidal silica and 2 ml of phosphoric acid), the fatty printing ink was applied and printing started. More than 1000 copies were printed with the plate thus prepared.

We claim:

1. A method for preparing a planographic printing plate wherein a sheet material comprising an outer hardenable hydrophilic colloid layer on the surface of which is concentrated a silver image which has been formed at that surface from complexed silver halide by silver complex diffusion transfer process is contacted with an aqueous lithographic fixer having a pH-value in the range from about 4.5 to about 6.2 and containing:

1. an iron(lll) ammonium salt of an aliphatic dicarboxylic acid which at least superficially oxidizes said silver imgage,

2. a compound yielding iodide ions for precipitating said silver ions, and

3. an organic heterocyclic nitrogen compound having in a 5- or fi-membered ring a thione group corre sponding to the following tautomeric structure:

for rendering said superficial oxidized silver image hydrophobic.

2. A method according to claim 1, wherein said lithographic fixer contains as said iron( III) salt from 20 to 120 g of iron(lll) ammonium malonate per litre.

3. A method according to claim 1 wherein said heter ocyelic nitrogen compound includes a sulphonic acid group in free acid or salt form.

4. A method according to claim 1, wherein said heterocyclic compound has the following structural for mula:

s N c \NH Qatari 7. An aqueous lithographic fixer according to claim 6 wherein said heterocyclic nitrogen compound includes a sulfonic acid group in free acid or salt form.

8. An aqueous lithographic fixer according to claim 6, wherein the heterocyclic nitrogen compound corresponds to the following structural formula:

9. An aqueous lithographic fixer according to claim 6, wherein said fixer contains a water-miscible solvent that improves the dissolving of the mercapto or thione compound in the fixer.

10. A lithographic fixer according to claim 6 of the following composition:

iron(lll) salt in the form of iron(lll) ammonium malonate 20 g to 120 g S\ /N\ Naons TH 0.5 gto 15 g \/U NC=S n-octylaminc H) g to ml potassium iodide 5 g to 40 g organic solvcnfls) n-propanol (1 ml to 200 ml ethylene glycol monoacctate 0 ml to [50 ml water to make I 1 pH adjusted to 6-6.2 by means of malonic acid and ammonium hydroxide.

Claims

1. AN IRON(III) AMMONIUM SALT OF AN AIPHATIC DICARBOXYLIC ACID WHICH AT LEAST SUPERFICIALLY OXIDIZES SAID SILVER IMGAGE,

1. A METHOD FOR PREPARING A PLANOGRAPHIC PRINTING PLATE WHEREIN A SHEET MATERIAL COMPRISING AN OUTER HARDENABLE HYDROPHILIC COHOID LAYER ON THE SURFACE OF WHICH IS CONCENTRATED A SILVER IMAGE WHICH HAS BEEN FORMED AT THAT SURFACE FROM COMPLEXED SILVER HALIDE BY SILVER COMPLEX DIFFUSION TRANSFER PROCESS IS CONTACTED WITH AN AQUEOUS LITHOGRAPHIC FIXER HAVING A PH-VALUE IN THE RANGE FROM ABOUT 4.5 TO ABOUT 6.2 AND CONTAINING:

2. A COMPOUND YIELDING IODIDE IONS FOR PRECIPITATING SAID SILVER IONS, AND

2. a compound yielding iodide ions for precipitating said silver ions, and

2. A method according to claim 1, wherein said lithographic fixer contains as said iron(III) salt from 20 to 120 g of iron(III) ammonium malonate per litre.

2. a compound yielding iodide ions for precipitating said silver ions, and

3. an organic heterocyclic nitrogen compound having in a 5- or 6-membered ring a thione group corresponding to the following tautomeric structure:

3. AN ORGANIC HETEROCYCILE NITROGEN COMPOUND HAVING IN A 5- RO 6- MEMBERED RING A THIONE GROUP CORRESPONDING TO THE FOLLOWING TAUTOMERIC STRUCTURE:

3. A method according to claim 1 wherein said heterocyclic nitrogen compound includes a sulphonic acid group in free acid or salt form.

4. A method according to claim 1, wherein said heterocyclic compound has the following structural formula:

5. A method according to claim 1, wherein the said lithographic fixer contains from 0.5 to 15 g of said organic thiol or thione compound per litre.

6. An aqueous lithographic fixer having a pH generally in the range of about pH 4.5-6.2 containing:

7. An aqueous lithographic fixer according to claim 6 wherein said heterocyclic nitrogen compound includes a sulfonic acid group in free acid or salt form.

10. A lithographic fixer according to claim 6 of the following composition: