US3582328A

US3582328A - Planographic printing plate from mercuric ion on silver diffusion transferred image

Info

Publication number: US3582328A
Application number: US697028A
Authority: US
Inventors: Louis Maria De Haes; Johannes Josephus Vanheertum; Hugo Karel Gevers
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1967-01-11
Filing date: 1968-01-11
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01
Also published as: DE1622331A1; NL6800431A; GB1213311A; BE709193A

Abstract

A PLANOGRAPHIC PRINTING PLATE IS PREPARED FROM SHEET MATERIAL CARRYING AN OUTER HYDROPHILIC COLLOID LAYER THEREON BY CREATING A PATTERN OF FINELY DIVIDED SILVER PARTICLES DISPOSED ESSENTIALLY AT THE SURFACE OF THE COLLOID LAYER AND TREATING THE COLLOID LAYER WITH AN AQUEOUS COMPOSITION CONTAINING MERCURY(II) IONS IN A SUFFICIENT CONCENTRATION OF ABOUT 5-50 GMS. PER LITER TO RENDER THE PATTERN OF SILVER PARTICLES RECEPTIVE TO A HYDROPHOBIC INK. IF NOT ALREADY HARDENED, THE COLLOID LAYER SHOULD BE HARDENED PRIOR TO PRINTING IN ANY CONVENTIONAL WAY IN ORDER TO PRECLUDE TRANSFER OF COLLOID MATERIAL FROM THE LAYER DURING PRINTING. THE PATTERN OF FINELY DIVIDED SILVER PARTICLES AT THE SURFACE OF THE LAYER IS PREFERABLY PRODUCED BY MEANS OF THE KNOWN SILVER COMPLEX DIFFUSION TRANSFER PROCESS, AND THE COLLOID LAYER CAN CONTAIN ONE OR MORE SUBSTANCES OFTEN REFERRED TO AS DEVELOPEMENT NUCLEI FOR PROMOTING THE DEPOSITION ON THE SURFACE THEREOF OF METALLIC SILVER PARTICLES FROM THE DIFFUSING COMPLEXED SILVER HALIDE, OR SUCH SUBSTANCES CAN BE SUPPLIED TO THE LAYER IN OTHER WAYS, SUCH VIA THE DEVELOPMENT BATH.

Description

United States Patent 3,582,328 PLANOGRAPHIC PRINTING PLATE FROM MERCURIC ION 0N SILVER DIFFUSION TRANSFERRED IMAGE Louis Maria De Haes, Edegem, Johannes Josephus Vanheertum, Zandhoven, and Hugo Karel Gevers, Edegem, Belgium, assignors to Gevaert-Agfa N.V., Mortsel, Belgium No Drawing. Filed Jan. 11, 1968, Ser. No. 697,028 Claims priority, application Great Britain, Jan. 11, 1967, 1,488/ 67 Int. Cl. G03c 5/54 US. CI. 96-29 9 Claims ABSTRACT OF THE DISCLOSURE A planographic printing plate is prepared from sheet material carrying an outer hydrophilic colloid layer thereon by creating a pattern of finely divided silver particles disposed essentially at the surface of the colloid layer and treating the colloid layer with an aqueous composition containing mercury(II) ions in a sufficient concentration of about 5-50 gms. per liter to render the pattern of silver particles receptive to a hydrophobic ink. If not already hardened, the colloid layer should be hardened prior to printing in any conventional way in order to preclude transfer of colloid material from the layer during printing. The pattern of finely divided silver particles at the surface of the layer is preferably produced by means of the known silver complex diffusion transfer process, and the colloid layer can contain one or more substances often referred to as development nuclei for promoting the deposition on the surface thereof of metallic silver particles from the diffusing complexed silver halide, or such substances can be supplied to the layer in other ways, such as via the development bath.

This invention relates to a method for the preparation of planographic printing plates by converting silver images into hydrophobic ink-receptive images.

The method for the preparation of a planographic printing plate according to the present invention comprises treating a sheet material, having an outer hydrophilic colloid layer carrying at its surface a pattern of finely divided silver particles, with an aqueous composition containing mercury(II) ions in a proportion whereby the character of the pattern of silver particles on the surface of the said outer hydrophilic colloid is modified so as to become receptive to a hydrophobic ink, the said outer hydrophilic colloid layer being hardened before, during or after the said treatment, and at least to such an extent that no substantial amount of colloid is transferred on printing.

This method is very simple and comprises only one real processing step. Any additional treatment usual in the preparation of planographic printing plates such as the strengthening of the printing parts, is not necessary and may be omitted.

The pattern of finely divided silver particles may be produced in different ways.

The silver particles may be deposited onto the outer colloid layer in an electrolytical way or by an electrochemical interaction.

According to a preferred embodiment the pattern of silver particles is produced in a photographic way.

A silver pattern obtained by image-Wise exposure and development of a common light-sensitive silver halide emulsion layer, however, is generally less suited in that the silver particles are located over the full depth of the light-sensitive layer and are not present to a sufficient degree at the surface thereof. Photographic images ob- 3,582,328 Patented June 1, 1971 tained in such a way, however, can generally be made more suitable for carrying out the method of the invention by intensifying the photographic silver image at the surface by means of an addition silver deposition i.e. by submitting the said silver image to an intensification generally known in the art.

A method according to which very suitable silver patterns can be obtained at the surface of an outer hydrophilic colloid layer is the generally known silver complex diffusion transfer process in all its possible embodiments, since according to this process the silyer deposition mainly occurs at the outer surface of the layer containing the substance and/ or substances for promoting the silver deposition from the diffusing complexed silver halide i.e. the so-called development nuclei.

According to a first embodiment there can be proceeded according to the common silver complex diffusion transfer process wherein a separate light-sensitive material and image-receiving material are used, the so-called development nuclei being present in the outer colloid layer of the image-receiving material whereby the deposition of the diffusion transfer silver occurs mainly at the surface of the said outer colloid layer.

In carrying out the diffusion transfer process, a waterpermeable hydrophilic colloid layer can be provided on top of the silver halide emulsion layer of the light-sensitive material as described in the British patent specifica tions 869,190; 998,955 and 998,956, or a special type of image-receiving material can be used as is known from the British patent specifications 1,013,344 and 1,054,252. It is also possible to incorporate at least part of the compounds that are essential or useful for carrying out the diffusion transfer image formation such as developing agents, preservatives for these developing agents, complexing agents, stabilizers, alkaline substances, black-toning agents, hardeners and softening agents in the materials used whereby the aqueous processing liquid can be reduced to an aqueous solution of alkaline substances and even to pure Water, the latter possibility being described in the British patent specification 1,013,343. For silver complex diffusion transfer processes in which the developing agents and preservatives for these developing agents are incorporated into the light-sensitive and/or imagereceiving material there can be referred to the British patent specifications 1,093,177; 1,000,115; 1,012,476; 1,042,477; 1,054,253 and 1,057,273. For embodiments according to which hardening agents and more particularly latent hardening agents are incorporated into the lightsensitive and/or image-receiving material there can be referred to British patent specification 962,483 and German patent specification 1,203,604. Suitable 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, mercaptanes and tin (1H) halides. Heavy metals or their salts and fogged silver halides are suitable too. The complexed salts of lead and zinc sulphides are active alone as well as mixed with thioacetamide, dithiobiuret and dithiooxamide. Heavy metals, preferably silver, gold, platina, palladium, and mercury may be used in their colloidal form. From these metals the noble metals are the most active ones. The support of the photographic material comprising the silver halide emulsion layer may be any usual flexible support sheet eg, a paper sheet, but preferably is a transparent hydrophobic usual film support, such as a support of cellulose triacetate or of a polyester e.g. polyethylene terephthalate, advantageously provided with an antihalation layer on its front side or on its backside or incorporating an antihalation dye or pigment in the transparent film support or in the silver halide emulsion layer. Preferably a red or black antihalation dye or pigment is applied. The silver halide emulsion layer preferably has a sensitivity of the order as normally required for camera exposure. The silver halide emulsion layer generally comprises an amount of silver halide equivalent to from about .5 g. to about 1.5 g. of silver nitrate and preferably amounting only to the equivalent of about 1 g. 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 apply to any embodiment for the production of a silver pattern substantially at the surface of a hydrophilic colloid layer according to the silver complex diffusion transfer process, also the embodiments described hereinafter.

According to a second diffusion transfer embodiment the development nuclei can be supplied to the lightsensitive material by the processing liquid for carrying out the diffusion transfer process. In this case it is sufficient to dispose of a light-sensitive material only, which is provided either or not with a colloid layer on top of the silver halide emulsion layer. The development nuclei will deposit from the processing liquid onto the surface of the light-sensitive material at the development stage and as a result the diffusion transfer silver deposition will also occur at this outer surface of the light-sensitive material. It is the latter diflusion transfer silver image that will be converted into the ink-receptive printing areas of a planographic printing plate and not the silver image resulting from the primary development of the image-wise exposed silver halide.

According to the embodiment wherein the development nuclei are supplied by the processing liquid and preferably according to said embodiment wherein also a colloid layer is provided on top of the silver halide emulsion layer it is also possible to transfer a diffusion transfer silver containing stratum to a suitable support and to use the resulting material as starting material for the preparation of a planographic printing plate according to the method of the invention. In connection with this method for the preparation of diffusion transfer images, more particularly the embodiment, wherein a colloid layer is provided on top of the silver halide emulsion layer, there can be referred to British patent specifications 1,001,558 and 1,052,022.

As a variant of the said second diffusion transfer embodiment the development nuclei for the diffusion transfer image formation, instead of being supplied by the processing liquid, can also be supplied to the image-receiving material by a pre-treatment with a liquid composition containing such nuclei.

According to a further diffusion transfer embodiment the development nuclei may be provided in a colloid layer on top of the silver halide emulsion layer at the preparation stage; in this way a multilayer material is obtained. Such a multilayer material is known among others from British patent specifications 746,186 and 758,627. After the diffusion transfer image formation, the said colloid top layer containing the diffusion transfer silver image is transferred to another sheet thus providing a colloid layer having on its free surface the pattern of finely divided silver particles as required for the preparation of a planegraphic printing plate according to the method of the invention. This transfer to another sheet may be avoided by substantially or completely concentrating the development nuclei at the free surface of the outer colloid layer of the multilayer material, whereby the diffusion transfer silver deposition substantially takes place at this outer free surface. In this connection there may be referred to British patent application 26,580/ 67.

The development nuclei, instead of being present in the said colloid layer on top of the silver halide emulsion layer, may also be provided between the light-sensitive emulsion layer and the said colloid layer. After the diffusion transfer image formation the said colloid layer is transferred to another sheet material and carries the diffusion transfer silver image on its free surface. In this way a material is provided which is suitable for the preparation of a planographic printing plate according to the method of the present invention.

It is also possible to use a multilayer material comprising a light-sensitive silver halide emulsion layer on top of an image-receiving layer containing development nuclei. Such a multilayer material is described i.a. in British patent specifications 654,631; 868,241; 868,243; 1,006,292 and 1,027,742. After the diffusion transfer image formation the light-sensitive emulsion layer may be removed by detaching in an aqueous rinsing bath as a coherent membrane or in flakes by dissolving or by stripping off either or not by means of an auxiliary sheet, whereupon the colloid image-receiving layer with the silver pattern formed on its surface becomes visible.

In order to obtain at the surface of the outer hydrophilic colloid layer a diffusion transfer silver deposition as high as possible the development nuclei are very often substantially or completely concentrated at the imagereceiving side of that layer. This can be very advantageously effected by adding the development nuclei to the processing liquid for carrying out the diffusion transfer image formation or to a separate liquid for wetting the image-receiving material just before the latter is brought in contact with the image-wise exposed lightsensitive material in the presence of the alkaline processing liquid for carrying through the silver complex diffusion transfer process. In order to keep the development nuclei in dispersion a minor amount of a hydrophilic protective colloid is often added to the dispersion. This amount of colloid does not suflice to form a layer and in most cases is hardened at the hardening stage of the hydrophilic colloid layer or by diffusion of hardener from said layer.

The above is a non-limitative list of methods for the preparation of a suitable sheet material for preparing a planographic printing plate according to the method of the present invention. The sheet materials used are generally of rather simple composition and comprise a suitable support such as a usual hydrophobic flexible film support or a paper sheet provided either directly 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. Often a silver halide emulsion layer is present between the colloid outer layer and the support and also antihalation dyes or pigments are provided. Various methods for producing this silver pattern have been described above. Photographic methods, especially the silver complex diffusion transfer process, if necessary combined with a chemical or physico-chemical after-treatment for intensifying the silver pattern at the surface of the outer colloid layer in or on which it has been produced, are particularly suitable.

For the preparation of the hydrophilic colloid outer layer any hardenable hydrophilic colloid is suitable. Although gelatin is favoured in this respect, other hardenable hydrophilic colloids such as polyvinylalcohol, 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.

Hardening of the hydrophilic colloid binder of the outer layer may occur before, during or after the treatment with the aqueous composition containing mercury(II) ions and must occur at least to such an extent that no substantial amount of colloid is transferred on printing neither to the rollers for applying water and ink to the printing plate nor 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. This explanation in our opinion will suflice for one skilled in the art.

When the silver pattern is produced in a photographic way, preferably according to the silver complex diffusion transfer process, the said hardening mostly occurs before the treatment with mercury(II) ions. In that case the said hardening may occur by addition of generally known hardening agents for gelatin and similar colloids such as formaldehyde, glyoxal, muccochloric 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 already referred to above, a coating composition comprising development nuclei, either or not together with a minor amount of a hydrophilic colloid to keep the development nuclei in dispersion 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. When the latter is formed according to a photographic method said hardening may occur by incorporating hardeners in at least one of the processing liquids and/or by incorporating latent hardeners, as already referred to above, into the photographic material to be hardened. 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 liquid composition. This liquid composition may be an aqueous treating composition applied before the treatment with mercury(II) ions, the aqueous treating composition containing mercury(II) ions itself or an aqueous treating composition applied after the treatment with mercury (II) ions.

The presence of certain hydrophilic colloid binders, e.g. carboxymethylcellulose, gum arabic, sodium alginate, propylene glycol ester of alginic acid, hydroxyethyl 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 properties of the non-printing areas of the printing plate finally obtained. Also hygroscopic substances likewise called hydrophilic softening agents, e.g., sorbitol, glycerol, trihydroxyethyl, ether of glycerol, turkish red oil and certain wetting agents, incorporated in at least one hydrophilic colloid layer of the sheet material carrying the silver image at its surface will improve the hydrophilic properties of the non-printing areas.

The hydrophilic colloid outer layer may advantageously comprise a considerable amount of pigment particles that will 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 5-20 g. thereof are present per sq. m. of the hydrophilic colloid outer layer. A similar anti-scumming effect may also be obtained by adding colloidal silica to the fountain solution used during the printing process.

For the production of the planographic printing plate the sheet material comprising an outer hydrophilic colloid layer having at its surface a pattern of finely divided silver particles is treated with an aqueous composition containing an operative amount of mercury(II) ions. At the moment this treatment starts the said outer colloid layer may be in dry as well as in wet condition. Said treatment can occur in different Ways, e.g. by spraying with, rubbing with or dipping into the aqueous composition containing mercury(II) ions. Generally, this treatment does not last long, on the average not longer than about 30 seconds and can be accelerated by raising the temperature of the aqueous composition and/or by increasing the concentration of the mercury(II) ions in the aqueous composition. The course of the reaction can be followed well since during the treatment the colour of the silver image changes from more or less black to light yellowgreyish white which means that the reaction has come to an end. At this moment the treatment with mercury(II) ions can be stopped and the silver image has become sufficiently hydrophobic i.e. ink-receptive to be suitable for printing.

The reaction mechanism according to which the pattern of finely divided silver particles, at the surface of the hydrophilic colloid outer layer, is converted into a hydrophobic i.e. ink-receptive pattern by the treatment with the aqueous composition containing mercury(II) ions cannot be explained with certainty. It is assumed that the silver particles are oxidized and form water-insoluble silver salts whereas the mercury (II) ions are reduced to mercury(I) ions, which probably form water-insoluble mercury(I) salts, and even to metallic mercury. It is possible that the silver salts formed by this redox-reaction are at least partly converted again into photolytic silver having a yellow colour and it is also possible that an amalgamation occurs between metallic mercury particles and the silver particles originally present or photolytically formed afterwards.

The aqueous composition containing mercury(II) ions is generally an aqueous solution of at least one more or less water-soluble mercury(II) salt or other mercury(II) compound that releases mercury(II) ions in an aqueous medium such as some mercury(II) complexes. The mercury(II) salt and/ or the other mercury(II) compounds is (are) incorporated into the aqueous treating composition in such concentration that an operative amount of mercury(II) ions is present. This means, an amount of mercury(II) ions that makes the aqueous composition suitable for the purpose intended i.e. for converting the silver pattern into a hydrophobic pattern. In general favourable results can be obtained with a concentration of mercury(II) ions comprised between about 5 and about g. per litre of aqueous composition. Particularly suitable water-soluble mercury(II) salts are: mercury(II) chloride, mercury(II) thiocyanate, mercury( II) nitrate, mercury(II) acetate, mercury(II) bromide and mercury- (II) lactate.

A-fter the treatment with the aqueous composition containing mercury(II) ions the planographic printing plate is theoretically ready for printing and can be braced on the offset machine. A further improvement of the hydrophobic i.e. ink-receptive character of the printing parts and/ or a mechanical strengthening of these parts by means of a hydrophobic lacquer is not necessary and may be omitted.

What is advantageous in most cases is to improve the hydrophilic character of the non-printing areas of the plate. This can be done by incorporating usual compounds such as carboxymethyl cellulose and arabic gum, colloidal silica and/or some wetting agents such as sodium lauryl sulphate into the aqueous composition containing mercury(II) ions in concentrations ranging preferably from about 5 to about 200 g. per litre. The compounds for improving the hydrophilic and thus ink-repelling properties of the non-printing areas of the planographic printing plate can also be provided by a separate after-treatrnent with an aqueous composition containing these compounds or just be added to the fountain solution used during the printing process.

Finally, in the method of the present invention it is desirable to neutralize the excess of mercury(II) ions in order to prevent that they affect anything the planographic printing plate comes into contact with, e.g. to prevent corrosion of the offset printing machine.

This neutralization can occur in a physical way e.g. by covering the planographic printing plate with a protective membrane. For this purpose an emulsifiable oil such as Turkish Red Oil can be added to the aqueous composition containing mercury(II) ions or said oil can be applied in a previous or subsequent treatment of the printing plate.

The neutralization of the excess of mercury(II) ions can also occur chemically e.g. by means of compounds forming with mercury(II) ions a mercury compound the ion product of which is very low. Examples of such compounds are: chelating compounds such as polyaminopolycarboxylic acids ethylene-diamine tetraacetic acid trisodium salt, N (2 hydroxyethyl)-N,N,N'-ethylenediamine triacetie acid and similar compounds disclosed in British patent specification 952,162 and polyamines such as triethylene tetraamine and 2,2,2"-triarnino-triethylamine; compounds comprising a mercapto group such as l-phenyl 5 mercapto-tetrazole, 5-methyl-3- mercapto 1,2,4 triazole, Z-mercapto-benzthiazole, 2- mercapto-benzimidazole, thiosalicylic acid and aliphatic mercaptans.

The chemical neutralization can also be effected by means of compounds having a labile sulphur atom forming mercury(II) sulphide with mercury(II) ions, e.g. thioacetamide, thiosulphates and thiourea. These compounds for chemically neutralizing the excess of mercury (II) ions may be applied to the planographic printing plate from a solution in a suitable solvent, after the treatment of said plate with the composition containing mercury(II) ions.

The following examples illustrate the method of the invention.

EXAMPLE 1 To a paper support of 135 g. per sq. m. a common high sensitive, negative gelatino silver chlorobromide emulsion layer, hardened by means of formaldehyde, is applied in such a way that an amount of silver halide equivalent to 1 g. of silver nitrate is present per sq. In. After drying of the gelatino silver halide emulsion layer, said layer is overcoated pro rata of g. sq. m. with the following composition:

Water 890 12.5% aqueous saponin 10 Aqueous colloidal nickel sulphide dispersion comprising per 100 cc. 0.2 g. of nickel sulphide and 10 g. of gelatin 100 The material obtained is exposed to an original and treated for sec. in the following processing composition:

G. Sodium hydroxide 10 Sodium sulphite (anhydrous) 75 Potassium bromide 1 Hydroquinone 16 1-phenyl-3-pyrazolidinone 1 Sodium thiosulphate (anhydrous) 10 Water up to 1000 cc.

The material is then rubbed in with a plug of wadding saturated with the following solution, until the dark positive diffusion transfer silver image produced at the surface of the material has disappeared:

Water 125 Aqueous mercury(II) acetate solution comprising per 100 cc. 5 g. of mercury(II) acetate 100 The material thus obtained is a positive planographic printing plate with very good printing characteristics.

EXAMPLE 2 To a paper support of 250 g. per sq. m. a common high sensitive negative gelatino silver chlorobromide emulsion layer, hardened by means of formaldehyde and comprising hydroquinone and 1 phenyl 3 pyrazolidinone, is applied in such a way that per sq. m. are present: an amount of silver halide equivalent to 1 g. of silver nitrate, 0.5 g. of hydroquinone and 0.25 g. of l-phenyl- 3-pyrazolidinone.

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

WaterlOOO cc.

Sodium phosphate-l2-water75 g.

Sodium sulphite (anhydrous)40 g.

Potassium bromide-05 g.

Sodium thiosulphate (anhydrous)10 g.

Aqueous colloidal nickel sulphide dispersion of Example 1-2O cc.

In this way, a positive diffusion transfer silver image is produced at the surface of the silver halide emulsion layer.

A positive planographic printing plate is then obtained by simply rubbing the material, until complete disappearance of the dark diffusion transfer silver image, with a plug of wadding saturated with the following solution:

Water 125 Aqueous mercury(II) thiocyanate solution comprising per cc. 5 g. of mercury(II) salt 100 EXAMPLE 3 Then the following liquid is applied pro rata of 22 g. per sq. m.:

Cc. Water 890 12.5% aqueous saponin 10 Aqueous colloidal nickel sulphide dispersion of Example 1100 The light-sensitive material obtained is image-wise exposed and then guided through an automatic two-bath processing device the baths of which have the following compositions respectively:

Water-1000 cc. Sodium phosphate-12-water-75 g. Sodium sulphite (anhydrous)--40 g. Potassium bromide-05 g. Sodium thiosulphate (anhydrous)10 g.

Water-- cc. Aqueous mercury (II) chloride solution comprising per 100 cc. 5 g. of mercury (II) salt-100 cc. 35% aqueous silicone emulsion marketed under the trade name Rhodorsil Emulsion E by Usines Chimiques Rhone-Poulenc Paris, Franee25 cc.

The material obtained after this treatment is ready for use as planographic printing plate with positive image values in respect of the original.

EXAMPLE 4 On a subbed cellulose triacetate film support having a thickness of 100 a layer is coated pro rata of 20 sq. m. per litre from the following composition:

Water-918 cc.

Gelatin40 g.

Aqueous colloidal nickel sulphide dispersion of Example 20% aqueous formaldehyde-2 cc.

After drying, this first layer is overcoated pro rata of 30 sq. m. per litre with the following composition:

Water-988 cc.

Hydroxyethyl starch having a substitution degree of 0.27

hydroxyethyl groups10 g.

Glyoxal1.6 cc.

The layer is dried whereupon a common gelatino silver chloride emulsion layer, hardened by means of formaldehyde, is applied in such a Way that an amount of silver halide equivalent to 1 g. of silver nitrate is present per The multilayer material thus obtained is image-wise exposed and then treated for 30 sec. in the processing composition of Example 1.

The emulsion layer is stripped off as a coherent membrane whereupon the underlying image-receiving layer carrying at its surface the diffusion transfer silver image is rubbed with a plug of wadding impregnated with the following solution to produce the planographic printing plate:

Water 125 Aqueous mercury (II) iodide solution comprising per 100 cc. 5 g. of mercury (II) iodide 100 The excess of mercury (II) ions is neutralized by rubbing the printing plate with a plug of wadding impregnated with a aqueous solution of sodium thiosulphate.

EXAMPLE 5 To a paper support of 135 g. per sq. m. a common highsensitive gelatino silver chlorobromide emulsion layer, hardened by means of formaldehyde, is applied in such a way that an amount of silver halide equivalent to 1 g. of silver nitrate is present per sq. m.

The light-sensitive material obtained is image-wise exposed and then developed in a processing composition as described in Example 1.

Thereupon the material is physically developed for 60 sec. by dipping into a bath consisting of a mixture of 5 parts of solution B below and 1 part of solution A below.

SOLUTION A Water-40 cc. p-Phenylene-diamine-2 g.

Water-60 cc. Sodium sulphite2 g.

SOLUTION B Water-350 cc. Sodium sulphite90 g.

Water50 cc. Silver nitrate3.75 g.

10 After this physical intensification of the silver image, the material is treated with the following solution to produce a planographic printing plate ready for printing:

Water 125 Aqueous mercury (II) chloride solution comprising per 100 cc. 5 g. of mercury (II) chloride 100 EXAMPLE 6 A light-sensitive material is prepared as follows:

A gelatino silver chloride emulsion (gelatin/ silver nitrate =l69) containing hydroquinone and l-phenyl-3-phenyl-3-pyrazolidinone and hardened in the usual way with formaldehyde is applied at 45 C. to a paper support of g. per sq. m. in such a way that an amount of silver chloride equivalent to 0.7 g. of silver nitrate, an amount of 0.16 g. of hydroquinone and an amount of 0.08 g. of 1-phenyl-3-pyrazolidinone are present per sq. m.

Onto this silver chloride emulsion layer a top layer is coated at 35 C. in a proportion of 1 litre per 31.7 sq. m. from the following composition:

Water5l0 cc.

Hydroxyethyl starch having a substitution degree of 0.27 of hydroxyethyl groups-40 g.

Ethanoll00 cc.

1-phenyl-3-pyrazolidinonel0 g.

20% aqueous formaldehydel0 cc.

12.5% aqueous saponin10 cc.

An image-receiving material is prepared by coating a paper support of 135 g. per sq. in. pro mm of g. per sq. m. with the following composition:

Water-800 cc.

Gelatin-28 g.

Propylene glycol ester of alginic acid-14 g.

56% aqueous dispersion of barium sulphatel00 g. 20% aqueous formaldehyde56 cc.

and then applying the following composition pro rata of 22 g. per sq. m.:

Cc. Water 890 Aqueous nickel sulphide dispersion of Example 1 100 12.5% aqueous saponin 10 The light-sensitive material is image-Wise exposed and then guided together with the image-receiving material through a conventional silver complex diffusion transfer apparatus comprising the following processing liquid:

Water1000 cc.

Sodium phosphate-12-water75 g. Sodium sulphite (anhydrous)40 g. Potassium bromide0.5 g.

Sodium thiosulphate (anhydrous)10 g.

After a contact time of the image-receiving material with the light-sensitive material of 30 sec. both materials are separated.

The image-receiving material showing the diffusion transfer silver image at its surface is then treated with the following composition to produce a planographic printing plate ready for printing:

Cc. Aqueous mercury(II) chloride solution comprising per 100 cc. 5 g. of mercury(I-I) chloride 40 5% aqueous solution of Adjupon LL (trade name of Adjubel N.V., Lembeek (Halle), Belgium for a white powder consisting of 35-40% of active sodium lauryl sulphate) 50 Turkish Red Oil 10 What we claim is:

1. Method for the preparation of a planographic printing plate, which method comprises treating a sheet material carrying an outer hydrophilic colloid layer having a pattern of finely divided silver particles disposed essentially at the surface of said layer, with an aqueous composition containing mercuryfll) ions in a concentration of about 5-50 gms. per liter, whereby the pattern of silver particles at the surface of the said outer hydrophilic colloid is rendered receptive to a hydrophobic ink, the said outer hydrophilic colloid layer being sufiiciently hardened prior to printing therewith that no substantial amount of colloid is transferred from said layer during such printing.

2. Method according to claim 1, characterized in that the outer hydrophilic colloid layer is a gelatin layer.

3. Method according to claim 1, characterized in that the pattern of finely divided silver particles is produced photographically at the layer surface using the silver complex diffusion transfer process wherein complexed silver halide diffuses from a separate exposed light-sensitive material onto the outer colloid layer of said sheet material in contact therewith, said outer colloid layer containing a substance for promoting deposition of metallic silver particles from the diffusing complexed silver halide.

4. Method according to claim 1, characterized in that the pattern of finely divided silver particles is produced photographically using the silver complex diffusion transfer process wherein said sheet material carries both said colloid layer and a silver halide emulsion layer for supplying complexed silver halide for diffusion during said transfer process, said colloid layer being supplied with a substance for promoting deposition of metallic silver particles from said diffusing complexed silver halide.

5. Method according to claim 3, characterized in that at least one of the light-sensitive material and the imagereceiving material contains at least part of the substances an aqueous solution of at least one mercury(II) salt.

8. Method according to claim 1, characterized in that any excess of mercury(II) ions on the planographic printing plate is neutralized.

9. Method according to claim 1, characterized in that the outer hydrophilic colloid layer contains a. considerable amount of pigment particles homogeneously dispersed therein.

References Cited FOREIGN PATENTS 1/1936 Great Britain 9629L OTHER REFERENCES Clerc: Photography Theory and Practice (2nd edition) Pitman & Sons, Ltd., New York (1937), pp. 307-308.

Hornsby: Basic Photographic Chemistry (1st edition), Rayelle Publications, Philadelphia, Pa. (1956), p. 79.

NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner U.S. Cl. X.R.