Patent GB-1433121-A (GB)
Title: Method of making a lithographic printing plate
IPC: G03F7/06
Filed: 1973-02-26
Abstract: 1433121 Photographic processes for producing lithographic plates FUJI PHOTO FILM CO Ltd 26 Feb 1973 [25 Feb 1972] 9436/73 Headings G2C and G2M Lithographic plates are produced by (i) forming on a support having an oleophilic resin surface a hydrophilic layer containing a hydrophilic resin, a resin which becomes hydrophilic on treatment with an alkaline developer or an oleophilic resin which becomes hydrophilic on brushing, the resin not being gelatin or nitrocellulose, the layer being formed by applying the resin dissolved or dispersed in an organic median which swells, softens or dissolves the resin surface, (ii) applying (a) a hydrophilic image-receiving layer for diffusion transfer or (b) a silver halide emulsion layer or both (a) and (b) in either order, (iii) forming a silver image (1) when (a) but not (b) is present by diffusion transfer, (2) when (b) but not (a) is present by imagewise exposure and development, (3) when (a) and (b) are present and (a) is uppermost, by diffusion transfer development of (a) and exposure of (b) through (a) followed by removal of (a) and development of (b) or (4) when (a) and (b) are present and (b) is uppermost, by imagewise exposure and development of (b) and diffusion transfer development of (a) followed by removal of (b) and (iv) etch-bleaching the silver image to remove or render removable the image and underlying hydrophilic layer and, if necessary, rubbing the image to remove it and the under-lying hydrophilic layer. In the examples, a support of cellulose triacetate or polyethylene terephthalate which has been treated with chromic/sulphuric/ phosphoric acid solution is coated on one side with an anti-halation layer and on the other side with an organic solution of maleic anhydride/ vinyl acetate or vinyl methyl ether copolymer, diethyl acrylamide/methacrylic acid copolymer, a polyvinyl acetal, hydroxyethyl cellulose, acrylamide/acrylic acid copolymer or vinyl pyrrolidose/ vinyl alcohol copolymer admixed with chromium sulphate or acetate, o-chlorophenol, resorcinol, benzylalcohol or acetic, monochloracetic or salicyclic acid to produce a hydrophilic intermediate layer firmly bonded to the support. This intermediate layer is coated with (a) optionally an acrylic acid/methyl methacrylate copolymer and then with a silver halide emulsion, (b) optionally a sodium alginate stripping layer and then a direct positive silver halide emulsion (c) an imagereceiving layer of nickel sulphide and gelatin or (d) an image-receiving layer, optionally a hydroxyethyl cellulose stripping layer and then a silver halide emulsion layer and all materials are coated with a protective gelatin layer. All materials are imagewise exposed (except (c) where a separate silver halide emulsion is used) and developed to produce a silver image, the silver halide emulsion layer removed for material (d), the silver image etch bleached with hydrogen peroxide/cupric chloride solution which weakens the hydrophilic and stripping layer (when present) underneath the silver image and then washing or rubbing to remove the weakened areas to produce a lithographic plate. In materials (a) and (b), preferably lith emulsions and lith developers are used and hydroquinone may be present in the emulsion. Oleophilic polymer coated metal supports or resin coated paper supports may also be used. The specified etch-bleach bath is cupric chloride, citric acid and hydrogen peroxide in water.