Procédé pour la production de clichés d'impression lithographiques perfectionnés

1,069,324. Photo-mechanical printing plates. GEVAERT PHOTO-PRODUCTION N. V. April 27, 1964 [April 26, 1963], No. 17330/64. Heading G2M. Offset printing plates are produced by treating a hydrophilic metal layer bearing a silver image with a solution of an organic compound containing an oleophilic radical ionized in solution and capable of reacting with the metal layer to produce a hydrophobic water-insoluble compound and then removing the silver image. The silver image is generally produced by the silver salt diffusion transfer process but it may be produced by selectively etching a silver layer on a hydrophilic metal layer, the silver areas which are not to be etched being shielded during etching. Aluminium and zinc are specified as the hydrophilic metals. The organic compound may be an anionic or amphoteric wetting agent or a fatty acid or a salt thereof. In the examples, a silver image, produced by the diffusion transfer process, on an aluminium or zinc foil is treated with an aqueous solution of sodium myristate, stearate or 10-sulpho-oleate, ethyl lauryl orthophosphate, laurylbenzene sodium sulphonate or a mixture of N-stearyl-and N-arachidoyl-methylaminoacetic acid and the silver image is then removed with a solution of ferricyanide, permanganate, dichromate, peroxydisulphate, iodide with iodine or ferric salt of E.D.T.A. The first solution may contain a thickening agent or be non aqueous e.g. stearic acid in glycerine/ethanol.