GB1025842A - Improvements in or relating to planographic printing - Google Patents

Abstract

1,025,842. Printing surfaces; etching. DICK CO. A.B. Nov. 8, 1962 [Nov. 28, 1961], No. 42536/61. Headings B6C and B6J. An imaged paper-base master for use in planographic printing is produced by imaging the surface of an oleophilic paper base, subjecting the imaged surface to the action of a pre-etch solution comprising an aqueous solution of a polyvalent metal salt such as zinc acetate, and then subjecting the imaged surface to the action of an aqueous etch solution containing an anion which reacts with the metal cation in the pre-etch solution to form an insoluble or sparingly soluble precipitate. The paper base used is described as non-lithographic, i.e. its imaged surface is incapable of being used directly in planographic printing when subjected to the action of, for instance, an aqueous phosphoric acid etch solution. The metal salt may be a salt of zinc, nickel, calcium, copper, cobalt, iron, lead, magnesium, cadmium, barium, manganese or aluminium. The salt may be derived from an organic or inorganic acid and suitable acids include acetic acid, hydrochloric acid, nitric acid and sulphuric acid. The pre-etch solution includes a hydrophilic colloid such as methyl cellulose, gum arabic, gelatine or polyvinyl alcohol to ensure good pick resistance and rapid pick-up of image, and a suspension of inert colloidal solids such as silica to improve the running properties of the master and to make it more robust. The pre-etch solution may also contain a surfaceactive agent, such as a condensation product of ethylene oxide with alkyl phenols, to improve wetting of the paper base. The etch solution may be a phosphoric acid solution with sodium dehydrogen phosphate and may contain a humectant, such as glycerol, to prevent drying out too quickly and also a wetting agent. Examples are given of compositions for suitable pre-etch solutions.