GB421217A - Method of preparing aluminium and zinc lithographic plates for planographic and off-set printing - Google Patents

Abstract

421,217. Printing surfaces. WOLF, O., 20, Halbgasse, Vienna. Oct. 11, 1933, No. 28025. [A Specification was laid open to inspection under Sect. 91 of the Acts, April 14, 1934.] [Class 100 (ii)] [See also Groups XX and XXXVI] Lithographic plates which are also suitable for offset printing are prepared by producing upon smooth ungrained plates of aluminium, zinc, and their alloys, before the application of a printing impression, a lithographic stone-like coating of the compounds of the metal of the plates by anodic electrolytic treatment. The voltage employed is a low direct current or alternating current voltage of less than 40 volts, and the electrolyte consists in the case of zinc and its alloys of a saturated solution of an alkali carbonate, with a current density of 2 to 3 amp/dm<2> for 10 to 30 minutes, and in the case of aluminium and its alloys of a <1>/3 to 5 per cent solution of a dilute acid such as nitric acid which does not dissolve the metal or its oxide, with a current density of 1 to 2 amp/dm<2> for 10 to 30 minutes. Examples given are : (a) for aluminium, ¢ per cent nitric acid, 1 to 2 amp /dm<2> with 7 to 10 volts A.C. for 15 to 20 minutes ; (b) for zinc, a saturated (37 per cent) solution of potassium carbonate solution, 2 to 3 amp/dm<2> with 10 to 12 volts D.C. for 10 to 12 minutes. After the formation of the coating, the surface is washed with dilute acetic or nitric acid, if zinc is used, or with water if aluminium is employed. The design is produced subsequently to the coating by transfer, drawing, e.g. in chalk or pencil, by a photomechanical process, or in any other way, and etching agents in the wetting fluid during the subsequent printing are unnecessary. Specifications 6701/00, 21322 /04, [both in Class 100], 223,994, 290,901, [both in Class 41], and 401,579 are referred to.