GB896563A - Improvements in or relating to the graining of lithographic plates - Google Patents

Abstract

896,563. Etching aluminium strip. ALGRAPHY Ltd. Dec. 6, 1960 [Dec. 10, 1959], No. 42061/59. Class 41. Aluminium or alloys thereof in sheet form are grained or etched by passing two webs of the metal each connected to the two poles of an A.C. source of energy, through an electrolyte, the greater part of each web facing a fixed metal plate acting as electrode mounted in a plane parallel with the web, the two fixed electrodes being connected together electrically, but not to an A.C. source or to the webs except through the electrolyte. No electrolytic action takes place between the webs themselves which may pass through the electrolyte in side-byside position, or may be treated in separate tanks. The etched sheet is suitable for use as lithographic plates. Two webs of aluminium strip 12, 12<1> are spaced apart and pass sideby-side over rollers 16 at the top of a bath 10 and under rollers 17 at the bottom. Fixed metal plate electrodes 13, 13<1> are mounted centrally between the upwardly and downwardly moving webs. Rollers are made of glass or synthetic resin, and the electrode plates 13 are of silver mesh to prevent collection of gas bubbles at the surface. As each plate extends across both faces of the two webs they need not be electrically connected, but may be if desired. The webs are connected, e.g. through feed rollers to the poles of an A.C. source. The electrolyte consists of HCl to which alkali metal or alkaline earth metal chlorides may be added.