GB969090A - Improvements in or relating to the production of electrotypes - Google Patents

Abstract

In the production of a copper shell for an electrotype, an electrically conductive film is first deposited on an electrotype mould, on this film a coating of copper is formed by displacement from a copper-containing solution by the introduction of a dispersion of a metal which is electrochemically more active than copper, and a further coating of copper is electrodeposited over it, preferably at a current density of at least 50 amps./sq. ft. Typically a forme of letterpress and graphic matter is coated with a plastic material such as wax, a phenol formaldehyde resin or a thermoplastic such as polyvinyl chloride which is preheated and cold pressed to form a mould from the forme. This mould is then coated with a thin conductive film of silver by spraying it simultaneously with solutions of silver nitrate and hydrazine sulphate from a twin orifice gun, spray washing the silver coating immediately with water, and without delay applying a copper coating, e.g. of 0.2 mils thickness, by displacement deposition by spraying simultaneously from a twin orifice gun with a copper sulphate-sulphuric acid solution containing ammonia and a zinc powder dispersion in distilled water. The copper-coated mould is then immersed as cathode in an acid copper sulphate electroplating bath using a copper anode and employing a current density of 120 amps./sq. foot of mould surface to give a copper thickness of 15 mils. The copper-plated mould is then removed from the bath and the plastic mould is stripped from the silver filmed front surface of the metal shell which is coated on its rear face with tin to assist adhesion of molten lead applied to form a rigid backing. As an alternative a plastic backing may be applied to the shell.