GB492900A - Improved process of protecting metal surfaces by electrodeposition - Google Patents

Abstract

492,900. Electrolysis. CROSSE & BLACKWELL, Ltd., SUMNER, C. G., JOHNSON, R. I., and CLAYTON, W. March 30, 1937, Nos. 8966/37 and 7732/38. [Class 41] A conductive surface (e.g. tinplate) is coated with an aluminous compound by anodic treatment in an aqueous medium containing in solution a compound of aluminium such that the ions containing the aluminium are negatively charged, e.g. sodium aluminate. The alkalinity of the solution may be reduced to such a value that the aluminous compound is only just held in solution in the absence of electrolysis, e.g. by addition of sodium bicarbonate, sodium dihydrogen phosphate or sodium bisulphite, or a depolarizer such as a reducing agent may be added. Also, the solution may contain a lacquer in dispersion, or colloidal material such as sodium silicate or gelatine, which is deposited simultaneously with the aluminous compound, or the film may be subsequently covered with lacquer, wax, cellulose, or like coating material by electrodeposition from an aqueous dispersion or by application in liquid form as in organic solvents, or by treatment with a dispersion coagulable by aluminium compounds, such as an emulsion of lacquer in dilute ammonia. In the case in which aluminous compound and lacquer are electrodeposited simultaneously, the colour and brightness of the film may be decreased by such additions as sodium hydroxide or ammonia, alkali-metal tartrate or citrate, or sodium silicate, and the brightness increased by addition of an emulsifying agent such as rosin soap, and both may be controlled by regulating the proportions of lacquer and aluminate and of the acidic constituents of the lacquer. The results obtained with various specified lacquers are described. The film may be stoved and, if desired, dyed in the manner usual for anodicallv-oxidized aluminium. Specifications 455,810, 479,681, and 490,851 are referred to.