method of formation of protective coatings on articles coloured aluminium or aluminium alloy

摘要

A process for the production of colored coatings on articles of aluminum or aluminum alloys, which are particularly adapted to be employed for architectural uses, involves first forming a hard, dense anodic coating on aluminum or aluminum base alloys by anodizing the aluminum in an electrolyte comprising sulfuric acid, a polyhydric alcohol of 3 to 6 carbon atoms and an organic carboxylic acid containing at least one reactive group in the alpha position in order to obtain a material having a film thickness of 5 to 28 microns and thereafter electrolytically coloring said anodized aluminum by passing alternating current between said anodized aluminum and a counter-electrode in an aqueous bath containing acid and a metal salt. The voltage may be modulated externally of the electrode system so as to apply voltage with controlled asymmetry to the electrodes.