PRODUCTION OF COLORED ALUMINUM BUILDING MATERIAL

PURPOSE:To surely color Al stock for building materials clear gray by successively subjecting the stock to anodic oxidation, immersion in an aq. acid soln. and cathodic electrolysis in an aq. soln. of a metal salt. CONSTITUTION:Al (alloy) stock for building materials is anodically oxidized to form an anodic oxide film of >= about 9mum thickness. The stock is then immersed in an aq. soln. of an acid such as sulfuric acid and subjected to cathodic electrolysis in an aq. soln. of a metal salt such as an Ni salt. The Al stock is uniformly colored clear gray and fine appearance can be obtd. even when the Al stock contains Si by such a small amt. as