GB837955A - Removing resin from metallic surfaces - Google Patents

Abstract

An organic resinous coating is removed from a metallic surface by treating the surface first with a stripping composition containing a phenol and/or a chlorinated hydrocarbon, and then with a solution of chromic acid. Examples of phenols and chlorinated hydrocarbons are, respectively, phenol, cresol and xylenol; and monochlor-, dichlor-, and trichlor-benzene, trichlortoluene, methylene chloride, ethylene dichloride, methyl chloroform, dichlorethylene, trichlorethylene and p perchlorethylene. The stripping composition may also contain a detergent emulsifier, e.g. an alkali metal (including ammonium), amine or alkanolamine salt of an organic acid, such as potassium oleate, or a non-ionic condensation product of ethylene oxide with aromatic materials and fatty alcohols, and an inhibitor, e.g. sodium phosphate and sodium chromate, and is preferably used as an aqueous solution. The chromic acid solution is preferably of 5-15% w/v strength, and may also contain an inhibitor such as barium and/or silver chromate. Between the treatments with the stripping composition and the chromic acid solution, the surface may be treated in an alkali solution, e.g. one containing an alkali metal silicate such as sodium metasilicate, an alkali metal carbonate, an alkali metal phosphate, an alkali hydroxide, or an aluminate. If necessary, the surface may again be treated in the alkali solution after treatment with the chromic acid solution, and then be treated again in the chromic acid solution. Metallic surfaces composed of aluminium alloys, magnesium alloys, steels and cadmium-plated steels, may be treated. Coatings formed of phenolic resin are referred to.