ORGANIC COMPOSITED COATED STEEL EXCELLENT IN WATER RESISTING SECONDARY ADHESION AND CORROSION RESISTANCE AFTER WORKING

摘要

PROBLEM TO BE SOLVED: To produce an organic composite coated steel excellent in water resisting secondary adhesion and corrosion resistance after working by applying the surface of a galvanized steel sheet with a silica-added chromate film and silica-dispersed water base coating material film both having specified compsns. by specified coating weights. SOLUTION: The surface of a galvanized or galvannealed steel sheet is applied with a silica-added chromate film by 5 to 500mg/m<2> coating weight expressed in terms of Cr. The content of Cr<6+> in this film is regulated to 25 to 70% to the whole Cr, and the ratio of Si/Cr therein is regulated to 1 to 5 by Auger electron spectroscopy. The upper layedr of this chromate film is applied with a water base coating material film formed by blending water- dispersed silica with a anionic or nonionic water base resin by 0.1 to 3g/m<2> coating weight (dry weight). As the water-dispersed silica, a water base silica sol or water-dispersed water base fumed silica having 0.05 to 2μm average particle size is preferably used, and the ratio thereof is preferably regulated to 10 to 100 pts.wt based on 100 pts.wt. of the organic resin.