ORGANIC COATED STEEL SHEET EXCELLENT IN CORROSION RESISTANCE

摘要

PROBLEM TO BE SOLVED: To provide an organic coated steel sheet capable of affording excellent corrosion resistance without being incorporated with a heavy metal such as sexivalent chromium. SOLUTION: The surface of a galvanized steel sheet or aluminized sheet is provided with an organic film with 0.1 to 5μm film thickness composed of a reaction product of a film forming organic resin (A) and an active hydrogen-contg. compd. (B) in which a part or the whole of the compd. is composed of a hydrazine derivative (C) having active hydrogen. By applying the hydrazine derivative to the film forming organic resin, the acting effects that the hydrazine derivative is attracted to or reacted with the surface of the plating film to form a dense passivated layer stably and tightly adhered to the plating surface, that the hydrazine traps zinc ions eluted at the time of the film formation to form an electrically neutral insoluble chelate compd. layer, so that the formation of an ion conducting layer on the boundary between the plating film and the organic resin layer is suppressed to suppress the progression of corrosion or the like, suppresses the progress of corrosion effectively, by which excellent corrosion resistance can be obtd.