STEEL SHEET COATED WITH COMPOSITE ORGANIC FILM AND EXCELLENT IN OUTSIDE RUSTPROOFNESS AND BRIGHTNESS, AND PRODUCTION THEREOF.

摘要

A steel sheet coated with a composite organic film and excellent in rustproofness and brightness when applied to the outside of an outer panel of an automobile. It is produced by coating the surface of a galvanized steel sheet with a chromate layer at a given chromium coverage and forming thereon an organic resin film with a thickness of 0.2 to 2 mu m prepared by adding a given proportion of a rustproofing additive to a block urethane-modified epoxy resin prepared by adding a given proportion of a block urethane comprising a polyol, a polyisocyanate and a blocking agent to a modified epoxy resin comprising an epoxy resin, a polyfunctional amine and, if necessary, a monoisocyanate or phosphoric acid.