ORGANIC COMPOSITE COATED STEEL SHEET EXCELLENT IN CONTACT RUSTING RESISTANCE AND CATIONIC ELECTRODEPOSITION COATING PROPERTY

摘要

PURPOSE: To improve contact rusting resistance and cationic electrodeposition coating property by specifying the composition, coating weight and film thickness of a coating film in a steel sheet made by forming a chromate coating film on the surface of a galvanized steel sheet and then a resin coating film composed of a urethane modified epoxy resin, containing a rust preventive pigment, and a polyfunctional polyisocyanate. ;CONSTITUTION: The urethane modified epoxy resin A having the epoxy equivalent of 1000-5000 is obtained by allowing a bisphenol and an isocyanate compound to react with a mixture of an epichlorohydrin-bisphenol A type epoxy resin and a polyalkylene glycol diglycidyl ether in the weight ratio of 100/300 to 100/10. A polyfunctional polyisocyanate compound B (containing ≥3 isocyanate groups) in an amount of 5-80 pts.wt. (hereafter the same) and the rust preventive additive C in the weight ratio (A+B)/C of 90/10 to 40/60 are added to 100 base body resin A, to which an alkanol amine is added, and the resultant resin composition is applied on the galvanized steel sheet, on which the chromate coating film has been formed in 5-200mg/m² coating weight expressed in terms of metal chromium, to form the coating film of 0.2-3.0μm dry film thickness.;COPYRIGHT: (C)1996,JPO