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

摘要

PURPOSE: To improve contact rusting resistance and electrodeposition coating property of an organic composite coated steel sheet. CONSTITUTION: A chromate coating film with 5-200mg/m<2> coating weight is formed on a galvanized steel sheet and, in the upper layer of the chromate coating film, 1-110 pts.wt. (solid portion) hydrophilic polyamide resin (B) 50-1000 in degree of polymerization and 5-80 pts.wt. (solid portion) polyfunctional polyisocyanate (C) having at least three isocyanate groups in a molecule per 100 pts.wt. (solid portion) urethane modified epoxy ester resin (A) having the number average molecular weight of 300-100000 are contained. Further, a resin coating film 0.2-3.0μm in dry film thickness is formed thereon by applying an organic solvent based coating material composition further containing a rust preventive agent (D) in the ratio ((A)+(B)+((C))/(D) of 90/10 to 40/60 by the weight of solid portion.