The organic composite coated steel sheet

PURPOSE:To impart high corrosion resistance capable of withstanding corrosive rust to the org. composite coated steel sheet while maintaining its electrodeposition coatability, weldability and press formability by specifying the compsn. and thickness of the org. resin coating layer of the steel sheet. CONSTITUTION:The upper layer of the org. composite coated steel sheet constituted by providing the surface of a galvanized steel sheet with a chromate film layer of the lower layer and an org. resin film layer of the upper layer is formed of the coating material compsn. having components A to D in an org. solvent and the thickness thereof is specified to 0.1 to 5mum. The component A is 100 pts.wt. epoxy resin having 500 to 10000 number average mol.wt., the component B is 10 to 60 pts.wt. polyvalent arom. amine compd. contg. 2 to 30wt.% phenolic and/or cresol reaction accelerator, the component C is 10 to 60 pts.wt. polyvalent isocyanate compd. and the component D is 10 to 40PHR colloidal silica and/or fumed silica. The PHR means the pts.wt. per 100 pts.wt. total of the epoxy resin + the polyvalent amine compd. contg. the reaction accelerator + the polyvalent isocyanate compd.