ORGANIC COMPOSITE COATED STEEL SHEET HAVING EXCELLENT ELECTRODEPOSITION COATABILITY AND CORROSION RESISTANCE AND ITS PRODUCTION

摘要

PURPOSE:To provide an org. composite coated steel sheet having an excellent water-resistant secondary adhesion property, rust preventiveness, low-temp. chipping resistance and spot weldability and further, having the excellent electrodeposition coatability (above all, brightness) comparable to the electrodeposition coatability of a cold rolled steel sheet and galvanized steel sheet. CONSTITUTION:The org. composite coated steel sheet has a chromate film 3 to 5 to 500mg/m<2> in terms of Cr on the front surface of the galvanized or galvannealed steel sheet 1 and has a resin layer 4 mainly formed by mainly compounding silica and binder resin of specific conditions and further adding at least one kind selected from the group consisting of a polyamide resin, polyamine resin and polyimine resin at 1 to 10wt.% thereto on the upper layer of this chromate film 3 to 0.0 to 3g/m<2> in dry weight. This production process is for such steel sheet. The average primary particle sizes of the silica constituting the resin layer are 5 to 30nm. The silica flocculates in the surface form of an average thickness of 0.2 to 2m and an average grain size of 5 to 300m in the resin layer 4.