| abstract |
Disclosed is a steel sheet having an organic composite plating layer excellent in press workability, spot weldability, electrodeposition coatability and corrosion resistance which comprises a zinc plated, aluminum plated or zinc base composite alloy steel sheet, a first layer of an insoluble chromate film of 5% or less in the content of water-soluble matter formed on the surface of the steel sheet at a coverage of 10-150 mg/m 2 in terms of chromium content and a second layer of a coating composition having the following composition coated at a thickness of 0.3-5 μm as a solid film on said first layer: n (A) a bisphenol type epoxy resin having a number-average molecular weight of 300-100,000 in an amount of 30% by weight or more of solid matter in the coating composition, n (B) at least one curing agent selected from the group consisting of a polyisocyanate compound and a block polyisocyanate compound at a weight ratio to solid matter in the epoxy resin of 1/10-20/10, n (C) fumed silica having an average particle size of 0.1-100 in an amount of 5-50% by weight of solid matter in the coating composition, and n (D) a ketone organic solvent in an amount of 40% by weight or more of the coating composition, and n the solid content of the coating composition being 10-50% by weight. |