| 摘要 |
<p>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 plated 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 mu m as a solid film on said first layer: (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, (B) at least one polyisocyanate compound or block polyisocyanate compound as a curing agent at a weight ratio to solid matter in the epoxy resin of 1/10 - 20/10, (C) fumed silica having an average particle size of 0.1-100 m mu in an amount of 5-50% by weight of solid matter in the coating composition, and (D) a ketone organic solvent in an amount of 40% by weight or more of the coating composition, and the solid content of the coating composition being 10-50% by weight.</p> |
