| 摘要 |
PROBLEM TO BE SOLVED: To improve the rust preventing property of a cut end part, especially in a relatively short period after the start of usage, of a coated steel sheet, of which the material is an aluminum-containing galvanized steel sheet, and to suppress the elution of harmful chromate ions. SOLUTION: This coated steel sheet has an undercoating film and a topcoating film on the surface of a surface treated steel sheet that is made by subjecting chemical conversion treatment to the galvanized steel sheet containing 3-70 wt.% of aluminum. The undercoating film has a thickness of 15μm or less, and is formed by baking an under coating material, of which the main resin is a polyester resin and/or an epoxy resin, in which 1-50 pts.wt. of calcium ion exchange silica is added to 50 pts.wt. of the resin solid content onto the surface of the steel sheet.
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