| 摘要 |
PURPOSE:To form chromate films having high rust preventing effect and causing no exfoliation on zinc-coated steel products by coating the products with an aq. soln. contg. chromic acid, a reduction product of chromic acid and silica sol followed by drying. CONSTITUTION:Zinc (alloy)-coated steel products are coated with an aq. soln. based on (A) chromic acid, (B) a reduction product of chromic acid and (C) silica sol, and the products are dried without washing to form chromate films. The ratio of the component (B) to the component (A) is 1:0.6-1.0 by wt. as CrO3, the concn. of (A) and (B) in total is 2-400 g/l as CrO3, and the ratio of the component (C) as SiO2 to (A) and (B) as CrO3 is 1:0.2-20. The drying temp. is pref. 40-150 deg.C, and the amt. of chromate adhered is regulated to above 30 mg/m<2> as Cr. |
