| 摘要 |
PURPOSE:To manufacture a galvanized steel sheet having superior corrosion resistance, weldability and coatability and leaving no fingerprint thereon by chromating a galvanized steel sheet with a chromating liq. contg. chromic acid, F ions, a silicic acid compound, a specified silane coupling agent and a water dispersible or soluble resin. CONSTITUTION:A galvanized steel sheet having said superior characteristics is manufactured by treating the surface of a galvanized steel sheet with a chromating liq. CrO3 in an aqueous soln. contg. 5-50g/l CrO3, 0.1-10g/l (expressed in terms of F ions) F ions or F complex ions such as HF and 5-100g/l (expressed in terms of SiO2) silicic acid compound is reduced to Cr2O3 by adding a reducing agent such as alcohol. After adjusting the soln. to 1.5-4pH, 0.1-5% gamma-(2- aminoethyl)aminoprophyltrimethoxysilane and 50-500g/l water dispersible or soluble resin which is stably miscible with chromic acid are added to the soln. to prepare said chromating liq. By surface treatment with the chromating liq., a chromate film is formed by 50-1500mg/m<2> as a dry film. |
