| 摘要 |
PROBLEM TO BE SOLVED: To obtain a chromate film excellent in weldability, adhesivity to coating materials and corrosion resistance on a continuous producing line with high productivity by subjecting a tinned steel sheet to cathode electrolysis in a bath of a specified temp. contg. CrO3 and a specified amt. of H2SO4, and next executing immersing treatment in a bath of a specified temp. contg. CrO3. SOLUTION: A tinned steel sheet is subjected to cathode electrolysis in a treating bath of <45 deg.C bath temp. contg. at least CrO3 and H2SO4 of 1/50 to 1/300 by the weight ratio to CrO3 and is subjected to immersing treatment in a treating bath of >=50 deg.C bath temp. at least contg. CrO3. By the reduction of the cathode electrolytic treating bath temp., the applicability of metallic chromium and hydrated chromium oxide (Ox-Cr) is good and, though the amt. of Ox-Cr increases, ol-type Ox-Cr in the upper layer in the Ox-Cr film formed at this time is large in the amt. of sulfuric acid ions to be precipitated, so that, it is high in meltability and can easily be melted by immersing treatment in a high temp. bath in the succeeding stage, and Ox-Cr remained at this time is the film high in oxs formation and excellent in adhesion.
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