| 摘要 |
PROBLEM TO BE SOLVED: To provide a tin base plated steel sheet with a uniform and fine plating appearance by preventing abnormal precipitation of Cr. SOLUTION: In the chemical conversion treatment method where a tin base plated steel sheet is subjected to cathode electrolysis at >20 to 150 A/dm<SP>2</SP>in a pre-stage low temperature bath with a bath temperature of <45°C storing a chromic anhydride base bath solution at least containing CrO<SB>3</SB>and H<SB>2</SB>SO<SB>4</SB>of 1/50 to 1/300 in the weight ratio to CrO<SB>3</SB>, and is successively subjected to dipping treatment and cathode electrolysis at 1 to 20 A/dm<SP>2</SP>in a post-stage high temperature bath with a bath temperature of≥50°C storing a chromic anhydride base bath solution at least containing CrO<SB>3</SB>and H<SB>2</SB>SO<SB>4</SB>of 1/50 to 1/300 in the weight ratio to CrO<SB>3</SB>, (i) (a) a part of the above bath solution fed from a bath solution storage tank for the pre-stage low temperature bath to the pre-stage low temperature bath is distributively supplied to a bath solution storage tank for the post-stage high temperature bath, and also, (b) a part of the above bath solution fed from the bath solution storage tank for the post-stage high temperature bath to the post-stage high temperature bath is distributively supplied to the bath solution storage tank for the pre-stage low temperature bath, thus the above bath solution is mutually exchanged, and (ii) the componential composition of the bath solution fed to the pre-stage low temperature bath and the componential composition of the bath solution fed to the post-stage high temperature bath are uniformized. COPYRIGHT: (C)2008,JPO&INPIT
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