Surface treatment agent composition for tin-plated steel, and tin-plated steel subjected to surface treatment

Abstract

A surface treatment agent composition which contains aluminum as the coating film formation component and exhibits excellent properties for removing tin ions within a treatment bath when subjecting a tin-plated steel to electrolytic surface treatment, thereby forming a coating film exhibiting excellent corrosion resistance and yellowing resistance. This surface treatment agent composition is used for subjecting a tin-plated steel or a tin-based alloy-plated steel to electrolytic surface treatment and contains aluminum ions, fluorine ions, and polycarboxylic acid. The tin ions that eluted from the tin-plated steel are precipitated within and removed from the treatment bath by using this surface treatment agent composition.

1 . A surface treatment agent composition for tin-plated steel to be used for electrolytic surface treatment of a tin- or tin-based alloy-plated steel, comprising aluminum ions, fluorine ions and a polycarboxylic acid. 
     
     
         2 . The surface treatment agent composition for tin-plated steel according to  claim 1 , wherein the polycarboxylic acid is a homopolymer containing a monomer selected from tl - group consisting of acrylic acid, methacrylic acid, maleic acid, and itaconic acid as a constitutional unit or a copolymer containing at least one of these monomers as the constitutional unit. 
     
     
         3 . The surface treatment agent composition for tin-plated steel according to  claim 1 , wherein a ratio [C group]/[Al] of a molar concentration [C group] of carboxyl groups contained in the polycarboxylic acid to a molar concentration [Al] of the aluminum ions is 0.005 to 2.0. 
     
     
         4 . The surface treatment agent composition for tin-plated steel according to  claim 1 , wherein a ratio [F]/[Al] of a molar concentration [F] of the fluorine ions to a molar concentration [Al] of the aluminum ions is 1 to 4. 
     
     
         5 . The surface treatment agent composition for tin-plated steel according to  claim 1 , wherein a mass concentration of the aluminum ions is 100 to 10,000 ppm. 
     
     
         6 . The surface treatment agent composition for tin-plated steel according to  claim 1 , wherein a pH value of the surface treatment agent at 25° C. is 1 to 5. 
     
     
         7 . The surface treatment agent composition for tin-plated steel according to  claim 1 , comprising tin ions, wherein a mass concentration of the tin ions is 500 ppm or less. 
     
     
         8 . A tin-plated steel which is surface-treated with the surface treatment agent composition for tin-plated steel according to  claim 1 . 
     
     
         9 . A method for electrolytic surface treatment of a tin- or tin-based alloy-plated steel, comprising electrolytically treating said tin- or tin-based alloy-plated steel with a surface treatment agent comprising aluminum ions, fluorine ions and polycarboxylic acid. 
     
     
         10 . The method according to  claim 9 , wherein the polycarboxylic acid is a homopolymer containing a monomer selected from acrylic acid, methacrylic acid, maleic acid, and itaconic acid as a constitutional unit or a copolymer containing at least one of these monomers as the constitutional unit. 
     
     
         11 . The method according to  claim 9 , wherein a ratio [C group]/[Al] of a molar concentration [C group] of carboxyl groups contained in the polycarboxylic acid to a molar concentration [Al] of the aluminum ions is 0.005 to 2.0. 
     
     
         12 . The method according to  claim 9 , wherein a ratio [F]/[Al] of a molar concentration [F] of the fluorine ions to a molar concentration [Al] of the aluminum ions is  1  to  4 .) 
     
     
         13 . The method according to  claim 9 , wherein a mass concentration of the aluminum ions is 100 to 10,000 ppm. 
     
     
         14 . The method according to  claim 9 , wherein a pH value of the surface treatment agent at 25° C. is 1 to 5. 
     
     
         15 . The method according to  claim 9 , comprising tin ions, wherein a mass concentration of the tin ions is 500 ppm or less.