Surface-treated steel sheet, organic resin-coated metal container and process for producing surface-treated steel sheet

Abstract

A surface-treated steel sheet and a process for its production. The surface-treated steel sheet has, on at least one surface of the steel sheet, a surface-treating layer that chiefly comprises zirconium and oxygen, and contains fluorine, the surface-treating layer containing an element of the Group II on the surface side thereof. The surface-treated steel sheet features excellent adhesion to the organic resin coating, excellent corrosion resistance, and can provide metal cans that feature excellent adhesion to the resin on the inner and outer surfaces of the cans and excellent resistance against the elution of fluorine.

1 . A surface-treated steel sheet having a steel sheet and a surface-treating layer on at least one surface of the steel sheet, the surface-treating layer including zirconium, oxygen and fluorine, wherein said surface-treating layer contains an element of the Group II on the surface side thereof. 
     
     
         2 . The surface-treated steel sheet according to  claim 1 , wherein the element of the Group II is present as a fluorine compound. 
     
     
         3 . The surface-treated steel sheet according to  claim 1 , wherein the element of the Group II is at least either calcium or magnesium. 
     
     
         4 . The surface-treated steel sheet according to  claim 1 , wherein a molar ratio AE/Zr of the element (AE) of the Group II and zirconium (Zr) in said surface-treating layer is not less than 0.2. 
     
     
         5 . The surface-treated steel sheet according to  claim 1 , wherein the thickness of zirconium in terms of weight is 100 to 200 mg/m 2 . 
     
     
         6 . An organic resin-coated surface-treated steel sheet obtained by forming an organic resin coating on the surface-treated steel sheet of  claim 1 . 
     
     
         7 . A metal container made from the organic resin-coated surface-treated steel sheet of  claim 6 . 
     
     
         8 . A can lid made from the organic resin-coated surface-treated steel sheet of  claim 6 . 
     
     
         9 . A process for producing a surface-treated steel sheet having a steel sheet and a surface-treating layer on at least one surface of the steel sheet, the surface-treating layer including zirconium, oxygen and fluorine, said process comprising the steps of:
 forming a coating by cathodically electrolyzing the steel sheet in an aqueous solution that contains Zr ions and F ions; and   thereafter, adjusting the surfaces by conducting any one or more of a dip treatment, a spray treatment or a cathodic electrolytic treatment by using an aqueous solution that contains an element of the Group II for adjusting the surface.   
     
     
         10 . The process for producing the surface-treated steel sheet according to  claim 9 , wherein the element of the Group II is at least one of calcium or magnesium. 
     
     
         11 . The process for producing the surface-treated steel sheet according to  claim 9 , wherein in the step of adjusting the surfaces, a reduction ratio of fluorine from that of the step of forming the coating is not more than 30%.