Method for manufacturing steel sheet coated with zinc-based coating layer (as amended)

Abstract

A steel sheet coated with a zinc-based coating layer having a reaction layer on the surface of the steel sheet is manufactured by a method that includes bringing a steel sheet coated with a zinc-based coating layer into contact for 1.0 second or more with an alkaline aqueous solution containing one or more chelating agents selected from among sodium gluconate, sodium glucoheptonate, sodium citrate, tartaric acid, arabonic acid, galactonic acid, sorbit, mannite, glycerin, EDTA, and sodium tripolyphosphate in a total amount of 0.050 mass % or more and having a pH of 10.0 or more as a pre-treatment before a formation of the reaction layer, and forming the reaction layer being an oxide layer containing a crystal-structured substance expressed by Zn 4 (SO 4 ) 1-X (CO 3 ) X (OH) 6 .nH 2 O.

1 . A method for manufacturing a steel sheet coated with a zinc-based coating layer having a reaction layer on the surface of the steel sheet, the method comprising:
 bringing a steel sheet coated with a zinc-based coating layer into contact for 1.0 second or more with an alkaline aqueous solution containing one or more chelating agents selected from the group consisting of sodium gluconate, sodium glucoheptonate, sodium citrate, tartaric acid, arabonic acid, galactonic acid, sorbit, mannite, glycerin, EDTA, and sodium tripolyphosphate in a total amount of 0.050 mass % or more and having a pH of 10.0 or more, and   thereafter forming the reaction layer being an oxide layer containing a crystal-structured substance expressed by Zn 4 (SO 4 ) 1-X (CO 3 ) X (OH) 6 .nH 2 O.   
     
     
         2 . The method for manufacturing a steel sheet coated with a zinc-based coating layer according to  claim 1 , wherein pH of the alkaline aqueous solution is 12.6 or more.