Zinc-based plated steel sheet having post-treated coating formed thereon and post-treatment method therefor

Abstract

Provided is a zinc-based plated steel sheet having a post-treated coating filmed thereon including: a steel sheet; a zinc plated layer formed on the steel sheet; and a post-treated coating formed on the plated layer, wherein the atomic ratio (O/M) of oxygen (O) to metals (M) contained in the post-treated coating is greater than 2 and less than 20, and a method for post-treating a zinc-based plated steel sheet. According to this, the zinc-based plated steel sheet having the post-treated coating formed thereon has the effects excellent in lubricity, weldability, adhesiveness, film-removing property and paintability. As the method of post-treating a zinc-based plated steel sheet of the present invention employs a simple coating method irrespective of the kind of plating layer, the process is simple and economical and the process operation cost is low.

1 . A zinc-based plated steel sheet having a post-treatment coating, the zinc-based plated steel sheet comprising:
 a steel sheet;   a zinc-based plating layer formed on the steel sheet; and   a post-treatment coating formed on the plating layer,   wherein   the post-treatment coating includes metal oxide salt and an organic compound, and   an atomic ratio (O/M) of oxygen (O) to metals (M) included in the post-treatment coating is greater than 2 and smaller than 20.   
     
     
         2 . The zinc-based plated steel sheet of  claim 1 , wherein
 the post-treatment coating includes a coating upper portion and a coating lower portion,   an atomic ratio (O/M) of oxygen and metal of the coating upper portion is greater than 5, and   an atomic ratio (O/M) of oxygen and metal of the coating lower portion is less than 5.   
     
     
         3 . The zinc-based plated steel sheet of  claim 2 , wherein
 an atomic ratio (O/M) of oxygen and metal of the coating upper portion is greater than 3.2, and   an atomic ratio (O/M) of oxygen and metal of the coating lower portion is less than 3.2.   
     
     
         4 . The zinc-based plated steel sheet of  claim 2 , wherein a thickness of the coating lower portion is ¼ to ¾ of the total thickness of the post-treatment coating. 
     
     
         5 . The zinc-based plated steel sheet of  claim 1 , wherein
 the metal oxide salt further includes one or more selected from the group consisting of molybdenum (Mo), boron (B), silicon (Si), titanium (Ti), and zirconium (Zr).   
     
     
         6 . A method for post-treating a zinc-based plated steel sheet, the method comprising:
 applying a post-treatment coating solution to a zinc-based plated steel sheet and drying the same to form a post-treatment coating,   wherein an atomic ratio (O/M) of oxygen (O) to metals (M) included in the post-treatment coating is greater than 2 and smaller than 20.   
     
     
         7 . The method of  claim 6 , wherein
 the post-treatment coating includes a coating upper portion and a coating lower portion,   an atomic ratio (O/M) of oxygen and metal of the coating upper portion is greater than 5, and   an atomic ratio (O/M) of oxygen and metal of the coating lower portion is less than 5.   
     
     
         8 . The method of  claim 7 , wherein a thickness of the coating lower portion is ¼ to ¾ of the total thickness of the post-treatment coating. 
     
     
         9 . The method of  claim 6 , wherein
 the post-treatment coating solution has pH ranging from 3.0 to 7.0.   
     
     
         10 . The method of  claim 6 , wherein
 the post-treatment coating has a coating weight ranging from 100 to 1000 mg/m 2 .