Chromium-free metal surface treatment agent

Abstract

Provided is a chromium-free metal surface treatment agent excellent in rust inhibitive performance which can be used in a surface treatment of metal products, in particular, galvanized metal products. The metal surface treatment agent consists essentially of a siliceous binder solution comprising water and/or alcohol as a solvent, and the concentration of the silica component is 8 to 25% by weight. In particular, a metal surface treatment agent containing an alcoholic solution of alkoxysilane oligomer having a weight averaged molecular weight of 1000 to 10000, which is obtained by hydrolyzed condensation polymerization of alkoxysilane, can suppress the occurrence of white rusting for a long time. It is preferred that 3 to 25 parts by weight of a dispersed nano-sized titanium dioxide powder having an average primary particle size of not more than 70 nm, per 100 parts by weight of the silica component be suspended in the siliceous binder solution. The rust inhibitive performance of the metal surface treatment agent can be further improved by using an alcohol-soluble polyvinyl butyral resin and by adding a silane coupling agent having a vinyl or epoxy group as a functional group, in combination with a dispersed nano-sized powder of titanium dioxide.

1 - 34 . (canceled) 
     
     
         35 . A chromium-free metal surface treatment agent which is a silica-based binder solution which consists essentially of:
 alkoxysilane oligomer having a weight averaged molecular weight of 1,500 to 10,000;   an alcohol-soluble resin component of 0.2 to 2% by weight; and   the balance being an alcohol solvent,   wherein the alkoxysilane oligomer is obtained by hydrolyzed condensation polymerization of tetraethoxysilane by adding water and acid catalyst; and   wherein the concentration of the alkoxysilane oligomer in the silica-based binder solution constitutes 8 to 25% by weight of the silica-based binder solution as silica component which is formed when the chromium-free metal surface treatment agent is applied and solidified.   
     
     
         36 . The chromium-free metal surface treatment agent according to  claim 35 , wherein the alcohol-soluble resin component is polyvinyl butyral. 
     
     
         37 . The chromium-free metal surface treatment agent according to  claim 35 , wherein the silica binder solution further comprises a silane coupling agent having a vinyl or epoxy group as a functional group. 
     
     
         38 . The chromium-free metal surface treatment agent according to  claim 35 , wherein 5 to 35% by weight of the alcohol contained in the silica-based binder solution is alcohol having a boiling point higher then 115° C. 
     
     
         39 . The chromium-free metal surface treatment agent according to  claim 38 , wherein the alcohol having a boiling point higher than 115° C. is glycol ether. 
     
     
         40 . A chromium-free metal surface treatment agent which is a silica-based binder solution which consists essentially of:
 alkoxysilane oligomer having a weight averaged molecular weight of 1,500 to 10,000;   a dispersed nano-sized titanium dioxide powder of 3 to 25 parts by weight per 100 parts by weight of the silica component contained in the silica-based binder solution and the balance being an alcohol solvent;   wherein the dispersed nano-sized titanium oxide powder is suspended in the silica-based binder solution, the dispersed nano-sized titanium dioxide powder has an average primary particle size of not more than 70 nm, and the alkoxysilane oligomer is obtained by hydrolyzed condensation polymerization of tetraethoxysilane by adding water and acid catalyst, and   wherein the concentration of the alkoxysilane oligomer in the silica-based binder solution constitutes 8 to 25% by weight of the silica-based binder solution as silica component which is formed when the chromium-free metal surface treatment agent is applied and solidified.   
     
     
         41 . The chromium-free metal surface treatment agent according to  claim 40 , where in the silica-based binder solution comprises a dispersed nano-sized titanium dioxide powder of 5 to 20 parts by weight per 100 parts by weight of the silica component contained in the silica-based binder solution, and wherein the dispersed nano-sized titanium dioxide powder has an average primary particle size of not more than 40 nm. 
     
     
         42 . The chromium-free metal surface treatment agent according to  claim 41 , wherein the silica-based binder solution further comprises an alcohol-soluble resin component of 0.2 to 2% by weight. 
     
     
         43 . The chromium-free metal surface treatment agent according to  claim 42 , wherein the alcohol-soluble resin component is polyvinyl butyral. 
     
     
         44 . The chromium-free metal surface treatment agent according to  claim 41 , wherein the silica based binder solution further comprises a silane coupling agent having a vinyl or epoxy group as functional group. 
     
     
         45 . The chromium-free metal surface treatment agent according to  claim 41 , wherein 5 to 35% by weight of the alcohol contained in the silica-based solution is alcohol having a boiling point higher than 115° C. 
     
     
         46 . The chromium-free metal surface treatment agent according to  claim 45 , wherein the alcohol having a boiling point higher than 115° C. is glycol ether. 
     
     
         47 . A metal product comprising a steel product and a coating formed by applying a chromium-free metal surface treatment agent,
 wherein the chromium-free metal surface treatment agent is a silica-based binder solution which consists essentially of:   alkoxysilane oligomer having a weight averaged molecular weight of 1,500 to  10,000; and      the balance being an alcohol solvent;   wherein the alkoxysilane oligomer is obtained by hydrolyzed condensation polymerization of tetraethoxysilane by adding water and acid catalyst, and   wherein the concentration of the alkoxysilane oligomer in the silica-based binder solution constitutes 8 to 25% by weight of the silica-based binder solution as silica component which is formed when the chromium-free metal surface treatment agent is applied and solidified; and   wherein the steel product is galvanized and the coating is formed on the surface of the galvanized steel product.   
     
     
         48 . A metal product comprising a steel product and a coating formed by applying the chromium-free metal surface treatment agent according to  claim 40 , wherein the steel product is galvanized and the coating is formed on the surface of the galvanized steel product. 
     
     
         49 . A metal product according to  claim 47 , wherein the silica-based binder solution further comprises an alcohol-soluble resin component of 0.2 to 2% by weight. 
     
     
         50 . A metal product according to  claim 49 , wherein the alcohol-soluble resin component is polyvinyl butyral. 
     
     
         51 . A metal product according to  claim 47 , wherein the silica-based binder solution further comprises a silane coupling agent having a vinyl or epoxy group as a functional group. 
     
     
         52 . A metal product according to  claim 47 , wherein 5 to 35% by weight of the alcohol contained in the silica-based binder solution is alcohol having a boiling point higher then 115° C. 
     
     
         53 . A metal product according to  claim 52 , wherein the alcohol having a boiling point higher then 115° C. is glycol ether. 
     
     
         54 . The chromium-free metal surface treatment agent according to  claim 38 , wherein the alcohol having a boiling point higher then 115° C. is ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether. 
     
     
         55 . The chromium-free metal surface treatment agent according to  claim 45 , wherein the alcohol having a boiling point higher than 115° C. is ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether. 
     
     
         56 . A metal product according to  claim 52 , wherein the alcohol having a boiling point higher then 115° C. is ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether. 
     
     
         57 . A metal product according to  claim 52 , wherein the coating formed by applying the chromium-free metal surface treatment agent is about 2 μm in thickness.