Patent ID: 7918931

Claim:
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 10000; 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 dioxide 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.