| abstract |
Disclosed is a chromium-free rust-inhibitive surface treatment agent to form a siliceous film that rarely cracks or peels off and yields an excellent rust-inhibitive performance on zinc surfaces of a metal part. The chromium-free rust-inhibitive surface treatment agent is an alcoholic solution of alkoxysilane oligomer having weight-averaged molecular weight of 1,000 to 10,000, and 2.5 to 15% of silicon in molecules of the alkoxysilane oligomer has been replaced with titanium. To prepare partly titanium-replaced alkoxysilane oligomer, titanium compound, in which about a half of alkoxy groups in titanium tetraalkoxide has been chelated, is reacted with tetraalkoxysilane monomer or alkoxysilane oligomer in the alcoholic solution. |