Patent ID: 8623503

Claim:
A method for surface treating comprising: adding an acid catalyst and water to an alcoholic solution containing alkoxysilane raw material to hydrolyze and condensation-polymerize the alkoxysilane raw material to synthesize alkoxysilane oligomer having weight-averaged molecular weight of 1,000 to 10,000, mixing an organic chelate titanium compound with the alcoholic solution of the synthesized alkoxysilane oligomer to obtain a chromium-free rust-inhibitive surface treatment agent, and surface treating a metal part with zinc surfaces with the chromium-free rust-inhibitive surface treatment agent, wherein silicon atoms in molecules of the alkoxysilane oligomer are partly replaced with titanium atoms from an organic chelate titanium compound, the alcoholic solution contains titanium of 2.5 to 15 atomic % to a total amount of silicon and titanium, and the total amount of silicon and titanium is 5 to 20 weight % in the alcoholic solution when silicon and titanium are converted to SiO 2 and TiO 2 , respectively, and wherein the organic chelate titanium compound is titanium alkoxide in which 40 to 60% of alkoxy groups are blocked or replaced by a chelate agent.