PLATED STEEL SHEET HAVING COMPOSITE COATING

摘要

PURPOSE:To obtain a surface treated steel sheet capable of satisfying each of rustproof treatment and prime-coating treatment by making the second layer a cured film of specified silane compd. in a plated steel sheet consisting of a chromate-treated film and an organic resin film. CONSTITUTION:A chromate-treated film is formed as the first layer on the surface of a plate steel sheet. A cured film having the following siloxane bond as a skelton is formed as the second layer wherein the siloxane bond is formed by coating and baking a soln. contg. one or more kinds of monomer of oligomer of di- or trialkoxysilane which has alkyl groups having the organic functional groups. In the film of the second layer, the silane compd. in itself is a film forming component and the cured film consisting of the siloxane skelton obtained by baking the silane compds. has not hydrophilic nature and also is sufficiently bonded to the chromatetreated film of the lower layer. Therefore, the corrosion resistance of the plated steel plate is remarkably increased and the electrodeposited painting properties are not throughly degraded within the limitation of the coating build-up of the second layer.