Abstract: The present invention relates to a highly corrosion resistant surface-treated steel plate. The steel plate of the invention comprises a zinc deposition or zinc alloy deposition film as the undercoat deposition layer, a chromate film formed on the undercoat deposition layer and a film of a resin composition formed on the chromate film. This resin composition comprises a substrate resin formed by adding at least one basic nitogen atom and at least two primary hydrogen groups to terminal of an epoxy resin, silica and sparingly water soluble Cr compound. The resin composition may comprise a polyisocyanate compound as the curing agent. Moreover, the resin composition may comprise a silane compound as the crosslinking agent for the substrate resin and silica.

Abstract: The present invention relates to a highly corrosion-resistant surface-treated steel plate. The steel plate of the present invention comprises a zinc deposition or zinc alloy deposition film as the undercoat deposition layer, a chromate film formed on the undercoat deposition layer and a film of a resin composition formed on the chromate film. This resin composition comprises a base resin formed by adding at least one basic nitrogen atom and at least two primary hydroxyl groups to terminals of an epoxy resin. The resin composition may comprise a polyisocyanate compound as the curing agent. Furthermore, the resin composition may comprise silica or a hardly soluble chromium compound as the additive for improving the corrosion resistance. Moreover, the resin composition may comprise a silane compound as the crosslinking agent for the base resin and silica.

Abstract: The present invention relates to a process for the preparation of a highly anticorrosive surface-treated steel plate. This process comprises the steps of subjecting a surface of a steel plate having a plating layer of the zinc or aluminum type deposited thereon to a chromate treatment to form a chromate film, treating the steel plate with an organic composite silica solution comprising an epoxy resin in an amount exceeding a certain level as an indispensable component and a curing agent optionally incorporated therein to form an organic composite silicate film comprising colloidal silica, organic resin and silane formed on the chromate film, and heat-treating the steel plate at a specific temperature.