PURPOSE: To extremely improve the corrosion resistance performance required for org. coated steel products by coating a surface treating liquid contg. prescribed chromic acid, a specific ratio of colloidal silica and water on the surface of steel products subjected to a cleaning treatment, then drying the coating.
CONSTITUTION: The surface treating liquid contg. chromic acid of ≤1 Cr3+/Cr6+ the colloidal silica of 0.4W0.8 Si/Cr at the atomic ratio with respect to Cr in the chromic acid, and the water is coated at 0.1W10g/m2 dry weight on the surface of the above-mentioned steel products and thereafter, the coating is dried at 50W300°C. ≥1 kinds of water of soluble org. material having a reducing property are further added to the above-mentioned treating liquid at ≤200pts.wt. per 100pts.wt. chromic acid. After the above-mentioned surface treatment is executed, the org. coating of an epoxy resin or the like is applied thereon, by which the org. coated steel products having the excellent corrosion preventive performance and adhesion are obtd.
MUKOHARA FUMINORI
KURISU TAKAO
