| 摘要 |
PURPOSE:To provide a steel plate painted on one side which is provided with weldability and corrosion preventiveness on paint films by forming mixed phosphates of specific compsns. on the surface of the steel plate then providing an undercoating layer of specific chromate type and a zinc-contg. top coating layer thereon. CONSTITUTION:A film of mixed phosphates mixed with iron phosphate and zinc phosphate-iron is formed on the surface of a steel plate regulated to 4-20mu surface roughness in a 1-500mg/m<2> range. A stabilized aq. soln. for coating consisting of 10pts.wt. chromium trioxide wherein the ratio of content of hexavalent chromium/content of chromium oxide attains 0-2.3, 3-4 parts phosphoric acid (100% H3PO4), 17-20 parts an acrylic emulsion polymer in solid contents, and 200-4,000 parts water is coated on said film and is dried, whereby an undercoating layer of 5-1,000mg/m<2> total content of Cr is formed. The top coating layer of the resin contg. zinc powder is formed on the undercoating layer in a 10-50mu range. This painted steel plate has excellent corrosion preventiveness, electric weldability and paint adhesive strength. |
