| 摘要 |
PURPOSE:To obtain the title org. coated multilayered steel sheet excellent in weldability and corrosion resistance by depositing a specified amt. of Cr on a galvanized steel sheet having specified surface roughness to form the lower film, and further forming the upper film of a specified resin having specified thickness thereon. CONSTITUTION:A partially reduced chromic acid-based chromating soln. is applied on a steel sheet plated with zinc or a zinc-based alloy, and baked to form the lower film contg. 10-150mg/m<2> Cr. A resin soln. is applied on the lower film, and baked at 80-300 deg.C to form the upper film having 0.2-4mum thickness. The resin soln. consists of an epoxy resin or a modified epoxy resin, and contains a cross-linking agent in such an amt. as to control the molar ratio of the functional group to the total amt. of the epoxy group and hydroxyl group to 0.1-0.2. In this case, the maximum height Rmax of the ruggedness of the base material of the plated steel sheet and the thickness (d) of the upper film fulfil Rmax>=12d, and the parameter PPI of the surface roughness (the number of peaks per inch, and the threshold value is 30% of Rmax) is controlled to >=30. By this method, an org. coated multilayered steel sheet excellent in spot welding, working adhesion, and suitability for electrodeposition coating is obtained. |
