| 摘要 |
PURPOSE:To obtain a coated steel sheet excellent in corrosion resistance and weldability by applying a coating material containing silica grains and a resin, in which number average molecular weight is regulated to a specific value or above, to a galvanized or Zn alloy plated steel sheet after specific chromate treatment. CONSTITUTION:Chromate treatment is applied to a galvanized or Zn alloy plated steel sheet. Chromate coating weight is regulated to 5-500mg/m<2> expressed in terms of chromium, and also the Cr<6+> content in the resulting chromate film is regulated to <=70%. A coating material containing silica sol and an organic resin having >=2000 number average molecular weight, such as epoxy resin, acrylic resin, and urethane resin, is applied to the chromate film by 0.2-3.0g/m<2> by dry weight and cured. The above silica sol is a dispersed solution of secondary grains in which primary grains of silica are agglomerated. By this method, a silica-containing film in which the number of secondary silica grains in an arbitrary cross section is regulated to 1X10<4>-1X10<9>pieces/mm<2> can be formed. |
