| 摘要 |
The coating solution having good weldability is prepared by (A) forming a solution composed of 5-25 g/l the total chromium ion containing 20-50% of 3-valent ion to the total chromium ions, 80-100 g/l colloidal silica with 0.001-0.003 micrometer particle size, 0.1-20 g/l vinyl or acryl based emulsion resin with 0.1-0.3 micrometer particle size, 0.1-5 g/l silane coupling agent and water, and (B) controlling the pH of that solution to 2-4 by adding at least one component selected from acetic acid, phosphoric acid and formic acid. 1-20 wt% of the total chromium ions are come from at least one component selected from strontium chromate, calcium chromate, zinc chromate and barium chromate as slightly insoluble chromic compounds, and the residues are come from at least one component selected from chromate, sodium dichromate, potassium dichromate and ammonium dichromate as water soluble chromic compounds.
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