| 摘要 |
I provide an aqueous coating composition to provide an outer protective coating for a metal selected from the group consisting of an aluminum, aluminum alloy, iron, iron alloy, zinc, zinc alloy, zinc coated iron, zinc coated iron alloy, and these metals and magnesium and magnesium alloys having a conversion coating thereon. The aqueous coating composition consists essentially of 60 to 90 parts by weight water, 0.5 to 10 parts by weight of a polyvinyl alcohol having a weight average molecular weight of at least 100,000 and being at least 95% hydrolyzed, 0.5 to 20 parts by weight of a polybasic acid or anhydride, and 0.0 to 3 parts by weight of a cross-linking agent or plasticizer to form a in-situ polyester conversion coating on the metal. The composition is applied directly to the metal or to the metal article which has a non-chromium conversion coating thereon and forms a thin film thereon. Then the metal with the film thereon is heated to between 300° to 550° F. to form an in-situ polyester conversion coating on the metal article.
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