| 摘要 |
Coatings of increased strength and reduced tackiness are anodically electrodeposited on metal sheets, and particularly alkali-cleaned aluminum sheets, by passing a unidirectional electrical current through an aqueous bath having dispersed therein carboxyl-functional copolymer particles and heat-hardening formaldehyde condensate for curing the same, and then through the metal sheet as anode to deposit a coating, and especially a clear coating, on the metal sheet. The copolymer particles are provided by copolymerization in the presence of free radical polymerization catalyst of monoethylenic carboxylic acid in an aqueous dispersion of the monomers in a liquid mixture containing at least 0.5% by weight of polyhydric alcohol having a molecular weight in the range of about 300 to about 6000, the copolymerization providing copolymer particles having an average molecular weight in the range of 10,000 to 50,000 and an acid value of 3-200. The copolymer particles are at least partially neutralized with a base to provide a bath pH of 6 or higher and electrodeposited coatings can be baked to cure the coating and provide a coated metal sheet in which the cured coating has sufficient strength to allow it to be permanently deformed. It is also possible to mechanically remove surface water from the electrodeposited coating and then to overcoat the same and cure the primer coating and the topcoating in a single baking operation.
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