| 摘要 |
In coating a metal substrate by passing an electric current between conductive anode and cathode in contact with an aqueous composition comprising a partially neutralized reaction product of a drying oil fatty acid ester or a semidrying oil fatty acid ester and an anhydride of an a :b -ethylenically unsaturated dicarboxylic acid and/or the acid thereof and/or fumaric acid, a portion of the composition is withdrawn from the electrodeposition bath and treated in a separate zone with a suitable cation exchange resin for a time sufficient to reduce the pH to 6 to 8.5 and is then returned to the bath. Additional coating material may be added to the bath as required. Neutralization of the reaction product may be effected with metal hydroxides or preferably ammonia or amines including tertiary amines. An ethylenically unsaturated monomer such as a styrene, acrylate, methacrylate, acrylonitrile or a diolefine may be reacted with the acid or anhydride before the reaction with the fatty acid ester. Pigments surface active agents and anti-oxidants may be included in the bath composition. The preferred cation exchange resins are weak carboxylic acid resins. As described the bath is agitated by external circulation and coatings are electrodeposited on phosphatized steel as anode and the deposited coating is baked. A pair of ion exchange resin treatment stations may be arranged in parallel in the bath composition regeneration path, one station being regenerated while the other is used to treat the bath composition. |
