GB1217002A - Electrodeposition of resins - Google Patents

Abstract

1,217,002. Coatings. DESOTO, Inc. 8 Feb., 1968 [10 Feb., 1967; 28 April, 1967], No. 6271/ 68. Heading B2E. [Also in Divisions C3 and C7] An electrically-conductive body is coated with a resin by immersing the body in an aqueous dispersion of a hydrophilic resin having an acid number of 8 to 70 and being a linear resin containing carboxyl groups and hydroxyl groups, the latter having been formed by reaction of some of the carboxyl groups with an epoxide and being positioned remote from the backbone of the resin, the resin being in the form of a salt with a base to provide dispersed particles of size less than 0.5 micron, passing a unidirectional current through the dispersion with the body as anode to form a film thereon and baking the film to cure it. The dispersion may also contain a waterinsoluble thermosetting aminoplast resin. The hydrophilic resin may be derived from a polyhydric polyether or an addition polymer. The polyether is preferably an aliphatic polycyolic polyether of the formula where n is 10 to 14. This is partially esterified with a monocarboxylic acid and the hydroxy ester is then reacted with a polybasic acid anhydride to provide carboxyl groups without cross-linking the resin. The product is then reacted with an epoxide in stoichiometric deficiency to form a hydroxy ester containing carboxyl groups. The epoxide is preferably a mono-epoxide but may comprise additionally or solely a polyepoxide, e.g. a diglycidyl ether of bis-phenol. The polyether may also comprise, instead of the above polycyclic compounds, glycidyl ethers of aromatic compounds or of glycols. The addition polymers which may be used are copolymers of hydroxyl-containing ethylenic compounds and carboxylcontaining ethylenic compounds. The first group includes hydroxyalkyl acrylates, methacrylates, maleates, crotonates and norbornene and alkyl, methalkyl and orotyl alcohols. The second group includes acrylic, methacrylic, crotonic, itaconic, maleic and fumaric acids and monobutyl maleate. The copolymers are reacted with epoxides as above. The aminoplast resin may be a urea-, melamine- or benzoguanamine-formaldehyde condensate in amount up to 40% by weight of total resin. A pigment, e.g. TiO 2 , and organic solvents may also be present. The base which may be used to convert the resin to a salt may be ammonia but is preferably an amine. The dispersion preferably contains 5 to 15% solids and may be maintained at a pH of up to 10. Voltages of at least 200 are suitable. In Example 1, a metal tank serves as cathode and steel and aluminium panels treated with zinc phosphate are used as the anodes for coating. The voltage is run up from zero to 500. The film is baked at 400‹ F. to cure.