Patent GB-1354532-A (GB)
Title: Electrodeposition of resins from aqueous dispersions
IPC: C09D167/00
Filed: 1971-04-19
Abstract: 1354532 Aqueous polymer compositions GENERAL ELECTRIC CO 19 April 1971 [12 March 1970] 21241/71 Heading C3R [Also in Division C7] An electrically conductive substrate is coated with a polymer by a method comprising the sequential steps of (a) preparing a solution of the polymer having free carboxyl groups in a watermiscible organic solvent, the polymer being selected from (1) aromatic polyamic acids derived by reacting an aromatic dianhydride and a diamine, (2) polyesters, (3) polyesterimides, and (4) ethylenemaleic anhydride polymers; (b) adding to the polymer solution a nitrogencontaining base in an amount sufficient to neutralize at least 4% of the free carboxyl groups of the polymer to render the polymer only partially water-soluble; (c) adding water to the base-modified polymer solution in an amount such as to effect precipitation of the polymer to form a stable electrodepositable polymer suspension in the aqueous-organic liquid medium; and (d) electrodepositing a coating of the polymer from the medium on to an electrically conductive substrate immersed therein. Coatings in excess of 2 mil. thick can be obtained. The thickness can be controlled by controlling the amounts of base and water used in preparing the suspension thereby adjusting the ratio of polymer in solution to that in suspension. The suspended polymer particle size may be 0À5 micron or less. The polymer suspension may include a wetting agent such as nonylphenol ethylene oxide adduct or carboxypropyl terminated dimethylsiloxanes. Cations of the base used to neutralize the carboxylic acid portion of the polymer can be removed by an ion exchange resin consisting of a copolymer of styrene and divinylbenzene in its sulphonic acid form. Specified materials which can be coated are Cu, Al, Sn, Zn, Fe and alloys of these materials. Examples of the above mentioned polymer systems are (1) a condensation product of benzophenonetetracarboxylic dianhydride with methylene dianiline; (2) a reaction product of dimethyl terephthalate, ethylene glycol and glycerine with added carboxyl groups through the reaction of trimellitic anhydride; (3) a condensation polymer made from ethylene glycol, terephthalic acid, reaction product of trimellitic anhydride and methylene dianiline, and trishydroxyethylcyanurate which polymer may be reacted with pyromellitic dianhydride; and (4) a partially neutralized half-ester of the copolymer of ethylene and maleic anhydride. For making other polyamic acid polymers (1), many aromatic dianhydride and organic diamine reactants are specified. Some of these diamines contain in their structures Si, O, S, or P. Many organic solvents (e.g. N-methyl-2- pyrrolidone or dimethyl sulphoxide) and nitrogen-containing bases (e.g. an alkanolamine, morpholine or ammonia) are specified. The polymer may be electrodeposited on a Cu wire anode of square cross-section placed between carbon cathodes within a glass container provided with a magnetic stirrer. The Cu wire is degreased, and acid cleaned before coating. Alternatively rectangular Cu wire may be coated using stainless steel cathodes (Example 2), cold drawn iron rods may be coated (Example 3), or Al foil may be coated using a cylindrical Pt cathode (Example 8). Heating of electrodeposited polyamic acid coatings converts them to polyimides.