Dual cure cathodic electrocoating process

Claim 1

In a process for electrodeposition from an aqueous electrocoating bath of an electrocoating composition onto a cathode substrate disposed within said bath, said electrocoating composition containing a polymer having pendant mercaptan groups and a polymer having pendant tertiary amine groups in combination with a cross-linking agent in an aqueous dispersion in said bath, said electrocoating composition being cross-linkable upon subsequent curing of the electrocoating on said cathode substrate, the improvement which comprises: (a) providing said electrocoating composition containing (1) a polymer having at least about 1% by weight pendant mercaptan groups, said mercaptan groups being protonated with acid to render said polymer water dispersible in said bath; (2) a polymer having at least about 1% by weight pendant tertiary amine groups, said pendant amine groups being attached to an alpha carbon of said polymer and said pendant amine groups being protonated with acid to render said polymer water dispersible in said bath; (3) at least about 5% bis-maleimide cross-linking agent by weight of said polymers; and (4) at least about 0.5% by weight of an ultraviolet photosensitizer by weight of said polymers; said pendant tertiary amine groups and said pendant mercaptan groups together comprising at least about 5% by weight of both said polymers; (b) applying an electromotive potential through said bath to electrodeposit said polymers, said cross-linking agent and said photosensitizer onto said cathode substrate, said pendant mercaptan groups and said pendant tertiary amine groups becoming de-protonated thereby; and (c) curing said electrocoating on said cathode substrate by heat flowing-out said electrocated composition to cross-link said polymer having pendant mercaptan groups with said bis-maleimide by addition polymerization with said de-protonated pendant mercaptan groups, followed by irradiating with ultraviolet radiation said electrocoated composition to fully cure said electrocoating by free radical polymerization of said bis-maleimide with said alpha carbon of said tertiary amine groups.