Nonyellowing cathodic electrocoat

Claim 1

A method of preventing the yellowing of the outermost clear coating of a multicoat top coat coating system comprising a. depositing onto a conductive substrate by cathodic electrodeposition a primer coating comprising at least one layer of an amine-epoxy resin adduct and a blocked cross-linking agent, and curing said primer coating to a hard durable film; b. depositing a pigmented base coat/clear outer coat coating system as a top coat onto the primer coating by initially depositing at least one layer of a pigmented film-forming base coat onto the primer, said base coat comprising pigment and resin, said base coat having a conventional viscosity and said base coat further having a dry film thickness of about 0.7 to about 1.4 mils, and then depositing directly onto the pigmented basecoat at least one layer of a clear film-forming outer coat, said clear coat having a dry film thickness of about 1.2 to about 1.8 mils, and then curing the base coat and clear coat to form the base coat/clear coat top coat coating, wherein the primer coating contains at least one blocked cross-linking agent selected from the group consisting of aliphatic polyisocyanates containing at least six carbon atoms, the isocyanurates of aliphatic polyisocyanates containing at least six carbon atoms, aromatic polyisocyanates having a molecular weight greater than 174, and the isocyanurates of aromatic diisocyanates having a molecular weight greater than 174, the polyisocyanate or isocyanurate blocked with a blocking agent.

Claim 2

A method of preventing the yellowing of the outermost clear coating of a multicoat top coat coating system comprising a. depositing onto a conductive substrate by cathodic electrodeposition a primer coating comprising at least one layer of an amine-epoxy resin adduct and a blocked cross-linking agent, and curing said primer coating to a hard durable film; b. depositing a pigmented base coat/clear outer coat coating system as a top coat onto the primer coating by initially depositing at least one layer of a pigmented film-forming base coat onto the primer, said base coat comprising pigment and resin, said base coat having a conventional viscosity and said base coat further having a dry film thickness of about 0.7 to about 1.4 mils, and then depositing directly onto the pigmented basecoat at least one layer of a clear film-forming outer coat, said clear coat having a dry film thickness of about 1.2 to about 1.8 mils, and then curing the base coat and clear coat to form the base coat/clear coat top coat coating, wherein the primer coating contains at least one blocked cross-linking agent selected from the group consisting of aliphatic polyisocyanates containing at least six carbon atoms, the isocyanurates of aliphatic polyisocyanates containing at least six carbon atoms, aromatic polyisocyanates having a molecular weight greater than 174, and the isocyanurates of aromatic diisocyanates having a molecular weight greater than 174, the polyisocyanate or isocyanurate blocked with a blocking agent.