Cathodic electrodeposition coatings containing an antioxidant additive
AssigneeE. I. Du Pont de Nemours and Company
InventorsDing Y. Chung, Kenneth S. Kirshenbaum
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Abstract
An improved aqueous electrocoating composition having a binder of an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent; wherein the improvement is the use of an antioxidant additive which is a combination of a phenolic antioxidant and a sulfur-containing antioxidant. The additive reduces overbake yellowing of the composition and the intercoat delamination of the composition and the topcoat upon exterior exposure.
Claims8
In a cathodic electrocoating composition comprising an aqueous carrier having dispersed therein a film forming binder comprising an epoxy-amine adduct and a blocked aromatic polyisocyanate crosslinking agent;
- wherein the improvement comprises the use of about 0.1-10% by weight, based on the weight of the binder, of an antioxidant mixture consisting of a phenolic antioxidant and a sulfur containing antioxidant;
- whereby the antioxidant mixture substantially reduces yellowing of the composition after electrodeposition to a substrate and subsequent baking and substantially reduces delamination of a topcoat applied to the electrodeposited composition.
In a method of preparing a cathodic electrocoating composition comprising the following steps:
- (a) preparing an epoxy-amine adduct;
- (b) preparing a blocked aromatic polyisocyanate crosslinking agent;
- (c) blending the epoxy-amine adduct with the blocked aromatic polyisocyanate crosslinking agent;
- (d) neutralizing the epoxy-amine adduct within an organic acid to form an emulsion of film forming binder;
- (e) adding about 0.1-10% by weight, based on the weight of this binder, of an antioxidant mixture to the electrocoating composition consisting of a phenolic antioxidant and a sulfurcontaining antioxidant;
- whereby the antioxidant mixture substantially reduces yellowing of the composition after electrodeposition to a substrate and subsequent baking and substantially reduces delamination of a topcoat applied to the electrodeposited composition.
Dependencies are inferred from the claim text.