Water-dispersible coating compositions and process

Claim 1

A process for preparing water-dispersible, block copolymer coating compositions, which process comprises: (1) forming a reaction mixture comprising (i) a water-indispersible, film-forming, organic polymer having an average of at least three hydroxyl groups per molecule (hereinafter referred to as "Reactant A"), (ii) an organic polymer, other than an ethylene-maleic anhydride copolymer, which has an average of at least two carboxylic acid anhydride groups per molecule and which, after hydrolysis and neutralization of at least some of the anhydride groups with a base, is dispersible in water, (hereinafter referred to as "Reactant B"), and (iii) an esterification catalyst; (2) reacting hydroxyl groups of Reactant A and anhydride groups of Reactant B to form ester groups and carboxy groups, such reaction being conducted to the extent necessary to produce a film-forming composition which, after neutralization of at least some of the carboxy groups with a base, is dispersible in a primarily aqueous medium having a pH over 5; and (3) controlling said reaction to prevent gelation of the composition by incorporating in said reaction mixture water or a low molecular weight organic compound containing one or two groups reactive with said anhydride groups.