Coating compositions containing starch half-esters and process for preparing same

Abstract

This invention is directed to aqueous compositions and to the process for preparing same which comprises a dispersion of polymeric resin binders and pigments in an aqueous system with a dispersant. The dispersant consists of half-esters of starch derived from (a) low molecular weight hydrolyzed starch having a plurality of anhydroglucose units or a derivative of said starch and (b) at least about 0.25 mole of at least one cyclic anhydride of a polycarboxylic acid for each anhydroglucose unit of the hydrolyzed starch and/or its derivatives. These half-ester starch dispersants are characterized as having pendant carboxyl groups and average molecular weights ranging up to about 100,000 with a high degree of substitution, i.e. wherein on an average of about 0.25 to 3.0 of the hydroxyl groups of each anhydroglucose unit are esterified. The unreacted carboxyl groups pendant from the backbone of the starch esters may be further reacted, i.e. neutralized with various reagents including, for example, metal compounds such as the alkali and alkaline earth metal hydroxides, amines, ammonia, alcohols, etc. to various degrees depending upon the hydrophilic/hydrophobic character desired of the products.

Dependencies are inferred from the claim text.