Predicting the Water-Sensitivity of Film-Forming Coatings Additives by Water Vapor Sorption: With Application to Thickeners and Rheology Modifiers

摘要

Although present in relatively low concentrations, additives such as thickeners, rheology modifiers, dispers-ants, and surfactants can contribute to the water sensitivity of coatings due to their inherent affinity for moisture. Because of the number of additives often present and the variable response possible within different formulations, a method was sought to examine the moisture affinity of individual additives in the absence of other coating components. A simple gravimetric procedure with high sensitivity and good repeatability was developed based on water vapor sorption (WVS). In this paper, the technique is applied to a variety of commercial thickeners and rheology modifiers commonly employed in water-borne coatings. Although alkali-swellable emulsions of the conventional (ASE) and associative (HASE) varieties are generally considered to be more water sensitive than nonionic thickener types, these car-boxyl functional polymers in their acid form actually showed much lower moisture affinities. WVS for the anionic ASE and HASE thickeners was a function of polymer composition, type of counter ion, base volatility, dry time, and the state of neutralization prior to conducting the test.