Dispersion Phase Diagrams for HEUR-Thickened Acrylic Paint Systems

By Tyler J. Bell, Raymond H. Fernando, Jason Ness, Carrie Street, Karl Booth, Stephen Korenkiewicz

Latex paint formulations are highly complex aqueous dispersions containing latex, pigment, and filler particles in the dispersed phase, and a range of additives such as thickeners, surfactants, and dispersing aids in the continuous aqueous phase. The ability to predict the stability of these dispersions is a highly desirable, but difficult task. In this study, dispersion phase diagrams (DPDs) were constructed for four commercial paint formulations.

A DPD is essentially a roadmap defining the good dispersion region and two different types of phase separation regions for a given paint formulation. The DPDs were constructed as a function of the concentration of two variables—an associative thickener and the external surfactant added to the formulations. The phase separated regions were determined via rheology and syneresis experiments. Each DPD was representative of a fully formulated, commercially available paint with the main components consisting of an all-acrylic latex; a combination of two hydrophobically modified, ethoxylated urethane (HEUR) thickeners; and a surfactant. Other variables included particle size of the latex and the nature of surfactant (nonionic vs anionic).

This approach was found to be successful in determining highly reliable representations of the different regions of dispersion for each system. Another part of the study involved using contour plots of the physical properties of the wet and dry paint samples, which were excellent for observing trends in gloss, infrared backscatter (IRBS), viscosity, and conductivity caused by the surfactant, thickener, or latex used in the system.