Pigment dispersion: II

Pigments are manufactured with the particle size distribution that gives the best compromise of properties, but the particles often become cemented together into aggregates during processing. Breaking these aggregates and forming stable dispersions of optimally sized pigment particles is a critical process in the manufactured of coatings. Making dispersions involves three aspects: (1) wetting, (2) separation, and (3) stabilization. Most authors agree that there are three aspects to dispersion but different terms are used, sometimes with conflicting meanings. Be careful reading papers to know how an author is using the terms. Because of effects of the high surface tension and polarity of water, consideration of pigment dispersion is separated in three sections. The first section (JCT, October 2001, page 145), dispersion in organic media, usually solutions of resins in organic solvent, was discussed. Dispersion in aqueous media is treated in the Formulation of Mill Bases section in this issue. The third section covers the use of Dispersion Equipment and Processes as well as the Evaluation of the Degree of Dispersion.