Pigment dispersion: II

Pigments are manufactured with the particle size distribution that gives th e best compromise of properties, but the particles often become cemented to gether into aggregates during processing. Breaking these aggregates and for ming 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 a gree that there are three aspects to dispersion but different terms are use d, sometimes with conflicting meanings. Be careful reading papers to know h ow an author is using the terms. Because of effects of the high surface tension and polarity of water, consi deration of pigment dispersion is separated in three sections. The first se ction (JCT, October 2001, page 145), dispersion in organic media, usually s olutions of resins in organic solvent, was discussed. Dispersion in aqueous media is treated in the Formulation of Mill Bases section in this issue. T he third section covers the use of Dispersion Equipment and Processes as we ll as the Evaluation of the Degree of Dispersion.