Production Equipment Dispersion and Grinding Overview

By Cynthia Challener

The dispersion of pigments in a final paint and coating product signifi­cantly impacts important properties of the formulation. Gloss, weather and chemical resistance, color strength and hiding power, adhesion, and durabil­ity can be enhanced or reduced depending on the nature of the dispersion. On the surface, dispersion-or the mixing of powder into a liquid by rapidly breaking apart agglomerates and uniformly distributing and wetting them­ seems to be one of the simpler aspects of producing paints and coatings. If one looks deeper, however, it quickly becomes apparent that dispersion is a complex process involving a multitude of variables, all of which can affect the desired outcome and, therefore, the quality of the final formulation. In this article, we focus on the different types of equipment used to disperse pigments.

It is important to remember, though, that the choice of dispersing equip­ment is only one of many factors affecting the nature of the dispersion. Pigment selection is also critical. Different pigments exhibit different behav­iors in different formulations, often times even if they appear to be identi­cal. Resins exhibit different wetting properties and rheological behaviors that play a role in the dispersion process. The vehicle often acts as a stabi­lizing agent, too, and a balance between wetting and stabilizing capabilities must be achieved. Many times, the same binder used for pigment disper­sion is used in the overall paint formulation. Yet while this seems to be a reasonable choice, it may not be due to the properties of the binder with re­gard to poor wettability.

The liquid base of a paint and coating is also important. Waterborne coat­ings will have different dispersion behaviors as compared to solvent-based formulations. Different solvents also have different dispersing properties. Surfactants must be considered as well, along with the interactions between all of the different components of a formulation.