The Dispersion Process

When producing pigmented coatings the basic physical process is to incorporate extremely fine solid particles into the surrounding vehicle, to produce a colloidal suspension. A colloidal suspension is characterized by its behavior that the finely divided small particles do not settle under the force of gravity.

The Dispersion process can be divided into three individual steps:
1. Wetting of the pigment particles by the fluid components of the mill base
2. Breakdown of the associated particles (agglomerates and aggregates) leading to smaller particle sizes
3. Stabilization of the dispersion preventing renewed association (flocculation)

Pigment particles can be divided into three classes:
– Primary particles = crystal
– Aggregates = Primary particles with surface to
  surface conatct
– Agglomerates = Primary particles touching each other
  via edges and corners

Pigments are classified according to their chemical nature as organic and inorganic pigments. Inorganic pigments are usually coarser than organic pigments, with the exception of carbon blacks and a few special pigment types, such as transparent red oxides. The diameter of the primary particles of inorganic pigments usually ranges between 0.2 and 0.5 microns; while organic pigments lie between 0.03 and 0.08 microns.