High quality coatings of high brilliance and color strength are characterized by:
- A perfect pigment dispersion
- Optimal pigment particle size
- Long-term stabilization of the dispersed particle in the formulation.
Most organic pigments show better transparency as dispersion improves, while in the case of the larger particle size inorganic pigments, opacity is improved by good dispersion.
The dispersion process consists of the permanent breaking down of agglomerates into, as far as possible, primary particles. There are four aspects to the dispersion process:
- Deagglomeration is the breaking down of the agglomerates and aggregates by the shear forces of the equipment being employed. A mixture of crushing action and mechanical shearing force is necessary.
- Wetting out occurs at the surface of a pigment when a binder (or surface active agent) sticks to the pigment's surface and acts as a connection between the pigment and the binder. The air and moisture are displaced from the surface. Between the particles of the pigment aggregates, agglomerates are replaced by the resin solution.
Wetting out time depends on the viscosity. Heat produced by the mechanical shearing process causes the temperature of the mixture to rise, thus helping the wetting out process. This increase in temperature reduces the viscosity as well as the effectiveness of deagglomeration which is a well-known phenomenon.
- Distribution demands the pigment to be equally dispersed throughout the binder system. A lower viscosity tends to lead to a more even pigment distribution.
- Stabilization prevents the pigments from re-agglomerating. The pigment dispersion is stabilized by dispersing agents in order to prevent the formation of uncontrolled flocculates. The resultant suspension is stabilized due to the adsorption of binder species or molecules at the pigment surface.