In the use of coatings, people often encounter problems such as flocculation, insufficient color or transparency, poor rheology or stability, which are closely related to the inadequate dispersion of pigments.
In pure theory, “good dispersion” means that each pigment particle in the system is completely free of flocculation, that is, each pigment particle is surrounded by a thin layer of paint binder or solvent. However, in practice, this is difficult to achieve. So, what effect does pigment dispersion have on coating performance? There are several as follows;
Pigment gloss: If the pigment is best dispersed, the gloss can be directly improved. In principle, the gloss depends on the properties of the paint binder. Adding the necessary pigments will only have an adverse effect on the gloss: If the pigment is not optimally dispersed, some pigment aggregates will have an adverse effect on the surface flatness, thereby reducing the gloss due to diffuse scattering of light.
Resistance: Weather resistance and chemical resistance will also be mainly determined by the choice of paint binder. Insufficient dispersion of pigment particles here will also reduce resistance. Pigment particles protruding from the surface provide attack points for chemicals and climatic factors. On the contrary, if the right pigment is correctly dispersed, the resistance of the coating system can only be increased by reflection (TiO2) or absorption of UV radiation (red iron oxide). The right pigment or pigments, if dispersed optimally, can increase the chemical resistance of the binder.
Product shelf life: The shelf life of a coating system depends largely on the quality of the pigment dispersion. The adverse effect of the sedimentation of coarse pigment particles can be easily understood when the proportion of coarse pigment particles in the system is too high. Such stability problems are caused by the so-called “post-wetting” of the pigment or conversely re-flocculation of the pigment. Post-wetting can occur if the pigment is not completely re-flocculated at the beginning of the dispersion to complete the dispersion. The reason for the re-flocculation of a previously properly dispersed pigment dispersion is that the pigment paste is sufficiently stable. This depends largely on the stability of the dispersed binder or the ratio of binder to solvent during the dispersion process. Solvents generally have excellent wetting properties, while binders contribute to stability. The problem is to obtain the ideal combination of wetting (= solvent) and stability (= binder).
Color, tinting strength, transparency and hiding power: All these properties depend largely on the “optimal dispersion” of the pigments used on the surface. In the case of complete dispersion of the pigment, shading pigments can lead to increased hiding power, greater color intensity of the toner (no flocculation); in the case of transparent pigments, better transparency. For all pigments, complete dispersion of the pigment leads to full display of the hue and “color purity” of the color.