Pigments and Paint Dispersions

Abstract

Signs of paint application have been found in caves, dating over 100,000 years ago. At that time, paint composition was based on natural resources. Nowadays, composition has changed considerably, because (1) many new constituents became available, (2) knowledge has increased and (3) new challenges and requirements have arisen. This chapter starts by listing the multitude of requirements for modern paints and overviews the relationship between composition and dispersion. The chapter deals with two paint types, viz. the conventional paint based on organic solvents and the modern water-based latex paint. Pigment particles provide the most important contribution to paint in terms of the desired optical properties (color, gloss and hiding power). These are explained and their relationships with refractive index, particle size distribution (PSD) and concentration of pigments and extenders are elucidated. The rheological, non-Newtonian behavior of paint is the second essential contribution to the performance of liquid paints. Adequate tuning of the viscosity at different shear rates is required for best performance at various stages during production and application. Especially where the concentration of solids comes close to their maximum packing density, attention should be paid to both concentration and packing density in relation to the PSD. Adequate de-agglomeration of pigments and extenders is necessary during their dispersion in view of both optical performance and minimum binder requirement. For water-based paints, both size and minimum film formation temperature of the colloidal polymer particles are extra points for attention. The quality of PSD measurement primarily depends on the presence of adequate analysis criteria and good sampling and dispersion methods that fulfill these criteria. Many measurement techniques are available, but they differ in requirements for concentration (dilution), precision, resolution and sensitivity.