Worldwide, paint is the largest filler market for pyrophyllite products. In the U.S., however, this is a minor market, after refractories and ceramics.8 Relatively coarse-ground grades are used to impart mud-crack resistance to high-build coatings such as textured paints and block fillers, and checking, cracking and frosting resistance to exterior latex paints. The platy nature of the pyrophyllite, mica and kaolin components promotes good dispersion by inhibiting the settling of pigments, helps film dry, and increases resistance to film cracking. Figure 1 shows the platy character of a filler-grade pyrophyllite product. The considerable quartz content of these products contributes hardness and wear resistance. Fine-ground grades have also been considered for use in powder coatings and traffic paints. Although the combination of soft, platy and hard, nodular particles in pyrophyllite products provides unique performance possibilities in coatings, their generally off-white color, and the safety concern relating to their high quartz content (up to 60%) have inhibited widespread use.
Chlorite is often associated with talc deposits, and offers many of the same benefits as talc in flatting ability, barrier properties and exterior durability. Chlorite is more hydrophilic, but generally lower in brightness than coatings grade talcs. Its use in coatings is limited.