The major inorganic pigment used in Ink is kaolin and the formulations are similar to those of paper coating and paint. Kaolin is used in ink to improve ink holdout and to extend both coloured and white pigments. The platelet shape of kaolinite reduces film permeability, which aids in the holdout of the vehicle (binder) on the surface. Fine particle size delaminated kaolin do this most effectively.
Gravure printing represents the biggest ink market for kaolin as it can accept relatively large amounts of kaolin. Kaolin extends the colorant, sharpens dot formation by imparting thixotropic and improves holdout. Kaolin is used in low viscosity inks for flexographic printing. Some kaolin is used to extend colorants and to provide thixotropic in offset printing. Silk screen printing uses relatively thick films that can tolerate the larger particles of calcined kaolin, which provides better light to improve opacity and whiteness. Surface modification of kaolin to make it hydrophobic increases its usefulness in oil-based inks.