Surface Treatments
Introduction
Surface treatment of pigments and fillers is used to improve performance in a variety of cosmetic formulations. Surface coatings improve skin feel by smoothing the rough pigment surfaces and reducing oil absorption. Treated pigments compress more easily, permitting formulation of pressed powders with lower binder content, further improving skin feel. In addition to the deagglomeration achieved by the coating process alone, surface characteristics can be modified to optimize wetting in a variety of vehicles. Surface treated pigments and fillers have permitted the development of new product forms, including cosmetically elegant water in oil foundations, cream to powder cosmetics, and powder to liquid formulations.
Surface treatments are applied by a variety of mechanisms:
Chemical Reaction – A permanent chemical bond is formed between the surface treatment molecule and the pigment surface, resulting in an insoluble, shear resistant coating. Chemically bonded treatments are recommended for use in aqueous and anhydrous dispersed systems. Precipitation – The treating compound is either precipitated by the pigment surface or is precipitated by addition of a polyvalent metal ion, forming a continuous, hydrophobic coating. Precipitated coatings are tenacious but may be dissolved from the pigment surface during prolonged heating in oil. Adsorption – Molecules can be adsorbed onto the surface of pigments or fillers, resulting in a shear resistant coating. Electrostatic – Under conditions of high shear, small particles are adhered to the surface of the larger pigment or fillers.
