TONY O’LENICK
Nascent Technologies Corporation, Lawrenceville Ga, USA

Abstract

In the personal care market, the color cosmetic segment is perhaps the most technically challenging class of products a formulator faces. This class of products generally includes several types of oils, silicones, wetting agents, film formers and pigments. The emulsion is generally invert (water in oil) and the consumer expectations are high. Since invert emulsions are very complicated and difficult, the formulator needs an approach to look at potential approaches to address emulsion instability. Additionally, the aesthetics include cushion, play time and feel of the invert emulsion, but also the feel of the final film after evaporation of a suitable solvent. Pigments are critical components that need to be properly wetted out for proper aesthetics of formulation out of the bottle, after evaporation of the volatile solvent and to deliver acceptable the proper color and color stability on the skin.
This article will suggest some screening techniques for pigmented emulsions.

Dispersions

Cosmetic dispersions typically contain a solid pigment(s). Typically, these solid pigments are inorganic particles.  Particle size of 3 – 5 mm is necessary for optimum color development.  Some examples of these inorganic particles are: titanium dioxide (TiO₂), zinc oxide (ZnO) and iron oxide (Fe₂O₃). These particles are insoluble in the formulation. Therefore, a uniform dispersion of these particles must be achieved in order to have a successful cosmetic product.  

The dispersion of these pigments becomes a critical part of the formulation.  Creating this dispersion is tricky, pigments cannot be simply stirred into the solvent (1).  To make it easier for the pigments to be incorporated into the solvent, a number of pigment treatments are available commercially. These “treatments” are typically a surface modification of the pigment, which makes the pigment easily dispersed into a media. There are two ways of treating the surface of a particle: covalently bonding an organic moiety onto the surface, or physically coating the particle’s surface with a surfactant. These surface treatments allo ...