Color Styling with Genuine Metallics in Plastics

Abstract

Aluminum and bronze pigments offer a wide range of unique coloristic effects, which are described in this chapter in relation to their different optical characteristics. The most brilliant metallic affects are achievable by aluminum or bronze pigments with a large particle size. The brilliance can be increased further by selecting products with a particle size distribution that is as narrow as possible, thereby reducing the amount of fines present. It is also important to allow the flake-like metallic pigments to orient themselves parallel to the surface to optimize the light reflection. It was found that the lower the viscosity of the plastic resin during processing, the more the metal flakes will orient and the better the metallic affect. Clear resins allow to achieve a brighter metallic shade compared to resins, which are turbid like polyolefins. Independent of the resin, the brightness of metallic pigments decreases with decreasing particle size, while their ability to hide increases. Encapsulated metallic pigments were developed to improve their chemical resistance allowing for instance their application in PVC. By encapsulating the bronze pigments, their heat resistance and storage stability was also substantially improved permitting them to be applied in most plastic resins without darkening. When incorporating metallic pigments into plastics care needs to be taken as not to damage the flake during the dispersing process, which would result in reduced brilliance. Since aluminum and bronze pigments disperse very easy, this represents no problem.