Colorant Materials, Additives in Plastic Technology

Abstract

Pigments and dyes are coloring substances, i.e., substances imparting a specific color to the substrate being colored (Carolin et al. 2015). Pigments and dyes are distinctly different types of colorants. A pigment is a finely divided solid which is essentially insoluble in its polymeric application medium. Pigments are incorpo-rated by a dispersion process into the polymer, while it is in a liquid phase, and after the polymer solidifies, the dispersed pigment particles are retained physi-cally within the solid polymer matrix. In contrast, a dye dissolves in the polymeric application medium and is usually retained as a result of an affinity between individual dye molecules and polymer molecules. Pigments are generally pre-ferred to dyes for the coloration of plastics mainly because of their superior fastness properties, especially migration resistance (Maile et al. 2005). Pigments may be introduced into plastics by a variety of methods. Direct dry coloring, in which the pigment is incorporated into the molten polymer often along with other additives using high-shear dispersing equipment, may be used. However, many manufacturers of plastic articles find it more convenient to make use of pre-dispersed concentrates or master batches of pigment in a liquid additive such as a plasticizer or in a compatible resin. Such concentrates are then easily incorporated by mixing into the final polymer composition at an appropriate stage of the processing sequence. Pigments are conveniently classified as either inor-ganic or organic types. The properties of a pigment are primarily dependent on its chemical constitution. However, other factors influence the properties as a result of the fact that pigments are used as solid crystalline particles.