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 incorporated 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 physically 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 preferred 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 inorganic 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.