Criteria for Selection of Pigments

Pigment Apparent Real Pigment Apparent Real 

and Size Distribution of Pigment Particles. As was mentioned previously, the stability of the suspension in the polymer matrix, the covering power, and the color shade are determined by the size of pigment particles. Large particles increase the heterogeneity of the system and they may lessen mechanical properties of plastic products. Practical size limits for pigment particles are 500 and 3000 nm. 

The shape of particles, as was also mentioned, affects the covering power and the permeation to gases and liquids. For example, lamellar pigments are used to color anticorrosive varnishes they form a protective thin layer against gases, liquids, and light. 

The quality of a pigment is also determined by the size distribution of the particles since pigment must fill all the interstices. In the case of a broad distribution, the presence of a little quantity of particles smaller than 500 nm does not affect the uniformity of coloring, but a distribution too close to the colloidal domain results in the formation of spots [12]. The surface of pigment particles affects also rheological properties of suspensions or plastisols [13]. 

Texture. The texture reflects the hardness of the pigment. Examples of soft pigments are anatase, white zinc, and talc. Ultramarine and rutile, are examples of hard-textured pigments. 

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