Pigment loadings in coatings are usually very high to obtain opacity in films that may be thinner than 1.0 mm. This high loading (20 to 60+ percent), unlike plastics, may approach what is known as the “critical pigment volume concentration” (CPVC). CPVC is the largest amount of pigments and fillers a coating vehicle system can tolerate and still maintain film integrity. In plastics, loadings such as these would severely compromise the physical properties of the colored resin, so pigment loadings are intentionally kept low.

Pigment selection for plastics and coatings is significantly different. A major plastic consideration is heat stability. Air dry and oven baked coatings normally do not have to meet the heat stability requirements that plastic pigment must exhibit during plastics processing. Pigments able to tolerate coating heat stability requirements may be unsuitable for thermoplastics.

Matching plastic materials to coated color standards can present difficult metamerism problems since different pigment systems may be employed. Dispersing pigments in many plastics is difficult, and it may be impossible to get a complete and stable dispersion. On the other hand, coatings usually employ dispersion aids in the coating formulation to assist the dispersion. This promotes a complete and stable dispersion.

These significant differences between coatings and plastics makes color matching a plastic material to a coating, textile, ceramic or other material very difficult. The physical property requirements, transparency/opacity differences, colorant differences, pigment loadings, pigment dispersion considerations and many other issues provide barriers to easily matching plastics to non-plastic materials. Obviously, ColorXpress* Services seeks to use all the tools at its disposal to match these targets, but it is important to realize that in some cases the “perfect” color match may be very difficult, if not impossible, to achieve.

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