Currently, the main coloring methods for plastics using colorants include dry mixing, liquid paste coloring, and masterbatch coloring.

① Dry Mixing Coloring Dry mixing coloring is also known as float coloring, powder coloring, and pure pigment coloring. In dry mixing coloring, white oil, turpentine, etc., are generally used as dispersants to allow the colorant to adhere to the resin granules, which can then be directly used in injection molding, extrusion, and other production processes. This method is suitable for production methods with a wide variety of pigments and products in small batches.

Dry mixing coloring is simple to operate, requires less equipment investment, and has low coloring costs. This method is particularly suitable for coloring pearlescent pigments and metallic flake pigments because it reduces the mixing and granulation process, avoiding the destruction of pigment flakes caused by over-mixing, which affects the shimmering coloring effect of the product. However, dry mixing coloring easily generates dust during mixing and feeding, polluting the environment and affecting worker health. Furthermore, when changing colors, the cleaning workload of the molding equipment hopper is large, making operation more troublesome. More importantly, the colorant dispersion effect is poor, therefore it cannot be used to color plastic products with high appearance requirements.

② Liquid Paste Coloring: Liquid paste coloring uses equipment such as a three-roll mill to grind the colorant together with plasticizers, polyols, and fatty acid glycerides (liquid carriers) into a paste-like pigment slurry, which is then used in production. This method produces a finer pigment with good dispersion, preventing pigment particle aggregation during production. Furthermore, the presence of a liquid carrier eliminates dust pollution during the coloring process. While less convenient and more expensive than dry coloring, liquid paste coloring is nearly one-third cheaper than masterbatch coloring. Currently, it is mainly used for coloring plastics such as PVC, UP, and PU.

③ Masterbatch Coloring: Masterbatch is a condensed form of pigment, containing 20%–80% pigment. The pigment is refined and fully dispersed in resin or dispersant to create various colors, supplied to the market in irregular and regular granular forms. Masterbatch coloring results in uniform pigment dispersion, accurate color, and high coloring quality; it is convenient to use, produces almost no dust, maintains a clean production environment, and has high production efficiency, but the cost is higher.