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1. Light resistance and weather resistance:
Some plastic products are required to have good light resistance and weather resistance, and certain pigments will change in different degrees under the irradiation of light. Among them, most inorganic pigments have good light resistance. Only a few varieties become darker or lighter due to changes in their crystal form or chemical composition after being irradiated with light. Organic pigments in plastic products will cause pigments after being irradiated with light. The change of molecular configuration affects the saturation and even fades to gray and white.
Weather resistance refers to the stability of a pigment under natural conditions. Generally, the sample is placed outdoors with an inclination angle of 15, and the front is facing south, and the color changes are regularly observed. Light fastness and weather fastness are actually a comprehensive index, usually considering the influence of acids, alkalis and smoke in the atmosphere. The thickness of colored plastic products is also closely related to light resistance.
2. Resistance to acids, alkalis, solvents and chemicals:
Industrial plastic products are often used to store chemicals and as pumps and pipes for transporting acids and alkalis. Therefore, the acid and alkali resistance of the pigments should be considered. Plastic products colored with ultramarine blue and spacer pigments should not be exposed to acids, and cadmium yellow should not be exposed to alkalis. The chemical resistance of pigments in colored plastic products should also include resin decomposition products, other additives in the products such as antioxidants, dispersants, etc., as well as detergents, bleaching agents and other substances in the use environment.
3. Toxicity:
Some colored plastic products are made into various containers, films are used to hold food, and some are made into toys. Therefore, we must pay attention to the toxicity of colorants. For food containers, packaging films, and colorants used in children's toys, all countries have standards for their safety, and toxicity tests can be carried out if necessary.
4. Mix compatibility:
The coloring of plastic products often uses more than two kinds of pigments. Therefore, it is necessary to understand their mixing and compatibility properties. At the same time, it is also necessary to understand whether the pigments react chemically with the additives (auxiliaries) in the plastic.
Generally, when copper and aluminum-containing pigments are mixed with sulfur-containing pigments, the color tends to become dark black. Chromium-containing pigments usually contain lead compounds, so they cannot be used with sulfur-containing stabilizers such as thiodipropionic acid dilaurate, which is a heat stabilizer in polypropylene.
Some lakes, azo organic pigments and chrome yellow will gradually weaken the red color after mixing. This is because the chromate in chrome yellow has strong oxidizing properties, which can cause organic pigments to oxidize and degrade or undergo other changes to fade.