The light resistance of the colorant directly affects the fading of the product. For outdoor products exposed to strong light, the light resistance (light fastness) level of the colorant used is an important indicator. The light resistance level is poor, and the product will fade quickly during use. So this is why, for example, anti-glare boards on highways, water horses, etc., will fade in color after being exposed to the sun after a few years of use, but generally when blow molding, quantitative anti-UV ingredients will be added to ensure that Persistence of product color retention time.
2. heat resistance
The thermal stability of the pigment refers to the degree of thermal weight loss, discoloration and fading of the pigment at the processing temperature. The components of inorganic pigments are metal oxides and salts, which have good thermal stability and high heat resistance. The pigments of organic compounds will undergo changes in molecular structure and a small amount of decomposition at a certain temperature. In fact, we need in the production process. If it is a plastic product that needs to be heated at high temperature, we need to choose a pigment with more heat resistance to ensure that the color changes and fades, and the overall appearance of the product is guaranteed.
Some organic pigments gradually fade due to the degradation of macromolecules or other changes after oxidation. This process is one of high temperature oxidation during processing, and the other is the oxidation of strong oxidants (such as chromate in chrome yellow). When lakes, azo pigments are mixed with chrome yellow, the red color will gradually decrease.
4. Acid and alkali resistance
The fading of colored plastic products is related to the chemical resistance (acid and alkali resistance, redox resistance) of the colorant. For example, molybdenum-chromium red is resistant to dilute acid, but is sensitive to alkali, and cadmium yellow is not acid-resistant. These two pigments and phenolic resin have a strong reducing effect on some colorants, which seriously affects the heat resistance and weather resistance of colorants and fades.