Second, the thermal stability of the heat-resistant pigment refers to the degree of heat loss, discoloration, and fading of the pigment at the processing temperature. The inorganic pigment is composed of metal oxides and salts, has good thermal stability and high heat resistance. However, the pigment of an organic compound undergoes a change in molecular structure and a small amount of decomposition at a certain temperature.
Especially for PP, PA, PET products, the processing temperature is above 280 °C. On the one hand, when selecting the coloring agent, attention should be paid to the heat resistance of the pigment. On the one hand, the heat resistance time of the pigment should be considered, and the heat resistance time is usually required to be 4-10 m.
Third, the oxidation resistance of some organic pigments after the oxidation of macromolecules undergoes degradation or other changes and gradually fade, this process is the high temperature oxidation in processing, and the second is the strong oxidant (such as chromate in chrome yellow) Oxidation that occurs. When the lake, azo pigment and chrome yellow are mixed, the red color will gradually decrease.
Fourth, the fading of acid-resistant and alkali-colored plastic products is related to the chemical resistance (acid and alkali resistance, oxidation-reduction) of colorants. For example, molybdenum chrome red is resistant to dilute acid, but sensitive to alkali, and cadmium yellow is not resistant to acid. These two pigments and phenolic resin have strong reduction effect on certain colorants, which seriously affect the heat resistance, weather resistance and fading of the colorant.