Inorganic pigments also increase the possibility of migration as the operating temperature increases. Therefore, when the operating temperature is close to the thermal stability temperature of the pigment or when the concentration of the pigment reaches saturation, we need to pay special attention to the possibility of migration. The thermal stability of inorganic pigments is an important parameter for plastics. Ultramarine pigment refers to the change in the total performance of the pigment at a certain time, a certain temperature and a certain concentration. The smaller the change, the more stable it is. Of course, the heat resistance of the resin itself should also be noted. Thermoplastic resins have different hot-melt operating temperatures, while thermosetting resins have different curing temperatures. Reasons for poor thermal stability? There are several possible reasons for the color change of inorganic pigments in polymer resins due to heat:
1. Thermal decomposition: When the operating temperature of the inorganic pigment ultramarine pigment is higher than its decomposition temperature, thermal decomposition occurs. For example, Pigment Red 38, its cracking temperature is 218 degrees, and the color immediately changes from red to brown. As for quinacridone, it is slowly cleaved at a temperature of 300: 350C.
2. Chemical substitution reaction: This phenomenon is unusual, but may occur. In polyvinyl chloride, when the temperature exceeds 160C, some methyl azo pigments will produce a color change, and the metal in the pigment molecule can be replaced by barium, cadmium or lead in the additive.
3. Crystal change: Polycrystalline ultramarine pigments will undergo crystal form conversion at high temperature. For example, the alpha form of phthalocyanine blue can be easily converted into a thermally stable beta form at high temperatures.
4. Growth of crystal size: In hot solvents (such as plasticizers), the particle size of the pigment can grow. When the particle size increases, the vividness and coloring power of the product will change relatively.
5. Solubility: When the inorganic pigment is operated at an excessively high temperature, it may sometimes cause partial or complete dissolution, resulting in color changes and performance changes.
