Migration of pigments
There are two phenomena of migration of pigments, one is frost spraying, if the pigment is dissolved in plastic products (which is very unlikely), the dissolved pigment moves from the inside to the surface, and the phenomenon is called frosting. The other is color seepage. When plastic products contain plasticizers, some organic pigments can be dissolved in the plasticizers, and when the plasticizers migrate to the surface of the plastics, they carry some organic pigments, so the color seepage occurs. Therefore, many organic pigments can not be used in plastics containing plasticizers, such as polyvinyl chloride or polyurethane. When the plasticizer is added, the high molecular structure is softened, which leads to the increase of the distance between the polymers, so the pigment is easy to migrate. With the increase of operating temperature, pigments also increase the possibility of migration. Therefore, when the operating temperature is close to the thermal stable temperature of the pigment or when the concentration of the pigment reaches saturation, we need to pay special attention to the possibility of migration.