Why do plastic coloring products fade?

1. Lightfastness of coloring agent The lightfastness of coloring agent directly affects the fading of the product. For outdoor products exposed to strong light, the lightfastness (lightfastness) rating of the coloring agent used is an important indicator, and the lightfastness is poor, and the product is in use. Will fade soon. The light resistance grade of weathering products should be no less than six grades, preferably seven or eight grades, and four or five grades of indoor products.

The light resistance of the carrier resin also has a great influence on the change of color, and the molecular structure of the ultraviolet-induced resin is changed to fade after irradiation. By adding a light stabilizer such as a UV absorber to the master batch, the light resistance of the colorant and the colored plastic article can be improved.

2. The thermal stability of heat-resistant pigments refers to the degree of thermal weight loss, discoloration, and fading of the pigment at processing temperatures. 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 4-10min. .

3. Antioxidation Some organic pigments gradually degrade after macromolecular degradation or other changes after oxidation. The first process is high temperature oxidation during processing, and the second is the occurrence of strong oxidants (such as chromate in chrome yellow). Oxidation. When the lake, azo pigment and chrome yellow are mixed, the red color will gradually decrease.

4. The fading of acid-resistant and alkali-colored plastic products is related to the chemical resistance (acid and alkali resistance, oxidation and reduction resistance) 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.

For the fading of plastic colored products, the above properties of the desired pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives should be comprehensively evaluated according to the processing conditions and application requirements of the plastic products.