Plastic coloring products may fade due to a variety of factors. The discoloration of plastic coloring products is related to the light resistance of pigments, dyes, oxidation resistance, heat resistance, acid and alkali resistance, and the characteristics of the resins used. According to the processing conditions and application requirements of plastic products, the above properties of the required pigments, dyes, surfactants, dispersants, carrier resins, and anti-aging aids may be selected after the masterbatch is produced.
1. Lightfastness The lightfastness of the colorant directly affects the fading of the product. Outdoor products exposed to strong light, the lightfastness (lightfastness) rating of the colorant used is an important indicator. The lightfastness grade is poor, and the product will soon be used. fade. The light-resistant grades used for weathering products should not be less than six grades, and the best ones are seven or eight grades. The indoor products can be graded four or five. The light resistance of the carrier resin also has a great influence on the color change, and the UV-induced resin changes its molecular structure and appears faded. Adding light stabilizers such as UV absorbers to the masterbatch can improve the light resistance of colorants and colored plastic products.
2. The thermal stability of heat-resistant pigments refers to the degree of thermal weight loss, discoloration, and discoloration of the pigments at the processing temperature. Inorganic pigments are metal oxides and salts, which have good thermal stability and high heat resistance. Organic pigments undergo molecular structure changes and small amounts of decomposition at a certain temperature. Especially for PP, PA and PET products, the processing temperature is above 280°C. When selecting colorants, one should pay attention to the heat resistance of the pigments. On the other hand, consider the heat-resistance time of the pigments. Usually, the heat-resisting time is 4 to 10 minutes. Hey.
3. Oxidation Resistance Some organic pigments undergo gradual degradation after macromolecule degradation or other changes after oxidation. This process involves high-temperature oxidation during processing. Second, the occurrence of strong oxidants (eg, chromate in chromium yellow) occurs. Oxidation. When lakes, azo pigments and chrome yellow are used in combination, the red color gradually decreases.
4. The discoloration of acid-alkaline stained plastic products is related to the chemical resistance (acid-alkali resistance, oxidation-reduction resistance) of colorants. For example, molybdenum chromium red is resistant to dilute acid, but sensitive to alkali, and cadmium yellow is not resistant to acid. These two pigments and phenolic resins can strongly reduce certain colorants, seriously affecting the heat resistance, weather resistance, and fading of colorants.
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