Plastic colored products will fade due to many factors. The fading of colored plastic products is related to the light resistance, oxygen resistance, heat resistance, acid and alkali resistance of the toner, and the characteristics of the resin used.
The following is a detailed analysis of the fading factors of plastic coloring:
1. Lightfastness of the colorant
The light fastness of the colorant directly affects the fading of the product. For outdoor products exposed to strong light, the light fastness (light fastness) level requirement of the colorant used is an important indicator. The light fastness level is poor, and the product will quickly fade during use. The light resistance grade selected for weather-resistant products should not be lower than six grades, preferably seven or eight grades, and indoor products can choose four or five grades.
The light resistance of the carrier resin also has a great influence on the color change, and the molecular structure of the resin changes and fades after being irradiated by ultraviolet rays. Adding light stabilizers such as ultraviolet absorbers to the masterbatch can improve the light resistance of colorants and colored plastic products.
2. Heat resistance
The thermal stability of a heat-resistant pigment refers to the degree of thermal weight loss, discoloration, and fading of the pigment at the processing temperature.
Inorganic pigments are composed of metal oxides and salts, with good thermal stability and high heat resistance. The pigments of organic compounds will undergo molecular structure changes and a small amount of decomposition at a certain temperature. Especially for PP, PA, PET products, the processing temperature is above 280℃. When selecting colorants, one should pay attention to the heat resistance of the pigment, and the heat resistance time of the pigment should be considered on the other hand. The heat resistance time is usually 4-10min. .
3. Antioxidant
Some organic pigments undergo macromolecular degradation or other changes after oxidation and gradually fade. This process is high temperature oxidation during processing, and oxidation when encountering strong oxidants (such as chromate in chrome yellow). After the lake, azo pigment and chrome yellow are used in combination, the red color will gradually fade.
4. Acid and alkali resistance
The fading of colored plastic products is related to the chemical resistance of the colorant (acid and alkali resistance, oxidation-reduction resistance). For example, molybdenum chrome red is resistant to dilute acid, but is sensitive to alkalis, and cadmium yellow is not acid resistant. These two pigments and phenolic resins have a strong reducing effect on certain colorants, which seriously affects the heat resistance and weather resistance of the colorants and causes fading.
For the fading of plastic colored products, it should be selected according to the processing conditions and use requirements of the plastic products, after comprehensive evaluation of the above-mentioned properties of the required pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives.
