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What are the reasons for the fading of plastic mold products

by:Vowin Rapid Prototyping     2023-02-09
In life, we often see that some plastic products fade after being used for a long time. This is actually related to the raw materials of plastic mold products and dyes. The raw materials of plastic parts should choose the correct pigment in the process of injection molding. When producing masterbatches, the above-mentioned properties of pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives can be selected after comprehensive evaluation, so as to ensure that plastic parts are not easy to fade after long-term use.

1. Lightfastness of lightfastness colorants

Light fastness 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 of the colorant used is an important indicator. If the light fastness level is poor, the product will fade quickly during use.

The light resistance grade of weather-resistant products should not be lower than grade 6, preferably grade 7 or 8, and indoor products can choose grade 4 or 5. The light resistance of the carrier resin also has a great influence on the color change, and the molecular structure of the resin caused by ultraviolet light will change and fade. Adding light stabilizers such as ultraviolet absorbers to the masterbatch can improve the light resistance of colorants and colored plastic products.

2. Thermal stability of heat-resistant pigments

The thermal stability of heat-resistant pigments refers to the degree of thermal weight loss, discoloration and fading of pigments at the processing temperature. The components of inorganic pigments are metal oxides and salts, which have good thermal stability and high heat resistance. The pigments of organic compounds will undergo changes in molecular structure and a small amount of decomposition at a certain temperature. Especially for PP, PA, and PET products, the processing temperature is above 280°C. When selecting colorants, we must pay attention to the heat resistance of the pigment on the one hand, and consider the heat resistance time of the pigment on the other hand.

3. Oxidation resistance

After oxidation, some organic pigments undergo macromolecule degradation or other changes and gradually fade. The first process is high-temperature oxidation during processing, and the second is oxidation that occurs when encountering strong oxidants (such as chromate in chrome yellow). After mixing lakes, azo pigments and chrome yellow, the red color will gradually fade.

4. Acid and alkali resistant colored plastic products

The fading of acid and alkali resistant colored plastic products is related to the chemical resistance of the colorant (acid and alkali resistance, redox resistance). For example, molybdenum chrome red is resistant to dilute acid, but is sensitive to alkali, and cadmium yellow is not acid resistant. These two pigments and phenolic resin have a strong reducing effect on some colorants, which seriously affect the heat resistance and weather resistance of the colorant and cause fading.

For the fading of plastic colored products, the above-mentioned properties of pigments, dyes, surfactants, dispersants, carrier resins and anti-aging additives should be comprehensively evaluated when producing masterbatches according to the processing conditions and use requirements of plastic products available only later.
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