What Causes Color Fading in Blown Plastic Products? Most plastic products are made through blow molding. What factors can influence the color fading in blown plastic? There are many factors that can affect the color fading of plastic products, including the acidity and alkalinity resistance, heat resistance, antioxidant properties, lightfastness, and the characteristics of the resin used in colored plastic products. Below, we will provide a detailed introduction:

Acid and alkali resistance

The fading of colored plastic products and the chemical resistance of the coloring agents (such as acid and alkali resistance, oxidation-reduction resistance) are related. For instance, molybdenum chrome red is resistant to dilute acid but sensitive to alkali, while cadmium yellow is not resistant to acid. These two pigments, along with phenolic resins, have a strong reducing effect on certain coloring agents, severely affecting their heat resistance, weather resistance, and causing fading.

2. Heat resistance

Colorant's thermal stability refers to the extent of heat loss, discoloration, and fading under processing temperatures. Inorganic pigments consist of metal oxides and salts, which have good thermal stability and high heat resistance. Organic compound pigments, however, may undergo molecular structure changes and slight decomposition at certain temperatures. Particularly for PP, PA, and PET products, with processing temperatures above 280°C, when selecting colorants, one must pay attention to both the heat resistance of the pigment and its heat resistance duration, typically requiring a duration of 4 to 10 hours.

3. Antioxidant properties

Certain organic pigments gradually fade due to the degradation of macromolecules or other changes after oxidation. This process involves both high-temperature oxidation during processing and oxidation caused by strong oxidizing agents (such as chromate in chrome yellow). When color precipitates, azo pigments, and chrome yellow are mixed, the red color will gradually fade.

4. Lightfastness

The lightfastness of colorants directly affects the discoloration of products. For outdoor products exposed to strong light, the lightfastness (sunfastness) grade of the colorants used is a critical indicator. A lower lightfastness grade leads to rapid discoloration of the products during use. The lightfastness grade chosen for weather-resistant products should not be lower than grade six, while grade seven or eight can be selected for indoor products. The lightfastness performance of the carrier resin also significantly impacts color changes, with the molecular structure of the resin altering and causing discoloration after exposure to UV rays. Adding UV absorbers and other light stabilizers to the masterbatch can enhance the lightfastness of colorants and colored plastic products.