Main factors affecting the fading of plastic products

Coloured plastic products can fade for several reasons. Light fastness, oxidation resistance, heat resistance, chemical resistance and the properties of the base resin all matter.

1. Light fastness. Products exposed to strong outdoor light need a higher light fastness grade than indoor products. The old-site guidance recommends at least grade 6 outdoors, preferably 7–8, and grades 4–5 indoors. A poorly selected colourant may fade quickly. In a masterbatch, the carrier resin also influences light fastness: ultraviolet light can change the resin structure. UV absorbers or other light stabilisers can improve performance.

2. Thermal stability. This describes pigment weight loss, colour change and fading at processing temperature. Inorganic pigments based on metal oxides and salts generally tolerate heat better. Organic pigments may change structure or decompose at elevated temperatures. Processing PC, PA or PET at temperatures above 280 °C can restrict the choice of organic pigments. Consider both the peak temperature and the exposure period; the old-site article gives a typical heat-resistance period of 4–10 minutes. Some metal ions in pigments can also promote resin degradation. Pigments containing copper, manganese, iron or cobalt may accelerate ageing in polyolefins more than some other metal-containing pigments.

3. Oxidation resistance. Some pigments, especially organic ones, can oxidise under processing heat or in contact with strong oxidants. The resulting reactions can degrade polymers and cause gradual fading. The old-site example is a lake or azo pigment used together with chrome yellow.

4. Acid and alkali resistance. Chemical resistance, including resistance to acids, alkalis and redox reactions, also affects fading. Molybdate red tolerates dilute acid but is sensitive to alkalis, while cadmium yellow is sensitive to acid. Such interactions can reduce heat and weather resistance.

Qingdao Yee Wo Cheong can customise lightfast and ageing-resistant masterbatch for specific product needs.