Why Do Colored Plastic Products Fade?
Colored plastic products may fade for a variety of reasons. The color stability of a plastic part is not determined by the pigment alone. It is related to the lightfastness of the pigment or dye, as well as its resistance to heat, oxidation, acids, alkalis, and the properties of the carrier resin used in the formulation.
For this reason, before producing a masterbatch or colored plastic product, the relevant properties of the selected pigment, dye, dispersant, carrier resin, and anti-aging additives should be evaluated together according to the processing conditions and final application requirements of the product.
1. Lightfastness and UV Resistance
The lightfastness of a colorant has a direct effect on whether a plastic product will fade during use. If a product is exposed to strong sunlight or outdoor conditions, poor lightfastness will cause the color to fade more quickly. For outdoor plastic products, the lightfastness grade of the colorant should generally be no lower than grade 6, and grade 7 or 8 is usually preferred. For indoor products, grade 4 or 5 may be acceptable depending on the application.
The light resistance of the carrier resin also affects color stability. Under ultraviolet exposure, the molecular structure of some resins may degrade or change, which can also contribute to fading. In practice, adding light stabilizers such as UV absorbers to the masterbatch can help improve the light resistance of both the colorant and the finished plastic product.
2. Thermal Stability and Heat Resistance
The thermal stability of a pigment refers to its resistance to heat loss, discoloration, and fading at the processing temperature. Inorganic pigments, which are often based on metal oxides or salts, usually have better heat resistance and stronger thermal stability. Organic pigments, however, may experience molecular structure changes or partial decomposition when exposed to elevated temperatures.
This is especially important for plastic materials such as PP, PA, and PET, where processing temperatures may exceed 280 degrees Celsius. When selecting a colorant for these materials, attention should be paid not only to the heat resistance temperature of the pigment, but also to its heat resistance duration. In many cases, the required heat resistance time is about 4 to 10 minutes depending on the actual process.
3. Oxidation Resistance
Some organic pigments gradually fade because of oxidation. This may happen during high-temperature processing or when the colorant is exposed to strong oxidizing substances. Under these conditions, the molecular structure of the pigment may degrade, leading to color change or reduced color stability over time.
For example, when certain lake pigments or azo pigments are mixed with strongly oxidizing components, the final color performance may become less stable. This is one reason why pigment compatibility must be reviewed carefully before mass production begins.
4. Resistance to Acids and Alkalis
The fading of colored plastic products is also related to the chemical resistance of the selected colorants. Some pigments are resistant to acids but sensitive to alkalis, while others may behave in the opposite way. If the product is used in an environment involving chemicals, cleaning agents, moisture, or specific resin systems, poor chemical compatibility may lead to fading, discoloration, or loss of performance.
For example, certain red and yellow pigments may show reduced stability when exposed to acids, alkalis, or reducing systems in the resin formulation. These effects may also reduce the weather resistance and heat resistance of the final colored product.
Why Masterbatch Formulation Matters
Because color fading is influenced by multiple factors, good color performance depends on the complete masterbatch system rather than on a single pigment choice. Pigments, dyes, surfactants, dispersants, carrier resins, UV stabilizers, and anti-aging additives all need to be selected as a compatible system according to the actual product application.
For outdoor products, long-term color stability usually requires stronger lightfastness and UV protection. For engineering plastic parts, heat resistance during molding becomes especially important. For products exposed to chemicals or harsh environments, acid and alkali resistance must also be considered in advance.
Plastic Part Manufacturing Support from FITMOLD
FITMOLD supports custom plastic part development and production for projects that require practical consideration of material performance, manufacturability, and final product quality. For colored plastic parts, early evaluation of material selection, color stability, and processing conditions is important in order to reduce fading risk and improve product reliability.
If you are looking for a manufacturing partner for custom plastic parts and injection mold development, FITMOLD can support your project from design review to tooling and production.
Contact us: sales@fitmold.com