The coating formed after the automobile is painted, in the actual use process, the yellowing often occurs due to the aging of the coating, which seriously affects its original performance requirements. So why does the paint coating age and yellow? Let’s take a look at the reasons and countermeasures below.

There are three main factors for the aging and yellowing of paint coatings:

1) The main film-forming substances of paint coating

Under the conditions of photo-oxygen and thermal-oxygen, two kinds of irreversible chemical reactions of degradation and cross-linking occur in the basic components of the main film-forming material. Alkyd resins containing drying oil (high degree of unsaturation), coumarone resins, epoxy resins containing aromatic rings, TDI polyurethanes, phenolic resins, etc. have a tendency to yellow. In addition, the coating absorbs ultraviolet light and undergoes Photo-fries rearrangement to generate primary aromatic amines, which are further degraded into yellowing products.

2) The influence of the substrate

2.1 The aging resistance of inorganic pigments in the basic components is poor

The paint that uses lead powder which is chemically reacted with lead oxide, carbon dioxide and water, that is, lead white as the pigment, is prone to yellowing or even blackening. Defensive paints are also prone to oxidative yellowing.

2.2 Influence of organic toner impurities in the return material of the substrate

When paint-coated plastic parts containing organic pigments such as yellow, red, blue, etc., are directly crushed and recycled into granules without fading treatment, or the substrates containing organic impurities in the black masterbatch are painted with a light-colored coating Afterwards, these impurities will escape under the action of light and heat, causing the coating to turn yellow.

3) External environmental factors

External environmental factors include physical factors, chemical factors and biological factors. Among them, sunlight, oxygen, heat, etc. are important factors that cause the aging and yellowing of paint coatings.

To sum up, choosing the correct, high-performance paint and establishing a suitable system for adding the substrate back to the material is an important means to reduce the yellowing of the paint coating.