The cause of yellowing of the car coat

The coating (the main component is aliphatic polyurethane acrylic resin), base film (aliphatic TPU), and glue (acrylic pressure-sensitive adhesive) are all polymer materials, so the main factors affecting yellowing are:

The influence of the performance of the polymer structure itself: there is bond energy between the bonds of the polymer macromolecular chain, and when the energy provided is greater than the bond energy, the molecular chain is easy to produce the active center, which will gradually degrade the polymer in the process of use and storage, resulting in yellowing.

Effect of light: When a material absorbs light energy, the molecular chain on the absorbed part will produce carbon-carbon bonds or cleavage of carbon-hydrogen bonds.

Effect of heat and oxygen: The oxidation of the material occurs, and the heat will accelerate the oxidation process of the material. After the formation of peroxide structure, free radicals are easily formed, resulting in discoloration of light and white materials.

Influence of other factors: Aging is also related to the additives added to the material, the presence of moisture, impurities and the processing process, and the inclusion of various chemical or mechanical impurities will reduce the stability of the polymer.

Figure: The yellowing index of aromatic TPU will be higher than 40 after 1000h irradiation with ultraviolet stabilizer even after 1000 hours, while the yellowing index of aliphatic TPU will still be lower than 10 after 1500 irradiation.