An excellent automotive paint protection film needs to meet the requirements of various indicators, after a roll of film is manufactured, there are some performance indicators that can be judged by the naked eye, such as crystal points, wrinkles and other problems, and some performance indicators need to be tested with the help of some experiments, such as weather resistance, so why do some car paint protection films appear yellowing problems after pasting? How does it work? How do you do the test experiments?
1. What is yellowing?
The phenomenon of yellowing under long-term exposure to natural sunlight and ultraviolet rays, or under the action of heat, oxygen, stress, trace moisture, impurities, improper processes, etc., is called yellowing.
2. Mechanism of yellowing
Thermal degradation: Mainly with the increase of ambient temperature, the movement of molecular chains intensifies, and when the energy absorbed by molecular chains exceeds the dissociation energy of intermolecular chemical bonds, thermal degradation of molecular chains or group shedding will occur
Photodegradation: UVB photosensitive groups react with polymers to form free radicals, which then react with oxygen to degrade polymers to form chromogenic substances;
Other reactions: The presence of NO2, SO2, H2S, O3 and other pollutants in the air will interact with polyurethane resin, resulting in discoloration, yellowing and other degradation of PU products.
3. Test method - QUV test
The test is carried out with high-power UV energy and high temperature for 15 minutes, and the comparison test is carried out with the top products, which cannot refer to the weather resistance period, and is only used to judge the gap between the product and the top product, and whether the product material selection is correct.
The UV aging resistance tester is used to test according to the European standard, which can be used for reference weather resistance of about 5 years, the standard is △E≤1.5, and the test conditions are as follows:
| Power and wavelength | Temperature and humidity | Time |
| 0.75W,313nm | 60ºC,90% | 2400H |
Taking the TPU original film produced by Kaiyang as an example, it can last for 3000 hours without yellowing after the QUV yellowing resistance test (using UVA bulb, 50ºC ultraviolet irradiation for 4 hours, and 60ºC condensation for 4 hours).
