Brief Analysis of Anti-yellowing Test of TPU Invisible Car Cover

Anti-yellowing is one of the most important properties of invisible car cover. As the name implies, it means that the car cover has no obvious yellowing defects within a certain period of time. It is the phenomenon that the color of the car cover turns yellow under long-term exposure to natural sunlight, ultraviolet rays, or under the action of heat, oxygen, stress, trace moisture, impurities, improper processes, etc.
1. Causes of yellowing of car cover
The coating (main component is aliphatic polyurethane acrylic resin), base film (aliphatic TPU), and glue (acrylic pressure-sensitive adhesive) of invisible car cover 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 polymer macromolecular chain bonds. When the energy provided is greater than the bond energy, the molecular chain is easy to produce active centers, which will cause the polymer to gradually degrade and yellow during use and storage. The influence of light: When the material absorbs light energy, the molecular chain at the absorption site will produce carbon-carbon bonds or carbon-hydrogen bonds. The influence of heat and oxygen: The material undergoes oxidation, and heat will accelerate the oxidation process of the material. After the peroxide structure is formed, it is easy to form free radicals, causing light and white materials to discolor. Influence of other factors: Aging is also related to the additives added to the material, the presence of moisture, impurities and processing technology. The mixing of various chemical or mechanical impurities will reduce the stability of the polymer.
2. Anti-yellowing test method
Understanding the cause of yellowing of TPU car cover, it is not difficult to understand its anti-yellowing test method. Anti-yellowing test, also known as weather resistance test, often uses ultraviolet aging test machine to simulate sunlight exposure, accelerate the aging process, and then calculate the yellowing color difference △E*ab before and after the test.
△E*ab is used to measure the degree of color deviation from the standard, which can also be called color deviation, or simply color difference. △E*ab＜2, almost no yellowing color difference; △E*ab＜4, there is yellowing color difference, but it is not very obvious; △E*ab＞6, yellowing color difference is obvious;
In other words, the simplest configuration of anti-yellowing test is a UV test machine + test operation manual.
The above is the summary of the anti-yellowing test of TPU invisible car cover, for reference only.