Solution to PU yellowing problem
Now most PU products, whether it is PU curing agent, soft Hard foam, PU leather or PU paint, mainly choose TDI or MDI as raw material. However, whether it is TDI or MDI, since the benzene ring is directly connected to the isocyanate group, the large pi bond on the benzene ring forms a conjugation with the adjacent NCO. , It will cause ammonia to solve the yellowing problem. The most essential method is not to use TDI and MDI, but to use HDI or IPDI and other benzene rings that are not directly connected to NCO as raw materials. However, the ester bonds of these raw materials are decomposed to form aromatic amines, and the benzene nuclei on the aromatic amines are oxidized and rearranged to form chromophoric groups such as quinone structures, so that the produced PU products are easy to yellow and cannot be maintained for a long time. Water white. There are such disadvantages: the price is relatively expensive, the chemical resistance is poor, and the rigidity is not enough… …which greatly limits the promotion of HDI on PU.
Another solution is to fill inert gas in the process of production and storage to isolate the contact with oxygen as much as possible. A more effective method is to add antioxidants and UV absorbers, which can effectively prevent and delay the yellowing of PU. There are many types of antioxidants, and selecting suitable products from them requires certain technical support and experience accumulation.
Classification of antioxidants, one is the main antioxidant: capture peroxide free radicals, mainly hindered phenol antioxidants; the other is auxiliary antioxidants: decompose hydroperoxides, mainly It is phosphite and thioester. In general, according to the production process and raw materials, solvents, additives, fillers of each manufacturer, whether it turns yellow during production or during storage, and the degree of yellowing is different, it is recommended to use different antioxidants.
The main culprit of PU oxidation and yellowing is ultraviolet rays. The source is mainly sunlight. Therefore, especially for customers who need to use the PU produced outdoors, we will recommend it in PU products. Adding a certain amount of ultraviolet absorber can effectively absorb ultraviolet rays and prevent PU from yellowing. Moreover, the use of ultraviolet rays and antioxidants together can have a synergistic effect, and the effect of 1 plus 1 is greater than 2.
Of course, the use of antioxidants and UV absorbers cannot fundamentally solve the problem of yellowing, but within a certain range and within a certain period of time, it can still effectively prevent PU products from oxidative yellowing. Keep the water color of the product transparent and improve the quality of the product.
Polyurethane Materials Co., Ltd.
20 years of industry experience in R&D, production and sales of polyurethane accessories;
10 years of research and development of weather resistance, anti-aging and anti-yellowing of polymer materials , unique formula combination;
Urethane amine catalyst, low odor and low VOC emission expert.
Label:   antioxidant UV absorber
