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Epoxy resin is widely used in electrical insulation casting, anticorrosive coating, metal bonding and other fields because of its high bonding strength, wide bonding area, low shrinkage, good stability, excellent electrical insulation, high mechanical strength, good processability and other advantages.

There are many factors that cause yellowing of epoxy products.

1. The aromatic epoxy bisphenol A structure is easy to oxidize to produce carbonyl groups to form yellowing groups.

2. Free amine in amine curing is polymerized with epoxy resin directly, which results in local temperature rising and yellowing.

3. Tertiary amine accelerators and nonylphenol accelerators are liable to discoloration under thermal oxygen and UV irradiation.

4. In the process of reaction, the temperature is too high. The residual impurities and metal catalysts in the system will induce yellowing.

The effective solution is to add antioxidants and ultraviolet absorbers, which can effectively prevent delayed yellowing. However, there are many kinds of antioxidants, so it needs a certain amount of technology and experience to select suitable products from them.

Classification of antioxidants, one is the main antioxidants: capture of peroxide radicals, mainly hindered phenol antioxidants; one is auxiliary antioxidants: decomposition of hydroperoxide, mainly phosphite esters, thioester. Generally speaking, different antioxidants are recommended according to the production process and raw materials, solvents, additives, fillers, which stages of yellowing, the degree of yellowing is different.

Ultraviolet radiation is the main cause of oxidative yellowing of epoxy system. The main source is sunlight. Therefore, we recommend adding a certain amount of ultraviolet absorbent to the product, especially for the customers who need to use it outdoors. It can effectively absorb ultraviolet radiation and delay yellowing. Moreover, ultraviolet radiation combined with antioxidants can have a synergistic effect, exceeding 1 plus 1 greater than 2.

Of course, the use of antioxidants and ultraviolet absorbers can not fundamentally solve the problem of yellowing, but in a certain range and a certain time, or can effectively prevent product oxidation yellowing, keep the product water color transparent, improve product grade.