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Solution to yellowing problem with UV epoxy resin

　　Epoxy UV light curing resin is widely used in electrical insulation casting, anticorrosive coating, metal bonding and other fields due to its high bonding strength, wide bonding surface, low shrinkage, good stability, excellent electrical insulation, high mechanical strength, good processability and other advantages. In recent years, epoxy UV curing resins as a booming industry.

　　But now most epoxy products have relatively weak weather resistance, especially in the production of epoxy adhesives, LED potting adhesives, epoxy UV curing resin ornament adhesives, etc., the product color requirements are strict, so as to put forward higher requirements on the anti-yellowing performance of the epoxy system.

　　There are many factors that cause easy yellowing of epoxy products: 1, aromatic epoxy UV light curing resin bisphenol A structure is easy to oxidize carbonyl group to form yellowing group; 2, amine curing agent in the free amine components directly and epoxy UV curing resin polymerization, leading to local temperature rise, accelerate yellowing; 3, tertiary amine accelerator, nonylphenol accelerator in hot oxygen, UV irradiation are easy to change color; 4. If the temperature is too high in the reaction process, residual impurities and metal catalysts in the system will induce yellowing.

　　The effective solution is to add antioxidant and ultraviolet absorbent, which can effectively prevent and delay the occurrence of yellowing. However, there are many kinds of antioxidants, from which the selection of suitable products, need some technical support and experience accumulation.

　　Antioxidant classification, one is the main antioxidant: capture peroxide free radicals, mainly blocked phenolic antioxidant; One is auxiliary antioxidant: decomposition of hydrogen peroxide, mainly phosphite ester, thioester. Under normal circumstances, according to the production process of each manufacturer and raw materials, solvents, additives, fillers, which stage of yellowing, yellowing degree is different, and it is recommended to use different antioxidant.

　　The main culprit of oxidation yellowing of epoxy system is ultraviolet ray, which is mainly from sunlight. Therefore, especially in the face of the production of products need to be used outdoors customers, we will recommend to add a certain amount of uv absorbent in the product, can effectively absorb uv, delay yellowing. What's more, ultraviolet light, combined with antioxidants, has a synergistic effect, making one plus one greater than two.

　　Of course, the use of antioxidant and ultraviolet absorbent can not fundamentally solve the problem of yellowing, but in a certain range and a certain period of time, or can effectively prevent the oxidation of the product yellowing, maintain the transparent color of the product, improve the grade of the product.