Epoxy UV curing resin is widely used in the fields of electrical insulation casting, anti-corrosion coating, metal bonding and so on because of its high bonding strength, wide bonding surface, low shrinkage, good stability, excellent electrical insulation, high mechanical strength and good processability. In recent years, epoxy UV curing resin as an industry has flourished.
However, at present, the weather resistance of most epoxy products is relatively weak, especially in the production of epoxy adhesive, led potting adhesive, epoxy UV curing resin jewelry adhesive, etc., the product color requirements are strict, which also puts forward higher requirements for the anti yellowing performance of epoxy system.
There are many factors that cause the yellowing of epoxy products: 1. The bisphenol a structure of aromatic epoxy UV curing resin is easy to oxidize to produce carbonyl to form yellowing group; 2. The free amine component in amine curing agent is directly polymerized with epoxy UV curing resin, resulting in local temperature rise and accelerated yellowing; 3. Tertiary amine accelerators and nonylphenol accelerators are easy to change color under hot oxygen and UV irradiation; 4. If the temperature is too high during the reaction, the residual impurities and metal catalysts in the system will induce yellowing.
The effective solution is to add antioxidant and ultraviolet absorber, which can effectively prevent and delay yellowing. However, there are many kinds of antioxidants, and selecting suitable products requires certain technical support and experience accumulation.
Classification of antioxidants: one is the main antioxidant: capture peroxide free radicals, mainly hindered phenol antioxidants; One is auxiliary antioxidant: decompose hydroperoxides, mainly phosphite esters and thioesters. In general, different antioxidants are recommended according to the production process, raw materials, solvents, additives and fillers of various manufacturers, which stage of yellowing and the degree of yellowing.
Ultraviolet light is also an important culprit causing oxidation yellowing of epoxy system, mainly from sunlight. Therefore, especially for customers whose products need to be used outdoors, we will recommend adding a certain amount of UV absorber to the products, which can effectively absorb UV and delay yellowing. Moreover, the use of ultraviolet and antioxidant can play a synergistic effect, with the effect that 1 plus 1 is greater than 2.
Of course, the use of antioxidants and ultraviolet absorbers can not fundamentally solve the problem of yellowing, but within a certain range and time, it can effectively prevent the oxidation yellowing of products, keep the water color of products transparent and improve the grade of products.
Post time: May-09-2022