How to solve the problem of unsaturated resin color yellowing?
data：2017/12/19 10:23:33
As a composite material, unsaturated polyester resin has been well applied in the fields of paint, glass fiber reinforced plastic, artificial stone, handicrafts and so on. However, the yellow color of unsaturated resin has always been a problem plaguing manufacturers. Usually unsaturated resin yellowing causes include the following:
1, unsaturated resin esterification synthesis process, due to high temperature caused by thermal aging yellowing, unsaturated resin general esterification temperature, 180 ~ 220℃ or even higher, at this temperature resin is easy to yellow due to thermal aging, affecting the appearance of resin products;
2, resin exposure to ultraviolet caused yellowing, the main factor is the benzene ring in the resin (including aromatic dibasic acid/anhydride and styrene introduced benzene ring), the reason may be that the aromatic compounds occur at high temperature thermal oxygen degradation, easy to occur π→π orbital electronic transition, making the resin yellow;
3, resin production process, due to the device sealing is not good and other reasons so that the raw material contact oxygen, general unsaturated polyester molecular chain not only contains ester, hydroxyl, carboxyl, but also contains double bonds and aromatic rings, trace oxygen can make its thermal oxidation degradation, the most obvious performance is the color of the resin yellow.
4, the influence of additives such as antioxidants, inhibitors, curing agents, etc., amine antioxidants are easy to transform into nitrogen oxygen free radicals and make products colored, commonly used inhibitors, such as hydroquinone, oxidized to quinones in the presence of trace oxygen, quinones themselves with color, thus affecting the color of the resin, Curing agent Some manufacturers still use peroxide acyl-tertiary amine system and peroxide ketone - metal soap system, because tertiary amine and metal soap have color, easy to color the resin.
Of course, there are other reasons why resin can turn yellow. In general, hot oxygen and ultraviolet light are the main causes of yellowing. The use of saturated dibasic acid (or acid anhydride) instead of aromatic dibasic acid (or acid anhydride), although it can make the resin color a little lighter to a certain extent, but considering the resin performance, cost and other factors, so this method is not ideal.
According to experts, in addition to filling inert gases in the production and storage process to isolate the contact with oxygen as much as possible, a more effective way is to add antioxidants and ultraviolet absorbers, which can effectively prevent yellowing with delayed polyester. The anti-yellowing solution of unsaturated resin recommended by experts is: the selection of amine-free antioxidants, and the use of a combination of main and auxiliary antioxidants, the main antioxidant is usually blocked phenols, can capture peroxide free radicals; The auxiliary antioxidants are phosphite esters, which can chelate metal ions while decomposing hydroperoxides to prevent resin oxidation and discoloration.
If you want to further improve the yellowing resistance and weather resistance, it is recommended to add ultraviolet absorbers. Adding ultraviolet absorbers can effectively inhibit the yellowing phenomenon of polymer materials under the action of ultraviolet light, and provide excellent protection for the product, effectively prevent the reduction of luster, cracks, bubbles, delamination, and significantly improve the weather resistance of the product. There is a good synergistic effect when used with antioxidants. Of course, the use of antioxidants and ultraviolet absorbers cannot fundamentally solve the yellowing problem, but within a certain range, it can effectively prevent the oxidation yellowing of unsaturated polyester products, maintain the transparency of the product's water color, and improve the grade of the product.
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