As a composite material, unsaturated resins are widely used in the fields of coatings, glass fiber reinforced plastics, artificial stones, handicrafts, etc., but the yellowing of unsaturated resins has always been a major problem that plagues manufacturers and customers. According to Foshan Kangdasi Chemical Experts believe that, generally speaking, the yellowing of unsaturated resins is mainly due to the following reasons:
1. In the process of synthesis of unsaturated resin esters, excessively high temperature may easily cause yellowing due to heat aging. Unsaturated resins generally have an esterification temperature of about 200 degrees or higher. At this temperature, the resin is easily changed due to heat aging Yellow, affect the appearance of resin products;
2. Unsaturated polyester resins can easily cause yellowing under long-term ultraviolet irradiation, specifically because the benzene rings present in the resin include aromatic dibasic acid/anhydride and styrene introduced by styrene. Thermal oxygen degradation occurs at high temperature, and the electronic transition on the orbit is easy to occur, which makes the resin appear yellow and produce a yellowing phenomenon;
3. In the production process of unsaturated resins, the poor sealing of the device will cause the raw materials to contact oxygen. The general unsaturated polyester molecular chain contains not only ester groups, hydroxyl groups, carboxyl groups, but also double bonds and aromatics. Ring, trace oxygen can make it thermally oxidatively degraded, thereby making the resin color yellow;
4. The influence of some additives, such as antioxidants, polymerization inhibitors, curing agents, etc., amine antioxidants are easily converted into nitroxide radicals to color the products, commonly used polymerization inhibitors, such as hydroquinone, in In the presence of trace oxygen, it oxidizes to quinones. The quinones themselves have a color, which affects the color of the resin. Some manufacturers still use acyl peroxide-tertiary amine systems and ketone peroxide-metal soap systems. Metal soaps are all colored, making it easy to color the resin.
In short, there are many reasons for resin yellowing, but thermal oxygen and ultraviolet light are the main reasons for yellowing. So how to solve it? Experts of Foshan Kangdasi Chemical pointed out that the use of saturated dibasic acid (or anhydride) instead of aromatic dibasic acid (or anhydride), although it can make the resin lighter to a certain extent, but considering the resin performance, cost and other factors, So this method is not very ideal.
One of the more effective solutions is to fill the inert gas during the production and storage process as far as possible from the contact with oxygen, and add antioxidants and ultraviolet absorbers, which can more effectively prevent and delay the yellowing of polyester. The unique solution recommended by Foshan Kangdasi experts is to choose antioxidants that do not contain amines, but to use a combination of primary and secondary antioxidants. The primary antioxidants are usually hindered phenols, which can capture free radicals; Oxygen agents are phosphite esters, which can chelate metal ions while decomposing hydroperoxides to prevent the resin from oxidizing and discoloring.
If you want to further improve the yellowing resistance and weather resistance, it is recommended to add ultraviolet absorbers to add in. 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 to effectively prevent The reduction of gloss, the generation of cracks, bubbles, and delamination significantly improve the weather resistance of the product, and it has a good synergistic effect when used together with antioxidants.
Finally, relevant experts of neweco Chemical pointed out that the use of antioxidants and ultraviolet absorbers does not completely solve the yellowing problem, but it can effectively prevent the unsaturated polyester products from oxidizing yellowing to a certain extent, thereby maintaining the product. The color of the water is transparent, and the grade of the product is improved.