UV absorber

Ultraviolet absorbers are substances that absorb sunlight or the ultraviolet light in a fluorescent source, but whose structure does not change. It can convert high-energy ultraviolet light energy into heat or non-destructive long light waves to protect the substances with UV absorbers from UV damage. It is mainly used as a light stabilizer for plastics, rubber, paints, dyes, etc. to prevent their photodecomposition under long-term exposure to sunlight. It is generally required to have a light color, good miscibility, heat resistance and chemical stability, and low volatility. It is also non-toxic and non-migratory when used in food packaging materials. When the wavelength of ultraviolet light is 290 nm or less, it is completely absorbed by the ozone layer before reaching the ground, and the problem is ultraviolet light of 290 to 400 nm, and the light energy is related to the aging of the polymer. The function of the ultraviolet absorber is to selectively absorb such high-energy ultraviolet rays, which are converted or consumed by energy conversion to become harmless energy. The ultraviolet wavelength which deteriorates depending on the type of the polymer is also different. The wavelengths that can be most affected are: polyethylene 300 nm, polyvinyl chloride 310 nm, polystyrene 318 nm, polyester 325 nm, polypropylene 310 nm, vinyl chloride-vinyl acetate copolymer 322-364 nm, polyacetal 300-320 nm, polycarbonate The ester is 295 nm, the nitrocellulose is 310 nm, the polymethyl methacrylate is 290 to 315 nm, the thermoplastic resin is 290 to 320 nm, and the unsaturated polyester is 325 nm. The sensitive wavelengths of various substances to ultraviolet light are different, and the range of light waves that various ultraviolet absorbers can absorb is also different. Appropriate selection can achieve satisfactory light stability. After the polymer is cured, discoloration occurs under the action of light for a long time. To reduce the effect of light on the polymer, a small amount of UV absorber can be added. Such as 2-hydroxy-4-methoxybenzophenone. Under the action of light, the ultraviolet absorber chelates and opens the ring, absorbing the energy of light; when the chelate ring is closed, the absorbed energy is released by other harmless energy. If the energy required to open the UV absorber is greater, the less energy is transferred to the polymer and the less the effect of light on the polymer. Since the ultraviolet absorber has the above characteristics, it is generally used in a small amount (0.1% to 1%) to exert a good effect. UV absorbers should have the following conditions: 1 can absorb ultraviolet light (especially the wavelength is 290 ~ 400nm); 2 good thermal stability, even in the process of processing will not change due to heat, low volatility; 3 good chemical stability , does not adversely react with other components in the material; 4 is miscible, can be uniformly dispersed in the material, does not spray, does not ooze out; 5 the photochemical stability of the absorbent itself is good, does not decompose, does not change color; Color, non-toxic, odorless; 7 resistant to dipping; 8 cheap, easy to get. The ultraviolet absorbers can be classified into the following categories according to their chemical structures: salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, and the like.