Introduction of UV absorber

Sunlight contains a lot of ultraviolet light that is harmful to colored objects. Its wavelength is about 290~460nm. These harmful ultraviolet rays cause the color molecules to decompose and fade through chemical oxidation-reduction reactions. The use of ultraviolet absorbers can effectively prevent or weaken the damage of ultraviolet rays to the protected objects.

UV absorber is a light stabilizer that can absorb the ultraviolet part of sunlight and fluorescent light sources without changing itself. Plastics and other polymer materials produce auto-oxidation reactions under sunlight and fluorescence due to the action of ultraviolet rays, which leads to the degradation and deterioration of polymers, and the deterioration of appearance and mechanical properties. After adding UV absorbers, this high-energy ultraviolet light can be selectively absorbed, turning it into harmless energy and released or consumed. Due to the different types of polymers, the wavelengths of ultraviolet rays that cause them to deteriorate are also different. Different UV absorbers can absorb ultraviolet rays of different wavelengths. When using, UV absorbers should be selected according to the type of polymer.

Types of UV absorber

Common types of UV absorbers include: benzotriazole(such as UV absorber 327), benzophenone(such as UV absorber 531), triazine(such as UV absorber 1164), and hindered amine(such as Light Stabilizer 622).

Benzotriazole UV absorbers are currently the most widely used variety in China, but the application effect of triazine UV absorbers is significantly better than that of benzotriazole. Triazine absorbers have excellent UV absorption properties and other advantages. They can be widely used in polymers, have excellent thermal stability, good processing stability, and acid resistance. In practical applications, triazine UV absorbers have a good synergistic effect with hindered amine light stabilizers. When the two are used together, they have better effects than when they are used alone.

Several commonly seen UV absorbers

(1) UV-531
Light yellow or white crystalline powder. Density 1.160g/cm³ (25℃). Melting point 48~49℃. Soluble in acetone, benzene, ethanol, isopropanol, slightly soluble in dichloroethane, insoluble in water. Solubility in some solvents (g/100g, 25℃) is acetone 74, benzene 72, methanol 2, ethanol (95%) 2.6, n-heptane 40, n-hexane 40.1, water 0.5. As a UV absorber, it can strongly absorb ultraviolet light with a wavelength of 270~330nm. It can be used in various plastics, especially polyethylene, polypropylene, polystyrene, ABS resin, polycarbonate, polyvinyl chloride. It has good compatibility with resins and low volatility. The general dosage is 0.1%~1%. It has a good synergistic effect when used with a small amount of 4,4-thiobis(6-tert-butyl-p-cresol). This product can also be used as a light stabilizer for various coatings.

(2) UV-327
As a UV absorber, its characteristics and uses are similar to those of benzotriazole UV-326. It can strongly absorb ultraviolet rays with a wavelength of 270~380nm, has good chemical stability and extremely low volatility. It has good compatibility with polyolefins. It is particularly suitable for polyethylene and polypropylene. In addition, it can also be used for polyvinyl chloride, polymethyl methacrylate, polyoxymethylene, polyurethane, unsaturated polyester, ABS resin, epoxy resin, cellulose resin, etc. This product has excellent resistance to heat sublimation, washing resistance, gas fading resistance and mechanical property retention. It has a significant synergistic effect when used in combination with antioxidants. It is used to improve the thermal oxidation stability of the product.

(3) UV-9
Light yellow or white crystalline powder. Density 1.324g/cm³. Melting point 62~66℃. Boiling point 150~160℃ (0.67kPa), 220℃ (2.4kPa). Soluble in most organic solvents such as acetone, ketone, benzene, methanol, ethyl acetate, methyl ethyl ketone, ethanol, but insoluble in water. The solubility in some solvents (g/100g, 25℃) is solvent benzene 56.2, n-hexane 4.3, ethanol (95%) 5.8, carbon tetrachloride 34.5, styrene 51.2, DOP 18.7. As a UV absorber, it is suitable for a variety of plastics such as polyvinyl chloride, polyvinylidene chloride, polymethyl methacrylate, unsaturated polyester, ABS resin, cellulose resin, etc. The maximum absorption wavelength range is 280~340nm, and the general dosage is 0.1%~1.5%. It has good thermal stability and does not decompose at 200℃. This product hardly absorbs visible light, so it is suitable for light-colored transparent products. This product can also be used in paints and synthetic rubber.