The structural molecule of the UV absorber contains at least one ortho hydroxyphenyl substituent. In this kind of compound, the ortho hydroxy forms a chelating ring with nitrogen atom or oxygen atom. After absorbing the UV, the hydrogen bond breaks to produce molecular isomerism, the internal structure of the molecule undergoes thermal vibration, the hydrogen bond is destroyed, the chelating ring opens, and the internal structure of the molecule changes. In this way, harmful UV light is turned into harmless heat energy, which protects the material,
3. In this process, the chelating ring formed in the molecule is the key to its UV absorption function. The energy sensitive range of opening this ring is just within the UV energy range of 290-400nm wavelength.
4. In addition, as an ultraviolet absorber, it must be able to avoid photochemical reaction under the action of ultraviolet light or visible light; Good stability to chemicals and water, and good stability to heat; Low volatility; Good compatibility with polymer materials and no solvent extraction.
Conditions for UV absorber
1. It can strongly absorb ultraviolet light (especially the wavelength is 290-400nm);
2. Good thermal stability, no change due to heat even during processing, and low thermal volatility;
3. Good chemical stability, no adverse reaction with material components in the product;
4. Good miscibility, can be evenly dispersed in the material, without frost spraying and seepage;
5. The absorbent itself has good photochemical stability, does not decompose and does not discolor;
6. Colorless, non-toxic and odorless;
7. Resistance to immersion;
8. Low price and easy to get;
9. Insoluble or insoluble in water.
Classification of UV absorbers
According to the chemical structure, UV absorbers can be divided into salicylates, benzones, benzotriazoles, substituted acrylonitrile, triazines and hindered amines.
This kind of compound is the product with the largest output and most varieties among UV absorbers, and the research at home and abroad is also very active. The synthesis of benzotriazole ultraviolet absorbers is generally to diazotize aromatic amines to form diazonium salts, and diazonium salts and phenolic compounds are coupled to form an intermediate azo pigment, which is then reduced and closed loop.
The output and variety of this type of ultraviolet absorber are only inferior to benzotriazole.
The synthetic route is basically a two-step reaction, namely, the synthesis of 2,4 - dihydroxybenzophenone and the synthesis of alkoxybenzophenone.
Research direction of ultraviolet absorber
1. High molecular mass
Reduce the volatility of auxiliaries and the loss in the reaction process
Groups with different functions in one stabilizer molecule can play multiple stabilizing roles (heat stabilizer, antioxidant...)
The reactive group is introduced into the light stabilizer molecule to bond it with the base polymer during processing, so that it can exist permanently in the polymer material
Application of ultraviolet absorber
1. Due to the different types of polymers, the UV wavelengths that degrade them are also different. Different UV absorbers can absorb different wavelengths of UV. When using, UV absorbers should be selected according to the types of polymers.
2. UV absorbers used in cosmetics can reduce or completely absorb UV rays and protect skin. However, excessive use or use of prohibited ultraviolet absorbers may cause skin irritation.
Composition: phenyl phthalate
Performance and application: colorless crystalline powder. It has a pleasant aromatic smell (holly oil smell). Density 1.250g/cm3, melting point 43, boiling point (1.6kPa) 173. Easily soluble in ether, benzene and chloroform, soluble in ethanol, almost insoluble in water and glycerin. The content is 99%.
This product is a kind of ultraviolet absorber used for plastic products, but the absorption wavelength range is narrow. Acrylic resin products approved by the U.S. Food and Drug Administration for use in contact with food.
UV-531 is a diphenylketone ultraviolet absorber, which can provide good light stabilization protection when used in combination with hindered amine light stabilizer. Good compatibility with polyolefin and soft PVC.
Application: UV-531 is used in combination with hindered amine, mainly used in agricultural film medium low density, linear low density polyethylene and EVA copolymer. It can also be used as a UV shielding agent to protect the contents of industrial/civil packaging. In addition, it can be used in combination with hindered amine light stabilizer for high-density polyethylene molded products, such as turnover boxes. UV-531 can also provide light stabilization protection for other polymers, such as soft PVC and rubber; UV-531 can be used in combination with antioxidant, phosphite ester and other light stabilizers.
Function: UV-531 is especially suitable for thick films (>100 µ m) and thick products. Its saturated steam pressure is low and the loss during processing is small. Low mobility, not easy to spray.
UV absorber JADEWIN BP-2
Chemical name: 2,2 ', 4,4' - tetrahydroxybenzophenone
Molecular formula: C13H10O5
Use: The absorption wavelength range is 320-400nm. There are symmetrical benzene rings and hydroxyl groups on both sides. Its thermo photochemical properties are stable and superior to BP-1. It is an anti ultraviolet additive for oily cosmetics. At present, it is widely used in polyester, coatings, cosmetics, etc. In recent years, its application on fabrics has attracted more and more attention from the textile industry, with a wider range.
UV absorber JADEWIN UV-326
Chemical name: 2 - (2-hydroxy-3-tert-butyl-5-methylphenyl) - 5-chlorobenzotriazole
Molecular formula: C17H18N3OCl
CAS NO. 3896-11-5
Main chemical indexes:
Appearance: pale yellow crystalline powder
Content: ≥ 99%
Melting point: 137-141 ° C
Loss on drying: ≤ 0.5%
Light transmittance: 460nm ≥ 97%
500nm ≥ 98%
Characteristics and purpose:
As a light stabilizer, this product can effectively absorb ultraviolet light with a wavelength of 270-380 nm, and is mainly used for PVC, polystyrene, unsaturated resin, polycarbonate, polymethyl methacrylate, polyethylene, ABS resin, epoxy resin, cellulose resin, etc. This product hardly absorbs visible light, and is especially suitable for colorless transparent and color finished products. The general dosage in thin products is 0.1-0.5%
Excerpted from- Rubber and plastic auxiliary products and application