Ultraviolet absorbers are the most widely used type of light stabilizers. They are those that can absorb the ultraviolet part of sunlight or fluorescent sources without changing their structure. A class of substances. It can convert high-energy ultraviolet light energy into heat energy or release non-destructive longer light waves, thereby protecting materials from ultraviolet damage.
1. The mechanism of action of ultraviolet absorbers is as follows:
The reason why ultraviolet absorbers can absorb ultraviolet light is because the molecules of this type of compounds contain conjugated π It is caused by two parts: the structure of the electronic system and the structure capable of moving hydrogen atoms. In some cases, it is only the former part. The structural molecules of UV absorbers contain at least one ortho-hydroxyphenyl substituent. In this type of compound, the ortho-hydroxyl group forms a chelate ring with a nitrogen atom or an oxygen atom. After absorbing ultraviolet light, the hydrogen bond breaks and molecular isomerism occurs. , the intramolecular structure undergoes thermal vibration, the hydrogen bond is destroyed, the chelate ring opens, and the intramolecular structure changes, thus converting harmful ultraviolet light into harmless heat energy and releasing it, thus protecting the material.
2. Classification of UV absorbers:
It is understood that UV absorbers are the most widely used type of light stabilizers. According to their structure, They are divided into salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, etc. The most widely used in industry are benzophenones and benzotriazoles.
(1) Benzophenones: Benzophenones UV absorbers are all derivatives of o-hydroxybenzophenone, including monohydroxy, dihydroxy, trihydroxy, tetrahydroxy and other derivatives This type of UV absorber is widely used in the finishing of polyethylene, polypropylene, polyvinyl chloride, ABS, polystyrene, polyamide, and other polymers as well as textile materials. This type of UV absorber is compatible with most high-quality polymers. The polymer has good compatibility. Good light and thermal stability. It does not decompose at 2D0℃, but has strong sublimation properties. It can be used in paints and plastics. The adding amount is 0.1~0.5.
(2) Benzotriazoles: Benzotriazole ultraviolet absorbers have better performance than benzophenones. They can strongly absorb ultraviolet light of 310~385pm and hardly absorb visible light. Its stability is also good, but it is more expensive.
(3) Triazines: Triazine ultraviolet absorbers have high absorption capacity for ultraviolet light of 280~380nm. Compared with benzotriazole stabilizers, it is a type of highly efficient absorption light stabilizer. It is a 2-hydroxyphenyltriazine derivative and contains a hydroxyl group in the ortho position. The ultraviolet absorption effect of this type of compound is related to the number of ortho-hydroxyl groups. The greater the number of ortho-hydroxyl groups, the stronger the ability to absorb ultraviolet rays. Introduce different substituents. It can reduce the alkalinity of the s-triazine ring, but improve the light fastness of the compound and its compatibility with resin. Its effect is better than the commonly used ultraviolet absorbers uV-9 uV-531 and uV-327. Its disadvantage is that it has poor compatibility with polymers and will cause coloring of the applied material.
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