Ultraviolet absorbers can absorb ultraviolet light due to the structure of the conjugated π-electron system in the molecule of this type of compound and the structure that can move hydrogen atoms. There are also cases where only the first part is present. Ultraviolet absorbers contain at least one ortho-hydroxy phenyl substituent in the structural molecule. In this type of compound, a chelate ring is formed by the ortho-hydroxy group and 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 broken, the chelating ring is opened, and the intramolecular structure changes, so that harmful ultraviolet light is turned into harmless heat energy to be released, thereby protecting the material. For the commonly used benzophenone and For benzotriazole ultraviolet absorbers, the above mechanism can be expressed by the following formula: benzophenone, benzotriazole
In this process, the chelating ring formed in the molecule is the key to its ultraviolet function. The energy sensitive range of opening this ring is exactly the ultraviolet energy range of 290-400 nm wavelength.
In addition, as an ultraviolet absorber, it must be able to not undergo photochemical reactions under the action of ultraviolet light or visible light; it has good stability to chemicals and water, and has good thermal stability; low volatility; compatibility with polymer materials It has good properties and is not extracted by solvents. Only compounds that meet the above conditions can be used as ultraviolet absorbers.
According to chemical structure, UV absorbers can be divided into benzotriazoles, benzophenones, triazines, salicylates and cyanoacrylates, etc.
