In order to prevent the aging of polymer materials, light stabilizers are usually used. The main light stabilizers currently used include light shielding agents, ultraviolet light absorbers, and energy transfer agents. wait.
1. Light shielding agent
Light-shielding agent mainly uses pigments to color high-molecular materials. Can reflect ultraviolet light. Preventing it from entering the interior of the polymer is like establishing a barrier between light and polymer materials. In this way, photo-oxidative aging can be avoided. Carbon black, oxygen. Zinc and other inorganic pigments, such as cadmium yellow, cadmium red, titanium white, and organic pigments, such as titanium blue and titanium green, can be used as light shielding agents, among which carbon black is the most effective. Add 1% carbon black to polyethylene. The service life is more than 30 years; due to the extensive use of carbon black (as reinforcing agent) in rubber. So the photostability is better. There is no need to use light stabilizer for it.
Due to the aging effect of ultraviolet light, it mainly produces harmful substances noodle. Therefore, coatings with the above pigments can also be used as coatings to achieve protection purposes. In addition, weather-resistant plastics, such as polytetrafluoroethylene, can also be used as a protective layer.
2. UV absorber
UV absorbers are the most important type of light stabilizers. According to their chemical structures, they can be divided into phenyl salicylate, o-hydroxy: benzophenone, O-HydroxybenzoM and triazine and other children,
This is the oldest type of ultraviolet absorber. The advantage is It is cheap and has good compatibility with resin. The disadvantage is that the ultraviolet absorption rate is low, the absorption wavelength band is narrow (below 340nm), and it is unstable to ultraviolet light. It will be emitted after illumination, and it will obviously absorb visible light, causing the product to be colored. Can be used for polyethylene, PVC, polyvinylidene chloride, polystyrene, polyester, cellulose ester, etc. The general dosage is 0.2%~0.5%. Individually it can reach 4%.
(2) Benzophenones Benzophenones are the most important ultraviolet absorbers. It has the structure of o-hydroxybenzophenone.
The synthesis of this type of compound is to first prepare the appropriate phenol, and then in the phenol The benzene ring is acylated with trichlorotoluene. Such as the production of 2-hydroxy-4-n-octyloxybenzophenone (UV-531).
