Product name: Dry film anti-mildew agent
Active substance content: 45%
Main application: used in oil-based coatings, polyethylene, polyurethane and other polymers and good compatibility with plastics
Decker et al. reported a benzotriazole UVA precursor 2 (2′-acetoxy-5′-methylphenyl) benzotriazole (Ⅰ), which caused photo-induced Fries weight under ultraviolet light irradiation. Exhaust, slowly form effective UVA 2 (2′-hydroxy-3′-acetyl 5′-methylphenyl) benzotriazole (Ⅱ), photo-induced transformation process and UV absorption tracking curve (in PMMA cured film) .
The conversion process of latent UVA is the opposite of photobleaching, that is, as the conversion degree increases, the UVA concentration in the film increases, and the light transmittance becomes lower and lower. Most of the effective photons are absorbed by the formed UVA, and the remaining precursors are converted more and more. The more difficult it is, the conversion of the precursor is a gradually slower process, so it is difficult to expect that after the photocuring process is completed, a sufficiently high concentration of UVA virgin ptfe powder will be formed in the film. In the long-term use process, the precursor may still be The transition occurs slowly.
The above types of light stabilizers have varying degrees of effect on improving the light stabilization of polymer coatings. Among them, excited state quenchers have obvious selectivity in application objects due to the energy matching problem. Other types of light stabilizers have a wide range of applications, but for coatings of different systems, screening tests are usually carried out to determine the matching light stabilizers. In coating light stabilization work, two light stabilizers of different mechanisms are often combined to obtain a more effective and lasting light stabilization effect on the coating.
The more classic combination is to use UVA and HALS together. The former protects the coating from photo-oxidation by filtering out harmful ultraviolet light in the sun, but it is inevitable that it will inevitably cause consumable secondary effects during the cycle. Grade transformation, irreversible transformations such as fading and photolysis occur, the effective concentration is reduced, and the light stabilization effect is gradually lost. Especially under the action of free radicals and peroxides, the phenolic structure of UVA will be attacked for the first time, and the intramolecular hydrogen bonds will be destroyed. Destroy, lose the function of cyclically dissolving harmful ultraviolet rays. HALS removes free radicals and peroxides in the coating, blocks the photo-oxidation process, maintains the gloss of the coating, and inhibits yellowing and embrittlement. However, the nitroxide radicals produced by HALS are colored and can absorb ultraviolet light, which may cause photolysis and consumption.
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