Physical properties composition
Morphology: white to off-white powder, ultra-fine powder
Stability: acid and alkali resistant, heat resistant, UV stable, decomposition temperature >180℃
Wide pH range: pH applicable range between 9 to 14
Although the large molecular weight HALS currently on the market overcomes the problems of compatibility and migration volatilization loss to a certain extent, it is still free in the cured coating after all. In the long term, there is still a hidden danger of migration loss. Liu Xiaoxuan acrylated hindered piperidinol [s 8] to obtain HALS copolymerized monomer, which was added to the light-curing coating formulation in ultra fine ptfe powder a smaller amount, and the light stabilization effect was better than that of free HALS.
Latent light stabilizer
UVA light stabilizers generally require strong absorption above 300nm to be able to shield polymer materials from ultraviolet light. However, in the photocuring system, UVA with strong light absorption will have a light shielding effect on the photoinitiator, resulting in a decrease in the photoinitiation efficiency of the system. In severe cases, the photocuring of the coating may be incomplete and the film performance may not meet the requirements.
Therefore, it is considered to design the UVA light stabilizer into a latent structure, that is, the UVA precursor is sensitive to ultraviolet light and can be slowly transformed into an ultraviolet light absorber with a stable structure under ultraviolet light irradiation. For example, phenyl benzoate with high steric hindrance substitution at the para position has an ultraviolet absorption wavelength below 300 nm. After absorbing ultraviolet light, photo-induced Fries rearrangement occurs  to generate 2-hydroxybenzophenone UVA. The reaction formula is as follows:
The rate of photo-induced Fries rearrangement is much lower than the rate of action of free radical photoinitiators. Therefore, at least in the initial stage of photopolymerization, latent UVA will not cause significant interference. In addition, the phenolic hydroxyl group is only generated after a period of irradiation, and will not inhibit the polymerization of the photocrosslinking carried out in advance. However, the photo-induced Fries rearrangement is not quantitative, and the secondary products produced at the same time of the rearrangement will complicate the reaction and may produce dark by-products.
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