1, Storage stability
The possibility of deterioration may occur when the paint is stored in the packaging container for a long time, especially if there are materials in the paint that are susceptible to bacterial erosion. The manifestation is viscosity decrease, discoloration, odor change, emulsion destruction delamination, etc.
2, Moldy coating film
After the construction of the coating film, the coating film, such as in wet conditions, or by the high humidity in the air climate and absorbed moisture, will also produce microbial growth conditions, thus growing mold on its surface, seriously affecting the appearance of the layer.
The mechanism of light stabilization is as follows:
Another new type of UVA additives are derivatives based on hydroxy phe-ny ls-triazines (HPT) , which have a wide range of UV absorption between 280 and 380 nm, and the mechanism of action is also The hydrogen bond between the ortho hydroxyl group of the phenyl ring attached to the triazine ring and the nitrogen atom will absorb and rearrange light to dissolve harmful ultraviolet rays.
The introduction of the R long-chain group is mainly to improve the compatibility with the coating system and inhibit the penetration and migration. This type of UVA has good light resistance L39J, weak alkalinity, and strong acid resistance . It is one of the ideal UV shielding additives for light stabilization of coatings. This type of UVA has a slightly lower light absorption intensity than BZ T UVA, has a longer duration of action, sasol microcrystalline wax and the light stabilization effect obtained in combination with HALS is usually much higher 41], in traditional solvent-based coatings, powder coatings and light-curing coatings Both are widely used.
As an ideal UVA molecule, in addition to the above-mentioned energy conversion mechanism, its chemical stability and light resistance are also very important indicators, which are related to the problem of the life of UVA additives in the coating. UVA is based on the premise of absorbing ultraviolet light of the appropriate wavelength. Their light absorption performance is often an aspect of concern to formulators. Choose a representative structure from the above-mentioned types of UVA, and use chloroform as the solvent. The UV absorption spectrum is shown in Figure 14-12. .
Due to its high conjugated structure and heteroatom substitution, ultraviolet absorbers have strong absorption in the wavelength range close to 400nm, which is easy to make the paint slightly yellow, which will become a defect in varnish and white paint.
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