Interaction of ultraviolet absorbers

Ultraviolet absorbers (UVA) are used in various fields, and their interactions with other additives have been studied. However, the interaction between UVA has not been studied in detail. In this study, the interaction of two UVA having maximum absorption in the range of UV-A (320-400 nm) or UV-B (290-320 nm) was studied. It was found that the photo-oxidation occurs by the fluorescence, which is emitted by a photo-excited UVA-B, if it has enough high energy, that is, its wavelength is within UV-A range. When a UVA-A coexists with such a UVA-B, however, the mixture of both UVA may show a synergism, because the UVA-A absorbs the fluorescence from UVA-B to make it harmless. Particularly, the mixture of hydrogen transfer-type UVA and charge separation-type UVA shows remarkable synergism. The synergistic mechanism is discussed.