whitening principle | fluorescent whitening agent 191 absorbs high energy near-ultraviolet light, the excited molecule then transitions to a lower energy ground state and emits fluorescence. Due to the energy loss, the wavelength of the fluorescent radiation becomes longer, and the blue light is about 450nm. The yellow color of the yellow article can be compensated by the blue light reflected by the fluorescent whitening agent, thereby increasing the apparent whiteness of the article. Since the intensity of the emitted light exceeds the intensity of the original visible light projected on the object to be treated, a whitening effect of slightly colored light is produced. Fluorescent whitening agent 191 with practical value, in addition to absorbing ultraviolet light and emitting purple blue fluorescence and high fluorescence efficiency, must also be close to colorless or yellowish, with the characteristics of ordinary dyes, it has good affinity, good solubility or dispersion properties and good fastness properties such as washing resistance, light resistance and hot resistance to whitened substances such as fibers. The whitening property of fluorescent whitening agent 191 is determined by the special structure of its molecule, and its intramolecular group will affect the nature and intensity of fluorescence. Some groups have little effect on the color system, but can change the application properties of fluorescent whitening agents and the affinity of fibers and plastics. |