Fluorescent whitening agent

In 1929, P. Krais discovered that 6,7-dihydroxycoumarin can fluoresce under ultraviolet light, and the fabric has a whitening effect after being immersed in its aqueous solution. The first commercially available fluorescent whitening agent was a derivative of 4,4'-bisazinyl stilbene-2,2' disulfonic acid produced by the Bayer Company of the Federal Republic of Germany in 1940. Since then, many optical brighteners have been developed and thus form a series in the dye. Fluorescent whitening agents are commonly known as "white dyes", also known as optical brighteners, referred to as brighteners. An organic compound that emits fluorescence under the illumination of ultraviolet light. The whitening effect is to use the optical complementary color principle to make the yellowing material not only reflect visible light but also absorb ultraviolet light other than visible light and convert it into visible light with purple blue or cyan. . An organic substance that can increase the whiteness of fiber fabrics and paper. The brightener can absorb ultraviolet light of 330-360 nm wavelength, and the blue-violet light of the reflected light wavelength is 400-440 nm, which is complementary to the yellow light originally reflected by the fabric which is still yellow after bleaching treatment. Add white to make the fabric white. After the whitening treatment, some of the ultraviolet light is also converted into visible light, and the total amount of reflection is increased compared with the untreated one. Therefore, the brightness of the treated fabric is also increased, so that the white fabric is more white, and the colored fabric increases the vividness. Fluorescent whitening differs from chemical bleaching in that it does not impair the color and strength of the fabric. However, if the fabric or paper of dark background is directly treated with a whitening agent without bleaching, a good effect cannot be obtained. The organic compound used as the fluorescent whitening agent has at least four conjugated double bonds in the molecular structure, such as —C=C—C=C—C=C—C=C— or —N=C—C=C— C=N —C=C—. There are four common types of chromophore structures: 1 stilbene type, such as whitening agent VBL. It is mainly used as a whitening component in cotton fiber whitening and advanced synthetic detergents. 2 Coumarin type, such as brightener WS. It has strong blue fluorescence and is a whitening agent for polyamide, wool and silk. 3 azole type. Mainly used for whitening of wool, polyamide and acrylic. 4 naphthalimide type, such as APL. Can be used for whitening of polyamide, polyester fiber and polyvinyl chloride plastics. Brighteners are mainly used in the textile printing and dyeing industry to improve the whiteness and gloss of various natural and synthetic fabrics. In recent years, applications in the paper, plastics, leather, soap, synthetic detergents and other commodity industries have also grown rapidly.