The colorless substance horse chestnut bark (scientific name: 6,7-dihydroxycoumarin) contained in horse chestnut bark can emit blue fluorescence under ultraviolet light. After soaking unbleached linen fabric in aqueous solution of horse chestnut bark, the whiteness of the fabric increased significantly. This was the earliest fluorescent whitening agent discovered. Since the affinity of horse bark to fiber is very low and its performance is not good, it has no practical value, but it is still a great discovery. The British ICI Company prepared the first chemical synthesis - a diacyl derivative of 4,4'-diaminostilbene-2,2'-disulfonic acid, and used it to treat cellulose fabrics and paper to produce Fluorescent whitening effect, and applied for a patent as a fluorescent whitening agent. 
horse chestnut bark
Industrially practical optical brighteners were first launched by Bayer Company in Germany. They are optical brighteners made from 4,4'-diaminodithelaethylene-2,2'-disulfonic acid (DSD acid) derivatives. Agents Blankophor B (C.I. Optical brightener 32) and Blankophor R (C.L. Optical brightener 30), as well as sulfonated 4,5-diphenyl imidazolone optical brightener Blankophor WT (C.I. Fluorescent Whitening Agent 48) has since realized the industrialization of optical brightening agents and has developed rapidly as a branch of the dye industry. In particular, stilbene-based optical brighteners still account for more than 50% of the world's optical brightener production, which shows its important position in optical brighteners. Ciba, Ilford, Geigy, BASF and other companies have successively developed different types of fluorescent whitening agents such as benzoxazoles, coumarins, pyrazoles, and naphthalimides. The product structure, variety, and output are constantly increasing, and the application fields are constantly expanding, from natural fibers to synthetic fibers, and from textiles to paper, synthetic detergents, plastics, coatings, anti-counterfeiting, laser detection and other non-textile fields. Today, fluorescent whitening Agents have become inseparable from our production and life. So far, there are nearly 2,500 product brands of optical brighteners in the world, belonging to 15 basic structural types. There are nearly 400 varieties of optical brighteners registered in the "Dye Index". World-renowned manufacturers and companies 16, located in 13 countries and regions around the world. 
Fluorescent whitening agent OB-1
There are currently no accurate numerical reports on the production of optical brighteners. According to foreign experts' predictions, the global demand for optical brighteners will grow at an annual rate of 7% to 8% in the next 3 to 5 years. In recent years, very few fluorescent whitening agents with new structures have been launched on the market. Foreign companies are focusing on supplementing their own varieties and improving product quality to enhance market competitiveness. Since my country began to produce the optical brightener VBL, the development of optical brighteners has been rapid, especially in recent years. According to incomplete statistics, there are 40 optical brighteners with different structures currently developed, researched and produced in our country. The application scope of multiple products has also evolved from being purely used in textiles in the past to now being used in non-textile fields such as detergents, papermaking and plastics. There are 48 optical brightener manufacturers of a certain scale. After years of development, Zhejiang Hongyi Chemical Co., Ltd. has become the largest optical brightener manufacturer in Zhejiang.
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