Also known as exhaustion, it is a term for dye application. The dyed object is immersed in a dye bath containing dyes and the required auxiliary agents, and the dye is gradually dyed onto the dyed object through the dye bath cycle or the movement of the dyed object. A dyeing method in which the textile is repeatedly immersed in the dye liquor to make it move relative to the dye liquor.
After vat dye leuco body and then become dyed insoluble dye. First, it becomes soluble leuco sodium salt through reduction in lye, which is adsorbed by cellulose fiber, and then it is oxidized to return to the original insoluble dye. Generally, it has high fastness to washing and light. For example, Shilin Blue and so on. It is mainly used for printing and dyeing cotton and polyester-cotton blended fabrics. Vinylon can also be colored. In the silk industry, it is used for rayon, rayon-rayon interweaving, and real silk discharge printing.
Vat dyes are not soluble in water. When dyeing, they must be reduced and dissolved into leuco sodium salt in an alkaline strong reducing solution to dye fibers. After oxidation, they will revert to insoluble dye lakes and be fixed on the fibers.
Vat dyes are dyes with excellent properties in all dyes. According to its main chemical structure, it can be divided into two categories: indigo and anthraquinone. Its color spectrum is relatively complete, its color is bright, and its soaping and light fastnesses are relatively high. However, due to its high price, some yellow and orange colors have photosensitive fragility, which limits their application.