Vat Dyes
Vat dyes are dyes that are reduced under alkaline conditions to color the fiber, and then oxidized to return to the original insoluble dye on the fiber for dyeing. They are used to dye cellulose fibers; insoluble vat dyes are made into sodium sulfate salts to become soluble vat dyes, which are mainly used for cotton printing.
Vat dyes are insoluble in water. When dyeing, they must be reduced and dissolved in an alkaline strong reducing solution to become leuco sodium salts before they can dye the fiber. After oxidation, they return to insoluble dye lakes and fix on the fiber. They are generally fast to washing and light. For example, Shilin Blue. It is mainly used for 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.
When dyeing with vat dyes, dip dyeing, roll dyeing or pad dyeing can be used. Generally, yarns and knitted fabrics are mostly dip dyed, and woven fabrics are mostly roll dyed and pad dyed.