Vat dye molecules do not contain water-soluble groups, it is insoluble in water; The molecular structure of the dye is large, the aromatic ring is good in coplanarity, and the affinity of the cellulose fiber is large. Therefore, the initial dyeing rate is high, the dyeing property is poor, and the dyeing unevenness is easy.
Mainly used for cotton, viscose and other fiber dyeing, dyeing methods are mainly leuco staining (dip method) and suspension dyeing method (padding method)。
Dyed fabric wet treatment fastness is very good, most of the dye has a high resistance to light fastness, is currently widely used in various types of goods dyes high-grade dyes. Vat dye molecules contain at least two carbonyl groups in the conjugated system, in the role of reducing agent is reduced to a enol structure of the leuco acid, leuco acid soluble in alkaline solution and fiber adsorption;The leuco (soluble sodium salt) adsorbed on the fiber is restored to the original water-insoluble carbonyl (quinone or ketone) state under the action of the acid and oxidizing agent, and is fixed inside the fiber. The dyestuffs of the dyestuffs are adsorbed on the surface of the fibers in the form of anions by means of van der Waals forces and hydrogen bonds with the fibers, and then diffused into the fibers.