The vat dye molecule does not contain a water-soluble group and is therefore insoluble in water; The dye has a large molecular structure, a good coplanarity of the aromatic ring, and a large affinity for the cellulose fiber, so the initial dyeing rate is high, the transferability is poor, and the uneven dyeing phenomenon is easy to occur;
It is mainly used for the dyeing of cotton, viscose and other fibers. The dyeing methods mainly include leuco staining method (dip dyeing method) and suspension dyeing method (rolling dyeing method);
Dyeing fabrics have good wet handling fastness, and most dyes have high light fastness. They are high-grade dyes widely used in various commercial dyes.
The vat dye molecule contains at least two carbonyl groups in a conjugated system, and is reduced to a leuco acid having an enol structure by a reducing agent, and the leuco acid is soluble in the alkaline solution and adsorbed by the fiber;
The leuco body (soluble sodium salt of the dye) adsorbed on the fiber returns to the original water-insoluble carbonyl (steroid or ketone body) state under the action of the acid and the oxidizing agent, and is fixed inside the fiber. The dyed leuco-dyed cellulose fibers are adsorbed on the surface of the fibers in an anionic form by van der Waals forces and hydrogen bonds with the fibers, and then diffused into the fibers.