Disperse dyes are a kind of non-ionic dyes with simple structure and very low water solubility. The chemical structure of disperse dyes is mainly azo and anthraquinones, but also heterocyclic disperse dyes.
Disperse dyes are mainly used for polyester fiber dyeing and printing, as well as vinegar ester fiber and polyamide fiber dyeing. The dye must be evenly dispersed in the dye solution with the aid of dispersant, and then all kinds of synthetic fibers are dyed.
Reductive dyes are mostly polycyclic aromatic compounds, and their molecular structures do not contain water-soluble groups such as sulfonic acid groups and carboxylic acid groups. Their basic feature is that they contain two or more carbonyl groups in the conjugated double bond system of molecules. Therefore, under the action of insurance powder, carbonyl group can be reduced to hydroxyl group, and become soluble leucomeric sodium salt in basic aqueous solution.
VAT dyes are mainly used for dyeing cellulose fibers. During dyeing, they are reduced to water-soluble cryptic sodium salt in alkaline solution containing reducing agent (such as Na2S2O4, sodium disulfite, commonly known as insurance powder), and then stained with fiber. After oxidation, they become insoluble dye again and fix on the fiber.