Vat dyes can be used for dyeing cotton, polyester cotton and vinylon cotton blended fabrics. According to the different dyeing forms of dyes, it can be divided into two types: cryptochrome dyeing and suspension pad dyeing. In addition, there is a cryptochrome staining method, which is not commonly used, so it is not discussed here.
1. Cryptochrome dyeing is a dyeing method in which dyes are reduced to Cryptochrome in advance, absorbed by fibers in dyeing bath, and then oxidized and soaped. It can be divided into dip dyeing, roll dyeing and pad dyeing. At present, it is mostly used in dip dyeing and pad dyeing. Leuco dip dyeing is suitable for yarn dyeing, but the core penetration degree of crimp dyeing is poor and there is white core phenomenon. According to the different properties of dyes, different reduction methods can be adopted.
(1) Dry vat method: in dip dyeing, some dyes have a slow reduction rate, so it is necessary to adopt more severe conditions to increase the reduction rate of dyes. This reduction method is called dry vat method.
Dry VAT reduction is to mix dyes into slurry with a small amount of water and Archaean oil or open powder, then add appropriate amount of warm water and specified amount of caustic soda and sodium hydrosulfite at the specified temperature for 10-15min. After the dye is fully reduced, it is filtered and added into the vat containing caustic soda and sodium hydrosulfite solution, and diluted to the required concentration for dyeing. Due to the little water consumption in the reduction, the concentration of caustic soda and sodium hydrosulfite is increased, and the reduction rate of dye is accelerated, so that the reduction reaction is completed normally.
(2) Full bath method: this reduction method is suitable for fast reduction of vat dyes. The method is to put the dye directly into the dyeing tank, add the required amount of caustic soda and sodium hydrosulfite to reduce the dye. After 10-15 minutes of reduction, the dye can be dyed. If this kind of dye is reduced violently, it is easy to cause the hydrolysis or excessive reduction of the dye, which will affect the quality of the finished product.