Several technical parameters in reactive dyeing

Due to the different reactive groups in the reactive dyes, the optimum dyeing temperature and the dosage of dyeing prescription aids are different.

Compared with direct dyes, reactive dyes have low directness. Therefore, inorganic salts are generally added during dyeing to improve directness. Usually about 50 g/L of Na2SO4 is used, and dyeing at different depths can be appropriately increased or decreased. In order to achieve the leveling effect, inorganic salts may be added in batches.

The role of alkali agents: Alkali is mainly used as a catalyst for dyes and dyes. It binds dye molecules and cellulose molecules. Therefore, it is important not to add the alkali post-staining solution pH average but to add the alkali. Under normal circumstances, the pH of dyeing liquor should be 11.5, and the pH after adding 20 g/L soda ash can reach about 11.5. There are also dyeing and finishing companies that use caustic soda (NaOH), but because it is a strong base, the pH is adjusted to 11.5, which is not easy to control, so it is less used.

When the grey cloth is dyed, in order to prevent the rope from being folded and fixed, a soft softener may be added in the dyeing bath to overcome the problem. When the quality of the dyeing water is hard, a metal chelating agent is added.

Second, bath ratio and dyeability

Commonly used low pressure bath ratio dyeing machine for dyeing cotton knitwear, low bath ratio commonly used are: 1:8, 1:5, etc., depending on the dyeing plant machinery and equipment to set. Since reactive dyes are direct dyes that are easily affected, it is extremely effective to use low bath ratio conditions for dye utilization and efficient use. The larger the bath ratio, the lower the dye uptake.

Third, the use of reactive dyeing alkali agents

When cellulose fibers are dyed with reactive dyes, the base serves as a reaction catalyst between the dye and the fibers, so an alkali agent must be used to promote the reaction. At this time, the type and amount of the alkali agent are not important, but it is necessary to pay attention to the management of the pH value of the dye bath. The optimum pH value for dyeing is based on the dyeing temperature. Generally, the pH of the medium temperature (60C) dye solution is set at about 11.5, the pH value of the high temperature dye solution is controlled at about 10-11, and the low pH value is controlled at 12.5 or so.

The addition of 20 G/L of sodium carbonate will generally result in 11.5. If a higher pH is required, sodium phosphate or sodium hydroxide may be used, and a low pH pH of available sodium bicarbonate may be used. Sodium hydroxide is an alkali that is difficult to control because of its pH, so it is not often used.