High-quality reactive dyes have good water solubility in commercial applications. The solubility and the concentration of the dye solution are related to the selected bath ratio, the amount of electrolyte added, the dyeing temperature and the amount of urea and other factors. The reactive dyes used in printing or pad dyeing should be selected from varieties with a solubility of about 100 g/L, and the dyes must be completely dissolved, free from turbidity, and no color spots. Hot water can accelerate the dissolution, urea has a solubilizing effect, and electrolytes such as salt and sodium sulfate will reduce the solubility of the dye. Alkaline agents should not be added at the same time when the reactive dyes are dissolved to prevent the dyes from being hydrolyzed.
Diffusion refers to the ability of the dye to move into the fiber, and the diffusion of dye molecules with temperature. Dyes with large diffusion coefficients have high reaction rate and fixation efficiency, as well as good level dyeing and penetrating dyeing. The diffusion performance depends on the structure and size of the dye. The larger the molecule, the more difficult it is to diffuse. Dyes with high affinity to fibers are strongly adsorbed by the fibers, and diffusion is difficult. Usually, the temperature is increased to accelerate the diffusion of the dyes. When electrolyte is added to the dye solution, the diffusion coefficient of the dye decreases.
Directness refers to the ability of reactive dyes to be absorbed by fibers in the dye liquor. Reactive dyes with high solubility tend to be low in directness, and low directness varieties should be used for continuous pad dyeing and printing. For dyeing equipment with large liquor ratios, such as rope piece dyeing and skein dyeing, dyes with high directness should be preferentially used. In the roll-coil (cold pad-batch) dyeing method, the dye solution is transferred to the fiber by padding. It is also easy to obtain level dyeing with dyes with lower directivity, with less color difference between the front and rear, and the hydrolyzed dyes are easy to wash.
4. Active response
The reactivity of reactive dyes usually refers to the ability of the dye to react with the cellulose hydroxyl group. The dyes with strong reactivity can be fixed under the conditions of room temperature and weak alkali. However, the stability of the dye in the reaction is relatively poor and easy It loses dyeing ability by hydrolysis. Dyes with weak reactivity need to be bonded to cellulose under relatively high temperature conditions, or use a strong alkali agent to activate the hydroxyl groups of the fiber yarn to promote the reaction and fixation of the dye on the fiber.