Basic properties of reactive dyes

Reactive dyes are reactive dyes, and there are certain differences in the dyeing performance of each dye. The color fixation reaction of dyes is easily affected by the fluctuation of process parameters, which makes it difficult to control the shade in continuous pad dyeing production. Middle right chromatic aberration.

(1) Dyeing eigenvalues of dyes: Dyeing eigenvalues of dyes include: directness S value, exhaustion rate E value, fixation rate R value and fixation rate F value.

①Substantivity S value: Substantivity refers to the percentage of the dye absorbed by the fiber after adding neutral salt to the dyeing solution for a certain period of time (generally 30 minutes), represented by S, which reflects the affinity between the dye and the fiber .

②Exhaustion rate E value: The exhaustion rate is the percentage of dye absorbed by the fiber at the end of dyeing after adding alkali in the dyeing solution (generally 60 minutes after adding alkali), expressed by E, which reflects the degree of affinity of the dye to the fiber.

③ Color fixing rate R value: the percentage of the color fixing value after adding alkali for 5 minutes to the final color fixing value, represented by R, which reflects the color fixing rate of the dye, that is, the reactivity of the dye.

④ Fixation rate F value: It is expressed by the percentage of the dye fixed on the fiber measured after the dyed fabric is washed with soap to remove the floating color, which reflects the reactivity and hydrolysis of the dye.

(2) Compatibility of dyes: Compatibility of dyes refers to the difference in the speed at which a group of dyes diffuse in fibers and the affinity of dyes to fibers during color matching. Small differences indicate good compatibility; otherwise, poor compatibility.

The diffusion of the dye in the dye solution is relatively rapid, while the diffusion in the fiber is relatively slow. The diffusion performance of dyes in fibers is determined by the properties of dyes and fibers, and changes with external conditions such as temperature and concentration. The freedom of movement of dye molecules in the dye solution is very small, molecular collisions are frequent, and the diffusion rate is low. In fibers, only those dye molecules that have sufficient kinetic energy to overcome this energy resistance can diffuse from one place to another. and spread more slowly.

The dye relies on its own diffusion and reaches the surface of the fiber through the diffusion boundary layer. The thicker the diffusion boundary layer, the longer the time it takes for the dye to pass through, which will affect the dyeing rate of the dye. If the difference in the dyeing rate is large, it is easy to produce head-to-tail color difference . Pad dyeing should choose dyes with low directness.