Water-soluble dyes generally contain water-soluble genes, such as sulfonic acid groups, carboxyl groups, etc. These dyes can be dissolved in aqueous solutions, and the solubility is related to the type of dye, temperature, and pH of the dye solution. Water-soluble dyes are generally electrolytes, and ionization occurs in the solution. According to the types of pigment ions generated after ionization, they are divided into anionic dyes and cationic dyes. Anionic dyes include direct dyes, reactive dyes, acid dyes, etc., which generate dye anions after ionization.
Disperse dyes and vat dyes are poorly soluble dyes, and their solubility in water is very small. During dyeing, the dyes mainly exist in a dispersed state in water, that is, the dye particles are adsorbed with the hydrophobic end of the dispersant through the action of the dispersant (surfactant). Rely on the hydrophilic group of the dispersant to disperse in the solution to form a stable suspension.
In the dye liquor, part of the dye is suspended in the dye liquor in the state of fine crystals, part of the dye is dissolved in the micelles of the dispersant, and a small part of the dye is in a dissolved state. These three states maintain a certain dynamic equilibrium relationship. When dyeing vat dyes and disperse dyes, the dispersion stability of the dye liquor must be ensured. If the dispersion stability of the dye liquor decreases, the dye particles are easy to precipitate, and it is easy to form a dye shelter on the cloth surface.
In the dyeing solution, there is not only a force (affinity) between the dye and the fiber, but also a force between the dye ions or between the dye ions and the dye molecules, which causes the dye ions or dye molecules to aggregate in different degrees to form dye aggregation. Body, so that the stability of the dye solution decreases. The aggregation tendency of dyes is related to the structure of dye molecules, dye solution temperature, electrolyte concentration, dye concentration and other factors.
There is a dynamic equilibrium between the dye ions, dye molecules and their aggregates in the dye liquor, that is, the dynamic equilibrium of aggregation and depolymerization. During dyeing, the dyeing of the dye to the fiber is carried out in a single molecule or ion state. As the dye molecules in the dye solution continue to dye the fiber, the concentration of the dye in the single molecule or ion state in the dye solution gradually decreases, and the dye aggregates continue to decompose. Gather until the dyeing reaches equilibrium.