The fixation mechanism of acid dye fixing agent is as follows:
(1) The quaternary ammonium group, tertiary amine group and secondary gum group in the color fixing agent molecule can be bonded with the sulfonic acid group that is not completely bound to the fiber in the acid dye molecule to close the water-soluble group, so as to increase the molecular weight of the dye and reduce the solubility, form precipitation in the gap of the fiber, reduce the swelling and falling off of the unfixed dye in the washing process, and improve the fastness to wet treatment. The reaction mechanism is as follows:
(2) fibers and nylon fibers contain amino, hydroxyl, sulfhydryl, carboxyl and amide groups, which can form hydrogen bonds with the polar groups containing hydrogen in the color fixing agent molecules and form multi-layer adsorption on the fibers: the color fixing agent with large molecular weight can also be adsorbed on the fiber macromolecules with the help of van der Waals force and dyes and fibers.
(3) There is electrostatic repulsion between the anion of the color fixing agent and the anion of the acid dye, which hinders the diffusion of the acid dye to the dye bath, promotes the diffusion of the dye on the surface of the fiber to the interior of the fiber, and reduces the probability of its dissolution.
(4) The color fixing agent containing reactive groups can react with the groups containing active hydrogen on the fiber and dye molecules to form a chemical bond. For example, epoxy (hydroxyl) and Chloroalkyl can react with hydroxyl, carboxyl and amino groups on the fiber.
(5) A film with network structure can be formed on the surface of the fiber to coat the dye and reduce its dissolution and falling off.
(6) A soft and smooth film can be formed on the fiber surface to make the fiber surface smooth, reduce the friction coefficient of the surface and improve the friction fastness.
