What is the role of fixing agent?

Although some dyes can dye brighter colors, the dyes have water-soluble groups, which make the wet treatment fastness poor, and the fading and staining phenomena are serious. Not only the appearance of the textile itself is old, but also the dye will stain Staining on white or other colored fibers will cause staining and color matching. For example, direct dyes and acid dyes are prone to such problems.

In addition, although reactive dyes can form covalent bonds with cellulose fibers, the presence of hydrolyzed dyes or insufficient soaping of unbonded dyes during dyeing will also reduce the wet treatment fastness; Reactive dyes that form covalent bonds may also decompose and break bonds under acidic or alkaline conditions, as well as problems such as insufficient color fastness to chlorine, perspiration, and insufficient fastness to light. In order to improve the color fastness of the fabric, fixation treatment can be carried out. These auxiliaries that can improve the fastness of various types of dyeing are called fixing agents.

The fixing mechanism of the fixing agent used to improve the wet processing fastness generally has the following effects:

(1) Generate insoluble lakes on the fabric, block the soluble groups, make the dye on the fabric difficult to dissolve when exposed to water, and achieve the purpose of improving the wet processing fastness. However, after this fixing agent is fixed, it is easy to change the shade of the dyed material or cause the light fastness to decrease.

(2) A net-like film is formed on the fabric to prevent the dye from falling off.

(3) Use the reactive groups in the fixing agent molecules to cross-link with the reactive groups on the dye molecules and the hydroxyl groups on the cellulose molecules to improve the fixation effect of the dye on the fiber.

(4) Utilize the molecular attraction between the fixing agent and the fiber to increase the fixing strength of the fixing agent, thereby improving the color fastness.