Color fixing agent molecules combine with dye molecules on the fabric to form insoluble colored precipitation. This is because there are a large number of cationic groups in the molecular chain of the color fixing agent. When these cationic groups meet with the anionic groups in the dye, they will form electrostatic binding, making the color fixing agent and the dye calm on the fiber. In order to reduce the water solubility of dyes in the environment with a large amount of water, so as to improve a series of color fastness of textiles. The fixing agent with this mechanism is usually called cationic surface active fixing agent. The research shows that the more the number of cationic groups on the fixing agent, the better the color fastness will be after fixing with it. According to this fixation principle, when cationic fixing agent is used to treat textiles dyed with dyes with anionic groups, the color fastness is improved by “salt formation”; After dyeing with acid dyes, textiles usually use chromium salt for fabric fixation treatment. After treatment, chelates will be formed between fibers and dyes, so as to reduce its water solubility and improve the color fastness. For example, PAMAM for acid and direct dyes. After etherification modification of the reagent, the amino group in its molecular structure will be grafted with many positive charged groups. When the group meets with the negative group in the dye, it will form lake deposition and realize color fixation.
The fastness to rubbing can be improved by using the film-forming property of the color fixing agent on the fiber surface and the low friction coefficient of the polymer film. The fixing agent with this mechanism is generally called resin type fixing agent. The experimental research shows that the better the film-forming performance of the color fixing agent, the better its color fixing effect. For example, many compounds polymerized with small olefin molecules can have a certain color fixing effect even if their molecular chain does not contain reactive groups. This is because the high polymer has ductility and will form a film on the surface of dyed textiles, so as to achieve the effect of sealing the dye on the fabric. It plays a “coating” role, thus reducing the solubility of the dye in water. At the same time, the molecular weight of color fixing agent can also affect the color fixing performance of color fixing agent to a certain extent. For example, polyamine color fixing agents mostly improve the color fastness by increasing the molecular weight. Previous scholars proposed to introduce some active groups into the synthesis process of polymer, which can not only form film, but also combine the above-mentioned “salt forming” mechanism on this basis, which will greatly improve the color fixing effect. Among them, the most typical color fixing agent using this color fixing mechanism belongs to the traditional color fixing agent y, but because its formaldehyde content seriously exceeds the standard, it is no longer used at present.
