Nylon, silk, wool and their blends are often dyed with acid dyes. The traditional acid dyes refer to the dyes with acid groups in the molecular structure. Most of the acid groups exist in the form of sulfonate, and only some varieties exist in the form of carboxylate. In the early stage of development, such dyes often need to be dyed under acidic conditions, so they are customarily called acid dyes. There are many kinds of acid dyes, which have the advantages of convenient use, complete chromatography, bright color and so on. When dyeing with acid dyes, there are two different attractive forces between dyes and protein fibers or nylon fibers: the intermolecular attraction between dyes and non-polar parts of fibers, including oxygen bond and van der Waals force; Dye molecules ionize into negatively charged anions in water and bind with positively charged amino groups on the fiber by ionic bonds. The process can be expressed as follows:
The sulfonic acid group and other water-soluble groups in the molecular structure of acid dyes can dye nylon, silk, wool and other fibers, which is also a very important reason for its poor wet treatment fastness. When the acid dye dyed fabric is washed or rubbed in water, the dye on which the anion part or all of the dye is not fixed with the fiber by ion bond is easy to dissolve out in water and fall off from the fabric, causing the fabric to fade or stain other fabrics in the same bath. In case of deep color or large amount of dye, there are more dyes that are not completely fixed with the fiber and are easy to fall off from the fiber, which is manifested in poor soaping fastness and wet rubbing fastness. The more sulfonic acid groups on the general dye molecules, the worse the mixing fastness, especially the wet rubbing fastness. The surface of protein fiber has scale layer structure, and the molecular structure of fiber contains reactive groups such as amino group, hydroxyl group and sulfhydryl group. There are a large number of amide groups (CONH -) in the structure of nylon fiber. The content of amino group is much lower than that of wool and silk, about one twelfth of that of wool. Therefore, the fastness of nylon fiber dyed with acid dye is worse than that of wool and silk. The wet treatment fastness of acid dyes is poor, which is difficult to meet the market requirements. Acid dye fixing agent must be used to further fix the dyes that are not completely combined with the fiber on the fiber, improve their color fastness, improve the utilization rate of dyes, reduce the dye content in wastewater and reduce the cost of wastewater treatment.
Acid dye fixing agent refers to the auxiliary agent that can more effectively fix the acid dye with egg fiber or nylon during or after dyeing, and can improve the wet treatment fastness and other fastness of acid dye dyed fabrics. 6 η, Such as tannic acid, synthetic tannin, etc
