Lead: Some dyes can dye bright-colored fabrics and the direct dye, acid dye and other anionic water-soluble dye have wild chromatogram.  But the water-soluble groups on the dyes makes the bad wet fastness.  Fading and staining will be appeared broadly, which will cause old appearance of the fabric, and the dropped dye will stain on other fiber, and causes staining on other fiber. The reactive dye. Although, the covalent bond formed by reactive dye and fiber is quite strong, but in fact,  the non-reacted reactants and hydrolysate of dye could not completely washed from the dyed fabric, this part of dye will fade. Moreover, fabric's covalent bond will be hydrolyzed and broken. In order to improve the fastness of the fabric, we need to fix the color. The auxiliaries that can improve the fastness is called color-fixing agent.

Dye-fixing agent's working principle.
Dyeing different fibers, the dyeing principle and fastness is different. So the dye-fixing principle and application is different.
(1)Reducing water solubility of dye: the dye-fixing agent and the dye will react and produce insolubility color lake, which will help to improve the wet-processing fastness. For example, the direct dye, acid dye and reactive dye contain hydrophilic  group. If we use cationic compound to fix color, it will combine with dye to form insoluble salt, which will decrease the water solubility and improve the color fastness.
(2)Crosslink thought reactiveness of the dye-fixing agent molecule, so as to reduce the water solubility and improve the wet fastness of dye. By crosslinking between dyes or  dye and fiber, the broken bond dye will not transfer to the fabrics from the dyes.
(3)By the film formed by dye-fixing agent, we can increase the dropping difficulty of the dye and improve its fastness. The experimental result shows that: the dye-fixing agent with good film-forming property, will have good fastness. The olefin polymer, even no reactive groups or cationic groups included, will form film in the fabric and reduce the drop of dye. With the increase of amine dye-fixing agent molecular weight, its fastness will increase. And If we introduce reactive groups or cationic groups, the fastness will increase.

Good dye-fixing agent should include the following advantages:
(1)Good substantivity, good reactivity, good stability, convenient application conditions, strong dye-fixing property, commonly used.
(2)Low cost, low-toxicity or non-toxicity, convenient application conditions
(3)It will improve the dye-fixing rate on fiber obviously ,but will not cause color change.
(4)It will improve fabric's wet fastness, rubbing fastness significantly. The good dyeing properties and finishing effect will be achieved at the same time.
(5)It will influence the hand-feeling of the fabric and decrease the strength of the fabric. In addition, it can be used with other auxiliary