What is the role of fixing agent?

The fixing agent in the printing and dyeing auxiliaries refers to the auxiliary auxiliaries added before or after the fiber is dyed with the dye to improve the color fastness. The dye can still be dyed without it, but the color fastness is poor. . Therefore, it can be said that the fixing agent in the printing and dyeing auxiliaries has the greatest relationship with the color fastness.

(1) Fixing mechanism

The dyeing mechanism of various dyes on different fibers is different, the color fastness is also different, and the fixing mechanism of the fixing agent used is also different. The covalent bond formed by reactive dyes and fibers is theoretically quite strong, but in fact, because the unreacted dyes will fall off the fabric, it needs to be fixed with a fixing agent, which is similar to the fixing of direct dyes. . Therefore, fixing agents used as reactive dyes can also be used for direct dyes.

Acid dyes can be used for dyeing wool, silk and nylon. The molecular weight of the dye is different, the number of water-soluble groups is different, and the object of the dye is different. Therefore, there are many fixing methods for acid dyes. Early acid dyes dyed wool with copper, titanium, tin or chromium salts have a good fixing effect. Acid dyes dye nylon with antimony tannin or synthetic tannins, which can improve the wet processing fastness and the soaping fastness of sulfur dyes. Alkylating agents or quaternary ammonium compounds can be used. In short, the fixing agents used by various dyes are different, and the fixing mechanism is also different, but there are roughly the following fixing theories:

①Reduce the water solubility of dyes to improve wet fastness. For example, direct dyes and reactive dyes are treated with cationic fixing agents to form lakes to improve wet fastness. Direct copper salt dyes are treated with copper salts to form chelate. , Reduce its water solubility to improve color fastness. Acid mordant dyes are treated with complex salts after dyeing to form a chelate compound between the dye and the fiber, reducing its water solubility and improving dye fastness.

②The formation of a film on the fiber surface increases the difficulty of dissolving the dye, thereby improving the wet processing fastness. For example, it is treated with a resin finishing agent to form a film on the fiber surface to reduce the dissolution of the dye during washing to improve the color fastness.

③Use a cross-linking agent to cross-link the dye and the fiber, such as directly cross-linking the dye. After using the cross-linking agent, the dye and the dye, and the dye and the fiber are cross-linked to improve the color fastness.

④Through metal salt treatment, the photochemical stability of the dye is improved, thereby improving the light fastness and also the wet fastness.

⑤ Fiber cationic denaturation treatment introduces cationic quaternary amine groups on the fiber molecules to improve the dyeing performance of reactive dyes and direct dyes, thereby improving wet processing fastness.