1. Post-treatment of metal salt (1) Fixing principle: D + Mn+→D-M dye metal ion complex (2) Commonly used fixing agents chromium salts: such as potassium dichromate, etc.; copper salts: such as copper sulfate, copper acetate, copper salt B, etc. (3) The fixation process is treated in a fixation solution at 50~60°C for about 20 minutes and then washed with water. To 2. Cationic fixing agent treatment (1) Type and principle *Ordinary cationic fixing agent Principle: D-SO3-Na++ F+X-→D-SO3F + NaX *Principle of resin type fixing agent: the primary shrinkage condenses to form a resin film on the surface of the fabric. *Reactive fixing agent principle: forming cross-links between dyes and fibers. (2) The fixation process can be processed in the fixation solution at 50~60°C for about 20 minutes. To Supplement: Direct dyes have molecular structures of water-soluble groups such as sulfonic acid groups arranged in a straight line, and the aromatic ring structure is in the same plane. Therefore, direct dyes have a greater affinity for cellulose fibers. They can be dyed directly in a neutral medium. Dye can be dyed by dissolving in dry water. The dye is adsorbed to the surface by the fiber in the solution, and then continuously diffuses into the amorphous area of ​​the fiber, forming a hydrogen bond and a combination of van der Waals force with the fiber macromolecules. Its derived dyes include direct lightfast dyes and direct copper salt dyes. Direct dyes contain water-soluble groups such as -S03Na and -COONa, and the solubility increases significantly with the increase of temperature. For direct dyes with poor solubility, soda ash can be added to help dissolve them. Direct dyes are not resistant to hard water, and most of them can combine with calcium and magnesium ions to form insoluble precipitates, causing stains on dyed fabrics. Therefore, direct dyes are dissolved in soft water. In the production of dyeing water, if the hardness is too high, soda ash or sodium hexametaphosphate can be added, which is not only conducive to the dissolution of dyes, but also has the effect of softening water. Direct dyes are more direct to cellulose fibers than other dyes. This is mainly due to the large molecular weight of direct dyes, linear molecular structure, good symmetry, long conjugation system, good coplanarity, and large van der Waals forces between dye and fiber molecules. At the same time, the direct dye molecule contains amino groups, hydroxyl groups, azo groups and other groups, which can form hydrogen bonds with the hydroxyl groups in cellulose fibers and the hydroxyl groups and amino groups in protein fibers to further improve the directness of the dye. Note: The mechanism of salt promotion When direct dyes are used to dye cellulose fibers, salt plays a role in accelerating dyeing. The dye-promoting mechanism is that the direct dye dissociates into pigment anions in the solution and dyes the cellulose fiber. The cellulose fiber is also negatively charged in water. There is a charge repulsion between the dye and the fiber. Adding salt to the dyeing solution can reduce the charge. Repulsion, increase the dyeing rate and the dyeing percentage. Different direct dye salts have different accelerating effects. The salt effect direct dyes with more sulfonic acid groups in the molecule, the salt has a significant effect of promoting dyeing, and the salt should be added in batches when accelerating dyeing to ensure uniform dyeing of the dye. Direct dyes with a low percentage of dyeing require more salt, and the specific dosage can be determined according to the type of dye and the depth of dyeing. For light-colored products with high level dyeing requirements, the amount of salt should be appropriately reduced to avoid local uneven dyeing and staining defects such as colored flowers. Note: The influence of temperature on the dyeing performance of different dyes The influence of temperature on the dyeing performance of different dyes is different. For direct dyes with high dyeing rate and good diffusion performance, the color will be deep at 60-70℃, but the dyeing rate will decrease above 90℃. When this type of dye is dyed, in order to shorten the dyeing time, the dyeing temperature is 80-90℃. After dyeing for a period of time, the temperature of the dye liquor gradually decreases, and the dye in the dye liquor continues to dye the fiber to increase the dye uptake percentage. For direct dyes with a high degree of aggregation, slow dyeing rate, and poor diffusion performance, increasing the temperature can speed up the dye diffusion, increase the dyeing rate, and promote the exhaustion of the dye in the dyeing solution to increase the dyeing percentage. During the regular dyeing time, the temperature at which a high percentage of dye uptake is obtained is called the highest dye uptake temperature. According to the difference of high dyeing temperature, direct dyes are often divided into low temperature dyes w