The dyeing of nylon fiber mainly uses acid dyes and some disperse dyes. Disperse dyes are mainly used in the case of relatively light colors, and the most used are acid dyes. Acid dyes are divided into level dyeing acid dyes (strong acid acid dyes); semi-level dyeing acid dyes (weak acid acid dyes) and neutral dye.
The choice of dyes is based on the shade of color:
1. Light color: disperse dyes and level dyeing acid dyes;
2. Medium and dark colors: semi-level dyeing acid dyes;
3. Dark color: neutral dye;
For particularly high washing fastness requirements, metal complex dyes are used. (Rarely used) The principle of dyeing nylon with acid dyes is that in an acid bath, the dye and fiber combine with covalent bonds and van der Waals forces, and are fixed on the fiber to color after fixing. The dye condition is a certain temperature, pH value and leveling agent.
The following is a process statement for different dyes:
1. Level dyeing acid dyes: also called strong acid acid dyes, which means that dyeing needs to be dyed under strong acid conditions, and glacial acetic acid is added to promote dyeing. It is characterized by excellent levelness but poor washing fastness. Therefore, a certain fastness can be achieved after fixing treatment.
2. Semi-level dyeing acid dyes: also called weak acid acid dyes, which means dyeing under weak acid conditions. Since the fastness of these dyes and fibers is acceptable, the amount of glacial acetic acid needs to be well controlled, and the addition of levelling agents is also very important to prevent the dyes from being dyed too fast and causing color difference and color blur.
3. Neutral dyes: need to be dyed under near-neutral conditions. Since these dyes are not easy to fall off after being combined with fibers, the amount of glacial acetic acid is very small or even unnecessary, and the addition of levelling agents is particularly important. The leveling agent plays a role of slowing down the dyeing.
Except for disperse dyes, which generally do not undergo color fixation, acid dye-dyed nylon fibers generally need to be fixed with a fixing agent to improve washing fastness. In general, the dyeing of nylon fibers should consider the combination of acid dyes and their washing fastness. Process control is based on different dyes and adopts different methods.