Issues that should be paid attention to when dyeing with disperse dyes

Problems such as uneven dyeing, recrystallization, agglomeration and focusing are prone to occur when dyeing with disperse dyes. How to prevent them are as follows:

1. Uneven dyeing:
The uniformity of dye absorption is related to the ratio between dye liquor flow rate and absorbance. During the color absorption phase, the liquid flow direction is changed every 8 cycles. Lowering the liquor ratio from 1:12 to 1:6 can change the uniformity of the migration stage, although the unevenness of dyeing is more obvious at the beginning. When blending dyes, simply choosing dyes with similar diffusion properties is not enough to ensure level dyeing.

Here, the mixing ratio plays an important role. If the three dyes used in color matching have the same amount, it is correct to use dyes with the same diffusion performance. However, if the dosage ratio of two of the dyes is larger, the diffusivity of the third dye should be lower, otherwise it will be absorbed faster than the other two dyes, which will easily cause uneven dyeing.

2. Recrystallization:
Disperse dyes often recrystallize particles larger than 1 nm due to repeated heating and cooling. Adding additional dispersants can reduce recrystallization to a minimum. When dyeing, when the dye bath is cooled from 130°C to 90°C, some dyes tend to recrystallize easily, resulting in poor friction fastness of the dyed goods, and even clogging of the filter in the high-temperature and high-pressure dyeing machine.

Preventive measures include:
① If the dye is kept at 100℃ for a long time, the dye is easy to condense. Adjust the heating speed from 100℃ to 130℃;
② If the dye in the dye bath recrystallizes after reaching the dyeing equilibrium, more dispersant must be added;
③ Some allium quinone type red disperse dyes such as C.I. Disperse Red 53, 60, 92, 121, 132, 159, etc. are prone to recrystallization when dyeing is near the end of dyeing, even if their concentration is much lower than the saturation level. When dyeing darker colors Especially obvious. Especially when dyeing with hard water, it is easy to chelate with metal ions. The resulting chelates are poorly soluble under dyeing conditions and can leave blue spots or streaks on the fabric.

Factors causing recrystallization include:
Additives, winding oil, alkaline residues, etc. added during spinning. These problems can be avoided by refining before dyeing or adding chelating agents to the dye bath (Dongguan Hongqi is a good manufacturer). Once stains occur, they can be eliminated with alkaline reduction cleaning or acid treatment.

3. Aggregation and focus:
The contributing factors are: weakening the dissolution effect of the dispersant, reducing electrostatic repulsion, and increasing the collision rate of dye particles and increasing their kinetic energy. Generally, the higher the dyeing concentration and temperature, and the longer the dyeing time, the greater the possibility of agglomeration and focusing. Dyeing auxiliaries such as carriers and leveling agents (Dongguan Hongqi’s is good) can easily replace the dispersant mixed in the dye, thereby reducing the dispersion stability.

Measures to improve stability during dyeing include:
①Disperse the dye at 40℃ and use concentrated dispersion;
②The temperature control is good when the dye liquor is heated;
③Use dispersants with protective colloidal effects;
④ No need for additives that have cloud points at high temperatures;
⑤ Wash away all dyes and yarn auxiliaries including emulsifiers before dyeing;
⑥During high-temperature dyeing, carriers and non-ionic leveling agents must not be added before most of the dye has been dyed on the fabric;
⑦ No salt is used, only acetic acid is used to adjust the pH value;
⑧The yarn or piece-dyed fabric should be properly pre-shaped, and laboratory tests should be conducted to ensure the dispersion stability of disperse dyes.

Source: Dr. Satin Moss Fabric