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Reasons And Solutions of Color Spots In Reactive Dyeing Process(II)

3.Characteristic values of S, E, R and F of reactive dyes
S value is direct, expressed by the adsorption value after adding salt;
E value is the exhaustion value, which is expressed by the final exhaustion value after adding alkali agent;
F value is the fixation value, which is expressed by the fixation value after soaping;
R value is the fixation rate, which is expressed by the ratio of the fixation value after adding alkali agent for 10 minutes to the final fixation value.
S value and the difference between s value and F value are the main factors determining the level dyeing. The difference between E value and F value indicates the floating dye, which determines the difficulty of washing.
Generally speaking, reactive dyes have lower directness, higher adsorption value after adding alkali, and alkali agent has a greater influence on dye uptake, which is the main influencing factor of spot color; Reactive turquoise blue KN-G has great directness, temperature has great influence on dye uptake, and E-F difference is large, which indicates that there are more floating colors after dyeing, and soaping and water washing should be strengthened.

4.Solution of active color spot in dip dyeing process
Reactive brilliant blue and turquoise blue are inevitable to be used in some colors (such as brilliant blue, bright green, green, etc.). Due to the special structure of these two dyes, they are more sensitive to process conditions (water quality, electrolyte, alkali, temperature, additives, etc.).
The s value of reactive turquoise KN-G is large. At room temperature, the dye molecules exist in the dye solution in the state of “aggregation”, and it is difficult to enter into the amorphous region of cotton fiber. There are few dyes for dyeing fabrics (the dyeing rate of reactive turquoise blue is obviously slower than other dyes at room temperature in overflow machine and spray dyeing). If the water quality is not good or some auxiliaries have influence on it, the dye is easy to form suspended matter, which shows as color spot on the fabric. Even if the temperature of the dye solution is increased, the dye suspended matter is difficult to dissolve in water again. When the dyeing solution temperature rises to the process temperature, there is enough energy between the dye molecules, from the “aggregation” state to the single molecule state. At this time, the s value becomes larger, and the emerald blue in the single molecule state is easy to enter the amorphous region of the rayon fiber, and the dyeing rate becomes faster. At this time, the dyeing flower phenomenon should be prevented. Therefore, the heating rate should be strictly controlled to increase the transfer time. Light or thin fabrics and elastic fabrics can increase the dyeing temperature. Use clear water to dissolve the alkali agent, the addition of alkali agent is slow first and then fast.
Here we need to emphasize that: for some fabrics such as rayon elastic knitted fabric, the process conditions (such as temperature, pH value, etc.) of auxiliaries (such as emulsifying degreaser) used in pretreatment must be clear, and demulsification must not be caused by improper use conditions. Once demulsification occurs, it is difficult to clean, and color spots are easy to appear during dyeing.

5.Solution of reactive brilliant blue and turquoise blue spots in rolling drying and steaming process.
The solution of reactive brilliant blue and turquoise blue in rolling, drying and steaming process in rolling, drying and steaming process, the dye and alkali agent are separated, the solubility of these two dyes is large in the case of no alkali, as long as the dye is fully dissolved, it will not be excellent in the backing part. Strictly control the pre drying and drying temperature, so as to avoid the streaks on the cloth due to the dye migration. The formation of color spots mainly occurs in the solid solution of dip rolling after steaming. This is due to the fact that when the fabric passes through the padding bath, some of the dyes are resolved in the fixing solution. In addition, there are some supplementary dyes in the padding bath. In the high concentration saline alkali solution, if the temperature of the padding bath is low, the water quality and some additives affect the solubility of the dyes, and the dyes appear in the fixing solution as “aggregation”, which is easy to combine with calcium and magnesium ions in water and suspended flocs, The formation of color spots on cloth surface (practice shows that some additives are easy to form flocculent suspension in high concentration saline alkali solution at low temperature). The solution: reduce the hardness of the water to below 70ppm, increase the temperature of the fixing solution in the high-level bath (above 80 ℃), ensure that the temperature of the fixing solution in the dip rolling bath is not less than 50%, speed up the movement of the dye molecules, so that the dye molecules are not easy to gather, which can effectively solve the color spot problem.

Post time: May-12-2021