Search

Reactive dyes are used to dye dark colors, and the dye dosage of 8% (owf) does not meet the depth requirement. What should we do?

Date:Oct 22, 2020

Reactive dyes are used to dye dark colors, and the dye dosage of 8% (owf) does not meet the depth requirement. What should we do?


8% (owf) of reactive dyes does not reach the depth of dyeing. This question asks what reactive dyes do you use?


    Is the dyeing process prescription reasonable? Because there are many types of reactive dyes and their grades are also complicated. Some reactive dyes have high affinity to cotton fiber, and some are not high. The depth of dyeing is not only related to the dye uptake rate, but also depends on the reaction ability of the dye and fiber. The quality of reactive dyes is also very different. Some commercial reactive dyes contain hydrolyzed dyes, which seriously affect their use value. Because reactive dyes lose their ability to react after being hydrolyzed, it is difficult to achieve a certain depth of dyeing even if the amount is large. There are many reasons for the hydrolysis of dyes, such as improper storage in the warehouse, damp or heat; the dye barrel is broken or the dye barrel is directly in contact with the cement floor; the plastic bag is not tightly closed or the lid is tightly closed after the dye barrel is opened. Long-term storage of dyes exceeds the shelf life, etc. These reasons can cause the dye to be hydrolyzed and cause quality degradation. Therefore, it is necessary to make a small sample to check the strength and quality of the dye before dyeing.

    When dyeing with reactive dyes, the choice of dye and dyeing process is also very important. Among the reactive dyes synthesized by cyanuric chloride, the fixation rate of dyeing with cellulose fiber is generally only about 60%. Among them, dichloro-s-triazine (X type) reactive dyes have a lower fixation rate, and monochloro-s-triazine ( The fixation rate of K-type reactive dyes is slightly higher. It is worth noting that the fixation rate of the same type of reactive dyes is not all the same, and sometimes they vary greatly. This is obviously due to the different molecular structures and physical and chemical properties of the specific varieties of each dye. In commercial reactive dyes, increasing the reactive groups in the reactive dye molecules can improve the dye fixation rate. The fixation rate of bis-chloro-s-triazine reactive dyes is significantly higher than that of mono-chloro-s-triazine reactive dyes. M-type reactive dyes are double active groups of vinyl sulfone and chloro-s-triazine, and the fixation rate is also higher. . In the chlorinated pyrimidine active material, difluoromonochloropyrimidine and monochlorotriazine and difluoromonochloropyrimidine double-reactive reactive dyes have good fixation rates. While increasing the number of active groups, dyes with high affinity are conducive to the exhaustion of dyes in the dyeing solution, and the color yield is also high.


    The application performance of reactive dyes mainly lies in the fixation rate and directness. During dyeing, the dye reacts with the fiber and also has hydrolysis. Therefore, how to reduce the dye hydrolysis and improve the fixation rate is very important. Another aspect that affects the fixation rate is to choose the dyeing process reasonably. There are two-bath method, one-bath two-step method and full-bath method for reactive dye dip dyeing. In the two-bath dyeing process, the dye uptake rate is high and the dye bath is relatively stable, but the fixing bath often contains dyes and dye accelerants that bring people from the dye bath, which makes the fixing bath unstable and the quality is not stable enough. The one-bath two-step method is not suitable for continuous vat dyeing, resulting in waste of dye. The full-bath method is generally only suitable for dyeing light colors. Dyeing bath ratio (use a small bath ratio as much as possible to get a deeper color), add salt to promote dyeing, add alkali (the choice of alkali agent), dyeing and fixing temperature and time must be strictly controlled. Dyes should be used as needed (alkaline agents should not be added when dissolving the dyes) to prevent the dyes from being hydrolyzed. Some reactive dyes have insufficient fixing alkali agent, the temperature is not high enough, and the time is short. After a certain period of time after dyeing, acid hydrolysis will occur, resulting in bond breakage, and a large amount of dye will fall off the cotton fiber, resulting in a decrease in dye depth. For this reason, in order to improve the dyeing performance of reactive dyes, we should start with the selection of dyes and a reasonable grasp of the dyeing process.