The water solubility of reactive dyes is very good, but this characteristic is greatly affected by some substances or auxiliaries, which is often overlooked. In the dyeing process of reactive dyes, the problem of color difference or poor dyeing reproducibility occurs from time to time, which is often related to this.
Reactive dyes must be used to fix the color of cotton fiber fabrics with alkaline agents, and at the same time, there is the problem of alkali hydrolysis. In fact, the solubility of reactive dyes is also affected by alkaline agents, and different types of reactive dyes are affected by alkaline agents to varying degrees. Therefore, if the alkaline agent is used improperly, it will significantly affect the dyeing effect.
First of all, the soda ash or sodium phosphate used in reactive dyeing is also a strong electrolyte, which, like the salts discussed earlier, also affects the solubility of the dye. It should be pointed out that the solubility of KN-type reactive dyes is greatly affected by alkali agents, which can easily cause the aggregation of dyes, and then cause the problem of color spots and color patterns on the fabric.
KN type reactive dyes are mostly fixed by nucleophilic addition reaction with cellulose. It can be noticed that the structure of the dye changes during this process: the sulfate ethyl group becomes the vinyl group. This is the reason why the solubility of many KN reactive dyes decreases significantly in the presence of alkali agents, which is much larger than that of salt agents.
Alkaline agent is a color-fixing agent. Adding an alkali agent during the dyeing process will cause the dye to fix too fast and cause insufficient dye migration. In addition, the characteristics of its electrolyte will speed up the dyeing speed, which will easily cause color flowers.
Therefore, regarding the use of alkaline agents, we recommend paying attention to the following aspects. First, when adding alkaline agent in the middle of dyeing, gradually increase the amount of alkaline agent added. For example, 10%, 30%, and 60% of the total alkali content are added in three times, and the addition interval is about 15 minutes. The longer the time interval, the better the effect; secondly, as with the salting agent, pay attention to the dissolution of the alkaline agent itself, to avoid the local concentration being too high, it is best to use the dissolved alkaline agent; thirdly, for those affected by the alkaline agent For large reactive dyes, pre-alkaline dyeing may be used, which can overcome the problem that the dye solution is affected by alkali agents to the greatest extent.