There are varying degrees of "uneven dyeing" in the process of dip dyeing with moderate temperature reactive dyes. The main performance is that it is easy to produce color stains or uneven color, and poor color fastness. This often results in rework and repair. Experiments show that the performance defects of the dye itself are the root cause of these quality problems.
1. In the fixing bath where salt and alkali coexist, the dye will have a higher concentration of electrolyte (salt, alkali), the salting-out effect is greater, and the "elimination reaction" of the active group of ß-hydroxyethyl sulfone sulfate will occur. The sudden drop of its own water-soluble capacity produces different degrees of "cohesion". Especially some vinyl sulfone dyes, the performance is getting worse. Such as C.I. Reactive Yuanqing 5, C.I. Reactive Brilliant Blue 19, C.I. Reactive Turquoise Blue 21 and so on. If the degree of "cohesion" of the dye is too large, it will inevitably cause uneven color, even color spots and stains, and also affect the purity of the shade and the fastness of the color.
2. In the alkali fixation stage (especially the initial stage of fixation), the dye in the dye bath will occur immediately due to the rapid bonding and fixation reaction, the rapid break of the original absorption balance, and the addition of soda ash (also electrolyte) , The concentration of electrolyte increases sharply, resulting in different degrees of "sudden dyeing", especially the performance of vinyl sulfone dyes. Too much "sudden dyeing" of the dye will undoubtedly cause obvious or even serious adverse consequences to the dyeing quality (level dyeing effect and dye fastness).
3. The fixation rate of medium-temperature reactive dyes is relatively low (60%～70%). In addition, the dyes have different degrees of "cohesion" and "sudden dyeing" problems in the fixing stage, so the fiber (or fabric The floating rate of the dyes (including hydrolyzed dyes, semi-hydrolyzed dyes and un-hydrolyzed and unfixed dyes) is high, and the requirements for soaping after dyeing are strict. If the soaping is not in place, its color fastness must be low.
Dyes with different structures have different dyeing properties. Practice has proved that the best dyeing result can be obtained only when the dyeing process is compatible with the practical performance of the dye. Therefore, the dyeing process cannot be one size fits all.