Medium-temperature reactive dyes have varying degrees of “uneven dyeing” problems in exhaust dyeing. The main manifestations are that it is easy to produce color spots, stains or uneven color, as well as 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.
Medium-temperature reactive dye exhaust dyeing There are three major defects
First, in the fixation bath where salt and alkali coexist, the dye will have a greater salting out effect due to the higher electrolyte (salt, alkali) concentration. As well as the occurrence of the “elimination reaction” of the active group of ß-hydroxyethyl sulfone sulfate, the water solubility of the product itself plummets, resulting in varying degrees of “aggregation”. Especially for some vinyl sulfone dyes, the performance is getting more serious. Such as C. I. Active Yuanqing 5, C. I. Reactive brilliant blue 19, C. I. Active Emerald Blue 21 etc. If the degree of “condensation” of the dye is too large, it will inevitably cause uneven and opaque color, and even color spots and stains. It will also affect the purity of the color and the fastness of the color.
Secondly, during the alkali fixation stage (especially the initial stage of color fixation), the dye in the dye bath will be absorbed due to the rapid occurrence of bonding fixation reaction and the original absorption. The rapid breaking of the color balance, the addition of soda ash (also an electrolyte), and the sudden increase in electrolyte concentration produce varying degrees of “flash dyeing”, with vinyl sulfone dyes being particularly prominent. If the degree of “snap dyeing” of dyes is too large, it will undoubtedly cause obvious or even serious adverse consequences to the dyeing quality (level dyeing effect and dyeing fastness).
Thirdly, the fixation rate of medium-temperature reactive dyes is relatively low (60% to 70%). In addition, the dyes have varying degrees of “agglomeration” during the fixation stage. “problem” and “flash dyeing” problem, so the floating rate of dyes on fibers (or fabrics) (including hydrolyzed dyes, semi-hydrolyzed dyes, and dyes that are not hydrolyzed and not fixed) is high, and the requirements for soaping after dyeing are strict. If the soaping is not done properly, the dye fastness will be low.
The process settings must be correct
Dye with different structures, Their dyeing properties vary. Practice has proved that the best dyeing results can be obtained only when the dyeing process is adapted to the practical performance of the dye. Therefore, the dyeing process cannot be one-size-fits-all.
Commonly used medium-temperature reactive dyes can be divided into three types based on their dyeing properties:
Dyeing performance can be divided into three types
1. The performance characteristics of this type of dye are: in a neutral salt bath, the affinity is greater, and the dye can be absorbed once The color quantity is higher. It is not too sensitive to alkali. In the early stage of alkali fixation, the fixation rate and color absorption rate of the dye are relatively slow, and there are no obvious “agglomeration” problems and “flash dyeing” problems. This type of dyes are mainly dyes containing heterobi-reactive groups (monochloro-s-triazine reactive group and ß-hydroxyethyl sulfone sulfate reactive group), such as the three primary colors of domestic medium-temperature reactive dyes: reactive yellow M-3RE. B- 4RFN, reactive red M-3BE, B-2BFN, reactive blue M-2GE, B-2GLN, etc. This type of dye is suitable for conventional dyeing-heating dyeing. Practice has proved that when this type of dye is dyed using conventional heating dyeing methods, it usually does not cause dyeing quality problems.
2. The performance characteristics of this type of dye are: weak affinity in a neutral salt bath, low color absorption at one time, and sensitive to alkali agents. In the early stage of color fixation by adding alkali, the fixation rate and color absorption rate of the dye are very fast, and the “agglomeration” phenomenon and “sudden dyeing” phenomenon are prominent. This type of dyes are mainly vinyl sulfone dyes, such as C. I. Reactive Brilliant Blue 19, C. I. Active bright yellow 160, C. I. Reactive Yuanqing 5 and other dyes are most suitable for pre-alkali dyeing. In the pre-alkali dyeing method, the fabric absorbs color in a weakly alkaline salt bath. Reactive dyes have greater affinity in alkaline baths, so the amount of color absorbed at one time can be significantly increased. Since the concentration of the dye liquor drops significantly before adding alkali, the aggregation phenomenon and flash dyeing phenomenon of the dye can be alleviated after adding alkali, so the quality problems caused by the performance defects of the dye can be effectively eliminated.
3. This type of dye is a blended dye, and its performance characteristics are poor level dyeing and poor color and light stability. More than half of the commonly used medium-temperature reactive blacks belong to this category. Such as reactive black KN-G2RC, reactive black GR, reactive black GWR, reactive black S-ED, reactive black N, reactive black ED, reactive black GFF, reactive black TBR, etc.
This type of reactive black is usually based on high concentration C. I. Active Yuanqing 5 (also known as active black KN-B, active navy blue B-GD) 60% ~ 80%, C. I. Active orange 82 is mainly composed of 10% to 20%, and a small amount of medium-temperature active yellow or active red is added. The performance defects of this type of reactive black are poor level dyeing and poor reproducibility. The reason is that the two blending components have different structures and poor compatibility, among which C. I. Reactive Yuanqing 5 is a disazo parent dye containing a bisvinyl sulfone reactive group. It has outstanding mid-temperature characteristics and is most suitable for color absorption and color fixation at 60 to 65°C. C． I. Reactive Orange 82 is a monoazo matrix dye containing isobi-reactive groups of vinyl sulfone and dichloro-s-triazine. It has significant low-temperature characteristics and is most suitable for color absorption and color fixation at 30 to 40°C.
Therefore, this type of reactive black is not a true medium-temperature dye, but a sub-medium-temperature dye. If it is used as a medium-temperature dye (dyed at 60°C), there will inevitably be two major consequences due to the incompatibility of the performance of the active orange component. First, the color absorption and color fixation of reactive orange are too rapid and the color is uneven, which can easily produce color flowers. Second, the hydrolysis of active orange is too fast, and process factors (temperature, time, pH value)Stimulate behavior to ensure stable dyeing quality.
The soaping process must be correct
The quality of the soaping effect , is the key factor that determines the color fastness of reactive dyes. Therefore, we must pay attention to the soaping process and overcome the wrong concept of focusing on dyeing and neglecting soaping.
The key points of the soaping process are:
(1) Soaping must be carried out on the basis of sufficient cleaning. That is, after dyeing, it must be washed with warm or hot water to remove residual salt, alkali, dye liquor and some floating dyes on the fabric to improve the freshness of the soaping solution and reduce the “re-staining” rate of the dye.
(2) When soaping with ordinary soaping agent, the key is that the soaping temperature must be kept above 90°C. Never use medium temperature (60-70℃) soaping in order to reduce fading and color correction. When using a low-temperature (60°C) soaping agent for soaping, the key is to choose a soaping agent with good wetting, penetration, solubilization (solubilization), and diffusion (dispersion) effects under low-temperature conditions to ensure good soaping. washing effect.
The author of this article: Cui Haoran, Changzhou Xinhao Printing and Dyeing Co., Ltd.
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