The dyeing principle of reactive dyes (reactiondye): also called reactive dyes. The molecules contain chemically active groups that can react with cotton, wool and other fibers in aqueous solution to form co-bonded dyes. Reactive dyes are composed of parent dyes, connecting groups and reactive groups, which enable them to form strong covalent bonds with fibers when used.
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. Therefore, medium-temperature reactive dyes often 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.
It is undeniable that the performance defects of the dye itself are the root cause of these quality problems. So the way to solve the technical problems of reactive dyes is mainly to improve their adsorption rate and fixation rate.
Three major defects in medium-temperature reactive dyeing
Medium-temperature reactive dyes have three major defects in exhaust dyeing as follows:
First, in the fixation bath where salt and alkali coexist, the dye will suffer from a greater salting out effect due to the higher electrolyte (salt, alkali) concentration, and the “β-hydroxyethyl sulfone sulfate active group” The occurrence of “elimination reaction” and the sudden drop in its own water solubility will lead to varying degrees of “aggregation”. Especially for some vinyl sulfone dyes, the performance is getting more serious. Such as C.I. Reactive Yuanqing 5, C.I. Reactive Brilliant Blue 19, C.I. Reactive Emerald Blue 21, etc. If the degree of “condensation” of the dye is too great, it will inevitably cause uneven and opaque color, and even color spots and stains. It will also affect the purity of the shade 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, Different degrees of “sudden dyeing” will occur due to the rapid occurrence of bonding and fixation reactions, the rapid break of the original color absorption balance, the addition of soda ash (also an electrolyte), and the sudden increase in electrolyte concentration. Vinyl sulfone dyes perform particularly well. 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).
Third, the fixation rate of medium-temperature reactive dyes is relatively low (60% to 70%). In addition, dyes have varying degrees of “aggregation” and “flash dyeing” problems during the fixation stage. Therefore, 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 relatively high, and the requirements for soaping after dyeing are stringent. If the soaping is not done properly, the dye fastness will be low.
The process setting must be correct
The dyeing properties of dyes with different structures are different. 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.
The first type. The performance characteristics of this type of dye are: in a neutral salt bath, it has greater affinity and a higher color absorption capacity at one time. 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 β-hydroxyethyl sulfone sulfate reactive group). For example, 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.
The second type. The performance characteristics of this type of dye are: weak affinity and low color absorption in a neutral salt bath. Moreover, it is sensitive to alkali agents. In the early stage of alkali fixation, the fixation rate and color absorption rate of the dye are very fast, and the “agglomeration” phenomenon and “sudden dyeing” phenomenon are prominent. Such dyes are mainly vinyl sulfone dyes. For example, C.I. Reactive Brilliant Blue 19, C.I. Reactive Yellow 160, C.I. Reactive Yuanqing 5, etc.
This type of dye is 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. Therefore, quality problems caused by dye performance defects can be effectively eliminated.
The pre-alkali dyeing process is as follows:
The third type. 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.
First,theadditionofsodaashmustItisbasedon”balancedcolorabsorptionanduniformcolorabsorption”. That is to say, the alkali agent can be added only after the color absorption balance is truly reached in the neutral salt bath (color absorption bath) and the color absorption is uniform through dye transfer. This is because after reaching the color absorption equilibrium, the residual dye liquor concentration is the lowest. The lower the dye liquor concentration, the smaller the tendency of dye aggregation after the addition of alkali agent, the milder the secondary color absorption rate, and the smaller the probability of dyeing defects. After the alkali agent is added, the dye on the fiber will lose its dye migration ability due to fixation. This can turn the unevenness created during the absorption phase into permanent blemishes.
Second, the application of alkali agent must be “less at first, then more, and added in batches.” Because the faster the alkali agent (soda ash) is added, the stronger the alkalinity of the fixation bath will be, the higher the salt-alkali mixing concentration will be, the more intense the aggregation and coloring behavior of the dye will be, and the easier it will be to produce dyeing quality problems. Practice has proved that the alkalinity of the fixation bath increases from weak to strong, the concentration of the salt-alkali mixture increases from low to high, and the concentration of the dye solution changes from thick to light, which can effectively alleviate the excessive behavior of the dye caused by the addition of alkali agents, thereby ensuring the dyeing quality. Achieve stability.
The soaping process must be correct
The soaping effect is a key factor in determining 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:
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 the 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.
When using ordinary soaping agents for soaping, 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</p