Reactive dyes, also known as reactive dyes. It is a type of dye that reacts chemically with fibers during dyeing. This type of dye molecules contains groups that can chemically react with fibers. During dyeing, the dyes react with the fibers and form a covalent bond between the two to form a whole, which improves the washing and rubbing fastness. Reactive dyes are a new type of dye. Reactive dye molecules include two main components: parent dye and reactive group. The group that can react with fiber is called reactive group.
Performance of reactive dyes
1. Solubility
High-quality reactive dye products should have good water solubility. The solubility and concentration of the prepared dye solution are related to the selected liquor ratio, the amount of electrolyte added, the dyeing temperature and the amount of urea and other factors. For reactive dyes used in printing or pad dyeing, varieties with a solubility of about 100 g/L should be selected. The dyes are required to be completely dissolved without turbidity or color spots. Hot water can accelerate the dissolution, urea has a solubilizing effect, and electrolytes such as salt and Yuanming powder will reduce the solubility of the dye. When dissolving reactive dyes, alkalis should not be added at the same time to prevent hydrolysis of the dyes.
2. Diffusion
Diffusivity refers to the diffusion of dye into fibers The ability to move internally, temperature has the effect of grounding the diffusion of dye molecules. Dyes with large diffusion coefficients have high reaction rates and fixation efficiency, as well as good level dyeing and through-dying. The quality of diffusion performance depends on the structure and size of the dye. The larger the molecule, the more difficult it is to diffuse. Dyes with a high affinity for fibers are strongly adsorbed by the fibers and have difficulty in diffusion. Dye diffusion is usually accelerated by increasing the temperature. When electrolyte is added to the dye liquor, the diffusion coefficient of the dye decreases.
3. Directness
Directness means that reactive dyes are The ability of dye liquor to be absorbed by fibers. Reactive dyes with high solubility tend to have low directness, so continuous pad dyeing and printing should use varieties with low directness. Dyeing equipment with a large liquor ratio, such as rope piece dyeing and skein dyeing, should give priority to dyes with high substantivity. In the pad coil (cold pad batch) dyeing method, the dye liquor is transferred to the fiber through padding. It is also easy to get level dyeing with dyes with slightly lower directness. The color difference between the front and back is small, and the hydrolyzed dye is easy to wash.
4. Reactivity
The reactivity of reactive dyes is usually It refers to the strength of the reaction ability between dyes and cellulose hydroxyl groups. Highly reactive dyes can be fixed at room temperature and under weak alkali conditions. However, the stability of dyes in this reaction is relatively poor and they are easily hydrolyzed and lose their dyeing ability. Weakly reactive dyes need to be bonded to cellulose under relatively high temperature conditions, or a strong alkali agent must be used to activate the hydroxyl groups of the fiber yarn to promote the dye reaction and fixation on the fiber.
Causes of color spots, stains and cloud-like flowers
Reactive dyes are dyed using a jet overflow machine. There are three main causes of color spots, color stains and cloud-like flowers:
1. Dyeing method Defects
The operation method of jet flow machine dyeing is that the dyed fabric enters the nozzle through the guide roller, and the hydraulic pressure generated by the circulation pump is used to send the fabric into the cloth conveying duct, and then from The tail of the machine is fed into the cylinder and slowly moves forward with the dye liquor. After reaching the head of the machine, it enters the nozzle through the guide roller, thus forming a circular circulation.
After the fabric enters the cylinder from the tail, there are five characteristics in the process of dipping into the dye solution:
① The fabric basically appears Rope bundle state;
② About 2/3 to 3/4 of the fabric is immersed in the liquid, and 1/3 to 1/4 of the fabric is floating on the liquid surface (especially Thin fabrics with small weight or fabrics with poor hydrophilicity);
③The stacking state of the fabrics in the cylinder is basically unchanged and is relatively static;
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④The fabrics are squeezed against each other and stacked tightly (especially when the fabrics are equipped with a large amount of cylinders);
⑤ The fabric remains statically stacked in the cylinder for a long time (the speed of domestic locomotives is relatively slow. When each tube is equipped with a cylinder of 700-800m, it usually takes 3-4 minutes to cycle once, especially when dyeing some delicate fabrics. When the nylon is on the front, nylon/cotton twill, nylon/cotton straight pattern, etc.). Sometimes in order to avoid scratches, the vehicle speed is often deliberately slowed down, so the stacking time will be longer.
Production practice shows that the above characteristics are one of the reasons why jet overflow dyeing is prone to uneven color. The reason is obvious, because when the fabrics are immersed in the dye solution in the cylinder, the fabrics are in the shape of ropes, squeezing each other, in close contact, and stacked relatively static for a long time. In addition, some of the fabrics are exposed above the liquid level. The following problems are bound to arise: on the surface of the outer layer of fabric, the flow and renewal speed of the dye liquor is fast, while on the surface of the inner layer of fabric, the flow and renewal speed of the dye liquor is much slower.
Because there is an objective difference in the exchange and update speed of the dye liquor on the inner and outer layers of the fabric, the concentration of the dye liquor inside the fabric is always lower than that of the main circulating dye liquor, so when the dye used is on If the dyeing speed is too fast or the feeding operation is improper, it can easily lead to uneven distribution of dye and color blooming.
2. Defects in dye performance
Medium-temperature reactive dye exhaust dyeing Dyeing has the problem of “unevenness” and is prone to color spots, stains, color blooms and other dyeing defects. This is because medium-temperature reactive dyes have two major defects in dyeing performance:
① The salt-alkali resistance medium has poor stability and is prone to “agglomeration”.
The molecular structure of medium-temperature reactive dyes generally contains 1-2 strongThe circulation speed quickly renews the dye liquor in contact with the inside and outside of the fabric (rope), thereby making the concentration of dyes and auxiliaries more consistent.
(2) The correct dyeing process must be adopted. Practice has proved that the dyeing process is compatible with the practical performance of the dye, which is the prerequisite for a successful dyeing. The practical properties of commonly used medium-temperature reactive dyes are not the same, so the dyeing method cannot be one-size-fits-all, and dyeing processes must be adapted to the dye properties.
For example:
The first type of dye (mainly dyes containing heterobi-reactive groups) uses conventional dyeing processes Dyeing, you can get good dyeing effect.
The dyeing performance of the second type of dye (mainly vinyl sulfone dye) is not suitable for conventional dyeing processes, and must be dyed using the “pre-alkali dyeing process”.
In the pre-alkali dyeing method, the fabric absorbs color in a weakly alkaline salt bath. The reactive dye has a greater affinity in the alkaline bath, so the amount of color absorbed at one time can be significantly increased. . Since the concentration of the dye solution drops significantly before adding alkali, the “agglomeration” and “flash dyeing” phenomena of the dye can be alleviated after adding alkali. Therefore, dyeing defects such as color spots, color stains, and color flowers caused by dye performance defects (see above) can be effectively eliminated.
The third type of dye (reactive black blended with low-temperature reactive orange C.1.82#) is neither suitable for conventional dyeing nor pre-added. For alkali dyeing, a special dyeing method – segmented dyeing must be used.
The segmented dyeing method is actually a one-bath two-stage method. That is, the low temperature (30~40℃) dyeing period is the best time to make C. 1. 82# active orange will color normally; the medium temperature (60~65℃) dyeing period is the best time for C. 1.5# reactive black is colored normally. Since this process meets the specific requirements for the dyeing properties of this type of reactive black, the resulting color is stable and has excellent level dyeing properties. Practice has proved that this process can fundamentally overcome the defects of this type of reactive black that are prone to color flowers and color differences, and can effectively improve the first-time success rate of dyeing.
Note: Among the commonly used reactive blacks, about 1/2 of the varieties are truly mid-temperature reactive blacks, because they completely abandon C. 1. 82# low temperature active orange component. Therefore, the reactive orange (C.1.107# orange) of the disazo parent bis vinyl sulfone reactive group, or the reactive orange of the monoazo parent with vinyl sulfone and monochloro-s-triazine isobi reactive groups is substituted. Since these new reactive oranges have medium-temperature active groups and do not contain low-temperature active groups – dichloro-s-triazine active groups, they have similar dyeing properties to C.1.5# reactive black and have good compatibility.
This type of reactive black includes: reactive black ED-NN, reactive black W-NN, reactive black NF, reactive black ED-R, reactive black HF-GRP, EX, reactive black Black RW et al.
This type of reactive black has good synchronicity in coloring of various blended components, so there is no need to use segmented dyeing. However, due to its main blending component C. 1.5 Reactive Yuanqing has the characteristics of the second type of dye, so it should be dyed with pre-added alkali dyeing instead of rising temperature dyeing.
③Dyeing auxiliaries must be applied correctly
3.1 Application of electrolytes
(1) The amount of electrolyte applied
After testing, most medium-temperature reactive dyes dye dark colors, and the maximum amount of electrolyte is <70 g/L is appropriate. For some reactive dyes, such as reactive turquoise blue BGFN, which dyes dark colors, the maximum electrolyte dosage must be <60g/L; reactive brilliant blue KN-R dyes dark colors, and the maximum electrolyte dosage must be <40 g/L. The reason is that if the amount of electrolyte is too high, the actual improvement of the color depth will not be much. However, in the early stage of adding alkali to fix the color, the mixing concentration of salt and alkali (soda ash is also an electrolyte) will be too high, resulting in the degree of "agglomeration" of the dye. The degree of "sudden dyeing" is too large, causing defects such as color spots, color stains, and color flowers.
(2) Electrolyte application method
Medium temperature reactive dye jet overflow machine (including air flow dyeing machine, electrolyte during dyeing It must be added first, and the dye must be added last. The order of adding materials is opposite to that of jig dyeing). This is because the electrolyte is added first so that the pre-mixed dye will not be dissolved or diluted in the reflux water containing the electrolyte, and harmful “agglomeration” or precipitation of the dye will not occur. (After testing, commonly used medium-temperature reactive dyes have good dissolution stability in neutral baths with electrolytes <80 g/L).
3.2 Application of alkali agent
(1) Application of soda ash Quantity
After testing, medium-temperature reactive dyes are commonly used to dye cotton, and their optimal fixation pH value is l0.5 ~ 11.0 (the pH value of reactive turquoise dyeing at 60°C is l2, The pH value of dyeing at 80°C is 11).
(2) Soda ash application method
Practice has proven that the following two principles must be followed when applying alkali:
First, the addition of soda ash must be based on “balanced color absorption and uniform color absorption”. 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:
①After reaching the color absorption balance, the residual dye solution concentration is the lowest, and the lower the dye solution concentration, the After the alkali agent is added, the tendency of dye aggregation is smaller, the secondary color absorption rate is milder, and the chance of dyeing defects is smaller.
② After the alkali agent is added, the dye on the fiber will lose its dye migration ability due to fixation. This can turn uneven color absorption stages into permanent blemishes.
The second is the application of alkali, which must be “less at first, then more, and added in batches.” This is 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 “agglomeration” and coloring behavior of the dye will be, and the easier it will be to produce color spots and color stains. , color flowers and other issues. Practice has proven 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 increases 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 dye is relatively strong, and the higher the salt-alkali mixing concentration, the more intense the “agglomeration” and coloring behavior of the dye, and the easier it is to produce color spots, color stains, color flowers and other problems. Practice has proven 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 increases 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. </p
