English Views: 20 Author: Site Editor Publish Time: 2022-05-30 Origin: Site
Reactive dyes are water-soluble dyes with reactive groups in the chemical structure. In the dyeing process, dyes react with fibers and eventually generate covalent bonds (ester and ether bonds). Reactive dyes are water-soluble and direct, and can be divided into X type, K type and KN type according to different structures.
(1) Excellent moisture absorption, soft feel, comfortable to wear
(2) The wet strength is greater than the dry strength, but on the whole strong and durable
(3) Good dyeing performance, soft luster, natural beauty
(4) Alkali resistance, high temperature resistance
(5) Poor wrinkle resistance and large shrinkage.
Cotton fabric refers to a textile woven with cotton yarn or cotton-type chemical fiber blended yarn, which has the following characteristics:
(1) Strong hygroscopic performance, relatively large shrinkage, about 4% ~ 10%.
(2) acid resistance, the fabric is very unstable to inorganic acid, even the weak acid will make the cotton fabric is damaged, but the organic acid on the cotton fabric is weak, almost no damage. Cotton fabric is more alkali resistant, general weak alkali does not produce action to cotton cloth at room temperature, but after strong alkali action, cotton cloth intensity will drop. Often use 20% burning lye cotton cloth, can get "mercerized" cotton cloth.
(3) Heat resistance is general, in the sun and the atmosphere cotton fabric will be slowly oxidized, so that the strength decreases. The cotton fabric will be damaged by long-term high temperature, but the cotton fabric can withstand short-term high temperature treatment of 125℃ ~ 150℃.
(4) Microbial damage to cotton fabric, cotton fabric is not resistant to mold.
Dyes can be dyed so quickly in a relatively short time because of the presence of reactive groups in reactive dyes that can react with fibers. The structure of reactive dyes is different from that of other dyes. Their structure can be expressed by the following general formula :S-D-B-R formula :S is a water-soluble group; D is the dye matrix; B is bridge foundation; R is the active group. Reactive group is the core of reactive dyes, through which dyeing and fiber chemical bond, this part determines reactive dyes reactivity, fixation rate, color fastness and application conditions. Dyeing of reactive dyes can be divided into three stages: upper dyeing, fixation and post treatment.
1. Dyeing stage
First dyes from dyeing fiber interface introversion, when the dye in the diffusion boundary layer near the fiber to a certain distance, dye molecules adsorbed by fiber surface rapidly, dye molecules and fiber surface intermolecular hydrogen bond, van der Waals force in combination with the dye adsorbed to the fiber surface, both inside and outside the fiber to form a concentration difference, thus spreading inside the fiber. This diffusion until the dye concentration between the fiber and the solution reached equilibrium, that is, the dye concentration inside and outside the fiber is approximately equal so far how much adsorption is the basis of fixation, the size of the dye fixation rate and this stage of adsorption has a great relationship. Therefore, the dye should be adsorbed as much as possible at this stage.
2. Fixation stage
With the addition of alkali agents, dyeing bath pH value increases, negative from the reaction of cellulose fibers and reactive dyes in the elimination reaction of sulfuric acid ester ethyl sayin successively occur, at the same time the water under the action of alkali dissociated into OH - step by step, at this time due to negative out of cellulose fibre dye fixation between fiber and quick start, but in fact, The fixation and hydrolysis reactions exist at the same time in the dyeing bath. The above reactions only list the situations in which one active group is involved in the reaction, but the actual fixation process occurs far more than these results. Is worthy of high attention: dye hydrolysis is almost completely irreversible, the hydrolysis of dye not only partly or completely lost the activity of the fixation with fiber, and has a close affinity with reactive dyes can be fiber adsorption become a part of the floating color, so the control response develop in a direction conducive to the fixation is the key to reactive dyeing.
3. Post-processing stage
The internal and surface attachments of reactive dye-dyed cotton fabric after alkali liquid fixation treatment include fixed dyes, floating dyes, excess base agents and electrolytes. Float dyes, excess alkalis and electrolytes have a great influence on the fastness of dyed fabrics. Therefore, after alkali fixing, sufficient washing and soap cooking must be done to remove excess alkalis, electrolytes and float to improve the fastness.
(1) Promotion of dyes: There are many factors that affect the promotion of reactive dyes, such as the type of dye structure, the purity of dye, the efficiency of fabric pretreatment, the quality and amount of salt used in dyeing, etc.
(2) Water solubility of dyes: the more water-soluble groups contained in the reactive dyes, the more conducive to the dissolution and dyeing of dyes in the dyeing process, but also conducive to the washing of floating color. But after dyeing, the "good water-soluble group" becomes a disadvantage to wet rubbing fastness. Because of the presence of water-soluble groups, the dye will have a tendency to disintegrate from cellulose and dissolve in water. The better the water solubility is, the easier the dye will be disconnected from the fiber.
(3) The directness of the dye: the directness of the reactive dye is mainly related to the polarity of the amount of the dye, the regularity of the structure, the active group and its position. The larger the amount, the stronger the polarity, the better the structure and shape of the regularity, the higher the directness of the dye, and the worse the diffusion performance, the easier the dye is to gather on the surface of the fabric and not easy to the fiber internal diffusion and transfer, is bound to cause too much floating color.
(4) Active group: different active groups react with fibers to form covalent bonds with different stability. Generally speaking, the higher the reactive activity of the reactive group, the worse the stability of the reaction.
(1) The utilization rate is not high enough, generally 60%~70%, producing a large number of colored sewage, its chroma is more than thousands of times, the COD value is generally between 8000 ~ 30000 PPM, the COD value of concentrated wastewater is more than 50000 PPM.
(2) In order to inhibit the charge on the fiber surface, reactive dyes need to consume a considerable amount of electrolyte when using, which not only increases the labor intensity, but also causes the chloride ion concentration in the wastewater to reach more than 100,000 PPM, greatly increasing the difficulty of treating reactive dyes dyeing wastewater.
(3) Some color fastness can not meet the market requirements, such as sweat sunlight fastness, wet rubbing fastness and azo red dye and azo blue dye in light color sun fastness.
(4) can replace vulcanized vulcanized materials and VAT dyes and other dark varieties are less.
At present, the main way to solve the technical problems of reactive dyes is to improve the adsorption rate and fixation rate. The most effective method is to introduce two different or identical active groups into reactive dyes, especially the former is to introduce two active groups -- chlorotriazine and vinyl sulfone. For the new reactive dyes composed of these two heterogeneous active groups and appropriate parent dyes and linked groups, in addition to the characteristics of each component of the active group, low alkaline hydrolysis rate, high acid hydrolysis bond breaking stability, excellent washability, good fastness and small difference between the absorption rate and fixed rate, Also has two different between the active group and increase effect and the new features, better resistant to acid hydrolysis and peroxide washing ability, higher fixation rate, wider scope of dyeing temperature, better dyeing reproducibility and is suitable for medium temperature, low temperature dyeing, short dyeing, high success rate (RFT), etc., Therefore, the production of reactive dyes has accounted for two thirds of all dyes used for dyeing, and has become the main dyes for cotton pad dyeing and immersion.
