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Notes on Reactive Dye Dyeing Process

Views: 11 Author: Site Editor Publish Time: 2023-11-22 Origin: Site

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reactive dye

textile dyes

dyeing process

Reactive dye definition

Reactive dyes are a type of dye that react 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. In 1956, the UK first produced the Procion brand of reactive dyes. Reactive dye molecules include two main components: parent dye and reactive group. The group that can react with fiber is called reactive group.

Reactive dye properties

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. The solubility of reactive dyes varies greatly. Please refer to the individual monographs. The solubility listed refers to the allowable range of the dye when used. 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

Diffusibility refers to the ability of a dye to move into the fiber. 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

Substantivity refers to the ability of reactive dyes to be absorbed by fibers in the dye liquor. 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 usually refers to the ability of the dye to react with the hydroxyl group of cellulose. Highly reactive dyes can be fixed at room temperature and under weak alkali conditions. However, the dyes in this reaction have relatively poor stability and are easy to fix. It is hydrolyzed and loses its 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.

Reactive dye dyeing precautions

1 When mixing the material, first use a small amount of cold water to mix the slurry. The temperature of the material should not be too high.

(1) First use a small amount of cold water to make the slurry to make the dye easily and fully wet. If the dye is poured directly into the water, the outer layer of the dye will form a gel and the dye particles will be wrapped, making it difficult for the dye particles to soak through and dissolve. , so you should first mix the paste with a small amount of cold water, and then use hot water to dissolve it.

(2) If the temperature of the chemical material is too high, it will cause hydrolysis of the dye and reduce the dye fixation rate.

2 Add ingredients slowly and evenly

The main thing is to prevent the dye from being dyed too fast. If the dye is added quickly at one time, the dyeing rate will be too fast, which will make the outer layer of the fiber dark and the inner layer shallow, which may easily cause stains or streaks.

3 After adding the dye, it takes a certain period of time (for example: 10 minutes) before adding salt.

Salt is a dye accelerator. When the dye is dyed to a certain extent, it has reached saturation and it is difficult to continue dyeing. Adding salt is to break this balance, but it takes about 10-15 minutes before adding salt to promote dyeing. Only then can it penetrate fully and evenly, otherwise it will easily cause streaks and colored flowers.

4 Add salt in batches

The purpose is to promote dyeing evenly to avoid promoting dyeing too quickly and causing color blooming.

5 After adding salt, it takes a certain amount of time (such as 20 minutes) to solidify the color.

(1) Let the salt dissolve evenly in the tank to fully promote dyeing

(2) Let the dyeing process enter the dyeing saturation stage and reach equilibrium, then add alkali to fix the color to achieve the highest dyeing amount.

6 Adding alkali will "fix the color"

Adding salt to reactive dyes only has the effect of promoting dyeing, but adding alkali will stimulate the activity of reactive dyes, causing the dye and fiber to react (chemical reaction) under alkaline conditions, thereby fixing the dye on the fiber, so it is also called "color fixation" because This type of color fixation undergoes a chemical reaction to achieve higher fastness. Once solidified, the color print will be difficult to achieve evenly.

7 Add alkali in stages

The purpose is to achieve uniform color fixation and prevent color blooming. If added at one time, it will easily cause excessive concentration of the local residual liquid and accelerate the reaction with the fiber, which will easily cause color blooming.

8 When adding materials, the steam must be turned off first.

(1) The purpose is to reduce stripe differences and prevent color blooming.

(2) When the temperature on both sides of the control cylinder rises above 3°C, dyeing will be affected. If the temperature exceeds 5°C, stripes will appear. If the temperature exceeds 10°C, the machine will be shut down for maintenance.

(3) The test found that the temperature inside the cylinder is basically uniform before and after the cylinder is turned for 10-15 minutes after steaming, and is equal to the surface temperature. Therefore, when adding materials, whether adding H202 during chlorine boiling or adding dye salt and soda ash during dyeing, the temperature should be the same. Turn off the steam before adding ingredients.

9 After adding alkali, it is necessary to ensure the process holding time.

The holding time should be calculated after the alkali is added and the temperature rises to the process holding temperature. Only when the panels are cut according to the process holding time can the quality be guaranteed, because the holding time is determined based on how much time it takes for a certain amount of dye to react. The laboratory also does proofing at this time.

10 Several types of plate shearing that do not follow process regulations cause unstable quality

(1) The time is not right for shearing.

Due to plate printing problems, material weighing problems, cloth weight and liquor ratio, etc., problems will cause color deviations. If the color has not been "corrected" before the time is up, this abnormality should be reported to the squad leader or craftsman. In any case, shorten the process and heat preservation time. , the dye reaction is not sufficient, the color does not change, the dyeing is uneven, there is no fullness, and the fastness is also a problem.

(2) The board is cut early and the material replenishment is inaccurate.

Dyeing can only be stable when the process heat preservation time is reached. The earlier the cutting time, the greater the change and the more unstable. If the cutting time is not up, (after boiling, scouring, washing, and blow-drying, the dye will be sent to the craftsman for color inspection From the time when the order is placed and the material is weighed, the actual heat preservation time of the vat cloth has been extended. At this time, the dyeing has also increased. After adding the supplementary material, the vat cloth is too dark and needs to be lightened again.

(3) Extend the time for shearing.

When the temperature is exceeded by the shearing board, the dye reaction has ended, and it is useless to dye again. Instead, some of the dyes that have been dyed will be re-hydrolyzed.

4-Notes on reactive dye dyeing process