Search

What are the common factors of reactive dyeing?

Date:Dec 30, 2020

Color flower is a quality problem often encountered in the production process of printing and dyeing enterprises. Establishing a reasonable dyeing process and paying attention to the problem-prone links is the key to improving the rate of genuine products. It is the focus of printing and dyeing enterprises to create a stable customer base under the pressure of energy saving, emission reduction and various costs.

Cotton 2


Cellulose, polyester and nylon are the three most common textile fibers on the market. However, dyeing cellulose fibers with reactive dyes is relatively complicated and requires the most attention during dyeing. The dyeing and finishing process is interlinked, and every step must be done well in order to finally obtain good quality. Next, let's discuss the factors that cause coloring in the reactive dyeing process and the conventional methods to avoid them.


1.cooking


Because of its natural fiber structure, cotton fiber must be strictly refined to ensure relatively uniform water absorption and dye uptake during the dyeing process. The so-called successful pre-processing is half the battle. The pretreatment must ensure sufficient scouring agent dosage and alkalinity as well as sufficient treatment time and temperature. Additives should be added in batches and steps. The effect of adding hydrogen peroxide at 70°C is the best. In case of problems such as entanglement and cylinder blockage, the insulation must be continued for a period of time. Ensure that the fiber has sufficient and uniform hair effect to ensure the uniformity of dyeing.


2. The scouring water stains are not clear, and the grey cloth is stained easily with alkali dyeing


After pretreatment, washing must be sufficient, and pickling can be carried out to ensure that the pH value of the fabric is neutral. Otherwise, under alkaline conditions, especially uneven alkaline conditions, the dyeing and coloring rate will be too fast, resulting in stains.


3. The residual oxygen treatment on the cloth surface is not clean after cooking


Reactive dyes are easily oxidized. Residues of hydrogen peroxide, especially uneven hydrogen peroxide residues, can damage the attached reactive dyes and cause them to change color. Resulting in color blur and inaccurate color. Nowadays, deoxygenase is generally used to remove residual hydrogen peroxide. Ensure the deaeration time and do an oxygen content test after deaeration to avoid such risks.


4. Uneven chemical materials and insufficient dye dissolution cause color blur


Stir fully and adjust the temperature of the chemical material appropriately. The solubility of different types of reactive dyes is different. The temperature of general reactive dyestuffs should not exceed 60℃, otherwise the high temperature will easily cause rapid hydrolysis of the dye. Because of the larger dye molecules, the dyestuffs such as turquoise blue and brilliant blue can increase the chemical temperature appropriately. In addition, it is necessary to strengthen the filtration and add a high-density filter at the feed port to prevent undissolved dye particles from directly entering the dyeing vat and contacting the cloth surface.


5. Adding speed of salt and alkali


Saline alkali is the key to control the dye adsorption rate and fixation rate. Too fast feeding speed will cause differences in the internal PH value of the dyeing solution, resulting in uneven coloring and coloring. Therefore, during the dyeing process, especially when dyeing lighter or more sensitive colors, salt and alkali must be slowly added step by step. After each feeding, it is necessary to rotate it thoroughly at an interval of 10~15min before proceeding to the next operation. When making artificial cotton or light colors, you can also add 1/10 alkali in advance to avoid drastic changes in the pH value in the later stage and avoid the production of colored flowers.


6. Bath ratio


Due to the limitation of energy saving and emission reduction, many factories are now reducing the bath ratio to reduce the cost and reduce the pressure of sewage treatment. Especially the air cylinder, because of the too small bath ratio, the process requirements are more stringent. Be sure to operate strictly and not carelessly.


7.soaping


After dyeing, the water is not clear, and the pH is too high and the temperature is too fast during soaping. At this time, it is necessary to wash out the residual alkali as much as possible before soaping, control the heating rate and ensure the soaping time. Acid soaping agent can also be used to neutralize part of the alkaline agent while soaping.


8. Unclean water, causing color blur


If the residual liquid after soaping is not washed out, the concentration of the residual liquid on the surface and the surface of the cloth will be different after the cloth is discharged. If it is not dried in time, it will cause stains, which is what we often call windmark. Therefore, at least one water wash is required after soaping to remove residual liquid.


9.Additive  color


Additive color is common in dyeing factories, but the amount of dyestuff is often very small. It is equivalent to one light color. Also, because there is a large amount of salt in the original tank, it will increase the coloring rate. Therefore, it is more important to control the feeding speed. If necessary, when the color depth is satisfied, part of the dye solution can be removed and water can be added to reduce the salt concentration. . Sometimes it is too risky to use reactive dyes to add color when the shades are not very different, you can choose disperse dyes for fine adjustment. Because disperse dyes are slower to color, they will only cause less staining on cotton fabrics. Therefore, when the shade is slightly different and the color is not bright, you can use disperse dyes for fine adjustment.