Six essential steps before fabric dyeing and finishing

Fabric dyeing and finishing is an important part of the fabric. Any slight mistake may cause the fabric dyeing and finishing to fail, causing defects in the entire batch of cloth, affecting quality and price. The following six steps will explain the details before dyeing and finishing the fabric. ⑴Gray fabric preparation: There are three main points for grey fabric preparation: grey fabric inspection-turning fabric (batch, box, printing)-sewing head. ⑵Singeing: The fluff on the surface of the fabric will affect the quality of the dyeing and finishing process and the performance.
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Fabric dyeing and finishing is an important part of the fabric. Any slight mistake may cause the fabric dyeing and finishing to fail, causing defects in the entire batch of cloth, affecting quality and price. The following six steps will explain the details before dyeing and finishing the fabric.

⑴Gray fabric preparation: There are three main points for grey fabric preparation: grey fabric inspection-turning fabric (batch, box, printing)-sewing head.

⑵ Scorching: The fluff on the surface of the fabric will affect the quality of the dyeing and finishing process and the wearability. It must be scorched to make the cloth smooth. Singing is to make the gray fabric pass through the flame of the sintering machine or rub the red hot metal surface in a flat width, causing the fluff on the cloth surface to burn due to rapid heating, while the fabric itself is denser, thicker, and warmer. Slow, when the temperature has not reached the ignition point, it has left the flame or red hot metal surface, so as to achieve the purpose of burning away fluff without damaging the fabric.
 

(3) Desizing: Before weaving the woven fabric, the warp yarns are generally subjected to sizing treatment to improve the strength, abrasion resistance and smoothness of the warp yarns, which is convenient for weaving. However, the slurry on the grey cloth is not good for printing and dyeing processing, because the presence of the slurry will contaminate the entire working fluid, consume dyeing materials, and even hinder the dyeing materials from fibers, which will affect the quality of printing and dyeing products. Therefore, the fabric must be desizing at the beginning of the dyeing and finishing process.
Desizing can be divided into enzyme desizing, alkali desizing, acid desizing and oxidizing agent desizing. Desizing alkali is currently the most common method used in printing and dyeing factories. It is used for pure cotton or blended fabrics and has the effect of removing most of the pulp. It also has a certain degree of decomposition and removal of natural impurities on cotton fibers, but because alkali desizing only reduces the adhesion between the pulp and the fabric, and cannot degrade the pulp, it must be washed with water after desizing, and the washing liquid must be constantly replaced . Because desalted caustic soda is generally waste soda, desizing cost is low.

⑷Cooking: After desizing of cotton fiber fabrics, most of the pulp and a small amount of natural impurities have been removed, but most of the natural impurities in cotton fibers, such as waxy substances, pectin, nitrogen-containing substances, and cottonseed shells And a small part of the oil agent and a small amount of slurry still remain on the fabric, making the cotton fiber fabric with a yellow surface and poor moisture absorption and permeability, which cannot meet the requirements of subsequent dyeing and finishing processes. In order to make the cotton fiber fabric have a certain water absorption and permeability, which is conducive to the adsorption and diffusion of dye additives during the dyeing and finishing process, it must be scoured after desizing to remove most of the residual impurities in the cotton fiber. .

⑸Bleaching: After the cotton fiber fabrics have been scoured, most of the impurities have been removed and the water absorption has been greatly improved. However, due to the existence of natural pigments on the fibers, the appearance is not white enough. Except for a few varieties, they are generally required. Bleach, otherwise it will affect the vividness of the color of dyeing or printing. The purpose of bleaching is to ensure that the fibers are not damaged, to destroy the natural pigments, to give the fabric the necessary and stable whiteness, and to remove the impurities (especially cottonseed husks) remaining after scouring. At present, the bleaching agents used for cotton fiber fabrics are mainly sodium hypochlorite, hydrogen peroxide (commonly known as hydrogen peroxide) and sodium chlorite. Each of these three bleaches has its own characteristics and uses.

⑹Mercerization: Mercerization refers to the fabric containing cotton fibers under a certain tension, treated with concentrated caustic soda, and maintaining the required size. As a result, the fabric has a silky luster. In addition, the fabric's strength and elongation The size and morphological stability have also been improved, and the chemical reaction ability of the fibers and the ability to adsorb dyes have also been improved. Therefore, mercerization of fiber-containing fabrics is one of the important tasks in dyeing and finishing.

The main factors affecting the mercerizing effect are the concentration of lye, temperature, action time and the tension applied to the fabric. The most commonly used method to test the mercerizing effect is the barium value method, which measures the cotton fiber's ability to absorb chemicals. The higher the barium value, the better the mercerizing effect. Normally, the barium value of this light cotton fiber fabric is 100. The barium value of mercerized thick fabrics is usually between 130 and 150, and a barium value above 150 indicates that the cotton fiber is fully mercerized.

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