Six essential steps before fabric dyeing and finishing
Fabric dyeing and finishing is an important part of fabric production. Any slight mistake may lead to fabric dyeing and finishing failure, causing defects in the entire batch of fabrics, affecting quality and price. The following six steps will explain in detail the details before dyeing and finishing fabrics.
⑴ Natural color cotton design: There are three main points in natural color cotton design: natural cotton inspection – turning (batch, box, print) – sewing head.
⑵Singeing: The fluff on the surface of the fabric will affect the quality of dyeing, finishing and wearing performance. It must be singed to make the cloth surface clean. Singeing is to make the natural cotton cloth quickly pass through the flame of the singeing machine or rub the red-hot metal surface in a flat shape, causing the fluff on the cloth surface to burn due to rapid heating, while the cloth itself has a relatively tight, thick and heated structure. Slowly, it has left the flame or red-hot metal surface before the temperature reaches the ignition point, thereby achieving the purpose of burning away the fluff without damaging the fabric.
⑶Desizing: Before weaving woven fabrics, the warp yarns generally undergo sizing treatment to improve the strength, wear resistance and smoothness of the warp yarns and facilitate weaving. However, the slurry on natural cotton cloth is not good for printing and dyeing, because the presence of slurry will contaminate the entire working fluid, consume dyeing materials, and even hinder the natural fibers of dyeing materials, affecting the quality of printing and dyeing products. Therefore, the fabric must undergo desizing at the beginning of dyeing and finishing.
Desizing can be divided into enzyme desizing, alkali desizing, acid desizing and oxidant desizing. Desizing alkali is a common method currently used in printing and dyeing factories. It is used on pure cotton or blended chemical fiber fabrics and can remove most sizing. It also has a certain decomposition and removal effect on natural impurities on cotton fibers. However, alkali desizing only reduces the adhesion between the sizing and the fabric, but does not degrade the sizing. Therefore, it must be fully washed after desizing, and the lotion must be constantly replaced. . Since the caustic soda used for desizing is generally waste alkali, the cost of desizing is low.
⑷ Cooking: After the cotton fiber fabric has been desized, most of the pulp and a small number of natural impurities have been removed, but most of the natural impurities in the cotton fiber, such as waxy substances, pectin, nitrogen-containing substances, and cotton seed hulls And a small amount of oil agent and a small amount of slurry still remain on the fabric, making the cotton fiber fabric surface yellower, with poor moisture absorption and permeability, and cannot meet the requirements of subsequent dyeing and finishing. In order to make the cotton fiber fabric have certain water absorption and permeability, which is beneficial 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. .
⑸Bleach: After scouring the cotton fiber fabric, most of the impurities have been removed and the water absorption has been greatly improved. However, due to the presence of natural pigments on the fiber, the appearance is not yet good.Snow white, except for a few varieties, generally needs to be bleached, otherwise it will affect the brightness of coloring or printing. The purpose of bleaching is to destroy the natural pigments and give the fabric the necessary and stable whiteness without causing obvious damage to the fibers, and at the same time remove the remaining impurities (especially cottonseed hulls) after scouring. The bleaching agents currently used for cotton fiber fabrics mainly include sodium hypochlorite, hydrogen peroxide (commonly known as hydrogen peroxide) and sodium chlorite. Each of these three types of bleach has its own characteristics and uses.
⑹Silk finish: Silk finish means that cotton fiber fabrics are treated with concentrated caustic soda under a certain tension and maintained at the required size. As a result, the fabric acquires a silky finish. In addition, the strength of the fabric , elongation, dimensional and morphological stability have also been improved, and the fiber’s chemical reaction ability and dye adsorption capacity have also been improved. Therefore, the silk finishing of fiber-containing fabrics is one of the important tasks in dyeing and finishing.
The main factors that affect the silk finishing effect are the concentration, temperature, action time of the alkali solution and the tension exerted on the fabric. The commonly used method to test the silk finishing effect is the barium value method, which measures the adsorption capacity of cotton fibers to chemicals. The higher the barium value, the better the silk finishing effect. Usually, the barium value of the finished cotton fiber fabric is 100. The barium value of the finished and thick fabric is usually between 130 and 150. A barium value above 150 means that the cotton fiber is fully finished.
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