Views: 2 Author: Site Editor Publish Time: 2021-12-03 Origin: Site
The best cloth surface effect of the fabric means that the fabric will not produce wrinkles that are difficult to eliminate due to mechanical external force or other factors, and the phenomenon of scratches and friction hairiness due to mechanical external force. Cotton knitted fabrics, especially single-sided varieties, are prone to wrinkles that are difficult to eliminate after finishing when they are rope-shaped scouring and bleaching. They are also called "dead wrinkles". This is a common product quality problem in the scouring and bleaching method of dyeing machines. .
1. Causes of "dead wrinkles" (difficult to eliminate after finishing) of cotton knitted fabrics
Cotton fiber absorbs water and swells in water, which will inevitably cause changes in yarn structure and loop structure. The change of yarn structure is manifested by the thickening of yarn, the shortening of yarn length and the increase of yarn twist; the change of loop structure is manifested by the increase of loop arc and the shortening of loop column. The result of these two changes causes the fabric to shrink and become dense.
In the process of shrinking and densification of the fabric, if it is subjected to irregular external forces (tension or pressure), it will cause unevenness in the density of the fabric after shrinking. The more loose the fabric, the more prominent this phenomenon; due to the structure of the fabric Constraint, although the fiber swelling process is reversible, the deformed fabric shape will not be restored due to the recovery of the fiber shape, so the shape (such as wrinkles) formed by the irregular external force of the fabric is retained. This is why cotton knitted fabrics appear "dead folds" during rope scouring, bleaching and dyeing.
2. Methods to prevent "dead wrinkles" (difficult to eliminate after finishing) of cotton knitted fabrics
The first method is to immerse the fabric in water in a completely loose state before being subjected to irregular tension and pressure, and make the fabric shrink freely and uniformly through fiber swelling; the uniformly shrinking and dense fabric will be constrained by the organizational structure. It is relatively stable and fixed, and there will be no "dead folds" due to pressure or tension (appropriate size) during subsequent processing. The anti-wrinkle effect of the "multifunctional, fully loose continuous boiling, bleaching, one-bath scouring and bleaching process scouring machine" is that the fabric is completely immersed in the water in a relaxed state through the set "relaxation anti-folding machine", and water is absorbed by the fiber Swelling causes the fabric to shrink and shrink freely and uniformly.
The second method is to wet the fabric under regular and appropriate external force (including horizontal and vertical) before the fabric is subjected to irregular tension and pressure. In this case, the fabric shape changes due to the swelling of the fiber due to water absorption. It is uniform and orderly. "Open-width, low-tension continuous scouring, bleaching, one-bath rolling and bleaching process scouring machine" uses this method to prevent wrinkles.
The third method is to perform irreversible swelling of fibers under regular external forces before the fabric is subjected to irregular tension and pressure. This process is mercerizing. Mercerized cotton knitted fabrics will not produce so-called "dead folds" during the rope scouring, bleaching and dyeing process. This is also the reason for the high dimensional stability of mercerized cotton fabrics.
3. How to ensure that the degree of oxidative damage suffered by cotton fibers is the lowest
The degree of oxidative damage to cotton fiber during scouring and bleaching will not only affect the strength of the fabric, but also affect the dyeing performance of the fiber. It is one of the important reasons for the appearance of color and color difference in dyeing, which must be paid attention to.
The fundamental measure to minimize the degree of oxidative damage of cotton fiber is to control the decomposition reaction of hydrogen peroxide to make it more conducive to the reaction of pigments and other impurities, and to avoid the ineffective decomposition of hydrogen peroxide (reaction to generate 02) as much as possible And inhibit the decomposition reaction (such as the formation of HO.) that has a bleaching effect but at the same time has a strong oxidative effect on the cotton fiber.
In particular, the effect of hydrogen peroxide scouring and bleaching and the degree of fiber damage are related to factors such as the amount of hydrogen peroxide, alkaline agent and pH value, scouring and bleaching temperature and time, and the selection of stabilizers, as well as the selection of scouring and bleaching equipment and the formulation of related processes. It is also an effective measure to control the degree of oxidative damage of cotton fiber. Cold-pressed reactor scouring and bleaching, the decomposition rate of hydrogen peroxide is slow at low temperature, and the cotton fiber damage is small; The high-temperature stage insulation steaming process can more effectively control the decomposition of hydrogen peroxide and minimize the degree of oxidative damage to the cotton fiber.
4. How to ensure that all impurities and their decomposition products and chemicals used are cleaned
Generally speaking, various impurities on cotton fabrics, such as waxy substances, pectin substances, etc., are easily washed out after the scouring and bleaching reaction, but the caustic soda absorbed in the cotton fibers must be neutralized by acid It can only be removed. If the acid is not completely neutralized, it will cause stains and chromatic aberrations in dyeing, local yellowing of bleached varieties, local discoloration of dyed varieties, and decreased color fastness. Therefore, the process used for acid neutralization, such as the selection of acid agent, the temperature and time of treatment, and the equipment to implement this process are very important.