Problems with creases caused by boiling and bleaching of cotton knitted fabrics

1. The boiling, bleaching and coloring finishing of cotton knitted fabrics are generally carried out in overflow tanks. During the entire finishing process, the fabrics remain in a rope-like state, and the fibers are continuously bent and deformed in the dyeing machine. The original Hydrogen bonds are constantly destroyed and new hydrogen bonds are constantly formed. Sometimes the newly formed hydrogen bonds cannot be fully restored, so chicken paw prints and dead creases are formed on the surface of the fabric.

2. In single-sided fabric structures, the tension of yarns spun on both sides is asymmetrical, and it is difficult for the fabric to recover after long-term one-way wrinkles. Therefore, plain weaves, sweatshirts, etc. are more common in various structures. Crease problems are prone to occur, especially on fabrics with less or larger weight per square meter. The occurrence of creases is also closely related to the yarn count and twist. The smaller the yarn count and the higher the twist, the greater the reverse untwisting of the spinning yarn, and the easier it is to have crease problems.

2. The main process step of crease generation-boiling and blanching

1. The general dyeing and finishing process is: preparing cloth → seaming → dropping into vat, boiling and bleaching → coloring → soaping → color fixation → soft → out of vat → dehydration → shock wave machine or hair dryer For machine-dried fabrics, many people generally think that creases are formed mainly in the dye vat. However, our engineers have proven through rigorous experiments: In fact, most cotton knitted fabrics have already formed creases during the cooking and bleaching stage, but they do not form before being dyed. Simply watch it out.

2. According to the many years of experience of our engineers, it has been confirmed that the fabrics and equipment that easily crease during the cooking and bleaching stage have the following aspects:

Fabric reasons: Single-sided cotton fabrics with a small or large weight per square meter (such as 300g per square meter), especially cotton stretch fabrics (with spandex);

Equipment reason: Compared with the L-type overflow cylinder, the J-type overflow cylinder is easier to produce creases due to its strong tensile force; while the air flow cylinder is less likely to produce creases because the fabric is at the nozzle The fibers are fully blown open by high-pressure gas, and the fibers get a “rest” from the tense state, which is conducive to the removal of internal stress and reduces crease problems;

Process reasons: Fabrics that have not been pre-shaped are more likely to have crease problems; the fabric is shaped under high temperature, which can improve fiber proximity and orientation, and the fiber shape is fixed, reducing the need for dyeing in the dye vat. The chance of change will help reduce creases.

3. Solutions to cooking and bleaching creases

1. General method: Add polyacrylamide type lubricant (such as Yuzhongbao F-306) during cooking, bleaching and coloring. The main function of this type of lubricant is to “reduce the fabric friction between fabrics and machinery”, but it is difficult to solve the creases formed during boiling and bleaching.

2. The solution in this article: Use the following additives, processes, and operations to improve creases during cooking and bleaching. It has been confirmed by multiple customer applications that it has satisfactory results.

Auxiliaries: A. Prefer low-foaming anti-wrinkle agent F-341 (non-ionic) in the bath, which is used to reduce friction between fabrics and between fabrics and machinery; B. Use new The bath softener F-342 (non-ionic) is used to give the fabric itself good softness and smoothness, and has level dyeing properties. The combined use of the above two auxiliaries is the core of this method.

Technology: Reduce the heating rate; the focus is on reducing the cooling rate, generally 1.0-1.5℃/min is better.

Operation: Before entering the cylinder, the natural cotton cloth should be placed in a place with high humidity in the workshop to fully regain moisture. When the fiber regains moisture, the fibers will definitely swell and the internal stress will be removed, which is beneficial to reducing creases; the natural cotton cloth will be loose After the cloth is allowed to pass freely through the J-shaped groove, it is simultaneously squeezed by the pressure roller or stretched by the roller, which is beneficial to removing internal stress and reducing creases.

3. Process examples (see next page):

Before boiling and bleaching, add scouring penetrant, bath anti-wrinkle agent F-341 and bath softener F-342. Do not raise the temperature first. After entering the cloth, circulate it for 20 minutes to fully moisturize the natural cotton cloth. When wet, the additives and fabric fibers react fully. If bleaching is required, caustic soda and hydrogen peroxide can be added before heating.

Reduce the heating rate; especially the cooling rate, generally 1.0-1.5℃/min is better; and the temperature must be completely cooled to 50℃ before the liquid can be drained for coloring.

4. Other matters to prevent creases

1. In order to prevent the occurrence of creases, it is recommended to add the anti-wrinkle agent F-341 in the bath when coloring, and reduce the cooling rate.

2. When dehydrating and drying the cloth, you can use the method of rolling the water-drying cloth in an open width, which improves the drying effect.�Efficiency and also helpful in solving the crease problem.

3. When stacking cloth on the cloth truck, it is recommended that the weight should not be too large and the time should not be too long, especially when storing wet cloth.

4. If the crease problem cannot be completely solved using this solution for cotton stretch fabrics (with spandex), pre-shaping technology can be considered.

5. Generally, slight creases can be solved by stretching and shaping with a setting machine. Stubborn creases can be returned to the washing tank, and the temperature is gradually raised to 85°C and then gradually cooled to 50°C. The process test returns It can be repaired, or it can be reshaped by adding steam shrinkage in an industrial polishing dryer. It can be repaired according to the respective equipment and crease conditions.

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