The boiling, bleaching and dyeing processing of textile fabrics are generally carried out in overflow tanks. During the entire processing process, the fabrics remain in a rope-like state. The fibers are constantly bent and deformed in the dyeing machine. The original hydrogen bonds are constantly destroyed, and new hydrogen bonds are formed. Bonds are constantly formed, and 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.
How to prevent “chicken paw prints” on fabrics during overflow machine dyeing?
When various fiber fabrics are dyed on an overflow machine, whether at normal temperature (100°C) or high temperature and high pressure (130°C/0.19 MPa), “chicken paw prints” (hereinafter referred to as folding marks) may be formed. print).
The main factors that cause folding are:
1. Potential factors in spinning and weaving
For example, the yarn is not dry enough Differences in twist and shrinkage after even twisting, differences in tension and density during weaving, especially high-count and high-density fabrics, will directly affect subsequent processes.
During the moist heat treatment process, folds are often formed due to different shrinkage of fibers (yarns). Therefore, to overcome folding, it is best for the fabric to undergo mercerization and preshrinking treatment. Especially after mercerization, the cotton fiber molecules are rearranged and the crystallinity is increased to reduce folding caused by spinning and weaving.
2. The thermal shrinkage of two or more fibers in the blended fabric is inconsistent
Sometimes the fabric is processed after pre-treatment A pre-forming step is added, but sometimes there is still residual stress, especially at 130°C, the difference in thermal shrinkage is more significant. Therefore, two or more fiber components will form folds due to their different thermal shrinkage rates. Although pre-shaped, sometimes it does not help (see the figure below).
1-boiling water shrinkage; 2-hot air shrinkage [190℃×15 min); 3-saturated steam shrinkage (Polyamide 6 is 125℃×3 min, nylon 66 and polyester are 130℃×3 min)
The author believes that pre-shaping before dyeing is one way. However, practice has proved that the pre-setting temperature is higher than the post-setting temperature and the effect is better. In addition, if conditions are met, comprehensive processing of flat width, rope shape and flat width can be adopted, and the effect will be better.
3. The dyeing bath ratio is too small, causing creases in the dyeing vat.
The liquor ratio is small, which is not only easy to dye flowers, but also easier to form fold marks, especially for light and high-density fabrics, such as polyester and pongee. The main factors that cause creases on elastic knitted fabrics in the dyeing vat are: nozzle pressure and lifting roller speed; wrapping, pressing vat, and cloth blocking; and dyeing temperature rise and fall speeds.
A. Nozzle pressure and lifting roller operation speed
Dyeing machine nozzle pressure and lifting roller operation during the dyeing process The cooperation and coordination between speed and speed is something that dyeing operators must control and master proficiently based on process practice and different types of fabrics. For heavy fabric dyeing machines, the nozzle pressure should be appropriately increased and the speed of the lifting roller should be slowed down. Smoothly promote the normal operation of the fabric; on the contrary, for light and thin fabrics, the nozzle pressure needs to be appropriately reduced, the speed of the lifting roller should be increased, and the tension between the water flow and the lifting roller and the fabric should be reduced, thereby reducing the surface stretch of the fabric in the dye vat. The crease phenomenon caused by.
B. Car wrapping, pressing cylinder, and blocking cloth
Caused by wrapping the car, pressing cylinder, and blocking cloth in the dyeing vat The creases on the fabric surface are generally caused by the following reasons:
First, the amount of dyeing vat is too large, the liquor ratio is small, the fabric circulates in the vat for a long time, folds and squeezes each other, and the cloth surface is easy to Generate chicken claw marks or creases. When arranging dyeing cylinders, you must pay attention to the size of the cylinder. Generally, the production is arranged according to 60% to 70% of the fabric capacity to avoid creases caused by poor fabric operation in the cylinder;
The second is the breakage of the fabric The broken fabric caused by yarn or weak joints before entering the cylinder is blocked in the cylinder. The creases in the cloth caused by being exposed to high temperatures for a long time and washed by water. Operators are required to stick to their posts, pay attention to the operating status of the gray fabric in the dye vat, discover it as early as possible, and handle it in time;
The third is regenerated cellulose fibers with poor wet strength, such as modal, viscose fiber, and bamboo fiber fabrics. Adding color and coloring in the dyeing vat for too long may cause fabric breakage and creases in the press vat. For this type of product, cut the samples and match the colors. If you find that the colors are very different, you should wash them out of the vat first, and then enter the vat for dyeing after the colors are close to each other. ; For serious stains, negotiate with the customer to change to a darker color. Try not to repair after stripping to avoid fiber breakage in the cylinder due to poor wet strength.
4. The heating/cooling speed is too fast
When dyeing on an overflow machine, heating and cooling will directly affect the shrinkage of the fiber. rate, thus forming a fold. For thermoplastic fibers such as nylon, once folds are formed, they are irreversible. Therefore, when dyeing, special attention should be paid to the need to slowly raise/lower the temperature within 10°C before and after the fiber glass transition temperature. Generally, a speed of 1°C/rain is appropriate.
The temperature rise and fall rate in the dyeing process not only affects the levelness of dyeing, but also restricts the feel of the dyed fabric and the degree of creases on the fabric surface. If the thermal processing temperature is improperly controlled, the surface temperature of the fabric will accumulate heat or cold, which will cause creases on the fabric surface due to thermal shrinkage of the fibers. In production practice, there have been cases of creases on the fabric surface, sometimes even serious creases, after the operator violated the process regulations and changed the heating and cooling from automatic computer control to manual control. Therefore, the dyeing process strictly follows the computer program, and the slow rise and fall of temperature is not only beneficial to level dyeing, and also helps reduce fabric creases. Therefore, it is necessary to strengthen employee craft discipline education to control creases in the dyeing process.
Of course, the temperature rise and fall speed can generally be increased beyond 10°C before and after the glass transition temperature to shorten the processing time. Sometimes in order to speed up the heating and cooling speed but also prevent folding, in addition to adding leveling agent during dyeing, you can also add 2-3 g/L of anti-wrinkle agent or bath softener in the bath to reduce the rigidity of the fabric and improve the softness. , reducing the chance of creases during dyeing. For example, for thick leather-like fabrics made of polyester/cotton and polyester/polyester microfibers, in addition to selecting a series of disperse dyes specifically designed for microfibers, in order to prevent folding during overflow dyeing, the above two can be added to the dye bath. kinds of auxiliaries.
There are many varieties of this type of additives. When selecting them, attention should be paid to: ① affinity and miscibility with dyes; ② low foaming or no foaming is required to prevent cloth clogging or excessive consumption of defoaming agent; ③ It must be resistant to high temperatures and weakly acidic media; ④ It needs to be selected after testing.
5. Fabrics after heat treatment cannot be cooled instantly
Practice has proved that no matter what kind of fabric, from the beginning of pre-treatment to the end of dyeing After each heat treatment, the machine cannot be shut down to discharge the residual liquid, and then replaced with cold water for cleaning. Otherwise, the very hot fabrics accumulated in the machine will form fold marks when exposed to cold in an instant, especially for synthetic fibers and their blended interwoven fabrics.
Therefore, do not rush to drain the liquid after stopping dyeing. Instead, gradually add cold water to the fabric until it overflows the dyeing machine, then wash it with running water for a while, and then drain the liquid after the temperature of the fabric and the machine body has dropped. fluid, or even fluid replacement and cleaning. This method can also reduce the occurrence of “pine board printing” if used in jigger dyeing machines. Hot and cold buffering facilitates the dyeing process.
6. Reasonable selection of processing equipment
Fabrics that can be processed by open-width equipment, such as nylon and polyester fabrics For cotton, high count and high density fabrics, etc., overflow machines should not be used as much as possible. In fact, the dyeing and finishing processing of various fabrics has its own suitable equipment, which should be selected according to the performance and end use of the fabric. </p
