Aiming at the problems that cotton knitted fabrics have poor dimensional stability during the dyeing and finishing process and are prone to wrinkles and creases, the reasons for shrinkage of cotton knitted fabrics and creases on the fabric surface are explained, and the reduction of shrinkage of cotton knitted fabrics from the aspects of equipment and technology The specific measures to prevent the occurrence of wrinkles and creases in cotton knitted fabrics provide a reference basis for the dimensional stability and cloth effect of cotton knitted fabrics during the dyeing and finishing process.
Author: Gaomi City Fuyuan Printing and Dyeing Co. Fu Ji Haidong deep ring
Common quality problems in cotton dyeing and finishing
The quality problems of cotton knitted fabrics during dyeing and finishing are manifested in four aspects:
1. Problems such as blooming, color difference, and poor color fastness are easy to occur in dyeing and printing;
2. The degree of fiber damage is large;
3. The fabric has high shrinkage and poor dimensional stability;
4. The folds and creases on the cloth surface are serious and there are many friction hairiness, that is, the cloth surface effect is poor.
Through the joint efforts of dye and auxiliary chemical workers and dyeing and finishing workers, the problems related to dyeing and the problem of heavy fiber damage have been better solved, but the cotton fabric has poor dimensional stability and poor cloth effect ( This problem has not been solved for a long time. This article will discuss the causes of shrinkage of cotton knitted fabrics, the anti-shrink technology and the causes and the methods of overcoming them.
Causes of shrinkage and creases on fabric
1. Reasons for shrinkage of cotton knitted fabrics
The shrinkage of the fabric is measured by the use of a drum-type washing machine, that is, the fabric shrinks freely in water. It is not only that the light gray fabrics and garments that have been dyed and finished will shrink when loosely washed. Knitted blanks also shrink in size when they are impregnated with water in a fully relaxed state. The shrinkage process of knitted fabrics washed with water or relaxed in water is completed by fiber shrinkage, yarn shrinkage, and fabric structure shrinkage.
1.1 Fiber shrinkage
In the spinning, spinning (chemical fiber), weaving, and dyeing and finishing processes with large tensile forces, the fibers will be stretched due to external force and form internal stress in the fibers, and they will be dried in the stretched state. The effect and cohesion between fibers and the interweaving resistance between yarns will temporarily fix the elongation and internal stress; when treated with water or water vapor, water molecules will weaken the force between fiber macromolecular segments , Reduce the retraction barrier of the macromolecular segment, the fiber will shrink under the effect of internal stress.
Filament fabrics, yarn fabrics with less twist, and regenerated cellulose fiber fabrics. In dyeing and finishing wet processing (such as bleaching and dyeing), fibers are easily stretched and stretched by external forces, which will cause a large shrinkage rate; For knitted fabrics, if the loosening and dyeing processes are used, the fibers will not be stretched, and the shrinkage rate due to fiber is small, but if the processing method with large tensile tension is used, Larger fiber shrinkage will occur. It is important to pay attention that the fiber deformation caused by external force will be difficult to recover due to the cohesion between the fibers and the intertwining (coil knot) resistance between the yarns. Therefore, we must pay attention to the training and drifting of cotton knitted fabric Control of tensile external force during dyeing.
1.2 Yarn shrinkage
Yarn shrinkage comes from two aspects: water absorption and swelling of the fibers and elongation of the yarn caused by external forces.
First of all, fiber swelling in water will cause the length of the yarn to shrink, and the greater the swelling of the fiber fabric, the greater the shrinkage caused by it.
Fiber swelling makes the effective diameter of the yarn increase, can not be extended or even shortened (measured by the length of the fiber around the yarn axis). In the case where it is impossible to untwist the yarn, the fiber can only be reduced by reducing the length of the yarn along the axis ( From L1 to L2) to adjust the position and posture in the yarn to shorten the yarn.
In addition, during the dyeing and finishing wet processing, the excessive tensile external force or the tensile external force is not excessive but it continuously acts on the fabric for a long time, so that the fabric has no chance of relaxation and shrinkage, which will inevitably lead to yarn elongation, yarn The twist of the yarn is reduced, and the water in the wet processing will fix the cellulose fiber yarn.
In the free state of the yarn, this stretching can be completely retracted, but the yarn in the fabric is difficult to recover due to the cohesion between the fibers and the interweaving resistance between the yarns. Finishing methods such as rubber blanket pre-shrinking are difficult to shrink, but in a drum washing machine or in the process of allowing the fabric to be completely relaxed, the yarn stretched by fiber swelling can be retracted.
1.3 Shrinking fabric
Cotton fibers absorb and swell in water, in addition to causing changes in the structure of the yarn and changes in the loop structure of the knitted fabric.
First of all, the swelling of the fiber increases the effective diameter of the yarn. In the case that the yarn cannot be untwisted and the yarn itself is shortened, the coil sleeve node can only be increased by increasing the coil width, shortening the coil height, or reducing the distance between the columns. Adjust the three-dimensional state of the knitting loop. This process may cause the fabric to shrink together in the longitudinal and transverse directions (b1 <b, a1 <a), and may also cause the fabric to shrink unidirectionally in both the longitudinal and transverse directions, and the other direction may even be somewhat different. Increase, that is, negative shrinkage (b1 <b, a1> a or b1> b, a1 <a), the direction and degree of shrinkage depends on the weaving and dyeing and finishing of the fabric.
In addition, during the wet processing of knitted fabrics that are easily stretched and deformed, even under a small external force, the stitches are prone to large deformation, which often manifests as an increase in stitch height and a decrease in stitch width. This kind of deformation of cotton knitted fabrics in the wet state is difficult to recover due to the effects of yarn interweaving resistance and cohesion between fibers at the knot point of the fabric loop, which will cause greater shrinkage space for the fabric.
It must also be noted that compared to the degree of fabric deformation caused by external force stretching of the yarn in wet processing, the degree of fabric deformation caused by the loop being stretched will be greater, because when the knitted fabric is stretched by external force in the longitudinal or transverse direction First, the loop height or width increases, the second is the yarn being stretched, and the second is the fiber being stretched. Of course, although the elongation of the fabric caused by the elongation of the coil caused by external force stretching is large, it is relatively easy to retract through appropriate finishing techniques (such as overfeeding and pre-shrinking of rubber blankets).
Causes of Wrinkles and Creases on Cotton Knitted Fabric (Single Side)
Cotton knitted fabrics, especially single-sided knitted fabrics, are prone to produce wrinkles and creases that cannot be eliminated after finishing during the dyeing and finishing process, which seriously affects the appearance of the fabric. The root cause of this phenomenon is also closely related to fiber swelling.
The swelling of cotton fibers will inevitably cause changes in the yarn structure and the coil structure. The changes in the yarn structure are manifested by the thickening, shortening and twist of the yarn, and the changes in the coil structure are represented by an increased loop arc and shortened loops or the distance between loops Shrinking, the result of these two changes results in shrinking and denser fabric. Due to the restriction of yarn interweaving resistance and cohesion between fibers on the fabric structure, although the fiber swelling process is reversible, the contracted and dense fabric form will not be restored by the recovery of fiber form.
