The Production Process Of "Dead Mark" And Unstable Size And Poor Cloth Effect In Cotton Dyeing And Finishing Are Solved.

In view of the problems of poor dimensional stability and wrinkle creases in cotton knitted fabric during dyeing and finishing process, the reasons for shrinkage of cotton knitted fabric and wrinkle of cloth fold are described. From the two aspects of equipment and technology, specific measures for reducing shrinkage rate of cotton knitted fabric and preventing wrinkle and wrinkle of cotton knitted fabric are put forward, which provides reference for dimensional stability and cloth effect of cotton knitted fabric during dyeing and finishing process.

Common quality problems in cotton dyeing and finishing

The quality problems often appeared in dyeing and finishing of cotton knitted fabrics are manifested in 4 aspects:

1. dyeing and printing are prone to problems such as color, color difference and poor color fastness.

2. fiber damage is relatively large.

3. the fabric has high shrinkage and poor dimensional stability.

4., the wrinkle of cloth fold is serious and the friction hairiness is more, that is, the cloth effect is poor.

Through the joint efforts of dye and auxiliaries, chemical workers and dyeing and finishing workers, problems related to dyeing and heavier fiber damage have been well solved. However, the problems of poor dimensional stability and poor cloth effect (manifested as fold creases and Mao Yu) have not been solved well for a long time. The reasons for shrinkage of cotton knitted fabrics, the technology of shrinkproof and the causes of wrinkle creases in cotton knitted fabrics and the methods to overcome them are discussed in this paper.

Causes of shrinkage and wrinkle of cloth fold

Reasons for shrinkage of 1. cotton knitted fabric

The shrinkage of the fabric is measured by the shrinkage of the washing machine, that is, the fabric is completely relaxed in the water. Not only after the dyeing and finishing process, the gray fabric and the garment will shrink when it is loosened, but also the size of the knitted billet that has just been knitted will also shrink when it is completely soaked in water. The shrinkage process of water washing or relaxation treatment of knitted fabric is accomplished by fiber shrinkage, yarn shrinkage and fabric shrinkage.

1.1 shrinkage of fibers

In spinning, spinning (chemical fiber), weaving and drawing, dyeing and finishing process, fiber will stretch and stretch inside the fiber due to tensile force and the internal stress in the fiber. The tensile state and the interlocking force between the fibers will make the elongation state and internal stress temporarily immobilized. When water or steam is used, the water molecules will weaken the force between the fiber macromolecular segments and reduce the retracting barriers of macromolecular segments, and the fibers will contract under the action of internal stress.

Filament fabrics, twisted yarn fabrics and regenerated cellulose fiber fabrics, in dyeing and finishing processes (such as scouring and bleaching and dyeing), fibers are easily stretched by external forces and elongate, resulting in larger shrinkage. Cotton knitted fabrics, if used in loose bleaching and dyeing processes, will not be stretched, and the shrinkage rate due to fiber causes is very small. But if the tensile strength is larger, the shrinkage will be larger. It must be emphasized that the fiber deformation caused by external force stretching is difficult to recover due to the force between the fibers and the interlacing between the yarns. Therefore, we must pay attention to the control of the tensile force in the process of scouring and bleaching and dyeing of cotton knitted fabrics.

1.2 shrinkage of yarn

Shrinkage of yarns comes from two aspects: swelling and swelling of fibers and elongation of yarns under external forces.

First, the swelling and absorption of fibers in water will lead to the shrinkage of yarns. The larger the swelling property, the greater the shrinkage rate. The swelling properties of several cellulose fibers are shown in Table 1.

　　 The swelling of the fibers makes the effective diameter of the yarn increase, and it can not stretch or even shorten (the fiber that can be measured by the fiber winding stroke) can not be twisted under the condition of yarn twisting. It can only adjust the position and posture of the yarn in the yarn by reducing the stroke along the yarn axis (from Ll to L2), so as to shorten the yarn.

In addition, in the wet finishing process, excessive tensile force or tensile force is not too large, but for a long time continuous action on the fabric, resulting in no relaxation of the fabric shrinkage chance, will inevitably lead to yarn elongation and yarn twist reduction, and the wet processing of water will play a role in twisting cellulose fiber yarn.

The yarn of free state 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 yarns. It is difficult to retract if it is finished by means of over feeding and rubber blanking. However, the yarn stretched by fiber swelling can be retracted in the barrel washing machine or during the process of completely relaxing water treatment.

1.3 shrinkage of fabric

Cotton fibers absorb water and expand in water, in addition to causing changes in yarn structure, and also causing changes in the coil structure of knitted fabrics.

First, the effective diameter of yarn increases with fiber swelling. When the yarn can not be twisted and the yarn itself is shortened, the three-dimensional space condition of the knitting coil can be adjusted by increasing the width of the coil, shortening the height of the coil or shortening the spacing between the rings. This process may cause longitudinal and transverse contraction of the fabric (B1 A or B1 >b, A1

In addition, in the wet process such as scouring and bleaching and dyeing, even when the external force is stretched, the deformation of the knitted fabric is easy to produce larger deformation. It is often shown that the height of the coil is increased and the width of the coil is reduced. The deformation of the cotton knitted fabric in wet condition is difficult to recover due to the weaving resistance and the interlocking force of the fibers, which will cause greater shrinkage space for the knitted fabric.

It must also be emphasized that compared with the degree of fabric deformation caused by external force stretching in the wet process, the deformation of the fabric caused by the stretching of the coil is greater, because when the fabric is stretched vertically or horizontally under external force, it first shows the increase of the height or width of the coil, followed by the stretching of the yarns, and then the stretching of the fibers. Of course, the elongation of the fabric caused by external force stretching is larger, but it is easier to retract by proper finishing technology, such as over feeding and rubber blanking.

Causes for wrinkle creases in cotton knitted fabric (one side)

Cotton knitted fabric, especially one side knitted fabric, easily produces wrinkles and wrinkles which can not be eliminated after finishing, which seriously affects the fabric appearance. The fundamental reason for this phenomenon is also closely related to the swelling of fibers.

Swelling of cotton fibers will inevitably lead to changes in yarn structure and coil structure. The yarn structure changes are thickened, shortened and twisted. The change of coil structure is manifested by the increase of ring arc and the shortening of the ring column or the reduction of the spacing between the columns. These two changes result in shrinkage and densification of the fabric. Due to the interleaving force of yarn and the binding force between fibers, the structure of the fabric is restrained. Although the swelling process of the fiber is reversible, the shrinkage of the compact fabric will not recover due to the recovery of fiber shape.

　　织密稀松的单面棉针织原坯布，在进行初次湿加工(如练漂)时，如果织物受到了不规则外力作用(大小不一、方向任意)，如织物绳状运行、压辊挤压、染色机喷嘴挤压、织物本身堆布挤压等，在纤维还未溶胀或溶胀效果还很差的时候，由于纤维抱合力较差、纱线交织阻力较小，纱线结构(表现为捻度)和织物结构(表现为套结点的三维空间)会产生不均匀的变化，这样织物因纤维溶胀发生的收缩致密效果也将是不均匀的，而这种织物密度不匀、套结点三维空间有异样的效果，却会因溶胀收缩后已经大大增高了的纤维抱合力，和纱线交织阻力的作用而无法复原，于是就形成了看似是褶皱折痕的现象。 Double knitted fabric, because of its fabric structure, has a very high yarn interleaving resistance and fiber holding force when it is in the gray cloth state. When the first wet processing (such as scouring and bleaching), the fabric is not easy to contract due to irregular external force.

Because the initial wet processing of cotton knitted fabrics is mostly scouring and bleaching, and dyeing machines are commonly used for rope drifting and bleaching, many dyeing and finishing factories erroneously believe that the wrinkle creases that can not be eliminated after finishing the finishing of single cotton knitted fabrics are caused by rope drifting and bleaching. Only flat width scouring and bleaching can overcome them.

Shrinkage proof technology of cotton knitted fabric

Shrinkage of cotton knitted fabric comes from three aspects, namely shrinkage of fibers, shrinkage of yarns and shrinkage of fabrics (coils), and all of them are related to tensile tension of fabrics. Therefore, shrinkage proofing methods and techniques can take four ways:

A. as far as possible, reduce the tensile force of cotton knitted fabric during wet processing.

B. before the scouring and bleaching and dyeing, the fabric is slack and wet treated to make the fabric compact and compact.

C. is mercerized.

After D. scouring, bleaching, dyeing and printing, shrink resistant finishing is carried out.

1. scouring, bleaching, dyeing and washing technology to reduce tension tension.

The characteristics of easy stretching and deformation of knitted fabrics make it difficult to control the tensile tension of fabrics during scouring, bleaching, dyeing and washing. This is also an important reason for the slow development of knitted fabric's continuous scouring and bleaching and dyeing technology. One of the advantages of the whole process such as bleaching, dyeing and washing with jet dyeing machines and other batch dyeing machines is that the fabric has good relaxation effect and is easy to control the dimensional stability and density of the fabric (the quality of the unit area).

This kind of good relaxation effect comes from the loose relaxation area during the running of the fabric and the low tension stretching area which can make the fabric run fast as long as it exerts little tension on the fabric.

The continuous scouring, bleaching, dyeing and washing methods of cotton knitted fabric can also be realized by referring to the working principle of the loose dyeing machine.

The continuous water washing unit adopts the blade rotary drum structure, the fabric is more relaxed than the jet dyeing machine, and it can be used for 3 kinds of knitted fabrics, which are cylinder, open width and edge.

Relaxation pretreatment technology for 2. cotton knitted fabric in water

Loosely woven cotton knitted grey fabric can be soaked and soaked in water, which makes the fabric shrink and dense through fiber swelling. Because of the interlocking effect between fibers and the interweaving of yarns, the fabric structure after compaction is quite stable. During subsequent processing, only when the external force is small or even the external force is larger, the time of action is very short, and the chance to relax in water can be obtained in time. The use of intermittent loosening dyeing machine can achieve good dimensional stability. The reason is that cotton knitted fabric has been loosely pretreated in the first step of dyeing and finishing process, and the dimension stability of some continuous scouring and bleaching equipment is not good. The reason is that the continuous wet washing machine has larger tensile tension or longer stretching time after the continuous rinsing machine, and the first step wet processing is also carried out under the tensile state.

3. mercerizing

Mercerization is a very important technology to reduce shrinkage and improve dimensional stability of cotton fabrics. First of all, mercerization will cause irreversible swelling of cotton fibers. When the mercerized cotton fabric is washed, the swelling degree of cotton fibers will be greatly reduced, so the shrinkage rate will be greatly reduced. In addition, mercerization will rearrange the macromolecular chain segments of cotton fibers, which can better eliminate the internal stress in fibers and improve the dimensional stability of fabrics.

It is worth mentioning that there are many factories using grey mercerization, because the surface mercerizing phenomenon is more serious, mercerizing can improve the fabric dimensional stability function can not be fully reflected, if the mercerizing and bleaching mercerizing, this problem can be solved; some factories use double mercerizing technology, that is, the two mercerization of cotton yarn mercerization + grey cloth mercerization, the fabric has obtained good dimensional stability, and the mercerization of cloth actually used the effect of mercerizing and mercerizing after mercerizing and double mercerizing, not two superimposed mercerizing effect.

4. shrink proof finishing technology

In the dyeing and finishing process of cotton knitted fabric in wet and dry conditions, it is unavoidable that the fabric is stretched and deformed. It needs to be improved through proper finishing process. There are two main methods of shrink proof finishing.

4.1 longitudinal over feeding and transverse extension

When the cotton knitted fabric is stretched lengthwise, it will also bring transverse contraction. The most direct way to reduce the longitudinal shrinkage and improve the dimensional stability is to lengthen the feed vertically and horizontally. The open fabric is stretched by needle chain, and the cylindrical fabric is expanded by long supporting plate. At the same time, a certain amount of moisture in the fabric is required, which can be achieved through the rolling water (combined with finishing liquid) or water vapor.

This longitudinal overfeeding and transverse stretching method reduces the degree of shrinkage of the fabric, because the yarn interleaving resistance is always difficult to get rid of by longitudinal transverse width. Sometimes, it may result in excessive shrinkage or excessive fabric density (the quality of the unit area).

4.2 forced retraction finishing

Forced retraction is to minimize the longitudinal length of fabric without requiring the fabric to be stretched or even smaller.

At present, the most effective method is the shrink proof technology of rubber blanket pre shrinking machine, which is also a common method of shrink proofing of woven fabrics.

Wrinkle proof technology for cotton knitted fabric

The effective step to prevent wrinkle creases which can not be eliminated after finishing of single cotton knitted fabric is the first step of wet treatment of cotton knitted fabric.

There are three specific methods:

Method 1

Before the fabric is subjected to irregular tension and pressure, it is immersed in water in a completely relaxed state, and the fabric is freely and evenly contracted through swelling of the fiber. The uniformly compressed and compact fabric will be relatively stable due to the interlocking force between fibers and the interleaving resistance between yarns, so that the dead folds will not be produced due to the effect of pressure or tensile force (proper size) in subsequent processing. For example, a multi-functional fully loosening continuous scouring and bleaching machine, the first unit of grey fabric is a loose crease which can make the fabric soaked in water in a completely relaxed state. The fabric is contracted freely and evenly through fiber swelling.

Method 2

Before the fabric is subjected to irregular tension and pressure, wet processing is carried out under regular and appropriate external force (including transverse and longitudinal). In this case, the fabric shape change caused by water swelling is uniform and orderly. There are some low tension continuous scouring and bleaching machines for flat knitting of open width fabric, which is to prevent wrinkles by using this method.

Method 3

Before the fabric is subjected to irregular tension and pressure, the irreversible swelling of the fibers is carried out under regular external force. This process is mercerization. The cotton knitted fabric after mercerization does not produce so-called Dead wrinkle in the process of rope drifting and dyeing. The reason why the mercerized cotton fabric is of high dimensional stability is also this.

Be careful

The shrinkage and wrinkle of cotton knitted fabric and single side knitted fabric have two common reasons, which are all related to the swelling property of cotton fiber, and are related to the external force of the fabric in wet processing such as scouring, bleaching, dyeing and washing. This is also the reason why the size stability and cloth effect of cotton knitted fabrics are summed up together.

How to improve the dimensional stability of cotton knitted fabrics and get good cloth effect (no wrinkle creases, frictional hairiness, etc.) is a topic of concern in the knitting industry for a long time. For this reason, a lot of process technology and related equipment have been researched and established, but it has not achieved satisfactory results. There are still some phenomena such as the size is not stable enough, and the wrinkle of cloth fold is serious.

Although the whole process of dyeing, washing, dyeing and washing has been improved to a certain extent, although the dimensional stability of the fabric has been improved to a certain extent, the problem is the increase of wrinkle, friction, hairiness and consumption of water, electricity and steam, as well as the instability of product quality. Flat width continuous scouring and bleaching technology and plain dyeing technology have been paid much attention in recent years, but most of the equipment used is compact continuous mode. Although the flat cloth effect can be obtained, there is a phenomenon of larger fabric shrinkage or lighter weight per unit area. From the past related technology, more attention is paid to loose machining process, such as intermittent loosening.

It can be seen that in order to get the most ideal dimensional stability and cloth effect, it is not enough to pay attention to the above mentioned "loose machining" and "flat width processing". We must also pay attention to the following three points:

First, the emphasis should be placed on the fabric form and deformation caused by water swelling of the cotton knitted fabric during the first wet treatment process and the effect on fabric dimensional stability and cloth surface effect. The best method is to put the fabric in a completely relaxed state in water and to shrink the fabric freely and evenly through the swelling of the fabric, thus achieving good dimensional stability and ensuring smooth cloth effect.

Second, attention should be paid to the "shaping" function of mercerizing process that can make irreversible swelling of cotton fibers to cotton knitted fabrics. The mercerized cotton knitted fabric is not only of high dimensional stability, but also large external force (pressure or tension) will not cause wrinkle creases.

Third, pay attention to shrink prevention finishing technology. "Over feeding and shrink proof technology" (over feeding expansion, over feeding drying, over feeding light, etc.) is not the whole content of shrink proof technology. Some mature cotton fabric fabric shrinkage prevention technologies, such as rubber blanket pre shrinking technology, should be applied in knitted fabric shrink proof finishing.