Prevention of dyeing and finishing production problems

Dyeing and finishing production is a complicated job. The production process is complex and meticulous, and problems can occur at any time if you are not careful.

In the dyeing and finishing production of textiles, because there are many links in the entire process, there are also many factors that affect the dyeing and finishing results. In addition to frequent color and luster quality defects such as color difference, other quality problems often occur.

Therefore, dyeing and finishing defects can be basically divided into the following three categories according to their phenomena:

  1. Color quality:

Problems such as color difference, uneven color (color flowers, color spots, color stains) and color fastness.

2.Intrinsic quality:

Problems such as fiber damage, loss of elasticity, skewed longitude and latitude, dense paths, shrinkage, gram weight and door width dimensions.

  1. Other qualities:

Problems such as stains on the finishing agent, pilling, crepe printing, and substandard finishing.

 

Causes of dyeing and finishing defects

  1. Yarn (silk) and gray cloth quality

The quality of yarn (silk) and gray cloth affects the quality of dyed finished products. This influence has a certain latent nature and is often exposed after dyeing. And this impact is often overlapped with problems that arise during the dyeing and finishing processes, increasing the complexity of dyeing and finishing defects. It also adds difficulty to the search for the causes of defects. Some dyeing and finishing defects are caused by yarn (silk) and gray cloth quality problems, such as width size, warp and weft skew, and expansion and contraction rate. Although it can be slightly adjusted in the post-processing process, it cannot fundamentally solve the problem. Therefore, the source of raw materials should be strictly controlled to ensure that the quality of yarn (silk) and gray cloth reaches the target to avoid the occurrence of defects in subsequent dyeing and finishing processes.

 

2.Dyeing and finishing process

The quality of the dyeing and finishing process is affected by both hardware and software.

 

Hardware:

The first is the applicability and integrity of hardware such as mechanical equipment and instruments.

The second step is the inspection and selection of the quality of raw materials such as dyes and auxiliaries.

 

Software:

It is mainly reflected in the implementation choices of process prescriptions, production processes, operating procedures, etc.

It is also reflected in the management level (including technical management and disciplinary management) and the overall quality of grassroots employees.

 

First of all, we must have a clear understanding of the variety adaptability of dyeing and finishing equipment. Because dyeing and finishing machinery is differentiated and specific for different fibers and different types of textiles, it is necessary to understand the fibers that the dyeing and finishing machinery can add and whether it is suitable for woven fabrics or knitted fabrics. If it is suitable for knitted fabrics, it needs to be distinguished whether it is suitable for warp knitted fabrics, weft knitted fabrics or horizontal knitted fabrics. It should also be understood whether the equipment is limited to a single variety, or a composite type that can be used in several categories.

 

for example:

The high-speed and high-pressure jet dyeing machine is suitable for dyeing polyester warp knitted fabrics, and is also suitable for dyeing polyester processed filament medium-thick wool-like style woven gray fabrics. But it is not suitable for dyeing polyester filament low-density thin woven fabrics (such as rain yarn, triclon and other silks). It is also not suitable for dyeing polyester-viscose, polyester-cotton and other blended fiber fabrics and weft-knitted fabrics. Otherwise, it is easy for cracks and seams to appear after dyeing (filament low-density thin woven fabrics) or pilling (polyester-viscose, polyester-cotton blended fiber fabrics) or the fabric’s original elastic characteristics will be lost (weft-knitted fabrics).

 

 

The jigger dyeing machine is suitable for dyeing small batches and multiple varieties of woven fabrics with a wide range of light weight and thickness. But it cannot be used for knitted fabrics with loop structure.

 

 

The overflow dyeing machine is suitable for weft knitted fabrics, polyester-viscose, polyester-cotton blended fibers and knitted fabrics with high elastic requirements, but it is not suitable for dyeing warp knitted and woven fabrics. Silk woven fabrics should be dyed on jig dyeing machines, but crepe fabrics and silk knitted fabrics, which are both woven from silk, should be dyed on specially designed machines that are significantly different from the overflow dyeing machine used for cotton.

 

 

Secondly, different dyes are suitable for different fibers, and are suitable for different deep, medium and light colors. Therefore, different types of dyes need to be selected differently. For example: S-type disperse dyes are suitable for dyeing with deep and intense colors, and type E dyes are suitable for dyeing with medium and light colors. Among the B-type reactive dyes, the BES type is suitable for medium and light color dyeing, and B-D types are suitable for deep and concentrated color dyeing. Due to the differences in fiber and fabric varieties, dyes, and dyeing and finishing machinery and equipment discussed above, the same additives will be used.

 

 

Only by fully understanding and recognizing the differences in raw materials, equipment, dyes, and auxiliaries and improving the quality and level of users can we ensure the quality of textile dyeing and finishing and avoid the occurrence of defects.

 

Defects in color quality

 

  1. Uneven color

Uneven color mainly manifests as color flowers, color spots and color stains. Among them, for the problem of color flowers, the selection of additives, the order of heating and adding materials, etc. should be properly controlled. Leveling agents need to be used just in case. Color spots and stains are mainly related to the cleaning work of dyes, auxiliaries and equipment. For example, some disperse dyes with low water solubility are affected by factors such as particle size, anti-agglomeration performance, process prescription, and whether the dyeing machine is thoroughly cleaned. If not properly controlled during use, color spots and color stains may easily occur.

  1. Color fastness

There are many color fastness items, including: soaping fastness, rubbing fastness, light fastness, perspiration fastness, chlorine resistance, weather fastness, etc. Among them, soaping fastness is mainly caused by subjective reasons. Light fastness, perspiration fastness and chlorine resistance are mainly affected by objective factors, namely the properties of the dye. Rubbing fastness and weather fastness are both related to subjective factors and are affected by objective factors (such as dyes and additive types). For example, the problem of wind marks in weather fastness is caused by uneven color caused by local discoloration. Mainly occurs on cotton fabrics, especially after using reactive dyes containing vinyl sulfone groups. Moreover, wind marks will not appear immediately after the fabric is dyed. Wind marks will not appear until the fabric is put into the warehouse or even after it is finished.

 

inherent quality defects

 

  1. Damage to fibers

Fiber brittleness is directly related to pre-treatment, and also related to too many times of stripping and re-dying, which will cause a sharp decrease in fiber strength. Severe fiber brittleness will form holes in the fabric, while minor fiber damage will cause needles to appear in the finished garment. Therefore, the pre-treatment process and the number of repairs should be strictly controlled.

 

  1. Lack of flexibility

For spandex-free weft knitted fabrics, the elasticity is formed by the combination of the weaving method (such as rib cloth) and the elasticity of the fiber raw material itself (such as elastic yarn). If the dyeing and finishing equipment is improperly selected, for example, this type of fabric is placed in a high-speed liquid jet dyeing machine with a nozzle pressure above 1 kg/cmz and a gray cloth operating speed of 400 to 600 m/min. Dyeing will expand the diameter of the fabric and reduce its elasticity. If the color is peeled off and repaired after dyeing defects occur, the elasticity will be further reduced. For fabrics with spandex involved, it is also necessary to reduce the number of repairs. The more the number of repairs, the greater the elasticity of the fabric will decrease. In severe cases, a large number of spandex filaments will break, which will affect the final service performance.

 

  1. Longitude and latitude oblique

Both woven fabrics and knitted fabrics are prone to warp skew, which is caused by both equipment and operations. Weft-knitted fabrics are prone to warp skew, also called longitudinal skew. This problem is mainly caused by weaving. The direction and degree of skew are jointly affected by the twist and twist direction of the yarn count, the length of the coil and the number of loop systems, as well as the rotation direction of the loom.

 

Although this can be corrected to a certain extent during tenter finishing in the post-finishing process, this is temporary for cotton weft-knitted fabrics. The skew will often return to its original position after the garment is washed, so preventive measures should be taken during the weaving process.

 

  1. Shrinkage, gram weight and door width size

The shrinkage rate, gram quality and door width of the dyed finished product are interrelated. And influence each other. In order to achieve the stability of these indicators, they should be strictly controlled during the weaving of gray fabrics. Standardize the operation in the dyeing and finishing process. If the weaving process of the raw fabric is not properly controlled and the above indicators cannot be achieved, although some compensation and adjustments can be made in the dyeing and finishing process, it can only be a limited correction within a certain range and cannot be corrected.

 

  1. Warp beams, rungs and sparse and dense road

Warp beams and rungs can occur on woven fabrics and knitted fabrics. From the appearance (such as rain-shaped stripes, horizontal color bars and color stripes, etc.), it is a problem of color quality. However, it is not caused by the dyeing step. The main reason is that the company failed to control the production plan management, the fiber raw material management was chaotic, and the fibers of different batch numbers were mixed and weaved.

This type of problem is not obvious on white blanks, so it is easy to be ignored. Although dyes with good hiding properties are screened during dyeing to control such problems to a certain extent, they cannot fundamentally solve the problem. Generally speaking, it is best to produce white fabrics with such problems, followed by black or printed fabrics. Density refers to the phenomenon that the fabric surface presents optical illusion properties after dyeing.

 

 

Similarly, sparse and dense road problems are not easily discovered when the blank is white and are often ignored. The occurrence of sparse paths is caused by the position of the knitting needles becoming loose after the knitting machine has been used for a long time, resulting in irregularities in the arrangement. Woven fabrics may be caused by the abnormal beat-up device of the loom. The occurrence of these problems is generally caused by the lack of technical quality of loom maintenance workers and the weak sense of management responsibility and inadequate management.

 

Therefore, it is necessary to improve the quality level of grassroots employees and strengthen the supervision of managers to avoid the occurrence of such defects.

 

inherent quality defects

 

  1. Finishing agent stains

 

There are many types of finishing, and their importance and influence on textiles is no less than that of dyeing. Finishing defects will inevitably occur during the finishing process. In terms of process design, in order to shorten the production process and save time, softness, antistatic, waterproof and oil-proof finishing are often combined. However, due to the compatibility issues of various additive varieties, it is more likely to cause defects such as spots and stains on the finishing agent.

 

And some finishing defects are irreparable for textiles with multiple colors in one yarn and multiple colors in one cloth. For example, the finishing of loose fibers, single yarn bobbins and hanks of cotton fiber after dyeing using silicone oil softeners is often done in a dyeing machine. After continuous use for a long time, this kind of softener will form accumulation on the inner wall of the processing equipment and its pipes. After a certain level, the accumulation may suddenly fall onto the fibers and cause silicone oil stains. It is very difficult to remove silicone oil stains from the fibers. In addition, people require the effects of finishing additives to be durable, but the better the durability, the greater the difficulty in repair and stripping.

 

 

For example, silicone softeners, fluorine-based three-proof finishing agents, coating agents, etc. are all types with excellent durability and difficult to remove. Therefore, when using such reagents, repairs should be avoided as much as possible, and the use process should be meticulous and standardized.

 

  1. Pilling and fluffing

Pilling is easy to occur in unmercerized and singed polyester-cotton blends, polyester-viscose blends, and polyester-nitrile blended fabrics.

 

  1. Crepe printing and crepe strips

Large area wrinkle printing is one of the problems caused by loose dip dyeing method. The root cause is mainly due to the dyeing form of the dyeing machine and its equipment characteristics. Anti-wrinkle additives are beneficial to avoid the appearance of wrinkles in liquid jet dyeing machines. The difference in shrinkage of fabrics in boiling water in the dyeing bath can also cause wrinkles. Straight wrinkles are mainly caused by the tight open-width dyeing equipment system that is not controlled and prevented. Therefore, the process should be strictly controlled.

 

  1. Post-processing is not up to standard

Functional finishing such as soft, waterproof and anti-static. If the functional indicators are not reached, finishing can be carried out again. However, the functional index saturation point of some finishing additives should be experimentally identified, otherwise repeated finishing will have little effect.

 

There are many factors that affect the quality of dyeing and finishing, such as fibers, gray fabrics, dyes and auxiliaries, as well as the matching of textile varieties and equipment. It also includes factors such as craftsmanship, technology, management and the quality of grassroots employees.

 

Therefore, the repair situation in dyeing and finishing production cannot be completely avoided, and it is also an indispensable technology in dyeing and finishing production. However, some defects cannot be repaired and returned to normal once they occur, especially some hard damage such as fiber brittleness, holes, fabric tissue cracks, fuzzing and pilling, etc. In addition, some textile types, such as multi-color yarns and multi-color fabrics, yarn-dyed and printed varieties, can be stripped and re-dyed. Repair of non-faulty defects, such as finishing agent stains, discoloration, color matching, staining, etc., is also not suitable for repairing certain defects in textiles and weaving. For example, excessively serious warps, rungs, dense paths, gram weight and door width dimensions are generally difficult to fundamentally correct during the dyeing and finishing process.

 

 

Therefore, comprehensive prevention-oriented strategies should be adopted promptly in all areas where problems may occur during the production process. Only in this way can quality problems in dyeing and finishing production be proactively and truly effectively reduced and avoided.

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