Shallow Discussion on the New Dyeing and Finishing Technology of Silk Knitted Fabrics

Silk clothing is the national costume with the longest history and cultural heritage in China. However, since silk knits started relatively late, the dyeing and finishing of silk knit fabrics is still behind. Both the processing technology and the dyeing auxiliaries have a large gap with foreign countries. In particular, the finishing technology of silk knitted fabrics is much wider than that of industrial developed countries, resulting in a large quantity of silk knitted garments in China, but the products are single, the grades are not high, the added value is low, and the competitiveness is weak. This is not only a kind of sadness for the people of the silk kingdom, which has been known for so long as it has a long tradition in the silk industry. In recent years, the proportion of thick and heavy silk knitted fabrics of 130g/m2 or more has been increasing. Customers are increasingly demanding the processing of silk knitted fabrics, and new types of silk knitted materials, composite yarns, wrapping yarns and various interwoven knitwear products have been continuously developed. The development, the compounding of raw materials, the thick and heavy fabrics, and the functionality of the product are three major trends, and new requirements have been put forward for the processing technology of scouring, dyeing, and finishing. To develop China's silk knitting industry and revitalize China's silk industry, we must strengthen research on dyeing and finishing technologies of silk knitted fabrics.
1 EKL-2 special foam agent characteristics and application
The raw silk used in the silk knitting factory is made of crepe and automatic reeling. The reeling factory's raw silk, especially the 44/48dtex automatic reeling yarn, has a large bending rigidity, and it is very difficult to make loops, resulting in the failure of knitting. Therefore, it is necessary to increase the flexibility and lubricity of the yarn by the foaming. The traditionally used foaming agents in silk knitting companies are representative of additives L and additives WS, but they are poor in softness and lack smoothness, even if some of them are soaked or alkali-pretreated and then soaked. Due to the complex process, the softness and smoothness of raw silk cannot meet the technical requirements of knitting production. As a result, the silk weft knitted fabrics are unevenly distributed, the fabrics are rough, and a large amount of the sericin powder is flaked, so that the needle grooves are blocked, and the tongue needles cannot be flexibly moved, resulting in sickles such as dilute road needles. And the white powder deposits on the fuselage, which affects the service life of the machine, and even the expensive imported needles cause broken needles due to repeated friction. The main reason is that the raw silk thread is not completely soaked. Some silk-knitting manufacturers had to apply a layer of white oil or sulphate with low sulfonation directly on the yarn during weaving. However, it caused a large amount of oil traces and filaments on the fabric blank so that the quality of the sliver was not improved. Good, the oil marks are hard to train, the oil in the scouring tanks gathers, and the stains are again contaminated. There are more than 10 types of foaming agents available in the country, including oil additives and wax-free (integrated) additives, among which the silk knitting special foaming agent EKL-2 has the best performance and the best results. EKL-2 foaming agent is mainly composed of a variety of surfactants and refined mineral oil, with a solid content of (25 ± 2)%, PH value of 6 ~ 7.5. The foaming agent has a simple application process and is easy to operate. The soaking process conditions of 60kg/piece 44/48dtex raw silk are shown in Table 1.
Table 1 44/48dtex raw silk soaking process
The soaking process of EKL-2 foaming agent is simple and does not need to be degummed in advance. Even if it is a kind of automatic twinning silk 44/48dtex, it can have very good softness and smoothness after soaking treatment according to Table 1 process. The coefficient of dynamic and static friction is significantly reduced, and its strength and cohesion performance are superior to those of other filaments soaked in silk. Not only can it be used smoothly for knitting, but also it can make the filaments resistant to friction and the white powder can be significantly reduced, thus protecting the machine and prolonging the life of the knitting needles. The surface of the fabric is also smooth and smooth, the coil is even, the scouring performance of the silk fabric is good, the whiteness is good, and the hand feels plump and smooth, and the quality is significantly improved.
2 The scouring of silk knits
The traditional scouring process of silk knitted fabrics is old and not optimized. Due to the long time, the saponification method is not easy to control because of the scouring process. It is not suitable for hard water, and the surface of the silk is easy to cause gray injury, crease marks, soap marks, etc., and it is easy to yellow. It is rarely used now. The enzymatic scouring process is complicated, the production efficiency is low, the cost is high, and there are not many manufacturers. In recent years, China successfully developed a new series of high-performance scouring agent EAT series, which is one of the representative varieties of a new generation of silk scouring agent in China. High-performance scouring agents EAT-2 and EAT-31 protect silk fibroin at high temperatures above 95°C, thereby avoiding gray injuries. For regions and manufacturers with poor water treatment conditions, river water, lake water, or tap water can be used directly. The scouring agents EAT-2 and EAT-31 not only have the silk fibroprotecting function, but also have a strong metal ion blocking function, can chelate and adsorb Ca2+, Fe3+ ions, so as to avoid rust spots on the silk; and can chelate calcium. , magnesium ions, reduce the hardness of water, no soap spots. When EAT is used as an efficient scouring agent, it is not necessary to add a mercerizing soap, dispersant WA, Remiphon A, additives 209 and 808, etc., and it is not necessary to add chelating agents such as EDTA. [Practice has proved that: EAT series silk high-performance scouring agent has three major characteristics of protecting silk fibroin, blocking metal ions and high efficiency and rapidity, and is worthy of being applied and promoted by silk knitted garment enterprises.
Staining of silk knit fabrics
When the silk knit fabric is dyed dark with a rope machine or an overflow machine, there are many gray injuries and more creases. Especially when heavy fabrics are dyed black or dark blue, defects such as color flowers, gray wounds and creases are often exposed. Some experts in the industry have proposed that the revolution in silk dyeing technology should be preceded by the addition of Pingping and O. Because Pingping plus O has a good affinity for anionic dyes, it is easy to combine with dyes into stable larger aggregates in low temperature areas, so it is difficult to dye at low temperatures. At high temperatures, the aggregates rapidly decompose, and the dye molecules released are rapidly dyed. For dyes with high dyeing speed, dyeing, coloring, stains, etc. occur. Especially when heavy silk is darkly stained, this is a common technical problem in the company. The development and application of high-performance, high-quality ESV-01, ESV-02 special effects leveling agents and processes to replace the decades-old flat-padded and O-old process are the key measures to solve the above problems and improve the dyeing quality of silk knitted fabrics.
In the rope machine or overflow dyeing machine, special process leveling agent ESV- 02 dyeing heavy silk knitted silk typical process formulae are shown in Table 2.

The knitted silk was dyed in a dye bath and dyed for 30 minutes at 25°C, warmed up to 40°C and then dyed for 20 minutes, and then continued to be dyed for 20 minutes at a heating rate of 2°C/min to 90°C. The special process leveler ESV- 02 process curve is shown in Figure 1.

The non-ionic surfactant compatible with the special leveling agent ESV makes the dyeing rate in the low, medium and high temperature areas tend to be uniform, so as to avoid competing dyeing in the high temperature area, and it is easy to dye defects. Some domestic silk knitwear manufacturers use special-effect leveling agent ESV, which solves the problems of color flowers, color willows, and white cores, especially in dyeing deep black, deep cyan, dark brown, etc., and dyeing more than 150g/m2. When knitted silk, special effects leveler ESV-01, ESV-02 played a superior role can not be compared to flat and O. The leveling agent ESV-02 is more effective than the leveling agent ESV-02. After testing and comparing, the ESV-02 performance leveler achieves the same level of imported leveling agent as Sandogen's Lyogen MS in Switzerland. Lower, is conducive to industry promotion.
4 Finishing of silk knitted fabrics
Silk knitted fabrics have excellent performance in their own use. Silk garments and accessories are made to be hygroscopic, light, smooth, gorgeous, comfortable, and flexible when worn, as well as special feel and drape. Therefore, during the process of collating, it is necessary not only to maintain its original unique style and excellent performance, but also to carry out the necessary special finishing in view of the fact that the silk product itself is prone to yellowing and wrinkling. The finishing of silk knitted fabrics, although they are numerous, can basically be divided into mechanical finishing and chemical finishing.
4.1 Mechanical finishing
After the scouring and dyeing of knitted silk, the coil structure is stretched in a straight or horizontal direction and is in an abnormal state. The width of the fabric is not uniform and the surface is not even. With mechanical finishing methods, smoothing the blanks and obtaining proper recovery of the deformed coils is an indispensable step in ensuring product quality and facilitating subsequent processing. For the finishing machinery of the silk weft-knitted fabric, it is best to use the Italian MONTI-203 type cylinder felt finishing machine and the SND-200 type felt finishing machine developed in China, both of which have basically the same performance. During the finishing process, the super-feeding expansion, steam heating and felt squeezing are used to increase the feel, elasticity and gloss of the fabric, improve the style of the knitted fabric, reduce the shrinkage rate, and reduce weft angle [1].
4.2 Chemical finishing
Silk knitted silk has different varieties such as white silk, dyed silk and printed silk. Conventional chemical finishing is mainly soft finishing and anti-static finishing.
a, soft finishing
A considerable number of China's real silk knitting manufacturers use cationic HC, Si-10 softeners and cationic sand softeners for soft finishing. These cationic surfactants are most irritating to human skin and mucous membranes. The softening agent ESN-33 is a non-ionic type, the main component of which is a derivative of a higher fatty acid amide, does not contain an amino group, and has the weakest irritation to human skin and mucous membranes. When used with various additives in the same bath, the hue and color of the dyestuffs are stable and will not yellow the silk. It is most suitable for the soft finishing of silk knitted silk and silk, and the soft and full effect is up to the level of softener Bicron 33N. It is the first choice for domestic softeners. After absorbing high-quality softeners, silk is smoother, fuller, and more flexible. It not only fully embodies the noble and luxurious style of silk, but also increases the comfort of taking.

b. Antistatic finishing
When the silk knitted fabric is softened and finished, it is necessary to add an antistatic agent to the bath to eliminate the electrostatic accumulation of the knitted fabric during drying, cutting, and sewing, so that the silk fabric will be free from aliasing and frequent needle breaks during cutting. At present, most of the silk knitters use cationic antistatic softener SN. This is an antistatic agent for synthetic fibers and can be used as an alkali reducer for polyester. Not only does it have a strong irritating effect on human skin, but it also has a serious impact on the hue and shade of anionic dyes, and it is easy to yellowish white silk. Non-ionic anti-static softeners ESF-1, ESF-930, completely avoid the above-mentioned disadvantages of cationic anti-static softener SN, performance is quite, but the price is low, is the best choice for silk knitting manufacturers.
5 Conclusion
In recent years, finishing, high-grade, and high added value are the directions for dyeing silk knitwear. Domestic and foreign customers are increasingly demanding the processing level of silk knit fabrics. The proportion of medium-thickness fabrics is increasing day by day. Various types of interwoven, blended, wrapped silk, composite yarns, and new silk raw material fabrics are continuously developed. The fabrics are heavy and composite. The three major trends in safety and health put forward higher requirements for the processing technology of scouring, dyeing and finishing. Through the finishing of silk knitted fabrics, it is necessary not only to maintain its original unique style and excellent performance, but also to conduct special sorting on the insufficiency of the silk products themselves. Therefore, the traditional training, dyeing auxiliaries and production processes can no longer adapt to the new situation.
a) EKL-2 special foam agent has the best performance and best effect. After being immersed in the EKL-2, the automatic twin silk 44/48dtex and other varieties have very good softness and smoothness, not only can weave smoothly and greatly improve the quality of the green silk, but also protect the machine equipment and extend the life of the needle.
b) The EAT series of efficient scouring agent formula is reasonable, which overcomes the shortcomings of traditional scouring agent. When the temperature is higher than 95°C, it has the three advantages of protecting silk fibroin, blocking metal ions, and high efficiency and rapidity.
The special leveling agent ESV can solve the problems of color flower, color and white core in dyeing, especially when dyeing various dark and heavy knitted fabrics, it has played a superior role that Pingping and O can not compare. After testing and comparison, the leveling agent ESV-02 achieves the same level of imported leveling agent as Sandogen's Lyogen MS from Switzerland, and the cost is lower, which is conducive to the promotion of the industry.
Mechanical finishing equipment is best to use Italy's MONTI-203 type cylinder felt finishing machine and China developed SND-200 type felt finishing machine. In chemical finishing, non-ionic softener ESN-33 has the weakest irritation to human skin and mucous membranes, and has the best softening effect. It is the first choice for domestic softeners. Non-ionic anti-static softeners ESF-1 and ESF-930 completely avoid many of the disadvantages of cationic antistatic SNs used by most manufacturers, and they are of similar performance and low price, and are increasingly welcomed by silk knitting manufacturers.
[1] Li Yiyou, Cheng Bin. Exploration of dyeing and finishing technology and equipment for silk knit fabrics [J]. Silk, 1993.6:21

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