Abstract: Based on the composition and property of T400T400 Denim/polyurethane twin-core yarn, this paper introduces its application in warp elastic denim and weft elastic denim and the related production processes. According to the performance comparison between twin-core yarn denim and conventional stretch denim, the twin-core yarn denim has better elasticity and dimensional stability. Its weft shrinkage rate is under 10%, and the elastic recovery rate can reach 96%. The wide use of twin-core yarn in denim fabrics makes the fabrics more comfortable and body-fit, which can also meet market demand.
Keywords: twin-core yarn; stretch denim; T400 fiber; property
Selection of T400 Denim raw materials
T400 Denim is a new type of elastic fiber. It has better elasticity and resilience than ordinary polyester and can avoid the occurrence of slack. At the same time, the stretchy denim woven by this fiber has good shape retention and wrinkle resistance. T400 Denim is made by the side-by-side composite spinning of PET and PTT (Figure 1). The difference in heat shrinkability and modulus of the two components of the fiber makes it have a tight crimped structure. The spiral fluctuations formed after spinning can be The woven double-core stretch denim provides excellent and long-lasting elasticity.
Preparation of double core yarn
Double core yarn is made by twisting and spinning short fiber as the outer material, and two kinds of filaments with different characteristics as the core yarn. Due to the other properties of the two core yarns have a strong complementarity, which makes the thread have more superior features.
Double core yarn refers to cotton bale T400 Denim fiber plus spandex. With the excellent expansion, excellent elastic recovery, dimensional stability, and superior strength of T400 fiber, coupled with the higher elasticity and repeated stretchability of spandex, it has good moisture absorption under the covering of cotton fiber. The fabric produced by the double-core yarn has no sense of restraint, looseness, etc., and has abrasion resistance, high tearing strength, low shrinkage rate, and good shape retention.
1. Production process technology
Double core yarn is used as warp yarn to weave warp denim fabric. Since the warp yarn needs to go through the production processes of batch warping, dyeing and sizing, and drawing-in, the coating quality of the double core yarn must be strictly controlled. Through the test, when the double core yarn is used as the warp, the core yarn content must be less than 25%; the core yarn must be completely caught when the yarn is broken; tape is attached 2 m before the warp beam to avoid yarn shrinkage.
2. Production process of double core yarn denim fabric
Customer incoming yarn → inspection → winding → warping → sizing and dyeing joint → drawing-in → weaving → cloth inspection → finishing → cloth inspection → rolling and packaging.
3. The main points of the double core yarn production process
Since the warp yarn is elastic and has a double-core yarn structure, the speed of the weaving process should be reduced as much as possible to reduce the accidental elongation of the string. At the same time, improve the technical level of car blocking, deal with broken filaments in time, and ensure the wrapping effect of warp yarns without naked core yarns.
In actual work, the application of T400 Denim fiber to stretch denim fabric can improve the strength of the material on the one hand. On the other hand, it can improve the elastic recovery and dimensional stability of the pure spandex denim fabric. For this reason, 29 texes ordinary spandex core-spun yarn and 29 tex double-core yarn are selected, and elastic denim fabrics are woven according to the same warp yarn, dense warp, and weft, and close width of the fabric. Another index of contrast elasticity, double-core yarn fabric stretch. The length rate is lower than the cotton/spandex core-spun fabric of the same specification. This may be due to the fact that T400 Denim filament hinders the stretching of spandex yarn to a certain extent during the pre-shrinking process of the double-core yarn fabric, so the elastic elongation of the double-core yarn fabric is relatively poor. After many tests, the current shrinkage rate in the weft direction of the T400/spandex twin-core yarn stretch denim fabric can be controlled within 10%, the elastic recovery rate can reach over 96%, and the fabric elongation rate is controlled within 35% ～ 50%.
The special structure of T400/spandex twin-core yarn can give full play to the characteristics of filament and short-coated short fiber, and the fabric feels comfortable and has excellent performance. The application of T400 Denim fiber to stretch denim fabric improves the strength of the fabric on the one hand, and on the other hand, improves the elastic recovery and dimensional stability of the pure spandex denim fabric. When weaving elastic warp fabric, the speed of each process is slightly lower than that of conventional varieties to reduce accidental elongation of double core yarn; when weaving elastic fabric, in order to increase elastic elongation and control the finished fabric width, the weft insertion length must be longer than that of ordinary cotton bales. The ammonia product is slightly longer than 3 to 5 cm. T400 fiber is not resistant to high temperature, the setting temperature is only 150 ℃, and spandex is not resistant to high temperature, so a low-temperature heat-setting process is adopted. After product trial production, the current shrinkage rate in the weft direction of the T400/spandex twin-core yarn stretch denim fabric can be controlled within 10%, the elastic recovery rate can reach over 96% and the fabric elongation rate is 35% to 50%. However, it was also found that the cost of dual-core yarn is slightly higher than that of ordinary cotton-covered spandex yarn products, so it is only suitable for the development of medium and high-end fabrics.