[Fiber knowledge] Spandex spinning method

Polyurethane fiber (spandex) is an elastic fiber (Spandex) made of a polymer compound with a linear chain structure containing more than 85% urethane. The trade name of our country is spandex. Due to the particularity of the structure, spandex has high strength, light specific gravity, excellent high elasticity and elastic recovery rate, its products are soft and elastic, close-fitting and unconstrained and relaxed, have good taking performance, and are widely used in Industry, medical, sports and other fields.

Polyurethane fiber (spandex) is an elastic fiber (Spandex) made of a polymer compound with a linear chain structure containing more than 85% urethane. The trade name of our country is spandex. Due to the particularity of the structure, spandex has high strength, light specific gravity, excellent high elasticity and elastic recovery rate, its products are soft and elastic, close-fitting and unconstrained and relaxed, have good taking performance, and are widely used in Industry, medical, sports and other fields. The research of spandex first began in Germany. In 1959, DuPont first realized the industrial production of dry spinning spandex. In the 1960 s, companies such as Asahi Kasei and Toyo Textile in Japan also developed spandex production technology. After the 1980 s, due to the development of spandex covered yarn and core-spun yarn technology, the application field of spandex continued to expand, and the market demand continued to increase. In 1989, China built the first spandex production plant in Yantai, Shandong Province, and a number of spandex enterprises also put into production in the 1990 s.

Main production methods of 1. spandex

According to the different spinning methods, the process route of spandex production can be divided into solution spinning method, melt spinning method, chemical reaction spinning method, in which the solution spinning is divided into dry solution spinning and wet solution spinning according to the different coagulation media. At present, dry spinning accounts for more than 80% of global spandex production worldwide, wet spinning accounts for about 10%, and the other two account for about 10%. And in our country so far there is no chemical reaction method. Due to the complex process, low spinning speed, high production cost, large equipment investment and environmental pollution of diamine, the chemical reaction spinning method has little possibility of development in the future.

1. Dry solution spinning

Dry spinning with polyether glycol and diisocyanate at a molar ratio of 1:2 under certain conditions of reaction temperature and time to form a prepolymer, prepolymer by solvent mixing dissolved, and then add diamine chain growth reaction, the formation of block copolymer solution, and then through mixing, filtration, defoaming and other processes, the performance of uniform spinning solution. Then the metering pump is used to quantitatively and evenly press into the spinning head. Under the action of pressure, the spinning solution is extruded from the capillary holes of the spinneret to form a thin stream of filaments and enters the tunnel. The tunnel is filled with hot air, so that the solvent in the filament stream is rapidly volatilized and taken away by the air. The concentration of the filament is continuously increased until it solidifies. At the same time, the filament stream is stretched and thinned, and finally wound into a certain package. The fineness range of spinnable spandex is 1.1-246.4tex, the spinning speed is 200-600 m/min, and some can be as high as 1000 m/min.

2. Wet solution spinning

Wet spinning, similar to the dry process, also forms a block copolymer solution, which is pressed into the spinneret by a metering pump. From the spinneret capillary hole out of the dope flow into the coagulation bath, the dope flow of the solvent to the coagulation bath, the concentration of the polymer continues to increase, in the coagulation bath precipitation to form a fiber, and then after washing and drying for winding. The spinning speed is generally 5-50 m/min, and the processing fineness is 0.55-44tex.

Dry spinning compared with wet spinning, spinning polymer concentration, viscosity is also high, can withstand a larger spinneret draw ratio, the fiber is finer than wet spinning. At the same time, dry spinning uses hot air as the coagulation medium, compared with the coagulation bath, the hydrodynamic resistance of the filament is small, the spinning speed is high, and the output is larger. Wet spinning has been gradually eliminated due to high production costs. The only two sets of wet spinning devices in China have been discontinued.

3. Melt spinning

The melt spinning method is to send the dried thermoplastic polyurethane chips into the screw extruder, the chips are melted due to heat, the melt is extruded at a certain pressure and transported to the spinning part, and then the melt is uniformly pressed to the spinning assembly by the spinning pump. The molten stream is extruded from the spinneret orifice and cooled in the shaft to solidify into fibers. Melt spinning is only suitable for fusible polyurethane block copolymers with good stability at melting temperature, and the spinning speed is 200-800 m/min.

Melt spinning production process is short, less investment, no solvent recovery, low cost. However, melt spinning spandex technology is still not mature enough, production costs, product quality is greatly affected by raw materials, and raw material slice production is subject to people. At the same time, due to the difference of spinning process and spinning raw materials, there are certain differences in the structure and performance between dry spinning spandex and melt spinning spandex. Dry spinning spandex has excellent performance, while melt spinning spandex will produce excessive crosslinking and gel when the residence time at high temperature is slightly longer. As a result, the physical mechanical energy of the finished product is worse than that of dry spinning, the product grade is low and the application range is small. At present, the scale of melt spinning spandex devices in China is small and the production capacity is low.

Main technologies of 2. spandex dry spinning

The dry spinning process is complex, the investment cost of the device equipment is large, and there is some pollution to the environment, but the process technology is mature, the spinning speed is high, the quality and performance of the fiber made is excellent, it occupies a dominant position in the spandex production technology, and will remain the mainstream of investment for quite a long time. At present, China's major spandex enterprises are using dry spinning technology, most of the projects under construction and to be built plan to use dry spinning technology, from the global spandex factory capacity situation, the use of dry spinning technology capacity is also dominant. Spandex dry spinning technology to the United States DuPont, South Korea Hyostar, Japan Toyo Spinning and other representatives, different production patent manufacturers of spinning polymer synthesis methods, fiber production technology and processing process has unique technical characteristics.

1. Invida and Xiaoxing Technology

Invitica (formerly DuPont) was the first to realize the industrialization of spandex dry spinning, and its spandex product "Lycra" is unique in product quality and brand promotion. Invida and Xiaoxing technology uses continuous polymerization and high-speed spinning, which has better product quality than regular batch polymerization and medium-speed spinning. At the same time, the output is high, the consumption of public works is low, and the unit production cost is low. However, the technical barriers to spandex production are very strong. The development strategy of Yingweida and Xiaoxing in China is mainly based on joint ventures and no technology transfer. China's spandex enterprises basically adopt Japanese technology.

2. Toyo Spinning Technology

Toyo Spinning is the earliest manufacturer of spandex and fiber in Japan. In 1963, it developed a dry production technology with intellectual property rights, using intermittent polymerization and continuous spinning process technology route. After years of exploration and improvement, the process is mature and the production process is stable. Spinning speed in 500-600 m/min, some domestic enterprises through technical transformation on this basis, the current spinning speed can reach 800 m/min. Product performance is excellent, complete specifications, from 20D to 210D, a wide range of applications, can be used for weaving, weft knitting, warp knitting, knitting socks, core yarn, covering yarn and so on. In terms of solvents, Toyo Spinning's new technology uses environmentally friendly solvent DMAC instead of DMF, which greatly reduces environmental pollution. Some of China's major spandex enterprises such as Yantai spandex, Zhejiang Huafeng, Lianyungang Duzhong, Jiangsu Shuangliang, Hangzhou Shuerzi, etc. are using Dongyang textile technology.

3. Nissing spinning technology

Riqing spinning also adopts the process technology of intermittent polymerization and continuous spinning, and the spinning speed can reach 600-800 m/min. Its technology has certain advancement in developing fine denier fibers and improving the elastic elongation of products. Some newly-built enterprises such as Longshan in Shaoxing, Zhejiang Province and Shuangliang in Jiangsu Province all adopt this technology.