From：spandex yarn manufacturing process Release time：2018-07-02
The spandex covered yarn is a stretch yarn formed by wrapping the elongated spandex yarn in a spiral shape with the spandex as the core.
According to the characteristics of the spinning process, the current production process of spandex includes solution dry spinning, solution wet spinning, reaction spinning and melt spinning. The following comparisons are made on the technical features and product features of several processes:
1. Dry solution method
Polyether glycol and diisocyanate with the molar ratio of 1:2, under the certain condition of reaction temperature and time of formation of prepolymer, prepolymer via solvent dissolves, add diamine chain extension reaction, formation of block copolymer solution, then through mixed with additives after pretreatment, filtration, deaeration, made the uniform performance of spinning dope. Then the metering pump is used to quantitatively and uniformly press the spinneret, and the spinneret fluid is extruded from the capillary hole of the spinneret plate to form a filament stream and enter the spinning passage. Filled with hot air in the tunnel (or nitrogen), make the strips trickle of solvent volatilization quickly, and was taken away by air (or nitrogen), concentration of strips to improve until solidification, spandex for multifilament commonly at the same time, before solidification after twisting it well, the final oiling, winding into a certain number of package.
Dry spinning is the most widely used method of spandex spinning in the world. Dry spinning is about 80% of the world's total production of spandex. Its size is 1.1-123tex, and its spinning speed is generally 200~ 600m /min, some of which can be as high as 1200 m/min. The dry spinning technology is mature and the fiber quality and performance are excellent. Dupont, bayer, dongyang spinning and other domestic manufacturers are all using solution dry spinning technology.
2. Wet solution method
First of all, polyester diol and diisocyanate were used to make block copolymer solution by similar dry spinning method. The solution was prepared before spinning and sent to the spinning machine. The fine flow of the raw liquid from the capillary of the spinneret into the coagulation bath. Coagulation bath with warm water (below 90 ℃) for coagulation medium, dope thread in the solvent diffusion to the coagulation bath, the dope thread in the polymer concentration, the formation of fiber, the winding after washing dry.
The wet spinning speed is generally 5~50 m/min, and the fiber size is 0.55 ~ 7.7dtex. The wet spinning process is complex, the equipment investment cost is large, the spinning speed is low, the production cost is high. The law has been phased out. At present, the production of wet spinning accounts for about 10% of the total production of spandex.
3. The reaction method
Reactive spinning, also known as chemical spinning, must undergo chemical reactions or control the rate at which the spinning fluid is converted into solid fibers. Reaction spinning is a process in which a high polymer is formed from a monomer or prepolymer at the same time as a fibrous process. The polyether or polyester prepolymer solution containing diisocyanate at both ends was pressed out through the nozzle into the coagulation bath, and reacted with the chain growth agent in the coagulation bath to form the primary fiber. Fiber winding after hardening treatment should also be in pressurized water, make the internal fiber has part of crosslinking reaction, thus transformed into a three-dimensional structure of polyurethane (pu) block copolymer.
The spinning speed of reactive spinning method is generally 50~ 150m /min, and its size is 0.56~ 38tex. This method is gradually eliminated due to the complicated process, low spinning speed, high production cost and large equipment investment. The world's reactive spinning now accounts for about 10% of the total production of spandex.
4. The melting method
Melt spinning is a method of fiber forming by using high polymer melt fluid. Melt spinning can only be used for polyurethane block copolymer with good thermal stability, such as polyurethane block copolymer obtained by condensation polymerization of 4-methylene diphenyl diisocyanate and 1, 4-butanediol. Spinning temperature is 160 ~ 220 ℃, the spinning speed is 200 ~ 800 m/min. The melt spinning of spandex is mainly completed by drying sections, melting, melt flow formation, cooling, extension and winding. As some macromolecular degradation occurs in the process of high temperature extrusion, a certain amount of crosslinking agent should be added in the extrusion equipment to reconnect the molecular chains containing the active -nco end group.
Due to melt spinning process characteristics, its products can achieve a high elongation at break, but because the molecular inter-atomic forces produced by the method of relative to other products is low, cause the restoring force is small, the elastic recovery is poor. Therefore, melt spinning spandex can only be used for socks and other less demanding purposes, and because the price of spandex slice is high, the promotion is limited.
But we should also see melt spinning spandex filament in investment cost, environmental advantages, if can solve the poor elastic recovery, will have higher competitive power, in fact, in recent years, foreign companies such as clock spinning by improving the crosslinking agent has occupied a strong advantage in the aspect of melt spinning spandex, in a this aspect has to be able to compete with dry spinning spandex. Therefore, while vigorously developing dry spinning, domestic manufacturers should continue to strengthen research and development investment in melt spinning, close to the frontier of international spandex technology development.
Production process of spandex covered yarn
The whole machine is divided into three parts: the feeding of spandex, the stretching coating and the winding. Work, 2 set of hollow spindle in dragon belt drive up and down, back in the opposite direction to convey, the cover on the hollow spindle silk by the rotary elicitation, twisting, and coated in the hollow spindle through the spandex core yarn. The covered yarn is wound into a parallel bobbin by a guide roller and a reciprocating guide.