Use a spinning pump (or metering pump) to continuously, quantitatively and evenly flow the spinning fluid from the capillary holes of the spinneret or spinneret. The process of extruding the fiber into a liquid stream and then solidifying it into a filament in air, water or coagulation bath is called spinning or fiber forming.
The newly spun filament is called primary fiber. Spinning is a key process in the production of chemical fibers. Changing the spinning process conditions can adjust the structure of the fiber within a wide range, thereby correspondingly changing the physical and mechanical properties of the resulting fiber.
According to the different properties of fiber-forming polymers, the spinning methods of chemical fibers mainly include melt spinning and melt spinning. In addition, there are special or unconventional spinning methods. Among them, according to the different coagulation methods, the melt spinning method is divided into two types: wet spinning and dry spinning. In the production of chemical fibers, most of them are produced by melt spinning, followed by wet spinning, and only a small amount are produced by dry or other unconventional spinning methods.
01 Melt spinning method
Also known as melt spinning, referred to as melt spinning. It is a chemical fiber spinning method in which the polymer is heated and melted, extruded through a spinneret, and cooled and solidified in the air to form fibers. Polymers used for melt spinning must be able to melt into a viscous flow state without significant decomposition. Polyester fibers, polyamide fibers and polypropylene fibers can all be produced by melt spinning.
Features:
The main feature of the melt spinning method is the spinning speed High (1000~7000m/min), no need for solvents and precipitants and their recovery and circulation systems, simple equipment and short process flow, it is an economical, convenient and efficient forming method. However, the number of spinneret holes is relatively small.
Process flow:
1. Preparation of spinning melt – continuous polymerization worthy of melt award-winning fiber formation after pre-crystallization and drying The polymer slices are added from the polymer hopper, and are melted, mixed, metered and extruded successively by the screw extruder heated in sections as required. The extruder sends the melt through the elbow between the spinning boxes to the melt metering pump. .
2. The melt is quantitatively extruded through the small hole of the spinneret through the metering pump in the spinning box to form a thin stream of melt.
3. After the thin stream of melt enters, it is cooled, solidified and formed into primary fibers at a lower temperature and cooling blowing environment.
4. The virgin fiber is then oiled, networked and wound into a cylinder.
5. This winding yarn is then subjected to subsequent drawing-heat setting and other secondary molding processes to produce a finished fiber with applicability.
Category:
Melt spinning method follows the melt preparation process It is further divided into direct spinning and slice spinning. The process of directly feeding the polymerized polymer melt into a metering pump for metering, extrusion and spinning becomes the direct spinning method; while the polymer pellets undergo pre-crystallization, drying and other necessary pre-spinning preparations, and then the Matsuri screw The technology of extruder melt spinning is called chip spinning. Direct spinning technology is often used in large-scale industrial production, which is beneficial to reducing production costs. However, it is difficult to produce differentiated fiber varieties, and only slight changes can be made in linear density and fiber cross-sectional shape. The chip spinning method is more flexible, easy to change varieties, and produces small batches of differentiated fibers with high added value.
02 Solution spinning method
Solution spinning is to dissolve fiber-forming polymers in a certain solvent to prepare a spinning solution with an appropriate concentration, and then spin the The solution is spit out from the tiny holes into the coagulation bath or hot gas, and the polymer precipitates into solid filaments. After stretching, shaping, washing, and drying, the finished fiber can be obtained.
Obviously, the solution spinning production process is more complicated than melt spinning. However, for some processes that occur before melting For decomposed polymers, you can only choose this spinning forming technology. Solution spinning can be divided into wet spinning, dry spinning, and dry and wet spinning.
01
Wet spinning
Wet spinning is referred to as wet spinning. A chemical fiber spinning method in which a polymer is dissolved in a solvent and a thin stream is ejected through a spinneret into a coagulation bath to form fibers. Fiber-forming polymers suitable for wet spinning have a decomposition temperature lower than the melting point or are easily discolored when heated, and can be dissolved in appropriate solvents. Synthetic fibers such as polyacrylonitrile fiber and polyvinyl alcohol fiber and man-made fiber varieties such as viscose fiber and cupro fiber are produced by wet spinning. Most of the fiber cross-sections obtained by wet spinning are non-circular and have an obvious sheath-core structure, which is mainly caused by the solidification of the coagulation liquid.
Features:
The speed of wet spinning is low, while the speed of jet spinning The number of holes in the silk plate is greater than that in melt spinning, and the process is complicated, with large investment times and high production costs. Generally, in the production of short fibers, multi-hole spinnerets or stepped spinnerets can be used to increase production capacity, thus Make up for the shortcomings of low spinning speed.
Process flow:
1. Prepare spinning solution.
2. Press the raw liquid out of the spinneret to form a thin stream.
3. The thin stream of raw liquid solidifies into primary fibers.
4. Primary growth The fiber is packaged or directly processed.
02
Dry spinning
Dry spinning is solution spinning A kind of fiber-forming polymer. If a fiber-forming polymer can find a solvent with a lower boiling point and good solubility to make a spinning solution, the spinning solution can be spit out from the tiny holes and enter the heated gas. In the process, the solvent in the spinning liquid evaporates, the polymer filaments gradually solidify, and the finished fiber can be obtained through post-processing processes such as stretching, shaping, washing, and drying. Acrylic, spandex, chlorine fiber, and vinylon all use dry spinning processes .
Features:
Dry spinning has continuous production and spinning speed It has the advantages of high efficiency, large output, and less pollution; the fiber quality, chemical resistance, and dyeing performance are better than wet-spun fibers. However, dry-process fibers have poor chlorine resistance, are technically difficult, require solvent recovery, and have relatively high production costs.
Dry spinning & wet spinning
The concentration of spinning solution is higher than that of wet spinning, generally up to 18%~45%, the corresponding viscosity is also high, and it can withstand larger spray than wet spinning The filament head is stretched (2 to 7 times), making it easier to produce finer fibers than wet spinning.
The mechanical resistance on the spinning line is much smaller than that of wet spinning. The spinning speed is higher than wet spinning, but due to the limitation of solvent evaporation speed, dry spinning speed is lower than melt spinning.
The number of spinneret holes is much smaller than that of wet spinning. This is because dry spinning The curing method is slow, and the threads are easy to stick before curing. Generally, the number of spinneret holes for dry-spun short fibers is about 1,200, while the number of holes for wet-spun short fibers is as high as tens of thousands, so the production capacity of a single spinning position in the dry method is far Lower than wet spinning, dry spinning is generally suitable for producing filaments.
Process flow:
03
Dry and wet method Spinning
Dry-wet spinning is a type of solution spinning, also known as dry-jet wet spinning. It combines the characteristics of wet spinning and dry spinning. , is particularly suitable for the molding and processing of liquid crystal polymers, so it is often called liquid crystal spinning.
That is, the fiber-forming polymer is dissolved in a certain solvent to prepare a spinning solution with an appropriate concentration, and then the spinning solution is spit out from a tiny hole. First, it passes through a very long period of time. In the short air interlayer, since the resistance of the filament is small, the polymer in the liquid crystal state is conducive to high orientation under high-stretch conditions, and then the filament enters the low-temperature coagulation bath to complete the solidification molding and make the liquid crystal The macromolecules are in a highly ordered frozen liquid crystal state, and the finished fiber has mechanical properties of high strength and high modulus.
At present, wet and dry spinning has been used in polyacrylonitrile fiber, polylactic acid fiber, chitosan fiber, dibutyryl chitin, polyvinyl chloride fiber, and aromatic polyamide fiber. , polybenzimidazole fiber and other fibers have been used in the preparation.
Features:
Dry and wet spinning can spin high viscosity spinning The original liquid is used to reduce solvent recovery and unit consumption. At the same time, the forming speed is high, the fiber structure obtained is uniform, the cross-section is metallic and circular, the strength and elasticity are improved, and the dyeability and color are good. A major disadvantage of wet and dry spinning is that after the thin stream of spinning dope breaks, the dope can easily flow along the spinneret. This means that if a single filament breaks during porous spinning, it is likely that the dope will overflow and the dope will flow. Causes other filaments to break, thereby destroying the continuity of the spinning process.
Process flow:
Dry and wet spinning, the spinning solution is from After the spinneret is pressed out, it first passes through a gas (usually air) layer (air gap) and then enters the coagulation bath. Therefore, some people also call this method air gap spinning. The post-processing process of the nascent fiber derived from the coagulation bath is the same as that of ordinary wet spinning.
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