Suzhou Zhanheng intelligent introduction: What is melt spinning method and solution spinning method? 

 The purification of polymers and the polymerization of chemical fibers are made from polymers. The high polymer can be directly derived from nature, or can be artificially synthesized from low molecular matter. The regenerated fiber is made from natural high polymer by chemical method. It is basically the same as the original polymer in chemical composition. For natural polymers, this requires purification to remove impurities. For example, the polymer used to manufacture viscose fiber is cellulose, which is purified from cellulose raw materials such as wool, wood, reed, and bagasse to make pulp, and then the pulp is used to manufacture fiber. The high polymer of synthetic fiber is made of low molecular compound (monomer) from coal, petroleum, natural gas, agricultural and sideline products, etc., and obtained by chemical addition or condensation polymerization. Finally, the polymer is processed to obtain synthetic fiber. Therefore, synthetic fibers are often named by the monomer of their polymer, and the "poly" is added before the single complete. Preparation of spinning fluid Fibrous polymers must be spun by a certain method before spinning the spinning fluid. At present, the commonly used methods are melt method and melt method. The melt method is to heat the fiber forming polymer above the melting point to become a melt. It is suitable for polymers whose decomposition point is higher than the melting point. If the decomposition point of the fiber forming polymer is lower than the melting point, the melting bar method must be adopted, which is to dissolve the fiber forming polymer into a spinning fluid with a certain viscosity with an appropriate solvent. In the actual industrial production, there are two main methods for the preparation of spinning melt: one is to directly send the high poly special melt obtained by polymerization to spinning, which is called direct spinning; The other is to make the polymer melt obtained by the process of casting tape, granulation and so on into a "slice", and then re-melt into the melt on the spinning machine and spin, this method is called slice spinning. There are also two methods for the preparation of solution spinning solutions such as polyacrylonitrile solutions. One is to directly use the polymer solution obtained after polymerization as the spinning stock, which is called one-step method; The second is to first make granular or powdered fiber forming polymer, and then deep solution to obtain spinning solution, this method is called two-step method. In order to make the spinning fluid have uniform and good spinning performance, the spinning fluid must be mixed, filtered, defrosted and other processes to remove impurities and bubbles before spinning. The deep agent for preparing spinning deep solution has good solubility, low toxicity, convenient recovery, low price and is not easy to burn and explode. In the preparation of spinning fluid, in order to improve the luster of the fiber, a matting agent can be added to produce a glossy, dull or semi-dull fiber. Spinning The spinning fluid is continuously, quantitatively and uniformly extruded from the capillary pores of the spinneret or spinneret by a spinning pump (or metering pump), and then solidified into strips in air, water or coagulation bath. The process is called spinning or fiber forming. Freshly spun silk strips are called primary fibers. Spinning is a key process in the process of chemical fiber production. Changing the spinning process conditions can adjust the structure of the fiber in a large range, so as to change the physical and mechanical properties of the fiber. According to the different properties of fiber forming polymers, the spinning methods of chemical fibers mainly include melt spinning method and melt spinning method, in addition, there are special or unconventional spinning methods. Among them, according to the different solidification methods, melt spinning is divided into wet spinning and dry spinning two kinds. 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. Melt spinning method Melt spinning method is that the spinning melt is quantitatively pressed out of the spinneret hole by the spinning pump through the screw extruder, so that it is shot into the air in a fine flow, and cooled into the spinning tube. At present, the spinning speed of melt spinning method is generally 1000-2000m/min. When adjusting spinning, it can reach 4000-6000m/min. The number of holes of the spinneret: the filament is 1-150 holes, the short fiber is 400-800 holes, and the many can reach 1000-2000 holes. The diameter of the spinneret is generally 0.2-0.4mm. The main characteristics of melt spinning method are high winding speed, no need for solvent and precipitator, simple equipment, short process flow, and it is an economic, convenient and efficient forming method. But the number of spinneret holes is relatively small. In recent years, on the basis of digestion and absorption of imported technology, China has developed low-speed porous and high-speed short-range spinning to produce polypropylene and polyester. Polyester, polyamide and polypropylene in synthetic fibers are all spun by melt spinning method. Solution spinning 1. Wet spinning Wet spinning process is to press the spinning solution from the fine hole of the spinneret head into a fine flow, and then solidify into silk in the solidifying solution. Due to the slow solidification of the filament, the spinning speed of wet spinning is low, generally 50-100m/min, and the number of holes of the spinnetting plate is more than that of melt spinning, generally up to 4000-2000 holes. The cross sections of the fibers obtained by mixed spinning method are mostly non-circular and have obvious skin core structure, which is mainly caused by the solidification of the solidifying liquid. Wet spinning is characterized by complex process flow, large casting, low spinning speed and high production cost. In general, in the production of short fibers, porous spinnerets or graded spinnerets can be used to improve the production capacity, so as to make up for the defects of low spinning speed. In general, fiber forming polymers that cannot be spun by melt method are wet-spun and produced as short fiber and filament bundles. Acrylic, vinylon, chlorylon and viscose are mostly wet-spun. 2, dry spinning Dry spinning process is to press the spinning solution prepared by solution spinning from the spinneret hole, in a fine flow, and then solidify into silk in hot air due to the sound speed of solvent volatilization. At present, the speed of dry spinning is generally 200-500m/min, and the spinning speed can be increased to 700-1500m/min when the spinning tube length is increased or the finer fibers are spun. The number of nozzle holes of dry spinning is less, which is 300-600 holes. The fiber produced by dry spinning has tight structure, high physical and mechanical properties and dyeing properties, and high fiber quality. However, the investment of dry spinning is larger than that of wet spinning, the production cost is high, and the environment is polluted. At present, the synthetic fibers produced by dry spinning are less, and only acetate fiber and vinylon can be used this method. In addition, for fibers that can be used for both dry spinning and wet spinning, dry spinning is more suitable for spinning filament. 3. Other spinning methods (1) Composite fiber spinning method The composite fiber spinning method is to prepare two or more spinning fluids with different chemical compositions or different concentrations through a spinneret with a special distribution system. Before entering the spinneret hole, the two components are separated from each other and do not mix, and at the moment of entering the spinneret hole, the two liquids contact, solidify and bond into a wire strip, thus opening into a composite fiber with two or more different components. The fibers produced by this method are divided into: parallel type, skin core type and spread type. (2) special-shaped fiber spinning This method uses non-circular spinneret holes to produce various profiled fibers of different cross sections. Common shape of different fibers are triangle, Y, star and hollow fibers. (3) Colored fiber spinning method This method is to add appropriate coloring agent to the spinning melt or solution of chemical fiber, and make colored fiber directly after spinning. This method can improve dyeing fastness, reduce dyeing cost and reduce environmental pollution. In addition, there are phase separation spinning, gel spinning, emulsion or suspension spinning, liquid crystal spinning and other spinning methods. The structure of the primary fiber obtained in the spinning process is not perfect, the physical and mechanical properties are poor, the specific performance is that the fiber strength is very low, the elongation is very large, the boiling water shrinkage rate is very high, can not be directly used to spin yarn, so the primary fiber must also go through a series of post-processing processes to improve the structure and improve the performance. Meet the requirements of textile processing and use. The specific process of chemical fiber post-processing varies with the variety and type of fiber (such as filament, staple fiber, etc.), but it can be basically divided into two types of staple fiber and filament.