The production process of polyester includes two parts: polyester melt synthesis and melt spinning. The raw materials for synthetic polyester are polyethylene terephthalic acid and ethylene glycol, which are mainly obtained from petroleum cracking, and can also be obtained from coal and natural gas. Heating and cracking of petroleum produces toluene, xylene and ethylene, etc. After chemical processing, terephthalic acid or dimethyl terephthalate and ethylene glycol can be obtained. In the early production of polyester, dimethyl terephthalate and ethylene glycol were used as raw materials because terephthalic acid was not easy to be refined. In 1965, the refining of terephthalic acid was successful, which reduced the production process and cost of polyester. Polyester produced from terephthalic acid and ethylene glycol has increased year by year. Polycondensation: Transesterify dimethyl terephthalate and ethylene glycol to produce diethylene glycol terephthalate oligomers, polycondensate at 280-290°C and vacuum conditions to obtain polyterephthalic acid Ethylene glycol ester; or direct esterification of terephthalic acid and ethylene glycol, and then polycondensation of ethylene terephthalate to obtain polyester melt. Polyester melts can be used to prepare polyester chips and melt direct spinning. Polyester chips are obtained by casting polyester melts and pelletizing them.
1. Spinning. After drying and melting, polyester chips can be used for spinning, preparing polyester films, polyester bottles, etc. During the melting process, the moisture contained in the chips can hydrolyze the polyester and affect the spinning performance and fiber quality. Therefore, it must be dried before spinning to reduce the moisture content of the chips to below 0.01%. In chip spinning, the dried polyester chips are heated and melted in the screw, extruded and sent to each spinning position of the spinning box, and after being accurately metered and filtered by the metering pump, they are sprayed from the spinneret holes of the spinneret. out. The diameter of the spinneret hole is generally 0.15 to 0.30 mm. The ejected melt stream is cooled and solidified into filaments by the cooling air flow. The cooled filaments are divided into polyester filaments and polyester staple fibers (or polyester staple filaments) according to different processing techniques.
2. Polyester staple. When spinning short fibers, multiple threads are gathered together, wetted and oiled, and then dropped into the silk barrel. Then the finished product is obtained through processes such as bundling, stretching, crimping, heat setting, and cutting. After stretching, after a tension heat setting at about 180°C, high-strength, low-elongation short fibers with a strength of more than 6cN/dtex and an elongation of less than 30% can be obtained. Polyester staple fiber is divided into cotton staple fiber (length 38mm) and wool staple fiber (length 56mm), which are used for blending with cotton fiber and wool respectively.
3. Polyester filament. When spinning filaments, the solidified filaments are wetted and oiled, and then wound on the bobbin at a speed of about 3500 m/min to obtain pre-oriented filaments (POY). POY cannot be directly used for weaving. POY is stretched and shaped, elasticized or twisted to obtain stretched yarn (DT), stretched textured yarn (DTY) or twisted yarn, which can be directly used for weaving or deformed. textured wire. After solidification, the filaments are oiled and stretched directly to wind up at 4500-5000m/min to obtain fully drawn filaments (FDY), which can be used for weaving. American commodity Kodel (kodel) is another polyester fiber that has been industrially produced. It is spun from a polymer obtained by polycondensation of terephthalic acid and 1,4-cyclohexanedimethanol. Compared with polyester, it has a lighter specific gravity of 1.22, a higher melting point of 290-295°C, stronger resistance to decomposition, and slightly lower fiber strength and elongation. It is suitable for blending with cotton, wool, etc. The resulting fabric has good elasticity, hand feeling, wrinkle resistance and anti-pilling performance, but poor strength and wear resistance.