Melt direct spinning-prepared single-vessel high and low viscosity pet bicomponent elastic fiber and preparation method therefor

Abstract

The present invention relates to a melt direct spinning-prepared single-vessel high and low viscosity PET bicomponent elastic fiber and a preparation method therefor. The method comprises: sequentially subjecting terephthalic acid, ethylene glycol, and a catalyst to esterification reactions in first and second esterification vessels, then performing pre-polymerization reactions in first and second pre-polymerization vessels to obtain a prepolymer; introducing the prepolymer into a final polymerization vessel to undergo polymerization, where the final polymerization vessel has a low viscosity melt outlet and a high viscosity melt outlet; separately outputting the low viscosity PET melt from the low viscosity melt outlet and the high viscosity PET melt from the high viscosity melt outlet; and spinning together the low viscosity PET melt and high viscosity PET melt are spun via the same side-by-side composite spinning assembly to obtain a PET bicomponent elastic fiber. In the present method, simultaneous polymerization of high and low viscosity components within the same final polymerization reactor can be achieved, resulting in fibers with good properties.

Description

A melt-spun single-reactor high- and low-viscosity PET bicomponent elastic fiber and its preparation method Technical Field

[0001] The invention relates to a melt-spun single-pot high- and low-viscosity PET two-component elastic fiber and a preparation method thereof. Background Art

[0002] The application scope of elastic fibers in the modern chemical fiber industry is becoming wider and wider. Especially in recent years, with the rapid development of the theory of bicomponent elastic fibers, we have a deeper understanding of the forming mechanism and elasticity generation mechanism of parallel bicomponent elastic fibers, and the varieties of elastic fibers and original technologies have also made great progress. Starting in the 1970s, DuPont first launched single-component spandex elastic fiber, which quickly became popular in the market for its unique style and characteristics. In the late 1970s, it launched the two-component parallel elastic fiber T800, which uses PBT / PET parallel composite to produce good elastic effect. However, due to the low glass transition temperature (26-42°C) of the PBT component of PBT / PET elastic fiber, the fiber undergoes rapid crystallization under stress, and the elastic recovery rate and shape retention of T800 fiber are poor. In the 21st century, with the successful industrialization of PDO by chemical and biological fermentation methods, PTT polyester has a unique molecular structure and excellent elastic recovery properties. DuPont's T400, PTT / PET two-component elastic fiber, was launched. The PTT / PET two-component parallel composite fiber has excellent elastic recovery rate and shape retention. The fabric will not deform after repeated stretching. Its elastic sustained-release effect overcomes the restraining feeling of spandex elastic fiber. With its excellent resistance to chlorine bleaching and light exposure, it has become the best elastic fiber variety in the fabric industry.

[0003] However, the price of PTT polyester raw materials is high, and PTT / PET two-component fibers are basically used in the category of high-end fabrics. For some fabrics with lower elasticity requirements, the cost-effectiveness is not outstanding. Therefore, the development of two-component elastic fibers has become a key area of ​​development in the industry in the past decade. The latest progress is to utilize the different orientation and crystallization behaviors between different viscosity components of PET polyester, and use high-viscosity PET and low-viscosity PET with a certain viscosity difference for parallel spinning to prepare PET / PET two-component elastic fibers. During the spinning process, the high-viscosity component and the low-viscosity component produce elastic curling due to the different speeds and percentages of transition from the orientation state to the crystallization state, forming a spring-like structure, thus showing a good elastic effect on the fabric. Patents such as CN111101237A, CN101126180A, CN106337212A, CN107964690A, CN101851812A, and CN115613159A respectively disclose a series of methods for preparing parallel composite elastic fibers such as PET / PET, PBT / PET, and PTT / PET, as well as methods for preparing easily dyed or deeply dyed elastic fibers by using modified PET with elasticity retention, such as high-viscosity ECDP, high-viscosity high-shrinkage polyester, high-viscosity disperse dye-easy polyester, high-viscosity CDP cationic polyester, etc., and low-viscosity PET polyester.

[0004] The preparation methods of the above-mentioned elastic fibers are all based on a slice spinning production process in which high-viscosity slices and low-viscosity slices are pre-crystallized and melted by a drying screw, and then formed into a composite spinning box and a composite parallel spinneret. Although the basic parallel composite spinning technology problems have been solved, the slice spinning technology has obvious defects such as long process, high cost, low production capacity, and poor product quality stability.

[0005] In the prior art, the synthesis of high-viscosity melt and low-viscosity melt is usually carried out in different polymerization kettles. The process of polymerizing in two kettles separately will increase the cost of polymerization on the one hand, and it is difficult to achieve precise control of the viscosity difference between high viscosity and low viscosity on the other hand. The existing high-viscosity melt has poor fluidity in the pipeline and is easily degraded during the melt transportation process, resulting in a decrease in viscosity, which in turn affects the quality of the final two-component elastic fiber.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a melt-spun single-reactor high- and low-viscosity PET two-component elastic fiber, which has very high elastic curl and low production cost. When preparing the elastic fiber, the viscosity of the high-viscosity and low-viscosity melts is controllable, the viscosity of the high-viscosity melt is high enough and can be well maintained during the melt conveying process, and the production capacity is high.

[0008] Another object of the present invention is to provide a method for preparing high-viscosity and low-viscosity PET bicomponent elastic fibers by melt direct spinning in a single reactor. The preparation method simultaneously polymerizes a high-viscosity melt component and a low-viscosity melt component in the same polymerization reactor, and then directly performs parallel composite spinning on the two-component melt. High-viscosity and low-viscosity PET bicomponent elastic fibers can be prepared simply and quickly, significantly reducing production costs and improving production efficiency.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for preparing melt-spun PET bicomponent elastic fiber, the method comprising the steps of sequentially passing terephthalic acid, ethylene glycol, and a catalyst through a first esterification kettle and a second esterification kettle for esterification reaction, and then through a first prepolymerization kettle and a second prepolymerization kettle for prepolymerization reaction to obtain an ethylene terephthalate prepolymer. The method further comprises passing the ethylene terephthalate prepolymer into a final polymerization kettle for polymerization, wherein the final polymerization kettle has a low-viscosity melt outlet and a high-viscosity melt outlet, and outputs low-viscosity PET from the low-viscosity melt outlets. melt, outputting a high-viscosity PET melt from a high-viscosity melt outlet; the intrinsic viscosity of the low-viscosity PET melt is 0.45-0.60, and the dynamic viscosity at 280°C is 90-300 Pa.s; the intrinsic viscosity of the high-viscosity PET melt is 0.68-0.80, and the dynamic viscosity at 284°C is 450-810 Pa.s; and the low-viscosity PET melt and the high-viscosity PET melt are spun through the same parallel composite spinning assembly to obtain the melt-spun PET two-component elastic fiber.

[0011] In the present invention, the intrinsic viscosity is measured in a mixed solvent of phenol and tetrachloroethane in a volume ratio of 3:2.

[0012] The present invention simultaneously synthesizes high-viscosity PET melt and low-viscosity PET melt in the same final polymerization kettle, discharges the high-viscosity PET melt and the low-viscosity PET melt from different positions of the final polymerization kettle respectively, and then spins the two in the same spinning assembly, so that a single kettle can simultaneously synthesize high-viscosity and low-viscosity two components, and the entire system can be a five-kettle system.

[0013] The preparation method of the PET two-component elastic fiber of the present invention adopts a five-reactor device system comprising a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, and a final polymerization reactor (high viscosity and low viscosity are in the same reactor).

[0014] The PET bicomponent elastic fiber of the present invention contains a high-viscosity and a low-viscosity bicomponent. The preparation method of the aforementioned PET bicomponent elastic fiber is a melt direct spinning method, that is, the melt obtained by polymerization is directly used for spinning without the melt cooling and slicing step and then melting and spinning.

[0015] In some embodiments, the PET bicomponent elastic fiber contains, by mass percentage, 30%-70% of a high-viscosity PET component and 70%-30% of a low-viscosity PET component, and the high-viscosity PET component and the low-viscosity PET component have different viscosities.

[0016] In some embodiments, the final polymerization kettle is a horizontal polymerization kettle and includes a main body containing a chamber inside, the main body includes a low viscosity zone, a medium-high viscosity zone, and a high viscosity zone arranged in sequence along the axial direction of the final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low viscosity zone, the medium-high viscosity zone, and the high viscosity zone increases in sequence, the low viscosity melt outlet is arranged at the rear end of the low viscosity zone, and the high viscosity melt outlet is arranged at the rear end of the high viscosity zone, the final polymerization kettle also includes a prepolymer feed port arranged at the front end of the final polymerization kettle, and two stirring shafts, one of which is arranged in the low viscosity zone, and the other stirring shaft is arranged in the medium-high viscosity zone and the high viscosity zone, and a weir plate arranged at the rear end of the low viscosity melt outlet, and the weir plate is used to prevent the melt in the medium-high viscosity zone from flowing into the low viscosity zone.

[0017] The final polymerization reactor of the present invention is divided into front and rear chambers with biaxial stirring. The front chamber completes the low-viscosity polymerization reaction, while the rear chamber completes the medium- and high-viscosity polyester polymerization reaction. A prepolymer feed port is provided at the front end of the reactor. A low-viscosity melt discharge port is designed at the rear end of the front chamber stirring to output low-viscosity PET polyester melt for production. A high-viscosity melt discharge port is designed at the rear end of the rear chamber stirring to output high-viscosity PET polyester melt for production. This final polymerization reactor design can achieve controllable output of two different intrinsic viscosities, low and high, from a single reactor. These melts are then transported via a spinning line to a two-component parallel composite spinning manifold, successfully producing PET / PET high- and low-viscosity parallel composite elastic fibers.

[0018] In some embodiments, the central axes of the two stirring shafts are located on the same straight line, and the final polymerization kettle further includes a support column arranged on the inner wall of the main body, the support column is used to support the two stirring shafts, and the support column is located at the rear end of the low viscosity zone.

[0019] In some embodiments, the length of the stirring shaft arranged in the low viscosity zone is two-thirds of the length of the final polymerization kettle, the length of the stirring shaft arranged in the medium-high viscosity zone and the high viscosity zone is one-third of the length of the final polymerization kettle, the length of the low viscosity zone is two-thirds of the length of the final polymerization kettle, and the length of the medium-high viscosity zone and the high viscosity zone is one-third of the length of the final polymerization kettle.

[0020] In the present invention, two-thirds and one-third are not the exact mathematical values ​​of two-thirds and one-third, but refer to values ​​approximately between two-thirds and one-third and thereabouts, and are approximately equal to two-thirds and one-third.

[0021] The present invention respectively arranges two stirring shafts in the low viscosity zone, the medium-high viscosity zone and the high viscosity zone, and controls the lengths of the two stirring shafts to be inconsistent, so that the stirring shaft in the low viscosity zone is longer. At the same time, a weir flow plate is arranged on the inner wall of the main body at the rear end of the low viscosity zone of the final polymerization kettle. The weir flow plate can separate the medium-high viscosity melt in the medium-high viscosity zone from flowing from the gap space between the disc reactor and the inner wall of the main body back to the low viscosity melt in the low viscosity zone, thereby realizing the simultaneous discharge of high viscosity melt and low viscosity melt in the same final polymerization kettle, which not only simplifies the production equipment and process, but also better controls the viscosity of the high viscosity melt and the low viscosity melt.

[0022] In some embodiments, multiple disc reactors are provided on the two stirring shafts, the disc reactor in the low viscosity zone is a multi-disc combination disc, 6 to 8 groups of multi-disc combination discs are provided in the low viscosity zone, and the disc reactor in the low viscosity zone is 35 to 50 discs; the disc reactor in the medium and high viscosity zone is a 4-disc combination disc or a 3-disc combination disc or a 2-disc combination disc, and the disc reactor in the medium and high viscosity zone is 15 to 25 discs; the disc reactor in the high viscosity zone is a single-disc design, and the disc reactor in the high viscosity zone is 6 to 15 discs.

[0023] In the present invention, the multi-disc assembly refers to a plurality of adjacent disc reactors that are assembled and fixed together so that they can achieve synchronous rotation relative to the stirring shaft.

[0024] Furthermore, the disc reactor in the low viscosity zone is a multi-disc combination disc with more than 4 discs, with a multi-disc combination disc of 8-10 discs designed at the front end of the low viscosity zone and a multi-disc combination disc of 4-5 discs designed at the rear end.

[0025] In some embodiments, the final polymerization kettle also includes a wall scraper arranged in the medium and high viscosity zone for scraping the melt on the inner wall of the final polymerization kettle, a disk scraper arranged in the high viscosity zone for scraping the melt on the disc reactor, a wall scraper arranged in the high viscosity zone for scraping the melt on the inner wall of the final polymerization kettle, and an axial scraper arranged in the high viscosity zone for scraping the melt on the stirring shaft.

[0026] In the prior art, although scrapers are provided in conventional polymerization kettles, the scraper structure is relatively simple and its role is relatively limited. In the high viscosity area of ​​the final polymerization kettle of the present invention, by adopting the composite scraper of the above-mentioned specific structure, the material renewal rate of the disc surface of the disc reactor, the surface of the stirring shaft and the wall of the polymerization kettle can be effectively controlled, so that the material in the three places will not accumulate too much, and the problems of hue degradation and large amounts of acetaldehyde generated during the production of high-viscosity melts can be effectively suppressed. The disc scraper portion of the composite scraper of the present invention can control the thickness of the disc melt film, the wall scraper portion can timely update the material on the wall of the polymerization kettle, and the axial scraper portion can clean the stirring shaft. By adopting a final polymerization kettle containing the above-mentioned composite scraper, the material residence time can be controlled at 75 to 120 minutes, which is much lower than the residence time of the conventional front and rear double-axis high-viscosity disc reactor, which is usually about 180 to 300 minutes. The significant reduction in residence time effectively reduces the level of side reactions, which is beneficial to the preparation of high-viscosity polyester melts.

[0027] In some embodiments, the weir plate is welded to the inner wall of the bottom of the main body, and in a cross section of the final polymerization kettle passing through the weir plate, the radian of the contact line between the weir plate and the inner wall of the bottom of the main body is greater than or equal to π / 6, and the lowest point of the upper edge of the weir plate is not lower than the secant of the cross section passing through the two end points of the contact line; preferably, the cross section of the weir plate is an inverted trumpet shape, and in the front and rear directions of the final polymerization kettle, the weir plate is adjacent to the low-viscosity melt outlet.

[0028] In some embodiments, the group spacing of multiple groups of disc reactors in the low viscosity zone and the disc spacing of each group of disc reactors, the group spacing of multiple groups of double-disc disc reactors in the medium and high viscosity zones and the disc spacing of two-piece combined discs, and the spacing between discs of single discs in the high viscosity zone increase successively; the diameters of multiple disc reactors in the high viscosity zone decrease successively from front to back, and the diameter of the disc reactor at the rear end of the high viscosity zone is 85%-90% of the diameter of the disc reactor at the front end of the high viscosity zone.

[0029] In the present invention, the overall disc design is based on the characteristic of gradually increasing axial viscosity. The width of the disc carrier surface gradually narrows, effectively reducing axial load. Simultaneously, for the high-viscosity individual disc assembly, the outer diameter of the rear disc is gradually reduced to expand the area of ​​​​the rear volatile flow space. The range of variation provided in this patent is that from the first individual disc at the rear to the last individual disc, the outer diameter of the disc gradually decreases to 85%-90% of the first individual disc. At the same time, the disc thickness gradually increases to meet the gradually increasing viscosity stress requirements. This disc reactor design is based on the characteristic of gradually increasing axial viscosity of the melt. The disc reactor radius gradually narrows, reducing the load on the stirring shaft and increasing the area of ​​​​the rear volatile flow space.

[0030] In some embodiments, the disc reactor in the high viscosity zone forms an angle of 1.0-3.0° with the vertical direction of the stirring shaft, and the upper end of the disc reactor faces the rear end of the high viscosity zone.

[0031] In the present invention, for the single-plate disc area located in the high-viscosity zone, in order to ensure the forward propulsion effect of the high-viscosity material, the single-plate disc and the rear chamber stirring shaft are designed to be set at an angle of 1.0-3.0° in the vertical direction, forming a certain driving force. While completing the devolatilization effect, it pushes the high-viscosity material forward to ensure that the material does not stagnate.

[0032] In some embodiments, the final polymerization kettle further comprises steam feed ports for introducing superheated ethylene glycol steam, which are arranged at the top of the main body at the rear end of the low viscosity zone, the rear end of the medium-high viscosity zone, and the rear end of the high viscosity zone. The preparation method further comprises the step of using a metering system to meter the superheated ethylene glycol steam and introduce it into the final polymerization kettle. The provision of the above-mentioned steam feed ports in the final polymerization kettle can achieve regular alcoholysis of the gel and carbonized materials produced in the high viscosity zone during the long-term operation of the device, thereby preventing carbonization at the top of the reactor, and timely reducing the viscosity and removing the materials from the high viscosity zone disc according to the pressure increase of the spinning assembly, depolymerizing and removing the deteriorated materials that have aged for a long period from the disc surface, reconstructing the material distribution of the disc, and extending the operation cycle of the device.

[0033] In some embodiments, the final polymerization kettle is connected to a vacuum pump, which is a liquid ring pump and a chilled water device for cooling the gas is provided at its inlet. The preparation method controls the suction volume of the vacuum pump to 200-350 kg / h, the ultimate vacuum degree of the vacuum pump to 50-65 Pa, and the vacuum degree in the final polymerization kettle is controlled to 100-180 Pa under the production state.

[0034] In the present invention, due to the increase in side reactions of materials in the high-viscosity zone and the overall decrease in the efficiency of devolatilization, the amount of volatile matter produced in the final polymerization kettle is 2.5 to 3.2 times that of a conventional polyester device with the same production capacity. The higher the viscosity of the high-viscosity outlet, the higher the amount of non-condensable gas produced. Therefore, the vacuum pump exhaust design is 2.0 to 3.0 times that of a conventional polyester device with the same production capacity, the ultimate vacuum design is: 50 to 65 Pa, the exhaust volume is: 200 to 350 kg / h, and a large-capacity chilled water device is designed at the inlet of the vacuum pump liquid ring pump to capture excess non-condensable acetaldehyde. In order to further maintain production stability, all ethylene glycol produced in the vacuum part of the device must be subjected to formaldehyde removal treatment before entering the system.

[0035] In some embodiments, a melt pump is used to transport high-viscosity PET melt and low-viscosity PET melt, a melt cooler is provided at the outlet of the melt pump, and the preparation method controls the temperature of the high-viscosity PET melt to 284-286°C after cooling by the melt cooler; a filter and a booster pump are provided between the melt pump and the parallel composite spinning assembly; the preparation method controls the transport time of the high-viscosity PET melt to 25-35 minutes; and a plurality of static slow-flow mixers are provided at the front end of the melt transport pipeline.

[0036] In the present invention, an ultra-short process high-viscosity polyester melt efficient melt conveying design is designed; a large-capacity melt cooler is equipped at the outlet of each melt pump to ensure that the melt temperature is quickly controlled at: 284-286°C, and then the melt is conveyed to the spinning unit through a filter and a booster pump. The ultra-short process design concept is to transfer the final polymerization kettle from the polymerization device to the top of the spinning device, and the melt is delivered to the spinning unit with the shortest conveying time. The conventional polyester melt conveying time is generally 50-70 minutes, and the high-viscosity melt conveying short process requires the conveying time to be compressed to: 25-35 minutes. A more stringent design is that the residual internal stress kinetic energy of the melt must be completely released within this residence time range. Therefore, a special front-end multi-position static slow-flow mixer is designed to quickly achieve a plug flow effect without increasing the residence time.

[0037] In some embodiments, the preparation method further includes the step of introducing a heat stabilizer, an antioxidant or a colorant into the second esterification kettle before the esterification reaction is carried out in the second esterification kettle; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; and the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

[0038] Introducing heat stabilizers and antioxidants into the second esterification kettle can improve the thermal stability and oxidation resistance of the high-viscosity PET polyester melt, thereby inhibiting the occurrence of side reactions during the esterification and polymerization process, and suppressing the viscosity drop caused by thermal degradation of the high-viscosity melt during the melt direct spinning process of up to 40 to 90 minutes. It also ensures that the intrinsic viscosity level of the melt remains high in the spinning box, thereby producing sufficient elastic curl.

[0039] In some embodiments, filters are respectively arranged between the low-viscosity melt outlet and the high-viscosity melt outlet of the final polymerization kettle and the parallel composite spinning components. The preparation method also includes the step of introducing a viscosity reducer into the high-viscosity PET melt through a pipeline syringe before the high-viscosity PET melt passes through the filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, normal pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, polypropylene terephthalate-1,3-trimethylene terephthalate PTT, and amorphous polyester; the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt.

[0040] An additive injection system is designed in front of the high-viscosity melt conveying filter to inject the viscosity reducer. The addition of the viscosity reducer can greatly improve the fluidity of the high-viscosity melt, improve the internal stress elimination effect of the high-viscosity melt, and enhance the plug flow effect. It can achieve a more stable spinning effect and an improved fiber curvature without affecting the basic indicators and quality of the final two-component elastic fiber product.

[0041] Preferably, the amount of the viscosity reducer is 0.5-2.0% of the total mass of the melt, more preferably 0.8-1.5%. Adding the viscosity reducer can significantly reduce the kinematic viscosity of the high-viscosity melt, improve the melt conveying efficiency, and reduce process degradation.

[0042] In some embodiments, the preparation method further includes the steps of passing a solid-phase smoothing agent into the ethylene terephthalate prepolymer before the ethylene terephthalate prepolymer is passed into the final polymerization kettle, and the step of passing the mixture of the solid-phase smoothing agent and the ethylene terephthalate prepolymer through a filter, wherein the solid-phase smoothing agent is in the form of a masterbatch and includes a polyester matrix and an inorganic powder, wherein the inorganic powder is selected from a combination of one or more of talc, montmorillonite, barium sulfate, hydrotalcite and nano-silica, and the amount of the solid-phase smoothing agent is 0.05% to 1.0% of the total mass of the melt.

[0043] Solid-phase lubricants are inert powders that create a good slip effect, reducing the rapid thickening of highly viscous melts. They also form vaporization centers, accelerating the overflow of small molecule materials, improving devolatilization efficiency, and reducing the temperature rise effect during melt conveying. This can significantly reduce the kinematic viscosity of highly viscous melts and improve melt conveying efficiency. The addition of solid-phase lubricants creates friction between the fluid surface and the pipe wall, which in turn increases the fluidity of the melt and reduces its viscosity.

[0044] Preferably, the amount of the solid phase smoothing agent is 0.06-0.8% of the total mass of the melt, more preferably 0.1-0.5%.

[0045] In some embodiments, filters are respectively arranged between the low-viscosity melt outlet and the high-viscosity melt outlet of the final polymerization kettle and the parallel composite spinning components, and the preparation method also includes the step of introducing a liquid lubricant into the high-viscosity PET melt before the high-viscosity PET melt passes through the filter; the liquid lubricant is selected from a combination of one or more of polyethylene glycol with a molecular weight of 8000 to 20000, polyetheramine with a molecular weight of 10000 to 20000, polybutylene adipate with a molecular weight of 5000 to 20000, polyethylene adipate with a molecular weight of 5000 to 20000, and polyacrylate, and the amount of the liquid lubricant is 0.1% to 2.0% of the total mass of the melt.

[0046] Preferably, the amount of the liquid lubricant is 0.3-1.5% of the total mass of the melt, more preferably 0.5-1.0%.

[0047] In some embodiments, the difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.18-0.35, and the difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 250-700 Pa.s.

[0048] In some embodiments, the final polymerization kettle is disposed on top of the spinning assembly, which can reduce the conveying distance of the high-viscosity and low-viscosity polyester melts synthesized in the final polymerization kettle, especially the high-viscosity melt, before spinning.

[0049] In some embodiments, the same spinning assembly is a composite spinning beam.

[0050] In some embodiments, the composite spinning beam includes a composite spinneret.

[0051] The present invention also provides a PET / PET bicomponent elastic fiber prepared by the above preparation method.

[0052] In some embodiments, the PET / PET bicomponent elastic fiber has a curl shrinkage rate of 12.0% to 36.0%.

[0053] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0054] The present invention simultaneously synthesizes a high-viscosity melt and a low-viscosity melt in the same final polymerization kettle, discharges the high-viscosity melt and the low-viscosity melt from different positions of the final polymerization kettle respectively, and then spins the two in the same spinning assembly, so that a single kettle can simultaneously synthesize high-viscosity and low-viscosity two components, and the entire system can be a five-kettle system.

[0055] The PET bicomponent elastic fiber of the present invention contains a high-viscosity and a low-viscosity bicomponent. The preparation method of the aforementioned PET bicomponent elastic fiber is a melt direct spinning method, that is, the melt obtained by polymerization is directly used for spinning without the melt cooling and slicing step and then melting and spinning.

[0056] The present invention respectively sets two stirring shafts in the low viscosity zone, the medium-high viscosity zone and the high viscosity zone, and controls the lengths of the two stirring shafts to be inconsistent, so that the stirring shaft in the low viscosity zone is longer. At the same time, a weir flow plate is set on the inner wall of the main body at the rear end of the low viscosity zone of the final polymerization kettle. The weir flow plate can separate the medium-high viscosity melt in the medium-high viscosity zone from flowing back from the gap space between the disc reactor and the inner wall of the main body to the low viscosity melt in the low viscosity zone. A low viscosity melt outlet is designed at the rear end of the low viscosity zone, and a high viscosity melt outlet is set in the high viscosity zone, thereby achieving the simultaneous discharge of high viscosity melt and low viscosity melt in the same final polymerization kettle, which not only simplifies the production equipment and process, but also better controls the viscosity of the high viscosity melt and the low viscosity melt.

[0057] In the present invention, the intrinsic viscosity of the high-viscosity melt at the first melt outlet (high-viscosity outlet) of the final polymerization reactor can reach 0.68 to 0.80, and its viscosity at 280-282°C is 550 to 800 Pa.s, which is much higher than the viscosity of the high-viscosity melt in the prior art. The difference in intrinsic viscosity between the high-viscosity melt and the low-viscosity melt in the final polymerization reactor can reach 0.23 to 0.45, which is much higher than that in the prior art.

[0058] In the PET bicomponent elastic fiber of the present invention, the intrinsic viscosity of the high-viscosity PET component (the first PET component) can reach 0.645 to 0.750. The crimp shrinkage rate of the PET bicomponent elastic fiber can reach 36.0%, which is much higher than that of existing bicomponent elastic fibers.

[0059] The preparation method of the present invention is used for industrial production of two-component elastic fibers, which can achieve a low-viscosity melt production capacity of 100,000 tons / year and a high-viscosity melt production capacity of 100,000 tons / year. When the product is melt-spun PET / PET high-low viscosity two-component elastic fiber, the comprehensive device production capacity is 200,000 tons / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG1 is a schematic diagram of a five-reactor polymerization system used in an embodiment of the present invention;

[0061] FIG2 is a schematic structural diagram of a final polymerization reactor used in an embodiment of the present invention;

[0062] FIG3 is another schematic structural diagram of the final polymerization kettle used in an embodiment of the present invention;

[0063] FIG4 is a schematic structural diagram of a composite scraper used in a final polymerization reactor according to an embodiment of the present invention;

[0064] Among them, 1-low viscosity zone, 2-medium and high viscosity zone, 3-high viscosity zone, 4-compound scraper, 5-disc scraper, 6-axial scraper, 7-wall scraper, 8-stirring shaft, 9-disc reactor, 10-first esterification kettle, 11-second esterification kettle, 12-first prepolymerization kettle, 13-second prepolymerization kettle, 14-final polymerization kettle, 15-melt pump, 16-high viscosity melt outlet, 17-low viscosity melt outlet, 18-weir plate, 19-steam feed port, 20-prepolymer feed port, 21-support column. DETAILED DESCRIPTION

[0065] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the basic principles, main features, and advantages of the present invention, and the present invention is not limited in scope by the following examples. The implementation conditions used in the examples can be further adjusted according to specific requirements. The implementation conditions not specified are generally those used in routine experiments. Unless otherwise specified in the following examples, all raw materials were purchased commercially or prepared by conventional methods in the art.

[0066] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

[0067] The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments of the present invention. In the following embodiments, it should be noted that the terms "front" and "rear" are based on the direction of material flow, with the direction in which the material flows first being the front and the direction in which the material flows later being the rear. For example, in FIG2 , the term "front" refers to the right side in FIG2 , and the term "rear" refers to the left side in FIG2 . Therefore, the directions and positional relationships described in the present invention are merely for the purpose of facilitating the description of the invention and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific direction, only have a specific direction, or be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0068] As shown in Figure 1, in the embodiment, a five-reactor system is used to prepare PET bicomponent elastic fibers: a first esterification reactor 10, a second esterification reactor 11, a first prepolymerization reactor 12, a second prepolymerization reactor 13, and a final polymerization reactor 14 (both high-viscosity and low-viscosity reactors are located in the same reactor). The five reactors are connected by necessary pipelines. A pump 15 and filters A and B are provided between the second prepolymerization reactor 13 and the final polymerization reactor 15. In actual production processes, filters A and B are not operated simultaneously. For example, filter A can be operated first, and after the system has been running for a period of time, filter B can be switched to use, at which point filter A can be cleaned.

[0069] 2 and 3 , the final polymerization kettle 14 is a horizontal polymerization kettle and includes a main body containing a chamber therein, the main body including a low viscosity zone 1, a medium-high viscosity zone 2, and a high viscosity zone 3 arranged in sequence along the axial direction of the final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low viscosity zone 1, the medium-high viscosity zone 2, and the high viscosity zone 3 increases in sequence, the low viscosity melt outlet 17 is arranged at the rear end of the low viscosity zone 1, and the high viscosity melt outlet 16 is arranged at the rear end of the high viscosity zone 3, the final polymerization kettle 14 also includes a prepolymer feed port 20 arranged at the front end of the final polymerization kettle 14, and two stirring shafts 8, one of which is arranged in the low viscosity zone 1, and the other is arranged in the medium-high viscosity zone 2 and the high viscosity zone 3, and a weir plate 18 arranged at the rear end of the low viscosity melt outlet 17, the weir plate 18 is used to prevent the melt in the medium-high viscosity zone 2 from flowing into the low viscosity zone 1.

[0070] The central axes of the two stirring shafts 8 are located on the same straight line. The final polymerization kettle 14 further includes a support column 21 arranged on the inner wall of the main body. The support column 21 is used to support the two stirring shafts 8. The support column is located at the rear end of the low viscosity zone 1.

[0071] The length of the stirring shaft 8 arranged in the low viscosity zone 1 is two-thirds of the length of the final polymerization kettle 14, the length of the stirring shaft 8 arranged in the medium-high viscosity zone 2 and the high viscosity zone 3 is one-third of the length of the final polymerization kettle 14, the length of the low viscosity zone 1 is two-thirds of the length of the final polymerization kettle 14, and the length of the medium-high viscosity zone 2 and the high viscosity zone 3 is one-third of the length of the final polymerization kettle 14. The above-mentioned one-third and two-thirds are not exact values, and they can be approximately equal to one-third and two-thirds.

[0072] Multiple disc reactors 9 are arranged on both stirring shafts 8. The disc reactor 9 in the low viscosity zone 1 is a multi-disc combination disc, and 6 to 8 groups of multi-disc combination discs are arranged in the low viscosity zone 1. A multi-disc combination disc of 8 to 10 discs is designed at the front end of the low viscosity zone 1, and a multi-disc combination disc of 4 to 5 discs is designed at the rear end. The number of disc reactors in the low viscosity zone 1 is 35 to 50; the disc reactor 9 in the medium and high viscosity zone 2 is a 4-disc combination disc, a 3-disc combination disc, or a 2-disc combination disc, and the number of disc reactors 9 in the medium and high viscosity zone 2 is 15 to 25; the disc reactor 9 in the high viscosity zone 3 is a single disc design, and the number of disc reactors 9 in the high viscosity zone 3 is 6 to 15.

[0073] The weir plate 18 is welded to the inner wall of the bottom of the main body, and in a cross section of the final polymerization kettle passing through the weir plate, the radian of the contact line between the weir plate 18 and the inner wall of the bottom of the main body is greater than or equal to π / 6, and the lowest point of the upper edge of the weir plate is not lower than the secant of the cross section passing through the two end points of the contact line; the cross section of the weir plate 18 is an inverted trumpet shape, and in the front and rear directions of the final polymerization kettle 18, the weir plate 18 is adjacent to the low-viscosity melt outlet 17.

[0074] As shown in Figures 2 and 4, the final polymerization kettle 14 also includes a wall scraper 7 arranged in the medium and high viscosity zone 2 for scraping the melt on the inner wall of the final polymerization kettle 14, a disk scraper 5 arranged in the high viscosity zone 3 for scraping the melt on the disc reactor 9, a wall scraper 7 arranged in the high viscosity zone 3 for scraping the melt on the inner wall of the final polymerization kettle 14, and an axial scraper 6 arranged in the high viscosity zone 3 for scraping the melt on the stirring shaft 8.

[0075] The spacing between the multiple groups of disc reactors in the low-viscosity zone 2, as well as the spacing between the discs in each group, the spacing between the multiple groups of double-disc disc reactors in the medium-to-high-viscosity zone 2, and the spacing between the discs in the single discs in the high-viscosity zone 3 increase sequentially. The diameters of the multiple disc reactors 9 in the high-viscosity zone 3 decrease sequentially from front to back, with the diameter of the disc reactor 9 at the rear end of the high-viscosity zone 3 being 85%-90% of the diameter of the disc reactor 9 at the front end of the high-viscosity zone 3. The disc reactors 9 in the high-viscosity zone 3 form an angle of 1.0-3.0° with the vertical direction of the stirring shaft 8, with the upper ends of the disc reactors 9 facing the rear end of the high-viscosity zone 3.

[0076] The final polymerization reactor 14 further includes steam feed ports 17 for introducing superheated ethylene glycol steam, which are arranged at the top of the main body at the rear end of the low viscosity zone 1, the rear end of the medium and high viscosity zone 2 and the rear end of the high viscosity zone 3.

[0077] The final polymerization reactor 14 is connected to a vacuum pump, which is a liquid ring pump with a chilled water device for cooling the gas at its inlet. A melt pump is used to transport high-viscosity PET melt and low-viscosity PET melt, and a melt cooler is set at the melt pump outlet.

[0078] The second esterification kettle 11 also includes feed ports for introducing heat stabilizer, antioxidant and colorant. The second esterification kettle adopts a three-chamber design, and each chamber is designed with a feed port for the three additives mentioned above.

[0079] A dynamic mixer and a filter are provided after the second prepolymerization kettle 13 and before the final polymerization kettle 14; and a solid phase smoothing agent injection system is provided before the dynamic mixer.

[0080] After the final polymerization reactor 14 and before the same spinning assembly, a dynamic mixer and a filter are arranged; before the dynamic mixer, a viscosity reducing agent injection system is arranged.

[0081] The same spinning assembly is a composite spinning beam, and the final polymerization reactor 14 is arranged on the top of the composite spinning beam to shorten the conveying distance of the melt, especially the high-viscosity melt.

[0082] Example 1

[0083] This embodiment provides a method for preparing a PET bicomponent elastic fiber, and the specific steps are as follows:

[0084] Using the above-mentioned five-reactor polymerization device, terephthalic acid, ethylene glycol, and catalyst ethylene glycol antimony are sequentially subjected to a first esterification reactor 310, a second esterification reactor 11 for esterification reaction, a first prepolymerization reactor 12, and a second prepolymerization reactor 13 for prepolymerization reaction to obtain ethylene terephthalate prepolymer, wherein the flow rate of terephthalic acid is 2500kg / h to 25000kg / h, the flow rate of ethylene glycol is 1000kg / h to 10000kg / h, and the mass content of the antimony element of the catalyst in the melt is 180 to 210ppm. Afterwards, the ethylene terephthalate prepolymer is introduced into the final polymerization kettle 14 for polymerization, and the high-viscosity PET melt is discharged from the high-viscosity melt outlet 16 of the final polymerization kettle 14, and the low-viscosity PET melt is discharged from the low-viscosity melt outlet 17; finally, the two are transported to the same parallel composite spinning box through the melt pipeline in a mass ratio of 5:5 for spinning to obtain PET two-component elastic fiber, which is FDY and has a specification of 83dtex / 36f.

[0085] The conditions of the five-reactor polymerization apparatus and the properties of the high-viscosity PET melt and the low-viscosity PET melt in the final reactor 14 are shown in Table 1. The intrinsic viscosity is measured by dissolving the melt in a mixed solvent of phenol and tetrachloroethane (3:2 volume ratio) and the unit is dL / g.

[0086] Table 1

[0087] Example 2

[0088] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 1, differing only in that a conventional titanium dioxide matting agent is added from the second esterification reactor 11 in an amount of 0.3% relative to the total mass of the melt. Furthermore, a heat stabilizer, antioxidant, and colorant are introduced from the second esterification reactor. Specifically, trimethyl phosphate, 1222, and blueing agent are added in amounts of 20 ppm, 50 ppm, and 1 ppm, respectively, relative to the molar amount of terephthalic acid. The intrinsic viscosity of the low-viscosity PET melt is controlled to be 0.47, and the intrinsic viscosity of the high-viscosity PET melt is controlled to be 0.72. After melt conveying, the online intrinsic viscosity of the low-viscosity PET melt is 0.463, and the online intrinsic viscosity of the high-viscosity PET melt is 0.673, with a difference of 0.200. Continuous spinning is performed on FDY of 83 dtex / 36 f. The fiber properties of the same spinning line at different spinning positions are shown in Table 2 below. The fiber properties of the present invention are tested according to the GBT 8960-2015 test standard:

[0089] Table 2

[0090] Example 3

[0091] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 2, except that the intrinsic viscosity of the low-viscosity PET melt is controlled to be 0.50, and the intrinsic viscosity of the high-viscosity PET melt is controlled to be 0.75. After melt conveying, the online intrinsic viscosity of the low-viscosity PET melt is 0.487, and the online intrinsic viscosity of the high-viscosity PET melt is 0.694, with a difference of 0.207. The fiber properties of the same spinning line at different spinning positions are shown in Table 3 below:

[0092] Table 3

[0093] Example 4

[0094] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 2, except that the intrinsic viscosity of the low-viscosity PET melt is controlled to be 0.55, and the intrinsic viscosity of the high-viscosity PET melt is controlled to be 0.80. After melt conveying, the online intrinsic viscosity of the low-viscosity PET melt is 0.541, and the online intrinsic viscosity of the high-viscosity PET melt is 0.744, with a difference of 0.203. The fiber properties of the same spinning line at different spinning positions are shown in Table 4 below:

[0095] Table 4

[0096] It can be seen from Examples 2 to 4 that, under the conditions of adding heat stabilizers, antioxidants and colorants, the viscosity drop level in the spinning process is greatly reduced, the degree of side reactions is effectively suppressed, the full roll rate of the fiber product is significantly increased, and the fiber curl shrinkage rate is significantly improved due to the increased viscosity difference between the two components. The fiber full roll rate level is between 91.5% and 93.8%.

[0097] Example 5

[0098] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 2, except that a viscosity reducer is also introduced via a pipe syringe. The specific type of the viscosity reducer is an amorphous polyester with an intrinsic viscosity of 0.64 (intrinsic viscosity test solvent: phenol:tetrachloroethane 3:2), and the amount of the viscosity reducer is 0.5% relative to the total mass of the melt. The intrinsic viscosity of the low-viscosity melt is controlled to be 0.47, and the intrinsic viscosity of the high-viscosity melt is controlled to be 0.72. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.463, and the online intrinsic viscosity of the high-viscosity melt is 0.670, with a difference of 0.207. The fiber properties of the same spinning line at different spinning positions are shown in Table 5 below:

[0099] Table 5

[0100] Example 6

[0101] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 5, with the only difference being that the intrinsic viscosity of the low-viscosity melt is controlled to be 0.50, and the intrinsic viscosity of the high-viscosity melt is controlled to be 0.75. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.488, and the online intrinsic viscosity of the high-viscosity melt is 0.690, with a difference of 0.202. The fiber properties of the same spinning line at different spinning positions are shown in Table 6 below:

[0102] Table 6

[0103] Example 7

[0104] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 5, differing only in that the viscosity reducer dosage is adjusted to 0.8%, the intrinsic viscosity of the low-viscosity melt is controlled to 0.55, and the intrinsic viscosity of the high-viscosity melt is controlled to 0.80. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.540, and the online intrinsic viscosity of the high-viscosity melt is 0.748, with a difference of 0.208. The fiber properties of the same spinning line at different spinning positions are shown in Table 7 below:

[0105] Table 7

[0106] It can be seen from Examples 5-7 that after adding the viscosity reducer, the basic physical and chemical indicators of the finished fiber line did not change significantly, but the spinning condition was significantly improved, and the full roll rate increased to 94.2% to 95.7%, indicating that the addition of the viscosity reducer not only improved the full roll rate of the product, but also significantly reduced irregular breakage during the spinning process.

[0107] Example 8

[0108] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 2, differing only in that a solid-phase smoothing agent is also introduced from the solid-phase smoothing agent injection system. Specifically, the agent is a polyester masterbatch of barium sulfate powder with a particle size of 20 to 100 nm, and the amount used is 0.2% of the total mass of the melt. The intrinsic viscosity of the low-viscosity melt is controlled to be 0.47, and the intrinsic viscosity of the high-viscosity melt is controlled to be 0.72. After melt transport, the online intrinsic viscosity of the low-viscosity melt is 0.460, and the online intrinsic viscosity of the high-viscosity melt is 0.665, with a difference of 0.205. The fiber properties of the same spinning line at different spinning positions are shown in Table 8 below:

[0109] Table 8

[0110] Example 9

[0111] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 8, differing only in that the amount of solid-phase smoothing agent is adjusted to 0.3%, the intrinsic viscosity of the low-viscosity melt is controlled to 0.50, and the intrinsic viscosity of the high-viscosity melt is controlled to 0.75. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.482, and the online intrinsic viscosity of the high-viscosity melt is 0.684, with a difference of 0.202. The fiber properties of the same spinning line at different spinning positions are shown in Table 9 below:

[0112] Table 9

[0113] Example 10

[0114] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 8, differing only in that the amount of solid-phase smoothing agent is adjusted to 0.4%, the intrinsic viscosity of the low-viscosity melt is controlled to 0.55, and the intrinsic viscosity of the high-viscosity melt is controlled to 0.80. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.535, and the online intrinsic viscosity of the high-viscosity melt is 0.736, with a difference of 0.201. The fiber properties of the same spinning line at different spinning positions are shown in Table 10 below:

[0115] Table 10

[0116] It can be seen from Examples 8 to 10 that after adding the solid-phase smoothing agent, the basic physical and chemical indicators of the finished fiber line did not change significantly, but the spinning condition was significantly improved, and the full roll rate increased to 93.5% to 94.9%. This shows that the addition of the solid-phase smoothing agent not only improves the full roll rate of the product, but also significantly reduces irregular breakage during the spinning process.

[0117] Example 11

[0118] This embodiment provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as that of Example 2, differing only in that a liquid lubricant is also introduced from the liquid lubricant injection system. Specifically, the lubricant is polyethylene adipate with a molecular weight of 8000, and the amount used is 0.2% relative to the total mass of the melt. The intrinsic viscosity of the low-viscosity melt is controlled to be 0.47, and the intrinsic viscosity of the high-viscosity melt is controlled to be 0.72. After melt transport, the online intrinsic viscosity of the low-viscosity melt is 0.463, and the online intrinsic viscosity of the high-viscosity melt is 0.668, with a difference of 0.205. The fiber properties of the same spinning line at different spinning positions are shown in Table 11 below:

[0119] Table 11

[0120] Example 12

[0121] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 11, differing only in that the amount of liquid lubricant is adjusted to 0.3% relative to the total mass of the melt, the intrinsic viscosity of the low-viscosity melt is controlled to 0.50, and the intrinsic viscosity of the high-viscosity melt is controlled to 0.75. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.489, and the online intrinsic viscosity of the high-viscosity melt is 0.687, with a difference of 0.198. The fiber properties of the same spinning line at different spinning positions are shown in Table 12 below:

[0122] Table 12

[0123] Example 13

[0124] This example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 11, differing only in that the amount of liquid lubricant is adjusted to 0.4%, the intrinsic viscosity of the low-viscosity melt is controlled to 0.55, and the intrinsic viscosity of the high-viscosity melt is controlled to 0.80. After melt conveying, the online intrinsic viscosity of the low-viscosity melt is 0.539, and the online intrinsic viscosity of the high-viscosity melt is 0.738, with a difference of 0.199. The fiber properties of the same spinning line at different spinning positions are shown in Table 13 below:

[0125] Table 13

[0126] It can be seen from Examples 10-13 that after adding and using the liquid lubricant, the basic physical and chemical indicators of the finished product line did not change significantly, but the spinning condition was significantly improved, and the full roll rate increased to 94.3% to 96.6%. Not only did it increase the full roll rate of the product, but the irregular breakage during the spinning process was significantly reduced.

[0127] Comparative Example 1

[0128] This comparative example provides a method for preparing PET bicomponent elastic fiber. This method is essentially the same as Example 2, differing only in that the heat stabilizer and antioxidant are not introduced into the second esterification reactor. The intrinsic viscosity of the low-viscosity melt was controlled to be 0.47, and the intrinsic viscosity of the high-viscosity melt was controlled to be 0.75. After melt transfer, the online intrinsic viscosity of the low-viscosity melt was 0.451, and the online intrinsic viscosity of the high-viscosity melt was 0.653, a difference of 0.202. The fiber properties of the same spinning line at different spinning positions are shown in Table 14 below:

[0129] Table 14

[0130] Comparative Example 2

[0131] This comparative example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 2, differing only in that the heat stabilizer and antioxidant are not introduced into the second esterification reactor. The intrinsic viscosity of the low-viscosity melt was controlled to be 0.50, and the intrinsic viscosity of the high-viscosity melt was controlled to be 0.78. After melt transport, the online viscosity of the low-viscosity melt was 0.467, and the online viscosity of the high-viscosity melt was 0.661, a significant difference of 0.143. Fiber properties from different spinning positions on the same spinning line are shown in Table 15 below:

[0132] Table 15

[0133] Comparative Example 3

[0134] This comparative example provides a method for preparing a PET bicomponent elastic fiber. This method is essentially the same as Example 2, differing only in that the heat stabilizer and antioxidant are not introduced into the second esterification reactor. The intrinsic viscosity of the low-viscosity melt was controlled to be 0.55, and the intrinsic viscosity of the high-viscosity melt was controlled to be 0.85. After melt transport, the online viscosity of the low-viscosity melt was 0.519, and the online viscosity of the high-viscosity melt was 0.667, a significant difference of 0.148. Fiber properties from different spinning positions on the same spinning line are shown in Table 16 below:

[0135] Table 16

[0136] It can be seen from Comparative Examples 1-3 that without adding heat stabilizers and antioxidants, the viscosity drop in the spinning process is high, the degree of side reactions is large, the product color is yellowish, the fiber full roll rate is low, and the fiber has a small viscosity difference between the two components, so the curl shrinkage rate and the actual width of the fabric are low.

[0137] The specific values ​​of the full roll rate of the fibers of Examples 2-13 and Comparative Examples 1-3 are shown in Table 17 below, where the full roll rate test method is carried out in accordance with the GBT 8960-2015 standard.

[0138] Table 17

[0139] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications based on the spirit and essence of the present invention are intended to be encompassed by the scope of protection of the present invention.

Claims

1. A method for preparing a melt-spun PET bicomponent elastic fiber, the method comprising the steps of sequentially passing terephthalic acid, ethylene glycol and a catalyst through a first esterification kettle and a second esterification kettle for esterification reaction, a first prepolymerization kettle and a second prepolymerization kettle for prepolymerization reaction, to obtain an ethylene terephthalate prepolymer, wherein: The preparation method also includes the steps of introducing the ethylene terephthalate prepolymer into a final polymerization kettle for polymerization, wherein the final polymerization kettle has a low-viscosity melt outlet and a high-viscosity melt outlet, and outputting a low-viscosity PET melt from the low-viscosity melt outlet and a high-viscosity PET melt from the high-viscosity melt outlet, respectively; the low-viscosity PET melt has a characteristic viscosity of 0.45 to 0.60, and a dynamic viscosity of 90 to 300 Pa.s at 280° C.; the high-viscosity PET melt has a characteristic viscosity of 0.68 to 0.80, and a dynamic viscosity of 450 to 810 Pa.s at 284° C.; and spinning the low-viscosity PET melt and the high-viscosity PET melt through the same parallel composite spinning assembly to obtain the melt-spun PET two-component elastic fiber.

2. The preparation method according to claim 1, characterized in that: The final polymerization kettle is a horizontal polymerization kettle, and includes a main body with a chamber inside, the main body includes a low viscosity zone, a medium-high viscosity zone, and a high viscosity zone arranged in sequence along the axial direction of the final polymerization kettle, the viscosity of the polyethylene terephthalate melt in the low viscosity zone, the medium-high viscosity zone, and the high viscosity zone increases in sequence, the low viscosity melt outlet is arranged at the rear end of the low viscosity zone, and the high viscosity melt outlet is arranged at the rear end of the high viscosity zone, the final polymerization kettle also includes a prepolymer feed port arranged at the front end of the final polymerization kettle, and two stirring shafts, one of which is arranged in the low viscosity zone, and the other is arranged in the medium-high viscosity zone and the high viscosity zone, and a weir flow plate arranged at the rear end of the low viscosity melt outlet, and the weir flow plate is used to prevent the melt in the medium-high viscosity zone from flowing into the low viscosity zone.

3. The preparation method according to claim 2, characterized in that: The central axes of the two stirring shafts are located on the same straight line. The final polymerization kettle also includes a support column arranged on the inner wall of the main body, the support column is used to support the two stirring shafts, and the support column is located at the rear end of the low viscosity zone.

4. The preparation method according to claim 2, characterized in that: The length of the stirring shaft arranged in the low viscosity zone is two-thirds of the length of the final polymerization kettle, the length of the stirring shaft arranged in the medium-high viscosity zone and the high viscosity zone is one-third of the length of the final polymerization kettle, the length of the low viscosity zone is two-thirds of the length of the final polymerization kettle, and the length of the medium-high viscosity zone and the high viscosity zone is one-third of the length of the final polymerization kettle.

5. The preparation method according to claim 4, characterized in that: A plurality of disc reactors are arranged on the two stirring shafts. The disc reactor in the low viscosity zone is a multi-disc combination disc. The low viscosity zone is provided with 6 to 8 groups of multi-disc combination discs, and the number of disc reactors in the low viscosity zone is 35 to 50. The disc reactor in the medium and high viscosity zone is a 4-disc combination disc, a 3-disc combination disc, or a 2-disc combination disc. The number of disc reactors in the medium and high viscosity zone is 15 to 25. The disc reactor in the high viscosity zone is a single-disc design. The number of disc reactors in the high viscosity zone is 6 to 15.

6. The preparation method according to claim 4, characterized in that: The final polymerization kettle also includes a wall scraper arranged in the medium and high viscosity zone for scraping the melt on the inner wall of the final polymerization kettle, a disk scraper arranged in the high viscosity zone for scraping the melt on the disc reactor, a wall scraper arranged in the high viscosity zone for scraping the melt on the inner wall of the final polymerization kettle, and an axial scraper arranged in the high viscosity zone for scraping the melt on the stirring shaft.

7. The preparation method according to claim 2, characterized in that: The weir plate is welded to the inner wall of the bottom of the main body, and in a cross section of the final polymerization kettle passing through the weir plate, the curvature of the contact line between the weir plate and the inner wall of the bottom of the main body is greater than or equal to π / 6, and the lowest point of the upper edge of the weir plate is not lower than the secant of the cross section passing through the two end points of the contact line; preferably, the cross section of the weir plate is an inverted trumpet shape, and in the front-to-back direction of the final polymerization kettle, the weir plate is adjacent to the low-viscosity melt outlet.

8. The preparation method according to claim 5, characterized in that: The group spacing of multiple groups of disc reactors in the low viscosity zone and the disc spacing of each group of disc reactors, the group spacing of multiple groups of double-disc disc reactors in the medium and high viscosity zones and the disc spacing of two combined discs, and the spacing between discs of the single disc in the high viscosity zone increase successively; the diameters of the multiple disc reactors in the high viscosity zone decrease successively from front to back, and the diameter of the disc reactor at the rear end of the high viscosity zone is 85%-90% of the diameter of the disc reactor at the front end of the high viscosity zone.

9. The preparation method according to claim 5, characterized in that: The disc reactor in the high viscosity zone forms an angle of 1.0-3.0° with the vertical direction of the stirring shaft, and the upper end of the disc reactor faces the rear end of the high viscosity zone.

10. The preparation method according to claim 2, characterized in that: The final polymerization kettle also includes steam feed ports for introducing superheated ethylene glycol steam, which are arranged at the top of the main body at the rear end of the low viscosity zone, the rear end of the medium and high viscosity zone, and the rear end of the high viscosity zone. The preparation method also includes the step of using a metering system to meter the superheated ethylene glycol steam and introducing it into the final polymerization kettle.

11. The preparation method according to claim 2, characterized in that: The final polymerization kettle is connected to a vacuum pump, which is a liquid ring pump, and a chilled water device for cooling the gas is provided at its inlet. The preparation method controls the suction volume of the vacuum pump to be 200-350 kg / h, the ultimate vacuum degree of the vacuum pump to be 50-65 Pa, and the vacuum degree in the final polymerization kettle is controlled to be 100-180 Pa under the production state.

12. The preparation method according to claim 2, characterized in that: A melt pump is used to transport high-viscosity PET melt and low-viscosity PET melt, a melt cooler is arranged at the outlet of the melt pump, and the preparation method controls the temperature of the high-viscosity PET melt to be 284-286°C after being cooled by the melt cooler; a filter and a booster pump are arranged between the melt pump and the parallel composite spinning component; the preparation method controls the transportation time of the high-viscosity PET melt to be 25-35 minutes; and a plurality of static slow-flow mixers are arranged at the front end of the melt transportation pipeline.

13. The preparation method according to claim 1 or 2, characterized in that: The preparation method also includes the step of introducing a heat stabilizer, an antioxidant or a colorant into the second esterification kettle before the esterification reaction is carried out in the second esterification kettle; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglycerol phosphate; the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

14. The preparation method according to claim 1 or 2, characterized in that: Filters are respectively arranged between the low-viscosity melt outlet and the high-viscosity melt outlet of the final polymerization kettle and the parallel composite spinning components. The preparation method also includes the step of introducing a viscosity reducer into the high-viscosity PET melt through a pipeline injector before the high-viscosity PET melt passes through the filter; the viscosity reducer is selected from a combination of one or more of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye-easy polyester ECDP, normal pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, polypropylene terephthalate-1,3-trimethylene terephthalate PTT, and amorphous polyester; the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt. Alternatively, the preparation method further comprises the steps of introducing a solid-phase smoothing agent into the ethylene terephthalate prepolymer before the ethylene terephthalate prepolymer is introduced into the final polymerization kettle, and passing a mixture of the solid-phase smoothing agent and the ethylene terephthalate prepolymer through a filter, wherein the solid-phase smoothing agent is in the form of a masterbatch and comprises a polyester matrix and an inorganic powder, wherein the inorganic powder is selected from a combination of one or more of talc, montmorillonite, barium sulfate, hydrotalcite and nano-silica, and the amount of the solid-phase smoothing agent is 0.05% to 1.0% of the total mass of the melt.

15. The preparation method according to claim 1 or 2, characterized in that: Filters are respectively arranged between the low-viscosity melt outlet and the high-viscosity melt outlet of the final polymerization kettle and the parallel composite spinning components. The preparation method also includes the step of introducing a liquid lubricant into the high-viscosity PET melt before the high-viscosity PET melt passes through the filter; the liquid lubricant is selected from a combination of one or more of polyethylene glycol with a molecular weight of 8000 to 20000, polyether amine with a molecular weight of 10000 to 20000, polybutylene adipate with a molecular weight of 5000 to 20000, polyethylene adipate with a molecular weight of 5000 to 20000, and polyacrylate, and the amount of the liquid lubricant is 0.1% to 2.0% of the total mass of the melt.

16. The preparation method according to claim 1 or 2, characterized in that: In terms of mass percentage, the PET bicomponent elastic fiber contains 30%-70% of a high-viscosity PET component and 70%-30% of a low-viscosity PET component, and the high-viscosity PET component and the low-viscosity PET component have different viscosities.

17. The preparation method according to claim 1 or 2, characterized in that: The difference between the intrinsic viscosity of the high-viscosity PET melt and the intrinsic viscosity of the low-viscosity PET melt is 0.18-0.35, and the difference between the dynamic viscosity of the high-viscosity PET melt and the dynamic viscosity of the low-viscosity PET melt is 250-700 Pa.s.

18. The PET / PET bicomponent elastic fiber prepared by the preparation method according to any one of claims 1 to 17.

19. The PET / PET bicomponent elastic fiber according to claim 18, characterized in that: The curling shrinkage rate of the PET / PET two-component elastic fiber is 12.0% to 36.0%.

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