Polymerization vessel for high viscosity PTT and method for producing high viscosity PTT / low viscosity pet bicomponent elastic fibers by direct melt spinning

Abstract

the present invention relates to a polymerization vessel for high viscosity PTT and a method for producing high viscosity PTT / low viscosity PET bicomponent elastic fibers by direct melt spinning. In a low viscosity zone of the polymerization vessel, cage-type combined circular tray reactors have been designed, a circular passage has been designed at the center of the combined disc reactors, and one stirring shaft is provided for both the medium high viscosity zone and the high viscosity zone. Preferably, material advancing components have been designed for the cage-type combined disc reactors. During the preparation of bicomponent elastic fibers, two production lines are used to separately produce a high viscosity PTT melt and a low viscosity PET melt, and then spinning is carried out. The high viscosity PTT production line includes a first esterification vessel, a second esterification vessel, a first pre-polymerization vessel, a second pre-polymerization vessel, and a high viscosity PTT polymerization vessel. By using the present method, low costs and high productivity are achieved, and the process is significantly shortened; the prepared elastic fibers have a fiber strength of 2.6-3.2 cN / dtex, a crimp contraction of 25-75%, and a crimp stability of 82-90%.

Description

Polymerization kettle for high-viscosity PTT and method for preparing melt-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fiber Technical Field

[0001] The invention relates to a polymerization kettle for high-viscosity PTT and a method for preparing melt-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fibers. 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] The development of bicomponent elastic fibers has been a key area of ​​industry development over the past decade. The latest advances utilize the differing orientation and crystallization behaviors of PET polyester components of varying viscosity. During the spinning process, the high-viscosity and low-viscosity components undergo elastic curling due to the varying speeds and percentages of transition from the oriented state to the crystallized state, forming a spring-like structure that exhibits excellent elastic properties on the fabric. Patents such as CN111101237A, CN101126180A, CN106337212A, CN107964690A, CN101851812A, and CN115613159A disclose a series of PET / PET, PBT / PET, and PTT / PET composite elastic fibers and their preparation methods, as well as methods for preparing easily or deeply dyed elastic fibers using modified PET fibers with retained elasticity, such as high-viscosity ECDP, high-viscosity high-shrinkage polyester, high-viscosity disperse dye-friendly polyester, and high-viscosity CDP cationic polyester, with low-viscosity PET polyester.

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

[0005] Although PTT polyester raw materials are expensive, the outstanding curl shrinkage, elastic recovery, and curl stability of PTT / PET bicomponent elastic fibers make them an ideal alternative to the more expensive spandex elastic fiber. PTT / PET fibers offer the advantage of being directly blended with fibers without the need for coating. Furthermore, PTT / PET bicomponent fibers exhibit superior stress-relieving properties, gradually relieving external forces. Therefore, garments woven from these fibers are more comfortable and well-fitted. However, existing PTT / PET bicomponent fibers lack sufficient curl shrinkage, curl stability, and quality consistency.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a high-viscosity PTT polymerization kettle, which is used to prepare a high-viscosity PTT melt. The high-viscosity PTT melt prepared by the polymerization kettle has a very high viscosity. When it is used to prepare melt-spun high-viscosity PTT / low-viscosity PET two-component elastic fiber, the performance of the fiber can be significantly improved.

[0008] The purpose of the present invention is to provide a melt-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fiber, which has significantly improved curl shrinkage, curl stability and quality stability.

[0009] Another object of the present invention is to provide a method for preparing melt-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fibers, which has significantly reduced costs, high production capacity, and a significantly shortened process flow. The curl shrinkage rate, curl stability, and quality stability of the prepared elastic fibers are significantly improved.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A high-viscosity PTT polymerization kettle, which is used to prepare a high-viscosity PTT melt, wherein the high-viscosity PTT melt is used to prepare a high-viscosity PTT / low-viscosity PET two-component elastic fiber. The high-viscosity PTT 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 high-viscosity PTT polymerization kettle. The viscosity of the PTT melt in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increases in sequence; the low-viscosity zone and the medium-high-viscosity zone are both provided with a combined disc reactor, and the high-viscosity zone is provided with multiple single-piece disc reactors; the high-viscosity PTT polymerization kettle also It includes a rotating shaft located at the front end of the low viscosity zone. The low viscosity zone of the high viscosity PTT polymerization kettle is designed with a cage-type combined disc reactor. The cage-type combined disc reactor includes multiple groups of combined disc reactors and an outer cage frame fixedly connected to the outer edge of the combined disc reactor. The rotating shaft drives the outer cage frame and the multiple groups of combined disc reactors in the low viscosity zone to rotate; and the axial area corresponding to the combined disc reactor in the low viscosity zone is not provided with a stirring shaft, and a circular channel is designed in the middle of the combined disc reactor; the medium-high viscosity zone and the high viscosity zone are provided with a stirring shaft in common, and the disc reactors in the medium-high viscosity zone and the high viscosity zone pass through the stirring shaft.

[0012] In the present invention, the combined disc reactor design refers to a plurality of adjacent disc reactors being fixedly connected together, and the disc reactors rotate together with the stirring shaft or the outer cage.

[0013] In some embodiments, the length of the low viscosity zone is half the length of the high viscosity PTT polymerization kettle, and the total length of the medium-high viscosity zone and the high viscosity zone is half the length of the high viscosity PTT polymerization kettle.

[0014] In some embodiments, the length of the stirring shaft disposed in the medium-high viscosity zone and the high viscosity zone is half the length of the high viscosity PTT polymerization kettle.

[0015] In the present invention, one-half does not mean an exact value of one-half, but refers to a value approximately at or around one-half, and is approximately equal to one-half.

[0016] In some embodiments, the high viscosity PTT polymerization kettle further includes a prepolymer inlet located at the bottom of the front end of the low viscosity zone and a high viscosity PTT melt outlet located at the bottom of the rear end of the high viscosity zone, and the high viscosity PTT melt outlet is in a bell-mouth shape.

[0017] In some embodiments, the outer cage includes a cage-shaped component with a gear-shaped front end, and a material pushing component extending along the axial direction of the high-viscosity PTT polymerization kettle by bending from each gear of the cage-shaped component. The outer cage is fixedly connected to the rotating shaft.

[0018] In some embodiments, the cross section of the material pushing component is wedge-shaped, with the thick end of the wedge facing the rotation direction of the disc reactor.

[0019] The outer cage frame of the present invention has a wedge-shaped structure, and the thick end of the wedge faces the rotation direction of the disc reactor, which can enhance the mixing effect in the bottom material area, push more materials to a higher position along the rotation direction, increase the residence time of the materials on the disc reactor, and improve the devolatilization efficiency of the disc reactor.

[0020] The cage-type combined disc reactor utilizes the pushing effect of the outer cage frame to improve the devolatilization efficiency of the low-viscosity zone in the front chamber, with the improvement degree reaching 25% to 40%. When the characteristic viscosity at the inlet position of the high-viscosity zone in the rear chamber is determined, the length of the low-viscosity zone in the front chamber can be shortened by 20% to 35% compared with the length of the conventional disc reactor, the total volume of the final polymerization kettle can be reduced by 18% to 25%, the material residence time is reduced by 18% to 25%, and the material mixing is more uniform, and the quality of the obtained PTT high-viscosity melt and the final fiber product will be effectively improved.

[0021] In some embodiments, the number of material propulsion components is 8 to 12. By providing 8 to 12 outer edge material propulsion components, the residence time of low-viscosity materials on the disc surface is significantly increased, effectively improving the devolatilization efficiency of the front kettle assembly disc and increasing the degree of polymerization reaction in the front kettle, thereby reducing the material residence time. The design volume of the high-viscosity reactor is reduced by 20% to 35%, and the length of the high-viscosity reactor is significantly reduced, reaching 65% to 80% of that of a conventional PTT disc reactor with the same viscosity.

[0022] In some embodiments, a support base for supporting a stirring shaft can be fixedly provided on the inner wall of the main body of the high-viscosity PTT polymerization kettle in the middle portion. The front ends of the stirring shafts arranged in the medium-high viscosity zone and the high viscosity zone are fixed on the support base.

[0023] In some embodiments, the disc reactor in the medium and high viscosity zone is designed with multiple groups of combined discs from front to back, namely a 4-piece combined disc design, a 3-piece combined disc design and a 2-piece combined disc design; in the 2-piece combined disc design in the medium and high viscosity zone, the distance between the combined disc groups and the distance between the two discs themselves gradually increases from front to back; the total number of disc reactors in the medium and high viscosity zone and the high viscosity zone is 25 to 35; the number of single-piece disc reactors in the high viscosity zone is 8 to 12, and the diameter of the disc reactor decreases from front to back, and the diameter of the last disc reactor in the high viscosity zone is 88%-92% of the diameter of the first disc reactor; the high viscosity zone is also provided with a composite scraper, which includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high viscosity PTT polymerization kettle and a disc scraper for scraping the melt on the disc reactor. The disc scraper is provided with two layers, and the material thickness on the disc reactor is controlled to be no more than 30 mm.

[0024] The first layer of disc scrapers ensures effective separation of high-viscosity materials, and the second layer of disc scrapers controls the thickness of the disc material, which can effectively control the effective separation of high-viscosity melt after the scraper and control the material thickness on the two disc reactors to not exceed 30mm, preferably 10-30mm.

[0025] The high-viscosity PTT polymerization kettle of the present invention adopts a unique design. The front chamber (low viscosity zone) adopts a cage-type multi-group disc reactor, and a circular channel is designed in the middle of the combined disc reactor. The cage-type combined disc reactor uses the pushing effect of the outer cage frame to improve the devolatilization efficiency of the front chamber by 25% to 40%. The rear chamber (medium-high viscosity zone and high viscosity zone) adopts a high-viscosity disc reactor design, and the rear end is designed with 8 to 12 groups of single discs and is equipped with an integrated scraper, including a disc scraper, a wall scraper, and an axial scraper. The upper disc scraper adopts a double-layer design. The first layer of scrapers scrapes the melt from the disc surface and produces effective separation, and the second layer of scrapers controls the thickness of the disc material to maintain at 10 to 30 mm; thus, a high-efficiency devolatilization effect can be achieved.

[0026] The antechamber of the high-viscosity PTT polymerization reactor of the present invention adopts the characteristics of a multi-stage combined disc combined with a cage structure. The outer edge of the combined disc is designed with a material propulsion component along the rotation direction. The antechamber is not provided with a central axis, and 8 to 12 material propulsion components on the outer edge are used as a support structure. The disc area ratio can reach 45% to 65%, which is higher than the 30% to 45% area ratio of ordinary disc reactors. The material can be expanded to the maximum extent to quickly complete the devolatilization of reaction by-products. A circular channel is designed in the middle of the disc group, and volatile components can be more smoothly discharged from the circular channel. Compared with the conventional central axis disc design, the effective devolatilization efficiency of the disc is increased by 30% to 55%.

[0027] In some embodiments, the aspect ratio of the high-viscosity PTT polymerization kettle is 3.5-4.0:1.0. This high aspect ratio is conducive to distributing more disc reactors to increase the effective devolatilization area and improve the vacuum degree of the reactor, thereby increasing the viscosity of the PTT melt and reducing the level of side reactions. It can also be combined with a high vacuum design to quickly increase the viscosity of the high-viscosity PTT melt.

[0028] The present invention also provides a method for preparing a high-viscosity PTT / low-viscosity PET bicomponent elastic fiber using the aforementioned high-viscosity PTT polymerization kettle, wherein the bicomponent elastic fiber contains a high-viscosity PTT component and a low-viscosity PET component, wherein the viscosity of the high-viscosity PTT component is greater than the viscosity of the low-viscosity PET component, and the preparation method comprises the steps of separately preparing a high-viscosity PTT melt and a low-viscosity PET melt, and spinning the high-viscosity PTT melt and the low-viscosity PET melt through the same parallel composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PTT melt is greater than the viscosity of the low-viscosity PET melt; the step of preparing the high-viscosity PTT melt comprises: The steps of sequentially passing terephthalic acid and 1,3-propylene glycol through a first esterification kettle and a second esterification kettle for esterification reaction, and then conducting a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PTT prepolymer, and then subjecting the PTT prepolymer to polymerization reaction in the aforementioned high-viscosity PTT polymerization kettle to obtain the high-viscosity PTT melt; the step of preparing a low-viscosity PET melt includes the steps of sequentially passing terephthalic acid and ethylene glycol through a first esterification kettle and a second esterification kettle for esterification reaction, and then conducting a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PET prepolymer, and then subjecting the PET prepolymer to polymerization reaction in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

[0029] In the present invention, PTT refers to poly(1,3-trimethylene terephthalate), and PET refers to polyethylene terephthalate.

[0030] The high-viscosity PTT / low-viscosity PET bicomponent elastic fiber of the present invention contains high-viscosity and low-viscosity components. The bicomponent elastic fiber is prepared by a melt-spinning method, whereby the melt obtained from polymerization is directly used for spinning, without undergoing the melt cooling and slicing steps before remelting and spinning.

[0031] In some embodiments, the bicomponent elastic fiber contains, by weight, 35%-65% of a high-viscosity PTT component and 65%-35% of a low-viscosity PET component.

[0032] In some embodiments, the high-viscosity PTT melt has an intrinsic viscosity of 0.92 to 1.16 and a dynamic viscosity of 320 to 1200 Pa.s (measured at 255°C); the low-viscosity PET melt has an intrinsic viscosity of 0.45 to 0.55 and a dynamic viscosity of 90 to 240 Pa.s (measured at 275°C).

[0033] In some embodiments, the high-viscosity PTT melt has an intrinsic viscosity of 0.95 to 1.10 and a dynamic viscosity of 430 to 900 Pa·s (measured at 255° C.).

[0034] In some embodiments, the high-viscosity PTT melt has an intrinsic viscosity of 0.97 to 1.05 and a dynamic viscosity of 500 to 750 Pa·s (measured at 255° C.).

[0035] In the present invention, the intrinsic viscosity is the result of measurement in a mixed solvent of phenol and tetrachloroethane at a volume ratio of 3:2.

[0036] In some embodiments, in the same parallel composite spinning assembly, the high-viscosity PTT melt has a dynamic viscosity of 350 to 800 Pa.s, and the low-viscosity PET melt has a dynamic viscosity of 70 to 220 Pa.s. This indicates that the high-viscosity PTT melt of the present invention experiences a minimal viscosity drop upon delivery to the spinning assembly.

[0037] In some embodiments, the preparation method controls the rotation speed of the rotating shaft in the low viscosity area to be 0-5.5 rpm.

[0038] In some embodiments, the preparation method controls the stirring speed of the stirring shafts in the medium-high viscosity zone and the high viscosity zone to be 0-3.0 rpm.

[0039] In some embodiments, the intrinsic viscosity of the PTT prepolymer introduced into the high-viscosity PTT polymerization kettle is 0.280 to 0.350. This range of prepolymer melt entering the high-viscosity PTT polymerization kettle effectively reduces the overall material loading on the high-viscosity PTT polymerization kettle, optimizes material residence time, significantly reduces the level of side reactions in the polymerization kettle, and minimizes the generation of non-condensable gas.

[0040] In some embodiments, the intrinsic viscosity of the PTT prepolymer introduced into the high-viscosity PTT polymerization kettle is 0.290 to 0.325.

[0041] In some embodiments, the intrinsic viscosity of the PTT prepolymer introduced into the high-viscosity PTT polymerization kettle is 0.295 to 0.310.

[0042] In some embodiments, when preparing a high-viscosity PTT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before performing the esterification reaction, and the esterification catalyst is selected from tetrabutyl titanate or tetraisopropyl titanate.

[0043] In some embodiments, the second esterification kettle used to prepare the high-viscosity PTT melt is a horizontal reactor and includes three chambers arranged in sequence in front and back. When preparing the high-viscosity PTT melt, the preparation method also includes a step of adding a catalyst blocking agent to the second chamber from the front to the back of the second esterification kettle after the esterification reaction is completed in the first chamber from the front to the back of the second esterification kettle to deactivate the esterification catalyst. The catalyst blocking agent is selected from trimethyl phosphate or phosphoric acid, and the mass of the catalyst blocking agent accounts for 15-30ppm of the mass of the high-viscosity PTT melt.

[0044] After the esterification catalyst completes the esterification reaction, it loses its ability to catalyze the polymerization reaction and can easily lead to an increase in side reactions in the polymerization vessel. Therefore, the esterification catalyst is treated with a catalyst blocking agent in the second chamber of the second esterification vessel. This blocking and deactivation treatment will not affect the subsequent polymerization reaction.

[0045] In some embodiments, when preparing a high-viscosity PTT melt, the preparation method further includes the step of adding a polymerization catalyst into the third sub-chamber from the front to the rear of the second esterification kettle.

[0046] In some embodiments, the polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the resultant in 1,3-propylene glycol.

[0047] In some embodiments, the titanate is selected from tetrabutyl titanate, tetraisopropyl titanate, or tetra(2-ethylhexyloxy) titanate.

[0048] In some embodiments, the protonic acid is selected from a combination of one or more of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid, and polyphosphoric acid.

[0049] In some embodiments, the mass ratio of the titanate to the protonic acid is 1:0.5-2.0.

[0050] In some embodiments, the mass percentage of titanium element in the polymerization catalyst is 1.0%-3.0%.

[0051] In some embodiments, the mass of the titanium element in the esterification catalyst accounts for 1 to 30 ppm of the mass of the high-viscosity PTT melt.

[0052] In some embodiments, the mass of the titanium element in the polymerization catalyst accounts for 30 to 100 ppm of the mass of the high-viscosity PTT melt.

[0053] In some embodiments, the high-viscosity PTT polymerization kettle further includes steam inlets for introducing superheated 1,3-propylene glycol vapor, located at the top of the main body at the rear ends of the low-viscosity zone, the rear ends of the medium-high viscosity zone, and the rear end of the high viscosity zone. The preparation method further includes the step of metering the superheated 1,3-propylene glycol vapor using a metering system and introducing it into the high-viscosity PTT polymerization kettle. This configuration allows the high-viscosity PTT polymerization kettle to form a gel-crosslinked carbonization at the upper rear end of the final polymerization kettle after a period of operation. The 1,3-propylene glycol vapor inlet facilitates regular cleaning of the entire polymerization apparatus without shutting down, thereby maintaining the apparatus's long-term operational capacity.

[0054] Three superheated 1,3-propylene glycol steam feed ports are set at the above three positions of the high-viscosity PTT polymerization kettle, and are equipped with a controllable flow device to provide sufficient superheated propylene glycol steam to the top of the high-viscosity zone reactor, to wet and promptly depolymerize the oligomeric by-product aggregates on the top of the reactor, so as to facilitate timely cleaning of the deposited materials on the top of the kettle wall and ensure long-term operation of the device.

[0055] In some embodiments, when used to prepare a high-viscosity PTT melt, the preparation method further includes the step of introducing a heat stabilizer, an antioxidant, or a colorant into the second esterification kettle before conducting the second esterification reaction; the heat stabilizer is selected from a combination of one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triphenyl phosphite, and triglyceride phosphate; the antioxidant is selected from a combination of one or more of antioxidant 168, antioxidant 1076, antioxidant 1010, antioxidant 1222, and benzothiazole antioxidants.

[0056] In some embodiments, the amount of the heat stabilizer or antioxidant is 30 to 300 ppm based on the total mass of the high-viscosity PTT melt.

[0057] To ensure the high-viscosity PTT melt's excellent resistance to heat and thermo-oxidative degradation during esterification and polymerization melt transport, a thermal stabilizer and antioxidant are compounded. To enhance the stability of the high-viscosity PTT melt, these additives can be added to improve the melt's thermal stability and antioxidant properties, respectively. The polymerization reaction of high-viscosity PTT melts experiences high temperatures, which can lead to thermal and thermo-oxidative degradation, generating acrolein and allyl alcohol, which accelerate degradation. During the spinning process, acrolein and allyl alcohol are released in large quantities, irritating the operator's eyes and respiratory system and potentially causing liver damage over time. To control the level of polymerization side reactions under high-temperature conditions, these thermal stabilizers and antioxidants are added. The antioxidants further reduce the risk of trace oxygen-induced thermal degradation during melt transport, significantly improving the melt's stability and resistance to degradation, and preventing problems caused by catalyst deposits in pipes and casings.

[0058] Thermal stabilizers and antioxidants help reduce viscosity drop during melt delivery. For high-viscosity PTT melts, with a pipeline residence time of 30 to 40 minutes, the viscosity drop is effectively controlled between 0.018 and 0.045, with an optimized viscosity drop of 0.015 to 0.055. Combined with a short-flow melt delivery design, the optimal viscosity drop is 0.018 to 0.030. Compared to the 0.120 to 0.140 viscosity drop achieved with existing high-viscosity PTT polyesters, this significantly reduces the melt's original intrinsic viscosity and effectively improves product quality. Furthermore, the melt spinning process does not produce the irritating odors of acrolein or allyl alcohol.

[0059] In some embodiments, the high-viscosity PTT polymerization kettle is connected to a vacuum pump with a maximum vacuum of 60-75 Pa. The preparation method controls the vacuum pump's extraction rate to 70-220 kg / h; the vacuum level during operation of the high-viscosity PTT polymerization kettle is controlled to 90-140 Pa. This configuration can meet the production capacity requirements of 30,000-100,000 tons / year of high-viscosity PTT polyester melt. Experimental research has shown that the volatile matter production of a high-viscosity (intrinsic viscosity of 1.05-1.16) PTT final polymerization kettle is 1.5-2.2 times that of a conventional (intrinsic viscosity of 0.92) PTT polyester unit with the same viscosity. As the high-viscosity outlet viscosity increases, the amount of non-condensable gas generated increases. Therefore, the vacuum pump extraction rate is designed to be 1.5-2.5 times that of a conventional polyester unit of the same production capacity. The vacuum pump extraction capacity is selected based on the production capacity of 30,000-100,000 tons / year, ranging from 70-220 kg / h. The design of the device's vacuum system takes into account the harmfulness of acrolein and allyl alcohol, adopts a fully enclosed design, and is equipped with a wastewater and waste gas neutralization device, which is sent to a stripping tower for treatment to ensure that the waste meets emission standards.

[0060] In some embodiments, a melt pump is used to transport high-viscosity PTT melt and low-viscosity PET melt, and a melt cooler is provided at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PTT melt to 254-256°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 PTT melt to 30-40 minutes.

[0061] In some embodiments, a distillation column is installed at the top of each of the first and second esterification reactors used to prepare the high-viscosity PTT melt. The preparation method further includes a step of recovering the 1,3-propylene glycol from the bottom of the distillation column. This recovery can be performed using a specialized recovery device. After recovery, impurities in the 1,3-propylene glycol are removed and the 1,3-propylene glycol is refined. The refined 1,3-propylene glycol can then be added back to the raw material slurrying system for subsequent esterification and polymerization reactions.

[0062] Preferably, the distillation tower at the upper end of the second esterification kettle is arranged in the third sub-chamber from the front to the back of the second esterification kettle.

[0063] In some embodiments, the low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its aspect ratio is 2.2-2.8:1.0.

[0064] In some embodiments, the preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PTT melt before the high-viscosity PTT 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, atmospheric pressure boiling dyeable polyester EDDP, polybutylene terephthalate PBT, and polypropylene terephthalate-1,3-propylene glycol terephthalate PTT.

[0065] Furthermore, the amount of the viscosity reducer is 0.2% to 3.0% of the total mass of the melt, preferably 0.5 to 2.0%, and more preferably 0.8 to 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.

[0066] In some embodiments, when used to prepare a high-viscosity PTT melt, the molar ratio of terephthalic acid to 1,3-propylene glycol is 1:1.05-1.65.

[0067] In some embodiments, the esterification reaction in the first esterification kettle for preparing the high-viscosity PTT melt is carried out at 250°C to 252°C.

[0068] In some embodiments, the esterification reaction in the first esterification kettle for preparing a high-viscosity PTT melt is carried out at a temperature of 0.7 to 1.8 kgf / cm 2 under pressure.

[0069] In some embodiments, the esterification reaction in the second esterification kettle for preparing the high-viscosity PTT melt is carried out at 250°C to 252°C.

[0070] In some embodiments, the esterification reaction in the second esterification kettle for preparing the high-viscosity PTT melt is carried out under normal pressure.

[0071] In some embodiments, the same spinning assembly is a composite spinning beam.

[0072] In some embodiments, the composite spinning beam includes a composite spinneret.

[0073] The present invention also provides a high-viscosity PTT / low-viscosity PET two-component elastic fiber prepared by the above preparation method.

[0074] In some embodiments, the bicomponent elastic fiber has a strength of 2.6 to 3.2 cN / dtex, a crimp shrinkage of 25% to 75%, and a crimp stability of 82% to 90%.

[0075] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0076] The high-viscosity PTT polymerization kettle of the present invention adopts an unconventional disc reactor design. The front chamber (low-viscosity zone) adopts an external cage frame combined disc design; the rear chamber (medium-high viscosity zone and high viscosity zone) adopts a combined disc combined with a single disc, as well as a composite scraper design, which can greatly improve the viscosity of the high-viscosity PTT melt, effectively reduce the level of side reactions during high-viscosity PTT polymerization, and ultimately achieve significant improvements in various properties of the two-component elastic fiber.

[0077] The present invention utilizes two different polyester production lines to produce high-viscosity PTT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PTT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-direct spinning high-viscosity PTT / low-viscosity PET parallel elastic fibers.

[0078] In the present invention, a special polymerization catalyst is adopted. The polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving the catalyst in 1,3-propylene glycol. The polymerization catalyst does not contain a Ti-OH group. The catalyst can significantly inhibit the hydrolysis of ordinary titanium-based catalysts in the polymerization stage, and further significantly inhibit the occurrence of side reactions in the polymerization stage, which is beneficial to improving the high-viscosity PTT melt performance and the final two-component elastic fiber performance.

[0079] In the present invention, the intrinsic viscosity of the high-viscosity PTT melt can reach 0.92-1.16, and the intrinsic viscosity of the low-viscosity PET melt is 0.45-0.55. The viscosity of the high-viscosity PTT melt is much higher than that of the prior art.

[0080] The bicomponent elastic fiber of the present invention has a strength of 2.6 to 3.2 cN / dtex, a crimp shrinkage of 25 to 75 percent, and a crimp stability of 82 to 90 percent, far exceeding the performance of existing bicomponent elastic fibers. The bicomponent elastic fiber of the present invention can be in various varieties, including FDY, POY, and DTY.

[0081] The preparation method of the present invention is used for industrial production of two-component elastic fibers, which can achieve a low-viscosity PET melt production capacity of 30,000 to 80,000 tons / year and a high-viscosity PTT melt production capacity of 30,000 to 80,000 tons / year. When the product is melt-spun high-viscosity PTT / low-viscosity PET two-component elastic fiber, the comprehensive device production capacity is 60,000 to 160,000 tons / year. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] FIG1 is a schematic diagram of a two-line polymerization system used in an embodiment of the present invention;

[0083] FIG2 is a schematic diagram of the internal structure of a high-viscosity PTT polymerization kettle used in an embodiment of the present invention;

[0084] FIG3 is a schematic diagram of a disc reactor and a material propulsion component of a high-viscosity PTT polymerization kettle used in an embodiment of the present invention;

[0085] FIG4 is another schematic diagram of the internal structure of a high-viscosity PTT polymerization kettle used in an embodiment of the present invention;

[0086] FIG5 is a schematic diagram of the disc reactor and outer cage structure of the high-viscosity PTT polymerization kettle used in an embodiment of the present invention;

[0087] FIG6 is a schematic structural diagram of a high-viscosity PTT polymerization kettle used in an embodiment of the present invention;

[0088] FIG7 is a schematic structural diagram of a composite scraper in a high-viscosity PTT polymerization reactor used in an embodiment of the present invention;

[0089] Among them, 1- low viscosity zone, 2- medium and high viscosity zone, 3- high viscosity zone, 4- composite scraper, 5- disk 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- high viscosity PTT polymerization kettle, 15- low viscosity PET final polymerization kettle, 16- melt pump, 17- prepolymer inlet, 18- high viscosity PTT melt outlet, 19- outer cage, 20- rotating shaft, 21- cage-shaped component, 22- material pushing component, 23- support seat. DETAILED DESCRIPTION

[0090] 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.

[0091] 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.

[0092] 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 FIG1 , the term "front" refers to the left side of FIG1 , and the term "rear" refers to the right side of FIG1 . 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 element 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.

[0093] As shown in Figure 1, when preparing high-viscosity PTT / low-viscosity PET two-component elastic fibers in the embodiment, two production lines are used. The first production line prepares a high-viscosity PTT melt. As shown in the first row of Figure 1, the production line includes a five-reactor device system consisting of a first esterification reactor 10, a second esterification reactor 11, a first prepolymerization reactor 12, a second prepolymerization reactor 13, and a high-viscosity PTT polymerization reactor 14. The five reactors are connected by necessary pipelines, and necessary vacuum systems, etc. are connected to the five reactors. Among them, a melt pump 16 and filters A and B are provided between the second prepolymerization reactor 13 and the high-viscosity PTT polymerization reactor 14. In the actual production process, filters A and B are not turned on at the same time. For example, filter A can be turned on first, and after the device has been running for a period of time, filter B can be switched to use. At this time, filter A can be cleaned.

[0094] The second production line produces low-viscosity PET melt, as shown in the second row of Figure 1. This line comprises a five-vessel system: a first esterification vessel 10, a second esterification vessel 11, a first prepolymerization vessel 12, a second prepolymerization vessel 13, and a low-viscosity PET final polymerization vessel 15. The five vessels are interconnected by necessary piping and are connected to the necessary vacuum systems. A melt pump 16 and filters A and B are located between the second prepolymerization vessel 13 and the low-viscosity PET final polymerization vessel 15. In actual production, filters A and B are not operated simultaneously. For example, filter A can be activated first, and after a period of operation, filter B can be switched to the system, allowing filter A to be cleaned.

[0095] As shown in Figure 6, a high-viscosity PTT polymerization kettle 14 is a horizontal polymerization kettle comprising a main body containing a chamber. The main body comprises a low-viscosity zone 1, a medium-high-viscosity zone 2, and a high-viscosity zone 3, arranged in sequence along the axis of the high-viscosity PTT polymerization kettle. The viscosity of the PTT melt in these zones increases in order. Both the low-viscosity zone 1 and the medium-high-viscosity zone 2 are equipped with a composite disc reactor 9, while the high-viscosity zone 3 is equipped with multiple single-disc reactors 9.

[0096] As shown in Figure 2-6, the high-viscosity PTT polymerization kettle 14 also includes a rotating shaft 20 located at the front end of the low-viscosity zone 1. The low-viscosity zone 1 of the high-viscosity PTT polymerization kettle 14 is designed with a cage-type combined disc reactor. The cage-type combined disc reactor includes multiple groups of combined disc reactors 9, and an outer cage frame 19 fixedly connected to the outer edge of the combined disc reactor 9. The rotating shaft 20 drives the outer cage frame 19 of the low-viscosity zone 1 and the multiple groups of combined disc reactors 9 to rotate; and the axial area corresponding to the combined disc reactor 9 in the low-viscosity zone 1 is not provided with a stirring shaft, and a circular channel is designed in the middle of the combined disc reactor 9; the medium-high viscosity zone 2 and the high viscosity zone 3 are provided with a stirring shaft 8, and the disc reactors 9 in the medium-high viscosity zone 2 and the high viscosity zone 3 pass through the stirring shaft 8.

[0097] The length of the low-viscosity zone 1 is one-half the length of the high-viscosity PTT polymerization kettle 14, and the combined length of the medium-high-viscosity zone 2 and the high-viscosity zone 3 is one-half the length of the high-viscosity PTT polymerization kettle 14. The length of the stirring shaft 8 provided in the medium-high-viscosity zone 2 and the high-viscosity zone 3 is one-half the length of the high-viscosity PTT polymerization kettle 14. It should be emphasized that the term "one-half" in this invention does not refer to an exact value of one-half, but rather to a value approximately equal to or around one-half.

[0098] The high-viscosity PTT polymerization kettle 14 further includes a prepolymer inlet 17 located at the front bottom of the low-viscosity zone 1 and a high-viscosity PTT melt outlet 18 located at the rear bottom of the high-viscosity zone 3. The high-viscosity PTT melt outlet 18 is in a bell-mouth shape.

[0099] As shown in Figures 2-5, the outer cage 19 comprises a gear-shaped cage member 21 at the front end and material pusher members 2 extending axially from each gear of the cage member 21. The outer cage 19 is fixedly connected to the rotating shaft 20. The material pusher members 22 have a wedge-shaped cross section, with the thick end of the wedge facing the direction of rotation of the disc reactor 9. There are 8 to 12 material pusher members 22.

[0100] The disc reactor 9 in the medium-high viscosity zone 2 is designed with multiple groups of combined discs from front to back, namely a 4-piece combined disc design, a 3-piece combined disc design and a 2-piece combined disc design; in the 2-piece combined disc design of the medium-high viscosity zone 2, the distance between the combined disc groups and the distance between the two discs themselves gradually increases from front to back; the total number of disc reactors 9 in the medium-high viscosity zone 2 and the high viscosity zone 3 is 25 to 35 pieces; there are 8 to 12 single-piece disc reactors 9 in the high viscosity zone, and the diameter of the disc reactor 9 decreases from front to back. The diameter of the last disc reactor 9 in the high viscosity zone 3 is 88%-92% of the diameter of the first disc reactor 9.

[0101] As shown in FIG7 , the high viscosity zone 3 is further provided with a composite scraper 4, which includes an axial scraper 6 for scraping the melt on the stirring shaft, a wall scraper 7 for scraping the melt on the inner wall of the high viscosity final polymerization reactor 14, and a disc scraper 5 for scraping the melt on the stirrer. The disc scrapers 5 are provided in two layers, and the material thickness on the disc reactor 9 is controlled to be no more than 30 mm.

[0102] As shown in FIG6 , the aspect ratio of the high-viscosity PTT polymerization kettle 14 is 3.5-4.0:1.0.

[0103] As shown in Figure 1, the second esterification vessel 11, used for preparing a high-viscosity PTT melt, is a horizontal reactor comprising three compartments arranged in a front-to-rear sequence. A distillation column is installed at the top of each of the first and second esterification vessels 10, 11, used for preparing a high-viscosity PTT melt. The distillation column at the top of the second esterification vessel 11 is located in the third compartment of the second esterification vessel 11, from the front to the rear.

[0104] High-viscosity PTT polymerization kettle 14 also includes steam inlets for introducing superheated 1,3-propylene glycol vapor, located at the top of the main body at the rear ends of low-viscosity zone 1, medium-high-viscosity zone 2, and high-viscosity zone 3. The high-viscosity PTT polymerization kettle is connected to a vacuum pump with a maximum vacuum of 60-75 Pa and a pumping capacity of 70-220 kg / h. The vacuum level within high-viscosity PTT polymerization kettle 14 is maintained at 90-120 Pa.

[0105] The high-viscosity PTT polymerization kettle 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 transports the high-viscosity PTT melt and the low-viscosity PET melt, and a melt cooler is provided at the melt pump outlet.

[0106] After the high-viscosity PTT polymerization reactor 14 and the low-viscosity PET final polymerization reactor 15, and before the same spinning assembly, a dynamic mixer and a filter are set; before the dynamic mixer, a viscosity reducer injection system is set.

[0107] Necessary melt pumps, vacuum pumps, conveying pipelines, etc. can be installed on the pipeline that serves as a connection between the five kettles on the two production lines.

[0108] The same spinning assembly is a composite spinning manifold, and a high-viscosity PTT polymerization kettle 14 is arranged on the top of the composite spinning manifold to shorten the conveying distance of the melt, especially the high-viscosity PTT melt. The composite spinning manifold contains a spinneret.

[0109] Example 1

[0110] This embodiment provides a method for preparing a high-viscosity PTT / low-viscosity PET bicomponent elastic fiber, and the specific steps are as follows:

[0111] The preparation method of the polymerization catalyst used in this embodiment is as follows:

[0112] Tetrabutyl titanate and acetic acid are mixed and subjected to an exothermic reaction in a mass ratio of 1:1. After the reaction, a titanium tetraacetate complex and a large amount of n-butanol by-product are generated. The reaction system is vacuum-purified at 50° C. for 2.0 hours to remove the generated n-butanol, and the temperature is lowered to room temperature. 1,3-propylene glycol is injected into the reaction system with stirring to prepare a 1,3-propylene glycol solution of a polymerization catalyst. The injection amount of 1,3-propylene glycol is controlled so that the titanium content in the polymerization catalyst solution is 1.0%.

[0113] The polymerization devices of the above two production lines are used to synthesize high-viscosity PTT melt and low-viscosity PET melt respectively.

[0114] For the high-viscosity PTT melt production line, the equipment includes a beating kettle, a first esterification kettle (with a distillation tower at the top), a second esterification kettle (three-chamber structure, with a distillation tower at the top), a first prepolymerization kettle, a second prepolymerization kettle, a high-viscosity PTT polymerization kettle, and a matching vacuum system and melt conveying system.

[0115] For the low-viscosity PET melt production line, the equipment includes a beating kettle, a first esterification kettle, a second esterification kettle, a first prepolymerization kettle, a second prepolymerization kettle, a low-viscosity PET final polymerization kettle, and a matching vacuum system and melt conveying system.

[0116] Synthetic high-viscosity PTT melt:

[0117] Purified terephthalic acid and 1,3-propylene glycol are sequentially subjected to esterification reactions in the first and second esterification kettles, followed by prepolymerization reactions in the first and second prepolymerization kettles to obtain a PTT prepolymer. The PTT prepolymer is then polymerized in a high-viscosity PTT polymerization kettle to obtain a high-viscosity PTT melt. The molar ratio of purified terephthalic acid to 1,3-propylene glycol is 1:1.25. The esterification temperature in the first esterification kettle is 250°C to 252°C, and the esterification reaction is carried out at a pressure of 0.7 to 0.8 kgf / cm 2The reaction is carried out under a pressure of (this pressure refers to the actual pressure in the first esterification kettle, which is lower than the atmospheric pressure, that is, the first esterification kettle is actually a reduced pressure reaction). The esterification temperature of the second esterification kettle is 250℃~252℃, and the esterification is carried out under normal pressure. Tetrabutyl titanate, an esterification catalyst, is added to the first esterification kettle in an amount such that the mass of the titanium element therein is 30ppm of the mass of the melt. Trimethyl phosphate, an esterification catalyst blocking agent, is introduced into the second sub-chamber from the front to the back of the second esterification kettle in an amount such that the mass of the titanium element therein is 100ppm relative to the total mass of the high-viscosity PTT melt, so that the esterification catalyst is deactivated. The polymerization catalyst prepared above is introduced into the third sub-chamber from the front to the back of the second esterification kettle in an amount such that the mass of the titanium element therein is 70ppm of the mass of the melt. Before the second esterification reaction in the second esterification reactor, a standard titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, with 10 wt% titanium dioxide and 90 wt% ethylene glycol) was added to the second esterification reactor via the corresponding pipeline. The titanium dioxide content was set to 0.32% of the total melt mass. The reaction temperature of the first prepolymerization reactor was 250°C and the vacuum level was 9.9 kPa; the reaction temperature of the second prepolymerization reactor was 251°C and the vacuum level was 1.15 kPa. The melt outlet temperature of the high-viscosity PTT polymerization reactor was 252.6°C and the vacuum level in the high-viscosity PTT polymerization reactor was 138 Pa. Superheated 1,3-propylene glycol was injected into the steam feed port of the high-viscosity PTT polymerization reactor via a steam jet pump. A double polycondensation circulating cooling system was installed to address the large amount of cyclic dimers produced during the polymerization process and facilitate cleaning of the vacuum system. The high-viscosity PTT melt discharged from the reactor had an intrinsic viscosity of 0.922 and a dynamic viscosity of 375 Pa.s. These intrinsic viscosities were measured in a 3:2 volume ratio of phenol and tetrachloroethane. The dynamic viscosity was measured at 252°C.

[0118] Synthetic low-viscosity PET melt:

[0119] Purified terephthalic acid and ethylene glycol are sequentially subjected to an esterification reaction in a first and second esterification reactors, followed by a prepolymerization reaction in a first and second prepolymerization reactors to produce a PET prepolymer. The PET prepolymer is then polymerized in a low-viscosity PET final polymerization reactor to produce a low-viscosity PET melt. The catalyst used for both esterification and polymerization is ethylene glycol antimony, in an amount such that the antimony content is 210 ppm relative to the total mass of the PET melt. This catalyst is added to the reaction system in the first esterification reactor. The first esterification reactor is pressurized esterification, while the second esterification reactor is atmospheric pressure esterification. Prior to the second esterification reaction in the second esterification reactor, a conventional titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, comprising 10 wt% titanium dioxide and 90 wt% ethylene glycol) is added to the second esterification reactor via corresponding pipelines in an amount such that the titanium dioxide accounts for 0.30% of the total mass of the melt. By adjusting the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, the polymerization temperature of the low-viscosity PET final polymerization kettle, etc.), the vacuum degree is controlled to be 180-200 Pa, the stirring rate of the medium-high viscosity zone and the high viscosity zone is 2.2-2.5 rpm, and the polymerization temperature is 272-273°C. Finally, a low-viscosity PET melt with an intrinsic viscosity of 0.452 and a dynamic viscosity of 90 Pa.s is obtained. The intrinsic viscosity is the result of measurement in a mixed solvent of phenol and tetrachloroethane with a volume ratio of 3:2. The dynamic viscosity is the test result at 270°C.

[0120] Spinning:

[0121] Finally, the high-viscosity PTT melt and the low-viscosity PET melt are transported to the composite spinning manifold at a mass ratio of 5:5, and spun through the composite spinning spinneret to obtain high-viscosity PTT / low-viscosity PET two-component elastic fiber.

[0122] The reaction conditions, parameters for high-viscosity PTT melt, and low-viscosity PET melt are shown in Tables 1-5. "-" indicates no parameters. Melt chip properties were tested according to GB / T 14190-2017. Intrinsic viscosity was measured in a 3:2 volume ratio of phenol and tetrachloroethane. Water, ash, iron, and agglomerated particles refer to the mass fractions of water, ash, iron, and agglomerated particles in the polyester, respectively.

[0123] Example 2-13

[0124] Example 2-13 provides a method for preparing a high-viscosity PTT / low-viscosity PET two-component elastic fiber. The specific steps are basically the same as Example 1, except that: when synthesizing the high-viscosity PTT melt, the parameters of the high-viscosity PTT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PTT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high viscosity zone and the high-viscosity zone, the inlet temperature of the PTT prepolymer melt (PTT low-viscosity melt), the residence time of the material in the final polymerization kettle, etc.); when synthesizing the low-viscosity PET melt, the parameters of the low-viscosity PET melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, the polymerization temperature of the low-viscosity PET final polymerization kettle, etc.). Among them, the parameters of the reaction conditions, high-viscosity PTT melt, and low-viscosity PET melt are shown in Tables 1-5.

[0125] Example 14

[0126] Example 14 provides a method for preparing a high-viscosity PTT / low-viscosity PET bicomponent elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing a high-viscosity PTT melt, the parameters of the high-viscosity PTT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PTT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high-viscosity zone and the high-viscosity zone, the inlet temperature of the PTT prepolymer melt (PTT low-viscosity melt), the residence time of the material in the final polymerization kettle, etc.); when synthesizing a low-viscosity PET melt, the reaction conditions are adjusted. (Including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, the polymerization temperature of the low-viscosity PET final polymerization kettle, etc., to adjust the parameters of the low-viscosity PET melt. In addition, a viscosity reducer is introduced from the viscosity reducer injection system. The specific type is amorphous polyester with an intrinsic viscosity of 0.55 (the intrinsic viscosity is tested using phenol:tetrachloroethane (3:2 volume ratio)), and the amount is 0.5% relative to the total mass of the melt. Among them, the reaction conditions, parameters of the high-viscosity PTT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0127] Example 15

[0128] Example 15 provides a method for preparing a high-viscosity PTT / low-viscosity PET bicomponent elastic fiber. The specific steps are basically the same as those in Example 1, except that: when synthesizing a high-viscosity PTT melt, the parameters of the high-viscosity PTT melt are adjusted by adjusting the reaction conditions (including the vacuum degree of the high-viscosity PTT polymerization kettle, the stirring rate of the low-viscosity zone, the stirring rate of the medium-high-viscosity zone and the high-viscosity zone, the inlet temperature of the PTT prepolymer melt (PTT low-viscosity melt), the residence time of the material in the final polymerization kettle, etc.); when synthesizing a low-viscosity PET melt, the reaction conditions are adjusted. (Including the vacuum degree of the low-viscosity PET final polymerization kettle, the stirring rate of the low-viscosity PET final polymerization kettle, the polymerization temperature of the low-viscosity PET final polymerization kettle, etc., to adjust the parameters of the low-viscosity PET melt. In addition, a viscosity reducer is introduced from the viscosity reducer injection system. The specific type is amorphous polyester with an intrinsic viscosity of 0.58 (the intrinsic viscosity is tested using phenol:tetrachloroethane (3:2 volume ratio)), and the amount is 0.8% relative to the total mass of the melt. Among them, the reaction conditions, parameters of the high-viscosity PTT melt, and the low-viscosity PET melt are shown in Tables 1-5.

[0129] Comparative Example 1

[0130] Comparative Example 1 provides a preparation method for melt-spinning high-viscosity PET / low-viscosity PET two-component elastic fiber. The preparation method adopts a six-reactor polymerization device, which includes a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, and a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor respectively connected to the second prepolymerization reactor. The high-viscosity PET melt obtained by the high-viscosity final polymerization reactor and the low-viscosity PET melt obtained by the low-viscosity final polymerization reactor are simultaneously transported to the same spinning assembly for parallel spinning. Among them, the second esterification reactor is provided with three sub-chambers. The high-viscosity final polymerization reactor and the low-viscosity final polymerization reactor both adopt conventional structures in the prior art.

[0131] Specifically, terephthalic acid, ethylene glycol, and an antimony ethylene glycol catalyst are sequentially subjected to an esterification reaction in a first esterification kettle and a second esterification kettle, followed by a prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to produce an ethylene terephthalate prepolymer. Prior to the second esterification reaction in the second esterification kettle, a conventional titanium dioxide matting agent paste (prepared by grinding and dispersing titanium dioxide and ethylene glycol, with titanium dioxide accounting for 10% by weight and ethylene glycol accounting for 90% by weight) is added to a chamber of the second esterification kettle via a corresponding pipeline. The molar ratio of terephthalic acid to ethylene glycol is 1:1.25, the catalyst is used in an amount such that the antimony element accounts for 210 ppm of the total mass of the melt, and the matting agent is used in an amount such that the titanium dioxide accounts for 0.3% of the total mass of the melt. The ethylene terephthalate prepolymer was then passed through a high-viscosity final polymerization reactor and a low-viscosity final polymerization reactor for polymerization, respectively, to produce high-viscosity PET melt and low-viscosity PET melt. Finally, the high-viscosity PET melt and the low-viscosity PET melt were directly passed through the same parallel composite spinning beam at a mass ratio of 5:5 for spinning to produce PET bicomponent elastic fiber. The parameters of the high-viscosity PET melt and the low-viscosity PET melt are shown in Table 3-5.

[0132] Comparative Example 2

[0133] Comparative Example 2 provides a method for preparing a slice-spun high-viscosity PBT / low-viscosity PET bicomponent elastic fiber. Specifically, high-viscosity PBT and low-viscosity PET melt chips are pre-crystallized and then melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 for spinning to produce a slice-spun bicomponent elastic fiber. The properties of the corresponding chips are shown in Tables 3-5. Both the high-viscosity PBT chips and the low-viscosity PET chips were commercially available and did not contain a matting agent (matting agents cannot be added to high-viscosity PBT chips).

[0134] Comparative Example 3

[0135] Comparative Example 3 provides a method for preparing a chip-spun bicomponent elastic fiber composed of high-viscosity EDDP (disperse dye atmospherically metadyed polyester) and low-viscosity PET. Specifically, high-viscosity EDDP and low-viscosity PET melt chips are pre-crystallized and melted using a dry screw. The two melts are then directly introduced into a parallel composite spinning manifold at a mass ratio of 5:5 for spinning, yielding the chip-spun bicomponent elastic fiber. The properties of the resulting chips are shown in Tables 3-5.

[0136] Table 1 Test indicators of high viscosity PTT polyester ester materials

[0137] Table 2 Test indexes of high viscosity PTT prepolymerization second kettle materials

[0138] Table 3 Test indexes of high viscosity PTT polyester chips

[0139] Table 4 Physical and chemical indicators of low-viscosity PET polyester chips

[0140] Table 5 High viscosity PTT polymerization kettle control data and high viscosity PTT, low viscosity PET related indicators

[0141] The properties of the composite elastic fibers obtained by spinning the high-viscosity melts and low-viscosity PET melts corresponding to Examples 1-15 and Comparative Examples 1-3 are shown in Table 6. The fiber type is FDY, with a specification of 83 dtex / 36 f. The fiber properties in this invention were tested in accordance with the GBT 8960-2015 test standard.

[0142] Table 6 Physical and chemical indicators of PTT / PET two-component composite elastic fibers

[0143] It can be seen that the present invention utilizes two different polyester production lines to produce high-viscosity PTT polyester and low-viscosity PET polyester respectively, and then transports the two melts with different viscosities to the same parallel composite spinning assembly through melt conveying. After composite spinning, high-viscosity PTT / low-viscosity PET two-component elastic fibers are prepared, thereby realizing the preparation of melt-spun high-viscosity PTT / low-viscosity PET parallel elastic fibers, and the obtained fibers have excellent performance.

[0144] 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 high-viscosity PTT polymerization kettle, which is used to prepare a high-viscosity PTT melt, and the high-viscosity PTT melt is used to prepare high-viscosity PTT / low-viscosity PET bicomponent elastic fibers, and is characterized in that: The high-viscosity PTT 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 axis of the high-viscosity PTT polymerization kettle. The viscosities of the PTT melts in the low-viscosity zone, the medium-high-viscosity zone, and the high-viscosity zone increase in sequence. The low-viscosity zone and the medium-high-viscosity zone are both provided with combined disc reactors, and the high-viscosity zone is provided with a plurality of single-piece disc reactors. The high-viscosity PTT polymerization kettle further includes a rotating shaft located at the front end of the low-viscosity zone. The low-viscosity zone of the high-viscosity PTT polymerization kettle is designed with a cage-type combined disc reactor. The cage-type combined disc reactor includes multiple groups of combined disc reactors and an outer cage frame fixedly connected to the outer edge of the combined disc reactor. The rotating shaft drives the outer cage frame and multiple groups of combined disc reactors in the low-viscosity zone to rotate. And in the axial region corresponding to the combined disc reactor in the low-viscosity zone, no stirring shaft is arranged, and a circular channel is designed in the middle of the combined disc reactor. The medium-high-viscosity zone and the high-viscosity zone are provided with a total of one stirring shaft, and the disc reactors in the medium-high-viscosity zone and the high-viscosity zone pass through the stirring shaft.

2. The high-viscosity PTT polymerization kettle according to claim 1, wherein: The length of the low-viscosity zone is one-half of the length of the high-viscosity PTT polymerization kettle, and the total length of the medium-high-viscosity zone and the high-viscosity zone is one-half of the length of the high-viscosity PTT polymerization kettle.

3. The high-viscosity PTT polymerization kettle according to claim 1, wherein: The length of the stirring shaft arranged in the medium-high-viscosity zone and the high-viscosity zone is one-half of the length of the high-viscosity PTT polymerization kettle; and / or, the high-viscosity PTT polymerization kettle further includes a prepolymer inlet located at the bottom of the front end of the low-viscosity zone and a high-viscosity PTT melt outlet located at the bottom of the rear end of the high-viscosity zone. The high-viscosity PTT melt outlet is in the shape of a flared mouth.

4. The high-viscosity PTT polymerization kettle according to claim 1, characterized in that: The outer cage frame includes a cage-shaped component with a gear shape at the front end and a material propulsion component extending axially along the high-viscosity PTT polymerization kettle and bent and extended from each gear of the cage-shaped component. The outer cage frame is fixedly connected to the rotating shaft.

5. The high-viscosity PTT polymerization kettle according to claim 4, wherein: The cross-section of the material propulsion component is wedge-shaped, and the thick end of the wedge faces the rotation direction of the disc reactor; and / or, the number of the material propulsion components is 8 to 12.

6. The high-viscosity PTT polymerization kettle according to claim 1, wherein: The disc reactors in the medium-high-viscosity zone are designed with multiple groups of combined discs from front to back, which are 4-piece combined disc design, 3-piece combined disc design, and 2-piece combined disc design in sequence. In the 2-piece combined disc design in the medium-high-viscosity zone, the distance between the combined disc groups and the distance between the two discs of itself gradually increase from front to back. The total number of disc reactors in the medium-high-viscosity zone and the high-viscosity zone is 25 to 35. The number of single-piece disc reactors in the high-viscosity zone is 8 to 12, and the diameters of the disc reactors decrease in sequence from front to back. The diameter of the last disc reactor in the high-viscosity zone is 88%-92% of the diameter of the first disc reactor. The high-viscosity zone is further provided with a composite scraper. The composite scraper includes an axial scraper for scraping the melt on the stirring shaft, a wall scraper for scraping the melt on the inner wall of the high-viscosity PTT polymerization kettle, and a disc scraper for scraping the melt on the disc reactor. The disc scraper is provided with two layers, and the material thickness on the disc reactor is controlled not to exceed 30 mm.

7. A method for preparing a high-viscosity PTT / low-viscosity PET bicomponent elastic fiber, the bicomponent elastic fiber containing a high-viscosity PTT component and a low-viscosity PET component, the viscosity of the high-viscosity PTT component being greater than the viscosity of the low-viscosity PET component, characterized in that: The preparation method includes the steps of separately preparing a high-viscosity PTT melt and a low-viscosity PET melt, and spinning the high-viscosity PTT melt and the low-viscosity PET melt through the same side-by-side composite spinning assembly to obtain the bicomponent elastic fiber; the viscosity of the high-viscosity PTT melt is greater than that of the low-viscosity PET melt; the step of preparing the high-viscosity PTT melt includes the steps of subjecting terephthalic acid and 1,3-propanediol to esterification reaction in a first esterification kettle and a second esterification kettle in sequence, and subjecting to prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PTT prepolymer, and subjecting the PTT prepolymer to polymerization reaction in a high-viscosity PTT polymerization kettle to obtain the high-viscosity PTT melt, and the high-viscosity PTT polymerization kettle is the high-viscosity PTT polymerization kettle according to any one of claims 1-6; the step of preparing the low-viscosity PET melt includes the steps of subjecting terephthalic acid and ethylene glycol to esterification reaction in a first esterification kettle and a second esterification kettle in sequence, and subjecting to prepolymerization reaction in a first prepolymerization kettle and a second prepolymerization kettle to obtain a PET prepolymer, and subjecting the PET prepolymer to polymerization reaction in a low-viscosity PET final polymerization kettle to obtain the low-viscosity PET melt.

8. The preparation method according to claim 7, wherein: By mass percentage, the bicomponent elastic fiber contains 35%-65% of high-viscosity PTT component and 65%-35% of low-viscosity PET component; and / or, the intrinsic viscosity of the high-viscosity PTT melt is 0.92-1.16, and the dynamic viscosity is 320-1200 Pa·s; the intrinsic viscosity of the low-viscosity PET melt is 0.45-0.55, and the dynamic viscosity is 90-240 Pa·s.

9. The preparation method according to claim 7, wherein: In the same side-by-side composite spinning assembly, the dynamic viscosity of the high-viscosity PTT melt is 350-800 Pa·s, and the dynamic viscosity of the low-viscosity PET melt is 70-220 Pa·s.

10. The preparation method according to claim 7, characterized in that: The preparation method controls the rotation rate of the rotating shaft in the low-viscosity region to be 0-5.5 rpm; and / or, the preparation method controls the stirring speed of the stirring shaft in the medium-high-viscosity region and the high-viscosity region to be 0-3.0 rpm.

11. The preparation method according to claim 7, characterized in that: The intrinsic viscosity of the PTT prepolymer fed into the high-viscosity PTT polymerization kettle is 0.280-0.

350.

12. The preparation method according to claim 7, characterized in that: When preparing the high-viscosity PTT melt, the preparation method further includes the step of adding an esterification catalyst to the first esterification kettle before the esterification reaction, and the esterification catalyst is selected from tetrabutyl titanate or tetraisopropyl titanate.

13. The preparation method according to claim 12, characterized in that: The second esterification kettle for preparing the high-viscosity PTT melt is a horizontal reaction kettle and includes three compartments arranged in sequence from front to back. When preparing the high-viscosity PTT melt, the preparation method further includes the step of adding a catalyst deactivator to the second compartment from front to back of the second esterification kettle after the esterification reaction is completed in the first compartment from front to back of the second esterification kettle to deactivate the esterification catalyst, and the catalyst deactivator is selected from trimethyl phosphate or phosphoric acid, and the mass of the catalyst deactivator accounts for 15-30 ppm of the mass of the high-viscosity PTT melt.

14. The preparation method according to claim 13, characterized in that: When preparing the high-viscosity PTT melt, the preparation method further includes the step of adding a polymerization catalyst to the third compartment from the front to the back of the second esterification kettle; the polymerization catalyst is prepared by reacting a titanate with a protonic acid under anhydrous conditions, removing alcohol by-products, and dissolving in 1,3-propanediol.

15. The preparation method according to claim 14, wherein: The titanate is selected from tetrabutyl titanate, tetraisopropyl titanate or tetra(2-ethylhexoxy) titanate; and / or, the protonic acid is selected from one or more combinations of formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, tripolyphosphoric acid and polyphosphoric acid; and / or, the mass ratio of the titanate to the protonic acid is 1:0.5-2.0; and / or, in the polymerization catalyst, the mass percentage of titanium element is 1.0%-3.0%.

16. The preparation method according to claim 12 or 14, characterized in that: The mass of titanium element in the esterification catalyst accounts for 1-30 ppm of the mass of the high-viscosity PTT melt; and / or, the mass of titanium element in the polymerization catalyst accounts for 30-100 ppm of the mass of the high-viscosity PTT melt.

17. The preparation method according to claim 7, characterized in that: The high-viscosity PTT polymerization kettle further includes steam inlets for introducing superheated 1,3-propanediol steam at the rear ends of the low-viscosity zone, the medium-high-viscosity zone and the high-viscosity zone at the top of the main body, and the preparation method further includes the step of metering the superheated 1,3-propanediol steam by a metering system and introducing it into the high-viscosity PTT polymerization kettle.

18. The preparation method according to claim 7, characterized in that: The high-viscosity PTT polymerization kettle is connected to a vacuum pump, the ultimate vacuum degree of the vacuum pump is 60-75 Pa, and the preparation method controls the gas extraction volume of the vacuum pump to be 70-220 kg / h; controls the vacuum degree of the high-viscosity PTT polymerization kettle during operation to be 90-140 Pa.

19. The preparation method according to claim 7, wherein: A melt pump is used to transport the high-viscosity PTT melt and the low-viscosity PET melt, and a melt cooler is arranged at the outlet of the melt pump; the preparation method controls the temperature of the high-viscosity PTT melt after being cooled by the melt cooler to be 254-256 °C; a filter and a booster pump are arranged between the melt pump and the coextrusion spinning assembly; the preparation method controls the transportation time of the high-viscosity PTT melt to be 30-40 min.

20. The preparation method according to claim 7, characterized in that: Rectification towers are arranged at the upper ends of the first esterification kettle and the second esterification kettle for preparing the high-viscosity PTT melt, and the preparation method further includes the step of recovering 1,3-propanediol by taking it out from the bottom of the rectification tower.

21. The preparation method according to claim 7, wherein: The low-viscosity PET final polymerization kettle is a horizontal polymerization kettle, and its length-to-diameter ratio is 2.2-2.8:1.

0.

22. The preparation method according to claim 7, characterized in that: The preparation method further includes the step of introducing a viscosity reducer into the high-viscosity PTT melt before the high-viscosity PTT melt passes through the filter; the viscosity reducer is selected from one or more combinations of polyethylene terephthalate-1,4-cyclohexanedimethanol ester PETG, cationic dyeable polyester CDP, cationic dye easy-dyeing polyester ECDP, atmospheric boiling dyeing polyester EDDP, polybutylene terephthalate PBT, poly(1,3-propanediol terephthalate) PTT.

23. The preparation method according to claim 7, characterized in that: When preparing high-viscosity PTT melt, the molar ratio of terephthalic acid to 1,3-propanediol is 1:1.05 to 1.65; and / or, the esterification reaction in the first esterification kettle for preparing high-viscosity PTT melt is carried out at 250°C to 252°C; and / or, the esterification reaction in the first esterification kettle for preparing high-viscosity PTT melt is carried out under a pressure of 0.7 to 1.8 kgf / cm 2 ².

24. The preparation method according to claim 7, characterized in that: The esterification reaction in the second esterification kettle for preparing high-viscosity PTT melt is carried out at 250°C to 252°C; and / or, the esterification reaction in the second esterification kettle for preparing high-viscosity PTT melt is carried out under normal pressure.

25. High-viscosity PTT / low-viscosity PET bicomponent elastic fibers prepared by the preparation method according to any one of claims 7 to 24.

26. The high-viscosity PTT / low-viscosity PET bicomponent elastic fiber according to claim 25, wherein: The strength of the bicomponent elastic fibers is 2.6 to 3.2 cN / dtex, the crimp shrinkage rate is 25% to 75%, and the crimp stability is 82% to 90%.

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