CN110983468B - Preparation method of high-strength liquid crystal polymer fiber - Google Patents

Preparation method of high-strength liquid crystal polymer fiber Download PDF

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Publication number
CN110983468B
CN110983468B CN201911326264.5A CN201911326264A CN110983468B CN 110983468 B CN110983468 B CN 110983468B CN 201911326264 A CN201911326264 A CN 201911326264A CN 110983468 B CN110983468 B CN 110983468B
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fiber
liquid crystal
crystal polymer
heat treatment
strength
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CN110983468A (en
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郑红专
金良文
梁永华
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Jiangmen Dengzhongtai Engineering Plastics Co ltd
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Jiangmen Dengzhongtai Engineering Plastics Co ltd
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    • DTEXTILES; PAPER
    • D01NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01DMECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D10/00Physical treatment of artificial filaments or the like during manufacture, i.e. during a continuous production process before the filaments have been collected
    • D01D10/02Heat treatment

Abstract

The invention discloses a preparation method of a high-strength liquid crystal polymer fiber, which comprises the following steps: winding the liquid crystal polymer fiber on a winding drum, and carrying out heat treatment under the negative pressure condition, wherein the temperature of the heat treatment is lower than the melting point of the liquid crystal polymer, and the thermal expansion coefficient of the winding drum is larger than that of the liquid crystal polymer. The method utilizes the difference of the thermal expansion coefficients of the winding drum and the liquid crystal polymer fiber to ensure that the liquid crystal polymer fiber is stretched in the heat treatment process, thereby ensuring the strength and uniformity of the fiber.

Description

Preparation method of high-strength liquid crystal polymer fiber
Technical Field
The invention relates to the technical field of high-performance fibers, in particular to a preparation method of a high-strength liquid crystal polymer fiber.
Background
The Liquid Crystal Polymer (LCP) has high strength, high modulus, high temperature resistance, chemical corrosion resistance and high dimensional stability, and is widely applied to the fields of aerospace, national defense and military industry and special industry. In view of the problems of high production cost, environmental pollution and the like of solution spinning, the melt spinning method for preparing the high-strength, heat-resistant, acid-resistant and alkali-resistant liquid crystal fiber is a development trend. The melt spinning of the liquid crystal polymer is different from the spinning process of the common polymer, the liquid crystal material has a flowable optical anisotropic structure between a melting point and a clearing point, molecular chains are easy to orient and present long orientation relaxation time, the orientation structure is maintained to a great extent in the cooling and solidifying process, and the high-performance special fiber is obtained.
In the prior art, the melt spinning is carried out by using a high molecular weight liquid crystal polymer, the spinnability and the fineness are difficult to be considered, the spinning temperature is high, and the fiber is easy to degrade. Spinning with a relatively low molecular weight polymer results in a low nascent fiber strength, and usually requires a long period of solid phase polymerization to improve the properties of liquid crystal polyester fibers such as strength, heat resistance, and thermal dimensional stability. However, in the case of performing the solid-phase polymerization reaction, there is a problem that unwinding occurs from the package shape, which causes a decrease in the uniformity and strength in the longitudinal direction of the fiber, and fibrillation of the fiber from the defect as a starting point.
Patent CN101622384A and patent CN102348841A heat-treat liquid crystal polymer fibers above their melting point for a short time to prepare high-strength, uniform-fineness, abrasion-resistant liquid crystal polymer fibers. Since the treatment temperature is higher than the melting point of the liquid crystal polymer fiber, the treatment time cannot be too long, and the effect of enhancing the strength of the material is insufficient, and the fiber strength is generally about 20 cN/dtex. And the control requirements on the heat treatment temperature, the rolling temperature and the like are very strict, and the preparation difficulty is increased invisibly.
In addition, there is a method of preparing a high-strength liquid crystal polymer fiber by controlling the take-up tension, but this method requires the use of an aromatic polyester having a specific melt viscosity, otherwise it is liable to break filaments.
Disclosure of Invention
The invention aims to at least solve one of the technical problems in the prior art and provides a preparation method of a high-strength liquid crystal polymer fiber, which utilizes the difference of the thermal expansion coefficients of a winding drum and the liquid crystal polymer fiber to stretch the liquid crystal polymer fiber in the heat treatment process, ensures the strength and uniformity of the fiber and has good industrial value.
The preparation method of the high-strength liquid crystal polymer fiber according to the embodiment of the invention comprises the following steps:
winding the liquid crystal polymer fiber on a winding drum, and carrying out heat treatment under the negative pressure condition; wherein the temperature of the heat treatment is lower than the melting point of the liquid crystal polymer, and the thermal expansion coefficient of the winding drum is larger than that of the liquid crystal polymer.
The inventor finds that LCP fiber is wound on a winding drum with higher thermal expansion coefficient and is subjected to heat treatment together, and the expansion of the winding drum plays a role in stretching the fiber in the heat treatment process, so that the strength of the fiber can be obviously improved, and the uniformity is ensured. To achieve the above effects, the thermal expansion coefficient of the winding drum is preferably controlled to be 10% to 800%, more preferably 50% to 500%, and even more preferably 60% to 300% greater than that of the LCP resin, so as to facilitate the effective stretching of the LCP fibers during the heat treatment process and avoid fiber breakage. The heat treated fiber can be rolled on a paper tube, and is convenient to store, transport and use. The method is simple and easy to implement, is easy to industrialize and has obvious application value.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Detailed Description
The embodiments of the present invention are described in detail below, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
This example provides a method for preparing a high strength liquid crystal polymer fiber, including: winding the liquid crystal polymer fiber on a winding drum, and carrying out heat treatment under the negative pressure condition, wherein the temperature of the heat treatment is lower than the melting point of the liquid crystal polymer, and the thermal expansion coefficient of the winding drum is larger than that of the liquid crystal polymer. According to the difference of the thermal expansion coefficients of the winding drum and the liquid crystal polymer fiber, the fiber is stretched by utilizing the expansion of the winding drum in the heat treatment process, so that the fiber strength is obviously improved, and the uniformity is ensured. The method creatively utilizes the difference of the thermal expansion coefficients of the winding drum and the liquid crystal polymer fiber to ensure that the liquid crystal polymer fiber is stretched in the heat treatment process, the mechanical property of the fiber is obviously improved, and the method is simple, convenient and easy to implement, is convenient to prepare thinner and stronger LCP fiber and has considerable application value.
Depending on the properties of the LCP resin structure, molecular weight, nascent fiber diameter, etc., the choice of take-up drum, heat treatment process, negative pressure conditions, etc. may vary, as may the diameter of the resulting fiber.
Specifically, in the present example, the type of the LCP resin is not particularly required, and a wholly aromatic polyester is preferably used. From the viewpoint of high strength and spinning facilitation, the LCP resin preferably has an intrinsic viscosity of 3 to 15dl/g, more preferably 5 to 10 dl/g. From the viewpoint of high temperature resistance and high rigidity, the melting point of the LCP resin is preferably higher than 280 ℃ and lower than 400 ℃. Wherein the intrinsic viscosity can be measured according to ISO-1628-5 using 50/50(v/v) mixture of pentafluorophenol and hexafluoroisopropanol.
The virgin fiber can be manufactured by a known spinning method, preferably by a melt spinning process, LCP resin is melt-extruded by a double-screw extruder, the LCP resin is metered by a melt pump, the LCP resin is filtered by a filter and then is sprayed out by a spinning nozzle, and protofilaments are wound by a winding machine so that the fibers are wound on a winding drum.
The heating temperature of the twin-screw extruder is not lower than the melting point of the LCP resin but not higher than the thermal decomposition temperature, and is preferably 400 to 450 ℃ in accordance with the preferable range of the melting point of the LCP resin. The heating mode includes but is not limited to electric heating or heat-conducting oil heating, and all heating processes related to the method preferably adopt heat-conducting oil indirect heating, which is more beneficial to the mildness and uniformity of the heating process, so that the melt is stable, and the spinning stability and yield are improved.
The diameter of the spinneret is preferably 0.1 to 0.5mm, and more preferably 0.2 to 0.4 mm. When the diameter of the spinneret is larger than 0.5mm, the LCP resin is not easily drawn to obtain a desired fiber diameter, and when the diameter of the spinneret is smaller than 0.1mm, the spinning yield is easily reduced.
The filtering mesh number of the filter is preferably 60-500 meshes, and more preferably 120-300 meshes. The filter has a filtering mesh number lower than 60 meshes, and the spinneret holes are easily blocked by gel substances or impurities. The filtering mesh number of the filter is higher than 500 meshes, which easily causes the pressure before the filter to be too high.
The winding speed of the winding machine is preferably 300-2000 m/min, and more preferably below 600-1800 m/min. The thermal expansion coefficient of the take-up drum is preferably 10% to 800%, more preferably 50% to 500%, still more preferably 60% to 300% larger than that of the LCP resin. Research shows that when the thermal expansion coefficient of the winding drum does not exceed 10 percent of that of the LCP resin, the reinforcing effect can be influenced; above 800%, fiber breakage may occur during subsequent heat treatment.
The heat treatment step is performed under a negative pressure below the melting point of the LCP resin, and the heat treatment temperature is preferably 20 to 40 ℃ below the melting point of the LCP resin. The negative pressure state is preferably 500Pa or less, and the vacuum state heating can well avoid the thermal oxidation of the LCP resin in the high temperature state. The heating process is preferably a slow ramp to better match the take-up drum expansion rate to the fiber draw rate. The heating rate is preferably 1 ℃/h to 100 ℃/h, and more preferably 10 to 50 ℃/h. The temperature rise speed is more than 100 ℃/h, which can cause fiber breakage; the temperature rise speed is less than 1 ℃/h, and the production efficiency is influenced. Preferably, a gradient heating mode is adopted, different heating rates are used in different temperature intervals, a relatively high heating rate can be adopted in the early stage of heating, the production efficiency is ensured, the heating rate is properly delayed along with the rise of the temperature, and the fiber performance is ensured. After heating to the heat treatment temperature, the temperature may be maintained for a certain period of time, for example, 1 hour or more, preferably 1 to 36 hours.
The heat-treated fiber is preferably rewound on a paper tube again, so that the fiber is convenient to store, transport and use.
The diameter of the LCP fiber treated by the steps can be controlled to be 1-50 mu m, and more preferably 5-25 mu m; the fiber strength is preferably 20.0cN/dtex or more, more preferably 40.0cN/dtex or more; the elongation is preferably 0.5% or more, more preferably 1.0% or more; the elastic modulus is preferably 500cN/dtex or more, more preferably 800cN/dtex or more.
The above method is explained in detail below by way of exemplary embodiments. In the following examples and comparative examples, the fiber diameter was measured by a metallographic microscope; the mechanical property is measured by a fiber strength tester, the stretching speed is 5cm/min, and the clamp distance is 5 cm; the titer was measured with a titer meter.
Example 1
Into a reactor equipped with a stainless steel type C stirrer, a torque meter, a nitrogen introduction tube, a thermometer, a pressure gauge and a reflux condenser were charged 685g of p-hydroxybenzoic acid, 311g of terephthalic acid, 104g of isophthalic acid, 465g of biphenol, 1071g of acetic anhydride, 400.0g of acetic acid. The reactor was purged by evacuation and flushing with dry nitrogen and 0.18g of 1-methylimidazole was added. Heating to 150 ℃ for 80min under the stirring of 300rpm in the nitrogen atmosphere, and refluxing at constant temperature for 3 h.
13.0g of phenol were added to the reactor and the temperature was raised to 360 ℃ within 120 min. During this time, the by-product acetic acid was removed by distillation. Keeping the temperature at 360 ℃ for 30min, gradually reducing the pressure to about 100Pa within 20min, keeping the vacuum until the torque is increased by more than 30%, finishing the reaction, taking out the prepolymer, cooling to room temperature, and crushing by a crusher. The pulverized prepolymer is subjected to solid phase in the following mannerPolymerization: the temperature is heated from room temperature to 260 ℃ in 4h, from 260 ℃ to 295 ℃ in 5h under the negative pressure of 100Pa, and the obtained aromatic polyester is used as a base resin for preparing fibers in the next step after the temperature is kept at 295 ℃. The melting point was found to be 340 ℃, the intrinsic viscosity was 6.5dl/g, Dk was 3.0, Df was 0.0015, the carboxyl end groups were 25 equivalents/mole, the hydroxyl end groups were 43 equivalents/mole, and the coefficient of thermal expansion was 1.5 x 10-5/K(20℃)。
The aromatic polyester was dried in a vacuum dryer at 150 ℃ for 12 hours to a water content of less than 10ppm, melt-extruded by a twin-screw extruder, measured by a gear pump, and supplied to a spinning pack. The spinning temperature from the outlet of the extruder to the pack was 360 ℃, the number of filter meshes of the filter was 240, and the resin was discharged through the spinneret at a discharge rate of 18 cc/min. The spinneret had 58 orifices of 0.25mm diameter, and 58 filaments were simultaneously wound at 800m/min onto an aluminum alloy web (coefficient of thermal expansion of 2.5 x 10)-5K (20 ℃)) to obtain LCP nascent fiber.
The aluminum alloy wound with LCP nascent fiber is placed in an environment with negative pressure of 100Pa, heated from room temperature to 280 ℃ for 6h, heated from 280 ℃ to 310 ℃ for 6h, and kept at 310 ℃ for 18h for heat treatment. And after the heat treatment, rewinding from the aluminum alloy winding drum to the paper tube at a speed of 400m/min to obtain the LCP finished product fiber. Tests show that the diameter of the finished product fiber is 10 mu m, and the fiber strength is 28 cN/dtex; the elongation was 0.87% and the elastic modulus was 950 cN/dtex.
Example 2
Example 1 was used as the basis, with the difference that an aluminium alloy coil (coefficient of thermal expansion of 2.5 x 10)-5K (20 ℃)) was replaced by a zinc alloy spool (coefficient of thermal expansion 3.5 x 10)-5K (20 ℃ C.)). Tests show that the diameter of the finished product fiber is 8 mu m, and the fiber strength is 33 cN/dtex; the elongation was 0.75% and the elastic modulus was 1050 cN/dtex.
Comparative example 1
Example 1 was used as the basis, with the difference that an aluminium alloy coil (coefficient of thermal expansion of 2.5 x 10)-5K (20 ℃)) was replaced by a stainless steel drum (coefficient of thermal expansion 1.6 x 10)-5K (20 ℃ C.)). Tests show that the diameter of the finished product fiber is 15 mu m, and the fiber strength is 15 cN/dtex; elongation percentage0.42% and an elastic modulus of 450 cN/dtex.
Comparative example 2
Based on example 1, the difference is that the "heating from room temperature to 280 ℃ over 6 h" and the "heating from 280 ℃ to 310 ℃ over 6 h" is replaced by "heating from room temperature to 310 ℃ over 1 h". After removal, the fibers were found to break, and this temperature rise rate was not applicable to the LCP as-spun fibers of this example.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims (7)

1. A method of making a high strength liquid crystalline polymer fiber, comprising:
winding the liquid crystal polymer fiber on a winding drum, and carrying out heat treatment under the negative pressure condition; wherein the temperature of the heat treatment is lower than the melting point of the liquid crystal polymer, and the thermal expansion coefficient of the winding drum is larger than that of the liquid crystal polymer; the heating rate of the heat treatment is 1-100 ℃/h; the heat treatment adopts gradient temperature rise, and the temperature rise rate of each stage is reduced along with the increase of the temperature; the thermal expansion coefficient of the winding drum is 60 to 300% greater than that of the LCP resin.
2. The method of preparing a high strength liquid crystalline polymer fiber according to claim 1, wherein the liquid crystalline polymer is a wholly aromatic polyester.
3. The method of preparing a high strength liquid crystalline polymer fiber according to claim 1, wherein the liquid crystalline polymer has an intrinsic viscosity of 3 to 15 dl/g.
4. The method of claim 1, wherein the liquid crystal polymer has a melting point of more than 280 ℃ and less than 400 ℃.
5. The method of claim 1, wherein the liquid crystal polymer fiber is prepared by a melt spinning process.
6. The method of claim 1, wherein the fiber diameter after the heat treatment is 1 to 50 μm.
7. The method of claim 1, further comprising the step of rewinding the heat-treated fiber on a paper tube.
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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1252461A (en) * 1998-09-10 2000-05-10 塞拉尼斯阿希德特Llc公司 Method for direct thermal treatment of thermotropic liquid crystal polymer high protein filament on bobbin
CN1189606C (en) * 1998-09-10 2005-02-16 塞拉尼斯阿希德特Llc公司 Method for preparing thermotropic liquid crystal polymer and its composite high-denier multi-bobed filament
CN1582250A (en) * 2001-11-06 2005-02-16 旭化成纤维株式会社 Polyester type conjugate fiber package
JP2009167584A (en) * 2007-12-21 2009-07-30 Sumitomo Chemical Co Ltd Liquid crystal polyester fiber, method for producing the same, and use of the same
CN103122493A (en) * 2007-02-28 2013-05-29 东丽株式会社 Liquid crystalline polyester fiber and process for production of the same
CN104746155A (en) * 2015-03-25 2015-07-01 无锡金通化纤有限公司 Thermotropic liquid crystal polyarylater monofilament heat treatment device and heat treatment method
CN107523894A (en) * 2017-08-31 2017-12-29 宋宏婷 A kind of liquid crystalline polyester fiber and preparation method thereof

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1252461A (en) * 1998-09-10 2000-05-10 塞拉尼斯阿希德特Llc公司 Method for direct thermal treatment of thermotropic liquid crystal polymer high protein filament on bobbin
CN1189606C (en) * 1998-09-10 2005-02-16 塞拉尼斯阿希德特Llc公司 Method for preparing thermotropic liquid crystal polymer and its composite high-denier multi-bobed filament
CN1582250A (en) * 2001-11-06 2005-02-16 旭化成纤维株式会社 Polyester type conjugate fiber package
CN103122493A (en) * 2007-02-28 2013-05-29 东丽株式会社 Liquid crystalline polyester fiber and process for production of the same
JP2009167584A (en) * 2007-12-21 2009-07-30 Sumitomo Chemical Co Ltd Liquid crystal polyester fiber, method for producing the same, and use of the same
CN104746155A (en) * 2015-03-25 2015-07-01 无锡金通化纤有限公司 Thermotropic liquid crystal polyarylater monofilament heat treatment device and heat treatment method
CN107523894A (en) * 2017-08-31 2017-12-29 宋宏婷 A kind of liquid crystalline polyester fiber and preparation method thereof

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