KR20220069432A - liquid crystalline polymer fiber and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a liquid crystalline polymer fiber and a manufacturing method therefor. The method for manufacturing a liquid crystalline polymer fiber comprises the steps of: (1) synthesizing a liquid crystalline polymer; (2) preparing a liquid crystalline polymer fiber by spinning the liquid crystalline polymer; and (3) performing heat-treatment of the liquid crystalline polymer fiber at 215-245 ℃ for 3-15 hours.

Description

Liquid crystal polymer fiber, and method for manufacturing the same {liquid crystalline polymer fiber and method for manufacturing the same}

The present invention relates to a liquid crystal polymer fiber and a method for manufacturing the same.

In recent years, as the demand for higher performance of synthetic fibers increases, synthetic fibers having various novel performances are provided in the market. In particular, among the novel performance fibers, the fiber composed of liquid crystal polyester has excellent mechanical properties. Liquid crystal polyester fibers are used in various products such as cord reinforcement materials for various electrical products, ropes, protective gloves, and plastic reinforcement materials.

Liquid crystalline polyester is a polymer having a rigid molecular structure. The method of forming a liquid crystal polyester into a fiber is generally to melt the liquid crystal polyester and then mold it by extruding and elongating it through pores. During melt spinning of liquid crystal polyester fibers, molecular chains are highly oriented in the fiber axis direction and heat treatment is performed at high temperature for a long time.

Since liquid crystal polymer fibers can be heat treated at high temperatures for a long time, the best strength and elasticity among melt-spun fibers can be expressed. This is because the molecular weight of the fiber increases and the melting point rises as the polymerization reaction proceeds during the high-temperature and long-term heat treatment process.

However, the liquid crystal polyester fiber of the prior art has a problem in that when heat treatment is performed at a temperature near the melting point, fusion between single yarns tends to occur due to heat. In addition, there is a problem in that the fiber performance is deteriorated as the fused portion is peeled off and fibrillation occurs at the time of disengagement. In addition, as the demand for more reinforced liquid crystal polyester fibers for various fabrics such as mesh fabrics for filters and fabrics for screen printing occurs, it is necessary to improve the strength and elasticity of the liquid crystal polyester fibers of the prior art.

As a similar prior literature on this, Korean Patent Application Laid-Open No. 10-2009-0127371 has been published.

Republic of Korea Patent Publication No. 10-2009-0127371 (2009.12.10.)

In order to solve the above problems, an object of the present invention is to provide a liquid crystal polymer fiber capable of heat treatment at a relatively low temperature, thereby reducing fiber damage due to high temperature heat treatment, and a method for manufacturing the same. Another object of the present invention is to provide a liquid crystal polymer fiber having excellent thermodynamic properties and improved strength and elasticity, and a method for manufacturing the same.

One aspect of the present invention for achieving the above object is (step 1) synthesizing a liquid crystal polymer;

(Step 2) preparing a liquid crystal polymer fiber by spinning the liquid crystal polymer; and

(Step 3) heat-treating the liquid crystal polymer fiber at 215 to 245° C. for 3 to 15 hours; It relates to a method for producing a liquid crystal polymer fiber comprising a.

In one aspect, in the first step, the liquid crystal polymer is synthesized by melt polymerization of a first compound satisfying the following Chemical Formula 1, a second compound satisfying the following Chemical Formula 2, and a third compound satisfying the following Chemical Formula 3 may be characterized.

[Formula 1]

[Formula 2]

[Formula 3]

In one aspect, the first compound: the second compound: the third compound may be melt-polymerized in a molar ratio of 1: 0.5 to 1.5: 2.5 to 3.5.

In one aspect, the liquid crystal polymer fiber heat-treated in step 3 may have a diameter of 60 to 110 nm.

In another aspect of the present invention, a liquid crystal polymer prepared by melt polymerization of a first compound satisfying the following Chemical Formula 1, a second compound satisfying the following Chemical Formula 2, and a third compound satisfying the following Chemical Formula 3 is heat-treated, The prepared liquid crystal polymer fiber, wherein the liquid crystal polymer fiber has a melting transition temperature (T _m ) and an isotropic transition temperature (T _i ) of a difference (ΔT _im (°C)) value of 40 to 45° C. It relates to a liquid crystal polymer fiber. .

[Formula 1]

[Formula 2]

[Formula 3]

In another aspect, the liquid crystal polymer fiber may have a maximum tensile strength of 35 to 120 MPa and an initial tensile modulus of 12 to 20 GPa.

In another aspect, the liquid crystal polymer may be characterized by melt polymerization of the first compound: the second compound: the third compound in a molar ratio of 1: 0.5 to 1.5: 2.5 to 3.5.

The liquid crystal polymer fiber according to the present invention can be heat-treated at a relatively low temperature, thereby reducing fiber damage caused by high-temperature heat treatment. In addition, by heat-treating the liquid crystal polymer fiber at 215 to 245° C. for 3 to 15 hours, excellent thermodynamic properties can be exhibited, and strength and elasticity can be improved.

1 is a graph showing the results of Differential Scanning Calorimetry (DSC) of liquid crystal polymer fibers.
2 is a graph showing the results of thermogravimetric analysis (TGA) of liquid crystal polymer fibers.
3 and 4 are observations of the liquid crystal (LC) intermediate phase of the liquid crystal polymer fiber, FIG. 3 is a polarization micrograph of the fibers of Examples 1 and Comparative Examples 1 to 4, and FIG. 4 is the fibers of Examples 1 to 4 is a polarization micrograph of
5 is an X-ray diffraction (XRD) pattern graph of a liquid crystal polymer fiber.
6 and 7 are observations of the morphology of the liquid crystal polymer fiber. 6 is a scanning electron microscope (SEM) photograph of the fibers of Examples 1 and 1 and Comparative Examples 1 to 4, and FIG. 7 is a scanning electron microscope photograph of the fibers of Examples 1 to 4.
8 is a scanning electron micrograph of the skin-core of Comparative Example 1 (As-spun) and Example 3 fibers.
9 is a schematic diagram of the microfiber structure of the liquid crystal polymer and a scanning electron microscope photograph of the fiber of Example 3;
10 and 11 show changes in mechanical tensile properties of liquid crystal polymer fibers, FIG. 10 shows the maximum tensile strength and initial tensile modulus of fibers of Examples 1 and Comparative Examples 1 to 4, and FIG. 11 is Examples 1 to 4 The maximum tensile strength and initial tensile modulus of the fibers are shown.

Hereinafter, a liquid crystal polymer fiber according to the present invention, and a manufacturing method thereof will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the summary of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

Since liquid crystal polymer fibers can be heat-treated at high temperatures for a long time, the best strength and elasticity among melt-spun fibers can be expressed. This is because the molecular weight of the fiber increases and the melting point rises as the polymerization reaction proceeds during the high-temperature and long-term heat treatment process. However, when the heat treatment of the liquid crystal polyester fiber of the prior art is performed at a temperature near the melting point in the form of a package, fusion between single yarns tends to occur due to heat. In addition, there is a problem in that the fiber performance is deteriorated as the fused portion is peeled off and fibrillation occurs at the time of disengagement. In addition, as the demand for more reinforced liquid crystal polyester fibers for various fabrics such as mesh fabrics for filters and silk fabrics for screen printing arises, it is necessary to improve the strength and elasticity of liquid crystal polyester fibers of the prior art. .

Accordingly, the present inventors can heat treatment at a relatively low temperature, thereby reducing damage caused by high-temperature heat treatment, as well as exhibiting excellent thermodynamic properties, and liquid crystal polymer fibers, characterized in that they exhibit improved strength and elasticity; and a manufacturing method thereof were found to complete the present invention.

In detail, the method for producing a liquid crystal polymer fiber according to the present invention comprises the steps of (step 1) synthesizing a liquid crystal polymer;

(Step 2) preparing a liquid crystal polymer fiber by spinning the liquid crystal polymer; and

(Step 3) heat-treating the liquid crystal polymer fiber at 215 to 245° C. for 3 to 15 hours; It may be characterized in that it includes.

In step 1, the liquid crystal polymer may be characterized in that it is synthesized by melt polymerization of a first compound satisfying the following Chemical Formula 1, a second compound satisfying the following Chemical Formula 2, and a third compound satisfying the following Chemical Formula 3 .

[Formula 1]

[Formula 2]

[Formula 3]

More specifically, the liquid crystal polymer may be melt-polymerized in a molar ratio of 1: 0.5 to 1.5: 2.5 to 3.5 of the first compound: the second compound: the third compound, and more preferably, the first compound: Second compound: The third compound may be melt-polymerized in a molar ratio of 1: 0.7 to 1.3: 2.8 to 3.2. By satisfying this, thermodynamic properties may be improved compared to the related art.

For example, the synthesized liquid crystal polymer (TLCP) has different thermal properties and different LC properties depending on the number of moles of the third compound. As a non-limiting example, the first compound: the second compound: the third compound may be melt-polymerized in a molar ratio of 1: 1: 3, and when the mole number of the third compound is 3 moles, the lowest melting point and excellent A liquid crystal intermediate phase is shown. As a result of measuring the liquid crystal intermediate phase of the fiber made of the liquid crystal polymer using a polarizing microscope, a yarn-like nematic shape appeared regardless of the temperature range of 190 to 270 ° C and the heat treatment time of 3 to 12 hours. In addition, the polymer fiber prepared by melt polymerization of the first compound: the second compound: the third compound in a molar ratio of 1: 1: 3 can have excellent thermal properties compared to the prior art.

In addition, as an example, the second compound and the third compound monomer, such as a rigid rod-like structure, have a high rotational barrier effect on bonding by a diethoxy side chain and make partial movement difficult. The liquid crystal polymer fiber synthesized in a molar ratio of the first compound: the second compound: the third compound is 1: 1: 3 may have better thermal properties than the prior art.

In addition, the method of spinning the liquid crystal polymer in step 2 is described in more detail by the following examples, but these examples are merely illustrative of the present invention and do not limit the scope of the present invention. Electrospinning, melt spinning, etc. may be carried out by a spinning method used in the manufacture of conventional liquid crystal polymer fibers.

More preferably, the third step may be characterized in that the liquid crystal polymer is heat-treated at 215 to 245° C. for 4 to 11 hours. More preferably, it may be characterized by heat treatment at 225 to 240 °C for 8 to 10 hours. Under the above conditions, more excellent thermodynamic properties and mechanical strength properties can be secured.

The liquid crystal polymer fiber heat-treated in step 3 may be characterized in that microfiber strands having a diameter of 60 to 110 nm are oriented in a nematic shape.

As an example, the diameter of the liquid crystal polymer fiber may be adjusted according to the diameter of the capillary during spinning, but may be, for example, 0.1 to 1 mm. The thinner the fiber, the easier it can be twisted into multiple strands. By satisfying this, mechanical tensile properties such as strength and elasticity can be improved compared to the prior art.

As a specific example, the liquid crystal polymer fiber heat-treated under the above conditions may have a maximum tensile strength of 80 to 120 MPa and an initial tensile modulus of 7 to 9 GPa.

In another aspect of the present invention, a liquid crystal polymer prepared by melt polymerization of a first compound satisfying Chemical Formula 1, a second compound satisfying Chemical Formula 2, and a third compound satisfying Chemical Formula 3 is heat-treated. liquid crystal polymer fiber, wherein the liquid crystal polymer fiber has a difference (ΔT _im (℃)) between a melting transition temperature (T _m ) and an isotropic transition temperature (T _i ) of 40 to 45° C. It may be characterized in that it is.

[Formula 1]

[Formula 2]

[Formula 3]

As a specific example, the difference between the melting transition temperature (T _m ) and the isotropic transition temperature (T _i ) (ΔT _im (°C)) may mean the stability of the intermediate phase. The liquid crystal polymer state can be stably maintained over a wider temperature range. The fibers of Examples 1 to 4 had a ΔT _im (° C.) value of 39° C. or higher, and compared to Comparative Examples 1 to 4, the ΔT _im (° C.) value was improved. Therefore, since the ΔT _im (°C) value of Examples 1 to 4 is larger than Comparative Examples 1 to 4, it may mean that the liquid crystal polymer fiber can be stable in a wider temperature range. The difference (ΔTi-m(°C)) between the melting transition temperature (Tm) and the isotropic transition temperature (Ti) may mean the stability of the intermediate phase. The liquid crystal polymer state can be stably maintained over a wider temperature range.

Meanwhile, the liquid crystal polymer fiber described above may have a maximum tensile strength of 30 to 120 MPa and an initial tensile modulus of 12 to 20 GPa.

More preferably, the liquid crystal polymer fiber may have a maximum tensile strength of 50 to 120 MPa and an initial tensile modulus of 15.5 to 18 GPa. Even more preferably, the maximum tensile strength may be 80 to 120 MPa, and the initial tensile modulus may be 7 to 9 GPa.

As a specific example, the ultimate tensile strength of the fiber (Comparative Example 1) immediately after spinning is 13 MPa. On the other hand, when the heat treatment was performed for 3 hours at a temperature of 230°C (Example 1), the maximum tensile strength was 36 MPa. Increasing the heat treatment temperature improves the maximum tensile strength. In addition, the maximum tensile strength of 102 MPa in the case where heat treatment was performed for 9 hours at a temperature of 230° C. (Example 3). By increasing the heat treatment temperature and time, the maximum tensile strength value is improved. The initial tensile modulus of elasticity of the fiber (Comparative Example 1) immediately after spinning was 9.22 GPa. On the other hand, when the heat treatment was performed for 3 hours at a temperature of 230° C. (Example 1), the initial tensile modulus of elasticity was 12.15 GPa. When the heat treatment temperature is increased, the initial tensile modulus of elasticity is improved. In addition, Examples 2 to 4 in which the heat treatment time was increased than in Example 1 exhibited higher initial tensile modulus. In particular, the initial tensile modulus of elasticity is 16.11 GPa when the heat treatment is carried out for 9 hours at a temperature of 230 °C (Example 3). It can be seen that when the heat treatment temperature and time are increased, the maximum tensile strength and the initial tensile modulus are more excellently improved.

In addition, the liquid crystal polymer may be characterized in that the first compound: the second compound: the third compound is melt-polymerized in a molar ratio of 1: 0.5 to 1.5: 2.5 to 3.5. By satisfying this, thermodynamic properties can be improved compared to the prior art. can..

Hereinafter, the liquid crystal polymer fiber according to the present invention, and a manufacturing method thereof will be described in more detail through examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention. In addition, the unit of additives not specifically described in the specification may be weight %.

[Characteristic evaluation]

1) Measurement of thermodynamic properties: All experiments were performed in a nitrogen atmosphere, and the temperature increase rate was set at 20 °C/min. Using a differential scanning calorimeter (DSC), the thermal properties of the fibers were measured in a temperature range of 30 to 350 °C. In addition, using a DuPont 910 instrument (New Castle, DE, USA) as a thermogravimetric analyzer (TGA), thermal stability was measured in a temperature range of 30 to 750 °C. The results are shown in Table 2 and FIGS. 1 to 2 below.

2) Liquid crystal (LC) mesophase and fracture morphology investigation: Liquid crystal using a polarizing microscope equipped with a Mettler FP-5 hot stage (Leitz, Ortholux, Lahn-Dill-Kreis, Germany) in the temperature range of 190 to 270 ° C. The mesophase was measured. The results are shown in FIGS. 3 and 4 below.

The fractured portion of the spun fiber was observed using a scanning electron microscope (SEM, JEOL JSM-6500F, Tokyo, Japan). The results are shown in FIGS. 6 to 9 below.

3) Measurement of wide-angle X-ray diffraction (XRD) values: a Rigaku (D/Max-IIIB) X-ray Diffractometer equipped with Ni-filtered Cu-Kα radiation (Tokyo, Japan). XRD) was used to measure wide-angle X-ray diffraction (XRD) values of the fibers at 25 °C. The scan rate was 2°/min at 2θ=2-37°. The results are shown in FIG. 5 .

4) Measurement of mechanical tensile properties: The mechanical tensile properties of the fibers were measured at room temperature at 20 mm/min crosshead speed using an Instron mechanical tester (Model 5564) (New York, USA). The experimental errors of the maximum tensile strength and the initial tensile modulus were within ±1 MPa and ±0.05 GPa, respectively, and it was shown as an average value of 10 samples, and the results are shown in Table 3 and FIGS. 10 to 11 below.

[Example 1]

A first compound satisfying the following formula (1): a second compound satisfying the following formula (2): a third compound satisfying the following formula (3) 1: 1: 3 in a molar ratio of a thermotropic liquid crystalline copolyester (TLCP) was synthesized. The synthesis conditions were carried out in steps 1 to 6 as described in Table 1 below.

[Formula 1]

[Formula 2]

[Formula 3]

Melt polymerization conditions of liquid crystal polymer fiber fusion Stage 1 Step 2 Step 3 Step 4 Step 5 Step 6 Temperature (℃) 240 260 280 300 310 310 time (min) 120 120 90 65 45 40 Pressure (Torr) 760 760 760 760 300 One

Liquid crystal polymer (TLCP) in powder form was dried in a vacuum oven at 60° C. for 24 hours, and spun through a die of a capillary rheometer (model 5460, Instron) at 240 to 245° C. The standard die diameter was 0.50 mm and the average residence time of the capillary viscometer was 2-3 minutes. At this time, the rotation speed of the fiber in the capillary viscometer was set to 15 m/min. The amount of the spinning polymer (liquid crystal polymer fiber) was 19 to 21 g. Thermotropic liquid crystal polymer (TLCP) fibers were heat treated at 230 °C for 3 hours.

[Examples 2 to 4 and Comparative Examples 1 to 4]

As described in Table 2, the same procedure as in Example 1 was performed except that the heat treatment temperature (°C) and time (hr) of the thermotropic liquid crystal polymer (TLCP) fiber were different.

The liquid crystal polymer fibers prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated according to the property evaluation method, and the results are shown in Tables 2 and 3 below.

process conditions thermodynamic properties Heat treatment temperature (℃) heat treatment
time (hr) T _g
(℃) T _m
(℃) T _i
(℃) ΔT _im
(℃) T _D
(℃) wt _R ⁶⁰⁰ (%) DC
(%) Example 1 230 3 98 280 322 42 366 35 36 Example 2 230 6 98 281 322 41 366 35 37 Example 3 230 9 102 285 325 40 362 34 36 Example 4 230 12 93 276 318 42 363 37 33 Comparative Example 1
(As-spun) - - 82 277 315 38 363 35 27 Comparative Example 2 190 3 92 279 317 38 366 34 30 Comparative Example 3 210 3 94 280 317 37 367 35 36 Comparative Example 4 250 3 97 287 321 34 367 36 37

process conditions mechanical tensile properties Heat treatment temperature (℃) Heat treatment time (hr) maximum tensile strength
(MPa) Initial tensile modulus
(GPa) Elongation (%) Example 1 230 3 36 12.15 10 Example 2 230 6 72 12.77 12 Example 3 230 9 102 16.11 10 Example 4 230 12 58 14.66 10 Comparative Example 1
(As-spun) - - 13 9.22 10 Comparative Example 2 190 3 16 9.25 10 Comparative Example 3 210 3 15 11.99 12 Comparative Example 4 250 3 34 11.56 10

As can be seen from Table 3, the fibers of Examples 1 to 4 had a maximum tensile strength of 35 MPa or more, and the maximum tensile strength was improved compared to Comparative Examples 1 to 4. In particular, the fiber of Example 3 increased by 89 MPa in maximum tensile strength compared to the fiber before heat treatment (Comparative Example 1). In addition, the initial tensile modulus of elasticity also increased by 6.99 MPa compared to Comparative Example 1. It can be seen that Example 3 shows the best mechanical tensile properties. It was clearly confirmed that when the spun fiber was heat-treated at a temperature of 225 to 240° C. for 8 to 10 hours, the mechanical tensile properties could be greatly improved without compromising the liquid crystallinity of the liquid crystal fiber.

In detail, as described in Table 2 and FIGS. 1 to 2, the glass transition temperature (T _g ) of Comparative Example 1 (fiber immediately after spinning) is 82 °C. On the other hand, in the case of Example 1 in which the heat treatment was performed for 3 hours at a temperature of 230 ° C., the glass transition temperature (T _g ) was increased by 16 ° C., indicating 98 ° C. In addition, the melting transition temperature (T _m ) of Comparative Example 1 was 277 ° C., and the isotropic transition temperature (T _i ) was 315 ° C. In the case of Example 1 in which the heat treatment was performed, the melting transition The temperature (T _m ) was increased by 3 °C, and the isotropic transition temperature (T _i ) was increased by 7 °C. After the heat treatment, it can be seen that the glass transition temperature (T _g ), the melting transition temperature (T _m ), and the isotropic transition temperature (T _i ) all rise. In addition, it can be seen that Example 3 has the greatest increase in thermal properties (T _g , T _m , and T _i ) than Comparative Example 1. The glass transition temperature (T _g ) was increased by 20 °C, the melting transition temperature (T _m ) by 8 °C, and the isotropic transition temperature (T _i ) by 10 °C. It can be seen that the thermal properties (T _g , T _m and T _i ) of Example 3 are the best.

In addition, the difference (ΔT _im (℃)) between the melting transition temperature (T _m ) and the isotropic transition temperature (T _i ) may mean the stability of the intermediate phase. The higher the ΔT _im (°C) value, the more stable the liquid crystal polymer state can be maintained over a wider temperature range. The more stable the fiber remains over a wide temperature range, the more the range of applications for fiber use can be increased. ΔT _im (°C) values of Comparative Examples 1 to 4 were 34 to 38°C. On the other hand, ΔT _im (°C) values of Examples 1 to 4 were 40 to 42°C. Therefore, since the ΔT _im (°C) values of Examples 1 to 4 are larger than those of Comparative Examples 1 to 4, Examples 1 to 4 can be stably maintained in a wider temperature range and the application range for using fibers is This could mean that it could increase further.

Degree of crystallinity (DC) is determined from the ratio of the peak area of the crystalline region to the peak area of the amorphous region. The crystallinity of Comparative Example 1 was 27%. On the other hand, the crystallinity of Examples 1 to 3 was 36 to 37%. Since the crystallinity values of Examples 1 to 3 are larger than those of Comparative Example 1, it may mean that the fibers of Examples 1 to 3 exhibit excellent properties.

3 to 4 are results of measuring the liquid crystal (LC) intermediate phase using a polarizing microscope in a temperature range of 190 to 270 °C. 3 is a photograph of the liquid crystal intermediate phase of Example 1 and Comparative Examples 1 to 4, and FIG. 4 is a photograph of the liquid crystal intermediate phase of Examples 1-4. In Examples 1 to 4 and Comparative Examples 1 to 4, a thread-like nematic shape was observed. It can be seen that the nematic liquid crystal phase appears regardless of the heat treatment temperature and time. However, in the case of Examples 3 to 4, a more hazy intermediate image than Comparative Examples 1 to 4 was shown. This is because the molecular weight and viscosity of the heat-treated fibers increased as the heat treatment time and temperature increased. Therefore, it may mean that the liquid crystal polymer fibers of Examples 3 to 4 and their manufacturing method are excellent.

5 is a result of measuring a wide-angle X-ray diffraction (XRD) value of the fiber at 25 ℃. In Comparative Example 1, a very weak and broad peak was observed at d=8.55Å (2θ=10.34°), and a medium-intensity peak was observed at d=4.45Å (2θ=19.92°). Also, a very small peak was observed at d=3.77Å (2θ=23.58°). On the other hand, as the heat treatment temperature and time increased, the intensity of the peak gradually increased and new peaks were also observed. It can be seen that the intensity of the peak gradually increases as the heat treatment temperature and time increase. This may mean that the fibers of Examples 1 to 4 subjected to the heat treatment process exhibit excellent thermodynamic properties.

6 and 7 are using a scanning electron microscope (Scanning Electron Microscopy, SEM), Examples 1 to 4 and Comparative Examples 1 to 4 The morphologies of the fibers were observed. 6 is a morphology of the fibers of Example 1 and Comparative Examples 1 to 4, and FIG. 7 is a morphology of the fibers of Examples 1 to 4. To improve the conductivity of the fiber, the cracked surface was sputtered with gold using an SPI-Module sputter coater. Examples 1 to 5 and Comparative Examples 1 to 3 were cut vertically in liquid nitrogen and cross-sections were measured. In FIG. 6 , in the case of Comparative Example 1 (a), it can be seen that the fibrous form is observed only in some parts and small spherical particles that are not well developed are observed. On the other hand, in the case of Example 1 (d), the form of extruded fibers is observed. It can be seen that the fibers heat-treated at a low temperature show weak orientation and fibrous morphology, and the fibers heat-treated at a high temperature have a highly oriented fibrous structure. As the heat treatment temperature increases, highly developed fibers may be exhibited. It may mean that the properties of the liquid crystal polymer fiber can be excellently improved by the heat treatment process. 7, it can be seen that the distribution of fibers of Examples 1 to 4 is constant regardless of the heat treatment time. In addition, it can be seen that a highly developed fibrous form can be seen as the heat treatment time increases. It can be seen that in Example 3(c), the micro-sized fibers were observed with the largest area than in Examples 1(a) to 2(b) and 4(e). This may mean that the liquid crystal polymer fiber of Example 3 and its manufacturing method are the most excellent.

8 is a scanning electron micrograph of the skin-core of Comparative Example 1 (As-spun) and Example 3 fibers. Figure 8(a) shows an enlarged SEM image of the cross section of Comparative Example 1. Fibers can be observed only in a very narrow area of the skin area. Also, it can be seen that most of the fibrous morphology is not certain. And in the core region, most of the clusters are maintained and a slightly pulled structure can be observed. However, in the case of the enlarged SEM image of the cross section of Example 3, microfilaments with a large aspect ratio can be observed in most of the skin region. The diameter of these fibers varies from several tens of nanometers to several hundred nanometers. And a small amount of fibers can be observed in the core region. The skin and core shape of Example 3, which is more developed than Comparative Example 1, may be due to the difference in shear and expansion flow ranges generated in the liquid crystal polymer fiber processing step. This may mean that the properties of the liquid crystal polymer fiber can be excellently improved by the heat treatment process.

9 is a schematic diagram of the microfiber structure of the liquid crystal polymer and a scanning electron microscope photograph of the fiber of Example 3; Through the schematic diagram of the microfiber structure of the liquid crystal polymer, it can be seen that the diameter of the conventional liquid crystal polymer microfiber is about 5 μm (5000 nm), and the generally observed fiber is about 0.5 μm (500 nm). can On the other hand, it can be seen that the diameter of the fiber of Example 3 is in the range of about 60 to 110 nm. This may mean that the properties of the liquid crystal polymer fiber can be excellently improved by the heat treatment process.

As shown in Table 3 and FIGS. 10 to 11 below, the ultimate tensile strength of Comparative Example 1 (fiber immediately after spinning) was 13 MPa. On the other hand, the maximum tensile strength of Example 1 was 36 MPa. It can be seen that the maximum tensile strength is improved by further increasing the heat treatment temperature. In addition, Examples 2 to 4 in which the heat treatment time was increased than in Example 1 exhibited higher maximum tensile strength. In particular, it can be seen that the maximum tensile strength of Example 3 is the highest at 102 MPa. This may mean that the manufacturing method according to Example 3 can have the most improved maximum tensile strength value. The initial tensile modulus of Comparative Example 1 (As-spun fiber) was 9.22 GPa. On the other hand, the initial tensile modulus of Example 1 was 12.15 GPa. It can be seen that the initial tensile modulus of elasticity is improved when the heat treatment temperature is further increased. In addition, Examples 2 to 4 in which the heat treatment time was increased than in Example 1 exhibited higher initial tensile modulus. In particular, it can be seen that the initial tensile modulus of Example 3 is 16.11 GPa, which is the highest. This may mean that the manufacturing method according to Example 3 can have the most improved initial tensile modulus. Therefore, it may mean that the mechanical tensile properties of Example 3 can be improved the most.

Although the present invention has been described with reference to specific matters and limited examples as described above, these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and the present invention belongs to Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (7)

(Step 1) synthesizing a liquid crystal polymer;
(Step 2) preparing a liquid crystal polymer fiber by spinning the liquid crystal polymer; and
(Step 3) heat-treating the liquid crystal polymer fiber at 215 to 245° C. for 3 to 15 hours; A method for producing a liquid crystal polymer fiber comprising a.
The method of claim 1,
In step 1, the liquid crystal polymer is a liquid crystal polymer fiber, characterized in that it is synthesized by melt polymerization of a first compound satisfying the following formula (1), a second compound satisfying the following formula (2), and a third compound satisfying the following formula (3) manufacturing method.
[Formula 1]

[Formula 2]

[Formula 3]

3. The method of claim 2,
The first compound: the second compound: the third compound is 1: 0.5 to 1.5: a method for producing a liquid crystal polymer fiber, characterized in that melt polymerization in a molar ratio of 2.5 to 3.5.
The method of claim 1,
The method for producing a liquid crystal polymer fiber, characterized in that the liquid crystal polymer fiber heat-treated in step 3 has a diameter of 60 to 110 nm.
A liquid crystal polymer fiber prepared by heat-treating a liquid crystal polymer prepared by melt polymerization of a first compound satisfying the following Chemical Formula 1, a second compound satisfying the following Chemical Formula 2, and a third compound satisfying the following Chemical Formula 3,
The liquid crystal polymer fiber has a melting transition temperature (T _m ) and an isotropic transition temperature (T _i ) of a difference (ΔT _im (°C)) value of 40 to 45° C., a liquid crystal polymer fiber.
[Formula 1]

[Formula 2]

[Formula 3]

6. The method of claim 5,
The liquid crystal polymer fiber has a maximum tensile strength of 35 to 120 MPa, and an initial tensile modulus of 12 to 20 GPa, a liquid crystal polymer fiber.
6. The method of claim 5,
The liquid crystal polymer is a liquid crystal polymer fiber prepared by melt polymerization of the first compound: the second compound: the third compound in a molar ratio of 1: 0.5 to 1.5: 2.5 to 3.5.

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