Liquid crystal polyester as well as preparation method and application thereof

Abstract

The invention discloses liquid crystal polyester as well as a preparation method and application thereof, and belongs to the technical field of polymer engineering plastics. The viscous flow activation energy and the shear viscosity at the shear rate of 1000s <-1 > of the liquid crystal polyester provided by the invention are in a proper range, the liquid crystal polyester can be effectively applied to spinning and is particularly suitable for liquid crystal polyester monofilament spinning, fibers are easy to fine without being snapped in the spinning process, and the continuous spinnability is excellent; the obtained liquid crystal polyester monofilament has excellent dimensional stability, strength stability and modulus stability, and meanwhile, the prepared liquid crystal polyester monofilament has excellent creep resistance and high strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer engineering plastics, and particularly relates to a liquid crystal polyester, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, the linear density of a single filament of commercial liquid crystal polymer (LCP) fiber is 5D, and a bundle of filaments consists of dozens or even hundreds of single filaments. Therefore, during the spinning process, even if there is a slight fluctuation in the size of the fiber single filaments, the impact on the strength and modulus of the entire bundle of filaments is relatively small. However, for the application scenarios of LCP single filaments, the fluctuation in the single filament diameter has a greater impact on the strength and modulus of the product. During melt spinning, the melt is rapidly stretched after passing through the spinneret. Due to the highly oriented molecular segments of LCP, it is not possible to perform secondary stretching during the spinning process, nor can it be stretched a second time, and fibers with a specific diameter are directly obtained. Moreover, the heat treatment process will not change the diameter of the fibers. Therefore, the diameter of the as-spun raw filaments is the diameter of the finished fibers. For LCP single filaments, the fluctuation in fiber diameter directly affects the quality of the fibers. If the fiber diameter fluctuates too much, it will directly affect its physical properties such as strength and modulus, and affect its downstream use.

[0003] Patent CN201911342689 discloses an all-aromatic liquid crystal polyester (LCP) resin suitable for preparing fibers. This resin has a P1 / P3 ratio greater than or equal to 3.0, and the melt viscosity of P3 is lower than 70 Pa·S. P1, P2, and P3 are the melt viscosities at a shear rate of 1000 s -1 under the conditions of the melting temperature (Tm), the temperature of Tm + 10°C, and the temperature of Tm + 20°C. Since the polymer melting process has a certain melting range, and the melting point is only at the highest point of the melting peak, when measuring the viscosity at the melting point, the material has not been completely melted, and the measured viscosity value is very large. Due to the characteristics of liquid crystal polymers, once the resin melts, the viscosity drops sharply. Therefore, a resin that meets this determination condition may not necessarily have spinnability. Patent CN202080016816 discloses a heat treatment method. The fiber passes through an oven at three different temperatures, and a certain tension is applied to the fiber to cause a very small amount of stretching, and the obtained fiber has a small deviation in initial modulus. However, this method is mainly for thick denier filaments, and the principle is to improve the bundling and parallelism between the fibers by stretching, thereby improving the quality of the fibers. However, this method still cannot optimize the fluctuation of the single filament diameter of the fiber itself. Patent CN201120017797 discloses adding a slow cooling device below the spinneret to slow down this cooling and solidification behavior. Conventional injection molding grade LCP resins still cannot prepare LCP single filament fibers or multifilament fibers by melt spinning.

[0004] Since there is no LCP resin molecule in the prior art that can be effectively used for spinning monofilaments, it is urgent to provide a liquid crystal polyester that can prepare monofilaments with excellent comprehensive properties. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a liquid crystal polyester with excellent continuous spinnability, easy to thin and not easy to break the spinning fiber during the spinning process, that is, conducive to the formation of monofilaments, with high size stability, small fluctuations in modulus and strength, and high strength and excellent creep resistance, as well as its preparation method and application.

[0006] To achieve the above object, in the first aspect of the present invention, the present invention provides a liquid crystal polyester, and the liquid crystal polyester satisfies the following conditions:

[0007] a. The viscous flow activation energy is 70 - 150 kJ / mol;

[0008] b. The shear viscosity at a shear rate of 1000 s -1 is 25 - 47 Pa·s.

[0009] The liquid crystal polyester provided by the present invention has excellent continuous spinnability by selecting the viscous flow activation energy of the liquid crystal polyester and the shear viscosity at a shear rate of 1000 s -1 within a specific range. It can be effectively applied to the preparation of liquid crystal polyester monofilaments. During the preparation of liquid crystal polyester monofilaments, the fiber is easy to be thinned without breaking, and the obtained liquid crystal polyester monofilaments have a uniform diameter distribution and high strength. In addition, the prepared liquid crystal polyester monofilaments also have excellent size stability, modulus stability, strength stability and good creep resistance.

[0010] It should be noted that the test method for the viscous flow activation energy of the liquid crystal polyester is as follows: measured by a Malvern capillary rheometer, using a die with an inner diameter of 1 mm and a length of 20 mm. The test temperature is the melting point T m + 5°C, melting point T m + 10°C, melting point T m + 20°C, melting point T m + 30°C, using a variable shear mode, the shear rate is 1000 - 5000 s -1 variable shear rate, taking points every 1000 s -1 and taking the viscosity data at a shear rate of 5000 s -1 at different test temperatures, measured with a die with an inner diameter of 1 mm and a length of 20 mm; after the measurement, use the Arrhenius equation to plot a graph, with the reciprocal of the test temperature (absolute temperature) as the X-axis and the natural logarithm of the melt viscosity as the Y-axis. After linearly fitting the points on the graph, the slope of the fitting line is the viscous flow activation energy of the liquid crystal polyester.

[0011] The melting point of the liquid crystal polyester is 275 - 325 °C.

[0012] It should be noted that the test method for the melting point of the liquid crystal polyester is as follows: measured by DSC 200F3 of NETZSCH company, with a heating rate of 20 °C / min, heated from room temperature to 360 °C above the melting point, then cooled to room temperature at a rate of 20 °C / min, and finally heated to 30 °C above the melting point at a rate of 20 °C / min; the highest point of the melting peak of the second heating curve is taken as the melting point.

[0013] Exemplarily, the viscous flow activation energy of the liquid crystal polyester can be any point value or any two-point range value between 70 - 150 kJ / mol, such as 80 - 120 kJ / mol, or can be 70 kJ / mol, 75 kJ / mol, 80 kJ / mol, 85 kJ / mol, 90 kJ / mol, 95 kJ / mol, 100 kJ / mol, 105 kJ / mol, 110 kJ / mol, 115 kJ / mol, 120 kJ / mol, 125 kJ / mol, 130 kJ / mol, 135 kJ / mol, 140 kJ / mol, 145 kJ / mol, 150 kJ / mol, etc.

[0014] It should be noted that the liquid crystal polyester at a shear rate of 1000 s -1 The test method for the shear viscosity is as follows: measured by a Malvern capillary rheometer, the test temperature is the melting point T m + 20 °C, the shear rate is 1000 s -1 , measured using a die with an inner diameter of 1 mm and a length of 20 mm, to obtain the shear viscosity of the liquid crystal polyester at a shear rate of 1000 s -1 .

[0015] Exemplarily, the shear viscosity of the liquid crystal polyester at a shear rate of 1000 s -1 can be any point value or any two-point range value between 25 - 47 Pa·s, such as 28 - 40 Pa·s, or can be 25 Pa·s, 27 Pa·s, 29 Pa·s, 31 Pa·s, 33 Pa·s, 35 Pa·s, 37 Pa·s, 39 Pa·s, 41 Pa·s, 43 Pa·s, 45 Pa·s, 47 Pa·s, etc.

[0016] As a preferred embodiment of the liquid crystal polyester of the present invention, the viscous flow activation energy of the liquid crystal polyester is 95 - 120 kJ / mol.

[0017] The viscous flow activation energy of the liquid crystal polyester is a physical quantity representing its viscosity-temperature dependence; the research of the present invention finds that if the viscous flow activation energy is too high, even if a slow cooling device is added below the die during the preparation of the liquid crystal polyester monofilament, due to the sharp increase in viscosity of the melt after it exits the spinneret, it is very difficult to draw the fiber thinner to obtain a fiber with a specific linear density of the liquid crystal polyester monofilament; if the viscous flow activation energy is too low, the viscosity of the melt rises slowly after it exits the spinneret, the strength is insufficient, and the fiber is prone to breakage; when further selecting the viscous flow activation energy of the liquid crystal polyester to be 95-120 kJ / mol, when the obtained liquid crystal polyester is applied to the preparation of the liquid crystal polyester monofilament, the comprehensive performance of the obtained liquid crystal polyester monofilament is better.

[0018] As a preferred embodiment of the liquid crystal polyester described in the present invention, the non-Newtonian index of the liquid crystal polyester at the melting point T m +25 °C is 0.44-0.62.

[0019] Exemplarily, the non-Newtonian index of the liquid crystal polyester at the melting point T m +25 °C can be any point value or any two-point range value between 0.44-0.62. For example, it can be 0.49-0.55, or it can be 0.44, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, etc.

[0020] Preferably, the non-Newtonian index of the liquid crystal polyester at the melting point T m +25 °C is 0.50-0.53.

[0021] It should be noted that the test method for the non-Newtonian index of the liquid crystal polyester at the melting point T m +25 °C is as follows: use a Malvern capillary rheometer for testing, and measure with a die having an inner diameter of 1 mm and a length of 20 mm. The test temperature is the melting point T m +25 °C, the shear rate is 1000-6000 s -1 , and take a point every 1000 s -1 . Respectively, with the natural logarithm of the obtained viscosity result as the Y-axis and the natural logarithm of the shear rate as the X-axis, after linearly fitting the points on the graph, the slope of the fitting line plus 1 is the non-Newtonian index of the liquid crystal polyester at the melting point T m +25 °C. The non-Newtonian index is a physical quantity of the viscosity-shear dependence of polymers. At the same time, to a certain extent, it can also indirectly characterize the molecular weight distribution of polymers. The higher the non-Newtonian index, the narrower the molecular weight distribution; the research of the present invention finds that if the non-Newtonian index is too high, it is very difficult to draw the fiber thinner during the preparation process; if the non-Newtonian index is too low, the instantaneous strength of the melt at the die exit is too low, and the fiber is prone to be broken; when further selecting the liquid crystal polyester at the melting point T mThe non-Newtonian index at +25°C is 0.44 - 0.62, especially when it is 0.50 - 0.53, when the obtained liquid crystal polyester is applied to the preparation of liquid crystal polyester monofilaments, the obtained liquid crystal polyester monofilaments have smaller diameter fluctuations, higher strength and smaller fluctuations, smaller modulus fluctuations and better creep resistance.

[0022] As a preferred embodiment of the liquid crystal polyester of the present invention, the shear viscosity of the liquid crystal polyester at a shear rate of 1000 s -1 is 35 - 40 Pa·s.

[0023] The present invention's research found that the shear viscosity also affects the properties of the obtained liquid crystal polyester monofilaments to a certain extent. When further selecting the shear viscosity of the liquid crystal polyester at a shear rate of 1000 s -1 to be 35 - 40 Pa·s, when the prepared liquid crystal polyester is applied to spin liquid crystal polyester monofilaments, the obtained liquid crystal polyester monofilaments have higher strength, more excellent dimensional stability, lower fluctuating modulus and better creep resistance.

[0024] As a preferred embodiment of the liquid crystal polyester of the present invention, the liquid crystal polyester includes monomer units represented by formula (1), formula (2) and formula (3):

[0025]

[0026] As a preferred embodiment of the liquid crystal polyester of the present invention, based on the total molar amount of all monomer units constituting the liquid crystal polyester, 65% < the molar content of formula (1) < 80%.

[0027] Exemplarily, based on the total molar amount of all monomer units constituting the liquid crystal polyester, the molar content of formula (1) can be 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, etc.

[0028] As a preferred embodiment of the liquid crystal polyester of the present invention, based on the total molar amount of all monomer units constituting the liquid crystal polyester, in the monomer units of formula (1), the molar content of the monomer units in which the hydroxyl group and the carboxyl group are in the meta position < 5%.

[0029] Exemplarily, based on the total molar amount of all monomer units constituting the liquid crystal polyester, in the monomer units of formula (1), the molar content of the monomer units in which the hydroxyl group and the carboxyl group are in the meta position can be 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 4.8%, 4.9%, etc.

[0030] As a preferred embodiment of the liquid crystal polyester of the present invention, based on the total molar amount of all monomer units constituting the liquid crystal polyester, 18% < the molar content of formula (2) < 35%.

[0031] Exemplarily, based on the total molar amount of all monomer units constituting the liquid crystal polyester, the molar content of formula (2) may be 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 35%, etc.

[0032] As a preferred embodiment of the liquid crystal polyester of the present invention, based on the total molar amount of all monomer units constituting the liquid crystal polyester, 0 ≤ the molar content of formula (3) < 2%.

[0033] Exemplarily, based on the total molar amount of all monomer units constituting the liquid crystal polyester, the molar content of formula (3) may be 0, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 1.9%, etc.

[0034] The present invention has found through research that when further selecting, based on the total molar amount of all monomer units constituting the liquid crystal polyester, the molar contents of the monomer units represented by formula (1), formula (2), and formula (3) are within the above ranges; at the same time, when the molar content of the monomer unit in which the hydroxyl group and the carboxyl group are in the meta position in the monomer unit of formula (1) is within the above range, the obtained liquid crystal polyester has better continuous spinnability, and the size stability of the liquid crystal polyester monofilaments formed by spinning is better, the creep resistance is better, and the strength is higher.

[0035] In the second aspect of the present invention, the present invention provides a method for preparing the liquid crystal polyester, and the preparation method includes the following steps: mixing an acylating agent, a monomer, and a catalyst, and then carrying out an acylation reaction at 100 - 145°C under an inert gas pressurized environment. After the acylation reaction is completed, the pressure is reduced to normal pressure and the temperature is raised to 300 - 360°C for a polycondensation reaction, then stirring is carried out under vacuum conditions, and finally discharging and pelletizing to obtain the liquid crystal polyester.

[0036] As a preferred embodiment of the preparation method of the present invention, the acylating agent includes acetic anhydride.

[0037] As a preferred embodiment of the preparation method of the present invention, the catalyst includes at least one of potassium acetate, magnesium acetate, titanium dioxide, antimony trioxide, alkoxytitanium, potassium sulfate, and boron trifluoride.

[0038] Preferably, the catalyst includes magnesium acetate.

[0039] As a preferred embodiment of the preparation method of the present invention, the monomer includes at least one of p-hydroxybenzoic acid and m-hydroxybenzoic acid and at least one of 2-hydroxy-6-naphthoic acid and terephthalic acid.

[0040] As a preferred embodiment of the preparation method of the present invention, based on the total moles of the monomers, the added molar amount of the acylating agent is 1.01 - 1.05 times the total molar amount of hydroxyl groups in the monomers, and the mass of the catalyst is 0.002 - 0.008% of the monomer feed amount.

[0041] As a preferred embodiment of the preparation method of the present invention, the inert gas includes at least one of nitrogen, argon, and helium.

[0042] As a preferred embodiment of the preparation method of the present invention, the heating rate during heating is 0.5 - 2 °C / min.

[0043] In the third aspect of the present invention, the present invention provides a liquid crystal polyester monofilament, which is prepared using the liquid crystal polyester of the present invention.

[0044] As a preferred embodiment of the liquid crystal polyester monofilament of the present invention, the average diameter of the liquid crystal polyester monofilament is 50 - 300 μm.

[0045] As a preferred embodiment of the liquid crystal polyester monofilament of the present invention, the fluctuation of the tensile modulus of the liquid crystal polyester monofilament is ≤ 9.3.

[0046] As a preferred embodiment of the liquid crystal polyester monofilament of the present invention, when the liquid crystal polyester monofilament is under a 30% load of the breaking strength, the creep rate after 100 h is ≤ 0.16%.

[0047] In the fourth aspect of the present invention, the present invention provides a preparation method of the liquid crystal polyester monofilament, and the preparation method includes the following steps: melting and plasticizing the liquid crystal polyester and then spinning to obtain the liquid crystal polyester monofilament.

[0048] Preferably, the winding speed during the spinning process is 30 - 420 m / min.

[0049] Preferably, the spinning temperature is 25 - 35 °C above the melting point temperature of the liquid crystal polyester.

[0050] In the fifth aspect of the present invention, the present invention provides a fiber structure, which includes the liquid crystal polyester monofilament of the present invention.

[0051] Exemplarily, the fiber structure includes, but is not limited to, cables, filter membrane materials, and fiber cloth.

[0052] Compared with the prior art, the beneficial effects of the present invention are:

[0053] The viscous flow activation energy of a liquid crystal polyester provided by the present invention and at 1000 s -1The shear viscosity at a specific shear rate is within a specific range, which can be effectively applied to spinning, especially suitable for the spinning of liquid crystal polyester monofilaments, and has excellent continuous spinnability. During the spinning process, the fiber is easily drawn thin without breaking, and the obtained liquid crystal polyester monofilaments have a uniform diameter distribution, excellent dimensional stability, and creep resistance. At the same time, the prepared liquid crystal polyester monofilaments have high strength, and small fluctuations in strength and modulus. Detailed Embodiments

[0054] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0055] The reagents, methods, and equipment used in the present invention are all conventional reagents, methods, and equipment in the art, unless otherwise specified.

[0056] p-Hydroxybenzoic acid, m-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, terephthalic acid, magnesium acetate, and acetic anhydride were all purchased from Aladdin Reagents.

[0057] Examples 1-9 and Comparative Examples 1-6

[0058] The embodiments and comparative examples of the present invention provide a liquid crystal polyester, and the preparation method of the liquid crystal polyester is as follows:

[0059] (1) Under nitrogen conditions, the monomers were mixed and added to the reaction kettle according to Table 1, and then an acylating agent (acetic anhydride) and a catalyst (magnesium acetate) were added for acylation reaction; wherein, based on the total moles of the monomers, the addition amount of the acylating agent was 105%, and the addition amount of the catalyst was 0.004%;

[0060] (2) After the acylation reaction was completed, the pressure was reduced to atmospheric pressure, and the temperature was raised to a specific temperature at a certain heating rate for polycondensation reaction, and by-products were discharged during the polycondensation reaction;

[0061] (3) After the polycondensation reaction was completed, the vacuum was evacuated and stirred at a speed of 50 rpm, and finally the material was discharged and pelletized to obtain the liquid crystal polyester;

[0062] Among them, the temperature and time of the acylation reaction, and the heating rate and the temperature after heating of the polycondensation reaction are as described in Table 1.

[0063] The melting point, viscous flow activation energy, non-Newtonian index at the melting point T m +25 °C, and the shear viscosity at a shear rate of 1000 s -1 and the continuous spinnability test methods are as follows:

[0064] 1) Melting point: measured by NETZSCH DSC 200F3, with a heating rate of 20°C / min, from room temperature to 360°C above the melting point, then cooled to room temperature at 20°C / min, and finally heated to 30°C above the melting point at 20°C / min; the highest point of the melting peak of the second heating curve is taken as the melting point;

[0065] 2) Viscous flow activation energy: tested using a Malvern capillary rheometer, using a die with an inner diameter of 1 mm and a length of 20 mm. The test temperature is the melting point T m +5℃、T m +10℃、T m +20℃、T m +30℃, variable shear rate mode, shear rate 1000-5000s -1 Variable shear rate, every 1000s -1 Take the shear rate of 5000s at different test temperatures -1 The viscosity data at 100° is measured with a die having an inner diameter of 1 mm and a length of 20 mm; after the measurement, the Arrhenius equation is used to draw a graph, with the inverse of the test temperature (absolute temperature) as the X-axis and the natural logarithm of the melt viscosity as the Y-axis. After the points on the graph are linearly fitted, the slope of the fitted straight line is the viscosity activation energy of the liquid crystal polyester;

[0066] 3) At the melting point T m Non-Newtonian index at +25°C: tested using a Malvern capillary rheometer, using a die with an inner diameter of 1 mm and a length of 20 mm. The test temperature is the melting point T m +25℃, shear rate 1000-6000s -1 , every 1000s -1 Take a point to get the natural logarithm of the viscosity result as the Y axis, the natural logarithm of the shear rate as the X axis, and after linear fitting of the points on the graph, the slope of the fitting line plus 1 is the liquid crystal polyester at the melting point T m Non-Newtonian index at +25°C;

[0067] 4) In 1000s -1 Shear viscosity at a shear rate of: tested using a Malvern capillary rheometer, the test temperature is the melting point T m +20℃, shear rate 1000s -1 , using a die with an inner diameter of 1 mm and a length of 20 mm, the liquid crystal polyester was measured at 1000 s -1 Shear viscosity at a shear rate of

[0068] 5) Continuous spinnability: The liquid crystal polyester is continuously spun at a temperature equal to the melting point T m+30 °C; The evaluation criteria are as follows: continuous filament spinning for more than 24 h is excellent; continuous filament spinning for 6 - 24 h is good; continuous filament spinning for 1 - 6 h is poor; and inability to form filaments is extremely poor.

[0069] Among them, the monomer composition (mole percentage) of the liquid crystal polyester, as well as the melting point, viscous flow activation energy, and non-Newtonian index of the prepared liquid crystal polyester at T m +25 °C, and the shear viscosity test results at a shear rate of 1000 s -1 are shown in Table 1;

[0070] It should be noted that when the liquid crystal polyester monomer composition and reaction parameters in Table 1 are the same, liquid crystal polyesters with different viscous flow activation energies, shear viscosities at a shear rate of 1000 s -1 and non-Newtonian indices can be obtained by adjusting the polycondensation reaction time;

[0071] Table 1

[0072]

[0073]

[0074] Application Examples 1 - 9 and Comparative Application Examples 1 - 3

[0075] The application examples and comparative application examples of the present invention provide a liquid crystal polyester monofilament. The preparation methods of the liquid crystal polyester monofilaments provided in Application Examples 1 - 9 and Comparative Application Examples 1 - 3 are as follows: After melting and plasticizing the liquid crystal polyester, spinning is carried out at the melting point T m +30 °C to obtain a liquid crystal polyester monofilament; among them, the winding speed during the spinning process is 100 m / min; after winding into a roll, it is baked in a nitrogen atmosphere at 40 °C below the melting point of the raw filament for 48 h to obtain a finished liquid crystal polyester monofilament roll.

[0076] The liquid crystal polyesters used in Application Examples 1 - 9 are the liquid crystal polyesters prepared in Examples 1 - 9 respectively. The liquid crystal polyester used in Comparative Application Example 1 is the liquid crystal polyester prepared in Comparative Example 1. The liquid crystal polyester used in Comparative Application Example 2 is the liquid crystal polyester prepared in Comparative Example 3. The liquid crystal polyester used in Comparative Application Example 3 is the liquid crystal polyester prepared in Comparative Example 4; Since the spinnability of the liquid crystal polyester prepared in Comparative Example 2 is extremely poor, it cannot be spun.

[0077] The only difference between Application Example 10 and Application Example 1 is that the winding speed during the preparation of the liquid crystal polyester monofilament is 400 m / min.

[0078] The only difference between Application Example 11 and Application Example 1 is that the winding speed during the preparation of the liquid crystal polyester monofilament is 36 m / min.

[0079] The only difference between Application Example 12 and Application Example 1 is that the spinning is carried out at 300 °C during the preparation of the liquid crystal polyester monofilament.

[0080] The only difference between Application Example 13 and Application Example 1 is that the spinning is carried out at 330 °C during the preparation of the liquid crystal polyester monofilament.

[0081] Effect Example

[0082] The effect example of the present invention explores the properties of the liquid crystal polyester monofilaments prepared in Application Examples 1-13 and Comparative Application Examples 1-3, including the following aspects:

[0083] 1) Diameter and diameter fluctuation: Take a 1 m long sample every 1000 m, place it in alcohol and ultrasonically clean to remove the sizing agent. After drying, randomly cut ten 1 cm long samples, place them on a sample stage with conductive adhesive and spread them out. Measure the fiber diameter using a scanning electron microscope (SEM). Take three samples from each roll of fiber, and calculate the average value of all results as the fiber diameter, and the standard deviation as the diameter fluctuation;

[0084] 2) Tensile strength and tensile strength fluctuation: Refer to the standard GB / T 19975-2005, and test using a universal tensile testing machine. The test fixture is a fiber fixture, the fixture spacing is 10 cm, the tensile speed is 50 mm / min, each sample is tested 5 times, calculate the average value to obtain the strength, and the standard deviation is the tensile strength fluctuation;

[0085] 3) Tensile modulus fluctuation: Refer to the standard GB / T 19975-2005, and test using a universal tensile testing machine. The test fixture is a fiber fixture, the fixture spacing is 10 cm, the tensile speed is 50 mm / min. In the strain range of 0.05%-0.25%, the slope of the stress-strain curve is the tensile modulus of the test sample. Each sample is tested 5 times, calculate the average value to obtain the tensile modulus, and the standard deviation is the tensile modulus fluctuation;

[0086] 4) Creep rate: Take a 1 m long sample every 1000 m, a total of 5 samples. Refer to the standard GB / T19975-2005, and test using a universal tensile testing machine. The test fixture is a fiber fixture, the fixture spacing is 1 m, the tensile speed is 50 mm / min, test the tensile force when the fiber breaks, and calculate the average value to obtain F; then take 5 samples of 1.5 m long every 1000 m, make two marks in the middle, and the mark spacing is 1 m (L 0 ). Hang a weight of 0.3F on each sample. After 100 h, re-measure the distance L between the two marks. Then the creep rate of the sample is (L-L 0 ) / L 0 *100%;

[0087] The results obtained are shown in Table 2;

[0088] Table 2

[0089]

[0090]

[0091] As can be seen from Table 2, the liquid crystal polyester monofilaments prepared by applying the liquid crystal polyester provided by the present invention have excellent comprehensive properties. Specifically, the diameter fluctuation is within 5.23, the tensile strength is above 8.7 cN / dtex, the tensile strength fluctuation is within 1.91, the tensile modulus is above 356 cN / dtex, the tensile modulus fluctuation is within 9.24, and the creep rate is below 0.16%.

[0092] As can be seen from Application Examples 1-9 and Comparative Application Examples 1-3, the viscous flow activation energy of the liquid crystal polyester and the shear viscosity at a shear rate of 1000 s -1 will have an obvious influence on the properties of the liquid crystal polyester monofilaments prepared; when further selecting the viscous flow activation energy of the liquid crystal polyester and the shear viscosity at a shear rate of 1000 s -1 within the preferred range, the comprehensive properties of the corresponding liquid crystal polyester monofilaments prepared are more excellent. Specifically, the diameter fluctuation is within 2.79, the tensile strength is above 11.5 cN / dtex, the tensile strength fluctuation is within 1.31, the tensile modulus is above 420 cN / dtex, the tensile modulus fluctuation is within 7.16, and the creep rate is below 0.13%.

[0093] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A liquid crystal polyester, characterized in that: The liquid crystal polyester meets the following conditions: a. Viscous flow activation energy is 70-150kJ / mol; b. In 1000s -1 The shear viscosity at the shear rate is 25-47 Pa·s.

2. The liquid crystal polyester according to claim 1, characterized in that: The liquid crystal polyester satisfies at least one of the following: c. Viscous flow activation energy is 95-120 kJ / mol; d. At the melting point T m The non-Newtonian index at +25°C is 0.44-0.62; e. In 1000s -1 The shear viscosity at a shear rate of 35-40 Pa·s.

3. The liquid crystal polyester according to claim 1, characterized in that: The liquid crystal polyester comprises monomer units represented by formula (1), formula (2) and formula (3):

4. The liquid crystal polyester according to claim 3, characterized in that: Based on the total molar amount of all monomer units constituting the liquid crystal polyester, at least one of the following is satisfied: f. 65%<the molar content of formula (1)<80%; g. In the monomer units of formula (1), the molar content of the monomer units in which the hydroxyl group and the carboxyl group are in the meta position is less than 5%; h. 18%<the molar content of formula (2)<35%; i.0≤The molar content of formula (3)<2%.

5. The method for preparing a liquid crystal polyester according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: The acylating agent, monomer and catalyst are mixed and subjected to acylation reaction at 100-145°C under an inert gas pressurized environment. After the acylation reaction, the pressure is reduced to normal pressure and the temperature is raised to 300-360°C for polycondensation reaction, followed by stirring under vacuum conditions, and finally discharge and pelletize to obtain liquid crystal polyester.

6. The preparation method according to claim 5, characterized in that: The acylating agent includes acetic anhydride; The catalyst includes at least one of potassium acetate, magnesium acetate, titanium dioxide, antimony trioxide, alkoxy titanium, potassium sulfate, and boron trifluoride; The monomers include at least one of p-hydroxybenzoic acid and m-hydroxybenzoic acid and at least one of 2-hydroxy-6-naphthoic acid and terephthalic acid.

7. A liquid crystal polyester monofilament, characterized in that: The liquid crystal polyester monofilament is prepared using the liquid crystal polyester as described in any one of claims 1 to 4.

8. The liquid crystal polyester monofilament according to claim 7, characterized in that: The average diameter of the liquid crystal polyester monofilament is 50-300 μm; and / or, the tensile modulus fluctuation of the liquid crystal polyester monofilament is ≤9.3; And / or, the liquid crystal polyester monofilament has a creep rate of ≤0.16% after 100 hours under a load of 30% of the breaking strength.

9. The method for preparing a liquid crystal polyester monofilament according to claim 7 or 8, characterized in that: The preparation method comprises the following steps: melting and plasticizing the liquid crystal polyester and then spinning it to obtain liquid crystal polyester monofilaments; Preferably, the winding speed during the spinning process is 30-420 m / min; Preferably, the spinning temperature is 25-35° C. above the melting point of the liquid crystal polyester.

10. A fiber structure, characterized in that: At least comprises the liquid crystal polyester monofilament as described in any one of claims 7 to 9.

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