Liquid crystal polyester, polymerization method thereof and liquid crystal polyester composition

Abstract

The invention discloses a liquid crystal polyester, which is derived from the following repetitive units in molar percentage:-40-70 mol% of O-Ar1-CO; 15 to 30 mol% of-CO-Ar < 2->-CO <->; 15 to 30 mol% of-O-Ar3-O <->; -O-Ar1-CO-is one of a phenylene group and a naphthylene group; -CO-Ar2-CO-is one of a phenylene group, a naphthylene group and a biphenylene group; -O-Ar3-O-is one of a phenylene group, a naphthylene group and a biphenylene group; the initial melting temperature of the liquid crystal polyester is more than 400 DEG C, and the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is less than 0.5. According to the invention, the liquid crystal polyester has high initial melting temperature and low melting enthalpy ratio (i.e., the ratio of melting enthalpy of the highest melting point to melting enthalpy of the lowest melting point is less than 0.50), so that the liquid crystal polyester has the characteristics of low corrosion rate and good fluidity at high temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a liquid crystal polyester and a polymerization method thereof and a liquid crystal polyester composition. Background Art

[0002] Fully aromatic liquid crystal polymer (LCP) is an anisotropic aromatic polymer material composed of rigid molecular segments. LCP has a rigid structure of aromatic rings and regular molecular segments. This microstructure determines that the material has excellent properties such as high fluidity, high heat resistance, low dielectric properties, excellent mechanical properties, self-flammability, and chemical corrosion resistance. The material is used in the fields of electronics and electrical, 5G communications, electronics and electrical appliances, aerospace, etc.

[0003] In recent years, the field of new energy vehicles has developed rapidly. As the core component of new energy vehicles, power batteries provide power for vehicles and largely determine the usability, reliability and safety of vehicles. The power cells and battery packs of new energy batteries need to be overlapped and butted in explosion-proof valves, poles, injection holes, shell seals, pole ears and busbars. With the continuous improvement of battery processing precision, the thickness of parts is less than 1 mm, and the supporting packaging materials also need to be refined. Thin parts require materials with good fluidity. However, the traditional arc welding method has a large welding area, and it is difficult to achieve satisfactory welding effects in the processing of miniaturized parts. A new laser welding method is required. Compared with traditional methods, laser arc welding has the characteristics of high energy density, high flexibility and good accessibility. In higher energy and higher temperature laser welding molding, the instantaneous temperature of the encapsulated polymer material is higher than 400°C. Such extreme working conditions require the material to have higher heat resistance. Therefore, the LCP material with higher heat resistance and high fluidity gradually replaces the traditional PPS material and becomes the development trend of industry material upgrading. Summary of the invention

[0004] The object of the present invention is to provide a liquid crystal polyester which is not easily eroded under high temperature melting and has good fluidity, a polymerization method thereof and a composition containing the liquid crystal polyester.

[0005] The present invention is achieved through the following technical solutions: A liquid crystal polyester derived, in mole percent, from the following repeating units: -O-Ar1-CO-unit 40-70 mol%; -CO-Ar2-CO- units 15-30 mol%; -O-Ar3-O-unit 15-30mol%; The -O-Ar1-CO- unit is derived from at least one of 4-hydroxybenzoic acid, 3-hydroxy-2-naphthoic acid, and 1-hydroxy-2-naphthoic acid; The -CO-Ar2-CO- unit is derived from at least one of terephthalic acid, 2,6-naphthalene dicarboxylic acid, and 4,4'-biphenyl dicarboxylic acid; The -O-Ar3-O- unit is derived from at least one of hydroquinone, 2,6-naphthalene diol, and 4,4'-dihydroxybiphenyl; The initial melting temperature of the liquid crystal polyester is greater than 400° C., the liquid crystal polyester has two melting peaks within the temperature range of 350-480° C., and the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is less than 0.5.

[0006] Initial melting temperature: measured by NETZSCH DSC 200 F3, from room temperature, the temperature is increased at a heating rate of 20℃ / min to the melting point + (20~80)℃ maximum temperature, and then the temperature is cooled to room temperature at a rate of 20℃ / min after staying at this temperature for 2 minutes. The test sample is kept at room temperature for 2 minutes and then heated again at a heating rate of 20℃ / min to the melting point + (20~80)℃ maximum temperature to obtain the second melting curve of the polymer. The tangent of the rising curve before the low-temperature peak and the baseline is selected, and the temperature corresponding to the intersection is the initial melting temperature (the initial melting temperature is the lowest melting point).

[0007] The testing method for the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point in the temperature range of 350-480°C is as follows: the temperature is increased from room temperature to a maximum temperature of 30°C higher than the highest melting point of the liquid crystal polyester at a heating rate of 20°C / min at a heating rate of 20°C / min, the temperature is kept constant at this temperature for 3 minutes, and then the temperature is lowered to room temperature at a rate of 20°C / min. After the test sample is kept at room temperature for 3 minutes, the temperature is again increased to a maximum temperature of 30°C higher than the highest melting point of the liquid crystal polyester at a heating rate of 20°C / min to obtain the second melting curve of the polymer. The melting peaks in the temperature range of the highest melting point and the lowest melting point are respectively selected and integrated to obtain the enthalpy value, and the ratio is the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point.

[0008] Preferably, the content of -O-Ar1-CO- units is 40-66 mol%, the content of -CO-Ar2-CO- units is 17-30 mol%, the content of -O-Ar3-O- units is 17-30 mol%, the initial melting temperature of the liquid crystal polyester is >403°C, the liquid crystal polyester has two melting peaks in the temperature range of 350-480°C, and the ratio of the melting enthalpy of the highest melting point / the melting enthalpy of the lowest melting point is <0.40.

[0009] More preferably, the content of -O-Ar1-CO- units is 40-62 mol%, the content of -CO-Ar2-CO- units is 19-30 mol%, the content of -O-Ar3-O- units is 19-30 mol%, the initial melting temperature of the liquid crystal polyester is >406°C, the liquid crystal polyester has two melting peaks in the temperature range of 350-480°C, and the ratio of the melting enthalpy of the highest melting point / the melting enthalpy of the lowest melting point is <0.35.

[0010] Preferably, the -O-Ar1-CO- unit is derived from 4-hydroxybenzoic acid, the -CO-Ar2-CO- unit is derived from terephthalic acid, and the -O-Ar3-O- unit is derived from 4,4'-dihydroxybiphenyl.

[0011] The melt viscosity of the liquid crystal polyester of the present invention is in the range of 20-200 Pa.s. Melt viscosity: tested by Dynisco LCR7000 capillary rheometer, with the test temperature being 20°C above the lowest melting point and the shear rate being 1000S -1 , using a die with an inner diameter of 1mm and a length of 40mm, and preheating for 4 minutes to obtain the data.

[0012] Preferably, the initial melting temperature range of the liquid crystal polyester of the present invention is greater than 400° C. and less than 420° C. Preferably, the liquid crystal polyester has two melting peaks in the temperature range of 350-480° C., and the ratio of the melting enthalpy of the highest melting point / the melting enthalpy of the lowest melting point of the liquid crystal polyester is greater than 0.25 and less than 0.5.

[0013] The liquid crystal polyester of the present invention can be obtained by a conventional polymerization method, and the conventional process is as follows: (1) Acylation stage: The monomers corresponding to the -O-Ar1-CO- unit and the -O-Ar3-O- unit, the acylating agent and the catalyst are simultaneously added into the reactor for acylation reaction at a temperature of 130-160°C for 1.5-5h; (2) Polycondensation stage: melt polycondense the acylated reactant in step (1) with the monomer corresponding to the -CO-Ar2-CO- unit, heat the temperature to 280°C at a heating rate of 0.3-1.5°C / min, control the heating rate so that the heating time in the 280-300°C heating stage is maintained at 1-3h, and finally continue to heat the temperature at a heating rate of 0.3-1.5°C / min to 10-30°C above the lowest melting point, and continuously distill out by-products during the heating period; (3) Decompression and compression polymerization section: Decompression and compression polymerization is carried out, the target vacuum degree is 0.1 kPa ~ 40 kPa, the decompression and compression polymerization time is controlled within 3 hours, and the temperature of the prepolymer melt is finally controlled to be 10 ~ 30 ° C above the lowest melting point when discharged; (4) Solid-phase thickening: After reaching the target melt viscosity through a one-step melt polymerization method, the melt is discharged in a molten state, and then cut or crushed after cooling to obtain a liquid crystal polyester.

[0014] Preferably, the liquid crystal polyester of the present invention is obtained by the following polymerization method, comprising the following steps: (1) Acylation stage: Add monomers, acylating agent and catalyst into the reactor and carry out acylation at 120-180°C for 0.5-6 hours; (2) Deacylation polycondensation: heating the temperature to 180-240°C at a heating rate of 0.5-2°C / min to carry out deacylation polycondensation reaction, during which the acylated byproduct acid is distilled out, and then heating the temperature at a heating rate of 0.083-0.25°C / min until the melt temperature is 20-50°C higher than the lowest melting point of the liquid crystal polymer, and the reaction is carried out at a constant temperature for 0-120 minutes; In the deacylation polycondensation step, the preferred range of the isothermal reaction time is 5-120 min; (3) Polymerization under reduced pressure: Polymerization under reduced pressure is carried out at a temperature between +10°C and +30°C, which is the lowest melting point of the liquid crystal polymer, and at a reduced pressure of 0.1-50 mmHg for 0.5-6 hours to obtain a prepolymer; (4) Solid phase viscosity enhancement: The generated prepolymer is solid-phase polymerized at a melting temperature below 10-80°C, and the vacuum degree is controlled below 1000 Pa.s. After 1-30 hours, a liquid crystal polyester with the expected melt viscosity is obtained.

[0015] The molar ratio of the acylating agent to the total molar amount of phenolic hydroxyl groups in the monomer is (1-1.2): 1; the acylating agent is selected from any one of acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, 2-ethylhexanoic anhydride, dichloroacetic anhydride or difluoroacetic anhydride; the amount of the catalyst added is 20-2000ppm of the theoretical output; the catalyst is selected from organic imidazole compounds; the organic imidazole compound is selected from any one of 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 4-ethylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole, 2,4-dimethylimidazole. A liquid crystal polyester composition, in parts by weight, comprises the following components: 45-78 parts of the liquid crystal polyester of the present invention; 22-55 parts of reinforcing material.

[0016] The reinforcing material is selected from at least one of a fibrous reinforcing filler and a granular reinforcing filler, wherein the aspect ratio of the fibrous filler is 600:1-100:1, and the average particle size of the granular reinforcing filler is less than 100 microns.

[0017] The testing method for the aspect ratio of the fibrous filler is: place the sample under a two-dimensional imaging instrument, measure the length and diameter of the fibrous filler after magnification, and calculate the ratio as the aspect ratio.

[0018] The average particle size of the granular reinforcing filler is measured by a laser particle size analyzer.

[0019] The fibrous reinforcing filler is selected from at least one of glass fiber, potassium titanate fiber, ceramic fiber, wollastonite fiber, metal carbide fiber, metal solidified fiber, asbestos fiber, alumina fiber, silicon carbide fiber, gypsum fiber, boron fiber, potassium titanate whisker, zinc oxide whisker, and aluminum borate whisker.

[0020] The granular reinforcing filler is selected from at least one of talc, carbon black, gypsum, asbestos, zeolite, sericite, kaolin, montmorillonite, clay, hectorite, synthetic mica, aluminosilicate, silicon dioxide, titanium oxide, aluminum oxide, zinc oxide, zirconium oxide, iron oxide, magnesium titanate, dolomite, aluminum sulfate, barium sulfate, magnesium sulfate, calcium carbonate, mica, quartz powder, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, glass beads, ceramic beads, boron nitride, and silicon carbide.

[0021] A thin-walled article is made from the liquid crystal polyester composition, wherein the wall thickness of the article is less than 1 mm.

[0022] The present invention also relates to the application of thin-walled parts in laser welding.

[0023] The present invention has the following beneficial effects: The present invention designs the liquid crystal polyester repeating unit, controls the initial melting temperature to be greater than 400°C, and the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point within the temperature range of 350-480°C to be less than 0.5, so that the liquid crystal polyester of the present invention exhibits a high temperature, low melting rate, and good fluidity, and is suitable for thin-walled parts that are suitable for laser welding. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0025] The sources of experimental raw materials used in the present invention are as follows: 4-Hydroxybenzoic acid: Sigma-Aldrich, purity>99%; 3-Hydroxy-2-naphthoic acid: Sigma-Aldrich, purity > 99%; 1-Hydroxy-2-naphthoic acid: Sigma-Aldrich, purity > 99%; 2-Hydroxy-6-naphthoic acid: Sigma-Aldrich, purity > 99%; Terephthalic acid: Sigma-Aldrich, purity > 99%; 2,6-Naphthalenedicarboxylic acid: Sigma-Aldrich, purity>99%; 4,4'-Biphenyldicarboxylic acid: Sigma-Aldrich, purity > 99%; Hydroquinone: Sigma-Aldrich, purity>99%; Resorcinol: Sigma-Aldrich, purity>99%; 2,6-Naphthalenediol: Sigma-Aldrich, purity>99%; 4,4'-Dihydroxybiphenyl: Sigma-Aldrich, purity>99%; Fiberglass: Owens Corning; Talc: Qingdao Kaiwell Powder Engineering Technology Co., Ltd.

[0026] Preparation method of liquid crystal polyester in Example A1-A6: Acylation stage: monomers corresponding to -O-Ar1-CO- unit and -O-Ar3-O- unit, acylating agent (acetic anhydride, the molar ratio of acetic anhydride to the total molar amount of phenolic hydroxyl groups in the monomer is 1.1:1), and catalyst (1-methylimidazole, 800 ppm of theoretical output) are simultaneously added into a reactor, and acylation reaction is carried out at 150°C for 3-4h; Polycondensation stage: melt polycondensation is carried out on the acylated reactants and the monomers corresponding to the -CO-Ar2-CO- unit, and the temperature is raised to 280°C at a heating rate of 1.0°C / min, and then the temperature is controlled to The heating rate is such that the heating time in the 280-300°C heating section is maintained at 1.5-2.5h, and finally the heating rate of 1°C / min is continued to be used to heat the temperature to 20°C above the lowest melting point, and by-products are continuously distilled during the heating period; reduced pressure polymerization section: reduced pressure polymerization is carried out, the target vacuum degree is 10kPa-20kPa, the reduced pressure polymerization time is controlled within 3 hours, and finally the temperature of the prepolymer melt is controlled to be 20°C above the lowest melting point during discharge; solid phase viscosity enhancement: after reaching the target melt viscosity through a one-step melt polymerization method, the melt is discharged in a molten state, and cut or crushed after cooling to obtain liquid crystal polyester.

[0027] Polymerization method of liquid crystal polyester of Examples A7-A16 and Comparative Examples B1-B7: Acylation stage: each monomer, acylating agent (acetic anhydride, the molar ratio of acetic anhydride to the total molar amount of phenolic hydroxyl groups in the monomer is 1.1:1), and catalyst (1-methylimidazole, 800 ppm of theoretical output) are added to the reactor, and acylation is carried out at 140° C. for 3 hours; Deacylation polycondensation: the temperature is raised to 180-240° C. at a heating rate of 1° C. / min to carry out deacylation polycondensation reaction, during which the acylation byproduct acid is distilled out, and then the acylation byproduct acid is obtained according to the table The recorded heating rate is to increase the temperature until the melt temperature is 30°C higher than the lowest melting point of the liquid crystal polymer, and the reaction is carried out at a constant temperature for 60 minutes; reduced pressure polymerization: the reduced pressure polymerization reaction is carried out at the lowest melting point of the liquid crystal polymer +10°C ~ +30°C and a reduced pressure of 10-20 mmHg for 4 hours to obtain a prepolymer; solid phase viscosity enhancement: the produced prepolymer is solid-phase polymerized at a melting temperature below 10-80°C, and the vacuum degree is controlled below 1000 Pa.s. After 1-30 hours, a liquid crystal polyester with an expected melt viscosity is obtained.

[0028] Various test methods: (1) Melting enthalpy of the highest melting point / melting enthalpy ratio of the lowest melting point (referred to as high / low melting enthalpy ratio in the table): measured using DSC 200 F3 manufactured by NETZSCH. The temperature was raised from room temperature to a maximum temperature of 30°C above the highest melting point of the liquid crystal polyester at a heating rate of 20°C / min. The temperature was kept constant at this temperature for 3 min and then cooled to room temperature at a rate of 20°C / min. The test sample was kept at room temperature for 3 min and then heated again to a maximum temperature of 30°C above the highest melting point of the liquid crystal polyester at a heating rate of 20°C / min. The second melting curve of the polymer was obtained. The melting peaks in the temperature range of the highest melting point and the lowest melting point were selected and integrated to obtain the enthalpy value. The ratio was the ratio of the melting enthalpy of the highest melting point / the melting enthalpy of the lowest melting point.

[0029] (2) Melt viscosity: tested using a Dynisco LCR7000 capillary rheometer at a temperature of 20°C above the lowest melting point and a shear rate of 1000S. -1 , using a die with an inner diameter of 1mm and a length of 40mm, and preheating for 4 minutes to obtain the data.

[0030] (3) Fluidity: The length of a rod-shaped sheet injection molding with a size of 5*0.3 mm in width*thickness is used to characterize the fluidity of the liquid crystal polyester. The injection temperature is at the lowest melting point + 20°C, and the average length of 100 rod-shaped sheet injection moldings is used as a parameter to measure the fluidity of the liquid crystal polyester and its molding composition. Under the same injection molding conditions, the longer the length of the rod-shaped sheet injection molding, the better its fluidity.

[0031] (4) Initial melting temperature: measured by NETZSCH DSC 200 F3, starting from room temperature, the temperature is increased at a rate of 20°C / min to the melting point + (20-80)°C, then kept at this temperature for 2 min and then cooled to room temperature at a rate of 20°C / min. The test sample is kept at room temperature for 2 min and then heated again at a rate of 20°C / min to the melting point + (20-80)°C to obtain the second melting curve of the polymer. The tangent line of the rising curve before the low-temperature peak and the baseline is selected, and the temperature corresponding to the intersection is the initial melting temperature.

[0032] (5) Ablation rate: At 5°C above the melting temperature of the liquid crystal polyester composition and at an injection speed of 60 mm / s, the liquid crystal polyester composition was molded into a thin sheet sample with a thickness of 0.5 mm and a length and width of 60 mm. After the sample was heated in a 400°C tin bath for 30 seconds, 100 thin sheet samples were placed under a two-dimensional imaging instrument and observed at a magnification of 100 times to see whether there were appearance ablation defects (uneven appearance, irregular stripes, or other non-smooth morphology), and the number of pieces was recorded. Ablation rate = number of pieces with appearance ablation defects / total number of pieces*100%.

[0033] Table 1: Liquid crystal polyester A repeating unit mol% content and test results A-1 A-2 A-3 A-4 A-5 A-6 4-Hydroxybenzoic acid 46 40 66 70 3-Hydroxy-2-naphthoic acid 46 1-Hydroxy-2-naphthoic acid 46 Terephthalic acid 27 30 17 15 2,6-Naphthalene dicarboxylic acid 27 4,4'-Biphenyldicarboxylic acid 27 4,4'-Dihydroxybiphenyl 27 30 17 15 2,6-Naphthalenediol 27 Hydroquinone 27 Melt viscosity, Pa.s 66.3 69.5 63.8 65.6 68.5 64.2 Initial melting temperature, °C 401 406 402 402 400 411 High / low melting enthalpy ratio 0.33 0.38 0.36 0.34 0.44 0.49 Flowability, mm 53.3 51.3 51.9 52.6 50.6 49.8 Ablation rate, % 0 0 0 0 0 0 Table 1 continued: A-7 A-8 A-9 A-10 A-11 A-12 A-13 A-14 A-15 4-Hydroxybenzoic acid 46 40 62 66 70 42 38 3-Hydroxy-2-naphthoic acid 46 6 1-Hydroxy-2-naphthoic acid 46 12 Terephthalic acid 27 30 19 17 15 20 2,6-Naphthalene dicarboxylic acid 27 6 4,4'-Biphenyldicarboxylic acid 27 25 4,4'-Dihydroxybiphenyl 27 30 19 17 15 26 9 2,6-Naphthalenediol 27 Hydroquinone 27 16 Heating rate℃ / min 0.25 0.25 0.25 0.15 0.2 0.25 0.25 0.083 0.25 Melt viscosity, Pa.s 65.1 70.3 68.2 66.7 71.5 68.9 67.3 71.8 72.1 Initial melting temperature, °C 404 411 406 405 409 403 415 410 403 High / low melting enthalpy ratio 0.26 0.32 0.31 0.29 0.34 0.39 0.46 0.34 0.32 Flowability, mm 55.6 55.3 54.2 53.3 52.8 51.8 50.2 54.8 54.2 Ablation rate, % 0 0 0 0 0 0 0 0 0 It can be seen from the above-mentioned Example A that the preferred process can further increase the initial melting temperature and reduce the high / low melting enthalpy ratio.

[0034] It can be seen from the above Examples A7-A15 that the preferred monomers have a lower high / low melting enthalpy ratio and higher fluidity when compared with the molar content.

[0035] Table 2: Liquid crystal polyester B repeating unit mol% content and test results B-1 B-2 B-3 B-4 B-5 B-6 B-7 4-Hydroxybenzoic acid 46 42 38 72 38 46 2-Hydroxy-6-naphthoic acid 46 6 12 Terephthalic acid 27 27 20 14 31 27 2,6-Naphthalene dicarboxylic acid 6 4,4'-Biphenyldicarboxylic acid 25 4,4'-Dihydroxybiphenyl 27 26 9 14 31 27 Resorcinol 27 16 Melt viscosity, Pa.s 73.9 70.5 72.9 67.4 66.2 69.5 70.1 Heating rate℃ / min 0.25 0.25 0.25 0.25 0.25 0.25 1.5 Initial melting temperature, °C 385 390 376 356 366 346 391 High / low melting enthalpy ratio 0.53 0.57 0.56 0.49 0.62 0.53 0.58 Flowability, mm 40.5 30.7 35.6 47.5 22.3 46.3 37.5 Ablation rate, % 8 25 13 2 35 3 16 It can be seen from Comparative Examples B1-B7 that when the initial melting temperature, or the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is not within the scope of the present invention, the technical effect of the present invention cannot be achieved.

[0036] Table 3: Weight parts of each component of the liquid crystal polyester composition of the embodiment and comparative example and test results Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Liquid crystal polyester A-1 A-3 A-5 A-7 A-9 A-11 A-13 Liquid crystal polyester content 60 60 60 60 60 60 60 Fiberglass 40 40 40 40 40 40 talcum powder 40 Flowability, mm 45.5 41.3 42.0 42.5 40.9 39.9 45.5 Ablation rate, % 0 0 0 0 0 0 0 Table 3: Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Liquid crystal polyester B-1 B-2 B-3 B-4 B-5 B-6 Liquid crystal polyester content 60 60 60 60 60 60 Fiberglass 40 40 40 40 40 40 talcum powder Flowability, mm 32.6 24.6 28.7 38.2 18.3 37.2 Ablation rate, % 5 16 9 1 20 3 The preparation method of the liquid crystal polyester composition is as follows: the liquid crystal polyester composition and talcum powder (if any) are extruded and granulated through a twin-screw extruder, glass fiber is side-fed (if any), the screw barrel temperature is set to 460°C, and the rotation speed is 150r / min.

[0037] From the above examples, it can be seen that the initial melting temperature of the liquid crystal polyester of the present invention is greater than 400°C, the liquid crystal polyester has two melting peaks in the temperature range of 350-480°C, the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is less than 0.50, the fluidity is greater than 49 mm, and the ablation rate can reach 0%. The composition composed of the liquid crystal polyester of the present invention can have a fluidity greater than 39 mm and a ablation rate of 0%.

Claims

1. A liquid crystal polyester, characterized in that: In mole percent, derived from the following repeating units: A: -O-Ar1-CO- unit 40-70 mol%; B: -CO-Ar2-CO- unit 15-30mol%; C: -O-Ar3-O-unit 15-30 mol%; The -O-Ar1-CO- unit is derived from at least one of 4-hydroxybenzoic acid, 3-hydroxy-2-naphthoic acid, and 1-hydroxy-2-naphthoic acid; The -CO-Ar2-CO- unit is derived from at least one of terephthalic acid, 2,6-naphthalene dicarboxylic acid, and 4,4'-biphenyl dicarboxylic acid; The -O-Ar3-O- unit is derived from at least one of hydroquinone, 2,6-naphthalene diol, and 4,4'-dihydroxybiphenyl; The initial melting temperature of the liquid crystal polyester is greater than 400° C., the liquid crystal polyester has two melting peaks within the temperature range of 350-480° C., and the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is less than 0.

50.

2. The liquid crystal polyester according to claim 1, characterized in that: The content of -O-Ar1-CO- units is 40-66 mol%, the content of -CO-Ar2-CO- units is 17-30 mol%, the content of -O-Ar3-O- units is 17-30 mol%, the initial melting temperature of the liquid crystal polyester is >403°C, the liquid crystal polyester has two melting peaks in the temperature range of 350-480°C, and the ratio of the melting enthalpy of the highest melting point / the melting enthalpy of the lowest melting point is <0.

40.

3. The liquid crystal polyester according to claim 2, characterized in that: The content of -O-Ar1-CO- units is 40-62 mol%, the content of -CO-Ar2-CO- units is 19-30 mol%, the content of -O-Ar3-O- units is 19-30 mol%, the initial melting temperature of the liquid crystal polyester is >406°C, the liquid crystal polyester has two melting peaks in the temperature range of 350-480°C, and the ratio of the melting enthalpy of the highest melting point to the melting enthalpy of the lowest melting point is <0.

35.

4. The liquid crystal polyester according to claim 1, characterized in that: The -O-Ar1-CO- unit is derived from 4-hydroxybenzoic acid, the -CO-Ar2-CO- unit is derived from terephthalic acid, and the -O-Ar3-O- unit is derived from 4,4'-dihydroxybiphenyl; the melt viscosity of the liquid crystal polyester is in the range of 20-220 Pa.s.

5. The method for polymerizing a liquid crystal polyester according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Acylation stage: Add monomers, acylating agent and catalyst into the reactor and carry out acylation at 120-180°C for 0.5-6 hours; (2) Deacylation polycondensation: heating the temperature to 180-240°C at a heating rate of 0.5-2°C / min to carry out deacylation polycondensation reaction, during which the acylated byproduct acid is distilled out, and then heating the temperature at a heating rate of 0.083-0.25°C / min until the melt temperature is 20-50°C higher than the lowest melting point of the liquid crystal polymer, and the reaction is carried out at a constant temperature for 0-120 minutes; (3) Polymerization under reduced pressure: Polymerization under reduced pressure is carried out at a temperature between +10°C and +30°C, which is the lowest melting point of the liquid crystal polymer, and at a reduced pressure of 0.1-50 mmHg for 0.5-6 hours to obtain a prepolymer; (4) Solid phase viscosity enhancement: The generated prepolymer is subjected to solid phase polymerization at a melting temperature below 10-80°C, and the vacuum degree is controlled below 1000 Pa.s. After 1-30 hours, a liquid crystal polyester with the expected melt viscosity is obtained.

6. The polymerization method according to claim 5, characterized in that The molar ratio of the acylating agent to the total molar amount of phenolic hydroxyl groups in the monomer is (1-1.2): 1; the acylating agent is selected from any one of acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, 2-ethylhexanoic anhydride, dichloroacetic anhydride or difluoroacetic anhydride; the added amount of the catalyst is 20-2000ppm of the theoretical output amount; the catalyst is selected from organic imidazole compounds; the organic imidazole compound is selected from any one of 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 4-ethylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole and 2,4-dimethylimidazole.

7. A liquid crystal polyester composition, characterized in that: By weight, it includes the following components: 45-78 parts of the liquid crystal polyester according to any one of claims 1 to 4; 22-55 parts of reinforcing material.

8. The liquid crystal polyester composition according to claim 7, characterized in that: The reinforcing material is selected from at least one of fibrous reinforcing fillers and granular reinforcing fillers, wherein the aspect ratio of the fibrous filler is 600:1-100:1, and the average particle size of the granular reinforcing filler is less than 100 microns; the fibrous reinforcing filler is selected from at least one of glass fiber, potassium titanate fiber, ceramic fiber, wollastonite fiber, metal carbide fiber, metal solidified fiber, asbestos fiber, aluminum oxide fiber, silicon carbide fiber, gypsum fiber, boron fiber, potassium titanate whisker, zinc oxide whisker, and aluminum borate whisker; the granular reinforcing filler is selected from at least one of talc, carbon black, gypsum, asbestos, zeolite, sericite, kaolin, montmorillonite, clay, hectorite, synthetic mica, aluminosilicate, silicon dioxide, titanium oxide, aluminum oxide, zinc oxide, zirconium oxide, iron oxide, magnesium titanate, dolomite, aluminum sulfate, barium sulfate, magnesium sulfate, calcium carbonate, mica, quartz powder, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, glass beads, ceramic beads, boron nitride, and silicon carbide.

9. A thin-walled product, characterized in that: The article is made using the liquid crystal polyester composition according to claim 8 or 9.

10. Use of the thin-walled workpiece according to claim 9 in laser welding.