阅读说明：本技术 一种高韧性液晶聚合物薄膜及其制备方法 (High-toughness liquid crystal polymer film and preparation method thereof ) 是由 王阳 任忠平 周捷 于 2021-09-08 设计创作，主要内容包括：本发明属于高分子聚合物技术领域,具体涉及一种高韧性液晶聚合物薄膜及其制备方法。本发明的液晶聚合物薄膜,包括液晶聚合物,所述的液晶聚合物由以下单体制成：对羟基苯甲酸、6-羟基-2-萘甲酸、联苯二酚、四氟对苯二甲酸。制备步骤为预聚、固相缩聚、混炼、熔融挤出、牵伸、卷绕、热处理。本发明通过引入新型单体四氟对苯二甲酸与对羟基苯甲酸、6-羟基-2-萘甲酸、联苯二酚共聚,可显著提高液晶聚合物薄膜的韧性,将其经过－60℃～200℃冷热循环后无开裂现象,使用寿命进一步延长,能够更好适用于温差较大的环境。(The invention belongs to the technical field of high molecular polymers, and particularly relates to a high-toughness liquid crystal polymer film and a preparation method thereof. The liquid crystal polymer film comprises a liquid crystal polymer, wherein the liquid crystal polymer is prepared from the following monomers: p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol, tetrafluoroterephthalic acid. The preparation steps comprise prepolymerization, solid-phase polycondensation, mixing, melt extrusion, drafting, winding and heat treatment. According to the invention, by introducing a novel monomer of tetrafluoroterephthalic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and diphenol for copolymerization, the toughness of the liquid crystal polymer film can be obviously improved, the liquid crystal polymer film does not crack after being subjected to cold and heat cycles at-60-200 ℃, the service life is further prolonged, and the liquid crystal polymer film can be better suitable for environments with large temperature difference.)

1. A high toughness liquid crystalline polymer film comprising a liquid crystalline copolymer made from the following monomers:

p-hydroxybenzoic acid, having the formula:

6-hydroxy-2-naphthoic acid, the structural formula of which is:

biphenol having the structural formula:

tetrafluoroterephthalic acid having the formula:

the molar percentage of the p-hydroxybenzoic acid is 32-53 mol%, the molar percentage of the 6-hydroxy-2-naphthoic acid is 29-40 mol%, the sum of the molar percentages of the diphenol and the tetrafluoroterephthalic acid is 18-28 mol%, and the sum of the molar percentages of the four monomers is equal to 100 mol%.

2. The method for preparing a high toughness liquid crystal polymer film according to claim 1, wherein said method comprises the steps of

S1: putting monomers of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, diphenol, tetrafluoro terephthalic acid, an acetylation reagent of acetic anhydride, a catalyst of 4-dimethylamino pyrimidine and an antioxidant of tin powder into a Hastelloy polymerization kettle for prepolymerization to prepare a prepolymer;

s2: discharging the prepolymer from the Hastelloy kettle, crushing, and performing solid-phase polycondensation in a nitrogen atmosphere to obtain liquid crystal polymer powder;

s3: mixing the prepared liquid crystal polymer powder by a screw extruder, and exhausting; melt extrusion, and side blowing cooling; drafting and winding to prepare a liquid crystal polymer nascent film;

s4: and carrying out heat treatment on the prepared nascent film to obtain a finished liquid crystal polymer film.

3. The method for preparing a high toughness liquid crystal polymer film according to claim 2, wherein said acetic anhydride is added in an amount of 1.5 to 2.5 times the total mole number of hydroxyl groups in p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and biphenol in step S1.

4. The method for producing a high-toughness liquid-crystalline polymer film according to claim 2, wherein 4-dimethylaminopyrimidine is added in an amount of 80 to 400ppm based on the total weight of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol, and tetrafluoroterephthalic acid in step S1.

5. The method for preparing a high-toughness liquid crystal polymer film according to claim 2, wherein the tin powder is added in an amount of 0.15 to 0.45% by weight based on the total weight of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol, and tetrafluoroterephthalic acid in step S1.

6. The method for preparing a high-toughness liquid crystal polymer film according to claim 2, wherein the step S1 is specifically: putting the raw materials into a Hastelloy polymerization kettle, and keeping the temperature at 135-145 ℃ for 3-8 h; heating to 300-; and (3) flushing 0.1-1.0MPa of nitrogen into the polymerization kettle, discharging the prepolymer through a discharge valve with 8-10 holes and the diameter of 2-4mm, crushing, sieving with a 20-30 mesh sieve, and drying at 150 ℃ for 2-3h to obtain the prepolymer.

7. The method for preparing a high-toughness liquid crystal polymer film according to claim 2, wherein the step S2 is specifically: and carrying out solid phase polycondensation on the prepared prepolymer for 12-36h in a rotary kiln at the temperature of 190-300 ℃ under the protection of nitrogen to prepare the liquid crystal polymer.

8. The method for preparing a high-toughness liquid crystal polymer film according to claim 2, wherein the extrusion temperature of the screw extruder in the step S3 is 305-350 ℃.

9. The method for producing a high-toughness liquid crystalline polymer film according to claim 2, wherein the cross-blowing temperature in step S3 is 35 to 50 ℃ and the drawing speed is 5 to 40 m/min.

10. The method for preparing a high-toughness liquid crystal polymer film as claimed in claim 2, wherein the heat treatment temperature in step S4 is 230-310 ℃ and the time is 12-36 h.

Technical Field

The invention belongs to the technical field of high molecular polymerization, and particularly relates to a high-toughness liquid crystal polymer film and a preparation method thereof.

Background

Liquid Crystal Polymer (Liquid Crystal Polymer) has a large number of rigid benzene ring structures on the molecular main chain, generally has Liquid crystallinity in a molten state, has excellent heat resistance and molding processability, and is widely concerned and applied due to the excellent properties of high strength, high modulus, low humidity, chemical corrosion resistance, good weather resistance, flame resistance, high temperature thermal stability and the like.

LCP material can be processed into film product, and because the molecular skeleton symmetry of material is high, and the motion of main chain is restricted owing to liquid crystal self structure in addition, it shows extremely low dielectric constant and dielectric loss in the high frequency band, based on its excellent performance especially dielectric property widely used in aspects such as high-speed connector, 5G base station antenna oscillator, 5G cell-phone antenna, high frequency circuit board. In order to better apply liquid crystal film products to high-frequency 5G scenes, the existing research focuses more on improvement of dielectric properties, but due to the fact that actual use environment conditions of high-frequency equipment such as 5G equipment are complex and changeable, particularly when temperature difference changes greatly, the film cannot meet the requirements of expansion with heat and contraction with cold due to toughness limitation, cracking of the film is caused, and application of the high-frequency equipment such as 5G equipment is further influenced.

The expansion with heat and contraction with cold is the performance of the material along with the change of temperature, and the environment with large temperature difference requires the material to have corresponding toughness to adapt to the change of temperature. The liquid crystal polymer has a large number of rigid benzene ring structures on the main molecular chain, so that the liquid crystal polymer is not easy to change along with the temperature, and a film product prepared from the liquid crystal polymer is easy to crack in an environment with large temperature difference. In daily life, cutting lines on roads and bridges are a method for solving the problem of expansion caused by heat and contraction caused by cold. However, since the liquid crystal polymer film cannot use the method of cutting the line, it is necessary to solve the problem from the material itself.

Disclosure of Invention

The present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a high-toughness liquid crystal polymer film, in which the toughness of the liquid crystal polymer film can be greatly improved by introducing monomers of tetrafluoroterephthalic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and biphenol into the liquid crystal polymer and copolymerizing the monomers.

The above object of the present invention can be achieved by the following technical solutions: a high toughness liquid crystalline polymer film comprising a liquid crystalline copolymer made from the following monomers:

p-hydroxybenzoic acid, having the formula:

6-hydroxy-2-naphthoic acid, the structural formula of which is:

biphenol having the structural formula:

tetrafluoroterephthalic acid having the formula:

the molar percentage of the p-hydroxybenzoic acid is 32-53 mol%, the molar percentage of the 6-hydroxy-2-naphthoic acid is 29-40 mol%, the sum of the molar percentages of the diphenol and the tetrafluoroterephthalic acid is 18-28 mol%, and the sum of the molar percentages of the four monomers is equal to 100 mol%.

Preferably, the molar ratio of the diphenol to the tetrafluoroterephthalic acid is 1: 1.

the second object of the present invention is to provide a method for preparing the above high-toughness liquid crystal polymer film, wherein the method specifically comprises the following steps:

s1: putting monomers of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, diphenol, tetrafluoro terephthalic acid, an acetylation reagent of acetic anhydride, a catalyst of 4-dimethylamino pyrimidine and an antioxidant of tin powder into a Hastelloy polymerization kettle for prepolymerization to prepare a prepolymer;

s2: discharging the prepolymer from the Hastelloy kettle, crushing, and performing solid-phase polycondensation in a nitrogen atmosphere to obtain liquid crystal polymer powder;

s3: mixing the prepared liquid crystal polymer powder by a screw extruder, and exhausting; melt extrusion, and side blowing cooling; drafting and winding to prepare a liquid crystal polymer nascent film;

s4: and carrying out heat treatment on the prepared nascent film to obtain a finished liquid crystal polymer film.

The monomer polymerization of the invention adopts the catalyst 4-dimethylamino pyrimidine, which is beneficial to the reaction process, improves the conversion rate, generates high molecular weight polymer with narrow molecular weight distribution range, and is convenient for the subsequent film preparation. Whereas conventional melt polycondensation catalysts are: at least one of zinc acetate, manganese acetate, potassium acetate, lithium titanate, dibutyltin laurate, dibutyltin oxide, antimony trioxide or antimony acetate participates in the polymerization reaction, side reactions are more, the conversion rate is lower, and the prepared liquid crystal polymer has low molecular weight and cannot be used for preparing a film.

Preferably, the amount of the acetic anhydride added is 1.5 to 2.5 times the total molar number of hydroxyl groups in the p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and biphenol.

Preferably, the 4-dimethylamino pyrimidine is added in an amount of 80 to 400ppm based on the total weight of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid.

Preferably, the addition amount of the tin powder is 0.15-0.45 percent of the total weight of the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid, the diphenol and the tetrafluoroterephthalic acid.

Preferably, the step S1 is specifically: putting the raw materials into a Hastelloy polymerization kettle, and keeping the temperature at 135-145 ℃ for 3-8 h; heating to 300-; and (3) flushing 0.1-1.0MPa of nitrogen into the polymerization kettle, discharging the prepolymer through a discharge valve with 8-10 holes and the diameter of 2-4mm, crushing, sieving with a 20-30 mesh sieve, and drying at 150 ℃ for 2-3h to obtain the prepolymer.

Preferably, the step S2 is specifically: and carrying out solid phase polycondensation on the prepared prepolymer for 12-36h in a rotary kiln at the temperature of 190-300 ℃ under the protection of nitrogen to prepare the liquid crystal polymer.

The weight average molecular weight of the liquid crystal polymer prepared by the polymerization reaction is 3.25 multiplied by 10⁴The above.

Preferably, the extrusion temperature of the screw extruder in the step S3 is 305-350 ℃.

Preferably, the cross-blowing temperature in the step S3 is 35-50 ℃ and the drawing speed is 5-40 m/min.

Preferably, the heat treatment temperature in the step S4 is 230-310 ℃, and the time is 12-36 h.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, the tetrafluoroterephthalic acid, the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid and the diphenol are introduced for copolymerization, so that the molecular chain flexibility of the liquid crystal polymer can be improved, the toughness of the liquid crystal polymer film is further remarkably improved, the film product does not crack after being subjected to cold and heat cycles at-60-200 ℃, the service life is further prolonged, and the film product can be better suitable for an environment with larger temperature difference.

Detailed Description

The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the present invention is not limited to these examples. In the present invention, unless otherwise specified, the starting materials or reagents used are conventional ones, and the methods used are conventional ones.

Detailed description of the preferred embodiments

A high toughness liquid crystalline polymer film comprising a liquid crystalline copolymer made from the following monomers:

p-hydroxybenzoic acid, having the formula:

6-hydroxy-2-naphthoic acid, the structural formula of which is:

biphenol having the structural formula:

tetrafluoroterephthalic acid having the formula:

the molar percentage of the p-hydroxybenzoic acid is 32-53 mol%, the molar percentage of the 6-hydroxy-2-naphthoic acid is 29-40 mol%, the sum of the molar percentages of the diphenol and the tetrafluoroterephthalic acid is 18-28 mol%, and the sum of the molar percentages of the four monomers is equal to 100 mol%.

The preparation method of the liquid crystal polymer film comprises the following steps:

s1: putting monomers of p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, diphenol, tetrafluoro terephthalic acid, an acetylation reagent of acetic anhydride, a catalyst of 4-dimethylamino pyrimidine and an antioxidant of tin powder into a Hastelloy polymerization kettle for prepolymerization to prepare a prepolymer;

s2: discharging the prepolymer from the Hastelloy kettle, crushing, and performing solid-phase polycondensation in a nitrogen atmosphere to obtain liquid crystal polymer powder;

s3: mixing the prepared liquid crystal polymer powder by a screw extruder, and exhausting; melt extrusion, and side blowing cooling; drafting and winding to prepare a liquid crystal polymer nascent film;

s4: and carrying out heat treatment on the prepared nascent film to obtain a finished liquid crystal polymer film.

In the above production method, the amount of acetic anhydride added is preferably 1.5 to 2.5 times the total molar number of hydroxyl groups in p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and biphenol.

In the above production method, it is preferable that the molar ratio of biphenyldiol to tetrafluoroterephthalic acid is 1: 1.

in the above production method, it is preferable that the 4-dimethylaminopyrimidine is added in an amount of 80 to 400ppm based on the total weight of the p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid.

In the above preparation method, the addition amount of the tin powder is preferably 0.15 to 0.45% of the total weight of the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid, the diphenol and the tetrafluoroterephthalic acid.

In the above preparation method, preferably, step S1 is specifically: putting the raw materials into a Hastelloy polymerization kettle, and keeping the temperature at 135-145 ℃ for 3-8 h; heating to 300-; and (3) flushing 0.1-1.0MPa of nitrogen into the polymerization kettle, discharging the prepolymer through a discharge valve with 8-10 holes and the diameter of 2-4mm, crushing, sieving with a 20-30 mesh sieve, and drying at 150 ℃ for 2-3h to obtain the prepolymer.

In the above preparation method, preferably, step S2 is specifically: and carrying out solid phase polycondensation on the prepared prepolymer for 12-36h in a rotary kiln at the temperature of 190-300 ℃ under the protection of nitrogen to prepare the liquid crystal polymer.

In the above preparation method, the extrusion temperature of the screw extruder in step S3 is preferably 305 ℃ to 350 ℃.

In the above production method, it is preferable that the cross-blow temperature in step S3 is 35 to 50 ℃ and the draft speed is 5 to 40 m/min.

In the preparation method, the heat treatment temperature in the step S4 is preferably 230-310 ℃ and the time is 12-36 h.

The embodiments of the present invention will be described in detail by the following examples and comparative examples. The monomer formulations of examples 1 to 5 of the present invention and comparative examples 1 to 2 are shown in Table 1:

table 1: monomer ratios in examples 1-5 and comparative examples 1-2

Example 1

Putting p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid, acetic anhydride accounting for 1.5 times of the total mole number of hydroxyl in the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid and the biphenol, 4-dimethylamino pyrimidine accounting for 80ppm of the total weight of the four monomers and tin powder accounting for 0.15 percent of the total weight of the four monomers into a Hastelloy polymerization kettle according to a formula of a No. 1 monomer, and keeping the mixture at 135 ℃ for 8 hours; heating to 300 ℃ at the speed of 0.2 ℃/min, and keeping the temperature for 2 h; flushing 0.1MPa nitrogen into a polymerization kettle, discharging the prepolymer through an 8-hole discharge valve with the diameter of 2mm, crushing, sieving with a 20-mesh sieve, and drying at 130 ℃ for 3 hours to obtain the prepolymer;

performing solid phase polycondensation on the prepared prepolymer in a rotary kiln at 190 ℃ for 36h under the protection of nitrogen to prepare liquid crystal polymer powder with the weight-average molecular weight of 3.93 multiplied by 10⁴；

Mixing the prepared liquid crystal polymer powder at 305 ℃ by a double-screw extruder, and exhausting; melt-extruding at a discharge rate of 25kg/h, and cooling by side-blowing at 35 ℃; drafting at 23m/min, and winding to obtain a liquid crystal polymer primary film with the average thickness of 25 μm;

heating the nascent film and aluminum foil with thickness of 50 μm at 280 deg.C under pressure of 10kg/cm²Pressing the film on a hot rolling device provided with a heat-resistant rubber roller and a heating metal roller at a speed of 3m/min to prepare a laminated body consisting of a thermoplastic liquid crystal polymer film/an aluminum foil, and placing the laminated body in a heat treatment furnace at 300 ℃ for 30 s; under the protection of nitrogen, the mixture is subjected to heat treatment at 230 ℃ for 36 h; after that, the aluminum foil was peeled off to obtain a finished film of a liquid crystal polymer having an average thickness of 25 μm.

Example 2

Putting p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid, acetic anhydride accounting for 2.0 times of the total mole number of hydroxyl in the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid and the biphenol, 4-dimethylamino pyrimidine accounting for 200ppm of the total weight of the four monomers and tin powder accounting for 0.3 percent of the total weight of the four monomers into a Hastelloy polymerization kettle according to a formula of a No. 2 monomer, and keeping the mixture at 140 ℃ for 4 hours; heating to 320 ℃ at the speed of 0.5 ℃/min, and keeping the temperature for 1 h; flushing 0.5MPa nitrogen into a polymerization kettle, discharging the prepolymer through an 8-hole discharge valve with the diameter of 4mm, crushing, sieving with a 30-mesh sieve, and drying at 140 ℃ for 2 hours to obtain the prepolymer;

performing solid phase polycondensation on the prepared prepolymer in a rotary kiln at 240 ℃ for 16h under the protection of nitrogen to prepare liquid crystal polymer powder with the weight-average molecular weight of 3.45 multiplied by 10⁴；

Mixing the prepared liquid crystal polymer powder at 320 ℃ by a double-screw extruder, and exhausting; melt-extruding at a discharge rate of 25kg/h, and cooling by side blowing at 40 ℃; drafting at 23m/min, and winding to obtain a liquid crystal polymer primary film with the average thickness of 25 μm;

heating the nascent film and aluminum foil with thickness of 50 μm at 280 deg.C under pressure of 10kg/cm²Pressing the film on a hot rolling device provided with a heat-resistant rubber roller and a heating metal roller at a speed of 3m/min to prepare a laminated body consisting of a thermoplastic liquid crystal polymer film/an aluminum foil, and placing the laminated body in a heat treatment furnace at 300 ℃ for 30 s; under the protection of nitrogen, the mixture is subjected to heat treatment at 260 ℃ for 15 h; after that, the aluminum foil was peeled off to obtain a finished film of a liquid crystal polymer having an average thickness of 25 μm.

Example 3

Putting p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid, acetic anhydride accounting for 1.8 times of the total mole number of hydroxyl in the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid and the biphenol, 4-dimethylamino pyrimidine accounting for 130ppm of the total weight of the four monomers and tin powder accounting for 0.2 percent of the total weight of the four monomers into a Hastelloy polymerization kettle according to a 3# monomer formula, and keeping the mixture at 135 ℃ for 6 hours; heating to 305 ℃ at the speed of 0.3 ℃/min, and keeping the temperature for 2 h; flushing 0.4MPa nitrogen into a polymerization kettle, discharging the prepolymer through an 8-hole discharge valve with the diameter of 3mm, crushing, sieving with a 25-mesh sieve, and drying at 135 ℃ for 2 hours to obtain the prepolymer;

performing solid phase polycondensation on the prepared prepolymer in a rotary kiln at 195 ℃ for 24 hours under the protection of nitrogen to prepare liquid crystal polymer powder with the weight average molecular weight of 3.76 multiplied by 10⁴；

Mixing the prepared liquid crystal polymer powder at 330 ℃ by a double-screw extruder, and exhausting; melt-extruding at a discharge rate of 25kg/h, and cooling by side blowing at 45 ℃; drafting at 23m/min, and winding to obtain a liquid crystal polymer primary film with the average thickness of 25 μm;

heating the nascent film and aluminum foil with thickness of 50 μm at 280 deg.C under pressure of 10kg/cm²Pressing the sheet at a speed of 3m/min in a hot rolling device equipped with a heat-resistant rubber roll and a heated metal roll to prepare a laminate of a thermoplastic liquid crystal polymer film/aluminum foil, and laminating the laminate on a pressPlacing in a heat treatment furnace at 300 ℃ for 30 s; under the protection of nitrogen, the mixture is subjected to heat treatment at 250 ℃ for 18 h; after that, the aluminum foil was peeled off to obtain a finished film of a liquid crystal polymer having an average thickness of 25 μm.

Example 4

Putting p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid, acetic anhydride accounting for 2.2 times of the total mole number of hydroxyl in the p-hydroxybenzoic acid, the 6-hydroxy-2-naphthoic acid and the biphenol, 4-dimethylamino pyrimidine accounting for 300ppm of the total weight of the four monomers and tin powder accounting for 0.4 percent of the total weight of the four monomers into a Hastelloy polymerization kettle according to a 4# monomer formula, and keeping the mixture at 140 ℃ for 4 hours; heating to 320 ℃ at the speed of 0.6 ℃/min, and keeping the temperature for 1 h; flushing 0.7MPa nitrogen into a polymerization kettle, discharging the prepolymer through an 8-hole discharge valve with the diameter of 4mm, crushing, sieving with a 20-mesh sieve, and drying at 145 ℃ for 3 hours to obtain the prepolymer;

performing solid phase polycondensation on the prepared prepolymer in a rotary kiln at 270 ℃ for 24 hours under the protection of nitrogen to prepare liquid crystal polymer powder with the weight average molecular weight of 3.84 multiplied by 10⁴；

Mixing the prepared liquid crystal polymer powder at 340 ℃ by a double-screw extruder, and exhausting; melt-extruding at a discharge rate of 25kg/h, and cooling by side-blowing at 35 ℃; drafting at 23m/min, and winding to obtain a liquid crystal polymer primary film with the average thickness of 25 μm;

heating the nascent film and aluminum foil with thickness of 50 μm at 280 deg.C under pressure of 10kg/cm²Pressing the film on a hot rolling device provided with a heat-resistant rubber roller and a heating metal roller at a speed of 3m/min to prepare a laminated body consisting of a thermoplastic liquid crystal polymer film/an aluminum foil, and placing the laminated body in a heat treatment furnace at 300 ℃ for 30 s; under the protection of nitrogen, the mixture is subjected to heat treatment at 290 ℃ for 20 h; after that, the aluminum foil was peeled off to obtain a finished film of a liquid crystal polymer having an average thickness of 25 μm.

Example 5

Putting p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, biphenol and tetrafluoroterephthalic acid, acetic anhydride accounting for 2.5 times of the total mole number of hydroxyl in the p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and biphenol, 4-dimethylamino pyrimidine accounting for 400ppm of the total weight of the four monomers and tin powder accounting for 0.45 percent of the total weight of the four monomers into a Hastelloy polymerization kettle according to a 5# monomer formula, and keeping the mixture at 145 ℃ for 3 hours; heating to 330 ℃ at the speed of 0.8 ℃/min, and keeping the temperature for 1 h; flushing 1.0MPa nitrogen into a polymerization kettle, discharging the prepolymer through a 10-hole discharge valve with the diameter of 2mm, crushing, sieving with a 30-mesh sieve, and drying at 150 ℃ for 2 hours to obtain the prepolymer;

performing solid phase polycondensation on the obtained prepolymer in a rotary kiln at 300 ℃ for 12 hours under the protection of nitrogen to obtain liquid crystal polymer powder with the weight average molecular weight of 3.25 multiplied by 10⁴；

Mixing the prepared liquid crystal polymer powder at 350 ℃ by a double-screw extruder, and exhausting; melt-extruding at a discharge rate of 25kg/h, and cooling by side blowing at 50 ℃; drafting at 23m/min, and winding to obtain a liquid crystal polymer primary film with the average thickness of 25 μm;

heating the nascent film and aluminum foil with thickness of 50 μm at 280 deg.C under pressure of 10kg/cm²Pressing the film on a hot rolling device provided with a heat-resistant rubber roller and a heating metal roller at a speed of 3m/min to prepare a laminated body consisting of a thermoplastic liquid crystal polymer film/an aluminum foil, and placing the laminated body in a heat treatment furnace at 300 ℃ for 30 s; under the protection of nitrogen, the mixture is subjected to heat treatment at 310 ℃ for 12 h; after that, the aluminum foil was peeled off to obtain a finished film of a liquid crystal polymer having an average thickness of 25 μm.

Comparative example 1

This comparative example differs from example 2 only in that polymerization was carried out using the 6# monomer formulation, which was otherwise the same as example 2, wherein the liquid crystalline polymer prepared had a weight average molecular weight of 3.31X 10⁴。

Comparative example 2

This comparative example differs from example 2 only in that polymerization was carried out using the 7# monomer formulation, which was otherwise the same as example 2, wherein the liquid crystalline polymer prepared had a weight average molecular weight of 3.59X 10⁴。

Comparative example 3

This comparative example differs from example 2 only in that an equimolar amount of terephthalic acid was used instead of tetraFluoroterephthalic acid, the other things being equal to example 2, wherein the weight average molecular weight of the liquid crystalline polymer prepared was 3.47X 10⁴。

Comparative example 4

This comparative example differs from example 2 only in that dibutyltin laurate was used instead of 4-dimethylaminopyrimidine as catalyst, and it is otherwise the same as example 2. The weight average molecular weight of the prepared liquid crystal polymer is 2.34 multiplied by 10⁴Meanwhile, the color of the prepared polymer is obviously deepened compared with that of the polymer prepared in examples 1-4 and comparative examples 1-2 due to more side reactions.

The following performance tests were conducted for the above examples and comparative examples, and the test results are shown in table 2:

(1) tensile strength: ASTM D882;

(2) dielectric constant and dielectric dissipation factor: SPDR,15 GHz;

(3) elongation percentage: ASTM D882;

(4) the prepared high-toughness LCP film material is tested according to a test method of the tensile property of a GB 13022-1991 plastic film, and whether the film cracks or not is observed after being treated for 3 hours each time at the temperature of minus 60-200 ℃ for 500 times, wherein the mark of no crack is OK, and the mark of crack is NG.

Table 2: results of property test of the liquid crystal polymer films prepared in examples 1 to 5 and comparative examples 1 to 4:

as can be seen from the performance test results in Table 2, the elongation of the film product prepared by the formulation of the invention in examples 1-5 is greatly improved, and the film is free from cracking through a-60-200 ℃ cold-hot cycle test, which shows that the film has better toughness in high and low temperature environments, thereby reducing the thermal expansion and cold contraction degree in high and low temperature environments, and enabling the film to be stably applied in an environment with larger temperature difference. It can also be seen from table 2 that when tetrafluoroterephthalic acid is introduced in an amount of less than 9% as required in the present invention, the toughness of the film is not significantly improved and the film is cracked in the cold-hot cycle test; when the amount is more than 14%, although the toughness of the film is greatly improved, the dielectric constant of the film is increased, which is not favorable for high frequency transmission. In addition, when the monomer tetrafluoroterephthalic acid is replaced by the conventional aromatic dicarboxylic acid in the prior art, the obtained liquid crystal polymer film has poor toughness, and the film can crack in a cold-hot cycle test, so that the liquid crystal polymer film cannot be better adapted to the environment with larger temperature difference.

It should be noted that, those skilled in the art can obtain films with different thicknesses by adjusting and controlling the discharge amount or the drawing speed of the liquid crystal polymer according to actual needs, and details are not repeated here.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.