Preparation method and application of liquid crystal polymer film

Abstract

The invention discloses a preparation method and application of a liquid crystal polymer film, and relates to the technical field of LCP films used for high-frequency communication.The preparation method at least comprises the following heat treatment steps that S1, a liquid crystal polymer and a carrier are subjected to high-temperature compounding at the temperature of 200-350 DEG C, and a composite film of the liquid crystal polymer and the carrier is obtained; s2, carrying out multi-gradient heating and cooling treatment on the composite film at 200-350 DEG C; and S3, stripping the carrier in the composite film to obtain a liquid crystal polymer film precursor, and carrying out heat treatment on the liquid crystal polymer film precursor at a temperature lower than the glass transition temperature of the liquid crystal polymer for 1-30 minutes to obtain a liquid crystal polymer film finished product. Through the heat treatment, the resin molecular weight of the liquid crystal polymer in the film is improved, the thermal expansion coefficient is improved to be close to the thermal expansion coefficient of the copper foil, and the resin melting point of the liquid crystal polymer is also improved to meet the lead-free reflow soldering process of the FPC.

Description

Technical Field

[0001] The present invention relates to the technical field of LCP films used in high-frequency communications, and in particular to a preparation method and application of a liquid crystal polymer film. Background Art

[0002] Liquid crystal polymers (LCPs) are an important class of polymers, typically fully aromatic molecules containing multiple heteroatom bonds, including ester and / or amide-ester bonds. When heated to a sufficiently high temperature, LCPs melt to form a liquid crystal melt phase (often called an "anisotropic phase") rather than an isotropic melt phase. Due to their unique molecular chain rigidity, LCPs exhibit minimal entanglement, a characteristic of polymers. Unlike conventional thermoplastic resins, LCPs exhibit significant orientation in the direction of flow. The molecular chain orientation relaxation time is long, allowing them to maintain their orientation in the direction of flow and solidify during injection molding and thermoforming. Therefore, LCPs exhibit significant anisotropy in terms of mechanical properties and other performance factors, and orientation of the liquid crystal molecules must be minimized during the LCP film forming process. Typically, LCPs are composed of linear molecules ("rigid rods") that align to form the desired liquid crystal sequence. LCPs exhibit excellent low hygroscopicity, heat resistance, dimensional stability, and a low dielectric constant.

[0003] With the widespread adoption and widespread promotion of 5G technology, the trend toward higher-frequency communications is becoming increasingly evident. The copper-clad laminate (CCL) material that forms the substrate for 5G antennas is primarily composed of metallic copper foil and an insulating film. Liquid crystal polymers (LCPs) are often used as the insulating film in CCLs. However, the CCL material that forms the antenna substrate requires good dimensional stability. To produce dimensionally stable CCL components, the coefficients of thermal expansion (CTE) of the copper foil and the LCP must be as close as possible. However, since one is composed of copper atoms and the other is composed of molecular covalent bonds, their CTEs are difficult to approximate. Furthermore, the CCL requires soldering (at a temperature of 288°C), which requires high-temperature resistance. This performance is determined by the melting point of the LCP. However, most existing LCPs do not reach 288°C. Therefore, to prepare LCPs suitable for use in CCLs, they must be treated to ensure that their thermal properties, such as CTE and melting point, meet the required standards.

[0004] When mounting components such as semiconductor devices or impedance devices directly on a circuit board, misalignment can easily occur if the thermal expansion coefficients of the circuit board and the components differ. When thermoplastic liquid crystal polymers (TLPs) are formed into films using extrusion methods such as blow molding, they typically have a negative thermal expansion coefficient. When using such TLP films as insulating layers on circuit boards, aligning their thermal expansion coefficient with that of the components requires increasing the thermal expansion coefficient of the TLP film during the circuit board manufacturing process. While the thermal expansion coefficient of TLP films can be adjusted through heat treatment, increasing the thermal expansion coefficient requires heat treatment at a temperature not lower than the film's melting point, as documented in Kuraray Japan's public documents. However, high-temperature heat treatment can easily lead to resin degradation due to excessive heat load. Higher heat treatment temperatures make it more difficult to precisely control the film's thermal expansion coefficient and can easily cause film deformation and other undesirable effects. This compromises energy efficiency, increases the restrictions on the mounting surface, and raises costs, presenting various challenges for industrial production.

[0005] To address this problem, one prior art method involves heat-treating a laminate (circuit board) composed of a thermoplastic liquid crystal polymer film and a metal foil before mounting a surface-mount component on it, thereby making the thermal expansion coefficient of the film constituting the laminate substantially the same as that of the mounted component (see, for example, Japanese Patent Application Laid-Open No. 10-157010). Various other methods have also been proposed, such as heat-treating a laminate composed of a thermoplastic liquid crystal polymer film and a metal foil to modify the physical properties of the film (see, for example, US Patent No. 5,529,740). Summary of the Invention

[0006] To address a series of issues with existing liquid crystal polymer films, such as delamination caused by insufficient cohesion, a low thermal expansion coefficient, a low melting point, and significant thermal shrinkage, the present invention provides a method for preparing and applying liquid crystal polymer films. The liquid crystal polymer films provided herein utilize a specific heat treatment method to increase the molecular weight of the liquid crystal polymer resin within the film, while also raising the thermal expansion coefficient to a value close to that of copper foil. This also increases the melting point of the liquid crystal polymer resin, making it suitable for lead-free reflow soldering of FPCs.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a liquid crystal polymer film, the method comprising at least the following heat treatment steps: S1: Compounding the liquid crystal polymer and the carrier at a high temperature of 200-350° C. to obtain a composite film of the liquid crystal polymer and the carrier; S2: subjecting the composite membrane to a multi-gradient temperature rise and fall treatment at 200°C-350°C; S3: Peeling off the carrier from the composite film to obtain a liquid crystal polymer film precursor, and heat-treating the liquid crystal polymer film precursor at a temperature lower than the glass transition temperature of the liquid crystal polymer for a time of 1 second to 30 minutes to obtain a finished liquid crystal polymer film.

[0008] Furthermore, the molecular weight of the liquid crystal polymer in step S1 is 20,000-500,000, and the thermal expansion coefficient is -100--1 ppm; the thermal expansion coefficient of the carrier is 12-16 ppm; preferably, the absolute value of the difference between the thermal expansion coefficients of the liquid crystal polymer and the carrier is 13-100 ppm.

[0009] Furthermore, the high-temperature compounding in step S1 uses a high-temperature roller press or a pressing roller with a high-temperature pressing temperature of 200-350°C.

[0010] Furthermore, the high-temperature roller press is selected from a five-axis high-temperature press or a three-axis high-temperature press; the temperature accuracy of the rollers used is within ±5°C; and the unit pressure of the high-temperature pressing is 1KN-15KN.

[0011] Furthermore, the carrier in step S1 is selected from aluminum foil, copper foil, steel strip, polytetrafluoroethylene, titanium, chrome steel or nickel.

[0012] Furthermore, the thickness of the carrier in step S1 is 5 μm-500 μm.

[0013] Furthermore, the multi-gradient heating and cooling treatment method of step S2 is as follows: in the first stage, the temperature is increased to 220°C at a heating rate of 20°C / min, in the second stage, the temperature is increased to 240°C at a heating rate of 5°C / min, in the third stage, the temperature is increased to 260°C at a heating rate of 5°C / min, in the fourth stage, the temperature is increased to 300°C at a heating rate of 5°C / min, the heating time of each stage is 0.5h~50h, and in the fifth stage, the temperature is reduced to 25°C at a cooling rate of 30°C / min.

[0014] Furthermore, the heating equipment for the heat treatment in step S2 is selected from a high-temperature furnace and a high-temperature oven as a heat source, and uses at least one selected from a hot air oven, a steam oven, an electric heater, an infrared heater, a ceramic heater, a hot rolling roller, a hot press and an electromagnetic wave irradiation machine.

[0015] Furthermore, the composite film of step S2 has a cohesive force greater than 7 N / cm, an elongation of 2-6%, and a melting point of 260-300°C.

[0016] Furthermore, the shrinkage rate of the liquid crystal polymer film in step S3 under the conditions of 150° C. and 30 min is less than 0.08% in the length direction and (or width direction).

[0017] In a second aspect, the present invention further provides a laminate comprising the liquid crystal polymer film according to the first aspect.

[0018] By applying the technical solution of the present invention, compared with the prior art, the present invention has the following beneficial effects: The liquid crystal polymer film provided by the present invention effectively solves a series of problems such as delamination caused by insufficient cohesion of the original liquid crystal polymer film, small thermal expansion coefficient, and large thermal shrinkage through a specific heat treatment method. The resin molecular weight of the liquid crystal polymer in the film is increased, and the thermal expansion coefficient is also increased to be close to the thermal expansion coefficient of the copper foil. The resin melting point of the liquid crystal polymer is also increased simultaneously. The heat resistance is no longer restricted by the melting point of the resin raw material, so that it meets the lead-free reflow soldering process of FPC. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 shows a cross-sectional schematic diagram of a liquid crystal polymer film provided according to an embodiment of the present invention; The above drawings include the following reference numerals: 1 is a liquid crystal polymer film; 2 is a carrier. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. In this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "comprise", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the sentence "comprising a ..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

[0021] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0022] Unless otherwise defined, technical or scientific terms used in the present disclosure shall have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0023] Liquid crystal polymers (LCPs) offer high strength, high modulus, high temperature resistance, chemical resistance, and high dimensional stability, making them widely used in aerospace, defense, and specialty industries. However, LCP films suffer from a series of issues, including delamination due to insufficient cohesion, a low coefficient of thermal expansion, and high thermal shrinkage.

[0024] In order to solve this problem, the present application provides a preparation method and application of a liquid crystal polymer film.

[0025] In a typical embodiment of the present application, in the first aspect, the present invention provides a method for preparing a liquid crystal polymer film, the preparation method comprising at least the following heat treatment steps: S1, compounding the liquid crystal polymer and the carrier at a high temperature of 200-350°C to obtain a composite film of the liquid crystal polymer and the carrier; S2, subjecting the composite film to a multi-gradient temperature rise and fall treatment at 200-350°C; S3, peeling off the carrier from the composite film to obtain a liquid crystal polymer film precursor, and heat-treating the liquid crystal polymer film precursor, wherein the heat treatment temperature is lower than the glass transition temperature of the liquid crystal polymer, and the heat treatment time is 1s-30min, to obtain a finished liquid crystal polymer film.

[0026] In step S2, the composite film is subjected to a multi-gradient temperature rise and fall treatment at 200° C.-350° C., which can control the molecular weight growth process and stably improve the film strength without causing excessive high or low local strength.

[0027] The heat treatment temperature in step S3 is lower than the glass transition temperature of the liquid crystal polymer because when the temperature is lower than the Tg point, the molecular chain ends cannot move and the heat treatment has no effect.

[0028] In a typical embodiment of the present application, the molecular weight of the liquid crystal polymer in step S1 is 20,000 to 500,000, and the coefficient of thermal expansion is -100 to -1 ppm; the coefficient of thermal expansion of the carrier is 12 to 16 ppm. Preferably, the absolute value of the difference between the coefficients of thermal expansion of the liquid crystal polymer and the carrier is 13 to 100 ppm. The coefficient of thermal expansion of the carrier used in the heat treatment process of step S1 is preferably greater than the coefficient of thermal expansion of the liquid crystal polymer before the heat treatment.

[0029] In a typical embodiment of the present application, based on the film's heat resistance and processability, the high-temperature lamination in step S1 utilizes a high-temperature roller press or a roller with a high-temperature pressing temperature of 200-350°C. Furthermore, the high-temperature roller press is selected from a five-axis high-temperature press or a three-axis high-temperature press; the roller temperature accuracy is within ±5°C; and the unit pressure of the high-temperature pressing is 1KN-15KN. If the unit pressure of the high-temperature pressing is less than 1KN, the LCP film cannot be bonded to the carrier; if the unit pressure of the high-temperature pressing is greater than 15KN, the LCP film cannot be properly separated from the support after heat treatment due to its close bonding to the support.

[0030] In a typical embodiment of the present application, the carrier in step S1 is selected from aluminum foil, copper foil, steel strip, polytetrafluoroethylene, titanium, chrome steel or nickel.

[0031] In a typical embodiment of the present application, the thickness of the carrier in step S1 is 5 μm to 500 μm. If the carrier is less than 5 μm, the LCP will wrinkle due to a lack of support. If the carrier is more than 500 μm, the carrier is too thick to be peeled off and the resulting roll will be difficult to remove, resulting in high costs.

[0032] In a typical embodiment of the present application, the multi-gradient temperature rise and fall treatment method of step S2 is as follows: the first stage is to heat up to 220°C at a heating rate of 20°C / min, the second stage is to heat up to 240°C at a heating rate of 5°C / min, the third stage is to heat up to 260°C at a heating rate of 5°C / min, the fourth stage is to heat up to 300°C at a heating rate of 5°C / min, the heating time of each stage is 0.5h~50h, and the fifth stage is to cool down to 25°C at a cooling rate of 30°C / min.

[0033] In a typical embodiment of the present application, the heating equipment for the heat treatment in step S2 is selected from at least one of a high-temperature furnace, a high-temperature oven, a hot air oven, a steam oven, an electric heater, an infrared heater, a ceramic heater, a hot rolling roller, a hot press and an electromagnetic wave irradiation machine.

[0034] In a typical embodiment of the present application, the composite film in step S2 has a cohesive force greater than 7 N / cm, an elongation of 2-6%, and a melting point of 260-320°C. This method is the only way to achieve a cohesive force greater than 7 N / cm, increase elongation, and elevate the melting point.

[0035] In a typical embodiment of the present application, the shrinkage rate of the liquid crystal polymer film in step S3 under the conditions of 150° C. and 30 min is less than 0.08% in the length direction and (or width direction).

[0036] In a second aspect, the present invention further provides a laminate comprising the liquid crystal polymer film according to the first aspect.

[0037] In a preferred embodiment of the present application, when the metal is copper foil, a laminate consisting of a liquid crystal polymer film and copper foil is formed, which can be used as a circuit substrate. The aforementioned multiple heat treatments can increase the thermal expansion coefficient of the liquid crystal polymer film, resulting in a well-tuned film with a desired thermal expansion coefficient. The resulting liquid crystal polymer film has a thermal expansion coefficient close to that of copper foil.

[0038] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0039] Example 1: A 50 μm thick film (thermal expansion coefficient of -30 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 40 μm aluminum foil (thermal expansion coefficient of 14 ppm) using a roller press at 265°C and 12 kN. The resulting composite was heat treated in a tunnel oven by raising the temperature from room temperature to 240°C and holding the temperature for 2 hours, then raising the temperature from 240°C to 260°C and holding the temperature for 6 hours, then raising the temperature to 270°C and holding the temperature for 6 hours, and then cooling the temperature to room temperature. The aluminum foil was peeled off from the heat-treated composite film, and after peeling, the LCP film was placed in a tunnel oven, heated to 230°C and heat-treated for 3 minutes, and then taken out to obtain a finished liquid crystal polymer film.

[0040] Example 2: A 50 μm thick film (thermal expansion coefficient of -1 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 40 μm aluminum foil (thermal expansion coefficient of 14 ppm) using a roller press at 265°C and 12 kN. The resulting composite was heat treated in a tunnel oven by raising the temperature from room temperature to 240°C and holding the temperature for 2 hours, then raising the temperature from 240°C to 260°C and holding the temperature for 6 hours, then raising the temperature to 270°C and holding the temperature for 6 hours, and then cooling the temperature to room temperature. The aluminum foil of the heat-treated composite film was peeled off, and after peeling, the LCP film was placed in a tunnel oven, heated to 230°C and heat-treated for 3 minutes, and then taken out to obtain a finished liquid crystal polymer film.

[0041] Example 3: A 50 μm thick film (thermal expansion coefficient of -100 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 40 μm aluminum foil (thermal expansion coefficient of 14 ppm) using a roller press at 265°C and 12 kN. The resulting composite was heat-treated in a tunnel oven by raising the temperature from room temperature to 240°C and holding the temperature for 2 hours, then raising the temperature from 240°C to 260°C and holding the temperature for 6 hours, then raising the temperature to 270°C and holding the temperature for 6 hours, and then cooling the temperature to room temperature. The aluminum foil of the heat-treated composite film was peeled off, and after peeling, the LCP film was placed in a tunnel oven, heated to 230°C and heat-treated for 3 minutes, and then taken out to obtain a finished liquid crystal polymer film.

[0042] Example 4: A 50 μm thick film (thermal expansion coefficient of -80 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 5 μm aluminum foil (thermal expansion coefficient of 14 ppm) using a roller press at 265°C and 12 kN. The resulting composite was heat-treated in a tunnel oven by raising the temperature from room temperature to 240°C and holding the temperature for 2 hours, then raising the temperature from 240°C to 260°C and holding the temperature for 6 hours, then raising the temperature to 270°C and holding the temperature for 6 hours, and then cooling the temperature to room temperature. The aluminum foil of the heat-treated composite film was peeled off, and after peeling, the LCP film was placed in a tunnel oven, heated to 230°C and heat-treated for 3 minutes, and then taken out to obtain a finished liquid crystal polymer film.

[0043] Example 5: A 50 μm thick film (thermal expansion coefficient of -80 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 500 μm thick aluminum foil (thermal expansion coefficient of 14 ppm) using a roller press at 265°C and 12 kN. The resulting composite was heat-treated in a tunnel oven by raising the temperature from room temperature to 240°C and maintaining it for 2 hours, then raising the temperature from 240°C to 260°C and maintaining it for 6 hours, then raising the temperature to 270°C and maintaining it for 6 hours, and then cooling it to room temperature. The aluminum foil of the heat-treated composite film was peeled off, and after peeling, the LCP film was placed in a tunnel oven, heated to 230°C and heat-treated for 3 minutes, and then taken out to obtain a finished liquid crystal polymer film.

[0044] Example 6: A 50 μm thick film (thermal expansion coefficient of -80 ppm) was prepared by blown film using Polyplastics A950RX resin. The film was then laminated onto a 40 μm aluminum foil (thermal expansion coefficient of 14 ppm) at 265°C and 12 kN using a roller press. The resulting composite was heat treated in a tunnel oven. In the first stage, the temperature was increased to 220°C at a heating rate of 20°C / min, in the second stage, the temperature was increased to 240°C at a heating rate of 5°C / min, in the third stage, the temperature was increased to 260°C at a heating rate of 5°C / min, and in the fourth stage, the temperature was increased to 300°C at a heating rate of 5°C / min. The heating time for each stage was 0.5 h to 50 h. In the fifth stage, the temperature was cooled to 25°C at a cooling rate of 30°C / min. The aluminum foil of the composite film after heat treatment was peeled off. After peeling, the LCP film was placed in a tunnel oven, heated to 230°C, and heat treated for 3 min before being taken out to obtain a finished liquid crystal polymer film.

[0045] Comparative Example 1: A 50 μm thick film (thermal expansion coefficient of -100 ppm) was produced by blown film using Polyplastics A950RX resin and tested directly without heat treatment.

[0046] Performance testing: (1) Melting point: Using a differential scanning calorimeter, heat the film at a rate of 20°C / min until it is completely melted. Then, rapidly cool the melt to 50°C at a rate of 50°C / min and heat it again at a rate of 20°C / min. The position of the endothermic peak that appears at this time is recorded as the melting point Tm of the film.

[0047] (2) Thermal expansion coefficient: Using a thermomechanical analyzer (TMA), a tensile load of 1 g was applied to both ends of a film 5 mm wide and 20 mm long. The film was heated from room temperature to 200°C at a rate of 5°C / min, then cooled to 30°C at a rate of 20°C / min. The film was then heated again at a rate of 5°C / min. The coefficient of thermal expansion was calculated from the change in length between 30°C and 150°C.

[0048] (3) Shrinkage rate: Take a 150mm*150mm square sample and use the template to make a size of 100mm×100mm. Use a blade to draw a "cross" at the corresponding position, measure the length dimension in the TD / MD direction at room temperature (two-dimensional element or vernier caliper), then put it in a 150℃ oven, bake it for 30 minutes, take it out, let it stand for 15 minutes, and measure the TD / MD length again to calculate the shrinkage dimension.

[0049] (4) Cohesion: The prepared LCP was double-sidedly laminated with copper foil. After lamination, a peeling force test was performed according to IPC TM650. At this time, the peeling force tested was greater than 7N / CM, and the damaged interface was no longer the delamination of the LCP layer.

[0050] (5) Elongation: Take an A4-sized sample and use the sample to make a jig with a size of 15 mm × 15 mm. Use a knife to cut 5 samples in TD / MD direction. Fix the sample in the tensile value instrument, set the preload / stress to 5N, the preload / stress speed to 20 mm / min, and the elongation rate in the test speed column to 100 mm / min. Wait for the instrument to stretch until the membrane breaks and read the value.

[0051] Table 1: Test results of Examples 1 to 6 and Comparative Example 1

[0052] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: the tensile strength of the embodiments of the present invention is significantly higher than that of Comparative Example 1, the melting point is lower than that of Comparative Example 1, and the shrinkage rate is significantly lower than that of Comparative Example 1. Because the composite film described in this application is subjected to a multi-gradient temperature rise and fall treatment at 200°C-350°C, the molecular weight growth process can be controlled to stably improve the film strength. If the thickness of the carrier is less than 5μm, the lack of support will cause wrinkles when the LCP is peeled off; if the thickness of the carrier is greater than 500μm, the carrier is too thick to be peeled off and the roll cannot be peeled off, and the cost is high.

[0053] The above embodiments are only intended to help understand the method of the present invention and its core concept. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a liquid crystal polymer film, characterized in that: The preparation method comprises at least the following heat treatment steps: S1: Compounding the liquid crystal polymer and the carrier at a high temperature of 200-350° C. to obtain a composite film of the liquid crystal polymer and the carrier; S2: subjecting the composite membrane to a multi-gradient temperature rise and fall treatment at 200°C-350°C; S3: Peeling off the carrier from the composite film to obtain a liquid crystal polymer film precursor, and heat-treating the liquid crystal polymer film precursor at a temperature lower than the glass transition temperature of the liquid crystal polymer for a time of 1 second to 30 minutes to obtain a finished liquid crystal polymer film.

2. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The molecular weight of the liquid crystal polymer in step S1 is 20,000-500,000, and the thermal expansion coefficient is -100--1 ppm; the thermal expansion coefficient of the carrier is 12-16 ppm; preferably, the absolute value of the difference between the thermal expansion coefficients of the liquid crystal polymer and the carrier is 13-100 ppm.

3. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The high-temperature compounding in step S1 uses a high-temperature roller press or a high-temperature pressing roller with a high-temperature pressing temperature of 200-350°C.

4. The method for preparing a liquid crystal polymer film according to claim 3, wherein: The high-temperature roller press is selected from a five-axis high-temperature press or a three-axis high-temperature press; the temperature accuracy of the rollers used is within ±5°C; and the unit pressure of the high-temperature pressing is 1KN-15KN.

5. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The carrier in step S1 is selected from aluminum foil, copper foil, steel strip, polytetrafluoroethylene, titanium, chrome steel or nickel.

6. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The thickness of the carrier in step S1 is 5 μm-500 μm.

7. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The multi-gradient heating and cooling treatment method of step S2 is as follows: in the first stage, the temperature is increased to 220°C at a heating rate of 20°C / min, in the second stage, the temperature is increased to 240°C at a heating rate of 5°C / min, in the third stage, the temperature is increased to 260°C at a heating rate of 5°C / min, in the fourth stage, the temperature is increased to 300°C at a heating rate of 5°C / min, the heating time of each stage is 0.5h~50h, and in the fifth stage, the temperature is reduced to 25°C at a cooling rate of 30°C / min.

8. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The composite film in step S2 has a cohesive force greater than 7 N / cm, an elongation of 2-6%, and a melting point of 260-320° C.

9. The method for preparing a liquid crystal polymer film according to claim 1, wherein: The shrinkage rate of the liquid crystal polymer film in step S3 at 150° C. for 30 minutes is less than 0.08% in the length direction and / or the width direction. 10 . A laminate comprising at least one layer of the liquid crystal polymer film according to claim 1 .

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