A composition for preparing a flexible composite film and use thereof

Abstract

This invention discloses a composition for preparing flexible composite films and its application, relating to the field of engineering plastic materials technology. The composition comprises the following raw materials by weight: 40-60 parts of lyotropic liquid crystal polymer, 20-40 parts of polytetrafluoroethylene powder, and 10-30 parts of modified Mg3B2O6 ceramic powder; the modified Mg3B2O6 ceramic powder is obtained by grinding Mg3B2O6 ceramic powder in an organic solvent with a surface modifier, followed by drying. The surface modifier is 1-3 wt% of the Mg3B2O6 ceramic powder and is selected from at least one of stearic acid and silane coupling agent KH550. This invention uses a surface modifier to modify the surface of Mg3B2O6 ceramic powder, which acts as a functional bridge between inorganic ceramic particles and LLCP / PTFE composite membrane, improves the interfacial compatibility between Mg3B2O6 ceramic powder and organic matter, promotes the uniform dispersion of Mg3B2O6 ceramic powder in organic matter, reduces the porosity of composite material, and is beneficial to reducing the thermal expansion coefficient and dielectric loss of composite membrane, thus giving the composite membrane better performance.

Description

Technical Field

[0001] This invention relates to the field of engineering plastic materials technology, and more particularly to a modified liquid crystal polymer-based flexible composite film and its application, and a preparation method thereof. Background Technology

[0002] With the continuous development of 5G communication technology, high-frequency and high-speed application scenarios place higher demands on the transmission characteristics of mobile phone antennas. Therefore, it is necessary to introduce a larger number of antennas, while simultaneously addressing new challenges related to the phone's back cover and wiring. Currently, the mainstream solution is to use flexible circuit boards to manufacture foldable antennas, which can be bent into any shape to adapt to the miniaturization and portability of devices. Antenna performance is affected by the dielectric properties and thermal expansion coefficient of the substrate. The lower the dielectric constant and dielectric loss of the substrate, the lower the signal transmission delay and loss. The closer the thermal expansion coefficient of the substrate is to that of copper foil, the less affected by temperature in application scenarios, and the better the antenna performance stability.

[0003] Currently, polyimide (PI) and modified polyimide (MPI) plastics are commonly used as substrates for mobile phone antennas both domestically and internationally. PI possesses excellent bending properties, mechanical properties, heat resistance, and stable chemical properties. However, PI substrates exhibit high dielectric loss at high frequencies and high water absorption, significantly limiting the commercial application of polyimide. Existing technologies often compensate for these shortcomings by adding fillers and compounding with PI polymers. To improve the dielectric properties of PI materials, low-dielectric-loss ceramic materials are often used for filler modification, thereby meeting the application scenarios of 4G mobile phone antennas. However, low-dielectric-loss ceramics often have high dielectric constants and poor mechanical properties. Excessive filling will lead to an increase in the dielectric constant of MPI, a decrease in mechanical properties, and a reduction in the flexibility of the film material. Currently, many large plastic companies both domestically and internationally have conducted extensive research on MPI substrates and their applications in mobile phone antennas. For example, Wotech has developed various thin-film LCPs, and the products are already in the testing and verification stage; Sunway Communication Co., Ltd. has developed LCP / PTFE composite polymer films with dielectric constants of 2.4-2.9 and dielectric losses of 3.0-3.9×10⁻⁶. -3 Simultaneously, hollow glass microsphere-modified liquid crystal polyester films were developed, with dielectric constants of 2.5-3.4 and linear expansion coefficients of 26-32 ppm / ℃. Junchi New Materials Co., Ltd. developed modified polyimide-modified liquid crystal polymer composite materials, whose dielectric properties were measured at 10 GHz, showing dielectric constants of 3.14-3.27 and dielectric losses of 2.2-3.4 × 10⁻⁶. -3 High-frequency copper-clad laminate substrate.

[0004] Lyotropic liquid crystal polymers (LLCPs) possess excellent high-frequency dielectric properties (tanδ = 0.004 @ 10 GHz), extremely low water absorption, excellent mechanical properties, and stable physicochemical properties. Currently, commercially available pure LLCP resins have a Vicat softening temperature of up to 220°C, easily handling the high-temperature (75°C) environment of mobile phone operation. Both LLCPs and polytetrafluoroethylene (PTFE) are crystalline polymers. LLCP / PTFE composites can compensate for the high dielectric constant and loss of LLCPs while ensuring good mechanical and thermal properties. While excessive PTFE filler can significantly reduce the dielectric loss of LLCP materials, it introduces pores into the material, leading to phase separation and deteriorating its mechanical properties. Furthermore, PTFE has a much higher coefficient of thermal expansion than copper foil and a lower surface energy, resulting in poor adhesion to copper foil. Therefore, the development of LLCP / PTFE composite products with excellent comprehensive performance is very difficult, and the commercialization of LLCP / PTFE composites has been slow. To meet the requirements of 5G mobile phone antenna applications, it is also necessary to find high-performance ceramic fillers to improve the dielectric properties and thermal expansion coefficient of LLCP / PTFE-based composite materials. Summary of the Invention

[0005] The ultimate goal of this invention is to provide a modified liquid crystal polymer-based flexible composite film for mobile phone antennas and its preparation method, addressing the shortcomings of existing technologies. This composite material has a dielectric constant below 3.5, a dielectric loss below 0.0031, a Vicat softening temperature above 200°C, and excellent mechanical properties, thus meeting the application requirements of flexible substrates for mobile phone antennas.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] Firstly, a composition for preparing a flexible composite film is provided, which is composed of the following raw materials in parts by weight: 40-60 parts of lyotropic liquid crystal polymer (LLCP), 20-40 parts of polytetrafluoroethylene powder (PTFE), and 10-30 parts of modified Mg3B2O6 ceramic powder.

[0008] The modified Mg3B2O6 ceramic powder is obtained by grinding Mg3B2O6 ceramic powder in an organic solvent with the addition of a surface modifier and then drying it; the surface modifier is 1-3 wt% of the mass of the Mg3B2O6 ceramic powder; the surface modifier is selected from at least one of stearic acid and silane coupling agent KH550.

[0009] Preferably, the mass ratio of Mg3B2O6 ceramic powder to organic solvent is 1:(3-5), and the organic solvent is selected from at least one of anhydrous ethanol, methanol, propanol, and butanediol. More preferably, the average particle size of the Mg3B2O6 ceramic powder is 2-5 μm; the mass ratio of Mg3B2O6 ceramic powder to organic solvent is 1:(3.5-4.5); and the surface modifier is 1.5-2.5 wt% of the mass of the Mg3B2O6 ceramic powder. Even more preferably, the mass ratio of Mg3B2O6 ceramic powder to organic solvent is 1:4, and the surface modifier is 2 wt% of the mass of the Mg3B2O6 ceramic powder.

[0010] Preferably, the specific operation of drying after grinding is to use zirconia balls as the ball milling medium, set the speed in the ball mill to 300-400 r / min for 6-12 hours, and after the ball milling is completed, put the slurry into a constant temperature forced air drying oven for drying.

[0011] Preferably, the particle size of the Mg3B2O6 ceramic powder is in the micrometer range; more preferably, the average particle size is 2-10 μm, and even more preferably, the average particle size is 2-5 μm.

[0012] Furthermore, the particle size of the polytetrafluoroethylene powder is in the micrometer range; preferably, the average particle size is 2-10 μm, and more preferably, the average particle size is 5 μm.

[0013] Furthermore, the lyotropic liquid crystal polymer has an electrical constant of 2.9-3.1 and a dielectric loss of 3.5 × 10⁻⁶. -3 -4.5×10 -3 The coefficient of thermal expansion is 35-40 ppm / ℃, and the Vicat softening temperature is above 190℃. Preferably, the lyotropic liquid crystal polymer has an electrical constant of 3.03, a dielectric loss of 4.00 × 10⁻³, a coefficient of thermal expansion of 38 ppm / ℃, and a Vicat softening temperature above 190℃. Preferably, the lyotropic liquid crystal polymer can be...

[0014] Secondly, the present invention also provides a modified liquid crystal polymer-based flexible composite film, comprising a liquid crystal polymer nonwoven fabric and a film layer coated on the liquid crystal polymer nonwoven fabric, wherein the film layer contains the above-mentioned composition.

[0015] Furthermore, the modified liquid crystal polymer-based flexible composite film has a liquid crystal polymer nonwoven fabric thickness of 12-20 μm and a dielectric loss of 0.002 (6-10 GHz). Preferably, the liquid crystal polymer nonwoven fabric can be VECRUS manufactured by Kuraray Co., Ltd. of Japan. TM -MBBK4F-F.

[0016] Preferably, the film thickness on the liquid crystal polymer nonwoven fabric is 100-1000 μm.

[0017] The preparation method of the above-mentioned modified liquid crystal polymer-based flexible composite film includes the following steps:

[0018] S1: Dissolve the aforementioned composition in N-methylpyrrolidone and stir at 130-150°C for 2-4 hours to obtain a gel-like solution; the content of the composition in the gel-like solution is 20-50%;

[0019] S2: The gel-like liquid is uniformly coated onto the liquid crystal polymer nonwoven fabric, and then baked to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film material).

[0020] Preferably, in step S1, the mixture is magnetically stirred at 140°C for 2 hours.

[0021] Preferably, in step S2, the baking temperature is 140±10℃ and the time is 1-3 hours. More preferably, the baking is carried out on a coating machine at a temperature of 140℃ for 2 hours.

[0022] Finally, the present invention also provides a modified liquid crystal polymer-based flexible composite film for mobile phone antennas, which is made from the above-mentioned modified liquid crystal polymer-based flexible composite film.

[0023] Preferably, the thickness of the liquid crystal polymer nonwoven fabric in the modified liquid crystal polymer-based flexible composite film is 16 μm; and the film layer thickness on the liquid crystal polymer nonwoven fabric is 500 μm.

[0024] The above-mentioned method for preparing the modified liquid crystal polymer-based flexible composite film for mobile phone antennas is as follows: the film layers of the modified liquid crystal polymer-based flexible composite film are stacked opposite each other and pressed together at a pressing temperature of 190-220℃.

[0025] Preferably, the pressing is performed using a vulcanizing machine at a pressing temperature of 202°C.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention employs a surface modifier to modify the surface of Mg3B2O6 ceramic powder, which acts as a functional bridge between the inorganic ceramic particles and the LLCP / PTFE composite membrane, improving the interfacial compatibility between the Mg3B2O6 ceramic powder and the organic material, promoting the uniform dispersion of the Mg3B2O6 ceramic powder in the organic material, and reducing the porosity of the composite material. The reduction in porosity is beneficial for lowering the coefficient of thermal expansion and dielectric loss of the composite membrane, resulting in superior performance.

[0028] 2. Due to the low dielectric constant, extremely low dielectric loss, and low coefficient of thermal expansion of the modified Mg3B2O6 ceramic powder of this invention, the dielectric properties of LLCP / PTFE are improved by filling with modified Mg3B2O6 ceramic powder, effectively reducing the dielectric loss (tanδ < 0.0031) and coefficient of thermal expansion (CTE = 27.35-41.80 ppm / ℃) of the modified LLCP / PTFE-based composite material, while maintaining a low dielectric constant (2.51-3.43). The modified LLCP / PTFE-based composite film prepared by this invention possesses excellent dielectric properties, a Vicat softening temperature above 205℃, excellent mechanical properties, and is easy to coat and form films. It can be used as a flexible plate material for mobile phone antennas, meeting the needs of most application scenarios of mobile phone antennas. Compared with the prior art, the flexible film material prepared by this invention can withstand high temperatures of 200℃ while having lower dielectric loss and coefficient of thermal expansion.

[0029] 3. The substrate contains high-performance LLCP as the main component, which greatly improves the dielectric properties and hydrophobicity at high frequencies compared with commonly used PI and MPI substrates at home and abroad, giving the device better high-frequency performance and expanding the scope of application of the present invention.

[0030] 4. This invention uses liquid crystal polymer nonwoven fabric as a carrier, which not only makes the film prepared by coating method easier to preserve, but also greatly reduces the brittleness of the film and improves its bendability and tear strength, so that the modified LLCP / PTFE-based composite film material has excellent comprehensive performance. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a scanning electron microscope image of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas prepared in Example 3 of the present invention.

[0033] Figure 2 The image shows a scanning electron microscope (SEM) image of the composite membrane prepared for Comparative Example 1.

[0034] Figure 3 The image shows a scanning electron microscope (SEM) image of the composite membrane prepared for Comparative Example 4.

[0035] Figure 4 The image shows a scanning electron microscope (SEM) image of the composite membrane prepared in Comparative Example 7. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0038] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas of the present invention includes the following steps:

[0039] (1) In a ball mill jar, Mg3B2O6 ceramic powder is dispersed in an organic solvent of 3-5 times its mass. Then, 1.0-3.0 wt% of a surface modifier is slowly and uniformly added to the solvent. Zirconia balls are used as the milling medium. The ball mill is set to a speed of 300-400 r / min and milled for 6-12 h. After milling, the slurry is poured onto a tray and placed in a constant temperature forced-air drying oven to dry, thus obtaining modified Mg3B2O6 ceramic powder. The particle size of the Mg3B2O6 ceramic powder is in the micrometer range, preferably with an average particle size of 2-10 μm, and more preferably with an average particle size of 2-5 μm.

[0040] (2) 40-60 parts of lyotropic liquid crystal polymer, 20-40 parts of polytetrafluoroethylene powder with a particle size of micrometers, and 10-30 parts of modified Mg3B2O6 ceramic powder are mixed to form a composition. The composition is then dissolved in N-methylpyrrolidone and magnetically stirred at 130-150℃ for 2-4 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid is 20-50%. The gel-like liquid is uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0041] The electrical constant of the lyotropic liquid crystal polymer is 2.9–3.1, and the dielectric loss is 3.5 × 10⁻⁶. -3 -4.5×10 -3 The coefficient of thermal expansion is 35-40 ppm / ℃, and the Vicat softening temperature is above 190℃. The particle size of the polytetrafluoroethylene powder is in the micrometer range, preferably with an average particle size of 2-10 μm, and more preferably with an average particle size of 5 μm. The film thickness is 100-1000 μm.

[0042] (3) The layers of the modified LLCP / PTFE-based composite film are stacked relative to each other and pressed at 190-220°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0043] To further illustrate the technical solution of this application and verify the technical effect of the present invention, the following embodiments, comparative examples, and test results are also provided.

[0044] In the following examples, the average particle size of both the Mg3B2O6 ceramic powder and the polytetrafluoroethylene powder is 5 μm; the liquid crystal polymer is... The dielectric constant is 3.03, and the dielectric loss is 4.00 × 10⁻⁶. -3 The coefficient of thermal expansion is 38 ppm / ℃, and the Vicat softening temperature is above 190℃; the liquid crystal polymer nonwoven fabric is VECRUS manufactured by Kuraray Co., Ltd. of Japan. TM -MBBK4F-F, with a thickness of 16μm and a dielectric loss of 0.002 (6-10GHz); the film layer on the liquid crystal polymer nonwoven fabric has a thickness of 500μm.

[0045] Example 1

[0046] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0047] (1) In the ball milling jar of the ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 4 times that of Mg3B2O6 ceramic powder. Then, 2.0 wt% of stearic acid of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 350 r / min for 9 h. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0048] (2) 60 parts of lyotropic liquid crystal polymer, 30 parts of polytetrafluoroethylene powder, and 10 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 2 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 35%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 2 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0049] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0050] Example 2

[0051] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0052] (1) In the ball milling jar of the ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 4 times that of Mg3B2O6 ceramic powder. Then, 2.0 wt% of stearic acid of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 350 r / min for 9 h. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0053] (2) A composition was prepared by mixing 50 parts of lyotropic liquid crystal polymer, 30 parts of polytetrafluoroethylene powder, and 20 parts of modified Mg3B2O6 ceramic powder. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 2 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 35%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 2 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0054] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0055] Example 3

[0056] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0057] (1) In the ball milling jar of the ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 4 times that of Mg3B2O6 ceramic powder. Then, 2.0 wt% of stearic acid of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 350 r / min for 9 h. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0058] (2) 40 parts of lyotropic liquid crystal polymer, 30 parts of polytetrafluoroethylene powder, and 30 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 2 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 35%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 2 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0059] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0060] Example 4

[0061] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0062] (1) In the ball milling jar of the ball mill, Mg3B2O6 ceramic powder is dispersed in propanol with a mass of 3 times that of Mg3B2O6 ceramic powder. Then, 1.0 wt% of silane coupling agent KH550 of ceramic powder is slowly and evenly added to it. Zirconia balls are used as the ball milling medium. The ball milling speed is set to 300 r / min for 6 h. After the ball milling is completed, the slurry is poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0063] (2) 40 parts of lyotropic liquid crystal polymer, 40 parts of polytetrafluoroethylene powder, and 20 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 130°C for 2 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 50%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 1 hour on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0064] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together at 190°C in a vulcanizing machine to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0065] Example 5

[0066] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0067] (1) In the ball mill jar of the ball mill, Mg3B2O6 ceramic powder was dispersed in butanediol at a mass of 5 times that of Mg3B2O6 ceramic powder. Then, 3.0 wt% of silane coupling agent KH550 of ceramic powder was slowly and evenly added. Zirconia balls were used as the ball milling medium. The ball mill was set to a speed of 400 r / min and milled for 12 h. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0068] (2) 50 parts of lyotropic liquid crystal polymer, 30 parts of polytetrafluoroethylene powder, and 20 parts of modified Mg3B2O6 ceramic powder are mixed to form a composition. The composition is then dissolved in N-methylpyrrolidone and magnetically stirred at 150°C for 4 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid is 20%. The gel-like liquid is uniformly coated on a liquid crystal polymer nonwoven fabric and then baked to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0069] (3) The layers of the modified LLCP / PTFE-based composite film are stacked opposite each other and pressed at 220°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0070] Example 6

[0071] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0072] (1) In the ball milling jar of a ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 4 times that of Mg3B2O6 ceramic powder. Then, 2.0 wt% of silane coupling agent KH550 of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 350 r / min for 8 hours. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0073] (2) 40 parts of lyotropic liquid crystal polymer, 30 parts of polytetrafluoroethylene powder, and 30 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 3 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 25%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 3 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0074] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0075] Example 7

[0076] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0077] (1) In the ball milling jar of a ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 3.5 times that of Mg3B2O6 ceramic powder. Then, 2.5wt% of stearic acid of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 300 r / min for 6 hours. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0078] (2) 40 parts of lyotropic liquid crystal polymer, 40 parts of polytetrafluoroethylene powder, and 20 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 2 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 40%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 2 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0079] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0080] Example 8

[0081] The preparation method of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas in this embodiment is as follows:

[0082] (1) In the ball milling jar of the ball mill, Mg3B2O6 ceramic powder was dispersed in anhydrous ethanol at a mass of 4.5 times that of Mg3B2O6 ceramic powder. Then, 2.5wt% of stearic acid of ceramic powder was slowly and evenly added to it. Zirconia balls were used as the ball milling medium. The ball milling speed was set to 350 r / min for 6 hours. After the ball milling was completed, the slurry was poured into a tray and placed in a constant temperature forced air drying oven to dry and obtain modified Mg3B2O6 ceramic powder.

[0083] (2) 45 parts of lyotropic liquid crystal polymer, 25 parts of polytetrafluoroethylene powder, and 30 parts of modified Mg3B2O6 ceramic powder were mixed to form a composition. The composition was then dissolved in N-methylpyrrolidone and magnetically stirred at 140°C for 3 hours to obtain a gel-like liquid. The content of the composition in the gel-like liquid was 45%. The gel-like liquid was uniformly coated onto a liquid crystal polymer nonwoven fabric and then baked at 140°C for 3 hours on a coating machine to form a film layer, thereby obtaining the modified liquid crystal polymer-based flexible composite film (modified LLCP / PTFE-based composite film).

[0084] (3) The modified LLCP / PTFE-based composite film layers are stacked opposite each other and pressed together in a vulcanizing machine at 202°C to obtain the modified liquid crystal polymer-based flexible composite film for mobile phone antennas.

[0085] The performance of the modified liquid crystal polymer-based flexible composite films for mobile phone antennas in Examples 1-8 above was tested. The test methods and standards are as follows:

[0086] Dielectric properties were tested according to the IEC 61189-2-721:2015 Split Dielectric Resonator (SPDR) method.

[0087] The flexural strength was tested according to ASTM D790 & ISO 178, the method for determining the flexural properties of plastics.

[0088] Tensile strength was tested according to ISO 527-1-2012, Test method for tensile properties of plastics.

[0089] The Vicat softening temperature was tested according to the ASTM D1525 method for determining the Vicat softening temperature of plastics.

[0090] The coefficient of thermal expansion was tested according to ISO 11359-2, the method for determining the coefficient of thermal expansion of plastics.

[0091] The test results are shown in Table 1 below.

[0092] Table 1 Performance test results of modified liquid crystal polymer-based flexible composite films for mobile phone antennas in Examples 1-8

[0093]

[0094] As can be seen from the performance test results in Table 1, the filling modification of Mg3B2O6 ceramic powder within the range described in this invention can result in a modified LLCP / PTFE-based composite film material with a dielectric constant of 2.51-3.43, a dielectric loss below 0.0031, a coefficient of thermal expansion of 27.35-41.80 ppm / ℃, and a Vicat softening temperature above 205.5℃. This indicates that modified LLCP / PTFE-based composite film materials with low coefficients of thermal expansion, low dielectric constants, and low losses can be prepared by filling modified Mg3B2O6 ceramic powder. Furthermore, compared to other commercially available modified LLCP-based flexible composite film materials, the modified LLCP / PTFE-based composite film material provided by this invention has reached commercially viable levels in dielectric, mechanical, and thermal properties, and exhibits even lower dielectric loss while withstanding temperatures up to 200℃.

[0095] The test results above show that the present invention comprehensively improves the high-frequency dielectric properties, mechanical properties, and thermal expansion properties of LLCP / PTFE composite materials by using a variety of methods. The resulting modified LLCP / PTFE-based composite film material has a dielectric constant below 3.5, a dielectric loss below 0.0031, a Vicat softening temperature above 205℃, and a thermal expansion coefficient of up to 27.35ppm / ℃. It can be used as a flexible FPC film material for 5G antennas, and can also meet the needs of other application scenarios such as flexible devices in 5G wearable communication devices.

[0096] In the course of this invention research, composite membranes of comparative examples 1-7 were also prepared, and the specific preparation methods are as follows.

[0097] Comparative Example 1: The difference between this comparative example and Example 3 is that the modified Mg3B2O6 ceramic powder of step (1) is not used, and 70 parts of lyotropic liquid crystal polymer and 30 parts of polytetrafluoroethylene powder are mixed into a composition in step (2).

[0098] Comparative Example 2: The difference between this comparative example and Example 1 is that in step (1), boron nitride ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified boron nitride ceramic powder, and in step (2), the prepared modified boron nitride ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0099] Comparative Example 3: The difference between this comparative example and Example 2 is that in step (1), boron nitride ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified boron nitride ceramic powder, and in step (2), the prepared modified boron nitride ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0100] Comparative Example 4: The difference between this comparative example and Example 3 is that in step (1), boron nitride ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified boron nitride ceramic powder, and in step (2), the prepared modified boron nitride ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0101] Comparative Example 5: The difference between this comparative example and Example 1 is that in step (1), alumina ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified alumina ceramic powder, and in step (2), the prepared modified alumina ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0102] Comparative Example 6: The difference between this comparative example and Example 2 is that in step (1), alumina ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified alumina ceramic powder, and in step (2), the prepared modified alumina ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0103] Comparative Example 7: The difference between this comparative example and Example 3 is that in step (1), alumina ceramic powder is used to replace Mg3B2O6 ceramic powder to prepare modified alumina ceramic powder, and in step (2), the prepared modified alumina ceramic powder is used to replace modified Mg3B2O6 ceramic powder.

[0104] The composite membranes of Comparative Examples 1-7 were subjected to performance tests using the same test methods and standards. The test results are shown in Table 2 below.

[0105] Table 2 shows the performance test results of the composite membranes in Comparative Examples 1-7.

[0106]

[0107] The scanning electron microscope image of the modified liquid crystal polymer-based flexible composite film for mobile phone antennas prepared in Example 3 of this invention is shown below. Figure 1 As shown, the scanning electron microscope image of the composite film prepared in Comparative Example 1 is as follows. Figure 2 As shown, the scanning electron microscope image of the composite film prepared in Comparative Example 4 is as follows. Figure 3 As shown, the scanning electron microscope image of the composite film prepared in Comparative Example 7 is as follows. Figure 4 As shown.

[0108] The modified liquid crystal polymer-based flexible composite film for mobile phone antennas of the present invention is densely packed (see...). Figure 1 The material has few pores and voids, resulting in low porosity. Simultaneously, the organic polymer effectively isolates the contact pathways between filler particles, and no significant agglomeration was observed. After surface modification with a surface modifier, the interfacial compatibility between Mg3B2O6 ceramic powder and the organic polymer is improved, reducing the agglomeration of Mg3B2O6 ceramic particles and promoting uniform dispersion of Mg3B2O6 ceramic powder in the organic matter, thereby reducing the material's porosity. The reduction in porosity is beneficial for lowering the coefficient of thermal expansion and dielectric loss of the composite membrane, resulting in superior performance.

[0109] contrast Figure 1 and Figure 2 It can be clearly seen that the addition of stearic acid-modified Mg3B2O6 ceramic powder not only improves the density of the composite material and fills the pores inside the material, but also greatly reduces the internal interfaces of the material, thus optimizing its performance.

[0110] contrast Figure 1 and Figure 3 , Figure 4It can be seen that the modified Mg3B2O6 ceramic powder is more tightly wrapped by the lyotropic liquid crystal polymer after filling, with a small amount of long fiber structure of liquid crystal polymer nonwoven fabric; while the composite film filled with modified boron nitride and alumina still has a small number of pores and the structure is relatively not dense, indicating that the modified Mg3B2O6 ceramic powder and the lyotropic liquid crystal polymer are better bonded.

[0111] As can be seen from the performance test results of Examples 1-3 in Table 1 and Comparative Examples 1-7 in Table 2, the dielectric properties of the composite film are greatly improved and the coefficient of thermal expansion is significantly reduced after the addition of modified Mg3B2O6 ceramic powder, which is better than the filling effect of modified boron nitride and alumina.

[0112] In the course of this invention research, composite membranes of comparative examples 8-16 were also prepared, and the specific preparation methods are as follows.

[0113] Comparative Example 8: The difference between this comparative example and Example 3 is that carbonate is used instead of stearic acid as a surface modifier in step (1).

[0114] Comparative Example 9: The difference between this comparative example and Example 3 is that the amount of stearic acid added in step (1) is 0.5 wt% of Mg3B2O6 ceramic powder.

[0115] Comparative Example 10: The difference between this comparative example and Example 3 is that the amount of stearic acid added in step (1) is 5 wt% of Mg3B2O6 ceramic powder.

[0116] Comparative Example 11: The difference between this comparative example and Example 3 is that in step (2), 45 parts of lyotropic liquid crystal polymer, 45 parts of polytetrafluoroethylene powder, and 10 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0117] Comparative Example 12: The difference between this comparative example and Example 3 is that in step (2), 55 parts of lyotropic liquid crystal polymer, 15 parts of polytetrafluoroethylene powder, and 20 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0118] Comparative Example 13: The difference between this comparative example and Example 3 is that in step (2), 45 parts of lyotropic liquid crystal polymer, 20 parts of polytetrafluoroethylene powder, and 35 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0119] Comparative Example 14: The difference between this comparative example and Example 3 is that in step (2), 55 parts of lyotropic liquid crystal polymer, 40 parts of polytetrafluoroethylene powder, and 5 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0120] Comparative Example 15: The difference between this comparative example and Example 3 is that in step (2), 70 parts of lyotropic liquid crystal polymer, 20 parts of polytetrafluoroethylene powder, and 10 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0121] Comparative Example 16: The difference between this comparative example and Example 3 is that in step (2), 30 parts of lyotropic liquid crystal polymer, 40 parts of polytetrafluoroethylene powder, and 30 parts of modified Mg3B2O6 ceramic powder are mixed into a composition.

[0122] The composite membranes of Comparative Examples 8-16 were subjected to performance tests using the same test methods and standards. The test results are shown in Table 3 below.

[0123] Table 3. Performance test results of composite membranes in Example 3 and Comparative Examples 8-16

[0124]

[0125] Comparing Example 3 and Comparative Example 8, it can be seen that, compared with carbonate, using stearic acid as a surface modifier can improve the compatibility of ceramic powder, resin and GF to a greater extent, thereby making the composite film have lower dielectric loss and better thermal and mechanical properties.

[0126] Comparing Example 3 with Comparative Example 9 and Comparative Example 10, it can be seen that when the amount of added stearic acid is too small or too large, stearic acid will have difficulty playing a good role in surface modification, resulting in the composite film having higher dielectric loss and worse thermal and mechanical properties.

[0127] Comparing Example 3 with Comparative Examples 11 and 12, it can be seen that when the amount of added polytetrafluoroethylene powder is too high, the thermal properties of the composite film will deteriorate; while when the amount of added polytetrafluoroethylene powder is too low, the dielectric loss of the composite film will be too high. This indicates that the content of polytetrafluoroethylene and lyotropic liquid crystal polymer in the composite film should be controlled within the range protected by this patent.

[0128] Comparing Example 3 with Comparative Examples 13 and 14, it can be seen that when the content of added modified Mg3B2O6 ceramic powder is too high, the mechanical properties of the composite film will deteriorate. In this case, the poor mechanical properties of the composite film will make it difficult to meet the mechanical property requirements of flexible thin film materials for 5G antennas and flexible devices. When the content of added modified Mg3B2O6 ceramic powder is too low, the dielectric loss of the composite film will be too high and the heat resistance will be poor. This also shows that the content of Mg3B2O6 ceramic powder in the composite film material should be controlled within the range protected by this patent.

[0129] Comparing Example 3 with Comparative Examples 15 and 16, it can be seen that when the content of added lyotropic liquid crystal polymer is too high, the dielectric loss of the composite film material will be too high; while when the content of added lyotropic liquid crystal polymer is too low, the mechanical properties of the composite film material will deteriorate. In this case, the mechanical properties of the composite film are poor, and it is difficult to meet the mechanical property requirements of flexible thin film materials for 5G antennas and flexible devices. This also shows that the content of lyotropic liquid crystal polymer in the composite film material should be controlled within the range protected by this patent.

[0130] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A composition for preparing a flexible composite membrane, characterized in that, The product is composed of the following raw materials in parts by weight: 40-60 parts of lyotropic liquid crystal polymer, 20-40 parts of polytetrafluoroethylene powder, and 10-30 parts of modified Mg3B2O6 ceramic powder. The modified Mg3B2O6 ceramic powder is obtained by grinding Mg3B2O6 ceramic powder in an organic solvent with the addition of a surface modifier and then drying it; the surface modifier is 1-3 wt% of the mass of the Mg3B2O6 ceramic powder; the surface modifier is selected from at least one of stearic acid and silane coupling agent KH550. The lyotropic liquid crystal polymer has an electrical constant of 2.9-3.1 and a dielectric loss of 3.5 × 10⁻⁶. -3 -4.5×10 -3 Its coefficient of thermal expansion is 35-40 ppm / ℃, and its Vicat softening temperature is above 190°C.

2. The composition according to claim 1, characterized in that, The particle size of the Mg3B2O6 ceramic powder is in the micrometer range, and the particle size of the polytetrafluoroethylene powder is in the micrometer range; the mass ratio of the Mg3B2O6 ceramic powder to the organic solvent is 1:(3-5), and the organic solvent is selected from at least one of anhydrous ethanol, methanol, propanol, and butanediol.

3. The composition according to claim 1, characterized in that, The specific operation of drying after grinding is as follows: using zirconia balls as the ball milling medium, the ball mill is set to a speed of 300-400 r / min for 6-12 hours. After the ball milling is completed, the slurry is placed in a constant temperature forced-air drying oven for drying.

4. A modified liquid crystal polymer-based flexible composite film, characterized in that, It includes a liquid crystal polymer nonwoven fabric and a film layer coated on the liquid crystal polymer nonwoven fabric, said film layer containing the composition as described in any one of claims 1-3.

5. The method for preparing the modified liquid crystal polymer-based flexible composite film as described in claim 4, characterized in that, Includes the following steps: The composition according to any one of claims 1-3 is dissolved in N-methylpyrrolidone and stirred at 130-150°C for 2-4 hours to obtain a gel-like solution, wherein the content of the composition in the gel-like solution is 20-50%; The gel-like liquid is uniformly coated onto the liquid crystal polymer nonwoven fabric, and then baked to form a film layer, thus obtaining the modified liquid crystal polymer-based flexible composite film.

6. The preparation method according to claim 5, characterized in that, The baking temperature is 140±10 °C, and the time is 1-3 hours.

7. A modified liquid crystal polymer-based flexible composite film for mobile phone antennas, characterized in that, It is made from the modified liquid crystal polymer-based flexible composite film as described in claim 4.

8. The modified liquid crystal polymer-based flexible composite film for mobile phone antennas according to claim 7, characterized in that, The modified liquid crystal polymer-based flexible composite film has a liquid crystal polymer nonwoven fabric thickness of 12-20 μm and a film thickness of 100-1000 μm.

9. The method for preparing a modified liquid crystal polymer-based flexible composite film for mobile phone antennas as described in claim 7 or 8, characterized in that, The modified liquid crystal polymer-based flexible composite film is made by stacking the film layers opposite each other and pressing them together at a pressing temperature of 190-220℃.

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