Preparation method of high-thermal-conductivity composite film and high-thermal-conductivity composite film

Abstract

This application provides a method for preparing a high thermal conductivity composite film and the high thermal conductivity composite film itself. The method includes dispersing boric acid and melamine in water, adding vacuum-dried montmorillonite and mixing uniformly to obtain a montmorillonite-containing precursor solution. The precursor solution is sintered under an ammonia atmosphere to obtain a sintered product. Hydrofluoric acid is added to the sintered product and mixed, then filtered and dried to obtain boron nitride nanosheets. The boron nitride nanosheets are then dispersed at high speed in deionized water to obtain a first slurry. A fluororesin emulsion and additives are added to the first slurry, mixed uniformly, and then vacuum-degassed to obtain a second slurry. The second slurry is coated onto a base film to form a film, which is then dried and sintered to obtain a cast film. The cast film is hot-pressed, and the base film is peeled off to obtain the high thermal conductivity composite film. The preparation of boron nitride nanosheets using the montmorillonite precursor achieves uniform synthesis of the boron nitride nanosheets. The prepared high thermal conductivity composite film exhibits excellent high-temperature resistance, insulation, and chemical corrosion resistance.

Description

Technical Field

[0001] This application relates to the field of composite heat dissipation materials technology, specifically to a method for preparing a high thermal conductivity composite film and the high thermal conductivity composite film itself. Background Technology

[0002] Boron nitride nanosheets (BNNS), as a typical two-dimensional material, possess atomically flat surfaces, excellent thermal conductivity (700 W / (m·K)), high-temperature resistance, and electrical insulation, making them an ideal reinforcing phase for polymer materials. Polytetrafluoroethylene (PTFE), on the other hand, is widely used in harsh working conditions due to its excellent chemical corrosion resistance, low coefficient of friction, and wide temperature range. Combining BNNS with PTFE can leverage the advantages of both, addressing the issues of low thermal conductivity and easy deformation at high temperatures associated with PTFE alone, and expanding its applications in high-end fields.

[0003] Traditional BNNS preparation methods (such as mechanical exfoliation and liquid phase exfoliation) are prone to causing sheet agglomeration and it is difficult to control the uniformity of sheet size. When BNNS powder is directly mixed with PTFE emulsion, the dispersibility is poor and local agglomerates are easily formed, which affects the mechanical and thermal properties of the composite membrane. Summary of the Invention

[0004] To address at least one of the above technical problems, embodiments of this application provide a method for preparing a high thermal conductivity composite film.

[0005] In addition, this application also provides a high thermal conductivity composite film prepared using this preparation method.

[0006] This application provides a method for preparing a high thermal conductivity composite film, comprising dispersing boric acid and melamine in water, and adding vacuum-dried montmorillonite and mixing evenly to obtain a precursor solution containing montmorillonite. The precursor solution is sintered under an ammonia atmosphere to obtain a sintered product. Hydrofluoric acid is added to the sintered product and mixed, then filtered and dried to obtain boron nitride nanosheets. The boron nitride nanosheets are dispersed in water to obtain a first slurry. A fluororesin emulsion and additives are added to the first slurry, mixed evenly, and then vacuum degassed to obtain a second slurry. The second slurry is coated onto a substrate film to form a film, dried, and sintered at 200°C to 350°C to obtain a cast film. The cast film is hot-pressed, and the substrate film is peeled off to obtain a high thermal conductivity composite film.

[0007] This application utilizes montmorillonite precursors to prepare boron nitride nanosheets, achieving uniform synthesis. The nanodispersion of the boron nitride nanosheets is optimized by dispersing them in water. A high thermal conductivity composite film is obtained through a stepwise process of casting, drying, high-temperature sintering, and high-temperature hot pressing. The synthesis of boron nitride nanosheets via montmorillonite precursors and dispersion in aqueous solution effectively improves the problems of layer agglomeration and poor dispersion in traditional mechanical / liquid phase exfoliation methods. High-temperature hot pressing allows for precise control of the thickness of the high thermal conductivity composite film, fundamentally solving the problems of residual organic additives, easy surface cracking, uneven thickness, and impaired mechanical / thermal properties in existing composite films, significantly improving the core quality of the composite film.

[0008] In some embodiments of this application, the solid content of the first slurry is 10% to 30%; the solid content of the second slurry is 20% to 40%.

[0009] In some embodiments of this application, the preparation method satisfies at least one of the following characteristics: (1) the vacuum degassing time is 2 h to 12 h; (2) the drying temperature is 50 ℃ to 100 ℃.

[0010] In some embodiments of this application, the concentration of hydrofluoric acid is from 1 wt% to 10 wt%.

[0011] In some embodiments of this application, the hot-pressing temperature is 200°C to 350°C. The hot-pressing pressure is 1 MPa to 10 MPa.

[0012] In some embodiments of this application, the base film is one of a fluorine film and a polyimide film.

[0013] In some embodiments of this application, the mass ratio of boric acid to melamine is 1:(0.1-10).

[0014] In some embodiments of this application, the vacuum drying temperature is 50 °C to 120 °C.

[0015] In some embodiments of this application, montmorillonite is one or more of sodium-based montmorillonite and calcium-based montmorillonite.

[0016] This application also provides a high thermal conductivity composite film, prepared using the aforementioned high thermal conductivity composite film preparation method. The high thermal conductivity composite film provided by this application exhibits excellent high-temperature resistance, insulation, and chemical corrosion resistance, and can be applied to scenarios such as heat dissipation packaging of electronic devices, anti-corrosion coatings for chemical equipment, and high-temperature dielectric isolation films. It is suitable for both laboratory research and development and large-scale industrial production. Detailed Implementation

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0018] This application provides a method for preparing a high thermal conductivity composite film, specifically including the following steps:

[0019] S1. Boric acid and melamine are dispersed in water, and vacuum-dried montmorillonite is added and mixed evenly to obtain a precursor solution containing montmorillonite.

[0020] Specifically, boric acid and melamine are added to deionized water and ultrasonically dispersed, and then vacuum-dried montmorillonite is added and stirred until homogeneous to obtain a precursor solution containing montmorillonite.

[0021] In some embodiments, the frequency of the ultrasound is 300 Hz to 450 Hz.

[0022] In some embodiments, the mass ratio of boric acid to melamine is 1:(0.1-10).

[0023] For example, the mass ratio of boric acid to melamine can be 1:0.1, 1:0.125, 1:0.2, 1:0.5, 1:1, 1:2, 1:5, 1:8, 1:10, or any value within the range of any two of the above values.

[0024] In some embodiments, the vacuum drying temperature is 50 °C to 120 °C. The vacuum drying time is 12 h to 14 h. Vacuum drying can remove adsorbed water and crystal water from montmorillonite, preventing residual moisture from affecting the adsorption and reaction of boron-nitrogen sources between montmorillonite layers. Simultaneously, it prevents high temperatures from damaging the regular layered template structure of montmorillonite, ensuring the directional growth of boron nitride nanosheets guided by montmorillonite and guaranteeing the uniformity of boron nitride nanosheet size. Exemplarily, the vacuum drying temperature can be 50 °C, 80 °C, 100 °C, 120 °C, or any value within the range of any two of the above values. Exemplarily, the drying time can be 12 h, 13 h, 14 h, or any value within the range of any two of the above values.

[0025] In some embodiments, the montmorillonite is cationic montmorillonite. The cationic montmorillonite is one or more of sodium-based and calcium-based montmorillonite. Both sodium-based and calcium-based montmorillonite have suitable interlayer spacing and ion exchange capacity, enabling efficient adsorption of boron nitrogen sources and providing a stable growth template. Mixed use allows for flexible adjustment of layered structure parameters, further optimizing the thickness and morphological regularity of boron nitride sheets, avoiding the growth limitation problem caused by a single type of montmorillonite, and improving the interfacial compatibility between boron nitride and polytetrafluoroethylene. Preferably, calcium-based montmorillonite is used. Due to its more stable interlayer structure, calcium-based montmorillonite is less prone to collapse and deformation during high-temperature sintering, providing a stable template for boron nitride synthesis and ensuring uniform boron nitride sheets and complete crystals.

[0026] In some embodiments, in step S1, the stirring rate is 1000 rpm to 5000 rpm.

[0027] For example, the stirring rate can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, or any value within the range of any two of the above values.

[0028] S2. Sinter the montmorillonite precursor under an ammonia atmosphere to obtain the sintered product.

[0029] Specifically, the montmorillonite precursor is loaded into a corundum boat, placed in a tube furnace, and sintered at high temperature by introducing ammonia gas. After cooling, a white sintered product is obtained.

[0030] In some embodiments, the sintering time is 1 h to 20 h, and the sintering temperature is 600 °C to 1000 °C.

[0031] For example, the sintering time can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, or any value within the range of any two of the above values. The sintering temperature can be 600 ℃, 700 ℃, 800 ℃, 900 ℃, 1000 ℃, or any value within the range of any two of the above values.

[0032] S3. Add hydrofluoric acid to the sintered product, stir and mix, filter and dry to obtain boron nitride nanosheets.

[0033] In some embodiments, the concentration of hydrofluoric acid is from 1 wt% to 10 wt%.

[0034] For example, the concentration of hydrofluoric acid can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any value within the range of any two of the above values. By using the above concentration, impurities can be selectively etched while preserving the complete atomically flat surface and layered structure of the boron nitride nanosheets, thereby enhancing its core performance as a reinforcing phase.

[0035] In some embodiments, the stirring rate is from 100 rpm to 1000 rpm. For example, the stirring rate can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, or any value within the range of any two of the above values.

[0036] S4. Add boron nitride nanosheets to deionized water and stir at high speed to disperse them, thus obtaining the first slurry.

[0037] In some embodiments, the solid content of the first slurry is 10% to 30%. The first slurry is a ceramic slurry. Exemplarily, the solid content can be 10%, 15%, 20%, 25%, 30%, or any value within the range of any two of the above values.

[0038] In some embodiments, the stirring rate in step S3 is 1000 rpm to 5000 rpm.

[0039] For example, the stirring rate can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 5000 rpm, or any value within the range of any two of the above values.

[0040] S5. Add the fluororesin emulsion and additives to the first slurry, stir and mix evenly, and then degas under vacuum to obtain the second slurry.

[0041] In some embodiments, the solid content of the second slurry is 20% to 40%. For example, the solid content can be 20%, 25%, 30%, 35%, 40%, or any value within the range of any two of the above values.

[0042] In some embodiments, the vacuum degassing time is 2 h to 12 h. If the degassing time is too short, bubbles cannot be completely removed, and residual bubbles will disrupt the continuity of the heat-conducting network and reduce mechanical properties; if the degassing time is too long, it can easily lead to slurry stratification and boron nitride sedimentation and agglomeration. This range can completely remove microbubbles while maintaining a uniform dispersion of boron nitride in the slurry, balancing degassing effect and production efficiency. For example, the degassing time can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or any value within the range of any two of the above values.

[0043] In some embodiments, the stirring rate in step S4 is from 100 rpm to 1000 rpm. For example, the stirring rate can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, or any value within the range of any two of the above values.

[0044] In some embodiments, the additives are thickeners, defoamers, and film-forming agents. The thickener is Dow TT935, the defoamer is BYK-028, and the film-forming agent is CAP-800.

[0045] Specifically, fluoropolymer emulsions can be polytetrafluoroethylene emulsions.

[0046] In some embodiments, the mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is (2-5):5.

[0047] For example, the mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion can be 3:7, 2:3, or 5:5.

[0048] S6. After coating the second slurry onto the base film to form a film, dry it and sinter it at 200 ℃ to 350 ℃ to obtain a cast film.

[0049] Specifically, the second slurry is coated onto the base film using a four-sided coating tool, and then the surface solvent is dried and sintered at 200 ℃ to 350 ℃ to obtain a cast film.

[0050] In some embodiments, the thickness of the four-sided coating apparatus is from 250 μm to 1000 μm.

[0051] For example, the thickness of the four-sided coating device can be 250 μm, 500 μm, 750 μm, 1000 μm or any value within the range of any two of the above values.

[0052] In some embodiments, the drying temperature is 50°C to 100°C. For example, the drying temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or any value within the range of any two of the above values.

[0053] In some embodiments, the base film is either a fluorinated film or a polyimide film. Fluorinated films and polyimide films possess high-temperature resistance and low surface energy, exhibiting moderate compatibility with the composite system of polytetrafluoroethylene and boron nitride nanosheets. They do not chemically react with the film layer and avoid film damage caused by adhesion. Simultaneously, their excellent mechanical strength supports the integrity of the film layer throughout the coating, drying, and sintering processes, ensuring regular edges and uniform thickness of the cast film, avoiding film defects caused by poor compatibility with the base film, and guaranteeing the composite effect of subsequent multilayer stacking and hot pressing. Preferably, the base film is a polyimide film.

[0054] S7. The cast film is hot-pressed and the base film is peeled off to obtain a high thermal conductivity composite film.

[0055] In some embodiments, the pressure of hot pressing is from 1 MPa to 10 MPa. For example, the pressure can be 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, or any value within the range of any two of the above values.

[0056] In some embodiments, the hot-pressing temperature is between 200°C and 350°C. Exemplarily, the temperature can be 200°C, 250°C, 300°C, 350°C, or any value within the range of any two of the above values.

[0057] In some embodiments, the hot pressing time is from 1 h to 5 h. For example, the time can be 1 h, 2 h, 3 h, 4 h, 5 h, or any value within the range of any two of the above values.

[0058] Compared with the existing technology, the method for preparing high thermal conductivity composite films in this application has the following advantages:

[0059] Boron nitride nanosheets were prepared using montmorillonite precursors, achieving uniform synthesis. The nanodispersion of the boron nitride nanosheets was optimized by dispersing them in water. A high thermal conductivity composite film was obtained through a stepwise process of casting, drying, high-temperature sintering, and high-temperature hot pressing. The synthesis of boron nitride nanosheets using montmorillonite precursors and dispersion in aqueous solution effectively improves the problems of layer agglomeration and poor dispersion in traditional mechanical / liquid phase exfoliation methods. High-temperature hot pressing allows for precise control of the thickness of the high thermal conductivity composite film, fundamentally solving the problems of residual organic additives, easy surface cracking, uneven thickness, and impaired mechanical / thermal properties in existing composite films, significantly improving the core quality of the composite film.

[0060] This application provides a high thermal conductivity composite film, prepared using the aforementioned high thermal conductivity composite film preparation method. The high thermal conductivity composite film provided by this application exhibits excellent high-temperature resistance, insulation, and chemical corrosion resistance, and can be applied to scenarios such as heat dissipation packaging of electronic devices, anti-corrosion coatings for chemical equipment, and high-temperature dielectric isolation films. It is suitable for both laboratory research and development and large-scale industrial production.

[0061] The preparation method of the aforementioned high thermal conductivity composite film will be further explained below through specific embodiments.

[0062] Example 1

[0063] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:10 and disperse by ultrasonication to obtain a precursor solution. Place calcium-based montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried calcium-based montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0064] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0065] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0066] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0067] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 3:7.

[0068] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0069] Step 7: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h, and peel it off to obtain a high thermal conductivity composite film.

[0070] Example 2

[0071] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:10 and disperse by ultrasonication to obtain a precursor solution. Place sodium montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried sodium montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0072] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0073] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0074] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0075] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 3:7.

[0076] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0077] Step 7: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h, and peel it off to obtain a high thermal conductivity composite film.

[0078] Example 3

[0079] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:1 and disperse by ultrasonication to obtain a precursor solution. Place calcium-based montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried calcium-based montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0080] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0081] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0082] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0083] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 3:7.

[0084] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0085] Step 7: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h, and peel it off to obtain a high thermal conductivity composite film.

[0086] Example 4

[0087] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:0.1 and disperse by ultrasonication to obtain a precursor solution. Place calcium-based montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried calcium-based montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0088] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0089] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0090] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0091] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 3:7.

[0092] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0093] Step 7: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h, and peel it off to obtain a high thermal conductivity composite film.

[0094] Example 5

[0095] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:1 and disperse by ultrasonication to obtain a precursor solution. Place calcium-based montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried calcium-based montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0096] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0097] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0098] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0099] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 4:6.

[0100] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0101] Step 7: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h, and peel it off to obtain a high thermal conductivity composite film.

[0102] Example 6

[0103] Step 1: Add boric acid and melamine to deionized water at a mass ratio of 1:1 and disperse by ultrasonication to obtain a precursor solution. Place calcium-based montmorillonite in a vacuum drying oven and dry at 80 °C for 12 h. Add the vacuum-dried calcium-based montmorillonite to the precursor solution and stir at a speed of 2000 rpm to mix evenly to obtain the montmorillonite precursor.

[0104] Step 2: The montmorillonite precursor is loaded into a corundum boat and placed in a tube furnace. Ammonia gas is introduced and the furnace is sintered at 800 °C for 12 h. After cooling, a white sintered product is obtained.

[0105] Step 3: Add 1 wt% hydrofluoric acid to the sintered product and stir at 250 rpm for 4 h. Filter and collect the filter cake. Place the filter cake in a vacuum drying oven at 80 ℃ for 12 h to obtain boron nitride nanosheets.

[0106] Step 4: Add boron nitride nanosheets to deionized water and stir at 1500 rpm to disperse them, so as to obtain a first slurry with a solid content of 20%.

[0107] Step 5: Under low-speed stirring at 500 rpm, add the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 to the first slurry and mix thoroughly. Degas under vacuum for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 5:5.

[0108] Step 6: Apply the second slurry to the polyimide film substrate using a 500 μm thick four-sided coating tool, dry the surface solvent at 60 °C, and then sinter at 340 °C for 5 h to obtain the cast film.

[0109] Step 7: Hot-press the cast film at 350 °C and 2 MPa for 4 h to obtain a high thermal conductivity composite film.

[0110] Comparative Example 1

[0111] Step 1: Add commercial boron nitride powder to deionized water and stir at 1500 rpm to disperse it, so as to obtain a first slurry with a solid content of 20%.

[0112] Step 2: Under low-speed stirring at 500 rpm, the polytetrafluoroethylene emulsion, Dow TT935, BYK-028, and CAP-800 were added to the first slurry and mixed thoroughly. Vacuum degassing was performed for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion was 3:7.

[0113] Step 3: The second slurry is coated onto the polyimide film substrate using a 500 μm thick four-sided coating tool. The surface solvent is dried at 60 °C, and then sintered at 340 °C for 5 h to obtain the cast film.

[0114] Step 4: The cast film is hot-pressed at 350 ℃ and 2 MPa for 4 h, and then peeled off to obtain a high thermal conductivity composite film.

[0115] Comparative Example 2

[0116] Step 1: Ball milled commercial boron nitride powder was added to deionized water and stirred at 1500 rpm to disperse it, resulting in a first slurry with a solid content of 20%.

[0117] Step 2: Under low-speed stirring at 600 rpm, the polytetrafluoroethylene emulsion and additives are added to the first slurry and mixed evenly. Vacuum degassing is performed for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 3:7.

[0118] Step 3: The second slurry is coated onto the polyimide film substrate using a 500 μm thick four-sided coating tool. The surface solvent is dried at 60 °C, and then sintered at 340 °C for 5 h to obtain the cast film.

[0119] Step 4: The cast film is hot-pressed at 350 ℃ and 2 MPa for 4 h, and then peeled off to obtain a high thermal conductivity composite film.

[0120] Comparative Example 3

[0121] Step 1: Ball milled commercial boron nitride powder was added to deionized water and stirred at 1500 rpm to disperse it, resulting in a first slurry with a solid content of 20%.

[0122] Step 2: Under low-speed stirring at 600 rpm, the polytetrafluoroethylene emulsion and additives are added to the first slurry and mixed evenly. Vacuum degassing is performed for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 4:6.

[0123] Step 3: The second slurry is coated onto the polyimide film substrate using a 500 μm thick four-sided coating tool. The surface solvent is dried at 60 °C, and then sintered at 340 °C for 5 h to obtain the cast film.

[0124] Step 4: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h to obtain a high thermal conductivity composite film.

[0125] Comparative Example 4

[0126] Step 1: Ball milled commercial boron nitride powder was added to deionized water and stirred at 1500 rpm to disperse it, resulting in a first slurry with a solid content of 20%.

[0127] Step 2: Under low-speed stirring at 600 rpm, the polytetrafluoroethylene emulsion and additives are added to the first slurry and mixed evenly. Vacuum degassing is performed for 12 h to obtain a second slurry with a solid content of 35%. The mass ratio of boron nitride nanosheets to polytetrafluoroethylene emulsion is 5:5.

[0128] Step 3: The second slurry is coated onto the polyimide film substrate using a 500 μm thick four-sided coating tool. The surface solvent is dried at 60 °C, and then sintered at 340 °C for 5 h to obtain the cast film.

[0129] Step 4: Hot-press the cast film at 350 ℃ and 2 MPa for 4 h to obtain a high thermal conductivity composite film.

[0130] The high thermal conductivity composite films obtained in Examples 1-6 and Comparative Examples 1-4 were subjected to the following tests, and the test results are shown in Table 1.

[0131] (1) Dielectric constant Dk and dielectric loss Df: The SPDR method was used for testing at a frequency of 10 GHz;

[0132] (2) Thermal conductivity: Thermal conductivity was tested using the ASTM D5470-2017 method;

[0133] (3) Mechanical strength: The mechanical strength was tested using the ASTM D882-23 method.

[0134] (4) Chemical resistance: Chemical resistance was tested using the ASTM D543 method.

[0135] Table 1: Performance test results of Examples 1-6 and Comparative Examples 1-4

[0136]

[0137] As can be seen from the results in Table 1, the overall performance of Example 3 is superior to that of other examples and comparative examples. This is because calcium-based montmorillonite has a more stable interlayer structure and is less prone to collapse and deformation during high-temperature sintering, providing a stable template for boron nitride synthesis and ensuring uniform boron nitride sheets and complete crystals. Compared with the sodium-based montmorillonite system (14.9% higher horizontal thermal conductivity and 13.1% higher tensile strength) and traditional methods (such as ball-milled boron nitride, with 42.5% higher horizontal thermal conductivity and 44.6% higher tensile strength), it significantly improves the performance of the composite film. Therefore, the high thermal conductivity composite film preparation method provided in this application achieves uniformity in the synthesis of boron nitride nanosheets by preparing boron nitride nanosheets using montmorillonite precursors. The nanodispersion of boron nitride nanosheets is optimized by dispersing them in water. Simultaneously, a stepwise process of casting, drying, high-temperature sintering, and high-temperature hot pressing is used to obtain the high thermal conductivity composite film. Boron nitride nanoparticles, synthesized via montmorillonite precursors and dispersed in aqueous solution, effectively address the issues of lamellar agglomeration and poor dispersion in traditional mechanical / liquid phase exfoliation methods. High-temperature hot pressing allows for precise control of the composite film thickness, fundamentally resolving problems such as residual organic additives, surface cracking, uneven thickness, and compromised mechanical / thermal properties in existing composite films, thus significantly improving the core quality of the composite film. The prepared high thermal conductivity composite film not only meets the needs of high-end fields such as electronic packaging and chemical corrosion protection, but also ensures large-scale production due to the stable process.

[0138] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a high thermal conductivity composite film, characterized in that, include: Boric acid and melamine were dispersed in water, and vacuum-dried montmorillonite was added and mixed evenly to obtain a precursor solution containing montmorillonite. The precursor solution was sintered under an ammonia atmosphere to obtain the sintered product. Hydrofluoric acid with a concentration of 1 wt% to 10 wt% was added to the sintered product and mixed. After filtration and drying, boron nitride nanosheets were obtained. Boron nitride nanosheets were dispersed in water to obtain a first slurry with a solid content of 10% to 30%. Fluoropolymer emulsion and additives are added to the first slurry, mixed evenly, and then vacuum degassed to obtain a second slurry with a solid content of 20% to 40%. The second slurry is coated onto the base film to form a film, then dried and sintered at 200 ℃ to 350 ℃ to obtain a cast film; The cast film is hot-pressed and the base film is peeled off to obtain a high thermal conductivity composite film. The mass ratio of boric acid to melamine is 1:(0.1-10); The montmorillonite is one or more of sodium-based montmorillonite and calcium-based montmorillonite; the base membrane is one of fluorine membrane and polyimide membrane.

2. The method for preparing the high thermal conductivity composite film according to claim 1, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The vacuum degassing time is 2 h to 12 h; (2) The drying temperature is 50 ℃ to 100 ℃.

3. The method for preparing the high thermal conductivity composite film according to claim 1, characterized in that, The hot pressing temperature is 200 ℃ to 350 ℃; the hot pressing pressure is 1 MPa to 10 MPa.

4. The method for preparing the high thermal conductivity composite film according to claim 1, characterized in that, The vacuum drying temperature is between 50 °C and 120 °C.

5. A high thermal conductivity composite film, characterized in that, The high thermal conductivity composite film was prepared using the preparation method described in any one of claims 1-4.

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