A polyimide thermal conductive film and its preparation method and application

Abstract

The present invention provides a polyimide thermally conductive film, its preparation method, and application, relating to the technical field of polyimide films. The preparation method comprises: cutting a polyimide fiber film to produce polyimide fiber filaments; surface treating the polyimide fiber filaments to produce active fiber filaments; coating the active fiber filaments with first thermally conductive particles to produce modified fiber filaments; dispersing the modified fiber filaments and second thermally conductive particles into a polyamic acid adhesive to produce a composite adhesive; and forming the composite adhesive into a film and imidizing it to produce a polyimide thermally conductive film. The present invention can simultaneously improve the out-of-plane thermal conductivity and mechanical properties of the polyimide thermally conductive film.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide films, and in particular to a polyimide thermal conductive film and a preparation method and application thereof. Background Art

[0002] With the miniaturization, integration and functionalization of microelectronics and portable devices, the heat generated per unit time during the operation of internal electronic components has increased dramatically, making thermal management a key issue. How to achieve efficient and rapid heat dissipation while maintaining excellent insulation has become an important technical challenge currently faced. Polyimide is at the top of the engineering material pyramid due to its excellent insulation properties, high and low temperature resistance, and stable chemical properties. However, its intrinsic out-of-plane thermal conductivity is poor (0.2-0.3W·m -1 ·K -1 ), which cannot meet the rapid heat dissipation needs of electronic components, greatly limiting the application of films in more new fields. In order to solve the heat dissipation problem, a new generation of polyimide-based film materials with both high insulation and high thermal conductivity is urgently needed. Researchers have conducted a lot of research on this, mainly using polyimide resin or polyamic acid solution to add inorganic thermal conductive particles for blending and doping to prepare thermally conductive polyimide composite films. The thermal conductive filler inside the polyimide-based composite film prepared by this method will settle during the preparation process, resulting in a low out-of-plane thermal conductivity. If the amount of inorganic thermal conductive particles added is increased, although a heat conduction path can be effectively constructed, the mechanical properties of the film are severely damaged, which greatly affects the comprehensive performance of the polyimide composite film. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0003] The object of the present invention is to provide a polyimide thermally conductive film and a preparation method and application thereof, which can simultaneously improve the out-of-plane thermal conductivity and mechanical properties of the polyimide thermally conductive film.

[0004] In a first aspect, the present invention provides a method for preparing a polyimide thermally conductive film, comprising: cutting a polyimide fiber membrane to obtain polyimide fiber filaments; surface-treating the polyimide fiber filaments to obtain active fiber filaments; coating the surface of the active fiber filaments with first thermally conductive particles to obtain modified fiber filaments; dispersing the modified fiber filaments and second thermally conductive particles into a polyamic acid adhesive to obtain a composite adhesive; and forming a film and imidizing the composite adhesive to obtain a polyimide thermally conductive film.

[0005] Optionally, the average length of the polyimide fiber filaments is 50 μm-100 μm.

[0006] Optionally, the particle sizes of the first thermally conductive particles and the second thermally conductive particles are independently 50 nm-5000 nm.

[0007] Optionally, the first thermally conductive particles and the second thermally conductive particles are independently made of one of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0008] Optionally, when surface treatment is performed on the polyimide fiber filaments, the polyimide fiber filaments are immersed in an alkaline solution to perform surface etching.

[0009] Optionally, the concentration of the alkaline solute in the alkaline solution is 0.5 mol / L-2 mol / L.

[0010] Optionally, the alkaline solute in the alkaline solution includes sodium hydroxide and potassium hydroxide.

[0011] Optionally, the polyimide fiber is soaked in an alkaline solution and ultrasonicated.

[0012] Optionally, the inner surface is etched in an alkaline solution for 1 min to 10 min.

[0013] Optionally, the surface is etched and then separated and dried.

[0014] Optionally, the active fiber filaments and the first heat-conductive particles are co-dispersed in an alcohol-water solution and then separated to obtain modified fiber filaments.

[0015] Optionally, the mass ratio of the active fiber filaments to the first thermally conductive particles is 100:(5-15).

[0016] Optionally, the alcohol aqueous solution includes low molecular alcohol, and the low molecular alcohol includes methanol, ethanol and / or isopropanol.

[0017] Optionally, the separation is followed by drying at 50°C-80°C.

[0018] Optionally, the mixture is co-dispersed in an alcohol-water solution for 5 min to 30 min.

[0019] Optionally, the mass ratio of the modified fiber filaments to the second thermally conductive particles is (5-20): (1-15).

[0020] Optionally, the mass concentration of the modified fiber in the composite glue is 5%-20%.

[0021] Optionally, the mass concentration of the second thermally conductive particles in the composite adhesive is 1%-15%.

[0022] Optionally, the solid content of the polyamic acid glue is 5%-25%.

[0023] Optionally, the polyamic acid glue includes glue prepared by polycondensation of diamine and dianhydride or glue prepared by dissolving molding powder.

[0024] Optionally, the polyimide fiber membrane is prepared by electrospinning and imidization of a precursor glue, wherein the precursor glue includes polyamic acid and a solvent for dissolving the polyamic acid.

[0025] Optionally, the precursor glue is subjected to electrospinning in an environment with a temperature of 25° C.-50° C. and / or a humidity of 25 RH%-50 RH%.

[0026] Optionally, the solvent includes one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0027] Optionally, the solid content of the precursor glue is 5%-25%.

[0028] Optionally, the first particles are immersed in a first modification solution for modification and dispersion, and then separated and dried to obtain the first thermally conductive particles.

[0029] Optionally, the second particles are immersed and dispersed in the second modified solution and then separated and dried to obtain the second thermally conductive particles.

[0030] Optionally, the active solutes in the first modified solution and the second modified solution are independently titanate coupling agents or amino-containing silane coupling agents.

[0031] In a second aspect, the present invention further provides a polyimide thermally conductive film prepared by any of the above optional preparation methods.

[0032] Optionally, the polyimide thermally conductive film carries 10 wt%-40 wt% of a thermally conductive filler, and the thermally conductive filler includes first thermally conductive particles and second thermally conductive particles.

[0033] In a third aspect, the present invention further provides an application of a polyimide thermally conductive film prepared by any of the above optional preparation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A structural block diagram of a method for preparing a polyimide thermally conductive film provided by the present invention;

[0035] Figure 2 1 is the stress-strain curve of the polyimide thermal conductive film of Example 1 of the present invention;

[0036] Figure 3 1 is the stress-strain curve of the polyimide thermally conductive film of Comparative Example 1 of the present invention;

[0037] Figure 4 This is the stress-strain curve of the polyimide thermally conductive film of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are 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 work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0039] See also Figure 1 The present invention provides a method for preparing a polyimide thermal conductive film, comprising the following steps:

[0040] S1, cutting the polyimide fiber membrane to obtain polyimide fiber filaments;

[0041] S2. Surface treating the polyimide fiber to obtain active fiber;

[0042] S3, coating the surface of the active fiber with first thermally conductive particles to obtain modified fiber;

[0043] S4, dispersing the modified fiber filaments and the second thermally conductive particles into a polyamic acid adhesive to prepare a composite adhesive;

[0044] S5. Forming a film on the composite adhesive solution and performing imidization to obtain a polyimide thermal conductive film.

[0045] In fact, the preparation method provided by the present invention obtains polyimide fiber filaments by cutting the polyimide fiber membrane, and adds the polyimide fiber filaments into the composite glue to form a film. The mechanical properties of the thermal conductive film can be improved by utilizing the fiber reinforcement effect. At the same time, the polyimide fiber filaments and the polyimide thermal conductive film are made of the same material, which can avoid interface bonding problems.

[0046] In addition, by coating the first thermally conductive particles on the surface of the polyimide fiber filaments, the first thermally conductive filler can be oriented on the surface of the fiber filaments, thereby forming an effective thermal conductive path in the thermal conductive film. At the same time, the addition of the second thermally conductive particles can bridge with the first thermally conductive particles on the surface of the fiber filaments, thereby forming more heat transfer channels, which can effectively improve the out-of-plane thermal conductivity of the polyimide thermal conductive film.

[0047] In some embodiments, the average length of the polyimide fiber filaments cut in step S1 is 50 μm-100 μm. This facilitates coating the fiber filament surface with the first thermally conductive particles and allows the fiber filaments to be evenly dispersed and interwoven within the composite adhesive, thereby providing fiber reinforcement. In practice, a femtosecond ultraviolet laser ultrafine processing system can be used to cut the polyimide fiber membrane.

[0048] In some embodiments, the polyimide fiber membrane used in step S1 can be a pre-prepared, unused fiber membrane, or a recycled, cleaned fiber membrane. In fact, when preparing the polyimide fiber membrane, the precursor glue used is a polyamic acid-based glue, that is, no inorganic filler is added to the precursor glue.

[0049] Specifically, the precursor glue includes polyamic acid and a solvent for dissolving the polyamic acid. Furthermore, the solvent for dissolving the polyamic acid is a polar aprotic solvent, specifically one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone. In practice, the precursor glue can be prepared by polycondensing a diamine and a dianhydride in a polar aprotic solvent, or by dissolving polyimide molding powder.

[0050] In some embodiments, when preparing the polyimide fiber membrane used in Example 1, a precursor solution with a solid content of 5%-25% can be used for electrospinning to produce the polyamic acid fiber membrane. In fact, electrospinning the precursor solution can effectively control the diameter of the fiber filaments after cutting the fiber membrane, thereby facilitating the production of fiber filaments with a larger aspect ratio.

[0051] Specifically, when preparing the polyimide fiber membrane used in Example 1, the nozzle of the electrospinning equipment can be set in an environment of 25°C-50°C and / or a humidity of 25RH%-50RH%, thereby facilitating the formation of the polyamic acid fiber membrane. In addition, after the polyamic acid fiber membrane is prepared, it can be pre-imidized in an environment of 80°C-120°C, and then placed at 380°C-420°C for 10min-60min to completely imidize, thereby preparing the polyimide fiber membrane.

[0052] In fact, by surface treating the polyimide fiber filaments in step S2, the active sites on the surface of the polyimide fiber filaments can be effectively increased, which is beneficial to the loading of the first thermally conductive particles in step S3, and further beneficial to improving the loading uniformity of the first thermally conductive particles on the fiber filament surface, and promoting the first thermally conductive particles to be oriented on the fiber filament surface along the length direction of the fiber filament.

[0053] In some embodiments, during step S2, the polyimide fiber filaments may be immersed in an alkaline solution for surface etching, thereby effectively increasing the degree of surface defects and modifying the surface hydroxyl groups. Furthermore, when immersed in the alkaline solution, the alkaline solute in the alkaline solution includes a strong inorganic base such as sodium hydroxide or potassium hydroxide, and the concentration of the alkaline solute may be 0.5 mol / L to 2 mol / L.

[0054] In some embodiments, during step S2, the polyimide fiber filaments may be immersed in an alkaline solution and ultrasonically treated. Ultrasonic treatment can effectively remove tiny bubbles attached to the surface of the polyimide fiber filaments, helping the alkaline solution to uniformly infiltrate the fiber surface and improve the uniformity of surface modification. Alternatively, the fiber filaments may be immersed in an alkaline solution for 1-10 minutes, then separated and dried to produce active fiber filaments.

[0055] In some embodiments, during step S3, the active fiber filaments and the first thermally conductive particles may be co-dispersed in an alcohol-water solution for 5-10 minutes before separation to obtain the modified fiber filaments. Dispersing the first thermally conductive particles in an alcohol-water solution facilitates uniform dispersion of the active fiber filaments, thereby effectively improving the uniformity of the coating of the first thermally conductive particles on the surface of the active fiber filaments.

[0056] Specifically, the alcohol-water solution used in step S3 comprises a mixture of a low-molecular-weight alcohol and water. Furthermore, the low-molecular-weight alcohol used includes methanol, ethanol, and / or isopropanol. Furthermore, the concentration of the low-molecular-weight alcohol in the alcohol-water solution is 80%-95%. Furthermore, the amount of the alcohol-water solution used in step S3 is sufficient to ensure uniform dispersion of the first thermally conductive particles and the active fiber filaments.

[0057] In some embodiments, during step S3, the mass ratio of the active fiber filaments to the first thermally conductive particles in the alcohol-water solution is 100:(5-15), which facilitates adjusting the amount of the first thermally conductive particles coating the surface of the active fiber filaments. Furthermore, after the co-dispersion in step S3 to coat the surface of the first thermally conductive particles, the modified fiber filaments are separated by filtration and dried at 50°C-80°C to obtain the modified fiber filaments.

[0058] In practice, in step S4, the modified fiber filaments and the second thermally conductive particles can be dispersed into the polyamic acid adhesive under mechanical action to improve the uniformity of the modified fiber filaments and the second thermally conductive particles in the composite adhesive. This facilitates the modified fiber filaments to play a fiber reinforcement role after film formation, and utilizes the second thermally conductive particles to bridge the modified fiber filaments to increase the number of heat transfer channels. Specifically, the mechanical action can be a commonly used solid-liquid mixing method in the art, such as stirring, oscillation, and ultrasound.

[0059] In some embodiments, the solid content of the polyamic acid glue used in step S4 is 5%-25%. In fact, the polyamic acid glue used in step S4 can be the same as the polyamic acid glue used in preparing the polyimide fiber membrane in step S1. Specifically, a polyamic acid glue with a solid content of 5%-25% can be prepared in advance, and a portion of the glue is used to make the polyimide fiber membrane, and the remaining amount of the glue is made into a composite glue. This not only helps to improve production efficiency, but also homogeneous fiber filaments and thermally conductive film have better interface bonding performance.

[0060] In practice, in step S4, the mass ratio of the modified fiber filaments to the second thermally conductive particles is (5-20):(1-15). Specifically, the mass concentration of the modified fiber filaments in the composite adhesive is 5%-20%, and the mass concentration of the second thermally conductive particles is 1%-15%. By adjusting the concentration of the modified fiber filaments and the second thermally conductive particles in the composite adhesive, it is beneficial to adjust the total loading of the thermally conductive film for the first and second thermally conductive particles, which can effectively improve the out-of-plane thermal conductivity.

[0061] In some embodiments, the first thermally conductive particles used in step S3 and the second thermally conductive particles used in step S4 each have a particle size independently ranging from 50 nm to 5000 nm. Furthermore, the first thermally conductive particles and the second thermally conductive particles each are independently selected from the group consisting of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0062] In some embodiments, in order to improve the coating performance of the first thermally conductive particles on the surface of the active fiber filaments and improve the dispersion performance of the second thermally conductive particles in the composite glue, and promote the bridging between the second thermally conductive particles and the modified fiber filaments, the first thermally conductive particles and the second thermally conductive particles can be surface modified to increase the active sites on the particle surface.

[0063] Specifically, the first particles can be infiltrated and modified in a first modifying solution, dispersed, separated, and dried to obtain first thermally conductive particles. Alternatively, the second particles can be infiltrated and modified in a second modifying solution, dispersed, separated, and dried to obtain second thermally conductive particles. In practice, the first and second particles are independently selected from the group consisting of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0064] In some embodiments, the active solutes in the first and second modifying solutions are independently titanate coupling agents or amino-containing silane coupling agents. Specifically, during the infiltration modification, the mass ratio of the active solute to the corresponding particles is 0.5%-2%. Furthermore, the titanate coupling agent includes at least one of PN-130, PN-101, and PN-102, and the silane coupling agent includes at least one of KH-540, KH-550, KH-560, KH-570, and KH-602.

[0065] In fact, the present invention also provides a polyimide thermally conductive film produced using any of the above-described methods, wherein the thermally conductive film contains 10% to 40% by weight of a thermally conductive filler (including first and second thermally conductive particles). Furthermore, the present invention provides applications of the polyimide thermally conductive film, which can be used for thermal management of electronic components.

[0066] Example 1

[0067] This embodiment 1 provides a method for preparing a polyimide thermally conductive film, comprising the following steps:

[0068] S0, adding pyromellitic dianhydride and 4,4'-diaminodiphenyl ether monomers in a molar ratio of 1:1 to N,N-dimethylacetamide to obtain a polyamic acid glue solution with a solid content of 15% by solution polycondensation; using an electrostatic spinning device, the polyamic acid glue solution is electrostatically spun at 25°C and 30RH% to obtain a polyamic acid fiber membrane; heating the polyamic acid fiber membrane to 100°C in a blast drying oven for pre-imidization, then fixing it in a pin plate frame, keeping it warm in an imidization furnace at 400°C for 15 minutes for imidization treatment, and cooling it to obtain a polyimide fiber membrane;

[0069] S1. Using a femtosecond ultraviolet laser ultrafine processing system to cut the polyimide fiber membrane to produce polyimide fiber filaments with an average length of 80 μm;

[0070] S2, infiltrating and dispersing the polyimide fiber in a 1 mol / L sodium hydroxide solution, performing surface etching treatment at room temperature for 5 minutes, and filtering and separating the solid to obtain active fiber;

[0071] S3. Boron nitride particles with a particle size of 1000 nm were immersed and dispersed in an alcohol-water solution containing KH-550 (ethanol content: 90%; mass ratio of KH-550 to boron nitride: 1.5%) for 10 minutes, and the solids were separated by filtration and dried to constant weight to obtain first thermally conductive particles. Active fiber filaments were immersed and dispersed in an alcohol-water solution containing 8% of the first thermally conductive particles for 25 minutes, and the obtained fiber filaments were separated by filtration and dried in a vacuum drying oven at 60° C. for 5 hours to obtain modified fiber filaments.

[0072] S4, adding the modified fiber filaments and the second thermally conductive particles (the first thermally conductive particles prepared in S3) to a polyamic acid adhesive solution with a solid content of 20% (prepared in step S0), stirring and dispersing the solution, and then vacuum degassing the solution to prepare a composite adhesive solution; wherein the mass fraction of the modified fiber filaments in the composite adhesive solution is 12%, and the mass fraction of the second thermally conductive particles is 7%;

[0073] S5. The composite adhesive liquid is coated on a smooth and clean glass plate to form a composite adhesive film, the composite adhesive film is gradually heated at 80°C-120°C (each temperature section is kept warm for 10 minutes) for partial imidization, and then the composite adhesive film is fixed in a needle plate frame clamp, and the temperature is gradually increased to 420°C in an imidization furnace and kept warm for 10 minutes to obtain a polyimide thermal conductive film with a boron nitride loading of 19.8wt%.

[0074] Example 2

[0075] This embodiment 2 provides a method for preparing a polyimide thermally conductive film, which differs from embodiment 1 in that, in step S4, the mass fraction of the modified fiber filaments in the composite adhesive is 15%, and the mass fraction of the second thermally conductive particles is 5%; in step S5, a polyimide thermally conductive film with a boron nitride loading of 18.6 wt% is prepared.

[0076] Example 3

[0077] This embodiment 3 provides a preparation method of a polyimide thermally conductive film, which differs from embodiment 1 in that, in step S3, the active fiber filaments are immersed in an alcohol aqueous solution containing 12% of the first thermally conductive particles and dispersed for 25 minutes; in step S5, a polyimide thermally conductive film with a boron nitride loading of 20.4 wt% is prepared.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing a polyimide thermally conductive film, comprising the following steps:

[0080] D1, adding pyromellitic dianhydride and 4,4'-diaminodiphenyl ether monomers at a molar ratio of 1:1 to N,N-dimethylacetamide to obtain a polyamic acid glue with a solid content of 20% by solution polycondensation;

[0081] D2. Boron nitride particles with a particle size of 1000 nm were immersed and dispersed in an alcohol aqueous solution containing KH-550 (ethanol content 90%; mass ratio of KH-550 to boron nitride 1.5%) for 10 minutes, and the solids were separated by filtration and dried to constant weight to obtain first thermally conductive particles;

[0082] D3, adding the first thermally conductive particles to a polyamic acid adhesive having a solid content of 20%, stirring and mixing to prepare a composite adhesive; the mass fraction of the first thermally conductive particles in the composite adhesive is 5%;

[0083] D4. The composite adhesive liquid is coated on a smooth and clean glass plate to form a composite adhesive film. The composite adhesive film is gradually heated at 80°C-120°C (keeping each temperature section for 10 minutes) for partial imidization. The composite adhesive film is then fixed in a needle plate frame clamp, and the temperature is gradually increased to 420°C in an imidization furnace and kept warm for 10 minutes to obtain a polyimide thermal conductive film with a boron nitride loading of 20.8wt%.

[0084] Comparative Example 2

[0085] Comparative Example 2 provides a method for preparing a polyimide thermally conductive film, which differs from Comparative Example 1 in that, in step D3, the mass fraction of the first thermally conductive particles in the composite adhesive is 14.3%; and in step D4, a polyimide thermally conductive film with a boron nitride loading of 45.5 wt% is prepared.

[0086] Performance testing

[0087] The polyimide thermal conductive films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to tensile strength tests based on the method described in ASTM D882. The test data are shown in Table 1 below. The stress-strain curves of the polyimide thermal conductive films in Example 1 and Comparative Examples 1 to 2 are shown in Table 1. Figures 2 to 4 shown.

[0088] The out-of-plane thermal diffusion coefficient α of the polyimide thermal conductive films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was measured using a flash thermal conductivity meter (Netzsch, Germany, LFA467). The specific heat capacity C was measured using a differential scanning calorimeter (Netzsch, Germany, DSC214). p The density ρ was measured using an electronic density balance (Shanghai Sunny Optical, FA2104J) and the out-of-plane thermal conductivity λ of the thermal conductive film was calculated (λ = α × ρ × C p ) as shown in Table 1.

[0089] Table 1 Performance test data of polyimide thermal conductive film

[0090]

[0091] As can be seen from Table 1, the polyimide thermally conductive films prepared in Examples 1 to 3 of the present invention have a significant strengthening effect by adding polyimide fiber filaments, so that the tensile strength of the thermally conductive films is greater than 90 MPa, and they have excellent mechanical properties. In contrast, although Comparative Example 1 has a loading capacity similar to that of Examples 1 to 3, the lack of fiber filaments results in a significant decrease in tensile strength. For example, Comparative Example 2 has an out-of-plane thermal conductivity close to that of Example 1, but the addition of a large amount of boron nitride particles results in a significant decrease in tensile strength.

[0092] Therefore, by aligning the thermally conductive particles along the polyimide nanofibers, the present invention facilitates the formation of a heat conduction path out of the plane of the polyimide thermally conductive film. Furthermore, the thermally conductive particles in the polyimide adhesive further create more bridge points between the aligned thermally conductive particles, significantly increasing the heat transfer path. The use of polyimide fibers acts as a fiber reinforcement for the polyimide thermally conductive film, resulting in high mechanical strength and high out-of-plane thermal conductivity.

[0093] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A method for preparing a polyimide thermally conductive film, characterized in that: include: cutting the polyimide fiber membrane to obtain polyimide fiber filaments; Surface treatment is performed on polyimide fiber filaments to obtain active fiber filaments; The modified fiber filaments are prepared by coating the first thermally conductive particles on the surface of the active fiber filaments, and the mass ratio of the active fiber filaments to the first thermally conductive particles is 100:(5-15); the modified fiber filaments and the second thermally conductive particles are dispersed in a polyamic acid adhesive to prepare a composite adhesive, and the mass ratio of the modified fiber filaments to the second thermally conductive particles is (5-20):(1-15); the composite adhesive is formed into a film and imidized to prepare a polyimide thermally conductive film; the polyimide thermally conductive film is loaded with 10wt%-40wt% of a thermally conductive filler, and the thermally conductive filler includes the first thermally conductive particles and the second thermally conductive particles.

2. The preparation method according to claim 1, characterized in that The average length of the polyimide fiber is 50 μm-100 μm.

3. The preparation method according to claim 1, characterized in that The particle sizes of the first thermally conductive particles and the second thermally conductive particles are independently 50 nm to 5000 nm.

4. The preparation method according to claim 1, characterized in that The first thermally conductive particles and the second thermally conductive particles are independently made of one of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

5. The preparation method according to claim 1, characterized in that When the polyimide fiber is subjected to surface treatment, the polyimide fiber is immersed in an alkaline solution to perform surface etching.

6. The preparation method according to claim 5, characterized in that The concentration of alkali solute in the alkali solution is 0.5 mol / L-2 mol / L.

7. The preparation method according to claim 5, characterized in that The alkaline solute in the alkaline solution includes sodium hydroxide and potassium hydroxide.

8. The preparation method according to claim 5, characterized in that The polyimide fiber is immersed in an alkaline solution and ultrasonicated.

9. The preparation method according to claim 5, characterized in that Etch the inner surface in alkaline solution for 1 min-10 min.

10. The preparation method according to claim 5, characterized in that After surface etching, the film is separated and dried.

11. The preparation method according to claim 1, characterized in that The active fiber filaments and the first heat-conducting particles are co-dispersed in an alcohol-water solution and then separated to obtain modified fiber filaments.

12. The preparation method according to claim 11, characterized in that The alcohol aqueous solution includes low molecular alcohol, and the low molecular alcohol includes methanol, ethanol and / or isopropanol.

13. The preparation method according to claim 11, characterized in that After separation, dry at 50-80°C.

14. The preparation method according to claim 1, characterized in that The mass concentration of the modified fiber in the composite glue is 5%-20%.

15. The preparation method according to claim 1, characterized in that The mass concentration of the second thermally conductive particles in the composite adhesive is 1%-15%.

16. The preparation method according to claim 1, characterized in that The solid content of the polyamic acid glue is 5%-25%.

17. The preparation method according to claim 1, characterized in that The polyamic acid glue includes a glue prepared by polycondensation of diamine and dianhydride or a glue prepared by dissolving molding powder.

18. The preparation method according to claim 1, characterized in that The polyimide fiber membrane is prepared by electrostatic spinning and imidization of a precursor glue solution, wherein the precursor glue solution includes polyamic acid and a solvent for dissolving the polyamic acid.

19. The preparation method according to claim 18, characterized in that The precursor glue is electrospun in an environment with a temperature of 25° C.-50° C. and / or a humidity of 25RH%-50RH%.

20. The preparation method according to claim 18, characterized in that The solvent includes one of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

21. The preparation method according to claim 18, characterized in that The solid content of the precursor glue is 5%-25%.

22. The preparation method according to claim 1, characterized in that The first particles are immersed, modified and dispersed in the first modification solution, and then separated and dried to obtain the first thermally conductive particles.

23. The preparation method according to claim 22, characterized in that The active solute in the first modified solution is a titanate coupling agent or an amino-containing silane coupling agent.

24. The preparation method according to claim 1, characterized in that The second particles are immersed and dispersed in the second modified solution, and then separated and dried to obtain the second thermally conductive particles.

25. The preparation method according to claim 24, characterized in that The active solute in the second modified solution is a titanate coupling agent or an amino-containing silane coupling agent.

26. A polyimide thermally conductive film prepared by the preparation method according to any one of claims 1 to 25.

27. Use of the polyimide thermally conductive film prepared by the preparation method according to any one of claims 1 to 25.

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