Polyimide heat-conducting film as well as preparation method and application thereof

Abstract

The invention provides a polyimide heat-conducting film as well as a preparation method and application thereof, and relates to the technical field of polyimide films. The preparation method provided by the invention comprises the following steps: cutting a polyimide fiber membrane to prepare polyimide fibers; performing surface treatment on the polyimide fibers to obtain active fibers; coating the surfaces of the active fibers with first heat-conducting particles to obtain modified fibers; dispersing the modified cellosilk and second heat-conducting particles into the polyamide acid glue solution to prepare a composite glue solution; and carrying out film formation and imidization on the composite glue solution to prepare the polyimide heat-conducting film. According to the invention, the out-of-plane thermal conductivity and mechanical properties of the polyimide heat-conducting film can be simultaneously improved.

Description

Technical Field

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

[0002] With the development of miniaturization, integration and functionality of microelectronics and portable devices, the heat generated per unit time by internal electronic components during operation has increased sharply, 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 materials pyramid due to its excellent insulation performance, high and low temperature resistance, stable chemical properties, etc. However, its intrinsic out-of-plane thermal conductivity is poor (0.2 - 0.3 W·m -1 ·K -1 ), which cannot meet the rapid heat dissipation requirements of electronic components and greatly limits the application of the film in more new fields. To solve the heat dissipation problem, there is an urgent need for a new generation of polyimide-based film materials with both high insulation and high thermal conductivity. Researchers have conducted a large number of studies on this, mainly by adding inorganic thermal conductive particles to polyimide resin or polyamic acid solution for blending and doping to prepare thermal conductive polyimide composite films. The thermal conductive fillers inside the polyimide-based composite films prepared by this method will settle during the preparation process, resulting in a low out-of-plane thermal conductivity. If the addition amount of inorganic thermal conductive particles is increased, although a thermal conductive path can be effectively constructed, the mechanical properties of the film are severely damaged, and the comprehensive performance of the polyimide composite film is greatly affected. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

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

[0004] In the first aspect, a preparation method of a polyimide thermal conductive film provided by the present invention includes: cutting a polyimide fiber film to obtain polyimide fiber filaments; performing surface treatment on the polyimide fiber filaments to obtain active fiber filaments; coating first thermal conductive particles on the surface of the active fiber filaments to obtain modified fiber filaments; dispersing the modified fiber filaments and second thermal conductive particles into a polyamic acid colloidal solution to obtain a composite colloidal solution; forming a film from the composite colloidal solution and imidizing to obtain a polyimide thermal 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 thermal conductive particles and the second thermal conductive particles are independently 50 nm - 5000 nm.

[0007] Optionally, the first heat-conducting particles and the second heat-conducting particles are independently selected from the group consisting of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0008] Optionally, when the polyimide fiber filaments are surface-treated, the polyimide fiber filaments are immersed in an alkali solution for surface etching.

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

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

[0011] Optionally, the polyimide fiber filaments are immersed in the alkali solution and ultrasonically treated.

[0012] Optionally, the surface etching is carried out in the alkali solution for 1 min - 10 min.

[0013] Optionally, after the surface etching, separation and drying are carried out.

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

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

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

[0017] Optionally, after separation, drying is carried out at 50°C - 80°C.

[0018] Optionally, the co-dispersion in the aqueous alcohol solution is carried out for 5 min - 30 min.

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

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

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

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

[0023] Optionally, the polyamic acid adhesive solution includes a solution prepared by polycondensing diamine and dianhydride or a solution prepared by dissolving molding powder.

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

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

[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 solution is 5% - 25%.

[0028] Optionally, the first particles are infiltrated, modified, dispersed in the first modification solution and then separated and dried to obtain the first thermally conductive particles.

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

[0030] Optionally, the active solutes in the first modification solution and the second modification solution are independently a titanate coupling agent or an amino-containing silane coupling agent.

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

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

[0033] In a third aspect, the present invention also provides an application of the polyimide thermally conductive film prepared by any of the above optional preparation methods. Description of the Drawings

[0034] Figure 1 It is a structural block diagram of a preparation method of a polyimide thermally conductive film provided by the present invention;

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

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

[0037] Figure 4 It is the stress-strain curve of the polyimide thermally conductive film of Comparative Example 2 of the present invention. Detailed Embodiments

[0038] To make the objectives, 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. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present invention pertains.

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

[0040] S1. Cutting a polyimide fiber film to obtain polyimide fiber filaments;

[0041] S2. Performing surface treatment on the polyimide fiber filaments to obtain active fiber filaments;

[0042] S3. Coating the surface of the active fiber filaments with first thermal conductive particles to obtain modified fiber filaments;

[0043] S4. Dispersing the modified fiber filaments and second thermal conductive particles into a polyamic acid colloidal solution to obtain a composite colloidal solution;

[0044] S5. Forming a film from the composite colloidal solution and imidizing it to obtain a polyimide thermal conductive film.

[0045] Actually, the preparation method provided by the present invention cuts a polyimide fiber film to obtain polyimide fiber filaments and adds the polyimide fiber filaments into a composite colloidal solution to form a film, which can improve the mechanical properties of the thermal conductive film by using the fiber strengthening effect. At the same time, the polyimide fiber filaments and the polyimide thermal conductive film are made of the same material, which can avoid the interface bonding problem.

[0046] In addition, by coating the surface of the polyimide fiber filaments with first thermal conductive particles, the first thermal conductive fillers can be oriented on the surface of the fiber filaments, thereby forming an effective heat conduction path in the thermal conductive film. At the same time, adding second thermal conductive particles can bridge with the first thermal 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, which is beneficial to coating the surface of the fiber filaments with first thermal conductive particles. At the same time, the fiber filaments can be uniformly dispersed and intertwined in the composite colloidal solution to play a fiber strengthening role. Actually, when cutting the polyimide fiber film, a femtosecond ultraviolet laser ultra-precision processing system can be used to cut the fiber film.

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

[0049] Specifically, the precursor colloidal solution includes polyamic acid and a solvent for dissolving polyamic acid. Further, the solvent used to dissolve polyamic acid is a polar aprotic solvent, which can specifically include one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone. In fact, the precursor colloidal solution can be prepared by polycondensation of diamine and dianhydride in a polar aprotic solvent, or can be prepared by dissolving polyimide molding powder.

[0050] In some embodiments, when preparing the polyimide fiber membrane used in Example 1, an electrostatic spinning method can be used with a precursor colloidal solution having a solid content of 5%-25% to obtain a polyamic acid fiber membrane. In fact, by electrospinning the precursor colloidal solution, the diameter of the fiber filaments after cutting the fiber membrane can be effectively controlled, which is beneficial to obtaining fiber filaments with a larger aspect ratio.

[0051] Specifically, when preparing the polyimide fiber membrane used in Example 1, the nozzle of the electrostatic spinning device can be placed in an environment with a temperature of 25°C - 50°C and / or a humidity of 25RH% - 50RH%, which is beneficial to the formation of the polyamic acid fiber membrane. In addition, after obtaining the polyamic acid fiber membrane, it can be pre-imidated in an environment of 80°C - 120°C and then placed at 380°C - 420°C for 10 min - 60 min for complete imidation to obtain 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 heat-conducting particles in step S3, and further beneficial to improving the loading uniformity of the first heat-conducting particles on the surface of the fiber filaments and promoting the first heat-conducting particles to be arranged in a direction along the length of the fiber filaments on the surface of the fiber filaments.

[0053] In some embodiments, when performing step S2, the polyimide fiber filaments can be immersed in an alkali solution for surface etching, so as to effectively increase the surface defect degree and perform hydroxyl modification on the surface. In addition, when immersed in the alkali solution, the alkali solute in the alkali solution includes inorganic strong bases such as sodium hydroxide and potassium hydroxide, and the concentration of the alkali solute can be 0.5 mol / L - 2 mol / L.

[0054] In some embodiments, when performing step S2, the polyimide fiber filaments can be infiltrated in an alkaline solution and subjected to ultrasonic treatment. In fact, ultrasonic treatment can effectively remove the minute air bubbles adhering to the surface of the polyimide fiber filaments, which helps the alkaline solution to uniformly infiltrate the surface of the fiber filaments and improve the uniformity of surface modification. In addition, the fiber filaments can be infiltrated in the alkaline solution for 1 min - 10 min and then separated and dried to obtain activated fiber filaments.

[0055] In some embodiments, when performing step S3, the activated fiber filaments and the first heat-conducting particles can be co-dispersed in an aqueous alcohol solution for 5 min - 10 min and then separated to obtain modified fiber filaments. In fact, dispersing in the aqueous alcohol solution is conducive to the uniform dispersion of the first heat-conducting particles and the activated fiber filaments, and thus can effectively improve the coating uniformity of the first heat-conducting particles on the surface of the activated fiber filaments.

[0056] Specifically, the aqueous alcohol solution used when performing step S3 includes a mixed solution of low-molecular-weight alcohol and water. Further, the low-molecular-weight alcohol used includes methanol, ethanol, and / or isopropanol. In addition, the concentration of the low-molecular-weight alcohol in the aqueous alcohol solution is 80% - 95%. Meanwhile, when performing step S3, the amount of the aqueous alcohol solution used is necessary to enable the uniform dispersion of the first heat-conducting particles and the activated fiber filaments.

[0057] In some embodiments, the mass ratio of the activated fiber filaments to the first heat-conducting particles in the aqueous alcohol solution when performing step S3 is 100:(5 - 15), which is conducive to adjusting the coating amount of the first heat-conducting particles on the surface of the activated fiber filaments. Meanwhile, after co-dispersing in step S3 to enable the surface coating of the first heat-conducting particles, filtration and separation are carried out and drying is performed at 50°C - 80°C to obtain modified fiber filaments.

[0058] In fact, in step S4, the modified fiber filaments and the second heat-conducting particles can be dispersed into the polyamic acid colloidal solution under mechanical action to improve the uniformity of the modified fiber filaments and the second heat-conducting particles in the composite colloidal solution, and thus is conducive to the modified fiber filaments playing a fiber strengthening role after film formation, and using the second heat-conducting particles to bridge with the modified fiber filaments to increase the number of heat transfer channels. Specifically, the mechanical action can be stirring, oscillation, ultrasonic, etc., which are common solid-liquid mixing methods in the art.

[0059] In some embodiments, the solid content of the polyamic acid colloidal solution used in step S4 is 5% - 25%. In fact, the polyamic acid colloidal solution used in step S4 can be the same as the polyamic acid colloidal solution when preparing the polyimide fiber film in step S1. Specifically, a polyamic acid colloidal solution with a solid content of 5% - 25% can be prepared in advance, and a part of the colloidal solution is made into a polyimide fiber film, and the remaining amount of the colloidal solution is made into a composite colloidal solution. In this way, not only is it conducive to improving production efficiency, but also the homogeneous fiber filaments and the heat-conducting film have better interfacial bonding performance.

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

[0061] In some embodiments, the particle sizes of the first heat-conducting particles used in step S3 and the second heat-conducting particles used in step S4 are independently 50 nm - 5000 nm. In addition, the types of the first heat-conducting particles and the second heat-conducting particles are independently one of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0062] In some embodiments, to improve the coating performance of the first heat-conducting particles on the surface of the active fiber filaments, improve the dispersion performance of the second heat-conducting particles in the composite adhesive solution, and promote the bridging between the second heat-conducting particles and the modified fiber filaments, the first heat-conducting particles and the second heat-conducting particles can be subjected to surface modification treatment to increase the active sites on the particle surface.

[0063] Specifically, the first particles can be infiltrated and modified in the first modification solution, separated and dried after dispersion to obtain the first heat-conducting particles, and the second particles can also be infiltrated and modified in the second modification solution, separated and dried after dispersion to obtain the second heat-conducting particles. In fact, the first particles and the second particles are independently one of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

[0064] In some embodiments, the active solutes in the first modification solution and the second modification solution are independently a titanate coupling agent or an amino-containing silane coupling agent. Specifically, the dosage of the active solute during infiltration modification and the mass ratio of the corresponding particles is 0.5% - 2%. Further, 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 heat-conducting film prepared by the preparation method of any of the above embodiments, in which 10 wt% - 40 wt% of heat-conducting fillers (including the first heat-conducting particles and the second heat-conducting particles) are loaded. At the same time, the present invention also provides the application of the polyimide heat-conducting film, which can be applied to the thermal management of electronic components.

[0066] Example 1

[0067] Embodiment 1 provides a method for preparing a polyimide thermal conductive film, comprising the following steps:

[0068] S0. Add pyromellitic dianhydride and 4,4'-diaminodiphenyl ether monomers in a molar ratio of 1:1 to N,N-dimethylacetamide, and prepare a polyamic acid colloidal solution with a solid content of 15% through solution polycondensation; use an electrospinning device to electrospin the polyamic acid colloidal solution at 25°C and 30% RH to obtain a polyamic acid fiber membrane; after pre-imidization by heating the polyamic acid fiber membrane to 100°C in a blast drying oven, fix it in a needle plate frame, and perform imidization treatment by holding it in an imidization furnace at 400°C for 15 min, and cool to obtain a polyimide fiber membrane;

[0069] S1. Use a femtosecond ultraviolet laser ultra-precision machining system to cut the polyimide fiber membrane to obtain polyimide fiber filaments with an average length of 80 μm;

[0070] S2. After infiltrating and dispersing the polyimide fiber filaments in a 1 mol / L sodium hydroxide solution, perform surface etching treatment at room temperature for 5 min, and filter and separate the solids to obtain active fiber filaments;

[0071] S3. After infiltrating and dispersing boron nitride particles with a particle size of 1000 nm in an alcohol aqueous solution containing KH-550 (ethanol content 90%; mass ratio of KH-550 to boron nitride is 1.5%) for 10 min, filter and separate the solids and dry to constant weight to obtain first thermal conductive particles; immerse the active fiber filaments in an alcohol aqueous solution containing 8% of the first thermal conductive particles and infiltrate and disperse for 25 min, then filter and separate, and dry the obtained fiber filaments in a vacuum drying oven at 60°C for 5 h to obtain modified fiber filaments;

[0072] S4. Add the modified fiber filaments and second thermal conductive particles (the first thermal conductive particles prepared in S3) to a polyamic acid colloidal solution with a solid content of 20% (the same as that prepared in step S0), stir and disperse, and then perform vacuum degassing to obtain a composite colloidal solution; wherein, the mass fraction of the modified fiber filaments in the composite colloidal solution is 12% and the mass fraction of the second thermal conductive particles is 7%;

[0073] S5. Coat the composite colloidal solution on a smooth and clean glass plate to form a composite colloidal film, perform partial imidization on the composite colloidal film by gradually heating from 80°C to 120°C (holding for 10 min at each temperature stage), then fix the composite colloidal film in a needle plate frame clip, and gradient heat it to 420°C in an imidization furnace and hold for 10 min to obtain a polyimide thermal conductive film with a boron nitride loading of 19.8 wt%.

[0074] Embodiment 2

[0075] Example 2 provides a method for preparing a polyimide thermal conductive film. The difference from Example 1 is that in step S4, the mass fraction of the modified fiber filaments in the composite adhesive solution is 15%, and the mass fraction of the second thermal conductive particles is 5%; in step S5, a polyimide thermal conductive film with a boron nitride loading of 18.6 wt% is obtained.

[0076] Example 3

[0077] Example 3 provides a method for preparing a polyimide thermal conductive film. The difference from Example 1 is that in step S3, the active fiber filaments are immersed in an alcohol aqueous solution containing 12% of the first thermal conductive particles and dispersed by infiltration for 25 min; in step S5, a polyimide thermal conductive film with a boron nitride loading of 20.4 wt% is obtained.

[0078] Comparative Example 1

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

[0080] D1. Add pyromellitic dianhydride and 4,4'-diaminodiphenyl ether monomers in a molar ratio of 1:1 to N,N-dimethylacetamide and carry out solution polycondensation to obtain a polyamic acid adhesive solution with a solid content of 20%;

[0081] D2. Immerse boron nitride particles with a particle size of 1000 nm in an alcohol aqueous solution containing KH-550 (ethanol content 90%; mass ratio of KH-550 to boron nitride is 1.5%) and disperse by infiltration for 10 min, then filter and separate the solid matter and dry it to constant weight to obtain the first thermal conductive particles;

[0082] D3. Add the first thermal conductive particles to the polyamic acid adhesive solution with a solid content of 20% and stir and mix to obtain a composite adhesive solution; the mass fraction of the first thermal conductive particles in the composite adhesive solution is 5%;

[0083] D4. Coat the composite adhesive solution on a smooth and clean glass plate to form a composite adhesive film. After partially imidizing the composite adhesive film by gradually heating it from 80 °C to 120 °C (holding for 10 min at each temperature stage), then fix the composite adhesive film in a needle plate frame clamp and gradually heat it to 420 °C in an imidization furnace and hold for 10 min to obtain a polyimide thermal conductive film with a boron nitride loading of 20.8 wt%.

[0084] Comparative Example 2

[0085] This comparative example 2 provides a method for preparing a polyimide thermal conductive film. The difference from Comparative Example 1 is that in step D3, the mass fraction of the first thermal conductive particles in the composite adhesive solution is 14.3%; in step D4, a polyimide thermal conductive film with a boron nitride loading of 45.5 wt% is obtained.

[0086] Performance testing

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

[0088] The out-of-plane thermal diffusivity α of the polyimide thermal conductive films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was respectively tested by a laser flash thermal conductivity analyzer (NETZSCH, LFA467), and the specific heat capacity C was measured by a differential scanning calorimeter (NETZSCH, DSC214) p , and the density ρ was measured by an electronic density balance (Shunyu, FA2104J). 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 films

[0090]

[0091] As can be seen from Table 1, for the polyimide thermal conductive films prepared in Examples 1 to 3 of the present invention, the addition of polyimide fiber filaments has an obvious strengthening effect, making the tensile strength of the thermal conductive films all greater than 90 MPa, and having excellent mechanical properties. Although Comparative Example 1 has a similar loading amount to Examples 1 to 3, the tensile strength decreased significantly due to the absence of fiber filaments. Another example is Comparative Example 2, which 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, in the present invention, by arranging the thermal conductive particles along the polyimide nanofibers, it is more conducive to forming a thermal conduction path in the out-of-plane direction of the polyimide thermal conductive film. At the same time, the thermal conductive particles in the polyimide colloidal solution further result in more bridging points between the directionally arranged thermal conductive particles, significantly increasing the heat transfer channels. The application of polyimide fiber filaments plays a fiber strengthening role in the polyimide thermal conductive film, thus having the excellent effects of high mechanical strength and high out-of-plane thermal conductivity.

[0093] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A preparation method of a polyimide heat-conducting film, characterized in that, Including: Cutting a polyimide fiber film to obtain polyimide fiber filaments; Performing surface treatment on the polyimide fiber filaments to obtain active fiber filaments; Coating the surface of the active fiber filaments with first heat-conducting particles to obtain modified fiber filaments; Dispersing the modified fiber filaments and second heat-conducting particles into a polyamic acid colloidal solution to obtain a composite colloidal solution; forming a film from the composite colloidal solution and imidizing it to obtain a polyimide heat-conducting film.

2. The preparation method according to claim 1, characterized in that, The average length of the polyimide fiber filaments is 50 μm - 100 μm; and / or, the particle sizes of the first heat-conducting particles and the second heat-conducting particles are independently 50 nm - 5000 nm; and / or, the types of the first heat-conducting particles and the second heat-conducting particles are independently one of boron nitride, silicon oxide, aluminum oxide, silicon nitride, and silicon carbide.

3. The preparation method according to claim 1, characterized in that, When performing surface treatment on the polyimide fiber filaments, immersing the polyimide fiber filaments in an alkali solution for surface etching; preferably, the concentration of the alkali solute in the alkali solution is 0.5 mol / L - 2 mol / L; preferably, the alkali solute in the alkali solution includes sodium hydroxide and potassium hydroxide; preferably, immersing and ultrasonically treating the polyimide fiber filaments in the alkali solution; preferably, performing surface etching in the alkali solution for 1 min - 10 min; preferably, separating and drying after surface etching.

4. The preparation method according to claim 1, characterized in that, Co-dispersing the active fiber filaments and the first heat-conducting particles in an aqueous alcohol solution and then separating to obtain modified fiber filaments; preferably, the mass ratio of the active fiber filaments to the first heat-conducting particles is 100:(5 - 15); preferably, the aqueous alcohol solution includes low-molecular-weight alcohols, and the low-molecular-weight alcohols include methanol, ethanol, and / or isopropanol; preferably, drying at 50°C - 80°C after separation; preferably, co-dispersing in the aqueous alcohol solution for 5 min - 30 min.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the modified fiber filaments to the second heat-conducting particles is (5 - 20):(1 - 15); and / or, the mass concentration of the modified fiber filaments in the composite colloidal solution is 5% - 20%; and / or, the mass concentration of the second heat-conducting particles in the composite colloidal solution is 1% - 15%; and / or, the solid content of the polyamic acid colloidal solution is 5% - 25%; and / or, the polyamic acid colloidal solution includes a colloidal solution prepared by polycondensation of diamine and dianhydride or a colloidal solution prepared by dissolving molding powder.

6. The preparation method according to claim 1, characterized in that, The polyimide fiber film is prepared by electrospinning a precursor colloidal solution and then imidizing it. The precursor colloidal solution includes polyamic acid and a solvent for dissolving the polyamic acid; preferably, electrospinning the precursor colloidal solution in an environment with a temperature of 25°C - 50°C and / or a humidity of 25RH% - 50RH%; preferably, the solvent includes one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone; preferably, the solid content of the precursor colloidal solution is 5% - 25%.

7. The preparation method according to claim 1, characterized in that, Immersing and modifying and dispersing the first particles in a first modifying solution and then separating and drying to obtain the first heat-conducting particles; and / or, immersing and dispersing the second particles in a second modifying solution and then separating and drying to obtain the second heat-conducting particles; preferably, the active solutes in the first modifying solution and the second modifying solution are independently a titanate coupling agent or an amino-containing silane coupling agent.

8. A polyimide thermal conductive film prepared by the preparation method according to any one of claims 1 to 7.

9. The polyimide heat-conducting film according to claim 8, wherein The polyimide thermal conductive film carries 10 wt% - 40 wt% of a thermal conductive filler, and the thermal conductive filler includes a first thermal conductive particle and a second thermal conductive particle.

10. An application of a polyimide thermal conductive film prepared by the preparation method according to any one of claims 1 to 7.

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