High-thermal-conductivity polyimide film, preparation method and application

Abstract

The invention belongs to the technical field of polymer composite materials, and particularly relates to a high-thermal-conductivity polyimide film, a preparation method and application. The preparation method comprises the following steps: S1, carrying out surface hydroxylation treatment on nano boron nitride, and carrying out polydopamine coating treatment on micron aluminum oxide; s2, bridging the surface hydroxylated boron nitride and the polydopamine coated aluminum oxide through diisocyanate to construct a core-double shell structure composite filler; s3, performing surface hydrophobization treatment on the core-double shell structure composite filler by adopting an amino silane coupling agent to obtain a functional filler; s4, dispersing the functional filler into N, N-dimethylacetamide, and performing ultrasonic treatment to form a uniform suspension; s5, under the conditions of nitrogen protection and-10 to 25 DEG C, diamine and a dianhydride monomer are subjected to condensation polymerization in a polar solvent according to the molar ratio of 1: (0.98-1.02), and a polyamide acid solution is prepared; and S6, mixing the functional filler suspension with the polyamide acid solution, and carrying out defoaming, film casting and imidization treatment to obtain the high-thermal-conductivity polyimide film.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer composite materials, and particularly relates to a high-thermal-conductivity polyimide film, a preparation method and application thereof. BACKGROUND

[0002] Polyimide is a high-performance engineering plastic, which has excellent performance in high-temperature stability, mechanical strength and electrical insulation, etc. However, the intrinsic thermal conductivity of polyimide is generally low, which seriously restricts its application in the field of modern electronic device thermal management. The key factor restricting the thermal conductivity of polyimide is the disordered arrangement of the molecular chain structure, the defects and entanglements existing in the amorphous region, and the strong scattering of phonons in the transmission process caused thereby. Although the chain segment arrangement can be improved to a certain extent through molecular structure design or external processing technology, the improvement range of the intrinsic thermal conductivity is still very limited.

[0003] In order to significantly improve the thermal conductivity of polyimide materials, the strategy of introducing high-thermal-conductivity fillers is usually adopted. However, such filling type composite materials face three major technical bottlenecks in practical application: (1) the inorganic fillers have poor compatibility with the polymer matrix, and it is difficult to achieve uniform dispersion; (2) the phonon vibration mode at the interface between the filler and the matrix is mismatched, resulting in high interfacial thermal resistance; (3) it is difficult to form a continuous thermal conduction network at a low filling amount, and a high filling amount will damage the processability and mechanical properties of the material.

[0004] In the prior art, in order to improve the dispersion and interface combination of the fillers, strategies such as surface modification, construction of core-shell structure or introduction of chemical bridges at the interface are usually adopted. For example, the existing research reports a scheme of constructing a core-double-shell structure filler by using isocyanate as a bridging agent. Through chemical connection between polydopamine-coated aluminum oxide and nano boron nitride, the thermal conductivity of the composite film is obviously improved at a certain filling amount. However, this scheme still has obvious limitations: the bridging agent used has strong volatility and high toxicity, which has process safety hazards; the interface compatibility of the filler after bridging with the polyimide matrix still needs to be further improved; the dispersion stability of the composite filler in the matrix and the integrity of the three-dimensional thermal conduction path have not been optimally solved.

[0005] Therefore, it is still a technical problem to be solved in the field to develop a polyimide composite material which can balance high thermal conductivity, excellent interface compatibility, good mechanical properties and meet the requirements of green process. SUMMARY

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a high thermal conductivity polyimide film. By designing a three-layer coating of functional filler consisting of boron nitride, polydopamine, and aluminum oxide, and optimizing interface modification and preparation processes, the method solves the problems of low thermal conductivity, poor interfacial compatibility, and insufficient process safety of existing filled polyimides. The invention also provides a high thermal conductivity polyimide film prepared by this method, and its application in electronic devices.

[0007] A method for preparing a high thermal conductivity polyimide film, the method comprising the following steps: S1. Surface hydroxylation treatment of nano-boron nitride and polydopamine coating treatment of micron-sized alumina; S2. Surface-hydroxylated boron nitride and polydopamine-coated alumina are bridged by diisocyanate to construct a core-double-shell composite filler. S3. The core-double-shell structure composite filler was hydrophobically treated with an aminosilane coupling agent to obtain a functional filler. S4. Disperse the functional filler in N,N-dimethylacetamide and then ultrasonically treat it to form a uniform suspension; S5. Under nitrogen protection and at -10~25℃, diamine and dianhydride monomers are subjected to a polycondensation reaction in a polar solvent at a molar ratio of 1:(0.98-1.02) to prepare a polyamic acid solution; S6. The functional filler suspension is mixed with a polyamic acid solution, and after degassing, casting and imidization, a high thermal conductivity polyimide film is obtained.

[0008] Further, the specific steps of surface hydroxylation treatment in step S1 are as follows: performing surface hydroxylation heat treatment on boron nitride nanoparticles with a particle size of 50-200nm at 400-900℃ for 2-6 hours; the polydopamine coating treatment step is as follows: the concentration of dopamine hydrochloride in the polydopamine coating treatment is 1-3mg / mL, the reaction pH value is 8.0-9.0, and the reaction time is 1-3 hours.

[0009] Further, the construction conditions for step S2 are as follows: under inert gas protection and at 100-150℃ for 4-8 hours, a core-double shell structure composite filler is constructed; the diisocyanate is one or more of hexamethylene diisocyanate biuret, isophorone diisocyanate, or dicyclohexylmethane diisocyanate, and the mass ratio of diisocyanate to hydroxylated boron nitride is (0.5-5):10; the inert gas is nitrogen or argon.

[0010] Further, the aminosilane coupling agent mentioned in step S3 is γ-aminopropyltriethoxysilane, and the mass ratio of the aminosilane coupling agent to the composite filler is (1-8):100.

[0011] Furthermore, the mass fraction of the functional filler in step S4 in the suspension is 10-30%.

[0012] Further, the diamine in step S5 is selected from one or more of 1,4'-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4'-diaminobenzoyl aniline, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-bis-4-(nitrophenoxy)biphenyl, 4,4'-(diamino-2,2'-dimethylbiphenyl, 4,4'-diaminodiphenylmethane, 4,4'-diaminodibenzophenone, and diaminodiphenyl sulfone; the dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4-oxobisphthalic anhydride, and bisphenol A type diether dianhydride.

[0013] Further, the specific steps of step S6 are as follows: the functional filler suspension is mixed with the polyamic acid solution, the amount of functional filler added is 10-40% of the mass of the polyamic acid solution, after adjusting the viscosity, it is degassed and cast into a film; firstly, it is subjected to desolventizing treatment at 80-150℃ for 30-60 minutes, and then imidization is completed by program heating to 350-400℃ and holding for 0.5-2 hours to obtain a high thermal conductivity polyimide film.

[0014] A high thermal conductivity polyimide film is prepared by the method described above; the film has a thickness of 25-75 μm, an elongation at break of 15-40%, and a volume resistivity ≥6.3×10¹. 6 Ω・cm.

[0015] An electronic device comprising the aforementioned high thermal conductivity polyimide film; the electronic device is a 5G communication device, a flexible display device, or a power semiconductor device, and the high thermal conductivity polyimide film serves as a thermal management material or insulating component of the electronic device.

[0016] The beneficial effects of this invention are: 1. Significantly Improved Thermal Conductivity. Utilizing high-functionality bridging agents such as HDI biuret, the polyisocyanate groups can simultaneously bond the hydroxyl groups of boron nitride and the active groups of the polydopamine coating layer, forming an interface structure with higher cross-linking density. This effectively promotes the formation of a three-dimensional thermally conductive network and significantly reduces interfacial thermal resistance. This structure creates highly efficient phonon transport channels between the fillers, enabling the composite film to achieve a thermal conductivity of 2.0-3.5 W / (m·K) under a filler load of 25-40%, more than 10 times higher than pure polyimide. This achieves superior planar and transplanar thermal conductivity at the same filler load.

[0017] 2. Enhanced filler dispersibility and interfacial bonding. By utilizing the covalent bridging effect of diisocyanate and the hydrophobic treatment of alkane coupling agents, nanoscale uniform dispersion and strong interfacial bonding of the filler are achieved, effectively preventing filler agglomeration and constructing a continuous three-dimensional thermally conductive network.

[0018] 3. Improved process safety and environmental friendliness. The use of low-volatility bridging agents such as HDI biuret, with HDI biuret being the preferred choice, results in a larger molecular weight and significantly reduced toxicity compared to traditional HDI monomers, thus improving production safety. The resulting film maintains high thermal conductivity while also possessing excellent mechanical properties (tensile strength ≥ 150 MPa) and electrical insulation properties (electrical strength ≥ 180 kV / mm), meeting the requirements for high-end electronic devices. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] A method for preparing a high thermal conductivity polyimide film, the method comprising the following steps: S1. Perform surface hydroxylation heat treatment on boron nitride nanoparticles with a particle size of 50-200 nm at 400-900 °C for 2-6 hours; perform polydopamine coating treatment on micron-sized alumina with a particle size of 1-5 μm, wherein the concentration of dopamine hydrochloride in the polydopamine coating treatment is 1-3 mg / mL, the reaction pH is 8.0-9.0, and the reaction time is 1-3 hours; S2. Surface-hydroxylated boron nitride and polydopamine-coated alumina are bridged by diisocyanate and reacted at 100-150℃ for 4-8 hours under inert gas protection to construct a core-double-shell structured composite filler; the diisocyanate is one or more of hexamethylene diisocyanate biuret, isophorone diisocyanate, or dicyclohexylmethane diisocyanate, and the mass ratio of diisocyanate to hydroxylated boron nitride is (0.5-5):10; S3. The core-double shell structure composite filler is subjected to surface hydrophobic treatment by refluxing for 2-6 hours using an aminosilane coupling agent to obtain a functional filler; the aminosilane coupling agent is γ-aminopropyltriethoxysilane, and the mass ratio of the aminosilane coupling agent to the composite filler is (1-8):100. S4. Disperse the functional filler in N,N-dimethylacetamide and sonicate for 0.5-2 hours to form a uniform suspension; the mass fraction of the functional filler in the suspension is 10-30%. S5. Under nitrogen protection and at -10~25℃, a polycondensation reaction is carried out between a diamine and a dianhydride monomer in a polar solvent at a molar ratio of 1:(0.98-1.02) to prepare a polyamic acid solution; the diamine is selected from 1,4'-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4'-diaminobenzoylaniline, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-bis-4-(nitrobenzyl)-phenylene oxide, etc. The dianhydride is selected from one or more of the following: 4,4'-(diamino-2,2'-dimethylbiphenyl), 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, and diaminodiphenyl sulfone; the dianhydride is selected from one or more of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4-oxobisphthalic anhydride, and bisphenol A type diether dianhydride. S6. Mix the functional filler suspension with the polyamic acid solution (the amount of functional filler added is 10-40% of the mass of the polyamic acid solution), adjust the viscosity, and then degas and cast the film. First, perform a solvent removal treatment at 80-150℃ for 30-60 minutes, and then complete the imidization by procedurally raising the temperature to 350-400℃ and holding it for 0.5-2 hours to obtain a high thermal conductivity polyimide film.

[0021] Example 1: S1. Place 10g of boron nitride nanoparticles with a particle size of 100nm in a muffle furnace and heat-treat at 500℃ in air atmosphere for 4 hours to obtain hydroxylated boron nitride; disperse 1.2g of spherical alumina with a particle size of 3μm in 150mL Tris-HCl buffer solution (pH=8.5), add 0.3g of dopamine hydrochloride, stir and react at room temperature for 2 hours, centrifuge, wash and vacuum dry at 80℃ for 12 hours to obtain polydopamine-coated alumina core-shell particles; S2. 0.1 g of hydroxylated boron nitride and 0.3 g of polydopamine-coated alumina were dispersed in 50 mL of N,N-dimethylacetamide. After ultrasonic treatment for 0.5 hours, 0.04 g of HDI biuret was added. The reaction was carried out at 120 °C for 6 hours under nitrogen protection. After the reaction was completed, the mixture was washed with N,N-dimethylacetamide, filtered, and vacuum dried at 100 °C for 24 hours to obtain a core-double shell structured composite filler. S3. Disperse 0.4g of composite filler in 40mL of anhydrous ethanol, add 0.02g of γ-aminopropyltriethoxysilane, reflux at 80℃ for 4 hours, centrifuge, wash and vacuum dry at 80℃ for 12 hours to obtain a surface-hydrophobic functional filler. S4. Disperse 0.4g of functional filler in 20g of N,N-dimethylacetamide and sonicate for 1 hour to form a uniform suspension; S5. Under nitrogen protection, add 0.1 mol of 4,4'-diaminodiphenyl ether to 200 g of N,N-dimethylacetamide. After complete dissolution, add 0.09 mol of pyromellitic dianhydride in batches and stir to react. Control the reaction temperature below 20°C and react for 6 hours to obtain a polyamic acid solution. S6. Mix the filler suspension with 80g of polyamic acid solution, stir mechanically for 4 hours, add 0.009mol of pyromellitic dianhydride to adjust the viscosity, form a stable resin, degas, cast into a film, and complete imidization by programmed temperature rise treatment at 80℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h, and 350℃ / 1h to obtain a polyimide composite film with a thickness of 50μm.

[0022] Example 2: The difference from Example 1 is that the bridging agent used in step (2) is isophorone diisocyanate (IPDI), the amount is 0.035g, the reaction temperature is 100℃, and the reaction time is 8 hours.

[0023] Example 3: The difference from Example 1 is that the bridging agent used in step (2) is dicyclohexylmethane diisocyanate (H). 12 MDI was used in an amount of 0.045g, the reaction temperature was 140℃, and the reaction time was 5 hours.

[0024] Comparative Example 1: The difference from Example 1 is that the filler treatment in steps (2) and (3) is not performed, and the mixture of boron nitride and alumina treated in (1) is used directly as filler.

[0025] Performance testing The thin films of the above embodiments and comparative examples were subjected to performance tests, and the test methods are as follows: Thermal conductivity: Laser flash method (ASTM E1461); Tensile strength and elongation at break: Universal testing machine (ASTM D882). Volume resistivity: High resistance meter (ASTM D257); Electrical strength: Breakdown voltage tester (ASTM D149).

[0026] The results are shown in the table below: I. Experimental data show that the thermal conductivity of Examples 1-3 is 2.18-2.41 W / (m·K), while that of Comparative Example 1 is only 0.76 W / (m·K). The thermal conductivity of the Examples is 2.8-3.2 times that of the Comparative Example. The difference mainly stems from the filler structure and interface design. The core-double-shell structure constructs a continuous thermal conductivity path: In the example, hydroxylated boron nitride (high thermal conductivity outer layer) and polydopamine-coated alumina (high thermal conductivity core) are connected by diisocyanate bridging to form a "core-double-shell structure". This structure can form a three-dimensional thermal conductivity network under 10-40% filler load, reducing "breaks" in heat flow transfer; while in the comparative example, the two fillers are directly mixed, without bridging effect, the filler is prone to agglomeration, only forming local thermal conductivity paths, and the thermal resistance is high.

[0027] Interface modification reduces interfacial thermal resistance: The γ-aminopropyltriethoxysilane modification in Example 3 makes the interface between the filler and the polyimide matrix more tightly bonded, reducing phonon scattering at the interface; the comparative example without hydrophobic treatment has gaps at the interface between the filler and the matrix, which hinders phonon transmission and leads to a significant decrease in thermal conductivity.

[0028] The slight effect of bridging agent type on thermal conductivity: The thermal conductivity of Examples 1 (hexamethylene diisocyanate biuret), 2 (isophorone diisocyanate), and 3 (dicyclohexylmethane diisocyanate) is similar (≤0.23W / (m・K)), indicating that all three diisocyanates can effectively bridge the filler. The slight performance fluctuations are due to differences in molecular structure (such as the activity of isocyanate groups), and all meet the high thermal conductivity requirements.

[0029] II. The tensile strength of the embodiment is 155-162 MPa and the elongation at break is 26-30%, while that of the comparative example is 125 MPa and 18%. The mechanical properties of the embodiment are superior to those of the comparative example, mainly due to the optimization of interface compatibility. Polydopamine coating enhances interfacial bonding: In the examples, the amino and hydroxyl groups of the polydopamine coating can form chemical bonds with diisocyanate and matrix molecules, making the filler and matrix "seamlessly bonded". When under stress, the stress can be transferred from the matrix to the filler, avoiding interfacial delamination. In the comparative example, without polydopamine coating, the filler and matrix are only physically mixed. When under stress, the interface is prone to cracking, and the tensile strength decreases by 20-23%.

[0030] Hydrophobic modification reduces filler agglomeration: The hydrophobic treatment in the example makes the filler uniformly dispersed in the matrix without obvious agglomerated particles, and will not break due to local stress concentration when under stress; in the comparison example, the filler agglomerates, and the agglomerated particles become "mechanical weak points", reducing the elongation at break by 40%.

[0031] III. The electrical strength of the embodiment is 188-203 kV / mm, and the volume resistivity is 8.5-9.2 × 10¹. 6 Ω・cm, while the comparative example is 142kV / mm, 6.3×10¹ 6 Ω・cm, the embodiment exhibits superior electrical performance, the key being the integrity of the material structure: Uniform dispersion avoids insulation "holes": The filler in the example is uniformly dispersed, without the "conductive channels" formed by agglomeration, resulting in high electrical strength; the filler in the comparative example agglomerates, and the agglomerated areas are prone to local electric field concentration, leading to a decrease in breakdown voltage (22-30% lower than the example).

[0032] The core-double-shell structure isolates the conductive path: In the example, the boron nitride outer layer (with excellent insulation) wraps around the alumina core, so even if there is local contact with the filler, no conductive path will be formed; in the comparative example, there is no outer layer, and the alumina particles are in direct contact, which may reduce the volume resistivity.

[0033] Comparative Example 2 Compared with Example 1, Comparative Example 2 has no core-double shell structure and uses only a single nano boron nitride filler (the amount of filler is the same as the total amount of filler in Example 1). Comparative Example 3 Compared with Example 1, it has a core-double shell structure, but no hydrophobic modification was performed (step S3 is omitted). Comparative Example 4 Compared to Example 1, pure hexamethylene diisocyanate (highly volatile) was used instead of hexamethylene diisocyanate biuret, while all other aspects remained unchanged.

[0034] Comparative Example 5 Compared to Example 1, the polydopamine coating layer is too thick (500 nm, far exceeding the 50-100 nm of Example 1).

[0035] 1. Comparing Example 1 and Comparative Example 2, it can be seen that: Comparative Example 2, using only single nano-boron nitride, has a thermal conductivity (0.92 W / m·K) that is 61% lower than that of Example 1 (2.35 W / m·K), and its tensile strength decreases by 18%. This is because single boron nitride is prone to agglomeration due to size effect (nanoscale), making it difficult to form a continuous thermally conductive network; while the "micron-sized alumina core + nano-sized boron nitride shell" of Example 1 constructs a three-dimensional pathway through size matching, and the high filling efficiency of alumina (micron-sized reduction of agglomeration) and the high thermal conductivity of boron nitride (layered structure facilitates phonon transfer) synergistically improve thermal conductivity.

[0036] 2. Comparing Example 1 and Comparative Example 3, it can be seen that: Comparative Example 3, omitting hydrophobic modification, resulted in a 34% decrease in thermal conductivity (1.56 W / m·K) and a 25% decrease in tensile strength (118 MPa). This is because the unmodified core-double-shell filler still has polar groups on its surface, leading to weak interfacial bonding with the weakly polar polyimide matrix, resulting in: ① uneven filler dispersion and breakage of the thermally conductive network; ② interfacial peeling under stress, leading to a decrease in mechanical properties. The γ-aminopropyltriethoxysilane modification in the example reduced interfacial tension through hydrophobic chains, resulting in uniform filler dispersion, confirming the beneficial effect of "interfacial compatibility optimization".

[0037] 3. Comparing Example 1 and Comparative Example 4, it can be seen that: Comparative Example 4, using pure hexamethylene diisocyanate (high volatility), has a lower thermal conductivity (2.03 W / m·K) than Example 1, indicating that the bridging function of the hexamethylene diisocyanate biuret used in the examples is improved. Because pure hexamethylene diisocyanate has a low boiling point (130℃), the volatilization rate during the reaction reaches 30%, requiring forced ventilation in the workshop and protective clothing for operators; the hexamethylene diisocyanate biuret used in the examples (with a larger molecular weight and boiling point >200℃) has a volatilization rate <5%, requiring no special protection, thus confirming the beneficial effect of "improved process safety and environmental friendliness".

[0038] 4. Comparing Example 1 and Comparative Example 5, it can be seen that: the coating layer of Comparative Example 5 is too thick (500 nm), and the thermal conductivity (1.35 W / m·K) decreases by 43%. This is because polydopamine is an organic layer (thermal conductivity ≈ 0.2 W / m·K), and if it is too thick, it will form a "thermal resistance layer" that hinders the transmission of phonons from the alumina core to the boron nitride shell. The thickness of Example 1 is controlled at 50-100 nm, which can provide sufficient active sites (to ensure bridging) without significantly increasing the interfacial thermal resistance, thus confirming the beneficial effect of "interfacial thermal resistance regulation".

[0039] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a high thermal conductivity polyimide film, characterized in that, The preparation method includes the following steps: S1. Surface hydroxylation treatment of nano-boron nitride and polydopamine coating treatment of micron-sized alumina; S2. Surface-hydroxylated boron nitride and polydopamine-coated alumina are bridged by diisocyanate to construct a core-double-shell composite filler. S3. The core-double-shell structure composite filler was hydrophobically treated with an aminosilane coupling agent to obtain a functional filler. S4. Disperse the functional filler in N,N-dimethylacetamide and then ultrasonically treat it to form a uniform suspension; S5. Under nitrogen protection and at -10~25℃, diamine and dianhydride monomers are subjected to a polycondensation reaction in a polar solvent at a molar ratio of 1:(0.98-1.02) to prepare a polyamic acid solution. S6. The functional filler suspension is mixed with a polyamic acid solution, and after degassing, casting and imidization, a high thermal conductivity polyimide film is obtained.

2. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The specific steps of surface hydroxylation treatment in step S1 are as follows: surface hydroxylation heat treatment of boron nitride nanoparticles with a particle size of 50-200nm at 400-900℃ for 2-6 hours; the polydopamine coating treatment is as follows: the concentration of dopamine hydrochloride in the polydopamine coating treatment is 1-3mg / mL, the reaction pH is 8.0-9.0, and the reaction time is 1-3 hours.

3. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The construction conditions for step S2 are as follows: under inert gas protection and at 100-150℃ for 4-8 hours, a core-double shell structure composite packing is constructed; the diisocyanate is one or more of hexamethylene diisocyanate biuret, isophorone diisocyanate, or dicyclohexylmethane diisocyanate, and the mass ratio of diisocyanate to hydroxylated boron nitride is (0.5-5):10; the inert gas is nitrogen or argon.

4. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The aminosilane coupling agent mentioned in step S3 is γ-aminopropyltriethoxysilane, and the mass ratio of the aminosilane coupling agent to the composite filler is (1-8):

100.

5. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The functional filler in step S4 has a mass fraction of 10-30% in the suspension.

6. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The diamine in step S5 is selected from one or more of 1,4'-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4'-diaminobenzoyl aniline, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-bis-4-(nitrophenoxy)biphenyl, 4,4'-(diamino-2,2'-dimethylbiphenyl, 4,4'-diaminodiphenylmethane, 4,4'-diaminodibenzophenone, and diaminodiphenyl sulfone; the dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4-oxobisphthalic anhydride, and bisphenol A type diether dianhydride.

7. The method for preparing a high thermal conductivity polyimide film according to claim 1, characterized in that: The specific steps of step S6 are as follows: the functional filler suspension is mixed with the polyamic acid solution, the amount of functional filler added is 10-40% of the mass of the polyamic acid solution, after adjusting the viscosity, it is degassed and cast into a film; firstly, it is subjected to solvent removal treatment at 80-150℃ for 30-60 minutes, and then imidization is completed by program heating to 350-400℃ and holding for 0.5-2 hours to obtain a high thermal conductivity polyimide film.

8. A high thermal conductivity polyimide film, characterized in that, The high thermal conductivity polyimide film is prepared by the method described in any one of claims 1 to 7; the film has a thickness of 25-75 μm, an elongation at break of 15-40%, and a volume resistivity ≥6.3×10¹. 6 Ω・cm.

9. An electronic device, characterized in that, The device includes the high thermal conductivity polyimide film as described in claim 8; the electronic device is a 5G communication device, a flexible display device, or a power semiconductor device, and the high thermal conductivity polyimide film serves as a thermal management material or insulating component of the electronic device.

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