A polyimide film, a method for preparing the same, and an application thereof

Abstract

This invention proposes a polyimide film, its preparation method, and its applications, relating to the field of thin film materials. By weight, it comprises the following raw materials: 50-100 parts dimethylformamide, 5-10 parts diaminodiphenyl ether, 10-20 parts phenylenediamine, 1-2 parts core-shell structured silica-alumina particles, 25-30 parts pyromellitic dianhydride, 1-2 parts organically modified montmorillonite, 1-2 parts aminated thermally conductive particles, 50-100 parts acetic anhydride, and 5-10 parts pyridine; wherein the core-shell structured silica-alumina particles are a composite material with polydopamine as the shell and nano-silica and nano-alumina as the core; the organically modified montmorillonite is obtained by intercalation modification of montmorillonite with an organic compound containing hydroxyl groups; the aminated thermally conductive particles are obtained by graft modification of nitrides with an organic compound containing amino groups. It exhibits good high-temperature resistance, high-pressure breakdown resistance, and thermal conductivity, as well as high mechanical strength and long service life.

Description

Technical Field

[0001] This invention relates to the field of thin film materials, and more specifically, to a polyimide film, its preparation method, and its application. Background Technology

[0002] Polyimide film, as a high-performance special engineering material, has unique high temperature resistance, mechanical strength, chemical stability and excellent electrical insulation properties, which enable it to exhibit extraordinary adaptability in many extreme environments. It is widely used in many key fields such as aerospace, electronics, automobiles, and biomedicine.

[0003] However, the low thermal conductivity and poor barrier properties of polyimide films limit their applications. To improve the thermal conductivity of polyimide films, high thermal conductivity inorganic fillers are typically introduced, such as boron nitride (BN), aluminum nitride (AlN), and graphene. These fillers enhance thermal conductivity by constructing continuous microscopic thermal conduction pathways and reducing interfacial thermal resistance. Further, surface modification of the fillers (such as silane coupling agent treatment or polyethyleneimine adsorption) can improve their compatibility with the polyimide matrix, reduce interfacial defects, and enhance interfacial adhesion strength, thereby reducing interfacial thermal resistance. Alternatively, structural design, such as multilayer porous composite membranes, can significantly improve thermal conductivity through the gradient distribution of fillers and the interfacial self-assembly effect. To improve the barrier properties of polyimide membranes, layered nanoparticles such as montmorillonite are typically added. Through intercalation polymerization, the montmorillonite layers are exfoliated and dispersed within the polyimide (PI) matrix, forming a "zigzag path" that extends the permeation path of the penetrating molecules and enhances barrier performance. Alternatively, nanoparticles such as nano-silica are added, utilizing their small size and surface effects to improve the density and barrier properties of the polyimide membrane. Another approach is to introduce rigid structures (such as benzene rings or biphenyls) into the molecular chain to increase the packing density and crystallinity, thereby reducing free volume and improving barrier performance. Introducing polar groups (such as fluorine or thioether groups) strengthens the intermolecular forces between PI molecular chains, further enhancing the membrane's density and barrier properties.

[0004] For example, patent CN202411244435.0 discloses a high-voltage breakdown resistant polyimide film and its preparation method. This method introduces hexagonal platen alumina, hexagonal boron nitride, and layered clay as inorganic fillers into the polyimide film. The structure of silicate minerals in the layered clay forms a layered shield, hindering the movement of charges. Simultaneously, the adsorption effect of the clay on the hexagonal platen alumina and hexagonal boron nitride allows them to adhere to the surface of the layered clay, further improving the film's high-temperature and high-voltage breakdown resistance. However, in this technical solution, the hexagonal platen alumina and hexagonal boron nitride bind to the layered clay through adsorption, and the bonding strength is limited. During use, the adsorption effect weakens, leading to a corresponding decrease in the performance of the polyimide film and a short service life. Summary of the Invention

[0005] The purpose of this invention is to provide a polyimide film that has good high temperature resistance, high pressure breakdown resistance, and thermal conductivity, as well as high mechanical strength and long service life.

[0006] Another objective of this invention is to provide a method for preparing a polyimide membrane, in which silicon-aluminum particles, organomontmorillonite, and aminated thermally conductive particles are added during the preparation process, resulting in high bonding strength between the functional particles and the membrane substrate, making it less prone to detachment and separation during use, thus extending the service life of the membrane.

[0007] The technical problem solved by this invention is achieved by the following technical solution.

[0008] On one hand, embodiments of the present invention provide a polyimide film comprising, by weight, the following raw materials:

[0009] 50-100 parts of dimethylformamide, 5-10 parts of diaminodiphenyl ether, 10-20 parts of phenylenediamine, 1-2 parts of core-shell structured silica-alumina particles, 25-30 parts of pyromellitic dianhydride, 1-2 parts of organically modified montmorillonite, 1-2 parts of aminated thermally conductive particles, 50-100 parts of acetic anhydride, and 5-10 parts of pyridine.

[0010] The core-shell structured silicon-aluminum particles are a composite material with polydopamine as the shell and nano-silica and nano-alumina as the core.

[0011] The organically modified montmorillonite is obtained by intercalating montmorillonite with an organic compound containing hydroxyl groups;

[0012] The amination thermally conductive particles are obtained by grafting nitrides with organic compounds containing amino groups.

[0013] On the other hand, embodiments of the present invention provide a method for preparing a polyimide film, comprising the following steps:

[0014] S1, mix dimethylformamide, diaminodiphenyl ether, and phenylenediamine, stir until homogeneous, then add core-shell structured aluminum silicate particles, stir until homogeneous, and obtain mixture A;

[0015] S2, pyromellitic dianhydride and organically modified montmorillonite are ultrasonically treated for 10-30 minutes, then added to mixture A and stirred evenly to obtain mixture B;

[0016] S3, mix dimethylformamide and amination thermally conductive particles, stir evenly to obtain mixture C;

[0017] S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution;

[0018] S5, after mixing the polyamic acid solution with acetic anhydride, pyridine is added, the mixture is stirred evenly, and then the film is laid, dried, and imidized to obtain the polyimide film.

[0019] In some embodiments of the present invention, the core-shell structured silicon-aluminum particles are prepared by the following method:

[0020] Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 10-20 minutes, centrifuged, and filtered to obtain silicon-aluminum particles.

[0021] The silicon-aluminum particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 8.5-9.0. Stirring was continued for 12-24 hours. The particles were then centrifuged, filtered, and washed to obtain the core-shell structured silicon-aluminum particles.

[0022] In some embodiments of the present invention, the mass ratio of the nano-silica to the nano-alumina is (1-1.2):1.

[0023] In some embodiments of the present invention, the organically modified montmorillonite is prepared by the following method:

[0024] Montmorillonite was added to an aqueous sodium chloride solution and stirred for 10-12 hours. After freeze-thaw treatment 3-5 times, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol with a molecular weight of less than 600, and silane coupling agent. Then, it was stirred at 80-100℃ for 6-12 hours and subjected to intermittent ultrasonic treatment. After filtration, washing, and drying, the organic modified montmorillonite was obtained.

[0025] In some embodiments of the present invention, the mass ratio of montmorillonite, ethylene glycol and polyethylene glycol is 1:(0.3-0.5):(0.3-0.5).

[0026] In some embodiments of the present invention, the amination thermally conductive particles are prepared by the following method:

[0027] In a mixed atmosphere of ammonia and nitrogen, nitrides are treated by plasma, and after cooling, pretreated particles are obtained.

[0028] p-phenylenediisocyanate, phenylenediamine, silane coupling agent and ethanol aqueous solution are mixed and stirred evenly to obtain grafting solution;

[0029] The pretreated particles are mixed with the grafting solution and stirred at 80-90°C for 5-10 hours. After filtration, washing, and drying, the amination thermally conductive particles are obtained.

[0030] In some embodiments of the present invention, the nitride is hexagonal boron nitride, silicon nitride, or a mixture of both. The mass-to-volume ratio of the terephthalic diisocyanate, phenylenediamine, silane coupling agent, and ethanol aqueous solution is (0.8-1) g : (0.2-0.5) g : (0.2-0.5) g : (1-2) ml. The volume fraction of the ethanol aqueous solution is 50-60%.

[0031] Thirdly, embodiments of the present invention provide an application of a polyimide film, based on which the above-mentioned polyimide film is used in insulating materials, such as in high-speed motors and new energy batteries as an insulating material.

[0032] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0033] The polyimide film and its preparation method provided by this invention introduce silicon-aluminum particles, organo-montmorillonite, and aminated thermally conductive particles during the preparation process, which can improve the high-temperature resistance, high-pressure breakdown resistance, thermal conductivity, mechanical strength, and barrier properties of the polyimide film. Specifically, by adding core-shell structured silicon-aluminum particles with polydopamine as the shell, the dispersibility of the particles in the polyimide film can be improved, making the silicon-aluminum particles uniformly dispersed in the polyimide film, reducing interface defects. Furthermore, the addition of nano-silicon-aluminum particles can polarize and dissipate charges at the interface of the polyimide film, suppressing electric field concentration, thereby improving the high-pressure breakdown resistance of the polyimide film. The addition of organo-modified montmorillonite containing hydroxyl groups allows for strong adsorption between the layered montmorillonite and the aminated thermally conductive particles, enabling amino groups to enter the intercalation of montmorillonite, thus improving the bonding strength between montmorillonite and the aminated thermally conductive particles. On the other hand, the active hydroxyl groups carried by montmorillonite can also form intermolecular forces and hydrogen bonds with amino groups, further enhancing the bonding strength between the two. Furthermore, the active hydroxyl groups also participate in the molecular structure of polyamide, acting as crosslinking agents to form a three-dimensional network structure through esterification, thus enabling montmorillonite to be firmly grafted onto the polyimide film.

[0034] In summary, the polyimide film provided by this invention exhibits high bonding strength between various functional particles and the film matrix, making it less prone to detachment during use, thereby improving the mechanical properties and high-temperature resistance of the polyimide film. Detailed Implementation

[0035] 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0037] A polyimide film comprises, by weight, the following raw materials:

[0038] 50-100 parts of dimethylformamide, 5-10 parts of diaminodiphenyl ether, 10-20 parts of phenylenediamine, 1-2 parts of core-shell structured silica-alumina particles, 25-30 parts of pyromellitic dianhydride, 1-2 parts of organically modified montmorillonite, 1-2 parts of aminated thermally conductive particles, 50-100 parts of acetic anhydride, and 5-10 parts of pyridine; wherein, phenylenediamine may be one or a mixture of two of 1,2-phenylenediamine, 1,3-phenylenediamine, and 1,4-phenylenediamine.

[0039] Its preparation method includes the following steps:

[0040] S1, mix dimethylformamide, diaminodiphenyl ether, and phenylenediamine, stir until homogeneous, then add core-shell structured aluminum silicate particles, stir until homogeneous, and obtain mixture A;

[0041] S2, pyromellitic dianhydride and organically modified montmorillonite are ultrasonically treated for 10-30 minutes, then added to mixture A and stirred evenly to obtain mixture B;

[0042] S3, mix dimethylformamide and amination thermally conductive particles, stir evenly to obtain mixture C; wherein, the mass ratio of dimethylformamide used in step S1 and step S3 is 1:(0.8-1).

[0043] S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution;

[0044] S5, after mixing the polyamic acid solution with acetic anhydride, pyridine is added, the mixture is stirred evenly, and then the film is laid, dried, and imidized to obtain the polyimide film.

[0045] The core-shell structured silicon-aluminum particles are a composite material with polydopamine as the shell and nano-silica and nano-alumina as the core; the preparation method is as follows:

[0046] Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 10-20 minutes, centrifuged, and filtered to obtain silicon-aluminum particles. The mass fraction of sulfuric acid in the mixture was 5%, and the volume fraction of ethanol was 10%. Under the action of sulfuric acid and ethanol, nano-silica and nano-alumina were activated, and the number of active sites on the surface of the nanoparticles increased, thereby improving the coating effect of polydopamine.

[0047] The silica-alumina particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 8.5-9.0, and stirring continued for 12-24 hours. The mixture was then centrifuged, filtered, and washed to obtain the core-shell structured silica-alumina particles. The mass ratio of nano-silica to nano-alumina was (1-1.2):1. Coating the nanoparticles with polydopamine improves their dispersibility, reduces agglomeration, and results in a more uniform distribution of nanoparticles within the polyimide membrane, leading to superior overall membrane performance.

[0048] The organically modified montmorillonite is obtained by intercalating montmorillonite with an organic compound containing hydroxyl groups; its preparation method is as follows:

[0049] Montmorillonite was added to a sodium chloride aqueous solution (mass fraction 10-15%), stirred for 10-12 hours, and subjected to freeze-thaw treatment 3-5 times. Then, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol with a molecular weight less than 600, and a silane coupling agent. The mixture was then stirred at 80-100℃ for 6-12 hours and subjected to intermittent ultrasonic treatment. After filtration, washing, and drying, the organically modified montmorillonite was obtained. The mass ratio of montmorillonite, ethylene glycol, and polyethylene glycol was 1:(0.3-0.5):(0.3-0.5). The intermittent ultrasonic treatment was performed at 20 kHz for 10 minutes, followed by a 10-minute pause.

[0050] Before use, montmorillonite needs to be purified. When montmorillonite is added to a sodium chloride aqueous solution, it absorbs water and swells with prolonged stirring, increasing the interlayer spacing. Subsequent repeated freeze-thaw treatments cause the water molecules between the montmorillonite layers to increase in volume after freezing, further widening the interlayer spacing. Furthermore, after repeated freeze-thaw treatments, the interlayer spacing of montmorillonite becomes relatively stable, facilitating subsequent intercalation modification. Under the action of a coupling agent, polyol molecules can enter the montmorillonite interlayer and form hydrogen bonds with montmorillonite molecules, resulting in hydroxyl groups on the montmorillonite molecules and increasing the bonding strength between montmorillonite and polyamide molecules.

[0051] The amination-modified thermally conductive particles are obtained by grafting an amino-group-containing organic compound onto a nitride. The preparation method is as follows: The nitride is plasma-treated under a mixed atmosphere of ammonia and nitrogen, and after cooling, pretreated particles are obtained. Terephthalic diisocyanate, phenylenediamine, a silane coupling agent, and an aqueous ethanol solution are mixed and stirred until homogeneous to obtain a grafting solution. The pretreated particles are mixed with the grafting solution and stirred at 80-90°C for 5-10 hours. The mixture is then filtered, washed, and dried to obtain the amination-modified thermally conductive particles. The nitride is hexagonal boron nitride, silicon nitride, or a mixture of both. The mass-to-volume ratio of terephthalic diisocyanate, phenylenediamine, silane coupling agent, and aqueous ethanol solution is (0.8-1) g : (0.2-0.5) g : (0.2-0.5) g : (1-2) ml. The volume fraction of the aqueous ethanol solution is 50-60%.

[0052] First, the nitrides are subjected to plasma treatment. During the plasma treatment, the number of active sites on the surface of the nitrides increases. At the same time, the ammonia in the mixed gas is decomposed into ammonium ions. The ammonium ions combine with the active sites on the surface of the nitrides to obtain pre-aminated nitrides. Subsequently, under the action of organic compounds such as p-phenylenediamine, phenylenediamine, and silane coupling agents, the amine groups in the organic compounds combine with the active sites, resulting in further amination. Combining plasma treatment with chemical grafting modification improves the degree of amination of the nitrides.

[0053] The polyimide film provided in this invention can be used as an insulating material in high-speed motors, electronic coils, and new energy batteries.

[0054] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0055] Example 1

[0056] 1. Prepare core-shell structured aluminum silicon particles using the following method:

[0057] Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 20 min, centrifuged, and filtered to obtain silicon-aluminum particles; wherein the mass fraction of sulfuric acid in the mixture was 5% and the volume fraction of ethanol was 10%.

[0058] The silica-alumina particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 9.0, and stirring continued for 24 hours. The mixture was then centrifuged, filtered, and washed to obtain the core-shell structured silica-alumina particles. The mass ratio of nano-silica, nano-alumina, and dopamine hydrochloride was 1.2:1:2.5.

[0059] 2. Prepare organically modified montmorillonite using the following method:

[0060] Montmorillonite was added to a 10% sodium chloride aqueous solution and stirred for 12 hours. The mixture was then subjected to three freeze-thaw cycles at -2°C. Next, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol (200 Da), and a silane coupling agent (KH-550). The mixture was then stirred at 100°C for 12 hours and intermittently sonicated. After filtration, washing, and drying, the organically modified montmorillonite was obtained. The mass ratio of montmorillonite, ethylene glycol, polyethylene glycol, ethanol, and silane coupling agent was 1:0.5:0.5:1:0.2. The intermittent sonication was performed at 20 kHz for 10 minutes, followed by a 10-minute pause, and this cycle was repeated.

[0061] 3. Prepare amination-modified thermally conductive particles using the following method:

[0062] Hexagonal boron nitride and silicon boron nitride (mass ratio 1:1) were plasma-treated, and after cooling, pretreated particles were obtained. A grafting solution was prepared by mixing terephthalic diisocyanate, 1,2-phenylenediamine, silane coupling agent (KH-550), and an aqueous ethanol solution (volume fraction 50%). The pretreated particles were then mixed with the grafting solution and stirred at 80°C for 10 hours. After filtration, washing, and drying, the amination-treated thermally conductive particles were obtained. The volume ratio of ammonia to nitrogen was 1:2, and the plasma treatment parameters were: power 100W, gas flow rate 1L / min, and treatment time 40min. The mass-volume ratio of terephthalic diisocyanate, phenylenediamine, silane coupling agent, and aqueous ethanol solution was 0.8g:0.2g:0.5g:2ml.

[0063] 4. Prepare the polyimide film of this embodiment according to the following formulation and method:

[0064] 100 parts of dimethylformamide, 10 parts of diaminodiphenyl ether, 20 parts of 1,2-phenylenediamine, 2 parts of core-shell structured silica-alumina particles, 30 parts of pyromellitic dianhydride, 2 parts of organically modified montmorillonite, 2 parts of aminated thermally conductive particles, 100 parts of acetic anhydride, and 10 parts of pyridine.

[0065] S1, mix 55 parts of dimethylformamide, 10 parts of diaminodiphenyl ether, and 20 parts of 1,2-phenylenediamine, stir until homogeneous, then add 2 parts of core-shell structured aluminum silicate particles, stir until homogeneous, and obtain mixture A;

[0066] S2, 30 parts of pyromellitic dianhydride and 2 parts of organic modified montmorillonite were ultrasonically treated for 30 minutes, and then added to mixture A and stirred evenly to obtain mixture B;

[0067] S3, mix 45 parts of dimethylformamide and 2 parts of aminated thermally conductive particles, stir evenly to obtain mixture C;

[0068] S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution;

[0069] S5. After mixing the polyamic acid solution with 100 parts of acetic anhydride, add 10 parts of pyridine, stir evenly, and then lay, dry and imidize the film to obtain the polyimide film.

[0070] Example 2

[0071] The difference from Example 1 is that the polyimide film of this example is prepared according to the following formulation and method:

[0072] 80 parts of dimethylformamide, 8 parts of diaminodiphenyl ether, 15 parts of 1,2-phenylenediamine, 1 part of core-shell structured silica-alumina particles, 30 parts of pyromellitic dianhydride, 1 part of organically modified montmorillonite, 1 part of aminated thermally conductive particles, 80 parts of acetic anhydride, and 8 parts of pyridine.

[0073] S1, mix 40 parts of dimethylformamide, 8 parts of diaminodiphenyl ether, and 15 parts of phenylenediamine, stir until uniform, then add 1 part of core-shell structured aluminum silicate particles, stir until uniform, and obtain mixture A;

[0074] S2, 30 parts of pyromellitic dianhydride and 1 part of organic modified montmorillonite are ultrasonically treated for 30 minutes, then added to mixture A and stirred evenly to obtain mixture B;

[0075] S3, mix 40 parts of dimethylformamide and 1 part of aminated thermally conductive particles, stir evenly to obtain mixture C;

[0076] S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution;

[0077] S5. After mixing the polyamic acid solution with 80 parts of acetic anhydride, add 8 parts of pyridine, stir evenly, and then lay, dry and form a film, and heat imidize (300℃) to obtain the polyimide film.

[0078] The raw materials used in this embodiment are the same as those in Example 1.

[0079] Example 3

[0080] The difference from Example 1 is that the polyimide film of this example is prepared according to the following formulation and method:

[0081] 50 parts of dimethylformamide, 5 parts of diaminodiphenyl ether, 10 parts of 1,2-phenylenediamine, 1 part of core-shell structured silica-alumina particles, 25 parts of pyromellitic dianhydride, 1 part of organically modified montmorillonite, 1 part of aminated thermally conductive particles, 50 parts of acetic anhydride, and 5 parts of pyridine.

[0082] S1, mix 25 parts of dimethylformamide, 5 parts of diaminodiphenyl ether, and 10 parts of phenylenediamine, stir until uniform, then add 1 part of core-shell structured aluminum silicate particles, stir until uniform, and obtain mixture A;

[0083] S2, 25 parts of pyromellitic dianhydride and 1 part of organic modified montmorillonite were ultrasonically treated for 30 minutes, and then added to mixture A and stirred evenly to obtain mixture B;

[0084] S3, mix 25 parts of dimethylformamide and 1 part of aminated thermally conductive particles, stir evenly to obtain mixture C;

[0085] S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution;

[0086] S5. After mixing the polyamic acid solution with 50 parts of acetic anhydride, add 5 parts of pyridine, stir evenly, and then lay, dry and imidize the film to obtain the polyimide film.

[0087] The raw materials used in this embodiment are the same as those in Example 1.

[0088] Example 4

[0089] The difference from Example 1 is that, in this example, the core-shell structured silicon-aluminum particles used are prepared by the following method:

[0090] Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 20 min, centrifuged, and filtered to obtain silicon-aluminum particles; wherein the mass fraction of sulfuric acid in the mixture was 5% and the volume fraction of ethanol was 10%.

[0091] The silica-alumina particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 9.0, and stirring continued for 24 hours. The mixture was then centrifuged, filtered, and washed to obtain the core-shell structured silica-alumina particles. The mass ratio of nano-silica, nano-alumina, and dopamine hydrochloride was 1:1:2.

[0092] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0093] Example 5

[0094] The difference from Example 1 is that, in this example, the core-shell structured silicon-aluminum particles used are prepared by the following method:

[0095] Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 20 min, centrifuged, and filtered to obtain silicon-aluminum particles; wherein the mass fraction of sulfuric acid in the mixture was 5% and the volume fraction of ethanol was 10%.

[0096] The silica-alumina particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 8.5-9.0, and stirring continued for 12-24 hours. The mixture was then centrifuged, filtered, and washed to obtain the core-shell structured silica-alumina particles. The mass ratio of nano-silica, nano-alumina, and dopamine hydrochloride was 1.1:1:2.5.

[0097] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0098] Example 6

[0099] The difference from Example 1 is that, in this example, the organically modified montmorillonite used is prepared by the following method:

[0100] Montmorillonite was added to a 10% sodium chloride aqueous solution and stirred for 12 hours. The mixture was then subjected to three freeze-thaw cycles at -2°C. Next, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol (200 Da), and a silane coupling agent (KH-550). The mixture was then stirred at 80°C for 12 hours and intermittently sonicated. After filtration, washing, and drying, the organically modified montmorillonite was obtained. The mass ratio of montmorillonite, ethylene glycol, polyethylene glycol, ethanol, and silane coupling agent was 1:0.3:0.3:1:0.2. The intermittent sonication was performed at 20 kHz for 10 minutes, followed by a 10-minute pause, and this cycle was repeated.

[0101] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0102] Example 7

[0103] The difference from Example 1 is that, in this example, the organically modified montmorillonite used is prepared by the following method:

[0104] Montmorillonite was added to a 10% sodium chloride aqueous solution and stirred for 12 hours. The mixture was then subjected to three freeze-thaw cycles at -2°C. Next, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol (200 Da), and a silane coupling agent (KH-550). The mixture was then stirred at 90°C for 10 hours and intermittently sonicated. After filtration, washing, and drying, the organically modified montmorillonite was obtained. The mass ratio of montmorillonite, ethylene glycol, polyethylene glycol, ethanol, and silane coupling agent was 1:0.3:0.5:1:0.2. The intermittent sonication was performed at 20 kHz for 10 minutes, followed by a 10-minute pause, and this cycle was repeated.

[0105] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0106] Example 8

[0107] The difference from Example 1 is that, in this example, the amination-modified thermally conductive particles are prepared by the following method:

[0108] Silicon nitride was plasma-treated in a mixed atmosphere of ammonia and nitrogen. After cooling, pretreated particles were obtained. A grafting solution was prepared by mixing terephthalic diisocyanate, 1,2-phenylenediamine, a silane coupling agent (KH-550), and an aqueous ethanol solution (50% by volume). The pretreated particles were then mixed with the grafting solution and stirred at 80°C for 10 hours. The mixture was then filtered, washed, and dried to obtain the amination-treated thermally conductive particles. The volume ratio of ammonia to nitrogen was 1:2. The plasma treatment parameters were: power 100W, gas flow rate 1L / min, and treatment time 40min. The mass-to-volume ratio of terephthalic diisocyanate, phenylenediamine, silane coupling agent, and aqueous ethanol solution was 1g:0.5g:0.2g:2ml.

[0109] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0110] Example 9

[0111] The difference from Example 1 is that, in this example, the amination-modified thermally conductive particles are prepared by the following method:

[0112] Hexagonal boron nitride was plasma-treated in a mixed atmosphere of ammonia and nitrogen, and after cooling, pretreated particles were obtained. A grafting solution was prepared by mixing terephthalic diisocyanate, 1,2-phenylenediamine, a silane coupling agent (KH-550), and an aqueous ethanol solution (50% by volume). The pretreated particles were then mixed with the grafting solution and stirred at 80°C for 10 hours. After filtration, washing, and drying, the amination-modified thermally conductive particles were obtained. The volume ratio of ammonia to nitrogen was 1:2, and the plasma treatment parameters were: power 100W, gas flow rate 1L / min, and treatment time 40min. The mass-to-volume ratio of terephthalic diisocyanate, phenylenediamine, silane coupling agent, and aqueous ethanol solution was 0.8g:0.5g:0.3g:2ml.

[0113] The remaining raw materials, the proportions of each raw material, and the preparation method of the polyimide film are the same as in Example 1.

[0114] Comparative Example 1

[0115] The difference from Example 1 is that equal amounts of nano-silica and nano-alumina are used instead of the core-shell structured silicon-aluminum particles in Example 1. All other raw materials, proportions, and preparation methods are the same as in Example 1.

[0116] Comparative Example 2

[0117] The difference from Example 1 is that an equal amount of montmorillonite was used instead of the organically modified montmorillonite in Example 1. All other raw materials, proportions, and preparation methods are the same as in Example 1.

[0118] Comparative Example 3

[0119] The difference from Example 1 is that equal amounts of hexagonal boron nitride and silicon boron nitride (mass ratio 1:1) are used instead of the amination thermally conductive particles in Example 1. All other raw materials, proportions, and preparation methods are the same as in Example 1.

[0120] Comparative Example 4

[0121] The difference from Example 1 is that equal amounts of nano-silica and nano-alumina are used instead of the core-shell structured silica-alumina particles in Example 1, and equal amounts of montmorillonite are used instead of the organically modified montmorillonite in Example 1. All other raw materials, proportions, and preparation methods are the same as in Example 1.

[0122] Comparative Example 5

[0123] The difference from Example 1 is that equal amounts of nano-silica and nano-alumina are used instead of the core-shell structured silicon-aluminum particles in Example 1, and equal amounts of hexagonal nitride and silicon boron nitride (mass ratio 1:1) are used instead of the amination thermally conductive particles in Example 1. All other raw materials, proportions, and preparation methods are the same as in Example 1.

[0124] Experimental Example

[0125] Using the polyimide films of Examples 1-9 and Comparative Examples 1-5 as test objects, the thickness, tensile strength, thermal conductivity, and corona resistance time of each polyimide film were tested according to the test methods and relevant regulations in GB / T13542.2-2021. The test conditions for corona resistance time were: experimental voltage 2kV, experimental frequency 20kHz, pulse rise time 50ns, bipolar pulse square wave, and 6mm cylindrical electrode. The results are shown in Table 1.

[0126] Table 1 Properties of various polyimide films

[0127] Thickness (um) Tensile strength (MPa) Thermal conductivity (W / m·K) Corona resistance duration (min) Example 1 30 231 1.212 223.2 Example 2 30 229 1.275 221.5 Example 3 30 228 1.289 201.3 Example 4 30 226 1.311 211.8 Example 5 30 230 1.269 208.5 Example 6 30 225 1.298 207.6 Example 7 30 226 1.301 210.3 Example 8 30 221 1.278 205.3 Example 9 30 219 1.269 202.1 Comparative Example 1 30 183 1.013 102.3 Comparative Example 2 30 189 1.011 189.3 Comparative Example 3 30 178 0.823 178.2 Comparative Example 4 30 171 0.923 89.3 Comparative Example 5 30 169 0.625 99.2

[0128] As can be seen from Table 1, the polyimide film of the embodiments exhibits excellent mechanical properties, high thermal conductivity, and high heat transfer efficiency, while the properties of comparative examples 1-5 show a decline in all aspects. In summary, the polyimide film provided by this invention has high bonding strength between various functional particles and the film matrix, making it less prone to detachment during use, thereby improving the mechanical properties and high-temperature resistance of the polyimide film.

[0129] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A polyimide film, characterized in that, By weight, it includes the following ingredients: 50-100 parts of dimethylformamide, 5-10 parts of diaminodiphenyl ether, 10-20 parts of phenylenediamine, 1-2 parts of core-shell structured silica-alumina particles, 25-30 parts of pyromellitic dianhydride, 1-2 parts of organically modified montmorillonite, 1-2 parts of aminated thermally conductive particles, 50-100 parts of acetic anhydride, and 5-10 parts of pyridine. The core-shell structured silicon-aluminum particles are a composite material with polydopamine as the shell and nano-silica and nano-alumina as the core. The organically modified montmorillonite is obtained by intercalation modification of montmorillonite with an organic compound containing hydroxyl groups; the organically modified montmorillonite is prepared by the following method: Montmorillonite was added to an aqueous sodium chloride solution and stirred for 10-12 hours. After freeze-thaw treatment 3-5 times, it was added to a mixed solution of ethanol, ethylene glycol, polyethylene glycol with a molecular weight of less than 600, and a silane coupling agent. Then, it was stirred at 80-100°C for 6-12 hours and subjected to intermittent ultrasonic treatment. After filtration, washing, and drying, the organic modified montmorillonite was obtained. The aminated thermally conductive particles are obtained by grafting nitrides with organic compounds containing amino groups; the aminated thermally conductive particles are prepared by the following method: Under a mixed atmosphere of ammonia and nitrogen, nitrides are plasma-treated and cooled to obtain pretreated particles; the nitrides are hexagonal boron nitride, silicon nitride, or a mixture of both. p-phenylenediisocyanate, phenylenediamine, silane coupling agent and ethanol aqueous solution are mixed and stirred evenly to obtain grafting solution; The pretreated particles are mixed with the grafting solution and stirred at 80-90°C for 5-10 hours. After filtration, washing, and drying, the amination thermally conductive particles are obtained.

2. A method for preparing the polyimide film as described in claim 1, characterized in that, Includes the following steps: S1, mix dimethylformamide, diaminodiphenyl ether, and phenylenediamine, stir until homogeneous, then add core-shell structured aluminum silicate particles, stir until homogeneous, and obtain mixture A; S2, pyromellitic dianhydride and organically modified montmorillonite are ultrasonically treated for 10-30 minutes, then added to mixture A and stirred evenly to obtain mixture B; S3, mix dimethylformamide and amination thermally conductive particles, stir evenly to obtain mixture C; S4. Mix mixture B and mixture C, stir until homogeneous, and obtain a polyamic acid solution; S5. After mixing the polyamic acid solution with acetic anhydride, pyridine is added, and the mixture is stirred evenly. After film laying, drying, and imidization, the polyimide film is obtained.

3. The method for preparing the polyimide film according to claim 2, characterized in that, The core-shell structured silicon-aluminum particles are prepared by the following method: Nano-silica and nano-alumina were added to an aqueous solution of sulfuric acid and ethanol, sonicated for 10-20 minutes, centrifuged, and filtered to obtain silicon-aluminum particles. The silicon-aluminum particles were added to a 0.1 mol / L Tris buffer solution with a pH of 8.5 and stirred until homogeneous. Dopamine hydrochloride was then added and stirred until dissolved. Ammonia was added dropwise to adjust the pH to 8.5-9.

0. Stirring was continued for 12-24 hours. The particles were then centrifuged, filtered, and washed to obtain the core-shell structured silicon-aluminum particles.

4. The method for preparing the polyimide film according to claim 3, characterized in that, The mass ratio of the nano-silica to the nano-alumina is (1-1.2):

1.

5. The method for preparing the polyimide film according to claim 2, characterized in that, The mass ratio of montmorillonite, ethylene glycol, and polyethylene glycol is 1:(0.3-0.5):(0.3-0.5).

6. An application of a polyimide film, characterized in that, Application of the polyimide film according to claim 1 or the polyimide film prepared by any one of claims 2-5 in insulating materials.