Flexible PI heat-conducting insulating film pad and preparation method thereof

Abstract

The invention discloses a flexible PI heat-conducting insulating film pad and a preparation method thereof, and relates to the field of film pads. The preparation method comprises the following steps: preparing Fe3O4 magnetic heat-conducting core and SiO2 insulating shell composite nanoparticles by a sol-gel method, treating and grafting epoxy groups by a silane coupling agent, performing ring-opening addition with one end amino group of amino-terminated polydimethylsiloxane, and reacting the other end amino group with polyethylene glycol diglycidyl ether, so that two flexible long chains are grafted on SiO2. Due to the modified composite nanoparticles and the flexible long-chain structure, the flexibility of the film pad is remarkably improved; thermal vibration of silicon-oxygen bonds and ether bonds promotes heat transfer, a hydrogen bond network is formed with a PI substrate to improve dispersion stability, particles are orderly arranged under the action of a high-frequency magnetic field to construct a three-dimensional heat conduction network, and heat conduction efficiency is enhanced; the SiO2 isolates the inner core from conducting and improves the insulating property of the film pad by virtue of good insulativity and no free charge in the flexible long-chain polymer. The flexible PI heat-conducting insulating film pad prepared by the invention has the effects of flexibility, heat conduction and insulation.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane pads, and in particular to a flexible PI thermally conductive insulating membrane pad and a preparation method thereof. Background Art

[0002] PI-based insulating materials are widely used in the electronics field due to their excellent high-temperature resistance and electrical insulation properties. However, their inherent thermal conductivity is low, and the introduction of traditional thermally conductive fillers can easily lead to problems such as decreased insulation performance, poor interface compatibility, and increased material rigidity. This makes it difficult to meet the needs of high-frequency, high-power electronic devices for insulating, thermally conductive, flexible materials.

[0003] In the existing technology, when the thermal conductivity of PI-based materials is improved through nanoparticle modification, the efficiency of thermal network construction is often low due to uneven dispersion of fillers and weak interface bonding with the matrix. At the same time, the use of conductive fillers will significantly damage the insulation performance.

[0004] To this end, the present invention proposes a self-made modified composite nanoparticle filler. By designing core-shell structured magnetic thermal conductive particles and grafting flexible long-chain polymers, the filler dispersion and interface interaction are enhanced while ensuring insulation. The magnetic field is used to induce the construction of a three-dimensional thermal conductive network, effectively solving the problems of imbalance in thermal conductivity and insulation performance and insufficient flexibility of existing materials. Summary of the Invention

[0005] The object of the present invention is to provide a flexible PI thermally conductive insulating film pad and a preparation method thereof, so as to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solution: a flexible PI thermally conductive insulating film pad, wherein the preparation method of the flexible PI thermally conductive insulating film pad comprises the following steps: (1) The magnetic composite nanoparticles were treated with a silane coupling agent, mixed with amino-terminated polydimethylsiloxane and a catalyst in a mass ratio of 1-1.5:3-5:0.05-0.1, stirred at 300-500 rpm at 50-70 ° C for 12-24 h, cooled to room temperature, precipitated by permanent magnet, washed with deionized water three times, and dried in an oven at 50 ° C with a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: catalyst were mixed in a mass ratio of 1:2-4:0.05-0.1, stirred at 300-500 rpm at 50-70 ° C for 12-24 h, cooled to room temperature, precipitated by permanent magnet, washed with deionized water three times, and dried in an oven at 50 ° C with a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles; (2) The homemade modified composite nanoparticles: PI resin: organic solvent were mixed in a mass ratio of 1~2:5~7:25~35, stirred at 60℃ and 500rpm for 2~3h, allowed to stand for degassing for 30min, poured onto the casting substrate, and scraped with an automatic scraper with a 350µm slit at a speed of 10mm / min to form a uniform wet film. After pre-curing at 80℃ in a vertical magnetic field under a nitrogen atmosphere for 1~2h, the imidization was completed by step thermal curing to obtain a flexible PI thermal insulating film pad with a thickness of 30~50µm.

[0007] Furthermore, the silane coupling agent in step (1) is: γ-glycidyloxypropyltrimethoxysilane.

[0008] Furthermore, the amino-terminated polydimethylsiloxane in step (1) has a molecular weight of 2000.

[0009] Furthermore, the catalyst in step (1) is triethylamine.

[0010] Furthermore, the polyethylene glycol diglycidyl ether in step (1) has a molecular weight of 800.

[0011] Furthermore, the permanent magnet in step (1) is a neodymium iron boron permanent magnet with a surface magnetic field strength of 4500 Gauss.

[0012] Furthermore, the PI resin in step (2) is: Mitsui Chemicals PL450C.

[0013] Furthermore, the organic solvent in step (2) is: N-methylpyrrolidone.

[0014] Furthermore, the casting substrate in step (2) is an ordinary glass carrier which is washed three times with deionized water and ethanol in sequence and then dried in an oven at 80° C. for 12 hours.

[0015] Furthermore, the vertical magnetic field in step (2) is: the magnetic orientation intensity in the vertical direction is 60 mT.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention achieves the effects of insulation and heat conduction by adding self-made modified composite nanoparticles to the PI substrate.

[0017] First, the present invention uses a sol-gel method to prepare composite nanoparticles with Fe3O4 as a magnetic heat-conducting core and SiO2 as an insulating shell; the composite nanoparticles are treated with a silane coupling agent and then grafted with epoxy groups, first undergoing ring-opening addition with amino-terminated polydimethylsiloxane, and then polyethylene glycol diglycidyl ether is added to react and bond with the amino group at the other end of the amino-terminated polydimethylsiloxane under the action of a catalyst, so that two flexible long-chain polymers are simultaneously grafted onto SiO2. The presence of two flexible long-chain molecular structures and modified composite nanoparticles significantly improves the flexibility of the membrane pad; the silicon-oxygen bonds in polydimethylsiloxane and the ether bonds in polyethylene glycol diglycidyl ether both have thermal vibration characteristics, which can promote heat transfer, and can also form hydrogen bond networks with hydrogen-containing polar groups in the PI substrate to improve dispersion stability. At the same time, under the action of a high-frequency magnetic field, the modified composite nanoparticles are arranged in an orderly manner inside the membrane pad, constructing a three-dimensional thermal conductive network, further promoting the thermal conduction efficiency of the membrane pad; in the modified composite nanoparticles, SiO2 not only isolates the Fe3O4 core to prevent it from conducting electricity, but also further improves the insulation performance of the membrane pad due to its good insulation properties. There is no free mobile charge in the two flexible long-chain polymers, both of which help to improve the insulation performance of the membrane pad. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] In order to more clearly illustrate the method provided by the present invention, the following examples are used to describe in detail the various index testing methods of the flexible PI thermally conductive insulating film pads prepared in the following examples. Flexibility test: Samples were prepared and tested in accordance with GB / T 1040.3-2006 (Plastics tensile properties test Part 3: Test conditions for film and sheeting), and the elongation at break of the samples was measured.

[0020] Thermal conductivity test: Samples were prepared in accordance with ISO 22007-2 and thermal conductivity was measured using a heat flow meter sensor.

[0021] Insulation test: Dielectric strength is tested according to the DC voltage method of GB / T 13542.2-2009.

[0022] Example 1 (1) Under nitrogen atmosphere, FeCl3·6H2O:FeCl2·4H2O:deionized water were mixed in a mass ratio of 2.5:1:100 and stirred at 300 rpm for 30 min to form an iron salt solution. 25 wt% ammonia water (3 times the volume of the iron salt solution) was quickly added, and the mixture was stirred at 800 rpm for 30 min in a constant temperature water bath at 80°C. After cooling to room temperature, the precipitate was washed twice with deionized water and dried in an oven at 60°C and a vacuum degree of 0.1 kPa to constant weight to obtain Fe3O4 nanoparticles with a particle size of 30 nm. (2) Fe3O4 nanoparticles, deionized water and tartaric acid were mixed in a mass ratio of 0.5:50:1, and then ultrasonically dispersed at 30kHz at 60°C for 30 minutes to obtain a water-based magnetic fluid; tetraethoxysilane, ethanol, deionized water and perchloric acid were mixed in a volume ratio of 1:1:1:0.01 and stirred at 300 rpm at room temperature for 1 hour to obtain a sol-gel precursor mixture; the water-based magnetic fluid and the sol-gel precursor mixture were mixed in a volume ratio of 1:6 and stirred at 500 rpm for 20 minutes, and then allowed to stand at room temperature until a wet gel was produced, and then dried in an oven at 105°C and a vacuum degree of 0.1 kPa for 48 hours to obtain a dry gel; the dry gel was placed in a quartz tube and treated at 800°C for 1.5 hours under a nitrogen atmosphere to obtain magnetic composite nanoparticles; (3) Magnetic composite nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol were mixed in a mass ratio of 1:0.3:50 and then ultrasonically dispersed at 30kHz for 30 minutes. After stirring and reflux at 80°C and 300 rpm for 12 hours, the mixture was adsorbed and precipitated by a NdFeB permanent magnet. After washing with deionized water three times, the mixture was dried to constant weight in an oven at 60°C and a vacuum degree of 0.1 kPa. The mixture was then mixed with amino-terminated polydimethylsiloxane and triethylamine in a mass ratio of 1:3:0.05 and stirred at 50°C and 300 rpm for 12 hours under a nitrogen atmosphere. After cooling to room temperature, the mixture was adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: triethylamine were mixed in a mass ratio of 1:2:0.05, and stirred at 50°C and 300 rpm under a nitrogen atmosphere for 12 hours. After cooling to room temperature, the mixture was adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles; (4) The homemade modified composite nanoparticles: Mitsui Chemicals PL450C resin: N-methylpyrrolidone were mixed in a mass ratio of 1:5:25, stirred at 60°C and 500 rpm for 2 hours, and then allowed to stand for degassing for 30 minutes. The mixture was poured onto a common glass carrier that had been washed three times with deionized water and ethanol and dried in an oven at 80°C for 12 hours. The mixture was then scraped with an automatic scraper with a 350µm slit at a speed of 10mm / min to form a uniform wet film. The film was then pre-cured at 80°C and a vertical magnetic field with a vertical magnetic orientation strength of 60mT for 1 hour in a nitrogen atmosphere. The pre-cured film was then heated to 120°C and cured for 2 hours, then heated to 200°C and cured for 2 hours, and finally heated to 250°C and cured for 1 hour in a nitrogen atmosphere at a heating rate of 2°C / min per stage. After imidization was completed, the film was naturally cooled to room temperature to obtain a flexible PI thermal insulating film pad with a thickness of 30µm.

[0023] Example 2 (1) Under nitrogen atmosphere, FeCl3·6H2O:FeCl2·4H2O:deionized water were mixed in a mass ratio of 2.75:1:100 and stirred at 300 rpm for 30 min to form an iron salt solution. 25 wt% ammonia water (4 times the volume of the iron salt solution) was quickly added, and the mixture was stirred at 800 rpm for 30 min in a constant temperature water bath at 80°C. After cooling to room temperature, the precipitate was washed three times with deionized water and dried in an oven at 60°C and a vacuum degree of 0.1 kPa to constant weight to obtain Fe3O4 nanoparticles with a particle size of 40 nm. (2) Fe3O4 nanoparticles, deionized water and tartaric acid were mixed in a mass ratio of 1:50:1, and then ultrasonically dispersed at 30kHz at 70°C for 30 minutes to obtain a water-based magnetic fluid; tetraethoxysilane, ethanol, deionized water and perchloric acid were mixed in a volume ratio of 1:1:1:0.01 and stirred at 300 rpm at room temperature for 1 hour to obtain a sol-gel precursor mixture; the water-based magnetic fluid and the sol-gel precursor mixture were mixed in a volume ratio of 2.5:6 and stirred at 500 rpm for 30 minutes, and then allowed to stand at room temperature until a wet gel was produced, and then dried in an oven at 105°C and a vacuum degree of 0.1 kPa for 48 hours to obtain a dry gel; the dry gel was placed in a quartz tube and treated at 800°C for 1.5 hours under a nitrogen atmosphere to obtain magnetic composite nanoparticles; (3) Magnetic composite nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol were mixed in a mass ratio of 1:0.3:50 and dispersed by 30kHz ultrasonic dispersion for 30min. After stirring and reflux reaction at 80℃ and 300rpm for 12h, the mixture was adsorbed and precipitated by NdFeB permanent magnet. After washing with deionized water three times, the mixture was dried to constant weight in an oven at 60℃ and a vacuum degree of 0.1kPa. The mixture was mixed with amino-terminated polydimethylsiloxane and triethylamine in a mass ratio of 1.25:4:0.075 and stirred at 60℃ and 400rpm under nitrogen atmosphere for 18min. h, after cooling to room temperature, the mixture was adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: triethylamine were mixed in a mass ratio of 1:3:0.075, stirred at 60°C and 400 rpm under a nitrogen atmosphere for 18 h, cooled to room temperature, adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles; (4) The homemade modified composite nanoparticles: Mitsui Chemicals PL450C resin: N-methylpyrrolidone were mixed in a mass ratio of 1.5:6:30, stirred at 60°C and 500 rpm for 2.5 hours, and then allowed to stand for degassing for 30 minutes. The mixture was poured onto a common glass carrier which had been washed three times with deionized water and ethanol and dried in an oven at 80°C for 12 hours. The mixture was then scraped with an automatic scraper with a 350µm slit at a speed of 10mm / min to form a uniform film. After uniformly wetting the film, it was pre-cured for 1.5 hours at 80°C in a nitrogen atmosphere and a vertical magnetic field with a vertical magnetic orientation intensity of 60mT. The pre-cured film was then heated to 120°C for curing for 2 hours, then to 200°C for curing for 2 hours, and finally to 250°C for curing for 1 hour in a nitrogen atmosphere at a heating rate of 2°C / min per stage. After imidization was completed, it was naturally cooled to room temperature to obtain a flexible PI thermal conductive insulating film pad with a thickness of 40µm.

[0024] Example 3 (1) Under nitrogen atmosphere, FeCl3·6H2O:FeCl2·4H2O:deionized water were mixed in a mass ratio of 3:1:100 and stirred at 300 rpm for 30 min to form an iron salt solution. 25 wt% ammonia water (5 times the volume of the iron salt solution) was quickly added, and the mixture was stirred at 800 rpm in a constant temperature water bath at 80°C for 30 min. After cooling to room temperature, the precipitate was washed with deionized water 4 times and dried in an oven at 60°C and a vacuum degree of 0.1 kPa to constant weight to obtain Fe3O4 nanoparticles with a particle size of 50 nm. (2) Fe3O4 nanoparticles, deionized water and tartaric acid were mixed in a mass ratio of 1.5:50:1, and then ultrasonically dispersed at 80°C and 30kHz for 30 minutes to obtain a water-based magnetic fluid; tetraethoxysilane, ethanol, deionized water and perchloric acid were mixed in a volume ratio of 1:1:1:0.01 and stirred at 300 rpm at room temperature for 1 hour to obtain a sol-gel precursor mixture; the water-based magnetic fluid and the sol-gel precursor mixture were mixed in a volume ratio of 4:6 and stirred at 500 rpm for 40 minutes, and then allowed to stand at room temperature until a wet gel was produced, and then dried in an oven at 105°C and a vacuum degree of 0.1 kPa for 48 hours to obtain a dry gel; the dry gel was placed in a quartz tube and treated at 800°C for 1.5 hours under a nitrogen atmosphere to obtain magnetic composite nanoparticles; (3) Magnetic composite nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol were mixed in a mass ratio of 1:0.3:50 and then dispersed by ultrasonic dispersion at 30kHz for 30min. After stirring and reflux reaction at 80℃ and 300rpm for 12h, the mixture was adsorbed and precipitated by NdFeB permanent magnet. After washing with deionized water three times, the mixture was dried to constant weight in an oven at 60℃ and a vacuum degree of 0.1kPa. The mixture was then mixed with amino-terminated polydimethylsiloxane and triethylamine in a mass ratio of 1.5:5:0.1 and stirred at 70℃ and 500rpm for 24h under nitrogen atmosphere. After cooling to room temperature, the mixture was adsorbed and precipitated by a neodymium iron boron permanent magnet, washed three times with deionized water, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: triethylamine were mixed in a mass ratio of 1:4:0.1, stirred at 70°C and 500 rpm under a nitrogen atmosphere for 12-24 hours, cooled to room temperature, adsorbed and precipitated by a neodymium iron boron permanent magnet, washed three times with deionized water, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles; (4) The homemade modified composite nanoparticles: Mitsui Chemicals PL450C resin: N-methylpyrrolidone were mixed in a mass ratio of 2:7:35, stirred at 60°C and 500 rpm for 3 hours, and then allowed to stand for degassing for 30 minutes. The mixture was poured onto an ordinary glass carrier that was washed three times with deionized water and ethanol and dried in an oven at 80°C for 12 hours. An automatic scraper with a 350µm slit was used to scrape the film at a speed of 10mm / min to form a uniform wet film. The film was pre-cured at 80°C and a vertical magnetic field with a vertical magnetic orientation strength of 60mT for 2 hours in a nitrogen atmosphere. The pre-cured film was then heated to 120°C and cured for 2 hours in a nitrogen atmosphere at a heating rate of 2°C / min per stage. The film was then heated to 200°C and cured for 2 hours, and finally heated to 250°C and cured for 1 hour to complete the imidization. The film was then naturally cooled to room temperature to obtain a flexible PI thermal insulating film pad with a thickness of 50µm.

[0025] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that step (2) is removed and step (3) is changed to: Fe3O4 nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol are mixed in a mass ratio of 1:0.3:50 and ultrasonically dispersed at 30kHz for 30min, stirred and refluxed at 80℃ and 300rpm for 12h, adsorbed and precipitated with NdFeB permanent magnet, washed with deionized water 3 times, dried to constant weight in an oven at 60℃ and a vacuum degree of 0.1kPa, mixed with amino-terminated polydimethylsiloxane and triethylamine in a mass ratio of 1.25:4:0.075, and stirred at 60℃ and 400rpm under a nitrogen atmosphere. The reaction was stirred at 0 rpm for 18 h, cooled to room temperature, precipitated by adsorption by a NdFeB permanent magnet, washed with deionized water 3 times, and dried in an oven at 50 ° C with a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: triethylamine were mixed in a mass ratio of 1: 3: 0.075, and stirred at 60 ° C and 400 rpm under a nitrogen atmosphere for 18 h. After cooling to room temperature, the mixture was precipitated by adsorption by a NdFeB permanent magnet, washed with deionized water 3 times, and dried in an oven at 50 ° C with a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles. The remaining steps were the same as in Example 2.

[0026] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that step (3) is changed to: the magnetic composite nanoparticles, amino-terminated polydimethylsiloxane and triethylamine are mixed in a mass ratio of 1.25:4:0.075, stirred at 400 rpm and 60°C for 18 h under a nitrogen atmosphere, cooled to room temperature, adsorbed and precipitated by a NdFeB permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa. The modified particles were dried to a constant weight to obtain preliminary modified particles; the preliminary modified particles: polyethylene glycol diglycidyl ether: triethylamine were mixed in a mass ratio of 1:3:0.075, and the mixture was stirred at 400 rpm at 60°C under a nitrogen atmosphere for 18 h. After cooling to room temperature, the mixture was adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water 3 times, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to a constant weight to obtain homemade modified composite nanoparticles. The remaining steps were the same as in Example 2.

[0027] Comparative Example 3 The difference between Comparative Example 3 and Example 2 lies in the difference in step (3). The difference lies in that step (3) is changed to: magnetic composite nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol are mixed in a mass ratio of 1:0.3:50 and then ultrasonically dispersed at 30kHz for 30min. After stirring and reflux at 80°C and 300rpm for 12h, the mixture is adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 60°C and a vacuum degree of 0.1kPa to constant weight. After that, the mixture is mixed with amino-terminated polydimethylsiloxane and triethylamine in a mass ratio of 1.25:4:0.075, stirred and reacted at 60°C and 400rpm under a nitrogen atmosphere for 18h, cooled to room temperature, adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1kPa to constant weight to obtain homemade modified composite nanoparticles. The remaining steps are the same as those in Example 2.

[0028] Comparative Example 4 The difference between Comparative Example 4 and Example 2 lies in the difference in step (3). The difference lies in that step (3) is changed to: magnetic composite nanoparticles, γ-glycidyloxypropyltrimethoxysilane and anhydrous ethanol are mixed in a mass ratio of 1:0.3:50 and then ultrasonically dispersed at 30kHz for 30min. After stirring and reflux at 80°C and 300rpm for 12h, the mixture is adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 60°C and a vacuum degree of 0.1kPa to constant weight. After that, the mixture is mixed with polyethylene glycol diglycidyl ether and triethylamine in a mass ratio of 1:3:0.075, stirred and reacted at 60°C and 400rpm under a nitrogen atmosphere for 18h, cooled to room temperature, adsorbed and precipitated by a neodymium iron boron permanent magnet, washed with deionized water three times, and dried in an oven at 50°C and a vacuum degree of 0.1kPa to constant weight to obtain homemade modified composite nanoparticles. The remaining steps are the same as those in Example 2.

[0029] Comparative Example 5 The difference between Comparative Example 5 and Example 2 lies in the difference in step (4). The difference lies in that step (4) is changed to: the homemade modified composite nanoparticles: Mitsui Chemicals PL450C resin: N-methylpyrrolidone are mixed in a mass ratio of 1.5:6:30, stirred at 60°C and 500 rpm for 2.5 hours, and then allowed to stand for degassing for 30 minutes. The mixture is poured onto an ordinary glass carrier which has been washed three times with deionized water and ethanol and dried in an oven at 80°C for 12 hours. The mixture is then separated by a 350 μm slit. After an automatic scraper is applied at a speed of 10 mm / min to form a uniform wet film, the film is pre-cured at 80°C for 1.5 hours in a nitrogen atmosphere. The pre-cured film is then heated to 120°C for curing for 2 hours, then to 200°C for curing for 2 hours, and finally to 250°C for curing for 1 hour in a nitrogen atmosphere at a heating rate of 2°C / min per stage. After imidization is completed, the film is naturally cooled to room temperature to obtain a flexible PI thermally conductive insulating film pad with a thickness of 40 µm. The remaining steps are the same as those in Example 2.

[0030] Comparative Example 6 The difference between Comparative Example 6 and Example 2 lies in the difference in step (4), which is that step (4) is changed to: homemade modified composite nanoparticles: Mitsui Chemicals PL450C resin: N-methylpyrrolidone are mixed in a mass ratio of 1.5:6:30, stirred at 60°C and 500 rpm for 2.5 hours, and then allowed to stand for degassing for 30 minutes, poured onto an ordinary glass carrier which has been washed three times with deionized water and ethanol and dried in an oven at 80°C for 12 hours, and then coated with an automatic scraper with a 350µm slit at a speed of 10mm / min to form a uniform wet film, and then pre-cured at 80°C and a vertical magnetic field with a vertical magnetic orientation strength of 60mT under a nitrogen atmosphere for 1.5 hours, and then the pre-cured film is heated to 250°C under a nitrogen atmosphere at a heating rate of 2°C / min and cured for 2 hours to complete imidization, and then naturally cooled to room temperature to obtain a flexible PI thermal insulating film pad with a thickness of 40µm. The remaining steps are the same as those in Example 2.

[0031] Comparative Example 7 The difference between Comparative Example 7 and Example 2 is that steps (1), (2), and (3) are removed, and step (4) is changed to: Mitsui Chemicals PL450C resin and N-methylpyrrolidone are mixed in a mass ratio of 6:30, stirred at 500 rpm for 2.5 h at 60 ° C, and allowed to stand for degassing for 30 min, poured onto a common glass carrier which has been washed with deionized water and ethanol three times in sequence and dried in an oven at 80 ° C for 12 h, and then scraped with an automatic scraper with a 350 μm slit at a speed of 10 mm / m After forming a uniform wet film by scraping at an in speed, the film was pre-cured for 1.5 hours at 80°C in a nitrogen atmosphere and a vertical magnetic field with a vertical magnetic orientation strength of 60mT. The pre-cured film was then heated to 120°C for 2 hours, then to 200°C for 2 hours, and finally to 250°C for 1 hour in a nitrogen atmosphere at a heating rate of 2°C / min per stage. After imidization was completed, the film was naturally cooled to room temperature to obtain a flexible PI thermal conductive insulating film pad with a thickness of 40µm.

[0032] Effect Examples Table 1 below shows the performance analysis results of the flexible PI thermally conductive insulating film pads of Examples 1 to 3 of the present invention and Comparative Examples 1 to 7.

[0033] Table 1

[0034] From the comparison of the experimental data of the elongation at break of the embodiment and the comparative example, it can be found that the present invention grafts two flexible long-chain polymers onto the thermally conductive outer shell of the magnetic composite nanoparticles, and the flexibility of the membrane pad is significantly improved under the joint action of the two flexible long-chain polymers and the modified composite nanoparticles; from the comparison of the experimental data of the thermal conductivity coefficient of the embodiment and the comparative example, it can be found that the silicon-oxygen bonds in polydimethylsiloxane and the ether bonds in polyethylene glycol diglycidyl ether both have thermal vibration characteristics, which can promote heat transfer, and can also form a hydrogen bond network with the hydrogen-containing polar groups in the PI substrate to improve the dispersion stability. At the same time, under the action of the high-frequency magnetic field, the modified composite nanoparticles are arranged in an orderly manner inside the membrane pad to construct a three-dimensional thermal conductive network, which further promotes the thermal conduction efficiency of the membrane pad; from the experimental data of the dielectric strength of the embodiment and the comparative example, it can be found that in the modified composite nanoparticles, SiO2 not only isolates the Fe3O4 core to prevent it from conducting electricity, but also further improves the insulation performance of the membrane pad due to its good insulation properties. There is no free mobile charge in the two flexible long-chain polymers, which helps to improve the insulation performance of the membrane pad.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A flexible PI thermally conductive insulating film pad, characterized in that: The following steps are involved: (1) The magnetic composite nanoparticles were treated with a silane coupling agent, mixed with amino-terminated polydimethylsiloxane and a catalyst in a mass ratio of 1-1.5:3-5:0.05-0.1, stirred at 300-500 rpm and 50-70 ° C under a nitrogen atmosphere for 12-24 hours, cooled to room temperature, precipitated by permanent magnets, washed with deionized water three times, and dried in an oven at 50 ° C and a vacuum degree of 0.1 kPa to constant weight to obtain preliminary modified particles; The preliminary modified particles: polyethylene glycol diglycidyl ether: catalyst were mixed in a mass ratio of 1:2-4:0.05-0.1, stirred at 300-500 rpm at 50-70°C under a nitrogen atmosphere for 12-24 hours, cooled to room temperature, adsorbed and precipitated using a permanent magnet, washed three times with deionized water, and dried in an oven at 50°C and a vacuum degree of 0.1 kPa to constant weight to obtain homemade modified composite nanoparticles; (2) The homemade modified composite nanoparticles: PI resin: organic solvent were mixed in a mass ratio of 1~2:5~7:25~35, stirred at 60℃ and 500rpm for 2~3h, allowed to stand for degassing for 30min, poured onto the casting substrate, and scraped with an automatic scraper with a 350µm slit at a speed of 10mm / min to form a uniform wet film. After pre-curing at 80℃ in a vertical magnetic field under a nitrogen atmosphere for 1~2h, the imidization was completed by step thermal curing to obtain a flexible PI thermal insulating film pad with a thickness of 30~50µm.

2. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The silane coupling agent in step (1) is: γ-glycidyloxypropyltrimethoxysilane.

3. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The amino-terminated polydimethylsiloxane in step (1) has a molecular weight of 1500-2000.

4. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The catalyst in step (1) is triethylamine.

5. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The polyethylene glycol diglycidyl ether in step (1) has a molecular weight of 600-800.

6. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The permanent magnet in step (1) is a neodymium iron boron permanent magnet with a surface magnetic field strength of 3000-5000 Gauss.

7. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The PI resin in step (2) is: Mitsui Chemicals PL450C.

8. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The organic solvent in step (2) is one of N-methylpyrrolidone and N,N-dimethylformamide.

9. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The casting substrate in step (2) is an ordinary glass carrier which is washed three times with deionized water and ethanol in sequence and then dried in an oven at 80°C for 12 hours.

10. The flexible PI thermally conductive insulating film pad according to claim 1, characterized in that: The vertical magnetic field in step (2) is: the magnetic orientation intensity in the vertical direction is 60 mT.

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