Surface-modified hexagonal boron nitride and polyimide composite heat-conducting film as well as preparation method and application thereof

Abstract

According to the surface-modified hexagonal boron nitride and polyimide composite heat-conducting film and the preparation method and application thereof, hexagonal boron nitride is subjected to surface treatment through a macromolecular modifier, and a large amount of polyamide-imide or polyimide polymer is successfully introduced to the surface of hexagonal boron nitride; furthermore, the compatibility of the surface modified hexagonal boron nitride and polyimide is effectively improved, so that the polyimide composite heat-conducting film prepared from the surface modified hexagonal boron nitride has excellent heat-conducting property and mechanical property.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer film preparation, and relates to a surface-modified hexagonal boron nitride and polyimide composite thermal conductive film, a preparation method and application thereof. Background Art

[0002] Polyimide films, due to their excellent heat resistance, dielectric properties, chemical stability, and mechanical properties, have been widely used in the electronics and microelectronics fields as insulating materials or flexible substrates. With the rapid development of electronic devices, the power and density of electronic components have increased dramatically, generating increasing amounts of heat during use. Therefore, thermal management of polyimide films in electronic applications faces significant challenges. However, the thermal conductivity of neat polyimide films without thermally conductive fillers is typically below 0.25 W / m·K, which is insufficient to meet the requirements for rapid heat dissipation. Consequently, extensive research has been conducted to improve the thermal conductivity of polyimide films. In the structural design of intrinsically thermally conductive polyimides, molecular structure, chain orientation, and density have significant influences on their thermal conductivity. Liquid crystal polyimides with highly ordered molecular chains have been reported to exhibit high thermal conductivity. However, these polyimides are limited by the difficulty in synthesizing novel dianhydride or diamine monomers with specialized structures.

[0003] As another effective way to improve the thermal conductivity of films, people are in urgent need of thermally conductive polyimide-based composite films. Thermally conductive polyimide-based composite films can be prepared by mixing inorganic fillers with polyamino acid (PAA) solutions. Thermally conductive fillers generally include metal materials (silver, copper, aluminum oxide, etc.), carbon materials (graphite, graphene, carbon nanotubes, etc.) and ceramic materials (boron nitride, aluminum nitride, silicon nitride, etc.). Among them, the incorporation of metal or carbon fillers has a negative impact on the insulation of polyimide films. Ceramic fillers are considered to be the preferred material for preparing high thermal conductivity composite insulating films due to their good insulating properties. Among many ceramic fillers, boron nitride is widely used to prepare composite films with both thermal conductivity and electrical insulation properties.

[0004] In the process of preparing filler-containing polyimide-based composite films, there are many key technical problems that need to be solved, such as the dispersion and agglomeration of fillers, the interface between inorganic fillers and organic matrices, and the construction of long-distance heat conduction channels. For example, filler particles are difficult to effectively disperse in PAA solutions, which usually have high viscosity. When a small amount of inorganic fillers is added, the inorganic fillers are mostly separated from each other in the polyimide matrix and cannot form an effective heat transfer network, and the improvement in the thermal conductivity of the composite film is very limited. When the amount of inorganic fillers added is increased to a higher level, the fillers can contact each other and form effective heat conduction channels, thereby significantly improving the thermal conductivity of the composite film. However, at the same time, a high amount of fillers added will affect flexibility and even film-forming properties. How to balance the thermal conductivity of the composite film with other properties, such as mechanical properties and insulation properties, is a difficult problem that needs to be solved.

[0005] Generally speaking, the interfacial interaction between the organic matrix and the inorganic filler is weak. Fillers exhibit poor interfacial compatibility, making it difficult to achieve uniform and effective dispersion within the matrix. Fillers tend to form large aggregates, resulting in numerous visible micropores and defects between the two phases. The large interfacial thermal resistance also limits the improvement of thermal conductivity, particularly severely impairing the mechanical properties of the composite membrane. To improve the interfacial compatibility of composite membranes, extensive research has been conducted on filler modification methods. The use of coupling agents is the most commonly used approach. For example, Ma et al. modified boron nitride with silane or titanate coupling agents, respectively, successfully preparing high-performance polyimide-based composite membranes. The results showed that silane coupling agents significantly improved the interfacial compatibility of the composite membranes, resulting in higher thermal conductivity at the same filler loading. Kizilkaya et al. used another silane coupling agent, Z-6020, to react with hydroxyl groups on the surface of boron nitride. To increase the number of hydroxyl groups on the filler surface, Zhang et al. first treated boron nitride with acid and then modified the surface with a silane coupling agent. Results show that this method effectively improves the interfacial interaction and dispersibility of fillers. At a 40 wt% addition, the thermal conductivity λ of the polyimide-based composite film reached 0.686 W / m·K, 4.6 times that of pure polyimide-based composite films. These studies demonstrate that surface modification of fillers can improve the thermal conductivity and even mechanical properties of composite films to a certain extent. However, the improvements in thermal conductivity and tensile strength are not significant. This can be attributed to the limited interphase region between the polyimide matrix and the modified filler, as most modified fillers are treated with short-chain silane coupling agents. In particular, the interaction between the coupling-agent-modified filler and the matrix is ​​weak, resulting in a high interfacial thermal resistance between the two phases. For polyimide-based composite films, how to more effectively modify the filler surface to enhance interfacial interaction and compatibility, and how to improve thermal conductivity while retaining excellent mechanical properties, remains an unresolved issue. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a surface-modified hexagonal boron nitride and polyimide composite thermally conductive film, its preparation method, and its application. This invention utilizes a polymer modifier to surface-treat the hexagonal boron nitride, successfully introducing a large amount of polyamide-imide or polyimide polymer onto the hexagonal boron nitride surface. This effectively enhances the compatibility of the surface-modified hexagonal boron nitride with polyimide, resulting in a polyimide composite thermally conductive film with excellent thermal conductivity and mechanical properties.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In one aspect, the present invention provides a surface-modified hexagonal boron nitride, wherein the surface-modified hexagonal boron nitride is obtained by surface-treating unmodified hexagonal boron nitride with a polymer modifier, wherein the polymer modifier is polyimide or polyamide-imide.

[0009] In the present invention, the surface of unmodified hexagonal boron nitride is treated with a polymer reagent, which effectively improves the dispersibility of hexagonal boron nitride in the polyamic acid solution and the compatibility with polyimide, greatly reduces the probability of generating voids at the interface between the two phases during the preparation of the composite film, and makes the final polyimide composite thermal conductive film have low structural defects and highly ordered orientation structure, forming an effective heat conduction channel, thereby having excellent thermal conductivity and mechanical properties.

[0010] Preferably, the unmodified hexagonal boron nitride is hexagonal boron nitride rich in hydroxyl groups or amine groups on the surface.

[0011] Preferably, the mass ratio of the unmodified hexagonal boron nitride to the polymer modifier is 10:(2-6), for example, 10:2, 10:2.2, 10:2.5, 10:3, 10:3.5, 10:4, 10:4.5, 10:5, 10:5.5 or 10:6. In the present invention, if the amount of the polymer modifier is too small, the heat conduction channel is difficult to form, and the thermal conductivity is low at the same addition amount, which affects the mechanical properties of the composite film. If the amount of the polymer modifier is too high, the thermodynamic properties of the composite film are affected, especially the high temperature resistance will be greatly reduced.

[0012] Preferably, the unmodified hexagonal boron nitride has a thickness of 2 to 100 nm, for example, 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0013] Preferably, the radial length of the unmodified hexagonal boron nitride is 0.1-100 μm, for example, 0.15 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0014] Preferably, the polymer modifier is a polymer modifier that is capped with a capping agent.

[0015] Preferably, the blocking agent is an isocyanate blocking agent.

[0016] Preferably, the isocyanate blocking agent is selected from any one of p-phenylene diisocyanate, bis(4-isocyanatephenyl)methane, toluene-2,4-diisocyanate or 4,4'-diisocyanate dicyclohexylmethane, or a combination of at least two thereof.

[0017] In a second aspect, the present invention provides a method for preparing the surface-modified hexagonal boron nitride as described in the first aspect, the preparation method comprising the following steps:

[0018] Unmodified hexagonal boron nitride reacts with a polymer modifier to obtain the surface-modified hexagonal boron nitride.

[0019] Preferably, the mass ratio of the unmodified hexagonal boron nitride to the polymer modifier is 10:1 to 6, for example, 10:1, 10:2.2, 10:2.5, 10:3, 10:4, 10:5 or 10:6.

[0020] Preferably, the reaction temperature is 80-130°C, such as 80°C, 85°C, 88°C, 90°C, 95°C, 100°C, 110°C, 120°C or 130°C, and more preferably, the reaction temperature is 90-110°C.

[0021] Preferably, the reaction time is 1-6 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h.

[0022] Preferably, the reaction is carried out in a solvent selected from one or a combination of at least two of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), γ-butyrolactone or DMSO.

[0023] Preferably, the total concentration of the boron nitride and the polymer modifier in the reaction system is 40-60wt%; for example, 40wt%, 43wt%, 45wt%, 48wt%, 50wt%, 53wt%, 55wt%, 58wt% or 60wt%. Furthermore, the reaction concentration is 45-55wt%. If the concentration is too low, the modification reaction time is long, and if the concentration is too high, the boron nitride modification is uneven.

[0024] Preferably, the polymer modifier is prepared by the following method:

[0025] The diacid, dianhydride and end-capping agent are polymerized to obtain the polymer modifier.

[0026] Preferably, the diacid is selected from one or a combination of at least two of terephthalic acid, isophthalic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid or sebacic acid.

[0027] Preferably, the dianhydride may optionally include any one or a combination of at least two of the following compounds:

[0028]

[0029] Preferably, the ratio of the diancid to the dianhydride is 0 to 10:1; for example, 0:1, 1:1, 2:1, 3:1, 4:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 8:1, 9:1 or 10:1;

[0030] Preferably, the blocking agent is isocyanate.

[0031] Preferably, the isocyanate includes any one of p-phenylene diisocyanate, bis(4-isocyanatephenyl)methane, toluene-2,4-diisocyanate, or 4,4'-diisocyanate dicyclohexylmethane, or a combination of at least two thereof.

[0032] Preferably, the molar ratio of the total mass of the diacid and dianhydride to the isocyanate is 100:101-120; more preferably 100:106-116.

[0033] Preferably, the polymerization reaction is carried out in a solvent selected from one or a combination of at least two of DMAc, NMP, γ-butyrolactone or DMSO.

[0034] Preferably, the total concentration of diacid, dianhydride and isocyanate in the reaction system during the polymerization reaction is 30-50 wt%, for example, 30 wt%, 33 wt%, 35 wt%, 40 wt%, 43 wt%, 45 wt%, 48 wt% or 50 wt%.

[0035] Preferably, the polymerization reaction temperature is 90-160°C, for example, 90°C, 95°C, 98°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C. More preferably, the polymerization reaction temperature is 110-120°C.

[0036] Preferably, the polymerization reaction time is 3-8 h, for example, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0037] In a third aspect, the present invention provides a surface-modified hexagonal boron nitride-doped polyamic acid slurry, wherein the surface-modified hexagonal boron nitride-doped polyamic acid slurry comprises the surface-modified hexagonal boron nitride as described above.

[0038] In a fourth aspect, the present invention provides a method for preparing the surface-modified hexagonal boron nitride-doped polyamic acid slurry as described above, the preparation method comprising the following steps:

[0039] (1) Under nitrogen protection, diamine is added to a solvent, and after dissolution, dianhydride is added to 80-90% of the mass of the diamine, and the reaction is carried out to obtain a polyamic acid slurry;

[0040] (2) adding surface-modified hexagonal boron nitride to the polyamic acid slurry and adding a solvent to adjust the solid content;

[0041] (3) adding the remaining dianhydride to the reaction solution to carry out a reaction to obtain the surface-modified hexagonal boron nitride-doped polyamic acid slurry.

[0042] Preferably, the diamine in step (1) is selected from any one or a combination of at least two of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzanilide, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 4,4'-diaminodiphenyl sulfone, 2-(4-aminophenyl)-5-aminobenzimidazole, 2,2-bis(4-hydroxy-3-aminophenyl)propane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-biphenyl or 9,9-bis(4-aminophenyl)fluorene;

[0043] Preferably, the solvent in step (1) and step (2) is selected from one or a combination of at least two of N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone or DMSO;

[0044] Preferably, the dianhydride in step (1) is selected from 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, (4-phthalic anhydride) formyloxy-4-phthalate, bis[(3,4-dianhydride)phenyl]terephthalate, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, p-phenylene-bis(triphenylene)phthalate Any one or a combination of at least two of ester dianhydride, 4,4'-terephthalic anhydride, pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxylic)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxybenzoyloxy)phenyl)hexafluoropropane dianhydride or 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride;

[0045] Preferably, the reaction temperature in step (1) is -5-50°C and the reaction time is 5-24h;

[0046] Preferably, the mass ratio of the surface-modified hexagonal boron nitride to the polyamic acid in step (2) is 20-60:100, further 30-50:100; in the present invention, if the amount of the surface-modified hexagonal boron nitride is too low, the thermal conductivity is not significant; if the amount of the surface-modified hexagonal boron nitride is too high, the mechanical properties of the composite film will be significantly reduced when it is used to prepare the polyimide composite thermal conductive film.

[0047] Preferably, the solid content is adjusted in step (2) to a solid content of 18-25 wt%, such as 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt% or 25 wt%.

[0048] Preferably, the reaction temperature in step (3) is -5 to 50°C, for example, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, and the reaction time is 3-8h, for example, 3h, 4h, 5h, 6h, 7h or 8h.

[0049] Preferably, the viscosity of the surface-modified hexagonal boron nitride-doped polyamic acid slurry obtained in step (3) is 15-22w cPs, for example, 15w cPs, 17w cPs, 18w cPs, 19w cPs, 20w cPs, 21w cPs or 22w cPs.

[0050] In a fifth aspect, the present invention provides a polyimide composite thermally conductive film, which is prepared from the surface-modified hexagonal boron nitride-doped polyamic acid slurry as described above.

[0051] In the present invention, the polyimide composite thermally conductive film is obtained by coating the surface-modified hexagonal boron nitride-doped polyamic acid slurry onto a peeling board to obtain a wet film, and then subjecting the wet film to a staged temperature-raising heat treatment.

[0052] Preferably, the staged temperature rising heat treatment is 80°C for 30 min, 100°C for 30 min, 120°C for 30 min, 200°C for 30 min, 300°C for 15 min, and 400°C for 10 min, with a heating rate of 5°C / min.

[0053] In a sixth aspect, the present invention provides the use of the polyimide composite thermally conductive film described above in the preparation of electronic device packaging materials, new energy products, nuclear energy, aerospace products, etc.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The modified boron nitride particles provided by the present invention are obtained by surface-treating hexagonal boron nitride through modification with polyamic acid imide or polyimide polymer; by reacting the active group of the polymer end group being isocyanate with the hexagonal boron nitride rich in hydroxyl or amine groups, the polymer is successfully introduced onto the surface of the hexagonal boron nitride, thereby effectively improving the compatibility of the obtained surface-modified hexagonal boron nitride with polyimide, so that the interior of the polyimide composite thermal conductive film made by the composite of the two has low structural defects and highly ordered structural orientation, thereby being able to have both excellent heat resistance and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The infrared spectra of hydroxyl-rich boron nitride, polymer modifier and boron nitride surface-treated with polymer modifier (i.e., modified boron nitride) are shown. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0058] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are conventional materials in the art.

[0059] Example 1

[0060] This embodiment provides surface-modified hexagonal boron nitride, its doped polyamic acid slurry, and polyimide composite thermal conductive film, the preparation method of which is as follows:

[0061] (1) NMP (354 g) was added to a 2 L reaction flask, followed by the addition of bis(4-isocyanatephenyl)methane (30.031 g, 120 mmol). After heating to 90°C, pyromellitic anhydride (10.906 g, 50 mmol) and adipic acid (7.307 g, 50 mmol) were added in batches. The temperature was then raised to 150°C for reaction for 3 h, and the temperature was lowered to 100°C to obtain a polymer modifier. Subsequently, hydroxyl-rich boron nitride (3M-CFP003, 241 g) was added to make the solid content of the reaction system 45 wt %. The reaction was then stirred at 90°C for 3 h. After the reaction was completed, the filter cake was collected and washed several times with DMAc and ethanol, and then dried at 80°C in a vacuum for 12 h to obtain surface-modified hexagonal boron nitride.

[0062] (2) DMAc (dimethylacetamide, 227.6 g) was added to a 5 L reaction flask, and ODA (4,4'-diaminodiphenyl ether, 20.024 g, 100 mmol) was added thereto with stirring. Subsequently, pyromellitic anhydride (19.63 g, 90 mmol) was added to the reaction flask in batches, and the reaction temperature was maintained at 50°C for 3 h. Subsequently, the surface-modified hexagonal boron nitride (27.89 g) obtained in (1) was added to the reaction flask, and the reaction was stirred for 1 h. Then, a solvent was added to maintain the solid content at 18 wt%. Subsequently, the remaining pyromellitic anhydride (2.182 g, 10 mmol) was added in batches, and the reaction was stirred for 2 h. The final slurry had a viscosity of 21.86 wcp and a solid content of 18.7 wt%.

[0063] (3) Preparation of thermal conductive film: The obtained slurry is coated on a peeling plate to obtain a wet film, and the wet film is subjected to a step-by-step temperature increase heat treatment program of 80°C×30min, 100°C×30min, 120°C×30min, 200°C×30min, 300°C×15min, and 400°C×10min, with a temperature increase rate of 5°C / min to obtain the polyimide composite thermal conductive film 1.

[0064] The infrared spectra of hydroxyl-rich boron nitride, polymer modifier and boron nitride surface treated with polymer modifier (i.e. modified boron nitride) were tested by Fourier transform infrared spectrometer (Thermo Fisher Scientific-Nicolet iS50). Figure 1 As shown by Figure 1 It can be seen that boron nitride and polymer modifiers can be effectively combined.

[0065] Example 2

[0066] All operations were identical to those in Example 1, except that 37.18 g of surface-modified boron nitride was added, the final viscosity was 23.41 wcp, and the solid content was 19.7 wt %. The polyimide composite thermally conductive film 2 was obtained by performing a stepwise temperature-raising heat treatment.

[0067] Example 3

[0068] All operations were identical to those in Example 1, except that 16.73 g of surface-modified boron nitride was added, the final viscosity was 18.71 wcp, and the solid content was 18.1 wt %. A stepwise heat treatment was performed to obtain the polyimide composite thermally conductive film 3.

[0069] Example 4

[0070] All operations were identical to those in Example 1, except that 60.41 g of surface-modified boron nitride was added, the final viscosity was 19.33 wcp, and the solid content was 23.4 wt %. The polyimide composite thermally conductive film 4 was obtained by performing a stepwise temperature-raising heat treatment.

[0071] Example 5

[0072] All operations were identical to those in Example 1, except that the surface-modified boron nitride was amino-rich (R-BN-0094, Xi'an Ruixi Biotechnology Co., Ltd.). The final viscosity was 18.66 wcp and the solid content was 20.1 wt %. A stepwise heat treatment was performed to obtain the polyimide composite thermally conductive film 5.

[0073] Example 6

[0074] All operations were identical to those in Example 1, except that the isocyanate used was changed to isophorone diisocyanate, the final viscosity was 18.54 wcp, and the solid content was 20.8 wt %. A stepwise heat treatment was performed to obtain the polyimide composite thermally conductive film 6.

[0075] Example 7

[0076] All operations were identical to those in Example 1, except that the acid anhydride used was changed to biphenyltetracarboxylic dianhydride, and the final viscosity was 17.76 wcp and the solid content was 19.8 wt %. The polyimide composite thermally conductive film 7 was obtained by performing a stepwise temperature-raising heat treatment.

[0077] Comparative Example 1

[0078] (1) NMP was added to a 2 L reaction flask, followed by the addition of bis(4-isocyanatephenyl)methane (24.72 g, 99 mmol). After heating to 90°C, pyromellitic anhydride (2.18 g, 10 mmol) and adipic acid (13.15 g, 90 mmol) were added in batches. The temperature was then raised to 150°C for 3 h. The temperature was then lowered to 100°C, followed by the addition of hydroxyl-rich modified boron nitride (241 g) to a solid content of 45 wt %. The reaction was then stirred at 90°C for 3 h. After the reaction was completed, the mixture was filtered and the filter cake was collected. The filter cake was washed several times with DMAc and ethanol, and then dried at 80°C in a vacuum for 12 h to obtain surface-modified hexagonal boron nitride.

[0079] (2) DMAc (227.6 g) was added to a 5 L reaction flask, and ODA (20.024 g, 100 mmol) was added thereto with stirring. Subsequently, pyromellitic anhydride (19.03 g, 90 mmol) was added to the reaction flask in batches. The reaction temperature was maintained at 50°C for 3 h. Subsequently, the surface-modified boron nitride (27.89 g) obtained in (1) was added to the reaction flask. After stirring for 1 h, solvent was added to maintain the solid content at 18 wt%. Subsequently, the remaining pyromellitic anhydride (2.182 g, 10 mmol) was added in batches and stirred for 2 h. The resulting slurry had a viscosity of 22.39 wcp and a solid content of 18.8 wt%.

[0080] (3) Preparation of thermal conductive film: The obtained slurry is coated on a peeling plate to obtain a wet film, and the wet film is subjected to a step-by-step heating treatment at a temperature of 80°C × 30 min, 100°C × 30 min, 120°C × 30 min, 200°C × 30 min, 300°C × 15 min, and 400°C × 10 min, with a heating rate of 5°C / min to obtain the polyimide composite thermal conductive film.

[0081] Comparative Example 2

[0082] (1) NMP was added to a 2 L reaction flask, followed by the addition of bis(4-isocyanatephenyl)methane (26.03 g, 104 mmol). After heating to 90°C, pyromellitic anhydride (2.18 g, 10 mmol) and adipic acid (13.15 g, 90 mmol) were added in batches. The temperature was then raised to 150°C for reaction for 3 h. The temperature was then lowered to 100°C, and ordinary boron nitride (241 g) (Xi'an Ruixi Biotechnology Co., Ltd., R-MJ-003) was added to achieve a solid content of 45 wt %. The reaction was then stirred at 90°C for 3 h. After the reaction was completed, the mixture was filtered and the filter cake was collected. The filter cake was washed several times with DMAc and ethanol, and then dried at 80°C in a vacuum for 12 h.

[0083] (2) DMAc (227.6 g) was added to a 5 L reaction flask, and ODA (20.024 g, 100 mmol) was added thereto with stirring. Subsequently, pyromellitic anhydride (19.03 g, 90 mmol) was added to the reaction flask in batches, and the reaction temperature was maintained at 50°C for 3 h. Subsequently, the modified boron nitride (27.89 g) in (1) was added to the reaction flask, and the reaction was stirred for 1 h. Then, a solvent was added to maintain the solid content at 18 wt%. Subsequently, the remaining pyromellitic anhydride (2.182 g, 10 mmol) was added in batches, and the reaction was stirred for 2 h. The final slurry had a viscosity of 22.39 wcp and a solid content of 18.8 wt%.

[0084] (3) Preparation of thermal conductive film: The obtained slurry is coated on a peeling plate to obtain a wet film, and the wet film is subjected to a step-by-step heating treatment at a temperature of 80°C × 30 min, 100°C × 30 min, 120°C × 30 min, 200°C × 30 min, 300°C × 15 min, and 400°C × 10 min, with a heating rate of 5°C / min to obtain the polyimide composite thermal conductive film.

[0085] Comparative Example 3

[0086] (1) DMAc (227.6 g) was added to a 5 L reaction flask. ODA (20.024 g, 100 mmol) was added thereto with stirring. Subsequently, pyromellitic anhydride (19.03 g, 90 mmol) was added to the reaction flask in batches. The reaction temperature was maintained at 50°C for 3 h. Unmodified boron nitride (30%) was then added to the reaction flask. After stirring for 1 h, solvent was added to maintain the solid content at 18 wt%. The remaining pyromellitic anhydride (2.182 g, 10 mmol) was then added in batches. The reaction was stirred for 2 h. The resulting slurry had a viscosity of 22.39 wcp and a solid content of 18.8 wt%.

[0087] (2) Preparation of thermal conductive film: The obtained slurry is coated on a peeling plate to obtain a wet film, and the wet film is subjected to a step-by-step heating heat treatment program of 80°C×30min, 100°C×30min, 120°C×30min, 200°C×30min, 300°C×15min, and 400°C×10min, with a heating rate of 5°C / min to obtain the polyimide composite thermal conductive film.

[0088] Comparative Example 4

[0089] (1) DMAc was added to a 5 L reaction flask, and ODA (40.048 g, 200 mmol) was added thereto with stirring. Subsequently, pyromellitic anhydride (43.624 g, 200 mmol) was added to the reaction flask in portions. The reaction temperature was maintained at 50°C for 5 h, and the reaction was stirred for 2 h. The resulting slurry had a viscosity of 25 wcp and a solid content of 17.1 wt%.

[0090] (2) Preparation of thermal conductive film: The obtained slurry is coated on a peeling plate to obtain a wet film, and the wet film is subjected to a step-by-step heating heat treatment program of 80°C×30min, 100°C×30min, 120°C×30min, 200°C×30min, 300°C×15min, and 400°C×10min, with a heating rate of 5°C / min to obtain the polyimide composite thermal conductive film.

[0091] The performance of the polyimide composite thermally conductive films prepared in the examples and comparative examples was tested using the following method:

[0092] (1) Thermal conductivity: The transient plane heat source method is used for testing, and the test method refers to ISO22007-2;

[0093] (2) Tensile strength, elongation at break and modulus: Tested according to the method provided in GB13022-91.

[0094] The test results are shown in Table 1:

[0095] Table 1

[0096] Thermal conductivity / W / (m·K) Tensile strength / MPa Elongation at break / % Modulus / GPa Application Example 1 0.546 153 72 3.2 Application Example 2 0.821 161 53 3.6 Application Example 3 0.381 177 88 2.8 Application Example 4 1.078 128 31 3.9 Application Example 5 0.551 161 75 3.2 Application Example 6 0.561 158 77 3.2 Application Example 7 0.538 166 81 3.2 Comparative Application Example 1 0.334 125 44 3.2 Comparative Application Example 2 0.313 118 43 3.2 Comparative Application Example 3 0.308 104 27 3.2 Comparative Application Example 4 0.18 168 93 2.6

[0097] In comparative application example 1, the boron nitride cannot be modified due to the failure of the excessive polymer isocyanate in the modified part to react with the boron nitride, and cannot form a regular heat conduction channel and a regular structure, resulting in low thermal conductivity and greatly reduced elongation at break of the film. In comparative application example 2, ordinary boron nitride cannot effectively react with the modified polymer, resulting in no regular heat conduction channel and regular structure, resulting in low thermal conductivity and greatly reduced elongation at break of the film. In comparative application example 3, due to direct mixing of boron nitride, no regular heat conduction channel and regular structure can be formed, resulting in low thermal conductivity and greatly reduced elongation at break of the film. In comparative application example 4, due to the lack of addition of boron nitride, the thermal conductivity coefficient is not significantly improved.

[0098] The applicant states that while the above-described embodiments illustrate the surface-modified hexagonal boron nitride and polyimide composite thermally conductive film, its preparation method, and its application, the present invention is not limited to these embodiments. This does not necessarily mean that the present invention must rely on these embodiments for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A surface-modified hexagonal boron nitride, characterized in that: The surface-modified hexagonal boron nitride is obtained by surface-treating unmodified hexagonal boron nitride with a polymer modifier, and the polymer modifier is polyimide or polyamide-imide.

2. The surface-modified hexagonal boron nitride according to claim 1, characterized in that: The unmodified hexagonal boron nitride is hexagonal boron nitride with a surface rich in hydroxyl groups or amine groups; Preferably, the mass ratio of the unmodified hexagonal boron nitride to the polymer modifier is 10:(2-6); Preferably, the thickness of the unmodified hexagonal boron nitride is 2 to 100 nm; Preferably, the radial length of the unmodified hexagonal boron nitride is 0.1 to 100 μm.

3. The surface-modified hexagonal boron nitride according to claim 1 or 2, characterized in that: The polymer modifier is a polymer modifier that is end-capped with an end-capping agent; Preferably, the blocking agent is an isocyanate blocking agent; Preferably, the isocyanate blocking agent is selected from any one of p-phenylene diisocyanate, bis(4-isocyanatephenyl)methane, toluene-2,4-diisocyanate or 4,4'-diisocyanate dicyclohexylmethane, or a combination of at least two thereof.

4. The method for preparing surface-modified hexagonal boron nitride according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: Unmodified hexagonal boron nitride reacts with a polymer modifier to obtain the surface-modified hexagonal boron nitride.

5. The preparation method according to claim 4, characterized in that The mass ratio of the unmodified hexagonal boron nitride to the polymer modifier is 10:1 to 6; Preferably, the reaction temperature is 80-130°C, more preferably, the reaction temperature is 90-110°C; Preferably, the reaction time is 1-6h; Preferably, the reaction is carried out in a solvent selected from one or a combination of at least two of N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone or DMSO; Preferably, the total concentration of the boron nitride and the polymer modifier in the reaction system is 40-60 wt %; preferably 45-55 wt %; Preferably, the polymer modifier is prepared by the following method: Carrying out polymerization reaction between diacid, dianhydride and end-capping agent to obtain the polymer modifier; Preferably, the diacid is selected from one or a combination of at least two of terephthalic acid, isophthalic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid or sebacic acid; Preferably, the dianhydride may optionally include any one or a combination of at least two of the following compounds: Preferably, the ratio of the diancid to the dianhydride is 0 to 10:1; Preferably, the blocking agent is isocyanate; Preferably, the isocyanate comprises any one or a combination of at least two of p-phenylene diisocyanate, bis(4-isocyanatephenyl)methane, toluene-2,4-diisocyanate or 4,4'-diisocyanate dicyclohexylmethane; Preferably, the molar ratio of the total mass of the diacid and dianhydride to the isocyanate is 100:101-120; more preferably 100:106-116; Preferably, the polymerization reaction is carried out in a solvent selected from one or a combination of at least two of DMAc, NMP, γ-butyrolactone or DMSO; Preferably, the total concentration of the diacid, dianhydride and isocyanate in the reaction system during the polymerization reaction is 30-50 wt %; Preferably, the polymerization reaction temperature is 90-160°C, and more preferably, the polymerization reaction temperature is 110-120°C; Preferably, the polymerization reaction time is 3-8 hours.

6. A surface-modified hexagonal boron nitride-doped polyamic acid slurry, characterized in that: The surface-modified hexagonal boron nitride-doped polyamic acid slurry comprises the surface-modified hexagonal boron nitride according to any one of claims 1 to 3.

7. The method for preparing the surface-modified hexagonal boron nitride-doped polyamic acid slurry according to claim 6, characterized in that: The preparation method comprises the following steps: (1) Under nitrogen protection, diamine is added to a solvent, and after dissolution, dianhydride is added to 80% to 90% of the mass of the diamine, and the reaction is carried out to obtain a polyamic acid slurry; (2) adding surface-modified hexagonal boron nitride to the polyamic acid slurry and adding a solvent to adjust the solid content; (3) adding the remaining dianhydride to the reaction solution to carry out a reaction to obtain the surface-modified hexagonal boron nitride-doped polyamic acid slurry.

8. The preparation method according to claim 7, characterized in that The diamine in step (1) is selected from any one or a combination of at least two of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzanilide, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 4,4'-diaminodiphenyl sulfone, 2-(4-aminophenyl)-5-aminobenzimidazole, 2,2-bis(4-hydroxy-3-aminophenyl)propane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-biphenyl or 9,9-bis(4-aminophenyl)fluorene; Preferably, the solvent in step (1) and step (2) is selected from one or a combination of at least two of N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone or DMSO; Preferably, the dianhydride in step (1) is selected from 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, (4-phthalic anhydride) formyloxy-4-phthalate, bis[(3,4-dianhydride)phenyl]terephthalate, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, p-phenylene-bis(triphenylene)phthalate Any one or a combination of at least two of ester dianhydride, 4,4'-terephthalic anhydride, pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxylic)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)hexafluoropropane dianhydride, 2,2-bis(4-(3,4-dicarboxybenzoyloxy)phenyl)hexafluoropropane dianhydride or 2,2'-bis(trifluoromethyl)-4,4'-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride; Preferably, the reaction temperature in step (1) is -5-50°C and the reaction time is 5-24h; Preferably, the mass ratio of the surface-modified hexagonal boron nitride to the polyamic acid in step (2) is 20-60:100, further 30-50:100; Preferably, the solid content is adjusted in step (2) to a solid content of 18-25 wt%; Preferably, the reaction temperature in step (3) is -5 to 50°C and the reaction time is 3 to 8 hours; Preferably, the viscosity of the surface-modified hexagonal boron nitride-doped polyamic acid slurry obtained in step (3) is 15-22 wcPs.

9. A polyimide composite thermally conductive film, characterized in that: The polyimide composite thermally conductive film is prepared from the surface-modified hexagonal boron nitride-doped polyamic acid slurry according to claim 7; Preferably, the polyimide composite thermally conductive film is obtained by coating the surface-modified hexagonal boron nitride-doped polyamic acid slurry onto a peeling plate to obtain a wet film, and then subjecting the wet film to a staged temperature-raising heat treatment. Preferably, the staged temperature rising heat treatment is 80°C for 30 min, 100°C for 30 min, 120°C for 30 min, 200°C for 30 min, 300°C for 15 min, and 400°C for 10 min, with a heating rate of 5°C / min.

10. Use of the polyimide composite thermally conductive film according to claim 9 in the preparation of electronic device packaging materials, new energy products, nuclear energy or aerospace products.

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