A high-concentration boron nitride dispersion, its preparation method and application

Abstract

This invention discloses a high-concentration boron nitride dispersion, its preparation method, and its application. The high-concentration boron nitride dispersion is composed of graphene oxide and boron nitride. The preparation method is as follows: boron nitride powder is added to the graphene oxide dispersion to obtain a high-concentration boron nitride dispersion with a boron nitride solid content of 0.1-99%. The boron nitride thermally conductive insulating film is prepared by conventional casting technology using the high-concentration boron nitride dispersion and then densified. The planar thermal conductivity of the film is approximately 36-45 W / m·K. The boron nitride thermally conductive insulating pad is prepared by focusing-expansion multi-flow field casting technology using the high-concentration boron nitride dispersion. The boron nitride dispersion is extruded onto a substrate through a microchannel with a shrinkage section and an expansion section. After curing, washing, freezing, drying, and heat treatment, a vertically oriented boron nitride block is obtained. A high thermal conductivity composite is obtained by impregnating it with silicone. The out-of-plane thermal conductivity is significantly higher than that of ordinary preparation methods.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, specifically to a high-concentration boron nitride dispersion, its preparation method, and its application. Background Technology

[0002] With the rapid development of 5G communications, new energy vehicles, fast-charging batteries, power electronic devices, and aerospace, electronic components are constantly evolving towards higher power density, miniaturization, and integration. This has led to a dramatic increase in heat generation, making thermal management a key factor limiting their reliability and lifespan. In these applications, many electronic devices have stringent requirements for electrical insulation—for example, power modules, LED lighting, battery packs, and high-frequency communication devices must use electrically insulating thermally conductive materials to avoid short-circuit risks. While carbon-based thermally conductive materials (such as graphene and carbon nanotubes) possess extremely high thermal conductivity, their intrinsic electrical conductivity prevents direct application in situations requiring electrical insulation. They typically require an additional insulating layer, which is complex and affects thermal conductivity. Therefore, developing thermally conductive materials that combine high thermal conductivity with high electrical insulation has significant engineering application value.

[0003] Hexagonal boron nitride (h-BN) is an ideal filler for preparing thermally conductive and insulating materials due to its high thermal conductivity, excellent electrical insulation, low dielectric constant, and low dielectric loss, offering advantages that carbon materials cannot replace in electrical insulation applications. However, existing technologies for preparing boron nitride-based thermally conductive and insulating materials still have some shortcomings: First, the low solid content of boron nitride dispersions makes it difficult to meet high-filling requirements. Boron nitride powder has a highly inert surface and lacks polar functional groups, making it difficult to disperse uniformly in polar solvents and prone to agglomeration and precipitation. Current methods to improve the dispersibility of boron nitride mainly include: surface covalent grafting modification (such as silane coupling agents, dopamine, isocyanate molecular grafting), surface coating modification (such as polymer coating, surfactant adsorption), and ultrasonic-assisted dispersion. However, these methods involve complex processes, and the intrinsic thermal conductivity and insulation properties of modified boron nitride may be affected, making it difficult to achieve stable dispersion with high solid content. The solid content of unmodified boron nitride dispersions in water or organic solvents typically does not exceed 0.2 wt%, limiting the increase in filler density in subsequent composite materials and thus restricting further improvements in thermal conductivity.

[0004] Secondly, the planar thermal conductivity of boron nitride (BN) thermally conductive films needs improvement. During the film casting process, BN nanosheets tend to align horizontally along the film surface, an orientation beneficial for planar thermal conductivity. However, the interfacial thermal resistance between the sheets is relatively high, resulting in a planar thermal conductivity far lower than the theoretical value for single-crystal BN. Achieving efficient in-plane overlap and dense stacking of BN nanosheets while ensuring film formation is a key challenge in improving the planar thermal conductivity of the films.

[0005] Third, improving the out-of-plane thermal conductivity of boron nitride thermal pads is difficult due to limitations in existing fabrication methods. To achieve efficient heat transfer along the thickness direction, the boron nitride sheets need to be vertically aligned within the pad. Currently, methods for constructing vertically oriented pads mainly include stacking and cutting, ice template methods, 3D printing, and electric / magnetic field-assisted orientation methods. However, these methods generally suffer from complex processes, difficulty in scaling up, high costs, or unsatisfactory thermal conductivity. Limited by these bottlenecks, existing methods struggle to achieve high out-of-plane thermal conductivity boron nitride pads while maintaining process efficiency, necessitating the development of new fabrication strategies.

[0006] Therefore, developing a preparation method that can achieve high solid content boron nitride dispersions and optimize the performance of films and gaskets for both planar and out-of-plane thermal conductivity requirements is of great significance for the industrial application of high-performance thermally conductive and insulating materials. Summary of the Invention

[0007] To address the problems of low solid content and difficulty in controlling the orientation of boron nitride nanosheets in existing boron nitride dispersions, this invention provides a high-concentration boron nitride dispersion, its preparation method, and its applications. This invention utilizes the confined dispersion effect of graphene oxide on boron nitride, achieving stable preparation of a high-concentration boron nitride dispersion with only a small amount of graphene oxide. The surface of graphene oxide sheets is rich in oxygen-containing functional groups, carrying a negative charge in polar solvents, achieving uniform dispersion through electrostatic repulsion. Simultaneously, graphene oxide confines boron nitride sheets between its layers through non-covalent interactions, forming "graphene-confined boron nitride" dispersion units. These units utilize the excellent dispersibility of graphene oxide to promote uniform dispersion of boron nitride, while effectively inhibiting the aggregation and precipitation of boron nitride through physical barriers between the sheets. Based on the synergistic effect of spatial confinement and electrostatic repulsion, a high-concentration, highly stable boron nitride dispersion can be obtained with simple stirring, without the need for complex surface modification or energy-intensive ultrasonic treatment.

[0008] One of the technical solutions of this invention provides a method for preparing a high-concentration boron nitride dispersion. The method involves preparing graphene oxide as a solution and then uniformly mixing it with boron nitride powder to obtain the high-concentration boron nitride dispersion. The mass ratio of graphene oxide to boron nitride powder is 1-50:50-99. The solvent of the solution is one or more of water, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc). The solid content of the high-concentration boron nitride dispersion is 0.1-50 wt%, preferably 30-50 wt%. The concentration of the graphene oxide solution is 0.1-1 wt%, preferably 0.8-1 wt%. The diameter of the graphene oxide flakes is not less than 1 μm, preferably 10-100 μm.

[0009] Large-size graphene oxide possesses spontaneous surface activity. Its hydrophobic surfaces combine with the boron nitride surface through π-π stacking interactions, while its hydrophilic edges extend into the aqueous phase, thereby reducing the solid-liquid interfacial tension and shielding the van der Waals forces between boron nitride sheets. This stabilizes a large amount of boron nitride and prevents its sedimentation. After large-size graphene oxide combines with boron nitride, physical steric hindrance is formed between adjacent boron nitride sheets, and the dispersed boron nitride sheets are bridged into a loose three-dimensional network structure through face-to-face or edge-to-face overlap. This network fixes the entire dispersion system, further suppressing boron nitride sedimentation due to gravity, thus achieving a high-concentration, long-term stable boron nitride-graphene oxide co-dispersion system. If high-intensity ultrasonic treatment is introduced, the large-size graphene oxide sheets undergo irreversible fragmentation, transforming into small fragments. These fragments lose their spontaneous surface activity, cannot construct a three-dimensional network, and cannot provide sufficient steric hindrance, causing the dispersion system to degenerate into an isolated suspended particle state. At this point, the van der Waals forces between the boron nitride layers become dominant, leading to a significant decrease in the stability of the dispersion, making it impossible to maintain high concentrations and long-term anti-sedimentation properties.

[0010] The second technical solution of this invention is to provide a high-concentration boron nitride dispersion. A high-concentration boron nitride dispersion is fundamental to achieving high-performance thermally conductive and insulating materials. This invention, by adding boron nitride powder to a graphene oxide dispersion, utilizes the confined dispersion effect of graphene oxide on boron nitride, effectively suppressing boron nitride agglomeration, significantly improving the solid content and stability of the dispersion, and laying the foundation for high filling density and orientation control in subsequent films and gaskets. In a preferred embodiment of this invention, the solid content of the obtained dispersion is above 38%, and boron nitride accounts for more than 95% of the solid component; therefore, the boron nitride concentration can reach above 0.36 g / mL.

[0011] The third technical solution of this invention lies in providing the application of the aforementioned high-concentration boron nitride dispersion. This invention employs conventional casting molding technology and focused-expansion multi-flow field casting molding technology to prepare boron nitride thermally conductive films with high planar thermal conductivity and boron nitride thermally conductive pads with high out-of-plane thermal conductivity.

[0012] Specifically, it includes the following steps: (1) A high-concentration boron nitride dispersion was coated onto a substrate and dried to remove the solvent, thus obtaining a primary film; (2) The nascent film is compressed and densified by calendering or cold pressing to obtain a boron nitride thermally conductive and insulating film.

[0013] The calendering process uses a two-roll or three-roll calender, with the calender rolls at room temperature and a roll speed of 0.5~20 m / min. The initial film undergoes one or more calendering cycles, reducing its thickness by 30%~70%.

[0014] The cold pressing process uses a flatbed hot press for cold pressing, with a pressure of 1~20 MPa and a holding time of 1~15 min.

[0015] The specific steps for fabrication using the focused-expansion multi-flow field casting technique are as follows: (1) A high-concentration boron nitride dispersion is sequentially flowed through the contraction section and expansion section of a microchannel and extruded onto a substrate to obtain a nascent gel membrane; the microchannel has a contraction and expansion structure in the height direction, wherein the height of the contraction section gradually decreases and the height of the expansion section gradually increases, and there is a contraction neck with a height of d0 between the contraction section and the expansion section, and the height d at the end of the expansion section is not less than twice d0; the initial height of the contraction section is d1, where d1 > d0; (2) The nascent gel membrane was sequentially cured, washed with water, frozen, dried and heat-treated to obtain a boron nitride block with a vertical orientation structure; (3) The boron nitride block is immersed in an organic polymer for vacuum-assisted impregnation, and then heated and dried to remove the solvent to form a composite block; (4) Cut the composite block vertically to the required thickness to obtain the boron nitride thermally conductive insulating pad.

[0016] Further, the curing solution used in step (2) is a metal salt solution or a polyamine solution, which undergoes a crosslinking reaction with graphene oxide; the freezing step is: freezing in a low-temperature environment of 0~-30℃ for 12 hours to induce the directional growth of ice crystals through low-temperature freezing. The drying step is: heating and drying at 50-100℃ until the solvent in the block is completely removed. The heat treatment is: heating to 400~600℃ in an air atmosphere and holding for 12 hours until the graphene oxide in the block is completely removed to obtain a pure boron nitride block; the organic polymer is a high molecular material, preferably one or more of silicone rubber, gel, polydimethylsiloxane, epoxy resin, phenolic resin, and thermoplastic elastomers (such as polyurethane, styrene-butadiene-styrene block copolymer).

[0017] The focused-expansion multi-flow field casting technology achieves control over the spatial arrangement of two-dimensional graphene oxide and boron nitride through microchannels with contraction and expansion sections.

[0018] When a high-concentration boron nitride dispersion flows through the constriction section of a microchannel, the cross-sectional area of ​​the channel gradually decreases, the fluid velocity gradually increases, and a transverse shear flow field is generated. The graphene oxide sheets are oriented along the flow direction, forming a preliminary orientation parallel to the flow direction.

[0019] In the dispersion, boron nitride sheets are confined between graphene oxide sheets. The orientation change of the graphene oxide drives the confined boron nitride to undergo synergistic orientation. As the dispersion flows through the expansion section, the cross-sectional area of ​​the microchannel gradually increases, generating a longitudinal shear flow field. The graphene oxide sheets flip in the shear flow field, changing from being parallel to the flow direction to being perpendicular to the flow direction, and synchronously driving the confined boron nitride sheets to flip as well, forming a stable vertical orientation at the outlet of the expansion region.

[0020] Through the synergistic effect of the aforementioned contraction and expansion sections, vertically aligned thermally conductive pathways with graphene oxide as a template and boron nitride uniformly dispersed are directly constructed within a single block. Subsequent heat treatment removes the graphene oxide from the block, yielding a vertically aligned pure boron nitride block. This block is then impregnated with a polymer material to fill the pores left after the removal of graphene oxide, resulting in a vertically aligned boron nitride-polymer composite block. Finally, the block is cut vertically to the desired thickness to obtain a boron nitride thermally conductive insulating pad. By adjusting the amount of graphene oxide added, the mass ratio of boron nitride to polymer material in the resulting composite block can be further adjusted. Increasing the amount of graphene oxide added increases the number of pores formed after heat treatment, increases the amount of polymer impregnated, and decreases the relative content of boron nitride in the composite block. Decreasing the amount of graphene oxide added reduces the number of pores formed after heat treatment, decreases the amount of polymer impregnated, and increases the relative content of boron nitride in the composite block.

[0021] This invention also provides a thermally conductive pad prepared by the above method and its application in the field of high-insulation thermal interface heat dissipation. The thermally conductive pad prepared by this invention has both high out-of-plane thermal conductivity and excellent electrical insulation, and can be used as an insulating thermal interface material for heat dissipation at the interface between heat-generating components (such as fast-charging batteries, power chips, and IGBT modules) and heat sinks, effectively avoiding the risk of short circuits.

[0022] The advantages of this invention are: (1) This invention utilizes the confined dispersion effect of graphene oxide on boron nitride, and only requires simple stirring to achieve stable preparation of high-concentration boron nitride dispersion, overcoming the technical difficulty of high-concentration dispersion of boron nitride in the prior art, and laying the foundation for the preparation of high-fill-density thermally conductive composite materials. The solid content of the dispersion is above 38%, and boron nitride accounts for more than 95% of the solid components.

[0023] (2) Utilizing the confined dispersion effect of graphene oxide on boron nitride, the graphene oxide in the dispersion liquid confines the boron nitride sheets between the sheets through non-covalent interactions. Conventional casting combined with calendering densification process is used to form a tight stack and efficient in-plane overlap of the boron nitride sheets, resulting in a thermally conductive film with high planar thermal conductivity. Using a focused-expansion multi-flow field casting technology, the graphene oxide sheets are oriented and flipped in the shrinkage and expansion sections, respectively, and drive the confined boron nitride to align in a coordinated manner, constructing a vertically aligned thermally conductive path for boron nitride, resulting in a thermally conductive pad with high out-of-plane thermal conductivity.

[0024] (3) The conventional casting molding technology and the focused-expansion multi-flow field casting molding technology adopted in this invention are simple in process, can be continuously produced, and have good industrial application prospects. Attached Figure Description

[0025] Figure 1 Cross-sectional morphology of a boron nitride thermally conductive insulating film prepared by conventional casting.

[0026] Figure 2 This is a schematic diagram of the focused-expansion microchannel structure of the present invention.

[0027] Figure 3 This is a cross-sectional morphology diagram of a graphene oxide-boron nitride bulk material with a vertically oriented structure prepared using microchannels. Detailed Implementation

[0028] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0029] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0030] The graphene oxide described in this invention can be any commercially available raw material. In the following examples, GX-GO-3 produced by Hangzhou Gaoxi Technology Co., Ltd. was used.

[0031] The embodiments of the present invention will be further described below with reference to several examples.

[0032] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0033] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0034] Example 1 (1) Graphene oxide with a sheet diameter of 10 μm was dispersed in water to prepare a graphene oxide solution with a concentration of 1 wt%. The graphene oxide solution was mixed with boron nitride powder so that the mass ratio of graphene oxide to boron nitride was 1:99. The solution was placed in a vacuum stirrer for stirring and degassing, and vacuum degassing was performed simultaneously to obtain a high-concentration boron nitride dispersion with a solid content of 50 wt%.

[0035] (2) The boron nitride dispersion was uniformly coated onto the substrate using a conventional casting process, with the doctor blade gap controlled at 200 μm. After drying to remove the solvent, a nascent film was obtained. The nascent film was then calendered and densified using a roll press to obtain a boron nitride thermally conductive and insulating film. The cross-sectional morphology of the obtained film is as follows: Figure 1 As shown, the film thickness is approximately 70 μm, and the density of the thermally conductive film is approximately 1.7 g / cm³. 3 Its planar thermal conductivity is approximately 41 W / m·K, and its volume resistivity is greater than 10. 13 Ω·cm.

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that the mass ratio of graphene oxide to boron nitride in the mixed solution in step (1) is 5:95. The other steps are the same as in Embodiment 1. Testing showed that the planar thermal conductivity of this thermally conductive film is approximately 45 W / m·K, and the volume resistivity is greater than 10⁻⁶ W / m·K. 11 Ω·cm.

[0037] Example 3 The difference between this embodiment and Embodiment 1 is that the mass ratio of graphene oxide to boron nitride in the mixed solution in step (1) is 10:90. The other steps are the same as in Embodiment 1. Testing showed that the planar thermal conductivity of this thermally conductive film is approximately 36 W / m·K, and the volume resistivity is greater than 10⁻⁶ W / m·K. 10 Ω·cm.

[0038] Example 4 (1) Graphene oxide with a sheet diameter of 10 micrometers was dispersed in water to prepare a graphene oxide solution with a concentration of 0.8 wt%. The graphene oxide solution was mixed with boron nitride powder so that the mass ratio of graphene oxide to boron nitride was 1:99. The solution was placed in a vacuum stirrer for stirring and simultaneous vacuum degassing to obtain a high-concentration boron nitride dispersion with a solid content of 45 wt%.

[0039] (2) The above dispersion is extruded onto a substrate through a mold integrated with focusing-expansion microchannels, wherein the expansion ratio R of the focusing-expansion microchannels is 6.0 ( The initial height of the contraction segment is d1, where d1 = 2d0, as follows. Figure 2 The diagram shows a schematic of the microchannel structure. The obtained gel membrane was sequentially immersed in a 5 wt% calcium chloride solution for cross-linking and curing, and then washed with deionized water to remove residual calcium ions. The cured gel membrane was frozen at -20°C for 12 hours, then dried in a 70°C oven to remove the solvent, and subsequently heat-treated at 600°C in air to remove graphene oxide, yielding a pure boron nitride bulk with a vertically oriented structure. The cross-sectional morphology of the obtained bulk is shown in the figure. Figure 3 As shown.

[0040] (3) The obtained boron nitride block was immersed in liquid silicone rubber and impregnated under vacuum for 30 minutes to ensure that the silicone rubber fully filled the internal pores of the block. Finally, it was heated to 80-100℃ and cured for 2 hours to crosslink and cure the silicone rubber, thus obtaining a boron nitride-silicone rubber composite block. The boron nitride content in the block was 70 wt%. The block was cut vertically to the required thickness to obtain a boron nitride thermally conductive insulating gasket with good flexibility. The density of the thermally conductive gasket was tested to be approximately ~1.65 g / cm³. 3 The vertical thermal conductivity is approximately 30 W / m·K, and the volume resistivity is greater than 10. 13 Ω·cm. At 50 psi pressure, a 0.5 mm thick gasket has a thermal resistance of approximately 0.40 K·cm² / W.

[0041] Example 5 The difference between this embodiment and Embodiment 4 is that the solid content of the boron nitride dispersion in step (1) is 38 wt%, while the other steps are the same as in Embodiment 4. The final boron nitride-silicone rubber composite block has a boron nitride content of 60 wt%. The density of the thermal pad was tested to be approximately 1.55 g / cm³. 3 The vertical thermal conductivity is approximately 22 W / m·K, and the volume resistivity is greater than 10. 13 Ω·cm. At 50 psi pressure, a gasket with a thickness of 0.5 mm has a thermal resistance of approximately 0.53 K·cm² / W.

[0042] Example 6 The difference between this embodiment and Embodiment 4 is that the solid content of the boron nitride dispersion in step (1) is 30 wt%, while the other steps are the same as in Embodiment 4. The final boron nitride-silicone rubber composite block has a boron nitride content of 50 wt%. The density of the thermal pad was tested to be approximately ~1.45 g / cm³. 3 The vertical thermal conductivity is approximately 13 W / m·K, and the volume resistivity is greater than 10.13 Ω·cm. At 50 psi pressure, a gasket with a thickness of 0.5 mm has a thermal resistance of approximately 0.70 K·cm² / W.

[0043] Example 7 The difference between this embodiment and Example 4 is that the mass ratio of graphene oxide to boron nitride is 1:1, and the solid content of the boron nitride dispersion is 9 wt%. The other steps are the same as in Example 4. The final boron nitride-silicone rubber composite block contains 20 wt% boron nitride. The density of the thermal pad was tested to be approximately ~1.15 g / cm³. 3 The vertical thermal conductivity is approximately 4 W / m·K, a significant improvement over the approximately 0.2 W / m·K of the silicone rubber matrix. At 50 psi pressure, a 0.5 mm thick gasket exhibits a thermal resistance of approximately 2.5 K·cm. 2 / W.

[0044] Comparative Example 1 The difference between this comparative example and Example 1 is that the concentration of the boron nitride dispersion prepared in step (1) is 5 wt%. The other steps are the same as in Example 1. The thermal conductivity of this thermally conductive film was tested to be approximately 26 W / m·K, and its volume resistivity was greater than 10⁻⁶ W / m·K. 13 Ω·cm, lower than in Example 1.

[0045] Comparative Example 2 The difference between this comparative example and Example 4 is that the expansion ratio R of the microchannel used in step (2) is 2.0, while the other steps are the same as in Example 4. The prepared thermally conductive pad was tested and found to have a vertical thermal conductivity of approximately 25 W / m·K. At 50 psi pressure, the 0.5 mm thick pad had a thermal resistance of approximately 0.46 K·cm² / W, lower than that of Example 1.

[0046] Comparative Example 3 The difference between this comparative example and Example 4 is that the expansion ratio R of the microchannel used in step (2) is 10.0, while the other steps are the same as in Example 4. The prepared thermally conductive pad was tested and found to have a vertical thermal conductivity of approximately 31 W / m·K. At 50 psi pressure, the pad with a thickness of 0.5 mm has a thermal resistance of approximately 0.38 K·cm² / W, which is close to that of Example 1.

[0047] Comparative Example 4 The difference from Example 1 is that graphene oxide was not added. Boron nitride powder was directly dispersed in water. Since boron nitride is difficult to disperse in water, the resulting dispersion precipitated severely, making it impossible to coat evenly and obtain a complete primary film. The subsequent calendering and densification process could not be implemented.

[0048] Comparative Example 5 The difference from Example 1 is that a small molecule surfactant (sodium dodecylbenzenesulfonate) is used instead of graphene oxide, and the amount added is 5.0% of the boron nitride mass. Due to the significant scale mismatch between the size of the surfactant (less than 10 nm) and the size of the boron nitride sheets (micrometers), even if instantaneous dispersion can be achieved, the solid content of the resulting boron nitride dispersion is less than 5 mg / mL, making it impossible to prepare a high-concentration boron nitride dispersion or achieve stable dispersion over a long period of time.

[0049] Comparative Example 6 The difference from Example 1 lies in the addition of a small-molecule surfactant (sodium dodecylbenzenesulfonate), at an amount of 5.0% of the boron nitride mass. The surfactant itself has poor thermal conductivity; its molecules adsorb at the interface between boron nitride and graphene oxide, introducing low-thermal-conductivity components into the thermally conductive film and hindering the effective transfer of phonons within the thermally conductive network. Simultaneously, the presence of the small-molecule surfactant disrupts the direct interfacial contact between boron nitride and graphene oxide and the construction of the three-dimensional thermally conductive network. The planar thermal conductivity of this thermally conductive film was tested to be approximately 18 W / m·K.

[0050] Comparative Example 7 The difference from Example 1 lies in the introduction of ultrasonic treatment. The ultrasonic treatment conditions were: ultrasonic power 150 W, ultrasonic time 30 min, and temperature controlled at 25 ℃ (maintained constant temperature using an ice-water bath). Ultrasonic treatment breaks the large-sized graphene oxide into smaller fragments, causing it to lose its spontaneous surface activity and thus failing to effectively bridge the boron nitride sheets, preventing the construction of a three-dimensional network structure. The resulting boron nitride dispersion has a low solid content and cannot achieve stable high-concentration dispersion. The orientation degree of the boron nitride sheets inside the thermally conductive film prepared from this dispersion decreases, resulting in a discontinuous three-dimensional thermally conductive network. Testing showed that the planar thermal conductivity of this thermally conductive film is approximately 15 W / m·K.

[0051] The above embodiments detail the structure, features, and effects of the present invention. The above descriptions are merely preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent variations, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a high-concentration boron nitride dispersion, characterized in that, A high-concentration boron nitride dispersion is obtained by uniformly mixing graphene oxide solution with boron nitride powder; the mass ratio of graphene oxide to boron nitride powder is 1-50:50-99; the solvent of the solution is one or more of water, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc); the solid content of the high-concentration boron nitride dispersion is 0.1-50 wt%; and the graphene oxide sheet diameter is not less than 1 μm.

2. The method according to claim 1, characterized in that, The graphene oxide is prepared as a solution with a concentration of 0.1-1 wt%.

3. A high-concentration boron nitride dispersion prepared by the method as described in claim 1.

4. An application of the high-concentration boron nitride dispersion as described in claim 3.

5. The application according to claim 4, characterized in that, It includes the following steps: (1) A high-concentration boron nitride dispersion was coated onto a substrate and dried to remove the solvent, thus obtaining a primary film; (2) The nascent film is compressed and densified by calendering or cold pressing to obtain a boron nitride thermally conductive and insulating film.

6. The application according to claim 4, characterized in that, It includes the following steps: (1) A high-concentration boron nitride dispersion is sequentially flowed through the contraction section and expansion section of a microchannel and extruded onto a substrate to obtain a nascent gel membrane; the microchannel has a contraction and expansion structure in the height direction, wherein the height of the contraction section gradually decreases and the height of the expansion section gradually increases, and there is a contraction neck with a height of d0 between the contraction section and the expansion section, and the height d at the end of the expansion section is not less than twice d0; the initial height of the contraction section is d1, where d1 > d0; (2) The nascent gel membrane was sequentially cured, washed with water, frozen, dried and heat-treated to obtain a boron nitride block with a vertical orientation structure; (3) The boron nitride block is immersed in an organic polymer for vacuum-assisted impregnation, and then heated and dried to remove the solvent to form a composite block; (4) Cut the composite block vertically to the required thickness to obtain the boron nitride thermally conductive insulating pad.

7. The application according to claim 6, characterized in that, The curing solution used in step (2) is a metal salt solution or a polyamine solution, which undergoes a cross-linking reaction with graphene oxide; the freezing step is: freezing in a low temperature environment of 0~-30℃ for 12 hours to induce the directional growth of ice crystals through low temperature freezing; the drying step is: heating and drying at 50-100℃ until the solvent in the block is completely removed; the heat treatment is: heating to 400~600℃ in an air atmosphere and holding for 12 hours until the graphene oxide in the block is completely removed to obtain a pure boron nitride block.

8. A boron nitride thermal pad, characterized in that, It is prepared from the high-concentration boron nitride dispersion described in claim 3.

9. An application of the boron nitride thermal pad as described in claim 8.

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