Hexagonal boron nitride material, method for preparing same, and use thereof

Abstract

The application provides a hexagonal boron nitride material and a preparation method and application thereof, and the preparation method comprises the following steps: performing hydrophilic modification treatment on a hexagonal boron nitride raw material to obtain a modified hexagonal boron nitride raw material; mixing the modified hexagonal boron nitride raw material, a surfactant, a polymer binder, a sintering aid and a dispersion medium to prepare a second slurry; performing spray drying on the second slurry to form a spherical particle product; and performing sintering on the spherical particle product to obtain the hexagonal boron nitride material. The application can improve the sphericity and size of the hexagonal boron nitride material, increase the filling amount of the hexagonal boron nitride material in a heat-conducting composite material, and reduce the viscosity of the heat-conducting composite material.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive materials, specifically to a hexagonal boron nitride material, its preparation method, and its applications. Background Technology

[0002] Hexagonal boron nitride (h-BN) is a novel ceramic material with a layered structure similar to graphene. Within each layer is an infinitely extending hexagonal network of alternating B and N atoms, while the layers are stacked in an ABAB pattern via van der Waals forces. Therefore, hexagonal boron nitride is an anisotropic thermally conductive material, with its thermal conductivity along the in-plane direction of the (002) plane being tens of times higher than that perpendicular to this direction. Due to its excellent thermal conductivity, it is often used as a filler in polymers to improve the thermal conductivity of the resulting composite materials. However, high thermal conductivity boron nitride polymer composites require the formation of continuous thermally conductive channels within them, typically using materials with high aspect ratios (such as nanotubes and fibers). Although this method easily yields thermal conductivity greater than 10 W·m... -1 ·k -1 Composite materials can be made, but increasing the amount of BN filler will lead to a sharp increase in the viscosity of the system, which is not suitable for industrial production. At the same time, the anisotropic thermal conductivity of materials with a high aspect ratio is also not conducive to practical applications.

[0003] Spherical fillers can improve the rheological properties of polymers. Preparing boron nitride into spherical shapes can improve the dispersibility of boron nitride particles in composite materials, while increasing the filling amount of boron nitride and reducing the viscosity of the system. However, in related technologies, boron nitride has low sphericity and small particle size (usually no more than 20 μm). Small-sized boron nitride particles (such as BN nanospheres and microspheres) have limited effect on improving the thermal conductivity of composite materials, mainly because their poor crystallinity and curved (002) surface cause severe phonon scattering. Therefore, the size of spherical particles needs to be increased to above 20 μm to have practical application value. Summary of the Invention

[0004] This invention provides a hexagonal boron nitride material, its preparation method, and its application, to at least solve the problems of low sphericity and small particle size of boron nitride in the prior art.

[0005] In one aspect, the present invention provides a method for preparing a hexagonal boron nitride material, comprising the following steps: subjecting a hexagonal boron nitride raw material to hydrophilic modification treatment to obtain a modified hexagonal boron nitride raw material; mixing the modified hexagonal boron nitride raw material, a surfactant, a polymer binder, a sintering aid, and a dispersion medium to prepare a second slurry; spray-drying the second slurry to form spherical particle products; and sintering the spherical particle products to obtain the hexagonal boron nitride material.

[0006] According to one embodiment of the present invention, hydrophilic groups are introduced onto the modified hexagonal boron nitride raw material through the hydrophilic modification treatment, wherein the hydrophilic groups include hydroxyl and / or amino groups; preferably, the hydrophilic modification treatment process includes: mixing the hexagonal boron nitride raw material with a modifier for introducing the hydrophilic groups onto the modified hexagonal boron nitride raw material and preparing a first slurry followed by ball milling; or sintering and oxidizing the hexagonal boron nitride raw material in an air atmosphere; or ultrasonically treating the hexagonal boron nitride raw material in a polar solvent; preferably, the modifier includes one or more of boric acid, glucose, and cellulose; preferably, the conditions for the sintering and oxidation treatment are: a temperature of 750–800°C and a time of 1–15 min.

[0007] According to one embodiment of the present invention, the hexagonal boron nitride raw material is flake-shaped hexagonal boron nitride; and / or, the surfactant includes an alkanolamine compound; preferably, the alkanolamine compound includes one or more of ethanolamine, diethanolamine, triethanolamine, and alkanolamine borate esters; and / or, the sintering aid includes amorphous hexagonal boron nitride and / or low-melting-point glass powder, wherein the melting point of the low-melting-point glass powder is 450–1200°C; and / or, the polymer binder includes one or more of polyethylene glycol, polyvinyl alcohol, and carboxymethyl cellulose.

[0008] According to one embodiment of the present invention, the mass ratio of the surfactant to the hexagonal boron nitride raw material is (1-10):100; and / or, the mass ratio of the polymer binder to the hexagonal boron nitride raw material is (0.5-2):100; and / or, the mass ratio of the sintering aid to the hexagonal boron nitride raw material is (0.5-5):100.

[0009] According to one embodiment of the present invention, the spray drying is performed using a spray dryer, wherein the inlet temperature of the spray dryer is 200-300°C and the outlet temperature is greater than or equal to 120°C.

[0010] According to one embodiment of the present invention, the spherical particle product is first subjected to a debinding treatment before sintering; wherein the debinding treatment is carried out in an air atmosphere and the temperature of the debinding treatment is 500-700°C.

[0011] According to one embodiment of the present invention, the sintering temperature is 1200-1700℃ and the sintering time is 2-10h.

[0012] According to one embodiment of the present invention, the sintering is carried out in an atmosphere containing a reducing gas and / or an inert gas.

[0013] In another aspect, the present invention provides a hexagonal boron nitride material prepared according to the above preparation method.

[0014] In another aspect, the present invention provides a thermally conductive composite material comprising a polymer matrix material and the aforementioned hexagonal boron nitride material.

[0015] In this invention, the hexagonal boron nitride raw material is first subjected to hydrophilic modification treatment, and then mixed with surfactant, polymer binder, sintering aid and dispersant to form a second slurry. The slurry is then spray-dried to form spherical particles, and the spherical particles are sintered to obtain the hexagonal boron nitride material. Through this preparation process, the sphericity and particle size of the obtained hexagonal boron nitride material can be improved (up to 20-150 μm), that is, larger spherical hexagonal boron nitride material is obtained. The thermal conductivity of the hexagonal boron nitride material and its dispersibility and filling amount in the polymer matrix material are improved, and the viscosity of the thermally conductive composite material composed of hexagonal boron nitride material and polymer matrix material is reduced. Thus, the thermal conductivity and rheological properties of the composite material are improved.

[0016] Furthermore, this invention can improve the structural stability and mechanical properties of hexagonal boron nitride materials, making them less prone to breakage during application and facilitating their practical application. For example, when hexagonal boron nitride materials are added to polymer matrix materials, they will not break during the mixing process, thereby improving the performance of the resulting composite material.

[0017] Furthermore, the present invention can improve the compatibility between hexagonal boron nitride materials and polymer matrix materials, reduce the viscosity of composite materials formed by modified hexagonal boron nitride materials and polymer systems, and increase the filling amount of hexagonal boron nitride materials. Attached Figure Description

[0018] Figure 1 SEM image of the spherical particle product in Example 1 ( Figure 1 (a) is a SEM image of the spherical particle product in the collection chamber. Figure 1 (b) is a SEM image of the spherical particle product collected from the wall of the drying chamber container;

[0019] Figure 2 Here is a SEM image of the hexagonal boron nitride material product prepared in Example 1;

[0020] Figure 3 Here is a SEM image of the hexagonal boron nitride material product obtained in Example 2;

[0021] Figure 4 This is a SEM image of the hexagonal boron nitride material product prepared in Example 3. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a method for preparing hexagonal boron nitride material, comprising the following steps: subjecting hexagonal boron nitride raw material to hydrophilic modification treatment to obtain modified hexagonal boron nitride raw material; mixing the modified hexagonal boron nitride raw material, surfactant, polymer binder, sintering aid and dispersion medium to prepare a second slurry; spray drying the second slurry to form spherical particle products; and sintering the spherical particle products to obtain hexagonal boron nitride material.

[0024] Specifically, through hydrophilic modification treatment, hydrophilic groups (functional groups introduced to the surface of the hexagonal boron nitride raw material) can be introduced onto the modified hexagonal boron nitride raw material. The hydrophilic groups may include hydroxyl and / or amino groups. In this way, the viscosity of the second slurry can be reduced and the solid content of the second slurry can be increased (the viscosity of the second slurry with high solid content can be reduced). Furthermore, due to the increased hydrophilicity of the modified hexagonal boron nitride raw material, the spherical particles formed during the spray drying process have better sphericity, thereby improving the sphericity of the obtained hexagonal boron nitride material.

[0025] Furthermore, by performing hydrophilic modification on hexagonal boron nitride raw materials, the affinity of hexagonal boron nitride raw materials for water can be increased, the amount of surfactant required can be reduced, making it easier to wet and disperse, and obtaining a second slurry with a higher solids content that can be spray-dried.

[0026] Generally, hexagonal boron nitride raw materials can be hydrophilic modified by methods such as ball milling, air oxidation (i.e., sintering in air), or ultrasonic treatment in polar solvents.

[0027] In some embodiments, the hydrophilic modification process may include: mixing hexagonal boron nitride raw material with a modifier for introducing hydrophilic groups onto the modified hexagonal boron nitride raw material and preparing a slurry, followed by ball milling. Specifically, the hexagonal boron nitride raw material, the modifier, and water may be mixed to prepare a first slurry, which is then placed in a ball mill for ball milling. Through ball milling, hydrophilic groups are introduced onto the surface of the hexagonal boron nitride raw material, thereby achieving hydrophilic modification. After ball milling, the first slurry after ball milling may be centrifuged, washed with water, and the resulting solid product may be dried to obtain the modified hexagonal boron nitride raw material.

[0028] The modifier may include one or more of boric acid, glucose, and cellulose. The mass ratio of the modifier to the hexagonal boron nitride raw material may be (0.1-2):100, for example, 0.1:100, 0.5:100, 0.8:100, 1:100, 1.3:100, 1.5:100, 1.8:100, 2:100 or any combination thereof. The ball milling time may be 0.5h-8h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or any combination thereof.

[0029] In other embodiments, the hydrophilic modification process may include: sintering and oxidizing the hexagonal boron nitride raw material in an air atmosphere (or air-firing oxidation). Air contains components such as moisture and oxygen. By sintering in an air atmosphere, hydroxyl and other reactive groups can be introduced onto the surface of the hexagonal boron nitride raw material, achieving hydrophilic modification. The sintering and oxidation temperature can be 750–800°C, for example, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any combination thereof, and the time can be 1–15 min, for example, 1 min, 3 min, 5 min, 8 min, 10 min, 12 min, 15 min, or any combination thereof.

[0030] In other embodiments, the hydrophilic modification process may include: ultrasonically treating the hexagonal boron nitride raw material in a polar solvent. During the ultrasonic treatment, a modifier may or may not be added. By ultrasonically treating the hexagonal boron nitride raw material in a polar solvent, hydroxyl and other polar groups can be introduced onto the surface of the hexagonal boron nitride raw material, thereby achieving hydrophilic modification.

[0031] The ultrasonic treatment time can be 5 min to 60 min, for example, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min or any combination thereof. The polar solvent can include one or more of alcohol solvents, ester solvents, amide solvents, etc., such as one or more of ethanol, ethyl acetate, N,N-dimethylformamide (DMF).

[0032] In practice, modified hexagonal boron nitride, surfactant, polymer binder, sintering aid and dispersion medium can be mixed and stirred evenly (i.e., mixing) to obtain the second slurry.

[0033] Specifically, the aforementioned hexagonal boron nitride raw material is plate-shaped hexagonal boron nitride (or layered hexagonal boron nitride, hexagonal boron nitride sheet, hexagonal boron nitride crystal). After hydrophilic modification treatment, the resulting modified hexagonal boron nitride raw material is also in the shape of a plate. After spray drying, the resulting spherical particle product is formed by the contact of plate-shaped hexagonal boron nitride particle powder (that is, the spherical particles in the spherical particle product are formed by the agglomeration of multiple modified hexagonal boron nitride crystal particles).

[0034] In this embodiment of the invention, the hexagonal boron nitride raw material used can be commercially available hexagonal boron nitride sheet powder.

[0035] In the above preparation process, the hexagonal boron nitride raw material is a hydrophobic material. By adding surfactants, the wettability of the hexagonal boron nitride raw material can be improved.

[0036] Specifically, surfactants may include alkanolamine compounds, which may include one or more of ethanolamine, diethanolamine, triethanolamine, and alkanolamine borate esters.

[0037] According to the inventors' research, the aforementioned non-polymeric alkanolamine compounds possess the dual functions of surfactants and sintering aids. Specifically, alkanolamine compounds, possessing hydroxyl and amino groups, enhance the affinity of boron nitride for water, facilitating its dispersion. Simultaneously, alkanolamine compounds are typically viscous liquids at room temperature, soluble in water but still exhibiting slight viscosity (due to their small molecular size, their impact on the viscosity of the second slurry is relatively small; however, compared to polar substances like methanol and ethanol, they can still increase the viscosity of the second slurry to some extent). Furthermore, their viscosity is lower than that of nonionic surfactants, thus contributing to a suitable viscosity for the second slurry. Moreover, by increasing the solid content of the modified hexagonal boron nitride raw material in the second slurry, less polymer binder can be added, resulting in a viscosity suitable for spray drying. In other words, less polymer binder is added to the second slurry to maintain a higher boron nitride content while simultaneously enabling spray drying to form spherical granular products.

[0038] Specifically, the reduced amount of polymer binder added to the second slurry facilitates mixing of the components. This is primarily because polymer binders are typically long-chain macromolecules, which can become entangled with boron nitride in the solid powder, leading to uneven boron nitride distribution. During mixing, the viscosity is lower at the stirring points and higher at the edges. Therefore, reducing the amount of polymer binder to a certain extent improves mixing and enhances the sphericity of the spherical particles formed after spray drying. Alkylamine compounds are small molecules, and their influence is relatively small, further improving the sphericity and other properties of the spherical particles formed during spray drying.

[0039] Furthermore, after spray drying, alkanolamine compounds remain in the spherical particle product. These compounds can form hydrogen bonds with the modified hexagonal boron nitride raw material. During sintering, the boron hydroxyl groups and the amino groups in the alkanolamine compounds combine and transform into boron nitride, becoming a welding agent (other impurity elements are discharged as gas). This enhances the connection between multiple primary particles forming spherical particles (spherical agglomerates), thereby improving the structural stability and mechanical properties of the prepared hexagonal boron nitride material, preventing particle breakage during application, and reducing sintering temperature, thus saving energy.

[0040] In some embodiments, the mass ratio of the surfactant to the hexagonal boron nitride raw material can be (1 to 10):100, for example, a range consisting of 1:10, 1:30, 1:50, 1:100 or any two of these.

[0041] In the above preparation process, the polymer binder can increase the viscosity of the second slurry, which is beneficial for forming spherical particles after spray drying. Specifically, the polymer binder may include one or more of polyethylene glycol, polyvinyl alcohol, and carboxymethyl cellulose.

[0042] In some embodiments, the mass ratio of the polymer binder to the hexagonal boron nitride raw material is (0.5 to 2):100, for example, 0.5:100, 1:100, 1.5:100, 2:100 or any combination thereof.

[0043] In addition, sintering aids may include amorphous hexagonal boron nitride and / or low-melting-point glass powder, wherein the melting point of the low-melting-point glass powder is 400 to 1200°C, for example, 400°C, 450°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C or any combination thereof, which is beneficial for reducing the sintering temperature.

[0044] According to the inventors' research, without the addition of sintering aids, the sintering temperature is high (usually requiring sintering for several hours at temperatures as high as 1700-2200°C), which leads to high energy consumption and places higher demands on sintering equipment. However, by adding the aforementioned sintering aids, the embodiments of the present invention can significantly reduce the sintering temperature of the sintering process, which is beneficial for industrial production.

[0045] Specifically, t-BN is an amorphous boron nitride with an amorphous structure. Under normal circumstances, t-BN will transform into regular h-BN at around 1300℃. At the same time, t-BN usually contains oxygen-containing substances (impurities), at least some of which can be converted into B2O3 (that is, the discharged oxygen impurities exist in the form of B2O3), which enhances the sintering performance. Specifically, B2O3 can act as a flux to enhance the connection between modified hexagonal boron nitride sheets, reduce the sintering temperature, and improve the mechanical properties of the obtained hexagonal boron nitride material. At the same time, the amount of t-BN added is small, which can also maintain the purity and other properties of the obtained hexagonal boron nitride material.

[0046] In some embodiments, the mass ratio of sintering aid to hexagonal boron nitride raw material can be (0.5 to 5):100, for example, 0.5:100, 1:100, 2:100, 3:100, 4:100, 5:100 or any combination thereof.

[0047] Specifically, t-BN may include boron nitride nanospheres (BN nanospheres) and / or boron nitride with irregular particle morphology. In embodiments of the present invention, t-BN can be prepared by conventional methods in the art. For example, boron nitride with irregular particle morphology can be prepared by reacting boric acid with a nitrogen source (including urea and / or melamine), and boron nitride nanospheres can be prepared by chemical vapor deposition of borate esters and ammonia. For example, the preparation process of BN nanospheres may include: reacting borate esters and ammonia to prepare a precursor (usually with a high oxygen content), and then pressing the precursor into a dense bulk; then heating the bulk to 800-1200°C at a rate of 1-20°C / min under an inert atmosphere and holding for 2-10 hours, and then washing, centrifuging, drying, etc., of the obtained product to obtain BN nanospheres; wherein the inert atmosphere may include nitrogen and / or argon, etc.

[0048] Specifically, in the second slurry, the expected mass content (BN solid content) of modified hexagonal boron nitride can be 20% to 50%, for example, a range of 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any combination thereof.

[0049] Specifically, in the second slurry, a dispersion medium (solvent) is used to disperse the components, and the dispersion medium may specifically include water.

[0050] Generally, before spray drying, the second slurry can be stirred at 40–90°C at a speed of 400–1500 r / min for 1–24 h, and then spray dried. In practice, the second slurry can be heated to 40–90°C and mechanically stirred for 2–8 h, and then the heated slurry can be spray dried.

[0051] Specifically, a spray dryer (spray drying instrument, spray drying device) is used for spray drying. The inlet (sample inlet) temperature of the spray dryer can be 200-300℃, and the outlet temperature can be greater than or equal to 120℃. This can shorten the drying time, that is, obtain dried spherical particle products in a shorter time.

[0052] In practice, after spray drying is completed, spherical particulate products are collected in the collection chamber and on the container wall of the drying chamber of the spray dryer, and then subjected to subsequent sintering and other treatments.

[0053] In the above preparation process, the spherical particles formed after spray drying are agglomerated from plate-like modified hexagonal boron nitride raw material particles, containing polymer materials such as polymer binders. Specifically, after spray drying, the spherical particle product can undergo a debinding treatment before sintering. The debinding treatment is carried out in an air atmosphere at a temperature of 500–700°C, such as 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, or any combination thereof. The debinding time can be 0.5 h–6 h, such as 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, or any combination thereof. Through debinding, carbonaceous materials can be pyrolyzed, preventing color changes during high-temperature calcination (sintering), thus ensuring the whiteness of the obtained hexagonal boron nitride material and improving its performance.

[0054] In the above preparation process, the sintering process is used to calcine the spherical particle product at high temperature, which can enhance the connection between the sheets (i.e., modified hexagonal boron nitride sheets), endow the prepared hexagonal boron nitride material with strong mechanical properties, avoid particle breakage during application, and maintain the integrity of its spherical morphology during application.

[0055] Generally, the sintering temperature is higher than the melting point of sintering aids and other additives to prevent these additives from remaining in the resulting hexagonal boron nitride material and to improve its purity and other properties. Therefore, in practice, the sintering temperature can be adjusted according to the type and melting point of the sintering aids and other additives used.

[0056] In some embodiments, the sintering temperature can be 1200-1700℃, for example, a range of 1200℃, 1300℃, 1400℃, 1500℃, 1600℃, 1700℃ or any two thereof, and the sintering time can be 2-10h, for example, a range of 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or any two thereof.

[0057] In practice, the spherical particle product can be heated to the sintering temperature (1200-1700℃) at a heating rate of 1-10℃ / min, and then held at this temperature for a preset sintering time (2-10h) to complete the sintering.

[0058] Specifically, sintering can be carried out in an atmosphere containing a reducing gas and / or an inert gas. The reducing gas may include ammonia.

[0059] In the above preparation process, the hexagonal boron nitride material obtained after sintering is usually white.

[0060] Compared to existing hexagonal boron nitride materials, the hexagonal boron nitride material prepared in this embodiment of the invention has a larger size, with an average particle size D50 greater than 20 μm. Generally, the hexagonal boron nitride material (sintered product) obtained after sintering has a certain size distribution. In specific implementation, the hexagonal boron nitride material is sieved using a standard sieve (i.e., the prepared hexagonal boron nitride material (powder) is passed through a standard mesh sieve) to remove a small number of excessively large particles, resulting in spherical particles (hexagonal boron nitride material).

[0061] Specifically, in this embodiment of the invention, the sintered product obtained after sintering is sieved to remove a small amount of large particles and impurities, thereby obtaining a hexagonal boron nitride material with an average particle size D50 of 20-150 μm. The mass of this hexagonal boron nitride material with an average particle size D50 of 20-150 μm accounts for more than 80% of the total mass of the sintered product (i.e., the hexagonal boron nitride material before sieving), generally between 80% and 90%.

[0062] For example, the average particle size D50 of the hexagonal boron nitride material can be a range of 20 μm, 30 μm, 50 μm, 80 μm, 100 μm, 130 μm, 150 μm or any combination thereof.

[0063] The hexagonal boron nitride material provided in this embodiment of the invention is prepared according to the above preparation method. It has good sphericity and can also have a large size. Its average particle size D50 and other parameters can be referred to the foregoing content, and will not be repeated here.

[0064] The thermally conductive composite material provided in this embodiment of the invention includes a polymer matrix material and the aforementioned hexagonal boron nitride material.

[0065] In this embodiment of the invention, hexagonal boron nitride material is used as a filler. It has good compatibility with the polymer matrix, which can increase the filling amount of hexagonal boron nitride material in the thermally conductive composite material, improve the thermal conductivity of the thermally conductive composite material, and not reduce its insulation. At the same time, it can reduce the viscosity of the thermally conductive composite material and improve its rheological properties.

[0066] Specifically, the thermally conductive composite material in the embodiments of the present invention can be liquid, that is, it has rheological properties, and can be used as a fluid encapsulation material, such as an encapsulating material.

[0067] In some embodiments, the polymer matrix material may include silicone oil and / or epoxy resin, such as vinyl silicone oil. By adding the hexagonal boron nitride material of the present invention, the rheological properties of these polymer matrix materials can be effectively improved, their viscosity reduced, and the application of the formed thermally conductive composite material facilitated. Simultaneously, the hexagonal boron nitride material has good compatibility with these polymer matrix materials, allowing for an increase in the filling amount of the hexagonal boron nitride material, thereby improving the thermal conductivity and other properties of the formed thermally conductive composite material without affecting its insulation properties.

[0068] In some embodiments, the filling amount of hexagonal boron nitride material in the thermally conductive composite material (i.e., the mass ratio of hexagonal boron nitride material to thermally conductive composite material) in the above-mentioned thermally conductive composite material can be 30% to 60%, for example, a range of 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any combination thereof.

[0069] In some embodiments, the preparation method of the above-mentioned thermally conductive composite material may include: mixing hexagonal boron nitride material and polymer material for forming a polymer matrix, stirring evenly, and then performing degassing and other treatments to obtain a thermally conductive composite material (liquid state). When applying the above-mentioned thermally conductive composite material, the thermally conductive composite material may be cured as needed.

[0070] The present invention will be further described below through specific embodiments.

[0071] Example 1

[0072] (1) Hydrophilic modification treatment

[0073] Flaky hexagonal boron nitride raw material and glucose were mixed at a mass ratio of 100:0.5, and water was added to prepare a first slurry. The first slurry was ball-milled for 4 hours, then centrifuged, washed with water, and the resulting solid product was dried to obtain modified hexagonal boron nitride raw material.

[0074] (2) Preparation of the second slurry

[0075] Modified hexagonal boron nitride raw material and t-BN nanosphere powder were mixed evenly in a mixer at a mass ratio of 20:1 and placed in a reaction vessel. A mixed solution of water and ethanolamine at a mass ratio of 40:1 was added to the reaction vessel, and the mixture was mechanically stirred at 500 r / min for 3 h to ensure that the modified hexagonal boron nitride raw material was completely wetted and mixed evenly. Then, PVA solution was added to obtain a second slurry. The mass ratio of modified hexagonal boron nitride raw material, ethanolamine, PVA, t-BN nanospheres, and water was 20:1:0.2:1:80 (the mass content of modified hexagonal boron nitride raw material in the second slurry was about 20%). The PVA solution was prepared as follows: PVA (polyvinyl alcohol) and water were mixed at a mass ratio of 0.2:40 and heated at 90℃ for 1 h to obtain a clear solution (i.e., PVA solution).

[0076] (3) Spray drying

[0077] The second slurry was mechanically stirred at 500 rpm for 2 hours in a 60℃ water bath. Then, the slurry was maintained at 60℃ in the water bath and spray-dried using a spray dryer with the inlet temperature set to 230℃ to ensure rapid drying of the particles after spraying. Spherical particles were collected in the collection chamber and on the walls of the drying chamber. (The microstructure of the spherical particles was observed using a scanning electron microscope; SEM images of the spherical particles are shown below.) Figure 1 ( Figure 1 (a) is a SEM image of the spherical particle product in the collection chamber. Figure 1 (b) is a SEM image of the spherical particle product collected from the wall of the drying chamber container;

[0078] (4) De-glue

[0079] The spherical particles are placed in a high-temperature furnace and heated to 500°C in an air atmosphere for 4 hours to remove the glue.

[0080] (5) Sintering

[0081] The spherical particle product was placed in a high-temperature furnace, and nitrogen protective gas was introduced. The temperature was increased to 1500℃ at a rate of 5℃ / min and held for 6 hours (i.e., sintering) to obtain the sintered product.

[0082] (6) Screening

[0083] The sintered product obtained in step (4) is passed through an 80-mesh standard sieve to remove a small amount of oversized particles and impurities, and hexagonal boron nitride material product is obtained.

[0084] Figure 2 The image shows a SEM image of the hexagonal boron nitride material product prepared in Example 1, with an average particle size D50 of 35 μm; from Figure 2As can be seen, the hexagonal boron nitride material product prepared in Example 1 has good sphericity and large size.

[0085] Example 2: The difference from Example 1 is that in step (2), the mass ratio of modified hexagonal boron nitride raw material to water is 20:40 (the mass content of modified hexagonal boron nitride raw material in the second slurry is about 33%), and the other conditions are the same as in Example 1; Figure 3 The image shows the SEM image of the hexagonal boron nitride material product prepared in Example 2; its average particle size D50 is 55 μm; the hexagonal boron nitride material prepared in Example 2 has good sphericity and large size, and the aggregate particles therein are more compact and have a higher tap density.

[0086] Example 3: The difference from Example 1 is that carboxymethyl cellulose (CMC) was used instead of PVA; all other conditions were the same as in Example 1. The SEM image of the hexagonal boron nitride material product obtained in Example 3 is shown below. Figure 4 It has good sphericity and large size, with an average particle size D50 of about 58 μm.

[0087] Example 4: The difference from Example 1 is that diethanolamine is used instead of ethanolamine, and the other conditions are the same as in Example 1; the hexagonal boron nitride material product obtained in Example 4 has good sphericity and large size.

[0088] Example 5: The difference from Example 1 is that low-melting-point glass powder (melting point 900-1000℃) is used instead of t-BN nanosphere powder, and the other conditions are the same as in Example 1; the hexagonal boron nitride material product obtained in Example 5 has good sphericity and large size.

[0089] Example 6: The difference from Example 1 is that in step (3), the water bath temperature of the second slurry is 70°C (that is, the second slurry is mechanically stirred at 500 r / min for 2 hours under the heating of a 70°C water bath, and then the second slurry is kept in the heating state of a 70°C water bath and spray dried by a spray dryer). The other conditions are the same as in Example 1. The hexagonal boron nitride material product obtained in Example 6 has good sphericity and large size.

[0090] Example 7: The difference from Example 1 is that in step (5), ammonia is used instead of nitrogen as the protective gas (i.e., the process of step (5) is: place the spherical particle product in a high-temperature furnace, introduce ammonia as protective gas, raise the temperature to 1500℃ at a heating rate of 5℃ / min and keep it at 6h to obtain hexagonal boron nitride material), and the other conditions are the same as in Example 1; the hexagonal boron nitride material product obtained in Example 7 has good sphericity and large size.

[0091] The average particle size D50 of the hexagonal boron nitride material products obtained after sieving in each embodiment (see product particle size D50 in Table 1) is summarized in Table 1. In each embodiment, the mass of the hexagonal boron nitride material products that reach the average particle size D50 accounts for more than 85% of the total mass of the hexagonal boron nitride material before sieving.

[0092] Table 1

[0093]

[0094] Performance testing

[0095] 1. Epoxy Resin System Testing

[0096] Using the flake-shaped hexagonal boron nitride raw material from Example 1 (Comparative Example 1) and the hexagonal boron nitride material products obtained in each example as fillers, thermally conductive composite materials were prepared according to the following process, and their viscosity and maximum filler loading were tested: 30g of boron nitride powder product was added to 70g of epoxy resin EPIKOTE828EL, and stirred thoroughly for 30 minutes to obtain a uniform adhesive solution. After standing to remove bubbles, the thermally conductive composite material was obtained (where the filler loading was 30%). The viscosity of the thermally conductive composite material with a 30% filler loading was tested, and the maximum filler loading was also tested (exceeding the maximum filler loading would result in excessively high viscosity of the thermally conductive composite material (exceeding 10%). 6 (mPa·s) cannot form a uniform system, and excess powder will be free outside the system. The results are shown in Table 2.

[0097] 2. Silicone oil system testing

[0098] Using the hexagonal boron nitride material products prepared in each embodiment as fillers, thermally conductive composite materials were prepared according to the following process, and their viscosity and maximum filler content were tested: 30g of boron nitride powder product was added to 70g of vinyl silicone oil and stirred thoroughly for 30 minutes to obtain a uniform adhesive solution. After standing to remove bubbles, the thermally conductive composite material was obtained (where the filler content was 30%). The viscosity of the thermally conductive composite material with a 30% filler content was tested, and the maximum filler content was also tested (exceeding the maximum filler content would result in excessively high viscosity of the thermally conductive composite material (exceeding 10%). 6 (mPa·s) cannot form a uniform system, and excess powder will be free outside the system. The results are shown in Table 2.

[0099] Table 2

[0100]

[0101] As can be seen from Table 2, compared with Comparative Example 1, the hexagonal boron nitride material products prepared by Examples 1 to 7 can significantly reduce the viscosity of the epoxy resin system and silicone oil system, improve the rheological properties of the prepared thermally conductive composite material, and at the same time, can significantly increase the filling amount of the hexagonal boron nitride material product in the composite thermally conductive material, thereby improving the thermal conductivity and other properties of the composite thermally conductive material.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hexagonal boron nitride material, characterized in that, Includes the following steps: Hexagonal boron nitride raw material is subjected to hydrophilic modification treatment. Through the hydrophilic modification treatment, hydrophilic groups are introduced onto the hexagonal boron nitride raw material to obtain modified hexagonal boron nitride raw material. The hydrophilic groups include hydroxyl and / or amino groups. The modified hexagonal boron nitride raw material, surfactant, polymer binder, sintering aid and dispersion medium are mixed to prepare a second slurry; the surfactant includes alkanolamine compounds; the sintering aid includes amorphous hexagonal boron nitride and low melting point glass powder, or amorphous hexagonal boron nitride, wherein the melting point of the low melting point glass powder is 450~1200℃. The second slurry is spray-dried to form spherical granular products; The spherical particle product is sintered to obtain the hexagonal boron nitride material; the sintering temperature is 1200-1700℃ and the sintering time is 2-10 h. The hexagonal boron nitride raw material is plate-shaped hexagonal boron nitride; The mass ratio of the surfactant to the hexagonal boron nitride raw material is (1~10):100; The mass ratio of the polymer binder to the hexagonal boron nitride raw material is (0.5~2):100; The mass ratio of the sintering aid to the hexagonal boron nitride raw material is (0.5~5):

100.

2. The method for preparing hexagonal boron nitride material according to claim 1, characterized in that, The hydrophilic modification process includes: mixing the hexagonal boron nitride raw material with a modifier for introducing the hydrophilic groups onto the modified hexagonal boron nitride raw material and preparing a first slurry, followed by ball milling; or sintering and oxidizing the hexagonal boron nitride raw material in an air atmosphere; or ultrasonically treating the hexagonal boron nitride raw material in a polar solvent.

3. The method for preparing hexagonal boron nitride material according to claim 2, characterized in that, The modifier includes one or more of boric acid, glucose, and cellulose.

4. The method for preparing hexagonal boron nitride material according to claim 2, characterized in that, The conditions for the sintering oxidation treatment are: temperature 750~800℃, time 1~15min.

5. The method for preparing hexagonal boron nitride material according to claim 1, characterized in that, The alkanolamine compounds include one or more of ethanolamine, diethanolamine, triethanolamine, and alkanolamine borate esters; And / or, the polymer binder includes one or more of polyethylene glycol, polyvinyl alcohol, and carboxymethyl cellulose.

6. The method for preparing hexagonal boron nitride material according to any one of claims 1-5, characterized in that, The spray drying is carried out using a spray dryer, wherein the inlet temperature of the spray dryer is 200~300℃ and the outlet temperature is greater than or equal to 120℃.

7. The method for preparing hexagonal boron nitride material according to any one of claims 1-5, characterized in that, The spherical particle product is first subjected to a debinding treatment before sintering; wherein the debinding treatment is carried out in an air atmosphere at a temperature of 500~700℃.

8. The method for preparing hexagonal boron nitride material according to any one of claims 1-5, characterized in that, The sintering is carried out in an atmosphere containing reducing gas and / or inert gas.

9. A hexagonal boron nitride material, characterized in that, It is prepared according to the preparation method described in any one of claims 1-8.

10. A thermally conductive composite material, characterized in that, It includes polymer matrix materials and the hexagonal boron nitride material as described in claim 9.

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