High-thermal-conductivity boron nitride composite film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heat-conducting composite materials, and particularly relates to a high-heat-conductivity boron nitride composite film and a preparation method and application thereof. The boron nitride composite film is prepared from the following raw materials: boron nitride nanosheets serving as heat-conducting filler; the cellulose nanofiber is used as a polymer matrix; wherein the mass ratio of the boron nitride nanosheets to the cellulose nanofibers is (4: 6)-(6: 4); the average transverse size of the boron nitride nanosheet is 3-20 [mu] m, the thickness is 48-201 nm, and the aspect ratio is greater than or equal to 200. Through combination of vacuum filtration and a cold pressing process and control of the size and the use amount of the boron nitride nanosheets, high in-plane orientation and close contact of the boron nitride nanosheets in the boron nitride composite film are realized, formation of an efficient heat conduction network is facilitated, the in-plane heat conductivity of the obtained film is up to 74.97 Wm <-1 > K <-1 >, and the in-plane heat conductivity of the obtained film is up to 74.97 Wm <-1 > K <-1 >. Meanwhile, the material has high insulativity, flexibility and thermal stability, and is suitable for the field of thermal management of electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive composite material technology, specifically relating to a high thermal conductivity boron nitride composite film, its preparation method, and its application. Background Technology

[0002] With the continuous increase in power density of electronic devices, thermal management has become a key factor restricting their performance and reliability. Polymer-based thermally conductive composite materials have attracted widespread attention due to their advantages such as lightweight, ease of processing, and insulation. Among them, two-dimensional boron nitride nanosheets (BNNS) are considered ideal fillers due to their high in-plane thermal conductivity and excellent insulation properties. However, boron nitride nanosheets tend to agglomerate in polymer matrices, have low orientation, and high interfacial thermal resistance, resulting in composite materials with thermal conductivity far lower than theoretical values.

[0003] In existing technologies, methods such as shear-induced orientation and evaporation self-assembly are often used to improve the orientation degree of boron nitride nanosheets in composite materials. However, these methods are often characterized by complex equipment, difficult process control, and low efficiency. These problems severely limit the application of boron nitride nanosheet composite materials in practical thermal management.

[0004] Patent application CN120111837A discloses a boron nitride thermal conductive film and its preparation method. The boron nitride thermal conductive film is prepared using coating technology and roll forming technology. Deionized water is selected as the solvent, which is environmentally friendly. The preparation method is simple, fast, efficient, and low-cost, and can be industrialized on a large scale. Through the coating process, the boron nitride nanosheets in the slurry can be oriented to form a thermally conductive network inside the boron nitride thermal conductive film, giving it excellent thermal conductivity. The in-plane thermal conductivity of the final thermal conductive film can reach 54.46 W / (m·K).

[0005] Patent application CN110922719A discloses a high thermal conductivity boron nitride / epoxy resin composite material, its preparation method, and its application. In this method, boron nitride powder is subjected to ultrasonic exfoliation and functionalization with a silane coupling agent, which covalently bonds boron nitride and epoxy resin, improving the interfacial compatibility and bonding strength between the two, thereby reducing interfacial thermal resistance and increasing the thermal conductivity of the composite material. Combined with spin coating and hot pressing, boron nitride can be oriented along the film plane, improving the in-plane thermal conductivity of the composite film.

[0006] However, effectively converting the high intrinsic thermal conductivity of boron nitride nanosheets into high macroscopic thermal conductivity of composite materials faces two major challenges: First, boron nitride nanosheets tend to randomly distribute and aggregate in polymer matrices, making it difficult to form continuous and efficient thermal conduction pathways; second, even if boron nitride nanosheets are oriented to a certain extent, the contact thermal resistance between their layers remains high, severely hindering the trans-interface transport of phonons. Currently, vacuum filtration is a commonly used technique for preparing oriented boron nitride nanosheet films, utilizing the directional flow of the liquid during filtration to align the boron nitride nanosheets in the in-plane direction. However, films obtained solely through vacuum filtration often exhibit nanoscale voids and large interlayer spacing between BNNS layers, and there is still room for improvement in orientation, resulting in an in-plane thermal conductivity typically limited to 20-30 W / m². -1 K -1 This makes it difficult to meet the heat dissipation requirements of future high-power devices. Although methods such as hot pressing and high-temperature sintering can improve density, they may cause thermal degradation of the polymer matrix, impairing its flexibility.

[0007] Therefore, developing a composite film with high orientation and good thermal conductivity of boron nitride nanosheets, and achieving low-energy, large-scale preparation of large-size boron nitride, remains a key problem that urgently needs to be solved. Summary of the Invention

[0008] The primary objective of this invention is to provide a high thermal conductivity boron nitride composite film. This boron nitride composite film exhibits high thermal conductivity, high insulation, and high orientation. By combining vacuum filtration with cold pressing processes, and by controlling the size and amount of boron nitride nanosheets, the in-plane orientation and interfacial contact of the boron nitride nanosheets in the boron nitride composite film are effectively improved, thereby significantly increasing the thermal conductivity of the composite material.

[0009] The second objective of this invention is to provide a method for preparing the boron nitride composite film as described above.

[0010] The third objective of this invention is to provide a heat dissipation device.

[0011] To achieve the first objective mentioned above, the present invention adopts the following technical solution: This invention discloses a high thermal conductivity boron nitride composite film, wherein the raw materials for forming the boron nitride composite film include: Boron nitride nanosheets (BNNS) are used as thermally conductive fillers. Cellulose nanofibers (CNF) serve as a polymer matrix; The mass ratio of boron nitride nanosheets to cellulose nanofibers is 4:6-6:4; for example, the mass ratio of boron nitride nanosheets to cellulose nanofibers can be 4:6, 5:5 or 6:4, etc. The boron nitride nanosheets have an average lateral dimension of 3-20 μm, a thickness of 48-201 nm, and an aspect ratio of ≥200.

[0012] Furthermore, the boron nitride nanosheets can achieve high in-plane orientation in the boron nitride composite film, with an orientation factor ≥ 0.62.

[0013] The lateral dimensions of boron nitride nanosheets significantly affect the thermal conductivity of the composite films prepared from them. Larger lateral dimensions result in weaker phonon scattering during heat conduction, which is more conducive to forming efficient heat transport pathways. Therefore, using large-size boron nitride with a high aspect ratio is one of the key strategies for improving the thermal conductivity of composite materials. Traditional preparation methods, such as physical vapor deposition and chemical exfoliation, can obtain large-size boron nitride nanosheets, but they suffer from problems such as long synthesis cycles, high energy consumption, and low cost-effectiveness. This invention provides an exemplary method for preparing large-size boron nitride with a high aspect ratio, the specific steps of which are as follows: The magnesium thermal combustion synthesis method was adopted, using boron oxide, magnesium oxide, and magnesium powder with a particle size of 75-125 μm as raw materials, and NH4Cl as catalyst. The raw materials were weighed according to the molar ratio of n(Mg):n(B2O3):n(MgO)=3.5:1:3, mixed, and ball-milled to obtain raw material powder. The raw material powder is loaded into a mold and placed in a high-pressure reaction chamber for combustion reaction under a nitrogen atmosphere of 0.4-0.6 MPa. After the reaction was completed, the sample was acid-washed and dried to obtain the boron nitride nanosheets.

[0014] Furthermore, the in-plane thermal conductivity of the boron nitride composite film is 56.23-74.97 W / m. -1 K -1 Volume resistivity ≥ 5.1 × 10⁻⁶ 8 Ωcm.

[0015] Furthermore, the thickness of the boron nitride composite film is 45-62 μm.

[0016] To achieve the second objective mentioned above, the present invention adopts the following technical solution: This invention discloses a method for preparing the boron nitride composite thin film as described above, comprising the following steps: A homogeneous slurry was obtained by mixing boron nitride nanosheets and cellulose nanofiber aqueous solution and then ultrasonically dispersing the mixture. Vacuum filtration yields the initial thin film. The nascent film is cold-pressed at a pressure of not less than 100 MPa to obtain a boron nitride composite film.

[0017] This invention achieves initial orientation of boron nitride nanosheets through vacuum filtration, followed by cold pressing to further compress the interlayer spacing, improve the orientation degree, increase the contact area between the boron nitride nanosheets, and form a continuous thermal conductivity network. After cold pressing, the film thickness decreases from 100-150 μm to 45-62 μm, the orientation factor increases from 0.2-0.3 to 0.51-0.62, and the thermal conductivity increases from 31.8-45.43 W / m². -1 K -1 Increased to 56.23-74.97 Wm -1 K -1 .

[0018] Furthermore, the concentration of the aqueous solution of the cellulose nanofibers is 1-3 wt%, and the length of the cellulose nanofibers is 2-4 μm.

[0019] Furthermore, the pressure of the vacuum filtration is ≤0.1 Pa, and the vacuum filtration time is 36-48 h.

[0020] Furthermore, the cold pressing pressure is 100-200 MPa, the cold pressing time is 10-20 min, and the cold pressing temperature is room temperature.

[0021] To achieve the third objective mentioned above, the present invention adopts the following technical solution: This invention discloses a heat dissipation device comprising the boron nitride composite thin film as described above.

[0022] Furthermore, the heat dissipation device consists of attaching the boron nitride composite film between the heat source and the heat sink, and enhancing the interface contact with thermal paste.

[0023] The beneficial effects of this invention are as follows: This invention prepares a BNNS / CNF composite film with high BNNS orientation, high thermal conductivity, and high insulation. The composite film has an in-plane thermal conductivity of up to 74.97 W / m. -1 K -1 It has good flexibility, thermal stability and cycle reliability, and its performance does not change after 100 cycles of testing. It is suitable for high-performance thermal management scenarios such as LED heat dissipation and CPU cooling.

[0024] This invention also provides a method for preparing BNNS / CNF composite films. By combining vacuum filtration and cold pressing processes, and by controlling the size and amount of boron nitride nanosheets, the orientation factor of boron nitride nanosheets in the composite film and the contact area between boron nitride nanosheets are greatly improved, which is conducive to forming a more continuous thermal conduction network, thereby achieving a breakthrough in the thermal conductivity of the composite film. Attached Figure Description

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0026] Figure 1 Electron micrographs of the boron nitride nanosheets used in Examples 1 and 5.

[0027] Figure 2 SEM images of the cross-sections of the composite thin films prepared in Example 1 and Comparative Example 1.

[0028] Figure 3 The 2D-WAXS patterns of the BNNS orientation in the composite films prepared in Example 1 and Comparative Example 1 are shown.

[0029] Figure 4 The temperature curves of the composite films prepared in Example 1 and Comparative Example 1 are compared in the LED heat dissipation test. Detailed Implementation

[0030] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0031] In this invention, the preparation methods are all conventional unless otherwise specified, and the raw materials used can be obtained from publicly available commercial sources or prepared according to existing technology unless otherwise specified.

[0032] The boron nitride nanosheets used in Examples 1-4 and Comparative Examples 1-2 were prepared according to the following process: The magnesium thermal combustion synthesis method (3Mg + B2O3 + N2 → 3MgO + 2BN) was adopted. The magnesium powder particle size was 125 μm, and the boron oxide powder particle size was 75 μm. 3.5 mol of magnesium powder, 1 mol of boron oxide powder and 3 mol of magnesium oxide powder were weighed out. The role of MgO was to inhibit the agglomeration of molten magnesium. 0.25 mol of NH4Cl was added as a catalyst. The mixture was mixed and ball-milled to obtain the raw material powder.

[0033] 200 g of loosely mixed raw material powder was packed into a porous graphite mold (100 mm wide, 200 mm long), and the mold was placed in a 30°C high-pressure reaction chamber filled with a 0.5 MPa N2 atmosphere. A current of approximately 60 A was applied to the adjacent tungsten coil for 3 seconds to ignite the reaction, which lasted approximately 120 seconds. After the reaction system cooled to room temperature, the sample was removed and surface impurities were cleaned. The product was then washed with a 1:1 mixture of 37 wt% concentrated HCl and 63 wt% concentrated HNO3 to thoroughly remove residual magnesium oxide and magnesium borate. Finally, the sample was dried at 80°C for 2 h to obtain the final product. The obtained boron nitride nanosheets had an average lateral dimension of 9.1 μm and a thickness of 48 nm. Electron micrographs of the boron nitride nanosheets are shown below. Figure 1 a.

[0034] Referring to the above method, by controlling the process steps and the particle size of magnesium powder, BNNS with an average lateral size of 6 μm and a thickness of approximately 48 nm can be obtained (used in Example 5 and Comparative Example 3). See the electron microscope images of the boron nitride nanosheets. Figure 1 b.

[0035] Example 1 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0036] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 20 g of 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain 100 g of uniform slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a nascent film. The nascent film was cold-pressed at 25 °C and 200 MPa for 10 min to obtain a boron nitride composite film, denoted as 50BNNS / 50CNF-200 MPa.

[0037] The boron nitride composite film was tested to have a thickness of 55 μm, an orientation factor of 0.62 for the boron nitride nanosheets, and an in-plane thermal conductivity of 74.97 W / m². -1 K -1 The thermal diffusivity is 28 mm. 2 / s, dielectric constant is 7.5, volume resistivity is 5.1×10 8 Ωcm.

[0038] Example 2 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0039] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.16 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 24 g of 1 wt% CNF solution, diluted with 75.84 g of water, and stirred at high speed for 3 min to obtain 100 g of uniform slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a nascent film. The nascent film was cold-pressed at 25 °C and 200 MPa for 10 min to obtain a boron nitride composite film, denoted as 40BNNS / 60CNF-200 MPa.

[0040] The boron nitride composite film was tested and found to have a thickness of 45 μm and an in-plane thermal conductivity of 56.23 W / m. -1 K -1 .

[0041] Example 3 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0042] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.24 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 16 g of 1 wt% CNF solution, diluted with 83.76 g of water, and stirred at high speed for 3 min to obtain a homogeneous slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a nascent film. The nascent film was cold-pressed at 25 °C and 200 MPa for 10 min to obtain a boron nitride composite film, denoted as 60BNNS / 40CNF-200 MPa.

[0043] The boron nitride composite film was tested and found to have a thickness of 62 μm and an in-plane thermal conductivity of 63.10 W / m. -1 K -1 .

[0044] Example 4 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0045] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain 100 g of uniform slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a nascent film. The nascent film was cold-pressed at 25 °C and 100 MPa for 10 min to obtain a boron nitride composite film, denoted as 50BNNS / 50CNF-100 MPa.

[0046] The boron nitride composite film was tested and found to have a thickness of 78 μm and an in-plane thermal conductivity of 58.3 W / m. -1 K -1 .

[0047] Example 5 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0048] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 6 μm and a thickness of approximately 48 nm was mixed with 20 g of 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain a homogeneous slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a boron nitride composite film.

[0049] The nascent film was cold-pressed at 25 °C and 200 MPa for 10 min to obtain a boron nitride composite film, denoted as 50BNNS / 50CNF-3-200 MPa.

[0050] The boron nitride nanosheets in the boron nitride composite film were tested to have an orientation factor of 0.61 and an in-plane thermal conductivity of 57.22 W / m². -1 K -1 .

[0051] Comparative Example 1 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0052] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain a homogeneous slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a boron nitride composite film.

[0053] Tests showed that the orientation factor of boron nitride nanosheets in the boron nitride composite film was 0.30, and the in-plane thermal conductivity was 45.43 W / m². -1 K -1 .

[0054] Comparative Example 2 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0055] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 9.1 μm and a thickness of about 48 nm was mixed with 20 g of 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain a homogeneous slurry. Pour 50 g of slurry into a flat mold and let it air dry to obtain a boron nitride composite film.

[0056] The obtained thin film has a thermal conductivity of 12.5 W / m². -1 K -1 .

[0057] Comparative Example 3 Raw materials: boron nitride nanosheets (BNNS), 1 wt% CNF aqueous solution.

[0058] This example provides a method for preparing a high thermal conductivity boron nitride composite thin film, the steps of which are as follows: 0.2 g of BNNS with an average transverse dimension of 6 μm and a thickness of approximately 48 nm was mixed with 20 g of 1 wt% CNF solution, diluted with 79.8 g of water, and stirred at high speed for 3 min to obtain a homogeneous slurry. 50 g of slurry was poured into a vacuum filtration device and filtered at 0.1 Pa for 48 h to obtain a boron nitride composite film.

[0059] Tests showed that the orientation factor of boron nitride nanosheets in the boron nitride composite film was 0.31, and the in-plane thermal conductivity was 32.8 W / m². -1 K -1 .

[0060] Figure 2 Electron microscopy images of the boron nitride composite films prepared in Example 1 and Comparative Example 1 are shown. The images demonstrate the effect of cold pressing on the alignment of boron nitride nanosheets (BNNS) in the composite films. Compared to Comparative Example 1 without cold pressing, the orientation order of the BNNS in the composite film prepared in Example 1 is significantly enhanced after cold pressing. The thickness of the composite film decreases from 120 μm in Comparative Example 1 to 55 μm in Example 1, while the interlayer distance is significantly reduced.

[0061] Figure 3 The 2D-WAXS spectra of the boron nitride composite films prepared in Example 1 and Comparative Example 1 are presented. The figures show the effect of cold pressing on the orientation structure of the BNNS. In Comparative Example 1 without cold pressing, the orientation factor (H) of the BNNS is 0.3, while in Example 1 with cold pressing, the orientation factor of the BNNS increases to 0.6, indicating that this process significantly improves the directional alignment of BNNS in the boron nitride composite film.

[0062] Figure 4 This paper demonstrates a performance comparison of the boron nitride composite films prepared in Example 1 and Comparative Example 1 for heat dissipation applications in high-power LED lamps. The boron nitride composite films prepared in Example 1 and Comparative Example 1 were respectively adhered tightly to the surface of a high-power light-emitting diode (LED) using highly thermally conductive silicone grease. The other side of the film was also connected to an aluminum heat sink using thermally conductive silicone grease to simulate a real heat dissipation scenario. Under the same input power (10 V voltage, 700 mA current) and 100 cycle tests, the LED containing the boron nitride composite film of Example 1 maintained a stable center temperature of approximately 68 °C, which is 28 °C lower than that containing the boron nitride composite film of Comparative Example 1. This fully demonstrates that the composite film provided by this invention possesses excellent heat dissipation capability and thermal stability.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A high thermal conductive boron nitride composite film, characterized by, The raw material for forming the boron nitride composite film comprises: boron nitride nanosheets as a heat-conducting filler; cellulose nanofibers as a polymer matrix; wherein the mass ratio of the boron nitride nanosheets to the cellulose nanofibers is 4:6-6:4; the boron nitride nanosheets have an average lateral dimension of 3-20 μm, a thickness of 48-201 nm, and an aspect ratio ≥200.

2. The boron nitride composite film according to claim 1, wherein the orientation factor of the boron nitride nanosheets in the boron nitride composite film is ≥0.

62.

3. The boron nitride composite film according to claim 1, wherein The boron nitride nanosheets are prepared by the following steps: a magnesium hot combustion synthesis method is used, boron oxide, magnesium oxide, and magnesium powder with a particle size of 75-125 μm are used as raw materials, NH4Cl is used as a catalyst, the raw materials are weighed according to the molar ratio of n(Mg):n(B2O3):n(MgO)=3.5:1:3, mixed, ball milled, and the raw material powder is obtained; the raw material powder is loaded into a mold and placed in a high-pressure reaction chamber for combustion reaction under a nitrogen atmosphere of 0.4-0.6 MPa; after the reaction is completed, the boron nitride nanosheets are obtained by acid washing and drying.

4. The boron nitride composite film according to claim 1, wherein The in-plane thermal conductivity of the boron nitride composite film is 56.23-74.97 Wm -1 K -1 , and the volume resistivity is ≥5.1×10 8 Ωcm.

5. The method of claim 1 to 4, wherein comprising the following steps: mixing the boron nitride nanosheets and the cellulose nanofiber aqueous solution, and obtaining a uniform slurry after ultrasonic dispersion; vacuum suction filtration to obtain a nascent film; cold pressing the nascent film at a pressure not less than 100 MPa to obtain the boron nitride composite film.

6. The preparation method according to claim 5, characterized in that, The concentration of the cellulose nanofiber aqueous solution is 1-3 wt%, and the length of the cellulose nanofibers is 2-4 μm.

7. The preparation method according to claim 5, characterized in that, The pressure of the vacuum suction filtration is ≤0.1 pa, and the time of the vacuum suction filtration is 36-48 h.

8. The preparation method according to claim 5, characterized in that, The pressure of the cold pressing is 100-200 MPa, and the time of the cold pressing is 10-20 min.

9. A heat dissipating device, characterized by, The boron nitride composite film according to any one of claims 1-4.

10. The heat dissipating device according to claim 9, wherein, The heat dissipation device is obtained by attaching the boron nitride composite film between a heat source and a heat sink and enhancing the interface contact through a heat-conducting paste.

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