BN-PI / BMI composite insulating material and preparation method and application thereof

Abstract

The invention discloses a BN-PI / BMI composite insulating material and a preparation method and application thereof, and belongs to the technical field of high-performance composite insulating materials and preparation thereof. The problems that the heat conductivity of an existing PI-based composite material is limited to be improved, the insulating property and the heat-conducting property are difficult to collaboratively optimize, and an efficient three-dimensional heat-conducting network construction method is lacked are solved. The BN / PI insulation paper layers and the BN / BMI adhesive layers are used for constructing a multi-layer composite structure, the BN / BMI adhesive layers are used as thermal bridges, BN filler in the adjacent BN / PI layers is effectively connected, the composite film with a three-dimensional heat conduction network penetrating through the thickness direction is successfully prepared, interlayer interface thermal resistance is remarkably reduced, and efficient cross-layer transfer of heat is achieved. Test results show that the in-plane thermal conductivity of the obtained composite film can reach 7.62 W.m <-1 >. K <-1 >, and is increased by about 38 times compared with that of a pure PI material (about 0.2 W.m <-1 >. K <-1 >).

Description

Technical Field

[0001] This invention relates to a BN-PI / BMI composite insulating material, its preparation method, and its application, belonging to the technical field of high-performance composite insulating materials and their preparation. Background Technology Polyimide (PI) is widely used in aerospace, microelectronics, and transportation fields due to its excellent heat resistance, mechanical strength, and electrical insulation properties. However, pure PI materials have extremely low intrinsic thermal conductivity (approximately 0.2 W·m). -1 ·K -1 The high thermal conductivity of polyimide (PI) severely limits its heat dissipation capabilities in high-power-density electronic devices. Localized heat accumulation during device operation can lead to thermal stress, material aging, and even device failure, affecting system stability and lifespan. Existing methods for improving PI thermal conductivity mainly include molecular structure design and filling with thermally conductive fillers. Molecular structure design is complex and difficult to scale up. Furthermore, while filling with metal or carbon-based fillers can improve thermal conductivity, it sacrifices the material's electrical insulation and increases density, making it unsuitable for applications with stringent weight and insulation requirements, such as aerospace. Ceramic fillers such as boron nitride (BN) offer the advantages of high thermal conductivity (up to 300 W·m³). -1 ·K -1 ) and excellent electrical insulation (>10) 14 With a thermal conductivity of Ω·cm, BN filler is an ideal choice. However, the poor interfacial bonding and severe phonon mismatch between BN filler and the PI matrix result in high interfacial thermal resistance, making it difficult to form an effective thermal conduction path and limiting the improvement of the overall thermal conductivity of the composite material. In addition, traditional uniformly dispersed or single-layer structures are difficult to construct a through-hole three-dimensional thermally conductive network, resulting in low thermal management efficiency. Therefore, there is an urgent need to develop a PI-based composite insulating material and its preparation method that can significantly improve thermal conductivity, maintain excellent electrical insulation properties, and construct an efficient 3D thermally conductive network. Summary of the Invention

[0002] This invention addresses the problems of limited improvement in thermal conductivity of existing PI-based composite materials, difficulty in synergistic optimization of insulation and thermal conductivity, and lack of efficient methods for constructing three-dimensional thermal conductive networks. It provides a BN-PI / BMI composite insulation material, its preparation method, and its applications.

[0003] The technical solution of the present invention: One objective of this invention is to provide a method for preparing a BN-PI / BMI composite insulating material, characterized by comprising: (1) After adding the dry BN powder to DMAc and mixing it evenly by ultrasonication, ODA is added under ice-water bath conditions and stirred until completely dissolved. PMDA is added in batches and the reaction is continued by stirring. After defoaming, the gel solution I is obtained. (2) After mixing the dry BN powder with BMI, add it to DMAc, heat and stir until uniformly dispersed to obtain solution II; (3) The adhesive solution I was treated by electrospinning process, and the obtained wet film was subjected to gradient heating imidization treatment to obtain BN / PI composite insulating paper; (4) Stack multiple sheets of BN / PI composite insulating paper, apply adhesive II evenly between the layers, and place them in a laminator for hot pressing and curing to obtain BN-PI / BMI composite insulating material.

[0004] Further specified, in (1) the molar ratio of ODA to PMDA is 1:1.

[0005] Further, in (1), the ratio of the total mass of ODA and PMDA to the mass of DMAc is 3.8~4.1:20.

[0006] Further, the ultrasound time in (1) is 1-2 hours.

[0007] Further specifying, the reaction time in (1) under ice-water bath conditions is 1.5-2.5h.

[0008] Further specifying, (1) the BN powder is in flake form with a particle size of 20~30μm.

[0009] Further specified, in (2) the mass ratio of BMI to BN powder is 1:1.

[0010] Further, in (2), the stirring temperature is 80-100℃ and the time is 0.5-1h.

[0011] Further specifying, the electrospinning process conditions in (3) are: positive voltage 14-18kV, negative voltage -3.0~-4.0kV, receiving distance 20-25cm, advancing speed 0.08-0.12mm / min, and spinning time 5-7h.

[0012] Further specifying, the electrospinning process conditions in (3) are: positive voltage 15kV, negative voltage -3.5kV, receiving distance 24cm, pushing speed 0.09mm / min, and spinning time 6h.

[0013] Further, in (3), the gradient heating imidization treatment has a heating rate of 5~10℃ / min and a temperature range of 80~350℃.

[0014] Further specifying, the gradient heating imidization process in (3) is as follows: heating at a rate of 5~10℃ / min and holding at 80~100℃ for 15-25min, continuing to heat to 120~140℃ and holding for 15-25min, continuing to heat to 160~180℃ and holding for 15-25min, continuing to heat to 200~220℃ and holding for 15-25min, continuing to heat to 250~270℃ and holding for 50-70min, continuing to heat to 300~320℃ and holding for 50-70min, and finally heating to 340~360℃ and holding for 50-70min.

[0015] Further specifying, (3) the mass fraction of BN powder in the obtained BN / PI composite insulating paper is 0~20%.

[0016] Furthermore, (3) the mass fraction of BN powder in the obtained BN / PI composite insulating paper is 5~20%.

[0017] Further specifying, the hot-press curing conditions in (4) are: under a constant pressure of 1MPa, preheat to 110℃ and keep warm for 1h; then heat up and cure according to the following procedure: keep warm at 110℃ for 1.5h, keep warm at 150℃ for 1.5h, keep warm at 180℃ for 1.5h, keep warm at 200℃ for 1.5h, keep warm at 230℃ for 3h, and finally cool naturally to room temperature.

[0018] Further specifying, the amount of BN / PI composite insulating paper in (4) is 3.

[0019] Further specifying, (4) the coating amount of adhesive solution II is 3~5 g / cm³. 2 .

[0020] The second objective of this invention is to provide a BN-PI / BMI composite insulating material obtained by the above preparation method.

[0021] Furthermore, the in-plane thermal conductivity of the BN-PI / BMI composite insulation material is specified to be no less than 7.62 W·m. -1 ·K -1 The DC breakdown strength is not less than 204.7 kV·mm. -1 , in 10 1 ~10 6 The dielectric loss of Hz is less than 0.02.

[0022] Further specifying, when the mass fraction of BN powder in the BN / PI composite insulating paper is 10%, the tensile strength of the obtained BN-PI / BMI composite insulating material is not less than 312 MPa.

[0023] Further specifying that when the mass fraction of BN powder in the BN / PI composite insulating paper is 20%, the ratio of in-plane to out-of-plane thermal conductivity of the obtained BN-PI / BMI composite insulating material is not less than 10.04.

[0024] The residual weight of BN-PI / BMI composite insulation material is further limited to not less than 40% at 25~800℃.

[0025] The third objective of this invention is to provide an application of the above-mentioned BN-PI / BMI composite insulating material in the thermal management and insulation protection of high-power electronic devices in aerospace.

[0026] Beneficial effects: (1) This invention constructs a multilayer composite structure using BN / PI insulating paper layers and BN / BMI adhesive layers. The BN / BMI adhesive layer acts as a "thermal bridge," effectively connecting the BN fillers in adjacent BN / PI layers. This successfully prepares a composite film with a three-dimensional (3D) thermally conductive network extending through the thickness direction, significantly reducing interlayer thermal resistance and achieving efficient cross-layer heat transfer. Furthermore, the hot-pressing curing process promotes the in-plane orientation of the BN sheets, further enhancing in-plane thermal conductivity. Experimental results show that the in-plane thermal conductivity of the obtained composite film can reach 7.62 W·m. -1 ·K -1 Pure PI material (approximately 0.2 W·m) -1 ·K -1 It increased by nearly 38 times.

[0027] (2) This invention constructs a multilayer composite structure by using a BN / PI insulating paper layer and a BN / BMI adhesive layer to form a heterogeneous PI / BN-BMI interface. This interface induces the Maxwell-Wagner-Sillars (MWS) polarization effect, forming an interface trap, which effectively suppresses carrier migration. This allows the material to maintain excellent electrical insulation performance under high thermal conductivity, with a breakdown strength as high as 204.7 kV·mm. -1 The dielectric loss is less than 0.02.

[0028] (3) The method of composite thin film with a three-dimensional (3D) thermal conductive network that runs through the thickness direction provided by the present invention is simple and controllable, easy to scale up production, and provides a high-performance integrated material solution for solving the heat dissipation and insulation problems of high-power electronic devices, and has broad application prospects. Attached Figure Description

[0029] Figure 1 Analysis of out-of-plane and in-plane thermal conductivity of composite films prepared for different embodiments; Figure 2 TG and DTG analysis chromatograms of composite films prepared for different embodiments; Figure 3 Breakdown field strength (Weibull distribution) performance analysis of composite films prepared for different embodiments; Figure 4 Analysis of dielectric constant and dielectric loss properties of composite films prepared for different embodiments; Figure 5 Mechanical property analysis diagrams of composite films prepared for different embodiments; Figure 6 The image shows the cross-sectional scan and surface scan elemental distribution analysis of the composite thin film prepared in Example 1. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0034] Example 1: The method for preparing BN-PI / BMI composite insulating material (10wt% BN / PI-BMI) in this embodiment includes the following steps: Step 1, Preparation of BN-PAA adhesive solution: Dissolve 1.88g ODA in 20mL DMAc, add 3.08g BN powder (particle size 20-30μm), and ultrasonically disperse for 1h. Under ice-water bath conditions, add 2.05g PMDA in 4 portions, and continue stirring for 2h after all the powder has been added to obtain BN / PAA gel.

[0035] Step 2, Preparation of BN / BMI adhesive: Mix 10g of BMI resin with 10g of BN powder (particle size 20-30μm) and stir in an oil bath at 90℃ for 0.5h to obtain a BN / BMI adhesive with a BN content of 100wt%.

[0036] Step 3, Preparation of BN / PI insulating paper: The BN-PAA adhesive solution obtained in step 1 was electrospun (positive voltage 15kV, negative voltage -3.5kV, receiving distance 24cm, feed speed 0.09mm / min, time 6h) to obtain a fiber membrane. This membrane was then placed in an oven and heated at a rate of 5℃ / min to 80℃ and held for 20min, then further heated to 120℃ and held for 20min, then further heated to 160℃ and held for 20min, then further heated to 200℃ and held for 20min, then further heated to 250℃ and held for 60min, then further heated to 300℃ and held for 60min, and finally further heated to 350℃ and held for 60min, resulting in a BN / PI insulating paper with a thickness of approximately 30μm (BN content 10wt%).

[0037] Step 4, Preparation of composite thin film: Stack three layers of BN / PI insulating paper prepared in step 3, and uniformly coat the BN / BMI adhesive prepared in step 2 between the layers, with a coating amount of 4 g / cm³. 2 The material is placed in a hot press, subjected to a pressure of 1 MPa, preheated at 110℃ for 1 hour, and then cured by heating at 110℃ for 1.5 hours, 150℃ for 1.5 hours, 180℃ for 1.5 hours, 200℃ for 1.5 hours, and 230℃ for 3 hours. After natural cooling, it is demolded to obtain a multilayer composite insulating film, named 10wt% BN / PI-BMI.

[0038] Example 2: The difference between this embodiment and Embodiment 1 is that the amount of BN powder added in step 1 is 1.46g, so that the BN content in the PI layer is 5wt%. The remaining process steps and parameter settings are the same as in Embodiment 1, and a composite insulating film is obtained, named 5wt%BN / PI-BMI.

[0039] Example 3: The difference between this embodiment and Embodiment 1 is that the amount of BN powder added in step 1 is 4.9g, so that the BN content in the PI layer is 15wt%. The remaining process steps and parameter settings are the same as in Embodiment 1, and a composite insulating film is obtained, named 15wt%BN / PI-BMI.

[0040] Example 4: The difference between this embodiment and Embodiment 1 is that the amount of BN powder added in step 1 is 6.16g, so that the BN content in the PI layer is 20wt%. The remaining process steps and parameter settings are the same as in Embodiment 1, and a composite insulating film is obtained, named 20wt%BN / PI-BMI.

[0041] Comparative Example 1: The difference between this comparative example and Example 1 is that the amount of BN powder added in step 1 is 0g, so that the BN content in the PI layer is 0wt%. The remaining process steps and parameter settings are the same as in Example 1, and a composite insulating film is obtained, named 0wt% BN / PI-BMI.

[0042] Example of effect The microstructure and properties of the composite insulating films prepared in Examples 1-4 and Comparative Example 1 were characterized. The specific experimental procedures and results are as follows: (1) The out-of-plane thermal conductivity and in-plane thermal conductivity of the composite insulating films prepared in Examples 1-4 and Comparative Example 1 were tested using the transient planar source method (TPS). The results are as follows: Figure 1 As shown in the figure, the in-plane (k∥) and out-of-plane (k⊥) thermal conductivity of the composite film gradually increases with the increase of BN content in the PI layer. When the BN content is 20wt%, k∥ reaches 7.62 W·m. -1 ·K -1 k⊥ reaches 0.759 W·m -1 ·K -1 This is significantly higher than that of the pure PI film in Comparative Example 1 (k∥≈0.2W·m). -1 ·K -1 ).

[0043] (2) The TGA and DTG test results of the composite insulating films prepared in Examples 1-4 and Comparative Example 1 are as follows: Figure 2 As shown in the figure, the introduction of BN significantly improves the thermal stability of the composite material. The initial decomposition temperature (T5%) of the 20wt% BN / PI-BMI sample is about 50℃ higher than that of pure PI.

[0044] (3) The insulation properties of the composite insulating films prepared in Examples 1-4 and Comparative Example 1 were tested. Figure 3 Breakdown field strength (Weibull distribution) performance analysis of composite films prepared for different embodiments; Figure 4 The graphs show the dielectric constant and dielectric loss properties of the composite films prepared for different embodiments. As can be seen from the graphs, the DC breakdown strength of the 10wt% BN / PI-BMI sample reaches a peak of 204.7 kV·mm. -1 Furthermore, its dielectric loss is below 0.02 over a wide frequency range, demonstrating excellent insulation performance.

[0045] (4) The mechanical properties of the composite insulating films prepared in Examples 1-4 and Comparative Example 1 were tested, and the test results are as follows: Figure 5 As shown in the figure, the tensile strength of the 10wt% BN / PI-BMI sample reached 312.14 MPa, and the tensile strength of the 20wt% BN / PI-BMI sample reached 244.67 MPa, which is better than that of the pure PI film. This indicates that the introduction of BN and the good interfacial bonding enhance the mechanical properties of the material.

[0046] (5) The 10wt% BN / PI-BMI composite film prepared in Example 1 was analyzed by scanning electron microscopy (SEM), and its cross-sectional morphology is as follows: Figure 6 As shown in the image, the BN / BMI adhesive layer (intermediate layer) is tightly bonded to the upper and lower BN / PI insulating paper layers, with no obvious cracks or pores at the interface, forming a continuous and dense multilayer structure. The BN filler is uniformly dispersed in the PI layer without obvious agglomeration. Furthermore, the elemental mapping diagram shows that B and N elements are continuously distributed throughout the entire cross-section (including the PI and BMI layers), confirming that the BN filler forms a through-layer physical connection, providing direct microstructural evidence for the construction of the three-dimensional thermally conductive network.

[0047] The above results fully demonstrate that the present invention successfully constructs a highly efficient 3D thermally conductive network through multi-layer structure design and the introduction of BN / BMI thermal bridges, which significantly improves thermal conductivity while synergistically optimizing the electrical insulation, thermal stability and mechanical properties of the material.

[0048] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a BN-PI / BMI composite insulating material, characterized in that, include: (1) After adding the dry BN powder to DMAc and mixing it evenly by ultrasonication, ODA is added under ice-water bath conditions and stirred until completely dissolved. PMDA is added in batches and the reaction is continued by stirring. After defoaming, the gel solution I is obtained. (2) After mixing the dry BN powder with BMI, add it to DMAc, heat and stir until uniformly dispersed to obtain solution II; (3) The adhesive solution I was treated by electrospinning process, and the obtained wet film was subjected to gradient heating imidization treatment to obtain BN / PI composite insulating paper; (4) Stack multiple sheets of BN / PI composite insulating paper, apply adhesive II evenly between the layers, and place them in a laminator for hot pressing and curing to obtain BN-PI / BMI composite insulating material.

2. The preparation method according to claim 1, characterized in that, (1) The molar ratio of ODA to PMDA is 1:1; the total mass of ODA and PMDA to the mass ratio of DMAc is 3.8~4.1:

20.

3. The preparation method according to claim 1, characterized in that, (2) The mass ratio of BMI to BN powder is 1:

1.

4. The preparation method according to claim 1, characterized in that, (3) The electrospinning process conditions are: positive voltage 14-18kV, negative voltage -3.0~-4.0kV, receiving distance 20-25cm, feed speed 0.08-0.12mm / min, and spinning time 5-7h.

5. The preparation method according to claim 1, characterized in that, (3) The heating rate of the gradient heating imidization treatment is 5~10℃ / min, and the temperature range is 80~350℃.

6. The preparation method according to claim 1, characterized in that, (3) The mass fraction of BN powder in the obtained BN / PI composite insulating paper is 0~20%.

7. The preparation method according to claim 1, characterized in that, (4) The hot-press curing conditions are as follows: under a constant pressure of 1MPa, preheat to 110℃ and keep warm for 1h; then heat up and cure according to the following procedure: keep warm at 110℃ for 1.5h, keep warm at 150℃ for 1.5h, keep warm at 180℃ for 1.5h, keep warm at 200℃ for 1.5h, keep warm at 230℃ for 3h, and finally cool naturally to room temperature.

8. The preparation method according to claim 1, characterized in that, (4) The amount of BN / PI composite insulating paper is 3; the coating amount of adhesive II is 3~5 g / cm³. 2 .

9. A BN-PI / BMI composite insulating material obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the BN-PI / BMI composite insulating material as described in claim 9 in the thermal management and insulation protection of high-power electronic devices in aerospace.

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