Phase-change material heat-conducting adhesive, heat-conducting insulating sheet and preparation method and application of phase-change material heat-conducting adhesive

Abstract

The invention relates to the technical field of heat-conducting materials, in particular to a phase-change material heat-conducting adhesive, a heat-conducting insulating sheet as well as a preparation method and application thereof, and the phase-change material heat-conducting adhesive comprises the following components in parts by weight: 11-14 parts of polydimethylsiloxane, 2-3 parts of paraffin, 58-65 parts of hexagonal boron nitride, 8-12 parts of aluminum oxide, 1.5-3 parts of nano silicon dioxide, 6-8 parts of paraffin oil, 0.5-1.5 parts of a cross-linking agent and 1-2 parts of a silane coupling agent. According to the phase-change material heat-conducting adhesive disclosed by the invention, by optimizing the components and proportion of the phase-change material heat-conducting adhesive, the heat conductivity is remarkably improved, the degree of supercooling is reduced, and the heat dissipation efficiency is effectively enhanced.

Description

Technical Field

[0001] This invention relates to the technical field of thermally conductive materials, and more specifically, to a phase change material thermally conductive adhesive, a thermally conductive insulating sheet, its preparation method, and its application. Background Technology

[0002] The on-board charger (OBC), a core component in electric or plug-in hybrid vehicles, is responsible for converting alternating current (AC) to direct current (DC) to charge the high-voltage battery. Under high-power operating conditions (400–800 V), power semiconductor devices such as MOSFETs (metal-oxide-semiconductor field-effect transistors) are the main heat-generating elements in the OBC, generating a significant amount of heat during operation. Therefore, highly efficient thermally conductive insulating sheets are needed to conduct this heat to a heat sink or cooling cavity. Simultaneously, it is essential to ensure that the thermally conductive insulating sheets possess high electrical insulation properties to prevent short circuits or breakdowns.

[0003] In existing technologies, the thermally conductive insulating sheet commonly used in OBCs is made by coating one side of an alumina ceramic substrate with thermally conductive adhesive or other materials and the other side with silicone, and then assembling it between the heat dissipation cavity and the MOSFET. However, the thermal conductivity of existing insulating sheets is relatively low, resulting in insufficient heat dissipation efficiency of the MOSFET. In addition, if the phase change material used has a high degree of supercooling, it will cause a delay in the phase change process, and the latent heat of phase change cannot be fully utilized, thereby reducing the instantaneous thermal management capability and potentially causing temperature fluctuations, affecting system stability. Summary of the Invention

[0004] The purpose of this invention is to overcome the low thermal conductivity of existing thermally conductive insulating sheets, which leads to insufficient heat dissipation efficiency. This invention provides a phase change material thermally conductive adhesive, a thermally conductive insulating sheet, its preparation method, and its application, thereby improving the thermal conductivity of the thermally conductive insulating sheet and reducing the temperature of the MOSFET.

[0005] A further object of the present invention is to provide a method for preparing the above-mentioned phase change material thermally conductive adhesive.

[0006] A further object of the present invention is to provide the application of the above-mentioned phase change material thermally conductive adhesive in the preparation of thermally conductive insulating sheets.

[0007] A further object of the present invention is to provide a thermally conductive insulating sheet prepared from the above-mentioned phase change material thermally conductive adhesive.

[0008] The above-mentioned objective of the present invention is achieved through the following technical solution: A phase change material thermally conductive adhesive comprises the following components by weight: 11-14 parts polydimethylsiloxane, 2-3 parts paraffin wax, 58-65 parts hexagonal boron nitride, 8-12 parts alumina, 1.5-3 parts nano-silica, 6-8 parts paraffin oil, 0.5-1.5 parts crosslinking agent, and 1-2 parts silane coupling agent.

[0009] The phase change material thermally conductive adhesive of the present invention uses polydimethylsiloxane, which provides flexibility, adhesion and mechanical stability, ensuring good adhesion between the phase change material thermally conductive adhesive and the thermally conductive substrate and MOSFET, reducing contact thermal resistance, ensuring the reliability of the thermally conductive adhesive during thermal cycling, and the high breakdown strength of polydimethylsiloxane can enhance the electrical insulation performance of the thermally conductive adhesive.

[0010] Paraffin wax is used as a phase change material to absorb heat from the MOSFET through a solid-liquid phase change, smoothing temperature fluctuations and protecting the device. Simultaneously, it works synergistically with polydimethylsiloxane to enhance the flexibility and adhesion of the thermally conductive adhesive. Further addition of a crosslinking agent promotes partial crosslinking of the molecular chains of polydimethylsiloxane and paraffin wax, constructing a three-dimensional network structure, which improves the material's thermal conductivity and effectively confines the molten paraffin wax, reducing supercooling.

[0011] Hexagonal boron nitride (BN) utilizes its high thermal conductivity to construct efficient heat conduction paths in composite materials, while simultaneously imparting excellent electrical insulation. Alumina fills the interlayer gaps in BN, optimizing the thermal conductivity network packing density. Nano-silica fills these tiny gaps, reduces defects, improves the density of the thermally conductive adhesive in phase change materials (PCMs), and assists BN and alumina in forming multi-scale heat conduction paths. These three components synergistically enhance the thermal conductivity of the PCM adhesive and reduce its undercooling.

[0012] Paraffin oil can reduce viscosity, improve the flowability of thermally conductive adhesives, assist in the dispersion of hexagonal boron nitride and alumina, and reduce bubbles and defects. Silane coupling agents improve the interface between thermally conductive fillers and matrix materials through siloxane bonds, reducing interfacial thermal resistance and electrical defects.

[0013] Preferably, the crosslinking agent is dicumyl peroxide.

[0014] Preferably, the phase change material thermally conductive adhesive further includes 0.25 to 0.75 parts of an antioxidant; the antioxidant is butylated hydroxytoluene.

[0015] Antioxidants inhibit the oxidative degradation of thermally conductive adhesive at high temperatures, and synergistically improve the dispersibility of fillers, the stability of cross-linked networks, and the heat aging resistance of materials, thereby ensuring the efficient and long-term reliable operation of thermally conductive insulating sheets.

[0016] Preferably, the phase change material thermally conductive adhesive further includes 0.5 to 1 part aluminum hydroxide. Aluminum hydroxide has high thermal conductivity and good insulation properties, and can be used as a nucleating agent to reduce supercooling during the phase change process, increase the crystallization rate, and enhance transient thermal management. Reducing supercooling can reduce enthalpy loss caused by supercooling, thereby improving the thermal cycling stability of the phase change material.

[0017] Preferably, the number-average molecular weight of the polydimethylsiloxane is in the range of 10,000 to 30,000.

[0018] Preferably, the paraffin wax has a melting point of 50~60°C, a latent heat of phase change of 220~240 J / g, a specific heat capacity of 2.2~2.8 J / g·K, and a thermal conductivity of 0.2~0.25 W / (m·K).

[0019] Preferably, the average particle size of the hexagonal boron nitride is 5-10 μm, the average particle size of the alumina is 10-15 μm, and the average particle size of the nano-silica is 20-30 nm.

[0020] The preparation method of the above-mentioned phase change material thermally conductive adhesive includes the following steps: S1. Pretreatment of thermally conductive filler: The hexagonal boron nitride, alumina, nano-silica, silane coupling agent and optional aluminum hydroxide are mixed to obtain thermally conductive filler; S2. Preparation of matrix material: The polydimethylsiloxane and paraffin are melt-mixed, stirred and then degassed under vacuum to obtain the matrix material; S3. Add the thermally conductive filler prepared in step S1 to the matrix material prepared in step S2 and stir; then add paraffin oil and crosslinking agent, disperse by ultrasonication and degas under vacuum to obtain the phase change material thermally conductive adhesive.

[0021] Preferably, in step S3, 0.5 to 1 part of low molecular weight silicone oil is added to replace an equal amount of the paraffin oil. Adding low molecular weight silicone oil to replace part of the paraffin oil further reduces viscosity, enhances flow field shear force, and promotes the alignment of the hexagonal boron nitride sheets along the direction parallel to the substrate during screen printing.

[0022] The application of the aforementioned phase change material thermally conductive adhesive in the preparation of thermally conductive insulating sheets is also within the scope of protection of this invention.

[0023] A thermally conductive insulating sheet comprises the aforementioned phase change material thermally conductive adhesive and an alumina ceramic insulating sheet, wherein the phase change material thermally conductive adhesive is coated on the surface of the alumina ceramic insulating sheet. By precisely controlling the alumina ceramic substrate, an ultra-thin design is achieved while ensuring mechanical strength and insulation, meeting the requirements of miniaturization and lightweighting, making it suitable for the compact design of on-board chargers. By optimizing the phase change thermally conductive adhesive formulation to achieve lower supercooling, it ensures that the material can rapidly undergo phase change at operating temperature and fill interfacial gaps, ultimately reducing interfacial contact thermal resistance and improving the heat dissipation efficiency of the thermally conductive insulating sheet.

[0024] Preferably, the alumina ceramic insulating sheet has a thickness of 0.22~0.28mm, the phase change material thermally conductive adhesive has a thickness of 0.06~0.08mm, the phase change material thermally conductive adhesive has a supercooling of 2~8°C, the thermally conductive insulating sheet has a thickness of 0.37~0.41mm, and the thermal conductivity of the thermally conductive insulating sheet is greater than or equal to 16.8W / m·K.

[0025] Preferably, the surface of the alumina ceramic insulating sheet includes a coated area and an uncoated area, wherein the area of ​​the uncoated area is 25-30% of the area of ​​the coated area. A partially blank uncoated area is provided on the alumina ceramic insulating sheet for positioning by the vacuum chuck on the MOSFET, ensuring precise alignment of the thermally conductive insulating sheet during assembly. The area of ​​the uncoated area can be dynamically adjusted according to the number and size of the MOSFETs and the distribution of the vacuum chuck.

[0026] Preferably, in the preparation process of the thermally conductive insulating sheet, a phase change material thermally conductive adhesive is coated onto the surface of the alumina ceramic insulating sheet using screen printing technology. The screen printing employs a polyurethane beveled squeegee, with the angle between the squeegee's working surface and the horizontal direction being 15~30°, the squeegee gap being 0.06mm~0.08mm, the printing speed being 0.1~0.5m / s, and the printing pressure being 0.5~1.5MPa. Polyurethane is a flexible material, and using a polyurethane squeegee can adapt to thermally conductive adhesives with high solids content, providing uniform pressure and reducing mesh clogging and coating defects in the thermally conductive adhesive. The beveled design of the squeegee increases shear force, promoting the alignment of the hexagonal boron nitride layers along the direction parallel to the substrate, which is superior to a rectangular squeegee. Excessive printing speed may disrupt the directional alignment of hexagonal boron nitride, while excessively low printing speed will reduce production efficiency. Selecting a moderate printing speed generates stable shear force, inducing the hexagonal boron nitride layers to align along the direction parallel to the substrate.

[0027] Preferably, during the screen printing process, low-frequency ultrasonic vibration is applied to the screen, with a vibration frequency of 20~40kHz and an ultrasonic power of 100~200 W. Applying low-frequency ultrasonic vibration during screen printing transmits it through the mesh to the thermally conductive adhesive, enhancing the fluidity of the hexagonal boron nitride sheets and aiding in their directional alignment.

[0028] Compared with the prior art, the beneficial effects of the present invention are: 1. The phase change material thermal conductive adhesive of the present invention significantly improves thermal conductivity, reduces supercooling, and effectively enhances heat dissipation efficiency by optimizing the composition and ratio of the phase change material thermal conductive adhesive. 2. The method for preparing the thermally conductive insulating sheet of the present invention employs processes such as ball milling, ultrasonic dispersion, and high-shear stirring to achieve uniform dispersion of fillers, further optimize thermal conductivity and insulation performance, and retain a portion of the uncoated area for vacuum chuck positioning to ensure rapid and accurate alignment during assembly. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the front structure of the thermally conductive insulating sheet; Figure 2 This is a schematic diagram of the structure on the back of the thermally conductive insulating sheet; In the attached diagram: 100, coated area; 200, uncoated area. Detailed Implementation

[0030] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0031] Examples 1-6 Examples 1-6 provide a series of phase change material thermally conductive adhesives, the formulations of which are shown in Table 1.

[0032] Table 1. Formulations (parts by weight) for Examples 1-6

[0033] Comparative Examples 1-4 Comparative Examples 1-4 provide a series of phase change material thermally conductive adhesives, the formulations of which are shown in Table 2.

[0034] Table 2 shows the formulations (parts by weight) for Comparative Examples 1-4.

[0035] In Examples 1-6 and Comparative Examples 1-4, the number-average molecular weight of polydimethylsiloxane was 20,000; the paraffin had a melting point of 50°C, a latent heat of phase change of 220 J / g, a specific heat capacity of 2.2 J / g·K, and a thermal conductivity of 0.25 W / (m·K); the average particle size of hexagonal boron nitride was 5 μm, the average particle size of alumina was 10 μm, and the average particle size of nano-silica was 20 nm.

[0036] The preparation methods of the phase change material thermally conductive adhesives in each embodiment and comparative example include: S1. Pretreatment of thermally conductive filler: Mix hexagonal boron nitride, alumina, nano silica, aluminum hydroxide (if any) and silane coupling agent evenly to obtain thermally conductive filler; S2. Preparation of matrix material: Polydimethylsiloxane and paraffin were melt-mixed in a constant temperature water bath at 100°C, and then stirred at a high shear speed of 1000 rpm for 20 min. Then, the antioxidant dibutylhydroxytoluene (BHT) was added and the mixture was degassed under vacuum at 0.09 MPa for 20 min to obtain the matrix material. S3. Preparation of thermally conductive adhesive for phase change material: The thermally conductive filler obtained in step S1 is added to the matrix material prepared in step S2 in 5 batches. After each addition, the filler is stirred at a high shear speed of 3000 rpm for 15 min. Then, paraffin oil and crosslinking agent dicumyl peroxide (DCP) are added and ultrasonically dispersed at an ultrasonic power of 1500 W for 40 min. Then, vacuum degassing is performed at 0.09 MPa for 40 min to obtain the thermally conductive adhesive for phase change material.

[0037] The phase change material thermally conductive adhesives of each embodiment and comparative example were used to make thermally conductive insulating sheets. The process was as follows: An alumina ceramic insulating sheet was plasma-cleaned for 5 minutes at a cleaning power of 100W. The phase change material thermally conductive adhesive prepared in step S3 was then coated onto the surface of the 0.25mm thick alumina ceramic insulating sheet using screen printing, resulting in a 0.40mm thick thermally conductive insulating sheet. During screen printing, a polyurethane beveled squeegee was used, with a 30° angle between the squeegee's working surface and the horizontal direction, a squeegee gap of 0.07mm, a printing speed of 0.3m / s, and a printing pressure of 1MPa. The thermally conductive insulating sheet was then placed in an oven and dried at 105°C for 12 minutes. The structure of the thermally conductive insulating sheet prepared in this comparative example is as follows. Figure 1 , Figure 2 As shown, one side is entirely coated area 100, and the other side includes coated area 100 and uncoated area 200. The area of ​​uncoated area 200 is 25% of the area of ​​coated area 100. In actual production, the shape and area of ​​the uncoated area on the thermally conductive insulating sheet can be dynamically adjusted according to the number and size of the MOSFETs and the distribution of the vacuum chucks.

[0038] According to the national standard GB / T22588-2008, the thermal conductivity and supercooling of the thermally conductive insulating sheets prepared in Examples 1, 2, 3, 4, 5, 6, Comparative Examples 1, 2, 3, and 4 were tested using the laser flare method. The supercooling was based on the theoretical box-changing temperature of the thermally conductive insulating sheet, 55°C. The experimental data are shown in Table 3.

[0039] Table 3. Experimental data of Examples 1-6 and Comparative Examples 1-4

[0040] Based on the experimental data from Examples 1-6, Comparative Examples 1-4, and Table 3 (Examples 1-6 and Comparative Examples 1-4), it can be seen that the thermal conductivity of the thermally conductive insulating sheets prepared in Examples 1-6 is greater than that of the thermally conductive insulating sheets prepared in Comparative Examples 1-4. Therefore, the heat dissipation effect of the thermally conductive insulating sheets prepared in Examples 1-6 is better. The supercooling degree of the thermally conductive insulating sheets prepared in Examples 1-6 is less than that of the thermally conductive insulating sheets prepared in Comparative Examples 1-4. Therefore, using the thermally conductive insulating sheets prepared in Examples 1-6 can reduce enthalpy loss caused by supercooling, thereby improving the thermal cycling stability of the phase change material.

[0041] In the specific implementation of the above embodiments, the technical features can be combined in any non-contradictory way. For the sake of brevity, not all possible combinations of the above technical features are described. However, as long as the combination of these technical features is not contradictory, it should be considered to be within the scope of this specification.

[0042] 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. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A phase change material thermally conductive adhesive, characterized in that, The product comprises the following components by weight: 11-14 parts polydimethylsiloxane, 2-3 parts paraffin wax, 58-65 parts hexagonal boron nitride, 8-12 parts alumina, 1.5-3 parts nano silica, 6-8 parts paraffin oil, 0.5-1.5 parts crosslinking agent, and 1-2 parts silane coupling agent.

2. The phase change material thermally conductive adhesive according to claim 1, characterized in that, The phase change material thermally conductive adhesive also includes 0.25 to 1 part of antioxidant.

3. The phase change material thermally conductive adhesive according to claim 1, characterized in that, The phase change material thermally conductive adhesive also includes 0.5 to 1 part aluminum hydroxide.

4. The phase change material thermally conductive adhesive according to claim 1, characterized in that, The number-average molecular weight of the polydimethylsiloxane is in the range of 10,000 to 30,000.

5. The phase change material thermally conductive adhesive according to claim 1, characterized in that, The paraffin wax has a melting point of 50~60°C, a latent heat of phase change of 220~240 J / g, a specific heat capacity of 2.2~2.8 J / g·K, and a thermal conductivity of 0.2~0.25 W / (m·K).

6. The phase change material thermally conductive adhesive according to claim 1, characterized in that, The average particle size of the hexagonal boron nitride is 5~10μm, the average particle size of the alumina is 10~15μm, and the average particle size of the nano-silica is 20~30nm.

7. A method for preparing the phase change material thermally conductive adhesive according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Pretreatment of thermally conductive filler: The hexagonal boron nitride, alumina, nano-silica, silane coupling agent and optional aluminum hydroxide are mixed to obtain thermally conductive filler; S2. Preparation of matrix material: The polydimethylsiloxane and paraffin are melt-mixed, stirred under high shear, and then degassed under vacuum to obtain the matrix material; S3. Add the thermally conductive filler prepared in step S1 to the matrix material prepared in step S2 and stir; then add paraffin oil and crosslinking agent, disperse by ultrasonication and degas under vacuum to obtain the phase change material thermally conductive adhesive.

8. The application of the phase change material thermally conductive adhesive according to any one of claims 1 to 6 in the preparation of thermally conductive insulating sheets.

9. A thermally conductive insulating sheet, characterized in that, It includes the phase change material thermally conductive adhesive as described in any one of claims 1 to 6 and the alumina ceramic insulating sheet, wherein the phase change material thermally conductive adhesive is coated on the surface of the alumina ceramic insulating sheet.

10. The thermally conductive insulating sheet according to claim 9, characterized in that, The surface of the alumina ceramic insulating sheet includes a coated area (100) and an uncoated area (200), wherein the area of ​​the uncoated area (200) is 25-30% of the area of ​​the coated area (100).

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