A high thermal conductivity composite gasket, its preparation method and application

Abstract

This invention provides a high thermal conductivity composite gasket, its preparation method, and its application. The preparation method includes the following steps: (1) mixing polyurethane prepolymer, two-dimensional filler, chain extender, and catalyst to obtain a composite slurry; (2) calendering the composite slurry into a sheet and pre-curing it to obtain a composite sheet; (3) rolling the composite sheet, stacking it, and rolling it again, repeating the stacking and rolling steps several times to obtain a composite film with a thickness of 0.02-0.07 mm; (4) cross-laminating a graphite film and a composite film to obtain a laminated preform; (5) hot-pressing the laminated preform to obtain a composite block; (6) slicing the composite block along the orientation direction perpendicular to the two-dimensional filler in the composite film to obtain the high thermal conductivity composite gasket. The composite gaskets prepared using this invention all have good thermal conductivity and good adhesion.

Description

Technical Field

[0001] This invention belongs to the field of thermal management materials technology, and relates to a high thermal conductivity composite gasket, its preparation method and application. Background Technology

[0002] With the rapid development of emerging technologies such as 5G, artificial intelligence, high-performance computing, and electric vehicles, the power density and integration of electronic components are constantly increasing. The resulting heat accumulation has become a key bottleneck restricting equipment performance, reliability, and lifespan. Thermal interface materials used to fill the micro-gaps between heat sources and heat sinks and reduce contact thermal resistance have become indispensable key materials in the electronics industry.

[0003] Currently, the mainstream thermal interface materials on the market mainly include thermal paste, thermal gel, phase change materials, and thermal pads. Among them, thermal pads are favored in many application scenarios due to their advantages such as solid form, ease of installation, and compressibility and resilience. Traditional thermal pads typically use polymers such as silicone rubber, epoxy resin, or polyurethane as the matrix, and fill them with traditional ceramic fillers such as alumina, zinc oxide, and boron nitride to improve thermal conductivity. However, these materials are limited by the low intrinsic thermal conductivity of the fillers themselves and the random distribution of the fillers in the matrix, and their thermal conductivity is usually difficult to exceed 20 W / (m·K), which can no longer meet the heat dissipation requirements of today's high heat flux density chips; on the other hand, if the filling amount of traditional ceramic fillers is too high, it will damage the flexibility and processability of the material.

[0004] Moreover, the preparation process of high-performance thermal conductive materials is often complex and costly, making it difficult to mass-produce. For example, methods such as vapor deposition and template methods require high-end equipment; complex chemical modification processes increase costs and environmental burden; and special structures (such as aerogels) have poor mechanical strength and are not easy to process.

[0005] To significantly improve the thermal conductivity of polymer-based composites, researchers have turned their attention to carbon-based nanomaterials with ultra-high intrinsic thermal conductivity. Theoretically, constructing a continuous three-dimensional carbon network within a polymer matrix is ​​an effective way to obtain high thermal conductivity composites. CN121108681A discloses a method for preparing a high thermal conductivity graphene fiber composite based on conjugated interface adaptation, achieving an in-plane thermal conductivity of 570 W / (m·K). However, the method of neatly arranging graphene fibers in a mold and injecting them into an epoxy resin matrix using a vacuum-assisted resin infusion method severely limits the size and production efficiency of the prepared product. CN121019042A utilizes a layer-by-layer stacking of carbon fiber / silicone composite layers and graphene films, ultimately obtaining a thermally conductive pad with a thermal conductivity of 176.5 W / (m·K) after slicing. However, the thermal conductivity of a thermally conductive pad obtained by layer-by-layer stacking of carbon fiber / silicone composite layers through a scraping process is only 20 W / (m·K), indicating that its orientation degree is still limited. Furthermore, the limited adhesion between the silicone substrate and graphene film, substrate, etc., leads to application risks such as thermal pad cracking and interface delamination.

[0006] Therefore, developing a novel high-performance thermal pad with simple process, controllable cost, and the ability to fully utilize the efficiency of high thermal conductivity fillers, as well as its preparation method, to meet the increasingly severe heat dissipation challenges of high-end electronic devices, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a high thermal conductivity composite pad, its preparation method and application.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a high thermal conductivity composite pad, the method comprising the following steps: (1) The polyurethane prepolymer, two-dimensional filler, chain extender and catalyst are mixed to obtain a composite slurry; (2) The composite slurry is calendered into sheets and pre-cured to obtain composite sheets; (3) Roll the composite sheet, stack the sheets and roll them again. Repeat the stacking and rolling steps several times to obtain a composite film with a thickness of 0.02-0.07 mm (e.g., 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, etc.); (4) Graphite film and composite film are cross-laminated to obtain a laminated preform; (5) Hot-press the laminated prefabricated body to obtain composite block material; (6) The composite block is sliced ​​along the orientation direction perpendicular to the two-dimensional filler in the composite membrane to obtain the high thermal conductivity composite pad.

[0009] In the preparation method provided by this invention, a two-dimensional filler is used as the filler, and a highly oriented composite film is obtained through multiple rolling processes, thus constructing an oriented thermally conductive network. By forming the composite material with the thermally conductive network into a thin film and creating an effective two-dimensional filler orientation structure, the heat transfer path in the low thermal conductivity polymer phase is shortened, thereby significantly improving its in-plane thermal conductivity. Furthermore, a layered composite structure design is adopted: the obtained composite film (responsible for in-plane heat transfer and interface bonding) is combined with a high in-plane thermal conductivity graphite film (responsible for in-plane heat diffusion), resulting in a sandwich-like thermally conductive pad. This invention employs a simple hot-pressing process, and all steps are based on mature industrial equipment, making it easy to scale up for production.

[0010] In step (3) of the present invention, during the rolling process, the molten PU matrix flows in the plane, which strongly induces the two-dimensional filler to orient along the in-plane direction, and a composite film with target thickness and high orientation of two-dimensional filler is formed in one step.

[0011] Preferably, the two-dimensional filler in step (1) includes any one or a combination of at least two of graphite, boron nitride, and graphene.

[0012] Preferably, the graphite comprises flake graphite.

[0013] Preferably, the chain extender in step (1) comprises 1,4-butanediol.

[0014] Preferably, the catalyst in step (1) comprises dibutyltin dilaurate.

[0015] Preferably, in step (1), the proportion of the two-dimensional filler is 30%-60% based on the total mass of the polyurethane prepolymer and the two-dimensional filler as 100%, for example, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, 52%, 54%, 55%, 56%, 58%, 60%, etc.

[0016] Preferably, in step (1), the molar ratio of the chain extender to the NCO groups in the polyurethane prepolymer is (1-1.1):1, for example, 1:1, 1.02:1, 1.04:1, 1.05:1, 1.06:1, 1.08:1, 1.1:1, etc.

[0017] Preferably, in step (1), the amount of catalyst used is 0.01%-0.05% of the mass of the polyurethane prepolymer, for example, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc.

[0018] Preferably, step (1) of mixing the polyurethane prepolymer, two-dimensional filler, chain extender, and catalyst specifically includes: First, the polyurethane prepolymer and the two-dimensional filler are mixed for the first time, then high-speed shear dispersion is carried out, and then chain extender and catalyst are added for the second mixing.

[0019] Preferably, the first mixing is low-speed stirring, with a rotation speed of 400-600 rpm, such as 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, etc., and a mixing time of 20-40 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, etc.

[0020] Preferably, the high-speed shear dispersion rotation speed is 7000-9000 rpm, such as 7000 rpm, 7500 rpm, 8000 rpm, 8500 rpm, 9000 rpm, etc., and the high-speed shear dispersion time is 50-70 min, such as 50 min, 55 min, 60 min, 65 min, 70 min, etc.

[0021] Preferably, the system temperature is controlled to be <40°C during the high-speed shear dispersion process, for example, 35°C, 30°C, etc.

[0022] Preferably, the high-speed shear dispersion is carried out in a high-speed homogenizer.

[0023] Preferably, the second mixing is a medium-speed stirring, with a rotation speed of 1000-1500 rpm, such as 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, etc., and a mixing time of 3-8 min, such as 3 min, 4 min, 5 min, 6 min, 8 min, etc.

[0024] Preferably, step (2) of calendering the composite slurry into sheets specifically includes: The composite slurry is molded into sheets with a thickness of 0.4-0.6 mm (e.g., 0.4 mm, 0.5 mm, 0.6 mm, etc.).

[0025] Preferably, the pre-curing temperature in step (2) is 70-90℃, such as 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the pre-curing time is 20-40min, such as 20min, 25min, 30min, 35min, 40min, etc.

[0026] Preferably, the rolling process in step (3) is performed in a two-roll mill.

[0027] Preferably, the rolling process in step (3) is carried out at 40-70°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc.).

[0028] Preferably, the repeated stacking and rolling steps in step (3) specifically refer to repeating the stacking and rolling steps 5-20 times (e.g., 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 12 times, 14 times, 15 times, 16 times, 18 times, 20 times, etc.).

[0029] Preferably, the orientation degree of the two-dimensional filler in the composite membrane obtained in step (3) is >90%, such as 92%, 93%, 94%, 95%, etc.

[0030] Preferably, the thickness of the graphite film in step (4) is 0.02-0.03 mm, such as 0.02 mm, 0.022 mm, 0.024 mm, 0.025 mm, 0.026 mm, 0.028 mm, 0.03 mm, etc.

[0031] Preferably, step (4) of cross-laminating the graphite film and the composite film specifically includes: The graphite film and composite film are stacked in a cross-layered manner in the order of "graphite film-composite film-graphite film-composite film-...".

[0032] Preferably, the thickness of the laminated preform obtained in step (4) is 25-35mm, such as 25mm, 26mm, 28mm, 30mm, 32mm, 33mm, 35mm, etc.

[0033] In actual production, step (4) can be carried out using a roll-to-roll composite process, as follows: the rolled composite film and the rolled graphite film are cross-layered.

[0034] Preferably, the hot pressing temperature in step (5) is 120-140℃, such as 120℃, 125℃, 130℃, 135℃, 140℃, etc., the hot pressing pressure is 4-6MPa, such as 4MPa, 4.5MPa, 5MPa, 5.5MPa, 6MPa, etc., and the hot pressing time is 20-40min, such as 20min, 25min, 30min, 35min, 40min, etc.

[0035] Preferably, the hot pressing in step (5) is performed in a flatbed hot press.

[0036] Preferably, the slicing in step (6) is performed in a precision slicer.

[0037] Preferably, the thickness of the high thermal conductivity composite pad obtained by slicing in step (6) is 0.4-0.6 mm, such as 0.4 mm, 0.42 mm, 0.44 mm, 0.45 mm, 0.46 mm, 0.48 mm, 0.5 mm, 0.52 mm, 0.54 mm, 0.55 mm, 0.56 mm, 0.58 mm, 0.6 mm, etc.

[0038] In summary, this invention systematically solves the problems of insufficient performance in the thickness direction and complex preparation of existing thermally conductive composite materials through material optimization, structural innovation, and process synergy. Specifically: (1) Material and microstructure control scheme: Constructing a thermally conductive network with preferred orientation This invention uses a two-dimensional filler with high intrinsic thermal conductivity as the filler and innovatively utilizes a controllable high-temperature roll pressing process to induce the two-dimensional filler to generate a preferred orientation along the in-plane direction in the polyurethane (PU) matrix, thereby obtaining a two-dimensional filler sheet, thus constructing a directional and efficient thermal conductive network. This solves the problems of the difficulty in breaking through the thermal conductivity of traditional polymer-based thermal pads and the low efficiency of the thermal conductive path caused by the disordered distribution of filler in the matrix.

[0039] When the composite material is subjected to in-plane shear and compressive forces during high-temperature rolling, the high aspect ratio two-dimensional fillers tend to align parallel to the shear direction (i.e., parallel to the film plane); and the thermal conductivity of the material is further improved through the following parameter optimization: 1) Filler content optimization: Determine the percolation threshold of two-dimensional filler in PU. If the content is too low, it will not be conducive to improving thermal conductivity; if the content is too high, it will not be conducive to mixing preparation and subsequent bonding of graphite film.

[0040] 2) Relationship between thickness reduction and orientation degree: During the pressing process of ultra-thin composite films (e.g., 0.05 mm), strong planar constraints and shear flow fields significantly improve the in-plane orientation and stacking density of the two-dimensional filler, thus forming more heat conduction shortcuts. There is an optimal thickness window (e.g., 0.02-0.07 mm). Within this window, the orientation enhancement effect caused by thinning dominates the improvement of thermal conductivity. However, when the thickness is too small, it may lead to the destruction of matrix continuity; when the thickness is too large, the orientation degree is insufficient, and the two-dimensional filler network becomes disordered.

[0041] (2) Hierarchical composite structure scheme: functional integration and anisotropic thermal management This invention uses a PU film with an optimal thickness (e.g., 0.05 mm) and a highly oriented two-dimensional filler network, obtained from the above-mentioned scheme, as the core thermally conductive interlayer. This film is then composited with a graphite film possessing ultra-high in-plane thermal conductivity to design a functional integrated gasket with a "sandwich"-like structure, further improving the thermal conductivity of the oriented structural material. The scientific principle is as follows: 1) Functional synergy principle: Highly Oriented Composite Film: The highly oriented and tightly stacked two-dimensional filler network greatly optimizes the phonon transport path in the thickness direction. At the same time, the soft PU matrix ensures the adhesion between the composite film and the graphite film to prepare a complete thermally conductive pad; it also ensures a tight fit between the pad and the surface to be cooled, filling microscopic gaps and reducing contact thermal resistance.

[0042] Graphite film: Graphite film is a highly anisotropic thermally conductive material with an in-plane thermal conductivity of 800-1500 W / (m·K). Its extremely high in-plane thermal conductivity enables the excellent heat dissipation performance of thermal pads.

[0043] 2) Composite Interface Optimization: This invention employs a hot-pressing process for lamination. The temperature and pressure of the hot press must be precisely controlled to allow the PU layer surface to soften and flow slightly, thereby forming a microscopically embedded, tight physical bond with the graphite film surface, minimizing interlayer thermal resistance. This process does not damage the already formed orientation structure of the two-dimensional filler.

[0044] (3) Scalable preparation process This invention integrates the entire preparation process into a process route that can be continuously or batch-scaled based on mature polymer processing equipment: pre-dispersion-precision pressing and orientation-composite. This process route is simple and efficient, with great industrialization potential, and overcomes the problems of complex and costly preparation processes for high-performance thermal conductive materials in existing technologies.

[0045] Based on the above technical solution, the technical effects achieved by the present invention are as follows: (A) Breakthrough improvement in thermal conductivity based on thickness-orientation synergistic control Technical problems and solutions: To address the problem of insufficient thermal conductivity of traditional filler / polymer composite materials, this invention achieves a breakthrough in the intrinsic thermal conductivity of composite materials through the preferred orientation arrangement of two-dimensional fillers.

[0046] Technical effects: Forming a highly efficient thermal conductivity pathway: By inducing a highly in-plane orientation structure in the PU matrix through a high-temperature rolling process, the composite film produced within the optimal thickness window (0.03-0.07 mm) exhibits a thermal diffusivity perpendicular to the thickness direction that is more than 200% higher than that of traditional composite materials with the same filler content but without orientation control. A thermally conductive pad produced by stacking 0.05 mm composite films can achieve a thermal conductivity of 50 W / (m·K).

[0047] Achieving optimal connectivity of the filler network: By controlling the content of two-dimensional filler near the percolation threshold, the integrity of the three-dimensional thermal conductivity network is ensured, while avoiding processing difficulties and mechanical property degradation caused by high filler content.

[0048] Precise determination of the thickness window: Through systematic study of the thermal conductivity and microstructure of samples with different thicknesses, an optimal thickness range was identified. Within this range, the orientation enhancement effect brought about by the thinning process is maximized, while the matrix continuity is maintained. This discovery provides clear process guidelines for the design of high-performance thermally conductive composite materials.

[0049] (B) Multi-dimensional thermal management capabilities based on hierarchical composite structure Technical problems and solutions: To address the problem that a single material cannot meet the requirements of anisotropic thermal conductivity, this invention adopts a sandwich-like composite structure design of "highly oriented composite film-graphite film" to achieve the division of labor and synergy of thermal management functions.

[0050] Technical Results: By optimizing the hot-pressing composite process parameters, the PU layer is moderately softened during the composite process, forming a microscopic embedded bond with the graphite film surface to create a precursor for the thermally conductive gasket. This precursor is then sliced ​​along a direction perpendicular to the two-dimensional filler orientation to obtain the final composite gasket. The extremely high in-plane thermal conductivity of the graphite film (≥800 W / (m·K)) enables efficient heat dissipation. The composite film ensures a tight fit between the gasket and the surface being cooled, filling microscopic gaps and reducing contact thermal resistance. The final composite gasket exhibits an out-of-plane thermal conductivity of 239 W / (m·K) measured at 25℃, while its adhesion performance reaches 1.6 MPa.

[0051] (C) Industrialization advantages based on simplified process routes Technical problems and solutions: To address the problem of complex preparation processes for high-performance materials, this invention has developed an integrated process route of "pre-dispersion-precision tableting and orientation-composite", which achieves a balance between high performance and ease of processing.

[0052] Technical effects: Continuous production capability: The entire process route is based on mature processing equipment (high-speed homogenizer, rolling mill, hot press), which facilitates scale-up from laboratory to pilot-scale and then to large-scale production. For large-volume continuous production, roll-to-roll composite processes can be used.

[0053] Cost control and quality stability: It avoids the use of expensive chemical vapor deposition (CVD) equipment or complex surface modification chemical treatments, significantly reducing raw material costs and production energy consumption.

[0054] Product processability and adaptability: The final composite gasket has good flexibility and adhesion (adhesion can reach 1.6 MPa), can adapt to uneven heat dissipation surfaces, and ensure low contact thermal resistance.

[0055] By adjusting the content of two-dimensional fillers, film thickness, and number of composite layers, products with different thermal conductivity levels and thicknesses can be flexibly designed to meet the needs of different application scenarios, from consumer electronics to industrial power supplies.

[0056] In a second aspect, the present invention provides a high thermal conductivity composite pad, which is prepared by the preparation method described in the first aspect; Preferably, the out-of-plane (thickness direction) thermal conductivity of the high thermal conductivity composite gasket is ≥140W / (m·K), such as 140W / (m·K), 150W / (m·K), 160W / (m·K), 180W / (m·K), 200W / (m·K), 210W / (m·K), 220W / (m·K), 230W / (m·K), 250W / (m·K), 270W / (m·K), etc., and more preferably 140-250W / (m·K).

[0057] Thirdly, the present invention provides an application of the high thermal conductivity composite pad as described in the second aspect in heat dissipation of electronic devices.

[0058] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention controls the thickness of the composite film to an ultra-thin scale (such as 0.02-0.07 mm) by multiple rolling, which can significantly improve the in-plane thermal diffusivity of polymer materials containing two-dimensional filler networks, and provides a new idea for improving the intrinsic thermal conductivity of composite materials.

[0059] (2) The gasket obtained by combining the above composite film and graphite film achieves excellent vertical heat transfer capability, which meets the requirements of electronic devices for the anisotropy of interface thermal conductive materials.

[0060] (3) The preparation method of the present invention is simple and involves only conventional steps such as mixing, tableting and hot pressing. It does not require complex equipment or harsh conditions and is easy to achieve large-scale production.

[0061] (4) The final product obtained by the present invention has high thermal performance while maintaining good flexibility and interfacial adhesion of the polymer matrix. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: Polyurethane prepolymer: synthesized based on polytetrahydrofuran diol (PTMG, Mn=2000 g / mol, CAS 25190-06-1) and diphenylmethane diisocyanate (MDI, CAS 101-68-8), with an NCO content of 6.5%. The synthesis method includes the following steps: PTMG and MDI are mixed at a functional group molar ratio of 1:3 and reacted at 60°C for 3 h.

[0064] Chain extender: 1,4-Butanediol (BDO, CAS: 110-63-4), the amount added is 1.05:1 molar ratio of BDO to NCO groups in polyurethane prepolymer.

[0065] Catalyst: Dibutyltin dilaurate (DBTDL, CAS: 77-58-7), the amount added is 0.02% of the mass of polyurethane prepolymer.

[0066] Graphite: flake graphite, purity ≥99.9%, flake diameter D50: 30μm.

[0067] Example 1 This embodiment provides a method for preparing a high thermal conductivity composite pad, the method comprising the following steps: (1) Slurry preparation and pre-dispersion: Weigh out polyurethane prepolymer and graphite (flake graphite) according to the formula. First, stir at low speed of 500 rpm for 30 minutes to initially wet the material. Then, transfer it to a high-speed homogenizer and disperse it at high speed of 8000 rpm for 60 minutes, while controlling the temperature to <40℃. After dispersion, add the metered chain extender (BDO) and catalyst (DBTDL) and stir at 1100 rpm for 5 minutes to obtain a uniform composite slurry.

[0068] (2) Pre-curing: The composite slurry is molded into a sheet with a thickness of 0.5 mm and immediately transferred to an 80℃ forced-air oven for pre-curing for 30 minutes to obtain a "raw rubber" composite sheet with a dry surface, certain cohesive strength and complete peelability.

[0069] (3) Two-dimensional material orientation (graphite sheet orientation): The graphite sheets in the prepared "raw rubber" composite sheet are induced to form a highly in-plane orientation structure in the PU matrix through a high-temperature rolling process. Specific conditions include: temperature control at 50°C, multiple passes through a double roller mill, and stacking to ensure orientation (15 times). During this process, the molten PU matrix is ​​subjected to strong in-plane shear and compression, which forces the sheet graphite to rotate. Its sheet planes are arranged parallel to the film surface, achieving a high degree of in-plane orientation. Finally, the composite film is obtained by producing the sheet with the target thickness.

[0070] (4) Interval stacking: The above composite film and graphite film (0.025mm thick) are stacked in a cross-stacked manner in the order of "graphite film-composite film-graphite film-composite film-..." to form a block-shaped stacked prefabricated body with a total thickness of about 30mm.

[0071] (5) Hot pressing composite: The block-shaped laminated preform is placed in a flat hot press and hot-pressed at 130°C and 5MPa for 30 minutes to soften and flow the PU layer, fully impregnate and bond the adjacent graphite film layer to form a dense composite block.

[0072] (6) Slicing: The composite block is fixed on a precision slicer, and the slicing direction is perpendicular to the orientation direction of the graphite sheets in the composite film (i.e., parallel to the stacking direction of the block), and sliced ​​into thin slices with a thickness of 0.5 mm to obtain the high thermal conductivity composite gasket. This slicing direction ensures that in the final gasket, the high thermal conductivity of the graphite sheets, which were originally oriented in the film plane, is parallel to the thickness direction of the gasket, thereby obtaining an extremely high out-of-plane (thickness direction) thermal conductivity.

[0073] (7) Post-processing: Cover both sides of the high thermal conductivity composite pad with release film to obtain the final thermal conductive pad product.

[0074] The amounts of polyurethane prepolymer and graphite, and the thickness of the composite film are shown in Table 1.

[0075] Examples 2-3, Comparative Examples 1-5 The only difference from Example 1 is that the amount of polyurethane prepolymer and graphite, the thickness of the composite film, etc. are different, as shown in Table 1.

[0076] Table 1 Note: (1) All examples and comparative examples used the same polyurethane prepolymer, chain extender, catalyst type and ratio; (2) Step (3) is not performed for Example 2; (3) The method for testing the orientation of graphite sheets in the composite film includes the following steps: The orientation of the sample is characterized by using a Bruker D8Advance X-ray diffractometer. The (002) crystal plane diffraction peak of the graphite crystal is usually used to characterize its layered stacking structure, while the (004) crystal plane, as the second-order diffraction of (002), can reflect the degree of regular arrangement of the graphite sheets along the in-plane direction.

[0077] ; and The values ​​represent the diffraction peak intensities of the test sample and the random sample on the (004) crystal plane, respectively.

[0078] Comparative Example 6 This comparative example provides a method for preparing a composite gasket, the method comprising the following steps: (1) Slurry preparation and pre-dispersion: Weigh out polyurethane prepolymer, graphite (flake graphite), and dichloromethane (30% of the mass of polyurethane prepolymer) according to the formula. First, stir at low speed of 500 rpm for 30 minutes to initially wet the material. Then, transfer it to a high-speed homogenizer and disperse it at high speed of 8000 rpm for 60 minutes, while controlling the temperature to <40℃. After dispersion, add the metered chain extender (BDO) and catalyst (DBTDL) and stir at 1100 rpm for 5 minutes to obtain a uniform composite slurry. The amount of polyurethane prepolymer and graphite used is the same as in Example 3.

[0079] (2) Pre-curing: The composite slurry is applied to the surface of the graphite film by spin coating. After drying at room temperature for 3 hours, it is transferred to an 80°C forced-air oven for pre-curing for 30 minutes to obtain the composite film.

[0080] (3) Lamination: The above graphite film is laminated to form a block-shaped laminated preform with a total thickness of about 30 mm.

[0081] (4) Hot pressing composite: The block-shaped laminated preform is placed in a flat hot press and hot-pressed at 130°C and 5MPa for 30 minutes to soften and flow the PU layer, fully impregnate and bond the adjacent graphite film layer to form a dense composite block.

[0082] (5) Slicing: The composite block is fixed on a precision slicer, and the slicing direction is perpendicular to the orientation direction of the graphite sheets in the composite film (i.e., parallel to the stacking direction of the block), and sliced ​​into thin slices with a thickness of 0.5 mm to obtain the composite gasket. This slicing direction makes the high thermal conductivity sheet plane direction of the graphite sheets originally oriented in the film plane parallel to the thickness direction of the gasket, thereby obtaining an extremely high out-of-plane (thickness direction) thermal conductivity.

[0083] (6) Post-processing: Cover both sides of the high thermal conductivity composite pad with release film to obtain the final thermal conductive pad product.

[0084] The composite gaskets and composite films obtained during the preparation process provided in the embodiments and comparative examples of the present invention were subjected to performance tests, and the test methods are as follows: (1) Thermal conductivity: The thermal conductivity of the material was tested using the Laser Flash Method (LFA), specifically according to standard ASTM E1461-13. The thermal conductivity λ (unit: W / (m·K)) was calculated by measuring the thermal diffusivity of the material and combining it with the specific heat capacity and density of the sample using the following formula: λ = α × Cp × ρ; In the formula: λ is the thermal conductivity; α is the thermal diffusivity directly measured by the laser flare method; Cp is the specific heat capacity of the material; ρ is the density of the material.

[0085] (2) Adhesive properties: Test standard: Refer to GB / T 2791-1995.

[0086] Method: The composite film or composite gasket to be tested (as an adhesive layer) is sandwiched between two surface-treated aluminum sheets (25 mm wide). After treatment at 40 psi and 70 ℃ for 30 min, an overlap shear test is performed on a universal testing machine at a tensile speed of 10 mm / min. The result is the average value of 5 samples.

[0087] (3) Processability evaluation: Calendering sheet formation: Record the edge integrity and whether the composite film obtained during the rolling process is broken, and conduct a qualitative evaluation (excellent / good / medium / poor).

[0088] The performance test results are shown in Table 2.

[0089] Table 2 As can be seen from Table 2, the composite gaskets prepared using the present invention all have good thermal conductivity (out-of-plane thermal conductivity: 140~249W / (m·K)) and good adhesive properties (peel strength: 0.7~1.6MPa).

[0090] Compared to Example 2, Comparative Example 1 did not use graphite, resulting in a pure PU film, and the thermal conductivity of the resulting composite gasket was significantly worse. Comparative Example 2 did not perform orientation control, and the graphite flakes in the composite film were randomly distributed, resulting in a significant decrease in the thermal conductivity of the resulting composite gasket. In Comparative Example 3, the amount of graphite added exceeded the percolation threshold, and although the resulting composite gaskets all had high thermal conductivity, the processing difficulty increased, and the film-forming properties were poor. In Comparative Example 4, the thickness of the composite film was too small, resulting in poor calendering and sheet formation of the composite film, film breakage, and a significant decrease in the thermal conductivity of the resulting composite gasket. In Comparative Example 5, the thickness of the composite film was too large, resulting in a decrease in the thermal conductivity of the resulting composite gasket.

[0091] Compared with Example 3, Comparative Example 6 directly composites the composite slurry with the graphite film, resulting in a composite gasket with poorer thermal conductivity.

[0092] The applicant declares that the present invention illustrates the high thermal conductivity composite gasket, its preparation method, and its application through the above embodiments. However, the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high thermal conductivity composite pad, characterized in that, The preparation method includes the following steps: (1) The polyurethane prepolymer, two-dimensional filler, chain extender and catalyst are mixed to obtain a composite slurry; (2) The composite slurry is calendered into sheets and pre-cured to obtain composite sheets; (3) Roll the composite sheet, stack the sheets and roll them again. Repeat the stacking and rolling steps several times to obtain a composite film with a thickness of 0.02-0.07 mm. (4) Graphite film and composite film are cross-laminated to obtain a laminated preform; (5) Hot-press the laminated prefabricated body to obtain composite block material; (6) The composite block is sliced ​​along the orientation direction perpendicular to the two-dimensional filler in the composite membrane to obtain the high thermal conductivity composite pad.

2. The preparation method according to claim 1, characterized in that, The two-dimensional filler in step (1) includes any one or a combination of at least two of graphite, boron nitride, and graphene; Preferably, the graphite comprises flake graphite; Preferably, the chain extender in step (1) comprises 1,4-butanediol; Preferably, the catalyst in step (1) comprises dibutyltin dilaurate; Preferably, in step (1), the proportion of the two-dimensional filler is 30%-60% based on the total mass of the polyurethane prepolymer and the two-dimensional filler being 100%; Preferably, in step (1), the molar ratio of the chain extender to the NCO groups in the polyurethane prepolymer is (1-1.1):1; Preferably, in step (1), the amount of catalyst used is 0.01%-0.05% of the mass of the polyurethane prepolymer.

3. The preparation method according to claim 1 or 2, characterized in that, Step (1) involves mixing the polyurethane prepolymer, two-dimensional filler, chain extender, and catalyst, specifically including: First, the polyurethane prepolymer and the two-dimensional filler are mixed for the first time, then high-speed shear dispersion is performed, and then chain extender and catalyst are added for the second mixing. Preferably, the first mixing is performed by low-speed stirring, with a rotation speed of 400-600 rpm and a mixing time of 20-40 min; Preferably, the high-speed shear dispersion rotation speed is 7000-9000 rpm, and the high-speed shear dispersion time is 50-70 min; Preferably, the system temperature is controlled to be <40°C during the high-speed shear dispersion process; Preferably, the high-speed shear dispersion is carried out in a high-speed homogenizer; Preferably, the second mixing is a medium-speed stirring, with a rotation speed of 1000-1500 rpm and a mixing time of 3-8 minutes.

4. The preparation method according to any one of claims 1-3, characterized in that, Step (2) of calendering the composite slurry into sheets specifically includes: The composite slurry is molded into sheets with a thickness of 0.4-0.6 mm; Preferably, the pre-curing temperature in step (2) is 70-90℃ and the pre-curing time is 20-40min.

5. The preparation method according to any one of claims 1-4, characterized in that, The rolling process described in step (3) is carried out in a two-roll mill; Preferably, the rolling process in step (3) is carried out at 40-70°C; Preferably, the repeated stacking and rolling steps in step (3) specifically refer to repeating the stacking and rolling steps 5-20 times; Preferably, the orientation degree of the two-dimensional filler in the composite membrane obtained in step (3) is >90%.

6. The preparation method according to any one of claims 1-5, characterized in that, The thickness of the graphite film in step (4) is 0.02-0.03 mm; Preferably, step (4) of cross-laminating the graphite film and the composite film specifically includes: The graphite film and composite film are stacked in a cross-layered manner in the order of "graphite film-composite film-graphite film-composite film-...". Preferably, the thickness of the laminated preform obtained in step (4) is 25-35 mm.

7. The preparation method according to any one of claims 1-6, characterized in that, The hot pressing temperature in step (5) is 120-140℃, the hot pressing pressure is 4-6MPa, and the hot pressing time is 20-40min; Preferably, the hot pressing in step (5) is performed in a flatbed hot press.

8. The preparation method according to any one of claims 1-7, characterized in that, The slicing in step (6) is performed in a precision microtome; Preferably, the thickness of the high thermal conductivity composite pad obtained by slicing in step (6) is 0.4-0.6 mm.

9. A high thermal conductivity composite pad, characterized in that, The high thermal conductivity composite pad is prepared by the preparation method described in any one of claims 1-8; Preferably, the out-of-plane thermal conductivity of the high thermal conductivity composite gasket is ≥140W / (m·K), and more preferably 140-250W / (m·K).

10. The application of the high thermal conductivity composite pad as described in claim 9 in heat dissipation of electronic devices.

Images