Composite heat-conducting gasket as well as preparation method and application thereof

Abstract

The embodiment of the invention provides a composite heat-conducting gasket and a preparation method and application thereof. The preparation method comprises the following steps: preparing an organic silicon boron nitride dispersion liquid; coating the organic silicon boron nitride dispersion liquid on the surface of one side of the first base film to form a first coating layer; covering the surface of one side of the first coating layer with glass fiber cloth, and coating the surface of one side of the glass fiber cloth with the organic silicon boron nitride dispersion liquid to obtain a first composite film; sequentially carrying out preheating treatment and pre-curing treatment on the first composite membrane to obtain a second composite membrane; covering one side surface of the second composite film with a second base film to obtain a third composite film; performing two-way stretching treatment and cooling treatment on the third composite film to obtain a fourth composite film; and performing cross-linking curing treatment on the fourth composite film to obtain the composite heat-conducting gasket. By optimizing the preparation process of the composite heat-conducting gasket, uniform dispersion and vertical arrangement of the boron nitride nanosheets in the organic silicon matrix are realized, so that the vertical heat-conducting network is constructed.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of composite materials, in particular, to a composite heat-conductive gasket, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of 5G communication, artificial intelligence chips, and new energy vehicle electronic control systems, traditional isotropic heat-conductive materials (such as silicone grease and ordinary gaskets) cannot meet the precise heat dissipation requirements in high-frequency and high-temperature scenarios due to serious lateral heat diffusion and high local thermal resistance. Vertical heat-conductive materials achieve efficient heat conduction in the Z-axis direction (the length direction and the width direction of the heat-conductive gasket are defined as the X-axis and the Y-axis, respectively, and the direction perpendicular to the X-Y plane, i.e., the direction perpendicular to the plane of the heat-conductive gasket, is the Z-axis direction) by directional arrangement of high-aspect-ratio fillers (such as boron nitride nanosheets and carbon nanotubes), which becomes a key breakthrough direction for solving chip-level heat dissipation and preventing electromagnetic interference. However, due to uneven dispersion of fillers in the group and their directional arrangement depending on magnetic fields / electric fields, there are problems such as high energy consumption and uneven orientation, which limit the improvement of vertical heat-conduction performance and the stability of mechanical properties of the material.

[0003] However, it is not easy to achieve efficient dispersion and directional arrangement of fillers, especially commonly used boron nitride nanosheets (BNNS), in composite materials. First, BNNS is prone to agglomeration due to its extremely high surface energy and layered structure, which can seriously affect its dispersion in the organic matrix and thus reduce the overall thermal conductivity of the composite material. Second, the interface compatibility between BNNS and polymer matrices such as silicone is poor, and direct mixing often leads to uneven distribution of BNNS, forming areas with low thermal conductivity and affecting the construction of the heat conduction network. Third, the vertical arrangement of BNNS usually requires complex external fields (such as magnetic fields and electric fields) for assistance, which not only increases the preparation cost but also may introduce additional processing difficulties such as magnetic field strength control, electric field uniformity, and strict environmental conditions, making it difficult to achieve large-scale industrial production.

[0004] That is, the composite heat-conductive gasket in the prior art has poor dispersion, interface compatibility, and vertical orientation of the heat-conductive fillers, making it difficult to achieve efficient heat conduction in the Z-axis direction while maintaining excellent mechanical strength.

[0005] Currently, there is no good solution to the above problems. SUMMARY

[0006] Embodiments of the present application provide a composite heat-conductive gasket, a preparation method and application thereof, to at least solve the technical problem of poor mechanical properties of the composite heat-conductive gasket in the prior art, and difficulty in achieving efficient heat conduction in the Z-axis direction.

[0007] According to an aspect of the embodiments of the present application, a preparation method of a composite heat-conducting gasket is provided, comprising: step S1, preparing a silane coupling agent, boron nitride nanosheets, a silicone resin, and ethanol into a silicone-boron nitride dispersion liquid; step S2, preparing a first base film, and coating the silicone-boron nitride dispersion liquid onto a side surface of the first base film to form a first coating layer; covering a glass fiber cloth on a side surface of the first coating layer away from the first base film, and coating the silicone-boron nitride dispersion liquid onto a side surface of the glass fiber cloth away from the first base film to form a second coating layer, thereby obtaining a first composite film; step S3, the first composite film is sequentially subjected to preheating treatment and pre-curing treatment to obtain a second composite film; covering a second base film on a side surface of the second composite film away from the first base film to obtain a third composite film; the third composite film has a length direction and a width direction perpendicular to each other; step S4, the third composite film is subjected to bidirectional stretching treatment so that the length direction and the width direction of the third composite film are both in a stretched state; step S5, the third composite film in the stretched state is subjected to cooling treatment so that the boron nitride nanosheets are vertically oriented in the planar direction of the third composite film, thereby obtaining a fourth composite film in the stretched state; step S6, releasing the tension applied to the fourth composite film, and subjecting the fourth composite film to cross-linking and curing treatment to obtain the composite heat-conducting gasket.

[0008] Further, in step S1, the weight ratio of the silane coupling agent, the boron nitride nanosheets, and the silicone resin is 1:(2-12):(8-17); and / or the viscosity of the silicone-boron nitride dispersion liquid is 2000 mPa·s-5000 mPa·s.

[0009] Further, in step S2, the coating surface density of the first coating layer is 2.0±0.2 g / cm -3 ; and / or the coating surface density of the second coating layer is 1.8±0.1 g / cm -3 .

[0010] Further, in step S3, the preheating treatment is performed at a temperature of 60±5℃ for 4-6 min; and / or the pre-curing treatment is performed at a temperature of 80±5℃ for 10-30 min.

[0011] Further, in step S4, the stretching rate of the bidirectional stretching is 0.1-10 mm / s; and / or the stretching strain of the bidirectional stretching is 50%-300%.

[0012] Further, in step S5, the cooling treatment comprises: cooling the third composite film to -30±2℃ at a cooling rate of 1℃ / min-20℃ / min, and maintaining the temperature for 30±5min; and / or, before the cooling treatment, step S5 further comprises: maintaining the third composite film in a stretched state for 10±1min, and then performing the cooling treatment on the third composite film in the stretched state.

[0013] Further, in step S6, the releasing rate of the tension is 0.01mm / s-5mm / s; and / or, the holding temperature of the cross-linking and curing treatment is 100±10℃, and the holding time is 60±10min.

[0014] Further, the thickness of the boron nitride nanosheet is 10nm-20nm, and the flake diameter is 500nm-2000nm; and / or, the silane coupling agent is selected from one or more of KH550, KH570, KH580, A-174, A-1160, A-1310, A-1630 and F8261; and / or, the silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methyl phenyl silicone resin, phenolic silicone resin, vinyl silicone resin, amino silicone resin and polyester silicone resin; and / or, the first base film and the second base film are both polydimethylsiloxane films, and the thickness of the polydimethylsiloxane film is 50μm-100μm; and / or, the glass fiber cloth is selected from one or more of EWR200-100 alkali-free and untwisted roving cloth, CWR300-90 medium alkali and untwisted roving cloth, HT800 heat-treated glass fiber cloth, 7628 electronic cloth and GTG115 ultra-thin glass fiber cloth, and the thickness of the glass fiber cloth is 50μm-500μm.

[0015] According to another aspect of the embodiments of the present application, there is also provided a composite heat-conductive gasket prepared by the preparation method of the composite heat-conductive gasket.

[0016] According to another aspect of the embodiments of the present application, there is also provided an application of the composite heat-conductive gasket as a heat-conductive gasket in the fields of communication, semiconductor, industrial equipment, aerospace and new energy.

[0017] In the embodiments of the present application, by adopting the mode of bidirectional stretching combined with cooling treatment, the uniform dispersion and vertical arrangement of boron nitride nanosheets in the silicone matrix are realized by optimizing the overall preparation process of the composite heat-conductive gasket, thereby constructing a vertical heat-conductive network, improving the vertical heat-conductive performance of the obtained composite heat-conductive gasket, and further solving the technical problems of low heat dissipation efficiency, high local thermal resistance of traditional isotropic heat-conductive materials in high-frequency and high-temperature scenarios, and uneven dispersion of fillers, high directional arrangement energy consumption and complex process in the preparation process of vertical heat-conductive materials. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0019] Figure 1 is a cross-sectional scanning electron microscope (SEM) characterization result of the composite heat-conductive gasket obtained in Embodiment 1 of the application. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the embodiments.

[0021] As described in the background, the composite heat-conductive gasket in the prior art is difficult to achieve efficient heat conduction in the Z-axis direction while maintaining superior mechanical strength due to poor dispersion, interface compatibility, and vertical orientation of the heat-conductive filler thereon. In order to solve the above technical problems, according to an embodiment of the present application, a preparation method of a composite heat-conductive gasket is provided, comprising: step S1, preparing a silane coupling agent, boron nitride nanosheets, silicone resin, and ethanol into a silicone-boron nitride dispersion liquid; step S2, preparing a first base film, and coating the silicone-boron nitride dispersion liquid onto one side surface of the first base film to form a first coating layer; covering a glass fiber cloth on the side surface of the first coating layer away from the first base film, and coating the silicone-boron nitride dispersion liquid onto the side surface of the glass fiber cloth away from the first base film to form a second coating layer, thereby obtaining a first composite film; step S3, the first composite film is sequentially subjected to preheating treatment and pre-curing treatment to obtain a second composite film; covering a second base film on the side surface of the second composite film away from the first base film to obtain a third composite film; the third composite film has a length direction and a width direction perpendicular to each other; step S4, the third composite film is subjected to bidirectional stretching treatment so that the length direction and the width direction of the third composite film are both in a stretched state; step S5, the third composite film in the stretched state is subjected to cooling treatment so that the boron nitride nanosheets are vertically oriented in the planar direction of the third composite film, thereby obtaining a fourth composite film in the stretched state; step S6, releasing the tension applied to the fourth composite film, and subjecting the fourth composite film to crosslinking and curing treatment to obtain a composite heat-conductive gasket.

[0022] The application adopts a method of bidirectional stretching combined with cooling treatment, realizes uniform dispersion and vertical arrangement of boron nitride nanosheets in the silicone matrix by optimizing the overall preparation process of the composite thermal conductive gasket, thereby constructing a vertical thermal conduction network and improving the vertical thermal conduction performance of the obtained composite thermal conductive gasket. Specifically, in the above preparation process: in step S1, the boron nitride nanosheets are efficiently dispersed and surface functionalized by using ethanol solvent and silane coupling agent modification, so that alkyl groups are grafted on the surface of the boron nitride nanosheets, the interfacial compatibility between the boron nitride nanosheets and the silicone matrix is improved, the voids in the obtained composite layer in the microcosmic aspect are reduced, thereby reducing the interfacial thermal resistance and enhancing the heat conduction efficiency. In step S2, the first base film serves as a carrier, the silicone boron nitride dispersion liquid is uniformly coated, then the glass fiber cloth is covered, and another layer of dispersion liquid is coated to form a "sandwich" structure, wherein the composite layer containing boron nitride nanosheets is sandwiched between the silicone and the glass fiber cloth, thereby increasing the mechanical strength of the finally obtained composite thermal conductive gasket while more effectively improving the heat dissipation and insulation dual performance. The preheating treatment in step S3 realizes the preliminary infiltration of the silicone resin into the glass fiber cloth, and the pre-solidification treatment further reaches a semi-crosslinked state, laying a foundation for the subsequent bidirectional stretching. In steps S4 and S5, the bidirectional stretching treatment combined with the cooling treatment changes the orientation of the boron nitride nanosheets in the composite thermal conductive gasket from random orientation to perpendicular to the plane of the gasket, thereby constructing a straight-through heat conduction path, significantly reducing the thermal resistance along the Z axis, and improving the heat conduction efficiency. In the final step S6, the crosslinking and curing treatment not only completes the curing of the silicone resin and firmly embeds the boron nitride nanosheets and the glass fiber cloth into the silicone matrix, but also further enhances the mechanical properties of the obtained composite gasket. In summary, the composite thermal conductive gasket prepared in the application embodiment not only achieves significant improvement in Z-axis thermal conductivity, but also maintains good mechanical strength and insulation performance, which is suitable for high thermal load and high mechanical stress environments in the fields of high-frequency communication device heat dissipation, power battery PACK, etc., solving the problems of low heat dissipation efficiency and insufficient mechanical performance of traditional thermal conductive gaskets.

[0023] Furthermore, compared with the magnetic field-induced vertical orientation of boron nitride, the above preparation method of the application can more effectively construct a vertical thermal conduction network of the filler by using bidirectional stretching combined with cooling treatment. At the same time, the distribution uniformity of the boron nitride nanosheet filler is more significantly optimized, and agglomeration is avoided, so that the mechanical properties are better balanced. Furthermore, in terms of actual production, the above bidirectional stretching and cooling treatment provided by the application have good compatibility with existing production lines and can be integrated into the production process without major modification, which is easy to realize large-scale automated production. However, the magnetic field induction technology usually requires special equipment to generate a high-strength magnetic field, which not only increases the initial investment cost, but also consumes a large amount of electric energy during operation.

[0024] It is worth mentioning that, in the above preparation method provided by the present application, the composite film is strictly controlled to be cooled while maintaining the stretched state during the process of cooling and fixing the resin molecules. This is because when the composite film is in the stretched state, the fillers such as boron nitride nanosheets inside the composite film will be forced to arrange along the stretching direction. This arrangement is temporary under mechanical action, and once the external force is removed, the fillers may return to a more disordered state due to molecular thermal motion. Therefore, immediate cooling treatment during the stretching process can quickly reduce the temperature of the material, freeze the arrangement state of the fillers, and thus solidify the structural changes generated during the stretching process. The rapid temperature drop during the cooling process slows down the movement of the molecular chains, and the orientation of the fillers is fixed. This process is similar to "freezing" the composite material in the stretched state, ensuring that the directional arrangement of the fillers will not be destroyed due to molecular motion. At the same time, during the stretching and cooling process, the stress distribution in the material is fixed, which helps to form a more uniform and stable microstructure, thereby improving the mechanical properties of the material, such as tensile strength and toughness.

[0025] In actual application, the above preparation method further includes ultrasonic cleaning of the glass fiber cloth with dilute hydrochloric acid to remove impurities and grease on the surface of the glass fiber, improve the adhesion of subsequent processing, and further improve the production efficiency. For bidirectional stretching, it can be achieved by multiple rollers. In the mixing process at each stage, the uniform mixing method can be at least one of manual stirring, magnetic stirring, ultrasonic stirring, high-speed stirring, etc.

[0026] In several embodiments, in order to promote the surface of the boron nitride nanosheet to be sufficiently modified, thereby more effectively enhancing the bonding force with the silicone resin, while reducing the problem of agglomeration and uneven dispersion of fillers caused by excessive boron nitride nanosheets, in step S1, the weight ratio of silane coupling agent, boron nitride nanosheet and silicone resin is preferably 1:(2-12):(8-17).

[0027] In several embodiments, the viscosity of the silicone boron nitride dispersion liquid is 2000-5000 mPa·s, so as to better control the coating quality during the coating process and improve the uniformity and stability of the first coating layer and the second coating layer. On this basis, it is further preferred that the viscosity of the silicone boron nitride dispersion liquid is 3000±200 mPa·s, so as to further optimize the rheological properties of the dispersion liquid, so that the stress distribution during the coating, pre-solidification and stretching and cooling processes is more uniform, which is more conducive to the vertical orientation of the boron nitride nanosheet and the forming of the composite film, thereby more significantly improving the Z-axis thermal conductivity and overall mechanical properties of the obtained composite thermal pad.

[0028] In several embodiments, it is preferred that the coating area density of the first coating layer in step S2 is 2.0±0.2 g / cm -3; and / or, the second coating layer has a coating surface density of 1.8±0.1 g / cm -3 , thereby helping to further optimize the balance between the thermal conductivity and the mechanical strength of the resulting composite heat-conductive gasket, so as to ensure good heat dissipation effect while having higher tensile strength.

[0029] In step S3, the temperature of the pre-treatment is preferably 60±5℃, and the time is 4min-6min, thereby promoting more sufficient infiltration of the silicone resin into the glass fiber cloth. In addition, the temperature of the pre-curing treatment is preferably 80±5℃, and the time is 10min-30min, so as to promote the resulting composite film to be in a semi-crosslinked state, thereby enhancing the stability of the resulting composite structure while leaving room for subsequent directional orientation treatment, so as to obtain a composite heat-conductive gasket with more superior comprehensive performance.

[0030] In several embodiments, the stretching rate of the bidirectional stretching in step S4 is 0.1mm / s-10mm / s, preferably 1±0.05mm / s, so as to promote the boron nitride nanosheet to be more smoothly vertically oriented under the condition of reducing disordered movement or excessive deformation. At the same time, the stretching strain of the bidirectional stretching is preferably 50%-300%, more preferably 200±20%, so as to reduce the cracks and fractures that may occur during the stretching process, while also more effectively achieving the efficient vertical orientation of the boron nitride nanosheet and the enhancement of the mechanical properties of the final resulting composite heat-conductive gasket.

[0031] Further, in order to more quickly freeze the molecular chain movement in the silicone resin, thereby more efficiently locking the vertical arrangement of the boron nitride nanosheet, optimizing the microstructure and thermal conductivity performance of the final resulting composite heat-conductive gasket, the cooling treatment in step S5 preferably includes: cooling the third composite film to -30±2℃ at a cooling rate of 1℃ / min-20℃ / min, and maintaining the temperature for 30±5min. It is further preferred that the cooling rate is 10±2℃ / min, so as to reduce the phenomenon of internal stress concentration on the basis of rapid cooling to fix the orientation, thereby further improving the microstructure integrity and overall mechanical properties of the resulting composite heat-conductive gasket.

[0032] Before the cooling treatment, step S5 preferably further includes: maintaining the third composite film in the stretched state for 10±1min, and then cooling the third composite film in the stretched state. The above preferred scheme can promote more sufficient optimization of the vertical orientation of the boron nitride nanosheet, provide a more sufficient time window for the subsequent cooling treatment and orientation fixation, thereby making the thermal conductivity in the Z-axis direction greater, while also making the mechanical properties of the composite heat-conductive gasket stable.

[0033] Further, in step S6, the release rate of the pulling force is preferably 0.01 mm / s to 5 mm / s, and more preferably 0.5 ± 0.02 mm / s, so as to further balance the stability of the vertical orientation of the boron nitride nanosheets and the ability of the composite film structure to recover. In addition, the holding temperature of the cross-linking and curing treatment is preferably 100 ± 10°C, and the holding time is preferably 60 ± 10 min, so as to facilitate the complete curing of the silicone resin and form a more stable three-dimensional network structure, i.e., the boron nitride nanosheets are more firmly embedded in the composite thermal pad, thereby not only significantly improving the thermal conductivity in the Z-axis direction, but also imparting more excellent mechanical properties to the obtained composite thermal pad.

[0034] In some embodiments, the thickness of the boron nitride nanosheets is 10 nm to 20 nm, and the flake diameter is 500 nm to 2000 nm, so as to facilitate the boron nitride nanosheets to have sufficient surface area to increase their contact with the silicone matrix, and further facilitate the establishment of the Z-axis thermal conduction path, while facilitating dispersion, and ultimately improving the anisotropic thermal conductivity of the obtained composite thermal pad as a whole. In addition, the silane coupling agent is preferably selected from one or more of KH550, KH570, KH580, A-174, A-1160, A-1310, A-1630, and F8261; and / or, the silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methyl phenyl silicone resin, phenolic silicone resin, vinyl silicone resin, amino silicone resin, and polyester silicone resin.

[0035] In addition, in order to enhance the bonding and compatibility between the layers and achieve more excellent mechanical properties, the first base film and the second base film are preferably both polydimethylsiloxane films, and the thickness of the polydimethylsiloxane film is 50 μm to 100 μm; and / or, the glass fiber cloth is selected from one or more of EWR200-100 alkali-free twisted roving cloth, CWR300-90 medium alkali twisted roving cloth, HT800 heat-treated glass fiber cloth, 7628 electronic cloth, and GTG115 ultra-thin glass fiber cloth, and the thickness of the glass fiber cloth is 50 μm to 500 μm.

[0036] The embodiments of the present application also provide a composite thermal pad prepared by the above-mentioned method for preparing a composite thermal pad. Due to the use of the above-mentioned preparation method, the obtained composite thermal pad has a unique vertical thermal conduction network in the microstructure, and the directional arrangement of the boron nitride nanosheets in the Z-axis direction makes the thermal conductivity of the pad in the vertical direction significantly higher than that of traditional isotropic materials. At the same time, the addition of the glass fiber cloth ensures the mechanical strength of the pad when it is subjected to pressure and bending. In addition, due to the improvement of the interface between the boron nitride nanosheets and the silicone matrix, the insulation of the pad is also enhanced, and finally the pad exhibits good mechanical properties and excellent thermal conductivity and heat dissipation in the Z-axis direction.

[0037] The embodiments of the present application also provide application of the above-mentioned composite heat-conducting gasket as a heat-conducting gasket in the fields of communication, semiconductors, industrial equipment, aerospace and new energy. Thanks to the optimization of the vertical orientation of the boron nitride nanosheets and the mechanical properties of the composite material in the preparation process of the above-mentioned composite heat-conducting gasket, the obtained composite heat-conducting gasket can meet the use requirements of various application fields. Especially in the fields of communication and semiconductors, the composite heat-conducting gasket obtained by the present application can cope with the heat dissipation challenge brought by high-frequency high-speed signals; and in the field of new energy, especially in the field of power battery PACK, the high thermal conductivity and good insulation of the gasket can effectively manage and reduce the heat accumulation in the battery pack, improve the safety and service life of the battery.

[0038] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0039] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0040] The present application will be further described in detail below in conjunction with specific embodiments, which cannot be understood as limiting the scope of protection claimed by the present application.

[0041] Unless otherwise defined, all professional terms used herein have the same meaning as understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0042] Embodiment 1

[0043] A preparation method of a composite heat-conducting gasket:

[0044] (1) Preparation of an organic silicon boron nitride dispersion liquid:

[0045] (1-1) Take 0.5 g of KH550 silane coupling agent, dissolve it in ethanol organic solvent to obtain a KH550 solution;

[0046] (1-2) Take 5 g of boron nitride nanosheet powder (thickness of 15 nm, flake diameter of 2000 nm), add it to the above KH550 solution, and probe ultrasonic and high-speed stirring to obtain a boron nitride nanosheet dispersion;

[0047] (1-3) Take 42.5 g of silicone resin (model: vinyl silicone resin DT-6901) and 2 g of KH550 silane coupling agent, mix and low-speed stir to obtain a silicone slurry;

[0048] (1-4) Add the boron nitride nanosheet dispersion to the above silicone slurry in batches, and realize uniform mixing by homogenizing with a homogenizer and high-speed stirring;

[0049] (1-5) Provide ethanol, add it to the above mixed slurry to adjust the slurry viscosity to 3000 mPa·s (Brookfield viscometer, 25°C), vacuum degassing to obtain a silicone boron nitride dispersion. In the obtained silicone boron nitride dispersion, the weight ratio of silane coupling agent, boron nitride nanosheet and silicone resin is 1:2:17.

[0050] (2) Take a polydimethylsiloxane (PDMS) base film with a thickness of 50 μm as a lower base film, and successively: coat the silicone boron nitride dispersion with a coating surface density of 2.0 g / cm -3 , cover a glass fiber cloth (i.e. fiberglass cloth, model: 7628 electronic cloth) with a thickness of 100 μm, and then coat the silicone boron nitride dispersion with a coating surface density of 1.8 g / cm -3 , to obtain a first composite film.

[0051] (3) Preheat the slurry at a temperature of 60°C for 5 min to make the slurry preliminarily infiltrate the fiberglass cloth, then increase the temperature to 80°C to pre-cure the slurry for 20 min to form a semi-crosslinked gel, to obtain a second composite film. Then cover a PDMS base film as an upper base film to form a laminated composite gel structure, i.e. a third composite film.

[0052] (4) Stretch the third composite film in two directions by using multi-stage rollers, so that the third composite film is in a stretched state in both the length direction and the width direction. That is, the strain is made to reach 200% at a stretching rate of 1 mm / s, so as to force the boron nitride nanosheets to vertically arrange.

[0053] (5) After maintaining the stretched state for 10 min, continue to cool the stretched state to -30°C at a rate of 10°C / min by using a water-cooled roller, and keep the temperature for 30 min, to freeze the resin molecular chain movement and fix the vertical orientation of the boron nitride nanosheets, thereby obtaining a fourth composite film.

[0054] (6) After slowly releasing the tension at a rate of 0.5 mm / s, the temperature is raised to 100°C, and the cross-linking and curing are carried out for 60 min, to obtain a boron nitride-silicone / glass fiber composite vertical heat-conducting gasket, i.e., a composite heat-conducting gasket.

[0055] The cross-sectional SEM characterization results of the obtained composite heat-conducting gasket are shown in Figure 1 .

[0056] Example 2

[0057] A method for preparing a composite heat-conducting gasket comprises the following steps:

[0058] This example is different from Example 1 only in step (1), specifically:

[0059] (1) Preparing a silicone-boron nitride dispersion liquid:

[0060] (1-1) 1 g of KH550 silane coupling agent is weighed and dissolved in an ethanol organic solvent to obtain a KH550 solution;

[0061] (1-2) 10 g of boron nitride nanosheet powder (15 nm in thickness and 1500 nm in diameter) is weighed and added to the above KH550 solution, and a boron nitride nanosheet dispersion liquid is obtained by probe ultrasonic and high-speed stirring;

[0062] (1-3) 37.5 g of silicone resin (model: Dow Corning 840 methyl phenyl silicone resin) and 1.5 g of KH550 silane coupling agent are weighed and mixed to obtain a silicone slurry by low-speed stirring;

[0063] (1-4) The boron nitride nanosheet dispersion liquid is added to the above silicone slurry in batches, and the uniform mixing is realized by homogenization and high-speed stirring;

[0064] (1-5) Ethanol is provided and added to the above mixed slurry to adjust the slurry viscosity to 3000 mPa·s (Brookfield viscometer, 25°C), and vacuum degassing is performed to obtain a silicone-boron nitride dispersion liquid. In the obtained silicone-boron nitride dispersion liquid, the weight ratio of the silane coupling agent, the boron nitride nanosheet, and the silicone resin is 1:4:15.

[0065] Example 3

[0066] A method for preparing a composite heat-conducting gasket comprises the following steps:

[0067] This example is different from Example 1 only in step (1), specifically:

[0068] (1) Preparing a silicone-boron nitride dispersion liquid:

[0069] (1-1) Take 1.5 g of KH550 silane coupling agent, dissolve it in ethanol organic solvent to obtain a KH550 solution;

[0070] (1-2) Take 30 g of boron nitride nanosheet powder (thickness of 20 nm, flake diameter of 1000 nm), add it to the above KH550 solution, and obtain a boron nitride nanosheet dispersion by probe ultrasonic and high-speed stirring;

[0071] (1-3) Take 20 g of silicone resin (model K328 amino silicone resin) and 1 g of KH550 silane coupling agent, mix them to obtain a silicone slurry by low-speed stirring;

[0072] (1-4) Add the boron nitride nanosheet dispersion to the above silicone slurry in batches, and realize uniform mixing by homogenizing and high-speed stirring;

[0073] (1-5) Provide ethanol, add it to the above mixed slurry to adjust the slurry viscosity to 3000 mPa·s (Brookfield viscometer, 25°C), vacuum degassing to obtain a silicone boron nitride dispersion. In the obtained silicone boron nitride dispersion, the weight ratio of silane coupling agent, boron nitride nanosheet and silicone resin is 1:12:8.

[0074] Example 4

[0075] A preparation method of a composite heat-conducting gasket:

[0076] The difference between this example and Example 1 is only that in the obtained silicone boron nitride dispersion in step (1), the weight ratio of silane coupling agent, boron nitride nanosheet and silicone resin is changed to 1:1:18.

[0077] Example 5

[0078] A preparation method of a composite heat-conducting gasket:

[0079] The difference between this example and Example 1 is only that in the obtained silicone boron nitride dispersion in step (1), the weight ratio of silane coupling agent, boron nitride nanosheet and silicone resin is changed to 1:14:5.

[0080] Example 6

[0081] A preparation method of a composite heat-conducting gasket:

[0082] The difference between this example and Example 1 is only that the viscosity of the obtained silicone boron nitride dispersion in step (1) is changed to 2000 mPa·s.

[0083] Example 7

[0084] A preparation method of a composite heat-conducting gasket:

[0085] This example differs from Example 1 only in that the viscosity of the silicone boron nitride dispersion obtained in step (1) is changed to 5000 mPa-s.

[0086] Example 8

[0087] A method for producing a composite heat-conducting gasket:

[0088] This example differs from Example 1 only in that in step (3), the temperature of the preheating treatment is changed to 50°C and the time is changed to 10 min; and in the pre-curing treatment, the temperature is changed to 70°C and the time is changed to 40 min.

[0089] Example 9

[0090] A method for producing a composite heat-conducting gasket:

[0091] This example differs from Example 1 only in that in step (3), the temperature of the preheating treatment is changed to 70°C and the time is changed to 3 min; and in the pre-curing treatment, the temperature is changed to 90°C and the time is changed to 5 min.

[0092] Example 10

[0093] A method for producing a composite heat-conducting gasket:

[0094] This example differs from Example 1 only in that in step (4), the stretching rate of the biaxial stretching is changed to 0.1 mm / s and the stretching strain is changed to 300%.

[0095] Example 11

[0096] A method for producing a composite heat-conducting gasket:

[0097] This example differs from Example 1 only in that in step (4), the stretching rate of the biaxial stretching is changed to 10 mm / s and the stretching strain is changed to 50%.

[0098] Example 12

[0099] A method for producing a composite heat-conducting gasket:

[0100] This example differs from Example 1 in the cooling conditions in step (5), i.e., the temperature is decreased to -40°C at a rate of 1°C / min.

[0101] Example 13

[0102] A method for producing a composite heat-conducting gasket:

[0103] The difference between this example and Example 1 is the cooling condition in step (5), i.e., cooling at a rate of 20°C / min to -20°C.

[0104] Example 14

[0105] A method for preparing a composite heat-conductive gasket:

[0106] The difference between this example and Example 1 is that, before the cooling treatment in step (5), the stretched state is not maintained for 10 min, but the cooling treatment is directly performed after the tensile strain reaches 200%.

[0107] Example 15

[0108] A method for preparing a composite heat-conductive gasket:

[0109] The difference between this example and Example 1 is that, in step (6), the release rate of the tension is changed to 0.01 mm / s, and the holding temperature for cross-linking and curing is changed to 120°C.

[0110] Example 16

[0111] A method for preparing a composite heat-conductive gasket:

[0112] The difference between this example and Example 1 is that, in step (6), the release rate of the tension is changed to 5 mm / s, and the holding temperature for cross-linking and curing is changed to 90°C.

[0113] Comparative Example 1

[0114] A method for preparing a composite heat-conductive gasket:

[0115] (1) Preparation of a silicone-boron nitride dispersion liquid: 20 g of a silicone resin and 30 g of boron nitride nanosheets and 5 g of KH550 silane coupling agent were weighed and mixed at low speed to obtain a silicone slurry; ethanol was provided and added to the above mixed slurry to adjust the slurry viscosity to 3000 mPa·s (Brookfield viscometer, 25°C), and vacuum degassing was performed to obtain a silicone-boron nitride dispersion liquid.

[0116] (2) The PDMS-based film was coated with the silicone slurry in sequence, and then pre-cured at 80°C for 20 min to form a semi-crosslinked gel, and then further heated to 100°C and held for 60 min to achieve cross-linking and curing, thereby obtaining a composite heat-conductive gasket.

[0117] Comparative Example 2

[0118] A method for preparing a composite heat-conductive gasket:

[0119] The difference between this comparative example and Example 1 is only that the freezing treatment of step (5) is not performed, but after maintaining the stretched state for 10 min, the tension is slowly released at a rate of 0.5 mm / s directly, and the subsequent steps are performed.

[0120] Comparative Example 3

[0121] A preparation method of a composite heat-conducting gasket:

[0122] The difference between this comparative example and Example 1 is only in steps (5) and (6), specifically:

[0123] (5) After maintaining the stretched state for 10 min, the tension is slowly released at a rate of 0.5 mm / s. Then, the temperature is lowered to -30℃ at a rate of 10℃ / min by a water-cooled roller, and the temperature is maintained for 30 min to freeze the molecular chain movement of the resin and fix the vertical orientation of the boron nitride nanosheet, thereby obtaining a fourth composite film.

[0124] (6) The obtained fourth composite film is heated to 100℃ and maintained for 60 min to achieve cross-linking and curing, thereby obtaining a boron nitride-organic silicon / glass fiber composite vertical heat-conducting gasket, i.e., a composite heat-conducting gasket.

[0125] That is, this comparative example does not cool under the stretched state, but first releases the stretched state, and then performs the cooling treatment.

[0126] Test method

[0127] Density (p): calculated by a conventional method.

[0128] Specific heat capacity (Cp): measured by a sapphire method using NETZSCH DSC3500.

[0129] Tensile strength: tested according to GB / T 528-2009 using a universal testing machine.

[0130] Thermal conductivity (perpendicular to the plane of the gasket): first, the thermal diffusivity a of each heat-conducting gasket sample is measured using a flash method thermal diffusivity tester (LFA-467), and then the corresponding vertical thermal conductivity is calculated according to λ = a·p·Cp. p

[0131] The heat-conducting gasket samples obtained in each example and comparative example are tested respectively according to the above test method, and the results are shown in Table 1.

[0132] Table 1

[0133] Vertical thermal conductivity (W m -1 ·K -1 )]]> Tensile strength (MPa) Example 1 1.00 40 Example 2 2.00 28 Example 3 3.50 25 Example 4 0.91 20 Example 5 0.89 21 Example 6 0.77 19 Example 7 0.79 18 Example 8 0.89 18 Example 9 0.91 20 Example 10 0.86 23 Example 11 0.88 24 Example 12 0.91 22 Example 13 0.89 20 Example 14 0.88 19 Example 15 0.86 17 Example 16 0.90 18 Comparative Example 1 0.70 22 Comparative Example 2 0.59 22 Comparative Example 3 0.66 23

[0134] ​From the above description, it can be seen that, compared with the various comparative examples, the composite heat-conducting gasket obtained by the above-mentioned embodiments of the present application has a unique vertical heat-conducting network in the microstructure. The directional arrangement of the boron nitride nanosheets in the Z-axis direction makes the thermal conductivity of the gasket in the vertical direction significantly higher than that of conventional isotropic materials. At the same time, the addition of the glass fiber cloth ensures the mechanical strength of the gasket when it is subjected to pressure and bending. In addition, due to the improvement of the interface between the boron nitride nanosheets and the silicone matrix, the insulation of the gasket is also enhanced, ultimately exhibiting good mechanical properties and superior heat-conducting and heat-dissipating properties in the Z-axis direction.

[0135] Furthermore, as can be seen from Examples 1 to 3, as the filling amount of the boron nitride nanosheets increases, the vertical thermal conductivity of the obtained composite heat-conducting gasket also increases, which is much greater than that of the silicone gasket of Comparative Example 1, indicating that the vertical thermal conductivity of silicone can be effectively improved by compounding boron nitride nanosheets and in the manner of stretching and freezing. Secondly, although the tensile strength gradually decreases as the content of boron nitride nanosheets increases, it can still maintain a relatively high value, which is because, on the one hand, the contact interface between the boron nitride nanosheets and the silicone can be effectively improved through silane modification, and on the other hand, the glass fiber can play a reinforcing role to a certain extent.

[0136] Further, as can be seen from the comparison of Examples 4 and 5 with Example 1, in step S1, the weight ratio of the silane coupling agent, the boron nitride nanosheets and the silicone resin in the silicone-boron nitride dispersion liquid can promote the surface of the boron nitride nanosheets to be sufficiently modified, thereby more effectively enhancing the bonding force with the silicone resin, while reducing the problems of agglomeration and uneven distribution of fillers caused by excessive boron nitride nanosheets, and ultimately obtaining a composite heat-conducting gasket with better comprehensive performance.

[0137] As can be seen from the comparison of Examples 6 and 7 with Example 1, also in step S1, the viscosity of the silicone-boron nitride dispersion liquid can further optimize the rheological properties of the dispersion liquid, so that the stress distribution in the process of coating, pre-curing and stretching and cooling is more uniform, which is more conducive to the vertical orientation of the boron nitride nanosheets and the formation of the composite film, thereby more significantly improving the Z-axis thermal conductivity and overall mechanical properties of the obtained composite heat-conducting gasket.

[0138] As can be seen from the comparison of Examples 8 and 9 with Example 1, in step S3, the preferred conditions of the pre-heating treatment and the pre-curing treatment can promote the silicone resin to more fully infiltrate the glass fiber cloth, while making the obtained composite film in a semi-crosslinked state, thereby enhancing the stability of the obtained composite structure while leaving room for the subsequent directional orientation treatment, and obtaining a composite heat-conducting gasket with more superior comprehensive performance.

[0139] Comparing example 10, 11 with example 1, it can be seen that in step S4, the stretching rate and stretching strain of the preferred bidirectional stretching can promote the more stable vertical orientation of the boron nitride nanosheet, and at the same time, more effectively realize the high-efficiency vertical orientation of the boron nitride nanosheet, and the enhancement of the mechanical properties of the final obtained composite thermal conductive gasket.

[0140] Comparing example 12, 13 with example 1, it can be seen that in step S5, the preferred cooling rate and temperature condition in the cooling process can more efficiently lock the vertical arrangement of the boron nitride nanosheet, and at the same time, on the basis of the rapid cooling fixation of the orientation, reduce the phenomenon of internal stress concentration, and further improve the microstructure integrity and overall mechanical properties of the obtained composite thermal conductive gasket.

[0141] Comparing example 14 with example 1, it can be seen that in step S5, the preferred cooling treatment after keeping the stretching state for a certain period of time can promote the more sufficient optimization of the vertical orientation of the boron nitride nanosheet, provide a more sufficient time window for the subsequent cooling treatment and orientation fixation, so as to make the thermal conductivity in the Z-axis direction larger, and at the same time, make the mechanical properties of the composite thermal conductive gasket stable.

[0142] Comparing example 15, 16 with example 1, it can be seen that in step S6, the preferred release rate of tension and holding temperature of crosslinking and curing can better balance the stability of the vertical orientation of the boron nitride nanosheet and the ability of the composite film structure to recover. At the same time, promote the complete curing of the silicone resin, form a more stable three-dimensional network structure, so as to not only more significantly improve the thermal conductivity in the Z-axis direction, but also endow the obtained composite thermal conductive gasket with more excellent mechanical properties.

[0143] In the above examples of the present application, the description of each example has its own emphasis, and the parts not described in detail in a certain example can be referred to the related description of other examples.

[0144] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be regarded as the protection scope of the present application.

Claims

1. A method for preparing a composite thermally conductive pad, characterized in that, include: Step S1: Prepare an organosilicon boron nitride dispersion by mixing silane coupling agent, boron nitride nanosheets, organosilicon resin and ethanol. Step S2: Prepare a first base film and coat the organosilicon boron nitride dispersion onto one side surface of the first base film to form a first coating layer; A glass fiber cloth is covered on the surface of the first coating layer away from the first base film, and the organosilicon boron nitride dispersion is coated onto the surface of the glass fiber cloth away from the first base film to form a second coating layer, thereby obtaining a first composite film. Step S3: The first composite film is subjected to preheating and pre-curing treatments in sequence to obtain a second composite film; a second base film is then applied to the surface of the second composite film away from the first base film to obtain a third composite film; the third composite film has mutually perpendicular length and width directions. Step S4: The third composite film is subjected to biaxial stretching treatment so that the length direction and the width direction of the third composite film are both in a stretched state. Step S5: Cool the third composite film in the stretched state to make the boron nitride nanosheets perpendicular to the plane of the third composite film, thereby obtaining the fourth composite film in the stretched state. Step S6: Release the tension applied to the fourth composite film and perform cross-linking curing treatment on the fourth composite film to obtain the composite thermal conductive pad.

2. The method for preparing the composite thermally conductive pad according to claim 1, characterized in that, In step S1 The weight ratio of the silane coupling agent, the boron nitride nanosheets, and the organosilicon resin is 1:(2-12). (8–17); and / or, The viscosity of the organosilicon boron nitride dispersion is 2000 mPa·s to 5000 mPa·s.

3. The method for preparing the composite thermally conductive pad according to claim 1, characterized in that, In step S2, the surface density of the first coating layer is 2.0 ± 0.2 g / cm³. -3 ; and / or, the areal density of the second coating layer is 1.8 ± 0.1 g / cm³. -3 .

4. The method for preparing the composite thermally conductive pad according to any one of claims 1 to 3, characterized in that, In step S3 The preheating treatment is performed at a temperature of 60±5℃ for a time of 4 to 6 minutes; and / or, The pre-curing treatment is performed at a temperature of 80±5℃ for a time of 10 min to 30 min.

5. The method for preparing the composite thermally conductive pad according to any one of claims 1 to 3, characterized in that, In step S4 The biaxial stretching rates are all from 0.1 mm / s to 10 mm / s; and / or, The tensile strain of the biaxial stretching is 50% to 300%.

6. The method for preparing the composite thermally conductive pad according to any one of claims 1 to 3, characterized in that, In step S5 The cooling process includes: cooling the third composite film to -30±2℃ at a cooling rate of 1℃ / min to 20℃ / min, and holding it at that temperature for 30±5min; and / or, Before the cooling treatment, step S5 further includes: first maintaining the third composite film in the stretched state for 10±1 min, and then performing the cooling treatment on the third composite film in the stretched state.

7. The method for preparing the composite thermally conductive pad according to any one of claims 1 to 3, characterized in that, In step S6 The release rate of the tension is 0.01 mm / s to 5 mm / s; and / or, The cross-linking curing treatment is held at a temperature of 100±10℃ for 60±10 min.

8. The method for preparing the composite thermally conductive pad according to any one of claims 1 to 3, characterized in that, The boron nitride nanosheets have a thickness of 10 nm to 20 nm and a diameter of 500 nm to 2000 nm; and / or, The silane coupling agent is selected from one or more of KH550, KH570, KH580, A-174, A-1160, A-1310, A-1630, and F8261; and / or, The silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, phenolic silicone resin, vinyl silicone resin, amino silicone resin, and polyester silicone resin; and / or, Both the first base film and the second base film are polydimethylsiloxane films, and the thickness of the polydimethylsiloxane film is 50 μm to 100 μm; and / or, The glass fiber cloth is selected from one or more of EWR200-100 alkali-free untwisted roving, CWR300-90 medium-alkali untwisted roving, HT800 heat-treated glass fiber cloth, 7628 electronic cloth and GTG115 ultra-thin glass fiber cloth, and the thickness of the glass fiber cloth is 50μm to 500μm.

9. A composite thermally conductive pad, characterized in that, The thermally conductive composite pad is prepared by the method for preparing a composite thermally conductive pad according to any one of claims 1 to 8.

10. The composite thermally conductive pad of claim 9 is used as a thermally conductive pad in the fields of communications, semiconductors, industrial equipment, aerospace, and new energy.

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