WO2022120700A1 - 一种石墨取向型热界面材料的制备方法 - Google Patents

一种石墨取向型热界面材料的制备方法 Download PDF

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WO2022120700A1
WO2022120700A1 PCT/CN2020/135210 CN2020135210W WO2022120700A1 WO 2022120700 A1 WO2022120700 A1 WO 2022120700A1 CN 2020135210 W CN2020135210 W CN 2020135210W WO 2022120700 A1 WO2022120700 A1 WO 2022120700A1
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graphite
mixture
thermal interface
interface material
lamellar
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French (fr)
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曾小亮
张晨旭
叶振强
任琳琳
张月星
许建斌
孙蓉
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中国科学院深圳先进技术研究院
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L75/00—Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
    • C08L75/04—Polyurethanes
    • C08L75/08—Polyurethanes from polyethers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
    • C08L83/04—Polysiloxanes
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/14—Solid materials, e.g. powdery or granular

Definitions

  • the invention belongs to the technical field of thermally conductive polymer-based composite materials, and in particular relates to a preparation method of a graphite-oriented thermal interface material.
  • thermal interface materials In order to effectively dissipate heat from electronic products, thermal interface materials must be used between the heat source and the heat sink.
  • the thermal interface material is usually a composite material with a flexible polymer material as a matrix and a thermally conductive filler, which can effectively fill the gap between the solid-solid interface and increase the effective contact area, thereby improving the heat dissipation efficiency.
  • Commonly used thermal interface materials include thermally conductive silicone grease, thermally conductive gel, and thermally conductive gaskets. Compared with other types of thermal interface materials, the thermal pad itself has higher thermal conductivity, and has the characteristics of simple operation and strong applicability.
  • the thermal conductive fillers of common thermal interface materials are mainly high thermal conductive ceramic particles or metal powders.
  • the thermal conductivity of the thermal interface material can be significantly improved, and the thermal conductivity is usually lower than 7W ⁇ m -1 ⁇ K -1 .
  • the rapid development of the electronics industry makes it increasingly difficult for traditional thermal interface materials to meet today's heat dissipation needs. Therefore, there is an urgent need to develop new thermal interface materials to solve the thermal management problems faced by the electronics industry.
  • Patent CN 102433105 B discloses a composition and method containing oriented graphite particles and acrylate-based macromolecular polymers. The method proposes that the mixture is obtained by mechanical mixing first, and then the sheet material is obtained by calendering or pressing, and then the above-mentioned sheet material is laminated and then cut along the direction perpendicular to the orientation of the graphite particles, so as to obtain a final product with an out-of-plane height Thermal pad material for thermally conductive features. Both the stirring process and the lamination process used in this method are operated in an air atmosphere, so it is inevitable that a large number of air bubbles will be introduced into the mixture, thereby seriously increasing the intrinsic thermal resistance of the thermally conductive gasket.
  • Patent CN 111267434 A discloses a thermally conductive electromagnetic shielding material with an orientation structure and a preparation method thereof.
  • the method uses thermoplastic polymer as the matrix, first dissolves the matrix by a solvent, then prepares a mixture by mechanical mixing, then prepares a sheet-like material by coating, and then adopts lamination processing and cutting processing to obtain a sheet-like filler along the surface Externally oriented thermally conductive gasket material.
  • the sheet filler can achieve a certain degree of orientation by this method, the porosity problem of the thermally conductive gasket material is still unsolved.
  • the hardness of the thermoplastic matrix increases rapidly after the filler is added, and the thermal contact resistance is large.
  • the purpose of the present invention is to provide a preparation method of a graphite-oriented thermal interface material .
  • the present invention provides a preparation method of a graphite-oriented thermal interface material, comprising the following steps:
  • the laminated samples are processed by means of vacuum pressure, and the temperature is slowly increased in the process, so that the mixture is transformed from a solid state to a viscous flow state, and a dense sample preform is obtained;
  • step 2 includes slit extrusion, blade coating, and double-roll coating;
  • the thickness of the lamellar mixture after the orientation treatment in step 2) is not greater than 20 times the average particle size of the graphite filler.
  • the freezing treatment described in step 3 includes liquid nitrogen treatment and liquid oxygen treatment.
  • the pressure is 5-30 psi
  • the temperature is 30-90° C.
  • the time is 4-12 hours.
  • the high-temperature curing described in step 6) is different for different material systems.
  • the curing temperature is 90 ⁇ 120° C., and the curing time is 1 ⁇ 4 hours; for epoxy systems, the curing temperature is 70 ⁇ 120°C. 160°C, the curing time is 0.5-3 hours; for silicone rubber systems, the curing temperature is 80-200°C, and the curing time is 0.5-4 hours.
  • step 7 includes laser cutting and ultrasonic cutting.
  • the present invention provides a graphite-oriented thermal interface material, comprising graphite fillers, microscopic thermally conductive fillers, and a polymer matrix;
  • the microscopic thermally conductive filler is a particulate filler with a micron size or a nanometer size
  • the preparation method of the graphite-oriented thermal interface material comprises the following steps:
  • the laminated samples are processed by means of vacuum pressure, and the temperature is slowly increased in the process, so that the mixture is transformed from a solid state to a viscous flow state, and a dense sample preform is obtained;
  • the graphite fillers include one or more of flake graphite, graphene, graphene microflakes and artificial graphite microflakes; preferably, the particle size of the graphite fillers is 10-1000 microns, preferably is 50 to 500 microns;
  • the microscopic thermally conductive filler is a metal material or an inorganic non-metallic material; more preferably, the metal material includes one or more of aluminum, copper, and silver; more preferably, the inorganic non-metallic material includes One or more of silicon nitride, silicon carbide, silicon dioxide, boron nitride, aluminum oxide, and zinc oxide; more preferably, the particle size of the microscopic thermally conductive filler is 0.5-100 microns, preferably 3- 20 microns;
  • the polymer matrix includes one or more of a polyurethane system, an epoxy resin system, and a silicone rubber system.
  • the total volume percentage of the graphite-based filler in the graphite-oriented thermal interface material is 1-80%, preferably 30-60%;
  • the microscopic thermally conductive filler accounts for 0-10% of the total volume of the graphite-oriented thermal interface material, preferably 2-8%;
  • the total volume percentage of the polymer matrix in the graphite-oriented thermal interface material is 20-95%, preferably 27-63%.
  • step 1) is carried out under vacuum environment
  • the orientation treatment described in step 2) includes slit extrusion, blade coating, and double-roll coating;
  • the thickness of the lamellar mixture after the orientation treatment described in step 2) is not greater than 20 times the average particle size of the graphite filler
  • the freezing treatment described in step 3) includes liquid nitrogen treatment and liquid oxygen treatment;
  • the pressure is 5-30 psi
  • the temperature is 30-90°C
  • the time is 4-12 hours
  • the high-temperature curing described in step 6) is different for different material systems.
  • the curing temperature is 70-120° C., and the curing time is 1-4 hours;
  • the curing temperature is 70 ⁇ 120°C. 160°C, the curing time is 0.5-3 hours;
  • silicone rubber matrix the curing temperature is 80-200°C, and the curing time is 0.5-4 hours;
  • the cutting process described in step 7) includes laser cutting and ultrasonic cutting.
  • the beneficial effects of the present invention are: (1) The graphite-oriented thermal interface material prepared by the preparation method of the graphite-oriented thermal interface material of the present invention has high compactness (low porosity) and low thermal resistance. (2) The present invention realizes that the graphite filler has a high degree of orientation by means of orientation treatment such as slit extrusion; the present invention effectively fixes the molecular chain of the oriented mixed material through ultra-low temperature freezing treatment, prevents the occurrence of viscous flow, and can The mixture can be operated in a glass state, which avoids the difficult operation of the viscous-fluid mixture, which facilitates subsequent cutting, lamination and vacuum exhaust processing, which is beneficial to obtain a high degree of orientation and low porosity.
  • the thermal interface material is obtained; the vacuum pressure treatment is carried out in the state of the glass state of the mixture, which can reduce the porosity inside the material to the greatest extent, thereby improving the compactness of the material.
  • the present invention can achieve a high degree of densification of the material while achieving a high degree of orientation of the graphite-based filler. Therefore, the thermal interface material can be made with a low filler content.
  • the thermal conductivity is very high. high, the thermal resistance is low.
  • the lower filler content also endows the thermal interface material with good flexibility and elasticity.
  • the graphite-oriented thermal interface material of the present invention has stable performance, high degree of orientation, high density, and high thermal conductivity, and at the same time ensures good flexibility and resilience, thereby ensuring high coverage of heat sources and heat sinks for electronic devices It can be filled at a high rate, thereby effectively realizing the efficient heat dissipation of electronic devices.
  • the microscopic thermally conductive filler in the graphite-oriented thermal interface material of the present invention can better build a thermal conduction path inside the system; it can fill the micro-voids between the matrix molecules and bridge the graphite fillers, thereby helping to improve the thermal conductivity. Thermal conductivity of interface materials.
  • FIG. 1 is a scanning electron microscope image of the cross section of the thermal interface material prepared in Example 1 of the present invention.
  • Example 2 is a scanning electron microscope image of a longitudinal section of the thermal interface material prepared in Example 1 of the present invention.
  • Example 3 is a schematic structural diagram of the thermal interface material prepared in Example 1 of the present invention before ultrasonic cutting.
  • the following example illustrates the graphite-based filler/polymer-based thermal interface material with oriented structure characteristics and the preparation method thereof.
  • a graphite-based filler/polymer-based thermal interface material with oriented structure features uses graphite-based filler as main thermally conductive filler, microscopic thermally conductive filler as secondary thermally conductive filler, and polymer as matrix, graphite-based filler and microscopic thermally conductive filler are uniform Being dispersed and oriented in the polymer matrix, the thermal interface material not only has excellent thermal conductivity, but also has good resilience.
  • graphite fillers have a two-dimensional lamellar structure, and have the characteristics of high thermal conductivity along the direction of the lamellae, so that the graphite fillers arranged after orientation can greatly improve the thermal conductivity of the polymer matrix and make the thermal interface material. There is also obvious anisotropy.
  • the main function of microscopic thermally conductive fillers is to promote the formation of thermally conductive paths inside the thermal interface material and to adjust the rheological properties of the mixture.
  • the volume percentage of the graphite fillers may be 1-80%, the total volume percentage of the thermal interface material by the microscopic thermally conductive fillers may be 0-10%, and the volume percentage of the polymer matrix may be 20-95% %. If the total fraction occupied by the matrix in the thermal interface material is too high, the effect of improving the thermal conductivity of the matrix will not be obvious; if the total fraction occupied by the matrix in the thermal interface material is too low, it is difficult to achieve uniform dispersion of fillers and easily lead to The filler-to-filler adhesion is low, resulting in a decrease in the mechanical properties of the thermal interface material. Further, the volume percentage occupied by the graphite fillers may be 30-60%, the volume percentage occupied by the microscopic thermally conductive fillers may be 2-8%, and the volume percentage occupied by the matrix may be 27-63%.
  • the length of the sheet diameter of the graphite-based filler may be 10-1000 microns, and the particle size of the microscopic thermally conductive filler may be 0.5-100 microns.
  • Graphite fillers are the main thermal conductive fillers of thermal interface materials, and their sheet diameters have a significant impact on the thermal conductivity of thermal interface materials. If the length of the graphite filler sheet is too large, it will increase the difficulty in the mixing process; if the length of the graphite filler sheet is too small, a large number of interfaces will be introduced, it is difficult to form a relatively continuous thermal conduction path, and the thermal conductivity of the material will be reduced. .
  • the particle size length of the microscopic thermally conductive filler is too large, it is easy to introduce defects and reduce the mechanical properties of the material. If the particle size length of the microscopic filler is too small, it will lead to difficulty in dispersion of the filler. Further, the particle size of the graphite-based filler may be 50-500 microns, and the particle size of the microscopic thermally conductive filler may be 3-20 microns.
  • the graphite-based filler includes one or more of materials with anisotropic characteristics, such as flake graphite, graphene, graphene microplatelets, and artificial graphite microplatelets.
  • the microscopic thermally conductive filler refers to a general term for a class of particle-based fillers with micron-sized or nano-sized particles. It is beneficial to improve the thermal conductivity of thermal interface materials.
  • Such microscopic thermally conductive fillers are metal materials or inorganic non-metallic materials, the metal materials include one or more of aluminum, copper or silver, and the inorganic non-metallic materials include silicon nitride, silicon carbide, silicon dioxide, One or more of boron nitride, aluminum oxide, and zinc oxide.
  • the polymer matrix includes, but is not limited to, at least one of polyurethane, epoxy resin, and silicone rubber. Such materials are liquid at normal temperature and have good fluidity; under the effect of high temperature and catalyst A cross-linking reaction will take place inside the material; controlling the content of different components of the polymer can form a matrix material with different degrees of cross-linking and resilience.
  • a preparation method of a graphite filler/polymer-based thermal interface material with oriented structure features comprising the following steps:
  • volume percentage weigh the corresponding mass of graphite-based fillers, microscopic thermally conductive fillers and polymer matrix.
  • the graphite-based filler, the microscopic thermally conductive filler and the polymer matrix are uniformly mixed by mechanical mixing (such as planetary stirring, centrifugal stirring) to obtain a mixture.
  • mechanical mixing such as planetary stirring, centrifugal stirring
  • the rotational speed of the stirring rod for planetary stirring is 100-250 rpm
  • the stirring time is 2-6 hours
  • the stirring temperature is -5-100°C
  • the stirring environment is a vacuum environment.
  • Orientation treatment (such as a slit extrusion process) is used to realize the orientation of graphite flakes in the mixture to obtain a lamellar mixture.
  • the slit extrusion orientation process uses shear force to promote the orientation of graphite-based fillers with two-dimensional lamellar structure. In the slit extrusion process, it can cooperate with the conveying device to adjust the extrusion speed to be consistent with the conveying speed of the conveying device, so that the continuous extrusion treatment of the mixture can be realized.
  • the thickness of the extrusion treatment is controlled to be no greater than 20 times the average particle size of the graphite filler, for example, for a graphite filler with an average particle size of 150 microns , the size of its extrusion opening is not more than 3 mm.
  • the lamellar mixture that has been subjected to the orientation treatment is sent to an ultra-low temperature freezing device for freezing and fixing to obtain a frozen flaky mixture.
  • the freezing device directly uses the ultra-low temperature characteristics of liquid nitrogen or liquid oxygen to freeze the mixture.
  • the purpose of freezing is to keep the polymer matrix in a vitrified state, fix the molecular chains of the matrix, and ensure that the graphite filler in the mixture maintains a good degree of orientation during the lamination process.
  • the frozen flaky mixture is mechanically cut in a solid state, and then the cut flaky mixture of fixed size is transferred to a designated mold for lamination processing.
  • the above-specified mold will be immersed in an ultra-low temperature heat preservation device containing liquid nitrogen or liquid oxygen to keep it solid. The number of layers of the stack will be determined according to the actual application requirements.
  • the purpose of the pressurization operation is to further promote the densification of the mixture.
  • the purpose of the heating operation is to make the mixture change from a glassy state to a viscous fluid state, so that the bonding between layers can be achieved.
  • the oven temperature is 90 to 120°C; for epoxy substrates, the curing temperature is 70 to 160°C; for silicone rubber substrates, the curing temperature is 80 to 200°C;
  • a certain cutting process (such as laser cutting or ultrasonic cutting) is used to cut the cured thermal interface material, and the laser cutting or ultrasonic cutting process is more likely to obtain a thermal interface material with a smooth surface.
  • the cutting direction is cut along the direction perpendicular to the orientation of the graphite-based filler, thereby producing thermal interface materials with high thermal conductivity out-of-plane and high thermal conductivity in-plane, respectively.
  • flake graphite with an average particle size of 180 microns is used as graphite fillers
  • aluminum powder with an average particle size of 5 microns is used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as substrates.
  • the volume percentage of flake graphite is 35%, and the volume percentage of aluminum powder is 3%.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the thickness of the slit was controlled to be 1 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 40, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture together to a blast drying oven the temperature of the drying oven is set to 150°C, and the holding time is 2 hours.
  • ultrasonic cutting is used to cut along the direction perpendicular to the graphite orientation, and finally a thermal interface material in which the flake graphite is oriented along the out-of-plane direction is obtained.
  • the obtained thermal interface material is scanned by electron microscope, and the scanning electron microscope image of the cross section of the obtained thermal interface material is shown in Figure 1. From Figure 1, it can be seen that the graphite filler has obvious orientation and arrangement characteristics.
  • the SEM image of the longitudinal section of the prepared thermal interface material is shown in Figure 2, and it can be seen from Figure 1 that the flake graphite is almost flat on the surface of the section.
  • FIG. 3 A schematic structural diagram of the prepared thermal interface material before ultrasonic cutting is shown in Figure 3, and the flake graphites are distributed in the polymer matrix in parallel with each other.
  • flake graphite with an average particle size of 280 microns is used as graphite fillers
  • aluminum powder with an average particle size of 5 microns is used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the volume percentage of flake graphite is 45%, and the volume percentage of aluminum powder is 3%.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the slit thickness was controlled to be 1.5 mm.
  • the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment.
  • the frozen glassy mixture is then mechanically cut into 60mm*60mm slices.
  • the sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize. After the vacuum degree dropped below 300pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours.
  • graphene microflakes with an average particle size of 60 microns are used as graphite fillers
  • alumina powders with an average particle size of 7 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the mixture is mixed by planetary stirring to form a mixture of 30% by volume of flake graphite and 5% by volume of alumina powder.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was oriented by means of slit extrusion, and the thickness of the slit was controlled to be 0.7 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 50, the laminated mixture is transferred to a vacuum hot press together with the mold, and then vacuumized quickly. After the vacuum degree dropped below 300pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours. After waiting for the end of the program, transfer the mold and the mixture together to a blast drying oven, the temperature of the drying oven is set to 150°C, and the holding time is 2 hours. After the mixture is completely solidified, ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material in which the graphene microplates are oriented along the out-of-plane direction is obtained.
  • graphene microflakes with an average particle size of 60 microns are used as graphite fillers
  • alumina powders with an average particle size of 7 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was oriented by means of slit extrusion, and the thickness of the slit was controlled to be 0.7 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 50, the laminated mixture is transferred to a vacuum hot press together with the mold, and then quickly vacuumized. After the vacuum degree dropped below 300pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours. After waiting for the end of the program, transfer the mold and the mixture together to a blast drying oven, the temperature of the drying oven is set to 150°C, and the holding time is 2 hours. After the mixture is completely solidified, ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material in which the graphene microplates are oriented along the out-of-plane direction is obtained.
  • flake graphite with an average particle size of 280 microns is used as a graphite filler
  • aluminum powder with an average particle size of 5 microns is used as a microscopic thermal conductive filler
  • hydrogen polyether glycol and diisocyanate with an average molecular weight of 3000 are used as the matrix.
  • the mixture is mixed into a polyurethane prepolymer mixture with a volume percentage of flake graphite of 35% and a volume percentage of aluminum powder of 3% by stirring.
  • the rotational speed of planetary stirring was 200 rpm, the total stirring time was 4 hours, and the stirring temperature was 70°C. Add the amine chain extender and continue stirring for 1 hour.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the slit thickness was controlled to be 1.5 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture together to a blast drying oven the temperature of the drying oven is set to 90°C, and the holding time is 3 hours.
  • ultrasonic cutting is used to cut along the direction perpendicular to the graphite orientation, and finally a thermal interface material in which the flake graphite is oriented along the out-of-plane direction is obtained.
  • flake graphite with an average particle size of 280 microns is used as a graphite filler
  • aluminum powder with an average particle size of 5 microns is used as a microscopic thermal conductive filler
  • hydrogen polyether glycol and diisocyanate with an average molecular weight of 3000 are used as the matrix.
  • the mixture was mixed in a stirring manner to form a mixture with a volume percentage of flake graphite of 45% and an aluminum powder volume percentage of 3%.
  • the rotational speed of planetary stirring was 200 rpm, the total stirring time was 4 hours, and the stirring temperature was 70°C. Add the amine chain extender and continue stirring for 1 hour.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the slit thickness was controlled to be 1.5 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture together to a blast drying oven the temperature of the drying oven is set to 90°C, and the holding time is 3 hours.
  • ultrasonic cutting is used to cut along the direction perpendicular to the graphite orientation, and finally a thermal interface material in which the flake graphite is oriented along the out-of-plane direction is obtained.
  • graphene microflakes with an average particle size of 60 microns are used as graphite fillers
  • alumina powders with an average particle size of 7 microns are used as microscopic thermal conductive fillers
  • hydrogen polyether glycols and diisocyanates with an average molecular weight of 3000 are used as the matrix.
  • the rotational speed of planetary stirring was 200 rpm
  • the total stirring time was 4 hours
  • the stirring temperature was 70°C.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the extrusion thickness was controlled to be 1 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 50, the laminated mixture is transferred to a vacuum hot press together with the mold, and then vacuumized quickly.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture to a blast drying oven the temperature of the drying oven is set to 120°C, and the holding time is 4 hours.
  • ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material in which the graphene microplates are oriented along the out-of-plane direction is obtained.
  • graphene microflakes with an average particle size of 60 microns are used as graphite fillers
  • alumina powders with an average particle size of 7 microns are used as microscopic thermal conductive fillers
  • hydrogen polyether glycols and diisocyanates with an average molecular weight of 3000 are used as the matrix.
  • planetary stirring was 200 rpm
  • the total stirring time was 4 hours
  • the stirring temperature was 70°C.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the extrusion thickness was controlled to be 1 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 40, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture to a blast drying oven the temperature of the drying oven is set to 120°C, and the holding time is 4 hours.
  • ultrasonic cutting is adopted to carry out cutting processing along the vertical graphite orientation direction, and finally the thermal interface material with the graphene microplates oriented in the out-of-plane direction is obtained.
  • artificial graphite flakes with an average particle size of 200 microns are used as graphite fillers
  • aluminum powders with an average particle size of 5 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the planetary stirring method is used to mix into a mixture with the volume percentage of artificial graphite microplates being 35% and the volume percentage of aluminum powder being 3%.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the slit thickness was controlled to be 1.5 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then quickly vacuumize.
  • the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi was applied to the lamination mixture during the process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture together to a blast drying oven the temperature of the drying oven is set to 150°C, and the holding time is 2 hours.
  • ultrasonic cutting is used to carry out cutting processing along the vertical graphite orientation direction, and finally a thermal interface material with artificial graphite microplates oriented along the out-of-plane direction is obtained.
  • artificial graphite flakes with an average particle size of 200 microns are used as graphite fillers
  • aluminum powders with an average particle size of 5 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the planetary stirring method is used to mix into a mixture with the volume percentage of artificial graphite microplates being 45% and the volume percentage of aluminum powder being 3%.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the slit thickness was controlled to be 1.5 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then rapidly vacuumize.
  • the vacuum hot press is heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi is applied to the laminated mixture during this process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture to a blast drying oven the temperature of the drying oven is set to 150°C, and the holding time is 2 hours.
  • ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material with artificial graphite microplatelets oriented along the out-of-plane direction is obtained.
  • artificial graphite flakes with an average particle size of 400 microns are used as graphite fillers
  • aluminum powders with an average particle size of 5 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the planetary stirring method is used to mix into a mixture with the volume percentage of artificial graphite microplates being 40% and the volume percentage of aluminum powder being 3%.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the thickness of the slit was controlled to be 2 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then rapidly vacuumize.
  • the vacuum hot press is heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi is applied to the laminated mixture during this process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture to a blast drying oven the temperature of the drying oven is set to 150°C, and the holding time is 2 hours.
  • ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material in which the artificial graphite microplates are oriented along the out-of-plane direction is obtained.
  • artificial graphite flakes with an average particle size of 400 microns are used as graphite fillers
  • alumina powders with an average particle size of 7 microns are used as microscopic thermal conductive fillers
  • hydrogen-containing silicone oil and vinyl silicone oil with an average molecular weight of 1000 are used as the matrix.
  • the rotational speed of the stirring rod for planetary stirring was 120 rpm, the stirring time was 3 hours, and the stirring temperature was 5°C. After stirring uniformly, the platinum-based catalyst was added, and stirring was continued for 30 minutes.
  • the above mixture was subjected to extrusion orientation treatment by means of slit extrusion, and the thickness of the slit was controlled to be 2 mm. Then, the extruded mixture is sent to a refrigeration device using liquid nitrogen as a refrigerant for freezing treatment. The frozen glassy mixture is then mechanically cut into 60mm*60mm slices. The sheet is then quickly transferred to a mold immersed in liquid nitrogen for lamination of the mix. After the number of laminated layers reaches 30, transfer the laminated mixture together with the mold to a vacuum hot press, and then rapidly vacuumize.
  • the vacuum hot press is heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 20 psi is applied to the laminated mixture during this process.
  • the above holding time is controlled at more than 12 hours.
  • transfer the mold and the mixture to a blast drying oven the temperature of the drying oven is set to 120°C, and the holding time is 4 hours.
  • ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material in which the artificial graphite microplates are oriented along the out-of-plane direction is obtained.
  • thermomechanical properties of the thermal interface material products of the above Examples 1 to 12 (using a dynamic thermal mechanical analyzer to test the thermal interface material at 150 ° C and 10 psi pressure for 5 minutes) After that, the material's rebound rate) was tested, and the results obtained are shown in the following table.
  • the thermal interface material has a huge difference between the in-plane and out-plane thermal conductivity, has obvious anisotropy characteristics, and has a very high thermal conductivity in the out-of-plane direction of the material. , and the material also has good flexibility and elasticity.
  • the graphite-based filler and the microscopic thermally conductive filler are uniformly mixed inside the polymer matrix by means of mechanical stirring.
  • the orientation and arrangement of the graphite-based fillers with anisotropic characteristics along the sheet layer direction can be realized by shearing force.
  • the ultra-low temperature freezing treatment the state of the mixture after the orientation and arrangement is effectively fixed, and the subsequent processing such as cutting, lamination and vacuum exhaust is convenient.
  • the densification of the oriented sample can be effectively achieved by vacuum pressure treatment, thereby effectively reducing the intrinsic thermal resistance of the cured sample.
  • the finally prepared thermal interface material with graphite as the main filler has the characteristics of high thermal conductivity and soft rebound along the out-of-plane direction.

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Abstract

本发明公开了一种石墨取向型热界面材料的制备方法，其包括以下步骤：将石墨取向型热界面材料的原料混合，得到混合料；将混合料进行取向处理，得到片层状混合料；将片层状混合料进行冷冻处理，得到冻结片层状混合料；将冻结片层状混合料进行切割处理，得到指定宽度和长度的片层状样品，并将片层状样品进行叠层处理；采用真空加压的方式对叠层后的样品进行处理，在该过程中缓慢升温，使得混合料发生从固态到粘流态的转变，得到致密的样品预制体；将致密的样品预制体进行高温固化处理，得到固化后的样品；对固化后的样品沿垂直片层状样品厚度的方向进行切割，得到石墨取向型热界面材料。该制备方法制备得到的石墨取向型热界面材料高致密性，热阻小。

Description

一种石墨取向型热界面材料的制备方法 技术领域
本发明属于导热聚合物基复合材料技术领域，具体涉及一种石墨取向型热界面材料的制备方法。
背景技术
5G通信、物联网、大数据和人工智能等新兴领域的兴起使得集成电路正朝着小型化、轻薄化和高度集成化的方向发展。然而，这一趋势会直接导致电子器件功率密度和工作温度的升高。如果电子器件的热量未能及时散出，不仅会显著降低其性能，而且严重时还会导致设备故障、报废，甚至安全隐患。因此，如何实现电子元器件的高效散热是当今电子产品设计与组装所面临的关键问题。尤其是对于有着很高集成度的便携式电子产品，散热甚至成为了整个产业的主要技术瓶颈。
为了使电子产品得到有效散热，热源与散热装置之间必须配合热界面材料(Thermal interfere materials)使用。热界面材料通常是一种以柔性高分子材料为基体结合导热填料的复合材料，它可以有效填补固固界面之间的空隙，增加有效接触面积，从而提高散热效率。常用的热界面材料有导热硅脂、导热凝胶和导热垫片等。相比于其他种类的热界面材料，导热垫片自身有着较高的热导率，并且有着操作简单、适用性强的特点。
目前，常见的热界面材料的导热填料主要以高导热陶瓷颗粒或者金属粉体为主。但是，这类填料通常只有在含量为60wt％以上时，热界面材料的热导率才会有较为明显改善，而且通常热导率都低于7W·m -1·K -1。然而，电子行业的快速发展使得传统热界面材料愈发难以满足如今的散热需求。因此，亟需开发新型热界面材料用以解决电子行业所面临的热管理问题。
专利CN 102433105 B公开了一种含有取向型石墨粒子和丙烯酸酯系高分子聚合物的组合物及方法。该方法提出首先通过机械混合得到混合料，然后采用压延或者压制得到片状材料，再将上述片材进行叠层处理，然后沿着垂直石墨微粒取向方向进行切割，从而得到最终的具有面外高导热特征的导热垫片材料。该方法所使用的搅拌工艺以及叠层工艺均是在空气气氛下进行操作，所以难免会在混合料中引入大量气泡，从而严重增大导热垫片的本征热阻。专利CN 111267434 A公布了一种具有取向结构的导热电磁屏蔽材料及其制备方法。该方法采用热塑性聚合物为基体，先通过溶剂将基体溶解，然后通过机械混合制备混合料，接着通过涂布的方式制备一次片状材料，然后再采用叠层处理和切割处理得到片状填料沿面外取向的导 热垫片材料。尽管通过该方法片状填料可以实现一定程度的取向，但是导热垫片材料的气孔率问题依旧没有解决。此外，热塑性基体添加填料之后硬度迅速变大，接触热阻较大。
发明内容
针对现有技术制备得到的石墨类填料/聚合物基热界面材料气孔率高，接触热阻和总热阻较大的问题，本发明的目的在于提供一种石墨取向型热界面材料的制备方法。
为了达到上述目的，本发明所采用的技术方案为：一方面，本发明提供了一种石墨取向型热界面材料的制备方法，包括以下步骤：
1)将石墨取向型热界面材料的原料组份混合均匀，得到混合料；
2)将混合料进行取向处理，得到片层状混合料；
3)将片层状混合料进行冷冻处理，得到冻结片层状混合料；
4)保持冻结片层状混合料的冻结状态，将冻结片层状混合料进行切割处理，得到指定宽度和长度的片层状样品，并将片层状样品再进行叠层处理；
5)采用真空加压的方式对叠层后的样品进行处理，在该过程中缓慢升温，使得混合料发生从固态到粘流态的转变，得到致密的样品预制体；
6)将致密的样品预制体进行高温固化处理，得到固化后的样品；
7)对固化后的样品沿垂直片层状样品厚度的方向进行切割，得到具有各向异性特征的石墨取向型热界面材料。
进一步地，步骤2)中所述的取向处理包括狭缝挤出、刮涂、双辊涂布；
优选地，步骤2)中所述取向处理后片层状混合料的厚度不大于石墨类填料平均粒径的20倍。
进一步地，步骤3)中所述的冷冻处理包括液氮处理、液氧处理。
进一步地，步骤5)中所述的真空加压处理过程中压力为5～30psi，温度为30～90℃，时间为4～12小时。
进一步地，步骤6)中所述的高温固化针对不同材料体系存在差异，针对聚氨酯体系，固化温度为90～120℃，固化时间为1～4小时；针对环氧类体系，固化温度为70～160℃，固化时间为0.5～3小时；针对硅橡胶类体系，固化温度为80～200℃，固化时间为0.5～4小时。
进一步地，步骤7)中所述的切割工艺包括激光切割、超声切割。
另一方面，本发明提供了一种石墨取向型热界面材料，包括石墨类填料、微观导热填料、聚合物基体；
所述微观导热填料为具有微米尺寸或纳米尺寸的颗粒类填料；
所述石墨取向型热界面材料的制备方法，包括以下步骤：
1)将石墨类填料、微观导热填料和聚合物基体搅拌混合均匀，得到混合料；
2)将混合料进行取向处理，得到片层状混合料；
3)将片层状混合料进行冷冻处理，得到冻结片层状混合料；
4)保持冻结片层状混合料的冻结状态，将冻结片层状混合料进行切割处理，得到指定宽度和长度的片层状样品，并将该片层状样品再进行叠层处理；
5)采用真空加压的方式对叠层后的样品进行处理，在该过程中缓慢升温，使得混合料发生从固态到粘流态的转变，得到致密的样品预制体；
6)将致密的样品预制体进行高温固化处理，得到固化后的样品；
7)对固化后的样品沿垂直片层状样品厚度的方向进行切割，得到具有各向异性特征的石墨取向型热界面材料。
进一步地，所述石墨类填料包括鳞片石墨、石墨烯、石墨烯微片、人造石墨微片中的一种或多种；优选地，所述石墨类填料的粒径为10～1000微米，优选为50～500微米；
优选地，所述微观导热填料为金属材料或无机非金属材料；更优选地，所述金属材料包括铝、铜、银中的一种或多种；更优选地，所述无机非金属材料包括氮化硅、碳化硅、二氧化硅、氮化硼、氧化铝、氧化锌中的一种或多种；更优选地，所述微观导热填料的粒径为0.5～100微米，优选为3～20微米；
优选地，所述聚合物基体包括聚氨酯体系、环氧树脂体系、硅橡胶体系中的一种或多种。
进一步地，所述石墨类填料所占石墨取向型热界面材料的总体积百分比为1～80％，优选为30～60％；
优选地，所述微观导热填料所占石墨取向型热界面材料的总体积百分比为0～10％，优选为2～8％；
优选地，所述聚合物基体所占石墨取向型热界面材料的总体积百分比为20～95％，优选为27～63％。
进一步地，步骤1)中所述搅拌混合在真空环境下进行；
优选地，步骤2)中所述的取向处理包括狭缝挤出、刮涂、双辊涂布；
优选地，步骤2)中所述取向处理后片层状混合料的厚度不大于石墨类填料平均粒径的20倍；
优选地，步骤3)中所述的冷冻处理包括液氮处理、液氧处理；
优选地，步骤5)中所述的真空加压处理过程中压力为5～30psi，温度为30～90℃，时间为4～12小时；
优选地，步骤6)中所述的高温固化针对不同材料体系存在差异，针对聚氨酯基体，固化温度为70～120℃，固化时间为1～4小时；针对环氧类基体，固化温度为70～160℃，固化时间为0.5～3小时；针对硅橡胶类基体，固化温度为80～200℃，固化时间为0.5～4小时；
优选地，步骤7)中所述的切割工艺包括激光切割、超声切割。
本发明的有益效果为：(1)本发明石墨取向型热界面材料的制备方法制备得到的石墨取向型热界面材料高致密性(气孔率低)，热阻小。(2)本发明通过狭缝挤出等取向处理方式实现石墨类填料具有高的取向程度；本发明通过超低温冷冻处理，有效的固定取向后混合料的分子链，防止粘性流动现象的发生，可以实现混合料在玻璃态的状态下进行操作，避免了粘流态混合料难以操作的问题，从而便于后续的切割、叠层以及真空排气等处理，进而有利于得到高取向程度和低气孔率的热界面材料；本发明在混合料玻璃态的状态下进行真空加压处理，可以最大限度的降低材料内部的气孔率，从而提高材料致密性。(3)本发明可以在实现石墨类填料较高的取向程度的同时实现材料很高的致密程度，因此，可以在较低填料含量的情况下，使得所制得的热界面材料热导率很高，热阻较低。较低的填料含量也同时赋予了热界面材料具有着良好的柔性和弹性。(4)本发明石墨取向型热界面材料性能稳定、兼具高取向度、高致密性、高热导率，同时保证其还有着良好的柔性和回弹性，从而保证电子器件热源和散热装置高覆盖率地填充，进而有效地实现电子器件地高效散热。(5)本发明石墨取向型热界面材料中的微观导热填料可以更好地构建体系内部的导热通路；可起到填补基体分子间的微空隙和桥接石墨类填料的作用，从而有利于提高热界面材料的导热性能。
附图说明
图1为本发明实施例1中所制得热界面材料的横截面的扫描电镜图。
图2为本发明实施例1中所制得热界面材料的纵截面的扫描电镜图。
图3为本发明实施例1中所制得热界面材料在超声切割处理之前的结构示意图。
具体实施方式
以下事例性地说明具有取向结构特征的石墨类填料/聚合物基热界面材料及其制备方法。
一种具有取向结构特征的石墨类填料/聚合物基热界面材料以石墨类填料为主要导热填料，以微观导热填料为次要导热填料，以聚合物为基体，石墨类填料和微观导热填料均匀分散且取向分布在聚合物基体中，使得该热界面材料不仅有着优异的导热性能，还有着良好的 回弹性。其中，石墨类填料有着二维的片层结构，并且有着沿片层方向高导热的特点，从而可以使得取向后排列的石墨类填料大幅度的提高聚合物基体的导热性能，并使得热界面材料也有着明显的各向异性。微观导热填料的主要作用是促进热界面材料内部导热通路的形成以及调整混合料的流变性能。
在可选的实施方式中，石墨类填料所占体积百分比可为1～80％，微观导热填料所占热界面材料的总体积百分比为0～10％，聚合物基体的体积百分比为20～95％。若热界面材料中基体所占的总体积分数过高，则对基体导热的改善效果不明显；若热界面材料中基体所占的总体积分数过低，则难以实现填料的均匀分散以及容易导致填料与填料间粘结力低，从而导致热界面材料的力学性能下降。进一步地，石墨类填料所占的体积百分比可为30～60％，微观导热填料所占的体积百分比为2～8％，基体所占的体积百分比为27～63％。
在可选的实施方式中，石墨类填料的片径长度可以为10～1000微米，微观导热填料的粒径大小可以为0.5～100微米。石墨类填料作为热界面材料的主要导热填料，其片径长度对热界面材料的导热性能影响显著。若石墨类填料片径长度过大，则会增大混料过程中的难度；若石墨类填料片径长度过小，则会引入大量界面，难以形成较为连续的导热通路，降低材料的导热性能。若微观导热填料的粒径长度过大，则容易引入缺陷，降低材料的力学性能。若微观填料的粒径长度过小，则会导致填料分散困难。进一步地，石墨类填料粒径大小可为50～500微米，微观导热填料的粒径大小可为3～20微米。
在可选的实施方式中，石墨类填料包括鳞片石墨、石墨烯、石墨烯微片和人造石墨微片等具有各向异性特征的材料中的一种或多种。
在可选的实施方式中，微观导热填料是指一类具有微米尺寸或纳米尺寸的颗粒类填料的统称，此材料可起到填补基体分子间的微空隙和桥接石墨类填料的作用，从而有利于提高热界面材料的导热性能。该类微观导热填料为金属材料或者无机非金属材料，所述金属材料包括铝、铜或银中的一种或多种，所述无机非金属材料包括氮化硅、碳化硅、二氧化硅、氮化硼、氧化铝、氧化锌中的一种或多种。在可选的实施方式中，聚合物基体包括但不限于聚氨酯、环氧树脂、硅橡胶中的至少一类，该类材料在常温下为液态，有着良好的流动性；在高温和催化剂的作用下，材料内部会发生交联反应；控制聚合物不同组分含量，可以形成具有不同交联程度且具有回弹特性的基体材料。
一种具有取向结构特征的石墨填料/聚合物基热界面材料的制备方法：包括以下步骤：
根据体积百分比，称量相应质量的石墨类填料、微观导热填料和聚合物基体。
将石墨类填料、微观导热填料和聚合物基体采用机械混合的方式(如行星搅拌、离心搅 拌)均匀混合，得到混合料。行星搅拌的搅拌杆转速为100～250转/分钟，搅拌时间为2～6小时，搅拌温度为-5～100℃，搅拌环境为真空环境。
采用取向处理(如狭缝挤出工艺)实现混合料中石墨微片的取向，得到片层状混合料。狭缝挤出取向工艺是利用剪切力促使具有二维片层结构的石墨类填料进行取向。在狭缝挤出过程中，可以与传送装置配合，调整挤出速度和传送装置的传送速度一致，可实现混合料的连续性挤出处理。为保证挤出混合料内部石墨类填料具有高的取向度，所述挤出处理的厚度控制为不大于石墨类填料平均粒径的20倍，例如，对于平均粒径为150微米的石墨类填料，其挤出口的尺寸不大于3毫米。
将已经经过取向处理后的片层状混合料送入超低温冷冻装置进行冷冻固定，得到冻结片层状混合料。为保证冷冻速度，该冷冻装置直接借助液氮或者液氧的超低温特性来对混合料进行冷冻。冷冻的目的主要是使得聚合物基体保持在玻璃化状态，固定基体的分子链，保证混合料中石墨类填料在叠层过程中一直保持着良好的取向程度。
设计好切割尺寸，将冻结片层状混合料在固态状态时进行机械切割，接着，将切割好的固定尺寸的片层状混合料转移至指定模具中进行叠层处理。为保证叠层过程中石墨类填料的取向状态不变，上述指定模具将浸泡在含有液氮或者液氧的超低温保温装置中继续保持固态。叠层的层数将根据实际应用需求来确定。
将已经叠有指定层数混合料的模具同混合料一同转移至真空热压装置中。接着对腔体迅速进行抽真空处理，去除混合料层与层之间的空气。待腔体内部真空度下降至30pa以下时，施加竖直方向上5～30psi的压力，并升高装置温度至30～90℃。加压操作的目的是为了进一步促进混合料的致密化。升温操作的目的是为了使得混合料从玻璃态转变为粘流态，从而可以实现层与层之间的粘结。
将经过真空加压致密化操作后的混合料转移至如烘箱，调整烘箱温度至指定温度并保温一定的时间，使得基体内部发生交联反应，从而赋予混合料一定的力学性能。根据不同的基体材料类型，制定不同的固化程序。针对聚氨酯类基体，固化温度为90～120℃；针对环氧类基体，固化温度为70～160℃；针对硅橡胶类基体，固化温度为80～200℃；
采用一定的切割工艺(如激光切割或者超声切割的方式)对固化后的热界面材料进行切割，激光切割或者超声切割工艺更容易获得表面平整的热界面材料。切割方向沿着垂直于石墨类填料取向的方向切割，从而制得分别具有面外高导热和面内高导热特征的热界面材料。
下面进一步例举实施例以详细说明本发明。同样应理解，以下实施例只用于对本发明进行进一步说明，不能理解为对本发明保护范围的限制，本领域的技术人员根据本发明的以下 内容作出的一些非本质的改进和调整均属于本发明的保护范围。下述示例具体的工艺参数等也仅是合适范围中的一个示例，即本领域技术人员可以通过本文的说明作出合适范围内的选择，而非限定于下文示例中的具体数值。下列实施例中未注明具体条件的试验方法，通常按照常规条件，例如是工艺手册中的条件，或按照厂商所建议的条件。
实施例1
首先以平均粒径为180微米的鳞片石墨为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成鳞片石墨体积百分比为35％，铝粉体积百分比为3％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到40层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得鳞片石墨沿面外方向取向的热界面材料。
对所制得热界面材料进行电镜扫描，所制得热界面材料的横截面的扫描电镜图如图1所示，从图1中可以看到石墨类填料有着明显的取向排列特征。所制得热界面材料的纵截面的扫描电镜图如图2所示，从图1中可以看到鳞片石墨几乎都平铺在截面表面。
所制得热界面材料在超声切割处理之前的结构示意图如图3所示，鳞片石墨均互相平行的分布于聚合物基体内部。
实施例2
首先以平均粒径为280微米的鳞片石墨为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成鳞片石墨体积百分比为45％，铝粉体积百分比为3％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1.5毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混 合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得鳞片石墨沿面外方向取向的热界面材料。
实施例3
首先以平均粒径为60微米的石墨烯微片为石墨类填料，以平均粒径为7微米的氧化铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成鳞片石墨体积百分比为30％，氧化铝粉体积百分比为5％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行取向处理，并控制狭缝厚度为0.7毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到50层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得石墨烯微片沿面外方向取向的热界面材料。
实施例4
首先以平均粒径为60微米的石墨烯微片为石墨类填料，以平均粒径为7微米的氧化铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成石墨烯微片体积百分比为40％，氧化铝粉体积百分比为5％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行取向处理，并控制狭缝厚度为0.7毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到50层之后，将叠层混合料同模具 一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得石墨烯微片沿面外方向取向的热界面材料。
实施例5
首先以平均粒径为280微米的鳞片石墨为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为3000的氢聚醚二元醇和二异氰酸酯为基体，通过行星搅拌的方式混合成鳞片石墨体积百分比为35％，铝粉体积百分比为3％的聚氨酯预聚体混合料。行星搅拌的转速为200转/分钟，搅拌总时间为4小时，搅拌温度为70℃。加入胺类扩链剂，并继续搅拌1小时。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1.5毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为90℃，保温时间为3小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得鳞片石墨沿面外方向取向的热界面材料。
实施例6
首先以平均粒径为280微米的鳞片石墨为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为3000的氢聚醚二元醇和二异氰酸酯为基体，通过行星搅拌的方式混合成鳞片石墨体积百分比为45％，铝粉体积百分比为3％的混合料。行星搅拌的转速为200转/分钟，搅拌总时间为4小时，搅拌温度为70℃。加入胺类扩链剂，并继续搅拌1小时。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1.5毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12 小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为90℃，保温时间为3小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得鳞片石墨沿面外方向取向的热界面材料。
实施例7
首先以平均粒径为60微米的石墨烯微片为石墨类填料，以平均粒径为7微米的氧化铝粉为微观导热填料，以平均分子量为3000的氢聚醚二元醇和二异氰酸酯为基体，通过行星搅拌的方式混合成石墨烯微片体积百分比为30％，氧化铝粉体积百分比为5％的混合料。行星搅拌的转速为200转/分钟，搅拌总时间为4小时，搅拌温度为70℃。加入胺类扩链剂，并继续搅拌1小时。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制挤出厚度为1毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到50层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为120℃，保温时间为4小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得石墨烯微片沿面外方向取向的热界面材料。
实施例8
首先以平均粒径为60微米的石墨烯微片为石墨类填料，以平均粒径为7微米的氧化铝粉为微观导热填料，以平均分子量为3000的氢聚醚二元醇和二异氰酸酯为基体，通过行星搅拌的方式混合成石墨烯微片体积百分比为40％，氧化铝粉体积百分比为5％的混合料。行星搅拌的转速为200转/分钟，搅拌总时间为4小时，搅拌温度为70℃。加入胺类扩链剂，并继续搅拌1小时。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制挤出厚度为1毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到40层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为120℃，保温时间为4小时。待混合料完全固化之后，采用超声切割的方式，沿垂直 石墨取向方向进行切割处理，最终制得石墨烯微片沿面外方向取向的热界面材料。
实施例9
首先以平均粒径为200微米的人造石墨微片为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成人造石墨微片体积百分比为35％，铝粉体积百分比为3％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1.5毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得人造石墨微片沿面外方向取向的热界面材料。
实施例10
首先以平均粒径为200微米的人造石墨微片为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成人造石墨微片体积百分比为45％，铝粉体积百分比为3％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为1.5毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得人造石墨微片沿面外方向取向的热界面 材料。
实施例11
首先以平均粒径为400微米的人造石墨微片为石墨类填料，以平均粒径为5微米的铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，通过行星搅拌的方式混合成人造石墨微片体积百分比为40％，铝粉体积百分比为3％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为2毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为150℃，保温时间为2小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得人造石墨微片沿面外方向取向的热界面材料。
实施例12
首先以平均粒径为400微米的人造石墨微片为石墨类填料，以平均粒径为7微米的氧化铝粉为微观导热填料，以平均分子量为1000的含氢硅油和乙烯基硅油为基体，，通过行星搅拌的方式混合成人造石墨微片体积百分比为45％，氧化铝粉体积百分比为5％的混合料。行星搅拌的搅拌杆转速为120转/分钟，搅拌时间为3小时，搅拌温度为5℃。待搅拌均匀后，加入铂类催化剂，并继续搅拌30分钟。通过狭缝挤出的方式，对上述混合料进行挤出取向处理，并控制狭缝厚度为2毫米。接着将挤出的混合料传送至液氮为制冷剂的制冷装置进行冷冻处理。再将冷冻为玻璃态的混合料进行机械切割，切割成60毫米*60毫米的片层。紧接着把该片层迅速转移至浸在液氮中的模具中，进行混合料的叠层处理。待叠层层数达到30层之后，将叠层混合料同模具一同转移至真空热压机，然后迅速进行抽真空处理。待真空度下降至300pa以下，以0.5℃/分钟的升温速率，使真空热压机升温至50℃，并在该过程中对叠层混合料施加20psi的压力。以上保温时间控制在12小时以上。等待程序结束后，将模具和混合料一同转移至鼓风干燥箱中，干燥箱温度设置为120℃，保温时间为4小时。待混合料完全固化之后，采用超声切割的方式，沿垂直石墨取向方向进行切割处理，最终制得人造石墨微片沿面外方向取向 的热界面材料。
分别对上述实施例1～12的热界面材料产品的面内热导率、面外热导率和热机械性能(采用动态热机械分析仪测试热界面材料在150℃，10psi压力条件下保持5分钟后，材料的回弹率)进行测试，所得结果如下表所示。
实施例 面外热导率W/mk 面内热导率W/mk 回弹率％
1 16.21 1.24 97
2 19.45 1.44 93
3 13.22 1.23 97
4 17.54 1.26 95
5 14.84 1.24 98
6 18.21 1.45 93
7 11.01 1.22 96
8 15.65 1.89 92
9 25.41 1.17 93
10 30.54 1.33 90
11 28.24 1.48 92
12 32.41 1.56 90
从上表实施例的测试结果可以看出，所制的热界面材料的面内、外热导率差异巨大，有着很明显的各向异性特征，在材料面外方向有着极高的热导率，同时材料还兼具良好的柔性和弹性。
综上，本发明通过机械搅拌的方式，使得石墨类填料和微观导热填料在聚合物基体内部均匀混合。通过狭缝挤出处理，可以利用剪切力实现具有各向异性特征的石墨类填料沿片层方向的取向排列。通过超低温冷冻处理，有效地固定混合料取向排列后的状态，并便于后续的切割、叠层以及真空排气等处理。通过真空加压处理可以有效实现取向后样品的致密化，从而有效降低固化后样品的本征热阻。最终所制备得到的以石墨类为主要填料的热界面材料具有沿面外方向高导热和柔软回弹的特性。
以上提供的实施例仅仅是解释说明的方式，不应认为是对本发明的范围限制，任何根据本发明的技术方案及发明构思加以同等替换或者改变的方法，都应涵盖在本发明的保护范围之内。

Claims (10)

  1. 一种石墨取向型热界面材料的制备方法，其特征在于，包括以下步骤：
    1)将石墨取向型热界面材料的原料组份混合均匀，得到混合料；
    2)将混合料进行取向处理，得到片层状混合料；
    3)将片层状混合料进行冷冻处理，得到冻结片层状混合料；
    4)保持冻结片层状混合料的冻结状态，将冻结片层状混合料进行切割处理，得到指定宽度和长度的片层状样品，并将片层状样品进行叠层处理；
    5)采用真空加压的方式对叠层后的样品进行处理，在该过程中缓慢升温，使得混合料发生从固态到粘流态的转变，得到致密的样品预制体；
    6)将致密的样品预制体进行高温固化处理，得到固化后的样品；
    7)对固化后的样品沿垂直片层状样品厚度的方向进行切割，得到具有各向异性特征的石墨取向型热界面材料。
  2. 根据权利要求1所述的石墨取向型热界面材料的制备方法，其特征在于，步骤2)中所述的取向处理包括狭缝挤出、刮涂、双辊涂布；
    优选地，步骤2)中所述取向处理后片层状混合料的厚度不大于石墨类填料平均粒径的20倍。
  3. 根据权利要求1所述的石墨取向型热界面材料的制备方法，其特征在于，步骤3)中所述的冷冻处理包括液氮处理、液氧处理。
  4. 根据权利要求1所述的石墨取向型热界面材料的制备方法，其特征在于，步骤5)中所述的真空加压处理过程中压力为5～30psi，温度为30～90℃，时间为4～12小时。
  5. 根据权利要求1所述的石墨取向型热界面材料的制备方法，其特征在于，步骤6)中所述的高温固化针对不同材料体系存在差异，针对聚氨酯体系，固化温度为70～120℃，固化时间为1～4小时；针对环氧类体系，固化温度为70～160℃，固化时间为0.5～3小时；针对硅橡胶类体系，固化温度为80～200℃，固化时间为0.5～4小时。
  6. 根据权利要求1所述的石墨取向型热界面材料的制备方法，其特征在于，步骤7)中所述的切割工艺包括激光切割、超声切割。
  7. 一种石墨取向型热界面材料，其特征在于，包括石墨类填料、微观导热填料、聚合物基体；
    所述微观导热填料为具有微米尺寸或纳米尺寸的颗粒类填料；
    石墨取向型热界面材料的制备方法包括以下步骤：1)将石墨类填料、微观导热填料和聚合物基体搅拌混合均匀，得到混合料；
    2)将混合料进行取向处理，得到片层状混合料；
    3)将片层状混合料进行冷冻处理，得到冻结片层状混合料；
    4)保持冻结片层状混合料的冻结状态，将冻结片层状混合料进行切割处理，得到指定宽度和长度的片层状样品，并将该片层状样品再进行叠层处理；
    5)采用真空加压的方式对叠层后的样品进行处理，在该过程中缓慢升温，使得混合料发生从固态到粘流态的转变，得到致密的样品预制体；
    6)将致密的样品预制体进行高温固化处理，得到固化后的样品；
    7)对固化后的样品沿垂直片层状样品厚度的方向进行切割，得到具有各向异性特征的石墨取向型热界面材料。
  8. 根据权利要求7所述的石墨取向型热界面材料，其特征在于，所述石墨类填料包括鳞片石墨、石墨烯、石墨烯微片、人造石墨微片中的一种或多种；优选地，所述石墨类填料的粒径为10～1000微米，优选为50～500微米；
    优选地，所述微观导热填料为金属材料或无机非金属材料；更优选地，所述金属材料包括铝、铜、银中的一种或多种；更优选地，所述无机非金属材料包括氮化硅、碳化硅、二氧化硅、氮化硼、氧化铝、氧化锌中的一种或多种；更优选地，所述微观导热填料的粒径为0.5～100微米，优选为3～20微米；
    优选地，所述聚合物基体包括聚氨酯体系、环氧树脂体系、硅橡胶体系中的一种或多种。
  9. 根据权利要求7所述的石墨取向型热界面材料，其特征在于，所述石墨类填料所占石墨取向型热界面材料的总体积百分比为1～80％，优选为30～60％；
    优选地，所述微观导热填料所占石墨取向型热界面材料的总体积百分比为0～10％，优选为2～8％；
    优选地，所述聚合物基体所占石墨取向型热界面材料的总体积百分比为20～95％，优选为27～63％。
  10. 根据权利要求7所述的石墨取向型热界面材料，其特征在于，步骤1)中所述搅拌混合在真空环境下进行；
    优选地，步骤2)中所述的取向处理包括狭缝挤出、刮涂、双辊涂布；
    优选地，步骤2)中所述取向处理后片层状混合料的厚度不大于石墨类填料平均粒径的20倍；
    优选地，步骤3)中所述的冷冻处理包括液氮处理、液氧处理；
    优选地，步骤5)中所述的真空加压处理过程中压力为5～30psi，温度为30～90℃，时间为4～12小时；
    优选地，步骤6)中所述的高温固化针对不同材料体系存在差异，针对聚氨酯基体，固化温度为70～120℃，固化时间为1～4小时；针对环氧类基体，固化温度为70～160℃，固化时间为0.5～3小时；针对硅橡胶类基体，固化温度为80～200℃，固化时间为0.5～4小时；
    优选地，步骤7)中所述的切割工艺包括激光切割、超声切割。
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