CN112679798A - Polyolefin-based graphite oriented thermal interface material and preparation method thereof - Google Patents
Polyolefin-based graphite oriented thermal interface material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a polyolefin-based graphite oriented thermal interface material and a preparation method thereof, wherein the polyolefin-based graphite oriented thermal interface material comprises a polyolefin matrix, modified graphite powder and filled heat-conducting filler; the filling type heat conduction filler is micron-sized or nano-sized particle, whisker, fiber or nanowire filler; the preparation method of the modified graphite powder, which is the coupling agent modified graphite powder, comprises the following steps: carrying out plasma etching pretreatment on graphite powder; carrying out hydroxylation treatment on the pretreated graphite powder; fully hydrolyzing the coupling agent in a solvent, and adding hydroxylated graphite powder into the fully hydrolyzed coupling agent. The polyolefin-based graphite oriented thermal interface material disclosed by the invention is stable in performance, has high orientation degree, high compactness and high thermal conductivity, and simultaneously ensures good flexibility and rebound resilience, so that a heat source and a heat dissipation device of an electronic device are filled at high coverage rate, and further, the electronic device is effectively and efficiently dissipated.
Description
Technical Field
The invention belongs to the technical field of heat-conducting polymer matrix composite materials, and particularly relates to a polyolefin-based graphite oriented thermal interface material and a preparation method thereof.
Background
The emerging fields of 5G communication, the Internet of things, big data, artificial intelligence and the like enable integrated circuits to be developed towards miniaturization, light weight and high integration. However, this trend directly leads to an increase in the power density and operating temperature of electronic devices. If the heat of the electronic device cannot be dissipated in time, the performance of the electronic device is obviously reduced, and equipment failure, scrapping and even potential safety hazards can be caused when the electronic device is serious. Therefore, how to realize efficient heat dissipation of electronic components is a critical issue faced by the design and assembly of current electronic products. Especially for portable electronic products with high integration, heat dissipation is even a major technical bottleneck in the whole industry.
In order to effectively dissipate heat of electronic products, a Thermal interface material (Thermal interface materials) must be used between the heat source and the heat dissipation device. The thermal interface material is a composite material which takes a flexible high polymer material as a matrix and is combined with a heat conduction filler, and can effectively fill up gaps between solid interfaces and increase effective contact area, thereby improving heat dissipation efficiency. Typical TIM materials include thermally conductive silicone grease, thermally conductive gel, and thermally conductive pads. Compared with other types of thermal interface materials, the heat conduction gasket has higher heat conductivity, and has the characteristics of simple operation and strong applicability.
At present, the heat-conducting filler of the common thermal interface material mainly takes high heat-conducting ceramic particles or metal powder as main material. However, such fillers generally provide a significant improvement in thermal conductivity only at levels above 60 wt%, and typically have thermal conductivities below 7W/mK. However, rapid developments in the electronics industry have made it increasingly difficult for conventional thermal interface materials to meet today's heat dissipation needs. Therefore, there is a need to develop new thermal interface materials to solve the thermal management problems faced by the electronics industry.
Disclosure of Invention
In order to solve the problems of the background art, the present invention is directed to a polyolefin-based graphite-oriented thermal interface material and a method for preparing the same.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: in one aspect, the invention provides a method for modifying graphite powder by a coupling agent, which comprises the following steps:
(1) carrying out plasma etching pretreatment on the graphite powder to obtain pretreated graphite powder;
(2) carrying out hydroxylation treatment on the pretreated graphite powder to obtain hydroxylated graphite powder;
(3) fully hydrolyzing the coupling agent in a solvent, and adding hydroxylated graphite powder into the fully hydrolyzed coupling agent to modify the graphite powder to obtain the modified graphite powder.
Further, the graphite powder in the step (1) comprises one or more of crystalline flake graphite, graphene micro-sheets and artificial graphite micro-sheets;
preferably, the particle size of the graphite powder is 10-2000 microns, and preferably 100-1000 microns.
Further, the atmosphere of the plasma treatment in the step (1) is pure oxygen, a mixed gas of argon and oxygen or a mixed gas of nitrogen and oxygen;
preferably, the volume ratio of argon to oxygen in the mixed gas of argon and oxygen is 1: 2-1: 1;
preferably, the volume ratio of the nitrogen to the oxygen in the mixed gas of the nitrogen and the oxygen is 1: 2-1: 1;
preferably, the pressure of the plasma cavity is 2-10 Pa;
preferably, the plasma etching pretreatment time is 10-20 minutes.
Further, the hydroxylation treatment in the step (2) is specifically to soak the pretreated graphite powder in a mixed solution of hydrogen peroxide and ammonia water for hydroxylation treatment;
preferably, the concentration of the hydrogen peroxide in the mixed solution of the hydrogen peroxide and the ammonia water is 0.2-0.8 mol/L, and the concentration of the ammonia water is 0.1-0.4 mol/L.
Further, the coupling agent in the step (3) comprises one or more of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent;
preferably, the silane coupling agent comprises one or more of WD-26, WD-21, WD-27, WD-22, WD-51, WD-71, KH-550, KH-560, KH-570, dodecyl trimethoxy silane, and hexadecyl trimethoxy silane;
preferably, the titanate coupling agent comprises one or more of TMC-201, TMC-102, TMC-101, TMC-105, TMC-TTS, TMC-114, TMC-401;
preferably, the aluminate coupling agent comprises one or more of DL-411, DL-411AF, DL-411D, DL-411 DF;
preferably, the mass of the coupling agent is 1-15% of that of the graphite powder, and preferably 3-10%;
preferably, the solvent is a mixed solution of ethanol and water, and the mass ratio of the ethanol to the water in the mixed solution of the ethanol and the water is 2: 1-4: 1;
preferably, the modification time of the graphite powder is 10-30 hours.
On the other hand, the invention provides modified graphite powder, which is prepared by any one of the methods for modifying graphite powder by using the coupling agent.
On the other hand, the invention provides a polyolefin-based graphite oriented thermal interface material, which comprises a polyolefin matrix, the modified graphite powder and a filled heat-conducting filler;
the filling type heat conduction filler is a micron-sized or nano-sized particle filler, a whisker filler, a fiber filler or a nanowire filler.
Further, the polyolefin matrix contains at least one polyolefin material having terminal hydroxyl groups and at least one polyolefin material grafted with maleic anhydride groups; preferably, the polyolefin matrix accounts for 7-90%, preferably 25-60% of the total volume of the polyolefin-based graphite oriented thermal interface material;
preferably, the modified graphite powder accounts for 10-85% of the total volume of the polyolefin-based graphite oriented thermal interface material, and preferably 40-70%;
preferably, the filled heat conducting filler is a metal material or an inorganic non-metal material; more preferably, the metal material comprises one or more of aluminum, copper, silver; more preferably, the inorganic non-metallic material comprises one or more of carbon fiber, diamond, aluminum nitride, silicon nitride, aluminum oxide, zinc oxide, boron nitride; more preferably, the particle size of the filled heat conduction filler particle filler is 0.5-100 microns, preferably 5-15 microns; more preferably, the length of the filled heat-conducting filler fiber filler is 20-150 micrometers, preferably 30-100 micrometers, the length-diameter ratio is 20-250, preferably 50-200; more preferably, the length of the filling type heat conduction filler whisker filler is 2-50 microns, preferably 8-40 microns, the length-diameter ratio is 5-30, and preferably 10-20; more preferably, the percentage of the filled heat conductive filler in the total volume of the polyolefin-based graphite oriented thermal interface material is 0-8%, and preferably 0-5%.
In another aspect, the present invention provides a method for preparing the polyolefin-based graphite oriented thermal interface material, including the following steps:
(1) uniformly stirring and mixing a polyolefin matrix, the modified graphite powder as described in claim 7 and a filled heat-conducting filler to obtain a mixture;
(2) carrying out orientation treatment on the mixture to obtain a lamellar mixture;
(3) freezing the lamellar mixture to obtain a frozen lamellar mixture;
(4) keeping the frozen state of the frozen lamellar mixture, cutting the frozen lamellar mixture to obtain a lamellar sample with specified width and length, and laminating the lamellar sample;
(5) processing the laminated sample in a vacuum pressurization mode, and slowly heating in the process to ensure that the mixture is converted from a solid state to a viscous state to obtain a compact sample preform;
(6) carrying out high-temperature curing treatment on the compact sample preform to obtain a cured sample;
(7) and cutting the cured sample along the direction vertical to the thickness of the sheet-shaped layered sample to obtain the polyolefin-based graphite oriented thermal interface material with anisotropic characteristics.
Further, the stirring and mixing in the step (1) are carried out in a vacuum environment;
preferably, the orientation treatment described in step (2) comprises calendering, knife coating, two-roll coating;
preferably, the thickness of the oriented laminar mixture in the step (2) is not more than 10 times of the average particle size of the graphite powder;
preferably, the freezing treatment in the step (3) comprises liquid nitrogen treatment and liquid oxygen treatment;
preferably, in the vacuum pressurization treatment process in the step (5), the pressure is 5-30 psi, the temperature is 30-90 ℃, and the time is 6-20 hours;
preferably, the high-temperature curing temperature in the step (6) is 90-170 ℃, and the high-temperature curing time is 1-5 hours;
preferably, the cutting process in step (7) comprises laser cutting and ultrasonic cutting.
The invention has the beneficial effects that: (1) the polyolefin-based graphite oriented thermal interface material disclosed by the invention has the characteristics of stable performance, high orientation degree, high compactness and high thermal conductivity, and simultaneously ensures good flexibility and rebound resilience, so that a heat source and a heat dissipation device of an electronic device are filled at high coverage rate, and further, the electronic device is effectively and efficiently dissipated. (2) The polyolefin matrix has the characteristics of simple formula and stable performance, can realize stable crosslinking without the help of additives such as a catalyst, a chain extender and the like, and avoids the occurrence of catalyst poisoning; and the matrix has the characteristics of flexibility and elasticity after being cured and crosslinked. (3) The invention adopts plasma etching treatment, can effectively activate the surface state of the graphite powder, is convenient for the treatment of grafting hydroxyl on the surface of the powder, and can better play the role of the coupling agent. The plasma treatment of the graphite powder is to introduce an oxygen-containing group having a high activity to the surface of the inert graphite powder and to increase the surface energy of the powder. The hydroxylation treatment of the graphite-based powder can introduce hydrogen elements into the surface of the graphite-based powder to form hydroxyl groups. The modification of the graphite powder by the graft coupling agent is to improve the interface combination between the graphite powder and the polyolefin matrix and reduce the interface thermal resistance. (4) The polyolefin-based graphite oriented thermal interface material prepared by the preparation method of the polyolefin-based graphite oriented thermal interface material has high compactness (low porosity) and small thermal resistance. (5) The invention realizes the stable and excellent orientation degree of the modified graphite powder by orientation treatment modes such as rolling treatment and the like; according to the invention, through ultralow temperature freezing treatment, molecular chains of the oriented mixture are effectively fixed, the viscous flow phenomenon is prevented, the mixture can be operated in a glass state, and the problem that the viscous state mixture is difficult to operate is avoided, so that subsequent processing such as cutting, laminating, vacuum exhaust and the like is facilitated, and further, the thermal interface material with high orientation degree and low porosity can be obtained; the invention carries out vacuum pressurization treatment in the state of the glass state of the mixture, can reduce the porosity in the material to the maximum extent, thereby improving the compactness of the material. (6) The invention can realize high degree of orientation of the modified graphite powder and high degree of compactness of the material, so that the prepared thermal interface material has high thermal conductivity and low thermal resistance under the condition of low filler content. The lower filler content also imparts good flexibility and elasticity to the thermal interface material. (7) The microscopic heat-conducting filler in the graphite oriented thermal interface material can better construct a heat-conducting passage in a system; the filling material can fill up micro-gaps among matrix molecules and bridge graphite fillers, thereby being beneficial to improving the heat-conducting property of the composite material.
Drawings
FIG. 1 is a SEM image of a cross-section of a thermal interface material prepared in example 1 of the present invention.
FIG. 2 is a MicroCT image of a thermal interface material made in example 1 of the present invention.
Fig. 3 is a schematic structural view of the thermal interface material produced in example 1 of the present invention before the ultrasonic cutting process.
Detailed Description
The following examples will illustrate the graphite-based powder/polyolefin-based thermal interface material having an oriented structure and the method for preparing the same.
The graphite powder/polyolefin-based thermal interface material with the oriented structure characteristic takes modified graphite powder as a main heat-conducting filler, takes filled heat-conducting filler as a secondary heat-conducting filler and takes polyolefin which can be crosslinked into a flexible and elastic material as a matrix, and the modified graphite powder and the filled heat-conducting filler are uniformly dispersed and oriented in the polyolefin matrix, so that the thermal interface material has excellent heat-conducting property. The modified graphite powder has a two-dimensional lamellar structure and has the characteristic of high heat conduction along the lamellar direction, so that the modified graphite powder arranged after orientation can greatly improve the heat conduction performance of a polyolefin matrix, and the thermal interface material also has obvious anisotropy. The main function of the filling type heat-conducting filler is to promote the formation of heat-conducting paths in the thermal interface material and adjust the rheological property of the mixture.
The modified graphite powder is coupling agent modified graphite powder; the modification method comprises the following steps: (1) carrying out plasma etching pretreatment on the graphite powder to obtain pretreated graphite powder; (2) carrying out hydroxylation treatment on the pretreated graphite powder to obtain hydroxylated graphite powder; (3) fully hydrolyzing the coupling agent in a solvent, and adding hydroxylated graphite powder into the fully hydrolyzed coupling agent to modify the graphite powder to obtain the modified graphite powder.
In an alternative embodiment, the polyolefin matrix refers to a crosslinkable material with flexibility and resilience, which contains at least one polyolefin material with terminal hydroxyl groups and at least one polyolefin material grafted with maleic anhydride groups, and under the action of high temperature, the maleic anhydride groups and the hydroxyl groups can undergo an addition reaction, so that the interior of the matrix is crosslinked; by controlling the content of different components of the polymer, matrix materials with different crosslinking degrees and both flexibility and elasticity can be formed.
In an optional embodiment, the filled heat-conducting filler is a general name of micron-sized or nano-sized particle, whisker-type, fiber-type and nanowire-type fillers, and the material can fill micro-gaps among matrix molecules and bridge modified graphite-type powder, so that the heat-conducting property of the heat interface material is improved. The filled type heat conducting filler is a metal material or an inorganic non-metal material, wherein the metal material comprises one or more of aluminum, copper and silver, and the inorganic non-metal material comprises one or more of carbon fiber, diamond, aluminum nitride, silicon nitride, aluminum oxide, zinc oxide and boron nitride.
In an alternative embodiment, the graphite-based powder includes one or more of materials with anisotropic characteristics, such as crystalline flake graphite, graphene micro-sheets, artificial graphite micro-sheets, and the like. The coupling agent comprises one or more of silane coupling agent, titanate coupling agent and aluminate coupling agent.
In an optional embodiment, the amount of the coupling agent is 1-15% of the mass of the graphite powder, if the content of the coupling agent is too low, the modification effect on the graphite filler is not obvious, and if the content is too high, the adverse effect on the matrix property is brought. Furthermore, the using amount of the coupling agent is 3-10% of the mass of the graphite filler.
In an optional embodiment, a certain amount of graphite powder is uniformly spread and placed in a cavity of a plasma etching machine, and the vacuum degree of the cavity is reduced to 3 × 10-3And after Pa, filling oxygen or oxygen-containing mixed gas until the pressure of the cavity reaches 2-10 Pa, and etching the plasma for 10-20 minutes.
And soaking the graphite powder subjected to plasma etching in a mixed solution of hydrogen peroxide and ammonia water for 2-4 hours, wherein the concentration of the hydrogen peroxide is 0.2-0.8 mol/L, and the concentration of the ammonia water is 0.1-0.4 mol/L.
Fully hydrolyzing the coupling agent in a mixed solution of ethanol and water, adding the hydroxylated graphite powder into the fully hydrolyzed coupling agent for powder modification, and cleaning and drying to obtain the modified graphite powder.
In an optional embodiment, the volume percentage of the polyolefin matrix is 7-90%, the volume percentage of the modified graphite powder is 10-85%, and the total volume percentage of the filled heat-conducting filler is 0-8%. If the total volume fraction of the matrix in the thermal interface material is too high, the improvement effect on the matrix heat conduction is not obvious; if the total volume fraction of the matrix in the thermal interface material is too low, uniform dispersion of the filler is difficult to achieve, and the adhesion between the filler and the filler is easy to cause low, so that the mechanical property of the thermal interface material is reduced. Furthermore, the volume percentage of the polyolefin matrix is 25-60%, the volume percentage of the modified graphite powder is 40-70%, and the volume percentage of the filled heat-conducting filler is 0-5%.
In an optional embodiment, the particle size of the graphite powder is 10-2000 microns, the particle size of the filled heat conduction filler particle filler is 0.5-100 microns, the length of the filled heat conduction filler fiber filler is 20-150 microns, the length-diameter ratio is 20-250, the length of the filled heat conduction filler whisker filler is 2-50 microns, preferably 8-40 microns, and the length-diameter ratio is 5-30. The modified graphite powder is used as a main heat-conducting filler of the thermal interface material, and the length of the sheet diameter of the graphite powder has obvious influence on the heat-conducting property of the thermal interface material. If the length of the graphite powder sheet diameter is too large, the difficulty in the material mixing process can be increased; if the length of the graphite powder sheet diameter is too small, a large number of interfaces are introduced, so that a relatively continuous heat conduction path is difficult to form, and the heat conduction performance of the material is reduced. If the particle size length of the filling type heat-conducting filler is too large, defects are easily introduced, and the mechanical property of the material is reduced. If the particle diameter length of the filled-type heat conductive filler is too small, dispersion of the filler becomes difficult. Further, the particle size of the graphite powder can be 10-1000 micrometers, the particle size of the particle filling type heat conduction filler can be 5-15 micrometers, the size of the fiber filling type heat conduction filler can be 30-100 micrometers, the length-diameter ratio can be 50-200, and the length-diameter ratio of the whisker filling type heat conduction filler can be 10-20. A preparation method of a graphite powder/polyolefin-based thermal interface material with an oriented structure characteristic comprises the following steps: the method comprises the following steps: and weighing the modified graphite powder, the filled heat-conducting filler and the polyolefin matrix according to the volume percentage.
The modified graphite powder, the filled heat-conducting filler and the polyolefin matrix are uniformly mixed by adopting a mechanical mixing mode (such as centrifugal stirring) to obtain a mixture. The centrifugal rotation speed of centrifugal stirring is 1000-2500 rpm, the stirring time is 5-15 minutes, and the stirring environment is a vacuum environment. In order to prevent the friction heating phenomenon during the centrifugal stirring process from being serious, a batch stirring program is adopted, namely stirring is carried out for one minute every time, then the stirring is suspended for one minute, and the stirring and the suspension are alternated until the program is finished, wherein the suspension time is not calculated in the stirring time period.
Orientation treatment (such as a calendaring process) is adopted to realize orientation of the modified graphite powder in the mixture, so that a lamellar mixture is obtained. The calendering and orienting process utilizes shearing force to promote the modified graphite powder with a two-dimensional lamellar structure to orient. The calendering treatment can realize continuous production of the mixture. And selecting whether to use a release film in the calendering process according to the characteristics and the actual requirements of the mixture. In order to ensure that the graphite filler in the calendering mixture has high orientation degree, the thickness of the calendering treatment is controlled to be not more than 10 times of the average grain diameter of the graphite filler.
And (3) sending the oriented lamellar mixture into an ultralow temperature refrigerating device for freezing and fixing to obtain a frozen lamellar mixture. In order to guarantee the freezing speed, the freezing device directly freezes the mixture by means of the ultralow temperature characteristic of liquid nitrogen or liquid oxygen. The freezing purpose is mainly to keep the polymer matrix in a vitrified state, fix the molecular chain of the matrix and ensure that the modified graphite powder in the mixture always keeps a good degree in the lamination process.
Designing a cutting size, mechanically cutting the frozen laminar mixture in a solid state, and transferring the cut frozen laminar mixture with a fixed size to a specified die for lamination. In order to ensure that the orientation state of the modified graphite powder is unchanged in the lamination process, the specified mould is soaked in an ultralow temperature heat preservation device containing liquid nitrogen or liquid oxygen to continuously keep the solid state. The number of layers of the laminate will be determined according to the requirements of the actual application.
And transferring the mold stacked with the specified layers of the mixed materials and the mixed materials to a vacuum hot-pressing device. And then, quickly vacuumizing the cavity to remove air between the mixed material layers. And when the vacuum degree in the cavity is reduced to be below 30pa, applying pressure of 5-30 psi in the vertical direction, and raising the temperature of the device to 30-90 ℃. The purpose of the pressing operation is to further promote densification of the mix. The purpose of the heating operation is to gradually transform the mixture from a glassy state to a viscous state, so that layer-to-layer bonding can be achieved.
Removing the pressure, keeping the vacuum state, and continuously heating to 90-170 ℃. The cross-linking reaction is carried out in the matrix, and the curing time is 1-5 hours, so that the mixture has certain mechanical properties (any device with the heating and heat-preserving functions can be used in the high-temperature curing process).
The cured composite material is cut by a certain cutting process (such as a laser cutting or ultrasonic cutting mode), and the thermal interface material with a flat surface can be obtained more easily by the laser cutting or ultrasonic cutting process. Cutting along the direction perpendicular to the orientation of the modified graphite powder, thereby preparing the thermal interface material with the characteristics of out-of-plane high thermal conductivity and in-plane high thermal conductivity.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in accordance with the following disclosure. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., a person skilled in the art can make a selection within suitable ranges through the description herein, and are not limited to the specific values in the following examples. The test methods in the following examples, in which specific conditions are not specified, are generally carried out under conventional conditions, for example, those in the handbook of the art, or under the conditions recommended by the manufacturer.
Example 1
Preparing modified graphite powder: (1) and (2) placing the flake graphite with the average particle size of 200 microns into a cavity of a plasma etching machine for etching treatment to obtain the pretreated flake graphite, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated crystalline flake graphite in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain hydroxylated crystalline flake graphite, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking hydroxylated crystalline flake graphite in the mixture for 24 hours, and cleaning and drying to obtain the modified crystalline flake graphite.
Preparing a polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with the average particle size of 10 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the two are 3000 and 3500 respectively) are mixed into a mixture with the flake graphite volume percentage of 40% and the aluminum powder volume percentage of 3% in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the flake graphite oriented along the out-of-plane direction.
The cross section of the prepared thermal interface material is subjected to electron microscope scanning, and the result is shown in figure 1, and the graphite filler has obvious orientation arrangement characteristics as can be seen from figure 1.
The prepared thermal interface material is subjected to micro computer tomography scanning, and the MicroCT result is shown in figure 2, wherein the orientation type of the gray lines respectively well represents the orientation distribution characteristics of the crystalline flake graphite in the matrix.
The schematic structural diagram of the prepared thermal interface material before ultrasonic cutting treatment is shown in fig. 3, and graphite micro-sheets are distributed in the polyolefin matrix in parallel.
Example 2
Preparing modified graphite powder: (1) and (2) placing the flake graphite with the average particle size of 200 microns into a cavity of a plasma etching machine for etching treatment to obtain the pretreated flake graphite, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated crystalline flake graphite in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain hydroxylated crystalline flake graphite, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking hydroxylated crystalline flake graphite in the mixture for 24 hours, and cleaning and drying to obtain the modified crystalline flake graphite.
Preparing a polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with the average particle size of 10 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the two are 3000 and 3500 respectively) are mixed into a mixture with the flake graphite volume percentage of 50% and the aluminum powder volume percentage of 3% in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the flake graphite oriented along the out-of-plane direction.
Example 3
Preparing modified graphite powder: (1) and (2) placing the flake graphite with the average particle size of 200 microns into a cavity of a plasma etching machine for etching treatment to obtain the pretreated flake graphite, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated crystalline flake graphite in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain hydroxylated crystalline flake graphite, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking hydroxylated crystalline flake graphite in the mixture for 24 hours, and cleaning and drying to obtain the modified crystalline flake graphite.
Preparing a polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with the average particle size of 10 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the two are 3000 and 3500 respectively) are mixed into a mixture with the flake graphite volume percentage of 60 percent and the aluminum powder volume percentage of 3 percent in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the flake graphite oriented along the out-of-plane direction.
Example 4
Preparing modified graphite powder: (1) and (2) placing the flake graphite with the average particle size of 200 microns into a cavity of a plasma etching machine for etching treatment to obtain the pretreated flake graphite, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated crystalline flake graphite in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain hydroxylated crystalline flake graphite, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking hydroxylated crystalline flake graphite in the mixture for 24 hours, and cleaning and drying to obtain the modified crystalline flake graphite.
Preparing a polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with the average particle size of 10 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the two are 3000 and 3500 respectively) are mixed into a mixture with the flake graphite volume percentage of 70% and the aluminum powder volume percentage of 3% in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the flake graphite oriented along the out-of-plane direction.
Example 5
Preparing modified graphite powder: (1) placing the graphene nanoplatelets with the average particle size of 100 microns in a cavity of a plasma etching machine for etching treatment to obtain the preprocessed graphene nanoplatelets, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated graphene nanoplatelets in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation treatment to obtain hydroxylated graphene nanoplatelets, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking the hydroxylated graphene nanoplatelets in the mixed solution, wherein the dosage of the dodecyl trimethoxy silane coupling agent is 3% of the mass of the graphene nanoplatelets, the soaking and stirring time is 24 hours, and obtaining the modified graphene nanoplatelets after cleaning and drying.
Preparing a polyolefin-based graphite oriented thermal interface material: modified graphene nanoplatelets, aluminum powder with the average particle size of 8 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the aluminum powder and the polybutadiene are 3000 and 3500 respectively) are mixed into a mixture with the volume percentage of the graphene nanoplatelets being 40% and the volume percentage of the aluminum powder being 8% in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the matrix in the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the graphene micro-sheets oriented along the out-of-plane direction.
Example 6
Preparing modified graphite powder: (1) placing the graphene nanoplatelets with the average particle size of 100 microns in a cavity of a plasma etching machine for etching treatment to obtain the preprocessed graphene nanoplatelets, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated graphene nanoplatelets in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation treatment to obtain hydroxylated graphene nanoplatelets, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking the hydroxylated graphene nanoplatelets in the mixed solution, wherein the dosage of the dodecyl trimethoxy silane coupling agent is 3% of the mass of the graphene nanoplatelets, the soaking and stirring time is 24 hours, and obtaining the modified graphene nanoplatelets after cleaning and drying.
Preparing a polyolefin-based graphite oriented thermal interface material: modified graphene nanoplatelets, aluminum powder with the average particle size of 8 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the aluminum powder and the polybutadiene are 3000 and 3500 respectively) are mixed into a mixture with the volume percentage of the graphene nanoplatelets being 60 percent and the volume percentage of the aluminum powder being 8 percent in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the matrix in the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the graphene micro-sheets oriented along the out-of-plane direction.
Example 7
Preparing modified graphite powder: (1) placing the artificial graphite microchip with the average particle size of 300 micrometers in a cavity of a plasma etching machine for etching treatment to obtain the pretreated artificial graphite microchip, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated artificial graphite micro-sheet in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain a hydroxylated artificial graphite micro-sheet, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking the hydroxylated artificial graphite microchip in the mixture, wherein the soaking and stirring time is 24 hours, and obtaining the modified artificial graphite microchip after cleaning and drying.
Preparing a polyolefin-based graphite oriented thermal interface material: modified artificial graphite micro-sheets, aluminum powder with the average particle size of 8 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the modified artificial graphite micro-sheets and the polybutadiene are 3000 and 3500 respectively) are mixed into a mixture with the artificial graphite micro-sheets volume percentage of 50 percent and the aluminum powder volume percentage of 1 percent in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the artificial graphite micro-sheets oriented along the out-of-plane direction.
Example 8
Preparing modified graphite powder: (1) placing the artificial graphite microchip with the average particle size of 300 micrometers in a cavity of a plasma etching machine for etching treatment to obtain the pretreated artificial graphite microchip, wherein the etching atmosphere is a mixed gas with the volume ratio of oxygen to argon being 1:1, the pressure of the cavity is 6Pa, and the etching time is 15 minutes. (2) And (3) soaking the pretreated artificial graphite micro-sheet in a mixed solution of 0.3mol/L hydrogen peroxide and 0.2mol/L ammonia water for hydroxylation to obtain a hydroxylated artificial graphite micro-sheet, wherein the soaking time is 4 hours. (3) Fully hydrolyzing dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of the ethanol to the water is 3:1), drying and soaking the hydroxylated artificial graphite microchip in the mixture, wherein the soaking and stirring time is 24 hours, and obtaining the modified artificial graphite microchip after cleaning and drying.
Preparing a polyolefin-based graphite oriented thermal interface material: modified artificial graphite micro-sheets, alumina powder with the average particle size of 8 microns, polybutadiene grafted with maleic anhydride and hydrogenated polybutadiene containing terminal hydroxyl (the average molecular weights of the two are 3000 and 3500 respectively) are mixed into a mixture with the volume percentage of flake graphite being 70 percent and the volume percentage of aluminum powder being 1 percent in a centrifugal stirring mode. The rotating speed of a stirring rod for centrifugal stirring is 1800 rpm, an interval stirring mode is adopted, and the effective stirring time is 13 minutes. The mixture is subjected to calendering orientation treatment by means of calendering, and the calendering thickness is controlled to be 1 mm. And conveying the rolled mixture to a refrigerating device using liquid nitrogen as a refrigerant for freezing treatment. And mechanically cutting the mixture which is frozen into the glass state into sheets of 60 mm by 60 mm. The sheet is then quickly transferred to a mould immersed in liquid nitrogen for lamination of the mix. And after the number of the laminated layers reaches 50, transferring the laminated mixture and the die to a vacuum hot press together, and then quickly performing vacuum-pumping treatment. After the vacuum was reduced to below 30pa, the vacuum hot press was allowed to warm to 50 ℃ at a rate of 0.5 ℃/minute and pressure was applied to the layered mix at 15psi during this process. The heat preservation time is controlled to be more than 12 hours. The temperature is continuously increased to 150 ℃, and the holding time is 5 hours. And after the internal matrix of the mixture is completely crosslinked, cutting along the direction vertical to the graphite orientation direction in an ultrasonic cutting mode, and finally preparing the thermal interface material with the artificial graphite micro-sheets oriented along the out-of-plane direction.
The in-plane thermal conductivity and the out-of-plane thermal conductivity of the thermal interface material products of examples 1 to 8 were measured, and the results are shown in the following table.
| Examples | Out-of-plane thermal conductivity W/mk | In-plane thermal conductivity W/ |
| 1 | 13.41 | 1.04 |
| 2 | 17.35 | 1.12 |
| 3 | 21.21 | 1.13 |
| 4 | 22.52 | 1.12 |
| 5 | 27.85 | 1.27 |
| 6 | 30.11 | 1.05 |
| 7 | 36.01 | 1.22 |
| 8 | 44.65 | 1.28 |
From the test results of the above table examples, it can be seen that the prepared thermal interface material has great difference of the in-plane and out-plane thermal conductivities, has obvious anisotropic characteristics, and has extremely high thermal conductivity in the out-of-plane direction of the material.
In conclusion, the modified graphite powder and the filled heat-conducting filler are uniformly mixed in the polyolefin matrix in a mechanical stirring manner. The orientation arrangement of the modified graphite powder with anisotropic characteristics along the lamellar direction is realized by rolling treatment and utilizing shearing force. Through ultra-low temperature freezing treatment, the state of the mixture after orientation arrangement is effectively fixed, and subsequent treatments such as cutting, lamination, vacuum exhaust and the like are facilitated. The densification of the oriented sample can be effectively realized through vacuum pressurization treatment, so that the intrinsic thermal resistance of the cured sample is effectively reduced. The finally prepared thermal interface material taking the modified graphite powder as the main filler has the characteristics of high heat conduction and soft resilience along the out-of-plane direction.
The above-mentioned embodiments are provided only for illustrative purposes and should not be construed as limiting the scope of the present invention, and any equivalent replacement or modification of the technical solution and the inventive concept of the present invention should be covered within the scope of the present invention.
Claims (10)
1. A method for modifying graphite powder by a coupling agent is characterized by comprising the following steps:
(1) carrying out plasma etching pretreatment on the graphite powder to obtain pretreated graphite powder;
(2) carrying out hydroxylation treatment on the pretreated graphite powder to obtain hydroxylated graphite powder;
(3) fully hydrolyzing the coupling agent in a solvent, and adding hydroxylated graphite powder into the fully hydrolyzed coupling agent to modify the graphite powder to obtain the modified graphite powder.
2. The method for modifying graphite powder by using coupling agent according to claim 1, wherein the graphite powder in step (1) comprises one or more of crystalline flake graphite, graphene micro-sheets and artificial graphite micro-sheets;
preferably, the particle size of the graphite powder is 10-2000 microns, and preferably 100-1000 microns.
3. The method for modifying graphite powder by using a coupling agent as claimed in claim 1, wherein the atmosphere of the plasma treatment in the step (1) is pure oxygen, a mixed gas of argon and oxygen, or a mixed gas of nitrogen and oxygen;
preferably, the volume ratio of argon to oxygen in the mixed gas of argon and oxygen is 1: 2-1: 1;
preferably, the volume ratio of the nitrogen to the oxygen in the mixed gas of the nitrogen and the oxygen is 1: 2-1: 1;
preferably, the pressure of the plasma cavity is 2-10 Pa;
preferably, the plasma etching pretreatment time is 10-20 minutes.
4. The method for modifying graphite powder by using a coupling agent according to claim 1, wherein the hydroxylation treatment in the step (2) is specifically performed by immersing the pretreated graphite powder in a mixed solution of hydrogen peroxide and ammonia water;
preferably, the concentration of the hydrogen peroxide in the mixed solution of the hydrogen peroxide and the ammonia water is 0.2-0.8 mol/L, and the concentration of the ammonia water is 0.1-0.4 mol/L.
5. The method for modifying graphite powder by using a coupling agent as claimed in claim 1, wherein the coupling agent in step (3) comprises one or more of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent;
preferably, the silane coupling agent comprises one or more of WD-26, WD-21, WD-27, WD-22, WD-51, WD-71, KH-550, KH-560, KH-570, dodecyl trimethoxy silane, and hexadecyl trimethoxy silane;
preferably, the titanate coupling agent comprises one or more of TMC-201, TMC-102, TMC-101, TMC-105, TMC-TTS, TMC-114, TMC-401;
preferably, the aluminate coupling agent comprises one or more of DL-411, DL-411AF, DL-411D, DL-411 DF;
preferably, the mass of the coupling agent is 1-15% of that of the graphite powder, and preferably 3-10%;
preferably, the solvent is a mixed solution of ethanol and water, and the mass ratio of the ethanol to the water in the mixed solution of the ethanol and the water is 2: 1-4: 1;
preferably, the modification time of the graphite powder is 10-30 hours.
6. A modified graphite powder, characterized by being prepared by the method for modifying graphite powder with a coupling agent according to any one of claims 1 to 5.
7. A polyolefin-based graphite oriented thermal interface material, which is characterized by comprising a polyolefin matrix, the modified graphite powder as described in claim 7 and a filled heat-conducting filler;
the filling type heat conduction filler is a micron-sized or nano-sized particle filler, a whisker filler, a fiber filler or a nanowire filler.
8. The polyolefin-based graphite oriented thermal interface material of claim 7, wherein the polyolefin matrix comprises at least one polyolefin material having terminal hydroxyl groups and at least one polyolefin material having maleic anhydride groups grafted thereto; preferably, the polyolefin matrix accounts for 7-90%, preferably 25-60% of the total volume of the polyolefin-based graphite oriented thermal interface material;
preferably, the modified graphite powder accounts for 10-85% of the total volume of the polyolefin-based graphite oriented thermal interface material, and preferably 40-70%;
preferably, the filled heat conducting filler is a metal material or an inorganic non-metal material; more preferably, the metal material comprises one or more of aluminum, copper, silver; more preferably, the inorganic non-metallic material comprises one or more of carbon fiber, diamond, aluminum nitride, silicon nitride, aluminum oxide, zinc oxide, boron nitride; more preferably, the particle size of the filled heat conduction filler particle filler is 0.5-100 microns, preferably 5-15 microns; more preferably, the length of the filled heat-conducting filler fiber filler is 20-150 micrometers, preferably 30-100 micrometers, the length-diameter ratio is 20-250, preferably 50-200; more preferably, the length of the filling type heat conduction filler whisker filler is 2-50 microns, preferably 8-40 microns, the length-diameter ratio is 5-30, and preferably 10-20; more preferably, the percentage of the filled heat conductive filler in the total volume of the polyolefin-based graphite oriented thermal interface material is 0-8%, and preferably 0-5%.
9. The method for preparing an oriented polyolefin-based graphite thermal interface material according to claim 7 or 8, comprising the steps of:
(1) uniformly stirring and mixing a polyolefin matrix, the modified graphite powder as described in claim 7 and a filled heat-conducting filler to obtain a mixture;
(2) carrying out orientation treatment on the mixture to obtain a lamellar mixture;
(3) freezing the lamellar mixture to obtain a frozen lamellar mixture;
(4) keeping the frozen state of the frozen lamellar mixture, cutting the frozen lamellar mixture to obtain a lamellar sample with specified width and length, and laminating the lamellar sample;
(5) processing the laminated sample in a vacuum pressurization mode, and slowly heating in the process to ensure that the mixture is converted from a solid state to a viscous state to obtain a compact sample preform;
(6) carrying out high-temperature curing treatment on the compact sample preform to obtain a cured sample;
(7) and cutting the cured sample along the direction vertical to the thickness of the sheet-shaped layered sample to obtain the polyolefin-based graphite oriented thermal interface material with anisotropic characteristics.
10. The production method according to claim 9, wherein the stirring and mixing in the step (1) is performed under a vacuum environment;
preferably, the orientation treatment described in step (2) comprises calendering, knife coating, two-roll coating;
preferably, the thickness of the oriented laminar mixture in the step (2) is not more than 10 times of the average particle size of the graphite powder;
preferably, the freezing treatment in the step (3) comprises liquid nitrogen treatment and liquid oxygen treatment;
preferably, in the vacuum pressurization treatment process in the step (5), the pressure is 5-30 psi, the temperature is 30-90 ℃, and the time is 6-20 hours;
preferably, the high-temperature curing temperature in the step (6) is 90-170 ℃, and the high-temperature curing time is 1-5 hours;
preferably, the cutting process in step (7) comprises laser cutting and ultrasonic cutting.
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