WO2022120691A1

WO2022120691A1 - Polyolefin-based graphite-oriented thermal interface material and preparation method therefor

Info

Publication number: WO2022120691A1
Application number: PCT/CN2020/135169
Authority: WO
Inventors: 曾小亮; 张晨旭; 叶振强; 任琳琳; 张月星; 许建斌; 孙蓉
Original assignee: 中国科学院深圳先进技术研究院
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-06-16

Abstract

Disclosed are a polyolefin-based graphite-oriented thermal interface material and a preparation method therefor. The polyolefin-based graphite-oriented thermal interface material comprises a polyolefin base, modified graphite powder, and a filling type heat conduction filler. The filling type heat conduction filler is a micron-sized or nanosized particle type, whisker type, fiber type, or nanowire type filler. The modified graphite powder is coupling agent-modified graphite powder. A preparation method for the coupling agent-modified graphite powder comprises the following steps: performing a plasma etching pretreatment on the graphite powder; performing hydroxylation processing on the pretreated graphite powder; and fully hydrolyzing a coupling agent in a solvent, and adding hydroxylated graphite powder to the fully hydrolyzed coupling agent. The polyolefin-based graphite-oriented thermal interface material of the present invention is stable in performance, has high orientation, high compactness, and high thermal conductivity. At the same time, the polyolefin-based graphite-oriented thermal interface material is ensured to also have good flexibility and resilience, so as to ensure that a heat source of an electronic device and a heat-dissipation device are filled at a high coverage rate, thereby effectively realizing efficient heat dissipation of the electronic device.

Description

A kind of polyolefin-based graphite oriented thermal interface material and preparation method thereof

technical field

The invention belongs to the technical field of thermally conductive polymer-based composite materials, and in particular relates to a polyolefin-based graphite-oriented thermal interface material and a preparation method thereof.

Background technique

The rise of emerging fields such as 5G communication, Internet of Things, big data and artificial intelligence makes integrated circuits develop in the direction of miniaturization, thinness and high integration. However, this trend will directly lead to an increase in the power density and operating temperature of electronic devices. If the heat of electronic devices is not dissipated in time, it will not only significantly reduce its performance, but also lead to equipment failure, scrapping, and even safety hazards in severe cases. Therefore, how to achieve efficient heat dissipation of electronic components is a key issue facing the design and assembly of electronic products today. Especially for portable electronic products with a high degree of integration, heat dissipation has even become the main technical bottleneck of the entire industry.

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 TIM 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.

At present, the thermal conductive fillers of common thermal interface materials are mainly high thermal conductive ceramic particles or metal powders. However, only when the content of such fillers is above 60wt%, the thermal conductivity of the thermal interface material will be significantly improved, and the thermal conductivity is usually lower than 7W/mK. However, 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.

SUMMARY OF THE INVENTION

In order to solve the problems raised in the above background technology, the purpose of the present invention is to provide a polyolefin-based graphite oriented thermal interface material and a preparation method thereof.

In order to achieve the above purpose, the technical scheme adopted in the present invention is as follows: on the one hand, the present invention provides a method for modifying a graphite powder by a coupling agent, comprising the following steps:

(1) performing 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 to the fully hydrolyzed coupling agent to modify the graphite powder to obtain a modified graphite powder.

Further, the graphite powder described in step (1) includes one or more of flake graphite, graphene, graphene microplatelets, and artificial graphite microplatelets;

Preferably, the particle size of the graphite powder is 10-2000 microns, preferably 100-1000 microns.

Further, the atmosphere of the plasma treatment described in step (1) is pure oxygen, a mixture of argon and oxygen, or a mixture of nitrogen and oxygen;

Preferably, the volume ratio of argon and oxygen in the mixture of argon and oxygen is 1:2 to 1:1;

Preferably, the volume ratio of nitrogen and oxygen in the mixture of nitrogen and oxygen is 1:2 to 1:1;

Preferably, the gas pressure of the plasma chamber is 2-10 Pa;

Preferably, the time for the plasma etching pretreatment is 10-20 minutes.

Further, the hydroxylation treatment described in step (2) is specifically that the pretreated graphite powder is soaked in a mixed solution of hydrogen peroxide and ammonia water for hydroxylation treatment;

Preferably, the concentration of hydrogen peroxide in the mixed solution of hydrogen peroxide and ammonia water is 0.2-0.8 mol/L, and the concentration of ammonia water is 0.1-0.4 mol/L.

Further, the coupling agent in step (3) includes one or more of a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent;

Preferably, the silane coupling agent includes WD-26, WD-21, WD-27, WD-22, WD-51, WD-71, KH-550, KH-560, KH-570, dodecyl One or more of trimethoxysilane and hexadecyltrimethoxysilane;

Preferably, the titanate coupling agent includes one or more of TMC-201, TMC-102, TMC-101, TMC-105, TMC-TTS, TMC-114, and TMC-401;

Preferably, the aluminate coupling agent comprises one or more of DL-411, DL-411AF, DL-411D, and DL-411DF;

Preferably, the mass of the coupling agent is 1-15% of the mass of the graphite powder, preferably 3-10%;

Preferably, the solvent is a mixed solution of ethanol and water, and the mass ratio of ethanol to water in the mixed solution of ethanol and water is 2:1 to 4:1;

Preferably, the modification time of the graphite powder is 10-30 hours.

On the other hand, the present invention provides a modified graphite-based powder, which is prepared by any of the above-mentioned methods for modifying the graphite-based powder with a coupling agent.

On the other hand, the present invention provides a polyolefin-based graphite oriented thermal interface material, comprising a polyolefin matrix, the modified graphite powder described above, and a filled thermally conductive filler;

The filled thermally conductive fillers are particle, whisker, fiber, and nanowire fillers with micron-sized or nano-sized.

Further, the polyolefin matrix contains at least one polyolefin material with terminal hydroxyl groups and at least one polyolefin material grafted with maleic anhydride groups; preferably, the polyolefin matrix accounts for the polyolefin group The total volume percentage of the graphite-oriented thermal interface material is 7-90%, preferably 25-60%;

Preferably, the total volume percentage of the modified graphite powder in the polyolefin-based graphite oriented thermal interface material is 10-85%, preferably 40-70%;

Preferably, the filled 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 Including 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 thermally conductive filler particles is 0.5-100 microns, preferably 5-15 microns; more preferably, the length of the filled thermally conductive filler fibrous filler is 20-150 microns, preferably 30-100 microns, and the aspect ratio is 20-250, preferably 50-200 ; more preferably, the length of the filled type thermal conductive filler whisker filler is 2-50 microns, preferably 8-40 microns, and the aspect ratio is 5-30, preferably 10-20; more preferably, the said The percentage by volume of the filled thermally conductive filler in the polyolefin-based graphite oriented thermal interface material is 0-8%, preferably 0-5%.

In another aspect, the present invention provides a method for preparing the above-mentioned polyolefin-based graphite-oriented thermal interface material, comprising the following steps:

(1) stirring and mixing the polyolefin matrix, the modified graphite powder described in claim 7, and the filled thermally conductive filler to obtain a mixture;

(2) orientation treatment is carried out to the mixture to obtain a lamellar mixture;

(3) freezing the lamellar mixture to obtain frozen lamellar mixture;

(4) maintaining the frozen state of the frozen lamellar mixture, and cutting the frozen lamellar mixture to obtain a lamellar sample with a specified width and length, and then laminating the lamellar sample;

(5) The laminated sample is processed by means of vacuum pressing, and the temperature is slowly raised 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;

(6) carrying out high temperature curing treatment to the dense sample preform to obtain the cured sample;

(7) Cutting the cured sample along the direction perpendicular to the thickness of the lamellar sample to obtain a polyolefin-based graphite oriented thermal interface material with anisotropic characteristics.

Further, the stirring and mixing described in step (1) is carried out under vacuum environment;

Preferably, the orientation treatment described in step (2) includes calendering, blade coating, and double-roll coating;

Preferably, the thickness of the lamellar mixture after the orientation treatment in step (2) is not greater than 10 times the average particle size of the graphite powder;

Preferably, the freezing treatment described in step (3) includes liquid nitrogen treatment and liquid oxygen treatment;

Preferably, the pressure in the vacuum pressurization process in step (5) is 5-30 psi, the temperature is 30-90°C, and the time is 6-20 hours;

Preferably, the temperature of the high-temperature curing in step (6) is 90-170° C., and the high-temperature curing time is 1-5 hours;

Preferably, the cutting process described in step (7) includes laser cutting and ultrasonic cutting.

The beneficial effects of the present invention are as follows: (1) The polyolefin-based graphite oriented thermal interface material of the present invention has stable performance, has the characteristics of high degree of orientation, high density and high thermal conductivity, and at the same time ensures that it also has good flexibility and resilience. Elasticity, so as to ensure that the heat source of the electronic device and the heat dissipation device are filled with a high coverage rate, thereby effectively realizing the efficient heat dissipation of the electronic device. (2) The polyolefin matrix of the present invention has the characteristics of simple formula and stable performance, which can realize stable cross-linking without the help of additives such as catalysts and chain extenders, and avoid the occurrence of catalyst poisoning; and, the matrix is cured. After cross-linking, it has the characteristics of flexibility and elasticity. (3) The present invention adopts plasma etching treatment, which can effectively activate the surface state of the graphite powder, facilitates the treatment of grafting hydroxyl groups on the surface of the powder, and can better play the role of the coupling agent. The purpose of plasma treatment of graphite powder is to introduce highly active oxygen-containing groups on the surface of inert graphite powder to increase the surface energy of the powder. Hydroxylation of graphite powders can introduce hydrogen on the surface of graphite powders to form hydroxyl groups. The purpose of modifying the graphite powder by grafting the coupling agent is to improve the interface bonding 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 of the present invention has high compactness (low porosity) and low thermal resistance. (5) The present invention realizes that the modified graphite powder has a stable and excellent degree of orientation through calendering treatment and other orientation treatment methods; the present invention effectively fixes the molecular chains of the oriented mixed material through ultra-low temperature freezing treatment, preventing the phenomenon of viscous flow. It can realize the operation of the mixture in the state of glass, avoiding the problem that the viscous-flow mixture is difficult to operate, so as to facilitate the subsequent cutting, lamination and vacuum exhaust processing, which is conducive to obtaining a high degree of orientation and Thermal interface material with low porosity; in the present invention, vacuum pressure treatment is performed in the state of the mixture glass, which can reduce the porosity inside the material to the greatest extent, thereby improving the compactness of the material. (6) The present invention can achieve a high degree of densification of the material while achieving a high degree of orientation of the modified graphite powder. Therefore, under the condition of a low filler content, the prepared thermal interface material can be made hot. High conductivity and low thermal resistance. The lower filler content also endows the thermal interface material with good flexibility and elasticity. (7) 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-based fillers, thereby helping to improve the composite Thermal conductivity of materials.

Description of drawings

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.

2 is a MicroCT image of the thermal interface material prepared in Example 1 of the present invention.

3 is a schematic structural diagram of the thermal interface material prepared in Example 1 of the present invention before ultrasonic cutting.

Detailed ways

The following example illustrates the graphite-based powder/polyolefin-based thermal interface material with oriented structure characteristics and the preparation method thereof.

A graphite powder/polyolefin-based thermal interface material with oriented structure features uses modified graphite powder as the main thermal conductive filler, filled thermal conductive filler as the secondary thermal conductive filler, and crosslinkable as both flexibility and thermal conductivity. The polyolefin of the elastic material is the matrix, and the modified graphite powder and the filled thermally conductive filler are uniformly dispersed and oriented in the polyolefin matrix, so that the thermal interface material has excellent thermal conductivity. Among them, the modified graphite powder has a two-dimensional lamellar structure, and has the characteristics of high thermal conductivity along the lamellar direction, so that the modified graphite powder arranged after orientation can greatly improve the thermal conductivity of the polyolefin matrix. , and make the thermal interface material also have obvious anisotropy. The main function of filled thermally conductive fillers is to promote the formation of thermal conduction paths inside the thermal interface material and to adjust the rheological properties of the mixture.

The modified graphite powder is a coupling agent modified graphite powder; the modification method includes the following steps: (1) performing plasma etching pretreatment on the graphite powder to obtain the 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 hydroxylation to the fully hydrolyzed coupling agent The graphite powder is modified by graphite powder to obtain modified graphite powder.

In an optional embodiment, the polyolefin matrix refers to a type of crosslinkable material with flexibility and resilience, the material contains at least one polyolefin material with terminal hydroxyl groups and at least one The polyolefin material grafted with maleic anhydride groups, under the action of high temperature, the maleic anhydride group and the hydroxyl group will undergo an addition reaction, so that the interior of the matrix will be cross-linked; controlling the content of different components of the polymer can form Matrix materials with varying degrees of crosslinking that combine flexibility and elasticity.

In an optional embodiment, the filled thermally conductive filler refers to a general term for a type of particle, whisker, fiber and nanowire filler with micron-sized or nano-sized, which can fill the matrix. Intermolecular micro-voids and bridging the role of modified graphite powders are beneficial to improve the thermal conductivity of thermal interface materials. This type of filled thermally conductive filler is a metal material or an inorganic non-metallic material, the metal material includes one or more of aluminum, copper, and silver, and the inorganic non-metallic material includes carbon fiber, diamond, aluminum nitride, nitride One or more of silicon, aluminum oxide, zinc oxide, and boron nitride.

In an optional embodiment, the graphite-based powder includes one or more of materials with anisotropic characteristics, such as flake graphite, graphene, graphene microplatelets, and artificial graphite microplatelets. The coupling agent includes one or more of a silane coupling agent, a titanate coupling agent, and an 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 adversely affect the properties of the matrix. Further, the dosage 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 evenly spread out and placed inside the cavity of the plasma etching machine. After the vacuum degree of the cavity drops to 3×10 ^-3 Pa, oxygen is filled Or the oxygen-containing mixed gas can reach 2-10 Pa in the chamber pressure, and the plasma etching time is 10-20 minutes.

The graphite powder after plasma etching is immersed in a mixed solution of hydrogen peroxide and ammonia water, the soaking time is 2 to 4 hours, the concentration of hydrogen peroxide is 0.2 to 0.8 mol/L, and the concentration of ammonia water is 0.1 to 0.4 mol /L.

The coupling agent is fully hydrolyzed in a mixed solution of ethanol and water, and the above-mentioned hydroxylated graphite powder is added to the fully hydrolyzed coupling agent to modify the powder, and the modified graphite is obtained after cleaning and drying. powder.

In an optional embodiment, the volume percentage of the polyolefin matrix is 7-90%, the volume percentage of the modified graphite powder can be 10-85%, and the total volume percentage of the composite material by the filled thermally conductive filler is 0 to 8%. 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 of the polyolefin matrix is 25-60%, the volume percentage of the modified graphite powder can be 40-70%, and the volume percentage of the filled thermally conductive 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 thermally conductive filler particle filler is 0.5 to 100 microns, and the filled thermally conductive filler fibrous filler The length of the filler is 20-150 microns, the aspect ratio is 20-250, the length of the filled thermally conductive filler whiskers is 2-50 microns, preferably 8-40 microns, and the aspect ratio is 5-30. Modified graphite powder is used as the main thermal conductive filler of thermal interface material, and the sheet diameter length of graphite powder has a significant influence on the thermal conductivity of thermal interface material. If the length of the graphite powder sheet diameter is too large, it will increase the difficulty in the mixing process; if the length of the graphite powder sheet diameter is too small, a large number of interfaces will be introduced, and it is difficult to form a relatively continuous thermal conduction path, reducing the material's thermal conductivity. Thermal conductivity. If the particle size of the filled thermally conductive filler is too large, defects are easily introduced and the mechanical properties of the material are reduced. If the particle size length of the filled thermally conductive filler is too small, the dispersion of the filler will be difficult. Further, the particle size of the graphite powder can be 10-1000 microns, the particle size of the particle-filled thermally conductive filler can be 5-15 microns, the size of the fiber-filled thermally conductive filler can be 30-100 microns, and the length The diameter ratio may be 50-200, and the length-diameter ratio of the whisker-filled thermally conductive filler may be 10-20. A method for preparing a graphite powder/polyolefin-based thermal interface material with oriented structure features: comprising the following steps: weighing corresponding mass of modified graphite powder, filled thermally conductive filler and polyolefin matrix according to volume percentage .

The modified graphite powder, the filled thermally conductive filler and the polyolefin matrix are uniformly mixed by means of mechanical mixing (such as centrifugal stirring) to obtain a mixture. The centrifugal 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 serious frictional heat generation during the centrifugal stirring process, an intermittent stirring program is adopted, that is, every one minute of stirring is followed by a one-minute pause, and so on until the program ends. The pause time is not included in the stirring time.

Orientation treatment (such as a calendering process) is used to realize the orientation of the modified graphite powder in the mixture to obtain a lamellar mixture. The calendering orientation process uses shear force to promote the orientation of the modified graphite powder with a two-dimensional lamellar structure. The calendering process can realize the continuous production of the compound. According to the characteristics and actual needs of the mixture, choose whether to use a release film during the calendering process. In order to ensure that the graphite-based filler in the calendered mixture has a high degree of orientation, the thickness of the calendering treatment is controlled to be no greater than 10 times the average particle size of the graphite-based filler.

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. In order to ensure the freezing speed, 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 chain of the matrix, and ensure that the modified graphite powder in the mixture maintains a good degree of extraction during the lamination process.

After designing the cutting size, the frozen flaky mixture is mechanically cut in a solid state, and then the cut frozen flaky mixture of fixed size is transferred to a designated mold for lamination processing. In order to ensure that the orientation state of the modified graphite powder remains unchanged during the lamination process, 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.

Transfer the mold that has been stacked with the specified number of layers of compound to the vacuum hot pressing device together with the compound. Then the cavity is quickly vacuumed to remove the air between the layers of the mixture. When the vacuum inside the cavity drops below 30pa, apply a pressure of 5-30psi in the vertical direction, and raise the temperature of the device to 30-90℃. The purpose of the pressurization operation is to further promote the densification of the mixture. The purpose of the heating operation is to gradually change the mixture from a glassy state to a viscous fluid state, so that the bonding between layers can be achieved.

The pressure was removed, the vacuum state was maintained, and the temperature was continued to rise to 90-170°C. The cross-linking reaction occurs inside the matrix, and the curing time is 1 to 5 hours, thereby giving the mixture certain mechanical properties (any device with heating and heat preservation function can be used in the high-temperature curing process).

A certain cutting process (such as laser cutting or ultrasonic cutting) is used to cut the cured composite material, and the laser cutting or ultrasonic cutting process is easier to obtain a thermal interface material with a smooth surface. The cutting direction is cut along the direction perpendicular to the orientation of the modified graphite powder, so as to obtain thermal interface materials with high thermal conductivity out of plane and high thermal conductivity in plane respectively.

The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the following contents of the present invention belong to the present invention. scope of protection. The specific process parameters and the like in the following examples are only an example in the suitable range, that is, those skilled in the art can make selections within the suitable range through the description herein, rather than being limited to the specific values in the following examples. In the following examples, the test methods without specific conditions are usually in accordance with conventional conditions, such as the conditions in the process manual, or in accordance with the conditions suggested by the manufacturer.

Example 1

Preparation of modified graphite powder: (1) Place graphite flakes with an average particle size of 200 microns in the cavity of a plasma etching machine for etching to obtain pretreated graphite flakes, and the etching atmosphere is oxygen and argon. The volume ratio of the mixed gas is 1:1, the chamber pressure is 6Pa, and the etching time is 15 minutes. (2) soaking the pretreated graphite flakes in a mixed solution of 0.3 mol/L hydrogen peroxide and 0.2 mol/L ammonia water for hydroxylation treatment to obtain hydroxylated graphite flakes, and the soaking time is 4 hours. (3) fully hydrolyze the dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of ethanol and water is 3:1), and the dodecyl trimethoxy silane coupling agent is fully hydrolyzed. The dosage is 3% of the mass of the graphite flakes, and the hydroxylated graphite flakes are dried and soaked in it, and the soaking and stirring time is 24 hours, and the modified graphite flakes are obtained after cleaning and drying.

Preparation of polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with an average particle size of 10 microns, polybutadiene grafted with maleic anhydride and polybutadiene containing terminal hydroxyl groups after hydrogenation treatment Graphene (the average molecular weight of the two are 3000 and 3500 respectively), and mixed by centrifugal stirring to form a mixture of 40% by volume of flake graphite and 3% by volume of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the perpendicular graphite orientation direction, and finally a thermal interface material with flake graphite oriented along the out-of-plane direction is obtained.

The cross-section of the prepared thermal interface material is scanned by electron microscope, and the results are shown in Figure 1. From Figure 1, it can be seen that the graphite-based filler has obvious orientation and arrangement characteristics.

The obtained thermal interface material was scanned by micro-computed tomography, and the results of MicroCT are shown in Figure 2, in which the orientation patterns of the gray lines represent the orientation distribution characteristics of flake graphite in the matrix respectively.

The schematic diagram of the structure of the prepared thermal interface material before ultrasonic cutting is shown in Figure 3, and the graphite microplates are distributed in the polyolefin matrix in parallel with each other.

Example 2

Preparation of polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with an average particle size of 10 microns, polybutadiene grafted with maleic anhydride and polybutadiene containing terminal hydroxyl groups after hydrogenation treatment Graphene (the average molecular weights of the two are 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture of 50% by volume of flake graphite and 3% by volume of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the perpendicular graphite orientation direction, and finally a thermal interface material with flake graphite oriented along the out-of-plane direction is obtained.

Example 3

Preparation of polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with an average particle size of 10 microns, polybutadiene grafted with maleic anhydride and polybutadiene containing terminal hydroxyl groups after hydrogenation Graphene (the average molecular weights of the two are 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture with a volume percentage of flake graphite of 60% and aluminum powder of 3% by volume. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the perpendicular graphite orientation direction, and finally a thermal interface material with flake graphite oriented along the out-of-plane direction is obtained.

Example 4

Preparation of polyolefin-based graphite oriented thermal interface material: modified flake graphite, aluminum powder with an average particle size of 10 microns, polybutadiene grafted with maleic anhydride and polybutadiene containing terminal hydroxyl groups after hydrogenation treatment ethylene (the average molecular weight of the two are 3000 and 3500 respectively), and mixed by centrifugal stirring to form a mixture of 70% by volume of flake graphite and 3% by volume of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the perpendicular graphite orientation direction, and finally a thermal interface material with flake graphite oriented along the out-of-plane direction is obtained.

Example 5

Preparation of modified graphite powder: (1) Place graphene micro-sheets with an average particle size of 100 microns in a plasma etching machine cavity for etching to obtain pre-treated graphene micro-sheets, and the etching atmosphere is: The mixed gas of oxygen and argon with a volume ratio of 1:1, the chamber pressure is 6Pa, and the etching time is 15 minutes. (2) soaking the pretreated graphene micro-sheets in a mixture of 0.3 mol/L hydrogen peroxide and 0.2 mol/L ammonia water for hydroxylation to obtain hydroxylated graphene micro-sheets, and the soaking time is 4 hours. (3) fully hydrolyze the dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of ethanol and water is 3:1), and the dodecyl trimethoxy silane coupling agent is fully hydrolyzed. The dosage is 3% of the mass of the graphene micro-flakes, and the hydroxylated graphene micro-flakes are dried and soaked in it, and the soaking and stirring time is 24 hours, and the modified graphene micro-flakes are obtained after cleaning and drying.

Preparation of polyolefin-based graphite oriented thermal interface material: modified graphene microplatelets, aluminum powder with an average particle size of 8 microns, polybutadiene grafted with maleic anhydride, and hydrogenated polybutadiene containing terminal hydroxyl groups were prepared. Butadiene (the average molecular weight of the two are 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture with a volume percentage of 40% by volume of graphene microplatelets and 8% by volume of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the direction perpendicular to the graphite orientation, and finally a thermal interface material in which the graphene microplates are oriented along the out-of-plane direction is obtained.

Example 6

Preparation of polyolefin-based graphite oriented thermal interface material: modified graphene microplatelets, aluminum powder with an average particle size of 8 microns, polybutadiene grafted with maleic anhydride, and hydrogenated polybutadiene containing terminal hydroxyl groups were prepared. Butadiene (the average molecular weight of the two is 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture with a volume percentage of graphene microplates of 60% and an aluminum powder volume percentage of 8%. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the direction perpendicular to the graphite orientation, and finally a thermal interface material in which the graphene microplates are oriented along the out-of-plane direction is obtained.

Example 7

Preparation of modified graphite powder: (1) Place the artificial graphite microflakes with an average particle size of 300 microns in the cavity of the plasma etching machine for etching treatment to obtain pretreated artificial graphite microflakes, and the etching atmosphere is: The mixed gas of oxygen and argon with a volume ratio of 1:1, the chamber pressure is 6Pa, and the etching time is 15 minutes. (2) soaking the pretreated artificial graphite flakes in a mixed solution of 0.3 mol/L hydrogen peroxide and 0.2 mol/L ammonia water for hydroxylation to obtain hydroxylated artificial graphite flakes, and the soaking time is 4 hours. (3) fully hydrolyze the dodecyl trimethoxy silane coupling agent in a mixed solution of ethanol and water (the mass ratio of ethanol and water is 3:1), and the dodecyl trimethoxy silane coupling agent is fully hydrolyzed. The dosage is 3% of the mass of the artificial graphite flakes, and the hydroxylated artificial graphite flakes are dried and soaked in it. The soaking and stirring time is 24 hours, and the modified artificial graphite flakes are obtained after cleaning and drying.

Preparation of polyolefin-based graphite oriented thermal interface material: modified artificial graphite microflakes, aluminum powder with an average particle size of 8 microns, polybutadiene grafted with maleic anhydride, and hydrogenated polybutadiene containing terminal hydroxyl groups were prepared. Butadiene (the average molecular weight of the two are 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture with a volume percentage of 50% of artificial graphite flakes and 1% of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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 30pa, the vacuum hot press was heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi was applied to the lamination mixture during the process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material with artificial graphite microplates oriented in the out-of-plane direction is obtained.

Example 8

Preparation of polyolefin-based graphite oriented thermal interface material: modified artificial graphite microflakes, alumina powder with an average particle size of 8 microns, polybutadiene grafted with maleic anhydride and hydrogenated hydroxyl-terminated Polybutadiene (the average molecular weights of the two are 3000 and 3500 respectively), mixed by centrifugal stirring to form a mixture of 70% by volume of flake graphite and 1% by volume of aluminum powder. The rotational speed of the stirring rod for centrifugal stirring is 1800 rpm, and the interval stirring method is adopted, and the effective stirring time is 13 minutes. By means of calendering, the above-mentioned mixture is subjected to calendering orientation treatment, and the calendering thickness is controlled to be 1 mm. The calendered 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. When the vacuum degree drops below 30pa, the vacuum hot press is heated to 50°C at a heating rate of 0.5°C/min, and a pressure of 15 psi is applied to the lamination mixture during this process. The above holding time is controlled at more than 12 hours. Continue to heat up to 150 ℃, the holding time is 5 hours. After the internal matrix of the mixture is completely cross-linked, ultrasonic cutting is used to cut along the vertical graphite orientation direction, and finally a thermal interface material with artificial graphite microplates oriented in the out-of-plane direction is obtained.

The in-plane thermal conductivity and out-of-plane thermal conductivity of the thermal interface material products of the above Examples 1 to 8 were tested respectively, and the obtained results are shown in the following table.

实施例Example	面外热导率W/mkOut-of-plane thermal conductivity W/mk	面内热导率W/mkIn-plane thermal conductivity W/mk
11	13.4113.41	1.041.04
22	17.3517.35	1.121.12
33	21.2121.21	1.131.13
44	22.5222.52	1.121.12
55	27.8527.85	1.271.27
66	30.1130.11	1.051.05
77	36.0136.01	1.221.22
88	44.6544.65	1.281.28

From the test results of the examples in the table above, it can be seen that the thermal interface material prepared has a huge difference in the in-plane and out-plane thermal conductivity, has obvious anisotropic characteristics, and has a very high thermal conductivity in the out-of-plane direction of the material. .

To sum up, in the present invention, the modified graphite powder and the filled thermally conductive filler are uniformly mixed inside the polyolefin matrix by means of mechanical stirring. Through the calendering treatment, the modified graphite powder with anisotropic characteristics is oriented along the sheet layer direction by using shear force. Through 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 modified graphite powder as the main filler has the characteristics of high thermal conductivity and soft rebound along the out-of-plane direction.

The embodiments provided above are only for explanation, and should not be considered as limiting the scope of the present invention. Any method that is equivalently replaced or changed according to the technical solutions and inventive concept of the present invention should be included in the protection scope of the present invention. Inside.

Claims

A method for modifying graphite powder by coupling agent, comprising the following steps:

(1) performing 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 to the fully hydrolyzed coupling agent to modify the graphite powder to obtain a modified graphite powder.
The method for modifying graphite powder by a coupling agent according to claim 1, wherein the graphite powder in step (1) comprises flake graphite, graphene, graphene microflakes, and artificial graphite microflakes one or more of;

Preferably, the particle size of the graphite powder is 10-2000 microns, preferably 100-1000 microns.
The method for modifying graphite powder by a coupling agent according to claim 1, wherein the atmosphere of the plasma treatment in step (1) is pure oxygen, a mixture of argon and oxygen, or nitrogen and oxygen gas mixture;

Preferably, the volume ratio of argon and oxygen in the mixture of argon and oxygen is 1:2 to 1:1;

Preferably, the volume ratio of nitrogen and oxygen in the mixture of nitrogen and oxygen is 1:2 to 1:1;

Preferably, the gas pressure of the plasma chamber is 2-10 Pa;

Preferably, the time of the plasma etching pretreatment is 10-20 minutes.
The method for modifying graphite powder by a coupling agent according to claim 1, wherein the hydroxylation treatment in step (2) is specifically immersing the pretreated graphite powder in a mixture of hydrogen peroxide and ammonia water Hydroxylation in solution;

Preferably, the concentration of hydrogen peroxide in the mixed solution of hydrogen peroxide and ammonia water is 0.2-0.8 mol/L, and the concentration of ammonia water is 0.1-0.4 mol/L.
The method for modifying graphite powder by a coupling agent according to claim 1, wherein the coupling agent in step (3) comprises a silane coupling agent, a titanate coupling agent, an aluminate coupling agent one or more of the combination agents;

Preferably, the silane coupling agent includes WD-26, WD-21, WD-27, WD-22, WD-51, WD-71, KH-550, KH-560, KH-570, dodecyl One or more of trimethoxysilane and hexadecyltrimethoxysilane;

Preferably, the titanate coupling agent includes one or more of TMC-201, TMC-102, TMC-101, TMC-105, TMC-TTS, TMC-114, and TMC-401;

Preferably, the aluminate coupling agent comprises one or more of DL-411, DL-411AF, DL-411D, and DL-411DF;

Preferably, the mass of the coupling agent is 1-15% of the mass of the graphite powder, preferably 3-10%;

Preferably, the solvent is a mixed solution of ethanol and water, and the mass ratio of ethanol to water in the mixed solution of ethanol and water is 2:1 to 4:1;

Preferably, the modification time of the graphite powder is 10-30 hours.
A modified graphite powder is characterized in that, it is prepared by the method for modifying the graphite powder with a coupling agent according to any one of claims 1-5.
A polyolefin-based graphite-oriented thermal interface material, characterized in that it comprises a polyolefin matrix, the modified graphite powder described in claim 7, and a filled thermally conductive filler;

The filled thermally conductive fillers are particle, whisker, fiber, and nanowire fillers with micron-sized or nano-sized.
The polyolefin-based graphite-oriented thermal interface material according to claim 7, wherein the polyolefin matrix contains at least one polyolefin material with terminal hydroxyl groups and at least one polyolefin material with maleic anhydride groups. branched polyolefin material; preferably, the polyolefin matrix accounts for 7-90% of the total volume of the polyolefin-based graphite oriented thermal interface material, preferably 25-60%;

Preferably, the total volume percentage of the modified graphite powder in the polyolefin-based graphite oriented thermal interface material is 10-85%, preferably 40-70%;

Preferably, the filled 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 Including 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 thermally conductive filler particles is 0.5-100 microns, preferably 5-15 microns; more preferably, the length of the filled thermally conductive filler fibrous filler is 20-150 microns, preferably 30-100 microns, and the aspect ratio is 20-250, preferably 50-200 ; more preferably, the length of the filled type thermal conductive filler whisker filler is 2-50 microns, preferably 8-40 microns, and the aspect ratio is 5-30, preferably 10-20; more preferably, the said The percentage by volume of the filled thermally conductive filler in the polyolefin-based graphite oriented thermal interface material is 0-8%, preferably 0-5%.
The preparation method of the polyolefin-based graphite oriented thermal interface material according to claim 7 or 8, characterized in that, comprising the following steps:

(1) stirring and mixing the polyolefin matrix, the modified graphite powder described in claim 7, and the filled thermally conductive filler to obtain a mixture;

(2) orientation treatment is carried out to the mixture to obtain a lamellar mixture;

(3) freezing the lamellar mixture to obtain frozen lamellar mixture;

(4) maintaining the frozen state of the frozen lamellar mixture, and cutting the frozen lamellar mixture to obtain a lamellar sample with a specified width and length, and then laminating the lamellar sample;

(5) The laminated sample is processed by means of vacuum pressing, and the temperature is slowly raised 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;

(6) carrying out high temperature curing treatment to the dense sample preform to obtain the cured sample;

(7) Cutting the cured sample along the direction perpendicular to the thickness of the lamellar sample to obtain a polyolefin-based graphite oriented thermal interface material with anisotropic characteristics.
The preparation method according to claim 9, wherein the stirring and mixing in step (1) is carried out in a vacuum environment;

Preferably, the orientation treatment described in step (2) includes calendering, blade coating, and double-roll coating;

Preferably, the thickness of the lamellar mixture after the orientation treatment in step (2) is not greater than 10 times the average particle size of the graphite powder;

Preferably, the freezing treatment described in step (3) includes liquid nitrogen treatment and liquid oxygen treatment;

Preferably, the pressure in the vacuum pressurization process in step (5) is 5-30 psi, the temperature is 30-90°C, and the time is 6-20 hours;

Preferably, the temperature of the high-temperature curing in step (6) is 90-170° C., and the high-temperature curing time is 1-5 hours;

Preferably, the cutting process described in step (7) includes laser cutting and ultrasonic cutting.