High-performance graphene fiber heat-conducting gasket and preparation method thereof

Abstract

The application provides a high-performance graphene fiber heat-conducting gasket and a preparation method thereof. Graphene fibers and silica gel precursor mixture materials are sprayed on the inner wall of a high-speed rotating roller, so that the silica gel precursor fully infiltrates the surface grooves of the graphene fibers under the action of centrifugal force, the interaction between the graphene fibers and the silica gel matrix is promoted, and the interface thermal resistance between the graphene fibers and the silica gel matrix is reduced. At the same time, the graphene fibers are oriented and drawn along the circumferential direction under the action of shear force, the graphene fiber layers are further stacked and densified during the drawing process, and thus the thermal conductivity is improved. After continuous spraying, a graphene fiber / silica gel composite sheet highly oriented along the circumferential direction is obtained. The graphene fiber / silica gel composite sheet is laminated and cut along the direction perpendicular to the fiber orientation to obtain a high-performance graphene fiber heat-conducting gasket, which is suitable for the thermal management of high-power parts of electronic equipment such as electronic base stations, communication radars, new energy vehicles and aerospace equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal management materials, and particularly relates to a high-performance graphene fiber thermal conductive gasket and a preparation method thereof. BACKGROUND

[0002] Thermal interface materials (TIMs) are a kind of thermal management materials used to fill the small gap between the heat source and the heat sink, thereby promoting the heat transfer at the interface. TIMs are widely used in electronic devices to prevent performance degradation or damage caused by overheating of components. Common TIMs include but are not limited to thermal paste, thermal adhesive, thermal pad, metal matrix composites, etc. The main function of TIMs is to provide a continuous thermal conduction path, so that heat can be effectively transferred from the heat source (such as a processor chip) to the heat sink or other cooling devices. An ideal TIM should have high thermal conductivity, low interfacial thermal resistance, and good mechanical stability.

[0003] Carbon fibers show great application potential in the field of thermal interface materials due to their excellent axial thermal conductivity and corrosion resistance. When carbon fibers are combined with a polymer matrix, the overall thermal conductivity of the material can be significantly improved. In addition, due to the lightweight and high-strength characteristics of carbon fibers, TIMs made from them are lightweight and have good physical and mechanical properties, making them suitable for portable electronic devices.

[0004] In order to obtain carbon fiber thermal conductive pads with high out-of-plane thermal conductivity, external electric or magnetic fields are usually used to align carbon fibers in a specific direction, and a high-performance thermal conductive pad is formed after the polymer matrix is cured. These methods can effectively control the orientation of carbon fibers and improve the thermal conductivity of the material in a specific direction, but there are still some key problems that need to be solved: (1) the interaction between carbon fibers and the polymer matrix is weak, and voids are generated at the interface of the material during the curing process, resulting in a significant increase in interfacial thermal resistance; (2) the bulk thermal conductivity of commonly used carbon fibers is generally lower than 600 W m -1 K -1 , and the performance of imported high-performance products is lower than 900 W m -1 K -1 , and the performance improvement has an upper limit. SUMMARY

[0005] In view of the fact that the existing carbon fiber-based heat-conducting gasket cannot solve the interface defect problem of carbon fiber and matrix material, and the bottleneck problem of the thermal conductivity of carbon fiber itself, the present application provides a preparation method of a high-performance graphene fiber heat-conducting gasket. The method uses a continuous centrifugal film casting process, and the centrifugal force generated during the centrifugal process makes the matrix material (silica gel) fully penetrate into the surface grooves of the graphene fiber, thereby reducing the interface thermal resistance between the matrix material and the heat-conducting reinforcing phase. Tests show that the high polymer matrix and the graphene fiber are tightly combined, and the area ratio of the interface gap in the entire material cross section is less than 0.01%. At the same time, the shear force generated during the centrifugal process makes the graphene fiber further stretch and densify during the orientation process, thereby breaking through the upper limit of the thermal conductivity (1000-1400 W m -1 K -1 ). The graphene fiber / silica gel composite sheet material obtained by centrifugal film casting is cut into graphene fiber heat-conducting gaskets, which have the advantages of high thermal conductivity, good flexibility, low compression modulus, etc. The bulk thermal conductivity of the graphene fiber heat-conducting gaskets ranges from 66.3 to 193.5 W m -1 K -1 , the equivalent thermal conductivity ranges from 37.1 to 86.8 W m -1 K -1 when a pressure of 50 psi is applied, the tensile strength is greater than 1 MPa, and the Shore hardness ranges from 20 to 60 HA.

[0006] The aforementioned preparation method specifically comprises the following steps:

[0007] (1) Mix graphene short fibers with a length of 200 μm-2 mm, vinyl silicone oil, hydrogen-containing silicone oil, a catalyst and an inhibitor uniformly as precursor materials; the mass ratio of the vinyl silicone oil, the hydrogen-containing silicone oil, the catalyst and the inhibitor is (1-260):1:(0.02-0.12):(0.01-0.1); the mass fraction of the graphene short fibers in the precursor materials is 5-60%; the density of the graphene fibers is 1.3-1.5 g cm -3 , and the thermal conductivity ranges from 900 to 1200 W m -1 K -1 .

[0008] (2) Attach a PET film as a substrate to the inner wall of a horizontally placed centrifugal drum, and spray the above-mentioned precursor materials on the inner wall of the rotating drum to form a film. During the film forming process, the graphene short fibers are induced to orient on the surface of the substrate under the action of the centrifugal shear force, and are stretched and gradually densified in the orientation direction. At the same time, the silica gel precursor fully penetrates into the surface grooves of the graphene fibers under the action of the centrifugal force and is preliminarily solidified. After a certain period of time, a highly oriented graphene fiber / silica gel composite sheet material with a desired thickness is obtained.

[0009] (3) Stack the sheets obtained in step 2 by hot pressing to bond the semi-cured silicone together and shape them to obtain a highly oriented graphene fiber / silicone composite block.

[0010] (4) The above-mentioned graphene fiber / silicone composite block is cut in a direction perpendicular to the orientation direction of the graphene fiber. The cutting rate is 0.1~5 mm / min, and the cutting spacing is 200 μm~5 mm, to obtain a high-performance graphene fiber thermal conductive pad with a thickness of 200 μm~5 mm. The perpendicular cutting direction mentioned in this invention refers to the cutting direction being at an angle of 80~90 degrees to the axial direction of the graphene fiber. o horn.

[0011] The thickness of a single sheet is controlled by the spraying rate and spraying time, while the orientation and densification of the graphene fibers are controlled by the roller rotation speed. Typically, the spraying rate is 1–50 mL / min. -1 The time is 1~120 min, and the roller speed ranges from 2000~5000 rpm; the resulting individual sheet size ranges from 5 μm to 3 cm; hot pressing (the pressure is 10~100 psi, and the temperature is 60~100℃) is also performed. o C, after hot pressing for 30~240 min, the overall density is 1.62~1.92 g / cm³. -3 .

[0012] The present invention also provides a high-performance graphene fiber thermally conductive pad, which is composed of a thermally conductive reinforcing phase and a polymer matrix phase, wherein the thermally conductive reinforcing phase is oriented graphene fiber and the polymer matrix phase is silicone.

[0013] Furthermore, the relative cross-sectional anisotropy of the oriented graphene fibers is between 0.4 and 0.6, and the thermal conductivity is not less than 1200 W / m. -1 K -1 The angle between the direction of the graphene fibers and the thickness direction of the thermal pad is between 80 and 90 degrees. o .

[0014] Furthermore, the density of the oriented graphene fibers is 1.4~1.8 g cm⁻¹. -3 It has an oxygen content of less than 1%, a crystal region size range of 50~200 nm, and a diameter of 5~20 μm.

[0015] Furthermore, the interfacial voids between the thermally conductive reinforcing phase and the polymer matrix phase account for less than 0.01% of the total cross-sectional area of ​​the material.

[0016] Furthermore, the silicone is formed by in-situ polymerization of vinyl silicone oil and hydrogen-containing silicone oil, and has a Shore hardness of 10~50HA.

[0017] Further, the density of the heat-conducting pad is 1.62-1.92 g cm -3 , and the mass fraction of the oriented graphene fiber is 5-60%.

[0018] Further, the thermal conductivity of the heat-conducting pad ranges from 66.3 to 193.5 W m -1 K -1 , the equivalent thermal conductivity ranges from 21.3 to 86.8 W m -1 K -1 , the tensile strength is greater than 1 MPa, and the Shore hardness ranges from 20 to 60 HA.

[0019] The present application has the following beneficial effects:

[0020] (1) The high polymer matrix is fully infiltrated into the surface grooves of the graphene fiber under the action of centrifugal force by the continuous centrifugal film casting method, the area ratio of the interface gap in the entire material cross section is less than 0.01%, the interface interaction between the heat-conducting reinforcing phase and the elastic component is maximally utilized, the thermal resistance therebetween is reduced, and the high thermal resistance problem caused by the weak interface interaction between the carbon fiber and the high polymer matrix in the traditional processing method is overcome.

[0021] (2) The graphene fiber is highly oriented and accumulated while being stretched under the action of shear force by the continuous centrifugal film casting method, the internal structure units of the graphene fiber are closely stacked by the stretching of the shear force generated in the centrifugal process, the overall structure is more densified, and the cross-sectional anisotropy is significantly reduced, so that the bulk thermal conductivity (1200-1400 W m -1 K -1 ) of the graphene fiber is improved, the upper limit of the thermal conductivity of the traditional pitch-based carbon fiber and the original graphene fiber is further broken through, and the performance breakthrough of the super-high thermal conductivity graphene fiber-based thermal interface material is realized.

[0022] (3) The graphene fiber heat-conducting pad prepared by the continuous centrifugal film casting method has the advantages of higher bulk thermal conductivity of the heat-conducting reinforcing phase, lower interface thermal resistance, higher orientation degree, and wider adjustable range of array density. On the one hand, the carbon fiber filling amount can be greatly reduced under the premise of maintaining the same thermal conductivity as the traditional carbon fiber-based thermal interface material, so as to reduce the material cost and optimize the electrical performance; on the other hand, the preparation of the super-high directional thermal conductivity carbon fiber-based thermal interface material with the same or higher carbon fiber array density can be realized by preparing the heat-conducting reinforcing phase with the same or higher carbon fiber array density, so as to meet the heat dissipation demand in high-end application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The scanning electron microscope photo of the micro-morphology of the graphene fiber heat-conducting pad of Example 1;

[0024] Figure 2 Micro-morphology scanning electron microscope photo of graphene fiber heat-conducting gasket of Example 2;

[0025] Figure 3 Micro-morphology scanning electron microscope photo of graphene fiber heat-conducting gasket of Example 3;

[0026] Figure 4 Micro-morphology scanning electron microscope photo of graphene fiber heat-conducting gasket of Example 4. DETAILED DESCRIPTION

[0027] The present application provides a preparation method of high-performance graphene fiber heat-conducting gasket. The method uses a continuous centrifugal film casting process, in which the polymer matrix is caused to fully penetrate into the grooves on the surface of the graphene fiber, effectively utilizing the groove area on the surface of the graphene fiber and reducing the interfacial thermal resistance between the heat-conducting reinforcing phase and the second elastic component. The graphene fiber is subjected to a drawing densification effect under the action of shear force, which not only reduces the relative cross-sectional irregularity and improves the orientation degree of the fiber, but also significantly improves the thermal conductivity of the material. After the centrifugal drawing process, the combination between the polymer matrix and the graphene fiber is more compact, and the area ratio of the interfacial gap on the entire material cross-section is reduced to below 0.01%. Since the surface of the graphene fiber has a rich wrinkle microstructure, the interface fusion is prone to be poor when the graphene fiber is compounded with the polymer material, resulting in a high interface gap ratio on the material cross-section. However, through the centrifugal drawing process, the polymer can more effectively penetrate into the grooves on the surface of the graphene fiber, significantly reducing the number of interface gaps and realizing effective combination between the materials, thereby greatly reducing the internal thermal resistance and effectively improving the overall heat-conducting performance of the material.

[0028] The embodiments of the present application are further described below in multiple examples.

[0029] It should be clear that the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] The raw materials used in the present application are conventional commercially available products unless otherwise specified, and the methods used in the present application are conventional methods in the art unless otherwise specified.

[0031] The terms used in the embodiments of the present application are merely for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a," "an," and "the" used in the embodiments of the present application and the appended claims are intended to include plural forms as well, unless the context clearly indicates otherwise. The terms "first," "second," and the like are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or an indicated number of technical features. Thus, features defined with "first," "second" can explicitly or implicitly include one or more of the features.

[0032] In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly limited.

[0033] In the description of the present application, it is to be understood that the terms "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0034] In addition, the technical terms involved in the present application are explained as follows:

[0035] As a matter of common knowledge in the art, the relative cross-section profile degree is referred to the standard FZ / T 50002-1991, by measuring the inscribed circle radius (r) of the cross-section profile of the enlarged profiled fiber, and the circumscribed circle radius (R) on the corresponding cross-section concentric with r, the relative cross-section profile degree = (R 2 -r 2 ) / R 2 *100%. The crystalline region size is tested by X-ray diffraction method on the graphene fiber crystalline region size, according to the shape and position of the diffraction peak, the grain size is calculated by Scherrer equation. The area ratio of interface gap on the whole material cross-section is obtained by Image-J statistics. The Shore hardness is tested according to GB / T 531.1-2008.

[0036] The bulk thermal conductivity is tested by laser flash method, referring to GB / T 22588-2008. The thermal resistance is the sum of the thermal resistance of the material itself and the thermal resistance between the contact surfaces, which is tested by ASTM D 5470 method, and the equipment is LW-9389MD interface material thermal resistance and thermal conductivity tester.

[0037] Example 1:

[0038] (1) The graphene fiber filament is cut into short fibers with a length of 1 mm using a pipe cutting machine, and the proportion of vinyl silicone oil, hydrogen-containing silicone oil, platinum-vinyl silicone complex and ethynyl cyclohexanol is 3:1:0.02:0.01, and the mass fraction of graphene fiber is controlled to be 20%. The material is placed in a homogenizer for 30 min, and defoaming for 5 min, and the density of graphene fiber is 1.5 g cm -3 , the thermal conductivity is 1203 W m -1 K -1 .

[0039] (2) Using a continuous centrifugal coating device, a PET film is attached to the inner wall of the transversely placed roller as a substrate, and the circumference of the roller is 2 m and the width is 0.1 m. The uniformly mixed graphene fiber / silica gel precursor material is transported by a delivery pump and sprayed through a nozzle on the inner wall of the rapidly rotating roller at a spraying rate of 20 mL min -1 , the roller rotates at 5000 rpm, and after spraying for 25 min, an oriented graphene fiber / silica gel composite sheet with a thickness of 2.4 mm is obtained.

[0040] (3) The highly oriented graphene fiber / silica gel composite sheet obtained in step (2) is stacked layer by layer, and the semi-cured silica gel is bonded to each other by applying a certain pressure and temperature to completely shape, and a highly oriented graphene fiber / silica gel composite block is obtained. The applied pressure is 50 psi, the heating temperature is 80 o C, and the hot pressing time is 120 min.

[0041] (4) The graphene fiber / silica gel composite block obtained in step (3) is cut, the cutting direction is 90 o ° to the orientation direction of the graphene fiber, the cutting rate is 0.2 mm / min, and the cutting interval is 1 mm.

[0042] The obtained graphene fiber heat-conducting gasket has a thickness of 1 mm, a density of 1.77 g cm -3 , a tensile strength of 5.8 MPa, a Shore hardness of 31.5 HA, and a thermal conductivity of 1401.3 W m -1 K -1 after removing the silica gel matrix using a silica gel dissolving agent and measuring using a T-type method, an oxygen content of 0.8%, a crystal size range of 50 nm, a diameter of 8 μm, a density of 1.8 g cm -3 , and a relative cross-sectional heterogeneity of 0.4. The obtained heat-conducting gasket microstructure is shown in Figure 1 , it can be found that the graphene fiber is highly oriented along the thickness direction, and the angle between the direction of the graphene fiber and the thickness direction of the heat-conducting gasket is 80~90 oThe graphene fibers are evenly distributed in the silica gel matrix and closely adhere to the silica gel matrix, and the area ratio of the interface gap in the entire material cross section is less than 0.01%. The out-of-plane thermal conductivity of the thermal conductive gasket is 143.5 Wm -1 K -1 , the compression rate at 50 psi is 51%, the equivalent thermal conductivity is 83.1 Wm -1 K -1 , and the thermal impedance is 0.059K cm 2 W -1 .

[0043] Example 2:

[0044] (1) The graphene fiber filaments are cut into short fibers with a length of 200 μm using a pipe cutting machine, and the addition ratio of vinyl silicone oil, hydrogen-containing silicone oil, platinum-divinyltetramethylsiloxane complex and 3-ethynylcyclohexanol is 1:1:0.02:0.01, and the mass fraction of graphene fibers is controlled to be 5%. The material is placed in a homogenizer for 60 min and defoamed for 10 min, and the density of the graphene fibers is 1.3 g cm -3 , and the thermal conductivity is 900 Wm -1 K -1 .

[0045] (2) A continuous centrifugal coating device is used, and a PET film is attached to the inner wall of the transversely placed roller as a substrate. The length of the roller is 2 m and the width is 0.1 m. The uniformly mixed graphene fiber / silica gel precursor material is transported by a delivery pump and sprayed through a nozzle on the inner wall of the rapidly rotating roller at a spraying rate of 1 mL min -1 , and the roller rotates at 2000 rpm. After spraying for 120 min, an oriented graphene fiber / silica gel composite sheet with a thickness of 0.58 mm is obtained.

[0046] (3) The highly oriented graphene fiber / silica gel composite sheet obtained in step (2) is stacked layer by layer, and the semi-cured silica gel is bonded to each other by applying a specific pressure and temperature to completely cure, thereby obtaining a highly oriented graphene fiber / silica gel composite block. The applied pressure is 10 psi, the heating temperature is 60 o C, and the hot pressing time is 30 min.

[0047] (4) The graphene fiber / silica gel composite block obtained in step (3) is cut, and the cutting direction is 90 o ° to the orientation direction of the graphene fibers, the cutting rate is 0.1 mm / min, and the cutting interval is 1 mm.

[0048] The obtained graphene fiber heat-conducting gasket has a thickness of 1 mm, a density of 1.69 g cm -3 , a tensile strength of 3.9 MPa, a Shore hardness of 20.0 HA, and a thermal conductivity of 1200.6 W m -1 K -1 after the removal of the silica gel matrix using a silica gel dissolving agent and the measurement of a single graphene fiber after centrifugal drawing using a T-type method. The graphene fiber has an oxygen content of 0.74%, a crystal size range of 100 nm, a diameter of 5 μm, a density of 1.4 g cm -3 , and a relative cross-sectional heterogeneity of 0.6. The graphene fiber heat-conducting gasket has an out-of-plane thermal conductivity of 66.3 W m -1 K -1 , a compression rate of 62% at 50 psi, an equivalent thermal conductivity of 21.3 W m -1 K -1 , and a thermal impedance of 0.178 K cm 2 W -1 .

[0049] Example 3:

[0050] (1) The graphene fiber filament is cut into short fibers with a length of 1 mm using a pipe cutting machine, and the vinyl silicone oil, hydrogen-containing silicone oil, platinum-vinyl siloxane complex, and 3,5-dimethyl-1-ethynylcyclohexanol are added in a ratio of 120:1:0.08:0.05, and the mass fraction of the graphene fiber is controlled to be 60%. The material is placed in a homogenizer for 30 min of homogenization and 5 min of degassing, and the graphene fiber has a density of 1.48 g cm -3 and a thermal conductivity range of 1248 W m -1 K -1 .

[0051] (2) The continuously centrifugal coating equipment is used, and a PET film is attached to the inner wall of the transversely placed roller as a substrate. The length of the roller is 2 m, and the width is 0.1 m. The uniformly mixed graphene fiber / silica gel precursor material is transported by a delivery pump and sprayed on the inner wall of the rapidly rotating roller through a spray head at a spraying rate of 50 mL min -1 , and the roller rotates at a speed of 5000 rpm. After 1 min of spraying, an oriented graphene fiber / silica gel composite sheet with a thickness of 0.25 mm is obtained.

[0052] (3) The highly oriented graphene fiber / silica gel composite sheet obtained in step (2) is stacked layer by layer, and the semi-cured silica gel is bonded to each other by applying a specific pressure and temperature to completely cure, thereby obtaining a highly oriented graphene fiber / silica gel composite block. The applied pressure is 50 psi, and the heating temperature is 100 oC, hot-pressing time is 240 min.

[0053] (4) The graphene fiber / silica gel composite block obtained in step (3) is cut, the cutting direction is 90 degrees to the orientation direction of the graphene fiber, the cutting speed is 0.5 mm / min, and the cutting interval is 0.2 mm. o

[0054] The obtained graphene fiber heat-conducting gasket has a thickness of 0.2 mm, a density of 1.65 g cm -3 , a tensile strength of 3.3 MPa, a Shore hardness of 46.0 HA, and a thermal conductivity of 1491.1 W m -1 K -1 after the silica gel matrix is removed using a silica gel dissolving agent and the thermal conductivity of a single graphene fiber after centrifugal stretching is measured using a T-type method, a density of 1.75 g cm -3 , an oxygen content of 0.45%, a crystal region size of 200 nm, a diameter of 7.5 μm, and a relative cross-section anisotropy of 0.43. The obtained heat-conducting gasket has a micro-morphology structure as shown in Figure 2 , and it can be found that the graphene fiber is highly oriented along the thickness direction, uniformly and densely distributed in the silica gel matrix, and closely combined with the silica gel matrix without obvious layering at the interface. The out-of-plane thermal conductivity of the heat-conducting gasket is 193.5 W m -1 K -1 , the compression rate at 50 psi is 31%, the equivalent thermal conductivity is 49.7 W m -1 K -1 , and the thermal impedance is 0.028 K cm 2 W -1 .

[0055] Example 4:

[0056] (1) The graphene fiber filament is cut into short fibers with a length of 1 mm using a pipe cutting machine, and the vinyl silicone oil, hydrogen-containing silicone oil, platinum-cyclohexyldimethylsiloxane complex, and 3-ethynylcyclohexanol are added in a ratio of 260:1:0.12:0.1, and the mass fraction of the graphene fiber is controlled to be 40%. The material is placed in a homogenizer for homogenization for 30 min, and defoaming for 5 min. The density of the graphene fiber is 1.5 g cm -3 , and the thermal conductivity ranges from 1203 W m -1 K -1 .

[0057] ​(2) Using a continuous centrifugal coating equipment, a PET film is attached to the inner wall of a horizontally placed roller as a substrate. The length of the roller is 2 m and the width is 0.1 m. The mixed graphene fiber / silica precursor material is transported by a delivery pump and sprayed on the inner wall of the rapidly rotating roller through a spray head. The spraying rate is 1 mL min -1 , the roller speed is 4000 rpm, and a 20 μm thick oriented graphene fiber / silica composite sheet is obtained after spraying for 1 min.

[0058] (3) The oriented graphene fiber / silica composite sheet obtained in step (2) is stacked layer by layer, and the semi-cured silica is bonded to each other by applying a specific pressure and temperature to completely shape the graphene fiber / silica composite block. The applied pressure is 100 psi, the heating temperature is 90 o C, and the hot pressing time is 120 min.

[0059] (4) The graphene fiber / silica composite block obtained in step (3) is cut, the cutting direction is 90 o degrees to the orientation direction of the graphene fiber, the cutting rate is 5 mm / min, and the cutting interval is 5 mm.

[0060] The obtained graphene fiber thermal pad has a thickness of 5 mm, a density of 1.65 g cm -3 , a tensile strength of 7.5 MPa, a Shore hardness of 41.2 HA, and a thermal conductivity of 1499.8 W m -1 K -1 after removing the silica matrix using a silica dissolving agent and measuring the thermal conductivity of a single graphene fiber using a T-type method. The density is 1.83 g cm -3 , the oxygen content is 0.86%, the crystal size range is 70 nm, the diameter is 20 μm, and the relative cross-sectional anisotropy is 0.48. The graphene fiber is highly oriented along the thickness direction, uniformly and densely distributed in the silica matrix, and tightly attached to the silica matrix without obvious delamination at the interface. The out-of-plane thermal conductivity of the thermal pad is 166.1 W m -1 K -1 , the compression rate under 50 psi is 45%, the equivalent thermal conductivity is 86.8 W m -1 K -1 , and the thermal resistance is 0.32 K cm 2 W -1 .

[0061] Comparative Example 1:

[0062] (1) The graphene fiber filament is cut into short fibers with a length of 200 μm using a pipe cutting machine, and the proportion of vinyl silicone oil, hydrogen-containing silicone oil, platinum-divinyltetramethylsiloxane complex and 3-ethynylcyclohexanol is 1:1:0.02:0.01, and the mass fraction of graphene fiber is controlled to be 5%. The material is placed in a homogenizer for 60 min, and defoaming for 10 min, and the density of the graphene fiber is 1.3 g cm -3 , the thermal conductivity is 900 W m -1 K -1 .

[0063] (2) Using a continuous centrifugal coating device, a PET film is attached to the inner wall of the transversely placed roller as a substrate, and the circumference of the roller is 2 m and the width is 0.1 m. The uniformly mixed graphene fiber / silica gel precursor material is transported by a delivery pump and sprayed through a nozzle on the inner wall of the rapidly rotating roller at a spraying rate of 1 mL min -1 , the roller rotates at 500 rpm, and after spraying for 120 min, an oriented graphene fiber / silica gel composite sheet with a thickness of 0.7 mm is obtained.

[0064] (3) The highly oriented graphene fiber / silica gel composite sheet obtained in step (2) is stacked layer by layer, and the semi-cured silica gel is bonded to each other by applying a certain pressure and temperature to completely shape, and a highly oriented graphene fiber / silica gel composite block is obtained. The applied pressure is 10 psi, the heating temperature is 60 o C, and the hot pressing time is 30 min.

[0065] (4) The graphene fiber / silica gel composite block obtained in step (3) is cut, the cutting direction is 90 o ° to the orientation direction of the graphene fiber, the cutting rate is 0.1 mm / min, and the cutting interval is 1 mm.

[0066] The graphene fiber heat-conducting gasket obtained above has a thickness of 1 mm, a density of 1.67 g cm -3 , a tensile strength of 3.2 MPa, a Shore hardness of 16.5 HA, and a thermal conductivity of 923.6 W m -1 K -1 after removing the silica gel matrix using a silica gel dissolving agent and measuring the thermal conductivity of a single graphene fiber using a T-type method, a density of 1.33 g cm -3 , a crystal size range of 30 nm, a diameter of 11 μm, and a relative cross-sectional anisotropy of 0.63. It can be found that compared with Example 2, the lower centrifugal speed only increases the carbon fiber density by 0.03 g cm -3 , and in addition, the fiber anisotropy is higher, which means that the densification effect of the carbon fiber is relatively poor.

[0067] The resulting thermal pad microstructure is as follows Figure 3 As shown, it can be observed that during the centrifugal casting process, when the drum speed is low, the graphene fibers exhibit poor orientation and low array density, and a distinct interface layer exists between them and the silicone substrate. The out-of-plane thermal conductivity, measured using transient laser scintillation, is 41.3 W / m². -1 K -1 The compressibility at 50 psi was measured to be 64% using the steady-state method, and the equivalent thermal conductivity was 11.3 W / m². -1 K -1 The thermal resistance is 0.318 K cm. 2 W -1 .

[0068] Comparative Example 2:

[0069] (1) Graphene fiber filaments were cut into short fibers with a length of 1 mm using a tube cutter. Vinyl silicone oil, hydrogen-containing silicone oil, platinum-divinyltetramethyldisiloxane complex, and 3-ethynylcyclohexanol were added in a ratio of 260:1:0.12:0.1 to control the mass fraction of graphene fibers to 30%. The material was homogenized in a homogenizer for 30 min and degassed for 5 min. The density of the graphene fibers was 1.5 g / cm³. -3 Thermal conductivity is 1200 W / m -1 K -1 .

[0070] (2) A continuous centrifugal coating equipment was used. A PET film was attached to the inner wall of a horizontally placed roller as a substrate. The roller had a circumference of 2 m and a width of 0.1 m. The uniformly mixed graphene fiber / silicone precursor material was transported by a pump and sprayed onto the inner wall of the rapidly rotating roller through a nozzle at a spraying rate of 50 mL / min. -1 The roller speed was 3000 rpm, and after spraying for 140 min, an oriented graphene fiber / silicone composite sheet with a thickness of 45 mm was obtained.

[0071] (3) The highly oriented graphene fiber / silicone composite sheet obtained in step (2) is completely shaped by applying specific pressure and temperature to bond the semi-cured silicone together, resulting in a highly oriented graphene fiber / silicone composite block. The applied pressure is 10 psi, and the heating temperature is 80°C. o C, the hot pressing time is 120 min.

[0072] (4) Cut the graphene fiber / silicone composite block obtained in step (3) at a 90° angle to the orientation direction of the graphene fiber. o The cutting rate is 0.2 mm / min and the cutting spacing is 1 mm.

[0073] The obtained graphene fiber thermal conductive gasket has a thickness of 1 mm and a density of 1.62 g cm -3 , a tensile strength of 2.9 MPa, a Shore hardness of 37 HA, and after the silica gel matrix is removed using a silica gel dissolving agent, it is found that the diameters of the graphene fibers are highly inconsistent and are distributed in a range of 5-10 μm, and the relative cross-sectional irregularity of the fibers is generally higher than 0.65. The micro-morphological structure of the obtained thermal conductive gasket is shown in Figure 4 , the graphene fibers are generally oriented along the thickness direction, there is a certain degree of delamination between the graphene fibers and the silica gel matrix, and the cross-sectional regularity of the fibers is poor. This is because the spraying time is too long and the spraying amount is too large, resulting in a large deviation in the centrifugal force received by the graphene fibers in the thickness direction. The graphene fibers near the center of the roller receive a small centrifugal force and cannot be effectively densified. The surface thermal conductivity of the thermal conductive gasket is measured to be 58.7 W m -1 K -1 , the compression rate at 50 psi is measured to be 43.7 %, the equivalent thermal conductivity is 14.4 W m -1 K -1 , and the thermal impedance is 0.39 K cm 2 W -1 .

[0074] Although the embodiments of the present application are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, and therefore, the scope of the present application is not limited to the disclosed content.

Claims

1. A method for preparing high performance graphene fiber heat conducting gasket, characterized in that, The method comprises the following steps: (1) mixing graphene short fibers with a length of 200 μm-2 mm, vinyl silicone oil, hydrogen-containing silicone oil, a catalyst and an inhibitor uniformly as a precursor material; the mass ratio of the vinyl silicone oil, the hydrogen-containing silicone oil, the catalyst and the inhibitor is (1-260):1:(0.02-0.12):(0.01-0.1); the mass fraction of the graphene short fibers in the precursor material is 5-60%; (2) attaching a PET film as a substrate to the inner wall of a horizontally placed roller, and spraying the precursor material on the inner wall of the rotating roller to form a film to obtain a graphene fiber / silica gel sheet; (3) stacking the graphene fiber / silica gel sheet layer by layer, and hot-pressing to obtain a graphene fiber / silica gel composite block; (4) slicing the graphene fiber / silica gel composite block to obtain a graphene fiber vertically oriented heat-conducting gasket.

2. The production method according to claim 1, characterized by, In step 2, the spraying rate was 1-50 mL min -1 , the time was 1-120 min, and the drum rotation speed was in the range of 2000-5000 rpm.

3. The preparation method according to claim 1, characterized in that, In Step 3, the hot pressing is performed at a pressure of 10 to 100 psi and a temperature of 60 to 100 o C for 30 to 240 minutes.

4. The method of claim 1, wherein, In step 4, the slicing cutting rate is 0.1-5 mm / min, and the cutting interval is 200 μm-5 mm.

5. The preparation method according to claim 1, characterized in that, The catalyst comprises a platinum-based catalyst, and the inhibitor comprises ethynylcyclohexanol and derivatives thereof.

6. The high performance graphene fiber heat conducting gasket prepared by the method of claim 1, wherein, The material is composed of a heat-conducting reinforcing phase and a polymer matrix phase; the heat-conducting reinforcing phase is oriented graphene fiber, and the polymer matrix phase is silica gel; the area ratio of the interface gap between the heat-conducting reinforcing phase and the polymer matrix phase in the entire material cross section is less than 0.01%.

7. The thermally conductive gasket of claim 6, wherein Density of the oriented graphene fiber is 1.4~1.8 g cm -3 , relative cross-section heterogeneity is 0.4~0.6, the included angle between the direction of the graphene fiber and the thickness direction of the heat-conducting gasket is 80~90 o , and the thermal conductivity is not less than 1200 W m -1 K -1 .

8. The thermal pad of claim 6, wherein The high-performance graphene fiber heat-conducting gasket has a density of 1.62-1.92 g / cm -3 .

9. The thermally conductive gasket of claim 6, wherein, The high-performance graphene fiber heat-conducting gasket has a thermal conductivity ranging from 66.3 to 193.5 W m -1 K -1 , a tensile strength greater than 1 MPa, and a Shore hardness ranging from 20 to 60 HA.

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