Carbon fiber-based heat-conducting composite material and preparation method thereof

Abstract

The invention provides a carbon fiber-based heat-conducting composite material and a preparation method thereof, and the heat-conducting composite material comprises a composite material, a vertical filler and a surface foil; the composite material comprises a prepreg and a filler, wherein the prepreg is a three-dimensional woven fabric woven by carbon fibers; a plurality of vertical fillers are arranged in the vertical direction of the prepreg; the filling material is filled in a filling body formed by the prepreg and the vertical filler; the composite material further comprises interfaces which are the upper surface and the lower surface of the composite material. The surface foil is disposed on the upper surface and the lower surface. Through the three-dimensional weaving structure of the heat-conducting composite material based on the carbon fibers and the preparation method of adding the vertical filler, the purpose of enhancing the heat-conducting property of the heat-conducting composite material based on the carbon fibers in the vertical direction is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and in particular to a thermally conductive composite material based on carbon fiber and a preparation method thereof. Background Art

[0002] The density of carbon fiber composite materials is generally 1.6-1.8g / cm3, with high specific strength. Carbon fiber composite materials have a great advantage in density over aluminum alloys. However, the thermal conductivity of carbon fiber is only 0.6-1.2W / m·K, which is much lower than the 80-180W / m·K of aluminum alloys. Therefore, it cannot meet the requirements in some fields that require heat dissipation, such as military electronic equipment structural parts.

[0003] Asphalt-based carbon fiber has high thermal conductivity in its radial direction, generally up to 600-800W / m·K, but the thermal conductivity in other directions is not high. In addition, the thermal conductivity of resin and filler is very low. Therefore, the thermal conductivity of general carbon fiber composite materials is not high, especially the thermal conductivity in the Z direction (vertical direction). Summary of the invention

[0004] In view of this, the embodiments of the present specification provide a carbon fiber-based thermally conductive composite material and a preparation method thereof, so as to achieve the purpose of enhancing the thermal conductivity of the carbon fiber-based thermally conductive composite material in the vertical direction.

[0005] The embodiments of this specification provide the following technical solutions:

[0006] A thermally conductive composite material based on carbon fiber, comprising:

[0007] Composite materials, vertical fillers and surface foils;

[0008] The composite material includes prepreg and filler, the prepreg is a three-dimensional woven fabric woven from carbon fibers;

[0009] A plurality of vertical fillers are arranged in the vertical direction of the prepreg;

[0010] The filler is filled in a filling body composed of the prepreg and the vertical filler;

[0011] The composite material also includes an interface, which is the upper and lower surfaces of the composite material;

[0012] Surface foils are provided on the upper surface and the lower surface.

[0013] Furthermore, the surface foil is a graphene film.

[0014] Furthermore, the vertical filler is one or a combination of carbon nanotubes and cylindrical high thermal conductivity carbon rods.

[0015] Furthermore, the filler is a mixture of high thermal conductivity epoxy resin and graphene.

[0016] Furthermore, the preparation method is used to manufacture the thermally conductive composite material, comprising:

[0017] Preparing a prepreg, and when performing a three-dimensional weaving process on the prepreg, filling a plurality of vertical fillers in the vertical direction of the prepreg so that the volume fraction of the vertical fillers in the prepreg reaches a set volume fraction;

[0018] A mixture of graphene and epoxy resin having a thermal conductivity reaching a set thermal conductivity is prepared as a filler, and the filler is filled into a filler body composed of a prepreg and a vertical filler to generate a composite material;

[0019] After hot pressing, the composite material forms two upper and lower interfaces;

[0020] The interface is covered with a surface foil to produce a carbon fiber-based thermally conductive composite material.

[0021] Further, preparing the prepreg comprises:

[0022] The surface of carbon fiber filaments is treated by surface electropolymerization technology to generate surface-reinforced carbon fiber;

[0023] The surface-reinforced carbon fibers are woven into prepreg using three-dimensional weaving technology.

[0024] Furthermore, a mixture of graphene and epoxy resin having a thermal conductivity reaching a set thermal conductivity is prepared as a filler, comprising:

[0025] In a room temperature environment, graphene is added to epoxy resin to generate a filling mixture;

[0026] After adding dispersant and coupling agent to the filling mixture, mechanical stirring is adopted;

[0027] During the stirring process, the system viscosity of the filling mixture is obtained. If the system viscosity is lower than the set viscosity, ultrasonic vibration is used for further dispersion to fully disperse the graphene in the epoxy resin matrix;

[0028] If the system viscosity is higher than the set viscosity, three-roll milling is used for further dispersion to fully disperse the graphene in the epoxy resin matrix.

[0029] Further, the thermal conductivity of the surface foil is 380 W / m·K to 400 W / m·K.

[0030] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0031] The thermal conductivity of the carbon fiber-based thermally conductive composite material in the vertical direction is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a schematic diagram of the structure of a three-dimensional woven fabric according to an embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of the three-dimensional structure of a thermally conductive composite material based on carbon fiber according to an embodiment of the present invention;

[0035] Figure 3 is a cross-sectional view of a thermally conductive composite material based on carbon fiber according to an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of the air-cooling heat dissipation effect based on aluminum alloy;

[0037] Figure 5 This is a schematic diagram of the natural heat dissipation effect based on aluminum alloy;

[0038] Figure 6 This is a schematic diagram of the air-cooling heat dissipation effect based on ordinary carbon fiber;

[0039] Figure 7 This is a schematic diagram of the natural heat dissipation effect based on ordinary carbon fiber;

[0040] Figure 8 This is a schematic diagram of the natural heat dissipation effect of the carbon fiber-based thermally conductive composite material according to an embodiment of the present invention;

[0041] Fig. 9 It is a schematic diagram of the air-cooling heat dissipation effect of the carbon fiber-based thermally conductive composite material according to an embodiment of the present invention.

[0042] Reference numerals in the figure: 1. composite material; 2. surface foil; 3. vertical filler; 4. interface. DETAILED DESCRIPTION

[0043] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0044] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0045] like Figure 2 and Figure 3 As shown, carbon fiber-based thermally conductive composite materials include:

[0046] Composite material 1, vertical filler 3, surface foil 2 and interface 4. Composite material 1 includes prepreg and filler, and prepreg is a three-dimensional woven fabric woven from carbon fibers. A plurality of vertical fillers 3 are arranged in the vertical direction of the prepreg, and the filler is filled in a filling body formed by the prepreg and the vertical filler 3.

[0047] The interface 4 is the upper and lower surfaces of the composite material 1. The surface foil 2 is arranged on the upper and lower surfaces.

[0048] Specifically, the interface 4 of the composite material 1 refers to the interface 4 formed by the contact between the reinforcement and the matrix in the composite material 1. In the past, the interface of the composite material was imagined as a surface without thickness, but in fact, the interface of the composite material is a new phase with a thickness of more than nanometers and a significant structural difference from the matrix phase and the reinforcement phase, which is called an interface phase or interface layer. When the heat flow passes through this interface layer, due to the micro-protrusions and dislocations of the contact interface and the lattice dislocations caused by pressure, the heat carriers will be scattered and reflected in this area. The passage of heat flow on the interface is mainly transferred by radiation. Therefore, due to the reflection and scattering of the heat carriers at the contact interface, the heat transfer is resisted at the interface, which is the reason for the generation of thermal resistance of the contact interface.

[0049] The first thing to consider at interface 4 is the contact and wetting process between the resin matrix and the reinforcing fibers. Since the reinforcing fibers have different adsorption capacities for various groups of matrix molecules or components in the matrix, they always adsorb substances that can reduce their surface energy, and give priority to those substances that can reduce their surface energy more. Therefore, the interfacial polymerization layer is different in structure from the polymer body. In addition, during the curing stage of the resin, the resin is cured through physical or chemical changes to form a fixed interface layer. The curing stage is affected by the first stage, and it directly determines the structure of the interface layer formed. For improving the thermal conductivity of fiber composite materials, reducing the thermal resistance of the thermal conductive interface of the composite material is an effective way to improve the thermal conductivity of the composite material.

[0050] In this embodiment, the research on reducing the interface thermal resistance mainly includes the following aspects.

[0051] (1) Interface characterization

[0052] Scanning electron microscopy and atomic force microscopy are test methods for characterizing the surface morphology of fibers. Surface energy is an important parameter for characterizing the surface characteristics of materials. The surface energy values ​​before and after modification can be used to characterize the surface modification effect of materials. The surface tension of carbon fibers is not easy to measure directly. The double liquid method is used to indirectly measure the wettability of carbon fibers. This experimental method has simple equipment and is easy to operate. It is an effective method for measuring the wettability changes of carbon fibers after surface treatment.

[0053] X-ray photoelectron spectroscopy is a testing method with important application value in the fields of material physics and chemistry. Many researchers use this method to characterize the surface characteristics of carbon fiber before and after modification. X-ray diffraction can also be used to analyze the changes in the bulk structure of carbon fiber before and after treatment.

[0054] (2) Carbon fiber surface treatment

[0055] The carbon fiber is subjected to surface modification. After surface treatment, the surface properties of the carbon fiber are improved. At present, various methods such as electrochemical modification, vapor deposition treatment, surface electropolymerization, coupling agent coating, and graft polymerization surface treatment are used to improve the surface properties of carbon fiber to improve the thermal conductivity interface bonding performance of composite materials. Among them, surface electropolymerization technology is a new technology for carbon fiber surface modification developed in recent years. Its principle is to make the material monomer undergo polymerization reaction on the surface of carbon fiber under the initiation of electric field to generate polymer coating, thereby introducing active groups to greatly improve the connection strength between the fiber and the matrix. Surface electropolymerization modification of carbon fiber has a good effect on the manufacture of fiber-reinforced resin-based composite materials with high thermal conductivity and mechanical properties. The application of coupling agent to improve the interface is very extensive. Coupling agent is a bifunctional molecule. One part of the functional group combines with the carbon fiber surface to form a chemical bond, and the other part forms a chemical bond with the resin. The coupling agent plays a chemical medium role on the surface of the resin and the carbon fiber, thereby firmly connecting the carbon fiber and the resin together, thereby reducing the interface thermal resistance in the composite material.

[0056] (3) Modification technology to reduce the thermal resistance of the resin interface

[0057] There are two main methods for modifying the interface of the resin matrix: chemical modification and physical modification. Chemical modification is achieved by changing the chemical structure of the cross-linked network, such as introducing "flexible segments" into the cross-linked network to improve the activity of the molecular chain or increase the distance between the cross-linking points, and controlling the unevenness of the molecular cross-linking state to form a favorable plastic deformation to achieve the purpose of reducing the interfacial thermal resistance. The physical modification method is mainly to achieve blending by directly adding fillers to the matrix. The filler and the resin can form a two-phase structure initiation mechanism, which plays a role in filling the interface gap at the interface between the fiber and the resin matrix.

[0058] A method for preparing a thermally conductive composite material based on carbon fiber comprises the following steps:

[0059] Preparing a prepreg, and when performing a three-dimensional weaving process on the prepreg, filling a plurality of vertical fillers 3 in the vertical direction of the prepreg so that the volume fraction of the vertical fillers 3 in the prepreg reaches a set volume fraction;

[0060] A mixture of graphene and epoxy resin having a thermal conductivity reaching a set thermal conductivity is prepared as a filler, and the filler is filled into a filling body composed of a prepreg and a vertical filler 3 to generate a composite material 1;

[0061] The composite material 1 is hot-pressed to form upper and lower interfaces 4;

[0062] The interface 4 is covered with a surface foil 2 to produce a heat-conducting composite material based on carbon fibers.

[0063] The preparation of the prepreg comprises the following steps:

[0064] The surface of carbon fiber filaments is treated by surface electropolymerization technology to generate surface-reinforced carbon fiber;

[0065] The surface-reinforced carbon fibers are woven into prepreg using three-dimensional weaving technology.

[0066] The preparation of the prepreg comprises the following steps:

[0067] In a room temperature environment, adding graphene to the epoxy resin to generate a filling mixture;

[0068] After adding dispersant and coupling agent to the filling mixture, mechanical stirring is adopted;

[0069] During the stirring process, the system viscosity of the filling mixture is obtained. If the system viscosity is lower than the set viscosity, ultrasonic vibration is used for further dispersion to fully disperse the graphene in the matrix of the epoxy resin;

[0070] If the system viscosity is higher than the set viscosity, three-roll grinding is used for further dispersion to fully disperse the graphene in the epoxy resin matrix.

[0071] Specifically, traditional fabrics are two-dimensional plane fabrics made of two mutually perpendicular yarn systems, namely warp and weft yarns, interwoven in a plane. Three-dimensional woven fabrics use weaving methods to interweave yarns of multiple systems into a spatial mesh structure. Figure 1 As shown, according to the interlaced structural characteristics of the yarns, three-dimensional woven fabrics are mainly divided into two categories: three-dimensional orthogonal structure braids and three-dimensional angle interlocking structure braids. The two types of braids are structurally distinguished by the different forms of connecting yarns in the thickness direction.

[0072] Three-dimensional woven composite materials are composite materials formed by weaving high-performance fiber bundles into the shape of the required structure using textile technology to form a structural woven preform, which is then used as a reinforcing skeleton and cured with the matrix. Three-dimensional woven composite materials have the characteristics of high specific strength, light weight, high specific stiffness, thermal conductivity, and highly designable material properties.

[0073] Graphene with a thermal conductivity of 600W / m·K is used as a thermal conductive filler. The preparation method is as follows: a low-viscosity resin at room temperature with a viscosity of about 300mPa·s is used. Graphene slurry can be directly added at room temperature without the use of solvents. The physical dispersion method in the resin matrix is ​​mainly as follows: first, mechanical stirring is used after adding a dispersant and a coupling agent, and then the viscosity of the system is judged. If the viscosity of the system is low, ultrasonic vibration is used for further dispersion. If the viscosity of the system is high, three-roll grinding is used for further dispersion, and finally the filler is fully dispersed in the resin matrix. Taking the dispersion of the dispersed graphene slurry added to the epoxy resin system for dispersion as an example, rheological tests are carried out on the graphene modified resin system with mechanical stirring, ultrasonic 1h after mechanical stirring, and ultrasonic 3h after mechanical stirring. The thermal conductivity of the high thermal conductivity resin finally formed is about 3W / m·K.

[0074] Currently, commonly used non-metallic thermal conductive fillers include graphene, graphite sheets, graphite powder, carbon nanotubes, etc. The embodiment of the present invention uses graphene as a thermal conductive filler. As a two-dimensional carbon material, graphene has an extremely high specific surface area, a very high single-layer theoretical in-plane thermal conductivity, and excellent mechanical properties. It has become an important thermal conductive and electrical conductive material with a thermal conductivity of 600W / mK, and has extremely important applications.

[0075] Low-viscosity epoxy resin at room temperature is used as epoxy resin, with a viscosity of about 300mPa·s. Graphene slurry can be directly added at room temperature without the use of solvents. The physical dispersion method in the epoxy resin matrix is ​​mainly: first, mechanical stirring is used after adding dispersant and coupling agent, and then according to the viscosity of the system, ultrasonic vibration is used for further dispersion if the system viscosity is low, and three-roll grinding is used for further dispersion if the system viscosity is high, and finally the filler is fully dispersed in the resin matrix.

[0076] The change of viscosity of the resin system during the dispersion process is tested by a rheometer. It is assumed that the viscosity of the resin system will change as the dispersion state of a certain amount of filler in the resin system changes. When the viscosity no longer changes, it is considered that the filler has been fully dispersed in the resin system. Taking the dispersion of dispersed graphene slurry added to the epoxy resin system as an example, rheological tests were performed on the graphene-modified resin system with mechanical stirring, ultrasonic treatment for 1 hour after mechanical stirring, and ultrasonic treatment for 3 hours after mechanical stirring. According to the viscosity, the resin viscosity dividing point of this type of filler is found. If the viscosity is lower than this, ultrasonic oscillation is selected as the method for further dispersion. If the viscosity is higher than this, three-roll grinding is selected until the filler is well dispersed in the matrix.

[0077] The thermal conductivity of carbon fiber in Z direction is calculated as follows: the thermal conductivity of asphalt-based carbon fiber is 800W / m·K, and the thermal conductivity of epoxy resin is increased to 3W / m·K after thermal modification. At the same time, cylindrical high thermal conductivity carbon rods are used as vertical thermal conductive channel reinforcements. The thermal conductivity of the carbon rods is 320W / m·K, and the volume fraction is set to 5%. According to the thermal conductivity calculation formula of carbon fiber composite materials:

[0078] k 11 =(1-v F ) M +v F k Fa ;

[0079] k 22 =k M +k M (k Fr -k M )vF / [k M +(1-v F )(k Fr -k M )0.5];

[0080] k 33Comp =k 11 d z-fiber +k 22 (1-d z-fiber );

[0081] d z-fiber =v Fz / v F ;

[0082] in:

[0083] ——k 11 is the thermal conductivity between the laminate layers in the 1,1 direction (out-of-plane);

[0084] ——k 22 is the thermal conductivity between the laminate layers in the 2,2 direction (out-of-plane);

[0085] ——k M is the thermal conductivity of epoxy resin;

[0086] ——k Fa is the axial thermal conductivity of carbon fiber;

[0087] ——k Fr is the radial thermal conductivity of carbon fiber;

[0088] ——v F is the volume fraction of carbon fiber;

[0089] ——v Fz is the fiber volume fraction in the z direction.

[0090] That is, the thermal conductivity of carbon fiber composite materials in the horizontal direction can reach more than 200W / m·K, and the thermal conductivity in the Z direction can reach more than 60W / m·K.

[0091] The embodiment of the present invention proposes a carbon fiber-based thermal conductive composite material and a preparation method through a three-dimensional weaving process, a low resin process, etc., while ensuring that its density is no more than 1.6g / cm3. The thermal conductivity of the carbon fiber-based thermal conductive composite material in the embodiment of the present invention is greater than 200W / m·K in the horizontal direction and greater than 30W / m·K in the vertical direction, which effectively broadens its application in environments requiring thermal conductivity.

[0092] The heat dissipation effect of using the carbon fiber-based thermal conductive composite material of the embodiment of the present invention and using other materials to make the chassis and module structural parts is compared as follows:

[0093] Take a computer that complies with HB7390 / ARINC600 as an example. There are 5 modules installed inside the product. Cooling air passes through the module surface from below to dissipate heat to the surrounding environment. The chassis and module structural parts of this product are made of aluminum alloy. There are two working conditions: natural heat dissipation and air cooling. The thermal simulation results at 70℃ are as follows: Figure 4 and Figure 5 shown.

[0094] It can be seen from the simulation results that under air cooling, the maximum temperature of the product is 82.8°C, and under natural heat dissipation, the maximum temperature of the components is 104°C, both of which are lower than the maximum operating temperature of military components of 125°C, meeting the long-term temperature operating requirements of the product.

[0095] When the material is changed to general carbon fiber, the thermal conductivity of carbon fiber is selected as 1, and the simulation results are as follows Figure 6 and Figure 7 As shown:

[0096] It can be seen from the simulation results that since the heat of the components cannot be transferred normally, the component temperatures in both working conditions exceeded 160°C, which is much higher than the maximum operating temperature of 125°C for military components and cannot meet product requirements.

[0097] When the thermal conductivity of carbon fiber reaches 200, 200, and 30 (thermal conductivity in the three directions of X-axis, Y-axis, and Z-axis), the simulation results are as follows: Figure 8 and Fig. 9 As shown:

[0098] From the simulation results, it can be seen that the thermal conductivity of carbon fiber has been greatly improved after thermal modification. The highest temperature of air-cooled heat dissipation components is 91.3℃, and the highest temperature of natural heat dissipation components is 110℃, which are 8.5℃ and 6℃ higher than aluminum alloy, respectively, meeting the product use needs and project index requirements.

[0099] Beneficial effects of the embodiments of the present invention:

[0100] Enhance the vertical thermal conductivity of carbon fiber-based thermal conductive composite materials. After the carbon fiber is thermally modified, the thermal conductivity in the vertical direction is greatly improved. The maximum temperature of air-cooled heat dissipation components is 91.3°C, and the maximum temperature of natural heat dissipation components is 110°C, which are 8.5°C and 6°C higher than aluminum alloy, respectively, meeting the product use needs and project index requirements.

[0101] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the scope of protection of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other, and with each other.

Claims

1. A thermally conductive composite material based on carbon fiber, characterized in that: include: Composite material (1), vertical filler (3) and surface foil (2); The composite material (1) comprises a prepreg and a filler, wherein the prepreg is a three-dimensional woven fabric woven from carbon fibers; A plurality of vertical fillers (3) are arranged in the vertical direction of the prepreg; The filler is filled in a filling body formed by the prepreg and the vertical filler (3); The composite material (1) further comprises an interface (4), the interface (4) being the upper surface and the lower surface of the composite material (1); A surface foil (2) is provided on the upper surface and the lower surface.

2. The carbon fiber-based thermally conductive composite material according to claim 1, characterized in that: The surface foil (2) is a graphene film.

3. The carbon fiber-based thermally conductive composite material according to claim 1, characterized in that: The vertical filler (3) is one or a combination of carbon nanotubes and cylindrical high thermal conductivity carbon rods.

4. The carbon fiber-based thermally conductive composite material according to claim 1, characterized in that: The filler is a mixture of high thermal conductivity epoxy resin and graphene.

5. A method for preparing a thermally conductive composite material based on carbon fiber, the method being used to manufacture the thermally conductive composite material according to any one of claims 1 to 4, characterized in that: include: Preparing a prepreg, and when performing a three-dimensional weaving process on the prepreg, filling a plurality of vertical fillers (3) in a vertical direction of the prepreg, so that the volume fraction of the vertical fillers (3) in the prepreg reaches a set volume fraction; A mixture of graphene and epoxy resin having a thermal conductivity reaching a set thermal conductivity is prepared as a filler, and the filler is filled into a filling body composed of the prepreg and the vertical filler (3) to generate a composite material (1); The composite material (1) is hot-pressed to form upper and lower interfaces (4); The interface (4) is covered with a surface foil (2) to produce a heat-conducting composite material based on carbon fibers.

6. The method for preparing a thermally conductive composite material based on carbon fiber according to claim 5, characterized in that: Preparing prepreg, comprising: The surface of carbon fiber filaments is treated by surface electropolymerization technology to generate surface-reinforced carbon fiber; The surface-reinforced carbon fibers are woven into the prepreg using a three-dimensional weaving technique.

7. The method for preparing a thermally conductive composite material based on carbon fiber according to claim 5, characterized in that: Preparing a mixture of graphene and epoxy resin having a thermal conductivity reaching a set thermal conductivity as the filler, comprising: In a room temperature environment, adding the graphene into the epoxy resin to generate a filling mixture; adding a dispersant and a coupling agent into the filling mixture and then stirring the mixture mechanically; During the stirring process, the system viscosity of the filling mixture is obtained. If the system viscosity is lower than the set viscosity, ultrasonic vibration is used for further dispersion to fully disperse the graphene in the epoxy resin matrix; If the system viscosity is higher than the set viscosity, three-roll grinding is used for further dispersion to fully disperse the graphene in the epoxy resin matrix.

8. The method for preparing a thermally conductive composite material based on carbon fiber according to claim 5, characterized in that: The thermal conductivity of the surface foil (2) is 380 W / m·K to 400 W / m·K.

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