Three-dimensional high-thermal-conductivity pitch-based carbon fiber composite material and preparation method thereof

Abstract

The application discloses a three-dimensional high-thermal-conductivity pitch-based carbon fiber composite material and a preparation method, relates to carbon fiber composite materials and thermal conductive materials, and comprises the following steps: selecting a base cloth with a required number of layers, and preparing a pitch-based carbon fiber prepreg with reserved pin holes; after pretreatment, pitch-based carbon fiber filaments are immersed in a resin solution, twisted, cut into a specified length, and dried to prepare pitch-based carbon fiber short-cut Z-pins; the pitch-based carbon fiber short-cut Z-pins are mixed with resin to prepare a pin-resin mixed solution; the pin-resin mixed solution is filled into the pin holes of the pitch-based carbon fiber prepreg, and a magnetic field is applied around the filled material; the whole material after the magnetic field is applied is cured; a high-thermal-conductivity material film is coated on the upper and lower surfaces of the cured pitch-based carbon fiber composite material, and secondary curing is carried out to complete the preparation. The Z-directional thermal conduction path is complete, and the in-plane thermal conductivity of the composite material is ensured.

Description

Technical Field

[0001] The present application relates to the fields of carbon fiber composite materials and thermal conductive materials, and in particular to a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material and a preparation method thereof. Background Art

[0002] Existing pitch-based carbon fiber composites have high in-plane thermal conductivity, reaching 300-400 W / m•K. However, because the carbon fiber layers are connected to the resin matrix, the resin's thermal conductivity is extremely low, blocking the heat transfer path in the z-direction. This results in a very low z-direction thermal conductivity, with the best achieving only around 0.8 W / m•K. Improving z-direction thermal conductivity is crucial for electronic devices to transfer heat from internal components to the outer surface of the housing.

[0003] There are several existing technologies for improving the Z-direction thermal conductivity of carbon fiber composite materials.

[0004] (1) Combining an asphalt-based carbon fiber resin matrix with carbon nanotubes, and utilizing the properties of carbon nanotubes to improve the Z-direction thermal conductivity of the material. For example, CN111319279A discloses a modified asphalt-based carbon fiber composite material for spacecraft payload structures. However, the technical disadvantage is that the fiber continuity within the plane is destroyed, thereby reducing the in-plane thermal conductivity. Another example is CN117326882A, which discloses a method for improving the Z-direction thermal conductivity of an asphalt-based carbon fiber composite material. However, the technical disadvantage is that the carbon fiber filaments are easily broken, resulting in an unstable Z-direction thermal conductivity path. As a result, the maximum Z-direction thermal conductivity shown in the example of the patent is only 3W / m•K.

[0005] (2) Improve the mechanism of asphalt fiber preparation to increase the Z-direction thermal conductivity of the material. For example, CN111962294A proposed by Hunan Dongying describes a high thermal conductivity composite material and its preparation method. However, the technical disadvantage is that the Z-direction thermal conductivity path is unstable and the Z-direction thermal conductivity parameters of the materials vary.

[0006] (3) Pins are implanted in the Z direction of the material to establish a heat conduction channel. For example, CN109049865A describes a three-dimensional heat transfer channel composite material and its preparation method. However, the technical disadvantage is that the Z-pin is subjected to resistance from the carbon fiber layer during implantation, resulting in breakage or damage, and the Z-direction heat conduction path is unstable. The results of the example shown in the patent show that the maximum Z-direction heat conduction rate is only 10 W / m•K. In addition, after the heat is extracted from one side of the material to the other side in the Z direction, it will gather at one point, resulting in extremely concentrated heat. Another example is CN109265919A describes a 3D heat-conducting composite material and its preparation method. The technical disadvantage of this method is that the Z-pin is inefficient and the accuracy cannot be guaranteed during manual insertion. Moreover, after the heat is extracted from the surface of the material, it cannot diffuse again, resulting in concentrated heat. Summary of the Invention

[0007] The embodiment of the present application provides a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material and a preparation method. Based on the method of prepreg reserved holes, the Z-Pin is not easy to break, ensuring the integrity of the constructed Z thermal conduction path; the reserved holes ensure the regularity of the Z thermal conduction path, and at the same time do not destroy the continuity of the planar layer fiber filaments, ensuring the in-plane thermal conductivity.

[0008] The present invention provides a method for preparing a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, comprising:

[0009] Selecting a required number of base fabric layers according to the required material thickness and performance, and preparing a pitch-based carbon fiber prepreg, wherein the prepared pitch-based carbon fiber prepreg is reserved with a plurality of distributed reserved pin holes;

[0010] After pre-treatment, the asphalt-based carbon fiber precursor is impregnated in a resin solution and twisted, and then cut into a specified length and dried to prepare asphalt-based carbon fiber chopped Z-pins;

[0011] Mixing pitch-based carbon fiber chopped Z-pin with resin to make a pin-resin mixture;

[0012] Filling the pin holes of a pitch-based carbon fiber prepreg with a pin-resin mixture and applying a magnetic field around the filled material so that the pitch-based carbon fiber chopped Z-pins at a target ratio in the pin-resin mixture are aligned in the Z direction;

[0013] solidifying the entire material after the magnetic field is applied;

[0014] The upper and lower surfaces of the cured asphalt-based carbon fiber composite material are coated with a high thermal conductivity material and then cured for a second time to complete the preparation.

[0015] The present application also provides a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, comprising:

[0016] Pitch-based carbon fiber prepreg, with pin holes reserved, is prepared by selecting the required number of layers of base fabric based on the required material thickness and performance;

[0017] Pitch-based carbon fiber chopped Z-pin is prepared by pre-treating the pitch-based carbon fiber precursor, impregnating it with a resin solution, twisting it, cutting it into a specified length, and drying it;

[0018] The asphalt-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the asphalt-based carbon fiber prepreg;

[0019] The upper and lower surfaces of the inserted composite material are covered with a high thermal conductivity material film.

[0020] The method of this application is based on the method of prepreg reserved holes. The Z-Pin is not easy to break, ensuring the integrity of the constructed Z-heat conduction path. The reserved holes ensure the regularity of the Z-heat conduction path, do not destroy the continuity of the planar layer fiber filaments, and ensure the in-plane thermal conductivity. Based on the method of erection in a strong magnetic field, the efficient erection of the Z-Pin is guaranteed, the efficiency is improved, and the erection ratio of the Z-Pin can be guaranteed by controlling the magnetic field, ensuring that the formed Z-heat conduction path is stable.

[0021] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0023] Figure 1 The basic process of the preparation method of the three-dimensional high thermal conductivity asphalt-based carbon fiber composite material according to the embodiment of the present application is schematically shown;

[0024] Figure 2 This is a schematic diagram of the structure of the asphalt-based carbon fiber composite material prepared in the embodiment of the present application;

[0025] Figure 3 This is a schematic diagram of the interweaving of warp and weft yarns in the preparation method of the embodiment of the present application;

[0026] Figure 4 This is a schematic diagram of the unidirectional weaving method in the preparation method of the embodiment of the present application;

[0027] Figure 5 This is a schematic diagram of the pin holes used in the unidirectional weaving method in the preparation method of the embodiment of the present application;

[0028] Figure 6 This is a schematic diagram of the Z-pin being erected by applying a magnetic field in the preparation method of the present application embodiment;

[0029] Figure 7 This is a schematic diagram of the cross-sectional structure of the asphalt-based carbon fiber composite material prepared in an embodiment of the present application;

[0030] Figure 8 A partial schematic diagram of a single reserved hole in the asphalt-based carbon fiber composite material prepared in an embodiment of the present application. DETAILED DESCRIPTION

[0031] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0032] With the rapid development of industries such as 5G / 6G communications, satellite internet, and radar detection, electronic products are rapidly evolving towards high power, miniaturization, and high density. As the power of electronic devices increases significantly, the heat dissipation space continues to shrink. Heat dissipation has become a prominent constraint on their development, significantly impacting device performance. The industry is exploring various approaches to address heat dissipation, with composite materials emerging as a leading approach. Pitch-based carbon fiber composites, with their excellent properties such as high temperature resistance, high strength and modulus, and low density, have become a preferred thermal conductive material. They can improve the mechanical properties and thermal conductivity of products while significantly reducing weight. Several Chinese companies have mastered the technology for mass production of pitch-based carbon fibers, with domestic companies producing mesophase pitch-based carbon fibers with a power of 900 W / m•K. Carbon nanotubes and graphene also offer excellent thermal conductivity, but their large-scale production remains difficult. Furthermore, the thermal conductivity of these two materials is unstable when fabricated into composite materials, limiting their widespread application in products. Due to their lightweight, high thermal conductivity, high modulus, and stability, pitch-based carbon fiber composites are widely used in thermal management systems for satellites, hypersonic vehicles, nuclear power, military, and electronics.

[0033] However, the asphalt-based carbon fiber composites currently available for engineering applications only have high thermal conductivity in the planar direction, averaging 300-400 W / m•K. Thermal conductivity in the Z-direction is extremely low, with only around 0.8 W / m•K achieved in good quality, though some laboratories and patents have reported reaching around 10 W / m•K. This is because carbon fiber composites are typically manufactured using a resin matrix as a bonding layer, but the resin's thermal conductivity is extremely low, thus blocking the Z-direction heat transfer path. However, the application of carbon fiber composites in products requires very high Z-direction thermal conductivity. Larger heat-generating components are attached to the wall and rely on Z-direction thermal conductivity to direct heat to the outer surface, where it then diffuses. This low Z-direction thermal conductivity restricts the material's application.

[0034] Currently, some public technologies are dedicated to improving the thermal conductivity of carbon fiber composites in the Z direction. However, common problems are: the thermal conductivity in the Z direction shown in the examples is general and unstable; and the diffusion after the heat is extracted is not taken into account, which can easily lead to heat concentration and damage to the device.

[0035] If a simple heat-conducting structure could be provided in the Z-direction of a carbon fiber composite material as a heat transfer path, it would not only solve the problem of impeded Z-direction heat transfer, but also provide good structural strength and relatively stable heat transfer. It would also enable low-cost, simple processing, and make mass production and engineering feasible. A similar invention to the present invention, and one that serves as a foundation for the present invention, is the three-dimensional heat transfer channel composite material and its preparation method disclosed in CN109049865A. This method involves constructing fiber Z-pins or metal needles as thermal reinforcements, which are then implanted in the Z-direction of the composite material to establish a heat transfer channel. This method can also improve interlaminar shear performance. However, the Z-pins mentioned in this method are sharpened for insertion into the composite material, which damages the carbon fiber layers and places high demands on operability. Furthermore, the Z-pins may break or break due to internal stamping resistance during insertion, resulting in a maximum Z-direction thermal conductivity of only 10 W / m·K. Furthermore, heat is concentrated at a single point on the composite material surface after being conducted through the sharpened Z-pins, preventing heat from dissipating on the outer surface of the material. Consequently, this method fails to provide both conduction and heat dissipation for electronic products.

[0036] The present application embodiment proposes a method for preparing a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, such as Figure 1 Shown, including:

[0037] In step S101, a base cloth with a required number of layers is selected according to the required material thickness and performance, and an asphalt-based carbon fiber prepreg is prepared, wherein the prepared asphalt-based carbon fiber prepreg is reserved with a plurality of distributed reserved Pin holes. In a specific example, the asphalt-based carbon fiber base cloth can be first woven with fiber filaments, and then the base cloth with a required number of layers is selected according to the required material thickness and performance, the holes are aligned and stacked, and the base cloth is impregnated in resin, or the resin is brushed between the base cloth layers. The method of the embodiment of the present application reserves Pin holes when the asphalt-based carbon fiber prepreg is woven and layered, so that the Z-pin implantation does not destroy its own performance, nor does it destroy the fiber continuity of the base cloth, thereby ensuring the in-plane thermal conductivity and mechanical properties.

[0038] In step S102, the asphalt-based carbon fiber precursor, after pretreatment, is impregnated with a resin solution and twisted. After twisting, the asphalt-based carbon fiber chopped Z-pins are cut into a specified length and dried to produce the asphalt-based carbon fiber chopped Z-pins. In a specific example, the asphalt-based carbon fiber precursor can be pretreated by removing surface curing agent residues using methods such as ultrasonic vibration; then impregnated and twisted, the carbon fiber filaments are immersed in the resin solution for 30-60 seconds and twisted, preferably with a twist specification of 20-30 twists / m; then pre-dried; and the fiber bundles are cut into a specified length c.

[0039] In step S103, the pitch-based carbon fiber chopped Z-pin is mixed with resin to prepare a pin-resin mixture. In a specific example, a large amount of pitch-based carbon fiber chopped Z-pin is mixed with resin to prepare a pin-resin mixture. The density of the pitch-based carbon fiber chopped Z-pin in the pin-resin mixture is about 1 cm 3 The mixture contains 200-1000 Z-pins.

[0040] Through the above steps, an uncured asphalt-based carbon fiber prepreg with a reserved array of pin holes and a pin-resin mixture of asphalt-based carbon fiber chopped Z-pins and resin have been formed. In step S104, the pin-resin mixture is filled into the pin holes of the asphalt-based carbon fiber prepreg, and a magnetic field is applied around the filled material to make the target proportion of asphalt-based carbon fiber chopped Z-pins in the pin-resin mixture consistent with the Z direction. In a specific example, the pin-resin mixture is filled into the reserved holes on the asphalt-based carbon fiber prepreg manually or automatically, and then the required magnetic field is created around it using an electromagnet, a permanent magnet or an electromagnetic coil. The anti-magnetism of the asphalt-based carbon fiber chopped Z-pins in the pin-resin mixture is used to receive a torque perpendicular to the direction of the magnetic force in the magnetic field and stand upright in a state consistent with the Z direction. The present application uses a magnetic field to make a large number of Z-pins stand up, thereby constructing a complete and stable Z-direction heat conduction path.

[0041] In step S105, the entire material after the magnetic field is applied is solidified;

[0042] In step S106, the upper and lower surfaces of the cured asphalt-based carbon fiber composite material are coated with a high thermal conductivity material, followed by secondary curing to complete the preparation. The method of the present application coats the upper and lower surfaces of the asphalt-based carbon fiber composite material with a high thermal conductivity material after curing and forming, and then curing and forming. Heat conducted to a point on the surface of the material is evenly diffused across the entire surface, forming secondary heat dissipation and comprehensive conduction. The entire process is highly efficient, low-cost, and easy to apply in engineering applications.

[0043] like Figure 2 As shown, the prepared carbon fiber composite material includes a pitch-based carbon fiber prepreg 1, a pin-resin mixed solution 2, a high thermal conductivity material film 3, a pitch-based carbon fiber base cloth 11, and a resin 12.

[0044] The method of prepreg reserved holes in the present application makes the Z-Pin less likely to break, thereby ensuring the integrity of the constructed Z-direction heat conduction path; the reserved holes ensure the regularity of the Z-direction heat conduction path, while not destroying the continuity of the planar layer fiber filaments, thereby ensuring the in-plane thermal conductivity.

[0045] This application provides two methods for woven base fabrics. In some embodiments, preparing a pitch-based carbon fiber prepreg includes:

[0046] It is woven by warp and weft yarns, and pin holes are reserved during weaving. Figure 3 As shown, a cluster of pitch-based carbon fiber tows is used as the warp yarn, using a plain weave or twill weave method. This method is simple to operate and is easy to form a uniform and certain number of interwoven holes. The arrangement of the interwoven holes is very regular, and it is easier to form a rectangular array, which is convenient for uniform heat transfer.

[0047] In the case of plain weave, a cluster of warp yarns or weft yarns includes 3K-6K fiber yarns / bundles, and the spacing between the warp yarns and the spacing between the weft yarns are both a, to ensure that the woven base cloth reserves an array of pin holes. The pin holes are rectangular holes with a side length of a and a spacing of b, satisfying: 0.8h<a<1.1h, 2a<b<4a, and h is the thickness of the asphalt-based carbon fiber prepreg.

[0048] The thickness of the woven base fabric can be 0.125mm-0.5mm. This method reserves pin holes without destroying the continuity of the fiber filaments, and is more controlled during operation. It is very convenient to obtain the required number and spacing of pin holes, which is convenient for forming arrays of rectangular, circular or other regular shapes.

[0049] Another way to weave the base fabric, in some embodiments, preparing the pitch-based carbon fiber prepreg includes:

[0050] Using a unidirectional weaving method, the pitch-based carbon fiber filaments are laid flat in one direction, such as Figure 4 As shown, insert a needle of the required diameter into the corresponding position in advance to reserve a pin hole.

[0051] Alternatively, a combined weaving method at different angles can be used to combine asphalt-based carbon fiber yarns along weaving layers at different angles to form multiple carbon fiber yarn layers. The single-weaved fiber yarns are spread out, and needles of the required diameter are inserted in advance at the corresponding positions to reserve pin holes, such as Figure 4 For example, asphalt-based carbon fiber yarns are braided at different angles of 0, 45, and 90 degrees to form multiple carbon fiber yarn layers. Similarly, needles of the required diameter are inserted in advance at the corresponding positions to reserve pin holes.

[0052] The pin hole to be inserted is a circular hole, such as Figure 5 As shown, the diameter is r, the Pin hole spacing is b, and it satisfies: 0.9h<r<1.2h, 2r<b<4r, and h is the thickness of the asphalt-based carbon fiber prepreg.

[0053] The thickness of the woven base fabric is between 0.125mm and 0.5mm. This method allows for the creation of pre-positioned pin holes without disrupting the continuity of the fibers. Furthermore, the operation is more controlled, allowing for the desired number and spacing of pin holes to be easily obtained, facilitating the formation of rectangular, circular, or other regularly shaped arrays.

[0054] After obtaining a pre-pinned base fabric using either of the two methods above, it is then impregnated with resin, or resin is applied between base fabric layers to form an uncured pitch-based carbon fiber prepreg with pre-pinned holes. Impregnation is recommended as it is more suitable for the brittle nature of pitch-based carbon fibers.

[0055] Regarding the values ​​of a, r, and b proposed in this application, the values ​​of a, r, and b designed in this application, within the range of the values ​​of a and r proposed in this application, optimize the internal Z-pin density and vertical integrity upon completion of subsequent steps, ensuring the Z-direction heat transfer path. Within the range of the values ​​of b proposed in this application, sufficient Z-direction heat transfer paths are ensured upon completion of subsequent steps, while also ensuring the most complete fiber heat transfer path within the plane.

[0056] In the implementation example of the present application, an asphalt-based carbon fiber prepreg with a thickness of 1.8 mm is prepared, and the base cloth woven by method one and method two is used, a is 2 mm, b is 6.5 mm, the thickness of each layer of base cloth is 0.2 mm, and the thickness of the resin layer is 0.6-0.7 mm, so that a high thermal conductivity asphalt-based carbon fiber composite material plate with a thickness of 2 mm can be obtained. In the subsequent steps, the thickness of the upper and lower surface coatings is about 0.1 mm.

[0057] In some embodiments, preparing pitch-based carbon fiber chopped Z-pins comprises:

[0058] After pretreatment, the asphalt-based carbon fiber precursor is immersed in a resin solution for 30-60 seconds, twisted, and pre-dried. The twisting specification is 20-30 twists / m, and then pre-dried. The pre-drying method is: the temperature is 120-180°C, and the present application is dried at 130°C for 10 minutes. The drying and curing method is the temperature of 180-250°C, and the present application is dried at 180°C for 50 minutes. The resin impregnated with the carbon fiber filaments is preferably epoxy resin, and the pin-resin mixture can be epoxy resin, which has good thermal conductivity and small curing shrinkage. In a specific example, the epoxy resin can be a glycidyl ether epoxy resin, or it can be a bisphenol A epoxy resin, a glycidyl ester epoxy resin, or a glycidyl amine epoxy resin.

[0059] The pre-dried fiber bundle is cut into a specified length c and cured to obtain pitch-based carbon fiber chopped Z-pins, where c>h+0.6mm (h is the thickness of the pitch-based carbon fiber prepreg). After drying and curing, the Z-pins have a diameter of 8-17μm.

[0060] The asphalt-based carbon fiber chopped Z-pin prepared in this application has a diameter of about 8-10 μm after being processed in the above steps; it is suitable for asphalt-based carbon fiber prepreg with a thickness of 1.8 mm, and the asphalt-based carbon fiber chopped Z-pin prepared in this application has a length of 2.4 mm.

[0061] The advantages of the Z-pin formed by the method of the present application are: surface curing molding reduces resin loss; the infiltration method helps to evenly distribute the resin; a semi-cured state is first formed under pre-drying to ensure that the resin is slightly cross-linked and has a certain viscosity, which is convenient for cutting; and finally, drying and curing are performed to ensure good fracture resistance.

[0062] Then a large amount of pitch-based carbon fiber chopped Z-pin is mixed with resin to make a pin-resin mixture. The density of pitch-based carbon fiber chopped Z-pin in the pin-resin mixture is about 1cm 3 The mixture contains 200-1000 Z-pins.

[0063] The above steps have formed an uncured pitch-based carbon fiber prepreg with a pre-reserved array of pin holes and a pin-resin mixture of pitch-based carbon fiber chopped Z-pins and resin. Based on this, in some embodiments, applying a magnetic field around the filled material includes:

[0064] Using magnetic equipment, the required magnetic field is generated around the prepreg filled with the resin mixture of asphalt-based carbon fiber chopped Z-pins, so that the generated magnetic field can be used to rotate the Z-pins around an axis perpendicular to the magnetic field, so that the long axis of the asphalt-based carbon fiber chopped Z-pins is parallel to the direction of the magnetic field.

[0065] In a specific example, Figure 6 As shown, the pin-resin mixture can be filled into the reserved holes on the asphalt-based carbon fiber prepreg manually or automatically, and then the required magnetic field is created around it using equipment such as electromagnets, permanent magnets or electromagnetic coils. The asphalt-based carbon fiber chopped Z-pins in the pin-resin mixture have anti-magnetic properties and are subjected to a torque perpendicular to the direction of the magnetic force in the magnetic field, so that they stand upright in a state consistent with the Z direction.

[0066] Since the length of the Z-pin c>h+0.6mm (h is the thickness of the pitch-based carbon fiber prepreg), the Z-pin can pass through the holes in the prepreg, such as Figure 6 As shown, the Z-pin is exposed on the upper and lower surfaces of the prepreg by about 0.3 mm, thus completing the implantation of the Z-pin in the reserved hole.

[0067] In this process, the benefits of the reserved holes in the asphalt-based carbon fiber prepreg of the embodiment of the present application are demonstrated.

[0068] First, there is little resistance when the Z-pin is implanted and erected, perforation is easy, and the implantation speed is fast, which can reduce the stress on the Z-pin. In addition, the uncured resin has a buffering effect on the Z-pin, making it less likely to break during insertion.

[0069] Secondly, the Z-pin erection process does not affect the fiber continuity of the original carbon fiber base cloth, ensuring its in-plane thermal conductivity path and mechanical properties. The existing implantation method is to directly insert the Z-pin into the uncured carbon fiber material. The puncturing of the hole will destroy the integrity of the carbon fiber plane layer; and the inserted Z-pin is subject to the resistance of the carbon fiber plane layer, the deflection angle is large, and it is easy to break, damaging the Z-direction thermal conductivity path. The deflection angle of the Z-pin inserted by the method provided by the present invention is measured to be an average of 3-5°, which is several to dozens of times smaller than the existing method of implanting Z-pins.

[0070] The method of filling the reserved hole with the PIN-resin mixture in this application can be manual filling or automatic filling. The specific implementation method is as follows:

[0071] Manual implantation involves using a dispensing tool to insert the pin-resin mixture into the pitch-based carbon fiber prepreg one by one. The pitch-based carbon fiber prepreg is secured with a fixture beforehand, and during manual implantation, care is taken to ensure that each pre-placed hole is completely filled. This method is simple and low-cost, but due to the large number of pre-placed holes, it is time-consuming and is therefore only used for non-batch production or large-area material production.

[0072] The automated infill method first secures the pitch-based carbon fiber prepreg with a fixture. Then, a dispensing machine or other tooling is used to pick up Z-pins in rows or arrays. These are aligned with the pre-determined holes in the prepreg to be formed, allowing for row or surface infill. This method is highly efficient, ensuring that multiple Z-pins are placed at the same angle and distance, ensuring uniform thermal conductivity. Using a dispensing machine for automated infill, the rate can reach 0.3 seconds per hole.

[0073] The specific method of using a magnetic field to erect the Z-pins is as follows. Because the pin-resin mixture filled in each reserved hole contains thousands of asphalt-based carbon fiber chopped Z-pins, these Z-pins are randomly positioned and their small diameter makes it difficult to pick them up and erect them. Therefore, a Z-direction heat transfer channel has not yet been established. This embodiment of the application proposes a method of applying a magnetic field to erect the Z-pins, including:

[0074] First, an electromagnet, permanent magnet, or electromagnetic coil is used to create the desired magnetic field around the prepreg filled with the pin-resin mixture. Because pitch-based carbon fibers are diamagnetic (their magnetic susceptibility is extremely low and negative), they experience a torque perpendicular to the magnetic field, producing a micromagnetization opposite to the direction of the external field (i.e., the magnetic flux lines). Furthermore, their axial diamagnetic properties are weaker than their radial diamagnetic properties, making them more susceptible to radial repulsion. This causes the Z-pin to rotate about an axis perpendicular to the magnetic field, ultimately aligning its long axis parallel to the magnetic field (the magnetic flux lines).

[0075] When a magnetic field is applied, the stronger the magnetic field strength, the higher the orientation of the Z-pins, but the higher the energy consumption. In some embodiments, 300-500 Z-pins / 1cm 3 Under the conditions of a pin-resin mixture density, a Z-pin diameter of 8-17 μm and a length of 1.5-3.5 mm, the magnetic field strength is 0.15T-1.5T, more preferably 0.3T-0.5T. When the magnetic field is constructed using permanent magnets, trapezoidal permanent magnets can be used, and the spacing between the upper and lower permanent magnets and the prepreg is maintained at 2-10 mm. Excessive spacing requires an increase in magnetic field strength, while too small a distance can easily cause the permanent magnets to become contaminated with the resin solution and become unreusable. Experimental results show that when the Z-pins are 2.4 mm long and 8-10 μm in diameter, the number of Z-pins does not significantly affect the magnetic field strength. However, the length and diameter of the Z-pins do affect the ratio of the Z-pins required to stand upright. The longer the length and the larger the diameter, the greater the magnetic field required to maintain the same standing ratio. In this embodiment, microscopic observation and calculation at 0.35 T and an appropriate concentration of epoxy resin can ensure that the Z-pin standing ratio is greater than 30%. If modified asphalt-based carbon fiber is used, that is, a magnetic layer such as nickel is coated on the outer surface of the fiber, the erection ratio is greater than 70%.

[0076] After applying a magnetic field to make the Z-pins of the appropriate ratio stand up, the magnetic field needs to be kept uniform and stable to ensure that the forces acting on the Z-pins are the same to achieve a regular arrangement state with the upper and lower parts aligned. Then the intensity and direction of the magnetic field can be fine-tuned, or a local magnetic field can be applied or adjusted, while an optical microscope is used for real-time observation to make the Z-pins slightly higher than the upper and lower surfaces of the asphalt-based carbon fiber prepreg. This is possible because the length of the Z-pin c>h+0.6mm (h is the thickness of the asphalt-based carbon fiber prepreg). The implementation experience of this application is to first apply a weak magnetic field to make the Z-pin stand up initially, and then gradually increase the uniform magnetic field to an intensity of 0.35T. It can be weakened and then increased again to achieve a basically consistent height of the Z-pins when they are standing, and basically aligned up and down and protruding from the prepreg surface.

[0077] In some embodiments, curing the entire material after applying the magnetic field includes:

[0078] The asphalt-based carbon fiber chopped Z-pins are inserted into the reserved holes of the asphalt-based carbon fiber prepreg, and the whole is placed in a mold for pressurized curing. The temperature is first increased in an autoclave or hot press molding machine at a heating rate of 2-5°C / min. After the temperature reaches 100-180°C, pressurization begins. Depending on the requirements of the material's applicable environment, the pressure is controlled at 0.4-1.2Mpa. For the general epoxy resin material used in the embodiment, the specific implementation method is to start pressurization after the temperature reaches 130-140°C, steadily increase the temperature at 3°C / min, and apply a pressure of 1 Mpa to ensure material quality and relatively save energy.

[0079] After curing, the carbon fibers are short and the Z-pins will slightly protrude from the upper and lower surfaces of the molded asphalt-based carbon fiber composite material, requiring shearing to ensure a smooth surface. The asphalt-based carbon fiber composite material is secured in place with a fixture and positioned using a guide block with perforations. The surface is then fine-sheared using a small grinder or polisher. If necessary, the surface smoothness can be checked using a laser or other equipment. The present invention, in accordance with the aforementioned embodiment, can achieve a surface flatness of ≤0.05 mm after Z-pin removal.

[0080] On the basis of the above steps, the asphalt-based carbon fiber composite material prepared in this application has established a stable Z-direction heat conduction path for the material. The path is complete without any breaks and the number is sufficient to conduct heat from one side of the material to the other. However, for actual electronic products with high heat consumption, the high heat points are usually more concentrated, such as on a certain component or chip. Therefore, after the heat is extracted, it needs to be diffused on the outer surface of the shell. In some embodiments, the upper and lower surfaces of the asphalt-based carbon fiber composite material are further coated with a high thermal conductivity material, such as Figure 7 、 Figure 8 As shown, the upper and lower surfaces of the composite material are covered with a high thermal conductivity material film 3. Figure 8 The prepreg includes most of the vertical Z-pins, which are then solidified and formed. This application proposes a method for preparing a high thermal conductivity material film on the upper and lower surfaces of an asphalt-based carbon fiber composite material, which can evenly diffuse the heat conducted to a point on the surface of the material over the entire surface, forming secondary heat dissipation and comprehensive conduction.

[0081] The upper and lower surfaces of the composite material are coated with a high thermal conductivity material, and the materials can be selected from metal copper, metal aluminum, carbon nanotubes, graphene, etc. In the specific implementation of the embodiment, copper can be coated on the Z-pin to increase thermal conductivity while ensuring low cost. Thermal spraying and electroplating can be used. When the area is small and the appearance quality requirements are not high, thermal spraying is selected to reduce costs and facilitate operation. When the area is large and the appearance quality requirements are high, electroplating is selected. In a specific example, after the surface is copper-plated, natural drying curing, heat curing, ultraviolet curing, adding a curing agent, etc. can be used. Ultraviolet curing can also be used, which has a lower cost and better curing effect.

[0082] The composite material prepared in this manner according to the embodiment of the present application was tested to have an in-plane thermal conductivity greater than 400 W / m•K and a Z-direction thermal conductivity greater than 50 W / m•K.

[0083] The method of the present application first weaves an asphalt-based carbon fiber base cloth with array pin holes reserved, and can adopt a two-dimensional weaving or unidirectional laying pin method to reserve holes without destroying the fiber continuity of the base cloth; then the base cloth is impregnated with resin to form a prepreg containing reserved holes; then an asphalt-based carbon fiber Z-pin is made from the asphalt-based carbon fiber filament and mixed with resin to form a pin-resin mixture; then the pin-resin mixture is filled into each reserved hole by manual or automatic implantation, and the short Z-pin in the mixture is erected parallel to the Z direction of the material by applying a magnetic field, and the magnetic field is adjusted to make the Z-pin height consistent, so as to ensure that there are a certain number of Z-direction conduction paths in the array holes; then the prepreg is cured and formed under high temperature and pressure, and the upper and lower protruding Z-pins are trimmed until they are flush with the upper and lower surfaces of the material; finally, a thin film of high thermal conductivity material is prepared on the upper and lower surfaces of the composite material, and cured again to form a surface heat diffusion path.

[0084] This application is based on a method of erecting in a strong magnetic field, which ensures the efficient erection of the Z-Pin and improves efficiency. By controlling the magnetic field, the erection ratio of the Z-Pin can be guaranteed, ensuring that the formed Z-direction heat conduction path is stable.

[0085] After the heat reaches the outer surface of the material through the Z direction, it can diffuse evenly for a second time, so that the heat of the device is quickly dispersed after being conducted out of the product, truly achieving the effect of heat dissipation.

[0086] The present application also provides a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, comprising:

[0087] Pitch-based carbon fiber prepreg, with pin holes reserved, is prepared by selecting the required number of layers of base fabric based on the required material thickness and performance;

[0088] Pitch-based carbon fiber chopped Z-pin is prepared by pre-treating the pitch-based carbon fiber precursor, impregnating it with a resin solution, twisting it, cutting it into a specified length, and drying it;

[0089] The asphalt-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the asphalt-based carbon fiber prepreg;

[0090] The upper and lower surfaces of the inserted composite material are covered with a high thermal conductivity material film.

[0091] In some embodiments, the pitch-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the pitch-based carbon fiber prepreg in the following manner:

[0092] Mixing pitch-based carbon fiber chopped Z-pin with resin to make a pin-resin mixture;

[0093] Filling the pin holes of a pitch-based carbon fiber prepreg with a pin-resin mixture and applying a magnetic field around the filled material so that the pitch-based carbon fiber chopped Z-pins at a target ratio in the pin-resin mixture are aligned in the Z direction;

[0094] The entire material to which the magnetic field is applied is solidified.

[0095] In some embodiments, 300-500 Z-pins / 1 cm 3 The density of the pin-resin mixed solution is 8-17 μm in diameter and 1.5-3.5 mm in length, and the magnetic field strength is 0.15 T to 1.5 T.

[0096] It should be noted that, in the various embodiments of the present application, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0097] The serial numbers of the above embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0098] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are protected by this application.

Claims

1. A method for preparing a three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, characterized in that: include: Selecting a required number of base fabric layers according to the required material thickness and performance, and preparing a pitch-based carbon fiber prepreg, wherein the prepared pitch-based carbon fiber prepreg is reserved with a plurality of distributed reserved pin holes; After pre-treatment, the asphalt-based carbon fiber precursor is impregnated with a resin solution and twisted, and then cut into a specified length and dried to prepare asphalt-based carbon fiber chopped Z-pins; Mixing pitch-based carbon fiber chopped Z-pin with resin to make a pin-resin mixture; Filling the pin holes of a pitch-based carbon fiber prepreg with a pin-resin mixture and applying a magnetic field around the filled material so that the pitch-based carbon fiber chopped Z-pins at a target ratio in the pin-resin mixture are aligned in the Z direction; solidifying the entire material after the magnetic field is applied; The upper and lower surfaces of the cured asphalt-based carbon fiber composite material are coated with a high thermal conductivity material and then subjected to secondary curing to complete the preparation; The preparation of pitch-based carbon fiber chopped Z-pins includes: After pretreatment, the asphalt-based carbon fiber precursor is immersed in a resin solution for 30s-60s, twisted, and pre-dried. The twist specification is 20-30 twists / m. The pre-dried fiber bundle is cut into a specified length c and cured to obtain pitch-based carbon fiber chopped Z-pins, c>h+0.6mm, where c is the cut Z-pin length and h is the thickness of the pitch-based carbon fiber prepreg; Applying a magnetic field around the filled material involves: Using magnetic equipment, the required magnetic field is generated around the prepreg filled with the resin mixture of asphalt-based carbon fiber chopped Z-pins, so that the generated magnetic field can be used to rotate the Z-pins around an axis perpendicular to the magnetic field, so that the long axis of the asphalt-based carbon fiber chopped Z-pins is parallel to the direction of the magnetic field.

2. The method for preparing a three-dimensional high thermal conductivity pitch-based carbon fiber composite material according to claim 1, wherein: The preparation of pitch-based carbon fiber prepreg comprises: It is woven by interweaving warp and weft yarns, with pin holes reserved during weaving, and adopts plain or twill weaving method; In the case of plain weave, a cluster of warp or weft yarns includes 3K-6K fiber yarns / bundles, and the spacing between the warp yarns and the spacing between the weft yarns are both a, to ensure that the woven base cloth has reserved arrays of pin holes. The pin holes are rectangular holes with a side length of a and a spacing of b, satisfying: 0.8h<a<1.1h, 2a<b<4a, and h is the thickness of the asphalt-based carbon fiber prepreg.

3. The method for preparing a three-dimensional high thermal conductivity pitch-based carbon fiber composite material according to claim 1, wherein: The preparation of pitch-based carbon fiber prepreg comprises: Using a unidirectional weaving method, the pitch-based carbon fiber filaments are laid flat in one direction, and a needle of the required diameter is inserted in advance at the corresponding position to reserve a pin hole; or, Using a combination weaving method at different angles, the asphalt-based carbon fiber yarns are combined along the weaving layers at different angles to form multiple carbon fiber yarn layers, and pin holes are reserved at the corresponding positions; The reserved pin holes are circular holes with a diameter of a and a pin hole spacing of b, satisfying the following conditions: 0.9h<a<1.2h, 2a<b<4a, where h is the thickness of the asphalt-based carbon fiber prepreg.

4. The method for preparing a three-dimensional high thermal conductivity pitch-based carbon fiber composite material according to claim 1, wherein: 300-500 Z-pins / 1cm 3 The density of the pin-resin mixed solution is 8-17 μm in diameter and 1.5-3.5 mm in length, and the magnetic field strength is 0.15 T to 1.5 T.

5. The method for preparing a three-dimensional high thermal conductivity pitch-based carbon fiber composite material according to claim 4, wherein: Solidifying the entire material after applying the magnetic field includes: Insert the asphalt-based carbon fiber chopped Z-pin into the reserved holes of the asphalt-based carbon fiber prepreg, and place the whole into the mold for pressurized curing. The temperature is first increased in the autoclave or hot pressing molding machine at a heating rate of 2-5℃ / min. After the temperature reaches 100-180℃, pressurization is started. The pressure is controlled at 0.4-1.2Mpa according to the different requirements of the material application environment. After curing, trim the excess Z-pins exposed on the upper and lower surfaces.

6. A three-dimensional high thermal conductivity asphalt-based carbon fiber composite material, characterized in that: include: asphalt The carbon fiber prepreg is pre-pinned and is prepared by selecting the required number of layers of base fabric according to the required material thickness and performance; Pitch-based carbon fiber chopped Z-pin is prepared by pre-treating the pitch-based carbon fiber precursor, impregnating it with a resin solution, twisting it, cutting it into a specified length, and drying it; The asphalt-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the asphalt-based carbon fiber prepreg; The upper and lower surfaces of the inserted composite material are covered with a film of high thermal conductivity material; The preparation of pitch-based carbon fiber chopped Z-pins includes: After pretreatment, the asphalt-based carbon fiber precursor is immersed in a resin solution for 30s-60s, twisted, and pre-dried. The twist specification is 20-30 twists / m. The pre-dried fiber bundle is cut into a specified length c and cured to obtain pitch-based carbon fiber chopped Z-pins, c>h+0.6mm, where c is the cut Z-pin length and h is the thickness of the pitch-based carbon fiber prepreg; The pitch-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the pitch-based carbon fiber prepreg, comprising: Using magnetic equipment, the required magnetic field is generated around the prepreg filled with the resin mixture of asphalt-based carbon fiber chopped Z-pins, so that the generated magnetic field can be used to rotate the Z-pins around an axis perpendicular to the magnetic field, so that the long axis of the asphalt-based carbon fiber chopped Z-pins is parallel to the direction of the magnetic field.

7. The three-dimensional high thermal conductivity asphalt-based carbon fiber composite material according to claim 6, wherein the asphalt The asphalt-based carbon fiber chopped Z-pins are implanted into the reserved pin holes of the asphalt-based carbon fiber prepreg in the following manner: Mixing pitch-based carbon fiber chopped Z-pin with resin to make a pin-resin mixture; Filling the pin holes of a pitch-based carbon fiber prepreg with a pin-resin mixture and applying a magnetic field around the filled material so that the pitch-based carbon fiber chopped Z-pins at a target ratio in the pin-resin mixture are aligned in the Z direction; The entire material to which the magnetic field is applied is solidified.

8. The three-dimensional high thermal conductivity asphalt-based carbon fiber composite material according to claim 7, characterized in that: 300-500 Z-pins / 1cm 3 The density of the pin-resin mixed solution is 8-17 μm in diameter and 1.5-3.5 mm in length, and the magnetic field strength is 0.15 T to 1.5 T.

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