Modified carbon fiber, preparation method thereof and heat-conducting composite material

Abstract

This invention discloses a modified carbon fiber, its preparation method, and a thermally conductive composite material. The preparation method includes: S1. Coating the surface of the carbon fiber with an insulating slurry containing a polyimide precursor and aminated boron nitride nanosheets, and then thermally imidizing and curing it to obtain a preliminary modified carbon fiber; S2. Under a magnetic field, coating the surface of the preliminary modified carbon fiber with a composite slurry containing magnetically anisotropic magnetic particles, boron nitride nanosheets, and a curable resin, and then curing it to obtain the modified carbon fiber. The modified carbon fiber provided by this invention has the advantages of high insulation and high thermal conductivity, as well as excellent magnetic anisotropy and strong magnetic response. It can achieve efficient orientation under low-intensity magnetic fields, thereby obtaining an anisotropic thermally conductive material with excellent performance.

Description

Technical Field

[0001] This invention belongs to the technical field of functional fiber modification and advanced thermal management materials, specifically relating to a modified carbon fiber and its preparation method, and a thermally conductive composite material. Background Technology

[0002] Carbon fiber possesses excellent axial ultra-high thermal conductivity, making it an ideal functional filler for constructing oriented high thermal conductivity composite materials. However, carbon fiber has intrinsic electrical conductivity, which can easily cause short circuits when used in thermally conductive composite materials, limiting its safety.

[0003] To address the insulation problem of carbon fiber, materials such as polyimide and sol-gel ceramics are commonly used to insulate carbon fiber. However, conventional insulating coatings generally suffer from poor thermal conductivity, and high interfacial thermal resistance is easily formed between the coating and the fiber and matrix, which significantly weakens the overall thermal conductivity of the composite material.

[0004] Meanwhile, the anisotropic thermal conductivity of carbon fibers dictates that they must be oriented within the composite material to fully leverage their high axial thermal conductivity. Current mainstream orientation methods rely on high shear flow fields or strong magnetic field environments greater than 1 T. Among these, shear flow field orientation has low efficiency and is difficult to adapt to the needs of high-performance, low-cost large-scale production. On the other hand, carbon fibers have extremely low magnetic susceptibility, and magnetic field orientation methods suffer from low efficiency and excessive energy consumption, which also cannot meet the application requirements of large-scale industrial preparation. This greatly restricts the industrial development and high-performance application of high thermal conductivity carbon fiber composite materials.

[0005] Therefore, developing a technology that can simultaneously impart excellent insulation and efficient thermal conductivity to carbon fibers, and significantly improve their magnetic responsiveness to achieve low-field orientation, has become crucial for the application of carbon fibers. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a modified carbon fiber and its preparation method, as well as a thermally conductive composite material. The modified carbon fiber provided by the present invention has the advantages of high insulation, high thermal conductivity, and strong magnetic response, and can be efficiently oriented under low-intensity magnetic fields.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing modified carbon fiber, the method comprising:

[0009] S1. The surface of carbon fiber is coated with an insulating slurry containing polyimide precursor and aminated boron nitride nanosheets, and then thermally imidized and cured to obtain preliminarily modified carbon fiber.

[0010] S2. Under a magnetic field, a composite slurry containing magnetic anisotropic magnetic particles, boron nitride nanosheets, and curable resin is coated onto the surface of the preliminarily modified carbon fiber and then cured to obtain the modified carbon fiber.

[0011] In the preparation method provided by this invention, polyimide and aminated boron nitride nanosheets are first introduced onto the surface of carbon fibers. Polyimide can improve the thermal conductivity and insulation of carbon fibers, and it can react with aminated boron nitride nanosheets to enhance the cross-linking effect, so that a dense and tough insulating underlayer is formed on the surface of carbon fibers. Then, a functional layer with both magnetic response and thermal conductivity is introduced on the outside of the insulating layer. Coating under a magnetic field can make the magnetically anisotropic magnetic particles and carbon fibers align along the direction of the magnetic field, so that the modified carbon fibers form a chain-like ordered structure, giving the modified carbon fibers excellent magnetic anisotropy and magnetization, while the boron nitride nanosheets give the carbon fibers excellent thermal conductivity.

[0012] Therefore, the modified carbon fiber provided by this invention has the advantages of high insulation and high thermal conductivity, as well as excellent magnetic anisotropy and strong magnetic response. It can achieve efficient orientation under low-intensity magnetic field, thereby obtaining an anisotropic thermally conductive material with excellent performance.

[0013] Preferably, the preparation method further includes performing S1' before step S1 to activate the carbon fiber surface.

[0014] Preferably, the activation method includes any one or a combination of at least two of oxygen plasma treatment, air / gas phase oxidation, liquid phase oxidation, or electrochemical anodizing.

[0015] Preferably, the parameters of the oxygen plasma treatment include: O2 or an O2 / Ar mixture, a power of 50-300 W, such as 50 W, 100 W, 150 W, 200 W, 250 W, 300 W or any of the above values, a flow rate of 10-100 sccm, such as 10 sccm, 30 sccm, 50 sccm, 70 sccm, 90 sccm, 100 sccm or any of the above values, and a treatment time of 1-10 min, such as 1 min, 3 min, 5 min, 7 min, 9 min, 10 min or any of the above values.

[0016] Preferably, the liquid-phase oxidation method includes immersion in concentrated nitric acid (60-70 wt%, for example 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, or any range thereof), a nitric acid / sulfuric acid mixture, or a hydrogen peroxide solution at a temperature of 60-110°C, for example 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or any range thereof, for a time of 30-120 min, for example 30 min, 50 min, 70 min, 90 min, 110 min, 120 min, or any range thereof.

[0017] Preferably, the electrochemical anodizing method includes using carbon fiber as the anode, with the electrolyte selected from ammonium bicarbonate solution (pH≈8-9), dilute sulfuric acid solution (pH≈2-3), or phosphate buffer, and the current density being 5-50 mA / cm². 2 For example, 5mA / cm 2 10 mA / cm 2 20 mA / cm 2 30 mA / cm 2 40 mA / cm 2 50 mA / cm 2 Or any of the above values ​​within a range of 1-10 minutes, such as 1 minute, 3 minutes, 5 minutes, 7 minutes, 9 minutes, 10 minutes or any of the above values ​​within a range of 1-10 minutes.

[0018] This invention introduces active functional groups by activating the surface of carbon fibers. During subsequent insulation coating, these functional groups react with the effective components (such as aminated boron nitride nanosheets) in the insulating slurry, thereby forming a chemically cross-linked insulating layer on the outside of the carbon fibers. The insulating layer is tightly bonded to the carbon fibers, which avoids the generation of high interfacial thermal resistance.

[0019] Preferably, the polyimide precursor has a mass percentage content of 10-30 wt%, for example, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, or any of the above values, based on the total mass of the insulating slurry.

[0020] Preferably, based on the total mass of the insulating slurry (100%), the mass percentage of the aminated boron nitride nanosheets is 0.5-3 wt%, for example, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, or any of the above values.

[0021] Preferably, the solvent used in the insulating paste is N-methylpyrrolidone (NMP) or N,N-dimethylacetamide (DMAc).

[0022] Preferably, the thermal imidization curing method is a gradient temperature curing method, which preferably includes: first holding at 80-120℃ (e.g., 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃ or any of the above values) for 30-60 min (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or any of the above values), then raising the temperature to 200-260℃ (e.g., 200℃, 210℃, 220℃, 230℃, 250℃, 260℃ or any of the above values) and holding at that temperature for 30-60 min (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or any of the above values). (e.g., 280-350℃ or any of the above values), and then raise the temperature to 280-350℃ (e.g., 280℃, 290℃, 310℃, 320℃, 340℃, 350℃ or any of the above values) and hold for 30-60 minutes (e.g., 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or any of the above values).

[0023] Preferably, in step S1, the amount of insulating slurry applied causes the carbon fiber to gain weight by 3-20 wt%, for example, 3 wt%, 5 wt%, 10 wt%, 12 wt%, 15 wt%, 20 wt%, or any of the above values.

[0024] Preferably, based on the total mass of the composite slurry as 100%, the content of the magnetically anisotropic magnetic particles is 15-60%, for example, 15%, 20%, 30%, 40%, 50%, 60% or any of the above values, and the content of boron nitride nanosheets is 5-25%, for example, 5%, 10%, 15%, 18%, 20%, 25% or any of the above values.

[0025] Preferably, the magnetically anisotropic particles include any one or a combination of at least two of the following: iron oxide nanorods, cobalt nanorods, or barium ferrite nanosheets.

[0026] Preferably, the curable resin includes a flexible curable resin, and further includes any one or a combination of at least two of the following: polyurethane acrylate, epoxy acrylate, modified epoxy resin (preferably UV-curable or thermosetting), and flexible polyurethane prepolymer (preferably NCO-terminated / OH-terminated).

[0027] The curable resin described in this invention can be a light-curable resin or a thermosetting resin. This invention does not impose any specific limitations, and any curable flexible resin that can achieve the purpose of coating can be used in this invention.

[0028] The curable resin described in this invention is a photocurable resin. The curing method includes performing a photocuring reaction under a magnetic field to fix the orientation structure of the magnetic particles and hexagonal boron nitride nanosheets. This enables the formation of a magnetic thermally conductive coating layer on the surface of the carbon fiber, in which the magnetic particles are oriented axially. Since the easy magnetization axis of the magnetic thermally conductive coating layer is parallel to the fiber axis, it can impart strong magnetic anisotropy to the carbon fiber.

[0029] The curable resin described in this invention is a thermosetting resin. The curing method includes prepolymerization under a magnetic field to fix the orientation, and then polymerization to obtain a magnetically thermally conductive coating layer.

[0030] Preferably, the coating amount of the composite slurry is such that the preliminarily modified carbon fiber gains 8-40 wt%, for example, 8 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, 40 wt%, or any of the above values.

[0031] Preferably, the strength of the magnetic field is 0.05-0.8 T, such as 0.05 T, 0.1 T, 0.2 T, 0.3 T, 0.4 T, 0.5 T, 0.6 T, 0.7 T, 0.8 T, etc.

[0032] Preferably, the magnetic field is applied in the desired axial direction of the carbon fiber.

[0033] In this invention, the expected axial direction of the carbon fiber refers to the desired arrangement direction of the carbon fiber. By applying a magnetic field of a specific direction and intensity, this invention enables the carbon fiber and the magnetic particles attached to the surface of the carbon fiber to be arranged along the direction of the magnetic field (i.e., the axial direction of the carbon fiber) and connected end to end to form a chain-like orderly arrangement. At the same time, the hexagonal boron nitride nanosheets are also oriented along the direction of the magnetic field to a certain extent.

[0034] Preferably, the coating methods in step S1 and step S2 are both spraying.

[0035] The present invention employs ultrasonic coating for both coating processes, which enables the formation of an insulating coating layer and a magnetic and thermally conductive coating layer on the carbon fiber surface, thereby imparting excellent properties to the modified carbon fiber.

[0036] In a second aspect, the present invention provides a modified carbon fiber obtained by the preparation method described in the first aspect.

[0037] Thirdly, the present invention provides a thermally conductive composite material comprising the modified carbon fiber described in the second aspect.

[0038] Preferably, the thermally conductive composite material comprises a silicone rubber matrix, spherical thermally conductive fillers, and modified carbon fibers.

[0039] Preferably, based on the total mass of the thermally conductive composite material as 100%, the content of the modified carbon fiber is 5-10 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any of the above values.

[0040] Preferably, the length of the modified carbon fiber is 50-300 μm, for example, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm or any of the above values.

[0041] Preferably, based on the total mass of the thermally conductive composite material as 100%, the content of the spherical thermally conductive filler is 55-70 wt%, for example, 55 wt%, 58 wt%, 60 wt%, 65 wt%, 68 wt%, 70 wt%, or any of the above values.

[0042] Fourthly, the present invention provides a method for preparing the thermally conductive composite material described in the third aspect, the method comprising:

[0043] A slurry is prepared by mixing a silicone rubber matrix, spherical thermally conductive filler and modified carbon fiber. The slurry is then allowed to stand and solidify under a magnetic field to obtain the thermally conductive composite material.

[0044] Preferably, the settling time is 1-10 min, such as 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0045] Preferably, the strength of the magnetic field is 0.1-0.5 T, such as 0.1 T, 0.2 T, 0.3 T, 0.4 T, 0.5 T, etc.

[0046] In the preparation method described above, under the action of a magnetic field, the magnetically anisotropic magnetic particles included in the modified carbon fiber will generate a large magnetic moment. The carbon fiber is subjected to sufficient magnetic torque, causing it to rotate and align in the direction of the magnetic field. Therefore, by introducing the modified carbon fiber into the thermally conductive composite material, the present invention enables the preparation of a thermally conductive composite material with highly oriented carbon fiber under a relatively low uniform magnetic field. At the same time, the boron nitride nanosheets included in the modified carbon fiber and the carbon fiber together construct a highly efficient three-dimensional thermally conductive network structure.

[0047] Fifthly, the present invention provides the application of the modified carbon fiber described in the second aspect or the thermally conductive composite material described in the third aspect in thermally conductive pads.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The modified carbon fiber provided by the present invention has the advantages of high insulation and high thermal conductivity, as well as excellent magnetic anisotropy and strong magnetic response, and can achieve efficient orientation under low intensity magnetic field.

[0050] (2) The modified carbon fiber provided by the present invention forms strong chemical bonds with both the insulating layer and the functional layer which has both magnetic and thermal conductivity, thus having long-term reliability.

[0051] (3) The preparation method provided by the present invention is simple and easy to implement. It only requires coating treatment to simultaneously achieve high insulation, high thermal conductivity and strong magnetic responsiveness of carbon fiber.

[0052] (4) The thermally conductive composite material provided by the present invention has excellent insulation strength and ultra-high axial thermal conductivity, wherein the insulation strength is ≥10 kV / mm and the directional thermal conductivity is ≥60 W / (m·K);

[0053] (5) The thermally conductive composite material containing the modified carbon fiber described in this invention can achieve an orientation degree of more than 95% under weak magnetic conditions of ≤0.5T, which greatly reduces the energy consumption and equipment cost of the orientation process and provides conditions for industrial production. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Unless otherwise specified, the raw materials involved in the following specific embodiments of the present invention are all conventional materials in the art, and can be purchased from commercially available products. Some raw material information is as follows:

[0056] Carbon fiber: Purchased from Toray Industries, Japan, model Torayca T300 (PAN-based carbon fiber tow, single filament diameter approximately 7 μm);

[0057] Polyimide precursor (polyamic acid PAA solution): purchased from Mingshi New Materials Co., Ltd., trade name PAE-8060S / PAA-15 series (solid content approximately 15-16 wt% in NMP).

[0058] Aminated boron nitride nanosheets: purchased from Xi'an Ruixi Biotechnology Co., Ltd., brand name BNNS-95;

[0059] Hexagonal boron nitride nanosheets (BNNS): purchased from Xi'an Ruixi Biotechnology Co., Ltd. (sheet diameter 100-500 nm, thickness 3-10 layers, purity ≥98%).

[0060] Iron oxide nanorods: purchased from Changsha Yimo Biotechnology Co., Ltd. (diameter 20-80 nm, length 100-500 nm, aspect ratio 3:1-10:1).

[0061] Polyurethane acrylate (PUA): Purchased from Sartomer (Arkema), model CN968 (hexafunctional aliphatic polyurethane acrylate, 100% solids content).

[0062] Spherical thermally conductive filler: purchased from Ya'an Baitu High-tech Materials Co., Ltd., grade HNA-5 spherical alumina micro powder;

[0063] Silicone rubber matrix: purchased from Dow Inc., trade name SYLGARD 184 Silicone Elastomer Kit.

[0064] Example 1

[0065] This embodiment provides a method for preparing modified carbon fiber and thermally conductive composite materials, as follows:

[0066] S1. Carbon fibers are treated with oxygen plasma at an O2 / Ar ratio of 80 / 20 sccm, a power of 150 W, and a duration of 3 min.

[0067] S2. Hyperbranched polyimide precursor (20 wt%) and amino-modified boron nitride nanosheets (1.5 wt%) were dispersed in NMP to obtain an insulating slurry. The insulating slurry was ultrasonically sprayed onto the surface of carbon fibers with a spraying amount that increased the weight of the carbon fibers by 10 wt%. Then, a gradient temperature curing method was used: first, the temperature was raised to 80℃ for 60 min, then raised to 220℃ for 60 min, and finally raised to 300℃ for 60 min to form an insulating underlayer, thus obtaining the preliminary modified carbon fibers.

[0068] S3. Iron oxide nanorods, hexagonal boron nitride nanosheets, and polyurethane acrylate were mixed in a mass ratio of 35:12:53 to obtain a composite slurry. Under a magnetic field of 0.5 T, the composite slurry was ultrasonically sprayed onto the surface of carbon fibers. The spraying amount was sufficient to increase the weight of the initially modified carbon fibers by 20 wt%, and the coating was applied at 365 nm with a light intensity of 100 mW / cm². 2 The modified carbon fiber was obtained by curing under a magnetic field for 3 minutes.

[0069] S4. Shorten the modified carbon fiber (150 μm), and mix it with the following contents: modified carbon fiber content is 8 wt%, spherical thermally conductive filler content is 67 wt%, and silicone rubber matrix content is 25 wt% to obtain a mixed slurry;

[0070] S5. The mixed slurry is left to stand in a uniform magnetic field of 0.3 T for 3 min to orient the modified carbon fibers, and then cured at 100℃ for 45 min to obtain a thermally conductive composite material.

[0071] Examples 2-5

[0072] This embodiment provides a method for preparing modified carbon fiber and thermally conductive composite materials.

[0073] The difference from Example 1 is that, in this example, by controlling the amount of insulating slurry sprayed in step S2, the carbon fiber weight increases by 3 wt% (Example 2), 20 wt% (Example 3), 1 wt% (Example 4), and 25 wt% (Example 5).

[0074] Examples 6-9

[0075] This embodiment provides a method for preparing modified carbon fiber and thermally conductive composite materials.

[0076] The difference from Example 1 is that, in this example, by controlling the amount of composite slurry sprayed in step S3, the weight gain of the initially modified carbon fiber is increased by 8 wt% (Example 6), 40 wt% (Example 7), 5 wt% (Example 8), and 50 wt% (Example 9).

[0077] Example 10

[0078] This embodiment provides a method for preparing modified carbon fiber and thermally conductive composite materials, as follows:

[0079] S1. Carbon fibers were soaked in hydrogen peroxide solution at 60°C for 60 min;

[0080] S2. Hyperbranched polyimide precursor (10 wt%) and amino boron nitride nanosheets (0.5 wt%) were dispersed in NMP to obtain an insulating slurry. The insulating slurry was ultrasonically sprayed onto the surface of carbon fibers, with a spraying amount that increased the weight of the carbon fibers by 10 wt%. Then, a gradient temperature curing method was used: first, the temperature was raised to 120℃ and held for 30 min, then raised to 200℃ and held for 60 min, and finally raised to 280℃ and held for 60 min to form an insulating underlayer, thus obtaining the preliminary modified carbon fibers.

[0081] S3. Iron oxide nanorods, hexagonal boron nitride nanosheets, and polyurethane acrylate were mixed in a mass ratio of 55:5:40 to obtain a composite slurry. Under a magnetic field of 0.1 T, the composite slurry was ultrasonically sprayed onto the surface of carbon fibers. The spraying amount was sufficient to increase the weight of the initially modified carbon fibers by 20 wt%, and the coating was applied at 365 nm with a light intensity of 100 mW / cm². 2 The modified carbon fiber was obtained by curing under a magnetic field for 3 minutes.

[0082] S4. Shorten the modified carbon fiber (300 μm), and mix it with the following contents: modified carbon fiber content is 5 wt%, spherical thermally conductive filler content is 70 wt%, and silicone rubber matrix content is 25 wt% to obtain a mixed slurry;

[0083] S5. The mixed slurry is left to stand in a uniform magnetic field of 0.1 T for 2 min to orient the modified carbon fibers, and then cured at 100℃ for 45 min to obtain a thermally conductive composite material.

[0084] Example 11

[0085] This embodiment provides a method for preparing modified carbon fiber and thermally conductive composite materials, as follows:

[0086] S1. Carbon fibers are treated with oxygen plasma at an O2 / Ar ratio of 80 / 20 sccm, a power of 150 W, and a time of 5 min.

[0087] S2. Hyperbranched polyimide precursor (30 wt%) and amino boron nitride nanosheets (3 wt%) were dispersed in NMP to obtain an insulating slurry. The insulating slurry was ultrasonically sprayed onto the surface of carbon fibers, with a spraying amount that increased the weight of the carbon fibers by 10 wt%. Then, a gradient temperature curing method was used: first, the temperature was raised to 100℃ and held for 40 min, then raised to 260℃ and held for 30 min, and finally raised to 350℃ and held for 30 min to form an insulating underlayer, thus obtaining the preliminary modified carbon fibers.

[0088] S3. Iron oxide nanorods, hexagonal boron nitride nanosheets, and polyurethane acrylate were mixed in a mass ratio of 15:25:60 to obtain a composite slurry. Under a magnetic field of 0.8 T, the composite slurry was ultrasonically sprayed onto the surface of carbon fibers. The spraying amount was sufficient to increase the weight of the initially modified carbon fibers by 20 wt%, and the coating was applied at 365 nm with a light intensity of 100 mW / cm². 2 The modified carbon fiber was obtained by curing under a magnetic field for 3 minutes.

[0089] S4. Shorten the modified carbon fiber (50 μm), and mix it with the following contents: modified carbon fiber content is 10 wt%, spherical thermally conductive filler content is 55 wt%, and silicone rubber matrix content is 35 wt% to obtain a mixed slurry;

[0090] S5. The mixed slurry is left to stand in a uniform magnetic field of 0.5 T for 10 min to orient the modified carbon fibers, and then cured at 100℃ for 45 min to obtain a thermally conductive composite material.

[0091] Comparative Example 1

[0092] This comparative example provides a thermally conductive composite material.

[0093] The difference from Example 1 is that in this comparative example, step S4 is performed directly: short-cut (150 μm) carbon fibers are mixed with silicone rubber and then left to stand and cure under a 2 T magnetic field.

[0094] Comparative Example 2

[0095] This comparative example provides a thermally conductive composite material.

[0096] The difference from Example 1 is that step S3 is not performed in this comparative example, and the magnetic field strength in step S4 is 2T.

[0097] Comparative Example 3

[0098] This comparative example provides a thermally conductive composite material.

[0099] The difference from Example 1 is that step S2 is not performed in this comparative example.

[0100] Comparative Example 4

[0101] This comparative example provides a thermally conductive composite material.

[0102] The difference from Example 1 is that, in this comparative example, no aminated boron nitride nanosheets are added to the insulating paste in step S2.

[0103] Comparative Example 5

[0104] This comparative example provides a thermally conductive composite material.

[0105] The difference from Example 1 is that, in this comparative example, no magnetically anisotropic magnetic particles are added to the composite slurry in step S3.

[0106] Performance testing

[0107] The performance of the thermally conductive composite materials provided in the examples and comparative examples was tested using the following methods:

[0108] (1) Carbon fiber orientation: Take micrographs of the cross section or sample surface after curing, and count the distribution of the angle θ between the long axis of the fiber and the magnetic field direction. At least 200 fibers are counted.

[0109] (2) Vertical thermal conductivity: Three samples with thicknesses of 1 / 2 / 3 mm were used and measured according to ASTM D5470 (steady-state heat flow method).

[0110] (3) Insulation strength: Tested according to ASTM D149. The sample is a disc (25 mm in diameter), the electrode system is Ø20 mm ball-plate, the voltage rise rate is 0.5 kV / s, and the average value of 5 samples in each group is taken.

[0111] The test results are as follows:

[0112] Table 1

[0113]

[0114] As can be seen from the examples and performance tests, the carbon fibers in the thermally conductive composite material provided by the present invention have excellent orientation and insulation strength, as well as ultra-high axial thermal conductivity, wherein the insulation strength is ≥10 kV / mm and the directional thermal conductivity is ≥60 W / (m·K).

[0115] As can be seen from the comparison of Examples 1-9, by limiting the amount of insulating slurry and composite slurry introduced onto the carbon fiber surface, the present invention enables the modified carbon fiber to have both excellent orientation and insulation strength when applied to thermally conductive composite materials.

[0116] As can be seen from the comparison of Example 1 and Comparative Examples 1-3, the present invention enables carbon fibers to be oriented under a lower magnetic field and has better insulation performance by introducing an insulating bottom layer and a magnetic response-thermal conduction functional layer.

[0117] As can be seen from the comparison of Example 1 and Comparative Examples 4-5, the components of the insulating bottom layer and the components of the magnetic response-thermal conductive functional layer defined in this invention are indispensable.

[0118] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing modified carbon fiber, characterized in that, The preparation method includes: S1. The surface of carbon fiber is coated with an insulating slurry containing polyimide precursor and aminated boron nitride nanosheets, and then thermally imidized and cured to obtain preliminarily modified carbon fiber. S2. Under a magnetic field, a composite slurry containing magnetic anisotropic magnetic particles, boron nitride nanosheets, and curable resin is coated onto the surface of the preliminarily modified carbon fiber and then cured to obtain the modified carbon fiber.

2. The preparation method according to claim 1, characterized in that, The preparation method further includes performing S1' before step S1 to activate the carbon fiber surface; Preferably, the activation method includes any one or a combination of at least two of plasma treatment, air / gas phase oxidation, liquid phase oxidation, or electrochemical anodizing.

3. The preparation method according to claim 1 or 2, characterized in that, In the insulating slurry, the polyimide precursor has a mass percentage content of 10-30 wt%. And / or, in the insulating slurry, the mass percentage of the aminated boron nitride nanosheets is 0.5-3 wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, The thermal imidization curing method is a gradient temperature curing method, which preferably includes: first holding at 80-120℃ for 30-60 min, then raising the temperature to 200-260℃ and holding for 30-60 min, and finally raising the temperature to 280-350℃ and holding for 30-60 min. And / or, in step S1, the amount of insulating slurry applied causes the carbon fiber to gain 3-20 wt% weight.

5. The preparation method according to any one of claims 1-4, characterized in that, Based on the total mass of the composite slurry as 100%, the content of the magnetically anisotropic magnetic particles is 15-60%, and the content of boron nitride nanosheets is 5-25%. And / or, the magnetically anisotropic magnetic particles include any one or a combination of at least two of the following: iron oxide nanorods, cobalt nanorods, or barium ferrite nanosheets; And / or, the curable resin includes a flexible curable resin, further including any one or a combination of at least two of polyurethane acrylate, epoxy acrylate, modified epoxy resin or flexible polyurethane prepolymer. And / or, in step S2, the amount of the composite slurry applied causes the pre-modified carbon fiber to gain 8-40 wt% weight.

6. The preparation method according to any one of claims 1-5, characterized in that, The strength of the magnetic field is 0.05-0.8T; And / or, the magnetic field is applied in the desired axial direction of the carbon fiber; And / or, the coating methods described in step S1 and step S2 are both spraying.

7. A modified carbon fiber obtained by the preparation method according to any one of claims 1-6.

8. A thermally conductive composite material, characterized in that, Including the modified carbon fiber as described in claim 7; Preferably, the thermally conductive composite material comprises silicone rubber, spherical thermally conductive filler, and modified carbon fiber; Preferably, the modified carbon fiber content is 5-10 wt% based on the total mass of the thermally conductive composite material (100%). Preferably, the length of the modified carbon fiber is 50-300 μm.

9. A method for preparing the thermally conductive composite material as described in claim 8, characterized in that, The preparation method includes: A slurry is prepared by mixing a silicone rubber matrix, spherical thermally conductive filler and modified carbon fiber. The slurry is then allowed to stand and solidify under a magnetic field to obtain the thermally conductive composite material. Preferably, the strength of the magnetic field is 0.1-0.5 T.

10. The application of the modified carbon fiber of claim 7 or the thermally conductive composite material of claim 8 in thermally conductive pads.

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