A carbon fiber oriented skeleton and a heat conducting composite material prepared therefrom

Abstract

The application provides a carbon fiber directional skeleton and a prepared heat-conducting composite material, and relates to the technical field of advanced functional materials.The application first provides a carbon fiber / phenolic resin preform, uses the preform to prepare the carbon fiber directional skeleton, and further prepares the heat-conducting composite material.The preparation of the carbon fiber directional skeleton is not affected by the viscosity of the base material; meanwhile, the magnetic field strength used in the application is low, and the material preparation process is not limited by expensive superconducting magnet equipment and low-viscosity polymer base, so that the universality is very strong.The carbon fiber directional skeleton is used to prepare the heat-conducting composite material with carbon fiber directional arrangement, and the heat-conducting composite material has excellent vertical heat-conducting performance or in-plane heat-conducting performance, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of advanced functional materials, and particularly relates to a carbon fiber directional skeleton and a prepared heat-conducting composite material. BACKGROUND

[0002] With the miniaturization, integration and energy consumption of electronic devices, the heat generated by the electronic devices gradually increases. If the heat cannot be dissipated in time, it will seriously affect the performance and service life of the electronic devices. Therefore, a heat management system composed of a heat sink and a thermal interface material is usually arranged in the electronic device to promote heat dissipation. However, the increase in the heat generated by the electronic devices has higher requirements for the heat management system. At present, most of the commercialized thermal interface materials are prepared by blending polymers and heat-conducting fillers. Since the heat-conducting fillers are randomly distributed, they cannot form efficient heat-conducting channels, and the thermal conductivity is less than 10 W / mK, so it is difficult to meet the increasing heat dissipation demand.

[0003] Compared with the traditional blending process, the directional arrangement of the fillers not only can play the heat-conducting performance of the one-dimensional and two-dimensional heat-conducting fillers in the advantageous direction, but also is beneficial to the mutual lapping of the fillers to form heat-conducting channels, thereby greatly improving the thermal conductivity in the orientation direction. The mesophase pitch-based carbon fiber as a one-dimensional heat-conducting filler has excellent axial heat-conducting performance, so how to arrange and orient the axial direction of the mesophase pitch-based carbon fiber along the required heat-conducting direction is the key to utilizing the axial high heat-conducting performance and designing the carbon fiber heat-conducting composite material. Since the mesophase pitch-based carbon fiber has anisotropic magnetic resistance, the fiber can be deflected under the action of a magnetic field, and is turned from a high-energy state to a low-energy state until the fiber axis is parallel to the magnetic induction line. Therefore, without the modification of magnetic particles, the fiber can be arranged and oriented under the action of a magnetic field. The patent application with the publication number CN101087511A of Hozumi Science and Technology Co., Ltd. discloses a method for preparing a heat-conducting sheet by using a magnetic field and vibration to arrange and orient the carbon fiber along the magnetic induction line direction in a polymer matrix. However, the arrangement and orientation effect of the carbon fiber is limited by the magnetic strength, the viscosity of the polymer matrix and the filler content. In order to achieve good arrangement and orientation effect, the patent requires that the viscosity of the matrix material at 25℃ is less than 1000 mPa·s, so the method has small applicability and is not suitable for high-viscosity and high-filler-content systems. The patent application with the publication number CN100366676C discloses a composite material with directional arrangement of reinforcing bodies. The composite material includes a filler reinforcing body (such as graphite powder, nanometer carbon tube or continuous or short-cut fiber body thereof, such as carbon fiber) with magnetic field response and a resin (thermosetting resin, phenolic resin is a thermosetting resin) and an additive, and after mixing to form a dispersion system, an external magnetic field (with a strength of 0.1-10T) is applied. With the curing of the resin system, the reinforcing bodies are arranged and oriented, but the method is to disperse the reinforcing bodies in the liquid resin, and the orientation structure is fixed by the resin curing after the magnetic field orientation, so the method is also not suitable for high-viscosity materials and has poor universality.

[0004] For high viscosity matrix material, in order to achieve the effect of filler reinforcement (such as carbon fiber) directional arrangement, it is often necessary to use high strength magnetic field (more than 5T) generated by superconducting magnet, but it is difficult in practical application. How to find a method to realize the directional arrangement of filler reinforcement (such as carbon fiber) in high viscosity matrix material in low magnetic field strength needs further study. SUMMARY

[0005] The main technical problem faced by the present application is that it is difficult to make carbon fibers directional arrangement in high viscosity system to prepare high thermal conductivity composite materials in low magnetic field strength. In view of the problems existing in the prior art, the purpose of the present application is to provide a carbon fiber directional skeleton and a thermal conductive composite material prepared therefrom.

[0006] The present application provides a carbon fiber / phenolic resin preform, which is obtained by placing a dispersion liquid containing carbon fibers and phenolic resin in a magnetic field, and then making the solvent of the dispersion liquid volatilize after the carbon fibers are directional distributed along the magnetic induction line under the action of the magnetic field.

[0007] Further,

[0008] The mass ratio of the phenolic resin to the carbon fibers in the dispersion liquid is 0.05-0.8;

[0009] And / or, the mass ratio of the carbon fibers to the solvent is 0.01-0.15;

[0010] Preferably, the mass ratio of the phenolic resin to the carbon fibers in the dispersion liquid is 0.06-0.5;

[0011] And / or, the mass ratio of the carbon fibers to the solvent is 0.03-0.1.

[0012] More preferably,

[0013] The mass ratio of the phenolic resin to the carbon fibers in the dispersion liquid is 0.2;

[0014] And / or, the mass ratio of the carbon fibers to the solvent is 0.05.

[0015] Further,

[0016] The carbon fibers are mesophase pitch-based carbon fibers;

[0017] And / or, the phenolic resin is a thermosetting phenolic resin or a modified product thereof;

[0018] And / or, the solvent of the dispersion liquid is a volatile organic solvent;

[0019] And / or, the strength of the magnetic field is 0.2-1T;

[0020] And / or, the liquid level height of the dispersion liquid is 2-30mm;

[0021] Preferably,

[0022] The thermal conductivity of the carbon fiber is greater than 600 W / mK; and / or, the length of the carbon fiber is 0.1-3 mm;

[0023] And / or, the dispersion solvent is one or more of methanol, ethanol, ethylene glycol, dichloromethane, acetone and tetrahydrofuran;

[0024] And / or, the magnetic field is a parallel magnetic field, parallel or perpendicular to the dispersion liquid surface;

[0025] And / or, the strength of the magnetic field is 0.25-1T;

[0026] And / or, the height of the dispersion liquid surface is 10 mm.

[0027] Preferably, the strength of the magnetic field is 0.35T.

[0028] The present application also provides a preparation method of the aforementioned carbon fiber / phenolic resin preform, which comprises the following steps:

[0029] (1) Dissolve the phenolic resin in a solvent, add carbon fibers, and uniformly disperse the carbon fibers to form a carbon fiber dispersion liquid;

[0030] (2) Place the carbon fiber dispersion liquid in a parallel magnetic field environment, so that the carbon fibers are deflected during the settling process and are distributed in a direction along the magnetic induction direction;

[0031] (3) Apply vibration to the carbon fiber dispersion liquid, and naturally dry to volatilize the solvent, thereby obtaining a carbon fiber / phenolic resin preform;

[0032] Preferably, in step (3), the amplitude of the vibration is 0.3-3 mm, the frequency is 20-50 Hz, and the time is 0.5-2 min.

[0033] The present application also provides a carbon fiber directional skeleton, which is obtained by sequentially subjecting the aforementioned carbon fiber / phenolic resin preform to curing, carbonization and graphitization treatment;

[0034] Preferably, the curing temperature is 150-200℃, and the time is 1-5h; and / or, the carbonization temperature is 600-1200℃, and the time is 0.5-3h; and / or, the graphitization temperature is 2800-3000℃, and the time is 0.5-3h.

[0035] The present application also provides the use of the aforementioned carbon fiber directional skeleton in the preparation of a thermal conductive composite material.

[0036] The present invention also provides a thermally conductive composite material, which is prepared from the following raw materials in the following weight ratio: 40-80 parts of a polymer fluid composition and 20-60 parts of the aforementioned carbon fiber oriented skeleton; wherein the polymer fluid composition is composed of a polymer matrix, a solvent and a thermally conductive filler;

[0037] Preferably, in the polymer fluid composition, the polymer matrix accounts for 30-100 wt% by mass, the solvent accounts for 0-70 wt% by mass, and the thermally conductive filler accounts for 0-40 wt% by mass.

[0038] And / or, the viscosity of the polymer fluid composition is less than 20,000 mPa·s.

[0039] Furthermore, the polymer matrix is ​​a thermoplastic polymer or a thermosetting polymer;

[0040] And / or, the solvent is a good solvent for the polymer matrix;

[0041] And / or, the thermally conductive filler is one or more of graphite, graphene, carbon nanotubes, diamond, boron nitride, alumina, aluminum nitride, silicon carbide, silver powder, and copper powder;

[0042] Preferably,

[0043] The thermoplastic polymer material is an olefin polymer, polyvinyl acetate, polyvinyl alcohol, polyethylene glycol, polyvinyl chloride, polystyrene, polymethacrylate polymer, polyacrylic acid polymer, polycarbonate, or polyamide polymer;

[0044] And / or, the thermosetting polymer material is cross-linked rubber, epoxy resin, phenolic resin, unsaturated polyester resin, or polyimide resin;

[0045] And / or, the solvent is water, aliphatic hydrocarbons, aromatic hydrocarbons, ester-cyclic hydrocarbons, halogenated hydrocarbons, alcohols, esters, ethers, ketones, amides, or sulfoxide solvents;

[0046] And / or, the size of the thermally conductive filler is ≤50μm;

[0047] More preferably,

[0048] The olefin polymer is a copolymer of polyethylene, polypropylene, polyvinyl alcohol, and ethylene propylene;

[0049] And / or, the crosslinked rubber is natural rubber, acrylic rubber, polybutadiene rubber, nitrile rubber, butyl rubber, EPDM rubber, polyurethane rubber, fluororubber, and silicone rubber.

[0050] The present invention also provides a method for preparing the aforementioned thermally conductive composite material, which includes the following steps:

[0051] The polymer fluid composition is cast into the aforementioned carbon fiber oriented skeleton, vacuum degassing, curing, surface polishing treatment, to obtain a thermal conductive composite material;

[0052] Preferably, the curing method is chemical crosslinking, solvent evaporation or cooling solidification.

[0053] The application also provides the use of the aforementioned thermal conductive composite material in the preparation of a thermal conductive device.

[0054] Preferably, the thermal conductive composite material has excellent vertical or in-plane thermal conductivity and can be used as a thermal interface material to reduce the contact thermal resistance between electronic devices and heat sinks, or as a high thermal conductive device substrate or shell to promote internal heat dissipation to the external environment.

[0055] Compared with the prior art, the application has the following beneficial effects:

[0056] The application first dissolves the resin used for pre-forming in a volatile solvent to obtain a low-viscosity resin solution, then disperses carbon fibers in the solution to form a carbon fiber dispersion, places the dispersion in a parallel magnetic field, and arranges the carbon fibers in a low magnetic field to prepare a carbon fiber oriented skeleton. Since the viscosity of the dispersion is low, the carbon fibers can be arranged in a low magnetic field, and the obtained carbon fiber oriented skeleton has a permeable pore structure, so that the polymer can be impregnated into the interior of the skeleton in the form of a melt or a solution to form a thermal conductive composite material. Therefore, the material preparation process is no longer limited by expensive superconducting magnet equipment and low-viscosity polymer matrix. It can be seen that the application has very strong universality. The carbon fiber oriented skeleton and the polymer fluid prepared by the application can make full use of the high axial thermal conductivity of the carbon fibers, build an efficient thermal conductive path, and greatly improve the thermal conductivity of the material in the direction of the arranged carbon fibers. In addition, when the polymer fluid cast in the carbon fiber oriented skeleton contains additional thermal conductive fillers, a three-dimensional thermal conductive network can be formed by the mutual lapping of the carbon fibers and the fillers, further improving the thermal conductivity. The thermal conductive composite material prepared by the application has excellent vertical or in-plane thermal conductivity and has excellent application prospects.

[0057] Obviously, according to the above content of the application, according to the ordinary technical knowledge and common means in the art, other various forms of modifications, replacements or changes can be made without departing from the above technical ideas of the application.

[0058] The above content of the application will be further described in detail through the following embodiment. However, it should not be understood that the above subject matter of the application is limited to the following examples. Any technology achieved based on the above content of the application belongs to the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 Actual microphotograph of carbon fiber oriented skeleton prepared in the present application (Example 1).

[0060] Figure 2 Scanning electron microscope photograph of carbon fiber oriented skeleton prepared in the present application (Example 1).

[0061] Figure 3 Scanning electron microscope photograph of heat conductive composite prepared in the present application (Example 1).

[0062] Figure 4 Scanning electron microscope photograph of carbon fiber three-dimensional skeleton (Comparative Example 1). DETAILED DESCRIPTION

[0063] The heat conductive composite of the present embodiment is prepared from carbon fiber oriented skeleton and polymer fluid composition. The raw materials and equipment used are known products, which are obtained by purchasing commercially available products.

[0064] In the present embodiment, the phenolic resin is thermosetting phenolic resin or its modified product. In order to ensure the overall strength of the carbon fiber oriented skeleton, reduce the viscosity of the carbon fiber dispersion liquid and the volume fraction of the carbonized product of the phenolic resin in the skeleton, the addition amount of the phenolic resin is preferably 0.05-0.8 times the mass of the carbon fiber, more preferably 0.06-0.5 times the mass of the carbon fiber.

[0065] In the present embodiment, the solvent of the carbon fiber dispersion liquid is one or more of methanol, ethanol, ethylene glycol, dichloromethane, acetone and tetrahydrofuran.

[0066] In the present embodiment, the carbon fiber is mesophase pitch-based carbon fiber. The carbon fiber is arranged in an oriented manner to form the heat conduction path of the heat conductive composite, and the thermal conductivity coefficient of the carbon fiber is preferably greater than 600 W / mK, more preferably greater than 800 W / mK, considering the high heat conduction performance of the heat conductive composite. The carbon fiber in the dispersion liquid is deflected and oriented under the action of the magnetic field during the sedimentation process. In order to ensure that the deflection process of the carbon fiber is not disturbed by spatial factors, the length of the carbon fiber is preferably 0.1-3 mm, and the addition amount is preferably 0.01-0.15 times the mass of the dispersion liquid.

[0067] In the present embodiment, the magnet is a permanent magnet or an electromagnet. In order to ensure the rapid orientation of the carbon fiber in the dispersion liquid, the strength of the parallel magnetic field generated is preferably 0.2-1 T.

[0068] In the present embodiment, the non-magnetic vessel bottom surface is in the parallel magnetic field range. To ensure that the carbon fibers have enough time to deflect during the settling process, while reducing the time consumption of the carbon fiber dispersion liquid during the drying process, the liquid level of the carbon fiber dispersion liquid in the vessel is preferably 2-30 mm.

[0069] In the present embodiment, the carbon fiber oriented skeleton is prepared by curing, high-temperature carbonization and graphitization of the carbon fiber / phenolic resin preform, and the carbon fibers are connected by the carbonization product of the phenolic resin. To ensure complete curing of the phenolic resin, the curing temperature is preferably 150-200°C, and the processing time is preferably 1-5h. To ensure that the phenolic resin can fully degrade and carbonize, reducing its volume fraction in the skeleton, the carbonization temperature is preferably 600-1200°C, and the processing time is preferably 0.5-3h. Since the carbonization of the phenolic resin produces amorphous carbon with low thermal conductivity, graphitization treatment is needed to further improve the thermal conductivity, with a graphitization temperature of 2800-3000°C and a processing time of 0.5-3h.

[0070] In the present embodiment, the polymer fluid composition comprises a polymer matrix, a solvent and a thermally conductive filler, wherein the polymer matrix accounts for 30-100wt%, the solvent accounts for 0-70wt%, and the thermally conductive filler accounts for 0-40wt%, and the viscosity of the polymer fluid composition is less than 20000mPa·s.

[0071] In the present embodiment, the polymer matrix is a thermoplastic polymer material or a thermosetting polymer material. As specific examples of thermoplastic polymer materials, there are olefin-based polymers such as polyethylene, polypropylene, polyvinyl alcohol, ethylene-propylene copolymer, polyvinyl acetate, polyvinyl alcohol, polyethylene glycol, polyvinyl chloride, polystyrene, polymethacrylate, polyacrylic acid, polycarbonate, and polyamide.

[0072] As specific examples of thermosetting polymer materials, there are cross-linked rubber, epoxy resin, phenolic resin, unsaturated polyester resin, and polyimide resin. As specific examples of cross-linked rubber, there are natural rubber, acrylic rubber, polybutadiene rubber, nitrile rubber, butyl rubber, ethylene-propylene-diene rubber, polyurethane rubber, fluororubber, and silicone rubber.

[0073] In the present embodiment, the solvent is a good solvent for the polymer matrix, and is selected according to the type of polymer matrix. As specific examples of solvents, there are water, aliphatic hydrocarbons, aromatic hydrocarbons, ester cyclic hydrocarbons, halogenated hydrocarbons, alcohols, esters, ethers, ketones, amides, and sulfoxides.

[0074] In the embodiment, the heat-conductive filler is one or more of graphite, graphene, carbon nanotube, diamond, boron nitride, aluminum oxide, aluminum nitride, silicon carbide, silver powder and copper powder, and the size of the heat-conductive filler is less than or equal to 50 μm.

[0075] In the embodiment, the solidification mode includes chemical cross-linking, solvent evaporation and cooling solidification, and is selected according to the type of the polymer fluid composition.

[0076] The following examples and comparative examples are listed to further illustrate the above embodiments.

[0077] Example 1: Carbon fiber oriented skeleton and preparation of heat-conductive composite material thereof

[0078] In the first step, 0.15 g of phenolic resin (thermosetting resol resin, solid, weight average molecular weight of about 500) is dissolved in 15 g of ethanol, and then 0.75 g of mesophase pitch-based carbon fiber is dispersed in the solution and stirred uniformly to form a carbon fiber dispersion (the viscosity of the dispersion is about 1.5 mPa·s), wherein the length of the carbon fiber is 0.25 mm and the thermal conductivity is 900 W / mK.

[0079] In the second step, the carbon fiber dispersion is poured into a non-magnetic container, and the container is immediately transferred to a 0.35 T parallel magnetic field formed by two neodymium-iron-boron permanent magnets. The two permanent magnets are arranged vertically so that the magnetic induction line is perpendicular to the bottom surface of the container. The liquid level of the carbon fiber dispersion in the container is 10 mm. During the settling process, the fibers are deflected and oriented along the magnetic induction line and then vertically settled to the bottom of the container.

[0080] In the third step, in the magnetic field, after the carbon fibers in the dispersion are deflected and settled to the bottom, a vibration with an amplitude of 0.5 mm and a frequency of 30 Hz is applied to the dispersion for 1 min to make the distribution of the carbon fibers more uniform and the stacking more compact. Then the vibration is turned off and the dispersion is naturally dried at room temperature. After the solvent is evaporated, a carbon fiber / phenolic resin preform is obtained. After the resin is precipitated, the carbon fibers are bonded and the orientation structure of the carbon fibers is fixed.

[0081] In the fourth step, the carbon fiber / phenolic resin preform is placed in an oven at 180°C for 5 h, and then carbonization at 1000°C for 1 h and graphitization at 2800°C for 1 h are carried out in an argon atmosphere. After the treatment, a carbon fiber oriented skeleton is obtained.

[0082] In the fifth step, a polymer fluid composition is prepared by mixing liquid silicone rubber and ethyl acetate at a mass ratio of 10:1. Then the polymer fluid composition is casted into the carbon fiber oriented skeleton, and the liquid level of the casting is flush with the height of the carbon fiber oriented skeleton. After vacuum degassing at room temperature for 4 h, curing at 80°C for 6 h and surface polishing treatment, a heat-conductive composite material is obtained.

[0083] The real micro-distance photos and scanning electron microscope photos of the carbon fiber directional skeleton prepared in this example are shown in Figure 1 and 2 The scanning electron microscope photos of the heat-conducting composite material are shown in Figure 3 .

[0084] Example 2, the carbon fiber directional skeleton of the present application and the heat-conducting composite material prepared therefrom

[0085] The up-and-down arrangement of the neodymium-iron-boron permanent magnet in the second step of Example 1 is changed to left-and-right arrangement. After the change, the magnetic induction lines are parallel to the bottom surface of the vessel, and the carbon fibers are horizontally settled on the bottom of the vessel after being oriented along the magnetic induction lines. The other process steps are the same as those of Example 1.

[0086] Example 3, the carbon fiber directional skeleton of the present application and the heat-conducting composite material prepared therefrom

[0087] The polymer fluid composition in the fifth step of Example 1 is changed to be prepared by mixing liquid silicone rubber, ethyl acetate and diamond in a mass ratio of 10:2:3. The other process steps are the same as those of Example 1.

[0088] Example 4, the carbon fiber directional skeleton of the present application and the heat-conducting composite material prepared therefrom

[0089] The use amounts of the mesophase pitch-based carbon fiber and the phenolic resin in the first step of Example 1 are reduced to 0.45 g and 0.09 g, respectively. The other process steps are the same as those of Example 1.

[0090] Comparative Example 1

[0091] The parallel magnetic field in the second step of Example 1 is removed, and the carbon fibers are naturally settled in the dispersion liquid. The other process steps are the same as those of Example 1.

[0092] The scanning electron microscope photos of the carbon fiber three-dimensional skeleton prepared in this comparative example are shown in Figure 4 . It can be seen that the carbon fibers are distributed irregularly.

[0093] Comparative Example 2

[0094] The graphitization process in the fourth step of Example 1 is omitted. The other process steps are the same as those of Example 1.

[0095] Comparative Example 3

[0096] The use amount of ethanol in the first step of Example 1 is reduced to 3.75 g, and the bottom area of the vessel is also reduced correspondingly to ensure that the liquid level of the dispersion liquid remains unchanged. The other process steps are the same as those of Example 1.

[0097] Comparative Example 4

[0098] The vessel bottom area in the second step of Example 1 was increased so that the liquid level of the dispersion in the vessel was reduced to 1.5 mm, and other process steps were the same as in Example 1.

[0099] Comparative Example 5

[0100] The parallel magnetic field strength used in the second step of Example 1 was reduced to 0.1 T, and other process steps were the same as in Example 1.

[0101] Comparative Example 6

[0102] The amount of phenolic resin used in the first step of Example 1 was reduced to 0.025 g, and other process steps were the same as in Example 1.

[0103] The thermal conductivity of the composite materials prepared in the examples and comparative examples was compared, and the thermal conductivity study method was as follows: the vertical and in-plane thermal diffusivity of the composite material was measured by laser flash method according to standard ISO22007-4, the specific heat and density were measured by DSC and drainage method respectively, and the thermal conductivity was obtained by multiplying the thermal diffusivity, the specific heat and the density.

[0104] The thermal conductivity results of each composite material are shown in Table 1.

[0105] Table 1. Comparison of thermal conductivity of each composite material

[0106]

[0107] Table 1 shows the thermal conductivity results of each example and comparative example. As can be seen from the table, the thermal conductive composite material prepared in Example 1 and Example 3 has excellent vertical thermal conductivity, and the thermal conductive composite material of Example 2 has excellent in-plane thermal conductivity. In Example 4, due to the reduction of the amount of carbon fiber, the packing density of the carbon fiber deposited on the bottom of the vessel decreases, and with the evaporation of the solvent, the carbon fiber is prone to tilt without the support of adjacent fibers, which reduces the overall order of the skeleton, so its thermal conductivity is slightly lower than that of Example 1.

[0108] Compared with Example 1, the magnetic field orientation process was omitted in Comparative Example 1, and the carbon fibers were randomly distributed in the dispersion and naturally settled on the bottom of the vessel, and the carbon fibers formed an unordered three-dimensional network skeleton by overlapping with each other, so that efficient thermal conduction channels could not be formed, and the thermal conductivity of the prepared thermal conductive composite material was low. In Comparative Example 2, the graphitization process of the carbon fiber directional skeleton was omitted, and the carbon fibers in the skeleton were connected by amorphous carbon formed by carbonization of phenolic resin, and the amorphous carbon produced a large thermal resistance in the skeleton due to its low thermal conductivity, so the thermal conductivity of the thermal conductive composite material decreased.

[0109] For the comparative example 3, the decrease of solvent amount makes the concentration of carbon fibers in the dispersion liquid increase, when exceeding a certain degree, the carbon fibers are easily hindered by the volume of adjacent fibers in the process of deflection orientation, so the order degree of the carbon fiber skeleton formed is low, and the vertical thermal conductivity of the prepared thermal conductive composite material is also reduced accordingly.

[0110] The carbon fibers need a certain time to complete the orientation deflection under the action of magnetic field, if the relaxation time of fiber orientation is less than the time of deposition to the bottom of the vessel during the deposition process, the fibers can complete the orientation process and deposit to the bottom of the vessel in the oriented arrangement. In the comparative example 4, due to the significant reduction of the liquid level of the dispersion liquid, the time of carbon fibers deposition to the bottom of the vessel is reduced, and there is not enough time for the carbon fibers to complete the deflection orientation, at the same time, due to the decrease of the packing density of carbon fibers at the bottom of the vessel, the order degree of the fibers in the obtained skeleton is reduced, so the thermal conductivity of the thermal conductive composite material is reduced. For the comparative example 5, the decrease of the magnetic field strength makes the orientation rate of carbon fibers in the dispersion liquid decrease, so the relaxation time of orientation is increased, and the order degree of the fibers in the obtained skeleton is reduced, so the thermal conductivity of the composite material is also reduced.

[0111] After the carbon fibers are deflected and deposited at the bottom of the vessel, with the evaporation of the solvent, the phenolic resin in the dispersion liquid gradually precipitates and bonds the oriented and arranged carbon fibers, when the resin content is too low, the overall strength of the obtained carbon fiber / phenolic resin preform is low, the carbon fibers are easy to peel off from the preform, and the carbon fiber directional skeleton cannot be self-supported, so the carbon fiber directional skeleton cannot be formed in the comparative example 6.

[0112] In summary, the resin used for preforming is first dissolved in a volatile solvent to obtain a low-viscosity resin solution, then the carbon fibers are dispersed in the solution to form a carbon fiber dispersion liquid, the dispersion liquid is placed in a parallel magnetic field, and the carbon fibers are oriented and arranged under a low magnetic field strength, and a carbon fiber directional skeleton is prepared through subsequent processes. Since the viscosity of the dispersion liquid is low, the oriented arrangement of the carbon fibers can be realized under a relatively low magnetic field strength, and the obtained carbon fiber directional skeleton has a permeable pore structure, and the polymer can be impregnated into the interior of the skeleton in the form of a melt or a solution to form a thermal conductive composite material, so the material preparation process is no longer limited by expensive superconducting magnet equipment and low-viscosity polymer matrix. It can be seen that the present application has very strong universality. The carbon fiber directional skeleton and the polymer fluid are used to prepare a thermal conductive composite material with carbon fibers arranged in a direction, which can make full use of the high axial thermal conductivity of the carbon fibers, and build a high-efficiency thermal conductive path, so that the thermal conductivity of the material in the arrangement direction of the carbon fibers is greatly improved. In addition, when the polymer fluid in which the carbon fiber directional skeleton is cast contains additional thermal conductive fillers, a three-dimensional thermal conductive network can be formed by interlacing with the carbon fibers, further improving the thermal conductivity. The thermal conductive composite material prepared by the present application has excellent vertical thermal conductivity or in-plane thermal conductivity, and has excellent application prospects.

Claims

1. A carbon fiber oriented scaffold, characterized by: It is obtained by sequentially treating the carbon fiber / phenolic resin preform through solidification, carbonization and graphitization; The carbon fiber / phenolic resin preform is obtained by placing the dispersion liquid containing carbon fiber and phenolic resin in a magnetic field, and making the carbon fiber directional distribution along the magnetic induction line direction after the carbon fiber is affected by the magnetic field, and then making the solvent of the dispersion liquid volatilize. The mass ratio of the phenolic resin to the carbon fiber in the dispersion liquid is 0.05-0.

8. The mass ratio of the carbon fiber to the solvent is 0.05-0.

15. The strength of the magnetic field is 0.2-1T. The liquid surface height of the dispersion liquid is 2-30mm.

2. The carbon fiber directional skeleton according to claim 1, wherein: The mass ratio of the phenolic resin to the carbon fiber in the dispersion liquid is 0.06-0.

5. And / or, the mass ratio of the carbon fiber to the solvent is 0.05-0.

1.

3. The carbon fiber directional skeleton according to claim 2, wherein: The carbon fiber is mesophase pitch-based carbon fiber. And / or, the phenolic resin is thermosetting phenolic resin or its modified product. And / or, the solvent of the dispersion liquid is volatile organic solvent.

4. The carbon fiber directional skeleton according to claim 3, wherein: The thermal conductivity of the carbon fiber is greater than 600W / mK; and / or, the length of the carbon fiber is 0.1-3mm. And / or, the solvent of the dispersion liquid is one or more of methanol, ethanol, ethylene glycol, dichloromethane, acetone and tetrahydrofuran. And / or, the magnetic field is parallel magnetic field, which is parallel or perpendicular to the liquid surface of the dispersion liquid. And / or, the strength of the magnetic field is 0.25-1T. And / or, the liquid surface height of the dispersion liquid is 10mm.

5. The carbon fiber oriented scaffold of any one of claims 1-4, wherein: The preparation method of the carbon fiber / phenolic resin preform comprises the following steps: (1) dissolving the phenolic resin in the solvent, adding the carbon fiber, and making the carbon fiber uniformly dispersed to form a carbon fiber dispersion liquid; (2) placing the carbon fiber dispersion liquid in a parallel magnetic field environment, and making the carbon fiber deflect and directional distribution along the magnetic induction direction during the sedimentation process; (3) applying vibration to the carbon fiber dispersion liquid, and naturally drying to make the solvent volatilize, thereby obtaining the carbon fiber / phenolic resin preform.

6. The carbon fiber oriented scaffold of claim 5, wherein: In step (3), the amplitude of the vibration is 0.3-3mm, the frequency is 20-50Hz, and the time is 0.5-2min.

7. The carbon fiber directional skeleton according to any one of claims 1-4, wherein: The solidification temperature is 150-200℃, and the time is 1-5h; and / or, the carbonization temperature is 600-1200℃, and the time is 0.5-3h; and / or, the graphitization temperature is 2800-3000℃, and the time is 0.5-3h.

8. Use of the carbon fiber directional skeleton according to any one of claims 1-7 in preparing a thermal conductive composite material.

9. A thermally conductive composite material, characterized by: It is prepared from the following raw materials in the following weight ratio: 40-80 parts of a polymer fluid composition, 20-60 parts of the carbon fiber directional skeleton according to any one of claims 1-7; the polymer fluid composition is composed of a polymer matrix, a solvent and a thermal conductive filler.

10. The thermally conductive composite material of claim 9, wherein: The polymer fluid composition comprises 30-100 wt% of the polymer matrix, 0-70 wt% of the solvent, and 0-40 wt% of the heat-conducting filler. The viscosity of the polymer fluid composition is less than 20000 mPa·s.

11. The thermally conductive composite material of claim 9 or 10, wherein: The polymer matrix is a thermoplastic polymer or a thermosetting polymer. The solvent is a good solvent for the polymer matrix. The heat-conducting filler is one or more of graphite, graphene, carbon nanotube, diamond, boron nitride, aluminum oxide, aluminum nitride, silicon carbide, silver powder, and copper powder.

12. The heat-conducting composite material of claim 11, wherein: The thermoplastic polymer is an olefin polymer, polyvinyl acetate, polyvinyl alcohol, polyethylene glycol, polyvinyl chloride, polystyrene, polymethacrylate polymer, polyacrylic polymer, polycarbonate, or polyamide polymer. The thermosetting polymer is cross-linked rubber, epoxy resin, phenolic resin, unsaturated polyester resin, or polyimide resin. The solvent is water, aliphatic hydrocarbon, aromatic hydrocarbon, ester cyclic hydrocarbon, halogenated hydrocarbon, alcohol, ester, ether, ketone, amide, or sulfoxide. The size of the heat-conducting filler is less than or equal to 50 μm.

13. The heat-conducting composite material of claim 12, wherein: The olefin polymer is polyethylene, polypropylene, or ethylene-propylene copolymer. The cross-linked rubber is natural rubber, acrylic rubber, polybutadiene rubber, nitrile rubber, butyl rubber, ethylene-propylene-diene rubber, polyurethane rubber, fluororubber, or silicone rubber.

14. Process for the preparation of a thermally conductive composite material according to any one of claims 9 to 13, characterized in that: The method comprises the following steps: The polymer fluid composition is cast into the carbon fiber oriented skeleton of any one of claims 1-6, and then vacuum degassing, curing, and surface polishing are performed to obtain the heat-conducting composite material.

15. The method of claim 14, wherein: The curing method is chemical cross-linking, solvent evaporation, or cooling solidification.

16. Use of the heat-conducting composite material of any one of claims 9-13 in the preparation of a heat-conducting device.

17. Use according to claim 16, characterized in that: The heat-conducting composite material can be used as a thermal interface material or a high-heat-conducting device substrate or shell.

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