A high-strength graphene thermal conductive film with bidirectional cross-sectional and in-plane properties, its preparation method, and its application.

Abstract

This invention discloses a bidirectional high-strength graphene thermally conductive film with in-plane and out-of-plane properties, its preparation method, and its applications. A small amount of epoxy resin is filled into the graphene film using a vacuum impregnation process. The mortise-and-tenon-like structure formed by the epoxy resin within the pores enhances the interlayer stress transfer efficiency and suppresses sheet slippage, resulting in an in-plane strength twice that of conventional films (63.3 MPa) and an out-of-plane strength six times that of conventional films (182.6 kPa). Simultaneously, due to the low proportion and discontinuous distribution of epoxy resin, the thermal conductivity remains at a high level of 1325 W / mK. This method utilizes readily available raw materials and involves a simple process, providing a feasible path for the industrialization of graphene materials.

Description

Technical Field

[0001] This invention relates to the field of graphene technology, specifically to a bidirectional high-strength graphene thermal conductive film with in-plane and out-of-plane properties, its preparation method, and its application. Background Technology

[0002] Graphene possesses the highest known tensile strength (130 GPa) and Young's modulus (1 TPa), and exhibits the highest carrier mobility (15000 cm² / Vs) and thermal conductivity (5000 W / mK). Since Professor AK Geim's team at the University of Manchester, UK, successfully exfoliated graphene in 2004, how to precisely transfer graphene's excellent physicochemical properties to its macroscopic assemblies has become a core research issue worldwide.

[0003] Graphene films are the primary application form of nanoscale graphene, with broad application prospects in fields such as optoelectronic sensing, aerospace lightweighting, and thermal management of electronic devices. Their preparation mainly involves the macroscopic assembly of graphene oxide or graphene nanosheets followed by high-temperature graphitization. High-temperature graphitization (typically above 2800 °C) helps repair lattice defects in graphene, significantly improving the electrical and thermal conductivity of the graphene film. However, after high-temperature graphitization, the mechanical strength of the graphene film is severely weakened, typically around 20 MPa. This mechanical weakness stems from the weak interlayer forces in graphene and structural defects (such as wrinkles and pores) introduced during the pressing process after high-temperature graphitization, severely restricting the widespread application of graphene films.

[0004] Currently, there are two main approaches to improving the mechanical strength of graphene films: First, strictly controlling the quality of the assembly raw material, graphene oxide or graphene nanosheets. For example, synthesizing ultra-large-sized, low-defect-density graphene oxide can reduce edge defects, thereby increasing graphene crystallinity and enhancing interlayer forces. Second, strictly controlling the assembly structure of graphene during the assembly and pressing processes. For example, plasticizing and stretching, and pressure graphitization can reduce structural defects, thereby increasing graphene crystallinity. However, while these methods improve in-plane tensile strength, they may significantly reduce out-of-plane delamination strength, leading to graphene film delamination failure. Summary of the Invention

[0005] To address the challenge of balancing in-plane and out-of-plane strength in existing technologies, this invention provides a bidirectional high-strength graphene thermally conductive film, its preparation method, and its applications. A small amount of epoxy resin is filled into the graphene film using a vacuum impregnation process. The mortise-and-tenon-like structure formed by the epoxy resin within the pores enhances interlayer stress transfer efficiency and suppresses sheet slippage. This results in in-plane strength being twice that of conventional films (63.3 MPa) and out-of-plane strength being six times (182.6 kPa). Simultaneously, due to the low proportion and discontinuous distribution of epoxy resin, the thermal conductivity remains at a high level of 1325 W / mK. This method utilizes readily available raw materials and involves a simple process, providing a feasible path for the industrialization of graphene materials.

[0006] Specifically, it includes the following steps:

[0007] (1) A graphene film was prepared by applying pressure to porous graphene material; the density of the graphene film was 1.65-1.85 g / cm³. 3 ;

[0008] (2) Prepare a mixed solution of modified bisphenol A epoxy resin and curing agent;

[0009] (3) Immerse the graphene film obtained in step (1) vertically into the mixed solution obtained in step (2) until it is completely submerged. Obtain the graphene / epoxy resin composite film by vacuum-assisted impregnation; (4) Clean the graphene / epoxy resin composite film obtained in step (3) repeatedly with heated anhydrous ethanol solution until there is no resin residue on its surface.

[0010] (5) Pressurized and heat-cured graphene film: The graphene film obtained in step (4) is placed in a flatbed hot press, the pressure is controlled at 5-20 MPa, initially cured at 50 ℃ for 4 h, and then cured at 70 ℃ for 8 h to obtain a graphene thermal conductive film. The porous graphene forms wrinkles after the initial pressing process. The resin injected in a vacuum environment permeates into the wrinkled area through the interlayer channels of the graphene, and finally constructs a mortise and tenon-like structure.

[0011] Furthermore, the porous graphene material described in step (1) includes, but is not limited to, open-cell materials such as graphene foam, graphene aerogel, and expanded graphite. The initial density of the porous graphene material is 0.1-0.2 g / cm³. 3 The thickness is 350-450 μm. Porous graphene materials have good thermal conductivity.

[0012] Furthermore, the pressure application method in step (1) includes, but is not limited to, rolling and hot pressing. The rolling direction is consistent with the horizontal direction of the porous graphene material. The final thickness of the graphene film can be controlled to be 25-30 μm and the density to be 1.65-1.85 g / cm³ by single or multiple rolling processes.3 .

[0013] Furthermore, in step (2), the mass ratio of modified bisphenol A epoxy resin to curing agent in the mixed solution is 10:3, and the mixture at this ratio exhibits good wettability to graphene. After mixing, the mixture is magnetically stirred at a rate of 200-500 rpm for a period of time, followed by ultrasonic degassing to remove residual bubbles from the mixture.

[0014] Furthermore, the vertical immersion in step (3) is to facilitate the escape of gas from inside the graphene film. The graphene film must be completely immersed in the mixture. The vacuum-assisted impregnation is performed with a vacuum level controlled at 15-50 mbar, an impregnation temperature controlled at 20-25 ℃, and an impregnation time controlled at 0.5-5 h. These temperature and vacuum levels prevent excessive resin injection pressure from damaging the microstructure inside the graphene film.

[0015] Furthermore, the temperature of the heated anhydrous ethanol solution in step (4) is controlled at 30-50 °C. The purpose of heating the anhydrous ethanol solution is to accelerate the dissolution of epoxy resin and improve cleaning efficiency. The criterion for determining the absence of resin residue is to observe the surface of the graphene film through an optical microscope.

[0016] This invention also provides a bidirectional, high-strength graphene thermal conductive film prepared by the above method. The thickness of this graphene thermal conductive film is 22-27 μm, and its density is 1.85-1.95 g / cm³. 3 The volume fraction of epoxy resin is 4-6%.

[0017] This invention also provides applications of the aforementioned bidirectional high-strength graphene thermally conductive film in high-strength, high-thermal-conductivity graphene materials. For example, it can be used to prepare multilayer composite components for heat dissipation substrates in electronic devices.

[0018] The beneficial effects of this invention are as follows: by filling the structural defects generated during the pressing of graphene films with a small amount of epoxy resin, its in-plane and out-of-plane strength and thermal conductivity can be simultaneously improved (in-plane strength reaches 63.3 MPa, twice that of conventional graphene films; out-of-plane strength reaches 182.6 kPa, six times that of conventional graphene films; thermal conductivity reaches 1325 W / mK). The epoxy resin forms a tenon-and-mortise-like connection structure within the pores of the graphene film, which not only improves the interlayer stress transfer efficiency but also dissipates a large amount of strain energy by inducing crack tip deflection, effectively suppressing graphene sheet slippage and achieving a synergistic improvement in in-plane and out-of-plane strength. Simultaneously, the low proportion and discontinuous distribution of epoxy resin within the film preserves the original continuous thermal conductivity path of graphene, ensuring that its excellent thermal conductivity remains unaffected. Furthermore, this method has the advantages of readily available raw materials, simple process, and low cost, which helps to accelerate the industrialization of graphene materials. Attached Figure Description

[0019] Figure 1 The in-plane tensile mechanical curves of the graphene thermal conductive films obtained in Example 1 and Comparative Example 1 are shown.

[0020] Figure 2 The out-of-plane delamination mechanical curves of the graphene thermal conductive films obtained in Example 1 and Comparative Example 1 are shown.

[0021] Figure 3 The images are scanning electron microscope (SEM) images of the fracture surfaces of Example 1 and Comparative Example 1 after in-plane tensile fracture, with a scale bar of 10 micrometers.

[0022] Figure 4 This is a scanning electron microscope image of a typical dissipative structure during in-plane stretching in Example 1, with a scale bar of 1 micrometer.

[0023] Figure 5 The mechanical enhancement mechanism of graphene thermal conductive film. Detailed Implementation

[0024] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0025] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0026] The embodiments of the present invention will be further described below with reference to several examples.

[0027] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0028] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0029] Example 1

[0030] (1) The initial density is 0.12 g / cm³. 3 Commercial graphene foam with a thickness of 450 μm was rolled in the same direction. Its thickness was gradually reduced through six stages of rolling, resulting in a final thickness of 30 μm and a density of 1.65 g / cm³. 3 , of the graphene film;

[0031] (2) Dissolve 3 parts by weight of curing agent in 10 parts by weight of modified bisphenol A epoxy resin, stir for 5 min at room temperature and stirring rate of 400 rpm, and then degas in an ultrasonic degassing instrument for 5 min to obtain a mixed solution of modified bisphenol A epoxy resin and curing agent.

[0032] (3) The graphene film obtained in step (1) is vertically and completely immersed in the mixed solution obtained in step (2) along the roller pressing surface, and then the whole thing is moved into a vacuum barrel. Under the conditions of setting the ambient temperature to 20 ℃ and the constant vacuum degree to 30 mbar, it is vacuum impregnated for 2 h to obtain a graphene / epoxy resin composite film.

[0033] (4) Remove the graphene / epoxy resin composite film from the mixed solution and immerse it in anhydrous ethanol preheated to 50 °C. Gently shake the beaker for 1 min, then replace the anhydrous ethanol and repeat the cleaning 3 times. Confirm that there is no residual epoxy resin on the surface of the composite film through an optical microscope to ensure that the cleaning is complete.

[0034] (5) The cleaned composite film is placed in the middle of the platen of the flatbed hot press, with a polytetrafluoroethylene release cloth placed on top and bottom. The pressure is set to 5 MPa, and the hot pressing temperature is 50 ℃ for 4 h for initial curing. Then the temperature is raised to 70 ℃ and held for 8 h for secondary curing. After curing, the aforementioned graphene thermal conductive film can be obtained.

[0035] (6) The graphene thermally conductive film obtained had a thickness of 27 μm and a density of 1.95 g / cm³. 3 The epoxy resin has a volume fraction of 6%. Its in-plane strength is 63.3 MPa, its out-of-plane strength is 182.6 kPa, and its thermal conductivity is 1325 W / mK.

[0036] Example 2

[0037] (1) The initial density is 0.1 g / cm³. 3 Commercial graphene foam with a thickness of 350 μm was rolled in the same direction. Its thickness was gradually reduced through eight stages of rolling, resulting in a final thickness of 28 μm and a density of 1.71 g / cm³. 3 , of the graphene film;

[0038] (2) Dissolve 3 parts by weight of curing agent in 10 parts by weight of modified bisphenol A epoxy resin, stir for 5 min at room temperature and at a stirring rate of 300 rpm, and then degas in an ultrasonic degassing instrument for 5 min to obtain a mixed solution of modified bisphenol A epoxy resin and curing agent.

[0039] (3) The graphene film obtained in step (1) is vertically and completely immersed in the mixed solution obtained in step (2) along the roller pressing surface, and then the whole thing is moved into a vacuum barrel. Under the conditions of setting the ambient temperature to 20 ℃ and the constant vacuum degree to 15 mbar, it is vacuum impregnated for 5 h to obtain a graphene / epoxy resin composite film.

[0040] (4) Remove the graphene / epoxy resin composite film from the mixed solution and immerse it in anhydrous ethanol preheated to 40 °C. Gently shake the beaker for 1 min, then replace the anhydrous ethanol and repeat the cleaning 4 times. Confirm that there is no residual epoxy resin on the surface of the composite film through an optical microscope to ensure that the cleaning is complete.

[0041] (5) The cleaned composite film is placed in the middle of the platen of the flatbed hot press, with a polytetrafluoroethylene release cloth placed on top and bottom. The pressure is set to 15 MPa, and the hot pressing temperature is 50 ℃ for 4 h for initial curing. Then the temperature is raised to 70 ℃ and held for 8 h for secondary curing. After curing, the aforementioned graphene thermal conductive film can be obtained.

[0042] (6) The graphene thermally conductive film obtained had a thickness of 26 μm and a density of 1.90 g / cm³. 3 The volume fraction of epoxy resin is 5.31%. Its in-plane strength is 59.8 MPa, its out-of-plane strength is 170.3 kPa, and its thermal conductivity is 1332 W / mK.

[0043] Example 3

[0044] (1) The initial density is 0.2 g / cm³. 3 Commercial graphene foam with a thickness of 400 μm was rolled in the same direction. Its thickness was gradually reduced through 10 stages of rolling, resulting in a final thickness of 25 μm and a density of 1.85 g / cm³. 3 Graphene film;

[0045] (2) Dissolve 3 parts by weight of curing agent in 10 parts by weight of modified bisphenol A epoxy resin, stir for 5 min at room temperature and at a stirring rate of 200 rpm, and then degas in an ultrasonic degassing instrument for 5 min to obtain a mixed solution of modified bisphenol A epoxy resin and curing agent.

[0046] (3) The graphene film obtained in step (1) is vertically and completely immersed in the mixed solution obtained in step (2) along the roller pressing surface, and then the whole is moved into the vacuum barrel. Under the conditions of setting the ambient temperature to 25 ℃ and the constant vacuum degree to 50 mbar, it is vacuum impregnated for 0.5h to obtain the graphene / epoxy resin composite film.

[0047] (4) Remove the graphene / epoxy resin composite film from the mixed solution and immerse it in anhydrous ethanol preheated to 30 °C. Gently shake the beaker for 1 min, then replace the anhydrous ethanol and repeat the cleaning 5 times. Confirm that there is no residual epoxy resin on the surface of the composite film through an optical microscope to ensure that the cleaning is complete.

[0048] (5) The cleaned composite film is placed in the middle of the platen of the flatbed hot press, with a polytetrafluoroethylene release cloth placed on top and bottom. The pressure is set to 20 MPa, and the hot pressing temperature is 50 ℃ for 4 h for initial curing. Then the temperature is raised to 70 ℃ and held for 8 h for secondary curing. After curing, the aforementioned graphene thermal conductive film can be obtained.

[0049] (6) The thickness of the graphene thermally conductive film was 22 μm and the density was 1.85 g / cm³. 3 The epoxy resin has a volume fraction of 4%. Its in-plane strength is 52.5 MPa, its out-of-plane strength is 139.8 kPa, and its thermal conductivity is 1345 W / mK.

[0050] Comparative Example 1

[0051] (1) The initial density is 0.11 g / cm³. 3 Commercial graphene foam with a thickness of 440 μm was rolled in the same direction. Its thickness was gradually reduced through 10 stages of rolling, resulting in a final thickness of 24 μm and a density of 1.90 g / cm³. 3 Graphene film;

[0052] (2) The comparative example is a conventional graphene thermal conductive film, which is not vacuum impregnated with epoxy resin;

[0053] (3) The graphene thermally conductive film obtained had a thickness of 24 μm and a density of 1.90 g / cm³. 3 The volume fraction of epoxy resin is 0%. Its in-plane strength is 29.2 MPa, its out-of-plane strength is 35.8 kPa, and its thermal conductivity is 1398 W / mK.

[0054] The in-plane and out-of-plane mechanical curves of the graphene thermal conductive film sample are as follows: Figure 1 , 2 As shown, vacuum impregnation with epoxy resin significantly improves the in-plane tensile strength and out-of-plane delamination strength of graphene thermal conductive film, reaching 63.3 MPa and 182.6 kPa, which are 2 times and 6 times that of conventional graphene film, respectively.

[0055] Characterized by scanning electron microscopy, such as Figure 3 The results show that vacuum impregnation with epoxy resin significantly improves the stress transfer efficiency between graphene thermal conductive films, inducing crack tip deflection, specifically manifested as a rough and rugged fracture surface, accompanied by numerous dissipative structures such as sheet pull-out and shear bands. Meanwhile, as... Figure 4 As shown, epoxy resin also provides bridging to dissipate a large amount of strain energy and inhibit the slippage of graphene sheets. Figure 5 As shown, these mechanisms endow graphene thermal conductive films with excellent in-plane and out-of-plane strength, laying a solid foundation for their wide application in many fields.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that the graphene foam was not rolled and was directly immersed in the epoxy resin solution. The resulting graphene film had poor thermal conductivity and significantly reduced strength. This is because the structure of the unrolled graphene foam was broken down when it was immersed in the epoxy resin solution, resulting in reduced thermal conductivity and strength.

[0058] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a bidirectional high-strength graphene thermally conductive film, characterized in that, Includes the following steps: (1) A graphene film is obtained by applying pressure to porous graphene material; the density of the graphene film is 1.65-1.85 g / cm³. 3 ; (2) Prepare a mixed solution of modified bisphenol A epoxy resin and curing agent; (3) The graphene film obtained in step (1) is vertically immersed in the mixed solution obtained in step (2) until it is completely submerged. Vacuum-assisted impregnation is used to obtain a graphene / epoxy resin composite film. In the vacuum-assisted impregnation, the vacuum degree is 15-50 mbar, the impregnation temperature is 20-25 ℃, and the impregnation time is 0.5-5 h. (4) The graphene / epoxy resin composite film obtained in step (3) is repeatedly washed with heated anhydrous ethanol solution until there is no resin residue on its surface. (5) Place the graphene film obtained in step (4) in a flat hot press, control the pressure at 5-20 MPa, pre-cur at 50 ℃ for 4 h, and then pre-cur at 70 ℃ for 8 h to obtain the graphene thermal conductive film.

2. The method according to claim 1, characterized in that, The porous graphene material mentioned in step (1) is one of graphene foam, graphene aerogel, or expanded graphite; the density of the porous graphene material is 0.1-0.2 g / cm³. 3 The thickness is 350-450 μm.

3. The method according to claim 1, characterized in that, The pressure applied in step (1) is either roller pressing or hot pressing.

4. The method according to claim 1, characterized in that, In step (2), the mass ratio of modified bisphenol A epoxy resin to curing agent in the mixed solution is 10:

3.

5. The method according to claim 1, characterized in that, The temperature of the anhydrous ethanol solution in step (4) is 30-50℃.

6. A bidirectional high-strength graphene thermally conductive film prepared by the method as described in claim 1, characterized in that, Thickness ranges from 22 to 27 μm, and density ranges from 1.85 to 1.95 g / cm³. 3 The volume fraction of epoxy resin is 4-6%.

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