Graphene copper composite material and preparation method thereof

Abstract

The invention relates to the technical field of conductive material preparation, in particular to a graphene copper composite material and a preparation method thereof. The preparation method comprises the following steps: firstly, pretreating spherical copper powder, then coating the spherical copper powder with a polyamide acid precursor solution, and forming a uniform polyimide coating layer on the surface of the copper powder through thermal imidization treatment; and then a small amount of graphene is compounded with the coated copper powder in a mechanical ball milling mode and the like, and finally the composite material is prepared through cold press molding and sintering densification. The core of the preparation method is that polyimide is used as an interface modifier, so that the key problems that graphene is easy to agglomerate in a copper matrix and the interface bonding is poor are effectively solved, and the thermal conductivity, the electrical conductivity and the mechanical strength of the composite material are remarkably improved. The method is simple in process, environment-friendly, easy to industrialize and suitable for preparing electronic devices, heat dissipation modules and other high-performance electric conduction and heat conduction parts.

Description

Technical Field

[0001] This invention relates to the field of conductive material preparation technology, specifically to graphene-copper composite materials and their preparation methods. Background Technology

[0002] Copper-based composite materials are widely used in electrical contacts, heat dissipation devices, and other fields due to their excellent electrical and thermal conductivity. To improve their overall performance, academia and industry have generally attempted to introduce reinforcing phases, such as two-dimensional materials like carbon nanotubes and graphene, into the copper matrix. However, in existing technologies, graphene is mostly introduced into copper powder through simple physical mixing and then sintered to prepare composite materials, which has the following main problems: graphene is unevenly distributed in the copper matrix and is prone to agglomeration; the interface between graphene and copper is poor, resulting in high interfacial thermal resistance; the material density is insufficient, affecting the overall performance; and the preparation process has poor repeatability and weak industrialization capability.

[0003] These issues result in limited improvement in the thermal conductivity of composite materials and unstable mechanical properties, making it difficult to meet the application requirements of high-end equipment manufacturing. For example, the thermal conductivity of traditional graphene / copper composites is only slightly higher than that of pure copper, but the electrical conductivity is lower, and the process stability is poor. Therefore, there is an urgent need for a new preparation method to improve graphene dispersion and interfacial bonding, and to enhance material density and performance consistency. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a graphene-copper composite material, which uses a polyimide coating layer as an interface modifier to effectively inhibit graphene agglomeration, improve interfacial bonding, reduce interfacial thermal resistance, and thus improve overall thermo-electric performance; the material has high density and is suitable for harsh service environments.

[0005] Another objective of this invention is to provide a method for preparing graphene-copper composite materials, which has a mild preparation process, uses non-toxic or low-toxic solvents, reduces environmental pollution, and has low energy consumption.

[0006] This invention is achieved using the following technical solution: The preparation method of the graphene-copper composite material includes the following steps: (1) Copper powder pretreatment: The spherical copper powder is cleaned and roughened. (2) Polyimide precursor coating: The pretreated copper powder is dispersed in a polyamic acid precursor solution, and the coating solution is formed by mechanical stirring and ultrasonic mixing. Then, the copper powder is obtained by filtration and drying. (3) Thermal imidization treatment: The polyamic acid-coated copper powder is heated to the imidization temperature under a protective atmosphere and kept at that temperature for a certain time to convert the polyamic acid into polyimide and form polyimide-coated copper powder. (4) Graphene introduction: Graphene is uniformly incorporated into polyimide-coated copper powder by mechanical ball milling or solution blending, with a graphene mass fraction of 0.1-5 wt%. (5) Molding and sintering: After the composite powder is cold-pressed into shape, it is sintered and densified under a protective atmosphere to form a composite material block.

[0007] The copper powder pretreatment in step (1) includes: Ultrasonic cleaning: Use organic solvents such as acetone or ethanol to ultrasonically clean copper powder for 10-60 minutes to remove oil and oxide film; Acid washing and activation: Soak in dilute sulfuric acid or hydrochloric acid solution for 1-10 minutes, rinse with pure water and dry.

[0008] In step (2), the solid content of the polyamic acid solution is 5-15 wt%, the solvent is N-methylpyrrolidone, and the mass ratio of copper powder to polyamic acid is 100:(1-10).

[0009] In step (3), the imidization temperature is 200-400℃, the holding time is 1-4h, and the protective atmosphere is nitrogen or argon.

[0010] In step (4), the mechanical ball milling parameters are: rotation speed 100-300 rpm, ball milling time 1-4 h, ball-to-material ratio 5:1 to 20:1, and ball milling medium is ethanol or acetone; or the solution is mixed by ultrasonic dispersion.

[0011] In step (5), the cold pressing pressure is 100-500 MPa, the sintering temperature is 800-1050℃, the sintering time is 1-4 h, and the protective atmosphere is hydrogen or nitrogen.

[0012] The preparation method of the graphene-copper composite material further includes the step of: hot isostatic pressing the sintered material at a temperature of 500-900℃, a pressure of 50-200MPa, and a time of 0.5-2h.

[0013] The graphene-copper composite material is prepared by the method described above, and the thermal conductivity of the composite material is not less than 425 W·m. -1 ·K -1 The conductivity is not less than 97% IACS and the density is not less than 98%.

[0014] The composite material is suitable for electronic devices, heat dissipation modules, or new energy equipment.

[0015] Polyimide, acting as an interface modifier, forms a uniform coating layer on the surface of copper powder, which is then transformed into a stable polyimide film through thermal imidization. This film not only prevents graphene agglomeration but also enhances the interfacial bonding between graphene and the copper matrix, reducing interfacial thermal resistance and electrical resistance, thereby improving the thermal and electrical conductivity of the composite material. Simultaneously, the polyimide coating layer partially carbonizes during sintering, forming a nano-carbon structure, further optimizing the interfacial properties.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) The preparation process of this invention is mild, uses non-toxic or low-toxic solvents, reduces environmental pollution, and has low energy consumption; the process steps are simple, easy to operate, can be achieved with conventional equipment, has good repeatability, and is easy to mass-produce.

[0017] (2) The raw material cost of this invention is low (the amount of copper powder and graphene can be controlled), and the polyimide coating layer is thin, which does not affect the cost, but significantly improves the performance. The thermal conductivity of the composite material can be increased to 425 W·m. -1 ·K -1 The electrical conductivity remains above 97.5% IACS, while mechanical strength is improved. The polyimide coating acts as an interface modifier, effectively inhibiting graphene agglomeration, improving interfacial bonding, and reducing interfacial thermal resistance, thereby enhancing overall thermo-electrical performance. The material has high density, making it suitable for harsh service environments. The method is applicable to copper powder and graphene of different specifications, and process parameters can be adjusted to meet various application requirements. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the graphene copper powder obtained in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the copper powder used in Example 1 of the present invention; Figure 3 The Raman spectrum of the graphene copper obtained in Example 1 of this invention; Figure 4 This is a comparison of the tensile properties of the graphene copper obtained in Example 1, the graphene copper obtained in Example 3, and the pure copper used in Example 1. Detailed Implementation

[0019] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below.

[0020] Example 1 Raw material information: Copper powder: Spherical gas-atomized copper powder, average particle size 35μm, manufacturer: Shanghai Shuitian Materials Technology Co., Ltd., grade: ST-35; Polyamic acid (PAA) solution: solid content 8 wt%, solvent is N-methylpyrrolidone (NMP), manufacturer: Sigma-Aldrich; Graphene: Multilayer graphene, sheet diameter 10-20μm, manufacturer: Changzhou Sixth Element Technology Co., Ltd., grade: SE1235.

[0021] The preparation method of graphene-copper composite material includes the following steps: (1) Copper powder pretreatment: Spherical copper powder was ultrasonically cleaned in acetone for 30 minutes to remove oil and oxide film; then it was soaked in 5% dilute sulfuric acid solution for 5 minutes to activate the surface, rinsed with pure water and dried.

[0022] (2) Polyimide precursor coating: The pretreated copper powder is dispersed in a polyamic acid precursor solution (the mass ratio of copper powder to PAA is 100:5), and a coating solution is formed by mechanical stirring for 30 min and ultrasonic treatment for 15 min. Then, the copper powder is obtained by filtration and drying.

[0023] (3) Thermal imidization treatment: The polyamic acid-coated copper powder is heated to 300°C under a nitrogen protective atmosphere and kept at that temperature for 2 hours to convert the polyamic acid into polyimide and form polyimide-coated copper powder.

[0024] (4) Introduction of graphene: Graphene (mass fraction 0.5wt%) was uniformly incorporated into polyimide-coated copper powder by mechanical ball milling. The ball milling parameters were: rotation speed 200rpm, ball milling time 2h, ball-to-material ratio 10:1, and ball milling medium was ethanol.

[0025] (5) Molding and sintering: The composite powder is cold-pressed into a Φ20mm disc under a pressure of 300MPa, and then sintered at 950℃ for 2h under a hydrogen protective atmosphere to form a composite material block.

[0026] Example 2 Raw material information: Copper powder: Spherical gas-atomized copper powder, average particle size 35μm, manufacturer: Shanghai Shuitian Materials Technology Co., Ltd., grade: ST-35; Polyamic acid (PAA) solution: solid content 8 wt%, solvent is N-methylpyrrolidone (NMP), manufacturer: Sigma-Aldrich; Graphene: Multilayer graphene, sheet diameter 10-20μm, manufacturer: Changzhou Sixth Element Technology Co., Ltd., grade: SE1235.

[0027] The preparation method of graphene-copper composite material includes the following steps: (1) Copper powder pretreatment: Spherical copper powder was ultrasonically cleaned in ethanol for 40 min to remove oil and oxide film; then it was soaked in 3% hydrochloric acid solution for 3 min to activate the surface, rinsed with pure water and dried.

[0028] (2) Polyimide precursor coating: The pretreated copper powder is dispersed in a polyamic acid precursor solution (the mass ratio of copper powder to PAA is 100:3), and a coating solution is formed by mechanical stirring for 40 min and ultrasonic treatment for 20 min. Then, the copper powder is obtained by filtration and drying.

[0029] (3) Thermal imidization treatment: The polyamic acid-coated copper powder is heated to 250°C under an argon protective atmosphere and kept at that temperature for 3 hours to convert the polyamic acid into polyimide and form polyimide-coated copper powder.

[0030] (4) Introduction of graphene: Graphene (1.0 wt%) was uniformly incorporated into polyimide-coated copper powder by solution blending and ultrasonic dispersion for 30 min to ensure uniform mixing.

[0031] (5) Molding and sintering: The composite powder is cold-pressed under a pressure of 200MPa and then sintered at 900℃ for 3h under a nitrogen protective atmosphere to form a composite material block.

[0032] Example 3 Raw material information: Copper powder: Spherical electrolytic copper powder, average particle size 10μm, manufacturer: Zhongtong New Materials Co., Ltd., grade: ZC-Cu10; Polyamic acid (PAA) solution: solid content 12wt%, solvent is N-methylpyrrolidone (NMP), manufacturer: Sigma-Aldrich; Graphene: Multilayer graphene, sheet diameter 10-20μm, manufacturer: Changzhou Sixth Element Technology Co., Ltd., grade: SE1235.

[0033] The preparation method of graphene-copper composite material includes the following steps: (1) Copper powder pretreatment: Spherical copper powder was ultrasonically cleaned in acetone for 20 minutes to remove oil and oxide film; then it was soaked in 5% dilute sulfuric acid solution for 8 minutes to activate the surface, rinsed with pure water and dried.

[0034] (2) Polyimide precursor coating: The pretreated copper powder is dispersed in a polyamic acid precursor solution (the mass ratio of copper powder to PAA is 100:8), and a coating solution is formed by mechanical stirring for 30 min and ultrasonic treatment for 15 min. Then, the solution is filtered and dried to obtain polyamic acid coated copper powder.

[0035] (3) Thermal imidization treatment: The polyamic acid-coated copper powder is heated to 350°C under a nitrogen protective atmosphere and kept at that temperature for 1 hour to convert the polyamic acid into polyimide and form polyimide-coated copper powder.

[0036] (4) Introduction of graphene: Graphene (mass fraction 0.2wt%) was uniformly incorporated into polyimide-coated copper powder by solution blending and ultrasonic dispersion for 40 min to ensure uniform mixing.

[0037] (5) Molding and sintering: The composite powder is cold-pressed under a pressure of 200MPa and then sintered at 1000℃ for 2h under a hydrogen protective atmosphere to form a composite material block.

[0038] (6) Hot isostatic pressing: The sintered material is subjected to hot isostatic pressing at a temperature of 600℃, a pressure of 100MPa, and a time of 1h.

[0039] Comparative Example 1 Using a physical mixing method, graphene (0.5 wt%) of the same specifications as in Example 1 was directly mechanically ball-milled with uncoated polyimide spherical copper powder (manufacturer: Shanghai Shuitian Materials Technology Co., Ltd., grade: ST-35) (parameters same as in Example 1), then cold-pressed and sintered at 950°C in a hydrogen atmosphere for 2 hours.

[0040] Comparative Example 2 The difference from Example 1 is that the polyimide precursor coating and thermal imidization steps are omitted, and the pretreated copper powder is directly mixed with graphene by mechanical ball milling and then cold-pressed and sintered.

[0041] The test data for Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0042] Table 1: Test data of Examples 1-3 and Comparative Examples 1-2

[0043] As shown in Table 1, the graphene-copper composite material prepared by the method of this invention is significantly superior to that prepared by traditional methods in terms of thermal conductivity, electrical conductivity, density, and mechanical strength. The polyimide coating effectively improves the dispersibility and interfacial bonding of graphene, reduces interfacial thermal resistance, and thus enhances the overall performance.

Claims

1. A method for preparing a graphene-copper composite material, characterized in that, Includes the following steps: (1) Copper powder pretreatment: The spherical copper powder is cleaned and roughened. (2) Polyimide precursor coating: The pretreated copper powder is dispersed in a polyamic acid precursor solution, and the coating solution is formed by mechanical stirring and ultrasonic mixing. Then, the copper powder is obtained by filtration and drying. (3) Thermal imidization treatment: The polyamic acid-coated copper powder is heated to the imidization temperature under a protective atmosphere and kept at that temperature for a certain time to convert the polyamic acid into polyimide and form polyimide-coated copper powder. (4) Graphene introduction: Graphene is uniformly incorporated into polyimide-coated copper powder by mechanical ball milling or solution blending, with a graphene mass fraction of 0.1-5 wt%. (5) Molding and sintering: After the composite powder is cold-pressed into shape, it is sintered and densified under a protective atmosphere to form a composite material block.

2. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, The copper powder pretreatment in step (1) includes: Ultrasonic cleaning: Use organic solvents such as acetone or ethanol to ultrasonically clean copper powder for 10-60 minutes to remove oil and oxide film; Acid washing and activation: Soak in dilute sulfuric acid or hydrochloric acid solution for 1-10 minutes, rinse with pure water and dry.

3. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, In step (2), the solid content of the polyamic acid solution is 5-15 wt%, the solvent is N-methylpyrrolidone, and the mass ratio of copper powder to polyamic acid is 100:(1-10).

4. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, In step (3), the imidization temperature is 200-400℃, the holding time is 1-4h, and the protective atmosphere is nitrogen or argon.

5. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, In step (4), the mechanical ball milling parameters are: rotation speed 100-300 rpm, ball milling time 1-4 h, ball-to-material ratio 5:1 to 20:1, and ball milling medium is ethanol or acetone; or ultrasonic dispersion is used for solution blending.

6. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, In step (5), the cold pressing pressure is 100-500 MPa, the sintering temperature is 800-1050℃, the sintering time is 1-4 h, and the protective atmosphere is hydrogen or nitrogen.

7. The method for preparing the graphene-copper composite material according to claim 1, characterized in that, It also includes the following steps: hot isostatic pressing of the sintered material at a temperature of 500-900℃, a pressure of 50-200MPa, and a time of 0.5-2h.

8. A graphene-copper composite material, characterized in that, The graphene-copper composite material is prepared by any one of the preparation methods of claims 1-7, wherein the composite material has a thermal conductivity of not less than 425 W·m. -1 ·K -1 The conductivity is not less than 97% IACS and the density is not less than 98%.

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