High-thermal-conductivity graphene heat dissipation film and preparation method thereof

Abstract

The application discloses a high-thermal-conductivity graphene heat-dissipation film and a preparation method thereof. The film is prepared by adopting a mode of semi-vacuum pressurized pre-reduction-vacuum hot-pressing pre-graphitization-vacuum calendering-atmosphere pressurized graphitization and by using appropriate technology for reduction. Through combination of vacuumizing, air passing, temperature rising technology and pressure, water vapor and other gases generated in the reduction process are quickly extracted to prevent water vapor from condensing. The film is pre-graphitized under appropriate pressure and technology, so that the expansion rate of the film can be effectively controlled and the structural integrity and high orientation of the film can be maintained. The film is graphitized under high pressure to promote the graphitization degree and improve the thermal conductivity, so that the graphene heat-dissipation film with high thermal conductivity is prepared.

Description

Technical Field

[0001] This invention belongs to the field of thermal management technology, specifically relating to a high thermal conductivity graphene heat dissipation film and its preparation method. Background Technology

[0002] Since its discovery, graphene has garnered attention from academia and industry for its extremely high electrical conductivity, extremely high thermal conductivity, superior mechanical properties, and excellent flexibility. Graphene heat dissipation films, with their high thermal conductivity, have become a preferred heat dissipation material in high-end electronic applications. The mainstream method for preparing graphene heat dissipation films involves using graphene oxide as raw material and a process of "dispersion-coating-drying-reduction-calendering." Typically, the coated graphene oxide film has a high water content and numerous oxygen-containing functional groups. During the reduction process, a large amount of gas is released, causing the graphene oxide film to expand significantly. Macroscopically, this manifests as bubbling and delamination; microscopically, it results in poor orientation of the graphene oxide sheets, and even large sheets breaking into smaller pieces. Excessive expansion also leads to numerous wrinkles in the graphene film during calendering, affecting phonon transport and causing the thermal conductivity of the graphene film to be far lower than expected.

[0003] Currently, the main method for suppressing the expansion of graphene oxide films and maintaining their high thermal conductivity is the limiting reduction method. This method involves using a graphite clamp with multiple sets of graphite screws and nuts to hold the graphene oxide film in place, followed by reduction in a carbonization furnace or graphite furnace. During reduction, the graphene oxide film is restricted by the graphite clamp and cannot expand, thus producing a low-expansion, high-thermal-conductivity graphene heat dissipation film. However, the graphite screws and nuts used to limit the expansion of the graphene oxide film in this method are often unable to withstand the forces generated by the expansion of the graphene film at high temperatures and are prone to breakage. Summary of the Invention

[0004] To address the aforementioned problems, this invention employs a semi-vacuum pressurized pre-reduction—vacuum hot-pressing pre-graphitization—vacuum calendering—atmosphere-pressurized graphitization process, coupled with appropriate techniques for reduction. By combining vacuuming, ventilation, heating, and pressure, the water vapor and other gases generated during reduction are rapidly extracted, preventing water vapor condensation. Pre-graphitization of the membrane under suitable pressure and process conditions effectively controls the membrane's expansion rate, maintaining structural integrity and high orientation. After pre-graphitization, the density is compressed to 2.0 g / cm³. 3 In summary, when the membrane undergoes graphitization under high pressure, the pressure can promote the degree of graphitization and improve the thermal conductivity.

[0005] One of the technical solutions of this invention is to provide a method for preparing a high thermal conductivity graphene heat dissipation film, comprising the following steps:

[0006] (1) Pressure reduction of graphene oxide film: vacuum degree is 5~20kPa, heating temperature is 200~500℃, holding time is 0.5h~8h, heating rate is 0.01~1℃ / min; pressure applied to graphene oxide film is 10~60kPa;

[0007] Heating in a vacuum environment can effectively accelerate the vaporization of free water in the graphene oxide film as a whole, while preventing the free water at the edges from vaporizing too quickly. Micro-ventilation can accelerate the removal of moisture from the air, preventing excessive ambient humidity from slowing down the vaporization of free water in the film. At the same time, appropriate pressure combined with an extremely slow heating rate can effectively suppress the expansion of the graphene oxide film caused by the vaporization of free water, reducing structural damage.

[0008] (2) Pre-graphitize the graphene oxide film after step 1 under vacuum pressure: under vacuum conditions, the heating rate is 0.2~10℃ / min to heat the temperature to 2000~2400℃ and the holding time is 0.5h~4h; the pressure applied to the graphene oxide film after step 1 is 0.02~1.5MPa;

[0009] The pre-graphitization temperature reaches 2000~2400℃, which reduces all functional groups in graphene oxide, preventing further reduction reactions and gas generation in subsequent processes, and also preventing graphitization structure rearrangement. The slow heating rate combined with a certain pressure can effectively suppress the expansion of graphene oxide film caused by gas generation during reduction, reduce structural damage between layers, and maintain a highly oriented structure.

[0010] (3) The pre-graphitized graphene film treated in step 2 was subjected to vacuum conditions, first by oscillating pressure to remove bubbles, and then by gradually increasing pressure to densify. The final pre-graphitized graphene film had a film density of 2.0~2.23 g / cm³. 3 ;

[0011] The oscillating pressure degassing method involves applying a constant pressure in the range of 0.5 to 5 MPa, holding the pressure for 5 to 20 seconds after each application, and then completely depressurizing to 0. The constant pressure of each oscillating pressurization gradually increases, and the total number of pressurizations is 20 to 50.

[0012] The progressive pressurization and densification process involves applying a pressure of 4.0~10MPa, gradually increasing the pressure to the maximum, and then holding the pressure for 120 seconds.

[0013] By repeatedly pressurizing and depressurizing under vacuum, the internal gas is gradually removed during the oscillating and degassing process, preventing the formation of micro-air pockets. The more times the pressure is applied, the better the degassing effect. Combined with a progressive pressurization and densification process, the density is compacted to 2.0 g / cm³. 3In addition, the high orientation structure is maintained while avoiding the micro-airbags from being crushed and causing structural damage. The high density will make the film surface smooth, and during subsequent graphitization, it is not easy for micro-folds to form between the spacers (graphite plates, carbon paper, artificial graphite films, etc.) and cause adhesion.

[0014] (4) Pressurized graphitization: Under inert gas protection, the pressure applied to the pre-graphitized graphene film is 1.5~40MPa; the heating temperature is 2600~3100℃, and the holding time is 0.5~8h. This step can be used to pressurize multiple pre-graphitized graphene films in a concentrated manner, and graphite plates, carbon paper, artificial graphite films, etc. can be used as spacers between the films. Under high pressure, the graphitization reaction will compress the interlayer spacing during the graphitization structure rearrangement process, reduce the diffusion distance between carbon atoms, and make it easier for carbon atoms to rearrange to form a graphite layer structure, thereby improving the degree of graphitization; at the same time, under high pressure, the growth direction of graphite crystals is restricted, making it easier to grow laterally and form larger graphite grains, all of which are beneficial to improving thermal conductivity. At the same time, the surface after compaction is smooth and will not be compressed and form micro-wrinkles during the structure rearrangement process, which can effectively prevent adhesion with the spacers.

[0015] Furthermore, the density of the graphene oxide film after step 1 treatment is 0.4~0.7 g / cm³. 3 .

[0016] Furthermore, the density of the graphene film after step 2 treatment is between 0.6 and 1.4 g / cm³. 3 .

[0017] Furthermore, the heating described in step 4 is carried out in a hot press furnace, an SPS discharge plasma sintering furnace, or a Joule hot flash evaporation device.

[0018] Furthermore, the density of the graphene film after step 4 treatment is 1.9~2.2 g / cm³. 3 .

[0019] Furthermore, the inert gas is argon.

[0020] The second technical solution of the present invention is to provide a high thermal conductivity graphene heat dissipation film prepared by the above preparation method.

[0021] The beneficial effects of this invention are as follows: by applying appropriate pressure and a slow heating rate during the reduction process, the expansion of the graphene film during reduction is suppressed, structural damage is reduced, and a highly oriented structure is maintained; through the oscillating degassing and compaction process, the gas inside the film is gradually vented while retaining the highly oriented structure, making the surface of the film smooth and dense, which can prevent adhesion to the spacers during subsequent structural rearrangement; finally, graphitization under high pressure can reduce the graphitization temperature, promote the repair of structural defects, reduce the interlayer spacing, make it easier for carbon atoms to rearrange to form a graphite structure, and affect the growth direction of graphite crystals, forming larger graphite grains with specific orientations, thereby preparing a graphene heat dissipation film with high thermal conductivity. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] The embodiments of the present invention will be further described below with reference to several examples.

[0025] 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.

[0026] 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.

[0027] Example 1

[0028] (1) A 270mm*270mm*300μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 260℃ at a heating rate of 0.1℃ / min under a vacuum of 20kPa and a weight of 15kPa, and holding it at that temperature for 2h. The pre-reduced film had a thickness of 320μm and a density of 0.7g / cm³. 3 ;

[0029] (2) Under vacuum conditions, the temperature was increased to 2300℃ at a rate of 2℃ / min under hydraulic pressure of 0.5MPa and held for 2h for vacuum pre-graphitization; the thickness after pre-graphitization was 130μm and the density was 0.89g / cm³. 3 ;

[0030] (3) Defoaming was performed by oscillation and pressurization, with the pressure gradually increased from 0.5 MPa to 4 MPa. After each pressurization, the pressure was held for 5 seconds and then completely depressurized to 0. The number of defoaming cycles was 35. The densification pressure was increased from 4 MPa to 9 MPa and held for 120 seconds. The thickness of the densified film was 54 μm and the density was 2.09 g / cm³. 3 ;

[0031] (4) Under argon atmosphere, the temperature was increased to 2800℃ and held for 4 hours at a heating rate of 2~10℃ / min in a 2800℃ hot press furnace with a pressure of 15MPa; after graphitization, the thickness of the film was 56μm and the density was 2.02g / cm³. 3 .

[0032] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 856 mm. 2 / s.

[0033] Example 2

[0034] (1) A 270mm*270mm*280μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 260℃ at a heating rate of 0.05℃ / min under a vacuum of 18kPa and a weight of 8.5kPa and holding it at that temperature for 2h. The pre-reduced film had a thickness of 300μm and a density of 0.52g / cm³. 3 ;

[0035] (2) Under vacuum conditions, the temperature was increased to 2300℃ at a rate of 2℃ / min under hydraulic pressure of 0.5MPa and held for 2h for vacuum pre-graphitization; the thickness after pre-graphitization was 135μm and the density was 0.77g / cm³. 3 ;

[0036] (3) Defoaming was performed by oscillation and pressurization, with the pressure gradually increased from 0.5 MPa to 4 MPa. After each pressurization, the pressure was held for 20 seconds and then completely depressurized to 0. The number of defoaming cycles was 35. The densification pressure was increased from 4 MPa to 9 MPa and held for 120 seconds. The thickness of the densified film was 49 μm and the density was 2.14 g / cm³. 3 ;

[0037] (4) Under argon atmosphere, the temperature was increased to 2800℃ and held for 4 hours at a heating rate of 10℃ / min in a 2800℃ hot press furnace with a pressure of 15MPa. After graphitization, the thickness of the film was 52μm and the density was 2.02g / cm³. 3 .

[0038] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 874 mm. 2 / s.

[0039] Example 3

[0040] (1) A 100mm*100mm*300μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 260℃ at a heating rate of 0.05℃ / min under a vacuum of 18kPa and a weight of 16kPa and holding it at that temperature for 8h. The pre-reduced film had a thickness of 310μm and a density of 0.54g / cm³. 3 ;

[0041] (2) Under vacuum conditions, the temperature was increased to 2300℃ at a rate of 1.5℃ / min under hydraulic pressure of 0.28MPa and held for 2h for vacuum pre-graphitization; the thickness after pre-graphitization was 145μm and the density was 0.72g / cm³. 3 ;

[0042] (3) Defoaming was performed by oscillation and pressurization, with the pressure gradually increased from 0.5 MPa to 5.0 MPa. After each pressurization, the pressure was held for 15 seconds and then completely depressurized to 0. The number of defoaming cycles was 50. The densification pressure was increased from 4 MPa to 9 MPa and held for 120 seconds. The thickness of the densified film was 48 μm and the density was 2.18 g / cm³. 3 ;

[0043] (4) Under argon atmosphere, the temperature was increased to 2800℃ in a 2800℃ hot press furnace at a pressure of 20MPa and a heating rate of 10℃ / min, and held for 5 hours; the thickness of the graphitized film was 49μm and the density was 2.14g / cm³. 3 .

[0044] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 886 mm. 2 / s.

[0045] Example 4

[0046] (1) A 50mm*50mm*300μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 260℃ at a heating rate of 0.05℃ / min under a vacuum of 16kPa and a weight of 15kPa, and holding it at that temperature for 2h. The pre-reduced film had a thickness of 320μm and a density of 0.51g / cm³. 3 ;

[0047] (2) Under vacuum conditions, the temperature was increased to 2000℃ at a rate of 1.5℃ / min under hydraulic pressure of 0.25MPa and held for 4h for vacuum pre-graphitization; the thickness after pre-graphitization was 150μm and the density was 0.69g / cm³. 3 ;

[0048] (3) Defoaming was performed by oscillation and pressurization, with the pressure gradually increased from 0.5 MPa to 4.5 MPa. After each pressurization, the pressure was held for 20 seconds and then completely depressurized to 0. The number of defoaming cycles was 30. The densification pressure was increased from 4 MPa to 8.5 MPa and held for 120 seconds. The thickness of the densified film was 50 μm and the density was 2.08 g / cm³. 3 ;

[0049] (4) Under argon atmosphere, the temperature was increased to 2700℃ for 0.5 hours at a heating rate of 50℃ / min using an SPS discharge plasma sintering furnace under a pressure of 40MPa; the thickness of the graphitized film was 49μm and the density was 2.13g / cm³. 3 The thermal diffusivity measured using an LFA467 thermal conductivity meter is 830 mm. 2 / s.

[0050] Example 5

[0051] (1) A 50mm*50mm*300μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 200℃ at a heating rate of 0.01℃ / min and holding it for 2h under a vacuum of 5kPa and a weight of 10kPa. The pre-reduced film had a thickness of 320μm and a density of 0.4g / cm³. 3 ;

[0052] (2) Under vacuum conditions, the temperature was increased to 2000℃ at a rate of 0.2℃ / min under hydraulic pressure of 0.02MPa and held for 4h for vacuum pre-graphitization; the thickness after pre-graphitization was 130μm and the density was 0.6g / cm³. 3 ;

[0053] (3) Defoaming was carried out by oscillation and pressurization. The pressure was gradually increased from 0.5MPa to 5.0MPa. After each pressurization, the pressure was held for 10s and then completely depressurized to 0. The number of defoaming cycles was 20. The densification pressure was increased from 4MPa to 9MPa and held for 120s. The thickness of the densified film was 50μm and the density was 2.01g / cm3.

[0054] (4) Under argon atmosphere, the temperature was increased to 2600℃ for 0.5 hours at a heating rate of 50℃ / min using an SPS discharge plasma sintering furnace with a pressure of 1.5MPa; after graphitization, the film thickness was 55μm and the density was 1.90g / cm³. 3 .

[0055] Example 6

[0056] (1) A 50mm*50mm*300μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 500℃ at a rate of 1℃ / min under a vacuum of 15kPa and a weight of 60kPa and holding it for 0.5h. The pre-reduced film had a thickness of 310μm and a density of 0.6g / cm³. 3 ;

[0057] (2) Under vacuum conditions, the temperature was increased to 2400℃ at a rate of 10℃ / min under hydraulic pressure of 1.5MPa and held for 0.5h for vacuum pre-graphitization; the thickness after pre-graphitization was 100μm and the density was 1.4g / cm³. 3 ;

[0058] (3) Defoaming was performed by oscillation and pressurization, with the pressure gradually increased from 0.5 MPa to 5.0 MPa. After each pressurization, the pressure was held for 5 seconds and then completely depressurized to 0. The number of defoaming cycles was 50. The densification pressure was increased from 4 MPa to 10 MPa and held for 120 seconds. The thickness of the densified film was 40 μm and the density was 2.23 g / cm³. 3 ;

[0059] (4) Under argon atmosphere, the temperature was increased to 3100℃ for 8 hours at a heating rate of 50℃ / min using an SPS discharge plasma sintering furnace with a pressure of 40MPa; after graphitization, the film thickness was 55μm and the density was 2.20g / cm³. 3 .

[0060] Comparative Example 1

[0061] (1) A 270mm*270mm*310μm graphene oxide film was pre-reduced in a semi-vacuum environment by heating it to 260℃ at a heating rate of 0.05℃ / min under a pressure of 8.2kPa and holding it at that temperature for 2h. The pre-reduced film had a thickness of 340μm and a density of 0.51g / cm³. 3 ,

[0062] (2) Vacuum carbonization was carried out in a vacuum environment by heating to 1600℃ at a rate of 2℃ / min and holding for 1h; the carbonized thickness was 450μm and the density was 0.27g / cm³. 3 ,

[0063] (3) Under argon atmosphere, the temperature was increased to 2800℃ at a rate of 2~10 min and held for 4 hours; after graphitization, the thickness of the film was 610 μm and the density was 0.19 g / cm³. 3 .

[0064] (4) After calendering, the thickness is 54 μm and the density is 2.15 g / cm³. 3

[0065] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 793 mm. 2 / s.

[0066] Comparative Example 2

[0067] (1) A 270mm*270mm*310μm graphene oxide film was pre-reduced in a semi-vacuum manner by heating it to 260℃ at a heating rate of 0.05℃ / min and holding it for 2h without applying external force; the pre-reduced film had a thickness of 410μm and a density of 0.42g / cm³. 3 And there are many bubbles on the surface;

[0068] (2) Vacuum pre-graphitization was carried out in a vacuum environment by heating to 2200℃ at a rate of 2℃ / min and holding for 2h; the thickness after pre-graphitization was 600μm and the density was 0.20g / cm³. 3 ,

[0069] (3) Under argon atmosphere, the temperature was increased to 2800℃ and held for 5 hours at a heating rate of 2~10℃ / min in a 2800℃ hot press furnace with a pressure of 20MPa; after graphitization, the thickness of the film was 65μm and the density was 1.59g / cm³. 3 Furthermore, the film easily adheres to the carbon paper and cannot be completely separated;

[0070] (4) Due to its high density, it was impossible to remove bubbles. After densification using a progressively pressurized densification process, the membrane thickness was 56 μm and the density was 1.84 g / cm³. 3 Furthermore, the surface of the membrane is covered with tiny air bubbles;

[0071] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 680 mm. 2 / s.

[0072] Comparative Example 3

[0073] (1) A 270mm*270mm*310μm graphene oxide film was pre-reduced in a semi-vacuum manner by heating it to 260℃ at a heating rate of 0.05℃ / min and holding it for 2h without applying external force; the pre-reduced film had a thickness of 420μm and a density of 0.41g / cm³. 3 And there are many bubbles on the surface;

[0074] (2) Vacuum carbonization was carried out in a vacuum environment by heating to 1600℃ at a rate of 2℃ / min and holding for 2h; the carbonized thickness was 580μm and the density was 0.20g / cm³. 3 ,

[0075] (3) Under argon atmosphere, the temperature was increased to 2800℃ and held for 5 hours at a heating rate of 2~10℃ / min in a 2800℃ hot press furnace with a pressure of 20MPa; after graphitization, the thickness of the film was 90μm and the density was 1.15g / cm³. 3Furthermore, the film easily adheres to the carbon paper and cannot be completely separated;

[0076] (4) Due to its high density, it was impossible to remove bubbles. After densification using a gradual pressurization process, the membrane thickness was 65 μm and the density was 1.59 g / cm³. 3 Furthermore, the surface of the membrane is covered with tiny air bubbles;

[0077] The thermal diffusivity measured using an LFA467 thermal conductivity meter is 652 mm. 2 / s.

[0078] 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 high thermal conductivity graphene heat dissipation film, characterized in that, It includes the following steps: (1) Pressure reduction of graphene oxide film: vacuum degree is 5~20kPa, heating temperature is 200~500℃, holding time is 0.5h~8h, heating rate is 0.01~1℃ / min; pressure applied to graphene oxide film is 10~60kPa; (2) The graphene oxide film after step 1 is pre-graphitized under vacuum conditions to obtain a graphene film: the temperature is heated to 2000~2400℃ at a heating rate of 0.2~10℃ / min under vacuum conditions, and the holding time is 0.5h~4h; the pressure applied to the graphene oxide film after step 1 is 0.02~1.5MPa; (3) The graphene film obtained in step 2 was subjected to vacuum conditions, first by oscillating pressure to remove bubbles, and then by gradually increasing pressure to densify it. The final graphene film had a density of 2.0~2.23 g / cm³. 3 ; The oscillating pressure degassing method involves applying a constant pressure in the range of 0.5 to 5 MPa, holding the pressure for 5 to 20 seconds after each application, and then completely depressurizing to 0. The constant pressure of each oscillating pressurization gradually increases, and the total number of pressurizations is 20 to 50. The progressive pressurization and densification process involves applying a pressure of 4.0~10MPa, gradually increasing the pressure to the maximum, and then holding the pressure for 120 seconds. (4) Pressurized graphitization: Under the protection of inert gas, apply a pressure of 1.5~40MPa to the graphene film obtained in step 3; heat to 2600~3100℃ and keep warm for 0.5~8h.

2. The preparation method according to claim 1, characterized in that, The density of the graphene oxide film after step 1 treatment is 0.4~0.7 g / cm³. 3 .

3. The preparation method according to claim 1, characterized in that, The graphene film obtained in step 2 has a density of 0.6~1.4 g / cm³. 3 .

4. The preparation method according to claim 1, characterized in that, The heating described in step 4 is carried out in a hot press furnace, an SPS discharge plasma sintering furnace, or a Joule hot flash evaporation device.

5. The preparation method according to claim 1, characterized in that, The density of the graphene film after step 4 treatment is 1.9~2.2 g / cm³. 3 .

6. The preparation method according to claim 1, characterized in that, The inert gas is argon.

7. A high thermal conductivity graphene heat dissipation film prepared by the preparation method according to claim 1.