A method for preparing a graphene film with high longitudinal thermal conductivity

Abstract

The application provides a preparation method of a graphene film with high longitudinal heat conduction performance, relates to the field of graphene heat conduction films, and comprises the following steps: coating slurry A1 on the surface of a substrate to form a film, and baking to surface dryness to obtain film B1; coating slurry A2 on the surface of film B1, combing the slurry layer of the wet film by using a comb-shaped doctor blade after coating, and baking to surface dryness to obtain composite film B2; coating slurry A1 on the surface of composite film B2 to form a film, and baking to obtain a composite film piece; and performing low-temperature heat treatment, high-temperature carbonization, graphitization and calendering on the composite film piece to obtain a graphene heat conduction film. The expanded graphite of the sandwich layer provides graphene structures perpendicular to the graphene films on both sides, and the edges of the graphene sheets provided by the sandwich layer form interconnected structures with the graphene films on both sides after calendering, so that the composite film has higher longitudinal heat conduction performance.

Description

Technical Field

[0001] This invention relates to the field of graphene thermal conductive film technology, and specifically to a method for preparing a graphene film with high longitudinal thermal conductivity. Background Technology

[0002] Graphene is a novel two-dimensional carbon material formed by the close-packing of carbon atoms in a hexagonal plane. As the thinnest known material in the world, graphene has attracted worldwide attention since its discovery in 2004 due to its unique and excellent physicochemical properties. Graphene films can be widely used in fields such as thermal conductivity, electromagnetic shielding, water treatment, and electric heating.

[0003] Currently, graphene thermal conductive films have become a "star" material in high-efficiency thermal management applications for mobile phones, batteries, and automotive products, and have the potential to replace currently commercially available polyimide films. With such thermal conductive films, the heat dissipation benefit is basically proportional to the thickness of the film without a significant decrease in thermal conductivity. Compared to simply increasing the thermal conductivity, increasing the thickness of the thermal conductive film is a more cost-effective way to improve performance. However, current graphene film preparation processes generally use graphene oxide slurry as a precursor, coating a thick wet film in a single step. During the drying process, the surface preferentially forms a film, thus preventing the evaporation of internal moisture, causing a series of problems such as incomplete drying. Chinese invention patent 202211115172.4 obtains a high thermal conductivity thick graphene film by first obtaining a single-layer graphene film and then sequentially laminating the single-layer thermally conductive graphene film using a graphene oxide solution as a binder. However, the graphene oxide dispersion applied is not graphitized, and the thermal conductivity may not be guaranteed.

[0004] Furthermore, with the rapid development of technology, the demand for vertical heat dissipation is increasing. With the advancement of graphene film preparation technology, the lateral thermal conductivity of graphene thermal conductive films has now exceeded 1500 W / m·K, but its vertical thermal conductivity can generally only reach 4 to 8 W / m·K, which is obviously increasingly unable to meet market demands.

[0005] In the prior art, Chinese invention patent 202310893433.3 discloses an ultra-soft graphene thermally conductive film with high longitudinal thermal conductivity and its preparation method. This technology uses a plasticizing foaming process to prepare a graphene film containing three-dimensional micropores, enabling self-connection between graphene layers and thus giving the graphene film high thermal conductivity in the longitudinal direction (perpendicular to the graphene layer direction). This method can improve longitudinal thermal conductivity, but it does not improve film thickness. In the prior art, the thickness of a single-layer coating is related to the solid content of the coating slurry; that is, the higher the solid content, the thicker the coated film. However, the higher the solid content of the slurry, the higher the viscosity, which is detrimental to the peeling and coating processes. Therefore, current methods for preparing thick films generally involve first preparing single-layer films separately, and then hot-pressing multiple layers together. This process is not only complex but also prone to separation between film layers, affecting the performance of the thick film.

[0006] To address the above issues, a more efficient preparation process needs to be developed in order to produce graphene films with high thermal conductivity. Summary of the Invention

[0007] This invention provides a method for preparing a graphene film with high longitudinal thermal conductivity to address the aforementioned problems existing in the prior art.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0009] On one hand, the present invention provides a method for preparing a graphene film with high longitudinal thermal conductivity, characterized in that: slurry A1 is coated onto a substrate surface to form a film, and dried to surface dryness to obtain film B1; slurry A2 is coated onto the surface of film B1, and after coating, a comb-shaped scraper is used to comb the slurry layer of the wet film, and dried to surface dryness to obtain composite film B2; slurry A1 is coated onto the surface of composite film B2 to form a film, and dried to obtain a composite film sheet; the composite film sheet is subjected to low-temperature heat treatment, high-temperature carbonization, graphitization, and calendering to obtain a graphene thermally conductive film.

[0010] Among them, slurry A1 is graphene oxide slurry, and slurry A2 is a mixture of graphene oxide and expanded graphite slurry.

[0011] Furthermore, the slurry A1 is a graphene oxide slurry with a pH of 6-8 and a concentration of 2%-10%.

[0012] Furthermore, the preparation process of the slurry A2 is as follows: expanded graphite is added to a graphene oxide slurry with a concentration of 3%-8%, wherein the mass ratio of expanded graphite to graphene oxide is 1:10-1:1, the pH is adjusted to 6-8, and the mixture is homogeneous.

[0013] Furthermore, the graphene oxide sheets used to prepare slurry A2 have a diameter of <5μm, and the expanded graphite used to prepare slurry A2 is pulverized worm graphite with a mesh size ≥100 mesh and a purity >99%.

[0014] Furthermore, the temperature of the low-temperature heat treatment is between 80 and 400°C.

[0015] Furthermore, the high-temperature carbonization temperature is between 600-1200℃.

[0016] On the other hand, the present invention provides a graphene film with high longitudinal thermal conductivity, characterized in that the graphene thermal conductive film prepared by the above preparation method has a sandwich structure, the core layer of which is a composite layer of graphene and expanded graphite, and the upper and lower surface layers are both graphene layers.

[0017] Furthermore, the thickness of the obtained graphene thermal conductive film is 75-225 μm.

[0018] The beneficial effects of this invention are as follows: This invention forms a film by coating three layers. The two outermost layers are graphene slurries, and the middle layer is a composite slurry of graphene and expanded graphite, designed as a composite sandwich structure, i.e., a three-layer sandwich structure. The surface of the composite film has high lateral thermal conductivity. The slurry of the sandwich layer is a composite slurry of expanded graphite and small-diameter graphene oxide slurry. The small-diameter graphene oxide can be inserted into the three-dimensional structure of the expanded graphene, improving the compactness of the sandwich layer. The expanded graphite in the sandwich layer provides a graphene structure perpendicular to the graphene films on both sides. After calendering, the sandwich layer... The graphene sheets provided in the core layer form interconnected structures with the graphene films on both sides, giving the composite film high longitudinal thermal conductivity, with a longitudinal thermal conductivity of over 53 W / m·K. At the same time, it can ensure the strength of the composite film and avoid film delamination. Moreover, the film sandwich layer prepared by this method contains a certain amount of expanded graphite, and after heat treatment, it is basically 100% carbon residue. Therefore, the film made with the same solid content of slurry is thicker than that made without expanded graphite, and there is no need to carry out film composite by hot pressing. Compared with the existing coating film production technology, it has a significant advantage in terms of film thickness. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the scraper blade of the comb-shaped scraper used in this invention;

[0020] Figure 2 This is the expanded graphite diagram used in this invention;

[0021] Figure 3 This is a cross-sectional SEM image of the graphene film prepared in Example 1 of this invention. Detailed Implementation

[0022] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0023] The specifications of the main raw materials used in the following examples are as follows:

[0024] Graphene oxide filter cake 1, with a solid content of 43% and graphene oxide sheet diameter of 10-20 μm;

[0025] Graphene oxide filter cake II, with a solid content of 42.3%, wherein the graphene oxide flakes have a diameter of <5μm;

[0026] Expanded graphite, worm graphite with a mesh size ≥100 mesh, and a purity >99%;

[0027] pH adjuster: Industrial grade ammonia;

[0028] Base material: Polypropylene fiber woven fabric.

[0029] Example 1

[0030] The method for preparing the graphene film in this embodiment includes the following steps:

[0031] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 2% slurry, and adjust the pH to 6 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare a 6% slurry, add expanded graphite at a mass ratio of 1:10 to expanded graphene oxide, adjust the pH to 6, and continue stirring until the mixture is uniform to obtain slurry A2.

[0032] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until it is surface dry to obtain film B1.

[0033] S3. Apply slurry A2 to the surface of membrane B1, with a slurry layer thickness of 3000 μm. After coating, use a comb-shaped doctor blade to repeatedly scrape and comb the slurry layer of the wet membrane. After combing, place it in an oven and dry until surface dry to obtain composite membrane B2; the cross-sectional shape of the doctor blade of the comb-shaped doctor blade is shown in [reference needed]. Figure 1 As shown, the bottom of the scraper has a comb-like structure with teeth that are 3mm long.

[0034] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0035] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 200℃ for 2 hours, high-temperature carbonization at 600℃ for 2.5 hours, graphitization treatment at 3200℃ for 0.5 hours, and calendering to obtain a graphene thermally conductive film with a thickness of 75 μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0036] Example 2

[0037] The method for preparing the graphene film in this embodiment includes the following steps:

[0038] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 10% slurry, and adjust the pH to 8 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare a 3% slurry, add expanded graphite at a mass ratio of 1:1 to expanded graphite oxide, adjust the pH to 7, and continue stirring until the mixture is uniform to obtain slurry A2.

[0039] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until it is surface dry to obtain film B1.

[0040] S3. Take slurry A2 and coat it on the surface of membrane B1. The slurry layer thickness is 3000μm. After coating, use the same comb-shaped scraper as in Example 1 to scrape and comb the slurry layer of the wet membrane back and forth. After combing, place it in an oven to dry until surface dry to obtain composite membrane B2.

[0041] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0042] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 400℃ for 2 hours, high-temperature carbonization at 600℃ for 1 hour, graphitization treatment at 3000℃ for 1 hour, and calendering to obtain a graphene thermally conductive film with a thickness of 225 μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0043] Example 3

[0044] The method for preparing the graphene film in this embodiment includes the following steps:

[0045] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 6% slurry, and adjust the pH to 7 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare an 8% slurry, add expanded graphite at a mass ratio of 1:4 to expanded graphite oxide, adjust the pH to 7, and continue stirring until the mixture is uniform to obtain slurry A2.

[0046] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until it is surface dry to obtain film B1.

[0047] S3. Take slurry A2 and coat it on the surface of membrane B1. The slurry layer thickness is 3000μm. After coating, use the same comb-shaped scraper as in Example 1 to scrape and comb the slurry layer of the wet membrane back and forth. After combing, place it in an oven to dry until surface dry to obtain composite membrane B2.

[0048] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0049] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 300℃ for 2 hours, high-temperature carbonization at 1000℃ for 2 hours, graphitization treatment at 2900℃ for 1 hour, and calendering to obtain a graphene thermally conductive film with a thickness of 175μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0050] Comparative Example 1

[0051] The graphene film in this comparative example only includes the core layer of the graphene thermally conductive film of Example 1, and its preparation method includes the following steps:

[0052] S1. Raw material preparation: Take graphene oxide filter cake 2 and prepare a 6% slurry. Add expanded graphite at a mass ratio of 1:10 of expanded graphite to graphene oxide, adjust the pH to 6, and continue stirring until the mixture is uniform to obtain slurry A2. (i.e., graphene oxide slurry A2 of the same example).

[0053] S2. Take slurry A2 and coat it on the substrate to form a film with a wet film thickness of 3000μm. After coating, use the same comb-shaped scraper as in Example 1 to scrape and comb the slurry layer of the wet film back and forth. After combing, place it in an oven to dry and obtain a composite film.

[0054] S3. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 200℃ for 2 hours, high-temperature carbonization at 600℃ for 2.5 hours, graphitization treatment at 3200℃ for 0.5 hours, and calendering to obtain a graphene thermally conductive film with a thickness of 35 μm. The graphene thermally conductive film has a single-layer structure, namely, the core layer of Example 1—a composite layer of graphene and expanded graphite.

[0055] Comparative Example 2

[0056] The preparation method of the graphene film in this comparative example is basically the same as that in Example 1, except that the step of drying to surface dryness in steps S2 and S3 is changed to drying to complete dryness, as shown in the following steps:

[0057] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 2% slurry, and adjust the pH to 6 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare a 6% slurry, add expanded graphite at a mass ratio of 1:10 to expanded graphene oxide, adjust the pH to 6, and continue stirring until the mixture is uniform to obtain slurry A2.

[0058] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until completely dry to obtain film B1.

[0059] S3. Take slurry A2 and coat it on the surface of membrane B1. The slurry layer thickness is 3000μm. After coating, use the same comb-shaped scraper as in Example 1 to scrape and comb the slurry layer of the wet membrane back and forth. After combing, place it in an oven to dry completely to obtain composite membrane B2.

[0060] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0061] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 200℃ for 2 hours, high-temperature carbonization at 600℃ for 2.5 hours, graphitization treatment at 3200℃ for 0.5 hours, and calendering to obtain a graphene thermally conductive film with a thickness of 75 μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0062] Comparative Example 3

[0063] The preparation method of the graphene film in this comparative example is basically the same as that in Example 1, except that the combing operation is not performed in step S3, as shown in the following steps:

[0064] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 2% slurry, and adjust the pH to 6 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare a 6% slurry, add expanded graphite at a mass ratio of 1:10 to expanded graphene oxide, adjust the pH to 6, and continue stirring until the mixture is uniform to obtain slurry A2.

[0065] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until it is surface dry to obtain film B1.

[0066] S3. Take slurry A2 and coat it on the surface of membrane B1. The slurry layer thickness is 3000μm. After coating, place it in an oven and dry it until it is surface dry to obtain composite membrane B2.

[0067] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0068] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 200℃ for 2 hours, high-temperature carbonization at 600℃ for 2.5 hours, graphitization treatment at 3200℃ for 0.5 hours, and calendering to obtain a graphene thermally conductive film with a thickness of 74 μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0069] Comparative Example 4

[0070] The preparation method of the graphene film in this comparative example is basically the same as that in Example 1, except that expanded graphite was not added to slurry A2, as shown in the following steps:

[0071] S1. Raw material preparation: Take graphene oxide filter cake one, add water to prepare a 2% slurry, and adjust the pH to 6 to obtain slurry A1; take graphene oxide filter cake two, add water to prepare a 6% slurry, adjust the pH to 6, and continue stirring until the mixture is uniform to obtain slurry A2.

[0072] S2. Take slurry A1 and coat it on the substrate surface to form a film with a wet film thickness of 3000μm. Place it in an oven and dry it until it is surface dry to obtain film B1.

[0073] S3. Take slurry A2 and coat it on the surface of membrane B1. The slurry layer thickness is 3000μm. After coating, use the same comb-shaped scraper as in Example 1 to scrape and comb the slurry layer of the wet membrane back and forth. After combing, place it in an oven to dry until surface dry to obtain membrane B2.

[0074] S4. Take slurry A1 and coat it on the surface of composite membrane B2 to form a film with a slurry layer thickness of 3000μm. Place it in an oven to dry and obtain a composite membrane.

[0075] S5. After peeling the composite film from the substrate, it undergoes low-temperature heat treatment at 200℃ for 2 hours, high-temperature carbonization at 600℃ for 2.5 hours, graphitization treatment at 3200℃ for 0.5 hours, and calendering to obtain a graphene thermally conductive film with a thickness of 72 μm. The graphene thermally conductive film has a sandwich structure, with its core layer being a composite layer of graphene and expanded graphite, and its upper and lower surface layers being graphene layers.

[0076] The longitudinal thermal conductivity of the graphene thermal conductive films prepared in the above embodiments and comparative examples was tested. The test standard adopted was ASTM E1461-01, and the test data are shown in Table 1.

[0077] Table 1

[0078]

[0079]

[0080] The data in the table show that the thermally conductive film prepared by the present invention has high longitudinal thermal conductivity, with longitudinal thermal conductivity coefficients all above 54 W / m·K. Furthermore, as shown in Example 1 and Comparative Example 4, the film thickness of the product prepared by the present invention also has certain advantages, and there is no delamination problem.

Claims

1. A method for preparing a graphene film with high longitudinal thermal conductivity, characterized in that, Slurry A1 is coated onto the substrate surface to form a film, and then dried to surface dryness to obtain film B1. Slurry A2 is coated onto the surface of film B1, and after coating, the slurry layer of the wet film is combed using a comb-shaped scraper and dried to surface dryness to obtain composite film B2. Slurry A1 is coated onto the surface of composite film B2 to form a film, and then dried to obtain composite film sheet. After peeling the composite film sheet from the substrate, it undergoes low-temperature heat treatment, high-temperature carbonization, graphitization, and calendering to obtain graphene thermal conductive film. Among them, slurry A1 is graphene oxide slurry, and slurry A2 is a mixture of graphene oxide and expanded graphite slurry.

2. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that, The slurry A1 is a graphene oxide slurry with a pH of 6-8 and a concentration of 2%-10%.

3. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that, The preparation process of the slurry A2 is as follows: expanded graphite is added to a graphene oxide slurry with a concentration of 3%-8%, wherein the mass ratio of expanded graphite to graphene oxide is 1:10-1:1, the pH is adjusted to 6-8, and the mixture is homogeneous.

4. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1 or 3, characterized in that, The graphene oxide sheets used to prepare slurry A2 have a diameter of <5 μm.

5. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that, The temperature of the low-temperature heat treatment is between 80 and 400°C.

6. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that, The high-temperature carbonization temperature is between 600-1200℃.

7. A graphene film with high longitudinal thermal conductivity, characterized in that, The graphene thermal conductive film is prepared by the preparation method according to any one of claims 1-6. The graphene thermal conductive film has a sandwich structure, the core layer of which is a composite layer of graphene and expanded graphite, and the upper and lower surface layers are graphene layers.

8. The graphene film with high longitudinal thermal conductivity according to claim 7, characterized in that, The thickness of the obtained graphene thermal conductive film is 75-225 μm.

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