Preparation method of graphene film with high longitudinal heat-conducting property

Abstract

The invention provides a preparation method of a graphene film with high longitudinal heat-conducting property, and relates to the field of graphene heat-conducting films.The preparation method comprises the steps that slurry A1 is taken to coat the surface of a substrate to form a film, the film is dried until the surface is dry, and a film B1 is obtained; coating the slurry A2 on the surface of the film B1, carding the slurry layer of the wet film by adopting a comb-shaped blade coating device after coating, and drying until the surface is dry to obtain a composite film B2; coating the slurry A1 on the surface of the composite film B2 to form a film, and drying to obtain a composite film; the expanded graphite of the sandwich layer provides a graphene structure perpendicular to the graphene films on the two sides, and after rolling, the edges of the graphene sheets provided by the sandwich layer and the graphene films on the two sides form interconnection structures respectively; the composite film is endowed with relatively high longitudinal heat-conducting property.

Description

Technical Field

[0001] The invention relates to the technical field of graphene thermal conductive films, and in particular to a method for preparing a graphene film with high longitudinal thermal conductivity. Background Art

[0002] Graphene is a new type of two-dimensional carbon material formed by hexagonal and closely packed carbon atoms in a plane. As the thinnest substance known in the world, graphene has attracted worldwide attention for its unique and excellent physical and chemical properties since its discovery in 2004. Graphene films can be widely used in thermal conductivity, electromagnetic shielding, water treatment, electric heating and other fields.

[0003] At present, graphene thermal conductive film has become a "star" material in the application of efficient thermal management of mobile phones, batteries, and automotive products, and there is a possibility of replacing the current commercial polyimide film. When the thermal conductivity of this type of thermal conductive film does not drop significantly, the heat dissipation benefit is basically proportional to the thickness of the thermal conductive film. Compared with simply increasing the thermal conductivity, increasing the thickness of the thermal conductive film is a more cost-effective way to improve performance, but the current preparation process of graphene film generally uses graphene oxide slurry as a precursor, and a thicker wet film is coated at one time. During the drying process of the wet film, the surface will preferentially form a film and prevent the evaporation of internal water, resulting in a series of problems such as inability to dry thoroughly. Chinese invention patent 202211115172.4 obtains a single-layer graphene film first and then uses a graphene oxide solution as a binder to sequentially bond the single-layer thermal conductive graphene film to obtain a secondary molded high thermal conductivity graphene thick film. However, the applied graphene oxide dispersion has not been graphitized, and the thermal conductivity may not be guaranteed.

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

[0005] In the prior art, Chinese invention patent 202310893433.3 discloses a super-soft graphene thermal conductive film with high longitudinal thermal conductivity and a preparation method thereof. The technology uses a plasticizing and foaming process to prepare a graphene film containing three-dimensional micropores, so that self-connection is formed between the graphene layers so that the graphene film exhibits high thermal conductivity in the longitudinal direction (perpendicular to the direction of the graphene layer). This scheme can improve the longitudinal thermal conductivity, but there is no improvement in film thickness. In the prior art, the thickness of a single-layer coating is related to the solid content of the slurry used for coating, that is, the higher the solid content, the thicker the coated film, but the higher the solid content of the slurry, the greater the viscosity, which is not conducive to the stripping and coating processes. Therefore, the current method for preparing thick films is generally to prepare single-layer films separately first, and then hot-press the multilayer film. Not only is the process complicated, but it is also easy to produce separation between film layers, affecting the performance of the thick film.

[0006] In view of the above problems, a more efficient preparation process needs to be optimized in order to prepare graphene films with high thermal conductivity. Summary of the invention

[0007] In view of the above problems existing in the prior art, the present invention provides a method for preparing a graphene film with high longitudinal thermal conductivity.

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

[0009] On the one hand, the present invention provides a method for preparing a graphene film with high longitudinal thermal conductivity, characterized in that slurry A1 is applied on the surface of a substrate to form a film, and dried until the surface is dry to obtain a film B1; slurry A2 is applied on the surface of film B1, and after coating, the slurry layer of the wet film is combed with a comb-shaped scraper, and dried until the surface is dry to obtain a composite film B2; slurry A1 is applied on the surface of the 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 thermal conductive film.

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

[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: adding expanded graphite 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, adjusting the pH to 6-8, and mixing uniformly.

[0013] Furthermore, the diameter of the graphene oxide sheet used to prepare the slurry A2 is less than 5 μm, and the expanded graphite used to prepare the slurry A2 is uncrushed worm graphite, with a mesh number of ≥100 meshes and a purity of >99%.

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

[0015] Furthermore, the temperature of the high temperature carbonization is 600-1200°C.

[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 obtained by the above-mentioned preparation method is a sandwich structure, its core layer is a composite layer of graphene and expanded graphite, and its upper and lower surface layers are both graphene layers.

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

[0018] The beneficial effects of the present invention are as follows: the present invention forms a film by coating in three layers, the two surface slurries are graphene slurries, the middle layer slurry is a composite slurry of graphene and expanded graphite, and is designed to form 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 to improve 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 The edges of the graphene sheets provided by the core layer form an interconnected structure with the graphene films on both sides, giving the composite film a higher longitudinal thermal conductivity, wherein the longitudinal thermal conductivity coefficient can reach above 53w / m·K, while ensuring the strength of the composite film and avoiding film stratification; and the sandwich layer of the membrane prepared by this scheme contains a certain amount of expanded graphite, and after heat treatment, there is basically 100% carbon residue, so the slurry with the same solid content is thicker than the membrane made without expanded graphite, and there is no need to perform membrane compounding by hot pressing, which has obvious advantages in terms of membrane thickness compared with the existing coating membrane making technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the cross-sectional structure of the scraper of the comb-shaped scraper used in the present invention;

[0020] Figure 2 It is the expanded graphite figure used in the present invention;

[0021] Figure 3 This is a cross-sectional SEM image of the graphene film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The principles and features of the present invention are described below. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

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

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

[0025] Graphene oxide filter cake 2, solid content 42.3%, wherein the flake diameter of graphene oxide is <5 μm;

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

[0027] pH regulator: industrial grade ammonia;

[0028] Base material: polypropylene fiber woven cloth.

[0029] Example 1

[0030] The method for preparing the graphene film of this embodiment comprises the following steps:

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

[0032] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry the surface to obtain film B1;

[0033] S3, take slurry A2 and apply it on the surface of film B1, the thickness of the slurry layer is 3000 μm, after application, use a comb-shaped scraper to scrape and comb the slurry layer of the wet film back and forth, and after combing, place it in an oven to dry the surface to obtain a composite film B2; wherein the cross-sectional shape of the scraper of the comb-shaped scraper is shown in FIG. Figure 1 As shown, the bottom of the scraper has a comb-tooth structure, and the tooth length is 3mm;

[0034] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0035] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 200°C for 2h, high-temperature carbonization at 600°C for 2.5h, graphitization treatment at 3200°C for 0.5h, and rolling to obtain a graphene thermal conductive film with a film thickness of 75μm. The graphene thermal conductive film is 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.

[0036] Example 2

[0037] The method for preparing the graphene film of this embodiment comprises the following steps:

[0038] S1. Raw material preparation: Take graphene oxide filter cake 1, add water to prepare a 10% slurry, and adjust the pH to 8 to obtain slurry A1; take graphene oxide filter cake 2, add water to prepare a 3% slurry, add expanded graphite according to the mass ratio of expanded graphite to graphene oxide of 1:1, adjust the pH to 7, and continue stirring until the mixture is uniform to obtain slurry A2;

[0039] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry the surface to obtain film B1;

[0040] S3, take slurry A2 and apply it on the surface of membrane B1, the thickness of the slurry layer is 3000 μm, after application, the slurry layer of the wet membrane is scraped and combed by a comb-shaped scraper as in Example 1, and after combing, the slurry layer is placed in an oven and dried to dryness, to obtain a composite membrane B2;

[0041] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0042] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 400°C for 2 hours, high-temperature carbonization at 600°C for 1 hour, graphitization treatment at 3000°C for 1 hour, and calendering to obtain a graphene thermal conductive film with a film thickness of 225 μm. The graphene thermal conductive film is 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.

[0043] Example 3

[0044] The method for preparing the graphene film of this embodiment comprises the following steps:

[0045] S1, raw material preparation: take graphene oxide filter cake 1, add water to prepare 6% slurry, and adjust the pH to 7 to obtain slurry A1; take graphene oxide filter cake 2, add water to prepare 8% slurry, add expanded graphite according to the mass ratio of expanded graphite to graphene oxide of 1:4, adjust the pH to 7, continue stirring until mixed evenly, and obtain slurry A2;

[0046] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry the surface to obtain film B1;

[0047] S3, take slurry A2 and apply it on the surface of membrane B1, the thickness of the slurry layer is 3000 μm, after application, the slurry layer of the wet membrane is scraped and combed by a comb-shaped scraper as in Example 1, and after combing, the slurry layer is placed in an oven and dried to dryness, to obtain a composite membrane B2;

[0048] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0049] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 300°C for 2h, high-temperature carbonization at 1000°C for 2h, graphitization treatment at 2900°C for 1h, and calendering to obtain a graphene thermal conductive film with a film thickness of 175μm. The graphene thermal conductive film is 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.

[0050] Comparative Example 1

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

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

[0053] S2, taking slurry A2 and coating it on a substrate to form a film, the wet film thickness is 3000 μm, after coating, the slurry layer of the wet film is scraped and combed back and forth using a comb-shaped scraper as in Example 1, and after combing, it is placed in an oven for drying to obtain a composite film;

[0054] S3, after the composite film is peeled off from the substrate, low temperature heat treatment is performed at 200°C for 2h, high temperature carbonization is performed at 600°C for 2.5h, graphitization is performed at 3200°C for 0.5h, and rolling is performed to obtain a graphene thermal conductive film with a film thickness of 35μm. The graphene thermal conductive film is a single-layer film structure, that is, a composite layer of the core layer-graphene and expanded graphite as in Example 1.

[0055] Comparative Example 2

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

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

[0058] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry it completely to obtain film B1;

[0059] S3, take slurry A2 and apply it on the surface of membrane B1, the thickness of the slurry layer is 3000 μm, after application, the slurry layer of the wet membrane is scraped and combed by a comb-shaped scraper as in Example 1, and after combing, the slurry layer is placed in an oven and dried to be completely dry, to obtain a composite membrane B2;

[0060] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0061] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 200°C for 2h, high-temperature carbonization at 600°C for 2.5h, graphitization treatment at 3200°C for 0.5h, and rolling to obtain a graphene thermal conductive film with a film thickness of 75μm. The graphene thermal conductive film is 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.

[0062] Comparative Example 3

[0063] The preparation method of the graphene film of this comparative example is basically the same as that of Example 1, except that no combing operation is performed in step S3, as shown in the following steps:

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

[0065] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry the surface to obtain film B1;

[0066] S3, take slurry A2 and apply it on the surface of membrane B1, the thickness of the slurry layer is 3000 μm, and after application, place it in an oven and bake it until the surface is dry to obtain composite membrane B2;

[0067] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0068] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 200°C for 2h, high-temperature carbonization at 600°C for 2.5h, graphitization treatment at 3200°C for 0.5h, and calendering to obtain a graphene thermal conductive film with a film thickness of 74μm. The graphene thermal conductive film is 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.

[0069] Comparative Example 4

[0070] The preparation method of the graphene film of this comparative example is basically the same as that of Example 1, except that no expanded graphite is added to the slurry A2, as shown in the following steps:

[0071] S1. Raw material preparation: Take graphene oxide filter cake 1, add water to prepare a 2% slurry, and adjust the pH to 6 to obtain slurry A1; take graphene oxide filter cake 2, add water to prepare a 6% slurry, adjust the pH to 6, and continue stirring until mixed evenly to obtain slurry A2.

[0072] S2, take slurry A1 and apply it on the surface of the substrate to form a film with a wet film thickness of 3000 μm, and place it in an oven to dry the surface to obtain film B1;

[0073] S3, take slurry A2 and apply it on the surface of film B1, the thickness of the slurry layer is 3000 μm, after application, the slurry layer of the wet film is scraped and combed by a comb-shaped scraper as in Example 1, and after combing, the film is placed in an oven and dried to dryness, to obtain film B2;

[0074] S4, taking slurry A1 and coating it on the surface of composite membrane B2 to form a film, the thickness of the slurry layer is 3000 μm, and placing it in an oven for drying to obtain a composite membrane sheet;

[0075] S5. After the composite film is peeled off from the substrate, it is subjected to low-temperature heat treatment at 200°C for 2h, high-temperature carbonization at 600°C for 2.5h, graphitization treatment at 3200°C for 0.5h, and calendering to obtain a graphene thermal conductive film with a film thickness of 72μm. The graphene thermal conductive film is 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.

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

[0077] Table 1

[0078]

[0079]

[0080] It can be seen from the data in the table that the thermally conductive film prepared by the present invention has high longitudinal thermal conductivity, and the longitudinal thermal conductivity coefficient is above 54 W / m·K; and it can be seen from Example 1 and Comparative Example 4 that the film thickness of the product prepared by the present invention also has certain advantages and there is no stratification problem.

Claims

1. A method for preparing a graphene film with high longitudinal thermal conductivity, characterized in that: Slurry A1 is applied on the surface of a substrate to form a film, and dried until the surface is dry to obtain film B1; slurry A2 is applied on the surface of film B1, and after coating, the slurry layer of the wet film is combed with a comb-shaped scraper, and dried until the surface is dry to obtain a composite film B2; slurry A1 is applied on the surface of composite film B2 to form a film, and dried to obtain a composite film sheet; the composite film sheet is peeled off from the substrate, and then subjected to low-temperature heat treatment, high-temperature carbonization, graphitization, and calendering to obtain a graphene thermal conductive film; Among them, slurry A1 is graphene oxide slurry, and slurry A2 is a mixed slurry of graphene oxide and expanded graphite.

2. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that: The slurry A1 is 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: adding expanded graphite to graphene oxide slurry with a concentration of 3%-8%, wherein the mass ratio of expanded graphite to graphene oxide is 1:10-1:1, adjusting the pH to 6-8, and mixing uniformly.

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

5. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1 or 3, characterized in that: The expanded graphite used for preparing slurry A2 is un-crushed vermicular graphite, with a mesh number of ≥100 mesh and a purity of >99%.

6. 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 80-400°C.

7. The method for preparing a graphene film with high longitudinal thermal conductivity according to claim 1, characterized in that: The temperature of the high temperature carbonization is 600-1200°C.

8. 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 to 7, wherein the graphene thermal conductive film is 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.

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

Images