Preparation method of large-thickness high-thermal-conductivity graphite film

Abstract

The invention relates to the technical field of thermal management material preparation, in particular to a preparation method of a large-thickness high-thermal-conductivity graphite film. According to the characteristics that a scanning centrifugal film preparation technology can be used for controllably preparing a high-orientation-degree laminated film and the structure and components of a laminated film unit layer can be finely regulated and controlled, a GO / PAA composite film formed by alternately stacking graphene oxide (GO) layers and polyamide acid (PAA) layers is prepared through double-channel alternate scanning centrifugal film preparation, and then the GO / PAA composite film is prepared through conventional heat treatment and compaction treatment. The graphite film material with high heat-conducting property can be prepared; by controlling the thickness of the GO / PAA unit layer and the number of alternate film preparation layers, the thickness of the obtained graphite film can be regulated and controlled in a large range from several microns to several millimeters, and the in-plane thermal conductivity of the graphite film can reach more than 1400 W / mK. The preparation method effectively solves the problem that the heat conductivity of the PI-based artificial graphite film is quickly reduced along with the increase of the thickness, is high in film preparation efficiency, can be used for industrial production, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of thermal management materials, and particularly to a method for preparing a high thermal conductivity graphite film with a large thickness. Background Art

[0002] With the increase in the operating frequency, integration level, and power of core electronic devices such as chips, heat dissipation has become a key factor restricting the operating efficiency, reliability, and service life of electronic devices. In portable electronic devices, spaceborne / airborne / missile-borne electronic devices, etc., due to the limitations of space size and weight, how to achieve effective heat dissipation of chips in a small-size space is a key technical problem faced by such electronic devices. With the continuous improvement of the performance requirements for such devices, the heat generation of their chips is also increasing continuously, and the requirements for the heat dissipation ability of chips are also continuously improving.

[0003] The key to chip heat dissipation lies in eliminating local hot spots, that is, heat spreading. It uses high thermal conductivity materials to quickly spread the heat generated during chip operation to a large area, thereby reducing the chip operating temperature while improving the efficiency of heat dissipation to the environment. High thermal conductivity graphite film is a widely used heat spreading material in current electronic devices. The heat spreading ability of the graphite film is not only related to its in-plane thermal conductivity but also closely related to its thickness. That is, at the same in-plane thermal conductivity, the greater the thickness of the graphite film, the stronger its heat spreading ability.

[0004] Conventional high thermal conductivity graphite film, also known as artificial graphite film, was first manufactured by Panasonic Corporation of Japan (in 1998) using a special polyimide (PI) film as the base material through heat treatment processes such as carbonization and graphitization, as well as rolling. However, PI-based artificial graphite films usually have the problem that their in-plane thermal conductivity decreases significantly with the increase in their thickness. For example, the thermal conductivity of a 10-μm-thick PI-based artificial graphite film can reach 1950 W / mK, but when the film thickness increases to 50-100 μm, its in-plane thermal conductivity is only 900-300 W / mK. And how to solve the problem that the in-plane thermal conductivity of artificial graphite film decreases with the increase in thickness is a key technical bottleneck problem in this field. Summary of the Invention

[0005] In order to solve the problem that the in-plane thermal conductivity of artificial graphite film decreases with the increase of thickness, the purpose of the present invention is to provide a preparation method of a large-thickness and high-thermal-conductivity graphite film. By using the characteristics of the scanning centrifugal film-making technology that can controllably prepare highly oriented laminated films and can finely regulate the structure and composition of the laminated film unit layers, through dual-channel alternating scanning centrifugal film-making, a GO / PAA composite film with alternating stacks of graphene oxide (GO) layers and polyamic acid (PAA) layers is prepared. Then, through conventional heat treatment and compaction treatment, a graphite film material with high thermal conductivity can be prepared; by controlling the thickness of the GO / PAA unit layer and the number of alternating film-making layers, the thickness of the obtained graphite film can be regulated within a large range from several micrometers to several millimeters, and the in-plane thermal conductivity of the graphite film can reach more than 1400 W / mK.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method of a large-thickness and high-thermal-conductivity graphite film, comprising the following steps:

[0008] (1) First, prepare a graphene oxide (GO) dispersion and a solution of polyamic acid (PAA), which is a prepolymer monomer of polyimide (PI). Then, using a multi-channel scanning centrifugal film-making machine, through dual-channel alternating scanning centrifugal film-making, a GO / PAA composite film with alternating stacks of GO layers and PAA layers is prepared;

[0009] (2) By controlling the thickness of the GO / PAA unit layer and the number of stacked layers, the thickness of the GO / PAA composite film is regulated;

[0010] (3) The GO / PAA composite film is successively subjected to heat treatment to obtain an artificial graphite film with a loose structure, and after compaction treatment of the artificial graphite film with a loose structure, a graphite film material with both large thickness and high in-plane thermal conductivity is prepared.

[0011] In the preparation method of the large-thickness and high-thermal-conductivity graphite film, the preparation of the GO dispersion uses a purified graphite oxide filter cake with a solid content of 40 wt.% to 50 wt.% as the raw material. By adding deionized water and successively performing mechanical stirring, shear dispersion, and high-pressure homogenization treatment, a uniformly dispersed GO aqueous solution is obtained. The concentration of the obtained GO aqueous solution is 0.1 wt.% to 10 wt.%, and the viscosity range of the GO aqueous solution is 5 to 1000 mPa·s. Preferably, the concentration of the GO aqueous solution is 0.5 wt.% to 2 wt.%, and the viscosity range of the GO aqueous solution is: 10 to 260 mPa·s.

[0012] The preparation method of the thick high - thermal - conductivity graphite film is as follows. The PAA solution is prepared by using a PAA / dimethylacetamide (DMF) solution with a solid content of 25 - 35 wt.% as the raw material. By adding a new DMF solvent to adjust its concentration and performing mechanical stirring, a stable dilute PAA / DMF solution is obtained, with a concentration of 0.05 wt.% - 20 wt.%, and the viscosity range of the PAA / DMF solution is 5 - 200 mPa·s. Preferably, the concentration of the PAA / DMF solution is 1 wt.% - 8 wt.%, and the viscosity range of the PAA / DMF solution is 4 - 80 mPa·s.

[0013] The preparation method of the thick high - thermal - conductivity graphite film. The two - channel alternating scanning centrifugal film - making using a multi - channel scanning centrifugal film - making machine means that during the film - making process of the scanning centrifugal film - making machine, first, a GO film of a single unit layer is prepared using one film - forming liquid injection channel of the film - making machine. After it is dried, a PAA film of a single unit layer is prepared using the other film - forming liquid injection channel of the film - making machine. After it is dried, repeating the above process realizes alternating film - making; by regulating the thickness of the GO unit layer and the PAA unit layer and controlling the number of repeated film - making, the microstructure, composition, and final film thickness of the GO / PAA composite film are regulated.

[0014] The preparation method of the thick high - thermal - conductivity graphite film. In the GO / PAA composite film, the thickness range of the PAA unit layer is 0.01 - 5 μm, and the thickness range of the GO unit layer is 0.005 - 1 μm; according to the final target film thickness and the thickness of the unit layer combination, the number of repeated alternating film - making is calculated. After using the multi - channel scanning centrifugal film - making machine to automatically complete the alternating film - making of the required number of repetitions, a GO / PAA composite film with the set target thickness is prepared. Preferably, the thickness range of the PAA unit layer is 0.5 - 3 μm, and the thickness range of the GO unit layer is 0.1 - 0.8 μm.

[0015] The preparation method of the thick high - thermal - conductivity graphite film. The heat treatment refers to three processes of thermal amideification treatment, medium - temperature sintering treatment, and high - temperature graphitization treatment that are sequentially carried out on the GO / PAA composite film in a freely placed state. Among them: the temperature range of the thermal amideification treatment is 250℃ - 450℃, and the time is 5 h - 20 h; the highest temperature range of the medium - temperature sintering treatment is 900℃ - 1500℃, and the time is 5 h - 15 h; the highest temperature range of the graphitization treatment is 2600℃ - 3200℃, and the time is 5 h - 11 h; after the heat treatment through the above - mentioned processes, the GO / PAA composite film is transformed into a graphite film with a porous structure. Preferably, the temperature of the thermal amideification treatment is 300℃ - 420℃, the time is 6 h - 16 h; the temperature of the medium - temperature sintering treatment is 1000℃ - 1400℃, the time is 7 h - 12 h; the temperature of the graphitization treatment is 2800℃ - 3000℃, and the time is 6 h - 9 h.

[0016] For the preparation method of the high thermal conductivity graphite film with large thickness, the compaction treatment refers to compacting the loose-structured graphite film obtained after heat treatment, and adopting vacuum flat pressing treatment or roll pressing treatment to remove the voids in the loose film structure and densify the film structure; when adopting vacuum flat pressing treatment, the required flat plate pressure is 100 - 500 MPa, and the required vacuum degree is -100 kPa - 0; when adopting roll pressing treatment, the required roll pressing pressure is 200 - 600 MPa, and the radius of curvature of the pressure roller is 200 - 1000 mm; the density of the graphite film obtained after compaction is 2.0 - 2.25 g / cm 3 , the thermal conductivity is 1400 - 1600 W / mK, and the thickness of the graphite film is 100 μm - 2.1 mm. Preferably, the flat plate pressure is 200 - 300 MPa, and the required vacuum degree is -99 kPa - -90 kPa; the roll pressing pressure is 300 - 450 MPa, and the radius of curvature of the pressure roller is 350 - 500 mm.

[0017] The technical principle of the present invention is as follows:

[0018] The inventors' research found that the thermal conductivity of PI-based artificial graphite films is closely related to the degree of molecular structure orientation of the raw material PI films. Only PI films with highly oriented molecular chains can be transformed into an ordered graphite crystal structure through graphitization treatment, thus having high thermal conductivity. Therefore, PI raw material films used for the preparation of artificial graphite films usually need to be ordered by polymer chain orientation techniques such as biaxial stretching. This orientation treatment is effective for PI films with a relatively small thickness (film thickness < 30 μm). However, when the film thickness increases to more than 50 μm, biaxial stretching treatment can only orient the surface of the PI film, while there are a large number of disordered structures inside. This structure is difficult to be transformed into graphite crystals through heat treatment, resulting in a decrease in the thermal conductivity of the thick graphite film. To solve the above problems, the present invention proposes a film-making method based on the Chinese invention patent with the publication number CN110274803A, which can precisely control the film thickness and area of nanoscale-thickness films, and prepares GO / PAA (PI prepolymer) composite films based on the scanning centrifugal film-making method. The centrifugal force generated by the high-speed rotation of the film-making drum and the shear force generated by the liquid flow during the centrifugal film-making process make the PAA molecular chains form an ordered orientation structure during the formation of the ultra-thin film. To avoid the disordered cross-linking of PAA molecular chains during amidation and heat treatment, which destroys their orientation, the present invention adds GO unit layers between the PAA thin layers, which can effectively inhibit the cross-linking effect of PAA in the thickness direction. In addition, by using the difference in the thermal expansion coefficients of the GO unit layer and the PAA (PI) unit layer, the GO film layer with a smaller deformation amount pins the PAA (PI) unit layer that is prone to deformation, so as to ensure that the PAA (PI) molecular chains always maintain a high degree of orientation during film formation and heat treatment, and then realize the efficient transformation of PI molecular chains into graphite crystal structures through graphitization treatment, thereby obtaining high thermal conductivity in the case of a large film thickness.

[0019] The advantages and beneficial effects of the present invention are as follows:

[0020] The technical solution of the present invention can effectively solve the problem that the thermal conductivity of PI-based artificial graphite films rapidly decreases with the increase of thickness. Using the technical solution of the present invention, the thickness of the graphite film can be controlled within a large range from several micrometers to several millimeters, and the in-plane thermal conductivity of the graphite film can reach more than 1400 W / mK, that is, the preparation of a graphite thermal conductive film material that can take into account both large thickness and high in-plane thermal conductivity is realized, which can effectively meet the technical requirements of high-efficiency heat dissipation and heat spreading of high-power electronic devices. In addition, this technical solution has high film-making efficiency and can be industrially produced, so it has good application prospects. Description of the Drawings

[0021] Figure 1 . Schematic diagram of the principle of preparing a thick high-thermal-conductivity graphite film. In the figure, 1 is a rotating drum, 2 is a GO unit layer, 3 is a PAA unit layer, 4 is a GO injection channel, 5 is a PAA injection channel, 6 is an optical wave tube, and 7 is a graphite plate.

[0022] Figure 2 . SEM photograph of the cross-sectional morphology of the graphite film based on the GO / PAA composite film prepared in Example 1.

[0023] Figure 3 . TEM photograph of the crystal structure of the graphite film based on the GO / PAA composite film prepared in Example 1 and its electron diffraction pattern (inset).

[0024] Figure 4 . SEM photograph of the cross-sectional morphology of the thermally imidized GO / PAA composite film with an inappropriate laminated structure ratio prepared in Comparative Example 1 (the PAA layer has a fracture structure).

[0025] Figure 5 . SEM photograph of the cross-sectional morphology of the graphite film based on the pure PAA film (PI film) prepared in Comparative Example 2.

[0026] Figure 6 . Selected-area TEM photograph of the cross-section of the graphite film based on the pure PAA film (PI film) prepared in Comparative Example 2 and its electron diffraction pattern (inset, glassy carbon structure). Detailed implementation manners

[0027] In the specific implementation process, the prepared graphene oxide (GO) dispersion and the polyimide (PI) prepolymer polyamic acid (PAA) solution of the present invention are laminated by a multi-channel scanning centrifugal film-forming machine in the lamination manner as shown in the appendix Figure 1 . First, the GO dispersion is injected into the inner surface of the rotating drum 1 through the GO injection channel 4 to prepare a single-unit GO unit layer 2, and it is quickly dried by heating with the light wave tube 6; after the GO unit layer 2 is dried, the PAA solution is then injected into the inner surface of the rotating drum 1 through the PAA injection channel 5 to prepare a single-unit PAA unit layer 3, and the above process is repeated after drying to achieve alternating film formation. By controlling the thicknesses of the PAA unit layer 3 and the GO unit layer 2 and the number of repeated film formations, the microstructure, composition, and final film thickness of the GO / PAA composite film can be regulated. The GO / PAA composite film is heat-treated successively between graphite plates 7, and the GO / PAA composite film can be converted into a graphite film with a loose structure. After compacting the loose graphite film, a graphite film material with both large thickness and high in-plane thermal conductivity can be prepared.

[0028] The preparation of the GO dispersion uses purified graphite oxide filter cake (solid content 40 wt.% - 50 wt.%) as the raw material. By adding deionized water and successively performing mechanical stirring, shear dispersion, and high-pressure homogenization treatment, a uniformly dispersed GO aqueous solution is obtained. The concentration of the obtained GO aqueous solution is 0.1 wt.% - 10 wt.%, and the optimized concentration of the GO aqueous solution is 0.5 wt.% - 2 wt.%; the viscosity range of the GO aqueous solution is 5 - 1000 mPa·s, and the optimized viscosity range of the GO aqueous solution is: 10 - 260 mPa·s.

[0029] The preparation of the PAA solution uses a commercial PAA / dimethylacetamide (DMF) solution (solid content ~30 wt.%) as the raw material. By adding a new DMF solvent to adjust its concentration and performing mechanical stirring, a stable dilute PAA / DMF solution is obtained, with a concentration of 0.05 wt.% - 20 wt.%, and the optimized concentration of the PAA / DMF solution is 1 wt.% - 8 wt.%. The viscosity range of the PAA / DMF solution is 5 - 200 mPa·s, and the optimized viscosity range of the PAA / DMF solution is: 4 - 80 mPa·s.

[0030] Next, the preparation process of the present invention will be described in more detail through specific examples, where the vacuum degree is the gauge pressure of the vacuum pressure gauge.

[0031] Example 1

[0032] In this example, the concentration of the prepared GO aqueous solution is 1.12 wt.%, and the viscosity is 89.6 mPa·s; the concentration of the PAA / DMF solution is 5.2 wt.%, and the viscosity is: 18.2 mPa·s. The lamination method for laminating film using a multi-channel scanning centrifugal film former is: first prepare a GO film with a thickness of 0.3 μm, dry it, and then prepare a PAA film with a thickness of 2 μm, dry it, and repeat the above lamination film formation, that is, alternately repeat scanning film formation 320 layers according to 1 layer of GO / 1 layer of PAA; after the film formation is completed, a GO / PAA composite film is obtained. The GO / PAA composite film is successively subjected to three heat treatment processes of thermal imidization at 350 °C for 9 h, medium-temperature sintering at 1200 °C for 10 h, and high-temperature graphitization at 2850 °C for 7 h to obtain a graphite film with a porous structure. Use a vacuum flat press to perform vacuum compaction treatment on the above porous graphite film, with the applied pressure being 240 MPa and the vacuum degree in the vacuum chamber being -99 KPa. The thickness of the compacted graphite film is 148 μm; the density is 2.14 g / cm 3 ; the thermal conductivity is 1546 W / mK. The microscopic morphology of the cross-section of this graphite film is as shown in the appendix Figure 2 and in the appendix Figure 3As shown, its microstructure is highly ordered and dense, with an obvious graphite layered crystal structure and no defect structure. This is an important structural feature for the graphite film prepared by the present technical invention to obtain high thermal conductivity.

[0033] Example 2

[0034] In this example, the basic process flow of film preparation is the same as that of Example 1. The main differences are that the concentration of the GO aqueous solution used is 0.85 wt.%, the viscosity is 46.3 mPa·s, the concentration of the PAA / DMF solution is 3.5 wt.%, and the viscosity is 4.8 mPa·s; the thickness of the prepared GO monolayer film is 0.2 μm, and the thickness of the PAA monolayer film is 1 μm; 1115 layers are prepared by alternately repeating the scanning injection of 4 layers of GO / 1 layer of PAA to obtain a GO / PAA composite film. The temperature and time for the thermal imidization, medium-temperature sintering, and graphitization treatments of the GO / PAA composite film are: 400 °C for 11 h, 1200 °C for 12 h, and 2950 °C for 8 h. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 260 MPa and a vacuum degree of -99 KPa. The thickness of the obtained graphite film after compaction is 156 μm; the density is 2.2 g / cm 3 ; the thermal conductivity is 1592 W / mK. Its microstructure is similar to that of the graphite film prepared in Example 1.

[0035] Example 3

[0036] In this example, the basic process flow of film preparation is the same as that of Example 1. The main differences are that the concentration of the GO aqueous solution used is 1.3 wt.%, the viscosity is 114.4 mPa·s, the concentration of the PAA / DMF solution is 4.3 wt.%, and the viscosity is 11.4 mPa·s; the thickness of the prepared GO monolayer film is 0.35 μm, and the thickness of the PAA monolayer film is 1.5 μm; 2560 layers are prepared by alternately repeating the scanning injection of 15 layers of GO / 1 layer of PAA to obtain a GO / PAA composite film. The temperature and time for the thermal imidization, medium-temperature sintering, and graphitization treatments of the GO / PAA composite film are: 380 °C for 6 h, 1200 °C for 8 h, and 3000 °C for 8.5 h. The compaction treatment after heat treatment is carried out using a pair-roll press, with a pressure of 350 MPa and the radius of curvature of the press roll being 400 mm. The thickness of the obtained graphite film after compaction is 440 μm; the density is 2.08 g / cm 3 ; the thermal conductivity is 1514 W / mK. Its microstructure is similar to that of the graphite film prepared in Example 1.

[0037] Example 4

[0038] In this embodiment, the basic process flow of film preparation is the same as that of Embodiment 1. The main differences are as follows: the concentration of the GO aqueous solution used is 1.46 wt.%, the viscosity is 124.4 mPa·s, the concentration of the PAA / DMF solution is 5.6 wt.%, and the viscosity is 28.6 mPa·s; the thickness of the prepared GO unit layer film is 0.38 μm, and the thickness of the PAA unit layer film is 2.3 μm; a GO / PAA composite film is prepared by alternately repeating 3105 layers of scanning injection in the order of 8 layers of GO / 1 layer of PAA. The temperatures and times for thermal imidization, medium-temperature sintering, and graphitization treatment of the GO / PAA composite film are 400°C for 10 h, 1300°C for 11 h, and 2850°C for 9 h, respectively. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 260 MPa and a vacuum degree of -98 KPa. The thickness of the obtained graphite film after compaction is 734 μm; the density is 2.13 g / cm 3 ; the thermal conductivity is 1578 W / mK. Its microstructure is similar to that of the graphite film prepared in Embodiment 1.

[0039] Embodiment 5

[0040] In this embodiment, the basic process flow of film preparation is the same as that of Embodiment 1. The main differences are as follows: the concentration of the GO aqueous solution used is 1.62 wt.%, the viscosity is 135.5 mPa·s, the concentration of the PAA / DMF solution is 5.6 wt.%, and the viscosity is 28.6 mPa·s; the thickness of the prepared GO unit layer film is 0.41 μm, and the thickness of the PAA unit layer film is 2.3 μm; a GO / PAA composite film is prepared by alternately repeating 5054 layers of scanning injection in the order of 18 layers of GO / 1 layer of PAA. The temperatures and times for thermal imidization, medium-temperature sintering, and graphitization treatment of the GO / PAA composite film are 410°C for 12 h, 1400°C for 9 h, and 2900°C for 7 h, respectively. The compaction treatment after heat treatment is carried out using a pair-roll press, with a pressure of 380 MPa and a roll curvature radius of 600 mm. The thickness of the obtained graphite film after compaction is 1 mm; the density is 2.06 g / cm 3 ; the thermal conductivity is 1555 W / mK. Its microstructure is similar to that of the graphite film prepared in Embodiment 1.

[0041] Embodiment 6

[0042] In this embodiment, the basic process flow of film preparation is the same as that of Embodiment 1. The main differences are that the concentration of the GO aqueous solution used is 1.7 wt.%, the viscosity is 142.1 mPa·s, the concentration of the PAA / DMF solution is 6.3 wt.%, and the viscosity is 47.6 mPa·s; the thickness of the GO unit layer film prepared is 0.5 μm, and the thickness of the PAA unit layer film is 2.6 μm; a GO / PAA composite film is prepared by alternately repeating 2598 layers of scanning injection in the order of 2 layers of GO / 1 layer of PAA. The temperatures and times for the thermal imidization, medium-temperature sintering, and graphitization treatments of the GO / PAA composite film are 320 °C for 13.5 h, 1350 °C for 10.5 h, and 3000 °C for 9 h, respectively. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 270 MPa and a vacuum degree of -97 KPa. The thickness of the obtained graphite film after compaction is 1.18 mm; the density is 2.11 g / cm 3 ; the thermal conductivity is 1586 W / mK. Its microstructure is similar to that of the graphite film prepared in Embodiment 1.

[0043] Embodiment 7

[0044] In this embodiment, the basic process flow of film preparation is the same as that of Embodiment 1. The main differences are that the concentration of the GO aqueous solution used is 1.88 wt.%, the viscosity is 178.9 mPa·s, the concentration of the PAA / DMF solution is 7.1 wt.%, and the viscosity is 62.2 mPa·s; the thickness of the GO unit layer film prepared is 0.62 μm, and the thickness of the PAA unit layer film is 3 μm; a GO / PAA composite film is prepared by alternately repeating 3971 layers of scanning injection in the order of 10 layers of GO / 1 layer of PAA. The temperatures and times for the thermal imidization, medium-temperature sintering, and graphitization treatments of the GO / PAA composite film are 350 °C for 14 h, 1000 °C for 7.5 h, and 2850 °C for 7.5 h, respectively. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 290 MPa and a vacuum degree of -95 KPa. The thickness of the obtained graphite film after compaction is 1.33 mm; the density is 2.09 g / cm 3 ; the thermal conductivity is 1533 W / mK. Its microstructure is similar to that of the graphite film prepared in Embodiment 1.

[0045] Embodiment 8

[0046] In this example, the basic process flow of film preparation is the same as that of Example 1. The main differences are that the concentration of the GO aqueous solution used is 1.9 wt.%, the viscosity is 183.5 mPa·s, the concentration of the PAA / DMF solution is 7.5 wt.%, and the viscosity is 75.8 mPa·s; the thickness of the prepared GO unit layer film is 0.66 μm, and the thickness of the PAA unit layer film is 3.2 μm; a GO / PAA composite film is prepared by alternately repeating 4725 layers of scanning injection in the order of 20 layers of GO / 1 layer of PAA. The temperatures and times for thermal imidization, intermediate temperature sintering, and graphitization treatment of the GO / PAA composite film are 350 °C for 14.5 h, 1100 °C for 11.5 h, and 2950 °C for 8.5 h respectively. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 290 MPa and a vacuum degree of -94 KPa. The thickness of the obtained graphite film after compaction is 1.47 mm; the density is 2.1 g / cm 3 ; the thermal conductivity is 1520 W / mK. Its microstructure is similar to that of the graphite film prepared in Example 1.

[0047] Example 9

[0048] In this example, the basic process flow of film preparation is the same as that of Example 1. The main differences are that the concentration of the GO aqueous solution used is 1.9 wt.%, the viscosity is 183.5 mPa·s, the concentration of the PAA / DMF solution is 3.5 wt.%, and the viscosity is 4.8 mPa·s; the thickness of the prepared GO unit layer film is 0.66 μm, and the thickness of the PAA unit layer film is 1 μm; a GO / PAA composite film is prepared by alternately repeating 1110 layers of scanning injection in the order of 3 layers of GO / 2 layers of PAA. The temperatures and times for thermal imidization, intermediate temperature sintering, and graphitization treatment of the GO / PAA composite film are 350 °C for 15 h, 1200 °C for 13 h, and 3000 °C for 9 h respectively. The compaction treatment after heat treatment is carried out using a vacuum flat press, with a pressure of 290 MPa and a vacuum degree of -92 KPa. The thickness of the obtained graphite film after compaction is 1.77 mm; the density is 2.1 g / cm 3 ; the thermal conductivity is 1487 W / mK. Its microstructure is similar to that of the graphite film prepared in Example 1.

[0049] Example 10

[0050] In this embodiment, the basic process flow of film preparation is the same as that of Embodiment 1. The main differences are that the concentration of the GO aqueous solution used is 1.12 wt.%, the viscosity is 89.6 mPa·s, the concentration of the PAA / DMF solution is 3.5 wt.%, and the viscosity is 4.8 mPa·s; the thickness of the prepared GO unit layer film is 0.3 μm, and the thickness of the PAA unit layer film is 1 μm; 1105 layers are prepared by alternately repeating scanning injection in the order of 10 layers of GO / 3 layers of PAA to obtain the GO / PAA composite film. The temperatures and times for thermal imidization, medium-temperature sintering, and graphitization treatment of the GO / PAA composite film are 350 °C for 16 h, 1200 °C for 7 h, and 3000 °C for 8 h respectively. The compaction treatment after heat treatment is carried out using a pair-roll press, with a pressure of 430 MPa applied and a roll curvature radius of 800 mm. The thickness of the obtained graphite film after compaction is 2.07 mm; the density is 2.02 g / cm 3 ; the thermal conductivity is 1419 W / mK. Its microstructure is similar to that of the graphite film prepared in Embodiment 1.

[0051] To demonstrate the characteristics and advantages of the above preparation technology, the following comparative examples and related descriptions are given:

[0052] Comparative Example 1

[0053] In this comparative example, the solutions used for film preparation and the basic process flow are the same as those in Embodiment 1. The main difference is that when using a multi-channel scanning centrifugal film-making machine for laminated film preparation, the laminated structure ratio of GO and PAA is different: laminated in the order of 10 layers of GO / 3 layers of PAA, that is, first prepare 10 layers of GO film with a thickness of 0.3 μm, dry it, and then prepare 3 layers of PAA film with a thickness of 2 μm, dry it, and repeat the above laminated film preparation. 533 layers are prepared by alternately repeating scanning injection to obtain the GO / PAA composite film. The GO / PAA composite film is subjected to the same heat treatment as in Embodiment 1. During the thermal imidization treatment at 350 °C for 9 h, obvious cracking occurs, and the PAA after the thermal imidization treatment of the GO / PAA composite film falls off in fragments. Its morphological structure is as shown in the appendix Figure 4 As shown, obvious PAA fracture and loss can be seen, indicating the inappropriateness of this laminated structure ratio. However, it also demonstrates the effect of regulating the thickness of the PAA layer and the pinning effect of the GO layer. When the thickness of the PAA unit layer is too large, the shrinkage force generated by the cross-linking of molecular chains during the thermal imidization process is also very large. Then, hindered by the pinning effect of the GO layer, the PAA layer breaks and the PI lamellae fall off. After the film with the PAA layer fracture structure is subjected to the same medium-temperature sintering, high-temperature graphitization treatment, and vacuum compaction treatment as in Embodiment 1, the thickness of the obtained graphite film is 108 μm; the density is 2.05 g / cm 3 ; the thermal conductivity is ~1200 W / mK. It shows that the fracture structure of the PAA (PI) layer will have a significant impact on the thermal conductivity of the product graphite film.

[0054] Comparative Example 2

[0055] In this comparative example, a 6.3 wt.% PAA / DMF solution was used alone for scanning centrifugal film formation. The solution viscosity was 47.6 mPa·s, the thickness of the PAA unit layer film was 2.6 μm, and the number of repeated scans was 235 times. The film formation heat treatment process was the same as that in Example 1. The GO / PAA composite film was subjected to three heat treatment processes: treatment at 350 °C for 9 h, intermediate temperature sintering treatment at 1200 °C for 10 h, and high temperature graphitization treatment at 2850 °C for 7 h. The PI-based artificial graphite film converted from the PAA film was hard and brittle and could not be compacted. The thickness of the graphite film was 145 μm, and the density was 1.55 g / cm 3 ; The thermal conductivity was only 408 W / mK. The microscopic morphology of the cross-section of this graphite film is shown in Attachment Figure 5 and Attachment Figure 6 . Most of the middle region is a non-graphite region without a layered structure, and only ultra-thin graphite layered structures are present on the upper and lower surfaces. This shows that the disordered cross-linking of the PAA (PI) molecular chains during amidation and heat treatment destroys their orientation, which is the main reason for the low thermal conductivity of the PI-based artificial graphite thick film.

[0056] The examples and comparative examples better illustrate that the lamination method of using a multi-channel scanning centrifugal film former for lamination can control the unit layer thickness and the number of stacked layers, and realize the regulation of the thickness of the GO / PAA composite film. It also better illustrates the pinning effect of the GO layer, which can effectively inhibit the cross-linking of PAA in the thickness direction, so as to ensure that the PAA (PI) molecular chains always maintain a high degree of orientation during film formation and heat treatment. Therefore, the problem that the thermal conductivity of the PI-based artificial graphite film rapidly decreases with the increase of film thickness is solved, and a high thermal conductivity can be obtained in the case of a large film thickness, meeting the technical requirements of efficient heat dissipation and heat spreading of high-power electronic devices.

[0057] The above-described embodiments only represent certain implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention; it should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention; therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A preparation method of a high thermal conductivity graphite film with a large thickness, characterized in that, It includes the following steps: (1) First, prepare a graphene oxide (GO) dispersion and a polyimide (PI) prepolymer polyamic acid (PAA) solution. Then, use a multi-channel scanning centrifugal film-forming machine to prepare a GO / PAA composite film with alternating GO layers and PAA layers by two-channel alternating scanning centrifugal film formation. (2) Control the thickness of the GO / PAA composite film by controlling the thickness of the GO / PAA unit layer and the number of stacked layers. (3) Heat-treat the GO / PAA composite film successively to obtain an artificial graphite film with a loose structure. After compacting the artificial graphite film with the loose structure, prepare a graphite film material with both large thickness and high in-plane thermal conductivity.

2. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 1, characterized in that, The preparation of the GO dispersion uses a purified graphite oxide filter cake with a solid content of 40 wt.% to 50 wt.% as the raw material. By adding deionized water and successively performing mechanical stirring, shear dispersion, and high-pressure homogenization treatment, a uniformly dispersed GO aqueous solution is obtained. The concentration of the obtained GO aqueous solution is 0.1 wt.% to 10 wt.%, and the viscosity range of the GO aqueous solution is 5 to 1000 mPa·s.

3. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 2, characterized in that, Preferably, the concentration of the GO aqueous solution is 0.5 wt.% to 2 wt.%, and the viscosity range of the GO aqueous solution is: 10 to 260 mPa·s.

4. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 1, characterized in that, The preparation of the PAA solution uses a PAA / dimethylacetamide (DMF) solution with a solid content of 25 to 35 wt.% as the raw material. Adjust its concentration by adding a new DMF solvent and perform mechanical stirring to obtain a stable PAA / DMF dilute solution with a concentration of 0.05 wt.% to 20 wt.%. The viscosity range of the PAA / DMF solution is 5 to 200 mPa·s.

5. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 4, characterized in that, Preferably, the concentration of the PAA / DMF solution is 1 wt.% to 8 wt.%, and the viscosity range of the PAA / DMF solution is: 4 to 80 mPa·s.

6. The preparation method of the thick high thermal conductivity graphite film according to claim 1, characterized in that, Using a multi-channel scanning centrifugal film-forming machine for two-channel alternating scanning centrifugal film formation means that during the film formation process of the scanning centrifugal film-forming machine, first use one film-forming liquid injection channel of the film-forming machine to prepare a unit layer of GO film. After it dries, use the other film-forming liquid injection channel of the film-forming machine to prepare a unit layer of PAA film. After it dries, repeat the above process to achieve alternating film formation; control the microstructure and composition of the GO / PAA composite film and the final film thickness by regulating the thickness of the GO unit layer and the PAA unit layer and controlling the number of repeated film formations.

7. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 1, characterized in that In the GO / PAA composite film, the thickness range of the PAA unit layer is 0.01 to 5 μm, and the thickness range of the GO unit layer is 0.005 to 1 μm; calculate the number of repeated alternating film formations according to the final target film thickness and the thickness of the unit layer combination. After using the multi-channel scanning centrifugal film-forming machine to automatically complete the alternating film formation with the required number of repetitions, a GO / PAA composite film with the set target thickness is prepared.

8. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 7, characterized in that, Preferably, the thickness range of the PAA unit layer is 0.5 to 3 μm, and the thickness range of the GO unit layer is 0.1 to 0.8 μm.

9. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 1, characterized in that Heat treatment refers to three processes of thermal amidation treatment, medium-temperature sintering treatment, and high-temperature graphitization treatment that are sequentially carried out on the GO / PAA composite film in a freely placed state, where: the temperature range of the thermal amidation treatment is 250°C to 450°C, and the time is 5h to 20h; the maximum temperature range of the medium-temperature sintering treatment is 900°C to 1500°C, and the time is 5h to 15h; the maximum temperature range of the graphitization treatment is 2600°C to 3200°C, and the time is 5h to 11h; after the heat treatment through the above processes, the GO / PAA composite film is transformed into a graphite film with a loose structure; preferably, the temperature of the thermal amidation treatment is 300°C to 420°C, and the time is 6h to 16h; the temperature of the medium-temperature sintering treatment is 1000°C to 1400°C, and the time is 7h to 12h; the temperature of the graphitization treatment is 2800°C to 3000°C, and the time is 6h to 9h.

10. The preparation method of the high thermal conductivity graphite film with large thickness according to claim 1, characterized in that, Compaction treatment refers to compacting the loose-structured graphite film obtained after heat treatment, using vacuum flat pressing treatment or roll pressing treatment to remove the voids in the loose film structure and densify the film structure; when using vacuum flat pressing treatment, the required flat plate pressure is 100 - 500 MPa, and the required vacuum degree is -100 kPa - 0; when using roll pressing treatment, the required roll pressing pressure is 200 - 600 MPa, and the radius of curvature of the press roll is 200 - 1000 mm; the density of the graphite film obtained after compaction is 2.0 - 2.25 g / cm 3 , the thermal conductivity is 1400 - 1600 W / mK, and the thickness of the graphite film is 100 μm - 2.1 mm; preferably, the flat plate pressure is 200 - 300 MPa, and the required vacuum degree is -99 kPa - -90 kPa; the roll pressing pressure is 300 - 450 MPa, and the radius of curvature of the press roll is 350 - 500 mm.

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