A bendable flexible graphite film for folding screen and preparation method thereof

Abstract

The present invention discloses a bendable flexible graphite film for folding screens and a preparation method thereof. The present invention introduces carbon nanofibers and two-dimensional covalent organic skeleton materials, interconnects with carbonized polyimide, fills the gaps between the sheets, and undergoes processes such as thermal imidization, hot pressing carbonization, and vacuum graphitization to produce a large number of microscopic wrinkles after graphitization of the film, thereby preparing a graphite film with high thermal conductivity and excellent mechanical strength and flexibility. The graphite film meets the needs of new display technologies such as folding screens and curved screens, ensures uniform heat dissipation of folding mobile phones, and does not affect the performance and service life of the mobile phone due to multiple bending and wrinkling of the graphite.

Description

Technical Field

[0001] The present invention belongs to the field of graphite films, and in particular relates to a bendable flexible graphite film for a folding screen and a preparation method thereof. Background Art

[0002] Heat dissipation in mobile phones is a critical design consideration, especially as high-performance smartphones become more and more popular. As processor speeds increase, screen brightness increases, and multifunctionality increases, the heat generated inside mobile phones is also increasing. If the heat cannot be effectively dissipated, it will not only affect the performance stability of the phone, but may also cause damage to the hardware and shorten the life of the phone.

[0003] At present, mobile phones are constantly developing in the direction of intelligence, diversification, and high-end. In order to cope with fierce competition, leading manufacturers have entered the folding screen track. Folding innovation has become a new trend in the development of smartphones. The highly anticipated folding screen mobile phones are expected to gradually become a symbol of the high-end smartphone market and gradually become popular. At present, graphite sheet heat conduction has become the first choice for preparing heat dissipation materials due to its superior heat dissipation performance and cost performance. Graphite sheets with conventional structures and their heat dissipation are only suitable for ordinary smartphones. In the folding screen design of 5G smartphones, the disconnection design will cause uneven heat dissipation of folding phones, and the one-piece design will easily cause creases or even breaks in the folding part of the phone, affecting the service life and heat dissipation of the phone.

[0004] As a special engineering material, polyimide (PI) has good high and low temperature resistance, environmental stability, mechanical properties and excellent dielectric properties. It has been widely used in many basic industries and high-tech fields and is known as the "gold of engineering plastics". In the early 1970s, scientists discovered that graphite can be obtained by pressurizing polyimide in an inert atmosphere and carbonizing it at 2800-3200℃. The prepared samples have the same high crystallinity as highly oriented pyrolytic graphite and highly preferential graphite layer orientation along the film surface. In the 1980s, the aerospace, electronics, chemical and other industries developed rapidly, and there was an urgent need for a material with good electrical and thermal conductivity and low relative density. As a result, the research and development of polyimide-based graphite films has entered the public eye, mainly focusing on the study of the graphitization mechanism and properties of polyimide. Domestic companies generally use the thermal imidization method to prepare polyimide films. Polyimide-based graphite films have high thermal conductivity, but the graphite films prepared by existing processes are relatively brittle and have many defects. The mechanical strength of the films is relatively poor. As a result, when used in folding mobile phones, the graphite films will be bent and wrinkled multiple times, which will affect the performance and service life of the mobile phone. Summary of the invention

[0005] The main technical problem solved by the present invention is to provide a bendable flexible graphite film for folding screens and a preparation method thereof. The present invention introduces carbon nanofibers and two-dimensional covalent organic skeleton materials, interconnects with carbonized polyimide, fills the gaps between the sheets, and undergoes processes such as thermal imidization, hot pressing carbonization, and vacuum graphitization to produce a large number of microscopic wrinkles after graphitization of the film, thereby preparing a graphitized graphene / polyimide composite film with high thermal conductivity, excellent mechanical strength, and flexibility.

[0006] The present invention is implemented by the following technical scheme: A method for preparing a bendable flexible graphite film for a folding screen, comprising the following steps:

[0007] (1) adding aromatic diamine, carbon nanofibers and a covalent organic framework into an organic solvent, stirring thoroughly, and then adding aromatic dianhydride, stirring to react, to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic framework;

[0008] (2) placing the polyamic acid composite solution in a vacuum drying oven for defoaming, filtering after degassing, and then uniformly coating it on the substrate by knife coating, roller coating or extrusion coating, drying at 120-250° C. to form a film, and then placing it in a vacuum furnace for thermal imidization treatment, heating the temperature to 450-500° C. while applying a pressure of 25 MPa, maintaining constant temperature and pressure for 10-20 minutes, and then starting to cool down, cooling at a uniform rate to room temperature and then releasing the pressure to obtain a polyimide composite film;

[0009] (3) subjecting the prepared polyimide composite film to a high-temperature carbonization treatment under a protective atmosphere to obtain a carbonized film;

[0010] (4) Placing the carbonized film in a graphite furnace for graphitization treatment to obtain a graphite film with a thickness of 17-80 μm.

[0011] Furthermore, in step (1), aromatic diamine, carbon nanofibers and a covalent organic skeleton are added to an organic solvent, and under 20-30kHz ultrasonic dispersion conditions, the stirring speed is 150-200r / min, and the aromatic dianhydride is added after sufficient stirring for 2-4h, and the reaction is stirred under the protection of an inert gas. The stirring reaction temperature is -20-60°C, and the reaction time is 1-12h to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic skeleton.

[0012] Furthermore, the aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminodiphenyl ketone, and 4,4'-diaminodiphenylmethane; the aromatic dianhydride is at least one of pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride; and the organic solvent is at least one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, tetrahydrofuran, γ-butyrolactone, hexamethylphosphoramide, dimethyl sulfoxide, and m-cresol.

[0013] Furthermore, the molar ratio of the aromatic diamine to the aromatic dianhydride is 1:(1-1.05).

[0014] Furthermore, the covalent organic framework is a two-dimensional organic covalent framework nanosheet.

[0015] Furthermore, the mass of the carbon nanofibers is 5-10%wt of the sum of the mass of the aromatic diamine and the aromatic dianhydride; and the mass ratio of the carbon nanofibers to the organic covalent skeleton is 1:1.5-2.

[0016] Furthermore, the protective atmosphere is nitrogen or an inert gas.

[0017] Furthermore, the specific steps of the high temperature carbonization treatment are: heating to 1350-1450°C at a heating rate of 2-10°C / min, while the carbonization pressure is 20-25MPa, maintaining constant temperature and pressure for 1-2.5h, and then cooling to room temperature to obtain a carbonized film.

[0018] Furthermore, the specific steps of the graphitization treatment are: placing in a vacuum furnace, evacuating to a vacuum degree of 15-20Pa, first heating to 1600°C at a heating rate of 5-10°C / min, and keeping warm for 0.5-1h; then heating to 2200°C at a heating rate of 5-10°C / min, and keeping warm for 0.5-1h; heating to 2700°C at a heating rate of 5-10°C / min, keeping warm for 2h, and then cooling to room temperature at a rate of 5°C / min to obtain a graphite film.

[0019] Furthermore, in step (4), the carbonized film is first immersed in ethanol, heated to 40-80°C and pressure is applied to 25 MPa, maintained at constant temperature and pressure for 1-3 hours, dried in air, and then placed in a graphite furnace for graphitization to obtain a graphite film.

[0020] Furthermore, after obtaining the graphite film, the method further comprises:

[0021] Based on the preset evaluation system, the graphite film is tested for quality and the test results are obtained;

[0022] Based on the countermeasure knowledge base, according to the detection results, the countermeasure suggestions and the corresponding credibility of the suggestions are decided;

[0023] When the suggested credibility is greater than or equal to the credibility threshold, based on the countermeasure suggestion, steps (1) to (4) are re-executed to perform countermeasures to obtain a new graphite film.

[0024] The present invention also provides a bendable flexible graphite film for a folding screen, which is prepared by the above preparation method, and the thickness of the graphite film ranges from 17 to 80 μm.

[0025] Beneficial effects of the present invention:

[0026] Through rigorous processing steps, the microstructure and preparation process of the graphite film are optimized, so that the finished composite graphite film material has good heat dissipation effect and long service life, which meets the actual application requirements. It can quickly and evenly transfer the heat generated by the mobile phone chip to the entire graphite film plane, eliminate local hot spots, and keep the chip in a suitable operating temperature range.

[0027] The present invention uses a specially designed polyimide film. By adding an appropriate amount of carbon nanotubes or carbon nanofibers and a two-dimensional covalent organic skeleton into the polyimide film and then carbonizing and graphitizing it, a large number of microscopic wrinkles are generated on the graphite film, which greatly improves the flexibility and makes it resistant to stretching and bending. The thermal conductivity and flexibility are reasonably balanced to meet the needs of new display technologies such as folding screens and curved screens. While ensuring uniform heat dissipation of foldable mobile phones, the performance and service life of the mobile phone will not be affected by the repeated bending and wrinkling of the graphite. The cost is low, the process is simple, and the practical value is high.

[0028] The final graphitization temperature of the embodiment of the present invention is only 2700° C., which is lower than the traditional 3000° C., indicating that the method provided by the embodiment of the present invention can significantly reduce the energy of graphitization while improving the graphitization degree of polyimide, thereby greatly saving energy. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0030] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0031] Example 1

[0032] A method for preparing a bendable flexible graphite film for a folding screen comprises the following steps:

[0033] (1) 4,4'-diaminodiphenyl ether, carbon nanofibers and two-dimensional organic covalent skeleton nanosheets are added to an organic solvent (N,N-dimethylformamide), the molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic anhydride is 1:1; the mass of the carbon nanofibers is 8%wt of the sum of the masses of 4,4'-diaminodiphenyl ether and pyromellitic anhydride; the mass ratio of the carbon nanofibers to the organic covalent skeleton is 1:1.8. Under 25kHz ultrasonic dispersion conditions, the stirring speed is 200r / min, and after sufficient stirring for 3h, pyromellitic anhydride is added, and the reaction is stirred under the protection of an inert gas (argon). The stirring reaction temperature is room temperature and the reaction time is 6h to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic skeleton;

[0034] (2) placing the polyamic acid composite solution in a vacuum drying oven for defoaming, filtering after degassing, and evenly coating it on the substrate by knife coating, roller coating or extrusion coating, drying at 200° C. to form a film, and then placing it in a vacuum furnace for thermal imidization treatment, heating the temperature to 450° C. while applying a pressure of 25 MPa, keeping the temperature and pressure constant for 20 minutes, and then starting to cool down, cooling at a uniform rate to room temperature and then releasing the pressure to obtain a polyimide composite film with a thickness of 65 μm;

[0035] (3) subjecting the prepared polyimide composite film to a high-temperature carbonization treatment under a protective atmosphere (nitrogen), heating the temperature to 1400°C at a heating rate of 5°C / min, while the carbonization pressure is 25 MPa, and then cooling to room temperature at a constant temperature and pressure for 2 hours to obtain a carbonized film;

[0036] (4) The carbonized film is first immersed in ethanol, heated to 60°C and pressure is applied to 25 MPa. After maintaining constant temperature and pressure for 2 hours, it is dried in air and then placed in a graphite furnace for graphitization treatment. It is placed in a vacuum furnace and evacuated to a vacuum degree of 20 Pa. The temperature is first increased to 1600°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is increased to 2200°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is heated to 2700°C at a heating rate of 5°C / min, kept at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min to obtain a graphite film.

[0037] In this embodiment, by optimizing the preparation process of the polyimide film, a heat-conducting network is formed in the polyimide matrix, with carbon nanotubes or carbon nanofibers as the main heat-conducting path and a two-dimensional covalent organic skeleton dispersed in the structure as the heat-conducting branch path. Then, a special sintering process is used in the carbonization and graphitization treatment of the modified polyimide film. Since the heat-conducting network will generate gas at high temperature, it will destroy the brittle characteristics of the highly regular graphite layered structure. After graphitization, a large number of microscopic wrinkles are generated. The ductility of the microscopic wrinkles enables it to withstand repeated folding, knotting, twisting, bending and other complex deformations, and is also more suitable for industrial-scale production. The polyimide graphite film prepared in this embodiment has a large number of wrinkled structures, and its density is 1.96g / cm 3 , thickness is 61μm, shrinkage rate is 6%, thermal conductivity is 1607W / (m·K), graphite film has excellent flexibility and is used in folding screen mobile phones. It can be bent 300,000 times without breaking, solving the problem that high thermal conductivity and high flexibility of macro materials cannot be taken into account at the same time.

[0038] Example 2

[0039] A method for preparing a bendable flexible graphite film for a folding screen comprises the following steps:

[0040] (1) Add p-phenylenediamine, carbon nanofibers and two-dimensional organic covalent skeleton nanosheets into an organic solvent (N-methylpyrrolidone), the molar ratio of p-phenylenediamine to 3,3',4,4'-biphenyltetracarboxylic acid anhydride is 1:1; the mass of carbon nanofibers is 5%wt of the sum of the mass of p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic acid anhydride; the mass ratio of carbon nanofibers to the mass of organic covalent skeleton is 1:1.5. Under 20kHz ultrasonic dispersion conditions, the stirring speed is 200r / min, and after sufficient stirring for 2h, 3,3',4,4'-biphenyltetracarboxylic acid anhydride is added, and the reaction is stirred under the protection of inert gas (argon). The stirring reaction temperature is room temperature and the reaction time is 6h to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic skeleton;

[0041] (2) placing the polyamic acid composite solution in a vacuum drying oven for defoaming, filtering after degassing, and evenly coating it on the substrate by knife coating, roller coating or extrusion coating, drying at 200° C. to form a film, and then placing it in a vacuum furnace for thermal imidization treatment, heating the temperature to 450° C. while applying a pressure of 25 MPa, keeping the temperature and pressure constant for 20 minutes, and then starting to cool down, cooling at a uniform rate to room temperature and then releasing the pressure to obtain a polyimide composite film with a thickness of 85 μm;

[0042] (3) subjecting the prepared polyimide composite film to a high-temperature carbonization treatment under a protective atmosphere (nitrogen), heating the temperature to 1350°C at a heating rate of 5°C / min, while the carbonization pressure is 20 MPa, maintaining the temperature and pressure constant for 2 hours, and then cooling to room temperature to obtain a carbonized film;

[0043] (4) The carbonized film is first immersed in ethanol, heated to 40°C and pressure is applied to 25 MPa. After maintaining constant temperature and pressure for 2 hours, it is dried in air and then placed in a graphite furnace for graphitization treatment. It is placed in a vacuum furnace and evacuated to a vacuum degree of 15 Pa. The temperature is first increased to 1600°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is increased to 2200°C at a heating rate of 5°C / min and kept at this temperature for 1 hour; then the temperature is heated to 2700°C at a heating rate of 5°C / min, kept at this temperature for 2 hours, and then cooled to room temperature at a rate of 5°C / min to obtain a graphite film.

[0044] The graphite film obtained in this embodiment has a large number of wrinkles and protrusions in the microstructure, and the density is 1.98g / cm 3 , thickness 80μm, shrinkage rate 7%, thermal conductivity 1572W / (m·K), used in folding screen mobile phones, can be bent 300,000 times without breaking.

[0045] Example 3

[0046] A method for preparing a bendable flexible graphite film for a folding screen comprises the following steps:

[0047] (1) 4,4'-diaminodiphenylmethane, carbon nanofibers and two-dimensional organic covalent skeleton nanosheets are added to an organic solvent (dimethyl sulfoxide), the molar ratio of 4,4'-diaminodiphenylmethane to 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride is 1:1; the mass of the carbon nanofibers is 10%wt of the sum of the masses of 4,4'-diaminodiphenylmethane and 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride; the mass ratio of the carbon nanofibers to the organic covalent skeleton is 1:2. Under 30kHz ultrasonic dispersion conditions, the stirring speed is 150r / min, and after sufficient stirring for 4h, 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride is added, and the reaction is stirred under the protection of an inert gas (argon). The stirring reaction temperature is room temperature and the reaction time is 6h to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic skeleton;

[0048] (2) placing the polyamic acid composite solution in a vacuum drying oven for defoaming, filtering after degassing, and then uniformly coating it on the substrate by knife coating, roller coating or extrusion coating, drying at 200° C. to form a film, and then placing it in a vacuum furnace for thermal imidization treatment, heating the temperature to 500° C. while applying a pressure of 25 MPa, keeping the temperature and pressure constant for 15 minutes, and then starting to cool down, cooling at a uniform rate to room temperature and then releasing the pressure to obtain a polyimide composite film with a thickness of 18 μm;

[0049] (3) subjecting the prepared polyimide composite film to a high-temperature carbonization treatment under a protective atmosphere (nitrogen), heating the temperature to 1450°C at a heating rate of 5°C / min, while the carbonization pressure is 25 MPa, and the temperature and pressure are kept constant for 2.5 hours, and then cooled to room temperature to obtain a carbonized film;

[0050] (4) The carbonized film is first immersed in ethanol, heated to 80°C and pressure is applied to 25MPa. After maintaining constant temperature and pressure for 2h, it is dried in air and then placed in a graphite furnace for graphitization treatment. It is placed in a vacuum furnace and evacuated to a vacuum degree of 20Pa. The temperature is first increased to 1600°C at a heating rate of 10°C / min and kept at this temperature for 1h; then the temperature is increased to 2200°C at a heating rate of 10°C / min and kept at this temperature for 1h; then the temperature is heated to 2700°C at a heating rate of 10°C / min, kept at this temperature for 2h, and then cooled to room temperature at a rate of 5°C / min to obtain a graphite film.

[0051] The polyimide graphite film prepared in this embodiment has a distinct wrinkle structure and a density of 1.94 g / cm 3 , thickness is 17μm, shrinkage rate is 7%, thermal conductivity is 1554W / (m·K), graphite film has excellent flexibility and is used in folding screen mobile phones. It can be bent 300,000 times without breaking.

[0052] Comparative Example 1

[0053] In this comparative example, a graphite film is prepared, which differs from Example 1 in that carbon nanofibers and two-dimensional organic covalent skeleton are not added; other steps and conditions are consistent with Example 1.

[0054] The graphite film obtained in this comparative example has a thickness of 49 μm, a shrinkage rate of 24%, and a thermal conductivity of 1252 W / (m·K). However, the layered structure of the graphite film is highly regular and the graphite film also exhibits brittle characteristics, resulting in relatively poor mechanical strength of the film.

[0055] Comparative Example 2

[0056] This comparative example prepares a graphite film, which differs from Example 1 in that the amount of carbon nanofibers and two-dimensional organic covalent skeleton added in step (2) is 2 wt % of the polyamic acid solution; the other steps and conditions are consistent with Example 1.

[0057] The graphite film obtained in this comparative example has a thickness of 55 μm, a shrinkage rate of 16%, and a thermal conductivity of 1341 W / (m·K). The addition of carbon nanofibers enhances the strength of the graphite film, but the graphite film still has obvious brittle characteristics and the flexibility is not improved.

[0058] Comparative Example 3

[0059] A graphite film is prepared in this comparative example, which differs from Example 1 in that: in step 4, the carbonized film is not soaked and dried, but is directly placed in a graphite furnace for graphitization treatment; the other steps and conditions are consistent with Example 1.

[0060] The graphite film obtained in this comparative example has a small amount of wrinkle structure, which is significantly less than that in Example 1. The thickness is 61μm, the shrinkage rate is 6%, and the thermal conductivity is 1691W / m·K. It is used in folding screen mobile phones and can be seen to break after 4000 bends. It shows that the microstructure on the surface of the graphite film can be controlled and adjusted by changing the concentration of the ethanol solution and the heat treatment temperature. After the carbonized film is immersed in the ethanol solution, the carbonized layer is given a certain degree of freedom through the pressurized swelling effect, which is conducive to the formation of the wrinkle structure, and the microstructure of the carbonized film is constructed by heat treatment at a relatively low temperature, which has low energy consumption and a simple method. After the heat treatment, the carbonized film is naturally dried in the air, and the volatilization of the ethanol solution contained in the film forms a huge capillary force, which causes the layer to spontaneously wrinkle and form a microstructure on the surface and inside of the graphite film.

[0061] Comparative Example 4

[0062] A graphite film is prepared in this comparative example, which differs from Example 1 in that: in step 3, no pressure is applied during the carbonization treatment, and in step 4, no vacuum is drawn during the graphitization treatment; the other steps and conditions are consistent with Example 1.

[0063] The surface wrinkle degree of the graphite film prepared in this comparative example is not high, which is significantly lower than that of Example 1, with a thickness of 60 μm, a shrinkage rate of 7%, and a thermal conductivity of 1640 W / m·K. It can be bent 5,000 times without breaking in a folding screen mobile phone, but then it starts to break. This shows that due to the lack of pressure, the gas discharge inside the material is reduced, so that the surface wrinkle degree of the final graphite film is not high, and the flexibility is also reduced.

[0064] The present invention adds an appropriate amount of carbon nanofibers and a two-dimensional covalent organic skeleton to a polyimide film, and then uses a special process control to perform carbonization and graphitization, so that a large number of microscopic wrinkles are generated after the composite film is graphitized. The microscopic wrinkles are an important structural factor for the bending graphite to have a very high number of bending times, so the flexibility of the graphite film is greatly improved, that is, the bending resistance of the graphite film is improved. However, the increase in microscopic wrinkles will destroy the highly regular graphite layered structure, causing its thermal conductivity to decrease. However, due to the carbon nanofibers and two-dimensional covalent organic skeletons added to the polyimide film, the carbon nanofibers overlap each other to form a network, and the fibers at the grid nodes are fused with each other, and then supplemented with a two-dimensional covalent organic skeleton to form a heat-conducting network, further improving the thermal conductivity, so that the graphite film prepared by the present invention has excellent flexibility while maintaining the high thermal conductivity of the original graphite film, and reasonably balancing thermal conductivity and flexibility. The graphite film with good flexibility and thermal conductivity of the present invention can be widely used in folding mobile phones and wearable devices. It has expanded the application of graphite film in the field of flexible electronic devices and increased the market share of graphite film.

[0065] Example 4

[0066] After obtaining the graphite film, it also includes:

[0067] Based on the preset evaluation system, the graphite film is quality tested to obtain the test results; the preset evaluation system has different indicators for quality testing of the graphite film, which can be set in advance by the technicians according to actual needs;

[0068] Based on the countermeasure knowledge base, according to the detection results, the countermeasure suggestions and the corresponding credibility of the suggestions are decided;

[0069] When the suggested credibility is greater than or equal to the credibility threshold, based on the countermeasure suggestion, steps (1) to (4) are re-executed to perform countermeasures to obtain a new graphite film.

[0070] Among them, there is a large amount of countermeasure knowledge in the countermeasure knowledge base, and the steps for obtaining countermeasure knowledge include:

[0071] Acquire the knowledge acquisition basis; wherein the knowledge acquisition basis includes: historical quality test results and historical countermeasure records of the graphite film obtained by executing steps (1) to (4) within the recent preset time;

[0072] Perform feature description on the knowledge acquisition basis to obtain a feature description vector;

[0073] Determine the knowledge acquisition strategy corresponding to the feature description vector from the knowledge acquisition strategy library; the knowledge acquisition strategy library contains knowledge acquisition strategies corresponding to different feature description vectors, which can be set in advance by technical personnel according to actual needs;

[0074] Based on the knowledge acquisition strategy, countermeasure knowledge and corresponding sub-credibility are acquired;

[0075] Among them, based on the countermeasure knowledge base and according to the detection results, countermeasure suggestions and corresponding suggestion credibility are decided, including:

[0076] Determine a target knowledge set corresponding to the detection result from the countermeasure knowledge base;

[0077] Based on the target knowledge set, make countermeasure recommendations;

[0078] The sum of the sub-credibility of each counter-knowledge in the target knowledge set is taken as the recommendation credibility.

[0079] In this embodiment, after the graphite film is obtained, its quality is evaluated, and the system adaptively determines countermeasure suggestions. Based on the countermeasure suggestions, a new graphite film countermeasure is performed to improve the quality of graphite film production.

[0080] Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a bendable flexible graphite film for a folding screen, characterized in that: The following steps are involved: (1) adding aromatic diamine, carbon nanofibers and a covalent organic framework into an organic solvent, stirring them thoroughly, and then adding aromatic dianhydride, stirring and reacting to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic framework; (2) placing the polyamic acid composite solution in a vacuum drying oven for defoaming, filtering after degassing, and evenly coating it on the substrate by knife coating, roller coating or extrusion coating, drying at 120-250°C to form a film, and then placing it in a vacuum furnace for thermal imidization treatment, heating the temperature to 450-500°C while applying a pressure of 25MPa, keeping the temperature and pressure constant for 10-20 minutes, and then starting to cool down, cooling to room temperature at a uniform rate and then releasing the pressure to obtain a polyimide composite film; (3) subjecting the prepared polyimide composite film to high-temperature carbonization treatment under a protective atmosphere to obtain a carbonized film; (4) placing the carbonized film in a graphite furnace for graphitization treatment to obtain a graphite film with a thickness of 17-80 μm; The mass of the carbon nanofibers is 5-10%wt of the sum of the mass of the aromatic diamine and the aromatic dianhydride; the mass ratio of the carbon nanofibers to the covalent organic framework is 1:1.5-2; The specific steps of the high temperature carbonization treatment are: heating to 1350-1450°C at a heating rate of 2-10°C / min, while the carbonization pressure is 20-25MPa, maintaining constant temperature and pressure for 1-2.5h, and then cooling to room temperature to obtain a carbonized film; The specific steps of the graphitization treatment are: placing in a vacuum furnace, evacuating to a vacuum degree of 15-20Pa, first heating to 1600°C at a heating rate of 5-10°C / min, and keeping warm for 0.5-1h; then heating to 2200°C at a heating rate of 5-10°C / min, and keeping warm for 0.5-1h; heating to 2700°C at a heating rate of 5-10°C / min, keeping warm for 2h, and then cooling to room temperature at a rate of 5°C / min to obtain a graphite film; In step (4), the carbonized film is first immersed in ethanol, heated to 40-80°C and pressure is applied to 25 MPa, maintained at constant temperature and pressure for 1-3 hours, dried in air, and then placed in a graphite furnace for graphitization to obtain a graphite film.

2. The method according to claim 1, characterized in that: In step (1), aromatic diamine, carbon nanofibers and a covalent organic skeleton are added to an organic solvent, and stirred at a speed of 150-200 r / min under 20-30 kHz ultrasonic dispersion conditions. After sufficient stirring for 2-4 hours, aromatic dianhydride is added, and the mixture is stirred and reacted under the protection of an inert gas. The stirring reaction temperature is -20-60°C, and the reaction time is 1-12 hours to obtain a polyamic acid composite solution containing carbon nanofibers and a two-dimensional covalent organic skeleton.

3. The method according to claim 1, characterized in that: The aromatic diamine is at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 4,4'-diaminodiphenyl ketone, and 4,4'-diaminodiphenylmethane; the aromatic dianhydride is at least one of pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride; and the organic solvent is at least one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, tetrahydrofuran, γ-butyrolactone, hexamethylphosphoramide, dimethyl sulfoxide, and m-cresol.

4. The method according to claim 1, characterized in that: The covalent organic framework is a two-dimensional covalent organic framework nanosheet.

5. The method according to claim 1, characterized in that: The protective atmosphere is nitrogen or an inert gas.

6. The method according to claim 1, characterized in that: After obtaining the graphite film, it also includes: Based on the preset evaluation system, the graphite film is tested for quality and the test results are obtained; Based on the countermeasure knowledge base, according to the detection results, the countermeasure suggestions and the corresponding credibility of the suggestions are decided; When the suggestion credibility is greater than or equal to the credibility threshold, based on the countermeasure suggestion, steps (1) to (4) are re-executed to perform countermeasures to obtain a new graphite film.

7. A bendable flexible graphite film for a folding screen, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.