Ternary composite conductive filler, conductive polyimide film, flexible electrothermal film and preparation method thereof

Abstract

The present application relates to ternary composite conductive filler, conductive polyimide film, flexible electrothermal film and preparation method thereof, and belongs to the technical field of conductive polymer composite material, ternary composite conductive filler includes carbon fiber film, conductive carbon black and sheet graphite; The sheet graphite is prepared from graphite by liquid phase stripping process; The mass ratio of the carbon fiber film, the conductive carbon black and the sheet graphite is (0.5-2):(1-3):(0.5-2); The conductive polyimide film includes polyimide matrix and the ternary composite conductive filler described above dispersed therein.The present application solves the problem that the mechanical property is significantly reduced due to the addition of high proportion of conductive filler to obtain good conductive property of the existing conductive polyimide material, and realizes the synergistic improvement of conductive property and mechanical property.

Description

Technical Field

[0001] This invention belongs to the field of conductive polymer composite materials technology, specifically relating to ternary composite conductive fillers, conductive polyimide films, flexible electrothermal films, and their preparation methods. Background Technology

[0002] Heating films are electrothermal conversion materials that transform electrical energy into uniform and stable heat energy. They are widely used in home heating (such as underfloor heating systems and electric heating paintings), wearable devices (such as heated clothing and smart blankets), industrial insulation (such as pipe heating and agricultural greenhouse temperature control), and transportation (such as thermal management of new energy vehicle battery packs and seat heating). With the development of flexible electronics, smart homes, and new energy technologies, the market demands heating films with higher efficiency, lower energy consumption, better flexibility, and integrated intelligence.

[0003] Polyimide (PI) is an ideal substrate material for high-performance heating films due to its excellent thermal stability, chemical resistance, and mechanical properties. In existing technologies, conductive films for electrothermal applications are mostly composite structures consisting of a coated conductive layer or metal foil, which generally suffer from defects such as poor adhesion between the heating layer and the substrate, easy detachment, poor bending resistance, and poor heating uniformity. To address this, the industry has proposed a polyimide-based conductive functional layer, whose structure uses polyimide as the substrate and is filled with conductive materials to form a conductive network. However, to achieve ideal conductivity, using a single conductive filler (such as conductive carbon black) typically requires extremely high filler addition levels. This not only limits the improvement of conductivity efficiency but also severely degrades the mechanical properties of the film, increasing its brittleness and reducing its tensile strength, making it prone to mechanical failure during bending or stretching, and failing to meet the requirements of high-end electrothermal elements for long-term reliable operation and flexibility.

[0004] To overcome the aforementioned shortcomings of single fillers, those skilled in the art have attempted improvements in two directions: First, introducing fillers with superior intrinsic conductivity (such as graphene) to enhance conductivity, but this can easily lead to increased film brittleness; second, introducing a one-dimensional conductive framework (such as carbon fiber) into the system. This framework itself possesses excellent conductivity and can synergistically construct a more three-dimensional conductive network with graphene and conductive carbon black. Through the synergistic effect of these two types of fillers, the overall conductivity can be improved while reducing the total filler content, thereby mitigating the adverse effects on the mechanical properties of the film. Simultaneously, how to efficiently composite and disperse these fillers of different dimensions using a simple and uniform process is also crucial for achieving industrial applications.

[0005] To address the aforementioned technical bottlenecks, this invention provides a novel solution. Summary of the Invention

[0006] The purpose of this invention is to provide ternary composite conductive fillers, conductive polyimide films, flexible electrothermal films, and their preparation methods. The aim is to overcome the shortcomings of existing technologies where high filler content leads to increased film brittleness, and to provide a solution that can construct an efficient three-dimensional conductive network with both high conductivity and high flexibility with low filler addition.

[0007] On the one hand, the present invention provides a ternary composite conductive filler, which adopts the following technical solution: Ternary composite conductive filler, including short carbon fibers, conductive carbon black and sheet graphene; The short carbon fibers are prepared by electrospinning polyimide fiber membranes, followed by high-temperature carbonization and low-speed ball milling. The sheet-like graphene is prepared from graphite using a liquid-phase exfoliation process; The mass ratio of the short carbon fibers, conductive carbon black and sheet graphene is (0.5-2):(1-3):(0.5-2).

[0008] Preferably, the temperature of the high-temperature carbonization treatment is 1000-1500℃; The liquid phase exfoliation process is a mechanically assisted liquid phase exfoliation process, specifically including dispersing graphite in a liquid medium and performing high-speed ball milling and shearing.

[0009] On the one hand, the present invention provides a conductive polyimide film, which adopts the following technical solution: A conductive polyimide film comprising a polyimide matrix and a ternary composite conductive filler as described above dispersed therein.

[0010] Preferably, the ternary composite conductive filler is added to the conductive polyimide film at a mass ratio of 7%-28%.

[0011] On the other hand, the present invention provides a method for preparing conductive polyimide films, which adopts the following technical solution: A method for preparing a conductive polyimide film includes the following steps: 1) Polyimide fiber membranes were prepared by electrospinning and then subjected to high-temperature carbonization at 1000-1500℃ to obtain carbon fiber membranes; 2) Graphite is dispersed in a liquid medium and sheet-like graphene is prepared by a mechanically assisted liquid-phase exfoliation process; 3) The carbon fiber membrane and conductive carbon black obtained in step 1) are mixed with the sheet graphene obtained in step 2) in a liquid medium at a mass ratio of (0.5-2):(1-3):(0.5-2). The carbon fiber membrane is broken into short carbon fibers by low-speed ball milling. The short carbon fibers, conductive carbon black and sheet graphene are ground and mixed evenly to obtain a ternary composite conductive filler. 4) The ternary composite conductive filler obtained in step 3) is uniformly dispersed in polyamic acid, and after coating, drying and imidization treatment, a conductive polyimide film is obtained.

[0012] Preferably, in step 1), the parameters of the electrospinning are: voltage -1.5kV to 15kV, spinning time 2-8 hours, and temperature 30-40℃. The polyimide fiber membrane has a thickness of 100-150 μm, and the carbon fiber membrane obtained after carbonization has a thickness of 90-120 μm.

[0013] Preferably, in step 2), the liquid medium is water; the liquid phase stripping process uses high-speed ball milling with a rotation speed of 4000-6000 rpm; In step 3), the liquid medium is ethanol; the mixing is performed using low-speed ball milling at a speed of 100-200 rpm.

[0014] Preferably, in step 4), the solid content of the polyamic acid is 10%-20%, the mass ratio of the ternary composite conductive filler is 7%-28%, and the imidization treatment temperature is 350°C.

[0015] Furthermore, the present invention also provides a flexible electrothermal film, employing the following technical solution: A flexible electrothermal film, comprising: The aforementioned conductive polyimide thin film layer; Electrode layers disposed on both sides of the conductive polyimide film layer; An insulating polyimide film layer is encapsulated on both sides of the conductive polyimide film layer; A high-temperature adhesive layer used to bond the insulating polyimide film layer and the conductive polyimide film layer.

[0016] Preferably, the electrode layer is a copper foil electrode; The high-temperature adhesive layer is made of any one of thermoplastic polyimide, silicone, or modified epoxy.

[0017] In summary, the present invention has the following beneficial technical effects: 1. This invention constructs a continuous three-dimensional conductive network through the synergistic effect of short carbon fibers, conductive carbon black, and sheet graphene. High conductivity (up to 600 S / m) can be achieved within a 7%-28% filler content range, completely solving the problem that existing conductive polyimide materials require a high proportion of a single conductive filler to achieve good conductivity, leading to significant degradation of the film's mechanical properties. Short carbon fibers serve as the conductive framework, and sheet graphene possesses excellent intrinsic conductivity. The synergistic combination of these two with conductive carbon black balances conductivity and mechanical properties across the entire content range, enabling the conductive polyimide film to possess excellent electrothermal conversion capabilities, allowing it to self-heat to over 200°C and operate stably.

[0018] 2. The flexible electrothermal film of the present invention is made by hot-pressing conductive polyimide film and insulating polyimide film. It has excellent radiation characteristics in the far-infrared band and meets the national standard (GB / T7287 Test Method for Infrared Radiation Heaters). It is suitable for applications such as human body thermal management and medical physiotherapy.

[0019] 3. The precursor of the conductive filler (electrospun polyimide fiber membrane) and the insulating film matrix material (polyimide) of this invention both originate from the same polyamic acid solution. This solution can be used to produce fiber membranes through electrospinning or directly coated to form an insulating layer, thus achieving efficient utilization of raw materials. At the same time, the electrospinning, liquid-phase ball milling peeling, and coating imidization processes are smoothly connected, the operation is controllable, and it is easy to achieve industrial mass production. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the microstructure of the ternary composite conductive filler prepared in Example 1 of the present invention. Figure 2 This is a schematic diagram of the stacked structure of the flexible electrothermal film in Embodiment 1 of the present invention; Figure 3 A comparative curve showing the change in resistivity of different conductive filler systems with the amount of filler added; Figure 4 This is a temperature-time response curve of the flexible electrothermal film prepared in Example 1 of the present invention under different applied voltages; Figure 5 Stress-strain curves of polyimide composites with different conductive filler systems; Figure 6 A comparison of the mechanical properties of polyimide composites with different conductive filler systems.

[0021] Explanation of reference numerals in the attached figures: 1. Insulating polyimide film layer; 2. High-temperature adhesive layer; 3. Electrode layer; 4. Conductive polyimide film layer. Detailed Implementation

[0022] The following examples, comparative examples, and appendices are used in conjunction with the embodiments. Figure 1-6 The present invention will be described in further detail below.

[0023] Example Example 1 The preparation method of the flexible electrothermal film includes the following steps: S1. Preparation of carbon fiber membrane A polyamic acid solution with a solid content of 12% was injected into an electrospinning device. The voltage was set to -1.5kV to 15kV (adjustable), the spinning distance was 20cm, the spinning time was 6h, and the spinning temperature was 30-40℃. A polyimide fiber membrane with a thickness of about 150μm was collected. The polyimide fiber membrane was placed in a tube furnace and subjected to high-temperature carbonization under the protection of an inert gas (nitrogen or argon). The carbonization temperature was 1000℃ and the treatment time was 8h to obtain a carbon fiber membrane with a thickness of approximately 120μm.

[0024] S2. Preparation of sheet-like graphene Using graphite with a particle size of 500 μm as a precursor, it was dispersed in water as a liquid medium and mechanically assisted in liquid phase exfoliation was performed by high-speed ball milling at a speed of 4000-6000 rpm for 12-16 h to obtain sheet-like graphene.

[0025] S3. Preparation of ternary composite conductive fillers The carbon fiber membrane obtained in step S1, the sheet graphene obtained in step S2, and the conductive carbon black with a particle size of 30 nm were mixed in a mass ratio of 1:1:2. Liquid medium ethanol was added, and the mixture was mixed by low-speed ball milling at a speed of 100 rpm for 12 hours to obtain a uniform and stable "carbon black-short carbon fiber-graphene" ternary composite conductive filler.

[0026] S4. Preparation of conductive polyimide films A polyamic acid adhesive with a solid content of 10% was mixed with the ternary composite conductive filler obtained in step S3. The mass ratio of the ternary composite conductive filler was 25%. After stirring evenly, the mixture was coated into a film, dried, and then imidized at 350°C to obtain a conductive polyimide film with a resistivity of 0.220Ω. cm.

[0027] Preparation of S5 insulating polyimide film A polyamic acid adhesive with a solid content of 20% was coated into a film, dried, and then imidized at 350°C to obtain an insulating polyimide film.

[0028] S6. Preparation of flexible electrothermal film Copper foil electrodes are attached to both ends of the conductive polyimide film obtained in step S4. Then, the insulating polyimide film obtained in step S5 is used as the upper and lower encapsulation layers. Thermoplastic polyimide adhesive is used for hot pressing encapsulation. The hot pressing temperature is 160-200℃ and the hot pressing time is 10-30min, forming a flexible electrothermal film with a "sandwich" structure.

[0029] Reference Figure 1 The conductive carbon black, liquid-phase exfoliated graphene, and ball-milled short carbon fibers are uniformly mixed. The carbon black particles are dispersed between the graphene sheets and the short carbon fibers, resulting in a dense and uniform overall structure without obvious agglomeration.

[0030] Reference Figure 2 The flexible electrothermal film has a symmetrical five-layer composite structure, which includes, from top to bottom: insulating polyimide film layer 1, high-temperature adhesive layer 2, electrode layer 3, conductive polyimide film layer 4, electrode layer 3, high-temperature adhesive layer 2, and insulating polyimide film layer 1.

[0031] The conductive polyimide film layer 4 is the core functional layer, achieving uniform heating under energized conditions. In this embodiment, the electrode layer 3 is preferably made of copper foil electrodes, which are disposed on both sides of the conductive polyimide film layer 4 as power input terminals. This effectively reduces the contact resistance between the electrodes and the conductive layer, ensuring uniform current distribution within the heating layer and improving electrothermal conversion efficiency and heating uniformity. The high-temperature adhesive layers 2 on the upper and lower sides of the conductive polyimide film layer 4 can achieve high-strength interfacial bonding with adjacent layers through their thermoplastic melting characteristics during the hot pressing process, eliminating interlayer gaps. The high-temperature adhesive layer 2 is made of at least one of thermoplastic polyimide, silicone, and modified epoxy resin. In this embodiment, thermoplastic polyimide is the preferred material for the high-temperature adhesive layer 2. The insulating polyimide film layers 1 on the upper and lower sides serve as the outer encapsulation structure, possessing both excellent electrical insulation and mechanical protection properties. This effectively prevents the internal conductive layer and electrodes from being exposed to moisture, oxidation, or mechanical damage, ensuring long-term stable operation of the heating film under complex conditions such as high temperature and humidity.

[0032] Example 2 The preparation method of the flexible electrothermal film differs from that in Example 1 in that the carbonization temperature of the polyimide fiber film in step S1 is 1400℃, and the resistivity of the conductive polyimide film in step S4 is 0.206Ω. cm; the remaining steps are the same as in Example 1.

[0033] Example 3 The preparation method of the flexible electrothermal film differs from that of Example 2 in that the mass ratio of carbon fiber film, sheet graphene, and conductive carbon black in step S3 is 1.2:1:2, and the resistivity of the conductive polyimide film in step S4 is 0.198Ω. cm; the remaining steps are the same as in Example 2.

[0034] Example 4 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 28%, while the remaining steps are the same as in Example 3. At this time, Example 5 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 25%, while the remaining steps are the same as those in Example 3.

[0035] Example 6 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 22%, while the remaining steps are the same as in Example 3. Example 7 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 19%, while the remaining steps are the same as those in Example 3.

[0036] Example 8 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 16%, while the remaining steps are the same as those in Example 3.

[0037] Example 9 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 13%, while the remaining steps are the same as those in Example 3.

[0038] Example 10 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 10%, while the remaining steps are the same as those in Example 3.

[0039] Example 11 The preparation method of the flexible electrothermal film differs from that of Example 3 in that the mass ratio of the ternary composite conductive filler added in step S4 is 7%, while the remaining steps are the same as those in Example 3.

[0040] Comparative Example 1 The method for preparing the electrothermal film includes the following steps: S1. Preparation of conductive filler Using conductive carbon black with a particle size of 30 nm as the sole conductive filler, it was dispersed in a liquid medium (N,N-dimethylacetamide (DMAc)) and ultrasonically dispersed for 3 hours to obtain a uniform single conductive carbon black filler.

[0041] S2, Preparation of conductive polyimide film A polyamic acid liquid with a solid content of 10% is mixed with a single conductive carbon black filler obtained in step S1. The mass ratio of the single conductive carbon black filler is 25%. After stirring evenly, the mixture is coated into a film, dried, and then subjected to imidization treatment at 350°C to obtain a conductive polyimide film.

[0042] S3, Preparation of insulating polyimide film A polyamic acid adhesive with a solid content of 20% was coated into a film, dried, and then imidized at 350°C to obtain an insulating polyimide film.

[0043] S4. Preparation of the electrothermal film Copper foil electrodes are attached to both ends of the conductive polyimide film obtained in step S2. Then, the insulating polyimide film obtained in step S3 is used as the upper and lower encapsulation layers. Thermoplastic polyimide adhesive is used for hot pressing encapsulation. The hot pressing temperature is 160-200℃ and the hot pressing time is 10-30min to form an electrothermal film.

[0044] Comparative Example 2 The method for preparing the electrothermal film includes the following steps: S1. Preparation of sheet-like graphene Using graphite with a particle size of 500 μm as a precursor, it was dispersed in water as a liquid medium and mechanically assisted in liquid phase exfoliation was performed by high-speed ball milling at a speed of 4000-6000 rpm for 12-16 h to obtain sheet-like graphene.

[0045] S2. Preparation of composite conductive fillers The sheet-like graphene and conductive carbon black with a particle size of 30 nm obtained in step S1 were mixed at a mass ratio of 1:2, and ethanol was added as a liquid medium. The mixture was then ultrasonically dispersed for 4 hours to obtain a uniform and stable composite conductive filler.

[0046] S3, Preparation of conductive polyimide films The polyamic acid liquid with a solid content of 10% was mixed with the composite conductive filler obtained in step S2. The mass ratio of the composite conductive filler was 22%. After stirring evenly, the mixture was coated into a film, dried, and then subjected to imidization treatment at 350°C to obtain a conductive polyimide film.

[0047] S4. Preparation of insulating polyimide film A polyamic acid adhesive with a solid content of 20% was coated into a film, dried, and then imidized at 350°C to obtain an insulating polyimide film.

[0048] S5. Preparation of flexible electrothermal film Copper foil electrodes are attached to both ends of the conductive polyimide film obtained in step S3. Then, the insulating polyimide film obtained in step S4 is used as the upper and lower encapsulation layers. Thermoplastic polyimide adhesive is used for hot pressing encapsulation. The hot pressing temperature is 160-200℃ and the hot pressing time is 10-30min to form an electrothermal film.

[0049] Test case Test Example 1 Reference Figure 3 In conjunction with Examples 4-11 (carbon black / graphene / carbon fiber) and Comparative Examples 1 (carbon black) and 2 (carbon black / graphene) of the present invention, the resistivity of the three conductive filler systems all exhibited typical conductive percolation behavior as the filler addition amount increased: In the low addition amount stage, the filler was isolated in the matrix and could not form a continuous conductive path, and the resistivity of the composite material remained at a high level; as the filler addition amount increased to near the percolation threshold, the filler particles came into contact with each other and formed a continuous conductive network, and the resistivity decreased sharply; when the addition amount exceeded the percolation threshold, the conductive network tended to be perfect, the rate of resistivity decrease slowed down and gradually stabilized.

[0050] Reference Figure 3 The percolation threshold of the ternary composite filler system of the present invention is significantly lower than that of the single conductive carbon black system and the carbon black / graphene binary composite system. Within the 7%-28% full filler addition range defined by the present invention, the resistivity of the system of the present invention is always much lower than that of the other two comparative systems at the same addition amount. In the low addition range (7%-19%), the ternary filler of this invention relies on a three-dimensional cooperative network to form a preliminary conductive path and achieve usable conductivity even when the filler addition is as low as 7%; this reduces the resistivity of the composite material to 0.3Ω. Below cm, a single carbon black system requires approximately 25 wt.% filler, a carbon black / graphene binary system requires approximately 22 wt.% filler, while the ternary composite system of this invention only requires 20 wt.%-21 wt.% filler to achieve the same conductivity.

[0051] During the medium-to-high filler addition range (19%-28%), the conductive network of the composite system of this invention maintained high stability, with resistivity consistently lower than the control group. Even when the filler addition was increased to 28%, no blockage of conductive pathways or resistivity rebound occurred. Specifically, when the ternary composite conductive filler addition reached 28%, the resistivity of the system of this invention could be reduced to approximately 0.167 Ω·cm (corresponding to a conductivity of approximately 600 S / m). This result confirms that the ternary composite filler of this invention possesses excellent conductivity and network structure stability throughout the entire protection range of 7%-28%.

[0052] Test Example 2 Reference Figure 4The flexible electrothermal film of this invention exhibits excellent electrothermal response characteristics. In the initial stage of energization, all three curves show a rapid temperature increase over time. The electrothermal film can heat up to 100℃, 150℃, and over 200℃ respectively within approximately 20 seconds, demonstrating an extremely fast electrothermal response speed that meets the application requirements of rapid heating scenarios. Once the target temperature is reached, under continuous energization, the surface temperature of the electrothermal film can be stably maintained near the target temperature for a long period with minimal fluctuations. This indicates that the flexible electrothermal film of this invention has excellent temperature control stability and uniform heating performance, without localized overheating or temperature drift. After the power is cut off after 60 seconds of energization, all three curves show a smooth and controllable cooling process without sudden temperature drops or abnormal fluctuations, reflecting the good thermal inertia and structural stability of the electrothermal film.

[0053] Reference Figure 4 Comparison of test results under different voltages shows that the flexible electrothermal film of the present invention can achieve wide-range temperature control by adjusting the applied voltage, achieving stable and uniform heating effects from 100℃ to over 200℃. This characteristic indicates that the flexible electrothermal film of the present invention combines rapid electrothermal response, wide temperature range adjustability, constant temperature stability, and high-temperature operating reliability, making it suitable for diverse application scenarios from low-temperature insulation to high-temperature heating, effectively overcoming the shortcomings of existing flexible electrothermal devices such as narrow temperature adjustment range, poor high-temperature stability, and slow response speed.

[0054] Test Example 3 Reference Figure 5 The flexible electrothermal films prepared in Example 6, Comparative Example 1, and Comparative Example 2 of this invention were tested to ensure they exhibited the same conductivity (resistivity of 0.3Ω). Mechanical properties under the condition of (cm). All three curves exhibit typical tensile behavior of ductile materials, successively experiencing elastic deformation, yielding, and plastic deformation stages, ultimately leading to fracture. A comparison shows that the elongation at break of the composite system of this invention is significantly higher than that of the single carbon black system and the binary composite system, while the tensile strength does not show a significant decrease, demonstrating superior overall mechanical properties.

[0055] Reference Figure 6 To achieve the same conductivity, a single carbon black system requires the addition of approximately 25 wt.% filler, resulting in a composite material with a tensile strength of approximately 104 MPa and an elongation at break of only about 13%. A carbon black / graphene binary composite system requires the addition of approximately 22 wt.% filler, increasing the tensile strength to approximately 115 MPa and the elongation at break to approximately 23%. The composite system of this invention further reduces the filler addition to 21 wt.%, achieving the target conductivity while maintaining a tensile strength of approximately 116 MPa and an elongation at break of approximately 30%, significantly superior to the previous two systems.

[0056] The above results demonstrate that the carbon black / graphene / carbon fiber ternary composite filler system employed in this invention, through the synergistic effect of fillers of different dimensions, can effectively reduce the total amount of filler while achieving high conductivity within a total filler addition range of 7%-28%. This reduces the damage to the continuity of the polyimide matrix caused by filler particles, and solves the defects of existing conductive polyimide materials that require high filler addition to achieve high conductivity, leading to deterioration of mechanical properties, high brittleness, and easy fracture. The composite material possesses both excellent conductivity and mechanical properties, meeting the application requirements of flexible electric heating devices that require long-term bending and repeated use.

[0057] The embodiments shown in this specification are only used to illustrate the technical solutions of the present invention and are intended to help those skilled in the art understand the principles and advantages of the present invention. They do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been specifically described, those skilled in the art can still make any modifications, equivalent substitutions or other reasonable variations to the implementation methods without departing from the spirit and scope of the present invention. All equivalent technical solutions resulting therefrom should be considered within the scope of protection of this patent.

Claims

1. A ternary composite conductive filler, characterized in that, Including short carbon fibers, conductive carbon black, and sheet-like graphene; The short carbon fibers are prepared by electrospinning polyimide fiber membranes, followed by high-temperature carbonization and low-speed ball milling. The sheet-like graphene is prepared from graphite using a liquid-phase exfoliation process; The mass ratio of the short carbon fibers, conductive carbon black and sheet graphene is (0.5-2):(1-3):(0.5-2).

2. The ternary composite conductive filler according to claim 1, characterized in that, The high-temperature carbonization treatment is performed at a temperature of 1000-1500℃. The liquid phase exfoliation process is a mechanically assisted liquid phase exfoliation process, specifically including dispersing graphite in a liquid medium and performing high-speed ball milling and shearing.

3. A conductive polyimide film, characterized in that, It includes a polyimide matrix and a ternary composite conductive filler as described in claim 1 or 2 dispersed therein.

4. The conductive polyimide film according to claim 3, characterized in that, The ternary composite conductive filler is added to the conductive polyimide film at a mass ratio of 7%-28%.

5. A method for preparing a conductive polyimide film as described in claim 3 or 4, characterized in that, Includes the following steps: 1) Polyimide fiber membranes were prepared by electrospinning and then subjected to high-temperature carbonization at 1000-1500℃ to obtain carbon fiber membranes; 2) Graphite is dispersed in a liquid medium and sheet-like graphene is prepared by a mechanically assisted liquid-phase exfoliation process; 3) The carbon fiber membrane and conductive carbon black obtained in step 1) are mixed with the sheet graphene obtained in step 2) in a liquid medium at a mass ratio of (0.5-2):(1-3):(0.5-2). The carbon fiber membrane is broken into short carbon fibers by low-speed ball milling. The short carbon fibers, conductive carbon black and sheet graphene are ground and mixed evenly to obtain a ternary composite conductive filler. 4) The ternary composite conductive filler obtained in step 3) is uniformly dispersed in polyamic acid, and after coating, drying and imidization treatment, a conductive polyimide film is obtained.

6. The method for preparing the conductive polyimide film according to claim 5, characterized in that, In step 1), the parameters for electrospinning are: voltage -1.5kV to 15kV, spinning time 2-8 hours, and temperature 30-40℃. The polyimide fiber membrane has a thickness of 100-150 μm, and the carbon fiber membrane obtained after carbonization has a thickness of 90-120 μm.

7. The method for preparing the conductive polyimide film according to claim 5, characterized in that, Step 2), the liquid medium is water; the liquid phase stripping process uses high-speed ball milling with a rotation speed of 4000-6000 rpm; In step 3), the liquid medium is ethanol; the mixing is performed using low-speed ball milling at a speed of 100-200 rpm.

8. The method for preparing the conductive polyimide film according to claim 5, characterized in that, In step 4), the solid content of the polyamic acid is 10%-20%, the mass ratio of the ternary composite conductive filler is 7%-28%, and the imidization treatment temperature is 350℃.

9. A flexible electrothermal film, characterized in that, include: The conductive polyimide film layer (4) as described in claim 3 or 4; Electrode layers (3) are disposed on both sides of the conductive polyimide film layer; Insulating polyimide film layers (1) are encapsulated on both sides of the conductive polyimide film layer. High-temperature adhesive layer (2) for bonding the insulating polyimide film layer (1) and the conductive polyimide film layer (4).

10. The flexible electrothermal film according to claim 9, characterized in that, The electrode layer (3) is a copper foil electrode; The high-temperature adhesive layer (2) is made of any one of thermoplastic polyimide, silicone, or modified epoxy.

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