Conductive polyimide thin films and their preparation methods

Abstract

This application provides a conductive polyimide film and its preparation method, belonging to the field of conductive materials. The method involves preparing a polyamic acid solution, mixing surface-coated rod-shaped silver powder with the polyamic acid solution, and then performing a casting process followed by gradient heating to obtain a polyamic acid film enriched with rod-shaped silver powder at the bottom. The rod-shaped silver powder-rich surface of the obtained polyamic acid film is then subjected to an ion exchange reaction with a silver nitrate solution. The ion-exchange film is then cleaned and subjected to thermal imidization treatment to obtain the conductive polyimide film. This application utilizes the ion exchange reaction and subsequent thermal curing process to reduce silver ions on the film surface, forming a silver-plated layer with excellent adhesion and conductivity. This material exhibits excellent reliability during use; even if the surface silver-plated film partially peels off due to wear, the conductive network built by the rod-shaped silver powder at the bottom can still serve as a backup conductive path, significantly improving its long-term stability in practical applications.

Description

Technical Field

[0001] This invention relates to the field of conductive materials technology, specifically to a conductive polyimide film and its preparation method. Background Technology

[0002] Polyimide films are widely used in flexible circuits, aerospace, and microelectronic packaging due to their excellent thermal stability, mechanical strength, and insulation. Conductive polyimide films are typically achieved by introducing conductive fillers or constructing intrinsically conductive structures. This imparts conductivity to the material while retaining the excellent high-temperature resistance, toughness, and flexibility of the matrix material, making it suitable for applications such as antistatic coatings, flexible electrodes, and electromagnetic shielding. However, existing technologies still have significant drawbacks: poor interfacial compatibility between the filler and the matrix easily leads to stress concentration and accelerates material aging; the material surface is prone to wear during long-term use, affecting overall conductivity. Therefore, existing technologies struggle to simultaneously achieve high conductivity, excellent mechanical properties, ease of processing, and long-term stability, necessitating the development of novel composite strategies or structural designs to overcome these bottlenecks.

[0003] In view of this, it is necessary to design an improved conductive polyimide film and its preparation method to solve the above problems. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a conductive polyimide film and its preparation method, aiming to solve the technical problems of mechanical property degradation, stress concentration and insufficient long-term stability caused by poor compatibility between filler and matrix interface of existing conductive polyimide films, as well as conductivity decay caused by easy surface wear.

[0005] In a first aspect, embodiments of this application provide a method for preparing a conductive polyimide film, comprising the following steps:

[0006] S1. Prepare a polyamic acid solution;

[0007] S2. The surface-coated rod-shaped silver powder is mixed with the polyamic acid solution, and a polyamic acid film with rod-shaped silver powder enriched at the bottom is obtained by casting and gradient heating heat treatment.

[0008] S3. The rod-shaped silver powder enrichment surface of the polyamic acid film obtained in step S2 is subjected to an ion exchange reaction with a silver nitrate solution;

[0009] S4. The ion-exchanged film is cleaned and subjected to thermal imidization to obtain a conductive polyimide film.

[0010] As a further improvement of this application, in step S3, the concentration of the silver nitrate solution is 0.1~0.3 g / mL, and the ion exchange reaction time is 20~40 min.

[0011] As a further improvement of this application, in step S4, the specific method of the thermal imidization treatment is as follows: the temperature is raised to 140~160℃ within 1 hour and held for 0.9~1.2 hours, and then the temperature is raised to 280~300℃ within 2 hours and held for 4~5 hours.

[0012] As a further improvement of this application, in step S2, the specific method of the gradient heating heat treatment is as follows: under vacuum conditions, the film is held at temperatures of 50°C, 70°C, 90°C, 120°C, and 150°C for 1.8 to 2.2 hours respectively.

[0013] As a further improvement of this application, in step S2, the coating agent used for the surface coating treatment of the rod-shaped silver powder includes silane coupling agent and 12-hydroxystearic acid.

[0014] As a further improvement to this application, the silane coupling agent is vinyltriacetoxysilane.

[0015] As a further improvement of this application, the amount of vinyltriacetoxysilane used is 0.05~0.1% of the mass of the rod-shaped silver powder, and the amount of 12-hydroxystearic acid used is 0.1~0.2% of the mass of the rod-shaped silver powder.

[0016] As a further improvement of this application, in step S2, the amount of the surface-coated rod-shaped silver powder added is 1 to 5% of the mass of the polyamic acid in the polyamic acid solution.

[0017] Secondly, embodiments of this application provide a conductive polyimide film, which is prepared by the method for preparing conductive polyimide film described in the first aspect. The conductive polyimide film includes: a three-dimensional network conductive structure formed by overlapping rod-shaped silver powders at the bottom of the film, and a surface silver film formed on the surface enriched by the rod-shaped silver powders through ion exchange and thermal reduction reaction; the surface silver film and the three-dimensional network conductive structure together constitute a dual conductive path.

[0018] The beneficial effects of this application are as follows:

[0019] This application provides a conductive polyimide film and its preparation method. The method involves preparing a polyamic acid solution, mixing surface-coated rod-shaped silver powder with the polyamic acid solution, and then performing a casting and gradient heating heat treatment to obtain a polyamic acid film with rod-shaped silver powder enriched at the bottom. The rod-shaped silver powder enriched surface of the obtained polyamic acid film undergoes an ion exchange reaction with a silver nitrate solution. The ion-exchanged film is then cleaned and subjected to thermal imidization treatment to obtain the conductive polyimide film. This application also provides a method for preparing a conductive polyimide composite material. By performing a special surface coating treatment on the rod-shaped silver powder, the silver powder can be uniformly dispersed in the polyamic acid and enriched at the bottom during polyimide film formation, forming a three-dimensional conductive network structure. Subsequently, the silver powder enriched surface undergoes an ion exchange reaction with a silver nitrate solution, reducing the silver ions during the thermal curing process and depositing a silver film on the surface, resulting in excellent adhesion and conductivity. Even if the outer silver-plated film wears down during use, the bottom of the silver film is protected by a silver wire base composed of rod-shaped silver powder, which can still maintain good conductivity, thus greatly improving the reliability of the material.

[0020] The mechanism of this application involves immersing the silver-rich side of the polyamic acid film in a silver nitrate solution during the polyamic acid film preparation stage. This allows hydrogen ions on the carboxyl groups of the polyamic acid to exchange with silver ions in the silver nitrate solution, ensuring the film surface is fully wetted with silver ions. Simultaneously, the silver-rich lines on one side provide more binding sites for subsequent silver ion reduction. During the subsequent thermosetting process, silver is easily reduced upon heating due to its very low standard reduction potential (Eo = 0.80 V). Furthermore, the poor compatibility between the metal and the polymer leads to silver aggregation and phase separation, resulting in a silver layer on the surface. Through the combination of these two methods, the silver-plated layer formed on the polyimide surface possesses excellent adhesion and is not easily detached. Moreover, even if partial wear and detachment of the surface silver plating causes conductivity failure during subsequent use, the conductive network built by the rod-shaped silver powder at the bottom can compensate for the conductivity loss caused by plating wear, significantly increasing the reliability of the material. The conductive polyimide film prepared by this method is simple to operate and exhibits excellent one-sided conductivity.

[0021] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Detailed Implementation

[0022] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0024] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] Existing conductive polyimide films suffer from poor interfacial compatibility between fillers and the substrate, which easily leads to stress concentration and accelerates material aging; the material surface is also prone to wear during long-term use, affecting the overall conductivity.

[0027] To address the technical problems of poor interfacial compatibility between existing conductive polyimide films and the substrate, and the degradation of conductivity due to surface wear, this application provides a conductive polyimide film and its preparation method. The method involves pre-constructing a polyamic acid film with rod-shaped silver powder enriched at the bottom, and then growing a conductive silver network tightly bonded to the substrate in situ via an ion exchange reaction. This eliminates the physical interface between the filler and the substrate, achieves an integrated structure, and forms a stable conductive pathway embedded in the surface, thus endowing the material with excellent wear resistance and long-term conductive stability.

[0028] In a first aspect, embodiments of this application provide a method for preparing a conductive polyimide film, comprising the following steps:

[0029] S1. Prepare a polyamic acid solution;

[0030] S2. The surface-coated rod-shaped silver powder is mixed with a polyamic acid solution, and a polyamic acid film with rod-shaped silver powder enriched at the bottom is obtained by casting and gradient heating heat treatment.

[0031] S3. The rod-shaped silver powder enriched surface of the polyamic acid film obtained in step S2 is subjected to an ion exchange reaction with silver nitrate solution;

[0032] S4. The ion-exchanged film is cleaned and subjected to thermal imidization to obtain a conductive polyimide film.

[0033] In the technical solution of this application embodiment, the preparation method combines the conductivity of silver powder and the high temperature resistance and high strength of polyimide, and through special surface treatment and ion exchange reaction, it achieves high conductivity, excellent mechanical properties, simple process and long-term stability of the material.

[0034] Specifically, the method for synthesizing polyamic acid solution is as follows: 10-15g of 4,4-diaminodiphenyl ether is added to a container, followed by 60-90g of dimethylacetamide. The mixture is stirred until fully dissolved, and then 10.9-16.4g of pyromellitic dianhydride is slowly added. Nitrogen gas is introduced for protection, and the mixture is stirred and reacted for 2 hours under ice-water bath conditions to obtain polyamic acid solution.

[0035] Furthermore, in some embodiments, in step S3, the concentration of the silver nitrate solution is 0.1~0.3 g / mL, and the ion exchange reaction time is 20~40 min.

[0036] In the technical solution of this application embodiment, a suitable concentration range ensures a sufficient supply of silver ions, resulting in a moderate silver film thickness that guarantees conductivity without affecting the film's mechanical properties. A suitable reaction time allows silver ions to fully wet the film surface while preventing excessive silver ion enrichment, ensuring the uniformity and stability of the silver film. By controlling the silver nitrate concentration and ion exchange time, and conducting the reaction under light-protected conditions, excessive silver ion enrichment can be avoided, thereby reducing the stress between the silver film and the polyimide matrix and improving the adhesion of the silver film. Through the above reaction, a large number of silver ions are effectively anchored on the rod-shaped silver powder enrichment surface of the polyamic acid film, achieving in-situ enrichment of silver ions in the shallow surface layer of the polymer matrix. The enriched rod-shaped silver powder not only constitutes the first conductive network itself but also provides a huge specific surface area and abundant reaction sites for ion exchange, greatly promoting the adsorption and reduction of silver ions. This results in a strong chemical and physical interlocking structure between the final surface silver film and the underlying silver powder network, rather than simple physical adhesion, thus achieving a dual conductive pathway between the surface silver film and the underlying silver powder network.

[0037] Furthermore, in some embodiments, the specific method of thermal imidization treatment in step S4 is as follows: the temperature is raised to 140~160℃ within 1 hour and held for 0.9~1.2 hours, and then the temperature is raised to 280~300℃ within 2 hours and held for 4~5 hours.

[0038] In the technical solution of this application embodiment, the ion-exchanged film is cleaned and subjected to thermal imidization treatment. During the thermal curing process, silver ions are reduced to form a surface silver film, while polyamic acid is imidized and converted into polyimide, ultimately obtaining a conductive polyimide film. Preliminary imidization at a relatively low temperature can avoid excessive oxidation of silver powder and prevent the polyimide film from shrinking or cracking. Subsequently, the temperature is increased to completely imidize the polyamic acid molecular chains, forming a stable polyimide structure. During the high-temperature imidization process, silver ions adsorbed on the film surface are reduced to metallic silver and a uniform and dense silver film is formed on the film surface. The staged heating thermal imidization treatment can effectively ensure that polyamic acid is completely converted into polyimide and optimize the morphology and properties of the silver film, thereby achieving high conductivity, excellent mechanical properties and long-term stability of the material.

[0039] Furthermore, in some embodiments, the gradient heating heat treatment in step S2 is specifically carried out by maintaining the film at temperatures of 50°C, 70°C, 90°C, 120°C, and 150°C for 1.8 to 2.2 hours in sequence under vacuum conditions.

[0040] In the technical solution of this application embodiment, the rod-shaped silver powder that has undergone surface coating treatment is enriched at the bottom of the film to form a conductive network through gradient heating heat treatment; the combination of gradient heating and vacuum conditions ensures the smooth diffusion and removal of solvent from the inside of the film to the surface, effectively preventing internal stress caused by uneven solvent evaporation, avoiding the curling, warping or formation of internal microcracks in the film, thereby obtaining a flat, uniform and defect-free polyamic acid film.

[0041] Furthermore, in some embodiments, in step S2, the coating agent used for the surface coating treatment of the rod-shaped silver powder includes a silane coupling agent and 12-hydroxystearic acid.

[0042] In the technical solution of this application embodiment, 12-hydroxystearic acid ensures good dispersibility of silver powder in solution, while silane coupling agent establishes a strong chemical bond between silver powder and matrix, ensuring that silver powder and matrix will not peel off during subsequent solvent evaporation, film forming and high-temperature imidization processes, and can be enriched at the bottom when polyimide film is formed, overlapping to form a three-dimensional network conductive structure.

[0043] Specifically, the synthesis method of rod-shaped silver powder is as follows: Under mechanical stirring, add 5-6g of silver nitrate to 100mL of deionized water, mix thoroughly, then add 0.2-0.3g of polyvinylpyrrolidone (PVP), dissolve completely, add ammonia dropwise until the solution is clear, then add 0-0.05g of sodium hydroxide, mix thoroughly, and continue adding ammonia dropwise until the solution is clear to obtain a silver solution; under constant temperature of 0-25℃ and mechanical stirring, add 10-15g of formalin to the silver solution, maintain mechanical stirring, and after 1 minute, add 4-5mL of 0.5% stearic acid ethanol solution. After mixing evenly, filter and wash to obtain rod-shaped silver powder.

[0044] The surface coating treatment method for rod-shaped silver powder is as follows: disperse the rod-shaped silver powder in an ethanol solution of 0.5% silane coupling agent and stir for 10-15 min; disperse the treated silver powder in an ethanol solution of 0.5% 12-hydroxystearic acid and stir for 10-15 min to obtain rod-shaped silver powder with surface coating treatment.

[0045] Furthermore, in some embodiments, the silane coupling agent is vinyltriacetoxysilane.

[0046] In the technical solution of this application embodiment, the vinyltriacetoxysilane, due to its unique molecular structure and chemical properties, ensures that the well dispersed silver powder can form a strong interfacial bond with the matrix in subsequent stages.

[0047] Furthermore, in some embodiments, the amount of vinyltriacetoxysilane used is 0.05 to 0.1% of the mass of the rod-shaped silver powder, and the amount of 12-hydroxystearic acid used is 0.1 to 0.2% of the mass of the rod-shaped silver powder.

[0048] In the technical solution of this application embodiment, the precise control of the amount of vinyltriacetoxysilane and 12-hydroxystearic acid can ensure that the silver powder can be uniformly dispersed in the precursor solution and can form a firm bond with the final matrix, while avoiding the negative impact introduced by excessive coating agent, thereby preparing a high-performance conductive polyimide film in the most economical and efficient way.

[0049] Furthermore, in some embodiments, in step S2, the amount of surface-coated rod-shaped silver powder added is 1 to 5% of the mass of polyamic acid in the polyamic acid solution.

[0050] In the technical solution of this application embodiment, the amount of rod-shaped silver powder added after surface coating treatment ensures that the silver powder is uniformly dispersed in the polyamic acid solution, and is enriched at the bottom and overlapped into a three-dimensional network conductive structure during film formation. At the same time, the polyimide matrix can still maintain its continuous phase, giving the material excellent high temperature resistance, toughness and flexibility.

[0051] Secondly, embodiments of this application provide a conductive polyimide film, which is prepared by the method for preparing conductive polyimide film described in the first aspect. The conductive polyimide film includes: a three-dimensional network conductive structure formed by overlapping rod-shaped silver powders at the bottom of the film, and a surface silver film formed on the surface of the rod-shaped silver powder enrichment through ion exchange and thermal reduction reaction; the surface silver film and the three-dimensional network conductive structure together constitute a dual conductive path.

[0052] This conductive polyimide film possesses a unique asymmetric composite structure. The surface silver film is generated through in-situ reduction on the polymer matrix via ion exchange and intercalates with the underlying pre-placed silver powder network. Its adhesion to the polyimide matrix is ​​far superior to that of metal layers formed through physical adhesion or ordinary chemical plating, effectively preventing peeling and flaking of the silver film. In practical applications, even if the surface silver film experiences localized wear or detachment due to long-term friction or external force, the three-dimensional conductive network structure built from rod-shaped silver powder at the bottom can still serve as a backup conductive path, ensuring that the overall conductivity does not completely fail. This significantly improves the long-term stability and reliability of the product under harsh operating environments such as dynamic bending and frictional contact. The surface resistivity of the silver film surface of the prepared conductive polyimide film is 3.5 × 10⁻⁶. -7 ~9.2×10 -7 Ω, the surface resistance of the insulating surface is 5.8 × 10⁻⁶. 13 ~9.3×10 13 Ω possesses excellent single-sided conductivity. Through its innovative dual conductive structure of surface silver film and bottom silver mesh, it successfully solves the technical bottlenecks in existing technologies, such as easy wear of conductive layers, poor interfacial bonding, and insufficient long-term stability, making it an advanced functional material with high conductivity, high reliability, and excellent mechanical properties.

[0053] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0054] Example 1

[0055] This embodiment provides a method for preparing a conductive polyimide film, including the following steps:

[0056] S1. Synthesis of polyamic acid solution: 10g of 4,4-diaminodiphenyl ether and 60g of dimethylacetamide were added to a three-necked flask and stirred until fully dissolved. Then, 10.9g of pyromellitic dianhydride was slowly added, and nitrogen gas was introduced for protection. The reaction was stirred for 2 hours under ice-water bath conditions to obtain polyamic acid solution.

[0057] S2. Preparation of silver solution: Under mechanical stirring, add 5g of silver nitrate to 100mL of deionized water, mix thoroughly, then add 0.2g of polyvinylpyrrolidone (model K30), dissolve completely, add ammonia dropwise until the solution is clear, then add 0.05g of sodium hydroxide, mix thoroughly, and continue adding ammonia dropwise until the solution is clear to obtain silver solution;

[0058] Redox reaction: Under constant temperature of 25℃ and mechanical stirring, 10g formalin was slowly added dropwise to the silver solution at a rate of 3mL / min. Mechanical stirring was maintained. After 1min, 4mL of 0.5% stearic acid ethanol solution was added. After mixing evenly, the mixture was filtered and washed with deionized water until the pH value of the silver powder surface was neutral to obtain rod-shaped silver powder.

[0059] Silver powder surface treatment: The washed rod-shaped silver powder was filtered and then dispersed in a 98% ethanol solution of vinyltriacetoxysilane with a mass concentration of 0.5% and the amount of silane coupling agent was 0.05% of the mass of the rod-shaped silver powder. The mixture was stirred for 10 min and then filtered. The treated silver powder was then dispersed in an ethanol solution of 12-hydroxystearic acid with a mass concentration of 0.5% and the amount of 12-hydroxystearic acid was 0.1% of the mass of the rod-shaped silver powder. The mixture was stirred for 10 min and then filtered to obtain rod-shaped silver powder with surface coating treatment.

[0060] Preparation of polyamic acid film: Weigh 10g of polyamic acid solution, add 3% of the above surface-coated rod-shaped silver powder by mass of polyamic acid, mix evenly, pour the solution evenly onto a glass plate, form a film by casting, place it in a vacuum constant temperature drying oven, and keep it at 50℃, 70℃, 90℃, 120℃, and 150℃ vacuum conditions for 2 hours each to obtain a polyamic acid film with rod-shaped silver powder enriched at the bottom;

[0061] S3. Remove the obtained polyamic acid film from the glass plate, immerse the rod-shaped silver powder enrichment surface in a 0.2 g / mL silver nitrate aqueous solution for ion exchange, and keep it in the dark for 30 min;

[0062] S4. Rinse the ion-exchanged film thoroughly with water, place it in a vacuum constant temperature drying oven, raise the temperature to 150℃ within 1 hour, maintain for 1 hour, then raise the temperature to 300℃ within 2 hours, maintain for 5 hours to fully imidize it, and obtain a conductive polyimide film.

[0063] Example 2

[0064] This embodiment provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the concentration of the silver nitrate solution is 0.1 g / mL, and it is kept under light-protected conditions for 20 min. The other conditions are basically the same as in Example 1.

[0065] Example 3

[0066] This embodiment provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the concentration of the silver nitrate solution is 0.3 g / mL, and it is kept under light-protected conditions for 40 min. The other conditions are basically the same as in Example 1.

[0067] Comparative Example 1

[0068] Comparative Example 1 provides a method for preparing a conductive polyimide film. The only difference from Example 1 is that no ion exchange reaction is performed in step S3, while the other conditions are basically the same as in Example 1.

[0069] Comparative Example 2

[0070] Comparative Example 2 provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the film is kept under light-protected conditions for 5 minutes, while the other conditions are basically the same as those in Example 1.

[0071] Comparative Example 3

[0072] Comparative Example 3 provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the film is kept under light-protected conditions for 80 minutes, while the other conditions are basically the same as in Example 1.

[0073] Comparative Example 4

[0074] Comparative Example 4 provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the concentration of the silver nitrate solution is 0.05 g / mL, and the other conditions are basically the same as in Example 1.

[0075] Comparative Example 5

[0076] Comparative Example 5 provides a method for preparing a conductive polyimide film. Compared with Example 1, the only difference is that in step S3, the concentration of silver nitrate solution is 0.4 g / mL, and the other conditions are basically the same as in Example 1.

[0077] The conductive polyimide films prepared in the above embodiments and comparative examples were subjected to resistance tests, and the results are shown in Table 1.

[0078] Table 1 Performance test results of conductive polyimide films

[0079]

[0080] As shown in Table 1, the resistivity of the silver film surface of the conductive polyimide thin film material prepared in this application is 4.1 × 10⁻⁶. -7 ~7.2×10 -7 It has excellent electrical conductivity (Ω·m), while the surface resistivity of the insulating surface is 6.5 × 10⁻⁶. 13 ~7.6×10 13 Ω, lacking conductivity. In Comparative Example 1, no ion exchange treatment was performed, and the rod-shaped silver powder enrichment surface only possessed antistatic properties, not excellent conductivity. In Comparative Example 2, the treatment time in the silver nitrate solution was too short, failing to form a complete large-area silver film on the rod-shaped silver powder enrichment surface, thus failing to significantly enhance conductivity. In Comparative Example 3, the polyimide film was immersed in the silver nitrate solution for too long, causing excessive swelling and hydrolysis of the polyamic acid film, resulting in brittleness and cracking of the final film, destroying the overall mechanical structure and making testing impossible. In Comparative Example 4, the silver nitrate concentration was too low, and the degree of ion exchange was insufficient, failing to form a complete silver film on the surface during the thermal imidization stage, thus failing to significantly enhance conductivity. In Comparative Example 5, the silver nitrate concentration was too high, resulting in a large amount of silver reduced during the thermal imidization stage. The rapid reduction and excessive aggregation of silver generated significant internal stress, leading to uneven thickness, brittleness, and a significant decrease in adhesion to the underlying substrate of the formed surface silver film, which to some extent damaged the mechanical structure of the polyimide itself, reducing reliability.

[0081] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a conductive polyimide film, characterized in that, Includes the following steps: S1. Prepare a polyamic acid solution; S2. The surface-coated rod-shaped silver powder is mixed with the polyamic acid solution, and a polyamic acid film with rod-shaped silver powder enriched at the bottom is obtained by casting and gradient heating heat treatment. S3. The rod-shaped silver powder enriched surface of the polyamic acid film obtained in step S2 is subjected to an ion exchange reaction with a silver nitrate solution under light-protected conditions; the concentration of the silver nitrate solution is 0.1~0.3 g / mL, and the ion exchange reaction time is 20~40 min; S4. The ion-exchanged film is cleaned and thermally imidized to obtain a conductive polyimide film; The specific method of the thermal imidization treatment is as follows: the temperature is raised to 140~160℃ within 1 hour and held for 0.9~1.2 hours, and then the temperature is raised to 280~300℃ within 2 hours and held for 4~5 hours.

2. The method for preparing the conductive polyimide film according to claim 1, characterized in that, In step S2, the specific method of the gradient heating heat treatment is as follows: under vacuum conditions, the film is held at temperatures of 50℃, 70℃, 90℃, 120℃, and 150℃ for 1.8~2.2h respectively.

3. The method for preparing the conductive polyimide film according to claim 1, characterized in that, In step S2, the coating agents used for the surface coating treatment of the rod-shaped silver powder include silane coupling agent and 12-hydroxystearic acid.

4. The method for preparing the conductive polyimide film according to claim 3, characterized in that, The silane coupling agent is vinyltriacetoxysilane.

5. The method for preparing the conductive polyimide film according to claim 4, characterized in that, The amount of vinyltriacetoxysilane used is 0.05~0.1% of the mass of the rod-shaped silver powder, and the amount of 12-hydroxystearic acid used is 0.1~0.2% of the mass of the rod-shaped silver powder.

6. The method for preparing the conductive polyimide film according to claim 1, characterized in that, In step S2, the amount of the surface-coated rod-shaped silver powder added is 1 to 5% of the mass of polyamic acid in the polyamic acid solution.

7. A conductive polyimide film, characterized in that, The conductive polyimide film is prepared by the method according to any one of claims 1-6, wherein the conductive polyimide film comprises: a three-dimensional network conductive structure formed by overlapping rod-shaped silver powders at the bottom of the film, and a surface silver film formed on the surface enriched by the rod-shaped silver powders through ion exchange and thermal reduction reaction; the surface silver film and the three-dimensional network conductive structure together constitute a dual conductive path.

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