3D curved surface high-toughness polyimide film and preparation method thereof

Abstract

The invention discloses a 3D curved surface high-toughness polyimide film and a preparation method thereof. After a substrate is cleaned and pretreated, the surface of the special-shaped curved surface substrate is coated with a polyamide acid solution through a tape casting method, and a polyimide film is formed through gradient heating and curing; and then soaking treatment is carried out by adopting a low-boiling-point organic solvent, molecular chains are promoted to be rearranged by utilizing a solvent swelling effect, the thermocuring residual stress is effectively eliminated, and the stress distribution and the form stability of the film are optimized. Compared with a traditional process, the method has the advantages that the mechanical property and the thermal stability of the PI film on a complex curved surface are remarkably improved, the tensile toughness is improved, and meanwhile, the stress concentration risk is reduced. The obtained film has excellent curved surface film layer fitting property and mechanical reliability, can meet the performance requirements of flexible electronics, wearable equipment and aerospace fields on curved surface film covering devices, still keeps structural integrity in an extreme environment, and has important application value.

Description

Technical Field

[0001] The present invention relates to a 3D conformal electronic technology and its application field, in particular to a preparation process of a polyimide (PI) film. Specifically, the present invention relates to a preparation method of a high-toughness polyimide film for building a curved electronic system, aiming to optimize the film forming efficiency, quality and stress distribution of the polyimide film, and improve its application performance in flexible electronic devices and high-performance film materials. Background Art

[0002] With the rapid development of 3D conformal electronics technology, the integration of functional materials and devices has gradually expanded to non-planar surfaces, promoting application innovation in wearable devices, medical devices, aerospace and other fields. As an important high-performance material, polyimide (PI) film has been widely used in flexible electronic devices, thin-film circuits and high-performance membrane materials due to its excellent heat resistance, chemical stability, mechanical flexibility and good electrical properties. However, although PI film has a mature preparation process on a flat substrate, how to achieve high-quality and precisely bonded PI film preparation on a more complex 3D curved surface is still a technical problem that needs to be solved urgently.

[0003] At present, the preparation research of three-dimensional conformal curved surface films is becoming more and more extensive, and researchers have proposed a variety of methods such as hot pressing and thermal curing for film preparation. For example, in the Chinese invention patent "A method for manufacturing a curved polyimide film and a mold" (CN202411157294.9), Wang Hu et al. proposed a method for manufacturing a curved polyimide film and a mold design. The polyamic acid precursor solution is evenly applied to the surface of the mold by spraying, brushing or dipping, and the edge of the polyimide acid film is fixed by a stretching fixture around the mold, and then the mold is placed in an oven as a whole for gradient high-temperature baking. After dehydration and imidization, the polyamic acid forms a curved polyimide film on the mold. However, during the preparation process, since the preparation of the polyimide film is a thermal curing process, the stresses in different parts will be inconsistent due to the different rates of heat evaporation of the polyimide solvent in the curved surface, thereby causing residual stress in the film, resulting in the deformation of the curved film due to the influence of the shaping. In addition, in the Chinese invention patent "A detachable biaxial spin coating equipment for preparing curved thin films" (CN202410388735.X), Yan Ying et al. proposed a detachable biaxial spin coating equipment for preparing curved thin films, including an atmosphere control module, an artificial gravity module, a spin coating module, a frame and an operation module. The present invention adopts biaxial spin coating technology, one shaft is attached to the artificial gravity module, and is used to provide artificial gravity of variable size; the other shaft is attached to the spin coating module, which is used to coat the liquid material on the surface of the substrate to form a curved thin film. The invention can provide different artificial gravity to adapt to curved substrates with different curvatures, so that the spin coating method is used to prepare curved thin films, which can improve the problem of poor uniformity of the film caused by uneven spin coating of the curved surface. However, due to the size problem of the curved thin film prepared by this method, it is not suitable for practical applications such as the preparation of curved protective films in the aerospace field. And after the curved thin film is prepared by this method, it is still impossible to determine whether the shape of the curved thin film will be deformed due to the residual stress of the film. Therefore, relatively speaking, the residual stress release of the film is still a key issue in the preparation process of curved films.

[0004] During the preparation of three-dimensional curved polyimide (PI) films, residual stress is often introduced due to volume changes during solvent evaporation, thermal curing, and cooling. These residual stresses not only affect the mechanical properties and dimensional stability of the film, but may also cause material failure in some special applications. Therefore, it is crucial to study and develop effective residual stress elimination methods to improve the performance of polyimide films. At present, the commonly used residual stress elimination method is thermal annealing. This method rearranges the molecular chains in the film by heating the film to a certain temperature and keeping it for a period of time, thereby reducing stress. Usually, the thermal annealing temperature is set at a temperature near or above the glass transition temperature (Tg) of the film. However, there are some problems in the thermal annealing method that cannot be ignored. For example, too high an annealing temperature may cause material degradation or excessive thermal expansion, thereby affecting the stability of the film. In addition, the annealing process requires precise control of temperature and time, otherwise it is easy to cause uneven stress distribution, which in turn affects the overall performance of the film. For example, in the Chinese invention patent "A polyimide film annealing method" (CN202210746774.3), Wang Shanhui and others proposed a new polyimide film annealing method, which can save energy and realize segmented processing of preheating, annealing and cooling, and improve the yield rate through more precise temperature control. However, its implementation steps are relatively complicated, and it is difficult to achieve precise control of each step in actual operation. In the Chinese patent "A thin film annealing device and annealing process with photothermal, electric and atmosphere synergy" (CN202211535218.8), Shi Lei and others proposed a thin film annealing device and process that integrates photothermal, electric heating and atmosphere synergy, which can optimize the thin film annealing process and finely control the annealing effect. Although this technology can improve the controllability of the annealing effect, its high cost and the use of organic solvent vapors have a high boiling point and potential safety hazards, resulting in certain dangers during high-temperature annealing operations. In general, although existing annealing methods and equipment have made some progress in improving film properties, there are still challenges in temperature control, cost and safety, which need to be further optimized and improved.

[0005] Therefore, the present invention proposes a method for chemical annealing of polyimide film using low-boiling point organic solvent. The chemical annealing method is to immerse the polyimide film in a specific chemical reagent so that the film material and the reagent react or interact to a certain extent, thereby changing the physical and chemical properties of the film and finally achieving the purpose of eliminating residual stress. The mechanism of action of the chemical annealing method is: the chemical reagent interacts with the polyimide molecular chain, which may cause partial depolymerization or relaxation of the molecular chain, thereby relieving the internal stress in the film. During the immersion process, the chemical reagent may react with certain groups in the polyimide, reduce the crosslinking degree between the molecular chains, and then release the stress inside the film. Many organic chemical reagents have the effect of swelling polymers. After the polyimide film contacts with a low-boiling point solvent, the surface of the film will swell, resulting in slight changes in the film structure. This process can help eliminate the stress caused by uneven expansion during the cooling process. As an innovative stress elimination method, the chemical annealing method has the advantages of low-temperature treatment, strong controllability and surface modification. It can effectively relieve the residual stress in the polyimide film and play a role through mechanisms such as molecular chain relaxation, swelling and microstructure regulation. Therefore, this method is suitable for production of different scales and can be widely used for stress relief of various types of polyimide films.

[0006] In summary, the present invention proposes a method for preparing a high-toughness polyimide film for a three-dimensional curved surface. The method is to coat a polyamic acid (PAA) solution on the surface of a special-shaped curved substrate, form a film through thermal curing, and then perform a chemical annealing method to reduce the residual stress, thereby obtaining a three-dimensional curved polyimide film with excellent mechanical properties, thermal stability and dimensional stability. From a chemical principle, the stress comes from the irregularity of the arrangement of polymer chains in the film. The technical solution proposed by the inventor draws on the principle of material recrystallization, and uses chemical annealing technology to effectively reduce the internal stress in the curved polyimide film, ensuring the dimensional stability of the 3D curved film, and breaking through the problem of deformation affecting the quality of products in the production of special-shaped circuits in the fields of wearable electronics, aerospace, etc. Summary of the invention

[0007] The purpose of the present invention is to provide a new method for preparing a polyimide film, which can obtain a high-quality PI film on a 3D conformal surface with excellent mechanical properties, thermal stability and stress distribution. To this end, the present invention provides a method for preparing a polyimide film based on a thermal imidization process, which can effectively improve the conformability, toughness and thermal stability of the film on a complex surface, and solve the problems of excessive film stress and unstable morphology in the prior art.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A method for preparing a 3D curved high-toughness polyimide film comprises the following steps:

[0010] Step 1: Surface pretreatment of special-shaped substrates: Pre-treat the special-shaped curved substrates by immersing the substrates in N,N-dimethylformamide (DMF) solution for 10 minutes to improve the wettability of the substrate surface and remove surface oil and impurities;

[0011] Step 2: Polyamic acid coating: a polyimide film is prepared by a casting method, and a polyamic acid (PAA) N, N-dimethylformamide solution is uniformly coated on the surface of the substrate after the pretreatment in step 1;

[0012] Step 3: Vacuum degassing: The curved substrate coated with the PAA solution is subjected to vacuum degassing to remove bubbles formed during the coating process and ensure uniformity of the film;

[0013] Step 4: thermal curing treatment: the coated substrate is heated and cured by a thermal imidization process to form a polyimide film;

[0014] Step 5: Film peeling: When the substrate temperature naturally cools down to room temperature, gently peel off the film to obtain a curved PI film sample;

[0015] Step 6: stress release: soaking the PI film in a low-boiling point organic solvent to make the polyimide film swell, prompting the molecular chains to rearrange, and releasing the residual stress of the film generated by the thermal curing process, thereby improving the morphological stability and mechanical properties of the film;

[0016] Step 7: Curved film shaping treatment: The polyimide film after the immersion treatment in step 6 is subjected to gradient drying treatment. The film is first dried at a low temperature below 60°C to remove most of the low-boiling point organic solvents, and then vacuum dried to remove the residual solvent in the film. After the film is dried, a curved polyimide film sample maintaining the desired three-dimensional curved surface structure is obtained.

[0017] As a preferred embodiment, the low boiling point organic solvent used in step six is ​​ethanol, acetone, or tetrahydrofuran.

[0018] As a preferred embodiment, the substrate immersion time in step 1 is 10 to 30 minutes.

[0019] As a preferred embodiment, the vacuum degassing treatment in step three is carried out at a vacuum degree of 0 to 40 kPa, and the degassing time is 1 to 2 hours.

[0020] As a preferred embodiment, the thermal imidization temperature in step 4 is 150°C to 300°C, and the thermal curing process includes the following temperature program: baking at 100°C for 1 hour, baking at 150°C for 1.5 hours, baking at 180°C for 1 hour, and baking at 300°C for 1.5 hours.

[0021] As a preferred embodiment, the soaking time in the low boiling point organic solvent in step six is ​​6 to 24 hours.

[0022] As a preferred method, after the immersion treatment in the low-boiling point organic solvent in step six, the PI film is placed in an oven for low-temperature drying at a temperature of 30° C. to 60° C., and then vacuum dried at a vacuum degree of 0 to 40 kPa.

[0023] As a preferred embodiment, the thickness of the PI film is controlled to be 50 to 150 μm.

[0024] The second object of the present invention is to provide a 3D curved high-toughness polyimide film obtained by the above-mentioned preparation method.

[0025] The working principle of the present invention is as follows:

[0026] By coating the target surface with a polyamic acid (PAA) solution and forming a PI film through a thermal imidization process, the film-forming efficiency and film quality are improved by optimizing the thickness of the PI film, the thermal curing procedure and other key parameters. In addition, the residual stress of the film is released by soaking in a low-boiling organic solvent, thereby significantly improving the morphological stability and mechanical properties of the film.

[0027] (1) Substrate surface pretreatment:

[0028] In order to improve the surface wettability of aluminum alloy substrates and avoid the generation of bubbles during the coating process of polyamic acid (PAA) solution, the substrate needs to be surface treated. Immersing the substrate in N,N-dimethylformamide (DMF) solution can effectively remove surface oil and impurities, significantly improve the wettability of the solution to the substrate, reduce the generation of bubbles in the gaps caused by surface roughness, and provide optimized conditions for subsequent coating processes.

[0029] (2) Polyamic acid coating:

[0030] Take out the pre-treated aluminum alloy substrate and ensure that its surface is clean and free of moisture. Apply the polyamic acid solution on the surface of the substrate to ensure that the polyamic acid can evenly cover the entire curved substrate.

[0031] (3) Vacuum degassing treatment:

[0032] In order to eliminate bubbles formed during the coating process and promote the uniformity of the polyamic acid film, the coated substrate is vacuum treated. This process can not only effectively remove bubbles and avoid their adverse effects in subsequent heat treatment, but also ensure surface uniformity and reduce thickness irregularities through the self-leveling effect of the film, thereby optimizing the film quality.

[0033] (4) Thermal curing treatment:

[0034] After the polyamic acid film is vacuum treated, it needs to be cured by heating and baking to complete the conversion of polyamic acid (PAA) to polyimide (PI). This process drives the dehydration reaction of polyamic acid through high temperature, promotes the conversion of amide groups into imide groups, and finally forms a chemically stable polyimide film. After the heat treatment, the substrate is naturally cooled to room temperature with the oven to ensure the quality and structural integrity of the film.

[0035] (5) Film peeling:

[0036] After the heat treatment, the polyimide (PI) film is firmly attached to the aluminum alloy substrate, but due to the residual stress generated during the curing process, the film may bend or warp after peeling. When the substrate temperature naturally cools to room temperature, gently peel off the film to obtain a curved PI film sample. During this process, care should be taken to operate gently to avoid damage to the film due to residual stress or external force.

[0037] (6) Stress release:

[0038] In order to eliminate the bending deformation of the polyimide (PI) film and achieve shaping, stress release treatment is required. First, the curved PI film is immersed in a solution of low-boiling organic solvent. The residual stress in the film is effectively released through the penetration and swelling of organic small molecules. The immersion time is controlled to be 12 hours. Subsequently, the film is taken out and placed in an oven for low-temperature drying to ensure the integrity of the film and shape it, and finally a stable curved PI film sample is obtained.

[0039] (7) Curved film shaping treatment:

[0040] The polyimide film soaked in low-boiling point organic solvent is taken out and subjected to gradient drying. The film is first dried at low temperature to remove most of the low-boiling point organic solvent, and then vacuum dried to remove the residual solvent in the film. The use of gradient volatilization can avoid secondary stress caused by rapid shrinkage of the film. After the film is dried, a curved polyimide film sample that maintains the desired three-dimensional curved surface structure can be obtained.

[0041] By testing the mechanical properties of the film before and after the optimization treatment, it can be seen that after the optimization of the thermal curing process and the low-boiling point organic solvent immersion treatment, the tensile strength of the film increased from 183.1MPa to 191.7MPa (an increase of about 4.7%), and the elongation at break increased from 41.76% to 57.42% (an increase of about 27.3%). It can be seen that the toughness of the film is significantly improved after optimization.

[0042] The beneficial effects of the present invention are:

[0043] (1) High toughness and good adhesion: By optimizing the thermal curing process and low-boiling point organic solvent immersion treatment, the toughness of the PI film and its adhesion performance on complex curved surfaces are significantly improved.

[0044] (2) Uniform stress distribution: Solvent immersion treatment effectively releases the residual stress of the film and reduces the morphological deformation and performance degradation caused by stress concentration.

[0045] (3) Good thermal stability and mechanical properties: By adjusting the process parameters, the thermal stability and mechanical properties of the film are optimized, so that it can maintain stable performance under high temperature and high stress environment.

[0046] (4) Broad application prospects: The preparation method of the present invention is suitable for wearable devices, flexible electronic devices, aerospace and other fields, and has broad industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the process of the present invention.

[0048] Figure 2 This is an optical picture of the curved PI film prepared in the present invention.

[0049] Figure 3 This is an AFM image of the curved PI film prepared in the present invention. DETAILED DESCRIPTION

[0050] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0051] The embodiment provides a method for preparing a 3D curved high-toughness polyimide film, comprising the following steps:

[0052] Step 1: Surface pretreatment of special-shaped substrates: Pre-treat the special-shaped curved substrates by immersing the substrates in N,N-dimethylformamide (DMF) solution for 10 minutes to improve the wettability of the substrate surface and remove surface oil and impurities;

[0053] Step 2: Polyamic acid coating: a polyimide film is prepared by a casting method, and a polyamic acid (PAA) N, N-dimethylformamide solution is uniformly coated on the surface of the substrate after the pretreatment in step 1;

[0054] Step 3: Vacuum degassing: The curved substrate coated with the PAA solution is subjected to vacuum degassing to remove bubbles formed during the coating process and ensure uniformity of the film;

[0055] Step 4: thermal curing treatment: the coated substrate is heated and cured by a thermal imidization process to form a polyimide film;

[0056] Step 5: Film peeling: When the substrate temperature naturally cools down to room temperature, gently peel off the film to obtain a curved PI film sample;

[0057] Step 6: stress release: soaking the PI film in a low-boiling point organic solvent to make the polyimide film swell, prompting the molecular chains to rearrange, and releasing the residual stress of the film generated by the thermal curing process, thereby improving the morphological stability and mechanical properties of the film;

[0058] Step 7: Curved film shaping treatment: The polyimide film after the immersion treatment in step 6 is subjected to gradient drying treatment. The film is first dried at a low temperature below 60°C to remove most of the low-boiling point organic solvents, and then vacuum dried to remove the residual solvent in the film. After the film is dried, a curved polyimide film sample maintaining the desired three-dimensional curved surface structure is obtained.

[0059] Preferably, in some embodiments, the low boiling point organic solvent used in step six is ​​ethanol, acetone, or tetrahydrofuran.

[0060] Preferably, in some embodiments, the substrate soaking time in step 1 is 10 to 30 minutes.

[0061] Preferably, in some embodiments, the vacuum degassing treatment in step three is performed at a vacuum degree of 0 to 40 kPa, and the degassing time is 1 to 2 hours.

[0062] Preferably, in some embodiments, the thermal imidization temperature in step 4 is 150°C to 300°C, and the thermal curing process includes the following temperature program: baking at 100°C for 1 hour, baking at 150°C for 1.5 hours, baking at 180°C for 1 hour, and baking at 300°C for 1.5 hours.

[0063] Preferably, in some embodiments, the soaking time in the low boiling point organic solvent in step six is ​​6 to 24 hours.

[0064] Preferably, in some embodiments, after the immersion treatment in the low-boiling point organic solvent in step six, the PI film is placed in an oven for low-temperature drying at a temperature of 30° C. to 60° C., and then vacuum dried at a vacuum degree of 0 to 40 kPa.

[0065] Preferably, in some embodiments, the thickness of the PI film is controlled to be 50 to 150 μm.

[0066] Example 1

[0067] This embodiment provides a method for preparing a 3D curved high-toughness polyimide film, comprising the following steps:

[0068] (1) Substrate surface pretreatment: The substrate was immersed in N,N-dimethylformamide (DMF) solution for 10 min.

[0069] (2) Polyamic acid coating: Take out the pre-treated aluminum alloy substrate and ensure that its surface is clean and free of moisture. Coat the polyamic acid solution on the surface of the substrate to ensure that the polyamic acid can evenly cover the entire curved substrate.

[0070] (3) Vacuum degassing treatment: The substrate coated with the polyamic acid solution was placed in a vacuum oven and evacuated at a vacuum degree of 20 kPa for 1 hour.

[0071] (4) Thermal curing treatment: After the polyamic acid film is vacuum treated, it needs to be thermally cured by heating and baking to complete the conversion of polyamic acid to polyimide (PI). The substrate is placed in a vacuum oven and heat treated according to a step-by-step heating program: baking at 100°C for 1 hour, 150°C for 1.5 hours, 180°C for 1 hour, and 300°C for 1.5 hours.

[0072] (5) Film peeling: When the substrate temperature naturally cools to room temperature, gently peel off the film to obtain a curved PI film sample. Due to the residual stress generated during the curing process, the film may bend or warp after peeling.

[0073] (6) Stress release: First, the bent PI film was immersed in an acetone solution for 12 h. The residual stress in the film was effectively released through the penetration and swelling of acetone.

[0074] (7) Curved film shaping treatment: After the polyimide film has been soaked in a low-boiling point organic solvent, it is taken out and subjected to a gradient drying treatment. The film is first dried at a low temperature to remove most of the low-boiling point organic solvent, and then vacuum dried to remove the residual solvent in the film. The use of gradient volatilization can avoid secondary stress caused by rapid shrinkage of the film. After the film is dried, a curved polyimide film sample that maintains the desired three-dimensional curved surface structure can be obtained.

[0075] Example 2

[0076] This embodiment provides a method for preparing a 3D curved high-toughness polyimide film, comprising the following steps:

[0077] (1) Substrate surface pretreatment: The substrate was immersed in N,N-dimethylformamide (DMF) solution for 20 min.

[0078] (2) Polyamic acid coating: Take out the pre-treated aluminum alloy substrate and ensure that its surface is clean and free of moisture. Coat the polyamic acid solution on the surface of the substrate to ensure that the polyamic acid can evenly cover the entire curved substrate.

[0079] (3) Vacuum degassing treatment: The substrate coated with the polyamic acid solution was placed in a vacuum oven and evacuated at a vacuum degree of 30 kPa for 1 hour.

[0080] (4) Thermal curing treatment: After the polyamic acid film is vacuum treated, it needs to be thermally cured by heating and baking to complete the conversion of polyamic acid to polyimide (PI). The substrate is placed in a vacuum oven and heat treated according to a step-by-step heating program: baking at 100°C for 1 hour, 150°C for 1.5 hours, 180°C for 1 hour, and 300°C for 1.5 hours.

[0081] (5) Film peeling: When the substrate temperature naturally cools to room temperature, gently peel off the film to obtain a curved PI film sample. Due to the residual stress generated during the curing process, the film may bend or warp after peeling.

[0082] (6) Stress release: First, the bent PI film was immersed in an ethanol solution for 12 h. The residual stress in the film was effectively released through the penetration and swelling of ethanol.

[0083] (7) Curved film shaping treatment: After the polyimide film has been soaked in a low-boiling point organic solvent, it is taken out and subjected to a gradient drying treatment. The film is first dried at a low temperature to remove most of the low-boiling point organic solvent, and then vacuum dried to remove the residual solvent in the film. The use of gradient volatilization can avoid secondary stress caused by rapid shrinkage of the film. After the film is dried, a curved polyimide film sample that maintains the desired three-dimensional curved surface structure can be obtained.

[0084] Example 3

[0085] This embodiment provides a method for preparing a 3D curved high-toughness polyimide film, comprising the following steps:

[0086] (1) Substrate surface pretreatment: The substrate was immersed in N,N-dimethylformamide (DMF) solution for 30 min.

[0087] (2) Polyamic acid coating: Take out the pre-treated aluminum alloy substrate and ensure that its surface is clean and free of moisture. Coat the polyamic acid solution on the surface of the substrate to ensure that the polyamic acid can evenly cover the entire curved substrate.

[0088] (3) Vacuum degassing treatment: The substrate coated with the polyamic acid solution was placed in a vacuum oven and evacuated at a vacuum degree of 40 kPa for 2 hours.

[0089] (4) Thermal curing treatment: After the polyamic acid film is vacuum treated, it needs to be thermally cured by heating and baking to complete the conversion of polyamic acid to polyimide (PI). The substrate is placed in a vacuum oven and heat treated according to a step-by-step heating program: baking at 100°C for 1 hour, 150°C for 1.5 hours, 180°C for 1 hour, and 300°C for 1.5 hours.

[0090] (5) Film peeling: When the substrate temperature naturally cools to room temperature, gently peel off the film to obtain a curved PI film sample. Due to the residual stress generated during the curing process, the film may bend or warp after peeling.

[0091] (6) Stress release: First, the bent PI film was immersed in a tetrahydrofuran solution for 12 h. The residual stress in the film was effectively released through the penetration and swelling effect of tetrahydrofuran.

[0092] (7) Curved film shaping treatment: After the polyimide film has been soaked in a low-boiling point organic solvent, it is taken out and subjected to a gradient drying treatment. The film is first dried at a low temperature to remove most of the low-boiling point organic solvent, and then vacuum dried to remove the residual solvent in the film. The use of gradient volatilization can avoid secondary stress caused by rapid shrinkage of the film. After the film is dried, a curved polyimide film sample that maintains the desired three-dimensional curved surface structure can be obtained.

[0093] like Figure 2 The optical images of the curved polyimide film prepared by the present invention are shown in Figure A. The polyimide film just peeled off from the substrate shows strong deformation under the action of its residual stress; Figure B shows the curved polyimide film after being immersed in a low-boiling point organic solvent and dried, which can maintain a normal curved surface morphology and has excellent shape stability. Figure 3 As shown in the figure, the surface roughness Ra of the obtained PI film is only 4nm, and the surface flatness is excellent. The surface characteristics of low roughness and high uniformity help to reduce interface defects, improve the dielectric properties, mechanical strength and environmental stability of the film, fully meet the application requirements of high-performance electronic devices, and reflect the superior quality and process controllability of polyimide materials.

[0094] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a 3D curved high-toughness polyimide film, characterized in that The following steps are involved: Step 1: Surface pretreatment of special-shaped substrates: Pre-treat the special-shaped curved substrates by immersing the substrates in N,N-dimethylformamide (DMF) solution for 10 minutes to improve the wettability of the substrate surface and remove surface oil and impurities; Step 2: Polyamic acid coating: a polyimide film is prepared by a casting method, and a polyamic acid (PAA) N, N-dimethylformamide solution is uniformly coated on the surface of the substrate after the pretreatment in step 1; Step 3: Vacuum degassing: The curved substrate coated with the PAA solution is subjected to vacuum degassing to remove bubbles formed during the coating process and ensure uniformity of the film; Step 4: thermal curing treatment: the coated substrate is heated and cured by a thermal imidization process to form a polyimide film; Step 5: Film peeling: When the substrate temperature naturally cools down to room temperature, gently peel off the film to obtain a curved PI film sample; Step 6: stress release: soaking the PI film in a low-boiling point organic solvent to make the polyimide film swell, prompting the molecular chains to rearrange, and releasing the residual stress of the film generated by the thermal curing process, thereby improving the morphological stability and mechanical properties of the film; Step 7: Curved film shaping treatment: The polyimide film after the immersion treatment in step 6 is subjected to gradient drying treatment. The film is first dried at a low temperature below 60°C to remove most of the low-boiling point organic solvents, and then vacuum dried to remove the residual solvent in the film. After the film is dried, a curved polyimide film sample maintaining the desired three-dimensional curved surface structure is obtained.

2. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The low boiling point organic solvent used in step 6 is ethanol, acetone, or tetrahydrofuran.

3. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The substrate soaking time in step 1 is 10 to 30 minutes.

4. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The vacuum degassing treatment in step 3 is carried out at a vacuum degree of 0 to 40 kPa, and the degassing time is 1 to 2 hours.

5. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The thermal imidization temperature in step 4 is 150° C. to 300° C., and the thermal curing process includes the following temperature program: baking at 100° C. for 1 hour, baking at 150° C. for 1.5 hours, baking at 180° C. for 1 hour, and baking at 300° C. for 1.5 hours.

6. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The soaking time in the low boiling point organic solvent in step six is ​​6 to 24 hours.

7. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: After the immersion treatment in the low boiling point organic solvent in step six, the PI film is placed in an oven for low temperature drying at a temperature of 30° C. to 60° C., and then vacuum dried at a vacuum degree of 0 to 40 kPa.

8. The method for preparing a 3D curved high-toughness polyimide film according to claim 1, characterized in that: The thickness of the PI film is controlled to be 50 to 150 μm.

9. A 3D curved high-toughness polyimide film, characterized in that The method is obtained by the preparation method according to any one of claims 1 to 8.

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