A polyimide-based light-shielding film and its preparation method

Abstract

The present invention relates to the technical field of polyimide film preparation, and particularly relates to a light-shielding film based on polyimide and a preparation method thereof. It includes: obtaining a polyamic acid solution by polymerizing diamine and dianhydride monomers in a solvent; preparing modified helical carbon fibers; accurately weighing the required mass of the modified helical carbon fibers; slowly adding the modified helical carbon fibers into the solvent, while turning on a high-speed stirrer and assisting with oscillation by an oscillator to ensure that the carbon fibers are fully dispersed in the N,N-dimethylacetamide solvent to form a stable suspension; adding the suspension into the polyamic acid solution and stirring to obtain a modified polyamic acid dispersion; uniformly coating the modified polyamic acid dispersion on a substrate and drying and curing it; and preparing the light-shielding film based on polyimide by a two-step imidization method. The advantages are that the transmittance of the film to infrared rays, visible light, and ultraviolet rays is all 0; a dense network structure is formed, improving the mechanical strength and heat resistance of the film; and the orderly arrangement of the structure and the optimization of the performance are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide film preparation, and particularly to a light-shielding film based on polyimide and a preparation method thereof. Background Art

[0002] The preparation technology of light-shielding films based on polyimide (PI) mainly involves the preparation, modification of PI films, and the composite process with light-shielding film substrates. PI films are widely used in electronic-grade films for high-end electronic devices and electrical-grade films for insulation due to their excellent thermal stability, mechanical properties, chemical stability, and electrical insulation properties. The preparation of light-shielding films usually includes the preparation of PI films, the selection of light-shielding film substrates, and the composite process between the two.

[0003] The defects of the existing technology include the following aspects:

[0004] (1) Complex preparation process: The preparation process of PI films involves multiple processes, including the synthesis of polyamic acid, forming (such as casting, stretching), imidization (thermal method, chemical method), and post-treatment. These processes require extremely high control of process parameters. Any deviation in any link may affect the quality consistency and stability of the PI film finished product. Especially in the imidization process, the technical barrier is high, and there is a balance problem between production efficiency and product quality.

[0005] (2) Material property limitations: Traditional PI films have limited light absorption, which restricts their application in the light-shielding field. Therefore, the preparation of high-temperature resistant and fully light-shielding PI films has become a technical problem. In addition, there are still certain gaps in the mechanical properties, thermal shrinkage rate, etc. of PI films compared with foreign similar products.

[0006] (3) Contradiction between light-shielding property and thickness: In order to simultaneously achieve miniaturization and high functionality of the application module, it is necessary to adjust the thickness while maintaining the performance of the light-shielding film. However, simply reducing the thickness of the light-shielding film will lead to a decrease in light-shielding property. How to reduce the film thickness while maintaining the light-shielding property is a challenge.

[0007] (4) High cost: The price of light-shielding material additives is high, and the preparation process of high-performance PI films is complex, resulting in high production costs and limiting their competitiveness in large-scale applications.

[0008] Based on the above problems, it is urgent to study a more efficient and stable PI film preparation process, reduce production costs, and improve the quality consistency and stability of products. Summary of the Invention

[0009] In order to solve the above problems, the present invention provides a light-shielding film based on polyimide and a preparation method thereof.

[0010] The first object of the present invention is to provide a method for preparing a light-shielding film based on polyimide, which specifically includes the following steps:

[0011] S1. Prepare a polyamic acid solution: Obtain a polyamic acid solution by polymerizing diamine and dianhydride monomers in a solvent;

[0012] S2. Prepare modified helical carbon fibers: Select a nickel sheet as a catalyst carrier, uniformly coat a catalyst suspension on the surface of the nickel sheet, and dry it; Mix absolute ethanol and an auxiliary agent in a certain proportion, place the mixture on the surface of the nickel sheet, and obtain modified helical carbon fibers through the catalytic pyrolysis reaction of the mixture on the surface of the nickel sheet;

[0013] S3. Prepare a modified polyamic acid dispersion; specifically including the following sub-steps:

[0014] S301. Accurately weigh the required mass of modified helical carbon fibers;

[0015] S302. Slowly add the modified helical carbon fibers to the solvent, stir at high speed and shake to form a stable suspension;

[0016] S303. Add the suspension prepared in step S302 to the polyamic acid solution and stir to obtain a modified polyamic acid dispersion;

[0017] S4. Preparation and curing of the film: Select a substrate and clean it thoroughly; Uniformly coat the modified polyamic acid dispersion on the substrate; Dry and cure the coated substrate;

[0018] S5. Prepare a light-shielding film based on polyimide by two-step imidization; including the following sub-steps:

[0019] S501. Transfer the dried film to an imidization furnace, first maintain it at 150 - 200 °C for 0.5 - 1.5 h to promote partial imidization of the polyamic acid;

[0020] S502. Subsequently, raise the temperature to 380 - 420 °C and maintain it for 1.5 - 3.5 h to complete the imidization reaction and obtain a light-shielding film based on polyimide.

[0021] Preferably, the total mass fraction of the added diamine and dianhydride monomers in step S1 accounts for 18 - 25% of the polyamic acid solution; The solvent is dimethylacetamide or N,N-dimethylformamide.

[0022] Preferably, the dianhydride monomer is 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, and the diamine is an aromatic diamine monomer; The temperature of the polymerization is room temperature.

[0023] Preferably, the auxiliary agent in step S2 is water or a combustible solvent containing water; the water content in the mixture of absolute ethanol and the auxiliary agent is less than 0.75%; the catalytic pyrolysis reaction heats the nickel sheet with an alcohol lamp to burn the mixture on the nickel sheet.

[0024] Preferably, the distance between the nickel sheet and the bottom of the wick of the alcohol lamp is 18 - 25 mm, and the combustion time is 40 - 75 min.

[0025] Preferably, the substrate is made of glass, silicon wafer or stainless steel plate.

[0026] Preferably, the drying and curing method is as follows: place the coated substrate in a drying oven with a set temperature, dry it at 120 - 150 °C for 1 - 2 h, and slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0027] Preferably, the modified helical carbon fiber accounts for 5 - 25% of the mass of the modified polyamic acid dispersion liquid.

[0028] Preferably, in step S501, it is first maintained at 180 °C for 1 h; in step S502, the temperature is raised to 400 °C at a heating rate of 5 - 10 °C / min and maintained for 2 h.

[0029] The second object of the present invention is to provide a light-shielding film based on polyimide, which is prepared by using a preparation method of a light-shielding film based on polyimide.

[0030] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0031] (1) Design of carbon fiber with specific wave absorption performance: By precisely controlling the catalyst coating on the catalyst carrier (such as nickel sheet), the mixing ratio of alcohol and auxiliary agent, and the combustion conditions, modified helical carbon fibers with specific wave absorption performance and surface defects are prepared. The carbon fibers not only have a unique morphology (helical shape), but their surface defects and helicity can be adjusted according to requirements, so as to optimize the electromagnetic wave absorption performance. Moreover, the transmittance of infrared, visible light and ultraviolet light of the film added with modified helical carbon fibers is 0.

[0032] (2) Through high-speed stirring and oscillator oscillation, it is ensured that the modified helical carbon fibers are fully dispersed in the DMAC solvent, avoiding agglomeration phenomena, improving the uniform distribution of carbon fibers in the PI film, and further enhancing the overall performance and stability of the film.

[0033] (3) Two-step imidization process: Through the control of the temperature program, it helps to form a dense PI network structure, improve the mechanical strength and heat resistance of the film; ensure the orderly arrangement of the PI structure and the optimization of performance.

[0034] (4) Optimize the addition ratio of the modified helical carbon fiber, which can not only ensure good light-shielding effect but also maintain the mechanical strength and processability of the film.

[0035] (5) Select dimethylacetamide (DMAC) as the solvent, not only because of its good solubility, but also because it can form a good dispersion system with polyamic acid (PAA) and the modified helical carbon fiber, which helps to improve the uniformity and stability of the film. Brief Description of the Drawings

[0036] Figure 1 It is a flowchart of a preparation method of a polyimide-based light-shielding film. Detailed Embodiments

[0037] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0039] The present invention aims to solve the following problems: (1) Optimize the preparation process: study a more efficient and stable preparation process for PI films, reduce production costs, and improve the consistency and stability of product quality; (2) Improve the material properties: prepare high-temperature resistant PI films through molecular structure design, new synthesis technologies, and nano-composite technologies, with a transmittance of 0 for visible light, ultraviolet light, and infrared light, and having a certain electromagnetic wave absorption ability; (3) Solve the contradiction between light-shielding property and thickness: develop a new light-shielding film structure, such as introducing a scattering layer, etc., to reduce the thickness of the light-shielding film while maintaining the light-shielding property, meeting the miniaturization requirements.

[0040] The present invention provides a preparation method of a polyimide-based light-shielding film, which specifically includes the following steps:

[0041] S1. Prepare a polyamic acid (PAA) solution: As the precursor of the polyimide-based light-shielding film, it is obtained by polymerizing diamine and dianhydride monomers in a solvent.

[0042] Specifically, the total mass fraction of the added diamine and dianhydride monomers is 18 - 25%; the solvent is dimethylacetamide (DMAC) or N,N-dimethylformamide (DMF); the polymerization temperature is room temperature, stirring is carried out during the polymerization process, and the stirring time is 6h.

[0043] S2. Preparation of modified helical carbon fibers: Select a nickel sheet as the catalyst support, evenly coat the catalyst suspension on the surface of the nickel sheet, and dry it; Mix absolute ethanol and an auxiliary agent in a certain proportion, place the mixture on the surface of the nickel sheet, put the nickel sheet above the alcohol lamp, and burn the mixture on the surface of the nickel sheet to obtain modified helical carbon fibers through catalytic pyrolysis reaction;

[0044] Specifically, the catalyst suspension is a mixture of stannous chloride and trimellitic acid, and the molar ratio of stannous chloride to trimellitic acid is 3:1 to 3; The auxiliary agent is water or a combustible solvent containing water; The water content in the mixture of absolute ethanol and the auxiliary agent is less than 0.75%; The distance between the nickel sheet and the bottom of the alcohol lamp wick is 18 to 25 mm, and the combustion time is 40 to 75 minutes;

[0045] In this step, under strictly controlled conditions, alcohol is mixed with a specific auxiliary agent and burned on the surface of the catalyst, and the catalytic pyrolysis reaction is used to promote the growth of helical nanofibers. By adjusting the type and concentration of the auxiliary agent, the morphology, helicity and surface defects of the carbon fibers can be effectively controlled, so as to achieve precise regulation of the light absorption and wave absorption properties. Prepare modified helical carbon fibers with specific wave absorption properties and surface defects. These carbon fibers not only have a unique morphology (helical shape), but also their surface defects and helicity can be adjusted according to requirements, so as to optimize the electromagnetic wave absorption performance. Moreover, the transmittance of the film added with modified helical carbon fibers to infrared rays, visible light and ultraviolet rays is 0.

[0046] S3. Preparation of modified polyamic acid dispersion; Specifically, it includes the following sub-steps:

[0047] S301. Accurately weigh the required mass of modified helical carbon fibers;

[0048] S302. Slowly add the modified helical carbon fibers to the solvent, and at the same time turn on the high-speed stirrer and assist with an oscillator to oscillate, ensuring that the modified helical carbon fibers are fully dispersed in the N,N-dimethylacetamide (DMAC) solvent to form a stable suspension; This process requires continuous and uniform dispersion of the modified helical carbon fibers in DMAC to avoid agglomeration;

[0049] S303. Add the suspension prepared in step S302 to the polyamic acid solution and stir to obtain a modified polyamic acid dispersion;

[0050] Specifically, the solid content range of the modified polyamic acid dispersion is 10 to 18%.

[0051] S4. Preparation and curing of the film: Select a flat and flawless substrate, thoroughly clean it to ensure that the surface is free of dust and oil; Evenly coat the modified polyamic acid dispersion on the substrate; Dry and cure the coated substrate;

[0052] Specifically, the substrate is made of glass, silicon wafer or stainless steel plate; the flatness error of the substrate is within 0.003 mm, and the thickness error is within ±0.2 mm; the coating is carried out by a precision coater or manual coating method; the drying and curing method is as follows: place the coated substrate in a drying oven with a set temperature, dry it at 120~150 °C for 1~2 h, and slowly remove most of the solvents to avoid uneven film surface or cracks caused by rapid drying.

[0053] S5. Preparation of a polyimide-based light-shielding film by a two-step imidization method; including the following sub-steps:

[0054] S501. Transfer the dried film to an imidization furnace, first keep it at 150~200 °C for 0.5~1.5 h to promote partial imidization of polyamic acid;

[0055] S502. Then raise the temperature to 380~420 °C and keep it for 1.5~3.5 h to complete the imidization reaction, and obtain a polyimide-based light-shielding film;

[0056] Specifically, in step S501, first keep it at 180 °C for 1 h; in step S502, raise the temperature to 400 °C at a heating rate of 5~10 °C / min and keep it for 2 h; during this process, the heating rate needs to be strictly controlled to ensure the orderly arrangement of the internal structure of the film and the optimization of performance, and improve the mechanical strength and heat resistance of the film.

[0057] Specifically, the modified spiral carbon fiber accounts for 5~25% of the mass of the modified polyamic acid dispersion liquid.

[0058] Example 1

[0059] This example provides a method for preparing a polyimide-based light-shielding film, which specifically includes the following steps:

[0060] S1. Preparation of a polyamic acid (PAA) solution: Obtain a polyamic acid solution by polymerizing diamine and dianhydride monomers in a solvent; the total mass fraction of the diamine and dianhydride monomers accounts for 20% of the polyamic acid solution; the dianhydride monomer uses an asymmetric dianhydride monomer 2,3,3',4'-diphenylether tetracarboxylic dianhydride (aODPA) containing an ether bond, and the diamine is an aromatic diamine monomer; the solvent is DMAC; the polymerization temperature is room temperature.

[0061] S2. Preparation of modified helical carbon fibers: Select a nickel sheet as the catalyst carrier, evenly coat the catalyst suspension on the surface of the nickel sheet, and dry it; Mix absolute ethanol and an auxiliary agent in a certain proportion, place the mixture on the surface of the nickel sheet after mixing, place the nickel sheet above the alcohol lamp, and make the mixture on the surface of the nickel sheet burn to obtain modified helical carbon fibers through catalytic pyrolysis reaction; The catalyst suspension is a mixture of stannous chloride and trimellitic acid (molar ratio 3:2); The auxiliary agent is water, and the water content in the mixture of absolute ethanol and water is less than 0.75%; The distance between the nickel sheet and the bottom of the alcohol lamp wick is 20 mm, and the burning time is 60 min;

[0062] S3. Preparation of modified polyamic acid dispersion; specifically including the following sub-steps:

[0063] S301. Accurately weigh the required mass of modified helical carbon fibers;

[0064] S302. Slowly add the modified helical carbon fibers to the solvent, and at the same time start the high-speed stirrer and assist with an oscillator to oscillate to ensure that the carbon fibers are fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension;

[0065] S303. Add the suspension prepared in step S302 to the polyamic acid solution and stir to obtain a modified polyamic acid dispersion; The solid content in the modified polyamic acid dispersion is 15%; The modified helical carbon fibers account for 12% of the mass of the modified polyamic acid dispersion.

[0066] S4. Preparation and curing of the film: Select a flat and flawless glass substrate, thoroughly clean it to ensure that the surface is free of dust and oil; Uniformly coat the modified polyamic acid dispersion on the substrate; Place the coated substrate in a drying oven set at a certain temperature, dry it at 120 °C for 2 h, and slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0067] S5. Two-step imidization to prepare a polyimide-based light-shielding film; including the following sub-steps:

[0068] S501. Transfer the dried film to an imidization furnace, first keep it at 180 °C for 1 h to promote partial imidization of the polyamic acid;

[0069] S502. Subsequently, raise the temperature to 400 °C at a heating rate of 8 °C / min and keep it for 2 h to complete the imidization reaction to obtain a polyimide-based light-shielding film.

[0070] Example 2

[0071] This example provides a method for preparing a polyimide-based light-shielding film, specifically including the following steps:

[0072] S1. Preparation of polyamic acid (PAA) solution: The polyamic acid solution is obtained by polymerizing diamine and dianhydride monomers in a solvent; the total mass fraction of the diamine and dianhydride monomers accounts for 25% of the polyamic acid solution; the solvent is DMF; the polymerization temperature is room temperature.

[0073] S2. Preparation of modified helical carbon fibers: Select a nickel sheet as the catalyst carrier, evenly coat the catalyst suspension on the surface of the nickel sheet, and dry it; mix absolute ethanol and an auxiliary agent in a certain proportion, place the mixture on the surface of the nickel sheet, place the nickel sheet above the alcohol lamp, and ignite the mixture on the surface of the nickel sheet to obtain modified helical carbon fibers through catalytic pyrolysis reaction; the catalyst suspension is a mixture of stannous chloride and trimellitic acid (molar ratio 3:2); the auxiliary agent is water, and the water content in the mixture of absolute ethanol and water is less than 0.75%; the distance between the nickel sheet and the bottom of the alcohol lamp wick is 25 mm, and the combustion time is 70 min;

[0074] S3. Preparation of modified polyamic acid dispersion; specifically including the following sub-steps:

[0075] S301. Accurately weigh the required mass of modified helical carbon fibers;

[0076] S302. Slowly add the modified helical carbon fibers into the solvent, and at the same time start the high-speed stirrer and assist with an oscillator to shake, ensuring that the carbon fibers are fully dispersed in the N,N-dimethylacetamide (DMAC) solvent to form a stable suspension;

[0077] S303. Add the suspension prepared in step S302 to the polyamic acid solution and stir to obtain a modified polyamic acid dispersion; the solid content in the modified polyamic acid dispersion is 10%; the modified helical carbon fibers account for 5% of the mass of the modified polyamic acid dispersion.

[0078] S4. Preparation and curing of the film: Select a flat and flawless glass substrate, thoroughly clean it to ensure that the surface is free of dust and oil; evenly coat the modified polyamic acid dispersion on the substrate; place the coated substrate in a drying oven set at a certain temperature, dry it at 150 °C for 1 h, and slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0079] S5. Two-step imidization to prepare a polyimide-based light-shielding film; including the following sub-steps:

[0080] S501. Transfer the dried film to an imidization furnace, first maintain it at 200 °C for 0.5 h to promote partial imidization of the polyamic acid;

[0081] S502. Subsequently, heat it up to 420 °C at a heating rate of 5 °C / min and maintain it for 1.5 h to complete the imidization reaction to obtain a polyimide-based light-shielding film.

[0082] Example 3

[0083] This embodiment provides a method for preparing a polyimide-based light-shielding film, which specifically includes the following steps:

[0084] S1. Prepare a polyamic acid (PAA) solution: The polyamic acid solution is obtained by polymerizing diamine and dianhydride monomers in a solvent; the total mass fraction of the diamine and dianhydride monomers accounts for 18% of the polyamic acid solution; the solvent is DMAC; the polymerization temperature is room temperature.

[0085] S2. Prepare modified helical carbon fibers: Select a nickel sheet as the catalyst carrier, evenly coat the catalyst suspension on the surface of the nickel sheet, and dry it; mix absolute ethanol and an auxiliary agent in a certain proportion, place the mixture on the surface of the nickel sheet, place the nickel sheet above an alcohol lamp, and make the mixture on the surface of the nickel sheet burn to obtain modified helical carbon fibers through a catalytic pyrolysis reaction; the catalyst suspension is a mixture of stannous chloride and trimellitic acid (molar ratio 3:2); the auxiliary agent is water, and the water content in the mixture of absolute ethanol and water is less than 0.75%; the distance between the nickel sheet and the bottom of the alcohol lamp wick is 20 mm, and the burning time is 50 min;

[0086] S3. Prepare a modified polyamic acid dispersion; specifically, it includes the following sub-steps:

[0087] S301. Accurately weigh the required mass of the modified helical carbon fibers;

[0088] S302. Slowly add the modified helical carbon fibers to the solvent, and at the same time turn on a high-speed stirrer and assist with an oscillator to ensure that the carbon fibers are fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension;

[0089] S303. Add the suspension prepared in step S302 to the polyamic acid solution and stir to obtain a modified polyamic acid dispersion; the solid content in the modified polyamic acid dispersion is 18%; the modified helical carbon fibers account for 15% of the mass of the modified polyamic acid dispersion.

[0090] S4. Preparation and curing of the film: Select a flat and flawless glass substrate, thoroughly clean it to ensure that the surface is free of dust and oil; evenly coat the modified polyamic acid dispersion on the substrate; place the coated substrate in a drying oven set at a certain temperature, dry it at 120°C for 2 h, and slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0091] S5. Two-step imidization to prepare a polyimide-based light-shielding film; it includes the following sub-steps:

[0092] S501. Transfer the dried film to an imidization furnace, first keep it at 150°C for 1.5 h to promote partial imidization of the polyamic acid;

[0093] Subsequently, it was heated to 400 °C at a heating rate of 5 °C / min and held for 2 h to complete the imidization reaction, obtaining a polyimide-based light-shielding film.

[0094] The polyimide-based light-shielding film prepared by polymerization in the examples was tested, and the test results are shown in Table 1:

[0095] Table 1 Performance test results of polyimide-based light-shielding films

[0096]

[0097] It can be seen from Table 1 that the addition of modified helical carbon fibers did not reduce the mechanical properties of polyimide.

[0098] The light transmittance test results show that while maintaining excellent heat stability, it also has good optical transparency, and the transmittance of infrared, visible, and ultraviolet light is all 0.

[0099] Comparative Example 1

[0100] This comparative example provides a method for preparing a polyimide-based light-shielding film, wherein the modified helical carbon fibers account for 3% of the mass of the modified polyamic acid dispersion, and the remaining preparation steps are the same as those in Example 1.

[0101] The optical transparency of the prepared light-shielding film was measured; the results show that with the decrease in the addition amount of modified helical carbon fibers, the transmittance of infrared, visible, and ultraviolet light all increased, and the light-shielding rate could only reach 80%, and the light-shielding property decreased compared with Examples 1-3.

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing a polyimide-based light-shielding film, wherein the modified helical carbon fibers account for 30% of the mass of the modified polyamic acid dispersion, and the remaining preparation steps are the same as those in Example 1.

[0104] The optical transparency of the prepared light-shielding film was measured; the results show that with the increase in modified helical carbon fibers, the mechanical properties of the polyimide-based light-shielding film decreased significantly, and the elongation at break was 1.06%, which was inferior to Examples 1-3.

[0105] The modified helical carbon fibers obtained by the present invention through precise control of preparation conditions have a unique helical morphology and adjustable surface defects. These characteristics enable the modified helical carbon fibers to more effectively absorb light and electromagnetic waves in the polyimide-based light-shielding film, thereby significantly improving the light absorption performance and wave absorption performance of the polyimide-based light-shielding film. This is of great significance for applications in fields such as electromagnetic wave shielding and stealth materials.

[0106] The uniform dispersion technology of the modified helical carbon fiber in this invention ensures the good distribution of the modified helical carbon fiber in the polyimide-based light-shielding film, avoiding agglomeration phenomena, thus enhancing the overall mechanical strength of the film. At the same time, the two-step imidization process and its precise temperature and time control also contribute to the formation of a dense PI network structure, further improving the mechanical strength and heat resistance of the film. The reasonable carbon fiber addition ratio enables the polyimide-based light-shielding film to have good mechanical strength and processability while maintaining excellent wave-absorbing performance. This allows the polyimide-based light-shielding film to be applied in more fields, such as electronics, communication, aerospace, etc.

[0107] In addition, the selection of dimethylacetamide (DMAC) as the solvent not only improves the preparation efficiency and stability of the film but also reduces the production cost. The good solubility of DMAC and its good dispersibility with PAA and the modified helical carbon fiber make the film preparation process smoother, reducing waste and loss in production.

[0108] In summary, through innovations such as the preparation and application of the modified helical carbon fiber, precise imidization process control, and key raw materials and addition ratios in the formulation, this invention has significantly improved the performance and application fields of the polyimide-based light-shielding film, while reducing the production cost, providing new ideas and methods for the preparation and application of the polyimide-based light-shielding film.

[0109] It should be understood that various forms of processes shown above can be used, reordering, adding or deleting steps. For example, the steps described in the disclosure of this invention can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solutions disclosed in this invention can be achieved. There is no limitation here.

[0110] The above specific embodiments do not constitute a limitation to the protection scope of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention shall be included within the protection scope of this invention.

Claims

1. A method for preparing a light-shielding film based on polyimide, characterized in that: The specific steps include: S1. Preparation of polyamic acid solution: a polyamic acid solution is obtained by polymerization of diamine and dianhydride monomers in a solvent; S2. Preparation of modified helical carbon fibers: A nickel sheet is selected as a catalyst carrier, a catalyst suspension is uniformly coated on the surface of the nickel sheet, and then dried; anhydrous ethanol and an additive are mixed in a certain proportion, the mixture is placed on the surface of the nickel sheet, and the modified helical carbon fibers are obtained by catalytic pyrolysis of the mixture on the surface of the nickel sheet; the catalyst suspension is a mixture of tin dichloride and trimellitic acid, and the molar ratio of tin dichloride to trimellitic acid is 3:1-3; the additive is water or a flammable solvent containing water; and the water content of the mixture of anhydrous ethanol and the additive is less than 0.75%; S3. Preparation of a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. The modified helical carbon fiber is slowly added to the solvent, stirred and shaken at high speed to form a stable suspension; S303. The suspension prepared in step S302 is added to the polyamic acid solution and stirred to obtain a modified polyamic acid dispersion; the modified helical carbon fiber accounts for 5% of the mass of the modified polyamic acid dispersion; S4. Preparation and curing of the film: Select a substrate and clean it thoroughly; evenly apply the modified polyamic acid dispersion on the substrate; dry and cure the coated substrate; S5. A two-step imidization method for preparing a polyimide-based light-shielding film; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 200°C for 0.5h to promote partial imidization of the polyamic acid; S502. The temperature is then raised to 380-420° C. and maintained for 1.5-3.5 hours to complete the imidization reaction, thereby obtaining a polyimide-based light-shielding film.

2. The method for preparing a polyimide-based light-shielding film according to claim 1, wherein: The total mass fraction of the diamine and dianhydride monomers added in step S1 accounts for 18-25% of the polyamic acid solution; and the solvent is dimethylacetamide or N,N-dimethylformamide.

3. The method for preparing a polyimide-based light-shielding film according to claim 2, wherein: The dianhydride monomer is 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, and the diamine is an aromatic diamine monomer; and the polymerization temperature is room temperature.

4. The method for preparing a polyimide-based light-shielding film according to claim 1, wherein: In step S2, the catalytic pyrolysis reaction heats the nickel sheet through an alcohol lamp to burn the mixture on the nickel sheet.

5. The method for preparing a polyimide-based light-shielding film according to claim 4, wherein: The distance between the nickel sheet and the bottom of the alcohol wick is 18-25 mm, and the burning time is 40-75 minutes.

6. The method for preparing a polyimide-based light-shielding film according to claim 1, wherein: The substrate is made of glass, silicon wafer or stainless steel plate.

7. The method for preparing a polyimide-based light-shielding film according to claim 1, wherein: The drying and curing method is as follows: placing the coated substrate in a drying channel with a set temperature, drying at 120-150° C. for 1-2 hours, slowly removing most of the solvent to avoid unevenness or cracks on the film surface caused by rapid drying.

8. The method for preparing a polyimide-based light-shielding film according to claim 1, wherein: In step S502, the temperature is raised to 400°C at a heating rate of 5-10°C / min and maintained for 2 hours.

9. A polyimide-based light-shielding film, characterized in that: The polyimide-based light-shielding film is prepared by the method for preparing the light-shielding film according to any one of claims 1 to 8.

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