Shading film based on polyimide and preparation method thereof

Abstract

The invention relates to the technical field of polyimide film preparation, in particular to a polyimide-based shading film and a preparation method thereof. Comprising the following steps: polymerizing diamine and dianhydride monomers in a solvent to obtain a polyamide acid solution; preparing modified helical carbon fibers; accurately weighing the modified helical carbon fiber with the required mass; slowly adding the modified helical carbon fiber into the solvent, starting a high-speed stirrer and assisting with an oscillator for oscillation at the same time, and ensuring that the carbon fiber is fully dispersed in the dimethylacetamide solvent to form a stable suspension; adding the suspension into the polyamide acid solution, and stirring to obtain a modified polyamide acid dispersion liquid; uniformly coating a substrate with the modified polyamide acid dispersion liquid, and drying and curing; the polyimide-based shading film is prepared through two-step imidization. The method has the advantages that the transmittance of infrared rays, visible light and ultraviolet rays of the film is 0; a compact network structure is formed, and the mechanical strength and heat resistance of the film are improved; and ordered arrangement of the structure and optimization of the performance are ensured.

Description

Technical Field

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

[0002] The light-shielding film preparation technology based on polyimide (PI) currently mainly involves the preparation and modification of PI film and its composite process with light-shielding film substrate. PI film is widely used as electronic-grade film in high-end electronic equipment and electrical-grade film in insulation and other fields due to its excellent thermal stability, mechanical properties, chemical stability and electrical insulation properties. The preparation of light-shielding film usually includes the preparation of PI film, the selection of light-shielding film substrate and the composite process between the two.

[0003] The defects of the prior art include the following aspects: (1) Complex preparation process: The preparation process of PI film involves multiple steps, including the synthesis of polyamic acid, molding (such as casting, stretching), imidization (thermal method, chemical method) and post-treatment. These processes have extremely high requirements for process parameter control. Deviations in any link may affect the quality consistency and stability of the finished PI film. In particular, the imidization process has high technical barriers and there is a balance between production efficiency and product quality.

[0004] (2) Material performance limitations: Traditional PI films have limited light absorption, which limits their application in the field of light shielding. Therefore, the preparation of high-temperature resistant and fully light-shielding PI films has become a technical challenge. In addition, the mechanical properties, thermal shrinkage rate and other properties of PI films are still somewhat different from those of similar foreign products.

[0005] (3) Contradiction between light-shielding property and thickness: In order to simultaneously achieve miniaturization and high functionality of application modules, 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 result in reduced light-shielding property. How to reduce the film thickness while maintaining light-shielding property is a challenge.

[0006] (4) High cost: The price of light-shielding material additives is relatively high, and the preparation process of high-performance PI films is complicated, resulting in high production costs, which limits its competitiveness in large-scale applications.

[0007] Based on the above problems, there is an urgent need to study more efficient and stable PI film preparation processes to reduce production costs and improve product quality consistency and stability. Summary of the invention

[0008] In order to solve the above problems, the present invention provides a polyimide-based light-shielding film and a preparation method thereof.

[0009] The first object of the present invention is to provide a method for preparing a light-shielding film based on polyimide, which specifically comprises the following steps: S1. Preparation of polyamic acid solution: obtaining a polyamic acid solution by polymerization of diamine and dianhydride monomers in a solvent; S2. Preparation of modified spiral carbon fiber: selecting a nickel sheet as a catalyst carrier, uniformly coating the catalyst suspension on the surface of the nickel sheet, and drying; mixing anhydrous ethanol and an additive in a certain proportion, placing the mixture on the surface of the nickel sheet, and obtaining a modified spiral carbon fiber by catalytic pyrolysis reaction of the mixture on the surface of the nickel sheet; S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, stirring and shaking 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; S4. Preparation and curing of the film: selecting a substrate and thoroughly cleaning it; evenly coating the modified polyamic acid dispersion on the substrate; drying and curing the coated substrate; S5. Two-step imidization method for preparing a light-shielding film based on polyimide; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 150-200°C for 0.5-1.5h 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.

[0010] Preferably, 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.

[0011] Preferably, 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.

[0012] Preferably, the auxiliary agent in step S2 is water or a flammable solvent containing water; the water content in the mixture of anhydrous ethanol and the auxiliary agent is less than 0.75%; the catalytic pyrolysis reaction heats the nickel sheet through an alcohol lamp to burn the mixture on the nickel sheet.

[0013] Preferably, the distance between the nickel sheet and the bottom of the alcohol wick is 18-25 mm, and the burning time is 40-75 min.

[0014] Preferably, the substrate is made of glass, silicon wafer or stainless steel plate.

[0015] Preferably, the drying and curing method is as follows: the coated substrate is placed in a drying tunnel with a set temperature, and dried at 120-150° C. for 1-2 hours to slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0016] Preferably, the modified helical carbon fiber accounts for 5-25% of the mass of the modified polyamic acid dispersion.

[0017] Preferably, in step S501, the temperature is first maintained at 180°C for 1 hour; in step S502, the temperature is increased to 400°C at a heating rate of 5-10°C / min and maintained for 2 hours.

[0018] The second object of the present invention is to provide a polyimide-based light-shielding film, which is prepared by a method for preparing a polyimide-based light-shielding film.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) Design of carbon fiber with specific absorption performance: By precisely controlling the catalyst coating on the catalyst carrier (such as nickel sheet), the mixing ratio of alcohol and additives, and the combustion conditions, modified helical carbon fiber with specific absorption performance and surface defects is prepared. The carbon fiber not only has a unique morphology (helical), but also its surface defects and helicity can be adjusted according to demand, thereby optimizing the electromagnetic wave absorption performance. In addition, the infrared, visible light and ultraviolet light transmittance of the film with modified helical carbon fiber is 0.

[0020] (2) Through high-speed stirring and oscillator vibration, the modified helical carbon fibers are fully dispersed in the DMAC solvent, which avoids agglomeration and improves the uniform distribution of carbon fibers in the PI film, thereby improving the overall performance and stability of the film.

[0021] (3) Two-step imidization process: Through the control of 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.

[0022] (4) Optimizing the addition ratio of modified spiral carbon fiber can not only ensure a good shading effect, but also maintain the mechanical strength and processability of the film.

[0023] (5) Dimethylacetamide (DMAC) was selected 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 modified helical carbon fibers, which helps to improve the uniformity and stability of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention is a flow chart of a method for preparing a light-shielding film based on polyimide. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying 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 of the present invention.

[0027] The present invention aims to solve the following problems: (1) Optimizing the preparation process: Researching a more efficient and stable PI film preparation process, reducing production costs, and improving product quality consistency and stability; (2) Improving material performance: Through molecular structure design, new synthesis technology, and nano-composite technology, a high-temperature resistant PI film is prepared, and the transmittance of visible light, ultraviolet light, and infrared light is 0, and it has a certain electromagnetic wave absorption capacity; (3) Solving the contradiction between light-shielding property and thickness: Developing a new light-shielding film structure, such as introducing a scattering layer, so that the light-shielding film can reduce the thickness while maintaining the light-shielding property to meet the miniaturization requirements.

[0028] The present invention provides a method for preparing a light-shielding film based on polyimide, which specifically comprises the following steps: S1. Preparation of polyamic acid (PAA) solution: as a precursor of a polyimide-based light-shielding film, obtained by polymerizing diamine and dianhydride monomers in a solvent; 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, and stirring is performed during the polymerization process for 6 hours.

[0029] S2. Preparation of modified spiral carbon fiber: selecting a nickel sheet as a catalyst carrier, uniformly coating the catalyst suspension on the surface of the nickel sheet, and drying; mixing anhydrous ethanol and an additive in a certain proportion, placing the mixture on the surface of the nickel sheet, placing the nickel sheet above an alcohol lamp, burning the mixture on the surface of the nickel sheet, and catalyzing a pyrolysis reaction to obtain a modified spiral carbon fiber; Specifically, 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 auxiliary agent is water or a flammable solvent containing water; the water content in the mixture of anhydrous ethanol and the auxiliary agent is less than 0.75%; 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; In this step, alcohol is mixed with a specific additive and burned on the catalyst surface under strictly controlled conditions, and the growth of spiral nanocarbon fibers is promoted by catalytic pyrolysis reaction. By adjusting the type and concentration of the additive, the morphology, helicity and surface defects of the carbon fibers can be effectively controlled, thereby achieving precise regulation of light absorption and wave absorption properties. A modified spiral carbon fiber with specific wave absorption properties and surface defects is prepared. This carbon fiber not only has a unique morphology (spiral), but also its surface defects and helicity can be regulated according to demand, thereby optimizing the electromagnetic wave absorption performance, and the film after adding the modified spiral carbon fiber has a transmittance of 0 for infrared, visible light and ultraviolet light.

[0030] S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, while turning on a high-speed stirrer and shaking with an oscillator to ensure that the modified helical carbon fiber is fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension; in this process, the modified helical carbon fiber needs to be continuously and evenly dispersed in the DMAC to avoid agglomeration; S303. The suspension prepared in step S302 is added to the polyamic acid solution and stirred to obtain a modified polyamic acid dispersion; Specifically, the solid content of the modified polyamic acid dispersion is in the range of 10-18%.

[0031] S4. Preparation and curing of the film: Select a flat and flawless substrate and clean it thoroughly to ensure that there is no dust and oil on the surface; evenly apply the modified polyamic acid dispersion on the substrate; dry and cure the coated substrate; Specifically, the material of the substrate is glass, silicon wafer or stainless steel plate; the flatness error of the substrate is within 0.003mm, and the thickness error is within ±0.2mm; the coating is applied by a precision coater or manual coating; the drying and curing method is as follows: place the coated substrate in a drying channel with a set temperature, and dry it at 120~150℃ for 1~2h to slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0032] S5. Two-step imidization method for preparing a light-shielding film based on polyimide; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 150-200°C for 0.5-1.5h to promote partial imidization of the polyamic acid; S502. Then, the temperature is raised to 380-420° C. and maintained for 1.5-3.5 hours to complete the imidization reaction, thereby obtaining a light-shielding film based on polyimide; Specifically, in step S501, the temperature is first maintained at 180°C for 1 hour; in step S502, the temperature is increased to 400°C at a heating rate of 5-10°C / min and maintained for 2 hours; 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 the performance, thereby improving the mechanical strength and heat resistance of the film.

[0033] Specifically, the modified helical carbon fiber accounts for 5-25% of the mass of the modified polyamic acid dispersion.

[0034] Example 1 This embodiment provides a method for preparing a light-shielding film based on polyimide, which specifically includes the following steps: S1. Preparation of polyamic acid (PAA) solution: polyamic acid solution is obtained by polymerizing diamine and dianhydride monomers in a solvent; the total mass fraction of diamine and dianhydride monomers accounts for 20% of the polyamic acid solution; the dianhydride monomer adopts an asymmetric dianhydride monomer containing an ether bond 2,3,3',4'-diphenyl ether tetraacid dianhydride (aODPA), and the diamine is an aromatic diamine monomer; the solvent is DMAC; and the polymerization temperature is room temperature.

[0035] S2. Preparation of modified spiral carbon fiber: nickel sheet is selected as catalyst carrier, catalyst suspension is evenly coated on the surface of nickel sheet, and dried; anhydrous ethanol and auxiliary agent are mixed in a certain proportion, and the mixture is placed on the surface of nickel sheet, and the nickel sheet is placed above an alcohol lamp to burn the mixture on the surface of nickel sheet, and catalytic pyrolysis reaction is performed to obtain modified spiral carbon fiber; the catalyst suspension is a mixture of tin dichloride and trimellitic acid (molar ratio 3:2); the auxiliary agent is water, and the water content in the mixture of anhydrous ethanol and water is less than 0.75%; the distance between the nickel sheet and the bottom of the alcohol wick is 20mm, and the burning time is 60min; S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, while turning on a high-speed stirrer and shaking with an oscillator to ensure that the carbon fiber is fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension; S303. Add the suspension prepared in step S302 to the polyamic acid solution, stir, and obtain a modified polyamic acid dispersion; the solid content of the modified polyamic acid dispersion is 15%; the modified helical carbon fiber accounts for 12% of the mass of the modified polyamic acid dispersion.

[0036] S4. Preparation and curing of thin film: Select a flat, flawless glass substrate and clean it thoroughly to ensure that there is no dust and oil on the surface; evenly apply the modified polyamic acid dispersion on the substrate; place the coated substrate in a drying channel with a set temperature, and dry it at 120°C for 2 hours to slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0037] S5. Two-step imidization method for preparing a light-shielding film based on polyimide; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 180° C. for 1 h to promote partial imidization of the polyamic acid; S502. Then, the temperature is raised to 400° C. at a heating rate of 8° C. / min and maintained for 2 hours to complete the imidization reaction, thereby obtaining a polyimide-based light-shielding film.

[0038] Example 2 This embodiment provides a method for preparing a light-shielding film based on polyimide, which specifically includes the following steps: S1. Preparation of polyamic acid (PAA) solution: polyamic acid solution is obtained by polymerizing diamine and dianhydride monomers in a solvent; the total mass fraction of diamine and dianhydride monomers accounts for 25% of the polyamic acid solution; the solvent is DMF; and the polymerization temperature is room temperature.

[0039] S2. Preparation of modified spiral carbon fiber: select nickel sheet as catalyst carrier, evenly apply catalyst suspension on the surface of nickel sheet, and dry; mix anhydrous ethanol and auxiliary agent in a certain proportion, place on the surface of nickel sheet after mixing, place nickel sheet above alcohol lamp, burn the mixture on the surface of nickel sheet, and catalyze pyrolysis reaction to obtain modified spiral carbon fiber; catalyst suspension is a mixture of tin dichloride and trimellitic acid (molar ratio 3:2); auxiliary agent is water, and the water content in the mixture of anhydrous ethanol and water is less than 0.75%; the distance between nickel sheet and the bottom of alcohol wick is 25mm, and the burning time is 70min; S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, while turning on a high-speed stirrer and shaking with an oscillator to ensure that the carbon fiber is fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension; S303. Add the suspension prepared in step S302 to the polyamic acid solution, stir, and obtain a modified polyamic acid dispersion; the solid content of the modified polyamic acid dispersion is 10%; the modified helical carbon fiber accounts for 5% of the mass of the modified polyamic acid dispersion.

[0040] S4. Preparation and curing of thin film: Select a flat, flawless glass substrate and clean it thoroughly to ensure that the surface is free of dust and oil; evenly apply the modified polyamic acid dispersion on the substrate; place the coated substrate in a drying channel with a set temperature, and dry it at 150°C for 1 hour to slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0041] S5. Two-step imidization method for preparing a light-shielding film based on polyimide; 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. Then, the temperature is raised to 420° C. at a heating rate of 5° C. / min and maintained for 1.5 h to complete the imidization reaction, thereby obtaining a polyimide-based light-shielding film.

[0042] Example 3 This embodiment provides a method for preparing a light-shielding film based on polyimide, which specifically includes the following steps: 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 diamine and dianhydride monomers accounts for 18% of the polyamic acid solution; the solvent is DMAC; and the polymerization temperature is room temperature.

[0043] S2. Preparation of modified spiral carbon fiber: nickel sheet is selected as catalyst carrier, catalyst suspension is evenly coated on the surface of nickel sheet, and dried; anhydrous ethanol and auxiliary agent are mixed in a certain proportion, and the mixture is placed on the surface of nickel sheet, and the nickel sheet is placed above an alcohol lamp to burn the mixture on the surface of nickel sheet, and catalytic pyrolysis reaction is performed to obtain modified spiral carbon fiber; the catalyst suspension is a mixture of tin dichloride and trimellitic acid (molar ratio 3:2); the auxiliary agent is water, and the water content in the mixture of anhydrous ethanol and water is less than 0.75%; the distance between the nickel sheet and the bottom of the alcohol wick is 20mm, and the burning time is 50min; S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, while turning on a high-speed stirrer and shaking with an oscillator to ensure that the carbon fiber is fully dispersed in the dimethylacetamide (DMAC) solvent to form a stable suspension; S303. Add the suspension prepared in step S302 to the polyamic acid solution, stir, and obtain a modified polyamic acid dispersion; the solid content of the modified polyamic acid dispersion is 18%; the modified helical carbon fiber accounts for 15% of the mass of the modified polyamic acid dispersion.

[0044] S4. Preparation and curing of thin film: Select a flat, flawless glass substrate and clean it thoroughly to ensure that there is no dust and oil on the surface; evenly apply the modified polyamic acid dispersion on the substrate; place the coated substrate in a drying channel with a set temperature, and dry it at 120°C for 2 hours to slowly remove most of the solvent to avoid uneven film surface or cracks caused by rapid drying.

[0045] S5. Two-step imidization method for preparing a light-shielding film based on polyimide; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 150° C. for 1.5 h to promote partial imidization of the polyamic acid; S502. Then, the temperature is raised to 400° C. at a heating rate of 5° C. / min and maintained for 2 hours to complete the imidization reaction, thereby obtaining a polyimide-based light-shielding film.

[0046] The polyimide-based light-shielding film prepared by polymerization in the example was tested, and the test results are shown in Table 1: Table 1 Test results of light-shielding films based on polyimide

[0047] It can be seen from Table 1 that the addition of modified helical carbon fibers does not reduce the mechanical properties of polyimide.

[0048] The results of light transmittance tests show that while maintaining excellent heat resistance and stability, it also has good optical transparency, with the transmittance of infrared, visible light and ultraviolet light all being 0.

[0049] Comparative Example 1 This comparative example provides a method for preparing a light-shielding film based on polyimide, wherein the modified helical carbon fiber accounts for 3% of the mass of the modified polyamic acid dispersion, and the remaining preparation steps are the same as those in Example 1.

[0050] The optical transparency of the prepared light-shielding film was measured; the results showed that as the amount of modified spiral carbon fiber added decreased, the transmittance to infrared, visible light and ultraviolet light increased, and the light-shielding rate could only reach 80%, which was lower than that of Examples 1 to 3.

[0051] Comparative Example 2 This comparative example provides a method for preparing a light-shielding film based on polyimide, wherein the modified helical carbon fiber accounts for 30% of the mass of the modified polyamic acid dispersion, and the remaining preparation steps are the same as those in Example 1.

[0052] The optical transparency of the prepared shading film was measured; the results showed that with the increase of modified spiral carbon fibers, the mechanical properties of the polyimide-based shading film were significantly reduced, and the elongation at break was 1.06%, which was lower than that of Examples 1 to 3.

[0053] The modified helical carbon fiber obtained by precisely controlling the preparation conditions of the present invention has a unique helical morphology and adjustable surface defects, which enable the modified helical carbon fiber to absorb light and electromagnetic waves more effectively in the polyimide-based shading film, thereby significantly improving the light absorption and wave absorption performance of the polyimide-based shading film. This is of great significance for applications in the fields of electromagnetic wave shielding, stealth materials, etc.

[0054] The uniform dispersion technology of the modified spiral carbon fiber of the present invention ensures the good distribution of the modified spiral carbon fiber in the polyimide-based shading film, avoids agglomeration, and thus enhances the overall mechanical strength of the film. At the same time, the two-step imidization process and its precise temperature and time control also help to form 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 shading film to have good mechanical strength and processability while maintaining excellent wave absorbing properties. This enables the polyimide-based shading film to be applied to more fields, such as electronics, communications, aerospace, etc.

[0055] In addition, the selection of dimethylacetamide (DMAC) as a solvent not only improves the efficiency and stability of film preparation, but also reduces production costs. The good solubility of DMAC and its good dispersibility with PAA and modified helical carbon fibers make the film preparation process smoother and reduce waste and loss in production.

[0056] In summary, the present invention significantly improves the performance and application areas of polyimide-based shading films through innovations such as the preparation and application of modified spiral carbon fibers, precise imidization process control, and key raw materials and addition ratios in the formula, while reducing production costs, providing new ideas and methods for the preparation and application of polyimide-based shading films.

[0057] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0058] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present 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: obtaining a polyamic acid solution by polymerization of diamine and dianhydride monomers in a solvent; S2. Preparation of modified spiral carbon fiber: selecting a nickel sheet as a catalyst carrier, uniformly coating the catalyst suspension on the surface of the nickel sheet, and drying; mixing anhydrous ethanol and an additive in a certain proportion, placing the mixture on the surface of the nickel sheet, and obtaining a modified spiral carbon fiber by catalytic pyrolysis reaction of the mixture on the surface of the nickel sheet; S3. Preparing a modified polyamic acid dispersion; specifically comprising the following sub-steps: S301. Accurately weigh the required mass of modified spiral carbon fiber; S302. slowly adding the modified helical carbon fiber into the solvent, stirring and shaking 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; S4. Preparation and curing of the film: selecting a substrate and thoroughly cleaning it; evenly coating the modified polyamic acid dispersion on the substrate; drying and curing the coated substrate; S5. Two-step imidization method for preparing a light-shielding film based on polyimide; comprising the following sub-steps: S501. The dried film is transferred to an imidization furnace and maintained at 150-200°C for 0.5-1.5h 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 light-shielding film based on polyimide according to claim 1, characterized in that: 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 light-shielding film based on polyimide according to claim 2, characterized in that: 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 light-shielding film based on polyimide according to claim 1, characterized in that: The auxiliary agent in step S2 is water or a flammable solvent containing water; the water content in the mixture of anhydrous ethanol and the auxiliary agent is less than 0.75%; 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 light-shielding film based on polyimide according to claim 4, characterized in that: The distance between the nickel sheet and the bottom of the alcohol wick is 18-25 mm, and the burning time is 40-75 min.

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

7. The method for preparing a light-shielding film based on polyimide according to claim 1, characterized in that: 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 uneven film surface or cracks caused by rapid drying.

8. The method for preparing a light-shielding film based on polyimide according to claim 1, characterized in that: The modified helical carbon fiber accounts for 5-25% of the mass of the modified polyamic acid dispersion.

9. The method for preparing a light-shielding film based on polyimide according to claim 1, characterized in that: In the step S501, the temperature is first maintained at 180°C for 1 hour; in the step S502, the temperature is increased to 400°C at a heating rate of 5-10°C / min and maintained for 2 hours.

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

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