A polyimide film, its preparation method and application

Abstract

The present invention provides a polyimide film, a preparation method thereof and an application thereof, relating to the technical field of polyimide film preparation. The preparation method provided by the present invention comprises the following steps: polycondensing diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid solution; performing surface modification on inorganic nano silicon oxynitride powder to obtain a modified filler; adding the modified filler to the polyimide solution in a mass ratio of 0.1-2.0% and stirring and dispersing to obtain a composite solution; coating the composite solution into a film, drying and subjecting to imidization treatment to obtain a polyimide film. By introducing the modified filler, the present invention can form good interfacial bonding in the polyimide system, improve the comprehensive properties of the polyimide film, effectively improve the heat resistance, mechanical properties and flexibility of the film, and reduce the linear expansion coefficient.

Description

Technical Field

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

[0002] Polyimide (PI) is a class of polymer compounds containing imide groups in its molecular structure. The imide ring contained in the main chain of the molecule is formed by the condensation of compounds containing diamine and dianhydride in a non-protonic polar solvent. It has excellent thermal stability and good electrical insulation properties. Currently, it has developed into various application forms such as thin films, composite materials, special engineering plastics, fibers and photoresists, and has been widely used in aerospace, electronics and electrical, bioengineering and other fields.

[0003] However, traditional polyimide films are generally fully aromatic. The electron-pushing conjugation effect of the internal diamine residues and the electron-withdrawing induction effect of the dianhydride residues lead to the movement of charges between and within molecules, forming a charge transfer complex (CTC), which reduces the transmittance of the polyimide film and makes it yellow or brownish yellow, limiting the application of polyimide films in microelectronics, optoelectronics, photovoltaics and other fields. In particular, with the increasing requirements for high-heat-resistant flexible substrate films, colorless and transparent polyimide (CPI) films have received widespread attention.

[0004] Currently, the preparation of CPI films is mainly done by introducing fluorinated groups into the polyimide backbone. Due to the high electronegativity and low polarizability of fluorine atoms, they can inhibit the formation of CTCs, thereby improving the light transmittance of the polyimide film. At the same time, the low surface energy and good hydrophobic effect of fluorine atoms make the film have low water absorption. The large volume of fluorine atoms can increase the free volume between molecules, thereby improving the dielectric properties of the polyimide material. However, the addition of fluorine atoms to the polyimide backbone can cause the mechanical properties, flexibility, and glass transition temperature of the polyimide film to decrease. Therefore, there is an urgent need to provide a solution to improve this problem. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyimide film and its preparation method and application, which can improve the comprehensive performance of the polyimide film, effectively improve the heat resistance, mechanical properties and flexibility of the film, and reduce the linear expansion coefficient.

[0006] In a first aspect, a method for preparing a polyimide film provided by the present invention includes the following steps: polycondensing diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid solution; surface-modifying inorganic nano silicon oxynitride powder to obtain a modified filler; adding the modified filler to the polyimide solution at a mass ratio of 0.1-2.0% and stirring and dispersing to obtain a composite solution; coating the composite solution into a film, drying and imidizing to obtain a polyimide film.

[0007] A method for preparing a polyimide film provided by the present invention can form good interfacial bonding in the polyimide system by introducing a modified filler into the polyimide system formed by diamine and dianhydride, improve the comprehensive properties of the polyimide film, effectively improve the heat resistance, mechanical properties and flexibility of the film, and reduce the linear expansion coefficient.

[0008] Optionally, when surface-modifying inorganic nano silicon oxynitride powder to obtain a modified filler, it includes: immersing the inorganic nano silicon oxynitride powder in a modifying solution for infiltration and dispersion, and then filtering and drying to obtain the modified filler; the modifying solution dissolves a surface modifier.

[0009] Optionally, when immersing the inorganic nano silicon oxynitride powder in the modifying solution for infiltration and dispersion, the mass ratio of the surface modifier dissolved in the modifying solution to the inorganic nano silicon oxynitride powder is 0.5-2.0%, and the surface modifier includes at least one of phthalate coupling agent and vinyl silane coupling agent.

[0010] Optionally, when polycondensing diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid solution, the diamine includes at least one of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-amino-2-trifluoromethyl)benzene, and the dianhydride includes at least one of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthrene tetracarboxylic dianhydride, bisphenol A type diether dianhydride.

[0011] Optionally, when those skilled in the art process based on the technical solution of this application using existing conventional preparation process technologies for improving the comprehensive properties of fluorinated polyimide films without creative labor, other embodiments obtained belong to the protection scope of this application. For example, adding monomers containing the following group structures, such as rigid non-planar groups, large-volume substituted groups, ether bond groups, alicyclic structures, etc., can be superimposed without changing the scope of the claims of the present invention.

[0012] Optionally, when polycondensing diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid solution, the molar ratio of the diamine to the dianhydride is 1:1.

[0013] Optionally, when the composite adhesive solution is coated into a film, dried and imidized to obtain a polyimide film, the imidization treatment includes any one of high-temperature thermal imidization and chemical imidization.

[0014] Optionally, when the composite adhesive solution is coated into a film, dried and subjected to chemical imidization treatment to obtain a polyimide film, it includes: adding a dehydrating agent and a catalyst to the composite adhesive solution, stirring and mixing to obtain a mixed adhesive solution, coating the mixed adhesive solution into a film and drying to obtain a mixed adhesive film, and subjecting the mixed adhesive film to gradient temperature rise imidization treatment to obtain a polyimide film.

[0015] Optionally, when adding a dehydrating agent and a catalyst to the composite adhesive solution and stirring and mixing, the dehydrating agent includes at least one of acetic anhydride, propionic anhydride, butyric anhydride, and benzoic anhydride, and the catalyst includes at least one of pyridine and its derivatives, methylpyridine and its derivatives, dimethylpyridine, N,N-dimethylaminopyridine, quinoline, isoquinoline, and triethylamine.

[0016] Optionally, after coating, forming a film and drying, the solvent residue content in the adhesive solution is 10 - 50%.

[0017] Optionally, after polyamic acid adhesive solution is prepared by polycondensation of diamine and dianhydride in a polar aprotic solvent, the solid content of the polyamic acid adhesive solution is 5 - 25%.

[0018] Optionally, when polyamic acid adhesive solution is prepared by polycondensation of diamine and dianhydride in a polar aprotic solvent, the polar aprotic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0019] In a second aspect, the present invention also provides a polyimide film prepared by any one of the above optional preparation methods, and the glass transition temperature Tg of the polyimide film is 340 - 345°C, the temperature T at which the thermal weight loss is 5% is 520 - 530°C, the temperature T at which the thermal weight loss is 10% is 545 - 550°C, the cut-off wavelength λ is 350 - 362 nm, the light transmittance T is 86.50 - 88.00%, the dielectric constant is 2.00 - 2.70, the linear expansion coefficient is 60.0 - 72.0 ppm·K 5％ is 520 - 530°C, the temperature T at which the thermal weight loss is 10% is 10％ 545 - 550°C, the cut-off wavelength λ is cutoff 350 - 362 nm, the light transmittance T is 500 86.50 - 88.00%, the dielectric constant is 2.00 - 2.70, the linear expansion coefficient is 60.0 - 72.0 ppm·K -1 and the tensile strength is 80.0 - 95.0 MPa.

[0020] In a third aspect, the present invention also provides an application of the polyimide film prepared by any one of the above optional preparation methods in the fields of microelectronics, optoelectronics, and photovoltaics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart of a method for preparing a polyimide film provided by the present invention;

[0022] Figure 2 DMA curve graph of the polyimide film prepared in Example 1 of the present invention;

[0023] Figure 3 Thermogravimetric analysis graph of the polyimide film prepared in Example 1 of the present invention;

[0024] Figure 4 Ultraviolet-visible transmission spectrum graph of the polyimide film prepared in Example 1 of the present invention;

[0025] Figure 5 Dielectric constant graph of the polyimide film prepared in Example 1 of the present invention from 1000 Hz to 10 MHz;

[0026] Figure 6 Linear expansion coefficient graph of the polyimide film prepared in Example 1 of the present invention from 50 °C to 200 °C.

[0027] Figure 7 Stress-strain curve of the polyimide film prepared in Example 1 of the present invention. Detailed implementation manners

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The words such as "including" used herein mean that the elements or items appearing before this word cover the elements or items listed after this word and their equivalents, without excluding other elements or items.

[0029] See Figure 1 , the embodiments of the present invention provide a method for preparing a polyimide film, including the following steps:

[0030] S1. Prepare a polyamic acid solution: Polycondense diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid solution;

[0031] S2. Prepare a modified filler: Perform surface modification on inorganic nano silicon oxynitride powder to obtain a modified filler;

[0032] S3. Preparation of polyimide film: The modified filler is added to the polyimide glue solution at a mass ratio of 0.1-2% and stirred and dispersed to obtain a composite glue solution. The composite glue solution is coated into a film, dried and imidized to obtain a polyimide film.

[0033] Actually, there is no special limitation on the order of performing step S1 and step S2. Step S2 can be performed first and then step S1, or step S1 and step S2 can be performed simultaneously.

[0034] In some embodiments, when preparing the polyamic acid glue solution in step S1, the diamine is a fluorine-containing group monomer. Specifically, the diamine may include at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 1,4-bis(4-amino-2-trifluoromethyl)benzene. The dianhydride is a fluorine-containing group monomer. Specifically, the dianhydride may include at least one of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthrene tetracarboxylic dianhydride.

[0035] In some embodiments, when preparing the polyamic acid glue solution in step S1, the molar ratio of diamine to dianhydride is 1:1, and after the polyamic acid glue solution is prepared, the solid content of the polyamic acid glue solution is 5-25%.

[0036] In some embodiments, when preparing the polyamic acid glue solution in step S1, the polar aprotic solvents used include at least one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0037] In some embodiments, when preparing the modified filler in step S2, it includes: immersing the inorganic nano-silicon oxynitride powder in the modified solution for infiltration and dispersion, and then filtering and drying to obtain the modified filler; wherein, the surface modifier is dissolved in the modified solution used, and the mass ratio of the surface modifier dissolved in the modified solution to the inorganic nano-silicon oxynitride powder is 0.5-2%.

[0038] Specifically, when preparing the modified filler in step S2, the surface modifier dissolved in the modified solution includes at least one of phthalate coupling agent and vinyl silane coupling agent; wherein, the phthalate coupling agent includes at least one of PN-130, PN-101, and PN-102, and the vinyl silane coupling agent includes at least one of KH-500, KH-550, and KH-560.

[0039] In some embodiments, when performing step S2 to prepare the modified filler, the solvent in the modification solution is a mixed solution of deionized water and low molecular weight alcohol, and the mass concentration of the low molecular weight alcohol in the mixed solution is 80-95%. Specifically, the low molecular weight alcohol can be at least one of methanol, ethanol, and isopropanol.

[0040] In some embodiments, when performing step S2 to prepare the modified filler, the inorganic nano silicon oxynitride powder adopts a conventional preparation process technology, which can be any one of the solid-phase reaction of SiO2 and Si3N4 mixed powder, the carbothermal reduction-nitridation reaction of SiO2 powder, the nitridation reaction of SiO2 powder in ammonia gas, the direct nitroxidation reaction of Si powder in nitrogen-oxygen mixed gas, and the solid-gas nitridation reaction of Si and SiO2 mixed powder.

[0041] In some embodiments, when performing step S3 to prepare the composite adhesive solution, the modified filler is added to the polyamic acid adhesive solution. After stirring and dispersing, filtering and vacuum degassing treatment, a stable polyimide composite adhesive solution is obtained. In fact, during the filtering process, the stirred and dispersed adhesive solution can be filtered through a 2500-mesh sieve.

[0042] In some embodiments, after performing step S3 to prepare the composite adhesive solution, the composite adhesive solution can be stored at a low temperature.

[0043] In some embodiments, when performing step S3 to coat the composite adhesive solution into a film, the composite adhesive solution is coated on a glass plate for casting film formation.

[0044] In some embodiments, when drying the composite adhesive solution after performing step S3 to coat it into a film, the formed composite adhesive solution film is treated at 60-120°C for 0.5-1 h, so that the solvent residue in the film formed by the composite adhesive solution is 10-50%.

[0045] In some embodiments, when performing step S3 for imidization treatment, the composite adhesive film formed after drying the composite adhesive solution is placed in an imidization furnace for gradient heating to perform high-temperature imidization treatment, thereby obtaining a colorless and transparent polyimide film.

[0046] In some embodiments, when performing step S3 for imidization treatment, it also includes performing chemical imidization treatment, including: adding a dehydrating agent and a catalyst to the composite adhesive solution, stirring and mixing to obtain a mixed adhesive solution, coating the mixed adhesive solution into a film and drying to obtain a mixed adhesive film, and performing gradient heating imidization treatment on the mixed adhesive film to obtain a polyimide film.

[0047] Specifically, when performing chemical imidization treatment, the dehydrating agent includes at least one of acetic anhydride, propionic anhydride, butyric anhydride, and benzoic anhydride, and the catalyst includes at least one of pyridine and its derivatives, methylpyridine and its derivatives, dimethylpyridine, N,N-dimethylaminopyridine, quinoline, isoquinoline, and triethylamine.

[0048] Example 1

[0049] Example 1 provides a method for preparing a polyimide film, which includes the following steps:

[0050] S1. Prepare a polyamic acid solution: Stir and dissolve 0.0164 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl in 37.5 mL of N,N-dimethylacetamide (DMAc) to obtain a biphenyl solution; Add 0.0164 mol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to the biphenyl solution and stir to dissolve it, and prepare a polyamic acid solution with a solid content of 25% through solution polycondensation;

[0051] S2. Prepare modified filler: Immerse 0.1263 g of inorganic nano-silicon oxynitride powder in the modification solution, after infiltration and dispersion, perform dispersion treatment under mechanical stirring at 80 rpm for 2 h, and then dry it in an oven at 60 °C to obtain the modified filler; Among them, 2.0 g of vinyl silane coupling agent is dissolved in the modification solution, and the solvent of the modification solution is deionized water and ethanol with a weight ratio of 2:8;

[0052] S3. Prepare a polyimide film: Add the modified filler to the polyamic acid solution at a ratio of 1% by weight, stir and disperse it, filter and perform vacuum degassing to obtain a stable polyamic acid composite solution. After coating the composite solution on a glass plate and casting it into a film, place it in a blast drying oven and dry it at 100 °C for 1 h, and the solvent residue is 30%. Peel the composite film and place it in an imidization furnace to raise the temperature gradient, and perform imidization treatment at 270 °C for 1.5 h to obtain the polyimide film.

[0053] Example 2

[0054] Example 2 provides a method for preparing a polyimide film, which includes the following steps:

[0055] S1. Prepare a polyamic acid solution: Stir and dissolve 0.0104 mol of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane in 40 mL of N,N-dimethylacetamide (DMAc) to obtain a diamine solution; Add 0.0104 mol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to the diamine solution and stir to dissolve it, and prepare a polyamic acid solution with a solid content of 20% through solution polycondensation;

[0056] S2. Prepare modified filler: Immerse 0.0125 g of inorganic nano-silicon oxynitride powder in the modification solution, after infiltration and dispersion, perform dispersion treatment under mechanical stirring at 80 rpm for 2 h, and then dry it in an oven at 60 °C to obtain the modified filler; Among them, 1.0 g of vinyl silane coupling agent is dissolved in the modification solution, and the solvent of the modification solution is deionized water and ethanol with a weight ratio of 1:9;

[0057] S3. Preparation of polyimide film: The modified filler is added to the polyamic acid solution at a ratio of 0.1% by weight, stirred and dispersed, filtered, and degassed under vacuum to obtain a stable polyamic acid composite solution. After the composite solution is cast into a film on a glass plate, it is placed in a blast drying oven and dried at 60 °C for 0.5 h, and the solvent residue is 46%. The composite film is peeled off and placed in an imidization furnace for gradient heating. After imidization treatment at 300 °C for 1 h, a polyimide film is obtained.

[0058] Example 3

[0059] Example 3 provides a method for preparing a polyimide film, which includes the following steps:

[0060] S1. Preparation of polyamic acid solution: 0.0096 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl is stirred and dissolved in 42.5 mL of N,N-dimethylacetamide (DMAc) to obtain a biphenyl solution; 0.0096 mol of 9,9-bis(trifluoromethyl)-2,3,6,7-xanthene tetracarboxylic dianhydride is added to the biphenyl solution and stirred to dissolve, and a polyamic acid solution with a solid content of 15% is prepared by solution polycondensation.

[0061] S2. Preparation of modified filler: 0.0758 g of inorganic nano silicon oxynitride powder is immersed in the modification solution, infiltrated and dispersed, and then dispersed under mechanical stirring at 80 rpm for 1.5 h, and then dried in a drying oven at 80 °C to obtain the modified filler; among them, 2.0 g of vinyl silane coupling agent is dissolved in the modification solution, and the solvent of the modification solution is deionized water and ethanol with a weight ratio of 2:8.

[0062] S3. Preparation of polyimide film: The modified filler is added to the polyamic acid solution at a ratio of 1% by weight, stirred and dispersed, filtered, and degassed under vacuum to obtain a stable polyamic acid composite solution. After the composite solution is cast into a film on a glass plate, it is placed in a blast drying oven and dried at 80 °C for 1 h, and the solvent residue is 36%. The composite film is peeled off and placed in an imidization furnace for gradient heating. After imidization treatment at 270 °C for 0.5 h, a polyimide film is obtained.

[0063] Example 4

[0064] Example 4 provides a method for preparing a polyimide film, which includes the following steps:

[0065] S1. Preparation of polyamic acid solution: 0.0051 mol of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane was stirred and dissolved in 45 mL of N,N-dimethylacetamide (DMAc) to obtain a diamine solution; 0.0051 mol of 9,9-bis(trifluoromethyl)-2,3,6,7-xanthene tetracarboxylic dianhydride was added to the diamine solution and stirred to dissolve, and a polyamic acid solution with a solid content of 10% was prepared by solution polycondensation;

[0066] S2. Preparation of modified filler: 0.1020 g of inorganic nano silicon oxynitride powder was immersed in the modification solution. After infiltration and dispersion, it was dispersed under mechanical stirring at 80 rpm for 1 h, and then dried in an oven at 80 °C to obtain the modified filler; among them, 2.0 g of vinyl silane coupling agent was dissolved in the modification solution, and the solvent of the modification solution was deionized water and ethanol with a weight ratio of 1:9;

[0067] S3. Preparation of polyimide film: The modified filler was added to the polyamic acid solution at a ratio of 2% by weight, stirred and dispersed, filtered and vacuum degassed to obtain a stable polyamic acid composite solution. The composite solution was cast on a glass plate to form a film, and then placed in a forced-air drying oven at 120 °C for drying treatment for 0.5 h, and the solvent residue was 28%. The peeled composite film was placed in an imidization furnace and heated at a gradient temperature, and imidization treatment was carried out at 300 °C for 1.5 h to obtain the polyimide film.

[0068] Comparative Example 1

[0069] This Comparative Example 1 provides a method for preparing a polyimide film, including the following steps:

[0070] Y1. Preparation of polyamic acid solution: 0.0164 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl was stirred and dissolved in 37.5 mL of N,N-dimethylacetamide (DMAc) to obtain a biphenyl solution; 0.0164 mol of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride was added to the biphenyl solution and stirred to dissolve, and a polyamic acid solution with a solid content of 25% was prepared by solution polycondensation;

[0071] Y2. Preparation of polyimide film: The polyamic acid solution was stirred and dispersed, filtered and vacuum degassed to obtain a stable polyamic acid solution. The solution was cast on a glass plate to form a film, and then placed in a forced-air drying oven at 100 °C for drying treatment for 1 h, and the solvent residue was 30%. The peeled composite film was placed in an imidization furnace and heated at a gradient temperature, and imidization treatment was carried out at 270 °C for 1.5 h to obtain the polyimide film.

[0072] Comparative Example 2

[0073] This Comparative Example 2 provides a method for preparing a polyimide film, including the following steps:

[0074] Y1. Preparation of polyamic acid solution: 0.0164 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was stirred and dissolved in 37.5 mL of N,N-dimethylacetamide (DMAc) to obtain a biphenyl solution; 0.0164 mol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added to the biphenyl solution and stirred to dissolve, and a polyamic acid solution with a solid content of 25% was prepared by solution polycondensation;

[0075] Y2. Preparation of modified filler: 0.1263 g of inorganic nano-silica powder was immersed in a modified solution, and after infiltration and dispersion, it was dispersed under mechanical stirring at 80 rpm for 2 h, and then dried in an oven at 60 °C to obtain a modified filler; wherein, 2.0 g of vinyl silane coupling agent was dissolved in the modified solution, and the solvent of the modified solution was deionized water and ethanol with a weight ratio of 2:8;

[0076] Y3. Preparation of polyimide film: The modified filler was added to the polyamic acid solution at a ratio of 1% by weight, stirred and dispersed, filtered and vacuum degassed to obtain a stable polyamic acid composite solution. The composite solution was cast on a glass plate to form a film, and then placed in a forced-air drying oven and dried at 100 °C for 1 h with a solvent residue of 30%. The peeled composite film was placed in an imidization furnace and heated at a gradient temperature, and imidized at 270 °C for 1.5 h to obtain a polyimide film.

[0077] Comparative Example 3

[0078] This Comparative Example 3 provides a method for preparing a polyimide film, including the following steps:

[0079] Y1. Preparation of polyamic acid solution: 0.0164 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl was stirred and dissolved in 37.5 mL of N,N-dimethylacetamide (DMAc) to obtain a biphenyl solution; 0.0164 mol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was added to the biphenyl solution and stirred to dissolve, and a polyamic acid solution with a solid content of 25% was prepared by solution polycondensation;

[0080] Y2. Preparation of polyimide film: The unmodified inorganic nano-silicon nitride powder was directly added to the polyamic acid solution at a ratio of 1% by weight, stirred and dispersed, filtered and vacuum degassed to obtain a stable polyamic acid composite solution. The composite solution was cast on a glass plate to form a film, and then placed in a forced-air drying oven and dried at 100 °C for 1 h with a solvent residue of 30%. The peeled composite film was placed in an imidization furnace and heated at a gradient temperature, and imidized at 270 °C for 1.5 h to obtain a polyimide film.

[0081] Performance detection

[0082] The polyimide films prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to the following tests, and the results are shown in Table 1 below:

[0083] The glass transition temperature Tg (°C) was measured based on a dynamic thermomechanical analyzer (DMA 242E, Netzsch, Germany) with a heating rate of 5 °C / min.

[0084] The temperatures T 5％ (°C) and T 10％ (°C) at 5% and 10% weight loss were measured based on a thermogravimetric analyzer (STA 2500, Netzsch, Germany) within the temperature range of room temperature (20 °C) - 1000 °C with a heating rate of 2 °C / min.

[0085] The cut-off wavelength λ cutoff (nm) was measured based on a spectrophotometer (Lambda750S, PerkinElmer, USA).

[0086] The transmittance T 500 (%) was measured based on a spectrophotometer (Lambda750S, PerkinElmer, USA) within the test wavelength range of 200 nm - 800 nm.

[0087] The dielectric constant was measured based on an impedance analyzer (E4990A, Keysight, USA) within the test frequency range of 1000 Hz - 10 MHz.

[0088] The linear expansion coefficient was measured based on a static thermomechanical analyzer (TMA 402F3, Germany) within the test temperature range of 50 °C - 200 °C.

[0089] The tensile strength was measured based on a universal tensile testing machine (XLM, China) at room temperature of 25 °C.

[0090] The glass transition temperature of the polyimide film prepared in Example 1 was tested using a dynamic thermomechanical analyzer (DMA 242E, Netzsch, Germany), and its DMA curve is as Figure 2 shown; the thermogravimetric analysis of the polyimide film prepared in Example 1 was performed using a thermogravimetric analyzer (STA 2500, Netzsch, Germany), and its thermogravimetric analysis graph is as Figure 3 shown; the ultraviolet-visible light analysis of the polyimide film prepared in Example 1 was carried out using a spectrophotometer (Lambda750S, PerkinElmer, USA), and its ultraviolet-visible transmission spectrum is as Figure 4As shown; the dielectric constant of the polyimide film prepared in Example 1 was tested using an impedance analyzer (E4990A, Keysight, USA) device, and its dielectric constant at 1000 Hz - 10 MHz is as Figure 5 shown; the coefficient of thermal expansion of the polyimide film prepared in Example 1 was analyzed using a static thermomechanical analyzer (TMA 402F3, Germany) device, and its linear expansion coefficient diagram is as Figure 6 shown; the tensile strength of the polyimide film prepared in Example 1 was analyzed using a universal tensile testing machine (XLM, China) device, and its stress-strain diagram is as Figure 7 shown.

[0091] Table 1 Performance data of polyimide films of Examples 1 to 4 and Comparative Examples 1 to 3

[0092]

[0093]

[0094] Combined with Examples 1 to 4, the polyimide film provided by the present invention has a relatively high Tg value, good thermal stability, mechanical properties and light transmittance. From Examples 1 to 2 and Example 4, it can be seen that by adjusting the mass content of the modified filler, the mechanical properties and dielectric properties of the polyimide film can be changed. For example, the tensile strength of the polyimide film in Example 1 decreased from 93.0 MPa to 81.5 MPa in Example 2 and 85.4 MPa in Example 4, but there is no obvious influence on the Tg value and thermal stability of the polyimide film.

[0095] From Examples 1 and 3, it can be seen that by adjusting the process parameters of the preparation method, it has a slight influence on the linear expansion coefficient and tensile strength of the final polyimide film, but has no obvious influence on the Tg value and thermal stability of the film.

[0096] From Examples 1 and Comparative Example 1, it can be seen that when no inorganic filler is added during the preparation of the polyimide film in Comparative Example 1, the Tg value of the prepared polyimide film is about 12 °C lower than that in Example 1, and the temperatures at 5% and 10% thermal weight loss are also significantly lower than those in Example 1. This shows that the addition of inorganic filler can improve the thermal stability of the polyimide film; at the same time, compared with Examples 1 to 4, the dielectric constant of the polyimide film prepared in Comparative Example 1 is significantly increased, which shows that the addition of inorganic filler can reduce the dielectric constant of the film.

[0097] Comparing Comparative Example 1 and Comparative Example 2, it can be seen that after modifying the inorganic nano-silica powder in Comparative Example 2 and adding the modified inorganic nano-silica powder into the polyimide film, there is no obvious effect on the thermal stability of the film, but it can improve the tensile strength and reduce its dielectric constant. At the same time, the addition of inorganic fillers may slightly reduce the light transmittance of the film.

[0098] Comparing Example 1 and Comparative Example 2, it can be seen that using the modified silicon oxynitride powder as the modified filler in Example 1 can significantly improve the Tg value, mechanical properties and thermal stability compared with Comparative Example 2. Comparing Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that using the unmodified silicon oxynitride powder as the inorganic filler in Comparative Example 3 also has a synergistic effect similar to that of the modified silica powder in Comparative Example 2, but it is significantly inferior to the modified filler in Example 1.

[0099] From Figure 2 it can be seen that the glass transition temperature of the film in Example 1 is 343.7 °C; from Figure 3 it can be seen that the thermal decomposition temperature of the film in Example 1 is relatively high; from Figure 4 it can be seen that the light transmittance of the film in Example 1 in the visible light range (greater than 85%) is relatively high; from Figure 5 it can be seen that the dielectric constant of the film in Example 1 is 2.04; from Figure 6 it can be seen that the thermal stability of the film in Example 1 is good; from Figure 7 it can be seen that the tensile strength of the film in Example 1 is relatively high, reaching more than 90 MPa.

[0100] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein may have other embodiments and can be implemented or realized in various ways.

Claims

1. A method for preparing a polyimide film, characterized in that: The method comprises the following steps: polycondensing diamine and dianhydride in a polar aprotic solvent to obtain a polyamic acid glue solution; immersing inorganic nano silicon oxynitride powder in a modified solution for infiltration and dispersion, and then filtering and drying to obtain a modified filler, wherein a surface modifier is dissolved in the modified solution, and the surface modifier includes at least one of a titanate coupling agent and a vinyl silane coupling agent; adding the modified filler at a mass ratio of 0.1-2.0% to the polyimide glue solution, stirring and dispersing the mixture to obtain a composite glue solution; coating the composite glue solution to form a film, drying the film, and performing imidization treatment to obtain a polyimide film.

2. The preparation method according to claim 1, characterized in that When the inorganic nano silicon oxynitride powder is immersed in the modification solution for infiltration and dispersion, the mass ratio of the surface modifier dissolved in the modification solution to the inorganic nano silicon oxynitride powder is 0.5-2.0%.

3. The preparation method according to claim 1, characterized in that When a diamine and a dianhydride are polycondensed in a polar aprotic solvent to prepare a polyamic acid glue, the diamine includes at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, and 1,4-bis(4-amino-2-trifluoromethyl)benzene, and the dianhydride includes at least one of 4,4'-(hexafluoroisopropylene)diphthalic anhydride, bisphenol A diether dianhydride, and 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthene tetracarboxylic dianhydride.

4. The preparation method according to claim 1 or 3, characterized in that When polyamic acid glue is prepared by polycondensing diamine and dianhydride in a polar aprotic solvent, the molar ratio of the diamine to the dianhydride is 1:

1.

5. The preparation method according to claim 1, characterized in that When the composite adhesive solution is coated to form a film, dried, and subjected to imidization treatment to prepare a polyimide film, the imidization treatment includes any one of high-temperature thermal imidization and chemical imidization.

6. The preparation method according to claim 5, characterized in that When the composite adhesive solution is coated to form a film, dried, and subjected to chemical imidization treatment to obtain a polyimide film, the method includes: adding a dehydrating agent and a catalyst to the composite adhesive solution, stirring and mixing, to obtain a mixed adhesive solution; coating the mixed adhesive solution to form a film, and drying to obtain a mixed adhesive film; and subjecting the mixed adhesive film to a gradient temperature imidization treatment to obtain a polyimide film.

7. The preparation method according to claim 6, characterized in that When a dehydrating agent and a catalyst are added to the composite glue and stirred and mixed, the dehydrating agent includes at least one of acetic anhydride, propionic anhydride, butyric anhydride, and benzoic anhydride, and the catalyst includes at least one of pyridine and its derivatives, methylpyridine and its derivatives, dimethylpyridine, N,N-dimethylaminopyridine, quinoline, isoquinoline, and triethylamine.

8. The preparation method according to claim 6, characterized in that After coating, film formation and drying, the residual solvent in the glue solution is 10-50%.

9. The preparation method according to claim 1, characterized in that After polycondensing diamine and dianhydride in a polar aprotic solvent to prepare a polyamic acid glue solution, the solid content of the polyamic acid glue solution is 5-25%.

10. The preparation method according to claim 1, characterized in that When polyamic acid glue is prepared by polycondensing diamine and dianhydride in a polar aprotic solvent, the polar aprotic solvent includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

11. A polyimide film prepared by the method according to any one of claims 1 to 10.

12. Use of the polyimide film prepared by the preparation method according to any one of claims 1 to 10 in the fields of microelectronics, optoelectronics and photovoltaics.

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