Porous polyimide film and preparation method thereof

Abstract

The invention relates to a porous polyimide film and a preparation method thereof. The preparation method comprises the following steps: in an inert atmosphere, completely dissolving a diamine monomer in an organic solvent, adding a dianhydride monomer, stirring at 30-80 DEG C for 2-48 hours, standing and defoaming to prepare a polyimide casting solution A; adding a poor solvent and a surfactant into the polyimide membrane casting solution A, stirring for 2-24 hours, standing and defoaming to obtain a polyimide membrane casting solution B; coating the polyimide membrane casting solution B on a substrate, and standing to obtain a primary membrane; the preparation method comprises the following steps: respectively stirring and mixing good solvents and poor solvents in different mass ratios to prepare a coagulating bath; sequentially immersing the primary membrane into a multi-stage coagulating bath for phase inversion to prepare a phase inversion membrane; and drying the phase conversion film, and carrying out thermal imidization treatment to obtain the porous polyimide film. The prepared membrane is a spongy porous membrane with uniform through holes and open holes in the upper and lower surfaces, the permeability of the membrane is improved, and the interception performance of the membrane is improved by the spongy structure.

Description

Technical Field

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

[0002] Membrane separation is one of the most commonly used separation forms in various fields. They are not only used in industry, but also in ordinary households. As a type of membrane, porous membranes exhibit a porous structure at the microscopic level. In the field of porous membranes, traditional materials such as PVC, PET, PES, PTFE, and PVDF are the main materials. However, polyimide materials have obvious advantages under some special conditions due to their high temperature resistance, chemical stability, and mechanical strength that ordinary polymer materials do not have, and have become a research hotspot in recent years.

[0003] The traditional method for preparing porous membranes is mainly phase transformation, which is divided into non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS) according to the different phase separation methods. The non-solvent induced phase separation preparation process is simple and has low energy consumption. It has been widely used in industry, but the film prepared by this method often has an asymmetric structure, which is generally composed of a thicker cortex and a finger-like support layer. It is difficult to improve the permeability and interception performance at the same time. In addition, the traditional NIPS method often uses a single poor solvent as a coagulation bath. When the good solvent in the casting solution contacts the poor solvent in the coagulation bath, rapid phase separation will occur at the contact surface between the membrane and the coagulation bath, thereby forming a dense cortex at the contact surface. The presence of the cortex limits the application range of the film. Although thermally induced phase separation has few influencing factors and the film-forming process is easy to control, it has high energy consumption.

[0004] Therefore, how to develop a new preparation method to produce porous polyimide films has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] Based on this, in order to solve the above problems, the present application provides a porous polyimide film and a preparation method thereof to solve the above technical problems.

[0006] The first aspect of the present application provides a method for preparing a porous polyimide film, comprising the following steps:

[0007] Under an inert atmosphere, the diamine monomer is completely dissolved in an organic solvent, and then the dianhydride monomer is added, stirred at 30° C. to 80° C. for 2 h to 48 h, and allowed to stand for degassing to obtain a polyimide casting solution A;

[0008] Adding a poor solvent and a surfactant to a polyimide film casting solution A, stirring for 2 hours to 24 hours, and standing to degas, to obtain a polyimide film casting solution B;

[0009] The polyimide film casting solution B is coated on the substrate and allowed to stand to obtain a primary film;

[0010] A good solvent and a poor solvent of different mass ratios are stirred and mixed respectively to prepare a coagulation bath; wherein the coagulation bath includes a multi-stage coagulation bath, the number of the multi-stage coagulation bath is N, N ≥ 3, and as the number of the coagulation baths increases, the mass proportion of the good solvent in the coagulation bath decreases;

[0011] The primary membrane sheets are sequentially immersed in multi-stage coagulation baths to undergo phase inversion reaction, thereby obtaining a phase inversion membrane;

[0012] After the phase conversion membrane is dried, it is placed in an oven for thermal imidization treatment to obtain a porous polyimide film.

[0013] In some embodiments, the molar ratio of the diamine monomer to the dianhydride monomer is (1-1.2):1.

[0014] In some embodiments, based on the total mass of the polyimide casting solution B, the sum of the masses of the diamine monomer and the dianhydride monomer is 10% to 20% of the total mass, the mass of the organic solvent is 30% to 65% of the total mass, the mass of the poor solvent is 10% to 15% of the total mass, and the mass of the surfactant is 5 to 10% of the total mass.

[0015] In some embodiments, based on the total mass of the coagulation bath, the good solvent accounts for 0% to 100% of the total mass, and the poor solvent accounts for 0% to 100% of the total mass.

[0016] In some embodiments, N is 5, and the coagulation bath includes level 1, level 2, level 3, level 4 and level 5 coagulation baths; based on the total mass of the coagulation bath, the good solvent in the level 1 coagulation bath is 100% of the total mass, the good solvent in the level 2 coagulation bath is 75% to 95% of the total mass, the good solvent in the level 3 coagulation bath is 55% to 70% of the total mass, the good solvent in the level 4 coagulation bath is 20% to 50% of the total mass, and the good solvent in the level 5 coagulation bath is 0% of the total mass.

[0017] In some embodiments, the phase inversion reaction is carried out in any one stage of the coagulation bath for 5 min to 60 min.

[0018] In some embodiments, the thermal imidization treatment is specifically as follows: heating the oven to 150° C. and 300° C. in sequence at a heating rate of 5° C. / min to 15° C. / min, and keeping the temperatures at 150° C. and 300° C. for 1 h to 5 h, respectively.

[0019] In some embodiments, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanol.

[0020] In some embodiments, the surfactant includes one or more of dimethyl silicone oil, polyethylene glycol, sodium dodecylbenzene sulfonate, and fluorocarbon surfactants.

[0021] In some embodiments, the poor solvent includes one or more of methanol, ethanol, n-butanol, acetone, xylene, ethyl acetate, isopropanol, tetrahydrofuran, glycerol, and water.

[0022] In some embodiments, the good solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0023] In some embodiments, the diamine monomer includes one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 2,2'-bis(trifluoromethyl)diaminobiphenyl, and 1,4-bis(4-aminophenoxy)benzene.

[0024] In some embodiments, the dianhydride monomer includes one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

[0025] The second aspect of the present application provides a porous polyimide film, which is prepared according to the preparation method provided in the first aspect.

[0026] The present application provides a multi-stage multi-solvent phase inversion method to prepare a porous polyimide film, by adjusting the content of organic solvent and poor solvent in the casting solution, the content of good solvent and poor solvent in the coagulation bath, using a multi-stage coagulation bath to perform phase inversion respectively, controlling the replacement rate of the solvent, reducing the phase inversion rate, reducing the formation of the cortex, and at the same time regulating the pore size inside the film, to obtain a sponge-like porous polyimide film with uniform sponge-like through holes and openings on the upper and lower surfaces. Among them, the surface opening structure can effectively improve the permeability of the polyimide film, and the sponge-like structure effectively increases the channel path inside the film, increasing the interception performance of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of a cross section of the porous polyimide film prepared in Example 2 of the present application.

[0028] Figure 2 This is a scanning electron microscope image of the upper surface (close to the coagulation bath side) of the porous polyimide film prepared in Example 2 of the present application.

[0029] Figure 3 This is a scanning electron microscope image of the lower surface (close to the glass side) of the porous polyimide film prepared in Example 2 of the present application.

[0030] Figure 4 This is a scanning electron microscope image of a cross section of the porous polyimide film prepared in Example 4 of the present application.

[0031] Figure 5 This is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Example 4 of the present application.

[0032] Figure 6 This is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Example 4 of the present application.

[0033] Figure 7 This is a scanning electron microscope image of a cross section of the porous polyimide film prepared in Example 6 of the present application.

[0034] Figure 8 This is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Example 6 of the present application.

[0035] Fig. 9 This is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Example 6 of the present application.

[0036] Fig.10 This is a scanning electron microscope image of the cross section of the porous polyimide film prepared in Comparative Example 1 of the present application.

[0037] Fig.11 This is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 1 of the present application.

[0038] Fig.12 This is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 1 of the present application.

[0039] Fig.13 This is a scanning electron microscope image of the cross section of the porous polyimide film prepared in Comparative Example 2 of the present application.

[0040] Fig.14 This is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 2 of the present application.

[0041] Fig.15 This is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 2 of the present application.

[0042] Fig.16 This is a scanning electron microscope image of the cross section of the porous polyimide film prepared in Comparative Example 3 of the present application.

[0043] Fig.17This is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 3 of the present application.

[0044] Fig.18 This is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0045] References to embodiments of the present application will now be provided in detail, one or more embodiments of which are described below. Each embodiment is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0046] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0047] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0048] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0049] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 100-150nm means that the units of the left endpoint "100" and the right endpoint "150" are both nm (nanometers).

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0052] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0053] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0054] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] The first aspect of the present application provides a method for preparing a porous polyimide film, comprising the following steps:

[0056] S1. Under an inert atmosphere, completely dissolve the diamine monomer in an organic solvent, then add the dianhydride monomer, stir at 30°C to 80°C for 2h to 48h, and stand to degas to obtain a polyimide casting solution A;

[0057] S2, adding a poor solvent and a surfactant to the polyimide casting solution A, stirring for 2h to 24h, standing for degassing, and obtaining a polyimide casting solution B;

[0058] S3, coating the polyimide film casting solution B on the substrate and allowing it to stand to obtain a primary film;

[0059] S4, respectively stirring and mixing good solvents and poor solvents of different mass ratios to prepare a coagulation bath; wherein the coagulation bath comprises a multi-stage coagulation bath, the number of the multi-stage coagulation baths is N, N ≥ 3, and as the number of the coagulation baths increases, the mass proportion of the good solvent in the coagulation bath decreases;

[0060] S5, immersing the primary membrane sheet in a multi-stage coagulation bath in turn to perform a phase inversion reaction, thereby obtaining a phase inversion membrane;

[0061] S6. After drying the phase conversion membrane, place it in an oven for thermal imidization treatment to obtain a porous polyimide film.

[0062] It is to be understood that in the present application, there is no specific limitation on the inert atmosphere in step S1, and illustratively, it may be a nitrogen atmosphere, an argon atmosphere, or the like.

[0063] In some embodiments, in step S1, the molar ratio of the dianhydride monomer to the diamine monomer is (1-1.2):1, including but not limited to 1:1, 1.1:1, and 1.2:1.

[0064] In some embodiments, in step S1, the diamine monomer includes one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 2,2'-bis(trifluoromethyl)diaminobiphenyl, and 1,4-bis(4-aminophenoxy)benzene.

[0065] In some embodiments, in step S1, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanol.

[0066] In some embodiments, in step S1, the dianhydride monomer includes one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

[0067] In some embodiments, in step S2, based on the total mass of the polyimide casting solution B, the sum of the masses of the diamine monomer and the dianhydride monomer is 10% to 20% of the total mass, the mass of the organic solvent is 30% to 65% of the total mass, the mass of the poor solvent is 10% to 15% of the total mass, and the mass of the surfactant is 5 to 10% of the total mass.

[0068] In some embodiments, in step S2, the poor solvent includes one or more of methanol, ethanol, n-butanol, acetone, xylene, ethyl acetate, isopropanol, tetrahydrofuran, glycerol, and water.

[0069] In some embodiments, in step S2, the surfactant includes one or more of dimethyl silicone oil, polyethylene glycol, sodium dodecylbenzene sulfonate, and fluorocarbon surfactants.

[0070] In some embodiments, in step S3, the substrate is a glass substrate.

[0071] In some embodiments, step S3 is specifically as follows: at room temperature, the polyimide casting liquid B is slowly poured onto the glass substrate, and the polyimide casting liquid B is scraped onto the glass substrate at a speed of 1 cm / s to 10 cm / s by a flat scraper, and allowed to stand in the air for 5 min to 60 min to obtain a primary film.

[0072] In some embodiments, in step S4, based on the total mass of the coagulation bath, the good solvent accounts for 0% to 100% of the total mass, and the poor solvent accounts for 0% to 100% of the total mass.

[0073] In some embodiments, in step S4, the good solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0074] In some embodiments, in step S4, the poor solvent includes one or more of methanol, ethanol, n-butanol, acetone, xylene, ethyl acetate, isopropanol, tetrahydrofuran, glycerol, and water.

[0075] In a specific embodiment, N is 3, that is, the coagulation bath includes a first-stage coagulation bath, a second-stage coagulation bath, and a third-stage coagulation bath.

[0076] Based on the total mass of the coagulation bath, the good solvent in the first-level coagulation bath accounts for 100% of the total mass, the good solvent in the second-level coagulation bath accounts for 40% to 80% of the total mass, and the good solvent in the third-level coagulation bath accounts for 0% of the total mass.

[0077] In a specific embodiment, N is 5, that is, the coagulation bath includes a 1st-stage coagulation bath, a 2nd-stage coagulation bath, a 3rd-stage coagulation bath, a 4th-stage coagulation bath and a 5th-stage coagulation bath.

[0078] Based on the total mass of the coagulation bath, the good solvent in the first-level coagulation bath is 100% of the total mass, the good solvent in the second-level coagulation bath is 75% to 95% of the total mass, the good solvent in the third-level coagulation bath is 55% to 70% of the total mass, the good solvent in the fourth-level coagulation bath is 20% to 50% of the total mass, and the good solvent in the fifth-level coagulation bath is 0% of the total mass.

[0079] In some embodiments, in step S5, the time for the phase inversion reaction in any one stage of the coagulation bath is 5 min to 60 min, including but not limited to 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min.

[0080] It can be understood that in step S5, immersing the primary membrane sheet in the multi-stage coagulation baths in sequence to perform phase conversion reaction means immersing the primary membrane sheet in the first-stage coagulation bath, the second-stage coagulation bath, the third-stage coagulation bath in sequence, and so on.

[0081] In some embodiments, in step S6, the drying treatment is specifically: after drying the phase conversion membrane at room temperature for 12 hours to 24 hours, transfer it to a vacuum oven at 50°C to 150°C and dry it for 12 hours to 24 hours to remove the residual non-solvent molecules in the phase conversion membrane.

[0082] In some embodiments, in step S6, the thermal imidization treatment is specifically: heating the oven to 150°C and 300°C in sequence at a heating rate of 5°C / min to 15°C / min, and keeping the temperatures at 150°C and 300°C for 1h to 5h respectively.

[0083] In some embodiments, the following steps are further included between steps S5 and S6:

[0084] The phase conversion membrane obtained in step S5 is peeled off from the glass plate and then immersed in water for 1 hour to 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0085] The second aspect of the present application provides a porous polyimide film, which is prepared according to the preparation method provided in the first aspect.

[0086] The present application provides a multi-stage multi-solvent phase inversion method to prepare a porous polyimide film, by adjusting the content of organic solvent and poor solvent in the casting solution, the content of good solvent and poor solvent in the coagulation bath, using a multi-stage coagulation bath to perform phase inversion respectively, controlling the replacement rate of the solvent, reducing the phase inversion rate, reducing the formation of the cortex, and at the same time regulating the pore size inside the film, to obtain a sponge-like porous polyimide film with uniform sponge-like through holes and openings on the upper and lower surfaces. Among them, the surface opening structure can effectively improve the permeability of the polyimide film, and the sponge-like structure effectively increases the channel path inside the film, increasing the interception performance of the film.

[0087] The present application realizes dynamic adjustment of the morphology, size, and porosity of the porous polyimide film by setting parameters such as a multi-stage coagulation bath, a ratio of a good solvent to a poor solvent in the coagulation bath, the solid content of the polyimide casting solution, and the material type of the polyimide casting solution.

[0088] The solvent used in this application has little environmental pollution and is easy to recycle.

[0089] The preparation method of the present application has the advantages of being simple and easy to operate, having a short production time, low cost, low operating temperature, and being convenient for actual production.

[0090] The porous polyimide film prepared in the present application has bidirectional openings on the upper and lower surfaces and presents a sponge-like structure. The production of a surface cortex is effectively avoided during the preparation process. The cross-section shows that the pore structure is sponge-like, the porosity is good, and the pore size is uniform.

[0091] The present application will be further described below with reference to specific embodiments and comparative examples.

[0092] Example 1

[0093] S1. Under room temperature and N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 h to obtain a homogeneous solution. After standing for 12 h to completely degas, a polyimide casting solution A was obtained.

[0094] S2. Weigh 100 g of polyimide casting solution A, add 15 g of ethanol and 7 g of polyethylene glycol, stir at 35° C. for 12 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0095] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the gap of the flat-plate scraper to 200 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0096] S4. Prepare a multi-stage coagulation bath, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1600g N-methylpyrrolidone and 400g ethanol are mixed together as the second-stage coagulation bath; 1200g N-methylpyrrolidone and 800g ethanol are mixed together as the third-stage coagulation bath; 800g N-methylpyrrolidone and 1200g ethanol are mixed together as the fourth-stage coagulation bath; deionized water is used as the fifth-stage coagulation bath.

[0097] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0098] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0099] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0100] Example 2

[0101] S1. Under room temperature and N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 142.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 h to obtain a homogeneous solution. After standing for 12 h to completely degas, a polyimide casting solution A was obtained.

[0102] S2. Weigh 100 g of polyimide casting solution A, add 15 g of ethanol and 7 g of polyethylene glycol, stir at 35° C. for 12 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0103] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 300 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0104] S4. Prepare a multi-stage coagulation bath, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1600g N-methylpyrrolidone and 400g ethanol are mixed together as the second-stage coagulation bath; 1200g N-methylpyrrolidone and 800g ethanol are mixed together as the third-stage coagulation bath; 800g N-methylpyrrolidone and 1200g ethanol are mixed together as the fourth-stage coagulation bath; deionized water is used as the fifth-stage coagulation bath.

[0105] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0106] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0107] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0108] Example 3

[0109] S1. Under room temperature and N2 atmosphere, 31.5378 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 452.7 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 48.3345 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added. The mixture was stirred at 35°C for 18 h to obtain a homogeneous solution. After standing for 24 h to completely degas, a polyimide casting solution A was obtained.

[0110] S2. Weigh 300 g of polyimide casting solution A, add 40 g of ethanol and 20 g of polyethylene glycol, stir at 35° C. for 15 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0111] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 400 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0112] S4. Prepare a multi-stage coagulation bath, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1600g N-methylpyrrolidone and 400g ethanol are mixed together as the second-stage coagulation bath; 1200g N-methylpyrrolidone and 800g ethanol are mixed together as the third-stage coagulation bath; 800g N-methylpyrrolidone and 1200g ethanol are mixed together as the fourth-stage coagulation bath; deionized water is used as the fifth-stage coagulation bath.

[0113] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0114] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0115] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0116] Example 4

[0117] S1. Under room temperature and N2 atmosphere, 20.024 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 280.2 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 29.422 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 15 h to obtain a homogeneous solution. After standing for 18 h to completely degas, a polyimide casting solution A was obtained.

[0118] S2. Weigh 100 g of polyimide casting solution A, add 15 g of propanol and 7 g of polyethylene glycol, stir at 35° C. for 12 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0119] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 400 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0120] S4. Prepare a multi-stage coagulation bath, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1600g N-methylpyrrolidone and 400g ethanol are mixed together as the second-stage coagulation bath; 1200g N-methylpyrrolidone and 800g ethanol are mixed together as the third-stage coagulation bath; 800g N-methylpyrrolidone and 1200g ethanol are mixed together as the fourth-stage coagulation bath; deionized water is used as the fifth-stage coagulation bath.

[0121] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0122] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0123] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0124] Example 5

[0125] S1. Under room temperature and N2 atmosphere, 24.0288 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 302.9 g of N,N-dimethylformamide (DMF). After sufficient stirring to dissolve, 29.422 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 15 h to obtain a homogeneous solution. After standing for 18 h to completely degas, a polyimide casting solution A was obtained.

[0126] S2. Weigh 100 g of polyimide casting solution A, add 15 g of ethanol and 7 g of polyethylene glycol, stir at 35° C. for 12 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0127] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 400 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0128] S4. Prepare a multi-stage coagulation bath, specifically: pure N,N-dimethylformamide (DMF) as the 1st stage coagulation bath; 1600g N,N-dimethylformamide (DMF) and 400g ethanol are mixed together as the 2nd stage coagulation bath; 1200g N,N-dimethylformamide (DMF) and 800g ethanol are mixed together as the 3rd stage coagulation bath; 800g N,N-dimethylformamide (DMF) and 1200g ethanol are mixed together as the 4th stage coagulation bath; deionized water is used as the 5th stage coagulation bath.

[0129] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0130] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0131] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0132] Example 6

[0133] S1. Under room temperature and N2 atmosphere, 31.5378 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 428.7 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 44.133 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 18 h to obtain a homogeneous solution. After standing for 24 h to completely degas, a polyimide casting solution A was obtained.

[0134] S2. Weigh 300 g of polyimide casting solution A, add 45 g of ethanol and 25 g of polyethylene glycol, stir at 35° C. for 15 h to obtain a homogeneous solution, and let it stand for 18 h to completely degas, thereby obtaining polyimide casting solution B.

[0135] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 400 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0136] S4. Prepare multi-stage coagulation baths, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1400g N-methylpyrrolidone and 600g ethanol are mixed together as the second-stage coagulation bath; 1000g N-methylpyrrolidone and 1000g ethanol are mixed together as the third-stage coagulation bath; 600g N-methylpyrrolidone and 1400g ethanol are mixed together as the fourth-stage coagulation bath; deionized water is used as the fifth-stage coagulation bath.

[0137] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion is complete, a phase conversion membrane is obtained.

[0138] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0139] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0140] Example 7

[0141] S1. Under room temperature and N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 142.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 h to obtain a homogeneous solution. After standing for 12 h to completely degas, a polyimide casting solution A was obtained.

[0142] S2. Weigh 100 g of polyimide casting solution A, add 15 g of ethanol and 7 g of polyethylene glycol, stir at 35° C. for 12 h to obtain a homogeneous solution, and let it stand for 12 h to completely degas, thereby obtaining polyimide casting solution B.

[0143] S3. Slowly pour the polyimide casting liquid B onto a clean glass plate, set the flat-plate scraper blade gap to 300 μm, and evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film is obtained.

[0144] S4. Prepare a multi-stage coagulation bath, specifically: pure N-methylpyrrolidone as the first-stage coagulation bath; 1200 g of N-methylpyrrolidone and 800 g of ethanol are mixed together as the second-stage coagulation bath; deionized water is used as the third-stage coagulation bath.

[0145] S5. Slowly transfer the primary membrane sheet to the first-level coagulation bath for 10 minutes; then transfer it to the second-level coagulation bath for 30 minutes; and transfer it to the third-level coagulation bath for 60 minutes. After the three-level phase conversion is complete, a phase conversion membrane is obtained.

[0146] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 hours to completely replace the good solvent and the poor solvent in the phase conversion membrane.

[0147] S6. After drying the phase conversion membrane at room temperature for 24 hours, transfer it to a 100°C vacuum oven and continue drying it for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after fixing the phase conversion membrane, place it in a high-temperature oven and heat it to 150°C and 300°C at a heating rate of 5°C / min, and keep it at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0148] Comparative Example 1

[0149] At room temperature, in a N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 142.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 hours to obtain a homogeneous solution. After standing for 12 hours for complete degassing, a polyimide casting solution A was obtained.

[0150] The polyimide casting liquid A was slowly poured onto a clean glass plate, the gap of the flat-plate scraper was set to 300 μm, and the scraper was used to evenly scrape the polyimide casting liquid A onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film was obtained.

[0151] Deionized water was used directly as the coagulation bath.

[0152] The primary membrane was slowly transferred to deionized water and immersed for 3 hours to obtain a phase conversion membrane.

[0153] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 h.

[0154] After the phase transformation membrane was dried at room temperature for 24 hours, it was transferred to a 100°C vacuum oven and continued to be dried for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after the phase transformation membrane was fixed, it was placed in a high-temperature oven and heated to 150°C and 300°C at a heating rate of 5°C / min, and kept at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0155] Comparative Example 2

[0156] At room temperature, in a N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 hours to obtain a homogeneous solution. After standing for 12 hours for complete degassing, a polyimide casting solution A was obtained.

[0157] The polyimide casting liquid A was slowly poured onto a clean glass plate, the gap of the flat-plate scraper was set to 300 μm, and the scraper was used to evenly scrape the polyimide casting liquid A onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film was obtained.

[0158] A multi-stage coagulation bath was prepared, specifically: pure N-methylpyrrolidone was used as the first stage coagulation bath; 1600 g N-methylpyrrolidone and 400 g ethanol were mixed together as the second stage coagulation bath; 1200 g N-methylpyrrolidone and 800 g ethanol were mixed together as the third stage coagulation bath; 800 g N-methylpyrrolidone and 1200 g ethanol were mixed together as the fourth stage coagulation bath; deionized water was used as the fifth stage coagulation bath.

[0159] The primary membrane sheet was slowly transferred to the first-level coagulation bath for 10 minutes; then transferred to the second-level coagulation bath for 20 minutes; the third-level coagulation bath for 30 minutes; the fourth-level coagulation bath for 60 minutes; the fifth-level coagulation bath for 60 minutes. After the five-level phase conversion was complete, a phase conversion membrane was obtained.

[0160] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 h.

[0161] After the phase transformation membrane was dried at room temperature for 24 hours, it was transferred to a 100°C vacuum oven and continued to be dried for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after the phase transformation membrane was fixed, it was placed in a high-temperature oven and heated to 150°C and 300°C at a heating rate of 5°C / min, and kept at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0162] Comparative Example 3

[0163] At room temperature, in a N2 atmosphere, 10.5126 g of 4,4'-diaminodiphenyl ether (ODA) was dissolved in 100.9 g of N-methylpyrrolidone (NMP). After sufficient stirring to dissolve, 14.711 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. The mixture was stirred at 35°C for 12 hours to obtain a homogeneous solution. After standing for 12 hours for complete degassing, a polyimide casting solution A was obtained.

[0164] 100 g of polyimide casting solution A was weighed, 15 g of ethanol and 7 g of polyethylene glycol were added, and the mixture was stirred at 35° C. for 12 h to obtain a homogeneous solution. After standing for 12 h to completely degas, polyimide casting solution B was obtained.

[0165] The polyimide casting liquid B was slowly poured onto a clean glass plate, the gap of the flat-plate scraper was set to 200 μm, and the scraper was used to evenly scrape the polyimide casting liquid B onto the glass plate at a speed of 1 cm / s. After standing in the air for 10 minutes, a primary film was obtained.

[0166] Deionized water was used directly as the coagulation bath.

[0167] The primary membrane was slowly transferred to deionized water and immersed for 3 hours to obtain a phase conversion membrane.

[0168] The phase conversion membrane was peeled off from the glass plate and continued to be immersed in pure water for 24 h.

[0169] After the phase transformation membrane was dried at room temperature for 24 hours, it was transferred to a 100°C vacuum oven and continued to be dried for 12 hours to remove the residual non-solvent molecules in the membrane. Then, after the phase transformation membrane was fixed, it was placed in a high-temperature oven and heated to 150°C and 300°C at a heating rate of 5°C / min, and kept at 150°C and 300°C for 1 hour respectively to obtain a porous polyimide film.

[0170] Test Case

[0171] The morphology of the porous polyimide film was observed by scanning electron microscopy. Figure 1 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Example 2 of the present application. Figure 2 As shown in FIG. 1 , it is a scanning electron microscope image of the upper surface (close to the coagulation bath side) of the porous polyimide film prepared in Example 2 of the present application. Figure 3 As shown, it is a scanning electron microscope image of the lower surface (close to the glass side) of the porous polyimide film prepared in Example 2 of the present application. Figure 4 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Example 4 of the present application. Figure 5 As shown in FIG. 1 , it is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Example 4 of the present application. Figure 6 As shown in FIG. 1 , it is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Example 4 of the present application. Figure 7 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Example 6 of the present application. Figure 8 As shown in FIG. 1 , it is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Example 6 of the present application. Fig. 9 As shown in FIG. 1 , it is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Example 6 of the present application. Fig.10 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Comparative Example 1 of the present application. Fig.11 As shown, it is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 1 of the present application. Fig.12 As shown, it is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 1 of the present application. Fig.13 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Comparative Example 2 of the present application. Fig.14 As shown, it is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 2 of the present application. Fig.15 As shown, it is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 2 of the present application. Fig.16 As shown in FIG. 1 , it is a cross-sectional scanning electron microscope image of the porous polyimide film prepared in Comparative Example 3 of the present application. Fig.17 As shown, it is a scanning electron microscope image of the upper surface of the porous polyimide film prepared in Comparative Example 3 of the present application. Fig.18 Shown is a scanning electron microscope image of the lower surface of the porous polyimide film prepared in Comparative Example 3 of the present application.

[0172] By electron microscopic comparison, it can be clearly observed that the porous polyimide film prepared by the multi-stage multi-solvent phase conversion method provided by the present application clearly shows that the pore morphology of the film is uniform honeycomb pores (see Figure 1 , Figure 4 and Figure 7 ), and both the upper and lower surfaces show obvious through-hole structures (see Figure 2 , 3 , 5, 6, 8, 9); while the porous membrane prepared by the single NIPS method provided in Comparative Example 1 shows an irregular membrane pore structure in cross section (see Fig.10 ), the upper and lower surfaces show no through holes, showing a dense cortical structure (see Fig.11 and Fig.12 In comparative example 2, although a multi-stage phase was used, the lack of a poor solvent in the casting solution resulted in the coexistence of finger-like pores and honeycomb pores (see Fig.13 ), the upper and lower surfaces also show no through holes, showing a dense cortical structure (see Fig.14 and Fig.15 In Comparative Example 3, a poor solvent was added to the casting solution but no multi-stage phase conversion was performed, and finger-like pores appeared in the membrane (see Fig.16 ), the upper surface also shows a dense cortical structure (see Fig.17 ), all of which limit the application scope of porous membranes.

[0173] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0174] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for preparing a porous polyimide film, characterized in that: The following steps are involved: Under an inert atmosphere, the diamine monomer is completely dissolved in an organic solvent, and then the dianhydride monomer is added, stirred at 30° C. to 80° C. for 2 h to 48 h, and allowed to stand for degassing to obtain a polyimide casting solution A; Adding a poor solvent and a surfactant to the polyimide casting solution A, stirring for 2 hours to 24 hours, and standing for degassing to obtain a polyimide casting solution B; The polyimide film casting solution B is coated on a substrate and allowed to stand to obtain a primary film; A good solvent and a poor solvent of different mass ratios are stirred and mixed respectively to prepare a coagulation bath; wherein the coagulation bath comprises a multi-stage coagulation bath, the number of the multi-stage coagulation bath is N, N≥3, and as the number of the stages of the coagulation bath increases, the mass proportion of the good solvent in the coagulation bath decreases; Sequentially immersing the primary membrane into the multi-stage coagulation bath to perform a phase inversion reaction to obtain a phase inversion membrane; After the phase conversion membrane is dried, it is placed in an oven for thermal imidization treatment to obtain a porous polyimide film.

2. The method for preparing a porous polyimide film according to claim 1, characterized in that: The molar ratio of the diamine monomer to the dianhydride monomer is (1-1.2):

1.

3. The method for preparing a porous polyimide film according to claim 1, characterized in that: Taking the total mass of the polyimide casting liquid B as a benchmark, the sum of the masses of the diamine monomer and the dianhydride monomer is 10% to 20% of the total mass, the mass of the organic solvent is 30% to 65% of the total mass, the mass of the poor solvent is 10% to 15% of the total mass, and the mass of the surfactant is 5 to 10% of the total mass.

4. The method for preparing a porous polyimide film according to claim 1, characterized in that: Based on the total mass of the coagulation bath, the good solvent accounts for 0% to 100% of the total mass, and the poor solvent accounts for 0% to 100% of the total mass.

5. The method for preparing a porous polyimide film according to claim 1, characterized in that: The number of the multi-stage coagulation baths is N, N is 5, and the coagulation baths include 1st, 2nd, 3rd, 4th and 5th stage coagulation baths; based on the total mass of the coagulation baths, the good solvent in the 1st stage coagulation bath is 100% of the total mass, the good solvent in the 2nd stage coagulation bath is 75% to 95% of the total mass, the good solvent in the 3rd stage coagulation bath is 55% to 70% of the total mass, the good solvent in the 4th stage coagulation bath is 20% to 50% of the total mass, and the good solvent in the 5th stage coagulation bath is 0% of the total mass.

6. The method for preparing a porous polyimide film according to claim 1, characterized in that: The time for the phase inversion reaction in any one stage of the coagulation bath is 5 to 60 minutes.

7. The method for preparing a porous polyimide film according to claim 1, characterized in that: The thermal imidization treatment is specifically as follows: the oven is heated to 150° C. and 300° C. in sequence at a heating rate of 5° C. / min to 15° C. / min, and kept at 150° C. and 300° C. for 1 h to 5 h, respectively.

8. The method for preparing a porous polyimide film according to claim 1, characterized in that: The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and methanol; And / or, the surfactant includes one or more of dimethyl silicone oil, polyethylene glycol, sodium dodecylbenzene sulfonate, and fluorocarbon surfactant; and / or, the poor solvent comprises one or more of methanol, ethanol, n-butanol, acetone, xylene, ethyl acetate, isopropanol, tetrahydrofuran, glycerol, and water; And / or, the good solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

9. The method for preparing a porous polyimide film according to claim 1, characterized in that: The diamine monomer includes one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobenzanilide, 2,2'-bis(trifluoromethyl)diaminobiphenyl, and 1,4-bis(4-aminophenoxy)benzene; And / or, the dianhydride monomer includes one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

10. A porous polyimide film, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 9.

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