JP5605566B2 - Method for producing porous polyimide membrane - Google Patents

Description

  The present invention relates to a porous polyimide, particularly a polyimide film having three-dimensionally ordered macroporous (hereinafter 3DOM). These porous membranes can be suitably used for battery membrane materials such as separators and ion exchange membranes, optical materials such as displays and optical waveguides, and catalyst supports.

  In recent years, porous polyimide has been studied as a lithium ion battery separator, a fuel cell electrolyte membrane, and a low dielectric constant material. For example, a method in which a block copolymer or a graft copolymer of polyimide and an easily decomposable component is heated to imidize to make it porous, and a technique in which a polyimide film is optically processed to form a continuous pore film are known. (See Patent Documents 1 to 4)

Japanese Patent Laid-Open No. 2004-2865 JP 2007-92078 JP 2004-171994 JP 2002-335949 A

  The films of Patent Documents 1 to 3 have a problem of reproducibility, such as a part that is not necessarily a communicating hole, or a change in porosity and hole diameter, resulting in variations in physical property values in application fields and application fields. In addition, the film of Patent Document 4 has a limited film thickness and hole diameter, and requires a special device to produce a large-area film, resulting in high costs.

  Therefore, an object of the present invention is to provide a method capable of producing a 3DOM polyimide film having continuous micropores arranged in a three-dimensional regular array with good reproducibility, a large area, and at low cost using the existing polyimide film production equipment. There is to do.

The present invention is a varnish production process for producing a varnish by mixing polyamide acid or polyimide, silica particles and a solvent, or polymerizing polyamide acid or polyimide in a solvent in which silica particles are dispersed, and
A composite film production process for producing a polyimide-silica composite film by completing imidization after film formation of the varnish produced in the varnish production process on a substrate;
In the method for producing a porous polyimide film having a silica removal step of removing silica of the polyimide-silica composite membrane produced in the composite membrane production step,
As the silica particles, silica particles having a sphericity ratio of 1.0 to 1.1, a particle size distribution index (d ₂₅ / d ₇₅ ) of 1.5 or less, and an average diameter of 100 to 2000 nm are used, and the silica / silica in the polyimide-silica composite film The present invention relates to a method for producing a porous polyimide film, wherein the mass ratio of polyimide is 2 to 6.
Preferably, the porous polyimide film has a porosity of 50% or more, and micropores having an average diameter of 100 to 2000 nm are in contact with each other to form a communication hole, and the diameter of the communication hole is 1000 nm or less. .

The present invention also provides a varnish production process for producing a varnish by mixing polyamic acid or polyimide, silica particles and a solvent, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed, and
A composite film production process for producing a polyimide-silica composite film by completing imidization after film formation of the varnish produced in the varnish production process on a substrate;
Combined with the silica removal step of removing the silica of the polyimide-silica composite membrane produced in the composite membrane production step ,
The sphericity index as silica particles 1.0 to 1.1, particle size distribution index (d ₂₅ / d ₇₅₎ is the Rukoto with 1.5 following silica particles,
Micropores having a porosity of 50% or more and an average diameter of 100 to 2000 nm are in contact with each other to form a communication hole, and a porous polyimide film having a diameter of the communication hole of 1000 nm or less is obtained. The present invention relates to a method for producing a porous polyimide film.

  The present invention has a continuous fine pores that are three-dimensionally arranged by removing silica after forming a polyamic acid or polyimide varnish in which predetermined silica particles are uniformly dispersed to obtain a silica-polyimide composite film. There are advantages that a 3DOM polyimide film can be manufactured with good reproducibility, a large area, and can be manufactured at low cost by using an existing polyimide film manufacturing apparatus.

It is a figure which shows the diameter of a micropore and a communicating hole. 2 is a drawing-substituting photograph of the 3DOM polyimide porous film obtained in Example 1. FIG. 6 is a drawing-substituting photograph of a polyimide film obtained in Comparative Example 1. FIG. 6 is a drawing-substituting photograph of a polyimide film obtained in Comparative Example 2. FIG.

  In the present invention, the varnish production process is performed by mixing a solvent in which predetermined silica particles are dispersed in advance and a polyamic acid solution or a polyimide solution polymerized in a solvent that can be mixed with the solvent at an arbitrary ratio, It can be obtained by polymerizing polyamic acid or polyimide in a previously dispersed solvent. The silica particles are preferably colloidal silica or monodispersed spherical silica particles. Silica particles having a particle diameter (average diameter) of 100 to 2000 nm are used.

  The sphericity of the silica particles used in the present invention is 1.0 to 1.1. This sphericity is defined as the average value of the longest diameter of particles / the average value of the shortest diameter of particles. Further, the particle size distribution index of the silica particles used in the present invention is 1.5 or less. The particle size distribution index is defined as d25 / d75, and d25 and d75 are values of the particle size when the cumulative frequency of the particle size distribution is 25% and 75%, respectively. Silica particles having these conditions are excellent in dispersibility in polyamic acid, and can be produced into a polyimide film having three-dimensional regular array holes by being closely packed in a drying step after film formation. Hereinafter, silica particles satisfying the true sphere ratio and the particle size distribution index are also referred to as monodispersed spherical silica particles. The monodispersed spherical silica particles are preferably not aggregated with each other.

  The varnish can be mixed at a ratio of silica / polyimide of 2 to 6 (mass ratio), preferably 3 to 5. When the mass ratio of silica / polyimide is less than 2, it tends to be difficult to obtain continuous pores, and when it exceeds 6, it is often difficult to produce a desired film.

  The varnish viscosity can be adjusted to 10 to 3000 poises, preferably 50 to 300 poises, using a Brookfield viscometer at 25 ° C. Solid content concentration can be adjusted with 5-50 mass%, Preferably it is 20-40 mass%. The solid content concentration is measured by weighing 5 g of a sample in an aluminum cup, applying a heat treatment at 200 ° C. for 2 hours, and calculating a {(residue mass) / (varnish mass)} × 100 after constant weight.

  By satisfying these conditions, the packing state of silica can be regularly ordered in three dimensions. Since the pores of the obtained porous membrane become regular three-dimensionally, it becomes easy to fill the electrolyte. Further, by using a monodispersed spherical shape, the packing state of silica becomes regular three-dimensionally.

  The silica particles include, as substances other than silica, spherical particles of acrylic resin and polystyrene, spherical fine particles of inorganic salts such as calcium carbonate, spherical fine particles of organic salts such as calcium alginate, and spherical particles obtained by microencapsulating organic and inorganic materials. Fine particles may be added.

The composite film production process forms a film on a substrate coated with a release agent at an arbitrary ratio, and after drying at 0 to 50 ° C., preferably 10 to 30 ° C. under normal pressure or vacuum, then a polyamic acid film or polyimide The film can be peeled off and heated or chemically post-treated to complete imidization to obtain a silica-polyimide composite film. As heating conditions for completing imidization, the temperature is raised from room temperature to 375 ° C in 3 hours, and then kept at 375 ° C for 20 minutes, or gradually raised from room temperature to 375 ° C in increments of 50 ° C. (Each step is held for 20 minutes), and a thermal imidation method such as finally holding at 375 ° C. for 20 minutes can be used.
Further, as a chemical post-treatment, after peeling off the formed film, it is immersed in a mixed solvent of acetic anhydride and isoquinoline as an imidizing agent, and then heated from room temperature to 375 ° C. in 3 hours, A chemical imidization method in which the temperature is maintained at 375 ° C for 20 minutes can be used.

  The resulting silica-polyimide composite film has an average film thickness of 5 to 500 μm, preferably 10 to 100 μm. The film thickness can be measured with, for example, Digimicro MH-15M manufactured by Nikon Corporation.

  The silica-polyimide composite film can be dissolved and removed with low-concentration hydrogen fluoride water or the like to produce a 3DOM polyimide film having continuous pores arranged three-dimensionally with good reproducibility.

  As the monodispersed spherical silica particles, particles having a diameter of 100 to 2000 nm manufactured by Nippon Shokubai Co., Ltd. are suitable. In such a range, it is easy to obtain good performance in an application field, for example, in an electrolyte membrane. According to the diameter of the silica particles, the fine pore diameter and the communication pore diameter are affected, and an improvement in performance based on the same diameter can be expected.

  These particles can be stably dispersed in a solvent usually used for polyimide polymerization such as dimethylacetamide.

  The polyamic acid (polyamic acid) or polyimide solution used in the varnish production process is obtained from any tetracarboxylic dianhydride and diamine.

  Examples of the tetracarboxylic dianhydride include, for example, ethylene tetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1,2, 4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, pyromellitic dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ) Ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic acid Dianhydride, 2,2,6,6-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-di Carboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-Hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoro Propane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic dianhydride, 4,4- (p-phenylenedioxy) diphthalic acid Anhydride, 4,4- (m-phenylenedioxy) diphthalic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2 , 3,6,7-ant Sen tetracarboxylic dianhydride, 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride, 9,9-bis phthalic anhydride fluorene, and the like. These tetracarboxylic dianhydrides can be used alone or in admixture of two or more.

  As diamine, fatty acid diamine, aromatic diamine, etc. can be mixed and used.

  The aliphatic diamine has, for example, about 2 to 15 carbon atoms, and specific examples include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

  Examples of the aromatic diamine include diamino compounds in which one phenyl group or about 2 to 10 phenyl groups are bonded. Specifically, phenylenediamine and derivatives thereof, diaminodiphenyl compounds and derivatives thereof, diaminotriphenyl compounds and derivatives thereof, diaminonaphthalene and derivatives thereof, aminophenylaminoindane and derivatives thereof, diaminotetraphenyl compounds and derivatives thereof, diaminohexa Phenyl compounds and derivatives thereof, cardo-type fluorenediamine derivatives.

  Phenylenediamine is m-phenylenediamine, p-phenylenediamine, etc., and the phenylenediamine derivative is a diamine to which an alkyl group such as methyl group or ethyl group is bonded, such as 2,4-triphenylenediamine.

  The diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other via another group. The bond is an ether bond, a sulfonyl bond, a thioether bond, a bond by alkylene or a derivative group thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a ureylene bond, or the like. The alkylene bond has about 1 to 6 carbon atoms, and the derivative group has one or more hydrogen atoms of the alkylene group substituted with a halogen atom or the like.

  Examples of diaminodiphenyl compounds include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodienyl sulfone, 3,4'-diaminodienyl Sulfone, 4,4'-diaminodienylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'- Diaminodienyl ketone, 3,4'-diaminodiphenyl ketone, 2,2-bis (p-aminophenyl) propane, 2,2'-bis (p-aminophenyl) hexafluoropropane, 4-methyl-2, 4-bis (p-aminophenyl) -1-pentene, 4-methyl-2,4-bis (p-aminophenyl) -2-pentene, iminodianiline, 4-methyl-2,4-bis (p- Aminophenyl) pentane, bis (p-a Nofeniru) phosphine oxide, 4,4'-aminoazobenzene, 4,4'-diaminodiphenyl urea, may be mentioned 4,4'-diaminodiphenyl amide.

  In the diaminotriphenyl compound, two aminophenyl groups and one phenylene group are both bonded via other groups, and the other groups are the same as those of the diaminodiphenyl compound. Examples of diaminotriphenyl compounds include 1,3-bis (m-aminophenoxy) benzene, 1,3-bis (p-aminophenoxy) benzene, 1,4-bis (p-aminophenoxy) benzene, and the like. be able to.

  Examples of diaminonaphthalene include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

  Examples of aminophenylaminoindane include 5 or 6-amino-1- (p-aminophenyl) -1,3,3-trimethylindane.

  Examples of diaminotetraphenyl compounds include 4,4'-bis (p-aminophenoxy) biphenyl, 2,2'-bis [p- (p'-aminophenoxy) phenyl] propane and 2,2'-bis [ and p- (p′-aminophenoxy) biphenyl] propane, 2,2′-bis [p- (m-aminophenoxy) phenyl] benzophenone, and the like.

  Examples of the cardo type fluorene derivative include 9,9-bisaniline fluorene.

  A compound in which the hydrogen atom of these aromatic diamines is substituted with at least one substituent selected from the group such as a halogen atom, a methyl group, a methoxy group, a cyano group, and a phenyl group may be used.

  There are no particular restrictions on the means for producing the polyamic acid and polyimide solution according to the present invention. For example, (1) a method of reacting an acid and a diamine component in an organic solvent, (2) chemical imidization or heating imidization of polyamic acid And a known method such as a method of dissolving in an organic solvent can be used.

  Solvents used here include aprotic polar solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, phenolic solvents such as cresols, glycols such as diglyme And system solvents. These solvents can be used alone or in combination of two or more. Although there is no restriction | limiting in particular in the usage-amount of a solvent, It is desirable that content of the polyimide to produce | generate shall be 5-50 mass%.

The polymerization temperature is generally −10 to 120 ° C., preferably 5 to 30 ° C.
The polymerization time varies depending on the raw material composition to be used, but is usually 3 to 24 Hr (hour).

  The intrinsic viscosity of the polyimide precursor and polyimide organic solvent solution obtained under such conditions is preferably in the range of 0.1 to 3.0 dl / g, and more preferably in the range of 0.2 to 1.5 dl / g.

  These varnishes are prepared by mixing a solvent in which silica particles are dispersed in advance and a polyamic acid solution or a polyimide solution polymerized in a solvent that can be mixed with the solvent in an arbitrary ratio, or in a solvent in which monodispersed spherical silica particles are dispersed in advance. The polyamic acid solution or the polyimide solution can be polymerized, and is preferably adjusted to 10 to 3000 poise. In the varnish adjusting step, the silica / polyimide ratio may be 2 to 6 (mass ratio). When the viscosity is out of the range, it is difficult to form a film uniformly. When the ratio of silica / polyimide is out of the range, it is difficult to stably obtain a silica-polyimide composite film due to cracking.

  In a preferred embodiment, the 3DOM polyimide film can be manufactured as follows. Silica by mixing a monodispersed spherical silica particle in advance with a polyamic acid solution or a polyimide solution in an arbitrary ratio, or polymerizing polyamic acid or polyimide in a solvent in which monodispersed spherical silica particles have been dispersed in advance. -A varnish can be manufactured so that the ratio (mass ratio) of a polyimide may be 2-6. Then, this varnish is formed on the substrate with an arbitrary film thickness so that the final film thickness is 5 to 500 μm, dried and peeled off from the substrate, and heated or chemically post-treated to complete imidization. Thus, a silica-polyimide composite film can be produced. Finally, the silica in the composite film is eluted and removed with hydrogen fluoride water to obtain 3DOM polyimide having continuous holes arranged in a three-dimensional order.

  The film-like 3DOM polyimide film obtained as described above has fine pores regularly arranged in three dimensions, and the porosity of the membrane is 50% or more, preferably 85% or less. The average diameter is 100 to 2000 nm, and the polyimide phase and the spatial phase form fine communication holes in the membrane or the like, and the diameter of the communication holes is 1000 nm or less, preferably 10 nm or more.

In a preferred example of the 3DOM polyimide film, the polyimide to be used is a polyamic acid represented by the repeating unit represented by the formula (1) obtained by thermal or chemical ring closure reaction, or a repeating unit represented by the formula (2). The polyimide shown may be dissolved in a solvent. Ar represents an aryl group.

  The 3DOM polyimide film can be formed into a film having an average film thickness of 10 to 300 μm. Preferably, the 3DOM polyimide film has a mass loss of at least 5% even in heat resistance of 350 ° C. or higher.

  In this production method, it is also possible to obtain a film having a side of 5 cm or more by applying to a large area substrate, and using a normal polyimide film production apparatus, a roll having a width of 5 cm or more. Can also be obtained.

The physical properties of the polyimide porous membrane were determined by the following measurement method.
1) Porosity
Porosity [%] = 100-(W / (A x L x d)) x 100
(Wherein, W is the mass of the film, A is the apparent area of the film, L is the film thickness, and d is the density of the polyimide.)
2) Micropore diameter The diameters D1 and D2 of the micropores P1 and P2 as shown in FIG. From the scanning electron microscope (SEM) photograph of the surface of the porous film, the diameters of the openings at a plurality of points were measured, and the average value was calculated.
3) Diameter of communication hole Refers to the diameter D3 of the communication hole Q of the fine holes P1 and P2 as shown in FIG. From the scanning electron micrograph of the cross section of the porous film, the diameter was measured for a plurality of apertures, and the average value was calculated.
4) Td 5% (5% mass loss temperature)
Measurement was performed under a nitrogen atmosphere using a TGA-60 manufactured by Shimadzu Corporation at a measurement temperature RT (room temperature) to 800 ° C., a temperature increase rate of 10 ° C./min.

  For a general description of a method for producing a porous polyimide comprising a varnish (resin composition) production process, a composite film production process, and a silica removal process, JP-A-11-21369, JP-T 2002-544331, JP It is described in Kaikai 2004-292537. Examples of resins other than polyimide are described in JP-A-56-8442, etc., where a silica / PVA mass ratio of 0.5 to 5 is used.

  30 parts by mass of monodispersed spherical silica particles (true sphere ratio: 1.0, particle size distribution index: 1.20) with an average diameter of 550 nm manufactured by Nippon Shokubai Co., Ltd. are dispersed in 30 parts by mass of dimethylacetamide, A mass part was produced. At the same time, a polyamic acid solution (B) was prepared by polymerizing pyromellitic dianhydride (PMDA) and diaminodiphenyl ether (ODA) at a molar ratio of 0.990 in dimethylacetamide. (B) had a B-type viscosity of 1500 P (poise) and a solid content concentration of 18% by mass. 60 parts by mass of (A) solution and 41.67 parts by mass of (B) solution were mixed and mixed so that the ratio of silica / polyimide was 4/1. Mixing was performed using a CONDITIONING MIXER AR-500 (conditioning mixer, AR-500) manufactured by THINKY (Shinky Co., Ltd.), with stirring at 1000 rpm × 5 minutes and defoaming at 1800 rpm × 3 minutes. This varnish was formed at a thickness of 250 μm on a glass plate spin-coated with a phosphate ester release agent. Film formation was performed with a doctor blade using an automatic film forming apparatus in an area of 10 cm × 10 cm. Leave this at room temperature for 5 hours, wait until the film spontaneously peels off from the glass plate, remove the release agent with methanol after peeling, then fix it to the SUS mold, 100 ° C → 200 ° C → 300 ° C → Heat treatment was performed stepwise at 400 ° C. to complete imidization, and a silica-polyimide composite film was obtained. The silica-polyimide composite film was immersed in 10% by mass hydrogen fluoride water, and the silica was dissolved and removed over 6 hours. After removal, it was carefully washed with water to obtain a 3DOM polyimide film. A cross-sectional SEM image of the obtained polyimide porous membrane is shown in FIG. Table 1 shows the physical properties.

  A monodispersed spherical silica particle (true sphere ratio: 1.0, particle size distribution index: 1.20) with an average diameter of 550 nm manufactured by Nippon Shokubai Co., Ltd. is dispersed in dimethylacetamide. (A) After preparing the solution, Pyromellitic dianhydride and diaminodiphenyl ether were added at a molar ratio of 0.990, mixed and then polymerized to prepare a varnish having a silica / polyimide ratio of 4/1. About this varnish, the same method as the film forming after Example 1 was performed, and a 3DOM polyimide film was obtained. Table 1 shows the physical properties.

  A 3DOM polyimide film was obtained by the method described in Example 1, using 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (S-BPDA) and p-phenylenediamine (PDA) as raw materials for the varnish. . Table 1 shows the physical properties.

  The monodispersed spherical silica particles used were changed to an average diameter of 1500 nm (true sphere ratio: 1.0, particle size distribution index: 1.20), and a 3DOM polyimide film was obtained by the method described in Example 1. Table 1 shows the physical properties.

[Comparative Example 1]
Polyamic acid obtained by polymerizing pyromellitic dianhydride and diaminodiphenyl ether at a molar ratio of 0.990 is formed on a glass plate, and the solvent is extracted with methanol to form a porous body. Acquired. A cross-sectional SEM image of the obtained polyimide porous membrane is shown in FIG. Table 1 shows the physical properties.

[Comparative Example 2]
A porous polyimide film was obtained in the same manner as in Example 1 using silica having an average diameter of 550 nm, a sphericity ratio of 1.72, and a particle size distribution index of 1.80. A SEM image is shown in FIG.

  As shown in FIG. 2 and Table 1, in the example, a 3DOM polyimide film having regular continuous fine pores is obtained, which is very useful in separators, electrolyte membranes, and the like. In the comparative example, continuous fine pores were obtained, but the pore size variation was large, which was insufficient for use as a separator or electrolyte membrane.

  3DOM polyimide membrane provides a porous membrane with three-dimensional regular array of continuous micropores and a porosity of 70% or more, and separators and fuel cell electrolyte membranes that require stable physical properties. It can also be used as a dielectric material.

P1, P2 Micro hole Q Communication hole D1, D2, D3 Diameter

Claims (3)

A varnish production process for producing a varnish by mixing polyamic acid or polyimide, silica particles and a solvent, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed, and
A composite film production process for producing a polyimide-silica composite film by completing imidization after film formation of the varnish produced in the varnish production process on a substrate;
In the method for producing a porous polyimide film having a silica removal step of removing silica of the polyimide-silica composite membrane produced in the composite membrane production step,
Silica particles having a sphericity ratio of 1.0 to 1.1, a particle size distribution index (d ₂₅ / d ₇₅ ) of 1.5 or less, and an average diameter of 100 to 2000 nm are used as the silica particles, and the polyimide-silica A method for producing a porous polyimide film, wherein the mass ratio of silica / polyimide in the composite film is 2-6.   The porous polyimide film has a porosity of 50% or more, micropores having an average diameter of 100 to 2000 nm are in contact with each other to form a communication hole, and the diameter of the communication hole is 1000 nm or less. The method for producing a porous polyimide film according to claim 1. A varnish production process for producing a varnish by mixing polyamic acid or polyimide, silica particles and a solvent, or polymerizing polyamic acid or polyimide in a solvent in which silica particles are dispersed, and
A composite film production process for producing a polyimide-silica composite film by completing imidization after film formation of the varnish produced in the varnish production process on a substrate;
Combined with the silica removal step of removing the silica of the polyimide-silica composite membrane produced in the composite membrane production step ,
The sphericity index as silica particles 1.0 to 1.1, particle size distribution index (d ₂₅ / d ₇₅₎ is the Rukoto with 1.5 following silica particles,
Micropores having a porosity of 50% or more and an average diameter of 100 to 2000 nm are in contact with each other to form a communication hole, and a porous polyimide film having a diameter of the communication hole of 1000 nm or less is obtained. A method for producing a porous polyimide film.

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