JP2016216695A - Method of producing porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a porous film enabling resin fine particles to be removed well from a film containing the resin fine particles by thermal decomposition or sublimation with heating.SOLUTION: The method of producing a porous film is provided which comprises a step (1) of laminating a layer (X) comprising (A1) organic fine particles and a layer (Y) comprising (A2) inorganic fine particles to form a laminated film (Z), a step (2) of removing the (A1) the organic fine particles and the (A2) inorganic fine particles from the laminated film (Z), the (A1) organic fine particles being removed by thermal decomposition or sublimation with heating in the step (2). In the method of producing a porous film, a matrix of the layer (X) contains a material which is thermally decomposed or sublimated at lower temperature than matrix of the layer (Y), and the (A1) organic fine particles composed of the material which is thermally decomposed or sublimated at lower temperature than the matrix of the layer (Y) is used.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a porous membrane.

  Conventionally, various porous membranes have been used for applications such as filters. In recent years, the porous membrane has also been applied to separator applications for secondary batteries such as lithium batteries.

  For example, as a method for producing a porous film of polyimide used for a separator, a varnish in which silica particles are dispersed in a solution of polyamic acid or polyimide is coated on a substrate, and then the coated film is heated as necessary. There is known a method of obtaining a polyimide film containing silica particles and then dissolving silica in the polyimide film in hydrofluoric acid (Patent Document 1).

JP 2012-107144 A

  However, hydrofluoric acid is corrosive and difficult to handle, and its use is problematic in terms of the environment. Therefore, it is desired to reduce the amount of hydrofluoric acid used in the production of the porous membrane. Examples of the method for reducing the amount of hydrofluoric acid used include a method in which at least a part of inorganic particles such as silica used for the production of the porous membrane is replaced with thermally decomposable organic fine particles.

  However, according to the study of the present inventor, organic fine particles are contained after thermally decomposable organic fine particles are dispersed in a film made of a resin having high heat resistance such as polyimide resin or a precursor of a heat resistant resin. When heating the heat, only a part of the organic fine particles can be removed from the film, and it has been found that a porous film having a desired porosity cannot be obtained.

  The present invention has been made in view of the above-described problems, and provides a method for producing a porous film that can favorably remove resin fine particles from a film containing resin fine particles by thermal decomposition by heating or sublimation. For the purpose.

  The present inventors (1) (A1) laminating a layer (X) containing organic fine particles and (A2) a layer (Y) containing inorganic fine particles to form a laminated film (Z); 2) A method of removing (A1) organic fine particles and (A2) inorganic fine particles from the laminated film (Z), and (A1) removing organic fine particles by thermal decomposition or sublimation in step (2). The material of the layer (X) contains a material that thermally decomposes or sublimes at a lower temperature than the matrix of the layer (Y), and is made of a material that decomposes or sublimes at a lower temperature than the matrix of the layer (Y) (A1). ) It has been found that the above problems can be solved by using organic fine particles, and the present invention has been completed.

The present invention is a method for producing a porous membrane,
(1) (A1) laminating a layer (X) containing organic fine particles and (A2) a layer (Y) containing inorganic fine particles to form a laminated film (Z);
(2) a step of removing (A1) organic fine particles and (A2) inorganic fine particles from the laminated film (Z),
In the step (2), (A1) the organic fine particles are removed by thermal decomposition or sublimation,
The matrix of the layer (X) comprises a material that pyrolyzes or sublimes at a lower temperature than the matrix of the layer (Y);
(A1) The present invention relates to a method in which organic fine particles are thermally decomposed or sublimated at a lower temperature than the matrix of the layer (Y).

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the porous membrane which can remove resin fine particle favorably by thermal decomposition by heating or sublimation from the film | membrane containing resin fine particle can be provided.

It is a figure which shows typically preferable embodiment of this invention. 2 is a diagram showing an electron microscope observation image of the surface of a porous film obtained in Example 1. FIG. FIG. 4 is an electron microscope observation image of the surface of the porous film obtained in Example 2. It is a figure which shows the electron microscope observation image of the surface of the heat-processed film | membrane obtained in the comparative example 1. FIG. It is a figure which shows the electron microscope observation image of the surface of the heat-processed film | membrane obtained in the comparative example 2. FIG.

The method for producing a porous membrane according to the present invention includes the following steps (1) and (2).
(1) A step of laminating a layer (X) containing (A1) organic fine particles and a layer (Y) containing (A2) inorganic fine particles to form a laminated film (Z).
(2) A step of removing (A1) organic fine particles and (A2) inorganic fine particles from the laminated film (Z).

  In step (2), (A1) organic fine particles are removed by thermal decomposition or sublimation. Further, the matrix of the layer (X) includes a material that is thermally decomposed or sublimated at a lower temperature than the matrix of the layer (Y). (A1) The organic fine particles include a material that is thermally decomposed or sublimated at a lower temperature than the matrix of the layer (Y).

  In addition, when the matrix of the layer (Y) includes a plurality of materials, regarding the requirement that pyrolysis or sublimation at a lower temperature than the matrix of the layer (Y), among the materials included in the matrix of the layer (Y), Based on the pyrolysis temperature or sublimation temperature of the material having the highest pyrolysis temperature or sublimation temperature.

For example, when a layer composed of a matrix material having high heat resistance such as a polyimide resin and (A1) organic fine particles dispersed in the matrix material is heated to (A1) above the thermal decomposition or sublimation temperature of the organic fine particles, (A1) It is difficult to remove organic fine particles from the layer.
This is presumably because (A1) the heat-resistant matrix material covering the periphery of the organic resin fine particles inhibits the decomposition product or the sublimation product from falling out of the layer.

However, in the method of the present invention, the matrix of layer (X) comprises a material that pyrolyzes or sublimes at a lower temperature than the matrix of layer (Y). For this reason, when (A1) organic fine particles are removed from the layer (X) by heating, at least a part of the matrix of the layer (X) is also thermally decomposed or sublimated. Then, by the decomposition or sublimation of the matrix, a fine channel through which the decomposition product or sublimation product of (A1) organic fine particles can flow is formed in the layer (X).
In the method of the present invention, the above-mentioned fine flow path is formed in the layer (X), so that the thermal decomposition product and sublimation product of the organic fine particles can be removed well from the layer (X).

  Hereinafter, step (1) and step (2) will be described in order.

≪Process (1) ≫
As described above, in step (1), (A1) layer (X) containing organic fine particles and (A2) layer (Y) containing inorganic fine particles are laminated to form a laminated film (Z).
The layer (X) is usually formed by applying a varnish containing (A1) organic fine particles, a matrix material, and a solvent for dissolving the matrix material on the substrate.
The layer (Y) is usually formed by applying a varnish containing (A2) inorganic fine particles, a matrix material, and a solvent for dissolving the matrix material on the layer (X).
Hereinafter, the layer (X) and the layer (Y) will be described in order.

[Layer (X)]
Hereinafter, essential components such as (A1) organic fine particles, a matrix material, and a solvent for dissolving the matrix material, and optional components such as a dispersant, which are included in the varnish for forming the layer (X) will be described. In addition, a method for forming the layer (X) will be described.

<(A1) Organic fine particles>
(A1) The material of the organic fine particles is not particularly limited as long as it is a material that does not dissolve in the solvent contained in the varnish for forming the layer (X) and does not become compatible with the matrix of the layer (X) when heated. .
(A1) Organic fine particles are made of high molecular weight olefin polymers (polypropylene, polyethylene, polybutadiene, polyisoprene, polytetrafluoroethylene, etc.), aromatic vinyl polymers such as polystyrene, acrylic resins (methyl methacrylate, methacrylic acid). Organic polymers such as isobutyl, polymethyl methacrylate (PMMA), epoxy resin, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, and polyether. These organic polymers may be copolymers. Further, (A1) organic fine particles of different materials may be used in combination.

(A1) The material of the resin fine particles is not limited to the above specific example, and can be selected from, for example, a normal linear polymer or a known depolymerizable polymer according to the purpose.
A normal linear polymer is a polymer in which molecular chains of the polymer are randomly cut during thermal decomposition. The depolymerizable polymer is a polymer that decomposes into a monomer upon thermal decomposition. Any of them can be removed from the layer (X) by being decomposed into monomers, low molecular weight substances, or CO ₂ upon heating.

  (A1) The thermal decomposition temperature or sublimation temperature of the resin fine particles is preferably 400 ° C. or lower, more preferably 200 to 320 ° C., and further preferably 230 to 260 ° C. When the thermal decomposition temperature or sublimation temperature is 200 to 320 ° C., (A1) the resin fine particles are easily removed from the layer (X) while suppressing damage due to heat applied to the matrix of the layer (Y).

  Among the above depolymerizable polymers, methyl methacrylate having a low thermal decomposition temperature or isobutyl methacrylate alone (polymethyl methacrylate or polyisobutyl methacrylate) or a copolymer having a main component thereof is used by heating. (A1) It is preferable in that the resin fine particles can be easily removed from the layer (X).

  Moreover, as a material of (A1) resin fine particles, a polyoxyalkylene resin is also preferable. Polyoxyalkylene resins are easily decomposed into low molecular weight hydrocarbons, ethers, etc. by heating. The resin fine particles (A1) containing the polyoxyalkylene resin are easily removed from the layer (X) by heating.

The polyoxyalkylene resin is not particularly limited. The polyoxyalkylene resin preferably contains polyoxypropylene, polyoxyethylene, or polyoxytetramethylene because (A1) resin fine particles are easily decomposed by heating. Among these, polyoxypropylene is more preferable.
In particular, the polyoxyalkylene resin preferably contains 5% by weight or more of polyoxypropylene because thermal decomposition is easy.

  Examples of the polyoxyalkylene resin include MS polymer (registered trademark) S-203, S-303, and S-903 (manufactured by Kaneka Corporation); Silyl (registered trademark) SAT-200, MA-403, and MA -447 (manufactured by Kaneka Co., Ltd.); Epion (registered trademark) EP103S, EP303S, and EP505S (manufactured by Kaneka Corporation); Commercially available resins such as those manufactured by the company can be used.

  (A1) The material of the resin fine particles may contain the above acrylic resin together with the polyoxyalkylene resin. Examples of acrylic resins include homopolymers of monomers such as ethyl acrylate, propyl acrylate, n-butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate. A copolymer is mentioned.

(A1) The acrylic resin or polyoxyalkylene resin, which is a material of the resin fine particles, may be one in which crosslinking is introduced by a crosslinkable monomer. When (A1) resin fine particles are made of a material into which cross-linking is introduced, (A1) compatibilization of resin fine particles with various materials contained in layers (X) and (Y), or (A1) resin fine particles It is easy to suppress swelling due to the solvent.
Examples of the crosslinkable monomer include acrylic polyfunctional monomers such as trimethylolpropane tri (meth) acrylate and divinylbenzene.

  (A1) The resin fine particles may contain a decomposition accelerator in order to promote thermal decomposition by heating. The decomposition accelerator is not particularly limited, and various additives conventionally used for promoting thermal decomposition of resins can be used. Specific examples of the decomposition accelerator include peroxides such as benzoyl peroxide and lauroyl peroxide; 2,2′-azobisisobutyronitrile, 2-carbamoylazoformamide, and 1,1′-azo. Examples include azo compounds such as biscyclohexane-1-carbonitrile.

  (A1) The number average molecular weight of the resin fine particles is not particularly limited. The lower limit of the number average molecular weight is preferably 300. The upper limit of the number average molecular weight is preferably 1,000,000.

(A1) The shape of the resin fine particles is not particularly limited, but spherical fine particles are preferable, and those having a high true sphericity are more preferable.
(A1) The particle diameter (average diameter) of the resin fine particles is not particularly limited. For example, the average diameter is preferably 10 to 2000 nm, more preferably 50 to 1500 nm, and more preferably 100 to 1000 nm.
The average diameter of (A1) resin fine particles and the average diameter of (A2) inorganic fine particles contained in the layer (Y) described later may be the same or different from each other, and the resulting porous membrane It may be changed as appropriate in consideration of the strength or uniformity of the pores, the particle size distribution index of each particle, or the like.

  The particle size distribution index (d25 / d75) of the resin fine particles (A1) may be appropriately changed according to the use application of the porous membrane, and is preferably 1 to 6, for example, and more preferably 1 to 3. In addition, d25 and d75 are values of particle diameters in which the cumulative frequency of the particle size distribution is 25% and 75%, respectively, and in this specification, d25 is the larger particle diameter.

The particle size distribution index of (A1) resin fine particles and the particle size distribution index of (A2) inorganic fine particles contained in the layer (Y) described later may be the same or different from each other. .
When the average pore diameter of (A1) resin fine particles and (A2) inorganic fine particles contained in the layer (Y) to be described later is the same, by using particles having different particle size distribution indexes, the same particle size distribution index The specific surface area of the pores can be increased as compared with the case where is used.

  The ratio of the (A1) resin fine particles in the volume of the layer (X) is not particularly limited, but the volume ratio is preferably 40 to 95%, more preferably 50 to 90%, further preferably 55 to 85%, and 65 to 81. % Is particularly preferred. When the layer (X) contains (A1) resin fine particles at such a ratio, the porosity corresponding to the layer (X) portion of the resulting porous membrane is sufficient. Further, it is easy to uniformly disperse the resin fine particles (A1) in the layer (X) without aggregating them.

<Matrix material>
As a matrix material contained in the varnish for forming the layer (X), a material soluble in a solvent described later is selected. The matrix material also includes a material that is pyrolyzed or sublimated at a lower temperature than the matrix of the layer (Y).
Hereinafter, a material that thermally decomposes or sublimes at a lower temperature than the matrix of the layer (Y) is also referred to as a “low heat resistant material”.

  Examples of the low heat-resistant material include (A1) organic polymers listed as materials for organic fine particles. As the low heat resistant material, (A1) a material incompatible with the organic fine particle material is selected. This is because (A1) the organic fine particles and the matrix of the layer (X) are not made compatible when the layer (X) is heated.

  For example, (A1) As a suitable combination of the material of the organic fine particles and the low heat-resistant material layer, a combination of cellulose and an acrylic resin, a copolymer of cellulose, an aromatic vinyl monomer, and an olefin (for example, styrene / butadiene) And a combination thereof. In this case, the acrylic resin is preferably a cross-linked acrylic resin because it has low compatibility with other materials contained in the layer (X) and the layer (Y) and is difficult to swell with a solvent.

The thermal decomposition temperature or sublimation temperature of the matrix material contained in the layer (X) is preferably 400 ° C. or lower, more preferably 200 to 320 ° C., and further preferably 230 to 260 ° C. When the thermal decomposition temperature or sublimation temperature is 200 to 320 ° C., the matrix material can be removed from the layer (X) while suppressing damage due to heat applied to the layer (Y) matrix.
When the matrix material includes a plurality of materials, the thermal decomposition temperature or sublimation temperature of the matrix material is the lowest temperature among the thermal decomposition temperatures or sublimation temperatures of the plurality of materials.

The matrix material is a material that is thermally decomposed or sublimated at a temperature equal to or higher than the thermal decomposition temperature or sublimation temperature of the matrix of the layer (Y) together with the resin that is decomposed or sublimated at a relatively low temperature, and that is not easily decomposed or sublimated even at a high temperature. May be included.
Hereinafter, a material that undergoes thermal decomposition or sublimation at a temperature equal to or higher than the thermal decomposition temperature or sublimation temperature of the matrix of the layer (Y) is also referred to as “high heat resistant material”.
As an example of the high heat resistance material, a matrix material included in a layer (Y) described later can be given.

  When the matrix material included in the layer (X) includes a low heat resistant material and a material that thermally decomposes or sublimes at a temperature equal to or higher than the thermal decomposition temperature or sublimation temperature of the matrix of the layer (Y), (A1) resin fine particles; By removing the low heat resistant material from the layer (Y) by heating, a layer derived from the layer (Y) and made of the high heat resistant material is formed.

<Solvent>
The solvent contained in the varnish for forming the layer (X) is not particularly limited as long as (A1) the organic fine particles are not dissolved and the matrix material is dissolved. The solvent is appropriately selected according to the material of (A1) organic fine particles and the type of matrix material.
As the solvent, an organic solvent is usually used. When the matrix material is a water-soluble material, water or an aqueous solution of an organic solvent can be used as the solvent.

Preferable examples of the solvent contained in the varnish for forming the layer (X) include polar solvents and water-soluble solvents, such as methyl alcohol, ethyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2 -Butanol, 2-methyl-1-propanol, 1-pentanol, 2-pentanol, 4-methyl-2-pentanol, 1,1-dimethylethanol, 2,2-dimethyl-1-propanol, tetrahydrofurfuryl Alcohols such as alcohol; organic solvents such as glycols such as ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and diethylene glycol are exemplified, and alcohols are preferable. When these organic solvents are water-soluble, the organic solvent may be used as an aqueous solution.
3-50 mass% is preferable and, as for the solid content density | concentration of a varnish, More preferably, it is 5-40 mass%.

<Dispersant>
The varnish for forming the layer (X) may contain a dispersant in order to satisfactorily disperse the (A1) resin fine particles. A well-known thing can be used for a dispersing agent, without being specifically limited. For example, palm fatty acid salt, castor sulfate oil salt, lauryl sulfate salt, polyoxyalkylene allyl phenyl ether sulfate salt, alkylbenzene sulfonic acid, alkylbenzene sulfonate, alkyl diphenyl ether disulfonate, alkylnaphthalene sulfonate, dialkyl sulfosuccinate Anionic surfactants such as nate salt, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salt, polyoxyethylene allyl phenyl ether phosphate salt; oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride , Behenyltrimethylammonium chloride, didecyldimethyl Cationic surfactants such as ammonium chloride; amphoteric surfactants such as coconut alkyldimethylamine oxide, fatty acid amidopropyldimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amidobetaine type activator, alanine type activator, lauryliminodipropionic acid Agent: polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene lauryl amine, polyoxyethylene oleylamine, polyoxyethylene polystyryl phenyl ether, polyoxyalkylene polystyryl phenyl ether, polyoxy Nonionic surfactant of alkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether, polyoxyethylene dilaur , Polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, fatty acid diethanolamide and other nonoxyalkylene nonions Surfactants; fatty acid alkyl esters such as octyl stearate and trimethylolpropane tridecanoate; and polyether polyols such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether and trimethylolpropane tris (polyoxyalkylene) ether However, it is not limited to these. Moreover, the said dispersing agent can also be used in mixture of 2 or more types.

<Other ingredients>
In addition to the above-mentioned components, antistatic agents, flame retardants, chemical imidizing agents, condensing agents, release agents for the purpose of antistatic, imparting flame retardancy, low-temperature firing, imparting release properties, improving coatability, etc. A known component such as a surface conditioner can be appropriately added to the varnish as necessary.

<Formation method of layer (X)>
The layer (X) is, for example, directly applied to a varnish on a substrate such as a glass substrate, and 0 to 120 ° C. (preferably 0 to 90 ° C.) under normal pressure or vacuum, more preferably 10 to 10 at normal pressure. It is formed by drying the coating film at 100 ° C. (more preferably 10 to 90 ° C.).
For example, the thickness of the layer (X) is preferably 0.1 to 50 μm, and more preferably 0.5 to 5 μm.

[Layer (Y)]
Hereinafter, the essential components such as (A2) inorganic fine particles, the matrix material, and the solvent for dissolving the matrix material, and the optional components such as the dispersant, which are contained in the varnish for forming the layer (Y) will be described. A method for forming the layer (Y) will be described.

<(A2) Inorganic fine particles>
As long as (A2) inorganic fine particles can be removed from the layer (Y) by a method such as chemical treatment or heating, the material of the (A2) inorganic fine particles is not particularly limited. (A2) Examples of the material of the inorganic fine particles include metal oxides such as silica (silicon dioxide), calcium carbonate, titanium oxide, and alumina (Al ₂ O ₃ ).
Preferred (A2) inorganic fine particles include silica fine particles such as calcium carbonate and colloidal silica.

(A2) The shape of the inorganic fine particles is not particularly limited, and may be spherical particles or plate-like particles, but spherical particles are preferable, and those having a high true sphericity are more preferable.
(A2) The particle size (average diameter) of the inorganic fine particles is not particularly limited. For example, the average diameter is preferably 10 to 2000 nm, more preferably 100 to 1500 nm, and more preferably 200 to 1200 nm.

  Moreover, 1-6 are preferable and, as for the particle size distribution index (d25 / d75) of (A2) inorganic fine particle, 1-5 are more preferable.

  The ratio of the (A2) inorganic fine particles in the volume of the layer (Y) is not particularly limited, but the volume ratio is preferably 40 to 95%, more preferably 50 to 90%, still more preferably 55 to 85%, and 65 to 81. % Is particularly preferred. When the layer (Y) contains (A2) inorganic fine particles in such a ratio, the porosity corresponding to the layer (Y) portion of the resulting porous film is sufficient. Moreover, it is easy to disperse | distribute uniformly (A2) inorganic fine particles in a layer (Y), without aggregating.

<Matrix material>
The matrix material contained in the layer (Y) is (A1) in the varnish for forming the layer (Y) without thermal decomposition or sublimation at the heating temperature when the resin fine particles are removed from the layer (X) by heating. If it is a soluble material, it will not specifically limit.
The matrix material may be a highly heat-resistant resin material or a thermosetting resin precursor that generates a highly heat-resistant resin by heating. The precursor of the thermosetting resin may be a polymer compound or a mixture of low-molecular monomers.

Suitable examples of the matrix material contained in the layer (Y) include polyimide resins, polyimide resins that are precursors of polyimide resins, polybenzoxazole resins, precursor polymers of polybenzoxazole resins, polybenzimidazole resins, Examples thereof include a precursor polymer of polybenzimidazole resin, aromatic nylon, polyvinylidene fluoride resin, and polyarylsulfone. The polyimide resin includes a polyimide resin and a polyamideimide resin.
Among these matrix materials, polyamic acid, polyimide resin, polyamideimide resin, and polyamideimide resin can be prepared because the varnish is easy to prepare and the resulting porous film is excellent in mechanical properties and thermal properties. Polyamic acid which is a precursor of is preferable.
Hereinafter, polyamic acid, which is a precursor of polyamic acid, polyimide resin, polyamidoimide resin, and polyamidoimide resin, which is suitable as a matrix material included in the layer (Y) will be described.

(Polyamide acid)
As the polyamic acid, one obtained by polymerizing an arbitrary tetracarboxylic dianhydride and diamine can be used without any particular limitation. Although the usage-amount of tetracarboxylic dianhydride and diamine is not specifically limited, It is preferable to use 0.50-1.50 mol of diamine with respect to 1 mol of tetracarboxylic dianhydrides, and 0.60-1. It is more preferable to use 30 mol, and it is particularly preferable to use 0.70 to 1.20 mol.

  The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides conventionally used as raw materials for synthesizing polyamic acid. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. From the viewpoint of the heat resistance of the resulting polyimide resin, the aromatic tetracarboxylic dianhydride may be used. Preference is given to using carboxylic dianhydrides. Tetracarboxylic dianhydride may be used in combination of two or more.

  Preferable specific examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxy). Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′- Biphenyltetracarboxylic dianhydride, 2,2,6,6-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2 , 3-Dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2- Bis (2,3-dicarboxy Enyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) Ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 4,4- (p-phenylenedioxy) diphthal Acid dianhydride, 4,4- (m-phenylenedioxy) diphthalic dianhydride, 1,2,5,6-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic acid di Anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride , 2, 3 6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bisphthalic anhydride fluorene, 3,3 ′, 4,4′-diphenylsulfone Tetracarboxylic dianhydride etc. are mentioned. Examples of the aliphatic tetracarboxylic dianhydride include, for example, ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 1, 2, Examples include 4,5-cyclohexanetetracarboxylic dianhydride and 1,2,3,4-cyclohexanetetracarboxylic dianhydride. Among these, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoint of price and availability. These tetracarboxylic dianhydrides can be used alone or in combination of two or more.

  The diamine can be appropriately selected from diamines conventionally used as a raw material for synthesizing polyamic acid. This diamine may be an aromatic diamine or an aliphatic diamine, but an aromatic diamine is preferred from the viewpoint of the heat resistance of the resulting polyimide resin. These diamines may be used in combination of two or more.

  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, diaminobiphenyl compounds 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, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

  Phenylenediamine is m-phenylenediamine, p-phenylenediamine, etc., and phenylenediamine derivatives include diamines to which alkyl groups such as methyl group and ethyl group are bonded, such as 2,4-diaminotoluene, 2,4-triphenylene. Diamines and the like.

  The diaminobiphenyl compound is a compound in which two aminophenyl groups are bonded to each other. For example, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl, and the like.

  The diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other via other groups. 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 in the alkylene group substituted with halogen atoms or the like.

  Examples of diaminodiphenyl compounds include 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl 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-aminophenyl) phosphine oxide, 4,4′- Diaminoazobenzene, 4,4′-diaminodiphenylurea, 4,4′-diaminodiphenylamide, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3 -Bis (3-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] Sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophene) ) Phenyl] hexafluoropropane, and the like.

  Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferable from the viewpoint of price and availability.

  The diaminotriphenyl compound is obtained by bonding two aminophenyl groups and one phenylene group via other groups, and the other groups are the same as those of the diaminodiphenyl compounds. 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, 2,2′-bis [ p- (p′-aminophenoxy) biphenyl] propane, 2,2′-bis [p- (m-aminophenoxy) phenyl] benzophenone, and the like.

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

  Aliphatic diamines having, for example, about 2 to 15 carbon atoms are preferred, and specific examples include pentamethylene diamine, hexamethylene diamine, and heptamethylene diamine.

  A compound in which the hydrogen atom of these 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 is no restriction | limiting in particular in the means to manufacture the polyamic acid used by this invention, For example, well-known methods, such as the method of making an acid and a diamine component react in an organic solvent, can be used.

  Reaction of tetracarboxylic dianhydride and diamine is normally performed in an organic solvent. The organic solvent used for the reaction of the tetracarboxylic dianhydride and the diamine is particularly capable of dissolving the tetracarboxylic dianhydride and the diamine and not reacting with the tetracarboxylic dianhydride and the diamine. It is not limited. An organic solvent can be used individually or in mixture of 2 or more types.

  Examples of the organic solvent used for the reaction of tetracarboxylic dianhydride and diamine include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N Nitrogen-containing polar solvents such as N, N-diethylformamide, N-methylcaprolactam, N, N, N ′, N′-tetramethylurea; β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone Lactone polar solvents such as γ-caprolactone and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, ethyl Ethers such as cellosolve acetate; include phenolic solvents cresols, and the like. These organic solvents can be used alone or in admixture of two or more. Of these, a combination of the nitrogen-containing polar solvent and the lactone polar solvent is preferable. Although there is no restriction | limiting in particular in the usage-amount of an organic solvent, It is desirable for content of the polyamic acid to produce | generate to be 5-50 mass%.

  Among these organic solvents, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N- Nitrogen-containing polar solvents such as diethylformamide, N-methylcaprolactam, N, N, N ′, N′-tetramethylurea are preferred. Further, from the viewpoint of film formability and the like, it may be a mixed solvent to which a lactone polar solvent such as γ-butyrolactone is added, and is preferably added in an amount of 1 to 20% by mass with respect to the whole organic solvent, and 5 to 15% by mass. % Is more preferable.

  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). Further, the intrinsic viscosity of the polyamic acid solution obtained under such conditions is preferably in the range of 1000 to 100,000 cP (centipoise), and more preferably in the range of 5000 to 70000 cP.

(Polyimide resin)
Any known polyimide resin can be used as long as it is a polyimide resin that can be dissolved in the organic solvent used for the varnish, without being limited by its structure or molecular weight. About a polyimide resin, you may have a functional group which accelerates | stimulates a crosslinking reaction etc. at the time of baking, or a functional group which can be condensed, such as a carboxy group.

  Use of a monomer to introduce a flexible bending structure into the main chain in order to obtain a polyimide resin soluble in an organic solvent, for example, ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane Aliphatic diamines such as 4,4′-diaminodicyclohexylmethane; 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3′-dimethoxybenzidine, 4,4′-diaminobenzanilide Aromatic diamines such as; polyoxyethylene diamine, polyoxypropylene diamine, polyoxyalkylene diamine such as polyoxybutylene diamine; polysiloxane diamine; 2,3,3 ′, 4′-oxydiphthalic anhydride, 3,4,3 ', 4'-oxydiphthalic anhydride, 2,2-bis (4 Hydroxyphenyl) propane dibenzoate-3,3 ', use of such 4,4'-tetracarboxylic dianhydride is valid. In addition, use of a monomer having a functional group that improves solubility in an organic solvent, for example, 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl, 2-trifluoromethyl-1,4 -It is also effective to use a fluorinated diamine such as phenylenediamine. Furthermore, in addition to the monomer for improving the solubility of the polyimide resin, the same monomer as described in the column for the polyamic acid can be used in combination as long as the solubility is not inhibited.

There is no particular limitation on the means for producing a polyimide resin that can be dissolved in an organic solvent used in the present invention. For example, a known method such as a method in which polyamic acid is chemically imidized or heated imidized and dissolved in an organic solvent is used. Can be used. Examples of such polyimide resins include aliphatic polyimide resins (total aliphatic polyimide resins) and aromatic polyimide resins, and aromatic polyimide resins are preferred. As the aromatic polyimide resin, a polyamic acid having a repeating unit represented by the formula (1) is obtained thermally or chemically by a ring-closing reaction, or a polyimide resin having a repeating unit represented by the formula (2) is dissolved in a solvent. Things can be used. In the formula, Ar represents an aryl group.

(Polyamideimide resin and its precursor polyamic acid)
Any known polyamideimide resin can be used as long as it is a polyamideimide resin that can be dissolved in the organic solvent used in the varnish according to the present invention without being limited to its structure and molecular weight. The polyamide-imide resin may have a condensable functional group such as a carboxy group on the side chain or a functional group that promotes a crosslinking reaction or the like during firing.

  Polyamide acid, which is a precursor of polyamideimide resin, is obtained by reacting any trimellitic anhydride with diisocyanate, or obtained by reacting any reactive derivative of trimellitic anhydride with diamine. What is obtained by imidating a precursor polymer can be used without being specifically limited.

  Examples of the arbitrary trimellitic anhydride or a reactive derivative thereof include trimellitic anhydride halides such as trimellitic anhydride and trimellitic anhydride chloride, trimellitic anhydride ester, and the like.

  Examples of the optional diisocyanate include metaphenylene diisocyanate, p-phenylene diisocyanate, o-tolidine diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 4,4′-oxybis (phenylisocyanate), and 4,4′-diisocyanate. Diphenylmethane, bis [4- (4-isocyanatophenoxy) phenyl] sulfone, 2,2'-bis [4- (4-isocyanatophenoxy) phenyl] propane, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate 4,4′-diphenylmethane diisocyanate, 3,3′-dimethyldiphenyl-4,4′-diisocyanate, 3,3′-diethyldiphenyl-4,4′-diisocyanate, isophorone Diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m- xylene diisocyanate, p- xylene diisocyanate, naphthalene diisocyanate, and the like.

  As said arbitrary diamine, the thing similar to what was illustrated in description of the said polyamic acid is mentioned.

<Solvent>
In the varnish used for forming the layer (Y), since the matrix material described above is usually insoluble in water, an organic solvent is used as the solvent.
The organic solvent is not particularly limited as long as it can dissolve a matrix material such as polyamic acid or polyimide resin and does not dissolve (A2) inorganic fine particles.
Specific examples of the organic solvent include those exemplified as the solvent used for the reaction between tetracarboxylic dianhydride and diamine. An organic solvent may be used independently and may be used in combination of 2 or more type.

  5-50 mass% is preferable and, as for the solid content density | concentration of a varnish, More preferably, it is 5-40 mass%.

<Other ingredients>
Similar to the varnish for forming the layer (X), the varnish for forming the layer (Y) may contain a dispersant. Further, the varnish for forming the layer (Y) is not only the above-mentioned components, but also for the purpose of antistatic, imparting flame retardancy, low-temperature firing, imparting releasability, improving coatability, etc. In addition, a known component such as a chemical imidizing agent, a condensing agent, a release agent, and a surface conditioner may be appropriately contained as necessary.

<Method for forming layer (Y)>
The layer (Y) is obtained by applying the above varnish on the layer (X), and at 0 to 120 ° C. (preferably 0 to 90 ° C.) under normal pressure or vacuum, more preferably 10 to 100 ° C. (more preferably). Is formed by drying the coating film at 10 to 90 ° C.).
The film thickness of the layer (Y) is preferably 1 to 100 μm, for example.

As described above, when the layer (X) and the layer (Y) are stacked to form the stacked film (Z), the layer (X) is interposed between the layers (X) and (Y). It is preferable to form a mixing layer in which the matrix and the matrix of the layer (Y) are mixed.
In this case, in the mixing layer, (A1) organic fine particles are present in a mixture of the matrix of the layer (X) and the matrix of the layer (Y).
Then, when (A1) organic fine particles in the mixing layer are removed by heating, even if the matrix of the layer (X) is completely pyrolyzed or sublimated, the matrix of the layer (Y) remains in the mixing layer. Remains.
As a result, by heating the mixing layer, the mixing layer is mainly composed of a matrix of the layer (Y), and (A1) changes to a porous film having pores derived from organic fine particles.

When the mixing layer is not formed, when the organic fine particles (A1) are removed from the layer (X) by heating, the matrix of the layer (X) is heated to form pores derived from the (A1) organic fine particles. Therefore, it is necessary to adjust the heating conditions so as not to disappear completely.
However, when the mixing layer is formed, pores derived from (A1) organic fine particles are necessarily formed in the mixing layer without adjusting special heating conditions.

≪Process (2) ≫
In the step (2), (A1) organic fine particles and (A2) inorganic fine particles are removed from the laminated film (Z).
As described above, (A1) organic fine particles are removed by thermal decomposition by heating or sublimation. (A1) The heating temperature for removing the organic fine particles is not particularly limited, and is appropriately selected depending on the type of (A1) organic fine particles and the type of the matrix material of the layer (X).
(A1) The heating temperature for removing the organic fine particles is preferably 250 to 400 ° C. The heating time is not particularly limited and varies depending on the heating temperature. Typically, 10 minutes to 10 hours are preferable, 30 minutes to 8 hours are more preferable, and 1 hour to 5 hours are particularly preferable.

When heating is performed, it is preferable to hold the laminated film in a state where the layer (X) side surface of the laminated film (Z) is not in contact with the substrate or the like. For example, in a state where the laminated film (Z) is placed on the substrate so that the surface on the layer (Y) side is in contact, or in a state where the end of the laminated film (Z) is held with a fixing jig or the like It is preferred to heat the membrane.
By doing so, it is possible to prevent the resin fine particles from being fused to the substrate or the like.
In addition, before performing heat processing, you may provide the immersion process to the solvent containing water, a press process, and the drying process after the said immersion process as arbitrary processes, respectively.

  (A2) The method for removing the inorganic fine particles is not particularly limited, and the inorganic fine particles can be removed with an alkaline solution or an acidic solution depending on the properties of the matrix and the fine particles. (A2) inorganic fine particles such as silica can be removed by bringing the laminated film into contact with low-concentration hydrogen fluoride water (HF) or the like and (A2) dissolving the inorganic fine particles. Further, (A2) When the inorganic fine particles are calcium carbonate, an aqueous hydrochloric acid solution can be used instead of HF.

  Regarding the porous film that is mainly composed of the matrix of the layer (Y) and is provided with the (A1) pore A derived from the organic fine particles, the matrix of the layer (Y) is made of a polyimide resin. In that case, as a chemical etching method, treatment with a chemical etching solution such as an inorganic alkali solution or an organic alkali solution may be performed. Thereby, it is easy to form an internal communication hole, and the aperture ratio can be improved.

  Examples of the chemical etching method include treatment with a chemical etching solution such as an inorganic alkali solution or an organic alkali solution. Inorganic alkaline solutions are preferred. Examples of inorganic alkaline solutions include hydrazine solutions containing hydrazine hydrate and ethylenediamine, solutions of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, ammonia solutions, alkali hydroxides And hydrazine and 1,3-dimethyl-2-imidazolidinone as etching components. Organic alkaline solutions include primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; dimethylethanolamine And alcohol amines such as triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and alkaline solutions such as cyclic amines such as pyrrole and pihelidine.

  About the solvent of said each solution, pure water and alcohol can be selected suitably. Moreover, what added a suitable amount of surfactant can also be used. The alkali concentration is, for example, 0.01 to 20% by mass.

When processing with a chemical etching solution is performed, it is preferable to perform a cleaning step of the porous film after processing.
As washing after chemical etching, water washing alone or acid washing alone may be used, or acid washing and water washing may be combined.
Moreover, you may heat-process a porous film again for the wettability improvement to the organic solvent etc. of the surface of a porous film. The heating conditions are the same as the heating conditions in step (2).

  Hereinafter, in the specification of the present application, (A1) a hole formed by removing organic fine particles is also referred to as a hole A. Further, (A2) a hole formed by removing inorganic fine particles is also referred to as a hole B.

When the mixing layer is not formed, when removing the organic fine particles (A1) from the layer (X) by heating, in order to form the hole A, the matrix of the layer (X) is not completely lost by heating. It is necessary to adjust the heating conditions.
However, when the mixing layer is formed, the hole A is surely formed without adjusting the special heating conditions.

<< Preferred Embodiment >>
In the following, a preferred embodiment of the porous membrane manufacturing method described above will be described with reference to FIG.

Among the manufacturing methods of the porous membrane according to the present invention described above,
Step (1)
A layer (X) forming step of forming the layer (X) 11 using a first varnish containing (A1) organic fine particles 13, (B1) resin, and (C1) a solvent;
Using a second varnish containing (A2) inorganic fine particles 17, (B2) a polyimide resin and / or a polyimide resin precursor, and (C2) an organic solvent, a layer (Y And 15) forming a layer (Y),
Step (2) is
By firing the laminated film (Z) 10, the (A1) organic fine particles 13 and the (B1) resin are removed from the laminated film (Z) 10, and (B3) a polyimide resin and (A2) A firing step for obtaining a composite film comprising inorganic fine particles 17;
A method including the step (A2) of removing the inorganic fine particles 17 from the composite film is preferable.

  In this method, (A1) organic fine particles 13 and (B1) resin are incompatible, (B1) resin and (C2) organic solvent are compatible, and (A1) organic fine particles 13 (C2) It is desired that the organic solvent is incompatible.

In this method, since the (B1) resin and the (C2) organic solvent are compatible, when the layer (X) 11 and the layer (Y) 15 are laminated, the layer (X) 11 is transferred to the layer (C2). Organic solvent infiltration occurs. At this time, (C2) the organic solvent and (B2) the polyimide resin and / or the polyimide resin precursor move from the layer (Y) 15 to the layer (X) 11.
Therefore, at the interface between the layer (X) 11 and the layer (Y) 15, the mixing layer 19 containing (B1) resin and (B2) polyimide resin and / or polyimide resin precursor as a matrix is essential. It is formed

  Specifically, first, as shown in FIG. 1A, a first varnish containing (A1) organic fine particles 13, (B1) resin, and (C1) a solvent is used on a substrate. Layer (X) 11 is formed. (B1) The resin becomes the matrix 12 of the layer (X) 11.

  Next, as shown in FIG. 1B, on the layer (X) 11, (A2) inorganic fine particles 17, (B2) a polyimide resin and / or a polyimide resin precursor, and (C2) an organic solvent. A layer (Y) 15 is formed using a second varnish containing: (B2) The polyimide resin and / or polyimide resin precursor becomes the matrix 16 of the layer (Y) 15.

  After the formation of the layer (Y) 15, as shown in FIG. 1 (c), the infiltration of the (C2) organic solvent and the matrix 16 of the layer (Y) from the layer (Y) 15 into the layer (X) Thus, the mixing layer 19 is formed.

  As shown in FIG. 1D, after the laminated film (Z) 10 is peeled from the substrate 1, the laminated film (Z) 10 is attached to the heat resistant substrate 1 so that the layer (Y) 15 side contacts the substrate 1. 'Place on top. When the substrate 1 has heat resistance, the same substrate 1 and heat resistant substrate 1 'may be used.

Thereafter, as shown in FIG. 1 (e), by heating the laminated film (A) under desired conditions, (B2) the polyimide resin and / or the layer (Y) 15 and the mixing layer 19 are included. The imidization of the polyimide resin precursor proceeds to change to the polyimide resin 20, and (A1) the organic fine particles 13 and the matrix 12 of the layer (X) are removed by thermal decomposition.
(A1) By removing the organic fine particles 13 from the laminated film (Z) 10, (A1) hole A 14 derived from the organic fine particles 13 is formed in the laminated film (Z) 10.

  After the laminated film (Z) 10 is heated, the laminated film (Z) 10 is peeled off from the heat-resistant substrate 1 ′ and brought into contact with a hydrofluoric acid aqueous solution or the like, whereby (A2) the inorganic fine particles 17 are dissolved and removed. Thereby, the hole B18 derived from the (A2) inorganic fine particles 17 is formed in the laminated film (Z) 10.

  And as needed, after laminating | stacking and drying the laminated film (Z) 10, it is made to peel from the board | substrate 1 and a porous film is obtained.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to these examples.

[Example 1]
On a PET film, a varnish consisting of resin fine particles (average diameter 800 nm) made of a crosslinked polymethylmethacrylate resin, a resin (water-soluble cellulose), and an aqueous isopropanol solution having a concentration of 30% by mass was applied, and then 90 ° C. for 2 minutes. The layer (X) with a film thickness of 2 μm was formed.
The solid content concentration of the varnish used for forming the layer (X) was 8.5% by mass. Further, the mass ratio of the amount of resin fine particles to the total amount of resin and resin fine particles was 68% (volume ratio: about 72%).

Next, a polyamic acid solution (polyamide acid equivalent: 20 parts by mass, solvent: N, N-dimethylacetamide) obtained by reacting pyromellitic dianhydride and 4,4′-diaminodiphenyl ether on the layer (X), After applying silica (80 parts by mass) having an average diameter of 700 nm and varnish prepared by adding N, N-dimethylacetamide, baking was performed at 90 ° C. for 5 minutes to form a layer (Y) having a thickness of 20 μm. Thus, a laminated film (Z) was obtained.
The solid concentration of the varnish used for forming the layer (Y) was 35% by mass. The mass ratio of the amount of silica particles to the total amount of polyamic acid and silica particles was 80%, and the volume ratio was about 72%.
In Example 1, when applying the varnish for forming the layer (Y) onto the layer (X), the polyamic acid infiltrated into the layer (X) together with the solvent of the varnish. For this reason, in Example 1, the mixing layer containing water-soluble cellulose and polyamic acid was formed between the layers (X) and (Y).

After the laminated film (Z) was peeled from the PET film, the laminated film (Z) was placed on the metal substrate such that the layer (Y) side of the laminated film (Z) was in contact with the substrate.
Next, the laminated film was heated (fired) at 350 ° C. for 4 hours to imidize the polyamic acid, and resin fine particles and water-soluble cellulose were removed from the laminated film (Z) by thermal decomposition.
The fired film was immersed in an aqueous HF solution having a concentration of 10% by mass for 10 minutes to remove silica particles in the laminated film.
After removal of the silica particles, washing with water and drying were performed to obtain a porous film.

  An image obtained by observing the obtained porous membrane with an electron microscope from the layer (X) side is shown in FIG. As can be seen from FIG. 2, the resin fine particles are satisfactorily removed from the laminated film (Z).

[Example 2]
A porous film was obtained in the same manner as in Example 1 except that the firing temperature of the laminated film was changed from 350 ° C. to 400 ° C.
FIG. 3 shows an image obtained by observing the obtained porous film with an electron microscope from the layer (X) side. According to FIG. 3, it can be seen that the resin fine particles are well removed from the laminated film (Z).

[Comparative Example 1]
A polyamic acid solution obtained by reacting pyromellitic dianhydride and 4,4′-diaminodiphenyl ether on a PET film (converted to polyamic acid: 55 parts by mass; solvent: N, N-dimethylacetamide) and a crosslinked poly After applying resin fine particles (average diameter 800 nm) made of methyl methacrylate resin and varnish prepared by adding N, N-dimethylacetamide, baking was performed at 90 ° C. for 5 minutes to obtain a coating film having a thickness of 20 μm. .
The solid content concentration of the varnish was 30% by mass. The mass ratio of the amount of resin fine particles to the total amount of polyamic acid and resin fine particles was 45% (volume ratio 50%).
The obtained coating film was baked at 350 ° C. for 2 hours, and then the surface of the baked coating film was observed with an electron microscope. An electron microscope audit image is shown in FIG. As can be seen from FIG. 4, when a film in which thermally decomposable resin fine particles are dispersed in polyamic acid is baked, the resin fine particles are not satisfactorily removed from the film.

[Comparative Example 2]
The varnish composition was changed so that the mass ratio of the amount of resin fine particles to the total amount of polyamic acid and resin fine particles was 40% (volume ratio 45%), and the heating was changed as follows. Evaluation was performed in the same manner as in Example 1.
After the obtained coating film was baked at 400 ° C. for 1 hour, the surface of the baked coating film was observed with an electron microscope. An electron microscope audit image is shown in FIG. According to FIG. 5, when a film in which thermally decomposable resin fine particles are dispersed in polyamic acid is fired, the resin fine particles are not removed well from the film even if the firing is performed at a high temperature by reducing the ratio of the resin fine particles. I understand that.

1 substrate 1 'heat resistant substrate 10 laminated film (Z)
11 layers (X)
12 Matrix of layer (X) 13 (A1) Organic fine particles 14 Hole A
15 layers (Y)
16 layer (Y) matrix 17 (A2) inorganic fine particles 18 pores B
19 Mixing layer 20 Polyimide resin

Claims (10)

A method for producing a porous membrane, comprising:
(1) (A1) laminating a layer (X) containing organic fine particles and (A2) a layer (Y) containing inorganic fine particles to form a laminated film (Z);
(2) removing the (A1) organic fine particles and (A2) inorganic fine particles from the laminated film (Z),
In the step (2), the (A1) organic fine particles are removed by thermal decomposition or sublimation,
The matrix of the layer (X) comprises a material that pyrolyzes or sublimes at a lower temperature than the matrix of the layer (Y);
(A1) The method in which the organic fine particles are thermally decomposed or sublimated at a lower temperature than the matrix of the layer (Y).   In the laminated film (Z), a mixing layer in which the matrix of the layer (X) and the matrix of the layer (Y) are mixed is formed between the layers (X) and (Y). The method for producing a porous membrane according to claim 1.   The method for producing a porous film according to claim 1 or 2, wherein the particle size distribution index of the (A1) organic fine particles and the particle size distribution index of the (A2) inorganic fine particles are different from each other. The step (1)
A layer (X) forming step of forming the layer (X) using a first varnish containing the (A1) organic fine particles, (B1) resin, and (C1) a solvent;
Using the second varnish containing (A2) inorganic fine particles, (B2) polyimide resin and / or polyimide resin precursor, and (C2) organic solvent, the layer (X) Y), forming a layer (Y), and
The step (2)
By firing the laminated film (Z), the (A1) organic fine particles and the (B1) resin are removed from the laminated film (Z), and (B3) the polyimide resin and the (A2) are removed. ) A firing step for obtaining a composite film composed of inorganic fine particles;
An inorganic fine particle removing step of removing the inorganic fine particles (A2) from the composite film,
The (A1) organic fine particles and the (B1) resin are incompatible,
The (B1) resin and the (C2) organic solvent are compatible with each other.
The method for producing a porous film according to any one of claims 1 to 3, wherein the (A1) organic fine particles and the (C2) organic solvent are incompatible.   The volume ratio of the (A1) organic fine particles in the volume of the layer (X) is 40 to 95%, and the volume ratio of the (A2) inorganic fine particles in the volume of the layer (Y) is The method for producing a porous membrane according to any one of claims 1 to 4, which is 40 to 95%.   The porous membrane according to any one of claims 1 to 5, wherein the (A1) organic fine particles have an average diameter of 10 to 2000 nm and the (A2) inorganic fine particles have an average diameter of 10 to 2000 nm. Method.   The method for producing a porous film according to any one of claims 1 to 6, wherein the (A1) organic fine particles and the matrix of the layer (X) are each thermally decomposed or sublimated at 400 ° C or lower.   The manufacturing method of the porous membrane of any one of Claims 1-7 whose calcination temperature in the said process (2) is 250-400 degreeC.   The production of the porous membrane according to any one of claims 1 to 8, wherein the layer (X) has a thickness of 0.1 to 50 µm, and the layer (Y) has a thickness of 1 to 100 µm. Method.   The particle size distribution index (d25 / d75) of the (A1) organic fine particles is 1 to 3, and the particle size distribution index (d25 / d75) of the (A2) inorganic fine particles is 1 to 5. 10. The method for producing a porous membrane according to any one of 9 above.