Polyimide porous membrane

Abstract

To provide a porous polyimide film having an excellent gas permeation rate.SOLUTION: A porous film is constituted from a porous material comprising either a polyimide resin or a polyimide resin composition including a polyimide resin and has gas permeability. At least one main surface of the porous film has a contact angle with water of 100° or greater or the at least one main surface has a content of fluorine atoms of 5 atm% or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous polyimide film. [Background technology]

[0002] BACKGROUND ART Various porous membranes have been used for applications such as filters.

[0003] For example, a porous polyimide film is known that is obtained by applying a varnish in which silica particles are dispersed in a solution of polyamic acid or polyimide onto a substrate, heating the applied film as necessary to obtain a polyimide film containing silica particles, and then eluting and removing the silica in the polyimide film with hydrogen fluoride water (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5605566 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, filters used for gas-liquid and solid-gas separation are required to have higher separation speeds, and therefore, porous membranes used as filters are required to have higher gas permeation speeds. In this regard, the conventionally known polyimide porous membranes described in Patent Document 1 and the like have room for improvement in terms of the gas permeation rate.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyimide porous membrane that has an excellent gas permeation rate. [Means for solving the problem]

[0007] The present inventors have found that the above-mentioned problems can be solved by making the water contact angle on at least one main surface of a porous membrane made of a porous material formed from a polyimide resin or a polyimide resin composition containing a polyimide resin 100° or more, or by making the amount of fluorine atoms on at least one main surface of the porous membrane 5 atm % or more, and have thus completed the present invention.

[0008] A first aspect of the present invention is a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin, The porous material has breathability, The polyimide porous film has a water contact angle of 100° or more on at least one of its main surfaces.

[0009] A second aspect of the present invention is a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin, The porous material has breathability, The polyimide porous film has a fluorine atom content of 5 atm % or more on at least one of its main surfaces. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a polyimide porous membrane that has an excellent gas permeation rate. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0012] <Porous polyimide film> The polyimide porous film is made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin. Hereinafter, the polyimide porous film may also be simply referred to as a "porous film." The porous material that constitutes the porous membrane is breathable. At least one of the main surfaces of the porous film has a water contact angle of 100° or more, or the amount of fluorine atoms is 5 atm % or more.

[0013] Hereinafter, a porous film having a water contact angle of 100° or more on at least one of its main surfaces will be referred to as a "first porous film," and a porous film having a fluorine atom content of 5 atm% or more on at least one of its main surfaces will be referred to as a "second porous film."

[0014] Below, common features between the first porous film and the second porous film will be described.

[0015] The porous film is made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin. The porous material is breathable. The shape of the pores in the porous material is not particularly limited as long as the porous membrane allows gas to pass from one main surface to the other main surface. The porous materials constituting the porous membrane each have a desired porosity, and preferably have a structure in which spherical pores are interconnected (hereinafter referred to as interconnected pores), as described below. When the porous membrane is a laminate, the same applies to the porous layers included in the laminate. The spherical shape of the hole is a concept that includes a perfect sphere, but is not necessarily limited to a perfect sphere. The spherical shape may be substantially a perfect sphere, and also includes a shape that can be recognized as a nearly perfect sphere when visually observing an enlarged image of the hole portion. Specifically, in the case of a spherical hole, the surface defining the hole portion is a curved surface, and the curved surface may define a hole having a perfect sphere or a nearly perfect sphere. When the porous film is a laminate, the porosity and the pore size of the spherical pores constituting the communicating pores may be the same or different for each porous layer constituting the laminate.

[0016] For example, in the case of a porous membrane, the individual spherical pores are typically formed by removing the individual particles present in the polyimide resin-particle composite membrane described below in a subsequent step. The interconnected pores are formed by removing a plurality of particles that are in contact with each other in the polyimide resin-particle composite film in a subsequent process in the porous film manufacturing method described below. The interconnected spherical pores in the interconnected pores are formed at locations where the plurality of particles were in contact with each other before being removed.

[0017] The diameter of the openings in the porous membrane is preferably 50 nm or more and 3000 nm or less, more preferably 100 nm or more and 2000 nm or less, and even more preferably 200 nm or more and 1000 nm or less, in order to achieve both an excellent gas passage rate and the strength of the porous membrane. The diameter of the opening is equal to or approximately equal to the diameter of the spherical hole that constitutes the communicating hole. The porous membrane has internal communicating pores that run through the membrane in the thickness direction and serve as fluid flow paths, allowing the fluid to pass from one main surface of the porous membrane to the other main surface. Furthermore, when a porous membrane is used as a filter, the fluid passes through the interior of the porous membrane while coming into contact with the curved surfaces that define the individual spherical pores. The contact area of ​​the fluid inside the porous membrane is quite large due to the presence of interconnected pores made of spherical pores. Therefore, when a fluid passes through a laminate including a porous membrane, it is thought that minute substances present in the fluid are likely to be adsorbed by the spherical pores in the porous membrane.

[0018] The porous membrane may be a single layer membrane made of only one type of membrane, or a laminated membrane made of two or more layers of two or more types of membranes laminated together.

[0019] When the porous film is a laminated film, the laminated film can be formed by a conventional method such as lamination. Alternatively, the porous film included in the laminated film may be sequentially formed on one of the porous films constituting the outermost layers of the laminated film. Alternatively, a precursor film of the porous film can be laminated by lamination, coating, or the like, and then the laminated film on which the precursor film is laminated can be made porous to form a laminated porous film. Examples of the precursor film include a layer containing fine particles in a resin matrix that can be removed by thermal decomposition or treatment with an organic solvent, water, acid, alkali, or the like.

[0020] The shape of the pores in the porous material that constitutes the porous membrane is not particularly limited as long as the porous membrane allows fluid to flow from one main surface to the other main surface. Each porous membrane has a desired porosity and preferably has a structure in which spherical pores are interconnected (hereinafter referred to as interconnected pores), as described below. When the porous membrane is a laminate, the same applies to the porous layers included in the laminate. The spherical shape of the hole is a concept that includes a perfect sphere, but is not necessarily limited to a perfect sphere. The spherical shape may be substantially a perfect sphere, and also includes a shape that can be recognized as a nearly perfect sphere when visually observing an enlarged image of the hole portion. Specifically, in the case of a spherical hole, the surface defining the hole portion is a curved surface, and the curved surface may define a hole having a perfect sphere or a nearly perfect sphere. When the porous film is a laminated film, the porosity and the pore size of the spherical pores that form the communicating pores may be the same or different for each porous film that constitutes the laminated film.

[0021] The thickness of the porous membrane is not particularly limited. The thickness of the porous membrane is appropriately determined depending on the use of the porous membrane. Typically, the thickness of the porous membrane is preferably 20 μm or more, more preferably 20 μm or more and 200 μm or less, and even more preferably 30 μm or more and 100 μm or less.

[0022] The thickness of a porous film, or, if the porous film is a laminated film, the thickness of each porous film included in the laminated film, can be determined, for example, by measuring the thickness at multiple locations using a micrometer or the like and averaging the results, or by observing the cross section of the film using a scanning electron microscope (SEM) and averaging the results.

[0023] The porosity of the porous membrane is preferably 60% or more, more preferably 65% ​​to 85%, and even more preferably 70% to 80%, in terms of excellent gas permeation rate.

[0024] The porosity indicates, for example, the proportion of voids per unit volume of a porous membrane, and can be calculated by the following formula (A). Porosity (%) = {volume of specimen (cm 3 ) - [Weight of test piece (g) / Specific gravity of polyimide resin or polyimide resin composition (g / cm 3 )]} / volume of test piece (cm 3 )×100···(A) As will be described later, the porosity can be adjusted to a desired value by appropriately adjusting the particle size and content of the fine particles used in producing the porous film.

[0025] <Method of manufacturing porous membrane> A preferred porous membrane, which contains interconnected pores formed by interconnecting spherical pores, can be produced, for example, by the following method.

[0026] in particular, an unsintered composite film forming step of forming an unsintered composite film on a substrate using the porous film-forming composition; a firing step of firing the unfired composite film to obtain a polyimide resin-particle composite film; and a particle removal step of removing the particles from the polyimide resin-particle composite film.

[0027] Hereinafter, the method for producing a porous film will be described in detail, including the composition for producing a porous film and a preferred method for producing the porous film.

[0028] [Composition for producing porous membrane] The composition for producing a porous membrane contains a compound capable of producing a polyimide resin. The compound capable of producing a polyimide resin may be a monomer for forming a polyimide resin, or may be a polyamic acid which is a precursor of a polyimide resin. The compound capable of producing a polyimide resin is preferably a polyamic acid.

[0029] Essential and optional components contained in the composition for producing a porous film will be described below.

[0030] [Polyamic acid] The polyamic acid may be any resin obtained by polymerizing any tetracarboxylic dianhydride and diamine. The amounts of the tetracarboxylic dianhydride and diamine used are not particularly limited. The amount of the diamine used per mole of the tetracarboxylic dianhydride is preferably 0.50 moles or more and 1.50 moles or less, more preferably 0.60 moles or more and 1.30 moles or less, and particularly preferably 0.70 moles or more and 1.20 moles or less.

[0031] The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides that have conventionally been used as raw materials for synthesizing polyamic acids. 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, it is preferable to use an aromatic tetracarboxylic dianhydride. The tetracarboxylic dianhydride may be used alone or in combination of two or more. As will be described later, in order to increase the water contact angle and the fluorine atom content (atm %) on the main surface of the porous film, a polyimide resin may contain a structural unit having a fluorine atom. In this case, a tetracarboxylic acid dianhydride containing a fluorine atom is used.

[0032] Specific preferred examples of the aromatic tetracarboxylic dianhydride include 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 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, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)methane ... (phenyl) ether dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4-(p-phenylenedioxy)diphthalic dianhydride, 4,4-(m-phenylenedioxy)diphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 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, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride. Examples of aliphatic tetracarboxylic dianhydrides include ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, and 1,2,3,4-cyclohexane tetracarboxylic dianhydride. Among these, 3,3',4,4'-biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride are preferred in terms of price, availability, and the like. These tetracarboxylic dianhydrides can be used alone or in combination.

[0033] Examples of tetracarboxylic acid dianhydrides containing fluorine atoms that are used when a polyimide resin contains a structural unit having a fluorine atom include (trifluoromethyl)pyromellitic dianhydride, di(trifluoromethyl)pyromellitic dianhydride, di(heptafluoropropyl)pyromellitic dianhydride, (pentafluoroethyl)pyromellitic dianhydride, bis[3,5-di(trifluoromethyl)phenoxy]pyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 5,5'-bis(trifluoromethyl)pyromellitic ... 2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone dianhydride, 1,4-bis(2-trifluoromethyl-3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(5-trifluoromethyl) 1,4-bis(2-trifluoromethyl-3,4-dicarboxyphenoxy)trifluoromethylbenzene dianhydride, 1,4-bis(5-trifluoromethyl-3,4-dicarboxyphenoxy)trifluoromethylbenzene dianhydride, 1,4-bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, 1,4-bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, 1,4-bis(dicarboxyphenoxy)-2,5-bis(trifluoromethyl)benzene dianhydride, 1,4-bis(dicarboxyphenoxy)-2,6 -Bis(trifluoromethyl)benzene dianhydride, 1,4-bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride, 2,2-bis[(4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride, 4,4'-bis(2-trifluoromethyl-3,4-dicarboxyphenoxy)biphenyl dianhydride, 4,4'-bis(5-trifluoromethyl-3,4-dicarboxyphenoxy)biphenyl dianhydride, 4,4'-bis(2-trifluoromethyl-3,4-dicarboxyphenoxy-3,3'-Bis(trifluoromethyl)biphenyl dianhydride, 4,4'-bis(5-trifluoromethyl-3,4-dicarboxyphenoxy-3,3'-bis(trifluoromethyl)biphenyl dianhydride, 4,4'-bis(2-trifluoromethyl-3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(5-trifluoromethyl-3,4-dicarboxyphenoxy)diphenyl ether dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)-3,3-bis(trifluoromethyl)biphenyl dianhydride, 2,5-difluoropyromellitic acid, 2-trifluoromethyl-5-fluoropyromellitic acid, 2,5-di(trifluoromethyl)pyromellitic acid, 2,5-di(pentafluoroethyl)pyromellitic acid ) pyromellitic acid, hexafluoro-3,3',4,4'-biphenyltetracarboxylic acid, hexafluoro-3,3',4,4'-benzophenonetetracarboxylic acid, 2,2-bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)hexafluoropropane, 1,3-bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)hexafluoropropane, 2,2-bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)hexafluoropropane, 1,4-bis(2,5,6-trifluoro-3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene, hexafluoro-3,3'-oxybisphthalic acid, and hexafluoro-3,3'-oxybisphthalic acid, etc.

[0034] The diamine can be appropriately selected from diamines conventionally used as raw materials for synthesizing polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine, but aromatic diamines are preferred from the viewpoint of the heat resistance of the resulting polyimide resin. These diamines may be used alone or in combination of two or more. As will be described later, in order to increase the water contact angle and the fluorine atom content (atm %) on the main surface of the porous film, a polyimide resin may contain a structural unit having a fluorine atom. In this case, a diamine containing a fluorine atom is used.

[0035] Examples of aromatic diamines include diamino compounds having one or two to ten phenyl groups bonded together, specifically phenylenediamine and its derivatives, diaminobiphenyl compounds and their derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindan and its derivatives, diaminotetraphenyl compounds and their derivatives, diaminohexaphenyl compounds and their derivatives, and cardo-type fluorenediamine derivatives.

[0036] Phenylenediamines include m-phenylenediamine and p-phenylenediamine, and phenylenediamine derivatives include diamines to which alkyl groups such as methyl groups and ethyl groups are bonded, such as 2,4-diaminotoluene and 2,4-triphenylenediamine.

[0037] Diaminobiphenyl compounds have two aminophenyl groups bonded together, such as 4,4'-diaminobiphenyl and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0038] Diaminodiphenyl compounds are compounds in which two aminophenyl groups are bonded to each other via another group. The bond may be an ether bond, a sulfonyl bond, a thioether bond, a bond via an alkylene or its derivative group, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, or a ureylene bond. The alkylene bond has about 1 to 6 carbon atoms, and the alkylene derivative group is an alkylene group substituted with one or more halogen atoms, etc.

[0039] Examples of the diaminodiphenyl compound include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl methane, 3,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane, 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) 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-aminophenoxy)phenyl]hexafluoropropane, and the like.

[0040] Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred in terms of price, availability, and the like.

[0041] A diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are bonded via other groups. The other groups are selected from the same groups as in the diaminodiphenyl compounds. Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, and 1,4-bis(p-aminophenoxy)benzene.

[0042] Examples of diaminonaphthalenes include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

[0043] Examples of aminophenylaminoindan include 5 or 6-amino-1-(p-aminophenyl)-1,3,3-trimethylindan.

[0044] 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, and 2,2'-bis[p-(m-aminophenoxy)phenyl]benzophenone.

[0045] Examples of cardo-type fluorenediamine derivatives include 9,9-bisanilinefluorene.

[0046] The number of carbon atoms in the aliphatic diamine is preferably, for example, about 2 to 15. Specific examples of the aliphatic diamine include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

[0047] The diamine may be a compound in which the hydrogen atom of the diamine is substituted with at least one substituent selected from the group consisting of a halogen atom, a methyl group, a methoxy group, a cyano group, a phenyl group, and the like.

[0048] Examples of diamines containing fluorine atoms that can be used when incorporating a structural unit having a fluorine atom into a polyimide resin include 4-(1H,1H,11H-eicosafluoroundecanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-butanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-heptanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-octanoxy)-1,3-diaminobenzene, 4-pentafluorophenoxy-1,3-diaminobenzene, 4-(2,3 ,5,6-tetrafluorophenoxy)-1,3-diaminobenzene, 4-(4-fluorophenoxy)-1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1-hexanoxy)-1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1-dodecanoxy)-1,3-diaminobenzene, 2,5-diaminobenzotrifluoride, 2,5-bis(trifluoromethyl)-1,4-phenylenediamine, 2,3-bis(trifluoromethyl)-1,4-phenylenediamine, 2,6-bis(trifluoromethyl)- 4,6-bis(trifluoromethyl)-1,3-phenylenediamine, 4,5-bis(trifluoromethyl)-1,3-phenylenediamine, 2,4-bis(trifluoromethyl)-1,3-phenylenediamine, 2,5-bis(trifluoromethyl)-1,3-phenylenediamine, 1,4-diaminotetra(trifluoromethyl)benzene, 1,3-diaminotetra(trifluoromethyl)benzene, 1,4-diamino-2-pentafluoroethylbenzene, 1,3-diamino-4-pentafluoroethylbenzene 1,3-diamino-5-pentafluoroethylbenzene, 1,4-diamino-2-perfluorohexylbenzene, 1,4-diamino-2-perfluorobutylbenzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, octafluorobenzidine, 4,4'-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(4-aminophenyl)hexafluoropropane, 1,4-bis(4-aminophenyl)octafluorobutane, 1,5-bis(4-aminophenyl)decafluoropentane, 1,7-bis(4-aminophenyl)tetradecafluoroheptane, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3',5,5'-tetrakis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminobenzophenone, 1,4 -bis(4-aminophenyl)benzene, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 1,4-bis(4-aminophenoxy)-2,5-bis(trifluoromethyl)benzene, 1,4-bis(4-aminophenoxy)-2,3-bis(trifluoromethyl)benzene, 1,4-bis(4-aminophenoxy)-2,6-bis(trifluoromethyl)benzene, 1,4-bis(4-aminophenoxy)tetrakis(trifluoromethyl)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoro Fluoropropane, 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(2-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]hexafluoropropane, 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(4-amino-3-trifluoromethylphenoxy)phenyl]hexafluoropropane, 2,2-bis[4-(4-amino phenoxy)-3,5-ditrifluoromethylphenyl]hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-amino-3-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)diphenyl sulfone, 4,4'-bis(3-amino-5-trifluoromethylphenoxy)diphenyl sulfone, 1,4-bis{2-[4-(4-aminophenoxy)phenyl]hexafluoropropan-2-yl}benzene, 4,Examples of such compounds include 4'-bis(4-aminophenoxy)octafluorobiphenyl, 3,4,5,6-tetrafluoro-1,2-phenylenediamine, 2,4,5,6-tetrafluoro-1,3-phenylenediamine, 2,3,5,6-tetrafluoro-1,4-phenylenediamine, 4,4'-diaminooctafluorobiphenyl, bis(2,3,5,6-tetrafluoro-4-aminophenyl)ether, bis(2,3,5,6-tetrafluoro-4-aminophenyl)sulfone, and hexafluoro-2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

[0049] There are no particular limitations on the means for producing the polyamic acid, and any known method can be used, such as a method of reacting an acid and a diamine component in a solvent.

[0050] The reaction between the tetracarboxylic dianhydride and the diamine is usually carried out in a solvent. The solvent used for the reaction between the tetracarboxylic dianhydride and the diamine is not particularly limited as long as it can dissolve the tetracarboxylic dianhydride and the diamine and does not react with the tetracarboxylic dianhydride and the diamine. One solvent may be used alone, or two or more solvents may be used in combination.

[0051] Examples of solvents used in the reaction of tetracarboxylic dianhydride with diamine include nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea; lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, and ethyl cellosolve acetate; and phenol-based solvents such as cresols and xylene-based mixed solvents. These solvents may be used alone or in combination of two or more. There is no particular limitation on the amount of solvent used, but it is desirable that the content of the produced polyamic acid be 5 to 50 mass %.

[0052] Among these solvents, nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea are preferred in terms of the solubility of the polyamic acid produced.

[0053] The polymerization temperature is generally from −10° C. to 120° C., preferably from 5° C. to 30° C. The polymerization time varies depending on the composition of the raw materials used, but is usually from 3 hours to 24 hours. The polyamic acid may be used alone or in combination of two or more kinds.

[0054] [Polyimide resin] The polyimide resin is not limited in structure or molecular weight, and known polyimide resins can be used. The polyimide may have a condensable functional group such as a carboxyl group in the side chain or a functional group that promotes a crosslinking reaction during baking. In addition, when the composition for producing a porous membrane contains a solvent, a soluble polyimide that can be dissolved in the solvent used is preferred.

[0055] To make the polyimide resin soluble in a solvent, it is effective to use a monomer for introducing a flexible, bent structure into the main chain, for example, aliphatic diamines such as ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, and 4,4'-diaminodicyclohexylmethane; aromatic diamines such as 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3'-dimethoxybenzidine, and 4,4'-diaminobenzanilide; polyoxyalkylene diamines such as polyoxyethylenediamine, polyoxypropylenediamine, and polyoxybutylenediamine; polysiloxane diamine; 2,3,3',4'-oxydiphthalic anhydride, 3,4,3',4'-oxydiphthalic anhydride, and 2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3',4,4'-tetracarboxylic dianhydride. It is also effective to use a monomer having a functional group that improves solubility in a solvent, for example, a fluorinated diamine such as 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl or 2-trifluoromethyl-1,4-phenylenediamine. Furthermore, in addition to the monomer for improving the solubility of the polyimide resin, the same monomers as those described in the polyamic acid section above can also be used in combination, as long as the solubility is not impaired. The polyimide resin and the monomer thereof may be used singly or in combination of two or more kinds.

[0056] The means for producing the polyimide resin is not particularly limited, and known methods such as chemical imidization or thermal imidization of polyamic acid can be used. Examples of such polyimide resins include aliphatic polyimide resins (fully aliphatic polyimide resins) and aromatic polyimide resins, with aromatic polyimide resins being preferred. Examples of aromatic polyimide resins include those obtained by thermally or chemically ring-closing polyamic acid having a repeating unit represented by formula (1), or polyimides having a repeating unit represented by formula (2). In the formula, Ar represents an aryl group. When the composition for producing a porous membrane contains a solvent, the polyimide resin may then be dissolved in the solvent used. [ka] [ka]

[0057] [Fine particles] The material of the microparticles is not particularly limited, and any known material can be used as long as it is insoluble in the solvent contained in the porous membrane-producing composition and can be subsequently removed from the polyimide resin-microparticle composite membrane. For example, inorganic materials include metal oxides such as silica (silicon dioxide), titanium oxide, and alumina (Al2O3), and organic materials include organic polymer microparticles such as high-molecular-weight olefins (polypropylene, polyethylene, etc.), polystyrene, epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyesters, and polyethers.

[0058] Specific examples of fine particles include colloidal silica, among which monodispersed spherical silica particles are preferred because they can form uniform pores.

[0059] Furthermore, it is preferable that the microparticles have a high sphericity and a small particle size distribution index. Microparticles that meet these conditions have excellent dispersibility in the composition for producing a porous membrane and can be used in a state where they do not aggregate with each other. The average particle size of the microparticles used is appropriately selected taking into consideration the opening size on the surface of the porous membrane and the thickness of the porous membrane. The average particle size of the microparticles is, for example, preferably 50 nm or more, more preferably 100 nm to 2000 nm, and even more preferably 200 nm to 1000 nm. By satisfying these conditions, the pore size of the porous membrane obtained by removing the microparticles can be made uniform. The fine particles may be used alone or in combination of two or more kinds.

[0060] [solvent] The solvent is not particularly limited as long as it dissolves the polyamic acid and / or polyimide resin and does not dissolve the fine particles. Suitable examples of the solvent include the solvents exemplified for the reaction between tetracarboxylic dianhydride and diamine. The solvent may be used alone or in combination of two or more.

[0061] [Dispersant] A dispersant may be added together with the microparticles in the porous film-forming composition to uniformly disperse the microparticles. Adding a dispersant allows the microparticles to be mixed more uniformly in the porous film-forming composition, and further allows the microparticles to be uniformly distributed in the film formed from the porous film-forming composition. As a result, dense openings can be formed on the surface of the finally obtained porous film, and the front and back surfaces can be efficiently connected, thereby improving the air permeability of the porous film. Furthermore, adding a dispersant tends to improve the drying properties of the porous film-forming composition and also tends to improve the peelability of the formed unfired composite film from the substrate, etc.

[0062] The dispersant is not particularly limited, and known dispersants can be used. For example, anionic surfactants such as coconut fatty acid salts, castor sulfated oil salts, lauryl sulfate salts, polyoxyalkylene allyl phenyl ether sulfate salts, alkyl benzene sulfonic acid, alkyl benzene sulfonate salts, alkyl diphenyl ether disulfonate salts, alkyl naphthalene sulfonate salts, dialkyl sulfosuccinate salts, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salts, and polyoxyethylene allyl phenyl ether phosphate salts; cationic surfactants such as oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, and didecyl dimethyl ammonium chloride; amphoteric surfactants such as coconut alkyl dimethyl amine oxide, fatty acid amidopropyl dimethyl amine oxide, alkyl polyaminoethyl glycine hydrochloride, amido betaine surfactants, alanine surfactants, and lauryliminodipropionic acid; Nonionic surfactants of polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers, such as ethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, and polyoxyalkylene polystyrylphenyl ether; other polyoxyalkylene-based nonionic surfactants, such as polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylenated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamides; 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, but are not limited to these.The above dispersants can also be used in combination of two or more.

[0063] In the composition for producing a porous film, the content of the dispersant is, for example, preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less, relative to the mass of the microparticles, from the viewpoint of film-forming properties.

[0064] [Suitable method for producing porous membrane] [Unfired composite film formation process] In the green composite film forming step, for example, the green composite film can be formed by applying the above-described composition for producing a porous film onto a substrate and drying it under normal pressure or in vacuum at a temperature of 0° C. to 100° C., preferably at normal pressure and 10° C. to 100° C. Examples of the substrate include a PET film, a SUS substrate, and a glass substrate.

[0065] Furthermore, when peeling the unfired composite film from the substrate, a substrate pre-formed with a release layer can be used to further enhance the film's releasability. When a release layer is pre-formed on the substrate, a release agent is applied to the substrate and dried or baked before applying the porous film-producing composition. The release agent used here can be any known release agent, such as an alkyl ammonium phosphate salt, a fluorine-based agent, or a silicone-based agent, without any particular restrictions. When peeling the dried unfired composite film from the substrate, a small amount of release agent remains on the peeled surface of the unfired composite film, which can cause discoloration during firing and adversely affect electrical properties, so it is preferable to remove it as much as possible. To remove the release agent, a cleaning step can be introduced in which the unfired composite film peeled from the substrate is washed with an organic solvent.

[0066] On the other hand, when the substrate is used as is without providing a release layer for forming the green composite film, the above-mentioned release layer forming step and the above-mentioned cleaning step can be omitted. Furthermore, in the production of the green composite film, the following optional steps may be provided before the firing step described below: a step of immersing in a solvent containing water, a pressing step, and a drying step after the immersion step.

[0067] [Firing process] The unsintered composite film is subjected to post-treatment (sintering) by heating to form a composite film (polyimide resin-particle composite film) consisting of polyimide resin and fine particles. The baking temperature in the baking step varies depending on the structure of the unsintered composite film and the presence or absence of a condensing agent, but is preferably 120°C to 450°C, more preferably 150°C to 400°C. Furthermore, when an organic material is used for the fine particles, the temperature must be set lower than their thermal decomposition temperature. It is preferable to complete the imidization in the baking step.

[0068] The firing conditions may include, for example, a method in which the temperature is raised from room temperature to 400°C over 3 hours and then held at 400°C for 20 minutes, or a stepwise drying-thermal imidization method in which the temperature is raised from room temperature to 400°C in 50°C increments (each step held for 20 minutes), and finally held at 400°C for 20 minutes.When an unfired composite film is formed on a substrate and then temporarily peeled off from the substrate, a method can be used in which the edges of the unfired composite film are fixed to a stainless steel mold or the like to prevent deformation.

[0069] [Particle removal process] By selecting an appropriate method to remove the particles from the polyimide resin-particle composite film formed as described above, a porous film having a desired structure can be produced with good reproducibility. When silica is used as the material of the fine particles, for example, the polyimide resin-fine particle composite film can be treated with low-concentration hydrogen fluoride water or the like to dissolve and remove the silica. When the fine particles are organic fine particles, the fine particles can also be removed from the polyimide resin-fine particle composite film by thermally decomposing the organic fine particles. Furthermore, when the fine particles are organic fine particles, a treatment liquid that dissolves the fine particles but does not dissolve the polyimide resin can be selected and used to remove the organic fine particles. Typically, an organic solvent is used as the treatment liquid. When the organic fine particles are soluble in an acid or an alkali, an acidic aqueous solution or an alkaline aqueous solution can also be used as the treatment liquid.

[0070] [Resin removal process] Before the particle removal step, at least a part of the resin portion of the polyimide resin-particle composite film may be removed, or after the particle removal step, a resin removal step of removing at least a part of the porous film may be carried out. By removing at least a portion of the resin portion of the polyimide resin-particle composite film before the particle removal step, or by removing at least a portion of the porous film after the particle removal step, it is possible to improve the porosity of the final porous film product compared to when removal is not performed.

[0071] The step of removing at least a portion of the resin portion of the polyimide resin-particle composite film or the step of removing at least a portion of the resin portion of the polyimide resin-particle composite film can be carried out by a conventional chemical etching method, a physical removal method, or a combination of these methods.

[0072] Chemical etching methods include treatment with chemical etching solutions such as inorganic alkaline solutions or organic alkaline solutions. 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, and sodium metasilicate; ammonia solutions; and etching solutions containing alkali hydroxides, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components. Examples of organic alkaline solutions include alkaline solutions of primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; and cyclic amines such as pyrrole and piheridine.

[0073] The solvent for each of the above solutions can be selected appropriately from pure water and alcohols. It is also possible to use a solution containing an appropriate amount of surfactant. The alkali concentration is, for example, 0.01 to 20% by mass.

[0074] Physical methods that can be used include dry etching using plasma (oxygen, argon, etc.) or corona discharge, and a method of dispersing an abrasive (e.g., alumina (hardness 9)) in a liquid and irradiating the surface of the porous membrane with this at a speed of 30 to 100 m / s to treat the membrane surface.

[0075] On the other hand, as a physical method applicable only to the resin removal process performed after the particle removal process, a method can be adopted in which the target surface is pressed onto a mount film (e.g., a polyester film such as a PET film) wetted with a liquid, and then the laminate is peeled off from the mount film either without drying or after drying. Due to the surface tension or electrostatic adhesion of the liquid, the porous film is peeled off from the mount film, leaving only the surface layer of the porous film present on the surface to be treated on the mount film.

[0076] <First porous membrane> The first porous film is the aforementioned polyimide porous film, and is a porous film having a water contact angle of 100° or more on at least one of its main surfaces. When the first porous film exhibits the above-mentioned contact angle with water on at least one of its main surfaces, the porous film exhibits an excellent gas permeation rate. The water contact angle is preferably 105° or more, more preferably 110° or more. There is no particular upper limit to the water contact angle, but in reality it is, for example, 150° or less, and may be 130° or less.

[0077] Here, the contact angle of water is a static contact angle, which can be measured, for example, using a Dropmaster 700 (manufactured by Kyowa Interface Science Co., Ltd.) by applying a 2.0 μL droplet of pure water to the surface of the porous membrane and measuring the contact angle 10 seconds after the droplet is dropped.

[0078] Furthermore, in the first porous film, the main surface having a water contact angle of 100° or more preferably has a dynamic water contact angle of 30° or more. The dynamic water contact angle may be 40° or more, or may be 50° or more. There is no particular upper limit to the dynamic water contact angle, but in reality it is, for example, 120° or less, and may be 100° or less.

[0079] The dynamic contact angle of water can be measured using, for example, a Dropmaster 700 (manufactured by Kyowa Interface Science Co., Ltd.) as follows: First, a 2.0 μL droplet of pure water is placed on the surface of the porous membrane. Next, pure water is supplied from a syringe needle to the droplet until the total amount of pure water reaches 50.0 μL, causing the droplet to expand. The measurement starts when the expanded state of the droplet is maintained for 3 seconds, and pure water is aspirated from the droplet at a rate of 6.0 μL / sec from the start of the measurement. The receding angle when the end of the droplet shrinks by 10 dots from the end at the start of the measurement due to the aspirated pure water is measured as the dynamic contact angle of water.

[0080] There are no particular limitations on the method for making the water contact angle of the main surface of the first porous membrane equal to or greater than 100°. Examples of such methods include a method of attaching or bonding a water repellent agent to the main surface of an untreated porous membrane prepared by the above-mentioned method, a method of incorporating a fluorine atom-containing structural unit into the polyimide resin contained in the porous material constituting the first porous membrane, and a method of incorporating a water repellent material into the polyimide resin composition constituting the first porous membrane.

[0081] The water repellent used in the method of adhering or bonding the water repellent to the main surface is not particularly limited as long as it can be attached to or bonded to the polyimide resin and can increase the contact angle of water on the main surface of the porous membrane to 100° or more. Preferred water repellent agents include silicone-based water repellent agents and fluorine-based water repellent agents. In terms of water repellency, fluorine-based water repellent agents are more preferred.

[0082] As the fluorine-based water repellent agent, typically, a fluorine-containing organic compound itself or a liquid composition containing a fluorine-containing organic compound is used. The fluorine-containing organic compound is not particularly limited as long as it is an organic compound containing a fluorine atom. The fluorine-containing organic compound may be a low-molecular-weight compound, an oligomer, or a polymer. In addition, the fluorine-containing organic compound may be an aliphatic compound, an aromatic compound, or a compound containing an aliphatic portion and an aromatic portion.

[0083] Examples of the fluorine-containing organic compound include fluoroalkanes, fluoroalkanols, bisfluoroalkyl ethers, fluoroalkyl alkyl ethers, fluorinated aliphatic ketones, fluorinated aliphatic carboxylic acids, fluorinated aliphatic carboxylic acid alkyl esters, fluorinated aliphatic carboxylic acid fluoroalkyl esters, aliphatic carboxylic acid fluoroalkyl esters, fluoroalkylbenzene carboxylic acids, fluoroalkylbenzene carboxylates, fluoroalkylbenzene sulfonic acids, and fluoroalkylbenzene sulfonates.

[0084] A fluorine-containing silane coupling agent is also preferably used as the fluorine-containing organic compound. On the surface of a porous membrane that has not been treated with a fluorine-containing organic compound, functional groups containing active hydrogen atoms, such as hydroxyl groups, amino groups, and carboxy groups, are often present. The fluorine-containing silane coupling agent can react with and bond to such a functional group containing an active hydrogen atom.

[0085] The fluorine-containing silane coupling agent is not particularly limited as long as it is a silane coupling agent containing a functional group containing fluorine. Examples of the fluorine-containing silane coupling agent include fluoroalkyltrialkoxysilane, difluoroalkyldialkoxysilane, fluoroalkylalkyldialkoxysilane, bis(trialkoxysilyl)fluoroalkane, fluoroalkyltriisocyanatesilane, bis(trichlorosilyl)fluoroalkane, and bis(triisocyanatesilyl)fluorinated chain aliphatic compound. Specific preferred examples of the fluorine-containing silane coupling agent include fluoroalkylalkoxysilanes such as perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorooctyltriethoxysilane, perfluorododecyltrimethoxysilane, perfluorododecyltriethoxysilane, perfluoropentyltriethoxysilane, perfluoropentyltrimethoxysilane, and 1H,1H,2H,2H-heptadecafluorodecyltrimethoxysilane; Fluoroalkyl triisocyanate silanes such as 1H,1H,2H,2H-heptadecafluorodecyl triisocyanate silane; Bis(trichlorosilyl)fluoroalkanes such as 1,6-bis(trichlorosilyl)-2,5-ditrifluoromethyl-2,3,3,4,4,5-hexafluoropropane; Examples of the fluorinated chain aliphatic bis(triisocyanatesilyl) compounds include 1,10-bis(triisocyanatesilyl)-1H,1H,2H,2H,9H,9H,10H,10H-dodecafluorodecane, 1,8-bis(triisocyanatesilyl)-3,6-ditrifluoromethyl-3,4,4,5,5,6-hexafluorooctane, N,N'-di(2-triisocyanatesilylethyl)-1,8-dodecafluorooctanedioic acid diamide, 1,4-di(2-triisocyanatesilylethoxy)-1,4-ditrifluoromethylhexafluorobutane, 1,2-di(2-triisocyanatesilylethoxy)tetrafluoroethane, and 1,2-di(2-triisocyanatesilylethylthio)tetrafluoroethane.

[0086] Fluorine resins are also suitable as fluorine-containing organic compounds. The type of fluorine resin is not particularly limited, and various resins containing fluorine atoms can be used. Suitable fluororesins include, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer (PFA), polyvinylidene fluoride (PVDF) and its copolymers, polyvinyl fluoride (PVA), and ethylene / tetrafluoroethylene copolymer (ETFE). Among these, polyvinylidene fluoride (PVDF) and its copolymers are preferred from the viewpoint of improving abrasion resistance. In the case of copolymers, examples of copolymerizable monomers include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride, etc. Alternatively, the water-repellent treatment may be carried out by preparing fine particles as described in JP-A-10-140144 using the above-mentioned fluorine-containing organic compound itself or a liquid composition containing the fluorine-containing organic compound, and then colliding the fine particles with a porous film in the atmosphere using a blasting device or the like.

[0087] By contacting the water repellent agent described above with the main surface of the porous membrane, the water repellent component, such as the fluorine-containing organic compound contained in the water repellent agent, adheres to or bonds with the main surface. The contact angle of water on the main surface can be adjusted by adjusting the amount of the water-repellent component attached to or bonded to the main surface, by adjusting the contact time between the main surface and the water-repellent agent or by adjusting the concentration of the water-repellent component in the water-repellent agent.

[0088] In the method of incorporating a structural unit containing a fluorine atom into the polyimide resin contained in the porous material constituting the first porous membrane, a polyimide resin prepared using at least one of the above-mentioned tetracarboxylic acid dianhydride containing a fluorine atom and the above-mentioned diamine containing a fluorine atom is used.

[0089] The amount of the structural unit derived from the fluorine atom-containing tetracarboxylic dianhydride and the amount of the structural unit derived from the fluorine atom-containing diamine in the polyimide resin are not particularly limited as long as the water contact angle of the main surface of the first porous membrane is a desired value. Generally, the more fluorine atoms there are on the main surface of the porous membrane, the higher the water contact angle tends to be. Therefore, the water contact angle on the main surface of the porous membrane can be adjusted by adjusting the ratio of fluorine atom-containing monomers in the monomers used to produce the polyimide resin, or by adjusting the fluorine atom content in the monomers.

[0090] In a method for incorporating a water-repellent material into the polyimide resin composition that constitutes the first porous membrane, for example, a method is adopted in which the water-repellent material is incorporated into the porous membrane manufacturing composition when forming the porous membrane.

[0091] The water-repellent material may be the component described above for the water-repellent agent. As described above, when forming a porous membrane, the unsintered composite membrane is sintered at a high temperature. Therefore, in terms of heat resistance, the water-repellent material is preferably the fluororesin described above. The form of the fluororesin is not particularly limited. In terms of facilitating uniform dispersion of the fluororesin in the polyimide resin composition, it is preferable to add fluororesin particles to the composition for producing a porous membrane.

[0092] The particle size of the fluororesin particles is not particularly limited as long as it is possible to form a porous film made of a polyamide resin composition containing uniformly dispersed fluororesin particles. The volume average particle size of the fluororesin particles is preferably 10 nm or more and 1,000 nm or less, more preferably 50 nm or more and 700 nm or less, and even more preferably 100 nm or more and 500 nm or less.

[0093] In the first porous film, the amount of fluorine atoms on the main surface having a water contact angle of 100° or more is preferably 5 atm% or more, more preferably 10 atm% or more, even more preferably 20 atm% or more, and particularly preferably 30 atm% or more. The upper limit of the amount of fluorine atoms on the main surface is not particularly limited as long as the contact angle with water is at least 100°. The upper limit of the amount of fluorine atoms is, for example, 68 atm % or less, and may be 50 atm % or less.

[0094] The amount of fluorine atoms on the main surface can be adjusted by adjusting the amount of fluorine-based water repellent agent used, the amount of fluorine atom-containing monomer used when preparing the polyimide resin, the fluorine atom content in the fluorine atom-containing monomer, or the amount of fluorine atom-containing water repellent agent added to the polyimide resin composition.

[0095] The amount of fluorine atoms on the main surface of the porous film can be measured by X-ray photoelectron spectroscopy.

[0096] In order to achieve both an excellent gas permeation rate and the strength of the porous membrane, The porosity is 60% or more, the average diameter of openings on the main surface where the water contact angle is 100° or more is 50 nm or more and 3000 nm or less; The film thickness is preferably 30 μm or more.

[0097] The stress at break of the first porous membrane is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. The breaking elongation of the first porous membrane is preferably 5% GL or more, more preferably 10% GL or more, even more preferably 15% GL or more, and particularly preferably 20% GL or more.

[0098] <Second porous membrane> The second porous film is the aforementioned polyimide porous film, and the amount of fluorine atoms on at least one of the main surfaces is 5 atm % or more. When the amount of fluorine atoms on at least one of the main surfaces of the second porous membrane is within the above range, the porous membrane exhibits an excellent gas permeation rate. The amount of fluorine atoms on the main surface is preferably 5 atm % or more, more preferably 10 atm % or more, further preferably 20 atm % or more, and particularly preferably 30 atm % or more. The upper limit of the amount of fluorine atoms on the primary surface is, for example, 68 atm % or less, and may be 50 atm % or less.

[0099] The amount of fluorine atoms on the main surface is adjusted by the same method as that described for the first porous film.

[0100] In order to achieve both an excellent gas permeation rate and the strength of the porous membrane, The porosity is 60% or more, the average diameter of the openings in the main surface in which the amount of fluorine atoms is 5 atm % or more is 50 nm or more and 3000 nm or less; The film thickness is preferably 30 μm or more.

[0101] The stress at break of the second porous membrane is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. The breaking elongation of the second porous membrane is preferably 5% GL or more, more preferably 10% GL or more, even more preferably 15% GL or more, and particularly preferably 20% GL or more. [Example]

[0102] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the following examples.

[0103] Example 1 Slurry A, containing 70 parts by mass of silica microparticles, 0.35 parts by mass of a nonionic surfactant as a dispersant, and 70 parts by mass of dimethylacetamide, was stirred in a 200 mL container at 400 rpm with a stirring blade for 15 minutes. The stirred slurry A was then subjected to five dispersion treatments at 200 MPa using a dispersing device (NVL-S008, manufactured by Yoshida Kikai Kogyo Co., Ltd.). Silica with an average particle diameter of 300 nm was used as the silica microparticles.

[0104] The dispersed slurry A was mixed with 30 parts by mass of polyamic acid to obtain slurry B. The polyamic acid was used as a dimethylacetamide solution with a solids concentration of 20% by mass. The polyamic acid used was a polymer obtained by polymerizing equimolar amounts of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (hereinafter referred to as 6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (hereinafter referred to as HFBAPP)). Slurry B contained dimethylacetamide and gamma-butyrolactone so that the solid content concentration was 29 mass %. The mass ratio of dimethylacetamide to gamma-butyrolactone in Slurry B was 90:10 (dimethylacetamide:gamma-butyrolactone).

[0105] The obtained slurry B was dispersed in a 200 mL container by stirring with a stirring blade at 400 rpm for 30 minutes to prepare a composition for producing a porous membrane. The composition for producing a porous membrane was applied to a PET film, and then heated at 90°C for 300 seconds to remove the solvent, forming a coating film with a thickness of approximately 40 μm.

[0106] The formed coating film was imidized by heat treatment (baking) at 380°C for 15 minutes to obtain a polyimide resin-particle composite film. The obtained polyimide resin-particle composite film was immersed in a 10% HF solution for 10 minutes to remove the silica particles contained in the film. After removing the silica particles, the film was washed with water and dried to obtain a porous film.

[0107] Comparative Example 1 A porous membrane was obtained in the same manner as in Example 1, except that the polyamic acid was changed to a polymer obtained by polymerizing equimolar amounts of pyromellitic anhydride (hereinafter referred to as PMDA) and 4,4'-diaminodiphenyl ether (hereinafter referred to as ODA).

[0108] Example 2 Slurry D was obtained in the same manner as in the preparation of Slurry B in Comparative Example 1, except that the amount of polyamic acid used was changed from 30 parts by mass to 25 parts by mass, and 5 parts by mass of polytetrafluoroethylene (PTFE) fine particles having an average particle size of 300 nm were added together with the polyamic acid. The PTFE fine particles were used as a dispersion in which PTFE fine particles with a solid content concentration of 40% by mass were dispersed in N-methyl-2-pyrrolidone. The mass ratio of dimethylacetamide, gamma-butyrolactone, and N-methyl-2-pyrrolidone in Slurry D was 87:10:3, calculated as dimethylacetamide:gamma-butyrolactone:N-methyl-2-pyrrolidone. A porous membrane was obtained in the same manner as in Comparative Example 1, except that slurry B was changed to slurry D.

[0109] Example 3 The porous membrane obtained in the same manner as in Comparative Example 1 was immersed in an alkaline etching solution for 180 seconds to remove a portion of the surface of the polyimide resin, thereby performing chemical etching. Specifically, the porous membrane was immersed in an isopropanol aqueous solution with a concentration of 10% by mass to perform pre-wetting, and then immersed in a tetramethylammonium hydroxide (TMAH) aqueous solution with a concentration of 1.00% by mass, and then the porous membrane was washed with water and dried, thereby performing chemical etching. The chemically etched porous film was again heated (baked) at 380°C for 10 minutes to imidize the alkali-opened moieties again, yielding a porous film. A water-repellent treatment was performed on the main surface of the obtained porous film by attaching a fluororesin to the film using a water-repellent agent containing fluororesin (Adlon (registered trademark) L-4614CR, manufactured by Fluorocoat Co., Ltd.), yielding a porous film.

[0110] Comparative Example 2 A porous membrane obtained by the same method as in Comparative Example 1 was immersed in an N-methyl-2-pyrrolidone solution containing polyvinylidene fluoride at a concentration of 0.25% by mass for 1 minute, and then the porous membrane was dried at 100°C for 5 minutes to obtain a porous membrane having polyvinylidene fluoride attached to its main surface.

[0111] The porous membranes of Examples 1 to 3, Comparative Example 1, and Comparative Example 2 obtained as described above were measured for air permeability, water contact angle (static contact angle and dynamic contact angle), stress at break, elongation at break, and fluorine atom content on the main surface. The air permeability, stress at break, elongation at break, and fluorine atom content on the main surface were measured according to the following methods. The water contact angle was measured by the method described above. Regarding the water contact angle, the surface on the air side is the surface that was not in contact with the PET film when the porous membrane was produced, and the surface on the substrate side is the surface that was in contact with the PET film when the porous membrane was produced. The measurement results are shown in Table 1.

[0112] <Air permeability measurement> Using a 5 cm x 5 cm porous membrane sample, the time it took for 100 mL of air to pass through the sample was measured using a Gurley densometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS P 8117. The smaller the air permeability value, the shorter the time it took for 100 mL of air to pass through, and the faster the gas passed through the sample.

[0113] <Measurement of stress at break and elongation at break> A rectangular porous membrane sample measuring 3 cm × 3 mm was used. The stress at break (MPa; tensile strength) and elongation at break (% GL) of the sample were evaluated using EZ Test (Shimadzu Corporation).

[0114] <Measurement of the amount of fluorine atoms on the main surface>

[0115] [Table 1]

[0116] According to Examples 1 to 3, when the water contact angle is 100° or more or the amount of fluorine atoms is 5 atm % or more on at least one main surface of the porous membrane, the gas permeation rate of the porous membrane is excellent. On the other hand, according to Comparative Examples 1 and 2, when the water contact angle on the main surface of the porous membrane is less than 100° or the amount of fluorine atoms is less than 5 atm %, the gas permeation rate of the porous membrane is poor.

Claims

1. The porous material is made of a polyimide resin or a polyimide resin composition containing a polyimide resin, The porous material has air permeability, A porous polyimide film having a water contact angle of 100° or more on at least one of its main surfaces.

2. 2. The polyimide porous film according to claim 1, wherein at least one of the main surfaces has a water contact angle of 100° or more and a water dynamic contact angle of 30° or more.

3. 3. The polyimide porous film according to claim 1, wherein a fluorine-containing organic compound is attached to or bonded to the main surface having a water contact angle of 100° or more.

4. The porous polyimide film according to claim 1 or 2, wherein the polyimide resin comprises a structural unit containing a fluorine atom.

5. The porous polyimide film according to claim 1 or 2, wherein the porous material is made of a polyimide resin composition, and the polyimide resin composition contains a fluororesin.

6. 6. The polyimide porous film according to claim 4, wherein the amount of fluorine atoms on the main surface having a water contact angle of 100° or more is 5 atm % or more.

7. The porosity is 60% or more, the average diameter of the openings on the main surface having a water contact angle of 100° or more is 50 nm or more and 3000 nm or less; The polyimide porous film according to any one of claims 1 to 6, having a film thickness of 30 µm or more.

8. The porous material is made of a polyimide resin or a polyimide resin composition containing a polyimide resin, The porous material has air permeability, A porous polyimide film having a fluorine atom content of 5 atomic % or more on at least one of its main surfaces.

9. The porosity is 60% or more, the openings in the main surface having an amount of fluorine atoms of 5 atomic % or more have an average diameter of 50 nm or more and 3000 nm or less; The polyimide porous film according to claim 8, having a film thickness of 30 μm or more.

10. The polyimide porous film according to claim 7 or 9, wherein the stress at break is 10 MPa or more.

11. The polyimide porous film according to claim 7 or 9, having a breaking elongation of 5% GL or more.

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