WO2022230546A1

WO2022230546A1 - Porous polyimide film

Info

Publication number: WO2022230546A1
Application number: PCT/JP2022/015189
Authority: WO
Inventors: 陽明森田; 巳季夫西端; 武引間
Original assignee: 東京応化工業株式会社
Priority date: 2021-04-28
Filing date: 2022-03-28
Publication date: 2022-11-03
Also published as: JP2022170261A; CN117202984A; KR20230174209A

Abstract

Provided is a porous polyimide film having an excellent gas permeation rate.　The 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.

Description

polyimide porous membrane

The present invention relates to polyimide porous membranes.

Conventionally, various porous membranes have been used for applications such as filters.

For example, as a porous film of polyimide resin, after applying a varnish in which silica particles are dispersed in a solution of polyamic acid or polyimide resin on a substrate, the coating film is heated as necessary to obtain a polyimide film containing silica particles. A porous film is known which is obtained by obtaining and then removing silica in a polyimide film by elution with hydrogen fluoride water (see Patent Document 1).

Japanese Patent No. 5605566

Filters generally used for gas-liquid separation and solid-gas separation are required to improve their separation speed. Therefore, porous membranes used as filters are required to improve gas passage speed.
In this regard, the conventionally known polyimide porous membranes described in Patent Document 1 and the like have room for improvement in terms of gas passage speed.

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 is excellent in gas passage speed.

The present inventors have found that the contact angle of water is 100° on at least one main surface of a porous membrane having air permeability, which is made of a polyimide resin or a polyimide resin composition containing a polyimide resin. The present inventors have found that the above problems can be solved by setting the amount of fluorine atoms in at least one main surface to 5 atm % or more, and have completed the present invention.

A first aspect of the present invention consists of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin,
Porous material has air permeability,
The porous polyimide membrane has a water contact angle of 100° or more on at least one main surface.

A second aspect of the present invention consists of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin,
Porous material has air permeability,
The polyimide porous membrane has a fluorine atom content of 5 atm % or more on at least one main surface.

According to the present invention, it is possible to provide a polyimide porous membrane with excellent gas passage speed.

Hereinafter, 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 purpose of the present invention. .

≪Porous polyimide membrane≫
The polyimide porous membrane is made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin. Hereinafter, the polyimide porous membrane is also simply referred to as "porous membrane".
The porous material forming the porous membrane has air permeability.
At least one main surface of the porous film has a water contact angle of 100° or more, or a fluorine atom content of 5 atm % or more.

Hereinafter, a porous membrane having a water contact angle of 100° or more on at least one main surface is also referred to as a "first porous membrane". Hereinafter, a porous film having a fluorine atom content of 5 atm % or more on at least one main surface is also referred to as a “second porous film”.

The points common to the first porous membrane and the second porous membrane will be described below.

The porous membrane is made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin.
The above porous material has air permeability.
The shape of the voids in the porous material is not particularly limited as long as the porous membrane allows gas to flow from one main surface to the other main surface.
Each of the porous materials constituting the porous membrane preferably has a desired porosity and, as will be described later, has a structure in which spherical pores communicate with each other (hereinafter abbreviated as communicating pores). When the porous membrane is a laminate, the same applies to the porous layer included in the laminate.
A spherical shape as to the shape of the hole is a concept that includes a true spherical shape, but is not necessarily limited to a true spherical shape. The spherical shape may be a substantially spherical shape. A spherical shape also includes a shape that can be recognized as a substantially spherical shape when an enlarged image of the hole is visually confirmed.
Specifically, in a spherical hole, the surface that defines the hole is a curved surface. It is sufficient that the curved surface defines a hole having a perfect spherical shape or a substantially spherical shape.
In addition, when the porous membrane is a laminate, the porosity and the diameter of the spherical pores forming the communicating pores may be the same or different for each porous layer constituting the laminate.

For example, in a porous film, individual spherical pores are typically formed by removing individual fine particles present in a polyimide resin-fine particle composite film described below in a post-process.
Further, the communicating pores are formed by removing, in a post-process, a plurality of fine particles present in contact with each other in the polyimide resin-fine particle composite film in the method for producing a porous film, which will be described later. The portion where the spherical holes communicate with each other in the communicating hole originates from the portion where the plurality of fine particles come into contact with each other before being removed.

The diameter of the opening of 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 200 nm or more and 1000 nm or less, from the viewpoint of achieving both an excellent gas passage speed and the strength of the porous membrane. More preferred.
The diameter of the opening is equal to or substantially equal to the diameter of the spherical hole forming the communicating hole.
The porous membrane has, inside the porous membrane, communication holes penetrating through the porous membrane in the thickness direction as fluid flow paths. This allows fluid to permeate from one major surface of the porous membrane to the other major surface.
Moreover, when the porous membrane is used as a filter, the fluid passes through the inside 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 considerably wide due to the provision of the communicating pores made up of spherical pores. For this reason, it is considered that when the fluid passes through the laminate including the porous membrane, minute substances present in the fluid are likely to be adsorbed to the spherical pores in the porous membrane.

The porous membrane may be a single-layer membrane consisting of only one type of membrane, or a laminated membrane in which two or more types of membranes are laminated in two or more layers.

When the porous film is a laminated film, the laminated film can be formed according to a conventional method such as a lamination method. Further, the porous films included in the laminated film may be sequentially formed on the porous film that constitutes one of the outermost layers of the laminated film. Also, after laminating a precursor film of a porous film by a lamination method, a coating method, or the like, the laminated film having the precursor film laminated thereon is made porous to form a porous film that is a laminated film. Examples of the precursor film include a layer containing fine particles that can be removed by heat decomposition or treatment with an organic solvent, water, acid, alkali, or the like in a resin matrix.

The shape of the voids of the porous material that constitutes the porous membrane is not particularly limited as long as the fluid can pass from one main surface to the other main surface of the porous membrane.
Each of the porous membranes preferably has a desired porosity and, as will be described later, has a structure in which spherical pores communicate with each other (hereinafter abbreviated as communicating pores). When the porous membrane is a laminate, the same applies to the porous layer included in the laminate.
A spherical shape as to the shape of the hole is a concept that includes a true spherical shape, but is not necessarily limited to a true spherical shape. The spherical shape may be substantially spherical, and includes a spherical shape that can be recognized as a substantially spherical shape when an enlarged image of the hole is visually confirmed.
Specifically, in a spherical hole, the surface that defines the hole portion is a curved surface, and the curved surface defines a true spherical or substantially spherical hole.
When the porous membrane is a laminated membrane, the porous membranes constituting the laminated membrane may have the same or different porosities and spherical pore diameters constituting communicating pores.

The film thickness of the porous membrane is not particularly limited. The film thickness of the porous membrane is appropriately determined according to the use of the porous membrane. Typically, the film 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.

The film thickness of the porous film, and the film thickness of each porous film contained in the laminated film when the porous film is a laminated film, is obtained by measuring the thickness at a plurality of locations with a micrometer, for example, and averaging the thicknesses. or by observing and averaging the cross section of the film with a scanning electron microscope (SEM).

The porosity of the porous membrane is preferably 60% or more, more preferably 65% or more and 85% or less, and even more preferably 70% or more and 80% or less, in terms of excellent gas passage speed.

The porosity indicates the ratio of voids per unit volume of the porous membrane. The porosity can be calculated by the following formula (A).
Porosity (%) = {volume of test piece (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 when producing the porous membrane.

<Method for producing porous membrane>
A porous membrane containing therein communicating pores in which spherical pores communicate with each other, which is a preferable porous membrane, is produced, for example, by the following method.

In particular,
an unfired composite film-forming step of forming an unfired composite film on a substrate using the composition for producing a porous film;
A baking step of baking the unbaked composite film to obtain a polyimide resin-fine particle composite film;
and a step of removing fine particles from the polyimide resin-fine particle composite film.

In the following, regarding the method for producing a porous membrane, the composition for producing a porous membrane and the preferred method for producing the above-mentioned porous membrane will be described in detail.

[Composition for producing porous membrane]
The porous film-producing composition contains a compound capable of forming a polyimide resin.
A compound capable of forming a polyimide resin may be a monomer for forming a polyimide resin, or may be a polyamic acid that is a precursor of a polyimide resin.
Polyamic acid is preferred as a compound capable of forming a polyimide resin.

The essential or optional components contained in the composition for producing a porous film are described below.

[Polyamide acid]
As the polyamic acid, any resin obtained by polymerizing any tetracarboxylic dianhydride and diamine can be used without particular limitation. The amounts of tetracarboxylic dianhydride and diamine to be used are not particularly limited. The amount of diamine used relative to 1 mol of tetracarboxylic dianhydride is preferably 0.50 mol or more and 1.50 mol or less, more preferably 0.60 mol or more and 1.30 mol or less, and 0.70 mol or more and 1.20 mol. Molar or less is particularly preferred.

The tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydrides conventionally used as synthetic raw materials for polyamic acid. The tetracarboxylic dianhydride may be either an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. It is preferable to use an aromatic tetracarboxylic dianhydride from the viewpoint of heat resistance of the resulting polyimide resin. Tetracarboxylic dianhydrides may be used singly or in combination of two or more.
As will be described later, in order to increase the contact angle of water and the fluorine atom content (atm %) on the main surface of the porous film, the polyimide resin may contain structural units having fluorine atoms. In this case, tetracarboxylic dianhydrides containing fluorine atoms are used.

Preferred specific examples of aromatic tetracarboxylic dianhydrides 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, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(2,3 -dicarboxyphenyl)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-anthracene Tetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bisphthalic anhydride fluorene, 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride things, etc. Examples of aliphatic tetracarboxylic dianhydrides include ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1,2, 4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride and the like. Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferred in terms of price, availability, and the like. Moreover, these tetracarboxylic dianhydrides can also be used individually by 1 type or in mixture of 2 or more types.

Tetracarboxylic dianhydrides containing a fluorine atom used when the polyimide resin contains a structural unit having a fluorine atom include (trifluoromethyl)pyromellitic dianhydride, di(trifluoromethyl)pyro Melellitic 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)-3,3′,4,4′-tetracarboxybiphenyl dianhydride 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-3,4-dicarboxyphenoxy)benzene dianhydride, 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)-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(trifluoro methyl) biphe nyl 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, 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, hexafluoro-3,3'-oxybisphthalic acid, and the like. be done.

The diamine can be appropriately selected from diamines conventionally used as raw materials for synthesizing polyamic acid. The diamine may be either an aromatic diamine or an aliphatic diamine, but is preferably an aromatic diamine from the viewpoint of heat resistance of the resulting polyimide resin. These diamines may be used individually by 1 type, and may be used in combination of 2 or more type.
As will be described later, in order to increase the contact angle of water and the fluorine atom content (atm %) on the main surface of the porous film, the polyimide resin may contain structural units having fluorine atoms. In this case, diamines containing fluorine atoms are used.

Examples of aromatic diamines include diamino compounds in which one or about two to ten 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 their derivatives, diaminohexaphenyl compounds and their derivatives, and cardo-type fluorenediamine derivatives.

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

In the diaminobiphenyl compound, two aminophenyl groups are bonded together. Examples include 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl and the like.

A diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded between phenyl groups via another group. The bond is ether bond, sulfonyl bond, thioether bond, bond by alkylene or derivative group thereof, imino bond, azo bond, phosphine oxide bond, amide bond, ureylene bond and the like. A derivative group of an alkylene group in which the number of carbon atoms in the alkylene bond is about 1 or more and 6 or less is an alkylene group substituted with one or more 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'-diaminodiphenyl sulfone, 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-aminophenoxy)phenyl ] hexafluoropropane and the like.

Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred in terms of price, availability, etc.

A diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are both bonded via another group. Other groups are selected from the same groups as in the diaminodiphenyl compound. Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, 1,4-bis(p-aminophenoxy)benzene and the like. be able to.

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

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

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

Cardo-type fluorenediamine derivatives include 9,9-bisaniline fluorene and the like.

The number of carbon atoms in the aliphatic diamine is preferably 2 or more and 15 or less, for example. Specific examples of aliphatic diamines include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

A compound in which the hydrogen atoms of these diamines are substituted with at least one substituent selected from the group of halogen atoms, methyl groups, methoxy groups, cyano groups, phenyl groups and the like may also be used.

Examples of the diamine containing a fluorine atom used when the polyimide resin contains a structural unit containing a fluorine atom 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-diamino Benzene, 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)-1,4-phenylenediamine, 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]hexafluoropropane, 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-aminophenoxy)-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)diphenylsulfone, 4,4'-bis(3-amino-5-trifluoromethylphenoxy)diphenylsulfone, 1,4-bis{2- [4-(4-aminophenoxy)phenyl]hexafluoropropan-2-yl}benzene, 4,4'-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, hexafluoro-2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and the like.

There are no particular restrictions on the means of producing polyamic acid. For example, a known technique such as a method of reacting an acid and a diamine component in a solvent can be used.

The reaction of tetracarboxylic dianhydride and diamine is usually carried out in a solvent. The solvent used for the reaction of the tetracarboxylic dianhydride and the diamine is 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. not. A solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

Examples of solvents 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-diethylformamide, N-methylcaprolactam, N,N,N',N'-tetramethylurea; β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, Lactone-based polar solvents such as γ-caprolactone and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; and ethers; cresols, and phenolic solvents such as xylene mixed solvents.
These solvents may be used individually by 1 type, and may be used in combination of 2 or more type. There are no particular restrictions on the amount of solvent used. The solvent is desirably used in such an amount that the content of the produced polyamic acid in the reaction solution is 5% by mass or more and 50% by mass or less.

Among these solvents, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethyl Nitrogen-containing polar solvents such as formamide, N-methylcaprolactam and N,N,N',N'-tetramethylurea are preferred.

The polymerization temperature is generally preferably −10° C. or higher and 120° C. or lower, more preferably 5° C. or higher and 30° C. or lower. Although the polymerization time varies depending on the raw material composition used, it is usually preferably 3 hours or more and 24 hours or less.
Polyamic acid may be used alone or in combination of two or more.

[Polyimide resin]
The structure and molecular weight of the polyimide resin are not limited. Various known polyimide resins can be used. The polyimide resin may have a condensable functional group such as a carboxyl group or a functional group that promotes a cross-linking reaction or the like during baking in the side chain. When the porous film-producing composition contains a solvent, a soluble polyimide resin that is soluble in the solvent is preferred.

In order to obtain a solvent-soluble polyimide resin, it is effective to introduce a flexible bent structure into the main chain. Examples of monomers capable of introducing a flexible bent structure into the main chain include fatty acids 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, 4,4'-diaminobenzanilide; polyoxyethylenediamine, polyoxy Polyoxyalkylene diamines such as propylene diamine and polyoxybutylene diamine; polysiloxane diamines; 2,3,3',4'-oxydiphthalic anhydride, 3,4,3',4'-oxydiphthalic anhydride, 2, 2-bis(4-hydroxyphenyl)propane dibenzoate-3,3',4,4'-tetracarboxylic dianhydride and the like. It is also effective to use a monomer having a functional group that improves solubility in solvents. Examples of monomers having functional groups that improve solubility in solvents include 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, 2-trifluoromethyl-1,4- Fluorinated diamines such as phenylenediamine are included. Furthermore, in addition to the monomer for improving the solubility of the polyimide resin, the monomers described in the polyamic acid section above can be used in combination within a range that does not impair the solubility.
Each of the polyimide resin and its monomer may be used alone or in combination of two or more.

There is no particular limitation on the means for producing the polyimide resin. For example, known techniques such as chemical imidization or thermal imidization of polyamic acid can be used. Examples of such polyimide resins include aliphatic polyimide resins (full-aliphatic polyimide resins), aromatic polyimide resins, and the like, with aromatic polyimide resins being preferred. The aromatic polyimide resin is a polyimide resin obtained by a ring closure reaction of a polyamic acid having a repeating unit represented by formula (1) by thermal or chemical means, or a polyimide resin having a repeating unit represented by formula (2). etc. In the formula, Ar represents an aryl group. When the porous film-producing composition contains a solvent, these polyimide resins are preferably dissolved in the solvent to be used.

[Fine particles]
The material of the fine particles is not particularly limited as long as it is insoluble in the solvent contained in the composition for producing a porous film and can be removed from the polyimide resin-fine particle composite film later. Various known materials that satisfy the above conditions can be used as the material of the fine particles. Examples of inorganic materials include silica (silicon dioxide); metal oxides such as titanium oxide and alumina (Al ₂ O ₃ ). Organic materials include organic polymers such as high-molecular-weight olefin polymers (polypropylene, polyethylene, etc.), polystyrene, epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyesters, and polyethers.

Specific examples of fine particles include colloidal silica. Among colloidal silica, monodisperse spherical silica particles are preferable because uniform pores can be formed.

Further, the fine particles preferably have a high sphericity and a small particle size distribution index. Fine particles satisfying these conditions are excellent in dispersibility in the composition for producing a porous film, and can be used in a state in which they do not aggregate with each other. The average particle diameter of the fine particles is appropriately selected in consideration of the opening diameter on the surface of the porous membrane and the thickness of the porous membrane. For example, the average particle diameter of the fine particles is preferably 50 nm or more, more preferably 100 nm or more and 2000 nm or less, and even more preferably 200 nm or more and 1000 nm or less. By satisfying these conditions, the pore size of the porous membrane obtained by removing fine particles can be made uniform.
Fine particles may be used singly or in combination of two or more.

[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 of the tetracarboxylic dianhydride and the diamine. A solvent may be used independently and may be used in combination of 2 or more type.

[Dispersant]
A dispersant may be used together with the fine particles for the purpose of uniformly dispersing the fine particles in the composition for producing a porous film. By adding a dispersant to the composition for producing a porous film, the fine particles can be more uniformly mixed in the composition for producing a porous film, and furthermore, the fine particles can be mixed more uniformly in the film formed from the composition for producing a porous film. , fine particles can be uniformly distributed. As a result, dense openings can be provided on the surface of the finally obtained porous membrane, and the front and back surfaces of the porous membrane can be efficiently communicated with each other, thereby improving the air permeability of the porous membrane. Furthermore, the use of a dispersant facilitates improvement in the drying property of the composition for producing a porous film, and also facilitates improvement in the peelability of the formed unfired composite film from a substrate or the like.

The dispersant is not particularly limited. Known dispersants can be used. Specific examples of dispersants include coconut fatty acid salts, castor sulfated oil salts, lauryl sulfate salts, polyoxyalkylene allylphenyl ether sulfate salts, alkylbenzenesulfonic acids, alkylbenzenesulfonates, alkyldiphenyletherdisulfonates, and alkylnaphthalenesulfones. Anionic surfactants such as acid salts, dialkyl sulfosuccinate salts, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salts, polyoxyethylene allylphenyl ether phosphate salts; oleylamine acetate, laurylpyridinium chloride, cetylpyridinium chloride, lauryltrimethylammonium cationic surfactants such as chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, didecyldimethylammonium chloride; coconut alkyldimethylamine oxide, fatty acid amidopropyldimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amidobetaine type active agent, Amphoteric surfactants such as alanine-type active agents and lauryliminodipropionic acid; Styryl phenyl ether, polyoxyalkylene polystyryl phenyl ether, etc., polyoxyalkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether nonionic surfactant, polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylenated castor oil , polyoxyethylenated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, other polyoxyalkylene-based nonionic surfactants such as fatty acid diethanolamide; octyl stearate, trimethylolpropane tridecanoate, etc. and polyether polyols such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris(polyoxyalkylene) ether. Two or more of the above dispersants may be mixed and used.

In the porous film-producing composition, the content of the dispersant is preferably 0.01% by mass or more and 5% by mass or less, and preferably 0.05% by mass or more, based on the mass of the fine particles, from the viewpoint of film-forming properties. 1% by mass or less is more preferable, and 0.1% by mass or more and 0.5% by mass is even more preferable.

[Suitable method for producing porous membrane]
[Unfired Composite Film Forming Step]
In the unfired composite film-forming step, for example, the above-described composition for producing a porous film is applied onto a substrate, and the temperature is 0° C. or higher and 100° C. or lower under normal pressure or vacuum, preferably 10° C. or higher and 100° C. or less under normal pressure. An unfired composite film can be formed by drying at . Examples of substrates include PET films, SUS substrates, and glass substrates.

In addition, when peeling the unfired composite film from the substrate, a substrate provided with a release layer can be used in order to further improve the peelability of the film. When the release layer is provided on the substrate in advance, the release agent is applied onto the substrate and dried or baked before the porous film-producing composition is applied. As the mold release agent, known mold release agents such as alkyl phosphate ammonium salt type, fluorine type or silicone can be used without particular limitation. When the dried unfired composite film is peeled off from the substrate, a slight release agent remains on the peeled surface of the unfired composite film. The release agent remaining on the peeled surface can cause discoloration of the composite film during firing and adversely affect the electrical properties of the finally obtained porous film. Therefore, it is preferable to remove the release agent remaining on the release surface as much as possible. For the purpose of removing the release agent, a washing step may be introduced in which the unfired composite film separated from the substrate is washed with an organic solvent.

On the other hand, when a substrate without a release layer is used for forming the unfired composite film, the process of forming the release layer and the cleaning process can be omitted. Moreover, in the production of the unfired composite film, a step of immersing in a solvent containing water, a pressing step, and a drying step after the immersing step may be provided as optional steps before the firing step described later.

[Baking process]
The unbaked composite film is subjected to post-treatment (baking) by heating to form a composite film (polyimide resin-fine particle composite film) composed of polyimide resin and fine particles. The firing temperature in the firing step is preferably 120° C. or higher and 450° C. or lower, more preferably 150° C. or higher and 400° C. or lower, although it varies depending on the structure of the unsintered composite film and the presence or absence of a condensing agent. Moreover, when using fine particles made of an organic material, it is necessary to set the firing temperature to a temperature lower than the thermal decomposition temperature of the organic material. It is preferable to complete the imidization in the firing step.

The firing conditions are, for example, a method of raising the temperature from room temperature to 400 ° C. in 3 hours and then holding it at 400 ° C. for 20 minutes, or raising the temperature from room temperature to 400 ° C. in steps of 50 ° C. (holding for 20 minutes at each step) ) and finally holding at 400° C. for 20 minutes. When an unsintered composite film is formed on a substrate and the unsintered composite film is once peeled off from the substrate, a method is adopted in which the ends of the unsintered composite film are fixed to a SUS formwork or the like to prevent deformation. can also

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

[Resin removal step]
It may have a resin removing step of removing at least part of the resin portion of the polyimide resin-fine particle composite film before the fine particle removing step, or removing at least part of the porous film after the fine particle removing step. .
By removing at least part of the resin portion of the polyimide resin-fine particle composite film before the fine particle removal step, or by removing at least part of the porous membrane after the fine particle removal step, compared to the case where no removal is performed. , it is possible to improve the porosity of the porous membrane, which is the final product.

The step of removing at least a portion of the resin portion of the polyimide resin-fine particle composite film, or the step of removing at least a portion of the resin portion of the polyimide resin-fine particle composite film can be performed by a normal chemical etching method, physical removal method, Alternatively, it can be carried out by a method combining these.

The chemical etching method includes treatment with a chemical etchant such as an inorganic alkaline solution or an organic alkaline solution. Inorganic alkaline solutions are preferred. Examples of inorganic alkaline solutions include hydrazine hydrate and ethylenediamine containing hydrazine hydrate; solutions of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate and sodium metasilicate; ammonia solution; Etching solutions containing alkali, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components are included. Examples of 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; and dimethylethanolamine. alcohol amines such as , triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; alkaline solutions such as cyclic amines such as pyrrole and pyreridine.

Pure water and alcohols can be appropriately selected as the solvent for each of the above solutions. An appropriate amount of surfactant can also be added to each of the above solutions. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

Physical methods include, for example, plasma (oxygen, argon, etc.), dry etching using corona discharge, etc., and dispersion of abrasives (e.g., alumina (hardness 9), etc.) on the surface of the porous film at 30 m/s or more. A method of treating the film surface by discharging at a speed of 100 m/s or less can be used.

On the other hand, as a physical method that can be applied only to the resin removal step that is performed after the fine particle removal step, a base film (for example, a polyester film such as a PET film) wetted with a liquid is pressed against the surface of the laminate to be treated, and then the backing film is removed. A method of peeling off the laminate from the mount film before drying or after drying the mount film can also be adopted. Due to the surface tension or electrostatic adhesion force of the liquid, the porous membrane is peeled off from the backing film while only the surface layer of the porous membrane existing on the surface to be treated remains on the backing film. .

<First porous film>
The first porous membrane is the polyimide porous membrane described above and has a water contact angle of 100° or more on at least one main surface.
Since the first porous membrane exhibits the above water contact angle on at least one main surface, the porous membrane exhibits an excellent gas passage rate.
The contact angle of water is preferably 105° or more, more preferably 110° or more. Although the upper limit of the contact angle of water is not particularly limited, it is realistically, for example, 150° or less, and may be 130° or less.

Here, the above water contact angle is a static contact angle. For the static contact angle of water, for example, using Dropmaster 700 (manufactured by Kyowa Interface Science Co., Ltd.), after applying 2.0 μL of pure water droplets to the surface of the porous membrane, the contact angle after 10 seconds of dropping It is measurable.

In addition, in the first porous membrane, it is preferable that the dynamic contact angle of water on the main surface where the contact angle of water is 100°C or more is 30° or more. The dynamic contact angle of water may be 40° or more, or 50° or more. Although the upper limit of the dynamic contact angle of water is not particularly limited, in reality it is, for example, 120° or less, and may be 100° or less.

The dynamic contact angle of water can be measured as follows using, for example, Dropmaster 700 (manufactured by Kyowa Interface Science Co., Ltd.). First, 2.0 μL of pure water droplets are dropped on the surface of the porous membrane. Next, pure water is supplied to the droplet from the syringe needle until the total amount of pure water reaches 50.0 μL, and the droplet of pure water is expanded. The measurement was started when the expanded state of the droplet was maintained for 3 seconds, and pure water was sucked from the droplet at a rate of 6.0 μL/sec from the start of the measurement. The value of the receding angle when the edge shrinks by 10 dots from the edge of the droplet at the start of measurement due to suction of pure water is measured as the dynamic contact angle of water.

In the first porous membrane, the method for making the contact angle of water on the main surface 100° or more is not particularly limited. Such methods include, for example, a method of adhering or bonding a water repellent agent to the main surface of the untreated porous membrane prepared by the above method, and a method of incorporating a water-repellent material into the polyimide resin composition constituting the first porous film.

The water repellent agent used in the method of adhering or bonding the water repellent agent to the main surface is capable of adhering or bonding to the polyimide resin, and is capable of increasing the contact angle of water on the main surface of the porous membrane to 100° or more. It is not particularly limited as long as it can be increased. Preferred water repellent agents include silicone water repellent agents and fluorine-based water repellent agents. A fluorine-based water repellent agent is more preferable in terms of the water repellent effect.

As the fluorine-based water repellent agent, a fluorine-containing organic compound itself or a liquid composition containing a fluorine-containing organic compound is typically 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. Moreover, the fluorine-containing organic compound may be an aliphatic compound, an aromatic compound, or a compound containing an aliphatic portion and an aromatic portion.

Examples of fluorine-containing organic compounds include fluoroalkanes, fluoroalkanols, bisfluoroalkyl ethers, fluoroalkyl alkyl ethers, fluorinated aliphatic ketones, fluorinated aliphatic carboxylic acids, fluorinated aliphatic carboxylic acid alkyl esters, fluorinated fatty group carboxylic acid fluoroalkyl esters, aliphatic carboxylic acid fluoroalkyl esters, fluoroalkylbenzene carboxylic acids, fluoroalkylbenzene carboxylates, fluoroalkylbenzene sulfonic acids, fluoroalkylbenzene sulfonates, and the like.

A fluorine-containing silane coupling agent is also suitably used as the fluorine-containing organic compound. Functional groups containing active hydrogen atoms such as hydroxyl groups, amino groups and carboxyl groups are often present on the surface of porous membranes that are not treated with a fluorine-containing organic compound.
A fluorine-containing silane coupling agent can react and bond with such functional groups containing active hydrogen atoms.

The fluorine-containing silane coupling agent is not particularly limited as long as it is a silane coupling agent containing a fluorine-containing functional group. Fluorine-containing silane coupling agents include fluoroalkyltrialkoxysilanes, difluoroalkyldialkoxysilanes, fluoroalkylalkyldialkoxysilanes, bis(trialkoxysilyl)fluoroalkanes, fluoroalkyltriisocyanatesilanes, and bis(trichlorosilyl)fluoroalkanes. , and bis(triisocyanatosilyl) fluorinated linear aliphatic compounds.
Preferred specific examples of fluorine-containing silane coupling agents include perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, perfluorooctyltrimethoxysilane, perfluorooctyltrimethoxysilane, fluorooctyltriethoxysilane, perfluorododecyltrimethoxysilane, perfluorododecyltriethoxysilane, perfluoropentyltriethoxysilane, perfluoropentyltrimethoxysilane, and 1H,1H,2H,2H-heptadecafluorodecyltrimethoxysilane fluoroalkylalkoxysilanes such as
fluoroalkyl triisocyanate silanes such as 1H,1H,2H,2H-heptadecafluorodecyltriisocyanate silane;
bis(trichlorosilyl)fluoroalkanes such as 1,6-bis(trichlorosilyl)-2,5-ditrifluoromethyl-2,3,3,4,4,5-hexafluoropropane;
1,10-bis(triisocyanatosilyl)-1H,1H,2H,2H,9H,9H,10H,10H-dodecafluorodecane, 1,8-bis(triisocyanatosilyl)-3,6-ditrifluoromethyl- 3,4,4,5,5,6-hexafluorooctane, N,N'-di(2-triisocyanatosilylethyl)-1,8-dodecafluorooctane diamide, 1,4-di(2- triisocyanatosilylethoxy)-1,4-ditrifluoromethylhexafluorobutane, 1,2-di(2-triisocyanatosilylethoxy)tetrafluoroethane, 1,2-di(2-triisocyanatosilylethylthio)tetrafluoro Bis(triisocyanatosilyl) fluorinated linear aliphatic compounds such as ethane can be mentioned.

A fluororesin is also suitably used as the fluorine-containing organic compound. The type of fluororesin 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), polyfluoride Examples include vinylidene (PVDF) and its copolymer, polyvinyl fluoride (PVA), and ethylene/tetrafluoroethylene copolymer (ETFE). Among these, polyvinylidene fluoride (PVDF) and its copolymer are preferable from the viewpoint of improving wear resistance. In the case of a copolymer, monomers to be copolymerized include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride and the like.
Further, fine particles are prepared as described in JP-A-10-140144 using the fluorine-containing organic compound itself or a liquid composition containing the fluorine-containing organic compound, and the prepared fine particles are subjected to a blasting apparatus or the like. The water-repellent treatment may be performed by colliding against the porous membrane in the atmosphere.

By bringing the above-described water repellent agent into contact with the main surface of the porous film, a water repellent component such as a fluorine-containing organic compound contained in the water repellent agent adheres or bonds to the main surface.
The contact angle of water on the main surface can be adjusted by adjusting the adhesion amount or bonding amount of the water repellent component to the main surface. The amount of adhesion or bonding of the water repellent component can be adjusted 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.

In the method of including structural units containing a fluorine atom in the polyimide resin contained in the porous material constituting the first porous film, the above-mentioned tetracarboxylic dianhydride containing a fluorine atom and the above-mentioned fluorine atom-containing A polyimide resin prepared using at least one of diamines is used.

In the polyimide resin, the amount of structural units derived from the above-mentioned tetracarboxylic dianhydride containing a fluorine atom and the amount of the structural units derived from the above-mentioned diamine containing a fluorine atom are the main components of the first porous film. There is no particular limitation as long as the contact angle of water on the surface is a desired value.
Generally, the contact angle of water tends to increase as the amount of fluorine atoms on the main surface of the porous membrane increases. Therefore, by adjusting the ratio of the fluorine atom-containing monomer in the monomer used for the production of the polyimide resin, or by adjusting the fluorine atom content in the monomer, the porous membrane can adjust the contact angle of water on the main surface of

In the method of including a water-repellent material in the polyimide resin composition that constitutes the first porous film, for example, a method of including a water-repellent material in the composition for producing a porous film when forming the porous film. Adopted.

As the water-repellent material, the components described above for the water-repellent agent can be used. As mentioned above, the green composite membrane is fired at a high temperature in forming the porous membrane. For this reason, the aforementioned fluororesin is preferable as the water-repellent material in terms of heat resistance. The form of the fluororesin is not particularly limited. The fluororesin particles are preferably added to the porous film-producing composition in order to facilitate uniform dispersion of the fluororesin in the polyimide resin composition.

The particle size of the fluororesin particles is not particularly limited as long as a porous film comprising a polyamide resin composition containing uniformly dispersed fluororesin particles can be formed. The volume average particle diameter of the fluororesin particles is preferably 10 nm or more and 1000 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.

In the first porous membrane, 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, further preferably 20 atm% or more, and 30 atm% or more. is particularly preferred.
The upper limit of the amount of fluorine atoms on the main surface is not particularly limited as long as the contact angle of water is 100° or more. The upper limit of the amount of fluorine atoms is, for example, 68 atm % or less, and may be 50 atm % or less.

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

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

In terms of achieving both excellent gas passage speed and strength of the porous membrane,
The porosity is 60% or more,
The average diameter of the openings on the main surface where the contact angle of water is 100° or more is 50 nm or more and 3000 nm or less,
It is preferable that the film thickness is 30 μm or more.

In addition, the stress at breakage 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 elongation at break of the first porous membrane is preferably 5% GL or more, more preferably 10% GL or more, still more preferably 15% GL or more, and particularly preferably 20% GL or more.

<Second porous membrane>
The second porous film is the polyimide porous film described above, and has a fluorine atom content of 5 atm % or more on at least one main surface.
In the second porous membrane, when the amount of fluorine atoms on at least one main surface is within the above range, the porous membrane exhibits an excellent gas passage rate.
The amount of fluorine atoms in the main surface is preferably 5 atm % or more, more preferably 10 atm % or more, still more preferably 20 atm % or more, and particularly preferably 30 atm % or more.
The upper limit of the amount of fluorine atoms in the main surface is, for example, 68 atm % or less, and may be 50 atm % or less.

The amount of fluorine atoms on the main surface is adjusted by a method similar to the method described for the first porous film.

In terms of achieving both excellent gas passage speed and strength of the porous membrane,
The porosity is 60% or more,
The average diameter of the openings in the main surface where the amount of fluorine atoms is 5 atm % or more is 50 nm or more and 3000 nm or less,
It is preferable that the film thickness is 30 μm or more.

In addition, the stress when the second porous membrane breaks is preferably 10 MPa or more, more preferably 15 MPa or more, and even more preferably 20 MPa or more. The elongation at break of the second porous membrane is preferably 5% GL or more, more preferably 10% GL or more, still more preferably 15% GL or more, and particularly preferably 20% GL or more.

Hereinafter, the present invention will be described more specifically with reference to Examples. The scope of the invention is not limited to the examples below.

[Example 1]
Slurry A containing 70 parts by mass of fine silica particles, 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 vessel at 400 rpm for 15 minutes with a stirring blade. Thereafter, the slurry A after stirring was subjected to dispersion treatment five times at 200 MPa using a dispersion device (NVL-S008, manufactured by Yoshida Kikai Kogyo Co., Ltd.). Silica having an average particle diameter of 300 nm was used as the silica fine particles.

Slurry A after dispersion treatment and 30 parts by mass of polyamic acid were mixed to obtain slurry B. Polyamic acid was used as a dimethylacetamide solution with a solid concentration of 20% by mass. Further, as the polyamic acid, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (hereinafter referred to as 6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexa A polymer obtained by polymerizing equimolar fluoropropane (hereinafter referred to as HFBAPP) was used.
Slurry B contained dimethylacetamide and gamma-butyrolactone at a solids concentration of 29% by weight. The mass ratio of dimethylacetamide and gamma-butyrolactone in slurry B was 90:10 as dimethylacetamide:gamma-butyrolactone.

The resulting slurry B was dispersed in a container with a capacity of 200 mL by stirring with a stirring blade at 400 rpm for 30 minutes to prepare a composition for producing a porous film. After coating the composition for producing a porous film on a PET film, the film was heated at 90° C. for 300 seconds to remove the solvent and form a coating film having a thickness of about 40 μm.

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

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

[Example 2]
Except for changing the amount of polyamic acid used from 30 parts by mass to 25 parts by mass and adding 5 parts by mass of fine particles of polytetrafluoroethylene (PTFE) having an average particle size of 300 nm together with the polyamic acid, in Comparative Example 1 A slurry D was obtained in the same manner as the slurry B preparation method. The PTFE microparticles were used as a dispersion liquid in which PTFE microparticles having a solid 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 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.

[Example 3]
Chemical etching was performed by immersing the porous film obtained in the same manner as in Comparative Example 1 in an alkaline etching solution for 180 seconds to partially remove the surface of the polyimide resin. Specifically, after pre-wetting the porous membrane by immersing it in an isopropanol aqueous solution with a concentration of 10% by mass, the porous membrane is immersed in an aqueous tetramethylammonium hydroxide (TMAH) solution with a concentration of 1.00% by mass. Then, chemical etching was performed by washing and drying the porous membrane.
The chemically etched porous film was again heat-treated (baked) at 380° C. for 10 minutes to re-imidize the ring-opened portion with alkali to obtain a porous film. The main surface of the obtained porous film is subjected to a water-repellent treatment to attach the fluororesin using a water repellent agent containing fluororesin (Adlon (registered trademark) L-4614CR, manufactured by Fluorocoat). A porous membrane was obtained.

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

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

<Measurement of air permeability>
Using a porous membrane sample with a size of 5 cm×5 cm, the time required for 100 mL of air to pass through the sample was measured according to JIS P 8117 using a Gurley densometer (manufactured by Toyo Seiki Co., Ltd.). The smaller the air permeability value, the shorter the passage time of 100 mL of air, and the higher the gas passage speed of the sample.

<Measurement of stress at break and elongation at break>
A strip-shaped porous membrane sample with a size of 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 (manufactured by Shimadzu Corporation).

A K-Alpha (registered trademark) XPS system (manufactured by Thermo Fisher Scientific) was used to measure the fluorine atomic weight on the main surface of the sample of the porous membrane.

According to Examples 1 to 3, when the contact angle of water on at least one main surface of the porous membrane is 100° or more, or the amount of fluorine atoms is 5 atm% or more, the gas of the porous membrane It can be seen that the passing speed is excellent.
On the other hand, according to Comparative Examples 1 and 2, when the contact angle of water is less than 100° or the amount of fluorine atoms is less than 5 atm % on the main surface of the porous membrane, the passage of gas through the porous membrane It can be seen that the speed is inferior.

Claims

Made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin,
The porous material has air permeability,
A polyimide porous membrane having a water contact angle of 100° or more on at least one main surface.
The porous polyimide membrane according to claim 1, wherein the contact angle of water is 100° or more and the dynamic contact angle of water is 30° or more on at least one main surface.
3. The polyimide porous membrane according to claim 1 or 2, wherein a fluorine-containing organic compound is adhered or bonded to the main surface having a water contact angle of 100° or more.
The polyimide porous membrane according to claim 1 or 2, wherein the polyimide resin contains structural units containing fluorine atoms.
The polyimide porous membrane according to claim 1 or 2, wherein the porous material comprises a polyimide resin composition, and the polyimide resin composition contains a fluororesin.
The polyimide porous membrane according to claim 4 or 5, wherein the amount of fluorine atoms on the main surface having a water contact angle of 100° or more is 5 atm% or more.
The porosity is 60% or more,
The average diameter of the 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 polyimide porous membrane according to any one of claims 1 to 6, which has a thickness of 30 µm or more.
Made of a porous material made of a polyimide resin or a polyimide resin composition containing a polyimide resin,
The porous material has air permeability,
A polyimide porous membrane having a fluorine atom content of 5 atm % or more on at least one main surface.
The porosity is 60% or more,
The average diameter of the openings in the main surface where the amount of fluorine atoms is 5 atm % or more is 50 nm or more and 3000 nm or less,
9. The polyimide porous membrane according to claim 8, which has a thickness of 30 μm or more.
The polyimide porous membrane according to claim 7 or 9, which has a stress at break of 10 MPa or more.
The polyimide porous membrane according to claim 7 or 9, which has a breaking elongation of 5% GL or more.