CN117202984A

CN117202984A - Polyimide porous film

Info

Publication number: CN117202984A
Application number: CN202280030410.3A
Authority: CN
Inventors: 森田阳明; 西端巳季夫; 引间武
Original assignee: Tokyo Ohka Kogyo Co Ltd
Current assignee: Tokyo Ohka Kogyo Co Ltd
Priority date: 2021-04-28
Filing date: 2022-03-28
Publication date: 2023-12-08
Also published as: JP2022170261A; KR20230174209A; WO2022230546A1

Abstract

Disclosed is a polyimide porous membrane having excellent gas passage rate. In a porous film having air permeability, which is formed of a polyimide resin or a polyimide resin composition containing a polyimide resin, the contact angle of water is set to 100 DEG or more on at least one main surface, or the amount of fluorine atoms in at least one main surface is set to 5atm% or more.

Description

Polyimide porous film

Technical Field

The present invention relates to a polyimide porous membrane.

Background

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

For example, as a porous film of a polyimide resin, a porous film is known which is obtained by coating a substrate with a varnish obtained by dispersing silica particles in a solution of a polyamic acid or a polyimide resin, heating the coated film as necessary to obtain a polyimide film containing silica particles, and then eluting and removing silica in the polyimide film with an aqueous solution of hydrogen fluoride (see patent document 1).

Prior art literature

Patent literature

Patent document 1: japanese patent No. 5605566

Disclosure of Invention

Problems to be solved by the invention

In general, a filter used for gas-liquid separation and solid-gas separation is required to increase the separation speed. Therefore, the porous membrane used as a filter is required to increase the gas passing rate.

In this regard, conventionally known polyimide porous membranes described in patent document 1 and the like have room for improvement in terms of the gas passing rate.

The present application has been made in view of the above-described circumstances, and an object thereof is to provide a polyimide porous membrane excellent in gas passage rate.

Means for solving the problems

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

The first aspect of the present application is a polyimide porous film formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin,

the porous material has air permeability and is provided with a plurality of air holes,

The contact angle of water on at least one main surface is 100 DEG or more.

The second aspect of the present invention is a polyimide porous film formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin,

the amount of fluorine atoms in at least one main surface is 5atm% or more.

Effects of the invention

According to the present invention, a polyimide porous membrane excellent in gas passage rate can be provided.

Detailed Description

The embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention.

Polyimide porous film

The polyimide porous film is formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin. Hereinafter, the polyimide porous membrane will also be simply referred to as "porous membrane".

The porous material constituting the porous membrane has air permeability.

The contact angle of water is 100 DEG or more or the amount of fluorine atoms is 5atm% or more on at least one main surface of the porous film.

Hereinafter, a porous film having a contact angle of 100 ° or more with respect to water on at least one main surface is also referred to as "1 st porous film". Hereinafter, the porous film having 5atm% or more of fluorine atoms on at least one main surface is also referred to as "the 2 nd porous film".

Hereinafter, the common points of the 1 st porous film and the 2 nd porous film will be described.

The porous film is formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin.

The porous material has air permeability.

The shape of the voids in the porous material is not particularly limited as long as the porous film can allow the gas to flow from one main surface to the other main surface.

The porous materials constituting the porous film preferably each have a desired void ratio and have a structure in which spherical pores communicate with each other (hereinafter, simply referred to as communication pores) as described later. In the case where the porous film is a laminate, the same applies to the porous layer included in the laminate.

The sphere related to the shape of the hole is a concept including a sphere, but is not necessarily limited to a sphere. The spherical shape may be substantially spherical. The shape that can be recognized as a substantially spherical shape when the enlarged image of the hole portion is visually recognized is also included in the spherical shape.

Specifically, in the spherical hole, the surface of the predetermined hole portion is a curved surface. The curved surface may define a hole having a spherical shape or a substantially spherical shape.

In the case where the porous film is a laminate, the porosity and the pore diameter of the spherical pores constituting the communication pores may be the same or different for each porous layer constituting the laminate.

For example, in the porous film, each spherical hole is typically formed by removing each particle present in a polyimide resin-particle composite film described later in a subsequent step.

In the method for producing a porous film described later, the communication holes are formed by removing a plurality of particles in contact with each other in the polyimide resin-particle composite film in a subsequent step. The portion where the spherical holes in the communication holes communicate with each other is derived from a portion where the plurality of fine particles before removal contact each other.

The diameter of the opening of the porous film is preferably 50nm to 3000nm, more preferably 100nm to 2000nm, and even more preferably 200nm to 1000nm, from the viewpoint of achieving both excellent gas passage rate and strength of the porous film.

The diameter of the opening is equal to or substantially equal to the diameter of the spherical hole constituting the communication hole.

The porous membrane has, as a fluid flow path, communication holes penetrating the porous membrane in the thickness direction inside the porous membrane. Thus, the fluid can permeate from one main surface to the other main surface of the porous membrane.

In the case of using a porous membrane as a filter, the fluid passes through the porous membrane while contacting the curved surface defining each spherical hole. Since the porous membrane has the communication holes formed by the spherical holes, the contact area of the fluid inside the porous membrane is quite wide. Therefore, when a fluid passes through a laminate including porous membranes, it is considered that minute substances present in the fluid are easily adsorbed in spherical pores in the porous membranes.

The porous film may be a single-layer film containing only 1 film, or may be a laminated film in which 2 or more films are laminated in 2 or more layers.

When the porous film is a laminated film, the laminated film may be formed by a usual method such as a lamination method. Further, the porous films included in the laminated film may be formed sequentially on any one of the porous films constituting the outermost layers of the laminated film. In addition, a porous film may be formed by laminating a precursor film of a porous film by a lamination method, a coating method, or the like, and then making the laminated film on which the precursor film is laminated porous. Examples of the precursor film include a layer containing fine particles which can be removed by thermal decomposition or treatment with an organic solvent, water, an acid, an alkali, or the like in a matrix formed of a resin.

The shape of the voids included in the porous material constituting the porous film is not particularly limited as long as the fluid can pass from one main surface to the other main surface of the porous film.

The porous films preferably each have a desired void ratio and have a structure in which spherical pores communicate with each other (hereinafter, simply referred to as communication holes) as described later. In the case where the porous film is a laminate, the same applies to the porous layer included in the laminate.

The sphere related to the shape of the hole is a concept including a sphere, but is not necessarily limited to a sphere. The spherical shape may be substantially spherical, and a shape that can be recognized as substantially spherical when the enlarged image of the hole portion is visually recognized is included in the spherical shape.

When the porous membrane is a laminated membrane, the porosity and the pore diameter of the spherical pores constituting the communication pores may be the same or different for each porous membrane constituting the laminated membrane.

The film thickness of the porous film is not particularly limited. The film thickness of the porous film can be appropriately determined depending on the application of the porous film, and the like. Typically, the film thickness of the porous film is preferably 20 μm or more, more preferably 20 μm or more and 200 μm or less, and still more preferably 30 μm or more and 100 μm or less.

The thickness of the porous film and the thickness of each porous film included in the laminated film when the porous film is a laminated film can be obtained by measuring the thicknesses of a plurality of portions by a micrometer or the like and averaging them, or by observing the cross section of the film by a Scanning Electron Microscope (SEM) and averaging them.

The porosity of the porous film 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, from the viewpoint of an excellent gas passing rate.

The void ratio represents the ratio of voids per unit volume of the porous film. The void fraction can be calculated by the following formula (a).

Void ratio (%) = { 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 diameter and the content of the fine particles used in the production of the porous film.

Method for producing porous film

The porous membrane including the interconnected pores in which the spherical pores are interconnected is preferably produced by, for example, the following method.

Specifically, the method comprises the following steps:

an unfired composite film forming step of forming an unfired composite film on a substrate using the porous film-producing composition;

a firing step of firing the unfired composite film to obtain a polyimide resin-microparticle composite film; and

and a fine particle removing step of removing fine particles from the polyimide resin-fine particle composite film.

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

[ composition for producing porous film ]

The composition for producing a porous film contains a compound capable of producing a polyimide resin.

The compound capable of forming a polyimide resin may be a monomer for forming a polyimide resin or a polyamic acid which is a precursor of a polyimide resin.

As the compound capable of producing a polyimide resin, polyamic acid is preferable.

Hereinafter, the essential or optional components contained in the composition for producing a porous film will be described.

Polyamic acid

As the polyamic acid, a resin obtained by polymerizing any tetracarboxylic dianhydride with a diamine can be used without particular limitation. The amount of the tetracarboxylic dianhydride and the diamine used is not particularly limited. The amount of diamine used is preferably 0.50 to 1.50 mol, more preferably 0.60 to 1.30 mol, and particularly preferably 0.70 to 1.20 mol, based on 1 mol of tetracarboxylic dianhydride.

The tetracarboxylic dianhydride may be appropriately selected from among tetracarboxylic dianhydrides conventionally used as raw materials for the synthesis of polyamic acids. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. From the viewpoint of heat resistance of the obtained polyimide resin, aromatic tetracarboxylic dianhydride is preferably used. The tetracarboxylic dianhydride may be used alone or in combination of 2 or more.

As described later, in order to increase the contact angle of water and the fluorine atom number (atm%) on the main surface of the porous film, the polyimide resin may contain a structural unit having a fluorine atom. In this case, a tetracarboxylic dianhydride containing a fluorine atom is used.

Examples of suitable aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 1-bis (2, 3-dicarboxyphenyl) acetic anhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, 3',4' -biphenyl tetracarboxylic dianhydride, 2, 3',4' -biphenyltetracarboxylic dianhydride, 2, 6-biphenyltetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) ether dianhydride, bis (2, 3-dicarboxyphenyl) ether dianhydride, 2',3,3' -benzophenone tetracarboxylic dianhydride, 4- (terephthaloxy) diphthalic dianhydride, 4- (isophthaloxy) diphthalic dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 1,2,3, 4-benzene tetracarboxylic dianhydride, 3,4,9, 10-perylene tetracarboxylic dianhydride, 2,3,6, 7-anthracene tetracarboxylic dianhydride, 1,2,7, 8-phenanthrene tetracarboxylic dianhydride, 9-diphthalic anhydride fluorene, 3',4' -diphenyl sulfone tetracarboxylic dianhydride, and the like. Examples of the aliphatic tetracarboxylic dianhydride 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',4' -biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoints of price, easy availability and the like. These tetracarboxylic dianhydrides may be used singly or in combination of two or more.

As the fluorine atom-containing tetracarboxylic dianhydride used in the case of containing a structural unit having a fluorine atom in a polyimide resin, examples thereof include (trifluoromethyl) pyromellitic dianhydride, bis (heptafluoropropyl) pyromellitic dianhydride, (pentafluoroethyl) pyromellitic dianhydride, bis [3, 5-bis (trifluoromethyl) phenoxy ] pyromellitic dianhydride, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride, 5' -bis (trifluoromethyl) -3,3',4,4' -tetracarboxylbiphenyl dianhydride, 2', 5' -tetra (trifluoromethyl) -3,3',4,4' -Tetracarboxydiphenyl dianhydride, 5' -bis (trifluoromethyl) -3,3', 4' -Tetracarboxydiphenyl ether dianhydride, 5' -bis (trifluoromethyl) -3,3', 4' -Tetracarboxydiphenyl ketone 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) trifluoromethyl benzene dianhydride, 1, 4-bis (5-trifluoromethyl-3, 4-dicarboxyphenoxy) trifluoromethyl benzene dianhydride, 1, 4-bis (dicarboxyphenoxy) trifluoromethyl benzene dianhydride, 1, 4-bis (dicarboxyphenoxy) -2, 5-bis (trifluoromethyl) benzenedianhydride, 1, 4-bis (dicarboxyphenoxy) -2, 6-bis (trifluoromethyl) benzenedianhydride, 1, 4-bis (dicarboxyphenoxy) tetrakis (trifluoromethyl) benzenedianhydride, 2-bis [ (4- (3, 4-dicarboxyphenoxy) phenyl ] hexafluoropropane dianhydride, 4' -bis (2-trifluoromethyl-3, 4-dicarboxyphenoxy) biphenyldianhydride, 4' -bis (5-trifluoromethyl-3, 4-dicarboxyphenoxy) biphenyldianhydride, 4' -bis (2-trifluoromethyl-3, 4-dicarboxyphenoxy-3, 3' -bis (trifluoromethyl) biphenyldianhydride 4,4' -bis (5-trifluoromethyl-3, 4-dicarboxyphenoxy-3, 3' -bis (trifluoromethyl) biphenyl dianhydride, 4' -bis (2-trifluoromethyl-3, 4-dicarboxyphenoxy) diphenyl ether dianhydride, 4' -bis (5-trifluoromethyl-3, 4-dicarboxyphenoxy) diphenyl ether dianhydride, 4' -bis (3, 4-dicarboxyphenoxy) -3, 3-bis (trifluoromethyl) biphenyl dianhydride, 2, 5-difluoropyromellitic acid, 2-trifluoromethyl-5-fluoropyromellitic acid, 2, 5-bis (trifluoromethyl) pyromellitic acid, 2, 5-bis (pentafluoroethyl) pyromellitic acid, hexafluoro-3, 3', 4' -biphenyltetracarboxylic acid, hexafluoro-3, 3', 4' -benzophenone tetracarboxylic acid, 2-bis (2, 5, 6-trifluoro-3, 4-dicarboxyphenyl) hexafluoropropane, 1, 3-bis (2, 5, 6-trifluoro-3, 4-dicarboxyphenyl) hexafluoropropane, 2-bis (2, 5, 6-trifluoro-3, 4-dicarboxyphenyl) hexafluoropropane, 1, 4-bis (2, 5, 6-trifluoro-3, 4-dicarboxyltrifluorophenoxy) tetrafluorobenzene, hexafluoro-3, 3' -oxydiphthalic acid, and the like.

The diamine may be appropriately selected from diamines conventionally used as a raw material for the synthesis of polyamide acids. The diamine may be an aromatic diamine or an aliphatic diamine, and is preferably an aromatic diamine in view of heat resistance of the obtained polyimide resin. These diamines may be used alone or in combination of 2 or more.

As described later, in order to increase the contact angle of water and the fluorine atom number (atm%) on the main surface of the porous film, the polyimide resin may contain a structural unit having a fluorine atom. In this case, a diamine containing a fluorine atom may be used.

Examples of the aromatic diamine include diamino compounds having 1 or more or about 2 or less to about 10 or less phenyl groups bonded thereto. Specifically, the compound is a phenylenediamine and its derivative, a diaminobiphenyl compound and its derivative, a diaminodiphenyl compound and its derivative, a diaminotriphenyl compound and its derivative, a diaminonaphthalene and its derivative, an aminophenylaminoindane and its derivative, a diaminotetraphenyl compound and its derivative, a diaminohexaphenyl compound and its derivative, and a Cardo type fluorene diamine derivative.

The phenylenediamine is meta-phenylenediamine, para-phenylenediamine, etc., and as the phenylenediamine derivative, diamines having an alkyl group such as methyl group or ethyl group bonded thereto, for example, 2, 4-diaminotoluene, 2, 4-triphenyldiamine, etc., are used.

In the diaminobiphenyl compound, 2 aminophenyl groups are bonded to each other. For example, 4' -diaminobiphenyl, 4' -diamino-2, 2' -bis (trifluoromethyl) biphenyl, and the like.

The diaminodiphenyl compound is a compound in which 2 aminophenyl groups are bonded to each other through other groups. The bond is an ether bond, a sulfonyl bond, a thioether bond, a bond based on an alkylene group or a derivative thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a urea bond, or the like. The derivative group of the alkylene group having 1 to 6 carbon atoms or less is an alkylene group substituted with 1 or more halogen atoms or the like.

As an example of the diaminodiphenyl compound, examples thereof include 3,3' -diaminodiphenyl ether, 3,4' -diaminodiphenyl ether, 4' -diaminodiphenyl ether, 3' -diaminodiphenyl sulfone, 3,4' -diaminodiphenyl sulfone, 4' -diaminodiphenyl sulfone, 3' -diaminodiphenyl methane, 3,4' -diaminodiphenyl methane, and 4,4' -diaminodiphenylmethane, 4' -diaminodiphenylsulfide, 3' -diaminodiphenylketone, 3,4' -diaminodiphenylketone, 2-bis (p-aminophenyl) propane, 2' -bis (p-aminophenyl) hexafluoropropane, 4-methyl-2, 4-bis (p-aminophenyl) -1-pentene 4-methyl-2, 4-bis (p-aminophenyl) -2-pentene, iminodiphenylamine, 4-methyl-2, 4-bis (p-aminophenyl) pentane, bis (p-aminophenyl) phosphine oxide, 4' -diaminoazobenzene, 4' -diaminodiphenylurea, 4' -diaminodiphenylamide, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (3-aminophenoxy) benzene, 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-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane, and the like.

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

The diaminotriphenyl compound is a compound in which 2 aminophenyl groups and 1 phenylene group are bonded via other groups. The other groups are selected as the same groups as those of the diaminodiphenyl compound. Examples of the diaminotriphenyl compound include 1, 3-bis (m-aminophenoxy) benzene, 1, 3-bis (p-aminophenoxy) benzene, and 1, 4-bis (p-aminophenoxy) benzene.

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

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

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

Examples of the Cardo type fluorene diamine derivative include 9, 9-bisaniline fluorene and the like.

The aliphatic diamine preferably has about 2 to 15 carbon atoms. Specific examples of the aliphatic diamine include pentamethylene diamine, hexamethylene diamine, heptamethylene diamine, and the like.

The diamine may be one in which a hydrogen atom of the diamine is substituted with at least 1 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.

As the diamine containing fluorine atoms used when the polyimide resin contains a structural unit having fluorine atoms, examples thereof include 4- (1H, 11H-twenty-fluoroundecyloxy) -1, 3-diaminobenzene, 4- (1H, 1H-perfluoro-1-butoxy) -1, 3-diaminobenzene, 4- (1H, 1H-perfluoro-1-heptyloxy) -1, 3-diaminobenzene, 4- (1H, 1H-perfluoro-1-octyloxy) -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, 2H-perfluoro-1-hexyloxy) -1, 3-diaminobenzene, and 4- (1H, 2H-perfluoro-1-dodecyloxy) -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-diaminotetrakis (trifluoromethyl) benzene, 1, 3-diaminotetrakis (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 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl, 3 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl, octafluorobenzidine, 4,4 '-diaminodiphenyl ether, 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) tetradecylfluoroheptane, 2' -bis (trifluoromethyl) -4,4 '-diaminodiphenyl ether, 3',5,5 '-tetra (trifluoromethyl) -4,4' -diaminodiphenyl ether, 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-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane, 2-bis [4- (3-aminophenoxy) phenyl ] hexafluoropropane, 2-bis [4- (2-aminophenoxy) phenyl ] hexafluoropropane 2, 2-bis [4- (4-aminophenoxy) -3, 5-dimethylphenyl ] hexafluoropropane, 2-bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl ] hexafluoropropane, 2-bis [4- (4-amino-3-trifluoromethylphenoxy) phenyl ] hexafluoropropane, 2-bis [4- (4-aminophenoxy) -3, 5-bis (trifluoromethyl) phenyl ] hexafluoropropane, 4 '-bis (4-amino-2-trifluoromethylphenoxy) biphenyl, 4' -bis (4-amino-3-trifluoromethylphenoxy) biphenyl, 4,4 '-bis (4-amino-2-trifluoromethylphenoxy) diphenylsulfone, 4' -bis (3-amino-5-trifluoromethylphenoxy) diphenylsulfone, 1, 4-bis {2- [4- (4-aminophenoxy) phenyl ] hexafluoropropan-2-yl } benzene, 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' -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.

The means for producing the polyamic acid is not particularly limited. For example, a known method such as a method of reacting an acid and a diamine component in a solvent can be used.

The reaction of the tetracarboxylic dianhydride with the diamine is usually carried out in a solvent. The solvent used in the reaction of the tetracarboxylic dianhydride and the diamine is not particularly limited as long as it is a solvent that can dissolve the tetracarboxylic dianhydride and the diamine and does not react with the tetracarboxylic dianhydride and the diamine. The solvent may be used alone or in combination of 2 or more.

Examples of the solvent used for the reaction of the tetracarboxylic dianhydride and the diamine include N-methyl-2-pyrrolidone, N-dimethylacetamide, N, nitrogen-containing polar solvents such as N-diethylacetamide, N-dimethylformamide, N-diethylformamide, N-methylcaprolactam, N' -tetramethylurea, etc.; 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 a phenol solvent such as a cresol-based and xylene-based mixed solvent.

These solvents may be used alone or in combination of 2 or more. The amount of the solvent used is not particularly limited. The solvent is preferably used in an amount such that the content of the polyamic acid formed in the reaction solution is 5% by mass or more and 50% by mass or less.

Among these solvents, N-methyl-2-pyrrolidone, N-dimethylacetamide and N are preferable from the viewpoint of solubility of the polyamide acid to be formed, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylcaprolactam, N, N, N ', N' -tetramethylurea and the like.

The polymerization temperature is usually preferably-10℃to 120℃and more preferably 5℃to 30 ℃. The polymerization time varies depending on the composition of the raw materials used, and is usually preferably 3 hours to 24 hours.

The polyamic acid may be used alone or in combination of 2 or more kinds.

[ polyimide resin ]

The polyimide resin is not limited in its structure and molecular weight. Various known polyimide resins can be used. The polyimide resin may have a condensable functional group such as a carboxyl group in a side chain or a functional group that promotes a crosslinking reaction during firing. When the composition for producing a porous film contains a solvent, a soluble polyimide resin that can be dissolved in the solvent is preferable.

In order to obtain a polyimide resin which is soluble in a solvent, it is effective to introduce a soft bending structure into the main chain. Examples of the monomer capable of introducing a soft bending structure into the main chain include: 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 '-dimethoxybenzidine, and 4,4' -diaminobenzanilide; polyoxyalkylene diamines such as polyoxyethylene diamine, polyoxypropylene diamine, and polyoxybutylene diamine; polysiloxane diamine; 2, 3',4' -oxydiphthalic anhydride, 3,4,3',4' -oxydiphthalic anhydride, 2-bis (4-hydroxyphenyl) propane dibenzoate-3, 3',4' -tetracarboxylic dianhydride, and the like. In addition, it is also effective to use a monomer having a functional group that improves solubility in a solvent. Examples of the monomer having a functional group that improves solubility in a solvent include fluorinated diamines such as 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl and 2-trifluoromethyl-1, 4-phenylenediamine. In addition to the monomer for improving the solubility of the polyimide resin, the monomer described in the column of the polyamic acid may be used in combination within a range not to inhibit the solubility.

The polyimide resin and the monomer thereof may be used alone or in combination of 2 or more.

The means for producing the polyimide resin is not particularly limited. For example, a known method such as a method of chemically imidizing a polyamic acid or a method of thermally imidizing a polyamic acid can be used. Examples of such polyimide resins include aliphatic polyimide resins (full aliphatic polyimide resins) and aromatic polyimide resins, and aromatic polyimide resins are preferable. Examples of the aromatic polyimide resin include a polyimide resin obtained by a ring-closure reaction of a polyamic acid having a repeating unit represented by the formula (1) by a thermal or chemical means, and a polyimide resin having a repeating unit represented by the formula (2). Wherein Ar represents an aryl group. When the porous film-producing composition contains a solvent, these polyimide resins may be subsequently dissolved in the solvent used.

[ chemical formula 1]

[ chemical formula 2]

[ particles ]

The material of the microparticles is not particularly limited as long as the microparticles are insoluble in the solvent contained in the composition for producing a porous film and can be removed from the polyimide resin-microparticle composite film after that. As the material of the fine particles, various known materials satisfying the above conditions can be used. For example, as an inorganic material, silicon dioxide (silicon oxide) is given; titanium oxide, aluminum oxide (Al ₂ O ₃ ) And metal oxides. Examples of the organic material include high molecular weight olefin polymers (polypropylene, polyethylene, etc.), polystyrene, epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, polyether, and other organic polymers.

Specifically, examples of the fine particles include colloidal silica. In the colloidal silica, monodisperse spherical silica particles are preferable because uniform pores can be formed.

Further, the fine particles preferably have a high positive sphere ratio and a small particle size distribution index. The microparticles having these conditions are excellent in dispersibility in the composition for producing a porous film and can be used in a state of not aggregating with each other. The average particle diameter of the fine particles can be appropriately selected in consideration of the opening diameter of the surface of the porous film and the film thickness of the porous film. The average particle diameter of the fine particles is, for example, preferably 50nm or more, more preferably 100nm or more and 2000nm or less, and still more preferably 200nm or more and 1000nm or less. By satisfying these conditions, the pore size of the porous membrane from which fine particles are removed can be made uniform.

The microparticles may be used alone or in combination of 2 or more.

[ solvent ]

The solvent is not particularly limited as long as the solvent dissolves the polyamic acid and/or polyimide resin and does not dissolve the microparticles. Suitable examples of the solvent include solvents exemplified for the reaction of tetracarboxylic dianhydride and diamine. The solvent may be used alone or in combination of 2 or more.

[ dispersant ]

For the purpose of uniformly dispersing the fine particles in the composition for producing a porous film, a dispersant may be used together with the fine particles. By adding the dispersing agent 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 further, the fine particles can be uniformly distributed in a film obtained by forming a film from the composition for producing a porous film. As a result, dense openings can be provided on the surface of the finally obtained porous film, and the front surface and the back surface of the porous film can be efficiently communicated with each other, thereby improving the air permeability of the porous film. Further, the use of the dispersing agent can easily improve the drying property of the composition for producing a porous film, and can easily improve the peeling property of the formed unfired composite film from a substrate or the like.

The dispersant is not particularly limited. Known dispersants may be used. Specific examples of the dispersant include anionic surfactants such as coco fatty acid salts, sulfated castor oil salts, lauryl sulfate salts, polyoxyalkylene allyl phenyl ether sulfate salts, alkylbenzenesulfonic acid, alkylbenzenesulfonate salts, alkyldiphenyl ether disulfonate salts, alkylnaphthalene sulfonate salts, dialkylsulfosuccinate salts, isopropyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, polyoxyethylene allyl phenyl ether phosphate salts, and the like; cationic surfactants such as oleylamine acetate, laurylpyridine chloride, cetylpyridine chloride, lauryltrimethylammonium chloride, stearyl trimethylammonium chloride, behenyl trimethylammonium chloride, and didecyldimethyl ammonium chloride; amphoteric surfactants such as cocoyl alkyl dimethyl amine oxide, fatty amidopropyl dimethyl amine oxide, alkyl polyamino ethyl glycine hydrochloride, amidobetaine type active agent, alanine type active agent, and laurylimino dipropionic acid; nonionic surfactants such as polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers, such as polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl amine, polyoxyethylene oleyl amine, polyoxyethylene polystyrene phenyl ether, and polyoxyalkylene polystyrene phenyl ether, nonionic surfactants such as polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylated castor oil, polyoxyethylated hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamide; fatty acid alkyl esters such as octyl stearate and trimethylolpropane tricaprate; polyether polyols such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, trimethylolpropane tris (polyoxyalkylene) ether, and the like. The above dispersant may be used by mixing 2 or more kinds.

In the composition for producing a porous film, for example, the content of the dispersant is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.05 mass% or more and 1 mass% or less, and even more preferably 0.1 mass% or more and 0.5 mass% or less, with respect to the mass of the fine particles, in view of film forming property.

[ method for producing porous film suitably ]

[ procedure for Forming unfired composite film ]

In the unfired composite film forming step, for example, the composition for producing a porous film is applied to a substrate and dried at a temperature of 0 ℃ to 100 ℃ under normal pressure or vacuum, preferably 10 ℃ to 100 ℃ under normal pressure, thereby forming an unfired composite film. Examples of the substrate include a PET film, an SUS substrate, and a glass substrate.

In addition, in the case of peeling the unfired composite film from the substrate, a substrate having a release layer may be used in order to further improve the peeling property of the film. When a release layer is provided on a substrate in advance, a release agent is applied to the substrate and dried or sintered before the porous film-producing composition is applied. As the release agent, known release agents such as an alkyl ammonium phosphate salt, fluorine, and silicone can be used without particular limitation. When the dried unfired composite film is peeled from the substrate, a slight amount of release agent remains on the peeled surface of the unfired composite film. The release agent remaining on the release surface causes discoloration of the composite film during firing and adversely affects the electrical characteristics of the final 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 cleaning step of cleaning the unfired composite film peeled from the substrate with an organic solvent may be introduced.

On the other hand, when a substrate having no release layer is used for forming the unfired composite film, the release layer forming step and the cleaning step may be omitted. In the production of the unfired composite film, a dipping step in an aqueous solvent, a pressurizing step, and a drying step after the dipping step may be provided as optional steps before the firing step described later.

[ firing step ]

The unfired composite film is subjected to a post-treatment (firing) by heating, thereby forming a composite film (polyimide resin-microparticle composite film) formed of a polyimide resin and microparticles. The firing temperature in the firing step varies depending on the structure of the unfired composite film and the presence or absence of the condensing agent, and is preferably 120 ℃ to 450 ℃, more preferably 150 ℃ to 400 ℃. In addition, when fine particles made of an organic material are used, the firing temperature needs to be set to a temperature lower than the thermal decomposition temperature of the organic material. The imidization is preferably completed in the firing step.

As for the firing conditions, for example, it is also possible to use: a method of raising the temperature from room temperature to 400 ℃ for 3 hours and then maintaining the temperature at 400 ℃ for 20 minutes; the temperature is raised stepwise from room temperature to 400 ℃ at 50 ℃ intervals (each step is maintained for 20 minutes), and finally the temperature is maintained at 400 ℃ for 20 minutes. In the case where an unfired composite film is formed on a substrate and the unfired composite film is temporarily peeled from the substrate, a method of fixing an end portion of the unfired composite film to a SUS-made plate or the like to prevent deformation may be employed.

[ procedure for removing particles ]

By selecting an appropriate method to remove fine particles from the polyimide resin-fine particle composite film formed in the above manner, a porous film having a desired structure can be produced with good reproducibility.

For example, in the case of using silica, the polyimide resin-microparticle composite film may be treated with a low-concentration aqueous hydrogen fluoride solution or the like to dissolve and remove the silica.

In the case where 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 fine particles are organic fine particles, a treatment liquid in which the fine particles are dissolved but the polyimide resin is not dissolved may be selected, and the organic fine particles may be removed by a treatment based on the treatment liquid. Typically, an organic solvent is used as the treatment liquid. When the organic fine particles are soluble in an acid or a base, an acidic aqueous solution or an alkaline aqueous solution can be used as the treatment liquid.

[ resin removal Process ]

The method may further include a resin removal step of removing at least a part of the resin portion of the polyimide resin-microparticle composite film before the microparticle removal step, or removing at least a part of the porous film after the microparticle removal step.

The removal of at least a part of the resin portion of the polyimide resin-microparticle composite film before the microparticle removing step or the removal of at least a part of the porous film after the microparticle removing step can increase the aperture ratio of the porous film as a final product as compared with the case where the removal is not performed.

The step of removing at least a part of the resin portion of the polyimide resin-microparticle composite film or the step of removing at least a part of the resin portion of the polyimide resin-microparticle composite film may be performed by a usual chemical etching method, a physical removal method, or a combination thereof.

Examples of the chemical etching method include a treatment with a chemical etching solution such as an inorganic alkaline solution or an organic alkaline solution. Preferably an inorganic alkaline solution. Examples of the inorganic alkali solution include hydrazine solution containing hydrazine and ethylenediamine, solution of alkali metal hydroxide such as potassium hydroxide, sodium carbonate, sodium silicate and sodium metasilicate, ammonia solution, and etching solution containing alkali hydroxide, hydrazine and 1, 3-dimethyl-2-imidazolidinone as main components. Examples of the organic alkali solution 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; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; basic solutions of cyclic amines such as pyrrole and piperidine.

The solvent of each solution may be appropriately selected from pure water and alcohols. An appropriate amount of surfactant may be added to each of the above solutions. The alkali concentration is, for example, 0.01 mass% or more and 20 mass% or less.

As the physical method, for example, there can be used: dry etching by plasma (oxygen, argon, etc.), corona discharge, or the like; a method of treating the surface of a porous membrane by discharging a dispersion of an abrasive (for example, alumina (hardness 9) or the like) onto the surface of the membrane at a rate of 30m/s to 100m/s inclusive; etc.

On the other hand, as a physical method applicable only to the resin removal process performed after the particulate removal process, the following method may be employed: after the interleaving paper film (for example, polyester film such as PET film) wetted with the liquid is pressed against the surface of the laminate to be treated, the laminate is peeled from the interleaving paper film before the interleaving paper film is dried or after the interleaving paper film is dried. The porous film is peeled off from the backing paper film in a state where only the surface layer of the porous film existing on the surface of the processing object remains on the backing paper film due to the surface tension or electrostatic adsorption force of the liquid.

< 1 st porous film >

The 1 st porous film is the polyimide porous film described above, and has a contact angle of water of 100 ° or more on at least one main surface.

The 1 st porous film exhibits the above-described contact angle of water on at least one main surface, whereby the porous film exhibits an excellent gas passing rate.

The contact angle of water is preferably 105 ° or more, more preferably 110 ° or more. The upper limit of the contact angle of water is not particularly limited, and may be, for example, 150 ° or less or 130 ° or less in reality.

Here, the contact angle of water is a static contact angle. The static contact angle of water can be determined, for example, as follows: the contact angle after dropping 2.0. Mu.L of pure water onto the surface of the porous film was used as the static contact angle by using Dropmaster 700 (made by Kogyo chemical Co., ltd.).

In the 1 st porous film, the dynamic contact angle of water on the main surface having a contact angle of water of 100 ℃ or higher is preferably 30 ° or higher. The dynamic contact angle of water may be 40 ° or more, or 50 ° or more. The upper limit of the dynamic contact angle of water is not particularly limited, and may be, for example, 120 ° or less or 100 ° or less in reality.

The dynamic contact angle of water can be measured, for example, by using DropMaster 700 (manufactured by Co., ltd.). First, 2.0. Mu.L of a droplet of pure water was dropped onto the surface of the porous membrane. Then, pure water was supplied from the injection needle to the droplets until the total amount of pure water became 50.0. Mu.L, and the droplets of pure water were spread. The time point at which the droplet was held in the expanded state for 3 seconds was set as the measurement start time, and pure water was sucked from the droplet at a rate of 6.0. Mu.L/sec from the measurement start time. The value of the receding angle when the end portion of the droplet was contracted by 10 dots by the suction of pure water as compared with the end portion of the droplet at the start of the measurement was measured as the dynamic contact angle of water.

The method for setting the contact angle of water on the main surface of the 1 st porous film to 100 ° or more is not particularly limited. Examples of the method include: a method of attaching or binding a hydrophobizing agent to the main surface of the untreated porous film produced by the above method; a method in which a polyimide resin contained in a porous material constituting the 1 st porous film contains a fluorine atom-containing structural unit; and a method in which a polyimide resin composition constituting the 1 st porous membrane is made to contain a hydrophobic material.

The hydrophobizing agent used in the method of attaching or bonding the hydrophobizing agent to the main surface is not particularly limited as long as it can be attached or bonded to the polyimide resin and can increase the contact angle of water on the main surface of the porous film to 100 ° or more. Preferred hydrophobizing agents include silicone hydrophobizing agents and fluorine hydrophobizing agents. From the viewpoint of the effect of hydrophobization, a fluorine-based hydrophobizing agent is more preferable.

As the fluorine-based hydrophobizing 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 compound, or may be an oligomer or a polymer. The fluorine-containing organic compound may be an aliphatic compound, an aromatic compound, or a compound containing an aliphatic moiety and an aromatic moiety.

Examples of the fluorinated organic compound include fluorinated alkanes, fluorinated alkanols, bis-fluorinated alkyl ethers, fluorinated aliphatic ketones, fluorinated aliphatic carboxylic acids, fluorinated aliphatic carboxylic acid alkyl esters, fluorinated aliphatic carboxylic acid fluoroalkyl esters, fluorinated alkylbenzene carboxylic acids, fluorinated alkylbenzene carboxylates, fluorinated alkylbenzene sulfonic acids, and fluorinated alkylbenzene sulfonates.

The fluorine-containing silane coupling agent is also suitable for use as a fluorine-containing organic compound. On the surface of a porous membrane which is not treated with a fluorine-containing organic compound, functional groups containing active hydrogen atoms such as hydroxyl groups, amino groups, carboxyl groups and the like are often present.

The fluorine-containing silane coupling agent can react with and bond to the functional group containing an active hydrogen atom.

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 fluoroalkyl trialkoxysilane, difluoroalkyl dialkoxysilane, fluoroalkyl alkyl dialkoxysilane, bis (trialkoxysilyl) fluoroalkane, fluoroalkyl triisocyanate silane, bis (trichlorosilyl) fluoroalkane, and bis (triisocyanatosilyl) fluorinated chain aliphatic compound.

Suitable specific examples of the fluorine-containing silane coupling agent include:

fluoroalkyl alkoxysilanes such as perfluorodecyl trimethoxysilane, perfluorodecyl triethoxysilane, trifluoropropyl trimethoxysilane, trifluoropropyl triethoxysilane, perfluorooctyl trimethoxysilane, perfluorooctyl triethoxysilane, perfluorododecyl trimethoxysilane, perfluorododecyl triethoxysilane, perfluoropentyl trimethoxysilane, and 1H, 2H-seventeen fluoro decyl trimethoxysilane;

fluoroalkyl triisocyanates such as 1H, 2H-heptadecafluorodecyl triisocyanates silane;

bis (trichlorosilyl) fluoroalkanes such as 1, 6-bis (trichlorosilyl) -2, 5-bis (trifluoromethyl) -2,3,3,4,4,5-hexafluoropropane;

bis (triisocyanatosilylethyl) -1H, 2H,9H, 10H-dodecane, 1, 8-bis (triisocyanatosilyl) -3, 6-bis (trifluoromethyl) -3,4,4,5,5,6-hexafluorooctane, N' -bis (2-triisocyanatosilylethyl) -1, 8-dodecafluorooctanoic acid diamide, 1, 4-bis (2-triisocyanatosilylethoxy) -1, 4-bis (trifluoromethyl) hexafluorobutane, 1, 2-bis (2-triisocyanatosilylethoxy) tetrafluoroethane, 1, 2-bis (2-triisocyanatosilylethylthio) tetrafluoroethane, and the like.

The fluororesin is also suitable for use as a fluorine-containing organic compound. The kind of the fluorine resin is not particularly limited, and various resins containing fluorine atoms can be used.

Examples of suitable fluororesin include Polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoro (alkyl vinyl ether) copolymer (PFA), polyvinylidene fluoride (PVDF) and its copolymer, polyvinyl fluoride (PVA), and ethylene/tetrafluoroethylene copolymer (ETFE). Among these, polyvinylidene fluoride (PVDF) and its copolymers are preferable in terms of improving abrasion resistance. In the case of the copolymer, examples of the monomer to be copolymerized include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride, and the like.

Alternatively, the above-mentioned fluorine-containing organic compound itself or a liquid composition containing the fluorine-containing organic compound may be used to prepare fine particles as described in Japanese unexamined patent publication No. 10-140144, and the prepared fine particles may be subjected to a hydrophobization treatment by being caused to collide with a porous film in the atmosphere by a blasting device or the like.

By bringing the hydrophobizing agent into contact with the main surface of the porous membrane as described above, the hydrophobizing component such as the fluorine-containing organic compound contained in the hydrophobizing agent adheres to or bonds to the main surface.

By adjusting the amount of the hydrophobizing component attached to or bonded to the main surface, the contact angle of water on the main surface can be adjusted. The amount of the hydrophobic component to be attached or bound can be adjusted by: adjusting the contact time between the main surface and the hydrophobizing agent; or adjusting the concentration of the hydrophobizing component in the hydrophobizing agent.

In the method of forming the polyimide resin containing the structural unit containing fluorine atoms in the porous material constituting the 1 st porous film, a polyimide resin prepared from at least one of the above-mentioned tetracarboxylic dianhydride containing fluorine atoms and the above-mentioned diamine containing fluorine atoms is used.

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 contact angle of water on the main surface of the 1 st porous film is a desired value.

In general, the larger the amount of fluorine atoms in the main surface of the porous film, the higher the contact angle of water tends to be. Therefore, the contact angle of water on the main surface of the porous film can be adjusted by adjusting the ratio of the fluorine atom-containing monomer or the fluorine atom content in the monomer among the monomers used for producing the polyimide resin.

In the method of incorporating a hydrophobic material into the polyimide resin composition constituting the 1 st porous film, for example, a method of incorporating a hydrophobic material into the composition for producing a porous film at the time of forming a porous film is employed.

As hydrophobic materials, the ingredients set forth above for the hydrophobizing agent may be used. As described above, when forming the porous film, the unfired composite film is fired at a high temperature. Therefore, the aforementioned fluororesin is preferable as a hydrophobic material in terms of heat resistance. The form of the fluororesin is not particularly limited. From the viewpoint of easy uniform dispersion of the fluororesin in the polyimide resin composition, the fluororesin particles are preferably added to the composition for producing a porous film.

The particle diameter of the fluororesin particles is not particularly limited as long as a porous film formed from a polyamide resin composition containing uniformly dispersed fluororesin particles can be formed. The volume average particle diameter of the fluororesin particles is preferably 10nm to 1000nm, more preferably 50nm to 700nm, still more preferably 100nm to 500 nm.

In the 1 st porous film, the amount of fluorine atoms in the main surface having a contact angle of water of 100 ° or more is preferably 5atm% or more, more preferably 10atm% or more, still more preferably 20atm% or more, and particularly preferably 30atm% or more.

The upper limit of the amount of fluorine atoms in 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, 68atm% or less, and may be 50atm% or less.

The amount of fluorine atoms in the main surface can be adjusted by adjusting the amount of the fluorine-based hydrophobizing agent used, the amount of the fluorine-containing monomer used in the preparation of the polyimide resin, the amount of fluorine atoms in the fluorine-containing monomer, the amount of the fluorine-containing hydrophobizing agent added to the polyimide resin composition, and the like.

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

In view of achieving both excellent gas passage rate and strength of the porous film, it is preferable that in the porous film,

the void ratio is more than 60 percent,

the average diameter of the openings in the main surface having a contact angle of water of 100 DEG or more is 50nm to 3000nm,

the film thickness is 30 μm or more.

The stress at the time of breaking the 1 st porous film is preferably 10MPa or more, more preferably 15MPa or more, and even more preferably 20MPa or more. The elongation at break of the 1 st porous film 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.

< 2 nd porous Membrane >

The 2 nd porous film is the polyimide porous film described above, and the amount of fluorine atoms in at least one main surface is 5atm% or more.

In the 2 nd porous film, when the amount of fluorine atoms in at least one main surface is the above amount, the porous film exhibits an excellent gas passing rate.

The amount of fluorine atoms in the main surface is preferably 5atm% or more, more preferably 10atm% or more, still more preferably 20atm% or more, and particularly preferably 30atm% or more.

The upper limit of the amount of fluorine atoms in the main surface is, for example, 68atm% or less, or 50atm% or less.

The amount of fluorine atoms in the main surface is adjusted by the same method as described for the 1 st porous film.

the void ratio is more than 60 percent,

the average diameter of the openings in the main surface having a fluorine atom content of 5atm% or more is 50nm to 3000nm,

the film thickness is 30 μm or more.

The stress at the time of breaking the 2 nd porous film is preferably 10MPa or more, more preferably 15MPa or more, and still more preferably 20MPa or more. The elongation at break of the 2 nd porous film 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.

Examples

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

[ example 1 ]

Slurry a containing 70 parts by mass of silica fine particles, 0.35 parts by mass of a nonionic surfactant as a dispersing agent, and 70 parts by mass of dimethylacetamide was stirred in a 200mL container at 400rpm for 15 minutes by a stirring blade. Then, the stirred slurry A was subjected to 5 times of dispersion treatment at 200MPa using a dispersing apparatus (NVL-S008, manufactured by Jitian mechanical Crypton Co., ltd.). As the silica fine particles, silica having an average particle diameter of 300nm was used.

And mixing the dispersed slurry A with 30 parts by mass of polyamide acid to obtain slurry B. The polyamic acid was used in the form of a dimethylacetamide solution having a solid concentration of 20% by mass. As the polyamic acid, a polymer obtained by polymerizing 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (hereinafter referred to as 6 FDA) and 2, 2-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane (hereinafter referred to as HFBAPP)) in equimolar amounts was used.

Slurry B contained dimethylacetamide and γ -butyrolactone in such a manner that the solid content concentration was 29 mass%. The mass ratio of dimethylacetamide to gamma-butyrolactone in the slurry B is as dimethylacetamide: gamma-butyrolactone is calculated as 90:10.

The slurry B thus obtained was stirred at 400rpm for 30 minutes with a stirring blade in a 200mL container, and dispersed, to prepare a composition for producing a porous film. After the porous film-producing composition was applied to the PET film, the solvent was removed by heating at 90℃for 300 seconds, and a coating film having a film thickness of about 40 μm was formed.

The formed coating film was heat-treated (fired) at 380 ℃ for 15 minutes, whereby imidization was performed to obtain a polyimide resin-fine particle composite film. The polyimide resin-microparticle composite film thus obtained was immersed in a 10% hf solution for 10 minutes, whereby silica microparticles contained in the film were removed. After removing the silica fine particles, washing with water and drying were performed to obtain a porous membrane.

Comparative example 1

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

[ example 2 ]

Slurry D was obtained by the same method as that for slurry B in comparative example 1, except that the amount of polyamic acid used was changed from 30 to 25 parts by mass, and 5 parts by mass of Polytetrafluoroethylene (PTFE) microparticles having an average particle diameter of 300nm were added together with the polyamic acid. The fine particles of PTFE are used in the form of a dispersion in which fine particles of PTFE having a solid content concentration of 40% by mass are dispersed in N-methyl-2-pyrrolidone.

The mass ratio of dimethylacetamide, gamma-butyrolactone and N-methyl-2-pyrrolidone in the slurry D is as follows: gamma-butyrolactone: n-methyl-2-pyrrolidone was found to be 87:10:3.

a porous film was obtained in the same manner as in comparative example 1, except that the slurry B was changed to the slurry D.

[ example 3 ]

A porous film obtained in the same manner as in comparative example 1 was immersed in an alkaline etching solution for 180 seconds, and a part of the surface of the polyimide resin was removed, whereby chemical etching was performed. Specifically, the porous film was immersed in an aqueous isopropanol solution having a concentration of 10 mass% for prewetting, then immersed in an aqueous tetramethylammonium hydroxide (TMAH) solution having a concentration of 1.00 mass%, and then washed with water and dried to thereby perform chemical etching.

The chemically etched porous film was subjected to heat treatment (firing) at 380 ℃ for 10 minutes again, whereby the alkali-opened portion was imidized again to obtain a porous film. The main surface of the obtained porous film was subjected to a hydrophobization treatment for attaching a fluororesin using a hydrophobizing agent containing a fluororesin (Adron (registered trademark) L-4614cr, manufactured by fluorocoat corporation), to obtain a porous film.

Comparative example 2

The porous film obtained in the same manner as in comparative example 1 was immersed in an N-methyl-2-pyrrolidone solution having a concentration of 0.25 mass% of polyvinylidene fluoride for 1 minute, and then dried at 100 ℃ for 5 minutes, whereby a porous film having polyvinylidene fluoride attached to the main surface was obtained.

The porous films of examples 1 to 3, comparative example 1, and comparative example 2 obtained in the above manner were measured for air permeability, contact angle of water (static contact angle and dynamic contact angle), stress at break, elongation at break, and fluorine atom content of the main surface. The air permeability, stress at break, elongation at break, and fluorine atom content of the main surface were measured by the following methods. The contact angle of water was measured by the method described above. The contact angle of water and the air side are surfaces which are not in contact with the PET film when the porous film is produced, and the substrate side is a surface which is in contact with the PET film when the porous film is produced. The measurement results are shown in Table 1.

< determination of air permeability >

A sample of a porous film having a size of 5 cm. Times.5 cm was used, and a time for passing 100mL of air through the sample was measured in accordance with JIS P8117 using a Gurley densitometer (Toyo Seisakusho). The smaller the value of the air permeability, the shorter the passage time of 100mL of air, and the faster the passage speed of the gas of the sample.

< measurement of stress at break and elongation at break >

A sample of a porous membrane in the form of a strip having a size of 3cm X3 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).

< measurement of fluorine atom on principal surface >

The fluorine atom weight in the main surface of the sample of the porous film was measured using a K-. Alpha. (registered trademark) XPS system (manufactured by ThermoFisher Scientific Co.).

TABLE 1

According to examples 1 to 3, it is apparent that the porous film is excellent in gas passage rate when the contact angle of water is 100 ° or more or the amount of fluorine atoms is 5atm% or more on at least one main surface of the porous film.

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 5atm%, the gas passing speed of the porous film is different.

Claims

1. A polyimide porous film formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin,

the porous material has air permeability, and the porous material has air permeability,

the contact angle of water on at least one main surface is 100 DEG or more.

2. The polyimide porous 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 attached or bonded to the main surface of the polyimide porous membrane having a contact angle of 100 ° or more with respect to water.

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

5. The polyimide porous membrane according to claim 1 or 2, wherein the porous material is formed of a polyimide resin composition containing a fluororesin.

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

7. The polyimide porous membrane according to any one of claim 1 to 6, which has a void ratio of 60% or more,

the average diameter of the openings in the main surface, the contact angle of which is 100 DEG or more, is 50nm to 3000nm,

the film thickness is 30 μm or more.

8. A polyimide porous film formed of a porous material containing a polyimide resin or a polyimide resin composition containing a polyimide resin,

The amount of fluorine atoms in at least one main surface is 5atm% or more.

9. The polyimide porous membrane according to claim 8, which has a void ratio of 60% or more,

the average diameter of the openings in the main surface, which has a fluorine atom content of 5atm% or more, is 50nm to 3000nm,

the film thickness is 30 μm or more.

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

11. The polyimide porous membrane according to claim 7 or 9, which has an elongation at break of 5% GL or more.