JP2021181552A - Varnish composition, method of manufacturing precursor film of polyimide porous film, and method of manufacturing polyimide porous film - Google Patents

Abstract

To provide a varnish composition that can form a polyimide porous film with a high opening ratio and has a uniform composition including organic fine particles, a method of manufacturing a precursor film of a polyimide porous film using the varnish composition, and a method of manufacturing a polyimide porous film using the precursor film.SOLUTION: The present invention discloses a varnish composition for forming a polyimide porous film, containing polyamic acid (A), organic fine particles (B) and a solvent (S). As the solvent (S), used is a combination of water (S-I) and/or a water-soluble organic solvent (S-II) and an organic solvent (S-III) excluding the water-soluble organic solvent (S-II). The total amount of use of the water (S-I) and/or the water-soluble organic solvent (S-II) is in a specific range.SELECTED DRAWING: None

Description

The present invention relates to a varnish composition, a method for producing a precursor film of a polyimide porous film, and a method for producing a polyimide porous film.

In recent years, polyimide and / or polyamide-imide porous membranes have been studied as filters used for gas or liquid separation membranes, separators for lithium ion batteries, fuel cell electrolyte membranes, and low dielectric constant materials.

For example, as a method for producing a porous polyimide film used for a separator, a varnish in which fine particles such as silica particles are dispersed in a polymer solution of polyamic acid or polyimide is applied onto a substrate, and then applied as necessary. A method is known in which a polyimide film containing fine particles is obtained by heating the film, and then fine particles such as silica particles in the polyimide film are removed using hydrofluoric acid to make the polyimide film porous (see Patent Document 1).

Japanese Patent No. 5605566

When forming a porous polyimide film by the method described in Patent Document 1, it is desirable to use a varnish having a uniform composition to form a coating film having a uniform thickness and composition. However, the handling of hydrofluoric acid used in the production method described in Patent Document 1 is not easy. Therefore, since the use of hydrofluoric acid is a factor that increases the production cost of the polyimide porous membrane, a method that does not use hydrofluoric acid is required. Therefore, it is conceivable to use other fine particles such as organic fine particles instead of silica fine particles. However, since organic fine particles are often prepared in an aqueous solvent, they are often distributed as a fine particle dispersion containing water. When a varnish is prepared using such a fine particle dispersion containing water, a varnish containing water is inevitably obtained.

In this respect, when the varnish containing polyamic acid does not contain fine particles, even if the varnish contains water, a varnish that can be applied may be obtained because there are few components that hinder the orientation of the polyamic acids.
However, when the varnish contains water and fine particles, the polyamic acid may not be compatible with the solvent containing water, and the inclusion of the polyamic acid and the fine particles may hinder the orientation of the polyamic acids and reduce the film strength. As a result, there is a problem that a mixture having a non-uniform composition that cannot form a coating film, including a mass of polyamic acid that encloses fine particles, is likely to be formed.

In order to avoid such a problem, it is conceivable to produce a substantially water-free varnish using completely dried organic fine particles. However, this method has a problem that it is difficult to obtain a polyimide porous film having a high aperture ratio by using the obtained varnish.

Therefore, a varnish containing organic fine particles, which can form a polyimide porous film having a high aperture ratio and has a uniform composition, a method for producing a precursor film of the polyimide porous film using the varnish, and a polyimide porous film A manufacturing method is desired.

The present invention has been made in view of the above problems, and is a varnish composition having a uniform composition containing organic fine particles capable of forming a polyimide porous film having a high aperture ratio, and a polyimide porous membrane using the above-mentioned varnish composition. It is an object of the present invention to provide a method for producing a precursor film and a method for producing a polyimide porous film using the precursor film.

In a varnish composition for forming a polyimide porous film containing a polyamic acid (A), organic fine particles (B), and a solvent (S), the present inventors use water (SI) as the solvent (S). ) And / or a water-soluble organic solvent (S-II) and an organic solvent (S-III) other than the water-soluble organic solvent (S-II) are used in combination, and water (SI) and water-soluble organic. We have found that the above problems can be solved by setting the total amount of the solvent (S-II) to be within a specific range, and have completed the present invention.

The first aspect of the present invention is a varnish composition for forming a polyimide porous film obtained by mixing a polyamic acid (A), organic fine particles (B), and a solvent (S).
The solvent (S) contains water (SI) and / or a water-soluble organic solvent (S-II) and an organic solvent (S-III) other than the water-soluble organic solvent (S-II).
The total ratio of the mass of water (SI) to the mass of the water-soluble organic solvent (S-II) to the mass of the solvent (S) is less than 30% by mass.
The water-soluble organic solvent (S-II) is a varnish composition selected from the group consisting of an ether solvent, a ketone solvent, and an alcohol solvent.

A second aspect of the present invention comprises a coating film forming step of applying the varnish composition according to the first aspect onto a substrate to form a coating film.
It is a method for producing a precursor film of a polyimide porous film, which comprises a precursor film forming step of removing a solvent (S) from a coating film and forming a precursor film of a polyimide porous film.

A third aspect of the present invention comprises a removal step of producing a precursor film of a polyimide porous film by the production method according to the second aspect, and then removing organic fine particles (B) from the precursor film. This is a method for manufacturing a membrane.

According to the present invention, a varnish composition having a uniform composition containing organic fine particles capable of forming a polyimide porous film having a high aperture ratio, a method for producing a precursor film of a polyimide porous film using the above-mentioned varnish composition, and the present invention. It is possible to provide a method for producing a polyimide porous membrane using a precursor membrane.

≪Varnish composition≫
The varnish composition comprises a polyamic acid (A), organic fine particles (B), water (SI) and / or a water-soluble organic solvent (S-II), and the above-mentioned water-soluble organic solvent (S-II). Included in combination with an organic solvent other than (S-III). The water-soluble organic solvent (S-II) is selected from the group consisting of an ether solvent, a ketone solvent, and an alcohol solvent.

Since the varnish composition contains the organic fine particles (B), the precursor film of the polyimide porous film can be formed by removing the solvent (S) from the coating film formed by using the varnish composition. By imidizing the polyamic acid (A) contained in the precursor film and removing the organic fine particles (B) from the precursor film, a polyimide porous film mainly made of a polyimide resin can be obtained.
Therefore, the varnish composition is used for forming a polyimide porous film.

When preparing a varnish composition containing water, when the polyamic acid (A), the organic fine particles (B), and the solvent (S) are mixed, a mass of the polyamic acid embracing the organic fine particles (B) is generated. It is often difficult to uniformly dissolve or disperse the polyamic acid (A) and the organic fine particles (B) in the solvent (S).
However, in the above varnish composition, when the solvent (S) contains water (SI), the mass of water (SI) and the water-soluble organic solvent (S-II) with respect to the mass of the solvent (S). The total ratio to the mass of is less than 30% by mass. By containing the above-mentioned solvent (S), the above-mentioned varnish composition has a uniform composition even when the solvent (S) contains water, and provides a polyimide porous film having a high aperture ratio.

Further, the organic fine particles (B) are often marketed as a slurry containing water. As described above, the varnish composition may contain less than 30% by mass of water (SI) with respect to the mass of the solvent (S) as long as the above-mentioned predetermined conditions are satisfied. Therefore, for the preparation of the varnish composition, a slurry of organic fine particles (B) containing water can be used as long as the content of water (SI) does not exceed a predetermined upper limit.

Hereinafter, essential or arbitrary ingredients used in the preparation of the varnish composition will be described.

<Polyamic acid (A)>
As the polyamic acid (A), a product obtained by polymerizing an arbitrary tetracarboxylic dianhydride and a diamine can be used without particular limitation. The amount of the tetracarboxylic acid dianhydride and the diamine used is not particularly limited, but it is preferable to use 0.50 mol or more and 1.50 mol or less of the diamine per 1 mol of the tetracarboxylic acid dianhydride, preferably 0.60 mol. It is more preferable to use 1.30 mol or more, and it is particularly preferable to use 0.70 mol or more and 1.20 mol or less.

The tetracarboxylic dianhydride can be appropriately selected from the tetracarboxylic dianhydrides conventionally used as a raw material for synthesizing polyamic acids. The tetracarboxylic acid dianhydride may be an aromatic tetracarboxylic acid dianhydride or an aliphatic tetracarboxylic acid dianhydride, but from the viewpoint of the heat resistance of the obtained polyimide resin, the aromatic tetra is used. It is preferable to use carboxylic acid dianhydride. The tetracarboxylic dianhydride may be used alone or in combination of two or more.

Suitable specific examples of aromatic tetracarboxylic acid dianhydride include pyromellitic acid dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, and bis (2,3-dicarboxyphenyl). Phenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3', 4'- Biphenyltetracarboxylic acid dianhydride, 2,2,6,6-biphenyltetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2) , 3-Dicarboxyphenyl) Propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropanedianhydride, 2,2- Bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, bis ( 3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic acid dianhydride, 4,4- (P-phenylenedioxy) diphthalic acid dianhydride, 4,4- (m-phenylenedioxy) diphthalic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5 , 8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10 -Perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracentetracarboxylic acid dianhydride, 1,2,7,8-phenanthrentetracarboxylic acid dianhydride, 9,9-bisfluorene phthalate anhydride , 3,3', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride and the like. Examples of the aliphatic tetracarboxylic dianhydride include ethylenetetracarboxylic dianhydride, butanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, 1,2, Examples thereof include 4,5-cyclohexanetetracarboxylic dianhydride and 1,2,3,4-cyclohexanetetracarboxylic dianhydride. Among these, 3,3', 4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoint of price, availability and the like. In addition, these tetracarboxylic dianhydrides may be used alone or in admixture of two or more.

The diamine can be appropriately selected from the diamines conventionally used as a synthetic raw material for polyamic acids. The diamine may be an aromatic diamine or an aliphatic diamine, but an aromatic diamine is preferable from the viewpoint of heat resistance of the obtained polyimide resin. These diamines may be used alone or in combination of two or more.

As the aromatic diamine, a diamino compound containing one benzene ring or an aromatic skeleton in which two or more and ten or less benzene rings are bonded or condensed via a single bond or a divalent linking group is used. Can be mentioned. Specifically, phenylenediamine and its derivatives, diaminobiphenyl compounds and their derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindane and its derivatives, diaminotetraphenyl. It is a compound and its derivative, a diaminohexaphenyl compound and its derivative, and a cardo-type fluorinated amine derivative.

The phenylenediamine is m-phenylenediamine, p-phenylenediamine or the like, and the phenylenediamine derivative is a diamine to which an alkyl group such as a methyl group or an ethyl group is bonded, for example, 2,4-diaminotoluene or 2,4-triphenylene. Diamine etc.

In the diaminobiphenyl compound, two aminophenyl groups are bonded to each other. For example, 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 to each other via another group. The bond is an ether bond, a sulfonyl bond, a thioether bond, a bond by an alkylene or a derivative group thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, a ureylene bond and the like. The number of carbon atoms in the alkylene bond is about 1 or more and 6 or less. The derivative group of the alkylene group 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'-Diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylketone , 3,4'-Diaminodiphenylketone, 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) phosphinoxide, 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 ] Sulphon, bis [4- (3-aminophenoxy) phenyl] sulphon, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane and the like can be mentioned.

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

The diaminotriphenyl compound is a compound in which two aminophenyl groups and one phenylene group are both bonded via another group. As the other group, a group similar to that of the diaminodiphenyl compound is selected. Examples of the diaminotriphenyl compound 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 aminophenylaminoindanes include 5 or 6-amino-1- (p-aminophenyl) -1,3,3-trimethylindanes.

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

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

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

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

The means for producing the polyamic acid (A) is not particularly limited, and for example, a known method such as a method of reacting an acid or 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 for the reaction between 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 done. One type of solvent may be used alone, or two or more types may be used in combination.

Examples of the solvent used for the reaction between the tetracarboxylic acid dianhydride and the 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; dimethylsulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellsolve acetate, ethyl cell solve acetate. Etc.; Examples thereof include phenol-based solvents such as cresols and xylene-based mixed solvents.
One of these solvents may be used alone, or two or more of these solvents may be used in combination. The amount of the solvent used is not particularly limited, but it is desirable that the content of the polyamic acid (A) produced 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, A nitrogen-containing polar solvent such as N-diethylformamide, N-methylcaprolactam, N, N, N', N'-tetramethylurea is preferable.

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

The content of the polyamic acid (A) in the varnish composition is not particularly limited, and is appropriately determined in consideration of the viscosity and coatability of the varnish composition and the solid content concentration of the varnish composition.
The viscosity of the varnish composition is not particularly limited as long as a coating film having a desired film thickness can be formed. For example, the viscosity of the varnish composition is preferably 300 cP or more and 20000 cP or less, more preferably 1000 cP or more and 15000 cP or less, and further preferably 1500 cP or more and 12000 cP or less. When the viscosity of the varnish composition is within this range, uniform film formation is easy.

The varnish composition has an organic fine particle (B) such that the ratio of the organic fine particles (B) / polyamic acid (A) is 0.5 to 4.0 (mass ratio) when the polyamic acid-fine particle composite film is formed. And polyamic acid (A) are preferably contained, and organic fine particles (B) and polyamic acid (A) are more preferably contained so that the above-mentioned ratio is 0.7 to 3.5 (mass ratio).
Further, when a polyamic acid-fine particle composite film is formed using the varnish composition, the volume ratio of the organic fine particles (B) / polyamic acid (A) in the composite film is 1.0 to 5.0. It preferably contains organic fine particles (B) and a polyamic acid. The above-mentioned volume ratio is more preferably 1.2 to 4.5. When the mass ratio or volume ratio of the organic fine particles (B) / polyamic acid (A) is at least the lower limit, it is easy to form pores having an appropriate density. When the mass ratio or volume ratio of the organic fine particles (B) / polyamic acid (A) is not more than the upper limit, a stable film formation is formed without causing problems such as an increase in the viscosity of the varnish composition and cracks in the film. be able to.

The solid content concentration of the varnish composition is not particularly limited, but is, for example, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and the upper limit is, for example, 60% by mass or less. It is preferably 30% by mass or less.

<Organic fine particles (B)>
The material of the organic fine particles (B) is not particularly limited as long as it is insoluble in the solvent (S) contained in the varnish composition and can be later removed from the precursor film of the polyimide porous film, and any known material can be used. It can be adopted.

The form of the organic fine particles (B) is not particularly limited. For the preparation of the varnish composition, a dried powder of the organic fine particles (B) may be used, or a dispersion liquid of the organic fine particles (B) may be used. The varnish composition may contain a specific amount of water (SI). Therefore, the varnish composition can be prepared by using the dispersion liquid in which the organic fine particles (B) are dispersed in water as the dispersion liquid of the organic fine particles (B). As the organic fine particles (B), a dispersion liquid is preferable because agglomeration of the organic fine particles (B) due to drying can be avoided and it is inexpensive and easily available. Therefore, a dispersion liquid in which the organic fine particles (B) are dispersed in water is preferable. More preferred.

Further, as the organic fine particles (B), fine particles having a high sphericity and a small particle size distribution index are preferable. The organic fine particles (B) having these conditions have excellent dispersibility in the varnish composition and can be used in a state where they do not aggregate with each other.

The average particle size (average diameter) of the organic fine particles (B) is, for example, preferably 2000 nm or less, more preferably 1000 nm or less, further preferably 700 nm or less, further preferably 10 nm or more and 600 nm or less, and particularly preferably 20 nm or more and 500 nm or less. It is preferably 30 nm or more and 450 nm or less, most preferably. By using fine particles having an average particle size within such a range, it is easy to form a polyimide porous film having fine pores having a desired pore diameter and having an excellent granulation effect.
The size of the pores derived from the fine particles formed in the polyimide porous membrane is the same as or close to the average particle size of the fine particles. Therefore, the average particle size of the fine particles is preferably 5 nm or more, more preferably 10 nm or more, from the viewpoint of fluid permeability when the polyimide porous membrane is used as a filter.
By satisfying these conditions, the pore diameters of the polyimide porous membrane obtained by removing the organic fine particles (B) can be made uniform, so that the applied electric field is uniform, especially when the polyimide porous membrane is used as a separator. It is preferable because it can be changed.

The material of the organic fine particles is not particularly limited as long as it is insoluble in the solvent (S), particularly the organic solvent (S-III) and can be selectively removed after the film formation. Resin is preferable as the material of the organic fine particles.

As the resin as a material for the organic fine particles, for example, a normal linear polymer or a known depolymerizable polymer can be used without limitation depending on the intended purpose. A normal linear polymer is a polymer in which the molecular chain of the polymer is randomly cut at the time of thermal decomposition, and a depolymerizable polymer is a polymer in which the polymer is decomposed into a monomer at the time of thermal decomposition. All of them disappear from the polyimide film by decomposing into a monomer, a low molecular weight substance, or CO _{2 at the time of heating.} The decomposition temperature of the resin fine particles used is preferably 200 ° C. or higher and 320 ° C. or lower, and more preferably 230 ° C. or higher and 260 ° C. or lower. When the decomposition temperature is 200 ° C. or higher, film formation can be performed even when a high boiling point solvent is used for the varnish composition, and the range of selection of firing conditions for polyimide is widened. Further, if the decomposition temperature is less than 320 ° C., only the resin fine particles can be eliminated without causing thermal damage to the polyimide.

As the linear polymer, for example, low-density or amorphous polyethylene, amorphous polypropylene, ethylene-vinyl acetate copolymer resin, polyamide and the like can be used. Further, as the depolymerizable polymer, for example, (meth) acrylic resin, α-methylstyrene resin, polyacetal homopolymer, copolymer and the like can be used.

The (meth) acrylic resin is obtained from (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. Examples thereof include a single polymer, a copolymer obtained by copolymerizing two or more kinds of the polymer, and the like. Further, the copolymer may be used by copolymerizing the above (meth) acrylic acid alkyl ester as a main component and copolymerizing with another monomer copolymerizable therewith (for example, glycidyl methacrylate, styrene, etc.).

Examples of the α-methylstyrene resin include a single polymer of α-methylstyrene and a copolymerized polymer containing α-methylstyrene as a main component and a copolymerizable product thereof. The depolymerizable polymer may be used alone or in combination.

Among these depolymerizable polymers, methyl methacrylate or isobutyl methacrylate having a low thermal decomposition temperature alone (polymethylmethacrylate or polyisobutylmethacrylate) or a copolymer polymer containing this as a main component is preferable for handling at the time of pore formation. ..

The polymer that is the material of the resin fine particles may be a crosslinked polymer in which crosslinks are introduced by a crosslinkable monomer. When the organic fine particles (B) are resin fine particles made of a crosslinked polymer, dissolution, deformation, swelling and the like of the resin fine particles due to the organic solvent (S-III) in the solvent (S) can be suppressed.
The crosslinkable monomer is not particularly limited as long as it is a polyfunctional monomer capable of introducing crosslinks into the polymer. When the polymer constituting the resin fine particles is, for example, polystyrene or (meth) acrylic resin, examples of the crosslinkable monomer include acrylic polyfunctional monomers such as trimethylolpropane tri (meth) acrylate and divinylbenzene. ..

Preferable examples of the resin fine particles into which crosslinks have been introduced by the crosslinkable monomer include resin fine particles containing a structural unit derived from a monofunctional styrene-based monomer (hereinafter, also simply referred to as “styrene-based structural unit”). For the resin fine particles containing the styrene-based constituent unit, the ratio of the mass of the styrene-based constituent unit to the mass of the resin fine particles is preferably 10% by mass or more and 99% by mass or less. The ratio of the mass of the styrene-based constituent unit to the mass of the resin fine particles is preferably 20% by mass or more, and more preferably 60% by mass or more. In such resin fine particles, the ratio of the mass of the structural unit derived from the polyfunctional crosslinkable monomer to the mass of the resin fine particles is preferably 1% by mass or more and 15% by mass or less. The amount of the structural unit derived from the polyfunctional crosslinkable monomer is preferably 1 part by mass or more and 20 parts by mass or less, with the amount of the structural unit derived from the monocyclic monomer as 100 parts by mass.
Such resin fine particles may be a copolymer of a monofunctional styrene-based monomer, the above-mentioned crosslinkable monomer, and the above-mentioned monofunctional monomer such as (meth) acrylic acid alkyl ester. When the resin constituting the resin fine particles contains a structural unit derived from another monofunctional monomer in addition to the structural unit derived from the monofunctional styrene-based monomer, the amount of the structural unit derived from the other polyfunctional monomer is particularly high. Not limited.
Examples of the monofunctional styrene-based monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene and the like.

In the resin fine particles made of the crosslinked polymer in which the crosslinkable group is introduced by the crosslinkable monomer described above, the mass ratio of the structural units derived from other monofunctional monomers other than the structural units derived from the monofunctional styrene-based monomer is determined. Of the mass of all the constituent units derived from the monofunctional monomer, 1% by mass or more and 100% by mass or less is preferable, and 50% by mass or more and 85% by mass or less is more preferable.

<Basic compound (C)>
The varnish composition may contain the basic compound (C) as long as the object of the present invention is not impaired. The basic compound (C) is not particularly limited as long as it is a compound generally recognized as a basic compound and the desired effect can be obtained by its use.
As the basic compound (C), a compound showing a pKa value of 7.5 or more in water is typically preferable. In the compound showing a plurality of pKa, it is not necessary that all pKa values are 7.5 or more, and it is preferable that all pKa values are 7.5 or more.
The value of pKa can be easily searched by SciFinder (registered trademark) known as a search service based on a database such as Chemical Abstract. Here, the pKa value calculated by Advanced Chemical Development (ACD / Labs) Software V11.02 (Copyright 1994-2011 ACD / Labs) was adopted.

When the varnish composition contains the basic compound (C), the pH of the varnish composition at 20 ° C. is 3.0 or more and 7.0 or less because the polyamic acid (A) dissolves in the solvent. Is preferable.

The basic compound (C) may be a basic organic compound or a basic inorganic compound. The basic compound (C) is basic because it is easily removed from the polyimide porous film in the imidization step and the step of removing the organic fine particles (B) and the polyimide porous film has little adverse effect on the product. Organic compounds are preferred.

As the basic organic compound, a nitrogen-containing basic organic compound is preferable. The nitrogen-containing basic organic compound may be an aliphatic compound that does not contain an aromatic ring, or may be an aromatic compound that contains an aromatic ring, and is good in that it does not easily remain in the polyimide porous film. It is preferably an aliphatic compound in that it exhibits basicity.
As the nitrogen-containing basic organic compound, a compound containing at least one primary nitrogen atom, a secondary nitrogen atom, or a tertiary nitrogen atom is preferable. The nitrogen-containing basic organic compound may have a heteroatom such as O, S, P, Si, or a halogen atom as long as the object of the present invention is not impaired.

Preferable examples of nitrogen-containing basic organic compounds include alkylamines, hydroxyalkylamines, piperidines, piperazines, morpholines, pyrrolidines, and guanidine and guanidine salts.

Alkylamines are amine compounds in which at least one aliphatic hydrocarbon group is bonded to a nitrogen atom. Examples of the aliphatic hydrocarbon group include a linear alkyl group, a branched alkyl group, a linear alkylene group, a branched alkylene group, a cycloalkyl group, and a cycloalkanediyl group. Alkylamines may contain two or more nitrogen atoms in one molecule. The number of nitrogen atoms contained in one molecule of alkylamines is preferably 1 or more and 4 or less. The number of carbon atoms of the alkyl group contained in the alkylamines on the nitrogen atom is preferably 1 or more and 6 or less, and more preferably 1 or more and 4 or less.

Specific examples of alkylamines include trimethylamine, diethylamine, dimethylethylamine, diethylmethylamine, triethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, Nn-propylethylamine, Nn-. Butylethylamine, ethylenediamine, N-methylethylenediamine, N, N-dimethylethylenediamine, N, N'-dimethylethylenediamine, N, N, N', N'-tetramethylethylenediamine, N-ethylethylenediamine, N, N-diethylethylenediamine , N, N'-diethylethylenediamine, N, N, N', N'-tetraethylethylenediamine, 1,3-propanediamine, diethylenetriamine, triethylenetetramine and the like.

Hydroxyalkylamines are compounds in which one or more hydroxyl groups are substituted for an aliphatic hydrocarbon group in the above-mentioned alkylamines. Specific examples of hydroxyalkylamines include ethanolamine, diethanolamine, triethanolamine and the like.

As the piperidines, unsubstituted piperidine or N-alkyl substituted piperidine is preferable. In the N-alkyl substituted piperidine, the number of carbon atoms of the alkyl group bonded on the nitrogen atom is preferably 1 or more and 6 or less, and more preferably 1 or more and 3 or less. Specific examples of piperidines include piperidine, N-methylpiperidine, N-ethylpiperidine and the like.

As the piperazines, unsubstituted piperazine, N-alkyl group-substituted piperazine, or N, N'-dialkyl-substituted piperazine are preferable. In the N-alkyl substituted piperazine and the N, N'-dialkyl substituted piperazine, the number of carbon atoms of the alkyl group bonded on the nitrogen atom is preferably 1 or more and 6 or less, and more preferably 1 or more and 3 or less. Specific examples of piperazines include piperazine, N-methylpiperazine, N-ethylpiperazine, N, N'-dimethylpiperazine, N, N'-diethylpiperazine and the like.

As the morpholins, unsubstituted morpholine or N-alkyl substituted morpholine is preferable. In the N-alkyl substituted morpholine, the number of carbon atoms of the alkyl group bonded on the nitrogen atom is preferably 1 or more and 6 or less, and more preferably 1 or more and 3 or less. Specific examples of morpholines include morpholine, N-methylmorpholine, N-ethylmorpholine and the like.

As the pyrrolidines, unsubstituted pyrrolidine or N-alkyl substituted pyrrolidine is preferable. In the N-alkyl substituted pyrrolidine, the number of carbon atoms of the alkyl group bonded on the nitrogen atom is preferably 1 or more and 6 or less, and more preferably 1 or more and 3 or less. Specific examples of pyrrolidines include pyrrolidine, N-methylpyrrolidin, N-ethylpyrrolidine and the like.

Examples of guanidine and guanidine salts include guanidine and salts of guanidine and a weak acid. Specific examples of guanidine and guanidine salts include guanidine, guanidine carbonate, guanidine oxalate, guanidine acetate and the like.

As the basic inorganic compound, an alkali metal hydroxide and a salt of the alkali metal and a weak acid are preferable. As the alkali metal, Na, K and Li are preferable, and Na and K are more preferable. As the weak acid, carbonic acid, oxalic acid, phosphoric acid, and an aliphatic carboxylic acid having 1 or more and 4 or less carbon atoms are preferable. Of these, carbonic acid, oxalic acid, acetic acid, and phosphoric acid are particularly preferred.
Specific examples of the basic inorganic compound include sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide, potassium carbonate, potassium hydrogencarbonate, sodium oxalate, potassium oxalate, sodium acetate, sodium phosphate, and potassium phosphate. , Disodium hydrogen phosphate, dipotassium hydrogen phosphate and the like.

<Solvent (S)>
The varnish composition contains a solvent (S). The solvent (S) includes water (SI) and / or a water-soluble organic solvent (S-II) and an organic solvent (S-III) other than the water-soluble organic solvent (S-II). The water-soluble organic solvent (S-II) is selected from the group consisting of an ether solvent, a ketone solvent, and an alcohol solvent.
The total ratio of the mass of water (SI) to the mass of the water-soluble organic solvent (S-II) to the mass of the solvent (S) is less than 30% by mass.
By containing the solvent (S) satisfying the above conditions, the varnish composition is uniform even when the solvent (S) contains water (SI), and the varnish composition is uniform. Can be used to form a polyimide porous film with a high aperture ratio.

The upper limit of the total ratio of the mass of water (SI) to the mass of the water-soluble organic solvent (S-II) with respect to the mass of the solvent (S) is less than 30% by mass, preferably 28% by mass or less. 25% by mass or less is more preferable, 23% by mass or less is further preferable, 20% by mass or less is further preferable, and 15% by mass or less is particularly preferable.
The lower limit of the total ratio of the mass of water (SI) to the mass of the water-soluble organic solvent (S-II) with respect to the mass of the solvent (S) is not particularly limited as long as it is less than 30% by mass. Specifically, as the lower limit, 0.1% by mass or more is preferable, 0.5% by mass or more is more preferable, and 1% by mass or more is further preferable. The lower limit may be 2% by mass or more, or 5% by mass or more.

When the total content of the water (SI) and the water-soluble organic solvent (S-II) in the solvent (S) is within the above range, it is particularly easy to form a polyimide porous film having a high aperture ratio. ..

As described above, the water-soluble organic solvent (S-II) is selected from the group consisting of an ether solvent, a ketone solvent, and an alcohol solvent.
Here, "water-soluble" refers to the property that 0.5 g or more of the solute is dissolved in 100 g of water at 25 ° C.

Within the specification and claims of the present application, compounds corresponding to ketones and ethers and having an alcoholic hydroxyl group are classified as alcohol-based solvents. In addition, compounds corresponding to both ketones and ethers are classified as ketone solvents.

The water-soluble organic solvent (S-II) preferably does not contain nitrogen atoms because it is easy to obtain a varnish composition that easily forms a polyimide porous film having a high aperture ratio.

Examples of the ether solvent corresponding to the water-soluble organic solvent (S-II) include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like.

Examples of the ketone solvent corresponding to the water-soluble organic solvent (S-II) include acetone, methyl ethyl ketone, cyclohexanone and the like.

Examples of alcohols corresponding to the water-soluble organic solvent (S-II) include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether. Diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5- Pentandiol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, and 1,2,6-hexane Triol and the like can be mentioned.

The type of the organic solvent (S-III) is not particularly limited as long as it is an organic solvent that does not correspond to the water-soluble organic solvent (S-II). The organic solvent (S-III) may be basic, but from the viewpoint of avoiding hydrolysis of the polyamic acid (A), the organic solvent (S-III) is a compound that is neutral or weakly basic in water. preferable. More specifically, the organic solvent (S-III) is preferably a compound having a pKa value of less than 7.5 in water.

Suitable examples of the organic solvent (S-III) include N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylisobutylamide, N, N-diethylacetamide, N, N-dimethylformamide (DMF), N, N-diethylformamide, N-methylcaprolactum, 1,3-dimethyl-2-imidazolidinone (DMI), pyridine, and N, N, N', N'- Nitrogen-containing polar solvent such as tetramethylurea (TMU); lactone-based polar solvent such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; dimethylsulfoxide Hexamethylphosphoric triamide; acetonitrile; aromatic solvents such as benzene, toluene, xylene and the like.

（式（Ｓ１）中、Ｒ^Ｓ１及びＲ^Ｓ２は、それぞれ独立に炭素原子数１以上３以下のアルキル基であり、Ｒ^Ｓ３は、水素原子、又は下記式（Ｓ１−１）若しくは下記式（Ｓ１−２）：

で表される基であり、Ｒ^Ｓ４は、水素原子又は水酸基であり、Ｒ^Ｓ５及びＲ^Ｓ６は、それぞれ独立に、水素原子、炭素原子数１以上３以下のアルキル基であり、Ｒ^Ｓ７及びＲ^Ｓ８は、それぞれ独立に水素原子、又は炭素原子数１以上３以下のアルキル基である。）
で表される含窒素有機溶媒、又はジメチルスルホキシドを含むのが好ましい。 The organic solvent (S-III) has the following formula (S1): from the viewpoint of dissolution or dispersion stability of the varnish composition and easy removal of the solvent (S) from the coating film.

(In the formula (S1), ^RS1 and ^RS2 are each independently an alkyl group having 1 or more and 3 or less carbon atoms, and ^RS3 is a hydrogen atom, or the following formula (S1-1) or the following formula (S1). -2):

^RS4 is a hydrogen atom or a hydroxyl group, and ^RS5 and ^RS6 are independently hydrogen atoms and alkyl groups having 1 or more and 3 or less carbon atoms, respectively, and ^RS7 and R are ^S8 is an independently hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms. )
It is preferable to contain a nitrogen-containing organic solvent represented by (1) or dimethyl sulfoxide.

Among the compounds represented by formula ^(S1), as a specific example of ^{R S3} is a group represented by the formula (S1-1) is, N, N-dimethylformamide, N, N- dimethylacetamide, N , N, 2-trimethylpropionamide, N-ethyl, N,2-dimethylpropionamide, N, N-diethyl-2-methylpropionamide, N, N,2-trimethyl-2-hydroxypropionamide, N-ethyl Examples thereof include -N, 2-dimethyl-2-hydroxypropionamide, N, N-diethyl-2-hydroxy-2-methylpropionamide and the like.

Among the compounds represented by formula ^(S1), as a specific example of ^{R S3} is a group represented by the formula (S1-2) is, N, N, N ', N'- tetramethyl urea, N , N, N', N'-tetraethylurea and the like.

Among the examples of the compound represented by the formula (S1), particularly preferable compounds are N, N-dimethylformamide, N, N-dimethylacetamide, N, N, 2-trimethylpropionamide, and N, N, N. ', N'-Tetramethylurea can be mentioned. Of these, N, N, 2-trimethylpropionamide and N, N, N', N'-tetramethylurea are preferred. The boiling point of N, N, 2-trimethylpropionamide under atmospheric pressure is 175 ° C, and the boiling point of N, N, N', N'-tetramethylurea under atmospheric pressure is 177 ° C. As described above, N, N, 2-trimethylpropionamide and N, N, N', N'-tetramethylurea have a relatively low boiling point in the organic solvent (S-III).
Therefore, when a varnish composition containing a solvent (S) containing at least one selected from N, N, 2-trimethylpropionamide and N, N, N', N'-tetramethylurea is used, When the precursor film of the polyimide porous film is heated, the solvent does not easily remain in the precursor film, and the tensile elongation of the obtained polyimide film is less likely to decrease.

Furthermore, N, N, 2-trimethylpropionamide, and N, N, N', N'-tetramethylurea are substances of very high concern under the REACH regulation in the EU (European Union). It is also useful in that it is a substance with low toxicity, as it is not designated as a substance of very high concern (Substance of Very High Concern).

The content of the nitrogen-containing organic solvent represented by the formula (S1) in the organic solvent (S-III) is not particularly limited as long as it does not impair the object of the present invention. The ratio of the mass of the nitrogen-containing organic solvent represented by the formula (S1) to the mass of the organic solvent (S-III) is typically 70% by mass or more, more preferably 80% by mass or more, and 90% by mass. % Or more is particularly preferable, and 100% by mass is most preferable.

Further, among the above-mentioned solvents described as the organic solvent (S-III), a solvent having good compatibility with the polyamic acid (A) and azeotropically boiling with water is preferable. Examples of such a solvent include N, N-dimethylacetamide, NMP, and γ-butyrolactone. When the organic solvent (S-III) is azeotropically heated with water, it is easy to remove the solvent (S) from the coating film made of the varnish composition.
Further, among the above-mentioned solvents described as the organic solvent (S-III), the solubility of the polyamic acid (A) and the dispersibility of the organic fine particles (B) are good, and the polyimide porous film has a high aperture ratio. Dimethyl sulfoxide is particularly preferable because it is easy to obtain a varnish composition that gives a varnish composition.

The content of the solvent (S) in the varnish composition is not particularly limited as long as it does not impair the object of the present invention. The content of the solvent (S) in the varnish composition is appropriately adjusted according to the solid content content of the varnish composition.

<Dispersant>
A dispersant may be further added together with the organic fine particles (B) for the purpose of uniformly dispersing the organic fine particles (B) in the varnish composition. By adding the dispersant, the polyamic acid (A) and the organic fine particles (B) can be mixed more uniformly, and further, the organic fine particles (B) in the formed film can be uniformly distributed. As a result, a dense opening can be provided on the surface of the finally obtained polyimide porous membrane, and the front and back surfaces can be efficiently communicated with each other, and the air permeability of the polyimide porous membrane is improved. Further, by adding the dispersant, the drying property of the varnish composition is likely to be improved, and the peelability of the formed polyimide porous film from the precursor film or the like is easily improved.

The dispersant is not particularly limited, and a known dispersant can be used. For example, palm fatty acid salt, castor sulfate oil salt, lauryl sulfate salt, polyoxyalkylene allylphenyl ether sulfate salt, alkylbenzene sulfonic acid, alkylbenzene sulfonate, alkyldiphenyl ether disulfonate, alkylnaphthalene sulfonate, dialkyl sulfosucci. Anionic surfactants such as nate salt, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salt, polyoxyethylene allylphenyl ether phosphate salt; oleylamine acetate, laurylpyridinium chloride, cetylpyridinium chloride, lauryltrimethylammonium chloride, stearyltrimethylammonium chloride. , Behenyltrimethylammonium chloride, didecyldimethylammonium chloride and other cationic surfactants; palm alkyldimethylamine oxide, fatty acid amide propyldimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amide betaine type activator, alanine type activator, lauryl Amphoteric surfactants such as iminodipropionic acid; polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, polyoxy Nonionic surfactant of polyoxyalkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether such as alkylene polystyrylphenyl ether, polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylated castor oil, polyoxyethylenated curing Other polyoxyalkylene-based nonionic surfactants such as castor oil, sorbitan lauric acid ester, polyoxyethylene sorbitan lauric acid ester, fatty acid diethanolamide; fatty acid alkyl esters such as octyl stearate, trimethylolpropane tridecanoate; poly Examples thereof include, but are not limited to, polyether polyols such as oxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropanthris (polyoxyalkylene) ether. Further, the above-mentioned dispersant may be used as a mixture of two or more kinds.

The content of the dispersant in the varnish composition is, for example, preferably 0.01% by mass or more and 5% by mass or less, and 0.05% by mass or more and 1% by mass or less with respect to the fine particles, in terms of film forming property. Is more preferable, and it is even more preferable that it is 0.1% by mass or more and 0.5% by mass or less.

The essential or optional components described above can be added to the essential or optional components described above according to a predetermined composition in consideration of the coatability of the varnish composition and various characteristics of the polyimide porous film to be produced. By mixing, a varnish composition is produced.

≪Manufacturing method of varnish composition≫
The method for producing a varnish composition is produced by mixing a predetermined amount of each of the above-mentioned various components.
As a preferable method for producing the varnish composition,
Examples thereof include a method of mixing a polyamic acid-containing liquid containing a polyamic acid (A) and an organic solvent (S-III) with a fine particle dispersion liquid containing organic fine particles (B).

Regarding the polyamic acid-containing liquid, the polyamic acid (A) and the organic solvent (S-III) are as described above. The polyamic acid-containing liquid may be prepared by dissolving the polyamic acid (A) produced by a well-known method in an organic solvent (S-III), or the polyamic acid (A) may be prepared in the organic solvent (S-III). May be prepared by synthesizing.
The polyamic acid-containing liquid may contain water (SI) and / or a water-soluble organic solvent (S-II). Further, the polyamic acid-containing liquid may contain any component other than the polyamic acid (A), the organic solvent (S-III), the water (SI), and the water-soluble organic solvent (S-II).

Regarding the fine particle dispersion liquid, the organic fine particles (B) are as described above. The dispersion medium contained in the fine particle dispersion is preferably one or more selected from water (SI), a water-soluble organic solvent (S-II), and an organic solvent (S-III), and water (SI). ) And / or a water-soluble organic solvent (S-II) is more preferable.
From the viewpoint of easy availability and low cost, the fine particle dispersion is preferably a dispersion in which the organic fine particles (B) are dispersed in water (SI).
Since the varnish composition contains water (SI) and / or a water-soluble organic solvent (S-II), at least one of the polyamic acid-containing liquid and the fine particle dispersion liquid is water (SI), and / Or contains a water-soluble organic solvent (S-II).

In the above method, when various materials constituting the varnish composition are mixed, the mixing is performed under heated conditions within a range in which the polyamic acid (A) and the organic fine particles (B) are not excessively decomposed or deformed. You may.
Further, various materials constituting the varnish composition may be mixed while dispersing the organic fine particles (B) using various dispersion devices.

≪Manufacturing method of precursor film of polyimide porous film≫
The method for manufacturing the precursor film of the polyimide porous film is
A coating film forming step of applying the above-mentioned varnish composition on a substrate to form a coating film, and
It includes a precursor film forming step of removing the solvent (S) from the coating film and forming a precursor film of the polyimide porous film.

Hereinafter, a method for forming a precursor film of a polyimide porous film (hereinafter, also simply referred to as “precursor film”) will be described. In the precursor film forming step, as described above, the precursor film is formed by using the above-mentioned varnish composition. At that time, the precursor film may be formed directly on the substrate, or may be formed on a lower layer film different from the precursor film formed on the substrate. Further, after the precursor film is formed by using the above-mentioned varnish composition, an upper film different from the precursor film may be further formed on the upper layer. In the present application, a method of providing a lower layer film on a substrate and a method of forming a precursor film on the upper layer after forming a precursor film using the above-mentioned varnish are also available. Included in the method of forming a precursor film on a substrate. However, when a material that does not require a firing step is used for the upper layer film, the upper layer film may be formed on the polyimide-fine particle composite film after firing.
For the precursor film, for example, the above-mentioned varnish composition is applied directly on the substrate or on the lower layer film formed on the substrate to form a coating film, and then the temperature is 0 ° C. or higher under normal pressure or vacuum. It can be formed by drying at 100 ° C. or lower, preferably 10 ° C. or higher and 100 ° C. or lower at normal pressure.
Examples of the base material include a PET film, a SUS substrate, a glass substrate and the like.

The lower layer film (or upper layer film) contains, for example, a resin composed of polyamic acid, polyimide, polyamide-imide precursor, polyamideimide and polyether sulfone, fine particles, and a solvent, and the content of the fine particles is the above. Examples thereof include a lower layer (or upper layer) unfired composite film formed by using a lower layer film (or upper layer film) forming varnish having a total of more than 40% by volume and 81% by volume or less with respect to the total of the resin and the fine particles. The lower unfired composite film may be formed on the substrate. When the content of the fine particles is more than 40% by volume, the fine particles are uniformly dispersed. Further, when the content of the fine particles is 81% by volume or less, the fine particles are dispersed without agglomeration, so that the pores are uniformly formed in the layer derived from the lower layer film (or upper layer film) in the polyimide porous film. Can be formed into. Further, when the content of the fine particles is within the above range, when the lower unfired composite film is formed on the substrate, the release property after the film formation is formed even if the release layer is not provided in advance on the substrate. Easy to secure.

The fine particles used in the varnish for forming the lower (or upper) film may be the same as or different from the organic fine particles (B) used in the above-mentioned varnish composition. In order to make the pores in the lower (or upper) unfired composite film more dense, the fine particles used for the lower (or upper) film-forming varnish have a particle size distribution more than that of the organic fine particles (B) used in the above-mentioned varnish composition. It is preferable that the exponent is small or the same. Alternatively, it is preferable that the fine particles used for the lower (or upper) film forming varnish have a smaller or the same sphericity ratio than the fine particles used for the above-mentioned varnish composition.

The average particle size of the fine particles used in the varnish for forming the lower (or upper) film is preferably 5 nm or more and 1000 nm or less, and more preferably 10 nm or more and 600 nm or less.

Further, the content of the fine particles in the lower (or upper) film forming varnish may be higher or lower than that of the above-mentioned varnish composition. Preferable examples of the components such as fine particles and the solvent contained in the varnish for forming the lower layer (or upper layer) film are the same as the above-mentioned varnish composition. The varnish for forming the lower layer (or upper layer) film can be prepared by the same method as the above-mentioned varnish composition.
The lower unfired composite film is, for example, coated with the above varnish for forming the lower layer film on a substrate and dried at 0 ° C. or higher and 100 ° C. or lower, preferably 10 ° C. or higher and 100 ° C. or lower under normal pressure or vacuum. By doing so, it can be formed. The same applies to the film forming conditions of the upper unfired composite film.

The lower (or upper) film is made of a fiber-based material such as a cellulosic resin or a non-woven fabric (for example, a polyimide non-woven fabric or the like (the fiber diameter is, for example, about 50 nm or more and about 3000 nm or less)). Membranes and polyimide films can also be mentioned.

By the method described above, the precursor film is formed on the substrate alone or, if necessary, together with the lower layer (or upper layer) film.

The method for producing a precursor film of a polyimide porous film preferably includes a peeling step of peeling the precursor film from the substrate after the above-mentioned precursor film forming step.
When the precursor film is peeled off from the substrate, the substrate is not required to have heat resistance that can withstand the temperature at which the precursor film is fired.
The precursor film of the polyimide porous film is often difficult to stretch and brittle. However, the precursor film obtained by drying the coating film made of the above-mentioned varnish composition has an elongation of 0.5% or more as measured according to the 0.5 grade of JIS B7721. Therefore, the precursor film formed by drying the coating film made of the above-mentioned varnish composition can be easily peeled off from the substrate without being damaged.
The elongation of the precursor film is preferably 1% or more, more preferably 2% or more.

When peeling the precursor film or the laminated film of the precursor film and the lower (or upper) unfired composite film from the base material, use a base material with a release layer in advance in order to further improve the peelability of the film. You can also. When the release layer is provided on the substrate in advance, the release agent is applied on the substrate and dried or baked before applying the above-mentioned varnish composition or the varnish for forming the lower layer film. As the release agent used here, a known release agent such as an alkyl phosphate ammonium salt type, a fluorine type or a silicone can be used without particular limitation. When the dried precursor film is peeled off from the substrate, if a small amount of the release agent remains on the peeled surface of the precursor film, the remaining mold release agent may cause discoloration during firing and adverse effects on electrical characteristics. Therefore, it is preferable that the release agent adhering to the peeled surface is removed as much as possible. For the purpose of removing the release agent, a cleaning step may be introduced in which a precursor film peeled from the substrate or a laminated film containing the precursor film is washed with an organic solvent.

When the base material is used as it is without providing the release layer, the above-mentioned peeling step and cleaning step can be omitted. Further, in the method for producing a precursor film, a dipping step of immersing the precursor film in water or a solvent containing water before the removal step described later, a pressing step of pressing the precursor film after the dipping step, and a precursor film after the dipping step. A drying step of drying the above may be provided as an arbitrary step.

In the method for producing a precursor film of a polyimide porous film, when the above peeling step is carried out, it is preferable to further carry out a winding step of winding the precursor film into a roll shape after the peeling step.
As described above, since the precursor film exhibits a certain degree of elongation, it is possible to wind up the precursor film without causing cracks or breakage. When the precursor film is wound into a roll, the roll-shaped precursor film can be fired in a small firing furnace. In addition, the precursor film can be easily transferred until the precursor film is fired, and space can be saved for storage.
Further, a roll-to-roll process can be applied to the process of firing the precursor film, and an efficient production of a polyimide porous film is possible.

≪Manufacturing method of polyimide porous membrane≫
The method for producing a polyimide porous membrane is a method including a removal step of removing organic fine particles (B) from the precursor film of the polyimide porous membrane described above. In the removal step, the removal of the organic fine particles (B) may be carried out while imidizing the polyamic acid (A), or may be carried out after imidizing the polyamic acid (A).

The method for imidizing the polyamic acid (A) is not particularly limited. The imidization may be either thermal imidization or chemical imidization. As the chemical imidization, a method such as immersing the precursor membrane containing the polyamic acid (A) in acetic anhydride or a mixed solvent of acetic anhydride and isoquinoline can be used.

Among the above-mentioned imidization methods, calcination, which is thermal imidization, is preferable because it is not necessary to remove the imidizing agent by washing. When imidization is performed by firing, if the organic fine particles (B) are resin fine particles, the resin fine particles can be removed together with the imidization.

In this case, if the organic fine particles (B) are resin fine particles made of a crosslinked polymer, the resin fine particles are easily removed by firing, and the resin fine particles made of the crosslinked polymer are of the organic solvent (SI). Since it is difficult to swell or deform due to the influence, it is easy to manufacture a polyimide porous film having pores of a desired size and shape.
Hereinafter, firing will be described.

When a lower layer (or upper layer) film is formed together with the precursor film when the precursor film is produced, the lower layer (or upper layer) film is fired together with the firing of the precursor film. The firing temperature varies depending on the structure of the polyamic acid (A) and the like, but is preferably 120 ° C. or higher and 500 ° C. or lower, more preferably 150 ° C. or higher and 450 ° C. or lower, and more preferably 300 ° C. or higher and 450 ° C. or lower.

The firing conditions are, for example, a method of raising the temperature from room temperature to about 400 to 450 ° C. in about 3 hours and then holding the temperature at the same temperature for about 2 to 30 minutes, or stepwise 400 from room temperature in increments of, for example, 50 ° C. It is also possible to use a stepwise drying-heat imidization method such as raising the temperature to ~ 450 ° C. (holding for about 20 minutes in each step) and finally holding at 400 to 450 ° C. for about 2 to 30 minutes. When a precursor film is formed on the substrate and the precursor film or the laminated film containing the precursor film is once peeled off from the substrate, the end of the precursor film or the laminated film is fixed to a SUS mold or the like to deform it. You can also take preventive measures.

The film thickness of the polyimide porous film or the polyimide resin-fine particle composite film obtained after firing can be obtained by measuring the thicknesses of a plurality of locations with a micrometer or the like and averaging them. What kind of average film thickness is preferable depends on the use of the polyimide porous membrane, but for example, when it is used for a separator or the like, it is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 100 μm or less, and 15 μm or more and 30 μm or less. Is even more preferable. When used for a filter or the like, it is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, and further preferably 20 μm or more and 150 μm or less.

The polyimide porous film thus obtained is a non-transparent or colored porous film. The overall film thickness of the polyimide porous film is not particularly limited, but for example, when the polyimide porous film is used for a separator or the like, the film thickness is preferably 5 μm or more and 500 μm or less, and 10 μm or more and 100 μm or less. More preferably, it is more preferably 15 μm or more and 30 μm or less. When the polyimide porous membrane is used for a filter or the like, the film thickness is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, and further preferably 20 μm or more and 150 μm or less. The above film thickness can be obtained by measuring and averaging the thicknesses of a plurality of locations with, for example, a micrometer, as in the case of measuring the polyimide resin-fine particle composite film. Further, regardless of the film thickness, the polyimide porous membrane is a porous membrane in which spherical pores communicate with each other throughout the membrane, and the front and back surfaces communicate with each other.

In the method for producing a polyimide porous film, at least a part of the polyimide resin portion of the polyimide resin-fine particle composite film is removed before the removal step, or at least a part of the polyimide porous film is removed after the removal step. It may have a resin removing step. By removing at least a part of the resin portion of the polyimide resin-fine particle composite film before the removal step, at least the above resin portion is formed when the organic fine particles (B) are removed and pores are formed in the subsequent removal step. It is possible to improve the pore size of the porous membrane of the final product as compared with the one in which a part is not removed. Further, by removing at least a part of the porous membrane after the removal step, the pore size of the polyimide porous membrane of the final product is improved as compared with the polyimide porous membrane in which at least a part of the porous membrane is not removed. It is possible to make it.

The step of removing at least a part of the resin portion or the step of removing at least a part of the polyimide porous film is performed by a normal chemical etching method, a physical removal method, or a method in which these are combined. Can be done.

Examples of the chemical etching method include treatment with a chemical etching solution such as an inorganic alkaline solution or an organic alkaline solution. Inorganic alkaline solutions are preferred. Examples of the inorganic alkaline solution include a hydrazine solution containing hydrazine hydrate and ethylenediamine, a solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate, and sodium metasilicate, an ammonia solution, and hydroxylation. Examples thereof include an etching solution containing alkali, hydrazine, and 1,3-dimethyl-2-imidazolidinone as main components. Examples of the organic alkaline 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; 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 piperidine.

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

As a physical method, for example, plasma (oxygen, argon, etc.), dry etching by corona discharge, polishing agent (for example, alumina (hardness 9), etc.) is dispersed in a liquid, and this is applied to the surface of the film. A method of surface treatment by irradiating at a speed of 30 m / s or more and 100 m / s or less can be used.

The above method is preferable because it can be applied either before or after the removal step of removing the organic fine particles (B).

On the other hand, as a physical method applicable only to the resin removing step performed after the removing step of removing the organic fine particles (B), the target surface is pressure-bonded to a mount film (for example, a polyester film such as PET film) wet with a liquid and then dried. It is also possible to adopt a method of peeling the porous film from the mount film without or after drying. Due to the surface tension or electrostatic adhesion of the liquid, the porous film is peeled off from the mount film while only the surface layer of the porous film is left on the mount film.

Hereinafter, the present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited thereto.

[Example 1]
As the polyamic acid, a polyamic acid obtained by condensing pyromellitic dianhydride (PMDA) as a tetracarboxylic dianhydride component and 4,4'-diaminodiphenyl ether (ODA) as a diamine component was used. A polyamic acid solution in which polyamic acid was dissolved in dimethylacetamide (DMAc) at a concentration of 20% by mass and crosslinked polystyrene fine particles having a volume particle diameter of 380 nm were added to the total of the mass of polyamic acid and the mass of the crosslinked polystyrene fine particles. The mixture was mixed so that the amount of the polyamic acid was 46% by mass and the mass of the crosslinked polystyrene fine particles was 54% by mass. Water (SI) and an organic solvent (S-III) are further added to the obtained mixture, and the composition of the solvent (S) in the entire final composition is water (SI): organic solvent (S-III) = 1. The mixture was mixed so as to have a solid content concentration of 18% by mass to obtain a varnish composition having a uniform composition of 99% by mass.
When the obtained varnish composition was allowed to stand at room temperature for one day to confirm the stability of the varnish, the varnish was uniform even after being allowed to stand for one day.

<Polyimide porous film forming method>
Using the obtained varnish composition, a polyimide porous film was obtained according to the following method. First, the varnish composition was applied onto a polyethylene terephthalate film (PET film) to form a coating film. The coating film was dried at 70 ° C. for 10 minutes to obtain a precursor film of a polyimide porous film. The obtained precursor film is peeled off from the polyethylene terephthalate film, and then the precursor film is fired in a firing furnace at 420 ° C. for 2 minutes to pyrolyze the polystyrene fine particles while imidizing the polyamic acid to make the polyimide porous. Obtained a membrane.
The pore area ratio of the obtained polyimide porous membrane was measured according to the following method.
The measurement of the pore area ratio was performed on the PET surface and the air surface of the polyimide porous membrane. Here, the PET surface is a surface that was in contact with the PET film in the state of the precursor film. The air surface is the surface opposite to the PET surface. The pore area ratio was determined by processing a scanning electron microscope (SEM) observation image of the PET surface or the air surface with image analysis software.
The results of these evaluations are shown in Table 2.

[Examples 2 to 4]
In Example 1, the composition of the solvent (S) in the entire final composition was changed to the composition shown in Table 1, and the varnish composition was prepared and the polyimide porous film was produced in the same manner as in Example 1. The pore area ratio was measured.

[Examples 5 to 7]
Except for changing the organic fine particles to the types of organic fine particles shown in Table 1, the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 4.

[Example 8]
Except for changing dimethylacetamide (DMAc) to dimethyl sulfoxide (DMSO), the varnish composition was prepared, the polyimide porous membrane was produced, and the pore area ratio was measured in the same manner as in Example 4.

[Example 9]
Except for changing water (SI) to methanol (MeOH), which is a water-soluble organic solvent (S-II), preparation of a varnish composition, production of a polyimide porous membrane, and emptying were performed in the same manner as in Example 4. The pore area ratio was measured.

[Example 10]
Polyacic acid was condensed with 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) as a tetracarboxylic acid dianhydride component and p-phenylenediamine (PDA) as a diamine component. Except for the change to polyamic acid, the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 8.

[Comparative Example 1]
Except for the addition of water (SI), the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 4.

[Comparative Example 2]
The composition of the solvent (S) in the entire final composition was changed to the composition shown in Table 1, and the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was the same as in Example 1. Measurements were made.

[Comparative Example 3]
Except for the addition of water (SI), the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 5.

[Comparative Example 4]
Except for the addition of water (SI), the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 6.

[Comparative Example 5]
Except for the addition of water (SI), the varnish composition was prepared, the polyimide porous film was produced, and the pore area ratio was measured in the same manner as in Example 7.

The abbreviations in Table 1 below are as follows.
PMDA: Pyromellitic acid dianhydride BPDA: 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride ODA: 4,4'-diaminobiphenyl ether PDA: p-phenylenediamine OP1: Crosslinked polystyrene fine particles OP2 : Styrene-methyl methacrylate copolymer cross-linked fine particles (styrene: methyl methacrylate = 2: 8 (mass ratio))
OP3: Styrene-methyl methacrylate copolymer cross-linked fine particles (styrene: methyl methacrylate = 3: 7 (mass ratio))
OP4: Crosslinked polymethylmethacrylate fine particles MeOH: Methanol DMAc: N, N-dimethylacetamide DMSO: Dimethyl sulfoxide

As can be seen from Tables 1 and 2, the varnish composition of the example containing the solvent (S) in which the total amount of water (SI) and the water-soluble organic solvent (S-II) is less than 30% by mass is one. It can be seen that it gives a polyimide porous film that is stable even when left to stand for a day and has a high aperture ratio (vacancy area ratio).
On the other hand, according to Comparative Examples 1 and 3 to 5, the varnish of the comparative example containing the solvent (S) in which the total amount of water (SI) and the water-soluble organic solvent (S-II) is 30% by mass or more. It can be seen that when the composition is used, it is difficult to form a polyimide porous film having a high aperture ratio (pore size ratio) even if it is stable when left to stand for one day.
Further, according to Comparative Example 2, it can be seen that the varnish composition containing neither water (SI) nor the water-soluble organic solvent (S-II) is inferior in stability over time.

Claims (9)

A varnish composition for forming a polyimide porous film obtained by mixing a polyamic acid (A), organic fine particles (B), and a solvent (S).
The solvent (S) contains water (SI) and / or a water-soluble organic solvent (S-II) and an organic solvent (S-III) other than the water-soluble organic solvent (S-II).
The total ratio of the mass of the water (SI) to the mass of the water-soluble organic solvent (S-II) to the mass of the solvent (S) is less than 30% by mass.
A varnish composition in which the water-soluble organic solvent (S-II) is selected from the group consisting of an ether solvent, a ketone solvent, and an alcohol solvent. The organic solvent (S-III) has the following formula (S1):

(In the formula (S1), ^RS1 and ^RS2 are each independently an alkyl group having 1 or more and 3 or less carbon atoms, and ^RS3 is a hydrogen atom, or the following formula (S1-1) or the following formula (S1). -2):

^RS4 is a hydrogen atom or a hydroxyl group, and ^RS5 and ^RS6 are independently hydrogen atoms and alkyl groups having 1 or more and 3 or less carbon atoms, respectively, and ^RS7 and R are ^S8 is an independently hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms. )
The varnish composition for forming a polyimide porous film according to claim 1, which is a nitrogen-containing organic solvent represented by 1 or dimethyl sulfoxide. The varnish composition for forming a polyimide porous film according to claim 1 or 2, wherein the ratio of the mass of the water-soluble solvent (S-II) to the mass of the solvent (S) is 1% by mass or more. The varnish composition for forming a polyimide porous film according to any one of claims 1 to 3, wherein the organic fine particles (B) are resin fine particles made of a crosslinked polymer. A coating film forming step of applying the varnish composition according to any one of claims 1 to 4 onto a substrate to form a coating film.
A method for producing a precursor film of a polyimide porous film, which comprises a step of forming a precursor film, which comprises removing the solvent (S) from the coating film to form a precursor film of the polyimide porous film. The method for producing a polyimide porous film according to claim 5, further comprising a peeling step of peeling the precursor film from the substrate after the precursor film forming step. The method for producing a precursor film of a polyimide porous film according to claim 6, further comprising a winding step of winding the precursor film into a roll shape after the peeling step. A polyimide porous membrane comprising a removal step of producing a precursor film of a polyimide porous membrane by the method according to any one of claims 5 to 7 and then removing the organic fine particles (B) from the precursor membrane. Membrane manufacturing method. The method for producing a polyimide porous membrane according to claim 8, wherein the organic fine particles (B) are resin fine particles made of a crosslinked polymer, and the method for removing the organic fine particles (B) is firing.