KR20200145732A - Varnish composition, method of producing varnish composition, method of producing precursor film of polyimide porous film, precursor film of polyimide porous film, and method of producing polyimide porous film - Google Patents

Abstract

The present invention relates to a varnish composition containing fine particles for forming a porous polyimide film, capable of forming a coating film having a uniform thickness or composition even though it contains water, to a production method of the varnish composition, to a production method of a precursor film of a porous polyimide film using the varnish composition, to a precursor film of a porous polyimide film, and to a production method of a porous polyimide film using the precursor film. When forming the varnish composition for forming a porous polyimide film comprising: polyamic acid (A); organic fine particles (B); and a solvent (S), the solvent (S) containing an organic solvent (SI) and a predetermined amount of water (S-II) is used while adding a basic compound (C) to the varnish composition.

Description

Varnish composition, method of producing a varnish composition, method of producing a precursor film of a porous polyimide film, a precursor film of a porous polyimide film, and a method of producing a porous polyimide film TECHNICAL FIELD [VARNISH COMPOSITION, METHOD OF PRODUCING VARNISH COMPOSITION, METHOD OF PRODUCING PRECURSOR FILM OF POLYIMROUS" FILM, PRECURSOR FILM OF POLYIMIDE POROUS FILM, AND METHOD OF PRODUCING POLYIMIDE POROUS FILM}

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

BACKGROUND ART In recent years, studies on porous polyimide and/or polyamideimide membranes have been conducted as filters used for gas or liquid separation membranes, separators for lithium ion batteries, electrolyte membranes for fuel cells, and materials with low dielectric constants.

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 on a substrate, and then the coating film is heated if necessary. Thus, there is known a method of obtaining a polyimide film containing fine particles, and then removing fine particles such as silica particles in the polyimide film using hydrofluoric acid to make it porous (see Patent Document 1).

Japanese Patent Publication No. 55605566

When forming a porous polyimide film by the method described in Patent Document 1 or the like, it is desired to use a varnish having a uniform composition to form a coating film having a uniform thickness and composition. However, handling of hydrofluoric acid used in the manufacturing method described in Patent Document 1 is not easy. Therefore, the use of hydrofluoric acid is a factor that increases the manufacturing cost of the porous polyimide film. For this reason, there is a demand for a method that does not use hydrofluoric acid. Therefore, it is conceivable to use other fine particles such as organic fine particles instead of the silica fine particles. However, since organic fine particles are often prepared in an aqueous medium, they are often circulated as fine particle dispersions containing water. When a varnish is prepared using such a water-containing fine particle dispersion, a varnish containing water is inevitably obtained.

From this point of view, when the varnish containing the polyamic acid does not contain fine particles, even if the varnish contains water, there are few components that inhibit the orientation of the polyamic acids and the like, so that a varnish that can be applied may be obtained.

However, when the varnish contains water and fine particles, the affinity between the polyamic acid and the solvent containing water is poor, but the orientation of the polyamic acids is inhibited and the film strength may decrease by including the polyamic acid and the fine particles. Due to such reasons, there is a problem in that a mixture of a non-uniform composition including a block of polyamic acid surrounding the fine particles is easily formed and a coating film cannot be formed.

For this reason, a coating film having a uniform thickness and composition can be formed, and a varnish containing fine particles for forming a porous polyimide film having a uniform composition, and a method for producing a precursor film of a porous polyimide film using the varnish , A method for producing a porous polyimide film is desired.

The present invention has been made in view of the above problems, and can form a coating film having a uniform thickness and composition even though it contains water, and also includes fine particles for forming a porous polyimide film of a uniform composition. To provide a varnish composition, a method for producing the varnish composition, a method for producing a precursor film of a porous polyimide film using the above-described varnish composition, a precursor film of a porous polyimide film, and a method for producing a porous polyimide film using the precursor film It aims to do.

The present inventors added a basic compound (C) to the varnish composition when forming a varnish composition for forming a porous polyimide film containing a polyamic acid (A), an organic fine particle (B), and a solvent (S). Together with the organic solvent (SI), by using a solvent (S) containing a predetermined amount of water (S-II), it was found that the above problems could be solved, and the present invention was completed.

A first aspect of the present invention is a varnish composition for forming a porous polyimide film obtained by mixing a polyamic acid (A), an organic fine particle (B), a basic compound (C), and a solvent (S),

The solvent (S) contains an organic solvent (S-I) and water (S-II),

It is a varnish composition wherein the ratio of the mass of water (S-II) to the mass of the solvent (S) is less than 50% by mass.

In a second aspect of the present invention, a polyamic acid-containing liquid containing a polyamic acid (A) and an organic solvent (SI) and a fine particle dispersion containing the organic fine particles (B) are mixed in the presence of a basic compound (C), or , or,

It is a method for producing a varnish composition for forming a porous polyimide film according to the first aspect, in which a basic compound (C) is added to the mixture after obtaining a mixed solution by mixing the polyamic acid-containing liquid and the fine particle dispersion liquid described above.

A third aspect of the present invention is a coating film forming step of forming a coating film by applying the varnish composition according to the first aspect on a substrate,

It is a method for producing a precursor film of a porous polyimide film including a precursor film formation step of removing the solvent (S) from the coating film and forming a precursor film of the porous polyimide film.

A fourth aspect of the present invention is a precursor film of a porous polyimide film formed by drying a coating film made of the varnish composition according to the first aspect,

It is a precursor film of a porous polyimide film having an elongation of 0.5% or more measured according to the 0.5 grade of JIS B7721.

A fifth aspect of the present invention is a method for producing a porous polyimide film including a removal step of removing organic fine particles (B) from the precursor film of the porous polyimide film according to the fourth aspect.

According to the present invention, a coating film having a uniform thickness and composition can be formed even though it contains water, and a varnish composition containing fine particles for forming a porous polyimide film having a uniform composition, and the varnish composition It is possible to provide a method for producing a polyimide porous film using the above varnish composition, a method for producing a precursor film for a porous polyimide film, a precursor film for a polyimide porous film, and a method for producing a polyimide porous film using the precursor film.

≪varnish composition≫

The varnish composition is a composition obtained by mixing a polyamic acid (A), an organic fine particle (B), a basic compound (C), and a solvent (S). The solvent (S) contains an organic solvent (S-I) and water (S-II). Since the varnish composition contains organic fine particles (B), the precursor film of the porous polyimide film can be formed by removing the solvent (S) from the coating film formed using the varnish composition. By imidizing the polyamic acid (A) contained in such a precursor film and removing the organic fine particles (B) from the precursor film, a porous polyimide film mainly composed of a polyimide resin is obtained.

For this reason, the varnish composition is used for formation of a porous polyimide film.

When preparing a varnish composition containing water, when mixing the polyamic acid (A), the organic fine particles (B), and the solvent (S), without generating a block of polyamic acid surrounding the organic fine particles (B) In many cases, it is difficult to uniformly dissolve or disperse the polyamic acid (A) and the organic fine particles (B) in the solvent (S).

However, by mixing the basic compound (C) together with the polyamic acid (A), the organic fine particles (B), and the solvent (S), in the solvent (S) containing water (S-II), the polyamic acid (A) , And a varnish composition in which the organic fine particles (B) are uniformly dissolved or dispersed can be prepared.

In addition, in the prepared varnish composition, it is difficult to clearly identify the polyamic acid (A) and the basic compound (C) in what state, respectively, by a chemical analysis method.

As described above, the solvent (S) contains an organic solvent (S-I) and water (S-II). However, the ratio of the mass of water (S-II) to the mass of the solvent (S) is less than 50 mass%.

When the varnish composition contains water (S-II) as the solvent (S), even when the boiling point of the organic solvent (SI) is high, removal of the organic solvent (SI) from the coating film made of the varnish composition is easy. . However, if the amount of water (S-II) is excessive, the stability of dissolution or dispersion of the polyamic acid (A) in the varnish composition may be impaired. In addition, when the amount of water (S-II) is excessive, the elongation of the precursor film obtained by removing the solvent (S) from the coating film formed using the varnish composition tends to be extremely inferior.

On the other hand, when the varnish composition contains water (S-II) as the solvent (S), for example, 30% by mass or less based on the mass of the varnish composition, the stability of the dissolution or dispersion of the polyamic acid in the varnish composition is good. Do. The content of water (S-II) with respect to the mass of the varnish composition is preferably 25% by mass or less, and more preferably 20% by mass or less.

Moreover, the organic fine particles (B) are often marketed as a slurry containing water. As described above, the varnish composition contains less than 50% by mass of water (S-II) based on the mass of the solvent (S). For this reason, in preparation of a varnish composition, as long as the content of water (S-II) does not exceed a predetermined upper limit, a slurry of organic fine particles (B) containing water can be used.

Hereinafter, essential or optional components used in the preparation of the varnish composition will be described.

<Polyamic acid (A)>

As polyamic acid (A), the product obtained by polymerizing arbitrary tetracarboxylic dianhydride and diamine is not specifically limited, and can be used. The amount of tetracarboxylic dianhydride and diamine used is not particularly limited, but it is preferable to use 0.50 mol or more and 1.50 mol or less of diamine, and 0.60 mol or more and 1.30 mol or less, based on 1 mol of tetracarboxylic dianhydride. It is more preferable, and it is particularly preferable to use 0.70 mol or more and 1.20 mol or less.

Tetracarboxylic dianhydride can be appropriately selected from tetracarboxylic dianhydride which has been conventionally used as a raw material for synthesis of polyamic acid. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. It is preferable to use an aromatic tetracarboxylic dianhydride from the viewpoint of the heat resistance of the polyimide resin obtained. Tetracarboxylic dianhydride may be used individually by 1 type, and may be used in combination of 2 or more types.

Preferred examples of aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, and bis(2,3-dicarboxyphenyl)methane 2 Anhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxyl Acid dianhydride, 2,2,6,6-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-di Carboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3 -Dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bis(3,4- Dicarboxyphenyl) ether dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4-(p-phenylenedi Oxy)diphthalic dianhydride, 4,4-(m-phenylenedioxy)diphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracar Acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxyl Acid dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 9,9-bis fluorene phthalate anhydride, 3,3 ',4,4'-diphenyl sulfone tetracarboxylic dianhydride, etc. are mentioned. As aliphatic tetracarboxylic dianhydride, for example, ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, 1, 2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride, etc. are mentioned. Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable from the viewpoint of price and availability. Moreover, these tetracarboxylic dianhydrides can be used individually by 1 type or in mixture of 2 or more types.

The diamine can be appropriately selected from diamines conventionally used as raw materials for synthesis of polyamic acid. The diamine may be an aromatic diamine or an aliphatic diamine. In view of the heat resistance of the obtained polyimide resin, aromatic diamine is preferable. These diamines may be used individually by 1 type, and may be used in combination of 2 or more types.

Examples of the aromatic diamine include diamino compounds containing an aromatic skeleton in which one benzene ring is included, or about 2 or more and 10 or less benzene rings are bonded or condensed via a single bond or a divalent linking group. Specifically, phenylenediamine and its derivatives, diaminobiphenyl compound and its derivatives, diaminodiphenyl compound and its derivatives, diaminotriphenyl compound and its derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindan and Derivatives thereof, diaminotetraphenyl compounds and derivatives thereof, diaminohexaphenyl compounds and derivatives thereof, and cardo-type fluorenediamine derivatives.

Examples of phenylenediamine are m-phenylenediamine and p-phenylenediamine. Examples of the phenylenediamine derivative are diamines to which an alkyl group such as a methyl group and an ethyl group is bonded, such as 2,4-diaminotoluene and 2,4-triphenylenediamine.

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

The diaminodiphenyl compound is a compound in which two aminophenyl groups are bonded to each other through different groups. Bonds are ether bonds, sulfonyl bonds, thioether bonds, bonds by alkylene or derivatives thereof, imino bonds, azo bonds, phosphine oxide bonds, amide bonds, ureylene bonds, 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 the diaminodiphenyl compound include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodi Phenylsulfone, 3,4'-diaminodiphenylsulfone, 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)phosphine oxide, 4,4'-dia Minoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy )Benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[ 4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexa And fluoropropane.

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

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

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

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

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

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

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

Further, the diamine may be a compound in which the hydrogen atom of the diamine is substituted with at least one substituent selected from the group 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 and a diamine component in a solvent can be used.

The reaction of tetracarboxylic dianhydride and diamine is usually carried out in a solvent. The solvent used for the reaction of tetracarboxylic dianhydride and diamine is not particularly limited as long as it can dissolve tetracarboxylic dianhydride and diamine, and does not react with tetracarboxylic dianhydride and diamine. The solvent may be used individually by 1 type, and may be used in combination of 2 or more types.

Examples of the solvent used in the reaction of tetracarboxylic dianhydride and diamine include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethyl Nitrogen-containing polar solvents such as formamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea; lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; Dimethyl sulfoxide; Acetonitrile; Fatty acid esters such as ethyl lactate and butyl lactate; Ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellosolve acetate, and ethyl cellosolve acetate; Phenolic solvents such as cresols and xylene-based mixed solvents may be mentioned.

These solvents may be used individually by 1 type, and may be used in combination of 2 or more types. Although there is no particular limitation on the amount of the solvent used, it is preferable that the content of the produced polyamic acid (A) is 5% by mass or more and 50% by mass or less.

Among these solvents, from the solubility of the resulting polyamic acid (A), N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide And nitrogen-containing polar solvents such as N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea.

The polymerization temperature is generally -10°C or more and 120°C or less, and preferably 5°C or more and 30°C or less. The polymerization time varies depending on the composition of the raw material used, but is usually 3 hours or more and 24 hours or less.

Polyamic acid (A) may be used individually by 1 type, and may be used in combination of 2 or more types.

The content of the polyamic acid (A) in the varnish composition is not particularly limited, and is appropriately determined in view 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 it can form a coating film having a desired film thickness. 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 still more 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 contains the organic fine particles (B) and the polyamic acid (A) so 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. It is preferable, and it is more preferable to contain organic fine particles (B) and polyamic acid (A) so that the above-described ratio is 0.7 to 3.5 (mass ratio).

In addition, when the polyamic acid-fine particle composite film is formed using the varnish composition, the organic fine particles (B) and the organic fine particles (B) and the volume ratio of the organic fine particles (B)/polyamic acid (A) in the composite film are 1.0 to 5.0. It is preferable to contain polyamic acid (A). The volume ratio mentioned above 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 more than the lower limit, it is easy to form pores of an appropriate density. When the mass ratio or volume ratio of the organic fine particles (B)/polyamic acid (A) is equal to or less than the upper limit, the film can be stably formed without causing problems such as an increase in the viscosity of the varnish composition or cracking in the film.

The solid content concentration of the varnish composition is not particularly limited, but is, for example, 1 mass% or more, preferably 5 mass% or more, and more preferably 10 mass% or more. The upper limit of the solid content concentration is, for example, 60% by mass or less, and 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 removed from the precursor film of the porous polyimide film afterwards, and a known material can be employed.

The form of the organic fine particles (B) is not particularly limited. For preparation of the varnish composition, the dried powder of the organic fine particles (B) may be used, or a dispersion of the organic fine particles (B) may be used. The varnish composition contains a specific amount of water (S-II). For this reason, a varnish composition can be prepared using a dispersion in which the organic fine particles (B) are dispersed in water as the dispersion of the organic fine particles (B). As the organic fine particles (B), a dispersion liquid is preferable from the viewpoint of avoiding agglomeration of the organic fine particles (B) by drying, and from the viewpoint of being inexpensive and easy to obtain, and a dispersion in which the organic fine particles (B) are dispersed in water is more desirable.

Moreover, as the organic fine particles (B), fine particles having a high sphericity ratio and a small particle size distribution index are preferable. The organic fine particles (B) provided with these conditions are excellent in dispersibility in the varnish composition, and can be used in a state in which they are not aggregated with each other.

As the average particle diameter (average diameter) of the organic fine particles (B), for example, 2000 nm or less is preferable, 1000 nm or less is more preferable, 700 nm or less is even more preferable, and 10 nm or more and 600 nm or less are even more. Preferably, 20 nm or more and 500 nm or less are particularly preferable, and 30 nm or more and 450 nm or less are most preferable. By using fine particles having an average particle diameter within such a range, it is easy to form a porous polyimide film having fine pores of a desired pore diameter and excellent in the granulation effect.

Further, the size of the pores formed in the porous polyimide film and originating from the fine particles is the same as or close to the average particle diameter of the fine particles. For this reason, from the viewpoint of fluid permeability and the like when the porous polyimide membrane is used as a filter, the average particle diameter of the fine particles is preferably 5 nm or more, and more preferably 10 nm or more.

By satisfying these conditions, since the pore diameter of the porous polyimide film obtained by removing the organic fine particles (B) can be uniform, in particular, when the porous polyimide film is used as a separator, the applied electric field can be made uniform, which is preferable.

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-I), and can be selectively removed after film formation. Resin is preferable as the material of the organic fine particles.

As the resin as the material of the organic fine particles, for example, a conventional linear polymer or a known depolymerizable polymer can be used without limitation depending on the purpose. A typical linear polymer is a polymer in which molecular chains of a polymer are randomly cut during thermal decomposition, and a depolymerizable polymer is a polymer in which the polymer is decomposed into monomers during thermal decomposition. All of them disappear from the polyimide film by decomposition to a monomer, a low molecular weight substance, or to CO ₂ upon heating. The decomposition temperature of the resin fine particles to be used is preferably 200°C or more and 320°C or less, and more preferably 230°C or more and 260°C or less. 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 the firing conditions of the polyimide is wide. Further, when 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, a (meth)acrylic resin, an α-methylstyrene resin, a polyacetal homopolymer or a copolymer can be used.

As the (meth)acrylic resin, a single polymer obtained from alkyl (meth)acrylates such as methyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, or 2 And a copolymerized polymer obtained by copolymerizing more than one species. Further, the above alkyl (meth)acrylate may be used as a main component, and a copolymer may be used by copolymerizing with another monomer copolymerizable therewith (eg, glycidyl methacrylate, styrene, etc.).

Examples of the α-methylstyrene-based resin include a single polymer of α-methylstyrene, a copolymer of α-methylstyrene as a main component, and other monomers that can be copolymerized therewith. 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 (polymethyl methacrylate or polyisobutyl methacrylate), or a copolymerized polymer containing this as a main component It is preferable for handling.

The polymer which is the material of the resin fine particles may be a crosslinked polymer in which a crosslinking group is introduced by a crosslinkable monomer. When the organic fine particles (B) are resin fine particles composed of a crosslinked polymer, dissolution, deformation, and swelling of the resin fine particles by the organic solvent (S-I) 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 a crosslinking group 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, divinylbenzene, etc. have.

Preferred examples of resin fine particles into which crosslinking has been introduced by a crosslinkable monomer include resin fine particles containing a structural unit derived from a monofunctional styrene monomer (hereinafter, also referred to simply as a "styrene structural unit"). . The ratio of the mass of the styrenic structural unit to the mass of the resin fine particles with respect to the resin fine particles containing the styrenic structural unit is preferably 10% by mass or more and 99% by mass or less. The ratio of the mass of the styrenic structural 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. In addition, 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 monofunctional monomer being 100 parts by mass.

Such resin fine particles may be a copolymer of a monofunctional styrene-based monomer, the aforementioned crosslinkable monomer, and a monofunctional monomer such as the aforementioned alkyl (meth)acrylate. When the resin constituting the resin microparticles contains structural units derived from other monofunctional monomers in addition to the structural units derived from monofunctional styrene monomers, the amount of the structural units derived from other polyfunctional monomers is not particularly limited. .

Examples of monofunctional styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, and α-methylstyrene.

In the resin fine particles composed of a crosslinked polymer in which crosslinking has been introduced with a crosslinkable monomer as described above, the ratio of the mass of the structural units derived from a monofunctional monomer other than the constitutional units derived from the monofunctional styrene monomer is the monofunctional monomer In the mass of all the structural units derived from, 1 mass% or more and 100 mass% or less are preferable, and 50 mass% or more and 85 mass% or less are more preferable.

<Basic compound (C)>

The basic compound (C) is not particularly limited as long as it is a compound generally recognized as a basic compound and a desired effect is obtained by its use.

As the basic compound (C), typically, a compound exhibiting a pKa value of 7.5 or more in water is 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 Uptrack. Here, the pKa value calculated by Advanced Chemistry Development (ACD/Labs) Software V11.02 (Copyright 1994-2011 ACD/Labs) was adopted.

The basic compound (C) may be a basic organic compound or a basic inorganic compound. In the step of imidation or the step of removing organic fine particles (B), a basic organic compound is preferable as the basic compound (C) because it is easily removed from the porous polyimide film and has little adverse effect on the product of the porous polyimide film. Do.

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 containing an aromatic ring, and it is difficult to remain in the polyimide porous film or exhibits good basicity. desirable.

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 hetero atom such as O, S, P, Si, or a halogen atom within a range that does not impair the object of the present invention.

Preferred examples of the nitrogen-containing basic organic compound 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 chain alkyl group, a linear alkylene group, a branched chain 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 the alkylamines is preferably 1 or more and 4 or less. The number of carbon atoms in the alkyl group that the alkylamines have 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, and Nn-propyl Ethylamine, 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, diethylenetri Amine, triethylenetetramine, etc. are mentioned.

Hydroxyalkylamines are compounds in which at least one hydroxyl group is substituted with an aliphatic hydrocarbon group in the aforementioned alkylamines. As a specific example of hydroxyalkylamines, ethanolamine, diethanolamine, triethanolamine, etc. are mentioned.

As 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, and N-ethylpiperidine.

As piperazines, unsubstituted piperazine, N-alkyl group substituted piperazine, or N,N'-dialkyl substituted piperazine is 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-methyl piperazine, N-ethyl piperazine, N,N'-dimethyl piperazine, and N,N'-diethyl piperazine.

As morpholines, 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, and N-ethylmorpholine.

As the pyrrolidines, unsubstituted pyrrolidine or N-alkyl substituted pyrrolidine is preferable. In the N-alkyl substituted pyrrolidine, the number of carbon atoms in 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-methylpyrrolidine, and N-ethylpyrrolidine.

Examples of guanidine and guanidine salts include guanidine and salts of guanidine and weak acids. Specific examples of guanidine and guanidine salts include guanidine, guanidine carbonate, guanidine oxalate, and guanidine acetate.

As the basic inorganic compound, an alkali metal hydroxide and a salt of an 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 aliphatic carboxylic acids having 1 to 4 carbon atoms are preferable. Among 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 hydrogen carbonate, potassium hydroxide, potassium carbonate, potassium hydrogen carbonate, sodium oxalate, potassium oxalate, sodium acetate, sodium phosphate, potassium phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate. And the like.

The content of the basic compound (C) used for preparing the varnish composition is not particularly limited as long as a desired effect is obtained.

The amount of the basic compound (C) to be used is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more with respect to the mass of the polyamic acid (A). The upper limit of the amount of the basic compound (C) used is not particularly limited as long as it does not impair the object of the present invention. From the point of easy preparation of the varnish composition, the upper limit of the use amount of the basic compound (C) is preferably 30% by mass or less, more preferably 20% by mass or less, and 10% by mass with respect to the mass of the polyamic acid (A). The following are more preferable.

<Solvent (S)>

The varnish composition contains a solvent (S). The solvent (S) contains an organic solvent (S-I) and water (S-II). The ratio of the mass of water (S-II) to the mass of the solvent (S) is less than 50% by mass.

The upper limit of the ratio of the mass of water (S-II) to the mass of the solvent (S) may be 45 mass% or less, 40 mass% or less, 35 mass% or less, or 30 mass% or less. .

The lower limit of the ratio of the mass of water (S-II) to the mass of the solvent (S) may be more than 0% by mass, 5% by mass or more, 10% by mass or more, or 15% by mass or more. , 20 mass% or more may be sufficient.

The kind of organic solvent (S-I) is not particularly limited as long as it does not impair the object of the present invention. The organic solvent (S-I) is usually a compound which does not have a group capable of reacting with a basic compound (C) such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Moreover, although the organic solvent (S-I) may exhibit basicity, from the viewpoint of avoiding hydrolysis of the polyamic acid (A), it is preferable that it is a compound exhibiting neutral or weak basicity in water. More specifically, the organic solvent (SI) does not have a group capable of reacting with a basic compound (C) such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group, and is preferably a compound showing a pKa value of less than 7.5 in water. .

Examples of preferred organic solvents (SI) include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylisobutylamide, N,N-diethylacet. Amide, N,N-dimethylformamide (DMF), N,N-diethylformamide, N-methylcaprolactam, 1,3-dimethyl-2-imidazolidinone (DMI), pyridine, and N,N Nitrogen-containing polar solvents such as ,N',N'-tetramethylurea (TMU); lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; Dimethyl sulfoxide; Hexamethylphosphoric triamide; 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, ethyl cellosolve acetate, glyme, and tetraethylene glycol dimethyl ether (tetraglyme) ; And aromatic solvents such as benzene, toluene, and xylene.

From the viewpoint of dissolution stability or dispersion stability of the varnish composition or the easy removal of the solvent (S) from the coating film, the organic solvent (S-I) is represented by the following formula (S1):

[Formula 1]

(In formula (S1), R ^S1 and R ^S2 are each independently an alkyl group having 1 or more and 3 or less carbon atoms, and R ^S3 is a hydrogen atom, or the following formula (S1-1) or the following formula (S1-2) ):

[Formula 2]

Is a group represented by, R ^S4 is a hydrogen atom or a hydroxyl group, R ^S5 and R ^S6 are each independently a hydrogen atom and an alkyl group having 1 or more and 3 or less carbon atoms, and R ^S7 and R ^S8 are each independently It is a 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.

In the compound represented by formula (S1), as a specific example in the case where R ^S3 is a group represented by formula (S1-1), 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-N, 2-dimethyl-2-hydroxypropionamide, and N,N-diethyl-2-hydroxy-2-methylpropionamide, and the like.

In the compound represented by formula (S1), as a specific example in the case where R ^S3 is a group represented by formula (S1-2), N,N,N',N'-tetramethylurea, N,N,N',N '-Tetraethylurea, etc. are mentioned.

Among the examples of the compound represented by formula (S1), particularly preferred compounds include N,N-dimethylformamide, N,N-dimethylacetamide, N,N,2-trimethylpropionamide, and N,N,N' And N'-tetramethylurea. Among 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. Thus, N,N,2-trimethylpropionamide and N,N,N',N'-tetramethylurea have relatively low boiling points in the organic solvent (S-I).

For this reason, 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, In heating when forming the precursor film of the mid-porous membrane, the solvent is difficult to remain in the precursor film, and it is difficult to cause a decrease in tensile elongation of the resulting polyimide film.

In addition, N,N,2-trimethylpropionamide, and N,N,N',N'-tetramethylurea are substances of concern for harmfulness in the REACH regulation in the EU (European Union), SVHC (Substance of Very High Concern), it is also useful in that it is a low-hazardous substance.

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

Moreover, among the above-described solvents described as the organic solvent (S-I), a solvent having good compatibility with a polyamic acid and azeotropic with water is preferable. Examples of such a solvent include N,N-dimethylacetamide, NMP, γ-butyrolactone, and tetraethylene glycol dimethyl ether (tetraglyme). When the organic solvent (S-I) is azeotroped with water, removal of the solvent (S) from the coating film made of the varnish composition is easy.

Further, among the above-described solvents described as the organic solvent (S-I), NMP is preferable from the viewpoint of good dispersibility of the polyamic acid and the fine particles.

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

<Dispersant>

For the purpose of uniformly dispersing the organic fine particles (B) in the varnish composition, a dispersing agent may be further added together with the organic fine particles (B). By adding a dispersant, the polyamic acid (A) and the organic fine particles (B) can be further uniformly mixed, and further, the organic fine particles (B) in the formed film can be uniformly distributed. As a result, a dense opening is formed in the surface of the finally obtained porous polyimide film, it is possible to efficiently communicate the front and back surfaces, and the air permeability of the porous polyimide film is improved. Further, by adding a dispersant, the drying property of the varnish composition is easily improved, and the peelability of the precursor film of the formed polyimide porous film from the substrate 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 sulfuric acid salt, lauryl sulfate salt, polyoxyalkylene allylphenyl ether sulfate salt, alkylbenzenesulfonic acid, alkylbenzenesulfonate, alkyldiphenyletherdisulfonate, alkylnaphthalenesulfonic acid Anionic surfactants such as salts, dialkyl sulfosuccinate salts, isopropyl phosphate, polyoxyethylene alkyl ether phosphate salts, and polyoxyethylene allyl phenyl ether phosphate salts; Cationic surfactants, such as oleylamine acetate, lauryl pyridinium chloride, cetyl pyridinium chloride, lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, and didecyl dimethyl ammonium chloride; Amphoteric surfactants such as palm alkyl dimethyl amine oxide, fatty acid amide propyl dimethyl amine oxide, alkyl polyaminoethyl glycine hydrochloride, amide betaine type activator, alanine type activator, and lauryl iminodipropionic acid; Polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polytyrylphenyl ether, polyoxyalkylene polytyrylphenyl ether, etc. , Polyoxyalkylene primary alkyl ether or polyoxyalkylene secondary alkyl ether nonionic surfactant, polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylenated castor oil, polyoxyethylene hardened castor Other polyoxyalkylene-based nonionic surfactants such as free, sorbitan lauric acid ester, polyoxyethylene sorbitan lauric acid ester, and fatty acid diethanolamide; Fatty acid alkyl esters such as octyl stearate and trimethylolpropane tridecanoate; Polyether polyols, such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris (polyoxyalkylene) ether, are mentioned, but are not limited to these. Further, the dispersant may be used in combination of two or more.

The content of the dispersant in the varnish composition is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 1% by mass or less with respect to the organic fine particles (B) from the viewpoint of film-forming properties. And it is even more preferable that it is 0.1 mass% or more and 0.5 mass% or less.

Varnish composition is prepared by mixing the essential or optional components described above according to a predetermined composition in consideration of the applicability of the varnish composition or various properties of the polyimide porous membrane to be produced. do.

≪Method for producing varnish composition≫

The manufacturing method of the varnish composition is manufactured by mixing the various components mentioned above in predetermined amounts, respectively.

As a preferred method for producing a varnish composition,

The polyamic acid-containing liquid containing the polyamic acid (A) and the organic solvent (S-I) and the fine particle dispersion containing the organic fine particles (B) are mixed in the presence of a basic compound (C), or,

A method of adding a basic compound (C) to the mixed solution after obtaining a mixed solution by mixing the above-described polyamic acid-containing liquid and the above-described fine particle dispersion is mentioned.

With respect to the polyamic acid-containing liquid, the polyamic acid (A) and the organic solvent (S-I) are as described above. The polyamic acid-containing liquid may be prepared by dissolving the polyamic acid (A) produced by a known method in an organic solvent (S-I), or may be prepared by synthesizing the polyamic acid (A) in an organic solvent (S-I).

The polyamic acid-containing liquid may contain water (S-II). Moreover, the polyamic acid-containing liquid may contain arbitrary components other than polyamic acid (A), organic solvent (S-I), and water (S-II).

With respect to the fine particle dispersion, the organic fine particles (B) are as described above. The dispersion medium contained in the microparticle dispersion liquid may be an organic solvent (S-I), water (S-II), or an aqueous solution containing an organic solvent (S-I) and water (S-II). From the viewpoint of being easily available and inexpensive, the fine particle dispersion is preferably a dispersion in which organic fine particles (B) are dispersed in water (S-II).

Further, since the varnish composition contains water (S-II), at least one of the polyamic acid-containing liquid and the fine particle dispersion contains water (S-II).

When the polyamic acid-containing liquid and the fine particle dispersion are mixed in the presence of the basic compound (C), after adding the basic compound (C) to at least one of the polyamic acid-containing liquid and the fine particle dispersion, both are mixed and the varnish composition Is prepared.

Further, a varnish composition can also be prepared by simultaneously mixing the polyamic acid-containing liquid, the fine particle dispersion, and the basic compound (C). In this case, the basic compound (C) may be used as it is as an individual or a liquid, or as a solution dissolved in an organic solvent (S-I) or water (S-II).

Further, as described above, after mixing the polyamic acid-containing liquid and the fine particle dispersion to obtain a mixed liquid, a varnish composition can also be prepared by adding a basic compound (C) to the mixed liquid. In this case, a part of the basic compound (C) may be added in advance to at least one of the polyamic acid-containing liquid and the fine particle dispersion.

In the above method, when mixing various materials constituting the varnish composition, mixing may be carried out under a heated condition in a range in which excessive decomposition or deformation of the polyamic acid (A) or organic fine particles (B) does not occur. .

Further, various materials constituting the varnish composition may be mixed while dispersing the organic fine particles (B) by using various dispersing devices.

≪Method for producing a precursor film of a porous polyimide film≫

The method for producing a precursor film of a porous polyimide film,

A coating film forming step of forming a coating film by applying the above-described varnish composition on a substrate,

It includes a precursor film forming step of removing the solvent (S) from the coating film and forming a precursor film of the porous polyimide film.

Hereinafter, a film-forming method of a precursor film of a porous polyimide film (hereinafter, also simply referred to as a "precursor film") will be described. In the precursor film formation step, as described above, a precursor film is formed using the varnish composition described above. In that case, 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 forming a precursor film using the above-described varnish composition, an upper layer film different from the precursor film may be further formed on the upper layer. In addition, in the present application, the method of forming the lower layer film on the substrate is also a method of forming an upper layer film different from the precursor film on the upper layer after forming the precursor film using the above-described varnish. Included in the method of forming the film. However, in the case of using a material that does not require a firing step for the upper layer film, an upper layer film may be formed on the polyimide-fine particle composite film after firing.

The precursor film is, for example, directly on the substrate or on the underlayer film formed on the substrate, after applying the above-described varnish composition to form a coating film, and then under normal pressure or vacuum, 0°C or more and 100°C or less, preferably It can be formed by drying at 10°C or more and 100°C or less at normal pressure.

As a base material, a PET film, a SUS substrate, a glass substrate, etc. are mentioned, for example.

As the lower layer film (or upper layer film), for example, a resin composed of polyamic acid, polyimide, polyamideimide precursor, polyamideimide and polyethersulfone, microparticles and a solvent are contained, and the content of the microparticles A lower layer (or upper layer) unfired composite film formed using a varnish for forming a lower layer film (or upper layer film) of more than 40% by volume and not more than 81% by volume with respect to the total of the resin and the fine particles is mentioned. The lower layer 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. In addition, if the content of the fine particles is 81% by volume or less, the fine particles are dispersed evenly without aggregation of the fine particles. Therefore, in the polyimide porous film, pores are uniformly formed in the layer derived from the lower layer film (or upper layer film). can do. In addition, when the content of the fine particles is within the above range, when the lower unfired composite film is formed on a substrate, it is easy to ensure the releasability after film formation, even if a release layer is not previously formed on the substrate.

In addition, the fine particles used in the varnish for forming the lower layer (or upper layer) film may be the same as or different from the organic fine particles (B) used in the above-described varnish composition. In order to make the pores in the lower layer (or upper layer) unfired composite film more dense, the fine particles used for the varnish for forming the lower layer (or upper layer) film have a particle size distribution index than that of the organic fine particles (B) used in the aforementioned varnish composition. It is preferred that is less than or equal to. Alternatively, the fine particles used in the varnish for forming the lower layer (or upper layer) film preferably have a smaller or equal sphericity ratio than the fine particles used in the above-described varnish composition.

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

In addition, the content of the fine particles in the varnish for forming the lower layer (or upper layer) film may be higher or lower than the varnish composition described above. Preferred examples of components such as fine particles and a solvent contained in the varnish for forming the lower layer (or upper layer) film are the same as those of the varnish composition described above. The varnish for forming a lower layer (or upper layer) film can be prepared by the same method as the varnish composition described above.

The lower-layer unfired composite film is, for example, coated on a substrate with the varnish for forming an under-layer film and dried at 0°C or more and 100°C or less, preferably 10°C or more and 100°C or less under normal pressure or vacuum, Can be formed. The film formation conditions of the upper unfired composite film are also the same.

In addition, as the lower layer (or upper layer) film, for example, a cellulose resin, a nonwoven fabric (for example, a nonwoven fabric made of polyimide, etc.) (the fiber diameter is, for example, about 50 nm or more and about 3000 nm or less. A film made of a fibrous material such as) and a polyimide film are also mentioned.

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

It is preferable that the manufacturing method of the precursor film of a polyimide porous film includes a peeling process of peeling the precursor film from a base material after the said precursor film formation process.

When the precursor film is peeled from the substrate, the substrate is not required to have heat resistance that can withstand the temperature at which the precursor film is fired.

Further, the precursor film of the porous polyimide film is difficult to extend and is often fragile. However, the precursor film formed by drying the coating film made of the above-described varnish composition has an elongation of 0.5% or more as measured according to the 0.5 grade of JIS B7721. For this reason, the precursor film formed by drying the coating film made of the above-described varnish composition can be easily peeled off from the substrate without being damaged.

The elongation of the precursor film is preferably 1% or more, and more preferably 2% or more.

When the precursor film or the laminated film of the precursor film and the lower layer (or upper layer) unbaked composite film is peeled from the substrate, in order to further increase the peelability of the film, a substrate having a release layer formed in advance may be used. In the case of forming a release layer on the substrate in advance, before applying the above-described varnish composition or the varnish for forming an underlayer film, a release agent is applied on the substrate and dried or baked. The releasing agent used herein can be used without particular limitation as a known releasing agent such as an alkyl phosphate ammonium salt, fluorine-based or silicone. When the dried precursor film is peeled from the substrate, if a releasing agent remains slightly on the peeling surface of the precursor film, the remaining releasing agent may cause discoloration during firing or adverse effects on electrical properties. For this reason, it is preferable that the release agent adhering to the peeling surface is removed as much as possible. For the purpose of removing the releasing agent, a washing step of washing the precursor film peeled off from the substrate or the laminated film containing the precursor film may be introduced using an organic solvent.

When the base material is used as it is without forming a release layer, the above-described peeling step and washing step can be omitted. Moreover, in the manufacturing method of a precursor film, before the removal process mentioned later, an immersion process of immersing the precursor film in water or a solvent containing water, a press process of pressing the precursor film after the immersion process, and a drying process of drying the precursor film after the immersion process You may form each as an arbitrary process.

In the method for producing a precursor film of a porous polyimide film, when performing the above-described peeling step, it is preferable to perform a winding-up step of winding up the precursor film in 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 fractures. When the precursor film is wound in a roll shape, it is possible to fire the roll-shaped precursor film in a small sintering furnace. Moreover, it is easy to transfer the precursor film until the precursor film is fired, and space saving can be achieved also for storage.

In addition, a roll-to-roll process can be applied to the process of firing the precursor film, and efficient production of a porous polyimide film is possible.

≪Method for producing a porous polyimide film≫

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

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

Among the above imidization methods, thermal imidization is preferable because removal by washing of the imidizing agent is unnecessary. When performing imidization by firing, if the organic fine particles (B) are resin fine particles, it is possible to remove the resin fine particles together with the imidization.

In this case, if the organic fine particles (B) are resin fine particles composed of a crosslinked polymer, the resin fine particles are easily removed by firing, and the resin fine particles composed of the crosslinked polymer swell under the influence of the organic solvent (SI). Since it is difficult to be deformed, it is easy to produce a porous polyimide film having pores of a desired size and shape.

Hereinafter, firing will be described.

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

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 maintaining the temperature at the same temperature for about 2 to 30 minutes, or stepwise from room temperature, for example, at 50°C intervals. It is also possible to use a stepwise dry-heat imidization method such as heating up to 400 to 450°C (holding for about 20 minutes each step), and finally holding at 400 to 450°C for 2 to 30 minutes. When a precursor film is formed on a substrate and the precursor film or a laminated film including the precursor film is once peeled from the substrate, a method of fixing the precursor film or the end of the laminated film to a mold made of SUS or the like to prevent deformation may be employed.

The film thickness of the porous polyimide film or the polyimide resin-fine particle composite film obtained after firing can be obtained by measuring and averaging the thickness of a plurality of points with, for example, a micrometer or the like. Which average film thickness is preferable varies depending on the use of the polyimide porous film, but for example, in the case of using a separator or the like, 5 µm or more and 500 µm or less are preferable, and 10 µm or more and 100 µm or less are more preferable, It is more preferably 15 µm or more and 30 µm or less. When used for a filter or the like, 5 µm or more and 500 µm or less are preferable, 10 µm or more and 300 µm or less are more preferable, and 20 µm or more and 150 µm or less are still more preferable.

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. It is more preferable and 15 micrometers or more and 30 micrometers or less are still more preferable. 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 even more preferably 20 µm or more and 150 µm or less. The above film thickness can be obtained by measuring and averaging the thickness of a plurality of points, for example, with a micrometer or the like in the same manner as in the measurement of the polyimide resin-fine particle composite film. In addition, at any film thickness, the polyimide porous film is a porous film in which spherical pores are communicated throughout the film, and the front and back surfaces are in communication.

The manufacturing method of the polyimide porous film includes a resin removal step of removing at least a part of the polyimide resin portion of the polyimide resin-fine particle composite film before the removal step, or removing at least a part of the polyimide porous film after the removal step. You may have it. By removing at least a part of the resin part of the polyimide resin-fine particle composite film before the removal process, compared to not removing at least part of the resin part when the organic fine particles (B) are removed and voids are formed in the subsequent removal process Thus, it becomes possible to improve the porosity of the porous membrane of the final product. Further, by removing at least a part of the porous film after the removal step, it becomes possible to improve the porosity of the polyimide porous film of the final product as compared to the polyimide porous film in which at least a part of the porous film is not removed.

The step of removing at least a part of the resin portion or the step of removing at least a part of the porous polyimide film can be performed by a conventional chemical etching method, a physical removal method, or a combination thereof.

As a chemical etching method, treatment with a chemical etching solution, such as an inorganic alkali solution or an organic alkali solution, is mentioned. Inorganic alkaline solutions are preferred. As an inorganic alkali solution, for example, a hydrazine solution containing hydrazine hydrate and ethylenediamine, a solution of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, sodium carbonate, sodium silicate and sodium metasilicate, ammonia solution, alkali hydroxide and hydrazine 1 , An etching solution containing 3-dimethyl-2-imidazolidinone as a main component, and the like. 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 dimethyl ethanol amine and triethanol amine; Quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide; And alkaline solutions such as cyclic amines such as pyrrole and piperidine.

For the solvent of each of the above solutions, pure water and alcohols can be appropriately selected. Further, it is also possible to use a surfactant added in an appropriate amount. The alkali concentration is, for example, 0.01% by mass or more and 20% by mass or less.

In addition, as a physical method, for example, plasma (oxygen, argon, etc.), dry etching by corona discharge, etc., an abrasive (e.g., alumina (hardness 9), etc.) is dispersed in a liquid, and this is By irradiating at a speed of 30 m/s or more and 100 m/s or less, a method of surface treatment or the like can be used.

The above-described method is preferable because it can be applied to 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 removal step performed after the removal step of removing the organic fine particles (B), to a base film (for example, a polyester film such as a PET film) moistened with a liquid After compression bonding, without drying, or after drying, a method of peeling the porous membrane from the base film may be employed. 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 remains on the mount film.

Example

Hereinafter, the present invention will be described in more detail by showing examples based on examples, but the scope of the present invention is not limited thereto.

[Example 1 and Example 2]

3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a tetracarboxylic dianhydride component, and p-phenylenediamine (PPD) or m-phenylenediamine (MPD) as a diamine component ) Was reacted in N,N,N',N'-tetramethylurea to obtain a polyamic acid solution containing polyamic acid at a concentration of 20% by mass. After mixing 25.7 parts by mass of the obtained polyamic acid solution and 30 parts by mass of a fine particle dispersion containing a crosslinked polystyrene fine particles having a volume particle diameter of 420 nm at a concentration of 40% by mass, 2 parts by mass of triethylamine (TEA) were added to the obtained mixture. , To obtain a varnish composition having an oily and uniform composition. In addition, with respect to the mixed solution before TEA addition, the amount of polyamic acid was 30% by mass, the amount of crosslinked polystyrene particles was 70% by mass, and the solid content concentration of the mixture was It is about 31% by mass.

The obtained varnish composition was applied onto a polyethylene terephthalate film to form a coating film. The coating film was dried at 80°C for 6 minutes to obtain a precursor film of a porous polyimide film. With respect to the obtained precursor film, measurement of the film thickness and evaluation of the elongation and tensile strength according to the 0.5 grade of JIS B7721 were performed. Table 1 shows the results of these evaluations. Moreover, by using the obtained varnish composition, the polyimide porous film could be formed without a problem by the following method.

<Method of forming a porous polyimide film>

The varnish composition was applied on a polyethylene terephthalate film to form a coating film. The coating film was dried at 70°C for 10 minutes to obtain a precursor film of a porous polyimide film. After peeling the obtained precursor film from the polyethylene terephthalate film, the precursor film was fired in a firing furnace at 420° C. for 2 minutes, and the polyamic acid was imidized while thermally decomposing the polystyrene fine particles to obtain a porous polyimide film.

[Example 3, and Example 4]

3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as a tetracarboxylic dianhydride component and 4,4'-diaminodiphenylamide (DABAN) as a diamine component, N It reacted in ,N,N',N'-tetramethylurea, and the polyamic acid solution containing polyamic acid at a concentration of 15 mass% was obtained. After mixing 34.3 parts by mass of the obtained polyamic acid solution and 30 parts by mass of a fine particle dispersion containing a crosslinked polystyrene fine particles having a volume particle diameter of 420 nm in a concentration of 40% by mass, 2 parts by mass of N-methylmorpholine (NMM) , N,N,N',N'-tetramethylurea, and water were added and adjusted to the solid content concentration shown in Table 1 to obtain a varnish composition having an oily uniform composition. In addition, with respect to the mixed solution before NMM addition, the amount of polyamic acid was 30% by mass, the amount of crosslinked polystyrene particles was 70% by mass, and the solid content concentration of the mixed solution with respect to the total mass of the polyamic acid and the mass of the crosslinked polystyrene fine particles It is about 27% by mass.

The obtained varnish composition was applied onto a polyethylene terephthalate film to form a coating film. The coating film was dried at 80°C for 6 minutes to obtain a precursor film of a porous polyimide film. About the obtained precursor film, the film thickness, elongation, and tensile strength were evaluated in the same manner as in Example 1. Table 1 shows the results of these evaluations. In addition, in Example 3 and Example 4, the film thickness of the precursor film was made different by adjusting the coating conditions.

[Example 5]

Film thickness in the same manner as in Example 1, except that N,N,N',N'-tetramethylurea in Example 1 was changed to NMP, and the solid content concentration and solvent composition ratio were changed as shown in Table 1. , Elongation, and tensile strength were evaluated. Table 1 shows the evaluation results.

[Comparative Example 1]

After changing N,N,N',N'-tetramethylurea in Example 1 to water, mixing PPD and TEA of 1.95 times the molar ratio of PPD, it was reacted with BPDA in an aqueous medium to prepare a polyamic acid solution. After obtaining, a comparative varnish composition 1 (solid content concentration 15% by mass) in which the volume ratio of the fine particles and the resin polyamic acid was 65:35 was prepared.

[Comparative Example 2]

Comparative varnish composition 2 was obtained in the same manner as in Comparative Example 1, except that the volume ratio of the fine particles and the resin polyamic acid in Comparative Example 1 was 78:22 and the solid content concentration was 18% by mass.

Using the comparative varnish composition 1 and the comparative varnish composition 2, formation of a porous polyimide film was attempted in the same manner as in Example 1. However, even when the varnish composition of any of the comparative examples was used, the precursor film was too brittle, and thus the precursor film could not be peeled off from the polyethylene terephthalate film due to breakage. For this reason, about Comparative Example 1 and Comparative Example 2, evaluation of the precursor film was not performed.

[Comparative Examples 3 to 5]

The varnish composition of Comparative Example 3 was prepared in the same manner as in Example 1, except that the basic compound was not added, and the varnish composition of Comparative Example 4 was prepared in the same manner as in Example 2, and in the same manner as in Example 3 The varnish composition of Comparative Example 5 was prepared. As a result, in any of Comparative Examples 3 to 5, a block of polyamic acid containing fine particles was produced, and a varnish composition having a uniform composition that can be applied was not obtained.

As can be seen from Table 1, by mixing a polyamic acid (A), an organic fine particle (B), a basic compound (C), and a solvent (S) having a water content of less than 50% by mass, good coating It can be seen that a varnish composition for forming a porous polyimide film having a possible and uniform composition can be obtained. Further, the precursor film for forming a porous polyimide film, formed using the varnish composition of Examples 1 to 5, exhibits good elongation and is easily peeled from the substrate.

Claims (12)

As a varnish composition for forming a porous polyimide film obtained by mixing a polyamic acid (A), an organic fine particle (B), a basic compound (C), and a solvent (S),
The solvent (S) contains an organic solvent (SI) and water (S-II),
The varnish composition, wherein the ratio of the mass of water (S-II) to the mass of the solvent (S) is less than 50% by mass. The method of claim 1,
The organic solvent (SI) is the following formula (S1):
[Formula 1]

(In formula (S1), R ^S1 and R ^S2 are each independently an alkyl group having 1 or more and 3 or less carbon atoms, and R ^S3 is a hydrogen atom, or the following formula (S1-1) or the following formula (S1-2) ):
[Formula 2]

Is a group represented by, R ^S4 is a hydrogen atom or a hydroxyl group, R ^S5 and R ^S6 are each independently a hydrogen atom and an alkyl group having 1 or more and 3 or less carbon atoms, and R ^S7 and R ^S8 are each independently It is a hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms.)
A varnish composition for forming a porous polyimide film, which is a nitrogen-containing organic solvent represented by. The method according to claim 1 or 2,
The varnish composition for forming a porous polyimide film, wherein the mass of the basic compound (C) is 1% by mass or more with respect to the mass of the polyamic acid (A). The method according to claim 1 or 2,
A varnish composition for forming a porous polyimide film, wherein the organic fine particles (B) are resin fine particles made of a crosslinked polymer. A polyamic acid-containing liquid containing the polyamic acid (A) and the organic solvent (SI), and a fine particle dispersion containing the organic fine particles (B) are mixed in the presence of the basic compound (C), or,
After mixing the polyamic acid-containing liquid and the fine particle dispersion to obtain a mixed liquid, the basic compound (C) is added to the mixed liquid, and the varnish composition for forming a porous polyimide film according to claim 1 or 2 Manufacturing method. A coating film forming step of forming a coating film by applying the varnish composition according to claim 1 or 2 on a substrate,
A method for producing a precursor film of a porous polyimide film, comprising a precursor film forming step of removing the solvent (S) from the coating film and forming a precursor film of the porous polyimide film. The method of claim 6,
A method for producing a precursor film of a porous polyimide film comprising a peeling step of peeling the precursor film from the substrate after the precursor film forming step. The method of claim 7,
After the peeling step, a method for producing a precursor film of a porous polyimide film comprising a winding step of winding up the precursor film in a roll shape. As a precursor film of a porous polyimide film obtained by drying a coating film made of the varnish composition according to claim 1 or 2,
A precursor film of a porous polyimide film having an elongation of 0.5% or more as measured in accordance with JIS B7721 grade 0.5. The method of claim 9,
A precursor film of a porous polyimide film in the form of a roll. A method for producing a porous polyimide film, comprising a removal step of removing the organic fine particles (B) from the precursor film of the porous polyimide film according to claim 9. The method of claim 11,
The method for producing a porous polyimide film, wherein the organic fine particles (B) are resin fine particles composed of a crosslinked polymer, and the method for removing the organic fine particles (B) is sintering.