WO2022091915A1

WO2022091915A1 - Varnish for production of polyimide porous membrane

Info

Publication number: WO2022091915A1
Application number: PCT/JP2021/038813
Authority: WO
Inventors: 拓也野口
Original assignee: 東京応化工業株式会社
Priority date: 2020-10-30
Filing date: 2021-10-20
Publication date: 2022-05-05
Also published as: TW202225347A; JPWO2022091915A1; CN116457394A

Abstract

[Problem] To provide: a varnish composition that has a uniform compositional makeup including organic fine particles from which it is possible to form a polyimide porous membrane having fine uniform spherical pores having a diameter equivalent to the median diameter of the particles; a production method for a precursor membrane of a polyimide porous membrane, using said varnish composition; and a production method for a polyimide porous membrane using said precursor membrane. [Solution] This varnish composition for forming a polyimide porous membrane is obtained by mixing a polyamic acid (A), organic fine particles (B), and a solvent (S). The organic fine particles (B) include vinyl-based resin particles of a polymer having a structural unit (a) derived from a vinyl-based monomer and a structural unit (b1) that is derived from a compound represented by general formula (I) and that is different from the structural unit (a). [In the formula, m represents an integer of 1-3, R represents a polymerizable unsaturated group, AO represents an alkyleneoxy group having 2-4 carbon atoms, n represents an integer of 0-100, and X represents a hydrogen atom or an anionic hydrophilic group.]

Description

Varnish for manufacturing polyimide porous membrane

The present invention relates to a varnish for producing a polyimide porous membrane.

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

It is not easy to handle hydrofluoric acid used when forming a porous polyimide film by the method described in Patent Document 1. Therefore, the use of hydrofluoric acid is a factor that increases the production cost of the polyimide porous membrane, and there is a demand for a method for producing a porous membrane without using hydrofluoric acid. For example, it is conceivable to use other fine particles such as organic fine particles instead of the above silica particles. Organic fine particles are often prepared in an aqueous solvent and are often distributed as a fine particle dispersion containing water. Therefore, when using organic fine particles, if a varnish containing polyamic acid or polyimide is prepared using a fine particle dispersion liquid containing water, a varnish containing water is inevitably obtained.

However, when the varnish contains water and fine particles, the orientation of the polyamic acids is hindered by the poor compatibility between the polyamic acid and the solvent containing water and the presence of the fine particles, and the polyamic acid lumps embracing the fine particles. There is a problem that a mixture having a non-uniform composition that can cause poor formation of the coating film is likely to be formed, which leads to a defect that causes a decrease in film strength.

In order to avoid such problems, it is conceivable to produce a varnish that is substantially free of water using completely dried organic fine particles. However, the dried organic fine particles have poor dispersion stability and solvent resistance to an organic solvent that dissolves polyamic acid, aggregates are generated, and pores are uniformly formed, and the polyimide porous membrane has good air permeability. There are problems such as difficulty in obtaining.

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

The present invention has been made in view of the above problems, and is uniform including organic fine particles capable of forming a polyimide porous film having uniform and fine spherical pores having a diameter equivalent to the median diameter of the particles. It is an object of the present invention to provide a varnish composition having a composition, a method for producing a precursor film of a polyimide porous film using the above-mentioned varnish composition, and a method for producing a polyimide porous film using the precursor film.

The present invention is intended for the following [1] to [7].
[1]
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 structural unit (a) in which the organic fine particles (B) are derived from a vinyl-based monomer and
A varnish composition containing vinyl-based resin particles which are polymers having a structural unit (b1) derived from a compound represented by the following general formula (I), which is different from the structural unit (a).

[During the ceremony,
m represents an integer of 1 to 3 and represents
R represents a group represented by the following formula (i) or formula (ii).

(In the formula, R ₁ represents a hydrogen atom or a methyl group),
AO represents an alkyleneoxy group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100.
X represents a hydrogen atom or -SO ₃ M, -COOM and -PO ₃ M (in the formula, M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group or an organic ammonium group). Represents an anionic hydrophilic group selected from the group consisting of. ]
[2]
The structural unit (a) derived from the vinyl-based monomer includes a structural unit (a0) derived from a monofunctional vinyl-based monomer and a structural unit (a3) derived from a polyfunctional vinyl-based monomer. The varnish composition of [1].
[3]
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 structural unit (a0) in which the organic fine particles (B) are derived from a monofunctional vinyl-based monomer and
The structural unit (a3) derived from the polyfunctional vinyl-based monomer and
Vinyl-based resin particles for producing a porous membrane, which is a polymer having a structural unit (b0) derived from a reactive emulsifier.
The ratio of the structural unit (a0) is 88 to 99% by mass, the ratio of the structural unit (a3) is 0.9 to 10% by mass, and the ratio of the structural unit (b0) is 0.1 to 2% by mass. A varnish composition containing vinyl-based resin particles for producing a porous film.
[4]
A coating film forming step of applying the varnish composition according to any one of [1] to [3] 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, wherein the solvent (S) is removed from the coating film to form a precursor film of the polyimide porous film.
[5]
The method for producing a polyimide porous film according to [4], which comprises a peeling step of peeling the precursor film from the substrate after the precursor film forming step.
[6]
The method for producing a precursor film of a polyimide porous film according to [5], which comprises a winding step of winding the precursor film into a roll after the peeling step.
[7]
A polyimide comprising a step of producing a precursor film of a polyimide porous film by the method according to any one of [4] to [6], and then removing the organic fine particles (B) from the precursor film. A method for producing a porous membrane.

The varnish composition of the present invention can provide a polyimide porous film having spherical pores having a diameter equivalent to the median diameter of the organic fine particles contained in the varnish with a uniform distribution.
Further, the method for producing a porous membrane of the present invention can produce a polyimide porous membrane having spherical pores having a uniform distribution.

FIG. 1 shows an SEM image of a porous membrane ((a) Example 1, (b) Example 2, (c) Example 3, and (d) Example 4). FIG. 2 shows an SEM image of the porous membrane (Comparative Example 1).

≪Varnish composition≫
The varnish composition targeted by the present invention contains a polyamic acid (A), specific organic fine particles (B), and a solvent (S).
By removing the solvent (S) from the coating film formed by using the varnish composition of the present invention, a precursor film of a polyimide porous film can be formed. 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 of the present invention can be used for forming a polyimide porous film.

Hereinafter, essential or arbitrary components used for preparing the varnish composition will be described.

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

The tetracarboxylic acid dianhydride can be appropriately selected from compounds conventionally used as a raw material for synthesizing polyamic acid. The tetracarboxylic acid dianhydride may be an aromatic tetracarboxylic acid dianhydride or an aliphatic tetracarboxylic acid dianhydride, but the heat resistance of the obtained polyimide resin and thus the porous film From the point of view, it is preferable to use aromatic tetracarboxylic acid dianhydride. The above tetracarboxylic acid dianhydride may be used alone or in combination of two or more.

Preferable specific examples of the aromatic tetracarboxylic acid dianhydride include, but are not limited to, pyromellitic acid dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, and bis. (2,3-dicarboxyphenyl) 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-hexafluoropropanedi Anhydride, 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 dianhydride Anhydride, 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, Examples thereof include fluorene 9-bisanhydride phthalate, 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, and so on. Examples thereof include 4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclohexanetetracarboxylic dianhydride and the like.
Among these, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride and pyromellitic acid dianhydride are preferable from the viewpoint of price, availability and the like.

The above diamine can be appropriately selected from compounds conventionally used as synthetic raw materials 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 and the porous membrane. These diamines may be used alone or in combination of two or more.

As the aromatic diamine, a diamino compound containing one benzene ring, a diamino compound containing an aromatic skeleton in which two or more and about 10 or less benzene rings are bonded by a single bond or via a divalent linking group. Alternatively, a diamino compound containing an aromatic skeleton in which 2 or more and 10 or less of the benzene rings are condensed can be mentioned.
Specifically, a phenylenediamine compound and its derivative, a diaminobiphenyl compound and its derivative, a diaminodiphenyl compound and its derivative, a diaminotriphenyl compound and its derivative, a diaminonaphthalene compound and its derivative, an aminophenylaminoindan compound and its derivative, Examples thereof include a diaminotetraphenyl compound and its derivative, a diaminohexaphenyl compound and its derivative, and a cardo-type fluorangeamine derivative.

Examples of the phenylenediamine compound include m-phenylenediamine, p-phenylenediamine and the like, and examples thereof include diamines in which the hydrogen atom on the benzene ring is substituted with an alkyl group such as a methyl group or an ethyl group, for example, 2. , 4-Diaminotoluene, 2,4-triphenylenediamine, etc.

The diaminobiphenyl compound and its derivative have a structure in which two aminophenyl groups are bonded to each other by a single bond. Specific examples thereof include 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis (trifluoromethyl) biphenyl and the like.

The diaminodiphenyl compound and its derivative have a structure in which two aminophenyl groups are bonded via another group (linking group). Examples of the linking group (bond) include an ether bond, a sulfonyl bond, a thioether bond, a carbonyl bond, a bond with an alkylene or a derivative group thereof, an imino bond, an azo bond, a phosphine oxide bond, an amide bond, and a ureylene bond. The number of carbon atoms of the alkylene bond is about 1 or more and 6 or less, and a double bond may be partially contained. Examples of the derivative group of the alkylene group include an alkylene group substituted with one or more halogen atoms and the like, and an alkylene group substituted with an alkenyl group or the like.

Examples of diaminodiphenyl compounds and derivatives thereof include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 3,4'-diamino. Diphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 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-penten, iminodianiline, 4-methyl-2,4-bis (p-aminophenyl) ) Pentan, bis (p-aminophenyl) phosphinoxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide and the like.

The diaminotriphenyl compound and its derivative are compounds having a structure in which two aminophenyl groups are bonded via a single bond and / or a linking group, respectively, with one phenylene group interposed therebetween. As the linking group, a group similar to the group mentioned in the diaminodiphenyl compound and its derivative is selected.
Examples of diaminotriphenyl compounds and their derivatives include 1,3-bis (m-aminophenoxy) benzene [also referred to as 1,3-bis (3-aminophenoxy) benzene] and 1,3-bis (p-amino). Phenoxy) benzene [also referred to as 1,3-bis (4-aminophenoxy) benzene], 1,4-bis (p-aminophenoxy) benzene [also referred to as 1,4-bis (4-aminophenoxy) benzene], 2 , 4-Triphenylenediamine and the like can be mentioned.

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

Examples of the aminophenylaminoindane compound and its derivative include 5 or 6-amino-1- (p-aminophenyl) -1,3,3-trimethylindane.

Examples of diaminotetraphenyl compounds and derivatives thereof include 4,4'-bis (p-aminophenoxy) biphenyl, bis [4- (p-aminophenoxy) phenyl] sulfone [bis [4- (4-aminophenoxy). Also called phenyl] sulfone], bis [4- (m-aminophenoxy) phenyl] sulfone [also called bis [4- (3-aminophenoxy) phenyl] sulfone], 2,2'-bis [p- (p') -Aminophenoxy) phenyl] propane [2,2-bis [4- (4-aminophenoxy) phenyl] propane], 2,2'-bis [p- (p'-aminophenoxy) phenyl] hexafluoropropane [2,2-bis [4- (4-aminophenoxy) phenyl] also referred to as hexafluoropropane], 2,2'-bis [p- (p'-aminophenoxy) biphenyl] propane, 2,2'-bis [P- (m-aminophenoxy) phenyl] benzophenone and the like can be mentioned.

Specific examples of the cardo-type fluorene amine derivative include 9,9-bisaniline fluorene and the like.

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

Examples of the aliphatic diamine include diamine compounds having 2 or more and 15 or less carbon atoms.
Specific examples of the aliphatic diamine include pentamethylenediamine, hexamethylenediamine, heptamethylenediamine and the like.

Even if the hydrogen atom of the carbon atom chain of these aliphatic diamines is substituted with at least one substituent selected from the group of halogen atom, methyl group, methoxy group, cyano group, phenyl group and the like. good.

The means for producing the polyamic acid (A) is not particularly limited, and a known method such as a method of reacting a tetracarboxylic acid dianhydride component with a diamine component in a solvent can be used.

The solvent used for the above-mentioned reaction between the tetracarboxylic acid dianhydride and the diamine is a solvent that can dissolve the tetracarboxylic acid dianhydride and the diamine and does not react with the tetracarboxylic acid dianhydride and the diamine. Not particularly limited. 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.
The amount of the solvent used is not particularly limited, but it is desirable to use it so 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.

As the temperature at the time of polyamic acid synthesis, an arbitrary temperature of −10 ° C. or higher and 120 ° C. or lower, preferably 5 ° C. or higher and 30 ° C. or lower can be selected.
The reaction time varies depending on the raw material composition used, but is usually 3 hours or more and 24 hours or less.
When the synthesis of the polyamic acid is carried out in the solvent (S) described later, the reaction solution of the polyamic acid can be used as it is as the polyamic acid-containing liquid in the preparation of the varnish composition.

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 polyamic acid (A) may be used alone or in combination of two or more.

<Organic fine particles (B)>
The organic fine particles (B) used in the varnish composition of the present invention are a structural unit (a) derived from a vinyl-based monomer and a structural unit (b1) derived from a compound represented by the general formula (I) described later. ), Which is a vinyl-based resin particle.
The organic fine particles (B) are a copolymer (copolymer) of a monomer component (mixture) containing a vinyl-based monomer and a compound represented by the general formula (I), which constitutes each of the above-mentioned structural units. It can be a polymer).

Further, in one embodiment of the present invention, the organic fine particles (B) used in the varnish composition include a structural unit (a0) derived from a monofunctional vinyl-based monomer described later and a polyfunctional vinyl-based monomer described later. Vinyl-based resin particles, which are polymers having a structural unit (a3) derived from the above and a structural unit (b0) derived from the reactive emulsifier described later, can be used.

In the present specification, the (meth) acrylic monomer means both an acrylic monomer and a methacrylic monomer. For example, (meth) acrylic acid alkyl ester refers to acrylic acid alkyl ester and methacrylic acid alkyl ester.
Further, in the present specification, "structural unit derived from vinyl-based monomer", "structural unit derived from monofunctional styrene-based monomer", "structural unit derived from monofunctional (meth) acrylic monomer", and "structural unit". Notations such as "structural unit derived from polyfunctional vinyl-based monomer" are vinyl-based monomer, monofunctional styrene-based monomer, monofunctional (meth) acrylic-based monomer, polyfunctional vinyl-based monomer. However, each indicates a structural unit formed when polymerized, and does not represent those monomers themselves.

[Structural unit derived from vinyl-based monomer (a)]
The structural unit (a) derived from the vinyl-based monomer is distinguished from the structural unit (b0) derived from the reactive emulsifier described later and the structural unit (b1) derived from the compound represented by the general formula (I). Is to be done.
The structural unit (a) can include a structural unit (a0) derived from a monofunctional vinyl-based monomer and a structural unit (a3) derived from a polyfunctional vinyl-based monomer, and is also monofunctional vinyl-based. The structural unit (a0) derived from the monomer includes a structural unit (a1) derived from a monofunctional styrene-based monomer and a structural unit (a2) derived from a monofunctional (meth) acrylic monomer. be able to.
In a preferred embodiment, the structural unit (a) includes both a structural unit (a0) derived from a monofunctional vinyl-based monomer and a structural unit (a3) derived from a polyfunctional vinyl-based monomer.

[Structural unit derived from monofunctional vinyl monomer (a0)]
<Structural unit derived from monofunctional styrene-based monomer (a1)>
As the structural unit (a0) derived from the monofunctional vinyl-based monomer, the structural unit (a1) derived from the monofunctional styrene-based monomer can be included. In general, structural units derived from styrene-based monomers can contribute to the formation of uniform spherical particles.
Examples of the monofunctional styrene-based monomer constituting the structural unit (a1) include styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2, Styrene such as 5-dimethylstyrene and 2,4,6-trimethylstyrene and derivatives thereof; styrene sulfonates such as sodium styrene sulfonate and ammonium styrene sulfonate can be mentioned. Among these, styrene, α-methylstyrene, and sodium styrene sulfonate can be mentioned as suitable ones.

<Structural unit derived from monofunctional (meth) acrylic monomer (a2)>
Further, as the structural unit (a0) derived from the monofunctional vinyl-based monomer, in addition to the structural unit (a1) derived from the monofunctional styrene-based monomer, it is derived from the monofunctional (meth) acrylic monomer. The structural unit (a2) to be used may be included. The structural unit derived from the (meth) acrylic monomer has the property of being easily decomposed (depolymerized) in the monomer unit regardless of whether it is monofunctional or polyfunctional, and has excellent thermal decomposition properties, and the heat of the organic fine particles (B). The decomposition temperature can be lowered.
Examples of the monofunctional (meth) acrylic monomer constituting the structural unit (a2) include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth). ) Isopropyl acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, n-pentyl (meth) acrylate, 3-methylbutyl (meth) acrylate, (meth) ) N-hexyl acrylate, cyclohexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, etc. (Meta) acrylic acid esters having a number of 1 to 18 can be mentioned.
Among these, methyl (meth) acrylate and ethyl (meth) acrylate are preferable as the (meth) acrylic acid-based monomer from the viewpoint of easily obtaining organic fine particles (B) having the same particle size. It can be mentioned as a thing, and methyl (meth) acrylate is particularly preferable.

[Structural unit derived from polyfunctional vinyl-based monomer (a3)]
The structural unit (a) can include a structural unit (a3) derived from a polyfunctional vinyl-based monomer in addition to a structural unit (a0) derived from a monofunctional vinyl-based monomer. A varnish composition (polyimide varnish) by containing the structural unit (a3) derived from a polyfunctional vinyl-based monomer to enhance the solvent resistance of the obtained organic fine particles (B) and swelling the organic fine particles (B). It is possible to suppress the decrease in viscosity of. Further, by including the structural unit (a3), the compressive strength is high and it becomes easy to obtain the organic fine particles (B) having the same particle size.
The structural unit (a3) includes a structural unit (a3-1) derived from a polyfunctional (meth) acrylic monomer and a structural unit (a3-2) derived from a polyfunctional (poly) vinyl monomer. ) Can be mentioned.

Specific examples of the polyfunctional (meth) acrylic monomer constituting the structural unit (a3-1) include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,3. -Butylene glycol di (meth) acrylate, 1,4-butylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, ethylene oxide modified 1,6-hexanediol di (meth) acrylate, 1,9 -Di (meth) acrylates of polyhydric alcohols having 1 to 10 carbon atoms such as nonanediol di (meth) acrylates, propylene oxide-modified neopentyl glycol di (meth) acrylates, and tripropylene glycol di (meth) acrylates; Polyethylene glycol di (meth) acrylate having 2 to 50 moles added, polypropylene glycol di (meth) acrylate having 2 to 50 moles of propylene oxide, tripropylene glycol di (meth) acrylate, etc. having 2 to 2 carbon atoms. Alkyldi (meth) acrylate in which the number of added moles of the alkylene oxide group of 4 is 2 to 50; ethoxylated glycerintri (meth) acrylate, propylene oxide-modified glycerol tri (meth) acrylate, ethylene oxide-modified trimethyl propanetri (meth) acrylate. , Trimethylol propanetri (meth) acrylate, pentaerythritol monohydroxytri (meth) acrylate, trimethylolpropanetriethoxytri (meth) acrylate and other polyhydric alcohol tri (meth) acrylates having 1 to 10 carbon atoms; penta Tetra (meth) acrylates of polyhydric alcohols having 1 to 10 carbon atoms such as erythritol tetra (meth) acrylates, dipentaerythritol tetra (meth) acrylates, and ditrimethylolpropane tetra (meth) acrylates; pentaerythritol penta (meth) acrylates. , Penta (meth) acrylate of polyvalent alcohol having 1 to 10 carbon atoms such as dipentaerythritol (monohydroxy) penta (meth) acrylate; multivalent of 1 to 10 carbon atoms such as pentaerythritol hexa (meth) acrylate. Hexa (meth) acrylate of alcohol and the like can be mentioned, but the present invention is not limited thereto.

Specific examples of the polyfunctional (poly) vinyl-based monomer constituting the structural unit (a3-2) include polyfunctional aliphatic vinyl monomers such as isoprene and butadiene; cyclopentadiene. , Cyclohexadiene and other polyfunctional alicyclic vinyl monomers; polyfunctional aromatic vinyl monomers such as divinylbenzene, divinyltoluene and divinylnaphthalene; divinyl adipate, divinyl maleate, divinyl phthalate, isophthalic acid Polyfunctional vinyl ester-based monomer such as divinyl; Polyfunctional allyl ester-based monomer such as diallyl maleate, diallyl phthalate, diallyl isophthalate, diallyl adipate; divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether Polyfunctional vinyl ether-based monomers such as, etc .; Polyfunctional allyl ether-based monomers such as diallyl ether, diallyl oxyetane, and triallyl oxyetane; Polyfunctional vinyl ketone-based monomers such as divinyl ketone and diallyl ketone; Polyfunctional nitrogen-containing vinyl monomers such as isocyanurate, diallyl cyanurate, methylenebis (meth) acrylamide, and bismaleimide; polyfunctional silicon-containing vinyl monomers such as dimethyldivinylsilane, divinylmethylphenylsilane, and diphenyldivinylsilane. Etc., but are not limited to these.

Among these, ethylene glycol di (meth) acrylates, 1, 3 are examples of the polyfunctional vinyl-based monomer constituting the structural unit (a3) from the viewpoint that organic fine particles (B) having the same particle size can be easily obtained. -Butylene glycol di (meth) acrylate, 1,4-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, divinylbenzene, divinyltoluene and the like are preferable. Further, from the viewpoint of excellent polymerization stability and easy acquisition of organic fine particles (B) with few aggregates, ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth). Examples thereof include ethylene glycol di (meth) acrylate, and ethylene glycol di (meth) acrylate is preferable.

The structural unit (a3) derived from the polyfunctional vinyl-based monomer is preferably 1% by mass to 10% by mass with respect to the total mass of the structural unit (a).

<Structural unit derived from other polymerizable monomers>
The polymer which is the organic fine particles (B) has the structural units (a0) [(a1), (a2)] and (a3) [(a3-1), (a3) as long as the effects of the present invention are not impaired. -2)] may contain structural units derived from other vinyl-based monomers (polymerizable monomers). That is, the organic fine particles (B) can be a copolymer of a monomer component (mixture) containing other polymerizable monomers.

For example, other than the monofunctional styrene-based monomer and the monofunctional (meth) acrylic-based monomer, other polymerizable monomers include monofunctional (meth) acrylonitrile-based single amounts such as (meth) acrylonitrile. Body; Monofunctional heterocycle-containing vinyl-based monomer such as N-vinylimidazole and N-vinyl-2-pyrrolidone; Simple such as vinyl acetate (vinyl acetate), isopropenyl acetate, vinyl propionate, vinyl decanoate and the like. Functional vinyl ester-based monomer; Monofunctional vinyl ether-based monomer such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, ethylene glycol vinyl ether; Other monofunctional vinyl compounds such as vinyl cyclopentane, vinyl cyclohexane, ethyl vinyl benzene, etc. Monomer: Monofunctional (meth) acrylic acid-based monomer such as (meth) acrylic acid and itaconic acid; Monofunctional (meth) acrylamide-based monomer such as (meth) acrylamide, N, N-dimethyl (meth) acrylamide. Examples thereof include, but are not limited to, monomers.

<Structural unit derived from reactive emulsifier and reactive emulsifier (b0)>
The reactive emulsifier is not particularly limited as long as it is an emulsifier reactive with the above-mentioned monomer or its polymer, but has a radically polymerizable double bond, a hydrophilic functional group, and a hydrophobicity in its molecular structure. Examples thereof include those having each group and having emulsifying, dispersing, and wetting functions similar to general emulsifiers.

Examples of the structure of the radically polymerizable double bond in the molecular structure include 1-propenyl group, 2-methyl-1-propenyl group, allyl group, methallyl group, vinyl group, acryloyl group, metaacryloyl group and the like. Can be mentioned.

Examples of the hydrophilic functional group in the molecular structure include anionic groups such as sulfate group, nitrate group, phosphate group, borate group and carboxyl group (-OSO _3- ^, -NO _3- ^, -OPO _3- ^, and so on. -B (OH) _4- ^, -COO- ^, etc.); Cationic groups such as amino groups ⁽ -NH ₃₊ , etc.); Polyoxyalkylene chains such as polyoxyethylene, polyoxymethylene, polyoxypropylene; hydroxy groups, etc. Can be mentioned.

Examples of the hydrophobic group in the molecular structure include an alkyl group, an alkenyl group, a phenyl group, an alkylphenyl group, a styrrified phenyl group, a naphthyl group and the like.

Reactive emulsifiers are classified into anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers and the like according to the type of hydrophilic functional group contained in the molecular structure.
Further, the radically polymerizable double bond, the hydrophilic functional group, and the hydrophobic group in the molecular structure of the reactive emulsifier can each have a plurality of types of structures and functional groups.

Among the above, the reactive emulsifier preferably has at least a polyoxyalkylene chain and a sulfuric acid group as hydrophilic functional groups inside the molecular structure.

The trade name generally commercially available as such a reactive emulsifier is not particularly limited, but for example, Adecaria Soap SR, ER, SE, NE, PP (ADEKA Corporation), Aqualon HS, BC, KH. (Daiichi Kogyo Seiyaku Co., Ltd.), Latemuru PD (Kao Co., Ltd.), Eleminor JS, RS (Sanyo Kasei Kogyo Co., Ltd.), Antox MS (Nippon Emulsifier Co., Ltd.) and the like.

[Structural unit (b1) derived from the compound represented by the general formula (I)]
As described above, the organic fine particles (B) can have a structural unit (b1) derived from the compound represented by the following general formula (I).
The compound represented by the following general formula (I) has a hydrophobic group and a hydrophilic group in the molecule, and also has a copolymerizable unsaturated group. Therefore, the compound represented by the following general formula (I) also functions as a reactive (copolymerizable) emulsifier (corresponding to the above-mentioned reactive emulsifier), and various problems in the conventional emulsion polymerization, for example, during emulsion polymerization. It can be expected to suppress / improve the polymerization instability, the foaming of the system, and the deterioration of the physical properties of the polymer obtained after the polymerization.

In the above general formula (I), m represents an integer of 1 to 3, and preferably represents 2 from the viewpoint of emulsifying property.

AO represents an alkyleneoxy group having 2 to 4 carbon atoms. Examples of the alkyleneoxy group having 2 to 4 carbon atoms include an ethyleneoxy group, a propyleneoxy group, and a butyleneoxy group. Among these, ethyleneoxy group is preferable as AO. Since the ethyleneoxy group is more hydrophilic than other alkyleneoxy groups and can form a resin emulsion having a dense hydration layer, the stability of the resin particles in the aqueous dispersion medium can be further improved.
n represents the number of repetitions of the alkyleneoxy unit (that is, the number of moles of the alkyleneoxy group added). n is an integer of 0 to 100, preferably an integer of 5 to 50, and more preferably an integer of 5 to 30, from the viewpoint of the stability of the resin particles in the aqueous dispersion medium.

X represents a hydrogen atom or -SO ₃ M, -COOM and -PO ₃ M (in the formula, M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group or an organic ammonium group). Represents an anionic hydrophilic group selected from the group consisting of.
Examples of the alkali metal atom include a sodium atom and a potassium atom. Examples of the alkaline earth metal atom include a calcium atom and a barium atom.
Considering the emulsifying property, X is preferably a hydrogen atom, -SO ₃ NH ₄ , -SO ₃ Na, or -SO ₃ K, and more preferably -SO ₃ NH ₄ .

R represents a polymerizable unsaturated group, specifically a group represented by the following formula (i) or formula (ii), and in the formula, R ₁ represents a hydrogen atom or a methyl group.

As a preferable example of the compound represented by the general formula (I), a compound represented by the following formula (I-1) can be mentioned.

(In the formula, m, AO, n, and X are as defined in the formula (I).)

Commercially available products can also be used as the compound represented by the general formula (I). For example, Aqualon AR series (AR-10, AR-1025, AR-20, AR-2020) manufactured by Daiichi Kogyo Kagaku Co., Ltd. ) Etc. can be mentioned.

In the organic fine particles (B) (polymer), when the total structural unit of the polymer is 100% by mass from the viewpoint of copolymerizability at the time of polymerization, for example, the ratio of the structural unit (a) is 98.0% by mass. The ratio of the structural unit (b0) (for example, the structural unit (b1)) to 99.9% by mass can be 0.1% by mass to 2.0% by mass.
Further, when the total structural unit of the organic fine particles (B) (polymer) is 100% by mass, the ratio of the structural unit (a0) is 88 to 99% by mass, and the ratio of the structural unit (a3) is 0.9. The ratio of the structural unit (b0) can be about 10% by mass and 0.1 to 2% by mass.
The ratio of the structural unit (b0) may be read as the ratio of the structural unit (b1), or the total of the structural unit (b1) and the structural unit (b0) other than the structural unit (b1). It may be read as a ratio.

From the viewpoint of obtaining resin particles having a uniform particle size and being stable to a solvent or the like, for example, the ratio of the structural unit (a1) derived from the monofunctional styrene-based monomer in the structural unit (a) is set. 10% by mass to 99% by mass, the ratio of the structural unit (a2) derived from the monofunctional (meth) acrylic monomer is 0% by mass to 80% by mass, and the structural unit derived from the polyfunctional vinyl-based monomer ( The ratio of a3) can be 1% by mass to 10% by mass, and the ratio of other structural units derived from the polymerizable monomer can be 0% by mass to 5% by mass (total of 100% by mass).

The content of the organic fine particles (B) 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 organic fine particles (B) may be used alone or in combination of two or more.

[Diameter of organic fine particles (B)]
The organic fine particles (B) are preferably particles having a median diameter D ₅₀ of 0.05 μm to 2.0 μm.
As the median diameter in the present invention, a value of 50% volume diameter based on a volume measured by a dynamic light scattering method can be adopted.
Generally, when the particle size is small, agglomeration of particles is likely to occur particularly during polymerization, but the organic fine particles (B) used in the present invention exert an excellent aggregation suppressing effect in the dispersion, so that the organic fine particles (B) have an excellent effect. The particle size can be in a relatively small range. By setting the median diameter in the above range, when a polyimide porous film is produced from the varnish composition described later, fine pores can be formed in the polyimide, and the obtained polyimide porous film can be used as a material having a low dielectric constant. It will be possible to provide.
However, if the median diameter is less than 0.2 μm, the particle size may be too small to contribute to the formation of sufficient pores. Further, if it exceeds 1.5 μm, the mechanical strength of the polyimide resin to be punctured may be lowered, or the desired dielectric property may not be obtained.

[Pyrolysis temperature of organic fine particles (B)]
It is preferable that the organic fine particles (B) have a pyrolysis temperature lower than the pyrolysis temperature of the thermosetting resin described later under atmospheric pressure.
In the present specification, the thermal decomposition temperature is a condition according to JIS K7120 (thermogravimetric analysis method for plastics), and the weight reduction due to thermal decomposition of a sample is measured by a thermogravimetric analyzer (TGA). Means the starting temperature.
Although it depends on the type of the target thermosetting resin, the thermal decomposition temperature of the organic fine particles (B) in a nitrogen atmosphere is, for example, 340 to 440 ° C, preferably 370 to 410 ° C.

[Manufacturing method of organic fine particles (B)]
The organic fine particles (B) can be obtained by emulsion polymerization of a monomer component containing the vinyl-based monomer and the reactive emulsifier (for example, a compound represented by the general formula (I)). .. The emulsification polymerization method is preferable in that particles having a small particle size can be easily obtained. As the vinyl-based monomer, various monomers mentioned in the above description [monofunctional vinyl-based monomer (monofunctional styrene-based monomer, monofunctional (meth) acrylic-based monomer), Polyfunctional vinyl-based monomers (polyfunctional (meth) acrylic monomers, polyfunctional (poly) vinyl-based monomers), and other polymerizable monomers] can be used as the reactive emulsifiers of the above-mentioned compounds and the like. Can be exemplified respectively.
A preferred embodiment of emulsion polymerization is to use a polymerization mixture containing the above-mentioned monomer component, a polymerization initiator, and optionally other additives (surfactant, protective colloid agent, chain transfer agent, pH adjuster, etc.) for emulsion polymerization. The emulsion polymerization step may be included, and if desired, an aging step of aging the reaction solution obtained in the emulsion polymerization step may be included.

The emulsion polymerization is usually carried out in an aqueous dispersion medium, and the aqueous dispersion medium is not particularly limited, and examples thereof include water and a mixed solution of water and an alcohol solvent. From the viewpoint of stability (non-aggregation) of the organic fine particles (B) formed after emulsion polymerization, water is preferable as the aqueous dispersion medium. The amount of the aqueous dispersion medium used can be appropriately set so that the content of the organic fine particles (B) present in the system after emulsion polymerization is a desired ratio. For example, the content of the organic fine particles (B) existing in the system is set to 1% by mass to 70% by mass, 10% by mass to 60% by mass, 20% by mass to 50% by mass, and the amount of the aqueous dispersion medium used. It may be set appropriately.

The polymerization initiator used for the emulsion polymerization is not particularly limited, and a known polymerization initiator can be used. For example, azobisisobutyronitrile, 2,2-azobis (2-methylbutyronitrile), 2,2-azobis (2,4-dimethylvaleronitrile), 2,2-azobis (2-diaminopropane) hydro. Chloride, 4,4-azobis (4-cyanovaleric acid), 2,2-azobis (2-methylpropion amidine), 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] Azo compounds such as tetrahydrate; persulfates such as potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide, ammonium peroxide and the like. However, the present invention is not limited to these examples. Among these, the azo compound and the peroxide can also function as a decomposition accelerator, that is, have a function of promoting the thermal decomposition of the organic fine particles (B) when producing the polyimide porous film described later. Therefore, it can be preferably used.
The amount of the polymerization initiator used is not particularly limited, but is preferably 0.05 parts by mass or more per 100 parts by mass of the monomer component, from the viewpoint of increasing the polymerization rate and reducing the residual amount of the unreacted monomer. Is 0.1 part by mass or more, and can be, for example, 5 parts by mass or less from the viewpoint of polymerization stability.

The reactive emulsifier and the compound represented by the general formula (I) also serve as an emulsifier and can satisfactorily initiate and complete emulsion polymerization, but are commonly used surfactants for emulsion polymerization (). (Emulsifier) may be further used as another additive.
As the surfactant, an anionic surfactant or a cationic surfactant and / or other nonionic surfactant may be used in combination.
For example, examples of anionic surfactants (anionic emulsifiers) include fatty acid sekken; sekken rosinate; alkyl sulfates such as ammonium dodecyl sulfate and sodium dodecyl sulphate; alkyl sulfonates such as ammonium dodecyl sulfonate and sodium dodecyl sulfonate; Alkylaryl sulfonates such as ammonium dodecylbenzene sulfonate, sodium dodecylbenzene sulfonate, sodium dodecylnaphthalene sulfonate; polyoxyalkylene alkyl sulfate; polyoxyalkylene aryl sulfate; polyoxyalkylene alkylaryl sulfate; dialkylsulfosuccinic acid Salts; arylsulfonic acid-formalin condensates; fatty acid salts such as ammonium laurylate, sodium stearilate and the like.
Examples of the cationic surfactant include stearyltrimethylammonium, cetyltrimethylammonium, and lauryltrimethylammonium.
Examples of the nonionic surfactant include polyoxyalkylene alkylphenyl ether, polyoxyalkylene alkyl ether, alkyl polyglucoside, polyglycerin alkyl ether, polyoxyalkylene fatty acid ester, polyglycerin fatty acid ester, total ruby monofatty acid ester and the like. Be done.
When a surfactant is separately used in the emulsion polymerization step, the amount used is, for example, 0.05 parts by mass or more, 0.1 parts by mass or more, or 0.3 parts by mass with respect to 100 parts by mass of the monomer component. The number may be 10 parts by mass or more, and the upper limit thereof may be, for example, 10 parts by mass, 8 parts by mass or less, and 5 parts by mass or less.

Further, for the purpose of improving the polymerization stability during emulsion polymerization, a known protective colloidal agent may be used in combination as another additive. Examples of the protective colloid agent include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, polyacrylic acid, and gum arabic.

Further, as another additive at the time of emulsion polymerization, a known chain transfer agent or pH adjuster may be used in combination.
Examples of the chain transfer agent include octyl mercaptan, dodecyl mercaptan, mercaptoethanol, thioglycolic acid, allyl alcohol, isopropyl alcohol, sodium hypophosphite and the like.
Examples of the pH adjusting agent include inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid; organic acids such as citric acid, succinic acid, apple acid and lactic acid; and inorganic bases such as sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate. Alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, isopropanol, aliphatic amines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, aromatic polyamines such as phenylenediamine and tolylenediamine, piperazine. , Organic bases such as heterocyclic polyamines such as aminoethylpiperazine and the like.

In the monomer component to be subjected to the emulsion polymerization, the amount of each monomer used (charge ratio) can be appropriately set.
For example, the ratio of the vinyl-based monomer to the total amount of all the monomers (total 100% by mass) is 98.0% by mass to 99.9% by mass, and is represented by a reactive emulsifier (for example, the general formula (I)). The proportion of the compound) can be 0.1% by mass to 2.0% by mass.
Further, for example, the ratio of the monofunctional vinyl-based monomer is 88% by mass to 99% by mass, and the ratio of the polyfunctional vinyl-based monomer is 0.9% by mass with respect to the total amount of all the monomers (total 100% by mass). The ratio of the reactive emulsifier can be from% to 10% by mass, and the ratio of the reactive emulsifier can be from 0.1 to 2% by mass.
Further, in the vinyl-based monomer (100% by mass in total), the monofunctional styrene-based monomer is 10% by mass to 99% by mass, the monofunctional (meth) acrylic monomer is 0% by mass to 80% by mass, and more. The functional vinyl-based monomer may be 1% by mass to 10% by mass, and the other polymerizable monomer may be 0% by mass to 5% by mass.

The emulsion polymerization may be carried out by a known emulsion polymerization method, and for example, a monomer dropping method, a pre-emulsion method, a batch charging polymerization method and the like can be adopted. From the viewpoint of industrial productivity, it is preferable to adopt the pre-emulsion method because it can be polymerized stably and a polymer (organic fine particles (B)) having few aggregates can be obtained.

In the emulsion polymerization, the method for charging the above-mentioned monomer component, polymerization initiator, and other additives is not particularly limited and may be appropriately set.
For example, in the case of emulsion polymerization by the pre-emulsion method, a vinyl-based monomer is pre-emulsified with a reactive emulsifier (for example, a compound represented by the general formula (I)) and an aqueous dispersion medium such as water. , Get a pre-emulsion. Then, the obtained pre-emulsion can be carried out by dropping it into a reaction vessel and appropriately adding a polymerization initiator to promote the emulsion polymerization reaction.
Further, after starting emulsion polymerization using a part of the polymerization mixture, the remaining polymerization mixture may be dropped or the like. Alternatively, after starting emulsion polymerization in advance using a mixed solution consisting of a part of the total amount of the monomer component and a part of the polymerization initiator (and other additives), the remaining monomer component and the remaining monomer component, and An operation such as dropping the polymerization initiator (and other additives) separately or by mixing them may be performed.

Further, the emulsion polymerization step is repeated by two or more steps, that is, in an embodiment including, for example, a first emulsion polymerization step and a second emulsion polymerization step, a core portion is formed by the first emulsion polymerization step, and a subsequent second emulsion polymerization step is carried out. By forming the shell portion on the surface of the core portion, the core-shell type resin particles can be formed. In this case, the second emulsion polymerization step may be performed a plurality of times, and when the second second emulsion polymerization step is performed, the surface of the shell portion formed by the first second emulsion polymerization step is newly formed. Resin particles on which a shell portion is formed can be obtained.
When the first emulsion polymerization step and the second emulsion polymerization step are included, the composition of the monomer component used in each step can be changed, and the monomer component used in each step can be changed to 1. It may be a monomer of the seed. That is, in the first emulsion polymerization step and the second emulsion polymerization step, different monomers (one kind) may be used, or a mixture of monomers and a monomer (one kind) may be used. Alternatively, a mixture of different monomers may be used in each step. When a mixture of monomers of the same type is used, a mixture in which the mixing ratio of the monomers is changed can be used. For example, in the first emulsion polymerization step, among the monofunctional vinyl-based monomers, the monofunctional styrene-based monomer, the polyfunctional vinyl-based monomer, and the reactive emulsifier (for example, represented by the general formula (I)) are represented. In the subsequent second emulsion polymerization step using the mixture containing the compound), the monofunctional styrene-based monomer, the monofunctional (meth) acrylic-based monomer, and the polyfunctional vinyl-based monomer among the monofunctional vinyl-based monomers are used. A mixture containing a monomer and a reactive emulsifier (for example, a compound represented by the general formula (I)) can be used.

The polymerization temperature in the emulsion polymerization may be appropriately set depending on the polymerization initiator and the like used, and may be, for example, 30 ° C to 90 ° C or 50 ° C to 80 ° C. The polymerization time may be appropriately set according to the reaction rate obtained from the charged amount of the monomer component and the residual amount in the reaction solution, but is usually about 1 hour to 12 hours, for example, about 2 hours to 8 hours. be.

Next, in the aging step, which is an arbitrary step, after the emulsion polymerization step, unreacted monomers are reduced, or the polymer particles (organic fine particles (B)) obtained by emulsion polymerization are stabilized. It is done for the purpose of polymerizing.
The aging temperature in the aging step can be, for example, 50 ° C. to 90 ° C., and can be, for example, 70 ° C. to 85 ° C. By keeping the aging temperature within the above range, it can be expected that the amount of the unreacted monomer mixture can be reduced while suppressing the aggregation of particles. The aging time may be appropriately set according to the reaction rate obtained from the total amount of the monomer components charged and the residual amount of the monomer components in the reaction solution, but is usually 1 hour to 12 hours, preferably 1 to 12 hours. It takes about 2 to 8 hours.

In the aging step, a surfactant may be added as necessary for the purpose of facilitating the suppression of aggregation of the organic fine particles (B) during aging.
As the surfactant used in the aging step, it is preferable to use the surfactant mentioned in the emulsion polymerization step described above, and it is also possible to use an anionic surfactant or a nonionic surfactant. ..
The amount of the surfactant used in the aging step is, for example, 0.05 parts by mass or more and 0.1 parts by mass or more with respect to 100 parts by mass of the total amount of the monomer components attached to the emulsion polymerization step. , 0.3 parts by mass or more, and for example, 10 parts by mass or less, 8 parts by mass or less, and 5 parts by mass.

After undergoing the emulsion polymerization step (and, if desired, the aging step), the organic fine particles (B) can be obtained in the form of a dispersion liquid containing the formed polymer in the aqueous dispersion medium.
In the varnish composition described later, the organic fine particles (B) can be used in the form of a fine particle dispersion liquid containing the organic fine particles (B) or as the organic fine particles (B) of the dry powder.

When the organic fine particles (B) are used as the organic fine particles (B) of the dry powder, the organic fine particles (B) in the form of the dispersion liquid contained in the above-mentioned aqueous dispersion medium are freeze-dried, hot-air dried, spray-dried, or the like. Therefore, the form of powder can be obtained.
When the organic fine particles (B) are used in the form of a fine particle dispersion liquid containing the organic fine particles (B), the dispersion liquid containing the organic fine particles (B) obtained through the above-mentioned emulsification polymerization step in the aqueous dispersion medium is used. It may be used as it is, the aqueous dispersion medium may be substituted with a solvent to obtain a fine particle dispersion, or the organic fine particles (B) in the powder form described above may be passed and then dispersed in an appropriate solvent to form a fine particle dispersion. good.
At this time, examples of the solvent that can be used include one or more selected from water (SI) and an organic solvent (S-III), which will be described later.

<Solvent (S)>
The varnish composition contains a solvent (S).
Examples of the solvent (S) include water (SI), an organic solvent (S-III), or a combination thereof.

The organic solvent (S-III) may be basic, but is preferably a compound that is neutral or weakly basic in water from the viewpoint of avoiding hydrolysis of the polyamic acid (A). ..

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-methylcaprolactam, 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; ether solvents such as tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, and diethylene glycol diethyl ether. Ketone solvents such as acetone, methyl ethyl ketone, and cyclohexanone; methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, ethylene glycol monomethyl ether, 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-pentanediol, 2-butene Alcohol-based solvents such as -1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, and 1,2,6-hexanetriol. Can be mentioned.
In the specification of the present application, in the classification of the above-mentioned solvent, for example, a compound corresponding to a ketone or an ether and having an alcoholic hydroxy group can be classified as an alcohol-based solvent. Further, compounds corresponding to both ketones and ethers can be classified as ketone solvents.

The solvent (S) is an organic solvent (S-III), particularly an organic solvent (S), because the varnish composition has solubility or dispersion stability and the solvent (S) can be easily removed from the coating film. S-III) is 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 hydroxy group, and ^RS5 and ^RS6 are independently hydrogen atoms and alkyl groups having 1 or more and 3 or less carbon atoms, respectively, and are represented by ^{RS7 and RS6} ^. ^RS8 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 the formula (S1), specific examples of the case where ^RS3 is a hydrogen atom or a group represented by the formula (S1-1) are N, N-dimethylformamide and N, N-dimethyl. Acetamide, N, N, 2-trimethylpropionamide, N-ethyl-N, 2-dimethylpropionamide, N, N-diethyl-2-methylpropionamide, N, N,2-trimethyl-2-hydroxypropionamide, Examples thereof include N-ethyl-N, 2-dimethyl-2-hydroxypropionamide, N, N-diethyl-2-hydroxy-2-methylpropionamide and the like.

Among the compounds represented by the formula (S1), specific examples of the case where ^RS3 is a group represented by the formula (S1-2) include N, N, N', N'-tetramethylurea, and N. , N, N', N'-tetraethylurea and the like.

Among the specific 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.

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

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.

When a dispersant is used, the content of the dispersant in the varnish composition is preferably 0.01% by mass or more and 5% by mass or less with respect to the fine particles, for example, in terms of film forming property. It is more preferably 05% by mass or more and 1% by mass or less, and even more preferably 0.1% by mass or more and 0.5% by mass or less.

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 the varnish composition is produced by mixing the above-mentioned various components in predetermined amounts, and the specific procedure thereof is not particularly limited.
As one of the preferable methods for producing the varnish composition, a polyamic acid-containing liquid containing a polyamic acid (A) and an organic solvent (S-III), and a fine particle dispersion liquid containing organic fine particles (B) or an organic dry powder are used. A method of mixing with the fine particles (B) can be mentioned.

Regarding the polyamic acid-containing liquid, the polyamic acid (A) and the organic solvent (S-III) are as described above. The polyamic acid-containing solution 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 synthesized and the reaction solution may be used as it is as a polyamic acid-containing solution.
The polyamic acid-containing liquid may contain water (SI). Further, the polyamic acid-containing liquid may contain an arbitrary component other than the polyamic acid (A), the organic solvent (S-III), and water (SI).

Regarding the fine particle dispersion liquid containing the organic fine particles (B), 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) and an organic solvent (S-III).

In the above method, when various materials constituting the varnish composition are mixed, the mixing is performed under warmed 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.

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 20,000 cP or less, more preferably 1,000 cP or more and 15,000 cP or less, and further preferably 1,500 cP or more and 12,000 cP or less. When the viscosity of the varnish composition is within this range, uniform film formation is easy.

The varnish composition has a ratio of organic fine particles (B) / polyamic acid (A) of 0.5 to 4.0 (mass ratio) when a polyamic acid-fine particle composite film (precursor film) described later is used. , Organic fine particles (B) and polyamic acid (A) are preferably contained, and the organic fine particles (B) have the above-mentioned (B) / (A) ratio of 0.7 to 3.5 (mass ratio). And more preferably containing the polyamic acid (A).
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 above-mentioned lower limit value, 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 equal to or less than the above upper limit value, the varnish composition is stably formed without causing problems such as an increase in viscosity and cracks in the film. Can be filmed.

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. The solid content concentration referred to here means the concentration of a component other than the solvent (S), and even a liquid component is included in the weight as a solid content.

≪Manufacturing method of precursor film of polyimide porous film≫
The method for producing a precursor film of a 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 removing the solvent (S) from the coating film to form a polyimide porous film. It includes a precursor film forming step of forming a precursor film of the film.

Examples of the substrate include PET films, SUS substrates, glass substrates and the like.
To remove the solvent (S) from the coating film, the above-mentioned varnish composition is applied onto a substrate to form a coating film, and then the temperature is 0 ° C. or higher and 100 ° C. or lower, preferably normal pressure, under normal pressure or vacuum. It may be dried at 10 ° C. or higher and 100 ° C. or lower.

Hereinafter, a procedure for forming a precursor film of a polyimide porous film (hereinafter, also simply referred to as “precursor film”) will be described.
The precursor film may be formed directly on the substrate, or may be formed on a lower film different from the precursor film formed on the substrate. Further, after forming a precursor film 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, both the aspect of providing the lower layer film on the substrate and the aspect of providing the upper layer film on the precursor film are included in the method of forming the precursor film on the substrate.

The lower layer film (or upper layer film) is, for example, a varnish containing a resin selected from the group consisting of polyamic acid, polyimide, polyamide-imide precursor, polyamideimide and polyether sulfone, fine particles, and a solvent. For example, the lower layer (or the upper layer) formed with a varnish for forming a lower layer film (or an upper layer film) having a content of the fine particles of 40% by volume or more and 81% by volume or less with respect to the total of the resin and the fine particles is formed. Upper layer) An unfired composite film can be mentioned. The lower unfired composite film may be formed on the substrate.
When the content of the fine particles in the varnish is more than 40% by volume, the fine particles are uniformly dispersed in the varnish, and when the content of the fine particles is 81% by volume or less, the fine particles do not aggregate with each other. Therefore, the pores can be uniformly formed in the layer derived from the lower layer film (or the upper layer film).
Further, when the content of the fine particles in the varnish is within the above range, when the lower unfired composite film is formed on the substrate, even if the base material is not provided with the release layer in advance, the film is formed. Easy to secure releasability.

The fine particles used for the lower (or upper) film forming varnish may be the same as or different from the organic fine particles (B) used for 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.

Further, the average particle size of the fine particles used for 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 components such as fine particles and a solvent contained in the lower (or upper) film-forming varnish are the same as those of 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.
For the lower unfired composite film, for example, the above-mentioned varnish for forming the lower layer film is applied 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 may be 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)). A film made of non-woven fabric, a polyimide film, and the like 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 may include 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.

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 type can be used without particular limitation. However, 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 a release layer, the above peeling step and cleaning step can be omitted. Further, before the removal step of removing the organic fine particles (B) in the method for producing a polyimide porous film described later, in the method for producing a precursor film, a dipping step and a dipping step of immersing the precursor film in water or a solvent containing water. A pressing step of pressing the precursor film afterwards and a drying step of drying the precursor film after the dipping step may be provided as arbitrary steps.

In the method for producing a precursor film of a polyimide porous film, when the above peeling step is carried out, a winding step of winding the precursor film into a roll may be further carried out after the peeling step.
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 includes a removal step of removing organic fine particles (B) from the precursor film of the polyimide porous membrane described above. In the removing step, the organic fine particles (B) may be removed while imidizing the polyamic acid (A) or after imidizing the polyamic acid (A). The organic fine particles (B) are preferably removed by heating, and may be removed by heating after chemical imidization described later, or at the same time as or during the imidization of the precursor film by calcination related to thermal imidization. , Or may be removed after imidization. By thermally decomposing the organic fine particles (B) by heating, a polyimide porous film having spherical pores with a uniform distribution can be obtained.

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. Hereinafter, calcination related to thermal imidization will be described.

When the 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 ° C. to 450 ° C. in about 3 hours and then holding the temperature at the same temperature for about 2 to 30 minutes, or stepwise from room temperature in increments of, for example, 50 ° C. Drying-heat including continuous or stepwise temperature raising operation such as raising the temperature to 400 ° C. to 450 ° C. (holding for about 20 minutes in each step) and finally holding at 400 ° C. to 450 ° C. for about 2 to 30 minutes. The imidization method can also be used.
When a precursor film is formed on a substrate, the precursor film or the laminated film containing the precursor film is once peeled off from the substrate, and the firing step is performed, the end portion of the precursor film or the laminated film is made of SUS. It is also possible to adopt a method of fixing to a mold or the like to prevent deformation due to firing.

The film thickness of the polyimide porous 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 yellow or brown colored porous 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.

The method for producing the polyimide porous film may include a resin removing step of removing at least a part of the polyimide porous film after the removing step of removing the organic fine particles (B). The resin removing step means a step of removing the resin (thinning the film thickness) in the film thickness direction of the porous film, and by removing at least a part of the porous film after the removing step, the porous film is described. It is possible to improve the pore size of the polyimide porous membrane of the final product as compared with the polyimide porous membrane which does not remove at least a part of the above.
It should be noted that a step of removing at least a part of the resin portion of the precursor film may be included before the step of removing the organic fine particles (B), for example, after the step of forming the precursor film. At this time, a part of the organic fine particles (B) contained in the precursor film may be removed. By including this step, when the organic fine particles (B) are removed and pores are formed in the subsequent fine particle removal step, the porous polyimide type of the final product is compared with the one in which the resin portion of the precursor film is not removed. It is possible to improve the aperture ratio of the resin film.

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, and the use of an inorganic alkaline solution is particularly preferable.
As an inorganic alkaline solution, for example, 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, sodium metasilicate; an ammonia solution; hydroxylation. Examples thereof include an etching solution containing an alkali metal compound, 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.
The alkaline concentrations of these inorganic alkaline solutions and organic alkaline solutions are, for example, 0.01% by mass or more and 20% by mass or less.

Pure water and alcohols can be appropriately selected as the solvent for each of the above solutions. Further, it is also possible to use a solution in which an appropriate amount of a surfactant is added.

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

As another physical removal method, a method is adopted in which the surface of the object is pressure-bonded to a mount film (for example, a polyester film such as PET film) wetted with a liquid, and then the porous film is peeled off from the mount film without drying or after drying. You can also do it. In this method, 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 due to the surface tension or electrostatic adhesion of the liquid.

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

In Examples and Comparative Examples, the following tetracarboxylic acid dianhydrides, diamines, polyamic acids, and organic solvents were used.
-Tetracarboxylic acid dianhydride: pyromellitic acid dianhydride-Diamine: 4,4'-diaminodiphenyl ether-Polyamic acid solution: Reaction product of pyromellitic acid dianhydride and 4,4'-diaminodiphenyl ether (solid content) 20% by mass (organic solvent: dimethylacetamide))
-Organic solvent: Dimethylacetamide (DMAc)

Synthesis example 1
In a glass container having an internal capacity of 1.0 L equipped with a stirrer, a thermometer, a temperature controller, a condenser, and a dropping device, 383.0 g of ion-exchanged water was placed and nitrogen gas was introduced while stirring to perform nitrogen substitution. After that, it was heated with a mantle heater and the temperature was controlled at 72 ± 2 ° C. to obtain a polymerization vessel.
122.4 g of ion-exchanged water in a glass container with a content of 1.0 L equipped with a stirrer, polyoxyethylene styrenated propenylphenyl ether sulfate ammonium salt as a compound (reactive emulsifier) represented by the general formula (I) ( Aqualon AR-1025 (25% aqueous solution) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. 12.8 g, styrene as a monofunctional monomer (styrene monomer manufactured by Asahi Kasei Co., Ltd.) 378.6 g, ethylene glycol dimethacrylate (Mitsubishi) as a polyfunctional monomer 22.2 g of Acryester ED manufactured by Chemical Co., Ltd. was added and stirred to obtain a monomer emulsion in which styrene and ethylene glycol dimethacrylate were emulsified in ion-exchanged water.
48.6 g of ion-exchanged water in a glass container with a content of 0.1 L equipped with a stirrer, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate as a polymerization initiator 3.1 g of a product (VA-057 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added and dissolved by stirring to obtain an aqueous polymerization initiator solution.
26.8 g from the prepared monomer emulsion and 5.0 g from the prepared aqueous polymerization initiator were placed in the polymerization vessel, and the initial polymerization was carried out for 120 minutes.
After the initial polymerization was carried out for 120 minutes, the remaining monomer emulsion and the polymerization initiator aqueous solution were each sent to the polymerization vessel over 240 minutes by a liquid feed pump, and the dropping polymerization was carried out. After the completion of the dropping, the liquid feeding line was co-washed with 9.0 g of ion-exchanged water.
After continuing the polymerization reaction for 120 minutes, the mixture was cooled to 40 ° C. to obtain a crosslinked polymer aqueous dispersion having a solid content of 40%.

Synthesis example 2
Polymerization was carried out in the same manner as in Synthesis Example 1, except that 374.2 g of styrene and 4.4 g of methyl methacrylate were used instead of 378.6 g of styrene in Synthesis Example 1, and trimethylolpropane trimethacrylate was used instead of ethylene glycol dimethacrylate. A crosslinked polymer aqueous dispersion having a solid content of 40% was obtained.

Synthesis example 3
Instead of 378.6 g of styrene in Synthesis Example 1, 388.8 g of styrene was contained, and instead of 22.2 g of ethylene glycol dimethacrylate, a divinylbenzene mixture (DVB570 manufactured by Nittetsu Chemical & Materials Co., Ltd., 57% divinylbenzene was contained. A crosslinked polymer having a solid content of 40%, which was polymerized in the same manner as in Synthesis Example 1 except that 12.0 g (divinylbenzene: 6.84 g, ethylvinylbenzene: 5.16 g) (containing 43% of ethylvinylbenzene) was used. An aqueous dispersion was obtained.

Synthesis example 4
In addition, 364.7 g of styrene and 4.0 g of methyl methacrylate were used instead of 378.6 g of styrene in Synthesis Example 1, and 32.1 g of 1,3-butylene glycol dimethacrylate was used instead of 22.2 g of ethylene glycol dimethacrylate. Was polymerized in the same manner as in Synthesis Example 1 to obtain a crosslinked polymer aqueous dispersion having a solid content of 40%.

Synthesis example 5
Nitrogen gas was introduced into a glass container having an internal capacity of 1.0 L equipped with a stirrer, a thermometer, a temperature controller, a condenser, and a dropping device, and nitrogen exchange was performed while stirring. After nitrogen substitution, 0.6 g of a 40% aqueous solution of triethanolamine lauryl sulfate (Alscope LS-40T manufactured by Toho Chemical Industry Co., Ltd.) was added as an emulsifier, heated with a mantle heater, and the temperature was controlled at 72 ± 2 ° C to form a polymerization vessel. ..
In a glass container with a content of 1.0 L equipped with a stirrer, 169.7 g of ion-exchanged water, 3.5 g of a 40% triethanolamine lauryl sulfate aqueous solution as an emulsifier, 364.9 g of styrene as a monofunctional monomer, and 2-hydroxyethyl methacrylate ( 11.1 g of Acryester HO manufactured by Mitsubishi Chemical Co., Ltd. was added and stirred to obtain a monomer emulsion in which styrene and 2-hydroxyethyl methacrylate were emulsified in ion-exchanged water.
49.1 g of ion-exchanged water in a glass container with a content of 0.1 L equipped with a stirrer, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate as a polymerization initiator 3.2 g of the product was added and dissolved by stirring to obtain an aqueous polymerization initiator solution.
28.4 g of the prepared monomer emulsion and 4.5 g of the prepared aqueous polymerization initiator were placed in the polymerization vessel, and the initial polymerization was carried out for 120 minutes.
After performing the initial polymerization for 120 minutes, the remaining monomer emulsion and the remaining polymerization initiator aqueous solution were each sent to the polymerization vessel over 300 minutes by a liquid feed pump, and the dropping polymerization was carried out.
After continuing the polymerization reaction for 120 minutes, the mixture was cooled to 40 ° C. to obtain a non-crosslinked polymer aqueous dispersion having a solid content of 40%.

Synthesis example 6
In place of 12.8 g of polyoxyethylene styrenated propenylphenyl ether sulfate ammonium salt (25% aqueous solution) in Synthesis Example 1, 8.0 g of lauryl sulfate triethanolamine (40% aqueous solution) was used, and 392.8 g of styrene and ethylene were used. Polymerization was carried out in the same manner as in Synthesis Example 1 except that glycol dimethacrylate was changed to 8.0 g to obtain a crosslinked polymer aqueous dispersion having a solid content of 40%.

[Example 1]
<Drying of organic fine particle aqueous dispersion>
The crosslinked polymer aqueous dispersion (organic fine particle aqueous dispersion) obtained in Synthesis Example 1 was spray-dried using a spray dryer ADL-311S-A (manufactured by Yamato Kagaku Co., Ltd.) to obtain powdery organic fine particles. ..

<Preparation of varnish composition>
10.7 parts by mass of organic fine particles of powder and 43.0 parts by mass of N, N-dimethylacetamide were stirred to prepare a dispersion, and 46.3 parts by mass of polyamic acid (20 mass% solution of dimethylacetamide) was added to the dispersion. In addition, it was dispersed with a three-roll mill to obtain a varnish composition having a uniform composition.

<Manufacturing of polyimide porous membrane>
The varnish composition was applied onto a polyethylene terephthalate film and then dried at 90 ° C. for 5 minutes to obtain a precursor film of a polyimide porous film. After the obtained precursor film was peeled off from the polyethylene terephthalate film, the precursor film was fired at 420 ° C. for 5 minutes in a firing furnace to imidize the polyamic acid while thermally decomposing the vinyl resin particles. The polyimide porous film of Example 1 was obtained.
The surfaces of the obtained porous film (film side and air surface side of the substrate) were observed with a scanning electron microscope (SEM). The obtained SEM image on the air surface side is shown in FIG. 1 (FIG. 1 (a)). From FIG. 1 (a), spherical pores of uniform size are formed in the polyimide porous material, and as a result of measuring the diameter of the pores using the SEM length measuring tool, the median diameter of the organic resin particles used It was confirmed that pores of the same size as the above could be formed.

[Examples 2 to 4]
Except for changing the organic fine particles to the types of organic fine particles shown in Table 1, the organic fine particle aqueous dispersion was dried, the varnish composition was prepared, and the polyimide porous film was produced in the same manner as in Example 1. In addition, SEM observation was performed for each porous membrane. The obtained SEM image on the air surface side is shown in FIG. 1 (FIG. 1 (b): Example 2, FIG. 1 (c): Example 3, FIG. 1 (d): Example 4).
As shown in FIGS. 1B, 1C and 1D, spherical pores of uniform size are formed in the polyimide porous material, and the diameter of the pores is determined using an SEM length measuring tool. As a result of the measurement, it was confirmed that the pores having the same size as the median diameter of the organic fine particles could be formed.

[Comparative Examples 1 and 2]
Except for changing the organic fine particles to the types of organic fine particles shown in Table 1, the organic fine particle dispersion was dried, the varnish composition was prepared, and the polyimide porous film was produced in the same manner as in Example 1. Further, regarding Comparative Example 1, SEM observation was performed, and the obtained SEM image is shown in FIG.
As shown in FIG. 2, in this example, spherical pores having a non-uniform size are formed in the polyimide porous material in a non-uniform distribution as compared with the examples, and the holes are vacant using the SEM length measuring tool. As a result of measuring the diameter of the pores, it was confirmed that the pores were larger than the median diameter of the organic fine particles. Further, it was confirmed that Comparative Example 2 was also formed with a non-uniform distribution as compared with Example, and the pores larger and smaller than the median diameter of the organic fine particles were sparse.

<Evaluation>
The following evaluation was performed for each of the porous membranes prepared as described above.
[Stress and elongation at break]
Each of the prepared porous membranes was cut into a size of 3 cm × 3 mm to obtain a strip-shaped sample. The stress (MPa; tensile strength) and elongation at break (% GL) at break of this sample were evaluated using EZ Test (manufactured by Shimadzu Corporation).

[Air permeability]
Each of the prepared porous membranes was cut into 5 cm squares to prepare a sample for measuring air permeability. Using a Garley type densometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), the time for 100 ml of air to pass through the sample was measured according to JIS P 8117.
The air permeability can be, for example, within 250 seconds or 200 seconds. The lower the value, the more preferable, so the lower limit is not particularly set, but considering the handleability of the porous membrane sample, it can be, for example, 30 seconds or more. If the Garley air permeability is within 250 seconds, it can be judged that it can be applied as a filter used for a separator of a lithium ion battery or a separation membrane for gas or liquid because it exhibits sufficiently high ion permeability.

As shown in Table 1 and FIGS. 1 to 2, the varnish composition of the example containing the organic fine particles defined in the present invention has better air permeability and uniform distribution than the varnish composition of the comparative example. It was confirmed that a polyimide porous membrane having spherical pores having a diameter equivalent to the median diameter of the organic fine particles can be produced. In the polyimide porous film made of the varnish composition of Example 4, the size of the pores opened on the surface was uniform, and the distribution state of the surface openings was also substantially uniform. The polyimide porous membrane made of the varnish compositions of Examples 1 to 3 had a uniform size of pores opened on the surface and the distribution state of the surface openings, and was a better polyimide porous membrane.

Claims

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 structural unit (a) in which the organic fine particles (B) are derived from a vinyl-based monomer and
A varnish composition containing vinyl-based resin particles which are polymers having a structural unit (b1) derived from a compound represented by the following general formula (I), which is different from the structural unit (a).

[During the ceremony,
m represents an integer of 1 to 3 and represents
R represents a group represented by the following formula (i) or formula (ii).

(In the formula, R 1 represents a hydrogen atom or a methyl group),
AO represents an alkyleneoxy group having 2 to 4 carbon atoms, and n represents an integer of 0 to 100.
X represents a hydrogen atom or -SO 3 M, -COOM and -PO 3 M (in the formula, M represents an alkali metal atom, an alkaline earth metal atom, an ammonium group or an organic ammonium group). Represents an anionic hydrophilic group selected from the group consisting of. ]
The structural unit (a) derived from the vinyl-based monomer includes a structural unit (a0) derived from a monofunctional vinyl-based monomer and a structural unit (a3) derived from a polyfunctional vinyl-based monomer. The varnish composition according to claim 1.
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 structural unit (a0) in which the organic fine particles (B) are derived from a monofunctional vinyl-based monomer and
The structural unit (a3) derived from the polyfunctional vinyl-based monomer and
Vinyl-based resin particles for producing a porous membrane, which is a polymer having a structural unit (b0) derived from a reactive emulsifier.
The ratio of the structural unit (a0) is 88 to 99% by mass, the ratio of the structural unit (a3) is 0.9 to 10% by mass, and the ratio of the structural unit (b0) is 0.1 to 2% by mass. A varnish composition containing vinyl-based resin particles for producing a porous film.
A coating film forming step of applying the varnish composition according to any one of claims 1 to 3 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, wherein the solvent (S) is removed 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 4, 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 5, further comprising a winding step of winding the precursor film into a roll 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 4 to 6 and then removing the organic fine particles (B) from the precursor membrane. Membrane manufacturing method.