CN113201190A

CN113201190A - Aqueous composition containing polyimide precursor, method for producing polyimide film, and method for producing porous polyimide film

Info

Publication number: CN113201190A
Application number: CN202110059607.7A
Authority: CN
Inventors: 鹿岛保伸; 吉村耕作; 佐佐木知也; 中田幸佑; 广瀬英一
Original assignee: Fujifilm Business Innovation Corp
Current assignee: Fujifilm Business Innovation Corp
Priority date: 2020-01-30
Filing date: 2021-01-15
Publication date: 2021-08-03

Abstract

The present invention relates to an aqueous composition containing a polyimide precursor, a method for producing a polyimide film, and a method for producing a porous polyimide film. An aqueous composition containing a polyimide precursor, which comprises at least one polymer material selected from the group consisting of water-insoluble fibrous organic substances and polyalkylene oxides having a viscosity average molecular weight of 500 ten thousand or more, a polyimide precursor, particles, and water.

Description

Aqueous composition containing polyimide precursor, method for producing polyimide film, and method for producing porous polyimide film

Technical Field

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

Background

Polyimide resins are materials having excellent properties in mechanical strength, chemical stability and heat resistance, and polyimide films having these properties have attracted attention.

Polyimide membranes are sometimes used in applications such as filters (e.g., filters, oil filters, fuel filters, etc.), secondary battery applications (e.g., separators for lithium secondary batteries, holders for solid electrolytes in all-solid-state batteries, etc.), and the like.

For example, patent document 1 describes a varnish for producing a porous film, which contains at least one resin (a) selected from the group consisting of polyamic acids, polyimides, precursors of polyamideimides and polyamideimides, fine particles (B), and a surfactant (C) containing a silicon atom and/or a fluorine atom having an alkylene oxide chain.

Patent document 1: japanese patent laid-open publication No. 2016-056225

When a polyimide film is produced using an aqueous composition containing a polyimide precursor, which contains a polyimide precursor, particles and water, the amount of the particles changes in the thickness direction of the polyimide film if the particles precipitate or float during the production process.

If the amount of particles varies in the thickness direction of the polyimide film, the physical properties vary in the thickness direction of the polyimide film (for example, in the case of a porous polyimide film, the porosity varies in the thickness direction), which is not preferable in some cases.

Disclosure of Invention

The present invention addresses the problem of providing an aqueous composition containing a polyimide precursor, which can suppress the precipitation of particles during the production of a polyimide film, compared with a composition containing a polyimide precursor, a polyalkylene oxide having a viscosity average molecular weight of less than 500 ten thousand, or a water-insoluble fibrous organic substance, namely, carboxymethyl cellulose, particles, and water.

The above problems can be solved by the following means. That is to say that the first and second electrodes,

<1>

an aqueous composition containing a polyimide precursor, which comprises at least one polymer material selected from the group consisting of water-insoluble fibrous organic substances and polyalkylene oxides having a viscosity average molecular weight of 500 ten thousand or more, a polyimide precursor, particles, and water.

<2>

The polyimide precursor-containing aqueous composition according to <1>, wherein,

the content of the polymer material is 0.5 mass% or more and 8.0 mass% or less with respect to the polyimide precursor.

<3>

The polyimide precursor-containing aqueous composition according to <2>, wherein,

the content of the polymer material is 1.0 mass% or more and 3.0 mass% or less with respect to the polyimide precursor.

<4>

The polyimide precursor-containing aqueous composition according to any one of <1> to <3>, wherein,

the content of the polymer material is 0.05 mass% or more and 15 mass% or less with respect to the particles.

<5>

The polyimide precursor-containing aqueous composition according to <4>, wherein,

the content of the polymer material is 0.1 mass% or more and 2.0 mass% or less with respect to the particles.

<6>

The polyimide precursor-containing aqueous composition according to any one of <1> to <5>, wherein,

the polyalkylene oxide is polyethylene oxide.

<7>

The polyimide precursor-containing aqueous composition according to any one of <1> to <6>, wherein,

the polyalkylene oxide has a viscosity-average molecular weight of 600 to 1,100 ten thousand.

<8>

The polyimide precursor-containing aqueous composition according to any one of <1> to <7>, wherein,

the fiber diameter of the water-insoluble fibrous organic substance is 1nm to 500 nm.

<9>

The polyimide precursor-containing aqueous composition according to any one of <1> to <8>, wherein,

the fiber length of the water-insoluble fibrous organic substance is 10nm to 10,000 nm.

<10>

The polyimide precursor-containing aqueous composition according to any one of <1> to <9>, wherein,

the particles are resin particles.

<11>

The polyimide precursor-containing aqueous composition according to <10>, wherein,

the resin particles are particles containing a resin containing a constituent unit derived from styrene.

<12>

The polyimide precursor-containing aqueous composition according to any one of <1> to <11>, wherein,

the content of the water is 70% by mass or more based on the total mass of the aqueous composition containing the polyimide precursor.

<13>

The polyimide precursor-containing aqueous composition according to any one of <1> to <12>, wherein,

the viscosity at 25 ℃ is 1 pas or more and 200 pas or less.

<14>

A method for producing a polyimide film, comprising the steps of:

a step of forming a coating film by applying the polyimide precursor-containing aqueous composition according to any one of <1> to <13> onto a substrate;

a step of drying the coating film to form a coating film containing at least one polymer material selected from the group consisting of the water-insoluble fibrous organic substance and a polyalkylene oxide having a viscosity average molecular weight of 500 ten thousand or more, the polyimide precursor, and the particles; and

and a step of imidizing the polyimide precursor contained in the coating film to form a polyimide film.

<15>

A method for producing a porous polyimide film, comprising the steps of:

a step of drying the coating film to form a coating film containing at least one polymer material selected from the group consisting of the water-insoluble fibrous organic substance and a polyalkylene oxide having a viscosity average molecular weight of 500 ten thousand or more, the polyimide precursor, and the particles;

a step of imidizing the polyimide precursor contained in the coating film to form a polyimide film; and

and removing the particles from the coating film or the polyimide film.

Effects of the invention

According to the invention of <1>, there is provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles in the production of a polyimide film, as compared with the case where the aqueous composition contains a polyalkylene oxide having a viscosity average molecular weight of less than 500 ten thousand or a water-insoluble fibrous organic substance, that is, carboxymethyl cellulose, a polyimide precursor, particles and water.

According to the invention as described in <2> or <3>, there is provided an aqueous composition containing a polyimide precursor, in which precipitation or floating of particles can be suppressed in a process of producing a polyimide film, as compared with a case where the content of the polymer material is less than 0.5% by mass or more than 8.0% by mass relative to the polyimide precursor.

According to the invention as described in <4> or <5>, there is provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles in the production process of a polyimide film, as compared with a case where the content of the polymer material is less than 0.05% by mass or more than 15% by mass relative to the particles.

According to the invention as described in <6>, there can be provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles in the production of a polyimide film, as compared with the case where the polyalkylene oxide is polypropylene oxide.

According to the invention as recited in <7>, there can be provided an aqueous composition containing a polyimide precursor which can suppress precipitation or floating of particles in the production of a polyimide film as compared with the case where the viscosity average molecular weight of the polyalkylene oxide is less than 600 ten thousand or more than 1,100 ten thousand.

According to the invention of <8>, there can be provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles during production of a polyimide film, as compared with the case where the fiber diameter of the water-insoluble fibrous organic substance is larger than 500 nm.

According to the invention as <9>, there can be provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles during production of a polyimide film, as compared with the case where the fiber length of the water-insoluble fibrous organic substance is less than 10nm or more than 10,000 nm.

According to the invention of <10>, there can be provided an aqueous composition containing a polyimide precursor, in which the specific gravity of resin particles is closer to that of a solution than in the case where the particles are inorganic particles, and the movement of the particles is more easily suppressed.

According to the invention of <11>, there can be provided an aqueous composition containing a polyimide precursor, in which the specific gravity of the particles is closer to the specific gravity of the solution than when the particles are polymethyl methacrylate-based particles, and the movement of the particles is easily suppressed.

According to the invention as described in <12>, there can be provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles in the production of a polyimide film, compared with a case where the content of water is less than 70% by mass based on the total mass of the aqueous composition containing a polyimide precursor.

According to the invention as described in <13>, there can be provided an aqueous composition containing a polyimide precursor, which can suppress precipitation or floating of particles in the production of a polyimide film, as compared with the case where the viscosity at 25 ℃ is more than 100 pas.

According to the invention of <14>, there is provided a method for producing a polyimide film, which can provide a polyimide film having less variation in the amount of particles in the thickness direction than when an aqueous polyimide precursor-containing composition containing a carboxymethyl cellulose, a polyimide precursor, particles and water, which is a polyalkylene oxide or a water-insoluble fibrous organic substance having a viscosity average molecular weight of less than 500 ten thousand, is used.

According to the invention of <15>, there is provided a method for producing a polyimide film, which can provide a porous polyimide film having less change in porosity in the thickness direction than when an aqueous composition containing a polyimide precursor, which contains a polyalkylene oxide having a viscosity average molecular weight of less than 500 ten thousand or a water-insoluble fibrous organic substance, that is, carboxymethyl cellulose, a polyimide precursor, particles and water, is used.

Drawings

Embodiments of the present invention will be described in detail with reference to the following drawings.

FIG. 1 is a schematic view showing a porous polyimide film produced using the polyimide precursor-containing aqueous composition according to the present embodiment;

fig. 2 is a schematic partial cross-sectional view showing an example of a lithium ion secondary battery including a porous polyimide film produced using the polyimide precursor-containing aqueous composition according to the present embodiment as a separator for a lithium ion secondary battery;

fig. 3 is a schematic partial cross-sectional view showing an example of an all-solid-state battery including a porous polyimide film produced using the aqueous composition containing a polyimide precursor according to the present embodiment.

Description of the symbols

10-porous polyimide film

10A-holes

31-substrate

51-peeling layer

100-lithium ion secondary battery

200-all-solid-state battery

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail.

In the present embodiment, the concept of "film" includes not only substances generally called "films" but also substances generally called "thin films" and "sheets".

In the present embodiment, the term "solid component" refers to a component other than water and a water-soluble organic solvent (i.e., an aqueous solvent).

< aqueous composition containing polyimide precursor >

The polyimide precursor-containing aqueous composition according to the present embodiment (hereinafter also referred to as "the aqueous composition according to the present embodiment") contains at least one polymer material selected from the group consisting of a water-insoluble fibrous organic substance and a polyalkylene oxide having a viscosity average molecular weight of 500 ten thousand or more, a polyimide precursor, particles, and water.

Here, the "aqueous composition" refers to a composition that contains water and has a total content of water and a water-soluble organic solvent (i.e., an aqueous solvent) of 50 mass% or more relative to the total mass of the aqueous composition according to the present embodiment.

The aqueous composition according to the present embodiment having the above-described configuration can suppress precipitation or floating of particles in the process of producing a polyimide film.

The reason is not clear, but is presumed as follows.

It is considered that the viscosity average molecular weight of the polyalkylene oxide contained in the aqueous composition according to the present embodiment is 500 ten thousand or more, and the polyalkylene oxide has a high molecular weight and contains a large amount of alkylene oxide (i.e., composed of — (C)_mH_2mO) -and m represents an integer of 2 or more), and therefore adjacent molecules interact with each other in an aqueous composition containing water to form a mesh structure.

In the aqueous composition containing water, the fibers are entangled with each other and are connected at intersections, whereby the water-insoluble fibrous organic material maintains a mesh structure.

Therefore, it is assumed that the particles in the aqueous composition according to the present embodiment are captured by the mesh structure to suppress sedimentation or floating.

In particular, since the water-insoluble fibrous organic substance and/or the polyalkylene oxide having a viscosity average molecular weight of 500 ten thousand or more can suppress precipitation or floating of particles even when added in a small amount, it is presumed that it is difficult to increase the viscosity of the aqueous composition according to the present embodiment and to affect the physical properties of the polyimide film (including the porous polyimide film) to be produced.

[ polyimide precursor ]

The aqueous composition according to the present embodiment includes a polyimide precursor.

The polyimide precursor is a resin having a repeating unit represented by the general formula (I) (polyimide precursor).

[ chemical formula 1]

(in the general formula (I), A represents a 4-valent organic group, and B represents a 2-valent organic group.)

In the general formula (I), the 4-valent organic group represented by a is a residue obtained by removing 4 carboxyl groups from tetracarboxylic dianhydride as a raw material.

On the other hand, the 2-valent organic group represented by B is a residue obtained by removing 2 amino groups from a diamine as a raw material.

That is, the polyimide precursor having the repeating unit represented by the general formula (I) is a polymer of tetracarboxylic dianhydride and diamine.

The tetracarboxylic dianhydride may be an aromatic or aliphatic compound, and is preferably an aromatic compound. That is, in the general formula (I), the 4-valent organic group represented by a is preferably an aromatic organic group, for example.

Examples of the aromatic tetracarboxylic acid dianhydride include pyromellitic acid dianhydride, 3 ', 4, 4 ' -benzophenone tetracarboxylic acid dianhydride, 3 ', 4, 4 ' -biphenyl sulfone tetracarboxylic acid dianhydride, 1, 4, 5, 8-naphthalene tetracarboxylic acid dianhydride, 2, 3, 6, 7-naphthalene tetracarboxylic acid dianhydride, 3 ', 4, 4 ' -diphenyl ether tetracarboxylic acid dianhydride, 3 ', 4, 4 ' -dimethyldiphenylsilane tetracarboxylic acid dianhydride, 3 ', 4, 4 ' -tetraphenylsilane tetracarboxylic acid dianhydride, 1, 2, 3, 4-furan tetracarboxylic acid dianhydride, 4, 4 ' -bis (3, 4-dicarboxyphenoxy) diphenyl sulfide dianhydride, 4, 4 ' -bis (3, 4-dicarboxyphenoxy) diphenyl sulfone dianhydride, 4, 4 ' -bis (3, 4-dicarboxyphenoxy) diphenylpropane dianhydride, 3, 3 ', 4, 4' -perfluoroisopropyldiphthalic dianhydride, 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride, 2, 3, 3 ', 4' -biphenyltetracarboxylic dianhydride, bis (phthalic acid) phenylphosphine oxide dianhydride, p-phenylene-bis (triphenylphthalic acid) dianhydride, m-phenylene-bis (triphenylphthalic acid) dianhydride, bis (triphenylphthalic acid) -4, 4 '-diphenyl ether dianhydride, bis (triphenylphthalic acid) -4, 4' -diphenylmethane dianhydride.

Examples of the aliphatic tetracarboxylic acid dianhydride include butanetetracarboxylic acid dianhydride, 1, 2, 3, 4-cyclobutanetetracarboxylic acid dianhydride, 1, 3-dimethyl-1, 2, 3, 4-cyclobutanetetracarboxylic acid dianhydride, 1, 2, 3, 4-cyclopentanetetracarboxylic acid dianhydride, 2, 3, 5-tricarboxycyclopentylacetic acid dianhydride, aliphatic or alicyclic tetracarboxylic acid dianhydrides such as 3, 5, 6-tricarboxynorbornane-2-acetic acid dianhydride, 2, 3, 4, 5-tetrahydrofurantetracarboxylic acid dianhydride, 5- (2, 5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1, 2-dicarboxylic acid dianhydride, bicyclo [2, 2, 2] -oct-7-ene-2, 3, 5, 6-tetracarboxylic acid dianhydride, and the like; 1, 3, 3a, 4, 5, 9 b-hexahydro-2, 5-dioxy-3-furanyl) -naphthalene [1, 2-c ] furan-1, 3-dione, 1, 3, 3a, 4, 5, 9 b-hexahydro-5-methyl-5- (tetrahydro-2, 5-dioxy-3-furanyl) -naphthalene [1, 2-c ] furan-1, 3-dione, 1, 3, 3a, aliphatic tetracarboxylic acid dianhydrides having an aromatic ring such as 4, 5, 9 b-hexahydro-8-methyl-5- (tetrahydro-2, 5-dioxy-3-furyl) -naphthalene [1, 2-c ] furan-1, 3-dione.

Among these, as the tetracarboxylic acid dianhydride, for example, an aromatic tetracarboxylic acid dianhydride is preferable, and specifically, pyromellitic acid dianhydride, 3, 3 ', 4, 4' -biphenyltetracarboxylic acid dianhydride, 2, 3, 3 ', 4' -biphenyltetracarboxylic acid dianhydride, 3, 3 ', 4, 4' -diphenyl ether tetracarboxylic acid dianhydride, and 3, 3 ', 4, 4' -benzophenonetetracarboxylic acid dianhydride are preferable, and pyromellitic acid dianhydride, 3, 3 ', 4, 4' -biphenyltetracarboxylic acid dianhydride, and 3, 3 ', 4, 4' -benzophenonetetracarboxylic acid dianhydride are more preferable, and 3, 3 ', 4, 4' -biphenyltetracarboxylic acid dianhydride is particularly preferable.

The tetracarboxylic dianhydride may be used alone or in combination of two or more.

When two or more kinds are used in combination and at the same time, the aromatic tetracarboxylic acid dianhydride and the aliphatic tetracarboxylic acid dianhydride may be used separately and at the same time, or the aromatic tetracarboxylic acid dianhydride and the aliphatic tetracarboxylic acid dianhydride may be combined.

On the other hand, the diamine compound is a diamine compound having 2 amino groups in the molecular structure. The diamine compound may be an aromatic compound or an aliphatic compound, and is preferably an aromatic compound. That is, in the general formula (I), the 2-valent organic group represented by B is preferably an aromatic organic group, for example.

Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4 '-diaminodiphenylmethane, 4' -diaminodiphenylethane, 4 '-diaminodiphenylether, 4' -diaminodiphenylsulfide, 4 '-diaminodiphenylsulfone, 1, 5-diaminonaphthalene, 3, 3-dimethyl-4, 4' -diaminobiphenyl, 5-amino-1- (4 '-aminophenyl) -1, 3, 3-trimethylindane, and 6-amino-1- (4' -aminophenyl) -1Phenyl) -1, 3, 3-trimethylindane, 4 ' -diaminobenzanilide, 3, 5-diamino-3 ' -trifluoromethylbenzanilide, 3, 5-diamino-4 ' -trifluoromethylbenzanilide, 3, 4 ' -diaminodiphenyl ether, 2, 7-diaminofluorene, 2-bis (4-aminophenyl) hexafluoropropane, 4 ' -methylene-bis (2-chloroaniline), 2 ', 5, 5 ' -tetrachloro-4, 4 ' -diaminobiphenyl, 2 ' -dichloro-4, 4 ' -diamino-5, 5 ' -dimethoxybiphenyl, 3, 3 ' -dimethoxy-4, 4 ' -diaminobiphenyl, 4, 4 '-diamino-2, 2' -bis (trifluoromethyl) biphenyl, 2-bis [4- (4-aminophenoxy) phenyl]Propane, 2-bis [4- (4-aminophenoxy) phenyl]Hexafluoropropane, 1, 4-bis (4-aminophenoxy) benzene, 4 ' -bis (4-aminophenoxy) -biphenyl, 1, 3 ' -bis (4-aminophenoxy) benzene, 9-bis (4-aminophenyl) fluorene, 4 ' - (p-phenyleneisopropyl) dianiline, 4 ' - (m-phenyleneisopropyl) dianiline, 2 ' -bis [4- (4-amino-2-trifluoromethylphenoxy) phenyl ] aniline]Hexafluoropropane, 4' -bis [4- (4-amino-2-trifluoromethyl) phenoxy]Aromatic diamines such as octafluorobiphenyl; aromatic diamines having 2 amino groups bonded to an aromatic ring and hetero atoms other than the nitrogen atom of the amino group, such as diaminotetraphenylthiophene; 1, 1-m-xylylenediamine, 1, 3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4-diaminoheptamethylenediamine, 1, 4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadiene diamine, hexahydro-4, 7-methyleneindanyldimethylenediamine, tricyclo [6, 2, 1,0^2.7]Aliphatic diamines such as undecene dimethyl diamine and 4, 4' -methylenebis (cyclohexylamine), and alicyclic diamines.

Among them, the diamine compound is preferably an aromatic diamine compound, and specifically, for example, p-phenylenediamine, m-phenylenediamine, 4 '-diaminodiphenylmethane, 4' -diaminodiphenyl ether, 3, 4 '-diaminodiphenyl ether, 4' -diaminodiphenyl sulfide, 4 '-diaminodiphenyl sulfone are preferable, and 4, 4' -diaminodiphenyl ether and p-phenylenediamine are particularly preferable.

The diamine compound may be used alone or in combination of two or more. When two or more kinds are used in combination and at the same time, the aromatic diamine compound or the aliphatic diamine compound may be used at the same time, or the aromatic diamine compound and the aliphatic diamine compound may be combined.

The weight average molecular weight of the polyimide precursor used in the present embodiment is, for example, preferably 5000 or more and 300000 or less, and more preferably 10000 or more and 150000 or less.

The weight average molecular weight of the polyimide precursor was measured by a Gel Permeation Chromatography (GPC) method under the following measurement conditions.

Color bars: TOSOH CORPORATION TSKgel alpha-M (7.8mm I.D. 30cm)

Eluent: DMF (dimethylformamide)/30 mM LiBr/60mM phosphoric acid

Flow rate: 0.6mL/min

Injection amount: 60uL

The detector: RI (differential refractive index detector)

The content of the polyimide precursor is, for example, preferably 0.1 mass% or more and 10 mass% or less, and more preferably 0.5 mass% or more and 8 mass% or less, based on the total mass of the aqueous composition according to the present embodiment.

[ particle ]

The aqueous composition according to the present embodiment includes particles.

The particles contained in the aqueous composition according to the present embodiment are in a dispersed state without being dissolved.

The material of the particles is not particularly limited as long as the particles are insoluble in the aqueous composition according to the present embodiment, and the particles are roughly classified into resin particles and inorganic particles described below.

In the present embodiment, the phrase "the particles do not dissolve" means that the particles do not dissolve in a target solution (specifically, an aqueous solvent contained in an aqueous composition containing a polyimide precursor) at 25 ℃, and further, the particles dissolve in a range of 3 mass% or less with respect to the target solution.

The particles may be contained in the polyimide film produced using the aqueous composition according to the present embodiment, or may be removed from the produced polyimide film.

The volume average particle diameter D50v of the particles is not particularly limited. The volume average particle diameter D50v of the particles is preferably 0.1 μm or more and 10 μm or less, for example. The lower limit of the volume average particle diameter D50v of the particles may be 0.2 μm or more, may be 0.3 μm or more, may be 0.4 μm or more, and may be 0.5 μm or more. The upper limit of the volume average particle diameter D50v of the particles may be 7 μm or less, 5 μm or less, 3 μm or less, or 2 μm or less.

The volume particle size distribution index (GSDv) of the particles is, for example, preferably 1.30 or less, more preferably 1.25 or less, and most preferably 1.20 or less.

The particle size distribution of the particles in the aqueous composition according to the present embodiment is measured by the following method.

The composition to be measured was diluted, and the particle size distribution of the particles in the solution was measured using a Coulter counter LS13 (manufactured by Beckman Coulter, inc.). Based on the measured particle size distribution, the particle size distribution is measured by plotting a volume cumulative distribution from the small diameter side for the divided particle size range (channel).

In the volume cumulative distribution drawn from the small diameter side, the particle diameter at cumulative 16% is set as the volume particle diameter D16v, the particle diameter at cumulative 50% is set as the volume average particle diameter D50v, and the particle diameter at cumulative 84% is set as the volume particle diameter D84 v.

Further, the volume particle size distribution index (GSDv) of the particles was calculated from the particle size distribution obtained by the above-mentioned method as (D84v/D16v)^1/2。

When it is difficult to measure the particle size distribution by the above method, the particle size distribution of the particles in the aqueous composition according to the present embodiment can be measured by a method such as a dynamic light scattering method.

The shape of the particles is preferably spherical, for example.

When the particles are removed from the polyimide film using spherical particles to produce a porous polyimide film, a porous polyimide film having spherical pores can be obtained.

In the present embodiment, "spherical" in the particles means both spherical and substantially spherical (a shape close to a sphere).

Specifically, the particles are present so that the ratio of the major axis to the minor axis (major axis/minor axis) is 1 or more and less than 1.5, and the proportion of the particles is more than 80%. The proportion of particles having a ratio of the major axis to the minor axis (major axis/minor axis) of 1 or more and less than 1.5 is preferably 90% or more, for example. The ratio of the major axis to the minor axis is approximately spherical as it approaches 1.

As the particles, any of resin particles and inorganic particles can be used, and resin particles are preferably used for the following reasons, for example.

Since both the resin particles and the polyimide precursor are organic materials, particle dispersibility in the aqueous composition containing a polyimide precursor or in a coating film formed from the aqueous composition containing a polyimide precursor, surface adhesion to a polyimide precursor, and the like can be improved more easily than when inorganic particles are used. In addition, in the imidization step in the production of the polyimide film, the resin particles easily absorb volume shrinkage, and therefore, cracks generated in the polyimide film due to the volume shrinkage are likely to be less likely to occur.

Specific materials of the resin particles and the inorganic particles are described below.

(resin particles)

The resin particles are not particularly limited as long as they are insoluble in the aqueous composition containing the polyimide precursor (specifically, the aqueous solvent contained in the polyimide precursor solution). For example, resin particles composed of a resin other than polyimide are preferable,

specific examples of the resin particles include vinyl resins represented by polystyrenes, poly (meth) acrylics, polyvinyl acetates, polyvinyl alcohols, polyvinyl butyrals, polyvinyl ethers, and the like; condensation resins represented by polyesters, polyurethanes, polyamides, and the like; hydrocarbon resins represented by polyethylene, polypropylene, polybutadiene, and the like; resin particles such as fluorine-based resins represented by polytetrafluoroethylene, polyvinyl fluoride, and the like.

Here, "(meth) acrylic acid" means that both "acrylic acid" and "methacrylic acid" are included. And, (meth) acrylic acids include (meth) acrylic acid, (meth) acrylic acid esters, (meth) acrylamides.

The resin particles may or may not be crosslinked.

When the resin particles are based on vinyl resin particles, they can be obtained by addition polymerization of monomers.

Examples of the monomer for obtaining the vinyl resin include styrenes having a styrene skeleton such as styrene, alkyl-substituted styrenes (e.g., α -methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, etc.; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, lauryl (meth) acrylate, and 2-ethylhexyl (meth) acrylate; vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and vinyl isopropenyl ketone; acids such as (meth) acrylic acid, maleic acid, cinnamic acid, fumaric acid, and vinylsulfonic acid; and bases such as ethyleneimine, vinylpyridine, and vinylamine.

The vinyl resin may be a resin using these monomers alone or a resin using a copolymer of two or more monomers.

As other monomers, monofunctional monomers such as vinyl acetate, difunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, nonane diacrylate and decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate and trimethylolpropane trimethacrylate may be used in combination.

By using a bifunctional monomer and a polyfunctional monomer at the same time, crosslinked resin particles can be obtained.

From the viewpoint of the productivity and the suitability for the particle removal step described later, the resin particles are preferably those based on, for example, polystyrenes, poly (meth) acrylics or polyesters, and more preferably those based on polystyrenes, styrene- (meth) acrylic copolymers or poly (meth) acrylics.

Here, polystyrenes refer to resins containing constituent units derived from styrenic monomers (monomers having a styrene skeleton). More specifically, for example, when the total of the constituent units constituting the resin is 100 mol%, the polystyrenes preferably contain 30 mol% or more of the constituent units, and more preferably 50 mol% or more of the constituent units.

The poly (meth) acrylic acid-based resin refers to a methacrylic resin and an acrylic resin, and includes a resin derived from a constituent unit of a (meth) acrylic monomer (a monomer having a (meth) acryloyl skeleton). More specifically, for example, when the total ratio of the constituent units derived from (meth) acrylic acid and/or the constituent units derived from (meth) acrylic acid ester (total of the compositions in the polymer) is 100 mol%, the poly (meth) acrylic acid compound preferably contains 30 mol% or more of the constituent units, and more preferably 50 mol% or more of the constituent units.

The polyester is a resin obtained by polycondensation of a polycarboxylic acid and a polyol, and has an ester bond in the main chain.

From the viewpoint of a small difference in specific gravity from the solution and easy suppression of the movement of the particles, the resin particles are preferably resin particles based on a resin including styrene-derived constituent units, and for example, when the total of constituent units constituting the resin is 100 mol%, the resin particles preferably include 30 mol% or more of styrene-derived constituent units, more preferably 50 mol% or more, further preferably 80 mol% or more, and particularly preferably 100 mol%.

These resin particles may be used alone or in combination of two or more.

The resin particles preferably retain the shape thereof, for example, during the production process of the aqueous composition according to the present embodiment, and during the application of the aqueous composition according to the present embodiment and the drying of the coating film (before removal of the resin particles) in the production of the polyimide film. From these viewpoints, the glass transition temperature of the resin particles is, for example, preferably 60 ℃ or higher, preferably 70 ℃ or higher, and more preferably 80 ℃ or higher.

The glass transition temperature is determined from a Differential Scanning Calorimetry (DSC) curve, more specifically, according to JIS K7121: 1987 "method for measuring transition temperature of Plastic", the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature.

(inorganic particles)

Specific examples of the inorganic particles include silica (silicon dioxide) particles, magnesium oxide particles, alumina particles, zirconia particles, calcium carbonate particles, calcium oxide particles, titanium dioxide particles, zinc oxide particles, and cerium oxide particles.

As described above, the shape of the particles is preferably, for example, spherical. From this viewpoint, the inorganic particles are preferably silica particles, magnesia particles, calcium carbonate particles, and alumina particles, more preferably silica particles, titania particles, and alumina particles, and still more preferably silica particles.

These inorganic particles may be used alone or in combination of two or more.

When the wettability and dispersibility of the inorganic particles with respect to the solvent of the aqueous composition according to the present embodiment are insufficient, the surfaces of the inorganic particles may be modified as necessary.

Examples of the method for modifying the surface of the inorganic particles include a method of treating with an alkoxysilane having an organic group represented by a silane coupling agent; and a method of coating with an organic acid such as oxalic acid, citric acid, or lactic acid.

The content of the particles may be determined depending on the use of the polyimide film, and is, for example, preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 20% by mass or less, and still more preferably 1% by mass or more and 20% by mass or less, based on the total mass of the aqueous composition according to the present embodiment.

In the aqueous composition according to the present embodiment, the content of the particles is, for example, preferably 10% by mass or more and 120% by mass or less, more preferably 25% by mass or more and 110% by mass or less, and still more preferably 30% by mass or more and 100% by mass or less with respect to the polyimide precursor.

By setting the content of such particles, a porous polyimide film having a high porosity can be easily obtained while maintaining the mechanical strength. The porous polyimide film having the mechanical strength and high porosity is effective as a separator for a secondary battery.

[ Water-insoluble fibrous organic substance and polyalkylene oxide having a viscosity average molecular weight of 500 ten thousand or more ]

The aqueous composition according to the present embodiment contains at least one polymer material selected from the group consisting of a water-insoluble fibrous organic substance and a polyalkylene oxide having a viscosity-average molecular weight of 500 ten thousand or more (hereinafter simply referred to as a high-molecular-weight polyalkylene oxide).

Hereinafter, the water-insoluble fibrous organic material and the high molecular weight polyalkylene oxide are collectively referred to as a specific polymer material.

[ Water-insoluble fibrous organic Material ]

The water-insoluble fibrous organic substance is a long and thin linear solid, and has a linear diameter of 1nm or more.

The type of fibrous organic material is not particularly limited, and is preferably a resin fiber, a plant fiber, or the like.

The term "water-insoluble fibrous organic material" means that the amount of fibrous organic material dissolved is less than 1 part by mass per 100 parts by mass of water at 25 ℃.

Examples of the material constituting the water-insoluble fibrous organic material include plant fibers (specifically, cellulose fibers) and aramid fibers.

The fiber diameter of the water-insoluble fibrous organic substance is preferably, for example, 1nm or more and 500nm or less from the viewpoint of suppressing precipitation or floatation of particles.

The fiber length of the water-insoluble fibrous organic substance is preferably 10nm or more and 10,000nm or less, for example, from the viewpoint of suppressing precipitation or floatation of particles.

The fiber diameter and the fiber length of the water-insoluble fibrous organic substance can be measured by the following methods.

As for the fiber length, the length of 20 fibers was measured using a Scanning Electron Microscope (SEM) and the average value thereof was taken. With respect to the fiber diameter, the maximum diameter of 20 fibers was measured in units of 1 end of each fiber and the average value thereof was taken.

The water-insoluble fibrous organic material is obtained by microfibrillating water-insoluble fibers as a raw material.

Here, microfibrillation refers to a state in which the raw material fiber is shredded into microfibers (microfibers) that constitute the essential component thereof, or a state in which microfibers in the raw material fiber are present on the surface of the fiber and are fluffy.

External force such as mechanical shearing force (e.g., high-pressure homogenizer) is used for microfibrillation, and the external force is changed to micronize the raw material fiber to the fiber diameter.

That is, the water-insoluble fibrous organic material used in the present embodiment may also be referred to as microfibrillated fiber.

As the water-insoluble fibrous organic substance, commercially available products can be used.

Commercially available products of water-insoluble fibrous organic materials include Serish (micro fibrous cellulose) manufactured by Daicel Miraziu Ltd., Tiara (micro fibrous aramid), and BiNFi-s (binfis, micro fibrous cellulose) manufactured by Sugino Machine Limited.

[ polyalkylene oxide having a viscosity average molecular weight of 500 tens of thousands or more ]

The polyalkylene oxide is a polyalkylene oxide comprising a copolymer of formula (I) and (II)_mH_2mO)_nA polymer compound which is a constituent unit of the above-mentioned formula (I), and is soluble in water. Here, m and n each independently represent an integer of 2 or more.

M is, for example, preferably 2 to 6, more preferably 2 to 3, from the viewpoint of easy availability, and the like, and is, for example, particularly preferably 2, from the viewpoint of the formation of a mesh structure, and from the viewpoint of high affinity with the particle surface and easy inhibition of the movement of the particles. That is, the polyalkylene oxide is preferably polyethylene oxide, for example, from the viewpoint that it has a higher affinity with the particle surface than polypropylene oxide and tends to inhibit the movement of the particles.

The number n may be an integer satisfying a viscosity average molecular weight of 500 ten thousand or more.

High molecular weight polyalkylene oxides are obtainable by ring-opening polymerization of cyclic ethers such as ethylene oxide, propylene oxide, oxetane and the like.

In addition, the terminal of the high molecular weight polyalkylene oxide may be modified within a range in which the effect of suppressing precipitation or floating of particles is not impaired.

The viscosity average molecular weight of the high molecular weight polyalkylene oxide is, for example, preferably 600 to 1,100 ten thousand, more preferably 700 to 1,100 ten thousand, and still more preferably 800 to 1,000 ten thousand, from the viewpoint of suppressing precipitation or floating of particles and from the viewpoint of easy availability.

The viscosity average molecular weight of the high molecular weight polyalkylene oxide can be determined by the following method.

1g of a measurement sample was uniformly dissolved in 100cm of methylene chloride³The specific viscosity η sp is measured by Ubbelohde viscometer under the measuring environment of 25 ℃, and the specific viscosity η sp/c is [ [ eta ] +0.45 [ eta ] ]²c (wherein c is concentration [ g/cm ]³]) Obtaining limiting viscosity [ eta ] (cm)³(g), and the viscosity average molecular weight is determined by the following formula (I) given by h.schnell.

Formula (I): [ eta ] -1.23X 10^-4Mv^0.83

As the high molecular weight polyalkylene oxide, commercially available products can be used.

Commercially available products of high molecular weight polyalkylene oxide include SUMITOMO SEIKA CHEMICALS CO, PEO (registered trademark) series of LTD (specifically, PEO-29, PEO-27, etc.), Alcox series of Meisei Chemical Works, Ltd (specifically, E-300, etc.), and the like.

In the aqueous composition according to the present embodiment, the specific polymer material may be used alone or in combination of two or more. Specifically, the specific polymer material may be one or two or more fibrous organic substances used alone or in combination, one or two or more high molecular weight polyalkylene oxides used alone or in combination, or one or more fibrous organic substances and one or more high molecular weight polyalkylene oxides used in combination.

The content of the specific polymer material is, for example, preferably 0.5% by mass or more and 8.0% by mass or less, more preferably 1.0% by mass or more and 3.0% by mass or less, and further preferably 1.5% by mass or more and 2.0% by mass or less with respect to the polyimide precursor.

The specific polymer material is a component that is difficult to remove in the coating and drying steps in the production process of the polyimide film, and therefore, for example, it is preferable to use a small amount.

In the aqueous composition according to the present embodiment, the content of the specific polymer material is, for example, preferably 0.05% by mass or more and 15.0% by mass or less, more preferably 0.1% by mass or more and 2.0% by mass or less, and further preferably 0.2% by mass or more and 1.5% by mass or less with respect to the particles, from the viewpoint of suppressing precipitation or floating of the particles.

[ Water ]

The aqueous composition according to the present embodiment contains water.

Examples of the water include distilled water, ion-exchanged water, deionized water, ultrafiltration water, and pure water.

The content of water is, for example, preferably 70% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, and particularly preferably 85% by mass or more, based on the total mass of the aqueous composition according to the present embodiment.

The upper limit of the water content may be determined depending on the use of the polyimide film, and may be 90% by mass, for example.

In the aqueous composition according to the present embodiment, the content of water in the aqueous solvent containing water is, for example, preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 85% by mass or more.

Here, the aqueous solvent is a generic name of water and a water-soluble organic solvent. Here, water solubility means that the target substance is dissolved in water at 25 ℃ by 1 mass% or more.

[ other Components ]

The aqueous composition according to the present embodiment may contain other components as needed, in addition to the polyimide precursor, the particles, the specific polymer material, and water.

(Water-soluble organic solvent)

Organic amine compounds

The aqueous composition according to the present embodiment preferably contains an organic amine compound as one of the water-soluble organic solvents.

The organic amine compound is a compound that is obtained by converting a polyimide precursor (carboxyl group thereof) into an amine to improve solubility in the aqueous solvent, and also functions as an imidization accelerator. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less, for example. The organic amine compound is a compound other than the diamine compound which is a raw material of the polyimide precursor.

The organic amine compound is preferably a water-soluble compound, for example. Water solubility means that the target substance is dissolved in water at 25 ℃ by 1 mass% or more.

Examples of the organic amine compound include a primary amine compound, a secondary amine compound, and a tertiary amine compound.

Among these, the organic amine compound is preferably at least one compound selected from the group consisting of secondary amine compounds and tertiary amine compounds (particularly, tertiary amine compounds). When a tertiary amine compound or a secondary amine compound (particularly, a tertiary amine compound) is used as the organic amine compound, the solubility of the polyimide precursor in a solvent can be more easily improved, the film formation property can be more easily improved, and the storage stability of the aqueous composition according to the present embodiment can be more easily improved.

The organic amine compound may be a 1-membered amine compound, and may be a 2-membered or more polyamine compound. When the polyamine compound having 2 or more members is applied, a pseudo-crosslinked structure is easily formed between molecules of the polyimide precursor, and the storage stability of the aqueous composition according to the present embodiment is easily improved.

Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, 2-amino-2-methyl-1-propanol, and the like.

Examples of the secondary amine compound include dimethylamine, 2- (methylamino) ethanol, 2- (ethylamino) ethanol, and morpholine.

Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine (e.g., N-methylmorpholine, N-ethylmorpholine), 1, 2-dimethylimidazole, 2-ethyl-4-methylimidazole, and N-alkylpiperidine (e.g., N-methylpiperidine, N-ethylpiperidine).

Among them, for example, tertiary amine compounds are preferable, N-alkylmorpholines are more preferable, and N-methylmorpholines are particularly preferable.

The organic amine compound may be used alone or in combination of two or more.

The content of the organic amine compound is, for example, preferably 40% by mass or more and 100% by mass or less, more preferably 45% by mass or more and 90% by mass or less, and still more preferably 50% by mass or more and 80% by mass or less with respect to the polyimide precursor.

Other water-soluble organic solvents-

The aqueous composition according to the present embodiment may contain other water-soluble organic solvent (excluding the organic amine compound) as needed.

Other water-soluble organic solvents include aprotic polar solvents, water-soluble ether solvents, water-soluble ketone solvents, water-soluble alcohol solvents, and the like.

Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N-Dimethylformamide (DMF), 1, 3-dimethyl-2-imidazolidinone (DMI), N-dimethylacetamide (DMAc), N-diethylacetamide (DEAc), dimethyl sulfoxide (DMSO), Hexamethylenephosphonamide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1, 3-dimethyl-2-imidazolidinone, and the like.

The water-soluble ether solvent is a water-soluble solvent having an ether bond in one molecule.

Examples of the water-soluble ether solvent include Tetrahydrofuran (THF), dioxane, trioxane, 1, 2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and the like. Among them, tetrahydrofuran and dioxane are preferable as the water-soluble ether solvent.

The water-soluble ketone solvent is a water-soluble solvent having a ketone group in one molecule.

Examples of the water-soluble ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. Among them, acetone is preferred as the water-soluble ketone solvent.

The water-soluble alcohol solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule.

Examples of the water-soluble alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, monoalkyl ether of ethylene glycol, propylene glycol, monoalkyl ether of propylene glycol, diethylene glycol, monoalkyl ether of diethylene glycol, 1, 2-propane diol, 1, 3-butane diol, 1, 4-butane diol, 2, 3-butane diol, 1, 5-pentane diol, 2-butene-1, 4-diol, 2-methyl-2, 4-pentane diol, glycerol, 2-ethyl-2-hydroxymethyl-1, 3-propane diol, and 1, 2, 6-hexanetriol. Among them, preferable examples of the water-soluble alcohol solvent include methanol, ethanol, 2-propanol, ethylene glycol, monoalkyl ethers of ethylene glycol, propylene glycol, monoalkyl ethers of propylene glycol, diethylene glycol, and monoalkyl ethers of diethylene glycol.

One or more of the other water-soluble organic solvents may be used alone or in combination.

The boiling point of the other water-soluble organic solvent is preferably 270 ℃ or lower, more preferably 60 ℃ or higher and 250 ℃ or lower, and still more preferably 80 ℃ or higher and 230 ℃ or lower, for example. When the boiling point of the water-soluble organic solvent is in the above range, the water-soluble organic solvent hardly remains in the polyimide film, and the polyimide film having high mechanical strength can be easily obtained.

The content of the aqueous solvent containing water is, for example, preferably 75% by mass or more, and more preferably 80% by mass or more, based on the total mass of the aqueous composition according to the present embodiment.

(other additives)

The aqueous composition according to the present embodiment may contain a catalyst for accelerating the imidization reaction, a leveling material for improving the film forming quality, and the like.

As the catalyst for promoting the imidization reaction, a dehydrating agent such as an acid anhydride, an acid catalyst such as a phenol derivative, a sulfonic acid derivative, or a benzoic acid derivative, and the like can be used.

The aqueous composition according to the present embodiment may contain a conductive material (e.g., having a volume resistivity of less than 10) as a conductive agent added to impart conductivity, for example, depending on the purpose of use of the polyimide film⁷Ω · cm) or semiconductive materials (e.g. volume resistivity 10)⁷Omega cm or more and 10¹³Ω · cm or less)).

Examples of the conductive agent include carbon black (for example, acidic carbon black having a ph of 5.0 or less); metals (e.g., aluminum or nickel, etc.); metal oxides (e.g., yttrium oxide, tin oxide, etc.); and ion conductive materials (for example, potassium titanate, LiCl, and the like).

These conductive materials may be used singly or in combination of two or more.

The aqueous composition according to the present embodiment may further contain LiCoO used as an electrode of a lithium ion battery₂、LiMn₂O, and the like.

[ physical Properties ]

The viscosity of the aqueous composition according to the present embodiment at 25 ℃ is, for example, preferably 1Pa · s or more and 200Pa · s or less, and more preferably 5Pa · s or more and 180Pa · s or less.

The aqueous composition according to the present embodiment can suppress precipitation or floating of particles even if it has the viscosity described above.

The viscosity of the aqueous composition according to the present embodiment at 25 ℃ is measured using an E-type viscometer (e.g., TVE-22H, TOKI SANGYO co., LTD).

In the aqueous composition according to the present embodiment, for example, the total content of the solid content is preferably 1% by mass or more and 35% by mass or less, more preferably 3% by mass or more and 30% by mass or less, and further preferably 5% by mass or more and 25% by mass or less, based on the total mass of the aqueous composition according to the present embodiment, from the viewpoint of achieving the viscosity at 25 ℃.

< method for producing polyimide film and method for producing porous polyimide film >

The method for producing a polyimide film according to the present embodiment includes the steps of: a step of applying the aqueous composition according to the present embodiment described above onto a substrate to form a coating film (also referred to as step 1); a step of drying the coating film to form a coating film containing the specific polymer material, the polyimide precursor, and the particles (also referred to as a2 nd step); and a step (also referred to as step 3) of imidizing the polyimide precursor contained in the film to form a polyimide film.

The method for producing a porous polyimide film according to the present embodiment includes the steps of: a step (1 st step) of applying the aqueous composition according to the present embodiment to a substrate to form a coating film; a step (2) of drying the coating film to form a coating film containing the specific polymer material, the polyimide precursor, and the particles; a step (3) of imidizing the polyimide precursor contained in the film to form a polyimide film; and a step of removing particles from the coating film or the polyimide film (also referred to as a 4 th step).

The 1 st step, the 2 nd step, and the 3 rd step are common steps, and therefore, the following description is given in conjunction with the common steps.

Hereinafter, an example of the method for producing a porous polyimide film according to the present embodiment will be described with reference to the drawings.

Fig. 1 is a schematic view showing the structure of a porous polyimide film obtained by the method for producing a porous polyimide film according to the present embodiment.

In fig. 1, 31 denotes a substrate, 51 denotes a release layer, 10A denotes a void, and 10 denotes a porous polyimide film.

[1 st step ]

In the step 1, the aqueous composition according to the present embodiment (i.e., the aqueous composition containing the specific polymer material, the polyimide precursor, the particles, and water) described above is applied to a substrate to form a coating film.

[ Process for producing aqueous composition ]

In step 1, first, the aqueous composition according to the present embodiment is prepared.

Hereinafter, in the step 1, a case where a high molecular weight polyalkylene oxide is used as the specific polymer material will be described as an example, but the same method is used also in a case where a water-insoluble fibrous organic substance is used as the specific polymer material.

The method for producing the aqueous composition used in the step 1 (i.e., the aqueous composition according to the present embodiment) is not particularly limited.

First, a high molecular weight polyalkylene oxide is dispersed or dissolved in an aqueous solvent to prepare a solution containing the high molecular weight polyalkylene oxide.

In the dispersion liquid of the particles, after a resin (polyimide precursor) is produced by polymerizing a tetracarboxylic dianhydride with a diamine compound, an aqueous composition is prepared by a method of adding the above-mentioned high molecular weight polyalkylene oxide-containing solution thereto.

When the particles are resin particles, the resin particles can be produced in an aqueous solvent to obtain the dispersion.

Specific examples of the method for producing the aqueous composition include the following methods.

First, a high molecular weight polyalkylene oxide is dispersed or dissolved in an aqueous solvent to obtain a solution containing the high molecular weight polyalkylene oxide. Further, resin particles are produced in an aqueous solvent to obtain a resin particle dispersion. Next, in the resin particle dispersion, a tetracarboxylic dianhydride and a diamine compound are polymerized in the presence of an organic amine compound to produce a resin (polyimide precursor), and a solution containing a high molecular weight polyalkylene oxide is added to obtain a mixed solution. To the resulting mixed solution is added a solution containing a high molecular weight polyalkylene oxide to form an aqueous composition.

Another example of the method for producing the aqueous composition includes the following steps: a method of preparing an aqueous composition by adding a solution containing a high molecular weight polyalkylene oxide to a dispersion in which particles are dispersed and synthesizing a polyimide precursor in the mixed solution, a method of mixing a solution obtained by dissolving a polyimide precursor in an aqueous solvent, resin particles in a dry state and the solution containing a high molecular weight polyalkylene oxide, a method of mixing a solution obtained by dissolving a polyimide precursor in an aqueous solvent, a dispersion in which resin particles are dispersed in an aqueous solvent in advance, and the solution containing a high molecular weight polyalkylene oxide.

In addition, in the preparation of the aqueous composition, a polyimide precursor-containing solution in which a tetracarboxylic dianhydride and a diamine compound are polymerized in an organic solvent such as an aprotic polar solvent (e.g., N-methylpyrrolidone (NMP)) to produce a resin (polyimide precursor), and then the resin (polyimide precursor) is precipitated by adding the resin to the aqueous solvent may be used.

[ application of polyimide precursor solution ]

In the step 1, the aqueous composition obtained by the above-described method is applied to a substrate to form a coating film. The obtained coating film comprises a specific polymer material, a polyimide precursor, particles and an aqueous solvent. Further, the particles in the coating film are distributed in a state in which aggregation is suppressed.

The substrate (substrate 31 in fig. 1) to which the aqueous composition is applied is not particularly limited.

Examples of the substrate include resin substrates such as polystyrene and polyethylene terephthalate; a glass substrate; a ceramic substrate; metal substrates such as iron and stainless steel (SUS); a composite substrate obtained by combining these materials, and the like.

If necessary, a release layer (release layer 51 in fig. 1) may be provided on the substrate by performing a release treatment with a silicone-based or fluorine-based release agent, for example. Further, it is also effective to roughen the surface of the base material to a size of the particle diameter of the particles and promote the exposure of the particles on the base material contact surface.

The method for applying the aqueous composition to a substrate is not particularly limited, and examples thereof include various methods such as a spray coating method, a spin coating method, a roll coating method, a bar coating method, a slit die coating method, and an inkjet coating method.

[2 nd step ]

In the 2 nd step, the coating film obtained in the 1 st step is dried to form a coating film containing the specific polymer material, the polyimide precursor, and the particles.

The method of drying the coating film formed on the substrate is not particularly limited, and examples thereof include various methods such as heat drying, natural drying, and vacuum drying.

More specifically, for example, the coating film is preferably formed by drying the coating film so that the solvent remaining in the coating film is 50% or less (for example, preferably 30% or less) of the solid content of the coating film.

In the step 2, a treatment of exposing the particles may be performed in the process of forming the coating film by drying. By performing the treatment of exposing the particles, the aperture ratio of the porous polyimide film can be increased.

Specific examples of the treatment for exposing the particles include the following methods.

In the process of drying the coating film to form a coating film containing the specific polymer material, the polyimide precursor, and the particles, the polyimide precursor in the formed coating film is in a state soluble in water as described above. Therefore, the coating film can be exposed to the particles by, for example, wiping with water or immersing in water. Specifically, for example, the polyimide precursor (and the solvent) covering the particles is removed by performing a treatment of exposing the particles by wiping the surface of the coating film with water. As a result, the particles are exposed on the surface of the treated coating film.

In particular, when a coating film in which particles are buried is formed, it is preferable to use, for example, the above-described treatment as a treatment for exposing the particles buried in the coating film.

[ 3 rd step ]

In the 3 rd step, the polyimide precursor contained in the coating film obtained in the 2 nd step is imidized to form a polyimide film.

In step 3, specifically, the coating film obtained in step 2 is heated and imidized to form a polyimide film.

In addition, the imidization rate increases as the imidization proceeds, and the polyimide film is difficult to dissolve in an organic solvent.

[ imidization ]

In the 3 rd step, for example, heating in multiple stages of 2 stages or more is used for heating for imidizing the polyimide precursor in the film.

For example, when the particles are resin particles and are heated in 2 stages, the heating conditions shown below are specifically employed

The heating condition in the 1 st stage is preferably a temperature at which the shape of the resin particles is maintained, for example. Specifically, for example, the temperature is preferably in the range of 50 ℃ to 150 ℃, and preferably in the range of 60 ℃ to 140 ℃. The heating time is preferably in a range of, for example, 10 minutes to 60 minutes. For example, the heating time is shorter as the heating temperature is higher.

The heating conditions in the 2 nd stage include, for example, heating at 150 to 450 ℃ (preferably 200 to 400 ℃), and at 20 to 120 minutes. By heating in this range, imidization reaction further proceeds. In the heating reaction, the heating is preferably performed by, for example, gradually raising the temperature in a stepwise manner or at a constant rate until the final temperature of the heating is reached.

The heating conditions are not limited to the 2-stage heating method, and for example, a method of heating in 1 stage may be employed. When the heating is carried out in 1 stage, the imidization may be terminated only under the heating condition shown in the above-mentioned 2 nd stage, for example.

[4 th step ]

In the 4 th step, particles are removed from the coating film obtained in the 2 nd step or the polyimide film obtained in the 3 rd step. After the 4 th step, the particle portion becomes a void (void 10A in fig. 1) to obtain a porous polyimide film (porous polyimide film 10 in fig. 1).

In the 4 th step, specifically, the removal of particles may be performed in the process of heating the coating film and imidizing the polyimide precursor of the coating film obtained in the 2 nd step, or may be performed in the 3 rd step from the polyimide film after the completion of imidization (after imidization).

As a method for removing particles from the coating, for example, a method for removing particles (preferably, resin particles) by decomposition by heating, a method for removing particles by dissolving the particles in an organic solvent, a method for removing resin particles by decomposition with a laser or the like, and the like are mentioned.

In addition, when the method of decomposing and removing particles by heating is used, the above-described step 3 can be also used. That is, the particles can be removed by heating in the 3 rd step.

These methods may be carried out by only one kind, or two or more kinds may be used simultaneously.

In the 4 th step, when the resin particles are decomposed and removed by heating, for example, the heating is preferably performed at a temperature equal to or higher than the dissolution temperature of the resin particles.

The resin particles can be removed under the heating condition for imidization in the 3 rd step.

When a method of dissolving and removing the resin particles with an organic solvent is used, specific examples thereof include a method of dissolving and removing the resin particles in an organic solvent by bringing the coating film or the polyimide film into contact with the organic solvent.

Examples of the method of contacting the coating film or the polyimide film with an organic solvent include a method of immersing the coating film or the polyimide film in an organic solvent, a method of coating the coating film or the polyimide film with an organic solvent, and a method of contacting the coating film or the polyimide film with an organic solvent vapor.

The organic solvent for dissolving the resin particles is not particularly limited as long as it is an organic solvent that does not dissolve the polyimide precursor and the polyimide and can dissolve the resin particles.

When the particles are resin particles, as the organic solvent, for example, ethers such as tetrahydrofuran and 1, 4-dioxane; aromatic compounds such as benzene and toluene; ketones such as acetone; and esters such as ethyl acetate.

Of these, ethers such as tetrahydrofuran and 1, 4-dioxane, and aromatic compounds such as toluene are preferable, and tetrahydrofuran and toluene are more preferable.

When a method of removing particles by dissolving the particles in an organic solvent is used, it is preferable to perform imidization of the polyimide precursor in the film at a rate of 10% or more, for example, from the viewpoint of removing the particles and suppressing the dissolution of the film itself in the organic solvent.

The method of adjusting the imidization ratio to 10% or more includes, for example, heating conditions in the 1 st stage in the 3 rd step.

That is, for example, it is preferable to remove the particles in the coating film by dissolving them in an organic solvent after the heating in the 1 st stage in the 3 rd step.

Here, the imidization rate of the polyimide precursor will be described.

Examples of the polyimide precursor partially imidized include precursors having a structure having a repeating unit represented by the following general formula (I-1), the following general formula (I-2) and the following general formula (I-3).

[ chemical formula 2]

In the general formula (I-1), the general formula (I-2) and the general formula (I-3), A represents a 4-valent organic group, and B represents a 2-valent organic group. l represents an integer of 1 or more, and m and n each independently represent 0 or an integer of 1 or more.

The definitions of A and B are the same as those of A and B in the general formula (I) described below.

The imidization ratio of the polyimide precursor is represented by the ratio of the number of bonding portions of imide ring closure (2n + m) to the total number of bonding portions (2l +2m +2n) at the bonding portions of the polyimide precursor (the reaction portions of the tetracarboxylic dianhydride and the diamine compound). That is, the imidization ratio of the polyimide precursor is represented by "(2 n + m)/(2l +2m +2 n)".

The imidization ratio of the polyimide precursor ("(2 n + m)/(2l +2m +2 n)") was measured by the following method.

Determination of the imidization ratio of the polyimide precursor-

Preparation of polyimide precursor sample

(i) A polyimide precursor solution to be measured is applied to a silicone wafer in a film thickness range of 1 μm to 10 μm to prepare a coating sample.

(ii) The coating film sample was immersed in Tetrahydrofuran (THF) for 20 minutes while the solvent in the coating film sample was replaced with Tetrahydrofuran (THF). The solvent to be impregnated is not limited to THF and can be selected from solvents that do not dissolve the polyimide precursor and that are miscible with the solvent components contained in the polyimide precursor solution. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane can be used.

(iii) Taking out the coating film sample from THF, and blowing N to THF adhered on the surface of the coating film sample₂Gas is removed. A polyimide precursor sample is prepared by treating a coating sample at 5 to 25 ℃ for 12 hours or more under a reduced pressure of 10mmHg or less, and drying the coating sample.

Preparation of 100% imidized Standard sample

(iv) A coating sample was prepared by applying a polyimide precursor solution to be measured onto a silicone wafer in the same manner as in (i) above.

(v) The coated sample was heated at 380 ℃ for 60 minutes to effect imidization reaction, thereby preparing a 100% imidization standard sample.

Determination and analysis

(vi) The infrared absorption spectra of the 100% imidization standard sample and the polyimide precursor sample were measured using a Fourier transform infrared spectrophotometer (HORIBA, FT-730, Ltd.). 1500cm of a 100% imidized standard sample was determined^-1Absorption peak (Ab' (1500 cm) derived from aromatic ring in the vicinity^-1) And 1780cm^-1Nearby absorption peak (Ab' (1780 cm) derived from imide bond^-1) Ratio I' (100).

(vii) Similarly, a polyimide precursor sample was measured to obtain 1500cm^-1Nearby absorption peak derived from aromatic ring (Ab (1500 cm)^-1) And 1780cm^-1Nearby absorption peak derived from imide bond (Ab (1780 cm)^-1) A ratio of (i), (x).

Then, the imidization ratio of the polyimide precursor was calculated based on the following formula using the measured absorption peaks I' (100), I (x).

Formula (la): imidization rate of polyimide precursor I (x)/I' (100)

Formula (la): i '(100) ═ Ab' (1780 cm)^-1))/(Ab’(1500cm^-1))

Formula (la): i (x) ═ Ab (1780 cm)^-1))/(Ab(1500cm^-1))

The measurement of the imidization rate of the polyimide precursor is suitable for the measurement of the imidization rate of the aromatic polyimide precursor. When the imidization rate of the aliphatic polyimide precursor is measured, a peak derived from a structure that does not change before and after the imidization reaction is used as an internal standard peak instead of an absorption peak of an aromatic ring.

The substrate used in the 1 st step may be peeled from the coating film after the 2 nd step, may be peeled from the polyimide film after the 3 rd step, or may be peeled from the obtained porous polyimide film after the 4 th step.

A polyimide film or a porous polyimide film was produced as above.

[ average film thickness of polyimide film or porous polyimide film ]

The average film thickness of the polyimide film or the porous polyimide film produced using the aqueous composition according to the present embodiment is not particularly limited, and may be selected according to the application.

For example, the average film thickness of the porous polyimide film may be, for example, 10 μm or more and 1000 μm or less. The average film thickness of the polyimide film or the porous polyimide film may be 20 μm or more, and may be 30 μm or more, and the average film thickness of the polyimide film or the porous polyimide film may be 500 μm or less, and may be 400 μm or less.

When the thickness is the above-mentioned thickness, a separator for a secondary battery, which will be described later, is preferable, for example.

The average film thickness of the polyimide film or the porous polyimide film in the present embodiment was calculated by measuring the film thickness of the polyimide film at 5 places using an eddy current film thickness meter CTR-1500E manufactured by Sanko Electronics co.

[ use of porous polyimide film ]

The porous polyimide film produced using the aqueous composition according to the present embodiment may be suitably used in applications such as a filter and a secondary battery.

In particular, the porous polyimide film is preferable as a separator for a lithium ion secondary battery, for example.

< lithium ion Secondary Battery >

A lithium ion secondary battery including a porous polyimide film produced using the aqueous composition according to the present embodiment as a separator for a lithium ion secondary battery will be described with reference to fig. 2.

Fig. 2 is a partially schematic sectional view showing an example of a lithium-ion secondary battery to which a separator for a lithium-ion secondary battery is applied.

As shown in fig. 2, the lithium ion secondary battery 100 includes a positive electrode active material layer 110, a separator layer 510, and a negative electrode active material layer 310 housed inside an exterior member not shown. The positive electrode active material layer 110 is disposed on the positive electrode collector 130, and the negative electrode active material layer 310 is disposed on the negative electrode collector 330. The separator layer 510 is provided so as to separate the positive electrode active material layer 110 and the negative electrode active material layer 310, and is disposed between the positive electrode active material layer 110 and the negative electrode active material layer 310 so that the positive electrode active material layer 110 and the negative electrode active material layer 310 face each other. The separator layer 510 includes a separator 511 and an electrolyte 513 filled in the pores of the separator 511. A porous polyimide film produced using the aqueous composition according to the present embodiment is applied to the separator 511. The positive electrode current collector 130 and the negative electrode current collector 330 are members provided as needed.

(Positive electrode collector 130 and negative electrode collector 330)

The material used for the positive electrode collector 130 and the negative electrode collector 330 is not particularly limited, and may be a known conductive material. For example, metals such as aluminum, copper, nickel, and titanium can be used.

(Positive electrode active material layer 110)

The positive electrode active material layer 110 is a layer containing a positive electrode active material. If necessary, known additives such as a conductive aid and a binder resin may be contained. The positive electrode active material is not particularly limited, and a known positive electrode active material can be used. For example, a composite oxide (LiCoO) containing lithium may be mentioned₂、LiNiO₂、LiMnO₂、LiMn₂O₄、LiFeMnO₄、LiV₂O₅Etc.), lithium-containing phosphates (LiFePO)₄、LiCoPO₄、LiMnPO₄And LiNiPO₄Etc.), conductive polymers (polyacetylene, polyaniline, polypyrrole, polythiophene, etc.), and the like. The positive electrode active material may be used alone or in combination of two or more.

(negative electrode active material layer 310)

The anode active material layer 310 is a layer containing an anode active material. If necessary, known additives such as a binder resin may be contained. The negative electrode active material is not particularly limited, and a known positive electrode active material can be used. Examples thereof include carbon materials (graphite (natural graphite, artificial graphite), carbon nanotubes, graphitized carbon, low-temperature sintered carbon, etc.), metals (aluminum, silicon, zirconium, titanium, etc.), metal oxides (tin dioxide, lithium titanate, etc.), and the like. The negative electrode active material may be used alone or in combination of two or more.

(electrolyte 513)

The electrolytic solution 513 may be a nonaqueous electrolytic solution containing an electrolyte and a nonaqueous solvent, for example.

The electrolyte includes, for example, a lithium salt electrolyte (LiPF)₆、LiBF₄、LiSbF₆、LiAsF₆、LiClO₄、LiN(FSO₂)₂、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)、LiC(CF₃SO₂)₃Etc.). One kind of electrolyte may be used alone, or two or more kinds may be used simultaneously.

Examples of the nonaqueous solvent include cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, and butylene carbonate), chain carbonates (e.g., diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ -butyrolactone, 1, 2-dimethoxyethane, and 1, 2-diethoxyethane), and the like. The nonaqueous solvent may be used alone or in combination of two or more.

(method for manufacturing lithium ion Secondary Battery 100)

An example of a method for manufacturing the lithium-ion secondary battery 100 will be described.

The positive electrode having the positive electrode active material layer 110 provided on the positive electrode current collector 130 is obtained by applying a coating liquid for forming the positive electrode active material layer 110 containing a positive electrode active material to the positive electrode current collector 130 and drying the coating liquid.

Similarly, a negative electrode having the negative electrode active material layer 310 provided on the negative electrode current collector 330 is obtained by applying a coating liquid for forming the negative electrode active material layer 310 containing a negative electrode active material to the negative electrode current collector 330 and drying the coating liquid. The positive electrode and the negative electrode may be respectively subjected to compression processing as needed.

Next, a laminate structure is obtained by disposing a separator 511 between the positive electrode active material layer 110 and the negative electrode active material layer 310 of the negative electrode so that the positive electrode active material layer 110 and the negative electrode active material layer 310 of the positive electrode face each other. In the laminate structure, a positive electrode (positive electrode current collector 130, positive electrode active material layer 110), a separator layer 510, and a negative electrode (negative electrode active material layer 310, negative electrode current collector 330) are laminated in this order. In this case, compression processing may be performed as necessary.

Next, the laminated structure is housed in the exterior member, and then an electrolyte solution 513 is injected into the laminated structure. The injected electrolyte 513 also penetrates the pores of the separator 511.

Thus, the lithium-ion secondary battery 100 was obtained.

< all solid State Battery >

Next, an all-solid-state battery to which a porous polyimide film produced using the aqueous composition according to the present embodiment is applied will be described. Hereinafter, description will be made with reference to fig. 3.

Fig. 3 is a partially sectional schematic view showing an example of the all-solid-state battery according to the present embodiment. As shown in fig. 3, all-solid battery 200 includes positive electrode active material layer 220, solid electrolyte layer 620, and negative electrode active material layer 420 housed inside an exterior member not shown. The positive electrode active material layer 220 is disposed on the positive electrode collector 240, and the negative electrode active material layer 420 is disposed on the negative electrode collector 440. The solid electrolyte layer 620 is disposed between the positive electrode active material layer 220 and the negative electrode active material layer 420 such that the positive electrode active material layer 220 and the negative electrode active material layer 420 face each other. The solid electrolyte layer 620 includes a solid electrolyte 624 and a holder 622 that holds the solid electrolyte 624, and the solid electrolyte 624 is filled in the hollow hole of the holder 622. The porous polyimide film produced using the aqueous composition according to the present embodiment is applied to the holder 622 holding the solid electrolyte 624. The positive electrode current collector 240 and the negative electrode current collector 440 are provided as needed.

(Positive electrode collector 240 and negative electrode collector 440)

Examples of the material used for the positive electrode current collector 240 and the negative electrode current collector 440 include the same materials as those described above for the lithium ion secondary battery.

(Positive electrode active material layer 220 and negative electrode active material layer 420)

Examples of the material used for the positive electrode active material layer 220 and the negative electrode active material layer 420 include the same materials as those described above for the lithium ion secondary battery.

(solid electrolyte 624)

The solid electrolyte 624 is not particularly limited, and known solid electrolytes can be used. Examples thereof include a polymer solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, and a nitride solid electrolyte.

Examples of the polymer solid electrolyte include fluororesins (individual polymers such as polyvinylidene fluoride, polyhexafluoropropylene, and polytetrafluoroethylene, and copolymers having these as constituent units), polyethylene oxide resins, polyacrylonitrile resins, and polyacrylate resins. For example, a sulfide-containing solid electrolyte is preferable from the viewpoint of excellent lithium ion conductivity. From the same viewpoint, for example, a sulfide solid electrolyte containing at least one of sulfur, lithium, and phosphorus as a constituent element is preferably contained.

As the oxide solid electrolyte, oxide solid electrolyte particles containing lithium can be cited. For example, Li is mentioned₂O-B₂O₃-P₂O₅、Li₂O-SiO₂And the like.

The sulfide solid electrolyte includes a sulfide solid electrolyte containing at least one of sulfur, lithium, and phosphorus as a constituent element. For example, 8Li is mentioned₂O·67Li₂S·25P₂S₅、Li₂S、P₂S₅、Li₂S-SiS₂、LiI-Li₂S-SiS₂、LiI-Li₂S-P₂S₅、LiI-Li₃PO₄-P₂S₅、LiI-Li₂S-P₂O₅、LiI-Li₂S-B₂S₃And the like.

Examples of the halide solid electrolyte include LiI.

As the nitride solid electrolyte, for example, Li is cited₃N, and the like.

(method for manufacturing all-solid-state battery 200)

An example of a method of manufacturing the all-solid battery 200 will be described.

The positive electrode having the positive electrode active material layer 220 provided on the positive electrode current collector 240 is obtained by applying a coating liquid for forming the positive electrode active material layer 220 containing a positive electrode active material to the positive electrode current collector 240 and drying the coating liquid.

Similarly, a negative electrode including the negative electrode active material layer 420 provided on the negative electrode current collector 440 is obtained by applying a coating liquid for forming the negative electrode active material layer 420 containing a negative electrode active material to the negative electrode current collector 440 and drying the coating liquid.

The positive electrode and the negative electrode may be respectively subjected to compression processing as needed.

Next, a coating liquid containing the solid electrolyte 624 for forming the solid electrolyte layer 620 is applied to the substrate and dried to form a layered solid electrolyte.

Next, a polyimide film (a porous polyimide film produced using the aqueous composition according to the present embodiment) as the holder 622 and a layered solid electrolyte 624 are stacked on the positive electrode active material layer 220 of the positive electrode as materials for forming the solid electrolyte layer 620. Then, a negative electrode is stacked on the material for forming the solid electrolyte layer 620 so that the negative electrode active material layer 420 of the negative electrode is on the positive electrode active material layer 220 side, thereby forming a stacked structure. In the laminate structure, a positive electrode (positive electrode current collector 240, positive electrode active material layer 220), a solid electrolyte layer 620, and a negative electrode (negative electrode active material layer 420, negative electrode current collector 440) are laminated in this order.

Next, the laminated structure is subjected to compression processing, and the solid electrolyte 624 is impregnated into the pores of the polyimide film serving as the holder 622, thereby holding the solid electrolyte 624.

Next, the laminated structure is housed in the exterior member.

Thus, the all-solid battery 200 is obtained.

Examples

The following examples are illustrative, but the present invention is not limited to these examples. In the following description, "part" and "%" are based on mass unless otherwise specified.

[ preparation of resin particle Dispersion ]

Resin particle dispersion (B1)

A monomer emulsion was prepared by mixing 180 parts by mass of styrene, 1 part by mass of a surfactant Dowfax2a1 (47% solution, The Dow Chemical Company) and 120 parts by mass of deionized water, and stirring and emulsifying The mixture by a dissolver while rotating The dissolver at 1,500 for 30 minutes. Next, 0.2 parts by mass of Dowfax2A1 (47% solution, manufactured by The Dow Chemical Company) and 300 parts by mass of deionized water were put into a reaction vessel. After heating to 75 ℃ under nitrogen atmosphere, 10 parts by mass of the monomer emulsion was added. Then, a polymerization initiator solution obtained by dissolving 2.0 parts by mass of ammonium persulfate in 12 parts by mass of deionized water was added dropwise over 10 minutes. After the reaction for 50 minutes, the remaining monomer emulsion was added dropwise over 180 minutes to further react for 180 minutes, and then the mixture was cooled to obtain a resin particle dispersion (B1). The solid content concentration of the resin particle dispersion (B1) was 30.0 mass%. The resin particles had an average particle diameter of 0.38. mu.m.

Resin particle dispersion (B2)

A resin particle dispersion (B2) was obtained in the same manner as the resin particle dispersion (B1) except that styrene was replaced with methyl methacrylate. The solid content concentration of the resin particle dispersion (B2) was 36.0 mass%. The resin had an average particle diameter of 0.37. mu.m.

[ preparation of a solution containing a polyalkylene oxide ]

Polyalkylene oxide-containing solutions (C1)

High molecular weight polyalkylene oxide (grade: PEO-29, polyethylene oxide having a viscosity average molecular weight of 800 to 1000 million, SUMITOMO SEIKA CHEMICALS CO., LTD.) was added to deionized water to obtain a high molecular weight polyalkylene oxide-containing solution (C1) having a solid content concentration of 0.5 mass%.

Polyalkylene oxide-containing solutions (C2)

High molecular weight polyalkylene oxide (grade: PEO-27, polyethylene oxide having a viscosity average molecular weight of 600 to 800 ten thousand, SUMITOMO SEIKA CHEMICALS CO., LTD.) was added to deionized water to obtain a high molecular weight polyalkylene oxide-containing solution (C2) having a solid content concentration of 0.5 mass%.

Polyalkylene oxide-containing solutions (C3)

High molecular weight polyalkylene oxide (grade: PEO-18, polyethylene oxide having a viscosity average molecular weight of 430 to 480 ten thousand, SUMITOMO SEIKA CHEMICALS CO., LTD.) was added to deionized water to obtain a high molecular weight polyalkylene oxide-containing solution (C3) having a solid content concentration of 0.5 mass%.

[ preparation of a solution containing carboxymethyl cellulose ]

Carboxymethyl cellulose-containing solution (C4)

Carboxymethyl cellulose (product No. 1160, Daicel Miraizu Ltd., also referred to as "CMC") was added to deionized water to obtain a carboxymethyl cellulose-containing solution (C4) having a solid content concentration of 0.5 mass%.

[ preparation of a solution containing a Water-insoluble fibrous organic substance ]

A solution (C5) containing water-insoluble fibrous organic substances

A water-insoluble fibrous organic matter-containing solution (C5) having a solid content of 0.5 mass% was obtained by adding microfibrous aramid (trade name: Tiara, product number: KY400S, Daicel Miraizu Ltd., fiber diameter 30nm, fiber length 3,000nm) to deionized water.

A solution (C6) containing water-insoluble fibrous organic substances

A water-insoluble fibrous organic matter-containing solution (C6) having a solid content of 0.5 mass% was obtained by adding microfibrous cellulose (trade name: Serish, product No. KY100G, Daicel Mirazu Ltd., fiber diameter 20nm, fiber length 3,000nm) to deionized water.

< example A1>

[ preparation of an aqueous composition containing a polyimide precursor (PAA-1) ]

To 170g of the resin particle dispersion (B1), 28g (96 mmol) of 3, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride (BPDA), 10g (96 mmol) of p-Phenylenediamine (PDA) and 360g of ion-exchanged water were added, and the mixture was stirred at 20 ℃ for 10 minutes.

Subsequently, N-methylmorpholine (organic amine compound): 20g (211 mmol) was dissolved and reacted by stirring for 24 hours while keeping the reaction temperature at 60 ℃ to produce a polyimide precursor (A1) based on BPDA and PDA, and 150g of a polyalkylene oxide-containing solution (C1) was slowly added thereto to obtain an aqueous composition (PAA-1) containing a polyimide precursor.

In the obtained polyimide precursor-containing aqueous composition (PAA-1), the content of the polyimide precursor was 5.1 mass%, the content of the resin particles was 6.8 mass%, the content of the high-molecular-weight polyalkylene oxide was 0.1 mass%, and the content of water was 85.1 mass%, based on the total mass of the composition.

Further, as a result of measurement by the above-described method, the viscosity of the polyimide precursor-containing aqueous composition (PAA-1) at 25 ℃ was 150 pas.

< example A2 to example A9, and comparative examples 1 to 2>

Aqueous compositions (PAA-2) to (PAA-11) containing a polyimide precursor were obtained in the same manner as in example a1, except that the kinds and amounts of the resin particle dispersion and the polyalkylene oxide-containing solution were changed as appropriate to obtain the content ratios of the components shown in table 1.

In comparative example 2, a solution containing carboxymethyl cellulose was used instead of the solution containing polyalkylene oxide.

< example B1 to example B9>

Aqueous compositions (PAA-12) to (PAA-20) containing polyimide precursors were obtained in the same manner as in example a1, except that the kind and amount of the resin particle dispersion were changed as appropriate, and a solution containing a water-insoluble fibrous organic substance was used instead of the solution containing a polyalkylene oxide, and the content of each component was set as shown in table 1.

< evaluation >

A porous polyimide film was produced using the polyimide precursor-containing aqueous composition obtained in each example.

(method for producing porous polyimide film)

First, an aluminum plate was prepared as a base material. An aluminum plate was provided with a release layer, which was coated with a solution obtained by dissolving a release agent KS-700(Shin-Etsu Chemical co., ltd.) in toluene so as to have a thickness of about 0.05 μm after drying, and heat-treated at 400 ℃.

Subsequently, the aqueous composition containing a polyimide precursor obtained in each example was applied to the release layer of an aluminum substrate so that the film thickness after drying became 30 μm to form a coating film, and the coating film was dried at 90 ℃ for 1 hour. Then, the temperature was raised from room temperature (25 ℃ C., the same applies hereinafter) to 390 ℃ at a rate of 10 ℃ per minute, and after keeping at 390 ℃ for 1 hour, the temperature was cooled to room temperature to obtain a porous polyimide film having a film thickness of about 30 μm.

In addition, since the aqueous polyimide precursor-containing composition (PAA-11) containing carboxymethyl cellulose of comparative example 2 has a high viscosity, the coatability in the above coating is deteriorated. As a result, a coating film having a large change in film thickness was formed.

(confirmation of precipitation or flotation of particles)

The obtained porous polyimide film was cut in the thickness direction thereof, and the resulting cut surface was observed with a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, FE-SEM S4700).

The cut surface was divided into 2 equal parts in the thickness direction, and the porosity of the cut surface above and below was measured by image analysis, and the obtained measurement values were substituted into the following formula (a) to obtain S.

Formula (A): s ═ 1- (void fraction of value "small")/(void fraction of value "large")

Here, the numerical value "small" porosity means that the measured values of the porosity are smaller in the upper and lower portions of the cut surface divided by 2 in the thickness direction, and the numerical value "large" porosity means that the measured values of the porosity are larger in the upper and lower portions of the cut surface divided by 2 in the thickness direction.

The degree of particle sedimentation or floatation was evaluated based on the value of S obtained by the above formula (a). The smaller the value of S, the less the particles settle or float, e.g., S is preferably less than 0.1.

The evaluation index is shown below.

Evaluation index-

G5: s is less than 0.03

G4: s is 0.03 or more and less than 0.05

G3: s is 0.05 or more and less than 0.1

G2: s is 0.1 or more and less than 0.2

G1: s is 0.2 or more

As is clear from the results shown in tables 1 and 2, the use of the aqueous composition containing a polyimide precursor according to the present example can suppress precipitation or floating of particles during the production of a polyimide film.

The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. The embodiments of the present invention do not fully encompass the present invention, and the present invention is not limited to the disclosed embodiments. It is obvious that various changes and modifications will be apparent to those skilled in the art to which the present invention pertains. The embodiments were chosen and described in order to best explain the principles of the invention and its applications. Thus, other skilled in the art can understand the present invention by various modifications assumed to be optimal for the specific use of various embodiments. The scope of the invention is defined by the following claims and their equivalents.

Claims

1. An aqueous composition containing a polyimide precursor, which comprises at least one polymer material selected from the group consisting of water-insoluble fibrous organic substances and polyalkylene oxides having a viscosity average molecular weight of 500 ten thousand or more, a polyimide precursor, particles, and water.

2. The polyimide precursor-containing aqueous composition according to claim 1,

3. The polyimide precursor-containing aqueous composition according to claim 2,

4. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 3,

5. The polyimide precursor-containing aqueous composition according to claim 4,

6. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 5,

the polyalkylene oxide is polyethylene oxide.

7. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 6,

8. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 7,

9. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 8,

10. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 9,

the particles are resin particles.

11. The polyimide precursor-containing aqueous composition according to claim 10,

12. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 11,

13. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 12,

the viscosity at 25 ℃ is 1 pas or more and 200 pas or less.

14. A method for producing a polyimide film, comprising the steps of:

a step of forming a coating film by applying the polyimide precursor-containing aqueous composition according to any one of claims 1 to 13 onto a substrate;

15. A method for producing a porous polyimide film, comprising the steps of:

and removing the particles from the coating film or the polyimide film.