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

Abstract

To provide a polyimide precursor-containing aqueous composition that gives a porous polyimide film with a reduced number of coarse holes.SOLUTION: A polyimide precursor-containing aqueous composition contains a polyimide precursor, resin particles having polyalkylene oxide groups, and a solvent containing water and an aprotic polar solvent.SELECTED DRAWING: None

Description

Technical Field

[0001] 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 Art

[0002] Polyimide resins are materials having excellent properties such as mechanical strength, chemical stability, and heat resistance, and polyimide films having these properties have attracted attention. Polyimide films may be applied to uses of filters (for example, filtration filters, oil filters, fuel filters, etc.), uses of secondary batteries (for example, separators of lithium secondary batteries, holders of solid electrolytes in all-solid-state batteries, etc.).

[0003] For example, Patent Document 1 describes a varnish for producing a porous film containing at least one resin (A) selected from the group consisting of polyamic acid, polyimide, polyamideimide precursor, and polyamideimide, fine particles (B), and a surfactant (C) containing a silicon atom and / or a fluorine atom having an alkylene oxide chain.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide an aqueous composition containing a polyimide precursor, from which a porous polyimide film having a reduced number of macropores can be obtained, as compared with an aqueous composition containing a polyimide precursor, resin particles, a solvent containing water, and a surfactant having a polyalkylene oxide group.

Means for Solving the Problems

[0006] Means for solving the above problems include the following aspects. <1> A polyimide precursor, resin particles having a polyalkylene oxide group, a solvent containing water and an aprotic polar solvent, and a polyimide precursor-containing aqueous composition having the same. <2> The polyimide precursor-containing aqueous composition according to <1>, wherein the polyalkylene oxide group is a group represented by the following general formula ( POA ). [Chemical formula] (In the general formula (POA), R POA1 represents a hydrogen atom, an alkyl group, or an aryl group. n represents an integer of 0 or 1 or more, m represents an integer of 0 or 1 or more, and n + m represents an integer of 2 or more and 50 or less.) <3> The polyimide precursor-containing aqueous composition according to <2>, wherein the group represented by the general formula ( POA ) is a group in which R POA1 represents an alkyl group having 1 or more and 12 or less carbon atoms, n represents 0, and m represents an integer of 2 or more and 30 or less. <4> The resin particles include a copolymer of a vinyl monomer A having a polyalkylene oxide group and a vinyl monomer B not having a polyalkylene oxide group, and the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is 1.5 / 1000 or more and 15 / 1000 or less. The polyimide precursor-containing aqueous composition according to any one of <1> to <3>. <5> The polyimide precursor-containing aqueous composition according to <4>, wherein the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is 2 / 1000 or more and 10 / 1000 or less. <6> The polyimide precursor-containing aqueous composition according to any one of <1> to <5>, wherein the mass ratio (the resin particles / the aprotic polar solvent) of the resin particles to the aprotic polar solvent is 1 or more and 8 or less. <7> The polyimide precursor-containing aqueous composition according to <6>, wherein the mass ratio of the resin particles to the aprotic polar solvent (the resin particles / the aprotic polar solvent) is 3 or more and 5 or less. <8> The polyimide precursor-containing aqueous composition according to any one of <1> to <7>, wherein the water content is 60% by mass or more based on the total mass of the polyimide precursor-containing aqueous composition. <9> A step of applying the polyimide precursor-containing aqueous composition according to any one of <1> to <8> onto a substrate to form a coating film; A step of drying the coating film to form a film; A step of imidizing the polyimide precursor contained in the film to form a polyimide film; Removing the Resin particles from the film or the polyimide film; Removing the having A method for producing a porous polyimide film. <10> The method for producing a porous polyimide film according to <10>, for producing a porous polyimide film having a film thickness of 50 μm or more.

Advantages of the Invention

[0007] According to the invention according to <1> or <2>, compared with the polyimide precursor-containing aqueous composition having a polyimide precursor, resin particles, a solvent containing water, and a surfactant having a polyalkylene oxide group, a porous polyimide film in which the number of large pores is suppressed is provided. According to the invention according to <3>, compared with the case where the group represented by the general formula ( POA ) is a group in which R POA1 represents an alkyl group having 1 or more and 12 or less carbon atoms, n represents 0, and m represents an integer exceeding 30, a polyimide precursor-containing aqueous composition in which the number of large pores is suppressed is provided. According to the invention according to <4>, compared with the case where the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is less than 1.5 / 1000, a polyimide precursor-containing aqueous composition in which the number of large pores is suppressed is provided. According to the invention according to <5>, a polyimide precursor-containing aqueous composition capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided as compared with the case where the mass ratio (A / B) of vinyl monomer A and vinyl monomer B is less than 2 / 1000.

[0008] According to the invention according to <6>, a polyimide precursor-containing aqueous composition capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided as compared with the case where the mass ratio (resin particles / aprotic polar solvent) of resin particles and aprotic polar solvent is less than 1 or more than 8. According to the invention according to <7>, a polyimide precursor-containing aqueous composition capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided as compared with the case where the mass ratio (resin particles / aprotic polar solvent) of resin particles and aprotic polar solvent is less than 3 or more than 5.

[0009] According to the invention according to <8>, a polyimide precursor-containing aqueous composition capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided, even when the water content is 70% by mass or more based on the total mass of the polyimide precursor-containing aqueous composition, as compared with a polyimide precursor-containing aqueous composition having a polyimide precursor, resin particles, a solvent containing water, and a surfactant having a polyalkylene oxide group.

[0010] According to the invention according to <9>, a method for producing a porous polyimide film capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided as compared with the case where a polyimide precursor-containing aqueous composition having a polyimide precursor, resin particles, a solvent containing water, and a surfactant having a polyalkylene oxide group is applied. According to the invention according to <10>, a method for producing a porous polyimide film capable of obtaining a porous polyimide film in which the number of macropores is suppressed is provided, even when the film thickness is 50 μm or more, as compared with the case where a polyimide precursor-containing aqueous composition having a polyimide precursor, resin particles, a solvent containing water, and a surfactant having a polyalkylene oxide group is applied.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. In this embodiment, the "membrane" is a concept that includes not only what is generally called a "membrane" but also what is generally called a "film" and a "sheet". Also, in this embodiment, the "solid content" refers to components excluding water and water-soluble organic solvents (i.e., aqueous solvents).

[0013] <Aqueous Composition Containing Polyimide Precursor> The aqueous composition containing a polyimide precursor according to this embodiment (hereinafter, also referred to as "the aqueous composition according to this embodiment") has a polyimide precursor, resin particles having a polyalkylene oxide group, and a solvent containing water and an aprotic polar solvent. Here, the "aqueous composition" refers to a composition that contains water and in which the total content rate of water and water-soluble organic solvents (i.e., aqueous solvents) is 50% by mass or more based on the total mass of the aqueous composition.

[0014] Due to the above configuration, the aqueous composition according to this embodiment can obtain a porous polyimide film with the number of macropores suppressed. The reason is presumed as follows.

[0015] Conventionally, a technique of using a surfactant to improve the dispersibility of resin particles in an aqueous composition containing a polyimide precursor has been known. However, when a coating film of an aqueous composition using an aprotic polar solvent together with water as a solvent is dried, at the end of drying, water evaporates and the proportion of the aprotic polar solvent in the solvent increases. When the proportion of the aprotic polar solvent in the solvent increases, the resin particles are likely to swell due to the aprotic polar solvent. Then, the interface between the solvent and the resin particles collapses, the surfactant separates from the surface of the resin particles, and it becomes difficult for the surfactant to function. Therefore, the resin particles are likely to aggregate. When a dry film containing the aggregated resin particles is heated to produce a porous polyimide film, large pores are formed. This phenomenon is particularly likely to occur when producing a thick porous polyimide film in which the time during which the proportion of the aprotic polar solvent in the solvent increases is long.

[0016] On the other hand, when resin particles having a polyalkylene oxide group are applied as the resin particles, aggregation of the resin particles is suppressed due to steric hindrance by the polyalkylene oxide group. Moreover, since the polyalkylene oxide group is in a state of being chemically bonded to the resin component of the resin particles, it does not separate from the resin particles even at the end of drying when the proportion of the aprotic polar solvent in the solvent increases. Therefore, aggregation of the resin particles is suppressed until drying is completed. That is, since a dry film containing resin particles with suppressed aggregation is obtained, a porous polyimide film with a reduced number of large pores is obtained.

[0017] From the above, it is presumed that the aqueous composition according to the present embodiment can obtain a porous polyimide film with a reduced number of large pores due to the above configuration.

[0018] 〔Polyimide Precursor〕 The aqueous composition according to the present embodiment contains a polyimide precursor. The polyimide precursor is a resin (polyimide precursor) having a repeating unit represented by the following general formula (I).

[0019] [Chem.]

[0020] (In general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

[0021] Here, in general formula (I), the tetravalent organic group represented by A is the residue obtained by removing four carboxyl groups from the tetracarboxylic dianhydride used as a raw material. On the other hand, the divalent organic group represented by B is the residue obtained by removing two amino groups from the diamine compound used as a raw material.

[0022] That is, the polyimide precursor having a repeating unit represented by general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound.

[0023] Examples of the tetracarboxylic dianhydride include both aromatic and aliphatic compounds, but aromatic compounds are preferred. That is, in general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

[0024] Examples of the aromatic tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, 3,3’,4,4’-biphenylsulfone tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3’,4,4’-biphenyl ether tetracarboxylic dianhydride, 3,3’,4,4’-dimethyl diphenylsilane tetracarboxylic dianhydride, 3,3’,4,4’-tetraphenylsilane tetracarboxylic dianhydride, 1,2,3,4-furan tetracarboxylic 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) diphenyl propane dianhydride, 3,3’,4,4’-perfluoroisopropylidene diphthalic dianhydride, 3,3’,4,4’-biphenyl tetracarboxylic dianhydride, 2,3,3’,4’-biphenyl tetracarboxylic 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, and the like.

[0025] Examples of the aliphatic tetracarboxylic dianhydride include aliphatic or alicyclic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; aliphatic tetracarboxylic dianhydrides having an aromatic ring such as 1,3,3a,4,5,9b-hexahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, etc.

[0026] Among these, as the tetracarboxylic dianhydride, aromatic tetracarboxylic dianhydrides are preferred. Specifically, for example, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride are preferred. Further, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride are preferred, and particularly 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferred.

[0027] The tetracarboxylic dianhydride may be used alone or in combination of two or more. In addition, when two or more of them are combined and used together, an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic acid may be used in combination, or an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride may be combined.

[0028] On the other hand, the diamine compound is a diamine compound having two amino groups in its molecular structure. Examples of the diamine compound include both aromatic and aliphatic compounds, but it is preferably an aromatic compound. That is, in the general formula (I), the divalent organic group represented by B is preferably an aromatic organic group.

[0029] Examples of the diamine compound include aromatic diamines such as p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide, 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)-biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4'-bis[4-(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl; and aromatic diamines having two amino groups bonded to an aromatic ring and a heteroatom other than the nitrogen atom of the amino group, such as diaminotetraphenylthiophene.1,1-Metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenenediamine, hexahydro-4,7-methanoindanylenemethylenediamine, tricyclo[6,2,1,0; 2.7 -undecylenemethyldiamine, aliphatic diamines such as 4,4'-methylenebis(cyclohexylamine), and alicyclic diamines, etc. are mentioned.

[0030] Among these, as the diamine compound, aromatic diamine compounds are preferable. Specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone are preferable. In particular, 4,4'-diaminodiphenyl ether and p-phenylenediamine are preferable.

[0031] The diamine compound may be used alone or in combination of two or more. Also, when used in combination of two or more, aromatic diamine compounds or aliphatic diamine compounds may be used in combination respectively, or an aromatic diamine compound and an aliphatic diamine compound may be combined.

[0032] The weight average molecular weight of the polyimide precursor used in this embodiment is preferably 5000 or more and 300000 or less, more preferably 10000 or more and 150000 or less.

[0033] The weight average molecular weight of the polyimide precursor is measured by gel permeation chromatography (GPC) method under the following measurement conditions. · Column: Tosoh TSKgel α-M (7.8 mm I.D × 30 cm) · Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acid · Flow rate: 0.6 mL / min · Injection volume: 60 μL · Detector: RI (Differential refractive index detector)

[0034] The content rate of the polyimide precursor is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, based on the total mass of the aqueous composition according to the present embodiment.

[0035] 〔Resin particles〕 The resin particles refer to those that are dispersed without dissolving in the aqueous composition. Here, "the resin particles do not dissolve in the aqueous composition" means that at 25°C, in addition to the resin particles not dissolving in the target liquid (specifically, the solvent containing water included in the aqueous composition containing the polyimide precursor), it also includes the resin particles dissolving within a range of 3% by mass or less in the target liquid.

[0036] The resin particles are resin particles having a polyalkylene oxide group. "The resin particles have a polyalkylene oxide group" means that a polyalkylene oxide group is chemically bonded to the polymerization unit of the resin constituting the resin particles.

[0037] Here, the polyalkylene oxide group is a group containing a structural unit represented by -(C m H 2m O) n -. Here, m and n each independently represent an integer of 2 or more.

[0038] Specifically, the polyalkylene oxide group is preferably a group represented by the following general formula ( POA ).

[0039]

Chemical formula

[0040] In the general formula (POA), R POA1represents a hydrogen atom, an alkyl group, or an aryl group. n represents an integer of 0 or 1 or more, m represents an integer of 0 or 1 or more, and n + m represents an integer of 2 or more and 50 or less. Note that n and m represent the average number of added moles of polyalkylene oxide.

[0041] In the general formula (POA), R POA1 Examples of the alkyl group represented by include linear or branched alkyl groups having 1 to 15 carbon atoms, 1 to 12 carbon atoms, 1 to 10 carbon atoms, 1 to 8 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms.

[0042] In the general formula (POA), R POA1 Examples of the aryl group represented by include aryl groups having 6 to 30 carbon atoms, 6 to 20 carbon atoms, or 6 to 15 carbon atoms. R POA1 Specific examples of the aryl group represented by include a phenyl group, a biphenyl group, and the like. R POA1 The aryl group represented by may be a substituted aryl group. Examples of the substituent of the substituted aryl group include an alkyl group (for example, an alkyl group having 1 to 12 carbon atoms, etc.).

[0043] In the general formula (POA), n + m represents an integer of 2 or more and 50 or less, but may also represent an integer of 2 or more and 40 or less, 2 or more and 30 or less, 2 or more and 15 or less, or 4 or more and 8 or less.

[0044] Among the groups represented by these general formulas ( POA ), from the viewpoint of obtaining a porous polyimide film with the number of macropores suppressed, as the polyalkylene oxide group, a group in which R POA1 represents an alkyl group having 1 to 12 carbon atoms, n represents 0, and m represents an integer of 2 or more and 30 or less (that is, a polyethylene oxide group) is preferable.

[0045] Examples of the resin particles include vinyl resins typified by polystyrenes, poly(meth)acrylic acids, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, and polyvinyl ether; condensation resins typified by polyesters, polyurethanes, and polyamides; hydrocarbon resins typified by polyethylene, polypropylene, and polybutadiene; and fluorine-based resins typified by polytetrafluoroethylene and polyvinyl fluoride.

[0046] Preferably, the resin particles are resin particles using a monomer having a polyalkylene oxide group as the monomer forming these resins.

[0047] Examples of the monomer having a polyalkylene oxide group include esters of polyethylene glycol monoalkyl ether and carboxylic acid monomers, esters of polyethylene glycol monoalkyl ether and sulfonic acid monomers, esters of polyethylene glycol monoalkyl ether and phosphoric acid monomers, vinyl group-containing urethanes formed from polyethylene glycol monoalkyl ether and isocyanate group-containing monomers, and macromonomers containing a polyvinyl alcohol structure. These vinyl monomers A may be used alone or in combination of two or more.

[0048] Here, “(meth)acryl” means including both “acryl” and “methacryl”. Further, poly(meth)acrylic acids include (meth)acrylic acid, (meth)acrylic acid esters, and (meth)acrylamides. Also, the resin particles may or may not be crosslinked.

[0049] From the viewpoint of obtaining a porous polyimide film in which a polyalkylene oxide group is introduced and the number of macropores is suppressed, vinyl resin particles are preferable as the resin particles. Specifically, the vinyl resin particles are preferably resin particles containing a copolymer of a vinyl monomer A having a polyalkylene oxide group and a vinyl monomer B not having a polyalkylene oxide group.

[0050] Here, from the viewpoint of obtaining a porous polyimide film with the number of large pores suppressed, the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is preferably 1.5 / 1000 or more and 15 / 1000 or less, and more preferably 2 / 1000 or more and 10 / 1000 or less. When the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is within the above range, the number of polyalkylene oxide groups on the surface of the resin particles is suppressed from increasing. Thereby, the film thickness variation is suppressed in the coating of the dry film due to the increase in liquid viscosity.

[0051] Examples of the vinyl monomer A having a polyalkylene oxide group include esters of polyethylene glycol monoalkyl ether and carboxylic acid monomers (for example,). Specifically, examples of the vinyl monomer A include polyalkylene glycol (meth)acrylates such as polypropylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; alkoxypolyalkylene glycol (meth)acrylates such as methoxypolyethylene glycol (meth)acrylate; and phenoxypolyalkylene glycol (meth)acrylate. Commercially available products of the vinyl monomer A include Brenmer (registered trademark, the same hereinafter) PME-100, Brenmer PME-200, Brenmer PME-400, Brenmer PME-1000, Brenmer PME-4000, Brenmer 50POEP-800B, Brenmer AME-400 manufactured by NOF Corporation; Methoxypolyethylene glycol acrylate AM-90G, Methoxypolyethylene glycol acrylate AM-230G, Methoxypolyethylene glycol methacrylate M-90G, Methoxypolyethylene glycol methacrylate M-230G manufactured by Shin-Nakamura Chemical Co., Ltd.

[0052] Examples of the vinyl monomer B without a polyalkylene oxide group 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; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, 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; bases such as ethyleneimine, vinylpyridine, and vinylamine; and the like.

[0053] The vinyl monomer B may be used in combination with other monomers other than those described above. Examples of other monomers include monofunctional monomers such as vinyl acetate, bifunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate, nonanediacrylate, and decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate and trimethylolpropane trimethacrylate. By using the bifunctional monomer and the polyfunctional monomer in combination, crosslinked resin particles can be obtained.

[0054] These vinyl monomers B may be used alone or in combination of two or more.

[0055] From the viewpoints of productivity and adaptability in the particle removal step, these resin particles are preferably resin particles made of polystyrenes or poly(meth)acrylic acids, and more preferably resin particles made of polystyrenes, styrene-(meth)acrylic acid copolymers, or poly(meth)acrylic acids.

[0056] Here, the polystyrenes are resins containing constituent units derived from styrenic monomers (monomers having a styrene skeleton). More specifically, the polystyrenes contain the constituent units in an amount of preferably 30 mol% or more, more preferably 50 mol% or more, when the total of the constituent units constituting the resin is 100 mol%. The poly(meth)acrylic acids mean methacrylic resins and acrylic resins, and are resins containing constituent units derived from (meth)acrylic monomers (monomers having a (meth)acryloyl skeleton). More specifically, the poly(meth)acrylic acids contain, for example, the total proportion of the constituent units derived from (meth)acrylic acid and / or the constituent units derived from (meth)acrylic acid ester in an amount of preferably 30 mol% or more, more preferably 50 mol% or more, when the total of the composition in the polymer is 100 mol%.

[0057] From the viewpoint that the movement of the particles is easily suppressed due to the small specific gravity difference from the liquid, the resin particles are preferably resin particles made of a resin containing constituent units derived from styrene. When the total of the constituent units constituting the resin is 100 mol%, it is preferably contained in an amount of 30 mol% or more, more preferably 50 mol% or more, still more preferably 80 mol% or more, and particularly preferably 100 mol%.

[0058] These resin particles may be used alone or in combination of two or more.

[0059] It is preferable that the shape of the resin particles is maintained during the process of manufacturing 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 the removal of the resin particles) when manufacturing the polyimide film. From these viewpoints, the glass transition temperature of the resin particles is preferably 60°C or higher, more preferably 70°C or higher, still more preferably 80°C or higher.

[0060] The glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, it is determined by the "extrapolated onset temperature of glass transition" described in the method for determining the glass transition temperature in JIS K 7121:1987 "Method for Measuring the Transition Temperature of Plastics".

[0061] The volume average particle diameter D50v of the resin particles is not particularly limited. The volume average particle diameter D50v of the resin particles is preferably, for example, 0.1 μm or more and 10 μm or less. The lower limit of the volume average particle diameter D50v of the resin particles may be 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, or 0.5 μm or more. Also, the upper limit of the volume average particle diameter D50v of the resin 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 resin particles is preferably 1.30 or less, more preferably 1.25 or less, and most preferably 1.20 or less.

[0062] The particle size distribution of the resin particles is measured by the following method. The composition to be measured is diluted and the particle size distribution of the particles in the liquid is measured using a Coulter Counter LS13 (manufactured by Beckman Coulter). Based on the measured particle size distribution, a volume cumulative distribution is drawn for the divided particle size ranges (channels) from the smaller diameter side to measure the particle size distribution. Then, among the volume cumulative distributions drawn from the smaller diameter side, the particle diameter at which the cumulative value is 16% is defined as the volume particle diameter D16v, the particle diameter at which the cumulative value is 50% is defined as the volume average particle diameter D50v, and the particle diameter at which the cumulative value is 84% is defined as the volume particle diameter D84v. And the volume particle size distribution index (GSDv) of the particles is (D84v / D16v) 1 / 2 calculated as follows from the particle size distribution obtained by the above method.

[0063] In addition, when it is difficult to measure the particle size distribution of the resin particles by the above method, it may be measured by a method such as the dynamic light scattering method.

[0064] The shape of the resin particles is preferably spherical. When particles of resin particles are used to remove the particles from the polyimide film to produce a porous polyimide film, a porous polyimide film having spherical pores can be obtained. Note that the "spherical" in the resin particles includes both spherical and substantially spherical (shapes close to spherical) shapes. Specifically, it means that the proportion of particles with a ratio of major axis to minor axis (major axis / minor axis) of 1 or more and less than 1.5 exceeds 80%. The proportion of particles with a ratio of major axis to minor axis (major axis / minor axis) of 1 or more and less than 1.5 is preferably 90% or more. The closer the ratio of the major axis to the minor axis is to 1, the closer it is to a true sphere.

[0065] The content of the resin particles may be determined according to the use of the polyimide film, and is 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.

[0066] The content of the resin particles is 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 based on the polyimide precursor. By setting the content of the resin particles, a porous polyimide film with a high porosity can be easily obtained while maintaining mechanical strength. A porous polyimide film having high mechanical strength and high porosity is useful as a separator for secondary batteries.

[0067] 〔Solvent〕 The solvent includes water and an aprotic polar solvent. The solvent may also include an aqueous solvent other than water and an aprotic polar solvent. Here, the aqueous solvent is a general term for water and a water-soluble organic solvent. Here, water-soluble means that at 25°C, the target substance dissolves in water by 1% by mass or more.

[0068] Examples of water include distilled water, ion-exchanged water, deionized water, ultrafiltration water, pure water, etc.

[0069] The water content is preferably 60% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more, and particularly preferably 85% by mass or more with respect to the total mass of the aqueous composition. Even when the water content with respect to the total mass of the aqueous composition is 60% by mass or more, a porous polyimide membrane with the number of large pores suppressed can be obtained. Note that the upper limit of the water content may be determined according to the use of the polyimide membrane, and for example, 90% by mass may be mentioned.

[0070] The water content is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 85% by mass or more with respect to the aprotic polar solvent. Even when the water content with respect to the aprotic polar solvent is 70% by mass or more, a porous polyimide membrane with the number of large pores suppressed can be obtained.

[0071] The aprotic polar solvent is preferably a solvent having a boiling point of 150°C or higher and 300°C or lower and a dipole moment of 3.0 D or higher and 5.0 D or lower. Examples of the aprotic polar solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-1,3-dimethyl-2-imidazolidinone (DMI), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide (DEAc), dimethyl sulfoxide (DMSO), hexamethylenephosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-imidazolidone, and the like. Among these, as the aprotic polar solvent, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-1,3-dimethyl-2-imidazolidinone (DMI), and N,N-dimethylacetamide (DMAc) are preferable.

[0072] The content rate of the aprotic polar solvent is preferably 1% by mass or more and 10% by mass or less, more preferably 1.5% by mass or more and 8% by mass or less, and still more preferably 2.0% by mass or more and 6% by mass or less, based on the total mass of the aqueous composition.

[0073] The content rate of the aprotic polar solvent is preferably 1.5% by mass or more and 15% by mass or less, more preferably 2.5% by mass or more and 10% by mass or less, and still more preferably 3.0% by mass or more and 8.0% by mass or less, based on the aqueous solvent containing water.

[0074] Here, from the viewpoint of obtaining a porous polyimide film with the number of macropores suppressed, the mass ratio of the resin particles to the aprotic polar solvent (resin particles / aprotic polar solvent) is preferably 1 or more and 8 or less, and more preferably 3 or more and 5 or less.

[0075] Examples of the water-soluble organic solvent include organic amine compounds. The organic amine compound is a compound that amine-chlorinates the polyimide precursor (its carboxyl group) to enhance its 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. The organic amine compound is a compound excluding the diamine compound that is a raw material of the polyimide precursor. Note that the organic amine compound is preferably a water-soluble compound. Water solubility means that the target substance dissolves in water at 25°C at 1% by mass or more.

[0076] Examples of the organic amine compound include primary amine compounds, secondary amine compounds, and tertiary amine compounds. Among these, as the organic amine compound, at least one selected from secondary amine compounds and tertiary amine compounds (particularly, tertiary amine compounds) is preferable. When a tertiary amine compound or a secondary amine compound is applied as the organic amine compound (particularly, a tertiary amine compound), the solubility of the polyimide precursor in the solvent is likely to increase, the film-forming property is likely to improve, and the storage stability of the aqueous composition according to the present embodiment is likely to improve.

[0077] In addition, as the organic amine compound, in addition to monovalent amine compounds, polyvalent amine compounds having two or more valences are also included. When a polyvalent amine compound having two or more valences is applied, a pseudo-crosslinked structure is likely to be formed between the molecules of the polyimide precursor, and the storage stability of the aqueous composition according to the present embodiment is likely to improve.

[0078] 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, morpholine, and the like. Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine (for example, N-methylmorpholine, N-ethylmorpholine, etc.), 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, N-alkylpiperidine (for example, N-methylpiperidine, N-ethylpiperidine, etc.), and the like. Among these, a tertiary amine compound is preferable, N-alkylmorpholine is more preferable, and N-methylmorpholine is particularly preferable.

[0079] The organic amine compound may be used alone or in combination of two or more.

[0080] The content rate of the organic amine compound is 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, based on the polyimide precursor.

[0081] Examples of the water-soluble organic solvent include other water-soluble organic solvents such as water-soluble ether solvents, water-soluble ketone solvents, and water-soluble alcohol solvents.

[0082] 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 these, tetrahydrofuran and dioxane are preferred as the water-soluble ether solvent.

[0083] 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, cyclohexanone, and the like. Among these, acetone is preferred as the water-soluble ketone solvent.

[0084] The water-soluble alcohol solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Water-soluble alcohol solvents include, for example, methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, monoalkyl ethers of ethylene glycol, propylene glycol, monoalkyl ethers of propylene glycol, diethylene glycol, monoalkyl ethers of diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexanetriol, and the like. Among these, as water-soluble alcohol solvents, 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 are preferred.

[0085] Other water-soluble organic solvents may be used alone or in combination of two or more.

[0086] In addition, other water-soluble organic solvents preferably have a boiling point of 270°C or lower, more preferably 60°C or higher and 250°C or lower, and even more preferably 80°C or higher and 230°C or lower. When the boiling point of the water-soluble organic solvent is within the above range, it becomes difficult for the water-soluble organic solvent to remain in the polyimide film, and it becomes easier to obtain a polyimide film with high mechanical strength.

[0087] The content of the aqueous solvent containing water is preferably 75% by mass or more, more preferably 80% by mass or more, based on the total mass of the aqueous composition according to this embodiment.

[0088] 〔Other Components〕 The aqueous composition according to this embodiment may contain other components as necessary.

[0089] In the aqueous composition according to this embodiment, it may contain a catalyst for promoting the imidization reaction, a leveling agent for improving the film formation quality, and the like. As the catalyst for promoting the imidization reaction, dehydrating agents such as acid anhydrides, acid catalysts such as phenol derivatives, sulfonic acid derivatives, benzoic acid derivatives, etc. may be used.

[0090] In addition, the aqueous composition according to this embodiment, depending on the purpose of use of the polyimide film, for example, as a conductive agent added for imparting conductivity, a conductive material (conductive (for example, volume resistivity less than 10 7 Ω·cm) or a semiconductive material (for example, volume resistivity 10 7 Ω·cm or more and 10 13 Ω·cm or less)) may be included. Examples of the conductive agent include carbon black (for example, acidic carbon black with pH 5.0 or less); metals (for example, aluminum, nickel, etc.); metal oxides (for example, yttrium oxide, tin oxide, etc.); ion conductive substances (for example, potassium titanate, LiCl, etc.); and the like. These conductive agents may be used alone or in combination of two or more.

[0091] In addition, the aqueous composition according to this embodiment may contain LiCoO2, LiMn2O, etc., which are used as electrodes of lithium ion batteries.

[0092] 〔Preferred physical properties〕 The aqueous composition according to this embodiment preferably has a viscosity at 25°C of 1 Pa·s or more and 200 Pa·s or less, and more preferably 5 Pa·s or more and 180 Pa·s or less. In the aqueous composition according to this embodiment, even if it has the above viscosity, Resin particles it is difficult to aggregate, and a porous polyimide film with the number of large pores suppressed can be obtained. The viscosity at 25°C of the aqueous composition according to this embodiment is measured using an E-type viscometer (for example, TVE-22H, Toki Sangyo Co., Ltd.).

[0093] From the perspective of achieving the viscosity at 25°C, the total solid content of the aqueous composition according to the present embodiment 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 still more preferably 5% by mass or more and 25% by mass or less with respect to the total mass of the aqueous composition according to the present embodiment.

[0094] <Method for manufacturing porous polyimide film> The method for manufacturing a porous polyimide film according to the present embodiment includes a step of applying the above-described aqueous composition according to the present embodiment onto a substrate to form a coating film (also referred to as the first step), and a step of drying the coating film to form a film containing a specific polymer material, a polyimide precursor, and particles (also referred to as the second step), a step of imidizing the polyimide precursor contained in the film to form a polyimide film (also referred to as the third step), and a step of removing particles from the film or the polyimide film (also referred to as the fourth step).

[0095] Hereinafter, an example of a preferred method for manufacturing a porous polyimide film according to the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the structure of a porous polyimide film obtained by the method for manufacturing a porous polyimide film according to the present embodiment. In FIG. 1, 31 represents a substrate, 51 represents a release layer, 10A represents pores, and 10 represents a porous polyimide film.

[0096] 〔First step〕 In the first step, the above-described aqueous composition according to the present embodiment (that is, an aqueous composition containing a specific polymer material, a polyimide precursor, particles, and water) is applied onto a substrate to form a coating film.

[0097] [Method for preparing aqueous composition] In the first step, first, the aqueous composition according to the present embodiment is prepared. As an example of the method for preparing the aqueous composition, specifically, the following methods can be mentioned. First, resin particles are granulated in an aqueous solvent to obtain a resin particle dispersion. Subsequently, in the resin particle dispersion, in the presence of an organic amine compound, a tetracarboxylic dianhydride and a diamine compound are polymerized to produce a resin (polyimide precursor), thereby obtaining an aqueous composition.

[0098] When preparing the aqueous composition, after polymerizing a tetracarboxylic dianhydride and a diamine compound in an organic solvent such as an aprotic polar solvent (e.g., N-methylpyrrolidone (NMP), etc.) to produce a resin (polyimide precursor), this may be used by introducing it into an aqueous solvent to precipitate the resin (polyimide precursor) to obtain a polyimide precursor-containing liquid.

[0099] [Coating of the polyimide precursor solution] In the first step, the aqueous composition obtained by the method described above is coated on a substrate to form a coating film.

[0100] The substrate (substrate 31 in FIG. 1) on which the aqueous composition is coated is not particularly limited. Examples of the substrate include resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); and composite material substrates in which these materials are combined. Further, on the substrate, if necessary, a release treatment may be performed with, for example, a silicone-based or fluorine-based release agent to provide a release layer (release layer 51 in FIG. 1). Also, it is effective to roughen the surface of the substrate to a size on the order of the particle diameter to promote the exposure of the organic particles at the substrate contact surface.

[0101] The method for coating the aqueous composition on the substrate is not particularly limited, and examples include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating.

[0102] [Second step] In the second step, the coating film obtained in the first step is dried to form a film (i.e., a dry film).

[0103] As a method for drying the coating film formed on the substrate, there are no particular restrictions, and examples thereof include various methods such as heat drying, natural drying, and vacuum drying. More specifically, it is preferable to dry the coating film so that the solvent remaining in the film is 50% or less (preferably 30% or less) with respect to the solid content of the film to form the film.

[0104] In the second step, in the process of drying to form a film, a treatment for exposing the organic particles may be performed. By performing the treatment for exposing the particles, the porosity of the porous polyimide film can be increased. Specific examples of the treatment for exposing the organic particles include, for example, the methods shown below. In the process of drying the coating film to form a film, the polyimide precursor in the formed film is in a state where it can be dissolved in water as described above. Therefore, by performing a treatment such as wiping the film with water or immersing the film in water, the organic particles can be exposed from the film. Specifically, for example, by performing a treatment for exposing the particles by wiping the film surface with water, the polyimide precursor (and solvent) covering the organic particles is removed. As a result, the particles are exposed on the surface of the treated film. In particular, when a film in which organic particles are buried is formed, it is preferable to employ the above treatment as a treatment for exposing the organic particles buried in the film.

[0105] [Third Step] In the third step, the polyimide precursor contained in the film obtained in the second step is imidized to form a polyimide film. Specifically, in the third step, the film obtained in the second step is heated to cause imidization to proceed, thereby forming a polyimide film. Note that as the imidization proceeds and the imidization rate increases, the polyimide film becomes less soluble in organic solvents.

[0106] [Imidization] In the third step, for heating to imidize the polyimide precursor in the film, for example, heating in two or more steps is preferably used. For example, when the particles are resin particles and heating is performed in two steps, specifically, the following heating conditions are adopted.

[0107] As the heating conditions for the first step, it is desirable that the temperature be such that the shape of the resin particles is maintained. Specifically, for example, the range of 50°C or higher and 150°C or lower is good, and the range of 60°C or higher and 140°C or lower is preferable. Also, as the heating time, the range of 10 minutes or more and 60 minutes or less is good. The higher the heating temperature, the shorter the heating time may be.

[0108] As the heating conditions for the second step, for example, heating can be performed at 150°C or higher and 450°C or lower (preferably 200°C or higher and 400°C or lower) under the conditions of 20 minutes or more and 120 minutes or less. By setting the heating conditions within this range, the imidization reaction further proceeds. During the heating reaction, before reaching the final temperature of heating, it is preferable to gradually increase the temperature stepwise or at a constant rate for heating.

[0109] Note that the heating conditions are not limited to the above two-step heating method, and for example, a method of heating in one step may be adopted. In the case of the one-step heating method, for example, imidization may be completed only by the heating conditions shown in the above second step.

[0110] 〔Fourth step〕 The fourth step is to remove from the film obtained in the second step or the polyimide film obtained in the third step Resin particles (also referred to as "organic particles") By going through the fourth step, the organic particle portion becomes pores (pores 10A in FIG. 1), and a porous polyimide film (porous polyimide film 10 in FIG. 1) is obtained. Specifically, in the fourth step, the removal of the organic particles may be performed by heating the film and removing the polyimide precursor from the film obtained in the second step during the process of imidizing the polyimide precursor, or may be removed from the polyimide film after the imidization is completed (after imidization) in the third step.

[0111] As a method for removing organic particles from the film, for example, there are a method of decomposing and removing particles (preferably resin particles) by heating, a method of dissolving and removing organic particles with an organic solvent, a method of removing resin particles by decomposition with a laser or the like. In addition, when using the method of decomposing and removing organic particles by heating, it may also serve as the aforementioned third step. That is, the organic particles may be removed by heating in the third step. These methods may be carried out using only one type, or two or more types may be used in combination.

[0112] In the case of the method of decomposing and removing resin particles by heating in the fourth step, it is preferable to heat at a temperature equal to or higher than the melting temperature of the resin particles. The resin particles can be removed under the heating conditions for imidization in the third step.

[0113] When using the method of dissolving and removing resin particles with an organic solvent, specifically, there is a method of bringing the film or polyimide film into contact with the organic solvent to dissolve and remove the resin particles in the organic solvent. As a method of bringing the film or polyimide film into contact with the organic solvent, for example, there are a method of immersing the film or polyimide film in the organic solvent, a method of applying the organic solvent to the film or polyimide film, a method of bringing the film or polyimide film into contact with the organic solvent vapor, and the like.

[0114] The organic solvent used for dissolving the resin particles is not particularly limited as long as it does not dissolve the polyimide precursor and polyimide and can dissolve the resin particles. As the organic solvent, for example, ethers such as tetrahydrofuran and 1,4-dioxane; aromatics such as benzene and toluene; ketones such as acetone; esters such as ethyl acetate; are used. Among these, ethers such as tetrahydrofuran and 1,4-dioxane; or aromatics such as benzene and toluene are preferable, and it is more preferable to use tetrahydrofuran or toluene.

[0115] When using a method of dissolving and removing organic particles with an organic solvent, it is preferably carried out when the imidization rate of the polyimide precursor in the film is 10% or more from the viewpoints of the removability of the organic particles and suppressing the dissolution of the film itself in the organic solvent. Examples of the method for making the imidization rate 10% or more include the heating conditions in the first stage of the third step. That is, after performing the heating in the first stage of the third step, it is preferable to dissolve and remove the organic particles in the film with an organic solvent.

[0116] Here, the imidization rate of the polyimide precursor will be described. Examples of the polyimide precursor partially imidized include precursors having a structure with repeating units represented by the following general formula (I-1), the following general formula (I-2), and the following general formula (I-3).

[0117]

Chemical formula

[0118] In general formula (I-1), general formula (I-2), and general formula (I-3), A represents a tetravalent organic group, and B represents a divalent 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.

[0119] Note that A and B have the same meanings as A and B in general formula (I) described later.

[0120] The imidization rate of the polyimide precursor represents the ratio of the number of imide ring-closed bond parts (2n + m) to the total number of bond parts (2l + 2m + 2n) at the bonding part (reaction part of the tetracarboxylic dianhydride and the diamine compound) of the polyimide precursor. That is, the imidization rate of the polyimide precursor is represented by "(2n + m) / (2l + 2m + 2n)".

[0121] Note that the imidization rate of the polyimide precursor (the value of "(2n + m) / (2l + 2m + 2n)") is measured by the following method.

[0122] -Measurement of Imidization Ratio of Polyimide Precursor- ·Preparation of Polyimide Precursor Sample (i) Apply the polyimide precursor solution to be measured onto a silicone wafer in the range of a film thickness of 1 μm or more and 10 μm or less to prepare a coated film sample. (ii) Immerse the coated film sample in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coated film sample with tetrahydrofuran (THF). The solvent for immersion is not limited to THF and can be selected from solvents that do not dissolve the polyimide precursor and 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) Take out the coated film sample from THF, blow N2 gas onto the THF adhering to the surface of the coated film sample to remove it. Treat the coated film sample under a reduced pressure of 10 mmHg or less in the range of 5 °C or more and 25 °C or less for 12 hours or more to dry the coated film sample and prepare a polyimide precursor sample.

[0123] ·Preparation of 100% Imidized Standard Sample (iv) Similar to (i) above, apply the polyimide precursor solution to be measured onto a silicone wafer to prepare a coated film sample. (v) Heat the coated film sample at 380 °C for 60 minutes to perform an imidization reaction and prepare a 100% imidized standard sample.

[0124] ·Measurement and Analysis (vi) Using a Fourier transform infrared spectrophotometer (manufactured by Horiba, Ltd., FT-730), measure the infrared absorption spectra of the 100% imidized standard sample and the polyimide precursor sample. Calculate the ratio I’(100) of the absorption peak (Ab’(1780 cm -1 )) derived from the imide bond near 1780 cm -1 to the absorption peak (Ab’(1500 cm -1 )) derived from the aromatic ring near 1500 cm -1 of the 100% imidized standard sample. (vii) Similarly, measurements are performed on the polyimide precursor sample, and the ratio I(x) of the absorbance peak (Ab(1780 cm -1 )) derived from the imide bond near 1780 cm -1 to the absorbance peak (Ab(1500 cm -1 )) derived from the aromatic ring near 1500 cm -1 is determined.

[0125] Then, using the measured absorbance peaks I’(100) and I(x), the imidization rate of the polyimide precursor is calculated based on the following formula. · Formula: Imidization rate of polyimide precursor = I(x) / I’(100) · Formula: I’(100) = (Ab’(1780 cm -1 )) / (Ab’(1500 cm -1 )) · Formula: I(x) = (Ab(1780 cm -1 )) / (Ab(1500 cm -1 ))

[0126] Note that the measurement of the imidization rate of this polyimide precursor is applicable to the measurement of the imidization rate of aromatic polyimide precursors. When measuring the imidization rate of an aliphatic polyimide precursor, instead of the absorption peak of the aromatic ring, a peak derived from a structure that does not change before and after the imidization reaction is used as the internal standard peak.

[0127] The substrate used in the first step may be peeled off from the film after the second step, may be peeled off from the polyimide film after the third step, or may be peeled off from the porous polyimide film obtained after the fourth step.

[0128] As described above, a polyimide film or a porous polyimide film is manufactured.

[0129] [Average film thickness of porous polyimide film] The average film thickness of the porous polyimide film produced using the aqueous composition according to this embodiment is not particularly limited and is 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 porous polyimide film may be 20 μm or more, may be 30 μm or more, and the average film thickness of the porous polyimide film may be 500 μm or less, may be 400 μm or less. In the case of the above film thickness, it is suitable for the separator for secondary batteries described later.

[0130] In particular, when manufacturing a porous polyimide film with a film thickness of 50 μm or more (preferably 100 μm or more), as described above, during drying, the time when the proportion of the aprotic polar solvent in the agent increases becomes longer, and the resin particles are likely to aggregate. However, in the method for manufacturing a porous polyimide film using the aqueous composition according to the present embodiment, even for a thick film with a film thickness of 50 μm or more, a porous polyimide film with the number of large pores suppressed can be obtained.

[0131] The average film thickness of the polyimide film or the porous polyimide film in the present embodiment is measured by using an eddy current type film thickness meter CTR-1500E manufactured by Sanko Electronics Co., Ltd. to measure the film thickness of 5 points of the polyimide film, and calculated by its arithmetic mean.

[0132] 〔Use of the porous polyimide film〕 The porous polyimide film manufactured using the aqueous composition according to the present embodiment may be applied to, for example, filter applications, secondary battery applications, etc. In particular, the above porous polyimide film is suitable as a separator for lithium ion secondary batteries.

[0133] <Lithium ion secondary battery> A lithium ion secondary battery provided with a porous polyimide film manufactured using the aqueous composition according to the present embodiment as a separator for lithium ion secondary batteries will be described with reference to FIG. 2.

[0134] FIG. 2 is a partial cross-sectional schematic view showing an example of a lithium ion secondary battery to which a separator for lithium ion secondary batteries 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, which are housed inside an exterior member (not shown). The positive electrode active material layer 110 is provided on a positive electrode current collector 130, and the negative electrode active material layer 310 is provided on a negative electrode current 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 such 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 electrolytic solution 513 filled inside the pores of the separator 511. The separator 511 is an applied porous polyimide film manufactured using the aqueous composition according to the present embodiment. Note that the positive electrode current collector 130 and the negative electrode current collector 330 are members provided as necessary.

[0135] (Positive electrode current collector 130 and negative electrode current collector 330) The materials used for the positive electrode current collector 130 and the negative electrode current collector 330 are not particularly limited as long as they are known conductive materials. For example, metals such as aluminum, copper, nickel, and titanium can be used.

[0136] (Positive electrode active material layer 110) The positive electrode active material layer 110 is a layer containing a positive electrode active material. If necessary, it may contain known additives such as a conductive assistant and a binder resin. The positive electrode active material is not particularly limited, and known positive electrode active materials are used. For example, composite oxides containing lithium (LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFeMnO4, LiV2O5, etc.), phosphates containing lithium (LiFePO4, LiCoPO4, LiMnPO4, LiNiPO4, etc.), conductive polymers (polyyne, polyaniline, polypyrrole, polythiophene, etc.), and the like can be mentioned. The positive electrode active material may be used alone or in combination of two or more.

[0137] (Negative electrode active material layer 310) The negative electrode active material layer 310 is a layer containing a negative electrode active material. Optionally, it may contain known additives such as a binder resin. The negative electrode active material is not particularly limited, and known positive electrode active materials are used. For example, carbon materials (graphite (natural graphite, artificial graphite), carbon nanotubes, graphitized carbon, low-temperature calcined carbon, etc.), metals (aluminum, silicon, zirconium, titanium, etc.), metal oxides (tin dioxide, lithium titanate, etc.), and the like can be mentioned. The negative electrode active material may be used alone or in combination of two or more kinds.

[0138] (Electrolyte 513) The electrolyte 513 can be, for example, a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent. Examples of the electrolyte include electrolytes of lithium salts (LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(FSO2)2, LiN(CF3SO2)2, LiN(C2F5SO2), LiC(CF3SO2)3, etc.). The electrolyte may be used alone or in combination of two or more kinds. Examples of the non-aqueous solvent include cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate, etc.), chain carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc.). The non-aqueous solvent may be used alone or in combination of two or more kinds.

[0139] (Method for manufacturing the lithium-ion secondary battery 100) An example of a method for manufacturing the lithium-ion secondary battery 100 will be described. A coating liquid for forming a positive electrode active material layer 110 containing a positive electrode active material is applied to and dried on the positive electrode current collector 130 to obtain a positive electrode provided with the positive electrode active material layer 110 provided on the positive electrode current collector 130. Similarly, a coating liquid for forming a negative electrode active material layer 310 containing a negative electrode active material is applied to and dried on a negative electrode current collector 330 to obtain a negative electrode provided with the negative electrode active material layer 310 provided on the negative electrode current collector 330. The positive electrode and the negative electrode may each be subjected to compression processing as required. Next, a separator 511 is disposed between the positive electrode active material layer 110 of the positive electrode and the negative electrode active material layer 310 of the negative electrode so that they face each other to obtain a laminated structure. The laminated structure is laminated in this order: 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). At this time, compression processing may be performed as required. Next, after accommodating the laminated structure in an exterior member, an electrolytic solution 513 is injected into the laminated structure. The injected electrolytic solution 513 also penetrates into the pores of the separator 511. In this way, a lithium ion secondary battery 100 is obtained.

[0140] <All-solid-state battery> Next, an all-solid-state battery to which a porous polyimide film manufactured using the aqueous composition according to the present embodiment is applied will be described. Hereinafter, it will be described with reference to FIG. 3.

[0141] FIG. 3 is a partial cross-sectional schematic view showing an example of an all-solid-state battery according to the present embodiment. As shown in FIG. 3, the all-solid-state battery 200 includes a positive electrode active material layer 220, a solid electrolyte layer 620, and a negative electrode active material layer 420, which are housed inside an exterior member (not shown). The positive electrode active material layer 220 is provided on a positive electrode current collector 240, and the negative electrode active material layer 420 is provided on a negative electrode current 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 so 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 inside the pores of the holder 622. The holder 622 that holds the solid electrolyte 624 is applied with a porous polyimide film manufactured using the aqueous composition according to the present embodiment. Note that the positive electrode current collector 240 and the negative electrode current collector 440 are members provided as necessary.

[0142] (Positive electrode current collector 240 and negative electrode current collector 440) Examples of the materials used for the positive electrode current collector 240 and the negative electrode current collector 440 include the same materials as those described for the lithium ion secondary battery above.

[0143] (Positive electrode active material layer 220 and negative electrode active material layer 420) Examples of the materials used for the positive electrode active material layer 220 and the negative electrode active material layer 420 include the same materials as those described for the lithium ion secondary battery above.

[0144] (Solid electrolyte 624) The solid electrolyte 624 is not particularly limited, and known solid electrolytes can be mentioned. For example, polymer solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, nitride solid electrolytes, etc. can be mentioned.

[0145] Examples of the polymer solid electrolyte include fluororesins (homopolymers such as polyvinylidene fluoride, polyhexafluoropropylene, and polytetrafluoroethylene, copolymers having these as constituent units, etc.), polyethylene oxide resins, polyacrylonitrile resins, polyacrylate resins, and the like. It is preferable to contain a sulfide solid electrolyte in terms of excellent lithium ion conductivity. Similarly, it is preferable to contain a sulfide solid electrolyte containing sulfur and at least one of lithium and phosphorus as constituent elements.

[0146] Examples of the oxide solid electrolyte include oxide solid electrolyte particles containing lithium. For example, Li2O-B2O3-P2O5, Li2O-SiO2, and the like can be mentioned. Examples of the sulfide solid electrolyte include sulfide solid electrolytes containing sulfur and at least one of lithium and phosphorus as constituent elements. For example, 8Li2O·67Li2S·25P2S5, Li2S, P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li3PO4-P2S5, LiI-Li2S-P2O5, LiI-Li2S-B2S3, and the like can be mentioned. Examples of the halide solid electrolyte include LiI and the like. Examples of the nitride solid electrolyte include Li3N and the like.

[0147] (Method for manufacturing the all-solid-state battery 200) An example of a method for manufacturing the all-solid-state battery 200 will be described. A coating liquid for forming the positive electrode active material layer 220 containing the positive electrode active material is applied to and dried on the positive electrode current collector 240 to obtain a positive electrode provided with the positive electrode active material layer 220 provided on the positive electrode current collector 240. Similarly, a coating liquid for forming the negative electrode active material layer 420 containing the negative electrode active material is applied to and dried on the negative electrode current collector 440 to obtain a negative electrode provided with the negative electrode active material layer 420 provided on the negative electrode current collector 440. The positive electrode and the negative electrode may each be subjected to compression processing as necessary. Next, a coating liquid containing the solid electrolyte 624 for forming the solid electrolyte layer 620 is applied onto a substrate and dried to form a layered solid electrolyte. Next, as a material for forming the solid electrolyte layer 620, a polyimide film as the retainer 622 (a porous polyimide film manufactured using the aqueous composition according to this embodiment) and the layered solid electrolyte 624 are superposed on the positive electrode active material layer 220 of the positive electrode. Further, the negative electrode is superposed on the material for forming the solid electrolyte layer 620 such that the negative electrode active material layer 420 of the negative electrode is on the positive electrode active material layer 220 side to form a laminated structure. The laminated structure is laminated in this order: positive electrode (positive electrode current collector 240, positive electrode active material layer 220), solid electrolyte layer 620, negative electrode (negative electrode active material layer 420, negative electrode current collector 440). Next, the laminated structure is subjected to compression processing to impregnate the pores of the polyimide film that is the retainer 622 with the solid electrolyte 624 and retain the solid electrolyte 624. Next, the laminated structure is housed in an exterior member. In this way, the all-solid-state battery 200 is obtained.

Examples

[0148] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0149] [Preparation of resin particle dispersion liquid] [Preparation of resin particle dispersion liquid (1)] 1000 parts by mass of styrene, 5 parts by mass of methoxypolyethylene glycol methacrylate ("Blemmer PME-400" manufactured by NOF Corporation), 24 parts by mass of surfactant Dowfax 2A1 (47% solution, manufactured by The Dow Chemical Company), and 580 parts by mass of ion-exchanged water are mixed and stirred and emulsified at 1,500 revolutions for 30 minutes using a dissolver to prepare a monomer emulsion. Subsequently, 1.1 parts by mass of Dowfax 2A1 (47% solution, manufactured by The Dow Chemical Company) and 1270 parts by mass of ion-exchanged water were charged into a reaction vessel. After heating to 75°C under a nitrogen stream, 75 parts by mass of the monomer emulsion was added. Then, a polymerization initiator solution prepared by dissolving 15 parts by mass of ammonium persulfate in 98 parts by mass of ion-exchanged water was added dropwise over 10 minutes. After reacting for 50 minutes after the addition dropwise, the remaining monomer emulsion was added dropwise over 220 minutes, and after reacting for an additional 180 minutes, it was cooled to obtain a resin particle dispersion (1) in which resin particles were dispersed. The solid content concentration of the resin particle dispersion (1) was 34% by mass. Also, the average particle diameter of these resin particles was 0.40 μm. Note that the average particle diameter of the resin particles is the volume average particle diameter measured by the method described above (the same shall apply hereinafter). The results are summarized in Table 1.

[0150] - Preparation of Resin Particle Dispersions (2) to (8), (101) - Resin particle dispersions were obtained in the same manner as the resin particle dispersion (1), except that the monomer species and amounts (parts by mass) were changed according to Table 1.

[0151]

Table 1

[0152] Details of the abbreviations in Table 1 are shown below. · St: Styrene · MMA: Methyl methacrylate · PME-400: Methoxypolyethylene glycol methacrylate (“Blemmer PME-400” manufactured by NOF Corporation), a monomer having a polyalkylene oxide group represented by the general formula ( POA ) in which R POA1 = methyl group, n = 0, m ≒ 9 · PME-1000: Methoxypolyethylene glycol methacrylate (“Blemmer PME-1000” manufactured by NOF Corporation), a monomer having a polyalkylene oxide group represented by the general formula ( POA ) in which R POA1 = methyl group, n = 0, m ≒ 23 · PP-1000: Polypropylene glycol monomethacrylate (“Blemmer PP-1000” manufactured by NOF Corporation), monomer having a polyalkylene oxide group represented by the general formula ( POA ) wherein R POA1 is a hydrogen group, n ≈ 5, and m = 0

[0153] <Example 1> [Preparation of Aqueous Composition Containing Polyimide Precursor (1)] To 170 g of the resin particle dispersion (1), 28 g (96 mmol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 10 g (96 mmol) of p-phenylenediamine (PDA), 360 g of ion-exchanged water, and N-methyl-2-pyrrolidone (NMP) as an aprotic polar solvent were added, and the mixture was stirred at 20°C for 10 minutes. Next, 20 g (211 mmol) of N-methylmorpholine (organic amine compound) was slowly added, and the mixture was stirred for 24 hours while maintaining the reaction temperature at 60°C to dissolve and react, thereby producing a polyimide precursor (A) from BPDA and PDA, and obtaining an aqueous composition containing a polyimide precursor (1). In the obtained aqueous composition containing a polyimide precursor, the amounts or addition amounts of ion-exchanged water and aprotic solvent were adjusted so as to have the amounts (mass% with respect to the aqueous composition) and mass ratios shown in Table 2.

[0154] <Examples 2 to 10, Comparative Example 1> An aqueous composition containing a polyimide precursor was obtained in the same manner as in Example 1, except that the type and amount of the resin particle dispersion were appropriately changed to have the content rates of the respective components as shown in Table 1.

[0155] <Evaluation> Using the aqueous composition containing a polyimide precursor obtained in each example, a porous polyimide film was produced.

[0156] (Method for Producing Porous Polyimide Film) First, an aluminum plate was prepared as the base material. The aluminum plate was provided with a release layer formed by applying a solution of a release agent KS-700 (manufactured by Shin-Etsu Chemical Co., Ltd.) dissolved in toluene so as to have a thickness of about 0.05 μm after drying, and then heat-treating at 400°C. Next, the polyimide precursor-containing aqueous composition obtained in each example was applied onto the release layer of the aluminum substrate so that the film thickness after imidization became 50 μm to form a coating film, which was then dried at 80°C for 2 hours. Thereafter, the temperature was raised from room temperature (25°C, the same hereinafter) to 390°C at a rate of 10°C / min, held at 400°C for 1 hour, and then cooled to room temperature to obtain a porous polyimide film with a size of 15 cm in length × 15 cm in width and a film thickness of 50 μm.

[0157] (Number of pinholes) The obtained porous polyimide film was observed, and the number of pinholes with a maximum diameter of 100 μm or more was counted. Then, it was evaluated according to the following evaluation criteria. A: Number of pinholes: 0 B: Number of pinholes: 1 C: Number of pinholes: 2 or more and 4 or less D: 5 or more

[0158] (Coatability) The film thickness of the obtained dried film was measured at 9 points evenly spaced in-plane, and the film thickness variation was quantified by the following calculation formula. Formula: Film thickness variation = (maximum film thickness value - minimum film thickness value) / average film thickness value Then, it was evaluated according to the following evaluation criteria. Note that passing is L-L3. L1: Less than 3.0 L2: 3.0 or more and less than 8.0 L3: 8.0 or more and less than 15.0 L4: 15 or more

[0159]

Table 2

[0160] From the above results, it can be seen that in this example, a porous polyimide film with the number of pinholes (i.e., the number of large pores) suppressed can be obtained compared to the comparative example.

Explanation of symbols

[0161] 10 Porous polyimide film 10A Pore 31 Substrate 51 Release layer 100 Lithium-ion secondary battery 200 All-solid-state battery

Claims

1. A polyimide precursor, resin particles having a polyalkylene oxide group, a solvent containing water and an aprotic polar solvent, and having wherein the resin particles contain a copolymer of a vinyl monomer A having a polyalkylene oxide group and a vinyl monomer B not having a polyalkylene oxide group, and the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is 1.5 / 1000 or more and 15 / 1000 or less. A polyimide precursor-containing aqueous composition which is resin particles.

2. The polyimide precursor-containing aqueous composition according to claim 1, wherein the polyalkylene oxide group is a group represented by the following general formula (POA). 【Chemical 1】 (In the general formula (POA), R ＰＯＡ１ represents a hydrogen atom, an alkyl group, or an aryl group. n represents an integer of 0 or 1 or more, m represents an integer of 0 or 1 or more, and n + m represents an integer of 2 or more and 50 or less.)

3. The group represented by the general formula (POA) is R ＰＯＡ１ The polyimide precursor-containing aqueous composition according to claim 2, wherein R represents an alkyl group having 1 to 12 carbon atoms, n represents 0, and m represents an integer of 2 or more and 30 or less.

4. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 3, wherein the mass ratio (A / B) of the vinyl monomer A to the vinyl monomer B is 2 / 1000 or more and 10 / 1000 or less.

5. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 4, wherein the mass ratio (the resin particles / the aprotic polar solvent) of the resin particles to the aprotic polar solvent is 1 or more and 8 or less.

6. The polyimide precursor-containing aqueous composition according to claim 5, wherein the mass ratio (the resin particles / the aprotic polar solvent) of the resin particles to the aprotic polar solvent is 3 or more and 5 or less.

7. The polyimide precursor-containing aqueous composition according to any one of claims 1 to 6, wherein the water content is 60% by mass or more based on the total mass of the polyimide precursor-containing aqueous composition.

8. A step of applying the polyimide precursor-containing aqueous composition according to any one of claims 1 to 7 onto a substrate to form a coating film; a step of drying the coating film to form a film; a step of imidizing the polyimide precursor contained in the film to form a polyimide film; a step of removing the resin particles from the film or the polyimide film; A method for producing a porous polyimide film having

9. The method for producing a porous polyimide film according to claim 8, for producing a porous polyimide film having a film thickness of 50 μm or more.

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