Polyimide precursor film, method for producing polyimide film

Abstract

To provide a polyimide precursor film that is less prone to breakage and has a self-standing capability.SOLUTION: The present invention discloses a polyimide precursor film, in which the total content of solvents including water and a solvent other than the water is 5 mass% or more and 40 mass% or less, and the mass ratio of the water to the other solvent is 0 or more and 2.5 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a polyimide precursor film and a polyimide film. [Background technology]

[0002] Patent Document 1 proposes a method for producing a polyimide film for displays, which comprises applying a solution of polyamic acid obtained by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydride and trans-1,4-diaminocyclohexane onto a support, heating the solution, peeling the film from the support, fixing the periphery of the film, and then subjecting the film to a further heat treatment.

[0003] Patent Document 2 proposes a polyimide film in which "both the linear expansion coefficient αMD in the film's machine direction (MD) and the linear expansion coefficient αTD in the width direction (TD) are 7 ppm / °C or less, and the anisotropy index AI value, when measured using the equation AI = (VMAX^2 - VMIN^2) / (VMAX^2 + VMIN^2) (where VMAX^2 is the square of the maximum pulse propagation velocity, and VMIN^2 is the square of the minimum pulse propagation velocity), is 15 or less across the entire width."

[0004] Patent document 3 proposes a polyimide film characterized by having a film width of 1 m or more, an orientation coefficient AI(45,135) value of 12 or less across the entire width, expressed by the formula AI(45,135) = |(V45^2 - V135^2) / ((V45^2 + V135^2) / 2) x 100|, where the orientation angle (θ) of the film is 45° and 135° relative to the machine direction (MD) of the film, and a dimensional change rate of the flexible metal laminate in the diagonal (45°, 135°) direction across the entire width before and after etching of the flexible metal laminate of -0.05 to 0.05%, and a thermoplastic polyimide layer having a thickness of 0.5 to 20 μm on at least one side.

[0005] Patent document 4 states, "An organic insulating film that is continuously produced and satisfies the following (1) to (3) across the entire width of the film. (1) The MOR-c value of the film is 1.05 or more and 5.0 or less; (2) The molecular chain main axis orientation angle is -30 to 30 degrees relative to the MD direction, (3) The difference between the maximum and minimum film MOR-c values ​​is 1.0 or less.

[0006] Patent Document 5 describes a method for producing a polyimide-based multilayer film having a plurality of resin layers containing a polyimide resin, (1) a multilayer liquid film forming step in which a multilayer liquid film is formed by laminating liquid films made of multiple types of resin solutions containing a polyimide resin or its precursor on a support using a multilayer co-extrusion die; (2) A gel film formation step in which the obtained multilayer liquid film is converted into a self-supporting multilayer gel film. wherein, of the plurality of liquid films constituting the polyimide-based multilayer film, the outermost liquid film in contact with the support contains an imidization catalyst but does not contain a chemical dehydrating agent, and the adhesive strength between the multilayer gel film formed on the support and the support is 0.2 kg / 20 cm to 2.4 kg / 20 cm. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-275090 [Patent Document 2] Japanese Patent Application Publication No. 2018-58923 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-10107 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-25967 [Patent Document 5] Japanese Patent Application Laid-Open No. 2012-158149 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a polyimide precursor film that is less susceptible to breakage and has self-supporting properties compared to when the total content of solvents, including water and solvents other than water, is less than 5 mass % or exceeds 40 mass %, or when the mass ratio of water to solvents other than water (water / solvents other than water) exceeds 2.5. [Means for solving the problem]

[0009] The above problems are solved by the following means: <1> a polyimide precursor; A polyimide precursor film having a total content of solvents including water and the solvent other than water of 5% by mass or more and 40% by mass or less, and a mass ratio of the water to the solvent other than water (water / solvent other than water) of 0 to 2.5. <2> a polyimide precursor; A polyimide precursor film having a total content of water and solvents other than water of 5% by mass to 40% by mass, and a tensile strength of 5 kPa to 40 kPa. <3> The total content of the solvent including the water and the solvent other than water is 8% by mass or more and 33% by mass or less. <1> or <2> The polyimide precursor film according to claim 1. <4> The mass ratio of the water to the solvent other than water (water / solvent other than water) is 0 or more and 1 or less. <1> or <2> The polyimide precursor film according to claim 1. <5> The solvent other than water includes a non-water-soluble solvent. <1> ~ <4> The polyimide precursor film according to any one of the preceding claims. <6> The non-water-soluble solvent is at least one selected from the group consisting of a secondary amine compound and a tertiary amine compound. <5> The polyimide precursor film according to claim 1. <7> The secondary amine compound and the tertiary amine compound are at least one selected from the group consisting of imidazoles represented by the following general formula (IM) and morpholines represented by the following general formula (MO): <6> The polyimide precursor film according to claim 1. [ka] (In the general formula (IM), R IM1 , R IM2 , R IM3 , and R IM4 each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. In the general formula (MO), R MO1 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. <8> Contains particles The particles have a volume average particle size of 0.1 μm or more and 1 μm or less, The content of the particles is 30% by mass or more and 85% by mass or less with respect to the total amount of the polyimide precursor and the particles. <1> ~ <7> The polyimide precursor film according to any one of the preceding claims. <9> The particles are resin particles. <8> The polyimide precursor film according to claim 1. <10> <1> ~ <9> 10. A method for producing a polyimide film, comprising the step of heating the polyimide precursor film according to any one of claims 1 to 9 to imidize the polyimide precursor to form a polyimide film. <11> <8> or <9> 1. A method for producing a polyimide film, comprising: a step of heating the polyimide precursor film according to any one of claims 1 to 9 to imidize the polyimide precursor to form a polyimide film, the step including a treatment to remove the particles. [Effects of the Invention]

[0010] <1> According to the present invention, a polyimide precursor film is provided that is less susceptible to breakage and has self-supporting properties compared to when the total content of solvents, including water and solvents other than water, is less than 5 mass % or exceeds 40 mass %, or when the mass ratio of water to solvents other than water (water / solvents other than water) exceeds 2.5. <2> According to the present invention, a polyimide precursor film is provided that is less susceptible to breakage and has self-supporting properties compared to a film in which the total content of solvents, including water and solvents other than water, is less than 5 mass % or more than 40 mass %, or the tensile strength is less than 5 kPa.

[0011] <3> According to the present invention, a polyimide precursor film is provided that is less susceptible to breakage and has self-supporting properties compared to when the total content of solvents, including water and solvents other than water, is less than 8 mass % or exceeds 33 mass %. <4> According to the invention, a polyimide precursor film is provided which is less susceptible to breakage and has self-supporting properties compared to when the mass ratio of water to the solvent other than water (water / solvent other than water) exceeds 1.0.

[0012] <5> According to the invention, a polyimide precursor film is provided which is less susceptible to breakage and has self-supporting properties compared to a case in which the solvent other than water is only a water-soluble solvent. <6> According to the invention, a polyimide precursor film is provided which is less susceptible to damage and has self-supporting properties compared to when the water-insoluble solvent is a primary amine compound. <7> According to the invention, a polyimide precursor film is provided which is less susceptible to damage and has self-supporting properties compared to when the water-insoluble solvent is a primary amine compound.

[0013] <8> , or <9> According to the invention, a polyimide precursor coating is provided that is less susceptible to breakage and has self-supporting properties, even when the content of particles having a volume average particle size of 0.1 μm or more and 1 μm or less is 30 mass % or more and 80 mass % or less of the total amount of polyimide precursor and particles, compared to when the total content of solvents including water and solvents other than water is less than 5 mass % or more than 40 mass %, or when the mass ratio of water to solvents other than water (water / solvents other than water) is more than 2.5.

[0014] <10> , or <11> According to the invention, a polyimide precursor film having a total content of solvents including water and solvents other than water of less than 5 mass % or more than 40 mass %, or a mass ratio of water to solvents other than water (water / solvents other than water) of more than 2.5 is produced. The present invention provides a polyimide precursor film that can provide a polyimide film with reduced damage compared to when the film is applied. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram illustrating the configuration of a porous polyimide film according to an embodiment of the present invention. [Figure 2] 1 is a partial cross-sectional schematic view showing an example of a lithium ion secondary battery including a porous polyimide film according to the present embodiment as a separator for the lithium ion secondary battery. [Figure 3] 1 is a partial cross-sectional schematic view showing an example of an all-solid-state battery including a porous polyimide film according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0017] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0018] The term "film" is a concept that encompasses not only what is generally called "films" but also what is generally called "membranes" and "sheets."

[0019] <Polyimide precursor film> -First embodiment- The polyimide precursor film according to the first embodiment contains a polyimide precursor, and has a total content of solvents, including water and solvents other than water, of 5% by mass or more and 40% by mass or less, and a mass ratio of water to solvents other than water (water / solvents other than water) of 0 to 2.5.

[0020] The polyimide precursor film according to the first embodiment has the above-described structure, making it less susceptible to breakage and self-supporting. This is presumably because the polyimide precursor film has flexibility due to the appropriate solvent content and the presence of a solvent other than water.

[0021] -Second embodiment- The polyimide precursor film according to the second embodiment contains a polyimide precursor, has a total content of water and solvents other than water of 5% by mass or more and 40% by mass or less, and has a tensile strength of 5 kPa or more and 40 kPa or less.

[0022] The polyimide precursor film according to the second embodiment also has the above-described structure, making it less susceptible to breakage and self-supporting.

[0023] The polyimide precursor film corresponding to both the polyimide precursor film according to the first and second embodiments (hereinafter also referred to as "the polyimide precursor film according to this embodiment") will be described in detail below.

[0024] The polyimide precursor film according to this embodiment contains a solvent in addition to the polyimide precursor. Specifically, the polyimide precursor film according to this embodiment is a dried film obtained by drying a coating of a polyimide precursor solution containing a polyimide precursor and a solvent containing water and the solvent other than water.

[0025] In the process of producing a polyimide film, the polyimide precursor film may be peeled off from the coated substrate, taken up in a roll, and then imidized. In producing a polyimide film in this manner, if the polyimide precursor coating is resistant to breakage when peeled from the coated substrate or when wound into a roll and has self-supporting properties, the coating is easy to handle and a polyimide film with reduced breakage can be obtained.

[0026] Here, the phrase "a film is self-supporting" means that after being formed on a solid substrate, the film itself can be peeled off from the solid substrate while maintaining its shape. Specifically, for example, when one end of a film measuring 150 mm long x 100 mm wide and having a thickness of 0.02 mm to 0.1 mm is grasped, the film does not bend and is self-supporting.

[0027] (Polyimide precursor) The polyimide precursor is a resin (polyimide precursor) having a repeating unit represented by the following general formula (I).

[0028] [ka]

[0029] (In general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

[0030] Here, in the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from the starting tetracarboxylic dianhydride. 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 the raw material.

[0031] That is, the polyimide precursor having the repeating unit represented by general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound.

[0032] The tetracarboxylic acid dianhydride may be either an aromatic or aliphatic compound, but is preferably an aromatic compound, i.e., the tetravalent organic group represented by A in general formula (I) is preferably an aromatic organic group.

[0033] Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenylethertetracarboxylic dianhydride, 3,3',4,4'-dimethyldiphenylsilanetetracarboxylic dianhydride, 3,3',4,4'-tetraphenylsilanetetracarboxylic dianhydride, 1,2,3,4-furantetracarboxylic dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride, 4,4 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 3,3',4,4'-perfluoroisopropylidenediphthalic 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'-diphenylether dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylmethane dianhydride, and the like.

[0034] Examples of aliphatic tetracarboxylic dianhydrides include butane tetracarboxylic dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentyl acetic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo[2,2,2]-oct-7-ene aliphatic or alicyclic tetracarboxylic acid dianhydrides 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, and 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione.

[0035] Among these, the tetracarboxylic acid dianhydride is preferably an aromatic tetracarboxylic acid dianhydride, specifically, for example, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-biphenylethertetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, further, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride is more preferable, and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is particularly preferable.

[0036] The tetracarboxylic dianhydrides may be used alone or in combination of two or more. When two or more kinds are used in combination, aromatic tetracarboxylic dianhydrides or aliphatic tetracarboxylic acids may be used in combination, or an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride may be used in combination.

[0037] On the other hand, a diamine compound is a diamine compound having two amino groups in its molecular structure. The diamine compound may be either an aromatic or aliphatic compound, but an aromatic compound is preferable. In other words, the divalent organic group represented by B in the general formula (I) is preferably an aromatic organic group.

[0038] Examples of the diamine compound include 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'-dimethicone 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 aromatic diamines such as 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, and 4,4'-bis[4-(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl; aromatic diamines having two amino groups bonded to an aromatic ring and a heteroatom other than the nitrogen atom of the amino groups, such as diaminotetraphenylthiophene;1,1-meta-xylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanidinediamine, tricyclo[6,2,1,0; 2.7 ]-undecylenedimethyldiamine, 4,4'-methylenebis(cyclohexylamine), and other aliphatic diamines and alicyclic diamines.

[0039] Among these, the diamine compound is preferably an aromatic diamine compound, 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, and particularly, 4,4'-diaminodiphenyl ether and p-phenylenediamine are preferred.

[0040] The diamine compounds may be used singly or in combination of two or more. When two or more diamine compounds are used in combination, aromatic diamine compounds or aliphatic diamine compounds may be used in combination, or an aromatic diamine compound and an aliphatic diamine compound may be used in combination.

[0041] The weight average molecular weight of the polyimide precursor is preferably 5,000 or more and 300,000 or less, and more preferably 10,000 or more and 150,000 or less.

[0042] The weight-average molecular weight of the polyimide precursor is measured by gel permeation chromatography (GPC) under the following measurement conditions. Column: Tosoh TSKgel α-M (7.8 mm ID x 30 cm) Eluent: DMF (dimethylformamide) / 30mM LiBr / 60mM phosphoric acid ·Flow rate: 0.6mL / min ·Injection volume: 60μL Detector: RI (Differential Refractive Index Detector)

[0043] The content of the polyimide precursor is preferably 5% by mass or more and 65% by mass or less, and more preferably 10% by mass or more and 40% by mass or less, based on the polyimide precursor film.

[0044] (solvent) The solvent includes water and solvents other than water. The total content of solvents including water and solvents other than water is 5% by mass or more and 40% by mass or less. From the viewpoint of improving breakage resistance and self-supporting property, the total content of solvents including water and solvents other than water is preferably 8% by mass or more and 33% by mass or less, and more preferably 10% by mass or more and 30% by mass or less.

[0045] The mass ratio of water to the solvent other than water (water / solvent other than water) is 0 or more and 2.5 or less. From the viewpoint of improving breakage resistance and self-supporting property, the mass ratio of water to the solvent other than water (water / solvent other than water) is preferably 0 or more and 2.0 or less, more preferably 0 or more and 1.0 or less.

[0046] Here, the total content of solvents including water and solvents other than water, and the mass ratio of water to solvents other than water can be adjusted by the drying temperature and drying time of the coating film of the polyimide precursor solution, and the type and amount of solvents other than water.

[0047] -water- Examples of water include distilled water, ion-exchanged water, ultrafiltered water, and pure water.

[0048] -Solvents other than water- Examples of solvents other than water include water-insoluble solvents and water-soluble solvents. Here, "water-insoluble" means that the target substance dissolves in water at less than 1% by mass at 25°C. "Water-soluble" means that the target substance dissolves in water at 25°C at 1% by mass or more.

[0049] As the solvent other than water, a non-water-soluble solvent is preferred from the viewpoint of improving breakage resistance and self-supporting property. Here, from the viewpoint of improving breakage resistance and self-supporting property, the proportion of the water-insoluble solvent in the solvents other than water is preferably 50% by mass or more, 70% by mass or more, or 90% by mass or more.

[0050] Non-aqueous solvents Examples of the non-aqueous solvent include organic amine compounds. Among these, from the viewpoint of improving breakage resistance and self-supporting property, organic amine compounds are preferred as the non-aqueous solvent.

[0051] The organic amine compound contained in the polyimide precursor film improves the breakage resistance and self-supporting properties of the polyimide precursor film through hydrogen bonding with the polyimide precursor. The organic amine compound converts the polyimide precursor (its carboxyl group) into an amine salt, thereby increasing its solubility in aqueous solvents and also functioning 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 preferably a compound other than the diamines that are raw materials for polyimide precursors.

[0052] The organic amine compound includes a primary amine compound, a secondary amine compound, and a tertiary amine compound. Among these, the organic amine compound is preferably at least one selected from 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 hydrogen bonding with the polyimide precursor is strong, and the breakage resistance and self-supporting ability of the polyimide precursor film are improved.

[0053] The organic amine compound may be a monovalent amine compound or a divalent or higher polyvalent amine compound. The use of a divalent or higher polyvalent amine compound facilitates the formation of a pseudo-crosslinked structure between the molecules of the polyimide precursor, improving the breakage resistance and self-supporting properties of the polyimide precursor film.

[0054] Examples of primary amine compounds include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, and 2-amino-2-methyl-1-propanol. Examples of secondary amine compounds include dimethylamine, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, and morpholine. Examples of tertiary amine compounds include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, and 2-ethyl-4-methylimidazole. From the viewpoints of the pot life of the polyimide precursor solution and the uniformity of the film thickness, a tertiary amine compound is preferred, and in this respect, at least one selected from the group consisting of 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, N-methylpiperidine, and N-ethylpiperidine is more preferred.

[0055] Here, as the organic amine compound, from the viewpoint of film-forming property, amine compounds having a nitrogen-containing heterocyclic structure (particularly, tertiary amine compounds) are also preferred. Examples of amine compounds having a nitrogen-containing heterocyclic structure (hereinafter referred to as "nitrogen-containing heterocyclic amine compounds") include isoquinolines (amine compounds having an isoquinoline skeleton), pyridines (amine compounds having a pyridine skeleton), pyrimidines (amine compounds having a pyrimidine skeleton), pyrazines (amine compounds having a pyrazine skeleton), piperazines (amine compounds having a piperazine skeleton), triazines (amine compounds having a triazine skeleton), imidazoles (amine compounds having an imidazole skeleton), morpholines (amine compounds having a morpholine skeleton), polyaniline, polypyridine, polyamine, etc.

[0056] From the viewpoint of film-forming properties, the organic amine compound is preferably at least one selected from the group consisting of morpholines, pyridines, piperidines, and imidazoles, and more preferably at least one selected from the group consisting of morpholines and imidazoles. In particular, from the viewpoint of improving breakage resistance and self-supporting properties, the organic amine compound is preferably at least one selected from the group consisting of imidazoles represented by the following general formula (IM) and morpholines represented by the following general formula (MO). Imidazoles represented by the following general formula (IM) and morpholines represented by the following general formula (MO) have high hydrogen bonding properties with polyimide precursors, which improves the breakage resistance and self-supporting properties of the polyimide precursor film.

[0057] [ka]

[0058] In the general formula (IM), R IM1 , R IM2 , R IM3 , and R IM4 each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. In the general formula (MO), R MO1 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

[0059] In general formula (IM) and general formula (MO), R IM1 ~R IM4 and R MO1 The alkyl group represented by may be either linear or branched. R IM1 ~R IM4 and R MO1 The alkyl group represented by is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms.

[0060] The organic amine compound is preferably a compound having a boiling point of 60° C. or higher (preferably 60° C. or higher and 200° C. or lower, more preferably 70° C. or higher and 150° C. or lower). When the boiling point of the organic amine compound is 60° C. or higher, the organic amine compound is prevented from volatilizing from the polyimide precursor film during storage, and deterioration in breakage resistance and self-supporting ability is more likely to be prevented.

[0061] The organic amine compounds may be used alone or in combination of two or more.

[0062] Water-soluble solvent The water-soluble solvents are: Examples of the solvent include water-soluble ether solvents, water-soluble ketone solvents, and water-soluble alcohol solvents.

[0063] A water-soluble ether solvent is a water-soluble solvent that has an ether bond in one molecule. Examples of water-soluble ether solvents include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc. Among these, tetrahydrofuran and dioxane are preferred as water-soluble ether solvents.

[0064] A 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 these, acetone is preferred as the water-soluble ketone solvent.

[0065] The water-soluble alcoholic solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Examples of the water-soluble alcoholic solvent include 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, and 1,2,6-hexanetriol. Among these, preferred water-soluble alcohol solvents are 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.

[0066] Examples of solvents other than water include aprotic polar solvents, which have a boiling point of 150° C. or higher and 300° C. or lower and a dipole moment of 3.0D or higher and 5.0D or lower. Specific examples of aprotic polar solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), hexamethylene phosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone (DMI), N,N'-dimethylpropyleneurea, tetramethylurea, trimethyl phosphate, and triethyl phosphate.

[0067] (particle) The polyimide precursor film according to this embodiment may contain particles.

[0068] Examples of the particles include resin particles and inorganic particles. The particles used are those that are insoluble in the polyimide precursor film and the solvent in the solution. "Insoluble" also includes the case where the target substance dissolves in the target liquid to a degree of 3% by mass or less at 25°C. The particles may be used alone or in combination of two or more kinds.

[0069] The particles are preferably resin particles. The resin particles are not particularly limited, but include resin particles made of resins other than polyimide. Examples include resin particles obtained by polycondensation of polymerizable monomers such as polyester resins and urethane resins, and resin particles obtained by radical polymerization of polymerizable monomers such as vinyl resins, olefin resins, and fluororesins. Examples of resin particles obtained by radical polymerization include resin particles of (meth)acrylic resins, (meth)acrylic acid ester resins, styrene-(meth)acrylic resins, polystyrene resins, and polyethylene resins. Among these, the resin particles are preferably at least one selected from the group consisting of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene-(meth)acrylic resin, and polystyrene resin. In this embodiment, "(meth)acrylic" means to include both "acrylic" and "methacrylic".

[0070] The resin particles may be crosslinked or non-crosslinked. Non-crosslinked resin particles are preferred because they effectively contribute to the relaxation of residual stress in the imidization step of the polyimide precursor. Furthermore, the polyimide precursor solution preferably contains vinyl resin particles obtained by emulsion polymerization as the resin particles because this simplifies the process of producing the polyimide precursor solution.

[0071] When the resin particles are vinyl resin particles, they are obtained by polymerizing a monomer. Examples of the vinyl resin monomer include the following monomers. For example, 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.), and styrenes having a styrene skeleton such as vinylnaphthalene; methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, 2-(meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, and 2-(meth)acrylate. Examples of vinyl resin units include those obtained by polymerizing monomers such as esters having a vinyl group, such as ethylhexyl and trimethylolpropane trimethacrylate (TMPTMA); 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 vinyl sulfonic acid; and bases, such as ethyleneimine, vinylpyridine and vinylamine. Other monomers that may be used in combination include monofunctional monomers such as vinyl acetate, bifunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate, and decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate and trimethylolpropane trimethacrylate. The vinyl resin may be a resin using one of these monomers alone, or may be a resin that is a copolymer using two or more types of monomers.

[0072] The resin particles preferably have acidic groups on their surfaces, which improve dispersibility and suppress the occurrence of pinholes. The acidic groups present on the surfaces of the resin particles are thought to function as a dispersant for the resin particles by forming salts with bases such as organic amine compounds used to dissolve the polyimide precursor in an aqueous solvent. This is thought to improve the dispersibility of the resin particles in the polyimide precursor solution.

[0073] The acidic group present on the surface of the resin particles is not particularly limited, but is preferably at least one selected from the group consisting of a carboxy group, a sulfonic acid group, and a phenolic hydroxyl group, and among these, a carboxy group is preferred.

[0074] The monomer for providing an acidic group on the surface of the resin particle is not particularly limited as long as it is a monomer having an acidic group, and examples thereof include a monomer having a carboxy group, a monomer having a sulfonic acid group, a monomer having a phenolic hydroxyl group, and salts thereof. Specific examples include monomers having sulfonic acid groups such as p-styrenesulfonic acid and 4-vinylbenzenesulfonic acid; monomers having phenolic hydroxyl groups such as 4-vinyldihydrocinnamic acid, 4-vinylphenol, and 4-hydroxy-3-methoxy-1-propenylbenzene; and monomers having carboxyl groups such as acrylic acid, crotonic acid, methacrylic acid, 3-methylcrotonic acid, fumaric acid, maleic acid, 2-methylisocrotonic acid, 2,4-hexadienedioic acid, 2-pentenoic acid, sorbic acid, citraconic acid, 2-hexenoic acid, and monoethyl fumarate; and salts thereof. These monomers having acidic groups may be polymerized in admixture with monomers not having acidic groups, or the monomers not having acidic groups may be polymerized and formed into particles, followed by polymerization of the monomers having acidic groups on the surface. These monomers may be used alone or in combination of two or more.

[0075] Among these, preferred are monomers having a carboxy group such as acrylic acid, crotonic acid, methacrylic acid, 3-methylcrotonic acid, fumaric acid, maleic acid, 2-methylisocrotonic acid, 2,4-hexadienedioic acid, 2-pentenoic acid, sorbic acid, citraconic acid, 2-hexenoic acid, monoethyl fumarate, and salts thereof. The monomers having a carboxy group may be used alone or in combination of two or more. In other words, it is preferable that the resin particles having acidic groups on their surfaces have a skeleton derived from a monomer having at least one carboxy group selected from the group consisting of acrylic acid, crotonic acid, methacrylic acid, 3-methylcrotonic acid, fumaric acid, maleic acid, 2-methylisocrotonic acid, 2,4-hexadienedioic acid, 2-pentenoic acid, sorbic acid, citraconic acid, 2-hexenoic acid, monoethyl fumarate, etc., and salts thereof.

[0076] When a monomer having an acidic group and a monomer not having an acidic group are mixed and polymerized, the amount of the monomer having an acidic group is not particularly limited, but if the amount of the monomer having an acidic group is too small, the dispersibility of the resin particles in the polyimide precursor solution may decrease, and if the amount of the monomer having an acidic group is too large, polymer aggregates may occur during emulsion polymerization. Therefore, the amount of the monomer having an acidic group is preferably 0.3% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 15% by mass or less, and particularly preferably 0.7% by mass or more and 10% by mass or less, of the total monomers. On the other hand, when a monomer having no acidic group is emulsion polymerized and then a monomer having an acidic group is further added and polymerized, the amount of the monomer having an acidic group is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 7% by mass or less, and particularly preferably 0.07% by mass or more and 5% by mass or less, of the total monomers, for the same reasons as above.

[0077] As mentioned above, it is preferable that the resin particles are not crosslinked. However, when crosslinking the resin particles, if a crosslinking agent is used as at least a part of the monomer component, the proportion of the crosslinking agent in the total monomer component is preferably 0% by mass or more and 20% by mass or less, more preferably 0% by mass or more and 5% by mass or less, and particularly preferably 0% by mass.

[0078] When the monomer used in the resin constituting the vinyl resin particles contains styrene, the proportion of styrene in the total monomer components is preferably 20% by mass or more and 100% by mass or less, more preferably 40% by mass or more and 100% by mass or less.

[0079] The resin particles may be commercially available products polymerized with a monomer having an acidic group on the surface. Specific examples of crosslinked resin particles include crosslinked polymethyl methacrylate (MBX series, manufactured by Sekisui Plastics Co., Ltd.), crosslinked polystyrene (SBX series, manufactured by Sekisui Plastics Co., Ltd.), and copolymer crosslinked resin particles of methyl methacrylate and styrene (MSX series, manufactured by Sekisui Plastics Co., Ltd.). Examples of non-crosslinked resin particles include polymethyl methacrylate (MB-series, manufactured by Sekisui Plastics Co., Ltd.) and (meth)acrylate-styrene copolymer (FS-series, manufactured by Nippon Paint Co., Ltd.).

[0080] Specific examples of inorganic particles include silica particles, titanium oxide particles, and aluminum oxide particles.

[0081] The silica particles may be sol-gel silica obtained by a sol-gel method or fumed silica obtained by a gas phase method. Furthermore, the silica particles may be synthesized or commercially available products. Furthermore, the silica particles may be in the form of an aqueous solvent dispersion (e.g., the Snowtex (registered trademark) series manufactured by Nissan Chemical Industries, Ltd.) or a dry powder (e.g., the Aerosil series manufactured by Evonik). From the viewpoint of dispersibility, it is preferable to use an aqueous dispersion of the silica particles.

[0082] The inorganic particles may also include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc, which are added to improve mechanical strength.

[0083] The volume average particle size of the particles is preferably 0.1 μm or more and 1 μm or less. The volume average particle size of the particles is more preferably 0.25 μm or more and 0.98 μm or less, and even more preferably 0.25 μm or more and 0.95 μm or less. The particle size distribution by volume (GSDv) is preferably 1.30 or less, more preferably 1.25 or less, and most preferably 1.20 or less.

[0084] The volume average particle size of particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (for example, the aforementioned Coulter Counter LS13, manufactured by Beckman Coulter, Inc.). For divided particle size ranges (channels), the cumulative distribution is subtracted from the small particle size side, and the particle size at which the cumulative 50% of all particles is measured is taken as the volume average particle size D50v. The particle volume size distribution index is calculated from the particle size distribution in the polyimide precursor solution as follows: (D84v / D16v) 1 / 2 In the cumulative volume distribution drawn from the smallest diameter side of the particle volume, the particle size at 16% of the cumulative volume is the volume particle size D16v, and the particle size at 50% of the cumulative volume is the volume average particle size D50v.

[0085] Here, the polyimide coating according to this embodiment preferably contains particles, the volume average particle size of the particles is 0.1 μm or more and 1 μm or less, and the particle content is 30 mass % or more and 85 mass % or less based on the total amount of the polyimide precursor and the particles. The polyimide film according to this embodiment has high breakage resistance and self-supporting properties, and even if the polyimide film contains particles in the above manner, the decrease in breakage resistance and self-supporting properties is suppressed. As a result, a polyimide film with suppressed breakage can be obtained.

[0086] (Other additives) The polyimide precursor film according to this embodiment may contain a catalyst for accelerating the imidization reaction, a leveling material for improving the quality of the film formation, and the like, which are contained in the polyimide precursor solution. As a 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 may be used.

[0087] In addition, the polyimide precursor film may contain, depending on the intended use, a conductive material (e.g., a material having a volume resistivity of 10 or less) added to impart conductivity as a material other than inorganic particles having a volume average particle diameter of 0.001 μm or more and 0.2 μm or less. 7 Ω·cm) or semi-conductive (e.g., volume resistivity 10 7 Ω cm or more 10 13 It may contain Ω·cm or less). Examples of conductive agents include carbon black (e.g., acidic carbon black having a pH of 5.0 or less), metals (e.g., aluminum, nickel, etc.), metal oxides (e.g., yttrium oxide, tin oxide, etc.), ion-conductive substances (e.g., potassium titanate, LiCl, etc.), etc. These conductive materials may be used alone or in combination of two or more.

[0088] (Mechanical properties of polyimide precursor solution) The tensile strength of the polyimide precursor film according to this embodiment is 5 kPa or more and 40 kPa or less, and preferably 8 kPa or more and 35 kPa or less. When the tensile strength of the polyimide precursor film is within the above range, the film has high breakage resistance and self-supporting ability, and even if the film contains particles in the above manner, the decrease in breakage resistance and self-supporting ability is suppressed. The tensile strength of the polyimide precursor film is measured by a tensile test according to ISO 527:2012.

[0089] <Method of manufacturing polyimide film> Hereinafter, an example of a preferred method for producing the polyimide film according to this embodiment will be described. The polyimide film according to this embodiment can be produced by the following method. 1) A method for producing a polyimide film, comprising the step of heating the polyimide precursor film according to this embodiment when the polyimide precursor film does not contain particles, to imidize the polyimide precursor and form a polyimide film. 2) When particles are contained in the polyimide precursor film, a method for producing a polyimide film includes a step of heating the polyimide precursor film according to the present embodiment to imidize the polyimide precursor to form a polyimide film, the step including a step of removing the particles. This production method results in a porous polyimide film.

[0090] Hereinafter, an example of a method for producing a particle-containing polyimide precursor film, as well as a method for producing a porous polyimide film using the particle-containing polyimide precursor film (hereinafter also referred to as the "method for producing a porous polyimide film according to this embodiment") will be described. The methods for producing a particle-free polyimide precursor film and for producing a non-porous polyimide film using a particle-free polyimide precursor film are similar to the methods for producing a particle-containing polyimide precursor film and for producing a porous polyimide film, except that the polyimide precursor solution used does not contain particles.

[0091] The porous polyimide film according to this embodiment can be produced, for example, by the following steps. The first step is to form a polyimide precursor film (hereinafter also simply referred to as "film") containing polyimide precursors and particles by applying a polyimide precursor solution containing particles to form a coating film and then drying the coating film. A second step of heating the coating to imidize the polyimide precursor and form a polyimide film, the second step including a treatment to remove particles.

[0092] In the description of the production method, reference is made to FIG. 1, which is a schematic diagram showing the structure of the porous polyimide film according to this embodiment. The same components are denoted by the same reference numerals in Fig. 1. In Fig. 1, 31 denotes a substrate, 51 denotes a release layer, 10A denotes holes, and 10 denotes a porous polyimide film.

[0093] (First step) In the first step, a polyimide precursor solution is prepared. A method for preparing a polyimide precursor solution will be described in detail below. As an example, a method for preparing a polyimide precursor solution containing resin particles (resin particle-dispersed polyimide precursor solution) will be described.

[0094] The polyimide precursor solution according to this embodiment can be prepared by the following methods (i) and (ii). (i) A method in which a polyimide precursor solution is prepared before dispersing resin particles, and then resin particles (powder or organic solvent dispersion) are mixed and dispersed. (ii) A method of synthesizing a polyimide precursor in an organic solvent dispersion of resin particles

[0095] (i) A method in which a polyimide precursor solution is prepared before dispersing resin particles, and then resin particles are mixed and dispersed. First, a polyimide precursor solution before dispersing resin particles can be prepared by polymerizing a tetracarboxylic dianhydride and a diamine compound in an organic solvent using a known method to generate a resin (polyimide precursor), thereby obtaining a polyimide precursor solution before dispersing resin particles. Next, the resin particles described in the section on resin particles are mixed and stirred with the polyimide precursor solution before the resin particles are dispersed. Alternatively, the resin particles may be redispersed in an organic solvent (which may be a single solvent or a mixed solvent) that does not dissolve the resin particles, and then mixed and stirred with the polyimide precursor solution. The methods of mixing, stirring, and dispersing are not particularly limited. In order to improve the dispersibility of the resin particles, a known nonionic or ionic surfactant may be added.

[0096] (ii) A method of synthesizing a polyimide precursor in an organic solvent dispersion of resin particles First, a solution is prepared in which resin particles are dispersed in an organic solvent that dissolves the polyimide precursor but not the resin particles. Next, a tetracarboxylic dianhydride and a diamine compound are polymerized in the solution to produce a resin (polyimide precursor), thereby obtaining an organic solvent solution of the polyimide precursor.

[0097] The polyimide precursor solution obtained by the above method is applied onto a substrate to form a coating film containing the polyimide precursor solution and particles, and the coating film formed on the substrate is dried to form a film containing the polyimide precursor and particles.

[0098] The substrate to which the polyimide precursor solution is applied is not particularly limited. Examples 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 combining these materials. If necessary, the substrate may be provided with a release layer by performing a release treatment using, for example, a silicone-based or fluorine-based release agent.

[0099] The method for applying the polyimide precursor solution onto the substrate is not particularly limited, and examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating.

[0100] The amount of polyimide precursor solution to be applied to obtain a coating film containing the polyimide precursor solution and particles may be set to an amount that will provide a predetermined film thickness.

[0101] After forming a coating film containing the polyimide precursor solution and the particles, the coating film is dried to form a film containing the polyimide precursor and the particles. Specifically, the coating film containing the polyimide precursor and the particles is dried by a method such as heat drying, natural drying, or vacuum drying to form a film.

[0102] (Second step) The second step is a step of heating the film containing the polyimide precursor and particles obtained in the first step to imidize the polyimide precursor and form a polyimide film. The second step also includes a step of removing the particles. After the particle removal step, a porous polyimide film is obtained.

[0103] In the second step, the polyimide film is formed by heating the film containing the polyimide precursor and particles obtained in the first step to promote imidization, and then further heating to form a polyimide film in which imidization has progressed. Note that as imidization progresses and the imidization rate increases, the polyimide film becomes less soluble in organic solvents.

[0104] Then, in the second step, a treatment for removing the particles is carried out. The particles may be removed during the process of heating the film to imidize the polyimide precursor, or may be removed from the polyimide film after the imidization is completed (post-imidization). In this embodiment, the process of imidizing the polyimide precursor refers to a process in which the film containing the polyimide precursor and particles obtained in the first step is heated to advance the imidization, resulting in a state prior to the completion of the imidization and the formation of the polyimide film.

[0105] In terms of particle removability, the particle removal treatment is preferably carried out when the imidization rate of the polyimide precursor in the polyimide film is 10% or more during the process of imidizing the polyimide precursor. When the imidization rate is 10% or more, the shape is easily maintained.

[0106] Next, the process of removing particles will be described. First, the process for removing the resin particles will be described. Examples of the treatment for removing the resin particles include a method for removing the resin particles by heating, a method for removing the resin particles with an organic solvent that dissolves the resin particles, a method for removing the resin particles by decomposition with a laser, etc. Among these, the method for removing the resin particles by heating and the method for removing the resin particles with an organic solvent that dissolves the resin particles are preferred.

[0107] As a method for removing the resin particles by heating, for example, the resin particles may be decomposed by heating to promote imidization during the process of imidizing the polyimide precursor. In this case, there is no need to perform an operation of removing the resin particles by a solvent, which is advantageous in terms of reducing the number of steps.

[0108] As a method for removing the resin particles using an organic solvent that dissolves the resin particles, for example, a method in which the resin particles are brought into contact with an organic solvent that dissolves the resin particles (for example, immersed in the solvent) to dissolve and remove the resin particles can be mentioned. Immersing the resin particles in this state in the solvent is preferable because it increases the efficiency of dissolving the resin particles.

[0109] The organic solvent for dissolving the resin particles to be removed is not particularly limited as long as it does not dissolve the polyimide film before imidization or the polyimide film after imidization and is soluble in the resin particles. Examples of the organic solvent include ethers such as tetrahydrofuran (THF), aromatic compounds such as toluene, ketones such as acetone, and esters such as ethyl acetate.

[0110] When resin particles are removed by dissolution to form a porous film, it is preferable to use a solvent that dissolves in a general-purpose solvent such as tetrahydrofuran, acetone, toluene, ethyl acetate, etc. Depending on the resin particles and polyimide precursor used, water may also be used. Furthermore, when the resin particles are removed by heating to form pores, the resin particles do not decompose at the drying temperature after application, but are thermally decomposed at a temperature that imidizes the polyimide precursor film. From this viewpoint, the thermal decomposition starting temperature of the resin particles is preferably 150°C or higher and 320°C or lower, more preferably 180°C or higher and 300°C or lower, and more preferably 200°C or higher and 280°C or lower.

[0111] Here, a treatment for removing inorganic particles when the inorganic particles are contained in the polyimide precursor film will be described. One example of a method for removing inorganic particles is to use a liquid (hereinafter sometimes referred to as a "particle removal liquid") that dissolves inorganic particles but not polyimide precursors or polyimides. The particle removal liquid is selected based on the inorganic particles used. Examples include aqueous solutions of acids such as hydrofluoric acid, hydrochloric acid, hydrobromic acid, boric acid, perchloric acid, phosphoric acid, sulfuric acid, nitric acid, acetic acid, trifluoroacetic acid, and citric acid; and aqueous solutions of bases such as sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, sodium carbonate, potassium carbonate, ammonia, and the organic amines mentioned above. Depending on the inorganic particles and polyimide precursor used, water alone may also be used.

[0112] In the second step, the coating obtained in the first step is heated to promote imidization and obtain a polyimide film by any heating method, and the heating method is not particularly limited. For example, a two-stage heating method can be used. When heating in two stages, the following heating conditions can be specifically used.

[0113] The heating conditions for the first stage are preferably a temperature at which the particle shape is maintained. Specifically, for example, the temperature is preferably in the range of 50°C to 150°C, and more preferably in the range of 60°C to 140°C. The heating time is preferably in the range of 10 minutes to 60 minutes. The higher the heating temperature, the shorter the heating time.

[0114] The heating conditions for the second stage include, for example, heating at 150°C to 450°C (preferably 200°C to 430°C) for 20 minutes to 120 minutes. By using heating conditions within this range, the imidization reaction can proceed further, and a polyimide film can be formed. During the heating reaction, it is preferable to gradually increase the temperature in stages or at a constant rate before reaching the final heating temperature.

[0115] The heating conditions are not limited to the two-stage heating method described above, and a one-stage heating method may also be used. In the case of a one-stage heating method, the imidization may be completed only under the heating conditions shown in the second stage above.

[0116] In the second step, in order to increase the porosity, it is preferable to carry out a treatment to expose the particles so that the particles are exposed. In the second step, the treatment to expose the particles is preferably carried out during the process of imidizing the polyimide precursor or after the imidization and before the treatment to remove the particles.

[0117] In this case, for example, when forming a film on a substrate using a polyimide precursor solution, the polyimide precursor solution is applied to the substrate to form a film with embedded particles. The film is then dried to form a film containing the polyimide precursor and particles. The film formed by this method has embedded particles. This film may be heated to imidize the polyimide precursor before performing a particle removal process, or may be subjected to a process to expose the particles from the polyimide film after imidization is complete (post-imidization).

[0118] In the second step, the treatment for exposing the particles can be carried out when the polyimide film is in the following state, for example. When the imidization rate of the polyimide precursor in the polyimide film is less than 10% (i.e., when the polyimide film is soluble in a solvent), the treatment for exposing the particles can be performed by wiping the particles off, immersing the particles in a solvent, etc. The solvent used in this case may be the same as or different from the solvent used in the polyimide precursor solution of this embodiment.

[0119] Furthermore, when the imidization rate of the polyimide precursor in the polyimide film is 10% or more (i.e., the polyimide precursor is not easily soluble in water or organic solvents) and when the polyimide film has been completely imidized, the particles can be exposed by mechanically cutting the polyimide precursor with a tool such as sandpaper, or, if the particles are resin particles, by decomposing the polyimide precursor with a laser or the like to expose the resin particles. For example, when mechanically cutting, a portion of the particle present in the upper region of the particle embedded in the polyimide film (i.e., the region of the particle away from the substrate) is cut away together with the polyimide film present above the particle, and the cut particle is exposed from the surface of the polyimide film.

[0120] Thereafter, the particles are removed from the polyimide film with the exposed particles by the particle removal treatment described above, and a porous polyimide film from which the particles have been removed is obtained (see FIG. 1).

[0121] Although the above describes the manufacturing process of a porous polyimide film in which the particle-exposing treatment is performed in the second step, the particle-exposing treatment may be performed in the first step in order to increase the porosity. In this case, the particle-exposing treatment may be performed in the first step, after obtaining a coating film, during the process of drying to form a film, to expose the particles. By performing this particle-exposing treatment, the porosity of the porous polyimide film can be increased.

[0122] For example, after obtaining a coating film containing a polyimide precursor solution and particles, the coating film is dried to form a film containing the polyimide precursor and particles. In this process, the polyimide precursor is in a state in which it can be dissolved in a solvent, as described above. When the film is in this state, the particles can be exposed by, for example, wiping or immersing in a solvent. Specifically, the polyimide precursor solution present in a region greater than or equal to the thickness of the particle layer is removed by, for example, wiping with a solvent to expose the particle layer. Then, the particles present in the upper region of the particle layer (i.e., the region of the particle layer farther from the substrate) are exposed from the surface of the film.

[0123] In the second step, the substrate used in the first step for forming the coating may be peeled off when a dried coating is formed, when the polyimide precursor in the polyimide film is in a state where it is difficult to dissolve in an organic solvent, or when imidization is completed and a film is formed.

[0124] A porous polyimide film is obtained through the above steps, and the porous polyimide film may be post-processed.

[0125] Here, the imidization rate of the polyimide precursor will be described. Examples of partially imidized polyimide precursors include precursors having a structure having repeating units represented by the following general formula (V-1), (V-2), and (V-3).

[0126] [ka]

[0127] In general formula (V-1), general formula (V-2), and general formula (V-3), A and B have the same meanings as A and B in formula (I). 1 represents an integer of 1 or more, and m and n each independently represent an integer of 0 or 1 or more.

[0128] The imidization ratio of a polyimide precursor represents the ratio of the number of imide ring-closed bonds (2n+m) to the total number of bonds (2l+2m+2n) in the bonds of the polyimide precursor (reaction sites between tetracarboxylic dianhydride and diamine compound). In other words, the imidization ratio of a polyimide precursor is expressed as "(2n+m) / (2l+2m+2n)".

[0129] The imidization rate of the polyimide precursor (the value of "(2n+m) / (2l+2m+2n)") is measured by the following method.

[0130] -Measurement of imidization rate of polyimide precursor- Preparation of polyimide precursor samples (i) The polyimide precursor solution to be measured is applied to a silicon wafer to a film thickness of 1 μm to 10 μm to prepare a coating sample. (ii) The coating sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating 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) The coating sample is removed from the THF, and the THF adhering to the surface of the coating sample is removed by blowing N2 gas. The coating sample is then dried under a reduced pressure of 10 mmHg or less at a temperature of 5 to 25°C for 12 hours or more to prepare a polyimide precursor sample.

[0131] Preparation of 100% imidized standard sample (iv) In the same manner as in (i) above, a polyimide precursor solution to be measured is applied to a silicon wafer to prepare a coating sample. (v) The coating sample is heated at 380°C for 60 minutes to carry out an imidization reaction, and a 100% imidized standard sample is prepared.

[0132] Measurement and analysis (vi) Using a Fourier transform infrared spectrophotometer (FT-730 manufactured by Horiba, Ltd.), the infrared absorption spectra of the 100% imidized standard sample and the polyimide precursor sample are measured. -1 The absorption peak at 1780 cm -1 The absorption peak (Ab') (1780 cm) derived from the imide bond -1 )) to find the ratio I'(100). (vii) Similarly, measurements were carried out on the polyimide precursor sample, and the -1 The absorption peak (Ab) derived from the aromatic ring near 1500 cm -1 )) to 1780cm -1 The absorption peak (Ab (1780 cm)) derived from the imide bond near -1 )) to find the ratio I(x).

[0133] Then, the imidization rate of the polyimide precursor is calculated using the measured absorption peaks I'(100) and I(x) based on the following formula. Formula: Imidization rate of polyimide precursor = I(x) / I'(100) ·Formula: I'(100)=(Ab'(1780cm -1 )) / (Ab'(1500cm -1 )) ·Formula: I(x)=(Ab(1780cm -1 )) / (Ab(1500cm -1 ))

[0134] This measurement of the imidization rate of a polyimide precursor is also applicable to the measurement of the imidization rate of an aromatic polyimide precursor. When measuring the imidization rate of an aliphatic polyimide precursor, a peak derived from a structure that remains unchanged before and after the imidization reaction is used as an internal standard peak instead of the absorption peak of the aromatic ring.

[0135] <Porous polyimide film> The porous polyimide film of this embodiment will be described below.

[0136] The porous polyimide film of this embodiment is produced by the method for producing a porous polyimide film according to the embodiment described above.

[0137] The porous polyimide film preferably has a porosity of 30% or more, preferably 40% or more, and more preferably 50% or more, although the upper limit of the porosity is not particularly limited, and preferably 90% or less.

[0138] The shape of the pores is preferably spherical or nearly spherical. Furthermore, the pores are preferably connected to one another. The pore diameter of the connected pores is preferably, for example, 1 / 100 to 1 / 2 of the maximum pore diameter, preferably 1 / 50 to 1 / 3, and more preferably 1 / 20 to 1 / 4. Specifically, the average pore diameter of the connected pores is preferably 5 nm to 1500 nm.

[0139] The pore diameter of the pores in the porous polyimide film is preferably in the range of 0.1 μm to 1 μm, more preferably in the range of 0.12 μm to 0.98 μm, and even more preferably in the range of 0.14 μm to 0.96 μm.

[0140] The pore size of the pores in the porous polyimide film is not limited to the above range, and is preferably changed depending on the application.

[0141] In the porous polyimide film of this embodiment, the ratio of the maximum diameter to the minimum diameter of the pores (the ratio of the maximum diameter to the minimum diameter of the pores) is 1 or more and 2 or less. It is preferably 1 or more and 1.9 or less, and more preferably 1 or more and 1.8 or less. Within this range, a ratio closer to 1 is even more preferable. When the ratio is within this range, variation in the pore diameter is suppressed. Furthermore, when the porous polyimide film of this embodiment is applied to, for example, a battery separator for a lithium ion battery, disturbance in the ion flow is suppressed, which makes it easier to suppress the formation of lithium dendrites. The "ratio of the maximum diameter to the minimum diameter of the pores" is a ratio expressed by the value obtained by dividing the maximum diameter of the pore by the minimum diameter (i.e., maximum pore diameter / minimum pore diameter).

[0142] The pore diameter and the pore diameter of the interconnected pores are values ​​observed and measured using a scanning electron microscope (SEM). Specifically, a porous polyimide film is first cut out to prepare a measurement sample. This measurement sample is then observed and measured using a KEYENCE VE SEM with the image processing software that comes standard with the device. Observation and measurement are performed on 100 pore portions of the cross section of the measurement sample, and the average, minimum diameter, maximum diameter, and arithmetic mean diameter are determined for each. If the pore shape is not circular, the longest part is used as the diameter.

[0143] The thickness of the porous polyimide film is not particularly limited, but is preferably 15 μm or more and 500 μm or less.

[0144] The film thickness of the porous polyimide film is measured using a length measuring device (Tokyo Seimitsu Co., Ltd., high-precision digital length measuring device MINIAX PH-13 and display unit DH-150) in an environment of 23°C ± 1°C.

[0145] (Applications of porous polyimide film) Examples of applications of the porous polyimide film according to this embodiment include battery separators for lithium batteries and the like; separators for electrolytic capacitors; electrolyte membranes for fuel cells and the like; battery electrode materials; gas or liquid separation membranes; low-dielectric-constant materials; and filtration membranes.

[0146] <Lithium-ion secondary battery> A lithium ion secondary battery including the porous polyimide film according to this embodiment as a separator for the lithium ion secondary battery will be described with reference to FIG.

[0147] FIG. 2 is a partial cross-sectional schematic diagram showing an example of a lithium ion secondary battery to which a lithium ion secondary battery separator 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, all of 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 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 solution 513 filled in the pores of the separator 511. The separator 511 is made of a porous polyimide film according to this embodiment. The positive electrode current collector 130 and the negative electrode current collector 330 are members that are provided as needed.

[0148] (Positive electrode current collector 130 and negative electrode current collector 330) There are no particular limitations on the material used for the positive electrode current collector 130 and the negative electrode current collector 330, and any known conductive material may be used. For example, metals such as aluminum, copper, nickel, and titanium may be used.

[0149] (Cathode active material layer 110) The positive electrode active material layer 110 is a layer containing a positive electrode active material. It may contain known additives such as a conductive additive and a binder resin, as needed. The positive electrode active material is not particularly limited, and known positive electrode active materials can be used. Examples include lithium-containing composite oxides (LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFeMnO4, LiV2O5, etc.), lithium-containing phosphates (LiFePO4, LiCoPO4, LiMnPO4, LiNiPO4, etc.), and conductive polymers (polyacetylene, polyaniline, polypyrrole, polythiophene, etc.). One type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0150] (Negative electrode active material layer 310) The negative electrode active material layer 310 is a layer containing a negative electrode active material. If necessary, 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 can be used. Examples include carbon materials (graphite (natural graphite, artificial graphite), carbon nanotubes, graphitized carbon, low-temperature fired carbon, etc.), metals (aluminum, silicon, zirconium, titanium, etc.), metal oxides (tin dioxide, lithium titanate, etc.), etc. One type of negative electrode active material may be used alone, or two or more types may be used in combination.

[0151] (Electrolyte 513) The electrolytic solution 513 may be, for example, a non-aqueous electrolytic solution containing an electrolyte and a non-aqueous solvent. Examples of the electrolyte include lithium salt electrolytes (LiPF, LiBF, LiSbF, LiAsF, LiClO, LiN(FSO), LiN(CFSO), LiN(CFS0), LiC(CFSO), etc.) One type of electrolyte may be used alone, or two or more types may be used in combination. Examples of non-aqueous solvents 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.), etc. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0152] (Method of 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 the positive electrode active material layer 110 containing the positive electrode active material is applied to the positive electrode current collector 130 and dried to obtain a positive electrode having the positive electrode active material layer 110 provided on the positive electrode current collector 130. Similarly, a coating solution for forming the negative electrode active material layer 310 containing the negative electrode active material is applied to the negative electrode current collector 330 and dried to obtain a negative electrode including 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 necessary. 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 the positive electrode active material layer 110 and the negative electrode active material layer 310 face each other, thereby obtaining a laminate structure. The laminate structure has a positive electrode (positive electrode current collector 130, positive electrode active material layer 110), separator layer 510, and negative electrode (negative electrode active material layer 310, negative electrode current collector 330) laminated in this order. At this time, compression processing may be performed as necessary. Next, after the laminated structure is housed in an exterior member, electrolyte solution 513 is poured into the interior of the laminated structure. The poured electrolyte solution 513 also permeates the pores of separator 511. In this way, the lithium ion secondary battery 100 is obtained.

[0153] <All-solid-state battery> Next, an all-solid-state battery using the porous polyimide film according to this embodiment will be described with reference to FIG.

[0154] FIG. 3 is a partial cross-sectional schematic diagram illustrating 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, all of 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 support 622 that holds the solid electrolyte 624, and the pores of the support 622 are filled with the solid electrolyte 624. The support 622 that holds the solid electrolyte 624 is made of the porous polyimide film according to the present embodiment. The positive electrode current collector 240 and the negative electrode current collector 440 are members that are provided as needed.

[0155] (Positive electrode current collector 240 and negative electrode current collector 440) Materials 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.

[0156] (Positive Electrode Active Material Layer 220 and Negative Electrode Active Material Layer 420) 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 above for the lithium ion secondary battery.

[0157] (Solid electrolyte 624) The solid electrolyte 624 is not particularly limited, and examples thereof include known solid electrolytes, such as polymer solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, and nitride solid electrolytes.

[0158] Examples of polymer solid electrolytes include fluororesins (homopolymers such as polyvinylidene fluoride, polyhexafluoropropylene, and polytetrafluoroethylene, and copolymers having these as structural units), polyethylene oxide resins, polyacrylonitrile resins, and polyacrylate resins. In terms of excellent lithium ion conductivity, it is preferable to contain a sulfide solid electrolyte. For the same reason, it is preferable to contain a sulfide solid electrolyte containing sulfur and at least one of lithium and phosphorus as constituent elements.

[0159] The oxide solid electrolyte may be a lithium-containing oxide solid electrolyte particle, such as Li2O-B2O3-P2O5 or Li2O-SiO2. Examples of sulfide solid electrolytes include sulfide solid electrolytes containing sulfur and at least one of lithium and phosphorus as constituent elements, such as 8Li2O 67Li2S 25P2S5, Li2S, P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li3PO4-P2S5, LiI-Li2S-P2O5, and LiI-Li2S-B2S3. The halide solid electrolyte may be, for example, LiI. The nitride solid electrolyte may be, for example, Li3N.

[0160] (Manufacturing method of 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 the positive electrode current collector 240 and dried to obtain a positive electrode having 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 the negative electrode current collector 440 and dried to obtain a negative electrode having 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 a solid electrolyte 624 for forming the solid electrolyte layer 620 is applied onto the substrate and dried to form a layer of the solid electrolyte. Next, a polyimide film (porous polyimide film according to this embodiment) serving as a support 622 and a layered solid electrolyte 624 are superimposed on the positive electrode active material layer 220 of the positive electrode, as materials for forming a solid electrolyte layer 620. Furthermore, a negative electrode is superimposed on the material for forming the solid electrolyte layer 620, with the negative electrode active material layer 420 facing the positive electrode active material layer 220, to form a laminated structure. The laminated structure has a positive electrode (positive electrode current collector 240, positive electrode active material layer 220), solid electrolyte layer 620, and negative electrode (negative electrode active material layer 420, negative electrode current collector 440) superimposed 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 that is the support 622, and the solid electrolyte 624 is supported. Next, the laminated structure is housed in an exterior member. In this way, the all-solid-state battery 200 is obtained. [Example]

[0161] 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 by mass.

[0162] <Preparation of particle dispersion> (Preparation of PSt particle dispersion) 670 parts by mass of styrene, 12.1 parts by mass of surfactant Dowfax 2A1 (47% solution, manufactured by Dow Chemical Company), and 670 parts by mass of ion-exchanged water were mixed, and the mixture was emulsified by stirring at 1,500 rpm for 30 minutes using a dissolver to prepare a monomer emulsion. A reaction vessel was charged with 1.10 parts by weight of Dowfax 2A1 (47% solution, manufactured by The Dow Chemical Company) and 1,500 parts by weight of ion-exchanged water. After heating to 75°C under a nitrogen stream, 70 parts by weight of the monomer emulsion was added, followed by the dropwise addition of a polymerization initiator solution (15 parts by weight of ammonium persulfate dissolved in 98 parts by weight of ion-exchanged water) over 10 minutes. After the dropwise addition, the mixture was allowed to react for 50 minutes. The remaining monomer emulsion was then added dropwise over 220 minutes. The mixture was allowed to react for another 50 minutes, and then cooled to obtain PSt particle dispersion-2. The average particle size of the resin particles was 0.81 μm.

[0163] Example 1 To prepare resin particle dispersion (1), 128 g of ion-exchanged water was added to 39.21 g of PSt particle dispersion (16.04 g particles, 23.17 g ion-exchanged water) to adjust the resin particle solids concentration to 9.6% by mass. To this resin particle dispersion, 1.61 g (14.89 mmol) of p-phenylenediamine (molecular weight 108.14), 0.24 g (1.20 mmol) of oxydianiline ether (molecular weight 200.24), and 4.74 g (16.1 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (molecular weight 294.22) were added and dispersed by stirring at 50°C for 10 minutes. Next, a mixture of 3.46 g (34.9 mmol) of N-methylpyrrolidone (organic amine compound), 2.93 g (29.0 mmol) of 4-methylmorpholine, and 22.40 g of ion-exchanged water was slowly added, and the mixture was stirred for 24 hours while maintaining the reaction temperature at 50°C to dissolve and react, yielding a polyimide precursor solution (PAA-1) in which resin particles were dispersed. The polyimide precursor solution was applied to a 1.0 mm thick glass substrate over an area of ​​15 cm x 15 cm using an applicator, and then dried in an oven at 80°C for 20 minutes, thereby obtaining a polyimide precursor film. The applicator gap was adjusted so that the average thickness of the dried film after drying was 0.55 μm.

[0164] <Example 2> A polyimide precursor film was obtained in the same manner as in Example 1, except that after coating the polyimide precursor solution, it was dried in an oven at 80°C for 10 minutes and then further dried in an oven at 150°C for 10 minutes.

[0165] Example 3 A polyimide precursor film was obtained in the same manner as in Example 1, except that after coating the polyimide precursor solution, it was dried in an oven at 80°C for 8 minutes.

[0166] Example 4 Resin particle dispersion (2) was prepared by adding 68 g of ion-exchanged water to 98.03 g of PSt particle dispersion (40.09 g of particles, 57.94 g of ion-exchanged water). 2.42 g (22.4 mmol) of p-phenylenediamine, 0.36 g (1.8 mmol) of oxydianiline ether, and 7.12 g (24.2 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride were added to the resin particle dispersion and dispersed by stirring at 50°C for 10 minutes. Next, a mixture of 5.20 g (52.5 mmol) of N-methylpyrrolidone, 4.41 g (43.6 mmol) of 4-methylmorpholine, and 14.39 g of ion-exchanged water was slowly added, and the mixture was stirred for 24 hours while maintaining the reaction temperature at 50°C to dissolve and react, yielding a polyimide precursor solution (PAA-2) in which resin particles were dispersed. A polyimide precursor film was obtained in the same manner as in Example 1, except that the coating liquid was changed to PAA-2.

[0167] <Example 5> To 20 g of PAA-1, 0.19 g (2.3 mmol) of 4-methylimidazole and 0.95 g (9.4 mmol) of 4-methylmorpholine were added and stirred to obtain a polyimide precursor solution (PAA-3). A polyimide precursor film was obtained in the same manner as in Example 1, except that after coating, PAA-3 was dried in an oven at 110°C for 20 minutes.

[0168] Example 6 To 20 g of PAA-1, 0.95 g (9.4 mmol) of 4-methylmorpholine and 19.05 g of ion-exchanged water were added and stirred to obtain a polyimide precursor solution (PAA-4). A polyimide precursor film was obtained in the same manner as in Example 1, except that after coating, PAA-4 was dried in an oven at 110°C for 10 minutes.

[0169] <Comparative Example 1> A polyimide precursor film was obtained in the same manner as in Example 1, except that after coating the polyimide precursor solution, it was dried in an oven at 80°C for 10 minutes, and then further dried in an oven at 150°C for 5 minutes and then in an oven at 200°C for 10 minutes.

[0170] <Comparative Example 2> A polyimide precursor film was obtained in the same manner as in Example 1, except that after the application of the polyimide precursor solution, it was dried in an oven at 60°C for 8 minutes.

[0171] <Comparative Example 3> A polyimide precursor film was obtained in the same manner as in Example 1, except that PAA-2 was used as the coating liquid, and the polyimide precursor solution (PAA-2) was applied and then dried in an oven at 60°C for 10 minutes.

[0172] <Evaluation> The polyimide precursor film of each example was evaluated as follows.

[0173] (tensile strength) The tensile strength of the polyimide precursor film was measured by a tensile test in accordance with ISO 527: 2012. Specifically, an ISO multipurpose test piece was prepared from the film, and the test piece was placed in a universal testing machine (Shimadzu Corporation, Autograph AG-Xplus) and subjected to a tensile test to determine the tensile strength (KPa). The tensile strength of the polyimide precursor films that were determined not to have self-supporting properties was not measured.

[0174] (Self-autonomy) The evaluation of self-reliance was carried out as follows. When a film can be peeled off from a solid substrate while maintaining its shape after being formed on the solid substrate, it is judged to have self-supporting properties.

[0175] [Table 1]

[0176] The above results show that the polyimide precursor film of this example has higher tensile strength, is less susceptible to breakage, and is self-supporting, compared to the polyimide precursor film of the comparative example. This also shows that the polyimide precursor coating of this example provides a polyimide film with reduced breakage compared to the polyimide precursor coating of the comparative example. [Explanation of symbols]

[0177] 10 Porous polyimide film 10A hole 31 PCB 51 Peeling layer 100 Lithium-ion secondary battery 200 Solid state battery

Claims

1. a polyimide precursor; a total content of water and the solvent other than water is 5% by mass or more and 40% by mass or less, and a mass ratio of the water to the solvent other than water (water / solvent other than water) is 0 to 2.5, The polyimide precursor film, wherein the solvent contains a morpholine.

2. a polyimide precursor; The total content of water and the solvent other than water is 5% by mass or more and 40% by mass or less, and the tensile strength is 5 kPa or more and 40 kPa or less, The polyimide precursor film, wherein the solvent contains a morpholine.

3. 3. The polyimide precursor film according to claim 1, wherein the total content of the solvents including the water and the solvent other than water is 8% by mass or more and 33% by mass or less.

4. 3. The polyimide precursor film according to claim 1, wherein a mass ratio of the water to the solvent other than water (water / solvent other than water) is 0 or more and 1.0 or less.

5. The polyimide precursor film according to any one of claims 1 to 4, wherein the morpholine is a morpholine represented by the following general formula (MO): 【Chemical 1】 (In the general formula (MO), R ＭＯ１ represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

6. Contains particles The particles have a volume average particle size of 0.1 μm or more and 1 μm or less, The polyimide precursor film according to any one of claims 1 to 5, wherein the content of the particles is 30% by mass or more and 80% by mass or less with respect to the total amount of the polyimide precursor and the particles.

7. The polyimide precursor film according to claim 6, wherein the particles are resin particles.

8. A method for producing a polyimide film, comprising the step of heating the polyimide precursor film according to any one of claims 1 to 7 to imidize the polyimide precursor to form a polyimide film.

9. 8. A method for producing a polyimide film, comprising: a step of heating the polyimide precursor film according to claim 6 to imidize the polyimide precursor to form a polyimide film, the step including a treatment to remove the particles.

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