Polyimide precursor solution, method for producing porous polyimide film, and porous polyimide film

Abstract

To provide a polyimide precursor solution capable of obtaining a dry film good in coating properties, and high in strength while securing dispersibility of particles.SOLUTION: A polyimide precursor solution includes: an aqueous solvent containing water; a particle; and a polyimide precursor, where the polyimide precursor has a high molecular region A including a high molecular weight side maximum value, and a low molecular region B including a low molecular weight side maximum value, in an elution curve by gel permeation chromatography, the weight average molecular weight of the high molecular region A is 50,000 or higher, the weight average molecular weight of the low molecular region B is 10,000 or higher and 30,000 or lower, and when an area of the high molecular region A is a, and an area of the low molecular region B is b, the a / (a+b) value is 0.60 or more and 0.98 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In Patent Document 1, "In the elution curve by gel permeation chromatography, The polyimide precursor solution contains a polyimide precursor having a region A including a maximum value and a region B including a low molecular weight maximum value, the weight average molecular weight of the region A being 10,000 or more and the weight average molecular weight of the region B being less than 10,000, in terms of polystyrene, and satisfying formula (1) (formula (1): a / (a+b)=0.70 or more and 0.98 or less), where a is the area of ​​the region A and b is the area of ​​the region B." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-044074 A Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, which can provide a dried coating film having good coatability and high strength while ensuring the dispersibility of particles, as compared with a case in which the polyimide precursor has a following a / (a+b) value of less than 0.60 or more than 0.98. [Means for solving the problem]

[0005] The above problems are solved by the following means: <1> The method includes the steps of: preparing a polyimide precursor; The polyimide precursor has a polymer region A including a maximum value on the high molecular weight side and a low molecular weight region B including a maximum value on the low molecular weight side in an elution curve by gel permeation chromatography, the weight average molecular weight of the polymer region A is 50,000 or more, the weight average molecular weight of the low molecular weight region B is 10,000 or more and 30,000 or less, and when the area of the polymer region A is a and the area of the low molecular weight region B is b, the a / (a + b) value is 0.60 or more and 0.98 or less. A polyimide precursor solution. <2> The polyimide precursor solution according to <1>, wherein the a / (a + b) value is 0.70 or more and 0.95 or less. <3> The polyimide precursor solution according to <1> or <2>, wherein the difference in weight average molecular weight between the polymer region A and the low molecular weight region B is 20,000 or more and 90,000 or less. <4> The polyimide precursor solution according to <3>, wherein the difference in weight average molecular weight between the polymer region A and the low molecular weight region B is 20,000 or more and 70,000 or less. <5> The polyimide precursor solution according to any one of <1> to <4>, comprising at least one selected from the group consisting of a secondary amine compound and a tertiary amine compound. <6> The polyimide precursor solution according to <5>, wherein 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).

Chemical formula

Advantages of the Invention

[0006] According to the invention according to <1>, in a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, compared with the case where the following a / (a + b) value in the polyimide precursor is less than 0.60 or more than 0.98, a polyimide precursor solution is provided that can obtain a dry film with good coatability and high strength while ensuring the dispersibility of the particles. According to the invention according to <2>, compared with the case where the a / (a + b) value is less than 0.70 or more than 0.95, a polyimide precursor solution is provided that can obtain a dry film with good coatability and high strength while ensuring the dispersibility of the particles.

[0007] According to the invention according to <3>, compared with the case where the difference in the weight average molecular weight between the high molecular weight region A and the low molecular weight region B is less than 20,000 or more than 90,000, a polyimide precursor solution is provided that can obtain a dry film with good coatability and high strength while ensuring the dispersibility of the particles. According to the invention according to <4>, a polyimide precursor solution is provided which can obtain a dried film with good coatability and high strength while ensuring the dispersibility of particles, as compared with the case where the difference in weight average molecular weight between the polymer region A and the low molecular region B is less than 20,000 or more than 70,000.

[0008] According to the invention according to <5>, a polyimide precursor solution is provided which can obtain a dried film with good coatability and high strength while ensuring the dispersibility of particles, as compared with the case where the polyimide precursor solution contains only a primary amine compound as an amine compound. According to the invention according to <6>, a polyimide precursor solution is provided which can obtain a dried film with good coatability and high strength while ensuring the dispersibility of particles, as compared with the case where the polyimide precursor solution contains only triethylamine, N-alkylpiperidine, or dimethylaminoethanol as a secondary or tertiary amine compound.

[0009] According to the invention according to <7>, in a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, compared with the case where the following a / (a + b) value in the polyimide precursor is less than 0.60 or more than 0.98, even when the volume content ratio of particles to the polyimide precursor (particles / polyimide precursor) is 40 / 60 or more and 80 / 20 or less, a polyimide precursor solution is provided which can obtain a dried film with good coatability and high strength while ensuring the dispersibility of particles. According to the invention according to <8>, in a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, compared with the case where the following a / (a + b) value in the polyimide precursor is less than 0.60 or more than 0.98, even when the content of particles is 30% by mass or more and 85% by mass or less with respect to the total amount of the polyimide precursor and particles, a polyimide precursor solution is provided which can obtain a dried film with good coatability and high strength while ensuring the dispersibility of particles.

[0010] According to the invention according to <9>, in a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, compared with the case where a polyimide precursor solution in which the following a / (a + b) value in the polyimide precursor is less than 0.60 or more than 0.98 is applied, a porous polyimide film having pores closer to being uniform, less surface unevenness, and suppressed breakage is obtained, and a method for producing a porous polyimide film is provided. According to the invention according to <10>, in a polyimide precursor solution containing an aqueous solvent containing water, particles, and a polyimide precursor, compared with the case where a polyimide precursor solution in which the following a / (a + b) value in the polyimide precursor is less than 0.60 or more than 0.98 is applied, a porous polyimide film having pores closer to being uniform, less surface unevenness, and suppressed breakage is provided.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments which are an example of the present invention will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0013] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, if there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0014] "Film" is a concept that includes not only what is generally called "film", but also what is generally called "membrane" and "sheet".

[0015] <Polyimide precursor solution> The polyimide precursor solution according to this embodiment includes an aqueous solvent containing water, particles, and a polyimide precursor. The polyimide precursor has a high molecular weight region A including a maximum value on the high molecular weight side and a low molecular weight region B including a maximum value on the low molecular weight side in the elution curve by gel permeation chromatography. The weight average molecular weight of the high molecular weight region A is 50,000 or more, the weight average molecular weight of the low molecular weight region B is 10,000 or more and 30,000 or less. When the area of the high molecular weight region A is a and the area of the low molecular weight region B is b, the value of a / (a + b) is 0.60 or more and 0.98 or less.

[0016] The polyimide precursor solution according to this embodiment can obtain a dry film with good coatability and high strength while ensuring the dispersibility of the particles. The reason is speculated as follows.

[0017] When the weight average molecular weight of the polyimide precursor (that is, polyamic acid) in the polyimide precursor solution in which the particles are dispersed is high, the viscosity becomes high. Therefore, when the polyimide precursor solution is applied, unevenness is likely to occur in the coating film. On the other hand, if the weight average molecular weight of the polyimide precursor (that is, polyamic acid) is lowered to reduce the viscosity of the solution, the strength of the dry film obtained by drying the coating film of the polyimide precursor solution decreases. When the strength of the dry film decreases, damage occurs when the dry film is peeled off from the coating substrate before imidization and when the dry film is wound into a roll. However, simply adjusting the "molecular weight characteristics by gel permeation chromatography" in the polyimide precursor for the purpose of improving coatability and the strength of the dried film as shown in Patent Document 1 will reduce the dispersibility of the particles.

[0018] On the other hand, when applying a polyimide precursor having the molecular weight characteristics by the above gel permeation chromatography, a dried film with good coatability and high strength can be obtained. In addition, the decrease in the dispersibility of the particles is suppressed, and the dispersibility of the particles is ensured. If the weight average molecular weight of the polyimide precursor is too low, the viscosity of the polyimide precursor solution in which the particles are dispersed becomes too low, and the particles may settle, resulting in a decrease in the dispersibility of the particles. In contrast, the polyimide precursor solution according to the present embodiment contains a polyimide precursor with a high weight average molecular weight (a polyimide precursor with a weight average molecular weight of 50,000 or more) and a polyimide precursor with a low weight average molecular weight (a weight average molecular weight of 10,000 or more and 30,000 or less). Therefore, it is considered that the viscosity of the polyimide precursor solution does not become too low, the particles do not settle, and the dispersibility of the particles is ensured.

[0019] It is presumed that the polyimide precursor solution according to the present embodiment can obtain a dried film with good coatability and high strength while ensuring the dispersibility of the particles. When applying the polyimide precursor solution according to the present embodiment, during the manufacturing process of the porous polyimide film, coating unevenness is suppressed, and breakage of the dried film is suppressed. Moreover, since the dispersibility of the particles is ensured, the particles are dispersed in a state close to uniform in the dried film. Therefore, a porous polyimide film having pores close to uniform, less surface unevenness, and suppressed breakage can be obtained.

[0020] Hereinafter, the details of the polyimide precursor solution according to the present embodiment will be described.

[0021] (Polyimide Precursor) The polyimide precursor has a polymer region A including a maximum value on the high molecular weight side and a low molecular weight region B including a maximum value on the low molecular weight side in the elution curve by gel permeation chromatography. That is, the polyimide precursor has two maximum values, namely, a maximum value on the high molecular weight side and a maximum value on the low molecular weight side, in the elution curve by gel permeation chromatography (GPC).

[0022] The weight average molecular weight of the polymer region A is 50,000 or more. When the weight average molecular weight of the polymer region A is less than 50,000, the strength of the dry film decreases. The upper limit of the weight average molecular weight of the polymer region A is, for example, 100,000 or less.

[0023] The weight average molecular weight of the low molecular weight region B is 10,000 or more and 30,000 or less. When the weight average molecular weight of the low molecular weight region B is less than 10,000, the strength of the dry film decreases. When the weight average molecular weight of the low molecular weight region B exceeds 30,000, the coatability decreases and coating unevenness occurs.

[0024] From the viewpoints of ensuring the dispersibility of particles, improving coatability, and improving the strength of the dry film, the difference in the weight average molecular weight between the polymer region A and the low molecular weight region B is preferably G20,000 or more and 90,000 or less, and more preferably 20,000 or more and 70,000 or less.

[0025] Here, the weight average molecular weights of the polymer region A and the low molecular weight region B are in the range in terms of polystyrene conversion.

[0026] When the area of the polymer region A is a and the area of the low molecular weight region B is b, the a / (a + b) value (hereinafter, also referred to as "GPC peak area ratio") is 0.60 or more and 0.98 or less. By setting the GPC peak area ratio within the above range, a dry film with good coatability and high strength can be obtained while ensuring the dispersibility of particles. When the GPC peak area ratio is less than 0.60, the strength of the dry film decreases. When the GPC peak area ratio exceeds 0.98, the coatability decreases and coating unevenness occurs.

[0027] From the viewpoints of ensuring the dispersibility of particles, improving coatability, and enhancing the strength of the dried film, the GPC peak area ratio is preferably 0.70 or more and 0.95 or less, more preferably 0.75 or more and 0.93 or less.

[0028] From the viewpoints of ensuring the dispersibility of particles, improving coatability, and enhancing the strength of the dried film, the weight average molecular weight of the entire polyimide precursor is preferably 20,000 or more and 200,000 or less, more preferably 30,000 or more and 150,000 or less, still more preferably 50,000 or more and 130,000 or less. Here, the weight average molecular weight of the entire polyimide precursor represents the weight average molecular weight in the entire region including the high molecular weight region A containing the high molecular weight side maximum value and the low molecular weight region B containing the low molecular weight side maximum value.

[0029] The weight average molecular weight of the polyimide precursor is measured by gel permeation chromatography (gel permeation chromatography: GPC) under the following measurement conditions. · Column: Tosoh TSKgel α-M (7.8 mm I.D × 30 cm) · Eluent: DMF (dimethylformamide) / 30 mM LiBr / 60 mM phosphoric acid · Flow rate: 0.6 mL / min · Injection volume: 60 μL · Detector: RI (differential refractive index detector)

[0030] On the other hand, the measurement methods for the area a of the high molecular weight region A and the area b of the low molecular weight region B are as follows. First, prepare a polyimide precursor solution to be measured. Next, measure the polyimide precursor in the polyimide precursor solution under the same conditions as the above GPC method. When measured by the GPC method, an elution curve is obtained. Identify the high molecular weight region A and the low molecular weight region B from the elution curve. Then, determine the weight average molecular weight of the high molecular weight region A and the low molecular weight region B in terms of polystyrene conversion. Determine the area a of the high molecular weight region A and the area b of the low molecular weight region B, and calculate the GPC peak area ratio (a / (a + b)).

[0031] The polyimide precursor solution containing the polyimide precursor having the above molecular weight characteristics can be obtained, for example, by mixing two polyimide precursor solutions having different molecular weights obtained by a method for producing a polyimide precursor solution. Specifically, by adjusting the polymerization conditions of the polyimide precursor such as the polymerization temperature and reaction time, a first polyimide precursor solution having a weight average molecular weight of 50,000 or more and a second polyimide precursor solution having a weight average molecular weight of 10,000 or more and 30,000 or less are prepared. Then, the first polyimide precursor solution and the second polyimide precursor solution are mixed so that the GPC peak area ratio satisfies the above range.

[0032] The polyimide precursor is a resin (polyimide precursor) having a repeating unit represented by the following general formula (I).

[0033]

Chemical formula

[0034] (In the general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

[0035] Here, in the general formula (I), the tetravalent organic group represented by A is the residue obtained by removing four carboxyl groups from the tetracarboxylic dianhydride as a raw material. On the other hand, the divalent organic group represented by B is the residue obtained by removing two amino groups from the diamine compound as a raw material.

[0036] That is, the polyimide precursor having a repeating unit represented by the general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound.

[0037] Examples of the tetracarboxylic dianhydride include both aromatic and aliphatic compounds, but aromatic compounds are preferred. That is, in the general formula (I), the tetravalent organic group represented by A is preferably an aromatic organic group.

[0038] Examples of the aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, 3,3’,4,4’-biphenylsulfone tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 3,3’,4,4’-biphenyl ether tetracarboxylic dianhydride, 3,3’,4,4’-dimethyldiphenylsilane tetracarboxylic dianhydride, 3,3’,4,4’-tetraphenylsilane tetracarboxylic dianhydride, 1,2,3,4-furan tetracarboxylic dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy) diphenyl sulfone dianhydride, 4,4’-bis(3,4-dicarboxyphenoxy) diphenyl propane dianhydride, 3,3’,4,4’-perfluoroisopropylidene diphthalic dianhydride, 3,3’,4,4’-biphenyl tetracarboxylic dianhydride, 2,3,3’,4’-biphenyl tetracarboxylic dianhydride, bis(phthalic acid) phenylphosphine oxide dianhydride, p-phenylene-bis(triphenylphthalic acid) dianhydride, m-phenylene-bis(triphenylphthalic acid) dianhydride, bis(triphenylphthalic acid)-4,4’-diphenyl ether dianhydride, bis(triphenylphthalic acid)-4,4’-diphenylmethane dianhydride, and the like.

[0039] Examples of the aliphatic tetracarboxylic dianhydrides include aliphatic or alicyclic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; aliphatic tetracarboxylic dianhydrides having an aromatic ring such as 1,3,3a,4,5,9b-hexahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, etc.

[0040] Among these, as the tetracarboxylic dianhydride, aromatic tetracarboxylic dianhydrides are preferred. Specifically, for example, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride are preferred. Further, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride are preferred. In particular, 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferred.

[0041] The tetracarboxylic dianhydride may be used alone or in combination of two or more. When two or more of them are combined and used in combination, an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic acid may be used in combination, or an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride may be combined.

[0042] On the other hand, the diamine compound is a diamine compound having two amino groups in the molecular structure. Examples of the diamine compound include both aromatic and aliphatic compounds, but it is preferably an aromatic compound. That is, in the general formula (I), the divalent organic group represented by B is preferably an aromatic organic group.

[0043] Examples of the diamine compound include aromatic diamines such as p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide, 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)-biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, 4,4'-bis[4-(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl; and aromatic diamines having two amino groups bonded to an aromatic ring and a hetero atom other than the nitrogen atom of the amino group, such as diaminotetraphenylthiophene.1,1-Metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenenediamine, hexahydro-4,7-methanoindanylenemethylenediamine, tricyclo[6,2,1,0; 2.7 -undecylenebismethyldiamine, aliphatic diamines such as 4,4'-methylenebis(cyclohexylamine), and alicyclic diamines and the like can be mentioned.

[0044] Among these, as the diamine compound, aromatic diamine compounds are preferable. Specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone are preferable. In particular, 4,4'-diaminodiphenyl ether and p-phenylenediamine are preferable.

[0045] The diamine compound may be used alone or in combination of two or more. Further, when two or more 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 combined.

[0046] The content (concentration) of the polyimide precursor is preferably 0.1% by mass or more and 40% by mass or less, more preferably 0.5% by mass or more and 25% by mass or less, and still more preferably 1% by mass or more and 20% by mass or less with respect to the polyimide precursor solution.

[0047] (Particles) Examples of the particles include resin particles and inorganic particles. As the particles, those that are insoluble in the polyimide precursor solution are used. In this embodiment, "not soluble" includes that the target substance dissolves in the target liquid within a range of 3% by mass or less with respect to the target liquid at 25°C. The particles may be used alone or in combination of two or more.

[0048] As the particles, resin particles are preferred. The resin particles are not particularly limited, but are resin particles made of a resin other than polyimide. For example, resin particles obtained by polycondensing polymerizable monomers such as polyester resin and urethane resin, and resin particles obtained by radical polymerization of polymerizable monomers such as vinyl resin, olefin resin, and fluororesin can be mentioned. Examples of the resin particles obtained by radical polymerization include resin particles of (meth)acrylic resin, (meth)acrylate resin, styrene-(meth)acrylic resin, polystyrene resin, and polyethylene resin. Among these, as the resin particles, it is preferable that they are at least one selected from the group consisting of (meth)acrylic resin, (meth)acrylate resin, styrene-(meth)acrylic resin, and polystyrene resin. In this embodiment, "(meth)acrylic" means including both "acrylic" and "methacrylic".

[0049] Further, the resin particles may or may not be crosslinked. In the imidization step of the polyimide precursor, uncrosslinked resin particles are preferred in terms of effectively contributing to the relaxation of residual stress. Furthermore, in terms of simplifying the process of manufacturing the polyimide precursor solution, it is more preferable that the polyimide precursor solution contains vinyl resin particles obtained by emulsion polymerization as the resin particles.

[0050] When the resin particles are vinyl resin particles, they are obtained by polymerizing monomers. Examples of monomers for vinyl resins include the monomers shown below. For example, styrenes having a styrene skeleton such as styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene; esters having a vinyl group such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, trimethylolpropane trimethacrylate (TMPTMA); vinyl nitriles such as acrylonitrile, methacrylonitrile; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone; acids such as (meth)acrylic acid, maleic acid, cinnamic acid, fumaric acid, vinylsulfonic acid; bases such as ethyleneimine, vinylpyridine, vinylamine; and vinyl resin units obtained by polymerizing these monomers. As other monomers, monofunctional monomers such as vinyl acetate, difunctional monomers such as ethylene glycol dimethacrylate, nonanediol diacrylate, decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate may be used in combination. Also, the vinyl resin may be a resin using these monomers alone or a copolymer resin using two or more monomers.

[0051] The resin particles preferably have an acidic group on the surface in terms of improved dispersibility and suppression of pinhole generation. The acidic group present on the surface of the resin particles is considered to function as a dispersant for the resin particles by forming a salt with a base such as an organic amine compound used to dissolve the polyimide precursor in an aqueous solvent. Therefore, it is considered that the dispersibility of the resin particles in the polyimide precursor solution is improved.

[0052] The acidic group possessed on the surface of the resin particles is not particularly limited, but may preferably be at least one selected from the group consisting of a carboxy group, a sulfonic acid group, and a phenolic hydroxyl group. Among these, a carboxy group is preferred.

[0053] The monomer for having an acidic group on the surface of the resin particles is not particularly limited as long as it is a monomer having an acidic group. For example, monomers having a carboxy group, monomers having a sulfonic acid group, monomers having a phenolic hydroxyl group, and salts thereof can be mentioned. Specifically, for example, monomers having a sulfonic acid group such as p-styrenesulfonic acid and 4-vinylbenzenesulfonic acid; monomers having a phenolic hydroxyl group such as 4-vinyldihydrocaffeic acid, 4-vinylphenol, and 4-hydroxy-3-methoxy-1-propenylbenzene; 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, and monoethyl fumarate; and salts thereof; can be mentioned. These monomers having an acidic group may be polymerized by mixing with a monomer not having an acidic group, or after polymerizing and granulating a monomer not having an acidic group, a monomer having an acidic group may be polymerized on the surface. Further, these monomers may be used alone or in combination of two or more.

[0054] Among these, 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, and monoethyl fumarate, and salts thereof are preferred. The monomers having a carboxy group may be used alone or in combination of two or more. That is, the resin particles having an acidic group on the surface preferably have a skeleton derived from at least one monomer having a 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.

[0055] When mixing and polymerizing a monomer having an acidic group and a monomer having no acidic group, the amount of the monomer having an acidic group is not particularly limited. However, 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. If the amount of the monomer having an acidic group is too large, aggregates of the polymer may occur during emulsion polymerization. Therefore, the monomer having an acidic group is preferably 0.3% by mass or more and 20% by mass or less of the total monomers, 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. On the other hand, when emulsion polymerizing a monomer having no acidic group and then adding and polymerizing a monomer having an acidic group, in the same manner as above, the amount of the monomer having an acidic group is preferably 0.01% by mass or more and 10% by mass or less of the total monomers, 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.

[0056] As described above, it is preferable that the resin particles are not crosslinked. However, when crosslinking the resin particles, when using a crosslinking agent as at least a part of the monomer component, the ratio of the crosslinking agent in all the monomer components 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.

[0057] When the monomer used for the resin constituting the vinyl resin particles contains styrene, the ratio of styrene in all the monomer components is preferably 20% by mass or more and 100% by mass or less, and more preferably 40% by mass or more and 100% by mass or less.

[0058] In addition, the resin particles may be those obtained by polymerizing a monomer having an acidic group on the surface of a commercially available product. Specifically, examples of the crosslinked resin particles include crosslinked polymethyl methacrylate (MBX series, manufactured by Sekisui Chemical Co., Ltd.), crosslinked polystyrene (SBX series, manufactured by Sekisui Chemical Co., Ltd.), copolymer crosslinked resin particles of methyl methacrylate and styrene (MSX series, manufactured by Sekisui Chemical Co., Ltd.), and the like. Examples of the non-crosslinked resin particles include polymethyl methacrylate (MB series, manufactured by Sekisui Chemical Co., Ltd.), (meth)acrylic acid ester / styrene copolymer (FS series: manufactured by Nippon Paint Co., Ltd.), and the like.

[0059] Specific examples of the inorganic particles include silica particles, titanium oxide particles, aluminum oxide particles, and the like.

[0060] The silica particles may be sol-gel silica obtained by the sol-gel method or fumed silica obtained by the vapor phase method. Further, the silica particles may be synthesized or commercially available products may be used. Furthermore, the silica particles may be an aqueous solvent dispersion (for example, Snowtex (registered trademark) series manufactured by Nissan Chemical Industries, Ltd.) or a dry powder (for example, Aerosil series manufactured by Evonik Industries AG). From the viewpoint of dispersibility, it is preferable to use an aqueous dispersion of silica particles.

[0061] In addition, the inorganic particles may contain particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc, which are added to improve mechanical strength.

[0062] The volume average particle diameter of the particles is preferably 0.1 μm or more and 1 μm or less. More preferably, the volume average particle diameter of the particles is 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 volume particle size distribution index (GSDv) of the particles is preferably 1.30 or less, more preferably 1.25 or less, and most preferably 1.20 or less.

[0063] The volume-average particle diameter is measured as the volume-average diameter D50v, which is the particle diameter at which the cumulative distribution reaches 50% for all particles, by using the particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (for example, the Coulter Counter LS13 described above, manufactured by Beckman Coulter, Inc.) and subtracting the cumulative distribution from the smaller particle size side for each divided particle size range (channel) with respect to volume. The volume particle size distribution index of the particles is calculated as (D84v / D16v) 1 / 2 from the particle size distribution of the particles in the polyimide precursor solution. Here, the particle diameter at which the cumulative distribution reaches 16% is defined as the volume particle diameter D16v, and the particle diameter at which the cumulative distribution reaches 50% is defined as the volume-average particle diameter D50v, both measured from the smaller particle size side of the volume cumulative distribution of the particles.

[0064] The volume content ratio of the particles to the polyimide precursor (particles / polyimide precursor) is preferably 40 / 60 or more and 80 / 20 or less, more preferably 45 / 55 or more and 78 / 22 or less, and even more preferably 50 / 50 or more and 74 / 26 or less. The content of the particles is preferably 30% by mass or more and 85% by mass or less, more preferably 35% by mass or more and 80% by mass or less, and even more preferably 40% by mass or more and 80% by mass or less, based on the total amount of the polyimide precursor and the particles. When the polyimide precursor solution contains particles within the above range, when the polyimide precursor solution is applied to form a coating film during the production of the porous polyimide film, the resin particles are likely to be present throughout the coating film. Therefore, the pores obtained by removing the resin particles are likely to be present throughout the film, and a structure in which the pores communicate with each other is more likely to be formed. Moreover, even when the polyimide precursor solution contains a large amount of particles within the above range, a dried film with good coatability and high strength can be obtained while ensuring the dispersibility of the particles.

[0065] (aqueous solvent) When polymerizing a tetracarboxylic dianhydride and a diamine compound in a resin particle and inorganic particle dispersion, the resin particles used in the preparation of the resin particle and inorganic particle dispersion and the aqueous solvent in the inorganic particle dispersion may be used as they are. Further, when polymerizing a tetracarboxylic dianhydride and a diamine compound, the aqueous solvent may be prepared so as to be suitable for polymerization.

[0066] The aqueous solvent is an aqueous solvent containing water. Examples of the water include distilled water, ion-exchanged water, ultrafiltration water, pure water, and the like.

[0067] The water content is preferably 50% by mass or more based on the total amount of the aqueous solvent. By setting the water content within the above numerical range, the boiling point of the aqueous solvent further decreases. Therefore, the aqueous solvent is more likely to boil in the gaps between the polyimide precursors. As a result, more pores formed by the volatilization of the aqueous solvent are formed, and a structure in which the pores communicate with each other is more likely to be formed.

[0068] The water content is more preferably 70% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less based on the total amount of the aqueous solvent.

[0069] The aqueous solvent may contain a solvent other than water. The solvent other than water is preferably water-soluble. Here, water-soluble means that the target substance dissolves in water by 1% by mass or more at 25°C.

[0070] Examples of the solvent other than water include water-soluble organic solvents and aprotic polar solvents. The solvent other than water is preferably an aprotic polar solvent.

[0071] Examples of the water-soluble organic solvent include water-soluble ether solvents, water-soluble ketone solvents, water-soluble alcohol solvents, and the like.

[0072] A water-soluble ether-based solvent is a water-soluble solvent having an ether bond in one molecule. Examples of the water-soluble ether-based solvent include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and the like. Among these, tetrahydrofuran and dioxane are preferable as the water-soluble ether-based solvent.

[0073] A water-soluble ketone-based solvent is a water-soluble solvent having a ketone group in one molecule. Examples of the water-soluble ketone-based solvent include acetone, methyl ethyl ketone, cyclohexanone, and the like. Among these, acetone is preferable as the water-soluble ketone-based solvent.

[0074] A water-soluble alcohol-based solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Examples of the water-soluble alcohol-based 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, 1,2,6-hexanetriol, and the like. Among these, methanol, ethanol, 2-propanol, ethylene glycol, monoalkyl ethers of ethylene glycol, propylene glycol, monoalkyl ethers of propylene glycol, diethylene glycol, and monoalkyl ethers of diethylene glycol are preferable as the water-soluble alcohol-based solvent.

[0075] Examples of the aprotic polar solvent include solvents having a boiling point of 150°C or higher and 300°C or lower and a dipole moment of 3.0 D or higher and 5.0 D or lower. Specific examples of the aprotic polar solvent include, for example, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone (DMI), N,N'-dimethylpropyleneurea, tetramethylurea, trimethyl phosphate, triethyl phosphate, and the like.

[0076] The aqueous solvent preferably contains an aprotic polar solvent as a solvent other than water. Further, the content of the aprotic polar solvent is preferably 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the particles.

[0077] When the aqueous solvent contains an aprotic polar solvent as a solvent other than water, the content of the aprotic polar solvent is more preferably 3 parts by mass or more and 45 parts by mass or less, and still more preferably 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the particles.

[0078] (Organic amine compound) The polyimide precursor solution preferably contains an organic amine compound. By containing an organic amine compound, the polyimide precursor solution is likely to have increased solubility in the solvent of the polyimide precursor, is likely to have improved film-forming properties, and is also likely to have improved storage stability.

[0079] The organic amine compound is a compound that amine-chlorinates the polyimide precursor (its carboxy group) to enhance its solubility in the aqueous solvent and also functions as an imidization accelerator. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less. The organic amine compound is preferably a compound excluding the diamine that is a raw material of the polyimide precursor.

[0080] The action of amine-chlorinating the polyimide precursor of the organic amine (its carboxy group) to enhance its solubility in the aqueous solvent and the action of promoting imidization are more enhanced when the water content in the aqueous solvent is 50% by mass or more based on the whole aqueous solvent. Therefore, the polyimide precursor solution preferably contains an organic amine compound and has a water content of 50% by mass or more based on the whole aqueous solvent. The organic amine compound is preferably a water-soluble compound.

[0081] Examples of the organic amine compound include primary amine compounds, secondary amine compounds, and tertiary amine compounds. Among these, as the organic amine compound, at least one selected from secondary amine compounds and tertiary amine compounds (particularly, tertiary amine compounds) is preferable. When a tertiary amine compound or a secondary amine compound is applied as the organic amine compound (particularly, a tertiary amine compound), the solubility of the polyimide precursor in the solvent is more likely to increase, the film-forming property is more likely to improve, and the storage stability of the polyimide precursor solution is more likely to improve.

[0082] In addition to monovalent amine compounds, the organic amine compound also includes polyvalent amine compounds having two or more valences. When a polyvalent amine compound having two or more valences is applied, a pseudo-crosslinked structure is likely to be formed between the molecules of the polyimide precursor, and the storage stability of the polyimide precursor solution is likely to improve.

[0083] Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, 2-amino-2-methyl-1-propanol, and the like. Examples of the secondary amine compound include dimethylamine, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, morpholine, and the like. Examples of the tertiary amine compound include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, and the like. From the viewpoints of the pot life of the polyimide precursor solution and the film thickness uniformity of the film, the tertiary amine compound is preferable. In this regard, it is more preferable that it is 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.

[0084] Here, as the organic amine compound, from the viewpoint of film forming properties, an amine compound having a heterocyclic structure containing nitrogen (particularly, a tertiary amine compound) is also preferable. Examples of the amine compound having a heterocyclic structure containing nitrogen (hereinafter referred to as "nitrogen-containing heterocyclic amine compound") 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, and the like.

[0085] As the organic amine compound, from the viewpoint of film forming properties, it 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, as the organic amine compound, from the viewpoints of ensuring the dispersibility of particles, improving coatability, and enhancing the strength of the dried film, it 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). The imidazoles represented by the following general formula (IM) and the morpholines represented by the following general formula (MO) amine-chlorinate the polyimide precursor (its carboxyl group), making it easier to increase the solubility of the polyimide precursor in the solvent and easier to improve the coatability. Also, a part of the organic amine salt of this polyimide precursor is considered to function as a dispersant for the particles, improving the dispersibility of the particles. Further, the imidazoles represented by the following general formula (IM) and the morpholines represented by the following general formula (MO) function as imidization accelerators, and it is easy to obtain a dried film with high strength. Therefore, it is easy to ensure the dispersibility of particles, improve coatability, and enhance the strength of the dried film.

[0086]

Chemical formula

[0087] In general formula (IM), R IM1 , R IM2 , R IM3 , and R IM4 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. In general formula (MO), R MO1 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

[0088] In general formulas (IM) and (MO), the alkyl groups represented by R IM1 ~R IM4 and R MO1 may be either linear or branched. R IM1 ~R IM4 and R MO1 The alkyl groups represented are preferably alkyl groups having 1 to 6 carbon atoms, more preferably alkyl groups having 1 to 4 carbon atoms.

[0089] As the organic amine compound, it 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, volatilization of the organic amine compound from the polyimide precursor solution is suppressed during storage, and a decrease in the solubility of the polyimide precursor in the solvent is likely to be suppressed.

[0090] The organic amine compound is preferably contained in an amount of 50 mol% or more and 500 mol% or less, preferably 80 mol% or more and 250 mol% or less, more preferably 90 mol% or more and 200 mol% or less, based on the carboxy group (-COOH) of the polyimide precursor in the polyimide precursor solution. When the content of the organic amine compound is within the above range, the solubility of the polyimide precursor in the solvent is likely to increase, and the film-forming property is likely to improve. Also, the storage stability of the polyimide precursor solution is likely to improve.

[0091] The above organic amine compound may be used alone or in combination of two or more.

[0092] (Other additives) The polyimide precursor solution according to this embodiment may contain a catalyst for promoting the imidization reaction, a leveling agent for improving the film-forming quality, and the like. As the catalyst for promoting the imidization reaction, dehydrating agents such as acid anhydrides, acid catalysts such as phenol derivatives, sulfonic acid derivatives, and benzoic acid derivatives may be used.

[0093] Further, 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, the polyimide precursor solution may contain, depending on the purpose of use, for example, a conductive material added for imparting conductivity (conductivity (e.g., volume resistivity less than 10 7 Ω·cm) or semiconductive (e.g., volume resistivity 10 7 Ω·cm or more and 10 13 Ω·cm or less)). Examples of the conductive agent include carbon black (e.g., acidic carbon black with 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.); and the like. These conductive materials may be used alone or in combination of two or more.

[0094] (Viscosity characteristics of the polyimide precursor solution) The viscosity of the polyimide precursor solution according to this embodiment varies depending on the coating method. For example, when the temperature of the polyimide precursor solution is 20°C or higher and 25°C or lower, and the solid content concentration of the polyimide precursor solution is 5% by mass or higher and 20% by mass or lower, the viscosity of the polyimide precursor solution is preferably 50 Pa·s or higher and 400 Pa·s or lower, more preferably 100 Pa·s or higher and 350 Pa·s or lower, and even more preferably 150 Pa·s or higher and 300 Pa·s or lower. The viscosity of the polyimide precursor solution is measured with a No. 3 rotor 3°×R14 using an E-type viscometer TV-H manufactured by Toki Sangyo Co., Ltd.

[0095] By having the viscosity characteristics of the polyimide precursor solution, it becomes easier to obtain a dried film with good coatability and high strength while ensuring the dispersibility of the particles.

[0096] <Method for manufacturing a porous polyimide film> Hereinafter, an example of a preferred manufacturing method for the porous polyimide film according to this embodiment will be described. The porous polyimide film according to this embodiment has, for example, the following steps. A first step of forming a coating film by applying a polyimide precursor solution and then drying the coating film to form a film containing the polyimide precursor and the particles. A second step of heating the film to imidize the polyimide precursor to form a polyimide film, the second step including a treatment for removing the particles.

[0097] In the description of the manufacturing method, FIG. 1 referred to is a schematic diagram showing the configuration of the porous polyimide film according to this embodiment. In FIG. 1, the same reference numerals are given to the same components. Among the reference numerals in FIG. 1, 31 represents a substrate, 51 represents a release layer, 10A represents pores, and 10 represents a porous polyimide film.

[0098] (First step) In the first step, first, a polyimide precursor solution is prepared. The method for preparing the polyimide precursor solution will be described in detail below. As an example, the method for preparing a polyimide precursor solution containing resin particles as particles will be described.

[0099] Examples of the method for preparing the polyimide precursor solution according to this embodiment include the methods (i) and (ii) below. (i) A method in which a polyimide precursor solution before dispersing resin particles is prepared, and then the resin particles (powder or organic solvent dispersion) are mixed and dispersed (ii) A method in which a polyimide precursor is synthesized in an organic solvent dispersion of resin particles

[0100] (i) A method in which a polyimide precursor solution before dispersing resin particles is prepared, and then the resin particles are mixed and dispersed First, for the polyimide precursor solution before dispersing resin particles, a method can be used in which a resin (polyimide precursor) is formed by polymerizing a tetracarboxylic dianhydride and a diamine compound in an organic solvent using a known method to obtain a polyimide precursor solution before dispersing resin particles. Next, the resin particles described in the resin particle section are mixed and stirred into the obtained polyimide precursor solution before dispersing resin particles. Or, after redispersing in an organic solvent (which may be a single solvent or a mixed solvent) that does not dissolve the resin particles, it may be mixed and stirred with the polyimide precursor solution. Note that the methods of mixing, stirring, and dispersing are not particularly limited. Also, in order to improve the dispersibility of the resin particles, a known nonionic or ionic surfactant may be added.

[0101] (ii) Method for synthesizing a polyimide precursor in an organic solvent dispersion of resin particles First, prepare a solution in which resin particles are dispersed in an organic solvent in which the resin particles do not dissolve and the polyimide precursor dissolves. Next, in this solution, a tetracarboxylic dianhydride and a diamine compound are polymerized to produce a resin (polyimide precursor), and an organic solvent solution of the polyimide precursor is obtained.

[0102] 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 the particles. Then, the coating film formed on the substrate is dried to form a film containing the polyimide precursor and the particles.

[0103] The substrate onto which the polyimide precursor solution is applied is not particularly limited. For example, resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); composite material substrates in which these materials are combined, and the like. Further, on the substrate, if necessary, a release layer may be provided by performing a release treatment with, for example, a silicone-based or fluorine-based release agent.

[0104] The method for applying the polyimide precursor solution onto the substrate is not particularly limited. For example, various methods such as spray coating method, spin coating method, roll coating method, bar coating method, slit die coating method, inkjet coating method, and the like can be mentioned.

[0105] The coating amount of the polyimide precursor solution for obtaining a coating film containing the polyimide precursor solution and the particles may be set to an amount that can obtain a predetermined film thickness.

[0106] After forming a coating film containing a polyimide precursor solution and particles, it is dried to form a film containing the polyimide precursor and particles. Specifically, the coating film containing the polyimide precursor solution and particles is dried by a method such as heat drying, natural drying, vacuum drying, etc. to form a film. More specifically, the coating film is dried so that the solvent remaining in the film is 50% or less, preferably 30% or less, based on the solid content of the film to form a film.

[0107] (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 to form a polyimide film. And the second step includes a treatment for removing particles. Through the treatment of removing particles, a porous polyimide film is obtained.

[0108] In the second step, the step of forming the polyimide film specifically involves heating the film containing the polyimide precursor and particles obtained in the first step to allow imidization to proceed, and further heating to form a polyimide film in which imidization has proceeded. Note that as imidization proceeds and the imidization rate increases, it becomes difficult to dissolve in an organic solvent.

[0109] And in the second step, a treatment for removing particles is performed. 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 imidization is completed (after imidization). Note that in this embodiment, the process of imidizing the polyimide precursor refers to the process of heating the film containing the polyimide precursor and particles obtained in the first step to allow imidization to proceed, and being in a state prior to becoming a polyimide film after imidization is completed.

[0110] The process of removing particles is preferably carried out when the imidization rate of the polyimide precursor in the polyimide film is 10% or more in the process of imidizing the polyimide precursor, in terms of particle removability and the like. When the imidization rate is 10% or more, it is easy to maintain the morphology.

[0111] Next, the process of removing particles will be described. First, the process of removing resin particles will be described. Examples of the process of removing resin particles include a method of removing resin particles by heating, a method of removing resin particles with an organic solvent that dissolves the resin particles, a method of removing resin particles by decomposition with a laser or the like. Among these, a method of removing resin particles by heating and a method of removing resin particles with an organic solvent that dissolves the resin particles are preferable.

[0112] As a method of removing by heating, for example, in the process of imidizing the polyimide precursor, the resin particles may be removed by decomposing them by heating for promoting imidization. In this case, it is advantageous for process reduction in that there is no operation of removing resin particles with a solvent.

[0113] Examples of the method of removing resin particles with an organic solvent that dissolves the resin particles include a method of bringing the resin particles into contact with (for example, immersing in) an organic solvent that dissolves the resin particles and dissolving and removing the resin particles. When in this state, immersion in the solvent is preferable in that the dissolution efficiency of the resin particles is high.

[0114] The organic solvent that dissolves the resin particles for removing the resin particles is not particularly limited as long as it does not dissolve the polyimide film before the completion of imidization and the polyimide film after the completion of imidization, and the resin particles are soluble. For example, ethers such as tetrahydrofuran (THF); aromatics such as toluene; ketones such as acetone; esters such as ethyl acetate; can be mentioned.

[0115] When removing resin particles by dissolution to make it porous, those that can be dissolved in general-purpose solvents such as tetrahydrofuran, acetone, toluene, and ethyl acetate are preferred. Depending on the resin particles and polyimide precursor used, water can also be used. Also, when removing resin particles by heating to make it porous, it does not decompose at the drying temperature after coating, and is thermally decomposed at the temperature at which the polyimide precursor film is imidized. From this perspective, the thermal decomposition start 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 even more preferably 200°C or higher and 280°C or lower.

[0116] Here, the treatment for removing inorganic particles when the polyimide precursor solution contains inorganic particles will be described. As a treatment for removing inorganic particles, there is a method of removing them using a liquid in which the inorganic particles dissolve but the polyimide precursor or polyimide does not dissolve (hereinafter sometimes referred to as a "particle removal liquid"). The particle removal liquid is selected according to the inorganic particles used. For example, 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; aqueous solutions of bases such as sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, sodium carbonate, potassium carbonate, ammonia, and the above-mentioned organic amines; can be mentioned. Depending on the inorganic particles and polyimide precursor used, water alone can also be used.

[0117] In the second step, the heating method for heating the film obtained in the first step to promote imidization to obtain a polyimide film is not particularly limited. For example, a method of heating in two steps can be mentioned. When heating in two steps, specifically, the following heating conditions can be mentioned.

[0118] As the heating conditions in the first stage, it is desirable that the temperature be such that the shape of the particles is maintained. Specifically, for example, a range of 50°C or higher and 150°C or lower is good, and a range of 60°C or higher and 140°C or lower is preferable. Also, as the heating time, a range of 10 minutes or longer and 60 minutes or shorter is good. The higher the heating temperature, the shorter the heating time can be.

[0119] As the heating conditions in the second stage, for example, heating can be carried out under conditions of 150°C or higher and 450°C or lower (preferably 200°C or higher and 430°C or lower) for 20 minutes or longer and 120 minutes or shorter. By setting the heating conditions within this range, the imidization reaction can further proceed, and a polyimide film can be formed. During the heating reaction, it is preferable to gradually increase the temperature stepwise or at a constant rate before reaching the final temperature of heating.

[0120] Note that the heating conditions are not limited to the two-stage heating method described above. For example, a method of heating in one stage may be adopted. In the case of the one-stage heating method, for example, imidization may be completed only under the heating conditions shown in the second stage above.

[0121] In the second step, in terms of increasing the aperture ratio, it is preferable to perform a treatment to expose the particles so that the particles are in an exposed state. In the second step, the treatment to expose the particles is preferably carried out during the process of imidizing the polyimide precursor or before the treatment of removing the particles after imidization.

[0122] In this case, for example, when forming a film on a substrate using a polyimide precursor solution, the polyimide precursor solution is applied onto the substrate to form a coating film in which the particles are buried. Next, the coating film is dried to form a film containing the polyimide precursor and the particles. The film formed by this method will have the particles buried. With respect to this film, before performing the particle removal treatment after heating, a treatment may be performed to expose the particles from the polyimide film during the process of imidizing the polyimide precursor or after imidization (after imidization is completed).

[0123] In the second step, the process of exposing the particles can be performed, for example, when the polyimide film is in the following state. When performing the process of exposing the particles when the imidization rate of the polyimide precursor in the polyimide film is less than 10% (that is, when the polyimide film can be dissolved in a solvent), examples of the process of exposing the particles buried in the polyimide film include a wiping process and a process of immersing in a solvent. The solvent used at that time may be the same as or different from the solvent used in the polyimide precursor solution of the present embodiment.

[0124] Also, when performing the process of exposing the particles when the imidization rate of the polyimide precursor in the polyimide film is 10% or more (that is, in a state where it is difficult to dissolve in water or an organic solvent), and when the polyimide film has been completely imidized, examples of the process of exposing the particles include a method of mechanically cutting with tools such as paper and sandpaper to expose the particles, and when the particles are resin particles, a method of decomposing with a laser or the like to expose the resin particles. For example, when mechanically cutting, a part of the particles existing in the upper region of the particles buried in the polyimide film (that is, the region on the side of the particles away from the substrate) is cut together with the polyimide film existing above the particles, and the cut particles are exposed from the surface of the polyimide film.

[0125] Thereafter, the particles are removed from the polyimide film in which the particles are exposed by the above-described particle removal process. Then, a porous polyimide film from which the particles have been removed is obtained (see FIG. 1).

[0126] Note that in the above, the manufacturing process of the porous polyimide film in which the process of exposing the particles is performed in the second step has been described. However, from the viewpoint of increasing the porosity, the process of exposing the particles may be performed in the first step. In this case, in the first step, after obtaining the coating film and drying to form the film, the process of exposing the particles may be performed to make the particles exposed. By performing this process of exposing the particles, the porosity of the porous polyimide film can be increased.

[0127] For example, after obtaining a coating film containing a polyimide precursor solution and particles, in the process of drying the coating film to form a film containing the polyimide precursor and particles, as described above, the film is in a state where the polyimide precursor can be dissolved in the solvent. When the film is in this state, for example, by a wiping process or a process of immersing in a solvent, the particles can be exposed. Specifically, by performing a process of exposing the particle layer by wiping the polyimide precursor solution present in a region thicker than the thickness of the particle layer with a solvent, for example, the polyimide precursor solution present in the region thicker than the thickness of the particle layer is removed. Then, the particles present in the region above the particle layer (that is, the region on the side of the film away from the substrate of the particle layer) are exposed from the surface of the film.

[0128] Note that in the second step, the substrate for forming the above-mentioned film used in the first step may be peeled off when it becomes a dried film, may be peeled off when the polyimide precursor in the polyimide film becomes difficult to dissolve in the organic solvent, or may be peeled off when it becomes a film in which imidization is completed.

[0129] Through the above steps, a porous polyimide film is obtained. And the porous polyimide film may be post-processed.

[0130] Here, the imidization rate of the polyimide precursor will be described. The polyimide precursor partially imidized includes, for example, precursors having a structure with repeating units represented by the following general formula (V-1), the following general formula (V-2), and the following general formula (V-3).

[0131]

Chemical formula

[0132] In General Formulas (V-1), (V-2), and (V-3), A and B have the same meanings as A and B in Formula (I). l represents an integer of 1 or more, and m and n each independently represent 0 or an integer of 1 or more.

[0133] The imidization rate of the polyimide precursor represents the ratio of the number of imide-ring-closed bond parts (2n + m) to the total number of bond parts (2l + 2m + 2n) at the bonding part (reaction part of the tetracarboxylic dianhydride and the diamine compound) of the polyimide precursor. That is, the imidization rate of the polyimide precursor is represented by "(2n + m) / (2l + 2m + 2n)".

[0134] Note that the imidization rate of the polyimide precursor (the value of "(2n + m) / (2l + 2m + 2n)") is measured by the following method.

[0135] -Measurement of the imidization rate of the polyimide precursor- ·Preparation of a polyimide precursor sample (i) The polyimide precursor solution to be measured is applied onto a silicone wafer in the range of a film thickness of 1 μm or more and 10 μm or less to prepare a coating film sample. (ii) The coating film sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating film sample with tetrahydrofuran (THF). The solvent for immersion is not limited to THF and can be selected from solvents that do not dissolve the polyimide precursor and are miscible with the solvent components contained in the polyimide precursor solution. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane can be used. (iii) The coating film sample is taken out from THF, and N2 gas is blown onto the THF adhering to the surface of the coating film sample to remove it. The coating film sample is dried by treating it under a reduced pressure of 10 mmHg or less in the range of 5 °C or more and 25 °C or less for 12 hours or more to prepare a polyimide precursor sample.

[0136] ·Preparation of a 100% imidized standard sample (iv) In the same manner as in (i) above, the polyimide precursor solution to be measured is applied onto a silicone wafer to prepare a coating film sample. (v) Heat the coating film sample at 380 °C for 60 minutes to carry out the imidization reaction and prepare a 100% imidized standard sample.

[0137] · Measurement and analysis (vi) Using a Fourier transform infrared spectrophotometer (FT-730 manufactured by Horiba, Ltd.), measure the infrared absorption spectra of the 100% imidized standard sample and the polyimide precursor sample. The absorption peak (Ab’(1780 cm -1 )) derived from the imide bond near 1780 cm is determined for the absorption peak (Ab’(1500 cm-1)) derived from the aromatic ring near 1500 cm of the 100% imidized standard sample. -1 )) of the ratio I’(100). -1 )) is determined. (vii) Similarly, measure the polyimide precursor sample, and determine the absorption peak (Ab(1780 cm -1 )) derived from the imide bond near 1780 cm for the absorption peak (Ab(1500 cm -1 )) derived from the aromatic ring near 1500 cm. -1 )) of the ratio I(x). -1 )) is determined.

[0138] Then, using the measured absorption peaks I’(100) and I(x), calculate the imidization rate of the polyimide precursor based on the following formula. · Formula: Imidization rate of polyimide precursor = I(x) / I’(100) · Formula: I’(100) = (Ab’(1780 cm -1 )) / (Ab’(1500 cm -1 )) · Formula: I(x) = (Ab(1780 cm -1 )) / (Ab(1500 cm -1 ))

[0139] Note that the measurement of the imidization rate of this polyimide precursor is applicable to the measurement of the imidization rate of aromatic polyimide precursors. When measuring the imidization rate of aliphatic polyimide precursors, instead of the absorption peak of the aromatic ring, a peak derived from a structure that does not change before and after the imidization reaction is used as the internal standard peak.

[0140] <Porous polyimide film> Hereinafter, the porous polyimide film of the present embodiment will be described.

[0141] The porous polyimide film of the present embodiment is manufactured by the manufacturing method of the porous polyimide film according to the above-described present embodiment.

[0142] The porous polyimide film is not particularly limited, but preferably has a porosity of 30% or more. Further, the porosity is preferably 40% or more, and more preferably 50% or more. The upper limit of the porosity is not particularly limited, but is preferably in the range of 90% or less.

[0143] The shape of the pores is preferably spherical or a shape close to spherical. Further, the pores are preferably in a shape in which the pores are connected to each other and continuous. The pore diameter of the portion where the pores are connected to each other is, for example, preferably 1 / 100 or more and 1 / 2 or less of the maximum diameter of the pores, preferably 1 / 50 or more and 1 / 3 or less, and more preferably 1 / 20 or more and 1 / 4 or less. Specifically, the average value of the pore diameter of the portion where the pores are connected to each other and continuous is preferably 5 nm or more and 1500 nm or less.

[0144] The pore diameter of the pores of the porous polyimide film is preferably in the range of 0.1 μm or more and 1 μm or less, more preferably in the range of 0.12 μm or more and 0.98 μm or less, and even more preferably in the range of 0.14 μm or more and 0.96 μm or less.

[0145] The pore diameter of the pores of the porous polyimide film is not limited to the above range, and is preferably changed according to the application.

[0146] The porous polyimide film of this embodiment has a ratio of the maximum pore diameter to the minimum pore diameter (the ratio of the maximum value to the minimum value of the pore diameter) of 1 or more and 2 or less. Preferably, it is 1 or more and 1.9 or less, more preferably 1 or more and 1.8 or less. Among this range, the closer to 1, the more preferable. By being within this range, the variation in the pore diameter is suppressed. Further, when the porous polyimide film of this embodiment is applied to, for example, a battery separator of a lithium-ion battery, the occurrence of disturbance in the ion flow is suppressed, so that the formation of lithium dendrites is likely to be suppressed. The "ratio of the maximum pore diameter to the minimum pore diameter" is a ratio represented by the value obtained by dividing the maximum pore diameter by the minimum pore diameter (that is, the maximum value of the pore diameter / the minimum value).

[0147] The pore diameter and the pore diameter of the portion where the pores are connected to each other are values observed and measured by a scanning electron microscope (SEM). Specifically, first, a porous polyimide film is cut out to prepare a measurement sample. Then, this measurement sample is observed and measured with the image processing software standardly equipped in a VE SEM manufactured by KEYENCE Corporation. The observation and measurement are performed 100 times for each of the pore portions in the cross-section of the measurement sample, and the average value, the minimum diameter, the maximum diameter, and the arithmetic mean diameter are obtained respectively. When the shape of the pore is not circular, the longest portion is taken as the diameter.

[0148] The film thickness of the porous polyimide film is not particularly limited, but it is preferably 15 μm or more and 500 μm or less.

[0149] The film thickness of the porous polyimide film is measured using a length measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., high-precision digital length measuring instrument MINIAX PH-13 and the company's display unit DH-150) under an environment of 23°C ± 1°C.

[0150] (Use of the porous polyimide film) Examples of applications where the porous polyimide film according to this embodiment is applied include, for example, battery separators such as lithium batteries; separators for electrolytic capacitors; electrolyte membranes for fuel cells; battery electrode materials; gas or liquid separation membranes; low dielectric constant materials; filtration membranes; and the like.

[0151] <Lithium Ion Secondary Battery> A lithium ion secondary battery provided with the porous polyimide film according to this embodiment as a separator for a lithium ion secondary battery will be described with reference to FIG. 2.

[0152] FIG. 2 is a partial cross-sectional schematic view showing an example of a lithium ion secondary battery to which a separator for a lithium ion secondary battery is applied. As shown in FIG. 2, the lithium ion secondary battery 100 includes a positive electrode active material layer 110, a separator layer 510, and a negative electrode active material layer 310, which are housed inside an exterior member (not shown). The positive electrode active material layer 110 is provided on a positive electrode current collector 130, and the negative electrode active material layer 310 is provided on a negative electrode current collector 330. The separator layer 510 is provided so as to separate the positive electrode active material layer 110 and the negative electrode active material layer 310, and is disposed between the positive electrode active material layer 110 and the negative electrode active material layer 310 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 electrolytic solution 513 filled inside the pores of the separator 511. The separator 511 is applied with the porous polyimide film according to this embodiment. Note that the positive electrode current collector 130 and the negative electrode current collector 330 are members provided as necessary.

[0153] (Positive Electrode Current Collector 130 and Negative Electrode Current Collector 330) The materials used for the positive electrode current collector 130 and the negative electrode current collector 330 are not particularly limited, and any known conductive material may be used. For example, metals such as aluminum, copper, nickel, and titanium can be used.

[0154] (Positive Electrode Active Material Layer 110) The positive electrode active material layer 110 is a layer containing a positive electrode active material. If necessary, it may contain known additives such as a conductive assistant and a binder resin. The positive electrode active material is not particularly limited, and known positive electrode active materials are used. For example, composite metal oxides containing lithium (LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFeMnO4, LiV2O5, etc.), phosphates containing lithium (LiFePO4, LiCoPO4, LiMnPO4, LiNiPO4, etc.), conductive polymers (polyacetylene, polyaniline, polypyrrole, polythiophene, etc.), and the like can be mentioned. The positive electrode active material may be used alone or in combination of two or more.

[0155] (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 negative electrode active materials are used. For example, 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.), and the like can be mentioned. The negative electrode active material may be used alone or in combination of two or more.

[0156] (Electrolyte 513) The electrolyte 513 can be, for example, a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent. Examples of the electrolyte include electrolytes of lithium salts (LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiN(FSO2)2, LiN(CF3SO2)2, LiN(C2F5SO2), LiC(CF3SO2)3, etc.). The electrolyte may be used alone or in combination of two or more. Examples of the non-aqueous solvent include cyclic carbonates (such as ethylene carbonate, propylene carbonate, and butylene carbonate), chain carbonates (such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, and 1,2-diethoxyethane), and the like. The non-aqueous solvent may be used alone or in combination of two or more kinds.

[0157] (Method for manufacturing lithium ion secondary battery 100) An example of a method for manufacturing the lithium ion secondary battery 100 will be described. A coating liquid for forming a positive electrode active material layer 110 containing a positive electrode active material is applied to and dried on a positive electrode current collector 130 to obtain a positive electrode provided with the positive electrode active material layer 110 provided on the positive electrode current collector 130. Similarly, a coating liquid for forming a negative electrode active material layer 310 containing a negative electrode active material is applied to and dried on a negative electrode current collector 330 to obtain a negative electrode provided with the negative electrode active material layer 310 provided on the negative electrode current collector 330. The positive electrode and the negative electrode may each be subjected to compression processing as 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 they face each other to obtain a laminated structure. The laminated structure is laminated in this order: a positive electrode (positive electrode current collector 130, positive electrode active material layer 110), a separator layer 510, and a negative electrode (negative electrode active material layer 310, negative electrode current collector 330). At this time, compression processing may be performed as necessary. Next, after the laminated structure is housed in an exterior member, an electrolytic solution 513 is injected into the laminated structure. The injected electrolytic solution 513 also penetrates into the pores of the separator 511. In this way, the lithium ion secondary battery 100 is obtained.

[0158] <All-solid-state battery> Next, an all-solid-state battery to which the porous polyimide film according to the present embodiment is applied will be described. Hereinafter, description will be made with reference to FIG. 3.

[0159] FIG. 3 is a partial cross-sectional schematic view showing an example of an all-solid-state battery according to the present embodiment. As shown in FIG. 3, the all-solid-state battery 200 includes a positive electrode active material layer 220, a solid electrolyte layer 620, and a negative electrode active material layer 420, which are housed inside an exterior member (not shown). The positive electrode active material layer 220 is provided on a positive electrode current collector 240, and the negative electrode active material layer 420 is provided on a negative electrode current collector 440. The solid electrolyte layer 620 is disposed between the positive electrode active material layer 220 and the negative electrode active material layer 420 so that the positive electrode active material layer 220 and the negative electrode active material layer 420 face each other. The solid electrolyte layer 620 includes a solid electrolyte 624 and a holder 622 that holds the solid electrolyte 624, and the solid electrolyte 624 is filled inside the pores of the holder 622. The holder 622 that holds the solid electrolyte 624 is applied with a porous polyimide film according to the present embodiment. Note that the positive electrode current collector 240 and the negative electrode current collector 440 are members provided as necessary.

[0160] (Positive electrode current collector 240 and negative electrode current collector 440) Examples of the materials used for the positive electrode current collector 240 and the negative electrode current collector 440 include the same materials as those described for the lithium-ion secondary battery above.

[0161] (Positive electrode active material layer 220 and negative electrode active material layer 420) Examples of the materials used for the positive electrode active material layer 220 and the negative electrode active material layer 420 include the same materials as those described for the lithium-ion secondary battery above.

[0162] (Solid electrolyte 624) The solid electrolyte 624 is not particularly limited, and known solid electrolytes can be mentioned. For example, polymer solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, nitride solid electrolytes, etc. can be mentioned.

[0163] Examples of the polymer solid electrolyte include fluororesins (such as homopolymers of polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, etc., copolymers having these as constituent units, etc.), polyethylene oxide resins, polyacrylonitrile resins, polyacrylate resins, and the like. In terms of excellent lithium ion conductivity, it is preferable to contain a sulfide solid electrolyte. Similarly, it is preferable to contain a sulfide solid electrolyte containing sulfur and at least one of lithium and phosphorus as constituent elements.

[0164] Examples of the oxide solid electrolyte include oxide solid electrolyte particles containing lithium. For example, Li2O - B2O3 - P2O5, Li2O - SiO2, etc. are mentioned. Examples of the sulfide solid electrolyte include sulfide solid electrolytes containing sulfur and at least one of lithium and phosphorus as constituent elements. For example, 8Li2O·67Li2S·25P2S5, Li2S, P2S5, Li2S - SiS2, LiI - Li2S - SiS2, LiI - Li2S - P2S5, LiI - Li3PO4 - P2S5, LiI - Li2S - P2O5, LiI - Li2S - B2S3, etc. are mentioned. Examples of the halide solid electrolyte include LiI and the like. Examples of the nitride solid electrolyte include Li3N and the like.

[0165] (Method for manufacturing the all - solid - state battery 200) An example of the method for manufacturing the all - solid - state battery 200 will be described. A coating liquid for forming the positive electrode active material layer 220 containing the positive electrode active material is applied to and dried on the positive electrode current collector 240 to obtain a positive electrode provided with the positive electrode active material layer 220 provided on the positive electrode current collector 240. Similarly, a coating liquid for forming the negative electrode active material layer 420 containing the negative electrode active material is applied to and dried on the negative electrode current collector 440 to obtain a negative electrode provided with the negative electrode active material layer 420 provided on the negative electrode current collector 440. The positive electrode and the negative electrode may each be subjected to compression processing as required. Next, a coating solution containing the solid electrolyte 624 for forming the solid electrolyte layer 620 is applied onto a substrate and dried to form a layered solid electrolyte. Next, as materials for forming the solid electrolyte layer 620, a polyimide film (the porous polyimide film according to this embodiment) as the retainer 622 and the layered solid electrolyte 624 are superposed on the positive electrode active material layer 220 of the positive electrode. Further, the negative electrode is superposed on the material for forming the solid electrolyte layer 620 such that the negative electrode active material layer 420 of the negative electrode is on the side of the positive electrode active material layer 220 to form a laminated structure. The laminated structure is laminated in this order: the positive electrode (positive electrode current collector 240, positive electrode active material layer 220), the solid electrolyte layer 620, and the negative electrode (negative electrode active material layer 420, negative electrode current collector 440). Next, the laminated structure is subjected to compression processing to impregnate the pores of the polyimide film that is the retainer 622 with the solid electrolyte 624 and hold the solid electrolyte 624. Next, the laminated structure is housed in an exterior member. In this way, the all-solid-state battery 200 is obtained.

Example

[0166] Examples will be described below, but the present invention is not limited to these examples in any way. In the following description, unless otherwise specified, all “parts” and “%” are based on mass.

[0167] <Preparation of Particle Dispersion Liquid>

[0168] (Preparation of PSt Particle Dispersion Solution - 1) 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 are mixed and stirred and emulsified at 1,500 revolutions for 30 minutes using a dissolver to prepare a monomer emulsion. 1.10 parts by mass of Dowfax 2A1 (47% solution, manufactured by Dow Chemical Company) and 1500 parts by mass of ion-exchanged water were charged into a reaction vessel. After heating to 75°C under a nitrogen stream, 70 parts by mass of the monomer emulsion was added, and then a polymerization initiator solution prepared by dissolving 15 parts by mass of ammonium persulfate in 98 parts by mass of ion-exchanged water was added dropwise over 10 minutes. After reacting for 50 minutes after the dropwise addition, the remaining monomer emulsion was added dropwise over 220 minutes, and after reacting for another 50 minutes, it was cooled to obtain PSt particle dispersion-1. The average particle size of these resin particles was 0.81 μm.

[0169] <Example 1> A flask equipped with a stir bar, thermometer, and dropping funnel was filled with 850 g of water. 27.28 g (252.27 mmol) of p-phenylenediamine (molecular weight 108.14) and 50.00 g (494.32 mmol) of N-methylmorpholine (organic amine compound) were added thereto, and the mixture was stirred at 20°C for 10 minutes for dispersion. Further, 72.72 g (247.16 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (molecular weight 294.22) was added to this solution, and the mixture was stirred for 12 hours for dissolution and reaction while maintaining the reaction temperature at 50°C to obtain a high molecular weight polyimide precursor solution with a solid content of 10%. A flask equipped with a stir bar, thermometer, and dropping funnel was filled with 850 g of water. 27.28 g (252.27 mmol) of p-phenylenediamine (molecular weight 108.14) and 50.00 g (494.32 mmol) of N-methylmorpholine (organic amine compound) were added thereto, and the mixture was stirred at 20°C for 10 minutes for dispersion. Further, 72.72 g (247.16 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (molecular weight 294.22) was added to this solution, and the mixture was stirred for 3 hours for dissolution and reaction while maintaining the reaction temperature at 50°C to obtain a low molecular weight polyimide precursor solution with a solid content of 10%. Then, the prepared high molecular weight polyimide precursor solution and the low molecular weight polyimide precursor solution were mixed while adjusting to the GPC peak area ratio shown in Table 1 to obtain a polyimide precursor solution. To this polyimide precursor solution, PSt particle dispersion liquid - 1 was added so that the volume content ratio of resin particles to polyimide precursor (resin particles / polyimide precursor) was 60 / 40, and it was stirred on a web rotor to obtain a resin particle-dispersed polyimide precursor solution.

[0170] <Examples 2 to 5> The high molecular weight polyimide precursor solution and the low molecular weight polyimide precursor solution prepared in Example 1 were mixed while adjusting to the GPC peak area ratio shown in Table 1 to obtain a polyimide precursor solution.

[0171] <Example 6> A resin particle-dispersed polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 10 hours and the stirring time of the low molecular weight polyimide precursor solution was 6 hours.

[0172] <Example 7> A resin particle-dispersed polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 20 hours.

[0173] <Example 8> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 18 hours.

[0174] <Example 9> A polyimide precursor solution was obtained in the same manner as in Example 1, except that 22.28 g (494.32 mmol) of ethylamine (organic amine compound) was added during the preparation of the high molecular weight polyimide precursor solution and 22.28 g (494.32 mmol) of ethylamine (organic amine compound) was added during the preparation of the low molecular weight polyimide precursor solution.

[0175] <Example 10> When preparing the high molecular weight polyimide precursor solution, add 2-(ethylamino)ethanol (organic amine compound): 44.06 g (494.32 mmol), and when preparing the low molecular weight polyimide precursor solution, except for adding 2-(ethylamino)ethanol (organic amine compound): 44.06 g (494.32 mmol), a polyimide precursor solution was obtained in the same manner as in Example 1.

[0176] <Example 11> When preparing the high molecular weight polyimide precursor solution, add dimethylaminoethanol (organic amine compound): 44.06 g (494.32 mmol), and when preparing the low molecular weight polyimide precursor solution, except for adding dimethylaminoethanol (organic amine compound): 44.06 g (494.32 mmol), a polyimide precursor solution was obtained in the same manner as in Example 1.

[0177] <Example 12> A polyimide precursor solution was obtained in the same manner as in Example 1, except that PSt particle dispersion - 1 was added so that the volume content ratio of resin particles to polyimide precursor (resin particles / polyimide precursor) was 40 / 60.

[0178] <Example 13> A polyimide precursor solution was obtained in the same manner as in Example 1, except that PSt particle dispersion - 1 was added so that the volume content ratio of resin particles to polyimide precursor (resin particles / polyimide precursor) was 80 / 20.

[0179] <Comparative Example 1> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 3 hours and the stirring time of the low molecular weight polyimide precursor solution was 2 hours.

[0180] <Comparative Example 2> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the prepared high molecular weight polyimide precursor solution and low molecular weight polyimide precursor solution were mixed while adjusting the GPC peak area ratio to a / (a + b)=1.

[0181] <Comparative Example 3> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 8 hours.

[0182] <Comparative Example 4> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the low molecular weight polyimide precursor solution was 2 hours.

[0183] <Comparative Example 5> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the high molecular weight polyimide precursor solution was 8 hours and the stirring time of the low molecular weight polyimide precursor solution was 2 hours.

[0184] <Comparative Example 6> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the stirring time of the low molecular weight polyimide precursor solution was 8 hours.

[0185] <Comparative Example 7> A polyimide precursor solution was obtained in the same manner as in Example 1, except that the prepared high molecular weight polyimide precursor solution and low molecular weight polyimide precursor solution were mixed while adjusting the GPC peak area ratio to a / (a + b)=0.5.

[0186] <Evaluation> The polyimide precursor solution of each example was applied onto a glass substrate with a thickness of 1.0 mm over an area of 10 cm × 10 cm using an applicator and dried in an oven at 80°C for 30 minutes. The gap of the applicator was adjusted so that the average value of the film thickness of the dried film after drying was 30 μm.

[0187] (Surface unevenness evaluation) The presence or absence of unevenness generated on the surface of the dried film was evaluated using an optical microscope. A: No unevenness was generated on the film surface. B: Unevenness was generated on a part of the film surface (less than 10% of the film surface area). C: Non-uniformity occurs on about half of the membrane surface. D: Non-uniformity occurs on almost the entire membrane surface.

[0188] (Dry film strength evaluation) The dry film was cut into a size of 1 cm × 8 cm, and the cut dry film was wrapped around a finger to evaluate the strength of the dry film. A: The film can be wrapped without breaking. B: Cracks appear in part of the film, but it can be wrapped. C: The film breaks.

[0189] (Particle dispersibility) The obtained resin particle-dispersed polyimide precursor solution was stored by standing at room temperature (25 °C), and the dispersion state of the resin particles was visually evaluated (when the dispersibility of the resin particles is low, sedimentation of the particles can be observed). A: No change in the solution even after more than 1 day from the start of storage B: Sedimentation of particles can be seen within 1 week after more than 1 day from the start of storage. C: Sedimentation of particles can be seen within 1 day from the start of storage

[0190]

Table 1

[0191] From the above results, it can be seen that the polyimide precursor solution of this example can obtain a dry film with good coatability and high strength while ensuring the dispersibility of particles, compared with the polyimide precursor solution of the comparative example. Thereby, it can also be seen that the polyimide precursor solution of this example can obtain a porous polyimide film that has pores closer to being uniform, less surface non-uniformity, and suppressed breakage, compared with the polyimide precursor solution of the comparative example.

Explanation of symbols

[0192] 10 Porous polyimide film 10A Pore 31 Substrate 51 Release layer 100 Lithium-ion secondary battery 200 All-solid-state battery

Claims

1. an aqueous solvent containing water, at least one resin particle selected from the group consisting of (meth)acrylic resins, (meth)acrylate resins, styrene-(meth)acrylic resins, and polystyrene resins, a polyimide precursor containing a first polyimide precursor having a weight average molecular weight of 50,000 or more and a second polyimide precursor having a weight average molecular weight of 10,000 or more and 30,000 or less, comprising, The polyimide precursor has, in an elution curve by gel permeation chromatography, a high molecular weight region A including a maximum value on the high molecular weight side and a low molecular weight region B including a maximum value on the low molecular weight side, the weight average molecular weight of the high molecular weight region A is 50,000 or more which is the weight average molecular weight derived from the first polyimide precursor, the weight average molecular weight of the low molecular weight region B is 10,000 or more and 30,000 or less which is the weight average molecular weight derived from the second polyimide precursor, and when the area of the high molecular weight region A is a and the area of the low molecular weight region B is b, a polyimide precursor solution in which the a / (a + b) value is 0.60 or more and 0.98 or less.

2. The polyimide precursor solution according to claim 1, wherein the a / (a + b) value is 0.70 or more and 0.95 or less.

3. The polyimide precursor solution according to claim 1 or claim 2, wherein the difference in weight average molecular weight between the high molecular weight region A and the low molecular weight region B is 20,000 or more and 90,000 or less.

4. The polyimide precursor solution according to claim 3, wherein the difference in weight average molecular weight between the high molecular weight region A and the low molecular weight region B is 20,000 or more and 70,000 or less.

5. The polyimide precursor solution according to any one of claims 1 to 4, comprising at least one selected from the group consisting of secondary amine compounds and tertiary amine compounds.

6. The polyimide precursor solution according to claim 5, wherein 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). [Chemical 1] (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.)

7. The polyimide precursor solution according to any one of claims 1 to 6, wherein the volume content ratio (resin particles / polyimide precursor) of the resin particles to the polyimide precursor is 40 / 60 or more and 80 / 20 or less.

8. The polyimide precursor solution according to any one of claims 7, wherein the content of the resin particles is 30% by mass or more and 85% by mass or less based on the total amount of the polyimide precursor and the resin particles.

9. A first step of forming a coating film by applying the polyimide precursor solution according to any one of claims 1 to 8, and then drying the coating film to form a film containing the polyimide precursor and the resin particles; A second step of heating the film to imidize the polyimide precursor to form a polyimide film, the second step including a treatment for removing the resin particles; A method for producing a porous polyimide film having the above steps.

10. A porous polyimide film produced by the method for producing a porous polyimide film according to claim 9.

Images