JP2024059027A - Resin composition for film capacitor, film for capacitor, and film capacitor - Google Patents

Abstract

To provide a resin composition for a film capacitor that can form a film for a capacitor that has a high dielectric constant and a low dielectric loss tangent, and a capacitor film and a film capacitor formed from a composition.SOLUTION: In a resin composition for a film capacitor containing a resin A having an imide structure, at least one terminal of the resin A is an acid anhydride site or an amino group, and the acid anhydride equivalent or the active hydrogen equivalent of the amine of the resin A is 20,000 or less.SELECTED DRAWING: None

Description

The present invention relates to a resin composition for film capacitors, a film for capacitors, and a film capacitor.

Capacitor films are used in a wide range of fields, including the automotive and home appliance fields. In recent years, there has been an increasing demand for smaller capacitors, higher capacity, and higher reliability, so capacitor films are also required to have higher performance. It is known that capacitor films can be made from resins such as polyetherimide and aromatic liquid crystal polyester. In order to improve the performance of capacitor films, active research is being conducted into modifying these resins to form films more suitable for capacitor films.

For example, Patent Document 1 proposes a technology for applying a polyetherimide film containing a predetermined amount of inorganic filler to a film for a capacitor. Such a polyetherimide film has a uniform film thickness despite its thinness, and can have a higher tensile strength.

JP 2012-60161 A

In recent years, capacitor films, particularly for electric vehicles and hybrid cars, are required to have a high dielectric constant and a low dielectric dissipation factor. In addition, there is a strong demand for properties such as high dielectric breakdown voltage, high strength, and high heat resistance. In particular, in capacitor films, the dielectric constant and the dielectric dissipation factor are in a trade-off relationship, so it has been considered difficult to form a capacitor film that has both a high dielectric constant and a low dielectric dissipation factor.

The present invention has been made in view of the above, and aims to provide a resin composition for film capacitors that can form a capacitor film having a high dielectric constant, a low dielectric tangent, and high strength, and a capacitor film and film capacitor formed from the composition.

As a result of extensive research into achieving the above objective, the inventors discovered that the above objective could be achieved by using a specific polyimide resin, leading to the completion of the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
In a resin composition for a film capacitor containing a resin A having an imide structure,
At least one end of the resin A is an acid anhydride moiety or an amino group,
The resin composition for a film capacitor, wherein the resin A has an acid anhydride equivalent or an amine active hydrogen equivalent of 20,000 or less.
Item 2
Item 2. The resin composition for a film capacitor according to item 1, further comprising a resin B that reacts with an acid anhydride or an amino group.
Item 3
Item 3. The resin composition for a film capacitor according to item 2, wherein the resin B is at least one selected from the group consisting of an epoxy resin, a maleimide resin, and a resin having an allyl group.
Item 4
Item 4. The resin composition for a film capacitor according to any one of items 1 to 3, further comprising an inorganic filler.
Item 5
Item 5. A film for a capacitor comprising a cured product of the resin composition for a film capacitor according to any one of items 1 to 4.
Item 6
A film capacitor comprising the capacitor film according to claim 5 .

The resin composition for film capacitors of the present invention can form a capacitor film that has a high dielectric constant, a low dielectric tangent, and high strength.

The embodiments of the present invention will be described in detail below. In this specification, the expressions "contain" and "include" include the concepts of "contain," "include," "consist essentially of," and "consist only of."

1. Resin Composition for Film Capacitor The resin composition for film capacitor of the present invention contains a resin A having an imide structure, at least one end of the resin A is an acid anhydride moiety or an amino group, and the acid anhydride equivalent or amine active hydrogen equivalent of the resin A is 20,000 or less.

The resin composition for film capacitors of the present invention can form a capacitor film having high strength, particularly a capacitor film having both high breaking strength and breaking elongation. Therefore, the resin composition for film capacitors of the present invention is suitable as a raw material for forming a capacitor film.

(Resin A)
As described above, the resin A has an imide structure, at least one end of which is an acid anhydride moiety or an amino group, and the type of the resin A is not particularly limited as long as the acid anhydride equivalent or the active hydrogen equivalent of the amine of the resin A is not more than 20000. Examples of the resin A include polyimide resins.

Specifically, the resin A may be a polyimide resin having an acid anhydride moiety or an amino group at at least one end.
-C(=O)-O-C(=O)-
A specific example of the acid anhydride moiety is a structure represented by the following formula (10).

The amino group is represented, for example, by —NH ₂ and can be a functional group derived from a primary amine.

Either the acid anhydride moiety or the amino group can be directly bonded (covalently bonded) to the end of resin A (e.g., a polyimide resin). In addition, for example, as in resin A represented by formula (4) described later, the acid anhydride moiety or the amino group may be bonded to the end of resin A via another divalent organic group.

The acid anhydride moiety or amino group may be bonded to only one end of resin A, or may be bonded to both ends, and it is preferable that they are bonded to both ends. In this case, the resin composition for film capacitors of the present invention can form a capacitor film having a high dielectric constant and a low dielectric tangent. When the acid anhydride moiety or amino group is bonded to both ends of resin A, the acid anhydride moiety or amino group bonded to one end and the acid anhydride moiety or amino group bonded to the other end may be the same or different. Also, one end may be an acid anhydride moiety and the other end may be an amino group. It is preferable that the structures of both ends are the same.

The method for introducing an acid anhydride moiety or an amino group to the end of resin A is not particularly limited. For example, as described below, an acid anhydride moiety or an amino group can be introduced to the end of resin A by adjusting the molar ratio of the raw materials (monomers) used in synthesizing resin A.

The acid anhydride equivalent of the resin A or the active hydrogen equivalent of the amine is 20,000 or less. That is, the acid anhydride equivalent of the resin A must be 20,000 or less, or the active hydrogen equivalent of the amine must be 20,000 or less. In this case, the resin composition for film capacitors of the present invention can form a film for capacitors having a high dielectric constant and a low dielectric tangent. The unit of the acid anhydride equivalent or the active hydrogen equivalent of the amine can be expressed as g/eq, but in this specification, the unit of the acid anhydride equivalent or the active hydrogen equivalent of the amine is unitless. The acid anhydride equivalent or the active hydrogen equivalent of the amine of the resin A can be calculated from the content of the acid anhydride moiety or the content of the amino group in the resin A, and the acid anhydride equivalent or the active hydrogen equivalent of the amine can also be calculated from the amount of each monomer blended when producing the resin A.

The acid anhydride equivalent of the resin A is preferably 15,000 or less, and more preferably 10,000 or less. The acid anhydride equivalent of the resin A is preferably 1,000 or more, and more preferably 2,000 or more.

The active hydrogen equivalent of the amine of the resin A is preferably 15,000 or less, and more preferably 10,000 or less. The active hydrogen equivalent of the amine of the resin A is preferably 1,000 or more, and more preferably 2,000 or more.

The structure of the resin A (polyimide resin) can be the same as that of the polyetherimide resin disclosed in the aforementioned Patent Document 1.

Examples of resin A include polyimide resins represented by the following formulas (1), (2), (3), and (4).

The weight average molecular weight of resin A is not particularly limited. For example, the weight average molecular weight of resin A measured by gel permeation chromatography using a polystyrene standard can be 10,000 or more and 200,000 or less. This makes it easy to form a capacitor film that has a high dielectric constant and a low dielectric tangent, and also has high mechanical strength and a high dielectric breakdown voltage.

The weight average molecular weight of resin A is preferably 2000 or more, more preferably 3000 or more, and is preferably 40000 or less, more preferably 20000 or less.

The method for adjusting the weight average molecular weight of resin A is not particularly limited, and for example, the weight average molecular weight can be adjusted by a method similar to a known method. Specific methods for adjusting the weight average molecular weight include a method in which the molar ratio of the acid anhydride and diamine used during the production of the resin is shifted from an equivalent of 1:1, and a method in which a small amount of a monovalent acid anhydride or monoamine is added during the production of the resin to prevent the chain length extension of the growing polymer chain.

The resin A contained in the resin composition for film capacitors of the present invention may be one type alone, or may be two or more types.

The method for producing resin A is not particularly limited, and for example, a wide variety of known production methods can be adopted. For example, resin A can be produced by a method similar to a known method for producing polyimide resin. For example, resin A can be produced by reacting a compound having two or more amino groups with a compound having two or more acid anhydrides, and specifically, a reaction between an aromatic compound having two or more acid anhydrides and an organic diamine can be mentioned.

Examples of organic diamines include aromatic diamine compounds, specifically 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, bis(4-(4-aminophenoxy)phenyl)methane, 2,2 -bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(2-(4-aminophenyl)-2-propyl)benzene, 1,4-bis(2-(4-aminophenyl)-2-propyl)benzene, 3,3'-diamino-4,4'-dihydroxyphenylmethane, 4,4'-diamino-3,3'-dihydroxyphenylmethane, 3,3'-diamino-4,4'-dihydroxyphenyl ether, bisaminophenylfluorene, bistruidinefluorene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diamino-3,3'-dihydroxyphenyl ether, 3,3'-diamino-4,4'-dihydroxybiphenyl, 4,4'-diamino-2,2'-dihydroxybiphenyl, etc. Among them, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (referred to as BAPP in this specification) is preferred.

Examples of aromatic compounds having two or more acid anhydrides include 4,4'-biphthalic anhydride, pyromellitic anhydride, 1,2,5,6-naphthalene tetracarboxylic anhydride, 2,3,6,7-naphthalene tetracarboxylic anhydride, 1,2,4,5-naphthalene tetracarboxylic anhydride, 1,4,5,8-naphthalene tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 3,3',4,4'-biphenyl ether tetracarboxylic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, Carboxylic acid anhydrides, 2,3,5,6-pyridinetetracarboxylic acid anhydride, 3,4,9,10-perylenetetracarboxylic acid anhydride, 4,4'-sulfonyldiphthalic anhydride, 1-trifluoromethyl-2,3,5,6-benzenetetracarboxylic acid anhydride, 2,2',3,3'-biphenyltetracarboxylic acid anhydride, 2,2-bis(3,4-dicarboxyphenyl)propane anhydride, 2,2-bis(2,3-dicarboxyphenyl)propane anhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane anhydride, 1,1 -Bis(3,4-dicarboxyphenyl)ethane, bis(2,3-dicarboxyphenyl)methane anhydride, bis(3,4-dicarboxyphenyl)methane anhydride, bis(3,4-dicarboxyphenyl)sulfone anhydride, bis(3,4-dicarboxyphenyl)ether anhydride, benzene-1,2,3,4-tetracarboxylic acid anhydride, 2,3,2',3'-benzophenone tetracarboxylic acid anhydride, 2,3,3',4'-benzophenone tetracarboxylic acid anhydride, phenanthrene-1,8,9,10-tetracarboxylic acid Examples of such anhydrides include bisphenol A dianhydride, pyrazine-2,3,5,6-tetracarboxylic anhydride, thiophene-2,3,4,5-tetracarboxylic anhydride, 2,3,3',4'-biphenyltetracarboxylic anhydride, 3,4,3',4'-biphenyltetracarboxylic anhydride, 2,3,2',3'-biphenyltetracarboxylic anhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide anhydride, and bisphenol A dianhydride (manufactured by SHPP Japan LLC under the name "BISDA-1000").

In the reaction between an aromatic compound having two acid anhydrides and an organic diamine, when the molar ratio of the aromatic compound having two acid anhydrides to the organic diamine is 1:1, no acid anhydride moiety or amino group is bonded to the end of the resulting resin A. Therefore, in the reaction between an aromatic compound having two acid anhydrides and an organic diamine, the molar ratio of the aromatic compound having two acid anhydrides to the organic diamine (aromatic compound having two acid anhydrides:organic diamine) is other than 1:1 and can be, for example, 1:0.5 to 1:1.5.

In the reaction between an aromatic compound having two acid anhydrides and an organic diamine, the temperature is not particularly limited and can be, for example, 100 to 170°C.

In the method for producing resin A, a solvent can be used. The type of the solvent is not particularly limited, and examples of the solvent include toluene, anisole, N,N-dimethylacetamide, etc., and a mixed solvent is also possible. In the method for producing resin A, it is also preferable to remove the solvent after resin A is produced. In this case, the solvent is removed so that the content of the solvent relative to resin A is 1% by mass or less, preferably 0.5% by mass or less, and more preferably 0.1% by mass or less.

(Resin B)
The resin composition for film capacitors of the present invention can contain a resin B that reacts with an acid anhydride or an amino group. When such a resin B is contained in the resin composition for film capacitors of the present invention, the resin B can react with, for example, an acid anhydride moiety or an amino group at the end of the resin A. As a result, the resin composition for film capacitors of the present invention can easily form a capacitor film having a high dielectric constant and a low dielectric tangent, and can also easily form a capacitor film having high mechanical strength and a high dielectric breakdown voltage.

The type of resin B is not particularly limited, so long as it is a resin that reacts with an acid anhydride or an amino group. Examples of resin B include epoxy resins, maleimide resins, and resins having an allyl group.

Epoxy resins include, for example, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol E type epoxy resins, bisphenol S type epoxy resins, 2,2'-diallyl bisphenol A type epoxy resins, hydrogenated bisphenol type epoxy resins, propylene oxide-added bisphenol A type epoxy resins, triazine type epoxy resins, resorcinol type epoxy resins, biphenyl type epoxy resins, sulfide type epoxy resins, diphenyl ether type epoxy resins, dicyclopentadiene type epoxy resins, naphthalene type epoxy resins, fluorene type epoxy resins, naphthylene ether type epoxy resins, phenol novolac type epoxy resins, orthocresol novolac type epoxy resins, dicyclopentadiene novolac type epoxy resins, biphenyl novolac type epoxy resins, naphthalene phenol novolac type epoxy resins, glycidyl amine type epoxy resins, alkyl polyol type epoxy resins, rubber modified epoxy resins, glycidyl ester compounds, etc.

Examples of maleimide resins include N,N'-(4,4'-diphenylmethane) bismaleimide, bisphenol A diphenyl ether bismaleimide, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)hexane, bis-(3-ethyl-5-methyl-4-maleimidophenyl)methane, m-phenylene Examples include bismaleimide (N,N'-1,3-phenylene bismaleimide), 1,6-bismaleimidehexane, 1,2-bismaleimideethane (N,N'-ethylene dimaleimide), N,N'-(1,2-phenylene) bismaleimide, N,N'-1,4-phenylene dimaleimide, N,N'-(sulfonyl di-p-phenylene) dimaleimide, and N,N'-[3,3'-(1,3-phenylenedioxy)diphenyl]bismaleimide.

Examples of resins having an allyl group include diallyl phthalate, diallyl isophthalate, diallyl terephthalate, diallyl maleate, diallyl fumarate, diallyl diphenate, diallyl 2,3-naphthalene carboxylate, diphenyl diallyl silane, 2,2'-diallyl bisphenol A, N,N-diallyl acrylamide, diallylamine, diallyl methacrylamide, triallyl trimellitate, triallyl isocyanurate, triallyl cyanurate, triallyl phosphate, tetraallyl pyromellitate, allyl glycidyl ether (Neoallyl G: manufactured by Daiso Co., Ltd.), trimethylolpropane diallyl ether (Neoallyl T- 20: manufactured by Daiso Co., Ltd.), pentaerythritol triallyl ether (Neoallyl P-30: manufactured by Daiso Co., Ltd.), glycerin monoallyl ether (Neoallyl E-10: manufactured by Daiso Co., Ltd.), 5-allyl-1,3-diglycidyl isocyanuric acid (MA-DGIC: manufactured by Shikoku Kasei Co., Ltd.), 1,3-diallyl-5-glycidyl isocyanuric acid (DA-MGIC: manufactured by Shikoku Kasei Co., Ltd.), 1,3-diallyl-5-methyl isocyanuric acid (MeDAIC: manufactured by Shikoku Kasei Co., Ltd.), diallyl bisphenol A type diglycidyl ether (RE-810NM: manufactured by Nippon Kayaku Co., Ltd.), diallyl bisphenol S type diglycidyl ether, etc.

Resin B may consist of one type alone or two or more types.

The method for producing resin B is not particularly limited, and for example, any known production method can be widely adopted. Resin B can also be obtained from commercial products, etc.

(Hardening agent)
When the resin composition for a film capacitor of the present invention contains the resin B, the resin B can function as a curing agent for curing the resin A, but the resin composition for a film capacitor of the present invention can contain another curing agent in addition to the resin B. In particular, when the resin composition for a film capacitor of the present invention contains the resin B in an amount equivalent to or greater than the amount of the resin A, it is preferable to contain another curing agent in addition to the resin B.

The curing agent (excluding resin B) is not particularly limited as long as it has the effect of curing various thermosetting resins or photocurable resins, and can be a wide variety of known curing agents. Examples of the curing agent include known epoxy resin curing agents, and specific examples include amine-based curing agents, imidazole-based curing agents, guanidine-based curing agents, thiol-based curing agents, phenolic resin-based curing agents, acid anhydride-based curing agents, and organic peroxide-based curing agents.

Examples of the amine curing agent include polyethylene polyamines such as ethylene diamine, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylene diamine, 2,2,4-trimethylhexamethylene diamine, 1,10-diaminodecane, 1,12-diaminododecane, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine; and ring-containing amines such as 1,2-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, metaxylylenediamine, norbornane diamine, 4,4'-diaminodicyclohexylmethane, or 2,2'-dimethyl-4,4'-diaminodicyclohexylmethane and 4,4'-diaminodiphenylmethane.

Examples of imidazole-based curing agents include imidazoles such as imidazole, 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzylimidazole, 1-benzyl-2-phenylimidazole, and 1-cyanoethyl-2-methylimidazole.

Examples of guanidine-based curing agents include dicyandiamide, tetramethylguanidine, biguanide, n-butylguanidine, guanylthiourea, etc.

Examples of thiol-based curing agents include tris(3-mercaptopropionate), butanediol bis(3-mercaptopropionate), ethylene glycol bis(3-mercaptopropionate), tetraethylene glycol bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), 1,4-bis(3- mercaptobutyryloxy)butane, pentaerythritol tetrakis (3-mercaptobutyrate), tris (3-mercaptobutyryloxyethyl) isocyanurate, trimethylolethane (3-mercaptobutyrate), trimethylolpropane tris (3-mercaptobutyrate), trisbutanediol bisthioglycolate, hexanediol thioglycolate, trimethylolpropane tristhioglycolate, pentaerythritol tetrakis thioglycolate, etc.

Examples of phenolic resin-based hardeners include phenol novolac resin, bisphenol novolac resin, and cresol novolac resin. Among phenolic resin-based hardeners, aminotriazine novolac resin is particularly suitable for use because it increases the dielectric constant. Examples of aminotriazine novolac resins include Phenolite LA1356, LA3018-50P, LA7053, LA7054, and LA7757.

Examples of acid anhydride curing agents include phthalic anhydride, hexahydrophthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 4-methyltetrahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, bicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride, methylbicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride, methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride, succinic anhydride, and octenylsuccinic anhydride.

Examples of organic peroxide curing agents include lauroyl peroxide, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate.

Examples of maleimide curing agents include radical polymerization initiators and compounds having an allylphenol group represented by the following formula (10).

The curing agent may be a single type, or two or more types.

(Resin composition for film capacitors)
When the resin composition for film capacitors of the present invention contains resin B, the content ratio of resin B is not particularly limited. For example, it is preferable that resin B is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of resin A. In this case, it is easy to form a film for capacitors having a higher dielectric constant. For 100 parts by mass of resin A, resin B is preferably contained in an amount of 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, particularly preferably 30 parts by mass or more, more preferably 80 parts by mass or less, and even more preferably 50 parts by mass or less.

When the resin composition for film capacitors of the present invention contains the curing agent, the content ratio is not particularly limited, and can be, for example, 10 to 1000 parts by mass, preferably 50 to 500 parts by mass, and more preferably 80 to 200 parts by mass, per 100 parts by mass of resin B.

The resin composition for film capacitors of the present invention may contain other components in addition to the resin A and the resin B. Examples of other components include inorganic fillers. When the resin composition for film capacitors of the present invention contains an inorganic filler, a film capacitor having a higher dielectric constant can be formed.

The type of inorganic filler is not particularly limited, and examples include mica, talc, smectite, vermiculite, barium titanate, lead zirconate titanate, calcium titanate, strontium titanate, calcium zirconate, calcium zirconate titanate, and magnesium titanate, with barium titanate being preferred.

The size of the inorganic filler is not particularly limited, and for example, the average particle size can be 0.05 μm to 1 μm, and is preferably 0.05 μm to 0.5 μm. The average particle size of the inorganic filler means a value measured by dynamic light scattering. The inorganic filler may be subjected to a surface treatment, for example, to make it hydrophilic or hydrophobic.

When the resin composition for film capacitors of the present invention contains an inorganic filler, the content ratio is not particularly limited. For example, it is preferable that the inorganic filler is contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the total mass of the resin A and the resin B. This makes it easier to form a capacitor film having a higher dielectric constant, and also makes it easier to form a capacitor film having a low dielectric tangent. It is more preferable that the inorganic filler is contained in an amount of 2 to 20 parts by mass per 100 parts by mass of the total mass of the resin A and the resin B.

The resin composition for film capacitors of the present invention can contain, in addition to inorganic fillers, components contained in known resin compositions for film capacitors, such as curing accelerators, curing catalysts, dispersants, light stabilizers, antioxidants, preservatives, flame retardants, pigments, colorants, mildew inhibitors, and lubricants. One or more of these additives may be contained in composition 1.

The resin composition for film capacitors of the present invention may contain a solvent. The type of such solvent is not particularly limited, and examples include a wide range of solvents contained in known resin compositions for film capacitors. Preferred solvents include toluene, xylene, anisole, N,N-dimethylformamide, N,N-dimethylacetamide, and the like. The solvent contained in the resin composition for film capacitors of the present invention may be one type alone or a mixture of two or more types.

When the resin composition for film capacitors of the present invention contains a solvent, the content of the solvent is not particularly limited, and for example, the solvent may be contained so that the solid content concentration is 10 to 50 mass%. It is more preferable that the solid content concentration of the resin composition for film capacitors of the present invention is 20 to 40 mass%.

The resin composition for film capacitors of the present invention preferably contains resin A and resin B in an amount of 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, of the total solid content.

The resin composition for film capacitors of the present invention can form a capacitor film that has a high dielectric constant and a low dielectric tangent. Furthermore, the capacitor film formed from the resin composition for film capacitors of the present invention has high mechanical strength and a high dielectric breakdown voltage. Therefore, the resin composition for film capacitors of the present invention can be suitably used as a raw material for forming film capacitors.

The method for preparing the resin composition for film capacitors of the present invention is not particularly limited, and for example, any known method can be widely adopted. For example, the resin composition for film capacitors of the present invention can be prepared by mixing predetermined amounts of resin A, resin B, inorganic filler, and solvent.

The portability of the resin composition for film capacitors of the present invention is not particularly limited, and may be, for example, a solid or liquid. If it is a solid, it may be in the form of, for example, a pellet or powder, and if it is a liquid, it may be in the form of, for example, a solution, dispersion, or paste.

2. Film for Capacitor and Film Capacitor The resin composition for a film capacitor of the present invention can be used to form a film for a capacitor.

The method for forming the capacitor film is not particularly limited, and for example, the capacitor film can be formed by a method of curing the resin composition for film capacitors of the present invention. Therefore, the capacitor film can contain a cured product of the resin composition for film capacitors of the present invention.

As a method for producing a capacitor film from the resin composition for a film capacitor of the present invention, various methods such as a solution casting method and an extrusion method can be used.

In the solution casting method, a resin composition for film capacitors containing a solvent is cast onto a substrate to form a casting liquid layer, and the solvent is removed from the casting liquid layer by an appropriate method to form a film for a capacitor. The conditions for removing the solvent are not particularly limited, and appropriate conditions can be adopted depending on the type of solvent, etc.

In the extrusion method, for example, a solid resin composition for film capacitors can be extruded using a single-screw or twin-screw extruder to produce a film for capacitors.

The thickness of the capacitor film obtained using the resin composition for film capacitors of the present invention is not particularly limited, and can be adjusted to, for example, the same thickness as that of known capacitor films. For example, the thickness of the capacitor film can be 1 to 20 μm.

A film capacitor can be manufactured using the capacitor film. Since such a film capacitor contains a capacitor film obtained using the resin composition for film capacitors of the present invention, it is possible to form a capacitor film that has a high dielectric constant and a low dielectric tangent.

The film capacitor may have a metal film on its surface. Examples of metals used for the metal film include aluminum, nickel, gold, silver, and copper. There are no particular limitations on the method for forming the metal film, and it can be formed by a known method such as a vacuum deposition method. A capacitor element can be manufactured using the film capacitor.

In identifying the inventions encompassed by this disclosure, the configurations (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. In other words, this disclosure encompasses all subject matter consisting of all combinations of the combinable configurations described in this specification.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Production Example 1)
A mixed solvent consisting of 160 g of N,N-dimethylformamide and 80 g of toluene was added to a 500 mL round-bottom flask equipped with a Teflon (registered trademark) stirrer. Then, 41 g (0.1 mol) of BAPP (manufactured by Seika Corporation, diamine) and 62 g (0.12 mol) of BISDA-1000 (manufactured by Savic Corporation, acid anhydride) were added to the mixed solvent in this order to prepare a mixture. The molar ratio of the aromatic compound having two acid anhydrides to the organic diamine in the mixture (aromatic compound having two acid anhydrides:organic diamine) was 0.12:0.10. A Dean-Stark tube and a condenser were attached to the flask, and the mixture was refluxed for 5 hours to obtain polyimide resin 1 having an acid anhydride at its terminal, represented by the formula (1). The calculated acid anhydride equivalent of the obtained polyimide resin was 2500.

(Production Example 2)
A mixed solvent consisting of 160 g of N,N-dimethylformamide and 70 g of toluene was added to a 500 mL round-bottom flask equipped with a Teflon (registered trademark) stirrer. Then, 45.1 g (0.11 mol) of BAPP (manufactured by Seika Corporation, diamine) and 52 g (0.1 mol) of BISDA-1000 (manufactured by Savic Corporation, acid anhydride) were added to the anisole in this order to prepare a mixture. The molar ratio of the aromatic compound having two acid anhydrides to the organic diamine in the mixture (aromatic compound having two acid anhydrides:organic diamine) was 0.10:0.11. A Dean-Stark tube and a condenser were attached to the flask, and the mixture was refluxed for 5 hours to obtain polyimide resin 2 having an amino group at the end represented by the formula (2). The calculated active hydrogen equivalent of the amine of the obtained polyimide resin was 2400.

(Production Example 3)
A mixed solvent consisting of 160 g of N,N-dimethylformamide and 60 g of toluene was added to a 500 mL round-bottom flask equipped with a Teflon (registered trademark) stirrer. Then, 45.1 g (0.11 mol) of BAPP (manufactured by Seika Corporation, diamine), 16.1 g (0.05 mol) of BISDA-1000 (manufactured by Sabic Corporation, acid anhydride), and 14.7 g (0.05 mol) of 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride were added to the anisole in this order to prepare a mixture. The molar ratio of the aromatic compound having two acid anhydrides to the organic diamine in the mixture (aromatic compound having two acid anhydrides:organic diamine) was 0.1:0.11. A Dean-Stark tube and a condenser were attached to the flask, and the mixture was refluxed for 5 hours to obtain polyimide resin 3 having an amino group at its terminal, represented by the formula (4). The calculated active hydrogen equivalent of the amine in the resulting polyimide resin was 2,100.

Example 1
90 parts by mass of the polyimide resin 1 solution obtained in Production Example 1, calculated as a solid content, 10 parts by mass of epoxy resin "NC-3000" manufactured by Nippon Kayaku Co., Ltd., and 1 part by mass of hardening accelerator "dimethylaminopyridine" manufactured by Tokyo Kasei Co., Ltd. were mixed together to obtain a resin composition for film capacitors.

Example 2
A resin composition for a film capacitor was obtained in the same manner as in Example 1, except that the polyimide resin 2 obtained in Production Example 2 was used instead of the polyimide resin 1.

Example 3
A resin composition for a film capacitor was obtained in the same manner as in Example 1, except that the polyimide resin 3 obtained in Production Example 3 was used instead of the polyimide resin 1.

Example 4
90 parts by mass of the solution of polyimide resin 3 obtained in Production Example 1, calculated as a solid content, 10 parts by mass of epoxy resin "HP-6000" manufactured by DIC Corporation, and 1 part by mass of hardening accelerator "dimethylaminopyridine" manufactured by Tokyo Chemical Industry Co., Ltd. were mixed together to obtain a resin composition for a film capacitor.

Example 5
90 parts by mass, calculated as solid content, of the solution of polyimide resin 3 obtained in Production Example 2 was mixed with 10 parts by mass of "maleimide resin BMI-70" manufactured by KI Chemical Industry Co., Ltd. This resulted in a resin composition for a film capacitor.

Example 6
90 parts by mass, calculated as solid content, of the solution of polyimide resin 3 obtained in Production Example 2 was mixed with 5 parts by mass of "TAIC (triallyl isocyanurate)" manufactured by Shinryo Corporation. This resulted in a resin composition for a film capacitor.

(Example 7)
90 parts by mass of the polyimide resin 2 solution obtained in Production Example 1 was mixed in terms of solid content with 10 parts by mass of epoxy resin "NC-3000" manufactured by Nippon Kayaku Co., Ltd., 5 parts by mass of barium titanate as an inorganic filler, and 1 part by mass of a curing accelerator "dimethylaminopyridine" manufactured by Tokyo Kasei Co., Ltd. This resulted in a resin composition for film capacitors.

(Example 8)
90 parts by mass of the polyimide resin 2 solution obtained in Production Example 1 was mixed with 10 parts by mass of epoxy resin "NC-3000" manufactured by Nippon Kayaku Co., Ltd., 10 parts by mass of barium titanate as an inorganic filler, and 1 part by mass of a curing accelerator "dimethylaminopyridine" manufactured by Tokyo Kasei Co., Ltd., in terms of solid content. This resulted in a resin composition for film capacitors.

(Comparative Example 1)
A solution of 90 parts by mass of polyimide resin PIAD300 (Arakawa Chemical Industries, Ltd.) having no acid anhydride moieties or amino groups at the ends was mixed with 10 parts by mass of epoxy resin "NC-3000" from Nippon Kayaku Co., Ltd., and 1 part by mass of hardening accelerator "dimethylaminopyridine" from Tokyo Kasei Co., Ltd. This resulted in a resin composition for film capacitors.

(Comparative Example 2)
50 parts by mass of epoxy resin "NC-3000" from Nippon Kayaku Co., Ltd., 50 parts by mass of epoxy resin hardener "MEHC7851H (phenolic resin)" from UBE (formerly Meiwa Kasei Co., Ltd.), and 1 part by mass of hardening accelerator "dimethylaminopyridine" from Tokyo Kasei Co., Ltd. were added to 100 g of methyl ethyl ketone, and dissolved by stirring. This produced a resin composition for film capacitors.

(Evaluation method)
(Preparation of Capacitor Film)
The solutions (resin compositions for film capacitors) obtained in each Example and Comparative Example were applied to a 50 μm-thick PET film (manufactured by Nakamoto Backs Co., Ltd.) with a release treatment on one side, using a doctor knife to form a coating film with a dry film thickness of 30 μm. The coating film was heated at 100° C. for 10 minutes, and then heat-cured at 170° C. for 30 minutes to form a resin film. This resin film was used as a capacitor film. Note that when the solution obtained in Comparative Example 1 was used, the film was brittle after drying and could not be peeled off, so the film was not evaluated.

<Film breaking strength and elongation>
The capacitor film thus prepared was cut into a sample having a width of 20 mm and a length of 100 mm. A tensile test was performed on the sample using a Tensilon tensile tester (Shimadzu Corporation, Autograph AGS-X 500N) at 25°C and a tensile speed of 510 mm/sec to measure the stress and elongation at break.

<Dielectric constant and dielectric tangent of film>
The capacitor film thus prepared was cut into a 40 mm square, and platinum electrodes with a diameter of 20 mm and a thickness of 0.1 microns were formed on both sides by sputtering to prepare a sample. The dielectric constant and dielectric loss tangent of this sample were measured at 25° C. and 1 kHz using an LCR meter (E4980AL manufactured by Keysight Corporation).

<Film breakdown voltage>
The capacitor film prepared as described above was cut into a 100 mm square to prepare a sample. The dielectric breakdown voltage of this sample was measured in silicone oil at 25° C. The measurement device used was a dielectric breakdown voltage measuring device (TOJ-200, oil test electrode device, manufactured by Tama Densoku Co., Ltd.), and the electrodes used were a cylindrical upper electrode with a diameter of 6.425 mm and cylindrical upper and lower electrodes with a diameter of 75 mm, and the dielectric breakdown voltage was measured at a voltage rise rate of 50 V/sec.

Table 1 shows the compounding conditions for the resin compositions for film capacitors obtained in each Example and Comparative Example, as well as the evaluation results of the resulting capacitor films. Note that blanks in Table 1 mean that the raw material was not used. In addition, in Table 1, "functional group equivalent" means acid anhydride equivalent or amine active hydrogen equivalent in the polyimide resin column, and functional group equivalent in other columns.

From Table 1, it can be seen that the capacitor film formed from the resin composition for film capacitors obtained in the examples had a high dielectric constant but a low dielectric tangent, and also had high mechanical strength and a high dielectric breakdown voltage.

Claims (6)

In a resin composition for a film capacitor containing a resin A having an imide structure,
At least one end of the resin A is an acid anhydride moiety or an amino group,
The resin composition for a film capacitor, wherein the resin A has an acid anhydride equivalent or an amine active hydrogen equivalent of 20,000 or less. The resin composition for film capacitors according to claim 1, further comprising a resin B that reacts with an acid anhydride or an amino group. The resin composition for film capacitors according to claim 2, wherein the resin B is at least one selected from the group consisting of epoxy resins, maleimide resins, and resins having an allyl group. The resin composition for film capacitors according to any one of claims 1 to 3, which contains an inorganic filler. A film for capacitors containing a cured product of the resin composition for film capacitors according to any one of claims 1 to 3. A film capacitor having the capacitor film according to claim 5.