JP7313013B2 - Electrode foil for electrolytic capacitor and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an electrode foil for an electrolytic capacitor, and more particularly to a method for producing an electrode foil for an aluminum electrolytic capacitor by photo-nanoimprinting. The present invention also relates to an electrode foil for electrolytic capacitors obtained by using the manufacturing method.

Photolithography has traditionally been used as a microfabrication technique in the manufacture of parts, including semiconductor manufacturing. It is known to use this photolithographic technique to form a large number of micropores in an aluminum foil as an electrode material for an electrolytic capacitor.

For example, Patent Document 1 discloses a method of manufacturing an electrode foil for a high-capacity aluminum electrolytic capacitor by applying a pattern of a resist film layer to the surface of an aluminum foil by photolithography and etching the pattern. Specifically, according to the method for manufacturing an aluminum foil for electrolytic capacitors described in Patent Document 1, after forming a resist film layer on the surface of the aluminum foil, the surface is exposed through a photomask and developed to form a porous resist film as a resistant film. After that, the aluminum foil (etching foil) for an electrolytic capacitor is manufactured by performing an etching treatment with an etchant and then removing the resist.

However, the method for producing an aluminum foil for an electrolytic capacitor described in Patent Document 1 has a problem that it is difficult to realistically provide a pattern controlled on the order of submicrometers. In order to apply a sub-micrometer sized pattern to the resist film layer, not only is an expensive exposure device such as a reduction projection exposure device required, but the flexible aluminum foil for electrolytic capacitors has a problem that pattern formation is difficult due to variations in the distance between the photomask and the resist film layer. Therefore, in the roll-to-roll production of aluminum foil for electrolytic capacitors, it is practically difficult to impart a pattern controlled on the order of submicrometers to the surface of the aluminum foil by the production method described in Patent Document 1.
On the other hand, according to the photo-nanoimprint method, a similarly flexible resin nanoimprint mold (pattern forming mold) is adhered to a flexible aluminum foil for electrolytic capacitors, and the resist pattern is photocured and released. Therefore, in principle, it is possible to impart a pattern controlled in the submicrometer order. However, when a commercially available resist material for photo-nanoimprinting is used to impart a pattern to the surface of an aluminum foil and perform electrolytic etching, resistance to a strongly acidic and high ionic strength etchant is weak, and etching pits cannot be aligned according to the given pattern period.

JP-A-61-51817

Accordingly, an object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a method for producing an electrode foil for an electrolytic capacitor, which is capable of aligning etching pits according to the given pattern period by using a resist material for photo-nanoimprinting, which has strong resistance to etching solutions and is capable of imparting a pattern controlled on the order of submicrometers to the surface of the electrode foil.

As a result of intensive research to solve the above problems, the present inventors have found that a photocurable composition using a monomer having a cationically polymerizable hydrocarbon group containing an ethylenically unsaturated bond as a resist material and an onium salt having a specific structure as a photoacid generator exhibits strong resistance to an etchant and can align etching pits according to the pattern period on the surface of an electrode foil by a photo-nanoimprint method, and completed the present invention.

Specifically, the above problems have been solved by means described in <1> to <6> below.
<1> A method for manufacturing an electrode foil for an electrolytic capacitor,
a resist layer forming step of providing a resist layer on the surface of the electrode foil;
a resist pattern forming step of patterning the resist layer into a predetermined pattern;
a wet electrolytic etching step of performing wet electrolytic etching using an etchant on the electrode foil surface on which the patterned resist layer is formed,
The resist material used to form the resist layer is a photocurable composition containing a photopolymerization initiator and a polymerizable compound,
(a) the photopolymerization initiator is a photocationic polymerization initiator (A) comprising an iodonium compound or a sulfonium compound;
(b) 35% by weight or more of the total weight of the polymerizable compound is a cationically polymerizable hydrocarbon compound (B) containing an ethylenically unsaturated bond consisting only of carbon atoms and hydrogen atoms;
(c) heteroatom content percentage representing the ratio of heteroatoms contained in the photocurable composition, calculated based on the following formula (1):
Heteroatom content percentage=100×Σ(Nh _i ×M _i )/Σ{(Nh _i +Nc _i )×M _i } (1)
[Wherein, _Nhi is the number of heteroatoms contained in each component in the photocurable composition (here, heteroatoms are all atoms other than carbon atoms and hydrogen atoms), Nc _i is the number of carbon atoms contained in each component in the photocurable composition, M _i represents the fraction of the substance amount of each component in the photocurable composition, ΣM _i = 1, and i is the component contained in the photocurable composition. and represents an integer of 1 or more. ]
is 6.0 or less.
The heteroatom content percentage of the photocurable composition and resist layer (cured film) of the present invention can be calculated from the weight percentage of each element determined by elemental analysis.
<2> The method for producing an electrode foil for an electrolytic capacitor according to <1>, wherein the photocurable composition contains one or more additives selected from the group consisting of a photosensitizer, a surfactant, a polymerization inhibitor, an antioxidant, and an adhesion imparting agent.
<3> The method for producing an electrode foil for an electrolytic capacitor according to <1> or <2>, wherein in the resist pattern forming step, the resist layer is patterned using a photo-nanoimprinting method.
<4> The method for producing an electrode foil for an electrolytic capacitor according to <3>, wherein, in the resist pattern forming step, a residual film remaining in the concave portions of the concave-convex pattern of the resist layer patterned using a photo-nanoimprint method is removed by oxygen-based dry etching.
<5> The method for producing an electrode foil for an electrolytic capacitor according to any one of <1> to <4>, wherein in the resist layer forming step, the photocurable composition is applied to the surface of the electrode foil by an inkjet method, a slit die coating method, or a small diameter gravure method to form the resist layer.
<6> An electrode foil for an electrolytic capacitor obtained by the method for producing an electrode foil for an electrolytic capacitor according to any one of <1> to <5>.

The photocurable composition used in the production method of the present invention is sensitive to light to generate an acid, can be cured by cationic polymerization, and forms a cured film with excellent resistance to etching solutions, and this effect is obtained by using a hydrocarbon compound having an extremely low heteroatom content other than carbon atoms and hydrogen atoms as a monomer.
In the production method of the present invention, a pattern controlled in the order of submicrometers can be imparted to the surface of an electrode foil (particularly an aluminum foil) by a photo-nanoimprinting method using the photocurable composition as a photo-nanoimprinting resist. By etching the pattern, the etching pits can be aligned according to the imparted pattern period, and an electrode foil for an electrolytic capacitor having a higher capacity than conventional can be produced.

FIG. 4 is a diagram showing steps in a preferred example of manufacturing an electrode foil for an electrolytic capacitor using the manufacturing method of the present invention. (a) is an SEM image (scanning electron micrograph) showing the surface state of an example of an aluminum electrode foil for electrolytic capacitors produced using the production method of the present invention, and (b) is an SEM image showing the surface state of the aluminum electrode foil when etching was performed without using a resist material.

The contents of the present invention will be described in detail below. The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In the specification of the present application, the term "~" is used to mean that the numerical values before and after it are included as the lower limit and the upper limit.

In the production method of the present invention, the resist material used to form the resist layer is a photocurable composition containing a photopolymerization initiator and a polymerizable compound,
(a) the photopolymerization initiator is a photocationic polymerization initiator (A) comprising an iodonium compound or a sulfonium compound;
(b) 35% by weight or more of the total weight of the polymerizable compound is a cationically polymerizable hydrocarbon compound (B) containing an ethylenically unsaturated bond consisting only of carbon atoms and hydrogen atoms;
(c) The heteroatom content percentage of the photocurable composition is 6.0 or less.
Each component contained in the above photocurable composition will be described below.

The photopolymerization initiator contained in the photocurable composition used in the production method of the present invention is a photocationic polymerization initiator (A) composed of an iodonium compound or a sulfonium compound, and as the photocationic polymerization initiator (A), any known iodonium compound or sulfonium compound can be used.

The iodonium compound and the sulfonium compound can be regarded as a combination of a cation moiety that absorbs light and causes a decomposition reaction and an anion moiety that is a source of acid generation, and can be selected from known iodonium or sulfonium cation moieties and anion moieties from the viewpoint of the wavelength of light to be absorbed, the solubility in a photocurable composition (resist material), the strength of the generated acid, and the like.

For example, specific examples of preferred iodonium cation moieties include diphenyliodonium cation, di-p-tolyliiodonium cation, 4-isopropylphenyl(p-tolyl)iodonium cation, bis(4-tert-butylphenyl)iodonium cation, 4-octyloxyphenylphenyliodonium cation, di-4-isopropylphenyliodonium cation, bis(2,4-diisopropylphenyl)iodonium cation, 4-hexylphenyl(p-tolyl)iodonium cation, -cyclohexylphenyl(p-tolyl)iodonium cation, bis(4-dodecylphenyl)iodonium cation, bis(4-methoxyphenyl)iodonium cation, bis(4-decyloxyphenyl)iodonium cation, 4-(2-hydroxytetradecyloxy)phenylphenyliodonium cation and the like.

For example, specific examples of preferred sulfonium cation moieties include triphenylsulfonium cation, 4-(phenylthio)phenyldiphenylsulfonium cation, bis[4-(diphenylsulfonio)phenyl]sulfide, 4-hydroxyphenylmethylbenzylsulfonium cation, tris(4-chlorophenyl)sulfonium cation, tris(4-fluorophenyl)sulfonium cation, 4-tert-butylphenyldiphenylsulfonium cation, diphenylphenacylsulfonium cation, and the like.

For example, specific examples of preferred anion moieties include hexafluorophosphate, hexafluoroantimonate, tetrakis(pentafluorophenyl)borate, tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, tetrakis(2,6-bis(trifluoromethyl)phenyl)borate, trifluoromethylpentafluorophosphate, bis(trifluoromethyl)tetrafluorophosphate, tris(trifluoromethyl)trifluorophosphate, pentafluoroethylpentafluorophosphate, bis(pentafluoroethyl)tetrafluorophosphate. phate, tris(pentafluoroethyl)trifluorophosphate, bis(n-heptafluoropropyl)tetraolophosphate, tris(n-heptafluoropropyl)trifluorophosphate, tris(heptafluoroisopropyl)trifluorophosphate, n-nonafluorobutylpentafluorophosphate, bis(n-nonafluorobutyl)tetrafluorophosphate, tris(n-nonafluorobutyl)trifluorophosphate, tris(nonafluoroisobutyl)trifluorophosphate etc.

Specific examples of preferred iodonium compounds include the following.

Specific examples of preferred sulfonium compounds include the following.

The content of the photocationic polymerization initiator (A) is preferably 0.2 to 10 parts by weight with respect to 100 parts by weight of the polymerizable compound ((B) + (C)) contained in the photocurable composition, more preferably 0.4 to 5 parts by weight, and even more preferably 0.6 to 4 parts by weight.
If the content of the photocationic polymerization initiator (A) is too high, an excessive amount of cations will be generated even at low exposure doses, making it difficult to control the reactivity. Conversely, if the content is too low, it will be difficult to generate a sufficient amount of cations to react the polymerizable compound, which may lead to poor curing. These photocationic polymerization initiators (A) may be used alone, or two or more of them may be used in combination. When two or more are used in combination, the total amount is preferably within the above range.

The polymerizable compound contained in the photocurable composition used in the production method of the present invention is a cationically polymerizable hydrocarbon compound (B) containing an ethylenically unsaturated bond composed only of carbon atoms and hydrogen atoms in an amount of 35% by weight or more of the total weight of the polymerizable compound. As the cationically polymerizable hydrocarbon compound (B), for example, an aliphatic unsaturated hydrocarbon compound (B1) having 4 to 35 carbon atoms or a hydrocarbon compound (B2) obtained by substituting an ethylenically unsaturated group in an aromatic compound having 6 to 18 carbon atoms can be used.

Of the aliphatic unsaturated hydrocarbon compounds (B1) having 4 to 35 carbon atoms, the compound (B11) having one unsaturated group includes 1-butene, 2-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 2-hexene, 3-methyl-1-pentene, 2,3-dimethyl-1-butene, 3,3-dimethyl-1-butene, vinylcyclopentane, 3,3-dimethyl-1- pentene, vinylcyclohexane, 1-octene, 2-octene, 2,4,4-trimethyl-1-pentene, vinylnorbornane, 1-decene, camphene, α-pinene, β-pinene, vinyladamantane and the like.
Examples of the compound (B12) having two or more unsaturated groups include butadiene, 1,4-pentadiene, cyclopentadiene, 1,5-hexadiene, 1,3-cyclohexadiene, 2,5-norborinadiene, dicyclopentadiene, 4-vinyl-cyclohexene, 5-vinyl-2-norbornene, 5-ethylidene-2-norbornene, or condensed polycyclic unsaturated hydrocarbons produced by Diels-Alder reaction of these. mentioned.

The hydrocarbon compound (B2) obtained by substituting an ethylenically unsaturated group on an aromatic compound having 6 to 18 carbon atoms means an aromatic hydrocarbon compound having 6 to 18 carbon atoms (excluding the number of carbon atoms of the substituent substituted on the aromatic compound), which is substituted with one or more ethylenically unsaturated groups (vinyl group, allyl group, etc.). It also includes those in which one ethylenically unsaturated group is substituted with a plurality of aromatic hydrocarbon compounds.
Aromatic compounds having 6 to 18 carbon atoms include monocyclic and polycyclic aromatic hydrocarbon compounds such as phenyl, naphthyl, anthryl, phenanthryl and pyrenyl.
As for the aryl group, in addition to the above, part of the hydrogen atoms in the aryl group may be substituted with an alkyl group having 1 to 18 carbon atoms, an (alkyl)aryl group having 6 to 18 carbon atoms, or the like.

Of the hydrocarbon compounds (B2) in which an ethylenically unsaturated group is substituted on an aromatic compound having 6 to 18 carbon atoms, specific examples of the compound (B21) having one unsaturated group include styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 3-ethylstyrene, 4-ethylstyrene, 3-propylstyrene, 4-isopropylstyrene, 3-butylstyrene, 4-tert-butylstyrene, 4-hexylstyrene, 4-octylstyrene, 3-(2-ethylhexyl ) styrene, 4-(2-ethylhexyl)styrene, 2,4-diphenyl-4-methyl-1-pentene, 1-vinylnaphthalene, 2-vinylnaphthalene, 2-isopropenylnaphthalene, 9-vinylanthracene, 1-vinylanthracene and the like.
Specific examples of the compound (B22) having two or more unsaturated groups include 1,3-divinylbenzene, 1,4-divinylbenzene, 1,3-diisopropenylbenzene, 1,4-diisopropenylbenzene, 1,4-divinylnaphthalene, 1,5-divinylnaphthalene, 1,4-diisopropenylnaphthalene, 9,10-divinylanthracene, allylstyrene, isopropenylstyrene, butenylstyrene, and octenylstyrene. etc.

Among these cationically polymerizable hydrocarbon compounds (B), alicyclic compounds and aromatic compounds are preferred because they provide cured films with high etchant resistance derived from rigid molecular structures.
These cationically polymerizable hydrocarbon compounds (B) may be used alone, or two or more of them may be used in combination. When two or more of them are used together, the total amount should be 35% by weight or more based on the total weight of the polymerizable compounds. When the content of the cationically polymerizable hydrocarbon compound (B) is within the above range, the hydrophilicity of the photocurable composition is greatly reduced, and chloride ions in the etching solution can be prevented from penetrating into the cured film obtained by curing.

In the present invention, in addition to the above (B), a heteroatom-containing cationically polymerizable compound (C) can be further used in combination within a range in which the heteroatom content percentage, which represents the ratio of heteroatoms in the photocurable composition, is 6.0 or less, preferably in the range of 0.9 to 6.0. When the heteroatom content percentage is within the above range, the hydrophilicity of the photocurable composition is greatly reduced, and chloride ions in the etching solution can be prevented from penetrating into the cured film obtained by curing.
However, the heteroatom content percentage of the photocurable composition as used herein is calculated based on the following formula (1).
Heteroatom content percentage=100×Σ(Nh _i ×M _i )/Σ{(Nh _i +Nc _i )×M _i } (1)

In formula (1), Nh _i is the number of heteroatoms contained in each component in the photocurable composition (here, heteroatoms are all atoms other than carbon atoms and hydrogen atoms), Nc _i is the number of carbon atoms contained in each component in the photocurable composition, M _i represents the fraction of the amount of each component in the photocurable composition, and ΣM _i =1. In addition, i represents the number of types of components contained in the photocurable composition and is an integer of 1 or more.
In the present invention, the components considered when calculating the heteroatom content percentage representing the ratio of heteroatoms contained in the photocurable composition are the photocationic polymerization initiator (A), the cationically polymerizable hydrocarbon compound (B), the heteroatom-containing cationically polymerizable compound (C) and the photosensitizer (D) only, but this is because the amount of the other components such as the surfactant (E) and the polymerization inhibitor (F) is small and can be ignored for calculation.

Examples of the heteroatom-containing cationically polymerizable compound (C) include compounds (C1 and C2) obtained by replacing some of the hydrogen atoms or carbon atoms in the above (B) with a heteroatom or a heteroatom-containing functional group, epoxy compounds (C3), and the like.

A compound in which a hydrogen atom or part of a carbon atom is replaced with a heteroatom or a heteroatom-containing functional group refers to, for example, a chemical structure in which a hydrogen atom of a hydrocarbon compound is replaced with an alkoxy group, an acyl group, a halogen atom, or the like, or a compound having the same chemical structure as a hydrocarbon compound in which a carbon atom (and a hydrogen atom bonded to the carbon atom) is replaced with an oxygen atom, a nitrogen atom, or the like.

The heteroatom-containing cationically polymerizable compound (C1) used in the present invention refers to a compound obtained by replacing some of the hydrogen atoms or carbon atoms of the aliphatic unsaturated hydrocarbon compound (B1) with a heteroatom or heteroatom-containing functional group. -tert-butoxy-1-pentene, 2-vinylcyclohexanone, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, tert-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-nonyl vinyl ether, cyclohexyl vinyl ether, cyclohexyl methyl vinyl ether, 4-methylcyclohexyl methyl vinyl ether, benzyl vinyl ether, dicyclopentenyl vinyl ether, 2-dicyclopentenoxyethyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether, n-butoxyethyl vinyl ether, methoxyethoxyethyl vinyl ether, ethoxyethoxyethyl vinyl ether, methoxypolyethylene glycol vinyl ether, tetrahydrofurfuryl vinyl ether, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, diethylene glycol monovinyl ether, polyethylene glycol vinyl ether, chloroethyl vinyl ether, chlorobutyl vinyl ether, ethylene glycol divinyl ether, propylene glycol divinyl ether, ethyl-1-propenyl ether, tert-butyl-1 -propenyl ether, 2-ethylhexyl-1-propenyl ether, nonyl-1-propenyl ether, dodecyl-1-propenyl ether, lauryl-1-propenyl ether, cyclohexyl-1-propenyl ether, cyclohexylmethyl-1-propenyl ether, hexanediol dipropenyl ether, trimethylolethanetripropenyl ether, trimethylolpropanetripropenyl ether, ditrimethylolpropanetetrapropenyl ether, glycyl and serine tripropenyl ether.

The heteroatom-containing cationically polymerizable compound (C2) used in the present invention refers to a compound obtained by replacing some of the hydrogen atoms or carbon atoms of the aromatic unsaturated hydrocarbon compound (B2) with heteroatoms or heteroatom-containing functional groups. -nitrostyrene, 4-vinylphenyl acetate, 2-vinylpyridine, 2-vinylthiophene, 2-vinylfuran, N-vinylcarbazole, 3-tert-butoxy-1,5-divinylbenzene and the like.

Examples of the epoxy compound (C3) used in the present invention include monofunctional epoxy compounds such as phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1,3-butadiene monoxide, 1,2-epoxydodecane, epichlorohydrin, 1,2-epoxydecane, styrene oxide and cyclohexene oxide, and bisphenol A. Diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, brominated bisphenol S diglycidyl ether, epoxy novolac resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane, bis(3,-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'-methylcyclohexanecarboxylate, methylenebis(3,4-epoxy) cyclohexane), dicyclopentadiene diepoxide, ethylene glycol di(3,4-epoxycyclohexylmethyl) ether, ethylenebis(3,4-epoxycyclohexanecarboxylate), dioctyl epoxyhexahydrophthalate, di-2-ethylhexyl epoxyhexahydrophthalate, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether Polyfunctional epoxy compounds such as sidyl ether, polypropylene glycol diglycidyl ethers, 1,1,3-tetradecadiene dioxide, limonene dioxide, 1,2,7,8-diepoxyoctane and 1,2,5,6-diepoxycyclooctane can be mentioned.

Among these heteroatom-containing cationically polymerizable compounds (C), alicyclic compounds and aromatic compounds are preferred because they provide cured films with high etching solution resistance derived from rigid molecular structures.
In addition, these heteroatom-containing cationically polymerizable compounds (C) may be used alone or in combination of two or more within a range in which the heteroatom content percentage of the photocurable composition is 6.0 or less.

The photocurable composition used in the production method of the present invention may further contain a photosensitizer (D) capable of promoting photodecomposition of the initiator by absorbing irradiated light and transferring the obtained energy to the initiator.

As the photosensitizer (D), for example, known photosensitizers disclosed in JP-A-11-279212 and JP-A-09-183960 can be used. Specific examples include naphthalene (1-naphthol, 2-naphthol, 1-methoxynaphthalene, 2-methoxynaphthalene, 1,4-dihydroxynaphthalene and 4-methoxy-1-naphthol); benzoquinone {1,4-benzoquinone, 1,2-benzoquinone, etc.}; naphthoquinone {1,4-naphthoquinone, 1,2-naphthoquinone, etc.}; anthraquinone {2-methylanthraquinone, 2-ethylanthraquinone, etc.}; 10-dipropoxyanthracene, etc.}; pyrene; 1,2-benzanthracene; perylene; tetracene; coronene; coumarin {7-(diethylamino)4-(trifluoromethyl)coumarin, 3,3′-carbonylbis(7-diethylaminocoumarin), 3-(2-benzothiazolyl)-7-(diethylamino)coumarin, 10-acetyl-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H,-[1]benzopyrano[6,7,8-ij]quinolidin-11-one , 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H,-[1]benzopyrano[6,7,8-ij]quinolidin-11-one etc.}; methyldiphenyl sulfide, bis(4,4'-dimethylamino)benzophenone and bis(4,4'-diethylamino)benzophenone, etc.}; carbazole {N-phenylcarbazole, N-ethylcarbazole, poly-N-vinylcarbazole and N-glycidylcarbazole, etc.}; chrysene {1,4-dimethoxychrysene and 1,4-di-α-methylbenzyloxychrysene, etc.}; phenanthrene {9-hydroxyphenanthrene, 9-methoxyphenanthine rene, 9-hydroxy-10-methoxyphenanthrene, 9-hydroxy-10-ethoxyphenanthrene, etc.} and the like.
In particular, in the present invention, a naphthoquinone-based, benzophenone-based, xanthone-based, anthraquinone-based, or thioxanthone-based photosensitizer is preferably used from the viewpoint of the electron-accepting property of the iodonium compound or sulfonium compound contained as the photopolymerization initiator, because a high sensitizing effect can be obtained.

The content of these photosensitizers (D) is not particularly limited, but is usually 0.005 to 10 parts by weight, preferably 0.01 to 5 parts by weight, more preferably 0.02 to 4 parts by weight relative to 100 parts by weight of the polymerizable compound (B) + (C). Moreover, a photosensitizer (D) may be used independently and may be used in combination of 2 or more types. When two or more are used in combination, the total amount is preferably within the above range.

The photocurable composition used in the production method of the present invention can contain a surfactant (E) that is commonly used to improve coatability on the electrode foil.
As the surfactant (E) that can be used in the present invention, a nonionic (nonionic) surfactant is preferred in order to prevent the surface of the cured film from becoming hydrophilic.
Examples of nonionic (nonionic) surfactants include fluorine-based surfactants and silicone-based surfactants. For example, fluorine surfactants include FC4432, 4430 (manufactured by 3M Japan), S-242, 243, 431 (manufactured by AGC Seimi Chemical Co., Ltd.) and the like, and silicone surfactants include KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.).

Although the content of these surfactants (E) is not particularly limited, it is 0.001 to 5 parts by weight, preferably 0.002 to 4 parts by weight, more preferably 0.005 to 3 parts by weight with respect to 100 parts by weight of the polymerizable compound (B) + (C). Surfactants (E) may be used alone or in combination of two or more. When two or more surfactants are used, the total weight is preferably within the range described above.

The photocurable composition may contain a polymerization inhibitor (F) generally used to improve storage stability over time. Examples of the polymerization inhibitor (F) used in the present invention include aromatic polyol compounds (4-tert-butylcatechol, 4-methoxyphenol, 4-methoxy-1-naphthol, etc.), quinone compounds (naphthoquinone, benzoquinone, etc.), hindered phenol compounds (2,6-di-tert-butylphenol, 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,4,6-tri -tert-butylphenol, etc.) can be used.

In the present invention, the content of these polymerization inhibitors (F) is not particularly limited. The polymerization inhibitor (F) may be used alone or in combination of two or more. When two or more polymerization inhibitors are used, the total weight is preferably within the range described above.

The photocurable composition may contain an antioxidant (G). Antioxidants have the ability to trap oxygen radicals and suppress fading due to heat, light irradiation, various oxidizing gases (eg, ozone, active oxygen, etc.) and the like. Examples of the antioxidant (G) used in the present invention include hindered phenol antioxidants (BASF Japan Irganox 1010, 1035, 1076, etc.), hindered amine antioxidants (BASF Japan Tinuvin PA 144, 765, etc.), thioether antioxidants (ADEKA ADEKA STAB AO-412S, AO-5). 03, etc.).

In the present invention, the content of these antioxidants (G) is not particularly limited, but is 0.001 to 1 part by weight, preferably 0.002 to 1 part by weight, more preferably 0.003 to 1 part by weight with respect to 100 parts by weight of the polymerizable compound (B) + (C). The antioxidant (G) may be used alone or in combination of two or more. When two or more polymerization inhibitors are used, the total weight is preferably within the range described above.

The photocurable composition for forming a resist layer may contain a solvent, an adhesion imparting agent (for example, a silane coupling agent), etc., if necessary.
Solvents include glycol ethers (ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), esters (ethyl acetate, butyl acetate, ethylene glycol alkyl ether acetate, propylene glycol alkyl ether acetate, etc.), aromatic hydrocarbons (toluene, xylene, mesitylene, limonene, etc.), alcohols (methanol, ethanol, normal propanol, isopropanol, butanol, geraniol, linalool and citronellol, etc.) and ethers (tetrahydrofuran and 1,8-cineole, etc.). These may be used alone or in combination of two or more.
Although the content of the solvent is not particularly limited, it is preferably 0 to 99% by weight, more preferably 0 to 95% by weight, and particularly preferably 0 to 90% by weight based on the total weight of the photocurable composition.

Examples of adhesion-imparting agents include bis(trimethylsilyl)amine, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, ureapropyltriethoxysilane, tris(acetylacetonate)aluminum and acetylacetatealuminum diisopropylate. Although the content of the adhesion-imparting agent is not particularly limited, it is preferably 0 to 20% by weight, more preferably 1 to 15% by weight, and particularly preferably 5 to 10% by weight based on the total weight of the photocurable composition.

The photocurable composition comprises a photocationic polymerization initiator (A) composed of an iodonium compound or a sulfonium compound, a cationically polymerizable hydrocarbon compound (B) containing an ethylenically unsaturated bond composed only of carbon atoms and hydrogen atoms, a heteroatom-containing cationically polymerizable compound (C) used if necessary, a photosensitizer (D) used if necessary, a surfactant (E) used if necessary, a polymerization inhibitor used if necessary (F), an antioxidant used if necessary (G), a solvent and an adhesion-imparting agent used if necessary, mixed with known stirring. It can be obtained by uniform mixing using a device (mixing vessel equipped with a stirrer, paint shaker, etc.) or kneading using a known kneader (ball mill, three-roll mill, etc.). The uniform mixing temperature and kneading temperature for preparing the photocurable composition are usually 10°C to 40°C, preferably 20°C to 30°C.

Each step of the method for manufacturing the electrode foil for an electrolytic capacitor of the present invention will be described below.
FIG. 1 shows steps in a preferred example of manufacturing an electrode foil for an electrolytic capacitor using the manufacturing method of the present invention.
In the present invention, as shown in FIG. 1, before the resist layer forming step of providing a resist layer made of the photocurable composition (resist material) on the surface of the electrode foil base material, an adhesion layer may be formed by coating the surface of the electrode foil for electrolytic capacitors, which is the substrate to be etched, with a substrate treating agent for the purpose of enhancing the adhesion between the resist layer and the electrode foil base material. For forming the adhesion layer, for example, the above-mentioned adhesion imparting agent can be used, and the adhesion layer can be provided on the substrate by thermal vapor deposition or coating-heating process. Further, instead of forming the adhesion layer, the photocurable composition may contain an adhesion-imparting agent.

The electrode foil base material for electrolytic capacitors used in the production method of the present invention is generally subjected to surface conditioning (flattening/smoothing) by a known method and then washed to remove foreign matter and dirt. When an aluminum foil is used as the electrode foil base material, any material may be used as long as it can be used as an electrode foil for an electrolytic capacitor. For example, a high-purity aluminum foil having a purity of 99.9 or more, a thickness of 20 to 300 μm, and a (100) plane orientation rate of 95% or more can be used, and the average roughness Ra of the aluminum foil is preferably 1/100 or less of the hole diameter of the pattern to be formed. For example, when forming a pattern with a hole diameter of 1.0 μm, Ra=0.01 μm.

Then, in the resist layer forming step, a resist layer is formed by applying the photocurable composition (resist material) on the surface of the electrode foil base material. The method of applying the photocurable composition in forming the resist layer can be appropriately selected, but an ink jet method in which fine droplets are continuously discharged, a slit die coating method, or a small diameter gravure method is preferable. Incidentally, in the small-diameter gravure method, coating is generally performed using a small-diameter gravure roll having a diameter of about 20 to 50 mm.
In the present invention, the film thickness of the resist layer can be appropriately selected, but it is preferably about 0.05 to 10 μm. If the film thickness is less than 0.05 μm, the resist resistance disappears and pits are not formed according to the resist pattern period. Further, when the film thickness exceeds 10 μm, the residual film thickness increases, and in the process of removing the residual film by oxygen reactive etching, the oxidation of the resist film progresses, the resistance of the resist deteriorates, and pit formation according to the resist pattern cycle may not be possible.
Note that the specific film thickness of the resist layer is set according to the pattern size, since it is necessary to impart a sub-micrometer to micrometer-sized pattern in accordance with the withstand voltage specification of the electrode foil.
For example, when forming (transferring) recesses in a resist using a cylindrical pattern (convex mold) with an aspect ratio of about 1, the diameter and height of the cylindrical column are about 0.2 μm for low-voltage electrode foil and about 2.0 μm for high-voltage electrode foil. The film thickness of the resist layer is preferably d/4 to d [μm], more preferably d/3 to 4d/5 [μm], where d [μm] is the diameter of the cylinder. From the viewpoint of facilitating the removal of the residual film, it is desirable that the residual film is small (no residual film is left), and the film thickness of the resist layer is preferably smaller than the height of the cylindrical pattern.
When the resist layer is formed using the photocurable composition, it can be usually carried out under a nitrogen gas atmosphere or an air atmosphere. Since oxygen inhibition, which is a problem in radical polymerization, does not occur, it is convenient and preferable to carry out in an air atmosphere, and in order to avoid the influence of moisture on curing, it is more preferable to carry out in a dry air atmosphere.

Then, in the next resist pattern forming step, as shown in FIG. 1, a light-transmitting nanoimprint mold having unevenness is pressed against the surface of the resist layer coated and formed on the surface of the electrode foil base material to form an uneven pattern on the resist layer (first step). Thereafter, the electrode foil having the resist layer pressed against the mold is irradiated with light (ultraviolet rays) from the mold side to cure the resist layer (second step), thereby forming a resist layer having surface unevenness corresponding to the uneven shape of the mold, and forming the resist layer with the mold. It is preferable to release from the mold (third step). The resist pattern forming process including the above process is effective in roll-to-roll, and is suitable for double-sided treatment of the substrate because the resist layer can be cured by UV irradiation.
Translucent molding materials suitable for the present invention include glass, quartz glass, polycarbonate resin, acrylate resin, transparent metal deposition film, polydimethylsiloxane, and the like. The pattern of the mold is convex cylinders (pillars), the diameter of the cylinders is preferably 0.2 to 2.0 μm, and the height is preferably about the same as the diameter (aspect ratio of about 1).
In the present invention, a resist pattern for wet electrolytic etching as shown in FIG. 1 can be formed by a photo-nanoimprint method using the photocurable composition.

The photocurable composition used in the production method of the present invention generates a strong acid by irradiating with light, promotes a curing reaction by cationic polymerization, and obtains a cured coating (resist layer). Therefore, when producing such a cured film, it is preferable to include a step of selecting a photosensitizer (D) according to the wavelength of the light used as the light source, and irradiating light using one contained in the photocurable composition for a resist, or irradiating light using a light source corresponding to the absorption wavelength of the used photosensitizer (D). Moreover, you may heat at the time of hardening reaction as needed. The heating temperature is usually 30°C to 150°C, preferably 35°C to 120°C, more preferably 40°C to 100°C.
In the present invention, as a light source for curing the photocurable composition, in addition to a commonly used high pressure mercury lamp, an ultrahigh pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp and a high power metal halide lamp, an argon ion laser, a helium cadmium laser, a helium neon laser, a krypton ion laser, various semiconductor lasers, a xenon lamp, or an LED light source can be used.

In the present invention, in the photo-nanoimprint method, light is irradiated to form unevenness on the surface of the resist layer, and after releasing the mold from the resist layer, the remaining film remaining in the recesses of the uneven pattern of the resist layer is removed by oxygen-based dry etching (fourth step). This is because the presence of the residual film makes it impossible to finely process the electrode foil by the subsequent wet electrolytic etching, and it is necessary to eliminate the wet etching resistance of the residual film before performing the wet electrolytic etching.
In the present invention, oxygen-based dry etching (dry etching using oxygen or ozone gas) is used when removing the residual film remaining in the recesses of the uneven pattern of the resist layer. For example, reactive ion etching, ultraviolet/ozone treatment, etc. are preferable.

Thereafter, in the present invention, the electrode foil base material exposed at the positions of the recesses formed on the surface of the resist layer is etched by wet electrolytic etching to form fine surface unevenness corresponding to the surface unevenness of the photo-nanoimprint mold on the surface of the electrode foil, and finally, by removing the layer present on the electrode foil, an electrode foil having fine surface unevenness can be obtained.
At this time, the wet electrolytic etching conditions are not particularly limited, but the etching treatment is generally performed for 30 to 60 seconds in a solution containing hydrochloric acid (1 to 7 M) or sulfuric acid (0.1 to 2 M) added thereto and heated to 50 to 70°C.

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these. Hereinafter, unless otherwise specified, % means % by weight, and part means part by weight.

[Preparation of photocurable composition]
[Example 1]
The following photocationic polymerization initiator A-1 (3 parts by weight), the following cationically polymerizable hydrocarbon compound B-1 (50 parts by weight), the following heteroatom-containing cationically polymerizable compound C-1 (50 parts by weight), the following photosensitizer D-1 (1.5 parts by weight), the following surfactant E-1 (0.01 parts by weight), and the following polymerization inhibitor F-1 (0.01 parts by weight) were added to prepare a photocurable composition for a resist of Example 1.

[Examples 2 to 8]
Compositions of Examples 2 to 8 were prepared in the same manner as in Example 1, except that the photocurable composition for resist was changed to the compound shown in Table 1 below.

[Comparative Examples 1 to 4]
Compositions of Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, except that the photocurable composition for resist was changed to the compound shown in Table 1 below.

[Formation of resist layer (hardened film)]
The compositions prepared above (Examples 1 to 8 and Comparative Examples 1 to 4) were applied to a film thickness of 1.5 μm using a spin coater on an aluminum substrate previously surface-treated with bis(trimethylsilyl)amine. A resist layer was formed by irradiating the spin-coated base film with ultraviolet rays (1 J/cm ² ) from a high-pressure mercury lamp.

[Evaluation of etching resistance]
Etching resistance was evaluated by a concentrated hydrochloric acid exposure test in which 1 mL of concentrated hydrochloric acid was dripped on the resist layer of the aluminum test piece coated with the cured film obtained above and allowed to stand under conditions of 23 ° C./50% RH for 1 hour.
After the test, the resist layer surface was washed with pure water, and then completely dissolved with dichloromethane. After the resist layer was completely wiped off, corrosion marks on the surface of the aluminum substrate were visually confirmed. Table 1 shows the results. Moreover, the evaluation criteria are as follows.
○: No corrosion on the aluminum substrate surface △: Partial corrosion on the aluminum substrate surface ×: Complete corrosion on the aluminum substrate surface

[Photocationic polymerization initiator (A)]
A-1: Cumyl-p-tolyliodonium tris(pentafluoroethyl) trifluorophosphate (molecular weight 782.2, number of carbon atoms 22, number of heteroatoms 20)
A-2: (4-phenylthio)phenyldiphenylsulfonium tris(pentafluoroethyl)trifluorophosphate (molecular weight 816.5, number of carbon atoms 30, number of heteroatoms 21)
A-3: Bis(tert-butylphenyl)iodonium tetrakis(pentafluorophenyl)borate (molecular weight 1072.4, number of carbon atoms 44, number of heteroatoms 22)
[Cationically polymerizable hydrocarbon compound (B)]
B-1: 4-tert-butylstyrene (molecular weight 160.3, number of carbon atoms 12, number of heteroatoms 0)
B-2: 1,4-diisopropenylbenzene (molecular weight 158.2, number of carbon atoms 12, number of heteroatoms 0)
B-3: 5-ethylidene-2-norbornene (molecular weight 120.2, number of carbon atoms 9, number of heteroatoms 0)
[Heteroatom-containing cationic polymerizable compound (C)]
C-1: 4-tert-butoxystyrene (molecular weight 176.3, number of carbon atoms 12, number of heteroatoms 1)
C-2: 4-methoxystyrene (molecular weight 134.2, number of carbon atoms 9, number of heteroatoms 1)
C-3: 4-n-octyloxystyrene (molecular weight 232.4, number of carbon atoms 16, number of heteroatoms 1)
C-4: 4-chlorostyrene (molecular weight 138.6, number of carbon atoms 8, number of heteroatoms 1)
C-5: 4-acetoxystyrene (molecular weight 162.2, number of carbon atoms 10, number of heteroatoms 2)
C-6: 2,2-bis(4-hydroxyphenyl)propane diglycidyl ether (molecular weight 340.4, number of carbon atoms 21, number of heteroatoms 4)
[Photosensitizer (D)]
D-1: 9,10-dibutoxyanthracene (molecular weight 322.4, number of carbon atoms 22, number of heteroatoms 2)
[Surfactant (E)]
E-1: KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.)
[Polymerization inhibitor (F)]
F-1: 4-tert-butyl catechol

As can be seen from Table 1, the photocurable composition (resist material) used in the production method of the present invention exhibited good etching resistance in the concentrated hydrochloric acid exposure test compared to the photocurable composition used as a comparative product. In particular, in Examples 1 to 8, no significant change was observed in the resist layer even after the concentrated hydrochloric acid exposure test. On the other hand, Comparative Example 1 is an example in which the ratio of the cationically polymerizable hydrocarbon compound (B) to the total weight of the polymerizable compounds is less than 35% by weight, and many pitting corrosion was observed in the resist layer by the concentrated hydrochloric acid exposure test. Comparative Examples 2 to 4 are examples in which the heteroatom content percentage is greater than 6.0, and swelling and cracking were observed in the entire resist layer by the concentrated hydrochloric acid exposure test. That is, the photocurable composition used in the production method of the present invention has excellent resistance to strongly acidic etchants.

[Production Example of Electrode Foil for Electrolytic Capacitors by Photonanoimprinting]
Uses 120 μm thick high-purity aluminum foil for electrolytic capacitors.
Electrode foils for electrolytic capacitors were produced according to the following manufacturing process, and the surface state of the aluminum electrode foils was observed with a scanning electron microscope (SEM).
Manufacturing conditions used:
・Surface adjustment The surface is smoothed by lapping so that the average roughness is 1 nm or less.
・Surface cleaning Immersed in a phosphoric acid (2M) solution (45°C) for 60 minutes to remove the work-damaged layer on the surface, and then washed with a neutral detergent and ultrapure water to remove foreign matter and stains adhering to the surface.
Formation of Adhesion Layer Bis(trimethylsilyl)amine was heated in an oven in a stainless steel container (50 μL per 300 cm ² , 150° C., 1 hour), and vapor deposition was performed on the cleaned aluminum foil surface.
Coating of Photocurable Composition for Forming Resist Layer The photocurable compositions prepared above (Examples 1 to 8 and Comparative Examples 1 to 4) were dropped onto the aluminum foil surface in an amount of 1 μL/cm ² .
・Optical nanoimprint (formation of uneven shape)
Place a nanoimprint mold for molding recesses of φ1.7 μm, recess depth of 1.7 μm, and pitch of 3.0 μm on the surface coated with the photocurable composition, and irradiate ultraviolet rays (wavelength: 365 nm) from the mold side to cure the photocurable composition, impart an uneven pattern to the surface of the aluminum foil, and then release the mold.
・Removal of residual film remaining in recessed portions of the pattern The residual film remaining in the recessed portions of the pattern applied to the surface of the aluminum foil is removed by oxygen reactive ion etching (oxygen RIE).
・Etching The patterned aluminum foil is etched in an etchant.
Etching conditions: Etching for 40 seconds under a predetermined current condition under standard conditions (an etchant prepared by adding sulfuric acid (1M) to hydrochloric acid (6M) and heated to 55°C).

From the SEM image of the aluminum foil surface after etching, when the photocurable compositions of Examples 1 to 8 were used, it was confirmed that the etching pits could be aligned according to the applied pattern after etching. On the other hand, when the photocurable compositions of Comparative Examples 1 to 4 were used, the etching pits could not be aligned according to the given pattern after etching.

[Pit formation comparison test with and without the use of the photocurable composition in the present invention]
FIG. 2 is an SEM image comparing the state of the aluminum foil surface after etching when the photocurable composition (resist material) having the composition of Example 8 is used and when it is not used, (a) shows the surface state of the aluminum electrode foil for electrolytic capacitors produced by the manufacturing method of the present invention (using the above nanoimprint mold), and (b) shows the surface state of the aluminum electrode foil when etching is performed without using the resist material.
From the comparison of these SEM images, it was confirmed that when the resist material according to the present invention is used (FIG. 2(a)), pit formation can be precisely controlled, and pit formation that matches the hole period of the resist can be performed. On the other hand, it was confirmed that when etching was performed without providing a resist film, the etching start point could not be controlled, and random pit formation occurred on the surface of the aluminum foil.

In the method for producing an electrode foil for an electrolytic capacitor of the present invention, a resist layer formed from a photocurable composition having a specific composition exhibits excellent resistance to an etchant. Therefore, when etching is performed by applying a pattern using a photonanoimprint method using this photocurable composition, etching pits can be formed with high accuracy, and an electrode foil suitable for high-capacity electrolytic capacitors can be produced.

Claims (5)

A method for manufacturing an electrode foil for an electrolytic capacitor, comprising:
a resist layer forming step of providing a resist layer on the surface of the electrode foil;
a resist pattern forming step of patterning the resist layer into a predetermined pattern;
a wet electrolytic etching step of performing wet electrolytic etching using an etchant on the electrode foil surface on which the patterned resist layer is formed,
The resist material used to form the resist layer is a photocurable composition containing a photopolymerization initiator and a polymerizable compound,
(a) the photopolymerization initiator is a photocationic polymerization initiator (A) comprising an iodonium compound or a sulfonium compound;
(b) 35% by weight or more of the total weight of the polymerizable compound is a cationically polymerizable hydrocarbon compound (B) containing an ethylenically unsaturated bond consisting only of carbon atoms and hydrogen atoms;
(c) heteroatom content percentage representing the ratio of heteroatoms contained in the photocurable composition, calculated based on the following formula (1):
Heteroatom content percentage=100×Σ(Nh _i ×M _i )/Σ{(Nh _i +Nc _i )×M _i } (1)
[Wherein, _Nhi is the number of heteroatoms contained in each component in the photocurable composition (here, heteroatoms are all atoms other than carbon atoms and hydrogen atoms), Nc _i is the number of carbon atoms contained in each component in the photocurable composition, M _i represents the fraction of the substance amount of each component in the photocurable composition, ΣM _i = 1, and i is the component contained in the photocurable composition. and represents an integer of 1 or more. ]
is 6.0 or less,
A method for producing an electrode foil for an electrolytic capacitor , wherein in the resist pattern forming step, the resist layer is patterned using a photo-nanoimprinting method . 2. The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the photocurable composition contains one or more additives selected from the group consisting of a photosensitizer, a surfactant, a polymerization inhibitor, an antioxidant, and an adhesion imparting agent. 3. The method for manufacturing an electrode foil for an electrolytic capacitor according to claim 1, wherein, in the resist pattern forming step, residual films remaining in recesses of the uneven pattern of the resist layer patterned using a photo-nanoimprint method are removed by oxygen-based dry etching. In the resist layer forming step, the photocurable composition is applied to the surface of the electrode foil by an inkjet method, a slit die coating method, or a small diameter gravure method to form the resist layer. A claim characterized byany one of 1 to 3The method for producing the electrode foil for an electrolytic capacitor according to 1. An electrode foil for an electrolytic capacitor obtained by the method for producing an electrode foil for an electrolytic capacitor according to any one of claims 1 to 4. .