WO2025127019A1 - Solid electrolytic capacitor and method for manufacturing same - Google Patents

Abstract

A solid electrolytic capacitor according to the present invention comprises: a porous body made of a valve metal; a dielectric layer formed on a surface of the porous body; and two or more conductive layers covering the dielectric layer. The two or more conductive layers include a first conductive layer formed on a surface of the dielectric layer, and a second conductive layer laminated on the first conductive layer. The second conductive layer contains a polyaniline composite in which a polyaniline is doped with a proton donor.

Description

Solid electrolytic capacitor and method of manufacturing same

The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

In solid electrolytic capacitors such as aluminum electrolytic capacitors and tantalum capacitors, conductive polymers are used as the material for the solid electrolyte layer. The outer layer of a solid electrolytic capacitor generally has a three-layered structure consisting of a conductive polymer layer, a carbon layer, and a silver paste layer. The electric charge stored inside the capacitor element is taken out through each of these layers.
Patent Document 1 discloses a tantalum capacitor in which a conductive polymer layer, a carbon layer, and a silver layer are formed in this order on a tantalum sintered body having a dielectric oxide layer (Patent Document 1).

JP 2023-99299 A

However, the conventional configuration disclosed in Patent Document 1 had the problem that the tantalum capacitor had low resistance to moisture and heat, limiting the environments in which it could be used.

As a result of extensive research, the inventors discovered that by adopting a specific configuration for each layer of a solid electrolytic capacitor, a solid electrolytic capacitor with excellent resistance to moist heat could be obtained, and thus completed the present invention.

The object of the present invention is to provide a solid electrolytic capacitor with excellent resistance to moist heat and a method for manufacturing the same.

The present invention provides the following solid electrolytic capacitors, etc.

１２．前記弁金属が、アルミニウム、タンタル、ニオブ、チタン、ハフニウム、ジルコニウム、亜鉛、タングステン、ビスマス、及びアンチモンからなる群から選択される、前記１～１１のいずれかに記載の固体電解コンデンサ。
１３．以下の工程（Ａ－１）又は（Ａ－２）と、工程（Ｂ）と、工程（Ｃ）とを含む、固体電解コンデンサの製造方法。
（Ａ－１）弁金属の酸化物を有する多孔質体の一部又は全体を、導電性高分子及び溶媒を含む第１の導電性高分子組成物に浸漬する工程
（Ａ－２）弁金属の酸化物を有する多孔質体の一部又は全体を、導電性高分子、溶媒、及びフェノール性化合物を含む第１の導電性高分子組成物に浸漬する工程
（Ｂ）前記多孔質体を、前記工程（Ａ－１）又は（Ａ－２）で用いた第１の導電性高分子組成物から取り出して、前記第１の導電性高分子組成物に含まれる溶媒の沸点以下の温度下で保持する工程
（Ｃ）前記工程（Ｂ）を経た後の前記多孔質体の一部又は全体を、前記第１の導電性高分子組成物と同一又は異なる導電性高分子、チキソトロピー性付与剤、及び溶媒を含む第２の導電性高分子組成物に浸漬し、乾燥する工程
１４．前記第２の導電性高分子組成物全体に対する、前記チキソトロピー性付与剤の含有率が、０．２～５質量％である、前記１３に記載の固体電解コンデンサの製造方法。
１５．前記第２の導電性高分子組成物が、以下の条件（Ｐ１）及び（Ｐ２）を満たす、前記１３又は１４に記載の固体電解コンデンサの製造方法。
　（Ｐ１）せん断速度１０（１／ｓ）のときの粘度が１Ｐａ・ｓ以上である。
　（Ｐ２）せん断速度１０（１／ｓ）で３０秒間せん断を印加した後、０．０００１（１／ｓ）のせん断速度としたときの直後の粘度が１０Ｐａ・ｓ以上であり、かつ下記式（Ｐ２－１）を満たす。

１６．前記１３～１５のいずれかに記載の固体電解コンデンサの製造方法により得られた固体電解コンデンサ。 1. A porous body made of a valve metal, a dielectric layer formed on the surface of the porous body, and two or more conductive layers covering the dielectric layer,
the two or more conductive layers include a first conductive layer formed on a surface of the dielectric layer and a second conductive layer laminated on the first conductive layer,
The second conductive layer comprises a polyaniline composite in which the polyaniline is doped with a proton donor.
2. The solid electrolytic capacitor according to 1 above, wherein the dielectric layer is made of an oxide of the valve metal.
3. The solid electrolytic capacitor according to 1 or 2 above, wherein the polyaniline complex is doped with sulfosuccinic acid.
4. The solid electrolytic capacitor according to any one of 1 to 3 above, wherein the second conductive layer further contains a thixotropy-imparting agent.
5. The solid electrolytic capacitor according to 4 above, wherein the thixotropy-imparting agent contains inorganic particles.
6. The solid electrolytic capacitor according to 5 above, wherein the inorganic particles contain at least one selected from the group consisting of silica, titania, alumina, and zirconia.
7. The solid electrolytic capacitor according to any one of 4 to 6 above, wherein the content of the thixotropy-imparting agent in the second conductive layer as a whole is 0.01 to 50 mass %.
8. The solid electrolytic capacitor according to any one of 1 to 7 above, wherein the second conductive layer further contains a thickener.
9. The solid electrolytic capacitor according to 8 above, wherein the thickener is a polyether compound or a cellulose compound.
10. The solid electrolytic capacitor according to 8 or 9 above, wherein the content of the thickener in the second conductive layer is 0.001 to 5 mass %.
11. The solid electrolytic capacitor according to any one of 1 to 10 above, wherein the second conductive layer is formed from a conductive polymer composition that satisfies the following conditions (P1) and (P2):
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

12. The solid electrolytic capacitor according to any one of 1 to 11 above, wherein the valve metal is selected from the group consisting of aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony.
13. A method for producing a solid electrolytic capacitor, comprising the following steps (A-1) or (A-2), (B), and (C):
(A-1) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer and a solvent; (A-2) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound; (B) A step of removing the porous body from the first conductive polymer composition used in the step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition; (C) A step of immersing a part or the whole of the porous body after the step (B) in a second conductive polymer composition containing a conductive polymer, a thixotropy-imparting agent, and a solvent, the same or different from the first conductive polymer composition, and drying the second conductive polymer composition; 14. The method for producing a solid electrolytic capacitor according to the above item 13, wherein the content of the thixotropy-imparting agent relative to the entire second conductive polymer composition is 0.2 to 5 mass %.
15. The method for producing a solid electrolytic capacitor as described in 13 or 14 above, wherein the second conductive polymer composition satisfies the following conditions (P1) and (P2):
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

16. A solid electrolytic capacitor obtained by the method for producing a solid electrolytic capacitor according to any one of 13 to 15 above.

The present invention provides a solid electrolytic capacitor with excellent resistance to moist heat and a method for manufacturing the same.

FIG. 1 is a schematic diagram of a solid electrolytic capacitor according to one embodiment of the present invention. FIG. 2 is an enlarged schematic view of a cross section of a solid electrolytic capacitor according to one embodiment of the present invention.

The solid electrolytic capacitor and the method for producing the same of the present invention will be described in detail below.
In this specification, "x to y" represents a numerical range of "not less than x and not more than y." The upper and lower limits described in relation to the numerical ranges can be combined in any combination.

[Solid electrolytic capacitor]
A solid electrolytic capacitor according to one embodiment of the present invention includes a porous body made of a valve metal, a dielectric layer formed on the surface of the porous body, and two or more conductive layers covering the dielectric layer, the two or more conductive layers including a first conductive layer formed on the surface of the dielectric layer and a second conductive layer laminated on the first conductive layer, the second conductive layer including a polyaniline complex in which polyaniline is doped with a proton donor.

The solid electrolytic capacitor according to one aspect of the present invention has the above-mentioned configuration, and therefore has excellent resistance to moist heat.

FIG. 1 is a schematic diagram of a solid electrolytic capacitor according to one embodiment of the present invention, and FIG. 2 is an enlarged schematic diagram of a cross section of the solid electrolytic capacitor.
A solid electrolytic capacitor 100 according to one aspect of the present invention in one embodiment includes an anode body 110 including a porous body 111 made of a valve metal and a dielectric layer 112 formed on the surface of the porous body, a first conductive layer 120 covering the dielectric layer, a second conductive layer 130 laminated on the first conductive layer, a carbon layer 140 laminated on the second conductive layer, and a silver layer 150 laminated on the carbon layer.
The solid electrolytic capacitor according to the aspect of the present invention may include a wire 160 including a valve metal. The wire 160 penetrates at least a portion of the porous body 111.

The first conductive layer 120 is also called an inner solid electrolyte layer, an inner coating layer, an inner layer, or the like.
The second conductive layer 130 is also called an outer coating layer, an outer layer, or the like.

The following describes each component that constitutes a solid electrolytic capacitor according to one embodiment of the present invention.

[Porous body]
The porous body is made of a valve metal and is a material having pores, preferably having a large number of pores with diameters of about 1 nm to 10 μm.
By using a porous body, the surface area of the valve metal can be increased, which in turn increases the capacitance of the capacitor, making it possible to realize a small-sized capacitor with large capacitance.

The shape of the porous body is not particularly limited, and may be, for example, a molded body or a film (foil) having a certain thickness.
The length, width and thickness of the porous body which is a molded article are not particularly limited, and are, for example, independently 15 μm or more and 5 mm or less.
The thickness of the porous body serving as the membrane (foil) is not particularly limited, and is, for example, 15 μm or more and 300 μm or less.

Porous structures include, but are not limited to, tunnel-like pits, spongy pits, or gaps between densely packed powder particles. The porous body may contain only one of these structures, or two or more of them.

The method for manufacturing the porous body is not particularly limited, but for example, a metal powder made of a valve metal may be sintered to form a porous body, or a film (foil) made of a valve metal may be etched to form a large number of holes.

In one embodiment, the porous body is a sintered body made of valve metal, which is obtained by sintering a compact containing a valve metal powder and a binder.
A sintered body made of a valve metal can be produced by mixing and stirring a valve metal powder, a binder, and a solvent in a certain ratio, compressing the mixed powder into a rectangular parallelepiped, and then sintering this at high temperature and high vibration.

Valve metals include metals such as aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony, with aluminum or tantalum being preferred.
These metals may be used alone or in combination of two or more.

Examples of binders include, for example, cellulosic binders.
Examples of the cellulose-based binder include one or more types selected from the group consisting of nitrocellulose, methylcellulose, ethylcellulose, and hydroxypropylcellulose. One type of binder may be used alone, or two or more types may be used in combination.

[Dielectric layer]
The dielectric layer is formed on the surface of the porous body.
In one embodiment, the dielectric layer comprises an oxide of a valve metal contained in a porous body.

The method for producing the dielectric layer is not particularly limited, but examples thereof include anodic oxidation, in which an oxide film grows on the surface layer by passing a current through a porous body as an anode in an electrolytic solution.
Examples of the electrolytic solution include, for example, phosphates, borates, citrates, adipates, etc. The electrolytic solution may be used alone or in combination of two or more kinds.

The thickness of the dielectric layer is designed according to the required withstand voltage, capacitance, etc., but is preferably 1 nm or more and 500 nm or less, and more preferably 10 nm or more and 100 nm or less.

[Anode body]
In this specification, the porous body made of valve metal and the dielectric layer formed on the surface of the porous body are collectively referred to as the anode body.
The submerged capacity of the anode body is, for example, preferably 100 μF or more and 2000 μF or less, and more preferably 500 μF or more and 1500 μF or less.
The submerged capacity of the anode body can be measured by the method described in the Examples.

[First conductive layer]
A first conductive layer (hereinafter also referred to as the "internal solid electrolyte layer") covers the dielectric layer.

The material constituting the first conductive layer is not particularly limited as long as it is a material capable of forming a conductive layer, but for example, it is preferable that the first conductive layer contains a conductive polymer.

In one embodiment, the first conductive layer includes one or more selected from the group consisting of polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives. Here, the polythiophene may be a polythiophene doped with a polyanion such as polystyrene sulfonic acid, or a self-doped polythiophene.

These conductive polymers may be polymerized after the monomer is impregnated into the anode body, or the polymer may be impregnated into the anode body.

These conductive polymers may be used alone or in combination of two or more.

In one embodiment, the first conductive layer comprises polyaniline or a polyaniline derivative.
The polyaniline preferably has a weight average molecular weight of 10,000 or more, more preferably 20,000 or more, even more preferably 30,000 to 1,000,000, still more preferably 40,000 to 1,000,000, and particularly preferably 52,000 to 1,000,000.

For example, when used in a solid electrolyte layer of a solid electrolytic capacitor, a conductive polymer having a larger molecular weight is generally preferred from the viewpoint of increasing the strength of the resulting electrolyte layer, but a larger molecular weight leads to a higher viscosity, which may make it difficult to impregnate the inside of the pores of a porous body.
The weight average molecular weight of polyaniline is measured by the method described in the Examples.

From the viewpoints of versatility and economy, the polyaniline is preferably an unsubstituted polyaniline.
When the aryl group has a substituent, examples of the substituent include linear or branched hydrocarbon groups such as a methyl group, an ethyl group, a hexyl group, and an octyl group; alkoxy groups such as a methoxy group and an ethoxy group; aryloxy groups such as a phenoxy group; and halogenated hydrocarbons such as a trifluoromethyl group ( _-CF3 group).

In one embodiment, the first conductive layer comprises a polyaniline composite in which polyaniline is doped with a proton donor, which tends to improve solubility in a solvent.
The doping of polyaniline with the proton donor can be confirmed by ultraviolet, visible, near infrared spectroscopy or X-ray photoelectron spectroscopy. The proton donor can be used without any particular limitation as long as it has sufficient acidity to generate carriers in polyaniline.

The proton donor may be, for example, a Bronsted acid or a salt thereof. Preferably, it is an organic acid or a salt thereof, and more preferably, it is a proton donor represented by the following formula (I).
M(XARn)m(I)

M in formula (I) is a hydrogen atom, an organic free radical, or an inorganic free radical.
Examples of organic free radicals include pyridinium, imidazolium, and anilinium groups, while examples of inorganic free radicals include lithium, sodium, potassium, cesium, ammonium, calcium, magnesium, and iron.
X in formula (I) is an anionic group such as, for example, a -SO ₃ ^- group, a -PO ₃ ^2- group, a -PO ₄ (OH) ^- group, a -OPO ₃ ^2- group, a -OPO ₂ (OH) ^- group, a -COO ^- group, etc., and is preferably a -SO ₃ ^- group.

A in formula (I) is a substituted or unsubstituted hydrocarbon group (having, for example, 1 to 20 carbon atoms).
The hydrocarbon group is a linear or cyclic saturated aliphatic hydrocarbon group, a linear or cyclic unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group.
Examples of the chain-like saturated aliphatic hydrocarbon group include linear or branched alkyl groups (having, for example, 1 to 20 carbon atoms).
Examples of the cyclic saturated aliphatic hydrocarbon group include cycloalkyl groups (having, for example, 3 to 20 carbon atoms) such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, and a cyclooctyl group.
The cyclic saturated aliphatic hydrocarbon group may be a group in which a plurality of cyclic saturated aliphatic hydrocarbon groups are condensed, such as a norbornyl group, an adamantyl group, and a condensed adamantyl group.
Examples of the chain unsaturated aliphatic hydrocarbon (having, for example, 2 to 20 carbon atoms) include linear or branched alkenyl groups.
Examples of the cyclic unsaturated aliphatic hydrocarbon group (having, for example, 3 to 20 carbon atoms) include a cyclic alkenyl group.
Examples of the aromatic hydrocarbon group (having, for example, 6 to 20 carbon atoms) include a phenyl group, a naphthyl group, and an anthracenyl group.

When A is a substituted hydrocarbon group, the substituent is an alkyl group (e.g., 1 to 20 carbon atoms), a cycloalkyl group (e.g., 3 to 20 carbon atoms), a vinyl group, an allyl group, an aryl group (e.g., 6 to 20 carbon atoms), an alkoxy group (e.g., 1 to 20 carbon atoms), a halogen atom, a hydroxy group, an amino group, an imino group, a nitro group, a silyl group, or an ester bond-containing group.

R in formula (I) is bonded to A and is a substituent represented by -H, -R ¹ , -OR ¹ , -COR ¹ , -COOR ¹ , -(C=O)-(COR ¹ ), or -(C=O)-(COOR ¹ ).
R ¹ is a hydrocarbon group which may contain a substituent, a silyl group, an alkylsilyl group, a -(R ² O)x-R ³ group, or a -(OSiR ³ ₂ )x-OR ³ group.
^R2 is an alkylene group, ^R3 is a hydrocarbon group, and x is an integer of 1 or more.
When x is 2 or more, multiple R ^2s may be the same or different, and multiple R ^3s may be the same or different.

Examples of the hydrocarbon group (having, for example, 1 to 20 carbon atoms) for ^R1 include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a pentadecyl group, an eicosanyl group, etc. The hydrocarbon group may be linear or branched.
The substituent of the hydrocarbon group is an alkyl group (having, for example, 1 to 20 carbon atoms), a cycloalkyl group (having, for example, 3 to 20 carbon atoms), a vinyl group, an allyl group, an aryl group (having, for example, 6 to 20 carbon atoms), an alkoxy group (having, for example, 1 to 20 carbon atoms), a halogen atom, a hydroxy group, an amino group, an imino group, a nitro group, or an ester bond-containing group. The hydrocarbon group of ^R3 is the same as that of ^R1 .

Examples of the alkylene group (having, for example, 1 to 20 carbon atoms) for ^R2 include a methylene group, an ethylene group, and a propylene group.
In formula (I), n is an integer of 1 or more. When n is 2 or more, multiple Rs may be the same or different.
In formula (I), m is the valence of M/the valence of X.

The compound represented by formula (I) is preferably a dialkylbenzenesulfonic acid, a dialkylnaphthalenesulfonic acid, or a compound containing two or more ester bonds.
The compound containing two or more ester bonds is more preferably a sulfophthalic acid ester or a compound represented by the following formula (II).

In formula (II), M and X are the same as those in formula (I), and X is preferably a -SO ₃ ^- group.
R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom, a hydrocarbon group or an R ⁹ ₃ Si- group. Each of the three R ^9s is independently a hydrocarbon group.
When R ⁴ , R ⁵ , and R ⁶ are hydrocarbon groups, examples of the hydrocarbon group include linear or branched alkyl groups having 1 to 24 carbon atoms, aryl groups containing an aromatic ring (having, for example, 6 to 20 carbon atoms), and alkylaryl groups (having, for example, 7 to 20 carbon atoms).
The hydrocarbon group for R ⁹ is the same as for R ⁴ , R ⁵ , and R ⁶ .

In formula (II), R ⁷ and R ⁸ are each independently a hydrocarbon group or a —(R ¹⁰ O) _q —R ¹¹ group.
R ¹⁰ is a hydrocarbon group or a silylene group.
R ¹¹ is a hydrogen atom, a hydrocarbon group, or R ¹² ₃ Si—.
q is an integer of 1 or more.
The three R ¹² are each independently a hydrocarbon group.

When ^R7 and ^R8 are hydrocarbon groups, examples of the hydrocarbon group include linear or branched alkyl groups having 1 to 24 carbon atoms, preferably 4 or more carbon atoms, aryl groups containing an aromatic ring (having, for example, 6 to 20 carbon atoms), and alkylaryl groups (having, for example, 7 to 20 carbon atoms).
Specific examples include a butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, and the like, all of which may be linear or branched.

In ^R7 and ^R8 , when ^R10 is a hydrocarbon group, examples of the hydrocarbon group include a linear or branched alkylene group having 1 to 24 carbon atoms, an arylene group containing an aromatic ring (having, for example, 6 to 20 carbon atoms), an alkylarylene group (having, for example, 7 to 20 carbon atoms), or an arylalkylene group (having, for example, 7 to 20 carbon atoms).
In addition, in R ⁷ and R ⁸ , when R ¹¹ and R ¹² are hydrocarbon groups, the hydrocarbon groups are the same as those in the cases of R ⁴ , R ⁵ and R ⁶ , and q is preferably 1-10.

（式中、Ｘは式（Ｉ）と同様である。） Specific examples of the compound represented by formula (II) in which R ⁷ and R ⁸ are —(R ¹⁰ O) _q —R ¹¹ groups include the two compounds represented by the following formulae.

(In the formula, X is the same as in formula (I).)

The compound represented by the above formula (II) is more preferably a sulfosuccinic acid derivative represented by the following formula (III).

In formula (III), M is the same as in formula (I).
m' is the valence of M.
R ¹³ and R ¹⁴ are each independently a hydrocarbon group or a -(R ¹⁵ O) _r -R ¹⁶ group.
R ¹⁵ is a hydrocarbon group or a silylene group, R ¹⁶ is a hydrogen atom, a hydrocarbon group or an R ¹⁷ ₃ Si- group, and r is an integer of 1 or more.
Each of the three R ^17s independently represents a hydrocarbon group.
When r is 2 or more, multiple R ¹⁵ may be the same or different.

When R ¹³ and R ¹⁴ are hydrocarbon groups, the hydrocarbon groups are the same as those for R ⁷ and R ⁸ .
In R ¹³ and R ¹⁴ , when R ¹⁵ is a hydrocarbon group, the hydrocarbon group is the same as R ¹⁰ above.
In addition, in R ¹³ and R ¹⁴ , when R ¹⁶ and R ¹⁷ are hydrocarbon groups, the hydrocarbon groups are the same as those for R ⁴ , R ⁵ and R ⁶ above.
It is preferable that r is an integer from 1 to 10.

Specific examples when R ¹³ and R ¹⁴ are the -(R ¹⁵ O) _r -R ¹⁶ group are the same as those of -(R ¹⁰ O) _q -R ¹¹ in R ⁷ and R ⁸ .
The hydrocarbon group of R ¹³ and R ¹⁴ is the same as that of R ⁷ and R ⁸ , and a butyl group, a hexyl group, a 2-ethylhexyl group, or a decyl group is preferred.

The compound represented by formula (I) is preferably di(2-ethylhexyl)sulfosuccinic acid or sodium di(2-ethylhexyl)sulfosuccinate.

It is known that the above-mentioned proton donor can control the electrical conductivity and solubility in a solvent of the polyaniline composite by changing its structure (Patent No. 3384566). In this embodiment, the optimal proton donor can be selected depending on the required characteristics for each application.

The doping ratio of the proton donor to the polyaniline is preferably 0.30 or more and 0.65 or less, more preferably 0.32 or more and 0.60 or less, further preferably 0.33 or more and 0.57 or less, and particularly preferably 0.34 or more and 0.55 or less. Usually, when the doping ratio is 0.30 or more, the solubility of the polyaniline complex in an organic solvent is sufficient.
The doping ratio is defined as (the number of moles of the proton donor doped in the polyaniline)/(the number of moles of the monomer unit of the polyaniline). For example, a doping ratio of 0.5 for a polyaniline complex containing unsubstituted polyaniline and a proton donor means that one proton donor is doped for every two monomer unit molecules of polyaniline.
The doping ratio can be calculated if the molar numbers of the proton donor and the polyaniline monomer unit in the polyaniline composite can be measured. For example, when the proton donor is an organic sulfonic acid, the molar number of sulfur atoms derived from the proton donor and the molar number of nitrogen atoms derived from the polyaniline monomer unit are quantified by organic elemental analysis, and the doping ratio can be calculated by taking the ratio of these values.

The polyaniline complex preferably contains unsubstituted polyaniline and sulfonic acid as a proton donor, and satisfies the following formula (1).
0.32≦ _S5 / _N5 ≦0.60 (1)
(In the formula, _S5 is the total number of moles of sulfur atoms contained in the polyaniline complex, and _N5 is the total number of moles of nitrogen atoms contained in the polyaniline complex.
The number of moles of nitrogen atoms and sulfur atoms is a value measured by, for example, organic elemental analysis.

The method for producing the polyaniline composite is not particularly limited, but it can be produced, for example, by the production method described below.
For example, the above-mentioned proton donor, aniline corresponding to the above-mentioned polyaniline, and optionally a surfactant (e.g., a nonionic emulsifier) are dissolved in a water-immiscible organic solvent (e.g., a hydrocarbon solvent (preferably toluene, xylene)), an acidic aqueous solution (e.g., an aqueous phosphoric acid solution) is added thereto, the reaction liquid having two liquid phases of the water-immiscible organic solvent and water is stirred, and a polymerization initiator (e.g., ammonium persulfate) is added to carry out polymerization.
After the polymerization, the water-immiscible organic solvent phase is separated by standing to obtain a polyaniline complex water-immiscible organic solvent solution. This solution is transferred to an evaporator to evaporate and remove the volatile matter to obtain a polyaniline complex (protonated polyaniline).

[Second Conductive Layer]
The second conductive layer (hereinafter also referred to as the "external coating layer") is laminated on the first conductive layer. As shown in FIG. 1, the first conductive layer impregnates the inside of the pores of the anode body, while the second conductive layer further coats the anode body and the first conductive layer from the outside.

The second conductive layer includes a polyaniline complex in which polyaniline is doped with a proton donor. The polyaniline complex in which polyaniline is doped with a proton donor may be used alone or in combination of two or more kinds.
For the polyaniline, the proton donor, and the polyaniline complex, the items described in the first conductive layer can be applied.

In one embodiment, the proton donor used in the second conductive layer is preferably a compound represented by the above formulas (I) to (III), and in particular, di(2-ethylhexyl)sulfosuccinic acid and sodium di(2-ethylhexyl)sulfosuccinate are preferred. The ponianiline complex doped with these proton donors has high solubility in organic solvents, making it easy to prepare the conductive polymer composition used in forming the second conductive layer. Specifically, it is possible to expand the options for solvents used in the conductive polymer composition. In addition, it is easy to adjust the viscosity (concentration) of the conductive polymer composition, making it easy to adjust the thickness of the second conductive layer. Furthermore, high solubility in organic solvents means high hydrophobicity, which is expected to lead to improved moist heat resistance of the capacitor.

In one embodiment, the second conductive layer further comprises a thixotropic agent.
The thixotropy-imparting agent can be blended, for example, in the conductive polymer composition for forming the second conductive layer. The second conductive layer can be formed by immersing the porous body on which the first conductive layer has been formed in the conductive polymer composition, thereby making it possible to incorporate the thixotropy-imparting agent in the second conductive layer.
When a thixotropy-imparting agent is contained, the conductive polymer composition has a property of increasing viscosity when the shear force is small and decreasing viscosity when the shear force is large. That is, the conductive polymer composition containing a thixotropy-imparting agent flows and has good usability when an anode body having a first conductive layer formed thereon is immersed in the composition, and increases in viscosity when the anode body is removed from the composition, facilitating the formation of a second conductive layer having a certain thickness.

The thixotropy-imparting agent can be any material capable of imparting thixotropy without any particular limitation. For example, inorganic particles, carbon nanotubes, carbon powder, fluororesin powder, etc. are listed. As the thixotropy-imparting agent, inorganic particles are preferred.
Examples of inorganic particles include silica, titania, alumina, and zirconia.
The surfaces of the inorganic particles may be modified with a silane coupling agent or the like, if necessary.

The thixotropic agent may be used alone or in combination of two or more.

The average particle size of the inorganic particles is not particularly limited as long as it is within a range capable of imparting thixotropy, and is, for example, 1 to 100 nm, preferably 1 to 50 nm, and more preferably 2 to 40 nm.
The average particle size of the inorganic particles can be determined by calculating the specific surface area by the BET method and converting the specific surface area. The calculation of the specific surface area by the BET method is performed under the conditions described in JIS Z8830 (2013).

In one embodiment, the content of the thixotropy-imparting agent in the entire second conductive layer is 0.01 to 50 mass %, preferably 0.1 to 40 mass %, and more preferably 1 to 20 mass %.

In one embodiment, the second conductive layer further comprises a thickener.
The thickener can be blended, for example, in the conductive polymer composition for forming the second conductive layer, in the same manner as the thixotropy-imparting agent. The second conductive layer can be formed by immersing the porous body on which the first conductive layer has been formed in the conductive polymer composition, thereby making it possible to incorporate the thickener into the second conductive layer.
When the conductive polymer composition for forming the second conductive layer contains a thickener, the second conductive layer can be easily formed with a desired thickness, particularly in the case of producing a rectangular capacitor, whereby the second conductive layer can be easily formed with a desired thickness at the side edge portion and the side flat portion.

The side edge portion refers to the corner portion of the side (the portion where adjacent side surfaces intersect) when the surface that was on the lower side during dipping in forming the second conductive layer of the rectangular capacitor is taken as the bottom surface.
The flat side surface portion refers to the surface portion of the side surface when the surface that was on the lower side during dipping in forming the second conductive layer of the rectangular capacitor is regarded as the bottom surface.

The thickness of the second conductive layer at the side edge portion (side edge thickness) and the thickness of the second conductive layer at the side flat portion (side flat thickness) can be measured by the method described in the examples.

In addition, if the conductive polymer composition for forming the second conductive layer contains a thickener, it becomes easier to reduce the number of dipping steps required to obtain a second conductive layer with the desired thickness.

Thickeners include polyether compounds and cellulose compounds.

Examples of polyether compounds include polyethylene oxide (EO)-polypropylene oxide (PO) copolymers (e.g., EP1550H (manufactured by Meisei Chemical Industry Co., Ltd.)).

Examples of cellulose compounds include cellulose ethers (e.g., ethyl cellulose, methyl cellulose), hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. Among these, cellulose ethers are preferably used from the viewpoint of high thickening effect and easy availability. Among cellulose ethers, ethyl cellulose is preferably used.

Commercially available cellulose compounds include EC-N300 (manufactured by Ashland), N200 (manufactured by Ashland), and Klucel G (manufactured by Ashland).

A single thickener may be used, or two or more may be combined.

In one embodiment, the content of the thickener relative to the entire second conductive layer is, for example, 0.001% by weight or more, 0.002% by weight or more, 0.005% by weight or more, 0.01% by weight or more, 0.02% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.2% by weight or more, or 0.3% by weight or more.
In one embodiment, the content of the thickener relative to the entire second conductive layer is, for example, 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less.
In one embodiment, the content of the thickener relative to the entire second conductive layer is 0.001 to 10 mass %, 0.001 to 5 mass %, 0.01 to 5 mass %, 0.1 to 5 mass %, or 0.3 to 1 mass %.

In one embodiment, the second conductive layer includes a thixotropic agent and a thickener.

In one embodiment, the second conductive layer is formed from a conductive polymer composition that satisfies the following conditions (P1) and (P2).
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

If the second conductive layer satisfies conditions (P1) and (P2), when the porous body on which the first conductive layer is formed is immersed to form the second conductive layer, a thick second conductive layer can be easily formed even with a small number of dipping operations.

In one embodiment, the conductive polymer composition used to form the second conductive layer has a viscosity at a shear rate of 10 (1/s) of 1 Pa·s or more, and may be 2 Pa·s or more, or 5 Pa·s or more.

In one embodiment, the conductive polymer composition used to form the second conductive layer has a viscosity of 10 Pa·s or more immediately after applying shear at a shear rate of 10 (1/s) for 30 seconds and then reducing the shear rate to 0.0001 (1/s), and may be 50 Pa·s or more, 100 Pa·s or more, or 500 Pa·s or more.

In one embodiment, the conductive polymer composition used to form the second conductive layer satisfies formula (P2-1), and may also satisfy the following formula (P2-2), or may also satisfy the following formula (P2-3).

The following describes the components that can be used in the solid electrolytic capacitor according to one embodiment of the present invention, as well as the materials that can form each layer.

[Carbon layer]
The carbon layer is laminated on the second conductive layer. The carbon layer contains a carbon material as a main component. The content of the carbon material in the carbon layer is, for example, 60 mass% or more, and preferably 70 mass% or more. When the content of the carbon material is in such a range, it is easy to ensure high adhesion between the second conductive layer and the silver layer.

Examples of carbon materials include activated carbon, carbon black, carbon nanohorns, graphene, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, carbon nanotubes, and carbon nanofibers.
These carbon materials may be used alone or in combination of two or more.

The carbon layer may contain other components such as known binders and additives.
The upper limit of the content of carbon particles in the carbon layer can be determined depending on the contents of other components, and is not particularly limited, but is, for example, 99 mass % or less.

The carbon layer is formed, for example, by a method of applying a carbon paste onto the surface of the second conductive layer and drying it.
The carbon paste can be applied by, for example, a dipping method, sponge transfer, screen printing, spray application, a dispenser, inkjet printing, or the like.

The carbon paste contains a carbon material and a dispersion medium. Examples of the dispersion medium include water, an organic medium, or a mixture of these. The carbon paste may contain other components such as known binders and additives.

In one embodiment, the carbon layer is laminated by impregnating the anode body having the first conductive layer and the second conductive layer described above with a dispersion medium in which the carbon material described above is dispersed, and then drying at a predetermined temperature to volatilize the organic solvent.

[Silver layer]
A layer of silver (Ag) is laminated to the carbon layer.

The silver layer contains silver as a main component. The silver content in the silver layer is, for example, 60% by mass or more, and preferably 70% by mass or more. When the silver content is within this range, sufficient conductivity is easily obtained.

The silver layer may contain other components such as known binders and additives.
The upper limit of the silver content in the silver layer can be determined depending on the contents of other components, and is not particularly limited, but is, for example, 99 mass % or less.

The silver layer is laminated, for example, by applying silver paste to the surface of the carbon layer and drying it. The silver paste that can be used is in the form of silver dispersed in a solvent.

As long as it can be dispersed in a solvent, the shape of the silver is not limited, and examples thereof include plate-like silver, granular silver, and the like.
The solvent is not particularly limited as long as it can disperse silver, and any known solvent can be used. Examples include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, esters, etc. In addition, specific examples of the solvent (b) described below can be used.
The silver paste can be applied by, for example, a dipping method, sponge transfer, screen printing, spray application, a dispenser, inkjet printing, or the like.

In one embodiment, the silver layer is laminated by impregnating the anode body having the above-mentioned first conductive layer, second conductive layer, and carbon layer with an organic solvent in which silver is dispersed, and then drying at a predetermined temperature to volatilize the organic solvent.

The solid electrolytic capacitor according to this embodiment can be manufactured, for example, by the manufacturing method of the present invention described below.

[Method of manufacturing solid electrolytic capacitor]
A method for producing a solid electrolytic capacitor according to one aspect of the present invention includes the following steps (A-1) or (A-2), (B), and (C).
(A-1) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer and a solvent; (A-2) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound; (B) A step of removing the porous body from the first conductive polymer composition used in the step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition; (C) A step of immersing a part or the whole of the porous body after the step (B) in a second conductive polymer composition containing a conductive polymer, a thixotropy-imparting agent, and a solvent that is the same as or different from the first conductive polymer composition, and drying the second conductive polymer composition.

The above steps (A-1) or (A-2) and (B) are steps for forming a first conductive layer on the surface of the anode body. The above step (C) is a step for forming a second conductive layer.

In one embodiment, a method for producing a solid electrolytic capacitor according to one aspect of the present invention includes steps (A-1), (B), and (C).
In one embodiment, a method for producing a solid electrolytic capacitor according to one aspect of the present invention includes steps (A-2), (B), and (C).

[First layer formation process]
<Steps (A-1) and (A-2)>
The step of forming the first layer includes any one of steps (A-1) and (A-2).
In the step (A-1), a part or the whole of a porous body having an oxide of a valve metal is immersed in a first conductive polymer composition containing a conductive polymer and a solvent.
In the step (A-2), a part or the whole of the porous body having an oxide of a valve metal is immersed in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound.

As for the porous body and the valve metal, the matters explained in the solid electrolytic capacitor according to one aspect of the present invention can be applied.
The first conductive polymer composition in step (A-1) contains a conductive polymer and a solvent.
The first conductive polymer composition in step (A-2) contains a conductive polymer, a solvent, and a phenolic compound.

[(a) Conductive polymer]
Examples of the conductive polymer (hereinafter also referred to as "component (a)") include polyaniline, polyaniline derivatives, polythiophene, and polythiophene derivatives.
These may be used alone or in combination of two or more.

The polyaniline, polyaniline derivatives, polythiophene, and polythiophene derivatives can be those described in the solid electrolytic capacitor according to one embodiment of the present invention.

In one embodiment, the first conductive polymer composition contains polyaniline or a polyaniline derivative. In order to impregnate the pores of the anode body with the first conductive polymer composition and to coat the surface of the dielectric layer with the first conductive layer, it is preferable that the weight average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition is smaller than the weight average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition described below. For example, it is preferable that the weight average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition is 100,000 or less.

In one embodiment, the first conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with a proton donor.
In one embodiment, the first conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with sulfosuccinic acid.

(b) Solvent
The solvent (hereinafter also referred to as "component (b)") is not particularly limited as long as it dissolves or disperses the conductive polymer. It is particularly preferable that the solvent (component (b)) dissolves the conductive polymer. However, the solvent does not include the component (c) described below.

The solvent is preferably an organic solvent, examples of which include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, and esters.
These may be used alone or in combination of two or more.

The organic solvent may be a water-soluble organic solvent, or may be an organic solvent that is substantially not miscible with water (a water-immiscible organic solvent).
As the water-soluble organic solvent, a highly polar organic solvent can be used, and it may be either a protic polar solvent or an aprotic polar solvent.
Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 1-ethoxy-2-propanol, 2-ethoxy-1-propanol, 1-butanol, 2-butanol, 2-pentanol, benzyl alcohol, and alkoxyalcohols (e.g., 1-methoxy-2-propanol, 3-methoxy-1-butanol, and 3-methoxy-3-methylbutanol); ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as tetrahydrofuran, 4-methyltetrahydropyran, dioxane, diethyl ether, and ethylene glycol mono-tert-butyl ether; and aprotic polar solvents such as N-methylpyrrolidone.

As the water-immiscible organic solvent, a low-polarity organic solvent can be used, and examples thereof include hydrocarbon solvents such as hexane, benzene, toluene, xylene, ethylbenzene, tetralin, etc.; halogen-containing solvents such as methylene chloride, chloroform, carbon tetrachloride, dichloroethane, tetrachloroethane, etc.; ester solvents such as ethyl acetate, isobutyl acetate, n-butyl acetate, ethyl lactate, methyl lactate, etc.; ketone solvents such as methyl isobutyl ketone (MIBK), methyl ethyl ketone, cyclopentanone, cyclohexanone, etc.; and ether solvents such as cyclopentyl methyl ether, etc.
Furthermore, an isoparaffin-based solvent containing one or more types of isoparaffin may be used as the hydrocarbon-based solvent.

Also, a commercially available solvent such as "Kyowasol C900" (manufactured by KH Neochem Co., Ltd.) can be used.

Of these, toluene, xylene, methyl isobutyl ketone, chloroform, trichloroethane, and ethyl acetate are preferred because they have excellent solubility for conductive polymers.

In addition, polyaniline complexes can be dissolved even in alcoholic solvents such as isopropyl alcohol, 1-butanol, 2-butanol, 2-pentanol, benzyl alcohol, and alkoxy alcohols. Alcohols are preferable from the viewpoint of reducing the environmental impact compared to aromatic solvents such as toluene.

When an organic solvent is used as the solvent, it is preferable to use a mixed organic solvent obtained by mixing a water-immiscible organic solvent and a water-soluble organic solvent in a ratio of 99 to 1:1 to 99 (mass ratio), since this can prevent the generation of gels or the like during storage and allows long-term storage.
The mixed organic solvent may contain one or more water-immiscible organic solvents, and may contain one or more water-soluble organic solvents.

The concentration of component (a) relative to the total amount of the solvent (component (b)) [component (a) x 100/(component (a) + component (b))] may be 0.01 mass% or more, 0.03 mass% or more, 0.05 mass% or more, or 2.0 mass% or more. It is usually 15.0 mass% or less, 13.0 mass% or less, 12.0 mass% or less, 10.0 mass% or less, 9.0 mass% or less, or 8.0 mass% or less.

When the conductive polymer composition further contains component (c) described below, the concentration of component (a) is usually 0.3 to 20 mass % relative to the conductive polymer composition, preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %, even more preferably 1 to 10 mass %, and even more preferably 1 to 7 mass %.

The amount of component (b) is not limited and can be adjusted appropriately depending on the amount of other components, but can be, for example, 200 to 20,000 parts by mass, 300 to 17,000 parts by mass, 500 to 12,000 parts by mass, 500 to 5,000 parts by mass, or 500 to 1,500 parts by mass per 100 parts by mass of component (a).

[(c) Phenolic Compound]
The phenolic compound (component (c)) is not particularly limited and is a compound represented by ArOH (wherein Ar is an aryl group or a substituted aryl group). Note that component (c) is a component different from component (b).

Specific examples of phenolic compounds include substituted phenols such as phenol, o-, m-, or p-cresol, o-, m-, or p-ethylphenol, o-, m-, or p-propylphenol, o-, m-, or p-butylphenol, o-, m-, or p-chlorophenol, salicylic acid, hydroxybenzoic acid, and hydroxynaphthalene; polyhydric phenolic compounds such as catechol and resorcinol; and polymeric compounds such as phenolic resins, polyphenols, and poly(hydroxystyrene).

（式中、ｎは１～５の整数である。ｎが２以上である場合、複数のＲ^２１はそれぞれ、同じであってもよく、また、異なっていてもよい。
　Ｒ^２１は、炭素数２～１０のアルキル基、炭素数２～２０のアルケニル基、炭素数１～２０のアルキルチオ基、炭素数３～１０のシクロアルキル基、炭素数６～２０のアリール基、炭素数７～２０のアルキルアリール基、又は炭素数７～２０のアリールアルキル基である。） Furthermore, a phenolic compound represented by the following formula (C1) can be used.

(In the formula, n is an integer of 1 to 5. When n is 2 or more, the multiple R ²¹ may be the same or different.
R ²¹ is an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkylthio group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms.

Examples of the alkyl group represented by ^R21 include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, and tertiary amyl.
The alkenyl group includes the above-mentioned alkyl groups each having an unsaturated bond in the molecule.
Cycloalkyl groups include cyclopentane, cyclohexane, and the like.
Alkylthio groups include methylthio, ethylthio, and the like.
Aryl groups include phenyl, naphthyl, and the like.
Examples of the alkylaryl group and the arylalkyl group include the substituents obtained by combining the above-mentioned alkyl group and aryl group.
Of these groups, R ²¹ is preferably a methyl group or an ethyl group.

Specific examples of phenolic compounds represented by formula (C1) include 4-tert-amylphenol, 2-isopropylphenol, 4-isopropyl-3-methylphenol, 2-isopropyl-5-methylphenol (thymol), 5-isopropyl-2-methylphenol (carbacrol), and 4-(1,1.3,3-tetramethylbutyl)phenol.

The content of component (c) is preferably 10 to 5000 parts by mass, more preferably 10 to 2000 parts by mass, and more preferably 10 to 1000 parts by mass, per 100 parts by mass of component (a).
The content of component (c) may be 100 to 10,000 parts by mass per 100 parts by mass of component (a).
The use of such a phenolic compound is preferable because it improves the electrical conductivity and improves the solubility in alcohol.

The content of component (c) in the conductive polymer composition is 1 to 80% by mass, more preferably 5 to 60% by mass, and even more preferably 10 to 40% by mass. Use of the phenolic compound is preferable because it improves the electrical conductivity and improves the solubility in alcohol.
Also, component (c) may be mixed with component (b) to be used as a mixed solvent. In this case, the concentration of component (a) in the solvent is calculated based on the combined mass of components (b) and (c).

[(d) Heat resistance stabilizer]
The conductive polymer composition may further contain (d) a heat resistance stabilizer (hereinafter also referred to as "component (d)").

The heat resistance stabilizer (component (d)) may be an acidic substance or a salt of an acidic substance. However, component (d) does not include component (c).

The acidic substance may be either an organic acid, which is an acid of an organic compound, or an inorganic acid, which is an acid of an inorganic compound, and is preferably an organic acid.
The acidic substance is preferably an organic acid containing one or more sulfonic acid groups.

The above-mentioned organic acid having a sulfonic acid group is preferably a cyclic, linear or branched alkylsulfonic acid, a substituted or unsubstituted aromatic sulfonic acid, or a polysulfonic acid, each of which has one or more sulfonic acid groups.
Examples of the alkylsulfonic acid include methanesulfonic acid, ethanesulfonic acid, and di(2-ethylhexyl)sulfosuccinic acid. The alkyl group is preferably a linear or branched alkyl group having 1 to 18 carbon atoms.
Examples of the aromatic sulfonic acid include those having 6 to 20 carbon atoms, such as sulfonic acids having a benzene ring, sulfonic acids having a naphthalene skeleton, and sulfonic acids having an anthracene skeleton. Examples of the aromatic sulfonic acid include substituted or unsubstituted benzenesulfonic acid, substituted or unsubstituted naphthalenesulfonic acid, and substituted or unsubstituted anthracenesulfonic acid.

The substituent may be, for example, one or more selected from the group consisting of an alkyl group (e.g., one having 1 to 20 carbon atoms), an alkoxy group (e.g., one having 1 to 20 carbon atoms), a hydroxy group, a nitro group, a carboxy group, and an acyl group.

（式（Ｄ１）中、ｌは１以上であり、ｍは０以上５以下の整数であり、ｎは０以上５以下の整数である。ｍ又はｎの一方が０の場合、他方は１以上である。）

（式（Ｄ２）中、ｑは１以上であり、ｐは０以上７以下の整数であり、Ｒは、それぞれ独立に炭素数１～２０のアルキル基、カルボキシ基、水酸基、ニトロ基、シアノ基、アミノ基である。） Specific examples of the aromatic sulfonic acid include compounds represented by the following formula (D1) or (D2).

(In formula (D1), l is 1 or more, m is an integer of 0 or more and 5 or less, and n is an integer of 0 or more and 5 or less. When one of m and n is 0, the other is 1 or more.)

(In formula (D2), q is 1 or more, p is an integer of 0 to 7, and R each independently represents an alkyl group having 1 to 20 carbon atoms, a carboxy group, a hydroxyl group, a nitro group, a cyano group, or an amino group.)

l is preferably an integer of 1 to 3. m is preferably an integer of 1 to 3. n is preferably an integer of 0 to 3.
q is preferably 1 to 3. p is preferably 0 to 3. R is preferably an alkyl group having 1 to 20 carbon atoms, a carboxy group, or a hydroxyl group.

Aromatic sulfonic acids include 4-sulfophthalic acid, 5-sulfoisophthalic acid, 5-sulfosalicylic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 2-hydroxy-6-naphthalenesulfonic acid, 1,5-naphthalenedisulfonic acid, 2,6-naphthalenedisulfonic acid, p-phenolsulfonic acid, toluenesulfonic acid, p-xylene-2-sulfonic acid, 4,4'-biphenyldisulfonic acid, dibenzofuran-2-sulfonic acid, flavianic acid, (+)-10-camphorsulfonic acid, monoisopropylnaphthalenesulfonic acid, 1-pyrenesulfonic acid, etc. Among these, from the viewpoint of improving heat resistance, 4-sulfophthalic acid, 5-sulfosalicylic acid, 5-sulfoisophthalic acid, 2-naphthalenesulfonic acid, dibenzofuran-2-sulfonic acid, flavianic acid, 2-hydroxy-6-naphthalenesulfonic acid, and 1-pyrenesulfonic acid are preferred.

Examples of the salts of acidic substances include salts of the compounds listed above. Examples of the counter ions of the salts include sodium, lithium, potassium, cesium, ammonium, calcium, barium, etc.
Component (d) may be a hydrate.

The content of component (d) is preferably 0.1 to 1000 parts by mass, more preferably 1 to 100 parts by mass, even more preferably 1 to 30 parts by mass, and even more preferably 2 to 8 parts by mass, per 100 parts by mass of component (a).

[(e) Additives]
In addition to the above components, the conductive polymer composition may contain an additive (hereinafter, also referred to as "component (e)") as necessary. However, component (e) does not include any of the above components (a) to (d).
The additives include an adhesion imparting agent, a filler, a rheology control agent, a binder resin, and the like.

Examples of the adhesion imparting agent include silane coupling agents such as isocyanate silane and glycidyl silane, and polymer coupling agents such as acidic polyester.
As a commercially available adhesion promoter, for example, "BYK-4510" (manufactured by BYK Additives & Instruments) can be used.
Examples of the filler include alumina, silica, titania, and zirconia.

The conductive polymer composition may essentially consist of components (a) and (b), and optionally components (c), (d), and (e). In this case, it may contain unavoidable impurities. For example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 98% by mass or more, 99% by mass or more, or 99.5% by mass or more of the conductive polymer composition may be components (a) and (b), and optionally components (c), (d), and (e). The conductive polymer composition may also consist only of components (a) and (b), and optionally components (c), (d), and (e).

The method of immersing the porous body having an oxide of a valve metal in the first conductive polymer composition is not particularly limited, and the entire porous body may be immersed in the conductive polymer composition in a single insertion operation, or the porous body may be immersed in the conductive polymer composition stepwise or continuously.
"Stepwise immersion" means that the porous body is moved in a number of separate steps to gradually immerse the porous body in the conductive polymer composition. In other words, "stepwise immersion" means that the immersion operation is carried out step by step, and after a series of stepwise immersion operations, the porous body is removed from the conductive polymer composition in step (B).
The term "continuously immersed" means that the porous body is moved continuously at a predetermined speed and gradually immersed in the conductive polymer composition.
By immersing the porous body in the conductive polymer composition stepwise or continuously, the conductive polymer can be smoothly impregnated into the pores of the porous body.

When the entire porous body is immersed in the conductive polymer composition in a single pouring operation, the time for which the porous body is held in the conductive polymer composition (hereinafter simply referred to as the immersion time) is usually 1 to 30 minutes, and preferably 1 to 10 minutes.

When the porous body is moved in several separate steps to gradually immerse the porous body in the conductive polymer composition, first, a portion of the porous body from the lower end to a predetermined height is immersed in the conductive polymer composition and maintained in the immersed state for, for example, 1 to 30 minutes, preferably 1 to 10 minutes.
Next, the porous body is moved so that a portion of the non-immersed portion is further immersed in the conductive polymer composition, and the immersion state is maintained for, for example, 1 to 20 minutes, preferably 1 to 10 minutes.

The temperature of the conductive polymer composition into which the porous body is immersed is not particularly limited, and is usually room temperature (e.g., 15 to 30°C, or 25°C).

<Process (B)>
Step (B) is a step of removing the porous body from the first conductive polymer composition used in step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition. This causes the liquid film formed at the openings of the pores in the porous body to disappear, and the liquid-sealed state can be eliminated. Therefore, the amount of the conductive polymer composition filled into the inside of the pores can be increased.

In step (B), the holding temperature is a temperature below the boiling point of the solvent contained in the first conductive polymer composition and may be appropriately selected depending on the type of solvent, for example, room temperature. The holding time is usually 30 seconds to 5 minutes, and preferably 1 minute to 2 minutes.

In one embodiment, a cycle of steps (A) and (B) may be repeated multiple times prior to step (C).
When a cycle of steps (A) and (B) is repeated multiple times before step (C), the multiple layers formed in a series of cycles are collectively referred to as an internal solid electrolyte layer (first conductive layer).

In one embodiment, a drying step (B1) may be performed after the step (B) and before the step (C). The temperature in the drying step does not need to be equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition. The drying temperature is usually 30 to 200° C., and preferably 100 to 180° C. The drying time is usually 10 to 120 minutes, and preferably 30 to 90 minutes.
Prior to the drying step (B1), the cycle of steps (A) and (B) may be repeated multiple times.

[Step of forming second conductive layer]
<Process (C)>
Step (C) is a step of immersing a part or the whole of the porous body after step (B) in a second conductive polymer composition containing a conductive polymer that is the same as or different from the first conductive polymer composition, a thixotropy imparting agent, and a solvent, and drying the second conductive polymer composition to form a second conductive layer.

The conductive polymer, solvent, and immersion can be the same as those described in step (A) above.

The matters described in the solid electrolytic capacitor according to one embodiment of the present invention can be applied to the thixotropy-imparting agent.

The content of the thixotropy-imparting agent in the entire second conductive polymer composition is not particularly limited as long as it is within a range that can impart thixotropy to the second conductive polymer composition. A person skilled in the art can appropriately select the content of the thixotropy-imparting agent in accordance with the composition of the second conductive polymer composition.
In one embodiment, the content of the thixotropy-imparting agent relative to the entire second conductive polymer composition is 0.2 to 5 mass % (preferably 0.3 to 4 mass %, more preferably 0.4 to 3 mass %).

In one embodiment, the second conductive polymer composition contains polyaniline or a polyaniline derivative. Since the second conductive polymer composition does not need to be impregnated into the pores of the anode body, the weight average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition can be larger than the weight average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition. This makes it possible to impart strength, heat resistance, etc. necessary for functioning as a coating layer. For example, the weight average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition is preferably 100,000 or more.

In one embodiment, the second conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with a proton donor.
In one embodiment, the second conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with sulfosuccinic acid.

In one embodiment, the second conductive polymer composition further comprises a thickener.

As for the thickener, the matters described in the solid electrolytic capacitor according to one embodiment of the present invention can be applied.

In one embodiment, the second conductive polymer composition satisfies the following conditions (P1) and (P2).
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

It is sufficient to confirm that the second conductive polymer composition satisfies the conditions (P1) and (P2) separately from step (C).

In step (C), the drying temperature is not particularly limited and may be appropriately selected depending on the type of solvent. The drying temperature is usually 30 to 200°C, preferably 100 to 180°C. The drying time is usually 10 to 120 minutes, preferably 30 to 90 minutes.

The method for manufacturing a solid electrolytic capacitor according to one embodiment of the present invention may include, after step (C), a step (D) of forming a carbon layer and a step (E) of forming a silver layer.

[Carbon layer forming process]
Step (D) is a step of immersing a part or the whole of the porous body after step (C) in a liquid containing a carbon paste and drying it.
As for the carbon paste, the matters described in the solid electrolytic capacitor according to one aspect of the present invention can be applied.

In the carbon layer forming step, the immersion time is usually 5 seconds to 1 minute, and preferably 10 to 30 seconds.
The drying temperature is usually 30 to 200° C., and preferably 100 to 180° C. The drying time is usually 10 to 120 minutes, and preferably 30 to 90 minutes.

[Silver layer formation process]
Step (E) is a step of immersing a part or the whole of the porous body after step (D) in a liquid containing silver paste and drying it.
As for the silver paste, the matters described in the solid electrolytic capacitor according to one aspect of the present invention can be applied.

In the silver layer forming step, the immersion time is usually from 5 seconds to 1 minute, and preferably from 10 to 30 seconds.
The drying temperature is usually 30 to 200° C., and preferably 100 to 180° C. The drying time is usually 10 to 120 minutes, and preferably 30 to 90 minutes.

The solid electrolytic capacitor according to one aspect of the present invention can be used as a circuit element mounted on an electric/electronic circuit board, particularly as a circuit element mounted on an automobile or the like.

In one embodiment, step (C) may be repeated multiple times. In this case, the multiple layers formed in a series of cycles are collectively referred to as the outer coating layer (second conductive layer).

The solid electrolytic capacitor according to one aspect of the present invention can be used as a circuit element mounted on an electric/electronic circuit board, particularly as a circuit element mounted on an automobile or the like.

Production Example 1 (Production of Polyaniline Composite 1)
A 1,000 mL separable flask was charged with 32.4 g of "Neocol SWC" (di-2-ethylhexyl sodium sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 13.3 g of aniline, and 0.9 g of "Sorbon T-20" (a nonionic emulsifier having a polyoxyethylene sorbitan fatty acid ester structure, manufactured by Toho Chemical Industry Co., Ltd.), and dissolved in 320.4 g of toluene. 450 g of an 8.5 mass % aqueous phosphoric acid solution was added thereto, and the reaction liquid having two liquid phases, toluene and water, was stirred and the internal temperature of the reaction liquid was cooled to 5°C.

When the internal temperature of the reaction solution reached 5° C., a solution prepared by dissolving 39.3 g of APS (ammonium persulfate) in 90.2 g of an 8.5 mass% aqueous phosphoric acid solution was added using a dropping funnel while stirring the reaction solution, and the mixture was stirred for 4 hours while maintaining the internal temperature of the solution at 5° C.
After stopping the stirring, the contents were transferred to a separating funnel, and the aqueous phase and the toluene phase (organic phase) were allowed to stand and separated. After separation, the toluene phase (organic phase) was washed once with 180.3 g of an 8.5 mass % aqueous phosphoric acid solution and five times with 328.0 g of ion-exchanged water to obtain a polyaniline complex toluene solution.

The solution was transferred to an evaporator, heated in a 60°C water bath, and reduced pressure to evaporate and remove the volatiles, yielding polyaniline complex 1 (protonated polyaniline). The weight-average molecular weight (Mw) of the polyaniline in polyaniline complex 1 was 73,000.

The weight average molecular weights of the polyanilines in the Polyaniline Composite 1 and the Polyaniline Composite 2 described below were measured as follows.
1.65 to 1.85 g of lithium bromide was dissolved in 2000 mL of NMP (N-methyl-2-pyrrolidone) to prepare a 0.01 M lithium bromide NMP solution. 14 μL of triethylamine was added to 10 mL of this 0.01 M lithium bromide NMP solution, and the solution was stirred to dissolve the triethylamine and obtain a homogeneous solution. 50 μL of the polyaniline complex toluene solution was then dropped and mixed by stirring, and the mixture was passed through a 0.45 μM filter to prepare a sample for gel permeation chromatography (GPC) measurement.

Using a sample for GPC measurement, the GPC measurement was carried out using a GPC column (Shodex KF-806M manufactured by Showa Denko KK, two columns connected) under the following measurement conditions.
Solvent: 0.01M LiBr in NMP
Flow rate: 0.70 mL/min Column temperature: 60° C.
Injection volume: 100μL
UV detection wavelength: 270 nM

The weight average molecular weight obtained by the above method is a value calculated in terms of polystyrene (PS).
The doping ratio of the proton donor (sodium di-2-ethylhexyl sulfosuccinate) to the polyaniline was 0.36.

Production Example 2 (Production of Polyaniline Composite 2)
A 1,000 mL separable flask was charged with 10.13 g of "Neocol SWC" (di-2-ethylhexyl sodium sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 4.17 g of aniline, and 0.32 g of "Sorbon T-20" (a nonionic emulsifier having a polyoxyethylene sorbitan fatty acid ester structure, manufactured by Toho Chemical Industry Co., Ltd.), and dissolved in 238.37 g of toluene. 353.70 g of a 17% by mass aqueous phosphoric acid solution was added thereto, and the reaction liquid having two liquid phases, toluene and water, was stirred and the internal temperature of the reaction liquid was cooled to -2°C.

When the internal temperature of the reaction solution reached −2° C., a solution prepared by dissolving 12.3 g of APS (ammonium persulfate) in 48 g of a 17% by mass aqueous phosphoric acid solution was added using a dropping funnel while stirring the reaction solution, and the solution was stirred for 18 hours while maintaining the internal temperature at −2° C.
After stopping the stirring, the contents were transferred to a separating funnel and the aqueous phase and the toluene phase (organic phase) were allowed to stand and separated. After separation, the toluene phase (organic phase) was washed once with 59.4 g of an 8.5 mass % phosphoric acid aqueous solution and three times with 108.14 g of ion-exchanged water to obtain a polyaniline complex toluene solution.

This solution was transferred to an evaporator, heated in a water bath at 60° C., and reduced pressure to evaporate and remove the volatile matter, thereby obtaining polyaniline composite 2 (protonated polyaniline). The weight average molecular weight (Mw) of polyaniline in polyaniline composite 2 was 112,000.
The doping ratio of the proton donor (sodium di-2-ethylhexyl sulfosuccinate) to polyaniline was 0.36.

Production Example 3 (Anode Body)
A voltage of up to 8.8 V was applied to 20 pellet-shaped tantalum powder sintered compacts (porous bodies of 1.71 mm × 3.01 mm × 2.89 mm) made from tantalum powder having a specific capacitance of 250,000 μFV/g in a 0.5% phosphoric acid electrolyte to subject them to anodization, forming a dielectric (tantalum oxide) on the surface of the tantalum powder sintered compact (porous body), thereby obtaining an anode body for a tantalum capacitor.
The submerged capacity of the anode body was measured using 10% by mass phosphoric acid as the electrolyte and a platinum black electrode as the counter electrode, and was found to be 961 μF.

Example 1
(1) Preparation of Conductive Polymer Composition D (First Conductive Polymer Composition) for Forming First Conductive Layer 49 g of 1-propanol (component (b), boiling point 97° C., manufactured by Tokyo Chemical Industry Co., Ltd.), 49 g of p-tert-amylphenol (component (c), manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 42 g of Kyowazole C900 (component (b), manufactured by KH Neochem Corporation) were mixed with stirring until homogenous, to prepare a mixed solvent α.
7 g of the polyaniline composite 1 (component (a)) obtained in Production Example 1 was dissolved in 133 g of the mixed solvent α to obtain a polyaniline composite solution A (polyaniline composite concentration: 5 mass %).

10 g of 2-naphthalenesulfonic acid hydrate (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 90 g of isopropyl alcohol (component (b), boiling point 82.5° C., manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a heat stabilizer solution B.
An adhesion-imparting solution C was prepared by dissolving 20 g of BYK-4510 (component (e), manufactured by BYK Additives & Instruments) in 100 g of the mixed solvent α.

0.237 g of heat-resistant stabilizer solution B and 0.105 g of adhesion-imparting solution C were added to 21 g of polyaniline complex solution A (polyaniline complex concentration: 5% by mass), and mixed with stirring to obtain a conductive polymer composition D (first conductive polymer composition) for forming a first conductive layer.

(2) Formation of Internal Solid Electrolyte Layer (First Conductive Layer) [First Immersion]
The anode body obtained in Production Example 3 was fixed to a metal bar and hung, and the anode body was immersed up to ⅓ of the height from the bottom end side in conductive polymer composition D and held for 2 minutes. Next, the anode body was immersed up to ⅔ of the height from the bottom end side in conductive polymer composition D and held for 2 minutes. Next, the entire anode body was immersed in conductive polymer composition D and held for 1 minute. In this manner, the first immersion of the anode body was completed.
Next, the anode body was pulled out from conductive polymer composition D and was held at room temperature for 1 minute in a state where the entire anode body was exposed to air.

[Second immersion]
Next, the anode body was immersed in conductive polymer composition D up to ⅓ of the height from the bottom end side and held for 2 minutes. Next, the anode body was immersed in conductive polymer composition D up to ⅔ of the height from the bottom end side and held for 2 minutes. Next, the entire anode body was immersed in conductive polymer composition D and held for 1 minute. In this manner, the second immersion of the anode body was performed.
Next, the anode body was pulled out from the conductive polymer composition D and dried at 40° C. for 7 minutes, and then further dried at 140° C. for 5 minutes to form an internal solid electrolyte layer (first conductive layer).

(3) Preparation of Conductive Polymer Composition G for Forming Second Conductive Layer (Second Conductive Polymer Composition) 30 g of 1-ethoxy-2-propanol (component (b), manufactured by Tokyo Chemical Industry Co., Ltd.), 30 g of 1-propanol, and 40 g of p-tert-amylphenol were mixed with stirring until the mixture became uniform, to prepare a mixed solvent ε.
10 g of the polyaniline composite 2 (component (a)) obtained in Production Example 2 was dissolved in 90 g of the mixed solvent ε to obtain a polyaniline composite solution E (polyaniline composite concentration: 10 mass %).

2 parts by mass (0.2 g) of fine silica: AEROSIL 380 (manufactured by Nippon Aerosil Co., Ltd.) was added to 10 g of polyaniline complex solution E, and the mixture was stirred and mixed at 1000 rpm for 5 minutes using a homodisper (PRIMIX homodisper 2.5 type) to prepare polyaniline complex/fine silica mixed solution H.

20 g of BYK-4510 (component (e), manufactured by BYK Additives & Instruments) was dissolved in 100 g of mixed solvent ε to prepare adhesion imparting solution F.

0.564 g of heat resistance stabilizer solution B and 0.075 g of adhesion imparting solution F were added to 7.5 g of polyaniline complex/fine silica mixed solution H (polyaniline complex concentration: 10% by mass), and mixed with stirring to obtain conductive polymer composition G (second conductive polymer composition) for forming a second conductive layer.

(4) Formation of Outer Coating Layer (Second Conductive Layer) First, the anode body obtained in (2) above was entirely immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol, and held for 10 minutes.
The anode element was then pulled out from the 4-sulfophthalic acid solution and dried at 150° C. for 60 minutes.
Next, the entire anode body was immersed in conductive polymer composition G for forming a second conductive layer and held there for 5 minutes.

Then, the anode body was pulled out of the conductive polymer composition G and dried at 100°C for a specified time of 30 to 60 minutes, and then dried at 150°C for a specified time of 30 to 60 minutes to coat the outside of the anode body. This process of immersing the conductive polymer composition for forming the second conductive layer and drying it is called dipping, and dipping was performed three times.

Next, the entire anode body was immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol, and was kept therein for 10 minutes.
The anode body was then pulled out of the 4-sulfophthalic acid solution and dried at 150° C. for 60 minutes to obtain an anode body having an inner solid electrolyte layer (first conductive layer) and an outer coating layer (second conductive layer).

(5) Formation of Carbon Layer The anode body (having the first conductive layer and the second conductive layer) obtained in (4) above was immersed in a carbon paste: FUAE (solvent: ketone-based, manufactured by Nippon Graphite Industries Co., Ltd.) as an undiluted solution for 10 seconds, and then dried at 150° C. for 30 minutes.

(6) Formation of Silver Layer Next, a silver paste: H9113-6 (granular, manufactured by Namics Corporation) was diluted 1.2 times with a dilution solvent: diethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), and the diluted solution was stirred and mixed to obtain a silver paste solution, in which the anode body obtained in (5) above was immersed for 10 seconds, dried at 100° C. for 30 minutes, and then further dried at 150° C. for 30 minutes to obtain a capacitor.

<Evaluation of Electrical Characteristics>
The capacitance (Cap) and dielectric loss (tan δ) at a frequency of 120 Hz, and the equivalent series resistance (ESR) at a frequency of 100 kHz were measured for the capacitor obtained above before and after the heat treatment using an LCR meter "Precision LCR Meter E4980A" (manufactured by Agilent Technologies Japan, Ltd.). The evaluation results are shown in Table 1.

<Evaluation of wet heat resistance>
The capacitor obtained above was exposed to an environment of 85% temperature and 95% RH (Relative Humidity) for 3 days, and then the element was dried at 100°C for 30 minutes. Then, the Cap and ESR were measured using an LCR meter "Precision LCR Meter E4980A" to evaluate the wet heat resistance. The evaluation results are shown in Table 1.
In Table 1, the case where the change in the Cap and ESR values compared to before exposure was within 30% was marked as O. The case where the change in the Cap and ESR values compared to before exposure was more than 30% or the Cap and ESR values were not measurable was marked as ×.

Example 2
A capacitor was manufactured and evaluated in the same manner as in Example 1, except that in forming the outer coating layer (second conductive layer), the dipping was performed once. The evaluation results are shown in Table 1.

Example 3
A capacitor was manufactured and evaluated in the same manner as in Example 1, except that in forming the outer coating layer (second conductive layer), a conductive polymer composition G' obtained by adding 0.564 g of heat resistance stabilizer solution B and 0.075 g of adhesion imparting solution F to 7.5 g of polyaniline complex solution E (polyaniline complex concentration: 10 mass %) and mixing them under stirring was used instead of the conductive polymer composition G. The evaluation results are shown in Table 1.

Comparative Example 1
A capacitor was produced and evaluated in the same manner as in Example 2, except that in forming the outer coating layer (second conductive layer), PEDOT/PSS (ethylene glycol-added product, manufactured by Sigma-Aldrich) was used without dilution instead of the conductive polymer composition G. The evaluation results are shown in Table 1.

Production Example 4 (Anode Body)
A tantalum powder sintered compact (porous body), which is an EIA standard compliant product with an EIA designation of 1206 (JIS designation of 3216) and a CV product of 120 kCV, was anodized by applying a voltage of up to 30 V in a 0.5% phosphoric acid electrolyte to form a dielectric (tantalum oxide) on the surface of the tantalum powder sintered compact (porous body), thereby obtaining an anode body for a tantalum capacitor.
The submerged capacity of the anode body was measured using 10% by mass phosphoric acid as the electrolyte and a platinum black electrode as the counter electrode. The submerged capacity of the anode body was 50 μF.

Example 4
(1) Formation of Internal Solid Electrolyte Layer (First Conductive Layer) An internal solid electrolyte layer (first conductive layer) was formed in the same manner as in Example 1, except that the anode body obtained in Production Example 4 was used instead of the anode body obtained in Production Example 3.

(2) Preparation of Conductive Polymer Composition K for Forming Second Conductive Layer (Second Conductive Polymer Composition) 30 g of 1-ethoxy-2-propanol (component (b), manufactured by Tokyo Chemical Industry Co., Ltd.), 30 g of 1-propanol, and 40 g of p-tert-amylphenol were mixed with stirring until the mixture became uniform, to prepare a mixed solvent ε.
10 g of the polyaniline composite 2 (component (a)) obtained in Production Example 2 and 0.4 g of ethyl cellulose Aqualon EC-N300 (manufactured by Ashland Inc.) were dissolved in 90 g of the mixed solvent ε at room temperature to obtain a polyaniline composite solution I (polyaniline composite concentration: 10 mass %).
To 10 g of the polyaniline composite solution I, 4 parts by mass (0.4 g) of fine silica: AEROSIL 380 (manufactured by Nippon Aerosil Co., Ltd.) was added, and the mixture was stirred and mixed at 3,000 rpm for 5 minutes using a Homo Disper (PRIMIX Homo Disper 2.5 type) to prepare a polyaniline composite/fine silica mixed solution J.

The polyaniline composite/fine silica mixed solution J was measured using an Anton Paar rheometer MCR302 with a P-PTD200/H-PTD200 for temperature control, with parallel plates of 25 mm diameter and a gap of 1 mm. The viscosity was 9 Pa·s at a shear rate of 10 (1/s), and after applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate was reduced to 0.0001 (1/s) was 1500 Pa·s, with a viscosity change of 11 times after 5 minutes.

20 g of BYK-4510 (component (e), manufactured by BYK Additives & Instruments) was dissolved in 100 g of mixed solvent ε to prepare adhesion imparting solution F.

0.564 g of heat resistance stabilizer solution B and 0.075 g of adhesion imparting solution F were added to 7.5 g of polyaniline complex/fine silica mixed solution J (polyaniline complex concentration: 10% by mass) and mixed with stirring to obtain conductive polymer composition K (second conductive polymer composition) for forming a second conductive layer.

(3) Formation of Outer Coating Layer (Second Conductive Layer) First, the anode body obtained in (1) above was entirely immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol, and held for 180 minutes.
The anode element was then removed from the 4-sulfophthalic acid solution and dried at 100° C. for 18 hours.
Next, the entire anode body was immersed in conductive polymer composition K for forming a second conductive layer and held there for 5 minutes.

Then, the anode body was removed from the conductive polymer composition K at a pulling speed of 1 second (a speed at which it takes 1 second for the entire anode body to come out of the conductive polymer composition K after starting to pull it up), and dried at 100°C for a specified time of 30 to 60 minutes, and then dried at 150°C for a specified time of 30 to 60 minutes to coat the outside of the anode body. This process of immersing the conductive polymer composition for forming the second conductive layer and drying it is called dipping, and dipping was performed once.

Next, the entire anode body was immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol, and was kept therein for 180 minutes.
The anode body was then pulled out of the 4-sulfophthalic acid solution and dried at 75° C. for 18 hours to obtain an anode body having an inner solid electrolyte layer (first conductive layer) and an outer coating layer (second conductive layer).

(4) Formation of Carbon Layer The anode body (having the first conductive layer and the second conductive layer) obtained in (3) above was immersed in a carbon paste: FUAE (solvent: ketone-based, manufactured by Nippon Graphite Industries Co., Ltd.) as an undiluted solution for 10 seconds, and then dried at 150° C. for 30 minutes.

(5) Formation of Silver Layer Next, a silver paste: EC209A (plate-like + granular, manufactured by Mitsuboshi Belting Co., Ltd.) was diluted 1.1 times with a dilution solvent: N-methylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd.), and the diluted solution was stirred and mixed to obtain a silver paste solution, in which the anode body obtained in (4) above was immersed for 10 seconds, dried at 100° C. for 30 minutes, and then further dried at 150° C. for 180 minutes to obtain a capacitor.

Example 5
A capacitor was manufactured and evaluated in the same manner as in Example 4, except that in forming the outer coating layer (second conductive layer), the dipping was performed twice. The evaluation results are shown in Table 2.

Example 6
A capacitor was manufactured and evaluated in the same manner as in Example 5, except that in the preparation of conductive polymer composition K (second conductive polymer composition) for forming the second conductive layer, the amount of fine silica added to the polyaniline complex solution I was 2 parts by mass (0.2 g). The evaluation results are shown in Table 2. Polyaniline complex/fine silica mixed solution J

Example 7
A capacitor was produced and evaluated in the same manner as in Example 4, except that in forming the outer coating layer (second conductive layer), the anode body was pulled up from the conductive polymer composition K at a pulling speed of 30 seconds. The evaluation results are shown in Table 2.

Example 8
A capacitor was manufactured and evaluated in the same manner as in Example 4, except that in the preparation of the conductive polymer composition K (second conductive polymer composition) for forming the second conductive layer, ethyl cellulose was not added, and in the formation of the outer coating layer (second conductive layer), the number of dipping steps was set to three. The evaluation results are shown in Table 2.

Example 9
A capacitor was manufactured and evaluated in the same manner as in Example 4, except that in preparing the conductive polymer composition K (second conductive polymer composition) for forming the second conductive layer, the amount of ethyl cellulose dissolved in the mixed solvent ε was 0.2 g, and in forming the outer coating layer (second conductive layer), the number of dipping operations was 3. The evaluation results are shown in Table 2.

Example 10
A capacitor was manufactured and evaluated in the same manner as in Example 4, except that in the preparation of the conductive polymer composition K (second conductive polymer composition) for forming the second conductive layer, fine silica was not added, and in the formation of the outer coating layer (second conductive layer), the number of dipping steps was set to three. The evaluation results are shown in Table 2.

<Evaluation of side edge thickness>
The surface of the capacitor obtained above that was the bottom surface during dipping was set as the bottom surface, and the capacitor was cut along a surface parallel to the bottom surface at a position 1/3 of the way from the bottom surface side in the bottom-top direction, and the thickness of the side edge portion and the side flat portion were measured by observing the cross section with an optical microscope. The evaluation results are shown in Table 2.

<Evaluation of wet heat resistance>
The moist heat resistance of the capacitor obtained above was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

All of the capacitors in Examples 4 to 10 had moist heat resistance.

The capacitors in Examples 4 to 6, which had a pull-up speed of 1 second, were found to have thicker side edge portions and flat side portions than the capacitor in Example 7, which had a pull-up speed of 30 seconds.

In addition, it was found that the capacitors of Examples 4 to 6, which contain both a thixotropic agent (silica) and a thickener (ethyl cellulose), have thicker side edge portions and flat side portions, even when dipping is performed only once or twice, compared to the capacitors of Examples 8 and 10, which contain only one of a thixotropic agent (silica) and a thickener (ethyl cellulose).

Furthermore, when comparing Example 6, in which the amount of thickener (ethyl cellulose) added is 0.36 mass%, with Example 9, in which the amount of thickener (ethyl cellulose) added is 0.18 mass%, it was found that while the amount of thixotropy-imparting agent (silica) added is both 1.8 mass%, the capacitor in Example 6 had thicker side edge portions and side flat portions even with fewer dipping cycles.

Although some embodiments and/or examples of the present invention have been described in detail above, those skilled in the art can easily make many modifications to these exemplary embodiments and/or examples without substantially departing from the novel teachings and advantages of the present invention, and therefore many such modifications are within the scope of the present invention.
The contents of all documents cited in this specification and of the application from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims (16)

The present invention includes a porous body made of a valve metal, a dielectric layer formed on a surface of the porous body, and two or more conductive layers covering the dielectric layer,
the two or more conductive layers include a first conductive layer formed on a surface of the dielectric layer and a second conductive layer laminated on the first conductive layer,
The second conductive layer comprises a polyaniline composite in which the polyaniline is doped with a proton donor. The solid electrolytic capacitor of claim 1, wherein the dielectric layer is made of an oxide of the valve metal. The solid electrolytic capacitor according to claim 1 or 2, wherein the polyaniline complex is doped with sulfosuccinic acid. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the second conductive layer further contains a thixotropic agent. The solid electrolytic capacitor according to claim 4, wherein the thixotropy-imparting agent contains inorganic particles. The solid electrolytic capacitor according to claim 5, wherein the inorganic particles include one or more selected from the group consisting of silica, titania, alumina, and zirconia. The solid electrolytic capacitor according to any one of claims 4 to 6, wherein the content of the thixotropy-imparting agent in the entire second conductive layer is 0.01 to 50 mass %. The solid electrolytic capacitor according to any one of claims 1 to 7, wherein the second conductive layer further contains a thickener. The solid electrolytic capacitor according to claim 8, wherein the thickener is a polyether compound or a cellulose compound. The solid electrolytic capacitor according to claim 8 or 9, wherein the content of the thickener in the entire second conductive layer is 0.001 to 5 mass %. 11. The solid electrolytic capacitor according to claim 1, wherein the second conductive layer is formed from a conductive polymer composition that satisfies the following conditions (P1) and (P2):
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

The solid electrolytic capacitor according to any one of claims 1 to 11, wherein the valve metal is selected from the group consisting of aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. A method for producing a solid electrolytic capacitor, comprising the following steps (A-1) or (A-2), (B), and (C):
(A-1) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer and a solvent; (A-2) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound; (B) A step of removing the porous body from the first conductive polymer composition used in the step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition; (C) A step of immersing a part or the whole of the porous body after the step (B) in a second conductive polymer composition containing a conductive polymer, a thixotropy-imparting agent, and a solvent that is the same as or different from the first conductive polymer composition, and drying the second conductive polymer composition. The method for producing a solid electrolytic capacitor according to claim 13, wherein the content of the thixotropy-imparting agent in the entire second conductive polymer composition is 0.2 to 5 mass %. 15. The method for producing a solid electrolytic capacitor according to claim 13, wherein the second conductive polymer composition satisfies the following conditions (P1) and (P2):
(P1) The viscosity at a shear rate of 10 (1/s) is 1 Pa·s or more.
(P2) After applying shear at a shear rate of 10 (1/s) for 30 seconds, the viscosity immediately after the shear rate is reduced to 0.0001 (1/s) is 10 Pa·s or more and satisfies the following formula (P2-1).

A solid electrolytic capacitor obtained by the method for producing a solid electrolytic capacitor according to any one of claims 13 to 15.

Images