JP2005252213A - Solid electrolytic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor having satisfactory characteristics as a capacitor, easy in manufacture and high in productivity, and to provide its manufacturing method. <P>SOLUTION: In a solid electrolytic capacitor having a metal body 11 comprising a valve action metal, a dielectric oxide film 12 that is formed on the surface of the metal body 11, and a solid electrolyte layer 13 adjacent to the dielectric oxide film 12, the solid electrolyte layer 13 has a first conductive polymer layer 13a that is formed on the surface of the dielectric oxide film 12 by the electrolytic polymerization or chemical oxidative polymerization of the precursor monomer of a conductive polymer and a second conductive polymer layer 13b that is formed by applying a conductive polymer containing coating on the first conductive polymer layer 13a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

 The present invention relates to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte layer and a method for manufacturing the same.

A solid electrolytic capacitor widely used for electronic parts is made of, for example, a valve metal such as aluminum or tantalum, a metal body serving as an anode, a dielectric oxide film formed on the surface of the metal body, And a solid electrolyte layer formed on the surface of the dielectric oxide film.
As a method for manufacturing such a solid electrolytic capacitor, for example, Patent Document 1 describes a manufacturing method in which a solid electrolyte layer is formed by an electrolytic polymerization method. In this manufacturing method, first, a dielectric oxide film is formed on the surface of a metal body made of aluminum or tantalum, and a precoat layer made of a metal or a conductive metal compound is formed on the dielectric oxide film. Then, using this precoat layer as an electrode, a conductive polymer precursor monomer such as pyrrole is electrolytically polymerized on the precoat layer to form a solid electrolyte layer made of a conductive polymer.

 Patent Document 2 describes a manufacturing method for forming a solid electrolyte layer by a chemical oxidative polymerization method. In this manufacturing method, a sintered body having a dielectric oxide film is alternately immersed in an oxidant solution and a monomer solution, and subjected to chemical oxidative polymerization to form a solid electrolyte layer made of a conductive polymer. Further, after the oxidant and the precursor monomer of the conductive polymer are mixed and the sintered body is immersed in a solution maintained at a temperature lower than the temperature at which the polymerization reaction proceeds, the sintered body is pulled up, and the polymerization start temperature is increased. A method has been proposed in which the polymerization reaction proceeds by heating to the above temperature.

Patent Document 3 describes a production method in which a solid electrolyte layer is formed by combining a chemical oxidative polymerization method and an electrolytic polymerization method. In this manufacturing method, a dielectric oxide film is formed on the surface of a metal body, and a first conductive polymer layer made of polypyrrole is formed on the dielectric oxide film by chemical oxidative polymerization of pyrrole using an oxidizing agent. Further, pyrrole is electrolytically polymerized on the first conductive polymer layer to form a second conductive polymer layer to form a solid electrolyte layer.
Furthermore, Patent Document 4 describes a method of forming a solid electrolyte layer made of a conductive polymer by a method other than electrolytic polymerization or chemical oxidative polymerization described in Patent Documents 1 to 3. Specifically, Patent Document 4 describes a method of forming a solid electrolyte layer by applying a polyaniline solution, which is a polymerized conductive polymer, to the surface of a dielectric oxide film on an anode and drying it. Yes.
JP 63-173313 A JP-A-2-15611 JP-A-63-158829 JP-A-3-35516

However, the electrolytic polymerization method described in Patent Document 1 is complicated because it is necessary to provide a precoat layer serving as an electrode on the surface of the dielectric oxide film in order to apply a voltage. Moreover, in order to continuously form a conductive polymer layer having a uniform thickness over a wide range, a uniform current must be continuously applied for a long time, resulting in low productivity.
The chemical oxidative polymerization method described in Patent Document 2 is complicated because it includes a step of discharging a monomer onto a sintered body and drying it, and a step of discharging an oxidant and polymerizing the monomer. To increase the thickness, the same operation had to be repeated many times, resulting in low productivity. In addition, in the method of immersing the sintered body in a solution in which the monomer solution and the oxidant solution are mixed in advance and performing chemical oxidative polymerization, there is a problem in that the characteristics of the capacitor obtained vary depending on the mixed state of the solution.
Since the production method described in Patent Document 3 is a combination of a chemical oxidative polymerization method and an electrolytic polymerization method, there is a problem similar to Patent Documents 1 and 2.

  Moreover, in the method of applying the solubilized polyaniline solution of Patent Document 4, the viscosity of the polyaniline solution is very high and does not penetrate the entire surface of the oxide film that has been finely expanded, and as a result, the capacity appearance rate (actually compared to the design value) There is a drawback that only capacitors with a remarkably small capacitance value can be manufactured. In contrast to this method, there is also a method of polymerizing an aniline monomer on an oxide film to form polyaniline, but even in this case, although the capacity appearance rate is satisfactory, polyaniline itself has a lower conductivity than polypyrrole, The obtained capacitor has the disadvantage that the characteristics in the high frequency region are inferior to those using polypyrrole.

Furthermore, the adhesion between the dielectric oxide film and the polyaniline may be insufficient. In order to solve this, an aromatic polyamic acid, a soluble aromatic polyimide, a polyalkylene glycol, a polymer of a vinyl compound, etc. are added and mixed in a range of 1 to 25% by weight with respect to the soluble polyaniline. Has been proposed. However, the solid electrolytic capacitor obtained by this method exhibits excellent performance in terms of capacity achievement rate, dielectric loss (tan δ), high frequency impedance, etc., but has a large leakage current and sufficient characteristics as a solid electrolytic capacitor. It was hard to say.
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a solid electrolytic capacitor that has simple characteristics and high productivity, and has good characteristics as a capacitor, and a method for manufacturing the same.

The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor having a metal body made of a valve metal, a dielectric oxide film formed on the surface of the metal body, and a solid electrolyte layer adjacent to the dielectric oxide film. ,
The solid electrolyte layer includes a first conductive polymer layer formed by electrolytic polymerization or chemical oxidation polymerization of a precursor monomer of a conductive polymer on the surface of the dielectric oxide film, and the first conductive polymer. And a second conductive polymer layer formed by applying a conductive polymer-containing coating on the layer.
In the solid electrolytic capacitor of the present invention, the conductive polymer-containing paint preferably includes a polymer resin compound and a π-conjugated conductive polymer.
When the conductive polymer-containing paint includes a polymer resin compound, the polymer resin compound is preferably a copolymer of a compound having a cyano group and a compound having a vinyl group.
Alternatively, in the solid electrolyte capacitor of the present invention, the conductive polymer-containing paint preferably includes a polyanion and a π-conjugated conductive polymer.
When the conductive polymer-containing paint contains a polyanion, the polyanion is substituted or unsubstituted polyalkylene, substituted or unsubstituted polyalkenylene, substituted or unsubstituted polyimide, substituted or unsubstituted polyamide, substituted or unsubstituted The polymer having at least one of the polyesters and comprising a structural unit having an anionic group and a structural unit not having an anionic group, wherein the number of structural units having an anionic group is m and having an anionic group It is preferable that m / n ≦ 1 is satisfied, where n is the number of structural units that are not present.
Further, the polyanion may have a main chain and an anion group, and further have an ester group between the main chain and the anion group.
In that case, the anion group and the ester group may be bonded via a substituted or unsubstituted alkylene or a substituted or unsubstituted aromatic ring.

The method for producing a solid electrolytic capacitor of the present invention includes a step of oxidizing a surface of a metal body made of a valve action metal to form a dielectric oxide film,
A conductive polymer precursor monomer is electrolytically polymerized or chemically oxidatively polymerized on the surface of the dielectric oxide film to form a first conductive polymer layer, and on the surface of the first conductive polymer layer. And a step of applying a conductive polymer-containing paint and drying to form a second conductive polymer layer and providing a solid electrolyte layer.

  According to the solid electrolytic capacitor and the manufacturing method thereof of the present invention, the manufacturing can be simplified, the productivity is high, and the characteristics as a capacitor are improved.

Hereinafter, embodiments of the solid electrolytic capacitor and the manufacturing method thereof according to the present invention will be described.
FIG. 1 is a diagram showing the configuration of the solid electrolytic capacitor of this embodiment. The solid electrolytic capacitor 1 includes a metal body 11 made of a valve metal, a dielectric oxide film 12 formed on the surface of the metal body 11, a solid electrolyte layer 13 formed on the dielectric oxide film 12, a solid electrolyte The cathode layer 14 formed on the electrolyte layer 13, the anode lead 15 and the cathode lead 16 that are external connection terminals, and a lead rod 17 that connects the anode lead 15 and the metal body 11 are schematically configured. Yes. Further, portions other than the tips of the anode lead 15 and the cathode lead 16 (the portions may be referred to as capacitor elements) are covered with a coating material 18 such as an epoxy resin.

Examples of the valve action metal forming the metal body 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Of these, aluminum used as a capacitor anode is aluminum. Tantalum and niobium are preferred.
Moreover, as shown in FIG. 2, the metal body 11 has unevenness on the surface. By forming irregularities on the surface of the metal body 11, the surface area is increased and the capacitance of the capacitor can be increased. Examples of the method for forming irregularities on the surface include a method of performing a roughening treatment and a method of using a sintered body of metal powder as a metal body.

  The dielectric oxide film 12 is formed, for example, by anodizing the surface of the metal body 11 in an electrolytic solution such as an ammonium adipate aqueous solution. Therefore, as shown in FIG. 2, the dielectric oxide film 12 has unevenness on the surface.

As shown in FIG. 2, the solid electrolyte layer 13 is divided into a first conductive polymer layer 13a and a second conductive polymer layer 13b.
Here, the first conductive polymer layer 13a is a layer made of a conductive polymer formed on the surface of the dielectric oxide film 12 by electrolytic polymerization or chemical oxidation polymerization of a precursor monomer of the conductive polymer. It is. As the conductive polymer, conductive polymers such as polypyrrole, polythiophene, polyethylenedioxythiophene, polyaniline, polyphenylene, polyfuran, polythiazyl, polyphenylene vinylene, polyacetylene, polyazulene are preferable, and among them, polypyrrole, polythiophene, polyethylene are preferable from the viewpoint of stability. Dioxythiophene, polyaniline, and derivatives thereof are preferred. In particular, poly (3,4-ethylenedioxythiophene) is more preferable because of its high conductivity and high capacitance. In addition, the precursor monomer of a conductive polymer is a monomer that becomes the conductive polymer by polymerization.
The first conductive polymer layer 13 a formed by electrolytic polymerization or chemical oxidative polymerization has a thin layer thickness, and the surface thereof has irregularities formed along the irregularities of the dielectric oxide film 12.

  In the case of forming the first conductive polymer layer 13a by electrolytic polymerization, it is necessary to form a conductive precoat layer on the surface of the dielectric oxide film 12. As the precoat layer, a thin film of manganese dioxide or the like is used. In addition, this precoat layer shall be contained in the 1st conductive polymer layer 13a.

The second conductive polymer layer 13b is a coating film formed by applying a conductive polymer-containing paint on the first conductive polymer layer 13a.
The conductive polymer-containing paint preferably contains a polymer resin compound or polyanion and a π-conjugated conductive polymer because it is easily solubilized in a solvent.
As the polymer resin compound, a copolymer of a compound having a cyano group and a compound having a vinyl group is particularly preferable because a π-conjugated conductive polymer can be solubilized. Furthermore, acrylonitrile and / or methacrylonitrile is preferable as the compound having a cyano group. Examples of the compound having a vinyl group include halogenated vinyl compounds, aromatic vinyl and / or derivatives thereof, heterocyclic vinyl compounds and / or derivatives thereof, aliphatic vinyl compounds and / or derivatives thereof, acrylic compounds, diene compounds, At least one selected from maleimide compounds is preferred.

  The polyanion has at least one of a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, a substituted or unsubstituted polyester, and an anion It is a polymer composed of a structural unit having a group and a structural unit having no anionic group.

  The polyalkylene constituting the polyanion is a polymer whose main chain is composed of repeating methylenes. Examples of polyalkenylene include a polymer composed of a constitutional unit containing one vinyl group in the main chain, and there is an interaction between an unsaturated bond and a π-conjugated conductive polymer, and a substituted or unsubstituted polymer. Since it is easy to synthesize using butadiene as a starting material, substituted or unsubstituted butenylene can be exemplified. Examples of polyimide include pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, 2,2,3,3-tetracarboxydiphenyl ether dianhydride, 2,2- [4,4 Examples include polyimides from acid anhydrides such as' -di (dicarboxyphenyloxy) phenyl] propane dianhydride and diamines such as oxydianiline, paraphenylenediamine, metaphenylenediamine, and benzophenonediamine. Examples of the polyamide include polyamide 6, polyamide 6,6, polyamide 6,10 and the like. Examples of the polyester include polyethylene terephthalate and polybutylene terephthalate.

  Examples of the substituent that the polymer constituting the polyanion has include an alkyl group, a hydroxy group, a carboxyl group, a cyano group, a phenyl group, a phenol group, an ester group, an alkoxy group, and a carbonyl group. Alkyl groups have excellent solubility and dispersibility in polar or nonpolar solvents, compatibility and dispersibility in organic resins, etc., and hydroxy groups easily form hydrogen bonds with other hydrogen atoms. It has excellent solubility in organic solvents, compatibility with organic resins, dispersibility, and adhesiveness. Moreover, the cyano group and the hydroxyphenyl group are excellent in compatibility and solubility in polar resins, and are excellent in heat resistance. Among the above substituents, an alkyl group, a hydroxy group, an ester group, and a cyano group are preferable.

Examples of the alkyl group include alkyl groups such as methyl, ethyl, propyl, butyl, isobutyl, t-butyl, pentyl, hexyl, octyl, decyl, and dodecyl, and cycloalkyl groups such as cyclopropyl, cyclopentyl, and cyclohexyl. In consideration of solubility in an organic solvent, dispersibility in a resin, steric hindrance, and the like, an alkyl group having 1 to 12 carbon atoms is more preferable.
Examples of the hydroxy group include a hydroxy group directly bonded to the main chain of the polyanion, a hydroxy group bonded to the terminal of the alkyl group having 1 to 7 carbon atoms bonded to the main chain of the polyanion, and 2 to 2 carbon atoms bonded to the main chain of the polyanion. And a hydroxy group bonded to the terminal of 7 alkenyl groups. Among these, a hydroxy group bonded to the terminal of an alkyl group having 1 to 6 carbon atoms bonded to the main chain is more preferable from the viewpoint of compatibility with a resin and solubility in an organic solvent.

  Examples of the ester group include an alkyl ester group directly bonded to the main chain of the polyanion, an aromatic ester group, and an alkyl ester group or an aromatic ester group having another functional group interposed therebetween.

  The cyano group includes a cyano group directly bonded to the main chain of the polyanion, a cyano group bonded to the terminal of the alkyl group having 1 to 7 carbon atoms bonded to the main chain of the polyanion, and 2 to 2 carbon atoms bonded to the main chain of the polyanion. And a cyano group bonded to the terminal of 7 alkenyl group.

  As the anion group of the polyanion, any functional group capable of causing chemical oxidation doping to the π-conjugated conductive polymer can be used. From the viewpoint of ease of production and stability, a monosubstituted sulfate group, a monosubstituted phosphate group, a carboxylic acid group, a sulfonic acid group, and the like are preferable. Furthermore, from the viewpoint of the doping effect of the functional group on the π-conjugated conductive polymer, a sulfonic acid group and a monosubstituted sulfate group are more preferable.

In general, in the doping of an anionic dopant into a π-conjugated conductive polymer, 1 mol of an anionic group is doped with respect to 3 to 4 mol of a π-conjugated conductive polymer monomer. In the polyanion according to the present invention, the number (m) of structural units having an anion group (hereinafter referred to as unit A) and the number (n) of contained structural units having no anionic group (hereinafter referred to as unit B). By appropriately adjusting the ratio m / n and the ratio of the π-conjugated conductive polymer and the polyanion, 1 mol of an anion group can be formed with respect to 3 to 4 mol of the π-conjugated conductive polymer monomer.
Further, there is a method in which the number of moles of anion groups contained in the polyanion is set to a number less than the number of moles necessary for doping, and an anion other than the polyanion is added for the shortage. By this method, it is possible to reduce residual ions and to control heat deterioration resistance and conductivity due to the dopant. Furthermore, the properties such as solvent solubility, dispersibility, and resin compatibility of the conductive polymer-containing coating are improved by appropriately selecting the type of anion other than the polyanion.

In the polyanion according to the present invention, the ratio of unit A to unit B is preferably 1 or less (m / n ≦ 1), more preferably less than 1, and 0.2 to 0.7. It is particularly preferred. By setting such a ratio, the unit A is widely dispersed in the polyanion, the anion distribution is expanded, and the main chain of the π-conjugated conductive polymer can be extended along the polyanion main chain. Further, the anion group in the polyanion can be effectively used for doping, and surplus residual ions can be greatly reduced.
When the number of anions increases beyond this range, the anion groups in the polyanion are too close to each other, leaving an anion group in a state where it is hindered by nearby anion groups and does not capture the π-conjugated conductive polymer. As a result, since the coating film obtained by applying and drying the π-conjugated conductive polymer becomes weak to water, humidity dependency tends to occur.

The degree of polymerization of such a polyanion is not particularly limited, but from the viewpoint of solubility in an organic solvent, the number average degree of polymerization is preferably 10 to 1,000.
The polyanion can be obtained by oxidative polymerization of the polymerizable monomer for unit A and the polymerizable monomer for unit B in the presence of an oxidizing agent or / and a polymerization catalyst.

  Examples of the polymerizable monomer for unit B include substituted or unsubstituted ethylene compounds, substituted or unsubstituted acrylic acid compounds, substituted or unsubstituted vinyl aromatic compounds, substituted or unsubstituted vinylamines as polyalkylene monomers. A substituted or unsubstituted acrylamide compound, a substituted or unsubstituted arbitrary substituted vinyl heterocyclic compound, a substituted or unsubstituted vinylphenol compound, and the like. Arbitrary substituted divir benzene compounds, arbitrary substituted silyl styrenes, arbitrary substituted phenol compounds, etc. are mentioned.

The polyanion may have a main chain and an anion group, and may further have an ester group between the main chain and the anion group. That is, the anion group may be bonded to the side chain. As described above, the polyanion in which the anion group is bonded to the side chain can easily dissolve the π-conjugated conductive polymer with a solvent.
The anion group and ester group in this polyanion may be bonded via another functional group. Other functional groups are preferably substituted or unsubstituted alkylene, substituted or unsubstituted alkenylene, substituted or unsubstituted aromatic ring, and substituted or unsubstituted heterocycle. When an anionic group is bonded to the side chain, it produces a doping effect with the π-conjugated conductive polymer, so the conductive properties of the resulting conductive polymer layer depend on the size, length, polarity, etc. of the side chain. This greatly affects the heat resistance and compatibility characteristics. Therefore, the other functional group is more preferably an optionally substituted alkylene having 1 to 9 carbon atoms, an optionally substituted alkenylene having 2 to 9 carbon atoms, 1 to 3 aromatic rings, and 1 to 3 heterocycles.
The ester group is preferably chemically bonded directly to the main chain, but another functional group may be interposed between the main chain and the ester group. Other functional groups are preferably substituted or unsubstituted alkylene, substituted or unsubstituted aromatic rings, and substituted or unsubstituted alkenylene.

Such polyanions include a method for anionizing a polymer compound containing an ester group or a carboxylic acid group compound in the side chain, a method for transesterifying the polymer compound, and a polymerizable monomer containing an ester group and an anion group. It can be obtained by a method of polymerizing.
Anionization treatment for anionizing a polymer compound containing an ester group and a carboxylic acid group compound in the side chain includes, for example, a method of introducing an anion group by transesterification using a compound having an anion group, fuming Examples thereof include a method of introducing a sulfonic acid group with sulfuric acid or concentrated sulfuric acid, a method of introducing a phosphoric acid group with phosphoric acid, and a method of introducing a sulfonic acid group with a sulfone compound.
Examples of the method of transesterification include transesterification of polyacrylate, polymethacrylate or a copolymer thereof with an anion group-containing hydroxy compound.
Examples of a method for polymerizing a polymerizable monomer containing an ester group and an anion group include a method in which a polymerizable monomer is appropriately dissolved or dispersed in a solvent and polymerized in the presence of an oxidizing agent and / or an oxidation polymerization catalyst. Can be mentioned.

Specifically, the π-conjugated conductive polymer contained in the conductive polymer-containing coating material comprises at least one selected from polypyrroles, polythiophenes, and polyanilines.
The π-conjugated conductive polymer can obtain sufficient compatibility and dispersibility with other additive components such as organic resin components even without being substituted, but it is an alkyl group effective for dispersion or dissolution in organic resin components and solvents. It is more preferable to introduce a functional group such as a carboxy group, a sulfonic acid group, an alkoxy group, or a hydroxy group into the π-conjugated conductive polymer.

  Specific examples of the π-conjugated conductive polymer include polypyrrole, poly (3-methylpyrrole), poly (3-butylpyrrole), poly (3-octylpyrrole), poly (3-decylpyrrole), poly (3, 4-dimethylpyrrole), poly (3,4-dibutylpyrrole), poly (3-hydroxypyrrole), poly (3-methyl-4-hydroxypyrrole), poly (3-methoxypyrrole), poly (3-ethoxypyrrole) ), Poly (3-octoxypyrrole), poly (3-carboxylpyrrole), poly (3-methyl-4-carboxylpyrrole), polythiophene, poly (3-methylthiophene), poly (3-butylthiophene), poly (3-octylthiophene), poly (3-decylthiophene), poly (3-dodecylthiophene), poly (3-methoxy Thiophene), poly (3-ethoxythiophene), poly (3-octoxythiophene), poly (3-carboxylthiophene), poly (3-methyl-4-carboxylthiophene), poly (3,4-ethylenedioxythiophene) ), Polyaniline, poly (2-methylaniline), poly (2-octylaniline), poly (2-isobutylaniline), poly (3-isobutylaniline), poly (2-anilinesulfonic acid), poly (3-aniline) Sulfonic acid) and the like.

The conductive polymer-containing coating is formed by dissolving solid components such as the above-described polymer resin compound or polyanion or π-conjugated conductive polymer in water or an organic solvent. Is preferred. Since the surface tension is small if the solvent is an organic solvent, the conductive polymer-containing paint can be sufficiently permeated into the recesses on the surface of the dielectric oxide film.
Examples of the organic solvent include methanol, ethanol, propylene carbonate, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, cyclohexanone, acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene and the like.

As a method for producing the above-mentioned conductive polymer-containing coating, a solid electrolyte capacitor having better characteristics can be obtained. Therefore, a precursor of a π-conjugated conductive polymer dispersed or dissolved in a solvent in the presence of a polyanion. A method having a step of chemically oxidatively polymerizing the monomer and a step of removing free ions by ultrafiltration after the chemical oxidative polymerization is preferable.
Further, in the preferable method for producing a coating material containing a conductive polymer, a proton-containing solution is added during or after the step of removing free ions, and the free ions are removed by ultrafiltration, thereby converting the ions to cations. It may be exchanged.

  Further, in the method for producing a conductive polymer-containing paint, the chemical oxidative polymerization step includes a step of preparing a polyanion, a step of preparing a precursor monomer of a π-conjugated conductive polymer, a polyanion and a π-conjugated conductive high Mixing and reacting precursor monomers of the molecule. The operation method and reaction conditions are not particularly limited as long as a mixed liquid of a polyanion and a π-conjugated conductive polymer can be prepared.

In the removal of free ions, a solution is circulated on an ultrafiltration membrane formed on a porous material with a constant diameter (hereinafter, the circulated solution is referred to as a circulating solution), and the ultrafiltration membrane is The solution is also brought into contact with the opposite side (hereinafter, the solution is referred to as a permeation solution). At this time, the pressure of the circulating solution is increased, but a part of the circulating solution moves to the permeate solution side to relieve the pressure of the circulating solution. Thus, a part of circulating solution moves to the permeate solution side, and a part of particles, ions, etc. in the circulating solution moves to the permeate solution side, so that free ions can be removed. This method is a dilution method, and impurities can be easily removed by increasing the number of dilutions.
Here, the ultrafiltration membrane to be used can be appropriately selected within the range of the molecular weight cutoff of 1,000 to 100,000 depending on the particle diameter of the particles to be removed and the ionic species.

The surface of the second conductive polymer layer 13b formed by application of such a conductive polymer-containing paint is smooth without following the irregularities of the first conductive polymer layer 13a. Therefore, the contact area with the cathode layer 14 provided on the second conductive polymer layer 13b can be increased, and the characteristics as a capacitor can be improved.
Further, since the soft second conductive polymer layer 13b is formed between the first conductive polymer layer 13a and the cathode layer 14, their contact resistance can be reduced, and the equivalent series resistance can be reduced. Can be reduced.

  The thickness of the first conductive polymer layer is 1 to 99 μm, and the thickness of the second conductive polymer layer is 1 to 99 μm. If it is less than 1 μm, the breakdown voltage is hardly improved. If it exceeds 100 μm, the breakdown voltage is improved, but the equivalent series resistance (ESR) becomes very large, resulting in inconvenience. Therefore, when the thickness of the first and second conductive polymer layers is 1 to 99 μm, good characteristics can be obtained without impairing the productivity of the solid electrolyte layer.

  The cathode layer 14 is a layer of a conductive material. In this embodiment, the cathode layer 14 includes a silver paste layer 14b made of a silver paste having a conductive carbon layer 14a containing conductive carbon such as carbon nanotubes provided on the surface. The conductive carbon layer 14 a is in contact with the solid electrolyte layer 13.

In order to manufacture the above-described solid electrolytic capacitor, first, a dielectric oxide film is formed by anodizing the surface of a metal body made of a valve metal and attached with a lead bar in an electrolytic solution.
Next, a conductive polymer precursor monomer is supplied onto the surface of the dielectric oxide film, and the monomer is electrolytically polymerized or chemically oxidized to form a first conductive polymer layer. In the case of electrolytic polymerization, a precoat layer is previously formed on the surface of the dielectric oxide film. Subsequently, a conductive polymer-containing paint is applied on the surface of the first conductive polymer layer, and dried to remove the solvent in the conductive polymer-containing paint to form a second conductive polymer layer. To do. Examples of the method for applying the conductive polymer-containing paint include a dipping method and a spray coating method. In this way, a solid electrolyte layer composed of the first conductive polymer layer and the second conductive polymer layer is provided.
Next, a solution containing conductive carbon such as carbon nanotubes is applied onto the solid electrolyte layer and dried to form a conductive carbon layer. A silver paste is applied onto the conductive carbon layer and dried to obtain a silver paste. Form a layer.
Next, an anode lead is provided on the lead bar, and a cathode lead is provided on the silver paste layer. The anode lead and the cathode lead can be provided by welding a lead wire, applying a conductive paste, or wiring by drying.
Finally, a portion other than the tips of the anode lead and the cathode lead is covered with a resin component such as an epoxy resin so that the tips of the anode lead and the cathode lead are exposed to obtain a solid electrolytic capacitor.

  In the embodiment described above, a first conductive polymer layer is formed by electrolytic polymerization or chemical oxidization polymerization on a dielectric oxide film having irregularities formed on the surface, and this first conductive polymer layer is formed. A second conductive polymer layer is formed by applying and drying a conductive polymer-containing paint on top. Since the formation of the coating film by application is a simple method, in this embodiment, the formation process of the solid electrolyte layer having a film thickness can be simplified, and the productivity of the solid electrolytic capacitor is improved. Further, in electropolymerization or chemical oxidative polymerization, the conductive polymer penetrates into the recess, so that the contact area between the dielectric oxide film and the solid electrolyte layer is increased, and the characteristics of the solid electrolytic capacitor are improved.

  The present invention is not limited to the above-described embodiment example. For example, as a solid electrolytic capacitor, as shown in FIG. 3, an anode foil 22 made of an aluminum foil having a dielectric oxide film 21 formed on the surface by roughening the surface by etching and then anodizing, and etching It may be a solid electrolytic capacitor 2 that has a cathode foil 23 made of an aluminum foil that has not been wound, and is wound with a nonwoven fabric separator 24 interposed therebetween. In this solid electrolytic capacitor, a solid electrolyte layer 25 is formed between the dielectric oxide film 21 of the anode foil 22 and the cathode foil 22. The solid electrolyte layer 25 includes a first conductive polymer layer formed on the surface of the dielectric oxide film 21 by electrolytic polymerization or chemical oxidation polymerization of a precursor monomer of the conductive polymer, and the first conductive layer. And a second conductive polymer layer formed by applying a conductive polymer-containing paint on the polymer layer. Therefore, the productivity is high and the characteristics as a capacitor are excellent.

Next, examples of the present invention and comparative examples will be described.
(Experimental Example 1) Formation of Conductive Polymer Layer by Electropolymerization of Pyrrole A metal body made of tantalum was anodized at a constant voltage at an electrolytic oxidation voltage of 20 V in a 5 mass% ammonium adipate aqueous solution, and a dielectric was formed on the surface thereof A tantalum oxide film as a body oxide film was formed. Next, an oxide film of manganese dioxide was formed on the tantalum oxide film to form a precoat layer. Next, a 10% by mass isopropylene alcohol aqueous solution containing 1 mol / l of pyrrole and 2% by mass of sodium arylsulfonate as an electrolyte is supplied to the entire surface of the precoat layer, and a voltage of 10V is applied for 5 minutes using the precoat layer as a positive electrode. The conductive polymer layer was formed by applying and electrolytic polymerization of pyrrole.

(Experimental example 2) Formation of a conductive polymer layer by chemical oxidative polymerization of 3,4-ethylenedioxythiophene A metal body, which is a tantalum sintered body, is electrolytically oxidized in an aqueous solution of ammonium adipate to form a dielectric on the surface. Tantalum oxide, which is a body oxide film, was formed. Next, the metal body on which the tantalum oxide film was formed was immersed in a solution in which 3,4-ethylenedioxythiophene and ferric paratoluenesulfonate were dissolved in butanol. Thereafter, heating and drying were performed, and 3,4-ethylenedioxythiophene was chemically oxidatively polymerized to form a conductive polymer layer made of poly (3,4-ethylenedioxythiophene) on the tantalum oxide film.

(Experimental example 3) Formation of conductive polymer layer by application of polyaniline solution An aqueous hydrochloric acid solution of ammonium persulfate cooled to 1 ° C and an aqueous hydrochloric acid solution of aniline were mixed at an ice water temperature. After mixing for about 1 hour, the mixture was filtered and the precipitate was thoroughly washed with an aqueous hydrochloric acid solution. After neutralization by adding aqueous ammonia to the precipitate, the precipitate was taken out and a hydrazine-methanol solution was added. Subsequently, the product chemically reduced by stirring in a ball mill was filtered, thoroughly washed with water, and then vacuum-dried to obtain a polyaniline powder. The polyaniline powder was dissolved in N-methyl-2-pyrrolidone to prepare a polyaniline solution.
An element obtained by superimposing anodized aluminum foil, separator paper, and cathode foil on the surface of the anodized foil, separator paper, and cathode foil is immersed in the polyaniline solution and dried to evaporate the solvent. A layer made of polyaniline was formed. Since the layer formed from polyaniline is a semiconductor as it is, it was immersed in a solution containing a protonic acid or a solution containing a dopant such as BF ₄ ions to form a conductor.

(Experimental Example 4) Preparation of Conductive Polymer-Containing Paint 1 20 g of acetonitrile, 10 g of styrene sulfonic acid and 20 g of methyl methacrylate were dissolved in 500 ml of toluene, and 2.5 g of benzoyl peroxide was added as a polymerization initiator at 60 ° C. Polymerized for 8 hours. Subsequently, the polymer produced | generated by superposition | polymerization was wash | cleaned with methanol, the deposit was filtered, and the polymer resin compound was obtained with the powder state.
Further, 10 g of the polymer resin compound and 7 g of anthraquinonesulfonic acid were dissolved in 90 g of acetonitrile and methanol (7: 3), 4 g of pyrrole was added, and the mixture was stirred at room temperature to prepare a monomer solution. Next, an oxidant solution prepared by dissolving 7 g of ferric chloride in acetonitrile and 60 ml of methanol (7: 3) was added to the monomer solution while maintaining the temperature at 0 ° C., and stirring was continued for 1 hour to polymerize pyrrole. After completion of the reaction, 500 ml of methanol is added to precipitate the product, the precipitate is filtered, washed with methanol and pure water until the filtrate becomes transparent, and powdered soluble π-conjugated conductive high I got a molecule. A soluble π-conjugated conductive polymer of this powder was dissolved in N-methyl-2-pyrrolidone to obtain a conductive polymer-containing coating material 1.

(Experimental example 5) Preparation of conductive polymer-containing coating material 2 (synthesis of polyanion)
In a mixed solvent of water (80 ml) and methanol (20 ml), 17 g (0.1 mol) of sodium isoprene sulfonate (trade name: IPS, manufactured by JSR) and 6.8 g (0.1 mol) of isoprene (Tokyo Chemical Industry) The product was added with a mixed oxidant solution of 0.228 g (0.001 mol) ammonium persulfate and 0.04 g (0.0001 mol) ferric sulfate previously dissolved in 10 ml of water while stirring at room temperature. Added dropwise for minutes.
The mixed solution was stirred at room temperature for 3 hours and further heated for 1 hour while refluxing, and then the solvent was removed under reduced pressure to obtain a pale yellow solid.
From the IR absorption spectrum, ESCA analysis, and GPC analysis of the obtained compound, this compound is a copolymer comprising isoprene sulfonic acid soda units and isoprene units in a ratio of 1: 1, and has a molecular weight of about 20 , Polyanion was confirmed. Therefore, this light yellow solid was used as a polyanion.

(Synthesis of paint containing conductive polymer)
6.80 g (0.1 mol) of pyrrole and 11.85 g (0.05 mol) of a polyanion were dissolved in 300 ml of water, and 2 g of a 10% by mass sulfuric acid solution was added to this solution and cooled to 0 ° C.
While maintaining this solution at 0 ° C., with stirring, 22.80 g (0.1 mol) of ammonium persulfate dissolved in 100 ml of water and 8.0 g (0.02 mol) of ferric sulfate oxidation catalyst solution were slowly added. Stir for 3 hours.
100 ml of ethanol was added to the resulting reaction solution, and the precipitate was filtered under reduced pressure to obtain a black-blue solid.
The obtained black-blue solid was uniformly dispersed in 200 ml of water, 100 ml of ethanol was added, and the precipitate was filtered under reduced pressure to wash the black-blue solid. The washing operation was performed three times to remove residual ions in the solid, and a soluble π-conjugated conductive polymer that was a black-blue solid containing polypyrrole and polyanion was obtained.
The obtained solid was dissolved in N-methyl-2-pyrrolidone to obtain a conductive polymer-containing coating material 2.

(Experimental example 6) Preparation of conductive polymer-containing paint 3 (synthesis of polyanion)
43.4 g of sodium ethyl sulfonate (trade name: Antox, manufactured by Nippon Emulsifier Co., Ltd.) was added to ion-exchanged water (100 ml), and the mixture was kept at 80 ° C. while stirring and dissolved in 10 ml of ion-exchanged water in advance. A complex oxidation solution of 0.114 g ammonium persulfate and 0.04 g ferric sulfate was added, and the mixture was stirred for 3 hours while maintaining at 80 ° C.
After completion of the reaction, the reaction solution was cooled to room temperature, 1000 ml of ion exchange water was added thereto, and then 30 g of 50% by mass sulfuric acid aqueous solution was added, and then the solution was concentrated to 300 ml. This operation was repeated 4 times.
Furthermore, the operation of adding 2000 ml of ion-exchanged water and concentrating to 300 ml was repeated until the permeated solution became neutral, and the concentrated solution was dried in an oven to obtain polyethyl methacrylatesulfonic acid.

(Synthesis of paint containing conductive polymer)
6.80 g (0.1 mol) of pyrrole and 2.91 g (0.015 mol) of polyanion were dissolved in 300 ml of ion exchange water, and this mixed solution was kept at 0 ° C. and dissolved in 100 ml of ion exchange water while stirring. After slowly adding 2.85 g (0.0125 mol) of ammonium persulfate and 0.1 g of ferric sulfate oxidation polymerization catalyst solution, the mixture was stirred for 3 hours.
2000 ml of ion-exchanged water was added to the resulting reaction solution, 20 g of 10% aqueous sulfuric acid solution was added, and the solution was concentrated to 300 g by ultrafiltration. This operation was repeated four more times to perform proton exchange. Furthermore, 3000 ml of ion-exchanged water was added to the ion-exchanged concentrated solution, and the solution was concentrated to 300 ml by ultrafiltration. This operation was repeated until the permeated solution became neutral, and the precipitate was filtered under reduced pressure to obtain a soluble π-conjugated conductive polymer that was a black-blue solid containing polypyrrole and polyanion.
The obtained solid was dissolved in N-methyl-2-pyrrolidone to obtain a conductive polymer-containing coating.

(Example 1)
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 1, the conductive polymer-containing coating material 1 prepared in Experimental Example 4 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

(Example 2)
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 2, the conductive polymer-containing coating material 1 prepared in Experimental Example 4 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

(Example 3)
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 1, the conductive polymer-containing coating material 2 prepared in Experimental Example 5 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

Example 4
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 2, the conductive polymer-containing paint 2 prepared in Experimental Example 5 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

(Example 5)
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 1, the conductive polymer-containing coating material 3 prepared in Experimental Example 6 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

(Example 6)
On the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 2, the conductive polymer-containing coating material 3 prepared in Experimental Example 6 is applied, heated, dried, and dried. Two conductive polymer layers were formed.

(Comparative Example 1)
A metal body, which is a tantalum sintered body, is electrolytically oxidized in an aqueous solution of ammonium adipate to form a dielectric oxide film on the surface, and the conductive polymer containing the conductive polymer prepared in Experimental Example 4 is formed on the surface of the dielectric oxide film. The paint 1 was applied, heated and dried to form a conductive polymer layer.

(Comparative Example 2)
The same procedure as in Comparative Example 1 was conducted except that the conductive polymer-containing coating 2 prepared in Experimental Example 5 was used instead of the conductive polymer-containing coating 1.

(Comparative Example 3)
The same procedure as in Comparative Example 1 was conducted except that the conductive polymer-containing coating 3 prepared in Experimental Example 6 was used instead of the conductive polymer-containing coating 1.

(Comparative Example 4)
Similar to the formation of the first conductive polymer layer on the surface of the first conductive polymer layer formed in Experimental Example 1, the operation of electrolytic oxidation polymerization is repeated to form the second conductive polymer layer. A layer was formed.

(Comparative Example 5)
Similar to the formation of the first conductive polymer layer on the surface of the first conductive polymer layer formed in Experimental Example 2, the operation of chemical oxidative polymerization is repeated to form the second conductive polymer layer. A layer was formed.

(Comparative Example 6)
A conductive polymer-containing coating is applied on the surface of the conductive polymer layer (first conductive polymer layer) formed in Experimental Example 3 in the same manner as the formation of the first conductive polymer layer. And heated and dried to form a second conductive polymer layer.

(Evaluation example)
As described above, after forming a solid electrolyte layer composed of one or two conductive polymer layers, colloidal carbon is applied to the surface of the solid electrolyte layer, and a silver paste is further applied thereon, followed by heating. And dried to form a cathode. Next, an anode lead serving as an anode terminal was provided by welding, and a cathode lead serving as a cathode terminal was provided by applying a silver paste. Thereafter, the whole was molded with an epoxy resin and the capacitor element was sealed, and then a voltage of 20 V was applied and aged to obtain a solid electrolytic capacitor (rated voltage: 16 V × rated capacitance: 10 μF).
As initial characteristics of the obtained capacitor, electrostatic capacity at 120 Hz, dielectric loss (tan δ) at 120 Hz, and equivalent series resistance (ESR) at 100 kHz were measured. Further, the voltage was applied while increasing the voltage at 0.5 V / min, and the voltage at which the dielectric oxide film was destroyed was measured to obtain the breakdown voltage. These measurement results are shown in Table 1.

In Examples 1 to 6, the first conductive polymer layer is formed on the dielectric oxide film by electrolytic polymerization or chemical oxidative polymerization, and the conductive polymer-containing coating is applied on the first conductive polymer layer. Thus, the second conductive polymer layer was formed and the solid electrolyte layer was provided, so that the productivity was excellent. Moreover, as shown in Table 1, in Examples 1 to 6, the capacitance, dielectric loss and breakdown voltage were large and the equivalent series resistance was small, so that the characteristics as a capacitor were excellent.
On the other hand, in Comparative Examples 1-3 and 6, since the solid electrolyte layer was provided only by application of the conductive polymer-containing paint, the breakdown voltage was large, but the capacitance was small.
In Comparative Example 4, the solid electrolyte layer was provided only by electrolytic polymerization, and in Comparative Example 5 only by chemical oxidation polymerization. However, although it exhibited sufficient characteristics, the productivity was low.

In addition, in the characteristics of the evaluated capacitors, the capacitance depends on the conductivity of the conductive polymer, and Examples 2, 4, and 4 in which the conductive polymer is poly (3,4-ethylenedioxythiophene). 6 and Comparative Example 5 had large capacitance.
In addition, the equivalent series resistance depends on the resistance values of the solid electrolyte layer, the negative anode conductor, the negative anode terminal, and the dielectric oxide film, which are conductive paths for the capacitor charging / discharging current. As described in JP-A-2000-133551, by providing a soft intermediate layer made of a conductive polymer between the solid electrolyte layer and the cathode layer, the contact resistance can be reduced and the equivalent series resistance is reduced. Can be reduced. In Examples 1 to 6 and Comparative Examples 1 to 3, since the second conductive polymer layer served as a soft intermediate layer, their equivalent series resistance was small.
In addition, the breakdown voltage increases when the conductive polymer layer is formed by applying the conductive polymer-containing paint. Therefore, the breakdown voltage of Examples 1-6 and Comparative Examples 1-3, 6 was large.

1 is a cross-sectional view showing an embodiment of a solid electrolytic capacitor according to the present invention. It is a principal part enlarged view of the solid electrolytic capacitor shown in FIG. It is a perspective view which shows the other embodiment example of the solid electrolytic capacitor which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Solid electrolytic capacitor 11 Metal body 12 Dielectric oxide film 13 Solid electrolyte layer 13a 1st conductive polymer layer 13b 2nd conductive polymer layer

Claims (8)

In a solid electrolytic capacitor having a metal body made of a valve action metal, a dielectric oxide film formed on the surface of the metal body, and a solid electrolyte layer adjacent to the dielectric oxide film,
The solid electrolyte layer includes a first conductive polymer layer formed by electrolytic polymerization or chemical oxidation polymerization of a precursor monomer of a conductive polymer on the surface of the dielectric oxide film, and the first conductive polymer. A solid electrolytic capacitor comprising: a second conductive polymer layer formed by applying a conductive polymer-containing paint on the layer.   The solid electrolytic capacitor according to claim 1, wherein the conductive polymer-containing paint includes a polymer resin compound and a π-conjugated conductive polymer.   3. The solid electrolytic capacitor according to claim 2, wherein the polymer resin compound is a copolymer of a compound having a cyano group and a compound having a vinyl group.   The solid electrolytic capacitor according to claim 1, wherein the conductive polymer-containing paint contains a polyanion and a π-conjugated conductive polymer. The polyanion has at least one of a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, a substituted or unsubstituted polyester, and an anion A polymer composed of a structural unit having a group and a structural unit having no anionic group,
5. The condition of m / n ≦ 1 is satisfied, where m is the number of structural units having an anionic group and n is the number of structural units having no anionic group. Solid electrolytic capacitor.   6. The solid electrolytic capacitor according to claim 4, wherein the polyanion has a main chain and an anion group, and further has an ester group between the main chain and the anion group.   The solid electrolytic capacitor according to claim 6, wherein the anion group and the ester group are bonded via a substituted or unsubstituted alkylene or a substituted or unsubstituted aromatic ring. Forming a dielectric oxide film by oxidizing the surface of a metal body made of a valve metal;
A conductive polymer precursor monomer is electrolytically polymerized or chemically oxidatively polymerized on the surface of the dielectric oxide film to form a first conductive polymer layer, and on the surface of the first conductive polymer layer. And a step of forming a second conductive polymer layer by applying a conductive polymer-containing coating material and drying to form a solid electrolyte layer.

Images