JP2000150309A - Manufacture of solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve productivity when excellent capacitor characteristic is stably realized and a solid-state electrolytic capacitor capable of stably obtaining excellent characteristic is manufactured, in a solid-state electrolytic capacitor having solid electrolyte composed of conductive high-molecular compound formed by electrolytic oxidation polymerization. SOLUTION: This manufacturing method is provided with a process for forming an insulating oxide film by oxidizing an anode base body composed of metal, a process for forming a conductive base layer on the oxide film, and a process for forming a high-molecular electrolyte layer containing conductive high-molecular compound on the base layer by performing electrolytic oxidation polymerization while applying a centrifugal force. Preferably the insulating oxide film and the conductive base layer are formed on both surfaces of the anode base body, and the high-molecular electrolyte layer is formed on the surfaces of both the conductive base layers, while applying the centrifugal force in such a manner that the direction of the centrifugal force intersects rectangularly the surface of the anode base body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte.

[0002]

2. Description of the Related Art Electrolytic capacitors use a metal having an insulating oxide film forming ability, for example, a so-called valve metal such as aluminum or tantalum as an anode, and anodize the surface of the metal to form an insulating oxide film which becomes a dielectric layer. After the coating is formed, an electrolyte layer which functions substantially as a cathode is formed, and a conductive layer such as graphite or silver is provided as a cathode.

[0003] For example, an aluminum electrolytic capacitor has a porous aluminum foil whose specific surface area is enlarged by etching as an anode, and a separator paper impregnated with an electrolytic solution between an aluminum oxide layer formed on the surface of the anode and a cathode foil. Is provided.

[0004] Electrolytic capacitors that use an electrolytic solution for the electrolyte layer between the insulating oxide film and the cathode have problems such as leakage from the sealing portion and the lifetime determined by evaporation of the electrolytic solution. In contrast, solid electrolytic capacitors using solid electrolytes made of metal oxides and organic compounds
It is preferable because there is no such problem. Manganese dioxide is typical as a solid electrolyte composed of a metal oxide. On the other hand, examples of solid electrolytes composed of organic compounds include, for example, JP-A-52-79255 and JP-A-58-19.
A 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex salt described in No. 1414 has been studied.

[0005] In recent years, with the increase in the frequency of the power supply circuit of electronic equipment, there has been a demand for electrolytic capacitors to have corresponding characteristics. Above all, reduction of impedance is a major issue. However, the solid electrolytic capacitor using the above-mentioned electrolyte layer made of manganese dioxide or TCNQ complex has the following problems. Solid electrolyte layer made of manganese dioxide, generally but formed by repeating the thermal decomposition of manganese nitrate by heating during the pyrolysis and by oxidation of the NO _x gas generated during thermal decomposition, dielectric Since the insulating oxide film, which is the body, is damaged or deteriorated, various characteristics of the finally obtained solid electrolytic capacitor tend to be low, such as an increase in leakage current value. Further, when manganese dioxide is used as a solid electrolyte, the impedance becomes high in a high frequency range. On the other hand, TCNQ
The complex salt has a conductivity of about 1 S / cm and is not sufficiently satisfactory with respect to the current demand for lowering the impedance of electrolytic capacitors. It has also been pointed out that the TCNQ complex salt has poor adhesion to an insulating oxide film, and lacks thermal stability when fixed by soldering and thermal stability over time, leading to lower reliability. . Furthermore, TCN
There is also a problem that the Q complex salt is expensive.

[0006] In order to compensate for these drawbacks and obtain more excellent properties, a high conductivity having relatively low production cost, relatively good adhesion to an insulating oxide film, and excellent thermal stability. There has been proposed a solid electrolytic capacitor using the above polymer compound.

[0007] For example, Japanese Patent No. 2725553 describes a solid electrolytic capacitor in which polyaniline is formed by chemical oxidation polymerization on an oxide film on the surface of an anode.

In Japanese Patent Publication No. 8-31400,
In the chemical oxidation polymerization method, a high-strength conductive polymer film cannot be formed on the anodized film, and since the anodized film is an electrical insulator, the electrolytic polymerization method forms an electrolytic polymerized film on the anodized film. It is impossible or very difficult to form a thin film of metal or manganese dioxide on an oxide film, and then form a conductive polymer film, which is a solid electrolyte, by an electrolytic polymerization method. Has been described. In addition, Japanese Patent Publication No. 4-74853 discloses the above-mentioned Japanese Patent Publication No. 8-74853.
No. 31400 describes a solid electrolytic capacitor provided with a conductive polymer film formed by chemical oxidation polymerization instead of a manganese dioxide thin film. In both these publications,
As a conductive polymer to be used, polypyrrole, polythiophene, polyaniline, and polyfuran are mentioned.

[0009]

Problems to be Solved by the Invention
As described in Japanese Patent Publication No. 00, a conductive polymer film having high strength cannot be formed on the anodic oxide film by the chemical oxidation polymerization method. On the other hand, in the electrolytic oxidation polymerization method, the reaction control is easier and the synthesis time can be shortened as compared with the chemical oxidation polymerization method. However, Electrochemistry, Vol. 65, No. 6, p. 495, 1
In 997, the problem that the film quality of polyaniline formed by the electrolytic oxidation polymerization method was coarse and the density was low was described.

It is an object of the present invention to stably realize good capacitor characteristics in a solid electrolytic capacitor having a solid electrolyte made of a conductive polymer compound produced by electrolytic oxidation polymerization. Another object of the present invention is to improve productivity when manufacturing a solid electrolytic capacitor having good characteristics stably obtained.

[0011]

This and other objects are achieved by the present invention which is defined below as (1) to (5). (1) a step of oxidizing a metal anode substrate to form an insulating oxide film, a step of forming a conductive underlayer on the insulating oxide film, and performing electrolytic oxidation polymerization while applying a centrifugal force. Forming a polymer electrolyte layer containing a conductive polymer compound on the conductive underlayer. (2) The insulating oxide film and the conductive underlayer are formed on both surfaces of the anode substrate, and the centrifugal force is applied so that the direction of the centrifugal force is orthogonal to the surface of the anode substrate. The method for producing a solid electrolytic capacitor according to the above (1), wherein the polymer electrolyte layer is formed on the surface of the conductive underlayer. (3) The conductive polymer compound contained in the polymer electrolyte layer contains a substituted or unsubstituted π-conjugated heterocyclic compound, a cyclic or chain π-conjugated hydrocarbon compound, and a hetero atom. The method for producing a solid electrolytic capacitor according to the above (1) or (2), wherein at least one compound selected from cyclic or chain π-conjugated hydrocarbon compounds is used as a starting monomer. (4) The conductive underlayer contains a conductive polymer compound, and the conductive polymer compound is a substituted or unsubstituted π-conjugated heterocyclic compound, cyclic or chain π-conjugated compound. Any of the above (1) to (3), wherein at least one compound selected from a hydrocarbon compound and a cyclic or chain π-conjugated hydrocarbon compound containing a hetero atom is used as a starting monomer. Manufacturing method of solid electrolytic capacitor. (5) The method for producing a solid electrolytic capacitor according to any one of the above (1) to (4), wherein the anode substrate is made of a metal or an alloy containing at least one of Al, Ta, Ti, Nb and Zr.

[0012]

According to the present invention, a polymer containing a conductive polymer compound is formed by sequentially forming an insulating oxide film and a conductive base layer on the surface of the anode substrate and then performing electrolytic oxidation polymerization while applying a centrifugal force. An electrolyte layer is formed. The polymer electrolyte layer formed by performing electrolytic oxidation polymerization while applying centrifugal force has a dense film quality. For this reason, conductivity becomes high,
Environmental resistance and mechanical properties as well as electrochemical properties are improved.

FIG. 2 shows a configuration example of an apparatus for performing electrolytic oxidation polymerization while applying a centrifugal force. This apparatus uses a general centrifuge, and an electrolysis cell 3 is arranged in one of a pair of centrifuge tubes 2. The details of the electrolytic cell 3 are shown in FIG. In the electrolysis cell 3, a pair of electrodes A and B
And a reference electrode (silver-silver chloride wire) 4 are arranged,
The electrodes A and B are connected to an external DC power supply via the rotating shaft 5. In FIG. 3, the electrode A whose surface is vertically upward with respect to the centrifugal force is referred to as a reverse electrode A in this specification.
The electrode B whose surface is vertically downward with respect to the centrifugal force is referred to as a forward electrode B in this specification. Therefore, in the electrolytic oxidation polymerization under the application of centrifugal force, when the reverse electrode A is used as the working electrode, the centrifugal force is opposite to the direction in which the conductive polymer film grows by polymerization, and the forward electrode B acts. When the poles are used, the centrifugal force has the same direction.

By the way, the present inventors have found that in the electrolytic oxidation polymerization under the application of centrifugal force, the polymer formed when the reverse electrode A is used as the working electrode and when the forward electrode B is used as the working electrode is formed. It was found that there was a remarkable difference in the film quality and molecular structure of the electrolyte layer.

In the reverse electrode A, the polymerization reaction speed increases as the centrifugal force increases, while in the forward electrode B, the polymerization reaction speed decreases. In the initial stage of polymerization, oligomers with a low degree of polymerization are generated, which are separated from the electrode interface,
The mechanism of re-dissolving in the electrolyte works. Reverse electrode A
Then, this mechanism is suppressed by the action of centrifugal force,
On the other hand, since it is not suppressed by the forward electrode B, it is considered that a difference appears not only in the polymerization reaction rate but also in the chemical structure and various physical properties of the polymer film as described above. This is supported by the fact that, when the forward electrode B is used as the working electrode, the amount of oligomer increases in the UV absorption spectrum of the electrolytic solution after electrolysis.

The properties of the formed polymer electrolyte layer are very fine microscopically composed of fine agglomerates in the reverse electrode A, while the properties of the forward electrode B are
It becomes macroscopically dense, consisting of relatively large and substantially spherical massive particles, and all become extremely stable. In any case, the adhesion between the polymer electrolyte layer and the underlying conductive layer is extremely good.

In the measurement by IR spectrum, there is a difference in the polymer structure of the polymer electrolyte layer between the forward direction and the reverse direction. Here, the case where the polymer electrolyte is polyaniline will be described. In polyaniline, it is known that a linear polymer structure (1,4-) in which an aniline molecule is repeatedly bonded to the para position (position 4) of the aniline skeleton is dominant, but in an actual reaction, It is said that not only this structure is generated, but also other bonding structures.

In the backward electrode A and the forward electrode B,
Comparing the abundance ratio of the other structure with respect to the basic 1,4-bond structure, the polyaniline formed on the forward electrode B has a 1,2-bond structure (the ortho position at the 2-position) in the reverse direction. Decrease compared to that of. Also, 1, 2,
The abundance ratio of the 4-bond structure also decreases, and the abundance ratio of the 1,4-bond structure increases. On the other hand, the structural state of the polyaniline formed on the reverse electrode A is similar to that formed by electrolytic oxidation polymerization under ordinary conditions without applying a centrifugal force.

The above-mentioned Synthetic Metals (Synthetic Metals)
Metals), 41-43, 715, 1991, that polyaniline has three oxidation states;
It also describes that high conductivity appears depending on the oxidation state. The molecular structure supported here is 1,
It is a 4-bond structure, and it is assumed that this structure also contributes to conductivity, and other structures are not discussed. Therefore, it is considered that the conductivity becomes better when at least the proportion of the 1,4-bond structure is increased. This is very generally supported by the theory of conductivity of organic molecules based on the conjugation of the electron configuration.

The Abstracts of the 65th Annual Meeting of the Electrochemical Society of Japan, 1M09, page 361, were prepared while applying centrifugal force.
It has been reported that a polyaniline film was formed on a platinum electrode by electrolytic oxidation polymerization. Here, it is described that the polymerization rate of polyaniline is affected by the application of centrifugal force. Specifically, it is described that the polymerization speed increases as the centrifugal acceleration increases in the reverse electrode A in FIG. 2 described above, and the polymerization speed decreases as the centrifugal acceleration increases in the forward electrode B. . And from this result,
He states that the effect of centrifugal force on the electropolymerization reaction is anisotropic and has been shown to depend on the orientation of the working electrode surface to the centrifugal force. However, this report does not state that a polyaniline film formed while applying a centrifugal force is applied to a polymer electrolyte layer of a solid electrolytic capacitor. Is not listed.

Incidentally, in a solid electrolytic capacitor, it is necessary to form an insulating oxide film and an electrolyte layer on both surfaces of an anode substrate. Therefore, also in the present invention, an insulating oxide film, a conductive underlayer, and a polymer electrolyte layer are sequentially formed on both surfaces of the anode substrate. At this time, based on the description in the above summary of the 65th meeting, 1M09, page 361,
Only one side of the working electrode may be used. That is, first,
A polymer electrolyte layer is formed on the conductive underlayer on one side of the anode substrate. Next, the anode substrate is turned over, and a polymer electrolyte layer is formed on the conductive underlayer on the other surface. The electrode used in this method is preferably the reverse electrode A because a very dense film can be formed microscopically.
However, in such a method of treating one surface at a time, it is necessary to perform the electropolymerization reaction at least twice, so that the process is complicated, the workability is reduced, and the cost of the product is increased.

Therefore, in a preferred embodiment of the present invention, an anode substrate having an insulating oxide film and a conductive underlayer formed on both surfaces is used as a working electrode, and the working electrode is arranged so that its surface is orthogonal to the direction of centrifugal force. In this state, a polymer electrolyte layer is simultaneously formed on the conductive underlayers on both sides. FIG. 1 shows a configuration example of an electrolytic cell used in this method. In FIG. 1, the upper electrode of the pair of electrodes is used as a working electrode, and both surfaces of the working electrode are in contact with the electrolyte 6. In the present specification, the relationship with respect to the direction of the centrifugal force is the reverse
Referred to as the reverse surface S _A working electrode surface has the same as,
The working electrode surface has the same as the forward electrode B in FIG. 3 is referred to as a forward surface S _B. Using this electrolytic cell, when the electrolytic oxidation polymerization while applying a centrifugal force to the downward in the figure, the reverse surface S _A and the forward surface S _B, and the reverse electrode A and the forward electrode B shown in FIG. 3 A similar polymer electrolyte layer is formed in each case. That is, in the reverse surface S _A, it is assumed that fine consisting massive particles microscopically very dense, while in the forward surface S _B, macroscopically consisting of substantially spherical massive particles in relatively large dense And all are in a very stable state. In any case, the adhesion between the polymer electrolyte layer and the underlying conductive layer is extremely good. Further, the forward surface S _B, the existence ratio of the forward electrode B as well as 1,4-linked structure increases.

[0023] As a result, the reverse surface S _A, due to the microscopically very compact structure, conductivity is improved. On the other hand, the forward face S _B, microscopically dense structure is not formed, conductivity becomes good due to the existence ratio of 1,4-bond structure is increased. Therefore, both polymer electrolyte layers formed on both surfaces of the working electrode have good conductivity and a small difference in electrical characteristics,
Excellent characteristics as a solid electrolytic capacitor can be obtained. The fact that good conductivity is obtained on both the reverse surface S _A and the forward surface S _B under the application of the centrifugal force as described above will be made clear for the first time by the present application. Forward plane S
_{The fact} that the abundance ratio of the 1,4-bond structure in _B increases and the uniformity of the molecular structure improves,
It is not described in the abstract of the 65th meeting, 1M09, page 361.

Even when the lower electrode in FIG. 1 is used as the working electrode, the same result is obtained depending on the direction of the centrifugal force on each surface of the working electrode.

[0025]

FIG. 4 shows a configuration example of a solid electrolytic capacitor manufactured according to the present invention. This electrolytic capacitor has an insulating oxide film 13 formed by anodic oxidation, a conductive underlayer 14, a polymer electrolyte layer 15, and a cathode 16 on an anode substrate 12. Hereinafter, a configuration and a forming method of each part of the solid electrolytic capacitor will be described.

Anode Substrate 12 The anode substrate can be composed of a group of valve metals or alloys thereof having the ability to form an insulating oxide film. Examples of such a metal or alloy include Al, Ta, Ti,
One of Nb and Zr or an alloy containing at least one of these is preferred. Then, these metals or alloys can be processed into shapes such as linear, foil, plate, and porous blocks, and if necessary, laminated and wound to form an anode substrate.

If necessary, the anode substrate is subjected to an etching treatment for increasing the specific surface area, and irregularities as shown in FIG. 4 are formed on the surface.

Insulating Oxide Film 13 The insulative oxide film is formed by oxidizing the surface of the anode substrate by a process such as anodic oxidation.

The thickness of the insulating oxide film may be appropriately determined according to the working voltage, but is generally about 10 nm to 1 μm.

Conductive Underlayer 14 The conductive underlayer is essential for forming the polymer electrolyte layer by electrolytic oxidation polymerization. The conductive underlayer may be made of any of a metal, a metal oxide having conductivity, and a conductive polymer compound, but is preferably made of a conductive polymer compound.

The conductive underlayer made of a conductive polymer compound is preferably formed by a chemical oxidation polymerization method. The chemical oxidative polymerization is preferably performed, for example, by the following procedure. First, an oxidizing agent is put on the insulating oxide film at 0.001.
A solution containing about 2.0 mol / l or a solution containing a compound giving a dopant species is uniformly deposited by a method such as coating or spraying. Next, the monomer of the conductive polymer compound is preferably at least 0.01 mol / l.
The solution or monomer itself containing the above is brought into direct contact with the insulating oxide film. Thereby, a conductive polymer compound is synthesized.

The oxidizing agent used in the chemical oxidative polymerization is not particularly limited, but typical examples thereof include halides such as iodine, bromine and bromine iodide, arsenic pentafluoride, antimony pentafluoride, Metal halides such as silicon fluoride, phosphorus pentachloride, phosphorus pentafluoride, aluminum chloride, and molybdenum chloride; protic acids such as sulfuric acid, nitric acid, fluorosulfuric acid, trifluoromethanesulfuric acid, and chlorosulfuric acid; sulfur trioxide; and nitrogen dioxide Oxygen compounds, persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; and peroxides such as hydrogen peroxide, potassium permanganate, peracetic acid, and difluorosulfonyl peroxide.

Examples of the compound for providing a dopant species, which is optionally contained, include the following.

The anions are hexafluoroline anion and hexafluoroarsenic anion, and the cation is lithium,
Sodium salt is an alkali metal cation such as potassium, for _{example, LiPF 6, LiAsF 6, NaPF} 6,
KPF ₆ and KAsF ₆ . In addition to these, boron tetrafluoride salt compounds such as LiBF ₄ , NaBF ₄ ,
_{NH 4 BF 4, (CH 3} ) 4 NBF 4, (n-C 4 H 9) 4 NB
F _4, and the like. Further, a sulfonic acid or a derivative thereof, for example, p-toluenesulfonic acid, p-ethylbenzenesulfonic acid, p-hydroxybenzenesulfonic acid,
Dodecylbenzenesulfonic acid, methylsulfonic acid, dodecylsulfonic acid, benzenesulfonic acid, β-naphthalenesulfonic acid and salts thereof, such as sodium 2,6-naphthalenedisulfonic acid, sodium toluenesulfonic acid, and tetrabutylammonium toluenesulfonic acid It is.

Metal halides such as ferric chloride, ferric bromide, cupric chloride, cupric bromide and the like.

Hydrohalic acid, inorganic acid or a salt thereof,
For example, hydrochloric acid, hydrogen bromide, hydrogen iodide, sulfuric acid, phosphoric acid,
Nitric acid, or an alkali metal salt, an alkaline earth metal salt or an ammonium salt thereof, a perhalic acid such as perchloric acid or sodium perchlorate, or a salt thereof.

Carboxylic acids such as acetic acid, oxalic acid,
Mono- or dicarboxylic acids such as formic acid, butyric acid, succinic acid, lactic acid, citric acid, phthalic acid, maleic acid, benzoic acid, salicylic acid, nicotinic acid, aromatic and heterocyclic carboxylic acids, and halogenated compounds such as trifluoroacetic acid Carboxylic acids and salts thereof.

The compounds capable of providing these oxidizing agents and dopant species are used in an appropriate solution, that is, in a state of being dissolved in water or an organic solvent. The solvents may be used alone or in combination of two or more. The mixed solvent is
It is also effective for increasing the solubility of the compound giving the dopant species. As the mixed solvent, those having compatibility between the solvents and those having compatibility with the compound are suitable. Specific examples of the solvent include organic amides, sulfur-containing compounds, esters, and alcohols.

The conductive polymer compound synthesized by chemical oxidative polymerization contains a substituted or unsubstituted π-conjugated heterocyclic compound, a cyclic or chain π-conjugated hydrocarbon compound and a hetero atom. It is preferable to use at least one compound selected from cyclic or chain π-conjugated hydrocarbon compounds as a starting monomer. Among these, polyaniline, polypyrrole, polythiophene or polyfuran is preferable, and polyaniline or polypyrrole is particularly preferable.

Representative examples of the monomer that provides such a conductive polymer compound include unsubstituted anilines, alkylanilines, alkoxyanilines, haloanilines, o
Phenylenediamines, 2,6-dialkylanilines, 2,5-dialkoxyanilines, 4,4′-diaminodiphenylether, pyrrole, 3-methylpyrrole, 3-ethylpyrrole, 3-propylpyrrole, thiophene, -Methylthiophene, 3-ethylthiophene and the like.

In addition to the above forming method, the conductive underlayer can also be formed by dissolving a conductive polymer compound synthesized in advance in an organic solvent to form a solution and applying the solution on an oxide film. It is possible to form.

The conductive underlayer has an effect of preventing the insulating oxide film from being destroyed by ultrasonic waves, and in particular, the conductive underlayer containing a conductive polymer compound has a large effect.

The conductive underlayer may be made of manganese dioxide. In this case, however, damage to the insulating oxide film when manganese dioxide is formed becomes relatively large.
On the other hand, if the conductive underlayer is made of a conductive polymer compound formed by chemical oxidation polymerization, damage to the insulating oxide film during formation of the conductive underlayer is small.

The conductive underlayer formed on the insulating oxide film by chemical oxidation polymerization has a relatively rough surface, but in the present invention, the conductive underlayer can be finally made dense. . In the present invention, after the formation of the conductive underlayer, electrolytic oxidative polymerization is subsequently performed under the application of centrifugal force.At this time, the monomer penetrates into the conductive underlayer having a rough structure, and adheres to the insulating oxide film. Polymerizes. Also, the monomer is
Also polymerizes with the conductive underlayer. As a result, the conductive underlayer becomes so dense that the boundary with the polymer electrolyte layer cannot be seen, and both layers are in a very stable state. Such an effect is realized when the polymer electrolyte layer is formed under the application of a centrifugal force, and as described in Japanese Patent Publication No. 4-74853, the chemical oxidized polymer layer and the electrolytic oxidized polymer layer are simply laminated. Does not happen.

The thickness of the conductive underlayer may be appropriately set so as not to cause any inconvenience during the electrolytic oxidation polymerization, and may be generally selected from the range of 0.5 to 10 μm. In addition,
The conductive underlayer is preferably a continuous film.

The polymer electrolyte layer 15 is formed by performing electrolytic oxidation polymerization while applying a centrifugal force as described above. The centrifugal force is
In a relatively small-scale process, it can be generated by a general centrifuge as shown in FIG. On the other hand,
In the case of a large-scale process, it can be generated using an annular or cylindrical centrifuge (one that has been put into practical use for isotope separation or the like). The constituent material of the electrolytic cell is not particularly limited, and may be, for example, any of glass, plastic, metal, and the like.

The acceleration applied to the working electrode is preferably at least 10 g (g is the gravitational acceleration). If the acceleration is too small, a sufficient effect cannot be obtained.

The electrolytic oxidation polymerization itself may be performed according to a known method. That is, electrolytic oxidative polymerization is performed by placing the conductive underlayer as a working electrode, placing it in an electrolytic solution together with the counter electrode, and applying a current.

The electrolytic solution contains a monomer for providing a conductive polymer compound and a supporting electrolyte, and further contains various additives as necessary.

The conductive polymer compound used for the polymer electrolyte layer is the same as the conductive polymer compound used for the conductive underlayer, and is a substituted or unsubstituted π-conjugated heterocyclic compound, Formula or chain π-conjugated hydrocarbon compound and cyclic or chain π containing hetero atom
It is preferable to use at least one compound selected from conjugated hydrocarbon compounds as a starting monomer. Among these, polyaniline, polypyrrole, polythiophene or polyfuran is preferable, and polyaniline or polypyrrole is particularly preferable. Polyaniline has the same electrical conductivity as polypyrrole and is more excellent in heat resistance and stability over time.

The monomers used for forming the polymer electrolyte layer are as follows:
What is necessary is just to select from the various monomers mentioned in the description of the conductive underlayer.

The supporting electrolyte is selected in each case according to the monomer and the solvent to be combined. Typical examples of the basic electrolyte include sodium hydroxide, potassium hydroxide, ammonium hydroxide and sodium carbonate. , Sodium bicarbonate and the like. Examples of the acidic compound include sulfuric acid, hydrochloric acid, nitric acid, hydrogen bromide, perchloric acid, trifluoroacetic acid, and sulfonic acid. Further, as the salt, sodium chloride, sodium bromide, potassium iodide, potassium chloride, potassium nitrate, sodium periodate, sodium perchlorate, lithium perchlorate, ammonium iodide, ammonium chloride, boron tetrafluoride salt compound , Tetramethylammonium chloride, tetraethylammonium chloride,
Tetramethylammonium bromide, tetraethylammonium bromide, tetraethylammonium perchloride, tetrabutylammonium perchloride, tetramethylammonium, p-toluenesulfonic acid chloride, triethylamine borodisalicylate, 1
Examples thereof include sodium 0-camphorsulfonate.

The dissolution concentration of the supporting electrolyte may be set so as to obtain a desired current density.
There is no particular problem if it is set within the range of 5 to 1.0 mol / l.

The solvent used in the electrolytic oxidation polymerization is not particularly limited, and may be appropriately selected from, for example, water, a protic solvent, an aprotic solvent, or a mixed solvent obtained by mixing two or more of these solvents. As the mixed solvent, those having compatibility between the solvents and those having compatibility with the monomer and the supporting electrolyte are suitable.

Examples of the protic solvent include formic acid, acetic acid, propionic acid, methanol, ethanol, n-propanol, isopropanol, tert-butyl alcohol, methyl cellosolve, diethylamine and ethylenediamine. Examples of aprotic solvents include methylene chloride, 1,2-dichloroethane, carbon disulfide, acetonitrile, acetone, propylene carbonate, nitromethane, nitrobenzene, ethyl acetate, diethyl ether,
Tetrahydrofuran, dimethoxyethane, dioxane,
N, N-dimethylacetamide, N, N-dimethylformamide, pyridine, dimethylsulfoxide and the like can be exemplified.

For the electrolysis, any of the constant voltage method, the constant current method and the potential sweep method may be used. Further, a method in which the constant current method and the constant voltage method are combined in the electrolytic polymerization process can also be used. The current density is not particularly limited, but is about 10 mA / cm ² at the maximum.

The temperature of the electrolytic bath may be between the freezing point and the boiling point of the electrolytic solution, but is usually about 0 to 60 ° C.

As shown in FIG. 4, the thickness of the polymer electrolyte layer may be appropriately determined so as to completely fill the irregularities on the surface of the anode substrate 1 formed by etching or the like. It is about 100 μm. The thickness in this case is the maximum thickness of the polymer electrolyte layer.

Other components The cathode 16 can be formed by applying a conductive paste containing silver, palladium, copper and the like. Note that a carbon layer is provided between the cathode 16 and the polymer electrolyte layer 15 as needed. For example, when a cathode is formed from a silver paste, the migration of silver can be prevented by providing a carbon layer. The carbon layer can be formed by immersing the polymer electrolyte layer in colloidal carbon.

Finally, after a cathode lead terminal is connected to a part of the cathode, exterior processing is performed by resin molding or encapsulation in a resin or metal case to obtain an electrolytic capacitor.

[0061]

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

A solid electrolytic capacitor having a conductive underlayer and a polymer electrolyte layer shown in Table 1 was produced in the following procedure.

As an anode substrate, an aluminum foil having a thickness of 100 μm was used, and the both surfaces thereof were etched to increase the surface area.
An insulating oxide film having a thickness of 20 nm made of aluminum oxide was formed to obtain an aluminum conversion foil of 75 μF / cm ² .
Thereafter, the aluminum conversion foil and the lead terminals were fixed by a caulking method, and a chemical conversion treatment was performed again. Next, the insulating oxide film was immersed in a 0.04 mol / l aqueous solution of ammonium persulfate under reduced pressure for 30 minutes, and then dried.

Next, a conductive underlayer was formed on both insulating oxide films. The conductive underlayer made of polypyrrole was formed by immersing an oxide film in an acetonitrile solution containing a purified pyrrole monomer under reduced pressure for 30 minutes to perform chemical oxidation polymerization. On the other hand, when forming a conductive underlayer made of polyaniline, first, undoped polyaniline synthesized in advance is dissolved in an N-methyl-2-pyrrolidone solution to a concentration of 0.5% by weight. Then, citric acid was dissolved therein as a dopant to a concentration of 0.2 mol / l. Next, after immersing the anode substrate in this solution for 5 minutes,
Dry at 0 ° C. for 1 hour. This process was repeated five times to obtain a conductive underlayer made of polyaniline. Note that the thickness of the conductive underlayer was 1 μm.

Next, the electrolytic cell shown in FIG. 1 was set in the centrifuge shown in FIG. 2 to prepare an electrolytic device. In addition, the cylinder type non-diaphragm cell made of acrylic resin was used for the electrolytic cell. For the upper electrode (working electrode), an aluminum conversion foil provided with the conductive underlayer (area 1 cm ² ) was used, and for the lower electrode (cathode), a platinum electrode (area 1 cm ² ) was used. In addition, the electrolyte solution contains aniline monomer at 0.2 mol /
l, oxalic acid 0.02 mol / l, tetrabutylammonium toluenesulfonate 0.05 mol / l as supporting electrolyte
An aqueous solution containing l was used.

Using this electrolysis apparatus, 0 to 1.0 V vs.
The potential sweeping electrolysis was repeated 50 times at a silver / silver chloride electrode and a sweep speed of 100 mV / s to form a polyaniline film on both surfaces of the working electrode. However, in sample No. 4, the current density was set to 0.
The polyaniline film was formed by performing constant current electrolysis for 20 minutes under the condition of 5 mA / cm ² . Table 1 shows the acceleration applied during the electrolysis. Note that the acceleration of 1 g is a state in which no centrifugal force is applied (only gravitational acceleration).

Next, cathodes were respectively formed on the surfaces of the polymer electrolyte layers on both sides using a carbon paste and a silver paste, and exterior treatment was performed with an epoxy resin to complete a solid electrolytic capacitor sample.

For these samples, the capacitance at 120 Hz, the impedance at 100 kHz, and the leakage current value were measured. Table 1 shows the results.

Further, in order to examine the adhesion between the insulating oxide film and the conductive underlayer and the polymer electrolyte layer, a peeling test using an adhesive tape was performed before forming the cathode. In this test, when the polymer electrolyte layer hardly adhered to the pressure-sensitive adhesive tape side and the polymer electrolyte layer remained on the insulating oxide film side, the adhesion was considered to be good,
A case where most of the polymer electrolyte layer adhered to the adhesive tape side and almost no polymer electrolyte layer remained on the insulating oxide film side was regarded as defective. Table 1 shows the results.

[0070]

[Table 1]

From Table 1, by applying a centrifugal force,
It can be seen that all of the capacitance, the impedance, and the leakage current value are improved. Further, it can be seen that the adhesion is improved by applying a sufficient acceleration.

The surface state of the polymer electrolyte layer after washing and drying was examined by a scanning electron microscope (SEM). As a result, those formed in the backward surface S _A, qualitatively, massive particles constituting the film becomes fine in accordance with the centrifugal acceleration increases were found to be significantly densified. On the other hand, which was formed in the forward surface S _B, massive particles be substantially spherical, it was found that there is a dense but is coarse in comparison with the case of the reverse direction. On the other hand, it was found that the surface state of the polymer electrolyte layer formed without applying a centrifugal force was extremely rough, and the polymer electrolyte layer was not densified.

[0073] In order to centrifugal forces investigate the effect on the polymer structure of the polymer electrolyte layer, a platinum electrode as a working electrode, each of the reverse surfaces S _A and the forward surface S _B, Table 1 A polymer electrolyte layer was formed in the same manner as in some of the samples shown in (1), and these were analyzed by IR spectrum. Table 2 shows the results. Table 2 shows the acceleration applied during electrolytic oxidation polymerization. In addition, 1,2,4-bond, 1,4-bond and 1,2
The peaks attributable to the bonds are 880 cm ⁻¹ and 83
0cm ^-1 and 710cm ^-1.

[0074]

[Table 2]

[0075] From Table 2, the forward surface S _B, l, 4
-It can be seen that the ratio of the bonding structure is increased and the uniformity of the molecular structure is improved.

[0076] Further, a polymer electrolyte layer formed on the reverse surface S _A platinum electrodes under centrifugal acceleration of 50 to 300 g,
After washing and drying, they were forcibly peeled off from the electrode surface and powdered. This powder was formed into a pellet, and the conductivity was measured by a four-terminal method. The result was in the range of ^{1 to} 10 S cm ^-1 , and it was found that good conductivity was obtained. It is considered that the reason why the conductivity is good is that the film is densified.
On the other hand, a polymer electrolyte layer formed on the forward surface S on _B is
Conductivity is 5~10S cm ^-1, it was comparable to that formed on the reverse surface S _A. In contrast, the conductivity of the polymer electrolyte layer formed without applying a centrifugal force is 0.01 to 0.0
It was within the range of 5 S cm ^-1 , and the result was significantly different from the case where centrifugal force was applied.

The effects of the present invention are apparent from the results of the above examples.

[Brief description of the drawings]

FIG. 1 is a front view showing a configuration example of an electrolytic cell used in the present invention.

FIG. 2 is a perspective view showing an experimental apparatus for performing electrolytic oxidation polymerization while applying a centrifugal force.

FIG. 3 is a front view showing a structure of an electrolytic cell in the experimental apparatus of FIG.

FIG. 4 is a cross-sectional view illustrating a configuration example of a solid electrolytic capacitor manufactured according to the present invention.

[Explanation of symbols]

2 Centrifuge tube 3 Electrolysis cell 4 Reference electrode 5 Rotation axis 6 Electrolyte A Reverse electrode B Forward electrode S _A Reverse surface S _B Forward surface 12 Anode substrate 13 Insulating oxide film 14 Conductive underlayer 15 Polymer electrolyte Layer 16 cathode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noriyoshi Nanba 1-13-1, Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation

Claims (5)

[Claims] 1. A step of oxidizing a metal anode substrate to form an insulating oxide film, a step of forming a conductive underlayer on the insulating oxide film, and electrolytic oxidation polymerization while applying centrifugal force. And forming a polymer electrolyte layer containing a conductive polymer compound on the conductive underlayer. 2. The insulating oxide film and the conductive underlayer are formed on both surfaces of the anode substrate, and the centrifugal force is applied so that the direction of the centrifugal force is orthogonal to the surface of the anode substrate. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein said polymer electrolyte layer is formed on surfaces of both conductive underlayers. 3. The conductive polymer compound contained in the polymer electrolyte layer may be a substituted or unsubstituted π-conjugated heterocyclic compound, a cyclic or chain π-conjugated hydrocarbon compound and a heteroatom. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein at least one compound selected from cyclic or chain π-conjugated hydrocarbon compounds containing 4. The conductive underlayer contains a conductive polymer compound, and the conductive polymer compound is a substituted or unsubstituted π-conjugated heterocyclic compound, cyclic or chain π. The solid according to any one of claims 1 to 3, wherein at least one compound selected from a conjugated hydrocarbon compound and a cyclic or chain π-conjugated hydrocarbon compound containing a hetero atom is used as a starting monomer. Manufacturing method of electrolytic capacitor. 5. The method according to claim 1, wherein the anode substrate is made of Al, Ta, Ti, N
The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 4, comprising a metal or an alloy containing at least one of b and Zr.