JP2000124075A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably realize satisfactory capacitor characteristics for a solid electrolytic capacitor having a solid electrolyte, composed of a conductive polymer compd. produced through electrolytic polymerization. SOLUTION: This manufacturing method comprises steps of oxidating a metal anode base 2 to form an insulative oxide film 3, forming a conductive base layer 4 on the insulative oxide film 3, and executing an electrolytic oxidation polymerization with the irradiation of an ultrasonic wave to form a polymer electrolyte layer 5 contg. a conductive polymer compd. on the conductive base layer 4. The electrolytic oxidation polymerization is executed in an electrolytic liq. which contains dispersed grains of a metal oxide inactive to electrolytic oxidation polymerizing reaction.

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 an electric 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.

Japanese Patent Application Laid-Open No. 3-280519 discloses a dielectric film (oxide film) provided on an anode valve metal.
A method of manufacturing a solid electrolytic capacitor by growing a polymer of a conductive polymer by an electrolytic polymerization method while irradiating ultrasonic waves on a conductive film made of manganese oxide formed thereon or on a manganese oxide formed thereon. Have been. The publication states that, by performing electrolytic polymerization while irradiating ultrasonic waves, monomers, supporting electrolytes, additives, etc. are distributed to every corner on the dielectric film, and the growth of the conductive polymer is smoothed. It also describes that an electropolymerized conductive polymer can be grown even in fine etching pits of the anode valve metal, so that the capacity achievement rate can be increased. The publication states that the ultrasound used here does not need to be special. 50kH in the embodiment
Although the ultrasonic wave of z is used, no other information is described about the ultrasonic wave. The publication describes pyrrole, thiophene, furan, and the like as monomers for forming a conductive polymer.

[0010]

SUMMARY OF THE INVENTION The present inventors carried out electrolytic oxidation polymerization while irradiating ultrasonic waves as described in the above-mentioned Japanese Patent Application Laid-Open No. 3-280519 to obtain a conductive polymer compound. A solid electrolyte layer was formed to produce a solid electrolytic capacitor. However, in the solid electrolytic capacitor manufactured in this way, various characteristics such as capacitance, impedance at high frequency, and leakage current value significantly vary depending on ultrasonic irradiation conditions, and industrial use is practically impossible. It turned out to be.

An object of the present invention is to stably realize good capacitor characteristics in a solid electrolytic capacitor having a solid electrolyte made of a conductive polymer compound produced by an electrolytic polymerization method.

[0012]

This and other objects are achieved by any one of the following (1) to (7). (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 irradiating ultrasonic waves. Forming a polymer electrolyte layer containing a conductive polymer compound on the conductive underlayer, wherein particles comprising a metal oxide inert to an electrolytic oxidation polymerization reaction are dispersed. The method for producing a solid electrolytic capacitor, wherein the electrolytic oxidation polymerization is performed in the above. (2) The method for manufacturing a solid electrolytic capacitor according to the above (1), wherein an ultrasonic output value when forming the polymer electrolyte layer is within ± 10% of a cavitation threshold. (3) The ultrasonic output value is set to the cavitation threshold of −10.
% And less than the cavitation threshold to form a part of the polymer electrolyte layer, and then set the ultrasonic output value to not less than the cavitation threshold and + 10% or less thereof to form the remainder of the polymer electrolyte layer. Manufacturing method of electrolytic capacitor. (4) The method for manufacturing a solid electrolytic capacitor according to any one of (1) to (3), wherein the frequency of the ultrasonic wave is 20 to 100 kHz. (5) The conductive polymer compound contained in the polymer electrolyte layer is a substituted or unsubstituted π-conjugated heterocyclic compound, conjugated aromatic compound or heteroatom-containing conjugated aromatic compound as a starting monomer. The above (1)
The method for manufacturing a solid electrolytic capacitor according to any one of (1) to (4). (6) The conductive underlayer contains a conductive polymer compound, and the conductive polymer compound is a substituted or unsubstituted π-conjugated heterocyclic compound, conjugated aromatic compound, or heteroatom-containing conjugated compound. The method for producing a solid electrolytic capacitor according to any one of the above (1) to (5), wherein an aromatic compound is used as a raw material monomer. (7) The method for producing a solid electrolytic capacitor according to any one of the above (1) to (6), wherein the anode substrate is made of a metal or an alloy containing at least one of Al, Ta, Ti, Nb and Zr.

[0013]

[Action and effect] Ultrasonic waves are one of the mechanical energies, and the wavelength when propagating in a medium is usually 10 to 1
It is a compression wave of about 0 ^-2 cm. When converted to electromagnetic waves, they correspond to long-wavelength radio waves. At the molecular level, it is insufficient to directly excite a reactive species and directly drive a chemical reaction. However, it is extremely rich in control energy for chemical reactions. When an ultrasonic wave propagates in a liquid, a low pressure region and a high pressure region are alternately generated at a cycle of about 10 ^-4 to 10 ^-6 seconds, and a small cavity is generated in the low pressure region. Disintegrates rapidly in cycles. At this time, an extremely high temperature (1000 K or more) and an extremely high pressure (100 atm or more) are locally generated. The repetition of the generation and collapse of the cavity is generally called cavitation, and the output value of the ultrasonic wave necessary to generate cavitation is generally called a cavitation threshold.

[0014] As an attempt to synthesize a conductive high molecular compound by performing electrolytic oxidation polymerization utilizing such a specific property of ultrasonic waves, for example, the following reports have been reported.

[0015] Synthetic Metals
ls), vol. 18, p. 145, 1987, and Polymer Physics, vol. 30, p. 19, 1
In 992, it was reported that a polythiophene film formed by electrolytic oxidation polymerization under ultrasonic irradiation had significantly improved physical properties in all of surface smoothness, doping properties, and redox properties. In addition, New Journal of Chemistr
y), Vol. 19, p. 989, 1996 reports that polypyrrole has the same effect. Also, Electrochemistry, Vol. 65, No. 6, p. 495, 19
In 1997, it was reported that polyaniline formed on a platinum electrode by electrolytic oxidation polymerization while irradiating ultrasonic waves had high adhesion and a high film quality.

The 65th Annual Meeting of the Electrochemical Society of Japan, Abstracts, 1M18, p. 364 reports that the film quality of a polyaniline polymer film formed on a platinum electrode largely depends on the occurrence of cavitation. I have. In particular,
Under the condition that the cavitation threshold is 10 W, when the ultrasonic output is set to 6 W which is less than the cavitation threshold and the electrolytic oxidation polymerization is performed, a rough structure and morphology in which agglomerates are entangled in the same manner as a film formed without irradiation of ultrasonic waves is obtained. On the other hand, when the ultrasonic output was set to 17 W exceeding the cavitation threshold, the SEM with a magnification of 10,000 times was used.
(Scanning electron microscope) It has been reported that a film was obtained which was so uniform that no agglomerates could be confirmed in the photograph. From this result, this report concludes that it has been clarified that irradiation of the aniline polymerization system with an ultrasonic wave having a cavitation threshold or higher causes uniformization and densification of the film surface. In this report, the cavitation threshold is measured by inserting the measurement probe of the cavitation meter into the electrolytic cell.

However, none of the above reports suggests that the conductive polymer compound film formed by electrolytic oxidation polymerization under ultrasonic irradiation can be applied to a solid electrolyte in a solid electrolytic capacitor. Also, there is no description regarding the conditions to be considered when applying to a solid electrolytic capacitor. Japanese Patent Application Laid-Open No. 3-280519 in which electrolytic oxidation polymerization under ultrasonic irradiation is applied to the production of a solid electrolytic capacitor.
In the publication, only the frequency of the ultrasonic irradiation condition is described.

Therefore, the present inventors have developed a conductive polymer compound film formed by electrolytic oxidation polymerization under ultrasonic irradiation,
An experiment applied to a solid electrolyte of an electrolytic capacitor was performed.
As a result, a problem peculiar to application to an electrolytic capacitor became apparent. That is, the above-mentioned IEICE 6th
As shown in the 5th Annual Meeting, Abstracts of Lectures, 1M18, page 364, it was found that the oxide film formed on the surface of the anode substrate of the electrolytic capacitor was easily broken when simply irradiating an ultrasonic wave having a cavitation threshold or more. When the oxide film is destroyed, the leakage current becomes extremely large, and a desired capacitance cannot be obtained.

The present inventors have conducted various experiments for the purpose of preventing damage and destruction of an oxide film when applying electrolytic oxidation polymerization under ultrasonic irradiation to the production of an electrolytic capacitor. As a result, they have found that this object can be achieved by using an electrolytic solution in which metal oxide particles are dispersed.

First, the case where an electrolytic solution which does not disperse metal oxide particles is used will be considered. The lower the oscillation frequency of the ultrasonic wave, the longer the period in which the low-pressure region and the high-pressure region occur in the electrolytic solution, which facilitates the generation of cavities and lowers the cavitation threshold, but increases the cavitation energy. In addition, the damage of the insulating oxide film increases. On the other hand, if the oscillation frequency is increased, damage to the insulating oxide film can be reduced, but the cavitation threshold increases exponentially with the increase in frequency, so that an expensive high-output oscillator is required,
It becomes impractical.

On the other hand, if an electrolytic solution in which metal oxide particles are dispersed is used, the cavitation threshold can be lowered without changing the oscillation frequency. Therefore, an expensive oscillator is not required to prevent damage to the insulating oxide film. Moreover, even if the oscillation frequency is the same, the damage of the insulating oxide film is reduced by using the electrolytic solution in which the metal oxide particles are dispersed.

By the way, the cavitation threshold varies greatly depending on the geometrical shape of the electrolytic cell, the electrode, the electrolytic reaction device, and the physical properties of the electrolytic solution even when the same ultrasonic wave source is used. In particular, the material of the electrolytic cell, the pressure in the reaction system, the amount and type of dissolved gas contained in the electrolytic solution,
The cavitation threshold varies depending on the type of the solvent.
Therefore, it is possible to lower the cavitation threshold by optimizing these conditions.
However, in the present invention, the cavitation threshold can be reduced under any conditions, and the cavitation threshold can be further reduced by applying the present invention after optimizing the above various conditions.

The Electrochemical Society, 1996 Spring Meeting Proceedings, 96-1, Vol. 1040, 129
On page 0, there is a report on the effect of ultrasonic irradiation on electrochemical reactions. According to this, as a result of promoting the reaction while dispersing alumina particles in the reaction solution and irradiating ultrasonic waves, the collision phenomenon between the electrodes and the particles was induced, and local heat was generated. Has been confirmed. This report is the same as the present invention in that an electrolytic solution in which alumina particles are dispersed is used, but the report does not pay any attention to electrode damage. And, of course, there is no description of application to the formation of a polymer electrolyte layer of an electrolytic capacitor.

The present inventors have made the above-mentioned Electrochemical Society No. 65
As shown in the Annual Meeting, Abstracts of Lectures, 1M18, p. 364, it was found that the rate of formation of the conductive polymer compound film was liable to be remarkably reduced when simply irradiating an ultrasonic wave having a cavitation threshold or higher. Further, they have found that even when the ultrasonic output is less than the cavitation threshold, a conductive polymer compound film having a sufficiently high function as a solid electrolyte can be formed, and the film formation speed can be improved. From these results, in a preferred embodiment of the present invention, when forming the solid electrolyte layer, the ultrasonic output is set at ± the cavitation threshold.
The electrolytic oxidative polymerization is performed at a setting within 10%. The cavitation threshold value in the present invention is the same as the cavitation threshold value described in the above-mentioned 65th Annual Meeting of the Institute of Electrical Engineers of Japan, Abstracts, 1M18, page 364. (The output value of the ultrasonic oscillator). Cavitation meters are commercially available.
Also in the present invention, commercially available products can be used.

The ultrasonic output is set to the cavitation threshold of -1.
By setting the range from 0% to less than the cavitation threshold, a uniform and dense solid electrolyte layer can be formed, and the formation rate of the solid electrolyte layer is increased. It has not been previously reported that a homogeneous and dense film can be obtained despite being below the cavitation threshold. That is, it was found for the first time by the present invention that the film quality can be improved by cavitation at a level that cannot be captured by a cavitation meter. On the other hand, if the ultrasonic output is set within the range from the cavitation threshold to + 10% of the cavitation threshold, a more uniform and denser solid electrolyte can be formed, and the insulating oxide film will not be destroyed. Despite the occurrence of cavitation, the insulating oxide film is not destroyed because the conductive underlayer, especially a conductive underlayer composed of a conductive polymer compound, has the effect of buffering ultrasonic waves. it is conceivable that.

On the other hand, the cavitation threshold of -1
When ultrasonic waves having an output of less than 0% are irradiated, the solid electrolyte layer becomes rough as in the case where no ultrasonic waves are irradiated, and it becomes difficult to obtain a high-performance solid electrolytic capacitor. This is considered to be because when the ultrasonic output falls below -10% of the cavitation threshold, the effect is merely the sound field.
In addition, when an ultrasonic wave having an output exceeding + 10% of the cavitation threshold is irradiated, the insulating oxide film is easily damaged or broken. When damage or destruction occurs, the leakage current value becomes extremely large, and the capacitor cannot function as a capacitor.

[0027]

FIG. 1 shows an example of the configuration of a solid electrolytic capacitor manufactured according to the present invention. This electrolytic capacitor includes an oxide film 3 formed by anodic oxidation, a conductive underlayer 4 and a polymer electrolyte layer 5 on an anode substrate 2.
And a cathode 6. Hereinafter, a configuration and a forming method of each part of the solid electrolytic capacitor will be described.

Anode Substrate 2 The anode substrate can be composed of a valve metal group or an alloy group thereof capable of forming 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. 1 are formed on the surface.

Insulating Oxide Film 3 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 4 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.

Further, examples of the compound for providing a dopant species, which is contained as necessary, 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 halide compounds such as ferric chloride, ferric bromide, cupric chloride and cupric bromide.

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.

As the conductive polymer compound synthesized by chemical oxidation polymerization, a substituted or unsubstituted π-conjugated heterocyclic compound, conjugated aromatic compound or heteroatom-containing conjugated aromatic compound is used as a starting monomer. Are preferred. Of these, polyaniline, polypyrrole,
Polythiophene or polyfuran is preferred, and polyaniline or polypyrrole is particularly preferred.

Representative examples of the monomer that gives 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 this solution on an oxide film. It is possible to form.

The conductive underlayer has an effect of preventing the destruction of the insulating oxide film by ultrasonic waves. 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 surface of the conductive underlayer formed by chemical oxidation polymerization on the insulating oxide film is relatively rough, 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 oxidation polymerization is subsequently performed under ultrasonic irradiation. 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 effects cannot be realized unless the formation of the polymer electrolyte layer is performed under ultrasonic irradiation. That is, as described in Japanese Patent Publication No. 4-74853, this cannot be realized by simply laminating a chemical oxidation polymerization layer and an electrolytic oxidation polymerization layer.

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

Polymer Electrolyte Layer 5 The polymer electrolyte layer is formed by electrolytic oxidation polymerization under ultrasonic irradiation. The ultrasonic irradiation conditions are as described above. On the other hand, the electrolytic oxidation polymerization itself may follow 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 metal oxide particles in addition to the monomer for providing the conductive polymer compound and the 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, conjugated aromatic compound. It is preferable to use an aromatic compound or a heteroatom-containing conjugated aromatic compound as a starting monomer. Among these, polyaniline, polypyrrole, polythiophene or polyfuran is preferable, and polyaniline or polypyrrole is particularly preferable. Polyaniline is
Compared to polypyrrole, the conductivity is the same, and the heat resistance and the stability over time are more excellent.

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.

The material of the particles to be dispersed in the electrolytic solution is not particularly limited as long as it is a metal oxide which is inert in an electrochemical reaction and does not change even at high temperature and high pressure when cavitation occurs. For example, aluminum oxide, titanium dioxide, zirconium oxide and the like can be exemplified,
At least one of these may be selected and used. Of these, aluminum oxide is particularly preferred. Such metal oxide particles do not participate in the electrolytic reaction at all, and serve as nuclei when cavitation occurs, and have the effect of promoting the occurrence of cavitation.

The dispersion concentration of the metal oxide particles in the electrolyte is preferably from 0.01 to 5% by weight, more preferably from 0.01 to 1% by weight. If the dispersion concentration is too low, the effect of lowering the cavitation threshold tends to be insufficient. On the other hand, if the dispersion concentration is too high, metal oxide particles are likely to be taken into the conductive polymer film formed by electrolytic oxidation polymerization.

The size of the cavity generated during the cavitation phenomenon is said to be on the order of several tens of micrometers. If the particle size of the metal oxide particles is smaller than the above-mentioned size, it can be a core of the cavity. Therefore, the average particle size of the metal oxide particles may be determined so as to be smaller than the size of the cavity. Specifically, the thickness is preferably 5 μm or less, more preferably 1 μm or less. Note that metal oxide particles having an extremely small average particle size are expensive and difficult to handle. Therefore, it is usually preferable to use metal oxide particles having an average particle size of 0.1 μm or more.

The ultrasonic oscillation frequency is preferably 20 to 1
00 kHz. If the oscillation frequency is too low, it is difficult to sufficiently prevent damage to the insulating oxide film. on the other hand,
If the oscillation frequency exceeds 100 kHz, the cavitation threshold value rises exponentially, so that cavitation hardly occurs in the device design. In addition, it is preferable that the oscillation frequency is low from the viewpoint of easy production of the oscillation device,
When attention is paid only to preventing damage to the insulating oxide film, the oscillation frequency is preferably set to 50 kHz or more.

The output value of the ultrasonic wave varies depending on various conditions such as the oscillation frequency and the size and structure of the electrolytic cell, but generally, about 5 to 20 W is sufficient.

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.

It is preferable that the ultrasonic oscillation device can control the output. Specifically, an ultrasonic transducer step horn is preferable. The ultrasonic vibrator step horn can easily control the output of ultrasonic energy and can introduce the ultrasonic oscillation source directly into the reaction system, so that the reproducibility of the reaction is good, High energy use efficiency.

The reason why the ultrasonic oscillator capable of controlling the output is used is to cope with the fluctuation of the cavitation threshold. Even if the output of the ultrasonic oscillation source is constant, the cavitation threshold depends on the geometric shape of the electrolytic reaction device such as the electrolytic cell, electrode, ultrasonic irradiation source, and the physical properties of the electrolytic solution such as the solution viscosity. It fluctuates strongly depending. Therefore,
In the present invention, it is preferable that the output value of the ultrasonic wave to be used is kept in a specific relationship with the cavitation threshold value. In order to perform a reaction with good reproducibility, it is preferable to control the output of the ultrasonic oscillation device.

A method of irradiating an ultrasonic wave without directly introducing an ultrasonic oscillation source into the reaction system can also be used. This method can be carried out, for example, by placing the electrolytic cell in an ultrasonic cleaner filled with water or the like. However, since the reaction in ultrasonic electrochemical is a solid-liquid heterogeneous reaction system, a method that directly introduces an ultrasonic oscillation source into the reaction system is used in view of its reproducibility, controllability, and efficiency. Is preferred.

Since the reaction field of the electrode reaction is at the electrode interface,
The ultrasonic effect largely depends on the distance between the tip of the step horn and the electrode, but if the distance is kept constant, the ultrasonic effect corresponding to the output intensity can be reproduced. Actually, there is no problem if the distance between the tip of the step horn and the electrode is set to 10 cm or less, preferably 5 cm or less. In addition, it is desirable that the surface of the electrode on which the conductive polymer compound is formed be arranged perpendicular to the step horn.

It is considered that there are various design techniques for the shape of the electrolytic cell. In other words, if the ultrasonic wave forms a standing wave in the reaction system, a node and an antinode are generated. Therefore, the effect should be different depending on whether the wave reaching the electrode surface is the node or the antinode. That is, since the wavelength of commonly used ultrasonic waves having a frequency of several tens of kilohertz in water is several centimeters, the ultrasonic effect is periodically generated every time the distance between the ultrasonic transducer horn and the electrode is increased or decreased by a quarter wavelength. Will be changed to However, the periodicity of the ultrasonic effect every quarter wavelength is actually unclear even though there is a complexity due to the exponential decrease of the arrival energy of the ultrasonic wave with respect to the distance from the sound source. there were. This is considered to be because the reflected waves from the wall surface in the electrolytic cell are complicatedly complicated.

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. Since ultrasonic energy is easily converted to heat energy, it is preferable to set the apparatus so as to minimize temperature fluctuation during the reaction.

In the present invention, the ultrasonic output may be suppressed at the initial stage of the electrolytic oxidation polymerization, and then the electrolytic oxidation polymerization may be performed under the original conditions. Specifically, after forming a part of the polymer electrolyte layer with the ultrasonic output value being −10% or more of the cavitation threshold and less than the cavitation threshold, the polymer is set so that the ultrasonic output value is not less than the cavitation threshold and + 10% or less thereof. The remainder of the electrolyte layer is formed. If the electrolytic oxidation polymerization is performed under such conditions, the initially formed portion functions as a protective film, so that the impact of ultrasonic waves under the original conditions can be reduced. Therefore, it is possible to improve the density of the polymer electrolyte layer while reducing damage to the insulating oxide film.

As shown in FIG. 1, 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 6 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 6 and the polymer electrolyte layer 5 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.

[0072]

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

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

As the anode substrate, an aluminum foil having a thickness of 100 μm was etched, and the surface area was increased by performing an etching process. Then, a chemical conversion process was performed by anodic oxidation to thereby form a 20-nm-thick insulating oxide film made of aluminum oxide. Was formed. Thereafter, the aluminum foil and the lead terminal 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 the insulating oxide film. The conductive underlayer made of polypyrrole is
The oxide film was formed by immersing the oxide film in an acetonitrile solution containing a pyrrole monomer purified by distillation 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 converted into N-methyl-
It was dissolved in a 2-pyrrolidone solution to a concentration of 0.5% by weight, and citric acid was further dissolved therein as a dopant to a concentration of 0.2 mol / l. Then
After dipping the anode substrate in this solution for 5 minutes, it was dried at 150 ° 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 aniline monomer was added at 0.2 mol / l,
Oxalic acid 0.02 mol / l, tetrabutylammonium toluenesulfonate 0.05 mol / l as supporting electrolyte
The aqueous solution containing the solution is placed in an electrolytic cell as an electrolytic solution.
The anode substrate on which the conductive underlayer was formed was immersed. In the electrolyte, Al ₂ O ₃ particles having an average particle diameter shown in Table 1 were added.
At the concentrations shown in Table 1. Also, for comparison, Al ₂
An electrolytic solution to which no O ₃ particles were added was also prepared. A non-diaphragm cell was used as the electrolytic cell, and an ultrasonic step horn was used as the ultrasonic irradiation source. The conductive underlayer serving as the working electrode (anode) was arranged vertically on the step horn, and the distance was fixed at 2.0 cm. In this state, the results of measuring the cavitation threshold value by using a commercially available cavitation meter and directly inserting the probe into the electrolytic cell are shown in Table 1. Table 1 shows the ultrasonic oscillation frequency.

Subsequently, a constant current electrolysis was performed using platinum as a cathode at a current density of 0.5 mA / cm ² under ultrasonic irradiation for 20 minutes to form a polymer electrolyte layer. The ultrasonic output at this time is shown in Table 1 as a relative value based on the cavitation threshold. Sample No. 2 and Sample No. 3
When comparing the amount of current during electrolysis for
No. 3 was about four times as large as Sample No. 2. This indicates that setting the ultrasonic output value to less than the cavitation threshold significantly improves the formation rate of the polymer electrolyte layer.

Next, a cathode was formed on the surface of the polymer electrolyte layer 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 carried out 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.

[0081]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, when the oscillation frequency is the same (20 kHz), the cavitation threshold is lowered from 10 W to 7 W by using the electrolyte in which the Al ₂ O ₃ particles are dispersed. Samples Nos. 1 to 3, 7, and 8 produced using an electrolyte in which Al ₂ O ₃ particles are dispersed have sufficiently high capacitance, low impedance, and low leakage current. On the other hand, in Sample No. 4 manufactured using an electrolyte solution containing no Al ₂ O ₃ particles, an increase in leakage current value, which is considered to be caused by damage to the insulating oxide film, is observed.

Sample No. 4 was prepared using an electrolytic solution containing no Al ₂ O ₃ particles. However, since the ultrasonic output was set to within ± 10% of the cavitation threshold during the preparation, the leakage current was reduced. The increase of the value is not so large.
On the other hand, in Sample No. 5, which was irradiated with high-output ultrasonic waves exceeding + 10% of the cavitation threshold value, all the characteristics except the adhesion were significantly deteriorated. this is,
This is probably because the insulating oxide film was destroyed by high-power ultrasonic waves, resulting in deterioration of the insulating property. On the other hand, the characteristics are low even in Sample No. 6 using low-power ultrasonic waves lower than −10% of the cavitation threshold. This is because the effect of improving the film quality by the ultrasonic irradiation was insufficient.

The polymer electrolyte layer made of polyaniline is
Sample No. 6 was dark green, and the other samples were light green. Further, when observed with a scanning electron microscope, the film quality of Sample No. 6 was coarse, but the other samples were dense.

In addition to the samples described above, a polymer electrolyte layer made of polypyrrole or polythiophene was formed using 3-methylpyrrole or 3-methylthiophene as a raw material monomer, respectively. When I made the capacitor,
According to the conditions at the time of forming the polymer electrolyte layer, the same results as in Table 1 above were obtained.

Example 2 An aluminum foil having a thickness of 100 μm was used as an anode substrate. The aluminum foil was subjected to an etching treatment to increase the surface area, and then subjected to a chemical conversion treatment by anodization to form an aluminum oxide insulating film having a thickness of 20 nm. A conductive oxide film was formed. Thereafter, the aluminum foil and the lead terminal were fixed by a caulking method, and a chemical conversion treatment was performed again. Next, the aluminum foil was placed in an electrolytic solution and irradiated with ultrasonic waves. The electrolyte used and the ultrasonic irradiation conditions used at this time were the same as those for producing Sample Nos. 1, 4 and 8 in Table 1, respectively.

The surface (insulating oxide film surface) state and cross section of these aluminum foils after ultrasonic irradiation were observed with a scanning electron microscope. As a result, sample N
o The aluminum foil irradiated with ultrasonic waves under the same conditions as in the production of Nos. 1 and 8 is more qualitative than the case of using the same conditions as in the production of Sample No. 4, but is considered to be damaged. There were fewer parts.

Example 3 A polyaniline thin film was formed by the following procedure in order to examine the effect of ultrasonic irradiation on the density of the polymer electrolyte layer.

First, 0.1 mol / l of an aniline monomer was added.
An electrolyte was prepared containing 4.0 mol / l of hydrochloric acid and 0.1% by weight of Al ₂ O ₃ particles having an average particle size of 0.5 μm. Then the anode,
Both cathodes are platinum electrodes, 0-1.0V vs SCE,
Potential sweep electrolysis was repeated 50 times at a sweep speed of 100 mV / s to form a polyaniline thin film on a platinum electrode. Ultrasonic waves were applied during electrolysis. Electrolysis conditions (including ultrasonic irradiation conditions) were the same as in Example 1. After the electrolysis, 0
Dedoping was performed while maintaining V vs SCE.

The weight of the polyaniline thin film was determined from the increase in weight of the platinum electrode, and the thickness of the thin film was measured with a surface roughness meter and an optical microscope. It was cm ^3. On the other hand, a polyaniline thin film was formed on a platinum electrode in the same manner as described above except that no ultrasonic wave was applied, and the density was determined to be 0.037 g / cm ³ . From this result, it can be seen that the film quality of the polyaniline thin film is significantly reduced when no ultrasonic wave is 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 sectional view showing a structure of a solid electrolytic capacitor manufactured according to the present invention.

[Explanation of symbols]

 2 Anode substrate 3 Insulating oxide film 4 Conductive underlayer 5 Polymer electrolyte layer 6 Cathode

Continuation of the front page (72) Inventor Noriyoshi Nanba 1-1-13 Nihonbashi, Chuo-ku, Tokyo FDT term in TDK Corporation 4G075 AA23 AA24 AA32 BA06 BC06 CA23 CA51 EC21 FB02 FB12 FC11

Claims (7)

[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 irradiating ultrasonic waves. Performing a step of forming a polymer electrolyte layer containing a conductive polymer compound on the conductive underlayer, and dispersing particles made of a metal oxide inert to an electrolytic oxidation polymerization reaction. A method for producing a solid electrolytic capacitor, wherein the electrolytic oxidation polymerization is performed in a liquid. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein an ultrasonic output value when forming the polymer electrolyte layer is within ± 10% of a cavitation threshold. 3. After forming a part of the polymer electrolyte layer with the ultrasonic output value being −10% or more of the cavitation threshold and less than the cavitation threshold, setting the ultrasonic output value to be not less than the cavitation threshold and not more than + 10% thereof. 3. The method according to claim 2, wherein the remaining portion of the polymer electrolyte layer is formed. 4. The ultrasonic wave has a frequency of 20 to 100 kHz.
The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein 5. The conductive polymer compound contained in the polymer electrolyte layer is a substituted or unsubstituted π-conjugated heterocyclic compound, conjugated aromatic compound or heteroatom-containing conjugated aromatic compound as a starting monomer. The method for producing a solid electrolytic capacitor according to any one of claims 1 to 4, wherein 6. The conductive underlayer contains a conductive polymer compound, and the conductive polymer compound contains a substituted or unsubstituted π-conjugated heterocyclic compound, conjugated aromatic compound, or heteroatom-containing compound. 6. The method for producing a solid electrolytic capacitor according to claim 1, wherein a conjugated aromatic compound is used as a raw material monomer. 7. The method according to claim 7, 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 6, comprising a metal or an alloy containing at least one of b and Zr.