JPH09320902A - Solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve characteristics such as tanδ, impedance and leakage current by spreading solution of conducting polymer containing carbon on an element wherein an oxide film is formed on a valve action metal, and arranging a conducting polymer film which forms at least a surface part. SOLUTION: In a capacitor element 1, a sintered body composed of fine particles of valve action metal or a body formed by laminating or winding valve action metal foils is used as a substratum, and an oxide film 2 is formed on the surface of the substratum. An anode lead 3 of tantalum or the like is led out from the element 1. A film 4 composed of conducting polymer is formed on the surface of the oxide film 2. Carbon 5 is mixed in at least the surface of the film 4. As the conducting polymer, polyaniline whose solubility to solvent is high is preferable. As carbon 5, a spherical form or a scale form or an undefined form is used. The average particle size is especially preferable to be 0.5-10μm. Its loadings to the conducting polymer is preferable to be 1:20-2:1 by volume ratio.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

[0002]

2. Description of the Related Art As a solid electrolytic capacitor, for example, a foil or a sintered body of a valve metal such as aluminum or tantalum is anodized to form an oxide film, and then a conductive polymer is formed on the surface of the oxide film. There is a structure in which a cathode layer is formed by forming a film made of and further laminating a carbon layer or a silver layer on the surface of this film. And, in the case of a chip type solid electrolytic capacitor, in order to maximize the internal volume ratio after forming the exterior by a molding method, etc.
The capacitor element has a rectangular parallelepiped shape. As the conductive polymer, π-conjugated organic conductive polymers such as polyacetylene, polythiophene, polypyrrole, and polyaniline are known. Then, in order to form a film of a conductive polymer, monomers of raw materials are polymerized to be polymerized. For example, a monomer is subjected to a polymerization reaction such as chemical oxidative polymerization, gas phase oxidative polymerization, and electrolytic polymerization on the surface of the oxide film. The conductive polymer such as polyaniline is formed by dipping the element after the oxide film is formed in a solution prepared by dissolving a prepolymerized polymer in a solvent, and then evaporating the solvent. ing.

[0003]

By the way, a conductive polymer solution such as an organic one has a large fluidity and a low viscosity. Then, a conductive polymer solution having a high fluidity such as an organic system is applied to a rectangular parallelepiped-shaped element, and when dried, due to surface tension, the planar portion of the element is thick and the ridges and corners are thick. A thin film of conductive polymer is formed.

Thermal stress is applied to each part of the capacitor element when forming a molded package on the capacitor element or mounting the capacitor. At this time, the ridges and corners of the capacitor element are relatively thin in thickness of the conductive polymer and are easily affected by thermal stress. Therefore, there are drawbacks that the characteristics such as tan δ, impedance, and leakage current of the solid electrolytic capacitor are easily deteriorated.

A conductive polymer film formed by applying a conductive polymer solution having a high fluidity such as an organic system is
It has the disadvantages that the surface is smooth, the contact resistance with the carbon layer, which is the cathode layer, etc., is relatively large, and the impedance at high frequencies is high.

An object of the present invention is to provide a solid electrolytic capacitor which is capable of improving the above-mentioned drawbacks and improving characteristics such as tan δ, impedance and leakage current.

[0007]

In order to solve the above problems, the present invention provides a solid electrolytic capacitor in which a film of a conductive polymer is laminated on an element having an oxide film formed on a valve metal, and a conductive material containing carbon is used. The present invention provides a solid electrolytic capacitor, characterized in that a conductive polymer film having at least a surface portion formed by applying a solution of a conductive polymer is provided.

When carbon is mixed in the solution of the conductive polymer, the fluidity of the solution is suppressed and the viscosity can be increased. For this reason, a thick conductive polymer film can be formed at the ridges and corners of the device. Therefore, when the mold exterior is formed, even if thermal stress is applied to the ridge line portion of the element, the effect thereof can be reduced. Therefore, characteristics such as tan δ and leakage current of the solid electrolytic capacitor can be improved.
Further, since the surface portion of the conductive polymer film is formed by applying a solution of a conductive polymer containing carbon,
It is uneven. Therefore, the contact area between the conductive polymer film and the carbon layer is increased. Also, carbon is electrically conductive. Therefore, the contact resistance between the conductive polymer film and the carbon layer can be lowered, and the equivalent series resistance and impedance can be lowered in the low frequency region to the high frequency region.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. First, tantalum, aluminum, or the like is used as the valve metal. Further, as shown in FIG. 1, the element 1 is basically a sintered body made of fine powder of valve metal or a laminated or wound valve metal foil, and an oxide film 2 is provided on the surface thereof. ing. An anode lead wire 3 of tantalum or the like is drawn out from the element 1.

A film 4 made of a conductive polymer is provided on the surface of the oxide film 2. Then, carbon 5 is mixed with at least the surface portion of the film 4. As the conductive polymer, simple substances such as polyaniline, polypyrrole, polythiophene, polyparaphenylene, and polyacetylene, and mixtures of these with polymers such as polystyrene, polyethylene, polymethylmethacrylate, and polyacrylonitrile butadiene-styrene are used. Among them, polyaniline has a high solubility in a solvent, and a relatively high concentration solution can be prepared.

The carbon has a spherical shape, a scaly shape, an amorphous shape, or the like, and is crystalline or amorphous. And the average particle diameter of this carbon is 0.1 to 50 μm.
The range of m is good, and the range of 0.5 to 10 μm is particularly preferable. When the average particle diameter is smaller than 0.1 μm, the fluidity of the solution of the conductive polymer is difficult to improve and the viscosity cannot be increased when the blending amount is small. And, the compounding amount of carbon in the conductive polymer solution is preferably in the range of 1:20 to 2: 1 by volume ratio with respect to the conductive polymer. If the blending amount is less than 1/20, it becomes difficult to improve the fluidity of the conductive polymer solution. On the other hand, if the blending amount is more than twice, the conductive polymer binding between the carbon particles is reduced, and it becomes difficult to improve the impedance characteristics and the like of the capacitor in the high frequency region. Further, the thickness of the carbon-containing surface portion of the conductive polymer film is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 50 μm.

On the surface of the conductive polymer film 4, a carbon layer 6 made of carbon paste and a silver layer 7 made of silver paste are laminated to form a cathode layer, and a capacitor element 8 is provided.
Is formed. Then, the cathode terminal 9 is connected to the silver layer 7 by the silver conductive paste 10, and the anode lead wire 3
The anode terminal 11 is welded to. And the whole is covered with the resin exterior 12.

Next, a method of manufacturing the solid electrolytic capacitor 13 of the above embodiment will be described. First, the element 1 having a predetermined shape is formed using tantalum, aluminum, or the like. Then, the element 1 is anodized using an aqueous solution of nitric acid, phosphoric acid or the like to form an oxide film 2.

After forming the oxide film 2, the element 1 is dipped in a conductive polymer solution containing no carbon 5 or sprayed with this solution to apply the conductive polymer solution to the surface of the oxide film 2. . After application, the solvent is evaporated and dried. The steps from application of the conductive polymer solution to drying are repeated as necessary to form a conductive polymer film containing no carbon 5 and having a predetermined thickness on the element 1.

After forming the conductive polymer film containing no carbon 5, the element 1 is dipped in a conductive polymer solution in which carbon 5 is dispersed to apply this solution, and then the solvent is evaporated and dried. . Then, the steps from application of the liquid to drying are repeated as necessary to form a conductive polymer film containing carbon 5 having a predetermined thickness.

When a polyaniline solution is used as the conductive polymer solution, a previously doped polyaniline solution is applied and the solvent is evaporated and dried to form a film, or a dedoped polyaniline solution is applied. After that, a doping solution is applied and doping is performed, and then a similar process is performed to form a film.

The doped polyaniline solution is prepared by mixing the undoped polyaniline with a protic acid and dissolving it in an organic solvent. Examples of the protonic acid include camphorsulfonic acid, dodecylbenzenesulfonic acid, P-toluenesulfonic acid, naphthalenesulfonic acid, styrenesulfonic acid, organic sulfonic acids such as polymers thereof, phthalic acid,
It is prepared by mixing with an carboxylic acid such as oxalic acid, maleic acid, citric acid, chloroacetic acid, dichloroacetic acid, benzoic acid, salicylic acid or the like, and dissolving them in an organic solvent. As the organic solvent, N-methyl-2-pyrrolidone, N, N′-dimethylpropyleneurea, chloroform, m-cresol, trichlorobenzene, xylene, decalin or the like is used. The doped polyaniline solution preferably has a polyaniline concentration of 0.1 to 2 wt% and a dopant concentration of 0.1 to 2 wt%.

The dedoped polyaniline solution is
Polyaniline produced by chemical oxidative polymerization of aniline is dedoped with an alkali and dissolved in a solvent to produce. For chemical oxidative polymerization of aniline, the aniline salt is oxidatively polymerized in an aqueous solution containing a protonic acid and an oxidizing agent. As the aniline salt, salts of aniline such as hydrochloric acid, sulfuric acid, and borofluoric acid are used. Also, as the protic acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, or the like is used. further,
As the oxidizing agent, a persulfate such as ammonium persulfate and potassium persulfate, a high valence compound such as hydrogen peroxide, potassium permanganate and ferric chloride, which can oxidize aniline, is used. When the aniline is chemically oxidatively polymerized, the temperature rises due to the heat of reaction, so the temperature is cooled to control the reaction temperature to 0 to 10 ° C., and the aqueous solution of the oxidant is reacted for a sufficient time. Further, the produced polymer is repeatedly washed and then dried. Thereafter, the produced polyaniline powder is suspended in aqueous ammonia, stirred, and separated by filtration to obtain dedoped polyaniline. Next, the dedoped polyaniline is dissolved in N-methyl-2-pyrrolidone or a mixed solvent of N-methyl-2-pyrrolid and another solvent to produce a dedoped polyaniline solution. At this time, the solubility can be increased by adding a reducing agent to the dedoped polyaniline to form the reduced dedoped polyaniline. In order to obtain the reduced type, a reducing agent is added to the undoped polyaniline solution, or the undoped polyaniline separated by filtration is dispersed in a non-solvent and the reducing agent is added. As the reducing agent, hydrazine compounds such as phenylhydrazine, hydrazine, hydrazine hydrate, and hydrazine sulfate, and hydrogenated metal compounds are used. At this time, the concentration of polyaniline is preferably in the range of 5 to 10%.

To form a conductive polymer film using a dedoped polyaniline solution, the solution is applied to form a film, and then a doping solution is applied to dope the film to impart conductivity. As the doping solution, a protic acid or a solution of a protic acid and an oxidizing agent in an organic solvent is used.
Organic solvents include, for example, ketones and esters, alcohols, aromatic hydrocarbons, nitriles, cellosolves,
A nitrogen-containing compound or the like is used. Further, as the oxidizing agent, for example, a disulfide compound, a benzothiazolylsulfenamide compound, a quinonedioxime compound, or the like is used.

After forming a conductive polymer film 4 consisting of a conductive polymer film containing no carbon and a conductive polymer film containing carbon, a carbon paste is applied to the surface of the film 4 to form a carbon layer 6. Then, a silver paste is applied to the surface of the carbon layer 6 to form the silver layer 7. After forming the silver layer 7, the cathode terminal 9 is connected to the silver layer 7 and the anode terminal 11 is connected to the anode lead wire 2. Then, the resin exterior 12 is formed by a resin molding method, a resin dipping method, or the like.

[0021]

Next, an embodiment of the present invention will be described. Example 1: Tantalum powder is used as the valve metal.
The capacitor element is a rectangular parallelepiped of 1.0 x 1.7 x 1.4 mm square, and the tantalum anode lead wire is pulled out. An oxide film is formed on the capacitor element, and a carbon-free polyaniline film is formed on the surface of the oxide film.
Carbon-containing polyaniline films are sequentially laminated, and a carbon-containing polyaniline film is arranged on the surface portion.
A carbon layer and a silver layer are sequentially laminated on the surface of the carbon-containing polyaniline film to form a cathode layer. An anode terminal is connected to the anode lead wire and a cathode terminal is connected to the silver layer. Further, the capacitor element is covered with an exterior made of epoxy resin. The rating of this solid electrolytic capacitor is 4V, 10 μF.

The solid electrolytic capacitor of Example 1 is manufactured as follows. First, a molded body of tantalum powder is formed, and this molded body is sintered at a temperature of 1450 ° C. After forming the sintered body, the sintered body is immersed in a 0.1% aqueous nitric acid solution and anodized at a voltage of 24 V to form an oxide film. Also, in an Erlenmeyer flask of 1 <<,
50 ml of aniline, 50 ml of 35% hydrochloric acid and 400 ml of pure water are prepared to prepare an aniline solution. Thereafter, the flask is kept in a cooling bath at a temperature of 0 ° C. Then, a solution prepared by dissolving 46 g of ammonium persulfate in 100 ml of pure water is added dropwise to the above aniline solution over about 2 hours, and stirring is continued for 3 hours to chemically oxidize and polymerize aniline.
Then, the precipitate is filtered, washed with pure water, and repeatedly decanted until the pH of the washing liquid becomes 6 to 7. Further, in order to remove water, the substrate is washed with ethanol and methanol, and then dried under reduced pressure at room temperature for 48 hours. After drying
10 g of the produced powder is stirred for 2 hours while being dispersed in 3% ammonia 1 << to be dedoped and filtered. After filtration, it is repeatedly washed with pure water and then with methanol.
After washing, it is dried under reduced pressure for 48 hours to produce undoped polyaniline powder. Next, 0.1 g of this dedoped polyaniline powder was added to N-methyl-2-pyrrolidone 10
Mix with g and treat in an ultrasonic bath for 2 hours. After this processing,
The undissolved material in the solution is decanted and removed to produce a dedoped polyaniline solution. Also, separately, P
-Toluenesulfonic acid 0.5 g and ammonium persulfate 0.2 g are dissolved in butanol 20 g to prepare a doping solution. Furthermore, carbon powder (particle size: 2 μm or less: 45% or more, 2-4 μm: 25%, 4-6 μm: 1) was added to 10 g of a dedoped polyaniline solution having a concentration of 10 wt%.
5%. ) 1 g is added and mixed well to produce a carbon-containing dedoped polyaniline solution. Then, first, the element having the oxide film formed thereon is immersed in a dedoped polyaniline solution containing no carbon for 5 minutes. After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After immersion, it is repeatedly washed with ethanol. After washing
It is dried at a temperature of 120 ° C. for 20 minutes and the solvent is evaporated to form a carbon-free polyaniline film on the surface of the oxide film. After forming a carbon-free polyaniline film, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 1 hour. After immersion, it is repeatedly washed with ethanol. After washing, the film is dried at a temperature of 120 ° C. for 20 minutes to evaporate the solvent and form a carbon-containing polyaniline film on the surface of the carbon-free polyaniline film. After forming a carbon-containing polyaniline film, the device is immersed in a colloidal carbon dispersion liquid to form a carbon layer. After forming the carbon layer, silver paste is applied to form the silver layer. After forming the silver layer, the anode terminal and the cathode terminal are connected to each other, and further a molding process is performed with an epoxy resin to form a resin exterior.

Example 2: The same conditions as in Example 1 are used except for the conductive polymer film laminated on the surface of the oxide film. The conductive polymer film is formed by the following method. That is, 0.1 g of the dedoped polyaniline powder produced under the same conditions as in Example 1 and 0.18 g of dodecylbenzenesulfonic acid are thoroughly mixed in a dry nitrogen atmosphere with a stirrer. After this, the mixture is dissolved in 20 g of xylene and treated in an ultrasonic bath for 48 hours.
After sonication, the undissolved material is decanted and removed to produce a dark green, 0.5 wt% doped polyaniline solution. Next, the element after the oxide film is formed is dipped in the doped polyaniline solution. Then, the device is pulled up, washed repeatedly with ethanol, and further dried at a temperature of 120 ° C. for 30 minutes. Then, the steps from the dipping to the drying are repeated four times to form a carbon-free polyaniline film. In addition, carbon powder (particle size: 1 μm or less: 82% or more, 1-2 μ
m: 8% and 2-3 μm: 5%. ) Add 0.1 g and mix well to produce a carbon-containing doped polyaniline solution. Then, the element on which the carbon-free polyaniline film is formed is dipped in this solution for 2 minutes. After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. The dipping and drying steps are repeated twice to form a carbon-containing polyaniline film.

Example 3: The same conditions as in Example 1 are used except that a conductive polymer film is laminated on the surface of the oxide film by the following method. That is, first, as the dedoped polyaniline solution containing no carbon, one prepared under the same conditions as in Example 1 is used. Then, carbon powder (particle size: 2 μm or less: 45% or more, 2 to 4 μm: 25) was added to 10 g of this dedoped polyaniline solution having a concentration of 10 wt%.
%, 4 to 6 μm: 15%. ) 1 g is added and mixed well to produce a carbon-containing dedoped polyaniline solution. In addition, dodecylbenzenesulfonic acid 0.
5 g and ferric hydroxide 0.2 g are sufficiently mixed, and this is dissolved in butanol 20 g to prepare a doping solution. Then, the element after the oxide film is formed is dipped in the dedoped polyaniline solution for 2 minutes. After immersion, temperature 120
Dry at 30 ° C. for 30 minutes. After drying, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After the immersion, the film is repeatedly washed with ethanol and dried in a constant temperature bath at a temperature of 120 ° C. to form a polyaniline film containing carbon on the surface portion.

Example 4: The same conditions as in Example 1 are used except that a conductive polymer film is laminated on the surface of the oxide film by the following method. That is, first, as the carbon-free dedoped polyaniline solution, one having a concentration of 10% manufactured under the same conditions as in Example 1 is used. Also, a concentration of 10
1 g of carbon beads having an average particle size of 2 to 10 μm is added to 10 g of this wt% dedoped polyaniline solution, and they are sufficiently mixed to produce a carbon-containing dedoped polyaniline solution. Further, 0.5 g of α-naphthalene sulfonic acid and 0.2 g of ammonium persulfate are sufficiently mixed, and this is dissolved in 20 g of butanol to prepare a doping solution. Then, the element after the oxide film is formed is first immersed in the dedoped polyaniline solution for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After immersion, it is repeatedly washed with ethanol. After washing
By drying in a constant temperature bath at a temperature of 120 ° C., a conductive polyaniline film containing carbon is formed on the surface portion.

Next, with respect to the tantalum solid electrolytic capacitors of Examples 1 to 4, the initial characteristics and the respective characteristics after the high temperature no-load leaving test of leaving them in a high temperature atmosphere of 150 ° C. for 10 hours were measured. The results are shown in Table 1. The measurement is performed by applying a capacitance and tan δ of 120 Hz, an impedance of 100 KHz and a leakage current of 4V. The manufacturing method of the comparative example is as follows.

Comparative Example 1 The conditions are the same as in Example 1 except that the carbon-free polyaniline film is further coated with a carbon-free dedoped polyaniline solution to form a polyaniline film.

Comparative Example 2: The same conditions as in Example 2 except that a carbon-free polyaniline film is formed on the surface of a carbon-free polyaniline film by using a carbon-free doped polyaniline solution. And

[0029]

[Table 1]

As is clear from Table 1, according to Examples 1 to 4, compared with Comparative Examples 1 and 2 in which only a carbon-free polyaniline film was formed, the initial characteristics
Tan δ, impedance, and leakage current are decreasing. That is, tan δ is about 82.2 to 92.9%, impedance is about 54.9 to 76.9%, and leakage current is about 9.3 to 20.5%. Further, even after the high temperature unloaded test, according to Examples 1 to 4, tan δ is about 52.9 to 6 as compared with Comparative Examples 1 and 2.
Impedance of about 47.7-64.7% at 2.5%
And the leakage current is reduced to a magnitude of about 1.5 to 2.8%, respectively.

[0031]

As described above, according to the present invention, when a conductive polymer film is provided on the surface of an oxide film, at least the surface portion of the film is coated with a carbon-containing conductive polymer solution. Because of the formed structure, tan δ
It is possible to obtain a solid electrolytic capacitor that can improve various characteristics such as impedance, impedance and leakage current.

[Brief description of drawings]

FIG. 1 shows a sectional view of an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Element, 3 ... Oxide film, 4 ... Conductive polymer film, 5 ... Filler, 13 ... Solid electrolytic capacitor.

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[Procedure amendment]

[Submission date] May 29, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Detailed description of the invention

[Correction method] Change

[Correction contents]

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte.

[0002]

2. Description of the Related Art As a solid electrolytic capacitor, for example, a foil or a sintered body of a valve metal such as aluminum or tantalum is anodized to form an oxide film, and then a conductive polymer is formed on the surface of the oxide film. There is a structure in which a cathode layer is formed by forming a film made of and further laminating a carbon layer or a silver layer on the surface of this film. And, in the case of a chip type solid electrolytic capacitor, in order to maximize the internal volume ratio after forming the exterior by a molding method, etc.
The capacitor element has a rectangular parallelepiped shape. As the conductive polymer, π-conjugated organic conductive polymers such as polyacetylene, polythiophene, polypyrrole, and polyaniline are known. Then, in order to form a film of a conductive polymer, monomers of raw materials are polymerized to be polymerized. For example, a monomer is subjected to a polymerization reaction such as chemical oxidative polymerization, gas phase oxidative polymerization, and electrolytic polymerization on the surface of the oxide film. The conductive polymer such as polyaniline is formed by dipping the element after the oxide film is formed in a solution prepared by dissolving a prepolymerized polymer in a solvent, and then evaporating the solvent. ing.

[0003]

By the way, a conductive polymer solution such as an organic one has a large fluidity and a low viscosity. Then, a conductive polymer solution having a high fluidity such as an organic system is applied to a rectangular parallelepiped-shaped element, and when dried, due to surface tension, the planar portion of the element is thick and the ridges and corners are thick. A thin film of conductive polymer is formed.

Thermal stress is applied to each part of the capacitor element when forming a molded package on the capacitor element or mounting the capacitor. At this time, the ridges and corners of the capacitor element are relatively thin in thickness of the conductive polymer and are easily affected by thermal stress. Therefore, there are drawbacks in that the characteristics such as tan δ, impedance, and leakage current of the solid electrolytic capacitor are easily deteriorated.

A conductive polymer film formed by applying a conductive polymer solution having a high fluidity such as an organic system is
It has the disadvantages that the surface is smooth, the contact resistance with the carbon layer, which is the cathode layer, etc., is relatively large, and the impedance at high frequencies is high.

The present invention remedies the above-mentioned drawbacks and provides tan δ
It is an object of the present invention to provide a solid electrolytic capacitor capable of improving various characteristics such as impedance, impedance and leakage current.

[0007]

In order to solve the above problems, the present invention provides a solid electrolytic capacitor in which a film of a conductive polymer is laminated on an element having an oxide film formed on a valve metal, and a conductive material containing carbon is used. The present invention provides a solid electrolytic capacitor, characterized in that a conductive polymer film having at least a surface portion formed by applying a solution of a conductive polymer is provided.

When carbon is mixed in the solution of the conductive polymer, the fluidity of the solution is suppressed and the viscosity can be increased. For this reason, a thick conductive polymer film can be formed at the ridges and corners of the device. Therefore, when the mold exterior is formed, even if thermal stress is applied to the ridge line portion of the element, the effect thereof can be reduced. Therefore, characteristics such as tan δ and leakage current of the solid electrolytic capacitor can be improved. Further, since the surface portion of the conductive polymer film is formed by applying a solution of the conductive polymer containing carbon, it has an uneven shape. Therefore, the contact area between the conductive polymer film and the carbon layer is increased. Also, carbon is electrically conductive. Therefore, the contact resistance between the conductive polymer film and the carbon layer can be lowered, and the equivalent series resistance and impedance can be lowered in the low frequency region to the high frequency region.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. First, tantalum, aluminum, or the like is used as the valve metal. Further, as shown in FIG. 1, the element 1 is basically a sintered body made of fine powder of valve metal or a laminated or wound valve metal foil, and an oxide film 2 is provided on the surface thereof. ing. An anode lead wire 3 of tantalum or the like is drawn out from the element 1.

A film 4 made of a conductive polymer is provided on the surface of the oxide film 2. Then, carbon 5 is mixed with at least the surface portion of the film 4. As the conductive polymer, simple substances such as polyaniline, polypyrrole, polythiophene, polyparaphenylene, and polyacetylene, and mixtures of these with polymers such as polystyrene, polyethylene, polymethylmethacrylate, and polyacrylonitrile butadiene-styrene are used. Among them, polyaniline has a high solubility in a solvent, and a relatively high concentration solution can be prepared.

The carbon has a spherical shape, a scaly shape, an amorphous shape, or the like, and is crystalline or amorphous. And the average particle diameter of this carbon is 0.1 to 50 μm.
The range of m is good, and the range of 0.5 to 10 μm is particularly preferable. When the average particle diameter is smaller than 0.1 μm, the fluidity of the solution of the conductive polymer is difficult to improve and the viscosity cannot be increased when the blending amount is small. And, the compounding amount of carbon in the conductive polymer solution is preferably in the range of 1:20 to 2: 1 by volume ratio with respect to the conductive polymer. If the blending amount is less than 1/20, it becomes difficult to improve the fluidity of the conductive polymer solution. On the other hand, if the blending amount is more than twice, the conductive polymer binding between the carbon particles is reduced, and it becomes difficult to improve the impedance characteristics and the like of the capacitor in the high frequency region. Further, the thickness of the carbon-containing surface portion of the conductive polymer film is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 50 μm.

On the surface of the conductive polymer film 4, a carbon layer 6 made of carbon paste and a silver layer 7 made of silver paste are laminated to form a cathode layer, and a capacitor element 8 is provided.
Is formed. Then, the cathode terminal 9 is connected to the silver layer 7 by the silver conductive paste 10, and the anode lead wire 3
The anode terminal 11 is welded to. And the whole is covered with the resin exterior 12.

Next, a method of manufacturing the solid electrolytic capacitor 13 of the above embodiment will be described. First, the element 1 having a predetermined shape is formed using tantalum, aluminum, or the like. Then, the element 1 is anodized using an aqueous solution of nitric acid, phosphoric acid or the like to form an oxide film 2.

After forming the oxide film 2, the element 1 is dipped in a conductive polymer solution containing no carbon 5 or sprayed with this solution to apply the conductive polymer solution to the surface of the oxide film 2. . After application, the solvent is evaporated and dried. The steps from application of the conductive polymer solution to drying are repeated as necessary to form a conductive polymer film containing no carbon 5 and having a predetermined thickness on the element 1.

After forming the conductive polymer film containing no carbon 5, the element 1 is dipped in a conductive polymer solution in which carbon 5 is dispersed to apply this solution, and then the solvent is evaporated and dried. . Then, the steps from application of the liquid to drying are repeated as necessary to form a conductive polymer film containing carbon 5 having a predetermined thickness.

When a polyaniline solution is used as the conductive polymer solution, a previously doped polyaniline solution is applied and the solvent is evaporated and dried to form a film, or a dedoped polyaniline solution is applied. After that, a doping solution is applied and doping is performed, and then a similar process is performed to form a film.

The doped polyaniline solution is prepared by mixing the undoped polyaniline with a protic acid and dissolving it in an organic solvent. Examples of the protonic acid include camphorsulfonic acid, dodecylbenzenesulfonic acid, P-toluenesulfonic acid, naphthalenesulfonic acid, styrenesulfonic acid, organic sulfonic acids such as polymers thereof, phthalic acid,
It is prepared by mixing with an carboxylic acid such as oxalic acid, maleic acid, citric acid, chloroacetic acid, dichloroacetic acid, benzoic acid, salicylic acid or the like, and dissolving them in an organic solvent. As the organic solvent, N-methyl-2-pyrrolidone, N, N′-dimethylpropyleneurea, chloroform, m-cresol, trichlorobenzene, xylene, decalin or the like is used. The doped polyaniline solution preferably has a polyaniline concentration of 0.1 to 2 wt% and a dopant concentration of 0.1 to 2 wt%.

The dedoped polyaniline solution is
Polyaniline produced by chemical oxidative polymerization of aniline is dedoped with an alkali and dissolved in a solvent to produce. For chemical oxidative polymerization of aniline, the aniline salt is oxidatively polymerized in an aqueous solution containing a protonic acid and an oxidizing agent. As the aniline salt, salts of aniline such as hydrochloric acid, sulfuric acid, and borofluoric acid are used. Also, as the protic acid, hydrochloric acid, sulfuric acid, hydrofluoric acid, or the like is used. further,
As the oxidizing agent, a persulfate such as ammonium persulfate and potassium persulfate, a high valence compound such as hydrogen peroxide, potassium permanganate and ferric chloride, which can oxidize aniline, is used. When the aniline is chemically oxidatively polymerized, the temperature rises due to the heat of reaction, so the temperature is cooled to control the reaction temperature to 0 to 10 ° C., and the aqueous solution of the oxidant is reacted for a sufficient time. Further, the produced polymer is repeatedly washed and then dried. Thereafter, the produced polyaniline powder is suspended in aqueous ammonia, stirred, and separated by filtration to obtain dedoped polyaniline. Next, the dedoped polyaniline is dissolved in N-methyl-2-pyrrolidone or a mixed solvent of N-methyl-2-pyrrolid and another solvent to produce a dedoped polyaniline solution. At this time, the solubility can be increased by adding a reducing agent to the dedoped polyaniline to form the reduced dedoped polyaniline. In order to obtain the reduced type, a reducing agent is added to the undoped polyaniline solution, or the undoped polyaniline separated by filtration is dispersed in a non-solvent and the reducing agent is added. As the reducing agent, hydrazine compounds such as phenylhydrazine, hydrazine, hydrazine hydrate, and hydrazine sulfate, and hydrogenated metal compounds are used. At this time, the concentration of polyaniline is preferably in the range of 5 to 10%.

To form a conductive polymer film using a dedoped polyaniline solution, the solution is applied to form a film, and then a doping solution is applied to dope the film to impart conductivity. As the doping solution, a protic acid or a solution of a protic acid and an oxidizing agent in an organic solvent is used.
Organic solvents include, for example, ketones and esters, alcohols, aromatic hydrocarbons, nitriles, cellosolves,
A nitrogen-containing compound or the like is used. Further, as the oxidizing agent, for example, a disulfide compound, a benzothiazolylsulfenamide compound, a quinonedioxime compound, or the like is used.

After forming a conductive polymer film 4 consisting of a conductive polymer film containing no carbon and a conductive polymer film containing carbon, a carbon paste is applied to the surface of the film 4 to form a carbon layer 6. Then, a silver paste is applied to the surface of the carbon layer 6 to form the silver layer 7. After forming the silver layer 7, the cathode terminal 9 is connected to the silver layer 7 and the anode terminal 11 is connected to the anode lead wire 2. Then, the resin exterior 12 is formed by a resin molding method, a resin dipping method, or the like.

[0021]

Next, an embodiment of the present invention will be described. Example 1: Tantalum powder is used as the valve metal.
The capacitor element has a rectangular parallelepiped shape of 1.0 × 1.7 × 1.4 mm square, and the tantalum anode lead wire is drawn out. An oxide film is formed on this capacitor element, a carbon-free polyaniline film and a carbon-containing polyaniline film are sequentially laminated on the surface of this oxide film, and a carbon-containing polyaniline film is arranged on the surface portion. ing. A carbon layer and a silver layer are sequentially laminated on the surface of the carbon-containing polyaniline film to form a cathode layer. An anode terminal is connected to the anode lead wire and a cathode terminal is connected to the silver layer. Further, the capacitor element is covered with an exterior made of epoxy resin. The rating of this solid electrolytic capacitor is 4V, 10 μF.

The solid electrolytic capacitor of Example 1 is manufactured as follows. First, a molded body of tantalum powder is formed, and this molded body is sintered at a temperature of 1450 ° C. After forming the sintered body, the sintered body is immersed in a 0.1% aqueous nitric acid solution and anodized at a voltage of 24 V to form an oxide film. Also, in the Erlenmeyer flask of 1,
Aniline 50ml, 35% hydrochloric acid 50ml, 400m
1 of pure water is prepared to produce an aniline solution. Thereafter, the flask is kept in a cooling bath at a temperature of 0 ° C. Then, a solution prepared by dissolving 46 g of ammonium persulfate in 100 ml of pure water was dropped into the above aniline solution over about 2 hours,
Further, stirring is continued for 3 hours to chemically polymerize aniline. Then, the precipitate is filtered, washed with pure water, and repeatedly decanted until the pH of the washing liquid becomes 6 to 7. Further, in order to remove water, the substrate is washed with ethanol and methanol, and then dried under reduced pressure at room temperature for 48 hours.
After drying, 10 g of the produced powder is stirred for 2 hours while being dispersed in 3% ammonia 1 to dedope, and filtered. After filtration, it is repeatedly washed with pure water and then with methanol. After washing, it is dried under reduced pressure for 48 hours to produce undoped polyaniline powder. Next, 0.1 g of this dedoped polyaniline powder is mixed with 10 g of N-methyl-2-pyrrolidone and treated in an ultrasonic bath for 2 hours. After this treatment, the undissolved material in the solution is decanted and removed to produce a dedoped polyaniline solution. Also,
Separately, 0.5 g of P-toluenesulfonic acid and 0.2 g of ammonium persulfate are dissolved in 20 g of butanol to prepare a doping solution. Furthermore, 10 g of dedoped polyaniline solution having a concentration of 10 wt% was added to carbon powder (particle size: 2
μm or less: 45% or more, 2 to 4 μm: 25%, 4 to 6 μm
m: 15% ) 1 g is added and mixed well to produce a carbon-containing dedoped polyaniline solution.
Then, first, the element having the oxide film formed thereon is immersed in a dedoped polyaniline solution containing no carbon for 5 minutes.
After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After immersion, it is repeatedly washed with ethanol. After washing
It is dried at a temperature of 120 ° C. for 20 minutes and the solvent is evaporated to form a carbon-free polyaniline film on the surface of the oxide film. After forming a carbon-free polyaniline film, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 1 hour. After immersion, it is repeatedly washed with ethanol. After washing, the film is dried at a temperature of 120 ° C. for 20 minutes to evaporate the solvent and form a carbon-containing polyaniline film on the surface of the carbon-free polyaniline film. After forming a carbon-containing polyaniline film, the device is immersed in a colloidal carbon dispersion liquid to form a carbon layer. After forming the carbon layer, silver paste is applied to form the silver layer. After forming the silver layer, the anode terminal and the cathode terminal are connected to each other, and further a molding process is performed with an epoxy resin to form a resin exterior.

Example 2: The same conditions as in Example 1 are used except for the conductive polymer film laminated on the surface of the oxide film. The conductive polymer film is formed by the following method. That is, 0.1 g of the dedoped polyaniline powder produced under the same conditions as in Example 1 and 0.18 g of dodecylbenzenesulfonic acid are thoroughly mixed in a dry nitrogen atmosphere with a stirrer. After this, the mixture is dissolved in 20 g of xylene and treated in an ultrasonic bath for 48 hours.
After ultrasonic treatment, the undissolved material is decanted and removed to produce a dark green, 0.5 wt% doped polyaniline solution. Next, the element after the oxide film is formed is dipped in the doped polyaniline solution. Then, the device is pulled up, washed repeatedly with ethanol, and further dried at a temperature of 120 ° C. for 30 minutes. Then, the steps from the dipping to the drying are repeated four times to form a carbon-free polyaniline film. In addition, carbon powder (particle size: 1 μm or less: 82% or more, 1-2 μ
m: 8% and 2-3 μm: 5%. ) Add 0.1 g and mix well to produce a carbon-containing doped polyaniline solution. Then, the element on which the carbon-free polyaniline film is formed is dipped in this solution for 2 minutes. After the immersion, it is dried in air at a temperature of 120 ° C. for 30 minutes. The dipping and drying steps are repeated twice to form a carbon-containing polyaniline film.

Example 3: The same conditions as in Example 1 are used except that a conductive polymer film is laminated on the surface of the oxide film by the following method. That is, first, as the dedoped polyaniline solution containing no carbon, one prepared under the same conditions as in Example 1 is used. Then, 10 g of this dedoped polyaniline solution having a concentration of 10 wt% was added to carbon powder (particle size: 2 μm or less: 45% or more, 2 to 4 μm: 25).
%, 4 to 6 μm: 15%. ) 1 g is added and mixed well to produce a carbon-containing dedoped polyaniline solution. In addition, dodecylbenzenesulfonic acid 0.
5 g and ferric hydroxide 0.2 g are sufficiently mixed, and this is dissolved in butanol 20 g to prepare a doping solution. Then, the element after the oxide film is formed is dipped in the dedoped polyaniline solution for 2 minutes. After immersion, temperature 120
Dry at 30 ° C. for 30 minutes. After drying, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After the immersion, the film is repeatedly washed with ethanol and dried in a constant temperature bath at a temperature of 120 ° C. to form a polyaniline film containing carbon on the surface portion.

Example 4: The same conditions as in Example 1 are used except that a conductive polymer film is laminated on the surface of the oxide film by the following method. That is, first, as the carbon-free dedoped polyaniline solution, one having a concentration of 10% manufactured under the same conditions as in Example 1 is used. Also, a concentration of 10
1 g of carbon beads having an average particle diameter of 2 to 10 μm is added to 10 g of this dedoped polyaniline solution of wt% and mixed sufficiently to produce a carbon-containing dedoped polyaniline solution. Further, 0.5 g of α-naphthalenesulfonic acid and 0.2 g of ammonium persulfate are sufficiently mixed, and this is dissolved in 20 g of butanol to prepare a doping solution. Then, the element after the oxide film is formed is first immersed in the dedoped polyaniline solution for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in a dedoped polyaniline solution containing carbon for 2 minutes. After the immersion, it is dried at a temperature of 120 ° C. for 30 minutes. After drying, the device is immersed in the doping solution for 3 hours. After immersion, it is repeatedly washed with ethanol. After washing
By drying in a constant temperature bath at a temperature of 120 ° C., a conductive polyaniline film containing carbon is formed on the surface portion.

Next, with respect to the tantalum solid electrolytic capacitors of Examples 1 to 4, the initial characteristics and the respective characteristics after the high temperature no-load leaving test of leaving them in a high temperature atmosphere of 150 ° C. for 10 hours were measured. The results are shown in Table 1. The measurement is performed by applying a capacitance and tan δ of 120 Hz, an impedance of 100 KHz, and a leakage current of 4V. The manufacturing method of the comparative example is as follows.

Comparative Example 1 The conditions are the same as in Example 1 except that a carbon-free polyaniline film is further coated with a carbon-free dedoped polyaniline solution to form a polyaniline film.

Comparative Example 2: The same conditions as in Example 2 except that a carbon-free polyaniline film is formed on the surface of a carbon-free polyaniline film by using a carbon-free doped polyaniline solution. And

[0029]

[Table 1]

As is clear from Table 1, according to Examples 1 to 4, compared with Comparative Example 1 and Comparative Example 2 in which only a carbon-free polyaniline film was formed, tan δ and impedance of initial characteristics, Leakage current is low.
That is, tan δ is about 82.2 to 92.9%, impedance is about 54.9 to 76.9%, and leakage current is about 9.3 to 20.5%. Further, even after the high temperature unloaded test, according to Examples 1 to 4, tan δ is about 5 as compared with Comparative Examples 1 and 2.
2.9 to 62.5% and impedance of about 47.7 to
The leakage current is reduced to 64.7%, and the leakage current is reduced to about 1.5 to 2.8%.

[0031]

As described above, according to the present invention, when a conductive polymer film is provided on the surface of an oxide film, at least the surface portion of the film is coated with a carbon-containing conductive polymer solution. Because of the formed structure, tan
A solid electrolytic capacitor capable of improving various characteristics such as δ, impedance, and leakage current can be obtained.

[Brief description of drawings]

FIG. 1 shows a sectional view of an embodiment of the present invention.

[Explanation of Codes] 1 ... Element, 3 ... Oxide film, 4 ... Conductive polymer film, 5 ... Filler, 13 ... Solid electrolytic capacitor.

Claims (1)

[Claims] 1. A solid electrolytic capacitor in which a conductive polymer film is laminated on an element having an oxide film formed on a valve metal, wherein a conductive polymer solution containing carbon is applied to form at least a surface portion of the conductive polymer. A solid electrolytic capacitor characterized by comprising a film of.