JP2001267185A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolytic capacitor capable of providing an excellent percentage of capacity achievement and further improving reliability, by suppressing a damage of a dielectric oxide film when a manganese oxide is formed. SOLUTION: The method for manufacturing the solid electrolytic capacitor comprises the steps of dipping an anode 1 formed of a dielectric oxide film layer 2 in a manganese nitrate solution, then dehydrating the anode to form an anhydrous manganese nitrate layer, then dipping the anode 1 in a permanganate aqueous solution, drying then anode 1 to form a manganese dioxide layer, and then forming a conductive polymer layer thereon by an electrolytic polymerization. Thus, a thermal decomposition reaction at a high temperature is eliminated in the formation of the manganese dioxide layer. A damage of the layer 2 is suppressed to reduce a leakage current. Further, since more manganeses oxide layer is formed to increase an area to be covered, the area to be coated of the conductive polymer due to the later electrolytic polymerization is improved, and the excellent percentage of capacity achievement can be exhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor, which is mainly based on a method for forming a solid electrolyte using a conductive polymer.

[0002]

2. Description of the Related Art With the recent digitization of electronic devices, capacitors used in these devices also have low impedance in a high-frequency region, and there is an increasing demand for small-sized and large-capacity capacitors. Examples of the capacitor include a plastic film capacitor, a mica capacitor, a multilayer ceramic capacitor and the like, as well as an aluminum dry electrolytic capacitor and an aluminum or tantalum solid electrolytic capacitor.

In the above-mentioned aluminum dry electrolytic capacitor, an etched anode / cathode aluminum foil is wound up through a separator and impregnated with a liquid electrolyte, and in an aluminum or tantalum solid electrolytic capacitor, the above-mentioned aluminum is used. The electrolyte is solidified to improve the characteristics of the dry electrolytic capacitor. The solid electrolyte is formed by immersing the anode body in a manganese nitrate solution and then thermally decomposing the anode body in a high-temperature furnace at about 250 to 350 ° C. to form a manganese oxide layer. In the case of such a solid electrolytic capacitor, since the electrolyte is solid, there are no drawbacks such as electrolyte loss at high temperatures, capacity reduction due to dry-up, and functional deterioration caused by solidification at low temperatures, and compared with liquid electrolytes. It shows good frequency characteristics and good temperature characteristics.

Further, according to the techniques disclosed in JP-A-60-37114 and JP-A-60-244017, electrolytic polymerization of a heterocyclic monomer such as pyrrole or thiophene using a supporting electrolyte is disclosed. It describes that a solid electrolytic capacitor having excellent frequency characteristics and temperature characteristics can be obtained using a conductive polymer containing an anion of a supporting electrolyte as a dopant as a solid electrolyte.

[0005]

However, in a conventional solid electrolytic capacitor using a conductive polymer as a solid electrolyte, a method for forming a conductive polymer on an electrode is disclosed in, for example, JP-A-63-173313. First, a conductive polymer layer is formed on a dielectric oxide film by chemical polymerization using an oxidizing agent, and the conductive polymer becomes a true electrolyte through the polymer of the conductive polymer layer. There is a method in which a conductive polymer is formed by electrolytic polymerization, but in such a method, the conductive polymer layer formed by the above chemical polymerization is used as a power supply portion in a later step of electrolytic polymerization. However, there has been a problem that productivity is remarkably inferior, cost is increased, and yield is poor.

A method of using manganese oxide as a conductive layer necessary for forming a conductive polymer layer on the surface of a dielectric oxide film by electrolytic polymerization has been widely adopted. The formation of manganese nitrate is performed by thermal decomposition of a manganese nitrate solution at a high temperature. In this method, the dielectric oxide film generated during the thermal decomposition is greatly damaged. Since the amount of oxides generated is small and dispersed in an island form, multiple thermal decomposition reactions are required to uniformly cover the surface of the dielectric oxide film, which further damages the dielectric oxide film. When a solid electrolytic capacitor is manufactured using such a capacitor, there is a problem that the leakage current characteristics are deteriorated.

For the purpose of suppressing such damage to the dielectric oxide film, the technique described in JP-A-6-124858 does not produce manganese oxide by a thermal decomposition reaction, but uses an aqueous solution of permanganate. In a method of obtaining manganese oxide by adhering and reducing this by heating, and in the technique described in JP-A-6-84706, manganese oxide is produced by a chemical oxidation-reduction reaction of acetate and permanganate. Although a method for producing an object is disclosed, it has been difficult to drastically solve the above-mentioned conventional problems even by such a technique.

The present invention solves such a conventional problem,
An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor capable of greatly improving performance, productivity and reliability by forming a manganese dioxide layer while suppressing damage to a dielectric oxide film. is there.

[0009]

According to a first aspect of the present invention, there is provided an anode body having a dielectric oxide film layer formed thereon, wherein the anode body is dehydrated after being immersed in a manganese nitrate solution. Thus, an anhydrous manganese nitrate layer is formed on the dielectric oxide film layer, then the anode body is immersed in a permanganate aqueous solution, and a manganese dioxide layer is formed on the dielectric oxide film layer by a chemical oxidation-reduction reaction. After the formation, it is a method of manufacturing a solid electrolytic capacitor so as to form a conductive polymer layer on these by electrolytic polymerization,
This method does not require a thermal decomposition reaction at a high temperature when forming a manganese dioxide layer, thereby suppressing damage to the dielectric oxide film layer and obtaining a high-performance solid electrolytic capacitor with reduced leakage current. It has the effect of being able to do so.

[0010] The invention described in claim 2 of the present invention is, in particular,
When the anode body is immersed in a manganese nitrate solution and then dehydrated to form an anhydrous manganese nitrate layer on the dielectric oxide film layer,
It is designed to be dried under reduced pressure, and by this method,
In addition to being able to be dried at low temperature, it has the effect that only manganese nitrate is supported on the dielectric oxide film, and even the water inside the anode body can be quickly dehydrated, as compared with the case of drying under normal pressure. .

[0011] The invention described in claim 3 of the present invention is, in particular,
Forming an anhydrous manganese nitrate layer, subsequently immersing the anode body in an aqueous solution of permanganate, and repeating the step of forming a manganese dioxide layer by a chemical oxidation-reduction reaction two or more times, By this method, more manganese dioxide layers can be formed and the covering area can be increased, so that the covering area of the conductive polymer by the subsequent electrolytic polymerization can be improved, and an excellent capacity achievement rate can be exhibited. It has the function and effect.

The invention described in claim 4 of the present invention particularly provides
A step of repairing the dielectric oxide film layer is provided before the step of forming the conductive polymer layer, and this method has an effect of improving the leakage current characteristics.

The invention according to claim 5 of the present invention particularly provides
The concentration of the aqueous solution of permanganate is set to 0.2 mol / L or less. According to this method, more manganese dioxide layers can be formed to increase the covering area. This has the effect of increasing the area covered with the conductive polymer and exhibiting an excellent capacity achievement rate. In addition, when the concentration of the aqueous solution of permanganate is 0.2 mol / L or more, the chemical oxidation reaction occurs rapidly only on the surface of the anode body, and the inside cannot be sufficiently filled with the solid electrolyte, which is not preferable.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a conceptual diagram schematically illustrating the structure of a solid electrolytic capacitor. In FIG. 1, reference numeral 1 denotes an anode body, and the anode body 1 uses an aluminum foil which is a valve action metal and has a surface thereof. Are roughened by etching.
Reference numeral 2 denotes a dielectric oxide film layer formed by anodizing the surface of the anode body 1, and 3 denotes a dielectric oxide film layer 2
The solid electrolyte layer 3 is composed of a manganese oxide layer and a conductive polymer layer. 4 is a carbon layer formed on the solid electrolyte layer 3 and 5 is a silver layer formed on the carbon layer 4. The carbon layer 4 and the silver layer 5 constitute a cathode layer. It is. In addition, + and-in the figure are an anode lead and a cathode lead respectively drawn from the anode body 1 and the cathode layer.

(Embodiment 1) Hereinafter, the first embodiment of the present invention will be described with reference to Embodiment 1.

First, as in the solid electrolytic capacitor shown in FIG. 1, an anode body 1 having a size of 3 mm × 4 mm made of aluminum having an anode lead connected to one end is prepared. Anodizing is performed for 60 minutes at an applied voltage of 12 V and an aqueous solution temperature of 70 ° C. for 60 minutes using an aqueous solution of ammonium acid, so that a dielectric oxide film layer 2
Was formed.

Next, the anode body 1 having the dielectric oxide film layer 2 formed thereon is immersed in a 30% manganese nitrate solution, pulled up, and subjected to a dehydration treatment at 120 ° C. for 10 minutes. After forming the anhydrous manganese nitrate layer on the layer 2, the anode body 1 on which the anhydrous manganese nitrate layer is formed is immersed in a potassium permanganate solution having a concentration of 0.2 mol / L and a pH of 3 to chemically A manganese dioxide layer to be a part of the solid electrolyte layer 3 was formed on the dielectric oxide film layer 2 by a redox reaction.

Next, the pyrrole monomer 0.5 mol / L
And sodium propylnaphthalenesulfonate 0.1mo
The anodic body 1 on which the manganese dioxide layer has been formed is immersed in a polymer solution for forming a solid electrolyte prepared by adding water as a solvent after pre-mixing 1 / L with each other. Bring the electrode for polymerization initiation close to the surface and set the temperature of the polymerization solution to 3
Electroconductive polymerization was performed at 0 ° C. and a polymerization voltage of 3 V to form a conductive polymer layer, thereby forming a solid electrolyte layer 3.

Thereafter, a colloidal carbon suspension is applied to the anode body 1 on which the solid electrolyte layer 3 is formed as a cathode extraction layer, and the suspension is dried to form a carbon layer 4.
Is formed, a silver paste is applied, and the silver paste is dried to form a silver layer 5 to provide a cathode layer. After connecting a cathode lead to this cathode layer, the anode body 1 is made of epoxy resin.
Was coated (not shown) to complete a solid electrolytic capacitor.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to Embodiment 2.

The second embodiment is different from the first embodiment in that the method of forming the anhydrous manganese nitrate layer on the dielectric oxide film layer is different from that of the first embodiment. Therefore, the description of the same portions will be omitted, and only different portions will be described.

In the method for forming an anhydrous manganese nitrate layer according to the second embodiment, the anode body 1 having the dielectric oxide film layer 2 formed thereon is immersed in a 30% manganese nitrate solution and pulled up, and dried under reduced pressure. An anhydrous manganese nitrate layer was formed on the dielectric oxide film layer 2 by performing a dehydration treatment at 30 ° C. for 10 minutes. That is, the dehydration process performed in the first embodiment is performed in a state of drying under reduced pressure.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described with reference to Embodiment 3.

The third embodiment is different from the first embodiment in that the method of forming the manganese dioxide layer is different. The other steps are the same as those of the first embodiment. The description is omitted, and only different parts will be described.

In the method of forming a manganese dioxide layer in the third embodiment, the anode body 1 on which the dielectric oxide film layer 2 is formed is immersed in a 30% manganese nitrate solution, pulled up, and dehydrated at 120 ° C. for 10 minutes. After forming an anhydrous manganese nitrate layer on the dielectric oxide film layer 2 by performing the treatment, the anode body 1 having the anhydrous manganese nitrate layer formed thereon is treated with a permanganese solution having a concentration of 0.2 mol / L and a pH of 3. The step of forming a manganese dioxide layer according to the first embodiment, wherein the manganese dioxide layer is formed as a part of the solid electrolyte layer 3 on the dielectric oxide film layer 2 by a chemical oxidation-reduction reaction by dipping in a potassium acid solution. Was repeated twice.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described with reference to Embodiment 4.

The fourth embodiment is different from the first embodiment in that a step of repairing the conductive oxide layer is provided before the step of forming the conductive polymer layer in the first embodiment. Since the configuration is the same as that of the first embodiment, a description of the same portions will be omitted, and only different portions will be described.

In the fourth embodiment, the anode body 1 on which the manganese dioxide layer is formed is immersed in a 3% aqueous solution of ammonium adipate, and anodized at a temperature of 70 ° C. for 30 minutes to perform dielectric oxidation. The coating layer 2 was repaired.

(Embodiment 5) Hereinafter, a fifth embodiment of the present invention will be described with reference to Embodiment 5.

The fifth embodiment is different from the first embodiment in the method of forming the manganese dioxide layer. Other than this, the fifth embodiment is the same as the first embodiment. The description is omitted, and only different parts will be described.

In the method for forming a manganese dioxide layer in the fifth embodiment, the anode body 1 on which the anhydrous manganese nitrate layer is formed is immersed in a potassium permanganate solution having a concentration of 0.1 mol / L and a pH of 3, A manganese dioxide layer to be a part of the solid electrolyte layer 3 was formed on the dielectric oxide film layer 2 by a chemical oxidation-reduction reaction. That is, the concentration of the potassium permanganate solution of the first embodiment is changed from 0.2 mol / L to 0.1 mol / L.

(Comparative Example) First, a conventional product was used as a comparative example.
3mm made of aluminum with anode lead connected to one end
An anode body having a size of × 4 mm was prepared, and the anode body was applied with a 3% ammonium adipate aqueous solution at an applied voltage of 12 V.
Anodization was performed at an aqueous solution temperature of 70 ° C. for 60 minutes to form a dielectric oxide film layer on the surface of the anode body. Next, the anode body on which the dielectric oxide film layer was formed was immersed in a 30% manganese nitrate solution, pulled up, air-dried, and then subjected to a thermal decomposition treatment at 300 ° C. for 10 minutes to obtain a solid electrolyte layer. A manganese dioxide layer that became part of the manganese dioxide was formed.

Next, the pyrrole monomer 0.5 mol / L
And sodium propylnaphthalenesulfonate 0.1mo
The manganese dioxide layer-formed anode body was immersed in a polymer solution for forming a solid electrolyte prepared by adding water as a solvent after mixing 1 / L in advance, and the surface of the anode body was immersed in the polymer solution. An electrode for polymerization initiation is brought close to the mixture and the temperature of the polymerization solution is set to 30.
A conductive polymer layer was formed by performing electropolymerization at a polymerization temperature of 3 ° C. and a polymerization voltage of 3 V, thereby forming a solid electrolyte layer.

Thereafter, a colloidal carbon suspension is applied as a cathode extraction layer to the anode body having the solid electrolyte layer formed thereon, and the suspension is dried to form a carbon layer. Further, a silver paste is applied and dried. Then, a cathode layer was formed by forming a silver layer, and a cathode lead was connected to the cathode layer. Then, an outer surface of the anode body was covered with an epoxy resin to complete a solid electrolytic capacitor.

Embodiments 1 to 5 manufactured as described above
And the solid electrolytic capacitor according to the comparative example (the number of each is 10), the capacitance at 120 Hz, tan δ, and the leakage current of one minute value when the rated voltage (2 V) was applied were measured, and the results were averaged. And (Table 1).

[0037]

[Table 1]

As is clear from Table 1, the solid electrolytic capacitor according to the present invention does not require a thermal decomposition reaction at a high temperature to form a manganese dioxide layer, so that the dielectric oxide film is not damaged. It can be seen that they exhibit extremely low leakage current characteristics. In addition, since the anode body immersed in the manganese nitrate solution is dehydrated, the manganese nitrate is retained to the inside, the oxidation-reduction reaction with potassium permanganate is easily promoted inside the anode body, and the thermal decomposition reaction Compared to the formation of the manganese oxide layer obtained, the manganese dioxide coating area is increased, and the formation of a conductive polymer by electrolytic polymerization, which is a subsequent step, is also formed to the inside of the anode body. Shows the achievement rate.

In the present embodiment, the case where aluminum is used as the material of the anode body has been described. However, the present invention is not limited to this, and other valve action metals such as tantalum and niobium may be used. May be.

Further, in the present embodiment, an example using polypyrrole as the conductive polymer material has been described. However, the present invention is not limited to this, and compounds obtained from aniline, thiophene and derivatives thereof are used. It may be.

Further, in the present embodiment, the case where a potassium permanganate solution is used as the aqueous solution of permanganate has been described. However, the present invention is not limited to this, and permanganate ions are used as anions. Any other salt may be used as long as it contains a salt.

Further, in the present embodiment, the case where sodium propylnaphthalenesulfonate is used as the supporting electrolyte has been described. However, the present invention is not limited to this, and it is possible to use a material having a high conductivity by doping. However, other than this may be used.

[0043]

As described above, according to the present invention, an anode body having a dielectric oxide film layer formed thereon is immersed in a manganese nitrate solution and then dehydrated to form an anhydrous manganese nitrate layer on the dielectric oxide film layer. Subsequently, the anode body is immersed in an aqueous solution of permanganate, a manganese dioxide layer is formed by a chemical oxidation-reduction reaction, and a conductive polymer layer is formed thereon by electrolytic polymerization. The formation of a manganese dioxide layer eliminates the need for a thermal decomposition reaction at high temperatures, thus suppressing damage to the dielectric oxide film layer and reducing leakage current. Can be obtained.
In addition, since the covering area can be enlarged by forming more manganese dioxide layers, the covering area of the conductive polymer by the subsequent electrolytic polymerization can be improved, and an excellent capacity achievement rate can be exhibited. is there.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram schematically showing a configuration of a solid electrolytic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 anode body 2 dielectric oxide film layer 3 solid electrolyte layer 4 carbon layer 5 silver layer

Claims (5)

[Claims] 1. A dielectric oxide film layer is formed by anodic oxidation on the outer surface of an anode body made of a valve metal, and then the anode body is immersed in a manganese nitrate solution and then dehydrated, whereby the dielectric oxide film is formed. After forming an anhydrous manganese nitrate layer on the layer, subsequently immersing the anode body in an aqueous solution of permanganate to form a manganese dioxide layer on the dielectric oxide film layer by a chemical oxidation-reduction reaction, A method for producing a solid electrolytic capacitor in which a conductive polymer layer is formed on a layer by electrolytic polymerization. 2. The solid electrolytic capacitor according to claim 1, wherein when the anode body is immersed in a manganese nitrate solution and then dehydrated to form an anhydrous manganese nitrate layer on the dielectric oxide film layer, the anode body is dried under reduced pressure. Manufacturing method. 3. The step of forming an anhydrous manganese nitrate layer, subsequently immersing the anode body in a permanganate aqueous solution, and forming a manganese dioxide layer by a chemical oxidation-reduction reaction is repeated twice or more. A method for manufacturing the solid electrolytic capacitor according to claim 1. 4. Prior to the step of forming a conductive polymer layer,
The method for manufacturing a solid electrolytic capacitor according to claim 1, further comprising a step of repairing the dielectric oxide film layer. 5. The concentration of the aqueous solution of permanganate is 0.2 m
2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor is at most ol / L.