JP2003037024A - Method of manufacturing solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid electrolytic capacitor using a polymerization solution for forming a solid electrolyte with which a large capacitance can be achieved, an impededance characteristic in a high-frequency range can be improved, and electrolytic polymerization time can be shortened while maintaining a leakage current characteristic. SOLUTION: An anionic surfactant of a molecular weight of 180 or larger, having a polymeric monomer and an alkyl group or an aromatic ring is mixed beforehand, and water, which is main solvent, is added to the mixture to obtain a solution. A pH regulator is added to adjust the solution to be pH 5 or lower, and thus a polymerization solution for forming a solid electrolyte is prepared. By using the polymerization solution, a solid electrolytic layer 8 is formed on a dielectric oxide film 7 formed on a surface of valve action metal by electrolytic polymerization so that the anionic surfactant is selectively taken in the solid electrolyte as a dopant.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a solid electrolytic capacitor using a polymerization liquid for forming a solid electrolyte.

[0002]

2. Description of the Related Art With the recent digitalization of electronic devices, the capacitors used for them have low impedance in the high frequency region, and there is an increasing demand for small and large capacitors. Conventionally, plastic film capacitors, mica capacitors, laminated ceramic capacitors and the like have been used as capacitors used for such high frequency regions. In addition, there are also aluminum dry electrolytic capacitors and aluminum or tantalum solid electrolytic capacitors. In the above aluminum dry electrolytic capacitors, the etched positive and negative electrode aluminum foil is wound around a separator and a liquid electrolyte is used. .

In addition, in the case of aluminum or tantalum solid electrolytic capacitors, solidification of the electrolyte is carried out in order to improve the characteristics of the above-mentioned aluminum dry type electrolytic capacitors. To form this solid electrolyte, the anode body is dipped in a manganese nitrate aqueous solution,
This is pyrolyzed in a high temperature furnace at about 250 to 350 ° C. to form a manganese oxide layer. In the case of this capacitor, since the electrolyte is a solid, there are no drawbacks such as electrolyte outflow at high temperature and capacity reduction due to dry-up, functional deterioration due to solidification in low temperature range, and better frequency characteristics and temperature characteristics than liquid electrolyte. Is shown.

Further, in recent years, in order to increase the electric conductivity of the solid electrolyte, a solid electrolytic capacitor in which a polymerizable monomer such as pyrrole or thiophene is polymerized to form a conductive polymer and which is used as a solid electrolyte has been put into practical use. .

[0005]

One of the methods for forming a solid electrolyte of a capacitor using a conductive polymer as the above solid electrolyte.
One is to form a precoat layer made of a conductive material such as manganese oxide or a conductive polymer on the surface of the dielectric oxide film of the valve metal, and then supply power from the external electrode in the polymerization liquid containing the polymerizable monomer. There is electrolytic polymerization to form a solid electrolyte of a conductive polymer, which makes it possible to produce a solid electrolytic capacitor having good characteristics stably in a relatively short time. Further, in the production of solid electrolytic capacitors, productivity can be further improved by increasing the polymerization rate of electrolytic polymerization to reduce the time required for forming the solid electrolyte.

However, as a method for increasing the polymerization rate in electrolytic polymerization, it is possible to increase the polymerization temperature, increase the polymerization voltage, etc. However, when the polymerization temperature is increased, the polymerizable monomer is likely to volatilize. However, there is a problem that the composition of the polymerization solution becomes unstable, and when increasing the polymerization voltage, another reaction different from the polymerization such as electrolysis of water is likely to occur in the polymerization solution containing water. In addition, the polymerization efficiency is reduced, and there are problems such as impedance deterioration due to the adhesion of bubbles generated by the electrolysis of water,
It was difficult to stably exhibit excellent product characteristics as a capacitor and to increase the electrolytic polymerization rate.

Further, when manganese oxide is used as a part of the solid electrolyte, when the manganese oxide is formed, the conventional pyrolysis method damages the dielectric oxide film due to the high temperature treatment and leaks. The phenomenon that the current becomes large is seen, and furthermore, the manganese oxide formed as a part of the solid electrolyte does not easily cover the inside of the electrode body, resulting in a low capacity drawing rate and poor impedance characteristics. There was a problem.

The present invention solves the above-mentioned conventional problems,
It is an object of the present invention to provide a method for producing a solid electrolytic capacitor using a polymerization solution for forming a solid electrolyte, which can simultaneously improve performance and reduce electrolytic polymerization time.

[0009]

In order to solve the above-mentioned problems, the present invention provides a mixture of a polymerizable monomer and an anionic surfactant having an alkyl group or an aromatic ring and having a molecular weight of 180 or more in advance. The main solvent, water, is added to form a solution, and the solution is adjusted to pH 5 or below.
A polymerization solution for forming a solid electrolyte is prepared by adding a regulator, and the polymerization solution for forming a solid electrolyte is used to form the anionic surfactant on the dielectric oxide film formed on the surface of the valve metal. Is a production method in which a solid electrolyte layer is formed by electrolytic polymerization so that is selectively incorporated into the solid electrolyte as a dopant.

According to the present invention, the polymerization rate is improved by selectively incorporating an anionic surfactant having excellent dedoping resistance as a dopant in the solid electrolyte, and the capacitor is left in the initial stage and in high temperature and high humidity. It is possible to manufacture a solid electrolytic capacitor having excellent impedance characteristics even under such conditions.

This is because when the anionic surfactant is present in the polymer electrolyte for forming a solid electrolyte containing water and the anionic surfactant takes a micellar structure incorporating a polymerizable monomer, There is an effect of improving the polymerization rate by facilitating drawing to the anode side forming a polymerized film using an anionic material as the activator, and the anionic surfactant present in the vicinity of the polymerizable monomer and as a dopant in the polymerized film is present. It is considered that a solid electrolytic capacitor having excellent impedance characteristics can be obtained because it is easily taken in.

Further, when two or more kinds of anionic surfactants are present in the polymerization liquid for forming a solid electrolyte, it is considered that a material that is easily compatible with the polymerizable monomer is selectively taken in, and thus a material that is more easily taken in is obtained. A solid electrolytic capacitor having excellent impedance characteristics can be obtained by using a material having an alkyl group and an aromatic ring and having a molecular weight of 180 or more. In addition, although it is considered that the pH adjuster is an anionic surfactant, by using a material having an alkyl group and an aromatic ring and having a molecular weight of 180 or more for a material that is more easily incorporated for the same reason as above, It is possible to obtain a solid electrolytic capacitor having excellent impedance characteristics.

Further, by using an acid having an alkyl group or an aromatic ring such as an alkyl phosphoric acid ester, an alkyl sulfonic acid or an aryl sulfonic acid as a pH adjusting agent, it is possible to compare with the case where an acid such as phosphoric acid or sulfuric acid is used. Then, there is an effect of reducing chemical stress on the dielectric oxide film of the valve action metal, and excellent leakage current characteristics and impedance characteristics can be obtained.

When manganese oxide is used as a part of the solid electrolyte, when the manganese oxide is formed, the dielectric oxide film formed on the valve action metal surface is p
By dipping in a manganese nitrate aqueous solution having a pH of 2 or less by adding an H-adjusting agent and thermally decomposing this to form a manganese oxide layer, the generated manganese oxide has a small particle size and is uniformly formed. Because
It is possible to coat even the inside of the smaller pores of the dielectric oxide film, and this can prevent deterioration of the dielectric oxide film.

Further, since the manganese oxide having a uniform particle size and a small size is coated over a wide range, the adhesion to the electrolytic polymerized film by the subsequent low pH solid electrolyte forming polymerization solution can be improved. In particular, when a low pH manganese nitrate aqueous solution containing nitric acid / hydrochloric acid / sulfuric acid / phosphoric acid / boric acid / acetic acid / phosphoric acid ester is thermally decomposed, a minute and uniform manganese oxide is formed. A gas generation path can be secured, the stress on the dielectric oxide film is small, and the effect of suppressing leakage current can be seen, and since the coverage is increased, a solid electrolytic capacitor with an excellent capacity extraction rate can be obtained. is there.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of the present invention will be described below, but the present invention is not limited thereto.

(Embodiment 1) (Example 1) FIG. 1 is a cross-sectional view showing a structure of a solid electrolytic capacitor according to an embodiment of the present invention. First, a 3 mm × 4 mm aluminum-etched aluminum plate with a lead as an anode. Foil 6 was used. An aqueous solution of 3% ammonium adipate was used for this with an applied voltage of 12 V and an aqueous solution temperature of 70 ° C.
Dielectric oxide film 7 was formed on the surface of aluminum etched foil 6 by performing anodic oxidation for minutes. Then p
The manganese oxide layer, which becomes a part of the solid electrolyte layer 8, is formed by immersing in a 30% aqueous solution of manganese nitrate having H of 3.73 and naturally drying, and then performing thermal decomposition treatment at 300 ° C. for 10 minutes. did.

Next, the pyrrole monomer 0.5 mol / L
And sodium propylnaphthalene sulfonate 0.1mo
After preliminarily mixing 1 / L, water as a solvent and propyl phosphate as a pH adjuster were added to prepare a polymerization solution for solid electrolyte formation in which the pH was adjusted to 2. The electrode was brought close to the element surface, and electrolytic polymerization was performed at a liquid temperature of 30 ° C. and a polymerization voltage of 3 V to form a solid electrolyte layer 8. Thereafter, a carbon layer 9 obtained by applying and drying a colloidal carbon suspension as a cathode extraction layer and a silver layer 10 obtained by applying and drying a silver paste are formed, and the carbon layer 9 and the silver layer 10 are combined. As a cathode lead-out portion. Then, it was packaged with epoxy resin to complete 10 solid electrolytic capacitors. The rated voltage of this solid electrolytic capacitor is 6.3V
Is.

Example 2 FIG. 1 is a sectional view showing the structure of a solid electrolytic capacitor according to an embodiment of the present invention, in which a lead-attached 3 mm × 4 mm aluminum etched foil 6 is used. An aqueous solution of 3% ammonium adipate was used to apply a voltage of 12 V and an aqueous solution temperature of 70
By performing anodization at 60 ° C. for 60 minutes, a dielectric oxide film 7 was formed on the surface of the aluminum etched foil 6. Then, nitric acid, which is a pH adjuster, was added to a 30% aqueous solution of manganese nitrate having a pH of 3.73, and the resultant was immersed in a solution having a pH of 2 and naturally dried, and then subjected to a thermal decomposition treatment at 300 ° C. for 10 minutes. By carrying out, a manganese oxide layer which becomes a part of the solid electrolyte layer 8 was formed.

Next, the pyrrole monomer 0.5 mol / L
And sodium propylnaphthalene sulfonate 0.1mo
After preliminarily mixing 1 / L, water as a solvent and propyl phosphate as a pH adjuster were added to prepare a polymerization solution for solid electrolyte formation in which the pH was adjusted to 2. The electrode was brought close to the element surface, and electrolytic polymerization was performed at a liquid temperature of 30 ° C. and a polymerization voltage of 3 V to form a solid electrolyte layer 8. Thereafter, a carbon layer 9 obtained by applying and drying a colloidal carbon suspension as a cathode extraction layer and a silver layer 10 obtained by applying and drying a silver paste are formed, and the carbon layer 9 and the silver layer 10 are combined. As a cathode lead-out portion. Then, it was packaged with epoxy resin to complete 10 solid electrolytic capacitors. The rated voltage of this solid electrolytic capacitor is 6.3V
Is.

Example 3 A solid electrolytic capacitor 1 was prepared in the same manner as in Example 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 1.5.
0 pieces were produced.

Example 4 Ten solid electrolytic capacitors were produced in the same manner as in Example 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 1.

(Embodiment 5) A solid electrolytic capacitor 1 was prepared in the same manner as in Embodiment 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0.5.
0 pieces were produced.

Example 6 A solid electrolytic capacitor 1 was manufactured in the same manner as in Example 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0.3.
0 pieces were produced.

(Embodiment 7) A solid electrolytic capacitor 1 was manufactured in the same manner as in Embodiment 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0.1.
0 pieces were produced.

(Example 8) A solid electrolytic capacitor 1 was prepared in the same manner as in Example 2 except that nitric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0 or less.
0 pieces were produced.

(Example 9) Solid electrolytic capacitor 1 was manufactured in the same manner as in Example 2 except that sulfuric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0 or less.
0 pieces were produced.

(Example 10) Ten solid electrolytic capacitors were produced in the same manner as in Example 2 except that hydrochloric acid was added to adjust the pH of a 30% manganese nitrate aqueous solution to 0 or less.

(Comparative Example 1) As in Example 1, a 3 mm × 4 mm aluminum etched foil 6 with a lead was used as an anode, and an aqueous solution of 3% ammonium adipate was used to apply an applied voltage of 12 V to the aqueous solution. 60 at 70 ℃
Dielectric oxide film 7 was formed on the surface of aluminum etched foil 6 by performing anodic oxidation for minutes. Then p
A manganese oxide layer which is a part of the solid electrolyte layer 8 is formed by immersing in a 30% aqueous solution of manganese nitrate having H of 3.73, naturally drying and then performing thermal decomposition treatment at 300 ° C. for 10 minutes. did.

Next, pyrrole monomer 0.5 mol / L
And sodium propylnaphthalene sulfonate 0.1mo
After mixing 1 / L in advance, water as a solvent was mixed to prepare a polymerization solution for solid electrolyte formation, and the polymerization initiation electrode was brought close to the element surface in this polymerization solution, and the solution temperature was 30 ° C. and the polymerization voltage was 3 V. Was subjected to electrolytic polymerization to form a solid electrolyte layer 8. Thereafter, a carbon layer 9 obtained by applying and drying a colloidal carbon suspension as a cathode extraction layer and a silver layer 10 obtained by applying and drying a silver paste are formed, and the carbon layer 9 and the silver layer 10 are combined. As a cathode lead-out portion. Then, it was packaged with epoxy resin to complete 10 solid electrolytic capacitors. The rated voltage of this solid electrolytic capacitor is 6.3V.

Comparative Example 2 As in Example 1, a 3 mm × 4 mm aluminum etched foil 6 with a lead was used as an anode, and a 3% ammonium adipate aqueous solution was used to apply an applied voltage of 12 V to the aqueous solution. 60 at 70 ℃
Dielectric oxide film 7 was formed on the surface of aluminum etched foil 6 by performing anodic oxidation for a minute. Then the pH
By adding nitric acid, which is a pH adjuster, to a 30% aqueous solution of manganese nitrate having a pH of 3.73, dipping it in a solution having a pH of 2 and allowing it to air-dry, and then performing thermal decomposition treatment at 300 ° C. for 10 minutes. A manganese oxide layer, which will be a part of the solid electrolyte layer 8, was formed.

Next, pyrrole monomer 0.5 mol / L
And sodium propylnaphthalene sulfonate 0.1mo
After mixing 1 / L in advance, water as a solvent was mixed to prepare a polymerization solution for solid electrolyte formation, and the polymerization initiation electrode was brought close to the element surface in this polymerization solution, and the solution temperature was 30 ° C. and the polymerization voltage was 3 V. Was subjected to electrolytic polymerization to form a solid electrolyte layer 8. Thereafter, a carbon layer 9 obtained by applying and drying a colloidal carbon suspension as a cathode extraction layer and a silver layer 10 obtained by applying and drying a silver paste are formed, and the carbon layer 9 and the silver layer 10 are combined. As a cathode lead-out portion. Then, it was packaged with epoxy resin to complete 10 solid electrolytic capacitors. The rated voltage of this solid electrolytic capacitor is 6.3V.

The solid electrolytic capacitors produced in Examples 1 to 10 and Comparative Examples 1 and 2 were aged, and then the initial characteristics of the solid electrolytic capacitors were measured. The average value of these results is shown in (Table 1).

[0034]

[Table 1]

Comparison between Comparative Example 1 and Example 1 and Comparative Example 2 and Example 2 shows that by adding a pH adjusting agent to adjust the pH of the manganese nitrate aqueous solution to 2 or less, the capacity withdrawing rate and the leakage current characteristics can be improved. Further, it has excellent impedance and ESR characteristics in a high frequency region. In addition, by comparing Examples 1 to 10 with Comparative Examples 1 and 2, it can be seen that by setting the pH at the time of electrolytic polymerization to 2, excellent capacity drawing rate, leakage current characteristics, and impedance characteristics can be obtained.

This excellent property is obtained by immersing in a manganese nitrate aqueous solution having a pH of 2 or less by adding a pH adjuster and thermally decomposing the manganese oxide layer to form a manganese oxide layer. When a conductive polymer layer is formed by electrolytic polymerization using, the particle size generated by the pyrolyzed manganese oxide is small and the particles are homogeneously formed. It is possible to coat even the inside of the pores, and this can prevent deterioration of the dielectric oxide film.

Further, since the manganese oxide having a uniform particle diameter and a small size is coated over a wide range, the adhesion with the electrolytic polymerized film by the low pH polymerization solution thereafter can be improved.
In particular, by thermally decomposing a low-pH manganese nitrate aqueous solution to which acids such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, acetic acid, and phosphoric acid ester have been added, minute and uniform manganese dioxide is formed. A gas generation path can be secured, the stress on the dielectric oxide film is small, and the effect of suppressing leakage current can be seen, and since the coverage is increased, a solid electrolytic capacitor with an excellent capacity extraction rate can be obtained. is there.

In the first embodiment described above, only the solid electrolytic capacitor using the valve action metal aluminum as the anode is described, but the present invention is not limited to this, and the dielectric oxide film is formed on the outer surface. It goes without saying that the same effect can be obtained even with other substances such as tantalum, niobium, and titanium which are valve-acting metals having.

In the first embodiment, the case where pyrrole is used as the polymerizable monomer constituting the conductive polymer has been described, but the present invention is not limited to this, and the conductive polymer is used. Needless to say, the same effect can be obtained by using other substances such as thiophene, aniline or their derivatives as the constituent monomers.

In the first embodiment described above, only the case where manganese oxide is used as the precoat layer which is a part of the solid electrolyte layer has been described, but the present invention is not limited to this, and the conductivity is not limited. Needless to say, the same effect can be obtained when other conductive materials such as polymers are used as the precoat.

[0041]

As described above, according to the present invention, a polymerizable monomer and an anionic surfactant having an alkyl group or an aromatic ring and having a molecular weight of 180 or more are mixed in advance, and water as a main solvent is added to the mixture. Add a solution and add p to this solution.
On the dielectric oxide film formed on the surface of the valve metal, a polymerization solution for solid electrolyte formation was prepared by adding a pH adjusting agent to H5 or less, and this polymerization solution for solid electrolyte formation was used. It is intended to form a solid electrolyte layer so that an anionic surfactant is selectively incorporated as a dopant into the solid electrolyte by electrolytic polymerization.
The anionic surfactant with excellent dedoping resistance improves the polymerization rate by being selectively incorporated as a dopant in the solid electrolyte, and the impedance characteristics are maintained even under the condition that the capacitor is left in the initial stage and in high temperature and high humidity. It is possible to produce a solid electrolytic capacitor having excellent characteristics, and as a result, it is possible to obtain a solid electrolytic capacitor having excellent capacity drawing ratio, leakage current characteristics, and impedance / ESR characteristics in a high frequency region.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a solid electrolytic capacitor according to a first embodiment of the present invention.

[Explanation of symbols]

6 Aluminum Etched Foil 7 Dielectric oxide film 8 Solid electrolyte layer 9 carbon layer 10 silver layers

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masato Ozawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (3)

[Claims] 1. A polymerizable monomer and an anionic surfactant having an alkyl group or an aromatic ring and having a molecular weight of 180 or more are mixed in advance, and water as a main solvent is added to the mixture to prepare a solution. p to keep pH below 5
A polymer electrolyte for forming a solid electrolyte was prepared by adding an H-adjusting agent, and the anionic surface active agent was formed on the dielectric oxide film formed on the surface of the valve metal by using the polymer liquid for forming a solid electrolyte. A method for producing a solid electrolytic capacitor, wherein a solid electrolyte layer is formed by electrolytic polymerization so that the agent is selectively incorporated into the solid electrolyte as a dopant. 2. A manganese oxide layer is formed on the dielectric oxide film layer by immersing in a manganese nitrate aqueous solution having a pH of 2 or less and thermally decomposing it before forming the solid electrolyte layer. 1. The method for manufacturing the solid electrolytic capacitor as described in 1. 3. The method for producing a solid electrolytic capacitor according to claim 2, wherein the pH adjustor added to the manganese nitrate aqueous solution is an acid.