JP2001237145A - Manufacturing method of solid-state electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a solid-state electrolytic capacitor by which a solid-state electrolytic layer composed of fine uniform conductive molecules is formed into a winding type capacitor element and which has excellent electrical characteristics and large capacitance. SOLUTION: The capacitor element 10 in which an anode electrode foil 1 and a cathode electrode foil 2 are wound through separators 3 is impregnated with a polymerizable monomer and an oxidizing agent in a solvent, and the conductive high molecules are formed by a chemical polymerization reaction by at least twice or more of heat treatment. The chemical polymerization reaction can be promoted by stages by executing at least twice or more of heat treatment for a fixed time, the solid-state electrolytic layer is formed into the etching pit 8 of the anode electrode foil 1, and the residue of the solvent can also be removed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly, to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

[0002]

2. Description of the Related Art Manganese dioxide and a complex of 7,7,8,8-tetracyanoquinodimethane (TCNQ) are known as solid electrolytes used for solid electrolytic capacitors.

A solid electrolyte layer made of manganese dioxide is
The anode element made of a sintered body of tantalum is immersed in an aqueous solution of manganese nitrate, and is produced by thermal decomposition at a temperature of about 300 to 400 ° C. In such a capacitor using a solid electrolyte layer, the oxide film layer is easily damaged during the thermal decomposition of manganese nitrate, which tends to increase the leakage current, and the specific resistance of manganese dioxide itself is high. It has been difficult to obtain sufficiently satisfactory impedance characteristics. In addition, the lead wire was damaged by the heat treatment, and it was necessary to separately provide an external terminal for connection as a later process.

As a solid electrolytic capacitor using a TCNQ complex, one described in Japanese Patent Application Laid-Open No. 58-191414 is known. An electrolyte layer is formed. This TCNQ complex has high conductivity and can obtain good results in frequency characteristics and temperature characteristics. However, since the TCNQ complex has the property of transferring to an insulator in a short time after being melted, it is difficult to control the temperature during the manufacturing process of the capacitor. In addition, the TCNQ complex itself lacks heat resistance, so it is difficult to mount it on a printed circuit board. A remarkable characteristic change is seen by the solder heat.

[0005] In order to solve the disadvantages of these manganese dioxide and TCNQ complexes, attempts have been made to use a conductive polymer such as polypyrrole as a solid electrolyte layer.
A conductive polymer represented by polypyrrole and polythiophene is mainly produced by a chemical oxidation polymerization method (chemical polymerization) or an electrolytic oxidation polymerization method (electrolytic polymerization).

When a solid electrolyte is produced by electrolytic polymerization, it is necessary to apply a voltage. Therefore, it is difficult to apply the solid electrolyte to an anode electrode for an electrolytic capacitor having an oxide film layer as an insulator formed on the surface. On the surface of the coating layer, there is a method in which a conductive precoat layer, for example, a conductive polymer film chemically polymerized using an oxidizing agent is used as a precoat layer, and then the electrolyte layer is formed by electrolytic polymerization using the precoat layer as an electrode. It has been proposed (JP-A-63-1733).
No. 13, JP-A-63-158829: manganese dioxide is used as a precoat layer). However, the manufacturing process is complicated because the pre-coat layer is formed in advance, and in the electrolytic polymerization, a solid electrolyte layer is generated from the vicinity of the polymerization external electrode arranged on the coating surface of the anode electrode, so that it is uniform over a wide range. It has been very difficult to continuously form a conductive polymer film having a large thickness.

Therefore, a foil-shaped anode electrode and a cathode electrode are
An electrolyte layer made of a conductive polymer film formed only by chemical polymerization by immersing a monomer solution such as pyrrole and an oxidizing agent into this capacitor element by winding it up through a separator to form a so-called winding type capacitor element Tried to form Such a wound-type capacitor element is well known in an aluminum electrolytic capacitor, but by avoiding the complexity of electrolytic polymerization by holding a conductive polymer layer with a separator, a foil-shaped capacitor having a large surface area. It was expected that the capacity would be expanded by the electrodes. Furthermore,
It was expected that the use of a wound-type capacitor element would maintain both electrodes and the separator with a constant tightening force and contribute to the adhesion between the electrodes and the electrolyte layer.

[0008]

However, when a capacitor element is impregnated with a mixed solution obtained by mixing a monomer solution and an oxidizing agent, a solid electrolyte layer is not formed even inside the capacitor element, and the expected electric power is not obtained. It turned out that the characteristic could not be obtained.

Therefore, when the monomer solution and the oxidizing agent are separately impregnated or the polymerization temperature of the solution at the time of the reaction is lowered, good electrical properties are obtained to some extent, but only the pressure resistance is insufficient. And the ESR characteristics are not satisfactory. The cause is that even with these means, the solid electrolyte layer formed near the end face of the capacitor element hinders the subsequent penetration of the solution, so that a sufficient solution has not penetrated into the inside, and as a result, It was considered that the reason was that a uniform solid electrolyte layer was not formed. In addition, when chemical polymerization is carried out at a low temperature, strict temperature control is required, and the production apparatus becomes complicated, resulting in an increase in product cost.

Therefore, a method of producing a solid electrolyte layer made of a dense and uniform conductive polymer inside a wound-type capacitor element and manufacturing a solid electrolytic capacitor having excellent electric characteristics and a large capacity was studied. As a result, the inventors have found a method for solving the above problems by impregnating the capacitor element with a polymerizable monomer and an oxidizing agent and then promoting the polymerization reaction by heat treatment.

[0011]

According to the present invention, there is provided a method for manufacturing a solid electrolytic capacitor, comprising: a polymerizable monomer and an oxidizing agent in a solvent formed on a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator. Is characterized in that a conductive polymer is generated by a chemical polymerization reaction by at least two or more heat treatments after impregnation.

The two or more chemical polymerization reactions by this heat treatment may be set at different temperatures as necessary, or may be set at different temperatures and successively higher temperatures.
Further, it is more preferable that the temperature of the first heat treatment in the chemical polymerization reaction is set at least lower than the boiling point of the solvent, and the temperature of the second and subsequent heat treatments is set higher than the boiling point of the solvent.

[0013] In each chemical polymerization reaction, it is preferable to perform heat treatment for at least 30 minutes or more.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows that in the method for manufacturing a solid electrolytic capacitor of the present invention, an anode electrode foil 1 made of a valve metal such as aluminum and having an oxide film layer formed on its surface and a cathode electrode foil 2 are mainly made of vinylon fiber or the like. Wound around a separator 3 made of non-woven fabric
0 is formed. Then, the capacitor element 10 is impregnated with 3,4-ethylenedioxythiophene, which is a polymerizable monomer, and an oxidizing agent in a solvent.
Polyethylene dioxythiophene, which is a conductive polymer produced by a chemical polymerization reaction in the inside, is held as a solid electrolyte layer 5 by a separator 3.

The anode electrode foil 1 is made of a valve metal such as aluminum. As shown in FIG. 2, the surface of the anode electrode foil 1 is roughened by electrochemical etching in a chloride aqueous solution to form a large number of etching pits. 8 are formed. Further, on the surface of the anode electrode foil 1, a voltage is applied in an aqueous solution of ammonium borate or the like to form an oxide film layer 4 serving as a dielectric. The cathode electrode foil 2 is made of aluminum or the like, similarly to the anode electrode foil 1, and has a surface subjected to only etching treatment.

Lead wires 6 and 7 for connecting the respective electrodes to the outside are connected to the anode electrode foil 1 and the cathode electrode foil 2 by known means such as stitching and ultrasonic welding. The lead wires 6 and 7 are made of aluminum or the like,
It comprises an external connection portion for electrically connecting the connection portion between the anode electrode foil 1 and the cathode electrode foil 2 and the outside, and is led out from the end face of the wound capacitor element 10.

The separator 3 is a non-woven fabric mainly composed of vinylon fibers, and a non-woven fabric obtained by mixing vinylon fibers with paper fibers such as glass fibers, polyester fibers, nylon fibers, rayon fibers, and manila paper. Can also. The nonwoven fabric has a basis weight of 6 to 36 g / m ² ,
Fiber diameter 5-30 μm, thickness 30-150 μm, density 0.
Those having a density of 2 to 0.5 g / m ³ are used.

The capacitor element 10 is formed by winding the above-mentioned anode electrode foil 1 and cathode electrode foil 2 with the separator 3 interposed therebetween. The dimensions of the bipolar electrode foils 1 and 2 are arbitrary according to the specifications of the solid electrolytic capacitor to be manufactured, and the separator 3 may have a width slightly larger than this according to the dimensions of the bipolar electrode foils 1 and 2. .

3,4-ethylenedioxythiophene as a polymerizable monomer can be obtained by a known production method disclosed in Japanese Patent Application Laid-Open No. 2-15611. As the oxidizing agent, ferric p-toluenesulfonate dissolved in a solvent was used, and the oxidizing agent was 40% by weight based on the solvent.
If the concentration exceeds the above range, good results can be obtained. The ratio of the solvent to the ferric p-toluenesulfonate in this oxidizing agent may be arbitrary, but the mixing ratio is from 1: 3 to 1:15.
Is suitable.

Then, the capacitor element 10 is impregnated with 3,4-ethylenedioxythiophene as a polymerizable monomer and an oxidizing agent in a solvent, and the capacitor element 10 is subjected to heat treatment at least twice or more. Produces polyethylenedioxythiophene by a chemical polymerization reaction in water.

Usually, when 3,4-ethylenedioxythiophene is mixed with an oxidizing agent in a solvent, the chemical polymerization reaction proceeds even at room temperature to produce polyethylenedioxythiophene. However, when the solvent is removed for a long time in the chemical polymerization reaction, the polymerization reaction does not proceed, and not only can not obtain a sufficient degree of polymerization,
Residue of the solvent in the capacitor element 10 increases and adversely affects various electric characteristics. On the other hand, although the chemical polymerization reaction can be promoted by performing the heat treatment, the solvent is removed before the polymerization proceeds into the etching pits 8 formed on the anode electrode foil 1 because the reaction speed is increased. As a result, a dense and uniform solid electrolyte cannot be produced.

Therefore, as in the present invention, at least 2
By performing heat treatment more than once for a certain period of time to promote the chemical polymerization reaction in a stepwise manner, a solid electrolyte layer is formed even inside the etching pit 8 of the anode electrode foil 1 and the solvent residue is efficiently removed. Will be able to do it.

The temperature and time of the heat treatment are optional depending on the type of the solvent, the process time, and the like, but may be set to different temperatures as needed, or may be set so as to become higher sequentially. In this case, the temperature is increased step by step, but the temperature may be increased temporarily. Further, it is more preferable that the temperature of the first heat treatment in the chemical polymerization reaction is set at least lower than the boiling point of the solvent, and the temperature of the second and subsequent heat treatments is set higher than the boiling point of the solvent.

[0024]

Next, a method for manufacturing a solid electrolytic capacitor according to the present invention will be specifically described. The anode electrode foil 1 and the cathode electrode foil 2 are made of a valve metal, for example, aluminum or tantalum, and their surfaces are subjected to an etching process in advance to increase the surface area. The anode electrode foil 1 is further subjected to a chemical conversion treatment to form an oxide film layer 4 made of aluminum oxide on the surface. The anode electrode foil 1 and the cathode electrode foil 2 are wound via a separator 3 made of a non-woven fabric mainly composed of vinylon fibers to obtain a capacitor element 10.

In this embodiment, the capacitor element 10
Has a diameter of 4φ, a vertical dimension of 7 mm, and a rated voltage of 20
It has a WV and a rated capacitance of 10 μF. Lead wires 6 and 7 are electrically connected to the anode electrode foil 1 and the cathode electrode foil 2 of the capacitor element 10, respectively, and project from the end face of the capacitor element 10.

The capacitor element 10 is impregnated with 3,4-ethylenedioxythiophene and an oxidizing agent. As the oxidizing agent, ferric p-toluenesulfonate dissolved in a ratio of 52% by weight to the solvent was used, and the oxidizing agent was impregnated with 3,4-ethylenedioxythiophene at a ratio of 1: 5.

Next, the capacitor element 10 impregnated with 3,4-ethylenedioxythiophene and an oxidizing agent
Heat treatment at 1 ° C. for 1 hour accelerates the chemical polymerization reaction. In the heat treatment at this time, the chemical polymerization reaction proceeds slowly, and polyethylene dioxythiophene, which is a conductive polymer, is generated inside the etching pits 8 of the anode electrode foil 1. On the other hand, the solvent is not completely removed and therefore
Even in the subsequent heat treatment, the chemical polymerization reaction proceeds.
Next, heat treatment is performed at 150 ° C. for 1 hour to further promote the chemical polymerization reaction to increase the degree of polymerization, and remove the solvent to eliminate the adverse effect of the residue on the electrical characteristics.

The anode electrode foil 1 thus formed
The capacitor element 10 in which the solid electrolyte layer 5 is held by the separator 3 interposed between the capacitor element 10 and the cathode electrode foil 2, after performing a post-process such as a normal aging process, and covering the capacitor device 10 with an exterior resin layer;
Alternatively, it is housed in an outer case to form a solid electrolytic capacitor.

Next, in the solid electrolytic capacitor according to the embodiment, changes in characteristics depending on the conditions of the heat treatment temperature will be described below.

[0030]

[Table 1]

As is evident from Table 1, at least two heat treatments provide good ESR characteristics, and a dense and uniform solid electrolyte is formed inside the etching pits of the anode electrode foil. Is understood.

[0032]

According to the present invention, there is provided a method for manufacturing a solid electrolytic capacitor, comprising the steps of impregnating a polymerizable monomer and an oxidizing agent in a solvent into a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator. Since a conductive polymer is generated by accelerating a stepwise chemical polymerization reaction by at least two or more heat treatments, a dense and uniform solid electrolyte layer can be formed inside the etching pit, and a residue of the solvent can be formed. Therefore, electrical characteristics such as ESR characteristics are improved, and the process time can be shortened.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a capacitor element used in the present invention.

FIG. 2 is a conceptual diagram of an anode electrode foil used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode electrode foil 2 Cathode electrode foil 3 Separator 4 Oxide film layer 5 Solid electrolyte layer 6, 7 Lead wire 8 Etching pit 10 Capacitor element

Claims (5)

[Claims] 1. A capacitor element in which an anode electrode foil and a cathode electrode foil are wound with a separator interposed therebetween is impregnated with a polymerizable monomer and an oxidizing agent in a solvent, and then subjected to a chemical polymerization reaction by heat treatment at least twice or more. A method for producing a solid electrolytic capacitor for producing a conductive polymer. 2. A method in which a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator is impregnated with a polymerizable monomer and an oxidizing agent in a solvent, and then subjected to at least two or more heat treatments at different temperatures. A method for producing a solid electrolytic capacitor that produces a conductive polymer by a polymerization reaction. 3. After impregnating a polymerizable monomer and an oxidizing agent in a solvent into a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator, at least two different temperatures and successively higher temperatures are obtained. A method for producing a solid electrolytic capacitor that produces a conductive polymer by a chemical polymerization reaction by at least one heat treatment. 4. The method according to claim 1, wherein the temperature of the first heat treatment in the chemical polymerization reaction is at least lower than the boiling point of the solvent, and the temperature of the second and subsequent heat treatments is higher than the boiling point of the solvent. The method for manufacturing a solid electrolytic capacitor according to any one of claims 1 to 3. 5. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein each heat treatment is performed for at least 30 minutes.