JP2733618B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte and having a small leakage current.

[Related Art] In recent years, as electronic devices have become smaller and lighter, a capacitor having a low impedance in a high frequency region and having a small size and a large capacity has been required.

Conventionally, mica capacitors, film capacitors, ceramic capacitors, and the like have been used as such high-frequency capacitors, but none of these capacitors is suitable for increasing the capacity.

On the other hand, as a small-sized and large-capacity capacitor, there are an aluminum electrolytic capacitor and a tantalum capacitor.

Aluminum electrolytic capacitors have the advantage that large capacity capacitors can be obtained at low cost.However, the use of an electrolytic solution causes capacity degradation due to evaporation of the electrolytic solution over time, and also has the disadvantage of poor high-frequency characteristics. was there.

On the other hand, a tantalum solid electrolytic capacitor overcomes disadvantages of an aluminum electrolytic capacitor such as capacity deterioration by using solid manganese dioxide or the like as an electrolyte. However, this solid electrolyte is formed by impregnating and attaching a manganese nitrate aqueous solution to a valve metal body, and then thermally decomposing manganese nitrate at about 350 ° C. Since it is necessary to repeat the process of impregnation and thermal decomposition ten times or more, there have been disadvantages such as damage of the oxide film as a dielectric during thermal decomposition, and low repairability of the manganese dioxide film.

Therefore, in order to eliminate these disadvantages, Japanese Patent Application Laid-Open No. 58-1760
No. 9,7,8,8-tetracyanoquinodimethane complex salt (hereinafter abbreviated as TCNQ complex salt) as an organic solid electrolyte having excellent repairability of dielectric oxide film and good conductivity
Have been proposed. Here, TC consisting of isoquinoline in which the position of N is substituted with an alkyl group and TCNQ
A solid electrolyte layer is disclosed in which an NQ complex salt is heated and melted, impregnated in a capacitor element, and then cooled and solidified to form a solid electrolyte layer.

It has also been proposed to use a polymer of a five-membered heterocyclic compound such as pyrrole or thiophene as a solid electrolyte.
[Problem to be Solved by the Invention] However, in such a solid electrolytic capacitor using the TCNQ complex salt, when cooling and solidifying after the impregnation,
Since the TCNQ complex salt crystallized and did not adhere sufficiently to the derivative oxide film, there was a problem that the desired capacitance could not be obtained.

In addition, a solid electrolytic capacitor using a conductive polymer compound such as polypyrrole or polythiophene as a solid electrolyte has better heat resistance and high-frequency characteristics than the TCNQ complex salt, but has a dielectric oxide film of the conductive polymer compound. There was a drawback that leakage current was large due to poor repairing ability.

[Means for Solving the Problems] The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor in which a solid electrolyte layer made of a conductive polymer compound is formed on a dielectric oxide film, wherein the conductive polymer compound is non-conductive. It is characterized in that it is formed on a dielectric oxide film in a solution to which an ionic surfactant is added.
Further, the method for producing a solid electrolytic capacitor of the present invention comprises the steps of: forming a solid electrolyte layer made of a conductive polymer compound on a dielectric oxide film by a chemical polymerization method or an electrolytic polymerization method in a solution to which a nonionic surfactant is added. Is formed.

As a method for forming the conductive polymer compound on the dielectric, a known chemical polymerization method or electrolytic polymerization method can be used. In the chemical polymerization method, a dielectric polymer oxide film is impregnated with a monomer of a conductive polymer compound, and then the dielectric oxide film is immersed in a solution containing an anion serving as a dopant, an oxidizing agent, and a nonionic surfactant. Thus, a conductive polymer compound can be formed on the dielectric oxide film. Also, after previously impregnating the dielectric oxide film with a solution containing an oxidizing agent and an anion serving as a dopant, the dielectric oxide film is immersed in a solution containing a conductive polymer compound monomer and a nonionic surfactant. You may. In the electrolytic polymerization method, an electrolytic solution in which a monomer of a conductive polymer compound is dissolved,
The conductive polymer compound can be formed on the dielectric oxide film by dissolving the anion serving as a dopant and the nonionic surfactant and electrolyzing the anode foil having the dielectric oxide film formed thereon as an anode. .

As the conductive polymer compound used in the present invention, polypyrrole, polythiophene, or a derivative thereof is preferable in terms of easiness of polymerization, stability, and conductivity.

The conductive polymer compound is formed on the dielectric oxide film by polymerization, but the dielectric oxide film is tens to thousands of square meters and is easily damaged, so capacitors using the conductive polymer compound may leak. There was a drawback that the current was large.

When a surfactant is added to a solution for forming a polymer compound or an electrolytic solution (hereinafter, referred to as a polymer solution), a smooth conductive polymer that is well adhered to the anode foil can be obtained.

Although the mechanism of this action is not always clear, the surfactant is considered to be a smooth polymer because it adsorbs to the growth point of the polymer and suppresses local abnormal growth.

Such a smooth polymer does not easily damage the dielectric oxide film and grows inside the fine irregularities of the anode foil.
It seems that a high capacity one can be obtained.

As a surfactant, a counter ion of an anionic surfactant or a cationic surfactant is taken into the conductive polymer compound as a dopant anion, and greatly affects the conductivity. For this reason, a nonionic surfactant which does not easily affect the conductivity of the conductive polymer compound is used as the surfactant. In particular, those which show solubility in water, acetonitrile, methanol, and the like, which are used for the polymerization, are preferable. Specific examples include polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester, and fatty acid monoglyceride.

The amount of these surfactants used is strictly determined by the solvent used for polymerization, but is generally 0.01 to 50% by weight,
Preferably, it is appropriate to employ about 0.1 to 30% by weight.

[Example] Example 1 Wound aluminum electrolytic capacitor element (Rating 2.2μ)
F, 25V) was vacuum impregnated with a pyrrole monomer. Next, this element was immersed in an aqueous solution containing 5% by weight of ammonium persulfate, 5% by weight of naphthalenesulfonic acid, 5% by weight of naphthylphosphoric acid, and 5% by weight of polyethylene glycol at 0 ° C. for 1 hour, and pyrrole was placed on the dielectric surface of the capacitor element. Polymerized. After the completion of the reaction, unreacted substances are washed off with water, and the temperature is 100 ° C in nitrogen.
Dried for 1 hour. The obtained capacitor element was housed in an aluminum case, and sealed with a resin to obtain a solid electrolytic capacitor. Table 1 shows the characteristics of this capacitor after aging by applying a voltage of 35 V for 2 hours at 105 ° C.

Example 2 The same capacitor element as in Example 1 was vacuum impregnated with a pyrrole monomer. Next, this device was treated with 10% by weight of ammonium persulfate, 5% by weight of toluenesulfonic acid, and 5% by weight of naphthyl phosphoric acid.
Wt%, polyethylene glycol monooleyl ether
Pyrrole was immersed in an aqueous solution containing 10% by weight at 0 ° C. for 1 hour to polymerize pyrrole on the dielectric surface of the capacitor element. This capacitor element was treated in the same manner as in Example 1 to produce a solid electrolytic capacitor, and the characteristics after aging were shown in Table 1.

Example 3 Using the same capacitor element as in Example 1, the capacitor element was immersed in an aqueous solution containing 7% by weight of pyrrole, 8% by weight of naphthalenesulfonic acid, and 10% by weight of polyethylene glycol monolauryl ether. mA current was applied for 1 hour. After the completion of the reaction, the capacitor element was washed with water and re-formed with an adipine oxidizing solution to produce a solid electrolytic capacitor. Table 1 shows the characteristics of the obtained capacitors.

Example 4 Using the same capacitor element as in Example 1, the capacitor element was immersed in an aqueous solution containing 7% by weight of pyrrole, 8% by weight of trienesulfonic acid, and 3% by weight of polyethylene glycol monostearate. mA current of 2
Flowed for hours. After the completion of the reaction, the capacitor element was washed with water and re-formed with an adipine oxidizing solution to produce a solid electrolytic capacitor. Table 1 shows the characteristics of the obtained capacitors.

Comparative Example 1 Using the same capacitor element as in Example 1, the capacitor element was immersed in an aqueous solution containing 7% by weight of pyrrole and 10% by weight of benzenesulfonic acid, and a current of 0.1 mA was passed between the anode and the cathode for 2 hours. After the completion of the reaction, the capacitor element was washed with water and re-formed with an adipine oxidizing solution to produce a solid electrolytic capacitor. Table 1 shows the characteristics of the obtained capacitors.

[Effects of the Invention] As described above, a capacitor using a conductive polymer compound as a solid electrolyte has excellent heat resistance and high-frequency characteristics, but has a disadvantage of high leakage current.

When a conductive polymer compound formed on a dielectric in a polymerization solution containing a nonionic surfactant as in the present invention is used as a solid electrolyte, the conductive polymer is smooth and has good dielectric properties. Therefore, a capacitor having very low leakage current and high capacity can be provided.

Claims (4)

(57) [Claims] 1. A solid electrolytic capacitor having a solid electrolyte layer made of a conductive polymer compound formed on a dielectric oxide film, wherein the conductive polymer compound is dissolved in a solution containing a nonionic surfactant. A solid electrolytic capacitor formed on a dielectric oxide film. 2. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer compound is polypyrrole, polythiophene or a derivative thereof. 3. A nonionic surfactant comprising polyethylene glycol, polyethylene glycol alkyl ether,
3. The solid electrolytic capacitor according to claim 1, which is a polyethylene glycol fatty acid ester or a fatty acid monoglyceride. 4. A solid electrolyte layer comprising a conductive polymer compound is formed on a dielectric oxide film by a chemical polymerization method or an electrolytic polymerization method in a solution to which a nonionic surfactant is added. Manufacturing method of solid electrolytic capacitor.