JP2725553B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

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 using polyaniline as a solid electrolyte, and more particularly, to a high-conductivity and high-reliability polyaniline easily formed by chemical oxidation to obtain a solid electrolyte. The present invention relates to a method for manufacturing a solid electrolytic capacitor having excellent heat resistance and a high capacitance appearance rate.

[0002]

2. Description of the Related Art With the progress of science and technology, there is a demand for miniaturization and improvement of reliability of electronic equipment. There is also a demand for the development of a small, large-capacity solid electrolytic capacitor that has good characteristics up to a high frequency range and has excellent reliability.

In general, a solid electrolytic capacitor comprises a first electrode (anode) formed of a porous film-forming metal such as tantalum or aluminum, a surface oxide film formed of a dielectric material, and a solid electrolyte formed thereon formed of a second electrode. Of the electrode (cathode). Since the solid electrolyte plays a role of electrically connecting the entire surface of the dielectric inside the porous body and the electrode leads, a substance having high conductivity is preferable from this viewpoint. On the other hand, the solid electrolyte is also required to have a function of repairing an electrical short circuit caused by a defect in the dielectric film. As a result, metals that have high conductivity but do not have a dielectric repair function cannot be used as a solid electrolyte, and manganese dioxide, which is transferred to an insulator due to heat due to short-circuit current, TC of organic compounds
NQ complex salts and the like have been used. Further, recently, an electrolytic capacitor using a conductive polymer such as polypyrrole, polyaniline, polythiophene, and polyparaphenylene as a solid electrolyte has been proposed, and an electrolytic capacitor using polypyrrole as a solid electrolyte has been put to practical use for one minute.

Some proposals have been made for capacitors using polyaniline as a solid electrolyte. JP 6
Japanese Patent Application Laid-Open No. 2-29124 discloses an electrolytic capacitor using ruco emeraldine polyaniline as a solid electrolyte. Further, JP 64 -24410 discloses, after the introduction of the monomers in the liquid phase, the production of electrolytic capacitors to form a polyaniline by introducing a solution of the oxidizing agent are allowed to coexist organic acid or salt thereof becomes solid electrolyte A method has been proposed. Furthermore, the present inventors have developed a method for producing emeraldine polyaniline, which has the same electrical conductivity as polypyrrole and has better stability over time than polypyrrole , and has demonstrated that it can be used for the solid electrolyte of electrolytic capacitors. (Japanese Patent Application No. 04-336882).

[0005]

The detailed study of MacDiamid et al. Has revealed that polyaniline has three oxidation states (Synthetic Metals,
41-43, p. 715, 1991), which are called pergranillin, emeraldine and rucoemeraldine, respectively, in the order of the degree of oxidation. It is now generally recognized that emeraldine polyaniline exhibits high conductivity by doping (proton acid treatment). However, what is disclosed in Japanese Patent Application Laid-Open No. 62-29124 is an electrolytic capacitor using polyaniline in a lucoemeraldine state as a solid electrolyte.
Since luco emeraldine does not exhibit high conductivity even when doped, it is considered that an electrolytic capacitor using this as a solid electrolyte cannot obtain sufficient characteristics. In Japanese Patent Application Laid-Open No. 64-24410, the formation of polyaniline as a solid electrolyte is carried out by sequentially introducing aniline, a protonic acid and an oxidizing agent onto an oxide film, followed by polymerization. However, polyaniline has three oxidation states,
When a solid electrolyte is formed by this method, the polyaniline may not be sufficiently oxidized or may be peroxidized and its electrical conductivity may not be maximized, and it is difficult to control the optimum conditions for forming the solid electrolyte.

An object of the present invention is to solve the above problems and to provide a method for manufacturing a solid electrolytic capacitor using polyaniline as a solid electrolyte. In this method, highly conductive and highly reliable polyaniline is easily formed by chemical oxidation to obtain a solid electrolyte. Another object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor having excellent high-frequency characteristics and heat resistance and a high capacitance appearance rate.

[0007]

The present inventors have studied various methods for forming a solid electrolyte on the oxide film surface of an electrolytic capacitor. Among them, a reaction mixture containing aniline, a protonic acid and an oxidizing agent is introduced unreacted onto a surface oxide film, and thereafter the reaction is started to polymerize aniline by oxidation to form polyaniline as a solid electrolyte. We studied in detail the possibility of a method of manufacturing an electrolytic capacitor. As a result, the present invention has been found that the solid electrolytic capacitor manufactured as described above has particularly excellent high-frequency characteristics and reliability and a high capacitance appearance rate.

More specifically, the present invention relates to a method for producing a solid electrolytic capacitor using a surface oxide film of a film-forming metal as a dielectric and polyaniline as a solid electrolyte.
Preparation of a mixed solution of water containing a protonic acid and an oxidizing agent and an organic solvent compatible with water and introduction of the mixed solution onto the surface oxide film at -5 ° C. or lower, and thereafter, the temperature is increased.
A method for producing a solid electrolytic capacitor, characterized in that the solid electrolyte is formed by oxidatively polymerizing aniline at a temperature of 0 ° C. or higher .

The above organic solvent is compatible with water and has a melting point of -30.degree.
The following is preferred. By using such a mixed solvent instead of water, which is a conventional solvent, the temperature of the reaction system can be controlled to -5 ° C or lower, and the rate of aniline polymerization can be controlled. The lower the polymerization temperature, the more the polymerization rate is controlled. In order to carry out the polymerization at a lower temperature, it is more effective to use an organic solvent having a low melting point. The ratio of the organic solvent in the mixed solvent of water and the organic solvent is preferably 10 to 85%. When the ratio of the organic solvent is 10% or less, the polymerization temperature cannot be effectively controlled. When the ratio is 85% or more, the conductivity of the obtained polyaniline is reduced.

Specific examples of particularly preferable organic solvents include methanol, ethanol, propanol, acetone, ethyl methyl ketone, and diethyl ketone.

The present invention also relates to a method for manufacturing a solid electrolytic capacitor using a surface oxide film of a film-forming metal as a dielectric and polyaniline as a solid electrolyte, wherein an oxidation reaction catalyst is introduced into the surface oxide film, and aniline and protonic acid are added. A method for producing a solid electrolytic capacitor, comprising introducing a mixture containing hydrogen and hydrogen peroxide into a surface oxide film and subjecting aniline to oxidative polymerization to form polyaniline as a solid electrolyte.

It is particularly preferred that the oxidation reaction catalyst is an Fe ^{2 +} salt.

The protonic acid used in the present invention is not particularly limited, but an aromatic sulfonic acid compound is preferable in order to obtain polyaniline having excellent thermal stability. For example, alkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, 1,5-naphthalenedisulfonic acid, 1,6-naphthalenedisulfonic acid, 2,6-naphthalenedisulfonic acid,
Anthraquinone-1,5-disulfonic acid, anthraquinone-2,6-disulfonic acid, anthraquinone-2-sulfonic acid, and the like, and derivatives thereof.

In claims 2 and 3 of the present invention, the oxidizing agent is not particularly limited, but in the process of oxidizing aniline, the pK value of a by-product formed from the oxidizing agent after accepting electrons.
An oxidizing agent that satisfies the condition that (K is an ionization constant and pK = -logK) is equal to or more than the pK value of the protonic acid is preferable. For example, hydrogen peroxide, potassium manganate,
Sodium manganate, ammonium manganate, potassium dichromate, sodium dichromate, ammonium dichromate, ferric aromatic sulfonic acid, ferric aromatic sulfonic acid, lead oxide and the like can be used.

In the present invention, the film-forming metal includes tantalum, aluminum, niobium, titanium, zirconium, magnesium, silicon, etc.
It can be used in the form of an etched product of a rolled foil.

In the production method of the present invention, after polyaniline is formed on the oxide film surface of the film-forming metal, it is washed with water or another appropriate organic solvent to remove the oxidizing agent and low molecular weight polyaniline which do not contribute to the conductivity. remove. In the present invention, the method of removing the oxidizing agent and the low-molecular-weight polyaniline is not particularly limited, and may be achieved by evaporation or the like in addition to cleaning. In the present invention, it is not necessary to completely remove the oxidizing agent and the low molecular weight polyaniline. However, the less the remaining oxidizing agent and low molecular weight polyaniline, the higher the high frequency characteristics and the heat resistance when the capacitor is assembled. After removing the oxidizing agent and the low molecular weight polyaniline, it is further treated (doped) with a protonic acid solution within a predetermined period of time to increase the conductivity of polyanine serving as a solid electrolyte. Thereafter, drying is performed, and a lead electrode is provided by a normal method, and assembled into a capacitor. Further, each step of the above-mentioned polymerization operation and assembling can be repeated.

[0017]

According to the present invention, a reaction mixture containing aniline, a protonic acid and an oxidizing agent can be sufficiently introduced into the pores of a porous dielectric material without substantially reacting, and the following effects are obtained. Since aniline, protonic acid and oxidizing agent are blended in an optimized composition, highly conductive and highly reliable polyaniline is easily formed on the dielectric surface. Polyaniline serving as a solid electrolyte can be formed on the oxide film surface at a high coverage. The polyaniline thus formed does not peel off from the oxide film surface even at a high temperature, and the reliability of the electrolytic capacitor is extremely high.

As described above, the capacitor according to the present invention is a solid electrolytic capacitor having good characteristics up to a high frequency range and excellent heat resistance.

[0019]

FIG. 1 is a diagram schematically showing a sectional structure of a solid electrolytic capacitor manufactured according to an embodiment of the present invention. The surface of the metal foil 1 serving as an anode is etched to form a large number of micropores to increase the surface area. The metal oxide dielectric thin film 2 is formed along the pore wall surface of this surface. On the surface of the dielectric thin film 2, a layer 3 of a solid electrolyte, polyaniline, which is the subject of the present invention, is formed so as to penetrate deep into its pores. A metal electrode 5 serving as a cathode is attached to the opposite side of the solid electrolyte layer 3. A graphite layer 4 may be used between the electrode 5 and the polyaniline layer 3 in order to maintain good contact. Electrode leads 6 and 7 are attached.

Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

(Example 1) 2 mm in diameter and 1.5 m in height
m, a columnar tantalum fine powder sintered pellet having a powder CV (product of capacity and formation voltage) of 20,000 was anodized at 100 V in a 0.05 wt% phosphoric acid aqueous solution, washed and dried. On the other hand, para-toluenesulfonic acid, aniline and ammonium dichromate are mixed in a mixed solvent of water / ethanol (volume ratio of 30:70) at a molar ratio of 9: 3: 1 so that the aniline concentration becomes 5 wt% while stirring. A mixed reaction solution was prepared sequentially and the temperature was lowered to -40 ° C. The tantalum pellets were immersed in the mixed solution for 30 seconds, filled with the reaction solution, taken out, and kept at room temperature for 30 minutes to perform polymerization. As a result, black polyaniline was formed on the dielectric surface. Thereafter, the resultant was washed with a 0.5 M solution of p-toluenesulfonic acid in water / ethanol (50:50) at room temperature and dried.

After repeating the above-mentioned filling of the reaction solution, polymerization, washing and drying three times, a silver paste was applied, a cathode lead was pulled out and sealed with an epoxy resin to complete a capacitor.

Comparative Example 1 A mixed solution of paratoluenesulfonic acid, aniline and ammonium dichromate of Example 1 was prepared at 0 ° C. This solution turned completely black 5 minutes after the preparation, and polymerization of aniline had occurred. Using this solution, a capacitor was fabricated in the same manner as in Example 1 using the tantalum pellets of Example 1 formed by etching to form an oxide film. (Comparative Example 2) Ethanol was used as a solvent instead of the mixed solvent of water / ethanol (volume ratio 30:70) used in the mixed solution of paratoluenesulfonic acid, aniline and ammonium dichromate of Example 1. Otherwise, a capacitor was manufactured in the same manner as in Example 1.

(Comparative Example 3) The mixture ratio of water: ethanol (30:70 by volume) used in the mixed solution of paratoluenesulfonic acid, aniline and ammonium dichromate in Example 1 was 5: 5. A 95 water / ethanol mixed solvent was used. When this mixed solvent was cooled to −40 ° C., a coagulation phenomenon occurred and a mixed solution could not be prepared.

(Embodiment 2) Using the tantalum pellets formed by etching to form an oxide film of Embodiment 1, Embodiment 1
Acetone was used in place of ethanol. Otherwise, polymerization, washing and drying of aniline were repeated in the same manner as in Example 1, and the leads were pulled out to complete the capacitor.

(Embodiment 3) Using the tantalum pellets formed by etching to form an oxide film in Embodiment 1, Embodiment 1
Butylnaphthalenesulfonic acid was used in place of paratoluenesulfonic acid. Otherwise, polymerization, washing and drying of aniline were repeated in the same manner as in Example 1, and the leads were pulled out to complete the capacitor.

(Embodiment 4) A film thickness of 200 μm, 1 × 0.5 cm in which the surface area is enlarged almost 20 times by etching.
₂ of the aluminum foil was anodized by 120V in a 0.1% ammonium borate solution, washed and dried. Thereafter, polymerization and washing of aniline were performed in the same manner as in Example 1.
The drying was repeated, and the leads were pulled out to complete the capacitor.

(Example 5) The tantalum pellets of Example 1 having an anodized oxide film formed thereon were used. First, at room temperature, the pellets were immersed in an aqueous solution in which the molar ratio of aniline, hydrogen peroxide, and paratoluenesulfonic acid was 1: 1: 3 and the concentration of aniline was 7 wt% for 30 seconds, and then the pellets were taken out. 30
After one minute, the pellets were immersed in a 0.05 wt% aqueous solution of iron p-toluenesulfonate (Fe (TSA) 2) for 30 seconds, taken out, and kept in the air for another 30 minutes to carry out polymerization. Then, it was washed with a 0.5 M solution of paratoluenesulfonic acid in water / ethanol (50:50) and dried.

Filling the above reaction solution, introducing an oxidation catalyst solution,
After repeating polymerization, washing and drying a total of 5 times, a silver paste was applied, a cathode lead was pulled out, and sealed with an epoxy resin to complete a capacitor.

(Embodiment 6) Using the tantalum pellets formed by etching to form an oxide film of Embodiment 1, Embodiment 5
Octylbenzenesulfonic acid was used as the protonic acid instead of paratoluenesulfonic acid. Other than this, Example 5
Polymerization, washing, and drying of aniline were repeated in the same manner as described above, and the lead was pulled out to complete the capacitor.

Example 7 Using the tantalum pellets of Example 1 having an anodized oxide film formed thereon, butyl naphthalene sulfonic acid was used in place of the paratoluenesulfonic acid of Example 5. Otherwise, polymerization, washing and drying of aniline were repeated in the same manner as in Example 5, and the lead was pulled out to complete the capacitor.

Example 8 Using the tantalum pellets of Example 1 on which an anodized oxide film was formed, iron chloride was used in place of iron p-toluenesulfonate of Example 5. Except for this, polymerization, washing and drying of aniline were repeated in the same manner as in Example 5, and the leads were pulled out to complete the capacitor.

Example 9 In Example 5, the order in which the tantalum pellets were immersed in the polymerization reaction solution and the oxidation catalyst solution was changed. First, the tantalum pellets were immersed in the oxidation catalyst solution, and then filled with the polymerization reaction solution. Otherwise, polymerization, washing and drying of aniline were repeated in the same manner as in Example 5, and the lead was pulled out to complete the capacitor.

(Embodiment 10) Using the aluminum foil of Embodiment 4 on which an oxide film was formed by etching, Embodiment 5 was carried out.
Polymerization, washing, and drying of aniline were repeated in the same manner as described above, and the lead was pulled out to complete the capacitor.

Example 11 Using the tantalum pellets of Example 1 on which an anodized oxide film was formed, copper p-toluenesulfonate was used instead of iron p-toluenesulfonate of Example 5. Otherwise, polymerization, washing and drying of aniline were repeated in the same manner as in Example 5, and the lead was pulled out to complete the capacitor.

For Examples 1 to 11 and Comparative Examples 1 to 3, immediately after the production of the obtained capacitors and at 125 ° C.
Table 1 shows the capacity appearance ratio (C / C0, capacity in the electrolyte solution is C0), the leakage current (LC), and the equivalent series resistance (ESR) at 100 kHz after holding for 00 hours. As can be seen from Table 1, the capacitor according to the present invention had a small equivalent series resistance at a high frequency, and showed almost no deterioration in characteristics even at a high temperature of 125 ° C., and was excellent in heat resistance.

[0037]

[Table 1]

[0038]

As described above, according to the present invention, a reaction mixture containing aniline, a protonic acid and an oxidizing agent is sufficiently introduced into the pores of a porous dielectric of an electrolytic capacitor while remaining substantially unreacted. The present invention provides a method for manufacturing a solid electrolytic capacitor having excellent high-frequency characteristics and heat resistance and a high capacitance appearance rate, which is easily formed by chemical oxidation of highly conductive and highly reliable polyaniline into a solid electrolyte. Is big.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a cross-sectional structure of a solid electrolytic capacitor manufactured according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film-forming metal foil 2 Dielectric thin film 3 Polyaniline layer which is a solid electrolyte 4 Graphite layer 5 Electrode 6, 7 Electrode lead

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaharu Sato Within NEC Corporation 5-7-1 Shiba, Minato-ku, Tokyo (56) References JP-A-4-245613 (JP, A) JP-A Sho 64-24410 (JP, A)

Claims (5)

(57) [Claims] 1. A method of manufacturing a solid electrolytic capacitor using a surface oxide film of a film-forming metal as a dielectric and polyaniline as a solid electrolyte, wherein the mixture containing aniline, protonic acid and an oxidizing agent is left unreacted. A method for producing a solid electrolytic capacitor, which comprises introducing the above-mentioned solid electrolyte into a film, and then starting the reaction to oxidize and polymerize aniline to form the solid electrolyte. 2. Preparation of a mixed solution of water containing aniline, a protonic acid and an oxidizing agent and an organic solvent compatible with water, and introduction of the mixed solution onto the oxide film on the capacitor surface at -5 ° C.
2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the method is carried out as follows, and thereafter, the temperature is raised and aniline is oxidized and polymerized at a temperature of 0 ° C. or higher to form polyaniline as a solid electrolyte. 3. The method according to claim 2, wherein the ratio of the organic solvent in the mixed solvent of water and the organic solvent is 10 to 85%. 4. Introducing an oxidation reaction catalyst into a surface oxide film;
2. The solid according to claim 1, wherein a mixture containing aniline, protonic acid, and hydrogen peroxide is introduced before and after the surface oxide film, and aniline is oxidatively polymerized to form polyaniline as a solid electrolyte. Manufacturing method of electrolytic capacitor. 5. A method for producing a solid electrolytic capacitor according to claim 4, wherein the oxidation catalyst is Fe ^{2 +} salts.