JPH06325984A - Solid electrolytic capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a reliable solid electrolytic capacitor having a small leak current and capable of breaking a current by using an electrolyte that is insulated when the overcurrent is carried. CONSTITUTION:A solid electrolytic capacitor has an electrolyte made of conductive polymer such that substituted pyrrole and pyrrole are copolymerized with a substituent of hydroxyl, acetyl or carboxyl. In a manufacturing step, as an example, after polypyrrole is formed on a surface of a molded body, on which an oxide film over a valve-action metal is used as a dielectric substance, the molded body is dipped in an alkali solution or acid anhydride of dicarbonyl compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte and a method for producing the same, and more particularly to a solid electrolyte comprising a copolymer of pyrrole and a substituted pyrrole, which has small leakage current and high reliability. To a solid electrolytic capacitor excellent in heat resistance and a method for manufacturing the same

[0002]

2. Description of the Related Art With the progress of science and technology, miniaturization of electronic devices and improvement of reliability are required. Regarding capacitors, there is an increasing demand for large-capacity solid electrolytic capacitors having excellent characteristics up to a high frequency range and having excellent reliability, and studies are being made to meet such demand. Normally, a solid electrolytic capacitor uses a porous molded body of a valve action metal such as tantalum or aluminum as a first electrode (anode), and uses its oxide film as a dielectric material for manganese dioxide or 7,7 ', 8,8'-. It has a structure in which a tetracyanoquinodimethane complex salt or the like is used as a part of the second electrode (cathode). In this case, the solid electrolyte of the capacitor is required to have a function of electrically connecting the entire surface of the dielectric inside the porous molded body and the electrode leads and a function of repairing an electrical short circuit caused by a defect in the dielectric film. It is said that. Recently, new materials have been developed also in the field of polymers, and as a result, conductive polymers obtained by doping a conjugated polymer such as polypyrrole or polyaniline with an electron-accepting compound have been obtained. Further, as one of its uses, a solid electrolytic capacitor using these conductive polymers as a solid electrolyte has been proposed. Japanese Patent Publication No. 4-56445 describes a capacitor using polypyrrole or an alkyl-substituted polypyrrole as a solid electrolyte. Since the electrolyte can be formed without heating at a high temperature, the leakage current is small and the withstand voltage is high. It has been shown to be a feature. Further, although polymers such as N-methylpyrrole and N-ethylpyrrole are shown as alkyl-substituted polypyrrole in the above publication,
No mention is made of any differences in the properties of these polypyrroles.

[0003]

In the conventional solid electrolytic capacitor using manganese dioxide as an electrolyte, the high frequency characteristics are insufficient due to the high resistance of the electrolyte.
In the case of using 8,8'-tetracyanoquinodimethane complex salt as an electrolyte, there is a problem in that it has no solder heat resistance because of its low melting point. Further, in a solid electrolytic capacitor using a conductive polymer as an electrolyte, the solid electrolyte has a high conductivity and sufficient heat resistance, but conversely, when a defect occurs in the dielectric film, an overcurrent continues to flow. Therefore, there was a problem of lack of reliability. In order to solve this problem, it is conceivable to repeat the re-formation to repair the defective portion, but in this case, the formed conductive polymer is immersed again in the electrolytic solution to apply a voltage. Oxidation of the conductive polymer proceeds and the characteristics are impaired. Due to the above reasons, it is possible to stably obtain a solid electrolytic capacitor which has a low resistance of the electrolyte, a sufficient heat resistance, does not flow an overcurrent even when a defect occurs in the dielectric film, and has excellent reliability. There was a problem that it was difficult.

[0004]

The present inventors have conducted various studies to solve the above problems. As a result, they have found that a solid electrolytic capacitor using a specific polypyrrole copolymer as an electrolyte has excellent high frequency characteristics due to the high conductivity of the electrolyte, and that it can be reduced even when an overcurrent flows, leading to the present invention. . That is, the present invention is a solid electrolytic capacitor having a substituted pyrrole and a pyrrole copolymer compound doped with an electron-accepting compound as an electrolyte, wherein the substituent of the substituted pyrrole is a hydroxyl group, an acetyl group or a carboxyl group. Is a solid electrolytic capacitor. In addition, the production method is a method for producing a solid electrolytic capacitor using a hydroxyl-substituted pyrrole doped with an electron-accepting compound or a copolymer compound of an acetyl-substituted pyrrole and pyrrole as an electrolyte, and an oxide film of a valve metal. In a molded body having a dielectric as a solid electrolyte layer, after forming polypyrrole as a solid electrolyte layer, it is immersed in an alkaline aqueous solution or a solution of an acid anhydride of a dicarbonyl compound, and re-doping as required. Alternatively, a method for producing a solid electrolytic capacitor using, as an electrolyte, an acetyl group-substituted pyrrole doped with an electron-accepting compound or a carboxyl group-substituted pyrrole-pyrrole copolymer compound is used. The molded body to be formed is N-acetylpyrrole or pyrrole-β-carboxylic acid and pillow. The characterized in that it comprises a step of oxidizing cationic polymerization as a monomer.

In the present invention, the electron-accepting compound is poly
Lewis acid compound used as a dopant for pyrrole
And, for example, Cl^-, Br^-, I^-Halogen ion such as H
SO_Four ^-, R-SO_Four ^-(R is an alkyl group or alkenyl
Group) sulfuric acid compound, benzene sulfonate anion,
p-toluenesulfonic acid anion, naphthalene sulfone
Acid anion, butylnaphthalene sulfonate anion, do
Aromatic sulfones such as decylbenzene sulfonate anion
Acid anion, HNO₃ ^-, H₂PO_Four ^-, CH₃COO^-Etc.
Can be mentioned. In the present invention, the copolymer constituting the solid electrolyte
The copolymerization ratio of the compound is not particularly limited, and in the homopolymer
If it is a copolymer, it is effective. These are the NMR spectra.
Molecular structure of polymers such as cuttle, IR spectrum, ESCA
It can be confirmed by a conventionally known method as a manufacturing analysis method.

Examples of the pyrrole substituted with a hydroxyl group in the present invention include 3-hydroxypyrrole and 3,4-dihydroxypyrrole, and the pyrrole substituted with an acetyl group includes 3-acetylpyrrole and 3,4-diacetylpyrrole. , N-acetylpyrrole and the like. Examples of the pyrrole substituted with a carboxyl group include 3-carboxypyrrole, 3,4-dicarboxypyrrole and N-carboxypyrrole.

In the present invention, a solid electrolytic capacitor having a copolymer of a hydroxyl-substituted pyrrole and a pyrrole as an electrolyte, a polypyrrole as a solid electrolyte layer is formed on a molded body having an oxide film of a valve metal as a dielectric, It is manufactured by immersing in an alkaline aqueous solution and re-doping as necessary. In the present invention, the method for forming polypyrrole is not particularly limited, and a conventionally known method such as electrolytic polymerization using pyrrole as a monomer or oxidative cation polymerization using a salt of a transition metal cation of a high number such as Fe ³⁺ as an oxidizing agent is used. Done in. In the present invention, the type and pH of the alkaline aqueous solution are not particularly limited as long as it is alkaline, and general aqueous solutions of ammonia water, sodium hydroxide, potassium hydroxide and the like are used. Also,
The dipping method, dipping time and temperature are also not particularly limited.

A solid electrolytic capacitor using the copolymer compound of acetyl group-substituted pyrrole and pyrrole of the present invention as an electrolyte is obtained by forming polypyrrole as a solid electrolyte layer on a molded body having an oxide film of a valve metal as a dielectric. It is manufactured by immersing it in a solution of an acid anhydride of a dicarbonyl compound and re-doping as necessary. Also in this method, the method of forming polypyrrole is not particularly limited, and conventionally known methods such as electrolytic polymerization using pyrrole as a monomer and oxidative cation polymerization using an expensive salt of a transition metal cation such as Fe ³⁺ as an oxidizing agent. Done in a way. Examples of the acid anhydride of the dicarbonyl compound include acetic anhydride, but are not particularly limited. Further, the dipping method, the dipping time, and the temperature are not particularly limited.

In the present invention, a solid electrolytic capacitor having a copolymer compound of N-acetylpyrrole and pyrrole as an electrolyte is a molded body having an oxide film of a valve metal as a dielectric, and a pyrrole and N-acetylpyrrole as monomers. Is produced by oxidative cation polymerization. The oxidizing cationizing agent is not particularly limited, but a salt of an expensive number of transition metal cations such as Fe ³⁺ and Cu ^{2+ which} are conventionally used for the polymerization of pyrrole can be used. As such an oxidizing cationizing agent,
Examples include ferric dodecylbenzene sulfonate, ferric butyl naphthalene sulfonate, cupric dodecyl benzene sulfonate, cupric butyl naphthalene sulfonate, and the like. The reaction proceeds by mixing the monomer and the oxidizing cationizing agent with an organic solvent such as methanol or water. A copolymer of N-acetylpyrrole and pyrrole is formed on the surface of the dielectric by the reaction, but in the present invention, it is washed with methanol or pure water as necessary. Further, the above polymerization can be repeated.

In the present invention, a solid electrolytic capacitor having a carboxyl group-substituted pyrrole and a pyrrole copolymer compound as an electrolyte is a molded body having an oxide film of a valve metal as a dielectric, and a pyrrole and a pyrrole-β-carboxylic acid. Is produced by oxidative cation polymerization using as a monomer. The oxidizing cationizing agent is not particularly limited, but a salt of an expensive number of transition metal cations such as Fe ³⁺ and Cu ^{2+ which} are conventionally used for the polymerization of pyrrole can be used. Examples of the oxidizing cationizing agent include ferric dodecylbenzene sulfonate, ferric butylnaphthalene sulfonate, cupric dodecylbenzene sulfonate, cupric butyl naphthalene sulfonate, and the like. The reaction proceeds by mixing the monomer and the oxidizing cationizing agent with an organic solvent such as methanol or water. A copolymer of carboxyl group-substituted pyrrole and pyrrole is formed on the surface of the dielectric by the reaction, but in the present invention, it is washed with methanol, pure water or the like as necessary. Further, the above polymerization can be repeated.

Copolymer compounds of hydroxyl-substituted pyrrole and pyrrole doped with the electron-accepting compound of the present invention,
Copolymer compound of acetyl group-substituted pyrrole and pyrrole,
In addition, the solid electrolytic capacitor using a carboxyl group-substituted pyrrole and a pyrrole copolymer compound as an electrolyte has a smaller leakage current and a higher withstand voltage than those using a polypyrrole homopolymer as an electrolyte. This is because in the capacitor of the present invention, when a current is concentrated in a defective portion of the dielectric film and heat is generated, one component of the copolymer, hydroxyl-substituted pyrrole, acetyl-substituted pyrrole, and carboxyl-substituted pyrrole undergoes some reaction. It is thought that this is because the electrical conductivity at that portion is lowered, but the details are unknown. According to the study conducted by the present inventors, even in a solid electrolytic capacitor using a homopolymer of polypyrrole and polyalkylpyrrole as an electrolyte, a phenomenon in which the current decreases with time when a voltage is applied is observed, and insulation of a defective portion due to concentration of current is observed. Is expected to occur, the degree of the hydroxyl group-substituted pyrrole and pyrrole copolymer compound of the present invention, acetyl group-substituted pyrrole and pyrrole copolymer compound and carboxyl group-substituted pyrrole and pyrrole copolymer compound It was smaller than the capacitor used as the electrolyte.

In the present invention, after forming the conductive polymer described above as an electrolyte layer, an electrode lead is attached by a conventionally known method using a silver paste and a carbon paste,
Further, molding is performed as necessary to complete a solid electrolytic capacitor.

[0013]

EXAMPLES Next, examples of the present invention will be described. Example 1 A 35 wt% solution of ferric dodecylbenzene sulfonate in methanol was placed in a glass container kept at -75 ° C., and stirred three times with respect to the number of moles of ferric dodecylbenzene sulfonate in the solution. A mixed solution of ferric dodecylbenzene sulfonate and pyrrole was prepared by dropping a certain number of moles of pyrrole. Next, length 3mm x 2mm x 2.5mm
0.05w of rectangular parallelepiped tantalum fine powder pellets
Anodic oxidation was carried out at 100 V in a t% aqueous phosphoric acid solution, followed by washing and drying to obtain pellets having a capacity of 10 μF in the electrolytic solution. The pellets were immersed in the mixed solution of ferric dodecylbenzene sulfonate / pyrrole at -75 ° C.
After 60 seconds, the pellets were removed and kept in air at 25 ° C for 30 minutes to polymerize the pyrrole, washed with methanol and dried to obtain a sample of tantalum pellets filled with polypyrrole doped with dodecylbenzene sulfonate anion. This sample was immersed in a 0.1 mol% aqueous ammonia solution and kept at room temperature for 30 minutes. Next, it was washed with methanol and dried under reduced pressure at 60 ° C. The X-ray photoelectron spectrum was measured before and after the treatment with the aqueous ammonia solution, and the C
When the 1s spectrum was subjected to peak separation, it was found that 3% of the whole pyrrole ring of the main chain of polypyrrole was converted to hydroxylated pyrrole after the treatment with the aqueous ammonia solution.
Furthermore, a lead was drawn out from the sample treated with ammonia water using a silver paste to complete a solid electrolytic capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 20 nA, which was 1/10 or less of the standard value. Also, when the voltage was raised at 1 V / min,
Destroyed at 88V. This withstand voltage value was more than twice as high as that of a capacitor using the same tantalum pellet and containing manganese dioxide as an electrolyte.

Comparative Example 1 Using the sample of tantalum pellets filled with polypyrrole of Example 1, the lead was pulled out using the silver paste as it was, and a solid electrolytic capacitor using polypyrrole as an electrolyte was completed. Apply 35V to this capacitor and 60
When the current value after a second was measured, it was 60 nA, which was lower than the standard value, but higher than that in the case of using the hydroxyl-substituted pyrrole-pyrrole copolymer of Example 1 as the electrolyte. Also, when the voltage was raised at 1 V / min, 55
Destroyed with V. This is also lower than the capacitor using the same tantalum pellet and using manganese dioxide as the electrolyte, but was inferior to the case where the copolymer of the hydroxyl-substituted pyrrole and pyrrole of Example 1 was used as the electrolyte.

Example 2 Using the sample of tantalum pellets filled with the polypyrrole of Example 1, the sample was immersed in a 0.1 mol% acetic anhydride aqueous solution,
Hold for 30 minutes at room temperature. Then wash with methanol, 60
It was dried under reduced pressure at ℃. X before and after treatment with acetic anhydride solution
When the line photoelectron spectrum was measured and the C1s spectrum was subjected to peak separation, it was found that 3% of the whole pyrrole ring of the main chain of polypyrrole was changed to acetylpyrrole after the treatment. Furthermore, a lead was pulled out from the treated sample using silver paste to complete a solid electrolytic capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 18 nA, which was 1 of the standard value.
It was / 10 or less. Moreover, when the voltage was increased at 1 V / min, it was broken at 86 V. This withstand voltage value was more than twice as high as that of a capacitor using the same tantalum pellet and containing manganese dioxide as an electrolyte.

Example 3 The rectangular parallelepiped tantalum fine powder pellets of Example 1 were anodized to form a dielectric layer. The pellets were immersed in 25 wt% ferric dodecylbenzene sulfonate in methanol. After 2 minutes, the pellets were taken out, immediately immersed in an aqueous solution of 0.01 M N-acetylpyrrole and 0.1 M pyrrole, and kept for 1 hour. Next, the pellet was washed with methanol and dried, X-ray photoelectron spectrum was measured for a part of the polymer formed on the surface, and the C1s spectrum was peak-separated. The obtained pellet had dodecylbenzenesulfonate anion as a dopant. It was found that the copolymer of N-acetylpyrrole and pyrrole was filled in, and the copolymerization ratio was 10:90. Furthermore, a lead was drawn from the obtained sample by using a silver paste to complete a solid electrolytic capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 18 nA, which was 1 of the standard value.
It was / 10 or less. Further, when the voltage was increased at 1 V / min, it was broken at 85 V. This withstand voltage value was more than twice as high as that of a capacitor using the same tantalum pellet and containing manganese dioxide as an electrolyte.

Example 4 The rectangular parallelepiped tantalum fine powder sintered body pellets obtained in Example 1 were anodized to form a dielectric layer. The pellets were immersed in 25 wt% ferric dodecylbenzene sulfonate in methanol. Two minutes later, the pellets were taken out, immediately immersed in an aqueous solution of 0.01 M pyrrole-β-carboxylic acid and 0.1 M pyrrole, and held for 1 hour. Next, the pellet was washed with methanol and dried to measure an X-ray photoelectron spectrum of a part of the polymer formed on the surface,
When the C1s spectrum was subjected to peak separation, the obtained pellets were filled with a copolymer of pyrrole-β-carboxylic acid and pyrrole having a dodecylbenzenesulfonate anion as a dopant, and the copolymerization ratio was 1
It was found to be 0:90. Furthermore, a lead was pulled out from the sample using silver paste to complete a solid electrolytic capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 19 nA, which was 1/10 or less of the standard value. Moreover, when the voltage was increased at 1 V / min, the device was broken at 89 V. This withstand voltage value was more than twice as high as that of a capacitor using the same tantalum pellet and containing manganese dioxide as an electrolyte.

Example 5 The rectangular parallelepiped tantalum fine powder pellets obtained in Example 1 were anodized to form a dielectric layer. The pellets were immersed in 25 wt% ferric dodecylbenzene sulfonate in methanol. After 2 minutes, the pellets were taken out, immediately immersed in a 0.1 M aqueous solution of pyrrole and kept for 1 hour to polymerize the pyrrole, washed with methanol and dried, and tantalum filled with polypyrrole doped with dodecylbenzenesulfonate anion. A pellet sample was obtained. This sample was treated with ammonia water in the same manner as in Example 1,
Leads were drawn out by the method of Example 1 to complete a capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 20 nA, which was 1/1 of the standard value.
It was 0 or less. Moreover, when the voltage was raised at 1 V / min, it was broken at 88 V. This withstand voltage value was more than twice as high as that of a capacitor using the same tantalum pellet and containing manganese dioxide as an electrolyte.

Example 6 Instead of the tantalum fine powder sintered body of Example 1, the surface area was increased 12 times by etching, and the film thickness was 50 μm and one side was 1 c.
m square aluminum foil was used, anodized, washed and dried in the same manner as in Example 1, immersed in the mixed solution of ferric dodecylbenzene sulfonate of Example 1 and pyrrole, and dried in air 25 When kept at 0 ° C. for 1 hour, an aluminum foil whose surface was coated with polypyrrole having a dodecylbenzene sulfonate anion as a dopant was obtained. This sample was treated with ammonia water in the same manner as in Example 1,
Leads were drawn out by the method of Example 1 to complete a capacitor. When 35 V was applied to this capacitor and the current value after 60 seconds was measured, it was 30 nA, which was 1/5 of the standard value.
It was below. When the voltage was increased at 1 V / min, it was found that this capacitor had a high withstand voltage that did not cause dielectric breakdown up to 50 V.

[0020]

As described above, according to the present invention, it is possible to provide a solid electrolytic capacitor excellent in high frequency characteristics and capable of reducing an overcurrent even when it flows, and its effect is large. is there.

Claims (3)

[Claims] 1. A solid electrolytic capacitor using a substituted pyrrole-pyrrole copolymer compound doped with an electron-accepting compound as an electrolyte, wherein the substituent of the substituted pyrrole is a hydroxyl group, an acetyl group or a carboxyl group. Solid electrolytic capacitor characterized by. 2. A method for producing a solid electrolytic capacitor using, as an electrolyte, a hydroxyl-substituted pyrrole doped with an electron-accepting compound or a copolymer compound of an acetyl-substituted pyrrole and a pyrrole, wherein an oxide film of a valve metal is formed. In the molded body as a dielectric, after forming polypyrrole as a solid electrolyte layer, it is immersed in an alkaline aqueous solution or a solution of an acid anhydride of a dicarbonyl compound, and a solid comprising a step of re-doping as required. Method of manufacturing electrolytic capacitor. 3. A method for producing a solid electrolytic capacitor using an acetyl group-substituted pyrrole doped with an electron-accepting compound or a copolymer compound of a carboxyl group-substituted pyrrole and pyrrole as an electrolyte, comprising an oxide film of a valve metal. A method for producing a solid electrolytic capacitor, which comprises a step of forming a molded body having a dielectric as a dielectric by oxidative cation polymerization using N-acetylpyrrole or pyrrole-β-carboxylic acid and pyrrole as monomers.