Electricity: electrical systems and devices – Safety and protection of systems and devices – Capacitor protection
Reexamination Certificate
2000-01-19
2002-10-15
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Capacitor protection
C361S058000, C361S115000
Reexamination Certificate
active
06466421
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a solid electrolytic capacitor and to a production method thereof. More specifically, the present invention relates to a solid electrolytic capacitor comprising a solid electrolyte having thereon an electrically conducting polymer having a n electron-conjugated system containing as a dopant at least one organic anion selected from (1) an alkoxy-substituted naphthalene monosulfonate anion, (2) a sulfonate anion of a heterocyclic compound, and (3) an anion of an aliphatic polycyclic compound and also relates to a production method of the capacitor. Preferably, the present invention relates to a solid electrolytic capacitor comprising a solid electrolyte additionally containing another anion having a dopant ability other than the organic anion dopant, and also relates to a production method of the capacitor.
BACKGROUND ART
A solid electrolytic capacitor is a device where an oxide film layer, a dielectric material, is formed on an anode substrate comprising a metal foil subjected to etching treatment, a solid semiconductor layer (hereinafter, simply referred to as a solid electrolyte) is formed as an opposing electrode outside the oxide dielectric layer and preferably an electric conductor layer such as an electrically conducting paste is further formed thereon. The device is actually used after the entire device is completely sealed by an epoxy resin or the like.
For the solid electrolyte, it has been heretofore known to use, for example, an inorganic semiconductor material such as manganese dioxide and lead dioxide, a tetracyanoquinodimethane (TCNQ) complex salt, an intrinsic electrically conducting polymer having an electric conductivity in the range of from 10
−3
, to 5×10
3
S/cm (JP-A-1-169914 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)(U.S. Pat. No. 4,803,596)) or a &pgr;-conjugated polymer such as polyaniline (JP-A-61-239617), polypyrrole (JP-A-61-240625), polythiophene derivative (JP-A-2-15611 (U.S. Pat. No. 4,910,645)) or polyisothianaphthene (JP-A-62-118511). Many of these electrically conducting polymers, which comprise a polymer main chain having a &pgr;-conjugated repeating structural unit and a dopant contained in the polymer chain, are used as an electrically conducting polymer layer (or a polymer-type charge-transfer complex). Furthermore, in recent years, not only dopants are used singly but also they are used in combination with, for example, manganese dioxide (JP-B-6-101418 (the term “JP-B” as used herein means an “examined Japanese patent publication” (U.S. Pat. No. 4,959,753)) or a filler (JP-A-9-320901).
With respect to the method for forming a solid electrolyte layer, a method of fusing and thereby forming an electrically conducting polymer layer on a dielectric layer provided on a valve-acting metal surface having a microfine void structure and a method of producing the above-mentioned electrically conducting polymer on a dielectric layer have been conventionally known. More specifically, for example, in the case of using a polymer of a 5-membered heterocyclic compound such as pyrrole or thiophene, a method of dipping an anode foil in a lower alcohol/water-based solution of a 5-membered heterocyclic compound and then dipping the anode foil in an aqueous solution having dissolved therein an oxidizing agent and an electrolyte to give rise to chemical polymerization, thereby forming an electrically conducting polymer (JP-A-5-175082), and a method of applying a 3,4-dioxyethylenethiophene monomer and an oxidizing agent each preferably in the form of a solution to an oxide coating layer of a metal foil separately differing in time or simultaneously to thereby form a solid electrolyte layer (JP-A-2-15611 (U.S. Pat. No. 4,910,645)) and JP-A-10-32145 (EP-A-820076(A2), (the term “EP-A” as used herein means an “unexamined published European patent application”)) are known.
In particular, JP-A-10-32145 discloses polymers of a monomer selected from pyrrole, thiophene, furan, aniline and derivatives thereof and doped with an aromatic polysulfonic acid (e.g., naphthalene disulfonic acid) having a plurality of sulfonic acid groups in the molecular structure thereof, and also discloses a polymerization method as the production method of the polymer, where a mixed solution of the above-described polymerizable monomer and an oxidizing agent is coated and dried or an oxidizing agent is introduced and then the polymerizable monomer is introduced.
Also, JP-A-10-32145 discloses a production method using the dopant of the above-described aromatic polysulfonic acid as a constituent component of the oxidizing agent (ferric salt), stating that the solid electrolytic capacitor comprising this dopant has excellent effects on the high temperature resistance or to prevent deterioration in the static capacitance.
Furthermore, JP-B-6-82590 (U.S. Pat. No. 4,959,753) discloses a solid electrolytic capacitor containing as a dopant an alkylnaphthalene sulfonate anion substituted by one or more alkyl groups, which has excellent effects on the initial property or leakage current property.
Known examples of the oxidizing agent for use, for example, in the chemical polymerization of 5-membered heterocyclic compounds such as thiophene include iron(III) chloride, Fe(ClO
4
)
3
, organic acid iron(III) salt, inorganic acid iron(III) salt, alkyl persulfate, ammonium persulfate (hereinafter simply referred to as “APS”), hydrogen peroxide, K
2
Cr
2
O
7
(see, JP-A-2-15611 (U.S. Pat. No. 4,910,645)), cupric compounds and silver compounds (see, JP-A-10-32145 (EP-A-820076(A2))).
However, the capacitor comprising a solid electrolyte using the manganese dioxide is disadvantageous in that the oxide dielectric film layer is ruptured at the thermal decomposition of manganese nitrate and the impedance property is not satisfied. In the case of using lead dioxide, its effect on the environment must be taken into account. The capacitor comprising a solid electrolyte using a TCNQ complex salt has good heat fusion workability and excellent electric conductivity but the TCNQ complex salt itself has a problem in the heat resistance and accordingly, the soldering heat resistance is poorly reliable. In order to overcome these problems, an electrically conducting polymer such as polypyrrole is applied to the solid electrolyte on the surface of a dielectric by electrolytic polymerization or chemical polymerization but satisfactory results cannot be obtained with respect to the homogeneity of film, soldering heat resistance, impedance property and the like.
Demands for the production of a capacitor device having high performance are recently increasing and to cope with this tendency, further improvements are required on the material for the solid electrolyte, production method thereof, heat stability, homogeneity of the film and the like.
DISCLOSURE OF THE INVENTION
Under these circumstances, an object of the present invention is to provide a solid electrolytic capacitor having excellent properties satisfying the requirements with respect to the reduction in the weight and size, high capacity, high frequency property, tan &dgr;, leakage current, heat resistance (reflow property), durability, etc. In particular, an object of the present invention is to provide a heat resistant solid electrolytic capacitor having excellent low impedance property and exhibiting durability in a sparking voltage test.
In order to attain the above-described objects, the present inventors have made extensive investigations on the kind, combination and content of a dopant anion in the electrically conducting polymer which works out to a solid electrolyte and as a result, they have now found that the above-described object of the present invention can be accomplished by provision of a specified organic anion in the solid electrolyte concerned in a solid electrolytic capacitor comprising opposing electrodes, one part electrode being a dielectric layer comprising a metal oxide and having a microfine structure provided on the surface of a valv
Furuta Yuji
Ikenoue Yoshiaki
Konuma Hiroshi
Monden Ryuji
Ohata Hideki
Jackson Stephen W.
Showa Denko K.K.
Sughrue & Mion, PLLC
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