Compositions – Electrically conductive or emissive compositions
Reexamination Certificate
1999-09-08
2003-12-16
Gupta, Yogendra N. (Department: 1751)
Compositions
Electrically conductive or emissive compositions
C361S523000, C361S524000, C361S525000, C361S526000, C361S437000
Reexamination Certificate
active
06663796
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electroconductive polymer, to a solid electrolytic capacitor containing an electroconductive polymer, and to methods for producing them. More specifically, the present invention relates to a solid electrolytic capacitor having a reduced size, high capacity, low impedance, good moisture resistant loading property and excellent heat resistance, and to a production method thereof as well as to a highly electroconductive polymer having a novel fibril structure for use in the capacitor and to a production method of the highly electroconductive polymer.
BACKGROUND ART
The solid electrolytic capacitor is a capacitor element manufactured by forming a dielectric oxide film layer on an anode substrate comprising a metal foil which has a large specific surface area and has generally been subjected to etching treatment, forming a solid semiconductor layer (hereinafter simply referred to as a solid electrolyte) as an counter electrode outside the dielectric layer, preferably further forming an electrically conductive layer such as an electroconductive paste on the outer face of the electrode, and connecting a lead wire thereto. The element as a whole is completely sealed with an epoxy resin or the like and is widely used as a capacitor part in electrical articles.
To cope with the demands for digitization of electrical appliances or higher speed processing of personal computers in recent years, the capacitor used therefor is also required to be compact, have a large capacity and give a low impedance in a high frequency region.
As the compact capacitor having a large capacity, solid electrolytic capacitors such as aluminum electrolytic capacitor and tantalum electrolytic capacitor have been used. However, the aluminum electrolytic capacitor has a problem in that since an ion conducting liquid electrolyte is used as the electrolytic solution, the impedance is high in the high frequency region and the temperature characteristics are bad. The tantalum electrolytic capacitor has a problem in that since a manganese oxide is used as the electrolyte and the manganese oxide has a relatively high resistivity, the impedance in the high frequency region is high.
As means to solve these problems, it has been proposed to use an electroconductive polymer having electrically conductive properties as the solid electrolyte. For example, use of an electroconductive organic material comprising a &pgr;-conjugated polymer such as polyaniline (see, JP-A-61-239617 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), a polypyrrole (see, JP-A-61-240625), a polythiophene derivative (see, JP-A-2-15611 (U.S. Pat. No. 4,901,645)), a polyisothianaphthene not containing a dopant (see, JP-A-62-118509), a doped polyisothianaphthene (see, JP-A-62-118511) or an intrinsic conducting polymer having an electroconductivity of from 10
−3
to 10
3
S/cm (see, JP-A-1-169914 (U.S. Pat. No. 4,803,596)) has been proposed.
That is, polymers having a conjugated double bond represented by polymers of aniline, pyrrole, thiophene or the like generally have a specific electroconductivity and therefore, various investigations and developments have heretofore been made thereon. In particular, the electric, magnetic and optical properties peculiar to the &pgr;-electron conjugated system of the electroconductive polymer have been taken notice of. These electroconductive polymers have been mainly produced by an electrolytic polymerization method and a chemical oxidative polymerization method.
However, according to the conventional production method, if the low molecular weight polymer obtained by the redox reaction performed on the electrode surface has poor adhesion to the electrode surface, the low molecular weight polymer dissolves or deposits in the electrolytic solution. Furthermore, if an article having a large area is intended to obtain, an electrode having a size in proportion thereto must be used, accordingly, a serious problem arises with respect to the production cost.
On the other hand, in the case of using the chemical oxidative polymerization method, an electroconductive polymer can be easily obtained by mixing a polymerizable monomer with an appropriate oxidizing agent, therefore, this simple polymerization method has been taken notice of in industry and studies and developments thereof have been made.
However, the chemical oxidative polymerization method has the following serious problem. Since the polymerization rate is proportional to the activity of the oxidizing agent, an oxidizing agent having high activity must be used. But if the polymerization is performed using a highly active oxidizing agent, an adverse side reaction readily takes place and only a polymer reduced in the structural order and having a low electroconductivity can be obtained. This problem is considered to occur because an electroconductive polymer having a conjugated double bond produced stays in the reaction system for a long period of time, therefore, the polymer skeleton having the conjugated double bond is partially destroyed by the effect of excess oxidizing agent in the reaction system, as a result, the electroconductivity decreases.
Furthermore, the electroconductive polymer obtained by the electrolytic polymerization or chemical oxidative polymerization is generally insoluble and infusible, therefore, there is an operational problem particularly in that its after processing is very difficult.
In order to solve these problems, various attempts have been made. For example, JP-A-7-130579 (U.S. Pat. No. 5,567,209) discloses a production method of a solid electrolytic capacitor using an oxide film formed on a valve-acting metal as the dielectric layer and an electroconductive polymer formed on the dielectric layer as the solid electrolyte comprising a step of coating a monomer compound solution on the surface of the above-described dielectric oxide layer and drying it to form a solid monomer compound, and a step of contacting the solid monomer compound with an oxidizing agent solution to form an electroconductive polymer layer, thereby producing a solid electrolytic capacitor having a high capacity occurrence ratio and good high-frequency properties.
JP-A-6-340754 discloses a technique of allowing polycyclic aromatic amine compound to adhere to or impregnate into an insulating substrate and contacting the substrate with a solution containing an oxidizing agent to thereby oxidatively polymerize the polycyclic aromatic amine compound inside or on the surface of the substrate.
JP-A-10-50558 discloses a production method of a solid electrolytic capacitor as an application of the electroconductive polymer, comprising impregnating an electroconductive polymer as the cathode electrolyte into a capacitor element comprising an anode member having thereon a chemical formed layer, wherein the capacitor element is immersed in a solution obtained by dissolving an oxidizing agent in a monomer which becomes an electroconductive polymer by the oxidative polymerization, thereby forming an electroconductive polymer layer within the capacitor element, so that a compact capacitor having a large capacity can be produced.
JP-A-10-50559 discloses a technique, which is an application of the electroconductive polymer to a solid electrolytic capacitor comprising a step of immersing a capacitor element in an oxidizing agent solution and then evaporating the solvent component, thereby precipitating an oxidizing agent within the capacitor element, and a step of immersing the capacitor element in a solution containing a monomer which becomes an electroconductive polymer by the oxidative polymerization, thereby allowing the oxidizing agent to act on the monomer, so that high-temperature load properties can be improved.
Furthermore, JP-A-9-289141 (EP-A-803885) proposes a production method of a solid electrolytic capacitor, comprising immersing a porous electrode material in a monomer salt solution kept at a temperature higher than the dissolution temperature, cooling the porous materia
Monden Ryuji
Ohata Hideki
Sakai Atsushi
Shirane Koro
Gupta Yogendra N.
Hamlin Derrick G.
Showa Denko K.K.
Sughrue & Mion, PLLC
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