Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
2002-01-24
2004-08-31
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
Reexamination Certificate
active
06783703
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
The present invention relates to a solid electrolytic capacitor comprising a solid electrolyte layer and an electrically conducting layer (an electrically conducting layer comprising metallic powder or an electrically conducting layer comprising an electrically conducting carbon layer and a layer formed thereon and comprising metallic powder) in which at least one of said layers contains a rubber-like elastic material and a production process thereof. More specifically, the present invention relates to a solid electrolytic capacitor which can be made compact and can be endowed with high-capacitance and low-impedance and is excellent in external force-relaxing properties, productivity, heat resistance and moisture resistance, etc., and a production process thereof.
The present invention also relates to a solid electrolyte, a conducting paste comprising metallic powder and an electrically conducting carbon paste for use in a solid electrolytic capacitor.
BACKGROUND ART
In general, a solid electrolytic capacitor is formed through the following steps: a dielectric oxide film layer is formed on a positive electrode substrate formed of a metallic foil which undergoes etching treatment and has a large specific surface area; a solid semiconducting layer (hereinafter referred to as “solid electrolyte layers”) serving as a counter electrode is formed outside the oxide film layer; preferably a conducting layer comprising metallic powder or a conducting layer comprising a conductive carbon layer and a layer formed thereon comprising metallic powder is further formed on the outer side of the solid electrolyte layer; and a lead wire is connected thereto, thereby forming the basic elements of a capacitor. Subsequently, the entirety of the elements is completely sealed by use of an epoxy resin or the like. The thus-obtained product is widely used as a capacitor component in electric appliances.
In recent years, in order to meet requirements for digitization of electric apparatuses and increase in processing speed of personal computers, solid electrolytic capacitors are demanded to have small size, high capacitance, and low impedance in a high-frequency range.
In order to meet demands for such solid electrolytic capacitors, suggestions have been made with regard to solid electrolytes, conducting materials, etc.
For the solid electrolyte, it is heretofore known to use, for example, an inorganic semiconductor material such as manganese dioxide and lead dioxide, an organic semiconductor material such as TCNQ complex salt, an intrinsic electrically conducting polymer having an electric conductivity 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”) corresponding to U.S. Pat. No. 4,803,596) or an electrically conducting polymer such as &pgr;-conjugated 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).
Capacitors using manganese dioxide for the solid electrolyte are disadvantageous not only in that when manganese nitrate is thermally decomposed to form manganese dioxide, the oxide dielectric film once formed on the anode foil is ruptured, but also in that the impedance property is not satisfied.
In the case of using lead dioxide, cares on the environment are additionally required.
Capacitors using a TCNQ complex salt solid for the solid electrolyte have good heat molten workability and excellent electric conductivity but are considered to show poor reliability in the heat resistance at the solder joining (soldering heat resistance) because the TCNQ complex salt itself has a problem in the heat resistance.
Capacitors using an electrically conducting polymer for the solid electrolyte are free of rupture of dielectric film and favored with high impedance property but disadvantageously deficient in the heat resistance, thermal shock resistance and vibration resistance.
With respect to the method for forming a solid electrolyte using an electrically conducting polymer, for example, a method of melting an electrically conducting polymer (solid electrolyte) as described above on a dielectric film layer on the surface of a valve-acting metal having fine void structures to form an electrically conducting polymer layer, and a method of depositing the above-described electrically conducting polymer on the dielectric film layer are known.
More specifically, in the case of using, for example, a polymer of a 5-membered heterocyclic compound such as pyrrole or thiophene for the solid electrolyte, there are known a method of forming an electrically conducting polymer layer having a necessary thickness by repeating a series of operations of dipping an anode foil having formed thereon a dielectric film in a lower alcohol and/or water-based solution of a 5-membered heterocyclic compound monomer and after pulling it up, again dipping the foil in an aqueous solution having dissolved therein an oxidizing agent and an electrolyte to cause chemical polymerization of the monomer (JP-A-5-175082), a method of coating simultaneously or not simultaneously a 3,4-ethylenedioxythiophene monomer and an oxidizing agent each preferably in the form of a solution on the oxide film layer of a metal foil to form an electrically conducting polymer layer (JP-A-2-15611 (U.S. Pat. No. 4,910,645) and JP-A-10-32145 (European Patent Laid-Open Publication 820076)), and the like.
As the oxidizing agent for use in conventional techniques, for example, chemical polymerization of 5-membered heterocyclic compounds such as thiophene, there are known 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
, etc., (JP-A-2-15611), cupric compounds, silver compounds, etc., (JP-A-10-32145 (European Patent Laid-Open Publication 820076)).
In recent years, a method for producing a polyaniline composite is proposed, where powdered polyaniline is used as an electrically conducting starting material, rubber and/or thermoplastic resin is used as the matrix material and the powdered polyaniline is dispersed and compounded in the rubber and/or thermoplastic resin to form a polyaniline composite having mechanical strength and flexibility (JP-A-64-69662).
Furthermore, a method for producing a capacitor is proposed, where a composite film is formed on the metal oxide of a capacitor electrode from a polyaniline solution containing from 1 to 25 mass % of a polymer binder and an electrically conducting polymer layer comprising polyaniline having added thereto anion is further formed on the composite film (JP-A-5-3138).
According to the above-descried methods, it is necessary for forming an electrically conducting polymer layer to previously form a thin electrically conducting layer on the oxide film as an insulator by chemical polymerization. Furthermore, there are problems mentioned below in suitability applying these methods to respective capacitors.
First, in the case of electrolytic polymerization, if the polymer has poor flexibility, the increase in viscosity causes reduction in capacitance. More specifically, when an aluminum foil having formed thereon a dielectric material obtained by etching the surface is dipped with an oxidizing agent solution and then dried, an oxide film having high viscosity is formed on the surface of a porous body. As a result, microfine pore openings present on the surface of the porous body are clogged. Furthermore, a polymer is formed on the surface by the contact with a monomer and the polymer is not formed inside the pores, which causes reduction in capacitance.
Second, in the case of chemical polymerization, the amount of polymer adhered by one polymerization step is small, accordingly, the dipping must be repeated with predetermined number of steps. Thus, a method advantageous in view of productivity is demanded.
Third,
Furuta Yuji
Konuma Hiroshi
Monden Ryuji
Ohata Hideki
Sakai Atsushi
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