Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
1999-11-30
2001-09-11
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S437000, C361S508000, C252S062200
Reexamination Certificate
active
06288889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electrolytic capacitor. Particularly, the invention relates to an electrolytic solution for electrolytic capacitor having a low impedance as well as good low temperature stability and other characteristics.
2. Description of the Related Art
A capacitor is a common electrical part and is generally used, in various electric and electronic products, mainly for power supply circuits, noise filters for digital circuits or the like.
Various types of capacitors are currently used. This invention pertains to an aluminum electrolytic capacitor. A typical aluminum electrolytic capacitor is fabricated by etching a high purity aluminum foil to increase its surface area, anodizing a surface of the aluminum foil to provide a dielectric surface film, preparing a laminate made up of the anode foil, an aluminum cathode foil which is opposed to the dielectric surface film of the anode foil and has etched surfaces, and a separator interposed between the anode and cathode foils, winding the laminate to provide an element of a wound structure, impregnating the element with an electrolytic solution, inserting the impregnated element in a case (typically made of aluminum), and sealing the case with an elastic sealant. There are electrolytic capacitors having structures other than such a wound structure.
In such an electrolytic capacitor, the characteristics of an electrolytic solution are important factors for deciding performance of the electrolytic capacitor. Particularly, miniaturization of electrolytic capacitors leads to the use of anode and cathode foils having a higher surface area by etching, which results in a high resistivity in the capacitors. Consequently, an electrolytic solution used in such a capacitor is always required to have a low resistivity (specific resistance) and a high electrical conductivity.
A typical electrolytic solution for a conventional electrolytic capacitor comprises a solvent made up of ethylene glycol (EG) as a main solvent and up to about 10% by weight of additional water, and an electrolyte dissolved in the solvent, the electrolyte being a carboxylic acid such as adipic acid or benzoic acid, or an ammonium salt thereof. Such an electrolytic solution has a specific resistance of the order of 1.5 &OHgr;-m (150 &OHgr;-cm).
Capacitors have to have a low impedance (z). The impedance of a capacitor is decided by various factors. For example, a capacitor having a larger electrode area shows a lower impedance and, accordingly, a larger capacitor naturally attains a lower impedance. In addition, there is approach to attempting to attain a lower impedance by improving a separator. However, particularly in smaller capacitors, the specific resistance of the electrolytic solution is a predominant factor for impedance.
Although electrolytic solutions of an aprotic type having a lower specific resistance (gamma-butyrolactone and the like) have recently been developed (JP-A-62-145713, JP-A-62-145714, and JP-A-62-145715), capacitors using an aprotic-type electrolytic solution have an unsatisfactory impedance compared to solid electrolytic capacitors using an electronic conductor which is known as a low specific resistance electrolyte.
In addition, an aluminum electrolytic capacitor has poorer low temperature stability due to use of an electrolytic solution and, in fact, has a ratio of impedance at −40° C. to impedance at 20° C. (Z(−40° C.)/Z(20° C.)) of about 40 at 100 kHz, which is significant.
On the other hand, water used as part of a solvent in an electrolytic solution for an aluminum electrolytic capacitor is a chemically active substance for the materials of the anode and cathode foils and, in general, tends to reduce the life of the electrolytic capacitor by acting on the anode and cathode foils (hydration reactions).
SUMMARY OF THE INVENTION
Thus, it is an object of the invention to provide an electrolytic solution for an aluminum electrolytic capacitor having a low impedance, excellent low temperature stability represented by a ratio of impedances at low temperature and normal temperature, and good other characteristics.
It is also an object of the invention to provide, using the electrolytic solution of the invention, an electrolytic capacitor having a lower impedance, improved low temperature stability, and a prolonged life.
The electrolytic solution for an electrolytic capacitor of the invention is characterized by comprising (1) a solvent made up of 20 to 80% by weight of an organic solvent and 80 to 20% by weight of water, (2) at least one electrolyte selected from the group consisting of carboxylic acids, salts of carboxylic acids, inorganic acids, and salts of inorganic acids, and (3) a chelate compound.
The chelate compound in the electrolytic solution of the invention prevents deterioration of aluminum electrode foils by inhibiting a hydration reaction of the electrode foil, to thereby provide an electrolytic capacitor with an elongated life. Use of a combination of an organic electrolyte of a carboxylic acid or salt thereof and an inorganic electrolyte of an inorganic acid or salt thereof has an effect on an electrolytic capacitor to provide it with a much longer life.
The electrolytic capacitor of the invention is characterized by using, as its electrolytic solution, the electrolytic solution of this invention. Specifically, the electrolytic capacitor comprises a sealed case and a wound element contained in the case, the element comprising a laminate made up of an anode foil formed of an aluminum foil having a dielectric surface film formed by anodization, a cathode foil of aluminum opposed to the dielectric surface film of the anode foil, and a separator interposed between the anode and cathode foils, and the element being impregnated with an electrolytic solution, wherein the electrolytic solution comprises (1) a solvent made up of 20 to 80% by weight of an organic solvent and 80 to 20% by weight of water, (2) at least one electrolyte selected from the group consisting of carboxylic acids, salts of carboxylic acids, inorganic acids, and salts of inorganic acids, and (3) a chelate compound. The anode foil may have a dielectric film on both surfaces.
REFERENCES:
patent: 4580855 (1986-04-01), Niwa
patent: 4652968 (1987-03-01), Shimamoto et al.
patent: 4664830 (1987-05-01), Shinozaki et al.
patent: 4734821 (1988-03-01), Morimoto et al.
patent: 4762632 (1988-08-01), Shinozaki et al.
patent: 5055974 (1991-10-01), Washio et al.
patent: 32-10531 (1957-12-01), None
patent: 56-73423 (1981-06-01), None
patent: 58-17609 (1983-02-01), None
patent: 61-79219 (1986-04-01), None
patent: 62-2514 (1987-01-01), None
patent: 62-219508 (1987-09-01), None
patent: 62-272514 (1987-11-01), None
patent: 1-168016 (1989-07-01), None
patent: 3-1817 (1991-01-01), None
patent: 3-42695 (1991-06-01), None
patent: 6-151251 (1994-05-01), None
patent: 9-115780 (1997-05-01), None
patent: 9-115782 (1997-05-01), None
patent: 9-115779 (1997-05-01), None
patent: 9-115781 (1997-05-01), None
Komatsu Akihiko
Ogawara Tetsushi
Ha Nguyen
Reichard Dean A.
Rubycon Corporation
Wallenstein & Wagner Ltd.
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