Compositions – Electrolytes for electrical devices
Reexamination Certificate
2000-08-17
2001-08-14
Koslow, C. Melissa (Department: 1755)
Compositions
Electrolytes for electrical devices
C361S504000, C361S505000
Reexamination Certificate
active
06274061
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrolyte for an electrolytic capacitor. More specifically, it relates to an electrolyte for an electrolytic capacitor having excellent high temperature life characteristics, and an electrolytic capacitor comprising the same. More particularly, it relates to an aluminum electrolytic capacitor having excellent high temperature life characteristics and moisture resistance.
BACKGROUND OF THE INVENTION
The general method for producing an electrolytic capacitor comprises winding, via an separator made of Manila paper, etc., an anodic electrode foil (A), which has been obtained by chemically or electrochemically etching a valve metal foil (for example, a band made of highly pure aluminum) to enlarge the foil surface and subjecting this foil to a anodizing treatment in an electrolyte such as an aqueous ammonium borate solution to thereby form an oxide coating layer on its surface, and a cathodic electrode foil (B) made of a highlypure foil subjected to etching treatment only. Next, the obtained capacitor device is impregnated with an electrolyte for driving electrolytic capacitors and putting in a bottomed outer case. The outer case is equipped at the opening with a sealer made of an elastic rubber and sealed by drawing.
The anodic electrode foil and the cathodic electrode foil are each connected to a lead wire by stitching, ultrasonic welding, etc. so as to lead the electrode. The lead wire employed as each electrode leading means is composed of a round bar, a connecting member being in contact with the electrode foil and an outer connecting member made of a solderable metal which has been fixed at the tip of the round bar by welding, etc.
There are various electrolytes, with which capacitor devices are to be impregnated for driving electrolytic capacitors, depending on the performance of the electrolytic capacitor employed. Among them, adipic acid solutions in ethyleneglycol are known as electrolytes which are suitable for low voltage and have excellent high temperature life characteristics.
FIGS. 1 and 2
show general structures of aluminum electrolytic capacitors. An aluminum foil of a high purity is chemically or electrochemically etched to thereby enlarge the aluminum foil surface. This aluminum foil is subjected to a anodizing treatment in an electrolyte such as an aqueous ammonium borate solution to give an anodic electrode foil (
2
) having an oxide coating layer formed on its surface. This anodic electrode foil (
2
) and a cathodic electrode foil (
3
) made of an aluminum foil of a high purity having been etched alone, are wound via a separator (
11
) made of Manila paper, etc. to give a capacitor device (
1
) as shown in FIG.
2
. As
FIG. 1
shows, this capacitor device (
1
) is impregnated with an electrolyte for driving electrolytic capacitors and then put into a bottomed outer case (
10
) made of aluminum etc., which is then sealed by drawing.
As
FIG. 2
shows, the anodic electrode foil (
2
) and the cathodic electrode foil (
3
) are provided respectively with lead wires (
4
) and (
5
), which are electrode-leadingmeans, by stitching, welding, etc. The lead wires (
4
) and (
5
) each employed as an electrode leading means is composed of a round bar (
6
) made of aluminum, a connecting member (
7
) being in contact with the electrode foil (
2
) or (
3
) and an outer connecting member (
8
) made of a solderable metal which has been fixed at the tip of the round bar (
6
) by welding, etc.
There are various electrolytes, with which the capacitor device (
1
) is impregnated for driving aluminum electrolytic capacitors, depending on the performance of the aluminum electrolytic capacitor employed. Among them, a solution comprising a quaternary ammonium salt dissolved in &ggr;-butyrolactone is known as an electrolyte having a high electric conductance. In recent years, there are further reported electrolytes wherein &ggr;-butyrolactone is employed as the main solvent and salts composed of quaternized cyclic amidin compounds (imidazolinium cation and imidazolium cation) as the cationic component and acid conjugated bases as the anionic component are dissolved therein as the solute (JP-A-8-321440 and JP-A-8-321441; The term “JP-A” as used herein means an “unexamined published Japanese patent application”).
With the recent tendency toward improved automobile functions, it has been more and more required in the field of vehicle equipments to use electronic parts in engine rooms operated at high temperatures. However, electrolytic capacitors with the use of the above-mentioned electrolytes cannot withstand these high temperatures. Regarding low temperature characteristics, furthermore, these electrolytic capacitors can withstand a temperature of −25° C. at lowest but vehicle equipments should generally withstand low temperatures of about −40° C. Namely, no electrolyte for electrolytic capacitors usable in this field has been provided in practice so far.
Although sulfolane has been known as a high-boiling solvent capable of imparting excellent high temperature life characteristics (JP-A-1-124210 and JP-A-8-31699), it fails to establish the desired characteristics as described above. Thus, sulfolane cannot be employed in vehicle equipments which should have excellent high temperature life characteristics and low temperature properties simultaneously.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an electrolytic capacitor having excellent high temperature life characteristics and excellent low temperature properties and an electrolyte to be used in these electrolytic capacitors.
Another object of the present invention is to provide an aluminum electrolytic capacitor having excellent high temperature life characteristics and moisture resistance, a low dielectric loss and good low temperature properties.
The above objects are achieved mainly by the following constitutions:
(1) A first electrolyte for electrolytic capacitors comprises a mixed solvent of sulfolane and at least one selected from the group consisting of 3-methyl sulfolane and 2,4-dimethyl sulfolane as a solvent;
the first electrolyte for electrolytic capacitors, wherein the content of sulfolane is from 20 to 70% by weight based on the mixed solvent;
the first electrolyte for electrolytic capacitors, which comprises a quaternized cyclic amidinium salt as a solute; and
an electrolytic capacitor, which comprises the first electrolyte,
(2) An aluminum electrolytic capacitor constructed by winding, via a separator, an anodic electrode foil provided with an anode leading means and a cathodic electrode foil provided with a cathode leading means made of aluminum to thereby form a capacitor device, and then impregnating said capacitor device with a second electrolyte in which a quaternized imidazolinium salt or a quaternized pyrimidinium salt is dissolved in a mixed solvent containing sulfolane and &ggr;-butyrolactone;
the aluminum electrolytic capacitor, wherein the second electrolyte contains &ggr;-butyrolactone in an amount of from 20 to 60% by weight based on the mixed solvent;
the aluminum electrolytic capacitor, wherein the cathodic electrode foil is an aluminum foil having provided on the whole or part of a surface thereof a coating made of a metal nitride selected from the group consisting of titanium nitride, zirconium nitride, tantalum nitride and niobium nitride or a metal selected from the group consisting of titanium, zirconium, tantalum and niobium; and
the aluminum electrolytic capacitor, wherein an aluminum oxide layer is formed by anodic oxidation on the whole or a part of the surface of the cathode leading means, and
(3) a third electrolyte for electrolytic capacitors which comprises a mixed solvent containing &ggr;-butyrolactone and at least two selected from the group consisting of sulfolane, 3-methyl sulfolane and 2,4-dimethyl sulfolane as a solvent and a quaternized imidazolinium salt or a quaternized pyrimidinium as a solute; and an electrolytic capacitor which comprises the third electrolyte.
REFEREN
Koslow C. Melissa
Nippon Chemi-Con Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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