Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2001-09-17
2002-12-10
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S503000, C361S511000, C361S523000, C252S062200, C029S025030
Reexamination Certificate
active
06493211
ABSTRACT:
INDUSTRIAL FIELD OF APPLICATION
The present invention relates to an electrolytic solution for an electrolytic capacitor.
PRIOR ART
An aluminum electrolytic capacitor generally has the following constitution. Specifically, a high-purity aluminum foil shaped in a strip form is subjected to a surface-enlargement treatment by chemical or electrochemical etching, and the aluminum foil whose surface has been subjected to an enlargement treatment is subjected to a formation treatment in a forming solution, such as an aqueous ammonium borate solution, to prepare an anodic foil comprising the aluminum foil having an oxide film layer formed thereon. Then, the anodic foil is overlapped and wound with a cathodic foil, which is prepared by subjecting a high-purity aluminum foil to a surface-enlargement treatment in a similar manner, via a separator, to prepare a capacitor element. The capacitor element is then dipped in an electrolytic solution for driving and housed in a metallic sheathed package in a closed-end cylindrical form. Further, a sealing member made of elastic rubber is inserted into an open-end section of the sheathed package, and the open-end section of the sheathed package is sealed by drawing, whereby an aluminum electrolytic capacitor is constituted.
As the electrolytic solution impregnated into the capacitor element of a compact aluminum electrolytic capacitor for low voltage, one having ethylene glycol as a main solvent and an ammonium salt of adipic acid, benzoic acid or the like as a solute, one having &ggr;-butyrolactone as a main solvent and a quaternary cyclic amidinium salt of phthalic acid, maleic acid or the like as a solute, and the like have been conventionally known.
Problems that the Invention is to Solve
Applications of the electrolytic capacitor include an electronic apparatus, such as an output smoothing circuit of a switching power supply or the like. While low impedance characteristics are demanded in these applications, such demand is being increased for an electrolytic capacitor along with the progress of miniaturization of the electronic apparatus. The conventional electrolytic solution cannot deal with the demand, and an electrolytic solution having a higher electroconductivity is demanded. The invention is to solve the problem, and one object thereof is to provide an electrolytic solution for an electrolytic capacitor that can realize a low impedance electrolytic capacitor, has a high electro-conductivity, and is excellent in high-temperature service life characteristics.
The conventional aluminum electrolytic capacitor has such problems that, upon allowing to stand, the capacitance is decreased, and the leakage current characteristics are deteriorated, which finally cause opening of a safety valve, and the reliability of the electrolytic capacitor is greatly influenced by the shelf characteristics, which are the characteristics after lapsing a long period of time under load or under no load.
Accordingly, when an aluminum electrolytic capacitor that had been deteriorated by allowing to stand for a long period of time was analyzed, it was found that the pH of the electrolytic solution is increased, and an anionic component, i.e., the solute, was attached to the surface of the electrode foil. It becomes apparent from these facts that aluminum on the surface of the electrode foil is reacted with the anionic component as the solute to attach on the electrode foil, and aluminum is dissolved to form a hydroxide, part of which is reacted with the anionic component as the solute to form a hydrogen gas through the reaction. The reaction is repeated to increase the pH, and finally it brings about deterioration of the electrode foil and opening of the valve.
Meanwhile, it has been well known that phosphoric acid is effective for prevention of the deterioration of an electrode foil, but it is not sufficient. This is because even when phosphoric acid is added, the phosphoric acid thus added is bonded to aluminum in the electrolytic solution to form a water-insoluble complex, and the insoluble complex is attached to the electrode foil, whereby the phosphoric acid is diminished from the electrolytic solution. Furthermore, when the addition amount is too large, such a problem arises that the leakage current is increased. However, the characteristics of the electrolytic capacitor are maintained in good conditions during the period where the phosphate ions remain in an appropriate amount before diminishment thereof, and therefore, the invention has been completed, another object of which is to improve the shelf characteristics of the electrolytic capacitor.
Means for Solving the Problems
The electrolytic solution for an aluminum electrolytic capacitor of the invention is characterized by containing a solvent containing water and a water-soluble aluminum complex having a phosphate ion combined thereto.
The water-soluble aluminum complex having a phosphate ion combined thereto can be formed by adding a compound forming a phosphate ion in an aqueous solution (a phosphate ion forming compound) and a chelating agent forming a water-soluble aluminum complex with aluminum. The phosphate ion forming compound can be selected from the phosphorus compounds described later, phosphoric acid, phosphorous acid, hypophosphorous acid, salts thereof, condensates thereof, and salts of the condensates.
In a preferred embodiment of the invention, at least one kind of adipic acid and a salt thereof is used as the solute.
The solvent contains water as a main component (i.e., in an amount of about 25% or more), and the content of water is generally from 35 to 100% by weight of the entire solvent.
The content of adipic acid or a salt thereof is generally from 5 to 20% by weight of the entire electrolytic solution.
The content of the phosphorus compounds, phosphoric acid, phosphorous acid, hypophosphorous acid, salts thereof, condensates thereof, and salts of the condensates is generally from 0.01 to 3.0% by weight of the entire electrolytic solution.
The content of the chelating agent is generally from 0.01 to 3.0% by weight of the entire electrolytic solution.
Mode for Carrying Out the Invention
The electrolytic solution for an aluminum electrolytic capacitor of the invention is an electrolytic solution, in which the compound forming a phosphate ion in an aqueous solution and the chelating agent are added to the solvent containing water to form a combined product of the water-soluble aluminum complex and a phosphate ion, and after being impregnated in the capacitor element, it reacts with aluminum eluted from the aluminum foil used as the electrode foil to the electrolytic solution, so as to form the combined product of the water-soluble aluminum complex and a phosphate ion.
As the solvent, a protonic polar solvent, an aprotonic solvent and a mixture thereof can be used in addition to water. Examples of the protonic polar solvent include a monohydric alcohol (such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, cyclopentanol, benzyl alcohol and the like), a polyhydric alcohol and an oxyalcohol compound (such as ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol and the like). Representative examples of the aprotic solvent include an amide series (such as N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, hexamethylphosphoric amide and the like), a lactone compound, a cyclic amide compound, a carbonate compound (such as &ggr;-butyrolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate and the like), a nitrile compound (such as acetonitrile and the like), an oxide compound (such as dimethyl sulfoxide and the like) and the like.
As the compound forming a phosphate ion in an aqueous solution (the phosphate ion forming compound), the following compounds can be exemplified. They are the phosphorus compounds described later, phosphoric acid, phosphorous acid, hypophosphorous acid, salts thereof, condensates thereof, and salts of the condensate
Itoh Hidehiko
Ozawa Masashi
Sakakura Masao
Sugiyama Takayuki
Tamamitsu Kenji
Ha Nguyen
Nippon Chemi-Con Corporation
Reichard Dean A.
Young & Thompson
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