JP2004040134A - Manufacturing method of solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor for reducing leakage current by suppressing the degradation of an anodized coating when a manganese dioxide layer is formed by thermal decomposition, for concurrently suppressing the increase of the leakage current when the capacitor is exposed to high temperatures and humidities without load, and for providing excellent impedance characteristics in the high-frequency region. <P>SOLUTION: The manufacturing method comprises the steps of: chemically reconverting an aluminum anodic body 1 in phosphate anion containing solution, of which anodic oxide coating film 2 is formed from aqueous solution of ammonium adipate; then forming a manganese dioxide layer 3 on the surface of the anodic body 1; then forming a conductive polymer layer 4 on the manganese dioxide layer 3; and further forming a cathode conductive layer 5 on the conductive polymer layer 4. <P>COPYRIGHT: (C)2004,JPO

Description

(4) The present invention relates to a method for manufacturing a solid electrolytic capacitor using aluminum having an anodized film as an anode body.

Conventionally, solid electrolytic capacitors using manganese dioxide as an electrolyte are well known, but manganese dioxide has a drawback of high impedance characteristics in a high-frequency region due to low conductivity. To improve this drawback, for example, as shown in Patent Document 1 and Patent Document 2, using a 7,7,8,8-tetracyanoquinodimethane complex as a solid electrolyte, or anodizing It has been proposed to form manganese dioxide on a film and then form a conductive polymer layer as a solid electrolyte.

In addition, since manganese dioxide is generally formed by thermally decomposing manganese nitrate, particularly when aluminum is used as the anode body, the anodic oxide film is significantly damaged, which has a disadvantage that the leakage current of the product increases. Things. As a method of solving this, for example, as shown in Patent Document 3 and Patent Document 4, a method of forming a conductive polymer layer and then re-forming in an electrolytic solution has been proposed.
JP-A-63-158829 JP-A-01-253226 JP-A-63-181310 JP-A-02-260516

However, in the above-mentioned conventional method, since the conductive polymer layer is formed and then re-chemically formed in the electrolytic solution, the electrolytic solution is hardly supplied to the anodic oxide film. Cannot be repaired, and there is a problem that the conductive polymer layer is deteriorated and the impedance characteristic is deteriorated depending on the formation conditions.

固体 Further, in the case of a solid electrolytic capacitor using aluminum as an anode body, there is a problem that the leakage current increases significantly when left without a load under high temperature and high humidity.

The present invention solves the above-mentioned conventional problems.In addition to suppressing the deterioration of the anodic oxide film that occurs when a manganese dioxide layer is formed by thermal decomposition, it is possible to reduce the leakage current, and at high temperature and high humidity. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor that can suppress an increase in leakage current when left unloaded and has excellent impedance characteristics in a high-frequency region.

According to the first aspect of the present invention, an aluminum anode body having an anodic oxide film formed from an aqueous solution of ammonium adipate is re-chemically formed in an aqueous solution containing phosphate anions, and then the surface of the anode body is thermally decomposed. Forming a manganese dioxide layer, and thereafter, forming a conductive polymer layer on the manganese dioxide layer, and further forming a cathode conductor layer on the conductive polymer layer, a manufacturing method comprising: According to the production method, since re-chemical conversion is performed in an aqueous solution containing a phosphate anion, an anodic oxide film is formed on a portion having no anodic oxide film, and the concentration of phosphorus in the anodic oxide film is not less than a certain level. The anodic oxide film is prevented from dissolving by manganese nitrate when the manganese dioxide layer is formed by the thermal decomposition due to the presence of the phosphorus, and the presence of heat or steam during the thermal decomposition. According hardly occur crystallization or hydration of the anodized film, these are those of the increase in leakage current can be suppressed.

According to a second aspect of the present invention, there is provided a production method wherein re-chemical formation in an aqueous solution containing a phosphate anion is performed at a chemical formation voltage within a range not exceeding a chemical formation voltage for forming an anodic oxide film with an aqueous solution of ammonium adipate. According to this method, re-chemical formation can be performed without impairing the characteristics of the anodic oxide film formed first, so that a solid electrolytic capacitor having a very small leakage current can be obtained. is there.

According to a third aspect of the present invention, there is provided a production method wherein the concentration of the aqueous solution containing a phosphate anion is in the range of 0.1 to 5.0% by weight. On the other hand, since the conductivity of the chemical conversion solution is low, the formation speed of the anodic oxide film becomes extremely slow, and the production efficiency is poor. On the other hand, when the concentration is 5.0% by weight or more, the dissolution reaction proceeds rapidly at the same time as the anodic oxidation reaction, which causes a problem such as a decrease in pressure resistance. Therefore, the concentration of the aqueous solution containing the phosphate anion is 0%. The range of 0.1 to 5.0% by weight is preferable.

According to the fourth aspect of the present invention, the temperature at the time of re-chemical formation of the aqueous solution containing the phosphate anion is set in the range of 50 to 100 ° C., and when the temperature is 50 ° C. or less, the anodic oxidation formed by the re-chemical formation is performed. This is undesirable because the number of defects in the coating increases. On the other hand, when the temperature is 100 ° C. or higher, the hydration reaction of the already formed anodic oxide film proceeds, which in turn causes a decrease in the pressure resistance, which is not preferable. The temperature is preferably in the range of 50 to 100 ° C.

According to the present invention, an aluminum anode body on which an anodized film is formed from an aqueous solution of ammonium adipate is re-formed in an aqueous solution containing phosphate anions, and thereafter, a manganese dioxide layer is formed on the surface of the anode body by thermal decomposition. Thereafter, a conductive polymer layer is formed on the manganese dioxide layer, and further, a cathode conductor layer is formed on the conductive polymer layer. Since the chemical conversion is carried out in an aqueous solution containing anions, the concentration of phosphorus in the anodic oxide film is maintained at a certain level, and the presence of this phosphorus forms a manganese dioxide layer by thermal decomposition. The dissolution of the anodic oxide film by manganese nitrate during the process is suppressed, and the crystallization or hydration reaction of the anodic oxide film due to the presence of heat or steam during thermal decomposition hardly occurs. Can reduce the leakage current during the production of solid electrolytic capacitors, suppress the increase in leakage current when left unloaded under high temperature and high humidity, and have low impedance in the high-frequency region. A capacitor can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a configuration of a capacitor element of a solid electrolytic capacitor according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an anode body made of an aluminum foil having an anodic oxide film 2 formed from an aqueous solution of ammonium adipate. A manganese dioxide layer 3 is formed on the surface of the anode body 1 by thermal decomposition. Reference numeral 4 denotes a conductive polymer layer formed of a polypyrrole film formed on the manganese dioxide layer 3. A cathode conductor layer 5 is formed on the conductive polymer layer 4 by sequentially applying a carbon paste and a silver paste. Then, after the leads are pulled out, the capacitor element is externally coated with a resin mold to form a solid electrolytic capacitor.

{Circle around (2)} The anodized film 2 of the anode body 1 is re-chemically formed in an aqueous solution containing a phosphate anion so that the concentration of phosphorus is maintained at a certain level or more. By the presence of phosphorus, when the manganese dioxide layer 3 is formed by thermal decomposition, the dissolution of the anodic oxide film 2 by manganese nitrate can be suppressed. Since the crystallization or hydration reaction of the oxide film hardly occurs, it is possible to suppress the increase of the leakage current.

Next, specific embodiments of the present invention will be described, but the present invention is not limited thereto.

(Embodiment 1)
An anode body made of aluminum foil of 3.5 mm × 4.0 mm (effective area of the capacitor element) subjected to electrolytic etching is applied with 12 V in an aqueous solution of ammonium adipate having a liquid temperature of 70 ° C. and a concentration of 5% by weight. A direct current voltage is applied for 10 minutes to form an anodic oxide film 2, and then a 12V direct current voltage is applied for 10 minutes in an aqueous solution of orthophosphoric acid having a liquid temperature of 70 ° C. and a concentration of 0.5% by weight. An oxide film is formed, and then the anode body is immersed in an aqueous solution of manganese nitrate and thermally decomposed at 300 ° C. for 5 minutes to form a manganese dioxide layer on the surface of the anode body. A conductive polymer layer made of a polypyrrole film is formed by a polymerization method. Thereafter, a carbon paste and a silver paste were sequentially applied on the conductive polymer layer to form a cathode conductor layer, and after the leads were pulled out, the package was applied with a resin mold to form a solid electrolytic capacitor.

(Embodiment 2)
An anode body made of an aluminum foil on which an anodic oxide film is formed under the same conditions as in Embodiment 1 is subjected to a punching process so that the effective area of the capacitor element is 3.5 mm × 4.0 mm. Anodized film was formed on the punched cross-section by applying a DC voltage of 12 V for 10 minutes in an aqueous solution of ammonium phosphate having a liquid temperature of 70 ° C. and a concentration of 1.0% by weight for 10 minutes. Thereafter, a manganese dioxide layer, a conductive polymer layer, and a cathode conductor layer were formed in the same manner as in Embodiment 1, and the leads were drawn out, followed by coating with a resin mold to form a solid electrolytic capacitor.

(Embodiment 3)
A solid electrolytic capacitor was configured in the same manner as in Embodiment 2 except that the solution temperature of the ammonium phosphate aqueous solution as the re-formation solution described in Embodiment 2 was set to 80 ° C.

(Embodiment 4)
A solid electrolytic capacitor was constructed in the same manner as in Embodiment 2 except that the concentration of the re-formation solution shown in Embodiment 2 was 0.5 wt% of normal phosphoric acid aqueous solution.

(Embodiment 5)
After forming the manganese dioxide layer in the second embodiment, the formation temperature (DC voltage of 12 V) for forming the anodic oxide film in an aqueous solution of ammonium phosphate having a solution temperature of 70 ° C. and a concentration of 1.0% by weight. An anodic oxide film was formed by applying a formation voltage within a range not exceeding, that is, applying a DC voltage of 11 V and performing re-formation. did.

(Comparative Example 1)
In the first embodiment, an anodic oxide film formed on an anode body made of an aluminum foil is formed only of an aqueous solution of ammonium adipate having a liquid temperature of 70 ° C. and a concentration of 5% by weight, and has a high conductivity made of a polypyrrole film. After forming a molecular layer, a liquid temperature was 40 ° C. and a DC voltage of 12 V was applied in an aqueous solution of ammonium adipate having a concentration of 5% by weight for 10 minutes to perform re-formation. A solid electrolytic capacitor was constructed in the same manner.

(Comparative Example 2)
Same as the first embodiment except that the anodic oxide film formed on the anode body made of aluminum foil in the first embodiment is formed only of an aqueous solution of ammonium adipate having a liquid temperature of 70 ° C. and a concentration of 5% by weight. The solid electrolytic capacitor was constructed according to the contents of the above.

(Table 1) shows average values of initial characteristics of ten solid electrolytic capacitors manufactured by the manufacturing methods of Embodiments 1 to 5 of the present invention and Comparative Examples 1 and 2, respectively. The measurement was performed at a temperature of 25 to 30 ° C., the content and tan δ were 120 Hz, the impedance was 400 kHz, and the leakage current was measured 30 seconds after applying a DC voltage of 6.3 V.

(Table 2) shows five solid electrolytic capacitors manufactured by the manufacturing methods of Embodiments 1 to 5 of the present invention and Comparative Examples 1 and 2, each having no load in saturated steam at 121 ° C. and 2 atm for 5 hours. It shows the average value of the leakage current after leaving the test. The measurement was performed at a temperature of 25 to 30 ° C., and the leakage current was measured by measuring a current value 30 seconds after applying a DC voltage of 6.3 V.

As is clear from Tables 1 and 2, the solid electrolytic capacitors manufactured by the manufacturing methods according to Embodiments 1 to 5 of the present invention are made of aluminum having an anodic oxide film formed from an aqueous solution of ammonium adipate. The anode body is re-formed in an aqueous solution containing phosphate anions, and a manganese dioxide layer formed on the surface of the anode body by thermal decomposition, a conductive polymer layer formed on the manganese dioxide layer, And the cathode conductor layer formed on the conductive polymer layer, so that reconversion is performed in an aqueous solution containing phosphate anions, so that the concentration of phosphorus in the anodic oxide film is maintained at a certain level or more. Therefore, the dissolution of the anodic oxide film by manganese nitrate when forming the manganese dioxide layer by thermal decomposition is suppressed, and the anodic oxide film due to the presence of heat or steam at the time of thermal decomposition. The crystallization or hydration reaction is also unlikely to occur, and from these facts, it is possible to reduce the leakage current at the time of manufacturing the solid electrolytic capacitor as compared with Comparative Examples 1 and 2, and leave the capacitor under no load under high temperature and high humidity. It is possible to suppress an increase in leakage current at the time of occurrence.

The present invention relates to a method for manufacturing a solid electrolytic capacitor using an aluminum body having an anodized film formed thereon as an anode body, and a solid electrolytic capacitor having improved impedance characteristics in a high frequency region can be obtained.

1 is a cutaway perspective view showing a configuration of a capacitor element of a solid electrolytic capacitor according to an embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Anode body 2 Anodized film 3 Manganese dioxide layer 4 Conductive polymer layer 5 Cathode conductor layer

Claims (4)

An aluminum anode body having an anodic oxide film formed from an aqueous solution of ammonium adipate is re-chemically formed in an aqueous solution containing phosphate anions, and then a manganese dioxide layer is formed on the surface of the anode body by thermal decomposition. A method for manufacturing a solid electrolytic capacitor, comprising forming a conductive polymer layer on a manganese layer, and further forming a cathode conductor layer on the conductive polymer layer. 2. The solid electrolytic capacitor according to claim 1, wherein the re-formation in the aqueous solution containing a phosphate anion is performed at a formation voltage within a range not exceeding a formation voltage for forming an anodic oxide film with an aqueous solution of ammonium adipate. Production method. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the concentration of the aqueous solution containing a phosphate anion is in the range of 0.1 to 5.0% by weight. The method for producing a solid electrolytic capacitor according to any one of claims 1 to 3, wherein a temperature at the time of re-chemical formation of the aqueous solution containing a phosphate anion is set in a range of 50 to 100C.

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