JP2007184301A - Method of manufacturing electrode foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode foil for an electrolytic capacitor which can positively restore even an electrode foil having high leakage current to make it usable. <P>SOLUTION: In reapplying anodic oxidation to an electrode foil obtained by applying anodic oxidation and drying to an aluminum etching foil, the electrode foil is immersed in an acid solution as depolarization processing ST1, and then, anodic oxidation is reapplied using in-solution power feed as restoring chemical treatment ST2. The acid solution is a nitric acid solution, a sulphuric acid solution or a phosphorous acid solution having acid density of 2.5-25.0 wt.%, and has a liquid temperature of 50-80°C. For second time anodic oxidation, a boric acid-based solution having pH of 3.0-5.0 is used as a chemical treatment liquid, its liquid temperature is set at 80-90°C, and its current density is set at 1.0-10.0 Adcm<SP>-2</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode foil for an electrolytic capacitor.

  Electrode capacitor electrode foils used as anodes in electrolytic capacitors are manufactured by anodizing aluminum etching foils (see, for example, Patent Document 1 and Non-Patent Document 1).

Such an electrode foil for an electrolytic capacitor is required to have a low leakage current level in addition to a high capacitance. Electrode capacitor electrode foils are also required not to undergo characteristic changes such as increased loss, decreased capacitance, increased leakage current, etc. when the electrolytic capacitor is left unloaded at high temperature.
JP-A-60-155699 Isaya Nagata “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nippon Electric Storage Co., Ltd., p. 306-307

Electrode capacitor electrode foils are generally stored after being anodized and dried on an aluminum etching foil and then wound into a roll. At this time, if stored for a long period of time, the leakage current may increase due to the influence of defects in the anodized film. In addition, in the inspection immediately after manufacturing, a product having a high leakage current may be produced.
Conventionally, such an electrode foil for an electrolytic capacitor has no measures other than disposal, which is very problematic from the viewpoint of resource saving and cost.

  In view of the above problems, an object of the present invention is to provide a method for manufacturing an electrode foil for an electrolytic capacitor that can be reliably restored and used even for an electrode foil having a high leakage current.

  In order to solve the above-mentioned problems, in the present invention, in an electrolytic capacitor electrode foil manufacturing method in which an aluminum etching foil is subjected to anodization, an anode is formed again with respect to the electrode foil obtained by subjecting the etching foil to anodization and drying. When oxidizing, the electrode foil is immersed in an acidic solution, and then anodized again.

In the present invention, when the leakage current of the anodized electrode foil is high, the electrode foil is first immersed in an acidic solution based on the knowledge that the leakage current cannot be reduced simply by performing anodization again. Then, after performing a depolarization treatment that exposes voids and cracks scattered in the anodized film, anodization is performed again.
For this reason, since the voids and cracks scattered in the anodic oxide film can be surely eliminated, the electrolytic capacitor electrode foil that has been regenerated is an electrolytic capacitor in which the phenomenon of increased leakage current has not occurred. The leakage current can be reduced to a level equal to or lower than that of the electrode foil, and the reliability is equal to or higher.

  In the present invention, the acidic solution is a nitric acid solution, a sulfuric acid solution, or a phosphoric acid solution having an acid concentration of 2.5 to 25.0 wt%, and the liquid temperature when the electrode foil is immersed in the acidic solution is 50. It is preferable to set it to -80 degreeC.

In the present invention, a boric acid solution having a pH of 3.0 to 5.0 is used as the chemical conversion solution for the re-anodic oxidation described above, the temperature of the boric acid solution is set to 80 to 90 ° C., and the current density Is preferably performed again under the condition of 1.0 to 10.0 A · dm ⁻² .

  In the present invention, it is preferable to supply power to the electrode foil by in-liquid power supply when performing the second anodic oxidation. Since an anodized film has already been formed on the electrode foil to be anodized again, if power is supplied to the electrode foil via the power supply roller, a spark is generated between the electrode foil and the power supply roller, resulting in dangers such as cutting. However, such a risk can be avoided by submerged power feeding.

  In the present invention, the anodized electrode foil is immersed in an acidic solution to expose voids and cracks scattered in the anodized film, and then anodized again. For this reason, since the voids and cracks scattered in the anodic oxide film can be surely eliminated, the electrolytic capacitor electrode foil which has been regenerated is an electrolytic capacitor in which the phenomenon of increased leakage current has not occurred. The leakage current can be reduced to a level equal to or lower than that of the electrode foil, and the reliability is equal to or higher. Therefore, the electrolytic capacitor electrode foil can be regenerated to be usable, which can contribute to both resource saving and cost.

FIG. 1 is a process diagram showing a method for producing an electrode foil for an electrolytic capacitor to which the present invention is applied.
As shown in FIG. 1, in the present invention, when anodization is again performed on an electrode foil obtained by anodizing and drying an aluminum etching foil, the electrode foil is immersed in an acidic solution as depolarization treatment ST1. Then, another anodization is performed as the repair conversion treatment ST2.
Here, when the anodic oxide film formed by re-anodic oxidation does not have water resistance, after dipping in the phosphoric acid aqueous solution in the phosphoric acid dipping treatment ST3, the drying treatment ST4 is performed to wind up the roll. .

  As described above, in the present invention, in the depolarization process ST1, the electrode foil is immersed in an acidic solution, and after performing the depolarization process that exposes voids and cracks scattered in the anodized film, in the repair chemical conversion process ST2, again. Therefore, voids and cracks scattered in the anodized film can be surely eliminated. Therefore, it is possible to reliably repair and use an electrode foil having a high leakage current.

Here, the acidic solution is a nitric acid solution, a sulfuric acid solution or a phosphoric acid solution having an acid concentration of 2.5 to 25.0 wt%, and the temperature of the electrode foil immersed in the acidic solution is 50 to 80 ° C. It is preferable that The nitric acid solution, the sulfuric acid solution, and the phosphoric acid solution do not vigorously dissolve the anodized film and the aluminum base portion like other inorganic acids. Therefore, it is possible to effectively expose the defective portion in the anodized film.
Moreover, about 80-80 degreeC is preferable about the liquid temperature of the acidic solution at the time of performing depolarization process ST1, and when it is lower than 50 degreeC, while it takes time to melt | dissolve an anodized film, when it is higher than 80 degreeC, melt | dissolution is intense. Therefore, control becomes difficult.
The acid concentration is preferably in the range of 2.5 to 25.0 wt%. When the concentration is lower than 2.5 wt%, voids and cracks in the anodized film are not exposed. Will be dissolved.

Further, in the repair chemical conversion treatment ST2, a boric acid solution having a pH of 3.0 to 5.0 is used as the chemical conversion solution, the temperature of the boric acid solution is set to 80 to 90 ° C., and the current density is 1.0. It is preferable to perform anodic oxidation again under a condition of ˜10.0 A · dm ⁻² . If the liquid temperature during the second anodic oxidation is lower than 80 ° C., the chemical conversion is reduced and the leakage current reduction effect is low. The risk of cutting the electrode foil on the chemical conversion machine increases. Therefore, the optimal liquid temperature is 80 to 90 ° C.
Also, if the pH of the chemical conversion solution is higher than 5.0, the anodic oxidation film formed by re-anodic oxidation becomes thick and the capacitance decreases, and if it is lower than 3.0, a large amount of boric acid is produced in the liquid preparation stage. The boric acid tends to precipitate. Therefore, the pH is optimally in the range of 3.0 to 5.0.
The current density, the optimum range of 1.0~10.0A · dm ^-2, defect repair not sufficiently when re-conversion is higher than 10.0A · dm ^-2, reduction of leakage current The effect is low, and if it is lower than 1.0 A · dm ⁻² , the amount of electricity for restoration conversion is reduced, and the effect of reducing leakage current is reduced.

Further, when the present invention is applied to an anodized electrode foil by a multi-tank continuous chemical conversion machine, it is preferable to supply power to the electrode foil by in-liquid power supply when performing anodization again.
Since the anodized film is already formed on the electrode foil to be anodized again, if power is supplied to the electrode foil via the power supply roller, a spark is generated between the electrode foil and the power supply roller, resulting in danger of cutting and the like. However, such a risk can be avoided by submerged feeding.

[Examples 1 to 16] Comparison of immersion treatment conditions (acid concentration, liquid temperature) in an aqueous nitric acid solution Hereinafter, examples according to the present invention will be described more specifically based on examples. First, an electrode foil subjected to chemical conversion treatment to the end is prepared. Here, as the electrode foil, for example, an electrode foil having a coating withstand voltage of 535 V according to the EIAJ method and a high leakage current level is prepared. Here, a nitric acid aqueous solution is used as the acidic solution, and the acid concentration is set to 2.5 to 25.0 wt%.

Next, in order to reduce the leakage current of the prepared electrode foil, first, the electrode foil is immersed for 5 minutes in a state where the nitric acid aqueous solution is set at a temperature of 50 to 80 ° C. Next, anodic oxidation is performed again by applying a voltage of 535 V in a chemical solution containing 110 g / l of boric acid and 0.20 ml / l of 28 wt% aqueous ammonia, and the voltage is maintained for 15 minutes after reaching the voltage of 535 V. The pH of the chemical conversion solution was 4.0, and the current density was 1.0 A · dm ⁻² . Next, it was immersed in an 8.5 wt% phosphoric acid aqueous solution for 5 minutes and then dried at 150 ° C. or higher to produce an electrode foil for an electrolytic capacitor.

(Comparative Example 1)
In addition, except having not immersed in said nitric acid aqueous solution, the reproduction | regeneration process similar to the said Example was performed, and the electrode foil for electrolytic capacitors was produced.

(Comparative Examples 2 to 5)
Next, as a comparative example, the acid concentration and the liquid temperature of the acidic solution are out of the range of the above-described examples, that is, the acid concentration is 1.0 wt%, 30.0 wt%, the liquid temperature of the acidic solution is 40 ° C., 90 An electrolytic capacitor electrode foil was prepared in the same manner as in the above example under the conditions of ° C. and other regeneration treatment conditions.

  Table 1 shows the conditions of the acidic aqueous solution used in performing the regeneration treatment and the evaluation results of the leakage current of the electrode foil for an electrolytic capacitor obtained by performing the regeneration treatment.

As can be seen from Table 1, in Examples 1 to 16 in which the regeneration process of the present invention was performed, the leakage current was improved as compared with the comparative example in which the regeneration process was not performed.
Here, the temperature at which the electrode foil is immersed in the acidic solution is optimally in the range of 50 to 80 ° C., and the reduction effect is particularly high at 60 ° C. and 70 ° C. (Examples 5 to 12). Since it takes time to dissolve the anodized film at 40 ° C., the leakage current becomes high (Comparative Example 2), and at 90 ° C., the dissolution of the anodized film is intense and the leakage current becomes high (Comparative Example 4).
The acid concentration is optimally in the range of 2.5 to 25.0 wt%. At 1.0 wt%, voids and cracks in the anodized film are not exposed and the leakage current becomes high (Comparative Example 3), and at 30.0 wt%, the entire anodized film can be dissolved (Comparative Example 4). Leakage current increases.

[Examples 17 to 24] Comparison of immersion treatment in phosphoric acid and sulfuric acid aqueous solution Next, an electrolytic capacitor was used under the same conditions as in Examples 5 to 8 except that an aqueous solution of phosphoric acid or sulfuric acid was used as the acidic solution. Electrode foils were prepared and leakage current was evaluated. Tables 2 and 3 show the evaluation results for the case of the phosphoric acid aqueous solution (Examples 17 to 20) and the case of the sulfuric acid aqueous solution (Examples 21 to 24).

Comparing Examples 17 to 24 in Tables 2 and 3 with Comparative Example 1 in Table 1, Examples 17 to 24 that were regenerated with phosphoric acid or sulfuric acid leaked from Comparative Example 1 that was not regenerated. It can be seen that the current is improved.
In Tables 1 to 3, when compared with the types of acidic solutions, the acidic solution having the highest leakage current reduction effect is phosphoric acid, the concentration is 5.0 wt%, and the electrode temperature is 60 ° C. The foil (Example 22) is most effective.

[Examples 25 to 32] Comparison of anodizing conditions again (pH of chemical conversion liquid, liquid temperature, current density) Next, Example 18 in which the effect of reducing leakage current was the highest among the conditions of immersion treatment in acidic solution. The electrode foil was used, and the regeneration treatment was performed by changing the pH, liquid temperature, and current density conditions of the chemical conversion solution during the anodic oxidation again.
Here, the pH was 3.0 to 5.0, the current density was 1 to 10 A · dm ⁻² , and the liquid temperature was 80 to 90 ° C.
The conditions for re-anodic oxidation are the same as those described above, and boric acid is 110 g / l, and the voltage is adjusted to 535 V in 28 wt% ammonia water, and a voltage of 535 V is applied for re-anodic oxidation. After reaching the voltage of 535 V, it was held for 15 minutes, then immersed in an 8.5 wt% phosphoric acid aqueous solution for 5 minutes, and then dried at 150 ° C. to produce an electrode foil for an electrolytic capacitor.

(Comparative example)
Next, as a comparative example, other regenerations were performed under the conditions of pH 2.0 and 6.0, current densities of 0.5 A · dm ⁻² and 15 A · dm ⁻² , and liquid temperature of 75 ° C. or 95 ° C. The processing conditions were the same as in the above example, and an electrode foil for an electrolytic capacitor was produced.

  Table 4 shows the results of evaluating the leakage current for the electrode foils for electrolytic capacitors of the above-described Examples and Comparative Examples.

As can be seen from Table 4, the optimum pH of the chemical conversion solution is in the range of 3.0 to 5.0. In 2.0, there is no increase in leakage current, but boric acid tends to break out at the chemical liquid preparation stage, and in 6.0, the anodic oxide film formed by re-anodizing becomes thicker and the capacitance is increased. Incurs a decline.
The current density is optimally in the range of 1.0 to 10.0 A · dm ⁻² . At 0.5 A · dm ^-2 , the amount of electricity required for repair formation is reduced, so the effect of reducing leakage current is reduced. At 15.0 A · dm ^-2 , the repair of defective parts becomes insufficient during repair formation, and leakage current is reduced. Reduction effect decreases.
Furthermore, the range of 80-90 degreeC is suitable for the liquid temperature of a chemical conversion liquid. At 75 ° C, the chemical conversion is reduced, and the effect of reducing leakage current is reduced. At 95 ° C, the chemical conversion of the chemical liquid is increased, and the effect of reducing leakage current is increased, but the risk of cutting and cutting the electrode foil on the chemical generator is high. Increases nature.

[Comparison of Example 26 with Acid Solution Soaking and Restoration Conversion]
Table 5 compares the leakage current of Comparative Example 12 where the regeneration treatment according to the present invention is not performed, Comparative Example 1 where only the anodic oxidation is performed again without performing the immersion treatment in the acidic solution, and Example 26 of the present invention. It is the result.
In Example 26, as described above, a 5 wt% aqueous phosphoric acid solution was used as the acidic solution, the liquid temperature during immersion was 60 ° C., and the immersion time was 5 minutes. The chemical conversion solution used for re-anodic oxidation is a boric acid-based chemical solution having a pH of 4.0 and a liquid temperature of 85 ° C., and the current density during re-anodic oxidation is 1.0 A · dm ⁻² .

  As can be seen from Table 5, according to Example 26 in which the regeneration process according to the present invention was performed, it was confirmed that the leakage current could be significantly reduced as compared with Comparative Examples 1 and 12.

  With respect to the above three types of electrolytic capacitor electrode foils, the VI characteristics indicating the voltage-leakage current relationship when the voltage was increased at a constant rate in an aqueous solution of boric acid 70 g / l were measured. As shown in FIG.

  As is apparent from FIG. 2, in Comparative Example 12, the leakage current value increases near 100 V, and such an increase occurs, so that many defect portions called voids and cracks remain in the anodized film. It is considered a thing. On the other hand, Example 26 has a low leakage current value, and it is considered that voids and cracks in the anodized film of the conversion foil are repaired. In Comparative Example 1 in which only the anodic oxidation was performed again, the leakage current value was lower than that in Comparative Example 12, but many voids remained in the anodic oxide film.

It is process drawing which shows the manufacturing method of the electrode foil for electrolytic capacitors to which this invention is applied. It is a graph which shows the measurement result of the VI characteristic of the electrode foil for electrolytic capacitors which concerns on Example 26 and Comparative Examples 1 and 12 of this invention.

Explanation of symbols

ST1 Depolarization treatment (immersion in acidic solution)
ST2 Repair conversion treatment (re-anodic oxidation)
ST3 Phosphate immersion treatment ST4 Drying treatment

Claims (4)

In the method for producing an electrode foil for an electrolytic capacitor obtained by anodizing an aluminum etching foil,
An electrode for an electrolytic capacitor, characterized in that, when anodizing and drying an electrode foil that has been anodized and dried on the etching foil, the electrode foil is immersed in an acidic solution and then anodized again. Foil manufacturing method. The acidic solution is a nitric acid solution, a sulfuric acid solution or a phosphoric acid solution having an acid concentration of 2.5 to 25.0 wt%,
The method for producing an electrode foil for an electrolytic capacitor according to claim 1, wherein the temperature of the electrode foil immersed in the acidic solution is 50 to 80 ° C. For the second anodic oxidation, a boric acid solution having a pH of 3.0 to 5.0 is used as a chemical conversion solution.
The liquid temperature of the boric acid-based solution is set to 80 to 90 ° C, and the anodic oxidation is performed again under the condition of a current density of 1.0 to 10.0 A · dm ^-2. 2. A method for producing an electrode foil for an electrolytic capacitor as described in 2.   The method for producing an electrode foil for an electrolytic capacitor according to any one of claims 1 to 3, wherein when the anodic oxidation is performed again, the electrode foil is fed by submerged feeding.

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