JP4576192B2 - Method for producing electrode foil for aluminum electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, and more particularly to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor that forms a uniform and difficult-to-dissolve chemical conversion film.

  In general, when the water content in the driving electrolyte increases, the chemical conversion film formed on the surface of the aluminum electrode foil not only tends to deteriorate due to a hydration reaction, but also various organic carboxyls added as solutes. The acid complex formation reaction is facilitated, and the deterioration of the electrode foil due to the dissolution reaction is promoted.

  In particular, when the water content of the electrolytic solution for driving an aluminum electrolytic capacitor exceeds 30%, it is required to improve the water resistance of the electrode foil used and to improve the dissolution resistance of the chemical conversion film. Formation is now required.

  Conventionally, in order to stabilize the chemical conversion film, a method of removing a film defect portion that occurs during the chemical conversion treatment and hinders the uniformity of the chemical conversion film (for example, heat treatment, acid immersion, etc., see Non-Patent Document 1), Known is a method for improving the water resistance of a chemical conversion film (for example, refer to Patent Document 1) and the like after performing chemical conversion with ammonium adipate and then performing chemical conversion with ammonium phosphate.

In addition, it is known that when a thermal oxide film or a hydrated oxide film is formed in advance as a chemical pretreatment, the capacity and characteristics of the chemical conversion foil are improved (for example, see Non-Patent Documents 1 and 2). For the purpose of improving the capacity of chemical conversion foil, improving chemical conversion efficiency (power saving), and reducing leakage current, it is immersed in boiling water in which an inhibitor is dissolved (for example, see Patent Document 2) or immersed in warm water. A method of forming a hydrated oxide film, a method of heat treatment in the atmosphere or an environment in which the oxygen partial pressure is controlled (for example, see Patent Documents 3 to 5), a method of heat treatment in a water vapor atmosphere (for example, Patent Document 6) is disclosed.
JP-A-52-92360 Japanese Patent Publication No.57-6250 JP-A-53-26960 Japanese Patent No. 3446115 JP 11-340102 A Japanese Patent No. 3407470 By Nagata Isaya, “Electrolyte Cathode Aluminum Electrolytic Capacitor (Aluminum Dry Type Electrolytic Capacitor Supplement Revised Version)”, Nihon Denki Kogyo Kogyo Co., Ltd., February 24, 1997, 2nd edition, 1st printing, P.A. 192-204, p. 261-314 Nagayama, Seiichi, “9th ARS Conference Text”, Surface Technology Association of Japan, 1992, p. 41

  However, even if any of the above-mentioned chemical pretreatments is used, an aluminum electrolytic capacitor in which the water content in the driving electrolyte exceeds 30%, or aluminum electrolysis that requires high reliability even if the water content is 30% or less For a capacitor, there has been a demand for a method for producing an electrode foil that can provide a conversion film that is insufficiently stabilized and that is more uniform and difficult to dissolve.

The present invention solves the above problems, and in the method for producing an electrode foil for an aluminum electrolytic capacitor to be subjected to chemical conversion treatment after etching the aluminum original foil,
Before the chemical conversion treatment, the etching foil is immersed in an alkaline solution, washed with water, subjected to a first heat treatment at 250 to 400 ° C. for 10 seconds to 5 minutes, and then at 100 to 250 ° C. for 10 minutes to 5 minutes. A second heat treatment is performed for a period of time, and then a third heat treatment is performed at 350 to 500 ° C. for 10 minutes to 5 hours, followed by a chemical conversion treatment. Is the method.

  The alkaline solution is a solution containing hydroxide ions, aluminate ions, or carbonate ions, and is a method for producing an electrode foil for an aluminum electrolytic capacitor.

  Furthermore, it is the manufacturing method of the electrode foil for aluminum electrolytic capacitors, wherein pH of the said alkaline solution is 10-12, and temperature is 40-60 degreeC.

  And it is a manufacturing method of the electrode foil for aluminum electrolytic capacitors characterized by performing 3rd heat processing in an atmosphere with a dew point of 30 degrees C or less.

  Moreover, the third heat treatment is performed in a nitrogen atmosphere, and this is a method for producing an electrode foil for an aluminum electrolytic capacitor.

  Furthermore, it is a manufacturing method of the electrode foil for aluminum electrolytic capacitors characterized by performing 3rd heat processing in a carbon dioxide atmosphere.

  By performing the above-mentioned chemical conversion pretreatment on the etching foil, it is possible to obtain a uniform chemical film with excellent dissolution resistance, and an electrode foil that can be applied to a driving electrolytic solution having a water content exceeding 30%. Can be manufactured.

After etching the aluminum foil for the aluminum electrolytic capacitor, it is immersed in an alkaline solution before chemical conversion treatment.
Immersion in an alkaline solution has an effect of removing an oxide film mixed with chemicals remaining on the surface of the etching foil and forming a clean hydroxide film on the surface of the etching foil.
The alkaline solution to be used is not a solution containing anions that easily bind aluminum such as silicate ions and phosphate ions in order to obtain a hydroxide film containing no impurity elements, but hydroxide ions or aluminate ions. Or the use of an alkaline solution of carbonate ions.
In order to minimize the dissolution of the aluminum foil by the alkaline solution, it is desirable to set the pH of the alkaline solution to 10 to 12 and the temperature to 40 to 60 ° C.
After immersion in the alkaline solution, the etching foil is washed with water.

Next, the first heat treatment is performed at 250 to 400 ° C. for 10 seconds to 5 minutes to remove the attached moisture.
This moisture removal suppresses the generation of a new hydrated oxide film on the surface of the etching foil immersed in an alkaline solution and in an active state.
Here, when the heat treatment conditions are less than 250 ° C. and less than 10 seconds, moisture is not completely removed, which is not preferable.
On the other hand, when the temperature exceeds 400 ° C., the hydroxide film on the etching foil surface is altered, and a new air oxide film is formed in a non-uniform and isolated form (see FIG. 1). It causes film defects and is not suitable.
In the first heat treatment, a large amount of water is evaporated, so that the partial pressure of water vapor in the furnace is increased. When the heat treatment time exceeds 5 minutes, a new hydrated oxide film is formed on the surface of the etching foil. In particular, the hydrated oxide film newly formed by water vapor is unevenly formed in the etching pits of the etching foil. Since it is formed (see FIG. 2), the chemical conversion film is not uniform in the subsequent chemical conversion.

Then, the 2nd heat processing was performed for 10 minutes-5 hours at the temperature of 100-250 degreeC, and the water | moisture content adsorb | sucked to the etching foil surface which cannot be removed by a short time heating (drying) was removed.
This moisture removal removes the unreacted moisture adsorbed on the fine etching pits while suppressing the formation of a new hydrated oxide film on the etching foil surface. The heating temperature is preferably 100 ° C. or higher, which is the boiling point of water, and is preferably 250 ° C. or lower so that the hydrated oxide film is not deteriorated. The heating time is 10 minutes or more, which can remove the adsorbed moisture. Although it is necessary, if it exceeds 5 hours, the hydrated oxide film will dissolve, which is not preferable.

Next, the third heat treatment is performed at a temperature of 350 to 500 ° C. for 10 minutes to 5 hours to dehydrate the hydroxide film uniformly formed on the surface of the etching foil and transfer it to a uniform oxide film.
The heating temperature is preferably 350 ° C. or higher at which the hydroxide film is transferred to the oxide film, and is preferably 500 ° C. or lower at which no new atmospheric oxide film is generated. The time is 10 minutes necessary for transfer to the oxide film. Although it is necessary to be above, if it exceeds 5 hours, dissolution of the oxide film occurs and the leakage current becomes large, which is not preferable.
The third heat treatment is desirably performed in an atmosphere having a dew point of 30 ° C. or lower in order to suppress generation of a new hydrated film.
In addition, the transition from a hydroxide film to an oxide film proceeds with heat treatment at a high temperature, but at the same time, a new oxide film is formed by reaction with oxygen. Or it is desirable to carry out in a carbon dioxide atmosphere.
Here, carbon dioxide acts as an inert gas on the etching foil in which a hydroxide film or an oxide film is uniformly formed, but in the weakened part of the hydroxide film or oxide film, Since it reacts with aluminum and is reduced to promote the formation of an oxide film, it has the effect of forming a more uniform film on the surface of the etching foil.

  After that, chemical conversion treatment is performed in an ammonium adipate solution. Ammonium adipate is a chemical commonly used as a chemical for chemical conversion, and has a higher molecular weight than boric acid and ammonium phosphate. Incorporation of ions is suppressed, and the formation of a conversion film that is uniform and difficult to dissolve is promoted.

  From the above, according to the method for producing an electrode foil of the present invention, the chemical conversion film is uniform and difficult to dissolve. Therefore, an aluminum electrolytic capacitor in which the water content of the driving electrolyte exceeds 30% and high reliability are required. As an aluminum electrolytic capacitor, an optimum electrode foil can be provided.

Here, the uniformity and dissolution resistance of the obtained chemical conversion film are measured by measuring the dissolution rate of the chemical conversion film by immersing it in a solution of phosphoric acid 4%, chromic acid 2% and a liquid temperature of 85 ° C. It can be evaluated by a phosphate chromic acid dissolution test).
Phosphoric acid chromic acid dissolution test is a widely used method for the evaluation of anodized and aluminum conversion coatings (anodized coatings). It dissolves only the conversion coating without dissolving the aluminum metal of the substrate. From the change in weight, the uniformity of the chemical conversion film and the dissolution resistance can be known.

FIG. 3 schematically shows the dissolution characteristics of the chemical conversion film and the state of dissolution of the film when the chromic acid phosphate dissolution test is performed.
In the case where the chemical conversion film is uniform but is easy to dissolve as a whole, as shown by the curve A in FIG.
Further, when the chemical film is a uniform film that is difficult to dissolve as a whole, as shown by a curve B in FIG. 3, the rising is slow and it takes a long time to dissolve.

  In the case where the chemical conversion film is non-uniform and is a film in which a portion that is easy to dissolve and a portion that is difficult to dissolve are mixed, first, as shown by curve C in FIG. Since the part that is difficult to dissolve also peels off, it becomes a curve that dissolves gradually after first dissolving greatly.

  Moreover, when the value of the film dissolution weight at a certain time (t) shown in FIG. 3 is compared with the film weight (total film weight) in the case of complete dissolution, it is found that the film is difficult to dissolve under the condition of this small value. It is possible to know the film uniformity and dissolution resistance quantitatively.

  Examples of the present invention will be described in detail below.

First, the first to third heat treatment conditions were examined.
Etching (roughening) and dechlorination treatment are performed on the aluminum foil by a known method to produce a sheet (20 cm × 50 cm) of the etching foil, and sodium hydroxide having a pH of 11 and a liquid temperature of 50 ° C. Was immersed in the solution for 3 minutes and washed with water.
Thereafter, the first to third heat treatment conditions were sequentially examined under the conditions shown in Tables 1 to 3, and then revised to JEITA RC-2364A 1999 with ammonium adipate: 150 g / L and liquid temperature: 85 ° C. In accordance with (hereinafter referred to as JEITA method), a constant voltage of 30 V was formed.
The evaluation was carried out by a chromic acid phosphate dissolution test, and the ratio of the film dissolution amount after 5 minutes and the film weight when dissolved completely (total film weight) was expressed in weight% (hereinafter referred to as film solubility). .

[Example 1] Examination of first heat treatment conditions, Table 1
The first stage heat treatment conditions were varied between 250 to 400 ° C. and 10 seconds to 5 minutes for comparison.
The heat treatment conditions for the second stage were fixed at 150 ° C. for 2 hours, and the heat treatment conditions for the third stage were fixed at 400 ° C. for 2 hours (dew point 0 ° C.).
As a comparative example, the case of the first stage temperatures of 200 ° C. and 450 ° C. was also investigated for the time of 5 seconds and 8 minutes.
The results are shown in Table 1.

As shown in Table 1, in the first stage heat treatment, the foil was not sufficiently dried by the heat treatment at 200 ° C. or 5 seconds, and incompleteness occurred, and 450 ° C. or 8 minutes Heating increases the solubility of the film, and the uniformity and dissolution resistance of the film are impaired.
Therefore, it is appropriate that the heat treatment conditions for the first stage are 250 to 400 ° C. and 10 seconds to 5 minutes.

[Example 2] Investigation of second heat treatment conditions, Table 2
The first stage heat treatment condition is fixed at 350 ° C. for 1 minute, the third stage heat treatment condition is fixed at 400 ° C. for 2 hours (dew point 0 ° C.), and the second stage heat treatment condition is 100 to 250 ° C. The comparison was made by changing between 10 minutes and 5 hours.
As a comparative example, in the case of the second stage temperature of 80 ° C. and 300 ° C., the case of 5 minutes and 8 hours was also investigated.
The results are shown in Table 2.

As shown in Table 2, in the second stage heat treatment, the film solubility increases at temperatures of 80 ° C. and 300 ° C. Regarding the time, in 5 minutes, the film solubility increased on the low heating temperature side, and in the 8 hour heat treatment, the film solubility increased on the high heating temperature side. .
Therefore, it is appropriate that the second heat treatment condition is 100 to 250 ° C. for 10 minutes to 5 hours.

[Example 3] Investigation of third heat treatment conditions, Table 3
The first stage heat treatment condition is fixed at 350 ° C. for 1 minute, the second stage heat treatment condition is fixed at 150 ° C. for 2 hours, and the third stage heat treatment condition is 350 to 500 ° C., 10 minutes to 5 minutes. Comparison was made by changing between times (dew point 0 ° C.).
As a comparative example, the case where the temperature of the third stage was 300 ° C. and 550 ° C. and the time was 5 minutes and 8 hours was also investigated.
The results are shown in Table 3.

As shown in Table 3, in the third stage heat treatment, the film solubility increased at a temperature of 300 ° C., and when heated at 550 ° C., the film solubility increased and the leakage current increased. With respect to the time, 5 minutes showed that the film solubility increased on the low heating temperature side, and 8 hours of heat treatment showed that the leakage current increased on the high heating temperature side.
Therefore, it is appropriate that the third heat treatment condition is 350 to 500 ° C. and 10 minutes to 5 hours.

Next, the alkaline solution (type, pH and temperature) used before the chemical conversion treatment was examined.
The specifications and processing conditions of the etching foil sample were the same as those in Examples 1 to 3.

[Example 4] Examination of alkaline solution (type), Table 4
The etching foil having the same specifications as those used in Examples 1 to 3 was immersed in an alkaline solution having the conditions shown in Table 4 for 3 minutes, washed with water, and then subjected to the third stage heat treatment under the conditions shown in Table 4. It was. In accordance with the JEITA method, a constant voltage of 30 V was formed at 150 g / L of ammonium adipate and the liquid temperature was 85 ° C., and a chromic acid phosphate dissolution test was performed to evaluate the film solubility.
The results are shown in Table 4.

  As shown in Table 4, when sodium silicate, potassium silicate, and sodium phosphate of comparative examples were used, the film solubility was slightly improved at a high heat treatment temperature in the third stage. Compared to those using a solution containing hydroxide ions such as sodium hydroxide, potassium hydroxide, calcium hydroxide, or aluminate ions such as sodium aluminate or potassium aluminate, or carbonate ions such as sodium carbonate. It can be seen that the film solubility is poor.

[Example 5] Examination of pH and temperature of alkaline solution, Table 5
The etching foil having the same specifications as those used in Examples 1 to 3 was immersed in an alkaline solution having the conditions shown in Table 5 for 3 minutes, washed with water, and then subjected to the third stage heat treatment under the conditions shown in Table 5. It was. Subsequent chemical conversion conditions and film solubility evaluation methods were the same as in Examples 1-3. Ammonium adipate: 150 g / L, liquid temperature: 85 ° C. According to the JEITA method, a constant voltage of 30 V was formed, and a phosphate chromic acid dissolution test was performed to evaluate the film solubility.
The results are shown in Table 5.

As shown in Table 5, in any solution of sodium hydroxide and calcium hydroxide, the film solubility becomes large at pH: 9 and a liquid temperature of 35 ° C., and the etching foil at pH: 13 and liquid temperature: 70 ° C. The dissolution reaction proceeds, and a decrease in capacity after chemical conversion is observed.
Therefore, it is appropriate that the alkaline solution has a pH of 10 to 12 and a temperature of 40 to 60 ° C.

[Example 6] Dew point study of third heat treatment conditions, Table 6
Etching foils having the same specifications as those used in Examples 1 to 3 were immersed in a sodium hydroxide solution having a pH of 11 and a liquid temperature of 50 ° C. for 3 minutes, washed with water, and subjected to the conditions shown in Table 6. Samples with different dew points in three stages of heat treatment conditions were prepared, and a constant voltage of 30 V was formed according to the JEITA method at ammonium adipate: 150 g / L, liquid temperature: 85 ° C., and dissolved in chromic phosphate Tests were conducted to evaluate film solubility.
The results are shown in Table 6.

As shown in Table 6, in the steam atmosphere with a dew point of -20 to 30 ° C, there is almost no change in the film solubility value, but at a dew point of 35 ° C, the film solubility is generally deteriorated.
Therefore, the dew point of the third heat treatment condition is suitably 30 ° C. or less.

[Example 7] Investigation of third heat treatment condition (in nitrogen atmosphere), Table 7
Etching foils having the same specifications as those used in Examples 1 to 3 were immersed in a sodium hydroxide solution having a pH of 11 and a liquid temperature of 50 ° C. for 3 minutes, washed with water, and subjected to the conditions shown in Table 7. 3 steps of heat treatment, ammonium adipate: 150 g / L, liquid temperature: 85 ° C., 30 V constant voltage formation according to JEITA method, chromic acid phosphate dissolution test, film solubility evaluated.
The results are shown in Table 7.

  As shown in Table 7, when performed in a nitrogen atmosphere, it can be seen that the film solubility in the heat treatment at a temperature of 500 ° C. or 5 hours is superior to that in the air atmosphere.

[Example 8] Investigation of third heat treatment condition (in carbon dioxide atmosphere), Table 8
Etching foils having the same specifications as those used in Examples 1 to 3 were immersed in a sodium hydroxide solution having a pH of 11 and a liquid temperature of 50 ° C. for 3 minutes, washed with water, and subjected to the conditions shown in Table 8. 3 steps of heat treatment, ammonium adipate: 150 g / L, liquid temperature: 85 ° C., 30 V constant voltage formation according to JEITA method, chromic acid phosphate dissolution test, film solubility evaluated.
The results are shown in Table 8.

  As shown in Table 8, when carried out in a carbon dioxide atmosphere, the film solubility is superior to that obtained by heat treatment in an air atmosphere as a whole, and the film solubility in a heat treatment at a temperature of 500 ° C. or 5 hours. It can be seen that the improvement effect is superior to that performed in the air atmosphere.

[Example 9] Confirmation of reliability with aluminum electrode foil An etching foil having the same specifications as those used in Examples 1 to 3 was subjected to three stages of heat treatment under the conditions shown in Table 10, and ammonium adipate: 150 g / liter. The liquid temperature was 85 ° C., and a constant voltage formation of 30 V was performed under the conditions in which film stabilization treatment (defect removal, water resistance treatment) was added to the JEITA method. The film was immersed under the conditions described above, and the degree of decrease in the withstand voltage of the film, ΔVt (initial withstand voltage−withstand voltage after immersion, according to JEITA method) and the film solubility were compared and evaluated.

As shown in Table 10, when the chemical conversion foil according to the present invention is used, when compared with a water content of 10 to 50 wt% of the driving electrolyte, the characteristics become slightly worse as the water content increases. It turns out that it is improving.
Therefore, the uniform and difficult-to-dissolve chemical conversion film according to the present invention can suppress deterioration of the film of the electrode foil even in an aluminum electrolytic capacitor in which the water content of the driving electrolyte exceeds 30%, thereby improving the reliability of the aluminum electrolysis. Capacitors can be provided.

It is a schematic diagram which shows the air oxide film formed in the nonuniform and isolated form. It is a schematic diagram which shows the hydrated oxide film formed nonuniformly by water vapor | steam within the etching pit of etching foil. It is the figure which showed the melt | dissolution characteristic of the chemical conversion film at the time of implementing a phosphoric acid chromic acid melt | dissolution test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching pit 2 Air oxide film 3 Hydrated oxide film A Dissolution curve B of a chemical film which is uniform but easy to dissolve as a whole C Dissolution curve C of a chemical film which is uniform and difficult to dissolve as a whole Dissolution curve of a conversion coating that contains both easy-to-melt and difficult-to-melt parts

Claims (6)

In the method for producing an electrode foil for an aluminum electrolytic capacitor to be subjected to chemical conversion treatment after etching the aluminum raw foil,
Before chemical conversion treatment, the etching foil is immersed in an alkaline solution, washed with water,
First heat treatment is performed at 250 to 400 ° C. for 10 seconds to 5 minutes,
Next, the second heat treatment is performed at 100 to 250 ° C. for 10 minutes to 5 hours,
Then, after performing the third heat treatment at 350 to 500 ° C. for 10 minutes to 5 hours,
A method for producing an electrode foil for an aluminum electrolytic capacitor, characterized by performing a chemical conversion treatment.   The method for producing an electrode foil for an aluminum electrolytic capacitor, wherein the alkaline solution according to claim 1 is a solution containing hydroxide ions, aluminate ions, or carbonate ions.   A method for producing an electrode foil for an aluminum electrolytic capacitor, wherein the alkaline solution according to claim 1 or 2 has a pH of 10 to 12 and a temperature of 40 to 60 ° C.   A method for producing an electrode foil for an aluminum electrolytic capacitor, wherein the third heat treatment according to claim 1 is performed in an atmosphere having a dew point of 30 ° C or lower.   The method for producing an electrode foil for an aluminum electrolytic capacitor, wherein the third heat treatment according to claim 1 is performed in a nitrogen atmosphere.   The method for producing an electrode foil for an aluminum electrolytic capacitor, wherein the third heat treatment according to claim 1 is performed in a carbon dioxide atmosphere.

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