JP2013247202A - Method for manufacturing aluminum electrode plate for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an aluminum electrode plate for electrolytic capacitors, capable of surely removing chlorine, etc., from an etching part while suppressing degradation in etching ratio due to dissolution of the etching part.SOLUTION: In the method for manufacturing an aluminum electrode plate for electrolytic capacitors, a cleaning step after an etching step includes alternately repeating two to four times a chemical cleaning treatment for immersing an etched plate for 20-60 sec in a nitric acid solution having a concentration of 1-2.5 mol/l and a temperature of 20-35°C and a shower-washing treatment for shower-washing the etched plate with water after the chemical cleaning treatment. Accordingly, the method can surely remove chlorine, etc., from an etching part while suppressing degradation in etching ratio due to dissolution of the etching part even when the etched plate has a spongy etching part with a depth of 70 μm or more per one side.

Description

  The present invention relates to a method for producing an aluminum electrode plate for electrolytic capacitors obtained by etching an aluminum plate.

  In order to manufacture an aluminum electrode plate of an aluminum electrolytic capacitor, an aluminum plate is etched in an etching solution to obtain an etched plate, and then the etched plate is washed to remove chlorine from the etched plate or etching. Remove aluminum hydroxide adhering to the pit. With regard to such cleaning, it has been proposed to immerse in an aqueous solution of an inorganic acid such as phosphoric acid, sulfuric acid, nitric acid, etc., then immerse in an aqueous solution of an organic acid such as oxalic acid, citric acid, tartaric acid, and then wash with pure water. (See Patent Document 1).

  Patent Document 1 describes that an etched plate is immersed in an aqueous nitric acid solution having a concentration of 5.04 wt% and a temperature of 60 ° C. as an example of chemical cleaning when nitric acid is used. Yes.

JP 11-354387 A

  In recent years, the aluminum electrode plate has been required to have a higher capacity, which requires deepening the etching site and increasing the etching magnification. However, when an etched plate having a deep etching site and a high etching magnification is subjected to chemical cleaning under the conditions described in Patent Document 1, there is a problem that the etching site is dissolved and the etching magnification is significantly reduced. In addition, since the etching site is deep, there is a problem that even if chemical cleaning is performed under conditions that dissolve the etching site, chlorine, aluminum hydroxide, and the like remain in the etching site.

  In view of the above problems, an object of the present invention is to provide an aluminum electrode plate for an electrolytic capacitor that can reliably remove chlorine and the like from an etching site while suppressing a decrease in etching magnification due to dissolution of the etching site. It is to provide a manufacturing method.

  In order to solve the above-described problems, a method for manufacturing an aluminum electrode plate for an electrolytic capacitor according to the present invention includes an etching step of obtaining an etched plate by etching an aluminum plate in an etching solution, and the etched plate after the etching step. A cleaning process for immersing the etched plate in a nitric acid solution having a concentration of 1 to 2.5 mol / liter and a temperature of 20 to 35 ° C. for 20 to 60 seconds. After the process and the chemical cleaning process, the shower cleaning process of shower-cleaning the etched plate with water is repeated alternately 2 to 4 times.

  In the present invention, in the cleaning step after the etching step, the concentration of nitric acid is set to a low concentration (1 to 2.5 mol / liter) and the temperature of the nitric acid solution is set to a low temperature (20 to 35 ° C.) during the chemical cleaning process. Since the dipping time is set to a short time (20 to 60 seconds), excessive dissolution of pits can be prevented. In addition, after the chemical cleaning process, a shower cleaning process with water is performed, and the chemical cleaning and the shower cleaning process are alternately repeated two to four times, so that chlorine and aluminum hydroxide remaining in the pits can be reliably ensured. Can be removed. As for chemical cleaning treatment, the effect of removing chlorine, aluminum hydroxide, etc. tends to be saturated even after immersion for more than 60 seconds. Since the shower method is adopted, the effect of removing chlorine, aluminum hydroxide and the like is remarkably improved. Therefore, chlorine, aluminum hydroxide, and the like can be reliably removed from the etching site while suppressing a decrease in etching magnification due to the dissolution of the etching site.

  The present invention is effective when applied in the etching step when AC etching is performed on the aluminum plate to form a spongy etching portion having a depth of 70 μm or more per side. When the etching site is deepened and the etching magnification is increased, the etching site is dissolved and the etching magnification is likely to decrease, and chlorine, aluminum hydroxide, etc. are likely to remain in the etching site. Chlorine and the like can be reliably removed from the etching site while suppressing a decrease in the etching magnification caused by dissolution.

  In this invention, in the manufacturing method of the aluminum electrode plate for electrolytic capacitors, in the cleaning step after the etching step, the etched plate is placed in a nitric acid solution having a concentration of 1 to 2.5 mol / liter and a temperature of 20 to 35 ° C. The chemical cleaning treatment soaked for 60 seconds and the shower cleaning treatment of showering the etched plate with water after the chemical cleaning treatment are alternately repeated 2 to 4 times. For this reason, even with an etched plate having a spongy etching portion with a depth of 70 μm or more per side, chlorine and the like are reliably removed from the etching portion while suppressing a decrease in etching magnification caused by dissolution of the etching portion. can do.

It is a figure showing the cross-sectional photograph of the aluminum electrode plate for electrolytic capacitors obtained by applying this invention.

  Hereinafter, as an embodiment of the present invention, a method for manufacturing an aluminum electrode plate (etched plate) for an electrolytic capacitor to which the present invention is applied will be described.

(Outline of manufacturing method)
FIG. 1 is a view showing a cross-sectional photograph of an aluminum electrode for electrolytic capacitors obtained by applying the present invention. As shown in FIG. 1, an aluminum electrode plate 1 (etched plate) for an electrolytic capacitor to which the present invention is applied has a spongy etching portion 3 on both sides of a core portion 2 and is used as an anode of an aluminum solid electrolytic capacitor. It is done.

  In manufacturing such an aluminum electrode plate for electrolytic capacitors, in this embodiment, in the etching process, the aluminum plate is etched and enlarged in an etching solution containing chlorine ions, and then the etched plate is cleaned and etched in the cleaning process. Remove chlorine, aluminum hydroxide, etc. from the site.

  Thereafter, the etched plate is used as an anode of an aluminum solid electrolytic capacitor after an anodized film (dielectric film) is formed by anodization. The solid electrolyte used in the aluminum solid electrolytic capacitor is not particularly limited, and may be a known solid electrolyte. For example, polypyrrole, polythiophene, polyaniline and the like are used.

In this embodiment, in the etching process, an aluminum plate having a thickness of 150 μm or more is AC-etched in an etching solution, and is etched to a deep position so that the thickness of the etched portion is 140 μm or more in total on both surfaces. More specifically, the etched plate is etched to a deep position so that the etching site is 70 μm or more, 100 μm or more, and further 120 μm or more on one side. For this reason, since the aluminum electrode plate (etched plate) for electrolytic capacitors to which the present invention is applied has a high etching magnification, a high capacitance can be obtained. In the present invention, since the cleaning process is performed under the conditions described later, only 1 mg / m ² or less of chlorine remains on the aluminum electrode plate (etched plate) for electrolytic capacitors.

(Detailed explanation of aluminum plate)
In this embodiment, the aluminum plate has, for example, an aluminum purity of 99.98% by mass or more. The aluminum plate preferably contains, for example, 5 to 50 ppm of iron and less than 30 ppm of copper as elements other than aluminum, 60 ppm or less of silicon, and preferably 40 ppm or less of silicon. This is because when iron or silicon exceeds the upper limit value, a crystallized product and a precipitate of a coarse intermetallic compound containing iron or silicon are generated, and the leakage current is increased. In the case of silicon, single silicon is also generated, which is not preferable for the same reason. If the copper exceeds the upper limit value, the corrosion potential of the matrix is greatly changed and no good etching may be performed.

The iron content of 5 to 50 ppm is preferable because it causes intermetallic compounds such as Al _m Fe, Al ₆ Fe, Al ₃ Fe, and Al—Fe—Si, and tends to be a pit starting point for AC etching. Further, if the content of copper is less than 30 ppm, the corrosion potential of the matrix can be stabilized in the presence of iron, and pits of a specific size can be easily drilled. The preferable content of copper is 25 ppm or less, the lower limit is 2 ppm or more, and more preferably 3 ppm or more. If it is less than the lower limit, abnormal growth of crystal grains occurs in the etching process of the etched plate, and the mechanical strength decreases. On the other hand, if the copper content exceeds 30 ppm, the dissolution during etching is accelerated abnormally, which is not preferable.

(Detailed description of etching process)
In this embodiment, at least a primary electrolytic treatment for generating etching pits in the aluminum plate and a main electrolytic treatment for growing the etching pits are performed as an etching process for the aluminum plate.

In the primary electrolytic treatment, AC etching is performed with a low-concentration hydrochloric acid aqueous solution. As a pretreatment, it is preferable to remove the surface oxide film from the aluminum plate by degreasing and light etching. In the primary electrolytic treatment, the low-concentration hydrochloric acid aqueous solution used as an etching solution is an aqueous solution containing, for example, 1.5 to 5.0 mol / liter hydrochloric acid and 0.05 to 0.5 mol / liter sulfuric acid, The liquid temperature is 40 to 55 ° C. As an AC etching condition, an AC waveform having a frequency of 10 to 50 Hz is used. As the AC waveform, a sine waveform, a rectangular waveform, an AC / DC superimposed waveform, or the like can be used. The current density at that time is 20 to 40 A / dm ^2. According to the etching conditions, a large number of pits can be drilled on the surface of the aluminum plate.

After the primary electrolytic treatment, in the main electrolytic treatment, the etching is progressed while growing the etching portion in a spongy manner. The etching solution used in this main electrolytic treatment is, for example, in an aqueous solution containing 4 to 7 mol / liter hydrochloric acid and 0.05 to 0.5 mol / liter sulfuric acid, and the solution temperature is lower than that of the primary electrolytic treatment. 25 ° C. or less, preferably 10 to 25 ° C. As an AC etching condition, an AC waveform having a frequency of 20 to 60 Hz is used. As the AC waveform, a sine waveform, a rectangular waveform, an AC / DC superimposed waveform, or the like can be used. In this case, the current density is set to 20 to 30 A / dm ^{2 which} is lower than that of the primary electrolytic treatment, the treatment time is set to a time during which treatment can be performed up to a predetermined etching site thickness, and pits drilled by the primary electrolytic treatment are further drilled.

After the primary electrolytic treatment, before the main electrolytic treatment, the main electrolytic treatment is etched using an AC / DC superimposed waveform so that the main electrolytic treatment proceeds reliably, and the pit surface drilled by the primary electrolytic treatment is activated and then the main electrolytic treatment is activated. You may make it transfer to electrolytic treatment. In this process, the etching process is performed for about 60 seconds under the condition that the duty ratio is about 0.7 to 0.9 and the current density is 12 to 17 A / dm ² .

  When etching is performed under such conditions, an etching site having a bulk specific gravity of 0.6 to 1.2 and having the following pits is formed. The diameter and number of pits can be measured with an image analyzer. For example, after the etched surface is polished at a predetermined interval in the depth direction, the hole diameter and number of each polished surface are measured with an image analyzer, and the ratio of the number of pits of 0.01 to 1 μmφ is calculated. Thus, the proportion of pits having a specific size diameter in each layer can be measured. The etched plate of this embodiment has a total of 150 μm or more on both sides, and at least one side has an etching site of 70 μm or more, 100 μm or more, and further 120 μm or more in the depth direction from the surface. When measured, the number of pits of 0.01 to 1 μmφ is 70% or more, preferably 75% or more of the total number of pits on each surface. If such an etched plate is anodized and used as an anode, an electrolytic capacitor having a large capacitance and low ESR can be realized. In addition, since the pit less than 0.001 μmφ does not contribute to the improvement of the capacitance, the diameter measured by the image analysis apparatus is set to 0.001 μmφ or more.

  Here, if there are many pits having a pit diameter exceeding 1 μmφ, the capacitance is lowered. Preferably it is 0.1 μmφ or less. The presence of pits of such a size is 70% or more, preferably 75% or more of the total number of pits on each surface, so that an electrolytic capacitor having a high capacitance and a low ESR can be manufactured. More preferably, it is 80% or more. The measurement position of the pit size is a position deeper than 20 μm from the surface because there is dissolution that does not contribute to the surface area expansion at the time of electrolytic etching and the pit diameter is increased by connecting the pits. In addition, since the boundary surface between the etching part and the core part is uneven and is not constant, the etching depth is set to a position 10 μm shallower from the position (boundary between the etching part and the core part) on the surface.

(Detailed explanation of cleaning process)
In this embodiment, after the etching step, the etching solution is removed from the etched plate by washing with water, and then the following washing step is performed. In this embodiment, as the cleaning step, after the chemical cleaning treatment in which the etched plate is immersed for 20 to 60 seconds in a nitric acid solution having a concentration of 1 to 2.5 mol / liter and a temperature of 20 to 35 ° C., and chemical cleaning treatment, The shower cleaning process of shower cleaning the etched plate with water is repeated alternately 2 to 4 times. In multiple shower cleaning processes, pure water may be used in any shower cleaning process, or pure water and well water may be used in combination. In the latter case, pure water is used at least in the final shower cleaning process.

  According to the cleaning under such conditions, excessive dissolution of the pits can be prevented during the chemical cleaning process, and pit collapse can be suppressed. That is, in the chemical cleaning process, the concentration of nitric acid is set to a low concentration (1 to 2.5 mol / liter), the temperature of the nitric acid solution is set to a low temperature (20 to 35 ° C.), and the immersion time is set to a short time (20 to 60). Second), excessive dissolution of pits can be prevented. Therefore, a high capacitance can be obtained.

In addition, after the chemical cleaning process, a shower cleaning process with water is performed, and the chemical cleaning and the shower cleaning process are alternately repeated two to four times, so that chlorine and aluminum hydroxide remaining in the pits can be reliably ensured. Can be removed. For example, the amount of residual chlorine on the etched plate can be set to 1 mg / m ² or less. That is, for chemical cleaning treatment, the effect of removing chlorine, aluminum hydroxide and the like tends to be saturated even if immersion is performed for more than 60 seconds. Since the shower method is adopted, the effect of removing chlorine, aluminum hydroxide and the like is remarkably improved. Therefore, chlorine, aluminum hydroxide, and the like can be reliably removed from the etching site while suppressing a decrease in etching magnification due to the dissolution of the etching site.

  Examples of the present invention will be described. The aluminum plate used in the following examples has an aluminum purity of 99.98% and a thickness of 350 μm.

In the etching process, in both the examples and the comparative examples, etching was performed under the following conditions, and AC etching was performed until the pit depth reached 150 μm / single side.
[First stage]
Etching solution: 4 mol / liter hydrochloric acid + 0.1 mol / liter sulfuric acid, 50 ° C.
Waveform: Sine wave AC, frequency 50Hz
Current density: 30 A / dm ²
[Second stage]
Etching solution: 5 mol / liter hydrochloric acid + 0.1 mol / liter sulfuric acid, 35 ° C.
Waveform: DC superimposed on sine wave AC, frequency 50Hz, duty ratio 0.80
Current density: 15 A / dm ²
[Third stage]
Etching solution: 5 mol / liter hydrochloric acid + 0.1 mol / liter sulfuric acid, 15 ° C.
Waveform: Sine wave AC, frequency 25Hz
Current density: 25 A / dm ²

  After the etching process was performed under the above conditions, running water was washed for 10 minutes in pure water before the cleaning process was performed under the conditions shown in Table 1.

  Next, after performing the cleaning process under the conditions shown in Table 1, the presence or absence of smut adhesion was visually confirmed on the dried etched plate. The etched plate was anodized in an ammonium adipate aqueous solution so that the withstand voltage of the film was 5 V, and then the capacitance was measured by the JEITA standard test method. In addition, the amount of chlorine was measured by the silver nitrate turbidimetric method. The evaluation results are shown in Table 1. Table 1 shows the concentration of nitric acid aqueous solution, temperature, time, number of repetitions, and water cleaning method during chemical cleaning. In Comparative Example 6, the sample was immersed in a sulfuric acid aqueous solution having a temperature of 60 ° C. and a concentration of 0.1 mol / liter for 2 minutes, followed by 5 minutes of pure water shower cleaning. Further, the temperature was 50 ° C. and the concentration was The film was immersed in an aqueous 0.1 mol / liter oxalic acid solution for 1 minute and 30 seconds, and then washed with pure water for 5 minutes.

  As can be seen from Table 1, a chemical cleaning treatment for immersing the etched plate in a nitric acid solution having a concentration of 1 to 2.5 mol / liter and a temperature of 20 to 35 ° C. for 20 to 60 seconds, and shower cleaning of the etched plate with water According to Examples 1 to 4 in which the shower cleaning process is alternately repeated 2 to 4 times, chlorine, aluminum hydroxide, and the like are reliably removed from the etching site while suppressing a decrease in capacitance (etching magnification). Can be removed.

In contrast, Comparative Example 1 in which the concentration of nitric acid during chemical cleaning is too low, Comparative Example 3 in which the number of repetitions is one, Comparative Example 4 in which water cleaning is running water cleaning, and comparison in which no chemical cleaning treatment with nitric acid aqueous solution is performed In Example 6, the residual chlorine exceeds 1 mg / m ² .

  In Comparative Example 5 in which the concentration of nitric acid during chemical cleaning is too high, in Comparative Example 2 in which the temperature during chemical cleaning is too high, and in Comparative Example 6 in which no chemical cleaning treatment with a nitric acid aqueous solution is performed, the capacitance (etching magnification) The decline is significant.

In addition to the above examples, as a result of evaluating various conditions, in particular, in the case of a spongy etching site having a depth of 70 μm or more per side, the etching site is dissolved and the etching magnification tends to decrease. Since there is a tendency, the result that the effect at the time of applying this invention is great is obtained. In addition, if the number of repetitions of the chemical cleaning treatment and the shower cleaning processing is four, the residual chlorine is sufficiently reduced to 1 mg / m ² or less. Therefore, in consideration of productivity, the number of repetitions is 2 to 4 times. preferable.

1 Aluminum Etched Plate for Electrolytic Capacitor 2 Core 3 Etching Site

Claims (2)

An etching step of etching an aluminum plate in an etchant to obtain an etched plate;
A cleaning step of cleaning the etched plate after the etching step;
Have
In the cleaning step, a chemical cleaning process in which the etched plate is immersed in a nitric acid solution having a concentration of 1 to 2.5 mol / liter and a temperature of 20 to 35 ° C. for 20 to 60 seconds, and after the chemical cleaning process, A method for producing an aluminum electrode plate for an electrolytic capacitor, wherein a shower cleaning process for shower cleaning an etched plate with water is alternately repeated 2 to 4 times.   2. The method for producing an aluminum electrode plate for an electrolytic capacitor according to claim 1, wherein in the etching step, the aluminum plate is subjected to AC etching to form a spongy etching portion having a depth of 70 [mu] m or more per side. .

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