JP2010021376A - Production process of electrode foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of an electrode foil for an electrolytic capacitor, which removes and replaces chlorine ion adhering to the foil while minimizing dissolution of a foil surface layer after etching, and can produce a high powered foil by improving chemical conversion property. <P>SOLUTION: This production method of an electrode foil for an electrolytic capacitor has: an etching process of surface roughening a foil made of aluminum or an aluminum alloy; and a chemical cleaning process of dipping the foil in a cleaning liquid, wherein it has: a primary steaming process of exposing the foil to a steam before the chemical cleaning process, the steam obtained by heating up a cleaning liquid; and a secondary steaming process of exposing the foil to a steam after the chemical cleaning process, the steam obtained by heating up the cleaning liquid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolytic capacitor etching foil. More specifically, the present invention relates to a processing technique / film formation technique for an etching foil after the etching process.

When manufacturing an electrolytic capacitor etching foil, a foil made of aluminum or an aluminum alloy is chemically or / and electrochemically etched in an etching solution to roughen the surface.
In that case, phosphoric acid, nitric acid, sulfuric acid, oxalic acid, etc. may be mix | blended with an etching liquid other than a chlorine ion.
An etched film containing chlorine ions is formed on the surface of the foil after etching. Chlorine ions existing in the film hinder the formation of the dielectric film and increase leakage current, corrosion, Reduces the withstand voltage, etc., and reduces the reliability of the electrolytic capacitor.

  Therefore, after the etching process, a chemical cleaning process is performed in which the etching foil is immersed in a cleaning solution containing phosphoric acid, nitric acid, sulfuric acid, and the like to dissolve the surface layer of the etching foil (for example, see Non-Patent Document 1).

Isaya Nagata, “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nippon Denki Kogyo Kogyo Co., Ltd., February 24, 1997, 2nd edition, 1st printing (P247-249)

  However, when the etching foil is immersed in a solution containing phosphoric acid, nitric acid, sulfuric acid, etc., and the surface layer of the etching foil is dissolved, in addition to the etching film, the base metal portion of the aluminum foil is also dissolved, and the etching magnification is reduced. End up.

  In view of the above problems, the object of the present invention is to remove chlorine ions adhering to the etching foil while minimizing the dissolution of the etching foil surface layer after the etching step, and to the anodic oxidation (chemical conversion) step. An object of the present invention is to provide a method for producing an electrode foil for an electrolytic capacitor capable of forming a better quality dielectric film.

In order to solve the above-mentioned problems, an electrolytic capacitor electrode foil manufacturing method according to the present invention includes an etching step of roughening a foil made of aluminum or an aluminum alloy in an etching solution, and immersing the foil in a cleaning solution. In the method for producing an electrolytic foil etching foil having a chemical cleaning step,
A first steam treatment step in which the cleaning solution is exposed to steam obtained by heating the cleaning solution before the chemical cleaning step; and a second steam treatment step in which the cleaning solution is exposed to steam obtained by heating after the chemical cleaning step. It is characterized by that.

  By the “first steam treatment”, the steam generated from the cleaning liquid can easily cause a reaction by the cleaning liquid immersion process, and the effect of promoting the removal of chlorine ions is obtained. Further, the dissolution of the surface layer of the etching foil by chemical cleaning can be minimized. By the “chemical cleaning”, chlorine ions that adhere in the etching process and have an adverse effect in the anodizing (chemical conversion) process can be removed and replaced. By performing the “second steam treatment” after the first steam treatment and the chemical cleaning, the quality of the formed film can be improved.

The cleaning liquid has a pH of 2 to 4.
When such a highly acidic cleaning solution is used, the concentration of nitrate ions and the like in the cleaning solution increases, the content in the steam increases, and chlorine ions can be removed and replaced in a short time. Nitric acid is used for adjusting the pH.

Further, the cleaning liquid contains at least one of aluminum nitrate, aluminum nitrite, aluminum oxalate, and aluminum phosphate.
Since the main cations of this treatment liquid are aluminum ions, even if the base metal part of the aluminum foil is dissolved, it can be suppressed to a minimum from the relationship of chemical equilibrium.

  The cleaning liquid contains 0.01 to 30.0 wt% aluminum salt.

  As the steam in the first and second steam treatment processes, steam evaporated from the cleaning liquid used in the chemical cleaning process is used.

The etching step includes at least a first-stage etching step for generating tunnel-like pits in the aluminum foil, and a second-stage etching step for expanding the hole diameter of the pits generated in the first-stage etching step,
In the second stage etching step, an etching solution containing at least one of nitrate ions, sulfate ions, phosphate ions and organic acid ions in addition to chlorine ions is used.

  Further, when the aluminum foil is subjected to AC etching or DC etching, an etching film having a large number of deep holes (for example, a diameter = 10 to 1600 nm, a depth = a hole 50 to 2000 times the diameter) is formed, and such a large number of holes are formed. Chlorine ions remain, but the chlorine ions can be removed and replaced by combining the three steps of the first steam treatment, the chemical cleaning, and the second steam treatment. At that time, a very small amount of dissolution of the etching film functions suitably during the anodic oxidation (chemical conversion) step, so that the etching magnification does not decrease.

In the present invention, when manufacturing an etching foil for medium and high voltage (for an electrolytic capacitor having a rated voltage of 160 WV or more) as an electrode foil for an electrolytic capacitor, in the etching step, a tunnel-like pit is generated in the aluminum foil. A step etching step and a second step etching step for enlarging the hole diameter of the pit generated in the first step etching step are performed.
In the second stage etching step, an etching solution containing at least one of nitrate ion, sulfate ion, phosphate ion and organic acid ion (oxalate ion, sulfonic acid, etc.) in addition to chlorine ion is used.
In the second-stage etching step, when such etching solution is used and direct current etching is performed using an aluminum foil as an anode, an etching film containing a large amount of chlorine ions is easily formed on the surface of the etching foil, but the present invention is applied. By doing so, chlorine ions in the etching film can be removed, dissolution can be suppressed, and a pit form effective for chemical conversion can be obtained.

  By configuring as described above, according to the present invention, it is possible to maintain the pit form while removing chlorine ions in the etching film, and to obtain an etching foil having improved capacitance without decreasing the etching magnification. it can.

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

FIG. 1 is a process flow diagram showing a method for producing an electrolytic capacitor etching foil according to the present invention.
FIG. 2 is an explanatory diagram showing the states of the first steam treatment process, the chemical cleaning process, and the second steam treatment process in the electrolytic capacitor etching foil manufacturing process according to the present invention.

  As shown in FIG. 1, the manufacturing method of the electrolytic capacitor etching foil according to the present invention includes a degreasing process ST1, a first stage etching process ST3, a second stage etching process ST5, a first steam treatment process ST7, and a chemical cleaning process ST8. The second steam treatment process ST9, the pure water treatment process ST10, and the drying heat treatment process ST11 are sequentially performed.

(Degreasing process) ST1
In the degreasing treatment step ST1, the aluminum foil was degreased by immersing it in, for example, sodium hydroxide, phosphoric acid, sodium phosphate, or a solution obtained by adding sodium silicate thereto.
Oil and dirt used in the rolling process are attached to the foil, and unevenness occurs in the attached part in the etching process, so that it is necessary to sufficiently degrease the foil. Next, water washing process ST2 was performed with respect to the aluminum foil after the said process.

(First stage etching process) ST3
Next, in the first stage etching step ST3, direct current electrolysis was performed in an etching solution using an aluminum foil as an anode to generate tunnel-like pits in the aluminum foil, and then a water washing step ST4 was performed.
In the first-stage etching step ST3, for example, in an etching solution having a liquid temperature of 80 ° C., sulfuric acid of 3.5 mol / L, and aluminum chloride of 0.50 mol / L, an aluminum foil is used as an anode, a current density of 150 mA / cm ² , It was subjected to electrolytic etching in the conditions of an amount 20C / cm ^2.

(Second stage etching process) ST5
Next, in the second stage etching step ST5, direct current electrolysis is performed in an etching solution using an aluminum foil as an anode to increase the diameter of the tunnel-like pit generated in the first stage etching step ST3, and then the water washing step ST6 is performed. went.
In the second stage etching step ST5, for example, an etching solution containing at least one of nitrate ion, sulfate ion, phosphate ion and organic acid ion in an aqueous solution mainly composed of hydrochloric acid 0.10 to 0.60 mol / L. Was used.
For example, at least one of nitrate ion, sulfate ion, phosphate ion and organic acid ion (oxalate ion, sulfonic acid, etc.) is added to an aqueous solution mainly composed of 0.10 to 0.60 mol / L of hydrochloric acid. Electrolytic etching was performed under the conditions of a liquid temperature of 70 to 90 ° C. and a current density of 15 to 35 mA / cm ² using an etching liquid containing 005 to 0.05 mol / L.

(First steam treatment process (first process)) ST7
Since the surface of the aluminum foil thus obtained contains chlorine ions used in the etching solution in the film formed during etching (etching film), in the present invention, the etched aluminum foil is washed with the cleaning liquid. The first steam treatment step ST7 was performed to expose the steam obtained by heating the metal and easily remove and replace chlorine ions in the etching film.
That is, by passing the roughened aluminum foil in a vapor containing a chemical cleaning component rather than in a liquid in which the etching film is easily dissolved, chlorine ions can be easily removed without dissolving the etching film. Was processed for.
Table 1 shows the first steam treatment conditions at that time. For example, 4.5 wt% aluminum nitrate, 2.5 wt% aluminum nitrite, 0.25 wt% aluminum oxalate, and 0.25 wt% aluminum phosphate are mixed, and the cleaning liquid whose pH is adjusted with nitric acid is heated. Steam treatment was performed for 5 minutes.

(Chemical cleaning process) ST8
As the cleaning solution, an acidic aqueous solution in which aluminum nitrate, aluminum nitrite, aluminum oxalate, and aluminum phosphate are mixed in the same composition as above and 5.0 wt% aluminum ions are contained is set to a liquid temperature of 70 ° C. Under the conditions, the chemical cleaning step ST8 was performed for 3.0 minutes.

(Second steam treatment process) ST9
In the second steam treatment step ST9, the etching foil after the chemical cleaning step ST8 was subjected to steam treatment at 55 ° C. for 2.5 minutes in the second steam treatment step ST9.
After the first steam treatment and chemical cleaning, the second steam treatment is performed. After the steam treatment with the cleaning liquid, the foil from which chlorine ions have been removed and replaced is further subjected to the steam treatment with the cleaning liquid, thereby anodizing. It is thought that a “post-treatment film” that improves the capacitance in the process can be formed.

(Pure water washing treatment process) ST10
After performing the steam treatment and film formation on the etching foil, in the pure water cleaning step ST10, the etching foil is treated with pure water having a conductivity of 1 mS / m or less (temperature is 20 to 25 ° C.) for 10 to 20 minutes, For example, it was washed with water for 15 minutes.

(Dry heat treatment process) ST11
Next, in the drying heat treatment step ST11, the etching foil was dried by removing water on the surface at a temperature of 200 to 250 ° C., and then heated and dried at 150 to 260 ° C. for 1 to 5 minutes.
Specifically, water on the surface was removed by drying at a temperature of 230 ° C., and then heat-dried at 250 ° C. for 2 minutes and 40 seconds. In this way, an etching foil for electrolytic capacitors was obtained.

By the above steps ST1 to ST11, the obtained etching foil was subjected to chemical conversion under the following conditions, and the obtained electrode foil sample was subjected to measurement of VT characteristics and capacitance.
In addition, the treatment conditions such as the treatment liquid composition were also examined as appropriately changed from the above.
The results are shown in Table 1.
[Formation conditions]
-Chemical conversion liquid Ammonium borate aqueous solution-Chemical conversion voltage 250V,-Current density 0.2A / cm ²
・ Temperature 85 ± 2 ℃
[V-T characteristics measurement conditions]
The voltage immediately before the occurrence of spark was measured by a standard method.
[Capacitance measurement conditions]
Measurements were made by standard techniques at room temperature in an aqueous ammonium borate solution.

(Main effects of this form)
As can be seen from Table 1, the electrical characteristics of the electrode foil samples of Examples 1 to 9 in which ST7 (first steam treatment process), ST8 (chemical cleaning process), and ST9 (second steam treatment process) were all performed are as follows. It is superior to the comparative examples 1 and 2 which did not perform any of 1 and 2nd steam processing, and the conventional example which did not perform both of these.
This is because in the first steam process in which the etching foil is vaporized as vapor from an acidic relatively high temperature cleaning solution, steam treatment is performed to promote chlorine ion removal / replacement in the next chemical cleaning. The chlorine ions adhering to the surface of the etching foil are removed and replaced while minimizing dissolution, and then the anode is formed by the ions of nitric acid, nitrous acid, oxalic acid, and phosphoric acid adhering to the foil in the second vapor. This is considered to be because the etching film can be effectively modified to improve the capacitance by oxidation.

In addition, the capacitance can be improved by performing the first vapor treatment, chemical cleaning, and second vapor treatment, but from Table 1, the concentration of the cleaning liquid (the total concentration when using a plurality of cleaning agents) is: When the content is 0.01 to 30.0 wt%, the capacitance value is remarkably improved, which is preferable.
Further, the pH of the cleaning solution is preferably an acidic solution in order to remove chlorine ions in the etching film, but is preferably 2 to 4 because a higher capacitance can be obtained.

Further, when the aluminum foil is subjected to AC etching or DC etching, an etching film in which a large number of deep holes (for example, a diameter = 10 to 1600 nm and a depth = a hole approximately 50 to 2000 times the diameter) is formed is formed. Although chlorine ions remain in the pores, in this embodiment, chlorine ions are removed and replaced by the first steam treatment process and chemical cleaning process, so the amount of etching film dissolved is controlled and dissolution of etching pits is suppressed. In addition, chlorine ions can be removed and replaced efficiently.
Therefore, according to the present embodiment, even after the etching foil is subjected to the cleaning liquid immersion treatment, the etching magnification of the etching foil is high, and a good quality post-treatment film is formed by the second vapor treatment. Can be improved.
Therefore, as compared with the conventional example in which only the chemical cleaning step is performed and the first and second steam treatment steps are not performed, the capacitance value is +1.32 to 6 in terms of the CV product ratio, as is apparent from Table 1. 34% improvement. Moreover, it is improved over Comparative Examples 1 and 2.

FIG. 2 shows a method for performing the first vapor treatment step ST7, the chemical cleaning step ST8, and the second vapor treatment step ST9 in one treatment layer. The vertically movable rollers 2 and 5 were disposed inside the processing tank 3 in which the cleaning liquid was stored, and the etching foil was caused to travel through the processing tank by the rollers 1, 4, and 7.
Here, the roller 7 was subjected to a cleaning liquid immersion treatment. At that time, the vertically movable roller 2 controls the time by the first steam treatment, the roller 7 controls the cleaning liquid immersion treatment time by the overflow position, and the vertically movable roller 5 has the time by the second steam treatment. Controlled.
Moreover, the vapor | steam is suck | inhaled from the upper part of a processing tank, is sent out to the intermediate part in a tank, and is heated and circulated. A temperature sensor is installed in the circulation path and is controlled and managed at the ambient temperature.
And the liquid level and the cleaning liquid immersion treatment time were managed by determining some overflow positions inside the tank. When such a configuration is adopted, the time in each process can be controlled.

(Other embodiments)
In the above embodiment, the present invention was applied to the production of an anode foil for electrolytic capacitors for medium and high pressures. However, the present invention may be applied to the production of an anode foil for electrolytic capacitors for low pressure. You may apply this invention to manufacture of cathode foil.
Moreover, in the said Example, although multiple types of cleaning agents were used, the same effect can be acquired also when it uses independently.

It is a process flow figure showing the manufacturing method of the anode foil of the electrolytic capacitor to which the present invention is applied. It is explanatory drawing which shows the state of a 1st steam processing process, a chemical cleaning process, and a 2nd steam processing process among the manufacturing processes of the etching foil of the electrolytic capacitor to which this invention is applied. The direction of the arrow is the direction in which the foil travels.

Explanation of symbols

1, 4, 7 Roller 2, 5 Vertically movable roller 3 Processing tank 6 Liquid level (control by overflow position)
8 Overflow drain

Claims (4)

In the method for producing an etching foil for an electrolytic capacitor, comprising an etching step of roughening a foil made of aluminum or an aluminum alloy in an etching solution, and a chemical cleaning step of immersing the foil in a cleaning solution,
A first steam treatment step in which the cleaning solution is exposed to steam obtained by heating the cleaning solution before the chemical cleaning step; and a second steam treatment step in which the cleaning solution is exposed to steam obtained by heating after the chemical cleaning step. The manufacturing method of the etching foil for electrolytic capacitors characterized by the above-mentioned.   The method of manufacturing an etching foil for an electrolytic capacitor according to claim 1, wherein the cleaning liquid has a pH of 2 to 4.   The method for manufacturing an etching foil for an electrolytic capacitor according to claim 2, wherein the cleaning liquid contains at least one of aluminum nitrate, aluminum nitrite, aluminum oxalate, and aluminum phosphate.   The manufacturing method of the etching foil for electrolytic capacitors according to claim 3, wherein the concentration of the cleaning liquid is 0.01 to 30.0 wt%.

Images