JP2005203529A - Method for manufacturing electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing electrode foil for aluminum electrolytic capacitor which has effectively improved static electricity capacitance of the electrode foil by improving pit density and pit growth property. <P>SOLUTION: In a method for manufacturing electrode foil for etching aluminum by impressing an alternative current in the electrolyte, an aqueous solution which is mainly composed of hydrochloric acid with addition of at least a kind of solution of sulfuric acid, oxalic acid, and phosphoric acid is used as the electrolyte, the maximum value is set at the start of the etching process as the step of the current density to impress the alternate current, the current density is gradually reduced from the maximum value, uniform and dense etching pit can be generated by setting the current density to 0 at the intermediate step before the step where the current density becomes 0, and the growth of etching pit can be improved in higher density. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing an electrode foil for an aluminum electrolytic capacitor, and more particularly to an etching technique for an anode foil used for a low-voltage aluminum electrolytic capacitor.

  In recent years, along with the downsizing and high reliability of electronic equipment, there has been a strong demand from users for aluminum electrolytic capacitors, and as a result, electrode foils used for aluminum electrolytic capacitors are more than per unit area. There is a need to increase the electrostatic capacity.

  A general aluminum electrolytic capacitor includes an anode foil in which a dielectric oxide film is formed by anodic oxidation on a surface of which an effective surface area is expanded by etching the aluminum foil, and a cathode foil in which the effective surface area is expanded by etching the aluminum foil. The capacitor element is formed by winding the capacitor element through a separator, and the capacitor element is impregnated with a driving electrolyte, and the capacitor element is sealed in a metal case.

  In this type of aluminum electrolytic capacitor, it is essential to increase the effective surface area of the anode foil and increase the capacitance per unit area in order to increase its capacitance or reduce its size. The development of etching technology that expands the effective surface area of silicon has been actively conducted.

  The etching treatment of the anode foil is performed chemically or electrochemically in an aqueous hydrochloric acid solution to which an acid for forming a film such as sulfuric acid, nitric acid, phosphoric acid, or oxalic acid is added. In the etching process of the foil, an infinite number of etching pits are formed stepwise in the aluminum foil by repeatedly performing the etching process by applying an alternating current in an electrolyte mainly composed of hydrochloric acid several times.

  In this etching process using an alternating current, an aluminum hydrate film is formed when a cathode current flows on the surface of the aluminum foil, and an etching pit is formed from a defective portion of the hydrate film when an anode current flows. It is known that countless etching pits are formed by repeating this reaction, and the electrolyte solution composition, the current density and frequency conditions of the alternating current are devised and improved, and the anode foil The characteristics such as capacitance and mechanical strength are improved.

For example, Patent Documents 1 and 2 are known as prior art document information relating to the invention of this application.
Japanese Patent Laid-Open No. 02-189912 Japanese Patent Laid-Open No. 2003-96599

  However, in the etching process in which an alternating current is applied to the aluminum foil in an electrolyte containing hydrochloric acid as a main component, a constant current density is used in the same etching treatment tank, and the surface area of the aluminum foil is controlled by regulating this frequency. Although the enlargement is attempted, since the mechanical strength is weakened when the surface area of the aluminum foil is excessive, there is a problem that the surface area of the aluminum foil can be expanded only to a certain region.

  Further, as shown in Patent Document 1 and Patent Document 2 and the like, an AC etching method in which various current densities are changed has been proposed, but an electrode satisfying the recent demand for an electrode foil for an aluminum electrolytic capacitor. It is difficult to provide a foil.

  The present invention is for solving the above-mentioned conventional problems, taking into account the chemical dissolution reaction, electrochemical reaction, and diffusion phenomenon of aluminum foil, increasing the surface area by generating dense and high-density etching pits, The present invention provides a method for producing an electrode foil for an aluminum electrolytic capacitor capable of increasing the capacitance.

  In order to achieve the above object, an invention according to claim 1 of the present invention is a method of manufacturing an electrode foil in which aluminum is etched by applying an alternating current in an electrolytic solution, and the electrolytic solution contains hydrochloric acid. Using an aqueous solution to which at least one of sulfuric acid, oxalic acid, and phosphoric acid is added as a main component, the current density step for applying the alternating current has a maximum value at the beginning of the etching process, and gradually decreases from the maximum value. It is a manufacturing method in which the current density is set to zero in the middle stage before becoming zero, and when the cathode current of the alternating current flows by gradually decreasing from the maximum value of the current density, It is possible to generate uniform and dense sponge-like etching pits that leave the surface with a thick hydroxide film, and the cathode hydroxide film is formed thin at high current density. It becomes possible to generate further etching pits at high density from the etching pits formed at the flow density, and as a result, the surface area of the aluminum foil is efficiently increased and the capacitance of the electrode foil for the aluminum electrolytic capacitor is increased. It has the effect of being able to.

  In addition, as a method of gradually decreasing from the maximum value of the current density, there are a method of linearly decreasing the slope, a method of decreasing in a step shape, a method of decreasing in a curved shape, and the like.

  The invention according to claim 2 of the present invention is a manufacturing method in which the step of current density for applying an alternating current is repeated a plurality of times, and the step is repeated a plurality of times.

  According to a third aspect of the present invention, the current density step for applying an alternating current is set to a maximum value at the beginning of the etching process, and after gradually decreasing from the maximum value, etching is performed for a certain period of time at the reduced current density. The present invention provides a manufacturing method in which the current density is reduced to 0 after processing, and the invention described in claim 4 is a manufacturing method in which the current density step is repeated a plurality of times. By gradually decreasing from the maximum value of the current density, when the alternating current cathode current flows, the hydroxide film is formed thick at a high current density, and a uniform and dense sponge-like etching pit is generated leaving the surface. The cathode hydroxide film is thinly formed by etching at a low current density for a certain period of time, and the etching pits formed at a high current density are formed. Stage of growth of etch pits becomes possible to prompt a high density, such an action can be enlarged surface area of the aluminum foil efficiently.

  The invention according to claim 5 of the present invention is a manufacturing method in which the current density at the beginning of the etching process for applying an alternating current is maintained for a certain period of time. When a cathode current having a high current density flows, The oxide film is formed thick, and has an effect that a large number of uniform and fine sponge-like etching pits leaving the surface of the aluminum foil can be generated.

  The invention according to claim 6 of the present invention is a manufacturing method in which the time until the current density is gradually reduced from the maximum value of the current density is 3 seconds or more, and etching pits formed at a high current density. Therefore, since it is possible to provide a sufficient amount of electricity to generate further etching pits at a high density, the density of the etching pits can be increased.

  According to the present invention, there is provided a method of manufacturing an electrode foil in which aluminum is etched by applying an alternating current in an electrolyte solution, the electrolyte solution containing hydrochloric acid as a main component and at least one of sulfuric acid, oxalic acid, and phosphoric acid. The step of current density in which the alternating current is applied using the added aqueous solution is set to the maximum value at the beginning of the etching process, gradually decreases from the maximum value, and the current density is reduced to zero in the middle stage before the current density becomes zero. By gradually reducing the current density from the maximum value of the current density, when the alternating current cathode current flows, the hydroxide film is formed thick at a high current density and the surface remains uniform and dense. Etching pits can be generated, and at a low current density, the cathode hydroxide film is formed thinly, which makes it possible to promote the growth of etching pits at a high density. The enlargement of the surface area of the aluminum foil efficiently performed, in which an effect that it is possible to increase the capacitance of the electrode foil for aluminum electrolytic capacitors.

  Hereinafter, embodiments of the present invention will be described in detail.

(Embodiment 1)
In the manufacturing method of the electrode foil for an aluminum electrolytic capacitor in Embodiment 1 of the present invention, an aluminum foil having a thickness of 100 μm and a purity of 99.98% is first used, and this is an aqueous solution of 90 ° C. having a phosphoric acid concentration of 1.0 wt%. For 60 seconds.

  Next, this aluminum foil is etched using an etching tank as shown in FIG.

  In this etching process, a pair of electrode plates 3 are arranged and electrolysis at a temperature of 30 ° C. adjusted to 5 wt% hydrochloric acid, 2 wt% aluminum chloride, 0.1 wt% sulfuric acid, 0.5 wt% phosphoric acid, and 0.2 wt% nitric acid. The aluminum foil 2 is immersed in an etching tank 4 filled with the liquid 5 (the aluminum concentration in the electrolytic solution is adjusted to 0.1 wt%), and an alternating current having a frequency of 35 Hz is applied to the pair of electrode plates 3 from the alternating current power supply device 1. The applied etching is performed for 100 seconds.

  As shown in FIG. 2, the current density to which the alternating current is applied is maximized at the initial current density, and gradually decreased from the maximum value, and the current density is reduced to 0 in the middle stage before the current density becomes zero. I made it a step.

  Finally, an immersion treatment is performed for 60 seconds with an aqueous solution of 10 wt% sulfuric acid at 60 ° C., and a heat treatment is performed at 250 ° C. for 120 seconds to produce an etching foil to be an electrode foil for an aluminum electrolytic capacitor.

  Hereinafter, specific examples of the first embodiment will be described.

(Example 1)
In the first embodiment, the initial current density of the waveform shown in FIG. 2 is set to 0.75 A / cm ² , and then gradually decreased to 0.25 A / cm ² (67% decrease from the initial current density), and thereafter An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

(Example 2)
In the first embodiment, the first current density of the waveform shown in FIG. 2 to 0.69A / cm ^2, (55% reduction from the initial current density) from there to 0.31A / cm ² is gradually reduced, then An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

(Example 3)
In the first embodiment, the first current density of the waveform shown in FIG. 2 to 0.63A / cm ^2, 0.38A / cm to ² (40% reduction from the initial current density) therefrom is gradually reduced, then An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

Example 4
In the first embodiment, the first current density of the waveform shown in FIG. 2 to 0.56A / cm ^2, (21% reduction from the initial current density) from there to 0.44 A / cm ² is gradually reduced, then An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

(Example 5)
In the first embodiment, the first current density of the waveform shown in FIG. 2 to 0.53A / cm ^2, (9% decrease from the initial current density) from to 0.48A / cm ² thereto is gradually reduced, then An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

(Example 6)
In the first embodiment, first the current density 0.56 A / cm ^2, up to 0.44A / cm ² (21% reduction from the initial current density) there from 25 seconds of the waveform shown in FIG. 2 gradually decreases Then, an etching foil was produced in the same manner as in Embodiment 1 except that the step of holding the current density at 0 for 10 seconds was repeated 4 times. The frequencies were set to 40, 30, 25, and 20 Hz in this order.

(Example 7)
In the first embodiment, the first current density of the waveform shown in FIG. 3 to 0.56A / cm ^2, (21% reduction from the initial current density) from there to 0.44 A / cm ² is gradually reduced, then An etching foil was produced in the same manner as in the first embodiment except that a step with a current density of 0 was applied.

(Example 8)
In the first embodiment, first the current density 0.56 A / cm ^2, up to 0.44A / cm ² (21% reduction from the initial current density) there from 25 seconds of the waveform shown in FIG. 3 gradually decreases Then, an etching foil was produced in the same manner as in Embodiment 1 except that the step of holding the current density at 0 for 10 seconds was repeated 4 times. The frequencies were set to 40, 30, 25, and 20 Hz in this order.

(Comparative Example 1)
In the first embodiment, an etching foil was produced in the same manner as in the first embodiment except that a constant current of 0.50 A / cm ² was applied as the current density of the alternating current.

  The results of evaluating the characteristics of the etching foils of Examples 1 to 8 and Comparative Example 1 thus produced are shown in (Table 1). The evaluation of the etching foil is a value measured based on the EIAJ standard (conforming to EIAJ RC-2364A), and the capacitance is a value when Comparative Example 1 is 100.

  As is clear from (Table 1), by gradually decreasing the current density to which the alternating current is applied from the initial maximum value, and then setting the current density to 0, the reduction rate is 21% to 55%. The surface area of the aluminum foil can be efficiently increased, and the capacitance of the etching foil can be improved.

  Further, by repeating the current density step of applying an alternating current as in Example 6, the capacitance of the etching foil can be further improved.

  Further, from the results of Examples 7 and 8, the capacitance can be further increased by gradually decreasing the maximum value of the current density in a curved shape.

  Note that when the rate of decrease from the maximum value of the current density is 9%, it is possible to obtain only substantially the same capacitance as in Comparative Example 1. Moreover, when the rate of decrease from the maximum value of the current density is 67%, the capacitance becomes lower than that of Comparative Example 1, and the surface area of the aluminum foil with high efficiency cannot be achieved.

(Embodiment 2)
In the first embodiment, the current density at which the alternating current is applied is set to the initial current density as shown in FIG. 4 and gradually reduced from the maximum value, and then the reduced current density is used. An etching foil was produced in the same manner as in the first embodiment except that the etching process was performed by performing the etching process for a certain time and then setting the current density to 0 as a step.

  A specific example of the second embodiment will be described below.

Example 9
In the second embodiment, the initial current density of the waveform shown in FIG. 4 is set to 0.69 A / cm ² and then from 0.51 to 0.31 A / cm ² (55% reduction from the initial current density). Etching foils were produced in the same manner as in the second embodiment except that the voltage was gradually decreased, and subsequently applied for 99.5 seconds at a current density of 0.31 A / cm ² , and then the step of setting the current density to 0 was applied.

(Example 10)
In the second embodiment, the first current density was to 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) at 1 second from the bottom of the waveform shown in FIG. 4 gradually decreases Subsequently, an etching foil was produced in the same manner as in Embodiment 2 except that a step was applied at a current density of 0.31 A / cm ² for 99 seconds and then a step in which the current density was reduced to 0 was applied.

(Example 11)
In the second embodiment, first the current density 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) in 3 seconds from there the waveform shown in FIG. 4 gradually decreases Subsequently, an etching foil was produced in the same manner as in Embodiment 2 except that a step of applying a current density of 0.31 A / cm ² for 97 seconds and then applying a step of setting the current density to 0 was applied.

(Example 12)
In the second embodiment, first the current density 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) there from 10 seconds of the waveform shown in FIG. 4 gradually decreases Subsequently, an etching foil was produced in the same manner as in the second embodiment except that a step was applied at a current density of 0.31 A / cm ² for 90 seconds and then a step in which the current density was reduced to 0 was applied.

(Example 13)
In the second embodiment, first the current density 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) there from 20 seconds of the waveform shown in FIG. 4 gradually decreases Subsequently, an etching foil was produced in the same manner as in the second embodiment except that a step of applying a current density of 0 was applied for 80 seconds at a current density of 0.31 A / cm ² and then applying a step of setting the current density to 0.

(Example 14)
In the second embodiment, first the current density 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) there from 50 seconds of the waveform shown in FIG. 4 gradually decreases Subsequently, an etching foil was produced in the same manner as in Embodiment 2 except that a step of applying a current density of 0 was applied at a current density of 0.31 A / cm ² for 50 seconds, and then applying a step of setting the current density to 0.

(Example 15)
In the second embodiment, first the current density 0.69A / cm ^2, up to 0.31A / cm ² (55% reduction from the initial current density) in 3 seconds from there the waveform shown in FIG. 4 gradually decreases Then, the etching foil was applied in the same manner as in Embodiment 2 except that the step of applying for 22 seconds at a current density of 0.31 A / cm ² and then applying the current density to 0 for 10 seconds was repeated four times. Produced. The frequencies were set to 40, 30, 25, and 20 Hz in this order.

  The results of evaluating the characteristics of the etching foils of Examples 9 to 15 produced in this way are shown in (Table 2). The evaluation of the etching foil is a value measured based on the EIAJ standard (conforming to EIAJ RC-2364A), and the capacitance is a value when Comparative Example 1 is 100.

  As is clear from Table 2, the surface density of the aluminum foil is efficiently increased even if the current density to which the alternating current is applied is decreased from the initial current density and etching is performed at the reduced current density. And the capacitance of the etching foil can be improved.

  Further, by repeatedly performing the step of current density in which an alternating current is applied as in Example 15, the capacitance of the etching foil can be further improved.

(Embodiment 3)
In the first embodiment, the current density to which an alternating current is applied is maintained for a certain period of time with the initial current density as a maximum value as shown in FIG. 5, and after gradually decreasing from the maximum value, the current density is then reduced to zero. An etching foil was produced in the same manner as in the first embodiment except that the etching process was performed in the step.

  A specific example of the third embodiment will be described below.

(Example 16)
In the third embodiment, the initial current density of the waveform shown in FIG. 5 is applied at 0.63 A / cm ² for 0.5 second, and then reaches 0.38 A / cm ² (40% decrease from the initial current density). ) Etching foil was manufactured in the same manner as in the third embodiment except that a step of gradually decreasing and then setting the current density to 0 was applied. The alternating current application time was 100 seconds and the frequency was 35 Hz.

(Example 17)
In Example 16, an etching foil was prepared in the same manner as in Example 16 except that the initial current density having the waveform shown in FIG. 5 was applied for 1.0 second.

(Example 18)
In Example 16, an etching foil was prepared in the same manner as in Example 16 except that the initial current density of the waveform shown in FIG. 5 was applied for 3.0 seconds.

(Example 19)
In Example 16, an etching foil was produced in the same manner as in Example 16 except that the initial current density of the waveform shown in FIG. 5 was applied for 5.0 seconds.

(Example 20)
In Example 16, an etching foil was produced in the same manner as in Example 16 except that the initial current density of the waveform shown in FIG. 5 was applied for 10.0 seconds.

  The results of evaluating the characteristics of the etching foils of Examples 16 to 20 produced in this way are shown in (Table 3). The evaluation of the etching foil is a value measured based on the EIAJ standard (conforming to EIAJ RC-2364A), and the capacitance is a value when Comparative Example 1 is 100.

  As is clear from (Table 3), the maximum value of the current density is initially maintained, and the surface area of the aluminum foil can be efficiently expanded by performing the etching process by gradually decreasing the current density. The capacitance of the etching foil can be improved.

  In addition, when the holding time of the maximum value of the current density is 0.5 seconds, it is possible to obtain only the same capacitance as that of the third embodiment.

(Embodiment 4)
In the first embodiment, the current density to which the alternating current is applied is maintained for a certain period of time with the initial current density as the maximum value as shown in FIG. 6, and gradually decreased from the maximum value, and then the reduced current density. Etching was performed in the same manner as in the first embodiment except that the etching process was performed for a certain period of time, and then the etching process was performed by setting the current density to zero.

  Hereinafter, specific examples of the fourth embodiment will be described.

(Example 21)
In the fourth embodiment, the initial current density of the waveform shown in FIG. 6 is applied at 0.56 A / cm ² for 3 seconds, and then from 0.44 A / cm ^{2 in} 10 seconds (21% from the initial current density) (Decrease) Gradually decrease, then apply for 37 seconds at a current density of 0.44 A / cm ² , and then repeat the step of applying the current density to 0 and holding for 10 seconds again, as in the fourth embodiment. Etching foil was produced. The frequency was set to 35 and 25 Hz in order.

(Example 22)
In the fourth embodiment, the initial current density of the waveform shown in FIG. 6 is applied at 0.56 A / cm ² for 3 seconds, and then from 0.44 A / cm ^{2 in} 10 seconds (21% from the initial current density) (Decrease) Gradually decrease, then apply for 12 seconds at a current density of 0.44 A / cm ² , then apply the same step as in the fourth embodiment except that the step of holding the current density at 0 for 10 seconds was repeated four times. Etching foil was prepared. The frequencies were set to 40, 30, 25, and 20 Hz in this order.

(Comparative Example 2)
In the first embodiment, except that the step of applying a constant current of 0.50 A / cm ² for 50 seconds and then holding the current density at 0 for 10 seconds was repeated again in the first embodiment. Etching foil was produced in the same manner as in Embodiment 1. The frequency was set to 40 and 25 Hz in this order.

(Comparative Example 3)
In the first embodiment, except that the step of applying a constant current of 0.50 A / cm ² for 25 seconds and then holding the current density at 0 for 10 seconds was repeated four times in the first embodiment. Etching foil was produced in the same manner as in Embodiment 1. The frequencies were set to 40, 30, 25, and 20 Hz in this order.

  The results of evaluating the characteristics of the etching foils of Examples 21 to 22 and Comparative Examples 2 to 3 produced in this way are shown in (Table 4). The evaluation of the etching foil is a value measured based on the EIAJ standard (conforming to EIAJ RC-2364A), and the capacitance of Example 21 is 100 in Comparative Example 2 and Example 22 is 100 in Comparative Example 3. This is the value when

  As is clear from Table 4, the current density to which the alternating current is applied is reduced from the initial maximum value, and the surface area of the aluminum foil can be efficiently increased even if the etching process is repeated at the reduced current density. The capacitance of the etching foil can be improved.

  The present invention can improve the capacitance of the electrode foil efficiently by improving the pit density and pit growth, and the aluminum electrolytic capacitor using this electrode foil can increase its rated capacity, Electronic devices can be miniaturized and highly reliable.

Sectional drawing which shows the structure of the etching tank used in embodiment of this invention Waveform diagram of current density for applying alternating current used in the first embodiment Waveform diagram of current density applied with alternating current used in other examples Waveform diagram of current density for applying alternating current used in the second embodiment Waveform diagram of current density for applying alternating current used in the third embodiment Waveform diagram of current density for applying alternating current used in the fourth embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply device 2 Aluminum foil 3 A pair of electrode plate 4 Etching tank 5 Electrolyte

Claims (6)

A method of manufacturing an electrode foil in which aluminum is etched by applying an alternating current in an electrolytic solution, wherein the electrolytic solution uses an aqueous solution to which hydrochloric acid is a main component and at least one of sulfuric acid, oxalic acid, and phosphoric acid is added, The step of the current density for applying the alternating current has a maximum value at the beginning of the etching process, and gradually decreases from the maximum value, so that the current density becomes zero in the middle stage before the current density becomes zero. Of manufacturing electrode foil for use. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the step of current density for applying an alternating current is repeated a plurality of times. The current density step for applying an alternating current is set to a maximum value at the beginning of the etching process, and after gradually decreasing from the maximum value, the etching process is performed for a certain period of time with the reduced current density, and then the current density is reduced to zero. The manufacturing method of the electrode foil for aluminum electrolytic capacitors of Claim 1 which was made to do. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 3, wherein the step of current density for applying the alternating current is repeated a plurality of times. The manufacturing method of the electrode foil for aluminum electrolytic capacitors as described in any one of Claims 1-4 which was made to hold | maintain the current density of the etching process start which applies an alternating current for a fixed time. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 3 or 4, wherein the time until the current density is gradually reduced from the maximum value is set to 3 seconds or more.

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