JP4758796B2 - Method for producing electrode foil for electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for producing an aluminum electrode foil for an electrolytic capacitor, and more particularly to a method for etching an electrode foil of a medium-high voltage electrolytic capacitor.

Aluminum foil used for an electrolytic capacitor is subjected to electrolytic etching, chemical etching, or both in order to increase the effective surface area and improve the capacitance.
The expansion of the surface area of aluminum foil by etching is necessary for effective utilization of aluminum resources and further miniaturization of products, and the demand is increasing.
Electrochemical etching has the advantage that the reaction can be easily controlled by electricity, and is currently the main method used in the production of etching foils. In the case of medium to high pressure etching, it is roughly divided into two steps: pretreatment and etching pit formation. (For example, refer to Patent Documents 1 to 3 and Non-Patent Document 1).
Among these, in the etching pit formation process, a method of dividing into a plurality of stages has been proposed for the purpose of more efficiently forming pits.

As shown in Patent Documents 1 to 3 and Non-Patent Document 1, the etching pit forming step is manufactured by performing the etching process in at least two stages.
The etching process was performed in the same step as the first etching process aiming to generate a large number of pits in an acidic etching solution, in which electrolytic etching by chemical application and chemical etching proceed in parallel. This is divided into a second etching process for the purpose of expanding the pits to a predetermined size.
JP-A-9-180965 JP 7-211153 A JP-A-7-272984 Isaya Nagata, “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nippon Storage Battery Industry Co., Ltd., February 24, 1997, Second Edition, First Printing P225-228

However, in the etching method described above, the second etching step that performs the pit hole diameter expanding step is a process that repeatedly expands the hole diameter with the same liquid composition, liquid temperature, and current density. As a result, the finished thickness after the etching process was reduced, and the tunnel pit length was shortened, resulting in a decrease in capacitance.
Therefore, in the second etching step, a method for efficiently expanding the hole diameter and suppressing surface dissolution has been required.

The present invention solves the above-described problem. In the method of manufacturing an electrolytic capacitor electrode foil in which the etching process is performed in two stages, a first etching process that mainly generates etching pits and a second that mainly enlarges the hole diameter. The second etching step consists of a plurality of stages, and the liquid temperature and the current are set higher sequentially, and the increase in the liquid temperature of the next stage relative to the previous stage is 5 to 25 ° C., the current density while maintaining the increase in the in the range of 8.3~30.0mA / cm2, have lines etched, the first stage of the second etching step, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, at least oxalic acid 1 include seeds, in the etching solution in the range concentration of 0.10~0.60mol / L, solution temperature 70-75 [° C., it is intended to perform at a current density 15~25mA / cm ^2, the second etching Engineering The current density of the final stage etching step is about 50.0 mA / cm ² or less .

In the aluminum foil etching method performed in two stages, after generating etching pits in the first etching step, when the second hole diameter expansion etching is performed in a plurality of stages, the increase in the liquid temperature of the next stage relative to the previous stage is 5 to 25 ° C., the current density increase is maintained in the range of 8.3 to 30.0 mA / cm ² , and the maximum current density of the final stage etching is set to 50.0 mA / cm ² or less. In the first stage, an etching solution containing one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and oxalic acid and having a concentration of 0.10 to 0.60 mol / L, a liquid temperature of 70 to 75 ° C., a current density of 15.0 to 25 By performing in the range of 0.0 mA / cm ² , the hole diameter can be efficiently expanded and dissolution of the etching foil surface can be suppressed. Therefore, the effect of suppressing the foil thickness reduction is obtained, and the capacity can be further increased.

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

  A high-purity aluminum foil having a purity of 99.99%, a thickness of 120 μm, and a (100) surface occupancy rate of 98% was pretreated by being immersed in a 5 wt% sodium hydroxide aqueous solution at 30 ° C. for 30 seconds.

In the first etching step, a current density of 150 mA / cm ² and an electric charge of 20 C / cm are applied to the aluminum foil 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. ^{In 2} , electrolytic etching was performed.

Next, in the second etching step, an aqueous hydrochloric acid solution is used as an etching solution under the etching conditions shown in Tables 1 to 7, and the electrolysis time is such that the total electric quantity from the first stage to the last stage is 30 C / cm ² . Then, the hole diameter expansion of the aluminum foil was performed by dividing the aluminum foil so as to obtain an equal amount of electricity at each stage, and an etching foil sample was produced.
The etching foil sample was washed with a 0.75 mol / L aluminum nitrate aqueous solution at 60 ° C. for 1 minute, and then subjected to a chemical conversion treatment of 573 V with a 50 g / L boric acid aqueous solution to determine the capacitance and the finished thickness after etching. It was measured.
Here, the finished thickness of the etching foil was measured using a micrometer.
Hereinafter, about Examples 1-47 and Comparative Examples 1-18, the measurement result of the etching conditions, the electrostatic capacitance after performing a chemical conversion treatment, and the finishing thickness after an etching is shown.

[Examples 1 to 9, Comparative Examples 1 and 2] Table 1, 1st and 2nd stage etching, current density increase ΔCD, liquid temperature increase ΔT comparison, final stage etching current density comparison (first stage etching liquid temperature : 70 ° C)
<First stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 70 ° C., current density 20.0 mA / cm ² , electric quantity 15 C / cm ²
<Second stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 to 95 ° C., current density 28.3 to 53.3 mA / cm ² , electric quantity 15 C / cm ²
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 1.

[Examples 10 to 17, Comparative Example 3] Table 2, first and second stage etching, current density increase ΔCD, liquid temperature increase ΔT comparison, final stage etching current density comparison (first stage etching liquid temperature: 75 ℃)
<First stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C., current density 20.0 mA / cm ² , electric quantity 15 C / cm ²
<Second stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 80 to 95 ° C., current density 28.3 to 53.3 mA / cm ² , electric quantity 15 C / cm ²
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 2.

[Examples 18 to 32, Comparative Example 4] Table 3, first to third stage etching, first stage etchant concentration comparison, liquid temperature increase ΔT comparison (first stage etchant temperature: 70 ° C.)
<First stage etching conditions>
Etching solution: 0.05 to 0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 70 ° C., current density of 15.0 to 25.0 mA / cm ² , electric quantity of 10 C / cm ²
<Second stage etching conditions>
Etching solution: 0.05 to 0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C. (Comparative Example 4: 73 ° C.), current density 25.0 to 35.0 mA / cm ² , electric quantity 10 C / cm ²
<Third stage etching conditions>
Etching solution: 0.05 to 0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 80 ° C. (Comparative Example 4: 76 ° C.), current density 35.0 to 45.0 mA / cm ² , electric quantity 10 C / cm ²
<First to third stage etching process>
Liquid temperature rise ΔT = 3 ° C or 5 ° C
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 3.

[Examples 33 to 47, Comparative Example 5] Table 4, first to third stage etching, first stage etching solution concentration comparison, liquid temperature rise ΔT comparison (first stage etching liquid temperature: 75 ° C.)
<First stage etching conditions>
Etching solution: 0.05 to 0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C., current density of 15.0 to 25.0 mA / cm ² , electric quantity of 10 C / cm ²
<Second stage etching conditions>
Etching solution: 0.05-0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 80 ° C. or 78 ° C., current density 25.0-35.0 mA / cm ² , electric quantity 10 C / cm ²
<Third stage etching conditions>
Etching solution: 0.05-0.75 mol / L hydrochloric acid aqueous solution, liquid temperature: 85 ° C. or 81 ° C., current density 35.0-45.0 mA / cm ² , electric quantity 10 C / cm ²
<1st to 3rd stage etching>
Liquid temperature rise ΔT = 3 ° C or 5 ° C
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 4.

(Comparative Examples 6 to 8) Table 5, comparison of the current density increase ΔCD below the lower limit until the first to third stage etching steps (first stage etching liquid temperature: 75 ° C.)
<First stage etching conditions>
Etching solution: 0.10-0.60 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C., current density 20.0 mA / cm ² , electric quantity 10 C / cm ²
<Second stage etching conditions>
Etching solution: 0.10 to 0.60 mol / L hydrochloric acid aqueous solution, liquid temperature: 80 ° C., current density 27.7 mA / cm ² , electric quantity 10 C / cm ²
<Third stage etching conditions>
Etching solution: 0.10-0.60 mol / L hydrochloric acid aqueous solution, liquid temperature: 85 ° C., current density 35.4 mA / cm ² , electric quantity 10 C / cm ²
<1st to 3rd stage etching>
Current density increase ΔCD = 7.7 ° C
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 5.

(Comparative Examples 9 to 14) Table 6, Comparison of liquid temperature of first to third stage etching and first stage etching exceeding upper limit and lower limit (liquid temperature: 65 ° C. or 80 ° C.)
<First stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution,
Liquid temperature: 65 ° C. or 80 ° C. (conditions outside 70-75 ° C.),
Current density: 15.0-25.0 mA / cm ² , Electricity: 10 C / cm ²
<Second stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 70 ° C. or 85 ° C., current density 25.0-35.0 mA / cm ² , electric quantity 10 C / cm ²
<Third stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C. or 90 ° C., current density of 35.0 to 45.0 mA / cm ² , electric quantity of 10 C / cm ²
<1st to 3rd stage etching>
Current density increase ΔCD = 10.0 mA / cm ²
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 6.

(Comparative Examples 15 to 18) Table 7, comparison of current density of first to third stage etching and first stage etching exceeding upper limit and lower limit (current density: 10.0 mA / cm ² or 30.0 mA / cm ² )
<First stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 70 ° C. or 75 ° C.,
Current density 10.0 mA / cm ² or 30.0 mA / cm ² , electric quantity 10 C / cm ²
<Second stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 75 ° C. or 80 ° C.,
Current density: 20.0 mA / cm ² or 40.0 mA / cm ² , electric quantity 10 C / cm ²
<Third stage etching conditions>
Etching solution: 0.35 mol / L hydrochloric acid aqueous solution, liquid temperature: 80 ° C. or 85 ° C., current density: 30.0 mA / cm ² or 50.0 mA / cm ² , electric quantity 10 C / cm ²
<1st to 3rd stage etching process>
Current density increase ΔCD = 10.0 mA / cm ^2, liquid temperature increase ΔT = 5 ° C.
Etching was performed under the above conditions to prepare an etching foil sample, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are shown in Table 7.

(Conventional example)
As a conventional example, etching is performed in the same manner as in Example 1 except that the current density is 30.0 mA / cm ² , the total electric quantity is 30 C / cm ² , and the liquid temperature is 80 ° C. through the first to final etching processes. A foil sample was prepared, and the capacitance after the chemical conversion treatment and the finished thickness after the etching were measured. The results are also shown in Tables 1-7.

[Comparison of current density rise ΔCD, liquid temperature rise ΔT, current density comparison of final stage etching]
-Table 1, Examples 1-9, 1st-2nd stage etching (1st stage etching liquid temperature: 70 degreeC)
・ To Table 2, Examples 10 to 17, first and second stage etching steps (first stage etching solution temperature: 75 ° C.)
The increase in the second stage liquid temperature relative to the first stage is maintained in the range of 5 to 25 ° C., and the increase in current density is maintained in the range of 8.3 to 33.3 mA / cm ^2. When the current density of the second-stage etching is 50.0 mA / cm ² or less at a current density of ˜75 ° C. and a current density of 20.0 mA / cm ² , the reduction in the finished thickness after etching is suppressed, The effect of increasing the capacitance is also obtained (Examples 1-9, 10-17).
However, when the current density of the second stage etching exceeded 50 mA / cm ² , the above effect was not observed (Comparative Examples 1 to 3).
Further, if the liquid temperature increase ΔT exceeds 25 ° C., it becomes close to the boiling point, and therefore, the foil is distorted in the liquid, which is not preferable.

[Comparison of 1st to 3rd stage etching solution concentration, ΔT comparison of liquid temperature increase]
Table 3, Examples 18 to 32, 1st to 3rd stage etching (first stage etchant temperature: 70 ° C.)
・ To Table 4, Examples 33 to 47, 1st to 3rd stage etching process (1st stage etchant temperature: 75 ° C.)
-Until Table 5, Comparative Examples 6-8, the 1st-3rd step etching process (1st step etching liquid temperature: 75 degreeC)
Maintain the temperature rise of the second stage with respect to the first stage and the third stage with respect to the second stage at 5 ° C. and the increase in current density at 10.0 mA / cm ² , and perform the first to third stage etching. Concentration 0.10 to 0.60 mol / L Hydrochloric acid aqueous solution is used, and the first stage etching is performed in the range of liquid temperature 70 to 75 ° C. and current density 15.0 to 25.0 mA / cm ² , and third stage etching. In the case where the current density is 35.0 to 45.0 mA / cm ² , the reduction in the finished thickness after etching is suppressed, and the effect of increasing the capacitance after formation is obtained (Example 21). -29, 36-44).
However, when the first to third stage etching is performed with a 0.05 mol / L hydrochloric acid aqueous solution, the capacitance does not increase (Examples 18 to 20, 33 to 35), and the concentration is 0.75 mol / L. In the case of using an aqueous hydrochloric acid solution, the capacitance did not increase, and the finished thickness after etching decreased (Examples 30 to 32, 45 to 47).
On the other hand, if the liquid temperature increase ΔT is 3 ° C., the effect of increasing the capacitance after chemical conversion cannot be obtained (Comparative Examples 4 and 5).

[First stage etchant temperature comparison]
Table 3, Examples 24-26, 1st to 3rd stage etching (first stage etchant temperature: 70 ° C.)
Table 4, Examples 39 to 41, 1st to 3rd stage etching (first stage etchant temperature: 75 ° C.)
Table 6, Comparative Examples 9 to 14, first to third stage etching (first stage etching solution temperature: 65 ° C. or 85 ° C.)
Maintain the temperature rise of the second stage with respect to the first stage and the third stage with respect to the second stage at 5 ° C. and the increase in current density at 10.0 mA / cm ² , and perform the first to third stage etching. The first stage etching is performed at a liquid temperature of 70 to 75 ° C. and a current density of 15.0 to 25.0 mA / cm ^{2 with} a concentration of 0.35 mol / L hydrochloric acid aqueous solution. In the case of 35.0-45.0 mA / cm ² , the reduction in the finished thickness after etching is suppressed, and the effect of increasing the capacitance after chemical conversion is obtained (Examples 24-26, 39). ~ 41).
However, when the first-stage etching is performed at a liquid temperature of 65 ° C., the capacitance does not increase (Comparative Examples 9 to 11). It decreased (Comparative Examples 12-14).

[First stage etching current density comparison]
Table 3, Examples 24-26, up to the third stage etching step (first stage etching solution temperature: 70 ° C.)
Table 4, Examples 39 to 41, up to the third stage etching step (first stage etching solution temperature: 75 ° C.)
Table 7, Comparative Examples 15 to 18, up to the third stage etching step (first stage etching solution temperature: 70 ° C. or 75 ° C.)
Maintaining the second stage liquid temperature with respect to the first stage and the third stage rise with respect to the second stage at 5 ° C. and the current density increase at 10.0 mA / cm ² , The first stage etching is performed at a liquid temperature of 70 to 75 ° C. and a current density of 15.0 to 25.0 mA / cm ^{2 with} a concentration of 0.35 mol / L hydrochloric acid aqueous solution. In the case of 35.0-45.0 mA / cm ² , the reduction in the finished thickness after etching is suppressed, and the effect of increasing the capacitance after chemical conversion is obtained (Examples 24-26, 39). ~ 41).
However, when the first-stage etching was performed at a current density of 10.0 mA / cm ² or 30.0 mA / cm ² , the capacitance did not increase and the finished thickness after etching decreased (Comparative Example) 15-18).

From the above results, when the second hole diameter expansion etching is performed in a plurality of stages after generating etching pits in the first etching step, the increase in the liquid temperature of the next stage relative to the previous stage is 5 to 25 ° C., current The increase in density is maintained in the range of 8.3 to 30.0 mA / cm ² , the maximum current density of the final stage etching is set to 50.0 mA / cm ² or less, and the first stage etching is performed with an etchant concentration of 0 .10 to 0.60 mol / L, liquid temperature of 70 to 75 ° C., current density of 15.0 to 25.0 mA / cm ² , so as to efficiently expand the hole diameter and suppress dissolution of the etching foil surface. can do. Therefore, the effect of suppressing the foil thickness reduction is obtained, and the capacity can be further increased.

  In the above embodiment, an aqueous hydrochloric acid solution was used as the first-stage etching solution. However, sulfuric acid, nitric acid, phosphoric acid, and oxalic acid can also be used, and hydrochloric acid, sulfuric acid, nitric acid, phosphorous can be used. Two or more of acid and oxalic acid can be mixed and used.

Claims (1)

In the manufacturing method of the electrode foil for electrolytic capacitors which performs an etching process in two steps,
A first etching step mainly generating etching pits;
Mainly comprising a second etching step for enlarging the hole diameter,
It said second etching step, with consists of a plurality of stages, are sequentially set the liquid temperature and the current is high, the rise of the next liquid temperature for the previous stage 5 to 25 ° C., the increase in the current density 8. and maintained in the range of 3~30.0mA / cm ^2, have rows etching,
The first stage of the second etching step is an etching solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and oxalic acid and having a concentration in the range of 0.10 to 0.60 mol / L. It is performed at 70 to 75 ° C. and a current density of 15 to 25 mA / cm ² ,
The method for producing an electrode foil for an electrolytic capacitor, wherein a current density in a final etching step of the second etching step is 50.0 mA / cm ² or less .