JP4793957B2 - Method for producing aluminum 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 mainstream method in the production of etching foils. In the case of medium to high pressure etching, it has two major 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. For example, as shown in Patent Documents 1 to 3 and Non-Patent Document 1, a method of dividing the etching process into at least two stages is taken when forming the etching pits. That is, it can be divided into a first etching process for generating a large number of pits and a second etching process for expanding the pits generated by the first etching process to a predetermined size. ing.
JP-A-9-180965 JP 7-211153 A JP-A-7-272984 Isaya Nagata, “Electrolyte Cathode Aluminum Electrolytic Capacitor”, Nippon Storage Battery Industry Co., Ltd., February 24, 1997, Second Edition, First Printing P225-241

  However, in the above etching method, since the second etching process for performing the pit hole diameter expanding step is a process of repeatedly expanding the hole diameter at the same liquid composition, liquid temperature, and current density, excessive surface dissolution near the foil surface. Will occur. For this reason, since the finished thickness after the etching process is thin, there is a problem that the tunnel pit length is short and the capacitance is low.

  In view of the above problems, an object of the present invention is to provide a method for producing an aluminum electrode foil for an electrolytic capacitor that can increase capacitance by suppressing surface dissolution when attempting to increase the pore size. is there.

  In order to solve the above-described problems, the present invention provides an electrolytic capacitor having a first etching process that mainly generates etching pits and a second etching process that mainly enlarges the hole diameter after the first etching process. In the method for producing an aluminum electrode foil, in the second etching process, a plurality of etching steps are performed using an etching solution in which at least one of sulfuric acid, nitric acid, phosphoric acid and oxalic acid is added as an additive to an aqueous hydrochloric acid solution. In the multi-stage etching process, both the concentration of the additive and the current density in the subsequent etching process are higher than those in the previous etching process.

In the present invention, the hydrochloric acid aqueous solution is an aqueous solution of hydrochloric acid of 0.10 to 0.60 mol / L, and the concentration of the additive in the subsequent etching step is higher than that in the previous etching step in the multiple etching step. Is 1.2 to 1.4 times, and the increase in current density is preferably 5 to ²⁰ mA / cm ² .

In the second etching process, in the first step, the concentration of the additive is 0.005 to 0.05 mol / L, and the temperature of the etching solution is 70 to 80 ° C. The current density is preferably 15 to 25 mA / cm ² .

Furthermore, in the second etching process, it is preferable that the current density of the last-stage etching process is 50 mA / cm ² or less.

In the medium-high pressure etching method performed in two stages, after generating etching pits in the first etching process, a multi-stage etching process is performed in the second etching process for expanding the hole diameter. At that time, the concentration of the additive in the next stage relative to the previous stage is maintained at 1.2 to 1.4 times, the increase in current density is maintained in the range of 5 to ²⁰ mA / cm ² , and the maximum current density in the final stage etching is 50 mA. / Cm ² or less, and the first stage of the second etching is 0.005 to 0.005 to any one of sulfuric acid, nitric acid, phosphoric acid and oxalic acid with 0.10 to 0.60 mol / L hydrochloric acid as the main additive. When etching is performed in the range of a liquid temperature of 70 to 80 ° C. and a current density of 15 to 25 mA / cm ² using one or more etching liquids mixed in a concentration range of 0.05 mol / L, the pore diameter is efficiently expanded. Thus, ineffective dissolution of the etching foil surface can be suppressed. Therefore, the foil thickness reduction suppressing effect can be obtained, and as a result, the foil capacitance obtained after the chemical conversion can be increased.

  In the method for manufacturing an aluminum electrode foil for electrolytic capacitors to which the present invention is applied, first, a first etching process that mainly generates etching pits, and a second etching process that mainly enlarges the hole diameter after the first etching process. It is characterized by having.

  Next, in the present invention, in the second etching process, a plurality of etching steps in an etching solution in which at least one of sulfuric acid, nitric acid, phosphoric acid and oxalic acid is added as an additive to an aqueous hydrochloric acid solution is performed. The multi-stage etching process is characterized in that both the concentration of the additive and the current density in the subsequent etching process are higher than those in the previous etching process.

Further, in the present invention, the aqueous hydrochloric acid solution is an aqueous solution of 0.10 to 0.60 mol / L hydrochloric acid, and in the multi-stage etching step, the additive in the subsequent etching step is larger than the previous etching step. The concentration is 1.2 to 1.4 times, and the increase in current density is 5 to 20 mA / cm ² . In the second etching process, in the first step, the concentration of the additive is 0.005 to 0.05 mol / L, and the temperature of the etching solution is 70 to 80 ° C. The current density is 15 to 25 mA / cm ² . Further, in the second etching process, the last etching step has a current density of 50 mA / cm ² or less.

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

  First, a high-purity aluminum foil having a purity of 99.99%, a thickness of 115 μm, and a (100) surface occupancy ratio of 98% was pretreated by being immersed in a 5 wt% sodium hydroxide aqueous solution at 30 ° C. for 30 seconds.

Next, in the first etching treatment, a current density of 150 mA / cm ² , an amount of electricity is 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. Electrolytic etching was performed at 20 C / cm ² .

Next, in the second etching process, an etching solution in which one or more of sulfuric acid, nitric acid, phosphoric acid, and oxalic acid is added as an additive to an aqueous hydrochloric acid solution under the etching conditions shown in Tables 1 to 6 is used. Then, the hole diameter of the aluminum foil was expanded under electrolysis conditions in which the total amount of electricity from the first stage to the last stage was 30 C / cm ² . At that time, the total amount of electricity was divided so that the amount of electricity was equal at each stage, and an etching foil sample was prepared.

  Next, the prepared 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 267 V with a 50 g / L boric acid aqueous solution. The finished thickness was measured. Here, the finished thickness of the etching foil was measured using a micrometer.

  Hereinafter, with respect to Conditions 1 to 155 and Conventional Examples 1 to 4, the measurement results of the etching conditions, the foil capacitance after the chemical conversion treatment, and the finished thickness after the etching are shown.

Conventional Example 1 has a total of two stages of pore size expansion, using an etching solution obtained by adding 0.025 mol / L sulfuric acid to a 0.50 mol / L hydrochloric acid aqueous solution, a current density of 20 mA / cm ² , and a total electric quantity. An etching foil sample at 30 C / cm ² and a liquid temperature of 75 ° C. 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 1-6. Etching foil samples were also prepared for nitric acid, phosphoric acid, and oxalic acid in addition to sulfuric acid, and the capacitance after chemical conversion and the finished thickness after etching were measured. The results are Conventional Examples 2 to 4, and the results are shown in Table 5.

[Comparison of additive concentration in the first stage and increase in current density in the second stage]
Table 1 shows data of Conditions 1 to 25 and Conventional Example 1. After the first etching process, a total of two etching steps are performed as the second etching process. At that time, the concentration of sulfuric acid added as an additive in the first-stage and second-stage etching processes was changed, and the capacitance was compared when the current density was changed. The concentration of the additive is set to 1.3 times in the second stage with respect to the first stage.

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: 0.003-0.060 mol / L sulfuric acid
Etching solution temperature: 75 ° C
Current density: 20 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: Sulfuric acid 0.0039-0.078 mol / L
Etching solution temperature: 75 ° C
Current density: 20 to 50 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 1, the horizontal axis represents the current density of the second stage, and each line L11 to L15 represents the concentration of the additive (sulfuric acid) of the etching solution used in the first stage,
Solid line L11: Sulfuric acid 0.003 mol / L
Solid line L12: sulfuric acid 0.005 mol / L
Solid line L13: sulfuric acid 0.025 mol / L
Solid line L14: 0.050 mol / L sulfuric acid
Solid line L15: sulfuric acid 0.060 mol / L
It is.

As can be seen from Table 1 and FIG. 1, the increase value of the current density of the next stage relative to the previous stage is set to +5 to 20 mA / cm ² (the range indicated by the arrow L1 in FIG. 1), and the additive in the first stage An increase in capacitance could be confirmed under conditions 7 to 9, conditions 12 to 14, and conditions 17 to 19 where the concentration was set to 0.005 to 0.05 mol / L.

More specifically, when the pore size is expanded in two stages, the first stage liquid temperature is fixed at 75 ° C., the current density is fixed at 20 mA / cm ² , and the sulfuric acid concentration in the 0.50 mol / L hydrochloric acid aqueous solution is The condition in which the current density in the second stage after that is in the range of 0.005 to 0.05 mol / L is increased in the range of +5 to +20 mA / cm ² with respect to the first stage is that after etching. There was a tendency that the decrease in the finished thickness was suppressed and the foil capacitance after the formation was increased (conditions 7-9, 12-14, 17-19). Among these, the condition in which the foil electrostatic capacity increased most was the condition 13, which has an effect of increasing the electrostatic capacity by 7.5% compared to the conventional example 1, and the finished thickness after the etching is also 100 μm conventionally. In contrast, it was 105 μm.

However, even if the current density in the second stage is increased in the range of +5 to +20 mA / cm ² with respect to the first stage, the concentration of sulfuric acid added to 0.50 mol / L hydrochloric acid in the first stage is In the etching conditions that do not satisfy the range of 0.005 to 0.05 mol / L, the foil capacitance decreased (Conditions 1 to 5, 21 to 25). From this, it can be seen that the concentration of sulfuric acid added as an additive in the first stage of pore diameter expansion is not preferable if it is less than 0.005 mol / L or more than 0.050 mol / L. If the additive is not in the optimum concentration range, it is considered that dissolution by hydrochloric acid proceeds excessively or is suppressed when the pore size is enlarged.

Even if the concentration of the sulfuric acid additive in the first stage is in the range of 0.005 to 0.050 mol / L, the increase value of the current density in the second stage with respect to the first stage is +5 to +20 mA / The foil capacitance decreased under conditions that did not satisfy cm ² (conditions 6, 10, 11, 15, 16, 20). From this, it can be seen that it is not preferable that the increase value of the current density in the second stage following the first stage is too small or too large. As the hole diameter increases and the pit diameter increases, the real area increases. Therefore, it is considered important to increase the current density value accordingly.

[Comparison of etchant temperature and current density at the first stage]
Table 2 shows the data of Conditions 26 to 50 and Conventional Example 1. After the first etching process, a total of two etching steps are performed as the second etching process. At that time, the concentration of sulfuric acid added as an additive in the etching process from the first stage to the second stage is changed, and when the current density is changed, the etching solution temperature and the current density value in the first stage are changed. Comparison of electrostatic capacity was performed. The concentration of the additive is set to 1.3 times the second stage with respect to the first stage, and the current density is increased by 15 mA / cm ² at the second stage relative to the first stage. is there. Further, the capacitance comparison was performed by changing the liquid temperature in the first and second etching steps.

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: 0.025 mol / L sulfuric acid
Etching liquid temperature: 65 to 85 ° C.
Current density: 10 to 30 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: Sulfuric acid 0.0325 mol / L
Etching liquid temperature: 65 to 85 ° C.
Current density: 25 to 45 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 2, the horizontal axis is the current density of the first stage, and each of the lines L21 to L25 indicates the temperature of the etchant,
Solid line L21: liquid temperature 65 ° C.
Solid line L22: Liquid temperature 70 ° C
Solid line L23: Liquid temperature 75 ° C
Solid line L24: Liquid temperature 80 ° C
Solid line L25: liquid temperature 85 ° C.
It is.

As can be seen from Table 2 and FIG. 2, the current density of the first stage is set to 15 to 25 mA / cm ² (the range indicated by the arrow L2 in FIG. 2), and the etching solution temperature is set to 70 to 80 ° C. The increased capacitance was confirmed under the conditions 32-34, conditions 37-39, and conditions 42-44.

More specifically, when the hole diameter is expanded in two stages, the etching solution temperature is in the range of 70 to 80 ° C. and the current density in the first stage is in the range of 15 to 25 mA / cm ² , and then The condition in which the current density at the second stage following the step increases by +15 mA / cm ^{2 with} respect to the current density at the first stage suppresses a decrease in the finished thickness after etching, and the foil capacitance after formation Also increased (conditions 32-34, 37-39, 42-44).

Among these, the conditions in which the foil capacitance increased most were the etching temperature of condition 38 at 75 ° C., the first stage current density of 20 mA / cm ² and the second stage current density of 35 mA / cm ^2. As a result, the capacitance was increased by 7.5% compared to the conventional example 1, and the finished thickness after the etching was 105 μm compared to the conventional 100 μm.

  However, if the liquid temperature in the first and second stages was too low at 65 ° C. or too high at 85 ° C., the foil capacitance was reduced (conditions 26-30, 46-50). From this, it is understood that the liquid temperature is an important factor for determining the foil capacitance, and the optimum liquid temperature is in the range of 70 to 80 ° C. If the liquid temperature is too low at 65 ° C., the pore diameter does not expand, and even if it is too high at 85 ° C., the pore diameter increases rapidly, resulting in surface collapse and a decrease in capacitance.

The etching liquid temperature even meet the range of 70 to 80 ° C. The current density of the first stage is 10 mA / cm ² and too low condition (condition 31,36,41) and, 30 mA / cm ² and too high condition (Conditions 35, 40, and 45) show that the foil electrostatic capacity is lowered and the finished thickness after etching is also reduced. It is necessary to set an optimum value as the current density according to the etched foil surface area.

[Comparison of increase in additive concentration in the first stage and increase in additive concentration in the second stage]
Table 3 shows data of Conditions 51 to 85 and Conventional Example 1. After the first etching process, a total of two etching steps are performed as the second etching process. At that time, the concentration of sulfuric acid added as an additive in the etching process from the first stage to the second stage is changed, and the current density is changed, so that the additive concentration in the first stage (0.003 to 0.0075 mol / L) is changed. ) Was compared with the volume when the amount of increase in additive concentration in the second stage was changed from 0.8 to 2.0 times. The current density is increased by 15 mA / cm ² in the second stage relative to the first stage.

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: 0.003-0.075 mol / L sulfuric acid
Etching solution temperature: 75 ° C
Current density: 20 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.50 mol / L
Additive: 0.8 to 2.0 times the first stage Etching liquid temperature: 75 ° C
Current density: 35 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 3, the horizontal axis is the concentration ratio of the second-stage additive (sulfuric acid) to the first stage, and each line L31 to L35 indicates the first-stage additive (sulfuric acid) concentration,
Solid line L31: first-stage additive (sulfuric acid) concentration 0.003 / mol / L
Solid line L32: first stage additive (sulfuric acid) concentration 0.005 / mol / L
Solid line L33: first stage additive (sulfuric acid) concentration 0.025 / mol / L
Solid line L34: first stage additive (sulfuric acid) concentration 0.050 / mol / L
Solid line L35: first stage additive (sulfuric acid) concentration 0.075 / mol / L
It is.

  As can be seen from Table 3 and FIG. 3, the additive (sulfuric acid) concentration in the second stage is set to 1.2 to 1.4 times (range indicated by arrow L3 in FIG. 3) with respect to the first stage. The capacitance increase was confirmed under conditions 60 to 62, conditions 67 to 69, and conditions 74 to 76 in which the sulfuric acid concentration in the first stage was set to 0.005 to 0.050 mol / L.

More specifically, when the pore size is expanded in two stages, the first stage liquid temperature is fixed at 75 ° C., the current density is fixed at 20 mA / cm ² , and the sulfuric acid concentration in the 0.50 mol / L hydrochloric acid aqueous solution is The concentration of sulfuric acid in the second stage that follows is increased by 1.2 to 1.4 times that of the first stage, and the value is 0.006 to 0. The conditions in the range of .05 mol / L suppressed the decrease in the finished thickness after etching, and increased the foil capacitance after formation (conditions 60 to 62, 67 to 69).

The first stage liquid temperature is fixed at 75 ° C., the current density is fixed at 20 mA / cm ² , the sulfuric acid concentration in the 0.50 mol / L hydrochloric acid aqueous solution is 0.05 mol / L, and the subsequent second stage Even if the sulfuric acid concentration increases by 1.2 to 1.4 times that of the first stage and the value is in the range of 0.06 to 0.07 mol / L, the finished thickness after etching is reduced. Was suppressed, and the foil capacitance after the formation was increased (conditions 74 to 76).

  Among these, the condition in which the foil capacitance increased most was the condition 68, which showed an effect of increasing the foil capacitance of 7.5% compared to the conventional example 1, and the finished thickness after the etching was 100 μm conventionally. On the other hand, it increased to 105 μm.

  However, even if the sulfuric acid concentration in the second stage is increased in the range of 1.2 to 1.4 times that in the first stage, the sulfuric acid concentration added to 0.50 mol / L hydrochloric acid in the first stage is Conditions that did not satisfy the range of 0.005 to 0.05 mol / L resulted in a decrease in foil capacitance (conditions 53 to 55, 81 to 83). From this, it can be seen that the additive concentration in the first stage of pore diameter expansion is not preferable if it is less than 0.005 mol / L or more than 0.050 mol / L.

  Moreover, even if the sulfuric acid as the additive in the first stage is 0.050 mol / L, the additive concentration in the next second stage is 1.2 to 1.4 times that in the first stage. It was found that the capacitance was lowered under conditions other than the conditions (conditions 72, 73, 77, 78).

  Similarly, even if the sulfuric acid concentration in the first stage satisfies the range of 0.005 to 0.05 mol / L, the concentration of sulfuric acid in the second stage is 1.2 to 1.4 times that in the first stage. The condition that is not satisfied results in a decrease in foil capacitance (conditions 58, 59, 63 to 66, 70 to 73, 77, and 78). From now on, even if the increase value of sulfuric acid, which is the additive in the second stage following the first stage, is too small, such as 0.8 times or 1.0 times, it is too much as 1.5 times or 2.0 times. It can also be seen that this does not lead to an increase in foil capacitance. It can be seen that there is an optimum additive concentration range in order to advance the pore diameter expansion so that the foil surface remains as much as possible.

  The etching conditions for the concentration of the first-stage additive (sulfuric acid) to deviate from 0.005 to 0.05 mol / L are the foil even if the sulfuric acid concentration in the next stage is 1.2 to 1.4 times that in the previous stage. The capacitance is reduced (conditions 51 to 57, 79 to 85).

[Comparison of hydrochloric acid concentration and additive concentration in the first stage]
Table 4 shows data for conditions 86 to 110 and Conventional Example 1. After the first etching process, a total of two etching steps are performed as the second etching process. At that time, the concentration of sulfuric acid added as an additive in the etching process from the first stage to the second stage was changed, and when the current density was changed, the hydrochloric acid concentration and the additive concentration in the first stage were changed. Comparison of capacitance was performed. The concentration of the additive was set to 1.3 times the second stage with respect to the first stage, and the current density was increased by 15 mA / cm ² at the second stage relative to the first stage. .

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.05 to 1.0 mol / L
Additive: Sulfuric acid 0.003 to 0.100 mol / L
Etching solution temperature: 75 ° C
Current density: 20 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.05 to 1.0 mol / L
Additive: Sulfuric acid 0.0039-0.1300 mol / L
Etching solution temperature: 75 ° C
Current density: 35 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 4, the horizontal axis represents the sulfuric acid addition concentration in the first stage, and each of the lines L41 to L45 represents the hydrochloric acid concentration,
Solid line L41: hydrochloric acid concentration 0.05 mol / L
Solid line L42: hydrochloric acid concentration 0.1 mol / L
Solid line L43: hydrochloric acid concentration 0.5 mol / L
Solid line L44: hydrochloric acid concentration 0.6 mol / L
Solid line L45: hydrochloric acid concentration 1.0 mol / L
It is.

  As can be seen from Table 4 and FIG. 4, the sulfuric acid addition concentration in the first stage is set to 0.005 to 0.050 mol / L (range indicated by the arrow L4 in FIG. 4), and the hydrochloric acid concentration in the etching solution is set to 0.00. An increase in capacitance could be confirmed under conditions 92 to 94, conditions 97 to 99, and conditions 102 to 104 set to 1 to 0.6 mol / L.

More specifically, when the pore size is expanded in two stages, the first stage liquid temperature is fixed at 75 ° C., the current density is fixed at 20 mA / cm ² , and the base hydrochloric acid and sulfuric acid added as an additive are added. The concentration value was changed. As a result, when the hydrochloric acid concentration is 0.1 to 0.6 mol / L and the sulfuric acid concentration is 0.005 to 0.050 mol / L, the decrease in the finished thickness after etching is suppressed, and the foil capacitance after formation is also reduced. A tendency to increase was obtained (conditions 92-94, 97-99, 102-104).

  Among these, the condition in which the foil capacitance increased most was the condition 98, which had an effect of increasing the capacitance by 7.5% with respect to the conventional example 1, and the finished thickness after completion of the etching was also compared with the conventional 100 μm. 105 μm.

  However, when the hydrochloric acid concentration is as low as 0.05 mol / L or as high as 1.0 mol / L, the foil capacitance decreases (conditions 86 to 90, 106 to 110). From this, it can be seen that the hydrochloric acid concentration in the first stage when the pore diameter is enlarged is less than 0.010 mol / L or more than 0.60 mol / L, resulting in a decrease in capacitance.

  In addition, even if the hydrochloric acid concentration satisfies the range of 0.10 to 0.60 mol / L, the condition that the sulfuric acid added as an additive is not in the range of 0.005 to 0.050 mol / L is a decrease in foil capacitance. (Conditions 91, 95, 96, 100, 101, 105).

  From this, it can be seen that not only the concentration of hydrochloric acid as a base but also the value of sulfuric acid added as an additive is too small or too large, which does not lead to an increase in capacitance.

[Comparison of additive type and additive concentration in the first stage]
Table 5 shows the data of Conditions 111 to 130 and Conventional Example 1. After the first etching process, a total of two etching steps are performed as the second etching process. At that time, changing the type of additive and the additive concentration in the first stage, changing the additive concentration in the etching process from the first stage to the second stage, and comparing the current density, the capacitance comparison Was done. The concentration of the additive is set to 1.3 times the second stage with respect to the first stage, and the current density is increased by 15 mA / cm ² at the second stage relative to the first stage. is there.

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.5 mol / L
Additive: Sulfuric acid 0.003 to 0.100 mol / L
: Nitric acid 0.003-0.100 mol / L
: Phosphoric acid 0.003-0.100 mol / L
: Oxalic acid 0.003 to 0.100 mol / L
Etching solution temperature: 75 ° C
Current density: 20 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.5 mol / L
Additive: Sulfuric acid 0.0039 to 0.130 mol / L
: Nitric acid 0.0039 to 0.130 mol / L
: Phosphoric acid 0.0039-0.130 mol / L
: Oxalic acid 0.0039 to 0.130 mol / L
Etching solution temperature: 75 ° C
Current density: 35 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 5, the horizontal axis represents the first-stage additive concentration, and each line L51 to L54 represents the type of additive,
Solid line L51: Additive: Sulfuric acid Solid line L52: Additive: Nitric acid Solid line L53: Additive: Phosphoric acid Solid line L54: Additive: Oxalic acid.

  As can be seen from Table 5 and FIG. 5, in any additive, the condition 112 in which the additive concentration in the first stage was set to 0.005 to 0.050 mol / L (range indicated by arrow L5 in FIG. 5). Up to 114, conditions 117 to 119, conditions 122 to 124, and conditions 127 to 129 were confirmed to have increased capacitance.

More specifically, when the pore size is expanded in two stages, the liquid temperature in the first stage is fixed at 75 ° C., the current density is fixed at 20.0 mA / cm ^2, and added in a 0.05 mol / L hydrochloric acid aqueous solution. The type of agent was changed from conventional sulfuric acid to other nitric acid, phosphoric acid, and oxalic acid. As the respective conventional examples, the conventional example 1 is used for sulfuric acid, the conventional example 2 is used for nitric acid, the conventional example 3 is used for phosphoric acid, and the conventional example 4 is used for oxalic acid. Even in the case of additives other than sulfuric acid, when the concentration to be added is in the range of 0.005 to 0.050 mol / L, the decrease in the finished thickness after etching is suppressed, and the capacitance after formation is increased ( Conditions 112-114, 117-119, 122-124, 127-129). Any additive can be used to increase the foil capacitance, but the condition that maximizes the foil capacitance was the condition 129 using oxalic acid.

  However, the foil capacitance decreases under conditions where the first-stage additive concentration does not satisfy the range of 0.005 to 0.05 mol / L (conditions 111, 115, 116, 120, 121, 125, 126, 130). ). From this, it can be seen that the additive concentration in the first stage of pore size expansion is less than 0.005 mol / L or more than 0.050 mol / L, which does not lead to an increase in foil capacitance.

[Comparison of additive concentration in the first stage and current density in the last stage]
Table 6 shows the data of Conditions 131 to 155 and Conventional Example 1. After the first etching process, a total of three etching steps are performed as the second etching process. At that time, capacitance comparison was performed when the additive concentration was changed in the etching process from the first stage to the third stage and the current density was further changed. Note that the concentration of the additive is set to 1.3 times that of the former stage in the latter stage, and the current density in the first stage is set to 20 mA / cm ² .

(First stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.5 mol / L
Additive: 0.003-0.060 mol / L sulfuric acid
Etching solution temperature: 75 ° C
Current density: 20 mA / cm ²
Electricity: 15 C / cm ²

(Second-stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.5 mol / L
Additive: Sulfuric acid 0.0039-0.0780 mol / L
Etching solution temperature: 75 ° C
Current density: 20 to 50 mA / cm ²
Electricity: 15 C / cm ²

(Third stage etching conditions)
Etching solution (hydrochloric acid aqueous solution): hydrochloric acid 0.5 mol / L
Additive: Sulfuric acid 0.0051 to 0.1014 mol / L
Etching solution temperature: 75 ° C
Current density: 20 to 60 mA / cm ²
Electricity: 15 C / cm ²

  Etching was performed under the above conditions to produce 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 and FIG.

In FIG. 6, the horizontal axis represents the current density of the third stage (final stage), and each line L61 to L65 represents the concentration of the additive (sulfuric acid) in the first stage,
Solid line L61: First stage additive (sulfuric acid) concentration 0.003 / mol / L
Solid line L62: first-stage additive (sulfuric acid) concentration 0.005 / mol / L
Solid line L63: first-stage additive (sulfuric acid) concentration 0.025 / mol / L
Solid line L64: concentration of the first stage additive (sulfuric acid) 0.050 / mol / L
Solid line L65: first stage additive (sulfuric acid) concentration 0.060 / mol / L
It is.

As can be seen from Table 6 and FIG. 6, the current density of the third stage is 50 mA / cm ² or less, preferably the current density of the third stage is 30 to 50 mA / cm ² (the range indicated by the arrow L6 in FIG. 6). In the conditions 137 and 138, the conditions 142 and 143, and the conditions 147 and 148 in which the additive concentration in the first stage was set to 0.005 to 0.050 mol / L, it was confirmed that the capacitance was increased.

More specifically, when the pore size is expanded in three stages, the first stage liquid temperature is 75 ° C., the current density is 20 mA / cm ² , and the sulfuric acid concentration in the 0.05 mol / L hydrochloric acid aqueous solution is 0.00. In the range of 003 to 0.060 mol / L, the current density of the subsequent stage is increased in the range of +5 to +20 mA / cm ² , and the sulfuric acid concentration is also 1.2 to 1.4 times that of the previous stage. Under the condition that the hole diameter was expanded in total of 3 steps by the method of adjusting to 1.3 times within the range of the above, the reduction of the finished thickness after etching was suppressed, and the foil capacitance after formation was also reduced There was a tendency to increase (conditions 137, 138, 142, 143, 147, 148).

However, the foil capacitance decreased under the conditions (conditions 139, 144, 149) in which the current density exceeded 50 mA / cm ² at the final stage of the hole diameter expansion. In addition, there are those in which the increase value of the current density of the next stage with respect to the previous stage is out of the range of +5 to +20 mA / cm ² and does not increase (conditions 136, 141, 146) or too high (conditions 140, 145, 150). Similarly, the foil capacitance decreased.

From these, it was found that it is important that the current density of the final stage does not exceed 50 mA / cm ² .

(Summary)
From the above results, in the method for manufacturing an electrolytic capacitor electrode foil in which the etching process is performed in two stages, the second etching process is performed when the first etching process for generating etching pits and the second etching process for expanding the hole diameter are performed. The liquid temperature in the etching process is 70 to 80 ° C., the etching liquid is mainly hydrochloric acid in the range of 0.10 to 0.60 mol / L, and additives (sulfuric acid, nitric acid, phosphoric acid, oxalic acid) are added to 0.005. Using a mixed solution to which ~ 0.05 mol / L was added, the concentration of the additive in the next stage relative to the previous stage was set to 1.2 to 1.4 times, and the increase in current density was set to the range of 5 to ²⁰ mA / cm ^2. , etching is performed in multiple stages, it is carried out in a range current density of 15~25mA / cm ² in the first hole diameter enlargement, with the hole diameter enlargement efficiently, suppressing the dissolution of the etching foil surface Rukoto can. Therefore, the effect of suppressing the foil thickness reduction is obtained, and the capacity can be further increased.

  In addition, in the above conditions, a liquid obtained by adding sulfuric acid to an aqueous hydrochloric acid solution was mainly used as an etching liquid at the time of pore size enlargement, but nitric acid, phosphoric acid, oxalic acid may be used in addition to this, hydrochloric acid, sulfuric acid, A mixture of two or more of nitric acid, phosphoric acid and oxalic acid may be used.

In a 2nd etching process, it is a graph which shows an electrostatic capacitance change at the time of changing the increase amount of the additive density in the 1st step, and the current density in the 2nd step. It is a graph which shows an electrostatic capacitance change at the time of changing etching liquid temperature and the current density in the 1st step in the 2nd etching process. In a 2nd etching process, it is a graph which shows an electrostatic capacitance change at the time of changing the increase amount of the additive concentration in the 1st step, and the additive concentration in the 2nd step. It is a graph which shows an electrostatic capacitance change at the time of changing hydrochloric acid concentration and additive concentration in the 1st step in the 2nd etching treatment. In a 2nd etching process, it is a graph which shows the electrostatic capacitance change at the time of changing the kind of additive and the additive density | concentration in the 1st step. In a 2nd etching process, it is a graph which shows an electrostatic capacitance change at the time of changing the additive density | concentration in the 1st step | paragraph, and the current density in the last step | paragraph.

Claims (4)

In the manufacturing method of an aluminum electrode foil for an electrolytic capacitor, which mainly includes a first etching process that generates etching pits and a second etching process that mainly enlarges the hole diameter after the first etching process.
In the second etching process, a multi-stage etching process is performed using an etching solution in which at least one of sulfuric acid, nitric acid, phosphoric acid, and oxalic acid is added to an aqueous hydrochloric acid solution as an additive,
In the multi-stage etching process, both the concentration of the additive and the current density in the subsequent etching process are higher than those in the previous etching process. . The hydrochloric acid aqueous solution is an aqueous solution of hydrochloric acid 0.10 to 0.60 mol / L,
In the multiple-stage etching process, the concentration of the additive in the subsequent etching process is 1.2 to 1.4 times that in the previous etching process, and the increase in current density is 5 to 20 mA / cm ^2. The manufacturing method of the aluminum electrode foil for electrolytic capacitors of Claim 1 characterized by the above-mentioned. In the second etching process, in the first etching step, the concentration of the additive is 0.005 to 0.05 mol / L, the temperature of the etching solution is 70 to 80 ° C., and the current is The method for producing an aluminum electrode foil for electrolytic capacitors according to claim ² , wherein the density is 15 to 25 mA / cm2. 4. The aluminum electrode foil for an electrolytic capacitor according to claim 1, wherein in the second etching process, a current density of the final etching process is 50 mA / cm ² or less. 5. Production method.

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