JPH0775215B2 - Method for etching aluminum foil for electrolytic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for etching an aluminum foil for an electrolytic capacitor, and more specifically to a method for etching an electrode foil for an aluminum electrolytic capacitor for medium and high voltage.

[Conventional technology]

For this type of electrode foil, an aluminum foil to be used as an electrode body is used which is electrically or chemically etched to increase the effective surface area.

Although various methods have been proposed for increasing the surface expansion rate, generally, aluminum foil is electrically etched in a chloride aqueous solution to which a film-forming acid such as sulfuric acid, oxalic acid, or phosphoric acid is added to form a pit. Pre-stage etching to form a large number of, and electrical or chemical etching in an aqueous solution containing at least one or more of chlorine ions, sulfate ions, nitrate ions, to dissolve aluminum along the inner wall of the pit,
It is performed in combination with post-stage etching that makes the pit diameter the target thickness.

[Problems to be Solved by the Invention]

The aluminum foil contains 10 to 50 ppm of copper as an impurity. Therefore, when continuous etching is industrially performed, a certain amount of copper increases in the electrolytic solution in each of the former and latter stages.

The presence of copper ions in the electrolytic solution promotes surface dissolution of the aluminum foil. This is proportional to the amount of copper ions present, and if the amount of copper ions increases, dissolution of the foil surface will occur more easily than dissolution of the inner diameter of the pits, resulting in a large reduction in surface expansion rate.

For this reason, conventionally, the electrolytic solution is regularly renewed or a special treatment facility is installed to remove copper ions, but this causes a problem of cost increase. In addition, since the line needs to be stopped each time the electrolytic solution is renewed, productivity is adversely affected.

[Means for Solving the Problems]

To solve the above problems, in the present invention, a first etching step of electrically etching an aluminum foil in a predetermined electrolytic solution to form a large number of pits,
In order to make the diameter of the pits formed in the same step the target thickness, the second step of performing electrical or chemical etching in an electrolytic solution containing at least one kind of chloride ion, sulfate ion and nitrate ion A method of etching an aluminum foil for an electrolytic capacitor, which comprises an etching step, is characterized in that a predetermined amount of carbon group metal element ions is added to the electrolytic solution used in the second etching step. In this case, the carbon group metal element ion is preferably selected from germanium ion, tin ion and lead ion. Moreover, the addition amount is preferably in the range of 0.01 to 1000 ppm.

Note that direct current electrolytic etching is particularly effective for electrical etching in the first etching step in which a large number of pits are generated. As the electrolytic solution, sulfuric acid, phosphoric acid, oxalic acid, etc. are added to a hydrochloric acid aqueous solution at a concentration of 1% or less. It is preferable to add it. In addition, hydrochloric acid was added to the sulfuric acid solution as an additive.
It is also preferable to add 0.5 to 10%. Furthermore, this first
The etching step may be divided into two steps, and after the above hydrochloric acid-based electrolytic etching, sulfuric acid-based electrolytic etching may be performed. Also, chemical soft etching may be performed before the first etching step.

There are two methods of chemical etching and electrolytic etching in the second etching step for increasing the pit diameter. In the former case, nitric acid solution with phosphoric acid or oxalic acid added at a concentration of 1% or less, hydrochloric acid solution with It is preferable to use sulfuric acid, phosphoric acid, oxalic acid or the like added at a concentration of 1% or less as an additive, or 0.5 to 10% hydrochloric acid added as an additive to the aqueous solution of sulfuric acid as an electrolytic solution. This electrolytic solution can also be used for electrolytic etching.

[Action]

By adding carbon group metal element ions to the electrolytic solution in the second etching step, surface dissolution of the aluminum foil by copper ions is suppressed.

〔Example〕

Hereinafter, an example of the present invention will be described in comparison with a conventional example.

[Conventional example] Aluminum foil used; thickness 104 μm, purity 99.99% First etching step; aluminum foil was immersed in an electrolyte solution containing hydrochloric acid 5 wt% and sulfuric acid 0.02 wt% at a liquid temperature of 80 ° C., and current density was 200 mA / Energize for 60 seconds with a DC current of cm ² .

Second etching step; aluminum foil having pits formed in the previous step is added with nitric acid 7 wt% and phosphoric acid 0.1 wt% at a liquid temperature of 85
Chemical etching is performed by immersing in the electrolytic solution at ℃ for 15 minutes.

First, the aluminum foil is etched in the first etching step to form pits on its surface, and then the copper ion concentration in the electrolytic solution in the second etching step is adjusted to 0.
Etching was carried out at 2, 0.4, 0.6, 0.8, and 1.0 ppm to obtain 6 types of aluminum foil which had been subjected to etching treatment as a conventional example including those without copper ions. Then, these aluminum foils were subjected to chemical conversion at a chemical conversion voltage of 200 V in a boric acid% aqueous solution (liquid temperature 85 ° C.), and the chemical conversion capacity was measured. The results are shown in Table 1 below. The graph is shown in FIG.

Example 1 Assuming that the aluminum foil and the first and second etching conditions were the same, lead nitrate was used in an electrolytic solution having a copper ion concentration of 1.0 ppm, which markedly reduces the capacity in the conventional example, to produce lead (Pb) ions. 0.01, 0.1, 1.0, 10, 100, 1000ppm respectively
Amount of Lead Ion Added to Etched Foil and Part 20
The measurement results of 0V conversion capacity are shown in Table 2 below.

Example 2 In place of the lead ions of Example 1, stannous chloride was used to add tin (Sn) ions to 0.01, 0.1, 1.0, 10, respectively.
Table 3 on the next page shows the measurement results of the amount of tin ion added to the etched foil after adding 100 and 1000 ppm and its 200V conversion capacity.

[Example 3] In place of the lead ions of Example 1, germanium chloride was used to add germanium (Ge) ions to 0.0
Table 4 on the next page shows the measurement results of the amount of germanium ion added to the foil etched by adding 1,0.1,1.0,10,100,1000 ppm and its 200V conversion capacity.

Further, FIG. 1 shows a characteristic graph of the carbon group metal element ion addition amount in Examples 1 to 3 above and the foil 200 V conversion capacity. As is clear from the graphs of Tables 2 to 4 and FIG.
Effective addition amount of Pb, Sn, Ge is about 0.01-1000ppm
However, the more preferable addition amount is 0.1 to 100 ppm.

[Example 4] First, in the first etching step, the same aluminum foil as described above was immersed in an electrolytic solution containing hydrochloric acid 7% and phosphoric acid 0.01% at a liquid temperature of 80 ° C, and a DC current having a current density of 300 mA / cm ² was applied. It was Next, as a second etching step, a current density of 25% was set in an electrolytic solution containing hydrochloric acid 7% and sulfuric acid 30% at a liquid temperature of 80 ° C.
A direct current of 0 mA / cm ² was applied. Further, in the third etching step, the aluminum foil subjected to the second etching step was immersed in an electrolytic solution containing hydrochloric acid 7% and phosphoric acid 0.01% at a liquid temperature of 80 ° C. to perform chemical etching. At that time, an aqueous solution of lead nitrate was added to the electrolytic solution having a copper ion concentration of 0.5 ppm in the electrolytic solution so that the content in the electrolytic solution was 5 ppm.

The thus-obtained etched aluminum foil was formed at 200 V and its capacitance was measured to be 2.04 μF / cm ²
Met. By the way, the capacitance without lead is 1.3μF
It was / cm ² .

Example 5 First, in the first etching step, the same aluminum foil as described above was immersed in an electrolytic solution containing sulfuric acid 30% and hydrochloric acid 1.5% at a liquid temperature of 70 ° C., and a DC current having a current density of 250 mA / cm ² was applied. It was Next, as a second etching step, sulfuric acid is used.
The aluminum foil was immersed in an electrolytic solution containing 30% and 2% hydrochloric acid at a liquid temperature of 85 ° C. to perform chemical etching. At that time, an aqueous lead nitrate solution was added to the electrolytic solution having a copper ion concentration of 0.5 ppm in the electrolytic solution so that the content in the electrolytic solution was 3 ppm.

The etched aluminum foil thus obtained was formed at 200 V and its capacitance was measured to be 2.62 μF / cm ²
Met. On the other hand, the capacitance without lead is 1.
It was 4 μF / cm ² .

〔The invention's effect〕

As described above, according to the present invention, chlorine ion,
Contains at least one or more of sulfate ion and nitrate ion,
0.01 to 10 carbon group metal element ions, especially lead ions, tin ions, and germanium ions, are added to the electrolytic solution used in the final etching step for adjusting the pit diameter to the target thickness.
The addition of 00 ppm suppresses the surface dissolution of the aluminum foil due to copper ions. Therefore, it is not necessary to regularly update the electrolytic solution or to process copper ions.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of carbon group metal element ions added and the chemical conversion capacity according to the present invention, and FIG. 2 is a graph showing the relationship between the copper ion in the electrolytic solution and the chemical conversion capacity.

Claims (3)

[Claims] 1. A first etching step in which a large number of pits are formed by electrically etching an aluminum foil in a predetermined electrolytic solution, and the diameter of the pits formed in the same step is adjusted to a target thickness. Therefore, in the method for etching an aluminum foil for an electrolytic capacitor, which comprises a second etching step of performing electrical or chemical etching in an electrolytic solution containing at least one or more of chloride ions, sulfate ions and nitrate ions, A method for etching an aluminum foil for an electrolytic capacitor, which comprises adding a predetermined amount of carbon group metal element ions to an electrolytic solution used in the etching step of 2. 2. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the carbon group metal element ions are selected from germanium ions, tin ions and lead ions. 3. The amount of the carbon group metal element ions added is 0.01.
The method for etching an aluminum foil for an electrolytic capacitor according to claim 1 or 2, wherein the etching amount is about 1000 ppm.