JP4811939B2 - Formation method of electrode foil for electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for forming an electrode foil for an electrolytic capacitor.

  Conventionally, in an electrolytic capacitor in which a high ripple current is applied or rapid charge / discharge is performed, a further reduction in leakage current is required. The aluminum electrode foil used in such an electrolytic capacitor has a rough surface. A porous film is formed by applying an electric current to the surface of the converted aluminum foil and applying an electric current in a chemical conversion solution containing at least one of sulfuric acid, oxalic acid and phosphoric acid that can form a porous film. And then producing an amorphous barrier-type film using a single aqueous solution of boric acid, adipic acid, phosphoric acid, or a salt thereof or a mixed aqueous solution thereof (for example, Non-Patent Document 1). reference).

Further, a chemical conversion method having a film shape in which a porous film remains at least 30 nm or more over the entire surface of the film after the generation of the barrier film is known (for example, patent document). 1).
In addition, there is a method in which a chemical treatment process is performed in which a chemical treatment of an aluminum foil is performed in the same solution as a chemical conversion solution capable of generating a porous film (see, for example, Patent Document 2).
Furthermore, there is also a method of forming a thin oxide film (Pre film) on the surface of the electrode foil before generating a film having a withstand voltage of 100 V or less (see, for example, Patent Document 3).
JP-A-8-293441 JP-A-6-302476 Japanese Patent Publication No. 07-082968 By Nagata Isaya, “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nippon Electric Storage Co., Ltd., February 24, 1997, P272-278

In response to the above-described reduction in leakage current, in the chemical conversion method having a film shape in which at least 30 nm or more of the porous film remains on the entire surface of the film after the generation of the barrier film described in Patent Document 1, the amount of electricity required for generating the porous film is It has increasing drawbacks.
Further, in the method of providing a chemical treatment step of performing chemical treatment of aluminum foil in the same solution as the chemical conversion solution capable of generating a porous film described in Patent Document 2, the dissolution of aluminum is remarkably high, and etching holes formed at high density are formed. The structure is broken and the electrostatic capacity is lowered.
Furthermore, in the method of forming a thin oxide film (Pre film) on the surface of the electrode foil before the generation of a film having a withstand voltage of 100 V or less described in Patent Document 3, it is effective if the film is thick as in the case of medium to high pressure conversion. Is small.
The present invention solves the above problems, prevents a decrease in electrostatic capacity due to dissolution of the etched portion, can reduce the leakage current even for high withstand voltage products without increasing the amount of chemical electricity, The present invention provides a method for producing an electrode foil for electrolytic capacitors that can withstand high ripple current and rapid charge / discharge.

That is, the present invention generates a porous film by using a chemical liquid containing at least one of sulfuric acid, oxalic acid, and phosphoric acid to form a porous film on the surface of the aluminum foil, and generates a barrier film. A film that is formed in the porous film forming process by providing a chemical treatment process with 0.02 to 0.20 g / L aqueous sodium hydroxide before the porous film forming process. The method for forming an electrode foil for an electrolytic capacitor, wherein the thickness is 50 to 80% of the thickness of the barrier type film .

  According to the present invention, compared with the prior art, the etched portion is not dissolved and the capacitance is not lowered. Therefore, even for a high voltage product, the leakage current can be reduced without increasing the amount of chemical formation. It is possible to provide an electrolytic capacitor electrode foil manufacturing method that can be realized and can withstand high ripple current and rapid charge / discharge.

  Examples of the present invention will be described below.

[ Examples 2 , 5, 8 , 9 and Comparative Examples 1 and 10] Sodium hydroxide treatment solution concentration comparison In Examples 2 , 5 , 8 , 9 and Comparative Examples 1 and 10, high ripple current and rapid charge and discharge were observed. In manufacturing the aluminum electrode foil used for the electrolytic capacitor to be loaded, in the chemical treatment step, as shown in Table 1, the liquid temperature is 60 ° C., and the concentrations are 0.01, 0.02, 0.04, 0, respectively. .10, 0.20, 0.30 g / L Aqueous solution of sodium hydroxide in an aqueous solution of sodium hydroxide (etching foil) for 5 minutes, and then in a porous film forming step, sulfuric acid having a liquid temperature of 45 ° C. and a concentration of 20 g / L In an aqueous solution, a direct current is applied for 11 minutes at a current density of 50 mA / cm 2 to form a porous film having a thickness of 560 nm on the surface of the aluminum foil.
Next, in the barrier type film forming step, 100 g of boric acid and 0.04 g of ammonium borate are dissolved in pure water to form a 1 L aqueous solution, heated to 90 ° C., and the aqueous solution (chemical conversion solution) Then, the aluminum foil on which the porous film is formed is immersed, formed at a current density of 25 mA / cm ² up to a formation voltage of 600 V, and held at the formation voltage for 30 minutes, thereby sealing the porous film. Further, a barrier-type film was formed on the porous-type film to produce an amorphous barrier-type film having a thickness of 840 nm (thickness ratio of porous-type / barrier-type film = 560 / 840≈66.7%). .

[Example 4-7, Comparative Example 3]-porous / barrier type thickness ratio Comparative Examples 4-7 of the film, in the chemical treatment step in Comparative Example 3, as shown in Table 1, the liquid temperature is 60 ° C., The etching foil is immersed in an aqueous sodium hydroxide solution having a concentration of 0.04 g / L for 5 minutes, and the subsequent porous film forming step is performed under the same conditions as in Comparative Example 1, respectively 7, 8, 11, 13, 14 For example, a direct current is applied for a minute to form a porous film of 380, 420, 560, 670, and 710 nm on the surface, and the subsequent barrier film formation process is performed under the same conditions as in Example 1. went.
As a result, the thickness ratio of the porous type / barrier type film was 380/840 (≈45.2%), 420/840 (= 50.0%), 560/840 (≈66.7%), 670 / 840 (≈79.8%) and 710/840 (≈84.5%) films were formed.

(Conventional example 1)
In Conventional Example 1, the chemical treatment process as in Comparative Example 1 was not provided, and the porous film generation process and the barrier film generation process were the same as in Comparative Example 1.

(Conventional example 2)
In Conventional Example 2, without providing the chemical processing steps such as Comparative Example 1, the porous type film generation process, except that the applied time 14 minutes was the same as Comparative Example 1, produces a porous type coating thickness 710nm Next, a barrier type film generation step was provided in the same manner as in Comparative Example 1.

(Conventional example 3)
In Conventional Example 3, in the chemical treatment step, the etching foil was immersed in a 20 g / L sulfuric acid aqueous solution having a liquid temperature of 45 ° C. for 2 minutes, and the subsequent porous type film generation step and barrier type film generation step were the same as in Comparative Example 1. It was.

[Examples 11 and 12] Comparison of chemical conversion liquids for producing a porous film In Examples 11 and 12, in the porous film production process of Example 5, instead of in a sulfuric acid aqueous solution having a liquid temperature of 45 ° C and a concentration of 20 g / L. In the same manner as in Example 1 except that an oxalic acid aqueous solution having a liquid temperature of 45 ° C., a concentration of 100 g / L, and a phosphoric acid aqueous solution having a concentration of 50 g / L were used, a chemical treatment and a barrier-type film formation were carried out. A film having a / barrier type film thickness ratio of 560/840 (≈66.7%) was produced.

About the electrode foil for electrolytic capacitors obtained by the above-described Examples 2, 4 to 6, 8 , 9 , 11 to 12, Comparative Examples 1, 3, 7, 10 and Conventional Examples 1 to 3, the liquid temperature was 90. The leakage current was measured in a boric acid aqueous solution at 100 ° C. and a concentration of 100 g / L, and then the capacitance was measured in an aqueous ammonium borate solution at a liquid temperature of 30 ° C. and a concentration of 100 g / L. Moreover, the amount of chemical electricity used for the anodic oxidation of the aluminum foil was also measured. The results are shown in Table 1.

[Sodium hydroxide treatment solution concentration comparison]
As is clear from Table 1 , the electrolytic capacitor electrode foils of Examples 2 , 5 , 8 , and 9 have reduced leakage current as compared with Conventional Example 1, and the capacitance is equivalent to Conventional Example 1. I understand.
In addition, the electrolytic capacitor electrode foils of Examples 2, 5, 8, and 9 have the same leakage current as that of Conventional Examples 2 and 3, and the capacitance is higher than that of Conventional Examples 2 and 3.
Moreover, it turns out that the range of 0.02-0.20 g / L is suitable for the density | concentration of sodium hydroxide aqueous solution (Example 2, 5, 8, 9). Dissolution occurs at 0.30 g / L, leading to a decrease in capacitance ( Comparative Example 10). Further, when the sodium hydroxide concentration is 0.01 g / L, the chemical treatment effect is hardly obtained and the leakage current reducing effect is hardly obtained ( Comparative Example 1).

[Comparison of thickness ratio of porous type / barrier type film]
Furthermore, as is clear from Table 1, it can be seen that the thickness ratio of the porous type / barrier type coating is preferably in the range of 50 to 80% (Examples 4 to 6). When the porous film is thin and the ratio is 45%, the leakage current is high ( Comparative Example 3), and when the porous film is thick and the ratio is 85%, the amount of chemical electricity is increased ( Comparative Example 7).

[Comparison of chemical liquids for porous film formation]
Furthermore, as apparent from Table 1, the chemical conversion liquid used in the porous film forming step can obtain the same effect as described above even when oxalic acid or phosphoric acid is used in addition to sulfuric acid ( Examples 11 and 12).

In the said Example, although the sulfuric acid, the oxalic acid, and phosphoric acid were used as a chemical conversion liquid used at a porous type | mold film | membrane production | generation process, these can also be used in mixture of 2 or more types.
In the above examples, an aqueous solution in which boric acid and ammonium borate were dissolved was used in the barrier type film forming step after the porous type film was formed. However, an aqueous solution of phosphoric acid or phosphate, adipic acid or adipine You may use the aqueous solution of an acid salt individually or in mixture.
Further, in the barrier-type film generation step, after reaching a predetermined formation voltage, so-called depolarization treatment such as heat treatment or acid immersion treatment and repair formation may be repeated.

Claims (1)

A porous film forming step of generating a porous film on the surface of the aluminum foil using a chemical conversion solution containing at least one of sulfuric acid, oxalic acid and phosphoric acid ;
A barrier type film generation step for generating a barrier type film,
Before the porous film production step, a chemical treatment step with 0.02 to 0.20 g / L sodium hydroxide aqueous solution is provided ,
A method for forming an electrode foil for an electrolytic capacitor , wherein the film thickness generated in the porous film forming step is 50 to 80% of the barrier film thickness .