JPH0812838B2 - Aluminum electrolytic capacitor electrode manufacturing method - Google Patents

Description

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

2. Description of the Related Art Generally, an aluminum electrolytic capacitor is small and has a large electrostatic capacity, and the rated working voltage is wide ranging from a low voltage class of several volts to a high voltage class of several hundred volts. It is used in many electronic devices ranging from industrial equipment. In particular, with the recent trend toward lighter, thinner, shorter, and smaller electronic devices in the consumer field, downsizing of electronic components,
In particular, miniaturization of aluminum electrolytic capacitors is strongly desired.

In order to miniaturize the aluminum electrolytic capacitor, it is indispensable to increase the electrode surface area of the aluminum electrolytic capacitor, and various electrolytic etching methods for this purpose have been studied.

This electrolytic etching method is roughly classified into a method using a direct current and a method using an alternating current. Generally, since a deep current is etched by a direct current, the etching shape has large irregularities, and an etching foil suitable for medium and high voltage is used. Is obtained. On the other hand, with an alternating current, etching is performed shallowly, so a fine uneven shape can be obtained, and an etching foil suitable mainly for low-voltage anodes and cathodes can be obtained.

Therefore, for the production of the low-voltage anode and cathode electrodes, an etching method using an alternating current is effective and variously developed and implemented.

That is, various etching methods have been carried out in which the AC current density is combined with various factors such as additives such as inorganic acids and organic acids to etching solutions such as hydrochloric acid and sodium chloride, and solution temperature.

Problems to be Solved by the Invention The present invention relates to a method for manufacturing an electrode of an aluminum electrolytic capacitor using this alternating current, and relates to the current density of the alternating current.

Conventionally, with respect to this current density, many developments have been made as an important factor that determines the magnitude of the etching magnification,
Although almost all of them have been implemented, they are devised so that the current density is made to flow uniformly from beginning to end, and careful attention is paid to how to make the current density uniform in the manufacturing process.

The inventors of the present invention have made a number of experiments on the current density that affects the etching magnification, and have found a new phenomenon here.

That is, very fine unevenness is required as the electrode foil for the low-voltage anode and the cathode, but when etching is performed at a constant current density throughout, the unevenness of the surface gradually increases as the etching progresses, Therefore, there is a problem that the etching magnification is lowered and the mechanical strength of the etching foil is weakened.

Means for Solving the Problems The present invention is to solve such problems, and an aluminum foil is subjected to an alternating current, and within about 1/3 of the total etching time is 0.05 to 0.30 A / cm ³ . Etching with a small current density, increasing the current density in sequence and remaining time 0.5-1.5A /
Etching is performed with a large current density of cm ³ .

According to such an etching method of the present invention, since the current density is changed, it is possible to prevent the unevenness of the surface from gradually increasing as in the case where the etching is performed at a constant current density all the time. As a result, fine irregularities are obtained on the etching surface, so that the mechanical strength of the etching foil does not become weak.

Examples Hereinafter, examples of the present invention will be described.

Example 1 Aluminum foil: Purity 99.993% Normal softening foil with a thickness of 60 μ Etching solution: H ₃ PO ₄ (phosphoric acid) 1.3% in hydrochloric acid 5% solution
Liquid with addition of: Current and current density: AC 60Hz 0.75A / cm ³ Etching time: 2 minutes Etching temperature: 50 ± 2 ° C Example 2 Aluminum foil: Purity 99.993% Normal softened foil of thickness 60μ Etching solution: Hydrochloric acid 5 % H ₃ PO ₄ (phosphoric acid) 1.3% solution
Current density and etching time: 0.15 A / cm ³ → 0.5 A / cm ³ →
0.8A / cm ³ → 1.2A / cm ³ 50 seconds → 45 seconds → 45 seconds → 20 seconds Etching temperature: 50 ± 2 ° C Example 3 Aluminum foil: Purity 99.993% 60 μm thick normal softening foil Etching solution: Hydrochloric acid H ₃ PO ₄ (phosphoric acid) 1.3% in 5% solution
Current with addition of: AC 60Hz Current density and etching time: 1.0A / cm ³ → 0.7A / cm ³ →
0.5A / cm ³ → 0.35A / cm ³ 20 seconds → 45 seconds → 50 seconds → 20 seconds Etching temperature: 50 ± 2 ° C Capacitance and formation voltage of the etching foils obtained in the above Examples 1, 2 and 3 The relationship is shown in the drawing. What is indicated by A and B in the drawing is the electrode foil for low voltage which is currently at the highest level in the world.

As is clear from this figure, in Example 2, the etching is performed with a small current density within about 1/3 of the total etching time, the current density is sequentially increased, and the remaining time is etched with a large current density. In comparison with Example 1 in which etching was performed at a constant current density, Example 3 in which the current density was sequentially decreased, and the low-voltage electrode foils A and B that are currently at the highest level in the world, As a result, one having a high electrostatic capacity can be obtained.

The bending strength of these electrode foils is shown in the table below.

The conditions for measuring the capacitance and the method for measuring the bending strength are as follows.

Capacitance forming liquid: boric acid 30g / l ammonium borate 30g
/ l aqueous solution formation temperature: 25 ± 2.5 ℃ Sample area: 10cm ² Formation method: Form until the formation current drops to 0.5mA / 10cm ³ .

Capacitance measurement method: Precision bridge is used in 8% ammonium borate solution, temperature 25 ± 2.5 ℃ Bending strength A 200g weight is hung on a foil with a width of 10mm. Rotate by 90 degrees until the foil is cut. However, once at 90 degrees. (Unit: 10mm width, thickness is the thickness of the foil) As is clear from the above table, in Example 2, the etching is performed with a small current density within about 1/3 of the total etching, and the current density is sequentially increased and the remaining time is etched with a large current density. In comparison with Example 1 in which etching was performed at a constant current density, Example 3 in which the current density was sequentially reduced, and the low-voltage electrode foils A and B that are currently at the highest level in the world, bending strength is also higher. It can be improved by about 10%, which results in an etching foil having excellent mechanical strength.

As described above, according to the method for manufacturing the electrode of the aluminum electrolytic capacitor of the present invention, the aluminum foil is subjected to an alternating current, and within about 1/3 of the total etching time, with a small current density of 0.05 to 0.30 A / cm ^3. Etching, increasing the current density in sequence and remaining time
Since the etching is performed with a large current density of 0.5 to 1.5 A / cm ³ , it is possible to prevent the surface irregularities from gradually increasing, which is the case when etching is performed with a constant current density all the time. As a result, since the unevenness of the etching surface is fine, the mechanical strength of the etching foil does not weaken, and the electrode foil can be made thinner as the mechanical strength of the etching foil improves. Therefore, when the electrode foil is thin, the aluminum electrolytic capacitor can be downsized and the cost can be reduced. Further, since the etching magnification can be improved as compared with the conventional one, a low-voltage electrode foil having a high capacitance can be obtained.

[Brief description of drawings]

The figure is a characteristic diagram of the electrostatic capacity and the formation voltage of the electrode obtained by the electrode manufacturing method of the aluminum electrolytic capacitor of the present invention and the conventional electrode at the highest level.

Continuation of the front page (72) Inventor Tameki Kiyoshi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-54-84261 (JP, A)

Claims (1)

[Claims] 1. An aluminum foil is etched with an alternating current at a small current density of 0.05 to 0.30 A / cm ³ within about 1/3 of the total etching time, and the current density is gradually increased to 0.
A method for manufacturing an electrode of an aluminum electrolytic capacitor, which comprises etching at a large current density of ^{5 to} 1.5 A / cm ³ .