JPH02146718A - Manufacture of aluminum material for electrolytic capacitor electrode - Google Patents

Abstract

PURPOSE:To obtain Al materials which are superior in etching performance and are able to secure high capacitance by forming an oxide film having a specific thickness on the surface of an Al foil while an average size of cells or subgrains is in a state that it is below a specified value and after that, by treating its film with heat at a high temperature and taking like steps within the limits of the thickness of the oxide film in total which does not exceed the specified value. CONSTITUTION:Before performing electro-chemical or chemical etching treatment, an oxide film having the thickness 5-50Angstrom is formed on the surface of an Al foil while an average size of cells or subgrains is in a state that it is below 10mum. After that, its film is treated with heat at a high temperature within the limits of the thickness in total of the oxide film which does not exceed 70Angstrom . For example, the Al foil having the thickness 100mum in which its purity is 99.99% and the average size of the cells or subgrains is 4mum is heated in an atmosphere containing H2O: 0.015kg/kg at a low temperature 100 deg.C for 10 hours and an initial oxide film having the thickness 32Angstrom is formed on the surface. Subsequently, its film is treated with heat at a high temperature 520 deg.C in a vacuum of 10<-4>Torr for an hour to make the thickness of the oxide film on the surface of the foil total to 43Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing aluminum material for electrolytic capacitor electrodes.

Prior Art and Problems Aluminum foil, which is generally used as an electrode material for aluminum electrolytic capacitors, is generally subjected to electrochemical or chemical etching treatment in order to expand its effective area and increase the capacitance per unit area. be done. but,
It was not possible to obtain sufficient capacitance by simply etching the foil.

Additionally, the present applicant has previously proposed an aluminum material for electrolytic capacitors that has improved etching performance by forming a crystallized γ-AΩ203 film of a certain thickness on the surface of an aluminum foil (Japanese Patent Publication No. 34925/1982). . This material made it possible to increase the surface area of the foil after etching, which in turn made it possible to increase the capacitance.

However, even with this material, there have been cases where it has not been possible to fully satisfy the recent demand for higher capacitance of electrolytic capacitors.

The present invention was made in view of the above circumstances, and it is an object of the present invention to provide an aluminum material for electrolytic capacitors that has excellent etching performance and can reliably obtain high capacitance.

Means for Solving the Problems Aluminum foil for electrolytic capacitors is generally manufactured by sequentially performing the steps of melting/casting, hot rolling, cold rolling, foil rolling, and final annealing.

Among these, recrystallization occurs in the final annealing, which has conventionally been carried out at a high temperature of 500° C. or higher in order to create a texture with many cubic orientations. In order to achieve the above object, the inventors conducted intensive research and found that the relationship between the formation of an oxide film formed on the surface of aluminum foil during final annealing and the structure of the foil at that time led to improved etching performance and static We found that this is extremely important for increasing capacitance. That is,
The positions where pits are generated by etching correspond to the cells or subgrains of the foil that exist at a relatively early stage of annealing. Therefore, in order to increase the number of etching pits and improve the area expansion ratio, it is necessary to It is possible to reduce the size of the etching pits and increase their number, but this is not enough to become the core of etching pit formation, and the oxide film on the foil surface at the stage where the cell or subgrain size is small is in the range of 5 to 50 particles. It has been found that it is necessary for the oxide film to be further applied thereafter to be as thin as possible.

This invention was made based on this knowledge,
Before electrochemical or chemical etching treatment,
A process of forming an oxide film with a thickness of 5 to 50 mm on the surface of an aluminum foil while the average cell or subgrain size is 10 μm or less, and then in a range where the total thickness of the oxide film does not exceed 70 mm. The above-mentioned problem can be solved by performing a high-temperature heat treatment step.

The aluminum foil preferably has a high purity of 99.99%, but is not limited to this, and may have a purity within the range used for electrolytic capacitors.

In the annealing process after foil rolling, the oxide film initially formed on the surface of the aluminum foil is limited to 5 to 50. By ensuring a film thickness within this range, cells or subgrains on the foil surface are This is because the nucleus of an etching pit consisting of a film defect can be effectively formed at a position corresponding to .

Particularly preferably, it is 15 to 45 people.

In addition, in the process of forming this oxide film, the average size of the cells or subgrains of the aluminum foil is limited to 10 μm or less, which reduces the size of the cells or subgrains to increase their number and improve the area ratio. This is to further increase the capacitance. In particular, it is preferably 5 μm or less. A specific method for forming an oxide film with a thickness of 5 to 50 people while the average size of cells or subgrains is 10 μm or less includes, for example, aluminum foil having an average cell or subgrain size of 10 μm or less after foil rolling. Examples include a method of heating at a low temperature in an atmosphere containing moisture or oxygen, an Ar atmosphere, or the like. Here, as a method to control the average size of cells or subgrains of aluminum foil to a microscopic size of 10 μm or less, the temperature of the foil is kept as low as possible by foil rolling, for example, the temperature of the coil is lowered to 150°C or less. Examples of methods include reducing the rolling speed, slowing down the rolling speed, and applying a large amount of rolling oil. In addition, in the above-mentioned low-temperature heating to form an oxide film with a thickness of 5 to 50 mm, moisture in the atmosphere (H20)
The amount is 0. It is preferable to set OIK'j/ to 'j or more, and the more water is recycled, the faster the desired film thickness can be obtained. Further, the lower the heating temperature during low-temperature heating, the smaller the cell or subgrain size can be kept, but since the heating time becomes longer, it is actually better to set the heating temperature to about 40 to 180°C. When the temperature exceeds 180° C., the size of cells or subgrains increases, and there is a possibility that the average size exceeds the requirement of 10 μm or less.

The heating time is preferably about 1 hour or more to ensure a film thickness of 5 Å or more, and for example, a film thickness of about 25 Å can be obtained in about 4 hours. Such low-temperature heating may be performed in only one stage, but may be performed in two or more stages with different heating temperatures and heating times.

The main purpose of the high-temperature heating carried out after forming an initial oxide film with a thickness of 5 to 50 mm is to change the structure of the aluminum foil into a texture with many cubic orientations, thereby improving the etching properties. In this high-temperature heat treatment, if the thickness of the oxide film further formed on the initial oxide film is too thick, the defective parts of the initial oxide film will be erased and sufficient etching pits will be formed during etching. I can't do anything. Therefore, the high-temperature heat treatment must be performed within a range where the total thickness of the oxide film including the initial oxide film is 70 Å or less. It is preferable to limit the thickness to 50 Å or less.

In order to keep the total thickness of the oxide film to 70 Å or less, moisture,
It is desirable to heat in an atmosphere that removes as much oxygen as possible.
Specifically, in an inert gas such as Ar gas or 1O-3
It is preferable to heat in a vacuum of about Torr or less. Further, it is desirable that the heating temperature is about 460° C. or higher and the heating time is about 1 to 5 hours.

The aluminum material produced as described above is then electrochemically or chemically etched and then used as an electrode material for an electrolytic capacitor.

Note that the manufacturing process of the aluminum foil used in the present invention is not limited to this, and may be intermediately annealed during the rolling process.

Effects of the Invention Since the present invention is as described above, it is possible to reliably and stably provide an electrolytic capacitor electrode shrine with excellent etching performance, which can form a large number of etching pits, and which has a large area expansion ratio and a large capacitance. .

Example (Example 1) Made of 99.99% pure aluminum with a thickness of 100μ
When producing aluminum foils of 50 to 800 m, various aluminum foils having average cell or subgrain sizes as shown in Table 1 were produced by adjusting the foil temperature, rolling speed, and amount of rolling oil during foil rolling.

Next, the above aluminum foil is heated in an atmosphere containing H20Jit as shown in Table 1 at a low temperature with various heating temperatures and heating times, so that the initial oxidation of the foil surface to the thickness shown in Table 1 is performed. A film was formed. Note that the thickness of the oxide film was measured by the Hunter-Hall method according to the following conditions. That is, a voltage was applied to the sample to be measured under the following conditions: Measurement liquid: 30'j/Q ammonium tartrate aqueous solution Temperature: 30°C Counter electrode: Carbon Measurement electrode: Sample to be measured Direct current voltage application acceleration: 5V/sec. The current/voltage characteristics shown in the figure were determined by ff111.

Then, the voltage difference χ shown in the same figure was measured, and the film thickness - χ×14
The film thickness was measured by converting using the formula: person/V.

Furthermore, when the average size of cells or subgrains in the aluminum foil at the end of heating was examined, it was found that it changed as shown in Table 1.

Next, each of the above aluminum foils was subjected to high-temperature heat treatment at 520°C for 1 hour in a vacuum of 1O-4 Torr, and then the total thickness of the oxide film on the foil surface was measured using the Hunter-Hall method as described above. It was as shown in Table 1.

Each of the aluminum materials obtained above was electrolytically etched in a 3% aqueous hydrochloric acid solution (85°C) at a current density of 10 A/d77j for 3 minutes, and then chemically etched in the same solution for 10 minutes. And then 5%
After chemical conversion treatment at 350V in a boric acid bath, the capacitance of each material was measured. The results are also shown in Table 1.

[Margin below (Example 2) Using an aluminum foil with a thickness of 100 μm and a purity of 99.99% and an average size of cells or subdaleins of 4 μm, the aluminum foil was heated to H20: 0. 015 to 9
Heating at a low temperature at 100°C for 10 hours in an atmosphere containing 7 and 9,
An initial oxide film with a thickness of 32 mm was formed on the surface. The average size of cells or subdaleins on the surface of the foil after low-temperature heating was 7 μm, and the average size was maintained at 10 μm or less throughout the low-temperature heating process.

Next, the aluminum foil was heated at a high temperature of 520°C while changing the heating time and degree of vacuum (10' to 10-5 Torr). The total thickness of the oxide film after high-temperature heating was determined by Δ1 using the Hunter-Hall method, and the results were as shown in Table 2.

Next, the above aluminum material was subjected to etching treatment and chemical conversion treatment under the same conditions as in Example 1, and the capacitance of the obtained material was measured. The results are shown in Table 2.

As can be seen from Tables 1 and 2, the product of the present invention forms a large number of etched pits and is etched with a high density, so it is possible to reliably obtain a large capacitance. It was something that could be done.

[Brief explanation of the drawing]

FIG. 1 is a current/voltage characteristic diagram for explaining the method of measuring the thickness of an oxide film by the Hunter-Hall method performed in the example. Denshiba t. one>

Claims (1)

[Claims] Before electrochemical or chemical etching treatment,
The surface of the aluminum foil is coated with a thickness of 5 to 50 Å while the average cell or subgrain size is 10 μm or less.
1. A method for producing an aluminum material for an electrolytic capacitor electrode, the method comprising: forming an oxide film; and then subjecting the oxide film to a high-temperature heat treatment such that the total thickness of the oxide film does not exceed 70 Å.