JPH0566006B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a method for manufacturing an aluminum material for electrolytic capacitor electrodes. Prior Art and Problems Aluminum foil, which is commonly 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 capacitance per unit area. be done. Conventionally, with the aim of improving etching performance, rolled aluminum foil was heated for 500 min in an inert gas such as argon or in a non-oxidizing atmosphere such as vacuum before etching.
Although high-temperature heat treatment at ~600°C for 2 to 10 hours has been carried out, satisfactory etching performance and capacitance have not been obtained. Therefore, the present applicant proposed an aluminum material for electrolytic capacitors in which a crystallized γ-Al ₂ O ₃ film of a constant thickness is formed 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, subsequent research has revealed that even with this material, there are cases in which it is not possible to obtain the desired sufficient capacitance. The present invention was made in view of this technical background, and aims to provide an aluminum material for electrolytic capacitors that has excellent etching performance and can reliably obtain high capacitance. Means for Solving the Problems The above aluminum material with a γ-Al ₂ O ₃ film formed on its surface was manufactured through a hydration film forming process and a high temperature heating process in a non-oxidizing atmosphere. In order to achieve the above objective, the inventor repeatedly conducted various experiments and research, and found that the formation conditions of the hydration film and the structure of the aluminum foil are closely related to the superiority of etching performance and the magnitude of capacitance. Based on this knowledge, we were able to complete this invention. That is, in order to achieve the above object, the method for producing an aluminum material for electrolytic capacitor electrodes according to the present invention is such that the average size of cells or subgrains is 10 μm or less before electrochemical or chemical etching treatment. Aluminum foil, heating temperature: 40 to 200℃, heating time: 10 minutes to 24 hours,
Atmospheric pressure: 2 atm or more, H ₂ O amount in the atmosphere: 0.01
It is characterized by a step of heating under conditions of Kg/Kg or more to form a hydration film on the foil surface, and then a step of heating at a high temperature in a non-oxidizing atmosphere. 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 structure of aluminum foil before hydration film formation, the average size of cells or subgrains is
The reason why it is limited to 10 μm or less is as follows. That is, according to the inventor's research, in an aluminum material that has undergone a hydration treatment process and a high-temperature heating process, the positions where pits are generated due to etching correspond to the cells or subgrains of the aluminum foil that are present during the hydration treatment. I found out. Therefore, in order to increase the area enlargement ratio by increasing the number of etching pits, it is sufficient to increase the number by decreasing the cell size or subgrain size. Therefore, the average size of cells or subgrains generated by processing aluminum foil was set to 10 μm or less. especially
Most preferably, the thickness is 5 μm or less. in this way,
One way to specify the average cell or subgrain size of aluminum foil to be as small as 10 μm or less is to reduce the temperature of the foil as much as possible by rolling the foil.
For example, methods include controlling the temperature of the wound coil to below 150°C, slowing down the rolling speed, and applying a large amount of rolling oil. However, the method is not limited to these methods, and the average size of cells or subgrains specifically present in the aluminum foil during hydration treatment is
A thickness of 10 μm or less satisfies the requirements of the present invention. The hydration treatment performed on the aluminum foil is performed by low temperature heating in a pressurized moisture atmosphere. The reason why the heating temperature is limited to 40 to 200°C is that the formation of the hydration film does not proceed at temperatures below 40°C, making it virtually impossible to form a sufficient film. The formation of a hydration film takes place in a shorter time as the temperature increases, but as the temperature rises above 200°C, the size of the cells or subgrains in the aluminum foil increases.
The number of etching pits decreases, and as a result, the capacitance cannot be increased. Particularly preferred heating temperature is 60-150℃
It is. The heating time is limited to 10 minutes to 24 hours because less than 10 minutes is insufficient to form an effective hydration film, and conversely, heating for more than 24 hours does not result in film formation. This is because the progress becomes saturated and costs increase due to wasted energy. It is particularly preferable to set the time to 30 minutes or more. The atmospheric pressure is limited to 2 atmospheres or more because 2
This is because if the pressure is less than the atmospheric pressure, the film formation rate is slow and a substantially sufficient film cannot be formed, resulting in a failure to obtain a high capacitance. Furthermore, the higher the pressure, the faster the film can be formed, but since it is not easy to achieve an atmosphere exceeding 10 atmospheres in terms of equipment, it is better to set the pressure in the range of 2 to 10 atmospheres during actual production. H ₂ O in the atmosphere is essential for the formation of a hydration film, but its content is 0.01Kg/Kg.
Since it is difficult to form a sufficient film at less than
Must be 0.01Kg/Kg or more. Particularly preferably, it is set to 0.02Kg/Kg or more. The main purpose of the high-temperature heating carried out after the formation of the hydration treatment film is to change the structure of the aluminum foil to a texture with many cubic orientations and improve the etching properties. It also has the effect of changing the film into a crystallized γ-Al ₂ O ₃ film. This high-temperature heating is performed in an inert gas such as Ar gas or in a vacuum of about 10 ^-2 Torr or less, at a heating temperature of about 500 to 600° C., and for a heating time of about 1 to 10 hours. The reason why the high temperature heating is performed in a non-oxidizing atmosphere is to prevent the film from becoming too thick and reducing the etching performance. In addition, when performing the above hydration treatment at a relatively low temperature, it is also recommended to heat at a temperature of 160 to 200 ° C before the high temperature heating step to prevent recrystallization from becoming coarse during high temperature heating. . In this case, the heating atmosphere may be air, Ar, or vacuum. The aluminum material produced as described above is then electrochemically or chemically etched and then used as an electrode material for an electrolytic capacitor. Effects of the Invention Since the present invention is as described above, it is possible to reliably and stably provide an electrolytic capacitor electrode material that has excellent etching performance, can form a large number of etching pits, and has a large area expansion ratio and thus a large capacitance. Examples Example 1 Thickness made of 99.99% pure aluminum
When producing 100 μm aluminum foil, the foil temperature, rolling speed, and amount of rolling oil during foil rolling were adjusted to produce various aluminum foils with various average cell or subgrain sizes as shown in Table 1. . Next, add the amount of H ₂ O to the aluminum foil above.
3 set in two types: 0.015Kg/Kg and 0.03Kg/Kg
Heating temperature 100℃ x heating time 5 in pressurized atmosphere
A hydration film was formed on the surface of the foil by heating it for a certain amount of time. Then, in an Ar gas atmosphere
High temperature heat treatment was performed at 550°C for 1 hour. The aluminum material obtained above was electrolytically etched for 3 minutes in a 3% aqueous hydrochloric acid solution (85°C) at a current density of 10 A/dm ² , and then chemically etched for 10 minutes in the same solution. After that, the capacitance of each material was measured after specific conversion treatment at 350V in a 5% boric acid bath. The results are shown in Table 1.

[Table] Example 2 A 100 μm thick aluminum foil with a purity of 99.99% and an average cell or subgrain size of 5 μm was used, and the hydration film formation process was performed at a heating temperature of 100°C and H ₂ O in the atmosphere. Various aluminum materials were obtained in the same manner as in Example 1, except that the amount was fixed at 0.03 Kg/Kg and the atmospheric pressure and heating time were varied. Then, the above aluminum material was subjected to etching treatment and chemical conversion treatment under the same conditions as in Example 1,
The capacitance of the obtained material was measured. The results are shown graphically in FIG. Example 3 The same aluminum foil as in Example 2 was used, and the hydration film forming process was carried out under the following conditions: atmospheric pressure: 3 atm, amount of H ₂ O in the atmosphere: 0.03 Kg/Kg, heating temperature and time. Various aluminum materials were obtained in the same manner as in Example 1, except that various aluminum materials were used. Then, the same etching treatment and chemical conversion treatment as in Example 1 were performed, and the capacitance of the obtained material was measured. The results are shown in FIG. In the product of the present invention, a large number of etching pits were formed and the etching state was high, so as can be seen from the above results, a large capacitance could be reliably obtained.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are graphs showing the test results of Examples 2 and 3, respectively.

Claims (1)

[Claims] 1. Before electrochemical or chemical etching treatment, aluminum foil with an average cell or subgrain size of 10 μm or less is heated at a heating temperature of 40 to 200°C, a heating time of 10 minutes to 24 hours, and an atmospheric pressure of: 2 atmospheres or more, H ₂ O amount in the atmosphere: 0.01Kg/
A method for producing an aluminum material for electrolytic capacitor electrodes, which comprises a step of heating under conditions of at least Kg to form a hydration film on the surface of the foil, and then a step of heating at a high temperature in a non-oxidizing atmosphere.