JPH0566007B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to an aluminum material for electrolytic capacitor electrodes and a method for manufacturing the same. BACKGROUND OF THE INVENTION Aluminum foil used as an aluminum electrode material for electrolytic capacitors is required to have as large a surface area as possible and a large capacitance per unit area. For this reason, it is generally done to enlarge the effective area of aluminum foil by electrochemical or chemical etching treatment, and furthermore, with the aim of increasing this area enlargement ratio as much as possible, etching holes are formed. In order to make the foil larger, deeper, and thicker, various studies are being conducted, including improving the material composition and metal structure, improving the etching method, and researching the manufacturing process of the foil. Problems to be Solved by the Invention However, in practice, in conventionally known etching techniques, the locations where etching nuclei, which form the basis of etching holes, are generated are generally non-uniform, and etching pits communicate with each other, resulting in coarse holes. As a result, there was a problem in that it was difficult to obtain the expected effect of increasing the area enlargement ratio. For this reason, photoresist technology has been developed as a manufacturing method for aluminum electrode materials for electrolytic capacitors, which can intentionally determine the locations where etching pits occur in advance and uniformly form many deep etching pits, resulting in an excellent area expansion ratio. Although methods using the method have also been proposed (for example,
(No.), which was expensive and impractical. This invention was made in view of this technical background, and it is possible to form a large number of deep etchings uniformly and with high density, and has excellent etching characteristics such as an excellent area enlargement ratio, that is, an excellent capacitance. This invention was developed with the intention of providing an aluminum material for electrolytic capacitor electrodes. Means for Solving the Problems For the above purpose, the aluminum material for electrolytic capacitor electrodes according to the present invention, as shown with reference to the reference numerals in the drawings, has a surface that is more oxidized than the aluminum before etching. Oxide-resistant particles 2 with an average particle diameter of 0.1-2μm are 70,000~
The aluminum foil 1 is characterized by being present in a fixed state at a rate of 400,000 particles/mm ² , and an oxide film 3 having a thickness of 70 to 5,000 Å is formed on the surface of the aluminum foil 1 except for the areas where these difficult-to-oxidize particles are present. It is something to do. Alternatively, in the method for manufacturing an aluminum material for electrolytic capacitor electrodes according to the present invention, before electrochemical or chemical etching treatment, the surface of the aluminum foil 1 is coated with an average particle size of 0.1 to 2 μm, which is less oxidized than aluminum. A step of causing oxidation-resistant particles 2 to exist in a fixed state at a rate of 70,000 to 400,000 particles/mm ² and a step of forming an oxide film 3 with a thickness of 70 to 5,000 Å on the surface of the aluminum foil 1 are sequentially carried out. It is characterized by: The aluminum foil 1 preferably has a high purity of 99.9% or higher, but is not limited to this, and may be any foil within the range used for electrolytic capacitors. As the above-mentioned hard-to-oxidize particles 2 that are less oxidized than aluminum, metal particles such as Ti, Au, etc.
Examples include non-metallic particles such as SiO ₂ and MgO, but the present invention is not limited to these, and any particulate substance that is less oxidizable than aluminum may be used.
The oxidation-resistant particles 2 are present in a fixed state on the surface of the aluminum foil 1, and the interface between the aluminum foil 1 and the oxidation-resistant particles 2 is preferentially corroded during subsequent etching. It serves as a nucleus for forming etching holes 4 in the areas where the oxidation-resistant particles 2 are present. The oxidant-resistant particles 2 may be present on one side of the foil 1, but preferably on both sides. If the average particle diameter of the oxide-resistant particles 2 is less than 0.1 μm, there will be many areas where no etching holes 4 will be formed during etching, and the effect of increasing capacitance due to the expansion of the surface area will not be sufficiently exhibited. On the other hand, if it exceeds 2 μm, etching hole 4
becomes too large, resulting in a decrease in the strength of the foil 1 after etching. The preferred average particle size is 0.2 to 0.5 μm. In addition, the number of difficult-to-oxidize particles 2 per mm ²
If the number is less than 70,000, the effect of expanding the surface area after etching will be small, and if it exceeds ^400,000 , the strength of the etched foil will decrease. Preferably, 150,000 to 250,000 particles are present per mm ² . One method for making the hard-to-oxidize particles 2 exist in a fixed state on the surface of the aluminum foil 1 is to embed the particles in the surface of the foil. The embedding can be performed, for example, by rolling using rolling oil to which the oxidation-resistant particles are added in a dispersed state. Other methods include attaching oxidant-resistant particles to the foil surface by vapor deposition or sputtering, or adsorbing them to the foil surface by a chemical method. The oxide film 3 formed on the surface of the aluminum foil except for the part where the oxidation-resistant particles are present serves to prevent the surface of the aluminum foil from dissolving in the film part. However, the thickness of oxide film 3 is 70Å
If it is less than that, the effect will be poor and the surface of the film-forming portion will dissolve, resulting in a small surface area. vice versa
If the thickness exceeds 5000 Å, there will be areas where no etching holes are formed even in areas where oxidation-resistant particles are present, resulting in the inability to increase the surface area.
It also has poor flexibility. Therefore, the thickness of the oxide film 3 formed on the surface of the aluminum foil, excluding the portion where the oxidation-resistant particles are present, must be in the range of 70 to 5000 Å. Preferably 100-2000
It is better to set it as Å. The formation of such an oxide film can be carried out, for example, by a method in which hard-to-oxidize particles are present on the surface of the aluminum foil and then subjected to high-temperature heat treatment in an oxygen atmosphere, or a method in which the aluminum foil is subjected to anodization treatment using a boric acid electrolyte. By performing such processing, an oxide film 3 grows on the surface of the aluminum foil 1, avoiding the oxidation-resistant particles 2, as shown in FIG. In either method, the requirements are satisfied as long as the oxide film 3 is formed with a thickness of 70 to 5000 Å, and the processing conditions therefor are not particularly limited. The aluminum foil 1 on which the oxide film 3 has been formed as described above is then electrochemically or chemically etched and used as an electrolytic capacitor electrode foil. In the above etching treatment, corrosion preferentially progresses from the interface between the oxidation-resistant particles and the aluminum foil, while surface dissolution of the oxide film-covered portion is prevented. As a result, as shown in FIG. 3, etching holes 4 are formed only in the areas where the oxidation-resistant particles 2 are present. Effects of the Invention As described above, when the aluminum material for electrolytic capacitor electrodes according to the present invention is etched, etching holes can be formed in the aluminum foil only in the areas where oxidation-resistant particles are present, and in other areas. can prevent surface dissolution due to the oxide film. Since such oxidation-resistant particles are present in a predetermined size and quantity, etching holes can be formed in a uniform and dense distribution, and communication between etching holes can be prevented. You can form each one into something thick and deep. As a result, it is possible to increase the area expansion ratio of the electrode foil, and as a result, it is possible to realize an increase in capacitance. Further, since the manufacturing method of the present invention does not use a photoetching method, an aluminum material having excellent etching properties as described above can be provided at a low cost. Examples Example 1 Using high purity aluminum material with a purity of 99.99%,
After hot rolling the aluminum material by a conventional method,
It was cold rolled to a thickness of 0.3 mm. Then, 50℃, 5%
The surface of the aluminum material was removed using caustic soda for 30 seconds. Then, when rolling the foil, by using rolling oil in which Ti particles are dispersed, the particles are adhered to and held on the surface of the aluminum material via the rolling oil, and then rolled to a thickness of 0.1 mm in which the Ti particles are embedded. I made multiple sheets of foil.
Here, by appropriately changing the particle size of the Ti particles and the number of particles dispersed in the rolling oil, the average particle size and number of Ti particles embedded in the surface of each foil can be adjusted to the first
I set it up as shown in the table. Next, each of the above foils was anodized in a 5 wt % boric acid solution to form an oxide film with a thickness of about 150 Å on its surface. Note that no oxide film was formed in the part where the Ti particles were embedded. Each aluminum material obtained above was heated to a DC current density of 10 A/dm ² in a 3% aqueous hydrochloric acid solution (85°C).
After performing electrolytic etching for 3 minutes, chemical etching was further performed for 10 minutes without changing the solution. The area enlargement magnification and strength of the aluminum electrode foil obtained after etching were examined and were as shown in Table 1.

【table】

[Table] Example 2 Using the same aluminum material as in Example 1, and using the same method, a plurality of aluminum foils each having a thickness of 0.1 mm and having Ti particles embedded in their surfaces were manufactured. Here, all Ti particles used had an average particle diameter of 0.25 μm, and the number of Ti particles distributed on the foil surface was also approximately 250,000 particles/mm ² . Next, each aluminum foil was anodized using the same boric acid electrolyte as in Example 1, and the treatment time was changed appropriately to apply various treatments as shown in Table 2 on the foil surface except for the areas where Ti particles were present. A thick oxide film was formed. Each of the aluminum materials obtained above was etched under the same conditions as in Example 1, and the area enlargement ratio and strength of the obtained electrode foils were measured, and the results were as shown in Table 2.

[Table] From the above results, it could be naturally expected that the aluminum material according to the present invention has a large area enlargement ratio after etching, and therefore a large capacitance can be obtained. It is also seen that the strength of the foil does not decrease after etching.

[Brief explanation of the drawing]

Figure 1 is a perspective view schematically showing a state in which oxidation-resistant particles are present in a fixed state on the surface of an aluminum foil, and Figure 2 is a diagram showing a state in which an oxide film is formed on the surface of an aluminum foil in which oxidation-resistant particles are embedded. The schematic cross-sectional view shown in FIG. 3 is a schematic cross-sectional view of the surface of the aluminum foil after etching. 1... Aluminum foil, 2... Hard-to-oxidize particles, 3...
Oxide film, 4...etching holes.

Claims (1)

[Claims] 1. On the surface of the aluminum foil before etching, an average particle size that is less likely to be oxidized than the aluminum is added.
70,000 to 400,000 0.1 to 2 μm oxidant-resistant particles/mm ²
An aluminum material for electrolytic capacitor electrodes, characterized in that the aluminum foil is present in a fixed state at a ratio of . 2. Before electrochemical or chemical etching treatment, oxidation-resistant particles with an average particle diameter of 0.1 to 2 μm, which are less oxidized than aluminum, are fixed on the surface of the aluminum foil at a rate of 70,000 to 400,000 particles/ ^mm2. 1. A method for producing an aluminum material for an electrolytic capacitor electrode, comprising sequentially carrying out a step of causing an oxide film to exist on the surface of an aluminum foil, and a step of forming an oxide film with a thickness of 70 to 5000 Å on the surface of an aluminum foil.