JPH032334B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing aluminum electrode foil for electrolytic capacitors. Structure of conventional examples and their problems In general, aluminum electrode foils for electrolytic capacitors are manufactured by subjecting rolled hard aluminum foil or annealed soft aluminum foil to chemical or electrical After chemically etching and expanding the surface area of the aluminum foil, a chemical conversion treatment is applied.
Manufactured by forming a dielectric oxide film on the surface. Since the capacitance of an aluminum electrode foil for an electrolytic capacitor is approximately proportional to the surface area of the aluminum foil, the larger the surface area expansion rate, the more desirable.
The surface area expansion rate of the aluminum foil due to this etching increases in proportion to the amount of etching, but beyond a certain limit, the increase slows down and eventually shows a tendency to decrease. In addition, the mechanical strength of the aluminum foil decreases with the amount of etching, so if the aluminum foil is excessively etched, there is a risk that it will break during electrolytic capacitor manufacturing processes such as etching, chemical formation, and assembly. . For these reasons, the optimum amount of etching is determined so that the aluminum foil has enough mechanical strength to prevent breakage during the manufacturing process of electrolytic capacitors and has as large a surface area expansion ratio as possible. On the other hand, for aluminum electrolytic capacitors,
As smaller size and larger capacity are desired, an aluminum electrode foil with sufficient mechanical strength and a larger surface area expansion ratio than the current one with a certain amount of etching is being desired, and much research is being carried out. OBJECTS OF THE INVENTION The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing an aluminum foil for an electrolytic capacitor having a surface area ratio higher than that of the conventional method. Structure of the Invention The method of manufacturing aluminum foil for electrolytic capacitors of the present invention includes implanting oxygen ions at 10 ¹³ to 10 ¹⁷ ions/cm ² into aluminum foil before etching, and then
It is heat treated at a temperature range of 200 to 500°C, and then chemically or electrochemically etched in an aqueous solution containing chlorine ions. In other words, after performing the above etching, a dielectric conversion film is further formed through a chemical conversion treatment to create an electrolytic capacitor with sufficient mechanical strength and a larger capacitance per unit area than conventional capacitors. Aluminum electrode foil can be manufactured. As mentioned above, aluminum foil for electrolytic capacitor anodes is chemically or electrochemically etched in an aqueous solution containing chlorine ions to increase its surface area and is chemically converted before use. The magnification rate depends on many factors such as the rolling process and annealing of the aluminum foil, the amount of impurities in the aluminum foil, the composition of the etching solution, and the electrolytic conditions. Etching of aluminum in an aqueous solution containing chlorine ions begins with the etch pit nucleus where chlorine ions are adsorbed on the surface, and as the etching progresses, corrosion of the aluminum foil occurs internally in the form of pitting corrosion, and the surface area gradually expands. . These chlorine ions preferentially adsorb to the weak points of the surface oxide film due to impurities or dislocations caused by rolling, etc., and become etch pit nuclei. Etching further proceeds along the dislocations, expanding the surface area. . Therefore, large surface area expansion requires that these dislocations be more numerous and uniformly distributed. Ion implantation of oxygen atoms into aluminum foil has the effect of straining the crystal lattice, increasing and uniformizing dislocations, and forming an aluminum oxide film uniformly on the surface. Generally, aluminum foil for electrolytic capacitors is made by mixing small amounts of several types of impurities into aluminum, and then melting, casting, rolling, and
Manufactured through processes such as annealing. The contained impurities mainly precipitate near the surface, but segregation is likely to occur and uniform dispersion is difficult to obtain. For this reason, dislocations are also non-uniformly distributed. This can be seen from the existence of overcrowded and depopulated areas in the etching pit due to etching. By the ion implantation of the present invention, dislocations in the aluminum foil are more uniformly dispersed, and an oxide film layer on the aluminum surface is uniformly formed by the implanted oxygen ions, so that etch pits are generated more uniformly. It is possible to measure the expansion of the surface area. The lower limit of the ion implantation amount is the minimum amount at which the effect of enlarging the surface area by etching is recognized, and the upper limit is the maximum amount limited by the adverse effect on the effect of enlarging the surface area due to concentration of etching pits. The ion implantation amount is 10 ¹² to 10 ¹⁸ ions/cm ² to exhibit the effect of expanding the surface area, but more preferably 10 ¹³ to 10 ¹⁷ ions/cm ²
is within the range of After ion implantation, heat treatment is performed at a temperature of 200 to 500°C. This is because when the ion implantation amount exceeds 10 ¹³ ions/cm ² , the implanted layer becomes amorphous and the surface tends to be etched uniformly, especially at 5×10 ¹⁴ ions/cm ²
This is because if the value exceeds 100%, the rate of surface area expansion by etching decreases, and therefore it is necessary to crystallize it by heat treatment. If the temperature of this heat treatment is below the lower limit, it will not be effective, and if it exceeds the upper limit, recrystallization of the Al foil itself will occur, and the surface area expansion rate will drop significantly. The subsequent etching is carried out in an aqueous solution containing chloride ions, as in the past, and is usually carried out in an aqueous solution such as hydrochloric acid or common salt at a current density of 0.1 to 1 A/cm ² at a current density of 50 to
A predetermined amount of etching is performed at a temperature of 90°C. Further, the chemical conversion treatment is also performed in the same manner as in the conventional method. The aluminum electrode foil for electrolytic capacitors obtained by the present invention has mechanical strength and tan δ comparable to those of conventional ones, has a large capacitance per unit area, and has a small leakage current. This makes it possible to make aluminum electrolytic capacitors smaller and larger in capacity. Note that, depending on the type and condition of the foil, mechanical processing such as rolling or stretching may be performed between the heat treatment and the subsequent etching. Description of Examples The present invention will be described below based on Examples. Oxygen ions were implanted at 10 ¹⁰ to 10 ¹⁹ ions/cm ² into both ends of a high purity aluminum foil sample with a purity of 99.99% and a thickness of 100 μm. Next, this sample was heat-treated in a temperature range of room temperature to 550°C for 30 minutes, and then etched in a 3% by weight hydrochloric acid aqueous solution at a temperature of 80°C and a current density of 0.15A/ ^cm2 for 8 minutes (etching 1cm x 1cm). In addition, boric acid 100
g/in an aqueous solution at a temperature of 80°C, capacitance, tanδ,
Leakage current was measured. The following table shows the amount of etching during etching, the capacitance after formation, tan δ, and leakage current. In addition,
Since the amount of etching has a close correlation with the surface area expansion rate and mechanical strength, it is shown as reference data for comparison at a constant amount of etching.

[Table] As is clear from the above table, by ion-implanting a predetermined amount of oxygen into aluminum foil, the effective surface area expansion rate during etching is improved, the capacitance per unit area is increased, and leakage is reduced. The current is also small,
Furthermore, an aluminum electrode foil for electrolytic capacitors having the same mechanical strength as the conventional aluminum foil can be obtained. Effects of the Invention As described above, the method for manufacturing aluminum electrode foil for electrolytic capacitors according to the present invention involves implanting oxygen ions into aluminum foil before etching, and then chemically or electrochemically implanting the aluminum foil in an aqueous solution containing chlorine ions. The aluminum electrode foil for electrolytic capacitors obtained by this method has a mechanical strength comparable to that of conventional foils, and a capacitance per unit area that is lower than that of conventional foils. Since the capacitor is larger and the leakage current can be made smaller than that of the conventional capacitor, it is possible to make the aluminum electrolytic capacitor smaller and larger in capacity, which is extremely effective in practice.

Claims (1)

[Claims] 1 Oxygen ions on aluminum foil 10 ¹³ ~ 10 ¹⁷
An aluminum electrode foil for electrolytic capacitors, which is characterized by being implanted with ions/ ^cm2 , then heat-treated in a temperature range of 200 to 500°C, and then chemically or electrochemically etched in an aqueous solution containing chloride ions. Production method.