JPH0336289B2 - - 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. Conventional Structures and Problems Generally, aluminum electrode foils for electrolytic capacitors are produced by applying a chemical or electrical process to rolled hard aluminum foil or annealed soft aluminum foil in an aqueous solution containing chlorine ions such as sodium chloride or hydrochloric acid. 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 has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing aluminum foil for electrolytic capacitors having a higher surface area expansion rate than conventional methods. Structure of the Invention The method of manufacturing aluminum foil for electrolytic capacitors of the present invention includes implanting oxygen ions at 5×10 ¹¹ to 5×10 ¹³ /cm ² into aluminum foil before etching, and then at a temperature of room temperature or higher and 200°C or lower. It is left in the area for a certain period of time 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 core where chlorine ions are adsorbed on the surface, and as the etching progresses, corrosion of the aluminum foil takes place in the form of pitting corrosion.
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, larger surface area expansion requires more and more uniformly distributed dislocations. Ion implantation of metal 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 is evenly formed on the aluminum surface by the implanted oxygen ions, making the etch pit more uniform. can be generated and the surface area can be expanded. 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 the concentration of etching pits. That is, in the present invention, the ion implantation amount is 5×10 ¹¹ to 5×
It shows the effect of increasing the surface area in the range of 10 ¹³ ions/cm ² , and when the ion implantation amount is less than the lower limit, no effect on etching is observed, and when it exceeds the upper limit, the surface area expansion rate decreases. After ion implantation, it is left at a temperature above room temperature and below 200° C. for a certain period of time, but if this standing temperature exceeds 200° C., the surface area expansion rate decreases, which is not preferable. The subsequent etching is carried out in an aqueous solution containing chloride ions, as in the past, and is usually carried out at a current density of 50 to 90°C at a current density of 0.1 to 1 A/cm ² in an aqueous solution such as hydrochloric acid or common salt.
It is etched by a predetermined amount at a temperature of . Further, the chemical conversion treatment is also performed in the same manner as in the conventional method. Note that, depending on the type of foil and the condition of the foil, mechanical processing such as rolling or stretching may be performed between the above-mentioned leaving treatment after ion implantation and subsequent etching. 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. Description of Examples The present invention will be described below based on Examples. Oxygen ions were implanted at 10 ¹⁰ to 10 ¹⁶ ions/cm ² into both sides of a high purity aluminum foil sample with a purity of 99.99% and a thickness of 100 μm. Next, this sample was left for 60 minutes at a temperature ranging from room temperature to 550℃, and then etched in a 20% by weight saline solution at a temperature of 90℃ and a current density of 0.35A/ ^cm2 for 4 minutes (etched area 1cm x 1cm). Further, it was chemically formed in an aqueous solution containing 1% by weight of boric acid at a temperature of 80°C and a formation voltage of 23V. The capacitance, tan δ, and leakage current of the obtained chemically formed foil were measured. The following table shows the amount of etching during etching, the capacitance and tan δ after chemical formation, and the leakage current. In addition,
Measurements were performed using an AC bridge at a temperature of 30°C using a Sn foil as a cathode in a 5wt% ammonium borate aqueous solution.
This was done at 120Hz. Furthermore, 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 implanting oxygen ions into aluminum foil, the effective surface area expansion rate during etching is improved, the capacitance per unit area is large, the leakage current is small, and Furthermore, an aluminum electrode foil for electrolytic capacitors having the same mechanical strength as conventional aluminum foils can be obtained. Effects of the Invention As described above, the method of 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 aluminum electrolytic capacitor is larger and the leakage current can be reduced, 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 are added to aluminum foil at 5×10 ¹¹ ~5
×10 ¹³ pcs/ ^cm2 After ion implantation, temperature above room temperature 200℃
1. A method for manufacturing an aluminum electrode foil for an electrolytic capacitor, which comprises leaving it in the following temperature range for a certain period of time, and then chemically or electrochemically etching it in an aqueous solution containing chlorine ions.