JPH0336288B2 - - 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,
There is a desire for smaller size and larger capacity, and an aluminum electrode foil with sufficient mechanical strength, an etched amount, and a larger surface area expansion ratio than the present one is 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 an aluminum foil for an electrolytic capacitor of the present invention includes adding atoms electrochemically more noble than aluminum and having a larger atomic radius than aluminum to the aluminum foil before etching in an amount of 5×10 ¹¹ to 5×
After implanting 10 ¹³ ions/cm ² ions, it is left for a certain period of time in a temperature range from room temperature to 200°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 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. The adsorption of chlorine ions is preferentially carried out at weak points in the oxide film on the surface due to impurities or dislocations caused by rolling, etc., forming etch pit nuclei, and further etching progresses along the dislocations, expanding the surface area. will be held. Therefore, larger surface area expansion requires more and more uniformly distributed dislocations. When metal atoms are ion-implanted into aluminum foil, the crystal lattice is strained, causing an increase and uniformization of dislocations. However, ion-implanting atoms with a larger atomic radius than aluminum causes an increase in dislocations,
Uniformity becomes noticeable. Generally, aluminum foil for electrolytic capacitors is manufactured by mixing a small amount of several kinds of impurities into aluminum and performing processes such as melting, casting, and annealing. The contained impurities mainly precipitate near the surface, but segregation is likely to occur and uniform dispersion is difficult to obtain. Therefore, 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 dispersed more and more uniformly, so
Generates etching pits uniformly and expands the surface area. The larger the atomic radius of the ion-implanted atoms is than that of aluminum, the greater the strain on the crystal lattice, which is effective in increasing and uniformizing dislocations. In addition, if the metal to be ion-implanted is electrochemically more noble than aluminum, the etching pit can be made more uniform due to the effect of accelerating the etching of aluminum due to the potential difference between the ion-implanted metal or intermetallic compound and the aluminum matrix. can be generated and the surface area can be expanded. The metal to be ion-implanted in the present invention is electrochemically nobler than aluminum and has a larger atomic radius than aluminum, but preferably Sn, In, Cd, Pb,
One type selected from Bi, Ag, and Au. 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 surface area enlarging effect due to excessive etching amount. That is,
In the present invention, the ion implantation amount is 5×10 ¹¹ to 5×10 ¹³ ions/
It shows the effect of increasing surface area in the range of ^cm2 ,
When the ion implantation amount is less than the lower limit, no effect on etching is observed, and when the ion implantation amount exceeds the upper limit, the etching of the aluminum foil surface becomes excessive, and the surface area expansion actually decreases. After ion implantation, the material is left at a temperature between room temperature and 200° C. for a certain period of time; however, if this 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 chlorine 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 and a current density of 50 to 90%.
It is etched by a predetermined amount at a temperature of °C. 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, tan δ, and leakage current comparable to conventional ones, and can increase capacitance per unit area. This makes it possible to make aluminum electrolytic capacitors smaller and larger in capacity. Description of Examples Hereinafter, the present invention will be described based on Examples. Metals that are electrochemically more noble than aluminum and have a larger atomic radius than aluminum, such as Sn, In, Cd, Pb, Bi, Ag, and Au, were placed on both sides of a high-purity aluminum foil sample with a purity of 99.99% and a thickness of 100μ. 10 ¹⁰
~10 ¹⁶ ions/ ^cm2 ions were implanted. Next, this sample was left for 60 minutes at a temperature range of room temperature to 550℃, and then placed in a 20% by weight saline solution at a temperature of 90℃ and a current density of
Etching was performed for 4 minutes at 0.35 A/cm ² (etched area 1 cm x 1 cm), and further chemical conversion was performed in an aqueous solution containing 1% by weight of boric acid at a temperature of 80° C. and a formation voltage of 23 V. The capacitance and tan δ of the obtained chemically formed foil were measured. The following table shows the amount of etching during etching, the capacitance after chemical formation, and tan δ. The measurement was carried out in a 5% by weight ammonium borate aqueous solution using a tin foil as a cathode at a temperature of 30° C. with an AC bridge at 120 Hz. 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 table above, by ion-implanting a metal that is electrochemically nobler than aluminum and has a larger atomic radius than aluminum into aluminum foil, the effective surface area expansion rate of aluminum foil during etching can be improved. It is possible to obtain an aluminum electrode foil for an electrolytic capacitor, which has an improved capacitance per unit area and a mechanical strength equivalent to that of a conventional aluminum foil. Note that although an anode foil is shown in the embodiment, the present invention can also be applied to a cathode foil. Effects of the Invention As described above, the method of manufacturing an aluminum electrode foil for an electrolytic capacitor according to the present invention includes ion-implanting a metal that is electrochemically nobler than aluminum and has a larger atomic radius than aluminum into an aluminum foil before etching. This method is then chemically or electrochemically etched in an aqueous solution containing chlorine ions, and the aluminum foil for electrolytic capacitors obtained by this method has good mechanical strength, tanδ, and leakage current. Since the electrostatic capacitance per unit area can be made larger than that of the conventional one, it is possible to make the aluminum electrolytic capacitor smaller and larger in capacity, making it extremely effective in practice.

Claims (1)

[Claims] 1. After electrochemically implanting 5×10 ¹¹ to 5×10 ¹³ ions/cm ² of a metal that is more noble than aluminum and whose atomic radius is larger than aluminum into aluminum foil, the metal is heated at room temperature or above 200°C. 1. A method for manufacturing an aluminum electrode foil for an electrolytic capacitor, which comprises leaving it at the following temperature for a certain period of time, and then chemically or electrochemically etching it in an aqueous solution containing chlorine ions. 2 Metals that are electrochemically more noble than aluminum and whose atomic radius is larger than aluminum are Sn, In,
The method for manufacturing an aluminum electrode foil for an electrolytic capacitor according to claim 1, wherein the aluminum electrode foil is one selected from Cd, Pb, Bi, Ag, and Au.