JPH032333B2 - - 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 configurations and their problems In general, aluminum electrode foils for electrolytic capacitors are made by processing rolled hard aluminum foil or annealed soft aluminum foil in a chemical solution containing chlorine ions such as sodium chloride or hydrochloric acid. After electrochemical etching is performed to expand the surface area of the aluminum foil, a chemical conversion treatment is performed to form 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 of breakage 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 ratio than conventional ones. 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 an atomic radius larger than that of aluminum to the aluminum foil before etching in an amount of 10 ¹³ to 5×.
After implanting 10 ¹⁶ ions/cm ² ions, heat treatment is performed at a temperature range of 200 to 500° C., and then chemical or electrochemical etching is performed in an aqueous solution containing chlorine ions. In other words, by applying the above etching and then forming a dielectric conversion film through chemical conversion treatment, aluminum for electrolytic capacitors has sufficient mechanical strength and has a larger capacitance per unit area than conventional ones. 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 etching pit adsorbed on the surface of the chlorine ions, and as etching progresses, corrosion of the aluminum foil occurs internally in the form of pitting corrosion.
The surface area gradually expands. The adsorption of chlorine ions is preferentially carried out on weak points in the surface oxide film caused by impurities or dislocations caused by rolling, etc., forming etched pit nuclei. Etching then proceeds along the dislocations, increasing the surface area. It will be done. 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 types of impurities into aluminum and performing processes such as melting, casting, rolling, and annealing. The contained impurities mainly precipitate near the surface, but segregation is likely to occur.
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 dispersed more and more uniformly, so that etch pits are uniformly generated and the surface area can be expanded. 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,
If the ion implantation amount is less than the lower limit, no effect on etching will be observed, and if it exceeds the upper limit, the etching of the aluminum foil surface will be excessive.
The surface area expansion actually shows a decrease, and if a large amount of implanted metal remains after etching, it deteriorates the conversion coating properties such as leakage current. The ion implantation amount exhibits the effect of increasing the surface area when it is 10 ¹² to 10 ¹⁸ ions/cm ² , but is more preferably in the range of 10 ¹³ to 5×10 ¹⁶ ions/cm ² . 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 implantation amount becomes amorphous and the surface tends to be uniformly etched, especially at 5×10 ¹⁴ ions/cm ²
This is because, if it exceeds this, the rate of surface area expansion by etching decreases, so it is necessary to crystallize it by heat treatment. If the heat treatment temperature 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 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 at a current density of 50 to 90%.
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 this heat treatment and the subsequent etching. The aluminum electrode foil for electrolytic capacitors obtained by the present invention has mechanical strength tanδ leakage current comparable to that of conventional ones, and can increase capacitance per unit area. It becomes possible to make electrolytic capacitors smaller and larger in capacity. Description of Examples The present invention will be described below based on Examples. Metals that are electrochemically more noble than aluminum and have larger atomic radii 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 ¹⁹ ions/ ^cm2 ions were implanted. Next, this sample was heat-treated for 30 minutes in the temperature range of room temperature to 550℃, and then
Temperature 80℃, current density in wt% chlorine aqueous solution
Etching was carried out at 0.15 A/cm ² for 8 minutes (etched area 1 cm x 1 cm), and further chemical formation was carried out in an aqueous solution containing 100 g of boric acid at a temperature of 80° C. and a formation voltage of 260 V. The electrostatic capacity and tan δ of the obtained chemically formed foil were measured. The following table shows the etching amount during etching, the capacitance after chemical formation, and tan δ. The measurement is 5wt%
Using tin foil as a cathode in an aqueous ammonium borate solution,
The etching was performed at 120Hz using an AC bridge at a temperature of 30°C.The etching amount is closely correlated with the surface area expansion rate and mechanical strength, so this data is shown as reference data for comparison at a constant etching amount. Ta.

【table】

[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 is
The mechanical strength, tanδ, and leakage current are comparable to conventional capacitors, and the capacitance per unit area can be increased compared to conventional capacitors, making it possible to make aluminum electrolytic capacitors smaller and larger in capacity. ,
This is extremely effective in practice.

Claims (1)

[Claims] 1. After electrochemically implanting 10 ¹³ to 5×10 ¹⁶ ions/cm ² of a metal that is more noble than aluminum and whose atomic radius is larger than aluminum into aluminum foil, at a temperature of 200 to 500°C. 1. A method for producing an aluminum electrode foil for an electrolytic capacitor, the method comprising heat-treating the foil at a temperature within a range 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,
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 In, Cd, Pb, Bi, Ag, and Au.