JPH057856B2 - - 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 electrolytic capacitor manufacturing process 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 for producing aluminum foil for electrolytic capacitors of the present invention includes electrochemically applying metals such as Fe, which are more noble than aluminum, to the aluminum foil before etching.
After implanting 5×10 ¹¹ to 5×13 ¹³ ions/cm ² of any one of Ni, Co, Cu, Cr, Zn, Mn, and Si,
Heat treated at a temperature range higher than room temperature and less than 200℃,
After that, etching is carried out chemically or electrochemically in an aqueous solution containing chloride 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 enlargement 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 etching composition, 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 occurs internally 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, increasing the surface area. It will be done. Therefore, larger surface area expansion requires more and more uniformly distributed dislocations. Electrochemically implanting ions of metals nobler than aluminum into aluminum foil strains the crystal lattice, increases and homogenizes dislocations, and increases the potential difference between these metals or intermetallic compounds and the aluminum matrix. Promotes etching of aluminum. 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 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, the number of dislocations in the aluminum foil is increased and uniformly dispersed, and furthermore, due to the effect of promoting aluminum etching due to the potential difference between the implanted metal or intermetallic compound and the aluminum matrix, Etch pits can be generated more uniformly 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 surface area enlarging effect due to excessive etching amount. That is,
In the present invention, the ion implantation amount is 5×10 ¹¹ ×5 to 10 ¹³ ions/cm ²
This indicates the effect of surface area expansion within the range of On the contrary, if a large amount of implanted metal remains after etching, the properties of the chemical conversion coating such as leakage current will deteriorate. After ion implantation, heat treatment is performed at a temperature higher than room temperature and less than 200°C, but if the heat treatment 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 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.
In addition, depending on the type of foil and the condition of the foil, there may be
Mechanical processing such as rolling and stretching may be performed. 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 The present invention will be described below based on Examples. Among metals more noble than aluminum, Fe, Ni, Co, Cu, Cr, Zn, Mn, and Si are coated on both sides of a high-purity aluminum foil sample with a purity of 99.99% and a thickness of ^100μ .
~10 ¹⁶ ions/ ^cm2 ions were implanted. Next, this sample was kept in the temperature range of room temperature to 550℃ for 60 minutes, and then
Temperature 90℃, current density in wt% saline solution
Etching was performed for 4 minutes at 0.35 A/cm ² (etched area 1 cm x 1 cm), and further chemical formation 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 5wt% ammonium borate aqueous solution using a tin foil as a cathode and
It was carried out at 120 Hz with an AC bridge at a temperature of °C.
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 ion-implanting a metal electrochemically more noble than aluminum into aluminum foil, the effective surface area expansion rate of aluminum foil during etching is improved, and the An aluminum electrode foil for electrolytic capacitors having a large capacitance and the same mechanical strength as conventional aluminum foils can be obtained. Note that although an anode foil is shown in the embodiment, the present invention can also be applied to an anode foil. Effects of the Invention As described above, in the method of manufacturing aluminum electrode foil for electrolytic capacitors according to the present invention, ions of a metal nobler than aluminum are electrochemically implanted into the aluminum foil before etching, and then chemically implanted in an aqueous solution containing chlorine ions. The aluminum foil for electrolytic capacitors obtained by this method has mechanical strength, tan δ, and leakage current comparable to those of conventional foils. Since the capacitance per unit area can be made larger than that of conventional capacitors, aluminum electrolytic capacitors can be made smaller and have larger capacities, making them extremely effective in practice.

Claims (1)

[Claims] 1 Aluminum foil with Fe, Ni, Co, Cu, Cr,
5×10 ¹¹ to 5 of any one of Zn, Mn, and Si
×10 ¹³ ions/cm ² After ion implantation, it is heat-treated in an atmosphere with a temperature higher than room temperature and less than 200℃, and then chemically or electrochemically etched in an aqueous solution containing chlorine ions. A method for manufacturing aluminum electrode foil for electrolytic capacitors.