JPS5992514A - Method of producing aluminum electrode foil for electrolyticcondenser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing aluminum electrode foil for electrolytic capacitors.

Structures of conventional examples and their problems In general, aluminum electrode foils for electrolytic capacitors are manufactured by subjecting rolled hard aluminum foils or annealed soft aluminum foils to chemical or chloride-containing aqueous solutions containing chlorine ions, such as sodium chloride or hydrochloric acid. Pages are manufactured by electrochemically etching the aluminum foil to enlarge its surface area, and then applying chemical conversion treatment 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. Also,
Since the amount of etching and the mechanical strength of the aluminum foil are reduced, if the aluminum foil is excessively etched, there is a risk that it will break during electrolytic capacitor manufacturing processes such as etching and chemical 9 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, aluminum electrolytic capacitors are desired to be more compact and have a larger capacity, and an aluminum electrode foil that has sufficient mechanical strength and a constant etching amount and a larger surface area expansion ratio than the current one. is highly desired, and much research is being conducted.

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 an aluminum foil for electrolytic capacitors having a higher surface area ratio than the conventional method.

Structure of the Invention The method of manufacturing aluminum foil for electrolytic capacitors of the present invention includes adding oxygen ions to the aluminum foil before etching.
After 3~1017 Keme ion implantation, 200~SOO
This process involves heat treatment in the temperature range of 10°C, followed by chemical or electrochemical etching in an aqueous solution containing chlorine ions. That is, after performing the above etching,
Furthermore, by forming a dielectric chemical conversion film by chemical conversion treatment, it is possible to manufacture an aluminum electrode foil for an electrolytic capacitor that has sufficient mechanical strength and has a larger capacitance per unit area than conventional ones.

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. is influenced by many factors such as the rolling process of the aluminum foil, annealing, 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 etch pit nuclei where chlorine ions are adsorbed on the surface, and as etching progresses, corrosion of the aluminum foil occurs internally in the form of pitting corrosion, and the surface area gradually expands. go. These hydrochloric acid ions preferentially adsorb to weak points in the surface oxide film caused by impurities or dislocations caused by rolling, etc., forming etch pit nuclei, and further etching progresses along the dislocations, expanding the surface area. Therefore, in order to increase the surface area to a large extent, it is necessary that these dislocations be more numerous and uniformly distributed.

The ion implantation of oxygen atoms into aluminum foil (5 vanes) 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 with aluminum, then melting, casting, and rolling.

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 presence of overcrowded and depopulated areas in the etch 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 the concentration of etch pits. This ion-67, -non-injected amount exhibits the effect of increasing the surface area at 10 to 10 ions/cd, but is more preferably in the range of 1013 to 1017 ions/cd.

When this happens, the injection layer becomes amorphous and the surface tends to be etched uniformly.Especially when it exceeds 5 x 1014 chips/cdi, the surface area expansion rate due to etching decreases.
This is because 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 A2 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 etched by a predetermined amount at a temperature of 60 to 90°C at a current density of 0.1 to 1 A in an aqueous solution such as 9-salt hydrochloric acid. be done. 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 capacitance per unit area of 7 vanes larger, and has a smaller 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 explained below based on examples.

Oxygen ions were implanted at 1010 to 1019 CrA ions 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 for 30 minutes in a temperature range of room temperature to 650°C, and then etched in a 3 weight ratio hydrochloric acid aqueous solution at a temperature of 80°C and a current density of 0.15 A/crA for 8 minutes (1 cm x 1 cm). , and further in an aqueous solution of 10 oy/L of boric acid at a temperature of 80°C.

Capacitance, tan δ, and leakage current were measured.

The following table shows the amount of etching during etching, the capacitance after chemical formation, tan δ, and leakage current. Since the amount of etching has a close correlation with the surface area expansion ratio 9 and mechanical strength, it is shown as reference data for comparison at a constant amount of etching.

As is clear from the table above on page 9, 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 large, and the leakage current is 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 of manufacturing aluminum electrode foil for electrolytic capacitors according to the present invention involves implanting oxygen ions into the 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 wide variety of mechanical strengths compared to conventional ones, and has a larger capacitance per unit area than conventional ones. Furthermore, since the leakage current can be made smaller than that of conventional capacitors, it is possible to make the aluminum electrolytic capacitor smaller and larger in capacity, making it extremely effective in practice.

Claims (1)

[Claims] It is characterized by implanting 10 to 10 oxygen ions/Ca ions into aluminum foil, then heat-treating it at a temperature range of 2oO to 500'C, and then chemically or electrochemically etching it in an aqueous solution containing chlorine ions. A method for manufacturing aluminum electrode foil for electrolytic capacitors.