JPS628492B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum alloy foil for electrolytic capacitor electrodes. In this specification, all "%" means "% by weight". Aluminum foils used as electrodes for electrolytic capacitors are generally etched in a solution such as a hydrochloric acid solution or a saline solution in order to expand their effective surface area and increase their electrostatic capacitance per unit volume. Therefore, in order to improve the performance of electrolytic capacitors, the foil material is required to have as large an area enlargement ratio as possible through etching. This area expansion ratio naturally depends on the etching conditions, but it also depends greatly on the composition of the material foil. This may lead to a decrease in capacity. The object of the present invention is to provide an aluminum alloy for electrolytic capacitor electrodes that can prevent such surface dissolution, always exhibit stable and excellent etching properties, and further increase capacitance without reducing mechanical strength. The purpose is to provide foil. The present invention was completed based on the discovery that the etching characteristics of aluminum alloy foil can be stabilized by containing a small amount of boron. That is, the aluminum alloy foil for electrolytic capacitor electrodes according to the present invention has a high purity of aluminum.
99.9% or more and contains more than 50ppm of boron
It is characterized in that the content is within a range of 300 ppm or less, and the content of titanium as an impurity is regulated to less than 2 ppm. If the content of boron in the foil is less than 50 ppm, the desired effect of improving etching characteristics and, by extension, increasing capacitance cannot be sufficiently achieved by adding boron alone. On the other hand, the content
When it exceeds 300 ppm, the surface of the foil is deeply and roughly etched, which tends to decrease the capacitance, and also causes a decrease in strength due to increased corrosion loss. Therefore, the content of boron in the foil is limited to a range of more than 50 ppm and less than 300 ppm, and a particularly preferable range is about 60 to 100 ppm. On the other hand, as an aluminum alloy foil material for electrolytic capacitor electrodes, aluminum purity is generally 99.9%.
The above requirements are well known, and it goes without saying that it is preferable to have as high a purity as possible. Therefore, in addition to containing boron, the aluminum alloy foil according to the present invention contains 0.01% of other elements such as copper, iron, and silicon as inevitable impurities.
It is of course permissible to include it within the range below. Also,
Conventionally, this type of aluminum alloy foil for capacitor electrodes has been actively added with other trace elements in order to increase the number of etched holes per unit area. In addition to the inclusion of these forcibly added elements, the scope also includes cases where such forcibly added elements are additionally included. Examples of such elements include strontium, vanadium, manganese, magnesium, zinc, indium, tin, lead, bismuth, silver, gallium, cadmium, zirconium, thorium, etc., and the content thereof is generally 0.1 to 5000 wt- Within ppm range. When these elements are contained in addition to boron, the effect may not only be the sum of the effects of boron and other elements, but also a more synergistic effect may be expected. As expected, this invention will
As long as the effect of containing boron is achieved, it is included within this range. Conventionally, in aluminum electrode foils, in view of the fact that the inclusion of titanium, which is unavoidably included as an impurity in the material gold, is a dominant factor in reducing capacitance, the content of titanium is allowed to be large. In order to maintain good capacitance, a technique has been proposed in which boron is forcibly added in coexistence with titanium (for example, JP-A-53-107657, JP-A-Sho 53-
113212). On the other hand, the present invention rather does not contain titanium substantially, but
By incorporating boron, the capacitance is increased even more effectively than by itself. Therefore, in the alloy foil of the present invention, the content of titanium as an impurity is limited to a very small amount, specifically less than 2 ppm.
If it exceeds this, the capacitance increasing effect intended by the present invention is reduced. Next, examples of this invention will be shown.

[Table] Various aluminum alloys made by homogenizing aluminum alloy slabs with various compositions shown in Table 1 at 600°C, hot rolling at 500°C to a thickness of 5 mm, cold rolling to 90 μm, and then annealing at 300°C. The foil was used as a sample. Each of these sample foils was etched in a 5% hydrochloric acid + 0.1% nitric acid aqueous solution with a bath temperature of 50°C for 5 minutes and 30 seconds through a current of 0.8A/cmPA, and then the temperature of the solution was lowered.
A chemical conversion treatment was performed in a 5% boric acid aqueous solution at 85° C. with a chemical conversion voltage of 20 V and an application time of 10 minutes, and the capacitance and tensile strength of each sample were measured. The capacitance was measured in a 10% ammonium borate aqueous solution at a liquid temperature of 30° C., with the measurement frequency set at 120 Hz. The measurement results are shown in Table 2.

[Table] As seen in the results in the table above, the aluminum alloy foil according to the present invention has a boron content of more than 50 ppm and less than 300 ppm, which leads to a decrease in mechanical strength. It is possible to obtain the effect of increasing capacitance without any interference, and has excellent performance as an electrolytic capacitor electrode.

Claims (1)

[Claims] 1. Aluminum for electrolytic capacitor electrodes, characterized in that the purity of aluminum is 99.9% or more, boron is contained in a range of more than 50 ppm and less than 300 ppm, and the content of titanium as an impurity is regulated to less than 2 ppm. Alloy foil.