JPH036647B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an aluminum foil for an electrolytic capacitor cathode. Conventional technology and its problems As aluminum foil for electrolytic capacitor cathode (hereinafter simply referred to as cathode foil), Al alloy foil containing 0.1 to 0.5% by weight of Cu is used because the surface area can be easily expanded by etching such as chemical etching. is widely used (Special Publication No. 44-25016).
In recent years, as the capacitance of anode foils has improved significantly, it has also become necessary to improve the capacitance of cathode foils, making it possible to perform more uniform and finer etching.
It is hoped that Al foil will emerge. In order to satisfy these conditions, the Al foil must have a large number of starting points for pitting during the etching operation and must have excellent foil strength. Furthermore, in current cathode foils, if tempering is performed after etching, the oxide film may become thicker and the capacity may decrease, so tempering by annealing is often performed before etching. However, in this case, the oxide film formed on the surface of the foil during annealing is strong, resulting in a decrease in chemical reactivity. Therefore, prior to etching, pretreatment is performed to activate the surface, and then etching is performed. For this reason, the etching line becomes complicated and the manufacturing cost increases. In addition, when producing foil, we take measures such as performing annealing at the step with the lowest oxygen concentration so that the oxide film is formed as uniformly and as thinly as possible. Means for Solving the Problems As a result of intensive research in view of the problems of the current technology as described above, the present inventor has discovered that a method containing a specific amount of Cu,
We have also found that Al foil containing a high concentration of Mg in the surface layer can substantially eliminate or greatly reduce the problems with cathode foils. That is, the present invention
In an aluminum foil for an electrolytic capacitor cathode containing 0.1 to 0.7% Cu and the remainder Al and unavoidable impurities, Mg is 0.3% in the surface layer up to 2 μm from the surface.
Mg is unevenly distributed at a concentration of ~30%, and Mg is 0.3~% in the inner layer.
The present invention relates to an aluminum foil for an electrolytic capacitor cathode, which is characterized in that it does not contain any of the above. In the present invention, Cu is unevenly distributed in the surface layer.
Since Mg and Mg act synergistically to produce a remarkable effect, it is not necessarily appropriate to discuss the relationship between each content and effect individually, but if we force the basis for specifying the content, it is as follows. be. First, Al
The Cu content is 0.1-0.7% by weight to increase the potential of the matrix and significantly promote chemical solubility.
shall be. If the Cu content is less than 0.1% by weight,
On the other hand, if the amount exceeds 0.7% by weight, the desired effect will not be sufficiently obtained, whereas the solubility will be excessive. Mg in the surface layer up to 2μm from the surface including the oxide film
If it is unevenly distributed at a concentration of 0.3 to 30% by weight, it will reduce the corrosion resistance of the oxide film, so the etching starting point will increase even if no pretreatment is performed prior to etching. If the concentration of Mg in the surface layer is less than 0.3% by weight, the desired effect will not be fully achieved, while if it exceeds 30% by weight, the entire surface will be etched and effective etching pits will not be obtained, and the foil will not be rewound. The foil may adhere to the point where it is no longer possible. The concentration of Mg is more preferably 0.5 to 10% by weight. Since the inner layer portion of the Al foil becomes the etched foil body, the Mg content is preferably set to an amount that does not substantially affect the etching properties, precipitation resistance, electrical characteristics of the capacitor, etc., more specifically, 0.3% by weight or less. is controlled to 0.1% by weight or less. Methods for unevenly distributing Mg in the surface layer include adding it during casting, vapor deposition or ion plating, and then annealing. Note that the higher the temperature during annealing, the more concentrated Mg will be on the foil surface, and the thicker the oxide film will be. Therefore, annealing should be carried out while paying attention to concentrating Mg as much as possible and making the thickness of the oxide film as thin as possible. It is desirable to do so. The cathode foil of the present invention is etched not only at the grain boundaries but also within the grains, as shown in Reference Drawing 2, which will be described later, and is characterized by more uniform etching. Therefore, the capacitance of the etched foil is greatly improved, the progress of local etching is suppressed, and the strength of the etched foil is also improved. Note that the cathode foil of the present invention may contain unavoidable impurities that are normally contained in Al base metal for cathode foil. For example, Fe, which is normally contained at about 0.05 to 0.8% by weight, does not have much effect on the performance of the cathode foil.
Rather, it improves foil strength and promotes chemical solubility. In addition, Si, which usually contains about 0.05 to 0.5% by weight,
also does not affect the performance of the cathode foil. Effects of the Invention The aluminum foil according to the present invention has the following remarkable effects. (1) The highly concentrated Mg unevenly distributed in the surface layer increases the number of defects in the oxide film, increasing the rate of erosion by the etching solution and increasing the pitting starting point. (2) As a result of the above, the reaction during etching proceeds rapidly and a high surface enlargement ratio is obtained, so surface activation by pretreatment before etching is no longer necessary. (3) Large capacitance as a cathode foil. (4) It has great strength. Examples Examples will be shown below to further clarify the features of the present invention. Example 1 An Al alloy obtained by adding Cu to a primary electrolytic Al ingot was cast, and hot rolled and cold rolled to a thickness of 60 μm.
It was made of Al foil. Metal Mg was vacuum-deposited on both sides of the obtained foil, and eight types of Al foils were prepared, each having a different deposition time. Next, the Al foil, which had been vacuum annealed at 400°C for 6 hours and then allowed to cool, was chemically etched by immersing it in a 10% HCl bath at a temperature of 100°C for 15 seconds. Next, after performing chemical conversion at 3V in a 5% boric acid solution, the
% ammonium borate solution. The results are shown in Table 1 as samples No. 1 to 8. In addition, the thickness of the surface layer is concentrated nitric acid: pure water = 1:
It was determined from the weight loss of the foil when immersed in an aqueous solution with a 2 volume ratio. At this time, the Al foil was cut into a size of 100 mm x 100 mm and immersed in the above aqueous solution until the weight loss was about 0.054 g (corresponding to a thickness of 2 μm). Furthermore, the concentration of Mg in the surface layer was determined by performing atomic absorption spectrometry of the eluate. Example 2 Different types of Cu are added to a different primary electrolytic Al ingot from Example 1 (however, sample No. 9 has no addition)
Except for this, Al foil was produced in the same manner as in Example 1, and Mg
(However, Nos. 9, 11 to 13, and 17 to 19 were excluded), chemical etching was performed, and the capacitance was measured. The results are shown in Table 1 as samples No. 9 to 22.

[Table] From the results shown in Table 1, the cathode foil of the present invention (sample No.
It is clear that Nos. 3 to 7, Nos. 14 to 16, and Nos. 20 to 22) have large capacitances. For reference, scanning electron micrographs of the surfaces of the etched foils of Sample No. 1 and Sample No. 4 are shown as a reference drawing and (1000x magnification). From the photographs, it is clear that in sample No. 1, only the grain boundaries are etched, whereas in sample No. 4, the grain boundaries and inside the grains are etched.

Claims (1)

[Claims] 1. In aluminum foil for electrolytic capacitor cathodes containing 0.1 to 0.7% Cu and the remainder Al and unavoidable impurities, Mg is added to the surface layer up to 2 μm from the surface.
is unevenly distributed at a concentration of 0.3 to 30%, and Mg is present in the inner layer.
Aluminum foil for electrolytic capacitor cathode, characterized in that it does not contain more than 0.3%.