JPS6144139B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel hard aluminum alloy foil for electrolytic capacitors containing thallium (Tl) and a soft special aluminum foil for electrolytic capacitors having a new configuration in which Tl is unevenly distributed in the surface layer of the aluminum foil. .

In this specification, "%" and "ppm" are expressed on a weight basis unless otherwise specified.

The aluminum foil used in electrolytic capacitors must have excellent etching properties, a large surface area expansion rate after etching, and a negligible leakage current after anodization. Conventionally, in order to obtain aluminum foil with such properties,
Although it has been proposed to add appropriate alloying components to high-purity aluminum, none of these methods can be said to be fully satisfactory in various respects. As a result of various studies while paying attention to the problems of known aluminum alloy foils, the present inventor found that a soft aluminum foil with a purity of 99.9% or more containing a specific amount of Tl has excellent etching properties, capacitance, chemical formation properties, etc. It has been found that this material exhibits excellent properties in terms of. Furthermore, according to the research of the present inventor, as described in claim 1,
When an aluminum alloy foil containing Tl is annealed, the alloying component Tl selectively migrates to the surface layer of the aluminum foil, resulting in a soft aluminum foil with a very unique structure containing a high concentration of Tl in the surface layer. It has been found that this product exhibits even more excellent properties for use in electrolytic capacitors.
That is, in the present invention, the Tl content (x) is 0.1 ppm<
Aluminum purity within the range of x≦0.7ppm
99.9% or more hard aluminum alloy foil for electrolytic capacitors (hereinafter referred to as the first invention) and
A soft aluminum foil for electrolytic capacitors with an aluminum purity of 99.9% or more, in which the Tl content (X) is within the range of 0.1 ppm < 2 invention).

In the present invention, the aluminum purity is 99.9%.
In addition to the above, the Tl content (x) is set within the range of 0.1 ppm<x≦0.7 ppm, more preferably 0.2 to 0.4 ppm, taking etching characteristics, capacitance, chemical formation characteristics, etc. into consideration comprehensively. Tl content is
If it is less than 0.1 ppm, there is a drawback that it is difficult to obtain uniform etching, while if it exceeds 0.7 ppm, capacitance, pit density, and chemical formation properties tend to deteriorate.

The hard aluminum alloy foil of the first invention of the present application is obtained by adding Tl content (x) such that the Tl content (x) becomes 0.1ppm<x≦0.7ppm when casting aluminum with a purity of 99.9% or more, and then performing a conventional foil manufacturing process. .

The soft aluminum foil of the second invention of the present application can be obtained by further annealing the aluminum alloy foil of the first invention of the present application in a conventional manner, for example, in a non-oxidizing atmosphere at 450° C. or higher or in a vacuum. In the obtained soft aluminum foil, since Tl is unevenly distributed in the surface layer at a high concentration, the surface oxide film is considered to be extremely defective. Therefore, during etching, Cl ^- ions easily penetrate and a large number of pits are formed in the early stage of etching. As etching progresses
The surface layer containing Tl is eluted, but once pits are formed, the pitting properties continue, so the inner layer made of high-purity aluminum continues to elongate, increasing the surface area expansion rate. .
After the surface layer portion is eluted, the process is similar to etching of ordinary high-purity aluminum foil, so the corrosion loss does not increase. Furthermore, the resulting etched foil has a high pit density, so it provides an electrolytic capacitor with higher capacity and even better chemical properties. Furthermore,
As is clear from the high L value of etched foil,
The aluminum soft foil of the second invention of the present application has good etching properties (etching efficiency). Furthermore,
Coarsening of crystal grains is also effectively prevented by the action of Tl.

Example 1 0 to 0.7 ppm of Tl was added to 99.99% Al during casting,
A 0.1 mm hard alloy foil was obtained by cold rolling according to a conventional method. In hard alloy foil containing Tl,
It was confirmed that Tl was uniformly distributed throughout. These hard foils are then heated under vacuum for 550°C.
It was annealed at ℃ for 3 hours to obtain a soft foil. In the soft foil containing Tl, it was confirmed that Tl was unevenly distributed in the surface layer at a high concentration.

(a) Next, the obtained soft foil is immersed in an etching bath containing 12.5 vol % of HCl, and etched for a predetermined period of time at a bath temperature of 80° C. and a DC current density of 30 A/dm ² . FIG. 1 shows the results of examining the relationship between the amount of Tl added and etching properties for each etching time. In Figures 1 to 3, curve A has an etching time of 30 seconds, curve B has an etching time of 90 seconds, and curve C has an etching time of 30 seconds.
The results for the case of 180 seconds are shown.

In Fig. 1, the L value (0°-45°) means the brightness (whiteness) of the etched foil surface measured by the 45° diffusion method (0°-45° method).
This was measured using a direct reading color measurement color difference computer (model CDE-SCH-4A) manufactured by Suga Test Instruments Co., Ltd. If the L value is low, it indicates that there are many unetched areas, while if it is too high, surface dissolution is too intense and pits are difficult to form. In Figure 1, the amount of Tl added is
Best results were obtained in the range of 0.3-0.4 ppm.

(b) The relationship between the amount of Tl added and the number of pits in each of the etched foils obtained in (a) above was investigated for each etching time, and the results are shown in FIG. If the amount of Tl added is too small, there will be few film defects and pitting initiation points, whereas if the amount of Tl added is too large, there will be too many film defects and the surface will be dissolved, and pits will extend in the thickness direction of the foil. It becomes difficult. In FIG. 2, the best results were obtained in the range of 0.2 to 0.4 ppm.

(c) Figure 3 shows the relationship between the amount of Tl added and the capacitance when the 90 second etched foil obtained in (a) above was subjected to 10V chemical conversion. In addition, 30 seconds etched foil and 180
The second-etched foil also shows the same tendency as the 90-second etched foil, so these results are not shown.

The best results have been obtained with Tl addition in the range of 0.2 to 0.4 ppm.

[Brief explanation of the drawing]

1 to 3 are graphs showing the physical properties of aluminum foil according to the present invention.

Claims (1)

[Claims] 1. Thallium content (x) is 0.1ppm<x≦
Aluminum purity 99.9% within 0.7ppm
Hard aluminum alloy foil for electrolytic capacitors. 2 Thallium content (x) is 0.1ppm＜x≦
Aluminum purity 99.9% with a concentration of 0.7ppm and thallium unevenly distributed in the surface layer.
Soft aluminum foil for electrolytic capacitors.