JPH0881725A - Aluminum foil for cathode of electrolytic capacitor - Google Patents

Abstract

PURPOSE: To develop Al foil for the cathode of an electrolytic capacitor high in capacitance and excellent in bending strength as the cathode material for an electrolytic capacitor by forming a high concn. layer of specified elements on the surface layer part of Al foil contg. specified elements by a sputtering method. CONSTITUTION: The ingot of Al having a compsn. contg., by weight, Ti, V, Zr and Ni respectively by <=20ppm concn. so as to regulate the total content o each element to >=0.4ppm, furthermore contg. 0.03 to 0.15% Fe and 0.02 to 0.15% Si, and the balance Al is subjected to homogenizing treatment and is thereafter subjected to hot rolling and cold rolling into Al foil having about 0.05mm thickness. The surface of this Al foil is treated by ion sputtering or the like to form a layer in which the total content of Ti, V, Zr and Ni in the surface layer part in the range of 0.2μm in the thickness direction from the surface is regulated to 0.6 to 8000ppm concn. The Al foil high in capacitance and excellent in bending strength as the cathode material of an electrolytic capacitor can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum foil for a cathode of an electrolytic capacitor, and more particularly to an improvement of an aluminum foil for a cathode of an electrolytic capacitor of a pure aluminum type which is subjected to AC electrolytic etching.

[0002]

2. Description of the Related Art Since the capacitance of an electrolytic capacitor is proportional to the surface area of an electrode, the aluminum foil for electrolytic capacitors is generally subjected to an etching treatment in order to increase the surface area. In the cathode aluminum foil, the etching method differs depending on the material system, in the case of a pure aluminum foil, constant current electrolytic etching by alternating current is performed in a hydrochloric acid solution, and in the case of an alloy foil added with copper or manganese. Chemical etching is performed by self-corrosion.

[0003] Of these, the pure aluminum-based cathode foil, which is subjected to electrolytic etching, is different from the anode foil in that it requires no chemical conversion treatment for forming a withstand voltage film, so that a normal-purity aluminum foil is used as the cathode foil. Although used, a material with a small chemical dissolution (corrosion) that does not lead to an increase in surface area is preferable for obtaining a high capacitance,
Ingenuity in terms of composition to improve etching characteristics by adjusting trace impurities, manufacturing ingenuity such that impurities are solid-solved in matrix by minimizing precipitation in solution treatment or hot rolling of ingot Is being done.

However, since the AC electrolytic etching of the pure aluminum foil for the cathode is performed in a hydrochloric acid solution, chemical dissolution is inevitable in addition to electrochemical dissolution, and the actual dissolution amount is larger than the theoretical amount. Always. This is because the walls of the etch pits formed by electrolysis are chemically dissolved, and this chemical dissolution action leads to an increase in the amount of dissolution, hindering the effect of increasing the surface area.

On the other hand, as an aluminum foil for an electrolytic capacitor used as an anode material, aluminum purity 99.9
% Or more, at least one of Ti, V, and Zr is contained in a trace amount range, and the total concentration of these elements in the foil surface layer portion is made higher than the concentration inside the foil to suppress dissolution of etch pits. Aluminum foil for electrolytic capacitors has been proposed in which the etch pits are deeply tunneled to obtain a large surface expansion ratio. (JP-A-4-62822)

[0006] The inventor focused on the above proposal, and based on this, in order to obtain a pure aluminum-based foil for a cathode having a high electrostatic capacity and strength, particularly excellent bending strength required for an electrolytic foil. , Multi-faceted study on the relationship between the generation and progress of etch pits in AC electrolysis, the dissolution and strength characteristics of etch pit walls, trace elements, trace impurities, and concentration distribution of these elements in the thickness direction of the foil As a result, they have found that excellent etching characteristics and strength can be imparted by adjusting the content and concentration distribution of a specific element in aluminum, and have reached the present invention.

[0007]

The present invention has been made based on the above studies and discoveries, and its purpose is to:
To provide an aluminum foil for an electrolytic capacitor cathode, in which chemical solubility in AC electrolytic etching is suppressed, electrostatic capacity is increased by forming etching pits with increased density, and strength required as an electrolytic foil, particularly bending strength is also good. is there.

[0008]

An aluminum foil for an electrolytic capacitor cathode according to the present invention for achieving the above object contains Ti, V, Zr and Ni in an amount of 20 ppm or less, respectively, and a total of 0.4 ppm or more. ~ 0.15%, Si 0.02-0.15
%, With the balance Al and unavoidable impurities, and the surface layer portion from the surface of the aluminum foil to 0.2 μm inside in the thickness direction contains Ti, V, Zr, and Ni in a total amount of 0.6 to The structural feature is that it exists at a concentration of 8000 ppm.

Explaining the significance and the reason for limitation of the trace amounts of components in the present invention, Ti, V, Zr and N are described.
i is related to the generation amount of the defective portion of the etching film at the time of AC electrolytic etching, and since it is an extremely small amount that affects the chemical solubility, it is necessary to strictly control it.

The contents of Ti, V, Zr and Ni are respectively
The content is 20 ppm or less, preferably 0.4 ppm or more in total. When each content exceeds 20 ppm, the number of defects in the etching film becomes too large, the dissolution of the etch pit wall increases rapidly, and the surface area decreases. More preferably 0.1 to 20 ppm
If the amount is less than 0.1 ppm, the number of defects in the etching film is small, the progress of etching is likely to be insufficient, and the effect of increasing the surface area is often not obtained. If the total amount is less than 0.4 ppm, the amount of defects in the etching film is too small,
Etching failure occurs.

Fe and Si are Al-Fe type and A type.
The l-Fe-Si-based compound is deposited to improve the strength of the aluminum foil, especially the bending strength. The preferable range of the Fe content is 0.03 to 0.15%, and if it is less than 0.03%, its effect is small. Since the wall of is melted, the capacitance is likely to decrease. The more preferable content range of Fe is 0.03 to 0.08.
%.

The preferred range of Si content is 0.02 to 0.15%
If less than 0.02%, its effect is small, and if it exceeds 0.15%, the chemical solubility increases during AC electrolytic etching, and the walls of the generated etch pits are dissolved.
The surface area is reduced, and the capacitance is likely to decrease. A more preferable content range of Si is 0.02 to 0.08%. Usually F
Both e and Si contain about 0.04 to 0.06%.

The aluminum purity is preferably 99.7% or more, and when the purity is 99.7% or less, the contents of Fe and Si easily exceed 0.15%, and the chemical solubility in hydrochloric acid increases. If the purity is high, for example, 99.9% or more, it is difficult to manufacture with primary refined aluminum ingot, and it is necessary to purify by the segregation purification method or the three-layer electrolysis method.Therefore, use aluminum with a purity of 99.7 or more and less than 99.9. Is preferred.

Ti, V, Zr is formed on the surface layer of the aluminum foil.
If Ni and Ni are present, a defective portion is generated in the oxide film on the foil surface in the AC electrolytic etching with hydrochloric acid, and the starting point of etching is easily formed. In order for the starting point of etching to be formed and for the etching to proceed evenly to the inside of the foil, Ti, V, Zr and Ni of 0.6 to 8000 ppm in total must be present in the surface layer portion from the foil surface to the inside of 0.2 μm in the thickness direction. It is preferably present at a concentration (average content in the surface layer portion). If it is less than 0.6 ppm, the formation of etching starting points is too small to obtain a sufficient surface expansion effect, and if it exceeds 8000 ppm, too many etching starting points are formed and the entire surface is likely to dissolve. From the foil surface in the thickness direction
A more preferable range of the average total amount of Ti, V, Zr and Ni in the surface layer portion up to 0.2 μm is 400 to 2000.
ppm.

The amount of TiV, Zr and Ni present inside the aluminum foil other than the surface layer is preferably a fraction to one tenth of the amount present in the surface layer, for example, 1 as an average value of the amount present. The range is / 2 to 1/80. T on the surface
As a method for unevenly distributing i, V, Zr, and Ni, an aluminum material containing predetermined amounts of these components, that is, 20 ppm each of Ti, V, Zr, and Ni, 0.4 ppm or more in total, is cast, and this is In the process of forming an aluminum foil, heating during hot rolling, heat treatment such as intermediate annealing, a method of concentrating these components in the surface layer portion,
There is a method of applying to the surface layer portion by a method such as ion sputtering or vapor deposition. In the present invention, Cu,
Even if each of Mn, Mg, Cr, Zn, and Ga is contained in the range of 0.02% or less, the effect of the present invention is not affected.

[0016]

In the present invention, Ti, V, Zr, Ni, and Fe, Si are contained in specific amounts, and Ti, V, Zr, and Ni are contained in specific amounts in the surface layer portion from the surface to 0.2 μm in the thickness direction When present, an aluminum foil for a cathode can be obtained in which chemical dissolution during AC electrolytic etching is suppressed, the etching property is improved, and the bending strength is excellent.

[0017]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 An aluminum ingot having a composition shown in Table 1 was produced, homogenized, and then hot-rolled and cold-rolled by a conventional method to give an aluminum foil having a thickness of 0.05 mm. Then, the surface layer of the aluminum foil is subjected to T by ion sputtering.
i, V, Zr and Ni were applied. Table 1 shows the total amounts of these elements in the surface layer portion. In Table 1, test material No. 8 is a conventional pure aluminum foil for cathode.

[0018]

[Table 1]

The bending strength and capacitance of the obtained aluminum foil were evaluated according to the following methods. Bending test: Using the JIS P 8115 MIT automatic bending tester, make a test piece with a width of 10 ± 0.3 mm and a length of 100 mm and set it in the tester, bending radius 0.5 ± 0.05 mm, load
A bending test was performed under the conditions of 2.5 ± 0.05 N, bending angle of 90 ± 2 degrees, and bending repetition rate of 6 times / s, and the number of times of bending until the test piece was broken was measured to evaluate the bending strength. The number of folds will be once for 90 degree bending and twice for undoing. Capacitance measurement: For aluminum foil, etching solution at 45 ° C (12.5% by volume hydrochloric acid + 0.5% by volume nitric acid + 0.6% by volume)
25 HZ AC electrolysis at a current density of 0.2 A / cm ² in phosphoric acid).
It went for 0 seconds. Then, it was subjected to chemical conversion treatment to 3 V in an ammonium adipate solution at 60 ° C, and the capacitance was measured with an LCR meter. Table 2 shows the number of times of bending and the capacitance. As shown in Table 2, each of the aluminum foils according to the present invention has superior capacitance and bending strength as compared with the conventional pure aluminum foil for cathode.

[0020]

[Table 2]

Comparative Example 1 An aluminum ingot having the composition shown in Table 3 was produced and treated in the same manner as in Example 1 to obtain an aluminum foil having a thickness of 0.05 mm. Then, Ti, V, Zr and Ni were applied to the surface layer of the aluminum foil by ion sputtering. Table 1 shows the total amounts of these elements in the surface layer portion. The bending strength and the capacitance of the obtained aluminum foil were evaluated in the same manner as in Example 1. The results are shown in Table 4. In Table 3, those that do not satisfy the conditions of the present invention are underlined.

[0022]

[Table 3]

[0023]

[Table 4]

As shown in Table 4, test materials No. 1 and No. 2
Does not contain a predetermined amount of Si and Fe, and has insufficient strength. Since the test material No. 3 contains too much Si and Fe, the chemical solubility at the time of etching is increased and the wall of the etching pit is dissolved, resulting in a decrease in capacitance. Since the test material No. 4 does not contain V or Zr, it has a low capacitance. Test material No. 5 contained too much Ti, Zr, and Ni, and Ti, V, Zr, and Ni in the surface layer portion
Also, since the total amount exceeds the limit range of the present invention, the etching start point becomes excessive and the entire surface is melted, resulting in a decrease in capacitance.

[0025]

As described above, according to the present invention, the chemical dissolution during electrolytic etching is suppressed and the electrostatic capacity is high.
In addition, an aluminum foil for cathode having good strength can be obtained.

Claims (1)

[Claims] 1. Ti, V, Zr and Ni are each 20 ppm
In the following, the total content is 0.4 ppm or more, Fe 0.03 to 0.15% (mass%, the same applies below), Si 0.02 to 0.15%, and the balance Al.
And an aluminum foil consisting of inevitable impurities,
In the surface layer portion from the surface of the aluminum foil to the inside of 0.2 μm in the thickness direction, the above Ti, V, Zr and Ni are contained in total.
Aluminum foil for electrolytic capacitor cathodes, characterized by being present in a concentration of 0.6 to 8000 ppm.