JPH10259442A - High purity aluminum for foil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high purity aluminum for foil in which the generation of blistering in a producing process is prevented, small in fraction defective and easy to rolling by regulating each content of Na and K as inevitable impurities in high purity aluminum having specified purity to specified value or below. SOLUTION: In high purity aluminum having >=99.85% purity, the content of Na as inevitable impurities is regulated to <=0.05 ppm and that of K to <=0.02 ppm. Furthermore, preferably, each content of Si and Fe is regulated to about <=700 ppm and that of Cu to about <=100 ppm. Moreover, in the case the contents of Na and K are high, by using flux of chloride, fluoride series or the like contg. no Na and K, the molten metal of aluminum is subjected to flux treatment, or by using gaseous chlorine or gaseous fluorine for degassing treatment to the molten metal, Na and K can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-purity aluminum which is mainly used by rolling into foil for electrolytic capacitors. It is intended to provide high-purity aluminum with low generation.

[0002]

2. Description of the Related Art High-purity aluminum can be used as a capacitor by utilizing the fact that the surface area can be enlarged by electrochemical etching and that a dense voltage-resistant oxide film is formed on the surface by anodic oxidation and can be used as a dielectric. It is used as a foil. For example, aluminum used for a low-voltage capacitor has a purity of 99.97% or more, and preferably 99.97% or more, as an anode foil because of its etching characteristics.
Based on aluminum of 98% or more, and for cathode use, based on aluminum of 99.85% to 99.9% purity, other significant or unavoidable impurity elements are blended or regulated within the required range. After smelting and performing processes such as degassing and removal of impurities by a filter, etc., a slab having a thickness of about 500 mm is cast by a DC casting method using a water-cooled mold with an open top and bottom, and then a liquefaction process,
Hot rolled and cold rolled to give a foil of about 0.3mm thickness,
Further, the foil is rolled into a foil for an electrolytic capacitor having a thickness of about 0.02 to 0.1 mm.

[0003] The foil ground or foil being rolled obtained as described above may be softened by heat annealing in order to facilitate rolling, and the foil may also be controlled by controlling the cubic orientation or bending. 200 to 550 ° C to facilitate
, And may be annealed by heating to a temperature of

[0004]

However, such foils as described above are very thin and are defective with slight scratches. That is, swelling (projection of 1 to 3 mm in diameter) occurs due to heat annealing, and it is difficult to provide a foil that does not cause swelling in the annealing process even if degassing or the like is performed on the molten metal. Pure aluminum has the disadvantage that the defective rate due to swelling during the production of the foil is high.

[0005]

The inventors of the present invention have studied to solve the problems in the prior art as described above, and as a result, have performed a heat annealing treatment by regulating a specific impurity level. The present inventors have found that high-purity aluminum with little swelling and poor occurrence in the production process of the foil can be obtained and completed the present invention, and are as follows.

A high-purity aluminum for foils, wherein the purity of Al is not less than 99.85%, Na as an unavoidable impurity is regulated to 0.05 ppm or less, and K is regulated to 0.02 ppm or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION
To further explain the details, first, the purity of Al is 99.85% or more, and 0.05 ppm of Na as an unavoidable impurity is contained.
Hereinafter, by controlling K to be 0.02 ppm or less, high-purity aluminum that can be easily rolled by foil and that does not cause swelling of the foil even after annealing treatment is obtained. Although other impurities are not particularly limited, Si and Fe are 700 ppm or less,
It is preferable to limit Cu to 100 ppm or less from the viewpoint of rollability of the foil and prevention of deterioration of etching characteristics.

[0008] However, the mechanism by which blisters are generated on the surface of the foil base or the foil when the foil is annealed by heating is considered as follows. That is, a small amount of water is present in the atmosphere or in the furnace atmosphere, and the aluminum foil has an annealing temperature of 350 ° C.
It is a well-known phenomenon that when heated to a temperature of at least ℃, water reacts with aluminum to generate hydrogen, and the hydrogen thus generated is partially released to the atmosphere, Some diffuse into the aluminum foil.

The aluminum foil is generally made of a polycrystalline material, and crystal grains are observed in a network in a plane, and a crystal grain boundary exists so as to surround the crystal grains. This crystal grain boundary is known as a kind of defect part because impurities are accumulated and the crystal lattice is irregular as compared with the inside of the crystal grain. By the way, the hydrogen generated by the reaction of the above-mentioned moisture and aluminum diffuses into the crystal grain boundaries having an irregular lattice, and relatively large crystallized substances and inclusions, or so-called grain boundaries which are densely present at the crystal grain boundaries. It is considered that the foil is likely to be adsorbed and aggregated at the defective portion as a triple point, and that the expansion pressure due to the heating of the aggregated gas causes a part of the foil that cannot withstand this pressure to expand. The gas originally contained in the foil is 0.2cc / 100g
Therefore, it is considered that the swelling does not have a strong influence because it is contained as a whole.

Further, since Na and K in the alkali metal hardly dissolve in solid aluminum and easily move in the aluminum during the annealing heating, they are crystal grains which are considered to be defective like the above-mentioned hydrogen. It easily migrates and assembles into the boundaries and precipitates to embrittle the grain boundaries. Therefore, it is considered that the aluminum foil having a large content of Na and K tends to soften the grain boundaries when heated and annealed, and cannot easily withstand the gas pressure of the aggregated gas, so that swelling is likely to occur. But for such Na and K,
In a foil material with an Al purity of 99.85% or more, the Na content is reduced to 0.0.
By controlling the K content to 5 ppm or less and the K content to 0.02 ppm or less, it was confirmed that the occurrence of blistering in the foil was clearly reduced even when annealing by heating.

Na and K as described above have an Al purity of 99.85.
% Of high-purity aluminum ingots
It is contained in an amount of about 0.01 to 0.10 ppm and 0.01 to 0.04 ppm in K. Also, as return materials, those from various uses are mixed, and as a result, Na and K may reach a considerably high range. Therefore, in order to smelt a foil material having a purity of the level of the present invention, a metal material having a small content of Na and K is used,
Also, it is preferable to select raw materials such as return materials, and as a result of dissolving them, when the content of Na and K is higher than the range of the present invention, a flux such as chloride or fluoride containing no Na and K is used. To remove Na and K in the molten metal by flux treatment, or use chlorine-based gas or fluorine-based gas for degassing of the molten metal.
Na and K can be removed.

[0012]

【Example】

(Example 1) A specific example of the present invention will be described. The metal is melted by using a base metal having an Al purity of not less than 99.98%, and chlorine gas is added to Na 0.09 ppm and K 0.04 ppm in the molten metal. Degassing using Na, the content of Na is 0.00
A molten metal having various contents within a range of 5 to 0.08 ppm and a K of 0.007 to 0.032 ppm is prepared.
After casting, the ingot was subjected to 10 mm face milling, kept at 600 ° C. for 4 hours, homogenized, hot-rolled and cold-rolled to a thickness of 0.1 mm.
A 4 mm aluminum foil substrate was manufactured. Other compositions of these foils are: 35-39 ppm Si, 33-37 pp Fe
m and Cu are 29 to 32 ppm, and the Al purity is 99.98%
That was all. The total gas volume measured by Lansley is
It was 0.1 to 0.15 cc / 100 g.

The foil rolling for each aluminum foil was rolled to a foil having a thickness of 0.1 mm only by cold rolling, followed by annealing.

The above-obtained Na
The swelling of each foil of 31 lots having different K levels was evaluated as follows. Heating pretreatment: The foil was immersed in a 1% NaOH aqueous solution at 50 ° C. for 60 seconds to perform a surface removal treatment. Atmosphere around heating furnace: 25 ° C, relative humidity is 70% or more Heating condition: 450 ° C x 5 hours in flowing electric furnace Quantification of swelling: Quantification of swelling in 3 x 3 cm ² range visually Criteria: As shown in Table 1 below. Element content analysis: glow discharge mass spectrometer

[0015]

[Table 1]

Table 2 below shows one example of the gas amount, Na amount, K amount and the result of the blister determination.

[0017]

[Table 2]

FIG. 1 is a graph showing the results of the swelling evaluation as described above in relation to the contents of Na and K. According to FIG. 1, 0.05 ppm of Na and 0.02 ppm of K are shown.
In the areas regulated below, the swelling amount of all foil
It is confirmed that the result is 0 pieces / 9 cm ² or less. Also, from the results in Table 2, it can be seen that even when the total gas amount in the foil is large as in the lot A of the present invention, no blistering occurs when Na and K are below the regulated values. On the other hand, even when the total gas amount in the foil is small as in the lot B of the comparative example, it is found that blistering occurs when Na and K exceed the regulated values.

(Example 2) Melting was performed using a base metal having an Al purity of not less than 99.98% and a return material of 20%.
Degassing treatment using chlorine gas for 10 ppm and K: 0.05 ppm, and Na content of 0.005 to 0.09 ppm, K
Was prepared having various contents in the range of 0.007 to 0.038 ppm, and a 0.4 mm-thick aluminum foil fabric was manufactured in the same manner as in Example 1. Other compositions of these foils are as follows: 35 to 39 ppm Si, 33 to 3 Fe
7 ppm, Cu is 29 to 32 ppm, and Al purity is 99.9.
8% or more. The total amount of gas measured by Lansley was 0.1 to 0.15 cc / 100 g.

The foil rolling on each aluminum foil substrate was performed by cold rolling only to a foil having a thickness of 0.1 mm and annealed in the same manner as in Example 1.

The above-obtained Na
The swelling of each foil of 15 lots having different K levels was evaluated in the same manner as in Example 1.

Table 3 below shows one example of the gas amount, the Na amount, the K amount, and the result of the blister case.

[0023]

[Table 3]

FIG. 2 is a graph showing the results of the swelling evaluation as described above in relation to the contents of Na and K. According to FIG. 2, 0.05 ppm of Na and 0.2 ppm of K are shown. In the area regulated below, the swelling amount of all foil
It is confirmed that the result is less than 9 pieces / 9 cm ² .
Further, from the results in Table 3, it can be seen that blistering does not occur when Na and K are below the regulated values even if the total gas amount in the foil is large as in lot C of the present invention. On the other hand, even if the total gas amount in the foil is small as in the lot D of the comparative example, when Na and K exceed the regulated values, blistering is found to occur.

[0025]

According to the high purity aluminum for foil according to the present invention as described above, the electrolytic capacitor is preferable because it does not generate much swelling even in the heat annealing treatment which is indispensable when rolling the foil to obtain various products. This is an invention having a large industrial effect because foils for use and the like can be obtained with a high yield.

[Brief description of the drawings]

FIG. 1 is a table summarizing the Na and K contents and the state of blistering during annealing in Example 1 according to the present invention.

FIG. 2 is a table showing the contents of Na and K and the occurrence of blistering during annealing in Example 2 of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yushi Inoue 161 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Inside the Nippon Light Metal Co., Ltd. Kambara Works (72) Inventor Hidehiko Ishii 1-11-1 Koike, Inazawa-shi, Aichi Japan Japan Inside the Nagoya Factory of Light Metal Co., Ltd. (72) Inventor: Shimizu Zun 3-6-8, Kutaro-cho, Chuo-ku, Osaka-shi, Osaka Inside Toyo Aluminum Co., Ltd. (72) Inventor: Yoshiya Ashidaka Kutaro-cho, Chuo-ku, Osaka-shi, Osaka 6-8, Toyo Aluminum Co., Ltd.

Claims (1)

[Claims] An Al purity of at least 99.85%, Na as an unavoidable impurity is 0.05 ppm or less, and K is 0.02 ppm.
High-purity aluminum for foil characterized by the following restrictions.