JP2005154897A - Aluminum alloy foil for cathode of electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy foil for the cathode of an electrolytic capacitor having a high capacitance, which is superior in etchability by electrochemical etching, and particularly in the etchability by alternating current etching. <P>SOLUTION: The aluminum alloy foil for the cathode of an electrolytic capacitor comprises 99.5 % or more Al, 0.01-0.05% Si, 0.01-0.1% Fe, 0.0005-0.005% Cu, 0.005-0.05% Mg, 0.001-0.02% Ga, 0.005-0.05% Zn and the balance with unavoidable impurities; includes 1,500 to 4,000/mm<SP>2</SP>Fe-containing crystallized products/precipitates with particle diameters of 0.1 to 5.0 μm; and when a Zn content is expressed by x% and the number of the Fe-containing crystallized products/precipitates with grain sizes of 0.1 to 5.0 μm is by y/mm<SP>2</SP>, has such x and y as to satisfy a relationship of (2,000-50,000x)≤y≤(5,000-50,000x). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an aluminum alloy foil for an electrolytic capacitor cathode, and more particularly to an aluminum alloy foil for an electrolytic capacitor cathode excellent in AC etching property.

  With the downsizing and high performance of electronic components, many attempts have been made to increase the capacitance per unit volume of aluminum electrolytic capacitors incorporated in electronic components.

  In order to increase the capacitance of the entire capacitor, it is first necessary to increase the capacitance of the aluminum foil for the anode. To fully demonstrate the capacity of the anode foil, The capacitance must also be increased.

  Usually, for aluminum foils for electrolytic capacitor cathodes, an ordinary etching hard aluminum foil having an Al purity of 99.3 to 99.8% made by a conventional method is subjected to an electrochemical etching treatment in a solution containing chlorine ions. Thus, a large number of holes called etch pits are formed to increase the surface area of the etched surface.

  In the electrochemical etching process, if the surface dissolution by etching is excessive, non-uniform dissolution occurs, and the capacitance and strength are reduced due to the lack of the surface. Further, if the surface dissolution by etching is too small, a sufficient surface expansion effect cannot be obtained. In order to make the surface dissolution of the foil moderate and uniform, it is necessary to improve not only the etching conditions but also the material surface. So far, many proposals regarding the control of the pit start point during etching have been made, and aluminum foil Various relations with the additive elements have been studied.

Among the additive elements, Cu, Mg, and Ga are known as elements that increase the pit start point during etching, and Zn is also known to increase the etching start point and increase the capacitance (patent). Reference 1).
Japanese Patent No. 2878487 (Japanese Patent Laid-Open No. 5-21288)

  In the process of studying the improvement of the electrostatic capacity of the aluminum alloy foil for electrolytic capacitor cathodes containing Cu, Mg, Ga and Zn, the inventors have studied the Zn content and the Al-Fe type (Al-Fe-Si type). It has been found that the relationship between the number of crystallized substances / precipitates (including the number of crystallized substances) affects the pit start point during the etching process, and has led to the present invention.

  An object of the present invention is to provide an aluminum alloy foil for an electrolytic capacitor cathode that is excellent in etching property in an electrochemical etching process, particularly AC etching property, and has improved electrostatic capacity.

The aluminum alloy foil for an electrolytic capacitor cathode according to claim 1 for achieving the above object includes Al 99.5% or more, Si 0.01 to 0.05%, Fe 0.01 to 0.1%, Cu 0.0005. -0.005%, Mg0.005-0.05%, Ga0.001-0.02%, Zn0.005-0.05%, the remainder consists of inevitable impurities, and the particle size is 0.1-5. There are 1500 μm / mm ² Fe-containing crystals / precipitates of 0 μm, Zn content is x%, and the number of Fe-containing crystals / precipitates with a particle size of 0.1-5.0 μm is y / mm ^2. X and y satisfy the relationship of (2000-50000x) ≦ y ≦ (5000-50000x).

  ADVANTAGE OF THE INVENTION According to this invention, the aluminum alloy foil for electrolytic capacitor cathodes which is excellent in the etching property in an electrochemical etching process, especially alternating current etching property, and has a high electrostatic capacitance is provided. When an aluminum alloy foil containing a large amount of Cu or Fe is used for a capacitor, an increase in leakage current, short circuit, or damage to the capacitor may occur. However, according to the aluminum alloy foil of the present invention, such a problem is caused. It does not occur.

  Explaining the significance and reasons for limitation of the components contained in the present invention, Si functions to improve the chemical solubility of the foil during etching and to uniformly dissolve the foil surface. The preferable content of Si is in the range of 0.01 to 0.05%. If it is less than 0.01%, the Si-containing compound such as an Al—Fe—Si-based compound decreases, and the solubility becomes insufficient. If it exceeds 0.05%, Si tends to precipitate as single particles, the solubility is increased and non-uniform dissolution occurs, and the capacitance and strength of the foil are lowered.

  Fe forms Fe-containing crystals / precipitates such as Al and Al—Fe, and the Al matrix around the Fe-containing crystals / precipitates dissolves during etching to generate pit start points. The preferable content of Fe is in the range of 0.01 to 0.1%. If it is less than 0.01%, the Fe-containing crystals / precipitates are small, so that the solubility becomes insufficient. Is easily dissolved, and the capacitance and strength are reduced.

  Cu functions as a solid solution in the Al matrix to enhance the etching property. The preferable content range of Cu is 0.0005 to 0.005%. If it is less than 0.0005%, the etching property is not sufficient, and if it exceeds 0.005%, excessive dissolution of the foil tends to occur.

Mg dissolves in the Al matrix to increase the strength of the original foil, and functions to enhance the etching property, and forms Mg ₂ Si, thereby preventing precipitation of single particles of Si and preventing excessive dissolution. . The preferable content range of Mg is 0.005 to 0.05%. If it is less than 0.005%, the etching property is not sufficient, and if it exceeds 0.05%, excessive dissolution of the foil tends to occur.

  Ga functions to enhance the etching property by dissolving in Al matrix. A preferable content range of Ga is 0.001 to 0.02%. If it is less than 0.001%, the etching property becomes insufficient, and if it exceeds 0.02%, excessive dissolution of the foil tends to occur.

  When the relationship between the Zn content and the number of Fe-containing crystals / precipitates is specified as described later, Zn lowers the corrosion potential of the Al matrix and increases the standard electrode potential difference with the Fe-containing crystals / precipitates. This increases the solubility during etching, and, like Mg, has the effect of preventing the excessive dissolution by suppressing the precipitation of single particles of Si. The preferable content of Zn is in the range of 0.005 to 0.05%. If it is less than 0.005%, the etching property becomes insufficient, and if it exceeds 0.05%, the foil is likely to be excessively dissolved. A more preferable content range of Zn is 0.005 to 0.035%.

  In the aluminum alloy foil of the present invention, the Al content is preferably 99.5% or more, and more preferably 99.8% or more. In addition to the above-mentioned components, the total content of elements contained as inevitable impurities is preferably 0.02% or less, and if it exceeds 0.02%, a local battery is formed with Al and etching is performed. Sometimes it tends to cause excessive dissolution.

In the aluminum alloy foil of the present invention, Fe-containing crystals / precipitates having a particle size (equivalent circle diameter) of 0.1 to 5.0 μm are present in the matrix in the range of 1500 to 4000 pieces / mm ² , and contain Zn. When the amount is x% and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm is y / mm ² , x and y are (2000-50000x) ≦ y ≦ (5000-50000x). ) Is important to satisfy the relationship. More preferably, the Fe-containing crystals / precipitates are present in the range of 2000 to 3500 pieces / mm ² , and the x and y satisfy the relationship of (2500−50000x) ≦ y ≦ (4250−50000x). More preferred.

Fe-containing crystals / precipitates less than 0.1 μm cannot exert a sufficient mechanism as the starting point of etch pits, and when the number exceeds 5.0 μm, the starting point of pits decreases. . When Fe content crystals and precipitation with a particle size 0.1~5.0μm is 1500 / mm not count pit is small enough surface enlarging rate obtained is less than ^2, there beyond the 4000 pieces / mm ^2, a pit Are combined to cause a lack of surface, making it difficult to obtain a sufficient area expansion ratio.

  The range of 0.005 ≦ x ≦ 0.05, 1500 ≦ y ≦ 4000, and (2000−50000x) ≦ y ≦ (5000−50000x) is the range indicated by the oblique lines in FIG. In this case, the area expansion ratio is increased, and an improved capacitance can be obtained.

  The aluminum alloy foil for an electrolytic capacitor cathode of the present invention is melted and cast in the same manner as in the prior art, and then homogenized at a temperature of, for example, 550 to 610 ° C. Hot rolling at 500 to 550 ° C., foil rolling, intermediate annealing as necessary, forming a hard aluminum alloy foil with a cold rolling rate of 90% or more, and the resulting hard foil is electrochemical Manufactured by etching treatment, the distribution of the Fe-containing crystals / precipitates in the present invention, the relationship between the Zn content and the number of Fe-containing crystals / precipitates, the ingot homogenization treatment conditions, hot rolling conditions Or by adjusting the combination of these conditions.

  The molten aluminum alloy adjusted to the component amount shown in Table 1 is ingoted by semi-continuous casting, and the resulting slab is subjected to homogenization treatment and hot rolling under the conditions shown in Table 2, and the rolling rate is 99.5. % Cold rolling to produce a hard foil having a thickness of 20 μm.

  Next, the capacitance and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm were measured for the hard foil by the following method. The results are shown in Table 2. Table 3 also shows the calculation results for the relationship between the Zn content and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm.

Capacitance measurement: In an etching solution at 30 ° C. (12.5% by volume hydrochloric acid + 0.5% by volume nitric acid + 0.6% by volume phosphoric acid), 25 Hz AC electrolysis at a current density of 0.2 A / cm ² for 60 seconds. Then, the capacitance was measured with an LCR meter in an ammonium adipate solution.

  Measurement of the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm: After electropolishing the surface of the hard foil in a nitric acid-hydrofluoric acid-hydrochloric acid solution, a reflection electron image of the foil surface using a scanning electron microscope The image was photographed at 50 magnifications for 50 fields of view and quantified with an image analyzer.

As shown in Tables 2-3, the test material according to the present invention has Fe-containing crystals / precipitates with a particle size of 0.1 to 5.0 μm, Zn content and Fe content with a particle size of 0.1 to 5.0 μm. The relationship with the number of crystals / precipitates satisfied the conditions of the present invention, and as shown in Table 2, all exhibited excellent capacitance exceeding 100 μF / cm ² .

Comparative Example 1

  The aluminum alloy melt adjusted to the component amount shown in Table 4 is ingoted by semi-continuous casting, and the obtained slab is subjected to homogenization treatment and hot rolling under the conditions shown in Table 5, and the rolling rate is 99.5. % Cold rolling to produce a hard foil having a thickness of 20 μm.

  Subsequently, the capacitance and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm were measured for the hard foil by the same method as in Example 1. The results are shown in Table 5. Table 6 shows the calculation results for the relationship between the Zn content and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm. In Tables 4-6, those outside the conditions of the present invention are underlined.

As shown in Tables 4-6, the test material No. Nos. 9 to 10 do not satisfy the relational expression between the Zn content and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm. No. 9 has a large number of Fe-containing crystals and precipitates having a particle size of 0.1 to 5.0 μm. 9 to 10 all had a capacitance of less than 100 μF / cm ² . Test material No. Since No. 11 has a small Zn content, the etching property is not sufficient and the electrostatic capacity is inferior. Test material No. No. 12 has a high Zn content. Since No. 13 has a high Ga content, excessive dissolution occurs in the electrolytic treatment, and the capacitance is low.

4 is a graph showing the relationship between the Zn content and the number of Fe-containing crystals / precipitates having a particle size of 0.1 to 5.0 μm in the aluminum alloy foil of the present invention.

Claims (1)

Al 99.5% (mass%, the same shall apply hereinafter) or more, Si 0.01-0.05%, Fe 0.01-0.1%, Cu 0.0005-0.005%, Mg 0.005-0.05% , Ga 0.001 to 0.02%, Zn 0.005 to 0.05%, the balance consists of inevitable impurities, and Fe-containing crystals / precipitates with a particle size of 0.1 to 5.0 μm are 1500 to 4000 / mm ² exist, the Zn content is set to x%, when the Fe content crystals, precipitates number particle size 0.1~5.0μm is y pieces / mm ^2, x and y are, (2000-50000x) An aluminum alloy foil for an electrolytic capacitor cathode, characterized by satisfying the relationship of ≦ y ≦ (5000-50000x).

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