JP2006169597A - Aluminum foil for electrolytic capacitor cathode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide aluminum alloy foil for an electrolytic capacitor cathode by which surface expansion ratio can be increased and high electrostatic capacity can be obtained by means of electrochemical etching treatment, particularly AC etching. <P>SOLUTION: The aluminum alloy foil has ≥99.7% aluminum purity and contains 0.01 to 0.10% Si, 0.02 to 0.10% Fe, 0.0005 to 0.005% Cu, 0.005 to 0.05% Mg and 0.005 to 0.05% Zn. Moreover, the amount of oil remaining on the surface of the aluminum alloy foil before etching treatment ranges from >400 to 3,500 μg/m<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  The production of aluminum foil for electrolytic capacitor cathodes is performed by subjecting the aluminum foil to electrochemical etching in a solution containing chlorine ions, thereby forming a large number of holes called etch pits to increase the surface area of the etched surface. The capacitance is increased.

  In the electrochemical etching process, if surface dissolution due to etching becomes excessive, non-uniform dissolution occurs, and the capacitance and strength decrease due to surface loss, etc., and if the surface dissolution is too small, a sufficient surface expansion effect is obtained. Therefore, in order to obtain an appropriate and uniform surface dissolution of the aluminum foil, not only the etching treatment conditions but also the influence of the elements contained in the aluminum foil has been studied and attempts have been made to improve the material surface.

For example, Cu, Mg, and Ga are known as elements that increase the etch pit start point during the etching process, and Zn also increases the etch pit start point to increase the capacitance. It is known as an element (see Patent Document 1). Further, it has been reported that the residual oil content on the surface of the aluminum foil before the etching process is involved in pit formation during the etching process, and that the performance is improved by adjusting the residual oil amount to a specific range (see Patent Document 2). ).
Japanese Patent No. 2878487 Japanese Patent No. 3537127

  Based on the above prior art, the inventors conducted further tests and studies on the relationship between the components contained in the aluminum foil for electrolytic capacitor cathodes, the amount of residual oil, and electrostatic characteristics. As a result, etching in an electrochemical etching process was performed. It has been found that the characteristics are influenced by the relationship between the contents of Mg and Zn and the amount of residual oil.

  The present invention has been made as a result of further studies based on the above-mentioned knowledge, and the object thereof is to obtain an increase in surface expansion ratio and high capacitance by electrochemical etching treatment, particularly AC etching. An object of the present invention is to provide an aluminum alloy foil for an electrolytic capacitor cathode that makes it possible.

In order to achieve the above object, an aluminum alloy foil for an electrolytic capacitor cathode according to claim 1 is composed of Si: 0.01 to 0.10%, Fe: 0.02 to 0.10%, Cu: 0.0005 to 0. 0.005%, Mg: 0.005 to 0.05%, Zn: 0.005 to 0.05% aluminum alloy foil having an aluminum purity of 99.7% or more, and the aluminum alloy before etching treatment wherein the residual oil amount of the surface of the foil is less than 3500μg / m ² over a 400 [mu] g / m ^2.

An aluminum alloy foil for an electrolytic capacitor cathode according to claim 2 is characterized in that, in claim 1, the total content X of Zn and Mg (Zn amount + Mg amount) is 0.01 to 0.1%, and the residual oil amount is Y μg. When / m ² , the following relationship is satisfied: (2X−500) ≦ Y ≦ (2X + 2000) (where X is a value converted to ppm).

  According to the present invention, there is provided an aluminum alloy foil for an electrolytic capacitor cathode capable of increasing an area expansion ratio and obtaining a high capacitance by electrochemical etching, particularly AC etching.

  Describing the significance and the limited range of the components contained in the aluminum foil in the present invention, Si and Fe are elements inevitably included as impurities, and preferable contents are Si: 0.01 to 0.10%, Fe : It is 0.02 to 0.10% of range. The aluminum purity is preferably 99.7% or more.

  Cu functions as a solid solution in the Al matrix to enhance the etching property. The preferable content of Cu is in the range of 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 occurs.

Mg functions as a solid solution in the Al matrix to enhance the etching property and to suppress precipitation of elemental Si by forming Mg ₂ Si. A preferable content of Mg is in the range of 0.005 to 0.05%.

  Zn is an element that increases the solubility at the time of etching treatment by lowering the potential of the Al matrix and increasing the potential difference from the Fe-containing crystals / precipitates, and the preferable content is 0.005 to 0.05%. Range.

  The aluminum alloy foil for an electrolytic capacitor cathode according to the present invention is manufactured by homogenizing an ingot of an aluminum alloy having the above composition, hot rolling in accordance with a conventional method, and then cold rolling and foil rolling. However, usually, rolling oil remains on the surface of the aluminum alloy foil after cold rolling, and rolling oil components such as mineral oil, fatty acid, and ester are detected.

  The remaining state of the rolling oil on the surface of the aluminum alloy foil is the adhering oil located in the outer layer part of the surface of the aluminum alloy foil and the adsorbing oil located in the inner layer part of the surface of the aluminum alloy foil and having an extremely high bonding force with the aluminum base. are categorized. Adhering oil is an oil component that dissolves in hexane, and adsorbed oil is oil that remains even if the oil on the foil surface is extracted with hexane. It is the adsorbed oil located in the inner layer that affects the generation of pits during the etching process. In the present invention, the residual oil refers to adsorbed oil.

In the present invention, it is important to control the residual oil amount 400 [mu] g / m ² over the 3500μg / m ² or less. If it is 400 μg / m ² or less, the protective action on the surface of the aluminum alloy foil is lost, the reaction between the aluminum substrate and the etching solution becomes intense, and excessive dissolution tends to occur. If it exceeds 3500 μg / m ² , the reaction with the etching solution becomes non-uniform, and there is a region where pits are partially concentrated, so that it is difficult to obtain a high capacitance.

  The amount of residual oil can be controlled by performing washing with an acid, an alkali, or an organic solvent after cold rolling. Even if washing is not performed, the amount of residual oil can be adjusted by cold rolling using a rolling oil having low adsorptivity or by performing heat treatment after cold rolling.

In the present invention, when the total content of Zn and Mg, (Zn amount + Mg amount) is X ppm, and the residual oil amount is Y μg / m ² , X is 0.01 to 0.1%, that is, 100 to 1000 ppm. Thus, when the relationship of (2X−500) ≦ Y ≦ (2X + 2000) is satisfied (region A shown in FIG. 1), appropriate solubility of the aluminum alloy foil and appropriate reaction between the aluminum alloy foil surface and the etching solution Can be obtained, and a further improved area expansion ratio can be achieved.

  When Y> (2X + 2000), since the residual oil is too much with respect to the total content X of Zn and Mg, the generation of pits is not uniform, and a sufficient surface expansion ratio cannot be obtained (2X−500). >, The total content X of Zn and Mg with respect to the residual oil becomes excessive and the etching property becomes too high, so that excessive dissolution tends to occur.

  The molten aluminum alloy having the composition shown in Table 1 is ingoted by semi-continuous casting, and the resulting ingot is homogenized and hot-rolled according to a conventional method, and then cold-rolled at a rolling rate of 95%. Thus, a hard foil having a thickness of 20 μm was obtained. In Table 1, those outside the conditions of the present invention are underlined.

  About the obtained hard foil (test material), the measurement of the amount of residual oil and the capacitance were performed by the following methods. The results are shown in Table 2. In Table 2, those outside the conditions of the present invention are underlined.

Measurement of residual oil: A test piece of 20 cm × 20 cm (surface area 400 cm ² ) was taken from the test material, immersed in 80 ml of hexane (5000 times concentrated test product), subjected to ultrasonic cleaning for 20 minutes, and outer layer After removing the adhering oil of the part with hexane, the test piece is immersed in a solution consisting of 90 ml of distilled water, 30 ml of hexane and 30 ml of 6N hydrochloric acid (hexane washed hydrochloric acid) until the surface of the test piece is completely decomposed. Then, the adsorbed oil (residual oil) was extracted.

  Subsequently, the extract was transferred into a 100 ml beaker and evaporated by heating until the extract was about 20 ml, and further evaporated at room temperature to about 5 ml. Then, it concentrated under reduced pressure with the suction desiccator, hexane was evaporated completely, and the adsorption | suction substance (residual oil) on the foil surface was obtained. This was dissolved in 100 μl of hexane, and 4 μl thereof was injected into a gas chromatograph to evaluate the amount of residual oil.

  The gas chromatograph analysis was performed using apparatus: GC-14B manufactured by Shimadzu Corporation, and detector: FID.

Capacitance measurement: The test material was 12.5% by volume hydrochloric acid, 0.5% by volume nitric acid, 0.6% by volume phosphoric acid in an electrolytic solution (temperature 30 ° C.) using an alternating current of 25 Hz. An AC electrolytic etching treatment was performed by energizing for 60 seconds at a current density of 0.2 A / cm ^2. After the treatment, the capacitance was measured with an LCR meter in an ammonium adipate solution.

  As shown in Tables 1-2, test material No. 1 according to the present invention. 1 to 7 all have (Zn content + Mg content) of 0.01 to 0.1%, that is, 100 to 1000 ppm, and satisfy the relationship of the above formula (2X−500) ≦ Y ≦ (2X + 2000). , Test material No. When the capacitance of 7 (comparative material) was 100%, an excellent capacitance exceeding 100% was exhibited.

  In contrast, test material No. No. 8 has a small amount of residual oil. No. 9 has a large amount of residual oil. No. 10 has low Mg content and Zn content. Since No. 11 has much Mg content and Zn content, both have inferior capacitance.

It is a figure which shows the preferable relationship of the amount of residual oil and (Mg + Zn) content in this invention.

Claims (2)

Si: 0.01-0.10% (mass%, the same shall apply hereinafter), Fe: 0.02-0.10%, Cu: 0.0005-0.005%, Mg: 0.005-0.05% Zn: 0.005 to 0.05% aluminum alloy foil with an aluminum purity of 99.7% or more, and the amount of residual oil on the surface of the aluminum alloy foil before the etching treatment exceeds 400 μg / m ² An aluminum alloy foil for an electrolytic capacitor cathode, characterized by being 3500 μg / m ² or less. When the total content X of Zn and Mg (Zn amount + Mg amount) is 0.01 to 0.1% and the residual oil amount is Y μg / m ² , (2X−500) ≦ Y ≦ (2X + 2000) 2. The aluminum alloy foil for an electrolytic capacitor cathode according to claim 1, wherein the relationship of (where X is a value converted to ppm) is satisfied.

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