JP4548834B2 - Aluminum foil for electrolytic capacitor electrode - Google Patents

Description

  The present invention relates to an aluminum foil for electrolytic capacitor electrodes, and more particularly to an aluminum foil for electrolytic capacitor electrodes having a high electrostatic capacity, in which a large number of uniform pits are formed by electrochemical etching.

  The production of aluminum foil for electrolytic capacitor electrodes is performed by electrochemically etching the aluminum foil in a solution containing chlorine ions to form a large number of holes called etch pits to increase the surface area of the etched surface. The capacitance is increased.

  With the recent miniaturization of electronic components, there has been a demand for further improvement in the capacitance of aluminum foil for electrolytic capacitor electrodes used in electronic components, and many attempts have been made to increase the capacitance. Has been done.

  Among these, regarding the relationship between the crystal structure of the aluminum foil and the capacitance, it is known that the capacitance is improved by increasing the (100) crystal plane occupancy, and the ideal cubic orientation ((100) crystal It has been proposed to increase the capacitance by reducing the crystal grains with a deviation of 10 to 20 ° to less than 20% with respect to the [010] crystal direction parallel to the sheet rolling direction. (See Patent Document 1).

  According to the above proposal, a considerable improvement in capacitance can be expected, but surface dissolution may occur during the etching process, and bending strength is reduced, and high capacitance is ensured. It remains difficult to obtain.

As a result of further tests and examinations based on the above-mentioned proposal, the inventors have formed a semi-cubic shape of the etch pits generated in the initial stage of etching, resulting in a tunnel-like dissolution in the <100> direction. For this reason, when there are many crystal grains having a small rotation angle with respect to the rolling direction (Rolling Direction = RD), that is, the rotation angle θ (see FIG. 1) with respect to RD (100) [100], as shown in FIG. Pits easily grow along the rolling direction (arrow direction in FIG. 2 (transverse pit growth direction)), surface dissolution occurs, causing a decrease in capacitance, and rotation with respect to RD (100) [100]. If there are many crystal grains with a large angle θ, as shown in FIG. 3, the lateral running of the pits stops at the portion of the rolling remainder D and the surface dissolution is suppressed, and as a result, the capacitance is improved. Heading was.
Japanese National Patent Publication No. 9-511360

  The present invention has been made as a result of further studies based on the above-mentioned knowledge, and its purpose is that the etch pit is deeply tunneled to the inside of the aluminum foil without causing surface dissolution by electrochemical etching treatment. It is an object of the present invention to provide an aluminum alloy foil for an electrolytic capacitor electrode that can increase the area expansion ratio and obtain a high capacitance.

An aluminum foil for an electrolytic capacitor electrode according to claim 1 for achieving the above object is an aluminum foil for use in an electrolytic capacitor electrode, wherein the surface of the aluminum foil is divided by a step of 40 μm per pixel. Among these, the deviation from the ideal cube orientation is less than 10 ° in the cube orientation, and the ratio of pixels having a rotation angle θ of 10 ° to 45 ° with respect to the rolling direction of the cube orientation is 5% or more of the total pixels. And

  The aluminum foil for electrolytic capacitor electrodes according to claim 2 is characterized in that, in claim 1, the center line average roughness Ra of the surface in the direction perpendicular to the rolling direction of the aluminum foil is 0.07 μm or more.

  The aluminum foil for electrolytic capacitor electrodes according to claim 3 is characterized in that, in claim 1 or 2, the aluminum purity of the aluminum foil is 99.90% or more.

  According to the present invention, the etch pit proceeds deeply into the inside of the aluminum foil without causing surface dissolution by the electrochemical etching process, and it is possible to increase the surface expansion ratio and obtain a high capacitance. An aluminum alloy foil for electrolytic capacitor electrodes is provided.

The aluminum foil for electrolytic capacitor electrodes according to the present invention is a cube orientation in which the deviation from the ideal cube orientation is less than 10 ° among the pixels obtained by dividing the surface of the aluminum foil in steps of 40 μm per pixel. The ratio of pixels having an angle θ of 10 ° to 45 ° is 5% or more of the entire pixels . If the ratio of pixels having a rotation angle θ of less than 10 ° is large, pits are likely to grow along the rolling direction, and surface dissolution occurs during the etching process, resulting in a decrease in capacitance (see FIG. 2).

It is desirable rotation angle θ is 10 ° to 45 °, when that having a rotation angle θ in this range, the surface dissolution is suppressed by stopping the partial lateral running of the pits in the rolling eyes remaining D An improvement in capacitance can be achieved (see FIG. 3). The ratio of pixels having a rotation angle θ of 10 ° to 45 ° is preferably 5% or more of the entire pixels.

  The reason why the deviation from the ideal cube orientation is limited to a cube orientation of less than 10 ° is that when it is 10 ° or more, the crystal orientation is uneven, and surface growth occurs due to pit growth.

  The measurement of the rotation angle θ (see FIG. 1) with respect to the rolling direction and the measurement of the shift angle with respect to the ideal cube orientation can be performed with a scanning microscope by an EBSD (Electron Back Scattering Diffraction) technique.

  In the aluminum foil for electrolytic capacitor electrodes of the present invention, the center line average roughness Ra on the surface of the aluminum foil in the direction perpendicular to the rolling direction of the aluminum foil is preferably 0.07 μm or more. An effect of reliably suppressing running can be obtained. The center line average roughness Ra is more preferably 0.10 μm or more. If the center line average roughness Ra is too large, melting of only the rolling marks is excessively promoted, resulting in nonuniform pit distribution. Therefore, the upper limit is made 0.70 μm or less.

  Although the aluminum foil for electrolytic capacitor electrodes of the present invention includes an aluminum foil and an aluminum alloy foil, it is preferable to apply an aluminum foil having an aluminum purity of 99.90% or more. It is more preferable to apply an aluminum foil having an aluminum purity of 99.96% or higher.

  In order to obtain the aluminum foil having the properties of the present invention, a method of rolling in the oblique direction in the hot rolling step, a method of performing oblique rolling in the cold rolling step, or a method of combining them is applied.

  Examples of the present invention will be described below in comparison with comparative examples. These examples show one embodiment of the present invention, and the present invention is not limited thereto.

  A molten aluminum alloy having a purity of aluminum of 99.90% or more was ingoted by semi-continuous casting, and the resulting ingot was homogenized and hot-rolled according to a conventional method to obtain a plate material having a thickness of 5 mm. Next, cold rolling was repeated to obtain an aluminum foil having a thickness of 0.1 mm. During the cold rolling, intermediate annealing was performed for 12 hours in the temperature range of 180 to 280 ° C. in the air at a thickness of 0.16 mm and 0.13 mm.

  Then, after performing additional rolling (skin pass rolling) in a direction of 0 to 45 ° with respect to the direction of cold rolling, final annealing is performed in an argon gas atmosphere at a heating rate of 30 to 200 ° C./h, a holding temperature. It carried out at 500-570 degreeC.

For the aluminum foil (test material) obtained through the above steps, as a primary electrolytic treatment, a current density of 20 A / dm in a mixed aqueous solution of hydrochloric acid 1.0 mol / l and sulfuric acid 3.0 mol / l (liquid temperature 83 ° C.). ^{As a} secondary electrolysis treatment, a direct current etching process was performed by energizing for 300 seconds under a current density of 10 A / dm ^{2 in} a 1.5 mol / l aqueous solution of nitric acid (liquid temperature 74 ° C.). Then, after chemical conversion to 250 V in an ammonium borate solution, the capacitance was measured using an LCR meter.

  The rotation angle θ with respect to the rolling direction is a cube whose deviation from the ideal cube orientation is less than 10 ° by measuring 3 fields of 2 mm × 1 mm in steps of 40 μm using the EBSD (TSL OIM 2.6). With respect to the orientation, the ratio of pixels having a rotation angle θ of 10 ° to 45 ° with respect to the rolling direction of the cube orientation was determined. As a pretreatment for performing the EBSD analysis, the surface of the aluminum foil was buffed and further electropolished in a perchloric acid ethanol solution.

  For each test material, the ratio (G%) of pixels whose deviation from the ideal cube orientation is less than 10 ° and whose rotation angle θ with respect to the rolling direction is 10 ° to 45 °, and perpendicular to the rolling direction. Tables 1 and 2 show the centerline average roughness (Raμm), aluminum purity, and capacitance of the surface in the direction.

  As can be seen from Table 1, the test material according to the present invention, in particular, the test material No. Each of Nos. 1 to 12 has an excellent capacitance of 100% or more.

  On the other hand, as shown in Table 2, test material No. with an aluminum purity of 99.94% was used. 13, test material No. with Ra of 0.05 μm. No. 14 has a somewhat lower capacitance. A test material No. having a G of 3% and deviating from the conditions of the invention 15 showed a low value of 92% electrostatic capacity.

It is a figure which shows rotation angle (theta) with respect to a rolling direction, and an arrow shows a rotation direction. In the formation of etch pits during the etching process viewed from the surface of the aluminum foil, it is a schematic diagram showing the growth direction of laterally running pits when the rotation angle θ with respect to the rolling direction is less than 10 ° . Sideways pits are running in the rolling direction. In the formation of etch pits during the etching process viewed from the aluminum foil surface, it is a schematic diagram showing the growth direction of laterally running pits when the rotation angle θ with respect to the rolling direction is 10 ° or more. The sideways pit stops at the remaining roll.

Explanation of symbols

  D Rolling remainder

Claims (3)

An aluminum foil for use in an electrolytic capacitor electrode, wherein the deviation of the surface of the aluminum foil with respect to the ideal cube orientation is less than 10 ° among pixels divided by a step of 40 μm per pixel, An aluminum foil for electrolytic capacitor electrodes, wherein a ratio of pixels having a rotation angle θ of 10 ° or more and 45 ° or less with respect to a rolling direction is 5% or more of the entire pixels. The aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein the center line average roughness Ra of the surface in a direction perpendicular to the rolling direction of the aluminum foil is 0.07 µm or more. The aluminum foil for electrolytic capacitor electrodes according to claim 1 or 2, wherein the aluminum purity of the aluminum foil is 99.90% (mass%, the same shall apply hereinafter) or more.

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