Aluminum material for electrolytic capacitor electrodes, method for producing same, and method for producing aluminum electrode material for electrolytic capacitors

Abstract

To provide an aluminum material for an electrolytic capacitor electrode directed to an aluminum material that is configured to: be formed with many recessed parts to serve as original points of etching pits in an aluminum base material; have excellent etching characteristics; enable enhancing an expanded surface rate so as to eventually enable acquisition of a large electrostatic capacitance, and to provide a method of manufacturing the same.SOLUTION: On an aluminum base material with a surface formed with an oxide film, many recessed parts that are portions to be formed with etching pits are formed. An inner surface of the recessed parts includes pit original point parts prescribed by such a straight line or a curved line that an inclination of the straight line or an inclination of a tangent of the curved line makes an angle of 20° to 90° with a plane of the aluminum base material, the straight line or the curved line configuring an outline of the recessed parts appeared in a cross section perpendicular to the plane of the aluminum base material. The maximum separation distance in a plan view of the pit original point parts on the whole inner surface of the recessed parts, is equal to or less than 1.9 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum material for electrolytic capacitor electrodes, a method for producing the same, and a method for producing an aluminum electrode material for electrolytic capacitors. [Background technology]

[0002] Aluminum foil, commonly used as an electrode material for electrolytic capacitors, undergoes electrochemical or chemical etching to increase its surface area in order to increase its capacitance. To increase the surface area, it is necessary to evenly space the etching initiation points and create more etching pits. To achieve this, a conventional method has been used to control the impurity distribution in the aluminum. However, this method has limitations in controlling the impurity distribution, making it impossible to precisely control the etching initiation points one by one. In other words, conventional methods have reached their limits in increasing the surface area through etching.

[0003] Therefore, a technology has been proposed in which depressions are formed in a desired pattern on the surface of an aluminum foil or on the surface of an aluminum foil having an oxide film by pressing a master mold having protrusions against the surface, and the starting point position is controlled by using these depressions as the starting point for etching, thereby producing an electrode foil with high surface expansion efficiency (see Patent Document 1). In addition, a technology has been proposed in which a mold with protrusions is pressed against the surface of a smooth aluminum material for electrode foil with a surface roughness (arithmetic mean roughness: Ra) of less than 0.30 to form indentations in a desired pattern, such as recesses that break through the aluminum oxide film or protrusions by indentation transfer, and these are used as starting points for etching, thereby controlling the starting point position and producing electrode foil with high surface expansion efficiency (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-74162 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-042789 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the inventors' research has revealed that even if a large number of recesses that serve as starting points for etching pits are formed by, for example, pressing the aluminum substrate surface against the matrix, it may not be possible to obtain the expected capacitance.

[0006] As a result of further research into the cause of this, the inventors discovered that the angle of the inner surface of the recessed portion formed on the surface of the aluminum base material and the size of the recessed portion have a significant effect on the occurrence and progression of etching pits.

[0007] The present invention was made based on this finding, and is directed to an aluminum material having a large number of recesses formed in the aluminum base material that serve as starting points for etching pits. It is an object of the present invention to provide an aluminum material for electrolytic capacitor electrodes that has excellent etching characteristics, can improve the surface expansion ratio, and can thereby obtain a large electrostatic capacitance, as well as a method for manufacturing the same and a method for manufacturing an aluminum electrode material for electrolytic capacitors. [Means for solving the problem]

[0008] The above object can be achieved by the following means. (1) A large number of recesses, which are the locations where etching pits are to be formed, are formed on an aluminum substrate on which an oxide film has been formed on the surface. the inner surface of the recess includes a pit initiation portion defined by a straight line or a curve constituting the outline of the recess appearing in a cross section perpendicular to the plane of the aluminum base, the angle between the slope of the straight line or the slope of the tangent to the curve and the plane of the aluminum base being 20° to 90°; An aluminum material for electrolytic capacitor electrodes, characterized in that the maximum distance between the pit initiation points on the entire inner surface of the recess in a plan view is 1.9 μm or less. (2) The aluminum material for electrolytic capacitor electrodes according to the preceding paragraph (1), wherein the oxide film is a natural oxide film or a chemically-formed oxide film. (3) The aluminum material for electrolytic capacitor electrodes according to (1) or (2) above, characterized in that etching pits can be formed by electrolytic etching or chemical etching, starting from the pit initiation portions. (4) An aluminum material for electrolytic capacitor electrodes according to any one of the preceding paragraphs (1) to (3), characterized in that the shape of the recesses corresponds to the shape of a large number of protrusions formed on a matrix that is pressed against the aluminum base. (5) A method for manufacturing an aluminum material for electrolytic capacitor electrodes, in which a matrix having a large number of protrusions is pressed against the surface of an aluminum base material having an oxide film formed thereon, thereby forming a large number of recesses in which etching pits are to be formed, the inner surface of the recess includes a pit initiation portion defined by a straight line or a curve constituting the outline of the recess appearing in a cross section perpendicular to the plane of the aluminum base, the angle between the slope of the straight line or the slope of the tangent to the curve and the plane of the aluminum base being 20° to 90°; A method for manufacturing an aluminum material for electrolytic capacitor electrodes, characterized in that the maximum distance between the pit initiation points in a plan view over the entire inner surface of the recess is 1.9 μm or less. (6) A method for producing an aluminum electrode material for electrolytic capacitors, comprising subjecting the aluminum material for electrolytic capacitors according to any one of the above items (1) to (4) to electrolytic etching or chemical etching. [Effects of the Invention]

[0009] The aluminum material for electrolytic capacitor electrodes according to the present invention has an aluminum base having an oxide film formed on its surface, and a large number of recesses formed therein where etching pits are planned to be formed. The inner surfaces of the recesses contain pit initiation portions defined by straight lines or curves that form the outline of the recesses as they appear in a cross section perpendicular to the plane of the aluminum base, and the inclination of the straight line or the inclination of the tangent to the curve and the plane of the aluminum base form an angle of 20° to 90°. Therefore, during etching, these pit initiation portions selectively serve as the initiation points of the etching pits, and the etching progresses, so that etching pits are reliably formed at the positions of the large number of recesses.

[0010] Furthermore, since the maximum distance between pit initiation points on the entire inner surface of the recess in a plan view is 1.9 μm or less, even if etching pits are generated starting from pit initiation points separated by the maximum distance, these etching pits will eventually connect to form a single etching pit at the position of the recess, thereby improving each area ratio and achieving a large capacitance.

[0011] According to the method for producing an aluminum material for electrolytic capacitor electrodes of the present invention, it is possible to produce an aluminum material for electrolytic capacitor electrodes that can improve each area ratio by etching and achieve a large electrostatic capacitance.

[0012] According to the method for producing an aluminum electrode material for electrolytic capacitors according to the present invention, an electrode material for electrolytic capacitors having a large capacitance can be produced. [Brief explanation of the drawings]

[0013] [Figure 1] 1(a) is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention, and FIG. 1(b) is a plan view. [Figure 2] FIG. 2 is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to another embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to still another embodiment of the present invention. [Figure 4] FIG. 10 is a cross-sectional view illustrating the angle of a recess for defining a pit start point. [Figure 5] FIG. 10 is a cross-sectional view illustrating the angle of a recess for defining a pit starting point. [Figure 6] 2(a) to 2(c) are schematic cross-sectional views showing, in time series, the state of etching an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention. [Figure 7] 1(a) to 1(c) are schematic cross-sectional views showing, in time sequence, the state when an aluminum material for electrolytic capacitor electrodes that deviates from the conditions of the present invention is etched. [Figure 8] 5(a) to 5(c) are schematic cross-sectional views showing, in time series, the state of etching an aluminum material for electrolytic capacitor electrodes according to another embodiment of the present invention. [Figure 9] FIG. 1 is a cross-sectional view illustrating a method for manufacturing an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention, showing the state before the matrix is ​​pressed against the aluminum substrate. [Figure 10] FIG. 10 is a cross-sectional view showing the state in which the matrix is ​​pressed against the aluminum substrate. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Aluminum material for electrolytic capacitor electrodes] An aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention has an aluminum base material having an oxide film on the surface thereof, and a large number of recesses that serve as starting points for etching pits are formed in the aluminum base material, and the recesses have a characteristic cross-sectional shape.

[0015] 1, 2, and 3 show schematic cross-sectional views of the aluminum material for electrolytic capacitor electrodes according to this embodiment.

[0016] Each aluminum material has an aluminum base 1 with an oxide film 2 formed on the surface thereof, and a large number of recesses 3 formed on the surface thereof.

[0017] In Fig. 1, each recess 3 has a shape obtained by dividing a sphere or an ellipsoid (for example, a hemisphere or a semi-ellipsoid). The cross section (hereinafter also referred to as a transverse section) of each recess 3 parallel to the plane of the aluminum substrate is circular or elliptical. The inner surface of each recess 3 is covered with an annular oxide film 5 on the side closer to the opening, and the entire bottom side is covered with an oxide film 4.

[0018] 2, each recess 3 has a cone shape, and the cross section of each recess 3 has a polygonal, circular, or elliptical shape. The inner surfaces of these recesses 3 are entirely covered with an oxide film 5.

[0019] 3, the shape of each recess 3 is a curved depression in which an inward convex curve and an outward convex curve are smoothly connected in a cross section perpendicular to the plane of the aluminum substrate 1 (hereinafter also referred to as a longitudinal section), and the cross section of each recess 3 is a polygon, circle, or ellipse. The bottom may be flat or curved. The inner surface of each recess 3 is coated with an annular oxide film 5 around the entire periphery of the middle part except for the opening and bottom sides, and the opening and bottom sides are coated with an oxide film 4.

[0020] In each of the aluminum substrates 1 shown in FIGS. 1 to 3, the spacing between the numerous recesses 3 is preferably 1 μm to 10 μm. The spacing between the recesses 3 refers to the minimum distance between the nearest recesses. If the spacing between the recesses 3 is less than 1 μm, the etching pits formed in the recesses 3 during etching may communicate with each other, hindering the surface-expanding effect of the etching pits. If the spacing between the recesses 3 exceeds 10 μm, the number of etching pits may decrease, again making it difficult to achieve a significant surface-expanding effect. A more preferred spacing between the recesses 3 is 2 μm to 5 μm.

[0021] In this embodiment, the recess 3 has the following characteristics. That is, the inner surface of the recess 3 includes pit initiation portions defined by straight lines or curves that constitute the outline of the recess 3 appearing in a vertical cross section of the aluminum base 1, and as shown in Figures 4 and 5, the angle θ (also referred to as the inclination angle) between the plane of the aluminum base 1 and the slope L (in the case of Figure 5) or the slope L of the tangent to the curve (in the case of Figure 4) is 20° to 90°. Note that the oxide films on the aluminum base 1 and the recess 3 are omitted from Figures 4 and 5.

[0022] 1 to 3, the portions where the oxide film 5 is formed are pit initiation portions, and in the examples shown in FIGS. 1 to 3, the pit initiation portions are formed in an annular band shape in the circumferential direction on the inner surface of the recess 3. The portions covered with the oxide film 4 shown in FIGS. 1 to 3 are non-pit initiation portions with an inclination angle θ of less than 20°.

[0023] The reason why the inclination angle θ of the pit starting point is set to 20° to 90° is as follows.

[0024] That is, in this embodiment, as will be described later, each recess 3 is formed by pressing a matrix having numerous protrusions against the surface of the aluminum base 1 on which the oxide film 2 has been formed. That is, each recess 3 corresponds to the shape of the protrusions formed on the matrix. When these protrusions are pressed against the aluminum base, different forces act on the portions of the inner surface of the recess 3 that are to be formed, depending on the shape of the protrusions.

[0025] If the angle of the inclined or curved portion of the protrusion is large, an inclined or curved portion coated with an oxide film 5 is formed on the inner surface of the recess 3, with an inclination angle θ of 20° to 90°. During this formation process, a shearing force acts along the inclined or curved portion of the protrusion diagonally downward (if the angle is other than 90°) or downward (if the angle is 90°), and this force causes numerous irregularities, voids, and cracks to form on the surface of the oxide film 2, thinning it and turning it into an oxide film 5, which then becomes the starting point of pits. On the other hand, if the angle of the inclined or curved portions of the projections of the matrix is ​​gentle, an oxide film 4 with an inclination angle θ of less than 20° will be formed, but this portion is a non-pit initiation portion, and in the process of forming this non-pit initiation portion, only a downward pressing force from the projections acts, and no large force acts in the shear direction. As a result, the occurrence of irregularities, voids, cracks, etc., such as those in the oxide film 5, is suppressed, and the reduction in thickness of the oxide film 4 is not as great as that of the oxide film 5.

[0026] Thus, the surface of the oxide film 5 has many irregularities, voids, and cracks, and its average thickness is thinner than those of the oxide film 2 and the oxide film 4, which serve as pit initiation points. The average thickness of the oxide film 4 is the same as or thinner than that of the oxide film 2. The average thickness of the oxide film 2 is preferably in the range of 1 nm to 50 nm, and more preferably in the range of 2 nm to 20 nm. The average thickness of the oxide film 4 is preferably in the range of 1 nm to 40 nm, and more preferably in the range of 2 nm to 10 nm. The average thickness of the oxide film 5 is preferably in the range of 0.5 nm to 40 nm, and more preferably in the range of 0.5 nm to 10 nm.

[0027] Differences in the average thickness of the oxide film result in differences in reactivity during etching. Utilizing this difference in reactivity, it is possible to provide selectivity for the generation of etching pits during etching. The thinner the oxide film, the higher the reactivity and the more likely pits are to occur. Of the oxide films 3, 4, and 5, it is the oxide film 5 that preferentially generates pits. Furthermore, oxide film 5 has many irregularities, voids, and cracks, which can become the starting points for etching pits. This, combined with the fact that etching pits preferentially occur in the areas covered by oxide film 5, in other words, the pit starting points.

[0028] 6, 7, and 8 are schematic cross-sectional views (a), (b), and (c) showing, in time sequence, the state of aluminum materials for electrolytic capacitor electrodes, each having a different shape of recesses 3, when etched in an electrolytic solution containing hydrochloric acid (the oxide film is not shown). In each case, (a) shows the state before electrolytic etching, (b) shows the state after electrolytic etching for 0.001 to 0.01 seconds to generate very initial pits, and (c) shows the state after electrolytic etching for 0.01 to 0.1 seconds to form initial pits by combining the very initial pits.

[0029] In Fig. 6, recess 3 is hemispherical, and the portion (pit initiation portion) covered with oxide film 5 having an inclination angle θ of 20° to 90° is formed in an annular shape over the entire circumferential direction, with a width from the opening on the inner surface of recess 3 to a position midway in the depth direction. Recess 3 shown in Fig. 6 is the same as that shown in Fig. 1, and the maximum distance between the pit initiation portions in plan view is diameter D1 of the opening of recess 3. Furthermore, the diameter of the bottom edge of the annular pit initiation portion in plan view is D2.

[0030] In Fig. 7, the shape of the recess 3 is a part of a shallow sphere, and the covered portion (pit initiation portion) of the oxide film 5 having an inclination angle θ of 20° to 90° is formed in an annular shape over the entire circumferential direction, with a width from the opening of the inner surface of the recess 3 to a position partway in the depth direction, as in the example of Fig. 6. In Fig. 7 as well, the maximum separation distance of the pit initiation portions in a plan view is the diameter D1 of the opening of the recess 3. Furthermore, the diameter of the bottom edge of the annular pit initiation portion in a plan view is D2.

[0031] In Fig. 8, the shape of the recess 3 is a cone or pyramid, and the covered portion (pit starting point) of the oxide film 5 having an inclination angle θ of 20° to 90° is formed on the entire inner surface of the recess 3. In Fig. 8, the maximum separation distance of the pit starting point in a plan view is the maximum distance D1 of the opening of the recess 3, and D2 is zero.

[0032] In this embodiment, the maximum separation distance D1 in plan view between pit start points where the inclination angle θ is 20° to 90° must be 1.9 μm or less. The maximum separation distance D1 in Figures 6 and 8 is 1.9 μm or less, while the maximum separation distance D1 in Figure 7 exceeds 1.9 μm.

[0033] As described above, etching pits start to form in the areas covered by the oxide film 5 where the inclination angle θ is 20° to 90°, and as shown in each of Figures 6 to 8(b), multiple initial pits 11 occur along these pit starting points. In each of Figures 6 to 8(b), the areas painted in light black indicate the initial pits 11.

[0034] In FIG. 6, where the maximum separation distance D1 is 1.9 μm or less, the multiple initial pits 11 that have occurred merge to form a single initial pit 12, as shown in (c). If etching is continued, a tunnel pit forms inward from the initial pit, and the final etching pit is formed around the recess 3 as desired. On the other hand, in FIG. 7, where the maximum separation distance D1 is greater than 1.9 μm, the distance between the initial pits 11 is so great that pit merging does not occur, and the initial pits 12 grow independently around the recess 3, as shown in (c). In FIG. 8, where the maximum separation distance D1 is 1.9 μm or less, multiple merged initial pits are formed around the recess 3, and no tunnel pit is formed around the recess 3 even if etching is continued.

[0035] To increase the effective area after etching, it is necessary to generate pits in the centers of the recesses 3. Otherwise, the effective area decreases due to the pits generated from adjacent recesses 3 joining together or the increase in voids where no pits are generated.

[0036] In other words, regardless of the value of D2, when the maximum separation distance D1 is 1.9 μm or less, the effective area can be increased, and thus a large capacitance can be obtained.

[0037] In the above description, the pit starting points, which are the portions covered with the oxide film 5, are continuous in the circumferential direction of the inner surface of the recess 3, but the pit starting points may not be continuous but may be scattered.

[0038] The proportion of recesses having pit starting points with θ of 20 to 90° is preferably 90% or more, particularly preferably 95% or more, and it is most desirable that all recesses have pit starting points with θ of 20 to 90°.

[0039] In the aluminum material for electrolytic capacitor electrodes according to this embodiment, the chemical composition of the aluminum constituting the aluminum substrate 1 is not limited, and aluminum commonly used as an electrolytic capacitor electrode material can be used as appropriate. Specifically, to limit the amount of impurities and prevent deterioration of etching characteristics due to excessive dissolution, the aluminum purity is preferably 99.9% or higher, and particularly 99.99% or higher. The cube orientation occupancy rate or (100) occupancy rate of the aluminum material is preferably 90% or higher, more preferably 95% or higher, and most preferably 99.9% or higher. The thickness of the aluminum material for electrolytic capacitor electrodes is also not limited, and includes aluminum foils with a thickness of 200 μm or less and aluminum plates with a thickness of more than 200 μm. The surface roughness (arithmetic mean roughness) of the aluminum substrate 1 is preferably less than 0.1 μm, and particularly preferably less than 0.05 μm. [Method of manufacturing aluminum material for electrolytic capacitor electrodes] The above-mentioned aluminum material for electrolytic capacitor electrodes can be produced, for example, by the following method.

[0040] An aluminum ingot having a predetermined chemical composition is subjected to a homogenization treatment, and then hot rolling, cold rolling, and final annealing are sequentially performed to form an oxide film, thereby producing an aluminum base material having an oxide film 2 on its surface. If the surface is smoothed by chemical polishing or electrolytic polishing after the final annealing, the aluminum base material is then exposed to the atmosphere to form a natural oxide film, thereby producing an aluminum base material. The oxide film 2 does not have to be a natural oxide film, but may be a chemical oxide film formed by chemical conversion treatment.

[0041] Next, a large number of recesses 3 are formed in the aluminum base 1 to prepare an aluminum material for electrolytic capacitor electrodes.

[0042] Although not limited to, the method of forming the recesses 3 may be, for example, a method in which a master die 100 having a large number of protrusions 101 as shown in Fig. 9 is pressed against the aluminum substrate 1 as shown in Fig. 10 to form the recesses 3 as indentations corresponding to the protrusions 101. By aligning the large number of protrusions 101 in the master die 100 with the arrangement of the recesses 3 described above, the recesses 3 can be formed in the aluminum substrate 1 at desired positions in a desired pattern.

[0043] The master mold 100 can be produced by any method that can realize a fine shape that can be patterned as desired, but is preferably produced using mold processing or lithography techniques. The material may be any material that is harder than the aluminum substrate 1, regardless of whether it is electrically conductive or not. The shape of the protrusions 101 may be any of a cone, column, sphere, and ellipsoid, and the outer surface shape of the protrusions will become the inner surface shape of the recesses 3.

[0044] When pressing the matrix 100 against the aluminum substrate 1, the protrusions 101 and the aluminum substrate 1 are in contact perpendicularly. The pressing pressure must be increased depending on the surface roughness of the aluminum substrate 1. In other words, if the aluminum substrate 1 is flat, uniform recesses 3 can be formed even with a low pressing pressure. The pressing method can be either flat or roll.

[0045] In the process of forming the recesses 3 by pressing the matrix 100 in using the method described above, if the inner surface of the recesses 3 has an inclination angle θ of 20° or more with respect to the plane of the aluminum substrate 1, stress is applied to the oxide film 2, resulting in irregularities, voids, cracks, and the like in the oxide film 5. If the matrix 100 is pressed in further, the oxide film 5 becomes more easily stretched as the angle increases, resulting in a decrease in its average thickness. As described above, in order to generate irregularities, voids, cracks, etc. in the oxide coating 5 and reduce the average thickness, the inclination angle θ needs to be 20° to 90°, and a particularly preferable inclination angle θ is 40° to 90°. Regardless of the shape of the protrusions 101 of the matrix 100, when the matrix 100 is pressed vertically, the aluminum substrate 1 undergoes plastic deformation, and therefore it is impossible in principle to set the inclination angle θ to an angle of 90° or more.

[0046] The aluminum material for electrolytic capacitor electrodes thus produced is then etched to increase the surface area. Etching pits are preferentially formed in the irregularities, voids, and cracks in the oxide film 5 on the inner surface of the recesses 3 due to their high reactivity during etching. Therefore, the recesses 3 become the starting points for etching pits, and erosion progresses parallel or perpendicular to the (100) plane of the crystal grains, forming tunnel pits. By generating etching pits in the desired recesses 3 that are regularly arranged, it is possible to reduce the reduction in effective area due to the joining of etching pits and the void areas of the etching pits. In other words, improving the pit occurrence rate in the desired recesses 3 leads to an increase in effective area.

[0047] The pit occurrence rate for the recess 3 at the desired position can be determined at the time of forming the initial pit before forming the tunnel pit. The initial pit here is a facet-type pit with a pit diameter and depth of 0.1 μm to 2 μm. The etching conditions are not limited, and either electrochemical etching or chemical etching may be used. The conditions for forming initial pits are shown below as an example. The treatment solution for electrochemical etching can be, for example, an aqueous hydrochloric acid solution, or a solution in which sulfuric acid, nitric acid, or phosphoric acid has been added to an aqueous hydrochloric acid solution. The treatment solution temperature is preferably 15°C to 80°C. Furthermore, a platinum electrode or a carbon electrode with an area sufficiently larger than that of the aluminum material is used as the counter electrode for the aluminum material, and the preferred current value is 100 mA / cm. 2 ~3000mA / cm 2 The preferred current application time is 0.01 s to 30.0 s. [Example]

[0048] Examples of the present invention and comparative examples are shown below.

[0049] By forming recesses 3 in an aluminum substrate 1 using a matrix 100 with projections, various aluminum materials for electrolytic capacitor electrodes were produced as shown in the following examples and comparative examples.

[0050] Each aluminum substrate 1 was an aluminum foil having a thickness of 130 μm and a composition of Si: 22 ppm, Fe: 16 ppm, Cu: 59 ppm, and Al purity of 99.99%, with an oxide film 2 having a thickness of 0.003 μm formed on the surface. The arithmetic mean roughness Ra of the surface of the aluminum substrate 1 was 0.05. Example 1 A master mold 100 made of nickel and having numerous pyramidal protrusions 101 with a height of 1.8 μm formed on its surface at intervals of 3.0 μm was pressed against the aluminum substrate 1 with a surface pressure of 20 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate 1. Example 2 A master mold 100 having numerous hemispherical protrusions 101 with a height of 1.9 μm formed on its surface at intervals of 3.0 μm was pressed against the aluminum substrate 1 with a surface pressure of 100 MPa, thereby forming recesses 3 corresponding to the spherical protrusions 101 on the surface of the aluminum substrate 1. Example 3 A large number of pyramidal protrusions 101 with a height of 0.5 μm were formed on the surface at intervals of 3.0 μm. The matrix was pressed against the aluminum base material 1 at a surface pressure of 40 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum base material. (Comparative Example 1) A master mold 100 having numerous pyramidal protrusions 101 with a height of 0.5 μm formed on its surface at intervals of 3.0 μm was pressed against the aluminum substrate 1 with a surface pressure of 5 MPa, thereby forming recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate 1. (Comparative Example 2) A master mold 100 having numerous pyramidal protrusions 101 with a height of 0.9 μm formed on its surface at intervals of 3.0 μm was pressed against the aluminum substrate 1 with a surface pressure of 100 MPa, thereby forming recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate 1.

[0051] For the aluminum materials for electrolytic capacitor electrodes according to the examples and comparative examples prepared as described above, the shapes of the recesses 3 were confirmed using an AFM, and the tilt angle θ and the maximum distance between the pit initiation points in a plan view were measured. The results are shown in Table 1. In comparative example 1, the tilt angle θ was 19°, and no pit initiation points were formed. Then, each aluminum material for electrolytic capacitor electrodes was immersed in a 6 mol / L hydrochloric acid solution at a temperature of 35°C, and a current of 800 mA / cm 2 The specimen was subjected to electrolytic etching treatment under the conditions of a current of 0.5 sec, washed with pure water and dried.

[0052] The state of etching pits in the etched aluminum material for electrolytic capacitor electrodes was observed using an SEM.

[0053] The results are shown in Table 1.

[0054] [Table 1]

[0055] As shown in Table 1, in the aluminum materials for electrolytic capacitor electrodes according to Examples 1 to 3, etching pits occurred in the center of 85% or more of the recesses 3. For this reason, it was expected that a large surface expansion ratio and a high capacitance would be obtained.

[0056] In contrast, in Comparative Example 1, in which the inclination angle θ was less than 20 degrees, and in Comparative Example 2, in which the maximum separation distance D1 in a plan view of the pit initiation point exceeded 1.9 μm, the proportions of recesses 3 in which etching pits occurred in the center were 50% and 70%, respectively, and it was expected that the surface expansion ratio would be smaller than in the Examples and that the capacitance would be inferior. [Industrial Applicability]

[0057] The aluminum material for electrolytic capacitor electrodes of the present invention can be etched to obtain a high surface area expansion ratio, and when used as an electrode material, is useful for improving the capacitance of electrolytic capacitors. [Explanation of symbols]

[0058] 1. Aluminum substrate 2. Oxide film 3 recess 4. Oxide film 5. Oxide film 100 Matrices 101 Protrusion

Claims

1. A large number of recesses, which are to be the locations for forming etching pits, are formed on an aluminum substrate having an oxide film formed on its surface, the inner surface of the recess includes a pit initiation portion defined by a straight line or a curve constituting the outline of the recess appearing in a cross section perpendicular to the plane of the aluminum base, the angle between the inclination of the straight line or the inclination of the tangent to the curve and the plane of the aluminum base being 20° to 90°; A method for manufacturing an aluminum material for electrolytic capacitor electrodes, in which electrolytic etching or chemical etching is performed while the inner surface of the recess is covered with the oxide film, characterized in that the maximum distance between the pit initiation points in a plan view across the entire inner surface of the recess is 1.9 μm or less.

2. 2. The method for producing an aluminum material for electrolytic capacitor electrodes according to claim 1, wherein the oxide film is a natural oxide film or a chemical oxide film.

3. 3. The method for producing an aluminum material for electrolytic capacitor electrodes according to claim 1, wherein etching pits can be formed by electrolytic etching or chemical etching, starting from the pit initiation portions.

4. 4. The method for manufacturing an aluminum material for electrolytic capacitor electrodes according to claim 1, wherein the shape of the recesses corresponds to the shape of a large number of protrusions formed on a matrix that is pressed against the aluminum base material.

5. A method for manufacturing an aluminum material for electrolytic capacitor electrodes, comprising the steps of: pressing a matrix having a large number of protrusions against the surface of an aluminum base material having an oxide film formed thereon, thereby forming a large number of recesses at which etching pits are to be formed; the inner surface of the recess includes a pit initiation portion defined by a straight line or a curve constituting the outline of the recess appearing in a cross section perpendicular to the plane of the aluminum base, the angle between the inclination of the straight line or the inclination of the tangent to the curve and the plane of the aluminum base being 20° to 90°; A method for manufacturing an aluminum material for electrolytic capacitor electrodes, in which electrolytic etching or chemical etching is performed while the inner surface of the recess is covered with the oxide film, characterized in that the maximum distance between the pit initiation points in a plan view across the entire inner surface of the recess is 1.9 μm or less.

6. A method for producing an aluminum electrode material for electrolytic capacitors, comprising: subjecting an aluminum material for electrolytic capacitor electrodes produced by the method for producing an aluminum material for electrolytic capacitor electrodes according to any one of claims 1 to 4 to electrolytic etching or chemical etching in a state in which the inner surfaces of the recesses are covered with the oxide film.

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