JP7754641B2 - Aluminum material for electrolytic capacitor electrodes, method for producing same, and method for producing aluminum electrode material for electrolytic capacitors - Google Patents

Description

The present invention relates to an aluminum material for electrolytic capacitor electrodes, a method for manufacturing the same, and a method for manufacturing aluminum electrode material for electrolytic capacitors.

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 capacitance. In order to increase the surface area, it is necessary to space the etching initiation points evenly and create more etching pit initiation points. To achieve this, the conventional method is to control the distribution of impurities contained in the aluminum. However, this method has limitations in terms of control over the impurity distribution, making it impossible to precisely control each individual etching initiation point. In other words, conventional methods have reached their limits in terms of increasing surface area through etching.

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 having protrusions is pressed against the surface of a smooth aluminum material for electrode foil having a surface roughness (arithmetic mean roughness: Ra) of less than 0.30 to form a desired pattern of indentations, 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 an electrode foil with high surface expansion efficiency (see Patent Document 2).

Japanese Patent Application Publication No. 11-74162 JP 2007-042789 A

However, the inventors' research has revealed that even if numerous 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.

After further research into the cause of this, the inventors discovered that the angle of the inner surface of the recesses formed on the surface of the aluminum substrate and the size of the recesses have a significant impact on the occurrence and progression of etching pits.

This invention was made based on this knowledge and targets aluminum materials in which numerous recesses that serve as starting points for etching pits are formed in the aluminum base material. Its objective is to provide an aluminum material for electrolytic capacitor electrodes that has excellent etching characteristics, can improve the surface expansion ratio, and ultimately can obtain a large electrostatic capacitance, as well as a method for manufacturing the same and a method for manufacturing aluminum electrode material for electrolytic capacitors.

The above object can be achieved by the following means.
(1) A large number of recesses, which are to be 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°;
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.
(2) The aluminum material for electrolytic capacitor electrodes according to the preceding item (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 the preceding item (1) or (2), 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 material.
(5) A method for producing 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 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, characterized in that the maximum distance between the pit initiation points in a plan view on 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 preceding items (1) to (4) to electrolytic etching or chemical etching.

The aluminum material for electrolytic capacitor electrodes according to this invention has an aluminum base material with an oxide film formed on its surface, and numerous recesses formed therein where etching pits are planned to be formed. The inner surfaces of the recesses include pit initiation regions defined by straight lines or curves that form the contours of the recesses as they appear in a cross section perpendicular to the plane of the aluminum base material, with the inclination of the straight line or the inclination of the tangent to the curve and the plane of the aluminum base material forming an angle of 20° to 90°. Therefore, during etching, these pit initiation regions selectively serve as the initiation points for etching pits, and etching proceeds, resulting in the reliable formation of etching pits at the locations of the numerous recesses.

In addition, 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 occur starting from pit initiation points that are the maximum distance apart, these etching pits will eventually connect to form a single etching pit at the recess. As a result, each area ratio can be improved, and a large capacitance can be achieved.

The method for manufacturing aluminum material for electrolytic capacitor electrodes according to the present invention allows for the improvement of each area ratio through etching, making it possible to manufacture aluminum material for electrolytic capacitor electrodes that can achieve a large electrostatic capacitance.

The method for manufacturing aluminum electrode material for electrolytic capacitors according to this invention makes it possible to manufacture electrode material for electrolytic capacitors with a large capacitance.

1A is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention, and FIG. 1B is a plan view thereof. FIG. 2 is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to another embodiment of the present invention. FIG. 2 is a cross-sectional view of an aluminum material for electrolytic capacitor electrodes according to still another embodiment of the present invention. FIG. 10 is a cross-sectional view illustrating the angle of a recess for defining a pit starting point. FIG. 10 is a cross-sectional view illustrating the angle of a recess for defining a pit starting point. 3A to 3C 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. 1A to 1C 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. 1A to 1C 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. 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. FIG. 10 is a cross-sectional view showing the state in which the matrix is pressed against the aluminum substrate.

[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.

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

Each aluminum material has a large number of recesses 3 formed on the surface of an aluminum base material 1 having an oxide film 2.

In Figure 1, each recess 3 has the shape of a divided sphere or ellipsoid (e.g., a hemisphere or semi-ellipsoid). The cross section (hereinafter also referred to as a transverse cross 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 coated with an annular oxide film 5 on the entire periphery on the side closer to the opening, and the entire bottom side is coated with an oxide film 4.

In Figure 2, each recess 3 has a conical shape, and the cross-sectional shape of each recess 3 is a polygon, circle, or ellipse. The inner surfaces of these recesses 3 are entirely covered with an oxide film 5.

In Figure 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 polygonal, circular, or elliptical. 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, excluding the opening and bottom sides, and the opening and bottom sides are coated with an oxide film 4.

In each of the aluminum substrates 1 shown in Figures 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 connect 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 decreases, and again, it may not be possible to achieve a significant surface-expanding effect. A more preferable spacing between the recesses 3 is 2 μm to 5 μm.

In this embodiment, the recess 3 has the following characteristics. That is, the inner surface of the recess 3 includes a pit initiation portion defined by a straight line or curve that constitutes the outline of the recess 3 that appears in a vertical cross section of the aluminum base material 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 material 1 and the slope L (in the case of Figure 5) or the slope L (in the case of Figure 4) of the tangent to the curve is 20° to 90°. Note that the oxide film on the aluminum base material 1 and the recess 3 has been omitted from Figures 4 and 5.

Specifically, the portions where the oxide film 5 shown in Figures 1 to 3 is formed are pit initiation portions, and in the example shown in Figures 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 by the oxide film 4 shown in Figures 1 to 3 are non-pit initiation portions with an inclination angle θ of less than 20°.

The reason why the pit starting point is specified to have an inclination angle θ between 20° and 90° is as follows:

In other words, in this embodiment, as described below, each recess 3 is formed by pressing a matrix having numerous protrusions against the surface of the aluminum base material 1 on which the oxide film 2 has been formed. In other words, each recess 3 corresponds to the shape of the protrusions formed on the matrix. When these protrusions are pressed against the aluminum base material, different forces act on the areas where the inner surfaces of the recess 3 are formed, depending on the shape of the protrusions.

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 the inclination angle θ being 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, reducing its thickness 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, the oxide film 4 is coated with an inclination angle θ of less than 20°, 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 projection acts, and no large force acts in the shear direction. Therefore, the occurrence of irregularities, voids, cracks, etc., such as those of 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.

As such, the surface of oxide film 5 has numerous irregularities, voids, and cracks, and its average thickness is thinner than oxide film 2 and oxide film 4, forming pit initiation points. The average thickness of oxide film 4 is the same as or thinner than oxide film 2. The average thickness of 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 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 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.

Differences in the average thickness of the oxide film result in differences in reactivity during etching. Utilizing these differences in reactivity can provide selectivity for the occurrence of etching pits during etching. The thinner the oxide film, the higher the reactivity and the more likely pits are to occur. Of oxide films 3, 4, and 5, pits occur preferentially in oxide film 5. Furthermore, oxide film 5 contains numerous irregularities, voids, and cracks, which can become the starting points for etching pits. This means that etching pits occur preferentially in areas covered by oxide film 5, in other words, from the pit starting points.

Figures 6, 7, and 8 (a), (b), and (c) are schematic cross-sectional views showing, in time sequence, the state of aluminum materials for electrolytic capacitor electrodes, each with a different shape of recess 3, when etched in an electrolyte containing hydrochloric acid; the oxide film is not shown. (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.

In Figure 6, the recess 3 is hemispherical, and the covered portion (pit initiation portion) of the oxide film 5, which has 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 the recess 3 to a position halfway in the depth direction. The recess 3 shown in Figure 6 is the same as in Figure 1, and the maximum distance between 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.

In Figure 7, the shape of the recess 3 is a portion of a shallow sphere, and the covered portion (pit initiation portion) of the oxide film 5, with 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 the recess 3 to a position halfway in the depth direction, as in the example of Figure 6. In Figure 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.

In Figure 8, the recess 3 has a conical or pyramidal shape, and the oxide film 5 covering the entire inner surface (pit initiation point) has an inclination angle θ of 20° to 90°. In Figure 8, the maximum distance between the pit initiation points in a plan view is the maximum distance D1 of the opening of the recess 3, and D2 is zero.

In this embodiment, the maximum separation distance D1 in a plan view of the pit start points where the inclination angle θ is between 20° and 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.

As mentioned above, etching pits originate from the covered portion of the oxide film 5 where the inclination angle θ is between 20° and 90°, and as shown in each of Figures 6 to 8 (b), multiple initial pits 11 occur along these pit initiation points. Note that in each of Figures 6 to 8 (b), the areas painted in light black indicate initial pits 11.

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

To increase the effective area after etching, it is necessary to generate pits in the centers of the recesses 3. Otherwise, the effective area will decrease due to pits generated from adjacent recesses 3 joining together or an increase in void areas where no pits are generated.

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, resulting in a large capacitance.

In the above explanation, we have described a case where the pit initiation portions, which are the portions covered by the oxide film 5, are continuous in the circumferential direction of the inner surface of the recess 3, but the pit initiation portions may not be continuous but may be scattered.

The proportion of recesses having pit origins with a θ of 20 to 90° is preferably 90% or more, and more preferably 95% or more, and it is most desirable for all recesses to have pit origins with a θ of 20 to 90°.

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 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, 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, as well as 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, 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.

An aluminum ingot of a specified chemical composition is subjected to a homogenization treatment, and then hot rolling, cold rolling, and final annealing are carried out in sequence to form an oxide film, producing an aluminum substrate having oxide film 2 on its surface. If chemical polishing or electrolytic polishing is carried out after final annealing to smooth the surface, the aluminum substrate is then exposed to the atmosphere to form a natural oxide film, resulting in an aluminum substrate. Oxide film 2 may not be a natural oxide film, but may be a chemical oxide film formed by chemical conversion treatment.

Next, a large number of recesses 3 are formed in the aluminum substrate 1 to produce an aluminum material for electrolytic capacitor electrodes.

The method of forming the recesses 3 is not limited to, but an example is to press a master mold 100 having numerous protrusions 101 as shown in Figure 9 against the aluminum substrate 1 as shown in Figure 10, to form the recesses 3 as indentations corresponding to the protrusions 101. By aligning the numerous protrusions 101 on the master mold 100 with the arrangement of the recesses 3 described above, the recesses 3 can be formed in the desired position and in the desired pattern on the aluminum substrate 1.

The master mold 100 can be produced by any method that can produce a micro-shape that can be patterned as desired, but is preferably produced using mold processing or lithography techniques. The material can be any material that is harder than the aluminum base material 1, regardless of whether it is electrically conductive or not. The shape of the protrusions 101 can be any of a cone, cylinder, sphere, or ellipsoid, and the outer shape of the protrusions will become the inner shape of the recesses 3.

When pressing the matrix 100 against the aluminum substrate 1, the protrusions 101 and the aluminum substrate 1 should be 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 lower pressing pressure. The pressing method can be either flat or roll.

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 coating 2, resulting in the oxide coating 5 having irregularities, voids, cracks, etc. If the matrix 100 is pressed further, the oxide coating 5 becomes more easily stretched as the angle increases, resulting in a decrease in average thickness.
As described above, in order to generate irregularities, voids, cracks, and the like 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.

The aluminum material for electrolytic capacitor electrodes thus produced is then etched to increase the surface area ratio. 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. This results in etching pits originating from the recesses 3, with erosion progressing parallel or perpendicular to the (100) plane of the crystal grains, forming tunnel pits. By generating etching pits in the desired regularly arranged recesses 3, it is possible to reduce the reduction in effective area due to the joining of etching pits and the void areas in the etching pits. In other words, improving the pit occurrence rate in the desired recesses 3 leads to an increase in effective area.

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 following shows an example of the conditions for forming initial pits. Examples of electrochemical etching treatment solutions include aqueous hydrochloric acid solutions, or solutions in which sulfuric acid, nitric acid, or phosphoric acid has been added to aqueous hydrochloric acid solutions. The treatment solution temperature is preferably 15°C to 80°C. Furthermore, a platinum electrode or a carbon electrode with an area significantly larger than that of the aluminum material is used as the counter electrode for the aluminum material, with a preferred current value of 100 mA/cm ² to 3000 mA/cm ² and a preferred current application time of 0.01 s to 30.0 s.

The following are examples of the present invention and comparative examples.

By forming recesses 3 in an aluminum substrate 1 using a protrusion-equipped matrix 100, various aluminum materials for electrolytic capacitor electrodes were produced as shown in the following examples and comparative examples.

Each aluminum substrate 1 was an aluminum foil having a thickness of 130 μm and a composition of 22 ppm Si, 16 ppm Fe, 59 ppm Cu, and 99.99% Al purity, 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, thereby forming 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.

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 by AFM, and the inclination 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 inclination angle θ was 19°, and no pit initiation points were formed.
Thereafter, each aluminum material for electrolytic capacitor electrodes was immersed in a 6 mol/L aqueous hydrochloric acid solution at a liquid temperature of 35°C, and subjected to electrolytic etching treatment under conditions of a current of 800 mA/ ^cm2 for 0.5 seconds, followed by washing with pure water and drying.

The occurrence of etching pits in etched aluminum material for electrolytic capacitor electrodes was observed using an SEM.

The results are shown in Table 1.

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. Therefore, it was expected that a large surface expansion ratio and high capacitance would be obtained.

In contrast, in Comparative Example 1, where the inclination angle θ was less than 20 degrees, and Comparative Example 2, where the maximum separation distance D1 of the pit initiation points in a plan view exceeded 1.9 μm, the proportions of recesses 3 where etching pits occurred in the center were 50% and 70%, respectively. Compared to the Examples, these had a smaller surface area expansion rate and were expected to have inferior capacitance.

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

1 Aluminum substrate 2 Oxide film 3 Recess 4 Oxide film 5 Oxide film 100 Master die 101 Protrusion

Claims (6)

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. 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. 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. 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. 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. 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.