JP7705277B2 - Method for manufacturing aluminium material for electrolytic capacitor electrodes, and method for manufacturing aluminium electrode material for electrolytic capacitors - Google Patents

Description

The present invention relates to a matrix used in the manufacture of aluminum material for electrolytic capacitor electrodes, a method for manufacturing aluminum material for electrolytic capacitor electrodes, and a method for manufacturing aluminum electrode material for electrolytic capacitors.

Aluminum foil, which is commonly used as an electrode material for electrolytic capacitors, undergoes an electrochemical or chemical etching process to expand the surface area of the aluminum foil in order to increase its capacitance. To expand the surface area, it is necessary to arrange the starting points from which etching begins at equal intervals and create more starting points for etching pits. To achieve this, a method has traditionally been used that controls the distribution of impurities contained in the aluminum. However, this method has limitations in terms of control over the impurity distribution, and it is impossible to precisely control each and every etching starting point. In other words, the conventional method has reached its limit when it comes to expanding the surface area through etching.

For this reason, 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 aluminum foil, and the starting point position is controlled by using these depressions as the starting points for etching, thereby producing an electrode foil with high surface area 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 multiple recesses that serve as the starting points for etching pits are formed by, for example, pressing the aluminum substrate surface against the master mold, 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 convex part of the master mold that corresponds to the concave part on the surface of the aluminum base material and the size of the concave part have a significant effect on the occurrence and progression of etching pits.

This invention was made based on such knowledge, and aims to provide a mother mold for use in the manufacture of aluminum material for electrolytic capacitor electrodes, which can form numerous recesses that serve as the starting points for etching pits, has excellent etching characteristics, can improve the surface expansion ratio, and can ultimately obtain a large electrostatic capacitance, a manufacturing method for aluminum material for electrolytic capacitor electrodes, and a manufacturing method for aluminum electrode material for electrolytic capacitors.

The above object can be achieved by the following means.
(1) A master mold having a large number of protrusions on its surface,
a pit origin forming portion defined by a straight line or a curve constituting the outline of a convex portion appearing in a cross section perpendicular to the plane of the matrix, the angle between the inclination of the straight line or the inclination of a tangent to the curve and the plane of the matrix being 20° to 90°;
A master mold is characterized in that it is pressed against an aluminum base having an oxide film formed on its surface, thereby forming a large number of recesses in the aluminum base where etching pits are to be formed, and the maximum distance in a planar view between the locations where the pit origin portions are to be formed on the entire surface of the convex portions of the master mold corresponding to the recesses is 1.9 μm or less.
(2) A master mold having a large number of protrusions on its surface,
a master mold having a pit origin portion forming region defined by a straight line or a curve constituting an outline of a protrusion appearing in a cross section perpendicular to a plane of the master mold, the angle between the inclination of the straight line or the inclination of a tangent to the curve and the plane of the master mold being 20° to 90°;
A method for manufacturing an aluminum material for electrolytic capacitor electrodes, characterized in that the master mold is pressed against an aluminum base having an oxide film formed on its surface, thereby forming a large number of recesses in the aluminum base, where etching pits are to be formed.
(3) The method for producing an aluminum material for electrolytic capacitor electrodes according to the preceding paragraph 2, wherein the oxide film is a natural oxide film or a chemically-formed oxide film.
(4) A method for producing an aluminum material for electrolytic capacitor electrodes according to the preceding paragraph 2 or 3, characterized in that an etching pit can be formed by electrolytic etching or chemical etching starting from a pit initiation portion formed in a recess of the aluminum base by a pit initiation portion formation site of the base material.
(5) A method for producing an aluminum material for electrolytic capacitor electrodes as described in any one of items 2 to 4 above, characterized in that the shape of the recesses corresponds to the shape of a number of protrusions formed on a matrix to be pressed against the aluminum base.
(6) A method for producing an aluminum electrode material for electrolytic capacitors, comprising subjecting the aluminum material for electrolytic capacitors produced by the method for producing an aluminum material for electrolytic capacitors according to any one of items 2 to 5 above to electrolytic etching or chemical etching.

The master mold according to the present invention has a large number of convex portions on its surface, and has pit initiation portion formation sites that are defined by straight lines or curves that form the outlines of the convex portions that appear in a cross section perpendicular to the plane of the master mold, and the angle between the inclination of the straight line or the inclination of the tangent of the curve and the plane of the master mold is 20° to 90°. Therefore, by pressing this master mold against an aluminum base material having an oxide film formed on its surface, a large number of recesses that are intended to be the formation sites of etching pits can be formed in the aluminum base material, and pit initiation portions can be formed on the inner surface of the recesses by the pit initiation portion formation sites of the master mold. When the aluminum base material is etched, the pit initiation portions in these recesses selectively become the starting points of the etching pits, and the etching proceeds, and thus etching pits are reliably formed at the positions of the numerous recesses.

In addition, the maximum distance in plan view between the pit initiation formation sites on the entire surface of the convex parts of the matrix corresponding to the concave parts formed in the aluminum base material is 1.9 μm or less. Therefore, when the aluminum base material is etched, even if etching pits occur in the concave parts of the aluminum base material starting from pit initiation parts that are the maximum distance apart, these etching pits will eventually connect and form a single etching pit at the position of the concave part. As a result, by using the matrix, it is possible to provide an aluminum material for electrolytic capacitor electrodes that can improve each surface ratio and achieve a large electrostatic capacitance.

The manufacturing method of the aluminum material for electrolytic capacitor electrodes according to the present invention allows the area ratios to be improved by etching, making it possible to manufacture aluminum material for electrolytic capacitor electrodes that can achieve a large electrostatic capacitance.

The manufacturing method of the aluminum electrode material for electrolytic capacitors according to the present invention makes it possible to manufacture electrode material for electrolytic capacitors with a large electrostatic capacity.

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. 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. 11 is a cross-sectional view for explaining the angle of a recess for defining a pit starting point portion. FIG. 11 is a cross-sectional view for explaining 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 when an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention is etched. 1A to 1C are schematic cross-sectional views showing, in time series, the state when an aluminum material for electrolytic capacitor electrodes that deviates from the conditions of the present invention is etched. 4A to 4C are schematic cross-sectional views showing in time series the state when an aluminum material for electrolytic capacitor electrodes according to another embodiment of the present invention is etched. FIG. 2 is a cross-sectional view illustrating a state before a master die is pressed against an aluminum substrate, illustrating a method for producing an aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention. FIG. 11 is a cross-sectional view showing the state in which the mother die is pressed against the aluminum base material. 11A is a cross-sectional view showing the shape of a matrix having protrusions corresponding to the recesses in FIG. 4, and FIG. 11B is a plan view of the matrix as viewed from the protrusion side (the lower side in FIG. 11). 6 is a cross-sectional view showing the shape of a matrix having protrusions corresponding to the recesses in FIG. 5 . FIG.

[Aluminum material for electrolytic capacitor electrodes]
The aluminum material for electrolytic capacitor electrodes according to one embodiment of the present invention has a large number of recesses, which are the starting points of etching pits, formed in an aluminum base material having an oxide film on its surface, and the recesses have a characteristic shape in cross section. The shape can be formed by pressing a matrix having a plurality of protrusions on its surface against the aluminum base material.

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 FIG. 1, each recess 3 has a shape obtained by dividing a sphere or an ellipsoid (e.g., a hemisphere or a semi-ellipsoid). The shape of a 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 oxide film 5 in an annular band on the entire circumference on the side closer to the opening, and the entire bottom side is covered with an oxide film 4.

In FIG. 2, each recess 3 has a cone 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 FIG. 3, the shape of each recess 3 is a curved depression in which an inwardly convex curve and an outwardly convex curve are smoothly connected in a cross section perpendicular to the plane of the aluminum base material 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 covered in an annular band with an oxide film 5 around the entire periphery of the middle part except for the opening side and bottom side, and the opening side and bottom side are covered 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 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 decreases, and it may not be possible to obtain 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 starting portion that is 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 θ1 (also called the inclination angle θ1) between the plane of the aluminum base material 1 and the straight line or curve that forms the slope L1 (in the case of Figure 5) or the slope L1 (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 is omitted in Figures 4 and 5.

Specifically, the portion where the oxide film 5 shown in Figs. 1 to 3 is formed is the pit initiation portion, and in the example shown in Figs. 1 to 3, the pit initiation portion is formed in an annular shape in the circumferential direction of the inner surface of the recess 3. The portion covered by the oxide film 4 shown in Figs. 1 to 3 is a non-pit initiation portion with an inclination angle θ1 of less than 20°.

The reason why the pit starting point is specified to have an inclination angle θ1 between 20° and 90° is as follows:

That is, in this embodiment, as described below, each recess 3 is formed by pressing a master die having numerous protrusions against the surface of the aluminum base material 1 on which the oxide film 2 is formed. That is, each recess 3 corresponds to the shape of the protrusions formed on the master die. When the protrusions are pressed against the aluminum base material, a force that differs according to the shape of the protrusions acts on the portion forming the inner surface of the recess 3.

If the angle of the inclined or curved portion of the protrusion is large, an inclined or curved portion covered with oxide film 5 is formed on the inner surface of recess 3, with an inclined or curved portion having an inclination angle θ1 of 20° to 90°. During the formation process, a shear force acts along the inclined or curved portion of the protrusion diagonally downward (when the angle is other than 90°) or downward (when the angle is 90°), and this force causes numerous irregularities, voids, and cracks to form on the surface of oxide film 2, reducing its thickness and turning it into oxide film 5, and this oxide film 5 becomes the initiation points of pits.
On the other hand, when the angle of the inclined or curved portions of the projections of the matrix is gentle, the oxide film 4 is covered with an inclination angle θ1 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 the downward pressing force of the projection acts, and no large force in the shear direction acts. Therefore, the occurrence of irregularities, voids, cracks, etc., as 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.

Thus, the surface of oxide film 5 has many irregularities, voids, and cracks, and its average thickness is thinner than oxide film 2 and oxide film 4, which become the origins of pits. 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. By utilizing this difference in reactivity, it is possible to provide selectivity in the generation of etching pits during etching. The thinner the oxide film, the higher the reactivity and the more likely pits will 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 of etching pits, and as a result, etching pits preferentially occur in the areas covered by oxide film 5, in other words, the pit starting points.

Figures 6, 7, and 8 (a), (b), and (c) are schematic cross-sectional views showing, in a time series, the state of aluminum materials for electrolytic capacitor electrodes, each having 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 when electrolytic etching is performed for 0.001 sec to 0.01 sec to generate very initial pits, and (c) shows the state when electrolytic etching is performed for 0.01 sec to 0.1 sec 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 with an inclination angle θ1 of 20° to 90° is formed in an annular shape over the entire circumferential area, with a width from the opening of 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 separation distance of the pit initiation portion in a plan view is the diameter D1 of the opening of the recess 3. In addition, 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 part of a shallow sphere, and the covered portion (pit initiation portion) of the oxide film 5 with an inclination angle θ1 of 20° to 90° is formed in an annular shape over the entire circumferential area, with a width from the opening of 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 portion in a plan view is the diameter D1 of the opening of the recess 3. Also, the diameter of the bottom edge of the annular pit initiation portion in a plan view is D2.

In Figure 8, the shape of the recess 3 is a cone or pyramid, and the covered portion (pit initiation portion) of the oxide film 5 with an inclination angle θ1 of 20° to 90° is formed on the entire inner surface of the recess 3. In Figure 8, the maximum distance in plan view of the pit initiation portion 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 θ1 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, and the maximum separation distance D1 in Figure 7 is greater than 1.9 μm.

As mentioned above, the starting point of the etching pits is the covered portion of the oxide film 5 where the inclination angle θ1 is 20° to 90°, and as shown in each of Figures 6 to 8 (b), multiple initial pits 11 are generated along this pit starting point. Note that in each of Figures 6 to 8 (b), the areas painted in light black indicate the initial pits 11.

In FIG. 6, where the maximum separation distance D1 is 1.9 μm or less, multiple initial pits 11 that have been generated combine to form one initial pit 12, as shown in (c). If etching is continued thereafter, a tunnel pit is formed inward from the initial pit, and the final etching pit is formed with the recess 3 at the center, as desired. On the other hand, in the case of FIG. 7, where the maximum separation distance D1 is greater than 1.9 μm, as shown in (c) in the same figure, the distance between the initial pits 11 is so far that no pit combination occurs, and the initial pits 12 grow independently around the recess 3. In FIG. 8(c), where the maximum separation distance D1 is 1.9 μm or less, multiple combined initial pits are formed in the recess 3, and even if etching is continued thereafter, no tunnel pit is formed with the recess 3 at the center.

To increase the effective area after etching, it is necessary to generate pits in the center of the recesses 3. Otherwise, the effective area will decrease due to the pits generated from adjacent recesses 3 joining together or the 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, and thus a large capacitance can be obtained.

In the above explanation, the pit initiation parts, which are the covered parts of the oxide film 5, are continuous in the circumferential direction of the inner surface of the recess 3, but the pit initiation parts may not be continuous but may be scattered.

The ratio of recesses having pit starting points with θ1 between 20 and 90° is preferably 90% or more, and more preferably 95% or more, and it is most preferable that all recesses have pit starting points with θ1 between 20 and 90°.

In the aluminum material for electrolytic capacitor electrodes according to this embodiment, the chemical composition of aluminum constituting the aluminum base material 1 is not limited, and materials used as electrolytic capacitor electrode materials can be used as appropriate. Specifically, in order to regulate the amount of impurities and prevent deterioration of etching characteristics due to over-dissolution, the aluminum purity is preferably 99.9% or more, and particularly preferably 99.99% or more. The cube orientation occupancy rate of the aluminum material, or the occupancy rate of (100) is preferably 90% or more, more preferably 95% or more, and most preferably 99.9% or more. In addition, the thickness of the aluminum material for electrolytic capacitor electrodes is not limited, and includes aluminum plates exceeding 200 μm in thickness in addition to aluminum materials called foils having a thickness of 200 μm or less. The surface roughness (arithmetic mean roughness) of the aluminum base material 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.

An aluminum ingot of a specified chemical composition is subjected to a homogenization treatment, and then hot rolling, cold rolling, and final annealing are performed in sequence to form an oxide film, 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, resulting in an aluminum base material. The 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 base material 1 to produce an aluminum material for electrolytic capacitor electrodes.

To form the recesses 3, a master mold 100 having numerous protrusions (corresponding to convex portions) 101 as shown in FIG. 9 is used, and this master mold 100 is pressed against the aluminum base material 1 as shown in FIG. 10 to form the recesses 3 as indentations corresponding to the protrusions 101. By aligning the numerous protrusions 101 in the master mold 100 to the arrangement of the recesses 3 described above, the recesses 3 can be formed in the desired pattern at the desired positions on the aluminum base material 1.

The master mold 100 can be produced by any method capable of producing a fine shape that can be subjected to the desired patterning, but is preferably produced using mold processing or lithography techniques. The material may 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 may be any of a cone, cylinder, sphere, or ellipsoid, and the outer shape of the protrusions becomes the inner shape of the recesses 3.

The master mold 100 has a hemispherical protrusion 101 that corresponds to the shape of the recess 3. In this embodiment, the protrusion 101 has the following characteristics. That is, the surface of the protrusion 101 includes a pit starting portion formation site that is defined by a straight line or curve that constitutes the outline of the protrusion 101 that appears in a longitudinal section of the master mold 100, and in which the angle θ2 (this angle is also called the inclination angle θ2) between the plane of the master mold 100 and the straight line or curve that forms the slope L2 (in the case of FIG. 13) or the slope L2 (in the case of FIG. 11) of the tangent to the curve is 20° to 90°, as shown in FIG. 11 and FIG. 12.

Figure 11 (a) shows the shape of the matrix 100 corresponding to the recess 3 in Figure 4, and Figure 11 (b) is a plan view of the matrix 100 as viewed from the protrusion direction side of the protrusion 101 (the lower side of Figure 11). In the example shown in Figure 11, as shown by the dashed-dotted hatching in Figure 11 (b), the pit start portion formation portion 102 is formed in an annular shape over the entire circumferential area, with a width from the base end of the protrusion 101 to a position halfway in the protrusion direction. The central apex of the protrusion 101 has an inclination angle θ2 smaller than 20°, and is not a pit start portion formation portion.

Figure 12 shows the shape of the matrix corresponding to the recess 3 in Figure 5. In Figure 12, the shape of the protrusion 101 is a cone or pyramid, and the pit start portion formation site with an inclination angle θ2 of 20° to 90° is formed on the entire surface (outer surface) of the protrusion 101.

In this way, by defining the pit initiation formation portion 102 in the protrusion 101 with an inclination angle θ2 of 20° to 90°, as described above, it is possible to form a pit initiation portion in the recess 3 of the aluminum base material 1 with an inclination angle θ1 of 20° to 90°, thereby improving the surface expansion rate after etching and achieving a large capacitance.

In this embodiment, the maximum separation distance D3 in plan view of the pit start portion forming portion 102 with an inclination angle θ2 of 20° to 90° from the protrusion 101 side must be 1.9 μm or less. The maximum separation distance D3 of the pit start portion forming portion 102 in FIG. 11 is the diameter of the protrusion 101. Also, the maximum separation distance D3 of the pit start portion forming portion 102 in the protrusion 101 in FIG. 12 is the maximum length of the cross section of the base end of the protrusion 101.

By setting the maximum distance D3 of the pit initiation portion forming portion 102 to 1.9 μm or less, the maximum distance D1 of the pit initiation portion in the recess 3 of the aluminum base material 1 can be set to 1.9 μm or less, and as described above, an etching pit can be formed centered on the recess 3.

In the above description, the pit starting portion forming portions 102 are continuous in the circumferential direction of the surface of the protrusion 101, but the pit starting portion forming portions 102 may not be continuous but may be scattered.

The proportion of protrusions 101 having pit start portion forming regions 102 with an inclination angle θ2 of 20 to 90° is preferably 90% or more, and more preferably 95% or more, and it is most preferable that all protrusions 101 have pit start portion forming regions 102 with an inclination angle θ2 of 20 to 90°.

When pressing the master mold 100 against the aluminum substrate 1, the protrusions 101 and the aluminum substrate 1 are in contact perpendicularly. The pressing pressure must be increased according to 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 a flat surface or a roll.

In the process of forming the recesses 3 by pressing the master die 100 in the above-described manner, if the inner surface of the recesses 3 has an inclination angle θ1 of 20° or more with respect to the plane of the aluminum base material 1, stress is applied to the oxide film 2, resulting in the oxide film 5 having irregularities, voids, cracks, etc. If the master die 100 is pressed further deeply, the oxide film 5 becomes more easily stretched as the angle increases, and the average thickness decreases.
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 θ2 of the protrusions 101 and, in turn, the inclination angle θ1 of the recesses 3 need 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 mother die 100, when the mother die 100 is pressed vertically, the aluminum base material 1 undergoes plastic deformation, and therefore it is impossible in principle to set the inclination angle θ1 to an angle of 90° or more.

The aluminum material for electrolytic capacitor electrodes thus produced is then etched to improve the surface area expansion 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, because they are highly reactive during etching. As a result, the recesses 3 become the starting point for etching pits, and erosion progresses parallel or perpendicular to the (100) plane of the crystal grains to form 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 improvement in the effective area.

The pit occurrence rate for the recess 3 at the desired position can be judged at the time of forming the initial pit before the formation of 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 may be electrochemical etching or chemical etching. As an example, the conditions for forming the initial pits are shown below. Examples of the treatment liquid for electrochemical etching include 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 liquid temperature is preferably 15°C to 80°C. In addition, a platinum electrode or a carbon electrode having 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 100mA/ ^cm2 to 3000mA/ ^cm2 , and the preferred current application time is 0.01s to 30.0s.

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

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

Each aluminum substrate 1 is 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%, and has an oxide film 2 having a thickness of 0.003 μm formed on its surface. The arithmetic mean roughness Ra of the surface of the aluminum substrate 1 is 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 base 1 with a surface pressure of 20 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum base 1. Each protrusion 101 of the master mold 100 had a pit origin formation site 102 with an inclination angle θ2 of 54°, and the maximum separation distance D3 of the pit origin formation sites 102 was 0.3 μm.
Example 2
A master mold 100 having a large number of 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 base material 1 with a surface pressure of 100 MPa to form recesses 3 corresponding to the spherical protrusions 101 on the surface of the aluminum base material 1. Each protrusion 101 of the master mold 100 had a pit origin formation site 102 with a maximum inclination angle θ2 of 90°, and the maximum separation distance D3 of the pit origin formation sites 102 was 1.9 μm.
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 mother mold was pressed against the aluminum base material 1 with a surface pressure of 40 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum base material. Each protrusion 101 of the mother mold 100 had a pit origin formation portion 102 with an inclination angle θ2 of 20°, and the maximum separation distance D3 of the pit origin formation portions 102 was 0.7 μm.
(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 base material 1 with a surface pressure of 5 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum base material 1. Each protrusion 101 of the master mold 100 had an inclination angle θ2 of 19°, and no pit origin formation sites 102 were formed.
(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 base 1 with a surface pressure of 100 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum base 1. Each protrusion 101 of the master mold 100 had a pit origin formation portion 102 with an inclination angle θ2 of 30°, and the maximum separation distance D3 of the pit origin formation portions 102 was 2.0 μm.

When the shapes of the recesses 3 of the aluminum materials for electrolytic capacitor electrodes according to the Examples and Comparative Examples prepared as described above were confirmed by AFM, it was found that in Examples 1 to 3 and Comparative Example 2, pit origin portions with inclination angles θ1 of 20 to 90°, which correspond to the inclination angle θ2 of the protrusions 101 of the matrix 100, were formed in the recesses 3. In addition, in Examples 1 to 3, the maximum separation distance D1 in a plan view of the pit origin portions was 1.9 μm or less in all cases, while in Comparative Example 3, the maximum separation distance D1 exceeded 1.9 μm. In Comparative Example 2, no pit origin portions with inclination angles θ1 of 20 to 90° 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 electrolytic etching was performed 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 a 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. For this reason, it was expected that a large surface expansion ratio and high capacitance would be obtained.

In contrast, in Comparative Example 1, in which the inclination angle θ2 of the protrusions 101 of the matrix 100 was less than 20 degrees, and in Comparative Example 2, in which the maximum separation distance D3 in a plan view of the pit initiation portion formation portion 102 exceeded 1.9 μm, the proportions of recesses 3 in which etching pits had occurred in the center were 50% and 70%, respectively, and it was expected that the surface expansion rate would be smaller than in the examples, resulting in inferior capacitance.

The master mold of the present invention is useful for producing aluminum material for electrolytic capacitor electrodes that can achieve a high surface area expansion ratio by etching.

Reference Signs List 1 Aluminum substrate 2 Oxide film 3 Recess 4 Oxide film 5 Oxide film 100 Mother mold 101 Protrusion (protruding portion)
102 Pit starting point formation site

Claims (5)

A master mold having a large number of protrusions on its surface,
a pit origin forming portion defined by a straight line or a curve constituting the outline of a convex portion appearing in a cross section perpendicular to the plane of the matrix, the angle between the inclination of the straight line or the inclination of a tangent to the curve and the plane of the matrix being 20° to 90°;
a mother mold is used, which is pressed against an aluminum base having an oxide film formed on its surface to form a large number of recesses in the aluminum base, which are intended to form etching pits, and which has a maximum separation distance in a plan view of 1.9 μm or less between the portions in the entire surface of the protrusions of the mother mold corresponding to the recesses, between the portions in the entire surface of the protrusions of the mother mold where the pit origin portions are to be formed ;
A manufacturing method of an aluminum material for electrolytic capacitor electrodes, in which electrolytic etching or chemical etching is performed with the inner surfaces of the recesses covered with the oxide film, characterized in that the master mold is pressed against an aluminum base having an oxide film formed on its surface, thereby forming a large number of recesses in the aluminum base, where etching pits are to be formed . 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 chemically-formed oxide film. 3. The method for producing an aluminum material for electrolytic capacitor electrodes according to claim 1 , characterized in that an etching pit can be formed by electrolytic etching or chemical etching, starting from a pit initiation portion formed in a recess of the aluminum base by a pit initiation portion formation site of the base material. 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 producing an aluminum electrode material for electrolytic capacitors , comprising the steps of: 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 surface of the recess is covered with the oxide film .

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