Method for producing mother die and aluminum material for electrolytic capacitor electrodes and method for producing aluminum electrode material for electrolytic capacitors

Abstract

To provide a mother die and the like used for manufacturing an aluminum material for an electrolytic capacitor electrode capable of obtaining a large electrostatic capacitance.SOLUTION: A mother die 100 with many convex parts 101 provided on its surface, has pit original point part formation portions 102 defined 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 mother die, the straight line or the curved line configuring an outline of the convex parts appeared in a cross section perpendicular to the plane of the mother die. Many recessed parts 3 to be formed with etching pits are formed on an aluminum base material 1 with a surface formed with an oxide film by pressing the mother die against the aluminum base material 1. A maximum separation distance in a plan view of the pit original point formation portions 102 in the whole surface of the convex parts 101 of the mother die 100 corresponding to the recessed parts 3 is equal to or less than 1.9 μm.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a master mold used for manufacturing an aluminum material for an electrolytic capacitor electrode, a method for manufacturing an aluminum material for an electrolytic capacitor electrode, and a method for manufacturing an aluminum electrode material for an electrolytic capacitor.

Background Art

[0002] As an electrode material for an electrolytic capacitor, an aluminum foil generally used is subjected to an electrochemical or chemical etching treatment to increase the surface area of the aluminum foil for the purpose of increasing the capacitance. To increase the surface area, it is necessary to arrange the starting points where etching starts at equal intervals to create more starting points for etching pits. Conventionally, a method of controlling by the distribution of impurities contained in aluminum has been adopted. However, in this method, there is a limit to the control of the impurity distribution, and it is impossible to precisely control each starting point of etching one by one. That is, in increasing the surface area by etching, the conventional method has reached its limit.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as a result of research by the inventors, it has been found that even if a large number of recesses serving as the starting points of etching pits are formed by pressing the aluminum base material plane against the mold or the like, the expected capacitance may not be obtained.

[0006] Regarding this cause, as a result of further research by the inventors, it has been found that the angle of the inner surface of the convex portion of the mold corresponding to the recess on the surface of the aluminum base material and the size of the recess greatly affect the generation and progress of etching pits.

[0007] This invention has been made based on such findings, and a large number of recesses serving as the starting points of etching pits are formed, and it has excellent etching characteristics and can improve the surface expansion rate, and thus can obtain a large capacitance. It aims to provide a mold used for manufacturing an aluminum material for an electrolytic capacitor electrode, a method for manufacturing an aluminum material for an electrolytic capacitor electrode, and a method for manufacturing an aluminum electrode material for an electrolytic capacitor.

Means for Solving the Problems

[0008] The above object is solved by the following means. (1) A mold having a large number of convex portions on the surface, A straight line or a curve that constitutes the contour of the convex portion appearing in a cross section perpendicular to the plane of the mold, and the angle formed by the inclination of the straight line or the inclination of the tangent of the curve and the plane of the mold is 20° to 90°. It has a pit starting point formation site defined by a straight line or a curve, By pressing against an aluminum substrate having an oxide film formed on its surface, a large number of recesses, which are portions where etching pits are to be formed, are formed in the aluminum substrate, and the maximum separation distance in a plan view of the pit starting point formation site over the entire surface of the convex portion of the master mold corresponding to the recesses is 1.9 μm or less. The master mold is characterized by this. (2) A master mold having a large number of convex portions on its surface, Using a master mold having a pit starting point formation site defined by a straight line or a curve that constitutes the contour of the convex portion appearing in a cross section perpendicular to the plane of the master mold, and the angle formed 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°. A method for manufacturing an aluminum material for an electrolytic capacitor electrode, characterized in that by pressing the master mold against an aluminum substrate having an oxide film formed on its surface, a large number of recesses, which are portions where etching pits are to be formed, are formed in the aluminum substrate. (3) The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to item 2 above, characterized in that the oxide film is a natural oxide film or a chemical conversion oxide film. (4) The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to item 2 or 3 above, characterized in that etching pits can be formed starting from the pit starting points formed in the recesses of the aluminum substrate by the pit starting point formation site of the base material by electrolytic etching or chemical etching. (5) The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to any one of items 2 to 4 above, characterized in that the shape of the recesses corresponds to the shape of a large number of protrusions formed on the master mold pressed against the aluminum substrate. (6) A method for manufacturing an aluminum electrode material for an electrolytic capacitor, characterized in that electrolytic etching or chemical etching is performed on the aluminum material for an electrolytic capacitor manufactured by the method for manufacturing an aluminum material for an electrolytic capacitor according to any one of items 2 to 5 above.

Advantages of the Invention

[0009] The master mold according to the present invention has a large number of convex portions on its surface, and is a straight line or a curve that forms the contour of the convex portion appearing in a cross section perpendicular to the plane of the master mold, and the angle formed by 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°. Since it has a pit starting point forming site defined by a straight line or a curve, by pressing this master mold against an aluminum substrate having an oxide film formed on its surface, a large number of concave portions, which are portions where etching pits are to be formed, can be formed on the aluminum substrate. Also, a pit starting point can be formed on the inner surface of the concave portion by the pit starting point forming site of the master mold. When etching the aluminum substrate, the pit starting point in this concave portion selectively serves as the starting point of the etching pit and the etching proceeds, and ultimately etching pits are surely formed at the positions of the large number of concave portions.

[0010] Moreover, since the maximum separation distance in plan view of the pit starting point forming site over the entire surface of the convex portion of the master mold corresponding to the concave portion formed on the aluminum substrate is 1.9 μm or less, when the aluminum substrate is etched, even if etching pits are generated starting from pit starting points separated by the maximum separation distance in the concave portion of the aluminum substrate, these etching pits will eventually communicate, and still one etching pit is formed at the position of the concave portion. As a result, by using the master mold, it becomes possible to provide an aluminum material for an electrolytic capacitor electrode that can improve each surface ratio and realize a large capacitance.

[0011] According to the manufacturing method of the aluminum material for an electrolytic capacitor electrode according to the present invention, an aluminum material for an electrolytic capacitor electrode that can improve each surface ratio by etching and realize a large capacitance can be manufactured.

[0012] According to the manufacturing method of the aluminum electrode material for an electrolytic capacitor according to the present invention, an electrode material for an electrolytic capacitor having a large capacitance can be manufactured.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0014] [Aluminum Material for Electrolytic Capacitor Electrodes] The aluminum material for electrolytic capacitor electrodes according to an embodiment of the present invention has a large number of recesses serving as the starting points of etching pits formed on the surface of an aluminum base material having an oxide film, and is characterized by the shape in the cross-section of the recesses. The form can be formed by pressing a master mold having a plurality of convex portions on the surface.

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

[0016] 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.

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

[0018] In Fig. 2, the shape of each recess 3 is a cone, and the shape of each recess 3 in the cross-section is a polygon, a circle, or an ellipse. The entire inner surface of these recesses 3 is covered with an oxide film 5.

[0019] In Fig. 3, the shape of each recess 3 is a form having a curved surface depression in which an inwardly convex curve and an outwardly convex curve are smoothly continuous in a cross-section (hereinafter also referred to as the longitudinal section) perpendicular to the plane of the aluminum base material 1, and the shape of each recess 3 in the cross-section is a polygon, a circle, or an ellipse. Note that the bottom may be a flat surface or a curved surface. Further, the entire circumference of the middle portion excluding the opening side and the bottom side of each recess 3 is covered in an annular shape with an oxide film 5, and the opening side and the bottom side are covered with an oxide film 4.

[0020] In each of the aluminum substrates 1 shown in FIGS. 1 to 3, the interval between a large number of recesses 3 is preferably 1 μm to 10 μm. The interval between the recesses 3 refers to the minimum separation distance between the closest recesses. If the interval between the recesses 3 is less than 1 μm, the etching pits formed in the recesses 3 during etching may communicate with each other adjacent to each other, and the surface area expansion effect by the etching pits may be inhibited. If the interval between the recesses 3 exceeds 10 μm, the number of etching pits decreases, and there is a possibility that a large surface area expansion effect cannot be obtained. A more preferable interval between the recesses 3 is 2 μm to 5 μm.

[0021] In this embodiment, the recess 3 has the following characteristic features. That is, on the inner surface of the recess 3, there is a straight line or a curve that constitutes the contour of the recess 3 appearing in the longitudinal section of the aluminum substrate 1, and as shown in FIGS. 4 and 5, the angle θ1 (this angle is also referred to as the inclination angle θ1) formed between the inclination L1 of the straight line (in the case of FIG. 5) or the inclination of the tangent of the curve (in the case of FIG. 4) and the plane of the aluminum substrate 1 is 20° to 90°. The recess 3 includes a pit starting portion defined by a straight line or a curve. In FIGS. 4 and 5, the oxide films of the aluminum substrate 1 and the recess 3 are omitted.

[0022] Specifically, the portion where the oxide film 5 illustrated in FIGS. 1 to 3 is formed is the pit starting portion, and in the examples shown in FIGS. 1 to 3, the pit starting portion is formed in an annular shape in the circumferential direction of the inner surface of the recess 3. The covered portion of the oxide film 4 shown in FIGS. 1 to 3 is a non-pit starting portion where the inclination angle θ1 is less than 20°.

[0023] The reason for defining the pit starting portion with the inclination angle θ1 of 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 master mold having a large number of protrusions against the surface of the aluminum substrate 1 on which the oxide film 2 is formed. That is, each recess 3 corresponds to the shape of the protrusion formed on the master mold. When this protrusion is pressed against the aluminum substrate, different forces act on the inner surface forming portion of the recess 3 according to the shape of the protrusion.

[0025] When the angle of the inclined portion or curved portion of the protrusion is large, an inclined portion or curved portion with an inclination angle θ1 of 20° to 90° covered with the oxide film 5 is formed on the inner peripheral surface of the concave portion 3. However, in the formation process, a shearing force acts obliquely downward (when it is other than 90°) or downward (when it is 90°) along the inclined portion or curved portion of the protrusion. Due to this force, numerous irregularities, voids, and cracks are generated on the surface of the oxide film 2, and its thickness also becomes thinner to form the oxide film 5, and this oxide film 5 becomes the pit starting point. On the other hand, when the angle of the inclined portion or curved portion of the protrusion of the master mold is gentle, an oxide film 4 with an inclination angle θ1 of less than 20° is covered. However, this portion is a non-pit starting point. In the formation process of this non-pit starting point, only a downward pressing force due to the protrusion acts, and a large shearing force does not act. Therefore, the generation of irregularities, voids, cracks, etc. like those of the oxide film 5 is suppressed, and the reduction in the thickness of the oxide film 4 is not as much as that of the oxide film 5.

[0026] Thus, numerous irregularities, voids, and cracks exist on the surface of the oxide film 5, and its average thickness is thinner than that of the oxide film 2 and the oxide film 4, making it the pit starting point. 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, particularly 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, particularly preferably 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, particularly preferably 0.5 nm to 10 nm.

[0027] Due to the difference in the average thickness of the oxide film, a difference in reactivity occurs during etching. Utilizing this difference in reactivity, selectivity can be imparted to the generation of etching pits during etching. The thinner the oxide film, the higher the reactivity and the easier it is for pits to occur. Among the oxide films 3, 4, and 5, pits are preferentially generated in the oxide film 5. Moreover, numerous irregularities, voids, and cracks exist in the oxide film 5, and combined with the fact that these can become the starting points of etching pits, etching pits preferentially occur from the covered portion of the oxide film 5, in other words, from the pit starting point.

[0028] Each (a), (b), and (c) in FIGS. 6, 7, and 8 is a schematic cross-sectional view showing the state of an aluminum material for an electrolytic capacitor electrode with different forms of the recess 3 during etching in an electrolytic solution containing hydrochloric acid in a time series, and the oxide film is omitted from the illustration. Each (a) is the state before electrolytic etching, (b) is when electrolytic etching is performed for 0.001 sec to 0.01 sec to generate initial pits, and (c) is a schematic cross-sectional view when electrolytic etching is performed for 0.01 to 0.1 sec and the initial pits are combined to form initial pits.

[0029] In FIG. 6, the recess 3 is hemispherical, and the covered portion (pit starting 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 direction with a width from the opening of the inner surface of the recess 3 to a position in the middle in the depth direction. The recess 3 shown in FIG. 6 is the same as that in FIG. 1, and the maximum separation distance in the plan view of the pit starting portion is the diameter D1 of the opening of the recess 3. Also, let the diameter in the plan view of the bottom edge of the annular pit starting portion be D2.

[0030] In FIG. 7, the shape of the recess 3 is a part of a shallow-bottomed sphere, and the covered portion (pit starting 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 direction with a width from the opening of the inner surface of the recess 3 to a position in the middle in the depth direction, similar to the example in FIG. 6. Also in FIG. 7, the maximum separation distance in the plan view of the pit starting portion is the diameter D1 of the opening of the recess 3. Also, let the diameter in the plan view of the bottom edge of the annular pit starting portion be D2.

[0031] In FIG. 8, the shape of the recess 3 is a cone or a pyramid, and the covered portion (pit starting portion) of the oxide film 5 with an inclination angle θ1 of 20° to 90° is formed over the entire inner surface of the recess 3. In FIG. 8, the maximum separation distance in the plan view of the pit starting portion 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 a plan view of the pit starting portion where the inclination angle θ1 is 20° to 90° needs to be 1.9 μm or less. The maximum separation distance D1 in FIGS. 6 and 8 is 1.9 μm or less, and the maximum separation distance D1 in FIG. 7 is assumed to exceed 1.9 μm.

[0033] As described above, the starting point of etching pit generation is the covered portion of the oxide film 5 where the inclination angle θ1 is 20° to 90°. As shown in each (b) of FIGS. 6 to 8, a plurality of very initial pits 11 are generated along this pit starting portion. In each (b) of FIGS. 6 to 8, the region painted in light black indicates the very initial pit 11.

[0034] In FIG. 6 where the maximum separation distance D1 is 1.9 μm or less, as shown in (c) at the same time, the generated plurality of very initial pits 11 combine to form one initial pit 12. Then, when etching is continued, tunnel pits are formed from the initial pit in the inward direction, and finally, etching pits are formed centering on the recess 3 as desired. On the other hand, in the case of FIG. 7 where the maximum separation distance D1 exceeds 1.9 μm, as shown in (c) of the same figure, since the distance between the very initial pits 11 is far, pit combination does not occur, and 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, a plurality of combined initial pits are formed in the recess 3, and even when etching is continued thereafter, tunnel pits centering on the recess 3 are not formed.

[0035] To increase the effective area after etching, it is necessary to generate pits at the center of the recess 3. Otherwise, the pits generated from adjacent recesses 3 combine with each other, or the void portions where no pits are generated increase, resulting in a decrease in the effective area.

[0036] That is, 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 case where the pit initiation portions, which are the coated portions of the oxide film 5, are continuous in the circumferential direction of the inner surface of the recess 3 has been described. However, the pit initiation portions may be discrete instead of being continuous.

[0038] The ratio of the recesses having pit initiation portions where θ1 is 20 to 90° is preferably 90% or more, particularly preferably 95% or more, and most preferably, pit initiation portions where θ1 is 20 to 90° are present in all the recesses.

[0039] In the aluminum material for an electrolytic capacitor electrode according to the present embodiment, the chemical composition of the aluminum constituting the aluminum base material 1 is not limited, and those used as electrolytic capacitor electrode materials can be appropriately used. Specifically, in order to regulate the amount of impurities and prevent a decrease in etching characteristics due to over-dissolution, the aluminum purity is preferably 99.9% or more, particularly preferably 99.99% or more. The cubic 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. Also, the thickness of the aluminum material for an electrolytic capacitor electrode is not limited, and in addition to the aluminum material of 200 μm or less called foil, aluminum plates of more than 200 μm are also included. The surface roughness (arithmetic mean roughness) of the aluminum base material 1 is preferably less than 0.1 μm, particularly preferably less than 0.05 μm. [Method for manufacturing aluminum material for electrolytic capacitor electrode] The aluminum material for an electrolytic capacitor electrode described above can be produced, for example, by the following method.

[0040] A homogenization treatment is performed on an aluminum ingot having a predetermined chemical composition, 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 the surface. When surface smoothing is performed by chemical polishing or electrolytic polishing after the final annealing, it is then exposed to the atmosphere to generate a natural oxide film to obtain the aluminum base material. The oxide film 2 may be a chemical conversion oxide film generated by chemical conversion treatment instead of a natural oxide film.

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

[0042] To form the recesses 3, as shown in FIG. 9, a master mold 100 having a large number of protrusions (corresponding to convex portions) 101 is used. The 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. In the master mold 100, by making the large number of protrusions 101 correspond to the arrangement of the above-described recesses 3, the recesses 3 can be formed in a desired pattern at desired positions on the aluminum base material 1.

[0043] The master mold 100 may be produced by any method as long as it can realize a fine shape capable of desired patterning processing, but it is preferably produced using die processing or lithography technology. The material may be anything as long as it is harder than the aluminum base material 1, regardless of the presence or absence of electrical conductivity. The shape of the protrusion 101 may be any of a cone, a cylinder, a sphere, and an ellipsoid, and the outer surface shape of the protrusion becomes the inner surface shape of the recess 3.

[0044] The master mold 100 has hemispherical protrusions 101 corresponding to the shape of the recesses 3. In this embodiment, the protrusions 101 have the following characteristics. That is, on the surface of the protrusion 101, there is a straight line or a curve that constitutes the contour of the protrusion 101 appearing in the longitudinal section of the master mold 100. As shown in FIGS. 11 and 12, the angle θ2 (this angle is also referred to as the inclination angle θ2) formed by the inclination L2 of the straight line (in the case of FIG. 13) or the inclination of the tangent of the curve (in the case of FIG. 11) and the plane of the master mold 100 is 20° to 90°. The pit starting point forming site defined by the straight line or the curve is included.

[0045] FIG. 11(a) shows the shape of the master mold 100 corresponding to the recess 3 in FIG. 4, and FIG. 11(b) is a plan view when the master mold 100 is viewed from the protruding direction side of the protrusion 101 (the lower side in FIG. 11). In the example shown in FIG. 11, as shown by the dashed-dotted hatching in FIG. 11(b), the pit starting point forming part 102 has a width from the base end part of the protrusion 101 to a position in the middle of the protruding direction, and is formed in an annular shape over the entire circumferential direction. The central top part of the protrusion 101 has an inclination angle θ2 less than 20° and is not a pit starting point forming part.

[0046] FIG. 12 shows the shape of the master mold corresponding to the recess 3 in FIG. 5. In FIG. 12, the shape of the protrusion 101 is a cone or a pyramid, and the pit starting point forming part where the inclination angle θ2 is 20° to 90° is formed on the entire surface (outer surface) of the protrusion 101.

[0047] Thus, by defining the pit starting point forming part 102 with an inclination angle θ2 of 20° to 90° in the protrusion 101, as described above, a pit starting point part with an inclination angle θ1 of 20° to 90° can be formed in the recess 3 of the aluminum base material 1, thereby improving the surface area expansion rate with etching and realizing a large capacitance.

[0048] In this embodiment, the maximum separation distance D3 in a plan view seen from the protrusion 101 side of the pit starting point forming part 102 with an inclination angle θ2 of 20° to 90° needs to be 1.9 μm or less. The maximum separation distance D3 of the pit starting point forming part 102 in FIG. 11 is the diameter of the protrusion 101. Also, the maximum separation distance D3 of the pit starting point forming part 102 in the protrusion 101 of FIG. 12 is the maximum length of the cross section at the base end part of the protrusion 101.

[0049] By setting the maximum separation distance D3 of the pit starting point forming part 102 to 1.9 μm or less, the maximum separation distance D1 of the pit starting point part in the recess 3 of the aluminum base material 1 can be made 1.9 μm or less, and as described above, etching pits can be formed around the recess 3.

[0050] In the above description, the case where the pit starting point forming portion 102 is continuous in the circumferential direction on the surface of the protrusion 101 has been described. However, the pit starting point forming portion 102 may be discontinuous and scattered.

[0051] The ratio of the protrusions 101 having the pit starting point forming portion 102 with the inclination angle θ2 of 20 to 90° is preferably 90% or more, particularly preferably 95% or more, and most preferably, the pit starting point forming portion 102 with the inclination angle θ2 of 20 to 90° exists in all the protrusions 101.

[0052] When pressing the master mold 100 against the aluminum base material 1, the protrusion 101 and the aluminum base material 1 should be in perpendicular contact. It is necessary to increase the pressing pressure according to the surface roughness of the aluminum base material 1. That is, even if the aluminum base material 1 is flat, uniform recesses 3 can be formed with a low pressing pressure. The pressing method can be either a flat surface or a roll.

[0053] In the process of forming the recess 3 by pressing the master mold 100 by the above method, when the inner surface of the recess 3 becomes 20° or more at the inclination angle θ1 with the flat surface of the aluminum base material 1, stress is applied to the oxide film 2, and the oxide film 5 with unevenness, voids, cracks, etc. is formed. When the master mold 100 is pressed deeper, the larger the angle, the easier the oxide film 5 is stretched and the average thickness decreases. As described above, in order to generate unevenness, voids, cracks, etc. in the oxide film 5 and reduce the average thickness, the inclination angle θ2 of the protrusion 101 and thus the inclination angle θ1 of the recess 3 need to be 20° to 90°, and the particularly preferable inclination angle θ is 40° to 90°. Regardless of the shape of the protrusion 101 of the master mold 100, when the master mold 100 is pressed vertically, it is impossible in principle to give an angle of 90° or more to the inclination angle θ1 because the aluminum base material 1 undergoes plastic deformation.

[0054] The aluminum material for the electrolytic capacitor electrode produced is then etched to improve the specific surface area. In the unevenness, voids, and cracks in the oxide film 5 on the inner surface of the recess 3, etching pits are preferentially formed because of the high reactivity during etching. Therefore, it becomes the starting point of the etching pits centered on the recess 3, and the etching progresses parallel or perpendicular to the (100) plane of the crystal grains, forming tunnel pits. By generating etching pits for the desired recesses 3 arranged regularly, it becomes possible to reduce the reduction of the effective area due to the combination of etching pits and the void area of the etching pits. That is, the improvement of the pit generation rate in the desired recess 3 leads to the improvement of the effective area.

[0055] The pit generation rate for the recess 3 at the desired position can be determined at the time of initial pit formation before the formation of tunnel pits. The initial pits mentioned here are faceted pits 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. As an example, the conditions for initial pit formation are shown. As the treatment solution for electrochemical etching, an aqueous hydrochloric acid solution, or a solution obtained by adding sulfuric acid, nitric acid, and phosphoric acid to an aqueous hydrochloric acid solution can be exemplified. The treatment solution temperature is preferably 15°C to 80°C. Also, as the counter electrode for the aluminum material, a platinum electrode or a carbon electrode having a sufficiently larger area than the aluminum material is used, and the preferred current value is 100 mA / cm 2 ~3000 mA / cm 2 exists, and the preferred current application time is 0.01 s to 30.0 s.

Example

[0056] Examples and comparative examples of the present invention are shown below.

[0057] By forming the recess 3 using the protrusion-attached master mold 100 on the aluminum base material 1, various aluminum materials for electrolytic capacitor electrodes shown in the following examples and comparative examples were produced.

[0058] All of the aluminum substrates 1 are aluminum foils with a thickness of 130 μm, consisting of (composition) Si: 22 ppm, Fe: 16 ppm, Cu: 59 ppm, and an aluminum purity of 99.99%. An oxide film 2 with a thickness of 0.003 μm is formed on the surface. Also, 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, with a large number of pyramidal protrusions 101 with a height of 1.8 μm formed at intervals of 3.0 μm on the surface, 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. Each protrusion 101 of the master mold 100 has a pit starting point forming part 102 with an inclination angle θ2 of 54°, and the maximum separation distance D3 of the pit starting point forming part 102 was 0.3 μm. (Example 2) A master mold 100 with a large number of hemispherical protrusions 101 with a height of 1.9 μm formed at intervals of 3.0 μm on the surface was pressed against the aluminum substrate 1 with a surface pressure of 100 MPa to form recesses 3 corresponding to the spherical protrusions 101 on the surface of the aluminum substrate 1. Each protrusion 101 of the master mold 100 has a pit starting point forming part 102 with an inclination angle θ2 of up to 90°, and the maximum separation distance D3 of the pit starting point forming part 102 was 1.9 μm. (Example 3) A large number of pyramidal protrusions 101 with a height of 0.5 μm are formed at intervals of 3.0 μm on the surface. The aluminum substrate 1 was pressed against the master mold with a surface pressure of 40 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate. Each protrusion 101 of the master mold 100 has a pit starting point forming part 102 with an inclination angle θ2 of 20°, and the maximum separation distance D3 of the pit starting point forming part 102 was 0.7 μm. (Comparative Example 1) A master mold 100 with a large number of pyramidal protrusions 101 with a height of 0.5 μm formed at intervals of 3.0 μm on the surface was pressed against the aluminum substrate 1 with a surface pressure of 5 MPa to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate 1. Each protrusion 101 of the master mold 100 has an inclination angle θ2 of 19°, and the pit starting point forming part 102 was not formed. (Comparative Example 2) A master mold 100 having a large number of 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 to form recesses 3 corresponding to the pyramidal protrusions 101 on the surface of the aluminum substrate 1. Each protrusion 101 of the master mold 100 had a pit starting point forming portion 102 with an inclination angle θ2 of 30°, and the maximum separation distance D3 of the pit starting point forming portion 102 was 2.0 μm.

[0059] Regarding the aluminum materials for electrolytic capacitor electrodes according to the examples and comparative examples prepared as above, when the shape of the recesses 3 was confirmed by AFM, in Examples 1 to 3 and Comparative Example 2, pit starting points with an inclination angle θ1 of 20 to 90° corresponding to the inclination angle θ2 of the protrusions 101 of the master mold 100 were formed in the recesses 3. Also, in Examples 1 to 3, the maximum separation distance D1 in a plan view of the pit starting points 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, pit starting points with an inclination angle θ1 of 20 to 90° were not formed. Thereafter, each aluminum material for electrolytic capacitor electrodes was immersed in a hydrochloric acid aqueous solution at a liquid temperature of 35°C and a concentration of 6 mol / L, and electrolytic etching treatment was performed under the conditions of a current of 800 mA / cm 2 for 0.5 seconds, washed with pure water, and dried.

[0060] The generation state of the etching pits of the aluminum materials for electrolytic capacitor electrodes subjected to the etching treatment was observed by SEM.

[0061] The results are shown in Table 1.

[0062]

Table 1

[0063] As shown in Table 1, in the aluminum materials for electrolytic capacitor electrodes according to Examples 1 to 3, for 85% or more of the recesses 3, etching pits were generated at their central portions. For this reason, it was expected that a large specific surface area and a high capacitance could be obtained.

[0064] On the other hand, in Comparative Example 1 where the inclination angle θ2 of the protrusion 101 of the master mold 100 was less than 20 degrees and Comparative Example 2 where the maximum separation distance D3 in plan view of the pit starting point formation site 102 exceeded 1.9 μm, the ratios of the recesses 3 in which etching pits were generated at their central portions were 50% and 70% respectively, and it was expected that the specific surface area was smaller and the capacitance was inferior compared to the examples.

Industrial Applicability

[0065] The master mold of the present invention is useful for manufacturing an aluminum material for an electrolytic capacitor electrode capable of obtaining a high specific surface area by etching.

Explanation of Reference Numerals

[0066] 1 Aluminum base material 2 Oxide film 3 Recess 4 Oxide film 5 Oxide film 100 Master mold 101 Protrusion (convex portion) 102 Pit starting point formation site

Claims

1. A master mold having a large number of convex portions on its surface, a straight line or a curve that constitutes the contour of the convex portion appearing in a cross section perpendicular to the plane of the master mold, and having a pit starting portion forming site defined by a straight line or a curve in which the angle formed between the slope of the straight line or the slope of the tangent of the curve and the plane of the master mold is 20° to 90°, using a master mold which, when pressed against an aluminum base material having an oxide film formed on its surface, forms a large number of recesses which are portions where etching pits are to be formed in the aluminum base material, and the maximum separation distance in a plan view of the pit starting portion forming site over the entire surface of the convex portion of the master mold corresponding to the recess is 1.9 μm or less, A method for manufacturing an aluminum material for an electrolytic capacitor electrode, wherein the master mold is pressed against an aluminum base material having an oxide film formed on its surface to form a large number of recesses which are portions where etching pits are to be formed in the aluminum base material, and electrolytic etching or chemical etching is carried out in a state where the inner surfaces of the recesses are covered with the oxide film.

2. The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to Claim 1, wherein the oxide film is a natural oxide film or a chemical conversion oxide film.

3. The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to Claim 1 or 2, wherein etching pits can be formed starting from the pit starting portions formed in the recesses of the aluminum base material by the pit starting portion forming site of the base material by electrolytic etching or chemical etching.

4. The method for manufacturing an aluminum material for an electrolytic capacitor electrode according to any one of Claims 1 to 3, wherein the shape of the recesses corresponds to the shape of the large number of convex portions formed on the master mold pressed against the aluminum base material.

5. A method for manufacturing an aluminum electrode material for an electrolytic capacitor, wherein electrolytic etching or chemical etching is carried out on an aluminum material for an electrolytic capacitor electrode manufactured by the method for manufacturing an aluminum material for an electrolytic capacitor electrode according to any one of Claims 1 to 4 in a state where the inner surfaces of the recesses are covered with the oxide film.

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