Method for producing chemically processed aluminum foil

Abstract

To provide chemically formed aluminum foil capable of preventing or suppressing breakage of aluminum foil due to bending when the aluminum foil having a porous layer made of a sintered body of powder is anodized, and a method for manufacturing the same.SOLUTION: Chemically formed aluminum foil 1 includes: aluminum foil 10 having a first porous layer 3 made of a sintered body of aluminum or aluminum alloy powder laminated on a first surface 2a of both surfaces of a foil-shaped base layer 2 made of aluminum or an aluminum alloy; and a first chemical conversion film 5 formed on the first porous layer 3. On the surface of the first porous layer 3, a plurality of cracks 7 extending in an in-plane direction in a Y direction with a length of 300 μm or more are formed at intervals of 30 μm to 150 μm in the in-plane direction in an X direction perpendicular to the Y direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a chemically formed aluminum foil obtained by chemically forming an aluminum foil having a porous layer made of a sintered body of aluminum or aluminum alloy powder, an electrode for an aluminum electrolytic capacitor, and a method for producing the chemically formed aluminum foil. [Background technology]

[0002] It is known that an aluminum electrolytic capacitor electrode is made of an aluminum foil having a porous layer made of a sintered body of aluminum powder and anodized. Such an aluminum foil has a problem that if the aluminum foil is bent during the anodization process in which the aluminum foil is anodized to form a chemical film, the aluminum foil breaks. In Patent Document 1, the surface of the sintered body is embossed to set the surface roughness of the sintered body within a predetermined range, and then the anodization process is performed, thereby reducing the breakage of the aluminum foil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 136804 Summary of the Invention [Problem to be solved by the invention]

[0004] The reason why the bending strength of the aluminum foil decreases in the anodizing process is that it becomes difficult to release stress from the aluminum foil as the chemical conversion film grows. That is, in the anodizing process, the chemical conversion film grows on the surface of the porous layer made of a sintered body of powder. As a result, adjacent powders are bonded via the chemical conversion film. In this state, if the aluminum foil is bent, the bond between the powders is strong, so the stress generated due to the deformation cannot be released from the aluminum foil. As a result, local cracks occur in the bonds between the powders. Furthermore, the cracks spread and the aluminum foil breaks.

[0005] Here, even when anodizing is performed on an aluminum foil with an embossed porous layer, the adjacent powder particles are bonded to each other via the chemical conversion film as the film grows. Therefore, even when the technology of Patent Document 1 is used, it is not easy to release the stress caused by deformation from the aluminum foil, and it is difficult to sufficiently suppress the decrease in the bending strength of the aluminum foil.

[0006] In view of the above problems, the present invention aims to provide an aluminum foil having a porous layer made of a sintered powder body, which can prevent or suppress breakage of the aluminum foil due to bending when the aluminum foil is anodized. Also, the present invention aims to propose a method for manufacturing such an aluminum foil. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides an aluminum chemically converted foil comprising an aluminum foil having a foil-like base layer made of aluminum or an aluminum alloy, on a first surface of which a first porous layer made of a sintered body of aluminum or an aluminum alloy powder is laminated, and a first chemical conversion coating is formed on the first porous layer, and a plurality of cracks extending in a first direction with a length of 300 μm or more in an in-plane direction are provided on the surface of the first porous layer at intervals of 30 μm to 150 μm in a second direction perpendicular to the first direction in the in-plane direction. It is characterized by:

[0008] The aluminum chemical foil of the present invention has a crack extending in a first in-plane direction with a length of 300 μm or more on the surface of the first porous layer. In addition, a plurality of cracks are provided at intervals of 30 μm to 150 μm in a second in-plane direction of the aluminum chemical foil. In the aluminum chemical foil having such a plurality of cracks, even if the aluminum foil in which adjacent powders are bonded via a first chemical conversion film is bent by anodizing the aluminum foil, the stress generated due to the deformation can be released from the part that becomes a crack after the completion of anodizing. This makes it possible to prevent or suppress the occurrence of local cracks in the bonds between the powders, and therefore to prevent or suppress the cracks from spreading and breaking the aluminum foil.

[0009] In the present invention, it is preferable that each of the cracks reaches the boundary between the base layer and the first porous layer, so that even if the aluminum foil is bent during anodization, the stress caused by the deformation can be easily released from the aluminum foil.

[0010] In the present invention, the aluminum foil may have a dimension in the second direction longer than a dimension in the first direction.

[0011] In the present invention, the first porous layer may have a thickness of 10 μm or more and 500 μm or less.

[0012] In the present invention, the average particle size of the powder may be 1 μm or more and 20 μm or less.

[0013] In the present invention, the base layer may have a thickness of 10 μm or more and 100 μm or less.

[0014] In the present invention, a second porous layer made of a sintered body of aluminum or aluminum alloy powder is laminated on a second surface of the base layer opposite to the first surface, a second chemical conversion coating is formed on the second porous layer, and a plurality of the cracks extending in the in-plane direction are provided at the above intervals on the surface of the second porous layer. In this way, even if the aluminum foil has porous layers on both sides of the base layer, the stress generated in the anodized aluminum foil can be released.

[0015] Here, the present invention can provide an electrode for an aluminum electrolytic capacitor, which is made of the above-mentioned chemically converted aluminum foil.

[0016] The aluminum electrolytic capacitor electrode of the present invention has a plurality of cracks in the first porous layer. Therefore, even if the aluminum foil is bent when the aluminum foil is anodized to manufacture the aluminum electrolytic capacitor electrode, breakage of the aluminum foil can be prevented or suppressed. In addition, since the aluminum electrolytic capacitor electrode has a plurality of cracks in the first porous layer, the specific surface area is increased compared to when the electrode does not have cracks. Therefore, the capacitance of the aluminum electrolytic capacitor electrode can be increased compared to when the first porous layer does not have a plurality of cracks.

[0017] In the present invention, the chemically formed aluminum foil may be in a roll shape wound in a spiral shape in the second direction. When the chemically formed aluminum foil is rolled to form a roll-shaped electrode for an aluminum electrolytic capacitor, the aluminum foil is wound in the second direction in which the multiple cracks are aligned. It is easy to roll. Therefore, the aluminum chemical foil having the cracks can be rolled in a shape close to a perfect circle compared to the aluminum chemical foil not having the cracks. That is, the aluminum chemical foil can be in a roll shape wound in the second direction without having a folded part in the middle. Here, if the aluminum electrolytic capacitor electrode in the roll shape in which the aluminum chemical foil is wound in a spiral curve is used as the capacitor element, the aluminum electrolytic capacitor electrode having a longer dimension in the second direction can be accommodated when the capacitor element is housed in the exterior case compared to the aluminum electrolytic capacitor electrode not wound in a spiral curve. This increases the surface area of ​​the aluminum electrolytic capacitor electrode, so that the capacitance of the aluminum electrolytic capacitor can be increased. In addition, if the aluminum chemical foil is rolled in a spiral curve, breakage of the aluminum chemical foil occurring at the folded part can be prevented compared to the case in which the aluminum chemical foil has a folded part in the middle. Therefore, the rollability of the aluminum chemical foil can be improved.

[0018] Next, another form of aluminum chemical foil of the present invention has an aluminum foil having a foil-shaped base layer made of aluminum or an aluminum alloy, on one of both sides of which a first porous layer made of a sintered body of aluminum or aluminum alloy powder is laminated, and a first chemical conversion coating formed on the first porous layer, wherein the surface of the first porous layer has a plurality of cracks extending in a first direction in the in-plane direction and spaced apart in a second direction perpendicular to the first direction, and each of the plurality of cracks reaches the boundary between the base layer and the first porous layer.

[0019] In the aluminum chemical foil of the present invention, a plurality of cracks extending in a first direction in the in-plane direction are provided on the surface of the first porous layer, the cracks being spaced apart in a second in-plane direction. In addition, each crack reaches the boundary between the base layer and the first porous layer. In the aluminum chemical foil having such a plurality of cracks, even if the aluminum foil in which adjacent powders are bonded via the first chemical film is bent by anodizing the aluminum foil, the stress generated due to the deformation can be released from the portion that becomes a crack after the completion of anodizing. This can prevent or suppress the occurrence of local cracks in the bonds between the powders, and therefore can prevent or suppress the cracks from spreading and breaking the aluminum foil.

[0020] Here, the present invention can provide an electrode for an aluminum electrolytic capacitor, which is made of the above-mentioned chemically converted aluminum foil.

[0021] The aluminum electrolytic capacitor electrode of the present invention has a plurality of cracks in the first porous layer. Therefore, even if the aluminum foil is bent when the aluminum foil is anodized to manufacture the aluminum electrolytic capacitor electrode, breakage of the aluminum foil can be prevented or suppressed. In addition, since the aluminum electrolytic capacitor electrode has a plurality of cracks in the first porous layer, the specific surface area is increased compared to when the electrode does not have cracks. Therefore, the capacitance of the aluminum electrolytic capacitor electrode can be increased compared to when the first porous layer does not have a plurality of cracks.

[0022] In the present invention, the chemically formed aluminum foil may be in a roll shape wound in a spiral shape in the second direction. When the chemically formed aluminum foil is wound to form a roll-shaped electrode for an aluminum electrolytic capacitor, it is easy to wind it in the second direction in which the multiple cracks are aligned. Therefore, the chemically formed aluminum foil having cracks can be wound in a shape closer to a perfect circle compared to a chemically formed aluminum foil having no cracks. In other words, the chemically formed aluminum foil having multiple cracks may be in a roll shape wound in the second direction without having any folded portions. Here, If the aluminum electrolytic capacitor electrode is a roll in which the aluminum chemical foil is wound in a spiral shape, the aluminum electrolytic capacitor electrode having a longer dimension in the second direction can be accommodated when the capacitor element is housed in an exterior case, compared to when the aluminum electrolytic capacitor electrode is not wound in a spiral shape. This increases the surface area of ​​the aluminum electrolytic capacitor electrode, thereby increasing the capacitance of the aluminum electrolytic capacitor. Furthermore, if the aluminum chemical foil is wound in a spiral shape into a roll, breakage of the aluminum chemical foil occurring at the folded portion can be prevented, compared to when the aluminum chemical foil has a folded portion in the middle. Therefore, the rollability of the aluminum chemical foil can be improved.

[0023] Next, the manufacturing method of the aluminum chemical foil of the present invention includes a chemical conversion step of forming a first chemical conversion coating on an aluminum foil having a first porous layer made of a sintered body of aluminum or aluminum alloy powder laminated on a first side of a foil-shaped base layer made of aluminum or an aluminum alloy, the chemical conversion step includes an anodizing step of anodizing the aluminum foil, the chemical conversion step includes a crack formation process that generates stress in the aluminum foil to provide a plurality of cracks extending in a first direction on the surface of the first porous layer and spaced apart in a second direction perpendicular to the first direction, and the anodizing step includes a post-crack formation anodizing process that anodizes the aluminum foil after the crack formation process.

[0024] According to the present invention, by generating stress in the aluminum foil in the chemical conversion step, a plurality of cracks extending in the first direction are provided on the surface of the first porous layer, spaced apart in the second direction. In addition, after the cracks are formed, the aluminum foil is anodized. Here, by forming cracks in the first porous layer during the chemical conversion step, even if the first chemical conversion film grows by the subsequent anodization, the cracks can be prevented from being closed by the first chemical conversion film. Thus, an aluminum chemical conversion foil having a plurality of cracks can be obtained. Therefore, even if the aluminum foil in which adjacent powders are bonded via the first chemical conversion film is bent as the first chemical conversion film grows, the stress generated due to the deformation can be released from the cracks. This makes it possible to prevent or suppress the occurrence of local cracks in the bonds between the powders, and therefore to prevent or suppress the local cracks from spreading and breaking the aluminum foil. In addition, since the aluminum foil is anodized after the cracks are formed, the first chemical conversion film can be reformed on the first porous layer after the cracks have occurred. This allows the newly formed aluminum surface (the exposed surface of the bare aluminum metal) exposed on the surface of the first porous layer due to the formation of cracks to be covered with the reformed first chemical conversion coating, thereby reducing leakage current from the aluminum foil or aluminum electrolytic capacitor electrode during anodization caused by cracks and preventing or suppressing breakage.

[0025] In the present invention, the crack formation treatment may be such that a plurality of cracks each having a length of 300 μm or more and extending in the first direction are provided at intervals of 30 μm to 150 μm in the second direction. By providing such cracks, even if the first chemical conversion coating grows by anodization, it is possible to prevent or suppress the cracks from being closed by the first chemical conversion coating.

[0026] In the present invention, it is preferable that the cracks are formed to reach the boundary between the base layer and the first porous layer in the crack formation process, so that the cracks are deep enough that even if the aluminum foil is bent during anodization, the stress caused by the deformation can be easily released from the cracks.

[0027] The thickness of the first chemical conversion film that grows until the voltage during anodization reaches a predetermined anodization voltage can be estimated. Therefore, if a pre-crack formation anodization process is performed in which the aluminum foil is anodized until the predetermined anodization voltage is reached before the crack formation process, the thickness of the first chemical conversion film that grows until the voltage during anodization reaches a predetermined anodization voltage can be estimated. This can prevent the first chemical conversion coating from becoming too thick and the aluminum foil from becoming too hard at the time of carrying out the process. This can prevent the aluminum foil from breaking when stress is applied to the aluminum foil. In addition, it is possible to uniformly provide multiple cracks on the surface of the first porous layer when stress is applied to the aluminum foil. Here, if multiple cracks are uniformly formed on the surface of the first porous layer, it is possible to suppress a decrease in bending strength even if the thickness of the first chemical conversion coating increases until the desired coating withstand voltage is reached.

[0028] The above-mentioned predetermined anodization voltage can be 400V or less. The time until the predetermined anodization voltage is reached includes the time when the predetermined anodization voltage is reached. In this way, compared with the case where the crack formation process is performed after the voltage during anodization reaches the predetermined anodization voltage, the first chemical conversion film does not become too thick and the aluminum foil does not become too hard at the time of forming the cracks. Therefore, when stress is generated in the aluminum foil, the aluminum foil is less likely to break. In addition, if the crack formation process is performed before the voltage during anodization reaches the predetermined anodization voltage, the first chemical conversion film does not become too thick and the aluminum foil does not become too hard, so that multiple cracks can be uniformly provided on the surface of the first porous layer by generating stress in the aluminum foil. Here, if multiple cracks can be uniformly provided on the surface of the first porous layer, the decrease in bending strength can be suppressed even when the first chemical conversion film is formed thick by anodization after the voltage during anodization reaches the predetermined anodization voltage.

[0029] In the present invention, the crack forming process may include contacting a first crack forming roller extending in the first direction with a second surface of the aluminum foil opposite to the first surface, and moving the aluminum foil and the first crack forming roller relatively in the second direction. In this way, stress is generated in the aluminum foil by the first crack forming roller, and cracks are formed in the first porous layer.

[0030] In the present invention, in the chemical conversion step, the aluminum foil is run in the second direction by a plurality of rollers arranged along the second direction, and among the plurality of rollers, a roller having a smaller diameter than the other rollers is arranged as the first crack forming roller. If a roller having a smaller diameter is used as the first crack forming roller, it becomes easy to generate stress in the aluminum foil by the first crack forming roller.

[0031] In the present invention, the aluminum foil has a second porous layer made of a sintered body of aluminum or aluminum alloy powder laminated on a second surface opposite to the first surface of the base layer, and in the chemical conversion step, a second chemical conversion film is formed on the second porous layer, and in the crack formation treatment, a second crack formation roller extending in the first direction is brought into contact with the first surface at a position different from the first crack formation roller in the second direction to relatively move the aluminum foil and the second crack formation roller in the second direction. In this way, stress can be generated in the aluminum foil by the second crack formation roller to form multiple cracks in the second porous layer. Therefore, even if the aluminum foil has porous layers on both sides of the base layer, or even if the aluminum foil is bent when anodized, the stress generated by the deformation can be released from the aluminum foil. Therefore, breakage of the aluminum foil can be prevented or suppressed.

[0032] In the present invention, the chemical conversion step includes a hydration step of forming a hydrated film on the aluminum foil before the anodization step, and the anodization step involves anodizing the aluminum foil on which the hydrated film has been formed, and the crack formation treatment can be performed during the hydration step. In this way, a hydrated film is formed on the surface of the first porous layer in the hydration step. Furthermore, cracks are provided in the first porous layer during the hydration step. As a result, the crack formation treatment causes the surface of the first porous layer to be cracked through the cracks. The newly formed aluminum surface is exposed. That is, at the fracture surface of the first porous layer caused by the crack, powders on which no hydrated film is formed are exposed. After that, a hydrated film is formed on the newly formed aluminum surface in the hydration process that is performed following the crack formation process. Here, the hydrated film that covers the newly formed aluminum surface inhibits or suppresses the bonding of the powders located on both sides of the crack through the first chemical conversion film in the anodization process. Therefore, if the crack formation process is performed during the hydration process, it is possible to prevent or suppress the cracks from being closed by the first chemical conversion film when the first chemical conversion film grows in the anodization process that is performed after the crack formation process and the hydration process.

[0033] In the present invention, the chemical conversion step includes a hydration step of forming a hydration film on the aluminum foil before the anodization step, and the anodization step includes anodizing the aluminum foil on which the hydration film is formed, and the crack formation treatment can be performed after the hydration step. In this way, a hydration film is formed on the surface of the first porous layer in the hydration step. Here, the hydration film becomes an obstacle when the powder particles bond together via the first chemical conversion film in the anodization step, and inhibits or suppresses the bonding between the powder particles. Therefore, if a crack formation treatment is provided after the hydration step during the chemical conversion step, it is easy to suppress the cracks formed in the first porous layer from being closed by the first chemical conversion film.

[0034] In the present invention, it is preferable to provide a rehydration treatment for forming a hydrated film on the aluminum foil following the crack formation treatment. In this way, a hydrated film is formed on the new aluminum surface exposed on the surface of the first porous layer due to the formation of cracks in the rehydration treatment performed following the crack formation treatment. Here, the hydrated film covering the new aluminum surface inhibits or suppresses the bonding of the powders located on both sides of the crack through the first chemical conversion film in the anodizing process. Therefore, if the rehydration treatment is performed following the crack formation treatment, it is possible to suppress the crack from being closed by the first chemical conversion film when the first chemical conversion film grows thereafter. Effect of the Invention

[0035] The aluminum chemical foil of the present invention has a crack extending in the first in-plane direction with a length of 300 μm or more on the surface of the first porous layer. The cracks are provided in a plurality of spaces at intervals of 30 μm to 150 μm in the second in-plane direction of the aluminum chemical foil. In the aluminum chemical foil having such a plurality of cracks, even if the aluminum foil is bent during anodization, the stress generated due to the deformation can be released from the portion that becomes the crack after the anodization is completed. This can prevent or suppress the occurrence of local cracks in the bonds between the powder particles, and therefore prevent or suppress the aluminum foil from breaking.

[0036] In another embodiment of the present invention, the aluminum chemical foil has a plurality of cracks extending in a first direction in the in-plane direction on the surface of the first porous layer, the cracks being spaced apart in a second in-plane direction. Each crack reaches the boundary between the base layer and the first porous layer. In the aluminum chemical foil having such a plurality of cracks, even if the aluminum foil is bent during anodization, the stress generated due to the deformation can be released from the portion that becomes a crack after the anodization is completed. This can prevent or suppress the occurrence of local cracks in the bonds between the powder particles, and therefore prevent or suppress the aluminum foil from breaking.

[0037] The method for producing a chemically-converted aluminum foil of the present invention includes a chemical conversion step of forming a first chemical conversion film on an aluminum foil having a first porous layer laminated thereon, and the chemical conversion step includes an anodizing step of anodizing the aluminum foil. In addition, in the chemical conversion step, cracks are formed in the first porous layer, and in the anodizing step, the aluminum foil is anodized after the cracks are formed. In this way, the chemical conversion step By forming cracks in the first porous layer during the process, it is possible to obtain an aluminum foil having a plurality of cracks. Thus, stress caused by deformation of the aluminum foil can be released from the cracks. This can prevent or suppress local cracks from occurring in the bonds between the powder particles, and therefore prevent or suppress the local cracks from spreading and breaking the aluminum foil. In addition, by performing anodizing after providing the cracks, the first chemical conversion film can be reformed on the first porous layer after the cracks have occurred. This allows the surface of the metal aluminum exposed by the formation of the cracks to be covered with the reformed chemical conversion film. Therefore, it is possible to prevent or suppress breakage while reducing the leakage current of the aluminum foil or the electrode for aluminum electrolytic capacitor during anodizing caused by the cracks. [Brief description of the drawings]

[0038] [Figure 1]1 is a photograph of the surface of an aluminum chemically formed foil taken under magnification by a scanning electron microscope. [Diagram 2] 1 is a photograph of a cross section of a chemically formed aluminum foil cut in the longitudinal direction, taken under magnification by a scanning electron microscope. [Diagram 3] FIG. 2 is an explanatory diagram of an aluminum chemical foil. [Figure 4] FIG. 2 is an explanatory diagram of a method for measuring the distance between cracks provided on the surface of a chemically formed aluminum foil. [Diagram 5] FIG. 2 is a schematic diagram of a roll-shaped aluminum electrolytic capacitor electrode. [Figure 6] FIG. 2 is an explanatory diagram of an aluminum foil serving as a base material for an aluminum chemical foil. [Figure 7] 1 is a flowchart showing a first manufacturing method of a chemically formed aluminum foil. [Figure 8] 4 is a flowchart showing a second method for producing a chemically formed aluminum foil. [Figure 9] 11 is a flowchart showing a third method for producing a chemically formed aluminum foil. [Figure 10] 13 is a flowchart showing a fourth manufacturing method of a chemically formed aluminum foil. [Figure 11] 13 is a flowchart showing a fifth method for producing a chemically formed aluminum foil. [Figure 12] FIG. 13 is an explanatory diagram of a crack formation process. [Figure 13] 1 is a table illustrating the timing of performing a crack formation treatment in the manufacturing methods of the chemically converted aluminum foils of Examples 1 to 5. [Figure 14] FIG. 2 is an explanatory diagram of the timing of performing a crack formation treatment in the method for producing the chemically converted aluminum foils of Examples 1 to 5. [Figure 15] 1 is a table showing the crack spacing, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foils for Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 16] 1 is a photograph taken by a scanning electron microscope under magnification of the surface of the chemically formed aluminum foil produced by the production method of Example 5. [Figure 17] 1 is a photograph of the surface of the chemically formed aluminum foil of Comparative Example 1 taken under magnification by a scanning electron microscope. [Figure 18] 1 is a photograph of a cross section of the chemically formed aluminum foil of Comparative Example 1 taken under magnification by a scanning electron microscope. [Figure 19] 1 is a table illustrating the timing of performing a crack formation treatment in the manufacturing methods of the chemically converted aluminum foils of Examples 6 to 8. [Figure 20] FIG. 1 is an explanatory diagram of the timing of performing a crack formation treatment in the method for producing the chemically converted aluminum foils of Examples 6 to 8. [Figure 21] 1 is a table showing the crack spacing, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foils for Examples 6 to 8. [Figure 22] 1 is a table illustrating the timing of performing a crack formation treatment in the manufacturing methods for the chemically converted aluminum foils of Examples 9 to 11. [Diagram 23] FIG. 13 is an explanatory diagram of the timing of performing the crack formation treatment in the method for producing the chemically converted aluminum foils of Examples 9 to 11. [Figure 24] 1 is a table showing the crack spacing, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foils for Examples 9 to 11. [Diagram 25] 13 is a flowchart showing a sixth manufacturing method of a chemically formed aluminum foil. [Figure 26] 13 is a flowchart showing a seventh manufacturing method of the chemically formed aluminum foil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, with reference to the drawings, an embodiment of the chemically formed aluminum foil and a method for manufacturing the chemically formed aluminum foil of the present invention will be described. However, the present invention is not limited to only the following embodiment. In addition, the components in the embodiment can be combined in part or in whole as appropriate. The chemically formed aluminum foil of this example is used as an electrode for an aluminum electrolytic capacitor. In the following, an aluminum electrolytic capacitor using the chemically formed aluminum foil as an electrode (anode foil) for an aluminum electrolytic capacitor will be described, and then the chemically formed aluminum foil and a method for manufacturing the chemically formed aluminum foil will be described. In this specification, when a numerical range is expressed by a lower limit value and an upper limit value using the symbol "~", both the lower limit value and the upper limit value are included.

[0040] (Aluminum electrolytic capacitor) To manufacture an aluminum electrolytic capacitor using aluminum chemical foil, an anode foil made of aluminum chemical foil (electrode for aluminum electrolytic capacitor) and a cathode foil are laminated with a separator between them and rolled to form a capacitor element. Next, the capacitor element is impregnated with an electrolytic solution (paste). Thereafter, the capacitor element containing the electrolytic solution is placed in an exterior case, and the case is sealed with a sealer.

[0041] When a solid electrolyte is used instead of an electrolytic solution, a solid electrolyte layer is formed on the surface of an anode foil made of aluminum chemical foil (electrode for aluminum electrolytic capacitors), a cathode layer is formed on the surface of the solid electrolyte layer, and then the solid electrolyte layer is covered with a resin or the like. At this time, an anode terminal that is electrically connected to the anode and a cathode terminal that is electrically connected to the cathode layer are provided. In this case, multiple anode foils may be laminated.

[0042] (Aluminum foil) Fig. 1 is a photograph of the surface of the chemically processed aluminum foil of the present invention taken by enlarging it with a scanning electron microscope. Fig. 2 is a photograph of a cross section of the chemically processed aluminum foil of Fig. 1 cut along the longitudinal direction, taken by enlarging it with a scanning electron microscope. Fig. 3 is an explanatory diagram showing the relationship between the powder constituting the porous layer and the chemically processed coating in the chemically processed aluminum foil. Fig. 3 shows a schematic diagram of the base layer, powder and chemically processed coating constituting the chemically processed aluminum foil. Fig. 4 is an explanatory diagram of a measurement method for measuring the interval between cracks provided on the surface of the chemically processed aluminum foil.

[0043] The chemically formed aluminum foil 1 is produced by anodizing an aluminum foil consisting of a base layer 2 and a porous layer (a first porous layer 3 and a second porous layer 4). The chemically formed aluminum foil 1 (electrode for an aluminum electrolytic capacitor) is long.

[0044] As shown in Fig. 2, the chemically formed aluminum foil 1 includes a foil-shaped base layer 2 made of aluminum or an aluminum alloy, a first porous layer 3 laminated on a first surface 2a of the base layer 2, and a second porous layer 4 laminated on a second surface 2b opposite to the first surface 2a of the base layer 2. The first porous layer 3 and the second porous layer 4 are each made of a sintered body of aluminum or aluminum alloy powder. The chemically formed aluminum foil 1 also has a first chemical conversion coating 5 formed on the first porous layer 3 and a second chemical conversion coating 6 formed on the second porous layer 4.

[0045] In the following description, the three mutually orthogonal directions are defined as the X direction, the Y direction, and the Z direction, and the X direction is the longitudinal direction of the chemically formed aluminum foil 1. The Y direction is the transverse direction of the chemically formed aluminum foil 1. The Z direction is the width direction of the first porous layer 3 and the second porous layer 4 laminated on the base layer 2. This is the direction it is heading in.

[0046] In this example, the base layer 2 is a foil made of pure aluminum. A foil made of an aluminum alloy can be used as the base layer 2. The aluminum alloy is aluminum to which at least one metal element selected from the group consisting of silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, and boron is added, or aluminum containing any of these elements as an inevitable impurity element. The thickness dimension T1 of the base layer 2 is usually 10 μm or more, preferably 20 μm or more, and usually 100 μm or less, preferably 50 μm or less.

[0047] The first porous layer 3 and the second porous layer 4 are sintered bodies of powder containing at least one selected from the group consisting of aluminum and aluminum alloys. As shown in FIG. 3, the first porous layer 3 and the second porous layer 4 have a three-dimensional network structure in which the powder particles are sintered and connected while maintaining voids. The first chemical conversion film 5 and the second chemical conversion film 6 are formed on the surface of the three-dimensional network structure of the powder particles 11. Here, the first porous layer 3 and the second porous layer 4 have a three-dimensional network structure, so that their surface areas are large. Therefore, when the aluminum chemical conversion foil 1 is used as an electrode for an aluminum electrolytic capacitor, a capacitor with a large electrostatic capacitance can be manufactured.

[0048] The aluminum powder 11 has an aluminum purity of 99.80 mass% or more. The aluminum alloy used as the powder 11 contains aluminum and at least one element selected from silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, zirconium, etc. The content of these elements in the aluminum alloy is desirably 100 mass ppm or less, particularly 50 mass ppm or less.

[0049] The thickness of the first porous layer 3 and the thickness of the second porous layer 4 are usually the same or approximately the same. However, the thickness of the first porous layer 3 and the thickness of the second porous layer 4 may be different. In this case, the thickness of the first porous layer 3 may be larger than the thickness of the second porous layer 4, and the thickness of the second porous layer 4 may be larger than the thickness of the first porous layer 3. In this example, the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4 are each 10 μm or more and 500 μm or less. Moreover, the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4 are preferably 50 μm or more and 200 μm or less. That is, the thickness of the porous layer obtained by adding up the thickness of the first porous layer 3 and the thickness of the second porous layer 4 is 20 μm or more and 1000 μm or less. Moreover, the thickness of the porous layer obtained by adding up the thickness of the first porous layer 3 and the thickness of the second porous layer 4 is preferably 100 μm or more and 400 μm. The powder 11 constituting the first porous layer 3 and the second porous layer 4 has an average particle diameter K of 1 μm or more and 20 μm or less.

[0050] The average particle diameter K of the powder 11 is obtained by measuring the cross section of the first porous layer 3 or the second porous layer 4 by observing it with a scanning electron microscope. Specifically, when the powder 11 is observed after sintering, it is found that some of the powder 11 are in a molten state or that the powder 11 are connected to each other, but the portions having an approximately circular shape can be approximately regarded as particles. Therefore, in the cross-sectional observation, the maximum diameter of each particle having an approximately circular shape is taken as the particle diameter of the particle, and the particle diameters of about 50 particles are measured, and the average of these is taken as the average particle diameter K of the powder 11 after sintering.

[0051] As shown in Fig. 1, a plurality of cracks 7 extending in the Y direction (first direction) with a length of 300 µm or more in the in-plane direction are provided on the surface of the first porous layer 3 at intervals of 30 µm to 150 µm in the X direction (second direction) in the in-plane direction. As shown in Fig. 2, each crack 7 provided in the first porous layer 3 reaches the boundary between the base layer 2 and the first porous layer 3. Similarly, a plurality of cracks 7, each having a length of 300 μm or more and extending in the Y direction, are provided on the surface of the second porous layer 4 at intervals of 30 μm to 150 μm in the X direction perpendicular to the Y direction. Each crack 7 provided in the second porous layer 4 reaches the boundary between the base layer 2 and the second porous layer 4.

[0052] The length and interval of each crack 7 in the first porous layer 3 and the second porous layer 4 are measured by observing with a scanning electron microscope. More specifically, as shown in FIG. 4, the aluminum chemical foil 1 is observed in a field of view of 500 μm or more in the X direction and 1000 μm or more in the Y direction, and an auxiliary line 8 is drawn in the X direction near the center of the field of view. Then, the number of intersections 9 with cracks 7 with a length of 300 μm or more is counted. Then, the length of the auxiliary line 8 converted from the scale is divided by the number of intersections 9 to calculate the interval between cracks 7 with a length of 300 μm or more. The average of such measurements and calculations performed in three or more fields of view is taken as the interval between adjacent cracks 7.

[0053] (Effects of chemically processed aluminum foil) The aluminum chemical foil 1 of this example has a crack 7 extending in the Y direction with a length of 300 μm or more on the surface of the porous layer (the first porous layer 3 and the second porous layer 4). A plurality of cracks 7 are provided at intervals of 30 μm to 150 μm in the X direction of the aluminum chemical foil 1. In the aluminum chemical foil 1 having such a plurality of cracks 7, even if the aluminum foil in which the adjacent powder particles 11 are bonded via the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film) is bent by anodization, the stress generated due to the deformation can be released from the portion that becomes the crack 7 after the completion of anodization. This makes it possible to prevent or suppress the occurrence of local cracks in the bonds between the powder particles 11, and therefore to prevent or suppress the cracks from spreading and breaking the aluminum foil.

[0054] Moreover, each of the multiple cracks 7 reaches the boundary between the base layer 2 and the porous layer (the first porous layer 3 and the second porous layer 4). Therefore, stress caused by deformation can be easily released from the aluminum foil.

[0055] Here, when the chemically formed aluminum foil 1 is used as an electrode for an aluminum electrolytic capacitor, the electrode for an aluminum electrolytic capacitor has a plurality of cracks 7 in the porous layer (first porous layer 3 and second porous layer 4). Therefore, the specific surface area of ​​the electrode for an aluminum electrolytic capacitor is larger than that of an electrode for an aluminum electrolytic capacitor in which the porous layer (first porous layer 3 and second porous layer 4) does not have the cracks 7. Therefore, when the chemically formed aluminum foil is used as an electrode for an aluminum electrolytic capacitor, the electrostatic capacitance can be increased.

[0056] Furthermore, when the chemically formed aluminum foil 1 is wound to form a roll-shaped electrode for an aluminum electrolytic capacitor, it is easy to wind it in the X direction in which the cracks 7 are aligned. Therefore, the chemically formed aluminum foil 1 having the cracks 7 can be wound in a shape closer to a perfect circle compared to a chemically formed aluminum foil not having the cracks 7.

[0057] FIG. 5 is a schematic diagram of an electrode for an aluminum electrolytic capacitor in which an aluminum chemically formed foil 1 is wound in a spiral shape in a second direction, and shows a side view of the aluminum chemically formed foil 1 seen from a first direction. In FIG. 5, the aluminum chemically formed foil 1 is wound around the outer circumferential surface of a roll 16 having a diameter of 1 mm to form a roll shape. Even when wound around such a roll 16, the aluminum chemically formed foil 1 (electrode for an aluminum electrolytic capacitor 15) is wound in a shape close to a perfect circle without bending along the way. That is, when an aluminum chemically formed foil without a crack 7 is wound, multiple bent parts are formed along the way of the aluminum chemically formed foil. In contrast, when an aluminum chemically formed foil 1 with multiple cracks 7 is wound, it forms a roll shape wound in the X direction without having any bent parts along the way.

[0058] Here, if the aluminum electrolytic capacitor electrode 15 in the form of a roll in which the aluminum chemical foil 1 is wound in a shape close to a perfect circle is used as the capacitor element, the aluminum electrolytic capacitor electrode 15 having a longer dimension in the X direction can be accommodated when the capacitor element is housed in an exterior case, compared to when the aluminum electrolytic capacitor electrode is not wound in a shape close to a perfect circle. This increases the surface area of ​​the aluminum electrolytic capacitor electrode 15, thereby increasing the capacitance of the aluminum electrolytic capacitor. In addition, if the aluminum chemical foil 1 is wound in a roll shape in a spiral curve, breakage of the aluminum chemical foil 1 occurring at the folded portion can be prevented, compared to when the aluminum chemical foil 1 has a folded portion in the middle. Therefore, the rollability of the aluminum chemical foil 1 can be improved.

[0059] (Method of manufacturing chemically-formed aluminum foil) Fig. 6 is an explanatory diagram of an aluminum foil that serves as a base material for the chemically formed aluminum foil 1. Fig. 6 shows a schematic diagram of the aluminum foil. Fig. 7 is a flowchart showing a first manufacturing method for the chemically formed aluminum foil 1. Fig. 8 is a flowchart showing a second manufacturing method for the chemically formed aluminum foil 1. Fig. 9 is a flowchart showing a third manufacturing method for the chemically formed aluminum foil 1. Fig. 10 is a flowchart showing a fourth manufacturing method for the chemically formed aluminum foil 1. Fig. 11 is a flowchart showing a fifth manufacturing method for the chemically formed aluminum foil 1.

[0060] Next, a manufacturing method of the chemically processed aluminum foil 1 will be described with reference to FIG. 6 to FIG. 11. As shown in FIG. 6, when manufacturing the chemically processed aluminum foil 1, an aluminum foil 10 is used as a base material. The aluminum foil 10 includes a foil-shaped base layer 2 made of aluminum or an aluminum alloy. A first porous layer 3 made of a sintered body of aluminum or aluminum alloy powder 11 is laminated on a first surface 2a of the base layer 2, and a second porous layer 4 made of a sintered body of aluminum or aluminum alloy powder 11 is laminated on a second surface 2b of the base layer 2. In this example, the powder 11 of the first porous layer 3 and the powder 11 of the second porous layer 4 are made of the same metal powder 11. In addition, the thickness of the first porous layer 3 and the thickness of the second porous layer 4 are the same or approximately the same.

[0061] As shown in Figs. 7 to 11, the manufacturing method of the aluminum chemically formed foil 1 includes a chemical conversion step ST1 in which a first chemical conversion film 5 is formed on the first porous layer 3 of the aluminum foil 10 (base material) and a second chemical conversion film 6 is formed on the second porous layer 4. The chemical conversion step ST1 includes, in this order, a hydration step ST2 in which a hydration treatment is performed to form a hydration film on the aluminum foil 10, and an anodization step ST3 in which an anodization treatment is performed on the aluminum foil 10 on which the hydration film has been formed. In this example, the anodization step ST3 includes a heat treatment ST31 in which the aluminum foil 10 is heated during the constant voltage chemical conversion treatment step to expose defects. That is, as shown in Figs. 7 to 11, in the anodization step ST3, an anodization treatment (not shown) is performed before and after the heat treatment ST31. This also applies to other cases in this specification where a flowchart is used.

[0062] In addition, in the chemical conversion process ST1, a crack formation process ST11 is performed in which stress is applied to the aluminum foil 10 to create multiple cracks 7 extending in the Y direction and spaced apart in the X direction on the surfaces of the first porous layer 3 and the second porous layer 4.

[0063] To explain the manufacturing method of the chemically formed aluminum foil 1 of this example in more detail, in the anodizing step ST3, after the crack formation treatment ST11, a post-crack formation anodizing treatment ST3A is performed in which the aluminum foil 10 is anodized. Note that the post-crack formation anodizing treatment ST3A is abbreviated to a post-anodizing treatment ST3A in the drawings and in the following description.

[0064] 7 and 11, the crack forming treatment ST11 is performed in the middle of the chemical conversion step ST1 and in the middle of the hydration treatment ST2. That is, in the hydration step ST2, hydration treatments (not shown) are performed before and after the crack forming treatment ST11.

[0065] 9 and 10, the crack formation treatment ST11 is performed in the middle of the chemical conversion step ST1 and in the middle of the anodization step ST3. That is, in the anodization step ST3, before the crack formation treatment ST11, a pre-crack formation anodization treatment ST3B is performed in which the aluminum foil 10 is anodized until the voltage during anodization reaches a predetermined anodization voltage. Note that the pre-crack formation anodization treatment ST3B is abbreviated to pre-anodization treatment ST3B in the drawings and in the following description. That is, when the crack formation treatment ST11 is performed in the middle of the anodization step ST3, the pre-anodization treatment ST3B, the crack formation treatment ST11, and the post-anodization treatment ST3A are performed in this order in the anodization step ST3.

[0066] In the hydration step ST2, the aluminum foil 10 is boiled in a hydration treatment liquid having a liquid temperature of 80° C. or more to form an aluminum hydrate film such as boehmite on the aluminum foil 10. Pure water can be used as the hydration treatment liquid. In addition, a rehydration treatment ST21 described later can be performed in the same manner.

[0067] In the anodizing step ST3, the aluminum foil 10 is immersed in a chemical conversion solution, and the voltage during anodizing (the voltage output from the power source) is made to reach a predetermined anodizing voltage. This forms a chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) on the aluminum foil 10. As the chemical conversion solution, sulfuric acid or its salt, selenic acid or its salt, boric acid or its salt, phosphoric acid or its salt, organic acid or its salt (e.g. adipic acid or its salt, citric acid or its salt, sebacic acid or its salt, oxalic acid or its salt, etc.), sodium hydroxide or its salt, etc. can be used. The anodizing voltage is set between 5V and 1000V. Needless to say, the anodizing treatment (post-anodizing treatment ST3A and pre-anodizing treatment ST3B) performed in the anodizing step ST3 can be performed in the same manner.

[0068] In the heat treatment ST31 performed during the anodization step ST3, the aluminum foil 10 is placed in, for example, a heat treatment furnace and heated. The atmosphere in the heat treatment furnace has a temperature of 300° C. or higher and 600° C. or lower. The atmosphere in the heat treatment furnace may be any of an air atmosphere, an inert gas atmosphere, and a water vapor atmosphere.

[0069] In the manufacturing method of the chemically converted aluminum foil 1 of this example, a crack formation treatment ST11 is performed during the hydration step ST2 before the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) are provided, or between the hydration step ST2 and the anodization step ST3. In this case, in the anodization step ST3 (post-anodization step ST3A) following the crack formation treatment ST11, anodization is performed on the aluminum foil 10 after the cracks are formed.

[0070] Alternatively, in the manufacturing method of the aluminum chemical foil 1 of this example, in the anodization step ST3, the crack formation step ST11 is performed before the voltage during anodization reaches the final target anodization voltage. In this case, since the crack formation step ST11 is performed in the middle of the anodization step ST3, the pre-anodization step ST3B and the post-anodization step ST3A are performed before and after the crack formation. In the post-anodization step ST3A, the aluminum foil 10 is subjected to anodization that reaches a higher anodization voltage than the predetermined anodization voltage reached in the pre-anodization step ST3B.

[0071] The above-mentioned predetermined anodization voltage is usually 400 V or less. The predetermined anodization voltage is preferably 300 V or less, and more preferably 250 V or less. In this example, in the anodization step ST3, the aluminum foil 10 is heated until the anodization voltage reaches the upper limit of the above-mentioned voltage. The aluminum foil 10 is anodized, and then the crack formation process ST11 is performed. This allows stress to be generated in the aluminum foil 10 at a timing when the chemical conversion film does not become too thick and the aluminum foil 10 does not become too hard. As a result, when stress is generated in the aluminum foil 10, the breakage of the aluminum foil 10 can be suppressed and a plurality of cracks can be uniformly provided on the surface of the porous layer. Here, the crack formation process ST11 may be performed before the chemical conversion film is formed as long as it is performed during the chemical conversion process ST1, so the lower limit of the predetermined anodization voltage is not particularly limited. Therefore, the lower limit of the predetermined anodization voltage is usually 0V or more. The lower limit of the predetermined anodization voltage is preferably 10V or more, and more preferably 50V or more. In addition, in the anodization process ST3, the final anodization voltage, which is the final target of the voltage during anodization, can be appropriately set according to the properties of the target aluminum chemical foil 1. Therefore, the final anodization voltage is not particularly limited, but can be set to, for example, 1000V or less.

[0072] In the anodizing step ST3, the aluminum foil 10 may be anodized by another known method.

[0073] Here, in the chemical conversion step ST1, when the anodizing step ST3 is completed, the aluminum foil 10 after chemical conversion, that is, the chemically converted aluminum foil 1, is taken up by a take-up roller to become a roll.

[0074] Specific examples of the method for producing the chemically formed aluminum foil 1 include the following first to fifth production methods which differ in the timing at which the crack formation treatment ST11 is carried out.

[0075] In the first manufacturing method of the chemically formed aluminum foil 1, a crack formation treatment ST11 is performed during the hydration step ST2, as shown in Fig. 7. Then, in the anodization step ST3 which follows the hydration step ST2, a post-anodization treatment ST3A is performed.

[0076] In the second manufacturing method of the chemically formed aluminum foil 1, a crack formation treatment ST11 is performed between the hydration step ST2 and the anodization step ST3, as shown in Fig. 8. Then, in the anodization step ST3 which is performed following the crack formation treatment ST11, a post-anodization treatment ST3A is performed.

[0077] In the third manufacturing method of the chemically formed aluminum foil 1, a crack formation treatment ST11 is performed during the anodization step ST3, as shown in Fig. 9. Specifically, in the anodization step ST3, a pre-anodization treatment ST3B is performed in which the aluminum foil 10 is anodized until a predetermined anodization voltage is reached, and the pre-anodization treatment ST3B is followed by a crack formation treatment ST11, and the crack formation treatment ST11 is followed by a post-anodization treatment ST3A.

[0078] In the fourth manufacturing method of the chemically formed aluminum foil 1, as shown in FIG. 10, the crack formation process ST11 is performed in the middle of the anodization process ST3, as in the third manufacturing method. Specifically, in the anodization process ST3, a pre-anodization process ST3B is performed in which the aluminum foil 10 is anodized until a predetermined anodization voltage is reached, and the pre-anodization process ST3B is followed by the crack formation process ST11. Furthermore, following the crack formation process ST11, a rehydration process ST21 is performed in which a hydrated film is formed on the aluminum foil 10, and the rehydration process ST21 is followed by the post-anodization process ST3A. That is, in the fourth manufacturing method of the chemically formed aluminum foil 1, the crack formation process ST11 and the rehydration process ST21 are performed continuously in the middle of the anodization process ST3.

[0079] In the fifth manufacturing method of the chemically processed aluminum foil 1, as shown in FIG. 11, the crack formation treatment ST11 is performed in the middle of the hydration step ST2. Also, the crack formation treatment ST11 is performed in the middle of the anodization step ST3. Specifically, in the hydration step ST2, the crack formation treatment ST1 In the anodizing step ST3, a pre-anodizing treatment ST3B is performed in which the aluminum foil 10 is anodized until a predetermined anodizing voltage is reached, and the pre-anodizing treatment ST3B is followed by the crack formation treatment ST11 and the rehydration treatment ST21 in succession, and the rehydration treatment ST21 is followed by the post-anodizing treatment ST3A.

[0080] Next, a specific method for generating stress in the aluminum foil 10 in the crack formation process ST11 will be illustrated. Fig. 12 is an explanatory diagram of the crack formation process ST11. As shown in Fig. 12, in the crack formation process ST11, the aluminum foil 10 is made to run along a plurality of rollers 21 arranged in the X direction.

[0081] Each of the rollers 21 has a rotation axis extending in the Y direction. Among the rollers 21 arranged in the X direction, a roller 21 having a smaller diameter than the other rollers 21 is arranged. Among these rollers 21 having a smaller diameter, the roller 21 that contacts the second surface 2b of the aluminum foil 10 that is traveling is arranged as a first crack forming roller 21(1) that generates stress in the aluminum foil 10 and generates cracks 7 in the first porous layer 3. Among these rollers 21 having a smaller diameter, the roller 21 that contacts the first surface 2a of the aluminum foil 10 that is traveling is arranged as a second crack forming roller 21(2) that generates stress in the aluminum foil 10 and generates cracks 7 in the second porous layer 4. The diameter dimension M of the first crack forming roller 21(1) and the second crack forming roller 21(2) is 5 mm to 60 mm. In this example, the first crack forming roller 21(1) and the second crack forming roller 21(2) have the same diameter M, but these diameters M may be different.

[0082] In this example, the first crack forming roller 21(1) and the second crack forming roller 21(2) are made of metal. A pressure roller 23 is pressed against the first crack forming roller 21(1) and the second crack forming roller 21(2). The surface of each pressure roller 23 is covered with an elastic member such as rubber. It is desirable that the diameter of each pressure roller 23 is larger than the diameter of the first crack forming roller 21(1) and the diameter of the second crack forming roller 21(2).

[0083] When the aluminum foil 10 travels between the first crack forming roller 21(1) and the pressing roller 23, stress is generated in the aluminum foil 10. Therefore, a plurality of predetermined cracks 7 are formed in the first porous layer 3. Moreover, when the aluminum foil 10 travels between the second crack forming roller 21(2) and the pressing roller 23, stress is generated in the aluminum foil 10. Therefore, a plurality of predetermined cracks 7 are formed in the second porous layer 4.

[0084] The wrap angle of the first crack forming roller 21(1) when the aluminum foil 10 runs between the first crack forming roller 21(1) and the pressing roller 23 is usually -180° to 180°, preferably -45° to 45°. The wrap angle of the second crack forming roller 21(2) when the aluminum foil 10 runs between the second crack forming roller 21(2) and the pressing roller 23 is usually -180° to 180°, preferably -45° to 45°. Furthermore, it is more preferable that the wrap angle of the first crack forming roller 21(1) and the second crack forming roller 21(2) is 0° or more. Therefore, the wrap angle of the first crack forming roller 21(1) and the second crack forming roller 21(2) is 0° to 180°, preferably 0° to 45°. Here, if the embrace angle of the first crack forming roller 21(1) is within the above range, it is easy to form the desired cracks 7 in the first porous layer 3 when the first crack forming roller 21(1) is brought into contact with the second surface 2b of the aluminum foil 10. Also, if the embrace angle of the second crack forming roller 21(2) is within the above range, it is easy to form the desired cracks 7 in the second porous layer 3 when the second crack forming roller 21(2) is brought into contact with the first surface 2a of the aluminum foil 10. It is easy to form the desired crack 7 in 4.

[0085] It should be noted that a plurality of first crack forming rollers 21(1) may be provided among the plurality of rollers 21. When a plurality of first crack forming rollers 21(1) are provided, it is preferable to provide the same number of second crack forming rollers 21(2) as the first crack forming rollers 21(1) among the plurality of rollers 21. In this case, it is preferable that the first crack forming rollers 21(1) and the second crack forming rollers 21(2) are brought into contact with the aluminum foil 10 at different positions.

[0086] (Action and effect) In the manufacturing method of the aluminum chemical foil 1 of this example, a stress is generated in the aluminum foil 10 in the chemical conversion step ST1, so that a plurality of cracks 7 extending in the Y direction are formed on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) at intervals in the X direction. After the cracks 7 are formed, the aluminum foil 10 is subjected to anodization, followed by an anodization treatment ST3A. Here, by forming the cracks 7 in the porous layer (the first porous layer 3 and the second porous layer 4) during the chemical conversion step ST1, even if the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) grows by the subsequent anodization, the cracks 7 can be prevented from being closed by the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6). Thus, an aluminum chemical conversion foil 1 having a plurality of cracks 7 can be obtained. Therefore, even if the aluminum foil 10 in which the adjacent powders 11 are bonded via the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6) is bent due to the growth of the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6), the stress generated due to the deformation can be released from the cracks 7. This makes it possible to prevent or suppress the occurrence of local cracks in the bonds between the powders 11, and therefore to prevent or suppress the local cracks from spreading and causing the aluminum foil 10 to break. In addition, since the aluminum foil 10 is anodized after the cracks 7 are formed, the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6) can be reformed on the porous layers (the first porous layer 3 and the second porous layer 4) after the cracks 7 are generated. This allows the newly formed aluminum surface (the exposed surface of metallic aluminum) exposed on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) due to the formation of the cracks 7 to be covered with the reformed chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6). Therefore, it is possible to prevent or suppress breakage while reducing leakage current of the aluminum foil 10 or the aluminum electrolytic capacitor electrode during anodization caused by the cracks 7.

[0087] In addition, in the chemical conversion step ST1, the thickness of the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) that grows until the voltage output from the power source during anodization reaches a predetermined anodization voltage can be estimated. Therefore, the thickness of the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) can be managed based on the voltage output from the power source during anodization. Therefore, if the pre-anodization process ST3B is performed on the aluminum foil 10 before the crack formation process ST11 until the voltage during anodization reaches a predetermined anodization voltage, and then the crack formation process ST11 is performed, it is possible to prevent the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) from becoming too thick and the aluminum foil 10 from becoming too hard at the time of performing the crack formation process ST11. Therefore, it is possible to prevent the aluminum foil 10 from breaking when stress is applied to the aluminum foil 10 in the crack formation process ST11.

[0088] Furthermore, in this example, since it is possible to prevent the aluminum foil 10 from becoming too hard when performing the crack formation treatment ST11, it is possible to uniformly provide a plurality of cracks 7 on the surface of the porous layer (first porous layer 3 and second porous layer 4) by generating stress in the aluminum foil 10. Here, if a plurality of cracks 7 are uniformly formed on the surface of the porous layer (first porous layer 3 and second porous layer 4), even if the thickness of the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6) is increased until the desired coating withstand voltage is reached, the bending strength is not reduced. This can prevent the following from happening:

[0089] Furthermore, in the crack formation treatment ST11, a plurality of cracks 7 each having a length of 300 μm or more and extending in the Y direction are provided at intervals of 30 μm to 150 μm in the X direction. By providing such cracks 7, even if the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) grow by anodization, it is possible to prevent or suppress the cracks 7 from being closed by the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6).

[0090] Furthermore, in the crack formation treatment ST11, the cracks 7 are caused to reach the boundaries between the base layer 2 and the porous layers (the first porous layer 3 and the second porous layer 4). This makes it easier to release the stress caused by the deformation from the cracks 7 even if the aluminum foil 10 is bent during anodization.

[0091] As shown in the examples described later, as long as the voltage during anodization (anodization voltage) is within the range of 250 V, the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6) does not become too thick, and the hardness of the aluminum foil 10 is suitable for forming the cracks 7. Therefore, in the chemical conversion step ST1, if a pre-crack formation anodization treatment ST3B is performed until the voltage reaches 250 V, and then a crack formation treatment ST11 is performed to apply stress to the aluminum foil 10, it is easier to uniformly form a plurality of cracks 7 on the surface of the porous layer (first porous layer 3 and second porous layer 4).

[0092] Furthermore, in the crack formation treatment ST11, stress is generated in the aluminum foil 10 by the crack formation rollers (the first crack formation roller 21(1) and the second crack formation roller 21(2)). Therefore, it is easy to form a plurality of cracks 7 in the porous layer (the first porous layer 3 and the second porous layer 4).

[0093] In the crack formation process ST11, among the multiple rollers 21 that run on the aluminum foil 10, rollers 21 having a smaller diameter than the other rollers 21 are arranged as crack formation rollers (first crack formation roller 21(1) and second crack formation roller 21(2)). By using the rollers with a smaller diameter as the crack formation rollers (first crack formation roller 21(1) and second crack formation roller 21(2)), it is easy to generate stress in the aluminum foil 10 and form cracks 7.

[0094] Furthermore, in the first and fifth manufacturing methods, the chemical conversion step ST1 includes a hydration step ST2 in which a hydration film is formed on the aluminum foil 10 before the anodization step ST3. Then, the crack formation treatment ST11 is performed during the hydration step ST2. In this way, first, a hydration film is formed on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) in the hydration step ST2. Then, cracks 7 are provided in the porous layer (the first porous layer 3 and the second porous layer 4) during the hydration step ST2. As a result, the crack formation treatment ST11 exposes a new aluminum surface (the exposed surface of metallic aluminum) on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) through the cracks 7. That is, the powder 11 on which a hydration film is not formed on the surface is exposed on the fracture surface of the porous layer (the first porous layer 3 and the second porous layer 4) caused by the cracks 7. Thereafter, a hydrated film is formed on the new aluminum surface in the hydration step ST2 which is carried out successively after the crack formation treatment ST11. Here, the hydrated film covering the new aluminum surface inhibits or suppresses bonding between the powder particles 11 located on both sides of the crack 7 via the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) in the anodizing step ST3. Therefore, if the crack formation treatment ST11 is carried out during the hydration step ST2, when the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) grows in the anodizing step ST3 which is carried out after the crack formation treatment ST11 and the hydration step ST2, the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) will not grow. 6) can prevent or suppress the crack 7 from being closed.

[0095] In the second, third and fourth manufacturing methods, the chemical conversion step ST1 includes a hydration step ST2 for forming a hydration film on the aluminum foil 10 before the anodization step ST3. In the anodization step ST3, the aluminum foil 10 on which the hydration film has been formed is anodized. In the second and third manufacturing methods, the crack formation treatment ST11 is performed after the hydration step ST2. In this way, a hydration film is formed on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) in the hydration step ST2. Here, the hydration film inhibits or suppresses the bonding of the powder particles 11 to each other via the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) in the anodization step ST3. Therefore, by performing the crack formation treatment ST11 after the hydration process ST2, it is easy to prevent the cracks 7 formed in the porous layers (first porous layer 3 and second porous layer 4) from being closed by the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) formed after the hydration process ST2.

[0096] In the fourth and fifth manufacturing methods, in the anodizing step ST3, a pre-crack formation anodizing step ST3B is performed until a predetermined anodizing voltage is reached, and then a crack formation step ST11 is performed. In addition, the crack formation step ST11 is followed by a rehydration step ST21 in which a hydration film is formed on the aluminum foil 10. Furthermore, the rehydration step ST21 is followed by a post-anodizing step ST3A. In this way, a hydration film is formed on the surface of the porous layer (the first porous layer 3 and the second porous layer 4) in the hydration step ST2. Here, the hydration film inhibits or suppresses the bonding of the powder particles 11 to each other through the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) in the anodizing step ST3. Therefore, it is easy to suppress the cracks 7 formed in the porous layer (the first porous layer 3 and the second porous layer 4) from being closed by the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6). Furthermore, a hydration film is formed on the newly formed aluminum surface exposed on the surface of the porous layer (first porous layer 3 and second porous layer 4) due to the formation of the cracks 7 in the rehydration treatment ST21 performed subsequently to the crack formation treatment ST11. Here, the hydration film covering the newly formed aluminum surface inhibits or suppresses the bonding of the powder particles 11 located on both sides of the cracks 7 via the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) in the subsequent anodization. Therefore, if the rehydration treatment ST21 is performed subsequent to the crack formation treatment ST11, it is possible to further suppress the cracks 7 from being closed by the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) when the chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) grows in the post-anodization treatment ST3A.

[0097] Here, in each manufacturing method, when the anodization step ST3 is completed, the aluminum foil 10 after the chemical conversion, that is, the aluminum chemical foil 1, is wound around a winding roller and is wound in a spiral shape. At this time, since the aluminum chemical foil 1 has a plurality of cracks 7, it is easy to wind it in the X direction. Therefore, the aluminum chemical foil 1 can be wound in a shape close to a perfect circle compared to when the aluminum chemical foil 1 does not have the cracks 7. That is, when the aluminum chemical foil 1 without the cracks is wound, a plurality of bent parts are formed in the middle of the aluminum chemical foil 1. In contrast, when the aluminum chemical foil 1 with the plurality of cracks 7 is wound, the roll shape is wound in the X direction without having any bent parts in the middle. As a result, the roll around which the aluminum chemical foil 1 is wound has a smaller outer dimension relative to the dimension in the X direction of the wound aluminum chemical foil 1 compared to when the aluminum chemical foil 1 does not have any cracks. In other words, when the roll is wound until the outer dimensions of the roll become the same, the roll on which the aluminum chemical foil 1 is wound has a longer dimension in the X direction of the wound aluminum chemical foil 1 compared to a roll in which the aluminum chemical foil 1 does not have cracks. Therefore, in this example, the work efficiency of the winding work of the aluminum chemical foil 1 into a roll is improved. Also, the aluminum chemical foil 1 is wound in a spiral curved shape into a roll shape. This makes it possible to prevent breakage of the chemically formed aluminum foil 1 at the folded portion, as compared with a case in which the chemically formed aluminum foil 1 has a folded portion in the middle, and therefore makes it possible to improve the rollability of the chemically formed aluminum foil 1.

[0098] (Example) Fig. 13 is a table explaining the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 1 to 5. Fig. 14 is an explanatory diagram of the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 1 to 5. The manufacturing methods of the chemically formed aluminum foil 1 of Examples 1 to 5 differ in the timing of performing the crack formation treatment ST11, but the treatment performed on the aluminum foil 10 in the chemical conversion step ST1 is the same.

[0099] In Examples 1 to 5, an aluminum foil 10 is used as a substrate, in which the thickness dimension T1 of the base layer 2 is 30 μm, the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4 are each 50 μm, and the average particle diameter K of the powder 11 forming the first porous layer 3 and the second porous layer 4 is 3 μm. In the hydration step ST2, pure water is used as a hydration treatment solution. In addition, in the hydration step ST2, the aluminum foil 10 is boiled at 95° C. for 10 minutes. In the anodization step ST3, a first anodization treatment ST41, a second anodization treatment ST42, and a third anodization treatment ST43 are performed. In addition, in the anodization step ST3, a heat treatment ST31 is performed between the second anodization treatment ST42 and the third anodization treatment ST43. In the heat treatment ST31, the aluminum foil 10 is heated in an atmosphere of 500° C. for 2 minutes to expose defects.

[0100] In the first anodizing treatment ST41, the aluminum foil 10 is anodized until the anodizing voltage reaches 400V. The chemical conversion treatment solution in the first anodizing treatment ST41 contains ammonium adipate. The amount of ammonium adipate in the chemical conversion treatment solution is 1 g / L. The temperature of the chemical conversion treatment solution is 80°C. In the second anodizing treatment ST42, the anodizing voltage is increased to 550V and maintained for another 30 minutes, thereby anodizing the aluminum foil 10. The chemical conversion treatment solution in the second anodizing treatment ST42 contains boric acid and ammonium pentaborate octahydrate. The amount of boric acid in the chemical conversion treatment solution is 80 g / L, and the amount of ammonium pentaborate octahydrate is 0.5 g / L. The temperature of the chemical conversion treatment solution is 80°C. In the third anodizing treatment ST43, the anodizing voltage is increased to 550 V and maintained for an additional 10 minutes to anodize the aluminum foil 10. In the third anodizing treatment ST43, the same chemical conversion treatment solution as in the second anodizing treatment ST42 is used. The temperature of the chemical conversion treatment solution is 80° C. The diameter M of the first crack forming roller 21(1) and the diameter M of the second crack forming roller 21(2) used in the crack forming treatment ST11 are 10 mm.

[0101] 13 and 14, Example 1 is a first manufacturing method in which a crack formation treatment ST11 is performed midway through the hydration step ST2. Example 2 is a second manufacturing method in which a crack formation treatment ST11 is performed between the hydration step ST2 and the anodizing step ST3. In Examples 1 and 2, the first anodizing treatment ST41, the second anodizing treatment ST42, and the third anodizing treatment ST43 correspond to the post-anodizing treatment ST3A.

[0102] Examples 3 to 5 are a third manufacturing method, in which a crack formation treatment ST11 is performed in the anodization step ST3 included in the chemical conversion step ST1 before the final target anodization voltage (550 V) is reached.

[0103] In Example 3, in the first anodizing treatment ST41, the crack formation treatment ST11 is performed when the anodizing voltage reaches 100 V. In Example 3, the period until the anodizing voltage reaches 100 V in the first anodizing treatment ST41 corresponds to the pre-anodizing treatment ST3B, and after the crack formation treatment ST11 in the first anodizing treatment ST41, the second anodizing treatment ST42 and the third anodizing treatment ST43 are performed. The anodizing treatment ST43 corresponds to the post-anodizing treatment ST3A.

[0104] In Example 4, in the first anodizing treatment ST41, the crack formation treatment ST11 is performed when the anodizing voltage reaches 200 V. In Example 4, the first anodizing treatment ST41 until the anodizing voltage reaches 200 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 after the crack formation treatment ST11 of the first anodizing treatment ST41 correspond to the post-anodizing treatment ST3A.

[0105] In Example 5, in the first anodizing treatment ST41, the crack formation treatment ST11 is performed when the anodizing voltage reaches 400 V. In Example 5, the first anodizing treatment ST41 until the anodizing voltage reaches 400 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 correspond to the post-anodizing treatment ST3A.

[0106] The manufacturing method of Comparative Example 1 does not include a crack formation treatment ST11 in the chemical conversion step ST1. In the manufacturing method of Comparative Example 2, the crack formation treatment ST11 is performed immediately after the second anodization treatment ST42 in the anodization step ST3. In the manufacturing method of Comparative Example 2, at the time when the crack formation treatment ST11 is performed, the voltage output from the power source during anodization exceeds a predetermined anodization voltage (400 V) and reaches the final anodization voltage (550 V) which is the final target voltage during anodization.

[0107] FIG. 15 is a table showing the intervals of cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the aluminum chemical foil 1, for Examples 1 to 5 and Comparative Examples 1 and 2. The manufacturing method of Comparative Example 1 does not include the crack formation treatment ST11. Therefore, as shown in FIG. 15, the aluminum chemical foil 1 obtained by the manufacturing method of Comparative Example 1 does not have cracks in the first porous layer 3 and the second porous layer 4. Therefore, the column of the crack interval in FIG. 15 is written as "not measurable."

[0108] Here, the bending strength, tensile strength, and capacitance were measured in accordance with the Electronic Industries Association of Japan standard "EIAJ RC-2364A". The bending strength is indicated by the number of times the aluminum chemical foil 1 is bent until it breaks. The number of times of bending is counted as one time when the aluminum chemical foil 1 extending in the X direction is bent 90° in the Z direction intersecting with the X direction and the Y direction, counted as two times when it is bent back, counted as three times when it is bent 90° in the Z direction opposite to the first time, counted as four times when it is bent back, and so on. From the fifth time onwards, the number of times is counted by folding in the same way as the first to fourth times. The tensile strength is the tensile force when the aluminum chemical foil 1 is pulled in the X direction until it breaks.

[0109] Fig. 16 is a photograph taken by a scanning electron microscope, enlarging the surface of the chemically formed aluminum foil 1 produced by the production method of Example 5. Fig. 1 is a photograph taken by a scanning electron microscope, enlarging the surface of the chemically formed aluminum foil 1 produced by the production method of Example 1. Fig. 2 is a photograph taken by a scanning electron microscope, enlarging the cross section of the chemically formed aluminum foil 1 produced by the production method of Example 1.

[0110] 1, 2 and 16, in the chemically formed aluminum foil 1 obtained by the manufacturing method of Examples 1 to 5, a plurality of cracks 7 each having a length of 300 μm or more and extending in the Y direction are provided at intervals of 30 μm to 150 μm on the surfaces of the first porous layer 3 and the second porous layer 4. Specifically, as shown in FIG. 15, a plurality of cracks 7 are provided at intervals of 95 μm to 110 μm.

[0111] In such a chemically-formed aluminum foil 1, even if bending occurs in the aluminum foil 10 when adjacent powder particles 11 are bonded via the chemically-formed coatings (the first chemically-formed coating 5 and the second chemically-formed coating 6) by subjecting the aluminum foil 10 to anodization, the bending is not caused by deformation. The stress can be released through the cracks 7. Therefore, the chemically formed aluminum foils 1 obtained by the manufacturing methods of Examples 1 to 5 have a bending strength of 150 or more times, and are stronger against bending than the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2.

[0112] Here, in the chemical aluminum foil 1 (see FIG. 1) obtained by the manufacturing methods of Examples 1 to 4, the intervals between the cracks 7 are narrower than in the chemical aluminum foil 1 obtained by the manufacturing method of Example 5 (see FIG. 16). Therefore, as shown in FIG. 15, the number of folds indicating the folding strength is greater than that of the chemical aluminum foil 1 obtained by the manufacturing method of Example 5, and the chemical aluminum foil 1 is more resistant to folding. Here, according to verification by the inventors, if the crack formation treatment ST11 is performed before the anodization voltage reaches 250V in the anodization step ST3, the chemical aluminum foil 1 can be made more resistant to folding than when the crack formation treatment ST11 is performed after the anodization voltage exceeds 250V.

[0113] Furthermore, when the chemically formed aluminum foils 1 obtained by the manufacturing methods of Examples 1 to 5 are used as electrodes for aluminum electrolytic capacitors, the capacitance is higher than when the chemically formed aluminum foils obtained by the manufacturing method of Comparative Example 1 are used as electrodes for aluminum electrolytic capacitors. That is, the chemically formed aluminum foils 1 obtained by the manufacturing methods of Examples 1 to 5 have cracks 7, and therefore have a larger specific surface area than the chemically formed aluminum foils 1 obtained by the manufacturing method of Comparative Example 1. As a result, the chemically formed aluminum foils 1 (electrodes for aluminum electrolytic capacitors) obtained by the manufacturing methods of Examples 1 to 5 have a higher capacitance.

[0114] Here, FIG. 17 is a photograph of the surface of the aluminum chemical foil 1' manufactured by the manufacturing method of Comparative Example 1, taken by enlarging it with a scanning electron microscope. FIG. 18 is a photograph of the cross section of the aluminum chemical foil 1' of Comparative Example 1, taken by enlarging it with a scanning electron microscope. As shown in FIG. 17 and FIG. 18, the aluminum chemical foil 1' manufactured by the manufacturing method of Comparative Example 1 does not have cracks. In such an aluminum chemical foil 1', when a chemical conversion film (first chemical conversion film 5 and second chemical conversion film 6) grows on the surface of the porous layer (first porous layer 3 and second porous layer 4) made of a sintered body of the powder 11 in the anodization step ST3, the adjacent powders 11 are bonded through the chemical conversion film. Therefore, when the aluminum foil is bent, the bond between the powders 11 is strong, so that the stress generated due to the deformation cannot be released from the aluminum foil. As a result, local cracks occur in the bonds between the powders 11. Furthermore, the cracks spread, and the aluminum foil breaks. Therefore, as shown in FIG. 15, the chemically formed aluminum foil 1' manufactured by the manufacturing method of Comparative Example 1 has low bending strength.

[0115] Fig. 19 is a table explaining the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 6 to 8. Fig. 20 is an explanatory diagram of the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 6 to 8.

[0116] Examples 6 to 8 are the fourth manufacturing method, and in the anodizing step ST3 included in the chemical conversion step ST1, a crack formation step ST11 and a rehydration step ST21 are performed consecutively before the final anodizing voltage (550 V) is reached as the final target. In Examples 6 to 8, the aluminum foil 10 used as the substrate is the same as that in Examples 1 to 5. That is, in Examples 6 to 8, the aluminum foil 10 used as the substrate has a thickness dimension T1 of 30 μm for the base layer 2, a thickness dimension T2 of the first porous layer 3 and a thickness dimension T3 of the second porous layer 4 each of 50 μm, and an average particle diameter K of the powder 11 forming the first porous layer 3 and the second porous layer 4 of 3 μm.

[0117] In addition, in the manufacturing method of the aluminum foil 1 of Examples 6 to 8, the treatment applied to the aluminum foil 10 in the chemical conversion step ST1 is the same as that of Examples 1 to 5. The diameter dimension M of the first crack formation roller 21(1) and the diameter dimension M of the second crack formation roller 21(2) used in the crack formation treatment ST11 are 10 mm. In the rehydration treatment ST21, pure water is used as the hydration treatment liquid. In the rehydration treatment ST21, the aluminum foil 10 is boiled at 95°C for 2 minutes.

[0118] Here, in Example 6, in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are successively performed when the anodizing voltage reaches 100 V. In Example 6, the first anodizing treatment ST41 until the anodizing voltage reaches 100 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 after the crack formation treatment ST11 and the rehydration treatment ST21 of the first anodizing treatment ST41 correspond to the post-anodizing treatment ST3A.

[0119] In Example 7, in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are successively performed when the anodizing voltage reaches 200 V. In Example 7, the first anodizing treatment ST41 until the anodizing voltage reaches 200 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 after the crack formation treatment ST11 and the rehydration treatment ST21 of the first anodizing treatment ST41 correspond to the post-anodizing treatment ST3A.

[0120] In Example 8, in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are successively performed when the anodizing voltage reaches 400 V. In Example 8, the first anodizing treatment ST41 until the anodizing voltage reaches 400 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 correspond to the post-anodizing treatment ST3A.

[0121] FIG. 21 is an explanatory diagram showing the intervals of the cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the aluminum chemical foil 1, in Examples 6 to 8. In the aluminum chemical foil 1 obtained by the manufacturing method of Examples 6 to 8, a plurality of cracks 7 extending in the Y direction with a length of 300 μm or more are provided on the surfaces of the first porous layer 3 and the second porous layer 4 at intervals of 30 μm to 150 μm. That is, as shown in FIG. 21, in the aluminum chemical foil 1 obtained by the manufacturing method of Examples 6 to 8, a plurality of cracks 7 are provided at intervals of 105 μm to 110 μm. Therefore, even if the aluminum foil 10 is bent when the adjacent powder particles 11 are bonded via the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) by subjecting the aluminum foil 10 to anodization, the stress generated due to the deformation can be released from the cracks 7.

[0122] Therefore, the chemically formed aluminum foils 1 obtained by the manufacturing methods of Examples 6 to 8 have a bending strength of 161 or more times, and are stronger against bending than the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2.

[0123] Furthermore, since the chemically converted aluminum foil 1 obtained by the manufacturing methods of Examples 6 to 8 is subjected to the crack formation treatment ST11 and the rehydration treatment ST21 successively in this order, when the chemically converted coating film (first chemical conversion coating film 5 and second chemical conversion coating film 6) grows in the anodizing step ST3, the cracks 7 are prevented or suppressed from being closed by the chemically converted coating film (first chemical conversion coating film 5 and second chemical conversion coating film 6). Furthermore, since the chemically converted coating film (first chemical conversion coating film 5 and second chemical conversion coating film 6) has the cracks 7, when the chemically converted aluminum foil 1 obtained by the manufacturing methods of Examples 6 to 8 is used as an electrode for an aluminum electrolytic capacitor, the cracks 7 are prevented or suppressed from being closed by the chemically converted coating film (first chemical conversion coating film 5 and second chemical conversion coating film 6) when the chemically converted aluminum foil 1 obtained by the manufacturing methods of Examples 6 to 8 is used as an electrode for an aluminum electrolytic capacitor. The electrostatic capacitance is higher than when the chemically formed aluminum foil 1 is used as an electrode for an aluminum electrolytic capacitor.

[0124] Here, in the aluminum chemical foil 1 obtained by the manufacturing method of Examples 6 and 7, the intervals of the cracks 7 are narrower than those of the aluminum chemical foil 1 obtained by the manufacturing method of Example 8. Therefore, as shown in Fig. 21, the aluminum chemical foil 1 obtained by the manufacturing method of Examples 6 and 7 has a greater number of folds, which indicates the folding strength, than the aluminum chemical foil 1 obtained by the manufacturing method of Example 8, and is therefore more resistant to folding. Furthermore, according to the inventors' verification, if the crack formation treatment ST11 and the rehydration treatment ST21 are performed before the anodization voltage reaches 250V in the anodization step ST3, the aluminum chemical foil 1 can be made more resistant to folding than the case where the crack formation treatment ST11 is performed after the anodization voltage exceeds 250V.

[0125] Fig. 22 is a table explaining the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 9 to 11. Fig. 23 is an explanatory diagram of the timing of performing the crack formation treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 9 to 11.

[0126] Examples 9 to 11 are the fifth manufacturing method, and the crack formation process ST11 is performed in the middle of the hydration process ST2 included in the chemical conversion process ST1. Furthermore, in Examples 9 to 11, in the anodization process ST3 included in the chemical conversion process ST1, the crack formation process ST11 and the rehydration process ST21 are performed continuously before the voltage output from the power source reaches the final anodization voltage (550 V) that is the final target. Furthermore, in Examples 9 to 11, an aluminum foil 10 is used as the substrate, in which the thickness dimension T1 of the base layer 2 is 30 μm, the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4 are each 100 μm, and the average particle diameter K of the powder 11 forming the first porous layer 3 and the second porous layer 4 is 3 μm. That is, in Examples 9 to 11, an aluminum foil 10 is used as the substrate, in which the thickness dimension of the porous layer (the sum of the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4) is 200 μm.

[0127] In Examples 9 to 11, the treatment applied to the aluminum foil 10 in the chemical conversion step ST1 is the same as that in Examples 1 to 8. The diameter M of the first crack forming roller 21(1) and the diameter M of the second crack forming roller 21(2) used in the crack forming treatment ST11 are 10 mm. In the rehydration treatment ST21, pure water is used as the hydration treatment liquid. In the rehydration treatment ST21, the aluminum foil 10 is boiled at 95°C for 2 minutes.

[0128] Here, in Example 9, in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are successively performed when the anodizing voltage reaches 100 V. In Example 9, the first anodizing treatment ST41 until the anodizing voltage reaches 100 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 after the crack formation treatment ST11 and the rehydration treatment ST21 of the first anodizing treatment ST41 correspond to the post-anodizing treatment ST3A.

[0129] In Example 10, in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are successively performed when the anodizing voltage reaches 200 V. In Example 10, the first anodizing treatment ST41 until the anodizing voltage reaches 200 V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 after the crack formation treatment ST11 and the rehydration treatment ST21 of the first anodizing treatment ST41 correspond to the post-anodizing treatment ST3A.

[0130] In Example 11, when the anodizing voltage reaches 400 V in the first anodizing treatment ST41, the crack formation treatment ST11 and the rehydration treatment ST21 are carried out consecutively. In FIG. 1, the first anodizing treatment ST41 until the anodizing voltage reaches 400V corresponds to the pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 correspond to the post-anodizing treatment ST3A.

[0131] FIG. 24 is an explanatory diagram showing the intervals of the cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the aluminum chemical foil 1, in Examples 9 to 11. In the aluminum chemical foil 1 obtained by the manufacturing method of Examples 9 to 11, a plurality of cracks 7 extending in the Y direction with a length of 300 μm or more are provided on the surfaces of the first porous layer 3 and the second porous layer 4 at intervals of 35 μm to 150 μm. That is, as shown in FIG. 24, a plurality of cracks 7 are provided at intervals of 135 μm to 150 μm. In such an aluminum chemical foil 1, even if the aluminum foil 10 is bent when the adjacent powders 11 are bonded via the chemical conversion coating (the first chemical conversion coating 5 and the second chemical conversion coating 6) by subjecting the aluminum foil 10 to anodization, the stress generated due to the deformation can be released from the cracks 7.

[0132] Therefore, the chemically formed aluminum foils 1 obtained by the manufacturing methods of Examples 9 to 11 have a bending strength of 120 or more times, and are stronger against bending than the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2.

[0133] Moreover, the aluminum chemical foil 1 obtained by the manufacturing method of Examples 9 to 11 is subjected to the crack formation treatment ST11 twice, the first crack formation treatment ST11 is performed in the middle of the hydration step ST2, and in the second crack formation treatment ST11, the rehydration treatment ST21 is performed continuously after the crack formation treatment ST11. Therefore, even when an aluminum foil 10 having a porous layer thickness dimension (the sum of the thickness dimension T2 of the first porous layer 3 and the thickness dimension T3 of the second porous layer 4) of 200 μm is used as the substrate, it is possible to prevent or suppress the crack 7 from being closed by the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) when the chemical conversion film (the first chemical conversion film 5 and the second chemical conversion film 6) grows in the anodization step ST3.

[0134] Furthermore, since the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) have cracks 7, when the aluminum chemical conversion foils 1 obtained by the manufacturing methods of Examples 9 to 11 are used as electrodes for aluminum electrolytic capacitors, the capacitance is higher than when the aluminum chemical conversion foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2 are used as electrodes for aluminum electrolytic capacitors.

[0135] Here, in the aluminum chemical foil 1 obtained by the manufacturing method of Examples 9 and 10, the intervals of the cracks 7 are narrower than those of the aluminum chemical foil 1 obtained by the manufacturing method of Example 11. Therefore, as shown in Fig. 24, the aluminum chemical foil 1 obtained by the manufacturing method of Examples 9 and 10 has a larger number of folds, which indicates the folding strength, than the aluminum chemical foil 1 obtained by the manufacturing method of Example 11, and is more resistant to folding. Furthermore, according to the verification by the inventors, if the crack formation treatment ST11 and the rehydration treatment ST21 are performed before the anodization voltage reaches 250V in the anodization step ST3, the aluminum chemical foil 1 can be made more resistant to folding than the case where the crack formation treatment ST11 is performed after the anodization voltage exceeds 250V.

[0136] In addition, in Examples 8 to 11, the porous layers (first porous layer 3 and second porous layer 4) laminated on the base layer 2 of the chemically formed aluminum foil 1 are thick. Therefore, when the chemically formed aluminum foils 1 manufactured by the manufacturing methods of Examples 8 to 11 are used as electrodes for aluminum electrolytic capacitors, the capacitance is higher than when the chemically formed aluminum foils 1 obtained by the manufacturing methods of other Examples are used as electrodes for aluminum electrolytic capacitors.

[0137] (Other embodiments) FIG. 25 is a flow chart of a sixth manufacturing method of the chemically formed aluminum foil 1. FIG. 26 is a flow chart of a seventh manufacturing method of the chemically formed aluminum foil 1. In the sixth manufacturing method of the chemically formed aluminum foil 1, the second manufacturing method shown in FIG. 8 is provided with a rehydration process ST21 for forming a hydration film on the aluminum foil 10 following the crack formation process ST11. That is, as shown in FIG. 25, in the sixth manufacturing method of the chemically formed aluminum foil 1, the crack formation process ST11 and the rehydration process ST21 are performed continuously between the hydration process ST2 and the anodization process ST3. In this way, a hydration film can be provided by the rehydration process ST21 on the new aluminum surface exposed through the cracks 7 provided by the crack formation process ST11. Therefore, when the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6) grows in the post-anodizing treatment ST3A in the subsequent anodizing process ST3, it is easy to prevent or suppress the crack 7 from being closed by the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6).

[0138] In addition, in the pre-anodizing treatment ST3B performed before the crack formation treatment ST11, if the predetermined anodizing voltage reached when anodizing is performed before the crack formation treatment ST11 is low, for example, if the predetermined anodizing voltage is set to 5 V or more and 150 V or less, the hydration step ST2 may be omitted. In other words, the chemical conversion step ST1 may include only the anodizing step ST3.

[0139] In the seventh manufacturing method in this case, as shown in FIG. 26, the crack formation process ST11 is performed in the anodization step ST3 by performing a pre-anodization process ST3B in which the aluminum foil 10 is anodized until the above-mentioned predetermined anodization voltage is reached, and then the crack formation process ST11 is performed. Then, after the crack formation process ST11, the post-anodization process ST3A is performed. Even in this way, a plurality of cracks 7 extending in the Y direction (Y direction) with a length of 300 μm or more can be provided on the surface of the first porous layer 3 at intervals of 30 μm to 150 μm in the X direction (X direction). In addition, a plurality of cracks 7 extending in the Y direction with a length of 300 μm or more can be provided on the surface of the second porous layer 4 at intervals of 30 μm to 150 μm in the X direction perpendicular to the Y direction. Therefore, even if the aluminum foil 10 is bent when adjacent powder particles 11 are bonded via the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) by anodizing the aluminum foil 10, the stress caused by the deformation can be released through the cracks 7.

[0140] In the manufacturing method of the chemically formed aluminum foil 1 described with reference to Figs. 7 to 11, 25, and 26, the heat treatment ST31 is performed after the post-anodizing treatment ST3A. The heat treatment ST31 may be performed in the middle of the anodizing step ST3, and may be performed before or after the pre-anodizing treatment ST3B, or before or after the post-anodizing treatment ST3A. The heat treatment ST31 may be performed in the middle of the pre-anodizing treatment ST3B, or may be performed in the middle of the post-anodizing treatment ST3A. The heat treatment ST31 may also be omitted.

[0141] Alternatively, an aluminum foil 10 including only a base layer 2 and a first porous layer 3 laminated on a first surface 2a of the base layer 2 may be used as the substrate of the chemically formed aluminum foil 1. In this case, in a crack formation treatment ST11 performed during the chemical conversion step ST1, cracks 7 are formed in the first porous layer 3 using only a first crack formation roller 21(1).

[0142] In the crack formation process ST11, the first crack formation roller 21(1) and the second crack formation roller 21(2) may be brought into contact with the aluminum foil 10, and either the first crack formation roller 21(1) or the second crack formation roller 21(2) may be moved to generate stress in the aluminum foil 10. That is, the crack formation In the process ST11, the cracks 7 can be formed in the aluminum foil 10 by moving the aluminum foil 10 relative to the first crack forming roller 21(1) and the second crack forming roller 21(2) in the X direction.

[0143] Furthermore, in the crack formation process ST11, the aluminum foil 10 may be made to run while being in contact with the first crack formation roller 21(1) or the second crack formation roller 21(2) at a predetermined wrap angle. That is, the aluminum foil 10 may be made to apply stress by the first crack formation roller 21(1) contacting the second surface 2b of the aluminum foil 10 or the second crack formation roller 21(2) contacting the first surface 2a, without running between the first crack formation roller 21(1) or the second crack formation roller 21(2) and the pressing roller 23. In this case, the wrap angle of the first crack formation roller 21(1) and the wrap angle of the second crack formation roller 21(2) may be usually greater than 0° and less than 180°. In this case, the wrap angle of the first crack forming roller 21(1) and the wrap angle of the second crack forming roller 21(2) are preferably greater than 0° and equal to or less than 45°. If the wrap angle of the first crack forming roller 21(1) and the wrap angle of the second crack forming roller 21(2) are within the above range, it is easy to form the desired cracks 7 in the first porous layer 3 or the second porous layer 4.

[0144] Here, the chemically formed aluminum foil 1 of the present invention can be used as a diffusion member that diffuses liquids such as test solutions and blood on its surface. In this case, the chemically formed aluminum foil 1 has cracks 7 on its surface, which makes it easy to diffuse liquids.

Claims

1. An aluminum foil having a foil-like base layer made of aluminum or an aluminum alloy and a first porous layer made of a sintered body of aluminum or an aluminum alloy powder laminated on a first surface of the foil-like base layer; a first chemical conversion coating formed on the first porous layer; having An aluminum chemical foil characterized in that a surface of the first porous layer has a plurality of cracks extending in a first direction with a length of 300 μm or more in an in-plane direction, the cracks being spaced apart from each other at intervals of 30 μm to 150 μm in a second direction perpendicular to the first direction in the in-plane direction.

2. The aluminum foil according to claim 1 , wherein each of the cracks reaches a boundary between the base layer and the first porous layer.

3. The aluminum foil according to claim 1 or 2, wherein the aluminum foil has a dimension in the second direction longer than a dimension in the first direction.

4. The chemically formed aluminum foil according to claim 1 , wherein the first porous layer has a thickness of 10 μm or more and 500 μm or less.

5. 5. The aluminum foil according to claim 1, wherein the powder has an average particle size of 1 μm or more and 20 μm or less.

6. The chemically formed aluminum foil according to any one of claims 1 to 5, wherein the base layer has a thickness of 10 µm or more and 100 µm or less.

7. a second porous layer made of a sintered body of aluminum or aluminum alloy powder is laminated on a second surface of the base layer opposite to the first surface; a second chemical conversion coating is formed on the second porous layer; The aluminum chemical foil according to any one of claims 1 to 6, characterized in that a plurality of cracks extending in an in-plane direction are provided at the intervals on the surface of the second porous layer.

8. An electrode for an aluminum electrolytic capacitor, comprising the aluminum foil according to claim 1 .

9. 9. The electrode for an aluminum electrolytic capacitor according to claim 8, wherein the aluminum foil is in a roll shape wound in a spiral shape in the second direction.

10. An aluminum foil having a foil-like base layer made of aluminum or an aluminum alloy and a first porous layer made of a sintered body of aluminum or an aluminum alloy powder laminated on a first surface of the foil-like base layer; a first chemical conversion coating formed on the first porous layer; having A surface of the first porous layer is provided with a plurality of cracks extending in a first direction in an in-plane direction and spaced apart in a second direction perpendicular to the first direction in the in-plane direction; An aluminum chemical foil, characterized in that each of the multiple cracks reaches the boundary between the base layer and the first porous layer.

11. An electrode for an aluminum electrolytic capacitor, comprising the aluminum foil according to claim 10.

12. 12. The electrode for an aluminum electrolytic capacitor according to claim 11, wherein the aluminum foil is in a roll shape wound in a spiral shape in the second direction.

13. The method includes a chemical conversion step of forming a first chemical conversion coating on an aluminum foil having a first porous layer made of a sintered body of aluminum or aluminum alloy powder laminated on a first surface of the aluminum foil having a foil-like base layer made of aluminum or an aluminum alloy, The chemical conversion step includes an anodizing step of anodizing the aluminum foil, In the chemical conversion step, a crack formation process is performed in which stress is generated in the aluminum foil to provide a plurality of cracks extending in a first direction on the surface of the first porous layer at intervals in a second direction perpendicular to the first direction, The method for producing an aluminum chemical foil, wherein the anodizing step includes a post-crack-formation anodizing treatment in which the aluminum foil is anodized after the crack formation treatment.

14. The method for producing an aluminum chemical foil according to claim 13, characterized in that, in the crack formation treatment, a plurality of cracks extending in the first direction with a length of 300 μm or more are provided at intervals of 30 μm to 150 μm in the second direction.

15. The method for producing a chemically formed aluminum foil according to claim 13 or 14, wherein in the crack formation treatment, each crack is allowed to reach a boundary between the base layer and the first porous layer.

16. In the anodizing step, a pre-crack formation anodizing treatment is performed in which the aluminum foil is anodized until a predetermined anodizing voltage is reached before the crack formation treatment, 16. The method for producing a chemically-formed aluminum foil according to claim 13, wherein the predetermined anodizing voltage in the pre-crack-formation anodizing treatment is 400 V or less.

17. 17. The method for producing an aluminum chemical foil according to any one of claims 13 to 16, characterized in that in the crack formation process, a first crack formation roller extending in the first direction is brought into contact with a second surface of both sides of the aluminum foil opposite to the first surface, and the aluminum foil and the first crack formation roller are moved relatively in the second direction.

18. In the chemical conversion step, the aluminum foil is run in the second direction by a plurality of rollers arranged along the second direction, The method for producing a chemically formed aluminum foil according to claim 17, characterized in that, among the plurality of rollers, a roller having a smaller diameter than the other rollers is arranged as the first crack forming roller.

19. A second porous layer made of a sintered body of aluminum or aluminum alloy powder is laminated on a second surface of the aluminum foil opposite to the first surface of the base layer, In the chemical conversion step, a second chemical conversion coating is formed on the second porous layer, The method for manufacturing an aluminum chemical foil according to claim 17 or 18, characterized in that in the crack formation process, a second crack formation roller extending in the first direction is brought into contact with the first surface at a position different from the first crack formation roller in the second direction, and the aluminum foil and the second crack formation roller are moved relatively in the second direction.

20. The chemical conversion step includes a hydration step of forming a hydrated film on the aluminum foil before the anodizing step, The anodizing step is a step of anodizing the aluminum foil on which the hydrated film is formed. 、 The method for producing a chemically converted aluminum foil according to any one of claims 13 to 19, wherein the crack formation treatment is carried out during the hydration step.

21. The chemical conversion step includes a hydration step of forming a hydrated film on the aluminum foil before the anodizing step, The anodizing step comprises anodizing the aluminum foil on which the hydrated film is formed, The method for producing a chemically converted aluminum foil according to any one of claims 13 to 19, wherein the crack formation treatment is carried out after the hydration step.

22. The method for producing a chemically converted aluminum foil according to claim 21, further comprising a rehydration process for forming a hydrated film on the aluminum foil subsequent to the crack formation process.

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