Manufacturing method of chemically formed 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 to use, as an electrode for an aluminum electrolytic capacitor, an aluminum chemically formed foil obtained by anodizing an aluminum foil having a porous layer made of a sintered body of aluminum powder. Such an aluminum chemically formed foil has a problem in that if the aluminum foil is bent during the anodizing process in which the aluminum foil is anodized to form a chemical conversion coating, the aluminum foil breaks. Patent Document 1 discloses that the surface of the sintered body is embossed to set the surface roughness of the sintered body within a predetermined range, and then the anodizing process is carried out, thereby reducing the risk of aluminum foil breakage. [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 aluminum foil decreases during the anodizing process is that it becomes difficult to release stress from the aluminum foil as the chemical conversion coating grows. That is, during the anodizing process, a chemical conversion coating grows on the surface of a porous layer made of a sintered powder. As a result, adjacent powder particles are bonded together via the chemical conversion coating. If the aluminum foil is bent in this state, the bonds between the powder particles are so strong that the stress generated by the deformation cannot be released from the aluminum foil. As a result, local cracks occur in the bonds between the powder particles. Furthermore, these cracks spread, causing the aluminum foil to break.

[0005] Here, even when anodizing is performed on an aluminum foil with an embossed porous layer, adjacent powder particles are bonded 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 a decrease in the bending strength of the aluminum foil.

[0006] In view of the above problems, an object of the present invention is to provide a chemically processed aluminum foil that can prevent or suppress breakage of the aluminum foil due to bending when anodizing the aluminum foil having a porous layer made of a sintered compact of powder, and to propose a method for manufacturing such a chemically processed aluminum foil. [Means for solving the problem]

[0023] To solve the above problems The method for producing a chemically formed aluminum foil of the present invention is Alternatively, 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 surface of a foil-like base layer made of an aluminum alloy, the chemical conversion step including an anodizing step of anodizing the aluminum foil, the chemical conversion step including a crack formation step of generating stress in the aluminum foil to form 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, and the anodizing step including a post-crack formation anodizing step of anodizing the aluminum foil after the crack formation step. the chemical conversion process includes a hydration process of forming a hydrated film on the aluminum foil before the anodization process, the anodization process is performed by anodizing the aluminum foil on which the hydrated film has been formed, the crack formation process is performed during the hydration process or after the hydration process and before the anodization process, and the crack formation process is performed by forming a plurality of cracks extending in the first direction with a length of 300 μm or more at intervals of 30 μm to 150 μm in the second direction.

[0024] According to the present invention, stress is generated in the aluminum foil during the chemical conversion process, thereby forming multiple cracks extending in a first direction and spaced apart in a second direction on the surface of the first porous layer. Furthermore, after the cracks are formed, the aluminum foil is anodized. Here, by forming cracks in the first porous layer during the chemical conversion process, even if the first chemical conversion film grows during subsequent anodization, the cracks are prevented from being closed by the first chemical conversion film. Therefore, an aluminum chemical conversion foil having multiple cracks can be obtained. Therefore, even if bending occurs in the aluminum foil in which adjacent powder particles are bonded via the first chemical conversion film as the first chemical conversion film grows, stress generated by deformation can be released from the cracks. This prevents or suppresses local cracks from occurring in the bonds between the powder particles, thereby preventing or suppressing the local cracks from spreading and causing the aluminum foil to break. Furthermore, 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 bare surface of the metallic aluminum) 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. According to the present invention, a hydrated film is formed on the surface of the first porous layer during the hydration process. The hydrated film acts as an obstacle to the bonding of powder particles via the first chemical conversion film during the anodization process, inhibiting or suppressing the bonding of the powder particles. Therefore, by providing a crack formation treatment after the hydration process during the chemical conversion process, it is easy to prevent cracks formed in the first porous layer from being closed by the first chemical conversion film. Furthermore, according to the present invention, a plurality of cracks extending in the first direction with a length of 300 μm or more are formed at intervals of 30 μm to 150 μm in the second direction. By forming such cracks, it is possible to prevent or suppress the first chemical conversion film from closing the cracks, even if the first chemical conversion film grows during anodization.

[0025] In the present invention, in the crack formation process, the cracks extending in the first direction with a length of 300 μm or more are formed in the second direction. 95 μm A plurality of cracks can be provided at intervals of 1 to 150 μm. 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 desirable that the cracks reach the boundary between the base layer and the first porous layer in the crack formation process, so that even if the aluminum foil is bent during anodization, the cracks are deep enough to easily release stress caused by deformation through the cracks.

[0027] The thickness of the first chemical conversion coating that grows until the voltage during anodizing reaches a predetermined anodizing voltage can be estimated. Therefore, if a pre-crack formation anodizing treatment is performed in which the aluminum foil is anodized until the predetermined anodizing voltage is reached before the crack formation treatment, the thickness of the first chemical conversion coating that grows until the voltage reaches a predetermined anodizing voltage can be estimated. This prevents the first chemical conversion coating from becoming too thick and the aluminum foil from becoming too hard when stress is applied to the aluminum foil. This prevents the aluminum foil from breaking when stress is applied to the aluminum foil. Furthermore, it is possible to uniformly form multiple cracks on the surface of the first porous layer when stress is applied to the aluminum foil. Here, by uniformly forming multiple cracks on the surface of the first porous layer, it is possible to prevent a decrease in bending strength even when the thickness of the first chemical conversion coating increases until the desired coating withstand voltage is reached.

[0028] The predetermined anodization voltage can be 400 V 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 to when the crack formation process is performed after the anodization voltage reaches the predetermined anodization voltage, the first chemical conversion coating does not become too thick and the aluminum foil does not become too hard when the cracks are formed. Therefore, the aluminum foil is less likely to break when stress is applied to the aluminum foil. Furthermore, if the crack formation process is performed before the anodization voltage reaches the predetermined anodization voltage, the first chemical conversion coating does not become too thick and the aluminum foil does not become too hard. Therefore, by applying stress to the aluminum foil, multiple cracks can be uniformly formed on the surface of the first porous layer. Here, if multiple cracks can be uniformly formed on the surface of the first porous layer, a decrease in bending strength can be suppressed even when the first chemical conversion coating is formed thick by anodization after the anodization voltage reaches the predetermined anodization voltage.

[0029] In the present invention, the crack formation process can be performed by bringing a first crack formation roller extending in the first direction into contact with a second surface of the aluminum foil opposite to the first surface, and moving the aluminum foil and the first crack formation roller relatively in the second direction. In this way, stress can be generated in the aluminum foil by the first crack formation roller, thereby forming cracks in the first porous layer.

[0030] In the present invention, in the chemical conversion step, the aluminum foil is made to travel 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 formation roller. If a roller having a smaller diameter is used as the first crack formation roller, it becomes easy to generate stress in the aluminum foil by the first crack formation roller.

[0031] In the present invention, the aluminum foil may have a second porous layer made of a sintered aluminum or aluminum alloy powder laminated on a second surface of the base layer opposite the first surface. In the chemical conversion step, a second chemical conversion coating is formed on the second porous layer. In the crack formation step, a second crack formation roller extending in the first direction may be 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 may be moved relative to each other in the second direction. In this manner, stress is generated in the aluminum foil by the second crack formation roller, forming 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 bends during anodization, stress generated by deformation can be released from the aluminum foil. This prevents or suppresses breakage of the aluminum foil.

[0034] In the present invention, it is desirable 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 bonding between the powder particles located on both sides of the crack via the first chemical conversion film during 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. [Effects of the Invention]

[0037] The method for producing a chemically processed aluminum foil of the present invention includes a chemical conversion step in which a first chemical conversion coating is formed on an aluminum foil laminated with a first porous layer, and an anodization step in which the aluminum foil is anodized. Furthermore, in the chemical conversion step, cracks are formed in the first porous layer, and in the anodization step, the aluminum foil is anodized after the cracks are formed. By forming cracks in the first porous layer during the chemical conversion step, a chemically processed aluminum foil having multiple cracks can be obtained. Therefore, stress generated due to deformation of the chemically processed aluminum foil can be released through the cracks. This prevents or suppresses local cracks from occurring in the bonds between the powder particles, thereby preventing or suppressing the local cracks from spreading and causing the aluminum foil to break. Furthermore, by performing an anodization treatment after forming the cracks, the first chemical conversion coating can be reformed on the first porous layer after the cracks have formed. This allows the metal aluminum surface exposed by the cracks to be covered with the reformed chemical conversion coating. Therefore, it is possible to prevent or suppress breakage while reducing leakage current from the aluminum foil or aluminum electrolytic capacitor electrode during anodization that would otherwise occur due to cracks. According to the present invention, a hydrated film is formed on the surface of the first porous layer during the hydration process. The hydrated film acts as an obstacle to the bonding of powder particles via the first chemical conversion film during the anodization process, inhibiting or suppressing the bonding of the powder particles. Therefore, by providing a crack formation treatment after the hydration process during the chemical conversion process, it is easy to prevent cracks formed in the first porous layer from being closed by the first chemical conversion film. Furthermore, according to the present invention, a plurality of cracks extending in the first direction with a length of 300 μm or more are formed at intervals of 30 μm to 150 μm in the second direction. By forming such cracks, it is possible to prevent or suppress the first chemical conversion film from closing the cracks, even if the first chemical conversion film grows during anodization. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a photograph of the surface of a chemically formed aluminum foil taken under magnification using a scanning electron microscope. [Figure 2] 1 is a photograph of a cross section of a chemically formed aluminum foil cut along its longitudinal direction, taken under magnification with a scanning electron microscope. [Figure 3] FIG. 1 is an explanatory diagram of a chemically formed aluminum foil. [Figure 4] FIG. 2 is an explanatory diagram of a measurement method for measuring the interval between cracks provided on the surface of a chemically formed aluminum foil. [Figure 5] FIG. 1 is a schematic diagram of a roll-shaped electrode for an aluminum electrolytic capacitor. [Figure 6] FIG. 1 is an explanatory diagram of an aluminum foil that serves as a substrate for a chemically formed aluminum foil. [Figure 7]1 is a flowchart showing a first method for producing a chemically formed aluminum foil. [Figure 8] 1 is a flowchart showing a second method for producing a chemically formed aluminum foil. [Figure 9] 10 is a flowchart showing a third method for producing a chemically formed aluminum foil. [Figure 10] 10 is a flowchart showing a fourth method for producing a chemically formed aluminum foil. [Figure 11] 10 is a flowchart showing a fifth method for producing a chemically formed aluminum foil. [Figure 12] FIG. 10 is an explanatory diagram of a crack formation process. [Figure 13] 1 is a table illustrating the timing of performing crack formation treatment in the manufacturing methods of chemically formed 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 formed 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 chemically formed aluminum foils for Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 16] 10 is a photograph taken under magnification by a scanning electron microscope 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 crack formation treatment in the manufacturing methods of chemically formed aluminum foils of Examples 6 to 8. [Figure 20] FIG. 10 is an explanatory diagram of the timing of performing the crack formation treatment in the method for producing the chemically formed 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 chemically formed aluminum foils for Examples 6 to 8. [Figure 22] 1 is a table illustrating the timing of performing crack formation treatment in the manufacturing methods of the chemically formed aluminum foils of Examples 9 to 11. [Figure 23] FIG. 10 is an explanatory diagram of the timing of performing the crack formation treatment in the method for producing the chemically formed 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 chemically formed aluminum foils for Examples 9 to 11. [Figure 25] 10 is a flowchart showing a sixth method for producing a chemically formed aluminum foil. [Figure 26] 10 is a flowchart showing a seventh method for producing a chemically formed aluminum foil. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, with reference to the drawings, embodiments of the chemically formed aluminum foil and the method for manufacturing the chemically formed aluminum foil of the present invention will be described. However, the present invention is not limited to the following embodiments. Furthermore, some or all of the components in the embodiments can be combined as appropriate. The chemically formed aluminum foil of this example is used as an electrode for an aluminum electrolytic capacitor. Below, an aluminum electrolytic capacitor using the chemically formed aluminum foil as an electrode (anode foil) for an aluminum electrolytic capacitor will be described, followed by an explanation of the chemically formed aluminum foil and the method for manufacturing the chemically formed aluminum foil. Note that in this specification, when a numerical range is expressed using the symbol "to" with a lower limit and an upper limit, both the lower limit and the upper limit are included.

[0040] (aluminum electrolytic capacitors) 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 wound to form a capacitor element. The capacitor element is then impregnated with an electrolytic solution (paste). The capacitor element containing the electrolytic solution is then 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 chemically formed foil (electrode for aluminum electrolytic capacitors), a cathode layer is formed on the surface of the solid electrolyte layer, and then the resulting product is packaged with a resin or the like. At this time, an anode terminal electrically connected to the anode and a cathode terminal electrically connected to the cathode layer are provided. In this case, multiple anode foils may be stacked.

[0042] (Chemical aluminum foil) Fig. 1 is a photograph of the surface of the chemically formed aluminum foil of the present invention taken under magnification using a scanning electron microscope. Fig. 2 is a photograph of a cross section of the chemically formed aluminum foil of Fig. 1 cut along the longitudinal direction, taken under magnification using a scanning electron microscope. Fig. 3 is an explanatory diagram showing the relationship between the powder constituting the porous layer and the chemical conversion coating in the chemically formed aluminum foil. Fig. 3 schematically shows the base layer, powder, and chemical conversion coating constituting the chemically formed aluminum foil. Fig. 4 is an explanatory diagram of a measurement method for measuring the spacing of cracks provided on the surface of the chemically formed aluminum foil.

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

[0044] As shown in Figure 2, the chemically formed aluminum foil 1 comprises 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 of the base layer 2 opposite the first surface 2a. 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 referred to 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 lateral direction of the chemically formed aluminum foil 1. The Z direction is the direction in which the first porous layer 3 and the second porous layer 4 are laminated on the base layer 2. This is the direction we are 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 has been added, or aluminum containing any of these elements as an inevitable impurity. The thickness T1 of the base layer 2 is typically 10 μm or more, preferably 20 μm or more, and typically 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 formed by sintering and connecting the powder particles while maintaining voids. The first chemical conversion coating 5 and the second chemical conversion coating 6 are formed on the surface of the three-dimensional network structure formed by the powder 11. Here, the first porous layer 3 and the second porous layer 4 have a large surface area due to their three-dimensional network structure. Therefore, when the chemically formed aluminum foil 1 is used as an electrode for an aluminum electrolytic capacitor, a capacitor with a large 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 one or more elements 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 preferably 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 greater than the thickness of the second porous layer 4, or the thickness of the second porous layer 4 may be greater 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. Furthermore, 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 total thickness of the porous layer, which is the sum of the thicknesses of the first porous layer 3 and the second porous layer 4, is 20 μm or more and 1000 μm or less. Furthermore, the total thickness of the porous layer, which is the sum of the thicknesses of the first porous layer 3 and 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 is in a molten state or that the powder particles 11 are connected to each other, but the portions having a substantially circular shape can be approximately regarded as particles. Therefore, in the cross section observation, the maximum diameter of each particle having a substantially circular shape is taken as the particle diameter of that 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 spacing of each crack 7 in the first porous layer 3 and the second porous layer 4 are measured by observation using a scanning electron microscope. More specifically, as shown in FIG. 4 , the aluminum chemically formed foil 1 is observed in a field of view that is 500 μm or more in the X direction and 1000 μm or more in the Y direction, and auxiliary lines 8 are drawn in the X direction near the center of the field of view. The number of intersections 9 with cracks 7 that are 300 μm or more in length is then counted. The length of the auxiliary lines 8, calculated from the scale, is then divided by the number of intersections 9 to calculate the spacing between cracks 7 that are 300 μm or more in length. The average of these measurements and calculations performed in three or more fields of view is taken as the spacing between adjacent cracks 7.

[0053] (Action and effect of chemically processed aluminum foil) The chemically formed aluminum foil 1 of this example has cracks 7 on the surfaces of the porous layers (first porous layer 3 and second porous layer 4) that extend in the Y direction with lengths of 300 μm or more. A plurality of cracks 7 are provided at intervals of 30 μm to 150 μm in the X direction of the chemically formed aluminum foil 1. In the chemically formed aluminum foil 1 having such a plurality of cracks 7, even if bending occurs in the aluminum foil in which adjacent powder particles 11 are bonded via chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating) due to anodization, stress generated by deformation can be released from the portions that become cracks 7 after completion of anodization. This prevents or suppresses local cracks from occurring in the bonds between the powder particles 11, thereby preventing or suppressing the cracks from spreading and causing the aluminum foil to break.

[0054] Furthermore, 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). This makes it easy to release stress caused by deformation 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 layers (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 when the porous layers (first porous layer 3 and second porous layer 4) do not have cracks 7. Therefore, when the chemically formed aluminum foil is used as an electrode for an aluminum electrolytic capacitor, the 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 multiple cracks 7 are aligned. Therefore, the chemically formed aluminum foil 1 having the cracks 7 can be wound in a shape that is closer to a perfect circle than an aluminum foil that does not have the cracks 7.

[0057] FIG. 5 is a schematic diagram of an electrode for an aluminum electrolytic capacitor in which a chemically processed aluminum foil 1 is wound in a spiral shape in a second direction, and shows a side view of the chemically processed aluminum foil 1 as viewed from a first direction. In FIG. 5, the chemically processed aluminum foil 1 is wound around the outer 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 chemically processed aluminum foil 1 (electrode 15 for an aluminum electrolytic capacitor) is wound in a shape close to a perfect circle without any bends. In other words, when a chemically processed aluminum foil without cracks 7 is wound, multiple bends are formed in the middle of the aluminum foil. In contrast, when a chemically processed aluminum foil 1 having multiple cracks 7 is wound, the aluminum foil is wound in the X direction without any bends in the middle.

[0058] Here, if the capacitor element is an aluminum electrolytic capacitor electrode 15 in a roll shape obtained by winding the aluminum chemically formed foil 1 in a shape close to a perfect circle, the capacitor element can accommodate an aluminum electrolytic capacitor electrode 15 that is longer in the X direction when 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. Furthermore, if the aluminum chemically formed foil 1 is wound in a spiral shape, breakage of the aluminum chemically formed foil 1 at the folded portion can be prevented compared to when the aluminum chemically formed foil 1 has folded portions. Therefore, the rollability of the aluminum chemically formed foil 1 can be improved.

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

[0060] Next, a manufacturing method of the chemically processed aluminum foil 1 will be described with reference to FIGS. 6 to 11. As shown in FIG. 6, when manufacturing the chemically processed aluminum foil 1, an aluminum foil 10 is used as a substrate. 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 compact 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 compact 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 powder 11 of the same metal. Furthermore, 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 method for producing the chemically converted aluminum foil 1 includes a chemical conversion step ST1 in which a first chemical conversion coating 5 is formed on the first porous layer 3 of the aluminum foil 10 (substrate) and a second chemical conversion coating 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 hydrated coating on the aluminum foil 10, and an anodization step ST3 in which anodization is performed on the aluminum foil 10 with the hydrated coating formed thereon. 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 explanations using flowcharts in this specification.

[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 will be abbreviated as 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 during the chemical conversion process ST1 and during the anodization process ST3. That is, in the anodization process ST3, a pre-crack formation anodization treatment ST3B is performed before the crack formation treatment ST11, 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 as pre-anodization treatment ST3B in the drawings and in the following description. That is, when the crack formation treatment ST11 is performed during the anodization process 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 process 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 higher to form an aluminum hydrate film such as boehmite on the aluminum foil 10. Pure water can be used as the hydration treatment liquid. A rehydration step ST21, which will be described later, can also be performed in the same manner.

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

[0068] In the heat treatment ST31 performed during the anodizing 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 air, inert gas, and water vapor.

[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 formed, or between the hydration step ST2 and the anodizing step ST3. In this case, in the anodizing step ST3 (post-anodizing treatment ST3A) following the crack formation treatment ST11, the aluminum foil 10 after the cracks are formed is anodized.

[0070] Alternatively, in the manufacturing method of the chemically formed aluminum foil 1 of this example, in the anodizing step ST3, the crack formation step ST11 is performed before the voltage during anodizing reaches the final target anodizing voltage. In this case, since the crack formation step ST11 is performed during the anodizing step ST3, a pre-anodizing step ST3B and a post-anodizing step ST3A are performed before and after the crack formation. In the post-anodizing step ST3A, the aluminum foil 10 is anodized to reach an anodizing voltage higher than the predetermined anodizing voltage reached in the pre-anodizing 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, 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 these upper limit values. The aluminum foil 10 is subjected to anodization, followed by the crack formation treatment ST11. This allows stress to be generated in the aluminum foil 10 at a timing that prevents the chemical conversion coating from becoming too thick and the aluminum foil 10 from becoming too hard. As a result, when stress is generated in the aluminum foil 10, breakage of the aluminum foil 10 is suppressed, and multiple cracks can be uniformly formed on the surface of the porous layer. Here, the crack formation treatment ST11 may be performed before the chemical conversion coating is formed as long as it is performed during the chemical conversion step 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 0 V or higher. The lower limit of the predetermined anodization voltage is preferably 10 V or higher, more preferably 50 V or higher. Furthermore, in the anodization step ST3, the final anodization voltage, which is the final target voltage during anodization, can be appropriately set depending on the properties of the desired aluminum chemically formed foil 1. Therefore, the final anodization voltage is not particularly limited, but can be set to, for example, 1000 V or lower.

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

[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 form 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 forming 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 that 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 that follows 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 anodizing step ST3, as shown in Fig. 9. Specifically, 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 then the pre-anodizing treatment ST3B is followed by the crack formation treatment ST11, and then the crack formation treatment ST11 is followed by the post-anodizing treatment ST3A.

[0078] In the fourth manufacturing method of the chemically formed aluminum foil 1, as shown in FIG. 10, a crack formation treatment ST11 is performed during the anodizing step ST3, as in the third manufacturing method. Specifically, 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. Furthermore, following the crack formation treatment ST11, a rehydration treatment ST21 is performed in which a hydrated film is formed on the aluminum foil 10, and the rehydration treatment ST21 is followed by the post-anodizing treatment ST3A. That is, in the fourth manufacturing method of the chemically formed aluminum foil 1, the crack formation treatment ST11 and the rehydration treatment ST21 are performed consecutively during the anodizing step ST3.

[0079] In the fifth manufacturing method of the chemically formed 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 anodizing 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 forming treatment ST11 and the rehydration treatment ST21, 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 treatment ST11 will be illustrated. Fig. 12 is an explanatory diagram of the crack formation treatment ST11. As shown in Fig. 12, in the crack formation treatment ST11, the aluminum foil 10 is made to run along a plurality of rollers 21 arranged in the X direction.

[0081] The rotation axis of each of the multiple rollers 21 extends in the Y direction. Among the multiple rollers 21 arranged in the X direction, rollers 21 having a smaller diameter than the other rollers 21 are arranged. Of these small-diameter rollers 21, the roller 21 that comes into contact with the second surface 2b of the traveling aluminum foil 10 is arranged as a first crack-forming roller 21(1) that generates stress in the aluminum foil 10 and causes cracks 7 in the first porous layer 3. Of these small-diameter rollers 21, the roller 21 that comes into contact with the first surface 2a of the traveling aluminum foil 10 is arranged as a second crack-forming roller 21(2) that generates stress in the aluminum foil 10 and causes 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 each 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 formation roller 21(1) and the second crack formation roller 21(2) are made of metal. A pressure roller 23 is pressed against each of the first crack formation roller 21(1) and the second crack formation roller 21(2). The surface of each pressure roller 23 is covered with an elastic material such as rubber. The diameter of each pressure roller 23 is preferably larger than the diameter of the first crack formation roller 21(1) and the diameter of the second crack formation 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. Furthermore, 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 formation roller 21(1) when the aluminum foil 10 runs between the first crack formation roller 21(1) and the pressure roller 23 is usually -180° to 180°, preferably -45° to 45°. The wrap angle of the second crack formation roller 21(2) when the aluminum foil 10 runs between the second crack formation roller 21(2) and the pressure roller 23 is usually -180° to 180°, preferably -45° to 45°. Furthermore, it is more desirable that the wrap angle of the first crack formation roller 21(1) and the second crack formation roller 21(2) be 0° or more. Therefore, the wrap angle of the first crack formation roller 21(1) and the second crack formation 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 set within the above range, when the first crack forming roller 21(1) is brought into contact with the second surface 2b of the aluminum foil 10, desired cracks 7 are easily formed in the first porous layer 3. Furthermore, if the embrace angle of the second crack forming roller 21(2) is set within the above range, when the second crack forming roller 21(2) is brought into contact with the first surface 2a of the aluminum foil 10, desired cracks 7 are easily formed in the second porous layer 3. 4, the desired crack 7 is easily formed.

[0085] It is to 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 desirable 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) contact the aluminum foil 10 at different positions.

[0086] (Action and effect) In the manufacturing method of the chemically formed aluminum foil 1 of this example, stress is generated in the aluminum foil 10 in the chemical conversion step ST1, thereby forming a plurality of cracks 7 extending in the Y direction and spaced apart in the X direction on the surfaces of the porous layers (first porous layer 3 and second porous layer 4). After the cracks 7 are formed, the aluminum foil 10 is subjected to a post-anodizing treatment ST3A in which the aluminum foil 10 is anodized. Here, by forming the cracks 7 in the porous layers (first porous layer 3 and second porous layer 4) during the chemical conversion step ST1, even if the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) grow during the subsequent anodization, the cracks 7 can be prevented from being closed by the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6). Therefore, it is possible to obtain a chemically formed aluminum foil 1 having a plurality of cracks 7. Therefore, even if bending occurs in the aluminum foil 10 in which adjacent powder particles 11 are bonded via the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) as the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) grow, the stress generated by the deformation can be released through the cracks 7. This prevents or suppresses local cracks from occurring in the bonds between the powder particles 11, thereby preventing or suppressing the local cracks from spreading and causing the aluminum foil 10 to break. Furthermore, because the aluminum foil 10 is anodized after the cracks 7 are formed, the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) can be reformed on the porous layers (first porous layer 3 and second porous layer 4) after the cracks 7 have formed. This allows the newly formed aluminum surfaces (exposed surfaces of the metallic aluminum) exposed on the surfaces of the porous layers (first porous layer 3 and second porous layer 4) due to the formation of cracks 7 to be covered with the reformed chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6). This reduces leakage current in the aluminum foil 10 or aluminum electrolytic capacitor electrode during anodization caused by cracks 7, while preventing or suppressing breakage.

[0087] Furthermore, in the chemical conversion step ST1, the thickness of the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 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 coating (first chemical conversion coating 5 and second chemical conversion coating 6) can be controlled based on the voltage output from the power source during anodization. Therefore, if a pre-anodizing treatment ST3B is performed on the aluminum foil 10 before the crack formation treatment ST11 until the voltage during anodization reaches a predetermined anodization voltage, and then the crack formation treatment ST11 is performed, the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6) can be prevented from becoming too thick and the aluminum foil 10 can be prevented from becoming too hard by the time the crack formation treatment ST11 is performed. Therefore, the aluminum foil 10 can be prevented from breaking when stress is applied to the aluminum foil 10 in the crack formation treatment ST11.

[0088] Furthermore, in this example, since the aluminum foil 10 can be prevented from becoming too hard when the crack formation treatment ST11 is performed, it is possible to uniformly form a plurality of cracks 7 on the surfaces of the porous layers (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 surfaces of the porous layers (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 will not decrease. This can prevent this from happening.

[0089] Furthermore, in the crack formation treatment ST11, multiple cracks 7 each having a length of 300 μm or more and extending in the Y direction are formed at intervals of 30 μm to 150 μm in the X direction. By forming such cracks 7, even if the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) grow due to 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, each crack 7 is made to reach the boundary between the base layer 2 and the porous layer (the first porous layer 3 and the second porous layer 4). This makes it easy to release stress caused by deformation from the crack 7 even if bending occurs in the aluminum foil 10 during anodization.

[0091] As will be described in the examples below, as long as the voltage during anodization (anodization voltage) is kept below 250 V, the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) will not become too thick and the hardness of the aluminum foil 10 will be suitable for forming cracks 7. Therefore, if pre-crack formation anodizing treatment ST3B is performed until the voltage reaches 250 V in the chemical conversion step ST1, and then crack formation treatment ST11 is performed to apply stress to the aluminum foil 10, it will be easier to uniformly form multiple cracks 7 on the surfaces of the porous layers (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] Furthermore, in the crack formation process ST11, among the multiple rollers 21 that run on the aluminum foil 10, rollers 21 that have 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)). If the rollers with a smaller diameter are used as the crack formation rollers (first crack formation roller 21(1) and second crack formation roller 21(2)), stress is generated in the aluminum foil 10, making it easy to form cracks 7.

[0094] Furthermore, in the first and fifth manufacturing methods, the chemical conversion step ST1 includes a hydration step ST2, which forms a hydrated film on the aluminum foil 10, before the anodizing step ST3. The crack formation treatment ST11 is performed during the hydration step ST2. In this manner, a hydrated film is first 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 formed 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 new aluminum surfaces (exposed metallic aluminum surfaces) on the surfaces of the porous layers (the first porous layer 3 and the second porous layer 4) through the cracks 7. That is, powder 11 without a hydrated film formed on the surface is exposed on the fracture surfaces of the porous layers (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 subsequent to 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 bond. 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, which forms a hydrated film on the aluminum foil 10, before the anodization step ST3. The anodization step ST3 anodizes the aluminum foil 10 on which the hydrated film has been formed. In the second and third manufacturing methods, the crack formation treatment ST11 is performed after the hydration step ST2. In this manner, a hydrated 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 hydrated film inhibits or suppresses bonding of the powder particles 11 to each other via the chemical conversion films (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 step ST2, it is easier 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 step ST2.

[0096] In the fourth and fifth manufacturing methods, in the anodizing step ST3, a pre-crack formation anodizing treatment ST3B is performed until a predetermined anodizing voltage is reached, followed by a crack formation treatment ST11. The crack formation treatment ST11 is followed by a rehydration treatment ST21, in which a hydrated film is formed on the aluminum foil 10. The rehydration treatment ST21 is followed by a post-anodizing treatment ST3A. In this manner, a hydrated 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. The hydrated film inhibits or suppresses bonding of the powder particles 11 to each other via the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 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 coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6). Furthermore, a hydrated film is formed on the newly formed aluminum surfaces exposed on the surfaces of the porous layers (first porous layer 3 and second porous layer 4) due to the formation of cracks 7 in a rehydration treatment ST21 performed subsequently to the crack formation treatment ST11. Here, the hydrated film covering the newly formed aluminum surfaces inhibits or suppresses bonding between the powder particles 11 located on both sides of the cracks 7 via the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) in the subsequent anodizing treatment. Therefore, performing the rehydration treatment ST21 subsequent to the crack formation treatment ST11 can further suppress the cracks 7 from being closed by the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) when the chemical conversion coatings (first chemical conversion coating 5 and second chemical conversion coating 6) grow in the post-anodizing treatment ST3A.

[0097] Here, in each manufacturing method, when the anodizing step ST3 is completed, the aluminum foil 10 after chemical conversion, i.e., the aluminum chemical foil 1, is taken up by a take-up roller and wound in a spiral curved shape into a roll. At this time, the aluminum chemical foil 1 has multiple cracks 7, making it easy to wind in the X direction. Therefore, the aluminum chemical foil 1 can be wound in a shape closer to a perfect circle than an aluminum chemical foil 1 without cracks 7. That is, when an aluminum chemical foil 1 without cracks is wound, multiple bends are formed in the aluminum chemical foil 1. In contrast, when an aluminum chemical foil 1 with multiple cracks 7 is wound, it is wound in the X direction without any bent portions. As a result, the roll around which the aluminum chemical foil 1 is wound has a smaller outer dimension relative to the X direction dimension of the wound aluminum chemical foil 1 than a roll without 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 formed foil 1 is wound has a longer dimension in the X direction of the wound aluminum chemical formed foil 1 compared to a roll in which the aluminum chemical formed foil 1 does not have cracks. Therefore, in this example, the work efficiency of the winding work of the aluminum chemical formed foil 1 into a roll is improved. Also, when the aluminum chemical formed foil 1 is wound in a spiral curved shape, This makes it possible to prevent breakage of the chemically formed aluminum foil 1 at the folded portion, compared to when 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 methods of the chemically formed aluminum foils 1 of Examples 1 to 5. Fig. 14 is an explanatory diagram showing the timing of performing the crack formation treatment ST11 in the manufacturing methods of the chemically formed aluminum foils 1 of Examples 1 to 5. The manufacturing methods of the chemically formed aluminum foils 1 of Examples 1 to 5 differ in the timing of performing the crack formation treatment ST11, but the treatments performed on the aluminum foils 10 in the chemical conversion step ST1 are the same.

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

[0100] In the first anodizing treatment ST41, the aluminum foil 10 is anodized until the anodizing voltage reaches 400 V. 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 550 V and maintained for an additional 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 forming treatment ST11 is performed in the anodizing step ST3 included in the chemical conversion step ST1 before the final target anodizing 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 up to when 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 ST3B 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 in 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 up to the time when 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 the crack formation treatment ST11 during the chemical conversion step ST1. In the manufacturing method of Comparative Example 2, the crack formation treatment ST11 is performed immediately after the second anodizing treatment ST42 in the anodizing 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 supply during anodizing exceeds the predetermined anodizing voltage (400 V) and reaches the final anodizing voltage (550 V), which is the ultimate target voltage during anodizing.

[0107] Fig. 15 is a table showing the spacing of cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the chemically formed aluminum foil 1, for Examples 1 to 5 and Comparative Examples 1 and 2. Note that the manufacturing method of Comparative Example 1 does not include the crack formation treatment ST11. Therefore, as shown in Fig. 15, the chemically formed aluminum 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 for crack spacing in Fig. 15 is marked "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 expressed as the number of times the aluminum chemical foil 1 is bent until it breaks. The number of times the aluminum chemical foil 1 extending in the X direction is bent 90° in the Z direction intersecting the X direction and the Y direction is counted as one bend, then returned to its original position and counted as two bends, then bent 90° in the Z direction opposite to the first bend and counted as a third bend, then returned to its original position and counted as a fourth bend, and so on. From the fifth bend onward, the bends are counted in the same way as the first to fourth bends. 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 with a scanning electron microscope, enlarged, of the surface of the chemically formed aluminum foil 1 produced by the production method of Example 5. Fig. 1 is a photograph taken with a scanning electron microscope, enlarged, of the surface of the chemically formed aluminum foil 1 produced by the production method of Example 1. Fig. 2 is a photograph taken with a scanning electron microscope, enlarged, of 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 foils 1 obtained by the manufacturing methods of Examples 1 to 5, a plurality of cracks 7 extending in the Y direction with lengths of 300 μm or more 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 (first chemically formed coating 5 and second chemically formed coating 6) by anodizing the aluminum foil 10, the bending does not occur due to 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 bending times, which is higher than that of the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2.

[0112] Here, in the chemical aluminum foils 1 obtained by the manufacturing methods of Examples 1 to 4 (see FIG. 1), the spacing of cracks 7 is 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, which indicates the bending 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 bending. Here, according to verification by the inventors, if the crack formation treatment ST11 is performed in the anodizing step ST3 before the anodizing voltage reaches 250 V, the chemical aluminum foil 1 can be made more resistant to bending than if the crack formation treatment ST11 is performed after the anodizing voltage exceeds 250 V.

[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 foil 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] FIG. 17 is a scanning electron microscope photograph of the surface of the chemically formed aluminum foil 1′ manufactured by the manufacturing method of Comparative Example 1. FIG. 18 is a scanning electron microscope photograph of the cross section of the chemically formed aluminum foil 1′ of Comparative Example 1. As shown in FIGS. 17 and 18, the chemically formed aluminum foil 1′ manufactured by the manufacturing method of Comparative Example 1 does not have cracks. In such a chemically formed aluminum foil 1′, when chemical conversion films (first chemical conversion film 5 and second chemical conversion film 6) grow on the surfaces of the porous layers (first porous layer 3 and second porous layer 4) made of a sintered body of powder 11 in the anodization step ST3, adjacent powder particles 11 are bonded together via the chemical conversion films. Therefore, when the aluminum foil is bent, the bonds between the powder particles 11 are strong, and the stress generated by the deformation cannot be released from the aluminum foil. As a result, local cracks occur in the bonds between the powder particles 11. Furthermore, these cracks propagate, causing the aluminum foil to break. 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 forming 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 forming treatment ST11 in the manufacturing method of the chemically formed aluminum foil 1 of Examples 6 to 8.

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

[0117] In addition, in the manufacturing method of the chemically formed 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 in Examples 1 to 5. The diameter M of the first crack formation roller 21(1) and the diameter 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] 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 in 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 spacing of cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the chemically formed aluminum foil 1, for Examples 6 to 8. In the chemically formed aluminum foil 1 obtained by the manufacturing method of Examples 6 to 8, multiple cracks 7 extending in the Y direction with lengths 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 chemically formed aluminum foil 1 obtained by the manufacturing method of Examples 6 to 8, multiple cracks 7 are provided at intervals of 105 μm to 110 μm. 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, stress generated by deformation can be released through 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 bending times, which is 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 formed aluminum foils 1 obtained by the manufacturing methods of Examples 6 to 8 are subjected to the crack formation treatment ST11 and the rehydration treatment ST21 successively in this order, when the chemically formed aluminum foils (first chemically formed aluminum foils 5 and second chemically formed aluminum foils 6) grow in the anodizing step ST3, the cracks 7 are prevented or suppressed from being closed by the chemically formed aluminum foils (first chemically formed aluminum foils 5 and second chemically formed aluminum foils 6) when the chemically formed aluminum foils 1 are used as electrodes for aluminum electrolytic capacitors, because the chemically formed aluminum foils 1 have cracks 7, the cracks 7 are prevented or suppressed from being closed by the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2. 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 chemical aluminum foils 1 obtained by the manufacturing methods of Examples 6 and 7, the spacing of the cracks 7 is narrower than in the chemical aluminum foil 1 obtained by the manufacturing method of Example 8. Therefore, as shown in Fig. 21, the chemical aluminum foils 1 obtained by the manufacturing methods of Examples 6 and 7 have a greater number of folds, which indicates their bending strength, than the chemical aluminum foil 1 obtained by the manufacturing method of Example 8, and are therefore more resistant to bending. Furthermore, according to verification by the inventors, if the crack formation treatment ST11 and the rehydration treatment ST21 are performed in the anodizing step ST3 before the anodizing voltage reaches 250 V, the chemical aluminum foil 1 can be made more resistant to bending than if the crack formation treatment ST11 is performed after the anodizing voltage exceeds 250 V.

[0125] Fig. 22 is a table explaining the timing of performing the crack forming 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 forming 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, in which a crack formation treatment ST11 is performed during the hydration step ST2 included in the chemical conversion step ST1. Furthermore, in Examples 9 to 11, in the anodization step ST3 included in the chemical conversion step ST1, the crack formation treatment ST11 and the rehydration treatment ST21 are performed consecutively before the voltage output from the power supply reaches the final target anodization voltage (550 V). 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 in Examples 1 to 8. The diameter M of the first crack formation roller 21(1) and the diameter 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.

[0128] 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 successively. In FIG. 1, the first anodizing treatment ST41 until the anodizing voltage reaches 400V corresponds to pre-anodizing treatment ST3B, and the second anodizing treatment ST42 and the third anodizing treatment ST43 correspond to post-anodizing treatment ST3A.

[0131] FIG. 24 is an explanatory diagram showing the spacing of cracks 7, bending strength, tensile strength, capacitance, and film withstand voltage of the aluminum foil 10 after chemical conversion treatment, i.e., the chemically converted aluminum foil 1, for Examples 9 to 11. In the chemically converted aluminum foil 1 obtained by the manufacturing method of Examples 9 to 11, multiple cracks 7 extending in the Y direction with lengths 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, multiple cracks 7 are provided at intervals of 135 μm to 150 μm. In such a chemically converted aluminum foil 1, even if bending occurs in the aluminum foil 10 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, stress generated by deformation can be released through 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, which is stronger against bending than the chemically formed aluminum foils 1 obtained by the manufacturing methods of Comparative Examples 1 and 2.

[0133] Furthermore, the chemically formed aluminum foil 1 obtained by the manufacturing methods of Examples 9 to 11 is subjected to the crack formation treatment ST11 twice, with the first crack formation treatment ST11 being performed during the hydration step ST2, and the second crack formation treatment ST11 being performed consecutively with the rehydration treatment ST21. Therefore, even when an aluminum foil 10 having a porous layer thickness (the sum of the thickness T2 of the first porous layer 3 and the thickness T3 of the second porous layer 4) of 200 μm is used as the substrate, it is possible to prevent or suppress the cracks 7 from being closed by the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6) when the chemical conversion coatings (the first chemical conversion coating 5 and the second chemical conversion coating 6) grow 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 chemical aluminum foils 1 obtained by the manufacturing methods of Examples 9 and 10, the spacing of the cracks 7 is narrower than in the chemical aluminum foil 1 obtained by the manufacturing method of Example 11. Therefore, as shown in Fig. 24, the chemical aluminum foils 1 obtained by the manufacturing methods of Examples 9 and 10 have a greater number of folds, which indicates their bending strength, than the chemical aluminum foil 1 obtained by the manufacturing method of Example 11, and are therefore more resistant to bending. Furthermore, according to verification by the inventors, if the crack formation treatment ST11 and the rehydration treatment ST21 are performed in the anodizing step ST3 before the anodizing voltage reaches 250 V, the chemical aluminum foil 1 can be made more resistant to bending than if the crack formation treatment ST11 is performed after the anodizing voltage exceeds 250 V.

[0136] Furthermore, 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 were thick. Therefore, when the chemically formed aluminum foils 1 manufactured by the manufacturing methods of Examples 8 to 11 were used as electrodes for aluminum electrolytic capacitors, the capacitance was higher than when the chemically formed aluminum foils 1 obtained by the manufacturing methods of the other Examples were used as electrodes for aluminum electrolytic capacitors.

[0137] (Other embodiments) FIG. 25 is a flowchart of a sixth method for producing a chemically formed aluminum foil 1. FIG. 26 is a flowchart of a seventh method for producing a chemically formed aluminum foil 1. The sixth method for producing a chemically formed aluminum foil 1 includes, in addition to the second production method shown in FIG. 8, a rehydration treatment ST21 for forming a hydration film on the aluminum foil 10 subsequent to the crack formation treatment ST11. That is, as shown in FIG. 25, the sixth method for producing a chemically formed aluminum foil 1 includes successively performing the crack formation treatment ST11 and the rehydration treatment ST21 between the hydration step ST2 and the anodization step ST3. In this way, a hydration film can be formed by the rehydration treatment ST21 on the newly formed aluminum surface exposed through the cracks 7 formed by the crack formation treatment 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 cracks 7 from being closed by the chemical conversion coating (first chemical conversion coating 5 and second chemical conversion coating 6).

[0138] Furthermore, 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 this case, in the seventh manufacturing method, as shown in FIG. 26, the crack formation treatment ST11 is performed in the anodization step ST3 by performing a pre-anodization treatment ST3B in which the aluminum foil 10 is anodized until the predetermined anodization voltage is reached, followed by the crack formation treatment ST11. Then, after the crack formation treatment ST11, a post-anodization treatment ST3A is performed. Even in this manner, a plurality of cracks 7 each having a length of 300 μm or more and extending in the Y direction (Y direction) can be formed on the surface of the first porous layer 3, at intervals of 30 μm to 150 μm in the X direction (X direction). Furthermore, a plurality of cracks 7 each having a length of 300 μm or more and extending in the Y direction (X direction) can be formed 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 generated 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 during 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 also be performed during the pre-anodizing treatment ST3B or during the post-anodizing treatment ST3A. The heat treatment ST31 may also be omitted.

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

[0143] Furthermore, in the crack formation process ST11, the aluminum foil 10 may be 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 not run between the first crack formation roller 21(1) or the second crack formation roller 21(2) and the pressing roller 23, but may be stressed 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. 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 typically be greater than 0° and less than or equal to 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 ranges, 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. The method includes a chemical conversion step of forming a first chemical conversion coating on an aluminum foil having a foil-like base layer made of aluminum or an aluminum alloy, the foil having a first porous layer made of a sintered body of aluminum or aluminum alloy powder laminated on a first surface of the foil-like base layer, 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, the cracks being spaced apart in a second direction perpendicular to the first direction, In the anodizing step, a post-crack-formation anodizing treatment is performed in which the aluminum foil is anodized after the crack formation treatment, 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 crack formation treatment is carried out after the hydration step and before the anodization step; a crack forming process for forming a plurality of cracks each having a length of 300 μm or more and extending in the first direction, the cracks being spaced apart from each other at intervals of 30 μm to 150 μm in the second direction;

2. 2. The method for producing an aluminum chemical foil according to claim 1, wherein the crack formation process includes providing a plurality of cracks extending in the first direction with a length of 300 μm or more at intervals of 95 μm to 150 μm in the second direction.

3. 3. The method for producing a chemically formed aluminum foil according to claim 1, wherein in the crack formation treatment, each crack is allowed to reach a boundary between the base layer and the first porous layer.

4. 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, The aluminum foil according to any one of claims 1 to 3, characterized in that the predetermined anodizing voltage in the pre-crack formation anodizing treatment is 400 V or less. Manufacturing method.

5. 5. The method for manufacturing an aluminum chemical foil according to claim 1, wherein 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 surfaces 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.

6. In the chemical conversion step, the aluminum foil is run in the second direction by a plurality of rollers arranged along the second direction, 6. The method for producing a chemically processed aluminum foil according to claim 5, wherein, of the plurality of rollers, a roller having a smaller diameter than the other rollers is disposed as the first crack forming roller.

7. 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, 7. The method for manufacturing an aluminum chemical foil according to claim 5, wherein 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 that of 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.

8. 2. The method for producing a chemically formed aluminum foil according to claim 1, further comprising a rehydration treatment for forming a hydrated film on the aluminum foil subsequent to the crack formation treatment.

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