Electrode material for aluminum electrolytic capacitors and its manufacturing method

Abstract

To provide an electrode material for an aluminum electrolytic capacitor, having excellent electrostatic capacitance and excellent bonding force between an aluminum foil base material and a sintered body, and a method for manufacturing the same.SOLUTION: There is provided an electrode material for an aluminum electrolytic capacitor which has a sintered body of at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, on at least one side of an aluminum foil base material. The electrode material for the aluminum electrolytic capacitor is characterized in that: (1) the aluminum foil base material has a through-hole and a protrusion protruding from an outer circumferential section of the through-hole; (2) the total thickness of the sintered body is 100-1,800 μm; (3) the mean particle diameter of the powder in the sintered body is 3-15 μm; and (4) the height of the protrusion is half the mean particle diameter of the powder or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode material for an aluminum electrolytic capacitor and a method for producing the same. [Background technology]

[0002] Aluminum electrolytic capacitors are widely used in the energy sector because they are inexpensive and can provide high capacitance. Aluminum foil is generally used as the electrode material for aluminum electrolytic capacitors.

[0003] The surface area of ​​aluminum foil can be increased by etching it to form etching pits. Anodizing the surface of the foil forms an oxide film, which functions as a dielectric. Therefore, by etching the aluminum foil and forming an anodized film on the surface at various voltages depending on the voltage used, various types of aluminum anode electrode foils for electrolytic capacitors can be manufactured to suit the application.

[0004] The etching pits formed by the etching process are processed to a shape that corresponds to the anodizing voltage. Specifically, for medium- to high-voltage capacitor applications, a thick oxide film must be formed. Therefore, to prevent the etching pits from being filled with such a thick oxide film, aluminum foil for medium- to high-voltage anodes is mainly subjected to DC etching to create tunnel-type etching pits with a width that corresponds to the voltage. On the other hand, for low-voltage capacitor applications, fine etching pits are required, and spongy etching pits are mainly formed by AC etching. Similarly, the surface area of ​​cathode foil is also expanded by etching.

[0005] Patent Document 1 proposes an electrode material for aluminum electrolytic capacitors, which is made of a sintered body of at least one of aluminum and an aluminum alloy. This electrode material has a larger surface area than conventional aluminum foils with etched pits, and can increase the capacitance of capacitors using this electrode material.

[0006] However, in recent years, aluminum electrolytic capacitors have been required to have a larger capacitance, and electrode materials for aluminum electrolytic capacitors are required to have a larger surface area.

[0007] Furthermore, in the case of electrode materials for aluminum electrolytic capacitors, in which a sintered body of aluminum powder or the like is molded into the shape of a capacitor, as in Patent Document 1, it is being considered to form the electrode lead-out portion (tab material) from an aluminum foil substrate or wire material.

[0008] However, the electrode material for aluminum electrolytic capacitors described above tends to have a weak bonding strength between the sintered body and the aluminum foil substrate (extraction portion). Therefore, in order to obtain a sufficient bonding strength, the sintering time of the sintered body must be extended, which causes excessive sintering of the sintered body, reducing the surface area of ​​the sintered body and resulting in a decrease in capacitance. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-98279 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an electrode material for an aluminum electrolytic capacitor that has excellent capacitance and excellent bonding strength between an aluminum foil base material and a sintered body, and a method for producing the same. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that by providing protrusions of a specific height on an aluminum foil base material that serves as a tab material or the like that serves as an electrode lead-out portion, and sintering the protrusions while they are embedded in a formed body made of a paste composition, it is possible to shorten the sintering time and increase the surface area of ​​the sintered body, which led to the completion of the present invention.

[0012] That is, the present invention relates to the following electrode material for an aluminum electrolytic capacitor and a method for producing the same. 1. An electrode material for an aluminum electrolytic capacitor having, on at least one surface of an aluminum foil substrate, a sintered body of at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, (1) The aluminum foil base material has a through hole and a protrusion protruding from the outer periphery of the through hole, (2) The total thickness of the sintered body is 100 to 1800 μm, (3) the average particle size of the powder in the sintered body is 3 to 15 μm; (4) The height of the protrusions is at least half the average particle size of the powder. Electrode material for aluminum electrolytic capacitors. 2. The electrode material for an aluminum electrolytic capacitor according to item 1, wherein the height of the protrusions is 30 μm or more. 3. The electrode material for an aluminum electrolytic capacitor according to item 1 or 2, wherein the height of the protrusions is 500 μm or less. 4. The electrode material for an aluminum electrolytic capacitor according to any one of items 1 to 3, wherein the sintered body is provided on both sides of the aluminum foil base, and the protrusions protrude from both sides of the aluminum foil base. 5. (I) Step 1 of forming through holes in an aluminum foil substrate and protrusions protruding from the outer periphery of the through holes; (II) Step 2 of laminating a paste composition containing at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, a binder resin, and a solvent on at least one surface of the aluminum foil base material; and (III) Step 3: sintering the paste composition to form a sintered body; and The total thickness of the sintered body is 100 to 1800 μm, The powder has an average particle size of 3 to 15 μm, The height of the protrusions is 1 / 2 or more of the average particle diameter of the powder. 1. A method for producing an electrode material for an aluminum electrolytic capacitor, comprising: [Effects of the Invention]

[0013] The electrode material for aluminum electrolytic capacitors of the present invention has excellent capacitance and excellent bonding strength between the aluminum foil substrate and the sintered body. Furthermore, the method for producing an electrode material for aluminum electrolytic capacitors of the present invention can easily produce an electrode material for aluminum electrolytic capacitors that has excellent capacitance and excellent bonding strength between the aluminum foil substrate and the sintered body. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 2] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 3] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 4] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 5] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 6] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 7] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 8] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. [Figure 9] 1 is a schematic diagram showing an example of an electrode material of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1. Electrode materials for aluminum electrolytic capacitors The electrode material for an aluminum electrolytic capacitor of the present invention is an electrode material for an aluminum electrolytic capacitor having, on at least one surface of an aluminum foil base, a sintered body of at least one kind of powder selected from the group consisting of aluminum powder and aluminum alloy powder, in which (1) the aluminum foil base has through holes and protrusions protruding from the outer peripheries of the through holes, (2) the total thickness of the sintered body is 100 to 1800 μm, (3) the average particle diameter of the powder in the sintered body is 3 to 15 μm, and (4) the height of the protrusions is at least 1 / 2 of the average particle diameter of the powder.

[0016] The electrode material for aluminum electrolytic capacitors of the present invention (hereinafter also referred to simply as "electrode material") has the above-mentioned features (1) and (4), so that the protrusions are sufficiently embedded in the sintered body, resulting in excellent bonding strength between the aluminum foil substrate and the sintered body. Furthermore, the electrode material of the present invention has the above-mentioned feature (1), which allows for a short sintering time due to the excellent bonding strength. Furthermore, the feature (2) and feature (3) allow for a thick sintered body and an appropriate average particle size of the powder, resulting in a high capacitance. Furthermore, the electrode material of the present invention has (1) through-holes, which facilitates degreasing during sintering and suppresses warping of the sintered body due to sintering, allowing for a thicker total thickness of the sintered body and a higher capacitance. In other words, the electrode material of the present invention, combined with the features (1) to (4), can achieve both high capacitance and high bonding strength between the aluminum foil substrate and the sintered body.

[0017] The electrode material of the present invention will be described in detail below.

[0018] FIG. 1 is a schematic diagram showing an example of an electrode material of the present invention. In FIG. 1, the electrode material 1 of the present invention has sintered bodies 3 on both sides of an aluminum foil substrate 2. FIG. 2(A) is a schematic diagram showing the electrode material of the present invention as viewed from the top, and FIG. 2(B) is a schematic diagram showing the electrode material of the present invention as viewed from the side. FIG. 2(B) shows the electrode material 1 of the present invention as viewed from the side along line X1 in FIG. 2(A). In FIGS. 2(A) and 2(B), the electrode material 1 of the present invention has an aluminum foil substrate 2 sandwiched between sintered bodies 3 on both sides, and the aluminum foil substrate 2 is provided with through holes 21 and protrusions 22 protruding from the outer peripheries of the through holes 21. In FIG. 2(B), the protrusions 22 protrude from either side of the aluminum foil substrate 2, and the protrusions 22 protruding from the outer peripheries of the same through holes 21 protrude in the same direction. 2, the electrode material of the present invention preferably has the sintered body 3 on both sides of the aluminum foil substrate 2, and the protrusions 22 protrude from both sides of the aluminum foil substrate 2. By adopting such a configuration, the capacitance of the electrode material of the present invention is further improved, and the bonding strength between the aluminum foil substrate and the sintered body is further improved.

[0019] Fig. 3 is a schematic diagram showing an electrode material of the present invention having a sintered body 3 on one side of the aluminum foil base material 2 used in the electrode material of Fig. 1 and Fig. 2. In Fig. 3, the aluminum foil base material 2 is laminated on the sintered body 3, and the protrusions protruding from the outer periphery of the through-hole 21 toward the sintered body 3 side are buried in the sintered body 3.

[0020] 4 and 5 are schematic diagrams showing an example of an electrode material of the present invention. In Fig. 4 and Fig. 5, an electrode material 1 of the present invention has a sintered body 3 on one side of an aluminum foil substrate 2. The aluminum foil substrate 2 has through holes 21 and protrusions 22 protruding from the outer periphery of the through holes 21. In Fig. 4 and Fig. 5, the protrusions 22 protrude from the surface of the aluminum foil substrate 2 that comes into contact with the sintered body 3 and are embedded in the sintered body 3.

[0021] 6 and 7 are schematic diagrams showing an example of an electrode material of the present invention. In Fig. 6 and Fig. 7, the area of ​​the surface of the aluminum foil substrate 2 to which the sintered body 3 is bonded is smaller than the area of ​​the surface of the sintered body 3 having the aluminum foil substrate 2. In Fig. 6 and Fig. 7, the protrusions 22 protruding from the outer peripheries of the through holes 21 of the aluminum foil substrate 2 all protrude from the surface in contact with the sintered body 3 and are embedded in the sintered body 3.

[0022] 8 and 9 are schematic diagrams showing an example of an electrode material of the present invention. The electrode material 1 of the present invention may have a configuration in which a plurality of sintered bodies 3 are provided on one side of an aluminum foil substrate 2 as shown in Fig. 8, or may have a configuration in which a plurality of sintered bodies 3 are provided on both sides of an aluminum foil substrate 2 as shown in Fig. 9.

[0023] (sintered body) The electrode material of the present invention has, on at least one surface of an aluminum foil substrate, a sintered body of at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder. The sintered body is a sintered body of at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder.

[0024] The sintered body may be formed on at least one side of the aluminum foil substrate, or may be formed on both sides. From the viewpoint of further improving the capacitance of the electrode material, it is preferable that the sintered body be formed on both sides.

[0025] The sintered body is preferably a porous sintered body having a three-dimensional network structure formed by sintering and bonding the powder particles together while maintaining voids. This structure increases the surface area of ​​the sintered body, making it possible to obtain an electrode material that can be used to manufacture aluminum electrolytic capacitors (hereinafter simply referred to as "capacitors") that exhibit high capacitance.

[0026] The aluminum content of the aluminum powder is preferably 99.80% by mass or more, more preferably 99.85% by mass or more, and even more preferably 99.99% by mass or more.

[0027] The aluminum alloy powder may contain one or more elements selected from silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), boron (B), zirconium (Zr), etc. The content of these elements in the aluminum alloy is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less. When the content of the above elements in the aluminum alloy powder is within the above range, the capacitance of the electrode material for aluminum electrolytic capacitors is further improved.

[0028] The above powders may be used alone or in combination of two or more.

[0029] The average particle size of the powder in the sintered body is 3 to 15 μm. If the average particle size is less than 3 μm or more than 15 μm, the capacitance of the electrode material will be insufficient. The average particle size of the powder in the sintered body is preferably 3 to 10 μm, and more preferably 3.5 to 6 μm.

[0030] In this specification, the average particle size of the powder in the sintered body can be measured by observing the cross section of the sintered body with a scanning electron microscope. Specifically, when the powder is sintered to form a sintered body, some of the particulate powder melts in the sintered body, resulting in a bonded state of the powder particles. In the cross section of the sintered body, the maximum diameter (longest diameter) of each bonded powder is taken as the particle size of that powder, and the particle sizes of 50 randomly selected powder particles are measured, and the arithmetic average of these is taken as the average particle size of the powder in the sintered body. The average particle size of the powder measured by the above measurement method is almost the same as the average particle size of the powder before sintering, with little change.

[0031] The total thickness of the sintered body is 100 to 1800 μm. If the total thickness of the sintered body is less than 100 μm, the capacitance of the electrode material is insufficient. A sintered body having a total thickness exceeding 1800 μm is difficult to form. The total thickness of the sintered body is preferably 300 μm or more, more preferably 400 μm or more. The total thickness of the sintered body is preferably 1200 μm or less, more preferably 900 μm or less. In this specification, the total thickness of the sintered body refers to the sum of the thicknesses of the sintered bodies formed on each side when the electrode material of the present invention has sintered bodies on both sides of the aluminum foil substrate. When the electrode material of the present invention has sintered bodies on only one side of the aluminum foil substrate, the thickness of the sintered body on one side is the total thickness.

[0032] (Aluminum foil substrate) As the aluminum foil forming the aluminum foil substrate, it is preferable to use an aluminum foil made of pure aluminum or an aluminum alloy foil.

[0033] The aluminum content of the aluminum foil made of pure aluminum is preferably 99.80% by mass or more, more preferably 99.85% by mass or more, and even more preferably 99.99% by mass or more.

[0034] The aluminum alloy used for the aluminum alloy foil may be an aluminum alloy containing at least one metal element selected from the group consisting of silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), and boron (B) added to aluminum within the required range, or an aluminum alloy containing the above element as an unavoidable impurity. The content of these elements in the aluminum alloy is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less. By containing the above elements in the aluminum alloy within the above range, the capacitance of the electrode material for aluminum electrolytic capacitors is further improved.

[0035] The thickness of the aluminum foil substrate is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more from the viewpoint of further improving the strength of the electrode material, and is preferably 80 μm or less, more preferably 60 μm or less, and even more preferably 40 μm or less from the viewpoint of further improving the capacitance per volume when used as an electrode material for a capacitor.

[0036] The area of ​​the surface of the aluminum foil base that comes into contact with the sintered compact may be larger than the area of ​​the surface of the sintered compact that comes into contact with the aluminum foil base, as shown in Figures 1 to 5, 8, and 9, or may be smaller as shown in Figures 6 and 7. Furthermore, as shown in Figures 6 and 7, the aluminum foil base may be in the form of a strip, at least a part of which comes into contact with the sintered compact, and the remaining part of which forms a protruding extraction part (tab) that can extract electric power.

[0037] The aluminum foil substrate has through holes and protrusions protruding from the outer periphery of the through holes. The method for forming the through holes and protrusions is not particularly limited. For example, the through holes and protrusions can be formed simultaneously by penetrating a needle or a prismatic tool from one side of the aluminum foil substrate.

[0038] The shape of the through-holes is not particularly limited, and examples thereof include circles and polygons, and more specifically, examples thereof include squares, rectangles, circles, ellipses, etc. From the viewpoints of ease of formation and ease of adjusting the height of the protrusions uniformly, squares and circles are preferred, and squares are more preferred.

[0039] When the through hole is square, the side length of the through hole is preferably 50 μm or more, more preferably 100 μm or more. Furthermore, the side length of the through hole is preferably 1000 μm or less, more preferably 200 μm or less. When the lower limit of the side length of the square through hole is within the above range, gas escapes well when the binder resin and solvent are burned and volatilized in step 3, and the effect of reducing warpage of the sintered body is further enhanced. However, if the side length of the through hole is too long, the strength of the aluminum foil substrate may decrease, and the aluminum foil substrate may break. Furthermore, when the upper limit of the side length of the square through hole is within the above range, the opposite occurs. When the side length of the square through hole is within the above range, the balance between the warpage reduction effect and the strength of the aluminum foil substrate is good, and the aluminum foil substrate can be suitably used as an electrode material for aluminum electrolytic capacitors.

[0040] When the through holes are circular, the diameter of the through holes is preferably 50 μm or more, more preferably 100 μm or more. Furthermore, the diameter of the through holes is preferably 1000 μm or less, more preferably 200 μm or less. When the lower limit of the diameter of the circular through holes is within the above range, gas escapes well when the binder resin and solvent are burned and volatilized in step 3, and the effect of reducing warpage of the sintered body is further enhanced. However, if the diameter of the through holes is too large, the strength of the aluminum foil substrate may decrease, and the aluminum foil substrate may break. Furthermore, when the upper limit of the diameter of the circular through holes is within the above range, the opposite occurs. When the diameter of the through holes is within the above range, a good balance is achieved between the warpage reduction effect and the strength of the aluminum foil substrate, making the material suitable for use as an electrode material for aluminum electrolytic capacitors.

[0041] The shape of the protrusions is not particularly limited, and examples thereof include triangles, rectangles, etc. When the protrusions have a triangular or rectangular shape, they are easily formed and the height of the protrusions can be more easily adjusted to be uniform.

[0042] The height of the protrusions is preferably 2 μm or more, more preferably 7.5 μm or more, even more preferably 15 μm or more, particularly preferably 30 μm or more, most preferably 50 μm or more, and most preferably 100 μm or more. By setting the lower limit of the protrusion height within the above range, the bonding strength between the aluminum foil substrate and the sintered body is further improved. Furthermore, the height of the protrusions is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less. The height of the protrusions depends on the formation method. When the through-holes have a circular or square shape, the height is approximately half the diameter or one side of the through-holes. Therefore, increasing the height of the protrusions increases the diameter of the through-holes, which may reduce the strength of the aluminum foil substrate and may cause the paste composition to ooze from the through-holes during the manufacturing process. Setting the upper limit of the protrusion height within the above range further suppresses these problems.

[0043] In the electrode material of the present invention, the height of the protrusions is at least 1 / 2 of the average particle diameter of the powder. If the height of the protrusions is less than 1 / 2 of the average particle diameter of the powder, the protrusions will not be sufficiently embedded in the sintered body, and the bonding strength between the aluminum foil substrate and the sintered body will be insufficient. This requires a longer sintering time, resulting in a low capacitance. The height of the protrusions is preferably at least 2 / 3 of the average particle diameter of the powder, more preferably at least 1 / 1, even more preferably at least 2 / 1, and particularly preferably at least 33 / 1. Furthermore, the height of the protrusions is preferably at most 334 / 1 of the average particle diameter of the powder, more preferably at most 200 / 1, and even more preferably at most 167 / 1.

[0044] 2. Manufacturing method for electrode material for aluminum electrolytic capacitors The method for producing an electrode material for an aluminum electrolytic capacitor of the present invention comprises the steps of: (I) Step 1 of forming through holes in an aluminum foil substrate and protrusions protruding from the outer periphery of the through holes; (II) Step 2 of laminating a paste composition containing at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, a binder resin, and a solvent on at least one surface of the aluminum foil base material; and (III) Step 3: sintering the paste composition to form a sintered body; and The total thickness of the sintered body is 100 to 1800 μm, The powder has an average particle size of 3 to 15 μm, In this manufacturing method, the height of the protrusions is at least half the average particle size of the powder.

[0045] The manufacturing method of the present invention includes (I) step 1 of forming through holes and protrusions in an aluminum foil substrate, so that the protrusions can be formed simultaneously with the formation of the through holes, and further includes (II) step 2 of laminating a paste composition on the surface of the aluminum foil substrate, and (III) step 3 of sintering the paste composition, so that the electrode material of the present invention can be easily manufactured.

[0046] The production method of the present invention will be described in detail below.

[0047] (Process 1) Step 1 is a step of forming through holes in an aluminum foil substrate and protrusions protruding from the outer periphery of the through holes.

[0048] As the aluminum foil substrate, the aluminum foil substrate explained in the above electrode material can be used.

[0049] In step 1, the height of the protrusions on the aluminum foil substrate is at least half the average particle size of the powder used in step 2. If the height of the protrusions is less than half the average particle size of the powder, the protrusions will not be sufficiently embedded in the sintered body in the produced electrode material, resulting in insufficient bonding strength between the aluminum foil substrate and the sintered body. This requires a longer sintering time, resulting in a low capacitance of the electrode material. The height of the protrusions is preferably at least 2 / 3 of the average particle size of the powder, more preferably at least 1 / 1, even more preferably at least 2 / 1, and particularly preferably at least 33 / 1. The height of the protrusions is preferably at most 334 / 1 of the average particle size of the powder, more preferably at most 200 / 1, and even more preferably at most 167 / 1.

[0050] The method for forming through holes and protrusions on an aluminum foil substrate is not particularly limited, and can be formed by known methods such as press working, Thomson working, embossing, etc. By forming through holes from one side of the aluminum foil substrate using the above method, protrusions protruding from the outer periphery of the through holes are formed, and through holes and protrusions can be formed simultaneously. Among these methods, press working is preferred from the viewpoint of excellent stability of the protrusion shape. Furthermore, Thomson working is preferred from the viewpoint of ease of processing and cost reduction.

[0051] By the above-described step 1, through holes and protrusions protruding from the outer peripheries of the through holes are formed in the aluminum foil base material.

[0052] (Process 2) Step 2 is a step of laminating a paste composition containing at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, a binder resin, and a solvent on at least one surface of the aluminum foil substrate.

[0053] The aluminum content of the aluminum powder is preferably 99.80% by mass or more, more preferably 99.85% by mass or more, and even more preferably 99.99% by mass or more.

[0054] The aluminum alloy powder may contain one or more elements selected from silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni), boron (B), zirconium (Zr), etc. The content of these elements in the aluminum alloy is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less. When the content of the above elements in the aluminum alloy powder is within the above range, the capacitance of the electrode material for aluminum electrolytic capacitors is further improved.

[0055] The above powders may be used alone or in combination of two or more.

[0056] The shape of the aluminum powder and aluminum alloy powder is not particularly limited, and any of spherical, irregular, flaky, fibrous, etc. can be suitably used, but spherical powder is preferred for industrial production.

[0057] The aluminum powder and aluminum alloy powder can be produced by known methods. Examples include atomization, melt spinning, rotating disk, rotating electrode, and rapid solidification methods. For industrial production, atomization, particularly gas atomization, is preferred. That is, it is preferable to use powder obtained by atomizing a molten metal.

[0058] The powder used in step 2 has an average particle size of 3 to 15 μm. If the average particle size is less than 3 μm or more than 15 μm, the capacitance of the produced electrode material will be insufficient. The average particle size of the powder is more preferably 3 to 9 μm, and even more preferably 3.5 to 6 μm.

[0059] In this specification, the average particle size of the powder used in step 2 can be measured by observing the powder with a scanning electron microscope. Specifically, the powder is observed with a scanning electron microscope, the maximum diameter (long diameter) of each powder is taken as the particle size of that powder, the particle sizes of 50 randomly selected powders are measured, and the arithmetic average of these is taken as the average particle size of the powder used in step 2. The average particle size of the powder measured by the above measurement method remains almost unchanged even after sintering and is approximately the same as the average particle size of the powder in the sintered body of the electrode material.

[0060] The content of the powder in the paste composition is preferably 30 to 80 mass %, more preferably 40 to 70 mass %, based on 100 mass % of the paste composition. When the lower limit of the powder content is within the above range, the capacitance of the produced electrode material is further improved. Furthermore, when the upper limit of the powder content is within the above range, the adhesive strength between the aluminum foil substrate and the paste composition is further improved.

[0061] The binder resin is not particularly limited, and known binder resins can be used. Examples of binder resins include synthetic resins such as carboxy-modified polyolefin resins, vinyl acetate resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymer resins, vinyl alcohol resins, butyral resins, vinyl fluoride resins, acrylic resins, polyester resins, urethane resins, epoxy resins, urea resins, phenolic resins, acrylonitrile resins, cellulose resins, paraffin wax, and polyethylene wax, as well as natural resins or waxes such as wax, tar, glue, urushi, pine resin, and beeswax. Depending on the molecular weight, type of resin, etc., these binder resins can be volatilized when heated or thermally decomposed to leave residues together with the aluminum powder. These binder resins can be used depending on the desired electrical properties, such as the electrostatic capacitance, of the electrode material to be manufactured. Examples include:

[0062] The binder resins may be used alone or in combination of two or more.

[0063] The content of the binder resin in the paste composition is preferably 0.5 to 35% by mass, and more preferably 0.75 to 10% by mass, based on 100% by mass of the paste composition. When the lower limit of the binder resin content is within the above range, the adhesive strength between the aluminum foil substrate and the paste composition is further improved. Furthermore, when the upper limit of the binder resin content is within the above range, degreasing is facilitated when the paste composition is sintered in Step 3 described below, and defects such as warping caused by remaining binder resin after sintering are further easily suppressed.

[0064] The solvent is not particularly limited, and known solvents can be used. Examples of the solvent include organic solvents such as water, toluene, alcohols, ketones, and esters, and more specifically, water, butyl acetate, propylene glycol methyl ether, ethyl lactate, butyl cellosolve, and isophorone.

[0065] The above solvents may be used alone or in combination of two or more.

[0066] The content of the solvent in the paste composition is preferably 20 to 70% by mass, more preferably 30 to 55% by mass, based on 100% by mass of the paste composition. When the lower limit of the solvent content is within the above range, the paste composition can be easily laminated on an aluminum foil substrate. Furthermore, when the upper limit of the solvent content is within the above range, the adhesive strength between the aluminum foil substrate and the paste composition is further improved.

[0067] The paste composition may contain other components such as a sintering aid, a surfactant, etc., as needed. These may all be known or commercially available. By including other components in the paste composition, a sintered body can be formed more efficiently.

[0068] The sintering aid is not particularly limited, and any known sintering aid can be used, such as fluorides such as aluminum fluoride, potassium fluoride, and calcium fluoride.

[0069] The surfactant is not particularly limited, and known surfactants can be used, such as betaine-based, sulfobetaine-based, and alkylbetaine-based surfactants.

[0070] In step 2, it is preferable to prepare a paste composition by mixing and kneading the above-mentioned powder, binder resin, solvent, and other components as necessary. By kneading, the paste composition becomes uniform, and the variation in capacitance between parts of the produced electrode material is further suppressed.

[0071] In step 2, the paste composition is laminated on at least one surface of an aluminum foil substrate. The method for laminating the paste composition is not particularly limited, and it can be laminated by a known method.

[0072] Examples of methods for laminating a paste composition on at least one surface of an aluminum foil substrate include (1) a method in which the paste composition is filled into a mold, dried, removed from the mold, and the dried paste composition is laminated on at least one surface of the aluminum foil substrate, and (2) a method in which the paste composition is applied to at least one surface of the aluminum foil substrate.

[0073] The drying conditions for the above method (1) are not particularly limited as long as the dried paste composition can maintain its shape without crumbling when removed, and examples of drying conditions include drying at a temperature in the range of 20 to 300°C for 1 to 30 minutes.

[0074] The shape of the mold used in the above method (1) may be selected arbitrarily depending on the shape of the sintered body of the electrode material to be obtained.

[0075] Specific examples of the method (2) include a method in which the paste composition is applied to at least one surface of an aluminum foil substrate by a coating method such as a roller, a brush, a spray, or a dipping method, and also a method in which the paste composition is applied by a known printing method such as silk screen printing.

[0076] In step 2, after preparing a green laminate by laminating the paste composition on at least one side of the aluminum foil substrate by the above method (1) or (2), the paste composition of the green laminate may be dried. The drying conditions are not particularly limited, and examples include drying at a temperature in the range of 20 to 300°C for 1 to 30 minutes.

[0077] The total thickness of the paste composition laminated on the aluminum foil substrate is preferably 100 to 1800 μm. By ensuring that the total thickness of the paste composition is within the above range, the total thickness of the sintered body formed in step 3 can be set to 100 to 1800 μm. The total thickness of the paste composition is preferably 300 μm or more, more preferably 400 μm or more. The total thickness of the paste composition is preferably 1200 μm or less, more preferably 900 μm or less. In this specification, the total thickness of the paste composition refers to the sum of the thicknesses of the paste compositions laminated on each side when the paste composition is laminated on both sides of the aluminum foil substrate. When the paste composition is laminated on only one side of the aluminum foil substrate, the total thickness is the thickness of the paste composition on one side.

[0078] The paste composition may be laminated on at least one surface of the aluminum foil substrate, that is, it may be laminated on one surface as shown in Figures 3 to 8, or on both surfaces as shown in Figures 1, 2, and 9.

[0079] By the above-described step 2, a paste composition containing at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, a binder resin, and a solvent is laminated on at least one surface of the aluminum foil substrate.

[0080] (Step 3) Step 3 is a step of sintering the paste composition to form a sintered body. In step 3, the powder in the paste composition laminated on the aluminum foil substrate is sintered to form a sintered body.

[0081] The sintering method is not particularly limited as long as it can sinter the powder in the paste composition. For example, the paste composition laminated on at least one surface of the aluminum foil substrate in step 2 can be placed together with the aluminum foil substrate in a heating furnace and heated to sinter.

[0082] The sintering temperature is preferably 490 to 650°C, more preferably 500 to 640°C, and even more preferably 550 to 630°C. When the lower limit of the sintering temperature is within the above range, the bonding strength between the aluminum foil substrate and the sintered body is further improved. Furthermore, when the upper limit of the sintering temperature is within the above range, a decrease in surface area due to melting of the powder is suppressed, and the capacitance of the produced electrode material is further improved.

[0083] The sintering time is preferably 5 to 10 hours, more preferably 6 to 10 hours. By setting the sintering time within the above range, the capacitance of the produced electrode material is further improved. Conventionally, in electrode materials in which through-holes and protrusions are not formed in the aluminum foil substrate, sintering of the powders forming the sintered body and sintering between the sintered body and the aluminum foil substrate were sufficient by setting the sintering time to more than 10 hours and not more than 24 hours. However, because the preferred sintering times for sintering of powders and sintering between the sintered body and the aluminum foil substrate differ, there was a risk of excessive sintering of the powders, resulting in a reduction in the surface area of ​​the sintered body. On the other hand, if the sintering time is set to 5 to 10 hours, even if the surface area of ​​the sintered body is sufficient, sintering between the sintered body and the aluminum foil substrate is insufficient, resulting in the sintered body peeling off. In the manufacturing method of the present invention, since the aluminum foil substrate has through-holes and protrusions, sintering of the sintered body and the aluminum foil substrate can be achieved by sintering the sintered body in a shorter sintering time, thereby suppressing a decrease in the surface area of ​​the sintered body and further improving the bonding strength between the sintered body and the aluminum foil substrate.

[0084] The sintering atmosphere is not particularly limited and may be, for example, a vacuum atmosphere, an inert gas atmosphere, an oxidizing gas atmosphere (air), a reducing atmosphere, etc. Among these, a vacuum atmosphere or a reducing atmosphere is preferred. The pressure condition of the sintering atmosphere may be any of normal pressure, reduced pressure, and increased pressure.

[0085] The total thickness of the sintered body formed in step 3 is 100 to 1800 μm. If the total thickness of the sintered body is less than 100 μm, the capacitance of the electrode material is insufficient. If the total thickness of the sintered body exceeds 1800 μm, it is difficult to form the sintered body. The total thickness of the sintered body is preferably 300 μm or more, more preferably 400 μm or more. Furthermore, the total thickness of the sintered body is preferably 1200 μm or less, more preferably 900 μm or less.

[0086] The paste composition is sintered to form a sintered body by the above-described step 3. By the above steps 1 to 3, the electrode material of the present invention can be produced.

[0087] (Step 4) The manufacturing method of the present invention may further include step 4 of anodizing the sintered body after step 3. By performing the anodizing treatment, an oxide film is formed on the surface of the sintered body, and the oxide film functions as a dielectric, making it useful as an electrode material for aluminum electrolytic capacitors.

[0088] The anodizing conditions are not particularly limited, and are usually performed in a boric acid aqueous solution or an ammonium adipate aqueous solution at a concentration of 0.01 to 5 mol and a temperature of 30 to 100°C, with a current of 10 mA / cm 2 More than 400mA / cm 2 The following current should be applied for at least 5 minutes:

[0089] The anodizing treatment voltage is preferably selected appropriately from 2 to 700 V. The anodizing treatment voltage is preferably a treatment voltage that corresponds to the operating voltage of an aluminum electrolytic capacitor when the electrode material is used as an electrode for an aluminum electrolytic capacitor.

[0090] According to the manufacturing method of the present invention, an excellent electrode material can be obtained without etching. By not including an etching step, treatment with hydrochloric acid or the like used in etching is not required, and environmental and economic burdens are further reduced. [Example]

[0091] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0092] (Example 1, Comparative Example 1) (Process 1) A 30 μm thick aluminum foil substrate (aluminum purity 99.99% by mass) was pressed so as to penetrate it with a prismatic tool, forming a square through-hole with the length of one side shown in Table 1 and a protrusion protruding from the outer periphery of the through-hole with the height shown in Table 1. The shape of the protrusion was triangular, as shown in protrusion 22 in FIG. 3. The protrusion was formed so as to protrude only from the surface on which the sintered body was to be formed. A plurality of through-holes were formed in the aluminum foil substrate.

[0093] (Process 2) An ethyl cellulose-based binder resin was added to butyl acetate as a solvent to prepare a binder resin solution at 5% by mass. 100 parts by mass of aluminum powder (manufactured by Toyo Aluminum Co., Ltd., JIS A1080) with an average particle size of 3 μm was added to 60 parts by mass of the binder resin solution and kneaded to prepare a paste composition. The paste composition was filled into a mold, dried in a dryer at 80°C for 3 minutes, and then removed to prepare a dried paste composition with a thickness of 900 μm. The dried paste composition was laminated on one side (the side with the protrusions) of the aluminum foil substrate processed in step 1 to prepare a green laminate. The green laminate was then heated at 100°C for 1.5 minutes to further dry the paste composition in the green laminate.

[0094] (Step 3) The unsintered laminate prepared in step 2 was heated in an argon gas atmosphere at 615°C for 5 hours to sinter the paste composition, forming a sintered body on the aluminum foil substrate to produce an electrode material. When the thickness of the sintered body after sintering was measured, it was found to be the same as the thickness of the paste composition of the unsintered laminate before sintering, and the thickness of the sintered body was 900µm. Because the sintered body was formed on only one side, the total thickness of the sintered body was also 900µm.

[0095] The average particle size of the powder in the sintered body was measured by observing the cross section of the sintered body with a scanning electron microscope. Specifically, the maximum diameter (longest diameter) of each powder in the bonded state in the cross section of the sintered body was taken as the particle size of that powder, and the particle sizes of 50 randomly selected powders were measured, and the arithmetic average of these was taken as the average particle size of the powder in the sintered body. The average particle size of the powder measured by the above measurement method was almost the same as the average particle size of the powder before sintering, with almost no change.

[0096] (Step 4) The produced electrode material was further subjected to anodizing treatment at a formation voltage of 10 to 900 V in accordance with the Japan Electronic Industries Association standard RC-2364A.

[0097] The electrode material produced through the above steps 1 to 4 was visually inspected for peeling between the aluminum foil substrate and the sintered body, and the bonding strength between the aluminum foil substrate and the sintered body was evaluated.

[0098] In the following Tables 1 to 6, the bonding strength evaluations of ◯, △, and × indicate the following evaluations. ◯: The aluminum foil substrate and the sintered body did not peel off during the chemical conversion. Δ: The aluminum foil substrate and the sintered body were slightly separated during the chemical conversion. ×: The aluminum foil substrate and the sintered body were peeled off during the chemical conversion.

[0099] The results are shown in Table 1.

[0100] [Table 1]

[0101] (Example 2, Comparative Example 2) An electrode material was produced and the bonding strength was evaluated in the same manner as in Example 1, except that the average particle size of the aluminum powder was set to 15 μm. The results are shown in Table 2.

[0102] [Table 2]

[0103] (Example 3, Comparative Example 3) An electrode material was produced in the same manner as in Example 1, except that the thickness of the sintered body on one side of the aluminum foil substrate was 100 μm and the total thickness of the sintered bodies was also 100 μm, and the bonding strength was evaluated. The results are shown in Table 3.

[0104] [Table 3]

[0105] (Example 4, Comparative Example 4) An electrode material was produced in the same manner as in Example 1, except that the average particle size of the aluminum powder was 15 μm, the thickness of the sintered body on one side of the aluminum foil substrate was 100 μm, and the total thickness of the sintered bodies was also 100 μm, and the bonding strength was evaluated. The results are shown in Table 4.

[0106] [Table 4]

[0107] Example 5 Electrode materials were manufactured in the same manner as in Example 1, except that the height of the protrusions was set to 500 μm, the total thickness of the sintered body was set to 900 μm, and the sintering time was changed within a range of 1 to 10 hours, and the bonding strength was evaluated. The results are shown in Table 5. In Example 5, when the sintering time was set to 1 to 4 hours, the sintering time was too short and no sintered body was yet formed.

[0108] [Table 5]

[0109] (Comparative Example 5) Except for not forming through holes or protrusions in the aluminum foil substrate and varying the sintering time within the range of 1 to 9 hours, electrode materials were produced in the same manner as in Example 5, and the bonding strength was evaluated. The results are shown in Table 6.

[0110] [Table 6]

[0111] (Comparative Examples 6 to 9) The aluminum foil substrate used had through holes but no protrusions. The electrode materials were manufactured in the same manner as in Example 5, except that the side lengths of the through holes were set to 1 to 2 μm, 1 mm, 2 mm, and 5 mm, respectively, and the bonding strength was evaluated. The results are shown in Table 7, and Example 5 is also shown in Table 7 for reference.

[0112] [Table 7]

[0113] (Examples 6 and 7, Comparative Examples 10 and 11) The average particle size of the powder and the presence or absence of through holes and protrusions were changed as shown in Table 8. A sintered body having a thickness of 900 μm was laminated on both sides of the aluminum foil substrate, with a total thickness of 1800 μm. Sintering was continued until the aluminum foil substrate and the sintered body were bonded. Except for this, an electrode material was produced in the same manner as in Example 5. The applied voltage was changed as shown in Table 8, and the capacitance was measured. The results are shown in Table 8.

[0114] [Table 8]

[0115] The electrode materials of Examples 6 and 7 were superior in bonding strength between the aluminum foil substrate and the sintered body compared to the corresponding electrode materials of Comparative Examples 7 and 11, respectively, and therefore were able to shorten the sintering time. As a result, the surface area of ​​the sintered body could be increased, and it was confirmed that the electrode material of the present invention can exhibit the high capacitance required for a capacitor. [Explanation of symbols]

[0116] 1. Electrode materials for aluminum electrolytic capacitors 2. Aluminum foil substrate 21.Through hole 22. Protrusion 3. Sintered body

Claims

1. An electrode material for an aluminum electrolytic capacitor having a sintered body of at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder on at least one surface of an aluminum foil substrate, (1) The aluminum foil base material has a through hole and a protrusion protruding from the outer periphery of the through hole, (2) The total thickness of the sintered body is 100 to 1800 μm, (3) the average particle size of the powder in the sintered body is 3 to 15 μm; (4) The height of the protrusions is at least half the average particle size of the powder. Electrode material for aluminum electrolytic capacitors.

2. 2. The electrode material for an aluminum electrolytic capacitor according to claim 1, wherein the height of the protrusions is 30 μm or more.

3. 3. The electrode material for an aluminum electrolytic capacitor according to claim 1, wherein the height of the protrusions is 500 μm or less.

4. The electrode material for an aluminum electrolytic capacitor according to any one of claims 1 to 3, wherein the sintered body is provided on both sides of the aluminum foil base, and the protrusions protrude from both sides of the aluminum foil base.

5. (I) Step 1 of forming through holes in an aluminum foil substrate and protrusions protruding from the outer periphery of the through holes; (II) Step 2 of laminating a paste composition containing at least one powder selected from the group consisting of aluminum powder and aluminum alloy powder, a binder resin, and a solvent on at least one surface of the aluminum foil base material; and (III) Step 3: sintering the paste composition for 5 to 10 hours to form a sintered body; and The total thickness of the sintered body is 100 to 1800 μm, The powder has an average particle size of 3 to 15 μm, The height of the protrusions is ½ or more of the average particle diameter of the powder.

1. A method for producing an electrode material for an aluminum electrolytic capacitor, comprising:

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