Capacitor manufacturing method and cathode electrode for chemical conversion

Abstract

To form a dielectric layer with less fault by a chemical treatment when manufacturing an electrolytic capacitor.SOLUTION: A method of manufacturing a capacitor element in which a dielectric layer is formed onto a front surface of a positive electrode substance constructed by a valve action metal, contains: a step (i) of electrically connecting a plurality of positive electrode substances to a first electrode provided along a first direction; and a step (ii) of forming the dielectric layer by oxidizing at least one part of a front surface of the positive electrode substance by flowing a current between a first electrode and a second plate-like electrode arranged along a bottom surface of a chemical treatment in a state where the positive electrode substance connected to the first electrode is immersed in chemical treatment liquid in a chemical treatment tank. The second electrode includes: a pair of convex parts by adjacent two each other or one concave part to an opposite surface opposite to the first electrode in each of the plurality of positive electrode substances. Each of the plurality of positive electrode substances is arranged at a position of the pair of concave parts or at the concave part in a second direction orthogonal to the first direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a capacitor and a cathode electrode for chemical conversion. [Background Art]

[0002] An electrolytic capacitor includes an anode body and a dielectric layer formed on a surface of the anode body. Generally, the dielectric layer is formed by subjecting the surface of the anode body to anodic oxidation (chemical conversion treatment).

[0003] For example, as disclosed in Patent Document 1, the chemical conversion treatment is performed by suspending a solid electrolytic capacitor element from a belt-shaped fixing plate via a wire rod made of valve metal, immersing the solid electrolytic capacitor element in a chemical conversion solution within a chemical conversion tank, and applying a voltage between a cathode disposed in the chemical conversion solution and the fixing plate. The cathode is usually a flat plate. [Prior Art Literature] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 11-150044 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] When an anode body has a large size and a porous body having a large surface area is used as the anode body, a larger current is required to uniformly form the dielectric layer on the porous surface of the anode, and a cathode with a large area is required. In the case of a flat-plate cathode, the area of the cathode required for the chemical conversion treatment of the anode body may be insufficient, resulting in insufficient chemical conversion, or a long-time chemical conversion treatment may be required.

[0006] If the chemical conversion treatment is insufficient, defects are likely to occur in the formed dielectric layer, and leakage current tends to increase. On the other hand, performing the chemical conversion treatment for a long time reduces productivity. [Means for Solving the Problem]

[0007] One aspect of the present disclosure relates to a method for manufacturing a capacitor element having a dielectric layer formed on the surface of an anode body made of a valve metal, comprising the steps of (i) electrically connecting a plurality of anode bodies to a first electrode provided along a first direction, and (ii) immersing the anode bodies connected to the first electrode in a chemical solution in a chemical tank, and oxidizing at least a portion of the surface of the anode bodies by passing an electric current between the first electrode and a plate-shaped second electrode arranged along the bottom surface of the chemical tank to form the dielectric layer, wherein the second electrode has a pair of adjacent convex portions or a single recess on a surface facing the first electrode, with respect to each of the plurality of anode bodies, and each of the plurality of anode bodies is positioned at the location of the recess or between two adjacent convex portions in a second direction perpendicular to the first direction.

[0008] Another aspect of the present disclosure relates to a plate-shaped cathode electrode for chemical conversion, which is positioned along the bottom surface of a chemical conversion tank to form a dielectric layer by immersing an anode body, made of a valve-acting metal, in a chemical conversion liquid in the tank with the anode body connected to an anode electrode, and passing an electric current through the anode body to oxidize at least a portion of the surface of the anode body, wherein the cathode electrode has a pair of adjacent protrusions on the surface facing the anode electrode. [Effects of the Invention]

[0009] According to this disclosure, a dielectric layer with fewer defects can be formed by chemical conversion treatment, thereby reducing the leakage current of the electrolytic capacitor. [Brief explanation of the drawing]

[0010] [Figure 1] This figure schematically shows the state inside the chemical conversion tank during the chemical conversion treatment, illustrating an example of the manufacturing method described herein. [Figure 2] This is a perspective view showing the schematic configuration of the second electrode (cathode electrode) used for chemical conversion in the manufacturing method of the present disclosure. [Figure 3]This figure schematically shows the state inside the chemical conversion tank during the chemical conversion treatment, illustrating an example of the manufacturing method described herein. [Figure 4A] This figure shows another example of the second electrode (cathode electrode). [Figure 4B] This figure shows another example of the second electrode (cathode electrode). [Figure 4C] This figure shows another example of the second electrode (cathode electrode). [Figure 4D] This figure shows another example of the second electrode (cathode electrode). [Figure 5A] This figure shows another example of the second electrode (cathode electrode). [Figure 5B] This figure shows another example of the second electrode (cathode electrode). [Figure 6] This is a schematic cross-sectional view showing an example of a capacitor element manufactured by the manufacturing method disclosed herein. [Figure 7] This is a schematic cross-sectional view showing an example of an electrolytic capacitor using a capacitor element manufactured by the manufacturing method of the present disclosure. [Modes for carrying out the invention]

[0011] The following describes embodiments of the manufacturing method relating to this disclosure with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B".

[0012] <Manufacturing method for capacitor elements> A method for manufacturing a capacitor element according to an embodiment of the present disclosure is a method for manufacturing a capacitor element in which a dielectric layer is formed on a surface of an anode body made of a valve-action metal, the method comprising: step (i) of electrically connecting a plurality of anode bodies to a first electrode (anode electrode) provided along a first direction; and step (ii) of forming the dielectric layer by oxidizing at least a part of the surface of the anode bodies to form the dielectric layer by passing a current between the first electrode and a plate-shaped second electrode (cathode electrode) arranged along the bottom surface of a formation tank, in a state where the anode bodies connected to the first electrode are immersed in a formation liquid in the formation tank.

[0013] The second electrode has a generally plate-like overall shape, and has, on a facing surface facing the first electrode, a pair of mutually adjacent projections or a single recess for each of the anode bodies. The groove shape formed between two adjacent projections or the hole shape that is a recess increases the surface area of the second electrode. This increases the current density flowing to the anode bodies during formation treatment, thereby accelerating the growth of the dielectric layer. As a result, the occurrence of defects in the dielectric layer is suppressed, and leakage current is reduced. The groove shape or hole shape allows the anode bodies to be brought close to the second electrode without contacting the second electrode. Further, by fixing the position of the anode bodies in the height direction perpendicular to the liquid surface of the formation liquid near the vertex height of the projections or near the opening of the hole shape in the recess, contact between the anode bodies and the second electrode can be prevented when the position of the anode bodies shifts in the second direction due to vibration, displacement or the like of the first electrode.

[0014] Each of the plurality of anode bodies is arranged at a position between the pair of projections or at a position of the single recess in a second direction orthogonal to the first direction. By arranging the anode bodies close to the space sandwiched between the pair of projections, the anode bodies can be arranged close to the cathode electrode, and the current density flowing to the anode bodies during formation treatment can be further increased. Similarly, by arranging the anode bodies close to the recessed space formed by the recess, the anode bodies can be arranged close to the cathode electrode, and the current density during formation treatment can be further increased.

[0015] In the second electrode having at least one pair of protrusions, a space is formed between the pair of protrusions. This space can be considered in the same way as the recessed space of the recess. Hereinafter, the space formed by two adjacent protrusions is referred to as a gap, to distinguish it from the recessed space of a recess.

[0016] For example, the protrusion is formed to include a portion protruding toward the outside of the second electrode relative to a reference plane (that is, in a direction approaching the first electrode). Similarly, the recess may be formed to include, for example, a portion recessed toward the inside of the second electrode relative to a reference plane (that is, in a direction away from the first electrode). The reference plane for the protrusion is the portion farthest from the first electrode on a facing surface that faces the first electrode (hereinafter also referred to as "element facing surface") (provided that the following-mentioned circulation inner circumferential surface of the hole is excluded). The reference plane for the recess may be the portion closest to the first electrode on the element facing surface (the opening portion where a hole shape is formed).

[0017] Further, a through-hole penetrating between the facing surface and the surface opposite to the facing surface may be formed in the second electrode, and the anode body may be arranged so as to overlap with the through-hole. In this case, the hole also has a function of flowing and circulating the chemical conversion solution.

[0018] Further, the statement that the anode body is arranged at a position between the pair of protrusions means that when considering the cross-section of the anode body and the second electrode on a plane parallel to the second direction and the direction perpendicular to the liquid surface of the chemical conversion solution at a certain position in the first direction, the range of the position in the second direction occupied by the anode body is limited between one vertex portion and the other vertex portion of the pair of protrusions, and does not overlap with any vertex portion.

[0019] When the anode is positioned at the location of the protrusion, the end of the anode on the second electrode side is positioned close to the protrusion. This allows for an increase in the current density at the end of the anode on the second electrode side, while making it difficult to increase the current density at the end of the anode on the first electrode side, which is further away from the protrusion. As a result, a difference in current density occurs between the first electrode side and the second electrode side of the anode during the chemical conversion process, making it easy for the dielectric layer to form unevenly. In contrast, by positioning the anode between the pair of protrusions, it is possible to increase the current density while suppressing the occurrence of differences in current density within the anode during the chemical conversion process. As a result, a uniform dielectric layer with fewer defects can be formed, improving the characteristics of the electrolytic capacitor, such as leakage current.

[0020] In one embodiment, a linear protrusion may be formed along a first direction on the opposing surface (i.e., the direction in which the first electrode (anode electrode) extends). Two protrusions extending along the first direction may form a groove extending in the first direction between the two protrusions. In this case, by arranging multiple anode bodies along the groove between the two protrusions, it becomes easier to arrange the anode bodies closer to the second electrode, and it becomes easier to increase the current density flowing through the anode bodies during the chemical conversion treatment.

[0021] In another embodiment, the second electrode may have multiple pairs of protrusions along the first direction of the opposing surface. In this case, the multiple pairs of protrusions may be arranged along the first direction corresponding to each of the multiple anode bodies. Each of the multiple anode bodies is positioned between the corresponding pair of protrusions in the second direction. In this case, it is easier to increase the surface area of ​​the second electrode and to increase the current density flowing through the anode body during the conversion treatment. The same applies when the second electrode has multiple recesses along the first direction of the opposing surface. If the second electrode has multiple pairs of protrusions or multiple recesses, each of the multiple anode bodies may be associated with one pair of protrusions or recesses. Alternatively, a single anode body may share two pairs of protrusions or two recesses that are adjacent to each other in the first direction.

[0022] In another embodiment, the recess may be a hole shape that penetrates the back surface of the opposing surface. The hole-shaped recesses may be arranged in a row for each anode along the first direction. If the first electrodes are arranged in multiple rows, the overall hole shape of the second electrodes may be arranged in a mesh shape. Each anode may be positioned at the opening of the mesh.

[0023] The height of the anode body in the chemical conversion tank (distance from the second electrode) is preferably as low as possible, insofar as contact between the second electrode and the anode body is suppressed. If the second electrode has at least one pair of protrusions, the height of the anode body in the chemical conversion tank may be higher or lower than the maximum height of the protrusions (e.g., the height of the apex of the protrusions) at its lowest position.

[0024] If the minimum height of the anode body in the chemical conversion tank is lower than the maximum height of the protrusions, a portion of the anode body is positioned in the gap between the two protrusions, making it easier to increase the current density during the chemical conversion treatment. If the minimum height of the anode body in the chemical conversion tank is higher than the maximum height of the protrusions, it is preferable that the difference between the maximum height of the protrusions and the minimum height of the anode body be 2 mm or less.

[0025] Similarly, if the second electrode has a recess, the height of the anode body in the chemical tank may be higher or lower than the height of the reference plane of the recess, at its lowest position. If the lowest height of the anode body in the chemical tank is higher than the height of the reference plane of the recess, the difference between the height of the reference plane of the recess and the lowest height of the anode body is preferably 2 mm or less.

[0026] The height within the chemical conversion tank refers to the height in the direction perpendicular to the surface of the chemical conversion solution (vertical direction). The maximum height of a convex portion is also the height of the point on the surface of the convex portion that is closest to the surface of the chemical conversion solution. The height of the reference plane of a concave portion is also the height of the point on the reference plane of the concave portion that is closest to the surface of the chemical conversion solution.

[0027] The maximum height of the anode body in the conversion tank may be greater than the maximum height at the apex of the protrusion. That is, at least a portion of the anode body may not be housed in the gap between the two protrusions, but rather positioned above the gap between the two protrusions. This reduces contact between the anode body and the second electrode when the anode body is immersed in the conversion solution, thereby improving productivity. Similarly, if the second electrode has a recess, the maximum height of the anode body in the conversion tank may be greater than the height of the reference plane of the recess.

[0028] The shape of the convex or concave portion is not particularly limited. In one embodiment, the cross-sectional shape of the convex portion in a cross-section perpendicular to the first direction may be triangular, trapezoidal, or rectangular. If the cross-sectional shape is triangular, the shape of the convex portion may be conical or pyramidal. If the cross-sectional shape is trapezoidal, the shape of the convex portion may be frustum of a cone or frustum of a polygon. If the cross-sectional shape is rectangular, the shape of the convex portion may be cylindrical or prism. The convex or concave portion may have a curved surface.

[0029] The second electrode may have a circulation hole through which the chemical solution flows and circulates, penetrating from one opposing surface to the opposite surface. The circulation hole may be formed on a surface adjacent to the hole shape of the recess, or on the recessed surface of the hole shape. The circulation hole may be formed in the groove between the two protrusions. When viewed from a direction perpendicular to the surface of the chemical solution, the circulation hole may be formed in a position that overlaps with the anode, or in a position that does not overlap with the anode.

[0030] The chemical treatment process is described in detail below.

[0031] (Step (i)) First, the anode is electrically connected to the first electrode. For example, if the anode has a porous anode and an anode wire planted from the planting surface, which is one of the main surfaces of the anode, the anode wire is connected to the first electrode. This electrically connects the anode to the first electrode via the anode wire. There are no limitations on the anode and anode wire, and known anodes and wires may be used. Alternatively, the anode may be manufactured by a known method. Examples of anodes and anode wires, and examples of methods for forming them, will be described later.

[0032] In this case, multiple anodes are arranged at intervals along a predetermined direction (here, the first direction) to form an anode group, and each anode in the anode group is electrically connected to the first electrode. For example, if the anode part has an anode wire, multiple anode parts are arranged at intervals along the first direction, and each of the multiple anode wires connected to the multiple anodes is connected to the first electrode. The multiple anodes may be arranged in a line, or if the multiple first electrodes are arranged in a line, they may be arranged in a matrix. The spacing between the multiple anode parts may be the same for all anode parts, or the spacing between one anode part and its adjacent anode parts may differ from that of others.

[0033] The shape of the first electrode is selected according to the arrangement of the anode group. For example, the first electrode may be linear (e.g., rod-shaped or plate-shaped), with multiple anodes arranged in a row along the first electrode. If multiple anodes are arranged in a matrix, the first electrode is composed of multiple rows of linear electrodes. The first electrode and the anode wire are electrically connected. Typically, the anode wire is fixed to the first electrode by a method such as welding. There are no particular limitations on the material of the first electrode; it may be a conductive metal (e.g., iron, iron alloy, aluminum, etc.). Multiple second electrodes may be formed corresponding to multiple first electrodes arranged in multiple rows, and the multiple second electrodes may be coupled to each other in a second direction to form a single integrated second electrode.

[0034] As the first electrode, metallic aluminum and its alloys can be preferably used due to their light weight and ease of handling.

[0035] There is no limit to the number of anodes included in the anode group; it may be in the range of 10 to 200 (for example, 40 to 100). There is also no particular limit to the spacing between adjacent anodes; this spacing may be in the range of 1 to 20 mm (for example, 2 to 6 mm). Normally, this spacing is constant, but it does not have to be constant.

[0036] (Step (ii)) Next, with the anode body electrically connected to the first electrode immersed in the chemical solution in the chemical tank, a DC voltage is applied between the first electrode and the second electrode to create a current. This oxidizes (anodic oxidation) at least a portion of the surface of the anode body, forming a dielectric layer.

[0037] In step (ii), the surface of the anode is oxidized and transformed into a dielectric layer. For example, if the anode is made of tantalum, an oxide tantalum layer is formed on the surface of the anode. There are no particular limitations on the conversion solution, and known conversion solutions used for the conversion treatment of anodes of electrolytic capacitors may be used. For example, any of acidic aqueous solutions, neutral aqueous solutions, or basic aqueous solutions may be used as the conversion solution. Examples of acidic aqueous solutions include phosphoric acid aqueous solutions, nitric acid aqueous solutions, acetic acid aqueous solutions, and sulfuric acid aqueous solutions. Other examples of conversion solutions include aqueous solutions of tartrate, oxalate, and tetraborate.

[0038] The second electrode is positioned along the bottom surface of the chemical conversion tank and immersed in the chemical conversion solution. It is preferable to use a metal that is stable during the chemical conversion process for the material of the second electrode. Examples of materials for the second electrode include iron alloys, nickel, chromium, gold, platinum, tantalum, titanium, and carbon. The second electrode can be created, for example, by machining the surface of a thick, plate-like material or by drilling holes. While a plate portion of the second electrode made of a mesh of metal wires improves the circulation of the chemical conversion solution, it results in a low current density, making it difficult to increase the current density.

[0039] The second electrode has a pair of protrusions or a single recess on the surface facing the first electrode. Multiple anodes (anode group) electrically connected to the first electrode are immersed in the chemical solution such that, when viewed from a direction perpendicular to the liquid surface, each is positioned at the location of the pair of protrusions or the single recess on the second electrode.

[0040] After step (ii), a capacitor element can be obtained by performing a step to form the necessary parts for an electrolytic capacitor, and an electrolytic capacitor can be manufactured. There are no limitations on these steps, and known methods may be applied.

[0041] In one example of a manufacturing method for an electrolytic capacitor in which the anode is a sintered body, an electrolyte layer is formed on a dielectric layer, and a cathode is formed on the electrolyte layer. In this way, a capacitor element is fabricated. Next, an anode lead terminal is connected to the anode wire, and a cathode lead terminal is connected to the cathode. Then, an outer casing is formed to cover the capacitor element, a portion of the anode lead terminal, and a portion of the cathode lead terminal. In this way, an electrolytic capacitor is obtained.

[0042] In a manufacturing method for an example of an electrolytic capacitor in which the anode is a wound metal foil, step (i) prepares a wound body in which the anode (metal foil), separator, and cathode foil are wound. The wound body includes an anode portion. The anode portion includes the anode (metal foil) and an anode wire protruding from the first end face of the anode (the first end face of the wound anode). Normally, a dielectric layer is formed on the surface of the anode (metal foil), but at least a portion of the end face of the anode does not have a dielectric layer. Therefore, in order to form a dielectric layer in the portion where the dielectric layer is not formed, a dielectric layer is formed by step (ii) above. After forming the dielectric layer, a capacitor element is manufactured by forming an electrolyte layer inside the wound body. A wound electrolytic capacitor is obtained by sealing the manufactured capacitor element in a case. The electrolyte layer may be a solid electrolyte layer or an electrolyte layer containing a liquid component. There are no particular limitations on their constituent elements and formation methods, and known constituent elements and formation methods may be used.

[0043] [First Embodiment] In the following, an example of manufacturing a capacitor element by applying a chemical conversion treatment to an anode body using a second electrode provided with at least one pair of protrusions will be described with reference to the drawings.

[0044] Figure 1 is a schematic diagram illustrating the chemical conversion process of the capacitor element manufacturing method according to this embodiment, and schematically shows the state inside the conversion tank 101 when a DC current is passed between a plurality of first electrodes (anode electrodes) 104 and a second electrode (cathode electrode) 105 to perform the chemical conversion process. The plurality of first electrodes 104 extend in a first direction (a direction perpendicular to the plane of the paper in Figure 1) parallel to the liquid surface 102a of the conversion liquid 102, and are also called carrier bars. The plurality of first electrodes 104 are arranged in a second direction perpendicular to the first direction. Figure 1 shows a cross-sectional view of the conversion tank 101 in a plane perpendicular to the first direction (a plane parallel to the second direction and the direction perpendicular to the liquid surface). Figure 2 is a perspective view showing the schematic configuration of the second electrode 105 arranged along the bottom surface of the conversion tank 101.

[0045] Multiple anode sections, each having an anode body 1 and an anode wire 2, are arranged at predetermined intervals along the carrier bar of a first electrode 104 and are electrically connected to the first electrode 104 via the anode wire 2. Therefore, although not clear from Figure 1, the multiple anode sections are arranged in a matrix along the first and second directions. Each of the anode bodies 1 in the multiple anode sections is immersed in the conversion solution 102 and is in contact with the conversion solution 102.

[0046] The second electrode 105 has multiple protrusions on the surface facing the first electrode 104. In the example shown in Figure 2, multiple pyramidal protrusions 110, which are square pyramidal in shape, are arranged two-dimensionally along the first and second directions on the surface facing the second electrode 105. The cross-sectional shape of the protrusions 110 in a cross section perpendicular to the first direction is triangular.

[0047] A gap 112 is formed between two pyramid-shaped protrusions 110 adjacent in the second direction. Since a plurality of protrusions 110 are arranged two-dimensionally, a plurality of gaps 112 are also formed. As shown in FIG. 1, each anode body 1 is arranged so as to be positioned inside any one of these gaps 112 when viewed from a direction perpendicular to the liquid surface 102a.

[0048] The protruding height H of the protrusion 110 in FIG. 1 is, for example, in the range of 1 to 20 mm. The spacing between the protrusions 110 in the second direction (in other words, the arrangement spacing of the plurality of second electrodes 105 arranged side by side in the second direction) is, for example, 5 to 20 mm.

[0049] In the example shown in FIG. 1, the minimum height h1 of each anode body 1 immersed in the formation liquid 102 is higher than the height h2 of the apex of the protrusion 110 (h1>h2), and the difference therebetween is 2 mm or less (h1-h2<2 mm). This makes it possible to obtain a high current density.

[0050] However, as shown in FIG. 3, the minimum height h1 of each anode body 1 immersed in the formation liquid 102 may be lower than the height h2 of the apex of the protrusion 110 (h1<h2). In that case, a part of the anode body 1 is accommodated in the gap 112 formed by two adjacent protrusions 110. In this case, a higher current density can be obtained.

[0051] In both cases of FIG. 1 and FIG. 3, the maximum height h3 of each anode body 1 immersed in the formation liquid 102 is higher than the height h2 of the apex of the protrusion 110. That is, at least a part of the first electrode side of the anode body 1 may not be accommodated in the gap 112 and may be located above the gap 112.

[0052] FIGS. 4A to 4D show another example of the second electrode 105 in which a protrusion is provided on the opposing surface. Each of FIGS. 4A to 4D corresponds to an arrangement in which only one row of first electrodes 104 is aligned, and is an enlarged perspective view showing the periphery of a region facing one anode body 1 within the second electrode 105, with a cross-section of the second electrode 105 cut away on a plane perpendicular to the first direction (a plane parallel to the second direction and the direction perpendicular to the liquid surface).

[0053] Figure 4A shows an example in which the apex of the pyramidal protrusion 110 of the second electrode 105 shown in Figure 2 is cut off, and the protrusion 110 is formed into a truncated square pyramidal shape. In this case, the cross-sectional shape of the protrusion 110 in a section perpendicular to the first direction is trapezoidal.

[0054] Figure 4B shows an example in which multiple protrusions 110 extending in a first direction are arranged. A groove is formed between two adjacent protrusions 110. Multiple anode bodies 1 can be arranged in the first direction along this groove. The cross-sectional shape of the protrusions 110 in a cross section perpendicular to the first direction is triangular.

[0055] Figure 4C, like Figure 4B, shows an example in which multiple protrusions 110 extending in the first direction are arranged, and a groove is formed between two adjacent protrusions 110. In Figure 4C, the cross-sectional shape of the protrusion 110 in a section perpendicular to the first direction is trapezoidal.

[0056] Figure 4D shows an example where multiple protrusions 110 extending in the first direction are arranged, similar to Figures 4B and 4C. A groove is formed between two adjacent protrusions 110. In Figure 4D, the cross-sectional shape of the protrusion 110 in a cross-section perpendicular to the first direction is a rectangle that is elongated in the direction of the protrusion. This forms a U-shaped groove between two adjacent protrusions 110. Multiple anodes 1 can be arranged along this groove.

[0057] In Figures 4A to 4D, a circulation hole 113 is provided at a predetermined position on the opposing surface of the second electrode 105, allowing the chemical solution to flow through from the opposing surface to the opposite surface, in order to promote the circulation of the chemical solution. The position of the circulation hole for the flow of the chemical solution is not particularly limited. From the standpoint of increasing the current density flowing through the anode, it is desirable that the circulation hole be positioned so as not to overlap with the anode, but it may also be positioned so as to overlap with the anode.

[0058] [Second Embodiment] A capacitor element may be manufactured by applying a chemical conversion treatment to the anode body using a second electrode provided with a recess. Figures 5A and 5B show examples of a second electrode 105 with a recess provided on its opposing surface. Figures 5A and 5B are perspective views that show an enlarged view of the area of ​​the second electrode 105 that faces one anode body 1, as well as a cutaway view of the cross-section of the second electrode 105 in a plane perpendicular to the first direction (a plane parallel to the second direction and the direction perpendicular to the liquid surface).

[0059] Figure 5A shows an example in which a recess 114 is formed on the opposing surface of the second electrode 105. In the example of Figure 5A, the recess 114 is a hole with a circular opening. The depth of the hole is not particularly limited and may be a hole that penetrates to the opposite surface of the opposing surface. Multiple recesses 114 may be arranged along the first direction. Each of the multiple anodes 1 is positioned so as to overlap with one of the recesses 114 when viewed from a direction perpendicular to the surface of the conversion solution.

[0060] Figure 5B shows that in Figure 5A, the recess 114 is a through-hole with a square-shaped opening. By arranging the square-shaped through-holes along the first direction, a second electrode 105 is formed in which multiple through-holes are arranged in a row.

[0061] In Figure 5B, the through-hole forming the recess 114 serves as a channel for the chemical solution to flow through. In Figure 5A, a separate through-hole (circulation hole) for circulating the chemical solution may be provided. The circulation hole for the chemical solution may be provided on the opposing surface (reference surface) where the recess 114 is not formed, or on the recessed surface of the recess 114.

[0062] <Capacitor elements and electrolytic capacitors> An example of the configuration and components of a capacitor element and electrolytic capacitor manufactured by the manufacturing method of this disclosure is described below, specifically in the case where a sintered anode is used. The example electrolytic capacitor described below includes a capacitor element, an outer casing, anode lead terminals, and cathode lead terminals. However, the configuration and components of an electrolytic capacitor manufactured by the method of this disclosure are not limited to the example below.

[0063] Figure 6 is a schematic cross-sectional view showing an example of a capacitor element manufactured by the manufacturing method according to this embodiment. Figure 7 is a schematic cross-sectional view of an electrolytic capacitor using a capacitor element manufactured by the manufacturing method according to this embodiment. However, the present invention is not limited to the configurations shown in these drawings.

[0064] The electrolytic capacitor 20 comprises a capacitor element 10 having an anode portion 6 and a cathode portion 7, an outer casing 11 that encloses the capacitor element 10, an anode lead terminal 13 electrically connected to the anode portion 6 and partially exposed from the outer casing 11, and a cathode lead terminal 14 electrically connected to the cathode portion 7 and partially exposed from the outer casing 11. The anode portion 6 has an anode body 1 and an anode wire 2. A dielectric layer 3 is formed on the surface of the anode body. The cathode portion 7 has a solid electrolyte layer 4 that covers at least a portion of the dielectric layer 3 and a cathode layer 5 that covers at least a portion of the surface of the solid electrolyte layer 4.

[0065] (Capacitor element) The following will provide a detailed explanation of the capacitor element 10, using the case where a solid electrolyte layer is provided as the electrolyte as an example.

[0066] (Anode part) The anode section 6 comprises an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connected to an anode lead terminal 13. The anode 1 is, for example, a rectangular porous sintered body obtained by sintering metal particles. As the metal particles, valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used. One or more types of metal particles are used in the anode 1. The metal particles may be an alloy composed of two or more metals. For example, an alloy containing a valve metal with silicon, vanadium, boron, etc. can be used. Alternatively, a compound containing a valve metal with a typical element such as nitrogen may be used. The valve metal alloy has a valve metal as its main component, for example, containing 50 atomic percent or more of the valve metal.

[0067] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited and, for example, in addition to the valve metal mentioned above, niobium, aluminum, aluminum alloy, etc. The materials constituting the anode body 1 and the anode wire 2 may be the same or different. The anode wire 2 has a first portion 2a embedded in the interior of the anode body 1 from one surface of the anode body 1 and a second portion 2b extending from the aforementioned surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited and, for example, circular, track-shaped (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), elliptical, rectangular, polygonal, etc.

[0068] The anode portion 6 is manufactured, for example, by pressure molding a rectangular parallelepiped shape with the first portion 2a embedded in the powder of the first metal particles, and then sintering it. As a result, the second portion 2b of the anode wire 2 is drawn out from one side of the anode body 1 so as to be embedded. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, so that the anode wire 2 and the anode lead terminal 13 are electrically connected. The welding method is not particularly limited and can include resistance welding, laser welding, etc.

[0069] A dielectric layer 3 is formed on the surface of the anode 1. The dielectric layer 3 is made of, for example, a metal oxide. The dielectric layer 3 is formed by immersing the anode 1 in a chemical conversion solution and anodic oxidizing the surface of the anode 1 by performing the chemical conversion treatment process described above.

[0070] (Cathode part) The cathode portion 7 has a solid electrolyte layer 4 and a cathode layer 5 that covers the solid electrolyte layer 4. The solid electrolyte layer 4 is formed to cover at least a portion of the dielectric layer 3.

[0071] For the solid electrolyte layer 4, for example, a manganese compound or a conductive polymer can be used. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used individually or in combination. The conductive polymer may also be a copolymer of two or more monomers. Polythiophene, polyaniline, and polypyrrole may be used because of their excellent conductivity. Polypyrrole may be used in particular because of its excellent water repellency.

[0072] The solid electrolyte layer 4 containing the conductive polymer is formed, for example, by polymerizing raw material monomers on the dielectric layer 3. Alternatively, it is formed by coating the dielectric layer 3 with a liquid containing the conductive polymer. The solid electrolyte layer 4 consists of one or more solid electrolyte layers. When the solid electrolyte layer 4 consists of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may differ.

[0073] In this specification, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, and polyaniline as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, and polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0074] Various dopants may be added to polymerization solutions, solutions, or dispersions of conductive polymers to improve the conductivity of the conductive polymer. The dopants are not particularly limited, but examples include naphthalene sulfonic acid, p-toluenesulfonic acid, and polystyrene sulfonic acid.

[0075] When conductive polymers are dispersed in a dispersion medium in the form of particles, the average particle size D50 is, for example, between 0.01 μm and 0.5 μm. If the average particle size D50 is within this range, the particles can easily penetrate into the interior of the anode 1.

[0076] The cathode layer 5 includes, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. However, the configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 is acceptable as long as it has a current collecting function.

[0077] (Anode lead terminal) The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 may be a metal such as copper, or a nonmetal. Its shape is not particularly limited as long as it is flat. The thickness of the anode lead terminal 13 (distance between the main surfaces of the anode lead terminal 13) may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less, from the viewpoint of reducing the profile.

[0078] One end of the anode lead terminal 13 may be joined to the anode wire 2 by conductive adhesive or solder, or by resistance welding or laser welding. The other end of the anode lead terminal 13 is led out to the outside of the housing 11 and is exposed from the housing 11. The conductive adhesive is, for example, a mixture of a thermosetting resin and carbon particles or metal particles, as described later.

[0079] (Cathode lead terminals) The cathode lead terminal 14 is electrically connected to the cathode portion 7 at the junction 14a. The junction 14a is the portion of the cathode lead terminal 14 that overlaps with the cathode layer 5 when viewed from the direction normal to the cathode layer 5.

[0080] The cathode lead terminal 14 is joined to the cathode layer 5, for example, via a conductive adhesive 8. One end of the cathode lead terminal 14 forms part of the joint 14a, for example, and is located inside the casing 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a portion of the cathode lead terminal 14, including the other end, is exposed from the casing 11.

[0081] The material of the cathode lead terminal 14 is not particularly limited, as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 may be a metal such as copper, or a nonmetal. Its shape is also not particularly limited, and for example, it may be long and flat. From the viewpoint of reducing the profile, the thickness of the cathode lead terminal 14 may be 25 μm to 200 μm, or 25 μm to 100 μm.

[0082] (Exterior) The outer casing 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is made of an insulating material (outer casing material). The outer casing material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0083] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0084] The anode body was treated using the following procedure. Tantalum metal particles were used as the valve metal. The tantalum metal particles were formed into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and then the formed body was sintered in a vacuum. This resulted in an anode section containing an anode body (1.7 mm × 3.3 mm × 4.4 mm) made of a porous sintered tantalum body, and an anode wire with one end embedded in the anode body and the remaining part planted from one side of the anode body. The anode wire is planted from the 1.7 mm × 3.3 mm surface.

[0085] Fifty-five anode units were arranged in a line at regular intervals (5 mm), and the anode wires were welded to a long, narrow plate-shaped first electrode. Next, the anode units welded to the first electrode and the second electrode were immersed in a conversion solution. A phosphoric acid aqueous solution was used as the conversion solution. Then, by applying a DC voltage (90 V) between the first and second electrodes and performing a conversion treatment, a dielectric layer of tantalum oxide (Ta2O5) was formed on the surface of the 55 anode units.

[0086] As a second electrode corresponding to the first electrode, which consisted of only one row of electrodes, the following pure copper cathode electrode was prepared, and the height of the anode body was appropriately changed relative to the cathode electrode, and a chemical conversion treatment was performed.

[0087] (Example 1) A second electrode having two adjacent protrusions as shown in Figure 4A was prepared and designated as the cathode electrode A1. The protruding height H of the truncated pyramidal protrusion 110 on the cathode electrode A1 was set to 10 mm. The truncated pyramid had an upper base that was a square with sides of 1 mm and a lower base that was a square with sides of 5 mm. The spacing between the protrusions 110 arranged in the first and second directions was set to 10 mm in the first direction from which the first electrode extends, and 10 mm in the second direction perpendicular to the first direction. In the second direction, the anode was immersed in the conversion solution so that it was positioned between the protrusions 110.

[0088] In Example 1, the anode body was immersed in the chemical conversion solution such that the minimum height h1 of the anode body in the conversion tank was at the same position as the maximum height h2 at the apex of the protrusion 110 (the upper base of the truncated square pyramid).

[0089] (Examples 2-4) A second electrode having two adjacent protrusions, as shown in Figure 4B, was prepared and designated as cathode electrode A2. The protrusion height H of the protrusions 110 on cathode electrode A2 was set to 2 mm. The spacing between the protrusions 110 extending in the first direction in the second direction was set to 10 mm. The anode body was immersed in the conversion solution so that it was positioned between the protrusions 110 in the second direction.

[0090] In Example 2, cathode electrode A2 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode in the conversion tank was at the same position as the maximum height h2 at the apex (ridge) of the protrusion 110.

[0091] In Example 3, cathode electrode A2 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode was 1 mm higher than the maximum height h2 of the protrusion 110.

[0092] In Example 4, cathode electrode A3 was used, with the protrusion height H of cathode electrode A2 changed to 5 mm, and the rest of the procedure was the same as in Example 2.

[0093] (Examples 5 and 6) A second electrode having two adjacent protrusions as shown in Figure 4C was prepared and designated as cathode electrode A4. The protrusion height H of the protrusions 110 on cathode electrode A4 was set to 10 mm. The cross-sectional shape of the protrusions 110 perpendicular to the first direction is an isosceles trapezoid with an upper base of 1 mm and a lower base of 3 mm. The spacing between the protrusions 110 extending in the first direction in the second direction was set to 10 mm. The anode body was immersed in the conversion solution so that it was positioned between the protrusions 110 in the second direction.

[0094] In Example 5, cathode electrode A4 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode in the conversion tank was at the same position as the maximum height h2 at the apex of the protrusion 110.

[0095] In Example 6, cathode electrode A4 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode was 1 mm higher than the maximum height h2 of the protrusion 110.

[0096] (Example 7) A second electrode having two adjacent protrusions as shown in Figure 4D was prepared and designated as cathode electrode A5. The protrusion height H of the protrusions 110 on cathode electrode A5 was set to 15 mm. The spacing between the protrusions 110 in the second direction was set to 10 mm. The anode body was immersed in the conversion solution so that it was positioned between the protrusions 110 in the second direction.

[0097] In Example 7, cathode electrode A5 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode in the conversion tank was at the same position as the maximum height h2 at the apex of the protrusion 110.

[0098] Furthermore, in cathode electrodes A1 to A5, the thickness of the second electrode, excluding the protrusion 110, was set to 3 mm.

[0099] (Example 8) A second electrode with a cylindrical hole shape and a concave shape, as shown in Figure 5A, was prepared and designated as the cathode electrode A6. The cathode electrode A6 had a thickness of 10 mm, and a hole with a diameter of 4 mm was arranged as a recess 114. The spacing of the recesses 114 in the first direction was 10 mm. The anode was immersed in the conversion solution so that the anode was positioned in the recess 114 in the second direction.

[0100] In Example 8, cathode electrode A6 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode in the conversion tank was at the same position as the height of the reference plane of the recess.

[0101] (Example 9) A second electrode with a rectangular prism-shaped hole and a concave shape, as shown in Figure 5B, was prepared and designated as cathode electrode A7. Cathode electrode A7 has a thickness of 5 mm, and a 3 mm x 3 mm square through-hole is arranged as a recess 114. The spacing between the recesses (center-to-center distance) in the first direction was set to 10 mm. The anode body was immersed in the conversion solution so that it was positioned in the recess 114 in both the first and second directions.

[0102] In Example 9, cathode electrode A7 was used, and the anode was immersed in the conversion solution such that the minimum height h1 of the anode in the conversion tank was at the same position as the height of the reference plane of the recess.

[0103] (Comparative Example 1) A 3mm thick flat plate was prepared as the second electrode and designated as cathode electrode B1. The anode was immersed in the chemical solution such that the minimum height h1 of the anode in the chemical tank was 1mm away from cathode electrode B1.

[0104] During the chemical conversion treatment, the current density of the 30th anode, located approximately in the center of the 55 anodes arranged in the first direction, was measured using an ammeter. The distribution of current density along a center line perpendicular to a 1.7 mm × 3.3 mm plane was determined on the 3.3 mm × 4.4 mm surface of the anode, and the average value of the current density was calculated. A The following was determined. The measurement results for Examples 1 to 9 and Comparative Example 1 are shown in Table 1.

[0105] [Table 1] [Industrial applicability]

[0106] This disclosure can be used in a method for manufacturing electrolytic capacitors. [Explanation of Symbols]

[0107] 20: Electrolytic capacitors 10: Capacitor element 1: Anode 2: Anode wire 2a:First part 2b:Second part 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Metal paste layer 6: Anode section 7: Cathode part 8: Conductive adhesive 11: Exterior 12: Resin protective layer 13: Anode lead terminal 14: Cathode lead terminals 14a: Joint 101:Chemical tank 102: Chemical liquid 102a:Liquid level 103: Bubbles 104: First electrode (anode electrode) 105: Second electrode (cathode electrode) 110: Convex part 112: Gap formed by the protrusion 113: Circulation hole 114: Recess

Claims

1. A method for manufacturing a capacitor element in which a dielectric layer is formed on the surface of an anode body made of a valve metal, Step (i) of electrically connecting a plurality of anodes to a first electrode provided along a first direction, The process includes (ii) immersing the anode body connected to the first electrode in a chemical solution in a chemical tank, and then passing an electric current between the first electrode and a plate-shaped second electrode positioned along the bottom surface of the chemical tank to oxidize at least a portion of the surface of the anode body and form the dielectric layer, The second electrode has, on the opposing surface facing the first electrode, a pair of adjacent convex portions or a single concave portion for each of the plurality of anode bodies. Each of the plurality of anode bodies is positioned between the pair of protrusions or at the position of the recess in a second direction perpendicular to the first direction. In step (ii) above, the chemical solution is present between the surface of the second electrode opposite to the opposing surface and the bottom surface of the chemical tank. The second electrode has a circulation hole through which the chemical solution circulates, penetrating from the opposing surface to the opposite surface. A method for manufacturing a capacitor element, wherein the anode body is located higher than the circulation hole in the chemical formation tank.

2. The method for manufacturing a capacitor element according to claim 1, wherein the diameter of the circulation hole is smaller than the thickness of the plate-shaped second electrode.

3. A method for manufacturing a capacitor element according to claim 1, wherein the protrusion is formed along the first direction of the opposing surface.

4. The opposing surfaces have a plurality of pairs of protrusions or a plurality of recesses along the first direction, A method for manufacturing a capacitor element according to claim 1, wherein a plurality of pairs of protrusions or a plurality of recesses are arranged along the first direction, corresponding to each of the plurality of anode bodies.

5. The method for manufacturing a capacitor element according to claim 4, wherein the plurality of recesses are in the shape of holes penetrating the back surface of the opposing surface.

6. The opposing surface has the convex portion, A method for manufacturing a capacitor element according to any one of claims 1 to 4, wherein the height of the lowest position of the anode body in the chemical formation tank is higher than the maximum height of the apex of the convex portion protruding toward the first electrode, and the difference between the maximum height and the height of the lowest position of the anode body is 2 mm or less.

7. The opposing surface has the convex portion, The height of the lowest position of the anode body in the chemical formation tank is lower than the maximum height of the apex of the protrusion projecting toward the first electrode. A method for manufacturing a capacitor element according to any one of claims 1 to 4.

8. The opposing surface has the recess, The height of the lowest position of the anode body in the chemical conversion tank is higher than the height of the reference surface of the recess on the opposing surface, and the difference between the height of the reference surface and the height of the lowest position of the anode body is 2 mm or less. A method for manufacturing a capacitor element according to claim 4 or 5.

9. The opposing surface has the recess, The method for manufacturing a capacitor element according to claim 4 or 5, wherein the height of the lowest position of the anode body in the chemical formation tank is lower than the height of the reference surface of the recess on the opposing surface.

10. A method for manufacturing a capacitor element according to any one of claims 1 to 4, 6, and 7, wherein the cross-sectional shape of the convex portion in a cross section perpendicular to the first direction is triangular.

11. A method for manufacturing a capacitor element according to any one of claims 1 to 4, 6, and 7, wherein the cross-sectional shape of the convex portion in a cross section perpendicular to the first direction is trapezoidal.

12. A method for manufacturing a capacitor element according to any one of claims 1 to 4, 6, and 7, wherein the cross-sectional shape of the convex portion in a cross section perpendicular to the first direction is rectangular.

13. A method for manufacturing a capacitor element according to any one of claims 1 to 12, wherein a plurality of second electrodes are formed and integrated with a plurality of first electrodes arranged in a plurality of rows.

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