Film capacitor

Abstract

A film capacitor 1 according to the present invention is provided with: a capacitor element 10 which comprises an element main body 11 and an external electrode 12 that is provided on an end face of the element main body 11; and a lead-out terminal 20 which is electrically connected to the external electrode 12. The element main body 11 is a multilayer body which comprises a metallized film (for example, a first metallized film 51) that is obtained by providing at least one main surface of a dielectric film (for example, a first dielectric film 53) with a metal layer (for example, a first metal layer 55). The external electrode 12 is connected to the metal layer (for example, the first metal layer 55). The lead-out terminal 20 is welded to the external electrode 12. The surface roughness Ra of the external electrode 12 is 20 µm to 45 µm; and the bite depth D of the lead-out terminal 20 from the surface of the external electrode 12 is 0.5 mm or more.

Description

Film capacitors

[0001] The present invention relates to a film capacitor.

[0002] One type of capacitor known is a film capacitor, which has a structure in which a flexible resin film is used as a dielectric film and metal layers are arranged facing each other across the dielectric film. The capacitor element that constitutes the film capacitor is manufactured, for example, by winding or laminating a metallized film, which has a metal layer provided on the surface of a dielectric film, to form a laminate, and then forming external electrodes (also called metallikon electrodes) on both end surfaces of the laminate.

[0003] The external electrodes of the capacitor element are connected to lead terminals such as lead wires or bus bars. Examples of methods for connecting the lead terminals include joining the lead terminals to the external electrodes of the capacitor element by soldering or resistance welding.

[0004] Patent Document 1 discloses a metallized film capacitor including a capacitor element having a metallikon electrode formed by winding or laminating a metallized film, and a metal bar solder-connected to the metallikon electrode, the metal bar having a protrusion for solder connection. According to Patent Document 1, the lead electrode joined to the capacitor element is a metal bar having a cross-sectional area required for the circuit, thereby enabling a structure capable of carrying a large current, and by providing the metal bar with a protrusion for solder connection, only the solder connection area is heated during soldering, thereby reducing the thermal impact on the capacitor element and ensuring reliability of the lead electrode connection and capacitor characteristics.

[0005] Patent Document 2 discloses a film capacitor that is composed of a capacitor element, metallikon electrodes formed by spraying molten metal such as lead or tin on both end faces of the element, and one lead wire connected and fixed to the metallikon electrode by an electric welder, etc. The film capacitor described in Patent Document 2 is characterized in that one of the metallikon bonding surfaces of the lead wire is formed continuously in a vertical direction in a generally mountain-like or generally sawtooth shape.

[0006] JP 2004-349447 A JP 2008-166457 A

[0007] As described in Patent Document 1, in the method of joining lead terminals such as lead wires to the external electrodes of a capacitor element by soldering, a high-temperature soldering iron is brought into contact with the joint, and the heat from the soldering iron is transferred to the inside of the capacitor element via the external electrodes, which can result in damage to the capacitor element due to heat, potentially leading to a deterioration in the performance of the film capacitor.

[0008] On the other hand, as described in Patent Document 2, in a method of joining a lead terminal such as a lead wire to an external electrode of a capacitor element by resistance welding, the external electrode and the lead terminal are pressed together with a welding electrode, and a large current is passed through the welding electrode to weld the lead terminal to the external electrode.

[0009] Although resistance welding uses a large current, the time the large current flows is very short, so compared to soldering, damage to the capacitor element due to heat is reduced. However, there is still room for improvement in terms of increasing the bond strength between the external electrodes of the capacitor element and the lead terminals.

[0010] An object of the present invention is to provide a film capacitor having a high bonding strength between the external electrodes of the capacitor element and the lead terminals.

[0011] The film capacitor of the present invention comprises a capacitor element including an element body and external electrodes provided on end surfaces of the element body, and lead terminals electrically connected to the external electrodes. The element body is a laminate including a metallized film having a metal layer provided on at least one main surface of a dielectric film. The external electrodes are connected to the metal layer. The lead terminals are welded to the external electrodes. The surface roughness Ra of the external electrodes is 20 μm or more and 45 μm or less, and the lead terminals penetrate the surfaces of the external electrodes to a depth of 0.5 mm or more.

[0012] According to the present invention, it is possible to provide a film capacitor having a high bonding strength between the external electrodes of the capacitor element and the lead-out terminals.

[0013] FIG. 1 is a perspective view schematically illustrating a film capacitor according to an embodiment of the present invention. FIG. 2 is a front view of the film capacitor shown in FIG. 1. FIG. 3A is a side view schematically illustrating an example of an external electrode and a lead terminal before welding, and FIG. 3B is a side view schematically illustrating an example of an external electrode and a lead terminal after welding. FIG. 4A is a front view schematically illustrating an example of an external electrode and a lead terminal before welding, and FIG. 4B is a front view schematically illustrating an example of an external electrode and a lead terminal after welding. FIG. 5 is a front view schematically illustrating an example of a lead terminal that has bitten into an external electrode. FIG. 6 is a front view schematically illustrating another example of a lead terminal that has bitten into an external electrode. FIG. 7 is a perspective view schematically illustrating an example of a capacitor element constituting a film capacitor of the present invention. FIG. 8 is a cross-sectional view of the capacitor element shown in FIG. 7 taken along line b-b. FIG. 9 is a perspective view schematically illustrating an example of an element body constituting the capacitor element shown in FIGS. 7 and 8. Fig. 10 is a perspective view schematically showing another example of an element body constituting the capacitor element shown in Fig. 7 and Fig. 8. Figs. 11A and 11B are perspective views schematically showing an example of a method of using the film capacitor shown in Fig. 1. Fig. 12 is a schematic view for explaining a tensile test.

[0014] The film capacitor of the present invention will be described below. Note that the present invention is not limited to the following configurations and may be modified as appropriate within the scope of the present invention. In addition, a combination of multiple individual preferred configurations described below also constitutes the present invention.

[0015] In this specification, terms indicating the relationship between elements (e.g., "perpendicular," "parallel," "orthogonal," etc.) and terms indicating the shape of elements are not expressions that only express a strict meaning, but are expressions that also include a range of substantial equivalence, for example, a difference of about a few percent.

[0016] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0017] Fig. 1 is a perspective view schematically illustrating a film capacitor according to an embodiment of the present invention, and Fig. 2 is a front view of the film capacitor shown in Fig. 1.

[0018] The film capacitor 1 shown in FIGS. 1 and 2 includes a capacitor element 10 and a lead terminal 20 .

[0019] The capacitor element 10 includes an element body 11 and external electrodes 12 provided on end surfaces of the element body 11. Specifically, a pair of external electrodes 12 is provided on both end surfaces of the element body 11. The configuration of the capacitor element 10 will be described later.

[0020] The lead-out terminals 20 are electrically connected to the external electrodes 12. Specifically, a pair of lead-out terminals 20 are electrically connected to each of the pair of external electrodes 12.

[0021] The pair of lead-out terminals 20 may extend from the external electrode 12 so that the distance between them is large, as shown in Figures 1 and 2. Alternatively, the pair of lead-out terminals 20 may extend from the external electrode 12 so that the distance between them is constant.

[0022] The lead-out terminal 20 is welded to the external electrode 12. Specifically, the lead-out terminal 20 is resistance-welded to the external electrode 12.

[0023] As shown in FIGS. 1 and 2, the welded portion of the lead-out terminal 20 may be flat.

[0024] As an example, the lead terminal 20 is a lead wire. In this case, the lead wire may or may not have a plating layer on its surface. The welded portion of the lead wire may be processed into a flat plate shape.

[0025] As another example, the lead terminal 20 is a bus bar. The bus bar has a flat plate shape as a whole, including the welded portion.

[0026] Fig. 3A is a side view showing an example of an external electrode and a lead-out terminal before welding, Fig. 3B is a side view showing an example of an external electrode and a lead-out terminal after welding, Fig. 4A is a front view showing an example of an external electrode and a lead-out terminal before welding, and Fig. 4B is a front view showing an example of an external electrode and a lead-out terminal after welding.

[0027] 3A and 4A, in resistance welding, a welding electrode 80 is pressed against the external electrode 12 and the lead terminal 20, and a large current is applied from the welding electrode 80. The large current generates heat at the interface between the external electrode 12 and the lead terminal 20, softening the external electrode 12. As a result, the lead terminal 20 bites into the external electrode 12, as shown in FIGS. 3B and 4B.

[0028] FIG. 5 is a front view schematically showing an example of a lead terminal that is biting into an external electrode.

[0029] The lead terminal 20 that has bitten into the external electrode 12 is unlikely to come off the external electrode 12 because the external electrode 12 receives the force indicated by the arrow in FIG.

[0030] FIG. 6 is a front view schematically showing another example of a lead terminal that is biting into an external electrode.

[0031] As shown in FIG. 6 , the entire lead terminal 20 may be embedded in the external electrode 12 .

[0032] The deeper the lead terminal 20 bites into the external electrode 12, the larger the contact area between the external electrode 12 and the lead terminal 20. Therefore, by increasing the depth to which the lead terminal 20 bites into the surface of the external electrode 12, the bonding strength between the external electrode 12 and the lead terminal 20 can be increased.

[0033] The film capacitor of the present invention is characterized in that the depth of the lead terminals from the surfaces of the external electrodes (the length indicated by D in FIGS. 3B and 4B) is 0.5 mm or more.

[0034] As will be explained in the examples below, if the depth of the lead terminal from the surface of the external electrode is 0.5 mm or more, sufficient bonding strength can be ensured.

[0035] The depth of the lead terminals can be easily controlled by adjusting the displacement of the welding machine, making it possible to manufacture film capacitors with consistent quality.

[0036] In this way, in the film capacitor of the present invention, the bond strength between the external electrode and the lead terminal can be controlled by the depth of the lead terminal's penetration. Therefore, sufficient bond strength can be ensured without alloying the lead terminal (e.g., a plating layer provided on the surface of a lead wire) and the external electrode by welding. Note that in the film capacitor of the present invention, the lead terminal and the external electrode may or may not be alloyed.

[0037] The embedding depth of the lead terminal from the surface of the external electrode can be measured, for example, by measuring the welded portion of the sample after welding strength measurement using 3D measurement with a digital microscope.

[0038] From the viewpoint of increasing the bonding strength between the external electrode and the lead terminal, it is preferable that the depth of the lead terminal from the surface of the external electrode be 0.7 mm or more.

[0039] The maximum depth of the lead terminal that can be inserted into the external electrode is up to the thickness of the external electrode, so the depth of the lead terminal from the surface of the external electrode is equal to or less than the thickness of the external electrode.

[0040] On the other hand, the lead terminal can only penetrate into the external electrode up to the thickness of the welded portion, so the penetration depth of the lead terminal from the surface of the external electrode is preferably equal to or less than the thickness of the welded portion of the lead terminal.

[0041] In order to ensure that the depth of the lead terminal from the surface of the external electrode is 0.5 mm or more, the thickness of the welded portion of the lead terminal is preferably 0.5 mm or more. Furthermore, in order to ensure that the depth of the lead terminal from the surface of the external electrode is 0.7 mm or more, the thickness of the welded portion of the lead terminal is more preferably 0.7 mm or more. There is no particular upper limit to the thickness of the welded portion of the lead terminal.

[0042] The film capacitor of the present invention is characterized in that the surface roughness Ra of the external electrodes is 20 μm or more and 45 μm or less.

[0043] As will be explained in the examples below, if the surface roughness Ra of the external electrode is 20 μm or more and 45 μm or less, welding can be performed at a temperature of 300° C. or less. Therefore, the lead terminal can be welded into the external electrode in a short time without damaging the capacitor element.

[0044] On the other hand, if the surface roughness Ra of the external electrodes exceeds 45 μm, problems such as a decrease in the strength of the external electrodes and a decrease in moisture resistance are likely to occur.

[0045] The surface roughness Ra of the external electrode can be determined, for example, by measuring the surface of the external electrode at two locations on both ends and three locations in the center using a laser microscope (VK-8700, manufactured by Keyence Corporation), and the average value can be used as the value of the surface roughness Ra.

[0046] In the film capacitor of the present invention, the element body constituting the capacitor element is a laminate including a metallized film having a metal layer provided on at least one main surface of a dielectric film, and the external electrodes constituting the capacitor element are connected to the metal layer.

[0047] The laminate is, for example, in the form of a column with an elliptical cross section, and external electrodes formed by, for example, metal spraying (metallicon) are provided on both end faces in the direction of the central axis.

[0048] The laminate may be a roll in which the metallized film is rolled up in a laminated state.

[0049] Hereinafter, as an example of a film capacitor, a wound film capacitor in which a metallized film is wound in a laminated state will be described, but a laminated film capacitor in which a metallized film is laminated may also be used.

[0050] Fig. 7 is a perspective view schematically showing an example of a capacitor element constituting the film capacitor of the present invention, and Fig. 8 is a cross-sectional view of the capacitor element shown in Fig. 7 taken along line bb.

[0051] 7 and 8 , element body 11 is a laminate including first metallized film 51 and second metallized film 52. For example, element body 11 is a wound body in which first metallized film 51 and second metallized film 52 are wound in a stacked state. A pair of external electrodes 12 are electrically connected to both end surfaces of element body 11.

[0052] As shown in Figure 8, the first metallized film 51 comprises a first dielectric film 53 and a first metal layer 55 provided on the surface of the first dielectric film 53, and the second metallized film 52 comprises a second dielectric film 54 and a second metal layer 56 provided on the surface of the second dielectric film 54.

[0053] 8, the first metal layer 55 and the second metal layer 56 face each other with the first dielectric film 53 or the second dielectric film 54 sandwiched therebetween. Furthermore, the first metal layer 55 is electrically connected to one of the external electrodes 12, and the second metal layer 56 is electrically connected to the other external electrode 12.

[0054] The first dielectric film 53 and the second dielectric film 54 may have different configurations, but preferably have the same configuration.

[0055] The first metal layer 55 is formed on one surface of the first dielectric film 53 so as to reach one edge but not the other edge. On the other hand, the second metal layer 56 is formed on one surface of the second dielectric film 54 so as to not reach one edge but to reach the other edge. The first metal layer 55 and the second metal layer 56 are made of, for example, an aluminum layer.

[0056] FIG. 9 is a perspective view schematically showing an example of an element body constituting the capacitor element shown in FIGS. 7 and 8. In FIG.

[0057] 8 and 9, the first dielectric film 53 and the second dielectric film 54 are laminated with a shift relative to each other in the width direction (the left-right direction in FIG. 8) so that the end of the first metal layer 55 that reaches the side edge of the first dielectric film 53 and the end of the second metal layer 56 that reaches the side edge of the second dielectric film 54 are both exposed from the laminated films. As shown in FIG. 9, the element body 11 becomes a roll of metallized films by winding the first dielectric film 53 and the second dielectric film 54 in a laminated state, and is stacked with the first metal layer 55 and the second metal layer 56 exposed at their ends.

[0058] In Figures 8 and 9, the second dielectric film 54 is wound so that it is on the outside of the first dielectric film 53, and the first metal layer 55 and the second metal layer 56 of each of the first dielectric film 53 and the second dielectric film 54 are wound so that they face inward.

[0059] FIG. 10 is a perspective view schematically showing another example of the element body constituting the capacitor element shown in FIGS. 7 and 8. In FIG.

[0060] When the capacitor element body 11 is made of a wound metallized film, it is preferably pressed into a flattened shape such as an ellipse or oval in cross section, as shown in Figure 10, which is more compact than a true circle in cross section, allowing the entire film capacitor to be made smaller.

[0061] The roll of the metallized film may include a cylindrical winding shaft that is disposed on the central axis of the rolled metallized film and serves as the winding shaft when the metallized film is wound.

[0062] The external electrodes 12 are formed by thermally spraying, for example, zinc onto each end face of the element body 11 obtained as described above. One external electrode 12 contacts an exposed end of the first metal layer 55, thereby being electrically connected to the first metal layer 55. The other external electrode 12 contacts an exposed end of the second metal layer 56, thereby being electrically connected to the second metal layer 56.

[0063] In the film capacitor of the present invention, the dielectric film constituting the element body of the capacitor element may contain a curable resin as a main component, or may contain a thermoplastic resin as a main component. From the viewpoint of improving the heat resistance of the film capacitor, it is preferable that the dielectric film contains a curable resin as a main component.

[0064] In this specification, the term "major component of the dielectric film" refers to the component with the largest weight percentage, preferably the component with a weight percentage of more than 50 wt %. Therefore, the dielectric film may contain components other than the major component, such as additives such as silicone resin, and uncured portions of starting materials such as the first organic material and second organic material described below.

[0065] The curable resin may be a thermosetting resin or a photocurable resin.

[0066] In this specification, thermosetting resin means a resin that can be cured by heat, and the curing method is not limited. Therefore, as long as it is a resin that can be cured by heat, resins that are cured by methods other than heat (for example, light, electron beam, etc.) are also included in thermosetting resins. Furthermore, depending on the material, a reaction may be initiated due to the reactivity of the material itself, and resins that proceed to cure without necessarily applying heat or light from the outside are also considered thermosetting resins. The same applies to photocurable resins, and the curing method is not limited.

[0067] The curable resin may or may not have at least one of a urethane bond and a urea bond. Examples of such resins include a urethane resin having a urethane bond and a urea resin having a urea bond. Alternatively, the curable resin may be a resin having both a urethane bond and a urea bond.

[0068] The presence of urethane bonds and / or urea bonds can be confirmed using a Fourier transform infrared spectrophotometer (FT-IR).

[0069] The curable resin is preferably a cured product of a first organic material and a second organic material, such as a cured product obtained by reacting a hydroxyl group (OH group) of the first organic material with an isocyanate group (NCO group) of the second organic material.

[0070] When a cured product is obtained by the above reaction, uncured portions of the starting material may remain in the film. For example, the dielectric film may contain at least one of an isocyanate group and a hydroxyl group. In this case, the dielectric film may contain either an isocyanate group or a hydroxyl group, or may contain both an isocyanate group and a hydroxyl group.

[0071] The presence of an isocyanate group and / or a hydroxyl group can be confirmed using a Fourier transform infrared spectrophotometer (FT-IR).

[0072] The first organic material is preferably a polyol having multiple hydroxyl groups in the molecule. Examples of polyols include polyether polyol, polyester polyol, and polyvinyl acetal. Two or more organic materials may be used in combination as the first organic material.

[0073] The second organic material is preferably an isocyanate compound, an epoxy resin, or a melamine resin having multiple functional groups in the molecule. Two or more organic materials may be used in combination as the second organic material. Among the second organic materials, an isocyanate compound is preferred.

[0074] Examples of the isocyanate compound include aromatic polyisocyanates such as diphenylmethane diisocyanate (MDI) and tolylene diisocyanate (TDI), and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI). Modified products of these polyisocyanates, such as modified products having carbodiimide or urethane, may also be used.

[0075] The epoxy resin is not particularly limited as long as it is a resin having an epoxy ring, and examples thereof include bisphenol A type epoxy resin, biphenyl skeleton epoxy resin, cyclopentadiene skeleton epoxy resin, and naphthalene skeleton epoxy resin.

[0076] The melamine resin is not particularly limited as long as it is an organic nitrogen compound having a triazine ring at the center of its structure and three amino groups on the periphery thereof, and examples thereof include alkylated melamine resins, etc. Modified melamine resins may also be used.

[0077] In the film capacitor of the present invention, the dielectric film constituting the element body of the capacitor element is preferably obtained by forming a resin solution containing the first organic material and the second organic material into a film, and then heat-treating it to harden it.

[0078] In the film capacitor of the present invention, the dielectric film constituting the element body of the capacitor element may contain a vapor-deposited polymer film as a main component. The vapor-deposited polymer film may or may not have at least one of a urethane bond and a urea bond.

[0079] The vapor deposition polymerized film refers to a film formed by vapor deposition polymerization, and is basically included in the category of curable resins.

[0080] In the film capacitor of the present invention, the dielectric film constituting the element body of the capacitor element may contain a thermoplastic resin as a main component, such as polypropylene, polyethersulfone, polyetherimide, or polyarylate.

[0081] In the film capacitor of the present invention, the dielectric film constituting the element body of the capacitor element may contain additives to impart other functions. For example, adding a leveling agent can impart smoothness. The additive is preferably a material having a functional group reactive with a hydroxyl group and / or an isocyanate group and forming part of the crosslinked structure of the cured product. Examples of such materials include resins having at least one functional group selected from the group consisting of epoxy groups, silanol groups, and carboxyl groups.

[0082] In the film capacitor of the present invention, the thickness of the dielectric film constituting the element body of the capacitor element is not particularly limited, but may be set appropriately according to the required capacitance and required element volume of the capacitor to be produced.

[0083] The thickness of the dielectric film can be measured using an optical film thickness meter.

[0084] In the film capacitor of the present invention, the type of metal contained in the metal layer constituting the element body of the capacitor element is not particularly limited, but it is preferable that the metal layer contains any one selected from the group consisting of aluminum (Al), titanium (Ti), zinc (Zn), magnesium (Mg), tin (Sn), and nickel (Ni).

[0085] In the film capacitor of the present invention, the thickness of the metal layer constituting the element body of the capacitor element is not particularly limited, but from the viewpoint of suppressing damage to the metal layer, the thickness of the metal layer is preferably 5 nm or more and 40 nm or less.

[0086] The thickness of the metal layer can be determined by observing a cross section of the metallized film cut in the thickness direction using an electron microscope such as a field emission scanning electron microscope (FE-SEM).

[0087] 11A and 11B are perspective views schematically showing an example of a method of using the film capacitor shown in FIG. 1. FIG.

[0088] As shown in FIG. 11A, first, the film capacitor 1 is housed in the exterior case 30.

[0089] The exterior case 30 may be a resin case or a metal case.

[0090] 11A, a rectangular parallelepiped space is formed inside the exterior case 30. Although not shown in Fig. 11A, the capacitor element 10 is preferably placed in the center of the interior of the exterior case 30 while being spaced apart from the inner surface of the exterior case 30.

[0091] The outer case 30 is, for example, a cylindrical shape with a bottom and an opening 31 at one end. In this case, the outer case 30 includes a bottom wall 32 that faces the opening 31 and seals the other end, and a side wall 33 that protrudes from the bottom wall 32 toward the opening 31.

[0092] 11A , the exterior case 30 has a generally rectangular opening 31 at one end, a bottomed square tubular shape including a bottom wall 32 that faces the opening 31 and seals the other end, and a square tubular side wall 33 that protrudes from the bottom wall 32 toward the opening 31. Note that instead of the square tubular side wall 33, the exterior case 30 may have a shape such as a bottomed cylindrical shape that includes a cylindrical side wall 33.

[0093] 11A, it is preferable that a recess 33a be provided on the side wall 33 of the outer case 30 on the edge on the opening 31 side. By providing the recess 33a on the opening surface of the outer case 30, when the film capacitor is mounted on a board, the film capacitor and the board are sealed, preventing an increase in internal pressure. Note that the outer case 30 does not necessarily have to be provided with the recess 33a.

[0094] Although not shown in FIG. 11A, the inner surface of the exterior case 30 may be provided with a guide groove for regulating the position of the lead-out terminal 20 .

[0095] 11B, the interior of the exterior case 30 is filled with a filling resin 40, thereby covering the periphery of the film capacitor 1 with the filling resin 40 and sealing the opening 31 of the exterior case 30. The lead-out terminals 20 protrude from the interior to the exterior of the exterior case 30. As shown in FIG. 11B, it is preferable that the distance between a pair of lead-out terminals 20 is constant.

[0096] The filling resin 40 can be appropriately selected depending on the required function. Examples of the filling resin 40 include epoxy resin, silicone resin, and urethane resin. An amine curing agent, an imidazole curing agent, and the like may be used as a curing agent for the epoxy resin. Alternatively, the filling resin 40 may consist solely of resin, but a reinforcing agent may be added to improve strength. Examples of the reinforcing agent include inorganic fillers such as silica and alumina, organic fillers such as polyethylene fibers and polyamide fibers, and organic-inorganic composite fillers in which the surface of inorganic powder is coated with an organic material such as a silane coupling agent.

[0097] The relationship between the height of the filling resin 40 and the height of the outer case 30 is such that the resin at the opening 31 of the outer case 30 is as thick as possible, and may be up to a position on the inside of the outer case 30, or may be just enough to fill it up, or may overflow slightly due to surface tension.

[0098] The film capacitor of the present invention is not limited to the above embodiment, as long as the lead terminals are welded to the external electrodes, the surface roughness Ra of the external electrodes is 20 μm or more and 45 μm or less, and the lead terminals penetrate the surfaces of the external electrodes to a depth of 0.5 mm or more. Therefore, various applications and modifications can be made within the scope of the present invention with respect to the configuration and manufacturing conditions of the film capacitor.

[0099] In the film capacitor of the present invention, when a pair of external electrodes are provided on both end surfaces of the element body and a pair of lead-out terminals are electrically connected to each of the pair of external electrodes, it is sufficient that at least one external electrode and the lead-out terminal electrically connected to that external electrode satisfy the relationship described in the above embodiment.

[0100] Although Figures 11A and 11B show an example in which a single capacitor element is housed inside a single outer case, multiple capacitor elements may be housed inside a single outer case, as described in, for example, Japanese Patent Application Laid-Open No. 2012-69840.

[0101] In the film capacitor of the present invention, the portion where the lead terminal, such as a lead wire, is electrically connected to the external electrode of the capacitor element is located in a small area of ​​the external electrode, so that if a load is applied to the lead terminal, the lead terminal may separate from the external electrode. Therefore, it is preferable that a filling resin is positioned inside the outer case on the outside of the external electrode of the capacitor element and the lead terminal to tightly fix them together. This allows the filling resin to reinforce the connection between the lead terminal and the external electrode, preventing them from separating, even if a load is applied to the protruding portion of the lead terminal.

[0102] The connection position between the external electrode and the lead-out terminal is not particularly limited, and may be, for example, the center of the external electrode as shown in FIG. 1, or may be on the case opening side as shown in FIG. 1 of Japanese Patent No. 4733566, or may be on the case bottom side.

[0103] The present specification discloses the following:

[0104] <1> A film capacitor comprising: a capacitor element including an element body and an external electrode provided on an end surface of the element body; and a lead terminal electrically connected to the external electrode, wherein the element body is a laminate including a metallized film having a metal layer provided on at least one main surface of a dielectric film, the external electrode being connected to the metal layer, the lead terminal being welded to the external electrode, the surface roughness Ra of the external electrode being 20 μm or more and 45 μm or less, and the embedding depth of the lead terminal from the surface of the external electrode being 0.5 mm or more.

[0105] <2> The film capacitor according to <1>, wherein the lead terminals have a depth of penetration from the surfaces of the external electrodes of 0.7 mm or more.

[0106] <3> The film capacitor according to <1> or <2>, wherein the depth of the lead terminal from the surface of the external electrode to which the lead terminal is inserted is equal to or less than the thickness of the welded portion of the lead terminal.

[0107] <4> The film capacitor according to any one of <1> to <3>, wherein the thickness of the welded portion of the lead-out terminal is 0.5 mm or more.

[0108] <5> The film capacitor according to any one of <1> to <4>, wherein the welded portion of the lead-out terminal is flat.

[0109] <6> The film capacitor according to any one of <1> to <5>, wherein the extraction terminal is a lead wire.

[0110] <7> The film capacitor according to any one of <1> to <6>, wherein the laminate is a wound body in which the metallized film is wound in a laminated state.

[0111] EXAMPLES Hereinafter, examples will be given that more specifically disclose the film capacitor of the present invention, but the present invention is not limited to these examples.

[0112] A film capacitor having the same structure as that shown in FIG. 1 was prepared.

[0113] A lead wire having an outer diameter of 1.2 mm was used as the lead terminal. The welded portion of the lead wire was processed into a flat plate having a thickness of 0.75 mm.

[0114] By changing the spraying conditions (for example, spray pressure) when forming the external electrodes, the surface roughness Ra of the external electrodes was adjusted to fall within the range of 20 μm to 45 μm.

[0115] By changing the displacement of the welding machine, the bite depth of the lead wire, which is the extraction terminal, was changed in the range of 0.2 mm to 0.75 mm.

[0116] The film capacitor was subjected to the following tensile test to evaluate the bonding strength between the external electrodes and the lead terminals.

[0117] FIG. 12 is a schematic diagram for explaining the tensile test.

[0118] As shown in FIG. 12, capacitor element 10 connected to lead-out terminal 20 was fixed, and lead-out terminal 20 was bent in the direction of the winding axis (the direction indicated by the arrow in FIG. 12), and the tensile strength in the same axis direction was measured.

[0119] One of the lead terminals was pulled outward in the direction of the winding axis, and the tensile strength at which the lead terminal peeled off from the external electrode was measured using a digital force gauge (ZTA-50N, manufactured by Imada Co., Ltd.). This tensile strength was taken as the bond strength between the external electrode and the lead terminal. The results are shown in Table 1.

[0120] A bonding strength of 7 N or more, preferably 8 N or more, was evaluated as having sufficient bonding strength. In Table 1, a minimum bonding strength of less than 7 N was evaluated as x (poor), a minimum bonding strength of 7 N or more but less than 8 N was evaluated as ◯ (good), and a minimum bonding strength of 8 N or more was evaluated as ⊚ (excellent).

[0121]

[0122] From Table 1, it can be seen that there is a correlation between the bite depth of the lead wire and the joint strength, and that sufficient joint strength is ensured when the bite depth of the lead wire is 0.5 mm or more.

[0123] Furthermore, when the surface roughness Ra of the external electrodes was 20 μm or more and 45 μm or less, the temperature at which the dimensional change rate measured by thermomechanical analysis (TMA) reached 5% was 300° C. or less. In contrast, when the surface roughness Ra of the external electrodes was 12 μm, for example, the temperature at which the dimensional change rate measured by TMA reached 5% was 383° C. From these results, it is believed that if the surface roughness Ra of the external electrodes is 20 μm or more and 45 μm or less, welding can be performed at a temperature of 300° C. or less, and therefore the lead terminal can be driven into the external electrode in a short time without damaging the capacitor element.

[0124] The dimensional change rate of the external electrode is calculated as follows. <TMA measurement mode> Penetration mode <TMA measurement method: Calculation of dimensional change rate> The external electrode is cut into a predetermined size to prepare a sample. The sample size can be approximately 5 mm x 5 mm. An indenter is placed in the center of the surface of the sample, and while applying a load of 100 gf to the indenter, the sample is heated to 450°C at a heating rate of 10°C / min. The penetration depth of the indenter from the start of measurement until the sample is heated to 450°C is measured. This penetration depth is divided by the thickness of the sample and multiplied by 100. This procedure is also performed on four samples obtained by cutting out other portions of the external electrode. The average of the five obtained values ​​is taken as the dimensional change rate of the external electrode.

[0125] In other words, when the surface roughness Ra of the external electrodes is 20 μm or more and 45 μm or less, when the electrodes are heated to 450°C and measured, the temperature at which the dimensional change rate of the external electrodes becomes 5% (the temperature at which the indenter penetrates 5%) is 300°C or less in all cases.

[0126] REFERENCE SIGNS LIST 1 film capacitor 10 capacitor element 11 element body 12 external electrode 20 lead terminal 30 exterior case 31 opening 32 bottom wall 33 side wall 33a recess 40 filled resin 51 first metallized film 52 second metallized film 53 first dielectric film 54 second dielectric film 55 first metal layer 56 second metal layer 80 welding electrode D penetration depth of lead terminal from surface of external electrode

Claims

1. A capacitor element including an element body and an external electrode provided on an end surface of the element body; a lead terminal electrically connected to the external electrode; the element body is a laminate including a metallized film having a metal layer provided on at least one main surface of a dielectric film, the external electrode is connected to the metal layer; The lead terminal is welded to the external electrode, The surface roughness Ra of the external electrode is 20 μm or more and 45 μm or less, A film capacitor, wherein the embedding depth of the lead terminal from the surface of the external electrode is 0.5 mm or more.

2. 2. The film capacitor according to claim 1, wherein a depth of the lead terminal from a surface of the external electrode to the lead terminal is 0.7 mm or more.

3. 3. The film capacitor according to claim 1, wherein a depth of the lead terminal from a surface of the external electrode to which the lead terminal is inserted is equal to or less than a thickness of a welded portion of the lead terminal.

4. 3. The film capacitor according to claim 1, wherein the welded portion of the leader terminal has a thickness of 0.5 mm or more.

5. The film capacitor according to claim 1 , wherein the welded portion of the leader terminal is flat.

6. The film capacitor according to claim 1 , wherein the lead terminal is a lead wire.

7. 3. The film capacitor according to claim 1, wherein the laminate is a wound body in which the metallized film is wound in a laminated state.