Stacked capacitor, connected capacitor, inverter, and electric vehicle

A stacked capacitor includes a body having opposing faces, first side faces in a first direction, and second side faces in a second direction. The body includes a first insulation margin without a first metal film and a second insulation margin without a second metal film. The first metal film includes a metal film edge overlapping the second insulation margin. The second metal film includes a metal film edge overlapping the first insulation margin. The first and second metal films each include multiple sub-films separated by multiple first slits. A first slit includes a first portion extending from the first or second insulation margin along the first side faces and a second portion located in the metal film edge and extending at an angle with the first side faces. The second portion has a length in the first direction greater than or equal to an interval between adjacent first slits.

FIELD

The present disclosure relates to a stacked capacitor, a connected capacitor, an inverter, and an electric vehicle.

BACKGROUND

A film capacitor includes, for example, a polypropylene resin film as a dielectric layer and a metal film deposited on the surface of the dielectric layer by vapor deposition. The metal film is used as an electrode. The film capacitor with this structure can have defective electrical insulation in the dielectric layer that may cause a short-circuit. In this case, the energy from the short-circuit causes a portion of the metal film around the defective portion to evaporate and diffuse to insulate the defective portion of the dielectric layer. Film capacitors have such self-healing properties and are unlikely to cause dielectric breakdown.

As described above, film capacitors are unlikely to ignite or to cause electric shocks upon short-circuiting of electrical circuitry. Thus, film capacitors are now increasingly used in, for example, power supply circuits for light-emitting diodes (LEDs), motor drives for hybrid vehicles, and inverter systems for photovoltaic power generation.

Film capacitors can be classified into wound capacitors and stacked capacitors. Stacked film capacitors are typically obtained by cutting from a stack of multiple dielectric layers and metal films. Cutting the dielectric layers and the metal films simultaneously causes the metal films to be exposed on each cut surface. To reduce insulation deterioration at the cut surface, a portion of the metal films at the cut position may be removed or the metal films may be sectioned for insulation at the cut surface (refer to Patent Literatures 1 and 2).

CITATION LIST

Patent Literature

BRIEF SUMMARY

A stacked capacitor according to an aspect of the present disclosure includes a body and external electrodes on surfaces of the body. The body is a rectangular prism including one or more stacks each including a dielectric layer, a first metal film, and a second metal film. The first metal film and the second metal film face each other across the dielectric layer. The body has a pair of opposing faces located in a thickness direction of the dielectric layer, a pair of opposing first side faces connecting the pair of opposing faces, and a pair of opposing second side faces receiving the external electrodes. The first side faces are located in a first direction, and the external electrodes are located in a second direction. The body includes an active area in which the first metal film and the second metal film overlap each other across the dielectric layer, a first insulation margin in which a portion without the first metal film extends continuously in the first direction, and a second insulation margin in which a portion without the second metal film extends continuously in the first direction. The first metal film includes a metal film edge in the second insulation margin. The second metal film includes a metal film edge in the first insulation margin. The first metal film includes a plurality of sub-films separated from one another by a plurality of first slits, and the second metal film includes a plurality of sub-films separated from one another by a plurality of first slits. A first slit of the plurality of first slits includes a first portion extending from the first insulation margin or the second insulation margin along the first side faces and across the active area and a second portion located in the metal film edge and extending at an angle with the first side faces. The second portion has a length in the first direction greater than or equal to an interval between adjacent first slits of the plurality of first slits. The second portion at the metal film edge of the first metal film extends from a first end of the second portion connecting with the first portion to a second end in a direction opposite to a direction in which the second portion at the metal film edge of the second metal film extends from a first end of the second portion connecting with the first portion to a second end.

A connected capacitor according to another aspect of the present disclosure includes a plurality of capacitors, and a busbar electrically connecting the plurality of capacitors. The plurality of capacitors include the above stacked capacitor.

An inverter according to another aspect of the present disclosure includes a bridge circuit including a switching element, and an active area connected to the bridge circuit. The active area includes the above stacked capacitor.

An electric vehicle according to another aspect of the present disclosure includes a power supply, an inverter connected to the power supply, a motor connected to the inverter, and a wheel drivable by the motor. The inverter includes the above inverter.

DETAILED DESCRIPTION

As shown inFIGS.1and2, a stacked capacitor includes a body3and a pair of first and second external electrodes4aand4b. The body3includes one or more stacks of a first dielectric layer1a, a first metal film2a, a second dielectric layer1b, and a second metal film2b. The body3is a rectangular prism having a pair of opposing faces located in the stacking direction, a pair of opposing first side faces3cand3dconnecting the pair of faces in the stacking direction, and a pair of opposing second side faces3aand3b. The first and second external electrodes4aand4bare formed on the second side faces3aand3bas metallic contact parts. The opposing first side faces3cand3dof the body3are free of external electrodes. The first and second external electrodes4aand4bmay be simply referred to as external electrodes4.

As shown inFIG.2, the body3in a stacked capacitor A includes first metallized layers5aand second metallized layers5balternately stacked on each other. Each first metallized layer5aincludes the first metal film2aon a first surface lac of the first dielectric layer1a. Each second metallized layer5bincludes the second metal film2bon a first surface1bcof the second dielectric layer1b. The first metal film2ais electrically connected to the first external electrode4aat the second side face3aof the body3. The second metal film2bis electrically connected to the second external electrode4bat the second side face3bof the body3. As shown inFIG.1, a first direction x refers to the direction in which the first side faces3cand3dfree of external electrodes are arranged, and a second direction y refers to the direction in which the first external electrode4aand the second external electrode4bare arranged. A third direction z refers to the thickness direction of the first dielectric layers1aand the second dielectric layers1b. The third direction z is also the direction in which the first dielectric layer1aand the second dielectric layer1bare stacked.

FIG.2is a cross-sectional view taken along line II-II inFIG.1. InFIG.2, the first direction x is the longitudinal direction of the first dielectric layer1a, the second dielectric layer1b, the first metal film2a, and the second metal film2b. The second direction y is the width direction of the films and layers. The third direction z is the thickness direction of the films and layers.

The first dielectric layer1ain the stacked capacitor A has the first surface lac and a second surface lad intersecting with the third direction z, and a first side surface1aeand a second side surface1afintersecting with the second direction y. The second dielectric layer1bhas the first surface1bcand a second surface1bdintersecting with the third direction z, and a first side surface1beand a second side surface1bfintersecting with the second direction y.

The first metallized layer5aincludes the first dielectric layer1aand the first metal film2alocated on the first surface lac of the first dielectric layer1a. The first metallized layer5ahas a first insulation margin6aon the first surface lac adjacent to the second side surface1af. The first insulation margin6aincludes an uncovered portion of the first dielectric layer1aextending continuously in the first direction x.

The second metallized layer5bincludes the second dielectric layer1band the second metal film2blocated on the first surface1bcof the second dielectric layer1b. The second metallized layer5bhas a second insulation margin6bon the first surface1bcadjacent to the second side surface1bf. The second insulation margin6bincludes an uncovered portion of the second dielectric layer1bextending continuously in the first direction x.

As shown inFIG.2, the metallized layers5aand5bare stacked on each other with a slight deviation from each other in the second direction y, which is the width direction. One or more sets of the metallized layers5aand5bare stacked in the third direction z.

A potential difference across the first metal film2aand the second metal film2bcauses capacitance charging in an active area7in which the first metal film2aand the second metal film2boverlap each other across the first dielectric layer1aor the second dielectric layer1b.

The stacked capacitor A described above is obtained in the manner described below. The first metallized layer5aand the second metallized layer5bboth in an elongated shape are stacked on each other with a slight deviation from each other in the second direction y or the width direction. This forms a stack. The external electrode4ais formed on the second side face3ain the second direction y of the resultant stack, and the second external electrode4bis formed on the second side face3b. The stack including the first external electrode4aand the second external electrode4bis cut at predetermined intervals in the first direction x into individual stacked capacitors A. After the stack is cut, the external electrodes4may be formed on each body3.

The characteristic parts commonly of the first metallized layers5aand the second metallized layers5bin the stacked capacitor A according to one or more embodiments will be described below. InFIG.3, the components may be simply referred to as a dielectric layer1, a metal film2, or a metallized layer5without the reference signs a and b.

FIG.3shows the metallized layer5in an example. The metallized layer5includes the dielectric layer1and the metal film2located on a first surface1cof the dielectric layer1. The first surface1cof the dielectric layer1has an insulation margin6uncovered with the metal film2. The metal film2has a portion2dlocated in the active area7and adjacent to the insulation margin6and a metal film edge2clocated opposite to the insulation margin6adjacent to the portion2d. The metal film2includes multiple sub-films2iseparated from one another by multiple first slits8.

Each first slit8has a first portion8jextending from a first end N1in contact with the insulation margin6along the first side faces3cand3dacross the active area7, and a second portion8klocated in the metal film edge2cand extending at an angle with the first side faces3cand3d.

In other words, the first portion8jof the first slit8extends in the second direction y, and the second portion8kextends at an angle with the second direction y. With the body3being a rectangular prism, the second portion8kalso extends at an angle with the first direction x. The first portion8jextending along the first side face3cand3dor in the second direction y refers to the first portion8jforming an angle of 15° or less with the first side faces3cand3dor the second direction y. The first portion8jmay form an angle of 0° with the first side faces3cand3dor the second direction y. The second portion8kextending at an angle with the first side face3cand3dor in the second direction y refers to the second portion8kforming an angle greater than 15° with the first side faces3cand3dor the second direction y. The second portion8kmay form an angle less than 75° with the first side faces3cand3dor the second direction y.

In the second direction y, the first portion8jof the first slit8has a second end N2opposite to the first end N1. The second portion8khas an end nearer the active area7matching the second end N2and a third end N3away from the active area7. The second end N2connects the first portion8jand the second portion8k.

InFIG.3, each sub-film2iincludes a strip-shaped first sub-film2diextending along the first side faces3cand3din the active area7and a strip-shaped second sub-film2ciextending at an angle with the first side faces3cand3dat an end of the sub-film2iopposite to the insulation margin6.

The first portion8jof the first slit8may extend further to the metal film edge2cfrom the portion2dlocated in the active area7. The second portion8klocated in the metal film edge2cdoes not extend to the portion2din the active area7. In other words, the second portion8khas its second end N2and third end N3both at the metal film edge2c.

The second portion8khas a length L1in the first direction x and a length L2in the second direction y. The length L1is equal to or greater than an interval g between adjacent first slits8in the first direction x.

For example, the metal film2may be cut in the second direction y along the broken line S as shown inFIG.3.FIG.4is a perspective view of two bodies3-1and3-2obtained by cutting a stack. The stack inFIG.4contains the metal film2shown inFIG.3. The body3-1in the left part ofFIG.4has the first side face3don the cut surface, and the body3-2in the right part ofFIG.4has the first side face3con its cut surface.

As shown inFIG.3, a portion of the metal film2on the left of the broken line S or a cut section S is located on the first side face3dof the body3-1, and a portion of the metal film2on the right of the cut section S is located on the first side face3cof the body3-2. InFIG.3, when the second portion8kof the first slit8having the length L1in the first direction x is greater than or equal to the interval g between adjacent first slits8, the first sub-film2diin the active area7and on the right of the cut section S in the active area7is insulated from the external electrodes4, independently of the position of the cut section S. InFIG.3, the double line arrows indicate the portion P of the metal film2insulated from the external electrodes4on the cut section S.

FIG.5is a diagram describing the arrangement of first slits8ain the first metal film2aand first slits8bin the second metal film2b. The first metallized layer5ashown in the upper part ofFIG.5and the second metallized layer5bshown in the lower part ofFIG.5are stacked on each other with a slight deviation from each other in the second direction y. One or more sets of the metallized layers are stacked on one another as shown inFIG.2. The portion2adof the first metal film2aand the portion2bdof the second metal film2boverlap each other across the first dielectric layer1aor the second dielectric layer1b, forming the active area7. The metal film edge2acof the first metal film2aoverlaps the second insulation margin6bof the second metallized layer5b. The metal film edge2bcof the second metal film2boverlaps the first insulation margin6aof the first metallized layer5a.

As shown inFIG.5, the second portion8akof the first metal film2aextends from the second end N2to the third end N3in a direction opposite to the direction in which the second portion8bkof the second metal film2bextends from the second end N2to the third end N3. In other words, in the first direction x, the second portion8akof the first metal film2aextends from the second end N2to the third end N3in a direction opposite to the direction in which the second portion8bkof the second metal film2bextends from the second end N2to the third end N3. The second portion8akextending from the second end N2to the third end N3in a direction opposite to the direction in which the second portion8bkextends from the second end N2to the third end N3may be simply referred as the second portion8akand the second portion8bkextending in opposite directions.

InFIG.5, the second portion8akof the first metal film2aand the second portion8bkof the second metal film2bextend in the opposite directions. In this case, the first metal film2ahas a portion indicated by the double line arrows Pa insulated from the external electrode4a, and the second metal film2bhas a portion indicated by the double line arrows Pb insulated from the external electrode4b. The double line arrows Pa indicate a portion of the first metal film2aon the right of the cut section S, or more specifically a portion including the first sub-films2adilocated in the active area7in the body3-2. The double line arrows Pb indicate a portion of the second metal film2bon the left of cut section S, or more specifically a portion including the first sub-films2bdilocated in the active area7in the body3-1. Hereafter, the double line arrows P may be simply referred to as arrows P, the double line arrows Pa may be as arrows Pa, and the double line arrows Pb may be as arrows Pb.

On the first side face3dof the body3-1on the left of the cut section S, the first sub-film2adifacing the first side face3dof the first metal film2aand in the active area7is electrically connected to the external electrode4athrough the second sub-film2aci. The first sub-film2bdifacing the first side face3dof the second metal film2band in the active area7is included in the portion indicated by the arrows Pb and insulated from the external electrode4b. On the first side face3cof the body3-2on the right of the cut section S, the first sub-film2adifacing the first side face3dof the first metal film2aand in the active area7is included in the portion indicated by the arrows Pa and electrically insulated from the external electrode4a. The first sub-film2bdifacing the first side face3cof the second metal film2band in the active area7is electrically connected to the external electrode4bthrough the second sub-film2bci.

Thus, on the first side faces3cand3d, either the first sub-film2adior the first sub-film2bdifacing the first side face3cor3dand in the active area7is electrically insulated from the external electrode4aor4b. With either the first sub-film2adior the first sub-film2bdibeing electrically insulated from the external electrode4aor4bon the first side face3cor3d, any contact between the first sub-film2adiand the first sub-film2bdion the first side face3cor3ddoes not increase the insulation deterioration on the first side faces3cand3d.

The third end N3may be aligned with the first side surface1aeof the dielectric layer1in the second direction y. The metal film2may include a portion extending continuously in the first direction x from the third end N3to the first side surface1ae.

The length L1of the second portion8kof each first slit8in the first direction x may be less than or equal to three times the interval g between adjacent first slits8. The first sub-film2dielectrically insulated from the external electrodes4does not contribute to capacitance charging near the first side faces3cand3d. When the first sub-film2di, not contributing to capacitance charging, has a large area, the stacked capacitor A has a smaller capacitance. With the length L1being less than or equal to three times the interval g, the area of the first sub-film2dinot contributing to capacitance charging can be smaller. The stacked capacitor A can thus have a larger capacitance.

The second portion8kof each first slit8in the second direction y may have a length L2less than the width w of the insulation margin6. More specifically, the second portion8akof each first slit8ain the first metal film2ain the second direction y may have a length La2less than the width wb of the second insulation margin6bof the second metallized layer5b. The second portion8bkof each first slit8bin the second metal film2bin the second direction y may have a length Lb2less than the width wa of the first insulation margin6aof the first metallized layer5a.

The first metallized layer5aand the second metallized layer5bare stacked on each other with a slight deviation from each other in the second direction y. The length La2may be less than or equal to the width wb. The length Lb2may be less than or equal to the width wa. The length La2is less than the sum of the width wb and the deviation width. The length Lb2is less than the sum of the width wa and the deviation width. With the length La2being less than the sum of the width wb and the deviation width, the second sub-film2acielectrically connected to the external electrode4aentirely overlaps the second insulation margin6bbut has no overlap with the second metal film2bin the third direction z. Thus, the second sub-film2aciand the second metal film2bare less likely to be in contact with each other on the cut surface S or on the first side faces3cand3d. With the length Lb2being less than the sum of the width wa and the deviation width, the second sub-film2bcielectrically connected to the external electrode4aentirely overlaps the first insulation margin6abut has no overlap with the first metal film2ain the third direction z. Thus, the second sub-film2bciand the first metal film2aare less likely to be in contact with each other on the cut surface S or on the first side faces3cand3d.

Each first sub-film2dimay include multiple small sections electrically connected with fuses10in the active area7. In the example shown inFIG.6, the first sub-film2didefined by the first slits8is divided into the small sections by multiple second slits9extending intermittently in the first direction x. Small sections adjacent to each other in the second direction y are electrically connected with a fuse10located between adjacent second slits9in the first direction x. Each second slit9may be at 0° with the first direction x. Each second slit9may be at 45° or less than 45° with the first direction x.

The arrangement shown inFIGS.3,5, and6may be reversed laterally.

FIG.7is a cross-sectional view of a series-connected stacked capacitor Ain an example. InFIG.7, the body3includes two capacitor units, or a first capacitor unit C1and a second capacitor unit C2connected in series.

Each first metal film2aincludes a first metal film2a1shown in the left part ofFIG.7and a first metal film2a2shown in the right part ofFIG.7. More specifically, the first metal film2aincludes the first metal film2a1and the first metal film2a2arranged in the second direction y. The first metal film2a1is electrically connected to the first external electrode4aat the second side face3aof the body3on the left. The first metal film2a2is electrically connected to the second external electrode4bat the second side face3bof the body3on the right.

Each first metallized layer5ahas, in its middle portion in the second direction y, a first insulation margin6aextending continuously in the first direction x. The first insulation margin6ais a portion of the first dielectric layer1ain which the first surface lac is uncovered with a metal film. The first metal films2a1and2a2are electrically insulated from each other by the first insulation margin6a.

Each second metallized layer5bhas, on its two ends in the second direction y, second insulation margins6b1and6b2that extend continuously in the first direction x. The second insulation margins6b1and6b2are portions of the second dielectric layer1bin which the first surface1bcis uncovered with a metal film. The second metal film2bis not electrically connected to the first external electrode4aor the second external electrode4b.

As shown inFIG.7, one or more sets of the first metallized layer5aand the second metallized layer5bare stacked on one another in the third direction z.

The series-connected stacked capacitor A includes the first capacitor unit C1and the second capacitor unit C2connected in series. The first capacitor unit C1is located in a portion of the active area7in which the first metal film2a1and the second metal film2bare stacked across the dielectric layer1aor1b. The second capacitor unit C2is located in a portion of the active area7in which the first metal film2a2and the second metal film2bare stacked across the dielectric layer1aor1b.

FIG.8shows a first metallized layer5ain an example. In the series-connected stacked capacitor A, the first metallized layer5aincludes the first metal film2a1shown in the lower part from the dot-and-dash line inFIG.8and the first metal film2a2shown in the upper part from the dot-and-dash line inFIG.8. The first metal film2a1includes a portion2a1dlocated adjacent to the first insulation margin6aand in the active area7and a metal film edge2a1clocated at the end of the portion2a1dopposite to the first insulation margin6a. The first metal film2a2includes a portion2a2dlocated adjacent to the first insulation margin6aand in the active area7and a metal film edge2a2clocated at the end of the portion2a2dopposite to the first insulation margin6a. InFIG.8, the width wa1or wa2of the first insulation margin6ain the first capacitor unit C1or the second capacitor unit C2is half the distance between the first metal film2a1and the first metal film2a2.

FIG.9shows a second metallized layer5bin an example, corresponding to the first metallized layer5ainFIG.8. The second metal film2bincludes a portion2b1dlocated adjacent to the second insulation margin6b1and in the active area7as shown in the lower part ofFIG.9, a portion2b2dlocated adjacent to the second insulation margin6b2and in the active area7as shown in the upper part ofFIG.9, and a metal film edge2bclocated between the portion2b1dand the portion2b2d. In other words, the metal film edge2bcis located at the end of the portion2b1dopposite to the second insulation margin6b1and at the end of the portion2b2dopposite to the second insulation margin6b2. For ease of explanation, although the metal film edge2bcis located in the middle of the second metallized layer5bin the second direction y inFIG.9, the position is referred to as, for ease of explanation, a metal film edge.

The series-connected stacked capacitor A may have the portions2a1d,2a2d,2b1d, and2b2dand the metal film edges2a1c,2a2c, and2bcarranged in the same manner as in the first slit8described above. This enhances the insulation at the first side faces3cand3dor the cut section. More specifically, the first metal films2a1and2a2and the second metal film2beach include the second portion8kwith a length La11, La12, Lb11, or Lb12in the first direction x greater than or equal to the interval g between adjacent first slits8in the first direction x. The second portion8akof the first slit8ain the first metal film2a1forming the first capacitor unit C1and the second portion8bkof the first slit8bin the second metal film2bextend in opposite directions, and the second portion8akof the first slit8ain the first metal film2a2forming the second capacitor unit C2and the second portion8bkof the first slit8bin the second metal film2bextend in opposite directions.

More specifically, in the first metal film2a1and the second metal film2bforming the first capacitor unit C1, the first metal film2a1extends in the first direction x from the second end N2to the third end N3in a direction opposite to the direction in which the second metal film2bextends from the lower second end N2to the lower third end N3. In the first metal film2a2and the second metal film2bforming the second capacitor unit C2, the first metal film2a2extends from the second end N2to the third end N3in the direction opposite to the direction in which the second metal film2bextends from the upper second end N2to the upper third end N3.

The third end N3of the first metal film2a1may be aligned with the first side surface1a1eof the first dielectric layer1ain the second direction y. The third end N3of the first metal film2a2may be aligned with the first side surface1a2eof the first dielectric layer1ain the second direction y. In this case, the second sub-films2a1ciand2a2ciare electrically connected to the external electrodes4. The first metal film2a1may include a portion extending continuously in the first direction x from the third end N3to the first side surface1a1e. The first metal film2a2may include a portion extending continuously in the first direction x from the third end N3to the first side surface1a2e. In this case, the portion of each metal film extending continuously in the first direction x is electrically connected to the corresponding external electrode4.

As shown inFIG.9, the second metal film2bmay or may not include, from the second sub-films2b1cito the second sub-films2b2ci, a portion extending continuously in the first direction x without being separated by slits.

In the example shown inFIGS.8and9, the first metal film2a1extends, in the first direction x, from the second end N2to the third end N3in the same direction as the first metal film2a2. The first metal film2a1may extend, in the first direction x, from the second end N2to the third end N3in the direction opposite to the direction in which the first metal film2a2extends from the second end N2to the third end N3. The second metal film2bmay extend, in the first direction x, from the upper second end N2to the upper third end N3in a direction opposite to the direction in which the second metal film2bextends from the lower second end N2to the lower third end N3.

The dielectric layers1in the stacked capacitor A may include resin films. In other words, the stacked capacitor A may be a stacked film capacitor including resin films as the dielectric layers1. Examples of insulating materials for the dielectric layers1in the film capacitor include polypropylene (PP), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), polyarylate (PAR), polyphenylene ether (PPE), polyetherimide (PEI), and cycloolefin polymers (COP). In particular, polyarylate (PAR) has a high dielectric breakdown voltage.

The resin films may have an average thickness of 0.7 μm or greater or 4 μm or less. Resin films having an average thickness of 0.7 μm or greater are highly slidable with the metal films2and have high dielectric breakdown voltage. Resin films having an average thickness of 4 μm or less can increase capacitance.

The metal films2may include, for example, aluminum as a main component. The metal films2have an average thickness of, for example, 14 to 70 nm. The metal films2having a thickness (an average thickness) of 14 to 70 nm closely adhere to the dielectric layers1and are less breakable under tension applied to the metallized layers5. The metal films2thus have a sufficient active area contributing to capacitance charging. The metal films2having an average thickness of 14 nm or greater are less likely to decrease capacitance at dielectric breakdown and increase the dielectric breakdown voltage. The metal films2having an average thickness of 70 nm or less remain self-healing and increase the dielectric breakdown voltage. The average thickness of the metal films2can be evaluated by observing cross sections of the metallized layers5processed by ion milling using, for example, a scanning electron microscope (SEM).

The metal films2may have a heavy-edge structure at least near the connection to the external electrodes4. Near the connections to the external electrodes4is, in other words, near the first side surfaces1eof the dielectric layers1. The metal films2with the heavy-edge structure is, for example, thicker and less electrically resistant near the connections to the external electrodes4than in the active area7in which the first metal film2aand the second metal film2boverlap each other. The heavy-edged portions of the metal films2near the connections to the external electrodes4may be referred to as heavy-edge portions.

The film thickness of the metal films2near the connections to the external electrodes4is, for example, twice or more the film thickness for enabling self-healing, or more specifically 20 nm or greater. The film thickness of the metal films2in the heavy-edge portions may be 80 nm or less. The metal films2with the heavy-edge portions have improved electrical connection to the external electrodes4. Additionally, the metal films2electrically connected to the external electrodes4with the less resistant heavy-edge portions can reduce the equivalent series resistance (ESR) of the stacked capacitor A.

The heavy-edge portions of the first metallized layers5aoverlap the insulation margins6bof the second metallized layers5b, and the heavy-edge portions of the second metallized layers5boverlap the insulation margins6aof the first metallized layers5a. The heavy-edge portions may have a width of, for example, 0.5 mm or greater in the second direction y. The heavy-edge portions may have a width of 3 mm or less in the second direction y.

The film capacitor, or more specifically the stacked capacitor A, including resin films as the dielectric layers1, may be fabricated in the manner described below. The dielectric layers1are first prepared. The dielectric layers1are obtained by, for example, preparing a resin solution in which an insulating resin is dissolved in a solvent, shaping the resin solution on the surface of a base film made of, for example, PET into a sheet, and drying the sheet to volatilize the solvent. The shaping method may be selected as appropriate from known film deposition methods including doctor blading, die coating, and knife coating. Examples of the solvent used for shaping include methanol, isopropanol, n-butanol, ethylene glycol, ethylene glycol monopropyl ether, methyl ethyl ketone, methyl isobutyl ketone, xylene, propylene glycol monomethyl ether, a propylene glycol monomethyl ether acetate, dimethylacetamide, cyclohexane, and an organic solvent containing a mixture of two or more solvents selected from the above solvents. In another example, a resin film formed by melt extrusion may be drawn.

The dielectric layers1may include the above insulating resin alone or may include other materials. The materials that may be included in the dielectric layers1other than resin include, for example, the above organic solvent and inorganic fillers. Example of the inorganic fillers include inorganic oxides such as alumina, titanium oxide, and silicon dioxide, inorganic nitrides such as silicon nitride, and glass. In particular, a material with a high relative dielectric constant such as a composite oxide having a perovskite structure may be used as an inorganic filler. In this case, the dielectric layer1has a higher relative dielectric constant in total and the stacked capacitor A can be smaller. The inorganic filler may be surface-treated by, for example, silane coupling or titanate coupling. The surface-treated inorganic filler is more compatible with the resin.

The dielectric layers1may be composite films containing less than 50 mass % of the above inorganic filler and 50 mass % or more than 50 mass % of resin. The dielectric layers1being composite films have a higher relative dielectric constant and other effects with the inorganic filler while remaining flexible as resin. The inorganic filler may have an average particle diameter of, for example, 4 to 1000 nm.

The resultant fabricated dielectric layers1are peeled off from the base film, and a metal component such as aluminum (Al) is deposited on one surface of each dielectric layer1by vapor deposition to form the metal films2. This forms the metallized layers5. The first slits8having a pattern may be formed on each metal film2by, for example, oil transfer patterning or laser patterning. In oil transfer patterning, each dielectric layer1is covered with an oil mask, and a metal component is deposited by vapor deposition. In laser patterning, a metal component is deposited on each dielectric layer1by vapor deposition, and the metal film2is then partially evaporated using a laser beam. The second slits9may be formed in the metal films2in the same manner.

The heavy-edge structure is formed by masking portions of the metallized layers5other than portions in which heavy-edge portions are to be formed as described above, and depositing, by vapor deposition, for example zinc (Zn) on the unmasked portions of the deposited metal component described above. The film to be deposited as the heavy-edge portions may have a thickness one to three times the thickness of the deposited metal component described above.

The first metallized layer5aand the second metallized layer5bare stacked on each other as a set with a slight deviation from each other in the width direction or the second direction y, and are wound around an annular winding core. The wound stack is cut in the second direction y to obtain the bodies3of stacked capacitors A. The annular winding core may also be referred to as a drum.

The external electrodes4aand4bare formed as metallic contact electrodes on the two end faces of each resultant body3in the second direction y or on the second side faces3aand3bto obtain the stacked capacitor A. For example, the external electrodes4may be formed by, for example, metal thermal spraying, sputtering, or plating. The external electrodes4may be formed before the stack is cut.

The outer surface of each resultant stacked capacitor A may be covered with an external package (not shown).

The external electrodes4may include metals such as Zn and alloys, other than Al described above.

The metallic contact electrodes may include at least one metal material selected from the group consisting of zinc, aluminum, copper, and solder.

FIG.10is a schematic perspective view of a connected capacitor in an example. InFIG.10, for ease of explanation, the external package covering the case and the surface of the capacitor is not shown. A connected capacitor B includes multiple capacitors D connected in parallel with a pair of busbars21and23. The busbars21and23include terminals21aand23afor external connection and lead terminals21band23b. The lead terminals21band23bare connected to the external electrodes of the capacitors D.

The connected capacitor B including the stacked capacitors A as the capacitors D achieves high insulation.

The connected capacitor B may include at least one stacked capacitor A, and may include two or more stacked capacitors A. The connected capacitor B includes multiple capacitors D, for example four capacitors D as inFIG.10, which are arranged side by side with the external electrodes on the two ends of each body connected to the busbars21and23with a bond.

The connected capacitor B may include the capacitors D arranged horizontally as shown inFIG.10or stacked vertically. The capacitors D may be arranged to have their external electrodes arranged vertically, or in the second direction y aligned with a vertical direction.

The capacitors D or the connected capacitor B may be placed in a case having a gap filled with resin to form a resin-molded capacitor or a case-molded capacitor.

FIG.11is a schematic diagram of an inverter in an example.FIG.11shows an inverter E that converts direct current to alternating current. As shown inFIG.11, the inverter E includes a bridge circuit31and a capacitor33. The bridge circuit31includes switching elements such as insulated gate bipolar transistors (IGBTs) and diodes. The capacitor33is located across the input terminals of the bridge circuit31to stabilize the voltage. The inverter E includes the stacked capacitor A as the capacitor33.

The inverter E is connected to a booster circuit35that raises the voltage of a DC power supply. The bridge circuit31is connected to a motor generator MG as a drive source.

FIG.12is a schematic diagram of an electric vehicle.FIG.12shows a hybrid electric vehicle (HEV) as an example of the electric vehicle.

An electric vehicle F includes a driving motor41, an engine43, a transmission45, an inverter47, a power supply49or a battery49, front wheels51a, and rear wheels51b.

The electric vehicle F includes an output unit, such as the motor41, the engine43, or both, as a drive source. The output from the drive source is transmitted to the pair of left and right front wheels51athrough the transmission45. The power supply49is connected to the inverter47, which is connected to the motor41.

The electric vehicle F shown inFIG.12also includes a vehicle electronic control unit (ECU)53and an engine ECU57. The vehicle ECU53centrally controls the entire electric vehicle F. The engine ECU57controls the rotation speed of the engine43and drives the electric vehicle F. The electric vehicle F further includes an ignition key55operable by, for example, a driver and driving components such as an accelerator pedal and a brake (not shown). The vehicle ECU53receives an input of a drive signal in response to an operation on a driving component performed by, for example, a driver. The vehicle ECU53outputs, based on the drive signal, an instruction signal to the engine ECU57, the power supply49, and the inverter47as a load. In response to the instruction signal, the engine ECU57controls the rotation speed of the engine43and drives the electric vehicle F.

The inverter47in the electric vehicle F includes the inverter E, which includes the stacked capacitor A as the capacitor33. The electric vehicle F includes the stacked capacitor A that is highly insulating and has insulation resistance less likely to decrease. In a harsh environment such as in an engine part of the electric vehicle F, the stacked capacitor A can have insulation resistance less likely to decrease over a long period. The electric vehicle F thus allows more stable current control performed by controllers such as ECUs.

In addition to EHVs, the inverter E according to the embodiment is also applicable to various power converting products such as electric vehicles (EVs), fuel cell vehicles, electric bicycles, power generators, and solar cells.

EXAMPLES

A dielectric layer with an average thickness of 3 μm was prepared with polyarylate (U-100, Unitika). Polyarylate was dissolved in toluene, applied onto a base film made of polyethylene terephthalate (PET) using a coater, and shaped into a sheet. After shaping, the sheet was heat-treated at 130° C. to remove toluene to form a dielectric layer.

The dielectric layer was peeled off from the base film and slit into strips each with a width of 200 or 130 mm. A metal film was then formed on one surface of the dielectric layer by vacuum deposition.

The dielectric layer with a width of 200 mm was coated with a metal film in the manner described below. First, the surface of the dielectric layer opposite to the surface previously facing the base film was covered with an oil mask. An Al metal film with a width of 52 mm was formed in the middle of the dielectric layer in the width direction or the first direction x. The average thickness of the Al metal film is 20 nm. Subsequently, using a metal mask, a Zn metal film with a width of 8.8 mm was formed in the middle of the Al metal film in the width direction as a heavy-edge portion. The average thickness of the Zn metal film is 40 nm.

The middle portion and the two ends in the width direction of the dielectric layer with the metal films were slit into a metallized layer with a width of 28 mm. The width of an insulation margin of the resulting metallized layer is 1 mm, and the width of the heavy-edge portion is 4.4 mm. The heavy-edge portion of the metallized layer is a continuous metal film.

As shown in Table 1, the first slits8shown in one ofFIG.5,13, or14were formed in each sample Al metal film using an oil mask. InFIG.5, the lengths La1and Lb1are equal, the length La2and Lb2are equal, and the widths wa and wb are equal. In Table 1 andFIG.13, L1indicates the lengths La1and Lb1, and L2indicates the lengths La2and Lb2. In Table 1 andFIGS.13and14, w indicates the widths wa and wb. The width of the first slit is 0.2 mm, with g indicating the interval between adjacent first slits, or more specifically the interval between the centers of the widths of the adjacent slits.

InFIG.5, as described above, the second portion of each first slit in the first metal film extends from the second end to the third end in a direction opposite to the direction in which the second portion of each first slit in the second metal film extends from the second end to the third end. InFIG.13, the second portion of each first slit in the first metal film extends from the second end to the third end in the same direction as the second portion of each first slit in the second metal film extends from the second end to the third end. InFIG.14, each first slit includes the first portion alone without the second portion.

A first metallized layer and a second metallized layer were stacked on each other with their heavy-edge portions located oppositely in the first direction x and protruding in the second direction y by 0.5 mm. The stacked first and second metallized layers were wound 450 times on a drum with a diameter of 200 mm to obtain a roll including multiple film capacitors connected annularly. The first metallized layer and the second metallized layer were stacked to have the dielectric layer between the first metal film and the second metal film.

The resultant roll was cut into stacks to be bodies with a width of 50 mm in the second direction y. Zn was arc sprayed onto the two ends of each resultant body at which the first metal film and the second metal film were exposed or onto the second (first) side face of each body, forming metallic contact electrodes as external electrodes. This completes fabrication of stacked film capacitors.

The capacitance, the dielectric loss (dissipation factor DF), and the withstand voltage of each fabricated stacked film capacitor were measured. The capacitance and the dielectric loss (DF) were measured using an LCR meter at 1 VAC and 1 kHz. The withstand voltage was evaluated by applying a DC voltage of 0 to 900 V to the stacked film capacitors using an insulation resistance meter. In the test, a DC voltage of 0 to 900 V was applied to the stacked film capacitors at a boosting rate of 10 V per second. The voltage at which the leakage current reached 0.01 A was determined as the withstand voltage of the stacked film capacitors.

For samples 1 to 3, the length L1is greater than or equal to the interval g, and the directions in which the second portions of the first slits in the first metallized layer extend and those in the second metallized layer extend are opposite. Samples 1 to 3 each show high insulation at the cut surface and a leakage current of 0.01 A or less under an applied DC voltage of 900 V.

Sample 4 has the same structure as sample 1 except that the second portions of the first slits in the first metallized layer and those in the second metallized layer extend in the same direction. Sample 4 shows a lower withstand voltage. Sample 5, with each first slit including the first portion alone without the second portion, shows a lower withstand voltage.

The present disclosure may be embodied in various forms without departing from the spirit or the main features of the present disclosure. The embodiments described above are thus merely illustrative in all respects. The scope of the present disclosure is defined not by the description given above but by the claims. Any modifications and alterations contained in the claims fall within the scope of the present invention.

REFERENCE SIGNS LIST