Film capacitor and method for producing film capacitor

Abstract

Provided is a film capacitor in which a dimensional change upon exposure to a high-temperature environment is suppressed. A film capacitor (10) comprises a capacitor element (20) including a winding element (21) having end faces (216) perpendicular to a winding axis (O), and end-face electrodes (22) provided on the end faces (216). The winding element (21) includes a wound body (211) and an outer wrapping film (215) wound around the outer periphery of the wound body (211). The wound body (211) is formed by winding, about the winding axis (O), a metallized film (212) including a dielectric film (213) and a metal film (214) provided on the dielectric film (213). An outer peripheral surface (30) of the capacitor element (20) has a pair of flat portions (31) facing each other. The dielectric film (213) sampled from the flat portion (31) exhibits a dimensional change rate of 0.6% or less in the direction along the winding axis (O) when heated from 25°C to 130°C at a heating rate of 5°C / min under a load of 0.3 MPa, as measured by thermomechanical analysis.

Description

Film Capacitor and Method for Manufacturing Film Capacitor

[0001] The present disclosure generally relates to a film capacitor and a method for manufacturing a film capacitor, and more specifically relates to a film capacitor including a capacitor element and a method for manufacturing this film capacitor.

[0002] Patent Document 1 discloses a wound film capacitor using a metal film laminated film. This metal film laminated film includes an olefin-based laminated film having breaking elongation, dimensional stability in a high-temperature region and insulation performance, and a metal film provided on at least one side of the olefin-based laminated film.

[0003] However, for the film capacitor using the olefin-based laminated film of Patent Document 1, when exposed to a high-temperature condition during heat treatment for removing residual stress in the manufacturing process and use of the film capacitor, the dimensional change of the capacitor element becomes large, which may cause problems such as poor connection with external equipment and deterioration of electrical characteristics.

[0004] International Publication No. WO2017 / 022706

[0005] An object of the present disclosure is to provide a film capacitor with suppressed dimensional change when exposed to a high-temperature environment and a method for manufacturing the film capacitor.

[0006] A film capacitor according to one aspect of the present disclosure includes a capacitor element including: a wound element having an end face perpendicular to a winding axis, the wound element including a wound body obtained by winding a metallized film around the winding axis, the metallized film including a dielectric film and a metal film provided on the dielectric film, and an exterior film wound around an outer periphery of the wound body; and an end face electrode provided on the end face. An outer peripheral surface of the capacitor element has a pair of flat portions facing each other. A dimensional change rate of the dielectric film sampled from the flat portion in a direction along the winding axis is 0.6% or less when the temperature is increased from 25°C to 130°C by thermomechanical analysis under the conditions of a load of 0.3 MPa and a temperature increase rate of 5°C / min.

[0007] A method for manufacturing a film capacitor according to one aspect of the present disclosure comprises a first step, a second step, a third step, a fourth step, and a fifth step. In the first step, a metallized film comprising a dielectric film and a metal film provided on the dielectric film is wound around a winding shaft to form a winding body. In the second step, an outer film is wound around the outer circumference of the winding body to form a winding element. In the third step, the winding element is pressed in one direction perpendicular to the winding shaft to form a flattened shape. In the fourth step, an end electrode is provided on the end face of the winding element perpendicular to the winding shaft to form a capacitor element. In the fifth step, the capacitor element is heated to a temperature of 130°C or higher. The outer surface of the capacitor element has a pair of flat portions facing each other. The dielectric film taken from the flat portion after the fifth step exhibits a dimensional change rate of 0.6% or less in the direction along the winding axis when heated from 25°C to 130°C under conditions of a load of 0.3 MPa and a heating rate of 5°C / min, as determined by thermomechanical analysis.

[0008] Figure 1 is a perspective view showing a film capacitor according to an embodiment. Figure 2 is a perspective view showing part of the manufacturing process of the film capacitor according to an embodiment. Figure 3 is a perspective view showing part of the manufacturing process of the film capacitor according to an embodiment. Figure 4 is a perspective view showing part of the manufacturing process of the film capacitor according to an embodiment. Figure 5 is a perspective view showing part of the measurement locations of the film capacitor in the evaluation of the embodiment. Figure 6 is a perspective view showing part of the measurement locations of the film capacitor in the evaluation of the embodiment. Figure 7 is a perspective view showing part of the measurement locations of the film capacitor in the evaluation of the embodiment.

[0009] The film capacitor according to the embodiment will be described below with reference to the drawings. The figures described in the following embodiments are schematic diagrams, and the ratios of the size and thickness of each component do not necessarily reflect the actual dimensional ratios. Furthermore, the configuration described in the following embodiments is merely one example of the disclosure. The disclosure is not limited to the embodiments described below, and various modifications are possible depending on the design, etc., as long as the effects of the disclosure can be achieved.

[0010] In Figures 1 and 4-7, the front-to-back, left-to-right, and up-to-down directions of the Cartesian coordinate system are defined. The terms used in this disclosure to indicate directions such as "front," "back," "up," "down," "left," and "right" are used solely to describe the embodiments, and these terms do not limit the usage conditions of the film capacitor.

[0011] Furthermore, in Figures 2 and 3, the Z, R, and θ directions of the cylindrical coordinate system are defined. The θ direction is the winding direction of the metallized film and is the mechanical direction (MD) of the dielectric film. The Z direction is the direction along the winding axis and is perpendicular to the mechanical direction (TD direction, width direction) in the dielectric film, corresponding to the front-to-back direction in the Cartesian coordinate system. The +Z direction is the direction from the second end face toward the first end face and corresponds to the "forward" direction. The -Z direction is the opposite direction of the +Z direction. The R direction is the radial direction of the winding element. The +R direction is the direction away from the winding axis. The -R direction is the opposite direction of the +R direction.

[0012] 1. Overview The film capacitor 10 comprises a winding body 211 in which a metallized film 212 comprising a dielectric film 213 and a metal film 214 provided on the dielectric film 213 is wound around a winding shaft O, and an outer film 215 wound around the outer circumference of the winding body 211, and a capacitor element 20 comprising a winding element 21 having an end face 216 perpendicular to the winding shaft O, and an end face electrode 22 provided on the end face 216. The outer circumferential surface 30 of the capacitor element 20 has a pair of opposing flat portions 31. The dielectric film 213 taken from the flat portions 31 has a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under the conditions of a load of 0.3 MPa and a heating rate of 5°C / min by thermomechanical analysis (TMA) in the direction along the winding shaft O.

[0013] By having the above configuration, the film capacitor 10 of this embodiment can suppress dimensional changes when exposed to a high-temperature environment.

[0014] In this disclosure, "high-temperature environment" refers to a temperature between 130°C and 145°C.

[0015] 2. Embodiments 2.1 Configuration The configuration of the film capacitor 10 according to the embodiment will be described with reference to Figures 1 to 4.

[0016] (Capacitor element) The capacitor element 20 has a rounded rectangular column shape extending in the front-to-back direction (see Figure 1). Therefore, the capacitor element 20 has a rounded rectangular shape when viewed from the front, and a rectangular shape when viewed from the top and side. A rounded rectangle is, for example, a shape in which semicircles with diameters equal to the short sides of a rectangle are attached to the two short sides of the rectangle. The shape of the capacitor element 20 is not limited to a rounded rectangular column, and examples include a cylindrical shape, an oval column shape, etc.

[0017] The capacitor element 20 comprises a wound element 21 and a pair of end-face electrodes 22. The pair of end-face electrodes 22 are a first end-face electrode 22a and a second end-face electrode 22b that face each other in the front-rear direction, and each has a rounded rectangular shape.

[0018] The capacitor element 20 has an outer circumferential surface 30 connecting a pair of end face electrodes 22. This outer circumferential surface 30 has a pair of opposing flat portions 31 and a pair of curved portions 32 connecting the pair of flat portions 31. The pair of flat portions 31 face each other in the vertical direction of the capacitor element 20. The pair of curved portions 32 face each other in the left-right direction of the capacitor element 20.

[0019] <Winding Element> The winding element 21 is the main body of the capacitor element 20. The winding element 21 may, for example, be a rounded rectangular column extending in the front-to-back direction, similar to the capacitor element 20, and its shape is not particularly limited.

[0020] The winding element 21 has a pair of end faces 216 and an outer circumferential surface. The pair of end faces 216 are a first end face 216a and a second end face 216b that face each other in the front-rear direction. When the winding element 21 is in the shape of a rounded rectangular column, the first end face 216a and the second end face 216b are each in the shape of a rounded rectangle. The outer circumferential surface is a surface other than the pair of end faces 216, and is the surface that connects the outer circumference of the first end face 216a and the outer circumference of the second end face 216b.

[0021] The winding element 21 comprises a winding body 211 and an outer film 215.

[0022] <<Wound Body>> The wound body 211 is formed by winding a metallized film 212 around a winding axis O (see Figure 2). Therefore, the winding axis O extends along the front-rear direction and extends so as to connect the center of the first end face 216a and the center of the second end face 216b. That is, the pair of end faces 216 are perpendicular to the winding axis O. In this embodiment, the wound body 211 is formed by winding a pair of metallized films 212 around a winding axis.

[0023] The metallized film 212 comprises a dielectric film 213 and a metal film 214 provided on the dielectric film 213. The metal film 214 is formed, for example, by metal deposition onto the dielectric film 213. The pattern of the metal film 214 formed on the dielectric film 213 in a pair of metallized films 212 is not particularly limited, as long as one metal film 214 is exposed at the first end face 216a and the other metal film 214 is exposed at the second end face 216b. In this embodiment, the metal film 214 is formed on one surface of each of the pair of metallized films 212 in such a way that they are mirror-symmetric when facing each other. The pattern of the metal film 214 on the metallized film 212 is not particularly limited, and for example, various known patterns can be used. In Figure 2, the pattern of the metal film 214 on the metallized film 212 is shown in a simplified manner. Furthermore, inside the wound body 211, the pair of metal films 214 face each other via the dielectric film 213. This results in the emergence of capacitance.

[0024] The metallized film 212 may further comprise a metal oxide film provided on the dielectric film 213 (not shown). The metal oxide film may be provided on the dielectric film 213, between the dielectric film 213 and the metal film 214, or on the metal film 214.

[0025] The winding body 211 may have a winding core 217. The winding core 217 is wound with an electrically insulating film and is arranged along the winding axis O. The material of the film is not particularly limited, but examples include polypropylene (PP) and polyethylene terephthalate (PET).

[0026] The dielectric film 213 is a high heat-resistant film. A high heat-resistant film in dielectric film 213 is defined as having a shrinkage initiation temperature measured by thermomechanical analysis in the width direction (TD direction) of the original film roll, for example, 130°C or higher, and a shrinkage initiation temperature measured by thermomechanical analysis in the winding direction (MD direction) when used as a film capacitor 10, for example, 135°C or higher. In this case, dimensional changes of the film capacitor 10 exposed to a high-temperature environment can be further suppressed. The material of the dielectric film 213 is not particularly limited as long as it satisfies the above-mentioned shrinkage initiation temperature, but examples include cyclic olefin (COC) resin, polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polyphenylene sulfide (PPS) resin, polycarbonate (PC) resin, polystyrene (PS) resin, etc.

[0027] Furthermore, the dielectric film 213 may further contain, for example, polypropylene (PP) resin, to improve film processability, etc., provided that the shrinkage initiation temperature determined by thermomechanical analysis does not fall outside the above range. When two or more resins are used as the material for the dielectric film 213, for example, multiple resins may be kneaded together to form a single form, or multiple film-like resins may be laminated together, and the form is not particularly limited.

[0028] The thickness of the dielectric film 213 is not particularly limited, but for example, it is 1.0 μm or more and 10.0 μm or less.

[0029] The material of the metal film 214 is not particularly limited, but examples include aluminum (Al), gold (Au), magnesium (Mg), zinc (Zn), tin (Sn), nickel (Ni), chromium (Cr), iron (Fe), copper (Cu), titanium (Ti), and alloys thereof.

[0030] The thickness of the metal film 214 is not particularly limited, but for example, it is between 3 nm and 100 nm.

[0031] The material of the metal oxide film is not particularly limited, but examples include aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), barium (Ba), calcium (Ca), and copper (Cu).

[0032] The thickness of the metal oxide film is not particularly limited, but for example, it is between 3 nm and 50 nm.

[0033] <Outer Film> The outer film 215 is wound around the outer circumference connecting the first end face 216a and the second end face 216b of the wound body 211 (see Figure 3). The thickness of the outer film 215 is not particularly limited, but for example, it is 1.0 μm or more and 30.0 μm or less.

[0034] The outer film 215 is a high heat-resistant film. A high heat-resistant film in the outer film 215 is defined as having a shrinkage initiation temperature in the width direction (TD direction) of the raw film, determined by thermomechanical analysis, of, for example, 160°C or higher. In this case, dimensional changes of the film capacitor 10 exposed to a high-temperature environment can be further suppressed. The material of the outer film 215 is not particularly limited as long as it satisfies the aforementioned shrinkage temperature, but examples include cyclic olefin (COC) resin, polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polyphenylene sulfide (PPS) resin, polycarbonate (PC) resin, and polystyrene (PS) resin.

[0035] <End face electrodes> A pair of end face electrodes 22 are provided on a pair of end faces 216 of the wound element 21 (see Figure 1). Specifically, the first end face electrode 22a is provided on the first end face 216a, and the second end face electrode 22b is provided on the second end face 216b.

[0036] The end face electrode 22 is a metal coating (metal spray coating) formed by metal spraying. Metal spraying is a process in which molten metal is atomized and sprayed onto the surface of a substrate (a pair of end faces in this embodiment) to form a metal coating. The material of the end face electrode 22 is not particularly limited, but examples include zinc (Zn), tin (Sn), and alloys thereof.

[0037] The first end electrode 22a is electrically connected to one metal film 214 exposed on the first end face 216a. The second end electrode 22b is not electrically connected to one metal film 214 that is not exposed on the second end face 216b. Similarly, the second end electrode 22b is electrically connected to the other metal film 214 exposed on the second end face 216b. The first end electrode 22a is not electrically connected to the other metal film 214 that is not exposed on the first end face 216a.

[0038] The thickness of the end electrode 22 is not particularly limited, but for example, it is 0.4 mm or more and 1.2 mm or less.

[0039] (Other Designs) The film capacitor 10 according to the embodiment may be designed in various ways, as long as it does not impair the effects of the present disclosure. For example, the film capacitor 10 may have a busbar connected to the end face electrode 22. Furthermore, the busbar is connected to an external device. Therefore, the film capacitor 10 can be electrically connected to an external device via the busbar. The external device is not particularly limited, but examples include components that constitute a power supply circuit such as an inverter device. That is, the film capacitor 10 may be, for example, part of an inverter device. The film capacitor 10 may also be housed in a case and sealed with a curable resin or the like.

[0040] 2.2 Manufacturing Method The manufacturing method of the film capacitor 10 according to the embodiment comprises a first step, a second step, a third step, a fourth step, and a fifth step. Each step will be described in detail below.

[0041] (First Step) In the first step, a metallized film 212 including a dielectric film 213 and a metal film 214 provided on the dielectric film 213 is wound around a winding axis O to form a wound body 211 (see FIG. 2).

[0042] Specifically, with reference to the winding axis O along the Z direction, a pair of metallized films 212 are wound in the θ direction to form a cylindrical wound body 211 (see FIG. 2). At this time, the pair of metallized films 212 are wound around the winding axis O such that an edge of one metal film 214 is exposed from the first end face 216a, an edge of the other metal film 214 is exposed from the second end face 216b, and the metal films 214 and the dielectric films 213 are alternately stacked.

[0043] (Second Step) In the second step, an exterior film 215 is wound around the outer periphery of the wound body 211 to form a winding element 21 (see FIG. 3). In this case, loosening of the wound body 211 is suppressed, and by restraining expansion of the dielectric film 213, dimensional change of the film capacitor 10 when exposed to a high-temperature environment is suppressed.

[0044] The method for winding the exterior film 215 is not particularly limited, and may be performed by any appropriate method. For example, the starting end of the exterior film 215 may be connected to the terminal end of the metallized film 212 of the wound body 211, and winding may be performed in the same manner as in the first step. The terminal end of the exterior film 215 is not particularly limited, and is adhered to the outer peripheral surface of the winding element 21 by, for example, heat welding or adhesion using an adhesive, an adhesive tape, or the like.

[0045] (Third Step) In the third step, the winding element 21 is pressed in one direction perpendicular to the winding axis O to be formed into a flat shape (see FIG. 4). By forming the winding element 21 into a flat shape, the first end face 216a and the second end face 216b become rounded rectangles.

[0046] The pressing method is not particularly limited as long as it is a method of pressing in one perpendicular direction by two parallel plate-shaped members 40 for forming the flat portion 31 on the outer peripheral surface 30 of the capacitor element 20. Examples of such a pressing method include a method using a press or the like. The flatness of the winding element 21 is not particularly limited, and is adjusted to an appropriate flat degree according to the usage environment, application purpose, and the like.

[0047] (Fourth Step) In the fourth step, the capacitor element 20 is formed by providing an end face electrode 22 on an end face 216 perpendicular to the winding axis O of the wound element 21.

[0048] As described above, the end face electrode 22 is formed by performing metal spraying on the end face 216 of the wound element 21. The metal spraying method is not particularly limited, and may be performed by a known method.

[0049] (Fifth Step) In the fifth step, the capacitor element 20 is heated at a temperature of 130°C or higher.

[0050] The fifth step is a step of removing residual stress in the capacitor element 20 by heating. The heating method is not particularly limited, and examples thereof include a method of placing the capacitor element in a constant temperature bath.

[0051] As described above, the heating temperature is 130°C or higher. If the heating temperature is lower than 130°C, the residual stress in the capacitor element 20 cannot be sufficiently removed, and the dimensional change of the capacitor element 20 when exposed to a high temperature environment cannot be sufficiently suppressed. The heating temperature is preferably 145°C or lower. If the heating temperature is 145°C or lower, the dimensional change of the film capacitor 10 caused by heating in the fifth step can be further suppressed.

[0052] 2.3 Functions and Effects In the film capacitor 10 according to the present embodiment, the dielectric film 213 collected from the flat portion 31 has a dimensional change rate of 0.6% or less when the temperature is increased from 25°C to 130°C under the conditions of a load of 0.3 MPa and a temperature increase rate of 5°C / min by thermomechanical analysis in the direction along the winding axis O (TD direction). Therefore, the dimensional change of the film capacitor 10 when exposed to a high temperature environment can be suppressed. This is presumed to be due to the following mechanism of action.

[0053] The dielectric film 213 used in the film capacitor 10 according to this embodiment has a shrinkage initiation temperature of, for example, 130°C or higher in the width direction (TD direction) of the original film, as determined by thermomechanical analysis, and a shrinkage initiation temperature of, for example, 135°C or higher in the winding direction (MD direction) when the film capacitor 10 is constructed, as determined by thermomechanical analysis. Therefore, it does not shrink when exposed to a high-temperature environment, but expands slightly. Thus, the dielectric film 213 is less likely to undergo excessive shrinkage in a high-temperature environment.

[0054] Furthermore, the film capacitor 10 is equipped with an outer film 215. The outer film 215 has a shrinkage initiation temperature of 160°C or higher, as determined by thermomechanical analysis in the width direction (TD direction) of the original film. Therefore, it does not shrink when exposed to a high-temperature environment, but expands slightly. Thus, the outer film 215 is less prone to excessive shrinkage in high-temperature environments.

[0055] Furthermore, the expansion rate of the outer film 215 at 130°C is equivalent to or smaller than that of the dielectric film 213. Therefore, the outer film 215 can suppress the loosening of the winding of the winding body 211.

[0056] As a result, the dielectric film 213 and the outer film 215 are less prone to excessive shrinkage due to high-temperature environments, and the expansion rate of the outer film 215 at 130°C is smaller than that of the dielectric film 213. Therefore, the dielectric film 213 taken from the flat portion 31 can have a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under the conditions of a load of 0.3 MPa and a heating rate of 5°C / min, as measured by thermomechanical analysis. This feature allows the film capacitor 10 according to this embodiment to suppress dimensional changes when exposed to high-temperature environments.

[0057] In the manufacturing method of the film capacitor 10 according to this embodiment, as described above, the heating temperature in the fifth step is 130°C or higher. At this temperature or higher, residual stress in the resin used in the dielectric film 213 and the outer film 215 is removed, so that the dielectric film 213 taken from the flat portion 31 can have a dimensional change rate of 0.6% or less when heated from 25°C to 130°C in the direction along the winding axis O by thermomechanical analysis under the conditions of a load of 0.3 MPa and a heating rate of 5°C / min.

[0058] Furthermore, in the manufacturing method of the film capacitor 10, as mentioned above, the heating temperature in the fifth step is preferably 145°C or lower. If the temperature exceeds 145°C, the dielectric film 213 may shrink excessively, and it may not be possible to suppress dimensional changes in the film capacitor 10.

[0059] As described above, the film capacitor 10 according to this embodiment has suppressed dimensional changes when exposed to high-temperature environments. Therefore, the yield rate in manufacturing is improved, and malfunctions when connecting to external devices are less likely to occur. Furthermore, since the shrinkage of the dielectric film 213 is suppressed in particular, a decrease in capacitance can be suppressed, and deterioration of insulation resistance due to deformation of the pattern of the metal film 214, damage to the dielectric film 213, etc. can be suppressed.

[0060] 3. Aspects As will be clear from the above embodiments, this disclosure includes the following aspects. Hereafter, reference numerals are enclosed in parentheses solely to indicate their correspondence with the embodiments.

[0061] A film capacitor (10) according to the first embodiment comprises a winding body (211) in which a metallized film (212) comprising a dielectric film (213) and a metal film (214) provided on the dielectric film (213) is wound around a winding shaft (O), and an outer film (215) is wound around the outer circumference of the winding body (211), and a capacitor element (20) comprising a winding element (21) having an end face (216) perpendicular to the winding shaft (O), and an end face electrode (22) provided on the end face (216). The outer surface (30) of the capacitor element (20) has a pair of opposing flat portions (31), and the dielectric film (213) taken from the flat portions (31) has a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under the conditions of a load of 0.3 MPa and a heating rate of 5°C / min, as measured by thermomechanical analysis in the direction along the winding axis (O).

[0062] According to this embodiment, dimensional changes in the film capacitor (10) when exposed to a high-temperature environment can be suppressed.

[0063] A method for manufacturing a film capacitor (10) according to a second embodiment comprises a first step, a second step, a third step, a fourth step, and a fifth step. In the first step, a metallized film (212) comprising a dielectric film (213) and a metal film (214) provided on the dielectric film (213) is wound around a winding shaft (O) to form a winding body (211). In the second step, an outer film (215) is wound around the outer circumference of the winding body (211) to form a winding element (21). In the third step, the winding element (21) is pressed in one direction perpendicular to the winding shaft (O) to form a flattened shape. In the fourth step, an end electrode (22) is provided on the end face (216) of the winding element (21) perpendicular to the winding shaft (O) to form a capacitor element (20). In the fifth step, the capacitor element (20) is heated to a temperature of 130°C or higher. The outer circumferential surface (30) of the capacitor element (20) has a pair of opposing flat portions (31). The dielectric film (213) taken from the flat portions (31) after the fifth step has a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under the conditions of a load of 0.3 MPa and a heating rate of 5°C / min, as measured by thermomechanical analysis in the direction along the winding axis (O).

[0064] According to this embodiment, a film capacitor (10) can be manufactured in which dimensional changes when exposed to a high-temperature environment are suppressed.

[0065] In the third embodiment of the method for manufacturing a film capacitor (10), the heating temperature in the fifth step is 145°C or lower, as in the second embodiment.

[0066] According to this embodiment, it is possible to manufacture a film capacitor (10) in which dimensional changes when exposed to a high-temperature environment are further suppressed.

[0067] The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited to the following examples.

[0068] 1. Fabrication of Film Capacitors (Example 1) First, two sheets of resin film #1 (thickness 3.5 μm) were prepared as dielectric films, the shrinkage initiation temperature in the width direction (TD direction) of the original film measured by thermomechanical analysis was 130°C or higher. Aluminum (Al) was deposited onto one surface of each of these two dielectric films in a mirror-symmetric pattern to form a metal film, thereby creating a pair of metallized films.

[0069] Next, the metal films of this pair of metallized films were superimposed so that they faced each other via a dielectric film, and then wound up to create a wound body. A resin film #3 (12 μm thick, PET resin), whose shrinkage onset temperature in the width direction (TD direction) of the original film, measured by thermomechanical analysis, was 160°C or higher, was wound around the outer circumference of this wound body as an outer film to create a wound element with a diameter of 4.64 cm.

[0070] The wound element was pressed with a parallel metal plate under a pressure of 0.15 MPa to create a flattened shape. Next, zinc (Zn) was sprayed onto both ends of the flattened wound element to a thickness of 0.5 mm to form end electrodes, thereby fabricating a capacitor element. Finally, the capacitor element was heated at 130°C for 8 hours to remove residual stress, thereby fabricating a film capacitor.

[0071] (Example 2) A film capacitor was manufactured in the same manner as in Example 1, except that the heating temperature for removing residual stress from the capacitor element was set to 140°C.

[0072] (Comparative Examples 1 and 2) Film capacitors were manufactured in the same manner as in Example 1, except that a resin film #4 (thickness 25 μm, PP resin) was used as the outer film, with a shrinkage initiation temperature of 105°C in the width direction (TD direction) of the raw film as determined by thermomechanical analysis, and the heating temperature for removing residual stress from the capacitor element was set to the temperatures shown in Table 2.

[0073] (Comparative Example 3) A film capacitor was fabricated in the same manner as in Comparative Example 1, except that a resin film #2 (thickness 3.5 μm) was used as the dielectric film, the shrinkage initiation temperature in the width direction (TD direction) of the original film as determined by thermomechanical analysis was 119°C.

[0074] 2. The dielectric film, outer film, and fabricated film capacitors used in the fabrication of the evaluated film capacitors were evaluated as follows. The results are shown in Tables 1 and 2.

[0075] (Dimensional change rate of dielectric film and outer film) The dimensional change rate at 130°C was measured for the dielectric film and outer film used in the fabrication of the film capacitor.

[0076] Test specimens of the dielectric film and outer film used in the fabrication of the film capacitors were taken from the original film rolls. The test specimens were cut so that they were 5 mm in the longitudinal direction (MD direction) and 10 mm in the width direction (TD direction) of the original film roll. Each test specimen was measured using a thermomechanical analyzer, and the results are shown in Table 1. In the embodiments of this disclosure, a positive number in "dimensional change rate" represents the change due to expansion, and a negative number represents the change due to contraction.

[0077] Test specimens of the dielectric film and outer film used in the fabrication of the film capacitor were taken from the central portion X of the flat section of the film capacitor (see Figure 7). The test specimens were cut to a size of 5 mm on the winding direction (MD direction) side of the capacitor element and 10 mm on the direction along the winding axis (TD direction). The measurement results are shown in Table 2.

[0078] The measurement conditions are as follows:

[0079] Measurement device: TMA402F3 Hyperion (manufactured by NETZSCH) Measurement mode: Tensile Tensile stress: 0.3 MPa Measurement atmosphere: Nitrogen atmosphere Temperature program: Heat from a starting temperature of 25°C to the set upper limit temperature at a heating rate of 5°C / min, and after reaching the upper limit temperature, cool down to 25°C at a cooling rate of 5°C / min. The upper limit temperature is set to 135°C for measurement of resin films #1, #2 and #4, and to 160°C for measurement of resin film #3.

[0080] (Shape distortion of film capacitors after residual stress removal) Shape distortion was measured for film capacitors after residual stress removal. Specifically, the lengths of the distance between end electrodes (LM) at nine locations (see Figure 5), the distance between flat sections (LT) at nine locations (see Figure 6), and the distance between the tips of curved sections (LW) at three locations (see Figure 7) were measured. Next, the difference between the maximum and minimum values ​​at each distance was calculated, and the sum of these differences was taken as the result. The calculated results are shown in Table 2.

[0081] The measurement sections for each shape distortion will be explained using the film capacitor 10 as an example, with reference to Figures 5 to 7.

[0082] The measurement point for LM is the distance between a pair of opposing points lm (point lma and point lmb) on a pair of end face electrodes 22 (see Figure 5). The opposing points lma and lmb, which are the measurement points for LM, are two locations on the most protruding part of the curved portion 32 of the pair of end electrodes 22 (lma4, lmb4; lma8, lmb8), four locations on the boundary between the curved portion 32 and the flat portion 31 of the pair of end electrodes 22 (lma1, lmb1; lma3, lmb3; lma5, lmb5; lma7, lmb7), one location at the intersection of the pair of end electrodes 22 and the winding axis O (lma9, lmb9), and two locations on the pair of end electrodes 22 at the intersection of a virtual line passing through the winding axis O and perpendicular to the flat portion 31 with the flat portion 31 (lma2, lmb2; lma6, lmb6).

[0083] The measurement area for LT is the distance between a pair of opposing points lt (points lta and ltb) on a pair of flat sections 31 (see Figure 6). The points lta and ltb, which are the measurement locations for LT, are two locations at the boundary between the curved section 32 and the flat section 31 at the rear end of the first end face electrode 22a of the pair of flat sections 31 (lta1, ltb1; lta7, ltb7), two locations at the boundary between the curved section 32 and the flat section 31 at the front end of the second end face electrode 22b of the pair of flat sections 31 (lta3, ltb3; lta9, ltb9), and a line passing through the winding axis O and perpendicular to the flat section 31 at the rear end of the first end face electrode 22a of the pair of flat sections 31. These are one intersection point with the flat portion 31 (lta4, ltb4), one intersection point with the flat portion 31 at the front end of the second end face electrode 22b of the pair of flat portions 31 with a virtual line passing through the winding axis O and perpendicular to the flat portion 31 (lta6, ltb6), one point at the centroid of the flat portion 31 (lta5, ltb5), and two intersection points with the boundary between the flat portion 31 and the curved portion 32 with a virtual line passing through the centroid of the flat portion 31 and extending parallel to the pair of end face electrodes 22 (lta2, ltb2; lta8, ltb8).

[0084] The measurement area for LW is the distance between a pair of opposing points lw (points lwa and lwb) on the protruding portions of the pair of curved surfaces 32 (see Figure 7). The points lwa and lwb, which are the measurement locations for LW, are two intersection points (lwa1, lwb1; lwa3, lwb3) of the protruding portions of the curved surfaces 32 and the pair of end face electrodes 22, and one midpoint (lwa2, lwb2) of the line segment connecting these intersection points.

[0085] (Dimensional deformation rate of film capacitors due to exposure to high-temperature environments) The dimensional deformation rate of film capacitors due to exposure to high-temperature environments was measured. Specifically, first, the distance between end electrodes (LM) was measured at nine locations (see Figure 5), the distance between flat sections (LT) at nine locations, and the distance between curved section tips (LW) at three locations (see Figure 7) in the film capacitor before heating, and the arithmetic mean of each distance was calculated. Next, the film capacitor was heated at 130°C for 2 hours. The arithmetic mean of each distance was calculated for the heated film capacitor in the same manner as before heating. Then, the rate of change of each distance was calculated using the following formula (1).

[0086] (Rate of change) = {(Arithmetic mean before heating) - (Arithmetic mean after heating)} / (Arithmetic mean before heating) ... (1).

[0087] Furthermore, the dimensional deformation rate of the film capacitor due to exposure to a high-temperature environment was calculated using the following formula (2). The calculated results are shown in Table 2.

[0088] (Dimension deformation rate) = {(Change rate of LM)^2 + (Change rate of LT)^2 + (Change rate of LW)^2}^0.5 ... (2)

[0089]

[0090]

[0091] Examples 1 and 2 used resin film #1 as the dielectric film, which had a shrinkage initiation temperature of 130°C or higher in the width direction (TD direction) of the base film as measured by thermomechanical analysis, and resin film #3 as the outer film, which had a shrinkage initiation temperature of 160°C or higher in the width direction (TD direction) of the base film as measured by thermomechanical analysis. As a result, the dielectric films of Examples 1 and 2 had a shrinkage initiation temperature of 135°C or higher in the winding direction (MD direction) when used as a film capacitor, as measured by thermomechanical analysis, and the dimensional change rate when the dielectric film sampled from the flat portion of the film capacitor was heated from 25°C to 130°C under conditions of a load of 0.3 MPa and a heating rate of 5°C / min was 0.6% or less in the direction along the winding axis (TD direction).

[0092] On the other hand, in Comparative Examples 1 and 2, where resin film #4 was used as the outer film, and the shrinkage initiation temperature in the width direction (TD direction) of the base film, as determined by thermomechanical analysis, was less than 160°C, the dimensional change rate as determined by the aforementioned thermomechanical analysis was greater than 0.6%. Furthermore, in Comparative Example 3, where resin film #4 was used as the outer film and resin film #2 was used as the dielectric film, and the shrinkage initiation temperature in the width direction (TD direction) of the base film, as determined by thermomechanical analysis, was less than 130°C, the dimensional change rate as determined by the aforementioned thermomechanical analysis was also greater than 0.6%.

[0093] Furthermore, a comparison of the element evaluations of the examples and comparative examples revealed that, even when aged at higher temperatures than the comparative examples, the shape distortion of the film capacitor after residual stress removal was found to be at the same level as, or even lower than, the comparative examples. In addition, it was confirmed that the dimensional deformation rate of the film capacitor due to exposure to high-temperature environments was reduced in the examples compared to the comparative examples.

[0094] 10 Film capacitor 20 Capacitor element 21 Winding element 211 Winding body 212 Metallized film 213 Dielectric film 214 Metal film 215 Outer film 216, 216a, 216b End faces 22, 22a, 22b End face electrodes 30 Outer surface 31 Flat portion O Winding shaft

Claims

1. A film capacitor comprising a winding body in which a metallized film comprising a dielectric film and a metal film provided on the dielectric film is wound around a winding shaft, and an outer film wound around the outer circumference of the winding body, the winding element having an end face perpendicular to the winding shaft, and an end face electrode provided on the end face, wherein the outer surface of the capacitor element has a pair of opposing flat portions, and the dielectric film taken from the flat portions has a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under thermomechanical analysis conditions of a load of 0.3 MPa and a heating rate of 5°C / min in the direction along the winding shaft.

2. A method for manufacturing a film capacitor, comprising: a first step of winding a metallized film comprising a dielectric film and a metal film provided on the dielectric film onto a winding shaft to form a winding body; a second step of winding an outer film onto the outer circumference of the winding body to form a winding element; a third step of pressing the winding element in one direction perpendicular to the winding shaft to flatten it; a fourth step of forming a capacitor element by providing an end electrode on the end face perpendicular to the winding shaft of the winding element; and a fifth step of heating the capacitor element to a temperature of 130°C or higher, wherein the outer surface of the capacitor element has a pair of opposing flat portions, and the dielectric film taken from the pair of flat portions after the fifth step has a dimensional change rate of 0.6% or less when heated from 25°C to 130°C under thermomechanical analysis conditions of a load of 0.3 MPa and a heating rate of 5°C / min in the direction along the winding shaft.

3. The method for manufacturing a film capacitor according to claim 2, wherein the heating temperature in the fifth step is 145°C or lower.

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