JP2020053564A - Metallized film - Google Patents

Abstract

To secure high withstand voltage in a film capacitor even when an insulation defect occurs in a dielectric film.SOLUTION: A metallized film 100 used for a film capacitor includes: a first dielectric film 121; a metal film 110 disposed on a first surface of the first dielectric film 121; and a second dielectric film 122 disposed on the second surface of the first dielectric film 122. The first dielectric film 121 and the second dielectric film 122 have the same thickness and the same dielectric constant.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a metallized film, and more specifically to a technique for improving the dielectric breakdown characteristics of a metallized film for a film capacitor.

  Polypropylene films are known to have excellent electrical properties such as high withstand voltage and low dielectric loss. Taking advantage of these excellent electrical properties, polypropylene films are used in electronic and electrical equipment, such as high-voltage capacitors, various switching power supplies, converters and inverters, and are used for insulating capacitors for capacitors such as filter capacitors or smoothing capacitors. It is used as a body film.

  In recent years, demands for electric vehicles, hybrid vehicles, and the like have been increasing, and polypropylene films have begun to be used as film capacitors for inverter power supply devices that control drive motors of these vehicles. High-capacity capacitors for automobiles are required to be further reduced in size, weight, and capacity, and to have high withstand voltage even under high voltage.

  Japanese Patent Application Laid-Open No. 2016-195250 (Patent Document 1) discloses a biaxially stretched polypropylene film for capacitors having high withstand voltage at high temperatures. Specifically, Japanese Patent Application Laid-Open No. 2016-195250 (Patent Document 1) discloses a biaxially stretched polypropylene film containing at least one kind of polypropylene resin and at least one kind of β crystal nucleating agent.

JP 2016-195250 A JP-A-2006-188361

  It is known that the dielectric breakdown strength of such a polypropylene film is not always uniform over the entire film, and that a portion having a low dielectric breakdown strength (hereinafter, also referred to as “insulation defect”) is partially generated. . The cause of the insulation defect may be due to a scratch at the time of manufacturing or contamination of a foreign substance, but may also be caused by fluctuation of a filling state of molecules. In the case of the latter factor, it is technically difficult to completely eliminate the occurrence at this stage, and an insulation defect occurs at a certain probability.

  The present disclosure has been made in order to solve the above problems, and an object thereof is to provide a film capacitor capable of realizing high withstand voltage even when an insulation defect occurs in a dielectric film. To provide a metallized film for use.

  The metallized film according to the present disclosure is a metallized film used for a film capacitor. The metallized film includes a first dielectric film, a metal film disposed on a first surface of the first dielectric film, and a second dielectric film disposed on a second surface of the first dielectric film. . The first dielectric film and the second dielectric film have the same thickness and the same dielectric constant.

  According to the metallized film for a film capacitor according to the present disclosure, the dielectric film is formed as a laminated structure of two dielectric films having the same thickness and the same dielectric constant. Thus, high withstand voltage can be realized even when an insulation defect occurs in one of the dielectric films.

FIG. 3 is a cross-sectional view of the metallized film according to the present embodiment. It is a perspective view of the metallized film according to this Embodiment. It is a perspective view which shows typically the laminated body which laminated | stacked the metallized film. FIG. 4 is a cross-sectional view of the stack taken along line IV-IV shown in FIG. 3. It is a figure for demonstrating the dielectric breakdown strength of the metallized film according to this Embodiment, and the metallized film of a comparative example.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

  1 and 2 are a cross-sectional view and a perspective view, respectively, of metallized film 100 according to the present embodiment. As shown in FIGS. 1 and 2, the metallized film 100 is formed by depositing a metal film 110 on one surface of a dielectric film 120. The metal film 110 is not deposited on the entire surface of the dielectric film 120. An insulation margin of about several mm where the metal film 110 is not formed is provided along one edge of the dielectric film 120. As a material of the metal film 110, for example, a metal material such as aluminum (Al) or zinc (Zn) can be used.

  The dielectric film 120 has a configuration in which a first dielectric film 121 and a second dielectric film 122 are laminated. That is, the metal film 110 is disposed on the first surface of the first dielectric film 121, and the second dielectric film 122 is disposed on the second surface of the first dielectric film 121.

  As a material of the first dielectric film 121 and the second dielectric film 122, for example, polyethylene terephthalate (PET), polypropylene (PP), polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), polyvinylidene fluoride (PVDF) Plastic films such as those described above can be used. The first dielectric film 121 and the second dielectric film 122 have the same thickness and the same dielectric constant, and are preferably formed of the same material.

  The dielectric film 120 is stretched. The dielectric film 120 is stretched at least in the stretching direction DR2 indicated by a double arrow in FIG. The dielectric film 120 may be a uniaxially stretched film stretched in one direction only in the stretching direction DR2, or biaxially stretched in two directions of a stretching direction DR2 and a stretching direction DR1 orthogonal to the stretching direction DR2. It may be a stretched film.

  FIG. 3 is a perspective view schematically showing a laminate 200 in which the metallized films 100 and 150 are laminated. FIG. 4 is a cross-sectional view of the stacked body 200 along the line IV-IV shown in FIG. The laminate 200 shown in FIGS. 3 and 4 includes the metallized film 100 described with reference to FIGS. 1 and 2, and a metallized film 150 different from the metallized film 100. The metallized film 150 is formed by depositing a metal film 160 on one surface of a dielectric film 170. The dielectric film 170 has a configuration in which two layers of dielectric films (a third dielectric film 171 and a fourth dielectric film 172) are laminated similarly to the dielectric film 120. The material of the metal film and the dielectric film constituting the metallized film 100 and the material of the metal film and the dielectric film constituting the metallized film 150 may be the same or different. .

  In the capacitor device, one of the metal film 110 of the metallized film 100 and the metal film 160 of the metallized film 150 functions as a cathode electrode, and the other functions as an anode electrode. The metal films 110 and 160 form two electrodes having different polarities.

  The laminated body 200 shown in FIG. 3 is formed by laminating one long metallized film 100 and one long metallized film 150 and winding them in the longitudinal direction. The metallized film 100 and the metallized film 150 are laminated so that their respective insulation margins do not coincide in the laminating direction to form a laminate 200.

  4, the lower surface of the dielectric film 120 of the metallized film 100 (the lower surface of the second dielectric film 122) is in contact with the upper surface of the metal film 160 of the metallized film 150. The lower surface of the dielectric film 170 of the metallized film 150 (the lower surface of the fourth dielectric film) is in contact with the upper surface of the metal film 110 of the metallized film 100. In the laminate 200, the metallized films 100 and the metallized films 150 are alternately laminated. In the laminate 200, a dielectric film 170, a metal film 160, a dielectric film 120, and a metal film 110 are sequentially laminated in this order.

  Note that the laminate is actually formed by stacking tens of thousands of metallized films 100 and 150. The laminated body 200 shown in FIG. 4 is a simplified one of the actual laminated body, and schematically shows a part of the actual laminated body.

  The laminated body 200 thus formed is subjected to a heat treatment, and a current collecting electrode is formed by spraying a metal on two electrode extraction surfaces at both ends of the laminated body 200 to form a capacitor element. Becomes Then, the obtained capacitor element is accommodated in a case and sealed, and a connection terminal is connected to the current collecting electrode to form a film capacitor device.

  A dielectric film used as a metallized film of such a film capacitor is required to have high withstand voltage. In particular, when used as a capacitor for a drive electric device of an electric vehicle or a hybrid vehicle, which has been increasing in demand in recent years, a withstand voltage under a high voltage (for example, 1 kV) is required.

  On the other hand, it is known that the dielectric breakdown strength of a dielectric film is not necessarily uniform over the entire film, and that a part (insulation defect) having a weak dielectric breakdown strength is partially generated. For example, in the case of a film having an average dielectric breakdown strength of 600 V / μm, the dielectric breakdown strength of a portion having an insulation defect indicates a portion of 300 V / μm or less.

  It is known that the insulation defect may be caused by scratches at the time of manufacturing or contamination of foreign matter, but may also be caused by fluctuation of the filling state of molecules. At this stage, it is difficult to completely control the packing state of the molecules in the manufacturing process, so that the insulating film inevitably contains insulation defects at a certain probability.

  In general, the thickness of a dielectric film used for a metallized film is 2 to 3 μm. For example, the dielectric breakdown strength of a portion having an insulation defect is 300 V / μm, and the thickness of the entire dielectric film is 3 μm. In this case, the total dielectric breakdown strength in the thickness direction of the insulation defect part is 900 V (= 300 V / μm × 3 μm), and cannot be applied to a power capacitor to which a voltage of 1 kV or more is applied.

  In addition, since the probability of the presence of insulation defects in the dielectric film is about 10%, the capacitance of the capacitor can be reduced by about 10% as a result. In general, it is preferable that the variation in the capacitance of the capacitor is less than 5%. Therefore, when an insulation defect exists, the capacitor may not satisfy the specification of the variation in the capacitance.

  In metalized film 100 according to the present embodiment, dielectric film 120 has a two-layer structure of first dielectric film 121 and second dielectric film 122. In each of the two laminated dielectric films 121 and 122, it is extremely rare that an insulation defect occurs at the same location. Therefore, even if an insulation defect occurs at a certain location on one of the dielectric films, the same is not true. The other dielectric film at the location is likely to be sound. Therefore, as in the case of the metallized film 100 of the present embodiment, by forming the dielectric film 120 into a two-layer structure, the dielectric breakdown strength of the entire dielectric film 120 can be secured.

  FIG. 5 shows the metallized film 100 (FIG. 5 (a)) according to the present embodiment and the metallized film 100 # (FIG. 5 (b)) of a comparative example having a single-layer dielectric film as in the prior art. FIG. 4 is a diagram for explaining dielectric breakdown strength.

  In the metallized film 100 # of the comparative example, the thickness of the dielectric film 120 # is d, and in the metallized film 100 of the present embodiment, the thickness of each of the dielectric films 121 and 122 is d / 2. In the metallized film 100 #, if an insulation defect 180 occurs in the dielectric film 120 #, the dielectric breakdown strength of the dielectric film 120 # as a whole decreases.

  On the other hand, in the metallized film 100 of the present embodiment, even if an insulation defect 180 occurs in one of the dielectric films, the other dielectric film is likely to be in a healthy state. In other words, even if the dielectric breakdown strength of the half of the dielectric film 120 in the thickness direction is reduced, the other half is maintained at a high dielectric breakdown strength.

  For example, the thickness of the dielectric film 120 is 3 μm, the thickness of each of the first dielectric film 121 and the second dielectric film 122 is 1.5 μm, and one of the dielectric films has an insulation breakdown strength of 300 V / μm. If a defect occurs, the total dielectric breakdown strength in the thickness direction of the dielectric film 120 is 1350 V (= 300 V / μm × 1.5 μm + 600 V / μm × 1.5 μm). Therefore, even when an insulation defect occurs in the dielectric film, it can be used as a power capacitor to which a voltage of 1 kV or more is applied.

  As described above, the probability of the presence of insulation defects in each dielectric film is about 10%. Therefore, when a dielectric film having a two-layer structure is employed as in the metalized film 100 according to the present embodiment, The probability that an insulation defect will occur at the same location of two dielectric films is 10% × 10% = 1%. Therefore, the variation in the capacitance of the capacitor due to the insulation defect is also 1%, which is suitable for the specification of the capacitance variation of the capacitor.

  In the above-described example, an example in which the dielectric film 120 has a two-layer structure has been described. However, the dielectric film 120 may be formed with three or more layers. Increasing the number of laminated dielectric films can further reduce the probability of occurrence of insulation defects at the same location in each dielectric film, so that the dielectric breakdown strength can be kept high and the capacitance fluctuation of the capacitor can be further reduced. Can be smaller. However, in the manufacturing process, the number of steps of laminating the dielectric films increases, and the thickness of each dielectric film decreases, so that the manufacturing cost may increase. Therefore, the number of laminated dielectric films to be used is determined in consideration of required specifications and manufacturing cost.

  As described above, it is desirable that the two dielectric films have the same thickness and the same dielectric constant. This is because if the film thickness or the dielectric constant is different, the voltage distribution applied to each dielectric film changes, and local electric field concentration may occur. Then, even in a portion where there is no insulation defect, insulation breakdown occurs due to electric field concentration, and as a result, insulation breakdown strength may be reduced.

  Further, it is preferable that the laminated dielectric films are not fixed to each other. When two dielectric films are fixed, a load is applied between the dielectric films at the time of hot pressing in the manufacturing process of the capacitor element, and the dielectric film is broken, which is the same as a single-phase dielectric film. There is a possibility that the workability of the steel cannot be ensured. Thus, from the viewpoint of the dielectric film workability, it is preferable that the laminated dielectric films are not fixed to each other.

  As described above, in the metallized film for a film capacitor according to the present embodiment, by using a dielectric film having a multilayer structure, there is a case where an insulating defect inevitably occurs in the dielectric film. In addition, the dielectric breakdown strength of the entire dielectric film can be secured, and high withstand voltage can be realized.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is defined by the terms of the claims, rather than the description of the embodiments, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  100, 100 #, 150 metallized film, 110, 160 metal film, 120-122, 120 #, 170-172 dielectric film, 180 insulation defect, 200 laminate.

Claims (1)

A metallized film used for a film capacitor,
A first dielectric film;
A metal film disposed on a first surface of the first dielectric film;
A second dielectric film disposed on a second surface of the first dielectric film,
A metallized film, wherein the first dielectric film and the second dielectric film have the same thickness and the same dielectric constant.

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