Capacitor and method for manufacturing the same

Abstract

The present invention provides a capacitor with low loss and excellent long-term durability at high temperatures, as well as a method for manufacturing the same. [Solution] The capacitor has a structure in which metallized films, each having metal layers B1, B2, C1, C2, D1, and D2 on both sides of a resin film, are adjacent to each other. This is equivalent to doubling the thickness of the electrode metal layers, thus achieving low resistance, which in practical terms suppresses heat generation and makes short-circuit failures less likely.

Description

Technical Field

[0001] The present invention relates to a capacitor and a method for manufacturing the same.

Background Art

[0002] Conventionally, capacitors such as film capacitors have been used in electronic and electrical devices. Examples of such capacitors include high-voltage capacitors, filter capacitors such as converters and inverters, and smoothing capacitors.

[0003] In power conversion devices such as the above-described converters and inverters, improvement in power conversion efficiency is required, and in the power transmission and distribution network, improvement in power transmission and distribution efficiency is required. In particular, since power is converted into heat due to power loss, the capacitor is required to have low loss.

[0004] <映 The above-described capacitors may be used at high temperatures depending on the application. In addition, with the recent improvement in the performance of electronic and electrical devices, the capacitor is loaded, and the capacitor may become hot due to self-heating, and a capacitor that can be used at high temperatures is required.

[0005] As a capacitor used at high temperatures, a capacitor formed by laminating and winding a metallized film having a metal layer on one side of a resin film such as a polypropylene film has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] While the capacitors mentioned above are excellent, there is room for improvement in terms of low loss characteristics and long-term durability at high temperatures. Patent Document 1 describes a capacitor formed by laminating a metallized film having a metal layer on one side of a resin film and winding it, but there is a need for the development of a new capacitor structure and a manufacturing method thereof that have even better characteristics.

[0008] In view of the above circumstances, the present invention aims to provide a capacitor with low loss and excellent long-term durability at high temperatures, and a method for manufacturing the same. [Means for solving the problem]

[0009] The inventors of the present invention conducted extensive research to solve the above problems and found that the above objective can be achieved by using a capacitor in which metallized films, each having a metal layer on both sides of a resin film, are adjacent to each other, thus completing the present invention.

[0010] In other words, the present invention relates to the following capacitor and method for manufacturing the same. 1. A capacitor characterized by having adjacent metallized films, each having a metal layer on both sides of a resin film. 2. The capacitor according to item 1, comprising winding or laminating the metallized film. 3. A capacitor according to item 1 or 2, wherein the void ratio in the thickness direction is 0.5% or more and 5% or less. 4. The capacitor described in any of items 1 to 3, wherein the film resistance of the metal layer is 5 to 25 Ω / □. 5. The capacitor according to any one of items 1 to 4, wherein the metal layer is formed by vapor deposition. 6. The capacitor according to any one of items 1 to 5, wherein the adjacent metal layers are drawn out to the same end face of the capacitor. 7. A method for manufacturing a capacitor, A manufacturing method characterized by comprising step 1 of winding or laminating a metallized film having metal layers on both sides of a resin film. 8. The manufacturing method according to item 7, wherein the capacitor has a void ratio in the thickness direction of 0.5% or more and 5% or less. 9. The manufacturing method according to item 7 or 8, wherein the film resistance of the metal layer is 5 to 25 Ω / □. 10. The manufacturing method according to any one of items 7 to 9, further comprising a metal deposition step of forming a metal layer on both sides of the resin film by vapor deposition before step 1. 11. The manufacturing method according to any one of items 7 to 10, further comprising step 2 of forming a pair of metallicon electrodes on both ends of the capacitor after step 1. [Effects of the Invention]

[0011] The capacitor of the present invention exhibits low loss and excellent long-term durability at high temperatures. Furthermore, the manufacturing method of the present invention allows for the easy production of the capacitor exhibiting the above characteristics. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram illustrating the capacitor of the present invention. [Figure 2] This is a schematic diagram showing the cross-section parallel to both end faces and the thickness of the capacitor of the present invention. [Figure 3] This is a schematic diagram showing a portion of the cross-section perpendicular to both end faces of the capacitor of the present invention. [Figure 4] This is a schematic diagram showing a conventional capacitor with stacked metallized films. [Figure 5] This is a schematic diagram showing a conventional capacitor with stacked metallized films. [Modes for carrying out the invention]

[0013] In this specification, the expression "consisting of" includes the concepts of "substantially consisting of" and "consisting of only."

[0014] In this specification, the expression "capacitor" includes the concepts of "capacitor", "capacitor element", and "film capacitor".

[0015] 1. Capacitor The capacitor of the present invention is a capacitor in which metallized films each having a metal layer on both sides of a resin film have an adjacent structure. The capacitor of the present invention having the above characteristics uses a metallized film having a metal layer on both sides of a resin film, and by having a structure in which the metallized films have an adjacent structure, the metal layers of the metallized films are adjacent to each other through a slight gap. As a result, it is equivalent to doubling the thickness of the metal layer, the ESR (equivalent series resistance) can be lowered, and the loss can be reduced. Therefore, in a circuit, the power loss is suppressed, and the power transmission and distribution efficiency and the conversion efficiency are improved. Further, even when a voltage is applied to the capacitor of the present invention at a high temperature, unlike the case of a single thick metal layer, since there is a gap between the two metal layers, the electrodes are likely to evaporate, so self-healing properties are imparted, dielectric breakdown is suppressed, and it has excellent long-term durability at high temperatures. Further, in the capacitor of the present invention, since there is almost no gap between the metal layers (electrodes) sandwiching the resin film, the capacitance increases, and for capacitors of the same volume, the capacitance becomes larger, and for capacitors of the same capacitance, a smaller capacitor can be obtained.

[0016] The capacitor of the present invention is a capacitor in which metallized films each having a metal layer on both sides of a resin film have an adjacent structure. The capacitor of the present invention is manufactured using metallized films each having a metal layer on both sides of a resin film, so that it is only necessary that the metallized films have an adjacent structure. Even if it is a small amount, a capacitor including a metallized film having a metal layer on one side of the resin film or a resin film having no metal layer may be included. That is, the capacitor of the present invention may substantially be a capacitor composed of metallized films each having a metal layer on both sides of a resin film. From the viewpoint of the capacitor having lower loss and the long-term durability of the capacitor at high temperature being further improved, the capacitor of the present invention is preferably a capacitor composed only of metallized films each having a metal layer on both sides of a resin film (not including a metallized film having a metal layer on one side of the resin film and a resin film having no metal layer).

[0017] The configuration of the capacitor of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the capacitor of the present invention. In FIG. 1, for the capacitor 10 of the present invention, between both end faces 11 and 12, a cross-section 13 parallel to the both end faces and a cross-section 14 perpendicular to the both end faces 11 and 12 are shown. Further, FIG. 2 shows a schematic diagram of the cross-section 13. The capacitor of the present invention shown in FIGS. 1 and 2 is a capacitor formed by winding a metallized film having a metal layer on both sides of a resin film (a wound capacitor), but the capacitor of the present invention may be a capacitor formed by laminating the metallized films (a laminated capacitor).

[0018] Figure 3 is a schematic diagram showing a portion of a cross-section 14 perpendicular to both end faces 11 and 12 of the capacitor of the present invention. In Figure 3, the capacitor of the present invention has a structure in which metallized films, each having a metal layer on both sides of a resin film, are adjacent to each other. The metallized films have metal layers on both sides of the resin film, and the metal layers B1 and B2, C1 and C2, and D1 and D2 are laminated in contact with each other. As a result, the thickness of the metal layer is equivalently doubled, which lowers the ESR (equivalent series resistance) and reduces power loss. Therefore, power loss in the circuit is suppressed, improving power transmission and distribution efficiency and conversion efficiency. Furthermore, even when a voltage is loaded onto the capacitor of the present invention at high temperatures, unlike the case of a single thick metal layer, the presence of air gaps between the two metal layers makes the electrodes more prone to evaporation, thus providing self-healing properties, suppressing dielectric breakdown, and resulting in excellent long-term durability at high temperatures.

[0019] Figures 4 and 5 are schematic diagrams showing a portion of the cross-section perpendicular to both end faces of a conventional capacitor. In Figure 4, the metallized film has a metal layer on one side of a resin film, and these metallized films are laminated. In Figure 5, the metallized film consists of alternating layers of metallized films with metal layers on both sides of the resin film and resin films without metal layers. In the conventional capacitors shown in Figures 4 and 5, since there is only one metal layer between the resin films, the ESR (equivalent series resistance) cannot be reduced, resulting in low losses. Power loss in the circuit is suppressed, and the transmission and distribution efficiency and conversion efficiency decrease.

[0020] The porosity in the thickness direction of the capacitor of the present invention is preferably 0.3% to 5%, more preferably 0.5% to 5%, even more preferably 0.7% to 3%, and particularly preferably 0.8% to 2.0%. Having the lower limit of the porosity within the above range further improves the long-term durability of the capacitor at high temperatures. Having the upper limit of the porosity within the above range further suppresses volume increase and stabilizes the shape of the capacitor.

[0021] In this specification, the measurement of the porosity in the thickness direction of the capacitor is performed according to the measurement method described in the examples. This will be explained in detail below.

[0022] The above void ratio measurement should be performed on the completed capacitor. If epoxy sealing is used, remove the sealing resin as needed before measurement.

[0023] The porosity of the capacitor is measured by the following method. Specifically, the porosity is calculated using the following formula, based on the difference between the measured thickness of the flat-type capacitor and the theoretical thickness of the capacitor obtained from the thickness of one metallized film. Void ratio (%) = [(Measured thickness) - (Theoretical thickness)] / (Theoretical thickness) × 100

[0024] Note that the measured thickness of the capacitor refers to the thickness of the flat portion of the element after the capacitor has been pressed and flattened, as shown in Figure 2.

[0025] The actual thickness of a capacitor can be measured using a two-dimensional shape measuring instrument, a three-dimensional shape measuring instrument, an X-ray CT scanner, a micrometer, calipers, etc. X-ray CT can measure non-destructively even if the capacitor is sealed with epoxy resin. Alternatively, the actual thickness of a capacitor may be measured using a molded object. There are no particular limitations on the mold, but it can be made using plaster or silicone rubber, or a mold gauge can be used. A mold gauge is particularly preferred because it causes less contamination of the capacitor element.

[0026] If the capacitor of the present invention is a capacitor made by winding a metallized film, the thickness d of one film sheet is calculated from the weight of the element (weight-based thickness). If the weight of the capacitor element is m, the winding length of the metallized film used for the element is h, and the film width of the metallized film is w, then it can be calculated by equation (1): d = m / 2hwρ. The coefficient 2 in equation (1) is the value due to the fact that two sheets are wound together. Also, ρ in equation (1) is the density of the metallized film. The density can be measured by known methods such as the density gradient tube method and the gas displacement method. When the resin film is polypropylene (PP), the density is mainly measured by the density gradient tube method (see JIS K7112:1999).

[0027] Furthermore, if the capacitor of the present invention is a capacitor formed by laminating metallized films, the formula for calculating the thickness d of one film is given by formula (2): d = m / ρLWn. In formula (2), m and ρ are the same as in formula (1) above. Also, in formula (2), L is the length and width dimension of the metallized film, W is the length and width dimension of the metallized film, and n is the number of layers.

[0028] The theoretical thickness is the film thickness d multiplied by the number of layers in the thickness direction. In the case of a wound type, the number of layers is four times the number of turns n, as two layers are wound together, as shown in Figure 2. In the case of a laminated type, the number of layers n is the number of layers. Therefore, if the film thickness is d and the number of turns is n, the theoretical thickness can be expressed as follows. For wound type: Theoretical thickness = 4th For laminated type: Theoretical thickness = nd

[0029] Regarding weight and density measurements, the difference between a metallized film and a resin film (non-metallized state) can be ignored. This is because the metal layer (metal vapor-deposited film) is very thin, and therefore its presence or absence does not affect the weight and density measurements.

[0030] When measuring the actual thickness and weight of a capacitor, it is preferable to remove parts other than the capacitor body, such as the outer film and core.

[0031] Methods for adjusting the void ratio include (i) adjusting the pressing pressure when flattening the capacitor during manufacturing. Higher pressure results in a smaller void ratio, while lower pressure results in a larger void ratio. Furthermore, (ii) adjusting the tension and contact pressure during element winding during capacitor manufacturing. Higher tension and contact pressure result in a smaller void ratio, while lower tension and contact pressure result in a larger void ratio.

[0032] The components constituting the capacitor of the present invention will be described in detail below.

[0033] (Resin film) The capacitor of the present invention uses a resin film as the dielectric. The resin film constituting the capacitor of the present invention is not particularly limited as long as it is a resin film used in capacitors, and any known resin film can be used.

[0034] Examples of resin films include polyethylene film (PE), polypropylene film (PP), polyethylene naphthalate film (PEN), polyethylene terephthalate film (PET), polyphenylene sulfide film (PPS), polycarbonate film (PC), and polystyrene film (PS). Among these, polypropylene film is preferred from the viewpoint of achieving lower capacitor losses and improving the long-term durability of the capacitor at high temperatures. The following is an illustrative description of polypropylene film used as the resin film.

[0035] The polypropylene film used as the resin film constituting the capacitor of the present invention preferably has polypropylene resin as its main component. It is more preferable that the resin component constituting the polypropylene film is polypropylene resin. The above "main component" means that the polypropylene film contains 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, on a solid content basis.

[0036] The above-mentioned polypropylene film may be a biaxially oriented polypropylene film. When the polypropylene film is a biaxially oriented polypropylene film, the stretching ratio in the flow direction is preferably 3.0 times or more and 7.0 times or less, and more preferably 4.0 times or more and 6.0 times or less. Furthermore, the stretching ratio in the transverse direction is preferably 6 times or more and 11 times or less, and more preferably 9 times or more and 11 times or less.

[0037] The polypropylene resin is not particularly limited, and a wide range of resins that can be used to form a polypropylene film can be used. Examples of polypropylene resins include propylene homopolymers such as isotactic polypropylene and syndiotactic polypropylene; long-chain branched polypropylene; and ultra-high molecular weight polypropylene. Preferably, propylene homopolymers are used, and among these, isotactic polypropylene is preferred from the viewpoint of heat resistance, and even more preferably isotactic polypropylene obtained by homopolymerizing propylene in the presence of an olefin polymerization catalyst. The polypropylene resin may be a single type or a blend of two or more types.

[0038] The polypropylene film can be made from a polypropylene resin composition (hereinafter also referred to simply as "polypropylene resin composition" in this specification) that contains a polypropylene resin and additives added as needed, as used in the manufacturing method described later.

[0039] The weight-average molecular weight (Mw) of the polypropylene resin in the above polypropylene resin composition is preferably 200,000 to 550,000, more preferably 200,000 to 500,000, even more preferably 200,000 to 450,000, and particularly preferably 250,000 to 400,000. Using such a polypropylene resin allows for appropriate resin fluidity during biaxial stretching, making biaxial stretching easier. For example, it becomes easier to obtain a thin-film biaxially oriented polypropylene film suitable for small, high-capacity capacitors. It is also preferable because it suppresses unevenness in the thickness of the biaxially oriented polypropylene film. Furthermore, the weight-average molecular weight (Mw) of the polypropylene resin in the above polypropylene resin composition is more preferably 250,000 or more from the viewpoint of uniformity of the thickness of the polypropylene film, mechanical properties, and thermal-mechanical properties. The weight-average molecular weight (Mw) of the polypropylene resin in the above polypropylene resin composition is more preferably 400,000 or less from the viewpoint of fluidity of the polypropylene resin and stretchability when obtaining a thin-film biaxially oriented polypropylene film.

[0040] The number-average molecular weight (Mn) of the polypropylene resin in the above-mentioned polypropylene resin composition is preferably 30,000 to 60,000, more preferably 40,000 to 60,000, and even more preferably 40,000 to 50,000. Using such a polypropylene resin allows for appropriate resin fluidity during biaxial stretching, making biaxial stretching easier. For example, it becomes easier to obtain a thin-film biaxially oriented polypropylene film suitable for small, high-capacity capacitors. It is also preferable because it suppresses unevenness in the thickness of the biaxially oriented polypropylene film. Furthermore, the number-average molecular weight (Mn) of the polypropylene resin in the above-mentioned polypropylene resin composition is more preferably 50,000 or less, from the viewpoint of the fluidity of the polypropylene resin and the stretchability when obtaining a thin-film biaxially oriented polypropylene film.

[0041] The average molecular weight distribution (Mw / Mn) of the polypropylene resin in the above-mentioned polypropylene resin composition, calculated as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is preferably 4 to 12, more preferably 5.5 to 10, and even more preferably 6 to 8. Using such a polypropylene resin makes it easier to obtain a thin, biaxially oriented polypropylene film with appropriate resin fluidity during biaxial stretching and without thickness variations. Furthermore, such a polypropylene resin is also preferable from the viewpoint of further improving the dielectric breakdown strength of the polypropylene film.

[0042] The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the polypropylene resin in the above-mentioned polypropylene resin composition can be measured using SEC (size exclusion chromatography) by the following method. Equipment: HLC-8321GPC / HT (Detector: Differential Refractometer (RI)) (Manufactured by Tosoh Corporation) Columns: TSKgel guardcolumnHHR(30)HT (7.5mm I.D. × 7.5cm) × 1 + TSKgel GMHHR-H(20)HT (7.8mm I.D. × 30cm) × 3 (Manufactured by Tosoh Corporation) Eluent: 1,2,4-Trichlorobenzene (for GPC, manufactured by Fujifilm Wako Pure Chemical Industries) + BHT (0.05%) Flow rate: 1.0mL / min Detection condition: polarization-(-) Injection volume: 0.3mL Column temperature: 140℃ Temperature: 40°C Sample concentration: 1 mg / mL Sample preparation: Weigh the sample, add the solvent (1,2,4-trichlorobenzene with 0.1% BHT added), and dissolve by shaking at 140°C for 1 hour. Then, filter by heating through a 0.5 μm sintered filter. Calibration Curve: A calibration curve of the fifth order approximation curve will be created using standard polystyrene manufactured by Tosoh Corporation. However, the molecular weight will be converted to the molecular weight of polypropylene using the Q-factor. From the calibration curve and SEC chromatogram obtained by the above method, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) can be obtained using analysis software for the measuring device. From Mw and Mn, the molecular weight distribution (Mw / Mn) can be calculated.

[0043] The layer structure of the polypropylene film is not particularly limited and may consist of multiple layers or a single layer. A single layer is preferred for the polypropylene film from the viewpoint of having metal oxides uniformly distributed throughout the polypropylene film and having excellent dielectric properties.

[0044] The thickness of the resin film (polypropylene film) is preferably 0.5 to 25 μm, more preferably 1 to 20 μm, even more preferably 1 to 10 μm, and particularly preferably 1 to 6 μm. When the lower limit of the thickness is within the above range, the dielectric strength is ensured and the breakage of the polypropylene film is further suppressed. When the upper limit of the thickness is within the above range, the shape of the capacitor can be made smaller if the capacitance is the same.

[0045] The method for measuring the thickness of the resin film (polypropylene film) is as described in the examples.

[0046] (Additives) The polypropylene film used as the resin film constituting the capacitor of the present invention may further contain additives. Examples of additives include primary antioxidants, secondary antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and colorants.

[0047] (Metallic film) The capacitor of the present invention is a metallized film having a structure in which metallized films, each having a metal layer on both sides of the resin film, are adjacent to each other.

[0048] The metal layer functions as an electrode. Examples of metals that can be used for the metal layer include individual metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, as well as mixtures of these metals and their alloys. Among these, zinc and aluminum are preferred due to their superior environmental impact, cost-effectiveness, and capacitor performance.

[0049] The method for laminating metal layers on both sides of a resin film is not particularly limited and includes, for example, vapor deposition and sputtering. From the viewpoint of productivity and economic efficiency, the metal layers are preferably formed by vapor deposition, and more preferably by vacuum deposition. Examples of vacuum deposition methods include the crucible method and the wire method, and the most suitable one can be selected as appropriate.

[0050] The margin pattern when laminating metal layers by vapor deposition is not particularly limited, but from the viewpoint of further improving the safety of the capacitor and further suppressing capacitor failure and short circuits, it is preferable to apply a pattern including so-called special margins, such as a fishnet pattern or a T-margin pattern, to the surface of the polypropylene film.

[0051] The method for forming the margin is not particularly limited and may be done by known methods such as the tape method or the oil method.

[0052] The film resistance of the metal layer is not particularly limited, but is preferably 5 to 25 Ω / □, and more preferably 10 to 20 Ω / □.

[0053] The capacitor of the present invention is preferably a capacitor formed by winding or laminating the above-mentioned metallized film. The metallized film can be wound or laminated using conventionally known methods to form a film capacitor.

[0054] The capacitor of the present invention preferably has a configuration in which adjacent metal layers are drawn out to the same end face of the capacitor, as shown in Figure 3. In Figure 3, the metal layers (B1) and (B2), (C1) and (C2), and (D1) and (D2) are adjacent to each other. Furthermore, (B1) and (B2), and (D1) and (D2) are in contact with the left end face with respect to the plane of the paper and are drawn out to the same end face of the capacitor. In addition, (C1) and (C2) are in contact with the right end face with respect to the plane of the paper and are drawn out to the same end face of the capacitor.

[0055] The above-described film capacitor may have a structure in which multiple metallized films are laminated, or it may have a wound metallized film. Such a film capacitor can be suitably used as a capacitor for inverter power supply equipment that controls drive motors in electric vehicles, hybrid vehicles, etc. It can also be suitably used in applications such as railway vehicles, wind power generation, solar power generation, and general home appliances.

[0056] 2. Method for manufacturing polypropylene film The method for producing the polypropylene film used as the resin film constituting the capacitor of the present invention is not particularly limited. For example, it can be produced by a manufacturing method that includes a step of melting a polypropylene resin composition containing at least a polypropylene resin and additives as needed, preferably at a temperature of 225°C to 270°C.

[0057] There are no particular limitations on the method for preparing the polypropylene resin composition, but examples include a method of dry blending polypropylene resin polymerization powder or pellets with additives as needed using a mixer, or a method of melt-kneading by supplying the mixture to a kneader.

[0058] The above-mentioned mixer and kneader are not particularly limited. The kneader may be a single-screw type, a double-screw type, or a multi-screw type with three or more screws. In the case of a double-screw type, the screws may rotate in the same direction or in opposite directions.

[0059] In the case of mixing by melt kneading, the mixing temperature is not particularly limited as long as a good mixture is obtained. Generally, it is in the range of 200°C to 300°C, and from the viewpoint of suppressing resin degradation, 230°C to 270°C is preferred. In addition, to suppress degradation during resin mixing, an inert gas such as nitrogen may be purged into the kneader. The melt-kneaded resin may be pelletized to an appropriate size using a generally known granulator. This allows for the preparation of polypropylene resin pellets.

[0060] In the above-described method for manufacturing polypropylene film, first, polypropylene resin pellets, dry-blended polypropylene resin pellets, or mixed polypropylene resin pellets prepared by pre-melting and kneading are supplied to an extruder and heated and melted.

[0061] The above polypropylene resin composition is preferably melted at a temperature of 170°C to 320°C, and more specifically, the extruder temperature set during the heating and melting of the polypropylene resin composition is preferably 225°C to 270°C. This further improves the dielectric strength of the manufactured polypropylene film.

[0062] Next, the molten polypropylene resin composition is extruded into a sheet using a T-die, and cooled and solidified in at least one metal drum to form an unstretched cast sheet. The surface temperature of the metal drum (the temperature of the metal drum that first comes into contact after extrusion) is preferably 10°C to 105°C, and more preferably 15°C to 100°C. The surface temperature of the metal drum can be determined according to the physical properties of the polypropylene resin used.

[0063] The thickness of the above cast sheet is not particularly limited, but is preferably 50 μm or more and 2000 μm or less, and more preferably 100 μm or more and 1000 μm or less.

[0064] If the above polypropylene film is a biaxially oriented polypropylene film, the biaxially oriented polypropylene film can be manufactured by performing a biaxial stretching treatment on the above cast sheet. Biaxial stretching, which orients the film biaxially in the longitudinal and transverse directions, is preferred, and a sequential biaxial stretching method is preferred as the stretching method. As an example of the above sequential biaxial stretching method, first, the cast sheet is kept at a temperature of 100°C to 180°C (preferably 120°C to 170°C) and stretched in the flow direction by passing it between rolls with a speed difference. The stretching ratio in the flow direction is preferably 3.0 to 7.0 times, and more preferably 4.0 to 6.0 times. Next, the sheet is guided to a tenter and stretched in the transverse direction. The temperature during transverse stretching is preferably 160°C to 180°C, and the stretching ratio in the transverse direction is preferably 3 to 11 times. Next, after transverse stretching, the sheet is relaxed, heat-set, and wound up.

[0065] The above biaxially oriented polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat-setting processes are completed, from the viewpoint of further improving adhesive properties in subsequent processes such as metal vapor deposition. Corona discharge treatment can be carried out using known methods. It is preferable to use air, carbon dioxide, nitrogen gas, or a mixture thereof as the atmospheric gas.

[0066] The manufacturing method described above makes it possible to produce polypropylene film, which can be used as a resin film.

[0067] 3. Method for manufacturing metallized film In the manufacture of the capacitor of the present invention, a metallized film having metal layers on both sides of a polypropylene film as the resin film described above is used. A metallized film having this configuration can be usefully used as a metallized film for capacitors.

[0068] The metal layer functions as an electrode. Examples of metals that can be used for the metal layer include individual metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, as well as mixtures of these metals and their alloys. Among these, zinc and aluminum are preferred due to their superior environmental impact, cost-effectiveness, and capacitor performance.

[0069] The method for laminating a metal layer onto a polypropylene film is not particularly limited and includes, for example, vacuum deposition and sputtering. From the viewpoint of superior productivity and economic efficiency, vacuum deposition is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, and the most suitable one can be selected as appropriate.

[0070] One method for laminating metal layers on both sides of a polypropylene film is to repeat the deposition process twice on one side when forming the metal layer by vapor deposition. Specifically, after the first deposition on one side of the resin film is completed, it is flipped over, wound up, and the second deposition is performed. Alternatively, if the vapor deposition machine for depositing the metal layer has two deposition mechanisms to allow deposition on both sides, the metal layer can be deposited on one side and then continuously deposited without winding up. In either case, it is preferable to accurately align the polypropylene film in the width direction during the second deposition so that the margin patterns on the front and back of the metallized film do not shift.

[0071] The margin pattern when laminating metal layers by vapor deposition is not particularly limited, but from the viewpoint of further improving the safety of the capacitor and further suppressing capacitor failure and short circuits, it is preferable to apply a pattern including so-called special margins, such as a fishnet pattern or a T-margin pattern, to the surface of the polypropylene film.

[0072] The method for forming the margin is not particularly limited and may be done by known methods such as the tape method or the oil method.

[0073] The capacitor of the present invention is a capacitor having a structure in which the above-mentioned metallized films are adjacent to each other. The metallized film can be used in the method for manufacturing the capacitor of the present invention, which will be described later.

[0074] 4. Capacitor manufacturing method The present invention relates to a method for manufacturing a capacitor, characterized by having step 1 of winding or laminating a metallized film having metal layers on both sides of a resin film. According to the manufacturing method of the present invention, the above-described capacitor can be easily manufactured. The manufacturing method of the present invention will now be described.

[0075] (Process 1) Step 1 is a step of winding or laminating a metallized film having metal layers on both sides of a resin film. As the metallized film having metal layers on both sides of a resin film, the metallized film that constitutes the capacitor of the present invention described above can be used. The characteristics of the capacitor manufactured by the manufacturing method of the present invention, such as the porosity in the thickness direction, the thickness of the resin film, and the thickness of the metal layer, are as described above. By manufacturing a capacitor using the metallized film described above, the capacitor of the present invention, which has low loss and excellent long-term durability at high temperatures, can be easily manufactured.

[0076] The method of winding (element winding) or laminating the metallized film is not particularly limited; it can be wound using conventionally known methods or laminated to form a film capacitor.

[0077] The above-described film capacitor may have a structure in which multiple metallized films are laminated, or it may have a wound metallized film. Such a film capacitor can be suitably used as a capacitor for inverter power supply equipment that controls drive motors in electric vehicles, hybrid vehicles, etc. It can also be suitably used in applications such as railway vehicles, wind power generation, solar power generation, and general home appliances.

[0078] In the manufacturing method of the present invention, the capacitor may be subjected to a flattening treatment after step 1. Flattening further reduces unnecessary space, thereby minimizing the element volume. The method of flattening is not particularly limited, and for example, one method is to press the capacitor using a known method such as a press machine. When flattening is performed by pressing, the size of the void can be adjusted by adjusting the pressure during pressing.

[0079] (Heat treatment process) The manufacturing method of the present invention may include a heat treatment step after step 1 above, in which the manufactured capacitor is heat-treated (aged).

[0080] The heat treatment method is not particularly limited, and heating can be done using conventionally known heating methods. For example, the capacitor can be placed in a heating device such as a constant temperature bath or a vacuum constant temperature bath and heated. From the viewpoint of suppressing oxidation of the polypropylene film, which is the resin film constituting the capacitor, it is preferable to heat under vacuum conditions using a vacuum constant temperature bath.

[0081] The heating time (aging time) in the heat treatment process is preferably 0.5 to 30 hours, more preferably 1 to 20 hours, even more preferably 1.5 to 18 hours, and particularly preferably 2 to 15 hours.

[0082] The heating temperature (aging temperature) in the heat treatment process is preferably 100 to 130°C, and more preferably 105 to 120°C.

[0083] (Process 2) The manufacturing method of the present invention may include a step 2 after step 1 above, in which a pair of metallicon electrodes are formed on both ends of the capacitor.

[0084] The method for forming metallicon electrodes on both ends of a capacitor is not particularly limited and includes known methods such as metallicon thermal spraying. By irradiating both ends of a capacitor with metallicon, extraction electrodes can be formed on the capacitor.

[0085] The manufacturing method of the present invention preferably includes a step after step 2 in which leads are attached to the extraction electrodes formed by the above-mentioned metallicon thermal spraying. The material used to form the leads is not particularly limited as long as it is conductive, and known metal wires used as capacitor leads, such as copper wires, can be used.

[0086] In the manufacturing method of the present invention, after attaching leads to the extraction electrodes as described above, preferably the electrodes are placed in a resin case, epoxy resin is filled into the gaps, and the epoxy resin is cured. Through this process, a capacitor coated with epoxy resin can be obtained. [Examples]

[0087] The present invention will be further described in detail by examples, but these examples are for illustrative purposes only and do not limit the present invention in any way. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0088] The raw materials used in the examples and comparative examples are as follows. (Polypropylene resin) • Polypropylene resin: Manufactured by Prime Polymer Co., Ltd. MFR 5g / 10min

[0089] Manufacturing of biaxially oriented polypropylene film <Examples and Comparative Examples> The polypropylene resin described above was supplied to an extruder and melt-kneaded at a temperature of 250°C to prepare resin pellets.

[0090] The resin pellets prepared as described above were supplied to an extruder, melted at a resin temperature of 250°C, and then extruded using a T-die. Next, the pellets were wound onto a metal drum with a surface temperature maintained at 95°C and allowed to solidify to produce an unstretched cast raw material sheet. The unstretched cast raw material sheet was kept at a temperature of 140°C and stretched 4.5 times in the flow direction by passing it between rolls with a speed difference, and then immediately cooled to room temperature. Next, the cast raw material sheet was guided to a tenter and stretched 10 times in the width direction at a transverse stretching temperature of 158°C, after which it was relaxed and heat-set to wind up a biaxially oriented polypropylene film with a thickness of 2.3 μm. After winding up the biaxially oriented polypropylene film, it was placed in an atmosphere of approximately 20-45°C for 24 hours to perform an aging treatment to produce a biaxially oriented polypropylene film.

[0091] Capacitor manufacturing A metallized film was manufactured by depositing aluminum onto both sides of the obtained biaxially oriented polypropylene film using a vacuum deposition method to form a metal layer. The metallized film was slit into 30 mm widths, and two films were used as a pair to fabricate a wound element using a Kaito Manufacturing Co., Ltd. automatic winding machine 3KAW-N2. Winding was performed under the conditions of a winding tension of 176 g, contact pressure of 255 g, and winding speed of 4 m / s, for a total of 1350 turns.

[0092] The wound element was flattened by pressing it with the load (pressing pressure) shown in Table 1. While still pressed, zinc metal was sprayed onto the end face of the element to a thickness of approximately 0.7 mm to form the film electrode extraction section. Next, heat treatment was performed under vacuum conditions at 120°C for 15 hours to manufacture a flattened capacitor. Lead wires were soldered to the end face of the flattened capacitor, and the entire element was sealed with epoxy resin.

[0093] In Example 1, the pressing pressure for the flattening process was twice that of Example 2. Furthermore, in Comparative Example 3, the film resistance value of the metal layer was twice that of Example 2.

[0094] For each example and comparative example, various characteristics were evaluated under the following measurement conditions.

[0095] <Thickness of resin film> The thickness of biaxially oriented polypropylene film used in the manufacture of capacitors was measured using an outside micrometer (Mitutoyo Corporation high-precision digital micrometer MDH-25MB) in accordance with the measurement method compliant with JIS K7130:199A.

[0096] <film resistance value> Because the thickness of the metal layer in metallized films is very thin (only a few nanometers), making measurement difficult, the film resistance (surface resistivity) is measured as a substitute for thickness. Since the film resistance is inversely proportional to the thickness, a smaller film resistance indicates a thicker film. Film resistance was measured using a Mitsubishi Analytec GP-MCP-T610 low-resistivity meter with a thin-film measurement electrode (PSP probe MCP-TP06PRMH112). The probe was placed on the surface of the metallized film and the value was read. Measures were taken at five solid areas near the center of the film width, and the average value was taken as the film resistance. Note that the film resistance values ​​shown in Table 1 represent the average value of all metal layers used. Specifically, in Table 1, the examples use two double-sided metallized films as a set, so the average value of the four metal layers is shown. In the comparative examples, either one double-sided metallized film or two single-sided metallized films as a set is used, so the average value of the film resistance of the two metal layers is shown.

[0097] <Porosity> The porosity of the capacitor was measured using the following method. Since the capacitor was epoxy-sealed, the measurement was performed after removing the sealing resin. Specifically, the porosity was calculated using the following formula, based on the difference between the measured thickness of the flat-type capacitor and the theoretical thickness of the capacitor determined from the thickness of one metallized film. Void ratio (%) = [(Measured thickness) - (Theoretical thickness)] / (Theoretical thickness) × 100

[0098] Note that the measured thickness of the capacitor refers to the thickness of the flat portion of the element after the capacitor has been pressed and flattened, as shown in Figure 2.

[0099] The actual thickness of the capacitor was measured using a shape gauge. The thickness d of a single film was calculated from the weight of the element (weight-based thickness). The formula d = m / 2hwρ was used, where m is the weight of the capacitor element, h is the length of the metallized film used for the element, and w is the film width. Here, ρ is the density of the resin film. The density was measured using the density gradient tube method (see JIS K7112:1999), yielding 0.90 g / cm³. 3 That was the case.

[0100] The theoretical thickness of the capacitor was calculated by multiplying the film thickness d by the number of layers in the thickness direction.

[0101] The above porosity measurements were performed on three capacitor elements, and the average value was used as the measured value.

[0102] <Capacitance and ESR> A Hioki 9140-10 four-terminal probe was attached to a Keysight E4980AL LCR meter. Two terminals (leads) of the capacitor were pinched with the four-terminal probe, and an AC voltage of 10mV-1kHz was applied from the LCR meter's built-in power supply. Once the displayed value stabilized, the capacitance and ESR values ​​were read. Other measurement conditions followed JIS C5101-16:2009, "4.2.2 Capacitance" and "4.2.3 Dielectric Loss Tangent (tanδ)". Measurements were performed on nine capacitor elements, and the average value was used as the measured value.

[0103] <High-temperature load test (life test)> The capacitor was placed in an environment of 115°C and a voltage of 750V was applied for 500 hours. The decrease in capacitance before and after the test was calculated according to the following formula. The test was stopped at 24 hours, 100 hours, 200 hours, 300 hours, and 400 hours, and capacitance and IR measurements were taken. After each measurement, the temperature and voltage loads were restarted. The test was performed on two capacitor elements. Capacity reduction rate (%) = [(Capacitance before test) - (Capacitance after test)] / (Capacitance before test) × 100 The evaluation was conducted according to the following evaluation criteria. ○: The capacity reduction rate (average of two units) over 500 hours is 5% or less. △: Capacity reduction rate (average of 2 units) exceeds 5% after 500 hours. ×: A short circuit failure occurs in at least one test.

[0104] In the high-temperature load test described above, a short-circuit failure refers to a state where the IR value falls below the lower limit of measurement for the HIOKI DSM8104 super insulation resistance meter, making measurement impossible (no value displayed). Specifically, when measuring with 500V applied, this corresponds to an IR value of less than 50kΩ. A normal capacitor (a capacitor without a failure) has an IR of around 1GΩ, so this is clearly different, and it is easy to determine whether or not a short-circuit failure has occurred.

[0105] <Insulation Resistance (IR)> A Hioki Electric Corporation DSM8104 super insulation resistance meter was connected to a SME-8350 shielding box. A capacitor was placed inside the shielding box, and a 500V DC voltage was applied. The insulation resistance value was read after 1 minute. Other measurement conditions were in accordance with JIS C 5101-16:2009, "4.2.4 Insulation Resistance".

[0106] Table 1 shows the results of the above characteristic evaluations for the examples and comparative examples.

[0107] [Table 1]

[0108] From the results in Table 1, it was found that the capacitance was almost the same in Comparative Examples 1 and 2. This is thought to be because, although the positions of the voids differed when winding or laminating the metallized film, the amount (volume) of the voids was similar. Therefore, the evaluation of ESR and high-temperature load tests is also considered to be equivalent.

[0109] Furthermore, in Comparative Example 3, the thickness of the metal layer (electrode) is doubled, and although the capacitance is about the same as in Comparative Examples 1 and 2, the ESR is reduced. This is thought to be due to the reduced electrode resistance. In Comparative Example 3, because of the low ESR, heat generation in actual operating circuits is suppressed, and it is thought that the lifespan will be longer. However, it was found that short-circuit failures were more likely to occur in high-temperature load tests, and the high-temperature durability decreased. Short-circuit failures in high-temperature load tests have a serious adverse effect on capacitors.

[0110] In contrast, in Examples 1 and 2, the capacitance is larger compared to Comparative Examples 1 to 3. Also, similar to Comparative Example 3, in which the thickness of the metal layer (electrode) is doubled, the ESR is lower, and unlike Comparative Example 3, the evaluation in the high-temperature load test was ○ or △, indicating that no short-circuit failure occurred. [Explanation of symbols]

[0111] 10: Capacitor element 11, 12: End face 13: Cross section parallel to both end faces 14: Cross section perpendicular to both end faces

Claims

1. A capacitor characterized by having adjacent metallized films, each having a metal layer on both sides of a resin film.

2. The capacitor according to claim 1, comprising winding or laminating the aforementioned metallized film.

3. The capacitor according to claim 1, wherein the porosity in the thickness direction is 0.5% or more and 5% or less.

4. The capacitor according to claim 1, wherein the film resistance of the metal layer is 5 to 25 Ω / □.

5. The capacitor according to claim 1, wherein the metal layer is formed by vapor deposition.

6. The capacitor according to claim 1, wherein the adjacent metal layers are drawn out to the same end face of the capacitor.

7. A method for manufacturing a capacitor, A manufacturing method characterized by comprising step 1 of winding or laminating a metallized film having metal layers on both sides of a resin film.

8. The manufacturing method according to claim 7, wherein the capacitor has a void ratio in the thickness direction of 0.5% or more and 5% or less.

9. The manufacturing method according to claim 7, wherein the film resistance of the metal layer is 5 to 25 Ω / □.

10. The manufacturing method according to claim 7, further comprising a metal deposition step of forming a metal layer on both sides of the resin film by vapor deposition before step 1.

11. The manufacturing method according to claim 7, further comprising step 2 of forming a pair of metallicon electrodes on both end faces of the capacitor after step 1.

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