Film capacitor and method for manufacturing a film capacitor

Abstract

A film capacitor according to the present invention is provided with: a wound body of a pair of dielectric films that are stacked in the thickness direction and have a metal vapor-deposited on the surfaces; and a pair of end face electrodes that are formed on both ends of the wound body. With respect to this film capacitor, a void part is formed between the pair of dielectric films; the wound body has such a shape that the length in a first direction is shorter than the length in a second direction that is perpendicular to the first direction in a cross-section along the direction of the plane in which the end face electrodes extend; and the ratio of the thickness of the void part in the height direction of the wound body to the thickness of the dielectric films in the first direction is 0.003 to 0.029.

Description

[Technical Field]

[0001] This invention relates to a film capacitor and a method for manufacturing a film capacitor. [Background technology]

[0002] Film capacitors in which a dielectric film is wound are known. For example, Patent Document 1 describes a film capacitor comprising a body in which a dielectric film and a first electrode film and a second electrode film are wound multiple times, and having an air gap between the dielectric film and the first electrode film or the second electrode film. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2021 / 125006 [Overview of the project] [Problems that the invention aims to solve]

[0004] The film capacitor described in Patent Document 1 still has room for improvement in terms of reducing the degree of anodic oxidation.

[0005] This invention provides a film capacitor with reduced degree of anodic oxidation, and a method for manufacturing a film capacitor. [Means for solving the problem]

[0006] The film capacitor of the present invention is A wound body of a pair of dielectric films, each with a metal vapor-deposited on its surface and overlapping in the thickness direction, A pair of end face electrodes formed at both ends of the winding body, Equipped with, A gap is formed between the pair of dielectric films. The wound body has a shape in which the dimension in the first direction is shorter than the dimension in the second direction orthogonal to the first direction in a cross-section along the plane in which the end face electrode extends, and the ratio of the thickness of the void portion to the thickness of the dielectric film in the first direction is 0.003 or more and 0.029 or less.

[0007] The method for manufacturing a film capacitor of the present invention includes a step of forming a wound body by winding a pair of dielectric films with metal vapor-deposited on their surfaces in the thickness direction, a step of pressing the wound body, and a step of forming end face electrodes at both ends of the wound body, and in the step of pressing the wound body, by controlling the pressing pressure within a predetermined range, the thickness of the void formed between the pair of dielectric films is controlled to be 0.003 or more and 0.029 or less with respect to the thickness of the dielectric film.

Effect of the Invention

[0008] According to the present invention, it is possible to provide a film capacitor with a reduced anodic oxidation degree.

Brief Description of the Drawings

[0009] [Figure 1] Perspective view showing a film capacitor according to Embodiment 1 of the present invention [Figure 2] Perspective view showing a wound body with protective winding omitted [Figure 3] Diagram schematically showing a cross-section of the wound body in FIG. 2 [Figure 4] Flowchart showing a method for manufacturing a film capacitor according to Embodiment 1 of the present invention [Figure 5] Schematic view showing a pair of dielectric films of the film capacitor in FIG. 1 [Figure 6] Schematic perspective view showing a state in which the dielectric film in FIG. 5 is wound [Figure 7] Schematic cross-sectional view showing a step of pressing the wound body of the dielectric film in FIG. 6 [Figure 8] Schematic cross-sectional view showing the process of pressing the wound body of the dielectric film of FIG. 6 [Figure 9] Table showing the measurement results of capacitance loss and anodic oxidation degree [Figure 10] Schematic diagram for explaining anodic oxidation of a film capacitor

Mode for Carrying Out the Invention

[0010] (Background of the Invention) In the film capacitor described in Patent Document 1, in a cross-section perpendicular to the winding axis of the wound body, the diameter of the effective part is made larger than the diameter of the metallicon electrode to reduce the volume ratio of the metallicon electrode, and it has been proposed to miniaturize and increase the capacitance of the film capacitor. In the film capacitor of Patent Document 1, by expanding a gas such as air remaining in the main body in which the dielectric film, the first electrode film, and the second electrode film are wound, a void is formed between the dielectric films to increase the diameter of the effective part.

[0011] On the other hand, in a film capacitor in which a dielectric film is laminated or wound, when a voltage is applied, anodic oxidation may be caused on the surface of the electrode film formed on the film due to the reaction of the electrode film with moisture or ionic impurities contained in the film.

[0012] FIG. 10 is a schematic diagram for explaining anodic oxidation in a film capacitor. As shown in FIG. 10, anodic oxidation is a phenomenon in which moisture (H2O), ionic impurities (Ion), etc. contained in the dielectric film 110 react with the electrode film 120 formed of aluminum or the like, and an oxide film 121 is formed on the surface. When anodic oxidation occurs, there is a problem that the effective electrode area of the electrode film 120 formed on the dielectric film 110 decreases, resulting in a decrease in the capacitance of the film capacitor or an increase in the ESR. In order to reduce anodic oxidation, providing a void between the dielectric films 110 has been studied.

[0013] ​The inventors have found that if the gaps between dielectric films are too large, the capacitance of the film capacitor will be smaller than the design value, and therefore it is important to appropriately control the size of the gaps.

[0014] In the film capacitor described in Patent Document 1, voids are formed by expanding gases such as air remaining in the film, making it difficult to control the size of these voids. As a result, the voids may become larger than desired, leading to a problem where the capacitance of the film capacitor decreases.

[0015] Therefore, the present inventors investigated the appropriate gap thickness and studied a film capacitor that can suppress the decrease in capacitance while reducing the degree of anodizing, and arrived at the following invention.

[0016] Hereinafter, Embodiment 1 of the present invention will be described with reference to the attached drawings. In addition, in each drawing, the elements are exaggerated to facilitate the explanation.

[0017] (Embodiment 1) [Overall structure] Figure 1 is a perspective view showing a film capacitor according to Embodiment 1 of the present invention. The X, Y, and Z directions in the figure represent the lateral, vertical, and height directions of the film capacitor 1, respectively.

[0018] As shown in Figure 1, the film capacitor 1 comprises a winding body 10 of a pair of dielectric films and a pair of end face electrodes 20 formed at both ends of the winding body 10.

[0019] The wound body 10 is formed by stacking a pair of dielectric films, each having a metal vapor-deposited electrode on its surface, in the thickness direction, then winding and pressing them into a flattened shape. Alternatively, the wound body 10 may be formed by stacking and pressing multiple dielectric films.

[0020] In the wound body 10, the cross-section in the direction along the plane (YZ plane) from which the end face electrode 20 extends has a shape in which the dimension τ1 in the first direction (Z direction) is shorter than the dimension d1 in the second direction (Y direction). In other words, the wound body 10 is formed in a columnar shape with an oval cross-section.

[0021] Figure 2 is a perspective view showing a winding body with the protective winding omitted. In this embodiment, a protective winding is formed on the surface of the winding body 10 to protect the dielectric film. As shown in Figure 2, the winding body 10 is formed by winding a pair of dielectric films 31 and 32 overlapping in the thickness direction. More specifically, after overlapping one dielectric film 31 and the other dielectric film 32, the pair of dielectric films 31 and 32 are wound up and pressed into a flattened shape to form a winding body 10 having an oval cross-section.

[0022] As the dielectric film, for example, a plastic film containing a thermoplastic resin such as polyethylene terephthalate, polypropylene, polyphenylene sulfide, or polyethylene naphthalate can be used, or a plastic film containing a thermosetting resin such as a cured product obtained by the reaction of hydroxyl groups (OH groups) of a first organic material and isocyanate groups (NCO groups) of a second organic material can be used. As the metal vapor deposition electrode formed on the surface of the dielectric film, for example, a metal such as aluminum or zinc can be used.

[0023] The end electrodes 20 can be formed on both ends of the wound body 10 by thermal spraying a metal such as zinc.

[0024] Figure 3 is a schematic diagram showing a cross-section of the wound body shown in Figure 2. As shown in Figure 3, a gap 41 is provided between the pair of dielectric films 31 and 32. For example, the gap 41 can be formed by overlapping and winding the pair of dielectric films 31 so that an air layer is included between the dielectric films 31 and 32. The formation of the gap 41 between the dielectric films 31 and 32 reduces the stress on the wound body 10 when an external force is applied, and also suppresses the anodic oxidation of the metal vapor-deposited electrodes formed on the surfaces of the dielectric films 31 and 32.

[0025] In the first direction (Z direction), the ratio of the thickness of the void in the height direction of the winding body 10 to the thickness of the dielectric films 31 and 32 is between 0.003 and 0.029.

[0026] The thickness of the dielectric films 31 and 32 represents the sum of the thicknesses f1 to f7 of the laminated dielectric films 31 and 32 in the first direction (Z direction) of the wound body 10. The thickness of the void 41 in the height direction (Z direction) of the wound body 10 represents the sum of the thicknesses s1 to s6 of the void 41 in the first direction. In other words, the ratio of the thickness of the void to the thickness of the dielectric films 31 and 32 represents the ratio of the sum of the thicknesses s1 to s6 of the void 41 to the sum of the thicknesses f1 to f7 of the dielectric films 31 and 32. To put it another way, the size of the void 41 is set such that the sum of the thicknesses s1 to s6 of the void 41 is between 0.003 and 0.029 relative to the sum of the thicknesses f1 to f7 of the dielectric films 31 and 32.

[0027] Furthermore, the void portion 41 does not necessarily have to be formed to a uniform thickness, and there may be areas where the dielectric films 31 and 32 are in contact.

[0028] [Manufacturing method] Figure 4 is a flowchart showing a method for manufacturing a film capacitor according to Embodiment 1 of the present invention. Figure 5 is a schematic diagram showing a pair of dielectric films of the film capacitor in Figure 1. Figure 6 is a schematic perspective view showing the dielectric film in Figure 5 in a wound state. Figure 7 is a schematic cross-sectional view showing the process of pressing the wound dielectric film in Figure 6. Figure 8 is a schematic cross-sectional view showing the process of pressing the wound dielectric film in Figure 6. The method for manufacturing the film capacitor 1 will be described with reference to Figures 4 to 8.

[0029] In step S1, the wound body 10 is formed. To form the wound body 10, first, as shown in Figure 5, a pair of dielectric films 31 and 32, on which metal is deposited on the surface, are stacked in the thickness direction. The dielectric films 31 and 32 are strip-shaped dielectric films of length L with metal-deposited electrodes 31a and 32a formed on their surfaces. The metal-deposited electrodes 31a and 32a are formed on the surface of the dielectric films 31 and 32, excluding the insulating margins 31b and 32b. In addition, pattern margins (not shown) on which metal is not deposited may be formed on the metal-deposited electrodes 31a and 32a.

[0030] As shown in Figure 5, the pair of dielectric films 31 and 32 are stacked with a length As offset in the width direction W. By stacking the dielectric films 31 and 32 in this manner, it is possible to suppress the occurrence of a short circuit between the metal deposition electrodes 31a and 32a and the end electrodes 20 after the end electrodes 20 are formed in a later process.

[0031] Next, when the pair of superimposed dielectric films 31 and 32 are wound, a cylindrical wound body 10 is formed, as shown in Figure 6. As shown in Figure 7, in the wound body 10 formed in step S1, the dimension h1 in the first direction (Z direction) and the dimension h2 in the second direction (Y direction) in the cross section perpendicular to the winding axis (YZ plane) are approximately the same, and the wound body 10 has a cylindrical shape with a substantially circular cross section.

[0032] In step S2, the winding body 10 is pressed. As shown in Figures 7 and 8, the sides of the cylindrical winding body 10 are pressed to form a flattened winding body 10. For example, a flattened winding body 10 can be formed by placing the cylindrical winding body 10 in a press device and applying pressure in the direction of arrow P. By adjusting the pressing pressure, the thickness of the gap 41 between the dielectric films 31 and 32 can be adjusted. More specifically, the greater the pressing pressure, the smaller the thickness of the gap 41. By pressing the winding body 10 in step S2, as shown in Figure 8, the dimension h3 in the first direction in the cross section perpendicular to the winding axis (YZ plane) becomes relatively smaller than the dimension h4 in the second direction.

[0033] In step S3, end electrodes 20 are formed on the pressed winding body to complete the film capacitor 1 shown in Figure 1. The end electrodes 20 can be formed on both ends of the winding body 10 by thermal spraying a metal such as zinc.

[0034] [Examples] In the film capacitor described in Embodiment 1, the thickness of the gap 41 was changed by varying the pressing pressure in the process of pressing the wound body 10 (step S2 in Figure 4), and the deviation from the design capacitance value of the film capacitor 1 and the degree of anodizing were measured. The specific results are shown in Figure 9.

[0035] <Film Capacitor> In the embodiment, the deviation from the design capacitance value and the degree of anodizing were measured using a film capacitor in which the ratio of the thickness of the void portion 41 to the thickness of the dielectric films 31 and 32 was varied from 0 to 0.06 by changing the press pressure in 11 steps.

[0036] <Thickness of the void> The ratio of the thickness of the void to the thickness of the dielectric film in each film capacitor was calculated using the following method.

[0037] First, measure the height τ1 in the first direction of the film capacitor (see Fig. 1). Next, disassemble the film capacitor to determine the number of windings of the dielectric film. Let the obtained number of windings be T film , and the film thickness of the dielectric film be d film . Note that the film thickness of the dielectric film includes the thickness of the metal vapor deposition electrode. Similarly, determine the number of windings of the pre-winding and protective winding other than the dielectric film in the film capacitor. The pre-winding is the part that serves as the core when winding the dielectric film, and the protective winding is the part wound around the outer periphery to protect the dielectric film and the metal vapor deposition electrode. Let the number of windings of the pre-winding be T in , the film thickness be d in , the number of windings of the protective winding be T out , and the film thickness be d out .

[0038] When assuming that no void is formed, the height τ0 in the first direction of the film capacitor is calculated by Equation (1).

[0039] τ0 = d in × T in × 2 + d out × T out × 2 + T film × d film × 4 ···(1)

[0040] Note that for the pre-winding and the protective winding, when wound once, two layers are included in the first direction. Therefore, the thickness in the first direction is calculated as "number of windings × film thickness × 2". For the dielectric film, since two sheets are wound as a pair, four layers are included in the first direction for one winding. Therefore, the thickness in the first direction is calculated as "number of windings × film thickness × 4".

[0041] By subtracting τ0 from τ1, that is, according to Equation (2), the thickness D of the void included in the film capacitor can be calculated.

[0042] D = τ1 - τ0 ···(2)

[0043] The thickness d of the void per sheet of the dielectric film airThis is calculated by equation (3).

[0044] d air =D / (4*T film ) ···(3)

[0045] Therefore, the ratio R of the thickness of the void to the thickness of the dielectric film is calculated by equation (4).

[0046] R=d air / d film ...(4)

[0047] <Design capacity value> The design capacitance value of a film capacitor can be calculated as follows:

[0048] The film capacitor is disassembled and the dielectric film is removed. The film width A0, effective electrode width A, insulating margin width Am, and dielectric film length L of the dielectric film are measured (see Figure 5). The effective electrode width A represents the width of the metal deposited electrode that actually acts as a capacitor. The permittivity of vacuum is ε0, and the relative permittivity of the dielectric film is ε film Let N be the effective electrode area ratio. The effective electrode area ratio N represents the ratio of the area of ​​the effective electrode, calculated by "effective electrode width A × dielectric film length L", to the area of ​​the part remaining after deducting the pattern margin, etc. Specifically, the effective electrode area ratio N can be calculated by "N = (L × A - Sp) / (L × A)". Sp represents the area where metal is not deposited, such as the pattern margin. The effective electrode width A can be calculated by "A = A0 - 2Am - As". The design capacitance value C0 of the film capacitor can be calculated by equation (5).

[0049] C0 = ε0ε film ×L×A×N / d film ...(5)

[0050] <Capacity loss relative to design capacity> The capacitance loss ΔC for each film capacitor relative to its design capacitance value C0 can be calculated using equation (6), with respect to the measured capacitance value C1 and the design capacitance value C0 of each film capacitor.

[0051] ΔC = (C0 - C1) / C0 × 100 ... (6)

[0052] <Measurement of Anodizing Degree> High-temperature and high-humidity tests were conducted on film capacitors whose air gap 41 thickness was adjusted by different pressing pressures, and the degree of anodic oxidation was measured after the high-temperature and high-humidity tests. The degree of anodic oxidation was measured by determining the percentage of the area where the metal deposition electrodes 31a and 32a of the dielectric films 31 and 32 had turned white.

[0053] In the high-temperature and high-humidity test, a voltage of 500V was applied for 1000 hours in an environment with a temperature of 85°C and a humidity of 85%RH.

[0054] After high-temperature and high-humidity testing, the film capacitor was disassembled, and the percentage of the effective electrode area that had turned white due to anodizing was calculated. The areas that had turned white due to anodizing were determined by visual inspection. The difference between the discolored and non-discolored areas was clearly visible, and there was no substantial difference in the area percentage results compared to when image processing technology was used.

[0055] Effective electrode area A all This was calculated using the formula "dielectric film length L × effective electrode width A". The area of ​​the part that has turned white due to anodizing is A. ox Therefore, the degree of anodic oxidation O can be calculated using equation (7).

[0056] O=A ox / A all ×100 ···(7)

[0057] <Measurement results> Figure 9 is a table showing the measurement results for capacity loss and degree of anodizing. Referring to Figure 9, we will consider the preferred range for the thickness of the void 41.

[0058] When the ratio R of the air gap thickness to the dielectric film thickness is 0.029 or less, the capacitance loss ΔC, which indicates how much the measured capacitance value C1 of the film capacitor has decreased relative to the design capacitance value C0, is within 10%. This is because the capacitance loss ΔC increases as the thickness of the air gap between the dielectric films increases. Since the product specifications for film capacitors require that the capacitance loss ΔC relative to the design capacitance value C0 be within 10%, it is desirable that the ratio R of the air gap thickness be 0.029 or less.

[0059] Furthermore, if the ratio R of the void thickness to the dielectric film thickness is 0.003 or higher, the degree of anodizing can be kept within 5%. A higher degree of anodizing increases the equivalent series resistance (ESR) when voltage is applied to the film capacitor. Film capacitor product specifications require that the ESR increase rate be within 50%, and keeping the degree of anodizing within 5% ensures that the product specifications are met more reliably. Therefore, it is desirable that the ratio R of the void thickness is 0.003 or higher. The ESR increase rate is an indicator showing, for example, how much the ESR increased before and after a high-temperature, high-humidity test.

[0060] Based on the above results, the ratio R of the void thickness to the dielectric film thickness is preferably between 0.003 and 0.029.

[0061] [effect] According to the above-described embodiment, the following effects can be achieved.

[0062] The film capacitor 1 comprises a winding body 10 and a pair of end electrodes 20. The winding body 10 is formed by winding a pair of dielectric films 31 and 32, which have metal deposited on their surfaces and overlap in the thickness direction. The end electrodes 20 are formed at both ends of the winding body 10. A gap 41 is formed between the pair of dielectric films 31 and 32. In a cross-section along the plane (YZ plane) from which the end electrodes 20 extend, the winding body 10 has a shape in which the dimension τ1 in the first direction (Z direction) is shorter than the dimension d1 in the second direction (Y direction) which is perpendicular to the first direction. The ratio of the thickness of the gap 41 in the height direction of the winding body 10 to the thickness of the dielectric films 31 and 32 in the first direction is 0.003 or more and 0.029 or less.

[0063] This configuration suppresses the anodic oxidation of the film capacitor 1. By providing a gap 41 between the dielectric films 31 and 32, the anodic oxidation of the metal deposition electrodes 31a and 32a can be prevented. On the other hand, by setting the thickness ratio of the gap 41 to 0.003 or more and 0.029 or less, the capacitance loss of the film capacitor 1 can be suppressed. Therefore, it is possible to provide a film capacitor 1 that is less prone to anodic oxidation and has low capacitance loss.

[0064] Furthermore, when the design capacitance value of film capacitor 1 is C0 and the measured capacitance value is C1, (C0-C1) / C0×100 is 10% or less.

[0065] This configuration makes it possible to provide a film capacitor 1 with low capacitance loss.

[0066] A method for manufacturing a film capacitor 1 includes the steps of forming a winding, pressing the winding, and forming end electrodes. The step of forming a winding includes winding a pair of dielectric films 31 and 32, each having a metal vapor-deposited on its surface, in overlapping directions in the thickness direction. The step of pressing the winding includes controlling the thickness of the gap 41 formed between the pair of dielectric films 31 and 32 by controlling the pressing pressure within a predetermined range.

[0067] This configuration makes it possible to provide a film capacitor 1 in which a gap of appropriate thickness is formed.

[0068] (Summary of the embodiment) (1) The film capacitor of the present invention comprises a winding body of a pair of dielectric films overlapping in the thickness direction, with a metal deposited on its surface, and a pair of end electrodes formed at both ends of the winding body, wherein a gap is formed between the pair of dielectric films, and the winding body has a shape in which the dimension in the first direction is shorter than the dimension in the second direction perpendicular to the first direction in a cross section along the direction on which the end electrodes extend, and the ratio of the thickness of the gap in the height direction of the winding body to the thickness of the dielectric film in the first direction is 0.003 or more and 0.029 or less.

[0069] (2) In the film capacitor of (1), when the design capacitance value of the film capacitor is C0 and the measured capacitance value is C1, (C0-C1) / C0×100 may be 10% or less.

[0070] (3) The method for manufacturing a film capacitor of the present invention includes the steps of forming a wound body by overlapping and winding a pair of dielectric films on which metal has been deposited on their surfaces in the thickness direction, pressing the wound body, and forming end electrodes at both ends of the wound body, wherein the step of pressing the wound body controls the thickness of the gap formed between the pair of dielectric films to 0.003 or more and 0.029 or less with respect to the thickness of the dielectric film by controlling the pressing pressure within a predetermined range. [Industrial applicability]

[0071] This invention is useful for film capacitors used in various electronic devices, electrical equipment, industrial equipment, vehicle equipment, etc. [Explanation of Symbols]

[0072] 1 Film Capacitor 10 coils 20 End electrode 31, 32 Dielectric film 31a, 32a Metal evaporated electrode 31b, 32b Insulation margin 41 Cavity

Claims

1. A wound body of a pair of dielectric films, each having a metal vapor-deposited on its surface and overlapping in the thickness direction, wherein the pair of dielectric films does not contain fillers, and A pair of end face electrodes formed at both ends of the winding body, Equipped with, A gap is formed between the pair of dielectric films such that the degree of anodic oxidation of the pair of dielectric films after applying a voltage of 500V for 1000 hours in an environment of 85°C and 85% RH is between 0 and 4.

2. The wound body has a cross-section in the direction along the plane from which the end face electrode extends, in which the dimension in the first direction is shorter than the dimension in the second direction perpendicular to the first direction, and the ratio of the thickness of the void to the thickness of the dielectric film in the first direction is 0.003 or more and 0.029 or less. Film capacitor.

2. When the design capacitance of the film capacitor is C0 and the measured capacitance is C1, (C0 - C1) / C0 × 100 is 10% or less. The film capacitor according to claim 1.

3. A step of forming a wound body by overlapping and winding a pair of dielectric films, each having a metal vapor-deposited on its surface, in the thickness direction, wherein the pair of dielectric films does not contain fillers. The steps include pressing the aforementioned wound body, The steps include forming end face electrodes at both ends of the winding body, Includes, The step of pressing the winding body involves controlling the pressing pressure within a predetermined range so that the thickness of the gap formed between the pair of dielectric films is controlled to be between 0.003 and 0.029 of the thickness of the dielectric films, such that the degree of anodic oxidation of the pair of dielectric films after applying a voltage of 500V for 1000 hours in an environment of 85°C and 85% RH is between 0 and 4.

2. A method for manufacturing film capacitors.

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