Polyolefin films, metal film laminates using the same, film capacitors, power control units, electric vehicles, and electric aircraft

Abstract

The present invention addresses the problem of providing a polyolefin-based film which is excellent in terms of withstand voltage characteristics and reliability in high-temperature environments and is suitable for use in, for example, capacitors to be used at high temperatures and high voltages. The present invention provides a polyolefin-based film that includes A layer, which includes a cycloolefin-based resin and a polypropylene-based resin, and that has a total light transmittance of 85% or higher and an internal haze of 4.0% or less.

Description

[Technical Field]

[0001] This invention relates to a polyolefin film particularly suitable for use in capacitor applications. [Background technology]

[0002] In recent years, the majority of electrical equipment has been converted to inverters, and consequently, the demand for smaller and larger capacitors has become increasingly strong. In particular, applications such as automobiles (including electric vehicles and hybrid cars), electric aircraft, solar power generation, and wind power generation are meeting these demands, requiring capacitor films to have improved voltage resistance, maintain productivity and processability in capacitor element manufacturing, as well as further thinning and improved heat resistance.

[0003] Among polyolefin films, polypropylene films are considered to have superior heat resistance and dielectric breakdown voltage. On the other hand, for applications in the aforementioned fields, it is important that the film exhibits excellent dimensional stability at the ambient temperature and stable electrical performance (such as dielectric strength) in the range 10 to 20°C higher than the ambient temperature. From the perspective of heat resistance, it is said that in the future, when considering power semiconductor applications using silicon carbide (SiC), the ambient temperature will be even higher.

[0004] Against this backdrop, capacitors are required to have further improvements in heat resistance and voltage resistance, and capacitor films are required to have improved dielectric breakdown voltage in high-temperature environments exceeding 110°C. However, as described in Non-Patent Literature 1, the upper limit of the operating temperature for polypropylene film is said to be about 110°C, and it has been extremely difficult for polypropylene film to stably maintain dielectric breakdown voltage in such a temperature environment.

[0005] To miniaturize film capacitors and improve their heat resistance, it is conceivable to use thinner films, films with high dielectric constants, and films with glass transition temperatures exceeding the operating temperature range of the capacitors. For example, a laminate structure has been proposed in which two layers with different dielectric constants are alternately stacked, with one layer being a cycloolefin polymer having a glass transition temperature exceeding 130°C and the other being a polypropylene layer, thereby maintaining a large capacitance while possessing heat resistance and dielectric strength (e.g., Patent Document 1). Furthermore, films with improved processability have been proposed by co-extrusion and co-stretching when forming the laminate of cycloolefin polymer and polypropylene (e.g., Patent Documents 2 and 3). Moreover, films with enhanced thermal dimensional stability in high-temperature environments have been proposed by blending cycloolefin polymer and polypropylene resin, forming the film, and biaxially stretching it (e.g., Patent Document 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-012076 [Patent Document 2] International Publication No. 2017 / 022706 [Patent Document 3] Japanese Patent Publication No. 2018-034510 [Patent Document 4] Japanese Patent Publication No. 2020-521867 [Non-patent literature]

[0007] [Non-Patent Document 1] Motonobu Kawai, "The Leap Forward of Film Capacitors: From Automobiles to Energy," Nikkei Electronics, Nikkei BP, September 17, 2012 issue, pp. 57-62. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, the film in Patent Document 1 is not a co-extruded laminate, but a laminate in which a cycloolefin polymer layer is formed on a polypropylene film by a coating method. As a result, the cycloolefin polymer layer is prone to peeling, and its performance and reliability when used as a capacitor are not entirely satisfactory. The film in Patent Document 2 also has a base layer made of cycloolefin polymer alone, making it difficult to increase the area stretching ratio and resulting in insufficient voltage resistance in high-temperature environments. As a result, its performance and reliability when used as a capacitor are not entirely satisfactory. The film in Patent Document 3 also has a base layer made of cycloolefin polymer, and although it contains an elastomer to improve stretchability and increase the area stretching ratio, its voltage resistance in high-temperature environments is not satisfactory. As a result, its performance and reliability when used as a capacitor are not entirely satisfactory. The film in Patent Document 4 is simply a film blended with cycloolefin polymer and polypropylene resin, making it difficult to increase the area stretching ratio and resulting in insufficient voltage resistance in high-temperature environments. As a result, its performance and reliability when used as a capacitor are not entirely satisfactory.

[0009] Therefore, the present invention aims to provide a polyolefin-based film that exhibits excellent voltage resistance and reliability in high-temperature environments and is suitable for applications such as capacitors used under high temperature and high voltage conditions. [Means for solving the problem]

[0010] The inventors of the present invention have conducted extensive research to solve the above problems and have come to invent the following first polyolefin film and second polyolefin film of the present invention. The first polyolefin film of the present invention is a polyolefin film having a layer containing a cyclic olefin resin and a polypropylene resin (such layer is conveniently referred to as "layer A"), having a total light transmittance of 85% or more, and an internal haze of 4.0% or less.

[0011] The second polyolefin-based film of the present invention has a layer containing a cyclic olefin-based resin and a polypropylene-based resin (this layer is referred to as "layer A" for convenience), wherein when a cross-section obtained by cutting said layer A along a plane parallel to the main orientation axis direction and the thickness direction is defined as cross-section X, in a 1 µm square defined in said cross-section X such that a pair of sides are parallel to the thickness direction, there are 3 or more domains of said cyclic olefin-based resin passing through the pair of sides parallel to the thickness direction, and the internal haze is 4.0% or less. This is a polyolefin-based film characterized by the above. [Effect of the Invention]

[0012] According to the present invention, there can be provided a polyolefin-based film that is excellent in voltage resistance characteristics and reliability under high-temperature environments, and is suitable for applications such as capacitors used under high temperature and high voltage conditions. [Brief Description of Drawings]

[0013] [Figure 1] It is a schematic diagram showing a 1 µm square defined in cross-section X of the polyolefin-based film according to one embodiment of the present invention such that a pair of sides are parallel to the thickness direction, and domains of the cyclic olefin-based resin passing through the pair of sides parallel to the thickness direction of said square. [Figure 2] It is an enlarged photograph (at a magnification of 20000×) of cross-section X of the polyolefin-based film according to one embodiment of the present invention (the embodiment of Example 2). [Figure 3] It is a schematic diagram showing a 1 µm × 2 µm rectangle defined in cross-section X of the polyolefin-based film according to one embodiment of the present invention such that a pair of short sides are parallel to the thickness direction, and domains of the cyclic olefin-based resin passing through the pair of sides parallel to the thickness direction of said rectangle. [Mode for Carrying Out the Invention]

[0014] The inventors of the present invention have conducted extensive research to solve the aforementioned problems and have concluded the following reasons why the films described in the above-mentioned Patent Documents 1 to 4 do not have sufficient dielectric breakdown voltage in high-temperature environments, and why their withstand voltage characteristics, reliability, and processability in high-temperature environments when used as capacitors are insufficient.

[0015] In other words, the film in Patent Document 1 is an unstretched film laminated by a coating method, and therefore we believe it has problems such as delamination between layers in high-temperature environments, insufficient mechanical properties, particularly insufficient elongation at break making it prone to breakage during capacitor element processing, and reduced dielectric strength in high-temperature environments. When considering the dielectric strength in high-temperature environments of the films in Patent Documents 2 and 3, we believe that the magnification ratio during longitudinal stretching in film formation is not necessarily sufficient, and the presence of a large amount of movable amorphous components in the film results in a low dielectric breakdown voltage at high temperatures. Similarly, when considering the dielectric strength in high-temperature environments of the film in Patent Document 4, we believe that the mixing ratio of the cycloolefin polymer and polypropylene resin is not sufficient, making it difficult to sufficiently increase the magnification ratio during longitudinal stretching in film formation, and the presence of a large amount of movable amorphous components in the film results in a low dielectric breakdown voltage at high temperatures.

[0016] Based on the above considerations, the inventors conducted further investigations and found that the above problem can be solved by providing a polyolefin film having a layer A containing a cyclic olefin resin and a polypropylene resin, having a total light transmittance of 85% or more, and an internal haze of 4.0% or less. Furthermore, they found that the above problem can be similarly solved by providing a polyolefin film having a layer A containing a cyclic olefin resin and a polypropylene resin, and a cross section X obtained by cutting the layer A with a plane parallel to the main orientation axis and the thickness direction, such that in a 1 μm square defined within the cross section X such that a pair of sides are parallel to the thickness direction, there are three or more domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction, and the internal haze is 4.0% or less.

[0017] In other words, the first polyolefin film of the present invention is a polyolefin film characterized in that, when a layer containing a cyclic olefin resin and a polypropylene resin is defined as layer A, it has the A layer, a total light transmittance of 85% or more, and an internal haze of 4.0% or less. The second polyolefin film of the present invention is a polyolefin film characterized in that, when a layer containing a cyclic olefin resin and a polypropylene resin is defined as layer A, and the A layer is cut by a plane parallel to the main orientation axis and the thickness direction, the A layer is present, and in a 1 μm square defined within the X cross section such that a pair of sides are parallel to the thickness direction, there are three or more domains of the cyclic olefin resin passing through the pair of sides, and the internal haze of 4.0% or less.

[0018] The first and second polyolefin films of the present invention will be described in detail below. When upper and lower limits are specified separately for preferred ranges, the combination thereof is arbitrary. Furthermore, the first and second polyolefin films of the present invention may be collectively referred to as the present invention or the polyolefin films of the present invention.

[0019] Furthermore, in this specification, polyolefin films may be simply referred to as "films." Note that the polyolefin film of the present invention is not a microporous film and therefore does not have a large number of pores. In other words, the polyolefin film of the present invention refers to polyolefin films other than microporous films. Here, a microporous film is defined as a film having a pore structure that penetrates both surfaces of the film and has an air permeability of 5,000 seconds / 100 ml or less for the transmission time of 100 ml of air at 23°C and 65% relative humidity using a Type B Gurley tester of JIS P 8117 (1998).

[0020] The polyolefin film of the present invention is required to have a layer A, which is a layer containing a cyclic olefin resin and a polypropylene resin, in order to achieve both thermal stability and dielectric strength. By adopting this configuration, the polyolefin film obtained will have excellent thermal stability and dielectric strength due to the effects of the high thermal stability of the cyclic olefin resin and the high dielectric strength of the polypropylene resin. The polyolefin film of the present invention may have any of the following configurations: a single film configuration consisting of only one layer A, a laminated configuration in which a total of two or more layers of layers A are laminated in the thickness direction, or a laminated configuration in which a total of two or more layers of layers other than layers A are laminated in the thickness direction. Furthermore, if the polyolefin film of the present invention has multiple layers A, their compositions may be the same or different.

[0021] Here, a polyolefin film refers to a sheet-like molded article containing more than 50% by mass and up to 100% by mass of polyolefin resin, when the total components constituting the film are considered to be 100% by mass. Here, a polyolefin resin refers to a resin containing more than 50 mol% and up to 100 mol% of olefin units, when the total constituent units constituting the resin are considered to be 100 mol%, and the same interpretation can be applied to polypropylene resins and cyclic olefin resins by replacing olefin units with propylene units and cyclic olefin units, respectively. The thickness direction refers to the direction perpendicular to the film surface.

[0022] The first polyolefin film of the present invention must have a total light transmittance of 85% or more and an internal haze of 4.0% or less, from the viewpoint of achieving both thermal stability and dielectric strength. Here, total light transmittance refers to the total light transmittance when light is incident perpendicularly to the film surface, in other words, the total light transmittance in the film thickness direction. Similarly, internal haze refers to the internal haze measured when light is incident perpendicularly to the film surface. From the viewpoint of thermal stability and dielectric strength, the total light transmittance is preferably 88% or more, more preferably 90% or more, and even more preferably 92% or more. There is no particular upper limit, but it is set to 99.9%. Furthermore, the internal haze of the first polyolefin film of the present invention is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less, from the viewpoint of thermal stability and dielectric strength. There is no particular lower limit, but it is set to 0.1%.

[0023] A total light transmittance of 85% or more and an internal haze of 4.0% or less indicates that, in a layer containing a cyclic olefin resin and a polypropylene resin, the formation of minute voids due to delamination at the sea-island interface of the sea-island structure (where the polypropylene resin is considered the sea and the cyclic olefin resin is considered the islands) is suppressed, and furthermore, the island structure (hereinafter sometimes referred to as the domain structure) is small or thin. As a result, the first polyolefin film of the present invention that satisfies the above requirements can obtain the effects of the high thermal stability of the cyclic olefin resin and the high dielectric strength of the polypropylene resin, and the dielectric breakdown voltage of the film can be increased in high-temperature environments. Furthermore, when such a film is used in a capacitor, it becomes less likely to cause short-circuit failure even when used for a long time in high-temperature environments, the dielectric strength is maintained, and high reliability can be obtained. The total light transmittance and internal haze can be measured with a known haze meter, and the detailed conditions will be described later.

[0024] In the first polyolefin film of the present invention, a method can be used to achieve a total light transmittance of 85% or more and an internal haze of 4.0% or less by controlling the domain structure (sea-island structure) of the A layer. For example, it is effective to prepare a compound resin raw material by pre-kneading a cyclic olefin resin and a polypropylene resin as the raw material for the A layer, to melt-extrude it into a sheet while controlling the content of the cyclic olefin resin, to perform biaxial stretching at an area stretching ratio of 35.0 times or more, and to perform a relaxation treatment while applying heat treatment after biaxial stretching.

[0025] Pre-preparing the compound resin raw materials as described above has the effect of increasing total light transmittance, lowering internal haze, and improving stretchability. This is presumed to be because, compared to simply mixing resins during film formation, the two types of resins are mixed more uniformly, causing the island component resin to be finely dispersed within the sea component resin, resulting in increased transparency and strength. Furthermore, using a diluted masterbatch of compound resin raw materials pre-mixed in a twin-screw extruder is also preferable because it improves the dispersibility of the cyclic olefin resin.

[0026] The second polyolefin film of the present invention requires that, when layer A is cut by a plane parallel to the main orientation axis and the thickness direction, the resulting cross-section X contains at least three domains of cyclic olefin resin passing through a 1 μm square defined such that a pair of sides are parallel to the thickness direction within cross-section X. The first polypropylene film of the present invention also preferably satisfies this requirement. In the polyolefin film of the present invention, the number of domains of cyclic olefin resin passing through the pair of sides (hereinafter sometimes referred to as a pair of sides parallel to the thickness direction) is preferably five or more, more preferably seven or more. There is no particular upper limit, but it is generally set at 100.

[0027] By creating three or more domains of cyclic olefin resin passing through a pair of sides parallel to the thickness direction, the high thermal stability of cyclic olefin resin and the high dielectric strength of polypropylene resin can be reflected in the polyolefin film, thereby increasing the dielectric breakdown voltage of the polyolefin film under high-temperature conditions. Furthermore, when such a film is used in a capacitor, it becomes less prone to short-circuit failure, especially during prolonged use in high-temperature environments, maintaining the dielectric strength of the capacitor and achieving high reliability.

[0028] Furthermore, in the second polyolefin film of the present invention, for the same reasons as in the first invention, it is necessary that the internal haze be 4.0% or less. The internal haze is preferably 3.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less. The lower limit is not particularly limited, but it is set at 0.1%. The definition of internal haze is as described above.

[0029] In the second polyolefin film of the present invention, a method can be used to control the domain structure (sea-island structure) of layer A to ensure that the number of cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction is three or more, and the internal haze is 4.0% or less. For example, it is effective to prepare a compound resin raw material by pre-kneading a cyclic olefin resin and a polypropylene resin as the raw material for layer A, to melt-extrude and form a sheet after controlling the content of the cyclic olefin resin, to perform biaxial stretching at an area stretching ratio of 35.0 times or more, and to perform a relaxation treatment while applying heat treatment after biaxial stretching. The same method can be used to ensure that the number of cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction is three or more in the first polyolefin film of the present invention.

[0030] In the polyolefin film of the present invention, "thickness direction" refers to the direction perpendicular to the film surface. "Longitudinal direction" refers to the direction corresponding to the flow direction in the film manufacturing process (hereinafter sometimes referred to as "MD"), and "width direction" refers to the direction perpendicular to the flow direction in the film manufacturing process within the film surface (hereinafter sometimes referred to as "TD"). If the film sample is in the shape of a reel or roll, the film winding direction can be said to be the longitudinal direction. When biaxial stretching is performed in the manufacturing of polyolefin film, stretching is performed in the longitudinal and width directions, but generally, the direction with the larger stretching ratio becomes the principal orientation axis direction. If the stretching direction (longitudinal and width directions) is determined but the stretching ratio is unknown, the maximum load until fracture can be measured in the tensile test described later, and the direction with the larger measured value can be determined as the principal orientation axis direction.

[0031] As described above, the principal orientation axis can be determined if the stretching direction and stretching ratio are known, but in the case of a film where these are unknown, the principal orientation axis can be determined by the following method. Specifically, prepare the film, orient it with an arbitrary direction upwards, and cut out a rectangular sample measuring 50 mm in length and 10 mm in width. <1> Sample <1> Define the direction of the longer side as 0°. Next, create a sample of the same size such that the direction of the longer side is rotated 15° to the right from the 0° direction. <2> Collect the sample. Similarly, rotate the rectangular sample by 15° along its longer side and collect the sample in the same manner. <3> ~ <12> A sample is taken. Next, each rectangular sample is set on a tensile testing machine (for example, Orientec's "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 20 mm so that the longer side is the tensile direction, and a tensile test is performed at a tensile speed of 300 mm / min in a room temperature atmosphere. At this time, the maximum load until the sample breaks is read, and the value obtained by dividing this by the cross-sectional area of ​​the sample before the test (film thickness × width) is calculated as the stress at the maximum point strength. The longer side of the sample with the highest value is designated as the main orientation axis of the polyolefin film and is designated as the width direction of the polyolefin film. The direction perpendicular to this is designated as the direction perpendicular to the main orientation axis of the polyolefin film and is designated as the longitudinal direction of the polyolefin film.

[0032] If the sample width is less than 50 mm and the above tensile test cannot be performed, the crystal orientation of the α(110) plane using wide-angle X-rays should be measured as follows, and the longitudinal and width directions of the film should be determined based on the following criteria. Specifically, X-rays (CuKα rays) should be incident perpendicular to the film surface, and the crystal peak at 2θ = approximately 14° (α(110) plane) should be scanned in the circumferential direction. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution should be considered the main orientation axis of the polyolefin film, and this should be considered the width direction of the polyolefin film. Alternatively, the direction perpendicular to this can be considered the longitudinal direction of the polyolefin film, or perpendicular to the main orientation axis of the polyolefin film.

[0033] The following describes, with reference to the drawings, a method for defining a 1 μm square within a cross-section X of the polyolefin film of the present invention such that a pair of sides are parallel to the thickness direction, and a method for determining the number of domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction. Figure 1 is a schematic diagram representing a 1 μm square defined within a cross-section X of a polyolefin film according to one embodiment of the present invention such that a pair of sides are parallel to the thickness direction, and domains of the cyclic olefin resin passing through the pair of sides of the square parallel to the thickness direction. Reference numerals 1 to 5 in Figure 1 represent, respectively, a part of the cross-section X, a sea portion, an island portion (domain), a 1 μm square defined within the cross-section X such that a pair of sides are parallel to the thickness direction, and a pair of sides parallel to the thickness direction. The left figure of Figure 2 is a part of the cross-section X, and the right figure is an enlarged view of the 1 μm square indicated by dashed lines within the cross-section X such that a pair of sides are parallel to the thickness direction. In the polyolefin film of the present invention, the sea portion is a polypropylene resin, and the island portion is a cyclic olefin resin.

[0034] When defining a 1 μm square within cross-section X such that a pair of sides are parallel to the thickness direction, the base of the square is set to the sea portion, and if a domain is located on the side opposite the base, it is considered not to exist and is not counted (no such domain exists in the example in Figure 1).

[0035] Here, "domains of cyclic olefin resin passing through a pair of edges parallel to the thickness direction" refers to domains of cyclic olefin resin passing through a pair of edges parallel to the thickness direction. In other words, in the example in Figure 1 (right figure), the 1st and 4th to 6th domains from the top fall into this category, while the 2nd and 3rd domains from the top do not. Therefore, in this example, there are four "domains of cyclic olefin resin passing through a pair of edges parallel to the thickness direction."

[0036] In the polyolefin film of the present invention, when the cross-section obtained by cutting the A layer with a plane parallel to the main orientation axis and the thickness direction is defined as cross-section X, it is preferable that, as shown in Figure 3, there are two or more domains of the cyclic olefin resin passing through a pair of short sides in a rectangle of 1 μm × 2 μm size, where the pair of short sides are defined to be parallel to the thickness direction. In the polyolefin film of the present invention, the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction is preferably four or more, more preferably six or more. There is no particular upper limit, but it is set to 100. By having two or more domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction, the cyclic olefin resin is more finely dispersed in a flattened manner within the plane, and the high thermal stability of the cyclic olefin resin and the high dielectric strength of the polypropylene resin can be reflected in the polyolefin film, thereby increasing the dielectric breakdown voltage of the polyolefin film in high-temperature environments. Furthermore, when such a film is used in a capacitor, it becomes less likely to cause short-circuit failure even when used for a long time in high-temperature environments, the dielectric strength of the capacitor is maintained, and high reliability can be obtained.

[0037] In the polyolefin film of the present invention, it is preferable that the average length in the thickness direction of the domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction is 1 nm or more and 300 nm or less. The average length in the thickness direction of the domains is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 99 nm or less, and particularly preferably 51 nm or less. By setting the average length in the thickness direction of the domains to 1 nm or more and 300 nm or less, the effects of the high thermal stability of the cyclic olefin resin and the high dielectric strength of the polypropylene resin can be reflected in the polyolefin film, and the dielectric breakdown voltage of the film in high-temperature environments can be increased. Furthermore, when such a film is used in a capacitor, it becomes less likely to cause short-circuit failure even when used for a long time in high-temperature environments, the dielectric strength is maintained, and high reliability can be obtained. The method for measuring the length in the thickness direction of the domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction, and the method for calculating the average value thereof are shown in the examples.

[0038] Furthermore, the average length of the domains in the thickness direction may be less than 1 nm. In such cases, for example, if the screw rotation speed is increased during pre-mixing in a twin-screw extruder, the resin temperature may rise above the set temperature due to shear heating, causing resin degradation. This can lead to foreign matter contamination and deterioration of reliability and voltage resistance when used as a capacitor. In other words, setting the average length of the domains in the thickness direction to 1 nm or more contributes to improving quality, reliability, and voltage resistance when used as a capacitor. From the above viewpoint, the lower limit of the average length of the domains in the thickness direction is preferably 5 nm, more preferably 10 nm, and even more preferably 20 nm.

[0039] In the polyolefin film of the present invention, a method can be used to set the average length in the thickness direction of the cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction to 1 nm or more and 300 nm or less. This can be the same as the method used in the first polyolefin film of the present invention, which sets the total light transmittance to 85% or more and the internal haze to 4.0% or less, or the method used in the second polyolefin film of the present invention, which sets the number of cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction to 3 or more and the internal haze to 4.0% or less.

[0040] In the polyolefin film of the present invention, the lower limit of the content of cyclic olefin resin in the total constituent components of layer A (or the film itself if the polyolefin film consists only of layer A) is preferably 1% by mass, more preferably 2% by mass, even more preferably 3% by mass, and particularly preferably 5% by mass, when the total resin components excluding various additives in the entire film, such as organic particles, inorganic particles, nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors, are taken as 100% by mass. On the other hand, the upper limit is preferably 39% by mass, more preferably 32% by mass, more preferably 25% by mass, even more preferably 19% by mass, particularly preferably 14% by mass, and most preferably 9% by mass. If the proportion of cyclic olefin resin in the entire film is high, the area magnification during stretching may not be increased, which may reduce the dielectric strength in high-temperature environments. If the proportion is low, the thermal dimensional stability in high-temperature environments may decrease, which may reduce the dielectric strength and reliability in high-temperature environments.

[0041] In the polyolefin film of the present invention, when the DSC chart obtained by raising the temperature from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC) shows the peak temperature of the largest absolute value of the heat flow on the vertical axis, the melting peak temperature Tm (°C) is preferably greater than 170°C and less than or equal to 200°C. Tm is more preferably 171°C or higher, even more preferably 172°C or higher, particularly preferably 173°C or higher, and most preferably 174°C or higher. The higher the Tm, the higher the crystallinity of the film, the better the thermal stability, and the higher the dielectric breakdown voltage in high-temperature environments. In other words, a Tm exceeding 170°C improves the dielectric strength characteristics in high-temperature environments and the reliability when used as a capacitor. On the other hand, the upper limit of Tm is preferably 200°C from the viewpoint of feasibility considering the olefin resin used in the film.

[0042] In this case, if two or more melting peaks are observed within the range of 170°C to 200°C, or if a multi-stage melting peak (a melting peak where two or more peaks overlap), known as a shoulder, is observed, Tm is defined as the temperature of the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart.

[0043] Tm can be measured as the endothermic peak temperature obtained when the film is heated from 30°C to 260°C at a rate of 20°C / min in a nitrogen atmosphere using a differential scanning calorimeter. Detailed measurement conditions will be described later.

[0044] In the polyolefin film of the present invention, to control the Tm to be between 170°C and 200°C or within the preferred range described above, for example, methods can be used to adjust the composition of the polyolefin resin or the stretching ratio. More specifically, it is effective to use a polypropylene resin with a high melting point as the polyolefin resin, or to increase the area stretching ratio to 35.0 times or more. It is also useful to prepare a compound resin raw material by pre-kneading a cyclic olefin resin and a polypropylene resin as a raw material for layer A.

[0045] From the viewpoint of dielectric strength, it is preferable that the polyolefin film of the present invention satisfies the following relationship between the MD (longitudinal direction) orientation parameter (MOP) and the TD (width direction) orientation parameter (TOP), which are determined from the Raman band intensity measured by Raman spectroscopy. MOP / TOP ≥ 0.11.

[0046] From the above viewpoint, MOP / TOP is preferably 0.15 or higher, more preferably 0.24 or higher, even more preferably 0.26 or higher, and most preferably 0.31 or higher. A preferred upper limit is 0.90 from the viewpoint of the possibility of achieving this while biaxial stretching. By increasing the value of MOP / TOP, the effect of high dielectric strength can be obtained, increasing the dielectric breakdown voltage of the film in high-temperature environments, and when used as a capacitor, it is less likely to cause short-circuit failure even when used for a long time in high-temperature environments, thus maintaining dielectric strength and achieving high reliability.

[0047] To control the MOP / TOP ratio to 0.11 or higher or within the preferred range described above, it is effective to, for example, dilute or melt-extrude a compound resin raw material containing a cyclic olefin resin and a polypropylene resin to form a sheet, and then biaxially stretch the resulting sheet under conditions where the area stretching ratio is 35.0 times or higher (preferably 40.0 times or higher) and the stretching ratio in the width direction is higher than the stretching ratio in the longitudinal direction, or to set the temperature of the preheating step immediately before stretching in the width direction to the stretching temperature in the width direction + 5 to +15°C in sequential biaxial stretching. Simultaneous biaxial stretching is also effective.

[0048] Here, the "longitudinal direction" (sometimes referred to as "MD") corresponds to the flow direction in the film manufacturing process, and the "width direction" (sometimes referred to as "TD") is the direction perpendicular to the longitudinal direction within the film plane. In other words, if the film sample is in the shape of a reel or roll, the winding direction is the longitudinal direction, and the direction parallel to the central axis of the winding core is the width direction.

[0049] From the viewpoint of using the polyolefin film of the present invention as a capacitor in a high-temperature environment, it is preferable that the loss tangent (tanδ0), determined by dynamic viscoelasticity measurement in the width direction at 0°C, is 0.06 or less. The loss tangent (tanδ) is the ratio of the storage modulus (E') (unit: Pa) to the loss modulus (E") (unit: Pa), and is calculated from the formula [tanδ = E" / E']. In other words, a smaller loss tangent (tanδ) suggests that molecular mobility is suppressed.

[0050] Since the polyolefin-based film of the present invention contains a polypropylene resin, the more the molecular mobility at 0°C, the glass transition temperature of the polypropylene resin, is suppressed, the higher the molecular chain constraint and the more stable the structure becomes. Furthermore, when the polyolefin-based film of the present invention is used as a capacitor, the film is usually wound in the longitudinal direction to process the capacitor element, so the winding direction (longitudinal direction) is constrained, but it is important to suppress the molecular mobility in the direction perpendicular to that (width direction). From the above viewpoint, tanδ0 is more preferably 0.05 or less, and even more preferably 0.04 or less. The lower limit is not particularly limited, but it is set to 0.001. By setting tanδ0 within this range, and the lower tanδ0 is, the higher the structural stability of the film, and the reliability is improved over long periods of time even when used as a capacitor in a high-voltage and high-temperature environment.

[0051] tanδ0 can be calculated by heating the film from -100°C to 180°C, plotting a viscoelastic-temperature curve using the dynamic viscoelastic method, and reading the storage modulus (E'0) and loss modulus (E''0) at 0°C from the resulting viscoelastic-temperature curve, then using the following formula. Detailed measurement conditions will be described later. Equation: tanδ0 = E''0 / E'0.

[0052] Methods for setting tanδ0 to 0.06 or less or within the above preferred range include, for example, using a polypropylene resin with a high mesopentade fraction and a high melting point, increasing the area stretching ratio to 35.0 times or more (preferably 40.0 times or more), setting the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction to the stretching temperature in the width direction + 5 to +15°C, and applying heat treatment after biaxial stretching. Simultaneous biaxial stretching is also effective.

[0053] The polyolefin film of the present invention, when used as a capacitor in a high-temperature environment, preferably has a widthwise shrinkage stress (135Tf) of 5.0 MPa or less, as determined by thermomechanical analysis (TMA). From the above viewpoint, 135Tf is preferably 3.5 MPa or less, more preferably 2.5 MPa or less, even more preferably 1.5 MPa or less, and most preferably 1.0 MPa or less. The lower limit of 135Tf is not particularly limited, but it is set to 0.01 MPa. Details of the TMA conditions, etc., will be described later.

[0054] To keep the shrinkage stress in the width direction (135Tf) below 5.0 MPa or within the preferred range mentioned above, it is effective to use a polypropylene resin with a high mesopentade fraction and a high melting point, to set the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction to the stretching temperature in the width direction + 5 to +15°C, and to perform a relaxation treatment with a relaxation rate greater than 5% during the heat treatment process after biaxial stretching.

[0055] When the polyolefin film of the present invention is used as a capacitor in a high-temperature environment, it is preferable that the thermal shrinkage rate (130S) in the longitudinal direction of the film after heating at 130°C for 10 minutes is greater than 2.0% and less than or equal to 5.0%, from the viewpoint of improving the reliability of the capacitor by ensuring that the capacitor elements are appropriately compressed during the heat treatment during element processing. From the above viewpoint, 130S is preferably 2.1% or more, more preferably 2.4% or more, even more preferably 2.8% or more, and most preferably 3.2% or more. 130S is preferably 4.8% or less, more preferably 4.4% or less, and even more preferably 4.0% or less.

[0056] To achieve the longitudinal thermal shrinkage rate (130S) within the preferred range described above, it is effective to, for example, use a polypropylene resin with a high mesopentad fraction and a high melting point, perform biaxial stretching at an area stretching ratio of 35.0 times or more, set the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction to the width direction stretching temperature + 5 to +15°C, and perform a relaxation treatment with a relaxation rate greater than 5% during the heat treatment process after biaxial stretching.

[0057] The layer structure of the polyolefin film of the present invention is not particularly limited as long as it has layer A, as described above, and may be a single-layer structure consisting only of layer A, or a laminated structure including layer A. However, from the viewpoint of exhibiting the stretchability of the film, excellent dielectric strength and reliability in high-temperature environments, and processability, it is preferable to have a layer B, where layer B is mainly composed of polypropylene resin, contains more polypropylene resin than layer A, and has a lower content of cyclic olefin resin.

[0058] Specific examples of such embodiments include a configuration having layer B on one side of layer A (a two-layer configuration of layer A / layer B), a configuration having layer B on both sides of layer A (a three-layer configuration of layer B / layer A / layer B), and a configuration of four or more layers with layer B as the outermost layer on both surfaces of the film. From the above viewpoint, a three-layer configuration of layer B / layer A / layer B and a configuration of four or more layers with layer B as the outermost layer on both surfaces of the film are more preferable, and a three-layer configuration of layer B / layer A / layer B is even more preferable. When there are multiple layers B, it is preferable that the composition of layer B contains a larger proportion of polypropylene resin than layer A and a smaller content (ratio) of cyclic olefin resin than layer A. With such a composition, each layer B may be the same or different.

[0059] Lamination methods that can be used in the polyolefin film of the present invention include, for example, a feed block method by co-extrusion, a multi-manifold method, and a coating method. However, from the viewpoint of production efficiency and production cost, a lamination method by co-extrusion (e.g., melt co-extrusion) is preferred.

[0060] When a polyolefin film has a laminated structure, the upper limit of the ratio of the thickness of layer A to the total thickness of the polyolefin film is preferably 99%, more preferably 95%, even more preferably 90%, and most preferably 85%, from the viewpoint of controlling film-forming properties and surface shape. The lower limit is preferably 10%, more preferably 15%, and even more preferably 20%. The ratio of the thickness of layer A can be determined, for example, in the case of a three-layer structure of layer B / layer A / layer B where layer B is directly laminated on both surfaces of layer A, by dividing the thickness of layer A (excluding the thickness of layer B on both surfaces) by the thickness of the polyolefin film and expressing it as a percentage. By having a ratio of layer A of 99% or less, the area multiplier during stretching can be sufficiently increased, and the decrease in dielectric strength in high-temperature environments can be reduced. On the other hand, by having a ratio of layer A of 10% or more, the decrease in thermal dimensional stability in high-temperature environments is reduced.

[0061] In the polyolefin film of the present invention, the polypropylene resin content of layer B is preferably 95% by mass or more, more preferably 96% by mass or more, and even more preferably 97% by mass or more, when the total components of layer B are considered as 100% by mass, from the viewpoint of obtaining high dielectric strength and excellent stretchability. There is no particular upper limit, but it is set to 100% by mass.

[0062] Next, we will describe resins that are preferable for use in the polyolefin-based film of the present invention.

[0063] The polyolefin film of the present invention preferably has a linear polypropylene resin (hereinafter sometimes referred to as polypropylene resin (A)) as its main component. Here, the main component refers to the component with the highest mass percentage (highest content) among all the components constituting the polyolefin film.

[0064] The lower limit of the number-average molecular weight (Mn) of the polypropylene resin (A) is preferably 30,000, more preferably 40,000, and even more preferably 50,000. On the other hand, the upper limit of Mn is preferably 90,000, and more preferably 80,000. By having the above properties in the polypropylene resin (A), deterioration of film formation stability, film strength, dimensional stability, and heat resistance can be reduced.

[0065] The mesopentade fraction of the polypropylene resin (A) is preferably 0.960 or higher. More preferably 0.965 or higher, even more preferably 0.970 or higher, particularly preferably 0.975 or higher, and most preferably 0.980 or higher. The mesopentade fraction is an index indicating the stereoregularity of the crystalline phase of polypropylene, measured by nuclear magnetic resonance (NMR) spectroscopy. A higher value indicates higher crystallinity and melting point, making it suitable for use at high temperatures, and is therefore preferable. There is no particular upper limit for the mesopentade fraction. To obtain a resin with such high stereoregularity, methods such as washing the resin powder obtained with a solvent such as n-heptane, or selecting a catalyst and / or co-catalyst and selecting the composition as appropriate are preferably employed.

[0066] The melting point of the polypropylene resin (A) is preferably 160°C or higher. More preferably 161°C or higher, even more preferably 162°C or higher, particularly preferably 164°C or higher, and most preferably 167°C or higher. A melting point of 160°C or higher for the polypropylene resin (A) reduces the decrease in dielectric strength under high-temperature environments when it is made into a film.

[0067] The melting point of the resin is defined as the melting peak temperature obtained when the resin is heated from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC). If two or more melting peak temperatures are observed within the aforementioned temperature range, or if a multi-stage peak known as a shoulder is observed, in such cases, the melting point of the resin is defined as the temperature of the peak with the largest absolute value of the heat flow (in mW) on the vertical axis of the DSC chart.

[0068] The polypropylene resin (A) is preferably composed mainly of a propylene homopolymer, but a propylene copolymer containing other unsaturated hydrocarbons as copolymer components may also be used, as long as it does not impair the objectives of the present invention. Examples of copolymer components included in the propylene copolymer include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and 5-methyl-2-norbornene.

[0069] In propylene copolymers, the copolymerization amount of components other than propylene is preferably less than 1 mol% from the viewpoint of dielectric breakdown voltage and heat resistance. Here, a copolymerization amount of components other than propylene being less than 1 mol% means that when the constituent components of the resin constituting the polypropylene resin (A) are set to 100 mol%, the constituent components other than propylene are less than 1 mol%. In other words, even when the polypropylene resin (A) consists of a polypropylene polymer with a copolymerization amount of less than 1 mol%, or when a copolymer of a polypropylene polymer with a copolymerization amount of 1 mol% or more and propylene (or a polypropylene polymer with a copolymerization amount of less than 1 mol%) is mixed such that the components other than propylene account for less than 1 mol% of the total, the copolymerization amount of components other than propylene is considered to be less than 1 mol%.

[0070] Furthermore, the polypropylene resin (A) may be blended with polymers whose main constituent component is a component other than propylene. Examples of main constituent components in such polymers include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, and cyclopentene. From the viewpoint of dielectric breakdown voltage and heat resistance, the amount of polymer blended with a component other than propylene as the main constituent component is preferably less than 1 part by mass per 100 parts by mass of the polypropylene resin (A).

[0071] This invention describes the cyclic olefin resin used in the polyolefin film of the present invention. A cyclic olefin resin is a resin obtained by polymerization from a cyclic olefin monomer, having an alicyclic structure in the main chain of the polymer, and refers to a polymer in which the total amount of components (constituent units) derived from the cyclic olefin monomer exceeds 20% by mass and is 100% by mass or less in 100% by mass of the polymer. It is preferable to use a polymer in which the content of these cyclic olefin monomer-derived components exceeds 50% by mass and is 100% by mass or less.

[0072] Examples of cyclic olefin monomers include monocyclic olefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, cyclopentadiene, and 1,3-cyclohexadiene, as well as bicyclo[2,2,1]hept-2-ene, 5-methyl-bicyclo[2,2,1]hepta-2-ene, 5,5-dimethyl-bicyclo[2,2,1]hept-2-ene, 5-ethyl-bicyclo[2,2,1]hept-2-ene, 5-butyl-bicyclo[2,2,1]hept-2-ene, 5-ethylidene-bicyclo[2,2,1]hept-2-ene, 5-hexyl-bicyclo[2,2,1]hept-2-ene, 5-octyl-bicyclo[2,2,1]hept-2-ene, 5-octadecyl-bicyclo[2,2,1]hept-2-ene, and 5-methylidene- Bicyclic olefins such as bicyclo[2,2,1]hepto-2-ene, 5-vinyl-bicyclo[2,2,1]hepto-2-ene, and 5-propenyl-bicyclo[2,2,1]hepto-2-ene, tricyclo[4,3,0,12.5]deca-3,7-diene, tricyclo[4,3,0,12.5]deca-3-ene, and tricyclo[4,3,0,12.5]undeca-3,7-diene N, tricyclo[4,3,0,12.5]undeca-3,8-diene, tricyclo[4,3,0,12.5]undeca-3-ene, 5-cyclopentyl-bicyclo[2,2,1]hepto-2-ene, 5-cyclohexyl-bicyclo[2,2,1]hepto-2-ene, 5-cyclohexenylbicyclo[2,2,1]hepto-2-ene, 5-phenyl-bicyclo[2,2,1] Tricyclic olefins such as hepta-2-ene, tetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, 8-methyltetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, 8-ethyltetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, 8-methylidenetetracyclo[4,4,0,12.5,17.10]dodeca-3- Tetracyclic olefins such as ene, 8-ethylidenetetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, 8-vinyltetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, and 8-propenyltetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, and 8-cyclopentyltetracyclo[4,4,0,12.5,17.10]dodeca-3-ene, and 8-cyclopentyltetracyclo[4,4,0,12.5,17.10) Dodeca-3-ene, 8-cyclohexyl-tetracyclo[4,4,0,12.5,17.10] Dodeca-3-ene, 8-cyclohexenyl-tetracyclo[4,4,0,12.5,17.10] Dodeca-3-ene, 8-phenyl-cyclopentyl-tetracyclo[4,4,0,12.5,17.10] Dodeca-3-ene, tetracyclo[7,4,13.6,01.9,02.7] Tetradeca-4,9,11,13-tetraene, tetracyclo[8,4,14.7,01.10,03.8] Pentadeca-5,10,12,14-tetraene, pentasi Examples include polycyclic olefins such as tetramers like chloro[6,6,13.6,02.7,09.14]-4-hexadecene, pentacyclo[6,5,1,13.6,02.7,09.13]-4-pentadecene, pentacyclo[7,4,0,02.7,13.6,110.13]-4-pentadecene, heptacyclo[8,7,0,12.9,14.7,111.17,03.8,012.16]-5-eicosene, heptacyclo[8,7,0,12.9,03.8,14.7,012.17,113.16]-14-eicosene, and cyclopentadiene. These cyclic olefin monomers can be used individually or in combination of two or more.

[0073] Among the cyclic olefin monomers mentioned above, from the viewpoint of productivity and surface properties, tricyclic olefins with 10 carbon atoms such as bicyclo[2,2,1]hepto-2-ene (hereinafter referred to as norbornene), tricyclic olefins with 12 carbon atoms such as tricyclo[4,3,0,12.5]deca-3-ene (hereinafter referred to as tricyclodecene), tetracyclic olefins with 12 carbon atoms such as tetracyclo[4,4,0,12.5,17.10]dodeca-3-ene (hereinafter referred to as tetracyclododecene), cyclopentadiene, or 1,3-cyclohexadiene are preferably used.

[0074] The cyclic olefin resin may be either a resin polymerized solely from the cyclic olefin monomer (hereinafter sometimes referred to as COP) or a resin copolymerized from the cyclic olefin monomer and a chain-like olefin monomer (hereinafter sometimes referred to as COC), as long as the total amount of components derived from the cyclic olefin monomer in 100% by mass of the cyclic olefin resin polymer exceeds 20% by mass but is 100% by mass or less. A suitable COP is, for example, "ZEONOR" (registered trademark) manufactured by Nippon Zeon Co., Ltd. A suitable COC is, for example, "APEL" (registered trademark) manufactured by Mitsui Chemicals, Inc., "ARTON" (registered trademark) manufactured by JSR Corporation, and "TOPAS" (registered trademark) manufactured by Polyplastics Corporation.

[0075] Known methods for producing COP include addition polymerization or ring-opening polymerization of cyclic olefin monomers. Examples include a method of ring-opening metathesis polymerization of norbornene, tricyclodecene, tetracyclodecene, and their derivatives followed by hydrogenation; an addition polymerization method of norbornene and its derivatives; and a 1,2-,1,4-addition polymerization of cyclopentadiene and cyclohexadiene followed by hydrogenation. Among these, the method of ring-opening metathesis polymerization of norbornene, tricyclodecene, tetracyclodecene, and their derivatives followed by hydrogenation is more preferred from the viewpoint of productivity and moldability.

[0076] In the case of COC, preferred chain-like olefin monomers include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Among these, ethylene is particularly preferred from the viewpoint of productivity and cost. Furthermore, known methods for producing resins copolymerized from cyclic olefin monomers and chain-like olefin monomers include, for example, addition polymerization of cyclic olefin monomers and chain-like olefin monomers, and among these, preferred methods include addition polymerization of norbornene and its derivatives with ethylene.

[0077] The cyclic olefin resin used in the polyolefin film of the present invention is preferably amorphous. Furthermore, the glass transition temperature of the amorphous cyclic olefin resin is preferably 125°C or higher, more preferably 130°C or higher, and even more preferably 135°C or higher, from the viewpoint of having dimensional stability and insulation performance in the high-temperature range suitable for applications such as capacitors. If the glass transition temperature is less than 125°C, thermal dimensional stability and dielectric breakdown voltage at high temperatures may be reduced. There is no particular upper limit, but it is set to 200°C from the viewpoint of film-forming properties. In the polyolefin film of the present invention, the cyclic olefin resin is defined as being amorphous if the melting peak temperature (Tm) obtained when the cyclic olefin resin is heated from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC) is not observed.

[0078] The polyolefin film of the present invention may contain various additives, such as organic particles, inorganic particles, nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and anticoloring agents, as long as they do not impair the objectives of the present invention.

[0079] When antioxidants are included in these materials, the selection of the type and amount of antioxidant is important from the viewpoint of long-term heat resistance. Specifically, such antioxidants should be sterically hindrance phenolic types, and at least one of them should preferably be a high molecular weight type with a molecular weight of 500 or more. Various specific examples can be given, but for example, it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) in combination with 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1,177.7).

[0080] The total content of high molecular weight antioxidants with a molecular weight of 500 or more is preferably in the range of 0.1 to 1.0 parts by mass relative to the total amount of resin. Too little antioxidant may result in poor long-term heat resistance. Too much antioxidant may adversely affect the capacitor element due to blocking at high temperatures caused by the bleeding out of these antioxidants. A more preferable total content is 0.2 to 0.7 parts by mass of the total mass of the resin, and particularly preferably 0.3 to 0.5 parts by mass. In the case of a laminated structure of two or more layers, it is preferable that each layer contains 0.3 to 0.5 parts by mass of high molecular weight antioxidants with a molecular weight of 500 or more, from the viewpoint of suppressing defects such as fisheyes and obtaining high quality and dielectric strength.

[0081] The polyolefin film of the present invention may contain resins other than polypropylene resin (A) and cyclic olefin resin, to the extent that it does not impair the objectives of the present invention. Specific examples of resins include vinyl polymer resins containing various polyolefin resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, polycarbonate resins, and olefin and styrene block copolymers, with polymethylpentene and syndiotactic polystyrene being particularly preferred examples. The content of resins other than polypropylene resin (A) and cyclic olefin resins is preferably less than 3% by mass, more preferably 2% by mass or less, and even more preferably 1% by mass or less, when the total resin components constituting the polyolefin film are considered as 100% by mass. If the content of resins other than polypropylene resin is 3% by mass or more, the influence of the domain interface becomes large, which may reduce the dielectric breakdown voltage in high-temperature environments.

[0082] The polyolefin film of the present invention preferably has a film dielectric breakdown voltage of 350 V / μm or higher at 135°C. More preferably, it is 375 V / μm or higher, even more preferably 400 V / μm or higher, and particularly preferably 420 V / μm or higher. There is no particular upper limit, but it is around 800 V / μm. When the film dielectric breakdown voltage at 130°C is 350 V / μm or higher, when used as a capacitor, it is less likely to cause short-circuit failure even when used for a long time in a high-temperature environment, maintaining its dielectric strength and providing high reliability.

[0083] To control the film dielectric breakdown voltage at 135°C within the above-mentioned range (350V / μm or higher), it is effective to use a raw material with a high mesopentad fraction as the polypropylene resin (A), pre-mix the cyclic olefin resin and the polypropylene resin in a twin-screw extruder, dilute or melt-extrude the resulting compound resin raw material to form a sheet, and to increase the TD side of the stretching ratio between MD and TD in biaxial stretching, and to increase the area stretching ratio to 35.0 times or higher.

[0084] The polyolefin film of the present invention is particularly suitable for use as a thin-film heat-resistant film capacitor required for automotive applications (including hybrid car applications) used in high-temperature environments, and therefore, the film thickness is preferably 0.5 μm or more and less than 25 μm. For the above-mentioned heat-resistant film capacitor applications, the upper limit is preferably 9.0 μm or less, more preferably 5.9 μm or less, and particularly preferably 3.9 μm or less, considering the balance between characteristics and capacitor size due to thinning.

[0085] The polyolefin film of the present invention is preferably used as a dielectric film for capacitors, but the type of capacitor is not limited. Specifically, in terms of electrode configuration, it may be a coiled capacitor with metal foil and film, or a metal vapor-deposited film capacitor, and it may also be preferably used in oil-immersion type capacitors impregnated with insulating oil, or in dry-type capacitors that do not use insulating oil at all. However, due to the characteristics of the film of the present invention, it is particularly preferably used as a metal vapor-deposited film capacitor. In terms of shape, it may be a wound type or a laminated type.

[0086] Polyolefin films typically have low surface energy, making it difficult to stably apply metal vapor deposition. Therefore, it is preferable to perform surface treatment before vapor deposition to improve adhesion to the metal film. Examples of surface treatments include corona discharge treatment, plasma treatment, glow treatment, and flame treatment. Typically, for example, in the case of polypropylene films, the surface wetting tension is about 30 mN / m. However, by performing these surface treatments, it is preferable to raise the wetting tension to preferably 37-75 mN / m, more preferably 39-65 mN / m, and most preferably 41-55 mN / m, as this results in excellent adhesion to the metal film and good security.

[0087] The polyolefin film of the present invention can be obtained by using raw materials capable of providing the above-described properties and subjecting them to biaxial stretching, heat treatment, and relaxation treatment. As for the biaxial stretching method, it can be obtained by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. Among these, sequential tenter biaxial stretching and simultaneous tenter biaxial stretching are preferred in terms of controlling the film formation stability, crystalline / amorphous structure, surface properties, and especially the mechanical properties and thermal dimensional stability while increasing the stretching ratio of the present invention.

[0088] Next, the method for producing the polyolefin film of the present invention will be explained using an example. First, a compound resin raw material, which is obtained by pre-kneading a cyclic olefin resin and a polypropylene resin, is diluted or melt-extruded onto a support to produce an unstretched film. This unstretched film is stretched in the longitudinal direction, and then in the width direction, and is successively biaxially stretched. After that, a heat treatment and a relaxation treatment are performed to produce a biaxially oriented polyolefin film. The following will be explained in more detail, but the present invention is not necessarily limited to this.

[0089] First, in the polyolefin film of the present invention, it is preferable to pre-mix the cyclic olefin resin, polypropylene resin, and antioxidant with the polyolefin resin (A) and compound them, in order to improve the dispersion state of the cyclic olefin resin and polypropylene resin (A) and obtain high transparency, and in particular from the viewpoint of increasing the dielectric breakdown voltage of the film at high temperatures. A short-screw extruder, a twin-screw extruder, etc. can be used for compounding, but from the viewpoint of good dispersion state and high transparency, it is particularly preferable to use a twin-screw extruder.

[0090] The amount of antioxidant is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the compound resin component. The preferred upper limit is 1.0 part by mass. Furthermore, setting the mesopentade fraction of the polypropylene resin (A) to 0.960 or higher is preferable because it raises the melting point and makes it suitable for use at high temperatures.

[0091] Next, a resin raw material, obtained by compounding a cyclic olefin resin and a polypropylene resin, is supplied to a single-screw extruder and, after passing through a filtration filter, is extruded from a slit-shaped die. The molten sheet extruded from the slit-shaped die is solidified on a casting drum (cooling drum) controlled to a temperature of 10 to 110°C, preferably 10 to 85°C, more preferably 10 to 65°C, to obtain an unstretched polyolefin film. From the viewpoint of increasing the area ratio, a laminated structure is preferred. In this case, a resin raw material, which is a compound of a cyclic olefin resin and a polypropylene resin, is supplied to a single-screw extruder for the inner layer (layer A), and the same polypropylene resin (A) used for layer A is supplied to a single-screw extruder for the outer layer (layer B). The resin, laminated in a three-layer structure of layer B / layer A / layer B using a feed block method by melt co-extrusion, is extruded as a molten sheet from a slit-shaped die and solidified on a cooling drum controlled to a temperature of 10 to 110°C, preferably 10 to 85°C, more preferably 10 to 65°C, to obtain an unstretched polypropylene film. Any of the following methods can be used to adhere the molten sheet to the casting drum: electrostatic application method, adhesion method using the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc. However, the air knife method is preferred because it provides good flatness and allows for control of surface roughness. Furthermore, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation process in order to prevent vibration of the film.

[0092] Next, the unstretched polyolefin film is biaxially stretched and biaxially oriented. More specifically, it is preferable to stretch the unstretched polyolefin film at a temperature above the glass transition temperature of the cyclic olefin resin and below the melting point of the polyolefin resin, more preferably 100 to 170°C, even more preferably 120 to 165°C, and stretch it in the longitudinal direction by preferably 2.0 to 12 times, more preferably 3.0 to 11 times, even more preferably 4.0 to 10 times, and most preferably 4.5 to 10 times, and then cool it to room temperature.

[0093] Next, the film, which has been uniaxially stretched in the longitudinal direction, is guided to a tenter while its ends are held with clips. In this invention, it is preferable to set the temperature of the preheating process immediately before stretching in the width direction to the width direction stretching temperature + 5 to +15°C, more preferably + 5 to +12°C, and even more preferably + 5 to +10°C, which further strengthens the fibril structure that is highly oriented in the longitudinal direction by uniaxial stretching and can increase the dielectric breakdown voltage of the polyolefin film. Furthermore, stabilizing molecular chains that are not sufficiently oriented after uniaxial stretching with high-temperature preheating is preferable from the viewpoint of improving thermal dimensional stability.

[0094] Next, the temperature at which the film is stretched in the width direction while its end is held with a clip (stretching temperature in the width direction) is preferably 150 to 175°C, more preferably 155 to 175°C.

[0095] From the viewpoint of increasing the dielectric breakdown voltage of the film, the stretching ratio in the width direction is preferably 6.0 to 20.0 times, more preferably 8.1 to 17.0 times, even more preferably 9.1 to 15.0 times, and particularly preferably 9.8 to 13.0 times. If the stretching ratio in the width direction is less than 6.0 times, the orientation contribution of the fibril structure, which is highly oriented in the longitudinal direction by uniaxial stretching, remains large, and when evaluating the dielectric breakdown voltage at high temperatures, the molecular chains in the film tend to move, which may result in a film with a poor dielectric breakdown voltage. Increasing the stretching ratio in the width direction more than in the longitudinal direction is preferable because it imparts orientation in the width direction while maintaining a high orientation state in the longitudinal direction, thereby increasing the molecular chain tension in the plane and obtaining the effect of increasing the dielectric breakdown voltage, especially at high temperatures.

[0096] Here, the area stretching ratio is preferably 35.0 times or more. By setting the area stretching ratio to 35.0 times or more, the molecular chain tension within the film surface increases, making the domain structure smaller or thinner, thus reducing internal haze and increasing the overall light efficiency. As a result, the resulting film has a particularly high dielectric breakdown voltage at high temperatures, and when used as a capacitor, it exhibits excellent reliability for long-term use in high-temperature environments. In the present invention, the area stretching ratio is the product of the stretching ratio in the longitudinal direction and the stretching ratio in the width direction. The area stretching ratio is more preferably 37.0 times or more, even more preferably 40.0 times or more, particularly preferably 44.0 times or more, and most preferably 49.0 times or more. There is no particular upper limit to the area stretching ratio, but from the viewpoint of feasibility, it is 90.0 times for sequential biaxial stretching and 150 times for simultaneous biaxial stretching. An important point in the present invention is to achieve a high area stretching ratio while keeping internal haze low and increasing the overall light efficiency. In other words, this can be achieved in the present invention by increasing the dispersibility of cyclic olefin resin domains dispersed in polypropylene resin and by applying a high temperature to the heat setting temperature after biaxial stretching, thereby reducing or eliminating minute voids at the domain interface that occur during stretching.

[0097] In the production of the polypropylene film of the present invention, in the subsequent heat treatment and relaxation treatment steps, it is preferable to perform heat treatment at 145°C to 170°C while tensioning the film in the width direction with clips and applying 2 to 20% relaxation in the width direction. This is preferable from the viewpoint of increasing the transparency of the film, increasing the dielectric breakdown voltage at high temperatures, and obtaining dielectric strength and reliability when used as a capacitor. From the above viewpoint, the heat treatment temperature is more preferably 150°C to 170°C, even more preferably 155°C to 170°C, and particularly preferably 160°C to 170°C. From the above viewpoint, the relaxation treatment rate is more preferably 5 to 18%, and even more preferably 7 to 15%.

[0098] After heat treatment and relaxation treatment, the film is guided to the outside of the tenter, the clips at the film ends are released in a room temperature atmosphere, the film edges are slit in the winder process, and a roll of film product with a film thickness of preferably 0.5 μm or more and less than 25 μm is wound up. Before winding the film, it is preferable to perform corona discharge treatment in air, nitrogen, carbon dioxide, or a mixture thereof in order to improve the adhesion of the vapor-deposited metal to the surface to be vapor-deposited.

[0099] To obtain the polyolefin film of the present invention, the manufacturing conditions that are considered are as follows. It is preferable to satisfy all of these manufacturing conditions, but it is not necessary to satisfy all of them and they may be combined as appropriate. For example, instead of "the preheating temperature before stretching in the width direction in sequential biaxial stretching is the stretching temperature in the width direction + 5 to + 15°C," simultaneous biaxial stretching may be used. • The mesopentadi fraction of polypropylene resin (A) must be 0.960 or higher. • Pre-compounding of cyclic olefin resin and polypropylene resin. • The area stretching ratio for biaxial stretching must be 35.0 times or more. • The stretch ratio in the width direction is higher than the stretch ratio in the length direction. • In sequential biaxial stretching, the preheating temperature before stretching in the width direction should be the stretching temperature in the width direction + 5 to +15°C. • The product has undergone heat treatment and relaxation treatment after biaxial stretching.

[0100] Next, a metal film laminated film using the polyolefin film of the present invention, a film capacitor using the same, and methods for manufacturing them will be described.

[0101] The metal film laminated film of the present invention has a metal film on at least one side of the polyolefin-based film of the present invention. This metal film laminated film can be obtained by providing a metal film on at least one side of the polyolefin-based film of the present invention described above.

[0102] In the present invention, the method for applying the metal film is not particularly limited, but a preferred method is to deposit aluminum or an alloy of aluminum and zinc onto at least one side of a polyolefin film to form a metal film such as a deposited film that will serve as the internal electrode of a film capacitor. At this time, other metal components such as nickel, copper, gold, silver, and chromium can be deposited simultaneously or sequentially with the aluminum. A protective layer such as oil can also be provided on the deposited film. If the surface roughness of the polyolefin film differs between the front and back sides, it is preferable to provide the metal film on the smoother surface side to form a metal film laminated film, from the viewpoint of improving dielectric strength.

[0103] In this invention, if necessary, after forming the metal film, the metal film laminate can be annealed or heat-treated at a specific temperature. Furthermore, for insulation or other purposes, at least one side of the metal film laminate can be coated with a resin such as polyphenylene oxide.

[0104] The film capacitor of the present invention is made using the metal film laminated film of the present invention. In other words, the film capacitor of the present invention has the metal film laminated film of the present invention.

[0105] For example, the film capacitor of the present invention can be obtained by laminating or winding the metal film laminate of the present invention described above in various ways. A preferred manufacturing method for a wound film capacitor is as follows.

[0106] Aluminum is deposited onto one side of a polyolefin film under reduced pressure. The aluminum is deposited in a stripe pattern with a margin running along the longitudinal direction. Next, a blade is inserted into the center of each deposited area and the center of each margin to create a tape-shaped reel with a margin on one side of the surface. Two of these tape-shaped reels, one with a left margin and one with a right margin, are stacked and wound together so that the deposited portion extends beyond the margin in the width direction, thereby obtaining a wound body.

[0107] When vapor deposition is performed on both sides, one side is vapor-deposited in a stripe pattern with a margin running along the longitudinal direction, and the other side is vapor-deposited in a stripe pattern so that the longitudinal margin is located in the center of the vapor-deposited area on the back side. Next, a blade is inserted into the center of the margin on both the front and back sides to make a slit, and a tape-shaped winding reel is created on both sides, each with a margin on one side (for example, if there is a margin on the right side of the front side, there will be a margin on the left side of the back side). The obtained reel and one unvapor-deposited laminated film are stacked on top of each other in the width direction so that the metallized film extends beyond the laminated film, and the two are wound together to obtain a wound body.

[0108] As described above, the core material is removed from the wound body and pressed, metallicon is sprayed onto both end faces to form external electrodes, heat treatment is performed under reduced pressure at a temperature of 125°C or higher, and lead wires are welded to the metallicon to obtain a wound film capacitor. The upper limit of the heat treatment temperature is 150°C. Here, heat treatment at a temperature of 125°C or higher in the state described above for the external electrodes is preferable from the viewpoint of easily obtaining voltage resistance and reliability when used as a capacitor in a high-temperature environment of 125°C or higher. Film capacitors have a wide range of applications, including railway vehicles, automobiles (hybrid cars, electric vehicles), electric aircraft, solar and wind power generation, and general home appliances, and the film capacitor of the present invention can be suitably used in these applications. In addition, the polyolefin film of the present invention can be used in various applications such as packaging films, release films, process films, sanitary products, agricultural products, building materials, and medical products, and is particularly suitable for applications that include a heating process in film processing.

[0109] The following describes the power control unit, electric vehicle, and electric aircraft of the present invention. The power control unit of the present invention has the film capacitor of the present invention. The power control unit is a system for managing power in electric vehicles, electric aircraft, and the like, which have mechanisms driven by electricity. By equipping the power control unit with the film capacitor of the present invention, it is possible to miniaturize the power control unit itself, improve its heat resistance and efficiency, and as a result, improve fuel efficiency.

[0110] The electric vehicle of the present invention is equipped with the power control unit of the present invention. Here, an electric vehicle refers to an automobile having a mechanism that is driven by electricity, such as an electric vehicle, hybrid vehicle, or fuel cell vehicle. As described above, the power control unit of the present invention can be miniaturized and also has excellent heat resistance and efficiency, so when an electric vehicle is equipped with the power control unit of the present invention, it leads to improved fuel efficiency and other benefits.

[0111] The electric aircraft of the present invention is equipped with the power control unit of the present invention. Here, an electric aircraft refers to an aircraft having an electric drive mechanism, such as a manned electric aircraft or a drone. As described above, the power control unit of the present invention can be miniaturized and also has excellent heat resistance and efficiency, so when an electric aircraft is equipped with the power control unit of the present invention, it leads to improved fuel efficiency and other benefits. [Examples]

[0112] The polyolefin film of the present invention will be described in more detail below with reference to examples. However, the polyolefin film of the present invention is not limited to these examples. The method for measuring characteristic values ​​and the method for evaluating effects in the present invention are as follows.

[0113] [Measurement and evaluation methods] (1) Film thickness The thickness of a polyolefin film was measured at 10 arbitrary points in an atmosphere of 23°C and 65% RH using a contact-type electronic micrometer (K-312A) manufactured by Anritsu Corporation. The arithmetic mean of these 10 thicknesses was defined as the film thickness of the polyolefin film (unit: μm).

[0114] (2) Total light transmittance A haze meter (HGM-2DP for C light source) manufactured by Suga Test Instruments Co., Ltd. was used. A 6.0 cm x 3.0 cm piece of polyolefin film was cut, and the transmittance of light rays incident perpendicularly to the surface of the polyolefin film was measured. The total light transmittance in the film thickness direction was obtained from the measured values. The measurement was performed five times, and the average value was taken as the total light transmittance.

[0115] (3) Internal haze A haze meter (HGM-2DP for C light source) manufactured by Suga Test Instruments Co., Ltd. was used. A polyolefin film was cut to 6.0 cm x 3.0 cm, and the polyolefin film was inserted into a quartz cell with a path length of 1 cm filled with purified water. Light was incident perpendicularly to the film surface, and the internal haze value was measured. The measurement was performed five times, and the average value was taken as the internal haze.

[0116] (4) MD orientation parameter (MOP) and TD orientation parameter (TOP), and MOP / TOP The film was embedded in bisphenol epoxy resin (Refinetech Co., Ltd., "Epomount Main Agent 27-771, Epomount Hardener 27-772") and cured for 24 hours. Then, using a microtome, measurement cross-sections in the longitudinal (MD) and width (TD) directions of the polyolefin film were cut out to prepare measurement samples. Polarized Raman spectroscopy (beam diameter 1 μm) was performed from the center position in the thickness direction of each measurement cross-section in the MD and TD directions of the polyolefin film using the apparatus and conditions described below to obtain polarized Raman spectra. Polarized Raman spectrum at 810 cm⁻¹ -1 and 840cm -1Using the Raman band intensities, the MD orientation parameter (MOP) and TD orientation parameter (TOP) were determined, and the MOP / TOP value was calculated.

[0117] The polarized Raman spectrum was obtained by incidenting linearly polarized light onto a film and detecting only the component parallel to the incident light from the resulting scattered light. However, to eliminate the anisotropy of the spectrometer, a λ / 4 plate was placed after the analyzer and before the grating to eliminate the polarization state of the scattered light before it was introduced to the grating.

[0118] Measurements for each cross-section were performed with a measurement count (hereinafter also referred to as n) of 5. The MD orientation parameter (MOP) was calculated for the MD cross-section at 810 cm². -1 and 840cm -1 The Raman band intensities (I810MD, I840MD, I810MZD, I840MZD) were calculated using the formula described below. The TD orientation parameter (TOP) was calculated at 810 cm in the TD cross section. -1 and 840cm -1 The Raman band intensities (I810TD, I840TD, I810TZD, I840TZD) were calculated using the formula described below.

[0119] <Details of measurement conditions for micro-Raman spectroscopy> Equipment: T-64000 (Jobin Yvon / Atago Bussan) Conditions: Measurement mode; Microscope Objective lens: ×100 Beam diameter: 1 μm Light source: Ar+ laser / 514.5nm Laser power: 100mW Diffraction grating: Single 1800gr / mm Slit: 100 μm Detector: CCD / Jobin Yvon 1024×256.

[0120] <Calculation of orientation parameters> MD orientation parameter (MOP) = (I810MD / I840MD) / (I810MZD / I840MZD) I810MD: 810 cm obtained when polarized light parallel to MD is incident on a film cross-section in the machine direction (MD) -1 Raman band intensity in the vicinity I840MD: 840 cm obtained when polarized light parallel to MD is incident on a film cross-section in the machine direction (MD) -1 Raman band intensity in the vicinity I810MZD: 810 cm obtained when polarized light parallel to the thickness direction (ZD) is incident on a film cross-section in the machine direction (MD) -1 Raman band intensity in the vicinity I840MZD: 840 cm obtained when polarized light parallel to the thickness direction (ZD) is incident on a film cross-section in the machine direction (MD) -1 Raman band intensity in the vicinity TD orientation parameter (TOP) = (I810TD / I840TD) / (I810TZD / I840TZD) I810TD: 810 cm obtained when polarized light parallel to TD is incident on a film cross-section in the transverse direction (TD) -1 Raman band intensity in the vicinity I840TD: 840 cm obtained when polarized light parallel to TD is incident on a film cross-section in the transverse direction (TD) -1 Raman band intensity in the vicinity I810TZD: 810 cm obtained when polarized light parallel to the thickness direction (ZD) is incident on a film cross-section in the transverse direction (TD) -1 Raman band intensity in the vicinity I840TZD: 840 cm obtained when polarized light parallel to the thickness direction (ZD) is incident on a film cross-section in the transverse direction (TD) -1 Raman band intensity in the vicinity.

[0121] (5) Melting peak temperature (Tm) of resin and film Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), a 3 mg film was heated from 30°C to 260°C at a rate of 20°C / min in a nitrogen atmosphere, held at 260°C for 5 minutes, and then cooled down to 30°C at a rate of 20°C / min. The endothermic peak temperature obtained during the heating process was defined as the melting peak temperature of the film. In this example, (Tm) was calculated from the average value of n=3 measurements. In some cases, two or more peak temperatures may be observed in the range between 170°C and 200°C, or a peak temperature that can be observed on a multi-stage DSC chart called a shoulder (observed when two or more peaks overlap) may appear. In this example, however, the temperature of the peak with the largest absolute value of the vertical axis heat flow (unit: mW) on the DSC chart was defined as (Tm) (°C). For the resin (Tm), the temperature was increased from 30°C to 260°C at a rate of 20°C / min, then held at 260°C for 5 minutes, and then cooled down to 30°C at a rate of 20°C / min. After holding at 20°C for 5 minutes, the temperature was increased again from 30°C to 260°C at a rate of 20°C / min. The endothermic peak temperature obtained during the reheating process was defined as the melting peak temperature of the resin.

[0122] (6) Glass transition temperature (Tg) of cyclic olefin resins Measurements were taken in accordance with JIS K7121-1987. Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), 3 mg of film or resin was heated from 30°C to 260°C at a rate of 20°C / min in a nitrogen atmosphere, held at 260°C for 5 minutes, and then cooled to 30°C at a rate of 20°C / min. After holding at 20°C for another 5 minutes, the temperature was raised again from 30°C to 260°C at a rate of 20°C / min. The glass transition temperature (Tg) was calculated from the DSC curve obtained during the reheating process using the following formula. Glass transition temperature = (Extracorporeal glass transition start temperature + Extracorporeal glass transition end temperature) / 2.

[0123] (7) Loss tangent (tanδ0) in the film width direction at 0°C Under the following apparatus and conditions, a rectangular polyolefin film (width (short side) 10 mm × length (long side) 20 mm), cut with the width direction as the long side, was attached to the apparatus chuck in a 23°C atmosphere and set in the furnace. The atmosphere inside the furnace with the film set was cooled with liquid nitrogen and the temperature was raised from -100°C to 180°C for measurement. A viscoelastic-temperature curve was drawn using the dynamic viscoelastic method, and the storage modulus (E'0) and loss modulus (E''0) at 0°C were read. Three measurements were taken, and the average values ​​of the storage modulus (E'0) and loss modulus (E''0) were calculated. The loss tangent (tanδ0) at 0°C in the film width direction was calculated using the following formula. Equation: tanδ0 = E''0 / E'0 <Equipment and Conditions> Device: EXSTAR DMS6100 (manufactured by Seiko Instruments Inc.) Test mode: Tensile mode Chuck spacing: 20mm Frequency: 10Hz Distortion amplitude: 10.0μm Gain: 1.5 Initial force amplitude: 400mN Temperature range: -100 to 180°C Heating rate: 5°C / min Measurement environment: Under air Measurement thickness: The film thickness specified in (1) above was used.

[0124] (8) Shrinkage stress (135Tf) in the film width direction at 135°C A polyolefin film was cut into a rectangular sample with a width of 4 mm and a length of 50 mm, with the measurement direction (width direction) as the longer side. The film was then clamped in a metal chuck to a test length of 20 mm. The sample clamped in the chuck was set in the apparatus described below, and the stress curve in the width direction of the film was obtained using the temperature program described below, while maintaining a constant test length. From the obtained stress curve, the shrinkage stress value at the temperature closest to 25°C was corrected as the zero point, and the shrinkage stress at 135°C (unit: MPa) was read. The average value of n=3 measurements was taken as 135Tf (unit: MPa). <Device and Temperature Program> Equipment: Thermomechanical analyzer TMA / SS6000 (manufactured by Seiko Instruments Inc.) Test mode: L control mode Trial length: 20mm Temperature range: 23~200℃ Heating rate: 10°C / min Starting displacement: 0 μm SS program: 0.1 μm / min Measurement atmosphere: Under nitrogen Measurement thickness: The film thickness specified in (1) above was used.

[0125] (9) Film dielectric breakdown voltage (V / μm) at 135°C The film was heated for 1 minute in an oven maintained at 135°C, and then measured in that atmosphere according to JIS C2330(2001)7.4.11.2 Method B (flat plate electrode method). However, for the lower electrode, a metal plate of the same dimensions as described in JIS C2330(2001)7.4.11.2 Method B, using "Conductive Rubber E-100" manufactured by Togawa Rubber Co., Ltd. <65> A sample containing the following was used. Dielectric breakdown voltage tests were performed 30 times, and the obtained values ​​were divided by the film thickness (measured in (1) above) to convert them to V / μm. The average of the 20 values ​​obtained by removing the 5 largest values ​​and the 5 smallest values ​​from the total of 30 measured values ​​(calculated values) was taken as the film dielectric breakdown voltage at 135°C.

[0126] (10) Number of cyclic olefin resin domains (domains / μm) passing through a pair of sides parallel to the thickness direction in a 1 μm square in layer A 2 ) Using a microtome, ultrathin sections with width-thickness cross-sections (TD / ZD cross-sections) were collected from the A layer of a polyolefin film. The collected sections were stained with RuO4, and the cross-sections were observed using a transmission electron microscope (TEM) under the following conditions. Note that cyclic olefin resins stained blacker than polypropylene resins. • Equipment: Hitachi, Ltd. Transmission Electron Microscope (TEM) HT7700 • Acceleration voltage: 100kV • Magnification: 20,000x In the image obtained from the aforementioned observation, a 1 μm square was drawn so that a pair of sides were parallel to the thickness direction, and the number of domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction within the square was counted. The same measurement was performed a total of 10 times, changing the position of the square in the image, and the average value of the number of domains obtained was calculated to determine the number of domains (domains / μm) of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction in layer A. 2 ) was determined. When defining a 1 μm square within cross-section X such that a pair of sides are parallel to the thickness direction, the base of the square was set in the sea portion, and if a domain was located on the side opposite the base, it was considered not to exist and was not counted. In addition, domains with constrictions were treated as connected domains by considering them as cyclic olefin resin domains that were dyed more darkly than the polypropylene resin portion in the sea portion.

[0127] (11) Number of cyclic olefin resin domains (domains / 2μm) passing through a pair of sides parallel to the thickness direction in a 1μm × 2μm rectangle in layer A 2 ) Observation was performed using the same method as in (10), and a rectangle was defined in the image obtained, with a pair of sides of 1 μm in the thickness direction and 2 μm in the direction perpendicular to the thickness direction, resulting in a 2 μm rectangle. 2 A rectangle was drawn enclosed by the four sides of the image, and the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction within that rectangle was counted. The same measurement was performed a total of 10 times, changing the position of the rectangle in the image, and the average value of the number of domains obtained was calculated to determine the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in layer A (domains / 2μm). 2 ) was defined. Furthermore, when defining a rectangle within cross-section X with a pair of sides measuring 1 μm in the thickness direction and 2 μm in the direction perpendicular to the thickness direction, the base of the rectangle was set to the sea portion, and if a domain was located on the side opposite the base, it was considered not to exist and was not counted. Domains with constrictions were also treated as connected domains.

[0128] (12) Thermal shrinkage rate in the longitudinal direction of the film after heat treatment at 130°C for 10 minutes (130S) A rectangular sample measuring 30 mm in length and 10 mm in width was cut from a polyolefin film, with the longitudinal direction as the longer side. Five of these rectangles were prepared. A mark parallel to the width direction was made 5 mm from the center of the shorter side of each rectangle, marking a test length of 20 mm (L0). Next, the test pieces were placed between sheets of paper and heated in an oven maintained at 130°C for 10 minutes. After removal and cooling to room temperature, the length between the two aforementioned markings (L1) was measured and the following formula was applied. Thermal shrinkage rate = {(L0-L1) / L0} × 100(%) The thermal shrinkage coefficient (130S) was calculated using the following method, and the arithmetic mean of the five values ​​was taken as the thermal shrinkage coefficient.

[0129] (13) Average length (nm) of the domains of the cyclic olefin resin in the A layer in the thickness direction. Under the same conditions as in (10) above, the cross-section of layer A of the polyolefin film was observed and an image was obtained. Next, a 1 μm square was drawn on the obtained image such that a pair of sides were parallel to the thickness direction, and the cyclic olefin resin domains passing through the pair of sides in the thickness direction of the square were identified. Subsequently, a straight line was drawn passing through the intersection of the diagonals of the square and parallel to the thickness direction, and the thickness direction length of each identified domain was measured along this straight line. The thickness direction length of the domains was measured for all cyclic olefin resin domains passing through the pair of sides parallel to the thickness direction of the square, by drawing lines at the top and bottom of the cyclic olefin resin domains that were darker than the polypropylene resin portion in the sea portion on the straight line passing through the intersection of the diagonals of the square and parallel to the thickness direction, and measuring the distance between them. Furthermore, the average value of the thickness direction length of the domains obtained in this way was calculated. Furthermore, the positions of the squares were arbitrarily changed and the same measurements were performed a total of 10 times (at this time, the squares were set so that none of the 10 squares overlapped). The average value was then calculated from the average values ​​of the thickness direction lengths of the domains in each measurement, and the resulting value was taken as the average value of the thickness direction lengths of the domains in the cyclic olefin resin (unit: nm).

[0130] (14) Evaluation of film capacitor characteristics (voltage withstand capability and reliability at 135°C) On one side of the film (if the wetting tension differs between the front and back sides, the side with the higher wetting tension is used), aluminum was deposited using an ULVAC vacuum deposition machine with a film resistance of 10Ω / sq and a margin section perpendicular to the longitudinal direction, resulting in a so-called T-shaped margin pattern (with a longitudinal pitch (period) of 17mm and a fuse width of 0.5mm due to masking oil). After slitting, a deposition reel with a film width of 50mm (end margin width of 2mm) was obtained. Next, capacitor elements were wound onto this reel using a Kaito Manufacturing Co., Ltd. element winding machine (KAW-4NHB), metallized, and then heat-treated under reduced pressure at 128°C for 12 hours. Lead wires were then attached to complete the capacitor elements. Using the 10 capacitor elements thus obtained, a so-called step-up test was performed in which a voltage of 150VDC was applied to the capacitor elements at a high temperature of 135°C, and after 10 minutes at this voltage, the applied voltage was gradually increased in a step-like manner by 50VDC / minute, and this process was repeated.

[0131] <Withstand Voltage Evaluation> In the step-up test, the change in capacitance was measured and plotted on a graph. The voltage at which the capacitance reached 70% of the initial value was divided by the film thickness (as described in (1) above) to determine the withstand voltage. The average value of 10 capacitor elements was calculated and evaluated according to the following criteria. A and B indicate usability, while C indicates poor practical performance. A: 330V / μm B: 320V / μm or more and less than 330V / μm C: Less than 320V / μm.

[0132] <Reliability Evaluation> After increasing the voltage until the capacitance decreased to 12% or less of the initial value, the single capacitor element that had the highest voltage rating among the 10 capacitor elements was disassembled, its state of failure was examined, and its reliability was evaluated as follows: A means usable, B means usable under certain conditions, and C means poor practical performance. A: No change in element shape was observed, and through-film fracture was observed across 1 to 5 layers. Alternatively, neither change in element shape nor through-film fracture was observed. B: No change in element shape was observed, but through-film fracture was seen across 6 to 10 layers. C: Changes were observed in the element shape, or through-layer fracture exceeding 10 layers was observed.

[0133] [Resin etc.] The following resins and other materials were used to produce the polyolefin films in each example and comparative example.

[0134] <Polypropylene resin> Polypropylene resin 1: A polypropylene resin with a mesopentad fraction of 0.982, a melting point of 167°C, and a melt flow rate (MFR) of 2.2 g / 10 min. Polypropylene resin 2: A polypropylene resin with a mesopentad fraction of 0.972, a melting point of 166°C, and a melt flow rate (MFR) of 2.2 g / 10 min. Polypropylene resin 3: A polypropylene resin (Borealis AG's "Borclean" (registered trademark) HC300BF) with a mesopentad fraction of 0.970, a melting point of 166°C, and a melt flow rate (MFR) of 3.3 g / 10 min. Polypropylene resin 4: A polypropylene resin with a mesopentad fraction of 0.984, a melting point of 168°C, and a melt flow rate (MFR) of 2.2 g / 10 min. Polypropylene resin 5: Polypropylene resin (F113G, manufactured by Prime Polymer Co., Ltd.) with a mesopentad fraction of 0.940, a melting point of 162°C, and a melt flow rate (MFR) of 2.9 g / 10 min. <Components other than polypropylene resin> Cyclic olefin resins: Polyplastics' "TOPAS" (registered trademark) 6013F-04 (a copolymer resin of ethylene and norbornene (COC), with a glass transition temperature of 138°C) Mitsui Chemicals' "APEL" (registered trademark) 5014CL(04) is a copolymer resin (COC) of ethylene and norbornene derivatives, with a glass transition temperature of 135°C, and is a cyclic olefin resin. ZEONOR® 1420R, manufactured by Nippon Zeon Corporation, is a cyclic olefin resin (COP) made from norbornene derivatives with a glass transition temperature of 135°C. Antioxidants: IRGANOX® 1010, manufactured by Ciba Specialty Chemicals.

[0135] <Polypropylene raw material> Polyolefin resin raw material (A1): Polypropylene resin 1 was mixed in an amount of 69.5 parts by mass, cyclic olefin resin "TOPAS" (registered trademark) 6013F-04 manufactured by Polyplastics in an amount of 30 parts by mass, and antioxidant in an amount of 0.5 parts by mass. The mixture was kneaded and extruded in a twin-screw extruder set to 260°C, and the strands were water-cooled and chipped to obtain polyolefin resin raw material (A1). Polyolefin resin raw materials (A2): Polypropylene resin 2 was mixed in an amount of 69.5 parts by mass, cyclic olefin resin "TOPAS" (registered trademark) 6013F-04 manufactured by Polyplastics in an amount of 30 parts by mass, and antioxidant in an amount of 0.5 parts by mass. The mixture was kneaded and extruded in a twin-screw extruder set to 260°C, and the strands were water-cooled and chipped to obtain polyolefin resin raw material (A2). Polyolefin resin raw materials (A3): As a cyclic olefin resin, 100 parts by mass of "TOPAS" (registered trademark) 6013F-04 manufactured by Polyplastics and 0.3 parts by mass of an antioxidant were mixed. After kneading and extruding in a twin-screw extruder set to 260°C, the strands were water-cooled and chipped to obtain polyolefin resin raw material (A3).

[0136] (Example 1) The polyolefin resin raw material (A1) was mixed in an amount of 30 parts by mass, polypropylene resin 1 in an amount of 69.6 parts by mass, and antioxidant in an amount of 0.4 parts by mass. This mixture was supplied to a single-screw melt extruder and melted at a temperature of 260°C. After removing foreign matter with an 80 μm cut sintering filter, the molten polymer was extruded from a T-die. Subsequently, the molten sheet was pressed tightly onto a casting drum maintained at 30°C using an air knife and cooled and solidified to obtain an unstretched polyolefin film. The unstretched polyolefin film was preheated in stages to 145°C using multiple roll groups, then maintained at 155°C and passed between rolls with different peripheral speeds, and stretched 5.1 times in the longitudinal direction. The film was then guided to a tenter, and while holding both ends of the film width with clips, it was preheated at a TD preheating temperature of 174°C (8°C higher than the TD stretching temperature), and then stretched 9.8 times in the width direction at a TD stretching temperature of 166°C. Furthermore, as a heat treatment and relaxation treatment, the film is heat-treated at 162°C while providing 8% relaxation in the width direction, then guided to the outside of the tenter to release the clips, and then 25 W·min / m is applied to the film surface (the side that contacts the casting drum). 2 A polyolefin film was obtained by performing corona discharge treatment in air at the specified treatment intensity. The evaluation results are shown in Table 1.

[0137] (Example 2) The polyolefin resin raw material (A1) was mixed in an amount of 66.6 parts by mass, polypropylene resin 1 in an amount of 30 parts by mass, and antioxidant in an amount of 0.4 parts by mass. This mixture was supplied to a single-screw melt extruder for layer A, and polypropylene resin 1 was supplied to a single-screw melt extruder for layer B. Both were melted at a temperature of 260°C, and after removing foreign matter with an 80 μm cut sintered filter, the extrusion amount was adjusted using a feed block to create a three-layer laminate of B / A / B with a layer thickness ratio (layer ratio) of 1 / 10 / 1 (the ratio of the inner layer A to the total film thickness is 83%). The molten laminated polymer was then extruded from a T-die. Subsequently, a polyolefin film was obtained in the same manner as in Example 1, except that the film formation conditions were as shown in Table 1. The evaluation results are shown in Table 1, and a photograph of the cross-section X is shown in Figure 2 (in Figure 2, the darker areas are the domains of the cyclic olefin resin). The thickness was adjusted by adjusting the extrusion amount (the same applies below).

[0138] (Example 3) A polyolefin film was obtained in the same manner as in Example 1, except that the following conditions were met: 90 parts by mass of polyolefin resin raw material (A1), 9.6 parts by mass of polypropylene resin 1, and 0.4 parts by mass of antioxidant. The mixture was supplied to a single-screw melt extruder and melted at a temperature of 260°C. After removing foreign matter with an 80 μm cut sintering filter, the molten polymer was extruded from a T-die, and the film-forming conditions were as shown in Table 1. The evaluation results are shown in Table 1.

[0139] (Example 4) A polyolefin film was obtained in the same manner as in Example 1, except that the following conditions were met: 53 parts by mass of polyolefin resin raw material (A2), 46.6 parts by mass of polypropylene resin 1, and 0.4 parts by mass of antioxidant. The mixture was supplied to a single-screw melt extruder and melted at a temperature of 260°C. After removing foreign matter with an 80 μm cut sintering filter, the molten polymer was extruded from a T-die, and the film-forming conditions were set as shown in Table 1. The evaluation results are shown in Table 1.

[0140] (Example 5) An unstretched polyolefin film was obtained in the same manner as in Example 1. The unstretched polyolefin film was then introduced into a simultaneous biaxial stretcher. With both ends of the film width held by clips, it was preheated at 164°C and then simultaneously biaxially stretched 4.1 times in the longitudinal direction and 10.8 times in the width direction. Further heat treatment, relaxation treatment, and corona discharge treatment were performed in the same manner as in Example 1 to obtain a polyolefin film. The evaluation results are shown in Table 1.

[0141] (Example 6) A polyolefin film was obtained in the same manner as in Example 1, except that polypropylene resin 1 was replaced with polypropylene resin 5 and the film-forming conditions were as shown in Table 1. The evaluation results are shown in Table 1.

[0142] (Example 7) A polyolefin film was obtained in the same manner as in Example 1, except that the heat treatment and relaxation treatment after biaxial stretching were performed under the film formation conditions shown in Table 1. The evaluation results are shown in Table 1.

[0143] (Example 8) A polyolefin film was obtained in the same manner as in Example 1, except that the following conditions were met: 6.6 parts by mass of polyolefin resin raw material (A1), 93.0 parts by mass of polypropylene resin 1, and 0.4 parts by mass of antioxidant, and the mixture was supplied to a single-screw melt extruder, with the film formation conditions set to those shown in Table 1. The evaluation results are shown in Table 1.

[0144] (Example 9) A polyolefin film was obtained in the same manner as in Example 1, except that instead of COC, ZEONOR® 1420R (a cyclic olefin resin with a glass transition temperature of 135°C) manufactured by Nippon Zeon Co., Ltd. was used as COP for the polyolefin resin raw material (A1), and the film was fabricated under the conditions shown in Table 1. The evaluation results are shown in Table 1.

[0145] (Example 10) A polyolefin film was obtained in the same manner as in Example 1, except that Mitsui Chemicals' "APEL" (registered trademark) 5014CL(04) (a cyclic olefin resin with a glass transition temperature of 135°C) was used as the cyclic olefin resin for the polyolefin resin raw material (A1), and the film was formed under the conditions shown in Table 1. The evaluation results are shown in Table 1.

[0146] (Comparative Example 1 and Comparative Example 6) 80 parts by mass of polypropylene resin 3, 20 parts by mass of Polyplastics' "TOPAS" (registered trademark) 6013F-04 as a cyclic olefin resin, and 0.3 parts by mass of an antioxidant were mixed and supplied to a single-screw extruder set to 260°C. After melting at 260°C, foreign matter was removed using an 80 μm cut sintering filter, and the molten single-layer polymer was extruded from a T-die. This was then cooled and solidified on a casting drum maintained at 90°C, with the film adhering tightly using an air knife, to obtain an unstretched polyolefin film. Subsequently, a polyolefin film was obtained in the same manner as in Example 1, except that the film-forming conditions were as shown in Table 2. The evaluation results are shown in Table 2.

[0147] (Comparative Example 2) An unstretched polyolefin film obtained in the same manner as in Comparative Example 1 was introduced into a simultaneous biaxial stretcher. With both ends of the film width held by clips, it was preheated at 163°C and then simultaneously biaxially stretched 3.8 times in the longitudinal direction and 8 times in the width direction. Next, without heat treatment or relaxation treatment, the film was introduced to the outside of the simultaneous biaxial stretcher, the clips at the film ends were released, and corona discharge treatment was performed in the same manner as in Example 1 to obtain a polyolefin film. The evaluation results are shown in Table 2.

[0148] (Comparative Example 3) A polyolefin film was obtained in the same manner as in Example 2, except that the raw material for layer A was melt-extruded using a single-screw melt-extruder without pre-kneading in a twin-screw extruder, and the film-forming conditions shown in Table 2 were used. The evaluation results are shown in Table 2.

[0149] (Comparative Example 4) Polyolefin resin raw material (A3) was used for layer A, and polypropylene resin 4 was used for layer B. The raw material for layer A was supplied to a single-screw melt extruder for layer A, and the resin for layer B was supplied to a single-screw melt extruder for layer B. Both were melted at a temperature of 260°C, and foreign matter was removed using an 80 μm cut sintered filter. Then, using a feed block, the extrusion amount was adjusted so that the layer thickness ratio (layer ratio) for a three-layer B / A / B laminate was 1 / 1 / 1 (the ratio of the inner layer A to the total film thickness was 33%), and the molten laminated polymer was extruded from a T-die. Using an air knife, the molten sheet was brought into close contact with a casting drum maintained at 70°C and cooled and solidified to obtain an unstretched polyolefin film. Subsequently, a polyolefin film was obtained in the same manner as in Example 1, except that the film formation conditions were as shown in Table 2. The evaluation results are shown in Table 2.

[0150] (Comparative Example 5) In the same manner as in Example 1, a single-layer structure consisting only of layer A was obtained, and an unstretched polyolefin film was acquired without biaxial stretching or heat fixing. The evaluation results are shown in Table 2.

[0151] [Table 1]

[0152] [Table 2]

[0153] In Tables 1 and 2, the content of cyclic olefin resin in the entire film was calculated by considering the total resin component as 100% by mass, without considering antioxidants. [Industrial applicability]

[0154] The polyolefin film of the present invention can be widely used in industrial applications such as capacitors, packaging, release agents, and tapes. In particular, it has excellent voltage resistance and reliability in high-temperature environments, making it suitable for use in capacitors that operate under high temperatures and high voltages. [Explanation of Symbols]

[0155] 1. Part of Section X 2 Sea part 3. Island portion (domain) 4. A 1 μm square defined within cross-section X such that one side is parallel to the thickness direction. 5. A pair of sides parallel to the thickness direction.

Claims

1. A polyolefin film having a layer containing a cyclic olefin resin and a polypropylene resin (such layer is conveniently referred to as "Layer A"), having a total light transmittance of 85% or more, an internal haze of 4.0% or less, and in a DSC chart obtained by raising the temperature from 30°C to 260°C at 20°C / min using a differential scanning calorimeter (DSC), the melting peak temperature Tm (°C) is defined as the temperature of the peak with the largest absolute value of heat flow among the melting peaks, wherein Tm is greater than 170°C and less than or equal to 200°C, and is characterized for use in film capacitors.

2. A polyolefin film having a layer containing a cyclic olefin resin and a polypropylene resin (such layer is conveniently referred to as "layer A"), wherein when layer A is cut by a plane parallel to the main orientation axis and the thickness direction, the cross section X is defined as such, and within a 1 μm square defined such that a pair of sides are parallel to the thickness direction, there are three or more domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction, the internal haze is 4.0% or less, and in a DSC chart obtained by heating from 30°C to 260°C at 20°C / min using a differential scanning calorimeter (DSC), when the melting peak temperature Tm (°C) is defined as the temperature of the peak with the largest absolute value of heat flow among the melting peaks, Tm is greater than 170°C and less than or equal to 200°C, the film is suitable for use in a film capacitor.

3. The polyolefin film according to claim 1 or 2, wherein the relationship between the longitudinal orientation parameter (MOP) and the width orientation parameter (TOP), determined from the Raman band intensity measured by Raman spectroscopy, satisfies the following equation. MOP / TOP≧0.11

4. The polyolefin film according to claim 1 or 2, wherein the loss tangent (tanδ0) determined by dynamic viscoelasticity measurement in the width direction at 0°C is 0.06 or less.

5. A polyolefin film according to claim 1 or 2, wherein the shrinkage stress in the width direction at 135°C (135Tf), as determined by thermomechanical analysis (TMA), is 5.0 MPa or less.

6. The polyolefin film according to claim 1 or 2, wherein the thermal shrinkage rate (130S) in the longitudinal direction of the film after heat treatment at 130°C for 10 minutes is greater than 2.0% and less than or equal to 5.0%.

7. The polyolefin film according to claim 1 or 2, wherein the cyclic olefin resin is an amorphous resin.

8. The polyolefin film according to claim 1 or 2, wherein the polyolefin film is a film having a laminated structure of three or more layers, and of which layer A is included as a layer other than the outermost layer, and the two outermost layers both mainly consist of a polypropylene resin, and contain more polypropylene resin than layer A, and have a smaller content of cyclic olefin resin than layer A.

9. The polyolefin film according to claim 1, wherein when the A layer is cut by a plane parallel to the principal orientation axis and the thickness direction, the cross section obtained by cutting the A layer is defined as cross section X, and within cross section X, in a 1 μm square defined such that a pair of sides are parallel to the thickness direction, there are three or more domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction.

10. The polyolefin film according to claim 1 or 2, wherein when the A layer is cut by a plane parallel to the principal orientation axis and the thickness direction, the resulting cross-section is defined as cross-section X, and within cross-section X, in a rectangle of 1 μm × 2 μm size defined such that a pair of short sides are parallel to the thickness direction, there are two or more domains of the cyclic olefin resin passing through the pair of short sides.

11. The polyolefin film according to claim 2, wherein the average length in the thickness direction of the domains of the cyclic olefin resin passing through the pair of sides is 1 nm or more and 300 nm or less.

12. A metal film laminated film having a metal film on at least one side of the olefin film according to claim 1 or 2.

13. A film capacitor comprising a metal film laminated film as described in claim 12.

14. The film capacitor according to claim 13, manufactured by subjecting a metal film laminate to heat treatment at 125°C or higher.

15. A power control unit having the film capacitor described in claim 13.

16. An electric vehicle having the power control unit described in claim 15.

17. An electric aircraft having the power control unit described in claim 15.

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