Polyolefin-based film, metallized film including same, film capacitor, power control unit, electric vehicle, 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

Polyolefin film, metal film laminated film using the same, film capacitor, power control unit, electric vehicle, and electric aircraft

[0001] The present invention relates to a polyolefin film that is particularly suitable for use in capacitors.

[0002] In recent years, the majority of electrical equipment has been converted to inverters, which has led to an ever-increasing demand for smaller capacitors with higher capacitance. This demand, particularly in applications such as automobiles (including electric vehicles and hybrid cars), electric aircraft, solar power generation, and wind power generation, requires capacitor films to have improved voltage resistance, maintain productivity and processability in the manufacture of capacitor elements, as well as thinner films and improved heat resistance.

[0003] Among polyolefin-based films, polypropylene films are considered to have excellent heat resistance and breakdown voltage. However, when applied to the aforementioned fields, it is important that the film exhibits excellent dimensional stability at the ambient temperature and stable electrical performance (such as voltage resistance) at temperatures 10 to 20°C higher than the ambient temperature. From the perspective of heat resistance, it is expected that the ambient temperature will become even higher in the future when considering power semiconductor applications using silicon carbide (SiC).

[0004] In light of this, further improvements in heat resistance and voltage resistance are required for capacitors, and capacitor films are required to have improved breakdown voltages in high-temperature environments exceeding 110° C. However, as described in Non-Patent Document 1, the upper limit of the usable temperature of polypropylene film is said to be approximately 110° C., and it has been extremely difficult for polypropylene films to stably maintain breakdown voltages in such temperature environments.

[0005] To miniaturize film capacitors and improve their heat resistance, it is possible to use thinner films, films with higher dielectric constants, and films with glass transition temperatures above the capacitor's operating temperature range. 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 with a glass transition temperature above 130°C and the other being a polypropylene layer, thereby maintaining heat resistance and voltage resistance while maintaining a large capacitance (see, for example, Patent Document 1). Furthermore, films have been proposed that improve processability by co-extrusion and co-stretching when forming a cycloolefin polymer and polypropylene laminate (see, for example, Patent Documents 2 and 3). Furthermore, a film with improved thermal dimensional stability in high-temperature environments has been proposed by blending a cycloolefin polymer and a polypropylene resin, forming the film, and biaxially stretching the film (see, for example, Patent Document 4).

[0006] JP 2015-012076 A International Publication No. 2017 / 022706 JP 2018-034510 A JP 2020-521867 A

[0007] Motonobu Kawai, "Film Capacitor Advances: From Automobiles to Energy," Nikkei Electronics, Nikkei BP, September 17, 2012, pp. 57-62

[0008] However, the film of Patent Document 1 is not a coextrusion laminate, but a laminate in which a cycloolefin polymer layer is formed on a polypropylene film by a coating method, so the cycloolefin polymer layer is prone to peeling, and the performance and reliability when used as a capacitor are not sufficient. The film of Patent Document 2 also has a base layer of a laminate structure consisting of a cycloolefin polymer alone, making it difficult to increase the areal stretch ratio and resulting in insufficient voltage resistance in high-temperature environments, and therefore, the performance and reliability when used as a capacitor are not sufficient. The film of Patent Document 3 also has a base layer of a laminate structure consisting of a cycloolefin polymer, and contains an elastomer to improve stretchability and increase the areal stretch ratio, but its voltage resistance in high-temperature environments is unsatisfactory, and the performance and reliability when used as a capacitor are not sufficient. The film of Patent Document 4 is a film simply made of a blend of a cycloolefin polymer and a polypropylene resin, so it is difficult to increase the areal stretch ratio and resulting in insufficient voltage resistance in high-temperature environments, and therefore, the performance and reliability when used as a capacitor are not sufficient.

[0009] Therefore, an object of the present invention is to provide a polyolefin film that has excellent voltage resistance and reliability in high-temperature environments and is suitable for use in capacitors and the like that are used under high temperatures and high voltages.

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

[0011] The second polyolefin film of the present invention is a polyolefin film characterized in that it has a layer containing a cyclic olefin resin and a polypropylene resin (such layer will be referred to as "layer A" for convenience), and when a cross section X is a cross section of layer A cut along a plane parallel to the main orientation axis direction and the thickness direction, in a 1 μm square within cross section X, where a pair of sides are parallel to the thickness direction, three or more domains of the cyclic olefin resin pass through a pair of sides parallel to the thickness direction, and the internal haze is 4.0% or less.

[0012] The present invention can provide a polyolefin film that has excellent voltage resistance and reliability in high-temperature environments and is suitable for use in capacitors and the like that are used under high temperatures and high voltages.

[0013] 1 is a schematic diagram showing a 1 μm square in a cross section X of a polyolefin film according to an embodiment of the present invention, the square having a pair of sides parallel to the thickness direction, and a domain of a cyclic olefin resin passing through a pair of sides parallel to the thickness direction of the square. 2 is an enlarged photograph (magnification 20,000 times) of the cross section X of a polyolefin film according to an embodiment of the present invention (embodiment of Example 2). 3 is a schematic diagram showing a 1 μm × 2 μm rectangle in a cross section X of a polyolefin film according to an embodiment of the present invention, the rectangle having a pair of short sides parallel to the thickness direction, and a domain of a cyclic olefin resin passing through a pair of sides parallel to the thickness direction of the square.

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems, and have concluded that the reason why the films described in Patent Documents 1 to 4 do not have sufficient breakdown voltage in a high-temperature environment, and when used as a capacitor, do not have sufficient voltage resistance characteristics, reliability, and processability in a high-temperature environment is as follows.

[0015] That is, the film of Patent Document 1 is an unstretched film laminated by a coating method, and therefore it is considered to have problems such as interlayer delamination in high-temperature environments, insufficient mechanical properties, particularly elongation at break, making it prone to breakage during capacitor element processing, and reduced voltage resistance in high-temperature environments. Regarding the films of Patent Documents 2 and 3, when considering voltage resistance in high-temperature environments, it is considered that the problems are that the ratio of stretching in the longitudinal direction during film formation is not necessarily sufficient, and the film contains a large amount of mobile amorphous components, resulting in low breakdown voltage at high temperatures. Regarding the film of Patent Document 4, when considering voltage resistance in high-temperature environments, it is considered that the mixing of the cycloolefin polymer and polypropylene resin is insufficient, making it difficult to sufficiently increase the ratio of stretching in the longitudinal direction during film formation, and the film contains a large amount of mobile amorphous components, resulting in low breakdown voltage at high temperatures.

[0016] Based on the above considerations, the present inventors have conducted further studies and found that the above problems can be solved by providing a polyolefin film having a total light transmittance of 85% or more and an internal haze of 4.0% or less, where Layer A is a layer containing a cyclic olefin resin and a polypropylene resin. Furthermore, the present inventors have found that the above problems can also be solved by providing a polyolefin film having a layer A containing a cyclic olefin resin and a polypropylene resin, where Layer A is a layer containing the cyclic olefin resin and a polypropylene resin, and where Cross Section X is a cross section of Layer A cut along a plane parallel to the main orientation axis direction and the thickness direction, in a 1 μm square defined in Cross Section X so that a pair of sides are parallel to the thickness direction, three or more domains of the cyclic olefin resin exist that pass through a pair of sides parallel to the thickness direction, and the internal haze is 4.0% or less.

[0017] That is, the first polyolefin film of the present invention is a polyolefin film characterized by having a layer containing a cyclic olefin resin and a polypropylene resin as Layer A, 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 by having a layer containing a cyclic olefin resin and a polypropylene resin as Layer A, a cross section of Layer A cut along a plane parallel to the main orientation axis direction and the thickness direction as Cross Section X, in which, in a 1 μm square defined in Cross Section X so 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 an internal haze of 4.0% or less.

[0018] The first and second polyolefin films of the present invention will be specifically described below. When the upper and lower limits of the preferred ranges are separately stated below, the combination of these limits can be arbitrary. The first and second polyolefin films of the present invention may be collectively referred to as the present invention or the polyolefin film of the present invention.

[0019] In addition, in this specification, polyolefin film may be simply referred to as film hereinafter. 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 means a polyolefin film other than a microporous film. Here, the 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 at 23°C and 65% relative humidity for 100 ml of air permeation time using a B-type Gurley tester according to JIS P 8117 (1998).

[0020] From the viewpoint of achieving both thermal stability and voltage resistance, the polyolefin film of the present invention must have an A layer, where the A layer is a layer containing a cyclic olefin resin and a polypropylene resin. By adopting such an embodiment, the high thermal stability of the cyclic olefin resin and the high voltage resistance of the polypropylene resin result in the resulting polyolefin film having excellent thermal stability and voltage resistance. The polyolefin film of the present invention may have a single-layer structure consisting of only one A layer, a laminate structure in which a total of two or more A layers are laminated in the thickness direction, or a laminate structure in which a total of two or more A layers and layers other than the A layer are laminated in the thickness direction. Furthermore, when the polyolefin film of the present invention has multiple A layers, the compositions thereof may be the same or different.

[0021] Here, the term "polyolefin film" refers to a sheet-like molded product containing more than 50% by mass and not more than 100% by mass of polyolefin resin, where the total components constituting the film are taken as 100% by mass. Here, the term "polyolefin resin" refers to a resin containing more than 50% by mass and not more than 100% by mass of olefin units, where the total structural units constituting the resin are taken as 100 mol%, and polypropylene resins and cyclic olefin resins can be interpreted in the same way by replacing the olefin units with propylene units and cyclic olefin units, respectively. The thickness direction refers to the direction perpendicular to the film surface.

[0022] From the viewpoint of achieving both thermal stability and voltage resistance, 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. Here, the 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, the internal haze refers to the internal haze measured when light is incident perpendicularly to the film surface. From the viewpoint of the above-mentioned thermal stability and voltage resistance, the total light transmittance is preferably 88% or more, more preferably 90% or more, and even more preferably 92% or more. The upper limit is not particularly limited, but is set to 99.9%. Furthermore, from the viewpoint of the above-mentioned thermal stability and voltage resistance, 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. The lower limit is not particularly limited, but 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 microvoids due to peeling at the sea-island interface of a sea-island structure in which the polypropylene resin is considered the sea and the cyclic olefin resin is considered the islands is suppressed, and the island structure (hereinafter sometimes referred to as a domain structure) is small or thin. As a result, the first polyolefin film of the present invention satisfying the above requirements can utilize the high thermal stability of the cyclic olefin resin and the high voltage resistance of the polypropylene resin, thereby increasing the film's breakdown voltage under high-temperature conditions. Furthermore, when such a film is used in a capacitor, it is less likely to cause short-circuiting, even when used for long periods of time, especially in high-temperature environments, and voltage resistance is maintained, resulting in high reliability. Total light transmittance and internal haze can be measured using a known haze meter; detailed conditions will be described later.

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

[0025] The effects of preparing the compound resin raw material in advance include increasing the total light transmittance, reducing the internal haze, and improving the stretchability. This is presumably because the two types of resins are mixed more uniformly than when the resins are simply mixed during film formation, and the island component resin is finely dispersed in the sea component resin, resulting in increased transparency and strength. It is also preferable to dilute the compound resin raw material pre-mixed in a twin-screw extruder and use it as a masterbatch, as this increases the dispersibility of the cyclic olefin resin.

[0026] In the second polyolefin film of the present invention, when a cross section X is defined as a cross section of layer A cut along a plane parallel to the main orientation axis direction and the thickness direction, in a 1 μm square defined in cross section X so that a pair of sides are parallel to the thickness direction, it is necessary that three or more domains of cyclic olefin resin pass through the pair of sides. It is also preferable that the first polypropylene film of the present invention also 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 5 or more, more preferably 7 or more. There is no particular upper limit, but it is generally 100.

[0027] By making the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction three or more, the high thermal stability of the cyclic olefin resin and the high voltage resistance of the polypropylene resin can be reflected in the polyolefin film, and the breakdown voltage of the polyolefin film in a high-temperature environment can be increased. Furthermore, when such a film is used in a capacitor, short circuit breakdown is less likely to occur, especially even when used for a long period of time in a high-temperature environment, and the voltage resistance of the capacitor is maintained, resulting in high reliability.

[0028] Furthermore, for the same reasons as in the first invention, the second polyolefin film of the present invention also needs to have an internal haze of 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 is set to 0.1%. The definition of internal haze is as described above.

[0029] In the second polyolefin film of the present invention, a method for controlling the domain structure (sea-island structure) of Layer A can be used to set 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. For example, it is effective to prepare a compound resin raw material for Layer A by pre-kneading a cyclic olefin resin and a polypropylene resin, control the content of the cyclic olefin resin, melt-extrude the resulting material into a sheet, biaxially stretch the resulting material at an areal stretching ratio of 35.0 times or more, and perform a relaxation treatment while performing a heat treatment after biaxial stretching. A similar method can also be used to set the number of cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction to 3 or more in the first polyolefin film of the present invention.

[0030] Here, in the polyolefin film of the present invention, the "thickness direction" refers to the direction perpendicular to the film surface. The "longitudinal direction" refers to the direction corresponding to the flow direction in the film production process (hereinafter sometimes referred to as "MD"), and the "width direction" refers to the direction perpendicular to the flow direction in the film production process within the film plane (hereinafter sometimes referred to as "TD"). When the film sample is in the form of a reel, roll, or the like, the film winding direction can be said to be the longitudinal direction. When biaxial stretching is performed in the production of polyolefin film, stretching is performed in the longitudinal direction and the width direction, and generally, the direction with the larger stretch ratio is the main orientation axis direction. When the stretching directions (longitudinal direction and width direction) are specified but the ratio is unknown, the maximum load until breakage can be measured in a tensile test described below, and the direction with the larger measured value can be considered the main orientation axis direction.

[0031] As described above, the main orientation axis direction can be determined if the stretching direction and stretch ratio are known. However, for films where these are unknown, the main orientation axis direction can be determined by the following method. Specifically, a film is prepared and cut into a rectangular shape 50 mm long x 10 mm wide with an arbitrary direction facing upward. This is designated sample <1>, and the direction of the long side of sample <1> is defined as 0°. Next, sample <2> of the same size is taken so that the long side direction is rotated 15° clockwise from the 0° direction. Similarly, the long side direction of each rectangular sample is rotated 15° at a time, and samples <3> to <12> are similarly taken. Next, each rectangular sample is placed in a tensile tester (e.g., Orientec's "Tensilon" (registered trademark) UCT-100) with an initial chuck distance of 20 mm so that the long side direction is the tensile direction, and a tensile test is performed at room temperature with a tensile speed of 300 mm / min. The maximum load until the sample breaks is read and divided by the cross-sectional area of ​​the sample before the test (film thickness x width) to calculate the stress at maximum strength, and the direction of the long side of the sample where this value is maximum is defined as the main orientation axis of the polyolefin film, which is the width direction of the polyolefin film. The direction perpendicular to this is defined as the direction perpendicular to the main orientation axis of the polyolefin film, which is the longitudinal direction of the polyolefin film.

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

[0033] Hereinafter, a method for defining a 1 μm square in the cross section X of the polyolefin film of the present invention, with a pair of sides parallel to the thickness direction, and a method for determining the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction, will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a 1 μm square defined in the cross section X of a polyolefin film according to one embodiment of the present invention, with a pair of sides parallel to the thickness direction, and domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction of the square. Reference numerals 1 to 5 in FIG. 1 respectively represent a portion of the cross section X, a sea portion, an island portion (domain), a 1 μm square defined in the cross section X with a pair of sides parallel to the thickness direction, and a pair of sides parallel to the thickness direction. The left side of FIG. 2 is a portion of the cross section X, and the right side is an enlarged view of a 1 μm square indicated by a dashed line in the cross section X, with a pair of sides 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 a square of 1 μm on each side is defined in the cross section X so 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 to the base, this is considered to be absent and is not counted in the number of domains (such domains do not exist in the example of FIG. 1 ).

[0035] Here, "domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction" refers to domains of the cyclic olefin resin passing through both of a pair of sides parallel to the thickness direction. That is, in the example of Figure 1 (right diagram), the first and fourth to sixth domains from the top correspond to this, but the second and third domains from the top do not, so there are four "domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction" in this example.

[0036] In the polyolefin film of the present invention, when a cross section X is defined as a cross section of the layer A cut along a plane parallel to the main orientation axis and the thickness direction, as shown in FIG. 3 , in a rectangle of 1 μm × 2 μm size defined so that a pair of short sides is parallel to the thickness direction, preferably, two or more domains of the cyclic olefin resin are present within the cross section X, passing through the pair of short sides. 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. The upper limit is not particularly limited, but is preferably 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 finely dispersed in a more flattened shape within the plane, which allows the high thermal stability of the cyclic olefin resin and the high voltage resistance of the polypropylene resin to be reflected in the polyolefin film, thereby increasing the breakdown voltage of the polyolefin film under high-temperature conditions. Furthermore, when such a film is used in a capacitor, short circuit breakdown is less likely to occur, especially even when used for long periods of time under high-temperature conditions, and the voltage resistance of the capacitor is maintained, resulting in high reliability.

[0037] In the polyolefin film of the present invention, the average thickness length of the cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction is preferably 1 nm or more and 300 nm or less. The average thickness length 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 thickness length of the domains to 1 nm or more and 300 nm or less, the high thermal stability of the cyclic olefin resin and the high voltage resistance of the polypropylene resin can be reflected in the polyolefin film, thereby increasing the dielectric breakdown voltage of the film in high-temperature environments. Furthermore, when such a film is used in a capacitor, it is less likely to cause short circuit breakdown, especially even when used for long periods of time in high-temperature environments, and voltage resistance is maintained, resulting in high reliability. Note that methods for measuring the thickness length of the cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction and calculating the average value are shown in the examples.

[0038] In addition, the average length of the domains in the thickness direction may be 1 nm or less. In such a case, for example, if the screw rotation speed during pre-mixing in a twin-screw extruder is increased, shear heating may cause the resin temperature to rise above the set temperature, resulting in resin degradation, which may cause foreign matter or may lead to deterioration in reliability and voltage resistance when used as a capacitor. In other words, making the average length of the domains in the thickness direction 1 nm or more contributes to improving the quality and reliability and voltage resistance when used as a capacitor. From the above perspectives, 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 for making the average thickness direction length of the cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction 1 nm or more and 300 nm or less can be used, for example, a method for making the total light transmittance 85% or more and the internal haze 4.0% or less in the first polyolefin film of the present invention, or a method similar to a method for making the number of cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction 3 or more and the internal haze 4.0% or less in the second polyolefin film of the present invention.

[0040] In the polyolefin film of the present invention, the lower limit of the content of the cyclic olefin resin in all constituents of Layer A (or the film itself when 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, based on 100% by mass of the total resin components excluding various additives in the entire film, such as organic particles, inorganic particles, crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, slipping agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors. 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 content of the cyclic olefin resin in the entire film is high, the areal ratio may not be increased during stretching, resulting in a decrease in voltage resistance in high-temperature environments. If the content is low, the thermal dimensional stability in high-temperature environments may be reduced, resulting in a decrease in voltage resistance and reliability in high-temperature environments.

[0041] In the polyolefin film of the present invention, when the melting peak temperature Tm (°C) is the temperature of the peak with the largest absolute value of the heat flow on the vertical axis in a DSC chart obtained by heating from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC), the Tm is preferably greater than 170°C and less than 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 and the more excellent its thermal stability, improving its breakdown voltage in high-temperature environments. In other words, a Tm exceeding 170°C improves the withstand voltage 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 based on the olefin resin used in the film.

[0042] In this case, two or more melting peak temperatures may be observed in the range of more than 170°C and not more than 200°C, or a multi-stage melting peak called a shoulder (a melting peak in which two or more peaks overlap) may be observed. In such cases, the temperature of the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart is taken as Tm.

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

[0044] In the polyolefin film of the present invention, the Tm can be controlled to be more than 170°C and not more than 200°C or within the above-mentioned preferred range by, for example, adjusting 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 areal 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 the raw material for the A layer.

[0045] From the viewpoint of voltage resistance, the polyolefin film of the present invention preferably has a relationship between the MD (machine direction) orientation parameter (MOP) and the TD (transverse direction) orientation parameter (TOP) determined from the Raman band intensity measured by Raman spectroscopy that satisfies the following formula: MOP / TOP≧0.11.

[0046] From the above viewpoints, MOP / TOP is preferably 0.15 or more, more preferably 0.24 or more, even more preferably 0.26 or more, and most preferably 0.31 or more. A preferred upper limit is 0.90 from the viewpoint of the possibility of realizing this while biaxially stretching. By increasing the value of MOP / TOP, the effect of high voltage resistance can be obtained, the dielectric breakdown voltage of the film in a high-temperature environment can be increased, and when used as a capacitor, short circuit breakdown is unlikely to occur even when used for a long period of time, particularly in a high-temperature environment, and voltage resistance can be maintained, resulting in high reliability.

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

[0048] Here, the "longitudinal direction" (sometimes referred to as "MD") refers to the direction corresponding to the flow direction in the film manufacturing process, and the "transverse direction" (sometimes referred to as "TD") refers to the direction perpendicular to the longitudinal direction within the film plane. In other words, when the film sample is in the form 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 transverse direction.

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

[0050] Since the polyolefin film of the present invention contains a polypropylene resin, the more suppressed the molecular mobility at 0°C, the glass transition temperature of the polypropylene resin, the more molecular chain restraint there is, resulting in a stable structure. Furthermore, when the polyolefin 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 molecular mobility in the direction perpendicular to that (width direction). From the above perspectives, tan δ0 is more preferably 0.05 or less, and even more preferably 0.04 or less. The lower limit is not particularly limited, but is set to 0.001. By setting tan δ0 within this range, and the lower tan δ0, the higher the structural stability of the film, and the longer the reliability when used as a capacitor under high-voltage and high-temperature environments is improved.

[0051] Tan δ0 can be calculated from the following formula by heating the film from -100°C to 180°C, drawing a viscoelasticity-temperature curve using a dynamic viscoelastic method, reading the storage modulus at 0°C (E'0) and the loss modulus at 0°C (E"0) from the viscoelasticity-temperature curve. Detailed measurement conditions will be described later. Formula: tan δ0=E"0 / E'0.

[0052] Methods for making tan δ0 0.06 or less or within the above-mentioned preferred range include, for example, using a polypropylene resin having a high mesopentad fraction and a high melting point, increasing the areal 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 carrying out heat treatment after biaxial stretching. Simultaneous biaxial stretching is also effective.

[0053] In order to improve reliability over a long period of time when used as a capacitor in a high-temperature environment, the polyolefin film of the present invention preferably has a widthwise shrinkage stress (135Tf) at 135°C as determined by thermomechanical analysis (TMA) of 5.0 MPa or less. From this 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 is set to 0.01 MPa. Details of the TMA conditions will be described later.

[0054] In order to make the shrinkage stress (135Tf) in the width direction 5.0 MPa or less or within the above-mentioned preferable range, it is effective to use a polypropylene-based resin having a high mesopentad 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 width direction stretching temperature +5 to +15°C, and to perform a relaxation treatment at a relaxation rate of more 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, the film preferably has a longitudinal heat shrinkage (130S) of more than 2.0% and not more than 5.0% when heated at 130°C for 10 minutes, in order to improve the reliability of the capacitor by appropriately winding and tightening the capacitor element during heat treatment during element processing. From this 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] In order to set the heat shrinkage rate (130S) in the longitudinal direction within the above-mentioned preferred range, it is effective to use a polypropylene-based resin having a high mesopentad fraction and a high melting point, to perform biaxial stretching at an areal stretching ratio of 35.0 times or more, to set the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction to a temperature higher than the stretching temperature in the width direction by 5 to 15°C, and to perform a relaxation treatment at a relaxation rate of more than 5% during the heat treatment step 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 of Layer A alone, or a laminate structure including Layer A. However, from the viewpoint of exhibiting the film's stretchability, excellent voltage resistance characteristics and reliability in high-temperature environments, and processability, it is preferable to have Layer B, which is a layer mainly composed of a polypropylene resin, contains more polypropylene resin than Layer A, and has a lower content of cyclic olefin resin.

[0058] Specific examples of such an embodiment include a structure having a B layer on one side of an A layer (a two-layer structure of A layer / B layer), a structure having a B layer on both sides of an A layer (a three-layer structure of B layer / A layer / B layer), and a four-layer or greater structure in which a B layer is the outermost layer on both surfaces of the film. From the above viewpoint, a three-layer structure of B layer / A layer / B layer or a four-layer or greater structure in which a B layer is the outermost layer on both surfaces of the film is more preferred, and a three-layer structure of B layer / A layer / B layer is even more preferred. Note that when there are multiple B layers, the composition of the B layers preferably contains a higher proportion of polypropylene-based resin than the A layer and a lower content (content ratio) of cyclic olefin-based resin than the A layer. As long as the composition is as described above, the B layers may be the same or different.

[0059] Examples of lamination methods that can be used in the polyolefin film of the present invention include a feed block method using coextrusion, a multi-manifold method, and a coating method. From the viewpoints of production efficiency and production costs, a lamination method using coextrusion (e.g., melt coextrusion) is preferred.

[0060] When the 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 formability and surface shape. The lower limit is preferably 10%, more preferably 15%, and even more preferably 20%. For example, in the case of a three-layer structure (layer B / layer A / layer B) in which layer B is directly laminated on both surfaces of layer A, the thickness ratio of layer A can be determined 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 the result as a percentage. By having the ratio of layer A be 99% or less, the area ratio in stretching can be sufficiently increased, and the decrease in voltage resistance in high-temperature environments can be reduced. On the other hand, by having the ratio of layer A be 10% or more, the decrease in thermal dimensional stability in high-temperature environments can be reduced.

[0061] In order to obtain high voltage resistance and excellent stretchability, the content of the polypropylene resin in Layer B of the polyolefin film of the present invention 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 amount of all components of Layer B is taken as 100% by mass. The upper limit is not particularly limited, but is set to 100% by mass.

[0062] Next, resins that are preferably used in the polyolefin film of the present invention will be described.

[0063] The polyolefin film of the present invention preferably contains a linear polypropylene resin (hereinafter sometimes referred to as polypropylene resin (A)) as a main component. Here, the main component refers to the component with the highest mass % (highest content) among all 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. When the polypropylene resin (A) has the above properties, deterioration of film formation stability, film strength, dimensional stability, and heat resistance can be reduced.

[0065] The mesopentad fraction of the polypropylene resin (A) is preferably 0.960 or more. It is more preferably 0.965 or more, even more preferably 0.970 or more, particularly preferably 0.975 or more, and most preferably 0.980 or more. The mesopentad fraction is an index of the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance (NMR). A higher mesopentad fraction indicates a higher crystallinity and melting point, making it suitable for use at high temperatures. There is no particular upper limit for the mesopentad fraction. To obtain a resin with such high stereoregularity, methods such as washing the resulting resin powder with a solvent such as n-heptane, or appropriately selecting a catalyst and / or co-catalyst and selecting the composition 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. When the polypropylene resin (A) has a melting point of 160° C. or higher, deterioration in voltage resistance characteristics in a high-temperature environment is reduced when the polypropylene resin (A) is formed into a film.

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

[0068] The polypropylene resin (A) is preferably composed mainly of a propylene homopolymer, but a propylene copolymer containing other unsaturated hydrocarbons as copolymerization components may also be used within the scope of the present invention. Examples of copolymerization components contained 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 view of breakdown voltage and heat resistance, the copolymerization amount of components other than propylene in a propylene copolymer is preferably less than 1 mol%. Here, "the copolymerization amount of components other than propylene is less than 1 mol%" means that when the constituent components of the resin constituting the polypropylene resin (A) are taken as 100 mol%, the constituent components other than propylene are less than 1 mol%. That is, even when the polypropylene resin (A) is made of a polypropylene polymer having a copolymerization amount of less than 1 mol%, or when a polypropylene polymer having a copolymerization amount of 1 mol% or more and a propylene copolymer (or a polypropylene polymer having a copolymerization amount of less than 1 mol%) are mixed so that the components other than propylene account for less than 1 mol% of the total, the copolymerization amount of components other than propylene is also considered to be less than 1 mol%.

[0070] Furthermore, the polypropylene resin (A) may be blended with a polymer whose main constituent is a component other than propylene. Examples of the main constituent component in such a polymer 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 viewpoints of breakdown voltage and heat resistance, the blend amount of the polymer whose main constituent is a component other than propylene is preferably less than 1 part by mass per 100 parts by mass of the polypropylene resin (A).

[0071] The cyclic olefin resin used in the polyolefin film of the present invention will be described. The cyclic olefin resin is a resin obtained by polymerizing a cyclic olefin monomer and having an alicyclic structure in the polymer main chain, and refers to a polymer in which the total amount of cyclic olefin monomer-derived components (structural units) is more than 20% by mass and not more than 100% by mass in 100% by mass of the cyclic olefin resin polymer. It is preferable to use one in which the content of the cyclic olefin monomer-derived components is more than 50% by mass and not more than 100% by mass.

[0072] Examples of cyclic olefin monomers include monocyclic olefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, cyclopentadiene, and 1,3-cyclohexadiene, bicyclo[2,2,1]hept-2-ene, 5-methyl-bicyclo[2,2,1]hept-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]hept-2-ene, 5-vinyl-bicyclo[2,2,1]hept-2-ene, and 5-propenyl-bicyclo[2,2,1]hept-2-ene, tricyclo[4,3,0,12.5]deca-3,7-diene, tricyclo[4,3,0,12.5]dec-3-ene, and tricyclo[4,3,0,12.5]undeca-3,7-diene, ene, 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]hept-2-ene, 5-cyclohexyl-bicyclo[2,2,1]hept-2-ene, 5-cyclohexenylbicyclo[2,2,1]hept-2-ene, 5-phenyl-bicyclo[2,2,1] ]hept-2-ene, tricyclic olefins such as tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-methyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-ethyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-methylidenetetracyclo[4,4,0,12.5,17.10]dodeca- tetracyclic olefins such as 8-cyclopentyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-ethylidenetetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-vinyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-propenyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, and 8-cyclopentyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-cyclohexyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-cyclohexenyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-phenyl-cyclopentyl-tetracyclo[4,4,0,12.5,17.10]dodec-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, penta Examples of the cyclic olefin monomer include polycyclic olefins such as tetramers of cyclo[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 alone or in combination of two or more.

[0073] Among the above-mentioned cyclic olefin monomers, from the viewpoints of productivity and surface properties, tricyclic olefins having 10 carbon atoms such as bicyclo[2,2,1]hept-2-ene (hereinafter referred to as norbornene), tricyclo[4,3,0,12.5]dec-3-ene (hereinafter referred to as tricyclodecene), tetracyclic olefins having 12 carbon atoms such as tetracyclo[4,4,0,12.5,17.10]dodec-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 obtained by polymerizing only the cyclic olefin monomer (hereinafter sometimes referred to as COP) or a resin obtained by copolymerizing the cyclic olefin monomer and a chain olefin monomer (hereinafter sometimes referred to as COC), as long as the total content of cyclic olefin monomer-derived components in 100% by mass of the cyclic olefin resin polymer is more than 20% by mass but not more than 100% by mass. Preferred examples of usable COP include "ZEONOR" (registered trademark) manufactured by Zeon Corporation. Preferred examples of usable COC include "APEL" (registered trademark) manufactured by Mitsui Chemicals, Inc., "ARTON" (registered trademark) manufactured by JSR Corporation, and "TOPAS" (registered trademark) manufactured by Polyplastics Co., Ltd.

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

[0076] In the case of COC, preferred chain 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 standpoints of productivity and cost. Furthermore, methods for producing resins obtained by copolymerizing cyclic olefin monomers and chain olefin monomers include, for example, known methods such as addition polymerization of cyclic olefin monomers and chain olefin monomers. Among these, a preferred method is 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 an amorphous resin. 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 dimensional stability and insulating performance in high-temperature ranges suitable for capacitor applications, etc. If the glass transition temperature is lower than 125°C, the thermal dimensional stability and breakdown voltage at high temperatures may decrease. The upper limit is not particularly limited, but is set to 200°C from the viewpoint of film formability. In the polyolefin film of the present invention, the cyclic olefin resin is defined as being amorphous 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) and no melting peak temperature (Tm) is observed.

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

[0079] When an antioxidant is added, the selection of the type and amount of antioxidant is important from the viewpoint of long-term heat resistance. Specifically, such antioxidants are preferably sterically hindered phenolic antioxidants, with at least one of them being a high-molecular-weight type having a molecular weight of 500 or more. Specific examples include various antioxidants, but 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" (registered trademark) 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox" (registered trademark) 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. If the amount of antioxidant is too small, long-term heat resistance may be poor. If the amount of antioxidant is too large, blocking at high temperatures due to bleed-out of these antioxidants may occur, adversely affecting the capacitor element. A more preferred 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 contain 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 achieving high quality and voltage resistance performance.

[0081] The polyolefin film of the present invention may contain resins other than the polypropylene resin (A) and the cyclic olefin resin, as long as the object of the present invention is not impaired. Specific resins include vinyl polymer resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, polycarbonate resins, olefin and styrene block copolymers, etc., including various polyolefin resins. Particularly preferred examples include polymethylpentene and syndiotactic polystyrene. The content of resins other than the polypropylene resin (A) and the cyclic olefin resin is preferably less than 3% by mass, more preferably 2% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the total resin components constituting the polyolefin film. If the content of resins other than the polypropylene resin is 3% by mass or more, the influence of the domain interface becomes greater, which may result in a decrease in the breakdown voltage in high-temperature environments.

[0082] The polyolefin film of the present invention preferably has a film breakdown voltage of 350 V / μm or more at 135°C. More preferably, it is 375 V / μm or more, even more preferably 400 V / μm or more, and particularly preferably 420 V / μm or more. The upper limit is not particularly limited, but is about 800 V / μm. When the film breakdown voltage at 130°C is 350 V / μm or more, when used as a capacitor, short circuit breakdown is unlikely to occur, even when used for a long time in a high-temperature environment, and voltage resistance is maintained, resulting in high reliability.

[0083] In order to control the film breakdown voltage at 135°C within the above-mentioned range (350 V / µm or more), for example, as described below, it is effective to use a raw material with a high mesopentad fraction as the polypropylene resin (A), to dilute or directly melt-extrude a compound resin raw material obtained by pre-kneading a cyclic olefin resin and a polypropylene resin in a twin-screw extruder to form a sheet, and to increase the TD side in the MD and TD stretching ratios in biaxial stretching and to increase the areal stretching ratio to 35.0 times or more.

[0084] The polyolefin film of the present invention is preferably 0.5 μm or more and less than 25 μm in thickness, from the viewpoint that it is suitable for thin-film heat-resistant film capacitors required for automotive applications (including hybrid car applications) used in high-temperature environments in particular. For the heat-resistant film capacitor application, 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, in view of the balance between the properties and the capacitor size due to the 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, from the viewpoint of electrode configuration, it may be either a laminated wound capacitor of metal foil and film or a metal-vapor-deposited film capacitor. It is also preferably used in an oil-immersion type capacitor impregnated with insulating oil or a dry capacitor that does not use insulating oil at all. However, due to the properties of the film of the present invention, it is particularly preferably used as a metal-vapor-deposited film capacitor. From the viewpoint of shape, it may be a wound type or a laminated type.

[0086] Polyolefin films usually have low surface energy, making it difficult to stably apply metal vapor deposition to them. Therefore, it is preferable to perform a surface treatment before vapor deposition in order to improve adhesion to the metal film. Specific examples of surface treatments include corona discharge treatment, plasma treatment, glow discharge treatment, and flame treatment. For example, polypropylene films usually have a surface wetting tension of about 30 mN / m. However, it is preferable to use these surface treatments to increase the wetting tension to preferably about 37 to 75 mN / m, more preferably about 39 to 65 mN / m, and most preferably about 41 to 55 mN / m, because this results in excellent adhesion to the metal film and good safety.

[0087] The polyolefin film of the present invention can be obtained by biaxially stretching, heat treatment, and relaxation treatment using raw materials that can impart the above-mentioned properties. As the biaxial stretching method, any of inflation simultaneous biaxial stretching, tenter simultaneous biaxial stretching, and tenter sequential biaxial stretching can be used. Among these, it is preferable to adopt tenter sequential biaxial stretching and tenter simultaneous biaxial stretching in terms of controlling the mechanical properties and thermal dimensional stability while increasing the film formation stability, crystalline / amorphous structure, surface properties, and particularly the stretch ratio of the present invention.

[0088] Next, the method for producing a polyolefin film of the present invention will be described using an example. First, a compound resin raw material, which is a pre-mixture of a cyclic olefin resin and a polypropylene resin, is melt-extruded onto a support, either diluted or as is, to form an unstretched film. This unstretched film is stretched in the longitudinal direction and then in the width direction, thereby sequentially biaxially stretching the film. Thereafter, a heat treatment and a relaxation treatment are performed to produce a biaxially oriented polyolefin film. The method will be described in more detail below, but the present invention should not be construed as being necessarily limited thereto.

[0089] First, in the polyolefin film of the present invention, it is preferable to preliminarily mix and compound the cyclic olefin resin, the polypropylene resin, and the antioxidant, in order to improve the dispersion state of the cyclic olefin resin and the polypropylene resin (A) to obtain high transparency, particularly to increase the dielectric breakdown voltage of the film at high temperatures. Compounding can be performed using a single-screw extruder, a twin-screw extruder, or the like, but from the viewpoints of good dispersion 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, by setting the mesopentad fraction of the polypropylene resin (A) to 0.960 or more, the melting point becomes high, making it suitable for use at high temperatures, which is preferable.

[0091] Next, the resin raw material obtained by compounding the cyclic olefin resin and the polypropylene resin is fed to a single-screw extruder, passed through a filtration filter, and then extruded from a slit die. The molten sheet extruded from the slit die is solidified on a casting drum (cooling drum) controlled at a temperature of 10 to 110°C, preferably 10 to 85°C, and more preferably 10 to 65°C, to obtain an unstretched polyolefin film. A laminated structure is preferred from the viewpoint of further increasing the area ratio, in which case a resin raw material obtained by pre-compounding a cyclic olefin resin and a polypropylene resin is fed to a single-screw extruder for the inner layer (A layer), and the same polypropylene resin (A) as used for the A layer is fed to a single-screw extruder for the surface layer (B layer), and the resin laminated in a three-layer structure of B layer / A layer / B layer by a feedblock method using melt co-extrusion is extruded as a molten sheet through a slit-shaped die and solidified on a cooling drum controlled at a temperature of 10 to 110°C, preferably 10 to 85°C, more preferably 10 to 65°C, to obtain an unstretched polypropylene film. The molten sheet may be adhered to the casting drum by any of the following methods: electrostatic application, adhesion methods utilizing the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc., although the air knife method is preferred because it provides good flatness and allows control of surface roughness. In addition, it is preferable to appropriately adjust the position of the air knife so that air flows downstream of the film production process to prevent vibration of the film.

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

[0093] Next, the film, uniaxially stretched in the longitudinal direction, is introduced into a tenter while the edges are held with clips. In the present invention, the temperature in the preheating step immediately before stretching in the width direction is preferably set 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 highly oriented in the longitudinal direction by uniaxial stretching and increases the dielectric breakdown voltage of the polyolefin film. Furthermore, stabilizing insufficiently oriented molecular chains by high-temperature preheating after uniaxial stretching is preferred from the viewpoint of improving thermal dimensional stability.

[0094] The temperature at which the film is stretched in the width direction while the edges of the film are held with clips (width direction stretching temperature) is preferably 150 to 175°C, more preferably 155 to 175°C.

[0095] From the viewpoint of increasing the 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 highly oriented in the longitudinal direction by uniaxial stretching remains large, which may result in a film with poor breakdown voltage when evaluating the breakdown voltage at high temperatures, as molecular chains in the film are more likely to move during evaluation. Increasing the stretching ratio in the width direction compared to 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 in-plane molecular chain tension and achieving the effect of increasing the breakdown voltage, particularly at high temperatures.

[0096] Here, the areal stretching ratio is preferably 35.0 times or more. By setting the areal stretching ratio to 35.0 times or more, the molecular chain tension in the film plane is increased, resulting in a smaller or thinner domain structure, thereby reducing internal haze and increasing the total light efficiency. As a result, the resulting film has a high breakdown voltage, particularly 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 areal stretching ratio is the product of the longitudinal stretching ratio and the widthwise stretching ratio. The areal 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. The upper limit of the areal stretching ratio is not particularly limited, but from the perspective 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 reduce internal haze and increase the total light efficiency while achieving a high areal stretching ratio. That is, in the present invention, this can be achieved by increasing the dispersibility of the cyclic olefin resin domains dispersed in the polypropylene resin and by performing heat setting at a high temperature after biaxial stretching, thereby reducing or eliminating microvoids that occur at the domain interface during stretching.

[0097] In the production of the polypropylene film of the present invention, in the subsequent heat treatment and relaxation treatment steps, the film is subjected to a heat treatment at 145°C to 170°C while being tension-held in the width direction with clips and relaxed by 2 to 20% in the width direction, which is preferable from the viewpoints of improving the transparency of the film, increasing the dielectric breakdown voltage at high temperatures, and obtaining voltage resistance and reliability when used as a capacitor. From these viewpoints, 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 these viewpoints, the relaxation treatment rate is more preferably 5 to 18%, and even more preferably 7 to 15%.

[0098] After the heat treatment and relaxation treatment, the film is led to the outside of the tenter, and the clips on the film edges are released in a room temperature atmosphere. The film edges are slit in a winding process, and a film product roll having a thickness of preferably 0.5 μm or more and less than 25 μm is wound up. Here, before winding the film, it is preferable to perform a corona discharge treatment in air, nitrogen, carbon dioxide gas, or a mixture of these gases to improve the adhesion of the vapor-deposited metal to the surface to be vapor-deposited.

[0099] Specific examples of production conditions that are important for obtaining the polyolefin film of the present invention are as follows. While it is preferable to satisfy all of these production conditions, they do not necessarily have to be satisfied, and suitable combinations of these conditions may be used. For example, instead of "the preheating temperature before widthwise stretching in the sequential biaxial stretching is the widthwise stretching temperature +5 to +15°C," simultaneous biaxial stretching may be employed. The mesopentad fraction of the polypropylene resin (A) is 0.960 or more. The cyclic olefin resin and the polypropylene resin are pre-compounded. The areal stretching ratio in the biaxial stretching is 35.0 times or more. The widthwise stretching ratio is higher than the longitudinal stretching ratio. The preheating temperature before widthwise stretching in the sequential biaxial stretching is the widthwise stretching temperature +5 to +15°C. Heat treatment and relaxation treatment are performed 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 producing them will be described.

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

[0102] In the present invention, the method for applying the metal film is not particularly limited. For example, a preferred method is to deposit a metal film, such as a vapor-deposited film of aluminum or an aluminum-zinc alloy, on at least one side of the polyolefin film to form an internal electrode of the film capacitor. In this case, other metal components, such as nickel, copper, gold, silver, or chromium, can be deposited simultaneously with or sequentially to the aluminum. A protective layer, such as oil, can also be deposited on the vapor-deposited film. When the surface roughness of the polyolefin film differs between the front and back, it is preferable to deposit a metal film on the smoother surface to form a metal film-laminated film, from the viewpoint of improving voltage resistance.

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

[0104] The film capacitor of the present invention is formed using the metal film laminated film of the present invention, that is, 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 laminated film of the present invention by various methods. A preferred example of a method for producing a wound type film capacitor is as follows.

[0106] Aluminum is vapor-deposited under reduced pressure on one side of a polyolefin film. This is done in stripes with longitudinal margins. Next, a blade is used to slit the center of each vapor-deposited area and the center of each margin on the surface, producing a tape-like take-up reel with a margin on one side of the surface. Two tape-like take-up reels with left and right margins are stacked and wound together so that the vapor-deposited area extends beyond the margin in the width direction, producing a wound body.

[0107] When vapor deposition is performed on both sides, one side is vapor deposited in stripes with a margin running in the longitudinal direction, and the other side is vapor deposited in stripes so that the longitudinal margin is located in the center of the vapor deposition area on the back side. Next, a blade is cut into the center of the margins on both sides to create a tape-like take-up reel with a margin on one side on each 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 on the back side). One of the resulting reels and one unvapor-deposited laminated film are overlapped and wound together so that the metallized film extends beyond the laminated film in the width direction, to obtain a wound body.

[0108] The core material is removed from the wound body prepared as described above, and the body is pressed. Metallicon is sprayed onto both end surfaces to form external electrodes. This is then heat-treated under reduced pressure at 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. Heat-treating the external electrodes at 125°C or higher is preferred because it facilitates achieving high 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. The film capacitor of the present invention can also be used in a variety of applications, such as packaging films, release films, processing films, sanitary products, agricultural products, construction products, and medical products, and is particularly suitable for applications involving heating processes in film processing.

[0109] The power control unit, electric vehicle, and electric aircraft of the present invention will be described below. The power control unit of the present invention includes the film capacitor of the present invention. The power control unit is a system that manages power in electric vehicles, electric aircraft, and the like that have mechanisms driven by electricity. By incorporating the film capacitor of the present invention into the power control unit, it is possible to reduce the size of the power control unit itself, improve its heat resistance, and increase its efficiency, resulting in improved fuel efficiency.

[0110] The electric vehicle of the present invention has the power control unit of the present invention. Here, the electric vehicle refers to a vehicle having a mechanism driven by electric power, such as an electric vehicle, a hybrid vehicle, or a fuel cell vehicle. As described above, the power control unit of the present invention can be made compact and has excellent heat resistance and efficiency, so that including the power control unit of the present invention in an electric vehicle leads to improved fuel efficiency, etc.

[0111] The electric aircraft of the present invention includes the power control unit of the present invention. Here, the electric aircraft refers to an aircraft with an electrically powered mechanism, such as a manned electric aircraft or a drone. As described above, the power control unit of the present invention can be made compact and has excellent heat resistance and efficiency, so that including the power control unit of the present invention in an electric aircraft can lead to improved fuel efficiency, etc.

[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 methods for measuring the property values ​​and evaluating the effects of the present invention are as follows.

[0113] [Measurement and Evaluation Methods] (1) Film Thickness The thickness of ten randomly selected points on the polyolefin film was measured in an atmosphere of 23°C and 65% RH using a contact-type electronic micrometer (K-312A model) manufactured by Anritsu Corporation. The arithmetic mean value of the thicknesses at the ten points was taken as the film thickness (unit: μm) of the polyolefin film.

[0114] (2) Total Light Transmittance A haze meter (HGM-2DP for C light source) manufactured by Suga Test Instruments Co., Ltd. was used. A polyolefin film was cut into a piece of 6.0 cm x 3.0 cm, and the transmittance of light irradiated perpendicularly to the surface of the polyolefin film was measured. The total light transmittance in the film thickness direction was obtained from the measured value. 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 into a size of 6.0 cm x 3.0 cm, and the polyolefin film was inserted into a quartz cell filled with purified water and having an optical path length of 1 cm. Light was incident perpendicularly to the film surface, and the internal haze value was obtained. 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 (manufactured by Refine Tech Co., Ltd., "Epomount base agent 27-771, Epomount hardener 27-772") and cured for 24 hours, and then measurement samples were cut out using a microtome to measure cross sections in the longitudinal direction (MD) and transverse direction (TD) of the polyolefin film. Polarized Raman measurements (beam diameter 1 μm) were performed using microscopic Raman spectroscopy from the center position in the thickness direction of each measurement cross section in the MD and TD of the polyolefin film using the following equipment and conditions to obtain polarized Raman spectra. The 810 cm of the polarized Raman spectrum －１ and 840 cm －１ The MD orientation parameter (MOP) and the TD orientation parameter (TOP) were determined using the Raman band intensities of the respective crystals, and the value of MOP / TOP was calculated.

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

[0118] The measurement of each cross section was performed five times (hereinafter also referred to as n number). The MD orientation parameter (MOP) was －１ and 840 cm －１ The TD orientation parameter (TOP) was calculated from the Raman band intensities (I810MD, I840MD, I810MZD, I840MZD) using the formula described below. －１ and 840 cm－１ The Raman band intensities (I810TD, I840TD, I810TZD, I840TZD) were calculated using the formula described below.

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

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

[0121] (5) Melting Peak Temperature (Tm) of Resin and Film Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of film was heated in a nitrogen atmosphere from 30°C to 260°C at a rate of 20°C / min, then held at 260°C for 5 minutes, and then cooled to 30°C at a rate of 20°C / min. The endothermic peak temperature obtained during the heating process was taken 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 were observed in the range of more than 170°C to 200°C, or a peak temperature observable on a multi-stage DSC chart known as a shoulder (observed in a chart where two or more peaks overlap) was observed. In this example, the temperature of the peak with the largest absolute value of the vertical axis heat flow (unit: mW) on the DSC chart was taken as (Tm) (°C). The resin (Tm) was measured by heating from 30°C to 260°C at a rate of 20°C / min, then holding at 260°C for 5 minutes, and then lowering the temperature to 30°C at a rate of 20°C / min. After holding at 20°C for 5 minutes, the resin was heated again from 30°C to 260°C at a rate of 20°C / min. The endothermic peak temperature obtained during the heating again process was taken as the melting peak temperature of the resin.

[0122] (6) Glass transition temperature (Tg) of cyclic olefin resin: Measured in accordance with JIS K7121-1987. Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of film or resin was heated from 30°C to 260°C at 20°C / min in a nitrogen atmosphere, then held at 260°C for 5 minutes, and then cooled to 30°C at 20°C / min. After further holding at 20°C for 5 minutes, the temperature was increased again from 30°C to 260°C at 20°C / min. From the DSC curve obtained during the reheating process, the glass transition temperature (Tg) was calculated using the following formula: Glass transition temperature = (extrapolated glass transition onset temperature + extrapolated glass transition end temperature) / 2.

[0123] (7) Loss tangent (tanδ0) at 0°C in the film width direction Using the apparatus and conditions shown below, a rectangular polyolefin film (width (short side) 10 mm x length (long side) 20 mm) cut with the width direction as the long side direction was attached to the chuck of the apparatus in an atmosphere of 23°C and set in a furnace. The atmosphere in the furnace in which the film was set was cooled with liquid nitrogen, and measurements were performed by raising the temperature from -100°C to 180°C. A viscoelasticity-temperature curve was drawn using a dynamic viscoelasticity method, and the storage modulus (E'0) at 0°C and the loss modulus (E"0) at 0°C were read. Note that the number of measurement tests was n=3, and the average values ​​of the storage modulus (E'0) and loss modulus (E"0) were calculated, and the loss tangent (tanδ0) at 0°C in the film width direction was calculated using the following formula. Formula: tan δ0=E"0 / E'0 <Apparatus and conditions> Apparatus: EXSTAR DMS6100 (manufactured by Seiko Instruments Inc.) Test mode: Tensile mode Chuck distance: 20 mm Frequency: 10 Hz Strain amplitude: 10.0 μm Gain: 1.5 Initial force amplitude: 400 mN Temperature range: −100 to 180° C. Heating rate: 5° C. / min Measurement atmosphere: Air Measurement thickness: The film thickness in (1) above was used.

[0124] (8) Shrinkage stress (135Tf) in film width direction at 135°C 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 long side, and the film was clamped between metal chucks so that the sample length was 20 mm. The sample clamped between the chucks was set in the following apparatus, and a stress curve in the width direction of the film was obtained while maintaining a constant sample length using the following temperature program. From the obtained stress curve, the shrinkage stress value at the temperature closest to 25°C was set as the zero point, and the shrinkage stress (unit: MPa) at 135°C was read, and the average value of n = 3 measurements was taken as 135Tf (unit: MPa). <Apparatus and temperature program> Apparatus: Thermomechanical analyzer TMA / SS6000 (Seiko Instruments Inc.) Test mode: L control mode Test length: 20 mm Temperature range: 23 to 200°C Heating rate: 10°C / min Start displacement: 0 µm SS program: 0.1 µm / min Measurement atmosphere: Nitrogen Measurement thickness: The film thickness in (1) above was used.

[0125] (9) Film Breakdown Voltage (V / μm) in a 135°C Environment After heating the film for 1 minute in an oven maintained at 135°C, the film was measured in that atmosphere in accordance with JIS C2330 (2001) 7.4.11.2 Method B (flat electrode method). However, for the lower electrode, a "Conductive Rubber E-100<65>" manufactured by Togawa Rubber Co., Ltd. of the same dimensions was placed on a metal plate described in JIS C2330 (2001) 7.4.11.2 Method B. The breakdown voltage test was performed 30 times, and the resulting value was divided by the film thickness (measured in (1) above) to convert it to V / μm. Of the 30 measured values ​​(calculated values), the five largest and five smallest were excluded, and the average of the remaining 20 values ​​was used as the film breakdown voltage at 135°C.

[0126] (10) The number of domains (domains / μm) of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in a 1 μm square in the layer A ２ ) Using a microtome, ultrathin sections having a cross section in the width direction-thickness direction (TD / ZD cross section) were taken from the A layer of the polyolefin film. ４The sample was stained with fluorine, and the cross section was observed using a transmission electron microscope (TEM) under the following conditions. Note that, at this time, the cyclic olefin resin was stained blacker than the polypropylene resin. Apparatus: Transmission electron microscope (TEM) HT7700 manufactured by Hitachi, Ltd. Acceleration voltage: 100 kV Observation magnification: 20,000x On the image collected in the observation, a 1 μm square was drawn with a pair of sides parallel to the thickness direction, and the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in the square was counted. The same measurement was performed 10 times in total by changing the position of the square in the image, and the average number of domains obtained was calculated, and the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in layer A (number / μm ２ ) In determining a square of 1 μm on each side in the cross section X so that a pair of sides were parallel to the thickness direction, the base of the square was set to the sea portion, and if a domain was located on the side opposite to the base, it was considered not to exist and was not counted in the number of domains. In addition, domains with constricted portions were also considered to be cyclic olefin-based resin domains dyed darker than the polypropylene-based resin part of the sea portion and were treated as connected domains.

[0127] (11) The number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in a 1 μm × 2 μm rectangle in the A layer (number / 2 μm ２ ) Observation was performed in the same manner as in (10), and a rectangle with a pair of sides of 1 μm in the thickness direction and 2 μm in the direction perpendicular to the thickness direction was defined on the collected image. ２ A rectangle was drawn around the four sides of the rectangle, and the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction of the rectangle was counted. The same measurement was carried out 10 times in total by changing the position of the rectangle in the image, and the average value of the obtained domain numbers was calculated to obtain the number of domains of the cyclic olefin resin (domains / 2 μm ２) In defining a rectangle in cross section X, with a pair of sides of 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 to the base, it was considered not to exist and was not counted in the number of domains. In addition, domains with constrictions were also treated as connected domains.

[0128] (12) Thermal Shrinkage (130S) in the Longitudinal Direction of the Film After Heat Treatment at 130°C for 10 Minutes A rectangular sample was cut out from the polyolefin film, measuring 30 mm in length and 10 mm in width, with the long side being the longitudinal direction. Five specimens were prepared. A marking line parallel to the width direction was made 5 mm from the center of each short side toward the center of the film, giving a test length of 20 mm (L0). Next, the test specimen was sandwiched between paper and heated in an oven maintained at 130°C for 10 minutes, then removed and cooled to room temperature. The length (L1) between the two marking lines was measured and calculated using the following formula: Thermal Shrinkage = {(L0 - L1) / L0} × 100 (%). The arithmetic average of the five specimens was taken as the thermal shrinkage (130S).

[0129] (13) Average Thickness Length (nm) of Cyclic Olefin Resin Domains in Layer A Under the same conditions as in (10), a cross section of Layer A of a polyolefin film was observed and an image was obtained. Next, a 1 μm square was drawn on the obtained image with a pair of sides parallel to the thickness direction, and the cyclic olefin resin domains passing through a pair of sides of the square in the thickness direction were identified. Then, a line passing through the intersection of the diagonals of the square and parallel to the thickness direction was drawn, and the thickness direction length of each identified domain on this line was measured. The thickness direction length of the domain was measured by drawing lines on a line passing through the intersection of the diagonals of the square and parallel to the thickness direction at the top and bottom of the cyclic olefin resin domains that were dyed darker than the polypropylene resin portion of the sea portion, and measuring the distance between them, for all cyclic olefin resin domains passing through a pair of sides parallel to the thickness direction of the square. Furthermore, the average thickness direction length of the domains obtained in this way was calculated. Furthermore, the position of the square was arbitrarily changed and similar measurements were performed a total of 10 times (at this time, the setting of the squares was set so that all 10 squares did not overlap), and an average value was calculated from the average values ​​of the thickness direction lengths of the domains in each measurement, and the obtained value was defined as the average value of the thickness direction length of the domains of the cyclic olefin resin (unit: nm).

[0130] (14) Evaluation of Film Capacitor Characteristics (Voltage Breakdown and Reliability at 135°C) Aluminum was deposited on one side of the film (if the wetting tension differed between the front and back sides, the side with the higher wetting tension was used) using a vacuum deposition machine manufactured by ULVAC, Inc., with a film resistance of 10 Ω / sq. The deposition pattern had a margin perpendicular to the longitudinal direction, i.e., a so-called T-shaped margin (a longitudinal pitch (period) of 17 mm and a fuse width of 0.5 mm, formed using masking oil). After slitting, a deposition reel with a film width of 50 mm (edge ​​margin width of 2 mm) was obtained. Next, this reel was used to wind the capacitor element on a device winding machine (KAW-4NHB) manufactured by Kaito Seisakusho, Inc., and after applying metallicon, the capacitor element was subjected to heat treatment at 128°C under reduced pressure for 12 hours. Lead wires were attached to complete the capacitor element. Using 10 of the capacitor elements thus obtained, a so-called step-up test was carried out in which a voltage of 150 VDC was applied to the capacitor elements at a high temperature of 135°C, and after 10 minutes at that voltage, the applied voltage was gradually increased in steps of 50 VDC / minute, and this was repeated.

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

[0132] <Reliability Evaluation> After increasing the voltage until the capacitance decreased to 12% or less of the initial value, one capacitor element out of the ten capacitor elements that had the highest withstand voltage was disassembled, and the state of breakdown was examined to evaluate reliability as follows. A means usable, B means usable depending on the conditions, and C means poor practical performance. A: No change in element shape, and penetration-like breakdown was observed in one to five film layers. Or, neither change in element shape nor penetration-like breakdown was observed. B: No change in element shape, and penetration-like breakdown was observed in six to ten film layers. C: A change in element shape was observed, or penetration-like breakdown was observed in more than 10 layers.

[0133] [Resins, etc.] The following resins, etc. were used in producing the polyolefin-based films in the examples and comparative examples.

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

[0135] <Polypropylene Raw Material> Polyolefin resin raw material (A1): 69.5 parts by mass of polypropylene resin 1, 30 parts by mass of Polyplastics' "TOPAS" (registered trademark) 6013F-04 as a cyclic olefin resin, and 0.5 parts by mass of an antioxidant were mixed and kneaded using a twin-screw extruder set at 260 ° C., and the strands were water-cooled and chipped to obtain polyolefin resin raw material (A1). Polyolefin resin raw material (A2): 69.5 parts by mass of polypropylene resin 2, 30 parts by mass of Polyplastics' "TOPAS" (registered trademark) 6013F-04 as a cyclic olefin resin, and 0.5 parts by mass of an antioxidant were mixed and kneaded using a twin-screw extruder set at 260 ° C., and the strands were water-cooled and chipped to obtain polyolefin resin raw material (A2). Polyolefin resin raw material (A3): 100 parts by mass of "TOPAS" (registered trademark) 6013F-04 manufactured by Polyplastics as a cyclic olefin resin and 0.3 parts by mass of an antioxidant were mixed together, kneaded and extruded in a twin-screw extruder set at 260°C, and the strands were water-cooled and then chipped to obtain polyolefin resin raw material (A3).

[0136] Example 1: 30 parts by weight of polyolefin resin raw material (A1), 69.6 parts by weight of polypropylene resin 1, and 0.4 parts by weight of antioxidant were mixed and fed into a single-screw melt extruder and melted at 260°C. After removing foreign matter with an 80 μm cutoff sintered filter, the molten polymer was extruded from a T-die. The molten sheet was then adhered to 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 stepwise to 145°C using a group of rolls, then passed through rolls maintained at 155°C and with different peripheral speeds, and stretched 5.1 times in the longitudinal direction. The film was then introduced into a tenter, and while both widthwise ends of the film were held 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. Further, as a heat treatment and relaxation treatment, the film was heat-treated at 162°C while being relaxed by 8% in the width direction, and then the film was led to the outside of the tenter and the clips were released. Then, the film surface (the side contacting the casting drum) was subjected to a 25 W·min / m ２ The results of the evaluation are shown in Table 1.

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

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

[0139] (Example 4) The polyolefin resin raw material (A2) was 53 parts by mass, the polypropylene resin 1 was 46.6 parts by mass, and the antioxidant was 0.4 parts by mass. The components were mixed and fed to a single-screw melt extruder, melted at a temperature of 260°C, and after removing foreign matter with a sintered filter with an 80 μm cutoff, the molten polymer was extruded from a T-die to obtain a polyolefin film in the same manner as in Example 1, except that the film-forming conditions in Table 1 were used. 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 stretching machine, and after preheating at 164°C while both ends of the film width were held with clips, it was simultaneously biaxially stretched at 4.1 times in the longitudinal direction and 10.8 times in the transverse direction. Further, heat treatment, relaxation treatment, and corona discharge treatment were carried out 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 changed to 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 carried out under the film-forming conditions shown in Table 1. The evaluation results are shown in Table 1.

[0143] (Example 8) A polyolefin-based film was obtained in the same manner as in Example 1, except that 6.6 parts by mass of polyolefin-based resin raw material (A1), 93.0 parts by mass of polypropylene resin 1, and 0.4 parts by mass of antioxidant were mixed and fed to a single-screw melt extruder under the film-forming conditions 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 "ZEONOR" (registered trademark) 1420R (a cyclic olefin resin having a glass transition temperature of 135°C) manufactured by Zeon Corporation was used as the COP instead of COC as the cyclic olefin resin of the polyolefin resin raw material (A1), and film formation was performed 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 "APEL" (registered trademark) 5014CL (04) (a cyclic olefin resin having a glass transition temperature of 135°C) manufactured by Mitsui Chemicals was used as the cyclic olefin resin of the polyolefin resin raw material (A1) and film formation was performed under the conditions shown in Table 1. The evaluation results are shown in Table 1.

[0146] (Comparative Examples 1 and 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 fed to a single-screw extruder set at 260°C. After melting at 260°C, foreign matter was removed using an 80 μm cut sintered filter, and the molten single-layer polymer was extruded from a T-die. This was placed on a casting drum maintained at 90°C, brought into close contact with an air knife, and cooled and solidified to obtain an unstretched polyolefin film. Thereafter, a polyolefin film was obtained in the same manner as in Example 1, except that the film-forming conditions shown in Table 2 were used. 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 stretching machine, and after preheating at 163°C while both ends of the film width were held with clips, it was simultaneously biaxially stretched 3.8 times in the longitudinal direction and 8 times in the width direction. Next, without heat treatment or relaxation treatment, it was introduced outside the simultaneous biaxial stretching machine, the clips on 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 in a single-screw melt extruder without being pre-mixed in a twin-screw extruder, and the film-forming conditions were set as shown in Table 2. The evaluation results are shown in Table 2.

[0149] Comparative Example 4: The raw material for Layer A was a polyolefin resin raw material (A3), and the resin for Layer B was polypropylene resin 4. The raw material for Layer A was fed into a single-screw melt extruder for Layer A, and the resin for Layer B was fed into a single-screw melt extruder for Layer B. Each was melted at 260°C, and foreign matter was removed using an 80 μm cutoff sintered filter. The extrusion rate was then adjusted using a feed block to achieve a three-layer B / A / B laminate with a lamination thickness ratio (lamination ratio) of 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. The molten sheet was brought into close contact with a casting drum maintained at 70°C using an air knife, and cooled and solidified to obtain an unstretched polyolefin film. A polyolefin film was then obtained in the same manner as in Example 1, except for the film-forming conditions shown in Table 2. The evaluation results are shown in Table 2.

[0150] Comparative Example 5 An unstretched polyolefin film was obtained in the same manner as in Example 1, having a single layer structure of only Layer A, without being subjected to biaxial stretching or heat setting. The evaluation results are shown in Table 2.

[0151]

[0152]

[0153] In Tables 1 and 2, the content of the cyclic olefin resin in the entire film was calculated assuming that the total resin component was 100% by mass, without taking into account the antioxidant.

[0154] The polyolefin film of the present invention can be widely used for industrial purposes such as capacitor applications, packaging applications, release applications, and tape applications, and since it has excellent voltage resistance characteristics and reliability in high-temperature environments, it can be suitably used for capacitor applications that are used under high temperatures and high voltages.

[0155] 1 Part of cross section X 2 Sea portion 3 Island portion (domain) 4 Square of 1 μm side defined in cross section X so that a pair of sides are parallel to the thickness direction 5 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 a 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 heating from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter, when the temperature of the peak with the largest absolute value of the heat flow among the melting peaks is defined as the melting peak temperature Tm (°C), the Tm exceeds 170°C and is 200°C or less.

2. A polyolefin film having a layer containing a cyclic olefin resin and a polypropylene resin (such a layer is conveniently referred to as "layer A"), when a cross-section obtained by cutting the layer A with a plane parallel to the main orientation axis direction and the thickness direction is defined as cross-section X, in a 1 μm square determined such that a pair of sides are parallel to the thickness direction within the cross-section X, there are 3 or more domains of the cyclic olefin resin passing through the pair of sides parallel to the thickness direction, having an internal haze of 4.0% or less, and in a DSC chart obtained by heating from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter, when the temperature of the peak with the largest absolute value of the heat flow among the melting peaks is defined as the melting peak temperature Tm (°C), the Tm exceeds 170°C and is 200°C or less.

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

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

5. The polyolefin film according to claim 1 or 2, wherein the widthwise shrinkage stress (135Tf) at 135°C obtained by thermomechanical analysis (TMA) is 5.0 MPa or less.

6. The polyolefin film according to claim 1 or 2, wherein the longitudinal thermal shrinkage rate (130S) of the film when heat-treated at 130°C for 10 minutes exceeds 2.0% and is 5.0% or less.

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

8. The polyolefin film is a film having a laminated structure of three or more layers. Among them, the A layer is included as a layer other than the outermost layer, and both of the two outermost layers mainly contain a polypropylene-based resin and contain more polypropylene-based resin than the A layer, and the content of the cyclic olefin-based resin is less than that of the A layer. The polyolefin-based film according to claim 1 or 2.

9. When a cross-section obtained by cutting the A layer in 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 such that a pair of sides are parallel to the thickness direction within the cross-section X, there are three or more domains of the cyclic olefin-based resin passing through the pair of sides parallel to the thickness direction. The polyolefin-based film according to claim 1.

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

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

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

13. A film capacitor using the metal film laminated film according to claim 12.

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

15. A power control unit having the film capacitor according to claim 13.

16. An electric vehicle having the power control unit according to claim 15.

17. An electric aircraft having the power control unit according to claim 15.