Biaxially oriented polypropylene film

Abstract

The present invention relates to a biaxially oriented polypropylene film that contains a resin A having an alicyclic structure in a side chain thereof. The present invention addresses the problem of providing a biaxially oriented polypropylene film that is excellent in processability, can be used as a dielectric for a film capacitor in a high temperature environment, and has an excellent service life when used as a film capacitor.

Description

Biaxially oriented polypropylene film

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

[0002] In recent years, the majority of electrical equipment has been converted to inverters, which has led to an even stronger demand for smaller, larger-capacity film capacitors. In response to these demands, particularly in the fields of automobiles (including electric vehicles and hybrid cars), electric aircraft, solar power generation, and wind power generation, there is a demand for films, which serve as the dielectric of film capacitors, to have improved voltage resistance and productivity, maintain processability in the manufacture of film capacitor elements, as well as thinner films and improved heat resistance.

[0003] To apply a film as a dielectric for film capacitors in the above fields, it is important that the film has excellent heat resistance (dimensional stability, etc.) at the ambient temperature of use and stable electrical performance (voltage resistance, etc.) in a temperature range 10°C to 20°C higher than the ambient temperature of use. Furthermore, considering future applications for power semiconductors using silicon carbide (SiC), it is said that the ambient temperature of use of film capacitors will become even higher, and it is estimated that the demand for heat resistance will also increase.

[0004] Currently, polypropylene film, which has relatively excellent heat resistance and voltage resistance among polyolefin films, is used as the dielectric of film capacitors. 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. However, due to the above circumstances, further improvements in heat resistance and voltage resistance are required for film capacitors, and films for film capacitors are also required to have improved breakdown voltage in high-temperature environments exceeding 110°C. In other words, it has been extremely difficult for conventional polypropylene films to stably maintain voltage resistance in such temperature environments.

[0005] In order to reduce the size of film capacitors and improve their heat resistance, various attempts have been made, including reducing the thickness of the film, using a film with a high dielectric constant, or using a film with a glass transition temperature that exceeds the operating temperature range of the film capacitor.

[0006] For example, a laminate has been proposed in which one layer is a cyclic olefin resin layer having a glass transition temperature exceeding 130° C. and the other layer is a polypropylene resin layer, and these layers are alternately laminated (for example, Patent Document 1). Such a laminate has a lamination structure in which two types of layers with different relative dielectric constants are alternately superimposed, and therefore can maintain a large capacitance while having excellent heat resistance and voltage resistance.

[0007] Also, films with improved processability have been proposed by co-extrusion and co-stretching when forming a laminate of a cyclic olefin resin and a polypropylene resin (e.g., Patent Documents 2 and 3).Furthermore, a film with improved thermal dimensional stability in a high-temperature environment has been proposed by blending a cyclic olefin resin and a polypropylene resin, forming the blend into a film, and biaxially stretching the film (e.g., Patent Document 4).

[0008] Japanese Patent Application Laid-Open No. 2015-012076 International Publication No. 2017 / 022706 Japanese Patent Application Laid-Open No. 2018-034510 Special Publication No. 2020-521867

[0009] Motonobu Kawai, "Film Capacitor Advances: From Automobiles to Energy," Nikkei Electronics, Nikkei BP, September 17, 2012, pp. 57-62

[0010] However, the film of Patent Document 1 is not a coextruded laminate, but a laminate in which a cyclic olefin resin layer is formed on a polypropylene film by a coating method. As a result, the cyclic olefin resin layer is prone to peeling, and the processability in high-temperature environments and the performance and reliability when used as a film capacitor are not sufficient. The film of Patent Document 2 also has a base layer of a laminate structure made of a single cyclic olefin resin. Therefore, it is difficult to increase the areal stretch ratio, and the voltage resistance in high-temperature environments is insufficient, making it difficult to achieve satisfactory performance and reliability when used as a film capacitor. The film of Patent Document 3 also has a base layer of a cyclic olefin resin and contains an elastomer to improve stretchability, thereby increasing the areal stretch ratio. However, the voltage resistance in high-temperature environments is unsatisfactory, making it difficult to achieve satisfactory performance and reliability when used as a film capacitor. The film of Patent Document 4 is a film simply made of a blend of a cyclic olefin resin and a polypropylene resin, making it difficult to increase the areal stretch ratio when stretched. As a result, the performance and reliability of these films when used as film capacitors were insufficient, including insufficient voltage resistance in high-temperature environments. Furthermore, while it is possible to stretch films at high areal stretch ratios by increasing the preheating and stretching temperatures during widthwise stretching, films stretched at high temperatures experience a significant decrease in voltage resistance from room temperature to high temperatures, resulting in unstable characteristics when used as film capacitors. Furthermore, these films also have issues such as being prone to breakage during production and processing, resulting in reduced yields, and a shortened lifespan when used long-term as a film capacitor.

[0011] Therefore, an object of the present invention is to provide a biaxially oriented polypropylene film that has excellent processability, can be used as a dielectric for a film capacitor in a high-temperature environment, and has an excellent life when used as a film capacitor.

[0012] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. The present invention is a biaxially oriented polypropylene film containing a resin A having an alicyclic structure in a side chain.

[0013] According to the present invention, it is possible to provide a biaxially oriented polypropylene film that has excellent processability, can be used as a dielectric of a film capacitor in a high-temperature environment, and has an excellent life when used as a film capacitor.

[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 are prone to breakage during processing, resulting in reduced yields, and why the life of a film capacitor is shortened when used for a long period of time as a dielectric of the film capacitor is as follows.

[0015] The films of Patent Documents 1 to 4 contain a cyclic olefin resin (hereinafter referred to as COP) having a cyclic olefin in the main chain in order to increase the withstand voltage at high temperatures. COP is generally brittle and has low impact resistance, so it is thought that these films break from the COP portion during processing, or that insulation breakdown progresses from the peeled portion due to impact, shortening the lifespan.

[0016] Furthermore, the films in the aforementioned patent documents have improved heat resistance by incorporating COP into polypropylene resin and then stretching it, but the dispersibility of the COP in the polypropylene resin and the ability of the COP domains to follow deformation during stretching may be insufficient. As a result, the stretchability of the unstretched film decreases, and the molecular chains of the polypropylene resin relax when the temperature rises instantaneously. This is thought to result in an increased equivalent series resistance and a shortened lifespan of the film capacitor when the resulting film is used as a dielectric in a film capacitor.

[0017] Based on the above considerations, the present inventors have conducted further research and have invented a biaxially oriented polypropylene film that solves the above problems. The biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film containing a resin A having an alicyclic structure in its side chain. The biaxially oriented polypropylene film of the present invention will be specifically described below. Note that hereinafter, the biaxially oriented polypropylene film may be simply referred to as a film. Furthermore, when the upper and lower limits of the preferred ranges are stated separately below, the combination thereof can be any.

[0018] In the present invention, biaxial orientation means that the molecules are oriented in two perpendicular directions within the film plane, which can be achieved by stretching an unstretched film in two perpendicular directions (for example, the longitudinal direction and the width direction). The longitudinal direction refers to the direction in which the film runs during the production process (corresponding to the winding direction in the case of a film roll), and the width direction refers to the direction within the film plane that is perpendicular to the longitudinal direction.

[0019] Furthermore, the biaxially oriented polypropylene film of the present invention is not a microporous film and therefore does not have a large number of pores. That is, the biaxially oriented polypropylene film of the present invention means a biaxially oriented polypropylene film other than a microporous film. Here, a microporous film is defined as a film having a pore structure penetrating both surfaces of the film and having an air permeability of 5,000 seconds / 100 ml or less, as measured at a temperature of 23°C and a relative humidity of 65% using a Gurley tester type B of JIS P 8117 (1998).

[0020] Biaxially oriented polypropylene film refers to a biaxially oriented sheet-like molded product whose main component is polypropylene resin, and the main component refers to a component that accounts for more than 50% by mass but not more than 100% by mass when all components constituting the film are taken as 100% by mass. Note that when a film contains multiple components equivalent to polypropylene resin, even if each component is less than 50% by mass, as long as the total of these components exceeds 50% by mass, the film is considered to have polypropylene resin as the main component.

[0021] The polypropylene resin is a resin that contains more than 50 mol % and 100 mol % or less of propylene units when all structural units constituting the resin are taken as 100 mol %, and does not fall under the category of "resin A having an alicyclic structure in a side chain" described below.

[0022] The biaxially oriented polypropylene film of the present invention contains a resin A having an alicyclic structure in a side chain (hereinafter, "resin A having an alicyclic structure in a side chain" may be referred to as "resin A"). Here, resin A refers to a resin containing 0.1 mol % to 100 mol % in total of structural units 1 to 4 represented by the following chemical formulas, when all structural units constituting the resin are taken as 100 mol %. The structural units contained in the molecular chain of resin A may be any one to four types. Furthermore, a structural unit refers to the smallest structural unit having two or more carbon atoms contained in the molecular chain of the resin. For example, in the case of polyethylene, structural unit 6 in which R1 and R2 are H is a structural unit. In the case of cyclohexylethylene-ethylene-butylene-cyclohexylethylene copolymer synthesized by hydrogenating styrene-butylene-styrene copolymer, structural units 1 in which R1 to R6 are H, structural unit 6 in which R1 to R2 are H, and structural unit 6 in which R1 is H and R2 is an ethyl group are structural units. In the case of polyethylene glycol, (C ２ H ４ O) is a structural unit.

[0023]

[0024] The other structural units constituting the resin A are arbitrary, but examples thereof include structural units 5 and 6 represented by the following chemical formulas.

[0025]

[0026] In structural units 1 to 6, R1 to R8 represent H or any substituent, and can be, for example, H, an alkyl group, a halogen group, a nitro group, a sulfone group, an amide group, a carbonyl group, or a carboxy group. R1 to R8 may all be different, or two or more may overlap. The wavy lines in structural units 1 to 6 indicate that the chemical structure beyond them is omitted.

[0027] However, R1 is preferably H or a methyl group from the viewpoint of increasing the degree of polymerization when producing Resin A. Furthermore, from the viewpoint of increasing dispersibility in polypropylene resin, R2 to R8 are preferably H, a linear alkyl group having 1 to 30 carbon atoms such as a methyl group or an ethyl group, an isopropyl group, an isobutyl group, a sec-butyl group, or the like.

[0028] In the biaxially oriented polypropylene film of the present invention, the heat resistance can be adjusted by adjusting the molecular structure of resin A, thereby adjusting the glass transition temperature of resin A. For example, the glass transition temperature of resin A can be increased by increasing the proportion of structural units 1 to 4 in resin A or decreasing the proportion of structural unit 6. The heat resistance of the biaxially oriented polypropylene film can also be adjusted by adjusting the content of resin A or by mixing multiple types of resin A. Specifically, the heat resistance of the biaxially oriented polypropylene film can be improved by increasing the content of resin A or by mixing a resin A with a high proportion of structural units 1 to 4 with a resin A with a high proportion of structural unit 6 and increasing the mixing ratio of the former.

[0029] On the other hand, from the viewpoint of the film formability of the biaxially oriented polypropylene film, particularly the ease of stretching, it is preferable to reduce the ratio of structural units 1 to 4 in resin A, reduce the content of resin A, or, when using multiple resins A, reduce the proportion of resins A with a high ratio of structural units 1 to 4. In other words, the heat resistance and film formability of a biaxially oriented polypropylene film are generally in a trade-off relationship, and from the viewpoint of achieving both, it is preferable to appropriately adjust the ratio of structural units 1 to 4 in resin A, the content of resin A, and, when using multiple resins A, the proportion of resins A with a high ratio of structural units 1 to 4.

[0030] The alicyclic structure contained in the side chains of structural units 1 to 4 not only increases the glass transition temperature and improves heat resistance, but also contributes to increasing affinity with polypropylene. Furthermore, if such an alicyclic structure is present in the main chain rather than the side chain, the flexibility of the molecular chain decreases, resulting in decreased stability and stretchability during molding. On the other hand, if an alicyclic structure is present in the side chain, the decrease in flexibility of the molecular chain is suppressed, making it possible to achieve both stability and stretchability during molding and a high glass transition temperature (heat resistance). In other words, in the biaxially oriented polypropylene film of the present invention, it is important to incorporate a resin (resin A) having an alicyclic structure in the side chain in order to achieve the effects of the invention.

[0031] Among the resins A, those containing the structural unit 1 are preferred because they can be synthesized by hydrogenating a styrene-based polymer, for which synthesis methods have been industrially established and high-quality raw materials are available. Note that a styrene-based polymer refers to a polymer polymerized using styrene as one of the monomers, and examples thereof include styrene-ethylene-butylene copolymer, styrene-ethylene copolymer, styrene-ethylene-propylene copolymer, styrene-butylene copolymer, styrene-ethylene-butylene-styrene copolymer, styrene-ethylene-styrene copolymer, styrene-butylene-styrene copolymer, styrene-propylene-styrene copolymer, and polystyrene.

[0032] More specifically, industrially applicable resins A suitable for use in the biaxially oriented polypropylene film of the present invention include hydrogenated polystyrene and hydrogenated styrene-α-olefin copolymers. In particular, from the viewpoint of suppressing interfacial delamination in polypropylene and increasing the storage modulus in the main orientation axis direction (described later) by enhancing dispersibility, it is preferable to use a copolymer having a residue of at least one of ethylene or α-olefin and a vinylcyclohexane residue as resin A, and it is more preferable to use a polymer synthesized by hydrogenating the unsaturated bonds derived from the styrene and α-olefin in a styrene-α-olefin copolymer. Furthermore, from the viewpoint of further enhancing heat resistance, it is preferable to use polyvinylcyclohexane obtained by hydrogenating polystyrene. Known examples of polyvinylcyclohexane include crystalline isotactic polyvinylcyclohexane obtained by hydrogenating isotactic polystyrene, crystalline syndiotactic polyvinylcyclohexane obtained by hydrogenating syndiotactic polystyrene, and amorphous atactic polyvinylcyclohexane obtained by hydrogenating atactic polystyrene. There have been reports of crystalline isotactic polyvinylcyclohexane being added in anticipation of its function as a nucleating agent for polypropylene (Japanese Patent No. 6592192, Japanese Patent No. 2075499, Macromolecules 2006, 39, 2832-2840).

[0033] In the present invention, amorphous atactic polyvinylcyclohexane is preferably used from the viewpoints of ensuring stability and stretchability during molding, increasing the film's withstand voltage by stretching without forming insulation defects, and extending its lifespan. As described in the above academic literature and publicly known literature, isotactic polyvinylcyclohexane and syndiotactic polyvinylcyclohexane have melting points higher than 300°C. Therefore, when a suitable content (described below) capable of enhancing the effects of the present invention is added, co-extrudability and moldability with polypropylene may be significantly impaired, making them undesirable resins from the viewpoints of economy and achieving the effects of the present invention. Furthermore, from the viewpoint of enhancing moldability, it is preferable that Resin A used in the present invention, when mixed with a specific polypropylene, has a crystallization temperature (Tmc) of 115°C or less during the cooling process as measured by differential scanning calorimetry, and thus has substantially no nucleating agent activity. Tmc can be measured in accordance with JIS K7121-1987, details of which will be described later. Examples of commercially available products that can be used industrially as Resin A include the "ViviOn" (registered trademark) series (1325, MDP-0011, etc.) from USI Corporation and "TEFABLOC" (registered trademark) from Mitsubishi Chemical Corporation. The "ViviOn" (registered trademark) series includes copolymers containing structural unit 1 in which R1 to R6 are all H, structural unit 6 in which R1 is H and R2 is an ethyl group, and homocopolymers of structural unit 1 in which R1 to R6 are all H, and as described above, any of these can be suitably used.

[0034] The biaxially oriented polypropylene film of the present invention is not particularly limited in terms of layer structure as long as it contains polypropylene resin as the main component and resin A, but from the viewpoint of achieving both stretchability and heat resistance, it preferably has at least one layer containing both polypropylene resin and resin A. Generally, polypropylene resin has better stretchability than resin A but inferior heat resistance. Therefore, by having a layer containing both polypropylene resin and resin A, a biaxially oriented polypropylene film with excellent stretchability and heat resistance can be obtained.

[0035] The polyolefin film of the present invention has a storage modulus E' in the main orientation axis direction at 145°C of 1.0 × 10 ８ Pa or more 1.0×10 １３ (Hereinafter, the storage modulus E' in the main orientation axis direction at 145°C may be simply referred to as "storage modulus E'".) The storage modulus E' can be measured by a dynamic viscoelastic method, and the details of the measurement method will be described later.

[0036] By setting the storage modulus E' to be equal to or greater than the lower limit of the above range, the biaxially oriented polypropylene film of the present invention can suppress an increase in equivalent series resistance when the temperature rises instantaneously. Therefore, when such a biaxially oriented polypropylene film is used as a dielectric of a film capacitor, the life of the film capacitor is improved. From the above viewpoint, the storage modulus E' of the biaxially oriented polypropylene film of the present invention is 1.2 × 10 ８ Pa or more, and more preferably 5.0 × 10 ８ Pa or more, and more preferably 5.5 × 10 ８ From the above viewpoint, the higher the storage modulus E' of the biaxially oriented polypropylene film of the present invention, the more preferable it is. １３ Pa or less, and more preferably 5.0 × 10 １０ Pa or less.

[0037] The storage modulus of the biaxially oriented polypropylene film of the present invention is 1.0 × 10 ８ Pa or more 1.0×10 １３Effective methods for adjusting the storage modulus E' to be less than or within the above-mentioned preferred range include, for example, biaxially stretching an unstretched polypropylene film containing resin A, or incorporating a resin A having a glass transition temperature of 140°C or higher in a suitable amount range described below. When multiple types of resin A are mixed and used so that the glass transition temperature is 140°C or higher, adjusting the storage modulus E' can also be facilitated by ensuring that the total content of the added resins A satisfies the suitable amount described below. The stretching conditions are not particularly limited, but it is preferable to perform biaxial stretching within a range of the glass transition temperature of resin A + 3°C to the glass transition temperature of resin A + 50°C, so that the areal stretching ratio is 35 times or more, preferably 40 times or more, more preferably 42 times or more, more preferably 50 times or more, and particularly preferably 55 times or more.

[0038] The main orientation axis direction in the biaxially oriented polypropylene film of the present invention will be described below. The main orientation axis direction refers to the direction in which the molecular chain orientation of the polypropylene resin is greatest within the plane of the film. When biaxial stretching is performed in the production of a biaxially oriented polypropylene film, stretching is usually performed in the longitudinal direction and the width direction, and generally, the direction with the greater stretching ratio is the main orientation axis direction. If the stretching directions (longitudinal direction and width direction) are specified but the stretching ratio is unknown, the maximum load until breakage can be measured for each direction in a tensile test at 23°C described below, and the direction with the greater measurement value can be determined as the main orientation axis direction.

[0039] As described above, if the stretching direction and stretch ratio are known, the main orientation axis direction can be easily determined. However, for films where these are unknown, the main orientation axis direction can be determined by the following method. Specifically, a rectangular sample measuring 50 mm in length and 10 mm in width is cut out to form sample <1>, and the direction of the long side of sample <1> is defined as 0°. Next, a rectangular sample <2> of the same size is taken so that the long side direction is rotated 15° clockwise from the 0° direction. Similarly, rectangular samples <3> to <12> are taken by rotating the long side direction of each rectangular sample by 15° each. Next, each rectangular sample is placed in a tensile tester with an initial chuck distance of 20 mm so that the long side direction is the tensile direction (measurement direction), and a tensile test is performed at a tensile speed of 300 mm / min in an atmosphere of 23°C. The maximum load until the sample breaks is read, and the value divided by the cross-sectional area of ​​the sample before the test (film thickness x width) is calculated as the stress at maximum strength. The long side direction of the sample with the largest value is defined as the main orientation axis of the biaxially oriented polypropylene film, and the direction perpendicular to this in the film plane is defined as the direction perpendicular to the main orientation axis of the biaxially oriented polypropylene film.

[0040] 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 can be measured using wide-angle X-rays as follows, and the direction of the main orientation axis can be 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, and the direction with the highest diffraction intensity in the obtained diffraction intensity distribution can be determined as the main orientation axis direction, and the direction perpendicular to this in the film plane can be determined as the direction perpendicular to the main orientation axis direction.

[0041] In the biaxially oriented polypropylene film of the present invention, the resin A is preferably amorphous. The use of an amorphous resin improves stretchability and makes it easier to prevent insulation defects from occurring during stretching, which can reduce the lifespan of the film capacitor. The amorphous nature of resin A can be confirmed by common measurement techniques such as powder X-ray diffraction. For example, in the case of polyvinylcyclohexane, crystalline polyvinylcyclohexane produces a peak in the 2θ = 5° to 20° range by powder X-ray diffraction, so the absence of a peak in this region can confirm that the resin A is amorphous.

[0042] The thickness of the biaxially oriented polypropylene film of the present invention can be adjusted appropriately depending on the application, but from the viewpoint of improving heat resistance by biaxial orientation, it is preferably 0.5 μm or more and 60 μm or less. From the same viewpoint, the upper limit of the thickness of the biaxially oriented polypropylene film is more preferably 40 μm, and even more preferably 30 μm.

[0043] Furthermore, when a biaxially oriented polypropylene film is used as a dielectric for a film capacitor, its thickness is preferably 10 μm or less, more preferably 6.0 μm or less, even more preferably 3.5 μm or less, and particularly preferably 3.0 μm or less, from the viewpoint of miniaturizing the film capacitor. The thickness of the biaxially oriented polypropylene film is preferably 1.0 μm or more, more preferably 1.5 μm or more, from the viewpoint of preventing film breakage during film formation. By making the thickness of the biaxially oriented polypropylene film 10 μm or less, the heat resistance improvement effect of resin A can be further enhanced, improving voltage resistance in high-temperature environments and also reducing the size of the film capacitor element. The thickness of the biaxially oriented polypropylene film can be measured using a known electronic micrometer, the details of which will be described later.

[0044] The thickness of the biaxially oriented polypropylene film can be adjusted by known methods. Specifically, the thickness of the biaxially oriented polypropylene film can be reduced by narrowing the lip gap of the die, reducing the amount of molten resin discharged from the extruder, increasing the rotation speed of the casting drum, increasing the stretch ratio, etc. These methods may be used in combination as appropriate.

[0045] The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage rate in the main orientation axis direction at 135°C of -10% or more and 5.0% or less. Adjusting the heat shrinkage rate in the main orientation axis direction at 135°C within the above range can improve dimensional stability when used as a dielectric in a film capacitor in a high-temperature environment. From the above perspective, the heat shrinkage rate is more preferably 2.5% or less, and even more preferably 1.2% or less. To ensure insulation from surrounding components, film capacitors are generally used in a form in which an exterior resin is filled around the components consisting of a film wound body and electrodes that function as a dielectric. Adjusting the heat shrinkage rate of the biaxially oriented polypropylene film of the present invention within the above range to improve the dimensional stability of the film capacitor can reduce the risk of the film capacitor peeling from the resin or the film capacitor itself deforming and breaking when used as described above.

[0046] The heat shrinkage rate in the main orientation axis direction at 135°C can be calculated by heating a biaxially oriented polypropylene film for 10 minutes in an oven maintained at 135°C and measuring the length in the main orientation axis direction before and after heating. The detailed measurement method will be described later.

[0047] Examples of a method for adjusting the heat shrinkage rate in the main orientation axis direction at 135°C to be −10% or more and 5.0% or less, or to fall within the above-mentioned preferred range, include a method in which the heat treatment temperature is set to be equal to or higher than the glass transition temperature of resin A and the relaxation treatment rate, which will be described later, is set to be 10% or more.

[0048] In the biaxially oriented polypropylene film of the present invention, the length in the thickness direction of the domain in the cross section in the main orientation axis direction-thickness direction is preferably 0.0010 μm or more and 1.0 μm or less. Herein, the main orientation axis direction-thickness direction cross section refers to a cross section obtained by cutting the biaxially oriented polypropylene film along a plane parallel to the main orientation axis direction and perpendicular to the film surface. Hereinafter, the "length in the thickness direction of the domain in the cross section in the main orientation axis direction-thickness direction" may also be referred to as the "length in the thickness direction of the domain."

[0049] By adjusting the thickness direction length of the domains within the above range, it is possible to suppress the occurrence of insulation defects in the domains, and when the biaxially oriented polypropylene film is used as a dielectric of a film capacitor, the life of the film capacitor can be extended. From the above viewpoint, the thickness direction length of the domains is more preferably 0.50 μm or less, even more preferably 0.20 μm or less, and particularly preferably 0.10 μm or less. From the above viewpoint, the shorter the thickness direction length of the domains, the better, but from the viewpoint of feasibility, it is preferably 0.0010 μm or more, more preferably 0.0050 μm or more.

[0050] The length of the domain in the thickness direction can be measured by cutting a biaxially oriented polypropylene film by a microtome method to obtain an ultrathin slice having a cross section in the main orientation axis direction-thickness direction, and observing and analyzing the ultrathin slice with a transmission electron microscope (TEM). The detailed measurement method will be described later.

[0051] Methods for adjusting the length of the domain in the thickness direction to 0.0010 μm or more and 1.0 μm or less, or within the above-mentioned preferred range, include using a resin A having a cyclic structure in the side chain with one of the preferred structures described above, a method of compounding the resin A having a cyclic structure in the side chain with polypropylene in advance by stretching at a high ratio (pre-mixing), and a method of lowering the extrusion temperature to increase the shear applied in the extruder. These methods can be combined as appropriate, but from the viewpoint of improving production stability, it is particularly preferable to use a resin A having a cyclic structure in the side chain with one of the preferred structures described above.

[0052] The biaxially oriented polypropylene film of the present invention preferably has an internal haze of 0.0% or more and 5.0% or less. By keeping the internal haze within this range, the biaxially oriented polypropylene film is less susceptible to dielectric breakdown, thereby extending the life of the film capacitor when used as a dielectric in a film capacitor. From the above perspective, the internal haze of the biaxially oriented polypropylene film is more preferably 2.0% or less. Theoretically, the lower limit of the internal haze of the biaxially oriented polypropylene film is 0.0%, but considering the enhanced life improvement effect of the resin A when used as a film capacitor, the lower limit is preferably 0.4%, more preferably 0.6%. The internal haze of the biaxially oriented polypropylene film can be measured using a known haze meter, and the measurement method will be described in detail below.

[0053] As a method for keeping the internal haze of a biaxially oriented polypropylene film between 0.0% and 5.0%, or within the above-mentioned preferred range, it is effective to set the glass transition temperature of the resin A used to 165°C or lower, preferably 160°C or lower, to ensure sufficient fluidity during stretching, and to perform stretching at a temperature higher than the glass transition temperature of resin A. The glass transition temperature of resin A can be increased, for example, by increasing the proportion of the aforementioned structural units 1 to 4 in the structural units of resin A, and can be decreased by increasing the proportion of the aforementioned structural unit 6. The internal haze of a biaxially oriented polypropylene film can also be reduced by reducing the amount of resin A.

[0054] In the biaxially oriented polypropylene film of the present invention, it is preferable that at least one resin A has a glass transition temperature of 120°C or higher and 160°C or lower. By adopting such an embodiment, it is possible to improve conformability to the polypropylene resin during molding processing, and it is easy to suppress a decrease in adhesion between resin A and the polypropylene resin, which leads to a decrease in impact strength. As a result, a film capacitor using such a biaxially oriented polypropylene film has improved reliability and a longer life because a decrease in equivalent series resistance when the temperature rises instantaneously is suppressed.

[0055] Furthermore, from the viewpoint of increasing the temperature at which the film capacitor can be used, the biaxially oriented polypropylene film more preferably contains resin A having a glass transition temperature of 127°C or higher, even more preferably contains resin A having a glass transition temperature of 137°C or higher, and particularly preferably contains resin A having a glass transition temperature of 143°C or higher.

[0056] Generally, when a cyclic olefin resin has a glass transition temperature of 143°C or higher, its stretchability significantly decreases when dispersed in polypropylene, making it difficult to achieve both productivity and heat resistance sufficient for use as a dielectric in a film capacitor in a high-temperature environment. By using resin A as a resin with excellent heat resistance, the biaxially oriented polypropylene film of the present invention can maintain stretchability even when the glass transition temperature is higher than 143°C, achieving both heat resistance sufficient for use as a dielectric in a film capacitor in a high-temperature environment and productivity. On the other hand, from the viewpoint of moldability, the glass transition temperature of resin A is preferably 160°C or lower, and even more preferably 150°C or lower.

[0057] In addition, containing two or more types of resin A is preferable from the viewpoint of achieving both film-forming ability and heat resistance, and containing both a resin A with a glass transition temperature of 140°C or higher and a resin A with a glass transition temperature lower than 140°C is more preferable because the former provides the effect of high heat resistance and the latter provides the effect of improved film-forming ability. Incidentally, containing two or more types of resin A means that the components corresponding to resin A are separated into two or more groups of components by known methods such as liquid chromatography or reprecipitation, and the molar fraction of each constituent unit is determined for each group when the total constituent units of the components corresponding to resin A are taken as 100 mol%. When the molar fractions of the constituent units are compared between the groups, there is at least one group in which the difference is 5 mol% or more. Furthermore, if it is difficult to measure the molar fraction, the glass transition temperature of the resin can be measured after separation into groups as described above. Even if the glass transition temperatures of the components corresponding to resin A differ by 5°C or more, the composition can also be considered to contain two or more types of resin A.

[0058] In the present invention, the glass transition temperature of a resin can be measured in accordance with JIS K7121-1987 as follows. Using a differential scanning calorimeter, 3 mg of resin is heated from 30°C to 260°C at a rate of 20°C / min in a nitrogen atmosphere, then held at 260°C for 5 minutes, and then cooled to 30°C at a rate of 20°C / min. After further holding at 20°C for 5 minutes, the resin is heated again from 30°C to 260°C at a rate of 20°C / min. From the DSC curve obtained during the reheating process, the glass transition temperature (Tg) is calculated using the following formula. The differential scanning calorimeter is not particularly limited as long as it is capable of performing measurements, and any known differential scanning calorimeter can be used; for example, an EXSTAR DSC6220 manufactured by Seiko Instruments, Inc. can be used. Glass transition temperature = (extrapolated glass transition onset temperature + extrapolated glass transition end temperature) / 2.

[0059] From the viewpoint of achieving both film formability and voltage resistance characteristics in a high-temperature environment, the biaxially oriented polypropylene film of the present invention preferably contains 0.2% by mass or more and 45% by mass or less of resin A, when the entire biaxially oriented polypropylene film is taken as 100% by mass. When multiple types of resin A are contained, the content of resin A is calculated by adding up all of the resins A.

[0060] In the biaxially oriented polypropylene film of the present invention, the content of resin A is 45% by mass or less, thereby improving stability and stretchability during molding. From the above viewpoints, the content of resin A is more preferably 30% by mass or less, and even more preferably 25% by mass or less. On the other hand, the content of resin A is 0.2% by mass or more, thereby improving heat resistance when used as a film capacitor. From the above viewpoints, the content of resin A in the biaxially oriented polypropylene film is more preferably 0.5% by mass or more, even more preferably 1.2% by mass or more, particularly preferably 5.0% by mass or more, very preferably 10% by mass or more, and extremely preferably 15% by mass or more.

[0061] In other words, by setting the content of resin A in the biaxially oriented polypropylene film to 0.2 mass% or more and 45 mass% or less, or even within the above-mentioned preferred range, the withstand voltage in high-temperature environments can be increased, making it easier to obtain a biaxially oriented polypropylene film that can be used as a dielectric for film capacitors with higher rated voltages.

[0062] Furthermore, from the viewpoint of reducing the areas of the film where the withstand voltage is partially low, minimizing the decrease in capacitance during use, and enabling the production of a small film capacitor, the content of resin A is preferably less than 10% by mass, and more preferably less than 3.0% by mass. Because there is a trade-off with the heat resistance mentioned above, in order to produce a small film capacitor while improving heat resistance, the content of resin A is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1.2% by mass or more; that is, 1.2% by mass or more and less than 3.0% by mass is most preferred. Furthermore, with the content of resin A in these preferred ranges, the storage modulus E' of the film in the main orientation axis direction at 145°C is 1.0 × 10 ８ Pa or more, and ８ As a method for controlling the storage modulus within the range while setting the content of resin A within the above-mentioned preferred range, a method using a highly stereoregular polypropylene resin with a mesopentad fraction of 0.973 or more, or a method of stretching the film so that the areal stretching ratio is preferably 55 times or more, more preferably 60 times or more, can be mentioned.

[0063] The biaxially oriented polypropylene 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. These additives may be used alone or in combination. Furthermore, when the biaxially oriented polypropylene film has a laminated structure, they may be contained in any layer.

[0064] When antioxidants are included among these additives, the type and amount thereof are 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).

[0065] 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 per 100 parts by mass of the total resin. Too little antioxidant may result in poor long-term heat resistance, while too much antioxidant may adversely affect the film capacitor element due to blocking at high temperatures caused by bleed-out of the antioxidants. From the above perspectives, the content of the antioxidant is more preferably 0.2 to 0.7 parts by mass, and even more preferably 0.3 to 0.5 parts by mass, per 100 parts by mass of the total resin. When the biaxially oriented polypropylene film has 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 viewpoints of suppressing defects such as fisheyes and improving quality and voltage resistance performance.

[0066] The biaxially oriented polypropylene film of the present invention may contain a resin other than the polypropylene resin and resin A, provided that the object of the present invention is not impaired. Specific examples of resins that can be contained in the biaxially oriented polypropylene film include vinyl polymer resins including various polyolefin resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, and polycarbonate resins, with particularly preferred examples being polymethylpentene and syndiotactic polystyrene.

[0067] The content of these resins is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, when the total resin components constituting the biaxially oriented polypropylene film is taken as 100% by mass. By keeping the content of resins other than polypropylene resin at 3% by mass or less, the influence of the domain interface can be suppressed, and a decrease in the breakdown voltage in a high-temperature environment can be reduced.

[0068] The biaxially oriented polypropylene film of the present invention can be preferably used as a dielectric for a film capacitor. The type of film capacitor is not limited here; specifically, from the viewpoint of electrode configuration, it can be either a laminated film capacitor of metal foil and film or a metal-vapor-deposited film capacitor. It can also be preferably used in oil-immersed film capacitors impregnated with insulating oil or dry capacitors that do not use insulating oil at all. However, due to the properties of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal-vapor-deposited film capacitor. From the viewpoint of shape, it can be either a wound type or a laminated type (the film capacitor of the present invention will be described later).

[0069] Since biaxially oriented polypropylene films usually have low surface energy and are difficult to stably apply metal vapor deposition to, 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.

[0070] The biaxially oriented polypropylene film of the present invention can be obtained by obtaining a polypropylene resin sheet using a resin composition containing a polypropylene resin as the main component and a resin A, and then biaxially stretching, heat treating, and relaxing the sheet. As the biaxial stretching method, any of the inflation simultaneous biaxial stretching method, tenter simultaneous biaxial stretching method, and tenter sequential biaxial stretching method may be used. Among these, tenter sequential biaxial stretching method and tenter simultaneous biaxial stretching method are preferred from the viewpoints of controlling the mechanical properties and thermal dimensional stability while increasing the film formation stability, crystalline / amorphous structure, and surface properties, particularly the stretch ratio of the present invention. Furthermore, tenter sequential biaxial stretching method is more preferred from the viewpoint of controlling the storage modulus at 145°C of the biaxially oriented polypropylene film of the present invention within the above-mentioned preferred range.

[0071] Next, a preferred method for producing the biaxially oriented polypropylene film of the present invention will be described. The biaxially oriented polypropylene film of the present invention can be produced by, in this order, a casting step in which a resin composition containing a polypropylene resin and resin A is melt-extruded onto a support to form a polypropylene resin sheet, and a stretching step in which the polypropylene resin sheet is stretched in the longitudinal and transverse directions. Incidentally, "having the casting step and stretching step in this order" means that the casting step and stretching step are present in this order, regardless of whether there are other steps upstream of the casting step, between the casting step and the stretching step, or downstream of the stretching step.

[0072] The production method includes a casting step in which a resin composition containing a polypropylene resin and a resin A is melt-extruded onto a support to form a polypropylene resin sheet. The resin composition containing a polypropylene resin and a resin A is not particularly limited as long as it contains a polypropylene resin as a main component and also contains a resin A, but it is preferable to use a compound resin composition in which the two are pre-kneaded in advance to improve the dispersibility of the resin A. The support is not particularly limited as long as it can be used to obtain a polypropylene resin sheet by cooling and solidifying the resin composition melt-extruded into a sheet form, and a cooling drum (casting drum) or the like can be used, for example.

[0073] In this production method, a stretching step of stretching the polypropylene resin sheet in the longitudinal and width directions is performed downstream of the casting step. "Stretching in the longitudinal and width directions" includes both a sequential biaxial stretching method in which stretching in the longitudinal direction is performed followed by stretching in the width direction, and a simultaneous biaxial stretching method in which stretching in the longitudinal and width directions is performed simultaneously. However, the sequential biaxial stretching method is preferred from the viewpoint of individually and preferably controlling the temperature conditions in the longitudinal stretching and the width stretching.

[0074] The method for producing the biaxially oriented polypropylene film of the present invention will be described in more detail below, although the biaxially oriented polypropylene film of the present invention is not limited to those obtained by the following method.

[0075] First, in producing the biaxially oriented polypropylene film of the present invention, it is preferable to compound resin A, polypropylene resin, and antioxidant in advance from the viewpoint of improving the dispersion state of resin A and polypropylene resin and increasing the breakdown voltage of the resulting biaxially oriented polypropylene film at high temperatures.

[0076] For compounding, a single-screw extruder, a twin-screw extruder, or the like can be used, but from the viewpoint of realizing a good dispersion state, it is particularly preferable to use a twin-screw extruder. The resin temperature during compounding is preferably within the following temperature range from the viewpoint of improving the dispersion state of the polymer having an alicyclic structure in the side chain and the polypropylene resin and further increasing the breakdown voltage of the obtained biaxially oriented polypropylene film at high temperatures. First, it is preferably 300°C or less, more preferably 280°C or less. On the other hand, it is preferably 200°C or more, more preferably 230°C or more.

[0077] From the viewpoint of the heat resistance of the resulting biaxially oriented polypropylene film, the content of resin A in the resin composition obtained by compounding is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 5% by mass or more, and particularly preferably 9% by mass or more, when the total compounding components are taken as 100% by mass. On the other hand, from the viewpoint of improving the dispersibility of resin A and improving stretchability, the content of resin A in the resin composition obtained by compounding is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0078] The amount of antioxidant is preferably 0.1 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 resin component in the resin composition obtained by compounding. The upper limit is 1.0 part by mass. Furthermore, by making the mesopentad fraction of the polypropylene resin 0.960 or more, the resulting biaxially oriented polypropylene film has a high melting point, which is suitable for use at high temperatures, and is therefore preferred.

[0079] Next, the resin composition obtained by compounding with the polypropylene resin is fed to a single-screw extruder after adjusting the amount of resin A to a desired level (preferably 0.2% by mass or more and 45% by mass or less, when the entire resin composition is taken as 100% by mass), and after passing through a filtration filter, is extruded into a sheet from a slit die. In this case, the extrusion temperature is preferably 200°C or more and 290°C or less. Thereafter, the molten sheet extruded from the slit die is solidified on a temperature-controlled casting drum to obtain a polypropylene resin sheet.

[0080] From the viewpoint of achieving both heat resistance and stretchability, the biaxially oriented polypropylene film of the present invention preferably has at least one layer containing both polypropylene resin and resin A. When the biaxially oriented polypropylene film of the present invention has a single-layer structure, it is preferable that the biaxially oriented polypropylene film consists only of a layer containing both polypropylene resin and resin A. When the biaxially oriented polypropylene film of the present invention has a laminate structure, it is preferable that the biaxially oriented polypropylene film has a two-type two-layer structure (layer A / layer B) or a two-type three-layer structure (layer B / layer A / layer B) from the viewpoint of suppressing film rupture when the areal stretch ratio is increased. In the above structure, it is preferable that at least layer A contains both polypropylene resin and resin A. In the above structure, the content of resin A in layer B is less than that in layer A, preferably 3% by mass or less, more preferably 1% by mass or less, when the mass of the entire layer B is taken as 100% by mass, and it is most preferable that layer B does not contain resin A. When layer B is laminated on both sides, the compositions of the layers B on both sides may be the same or different. Furthermore, when the biaxially oriented polypropylene film of the present invention is produced in a laminated structure, only one of the multiple layers may contain Resin A, or two or more layers may contain Resin A. The biaxially oriented polypropylene film of the present invention has a laminated structure, which increases the stretchability, and even if the content of Resin A is increased to the preferred range, it can be stretched at a high areal ratio within the preferred range, making it easy to significantly increase the lifespan of a film capacitor when used as such.

[0081] The method for forming the biaxially oriented polypropylene film of the present invention into a laminated structure is not particularly limited, but the following method can be used, for example. As the raw material for Layer A, a resin composition obtained by compounding polypropylene resin and Resin A is mixed and fed into a single-screw extruder, and as the raw material for Layer B, only the polypropylene resin is fed into another single-screw extruder. Thereafter, the molten resin is laminated into a two-layer structure (Layer A / Layer B) or a three-layer structure (Layer B / Layer A / Layer B) using a feedblock method by melt coextrusion, and this is extruded into a sheet from a slit-shaped die and solidified on a temperature-controlled casting drum to obtain an unstretched polypropylene film.

[0082] Regardless of whether the film has a single-layer structure or a laminated structure, from the viewpoint of cooling and solidifying the molten resin composition while appropriately controlling crystal growth, the temperature of the casting drum is preferably 10°C or higher and 110°C or lower, and more preferably 10°C or higher and 95°C or lower.

[0083] The method for adhering the molten sheet to the casting drum may be any of electrostatic application, adhesion methods utilizing the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc., but the air knife method is preferred because it provides good flatness and allows control of surface roughness. It is also preferred to appropriately adjust the position of the air knife so that air flows downstream of the film formation process to prevent vibration of the film. The air temperature of the air knife is preferably 5°C or higher and 130°C or lower.

[0084] Next, the unstretched polypropylene film is biaxially stretched to obtain biaxial orientation. The stretching for biaxial orientation may be performed by either a sequential biaxial stretching method in which stretching is performed sequentially in the longitudinal direction and the width direction, or a simultaneous biaxial stretching method in which stretching is performed simultaneously. The sequential biaxial stretching method will be described below. First, during stretching, the unstretched polypropylene film is brought into contact with a roll set to a predetermined longitudinal stretching temperature and stretched in the longitudinal direction at a predetermined magnification. The longitudinal stretching temperature is preferably 140°C or higher from the viewpoint of suppressing film rupture. In particular, when the glass transition temperature of resin A is 140°C or higher, it is preferably set to a temperature equal to or higher than the glass transition temperature of resin A from the viewpoint of increasing the conformability of resin A to the polypropylene resin and increasing the high-temperature withstand voltage of the biaxially oriented polypropylene film obtained. On the other hand, from the viewpoint of preventing melting of the polypropylene resin, the longitudinal stretching temperature is preferably 170°C or lower, more preferably 165°C or lower, and even more preferably 160°C or lower.

[0085] Furthermore, the stretching ratio in the longitudinal direction is preferably 3.5 times or more, more preferably 4.0 times or more, and even more preferably 5.0 times or more, from the viewpoint of increasing the areal stretching ratio and thereby increasing the breakdown voltage at high temperatures. On the other hand, from the viewpoint of suppressing film rupture, the stretching ratio in the longitudinal direction is preferably 15 times or less, more preferably 10 times or less. After stretching the unstretched polypropylene film in the longitudinal direction in this manner, it is cooled to room temperature to obtain a uniaxially oriented polypropylene film.

[0086] Next, while both widthwise ends of the obtained uniaxially oriented polypropylene film are held with clips, the film is introduced into a preheating chamber of a tenter, preheated to a temperature of ±3°C of the atmospheric temperature of the stretching chamber, and then introduced into a stretching chamber, where the uniaxially oriented polypropylene film is stretched in the width direction while both widthwise ends are held with clips. The atmospheric temperature of the stretching chamber (widthwise stretching temperature) at this time is preferably 150°C or higher, more preferably 155°C or higher, and even more preferably 160°C or higher, from the viewpoint of uniformly stretching Resin A, which has a high glass transition temperature, and improving the heat resistance of the biaxially oriented polypropylene film. On the other hand, from the above viewpoints, the widthwise stretching temperature is preferably 190°C or lower, more preferably 185°C or lower.

[0087] From the viewpoint of increasing the breakdown voltage of the resulting biaxially oriented polypropylene film, the stretching ratio in the width direction is preferably 5.0 times or more, more preferably 6.5 times or more, and even more preferably 8.3 times or more. On the other hand, from the viewpoint of stable film production, the stretching ratio in the width direction is preferably 20.0 times or less, more preferably 17.0 times or less, and even more preferably 15.0 times or less.

[0088] The areal stretching ratio is preferably 20.0 times or more from the viewpoint of forming a thin film and suppressing orientation relaxation of the polypropylene resin when the temperature rises instantaneously. In the present invention, the areal stretching ratio is the longitudinal stretching ratio multiplied by the widthwise stretching ratio. Note that in the present invention, the widthwise stretching ratio refers to the stretching ratio after stretching in the widthwise direction and before relaxation treatment. In order to increase the usable temperature, the areal stretching ratio is more preferably 31 times or more, even more preferably 39 times or more, and particularly preferably 45 times or more. There are no particular limitations on the upper limit of the areal stretching ratio, but from the viewpoint of feasibility, it is 90 times in the case of sequential biaxial stretching and 150 times in the case of simultaneous biaxial stretching.

[0089] In the production of the biaxially oriented polypropylene film of the present invention, it is preferable to include a heat treatment and relaxation treatment step after biaxial stretching. In this step, the biaxially oriented polypropylene film is subjected to a heat treatment at a tenter atmosphere temperature of 150°C to 190°C while providing 2 to 30% relaxation in the width direction while tensilely holding both widthwise ends with clips. This is preferable from the viewpoint of improving the reliability of film capacitors when the biaxially oriented polypropylene film is used as a dielectric of a film capacitor. From this viewpoint, the heat treatment temperature is preferably 150°C to 167°C. Furthermore, from the viewpoint of improving the reliability and lifespan of the biaxially oriented polypropylene film when used as a dielectric of a film capacitor, the relaxation treatment rate is preferably 5% or more, more preferably 7% or more, even more preferably 9% or more, particularly preferably 10% or more, and most preferably 15% or more. On the other hand, from the viewpoint of increasing the breakdown voltage of the biaxially oriented polypropylene film, the relaxation treatment rate is more preferably 25% or less, even more preferably 18% or less.

[0090] After the heat treatment and relaxation treatment, the biaxially oriented polypropylene film is guided to the outside of the tenter, and the clips on both widthwise ends are released in a room temperature atmosphere. The edges of the film are then slit in a winding process, and the biaxially oriented polypropylene film is wound into a roll. Before winding the biaxially oriented polypropylene film, it is preferable to perform a surface treatment such as corona discharge treatment on at least one side in air, nitrogen, carbon dioxide, or a mixture of these gases to improve the adhesion of the vapor-deposited metal.

[0091] Specific examples of production conditions that are important for obtaining the biaxially oriented polypropylene film of the present invention are as follows. While it is preferable to satisfy all of these production conditions, they do not necessarily need to be satisfied, and appropriate combinations may be used. For example, instead of "in sequential biaxial stretching, the preheating temperature before width direction stretching is the width direction stretching temperature +5°C or more and +15°C or less," simultaneous biaxial stretching may be employed. - Resin A is contained. - The polypropylene resin, which is the main component, has a mesopentad fraction of 0.960 or more. - Resin A and polypropylene resin are pre-kneaded. - The content of Resin A is 0.2% by mass or more and 45% by mass or less, when the total components of the biaxially oriented polypropylene film are taken as 100% by mass. - The areal stretch ratio of the biaxial stretching is 20.0 times or more. - The width direction stretch ratio is 5.0 times or more. - Heat treatment and relaxation treatment are performed after biaxial stretching. The heat treatment temperature after biaxial stretching is 150°C or higher and 190°C or lower.

[0092] Next, a metal film laminated film using the biaxially oriented polypropylene film of the present invention, a film capacitor using the same, and methods for producing them will be described.

[0093] The metal film laminated film of the present invention has a metal film on at least one side of the biaxially oriented polypropylene film of the present invention. This metal film laminated film can be obtained by providing a metal film on at least one side of the biaxially oriented polypropylene film of the present invention described above.

[0094] In the present invention, the method for forming 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 a biaxially oriented polypropylene film to form an internal electrode of a 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 biaxially oriented polypropylene film differs between the front and back sides, 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.

[0095] The metal film laminated film of the present invention can be annealed or heat-treated at a specific temperature as needed after forming the metal film. The annealing temperature is preferably in the range of T°C to (T+50)°C, where T [°C] is the temperature expected for use, and more preferably in the range of (TgA-50)°C to (TgA+20)°C, where TgA [°C] is the glass transition temperature of resin A used in the metal film laminated film of the present invention. Furthermore, for insulation or other purposes, a resin coating such as polyphenylene oxide can be applied to at least one side of the metal film laminated film.

[0096] The film capacitor of the present invention is made 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. For example, the film capacitor of the present invention can be obtained by laminating or winding the above-mentioned metal film laminated film of the present invention by various methods. An example of a preferred method for producing a wound film capacitor is as follows.

[0097] Aluminum is vapor-deposited under reduced pressure on one side of a biaxially oriented polypropylene 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 tape-like take-up reels with a margin on one side of the surface. Two tape-like take-up reels with a left margin and one with a right margin are stacked and wound together so that the vapor-deposited area extends beyond the margin in the width direction, producing a wound body.

[0098] 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.

[0099] A method for obtaining a film capacitor of the present invention using the metal layer laminated film of the present invention includes, for example, removing the core material from the wound body prepared as described above, pressing the wound body, spraying metallikon on both end faces to form external electrodes, and welding lead wires to the metallikon to form a wound film capacitor. Film capacitors have a wide range of applications, including power control units for electric vehicles (e.g., electric vehicles, hybrid vehicles, and fuel cell vehicles) and electric aircraft (e.g., drones), railroad vehicles, solar and wind power generation, and general home appliances. The film capacitor of the present invention can also be suitably used for these applications. The biaxially oriented polypropylene film of the present invention can also be used for various 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 a heating process in film processing.

[0100] 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, the power control unit itself can be made smaller, have improved heat resistance, and become more efficient, resulting in improved fuel efficiency for electric vehicles, electric aircraft, and the like that incorporate the power control unit of the present invention.

[0101] 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.

[0102] 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.

[0103] The present invention will be described in more detail below using examples, but the present invention is not limited to the embodiments described below.

[0104] [Measurement and evaluation methods] (1) Thickness of biaxially oriented polypropylene film The thickness of the biaxially oriented polypropylene film was measured at 10 random locations using a contact-type electronic micrometer (K-312A model) manufactured by Anritsu Corporation in an atmosphere of 23°C and 65% RH. The arithmetic mean value of the thicknesses at the 10 locations was taken as the thickness (unit: μm) of the biaxially oriented polypropylene film.

[0105] (2) Direction of the main orientation axis and direction perpendicular to the main orientation axis of biaxially oriented polypropylene film For each example and comparative example, the direction of the main orientation axis of the biaxially oriented polypropylene film was determined as follows according to the following method (tensile test). The direction perpendicular to the main orientation axis of the biaxially oriented polypropylene film was the direction perpendicular to the main orientation axis direction in the film plane. Examples 1 to 10, Comparative Examples 1 and 3: The width direction was the main orientation axis direction of the biaxially oriented polypropylene film.

[0106] <Tensile Test> First, a biaxially oriented polypropylene film was cut into a rectangular shape measuring 50 mm in length and 10 mm in width to form sample <1>. The direction of the long side of sample <1> was defined as 0°. Next, a rectangular sample <2> of the same size was taken so that the long side direction was rotated 15° clockwise from the 0° direction. Similarly, rectangular samples <3> to <12> were taken by rotating the long side direction of the rectangular sample by 15° each time. Next, each rectangular sample was placed in a tensile tester with an initial chuck distance of 20 mm so that the long side direction was the tensile direction (measurement direction), and a tensile test was performed at a tensile speed of 300 mm / min in an atmosphere of 23°C. The maximum load until the rectangular sample broke was read, and this value was divided by the cross-sectional area (film thickness x width) of the sample before the test to calculate the stress at maximum strength. The long side direction of the sample with the largest value was defined as the main orientation axis direction of the biaxially oriented polypropylene film.

[0107] (3) Melting Point and Glass Transition Temperature (Tg) of Resin The melting point and glass transition temperature (Tg) of the resin were measured in accordance with JIS K7121-1987. Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of film or polymer 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. In the DSC curve obtained during the reheating process, the peak temperature of the endothermic peak was taken as the melting point of the resin, and the glass transition temperature (Tg) was calculated using the following formula. Note that when multiple endothermic peaks were observed in a single measurement, the peak temperature of the endothermic peak with the highest peak temperature was taken as the peak temperature of that measurement. Glass transition temperature = (extrapolated glass transition onset temperature + extrapolated glass transition end temperature) / 2.

[0108] (4) The storage modulus E' in the direction of the main orientation axis at 145°C was measured using the following equipment and conditions. First, a rectangular biaxially oriented polypropylene film sample (width (short side) 10 mm x length (long side) 20 mm) cut with the main orientation axis direction as the long side direction was attached to the chuck of the equipment in an atmosphere of 23°C and placed in a furnace. The furnace was then cooled with liquid nitrogen, and the sample was heated from -100°C to 180°C. A viscoelasticity-temperature curve was drawn using a dynamic viscoelasticity method, and the storage modulus E' in the direction of the main orientation axis at 145°C was read. Note that three measurements were performed, and the average value of the storage modulus E' in the direction of the main orientation axis at 145°C was calculated. The obtained value was used as the storage modulus E' (Pa) in the direction of the main orientation axis of the biaxially oriented polypropylene film at 145°C. <Apparatus and conditions> Apparatus: EXSTAR DMS6100 (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 described in (1) above was used.

[0109] (5) Internal Haze A haze meter (HGM-2DP for C light source) manufactured by Suga Test Instruments Co., Ltd. was used. A biaxially oriented polypropylene film sample was cut into a size of 6.0 cm x 3.0 cm and inserted into a quartz cell with an optical path length of 1 cm filled with purified water. Then, light was incident perpendicularly to the sample surface to measure the haze. The same measurement was performed five times, and the average value obtained was taken as the internal haze of the biaxially oriented polypropylene film.

[0110] (6) Length of domain in thickness direction in cross section of film in main orientation axis direction-thickness direction Using a microtome, an ultrathin section of a biaxially oriented polypropylene film was prepared (the main orientation axis direction-thickness direction cross section refers to a direction parallel to the main orientation axis direction and perpendicular to the film surface). ４ After staining, the cross section was observed using a transmission electron microscope (TEM) under the following conditions, and an image was obtained. Since resin A stained darker than the polypropylene resin, the black-stained areas were used as domains for the following measurements. Apparatus: Hitachi, Ltd., Transmission Electron Microscope (TEM) HT7700, Acceleration Voltage: 100 kV, Observation Magnification: 20,000x. To measure the thickness direction length of the domains, five domains were selected from the top of the acquired image in ascending order of proximity to the center of the field of view without moving the field of view from the center of the layer containing both polypropylene resin and resin A, and then five domains were selected from the bottom. The thickness direction lengths of the selected domains were measured, and the average value was used as the thickness direction length of the resin A domain. If the selected domain had an end outside the field of view, the field of view was moved from one end to the other to obtain multiple images, and the length of the domain in the direction of the main orientation axis was determined from the combined image. If 10 domains could not be selected in one field of view, the field of view was moved to another field of view, and observation was continued until the measurement of 10 domains was completed.

[0111] (7) Heat Shrinkage in the Main Orientation Axis Direction at 135°C A biaxially oriented polypropylene film was cut into a rectangular shape with a length of 30 mm (measurement direction) and a width of 10 mm, with the main orientation axis direction being the long side. A marking line parallel to the width direction was made 5 mm from the center of each short side of the sample, and the length between the marking lines was determined as a test length of 20 mm (L0). Next, the sample was sandwiched between paper and heated in an oven maintained at 135°C for 10 minutes, then removed and cooled to room temperature. The length between the two marking lines (L1) was measured, and the heat shrinkage was calculated using the following formula. Similar measurements were performed five times, and the arithmetic average value was used as the heat shrinkage in the main orientation axis direction at 135°C. Heat shrinkage = {(L0 - L1) / L0} x 100 (%).

[0112] (8) Performance Evaluation of Biaxially Oriented Polypropylene Film <Lifespan Evaluation> The wet tension of each surface of a biaxially oriented polypropylene film was measured in accordance with JIS K 6768-1995. Aluminum was vapor-deposited onto the surface with higher wet tension using a vacuum vapor deposition machine manufactured by ULVAC, Inc., so that the film resistance was 10 Ω / sq. During vapor deposition, a vapor-deposited film A was formed with a vapor-deposited pattern having a so-called T-shaped margin (longitudinal pitch (period) of 17 mm, fuse width of 0.5 mm) in which a margin was provided in a direction perpendicular to the longitudinal direction using masking oil, and a vapor-deposited film B was formed without a vapor-deposited pattern having a T-shaped margin. The obtained vapor-deposited films A and B were each slit to obtain vapor-deposited reels A and B with a film width of 50 mm (edge ​​margin width of 2 mm). Next, the vapor deposition reels A and B were alternately stacked, and the vapor deposition film was wound using a device winding machine (KAW-4NHB) manufactured by Kaito Manufacturing Co., Ltd., so that the finished film capacitor element would have a capacitance of 10 μF. Metallicon processing was then performed. The biaxially oriented polypropylene film was then heat-treated for 12 hours under reduced pressure in an atmosphere at −5°C, the glass transition temperature of Resin A used in the film, and lead wires were attached to complete the film capacitor element. Ten film capacitor elements thus obtained were heated for 5 hours at a heat shock temperature T (described below). A voltage of (film thickness (μm) × 300 VDC / μm) was applied to the film capacitor element at 120°C for 500 hours, after which the capacitance of the 10 elements was measured, and the average value was taken as the element capacitance at the heat shock temperature T. Heat shock temperatures T were measured at three conditions: T = 125°C, 130°C, and 140°C. The film performance was evaluated according to the following criteria. S and A mean that the capacitor has a sufficient lifespan and can be used suitably even after being exposed to high temperatures, B and C mean that it is usable but has poor practical performance, and D means that it is difficult to use. S: The element capacitance after the test was 9.3 μF or more at all of T = 125°C, 130°C, and 140°C. A: The element capacitance after the test was 8.5 μF or more at all of T = 125°C, 130°C, and 140°C, and the element capacitance after the test at T = 140°C was less than 9.3 μF.B: When T = 140°C, the element capacitance after the test was less than 8.5 μF, but when T = 125°C and 130°C, the element capacitance after the test was 8.5 μF or more. C: When T = 130°C and 140°C, the element capacitance after the test was less than 8.5 μF, but when T = 125°C, the element capacitance after the test was 8.5 μF or more. D: When T = 125°C, 130°C, and 140°C, the element capacitance after the test was less than 8.5 μF.

[0113] <Evaluation of Stability and Stretchability During Molding> The thickness of biaxially oriented polypropylene films produced under the conditions described in the Examples and Comparative Examples was measured at 50 points at 5 cm intervals in the longitudinal direction using a contact-type electronic micrometer (K-312A) manufactured by Anritsu Corporation in an atmosphere of 23°C and 65% RH. The standard deviation of the thicknesses obtained at the 50 points was designated as σ and the average as Z, and the film performance was evaluated according to the following criteria. A indicates a biaxially oriented polypropylene film that exhibited high stability and stretchability during molding, resulting in reduced thickness unevenness, excellent voltage resistance and reduced yield during processing into film capacitors, and suitable for use as a film for film capacitors. B indicates a biaxially oriented polypropylene film with moderate thickness unevenness and poor practical performance, but usable for film capacitors. C indicates a film that is difficult to use as a film capacitor. A: σ / Z≦0.060. B: 0.060<σ / Z≦0.10. C: 0.10<σ / Z.

[0114] <Evaluation of Dimensional Stability> Biaxially oriented polypropylene films manufactured under the conditions described in the Examples and Comparative Examples were processed in the same manner as in the life evaluation described above to produce film capacitor elements. The obtained elements were placed in a thermostatic chamber and heated at 130°C for 10 hours, after which the shape of the elements was visually observed and compared with the shape of the elements before heating to evaluate dimensional stability according to the following criteria: A means that the element can be used appropriately in a 130°C environment, B means that the element can be used in a 130°C environment depending on the conditions, and C means that the element cannot be used in a 130°C environment. A: No noticeable deformation was observed in the film capacitor element. B: The film capacitor element was curved, expanded, or contracted, but the metallikon was not deformed. C: The metallikon of the film capacitor element was deformed.

[0115] <Evaluation of Film Low-Voltage Breakdown> The extent to which regions of low withstand voltage existed at 130°C in biaxially oriented polypropylene films manufactured under the conditions described in the Examples and Comparative Examples was determined by heating the film for 1 minute in an oven maintained at 130°C and then measuring the low-voltage breakdown voltage in the same 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. The average of the values ​​at the 4th to 6th points, in ascending order from the smallest to the smallest, of the 30 measured (calculated) points was calculated as the low-voltage breakdown value. Based on the evaluated low-voltage breakdown values, the lack of regions with low withstand voltage was evaluated as follows: S means that there is almost no region with low withstand voltage, making it suitable for use in a small size even with a film capacitor that has a high rated voltage at high temperatures; A, B, and C mean that it can be used in a small size for a film capacitor with a low rated voltage; and D means that the film capacitor becomes too large and is therefore not suitable for use. S: The low-voltage breakdown value was 280 V / μm or more. A: The low-voltage breakdown value was 240 V / μm or more but less than 280 V / μm. B: The low-voltage breakdown value was 200 V / μm or more but less than 240 V / μm. C: The low-voltage breakdown value was 150 V / μm or more but less than 200 V / μm. D: The low-voltage breakdown value was less than 150 V / μm.

[0116] (9) Mesopentad Fraction When measuring the mesopentad fraction of a polypropylene resin, 1 g of polypropylene resin was freeze-pulverized and extracted with 50 mL of n-heptane for 2 hours by the Soxhlet extraction method to remove impurities and additives in the polypropylene, and the n-heptane-insoluble matter was recovered and dried in vacuum at 130°C for 2 hours or more to obtain a sample. The sample was dissolved in a solvent and １３ The mesopentad fraction (mmmm) was determined using C-NMR under the following conditions. Measurement conditions: Apparatus: DRX-500 manufactured by Bruker Measurement nucleus: １３C nucleus (resonance frequency: 125.8 MHz) Measurement concentration: 10 wt % Solvent: benzene: deuterated orthodichlorobenzene = 1:3 mixed solution (volume ratio) Measurement temperature: 130°C Spin rotation speed: 12 Hz NMR sample tube: 5 mm tube Pulse width: 45° (4.5 μs) Pulse repetition time: 10 seconds Data points: 64 K Number of accumulations: 10,000 Measurement mode: complete decoupling Analysis conditions Fourier transform was performed with LB (line broadening factor) set to 1, and the mmmm peak was determined to be 21.86 ppm. Peak splitting was performed using WINFIT software (manufactured by Bruker). In this case, peak division was performed from the peak on the high magnetic field side as follows, and automatic software fitting was further performed to optimize the peak division. The sum of the peak fractions of mmmm and ss (spinning side band peak of mmmm) was then determined as the mesopentad fraction (mmmm): (1) mrrm (2) (3) rrrm (divided into two peaks) (4) rrrr (5) mrmm + rmrr (6) mmrr (7) mmmr (8) ss (spinning side band peak of mmmm) (9) mmmm (10) rmmr Similar measurements were performed five times on the same sample, and the average of the obtained mesopentad fractions was taken as the mesopentad fraction of the sample.

[0117] When measuring the mesopentad fraction of a film, the mesopentad fraction was measured in the same manner except that a film was used instead of the polypropylene resin.

[0118] (10) Melt Flow Rate (MFR) The MFR of the resin was measured in accordance with JIS K 7210-1 (2014), condition M (230°C, 2.16 kg).

[0119] [Resins, etc.] The following resins, etc. were used in the production of the biaxially oriented polypropylene films in each of the Examples and Comparative Examples.

[0120] (11) Crystallization temperature (Tmc) of polypropylene during cooling process The crystallization temperature (Tmc) of polypropylene during cooling process when Resin A was mixed with polypropylene was measured in accordance with JIS K7121-1987 as follows. The components were mixed so that 5 parts by mass of Resin A and 95 parts by mass of Polypropylene Resin 1 described below were mixed, kneaded and extruded using a twin-screw extruder set at 260 ° C., and the strands were water-cooled and chipped to prepare a Resin A mixed sample. Next, using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments, Inc.), 3 mg of the Resin A mixed sample was heated from 30 ° C. to 260 ° C. at a rate of 20 ° C. / min in a nitrogen atmosphere. Next, after holding at 260 ° C. for 5 minutes, the temperature was lowered to 30 ° C. at a rate of 20 ° C. / min, and the peak temperature of the exothermic peak obtained during the cooling process was measured. The same measurement was carried out three times, and the average of the obtained peak temperatures was taken as the crystallization temperature (Tmc) of the polypropylene in the cooling process when Resin A was mixed with polypropylene. When multiple exothermic peaks were observed in one measurement, the peak temperature of the exothermic peak with the highest peak temperature was taken as the peak temperature of that measurement.

[0121] <Polypropylene Resin> Polypropylene Resin 1: Homopolypropylene resin having a mesopentad fraction of 0.970, a melting point of 166°C, and a melt flow rate (MFR) of 3.3 g / 10 min (Borealis AG's "Borclean" (trade name) HC300BF). Polypropylene Resin 2: Polypropylene resin manufactured by Prime Polymer Co., Ltd. having a mesopentad fraction of 0.984, a melting point of 168°C, and a melt flow rate (MFR) of 2.5 g / 10 min. <Resin Components Other than Polypropylene Resin> Raw Material (C1): USI's "ViviOn" (registered trademark) product name 1325. Resin having an alicyclic structure in the side chain (corresponding to Resin A). Glass transition temperature is 128°C, and MFR is 13 g / 10 min. Raw material (C2): "ViviOn" (registered trademark) manufactured by USI, product name MDP-0011. A resin having an alicyclic structure in the side chain (corresponding to resin A). It has a glass transition temperature of 147°C and an MFR of 6.0 g / 10 min. Raw material (C3): "TOPAS" (registered trademark) 6013F-04 manufactured by Polyplastics (a resin (COC) obtained by copolymerizing ethylene and norbornene, not corresponding to resin A. It has a glass transition temperature of 138°C and is amorphous). Raw material (C4): "TOPAS" (registered trademark) 6017S-04 manufactured by Polyplastics (a resin (COC) obtained by copolymerizing ethylene and norbornene, not corresponding to resin A. It has a glass transition temperature of 178°C and is amorphous).

[0122] <Components other than resin component> Antioxidant: "IRGANOX" (registered trademark) 1010 manufactured by Ciba Specialty Chemicals.

[0123] <Pre-kneaded raw materials> Raw material (A1): The components were mixed so that the polypropylene resin 1 was 59.5 parts by mass, the raw material (C1) was 40 parts by mass, and the antioxidant was 0.5 parts by mass, and the mixture was kneaded and extruded in a twin-screw extruder set at 260°C, and the strand was water-cooled and then chipped. Raw material (A2): The components were mixed so that the polypropylene resin 1 was 59.5 parts by mass, the raw material (C2) was 40 parts by mass, and the antioxidant was 0.5 parts by mass, and the mixture was kneaded and extruded in a twin-screw extruder set at 260°C, and the strand was water-cooled and then chipped. Raw material (A3): The components were mixed so that the polypropylene resin 1 was 59.5 parts by mass, the raw material (C3) was 40 parts by mass, and the antioxidant was 0.5 parts by mass, and the mixture was kneaded and extruded in a twin-screw extruder set at 260°C, and the strand was water-cooled and then chipped. Raw material (A4): 59.5 parts by mass of polypropylene resin 1, 40 parts by mass of raw material (C4), and 0.5 parts by mass of 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.

[0124] Example 1 A resin composition containing 30.0 parts by mass of raw material (A1), 69.7 parts by mass of polypropylene resin 1, and 0.3 parts by mass of antioxidant was fed to a single-screw extruder. The resin composition was melted in the single-screw extruder at 250°C. After removing foreign matter using an 80 μm cutoff sintered filter adjusted to 250°C, the molten resin composition was extruded into a sheet from a T-die. The molten sheet was then adhered to a casting drum maintained at a surface temperature of 90°C using an air knife (air temperature: 23°C) and cooled and solidified to obtain an unstretched polypropylene film. The unstretched polypropylene film was heated to 145°C using a group of rolls and stretched 4.0 times in the longitudinal direction between rolls with different peripheral speeds to obtain a uniaxially oriented polypropylene film. Subsequently, the uniaxially oriented polypropylene film was guided into a tenter while holding both widthwise ends with multiple clips, preheated to 172°C, and then stretched 6.0 times in the widthwise direction at the same temperature. Further heat treatment and relaxation treatment were performed at 158°C while providing 12% relaxation in the widthwise direction, and the film was guided to the outside of the tenter and the clips were released. Furthermore, the film surface after heat treatment (the side contacting the casting drum) was heated at 25 W min / m in air.２ The results of the evaluation are shown in Table 1.

[0125] (Examples 2 to 13, Comparative Examples 1 to 5) Biaxially oriented polypropylene films were obtained in the same manner as in Example 1, except that the raw material formulation and film-forming conditions were as shown in Tables 1 and 2. The evaluation results are shown in Tables 1 and 2. The film thickness was adjusted by increasing or decreasing the discharge rate of the extruder. In Comparative Example 2, an attempt was made to obtain a biaxially oriented polypropylene film with a thickness of 5.5 μm, but film formation was not possible due to film breakage (since a biaxially oriented polypropylene film could not be obtained, the evaluation in Table 1 is shown as "-"). In Comparative Example 4, the film was cooled on a casting drum without being stretched longitudinally or transversely, and the side of the film that contacted the casting drum was stretched in air at 25 W·min / m ２ A corona discharge treatment was carried out at a treatment intensity of 1000 to obtain a polypropylene film.

[0126] (Example 14) A resin composition obtained by mixing the components so that the raw material (A1) was 30.0 parts by mass, the polypropylene resin 1 was 69.7 parts by mass, and the antioxidant was 0.3 parts by mass was supplied to a single-screw extruder for the A layer, and a resin composition obtained by mixing the components so that the polypropylene resin 2 was 99.7 parts by mass and the antioxidant was 0.3 parts by mass was supplied to a single-screw extruder for the B layer. In each single-screw extruder, the resin composition and polypropylene resin 1 were melted at 250 ° C., and foreign matter was removed using an 80 μm cut sintered filter adjusted to 230 ° C., and then the resin composition (for A layer) and polypropylene resin 1 (for B layer) were laminated using a feed block to form a three-layer structure of B layer / A layer / B layer with a lamination thickness ratio of 1 / 10 / 1. The resin composition was melted in the single-screw extruder at a temperature of 250°C, and after removing foreign matter with an 80 μm cut-off sintered filter adjusted to 250°C, the molten resin composition was extruded into a sheet from a T-die. As described above, a biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that two extruders were used to form a three-layer resin sheet, and the raw material formulation and film-forming conditions were as shown in Table 1. The evaluation results are shown in Table 2. As described above, the formulation shown in the raw material formulation in Table 1 is the raw material for the single-screw extruder for layer A, and the formulation shown in the surface layer formulation is the raw material for the single-screw extruder for layer B.

[0127]

[0128]

[0129] Note that none of the polypropylene films described in Examples 1 to 14 and Comparative Examples 1 and 3 to 5 had sufficient air permeability to achieve a 100 ml air permeation time of 5,000 seconds / 100 ml or less as measured at a temperature of 23°C and a relative humidity of 65% using a Type B Gurley tester in accordance with JIS P 8117 (1998). Therefore, they were determined not to be microporous films. Furthermore, the mesopentad fractions of the films were all the same as those of the polypropylene resin, which was the main component.

[0130] The biaxially oriented polypropylene film of the present invention can be widely used for industrial purposes such as film capacitor applications, packaging applications, release applications, tape applications, etc. In particular, since it has excellent voltage resistance characteristics and reliability in high-temperature environments, it can be suitably used for film capacitor applications used under high temperatures and high voltages.

Claims

1. A biaxially oriented polypropylene film containing resin A having an alicyclic structure in its side chain.

2. The biaxially oriented polypropylene film according to claim 1, having at least one layer containing both a polypropylene resin and said resin A.

3. The storage modulus E' in the main orientation axis direction at 145°C is 1.0 x 10 ８ Pa or more 1.0×10 １３ The biaxially oriented polypropylene film according to claim 1 or 2, having a modulus of elasticity of 100 Pa or less.

4. The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein resin A is an amorphous resin.

5. The biaxially oriented polypropylene film according to any one of claims 1 to 4, having an internal haze of 0.0% or more and 5.0% or less.

6. A biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein the glass transition temperature of at least one of said resins A is 120°C or higher and 160°C or lower.

7. A biaxially oriented polypropylene film according to any one of claims 1 to 6, containing 0.2% by mass or more and 45% by mass or less of said resin A when the entire biaxially oriented polypropylene film is taken as 100% by mass.

8. A biaxially oriented polypropylene film according to any one of claims 1 to 6, containing 0.5% by mass or more and 45% by mass or less of said resin A when the entire biaxially oriented polypropylene film is taken as 100% by mass.

9. A biaxially oriented polypropylene film according to any one of claims 1 to 6, containing 1.2 mass% or more and less than 3.0 mass% of said resin A when the entire biaxially oriented polypropylene film is taken as 100 mass%.

10. The biaxially oriented polypropylene film according to any one of claims 1 to 9, having a thickness of 0.5 μm or more and 60 μm or less.

11. A biaxially oriented polypropylene film according to any one of claims 1 to 10, having a heat shrinkage rate in the main orientation axis direction at 135°C of -10% or more and 5.0% or less.

12. A biaxially oriented polypropylene film according to any one of claims 1 to 11, wherein the length of the domain in the thickness direction in the cross section in the main orientation axis direction-thickness direction is 0.0010 μm or more and 1.0 μm or less.

13. A biaxially oriented polypropylene film according to any one of claims 1 to 12, comprising two or more types of resin A.

14. The biaxially oriented polypropylene film according to any one of claims 1 to 13, comprising a copolymer having residues of at least one of ethylene or an α-olefin and vinylcyclohexane residues.

15. The biaxially oriented polypropylene film according to any one of claims 1 to 14, wherein the mesopentad fraction of the film is 0.973 or more.

16. The biaxially oriented polypropylene film according to any one of claims 1 to 15, which is used as a dielectric for a film capacitor.

17. A metal film laminated film having a metal film on at least one side of the biaxially oriented polypropylene film according to any one of claims 1 to 16.

18. A film capacitor comprising the metal film laminated film according to claim 17.

19. A power control unit comprising the film capacitor according to claim 18.

20. An electric vehicle having the power control unit according to claim 19.

21. An electric aircraft having a power control unit according to claim 19.

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