Biaxially oriented polypropylene film

Abstract

The present invention relates to a biaxially oriented polypropylene film containing a resin A having an alicyclic structure in a side chain. The objective of the present invention is 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.

Description

[Technical field]

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

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

[0003] In order to use 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 operating temperature and stable electrical performance (voltage resistance, etc.) in a temperature range 10°C to 20°C higher than the operating temperature. In addition, when considering future applications for power semiconductors using silicon carbide (SiC), it is said that the operating temperature of film capacitors will become higher, and it is estimated that the requirements for heat resistance will 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, but as described in Non-Patent Document 1, the upper limit of the usage temperature of polypropylene film is said to be about 110°C. However, due to the above circumstances, further improvement in heat resistance and voltage resistance is required for film capacitors, and improvement in the dielectric breakdown voltage in high-temperature environments exceeding 110°C is also required for films for film capacitors. 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, such as making the film thinner, 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). Since such a laminate has a laminated structure in which two types of layers with different relative dielectric constants are alternately laminated, it is possible to maintain a large capacitance while having excellent heat resistance and voltage resistance.

[0007] Also, a film with improved processability has 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 also been proposed by blending a cyclic olefin resin with a polypropylene resin, forming the blend into a film, and biaxially stretching the film (e.g., Patent Document 4). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2015-012076 A [Patent Document 2] International Publication No. 2017 / 022706 [Patent Document 3] JP 2018-034510 A [Patent Document 4] Special Publication No. 2020-521867 [Non-patent literature]

[0009] [Non-Patent Document 1] Motonobu Kawai, "Film Capacitor Advances: From Cars to Energy," Nikkei Electronics, Nikkei BP, September 17, 2012, pp. 57-62 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the film of Patent Document 1 is not a laminate by coextrusion, but a laminate in which a cyclic olefin resin layer is formed on a polypropylene film by a coating method. Therefore, the cyclic olefin resin layer is easily peeled off, and the processability in a high-temperature environment and the performance and reliability when used as a film capacitor are not sufficient. The base layer of the laminated structure of the film of Patent Document 2 is also a single cyclic olefin resin. Therefore, it is difficult to increase the areal stretch ratio, and the voltage resistance in a high-temperature environment is insufficient, so the performance and reliability when used as a film capacitor are not sufficient. The base layer of the laminated structure of the film of Patent Document 3 is also a cyclic olefin resin, and an elastomer is contained to improve the stretchability to increase the areal stretch ratio, but the voltage resistance in a high-temperature environment is not satisfactory, and the performance and reliability when used as a film capacitor are not sufficient. The film of Patent Document 4 is a film simply made by blending a cyclic olefin resin and a polypropylene resin, so it is difficult to increase the areal stretch ratio when stretched. Therefore, the performance and reliability of the film capacitors were not sufficient, for example, the voltage resistance in high-temperature environments was insufficient. In addition, although it is possible to stretch at a high areal stretch ratio by increasing the preheating temperature and stretching temperature during width-direction stretching, there was also the issue that the film stretched at a high temperature had a large decrease in voltage resistance from room temperature to high temperatures, and the characteristics were not stable when used as a film capacitor. In addition, these films also had issues such as being prone to breakage during production and processing, resulting in low yields, and a short lifespan when used for long periods 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 of a film capacitor in a high-temperature environment, and has an excellent life when used as a film capacitor. [Means for solving the problem]

[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. Effect of the Invention

[0013] According to the present invention, it is possible to provide a biaxially oriented polypropylene film which 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems, and have concluded that the reasons why the films described in the above 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 are as follows.

[0015] In the films of Patent Documents 1 to 4, a cyclic olefin resin (hereinafter referred to as COP) having a cyclic olefin in the main chain is contained in order to increase the withstand voltage at high temperatures. Since COP is generally brittle and has low impact resistance, it was 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] In addition, the film in the above-mentioned patent document is improved in heat resistance by incorporating COP into polypropylene resin and then stretching it, but the dispersibility of COP in polypropylene resin and the ability of 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. It was thought that when the obtained film is used as a dielectric in a film capacitor, the equivalent series resistance increases and the life of the film capacitor is shortened.

[0017] Based on the above considerations, the present inventors have further studied and 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 the 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. In addition, when the upper and lower limits of the preferred ranges are described separately below, the combination of the upper and lower limits may be arbitrary.

[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 perpendicular to the longitudinal direction within the film plane.

[0019] In addition, the biaxially oriented polypropylene film of the present invention is not a microporous film, and therefore does not have many pores. That is, the biaxially oriented polypropylene film of the present invention means a biaxially oriented polypropylene film other than a microporous film. Here, the 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, measured at a temperature of 23°C and a relative humidity of 65% using a B-type Gurley tester according to 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 is contained in an amount of more than 50% by mass and not more than 100% by mass when all components constituting the film are taken as 100% by mass. Note that when the 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 main component is polypropylene resin.

[0021] A polypropylene resin is a resin that contains more than 50 mol% and not more than 100 mol% 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 the 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% or more and 100 mol% or less of structural units 1 to 4 represented by the following chemical formulas in total, when all structural units constituting the resin are taken as 100 mol%. The above structural units contained in the molecular chain of resin A may be any one of 1 to 4 types. Moreover, the structural unit refers to the smallest structural unit having 2 or more carbon atoms contained in the molecular chain of the resin. For example, in the case of polyethylene, the structural unit 6 in which R1 and R2 are H is a structural unit, and in the case of cyclohexylethylene-ethylene-butylene-cyclohexylethylene copolymer synthesized by hydrogenating a styrene-butylene-styrene copolymer, the structural units are those in which R1 to R6 are H in structural unit 1, those in which R1 to R2 are H in structural unit 6, and those in which R1 is H and R2 is an ethyl group in structural unit 6. In the case of polyethylene glycol, the structural units (C 2 H 4 O) is the building block.

[0023] [ka]

[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] [ka]

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

[0027] However, from the viewpoint of increasing the degree of polymerization when producing resin A, R1 is preferably H or a methyl group. Also, 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 glass transition temperature of resin A can be adjusted by adjusting the molecular structure of resin A, thereby adjusting the heat resistance. For example, the glass transition temperature of resin A can be increased by increasing the ratio of structural units 1 to 4 in resin A or decreasing the ratio 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 increased by increasing the content of resin A or by mixing resin A having a high ratio of structural units 1 to 4 with resin A having a high ratio 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 multiple resins A are used, reduce the proportion of resin A having a high ratio of structural units 1 to 4. That is, 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 multiple resins A are used, the proportion of resin A having a high ratio of structural units 1 to 4.

[0030] The alicyclic structure contained in the side chain of the structural units 1 to 4 not only increases the glass transition temperature and improves heat resistance, but also contributes to increasing the affinity with polypropylene. In addition, when such an alicyclic structure is present in the main chain rather than in the side chain, the flexibility of the molecular chain is reduced, and the stability and extensibility during molding are reduced. On the other hand, when the side chain has an alicyclic structure, the decrease in the flexibility of the molecular chain is suppressed, and it is possible to achieve both stability and extensibility during molding and a high glass transition temperature (heat resistance). That is, in the biaxially oriented polypropylene film of the present invention, it is important to include a resin (resin A) having an alicyclic structure in the side chain in order to obtain the effects of the invention.

[0031] Among them, resin A containing structural unit 1 is preferable because it can be synthesized by hydrogenating a styrene-based polymer, for which the synthesis method has 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, examples of resin A suitable for use in the biaxially oriented polypropylene film of the present invention that can be used industrially include hydrogenated polystyrene and hydrogenated styrene-α-olefin copolymers. In particular, from the viewpoint of suppressing interfacial peeling in polypropylene and increasing the storage modulus in the main orientation axis direction described below by increasing dispersibility, it is preferable to use a copolymer having at least one residue 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 styrene and α-olefin in a styrene-α-olefin copolymer. In addition, from the viewpoint of further increasing 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 the addition of crystalline isotactic polyvinylcyclohexane in the hope that it will act as a nucleating agent for polypropylene (Patent Publication No. 6592192, Patent Publication No. 2075499, Macromolecules 2006, 39, 2832-2840).

[0033] In the present invention, it is preferable to use amorphous atactic polyvinylcyclohexane from the viewpoints of ensuring stability and stretchability during molding, increasing the film voltage resistance by stretching so as not to form insulation defects, and increasing the lifespan. As described in the above academic literature and publicly known literature, isotactic polyvinylcyclohexane and syndiotactic polyvinylcyclohexane have melting points higher than 300°C, and when a suitable content (described later) capable of enhancing the effects of the present invention is attempted to be contained, co-extrusion and moldability with polypropylene may be significantly deteriorated, making them undesirable resins from the viewpoints of economy and obtaining the effects of the present invention. Also, from the viewpoint of enhancing moldability, it is preferable that the resin A used in the present invention has a crystallization temperature (Tmc) of 115°C or less during the temperature-lowering process measured by differential scanning calorimetry of polypropylene when mixed with a specific polypropylene, and has the characteristic of substantially not having a nucleating agent action. Tmc can be measured in accordance with JIS K7121-1987, the details of which will be described later. Examples of commercially available products that can be industrially used as resin A include the "ViviOn" (registered trademark) series (1325, MDP-0011, etc.) from USI Corporation and "TEFABLOCK" (registered trademark) from Mitsubishi Chemical Corporation. The "ViviOn" (registered trademark) series includes copolymers containing a structural unit 1 in which R1 to R6 are all H, a structural unit 6 in which R1 is H and R2 is an ethyl group, and a homopolymer of a 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 is preferable to have at least one layer containing both polypropylene resin and resin A. Generally, polypropylene resin has better stretchability than resin A, but has poorer 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] In order to improve the life of a film capacitor when used as a dielectric of the film capacitor, 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 More preferably, the pressure is 5.0×10 Pa or more. 8 More preferably, the pressure is 5.5×10 Pa or more. 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 13As a method for adjusting the storage modulus E' to 30 Pa or less or to the above-mentioned preferred range, for example, biaxial stretching of an unstretched polypropylene film containing resin A, or inclusion of a resin A having a glass transition temperature of 140°C or more in a suitable amount range described later, is effective. When a plurality of types of resin A are mixed and used so that the glass transition temperature is 140°C or more, the storage modulus E' can be easily adjusted by making the total content of the added resin A satisfy the suitable amount described later. The stretching conditions are not particularly limited, but it is preferable to perform biaxial stretching in the 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 in the film plane. 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 of the larger stretching ratio is the main orientation axis direction. When the stretching directions (longitudinal direction and width direction) are specified but the ratio is unknown, the maximum load until breakage is measured for each direction in a tensile test at 23°C described later, and the direction with the larger measured value can be determined as the main orientation axis direction.

[0039] As mentioned above, if the stretching direction and stretching ratio are known, the main orientation axis direction can be easily identified, but if these are unknown, the main orientation axis direction can be identified by the following method. Specifically, a sample is cut into a rectangle of 50 mm length x 10 mm width. <1> Then, the sample <1> The direction of the long side of is defined as 0°. Next, a rectangular sample of the same size is created so that the long side direction is rotated 15° to the right from the 0° direction. <2> The rectangular sample is then rotated 15° in the same manner to obtain a rectangular sample. <3> ~ <12> Next, each rectangular sample is set 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 divided by the cross-sectional area of ​​the sample before the test (film thickness x width) to calculate the stress at the maximum point strength. The long side direction of the sample where this value is maximum is defined as the main orientation axis direction 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 width of the sample is less than 50 mm and the above tensile test cannot be carried out, the crystal orientation of the α crystal (110) plane can be measured using wide-angle X-rays as follows, and the main orientation axis direction can be determined based on the following criteria: That is, X-rays (CuKα rays) are irradiated perpendicularly 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 is determined as the main orientation axis direction, and the direction perpendicular to this in the film plane is 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. By using an amorphous resin, it is possible to increase the stretchability and easily suppress the occurrence of insulation defects during stretching, which leads to a decrease in the life of the film capacitor. The fact that the resin A is amorphous can be confirmed by a general measurement method such as powder X-ray diffraction. For example, in the case of polyvinylcyclohexane, crystalline polyvinylcyclohexane produces a peak in the range of 2θ=5° to 20° by powder X-ray diffraction, so that 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 appropriately adjusted 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] In addition, when the biaxially oriented polypropylene film is used as a dielectric for a film capacitor, the 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 suppressing film breakage during film formation. By making the thickness of the biaxially oriented polypropylene film 10 μm or less, the effect of improving heat resistance by resin A can be made greater, the voltage resistance in a high-temperature environment can be improved, and the size of the film capacitor element can be reduced. The thickness of the biaxially oriented polypropylene film can be measured with 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 a known method. 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. By adjusting the heat shrinkage rate in the main orientation axis direction at 135°C to the above range, the dimensional stability can be improved when used as a dielectric of a film capacitor in a high temperature environment. From the above viewpoint, the heat shrinkage rate is more preferably 2.5% or less, and even more preferably 1.2% or less. In order to ensure insulation from surrounding parts, a film capacitor is generally used in a form in which an exterior resin is filled around the parts consisting of a film roll and electrodes that function as a dielectric. By adjusting the heat shrinkage rate of the biaxially oriented polypropylene film of the present invention to the above range to increase the dimensional stability of the film capacitor, the risk of the film capacitor peeling off from the resin or the film capacitor itself being deformed and broken when used as described above can be reduced.

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

[0047] Examples of a method for adjusting the thermal shrinkage rate in the main orientation axis direction at 135°C to be −10% or more and 5.0% or less or 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 described below 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 cross section in the main orientation axis direction-thickness direction refers to a cross section of the biaxially oriented polypropylene film cut 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 be referred to as the "length in the thickness direction of the domain".

[0049] By adjusting the thickness direction length of the domain within the above range, it is possible to suppress the domain from becoming an insulation defect, and when the biaxially oriented polypropylene film is used as a dielectric of a film capacitor, the life of the film capacitor can be increased. From the above viewpoint, the thickness direction length of the domain is more preferably 0.50 μm or less, further 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 domain, 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 the 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] Examples of methods for making the length of the domain in the thickness direction 0.0010 μm or more and 1.0 μm or less or within the above-mentioned preferred range include a method of using the resin A having a cyclic structure in the side chain with the above-mentioned preferred structure, a method of compounding the resin A having a cyclic structure in the side chain with polypropylene in advance (pre-mixing) by stretching at a high ratio, and a method of lowering the extrusion temperature to increase the shear applied in the extruder. These methods can be combined as appropriate, but it is particularly preferable to use the resin A having a cyclic structure in the side chain with the above-mentioned preferred structure from the viewpoint of increasing production stability.

[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 likely to undergo dielectric breakdown, and when used as a dielectric of a film capacitor, the life of the film capacitor can be increased. From the above perspective, the internal haze of the biaxially oriented polypropylene film is more preferably 2.0% or less. The lower limit of the internal haze of the biaxially oriented polypropylene film is theoretically 0.0%, but in consideration of the viewpoint of enhancing the life improvement effect when made into a film capacitor brought about by the improvement in heat resistance by resin A, it is preferably 0.4%, more preferably 0.6%. The internal haze of the biaxially oriented polypropylene film can be measured by a known haze meter, and the details of the measurement method will be described later.

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

[0054] In the biaxially oriented polypropylene film of the present invention, the glass transition temperature of at least one resin A is preferably 120° C. or more and 160° C. or less. By adopting such an embodiment, it is possible to improve the conformity to the polypropylene resin during molding processing, and it becomes easy to suppress the decrease in adhesion between the 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 the decrease in equivalent series resistance when the temperature rises instantaneously is suppressed.

[0055] In addition, 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] In general, when the glass transition temperature of a cyclic olefin resin is 143°C or higher, the stretchability is significantly reduced when dispersed in polypropylene, making it difficult to achieve both productivity and heat resistance sufficient to be used as a dielectric of 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, and can achieve both heat resistance sufficient to be used as a dielectric of 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 more preferably 160°C or lower, and even more preferably 150°C or lower.

[0057] In addition, it is preferable to contain two or more types of resin A from the viewpoint of achieving both film-forming properties and heat resistance, and it is more preferable to contain both resin A with a glass transition temperature of 140 ° C or more and resin A with a glass transition temperature lower than 140 ° C, because the former has the effect of increasing heat resistance and the latter has the effect of improving film-forming properties. Incidentally, the inclusion of 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 a known method such as liquid chromatography or reprecipitation, and the molar fraction of each constituent unit is calculated for each group when the total constituent units of the components corresponding to resin A are taken as 100 mol%, and the molar fractions of the constituent units are compared between the groups, and there is at least one group that differs by 5 mol% or more. In addition, if it is difficult to measure the molar fraction, the glass transition temperature of the resin is measured after separation into groups as described above, and it can also be considered that two or more types of resin A are contained when the glass transition temperatures of the components corresponding to resin A differ by 5 ° C or more.

[0058] In the present invention, the glass transition temperature of the resin can be measured according to JIS K7121-1987 as follows. Using a differential scanning calorimeter, 3 mg of the resin is heated from 30°C to 260°C at 20°C / min in a nitrogen atmosphere, then held at 260°C for 5 minutes, and cooled to 30°C at 20°C / min. After being held at 20°C for 5 minutes, the temperature is raised again from 30°C to 260°C at 20°C / min. From the DSC curve obtained during the reheating process, the glass transition temperature (Tg) is calculated according to the following formula. The differential scanning calorimeter is not particularly limited as long as it is capable of measurement, and any known one can be used, for example, EXSTAR DSC6220 manufactured by Seiko Instruments. Glass transition temperature=(extrapolated glass transition onset temperature+extrapolated glass transition finish 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 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, so that the stability and extensibility during molding can be improved. From the above viewpoint, 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, so that the heat resistance when used as a film capacitor can be improved. From the above viewpoint, 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 be 0.2 mass% or more and 45 mass% or less, or even within the above-mentioned preferred range, the voltage resistance in high-temperature environments can be increased, making it easy to obtain a biaxially oriented polypropylene film that can be used as a dielectric for film capacitors with higher rated voltages.

[0062] From the viewpoint of reducing the areas where the withstand voltage of the film is partially low and minimizing the capacity loss during use, and thus 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. Since there is a trade-off with the heat resistance described 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, it is most preferable that it is 1.2% by mass or more and less than 3.0% by mass. Furthermore, with the content of resin A being within these preferred ranges, the storage modulus E' of the film in the main orientation axis direction at 145°C is set to 1.0×10 8 Pa or more, and 5.0×10 8 It is more preferable that the storage modulus is set to 5 Pa or more. As a method for controlling the storage modulus within the above-mentioned range while setting the content of resin A within the above-mentioned preferable range, there may be mentioned a method for using a highly stereoregular polypropylene resin having a mesopentad fraction of 0.973 or more, or a method for stretching the film so that the areal stretch ratio is preferably 55 times or more, more preferably 60 times or more.

[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, within the scope of the present invention. These additives may be used alone or in combination. In addition, 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 of antioxidants are important from the viewpoint of long-term heat resistance. In other words, such antioxidants are sterically hindered phenols, and at least one of them is preferably a high molecular weight type with a molecular weight of 500 or more. Specific examples include various types, 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), etc.

[0065] The total content of the high molecular weight antioxidants having a molecular weight of 500 or more is preferably in the range of 0.1 to 1.0 parts by mass relative to 100 parts by mass of the total resin. If the amount of antioxidant is too small, the long-term heat resistance may be poor, and if the amount of antioxidant is too large, blocking at high temperatures due to bleed-out of the antioxidants may adversely affect the film capacitor element. From the above viewpoint, 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, relative to 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 the amount of the high molecular weight antioxidants having a molecular weight of 500 or more in each layer is 0.3 to 0.5 parts by mass from the viewpoint of suppressing defects such as fish eyes 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, and particularly preferred examples include 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 to 3% by mass or less, the effect of the domain interface can be suppressed, and the 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, and specifically, from the viewpoint of the electrode configuration, it may be either a laminated film capacitor of a metal foil and a film, or a metal-deposited film capacitor, and it is also preferably used for an oil-immersed type film capacitor impregnated with insulating oil, or a dry type capacitor that does not use insulating oil at all. However, due to the characteristics of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal-deposited film capacitor. From the viewpoint of the shape, it may be 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 it is difficult to stably apply metal vapor deposition to them, it is preferable to perform a surface treatment before vapor deposition in order to improve adhesion to the metal film. Specific examples of the surface treatment 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 a main component and a resin A, and biaxially stretching, heat treating and relaxing the sheet. As the method of biaxial stretching, any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method and the tenter sequential biaxial stretching method may be used. Among them, the tenter sequential biaxial stretching method and the tenter simultaneous biaxial stretching method are preferably used in terms of controlling the mechanical properties and thermal dimensional stability while increasing the film forming stability, crystalline / amorphous structure, surface properties, and particularly the stretch ratio of the present invention. Furthermore, it is more preferable to use the tenter sequential biaxial stretching method from the viewpoint of bringing the storage modulus at 145°C of the biaxially oriented polypropylene film of the present invention into 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 through 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, in that order. Incidentally, having a casting step and a stretching step in this order means that the casting step and the 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 manufacturing method includes 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. The resin composition containing a polypropylene resin and resin A is not particularly limited as long as it contains polypropylene resin as a main component and resin A, but it is preferable to use a compound resin composition in which the two are pre-kneaded in advance to increase the dispersibility of resin A. The support is not particularly limited as long as it can cool and solidify the resin composition melt-extruded into a sheet to obtain a polypropylene resin sheet, and for example, a cooling drum (casting drum) or the like can be used.

[0073] In this production method, downstream of the casting step, there is a stretching step in which the polypropylene resin sheet is stretched in the longitudinal direction and the width direction. The term "stretching in the longitudinal direction and the width direction" 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 direction and the width direction 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. However, the biaxially oriented polypropylene film of the present invention is not limited to the one obtained by the method described below.

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

[0076] A single screw extruder, a twin screw extruder, etc. can be used for compounding, 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 dielectric breakdown voltage at high temperatures of the obtained biaxially oriented polypropylene film. 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 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 the 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 the 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 set to 1.0 part by mass. In addition, by making the mesopentad fraction of the polypropylene resin 0.960 or more, the obtained biaxially oriented polypropylene film has a high melting point and is suitable for use at high temperatures, which is preferable.

[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-shaped die. At this time, the extrusion temperature is preferably 200° C. or more and 290° C. or less. The molten sheet-like material extruded from the slit-shaped die is then 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 is composed 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, from the viewpoint of suppressing film breakage when the areal stretch ratio is increased, a two-type two-layer structure of layer A / layer B, a two-type three-layer structure of layer B / layer A / layer B, etc. are preferable. 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 of layer A, preferably 3% by mass or less, more preferably 1% by mass or less, when the mass of the entire layer B is 100% by mass, and it is most preferable that layer B does not contain resin A. In addition, when layer B is laminated on both sides, the composition of layer B on both sides may be the same or different from each other. In addition, 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 area ratio within the preferred range, making it easy to significantly increase the life of a film capacitor.

[0081] The method for forming the biaxially oriented polypropylene film of the present invention into a laminated structure is not particularly limited, but for example, the following method can be adopted. As the raw material for the A layer, a resin composition obtained by compounding polypropylene resin and resin A is mixed and fed to a single screw extruder, and as the raw material for the B layer, only the polypropylene resin is fed to another single screw extruder. Thereafter, the molten resin is laminated into a two-layer structure of A layer / B layer or a three-layer structure of B layer / A layer / B layer by a feed block method using 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 of adhering the molten sheet to the casting drum may be any of the following: electrostatic application method, adhesion method using 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 in order 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 be biaxially oriented. For the stretching to achieve biaxial orientation, either a sequential biaxial stretching method in which the film is stretched sequentially in the longitudinal direction and the width direction, or a simultaneous biaxial stretching method in which the film is stretched simultaneously, may be used. Hereinafter, the sequential biaxial stretching method will be described. 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 breakage, and in particular, when the glass transition temperature of resin A is 140° C. or higher, it is preferable to set the temperature to a temperature equal to or higher than the glass transition temperature of resin A from the viewpoint of increasing the compatibility of resin A with the polypropylene resin to increase the withstand voltage at high temperatures of the biaxially oriented polypropylene film obtained by increasing the compatibility of resin A with the polypropylene resin. 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] In addition, 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 increasing the dielectric 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, the obtained uniaxially oriented polypropylene film is introduced into a preheating chamber of a tenter while both ends in the width direction are held by clips, and after preheating at a temperature of ±3°C of the atmospheric temperature of the stretching chamber, it is introduced into a stretching chamber and stretched in the width direction while both ends in the width direction of the uniaxially oriented polypropylene film are held by clips. The atmospheric temperature of the stretching chamber at this time (width direction stretching temperature) 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 the resin A having a high glass transition temperature and improving the heat resistance of the biaxially oriented polypropylene film. On the other hand, from the above viewpoint, the width direction stretching temperature is preferably 190°C or lower, more preferably 185°C or lower.

[0087] From the viewpoint of increasing the dielectric breakdown voltage of the obtained 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 formation, 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 the 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. In the present invention, the widthwise stretching ratio refers to the stretching ratio after stretching in the width direction and before performing a 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 is no particular limit to the upper limit of the areal stretching ratio, but in terms 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 provide a heat treatment and relaxation treatment process after biaxial stretching. In this process, it is preferable to perform heat treatment at a temperature of 150°C or more and 190°C or less in the tenter atmosphere temperature while providing 2 to 30% relaxation in the width direction while keeping both ends in the width direction tensely held by clips, from the viewpoint of improving the reliability of the film capacitor when the biaxially oriented polypropylene film is used as a dielectric of the film capacitor. From the above viewpoint, the heat treatment temperature is preferably 150°C or more and 167°C or less. In addition, from the viewpoint of improving the reliability and life of the biaxially oriented polypropylene film when used as a dielectric of the 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 dielectric breakdown voltage of the biaxially oriented polypropylene film, the relaxation treatment is more preferably 25% or less, and 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 at both ends in the width direction are released in a room temperature atmosphere. Then, in a winder process, the film edge is slit and the biaxially oriented polypropylene film is wound into a roll. Here, before winding the biaxially oriented polypropylene film, it is preferable to perform a surface treatment such as a corona discharge treatment on at least one side in air, nitrogen, carbon dioxide gas, or a mixture of these gases in order to improve the adhesion of the evaporated metal.

[0091] Specific examples of the manufacturing conditions that are focused on in order to obtain the biaxially oriented polypropylene film of the present invention are as follows. It is preferable to satisfy all of these manufacturing conditions, but they do not necessarily have to be all present and may be combined as appropriate. For example, instead of "in the sequential biaxial stretching, the preheating temperature before the width direction stretching is the width direction stretching temperature +5°C or more and +15°C or less," simultaneous biaxial stretching may be adopted. Contains resin A. The mesopentad fraction of the main component, polypropylene resin, is 0.960 or more. Pre-mix resin A with polypropylene resin. When the total components of the biaxially oriented polypropylene film are taken as 100% by mass, the content of resin A must be between 0.2% and 45% by mass. The area stretch ratio of biaxial stretching must be 20.0 times or more. The stretch ratio in the width direction must be 5.0 times or more. -Heat treatment and relaxation treatment are performed after biaxial stretching. The heat treatment temperature after biaxial stretching is 150℃ or higher and 190℃ 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 of forming the metal film is not particularly limited, but for example, a method of depositing a metal film such as a deposition film that becomes an internal electrode of a film capacitor by depositing aluminum or an alloy of aluminum and zinc on at least one side of a biaxially oriented polypropylene film is preferably used. At this time, other metal components such as nickel, copper, gold, silver, and chromium can be deposited simultaneously with or successively to the aluminum. Also, a protective layer can be provided on the deposition film using oil or the like. When the surface roughness of the biaxially oriented polypropylene film is different on the front and back sides, it is preferable to provide a metal film laminated film by providing a metal film on the surface side with a smoother roughness from the viewpoint of increasing the voltage resistance.

[0095] The metal film laminated film of the present invention can be annealed or heat-treated at a specific temperature as necessary 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 assumed 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 the resin A used in the metal film laminated film of the present invention. In addition, for insulation or other purposes, at least one side of the metal film laminated film can be coated with a resin such as polyphenylene oxide.

[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. A preferred method for producing a wound type film capacitor is as follows.

[0097] Aluminum is vapor-deposited under reduced pressure on one side of a biaxially oriented polypropylene film. At this time, the film is vapor-deposited in stripes with margins running in the longitudinal direction. Next, a blade is used to slit the center of each vapor-deposited portion and the center of each margin on the surface, producing a tape-like take-up reel with a margin on one side of the surface. Two tape-like take-up reels with a left margin and one with a right margin are stacked and wound together so that the vapor-deposited portion extends beyond the margin in the width direction, to obtain 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). The resulting reel and one unvapor-deposited laminated film are overlapped and wound in two so that the metallized film protrudes from the laminated film in the width direction to obtain a wound body.

[0099] As a method for obtaining the film capacitor of the present invention using the metal layer laminated film of the present invention, for example, the core material is removed from the wound body prepared as described above, pressed, metallicon is sprayed on both end faces to form external electrodes, and lead wires are welded to the metallicon to form a wound film capacitor. The uses of film capacitors are diverse, including power control units for electric automobiles such as electric vehicles, hybrid vehicles, and fuel cell vehicles, electric aircraft such as drones, railway vehicles, solar power generation and wind power generation, and general home appliances, and the film capacitor of the present invention can also be suitably used for these uses. In addition, the biaxially oriented polypropylene film of the present invention can be used for various uses such as packaging films, release films, processing films, sanitary products, agricultural products, building products, and medical products, and can be particularly preferably used for uses including a heating process in film processing.

[0100] The power control unit, electric automobile, and electric aircraft of the present invention will be described below. The power control unit of the present invention has the film capacitor of the present invention. The power control unit is a system that manages power in an electric automobile, electric aircraft, or the like that has a mechanism driven by electricity. By mounting the film capacitor of the present invention in the power control unit, it is possible to reduce the size of the power control unit itself, improve its heat resistance, and increase its efficiency, resulting in improved fuel efficiency for an electric automobile, electric aircraft, or the like that is equipped with 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 equipping an electric vehicle with the power control unit of the present invention leads to improved fuel efficiency, etc.

[0102] The electric aircraft of the present invention has the power control unit of the present invention. Here, the electric aircraft refers to an aircraft having a mechanism driven by electric power, 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 equipping an electric aircraft with the power control unit of the present invention leads to improved fuel efficiency, etc. EXAMPLES

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

[0105] (2) The main orientation axis direction and the perpendicular direction to the main orientation axis direction of biaxially oriented polypropylene film In each of the Examples and Comparative Examples, the main orientation axis direction 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, cut the biaxially oriented polypropylene film into a rectangular sample measuring 50 mm in length and 10 mm in width. <1> Then, the sample <1> The direction of the long side of the sample was defined as 0°. Next, a rectangular sample of the same size was created so that the long side direction was rotated 15° to the right from the 0° direction. <2> The rectangular sample is then rotated 15° in the same manner to obtain a rectangular sample. <3> ~ <12> Next, each rectangular sample was set 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 the value divided by the cross-sectional area (film thickness x width) of the sample before the test was calculated as the stress of the maximum point strength. The long side direction of the sample where this value was maximum was determined 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 according to JIS K7121-1987. Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments), 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 cooled to 30°C at 20°C / min. After holding at 20°C for 5 minutes, the temperature was raised 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 according to the following formula. When multiple endothermic peaks were observed in one measurement, the peak temperature of the endothermic peak with the highest peak temperature was taken as the peak temperature of the measurement. Glass transition temperature=(extrapolated glass transition onset temperature+extrapolated glass transition finish temperature) / 2.

[0108] (4) Storage modulus E' in the direction of the main orientation axis at 145°C Measurements were performed using the following equipment and conditions. First, a rectangular biaxially oriented polypropylene film sample (width (short side) 10 mm × 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 a 23 ° C atmosphere and set in the furnace. Then, the furnace was cooled with liquid nitrogen, the sample was heated from -100 ° C to 180 ° C, a viscoelasticity-temperature curve was drawn by the dynamic viscoelasticity method, and the storage modulus E' in the main orientation axis direction at 145 ° C was read. The number of measurement tests was n = 3, and the average value of the storage modulus E' in the main orientation axis direction at 145 ° C was calculated. The obtained value was adopted as the storage modulus E' (Pa) in the main orientation axis direction at 145 ° C of the biaxially oriented polypropylene film. <Apparatus and conditions> Equipment: EXSTAR DMS6100 (Seiko Instruments Inc.) Test mode: Tensile mode Chuck distance: 20mm Frequency: 10Hz Distortion amplitude: 10.0μm Gain: 1.5 Initial force amplitude: 400mN Temperature range: -100~180℃ Heating rate: 5℃ / min Measurement atmosphere: Air Measurement thickness: The film thickness described in (1) above was used.

[0109] (5) Internal haze A haze meter (HGM-2DP C light source) manufactured by Suga Test Instruments Co., Ltd. was used. A biaxially oriented polypropylene film sample was cut to 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. The haze was then measured by irradiating light perpendicularly to the sample surface. 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 at cross section along film's main orientation axis - thickness direction Using a microtome, ultrathin sections of biaxially oriented polypropylene film were prepared (the section in the main orientation direction-thickness direction refers to the direction parallel to the main orientation direction and perpendicular to the film surface). 4 After staining with , the cross section was observed and images were taken using a transmission electron microscope (TEM) under the following conditions. Since Resin A was stained blacker than the polypropylene resin, the black stained areas were used as domains for the following measurements. Equipment: Hitachi Transmission Electron Microscope (TEM) HT7700 Acceleration voltage: 100kV Magnification: 20,000x The thickness direction length of the domain was measured by first selecting five domains in the upward direction from the center of the layer containing both polypropylene resin and resin A in the acquired image, and then selecting five domains in the downward direction in order of proximity to the center of the field of view without moving the field of view. The thickness direction length of the selected domains was measured, and the average value was taken as the thickness direction length of the domain of resin A. If the selected domain had an end outside the field of view, the field of view was moved from one end to the other end to obtain multiple images, and the length of the domain in the main orientation axis direction was determined from the image that was stitched together. 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) Thermal shrinkage in the main orientation direction at 135°C A sample was cut into a rectangle of 30 mm (measurement direction) x 10 mm width with the main orientation axis direction of the biaxially oriented polypropylene film as the long side. A mark 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 mark lines was set as a test length of 20 mm (L0). Next, the sample was sandwiched between paper and heated in an oven kept at 135°C for 10 minutes, then removed and cooled to room temperature, after which the length between the two mark lines (L1) was measured and the heat shrinkage was calculated using the following formula. The same measurement was performed five times, and the arithmetic average value was taken as the heat shrinkage in the main orientation axis direction at 135°C. Thermal shrinkage rate = {(L0-L1) / L0} x 100 (%).

[0112] (8) Performance evaluation of biaxially oriented polypropylene film <Life evaluation> The wetting tension of each surface of the biaxially oriented polypropylene film was measured according to JIS K 6768-1995. On the surface with higher wetting tension, aluminum was deposited by a vacuum deposition machine manufactured by ULVAC, Inc., so that the film resistance was 10Ω / sq. During deposition, a deposition film A was formed with a deposition 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 the direction perpendicular to the longitudinal direction by masking oil, and a deposition film B was formed without a deposition pattern having a T-shaped margin. The obtained deposition films A and B were slit, respectively, to obtain deposition reels A and B with a film width of 50 mm (edge ​​margin width of 2 mm). Next, the deposition reels A and B were alternately overlapped, and the deposition film was wound up using an element winding machine (KAW-4NHB) manufactured by Kaito Seisakusho, Inc., so that the element capacitance after finishing as a film capacitor element was 10μF, and metallicon processing was performed. Thereafter, the biaxially oriented polypropylene film was subjected to a heat treatment for 12 hours while reducing the pressure in an atmosphere at the glass transition temperature of the resin A used in the biaxially oriented polypropylene film -5°C, and a lead wire was attached to complete a film capacitor element. Ten film capacitor elements thus obtained were heated for 5 hours at a heat shock temperature T described later, and then 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 ten elements was measured, and the average value was taken as the element capacitance at the heat shock temperature T. The heat shock temperature T was measured under three conditions of T = 125°C, 130°C, and 140°C, and the performance of the film was evaluated according to the following criteria. S and A mean that the film has a sufficient life and can be used suitably even after being exposed to high temperatures, B and C mean that the film has poor practical performance but can be used, and D means that it is difficult to use. In all cases where S:T was 125°C, 130°C, or 140°C, the element capacitance after the test was 9.3 μF or more. A: In all cases where T was 125° C., 130° C., and 140° C., the element capacitance after the test was 8.5 μF or more, and in the test at T=140° C., the element capacitance after the test was smaller 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. In all cases where D:T was 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 the biaxially oriented polypropylene film 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 type) manufactured by Anritsu Corporation under an atmosphere of 23°C and 65% RH. The standard deviation of the thickness at the 50 points obtained was designated as σ, and the average as Z, and the film performance was evaluated according to the following criteria. A means that the biaxially oriented polypropylene film had high stability and extensibility during molding, resulting in small thickness unevenness, and was excellent in terms of voltage resistance and reduction of yield during processing into a film capacitor, making it suitable for use as a film for a film capacitor; B means that the biaxially oriented polypropylene film had moderate thickness unevenness and was inferior in practical performance but was usable for a film capacitor; and C means that it was difficult to use for 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> The biaxially oriented polypropylene films manufactured under the conditions described in the Examples and Comparative Examples were processed in the same manner as in the above-mentioned life evaluation 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 the dimensional stability according to the following criteria: A means that it can be used suitably in a 130°C environment, B means that it can be used in a 130°C environment depending on the conditions, and C means that it 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 bent or expanded or contracted, but the Metallicon was not deformed. C: The metallicon of the film capacitor element was deformed.

[0115] <Evaluation of low voltage breakdown of film> The extent to which the biaxially oriented polypropylene film produced under the conditions described in the Examples and Comparative Examples has a region with low withstand voltage at 130°C was measured in the atmosphere after heating the film for 1 minute in an oven maintained at 130°C in accordance with JIS C2330 (2001) 7.4.11.2 Method B (plate electrode method). However, for the lower electrode, a conductive rubber E-100 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. <65> The test specimens were used that had the "Low Voltage Breakdown Value" printed on them. The breakdown voltage test was performed 30 times, the value obtained was divided by the film thickness (measured in (1) above) to convert it to V / μm, and the average of the three values ​​from the 4th to the 6th points, in ascending order from the smallest to the smallest, of the 30 measured values ​​(calculated values) was calculated as the low voltage breakdown value. From the evaluated low voltage breakdown values, the lack of areas with low voltage was evaluated as follows: S means that there are almost no areas with low voltage resistance, 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 a film capacitor with a low rated voltage can be used in a small size; and D means that the film capacitor is not suitable for use because it is too large. S: The low voltage breakdown value was 280 V / μm or more. A: The low voltage breakdown value was 240 V / μm or more and less than 280 V / μm. B: The low voltage breakdown value was 200 V / μm or more and 240 V / μm or more. C: The low voltage breakdown value was 150 V / μm or more and 200 V / μm or less. D: The low voltage breakdown value was lower than 150 V / μm.

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

[0117] When the mesopentad fraction of a film was measured, 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] [Resin etc.] The following resins and the like 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 The crystallization temperature (Tmc) of polypropylene during the cooling process when resin A was mixed with polypropylene was measured according to JIS K7121-1987 as follows. Each component was mixed so that resin A was 5 parts by mass and polypropylene resin 1 described later was 95 parts by mass, and the components were kneaded and extruded with a twin-screw extruder set at 260 ° C., and then the strand was water-cooled and chipped to prepare a resin A mixed sample. Next, using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments), 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 performed three times, and the average value of the peak temperatures obtained was taken as the crystallization temperature (Tmc) of polypropylene during the cooling process when resin A was mixed with polypropylene. When a plurality of exothermic peaks were observed in one measurement, the peak temperature of the highest exothermic peak was regarded as the peak temperature of that measurement.

[0121] <Polypropylene resin> Polypropylene resin 1: A 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. with a mesopentad fraction of 0.984, a melting point of 168°C, and a melt flow rate (MFR) of 2.5g / 10min. <Resin components other than polypropylene resin> Raw material (C1): "ViviOn" (registered trademark) manufactured by USI, product name 1325. Resin with an alicyclic structure in the side chain (corresponding to resin A). The glass transition temperature is 128°C and the MFR is 13g / 10min. Raw material (C2): "ViviOn" (registered trademark) manufactured by USI, product name MDP-0011. Resin with an alicyclic structure in the side chain (corresponding to resin A). Glass transition temperature is 147°C, MFR is 6.0g / 10min. Raw material (C3): Polyplastics "TOPAS" (registered trademark) 6013F-04 (a resin made by copolymerizing ethylene and norbornene (COC), not applicable to Resin A. Glass transition temperature is 138°C, amorphous) Raw material (C4): Polyplastics "TOPAS" (registered trademark) 6017S-04 (a resin copolymerized with ethylene and norbornene (COC), not applicable to Resin A. Glass transition temperature is 178°C, amorphous).

[0122] <Components other than resin components> Antioxidants: “IRGANOX”(Registered Trademark) 1010 manufactured by Ciba Specialty Chemicals.

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

[0124] ( reference Example 1) A resin composition in which the raw material (A1) was mixed at 30.0 parts by mass, the polypropylene resin 1 was mixed at 69.7 parts by mass, and the antioxidant was mixed at 0.3 parts by mass was fed to a single-screw extruder. In the single-screw extruder, the resin composition was melted at a temperature of 250°C, and foreign matter was removed using a sintered filter with a cutoff of 80 μm and adjusted to a temperature of 250°C. The molten resin composition was then discharged from a T-die in the form of a sheet. Thereafter, the molten sheet was adhered to a casting drum whose surface temperature was kept at 90°C by an air knife (air temperature: 23°C) and cooled and solidified to obtain an unstretched polypropylene film. The unstretched polypropylene film was heated to a temperature of 145°C by a group of rolls, and stretched 4.0 times in the longitudinal direction between rolls with a difference in peripheral speed to obtain a uniaxially oriented polypropylene film. Next, the uniaxially oriented polypropylene film was guided into a tenter with both ends in the width direction held by multiple clips, preheated to 172°C, and then stretched 6.0 times in the width direction at the same temperature. It was then heat-treated at 158°C while being relaxed by 12% in the width direction as heat treatment and relaxation treatment, and was then guided outside the tenter and the clips were released. Furthermore, the film surface after heat treatment (the side in contact with the casting drum) was subjected to a 25 W·min / m2 current in air. 2 The results are shown in Table 1.

[0125] ( Reference Example 1, Examples 2 to 5, Reference Example 6, Examples 7, 8, Reference Examples 9, 10, Examples 11, 12, Reference Example 13 , Comparative Examples 1 to 5) A biaxially oriented polypropylene film was 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 was not obtained, the evaluation in Table 1 is shown as "-"). In Comparative Example 4, longitudinal and transverse stretching was not performed, and the film was cooled on the casting drum, and the contact surface of 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 each component 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 each component 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 the polypropylene resin 1 were melted at 250 ° C., and foreign matter was removed with a sintered filter with a cut of 80 μm whose temperature was adjusted to 230 ° C., and then the resin composition (for A layer) and the polypropylene resin 1 (for B layer) were laminated using a feed block so that the layer thickness ratio was 1 / 10 / 1 in a three-layer structure of B layer / A layer / B layer. In the single screw extruder, the resin composition was melted at a temperature of 250 ° C., and foreign matter was removed with a sintered filter with a cut of 80 μm whose temperature was adjusted to 250 ° C., and then the molten resin composition was discharged from a T die into a sheet shape. As described above, a biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the resin was formed into a sheet in a three-layer configuration using two extruders, 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] [Table 1]

[0128] [Table 2]

[0129] In addition, Reference Example 1, Examples 2 to 5, Reference Example 6, Examples 7, 8, Reference Example 9, 10, Examples 11, 12, Reference Example 13, Examples The polypropylene films described in 14, Comparative Examples 1, and 3 to 5 did not have sufficient air permeability to achieve a permeation time of 5,000 seconds / 100 ml or less for 100 ml of air measured at 23°C and 65% relative humidity using a B-type Gurley tester according to JIS P 8117 (1998). Therefore, they were determined not to be microporous films. In addition, the mesopentad fractions of the films were all the same as those of the polypropylene resin, which was the main component. [Industrial Applicability]

[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 temperature and high voltage conditions.

Claims

1. A biaxially oriented polypropylene film comprising 0.5% by mass or more and 45% by mass or less of resin A having an alicyclic structure in a side chain, when the entire biaxially oriented polypropylene film is taken as 100% by mass, The storage modulus E' in the main orientation axis direction at 145°C is 1.0 x 10 8 Pa or more and 1.0 x 10 13 Pa or less; The internal haze is 0.0% or more and 5.0% or less, The heat shrinkage rate in the main orientation axis direction at 135°C is -10% or more and 5.0% or less. Biaxially oriented polypropylene film.

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

3. 2. The biaxially oriented polypropylene film according to claim 1, wherein resin A is an amorphous resin.

4. 2. The biaxially oriented polypropylene film according to claim 1, wherein the glass transition temperature of at least one of the resins A is 120°C or higher and 160°C or lower.

5. The biaxially oriented polypropylene film according to claim 1, wherein the resin A is contained in an amount of 1.2% by mass or more and less than 3.0% by mass when the entire biaxially oriented polypropylene film is taken as 100% by mass.

6. The biaxially oriented polypropylene film according to claim 1, having a thickness of 0.5 μm or more and 60 μm or less.

7. The biaxially oriented polypropylene film according to claim 1, 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.

8. The biaxially oriented polypropylene film according to claim 1 , comprising two or more types of resin A.

9. 2. The biaxially oriented polypropylene film of claim 1, comprising a copolymer having residues of at least one of ethylene or an α-olefin and vinylcyclohexane residues.

10. 2. The biaxially oriented polypropylene film of claim 1, wherein the mesopentad fraction of the film is 0.973 or more.

11. The biaxially oriented polypropylene film according to claim 1, which is used as a dielectric for a film capacitor.

12. 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 11.

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

14. A power control unit comprising the film capacitor according to claim 13.

15. An electric vehicle comprising the power control unit according to claim 14.

16. An electric aircraft comprising the power control unit according to claim 14.

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