Stretched film, metal laminated film, and film capacitor

Abstract

Provided is a stretched film having high dielectric breakdown strength even under a high temperature environment of 120°C or higher, and further capable of imparting excellent withstand voltage performance to a capacitor element even under a room temperature (for example, 25°C) and a high temperature environment of 120°C or higher.　The present invention is a stretched film that contains a polypropylene-based resin, and the number of regions R1 measured by a prescribed method is 10 or more. Alternatively, the present invention is a stretched film that contains a polypropylene-based resin, and the average value of the maximum lengths of regions 2 in the thickness direction, which are measured by a prescribed method, is 10-300 nm. Alternatively, the present invention is a stretched film that contains a polypropylene-based resin, and the average value of the maximum lengths of regions 3 in a direction orthogonal to the thickness direction, which are measured by a prescribed method, is 30 nm or more.

Description

Stretched films, metal laminated films, and film capacitors

[0001] The present invention relates to a stretched film formed from a polypropylene resin, a metal laminated film having the stretched film, and a film capacitor.

[0002] Stretched films primarily composed of polypropylene are used in film capacitor applications due to their excellent electrical properties. In electronic and electrical equipment, film capacitors made from stretched polypropylene are used, for example, as high-voltage capacitors, various switching power supplies, filter capacitors in converters and inverters, and smoothing capacitors. Film capacitors are also increasingly used in automobiles, such as electric vehicles and hybrid vehicles, where demand has been growing in recent years, for example, in inverters and converters that control drive motors.

[0003] Film capacitors, particularly automotive film capacitors, are increasingly being used in high-temperature environments. For example, in devices that control automotive drive motors (inverters, converters, etc.), the use of highly heat-resistant semiconductors (such as silicon carbide semiconductors) has increased in recent years. Consequently, capacitors used in these devices are required to have high heat resistance, such as 120°C or higher, preferably 130°C or higher. Conventional capacitors using polypropylene film are said to have an upper limit of operating temperature of about 110°C, and it is extremely difficult to stably maintain electrical insulation in high-temperature environments exceeding this.

[0004] One example of a resin film with high heat resistance is a film made of a resin composition containing a polyolefin mainly composed of polypropylene and a hydrogenated block copolymer, which is excellent in heat resistance and especially in its ability to block water vapor (Patent Document 1).

[0005] Japanese Patent Publication No. 2014-37532

[0006] Resin films primarily composed of polypropylene tend to exhibit a decline in physical properties, such as reduced rigidity and decreased electrical insulation, as the operating temperature increases. In this regard, stretching a polypropylene-based resin film in at least one direction, preferably two directions, improves rigidity and electrical insulation, allowing these properties to be maintained even in high-temperature regions exceeding 110°C. However, at operating temperatures above 120°C, and even above 130°C, maintaining rigidity and electrical insulation becomes difficult even with a stretched film, and furthermore, improving the characteristics of the capacitor element becomes challenging.

[0007] The present invention has been made in view of the above, and aims to provide a stretched film that has high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and that can impart excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher. The present invention also aims to provide a metal laminated film and a film capacitor comprising the stretched film.

[0008] The inventors of this invention conducted extensive research to achieve the above objective and, as a result, discovered that the above objective can be achieved by adjusting the number or size of the layered structure present in the cross-section to an appropriate range, thus completing the present invention.

[0009] In other words, the present invention encompasses, for example, the subject matter described in the following sections. Section 1 A stretched film comprising a polypropylene resin, wherein the number of regions R1 measured by the following measurement method 1 in atomic force microscopy (AFM) observation of the cross-section is 10 or more. <Measurement method 1> Regions in which the Stiffness approach value of the film cross-section measured by the force distance curve measurement method is 90 N / m or more are extracted by imaging processing, and the number of such regions located on line segments per 5 μm in the thickness direction of the cross-section is counted as R1. Section 2 A stretched film comprising a polypropylene resin, wherein the average value of the maximum length in the thickness direction of region 2 measured by the following measurement method 2 in atomic force microscopy (AFM) observation of the cross-section is 10 nm or more and 300 nm or less. <Measurement Method 2> By force distance curve measurement, regions in the film cross-section where the Stiffness approach value is 90 N / m or more are extracted by imaging processing. Region 2 is defined as the region located within the field of view enclosed by a rectangle of 5 μm in the thickness direction and 1 μm in the direction perpendicular to the thickness of the cross-section, and the average value of the maximum length in the thickness direction of region 2 is measured. Item 3 A stretched film containing a polypropylene resin, wherein, in atomic force microscopy (AFM) observation of the cross-section, the average value of the maximum length in the direction perpendicular to the thickness direction of region 3, measured by the measurement method 3 below, is 30 nm or more. <Measurement Method 3> By force distance curve measurement, regions where the Stiffness approach value of the film cross-section is 90 N / m or more are extracted by image processing. Region 3 is defined as the region located within a field of view enclosed by a rectangle of 5 μm in the thickness direction and 1 μm in the direction perpendicular to the thickness of the cross-section, and the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 is measured. Item 4 A stretched film according to any one of items 1 to 3, wherein the temperature dispersion data in the TD direction at a frequency of 1 Hz obtained from dynamic viscoelasticity measurement has a peak in the loss tangent tanδ in the region of 140°C or higher. Item 5 A stretched film according to any one of items 1 to 4, wherein the temperature dispersion data in the TD direction at a frequency of 1 Hz obtained from dynamic viscoelasticity measurement has a loss tangent tanδ at 100°C of 0.15 or less.Item 6: A stretched film according to any one of items 1 to 5, wherein at least one surface has irregularities, and the average value of the major axis of the irregularities, whose contour is observed to be elliptical by microscopic observation, is 150 μm or less. Item 7: A film having irregularities on at least one surface, wherein the density of the irregularities, whose contour is observed to be elliptical by microscopic observation, is 30 irregularities / mm². ２ The stretched film described in any one of items 1 to 6. Item 8: In infrared absorption spectroscopy, 880 to 890 cm⁻¹ －１ Absorption peaks are observed in the range, and at 1450 cm. －１ A stretched film according to any one of claims 1 to 7, having at least one of the shoulder peaks due to absorption in the vicinity. Claim 9 A stretched film according to any one of claims 1 to 8, wherein the polypropylene resin contains 80% to 99% by mass of an isotactic polypropylene resin and 1% to 20% by mass of a polymer having an alicyclic structure. Claim 10 A stretched film according to claim 9, wherein the polymer having an alicyclic structure comprises two or more polymers with different glass transition temperatures. Claim 11 A stretched film according to claim 9 or 10, wherein the polymer having an alicyclic structure comprises polymer B1 having an alicyclic structure with a glass transition temperature of 133°C to 155°C and polymer B2 having an alicyclic structure with a glass transition temperature of 70°C to less than 133°C. Claim 12 A stretched film according to claim 11, wherein the mass ratio B2 / B1 of polymer B2 to polymer B1 is less than 0.85. Item 13 A stretched film according to any one of items 9 to 12, wherein the polymer having an alicyclic structure contains hydrogenated polystyrene. Item 14 A stretched film according to item 13, wherein the hydrogenated polystyrene has an atactic structure and a hydrogenation rate of 95% or more. Item 15 A stretched film according to any one of items 1 to 14, having a thickness of 1.8 μm or more and 10 μm or less, and a total light transmittance of 80% or more. Item 16 A metal laminated film having a metal layer on one or both sides of the stretched film according to any one of items 1 to 15. Item 17 A film capacitor comprising the metal laminated film according to item 16.

[0010] The stretched film of the present invention has high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and moreover, it can impart excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher.

[0011] Figures (a) to (c) are schematic diagrams illustrating the "crater-like micro-irregularities" present on the roughened surface of the stretched film. (a) is an AFM image of the stretched film obtained in Example 1, and (b) is its binarized image. (a) is a binarized image of the stretched film obtained in Comparative Example 1, and (b) is a binarized image of the stretched film obtained in Comparative Example 3.

[0012] Embodiments of the present invention will be described in detail below. In this specification, the expressions "containing" and "including" include the concepts of "containing," "including," "substantially consisting of," and "consisting only of."

[0013] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. In the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Furthermore, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0014] 1. Stretched Film The stretched film of the present invention includes the following stretched film A, stretched film B, and stretched film C.

[0015] Stretched film A: Contains a polypropylene resin, and in atomic force microscopy (AFM) observation of the cross-section, the number of regions R1 measured by the following measurement method 1 is 10 or more. <Measurement method 1> Regions of the film cross-section with a Stiffness approach value of 90 N / m or more, measured by force distance curve measurement, are extracted by image processing, and the number of such regions located on line segments of 5 μm in the thickness direction of the cross-section is counted as R1.

[0016] Stretched film B: Contains a polypropylene resin, and in atomic force microscopy (AFM) observation of the cross-section, the average value of the maximum length in the thickness direction of region 2 measured by the measurement method 2 below is 10 nm or more and 300 nm or less. <Measurement method 2> Regions in which the Stiffness approach value of the film cross-section measured by the force distance curve measurement method is 90 N / m or more are extracted by image processing, and the region that exists within the field of view enclosed by a rectangle of 5 μm in the thickness direction and 1 μm in the direction perpendicular to the thickness of the cross-section is defined as region 2, and the average value of the maximum length in the thickness direction of region 2 is measured.

[0017] Stretched film C: Contains a polypropylene resin, and in atomic force microscopy (AFM) observation of the cross-section, the average value of the maximum length in the direction perpendicular to the thickness direction of region 3, measured by the measurement method 3 below, is 30 nm or more. <Measurement method 3> Regions in which the Stiffness approach value of the film cross-section measured by the force distance curve measurement method is 90 N / m or more are extracted by image processing, and the region located within the field of view enclosed by a rectangle of 5 μm in the thickness direction and 1 μm in the direction perpendicular to the thickness is defined as region 3, and the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 is measured.

[0018] The stretched films A, B, and C of the present invention have high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and can impart excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher. Furthermore, the stretched films A, B, and C of the present invention have high volume resistivity even in high-temperature environments.

[0019] The stretched films A, B, and C of the present invention all have a phase-separated structure in their cross-sections, and for example, a layered structure exists in the cross-section. In the present invention, by controlling the number or size of a specific layered structure, it is possible to have a high dielectric breakdown strength even in a high-temperature environment and to reduce the change in the dielectric breakdown strength in a high-temperature environment with respect to the dielectric breakdown strength at room temperature (for example, 25°C). It has been found that such a layered structure can be easily formed, for example, when the stretched films A, B, and C are manufactured using a polypropylene-based resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure, as described below.

[0020] Here, in the stretched film, that the change in the dielectric breakdown strength in a high-temperature environment with respect to the dielectric breakdown strength at room temperature (for example, 25°C) is small specifically means that when the dielectric breakdown strength of the stretched film at 25°C is V25 (Vdc / μm) and the dielectric breakdown strength at 140°C is V140 (Vdc / μm), the value of the strength ratio "V140 / V25" is close to 1. The value of V140 / V25 is usually 1 or less.

[0021] Incidentally, hereinafter, the value of "V140 / V25" representing the degree of change in the dielectric breakdown strength at 140°C (under high temperature) with respect to room temperature (for example, 25°C) may be simply abbreviated as the "ratio of dielectric breakdown strength".

[0022] In the stretched film A, the number of R1 is 10 or more. When the number of R1 is less than 10, the ratio of dielectric breakdown strength becomes small, and the volume resistivity also becomes low even in a high-temperature environment.

[0023] In the stretched film A, the number of R1 is preferably 15 or more, more preferably 18 or more, still more preferably 20 or more, and preferably 50 or less, more preferably 40 or less, still more preferably 35 or less.

[0024] The number of R1 in the stretched film A of the present invention can be measured by observing the cross-section of the stretched film A with an atomic force microscope (AFM), and more specifically, it can be measured as follows.

[0025] First, the stretched film A is cut so that its cross-section is exposed. This cut is made along the TD direction of the stretched film A. The atomic force microscope used is the Park Systems NX-10. The AFM observation conditions are as follows: a cantilever with a spring constant of 42 N / m (tip radius of curvature R is 30 nm) with a probe made of a Si single crystal tip is used, the scanning frequency is 330 Hz, the resolution is 512 (points) × 512 (points), and the observation environment is 23°C in an atmospheric atmosphere. Under these observation conditions, the force distance curve is measured by scanning within a 5 μm square cross-section in the lateral direction (TD direction) using Pinpoint nanomechanical mode, and the Stiffness approach value is calculated using the built-in software (XEI) while obtaining an AFM image of the film cross-section. Similarly, another part of the film cross-section is observed to obtain an AFM image. This allows us to obtain two AFM images of the cross-section of stretched film A. Using the programming language Python, each of the obtained AFM images is used to extract the region S in which the Stiffness approach value is 90 N / m or higher, and an adaptively binarized image is obtained in which the extracted region S becomes white. The Gaussian filter used is the filters.gaussian function of scikit-image (image, sigma=1, output=<DEPRECATED>, mode=nearest, cval=0, preserve_range=False, trunk=4.0, *, channel_axis=None, out=None). In each of the obtained binarized images, five line segments (with a length of 5 μm) parallel to the thickness direction are drawn randomly, and the regions S located on these line segments are defined as R1. The number of R1s is determined according to the method for determining the number of R1s described below.

[0026] <<Method for Determining the Number of R1s>>In one of the two binary images, using Python, randomly draw five line segments each 5 μm long parallel to the thickness direction. Taking the locations shown in white (i.e., the region S) as "0" and the locations shown in black as "1", count the number of times the switch from "1" to "0" occurs on each line segment, and take the average value of these numbers as the number (pieces) of R1s. However, R1s with a thickness direction length of 5 nm or less are excluded without being counted. In the same procedure, also count the number (pieces) of R1s in the other binary image. Calculate the average value of the number of R1s in each of the obtained binary images, and use this value as the number of R1s in the stretched film A.

[0027] The method for adjusting the number of R1s in the stretched film A of the present invention is not particularly limited. For example, by manufacturing the stretched film A from a polypropylene-based resin containing an isotactic polypropylene resin, it becomes easier to adjust the number of R1s to 10 or more. Among them, as will be described later, when the stretched film A is manufactured using a polypropylene-based resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure, it becomes even easier to adjust the number of R1s to 10 or more. Also, by adjusting the melting temperature of the raw material resin used during the manufacture of the stretched film A, or the metal drum temperature described later, it also becomes easier to adjust the number of R1s to 10 or more.

[0028] In the stretched film B, the average value of the maximum length in the thickness direction of the region 2 is 10 nm or more and 300 nm or less. When the average value of the maximum length in the thickness direction of the region 2 is less than 10 nm or exceeds 300 nm, the ratio of the dielectric breakdown strength becomes small, and the volume resistivity also becomes low even in a high-temperature environment.

[0029] In the stretched film B, the average value of the maximum length in the thickness direction of the region 2 is preferably 20 nm or more, more preferably 40 nm or more, still more preferably 60 nm or more, particularly preferably 80 nm or more, and preferably 250 nm or less, more preferably 200 nm or less, still more preferably 170 nm or less, particularly preferably 150 nm or less.

[0030] The average of the maximum length in the thickness direction of region 2 in the stretched film B of the present invention can be measured by observing the cross-section of the stretched film B with an atomic force microscope (AFM), and more specifically, it can be measured as follows.

[0031] First, using the same procedure as for observing the AFM image of the cross-section of the stretched film A described above, an AFM image is obtained, and then two adaptively binarized binarized images are acquired in the same manner. Using these binarized images, the average value of the maximum length in the thickness direction of region 2 is determined according to the method for determining the average value of the maximum length in the thickness direction of region 2 described below.

[0032] ≪Method for Determining the Average Value of the Maximum Length in the Thickness Direction of Region 2≫ Region 2 is defined as the region S (i.e., the white area) that exists within the field of view enclosed by a rectangle with a thickness of 5 μm in the cross-sectional thickness direction and a thickness of 1 μm in the direction perpendicular to the thickness in one of the two binarized images. The maximum length in the thickness direction of all regions 2 within the field of view is measured using Python, and the average value of these measurements is taken as the average value of the maximum length in the thickness direction of Region 2. However, regions 2 with a thickness length of 5 nm or less are excluded.

[0033] The method for adjusting the average value of the maximum length in the thickness direction of region 2 in the stretched film B of the present invention is not particularly limited. For example, by manufacturing the stretched film B with a polypropylene resin containing an isotactic polypropylene resin, it becomes easier to adjust the average value of the maximum length in the thickness direction of region 2 to between 10 nm and 300 nm. In particular, as described later, when the stretched film B is manufactured using a polypropylene resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure, it becomes even easier to adjust the average value of the maximum length in the thickness direction of region 2 to between 10 nm and 300 nm. Furthermore, by adjusting the melting temperature of the raw material resin used in the manufacture of the stretched film B, or the metal drum temperature described later, it also becomes easier to adjust the average value of the maximum length in the thickness direction of region 2 to between 10 nm and 300 nm.

[0034] The stretched film C has an average maximum length of 30 nm or more in the direction perpendicular to the thickness direction of region 3. If the average maximum length of 3 in the direction perpendicular to the thickness direction of region 3 is less than 30 nm, the ratio of dielectric breakdown strengths becomes smaller, and the volume resistivity also becomes lower even in high-temperature environments.

[0035] In the stretched film C, the average value of the maximum length in the direction perpendicular to the thickness direction of the region 3 is preferably 50 nm or more, more preferably 100 nm or more, even more preferably 130 nm or more, particularly preferably 180 nm or more, and also preferably 600 nm or less, more preferably 500 nm or less, even more preferably 400 nm or less, and particularly preferably 300 nm or less.

[0036] The average of the maximum length in the direction perpendicular to the thickness direction of the region 3 in the stretched film C of the present invention can be measured by observing the cross-section of the stretched film C with an atomic force microscope (AFM), and more specifically, it can be measured as follows.

[0037] First, using the same procedure as for observing the AFM image of the cross-section of the stretched film A described above, an AFM image is obtained, and then two adaptively binarized binarized images are acquired in the same manner. Using these binarized images, the average value of the maximum length of region 3 is determined according to the method for determining the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 described below.

[0038] ≪Method for determining the average value of the maximum length in the direction perpendicular to the thickness direction of region 3≫ In one of the two binarized images, region S (i.e., the white area) that exists within the field of view enclosed by a rectangle with a thickness of 5 μm in the cross-sectional thickness direction and a thickness of 1 μm perpendicular to the thickness is defined as region 3. The maximum length in the thickness direction of all regions 3 within the field of view is measured using Python, and the average value of these measurements is defined as the average value of the maximum length in the direction perpendicular to the thickness direction of region 3. However, regions 3 whose length in the direction perpendicular to the thickness direction is 5 nm or less are excluded.

[0039] The method for adjusting the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 in the stretched film C of the present invention is not particularly limited. For example, by manufacturing the stretched film C with a polypropylene resin containing isotactic polypropylene resin, it becomes easier to adjust the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 to 30 nm or more. In particular, as described later, when the stretched film C is manufactured using a polypropylene resin containing isotactic polypropylene resin and a polymer having an alicyclic structure, it becomes even easier to adjust the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 to 30 nm or more. Furthermore, by adjusting the melting temperature of the raw material resin used in the manufacture of the stretched film C, or the metal drum temperature described later, it also becomes easier to adjust the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 to 30 nm or more.

[0040] Both the stretched film B and the stretched film C of the present invention may possess the characteristics of the stretched film A of the present invention. That is, either or both of the stretched film B and the stretched film C of the present invention may have 10 or more of the aforementioned regions R1. Furthermore, the stretched film B of the present invention may possess the characteristics of the stretched film C of the present invention (i.e., a configuration in which the average value of the maximum length in the direction perpendicular to the thickness direction of the region 3 is 30 nm or more). Furthermore, the stretched film C of the present invention may possess the characteristics of the stretched film B of the present invention (i.e., a configuration in which the average value of the maximum length in the thickness direction of the region 2 is 10 nm or more and 300 nm or less).

[0041] In the stretched films A, B, and C of the present invention, it is preferable that the region S is formed so as to appear layered in cross-section. More specifically, the region S may be formed in the shape of a rod in the stretched film, for example. When the region S is formed in the shape of a rod, it is preferable that the rod is arranged so that its major axis (height of the cylinder) is stretched along the MD direction of the stretched film. In this case, when the cross-section of the film in the MD direction-thickness direction is observed, the rod is seen as layered, and when the cross-section of the film in the TD direction-thickness direction is observed, the rod is seen as circular.

[0042] The following details the characteristics that the stretched films A, B, and C of the present invention share in common. In the following description, the stretched films A, B, and C of the present invention will be collectively referred to as "the stretched films of the present invention."

[0043] The stretched film of the present invention preferably has a peak in the loss tangent tanδ in the region of 140°C or higher in the temperature dispersion data in the TD direction at a frequency of 1 Hz obtained from dynamic viscoelasticity measurement. As a result, the stretched film can have high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and the change in dielectric breakdown strength is also small (the V140 / V25 ratio becomes larger).

[0044] In this specification, "having a peak in the loss tangent (tanδ) in the region above 140°C" specifically means that, in the temperature dispersion data (also called temperature-dependent data) of dynamic viscoelasticity, the loss tangent (tanδ) has a clear principal dispersion peak (i.e., the peak with the largest tanδ value) in the region above 140°C.

[0045] Here, "having a clear principal dispersion peak in the region above 140°C" can mean, for example, that in the temperature range of 140 to 160°C of the temperature dispersion data (also called temperature-dependent data) of the dynamic viscoelasticity, the difference between the maximum and minimum values ​​of the tanδ (range of change in the temperature range) is ±0.03 or more, preferably ±0.04 or more, more preferably ±0.05 or more, and particularly preferably ±0.06 or more.

[0046] In the stretched film of the present invention, the method for having a loss tangent (tanδ) peak in the region of 140°C or higher is not particularly limited. For example, known methods for raising the glass transition temperature or methods using resin blends can be widely employed. In particular, a method of producing the stretched film using a polypropylene resin containing an isotactic polypropylene resin is preferred. Among these, as described below, when the stretched film is produced using a polypropylene resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure, it is easy to obtain a loss tangent (tanδ) peak in the region of 140°C or higher.

[0047] In the stretched film of the present invention, temperature dispersion data can be obtained by dynamic viscoelasticity measurement of each stretched film.

[0048] Specifically, for example, temperature dispersion data can be obtained by performing dynamic viscoelasticity measurements in accordance with JIS-K7244-1 and -4 (1999 edition) using test pieces cut from the stretched film of the present invention into strips. The conditions for such dynamic viscoelasticity measurements are tensile mode, vibration frequency of 1 Hz, chuck distance of 20 mm, strain amplitude of 10 μm, minimum tension of 20 mN, and heating rate of 2 °C / min. The tensile direction of the stretched film is perpendicular to the flow direction (MD direction) of the stretched film, i.e., the TD direction. By performing dynamic viscoelasticity measurements of the stretched film in this way, the relationship between temperature (X axis) and storage modulus E' (Y axis) and / or loss tangent tanδ (Y axis) can be obtained as temperature dispersion (also called temperature dependence) data.

[0049] Preferably, the stretched film of the present invention has a loss tangent (tanδ) of 0.15 or less at 100°C, obtained based on the temperature dispersion data. This allows the stretched film to have high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and the change in dielectric breakdown strength is also reduced (the V140 / V25 ratio increases).

[0050] In the stretched film of the present invention, the loss tangent (tanδ) at 100°C is preferably 0.145 or less, more preferably 0.140 or less, even more preferably 0.135 or less, and particularly preferably 0.130 or less. In the stretched film of the present invention, the loss tangent (tanδ) at 100°C is, for example, 0.05 or more, preferably 0.08 or more, more preferably 0.10 or more, and even more preferably 0.11 or more.

[0051] Here, in the stretched film of the present invention, a loss tangent (tanδ) of 0.15 or less at 100°C means that the temperature dispersion (temperature dependence) data of the tanδ value described above does not substantially have a peak at 100°C. The absence of a substantially peak at 100°C means that, in the loss tangent tanδ temperature dispersion data, there is almost no fluctuation in the value of the loss tangent tanδ around 100°C (for example, in the range of 80 to 120°C), and the characteristic increase in the tanδ value in this temperature range due to the movement based on the lattice relaxation of polypropylene does not occur. In other words, the movement of lattice relaxation is suppressed, and for example, in the range of 80 to 120°C, there is a simple increase toward the main dispersion peak of tanδ.

[0052] The method for adjusting the 100°C loss tangent (tanδ) of the stretched film of the present invention to 0.15 or less is not particularly limited. For example, known methods that can be used to suppress the lattice relaxation motion of isotactic polypropylene can be widely employed. In particular, it is easier to adjust the 100°C loss tangent (tanδ) to 0.15 or less by manufacturing the stretched film with a polypropylene resin containing an isotactic polypropylene resin. In particular, as described below, it is easier to adjust the 100°C loss tangent (tanδ) to 0.15 or less when the stretched film is manufactured using a polypropylene resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure.

[0053] The stretched film of the present invention preferably has irregularities on at least one surface, and the average value of the major axis of the irregularities, whose outline is observed to be elliptical under a microscope, is 150 μm or less. That is, the stretched film of the present invention preferably has a so-called roughened surface (crater-like fine irregularities) on one surface, and the average value of the major axis of the irregularities, whose outline is observed to be elliptical under a microscope, is 150 μm or less.

[0054] The roughened surface may be formed on only one side of the stretched film, or on both sides, preferably on both sides. The method for forming the roughened surface is not particularly limited, and for example, a wide range of known methods can be employed. To give a specific example, the roughened surface can be formed by stretching a sheet on which β crystals have been generated.

[0055] In the present invention, if crater-like fine irregularities (roughened surface) are formed on both surfaces, the surface roughness of both surfaces is measured, and the surface with greater surface roughness is designated as the roughened surface. This roughened surface can satisfy the condition that "the average major axis of the irregularities, whose outline is observed as elliptical under a microscope, is 150 μm or less." Alternatively, if crater-like fine irregularities (roughened surface) are formed on only one surface, that surface only needs to satisfy the condition that "the average major axis of the irregularities, whose outline is observed as elliptical under a microscope, is 150 μm or less."

[0056] Figure 1(a) is a schematic perspective view illustrating crater-like micro-irregularities, Figure 1(b) is a schematic cross-sectional view thereof, and Figure 1(c) is a longitudinal cross-sectional view along the line I-I' in (b). For the sake of clarity, Figures 1(a) to 1(c) are schematic diagrams for explaining "crater-like micro-irregularities" and do not represent the surface shape of stretched films, etc., according to the embodiments described later.

[0057] Many of the crater-like micro-irregularities are observed, for example, with an optical microscope as two paired arc shapes or roughly arc shapes whose contours are curved in opposite directions (hereinafter, arc shapes and roughly arc shapes are collectively referred to as "(abbreviated) arc shapes"). When the observed paired (abbreviated) arc-shaped portions are connected by interpolation, an elliptical shape or roughly elliptical shape is formed (hereinafter, elliptical shapes and roughly elliptical shapes are collectively referred to as "(abbreviated) elliptical shape") (20 in Figure 1). These paired (abbreviated) arc-shaped portions form protrusions and depressions between them (see Figure 1(a)). These protrusions (20a, 20b in Figure 1) and depressions (20c in Figure 1) are based on the above-mentioned crater-like micro-irregularities (see also Figures 1(b) and 1(c)). Furthermore, the two (omitted) arc shapes may combine to form a circle or a nearly circle (hereinafter, the circle and nearly circle shapes will be collectively referred to as "(omitted) circle shape") or an (omitted) ellipse shape. In this case, the cross-section of the projection will be an annular or nearly annular shape (hereinafter, the annular and nearly annular shapes will be collectively referred to as "(omitted) annular") or an elliptical annular or nearly elliptical annular shape (hereinafter, the elliptical annular and nearly elliptical annular shapes will be collectively referred to as "(omitted) elliptical annular". In addition, they may be observed as a single (omitted) arc shape without forming a pair.

[0058] In this specification, the observation of a contour based on irregularities as described above is referred to as "the contour being observed to be elliptical." For convenience, in the following explanation, "irregularly observed irregularities" will simply be referred to as "ellipse."

[0059] In the stretched film of the present invention, as described above, it is preferable that the average value of the major axis of the ellipse, which is observed as an elliptical contour by microscopic observation, is 150 μm or less.

[0060] The average major axis of the ellipse in the stretched film of the present invention can be measured as follows. First, using a digital scope (digital microscope VHX-X1 manufactured by Keyence Corporation), the roughened surface of the stretched film is observed at a lens magnification of 150x, with three randomly selected areas of a field of view of 2.4 mm × 1.8 mm. This observation is performed by reflection measurement. For each image of the three observed field of view areas, the area measurement function of the plane measurement function, which is a dedicated software attached to the digital scope, is used to perform binarization processing with the brightness range set to 100 to 200, and the contours of each ellipse are extracted. Next, the major axis length (longest diameter) and minor axis length (shortest diameter) of each ellipse are manually measured using the two-point distance measurement of the plane measurement, and when the major axis length (longest diameter) is L μm and the minor axis length (shortest diameter) is S μm, only ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 are extracted. In other words, within each of the three fields of view, only ellipses satisfying S ≤ L and 1 ≤ L ≤ 300 are extracted. The average value of the major axis length (longest diameter) L (μm) of all extracted ellipses is calculated, and this average value is taken as the "average value of the major axis of the irregularities whose contours are observed to be elliptical by microscopic observation" (also referred to as the average value of the major axis of the ellipses) in the stretched film A.

[0061] When the stretched film of the present invention has an average value of the major axis of the irregularities whose outline is observed to be elliptical by microscopic observation of 150 μm or less, it can have high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and moreover, it can provide excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher, while also exhibiting small changes in dielectric breakdown strength.

[0062] In the stretched film of the present invention, the lower limit of the average value of the major axis of the unevenness is preferably 91 μm or more, more preferably 101 μm or more, and even more preferably 111 μm or more.

[0063] In the stretched film, the average value of the major axis of the irregularities (the average value of the major axis of the ellipse) being 150 μm or less may be satisfied on at least one side (the roughened surface) or on both sides.

[0064] The method for adjusting the average value of the major axis of the irregularities in the stretched film of the present invention is not particularly limited, and a wide range of known methods that can be used to suppress the lattice relaxation movement of isotactic polypropylene can be employed. In particular, by manufacturing the stretched film with a polypropylene resin containing isotactic polypropylene resin, it becomes easier to adjust the average value of the major axis of the irregularities to 150 μm or less. In particular, as described later, when the stretched film is manufactured using a polypropylene resin containing isotactic polypropylene resin and a polymer having an alicyclic structure, it becomes even easier to adjust the average value of the major axis of the irregularities to 150 μm or less. Furthermore, by adjusting the melting temperature of the raw material resin used during the manufacture of the stretched film, or the metal drum temperature described later, it also becomes easier to adjust the average value of the major axis of the irregularities to 150 μm or less.

[0065] The stretched film of the present invention has irregularities on at least one surface, and the density of these irregularities, whose outline is observed to be elliptical under a microscope, is 30 irregularities / mm². ２ Preferably, the above conditions are met. That is, the stretched film of the present invention has a so-called roughened surface (fine crater-like irregularities) on one surface, and the density of the ellipses on that surface is 30 / mm². ２ It is preferable that the above conditions are met.

[0066] In this invention, if crater-like fine irregularities (roughened surface) are formed on both surfaces, the surface roughness of both surfaces is measured, and the surface with greater surface roughness is designated as the roughened surface. The roughened surface is defined as having a density of 30 irregularities / mm² where the outline is observed to be elliptical under a microscope. ２ The above conditions can be met. Furthermore, in the present invention, if crater-like fine irregularities (roughened surface) are formed on one side, the density of the irregularities whose outline is observed as elliptical by microscopic observation is 30 pieces / mm². ２ It is sufficient to satisfy the condition that "it is the above."

[0067] The density of the ellipses in the stretched film of the present invention can be measured as follows. First, using a digital microscope (Digital Microscope VHX-X1 manufactured by Keyence Corporation), the roughened surface of the stretched film is randomly determined at three locations in a region with a field-of-view range of 2.4 mm × 1.8 mm at a lens magnification of 150 times and observed respectively. This observation is performed by reflection measurement. In each of the images of the three observed field-of-view ranges, using the area measurement function among the plane measurement functions of the dedicated software attached to the digital microscope, the brightness range is set to 100 to 200 and binarization processing is performed to extract the contour of each ellipse. Next, for each ellipse, using the two-point distance measurement in plane measurement, the major axis length (longest diameter) and the minor axis length (shortest diameter) are manually measured. When the major axis length (longest diameter) is L μm and the minor axis length (shortest diameter) is S μm, only the ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 are extracted. That is, in each of the three field-of-view ranges, only the ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 are extracted. In each of the three field-of-view ranges thus extracted, the number of ellipses is counted, and the value obtained by dividing the number by the area of the field-of-view range is calculated. Since this value is obtained for each of the three field-of-view ranges, their average value is calculated, and this is defined as the "density of the concavities and convexities whose contours are observed to be elliptical by microscopic observation" (also referred to as the density of ellipses).

[0068] When the density of the concavities and convexities (the density of the ellipses) of the stretched film of the present invention is 30 pieces / mm ２ or more, it has a high dielectric breakdown strength even in a high-temperature environment of 120°C or higher, and moreover, it can impart excellent withstand voltage performance to capacitor elements even at room temperature (for example, 25°C) and in a high-temperature environment of 120°C or higher, and the change in dielectric breakdown strength is small.

[0069] The upper limit of the density of the concavities and convexities of the stretched film of the present invention is preferably, for example, 90 pieces / mm ２ or less, more preferably 85 pieces / mm ２ or less, and even more preferably 80 pieces / mm ２ or less.

[0070] In the stretched film, when the density of the concavities and convexities is 30 pieces / mm ２The above conditions may be met by at least one side (the roughened surface) or by both sides.

[0071] The method for adjusting the density of the irregularities in the stretched film of the present invention is not particularly limited, and a wide range of known methods that can be used to suppress the lattice relaxation motion of isotactic polypropylene can be employed. In particular, by manufacturing the stretched film with a polypropylene resin containing isotactic polypropylene resin, the density of the irregularities can be reduced to 30 irregularities / mm². ２ This makes it easier to adjust. In particular, as will be described later, when the stretched film is manufactured using a polypropylene resin containing an isotactic polypropylene resin and a polymer having an alicyclic structure, the density of the bumps is set to 30 bumps / mm². ２ This makes it easier to adjust the above. Furthermore, the density of the bumps can also be increased to 30 bumps / mm by adjusting the melting temperature of the raw resin used in the stretched film manufacturing process, or by adjusting the metal drum temperature described later. ２ This makes it easier to adjust the settings.

[0072] The thickness of the stretched film of the present invention can be adjusted to an appropriate range depending on the application, and can be, for example, to the same range as the thickness of stretched film used for capacitor applications. For example, the stretched film of the present invention preferably has a thickness of 1.8 μm or more and 10 μm or less. The thickness of the stretched film is measured in accordance with JIS-C2330:2014, except that it was measured at 100 ± 10 kPa using a paper thickness gauge MEI-11 manufactured by Citizen Seimitsu Co., Ltd.

[0073] From the viewpoint of having high transparency, the stretched film of the present invention preferably has a total light transmittance of 80% or more. In particular, the stretched film of the present invention preferably has a thickness of 1.8 μm or more and 10 μm or less, and a total light transmittance of 80% or more. In this case, the stretched film of the present invention can be used particularly suitably for capacitor applications. The stretched film of the present invention is even more preferably 5 μm or more in thickness.

[0074] The stretched film of the present invention exhibits an infrared absorption spectrum of 880-890 cm⁻¹. －１ Absorption peaks are observed in the range, and at 1450 cm. －１ It is preferable that the stretched film has at least one of the shoulder peaks due to absorption in the vicinity. In this case, the stretched film can have a higher dielectric breakdown strength even in high-temperature environments of 120°C or higher, and the change in dielectric breakdown strength is also likely to be smaller. The stretched film of the present invention has an infrared absorption spectrum of 880 to 890 cm⁻¹. －１ Absorption peaks are observed in the range, and at 1450 cm. －１ It is more preferable to have both a shoulder peak due to absorption in the vicinity.

[0075] 880-890 cm －１ Absorption peaks in the range of and / or 1450 cm －１ To obtain a shoulder peak due to absorption in the vicinity, for example, the composition ratio of each component in the polypropylene resin used to form the stretched film can be adjusted. For example, the characteristic infrared absorption peak of the polymer having the alicyclic structure described later is 880-890 cm². －１ The range, and / or 1450 cm －１ Because it is present in the vicinity, it is preferable that the polypropylene resin contains a polymer component having the alicyclic structure. For example, the content of the polymer component having the alicyclic structure described below in the polypropylene resin for forming a stretched film should be adjusted to 6% by mass or more, preferably 10% by mass or more.

[0076] In the stretched film of the present invention, the V140 / V25 value is preferably 0.75 or higher, more preferably 0.78 or higher, even more preferably 0.79 or higher, and particularly preferably 0.80 or higher. The V140 / V25 value is usually 1 or less, preferably 0.99 or less, and more preferably 0.95 or less.

[0077] The stretched film of the present invention may have a single-layer structure or a multilayer structure in which multiple layers are laminated. If the stretched film has a multilayer structure, some or all of the layers may be different. In this case, at least one layer is a layer containing the polypropylene resin.

[0078] (Polypropylene Resin) Next, the polypropylene resin included in the stretched film of the present invention will be described. The stretched film of the present invention is formed using a polypropylene resin.

[0079] A wide variety of polypropylene resins can be included in the stretched film. In particular, it is preferable that the polypropylene resin contains at least an isotactic polypropylene resin and a heat-resistant resin having a high glass transition temperature, as this makes it easier to adjust the average value of the major axis of the unevenness and the density of the unevenness of the stretched film to a desired range. The heat-resistant resin having a high glass transition temperature can be crystalline or amorphous, but an amorphous resin is preferable in order to better demonstrate the effect of having a high glass transition temperature. In particular, it is preferable that the polypropylene resin contains an isotactic polypropylene resin and a polymer having an alicyclic structure. In this case, it is possible to have a higher dielectric breakdown strength even in high-temperature environments of 120°C or higher, and the change in dielectric breakdown strength tends to be smaller.

[0080] As described above, in the stretched film of the present invention, the polypropylene resin is preferably a resin (so-called blended resin) that includes an isotactic polypropylene resin and a polymer having an alicyclic structure.

[0081] <Isotactic Polypropylene Resin> For the isotactic polypropylene resin, for example, known isotactic polypropylenes can be widely used.

[0082] The melt mass flow rate (MFR) of the isotactic polypropylene resin is preferably 0.5 g / 10 min or more and 6 g / 10 min or less, more preferably 1 g / 10 min or more and 5 g / 10 min or less, and even more preferably 1.5 g / 10 min or more and 4 g / 10 min or less, as measured at 230°C and 2.16 kgf. In this case, appropriate resin fluidity is obtained when stretching the film, and the stretchability is improved.

[0083] The melting point of the isotactic polypropylene resin is preferably 155°C or higher. In this case, the electrical insulation and stretchability at high temperatures are improved. The melting point is more preferably 160°C to 180°C, and even more preferably 164°C to 175°C.

[0084] The mesopentad fraction of the isotactic polypropylene resin is preferably 95 mol% or more and 99.9 mol% or less. A fraction of 95 mol% or more tends to improve the rigidity and electrical insulation of the stretched film of the present invention, while a fraction of 99.9 mol% or less tends to improve the stretchability. The mesopentad fraction is more preferably 96 mol% or more and 99.5 mol%, even more preferably 96 mol% or more and 99 mol%, and particularly preferably 97 mol% or more and 98 mol%.

[0085] The heptane-insoluble content (HI) of the isotactic polypropylene resin is preferably 94% by mass or more and 99.9% by mass or less. If it is 94% by mass or more, the rigidity and electrical insulation of the stretched film tend to improve, and if it is 99.9% by mass or less, the stretchability tends to improve. The heptane-insoluble content is more preferably 96% by mass or more and 99.5% by mass or less, even more preferably 97% by mass or more and 99.2% by mass or less, and particularly preferably 98% by mass or more and 99% by mass or less.

[0086] The number-average molecular weight (Mn) of the isotactic polypropylene resin is preferably between 30,000 and 70,000, and more preferably between 35,000 and 65,000. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention tend to improve.

[0087] The weight-average molecular weight (Mw) of the isotactic polypropylene resin is preferably between 250,000 and 500,000, and more preferably between 300,000 and 450,000. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention tend to improve.

[0088] The molecular weight distribution (Mw / Mn) of the isotactic polypropylene resin is preferably 3 or more and 12 or less, more preferably 5 or more and 10 or less, and even more preferably 5.5 or more and 9.5 or less. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention are easily improved.

[0089] The z-average molecular weight (Mz) of the isotactic polypropylene resin is preferably between 700,000 and 3,000,000, and more preferably between 1,000,000 and 2,500,000. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention tend to improve.

[0090] The Mz / Mw of the isotactic polypropylene resin is preferably 2 to 7, more preferably 2.5 to 6, and even more preferably 3 to 5. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention tend to improve.

[0091] Isotactic polypropylene resin can be manufactured, for example, by known methods, or it can be obtained from the market.

[0092] Polymerization methods for obtaining isotactic polypropylene resins include, for example, gas-phase polymerization, bulk polymerization, and slurry polymerization. Polymerization may be a single-step polymerization using one polymerization reactor, or a multi-step polymerization using two or more polymerization reactors. Hydrogen or comonomers may also be added to the reactor as molecular weight modifiers during polymerization. Conventional known Ziegler-Natta catalysts or metallocene catalysts can be used as polymerization catalysts, and the polymerization catalysts may contain co-catalyst components or donors. The mesopentade fraction, melt mass flow rate, molecular weight, and molecular weight distribution of the polypropylene resin can be controlled by appropriately adjusting the polymerization catalyst and other polymerization conditions.

[0093] The polypropylene resin may contain one or more isotactic polypropylene resins.

[0094] Furthermore, when the polypropylene resin includes isotactic polypropylene resin, the X-ray diffraction intensity measurement of the stretched film reveals diffraction peaks from the (110) plane originating from the α-crystal of the isotactic polypropylene mentioned above.

[0095] <Polymers with Alicyclic Structures> Polymers with alicyclic structures are polymers that have alicyclic structures in their main chain or side chains. Typically, the alicyclic structure exists covalently bonded to the main chain or side chains.

[0096] An alicyclic structure is defined as comprising one or more saturated and / or unsaturated carbon ring structures that do not possess aromaticity. There may be two or more such carbon ring structures. The carbon ring structures may have branching aliphatic hydrocarbon structures. The carbon ring structures are bonded directly or via hydrocarbon chains to the hydrocarbon chains of the polymer backbone.

[0097] Examples of the aforementioned carbocyclic structures include cycloalkane structures such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, and cyclododecane, as well as cycloalkene structures such as cyclopropene, cyclobutene, cyclopropene, cyclohexene, cycloheptene, and cyclooctene. Examples of bicyclic structures include bicyclic alkane structures such as bicycloundecane, and bicyclic alkene structures such as norbornene and norbornadiene, which can be suitably used. In particular, having a carbocyclic structure with 4 to 8 carbon atoms is preferred from the viewpoint of extensibility, having a monocyclic carbocyclic structure with 4 to 8 carbon atoms is more preferred, having a monocyclic cycloalkane carbocyclic structure with 4 to 8 carbon atoms is even more preferred, and having a cyclohexane structure is particularly preferred.

[0098] The main chain of a polymer having an alicyclic structure can be mainly composed of aliphatic hydrocarbons. The aliphatic hydrocarbons in the polymer main chain may have branches of aliphatic hydrocarbon structures and / or aromatic hydrocarbon structures. The main chain of a polymer having an alicyclic structure may further contain the alicyclic structure, but it is preferable that the main chain does not have an alicyclic structure, and that it is contained in the side chains, in order to easily maintain high dielectric breakdown strength even in high-temperature environments of 120°C or higher. Therefore, it is preferable that a polymer having an alicyclic structure is a polymer in which the side chain has an alicyclic structure.

[0099] A polymer having an alicyclic structure in its side chain may be a homopolymer whose constituent units are structures having an alicyclic structure in its side chain. For example, it may be a polyvinylcycloolefin obtained by homopolymerizing vinylcycloolefins. Examples of polyvinylcycloolefins include polyvinylcyclopropane, polyvinylcyclobutane, polyvinylcyclopentane, polyvinylcyclohexane, polyvinylcycloheptane, polyvinylcyclooctane, polyvinylcyclononane, polyvinylcyclodecane, polyvinylcycloundecane, and polyvinylcyclododecane. In the case of a homopolymer, it is preferable that rigidity and electrical insulation properties tend to be high in high-temperature environments. Among these, polyvinylcyclopentane, polyvinylcyclohexane, and polyvinylcycloheptane are preferred, with polyvinylcyclohexane being the most preferred.

[0100] Another example of a polymer having an alicyclic structure in its side chain is a hydrogenated block copolymer. The type of hydrogenated block copolymer is not particularly limited, and for example, known hydrogenated block copolymers can be broadly mentioned. A hydrogenated block copolymer can be, for example, a copolymer obtained by hydrogenating a block copolymer having at least a vinyl aromatic polymer block and a conjugated diene polymer block. That is, a hydrogenated block copolymer is a copolymer having at least a hydrogenated vinyl aromatic polymer block and a hydrogenated conjugated diene polymer block. Hydrogenated block copolymers will be described below.

[0101] ≪Hydrogenated Vinyl Aromatic Polymer Block≫ The hydrogenated vinyl aromatic polymer block contains constituent units derived from vinyl aromatic compounds, which have been hydrogenated. The hydrogenated vinyl aromatic polymer block contains 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass, constituent units derived from vinyl aromatic compounds. By having 50% by mass or more of constituent units derived from vinyl aromatic compounds, rigidity and electrical insulation properties in high-temperature environments are easily improved.

[0102] Examples of vinyl aromatic compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, vinyltoluene, 1-vinylnaphthalene, and 2-vinylnaphthalene. The vinyl aromatic compound is preferably selected from styrene and α-methylstyrene, and more preferably styrene.

[0103] The hydrogenated vinyl aromatic polymer block may consist of only one of the vinyl aromatic compounds, or it may consist of two or more. The hydrogenated vinyl aromatic polymer block may contain other constituent units other than those derived from the vinyl aromatic compounds. Examples of other constituent units include those derived from isoprene, butadiene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene, and the like.

[0104] The content of the vinyl hydrogenated aromatic polymer block is preferably 50% by mass or more and less than 100% by mass, relative to 100% by mass of the total of the vinyl hydrogenated aromatic polymer block and the hydrogenated conjugated diene polymer block. A content of 50% by mass or more tends to increase rigidity and electrical insulation at high temperatures. More preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

[0105] ≪Hydrogenated Conjugated Diene Polymer Block≫ The hydrogenated conjugated diene polymer block contains constituent units derived from a conjugated diene, which has been hydrogenated. The hydrogenated conjugated diene polymer block contains 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass of constituent units derived from a conjugated diene.

[0106] Examples of conjugated dienes include butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-butadiene, 1,3-pentadiene, and 1,3-hexadiene. The conjugated diene is preferably selected from butadiene and isoprene, and more preferably butadiene.

[0107] The hydrogenated conjugated diene polymer block may contain structural units derived from a conjugated diene without side chains. Examples of conjugated dienes without side chains include butadiene, 1,3-pentadiene, and 1,3-hexadiene. Butadiene is preferred as the conjugated diene without side chains.

[0108] In hydrogenated conjugated diene polymer blocks, the bonding configuration of the conjugated dienes, i.e., the microstructure, is not particularly limited. For example, butadiene can have 1,2-bonds and 1,4-bonds. Isoprene can have 1,2-bonds, 3,4-bonds, and 1,4-bonds. Only one of these bonding configurations may be present, or two or more may be present. If two or more bonding configurations are present, the proportion of each configuration is not particularly limited.

[0109] Hydrogenated conjugated diene polymer blocks may contain other constituent units besides those derived from conjugated dienes. Examples of other constituent units include those derived from styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, vinyltoluene, 1-vinylnaphthalene, 2-vinylnaphthalene, and the like.

[0110] The content of the hydrogenated conjugated diene polymer block is preferably more than 0% by mass (e.g., 1% by mass or more) and 50% by mass or less, based on 100% by mass of the total of the hydrogenated vinyl aromatic polymer block and the hydrogenated conjugated diene polymer block. A content of 50% by mass or less is preferable because it tends to increase rigidity and electrical insulation at high temperatures. More preferably, it is 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less.

[0111] ≪Hydrogenation Rate≫ In the hydrogenated vinyl aromatic polymer block according to this embodiment, the hydrogenation rate of the aromatic ring of the hydrogenated vinyl aromatic polymer block is preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, particularly preferably 90 mol% or more, and even more preferably 95 mol% or more. The hydrogenation rate may be 100 mol%. Furthermore, the hydrogenation rate of the carbon-carbon double bond derived from the conjugated diene in the hydrogenated conjugated diene polymer block is preferably 90 mol% or more, more preferably 95 mol% or more. The hydrogenation rate may be 100 mol%.

[0112] By setting the hydrogenation rate of the aromatic rings in the vinyl hydrogenated aromatic polymer block and / or the hydrogenation rate of the carbon-carbon double bonds derived from the conjugated diene in the hydrogenated conjugated diene polymer block within the above-mentioned range, the stretchability is improved, and the glass transition temperature (Tg) tends to be 100°C or higher, which is preferable.

[0113] ≪Bonding patterns of hydrogenated block copolymers≫ The bonding patterns of polymer blocks in hydrogenated block copolymers may be linear, branched, or radial, or a combination thereof.

[0114] For example, if we represent a hydrogenated vinyl aromatic polymer block as "X" and a hydrogenated conjugated diene polymer block as "Y", the bonding modes include diblock copolymers (X-Y), triblock copolymers (X-Y-X), tetrablock copolymers (X-Y-X-Y), and pentablock copolymers (X-Y-X-Y-X, or Y-X-Y-X-Y). From the viewpoint of ease of manufacture, the bonding modes are preferably diblock copolymers, triblock copolymers, or tetrablock copolymers.

[0115] Specific examples of hydrogenated block copolymers include hydrogenated block copolymers obtained by hydrogenating styrene-isoprene diblock copolymer (SI), styrene-butadiene diblock copolymer (SB), styrene-isoprene-styrene triblock copolymer (SIS), styrene-butadiene / isoprene-styrene triblock copolymer (SB / IS), and styrene-butadiene-styrene triblock copolymer (SBS), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), and styrene-butylene-butadiene-styrene copolymer (SBBS). Among these, hydrogenated block copolymers obtained by hydrogenating styrene-butadiene diblock copolymer (SB) are particularly preferred.

[0116] ≪Method for Producing Hydrogenated Block Copolymers≫ The method for producing hydrogenated block copolymers is not particularly limited, and known methods such as anionic polymerization can be used. Specifically, hydrogenated block copolymers can be produced by a polymerization reaction using an alkyllithium compound as an initiator to sequentially polymerize a vinyl aromatic compound and a conjugated diene; a method using an alkyllithium compound as an initiator to sequentially polymerize a vinyl aromatic compound and a conjugated diene, and then adding a coupling agent for coupling; or a method using a dilithium compound as an initiator to sequentially polymerize a conjugated diene, and then a vinyl aromatic compound, followed by a hydrogenation reaction.

[0117] Examples of alkyllithium compounds include methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, and pentyllithium.

[0118] Examples of coupling agents include polyvalent epoxy compounds such as divinylbenzene, epoxidized 1,2-polybutadiene, epoxidized soybean oil, and 1,3-bis(N,N-glycidylaminomethyl)cyclohexane; halogen compounds such as dimethyldichlorosilane, dimethyldibromosilane, trichlorosilane, methyltrichlorosilane, tetrachlorosilane, and tetrachlorotin; ester compounds such as methyl benzoate, ethyl benzoate, phenyl benzoate, diethyl oxalate, diethyl malonate, diethyl adipate, dioctyl adipate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate, and dimethyl terephthalate; carbonate ester compounds such as dimethyl carbonate, diethyl carbonate, and diphenyl carbonate; and alkoxysilane compounds such as dimethyldimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, bis(trimethoxysilyl)hexane, and bis(triethoxysilyl)ethane.

[0119] Examples of dilithium compounds include naphthalenedithium and dilithiohexylbenzene.

[0120] The polymerization reaction is preferably carried out in the presence of a solvent. The solvent is not particularly limited as long as it is inert to the initiator and does not adversely affect the reaction. Examples include saturated aliphatic hydrocarbons such as hexane, cyclohexane, heptane, octane, and decane; and aromatic hydrocarbons such as toluene, benzene, and xylene. The polymerization reaction temperature is usually preferably 0 to 100°C, more preferably 30 to 90°C, even more preferably 40 to 80°C, and particularly preferably 50 to 80°C, from the viewpoint of microstructure control. The polymerization reaction time is preferably 0.5 to 50 hours, from the viewpoint of microstructure control.

[0121] Furthermore, Lewis bases may be used as co-catalysts during polymerization reactions. Examples of Lewis bases include ethers such as dimethyl ether, diethyl ether, and tetrahydrofuran; glycol ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and amines such as triethylamine, N,N,N',N'-tetramethylethylenediamine, and N-methylmorpholine. These Lewis bases may be used individually or in combination of two or more.

[0122] The hydrogenation reaction may be carried out immediately after the polymerization reaction, or it may be carried out after the block copolymer has been isolated following the polymerization reaction.

[0123] To isolate a block copolymer after a polymerization reaction, the polymerization reaction solution obtained after the polymerization reaction can be poured into a poor solvent for the block copolymer, such as methanol, to solidify the block copolymer. Alternatively, the polymerization reaction solution can be poured into hot water along with steam to remove the solvent by azeotropic removal (steam stripping), and then the block copolymer can be isolated by drying.

[0124] The hydrogenation reaction of block copolymers can be carried out, for example, by reacting them for 0.1 to 100 hours under conditions of a reaction temperature of 20 to 200°C and a hydrogen pressure of 0.1 to 20 MPa in the presence of a hydrogenation catalyst.

[0125] Examples of hydrogenation catalysts include Raney nickel; heterogeneous catalysts in which metals such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and nickel (Ni) are supported on carriers such as carbon, alumina, and diatomaceous earth; Ziegler catalysts consisting of combinations of transition metal compounds (nickel octoate, nickel naphthenate, nickel acetylacetonate, cobalt octoate, cobalt naphthenate, cobalt acetylacetonate, etc.) and organoaluminum compounds such as triethylaluminum and triisobutylaluminum, or organolithium compounds; and metallocene catalysts consisting of combinations of bis(cyclopentadienyl) compounds of transition metals such as titanium, zirconium, and hafnium and organometallic compounds consisting of lithium, sodium, potassium, aluminum, zinc, or magnesium.

[0126] When the hydrogenation reaction is carried out immediately following the polymerization reaction, the hydrogenated block copolymer can be isolated by pouring the hydrogenation reaction solution into a poor solvent for the hydrogenated block copolymer, such as methanol, and allowing it to solidify, or by pouring the hydrogenation reaction solution into hot water with steam to remove the solvent by azeotrope (steam stripping), followed by drying.

[0127] <Polymers having an alicyclic structure in the main chain> In polymers having an alicyclic structure, the alicyclic structure may be present in the main chain. As polymers having an alicyclic structure in the main chain, known cycloolefin copolymers (so-called COCs) can be widely applied, for example. Specifically, a polymer in which an alkylene skeleton is the main chain and a part of the alkylene is replaced with an alicyclic structure can be given as an example. The alkylene skeleton may be, for example, an ethylene unit (-CH ２ -CH ２ -) is one example.

[0128] A specific example of a polymer having an alicyclic structure in its main chain is a polymer of norbornene and ethylene. In this case, the polymer having an alicyclic structure in its main chain is a polymer in which an alicyclic structure derived from norbornene is introduced into the polyethylene main chain. Polymers having an alicyclic structure in their main chain can be manufactured by known methods or obtained from commercially available products. Examples of commercially available polymers having an alicyclic structure in their main chain include the "Topas (registered trademark) COC" series from Polyplastics Co., Ltd., such as "COC6013F-04" (glass transition temperature Tg of 137°C) and "COC8007F-04" (Tg of 76°C).

[0129] <Preferred Embodiments of Polymers Having an Alicyclic Structure> As described above, polymers having an alicyclic structure may be homopolymers or copolymers. When the polymer having an alicyclic structure is a homopolymer, it is preferable that such polymer is a hydrogenated polymer, a so-called hydrogenated polymer. When the polymer having an alicyclic structure in its side chain is a hydrogenated polymer, a specific example is hydrogenated polystyrene (for example, polyvinylcyclohexane). The stereoregularity of the hydrogenated polystyrene may be isotactic, syndiotactic, or atactic, but in order to better demonstrate the effect of having a high glass transition temperature, it is more preferable that it be an atactic amorphous resin.

[0130] When the polymer having the alicyclic structure contains hydrogenated polystyrene, it has high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and moreover, it easily imparts excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher. The hydrogenated polystyrene preferably has an atactic structure and a hydrogenation rate of 95% or more.

[0131] When the polymer having an alicyclic structure is a copolymer, a block copolymer having at least a vinyl aromatic polymer block and a conjugated diene polymer block is preferred, and a hydrogenated block copolymer obtained by hydrogenating a styrene-butadiene diblock copolymer (SB) is particularly preferred.

[0132] The glass transition temperature (Tg) of a polymer having an alicyclic structure is preferably, for example, 100°C to 180°C. Setting the glass transition temperature to 100°C or higher tends to increase rigidity and electrical insulation at high temperatures, while setting it to 180°C or lower can improve stretchability. The glass transition temperature is more preferably 120°C to 165°C, more preferably 130°C to 160°C, and particularly preferably 140°C to 155°C.

[0133] In particular, polymers having an alicyclic structure preferably contain two or more polymers with different glass transition temperatures.

[0134] In this case, it is preferable that the polymer having an alicyclic structure includes polymer B1 having an alicyclic structure with a glass transition temperature of 133°C to 155°C and polymer B2 having an alicyclic structure with a glass transition temperature of 70°C to less than 133°C. In this case, heat resistance is improved by B1, and compatibility between polypropylene and B1 is increased by B2, resulting in high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and also making it easier to impart excellent dielectric strength to capacitor elements at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher. Hereinafter, polymer B1 having an alicyclic structure with a glass transition temperature of 133°C to 155°C will be abbreviated as "polymer B1", and polymer B2 having an alicyclic structure with a glass transition temperature of 70°C to less than 133°C will be abbreviated as "polymer B2".

[0135] The glass transition temperature of polymer B1 is preferably 135°C or higher. Furthermore, the glass transition temperature of polymer B2 is preferably 80°C or higher, more preferably 90°C or higher, even more preferably 100°C or higher, and particularly preferably 110°C or higher.

[0136] The mass ratio of polymer B2 to polymer B1, B2 / B1 (where B2 represents the content (parts by mass) of polymer B2 in a polymer having an alicyclic structure, and B1 represents the content (parts by mass) of polymer B1 in a polymer having an alicyclic structure), is not particularly limited. For example, it is preferable that the mass ratio of polymer B2 to polymer B1, B2 / B1, is less than 0.85. In this case, the compatibility between polymer B1 and polymer B2 is increased, which results in a particularly high dielectric strength at room temperature, and moreover, it is easier to impart excellent dielectric strength to the capacitor element even at room temperature (e.g., 25°C) and high-temperature environments of 120°C or higher. B2 / B1 is preferably 0.80 or less, more preferably 0.75 or less, even more preferably 0.70 or less, particularly preferably 0.65 or less, and also preferably 0.10 or more, more preferably 0.20 or more, even more preferably 0.25 or more, and particularly preferably 0.30 or more.

[0137] Even when the polymer having an alicyclic structure includes polymer B1 and / or polymer B2, it is preferable that both polymer B1 and polymer B2 are the aforementioned hydrogenated polystyrene, block copolymer, etc. For example, a combination can be given in which polymer B1 is hydrogenated polystyrene and polymer B2 is a block copolymer (for example, a hydrogenated block copolymer obtained by hydrogenating a styrene-butadiene diblock copolymer).

[0138] The Vicat softening point (1 kg, 50°C / hr) of polymers having an alicyclic structure is preferably between 100°C and 170°C. Setting the Vicat softening point above 100°C tends to increase rigidity and electrical insulation at high temperatures, while setting it below 170°C improves stretchability. A Vicat softening point of 120°C to 165°C is more preferable, 130°C to 160°C is even more preferable, and 140°C to 155°C is particularly preferable.

[0139] The glass transition temperature (Tg) and Vicat softening point of polymers having an alicyclic structure can be adjusted by the type of constituent unit having an alicyclic structure in the side chain, or by the type and ratio of one or more other constituent units.

[0140] The weight-average molecular weight (Mw) of the polymer having an alicyclic structure is preferably, for example, 50,000 to 400,000. In this case, the rigidity, electrical insulation, and stretchability of the stretched film of the present invention are easily improved.

[0141] The melt mass flow rate (MFR) of a polymer having an alicyclic structure is preferably 1 g / 10 min or more and 40 g / 10 min or less, more preferably 2 g / 10 min or more and 20 g / 10 min or less, and even more preferably 3 g / 10 min or more and 15 g / 10 min or less, as measured at 260°C and 2.16 kgf. In this case, appropriate resin fluidity is obtained when stretching the film, and the stretchability is easily improved.

[0142] Polymers having an alicyclic structure can be manufactured, for example, by known methods, or can be obtained from the market. An example of a commercially available product is ViviOn® (manufactured by USI Corporation).

[0143] Polypropylene resins may contain polymers having one or more alicyclic structures.

[0144] <Method for producing polymers having an alicyclic structure> The method for producing polymers having an alicyclic structure is not particularly limited and can be produced using known methods such as radical polymerization, ionic polymerization (anionic polymerization, coordination anionic polymerization, etc.), bulk polymerization, solution polymerization, suspension polymerization, etc. Specifically, polymers having an alicyclic structure can be produced by carrying out a polymerization reaction using known initiators such as alkyllithium compounds and dilithium compounds to sequentially polymerize monomers having an alicyclic structure (e.g., vinylcycloolefins); or by sequentially polymerizing monomers having an alicyclic structure and then adding a coupling agent to perform coupling.

[0145] In particular, polymers having an alicyclic structure in their side chains can be produced by polymerizing a monomer having an aromatic ring structure (e.g., styrene) by a known method, followed by a hydrogenation reaction. The hydrogenation reaction can be carried out, for example, by the method described later in the method for producing hydrogenated block copolymers.

[0146] When a hydrogenation reaction is carried out, the hydrogenation rate to the aromatic ring structure is preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, particularly preferably 90 mol% or more, and even more preferably 95 mol% or more. The hydrogenation rate may also be 100 mol%. It is preferable to set the hydrogenation rate within the above range because it improves the stretchability while also tending to result in a glass transition temperature (Tg) of 100°C or higher.

[0147] A polymer having an alicyclic structure may be, for example, a copolymer having structural units with an alicyclic structure in their side chains and one or more other structural units. The copolymer may be a random copolymer or a block copolymer having at least two polymer blocks. From the viewpoint of stretchability, copolymers are preferred, and block copolymers are more preferred. Examples of other structural units include ethylene, propylene, butene, pentene, hexene, heptene, octene, etc., and may or may not have side chains. It may also contain both structural units with side chains and structural units without side chains. Examples of structural units with side chains include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, etc. The other structural units may be unsaturated hydrocarbons, but saturated hydrocarbons are preferred from the viewpoint of electrical insulation.

[0148] When a polymer having an alicyclic structure contains propylene as another constituent unit, the propylene content in the polymer is less than 50% by mass, preferably 20% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the polymer.

[0149] Polymers having an alicyclic structure can be obtained, for example, by polymerizing monomers having their respective constituent units using known methods. Furthermore, if the side chain has an aromatic ring structure, a polymer with an alicyclic structure in the side chain can be obtained by hydrogenation. Hydrogenation of polymers with aromatic ring structures in the side chain allows for the industrially inexpensive production of polymers with an alicyclic structure in the side chain.

[0150] <Polypropylene Resin> The polypropylene resin contained in the stretched film of the present invention preferably contains the isotactic polypropylene resin described above and the polymer having the alicyclic structure described above, more preferably containing the isotactic polypropylene resin and hydrogenated polystyrene (e.g., polyvinylcyclohexane), and even more preferably containing the isotactic polypropylene resin and hydrogenated polystyrene (polyvinylcyclohexane) having an atactic structure and a hydrogenation rate of 95% or more. Furthermore, the polypropylene resin contained in the stretched film of the present invention may contain the isotactic polypropylene resin and the block copolymer, or it may contain the isotactic polypropylene resin and the polymer B1 and the polymer B2.

[0151] When the polypropylene resin contains an isotactic polypropylene resin and the polymer having the aforementioned alicyclic structure, it is preferable that the isotactic polypropylene resin is present in an amount of 80% to 99% by mass and the polymer having the alicyclic structure is present in an amount of 1% to 20% by mass relative to the total mass of the polypropylene resin. In this case, it is easier to adjust the average value of the major axis of the irregularities and the density of the irregularities to a desired range. Furthermore, the range of the polymer having the alicyclic structure, which is a high heat-resistant component, becomes more appropriate, and the orientation of the film tends to be within a good range. As a result, it is possible to have particularly high dielectric breakdown strength even in high-temperature environments of 120°C or higher, and the change in dielectric breakdown strength tends to be particularly small. In addition, the dielectric strength of the capacitor element in high-temperature environments tends to be improved.

[0152] The polypropylene resin more preferably contains 83% by mass or more of isotactic polypropylene resin, even more preferably 85% by mass or more, even more preferably 87% by mass or more, and more preferably 97% by mass or less, and even more preferably 95% by mass or less.

[0153] The polypropylene resin more preferably contains 3% by mass or more of a polymer having an alicyclic structure, even more preferably 5% by mass or more, even more preferably 17% by mass or less, and even more preferably 15% by mass or less. In these cases as well, the polymer having an alicyclic structure may preferably be, for example, hydride polystyrene (polyvinylcyclohexane) or the block copolymer, or the polymer having an alicyclic structure may include polymer B1 and polymer B2.

[0154] Polypropylene resins may include other resins besides isotactic polypropylene resins and polymers having an alicyclic structure. Examples of other resins include polyolefin resins and copolymer resins thereof, such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), and poly(4-methyl-1-pentene), such as ethylene-propylene copolymers, propylene-butene copolymers, ethylene-butene copolymers, and ethylene-(4-methyl-1-pentene) copolymers, such as copolymers of α-olefins. Other examples include polystyrene resins, elastomers, polyvinyl resins, polyester resins, polyurethane resins, nylon resins, and copolymers thereof. Commercially available resins may be used as other resins, for example, Tuffmer® (manufactured by Mitsui Chemicals, Inc.) is an example of a copolymer of α-olefins and can be suitably used for the aforementioned purposes.

[0155] The polypropylene resin preferably contains 90% by mass or more of isotactic polypropylene resin and polymers having an alicyclic structure, more preferably 95% by mass or more, and even more preferably 99% by mass or less. The polypropylene resin also preferably does not contain any resins other than isotactic polypropylene resin and polymers having an alicyclic structure.

[0156] If the polypropylene resin includes isotactic polypropylene resin and a polymer having an alicyclic structure, the average value of the major axis of the surface irregularities is 150 μm or less, or the density of the surface irregularities is 30 irregularities / mm². ２ The above is easy to fulfill.

[0157] When polypropylene resins contain isotactic polypropylene resin and polymers with alicyclic structures, they may exhibit a clear peak in the loss tangent (tanδ) in the region above 140°C. Such a peak is the main dispersion peak and may correspond to the glass transition temperature (Tg) of the polymer with an alicyclic structure (e.g., hydride polystyrene). This peak becomes clearer as the content of the polymer with an alicyclic structure (e.g., hydride polystyrene) increases. At the same time, the gentle bulge around 100°C present in polypropylene (100% polypropylene) (which may correspond to lattice relaxation in typical isotactic polypropylene) is lost with the addition of polymers with alicyclic structures because molecular mobility due to lattice relaxation is suppressed. That is, the loss tangent (tanδ) at 100°C becomes more easily satisfied with a value of 0.15 or less.

[0158] While we do not necessarily desire a restrictive interpretation, the fact that the loss tangent (tanδ) at 100°C is easily less than 0.15, or that there is a peak in the loss tangent (tanδ) in the region above 140°C, may indicate that the isotactic polypropylene resin and the polymer having an alicyclic structure have a phase-separated structure upon mixing. The structure consisting of the isotactic polypropylene resin and the polymer having an alicyclic structure is by no means a brittle phase-separated structure, and this can be judged from the fact that the film is not cloudy, that it maintains a high Tg (the presence of the aforementioned main dispersion peak), that the loss tangent (tanδ) at 100°C is small, that the lattice relaxation motion of polypropylene is contained (motion suppression effect), and that the temperature dependence of the storage modulus is small and flat with respect to temperature.

[0159] When a polypropylene resin contains isotactic polypropylene resin and polymers having an alicyclic structure, the presence of polymers having an alicyclic structure can be confirmed, for example, by changes in the infrared absorption spectrum. In particular, changes in the infrared absorption spectrum are more likely to occur when the polymer having an alicyclic structure contains hydrogenated polystyrene.

[0160] When the polypropylene resin contains isotactic polypropylene resin and polymers having an alicyclic structure, dynamic viscoelasticity measurements suggest that a "phase separation structure" is formed. By forming such a "phase separation structure," the relaxation motion (molecular chain motion) of polypropylene that occurs at high temperatures can be suppressed. As a result, the decrease in dielectric strength at high temperatures can be suppressed, and the stretched film of the present invention has high dielectric strength even in high-temperature environments of 120°C or higher, and moreover, the change in dielectric strength at high temperatures compared to room temperature (e.g., 25°C) is small.

[0161] When the polypropylene resin contains isotactic polypropylene resin and polymers having an alicyclic structure, the ratio of dielectric breakdown strength (V140 / V25) can be closer to 1, and when it contains 10% by mass or more of polymers having an alicyclic structure, the V140 / V25 value becomes particularly close to 1.

[0162] While it is preferable in one embodiment that the polypropylene resin includes isotactic polypropylene resin and polymers having an alicyclic structure, the polypropylene resin may be composed of other resins, for example, propylene homopolymers such as syndiotactic polypropylene; copolymers of propylene and other olefins (e.g., ethylene, 1-butene, etc.) (the copolymer may be a random copolymer or a block copolymer having at least two polymer blocks); long-chain branched polypropylene; or polypropylene resin produced from plant-derived raw materials. In this case, the MFR, melting point, mesopentade fraction, heptane insoluble matter (HI), Mn, Mw, Mw / Mn, Mz, and Mz / Mw of the polypropylene resin can all be within the same range as the isotactic polypropylene resin described above.

[0163] (Other features of the stretched film of the present invention) The stretched film of the present invention can be obtained using the polypropylene resin described above. The stretched film of the present invention is stretched in at least one direction. Preferably, the stretched film of the present invention is a biaxially oriented film stretched in two directions. Preferably, such a biaxially oriented film is stretched in the MD (flow) direction and the TD (width) direction, respectively.

[0164] The stretched film of the present invention may also contain various additives, to the extent that the effects of the present invention are not impaired. Examples of additives include those found in stretched films used in known capacitor applications, such as antioxidants, necessary stabilizers such as chlorine absorbers and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, and colorants.

[0165] Examples of antioxidants include hindered phenol antioxidants. Among hindered phenol antioxidants, examples of hindered phenol antioxidants having a carbonyl group include triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (trade name: Irganox 245), 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 259), pentaerythrultyl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010), 2,2- Examples include o-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1035), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), and N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) (trade name: Irganox 1098), but pentaerythrutyl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which has excellent heat resistance, is particularly preferred. All Irganox® products are manufactured by BASF Japan Ltd.

[0166] When the stretched film of the present invention contains an antioxidant, the amount is preferably 1,000 ppm by mass or more and 7,000 ppm by mass or less, and more preferably 2,000 ppm by mass or more and 6,000 ppm by mass or less, relative to the total mass of the stretched film. In general, the amount of the hindered phenol antioxidant remaining after the extrusion process during the stretched film formation process is 60 to 80% by mass of the above-mentioned content, as some of it is oxidized and decomposed during the extrusion process.

[0167] The stretched film of the present invention can be applied to capacitor applications, as well as various other applications such as packaging and separator applications. In particular, the stretched film of the present invention can be suitably used in capacitor applications, and is suitable for use in high-temperature environments of 120°C or higher, and is extremely suitable for small and high-capacitance capacitors (for example, 5 μF or more, preferably 10 μF or more, and even more preferably 20 μF or more).

[0168] The method for producing the stretched film of the present invention is not particularly limited. For example, the stretched film of the present invention can be produced by manufacturing a cast raw material sheet (unstretched film) using the polypropylene resin and then stretching the cast raw material sheet.

[0169] If the polypropylene resin includes an isotactic polypropylene resin and a polymer having an alicyclic structure, it can be obtained by mixing each resin in a predetermined ratio. For example, melt blending can be used as a mixing method. The polypropylene resin may be subjected to drying treatment or the like as needed.

[0170] The method for manufacturing the cast raw material sheet (unstretched film) is not particularly limited, and a wide range of known methods can be employed. For example, the cast raw material sheet can be manufactured by melt-kneading a polypropylene resin and then extruding it. As for the melt-kneading method, a single-screw type, twin-screw type, or multi-screw type melt-kneader can be used. The melt-kneading temperature (melting temperature) is preferably 200°C to 270°C, and more preferably 220°C to 260°C, as it allows for easy adjustment of the average value of the major axis of the unevenness and the density of the unevenness to a desired range. During melt-kneading, it is preferable to purge the kneader with an inert gas such as nitrogen to suppress the deterioration of the resin.

[0171] The extrusion molding method is not particularly limited; for example, a cast raw material sheet (unstretched film) can be obtained by extruding a molten and kneaded polypropylene resin into a film extruder. The extrusion molding method is not particularly limited, and known extrusion molding methods can be used. The molten and kneaded polypropylene resin may be filtered beforehand. The temperature during extrusion molding is not particularly limited, for example, 200 to 300°C, preferably 210 to 280°C, more preferably 215 to 270°C, and even more preferably 220 to 260°C.

[0172] Extruded, molten polypropylene resin can be cooled using cooling rolls such as metal drums. Typically, the surface that comes into contact with the cooling rolls becomes rougher, resulting in a greater surface roughness than the surface that does not come into contact with the cooling rolls.

[0173] The cooling roll surface temperature (metal drum surface temperature) is preferably 80 to 100°C, as this makes it easier to adjust the average value of the major axis of the unevenness and the density of the unevenness to a desired range. If the cooling roll surface temperature (metal drum surface temperature) falls below 80°C, it may become difficult to adjust the average value of the major axis of the unevenness and the density of the unevenness to a desired range.

[0174] The above procedure yields a cast raw material sheet. The thickness of the cast raw material sheet is not particularly limited, but is, for example, 20 to 300 μm.

[0175] The stretched film of the present invention can be obtained by stretching a cast raw material sheet. The stretching method is not particularly limited, and examples include: a method of stretching the cast raw material sheet in the longitudinal direction (flow direction, MD) by heating it with a heating roll (longitudinal uniaxial roll stretching method); a method of stretching the cast raw material sheet in the transverse direction (width direction, TD) in an oven at a predetermined temperature (generally called a tenter) (transverse uniaxial stretching method); a method of performing transverse uniaxial stretching after longitudinal uniaxial roll stretching (sequential biaxial stretching method); a method of performing transverse uniaxial stretching after longitudinal uniaxial roll stretching, and then longitudinal uniaxial (roll or tenter method) stretching (multi-stage sequential biaxial stretching method); a method of sequentially stretching the cast raw material sheet longitudinally and transversely in a tenter at a predetermined temperature (tenter method sequential biaxial stretching method); a method of simultaneously stretching the cast raw material sheet longitudinally and transversely in a tenter (simultaneous biaxial stretching method); and so on. As for the stretching method, a method in which longitudinal uniaxial roll stretching is followed by transverse uniaxial stretching (sequential biaxial stretching method) is preferable because it provides excellent rigidity, electrical insulation, and stretchability of the stretched film.

[0176] One example of a sequential biaxial stretching method is to maintain a cast raw material sheet at a temperature of approximately 100 to 180°C (longitudinal stretching temperature), pass it between rolls with a speed difference to stretch it 3 to 7 times (longitudinal stretching ratio) in the flow direction, and immediately cool it to room temperature. After cooling, the stretched film is guided to a tenter and stretched at a stretching angle of 5 to 17° (transverse stretching angle) at a temperature of 150°C or higher (transverse stretching temperature) to approximately 3 to 11 times (transverse stretching ratio) in the width direction, after which it can be relaxed, heat-set, and wound up. The wound film can be aged in an atmosphere of approximately 20 to 45°C and then cut to the desired product width. The transverse stretching angle is defined as the angle between a straight line Lx connecting one edge Px in the width direction of the stretched film at the start of the transverse stretching process and the other edge Py (on the same side as Px) in the width direction of the stretched film at the end of the transverse stretching process, and a straight line Ly that starts at Px and is parallel to the extrusion direction.

[0177] The resulting stretched film may be subjected to corona treatment, electrostatic discharge treatment, heating treatment, etc. Appropriate implementation of corona treatment, electrostatic discharge treatment, heating treatment, etc. can improve passability to the vapor deposition process. The heating treatment temperature is preferably 20°C to 80°C, more preferably 25°C to 60°C, and even more preferably 30°C to 55°C. The heating treatment time is preferably 3 hours to 50 hours, and more preferably 6 hours to 30 hours.

[0178] 2. Metal Laminate Film / Film Capacitor The stretched film of the present invention may have a metal layer on one or both sides thereof. That is, a metal laminate film having a metal layer on one or both sides of the stretched film can be obtained using the stretched film of the present invention.

[0179] In a metal laminated film, the metal film can act as an electrode. Examples of the metal film include metal foil, paper with at least one side metallized, and plastic film with at least one side metallized. The metal can be a single metal such as zinc, lead, silver, chromium, aluminum, copper, and nickel, a mixture of several of these, or an alloy thereof. However, considering the environment, economy, and capacitor performance, zinc and aluminum are preferred.

[0180] The metal film can be formed, for example, by vacuum deposition and sputtering, and vacuum deposition is preferred from the viewpoint of productivity and economic efficiency. Vacuum deposition methods generally include the crucible method and the wire method.

[0181] The film resistance of the metal film is preferably about 1 to 100 Ω / □, more preferably 5 Ω / □ or higher, and even more preferably 10 Ω / □ or higher, from the viewpoint of the electrical characteristics of the capacitor. Furthermore, from the viewpoint of safety as a capacitor, the film resistance of the metal film is more preferably 50 Ω / □ or lower, and even more preferably 30 Ω / □ or lower. The film resistance of the metal film can be measured during metal deposition, for example, by the four-terminal method known to those skilled in the art. The film resistance of the metal film can be adjusted, for example, by adjusting the output of the evaporation source to adjust the evaporation rate. For the sake of clarity, in this specification, the unit "Ω / □" means "Ω / square".

[0182] When forming a metal film on one side of the film, an insulating margin is formed from one end of the film without deposition for a certain width, so that the film acts as a capacitor when wound. Furthermore, to strengthen the bond between the metal laminated film and the metallicon electrode, it is preferable to form a heavy edge structure at the end opposite the insulating margin. The film resistance of the heavy edge is usually about 1 to 8 Ω / □, and preferably about 1 to 5 Ω / □. The thickness of the metal film is not particularly limited, but for example, 1 to 200 nm is preferred.

[0183] There are no particular restrictions on the margin pattern, and from the standpoint of improving characteristics such as the safety of the capacitor, patterns including so-called special margins such as fishnet patterns and T-margin patterns can be used. As for the method of forming the margin, any known method can be used without any restrictions, such as the tape method, which involves masking with tape during vapor deposition, or the oil method, which involves masking by applying oil.

[0184] The metal laminated film can be processed into the capacitor of the present invention, as described later, by winding it along the longitudinal direction of the film. Specifically, two metal laminated films are stacked as a pair, with the metal vapor-deposited film and polypropylene film alternately laminated and wound together. Then, a pair of metal-coated electrodes are formed on both end surfaces by thermal spraying to produce a film capacitor.

[0185] A capacitor can be manufactured using the above-mentioned metal laminated film for capacitors. As long as the capacitor includes the above-mentioned metal laminated film for capacitors, its other components are not particularly limited; for example, it can have a configuration similar to that of a known capacitor.

[0186] Since the capacitor described above is equipped with the stretched film of the present invention, it can have a high dielectric breakdown voltage, and moreover, the change in dielectric breakdown strength under high-temperature environments is small compared to the dielectric breakdown strength at room temperature (e.g., 25°C). Therefore, even when a voltage of, for example, 200 (Vdc / μm) is continuously applied to the capacitor at a high temperature of 135°C or higher, it will not short circuit and can maintain its insulation and capacitance for more than 500 hours. In other words, the capacitor does not short circuit at 135°C and exhibits little decrease in capacitance even under continuous voltage load.

[0187] The capacitor of the present invention, utilizing the stretched film of the present invention, is suitable for use in high-temperature environments and can be made into a small and high-capacitance capacitor (for example, 5 μF or more, preferably 10 μF or more, and even more preferably 20 μF or more). Therefore, the capacitor of the present invention can be used in electronic equipment, electrical equipment, etc., as a high-voltage capacitor; various switching power supplies; filter capacitors and smoothing capacitors for converters, inverters, etc. Furthermore, the capacitor of the present invention can be suitably used as an inverter capacitor and converter capacitor for controlling drive motors in electric vehicles, hybrid vehicles, etc., for which demand has been increasing in recent years.

[0188] In specifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein.

[0189] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to the embodiments of these examples.

[0190] (1) Measurement Methods The various measurement methods are as follows:

[0191] (1-1) Mn, Mw, Mz, Mw / Mn, and Mz / Mw of isotactic polypropylene resin The number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mw) of isotactic polypropylene resin were measured using GPC (gel permeation chromatography) under the following conditions.

[0192] Specifically, a high-temperature GPC instrument with a built-in differential refractometer (RI), the HLC-8121GPC-HT model, manufactured by Tosoh Corporation, was used. Three TSKgel GMHHR-H(20)HT columns, also manufactured by Tosoh Corporation, were used in conjunction. Measurements were taken at a column temperature of 140°C, with trichlorobenzene flowing as the eluent at a flow rate of 1.0 ml / min. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to the molecular weight of polypropylene using the Q-factor to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). The molecular weight distribution (Mw / Mn) was obtained using the Mw and Mn values. The molecular weight distribution (Mz / Mw) was also obtained using the Mz and Mw values.

[0193] (1-2) Mesopentad fraction of isotactic polypropylene resin The isotactic polypropylene resin was dissolved in a solvent and measured using a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR) under the following conditions. High-temperature nuclear magnetic resonance (NMR) spectrometer: JEOL Ltd., high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR), JNM-ECP500 Observed nucleus: 13C (125 MHz) Measurement temperature: 135°C Solvent: Ortho-dichlorobenzene (ODCB: mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4 / 1)) Measurement mode: Single pulse proton broadband decoupling Pulse width: 9.1 μsec (45° pulse) Pulse interval: 5.5 sec Number of integrations: 4,500 Shift reference: CH3 (mmmm) = 21.7 ppm The mesopentad fraction, which represents the degree of stereoregularity, was calculated as a percentage (%) from the integral intensity values ​​of each signal derived from combinations of five pentads (mmmm, mrrm, etc.) consisting of pentads arranged in the same direction ("meso (m)") and pentads arranged in opposite directions ("racemo (r)"). For the assignment of each signal derived from mmmm, mrrm, etc., spectral descriptions such as "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" were consulted.

[0194] (1-3) Melt Mass Flow Rate (MFR) The melt flow rate (MFR) was measured in accordance with JIS K 7210-1:2014 using a melt indexer from Toyo Seiki Co., Ltd. Specifically, first, 4 g of raw material was inserted into a cylinder heated to the test temperature (230°C for isotactic polypropylene resin, and 260°C for polymers with an alicyclic structure), and preheated for 3.5 minutes under a load of 2.16 kgf. Then, the weight of the resin extruded from the bottom hole in 30 seconds was measured, and the MFR (g / 10 min) was determined. The above measurement was repeated three times, and the average value was taken as the measured value of MFR.

[0195] (1-4) Melting point and glass transition temperature The melting point and glass transition temperature were calculated using a Perkin-Elmer input-compensated DSC, DiamondDSC, following the procedure below. 5 mg of each resin was weighed out, packed into an aluminum sample holder, and set in the DSC apparatus. The temperature was increased from 30°C to 230°C at a rate of 20°C / min under a nitrogen flow, held at 230°C for 5 minutes, cooled to 30°C at a rate of 20°C / min, and held at 30°C for 5 minutes. The melting point and glass transition temperature were then determined from the DSC curve when the temperature was increased again to 230°C at a rate of 20°C / min. Specifically, the melting peak (the largest melting peak if multiple melting peaks are shown) as defined in JIS-K7121:1987 9.1(1) was used as the melting point, and the midpoint glass transition temperature as defined in JIS-K7121:1987 9.3(1) was used as the glass transition temperature.

[0196] (1-5) Heptane-insoluble content (HI) of polypropylene resin A sample of approximately 3 g was prepared for measurement by press-molding polypropylene resin to 10 mm x 35 mm x 0.3 mm. Next, approximately 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble content was calculated from the sample mass before and after extraction.

[0197] (2) In order to prepare the polypropylene resin for obtaining the stretched raw material film, the following isotactic polypropylene resin and polymer having an alicyclic structure were prepared. [A1; Isotactic Polypropylene Resin A1] As isotactic polypropylene resin A1, an isotactic polypropylene resin "Prime Polypro (registered trademark); manufactured by Prime Polymer Co., Ltd." having the following physical properties was prepared. In addition, 3500 ppm by mass of "Irganox 1010" manufactured by BASF Japan Ltd. was pre-mixed into isotactic polypropylene resin A1 as an antioxidant. MFR: 3.5 g / 10 min (measurement temperature 230°C, 2.16 kgf) Melting point: 164°C Mesopentadione fraction: 98.6 mol% Heptane insoluble matter: 98.1 mass% Number average molecular weight (Mn): 49000 Weight average molecular weight (Mw): 390000 Z average molecular weight (Mz): 1,520000 Molecular weight distribution (Mw / Mn): 8.0 Molecular weight distribution (Mz / Mw): 3.9

[0198] [B1; Polymer B1 having an alicyclic structure] As polymer B1 having an alicyclic structure, hydrogenated polystyrene "Vivion® 0645; manufactured by USI Corporation" having the following physical properties was prepared. Glass transition temperature: 143°C (measured by DSC) MFR: 5.5 g / 10 min (measurement temperature 260°C, 2.16 kgf) Such polymer is a polymer having an alicyclic structure with a cyclohexane structure in the side chain, and the cyclohexane structure is formed by hydrogenation of the aromatic ring structure, with a hydrogenation rate of 99 mol% or more.

[0199] [B2; Polymer B2 having an alicyclic structure] As polymer B1 having an alicyclic structure, "Vivion® 1325; manufactured by USI Corporation" having the following physical properties was prepared. Glass transition temperature: 128°C MFR: 13 g / 10 min (measurement temperature 260°C, 2.16 kgf) Polymer B2 is a polymer having an alicyclic structure with a cyclohexane structure in its side chain, and is a hydrogenated block copolymer obtained by hydrogenating a styrene-butadiene diblock copolymer, and is not a hydrogenated polystyrene polymer. The cyclohexane structure is formed by hydrogenation of the aromatic ring structure derived from styrene, and the other structures are formed by hydrogenation of the carbon-carbon double bond derived from butadiene, with a hydrogenation rate of 99 mol% or more.

[0200] (Example 1) The isotactic polypropylene resin A1 and the polymer B1 having an alicyclic structure were blended and mixed in amounts of 90% by mass and 10% by mass, respectively (i.e., A1:B1 = 90:10 by mass ratio) to prepare a raw material. After dry blending this raw material, it was supplied to a single-screw type film extruder (GM-50, L / D = 32, manufactured by GM Engineering Co., Ltd.) and melted at a melting temperature of 260°C. The molten raw material was extruded using a T-die, and then wrapped around a metal drum with a surface temperature maintained at 95°C to solidify, thereby producing a cast raw material sheet (unstretched film) with a thickness of approximately 96 μm. Subsequently, this cast raw material sheet was stretched four times in the flow direction at a temperature of 158°C, immediately cooled to room temperature, and then stretched eight times in the transverse direction at a temperature of 165°C using a tenter to obtain a biaxially oriented film with a thickness of 3 μm.

[0201] (Example 2) A biaxially oriented film was obtained in the same manner as in Example 1, except that the isotactic polypropylene resin A1 and the polymer B1 having the alicyclic structure were blended in amounts of 85% by mass and 15% by mass, respectively (i.e., the mass ratio A1:B1 = 85:15).

[0202] (Example 3) A biaxially oriented film with a thickness of 3 μm was obtained in the same manner as in Example 1, except that the isotactic polypropylene resin A1 and the polymers B1 and B2 having the alicyclic structure were blended in amounts of 92% by mass, 6% by mass, and 2% by mass, respectively (i.e., the mass ratio A1:B1:B2 = 92:6:2).

[0203] (Example 4) A biaxially oriented film with a thickness of 3 μm was obtained in the same manner as in Example 1, except that the isotactic polypropylene resin A1 and the polymers B1 and B2 having the alicyclic structure were blended in amounts of 86% by mass, 10% by mass, and 4% by mass, respectively (i.e., the mass ratio A1:B1:B2 = 86:10:4).

[0204] (Comparative Example 1) A biaxially oriented film was obtained in the same manner as in Example 1, except that only isotactic polypropylene resin A1 was used instead of polymer B1 having the alicyclic structure (i.e., mass ratio A1:B1 = 100:0).

[0205] (Comparative Example 2) A biaxially oriented film was obtained in the same manner as in Example 1, except that the isotactic polypropylene resin A1 and the polymer B1 having the alicyclic structure were blended in amounts of 95% by mass and 5% by mass, respectively (i.e., the mass ratio A1:B1 = 95:5).

[0206] (Comparative Example 3) A biaxially oriented film was obtained in the same manner as in Example 1, except that the melting temperature was changed to 220°C.

[0207] (Evaluation Method) <Atomic Force Microscopy Observation> Sample Preparation Samples for AFM observation were prepared using the following procedure. Forty stretched films, cut to 40 mm in the MD direction and 40 mm in the TD direction, were stacked on a 120 μm thick aluminum press frame with a 40 mm square hole in the center and left to stand. Hot pressing was performed for 1 hour at 165°C and 20 MPa to obtain a laminate of stretched films. In preparing this laminate, the thickness of the aluminum press frame or the number of layers was adjusted so that the thickness of the aluminum press frame and the thickness of the film laminate matched. Using the above laminate, a smooth surface (cut surface) was prepared by cutting in a direction perpendicular to the stacking direction (i.e., along the TD direction) at -120°C and 0.6 mm / s using an ultramicrotome (ULTRACUTS FCS, Leica). Next, the sample was fixed to the sample fixing jig using carbon double-sided tape so that the smooth surface was facing upwards. Then, the sample was placed on the sample stage of the atomic force microscope so that the direction perpendicular to the scanning direction (lateral) of the cantilever (Y-axis direction) was the stacking direction of the sample. After this, the number of regions R1 was measured according to the atomic force microscope observation procedure described below.

[0208] For acquiring the binarized image, a Park Systems NX-10 atomic force microscope was used. The AFM observation conditions were as follows: a cantilever with a spring constant of 42 N / m (tip radius of curvature R of 30 nm) with a probe made of a Si single crystal tip was used, the scanning frequency was 330 Hz, the resolution was 512 (points) × 512 (points), and the observation environment was 23°C under atmospheric conditions. Under these observation conditions, the force distance curve was measured by scanning within a 5 μm square cross section in the lateral direction (TD direction) using Pinpoint nanomechanical mode, and the Stiffness approach value was calculated using the built-in software (XEI) to obtain an AFM image of the film cross section (the smooth surface). An AFM image was obtained by observing another part of the film cross section using the same method. As a result, two AFM images of the stretched film cross section were obtained. Using the Python programming language, regions S with a Stiffness approach value of 90 N / m or higher were extracted from each obtained AFM image, and a binarized image was obtained by adaptively binarizing the extracted regions S so that they appear white. The Gaussian filter used was the filters.gaussian function of scikit-image (image, sigma=1, output=<DEPRECATED>, mode=nearest, cval=0, preserve_range=False, trunk=4.0, *, channel_axis=None, out=None).

[0209] <Method for measuring the number of regions R1> The number of regions R1 was measured using the binarized images obtained from atomic force microscopy (AFM) observations of the stretched film cross-section. First, five line segments (length 5 μm) parallel to the thickness direction were randomly drawn in the two obtained binarized images, and the regions S located on these line segments were defined as R1. The number of these R1 regions was determined according to the following <Method for determining the number of R1 regions>. <Method for determining the number of R1 regions> In one of the two binarized images, five line segments with a length of 5 μm parallel to the thickness direction were randomly drawn using Python. The areas displayed in white (i.e., the regions S) were designated as "0", and the areas displayed in black were designated as "1". The number of times the values ​​switched from "1" to "0" was counted on each line segment, and the average value of these counts was taken as the number of R1 regions. The number of R1 regions was counted in the other binarized image using the same procedure. The average value of the number of R1 elements in each of the obtained binarized images was calculated, and this value was used as the number of R1 elements in the stretched film. However, R1 elements with a length of 5 nm or less in the thickness direction were not counted and were excluded.

[0210] <Average Value of Maximum Length in the Thickness Direction of Region 2> The average value of the maximum length in the thickness direction of Region 2 was measured using the two binarized images obtained from atomic force microscopy (AFM) observations of the stretched film cross-section. Specifically, the average value of the maximum length in the thickness direction of Region 2 was determined according to the following method: <Method for Determining the Average Value of Maximum Length in the Thickness Direction of Region 2> In one of the two binarized images, Region S (i.e., the white area) located within the field of view enclosed by a rectangle with a thickness of 5 μm in the thickness direction of the cross-section and a thickness of 1 μm in the direction perpendicular to the thickness was defined as Region 2. The maximum length in the thickness direction of all Region 2 located within the field of view was measured using Python, and the average value of these measurements was defined as the average value of the maximum length in the thickness direction of Region 2. However, Region 2 with a thickness of 5 nm or less was excluded.

[0211] <Average value of the maximum length in the direction perpendicular to the thickness direction of region 3> In one of the two binarized images, region S (i.e., the white area) located within the field of view enclosed by a rectangle with a thickness of 5 μm in the cross-sectional thickness direction and a thickness of 1 μm perpendicular to the thickness was defined as region 3. The maximum length in the thickness direction of all regions 3 located within the field of view was measured, and the average value of these measurements was defined as the average value of the maximum length in the direction perpendicular to the thickness direction of region 3. <Method for determining the average value of the maximum length in the direction perpendicular to the thickness direction of region 3> In one of the two binarized images, region S (i.e., the white area) located within the field of view enclosed by a rectangle with a thickness of 5 μm in the cross-sectional thickness direction and a thickness of 1 μm perpendicular to the thickness was defined as region 3. The maximum length in the thickness direction of all regions 3 located within the field of view was measured using Python, and the average value of these measurements was defined as the average value of the maximum length in the direction perpendicular to the thickness direction of region 3. However, regions 3 with a length of 5 nm or less in the direction perpendicular to the thickness direction were excluded.

[0212] <Volume Resistivity> The volume resistivity was measured using the following procedure. However, unless otherwise specified in the following description, the measurement conditions conformed to JIS C 2139-3-1:2018. First, a jig for volume resistivity measurement (hereinafter simply referred to as "the jig") was placed in a constant temperature bath at 145°C. The configuration of the volume resistivity measurement jig was as follows. A DC power supply and a DC ammeter were connected to each electrode of the jig. The jig consisted of a main electrode (diameter 50 mm) and a counter electrode (diameter 85 mm), with a ring-shaped guard electrode (outer diameter 80 mm, inner diameter 70 mm) surrounding the main electrode. Each electrode was made of gold-plated copper, and conductive rubber was attached to the surface in contact with the sample. The conductive rubber used was EC-60BL (W300) manufactured by Shin-Etsu Silicone Co., Ltd., and the glossy side of the conductive rubber was attached to the gold-plated copper. Next, the stretched film (hereinafter also referred to as the sample) was set in a jig inside a constant temperature bath. Specifically, the main electrode and guard electrode were placed in close contact with one side of the stretched film, and the counter electrode was placed in close contact with the other side, and the stretched film and each electrode were brought into close contact with a load of 5 kgf. After that, it was left to stand for 30 minutes, and then a voltage was applied to the sample so that the potential gradient was 100 V / μm. The current value was read after 1 minute had elapsed since the application of the voltage, and the volume resistivity was calculated using the following formula. A Keithley 2290-10 (DC power supply) was used to apply the voltage, and a Keithley 2635B (DC ammeter) was used to measure the current value. The volume resistivity was calculated using the following formula: Volume resistivity = [(effective electrode area) × (applied voltage)] / [(thickness of stretched film) × (current value)] Here, the effective electrode area was determined using the following formula. (Effective electrode area) = π × [[[(Diameter of main electrode) + (Inner diameter of guard electrode)] / 2] / 2] ２ Here, the effective electrode area is S (cm²). ２ If the diameter of the main electrode is DM (cm) and the inner diameter of the guard electrode is DG (cm), then S = π × [{(DM + DG) ÷ 2} ÷ 2] ２ Therefore, a simplified version is given by the following equation: S = π × (DM + DG) ２ / 16 In this measurement, the effective electrode area was not defined as the area of ​​the main electrode, but rather as the portion of the space between the main electrode and the guard electrode that is the same distance from or closer to the main electrode. This enabled more accurate measurement of the current value. Furthermore, in this measurement, the volume resistivity ρ at 145°C was used. Ｖ１４５℃ ρ was calculated using the following formula I. Ｖ１４５℃ = (S × V) / (D × A １ ) (I) In equation (I), V is the applied voltage and is in the range of V = 270 to 320 V, and S is the effective electrode area and is S = 28.27 cm² ２ D is the thickness of the stretched film (0.00027 to 0.00032 cm), and A １ This is the current value at 1 minute after 145°C, and A １ = 0.9 × 10 －８ ~8 x 10 －８ I chose A.

[0213] <Dynamic Viscoelasticity Measurement> A "Viscoelasticity Measuring Device (Model: DMS6100)" manufactured by Seiko Instruments was used as the dynamic viscoelasticity measuring instrument. As the measurement sample, the stretched film was cut into strips of 50 mm in the vertical direction and 10 mm in the horizontal direction, with the TD direction being perpendicular to the film flow direction (MD direction), i.e., with the TD direction as the long axis. The temperature dependence (temperature dispersion data) of the dynamic viscoelasticity of the film was measured according to JIS-K7244 (1999 edition) under the measurement conditions shown below. Test mode: Tensile mode Chuck distance: 20 mm Vibration frequency: 1 Hz Strain amplitude: 10 μm Minimum tension: 20 mN Tension gain: 1.2 Initial force amplitude: 100 mN Temperature range: -30 to 180 °C Heating rate: 2 °C / min Measurement atmosphere: Air Measurement thickness: Approximately 3.0 μm From the measurement results using the above measurement method, temperature dispersion data of the dynamic viscoelasticity of the stretched film was obtained. From this temperature dispersion data, the temperature of the main dispersion peak of the loss tangent (tanδ), the loss tangent (tanδ) value at 100 °C, and the storage modulus (E') at 25 °C and 135 °C were determined. An example of the measurement results of the logarithmic value of the storage modulus (log E') and the temperature dependence of the loss tangent (tanδ) is shown in Figure 2.

[0214] <Ellipse Density> Using a digital microscope (Keyence Corporation VHX-X1), the roughened surface of the stretched film (the surface in contact with the metal drum) was observed at a lens magnification of 150x, with three randomly selected areas of a field of view of 2.4 mm × 1.8 mm. This observation was performed by reflection measurement. For each image of the three observed field of view areas, the area measurement function of the dedicated planar measurement function included with the digital microscope was used to perform binarization with a brightness range of 100 to 200, and the contours of each ellipse were extracted. Next, the major axis length (longest diameter) and minor axis length (shortest diameter) of each ellipse were manually measured using the two-point distance measurement of the planar measurement function. When the major axis length (longest diameter) is L μm and the minor axis length (shortest diameter) is S μm, only ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 were extracted. Specifically, within each of the three aforementioned field of view areas, only ellipses satisfying S ≤ L and 1 ≤ L ≤ 300 were extracted. Within each of the three extracted field of view areas, the number of ellipses was counted, and the value obtained by dividing that number by the area of ​​the field of view area was calculated. After obtaining this value for each of the three field of view areas, the average value was calculated and this was defined as the "density of the irregularities whose contours are observed as elliptical by microscopic observation" (also called the density of ellipses). This calculation was performed on both sides of the stretched film, and the side with the larger value (usually the side in contact with the metal drum) was used as the density of ellipses of the stretched film.

[0215] <Average value of the major axis of the ellipse> Using a digital scope (digital microscope VHX-X1 manufactured by Keyence Corporation), the roughened surface of the stretched film was observed at a lens magnification of 150x, with three randomly selected areas of a field of view of 2.4 mm × 1.8 mm. This observation was performed by reflection measurement. For each image of the three observed field of view areas, the area measurement function of the plane measurement function of the dedicated software attached to the digital scope was used to perform binarization processing with the brightness range set to 100 to 200, and the contours of each ellipse were extracted. Next, the major axis length (longest diameter) and minor axis length (shortest diameter) of each ellipse were manually measured using the two-point distance measurement of the plane measurement, and when the major axis length (longest diameter) was L μm and the minor axis length (shortest diameter) was S μm, only ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 were extracted. In other words, within each of the three fields of view, only ellipses satisfying S ≤ L and 1 ≤ L ≤ 300 were extracted. The average value of the major axis length (longest diameter) L (μm) of all extracted ellipses was calculated, and this average value was taken as the "average value of the major axis of the irregularities whose contours are observed to be elliptical by microscopic observation" (also called the average value of the major axis of the ellipses) in the stretched film A. The average value of the major axis of the ellipses was calculated on the same surface as the surface in which the measured density of the ellipses was larger.

[0216] <Method for Calculating the Ratio of Dielectric Breakdown Strength (V140 / V25)> The ratio of the dielectric breakdown strengths of the stretched films obtained in the examples and comparative examples at 140°C and 25°C under high temperature conditions was evaluated as follows. First, a measuring apparatus conforming to JIS C2151:2006 17.2.2 (Plane Electrode Method) was prepared. However, instead of the elastic material described in JIS C2151:2006 17.2.2, conductive rubber (E12S10 manufactured by Seiwa Electric Co., Ltd.) was used as the lower electrode, and no aluminum foil wrapping was performed. The measurement environment was a forced-circulation oven with a set temperature of 140°C or 25°C. The electrodes and films were used after being conditioned in the oven for 30 minutes. The voltage increase was started from 0V and increased at a rate of 100V / second, and the voltage when the current value exceeded 5mA was defined as the dielectric breakdown voltage. The dielectric breakdown voltage was measured 20 times. Each dielectric breakdown voltage value Vdc was divided by the thickness of the stretched film (μm), and the average of the 16 values ​​obtained by excluding the top 2 and bottom 2 values ​​from the 20 calculations was taken as the dielectric breakdown strength (Vdc / μm). The obtained dielectric breakdown strength was taken as the dielectric breakdown strength of the stretched film, and the dielectric breakdown strength V140 (Vdc / μm) of the stretched film at high temperature (140°C environment) was divided by the dielectric breakdown strength of the stretched film at room temperature (25°C) to calculate the dielectric breakdown strength ratio "V140 / V25". In Table 1 shown below, the dielectric breakdown strength ratio is given as the value obtained by multiplying the "V140 / V25" value by 100 (%).

[0217] <Infrared Absorption Spectrum Measurement (IR)> The infrared absorption spectrum of the stretched film was measured using a Fourier transform infrared spectrophotometer (manufactured by JASCO Corporation). A prism was placed in close contact with the stretched film (sample), and the absorbance spectrum against wavenumber was measured using the ATR method under the following conditions: Measurement device: JASCO Corporation, Fourier transform infrared spectrophotometer FT / IR-4000 ATR unit: ATR-PRO410-M Prism: ZnSe Incident angle: 45° Scanning range: 4000 cm －１ ~650cm －１ Integration number: Auto (121 times) Resolution: 4cm －１ Gain: Auto Aperture: Auto Scan Speed: Auto Filter: Auto

[0218] <Film Thickness> The thickness of the stretched film was measured in accordance with JIS-C2330:2014, except that it was measured at 100 ± 10 kPa using a Citizen Seimitsu MEI-11 paper thickness gauge.

[0219] <Total Light Transmittance> The total light transmittance of the stretched film was measured using a haze meter NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS-K7361:1997.

[0220] (Evaluation Results) Table 1 shows the physical properties and evaluation results of the stretched film. In Table 1, A1 refers to isotactic polypropylene resin A1, B1 refers to "polymer B1 having an alicyclic structure", and B2 refers to "polymer B2 having an alicyclic structure".

[0221] In Table 1, "ellipse size" refers to the average value of the major axis of the ellipse (i.e., the average value of the major axis of the irregularities observed to have an elliptical contour), and "ellipse density" refers to the density of the irregularities observed to have an elliptical contour. "Temperature at which the main dispersion peak was observed" means the loss tangent (taaδ) peak clearly observed in the region above 140°C, and "tanδ at 100°C" means the loss tangent (tanδ) at 100°C obtained based on the temperature dispersion data. In Table 1, the infrared absorption spectrum is 880–890 cm⁻¹. －１ Absorption peaks are observed in the range, and at 1450 cm. －１ If a shoulder peak due to absorption was observed in the vicinity, it was indicated as "present," and if not observed, it was indicated as "absent." Also, as mentioned above, the ratio of dielectric breakdown strength shown in Table 1 is the value obtained by multiplying the "V140 / V25" value by 100 (%).

[0222] Figure 2 shows the AFM image (Figure 2(a)) and the binarized image (Figure 2(b)) of the stretched film obtained in Example 1. In Figure 2(b), the area shown in white indicates region S. From these figures, it can be seen that in the cross-section of the stretched film obtained in Example 1, regions with a Stiffness approach value of 90 N / m or more are formed in layers.

[0223] Figure 3(a) shows a binarized image of the stretched film obtained in Comparative Example 1, and (b) shows a binarized image of the stretched film obtained in Comparative Example 3. From Figure 3(a), it can be seen that the stretched film obtained in Comparative Example 1 does not have region S. In addition, although region S exists in the stretched film obtained in Comparative Example 3, region S is not formed in layers but exists in an aggregated state, and therefore does not satisfy any of the following conditions: "the number of R1 is 10 or more", "the average maximum length in the thickness direction of region 2 is 10 nm or more and 300 nm or less", and "the average maximum length in the direction perpendicular to the thickness direction of region 3 is 30 nm or more".

[0224] Table 1 shows that the stretched films obtained in the examples had a high ratio of dielectric breakdown strength at 140°C to room temperature (e.g., 25°C), "V140 / V25" (close to "1"), indicating that the change in dielectric breakdown strength between high and low temperatures was small, and that the dielectric breakdown strength was maintained. Furthermore, the stretched films obtained in the examples also had high volume resistivity in high-temperature environments.

[0225]

Claims

A stretched film containing a polypropylene resin, A stretched film in which the number of regions R1 measured by the measurement method 1 below is 10 or more in cross-sectional atomic force microscopy (AFM) observation. <Measurement method 1> Regions of the film cross-section where the Stiffness approach value is 90 N / m or more, as measured by the force distance curve measurement method, are extracted by image processing, and the number of such regions located on line segments of 5 μm in the thickness direction of the cross-section is counted, with R1 being the value of these regions. A stretched film containing a polypropylene resin, A stretched film in which, in cross-sectional atomic force microscopy (AFM) observation, the average value of the maximum length in the thickness direction of region 2, measured by the measurement method 2 below, is 10 nm or more and 300 nm or less. <Measurement method 2> Regions of the film cross-section where the Stiffness approach value is 90 N / m or higher, as measured by the force distance curve measurement method, are extracted by image processing. Region 2 is defined as the region located within the field of view enclosed by a rectangle with a thickness of 5 μm in the thickness direction and a thickness of 1 μm in the direction perpendicular to the thickness of the cross-section, and the average value of the maximum length in the thickness direction of region 2 is measured. A stretched film containing a polypropylene resin, A stretched film in which, in cross-sectional atomic force microscopy (AFM) observation, the average value of the maximum length in the direction perpendicular to the thickness direction of region 3, measured by the measurement method 3 below, is 30 nm or more. <Measurement method 3> Regions where the Stiffness approach value of the film cross-section, measured by the force distance curve measurement method, is 90 N / m or higher are extracted by image processing. Region 3 is defined as the region located within the field of view enclosed by a rectangle with a thickness of 5 μm and a thickness of 1 μm perpendicular to the thickness of the cross-section, and the average value of the maximum length in the direction perpendicular to the thickness direction of region 3 is measured. A stretched film according to any one of claims 1 to 3, wherein the temperature dispersion data in the TD direction at a frequency of 1 Hz, obtained from dynamic viscoelasticity measurement, has a peak in the loss tangent tanδ in the region of 140°C or higher. A stretched film according to any one of claims 1 to 3, wherein the loss tangent tanδ at 100°C in the temperature dispersion data in the TD direction at a frequency of 1 Hz, obtained from dynamic viscoelasticity measurement, is 0.15 or less. Having irregularities on at least one surface, The stretched film according to any one of claims 1 to 3, wherein the average value of the major axis of the irregularities, whose outline is observed to be elliptical by microscopic observation, is 150 μm or less. Having irregularities on at least one surface, The density of the aforementioned irregularities, whose outlines are observed to be elliptical under a microscope, is 30 particles / mm². ２ The stretched film according to any one of claims 1 to 3. In infrared absorption spectroscopy measurements, 880–890 cm⁻¹ －１ Absorption peaks are observed in the range, and at 1450 cm. －１ A stretched film according to any one of claims 1 to 3, having at least one of the shoulder peaks due to absorption in the vicinity. The aforementioned polypropylene resin is An isotactic polypropylene resin comprising 80% by mass or more and 99% by mass or less, Polymers having an alicyclic structure in an amount of 1% to 20% by mass A stretched film according to any one of claims 1 to 3, comprising the above. The stretched film according to claim 9, wherein the polymer having the alicyclic structure comprises two or more polymers with different glass transition temperatures. The stretched film according to claim 9, wherein the polymer having an alicyclic structure comprises polymer B1 having an alicyclic structure with a glass transition temperature of 133°C or more and 155°C or less, and polymer B2 having an alicyclic structure with a glass transition temperature of 70°C or more and less than 133°C. The stretched film according to claim 11, wherein the mass ratio B2 / B1 of polymer B2 to polymer B1 is less than 0.

85. The stretched film according to claim 9, wherein the polymer having the alicyclic structure contains hydrogenated polystyrene. The aforementioned hydride polystyrene has an atactic structure, The stretched film according to claim 13, having a hydrogenation rate of 95% or more. A stretched film according to any one of claims 1 to 3, having a thickness of 1.8 μm or more and 10 μm or less, and a total light transmittance of 80% or more. A metal laminated film having a metal layer on one or both sides of a stretched film according to any one of claims 1 to 3. A film capacitor comprising the metal laminated film described in claim 16.

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