Biaxially oriented polypropylene film, metal film laminated film, and film capacitor

Abstract

To provide a biaxially oriented polypropylene film having surface quality capable of uniformly controlling an air amount and a gap distance between film layers of a film capacitor to acquire proper processability and security in the film capacitor having excellent voltage resistance even at elevated temperature and mainly high capacity.SOLUTION: A biaxially oriented polypropylene film has a protrusion peak density Spd of 250 / mm2 or more and 800 / mm2 or less and a protrusion height Spk of 35 nm or more and 80 nm or less on at least one face.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polypropylene film, a metal film laminate, and a film capacitor using the same, which have high voltage resistance in high-temperature and high-voltage environments when used as a dielectric in a film capacitor. [Background technology]

[0002] Biaxially oriented polypropylene film is used in a variety of applications, including packaging, tape, cable wrapping, and electrical applications such as film capacitors, due to its excellent transparency, mechanical properties, and electrical properties.

[0003] In particular, in film capacitor applications, it is especially preferred as a dielectric material due to its excellent high voltage resistance and low loss characteristics. Recently, various electrical equipment is being converted to inverters, and consequently, the demand for smaller and larger capacity film capacitors is increasing. Furthermore, especially in automotive applications (including hybrid cars and electric vehicles), solar power generation, and wind power generation applications, the operating environment is getting hotter (85°C to 125°C), and the demand for heat resistance in film capacitors is also increasing.

[0004] Improving the heat resistance of film capacitors means improving their voltage resistance at high temperatures. To achieve this simultaneously with miniaturization, it is necessary to balance the thinning of the biaxially oriented polypropylene film used in film capacitors with improved voltage resistance. Controlling the surface shape (surface roughness, protrusion height, and number of protrusions) is considered an effective method for improving the voltage resistance of biaxially oriented polypropylene film, and various studies have been conducted to date.

[0005] Methods for roughening the surface of a film include mechanical methods such as embossing and sandblasting, chemical methods such as chemical etching with solvents, stretching a sheet mixed with different polymers such as polyethylene, and a method utilizing the crystal transition from β-crystal to α-crystal of polypropylene (hereinafter referred to as the β-crystal method) (see, for example, Patent Documents 1 and 2). This method utilizing the crystal transition is preferred as a method for roughening biaxially oriented polypropylene films for film capacitors because it does not require the incorporation of impurities such as additives that may worsen the dielectric strength.

[0006] Methods focusing on controlling surface shape include adding high melt-tension polypropylene to control the number of protrusions (see, for example, Patent Document 3) and mixing highly stereoregular polypropylene resins with different stereoregularities to control the protrusion height (see, for example, Patent Documents 4 and 5). The method of adding high melt-tension polypropylene allows for the control of the number of surface protrusions by controlling the spherulite size of the polypropylene. Furthermore, the method of mixing highly stereoregular polypropylene resins with different stereoregularities allows for the control of the surface protrusion height and the depth of the surface valleys, and by appropriately adjusting the amount of air and gap distance between film layers, it is possible to provide a film with excellent long-term durability at high temperatures. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-133446 [Patent Document 2] Japanese Patent Publication No. 2014-077057 [Patent Document 3] Japanese Patent Publication No. 2011-122143 [Patent Document 4] Japanese Patent Publication No. 2019-172972 [Patent Document 5] Japanese Patent Publication No. 2020-100800 [Overview of the project]

Problems to be Solved by the Invention

[0008] When applying the β-crystal method described in Patent Documents 1 and 2 using a general high stereoregular polypropylene film, crater-shaped steep convex and concave portions are formed at a low density. Therefore, the concave portions are likely to cause dielectric breakdown, and there are problems with the withstand voltage characteristics at high temperatures. When using the method described in Patent Document 3, although the convex portions on the surface become fine, the concave portions still exist at a high density. Therefore, the concave portions are likely to cause dielectric breakdown, and it has been difficult to obtain a film that meets market requirements in a high-temperature and high-voltage environment. Further, when using the methods described in Patent Documents 4 and 5, simply controlling the protrusion height and the depth of the valleys was insufficient to make the gaps between the film layers uniform when processed into a film capacitor. Therefore, in recent high-temperature and high-voltage environments, there have been problems with the withstand voltage characteristics when used as a film capacitor.

[0009] Therefore, an object of the present invention is to provide a biaxially oriented polypropylene film having a surface property capable of uniformly controlling the amount of air and the gap distance between the film layers of a film capacitor in order to have excellent withstand voltage properties even at high temperatures and to obtain appropriate processability and safety mainly in large-capacity film capacitors.

Means for Solving the Problems

[0010] To achieve the above-described problems, the present invention has the following configuration. That is, on at least one side, a biaxially oriented polypropylene film characterized in that the peak density Spd of the mountains is 250 / mm 2 or more and 800 / mm 2 or less, and the height Spk of the protruding mountain portions is 35 nm or more and 80 nm or less.

Effects of the Invention

[0011] According to the present invention, it is possible to provide a biaxially oriented polypropylene film, a metal film laminated film, and a film capacitor using these, which have excellent withstand voltage properties even at high temperatures and have a surface property capable of more uniformly controlling the air amount and gap distance between film layers in a film capacitor, mainly for obtaining proper processability and safety in a large-capacity film capacitor.

Mode for Carrying Out the Invention

[0012] Hereinafter, the biaxially oriented polypropylene film, the metal film laminated film, and the film capacitor of the present invention will be described in more detail. The biaxially oriented polypropylene film of the present invention has, on at least one side, a peak density Spd of 250 / mm 2 or more and 800 / mm 2 or less, and a protrusion peak height Spk of 35 nm or more and 80 nm or less. Here, "on at least one side, the peak density Spd is 250 / mm 2 or more and 800 / mm 2 or less, and the protrusion peak height Spk is 35 nm or more and 80 nm or less" means that at least one side has a surface with a peak density Spd of 250 / mm 2 or more and 800 / mm 2 or less and a protrusion peak height Spk of 35 nm or more and 80 nm or less, and it is preferable that both sides satisfy the above requirements. In addition, even if one side satisfies "the peak density Spd is 250 / mm 2 or more and 800 / mm 2 or less" and the other side satisfies "the protrusion peak height Spk is 35 nm or more and 80 nm or less", if the two requirements are not satisfied on one side, it is considered not to satisfy the above requirements.

[0013] Biaxially oriented polypropylene film is a biaxially oriented polypropylene film produced by stretching a cast sheet in two orthogonal directions. In other words, biaxial orientation here means stretching in two orthogonal directions (mainly the longitudinal and width directions). The longitudinal direction refers to the direction in which the film travels during the film manufacturing process (the winding direction of the film in the case of a film roll), and the width direction refers to the direction parallel to the film surface and perpendicular to the longitudinal direction.

[0014] The biaxially oriented polypropylene film of the present invention has polypropylene resin as its main component. "Main component" means that the film contains more than 50% by mass and up to 100% by mass of polypropylene resin in 100% by mass of all components constituting the film. Furthermore, polypropylene resin refers to a resin that, when the total constituent units of the resin are considered as 100 mol%, contains more than 50 mol% and up to 100 mol% of propylene units.

[0015] In addition, the biaxially oriented polypropylene film of the present invention is not particularly limited in terms of the details of the polypropylene resin as long as it is mainly composed of polypropylene resin. However, when a highly stereoregular polypropylene resin is called a highly stereoregular polypropylene resin (A), and among high melt-tension polypropylene resins, those with a high melt-fluidity index (MFR) at 230°C are called a high melt-tension polypropylene resin (H), and those with a low melt-tension polypropylene resin (I), it is preferable that the film contains a highly stereoregular polypropylene resin (A) as the main component, and further contains a high melt-tension polypropylene resin (H) and a high melt-tension polypropylene resin (I). Details of the highly stereoregular polypropylene resin (A), the high melt-tension polypropylene resin (H), and the high melt-tension polypropylene resin (I) will be described later.

[0016] Here, "primarily composed of highly stereoregular polypropylene resin (A)" means that the biaxially oriented polypropylene film contains more than 50% by mass and 100% by mass of highly stereoregular polypropylene resin (A) in 100% by mass of the total resin components, more preferably 90% by mass or more and less than 100% by mass, and even more preferably 90% by mass or more and 99% by mass or less. By adopting this configuration, it becomes easy to achieve both heat resistance and dielectric strength at high temperatures.

[0017] The biaxially oriented polypropylene film of the present invention may contain various additives, such as nucleating agents, antioxidants, heat stabilizers, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and anticoloring agents, as long as they do not impair the objectives of the present invention. Furthermore, these components may be one type or multiple types, as long as they do not impair the effects of the present invention.

[0018] Among the additives mentioned above, the selection of the type and content of antioxidants is important from the viewpoint of long-term heat resistance. Specifically, sterically hindered phenolic antioxidants are preferred, and at least one of them is preferably a high molecular weight type with a molecular weight of 500 or more. Specifically, for example, it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), BASF Japan's "Irganox" (registered trademark) 1330 (molecular weight 775.2), BASF Japan's "Irganox" (registered trademark) 1010 (molecular weight 1177.7), etc., either alone or in combination. The total content of the above additives is preferably 0.01 parts by mass or more and 1.00 parts by mass or less, more preferably 0.10 parts by mass or more and 0.90 parts by mass or less, and even more preferably 0.15 parts by mass or more and 0.60 parts by mass or less, when the resin component of the biaxially oriented polypropylene film is 100 parts by mass.

[0019] The biaxially oriented polypropylene film of the present invention, from the viewpoint of achieving both high voltage resistance and device processability at high temperatures, has a peak density Spd of 250 / mm² on at least one side. 2 More than 800 / mm 2 It is important that the following is true: 300 / mm2 More than 750 / mm 2 Preferably, it is 350 / mm 2 More than 700 / mm 2 It is more preferable that it be less than or equal to 400 / mm 2 More than 650 / mm 2 It is even more preferable that the following conditions apply: 550 / mm 2 More than 650 / mm 2 The following are particularly preferable.

[0020] The peak density Spd is one of the three-dimensional parameters of surface texture defined in ISO 25178-2 (2012), and is used as an indicator of the density of protrusions present on a surface. The peak density Spd can be determined by counting peaks with a height of 5% or more of the maximum amplitude of the contour surface, and dividing the number of peaks included in the contour surface by the field of view area of ​​the contour surface. The measuring device for the peak density Spd is not particularly limited as long as it is capable of the above measurement, but for example, the non-contact surface and layer cross-sectional shape measurement system "VertScan" (registered trademark) 2.0 manufactured by Ryoka Systems Co., Ltd. can be used.

[0021] On at least one side, the peak density Spd is 250 / mm². 2 By doing so, slipperiness is maintained. Therefore, in the conveying process during the processing of biaxially oriented polypropylene film, the occurrence of wrinkles and deterioration of the winding shape of the film roll can be prevented, improving processability. In addition, the peak density Spd is 800 / mm 2 By doing the following, blocking is suppressed during the film transport process in processing. As a result, the occurrence of wrinkles during processing of biaxially oriented polypropylene film is suppressed, the winding appearance of the film roll is improved, and film breakage is also reduced.

[0022] On at least one side, the peak density Spd is 250 / mm². 2 More than 800 / mm 2To achieve the following or above preferred range, a method of incorporating a high melt-tension polypropylene resin (H) having an appropriate MFR is preferably used. When using a method of incorporating a high melt-tension polypropylene resin (H), increasing the content of the high melt-tension polypropylene resin (H) tends to increase the peak density Spd of the mountain.

[0023] From the viewpoint of suitability for use in film capacitor applications, the biaxially oriented polypropylene film of the present invention is important in that the peak height Spk is 35 nm or more and 80 nm or less on at least one side, preferably 40 nm or more and 70 nm or less, more preferably 45 nm or more and 65 nm or less, and even more preferably 45 nm or more and 60 nm or less. Herein, "at least one side" means "peak density Spd is 250 / mm²". 2 More than 800 / mm 2 This means at least one of the faces that satisfy the following conditions.

[0024] The protruding peak height Spk is a type of functional parameter defined in ISO 25178-2 (2012). It represents the average height of the portion (protruding peak) above the intersection point of the bearing curve of height data (where the frequency at a given height is accumulated from the highest to the lowest, and expressed as a percentage with the total number of height data points set to 100%; the load area ratio at a given height C is given by Smr(C)) and the load area ratio = 0%. If the protruding peak height Spk is less than 35 nm, the amount of interlayer air in the film is reduced during film capacitor element formation, making the film capacitor more prone to short-circuit failure when used. On the other hand, if the protruding peak height Spk is greater than 80 nm, the amount of interlayer air in the film is increased during film capacitor element formation, making the capacitance more likely to decrease when the film capacitor is used at high temperatures for a long period of time.

[0025] To achieve a protruding peak height Spk of 35 nm to 80 nm or within the above preferred range on at least one side, a method of incorporating high melt-tension polypropylene resin (I) is preferably used. When using a method of incorporating high melt-tension polypropylene resin (I), increasing the content of high melt-tension polypropylene resin (I) tends to decrease the protruding peak height Spk.

[0026] From the viewpoint of suitability for use in film capacitors, the biaxially oriented polypropylene film of the present invention preferably satisfies the relationship shown in Equation 1 below, where the side with a large Spd is the X-plane, the side with a small Spd is the Y-plane, the Spd of the X-plane is Spd(x), and the Spd of the Y-plane is Spd(y). Formula 1: 1.00 <Spd(x) / Spd(y)≦1.50 From the above viewpoint, it is more preferable that Spd(x) / Spd(y) is between 1.05 and 1.40, and even more preferable that it is between 1.10 and 1.30.

[0027] Setting Spd(x) / Spd(y) within the above range suppresses the difference in slipperiness between the front and back sides of the biaxially oriented polypropylene film, making it easier to stabilize the amount of winding air during the winding process when processing film capacitor elements, and making it easier to achieve uniform interlayer gaps and air volume after the heat treatment process. Therefore, it is possible to prevent the safety features from being too strong or too weak when using film capacitors, which reduces the lifespan of the film capacitors or makes short-circuit failures less likely.

[0028] To set Spd(x) / Spd(y) to greater than 1.00 and 1.50 or within the above preferred range, it is effective to include at least one of high melt-tension polypropylene resin (H) and high melt-tension polypropylene resin (I), or to adjust the casting conditions. Including high melt-tension polypropylene resin tends to lower Spd(x) / Spd(y), and reducing the temperature difference between the casting drum temperature and the air temperature of the air knife also tends to lower Spd(x) / Spd(y).

[0029] From the viewpoint of suitability for use in film capacitors, it is preferable that the biaxially oriented polypropylene film of the present invention satisfies the relationship between Spd and Spk in the following formula 2 on at least one side. Equation 2: 0.05≦Spk / Spd≦0.30 From the above viewpoint, it is more preferable that the Spk / Spd ratio on at least one side is 0.05 or more and 0.25 or less, even more preferable that it is 0.05 or more and 0.20 or less, particularly preferable that it is 0.10 or more and 0.18 or less, and most preferable that it is 0.10 or more and 0.15 or less.

[0030] By setting Spk / Spd to 0.30 or less, or within the preferred range described above, the peak density Spd and the protruding peak height Spk can be controlled to appropriate values, achieving both high voltage resistance and ease of device processing at high temperatures. The lower limit of 0.05 for Spk / Spd was set from a feasibility standpoint.

[0031] To achieve a Spk / Spd ratio of 0.05 to 0.30 or within the preferred range described above, it is effective to include high melt-tension polypropylene resin (H) and high melt-tension polypropylene resin (I), and to control the difference in MFR between the two within an appropriate range. More specifically, increasing the difference in MFR between high melt-tension polypropylene resin (H) and high melt-tension polypropylene resin (I) tends to lower the Spk / Spd ratio.

[0032] The biaxially oriented polypropylene film of the present invention preferably has a thickness of 1.0 μm to 3.0 μm, from the viewpoint of mechanical strength, high-temperature withstand voltage characteristics, and capacitance per unit volume when used as a film capacitor dielectric. From the above viewpoint, a thickness of 1.2 μm to 2.8 μm is more preferable, and a thickness of 1.5 μm to 2.5 μm is even more preferable. By setting the thickness to 1.0 μm or more, the biaxially oriented polypropylene film can be made to have excellent mechanical strength and high-temperature withstand voltage characteristics, and its breakage during film formation and processing can be prevented. On the other hand, by setting the thickness to 3.0 μm or less, the capacitance per unit volume can be made larger when used as a film capacitor dielectric. The thickness shall be measured by the micrometer method in accordance with JIS C 2330 (2014).

[0033] Next, the polypropylene resin raw materials used in the biaxially oriented polypropylene film of the present invention will be described. The biaxially oriented polypropylene film of the present invention preferably contains a high-stereoregularity polypropylene resin (A), a high-melt-tension polypropylene resin (H), and a high-melt-tension polypropylene resin (I).

[0034] The highly stereoregular polypropylene resin (A) used as a raw material for the biaxially oriented polypropylene film of the present invention refers to an isotactic polypropylene resin, more specifically, a polypropylene resin whose melt tension (MS) (unit: cN) measured at 230°C is less than 1.0 cN. This isotactic polypropylene resin is known as a polypropylene resin commonly used in film capacitor applications. MS refers to the tension when the polypropylene resin is heated to 230°C to melt, the molten polypropylene is extruded as a strand at an extrusion speed of 15 mm / min, and this strand is taken up at a speed of 6.5 m / min.

[0035] The highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention preferably has a weight-average molecular weight (Mw) of 200,000 to 500,000 and a number-average molecular weight (Mn) of 40,000 to 90,000, as measured by GPC. Furthermore, the molecular weight distribution (Mw / Mn) is preferably 4.0 to 8.0, and more preferably 5.0 to 7.0. A high molecular weight distribution (Mw / Mn) means a broad molecular weight distribution, and by using a highly stereoregular polypropylene resin (A) within the above range, it is easier to achieve both film formation stability and improved voltage resistance at high temperatures.

[0036] The cold xylene-soluble portion (CXS) of the highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention is preferably 0.5% by mass or more and 4.0% by mass or less, more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less. CXS refers to the polypropylene components dissolved in xylene when the film is completely dissolved in xylene at 135°C and then precipitated at 20°C. This is considered to correspond to components that are difficult to crystallize due to reasons such as stereoregularity and low molecular weight. When the CXS of the highly stereoregular polypropylene resin (A) is 0.5% by mass or more and 4.0% by mass or less, it is easier to improve the high-temperature voltage resistance characteristics and dimensional stability of the biaxially oriented polypropylene film.

[0037] CXS can be quantified by the following procedure. First, 0.5 g of polypropylene resin is dissolved in 100 ml of boiling xylene at 135°C, allowed to cool, and then recrystallized in a constant temperature water bath at 20°C for 1 hour, followed by filtration. Next, the polypropylene components dissolved in the filtrate are quantified by liquid chromatography, and CXS is calculated from the following formula 3, with X0 (g) being the mass of polypropylene resin before dissolution in boiling xylene and X (g) being the mass of polypropylene components dissolved in the filtrate. Equation 3: CXS(mass%)=(X / X0)×100.

[0038] The mesopentad fraction (mmmm) of the highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention is preferably 0.960 or more and 0.995 or less, more preferably 0.960 or more and 0.995 or less, and even more preferably 0.970 or more and 0.995 or less. The mesopentad fraction (mmmm) is an index indicating the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance (NMR) spectroscopy. Higher values ​​are preferable because they indicate higher crystallinity and melting point, and superior dielectric strength at high temperatures. When the mesopentad fraction of the highly stereoregular polypropylene resin (A) is 0.960 or more, it is easier to maintain high-temperature dielectric strength and dimensional stability. On the other hand, when the mesopentad fraction of the highly stereoregular polypropylene resin (A) is 0.995 or less, it is easier to maintain film-forming properties and obtain a stable biaxially oriented polypropylene film. The mesopentad fraction is determined by dissolving the polypropylene resin sample in a solvent. 13 The measurement can be performed using 1C-NMR, and the detailed conditions are shown in the examples.

[0039] The melt-fracture-free (MFR) of the highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention is preferably 1.0 g / 10 min to 5.0 g / 10 min, more preferably 1.0 g / 10 min to 4.5 g / 10 min, and even more preferably 1.0 g / 10 min to 4.0 g / 10 min, when measured in accordance with JIS K 7210-1 (2014) at 230°C and 2.16 kg. Setting the MFR of the highly stereoregular polypropylene resin (A) to 1.0 g / 10 min or higher makes it easier to obtain a stable biaxially oriented polypropylene film while maintaining film-forming properties. On the other hand, setting the MFR of the highly stereoregular polypropylene resin (A) to 5.0 g / 10 min or lower makes it easier to maintain dimensional stability and high-temperature withstand voltage characteristics. The same measurement method and conditions for the MFR of the high melt-fracture-free polypropylene resin (H) and high melt-fracture-free polypropylene resin (I) are applied below.

[0040] Next, we will explain high melt-tension polypropylene resin (H). In this invention, high melt-tension polypropylene resin (H) refers to a high melt-tension polypropylene resin having a melt tension (MS, unit: cN) of 1.0 cN or more at 230°C.

[0041] The biaxially oriented polypropylene film of the present invention preferably contains 0.1% to 1.0% by mass of high melt-tension polypropylene resin (H) in 100% by mass of all resin components constituting the film, more preferably 0.1% to less than 1.0% by mass, and even more preferably 0.2% to 0.9% by mass. If multiple components corresponding to high melt-tension polypropylene resin (H) are contained in the biaxially oriented polypropylene film, the content thereof shall be determined by summing all the corresponding components, and this also applies to the high melt-tension polypropylene resin (I) described later.

[0042] By setting the content of high melt-tension polypropylene resin (H) in 100% by mass of all components constituting the film within the above range, it becomes easy to control the peak density Spd to the aforementioned preferred range.

[0043] Next, we will describe the high melt-tension polypropylene resin (I). In this invention, the high melt-tension polypropylene resin (I) is a high melt-tension polypropylene resin having a melt tension (MS, unit: cN) of 1.0 cN or more at 230°C, and a lower MFR than the high melt-tension polypropylene resin (H).

[0044] The biaxially oriented polypropylene film of the present invention preferably contains 1.0% by mass or more and 5.0% by mass or less of high melt tension polypropylene resin (I) in 100% by mass of all resin components constituting the film, more preferably 1.0% by mass or more and less than 5.0% by mass, and even more preferably greater than 1.0% by mass and less than 5.0% by mass.

[0045] By setting the content of high melt-tension polypropylene resin (I) in 100% by mass of all components constituting the film to the above range, it becomes easy to control the peak protrusion height Spk to the aforementioned preferred range.

[0046] To obtain high melt tension polypropylene resins (H) and (I), preferred methods include using high-energy ionization radiation on the polypropylene resin (e.g., Japanese Patent Publication No. 62-121704), reacting the polypropylene resin with a specific organic peroxide (e.g., Japanese Patent Publication No. 2869606), reacting the polypropylene resin with a pyrolytic radical-forming agent and an ethylene-based polyfunctional unsaturated monomer (e.g., Japanese Patent Publication No. 10-330436), and using a specific catalyst during the polymerization of the polypropylene resin (e.g., Japanese Patent Publication No. 2009-057542).

[0047] More specifically, as the high melt-tension polypropylene resin (H), products such as "WAYMAX" (registered trademark) (MFX3) manufactured by Nippon Polypropylene Co., Ltd. can be used. Furthermore, as the high melt-tension polypropylene resin (I), products such as "Profax" (registered trademark) (PF-814) manufactured by Lyondell Basell, and "Daploy" (trademark) (WB130HMS, WB135HMS) manufactured by Borealis can be used. Note that the combinations are not limited to those described above, and the combination can be determined by considering the magnitude of the MFR at 230°C.

[0048] The high melt-tension polypropylene resins (H) and (I) contained in the biaxially oriented polypropylene film of the present invention preferably have a branched structure in their molecular chains. A polypropylene resin having a branched structure is a polypropylene resin having five or fewer internal trisubstituted olefins per 10,000 carbon atoms, and the presence of these internal trisubstituted olefins is important. 1This can be confirmed by the proton ratio of the H-NMR spectrum. High melt-tension polypropylene resins (H) and (I) act as α-nucleating agents, and within a certain range of addition amounts, they can also form rough surfaces due to crystalline morphology. In other words, the size of the polypropylene spherulites generated during the cooling process of the melt-extruded resin sheet can be controlled to be small, and a biaxially oriented polypropylene film with excellent high-temperature voltage resistance can be obtained.

[0049] The high melt-tension polypropylene resin (H) and high melt-tension polypropylene resin (I) constituting the biaxially oriented polypropylene film of the present invention are preferably a combination in which the difference obtained by subtracting the MFR of high melt-tension polypropylene resin (I) from the MFR of high melt-tension polypropylene resin (H) is 4.0 or more and 8.0 or less, and more preferably a combination in which it is 4.0 or more and 7.0 or less. By keeping the difference obtained by subtracting the MFR of high melt-tension polypropylene resin (I) from the MFR of high melt-tension polypropylene resin (H) within the above range, it becomes easy to achieve both the peak density Spd and the protruding peak height Spk within the aforementioned preferred range, and a biaxially oriented polypropylene with both voltage resistance and device processability can be obtained.

[0050] The biaxially oriented polypropylene film of the present invention preferably has a surface wetting tension of 38 mN / m or more and 52 mN / m or less on at least one side, more preferably 40 mN / m or more and 50 mN / m or less, and even more preferably 42 mN / m or more and 48 mN / m or less. A surface wetting tension of 38 mN / m or more makes it easier to achieve sufficient adhesion with the metal during metal deposition. On the other hand, a surface wetting tension of 52 mN / m or less makes it easier to maintain dielectric strength at high temperatures. Biaxially oriented polypropylene films typically have low surface energy and a surface wetting tension of about 30 mN / m. In order to achieve a surface wetting tension within the above range, a method of surface treatment after biaxial stretching is preferably employed during film formation. Specifically, corona discharge treatment, plasma treatment, glow treatment, flame treatment, etc., can be employed.

[0051] The biaxially oriented polypropylene film of the present invention is preferably obtained by molding a polypropylene resin composition consisting of the above-described high stereoregularity polypropylene resin (A) and high melt tension polypropylene resins (H) and (I) into a sheet and then biaxially stretching it. The biaxial stretching can be performed by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. However, sequential tenter biaxial stretching is preferred from the viewpoint of film formation stability and thickness uniformity. In particular, it is preferable to stretch in the longitudinal direction first, and then in the width direction.

[0052] Next, the method for producing the biaxially oriented polypropylene film of the present invention will be described below, but is not necessarily limited thereto.

[0053] First, the aforementioned high stereoregularity polypropylene resin (A) and high melt tension polypropylene resins (H) and (I) are dry-blended and supplied to a single-screw melt extruder, where melt extrusion is performed at 200-260°C. Next, foreign matter and modified polymers are removed using a filter installed in the middle of the polymer tube. Then, the mixture is discharged from the T-die onto a cast drum to form a cast sheet, which is then cooled by a cooling roll.

[0054] The temperature of the casting drum is preferably 80°C to 120°C, more preferably 85°C to 115°C, and even more preferably 85°C to 110°C, from the viewpoint of appropriately generating β-crystals and spherulites. Setting the casting drum temperature to 80°C or higher prevents the formation of too few β-crystals in the cast sheet, thus maintaining the slipperiness of the film obtained after biaxial stretching, and preventing wrinkles from forming and deterioration of the film roll's winding shape during the film transport process in film formation and processing. On the other hand, setting the casting drum temperature to 120°C or lower prevents the excessive formation of β-crystals in the cast sheet, reducing meandering during the film transport process in film formation and processing and minimizing deterioration of the film roll's winding shape.

[0055] Preferably, the molten sheet discharged from the T-die lands on the casting drum and remains in contact with the drum for 1 second to 3 seconds. If the contact time is 1 second or longer, the molten sheet solidifies more easily, reducing breakage in the subsequent stretching process. On the other hand, if the contact time is 3 seconds or less, it is possible to prevent the excessive formation of β crystals in the cast sheet, reducing meandering during the film transport process in film formation and processing, and reducing deterioration of the winding shape of the film roll.

[0056] Methods for adhering the molten sheet to the casting drum include electrostatic application, air knife method, nip roll method, and underwater casting method. However, the air knife method is preferred from the viewpoint of suppressing thickness unevenness, high-speed film formation, and controlling the surface properties of the film. The air temperature of the air knife is preferably 60°C to 125°C, and more preferably 60°C to 100°C. Setting the air knife temperature to 60°C or higher prevents excessive formation of β crystals in the cast sheet, maintaining the slipperiness of the film obtained after biaxial stretching. This reduces wrinkle formation and deterioration of the film roll's winding shape during film formation and processing. On the other hand, setting the air knife temperature to 125°C or lower prevents excessive formation of β crystals in the cast sheet, reducing meandering and deterioration of the film roll's winding shape during film formation and processing.

[0057] The temperature difference between the cast drum temperature and the air knife temperature (the lower temperature being the lower temperature) is preferably 30°C or less, more preferably 20°C or less, and even more preferably 15°C or less, from the viewpoint of maintaining high slipperiness when equivalent β-crystals are formed on both sides of the cast sheet to create a biaxially oriented polypropylene film. When this temperature difference is 30°C or less, the discrepancy in cooling conditions on both sides is suppressed, making it difficult for different irregularities to form on the front and back of the cast sheet, and making it easier for the slipperiness to be equivalent on both sides of the film. Therefore, when the resulting biaxially oriented polypropylene film is used in capacitor element processing, the amount of air wound in during the winding process is stable, and the gaps between layers and the amount of air in the film tend to become uniform after the heat treatment process. As a result, high safety can be achieved when used as a capacitor, and the reduction in capacitor lifespan is reduced. Furthermore, setting the temperature difference between the cast drum temperature and the air knife temperature within the above range is also effective as a means of setting the peak density Spd of the resulting biaxially oriented polypropylene film within a desired range.

[0058] On the other hand, there is no particular lower limit to this temperature difference, and theoretically it can be 0°C. However, considering the stability of film formation, it is preferable to make the cast drum temperature relatively higher than the air temperature of the air knife, and it is preferable that the difference between the cast drum temperature and the air temperature of the air knife be 1°C or more, and more preferably 5°C or more. In the cooling process using a cast drum and an air knife, if the cast drum temperature is equal to the air temperature of the air knife, the cooling efficiency of the surface that is air-cooled by the air from the air knife is inferior to the surface that is cooled in close contact with the cast drum. Therefore, by making the cast drum temperature relatively higher than the air temperature of the air knife, it becomes easier to make the cooling efficiency of both sides roughly the same, and as a result of reducing the unevenness of the physical properties of the cast sheet due to differences in cooling conditions, the film formation becomes more stable.

[0059] Next, the cast sheet is stretched in the longitudinal direction in the longitudinal stretching process. The cast sheet is passed through rolls controlled to a temperature of 120°C to 150°C, and stretched in the longitudinal direction (longitudinal stretching) at a predetermined stretching speed and stretching ratio due to the difference in peripheral speed between the rolls. The longitudinal stretching ratio is preferably 4.0 to 7.0 times, and more preferably 5.0 to 7.0 times. By setting the stretching ratio to 4.0 times or higher, the surface properties of the film become uniform and the high-temperature withstand voltage characteristics are also improved. If the longitudinal stretching ratio is 7.0 times or lower, film breakage in the longitudinal stretching process and the subsequent transverse stretching process is reduced.

[0060] When stretching a film in the longitudinal direction, a phenomenon called "neck-down" occurs, in which the film width decreases. However, from the viewpoint of thickness variation, a neck-down rate (film width after stretching / film width before stretching × 100) of 90-99% is preferable.

[0061] Next, the uniaxially oriented film obtained by longitudinal stretching is held at both ends in the width direction with clips and stretched in the width direction at a stretching ratio of 5 to 15 times using a tenter-type stretcher controlled at a temperature of 140°C to 170°C. Furthermore, it is heat-set at a temperature of 150 to 170°C while being relaxed by 5 to 15% in the width direction.

[0062] Next, the biaxially oriented film is subjected to corona discharge treatment in air, nitrogen, carbon dioxide, or a mixture thereof. The edges of the film, held with clips, are cut and removed, and the film with the edges removed is wound onto a winding machine as a master roll. Finally, the film unwound from the master roll is slit to a specific width using a slitter, and wound onto a core as a film roll to obtain the biaxially oriented polypropylene film of the present invention.

[0063] The biaxially oriented polypropylene film of the present invention is preferably used as a dielectric for film capacitors, but is not limited to the type of film capacitor. Specifically, in terms of electrode configuration, it may be either a foil-wound film capacitor or a metal-deposited film capacitor, and it is also preferably used in oil-immersion type film capacitors containing insulating oil or dry-type film capacitors that do not use insulating oil at all. Furthermore, in terms of shape, it may be either a wound type or a laminated type. Due to the properties of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal-deposited film capacitor.

[0064] The metal film laminate of the present invention has a metal film on at least one side of the biaxially oriented polypropylene film of the present invention. The method for forming the metal film is not particularly limited, but a preferred method is to deposit aluminum on at least one side of the film to provide a metal film such as an aluminum vapor-deposited film that serves as an internal electrode for a film capacitor. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can be deposited simultaneously or sequentially with the aluminum. Furthermore, a protective layer such as oil can be provided on the vapor-deposited film.

[0065] The thickness of the metal film in the metal film laminate is preferably between 20 nm and 100 nm. This range prevents excessive thermal effects during deposition, thus maintaining the film's dielectric strength and improving productivity. Similarly, the surface resistance of the metal film is preferably between 1 Ω / sq and 20 Ω / sq. The surface resistance can be controlled by the type of metal used and the film thickness.

[0066] In this invention, if necessary, after forming a metal film, the metal film laminate can be subjected to aging treatment or heat treatment at a specific temperature. Furthermore, a coating such as polyphenylene oxide can be applied to at least one side of the metal film laminate for insulation or other purposes.

[0067] The film capacitor of the present invention has a structure in which the metal film laminate of the present invention is laminated or wound. In other words, the film capacitor of the present invention includes both a laminated film capacitor obtained by laminating the metal film laminate of the present invention and a wound film capacitor obtained by winding the metal film laminate. A preferred method for manufacturing the wound film capacitor will be described below, but is not necessarily limited thereto.

[0068] First, aluminum is vacuum-deposited onto one side of the biaxially oriented polypropylene film of the present invention to form a metal film laminate. At this time, the aluminum is deposited in a stripe pattern having a margin running along the longitudinal direction of the film. Next, a blade is inserted into the center of each deposited portion and the center of each margin portion on the surface to create a tape-shaped winding reel with a margin on one side of the surface. Two tape-shaped winding reels, one with a left margin and one with a right margin, are overlapped and wound together so that the deposited portion extends beyond the margin in the width direction to obtain a wound body. After heat treatment of the wound body, metallicon is sprayed onto both ends in the width direction to form external electrodes, and lead wires are welded to the metallicon to obtain a wound film capacitor.

[0069] Film capacitors have a wide range of applications, including those for vehicles, home appliances (such as televisions and refrigerators), general dust protection, automobiles (hybrid cars, power windows, wipers, etc.), and power supplies. The film capacitor of the present invention can also be suitably used in these applications. [Examples]

[0070] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The properties were measured and evaluated by the following methods, and the following raw materials were used.

[0071] [Measurement and evaluation methods] (1) Mesopentad fraction (mmmm) Dissolve the polypropylene resin sample in a solvent. 13The mesopentade fraction (mmmm) was determined using 1C-NMR under the following conditions (Reference: New Edition Polymer Analysis Handbook, edited by The Japan Society for Analytical Chemistry and the Polymer Analysis Research Group, 1995, pp. 609-611).

[0072] A. Measurement conditions Equipment: Bruker DRX-500 Nucleus for measurement: 13 C nucleus (resonance frequency: 125.8MHz) Measured concentration: 10% by mass Solvent: Benzene / deuterium dichlorobenzene = mass ratio 1:3 mixed solution Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Number of conversions: 10,000 Measurement mode: complete decoupling B.Analysis conditions A Fourier transform was performed with a line broadening factor (LB) of 1.0, resulting in a mmmm peak of 21.86 ppm. Peak splitting was then performed using WINFIT software (Bruker). The peak splitting was performed starting from the high-field side, and automatic fitting was then performed using the accompanying software. After optimizing the peak splitting, the sum of the mmmm peak fractions was calculated. This measurement was performed five times, and the average value was taken as the mesopentad fraction (mmmm) of this sample. peak (a)mrrm (b)(c)rrrm (split into two peaks) (d)rrrr (e)mrmr (f)mrmm+rmrr (g)mmrr (h)rmmr (i)mmmr (j)mmmm.

[0073] (2) Melt Flow Index (MFR) (Unit: g / 10min) Measurements were taken at 230°C and with a weight of 2.16 kg, in accordance with JIS K 7210-1 (2014).

[0074] (3) Melt tension (MS) (unit: cN) The following procedure was used to measure the tension using a melt tension tester (capillary diameter 2.1 mm, cylinder diameter 9.55 mm) manufactured by Toyo Seiki Seisakusho Co., Ltd. First, polypropylene resin was heated to 230°C and melted. Next, the molten polypropylene resin was extruded into strands at an extrusion speed of 15 mm / min, and the tension was measured when these strands were pulled back at a speed of 6.5 m / min. The obtained value was defined as the MS (Magnetic Stress Test).

[0075] (4)Cold xylene soluble part (CXS) 0.5 g of polypropylene resin was dissolved in 100 ml of boiling xylene at 135°C, allowed to cool, and then recrystallized in a constant temperature water bath at 20°C for 1 hour. The polypropylene components dissolved in the filtrate were quantified by liquid chromatography. When the mass of polypropylene resin before dissolution in boiling xylene was X0 (g) and the mass of polypropylene components dissolved in the filtrate was X (g), CXS was calculated using the following equation 3. Formula 3: CXS(mass%)=(X / X0)×100 (5) Height of the protruding peak Spk Measurements were taken using the "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) non-contact surface and layer cross-sectional shape measurement system manufactured by Ryoka Systems Co., Ltd. Ten measurement points were randomly selected from the film roll corresponding to the center position in the width direction from the center position of the film roll, and the average of the measurements from these ten points was defined as the height of the protruding peaks (Spk) of the surface characteristics of the sample. The detailed conditions for each measurement were as follows. Note that one field of view (field of view area: 939 μm vertical × 1,252 μm horizontal = 1,175,628 μm) was used for each measurement. 2 Measurements were taken of the following:

[0076] A. Measurement conditions CCD camera: SONY HR-57 1 / 2” Objective lens: 10X Lens tube: 0.5X BODY Wavelength filter: 530 white Measurement mode: Wave Field of view size: 640 x 480 Scan range: (Start) 5μm, (Stop) -5μm.

[0077] B.Measurement method A dedicated sample holder was used to secure the film during measurement. The sample holder consists of two detachable metal plates with a circular hole in the center. The film was placed between these plates, ensuring it was wrinkle-free, and measurements were taken on the central circular portion of the film. The film and sample holder were positioned so that the longitudinal direction of the film roll aligned with the vertical direction of the measurement field of view.

[0078] C. Analysis method The data obtained from the above measurements was analyzed using the image analysis software VS-Viewer of "VertScan" (registered trademark) 2.0. First, noise was removed using a median filter (5x5), and then undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, the surface texture protrusion height Spk, as defined in ISO25178-2 (2012), was calculated using the "ISOPara" function. In the "ISOPara" function, the S-Filter was set to 6.0 μm.

[0079] (6) Peak density Spd Measurements were performed using the non-contact surface and layer cross-sectional shape measurement system "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) manufactured by Ryoka Systems Co., Ltd. Ten measurement points were randomly selected from the film roll corresponding to the center position in the width direction, extending longitudinally from the center position of the film roll. At these ten points, peaks with a height of 5% or more of the maximum amplitude of the contour curve were counted. The average of the number of peaks included in the contour curve, calculated by dividing by the field of view area of ​​the contour curve, was defined as the peak density Spd of the surface characteristics of the sample. The detailed conditions for a single measurement are as follows. Note that one field of view (field of view area: 939 μm vertical × 1,252 μm horizontal = 1,175,628 μm) was used for one measurement. 2 Measurements were taken of the following:

[0080] A. Measurement conditions CCD camera: SONY HR-57 1 / 2” Objective lens: 10X Lens tube: 0.5X BODY Wavelength filter: 530 white Measurement mode: Wave Field of view size: 640 x 480 Scan range: (Start) 5μm, (Stop) -5μm.

[0081] B.Measurement method A dedicated sample holder was used to secure the film during measurement. The sample holder consists of two detachable metal plates with a circular hole in the center. The film was placed between these plates, ensuring it was wrinkle-free, and measurements were taken on the central circular portion of the film. The film and sample holder were positioned so that the longitudinal direction of the film roll aligned with the vertical direction of the measurement field of view.

[0082] C. Analysis method The data obtained from the above measurements was analyzed using the image analysis software VS-Viewer of "VertScan" (registered trademark) 2.0. First, noise was removed using a median filter (5x5), and then undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, the surface texture peak density Spd, as defined in ISO25178-2 (2012), was calculated using the "ISOPara" function. In the "ISOPara" function, the S-Filter was set to 6.0 μm.

[0083] (7) Thickness The thickness was measured using the micrometer method in accordance with JIS C 2330 (2014).

[0084] (8)GPC analysis The weight-average molecular weight, number-average molecular weight, and molecular weight distribution were determined using gel permeation chromatography (GPC). The GPC analysis equipment and conditions were as follows. Equipment: HLC-8321GPC / HT (Detector: RI) (Manufactured by Tosoh Corporation) Column: TSKgel GMHHR-H(20)HT (7.8mm I.D × 30cm) × 3 pieces (manufactured by Tosoh Corporation) Eluent: 1,2,4-Trichlorobenzene (for Fujifilm Wako Pure Chemical Industries GPC) + BHT (0.05%) Flow rate: 1.0mL / min Injection volume: 0.3mL Column temperature: 140℃ Sample concentration: 1 mg / ml Calibration curve: A fifth-order approximation curve was used, based on standard polystyrene manufactured by Tosoh Corporation. However, molecular weight was converted to polypropylene value using the Q-factor.

[0085] (9) Evaluation of processability of components in film capacitor manufacturing Aluminum was vacuum-deposited onto the corona-treated side of a biaxially oriented polypropylene film using a vacuum deposition machine manufactured by ULVAC, Inc., to achieve a surface resistance of 15 Ω / sq. The aluminum was deposited in a stripe pattern with a margin running along the longitudinal direction (a repeating pattern of 79.0 mm width in the deposited area and 1.0 mm width in the margin). Next, slits were made by cutting into the center of each deposited area and each margin, creating a tape-like winding reel with a total width of 40 mm and a 0.5 mm margin at either the left or right end. Two of these reels, one with the left margin and one with the right margin, were overlapped and wound together so that the deposited portion extended 0.5 mm beyond the margin in the width direction, resulting in a winding body with a capacitance of 120 μF. KAW-4NHB, manufactured by Kaito Seisakusho Co., Ltd., was used for winding. Finally, the winding body was heat-treated for 10 hours in a reduced-pressure atmosphere at 140°C. The coiled bodies were visually inspected, and any with wrinkles or distortions in their appearance or shape were deemed defective. 200 more coiled bodies were produced in the same manner, and the same evaluation was repeated. The processability of the coiled bodies was then assessed according to the following criteria. ◎: No defective products 〇: Less than 1 defective product △: Two or more defective items but less than three. ×: 4 or more defective items.

[0086] (10) Life evaluation of film capacitors A winding with a capacitance of 120 μF was obtained by the method described in (9). The winding was then heat-treated for 10 hours in a reduced-pressure atmosphere at 140°C, and metallicon was sprayed onto both ends in the width direction to serve as external electrodes. Lead wires were then welded to the metallicon to obtain a film capacitor. Next, the life evaluation of 15 film capacitors was performed using the following procedure. First, the capacitance (C0) was measured at room temperature. Then, a voltage of 325 VDC / μm (650 V when the thickness is 2.0 μm) was applied to the film capacitor at a high temperature of 120°C for 500 hours. After that, the capacitance (C) was measured at room temperature, and the rate of change of capacitance (ΔC) before and after voltage application was calculated from equation 5 below. The capacitance was measured using an LCR high-tester 3522-50 manufactured by HIOKI E.E. CORPORATION. Equation 4: ΔC=((C0-C) / C0)×100 The average of the rate of change (ΔC) of capacitance before and after voltage application for 15 film capacitors was used as the rate of change of capacitance before and after voltage application for that sample, and it was evaluated according to the following criteria. A smaller rate of change (ΔC) of capacitance before and after voltage application indicates that the decrease in capacitance at high temperatures is suppressed, and the lifespan evaluation of the film capacitor is considered good. ◎: ΔC is less than 2% ○: ΔC is between 2% and less than 3% △: ΔC is between 3% and less than 5% ×: ΔC is 5% or more.

[0087] (11) Film formation stability The film formation stability of biaxially oriented polypropylene films was evaluated according to the following criteria. The time from when film formation was stopped due to film tearing until it was resumed was excluded from the observation time. ◎: No film tears occurred for more than 48 hours from the start of film formation. ○: One film tear occurred 48 hours after the start of film formation. △: Two to three film tears occurred within 48 hours of the start of film formation. ×: More than four film tears occurred within 48 hours of the start of film formation.

[0088] [Raw materials] (1) Resin Highly stereoregular polypropylene resin (A): A highly stereoregular polypropylene resin (manufactured by Prime Polymer Co., Ltd.) with a mesopentad fraction of 0.980, an MFR of 2.8 g / 10 min, an MS of 0.9 cN, a CXS of 1.5 mass%, a weight-average molecular weight of 400,000, and a number-average molecular weight of 65,000.

[0089] High melt-tension polypropylene resin (H1): "WAYMAX" (registered trademark) (MFX3), manufactured by Nippon Polypropylene Co., Ltd., is a high melt-tension polypropylene resin with an MFR of 9.0 g / 10 min and an MS of 5.0 cN.

[0090] High melt-tension polypropylene resin (H2): WAYMAX (registered trademark) (EX6000), manufactured by Nippon Polypropylene Co., Ltd., is a high melt-tension polypropylene resin with an MFR of 2.9 g / 10 min and an MS of 9.0 cN.

[0091] High melt-tension polypropylene resin (I): Borealis' "Daploy" (trademark) (WB135HMS) is a high melt-tension polypropylene resin with an MFR of 2.5 g / 10 min and an MS of 32.0 cN.

[0092] (2) Antioxidants Antioxidant 1: BASF Japan's "Irganox" (registered trademark) 1010.

[0093] Antioxidant 2: 2,6-di-t-butyl-p-cresol (BHT).

[0094] (Example 1) A polypropylene resin mixture was prepared by mixing high stereoregularity polypropylene resin (A), high melt-tension polypropylene (H1), and high melt-tension polypropylene resin (I) in a mass ratio of 96.5:0.5:3.0. Antioxidant 1 and Antioxidant 2 were dry-blended in a mass ratio of 99.5:0.4:0.1 and supplied to a single-screw melt extruder, where it was melt-extruded at 250°C. After that, foreign matter was removed from the extruded molten polypropylene resin composition using a 25 μm cut sintered filter, and the mixture was further extruded in a sheet form through a T-type slit die. Furthermore, the sheet-like molten polypropylene resin composition was solidified by adhering it to a cast drum maintained at a temperature of 90°C using an air knife with an air temperature of 80°C, and then cooled on a cooling roll maintained at a temperature of 30°C to obtain a cast sheet. At this time, the temperature difference between the cast drum temperature and the air knife temperature was controlled to 10°C, and the time during which the sheet-like molten polypropylene resin composition was in close contact with the cast drum and the cooling roll was 1.5 seconds each (hereinafter, the side that was in contact with the cast drum will be referred to as the drum surface (D surface), and the side that was not in contact will be referred to as the non-drum surface (non-D surface)). Next, the obtained cast sheet was stretched in the longitudinal direction at a stretching ratio of 5.5 times using a longitudinal stretching roll at a temperature of 145°C to obtain a uniaxially oriented film. Furthermore, the widthwise end was gripped with a clip and guided to a tenter, where it was stretched in the widthwise direction under conditions of a temperature of 160°C and a stretching ratio of 11 times. Subsequently, a 12% relaxation treatment was performed in the widthwise direction at a temperature of 158°C, and it was slowly cooled to room temperature, with a cooling rate of 25 W·min / m on the D surface side. 2 Corona discharge treatment was performed at the specified treatment intensity. The widthwise end of the obtained biaxially oriented polypropylene film, held by clips, was cut off and wound up on a winding machine. Next, it was slit using a slitter to a film width of 0.82 m, and 30,000 m was wound onto a core in the longitudinal direction to obtain a biaxially oriented polypropylene film roll with a thickness of 2.0 μm. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1. Note that, from the results of the peak density Spd, the X-plane was on the non-drum plane (non-D-plane) side.

[0095] (Examples 2-7, Comparative Examples 1-6) A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the composition and manufacturing conditions of the polypropylene resin were as shown in Table 1. The physical properties and evaluation results of the obtained biaxially oriented polypropylene film are shown in Table 1. Note that the X-plane was the non-drum plane (non-D-plane) side based on the peak density Spd results.

[0096] [Table 1]

[0097] The polypropylene resin composition was calculated assuming the total polypropylene resin was 100% by mass. [Industrial applicability]

[0098] The present invention provides a biaxially oriented polypropylene film, a metal film laminated film, and a film capacitor using these, which have surface properties that enable uniform control of the amount of air and gap distance between film layers in a film capacitor, in order to obtain high productivity, processability, voltage resistance, and proper safety, mainly in high-temperature and high-voltage environments for large-capacity film capacitors.

Claims

1. A film comprising a highly stereoregular polypropylene resin (A) having a melt tension of less than 1.0 cN at 230°C as the main component, wherein 100% by mass of the total resin components constituting the film contains 0.1% by mass or more and 1.0% by mass or less of a high melt tension polypropylene resin (H) having a melt tension of 1.0 cN or more at 230°C, and contains 1.0% by mass or more and 5.0% by mass or less of a high melt tension polypropylene resin (I) having a melt tension of 1.0 cN or more at 230°C and a melt flux index (MFR) lower than that of the high melt tension polypropylene resin (H), On both sides, the peak density Spd is 250 / mm². ２ More than 800 / mm ２ A biaxially oriented polypropylene film characterized by having the following properties, and having a protruding peak height Spk of 35 nm or more and 80 nm or less.

2. The biaxially oriented polypropylene film according to claim 1, wherein the surface with a large Spd is the X-plane, the surface with a small Spd is the Y-plane, the Spd of the X-plane is Spd(x), and the Spd of the Y-plane is Spd(y), and the relationship shown in formula 1 below is satisfied. Formula 1: 1.00<Spd(x) / Spd(y)≦1.50

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein on at least one side, Spd and Spk satisfy the relationship of formula 2 below. Formula 2: 0.05≦Spk / Spd≦0.30

4. A biaxially oriented polypropylene film according to any one of claims 1 to 3, used as a dielectric for film capacitors.

5. A metal film laminated film having a metal film on at least one side of a biaxially oriented polypropylene film according to any one of claims 1 to 4.

6. A film capacitor having a configuration in which the metal film laminated film described in claim 5 is laminated or wound.

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