JP2024035063A - Biaxially oriented polypropylene film - Google Patents

Abstract

[Problem] The object of the present invention is to provide a biaxially oriented polypropylene film having excellent voltage resistance even at high temperatures, and surface properties that enable uniform control of the amount of air and gap distance between film layers of a film capacitor in order to obtain appropriate processability and safety, mainly in large-capacity film capacitors.Solution] A biaxially oriented polypropylene film, characterized in that at least one side is side A, where side A is the side with an interfacial developed surface area ratio (Sdr) of 0.0001% or more and less than 0.0004%. [Selected Figure] None

Description

The present invention relates to a biaxially oriented polypropylene film that has high voltage resistance under high temperature and high voltage environments when used as a dielectric of a film capacitor.

Biaxially oriented polypropylene film has excellent transparency, mechanical properties, and electrical properties, so it is used in a variety of applications including packaging, tape, cable wrapping, and electrical applications such as film capacitors.

Among these, in film capacitor applications, it is particularly preferably used as a dielectric material for film capacitors due to its excellent high withstand voltage characteristics and low loss characteristics. Recently, inverters are being used in various electrical equipment, and as a result, demands for smaller size and larger capacity film capacitors are becoming stronger. Furthermore, especially in automotive applications (including hybrid cars and electric vehicles), solar power generation, and wind power generation applications, the operating environment is becoming increasingly hot (85°C or higher and 125°C or lower), and film capacitors are required to be more heat resistant. is increasing.

Therefore, there is a need to make the dielectric biaxially oriented polypropylene film thinner, more heat resistant, and to improve the withstand voltage per thickness, and there is also a need to improve the safety of the film capacitor. Here, the safety of film capacitors refers to the property of maintaining insulation by scattering the deposited metal due to discharge energy during abnormal discharge in metal deposited film capacitors whose electrodes are metal deposited films formed on dielectric films. This is an important property in preventing short circuits and destruction of film capacitors. Controlling the surface properties of a polypropylene film is considered to be an effective means of achieving both high voltage resistance per thickness and safety for film capacitors, and various studies have been conducted to date.

As a method for controlling the surface properties of polypropylene films, a method that utilizes the crystal transition from β crystal to α crystal of polypropylene (hereinafter referred to as β crystal method) is known. This method that utilizes crystal transition is preferably used as a method for roughening the surface of biaxially oriented polypropylene films for film capacitors because it is not necessary to mix in impurities such as additives that may deteriorate the withstand voltage ( For example, see Patent Documents 1 and 2).

Techniques that focus on the density of surface roughness and uniformity of protrusions include a method of adding branched polypropylene (for example, see Patent Documents 3 and 4) and a method of mixing polypropylene with different molecular weights and molecular weight distributions (for example, the patent (see document 5) has been proposed. Since these methods can control the spherulite size to a small size, it is possible to form convex portions with uniform height and high density.

Further, as a technique that focuses on the convex portions and concave portions of the surface roughness, a method of subjecting a longitudinally stretched sheet to high temperature pressure treatment (for example, see Patent Document 6) has been proposed. With this method, the heights of the convex portions and concave portions can be uniformly controlled.

Japanese Patent Application Publication No. 2008-133446 Japanese Patent Application Publication No. 2014-077057 WO2007/094072 publication WO2012/121256 publication Japanese Patent Application Publication No. 2014-231584 JP 2019-172973 Publication

However, when the β-crystal method described in Patent Documents 1 and 2 is applied to a film made of general linear polypropylene, sharp crater-like convex portions and concave portions are formed at a low density. Dielectric breakdown was particularly likely to occur in the recesses, and there were issues with voltage resistance under high-temperature conditions. In addition, cases where the methods described in Patent Documents 3, 4, and 5 are applied to form convex portions with uniform height at high density, and patent documents where the heights of convex portions and concave portions of surface roughness are controlled uniformly are applied. When the method described in 6 is applied, it is not possible to suppress localized coarse protrusions and concave shapes, which affects workability during film capacitor production and voltage resistance and safety in recent high-temperature and high-voltage environments. It could not be said that the amount of air between the film layers could be controlled sufficiently.

Therefore, an object of the present invention is to suppress the formation of local coarse protrusions and recesses on the film surface in order to have high processability and voltage resistance, and to obtain appropriate safety mainly in large-capacity film capacitors. An object of the present invention is to provide a biaxially oriented polypropylene film having surface properties that allow uniform control of the amount of air and gap distance between film layers of a film capacitor.

The above-mentioned problems can be achieved by the following. That is, in the biaxially oriented polypropylene film of the present invention, at least one side is the A side, when the surface with the developed surface area ratio (Sdr) of the interface is 0.0001% or more and less than 0.0004% is the A side. A biaxially oriented polypropylene film characterized by:

Further, the biaxially oriented polypropylene film of the present invention can also be made into the following embodiments, and can also be made into a metal film laminate film or a film capacitor.
(1) Biaxially oriented polypropylene characterized in that at least one side is A-side, where A-side is a surface with an interface developed surface area ratio (Sdr) of 0.0001% or more and less than 0.0004%. film.
(2) The biaxially oriented polypropylene film according to (1), wherein the five-point valley region depth (S5v) of the A side is 30 nm or more and less than 70 nm.
(3) The biaxially oriented polypropylene film according to (1) or (2), wherein the five-point peak region height (S5p) of the A side is 50 nm or more and less than 80 nm.
(4) The biaxially oriented polypropylene film according to any one of (1) to (3), wherein the film thickness (t) is 1.0 μm or more and 4.0 μm or less.
(5) The maximum value, minimum value, and average value of BDV in the dielectric breakdown voltage (BDV) test conducted in accordance with JIS C 2330 (2014) at 23 ° C. and 65% RH atmosphere are Vmax, Vmin, and Vave, respectively. The biaxially oriented polypropylene film according to any one of (1) to (4), wherein (Vmax-Vmin)/Vave is 0.01 or more and 0.10 or less.
(6) Highly stereoregular polypropylene resin (A) is a highly stereoregular polypropylene resin, and among high melt tension polypropylene resins, one with a high melt flow rate index (MFR) at 230°C is a high melt tension polypropylene resin (H). ), when a low one is used as a high melt tension polypropylene resin (I), it contains a high stereoregular polypropylene resin (A) as a main component, and further contains a high melt tension polypropylene resin (H) and a high melt tension polypropylene resin (I). ) The biaxially oriented polypropylene film according to any one of (1) to (5).
(7) A metal film laminate film using the biaxially oriented polypropylene film according to any one of (1) to (6).
(8) A film capacitor using the metal film laminated film of (7).

According to the present invention, a biaxially oriented polypropylene film having high processability and voltage resistance can be provided. Further, by using the biaxially oriented polypropylene film of the present invention as a dielectric material of a film capacitor, it is possible to uniformly control the amount of air between film layers and the interlayer distance during processing into a film capacitor. Therefore, by using the biaxially oriented polypropylene film of the present invention in a film capacitor, the film capacitor exhibits high safety even under high temperature and high voltage environments, and its life span is also improved.

Hereinafter, the biaxially oriented polypropylene film, metal film laminate film, and film capacitor of the present invention will be explained in more detail. In addition, in the numerical range expressed using "~" below, the upper limit value and the lower limit value shall be included in the range, and the units of the upper limit value and the lower limit value shall be the same.

The biaxially oriented polypropylene film of the present invention is a biaxially oriented polypropylene film obtained by stretching a cast sheet in two orthogonal directions. In other words, the biaxial orientation here means stretching in two orthogonal directions (mainly the longitudinal direction and the width direction). Further, the longitudinal direction refers to the direction in which the film travels in 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.

The biaxially oriented polypropylene film of the present invention has a polypropylene resin as a main component. Note that the term "main component" refers to a component that is contained in an amount of more than 50% by mass and 100% by mass or less in 100% by mass of all components constituting the film. Moreover, polypropylene resin refers to a resin containing more than 50 mol% of propylene units and 100 mol% or less when the total constituent units constituting the resin are 100 mol%.

Note that the details of the polypropylene resin are not particularly limited as long as the biaxially oriented polypropylene film of the present invention has a polypropylene resin as a main component, but the highly stereoregular polypropylene resin (A), the highly stereoregular polypropylene resin (A), and the Among the melt tension polypropylene resins, when one with a high melt flow rate index (MFR) at 230°C is designated as a high melt tension polypropylene resin (H), and one with a low melt flow rate index (MFR) is designated as a high melt tension polypropylene resin (I), high stereoregularity is obtained. It is preferable that the composition contains a polypropylene resin (A) as a main component, and further contains a high melt tension polypropylene resin (H) and a high melt tension polypropylene resin (I). The 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.

Here, "mainly composed of highly stereoregular polypropylene resin (A)" means that 50% by mass of highly stereoregular polypropylene resin (A) is contained in 100% by mass of the total resin components of the biaxially oriented polypropylene film. It means containing more than 100% by mass, more preferably 90% by mass or more and less than 100% by mass, still more preferably 90% by mass or more and 98.9% by mass or less. By adopting such an aspect, it becomes easy to achieve both heat resistance and withstand voltage at high temperatures.

The biaxially oriented polypropylene film of the present invention may contain various additives, such as crystal nucleating agents, antioxidants, heat stabilizers, antistatic agents, antiblocking agents, fillers, viscosity A regulating agent, a coloring inhibitor, etc. may be included. Moreover, these components may be one type or multiple types as long as they do not impair the effects of the present invention.

Among the above additives, selection of the type of antioxidant and adjustment of the content are important from the viewpoint of long-term heat resistance of the biaxially oriented polypropylene film. From the above viewpoint, the antioxidant is preferably a phenolic one having steric hindrance, and specific examples thereof include 2,6-di-t-butyl-p-cresol (BHT), " Examples include "Irganox" (registered trademark) 1330 and "Irganox" (registered trademark) 1010 manufactured by BASF Japan. Note that these antioxidants can be used alone or in combination as long as they do not impair the effects of the present invention.

The total content of the above additives is preferably 0.01 parts by mass or more and 1.00 parts by mass or less, and 0.10 parts by mass or more and 0.01 parts by mass or less, based on 100 parts by mass of the resin component of the biaxially oriented polypropylene film. It is more preferably .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. By setting the antioxidant content in the polypropylene resin composition to 0.01 parts by mass or more, the antioxidant effect can be easily obtained, and the resulting biaxially oriented polypropylene film can easily maintain long-term heat resistance. On the other hand, by controlling the antioxidant content in the polypropylene resin composition to 1.00 parts by mass or less, it is easy to maintain voltage resistance characteristics at high temperatures.

Next, the polypropylene resin used in the biaxially oriented polypropylene film of the present invention will be explained in more detail. As described above, the biaxially oriented polypropylene film of the present invention preferably contains a high stereoregular polypropylene resin (A), a high melt tension polypropylene resin (H), and a high melt tension polypropylene resin (I).

The highly stereoregular polypropylene resin (A) used as a raw material for the biaxially oriented polypropylene film of the present invention is an isotactic polypropylene resin, more specifically, the melt tension (MS) when measured at 230°C ( Unit: cN) means a polypropylene resin having a value of 1.0 cN or less. Such isotactic polypropylene resins are known as polypropylene resins commonly used in film capacitor applications.

Note that MS refers to the tension when polypropylene resin is heated to 230°C to melt it, the molten polypropylene is extruded into a strand at an extrusion speed of 15 mm/min, and this strand is taken off at a speed of 6.5 m/min (details). (The measurement method will be described later.) The MS measurement method and conditions are the same for the high melt tension polypropylene resin (H) and the high melt tension polypropylene resin (I).

The highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention has a weight average molecular weight (Mw) of 200,000 to 500,000 and a number average molecular weight (Mn) of 4, as measured by GPC method. It is preferably 90,000 or more and 90,000 or less. Further, the molecular weight distribution (Mw/Mn) is preferably 4.0 or more and 8.0 or less, more preferably 5.0 or more and 7.0 or less. A high molecular weight distribution (Mw/Mn) means a wide molecular weight distribution, and by using a highly stereoregular polypropylene resin (A) in the above range, it is possible to improve film formation stability and withstand voltage at high temperatures. Easy to balance.

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, and 3 It is more preferably .0% by mass or less, and particularly preferably 2.0% by mass or less. CXS is a polypropylene component dissolved in xylene when a film is completely dissolved in xylene at 135°C and then precipitated at 20°C. This is considered to correspond to a component that is difficult to crystallize due to reasons such as stereoregularity and low molecular weight. Since 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 easy to improve the high temperature withstand voltage characteristics and dimensional stability of the biaxially oriented polypropylene film. Become.

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, left to cool, recrystallized in a constant temperature water bath at 20°C for 1 hour, and filtered. Next, the polypropylene component dissolved in the filtrate was quantified by liquid chromatography, and the mass of the polypropylene resin before dissolving in boiling xylene was determined as X0 (g), and the mass of the polypropylene component dissolved in the filtrate as X ( As g), CXS is determined from the following formula 1.
Formula 1: CXS (mass%) = (X/X0) x 100.

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, and 0.960 or more and 0.995 or less. More preferably, it is 0.970 or more and 0.995 or less. The mesopentad fraction (mmmm) is an index showing the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance method (NMR method). It is preferable because it has excellent withstand voltage characteristics. When the mesopentad fraction of the highly stereoregular polypropylene resin (A) is 0.960 or more, high-temperature withstand voltage characteristics and dimensional stability can be easily maintained. On the other hand, when the mesopentad fraction of the highly stereoregular polypropylene resin (A) is 0.995 or less, film forming properties are maintained and a biaxially oriented polypropylene film is easily obtained stably. The mesopentad fraction can be measured by dissolving a polypropylene resin sample in a solvent and using ¹³ C-NMR, and detailed conditions are shown in Examples.

The MFR of the highly stereoregular polypropylene resin (A) used in the biaxially oriented polypropylene film of the present invention is measured at 230°C and 2.16 kg in accordance with JIS K 7210-1 (2014). It is preferably 1.0 g/10 minutes or more and 5.0 g/10 minutes or less, more preferably 1.0 g/10 minutes or more and 4.5 g/10 minutes or less, and 1.0 g/10 minutes or more and 4.0 g /10 minutes or less is more preferable. When the MFR of the highly stereoregular polypropylene resin (A) is 1.0 g/10 minutes or more, a biaxially oriented polypropylene film can be easily obtained stably while maintaining film formability. On the other hand, when the MFR of the highly stereoregular polypropylene resin (A) is 5.0 g/10 minutes or less, dimensional stability and high temperature withstand voltage characteristics are easily maintained. Note that the MFR measurement method and conditions are the same for the high melt tension polypropylene resin (H) and the high melt tension polypropylene resin (I) below.

Next, the high melt tension polypropylene resin (H) will be explained. The high melt tension polypropylene resin (H) as used in the present invention is a polypropylene resin having a melt tension (MS, unit: cN) at 230° C. exceeding 1.0 cN.

The biaxially oriented polypropylene film of the present invention preferably contains 0.1% by mass or more and 1.0% by mass or less of high melt tension polypropylene resin (H) in 100% by mass of the total resin components constituting the film, and 0.1% by mass or more and 1.0% by mass or less It is more preferable that it is .1 mass % or more and 0.9 mass % or less, and even more preferably that it is 0.3 mass % or more and 0.8 mass % or less. In addition, if multiple components corresponding to high melt tension polypropylene resin (H) are contained in the biaxially oriented polypropylene film, the content shall be determined by adding up all the corresponding components, and this point will be explained later. The same applies to the high melt tension polypropylene resin (I). (We will discuss later whether it should be treated as such.)

By setting the content of the high melt tension polypropylene resin (H) to 0.1% by mass or more in 100% by mass of all components constituting the film, excessive smoothing of the surface of the biaxially oriented polypropylene film is suppressed. Therefore, the transportability in the processing process is improved and the element processability is improved. Furthermore, by adopting such an aspect, it is also possible to form a thin film more stably when biaxially stretching the thin film. In addition, by setting the content of the high melt tension polypropylene resin (H) to 1.0% by mass or less, the spherulite size does not become too large when forming the molten polymer into a sheet shape, and the biaxially oriented polypropylene film can be used as a biaxially oriented polypropylene film. Since the decrease in stereoregularity is reduced, it is easier to maintain voltage resistance at high temperatures.

Next, the high melt tension polypropylene resin (I) will be explained. The high melt tension polypropylene resin (I) in the present invention is a polypropylene resin whose melt tension (MS, unit: cN) at 230°C exceeds 1.0 cN and which has a lower MFR than the high melt tension polypropylene resin (H). It is.

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 the total resin components constituting the film, and 2 It is more preferably .0 mass % or more and 5.0 mass % or less, and even more preferably more than 3.3 mass % and 4.3 mass % or less.

By setting the content of high melt tension polypropylene resin (I) to 1.0% by mass or more in 100% by mass of all components constituting the film, the spherulites generated when molding the molten polymer into a sheet shape Since the size of the spherulite is suppressed, the decrease in voltage resistance characteristics caused by the unevenness of the large spherulites is reduced. Furthermore, by adopting such an embodiment, it becomes possible to form a thin film more stably when biaxially stretching the thin film. In addition, by setting the content of the high melt tension polypropylene resin (I) to 5.0% by mass or less, the size of the spherulites formed when molding the molten polymer into a sheet shape does not become too small, and the biaxial Since the smoothness of the surface of the oriented polypropylene film is maintained, the processability of the device as a biaxially oriented polypropylene film is improved.

High melt tension polypropylene resins (H) and (I) can be obtained by applying high-energy ionizing radiation to polypropylene resin (for example, JP-A-62-121704), or by applying a specific organic peroxide to polypropylene resin. A method of reacting (for example, Japanese Patent No. 2869606), a method of reacting a thermally decomposable radical forming agent and an ethylenic polyfunctional unsaturated monomer with a polypropylene resin (for example, Japanese Patent Application Laid-open No. 10-330436), polymerization of polypropylene resin Sometimes a method using a specific catalyst (for example, JP-A-2009-057542) is preferably used.

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

The following describes how to handle the case where three or more types of polypropylene resins having a melt tension MS exceeding 1.0 cN are included. In such a case, among the polypropylene resins with a melt tension MS exceeding 1.0 cN, the one with the largest MFR is designated as the high melt tension polypropylene resin (H), and all others are designated as the high melt tension polypropylene resin (I). handle. In addition, if there are multiple polypropylene resins having a melt tension MS exceeding 1.0 cN and having the largest MFR, all of these are treated as high melt tension polypropylene resins (H).

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. Note that the polypropylene resin having a branched structure in the molecular chain is a polypropylene resin having internal trisubstituted olefins at 5 or less locations per 10,000 carbon atoms, and the presence of this internal trisubstituted olefin results in ¹ H - It can be confirmed by the proton ratio in the NMR spectrum. The high melt tension polypropylene resins (H) and (I) have the function of an α-crystal nucleating agent, and can also form a rough surface due to crystal morphology if added in a certain range of amounts. That is, by containing high melt tension polypropylene resins (H) and (I), the spherulite size of polypropylene produced in the cooling process of the melt-extruded resin sheet can be controlled to a small size, and the resin has excellent voltage resistance characteristics under high temperatures. A biaxially oriented polypropylene film can be obtained.

Regarding the high melt tension polypropylene resin (H) and the high melt tension polypropylene resin (I) constituting the biaxially oriented polypropylene film of the present invention, from the MS of the high melt tension polypropylene resin (I) to the high melt tension polypropylene resin (H), The difference after subtracting MS is preferably 1.0 or more and 30.0 or less, more preferably 3.0 or more and 29.0 or less, and even more preferably 4.0 or more and 28.0 or less. Biaxially oriented polypropylene film with excellent film formability and high-temperature withstand voltage characteristics by keeping the difference between the MS of high melt tension polypropylene resin (I) and the MS of high melt tension polypropylene resin (H) within the above range. Easy to get.

Biaxially oriented polypropylene films are used as dielectrics in film capacitors by metal vapor deposition on their surfaces, but biaxially oriented polypropylene films usually have low surface energy, and adhesion of the vapor-deposited metals may be an issue. be. Therefore, it is preferable to subject the biaxially oriented polypropylene film to surface treatment after biaxial stretching. As a specific surface treatment method, for example, corona discharge treatment, plasma treatment, glow treatment, flame treatment, etc. can be adopted.

In the biaxially oriented polypropylene film of the present invention, from the viewpoint of achieving both processability and withstand voltage characteristics, when the surface where the developed surface area ratio (Sdr) of the interface is 0.0001% or more and less than 0.0004% is defined as the A side. It is important that at least one side is the A side. From the above viewpoint, it is more preferable that the developed surface area ratio Sdr of the interface on the A side is 0.0001% or more and less than 0.0003%.

The developed surface area ratio Sdr of the interface is a complex parameter for evaluating the three-dimensional surface texture (surface roughness) defined in ISO25178-2 (2012), and the developed area (surface area) of the defined area is It shows how much it has increased relative to the area of . If the developed area of the defined area has no surface irregularities, it will be the same as the area of the defined area, so Sdr=0%. The device for measuring the developed surface area ratio Sdr of the interface is not particularly limited as long as it can perform the above measurement, but for example, the non-contact surface/layer cross-sectional shape measurement system “VertScan” (registered trademark) manufactured by Ryoka System Co., Ltd. )2.0 can be used.

By setting the developed surface area ratio Sdr of the interface to 0.0001% or more on at least one side, the slipperiness of the film is maintained. Therefore, it is possible to prevent the occurrence of wrinkles and deterioration of the winding shape of the film roll in the conveying step during processing of the biaxially oriented polypropylene film, and the processability is improved. Furthermore, it is possible to prevent the interlayer gap of the film from becoming narrow during the formation of a film capacitor element, thereby making it difficult to cause short-circuit damage when the film capacitor is used.

On the other hand, the fact that the developed surface area ratio Sdr of the interface is less than 0.0004% means that there are no excessive irregularities on the surface. Therefore, when the developed surface area ratio Sdr of the interface is less than 0.0004% on at least one side, the interlayer gap of the film is kept narrow during the formation of a film capacitor element, and an excessive increase in safety can be suppressed. That is, by adopting such an embodiment, the decrease in voltage resistance characteristics caused by unevenness on the surface of the biaxially oriented polypropylene film can be reduced, and as a result, the life of the film capacitor can be extended.

That is, since at least one side of the polypropylene film of the present invention is the A side, appropriate unevenness is maintained on the surface, and excellent workability and voltage resistance performance can be improved. In addition, when the developed surface area ratio Sdr of the interface is 0.0001% or more and less than 0.0004% on both surfaces or satisfies the above preferable range (i.e., when both surfaces are A side), the processability and withstand voltage performance are even better. This result is more preferable.

In order to set the developed surface area ratio Sdr of the interface to 0.0001% or more and less than 0.0004% or the above preferable range on at least one side, the above-mentioned polypropylene resin is used, and as described later, the longitudinal stretching during film formation is One example is a method in which the preheating step is performed under specific conditions. More specifically, by applying heat locally using a radiation heater or the like to a cast sheet whose constituent component is the polypropylene resin described above, the β crystals in the cast sheet are instantaneously transformed into α crystals, and the surface Controlling the structure is effective. At this time, by increasing the processing time of the radiation heater, Sdr can be increased.

In the biaxially oriented polypropylene film of the present invention, the depth of the five-point valley region (S5v) on the A side is preferably 30 nm or more and less than 70 nm, more preferably 40 nm or more and less than 60 nm, and preferably 50 nm or more and less than 55 nm. It is even more preferable. The five-point valley region depth S5v is a feature parameter for evaluating the three-dimensional surface texture (surface roughness) defined in ISO25178-2 (2012), and is defined in the defined region in descending order from the deepest valley point. The average height of the valley regions up to the fifth is shown. The measuring device for the five-point valley depth S5v is not particularly limited as long as it can perform the above measurements, but for example, the non-contact surface/layer cross-sectional shape measuring system “VertScan” (registered) manufactured by Ryoka System Co., Ltd. Trademark) 2.0 can be used.

By setting the S5v of the A side to 30 nm or more and less than 70 nm, it is possible to suppress the occurrence of blocking and transport wrinkles in the film transport process during film formation and film capacitor element processing. Defects in appearance and internal shape can be reduced. Furthermore, it is possible to prevent the gap between the layers of the film from becoming narrow during the formation of a film capacitor element, and to suppress the occurrence of short-circuit damage when using the film capacitor. Furthermore, setting the S5v of the A surface to be less than 70 nm means that the depth of the recesses existing on the surface is shallow. By adopting such an aspect, the deterioration of the withstand voltage characteristics caused by the recesses is reduced, so that the life of the film capacitor can be extended. That is, if at least one side is the A side and the S5v is within the above range on that side, the biaxially oriented polypropylene film can maintain appropriate recesses and has excellent processability and voltage resistance performance. . From the above point of view, especially when both surfaces are A-side and the five-point valley region depth S5v is 30 nm or more and less than 70 nm on both surfaces or satisfies the above preferable range, the result is even better workability and withstand voltage performance. preferable.

In order to set the S5v of the A side to 30 nm or more and less than 70 nm or the above preferable range, there is a method in which the above-mentioned polypropylene resin is used and the longitudinal stretching preheating step during film formation is set to specific conditions as described later. It will be done. S5v can also be increased by locally applying heat using a radiation heater or the like.

In the biaxially oriented polypropylene film of the present invention, the height of the five-point peak region (S5p) on the A side is preferably 50 nm or more and less than 80 nm, more preferably 55 nm or more and less than 80 nm, and preferably 61 nm or more and less than 80 nm. It is more preferable that the thickness be 61 nm or more and 70 nm or less. The five-point mountain area height S5p is a morphological parameter for evaluating the three-dimensional surface texture (surface roughness) defined in ISO25178-2 (2012), and is determined in ascending order from the highest peak in the defined area. It represents the average height of the 5th mountain area. The measuring device for the five-point mountain area height S5p is not particularly limited as long as it can perform the above measurement, but for example, the non-contact surface/layer cross-sectional shape measuring system “VertScan” (registered) manufactured by Ryoka System Co., Ltd. Trademark) 2.0 can be used.

By setting the S5p of the A side to 50 nm or more, blocking and transport wrinkles can be suppressed in the film transport process during film formation and film capacitor element processing, thereby reducing the deterioration of the winding appearance of the film roll and the appearance of the film capacitor element. Internal shape defects can be reduced. Furthermore, by setting the five-point peak region height S5p to less than 80 nm, slipperiness can be moderately suppressed, and it is possible to reduce winding misalignment and meandering in the conveyance process during processing of biaxially oriented polypropylene film. Since the interlayer gap of the film does not become excessively wide during the formation of the capacitor element, the safety is not excessive, and as a result, the life of the film capacitor can be extended. That is, if at least one side is the A side and S5p is 50 nm or more and less than 80 nm on that side, the biaxially oriented polypropylene film can maintain appropriate convex portions and has excellent processability and voltage resistance performance. becomes. From the above point of view, it is particularly preferable that S5p satisfies the above range on both surfaces, as this results in even better workability and withstand voltage performance.

In order to set the S5p of the A side to 50 nm or more and less than 80 nm or the above preferable range, there is a method in which the above-mentioned polypropylene resin is used and the longitudinal stretching preheating step during film formation is set to specific conditions as described later. It will be done. The S5p value can also be increased by locally applying heat using a radiation heater or the like.

The biaxially oriented polypropylene film of the present invention is produced by molding a polypropylene resin composition containing the above-described highly stereoregular polypropylene resin (A) and high melt tension polypropylene resins (H) and (I) into a sheet shape, and biaxially stretching the polypropylene resin composition. It is preferable to obtain it by. Biaxial stretching can be achieved by any of the simultaneous inflation biaxial stretching method, simultaneous tenter biaxial stretching method, and sequential tenter biaxial stretching method. It is preferable to employ a biaxial stretching method. In particular, it is preferable to stretch in the width direction after stretching in the longitudinal direction.

The biaxially oriented polypropylene film of the present invention preferably has a thickness of 1.0 μm or more and 4.0 μm or less from the viewpoint of mechanical strength, high-temperature withstand voltage characteristics, and capacity per volume when used as a dielectric of a film capacitor. preferable. From the above viewpoint, the thickness of the biaxially oriented polypropylene film is more preferably 1.2 μm or more and 3.8 μm or less, and even more preferably 1.4 μm or more and 3.0 μm or less. By setting the thickness to 1.0 μm or more, the biaxially oriented polypropylene film can have excellent mechanical strength and high-temperature withstand voltage characteristics, and can also reduce breakage during film formation and processing. . On the other hand, by setting the thickness to 4.0 μm or less, the capacitance per volume can be increased when used as a dielectric of a film capacitor. In addition, the thickness shall be measured by a micrometer method according to JIS C 2330 (2014).

The thickness of the biaxially oriented polypropylene film can be adjusted, for example, by adjusting the slit width of the T-die, the discharge amount from the T-die, the rotational speed of the cast drum, the product of the stretching ratio, etc. More specifically, the thickness of the biaxially oriented polypropylene film can be reduced by reducing the slit width of the T-die, reducing the discharge amount from the T-die, increasing the rotation speed of the cast drum, and increasing the product of the stretching ratio. can do. Note that these methods may be used in combination as appropriate.

The biaxially oriented polypropylene film of the present invention has the maximum value, minimum value, and average value of BDV in a dielectric breakdown voltage (BDV) test conducted in accordance with JIS C 2330 (2014) at 23°C and 65% RH atmosphere. , Vmax, Vmin, and Vave, respectively, it is preferable that (Vmax−Vmin)/Vave is 0.01 or more and 0.10 or less, more preferably 0.01 or more and 0.05 or less.

Vmax, Vmin, and Vave in measuring the dielectric breakdown voltage (BDV) can be measured by the following procedure (details will be described later). First, a biaxially oriented polypropylene film is divided into 30 equal parts in the width direction to obtain square test pieces in which the length of each piece is 1/30 of the length in the width direction (at this time, the center part of the test piece is (Take samples so that they are located on a straight line parallel to the width direction.) Next, a BDV test according to JIS C 2330 (2014) was carried out on the central part of the 30 test pieces obtained at 23°C and 65% RH, and out of a total of 30 measured values (calculated values), The maximum value, minimum value, and average value are determined from 20 points excluding the 5 points with the highest breakdown voltage and the 5 points with the lowest breakdown voltage, and these are set as Vmax, Vmin, and Vave in that order. Note that if the width direction is unknown or if it is not possible to obtain a test piece of a measurable size by dividing the test piece into 30 equal parts in the width direction, it is possible to arbitrarily obtain 30 test pieces and perform the same evaluation. Furthermore, when a single intermediate product roll is slit parallel to the longitudinal direction to produce a plurality of identical film rolls, test pieces may be sampled from the intermediate product roll as described above.

A small value of (Vmax-Vmin)/Vave means that the withstand voltage characteristics throughout the biaxially oriented polypropylene film are more uniform. In other words, by setting (Vmax-Vmin)/Vave to 0.10 or less, the withstand voltage performance becomes more uniform throughout the biaxially oriented polypropylene film, which improves the life of the resulting film capacitor and reduces variations. Ru. In addition, the lower limit of (Vmax-Vmin)/Vave is preferably smaller from the viewpoint of the life of the film capacitor, but from the viewpoint of feasibility it is 0.01, and from the viewpoint of device processability, it is 0.04. preferable.

As a method for adjusting (Vmax-Vmin)/Vave to 0.01 or more and 0.10 or less, the above-mentioned polypropylene resin is used in the above-mentioned preferred amount, and as described later, the longitudinal stretching preheating step during film production is performed. An example of this method is to set the condition as a specific condition. Further, the breakdown voltage (BDV) can be set within a preferable range by locally applying heat using a radiation heater or the like.

Next, the method for producing a biaxially oriented polypropylene film of the present invention will be explained in more detail below using specific examples, but the method for producing a biaxially oriented polypropylene film of the present invention is not necessarily limited to this. .

First, the above-mentioned highly stereoregular polypropylene resin (A) and high melt tension polypropylene resins (H) and (I) are dry-blended so that each component has the above-mentioned preferred amount, and then placed in a single-screw melt extruder. and melt extrusion at 200-260°C. Next, a filter installed in the middle of the polymer tube removes foreign substances and modified polymers. Then, the molten polymer formed into a sheet is discharged from a T-die onto a cast drum, cooled and solidified to form a cast sheet, and this is cooled by a cooling roll.

The temperature of the cast drum is preferably 80°C or more and 120°C or less, more preferably 85°C or more and 115°C or less, and even more preferably 85°C or more and 110°C or less, from the viewpoint of appropriately generating β crystals and spherulites. Even more preferred. By setting the cast drum temperature to 80°C or higher, the β-crystals formed in the cast sheet will not decrease too much, and the film obtained after biaxial stretching will maintain its slipperiness. It is possible to prevent the occurrence of wrinkles during the conveyance process and deterioration of the winding appearance of the film roll. On the other hand, by keeping the cast drum temperature below 120°C, it is possible to prevent excessive formation of β-crystals in the cast sheet, which can prevent meandering in the film conveyance process during film forming and processing, and prevent film rolls from forming. The deterioration of the winding appearance is reduced.

The molten sheet discharged from the T-die lands on the cast drum and is in close contact with the drum for preferably 0.8 seconds or more and 3.0 seconds or less, and preferably 1.0 seconds or more and 3.0 seconds or less. It is more preferable that there be. When the contact time is 0.8 seconds or more, the molten sheet can be easily solidified, and breakage in the subsequent stretching process can be reduced. On the other hand, if the contact time is 3.0 seconds or less, excessive formation of β-crystals in the cast sheet can be prevented, and the occurrence of meandering in the film conveyance process during film formation and processing can be prevented. Deterioration in the appearance of the film roll is reduced.

Methods such as electrostatic application, air knife method, nip roll method, and underwater casting method can be used to bring the molten sheet into close contact with the cast drum. The air knife method is preferred from the viewpoint of property control. The air temperature of the air knife is preferably 60°C or more and 100°C or less. By setting the air knife temperature to 60°C or higher, the β crystals formed in the cast sheet do not decrease too much, and the slipperiness of the film obtained after biaxial stretching is maintained. The occurrence of wrinkles and deterioration of the film roll appearance during the conveyance process are reduced. On the other hand, by setting the air knife temperature to 100°C or less, β crystals are not excessively formed in the cast sheet, and the occurrence of meandering in the film conveyance process during film forming and processing and deterioration of the winding shape of the film roll are avoided. Reduced.

Next, the obtained cast sheet is biaxially stretched. As specific stretching conditions, first, the temperature at which the cast sheet is stretched in the longitudinal direction is controlled. Examples of temperature control methods include a method using a temperature-controlled rotating roll and a method using a hot air oven.

In the longitudinal stretching preheating step, the cast sheet is first preheated with rolls kept at 100 to 120°C, and then preheated with rolls kept at 120 to 145°C. Furthermore, by installing a radiation heater on the roll kept at a temperature of 135 to 150°C above the previous roll temperature, preferably above the previous roll temperature and 140 to 150°C, and applying heat locally. , to control the cast sheet surface structure.

From the viewpoint of controlling the developed surface area ratio Sdr of the interface of the obtained biaxially oriented polypropylene film within an appropriate range, it is preferable to locally apply the amount of heat using a radiation heater. When the distance between the cast sheet and the radiation heater is 5.0 mm, and the output of the radiation heater is 5.0 kW, the processing time using the radiation heater is preferably 0.1 seconds or more and 1.0 seconds or less, and 0.2 seconds or more and 0.2 seconds or more. The time is more preferably 0.8 seconds or less, and even more preferably 0.3 seconds or more and 0.7 seconds or less. By setting the treatment time with the radiation heater to 0.1 seconds or more, the amount of heat required for surface control can be reached, and the developed surface area ratio Sdr of the interface of the resulting biaxially oriented polypropylene film can be lowered to an appropriate level. . On the other hand, by setting the treatment time using the radiation heater to 1.0 seconds or less, it is possible to prevent film breakage due to excessive heat and an excessive increase in the developed surface area ratio Sdr of the interface of the resulting biaxially oriented polypropylene film. .

The distance between the radiation heater and the cast sheet is preferably 1.0 to 10 mm, and the output of the radiation heater is preferably 1.0 to 10 kW. When adjusting the distance between the radiation heater and the cast sheet and the output of the radiation heater within this range, set these to 5.0 mm and 5.0 kW, respectively, and set the processing time to 0.1 seconds or more and 1.0 seconds or less. The treatment time can be adjusted to provide the same amount of heat.

Next, the cast sheet is stretched in the longitudinal direction in a longitudinal stretching step. The cast sheet that has gone through the preheating process for longitudinal stretching is passed through rolls whose temperature is controlled at 120° C. or higher and 140° C. or lower, and stretched in the longitudinal direction (longitudinal stretching) at a predetermined stretching speed and stretching ratio depending on the peripheral speed difference between the rolls. The stretching ratio in the longitudinal direction is preferably 4.0 times or more and 7.0 times or less, and more preferably 5.0 times or more and 7.0 times or less. By setting the stretching ratio to 4.0 times or more, the surface texture of the resulting biaxially oriented polypropylene film becomes more uniform, and the withstand voltage characteristics at high temperatures are improved. When the longitudinal stretching ratio is 7.0 times or less, breakage of the film in the longitudinal stretching process and the next horizontal stretching process is reduced.

Next, both ends in the width direction of the uniaxially oriented film obtained by longitudinal stretching are held with clips, and stretched in the width direction at a stretching ratio of 5 times to 15 times using a tenter-type stretching machine controlled at a temperature of 140°C to 170°C. Stretch to. Further, it is heat set at a temperature of 150 to 170°C while relaxing by 5 to 15% in the width direction.

Next, the biaxially stretched film is subjected to a corona discharge treatment on the side that is in contact with the cast drum (drum surface (D surface)) in air, nitrogen, carbon dioxide, or a mixture of these. The edges of the film held by the clip are cut and removed, and the film with the edges removed is wound up as a master roll by a winder. Finally, the film unwound from the master roll is slit to a specific width using a slitter, and wound around a core as a film roll to obtain the biaxially oriented polypropylene film of the present invention.

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, from the viewpoint of electrode configuration, either a foil-wound film capacitor or a metal-deposited film capacitor may be used, an oil-immersed film capacitor containing insulating oil, or a dry film capacitor that does not use any insulating oil. It is also preferably used in capacitors. Moreover, from the viewpoint of shape, it does not matter if it is a winding type or a laminated type. Due to the characteristics of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal vapor deposited film capacitor.

Next, the metal film laminate film of the present invention will be explained. The metal film laminate film of the present invention uses the biaxially oriented polypropylene film of the present invention. As a method for forming a metal film on the polypropylene film of the present invention, a method is preferably used in which a metal such as aluminum is vapor-deposited on at least one side of a biaxially oriented polypropylene film to provide a metal film that will become an internal electrode of a film capacitor. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can also be deposited simultaneously or sequentially with the aluminum. Further, a protective layer may be provided on the metal film using oil or the like. The thickness of the metal film is preferably 20 nm or more and 100 nm or less from the viewpoint of electrical properties and safety of the film capacitor. Further, for the same reason, it is preferable that the surface resistance value of the metal film is 1 Ω/sq or more and 20 Ω/sq or less. The surface resistance value can be controlled by the metal type and film thickness used.

Next, the film capacitor of the present invention will be explained. The film capacitor of the present invention uses the metal film laminate film of the present invention, and has a structure in which the metal film laminate films are laminated or wound. An example of a method for manufacturing a wound film capacitor will be described below. First, aluminum is vacuum-deposited on one side of a biaxially oriented polypropylene film to obtain a metal film laminate film. At this time, aluminum is vapor-deposited in the form of a stripe with a margin running in the longitudinal direction of the film. Next, a blade is inserted into the center of each vapor-deposited part and the center of each margin part on the surface to make a slit, thereby producing a tape-shaped take-up reel whose surface has a margin on one side. Two tape-shaped take-up reels with a margin on the left or right are wound, one on the left margin and one on the right margin, one on top of the other so that the vapor-deposited part protrudes from the margin in the width direction to create a wound body. get. After the wound body is heat-treated, metallicon is thermally sprayed on both end faces in the width direction to form external electrodes, and lead wires are welded to the metallicon to obtain a wound film capacitor. Film capacitors are used in a wide variety of applications, including vehicles, home appliances (TVs, refrigerators, etc.), general miscellaneous protection, automobiles (hybrid cars, power windows, wipers, etc.), and power supplies. The film capacitor used can also be suitably used for these purposes.

EXAMPLES Hereinafter, the present invention will be explained in detail 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 materials were used as raw materials.

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

A. Measurement conditions device: Bruker DRX-500
Measurement nucleus: ^13C nucleus (resonance frequency: 125.8MHz)
Measured concentration: 10% by mass
Solvent: benzene/heavy orthodichlorobenzene = mass ratio 1:3 mixed solution Measurement temperature: 130°C
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 times Measurement mode: complete decoupling.

B. Analysis Conditions Fourier transform was performed with LB (line broadening factor) set to 1.0, mmmm peak was set at 21.86 ppm, and peak division was performed using WINFIT software (manufactured by Bruker). At that time, we performed peak division as shown below starting from the peak on the high magnetic field side, and then performed automatic fitting using the attached software. After optimizing the peak division, the sum of mmmm peak fractions was determined. The above measurement was performed five times, and the average value was taken as the mesopentad fraction (mmmm) of this sample.
(Peak splitting)
(a) mrrm
(b) (c) rrrm (split as two peaks)
(d)rrrr
(e) mrmr
(f) mrmm+rmrr
(g)mmrr
(h)rmmr
(i)mmmr
(j)mmmm.

(2) Melt flow index (MFR) (unit: g/10min)
Measured at 230°C and 2.16 kg in accordance with JIS K 7210-1 (2014).

(3) Melt tension (MS) (unit: cN)
The measurement was performed using a melt tension tester manufactured by Toyo Seiki Seisakusho Co., Ltd. (capillary diameter 2.1 mm, cylinder diameter 9.55 mm) according to the following procedure. First, polypropylene resin was heated to 230°C and melted. Next, the molten polypropylene resin was extruded into a strand at an extrusion speed of 15 mm/min, and the tension when this strand was taken off at a speed of 6.5 m/min was measured, and the obtained value was taken as the MS of the polypropylene resin.

(4) Cold xylene soluble part (CXS unit: mass%)
0.5 g of polypropylene resin was dissolved in 100 ml of boiling xylene at 135°C, left to cool, and then recrystallized in a constant temperature water bath at 20°C for 1 hour. Thereafter, solid substances such as crystals were removed by filtration, and the polypropylene components dissolved in the filtrate were quantified by liquid chromatography. CXS was determined from the following formula 1, where the mass of the polypropylene resin before dissolving in boiling xylene was defined as X0 (g), and the mass of the polypropylene component dissolved in the filtrate was defined as X (g).
Formula 1: CXS (mass%) = (X/X0) x 100.

(5) Interface developed surface area ratio Sdr (unit: %), five-point valley region depth S5v (unit: nm), five-point peak region height S5p (unit: nm)
The measurement was performed using a non-contact surface/layer cross-sectional shape measurement system "VertScan" (registered trademark) 2.0 (model: R3300GL-Lite-AC) manufactured by Ryoka System Co., Ltd. First, 10 test pieces of 100 mm x 100 mm were obtained from the center of the film roll in parallel to the longitudinal direction. Next, the developed surface area ratio (Sdr) of the interface, the depth of the five-point valley region (S5v), and the height of the five-point peak region (S5p) were measured using the center portions of the ten test pieces obtained as measurement points. Thereafter, the average of the measured values obtained for each parameter was calculated, and these values were defined as Sdr, S5v, and S5p of the films to be measured, respectively. The detailed conditions for one measurement were as follows. Note that one field of view (field area: 939 μm vertically×1,252 μm horizontally = 1,175,628 μm ² ) was measured for each measurement.

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

B. Measurement method A special sample holder was used to fix the film during measurement. The sample holder was two removable metal plates with a circular hole in the center, and the film was sandwiched and fixed between them without wrinkles, and the film in the central circular part was measured. Note that the film and sample holder were installed so that the longitudinal direction of the film roll coincided with the longitudinal direction of the measurement field of view.

C. Analysis method The data obtained from the above measurements were analyzed using "VertScan" (registered trademark) 2.0 image analysis software VS-Viewer. First, noise was removed using a median filter (5×5), and undulation components were removed using a Gaussian filter with a cutoff value of 250 μm. Next, the developed surface area ratios Sdr, S5v, and S5p of the interface of the surface texture defined in ISO25178-2 (2012) were calculated using the "ISOPara" function. Note that in the "ISOPara" function, the S-Filter was set to 6.0 μm.

(6) Thickness (unit: μm)
It was measured by a micrometer method according to JIS C 2330 (2014).

(7) Breakdown voltage (BDV): BDV (V/μm) at 23°C (Vave, Vmax, Vmin)
From an intermediate product roll with a length of 6,500 mm in the width direction, 250 mm was cut from both ends in the width direction to obtain a biaxially oriented polypropylene film sample measuring 200 mm (longitudinal direction) x 6000 mm (width direction). It was divided into equal parts to obtain test pieces of 200 mm x 200 mm. Next, using the center part of the obtained test piece as the measurement site, it was measured at 23°C and in a 65% RH atmosphere as described in JIS C2330 (2014) "JIS C2151 17.2.2 (flat plate electrode method)". A BDV test was conducted in accordance with the above, and the average value, maximum value, and minimum value of 20 points were obtained by excluding the 5 points with the highest breakdown voltage and 5 points with the lowest breakdown voltage out of a total of 30 measured values (calculated values). The values were calculated and set as Vave, Vmax, and Vmin, respectively. In addition, in the production of biaxially oriented polypropylene films in each example, a method was adopted in which multiple final product rolls were obtained from one intermediate product roll, and there was no difference in the properties of each final product roll. Since this is expected, test pieces were taken from the intermediate product roll.

(8) Element processability evaluation in film capacitor manufacturing Aluminum was vacuum-coated on the corona-treated side of the biaxially oriented polypropylene film using a vacuum evaporation machine manufactured by ULVAC Co., Ltd. so that the surface resistance value was 15Ω/sq. Deposited. At that time, aluminum was vapor-deposited in a stripe shape having a margin part running in the longitudinal direction (width of the vapor-deposited part was 79.0 mm, width of the margin part was 1.0 mm, repeated). Next, a blade was inserted into the center of each vapor deposition part and the center of each margin part to make a slit, thereby producing a tape-shaped take-up reel with a total width of 40 mm and a margin part of 0.5 mm at either the left or right end. One reel from the left margin and one from the right margin of the obtained reel were wound by overlapping each other so that the vapor-deposited part protruded 0.5 mm from the margin part in the width direction to form a wound body with a capacitance of 120 μF. I got it. Note that KAW-4NHB manufactured by Kaito Seisakusho Co., Ltd. was used for winding. Finally, the wound body was heat treated in a reduced pressure atmosphere at 140°C for 10 hours. This rolled body was visually observed, and those with wrinkles or distortion in shape on the outside or inside were judged to be defective. 200 wound bodies were produced in the same manner, the same evaluation was repeated, and the workability of the wound bodies was evaluated according to the following criteria.
〇: No defective products △: 3 or less defective products ×: 4 or more defective products.

(9) Lifespan evaluation of film capacitor A wound body with a capacitance of 120 μF was obtained by the method described in (8). Thereafter, the non-defective wound bodies were heat-treated in a reduced pressure atmosphere at 140° C. for 10 hours, metallicon was thermally sprayed on both end faces in the width direction to form external electrodes, and lead wires were welded to the metallicon to obtain a film capacitor. Next, the lifespan of the 15 film capacitors was evaluated according to the following procedure. First, capacitance (C0) was measured at room temperature. Next, a voltage of 325 VDC/μm (when the thickness was 2.0 μm, the applied voltage was 650 V) was applied to the film capacitor for 1000 hours at a high temperature of 120°C. Thereafter, the capacitance (C) was measured at room temperature, and the rate of change in capacitance (ΔC) before and after voltage application was calculated from Equation 2 below. Note that the capacitance was measured using LCR High Tester 3522-50 manufactured by Hioki Electric Co., Ltd.
Formula 2: ΔC=((C0-C)/C0)×100
The average value of the capacitance change rate (ΔC) before and after voltage application of the 15 film capacitors was taken as the capacitance change rate of the sample before and after voltage application, and evaluation was made according to the following criteria. The smaller the rate of change in capacitance (ΔC) before and after voltage application, the more suppressed the decrease in capacitance under high temperatures is, and it can be said that the life evaluation of the film capacitor is good.
○: ΔC is less than 2% Δ: ΔC is 2% or more and less than 5% ×: ΔC is 5% or more.

[material]
(1) Resin Highly stereoregular polypropylene resin (A):
(Used in Examples 1 to 6 and Comparative Examples 1 to 7)
"Borclean" (trademark) HC300BF manufactured by Borealis Corporation A highly stereoregular polypropylene resin having a mesopentad fraction of 0.980, CXS of 1.2% by mass, MFR of 3.3 g/10 min, and MS of 1.0 cN.
(Used in Example 7)
"Prime Polypro" (registered trademark) manufactured by Prime Polymer Co., Ltd. Highly stereoregular polypropylene resin with a mesopentad fraction of 0.980, CXS of 0.9% by mass, MFR of 2.8 g/10 min, and MS of 0.9 cN .

High melt tension polypropylene resin (H):
(Used in Examples 1 to 7 and Comparative Examples 1 to 7)
"WAYMAX" (registered trademark) (MFX3) manufactured by Nippon Polypro Co., Ltd. High melt tension polypropylene resin with MFR of 9.0 g/10 min and MS of 5.0 cN.

High melt tension polypropylene resin (I):
(Used in Examples 1 to 7 and Comparative Examples 1 to 6)
"Daploy" (trademark) (WB135HMS) manufactured by Borealis, Inc. High melt tension polypropylene resin with MFR of 2.5 g/10 min and MS of 32.0 cN.
(Used in Comparative Example 7)
"Daploy (trademark) WB140HMS manufactured by Borealis, a high melt tension polypropylene resin having an MFR of 2.1 g/10 min and an MS of 36.0 cN.

(2) Antioxidant Antioxidant 1: "Irganox" (registered trademark) 1010 manufactured by BASF Japan Co., Ltd.
Antioxidant 2: 2,6-di-t-butyl-p-cresol (BHT).

(Example 1)
A polypropylene resin mixture in which a highly stereoregular polypropylene resin (A), a high melt tension polypropylene resin (H), and a high melt tension polypropylene resin (I) are mixed at a ratio of 96.0:0.4:3.6 (mass ratio), Antioxidant 1 and antioxidant 2 were dry blended at a ratio of 99.5:0.4:0.1 (mass ratio), supplied to a single screw melt extruder, and melt extruded at 250°C. . Thereafter, foreign matter was removed from the extruded molten polypropylene resin composition using a sintered filter with a cut of 25 μm, and the composition was discharged into a sheet from a T-shaped slit die. Furthermore, the sheet-shaped molten polypropylene resin composition was solidified by being brought into close contact with a cast drum maintained at a temperature of 92°C using an air knife at an air temperature of 80°C, and then placed on a cooling roll maintained at a temperature of 30°C. A cast sheet was obtained by cooling. At this time, the time during which the sheet-shaped molten polypropylene resin composition was in close contact with the cast drum and the cooling roll was 1.0 seconds, respectively. ), and the surface that does not touch the ground is called the non-drum surface (non-D surface).

Subsequently, in a preheating step before longitudinal stretching, the cast sheet was preheated by passing it through rolls kept at 120°C, and further preheated by passing it through rolls kept at 145°C. Further, the cast sheet was heated for 0.4 seconds using a radiation heater on a roll maintained at 145°C. At this time, the distance between the cast sheet and the radiation heater was 5.0 mm, and the output of the radiation heater was 5.0 kW. Thereafter, the cast sheet that had undergone a preheating step before longitudinal stretching was stretched in the longitudinal direction at a stretching ratio of 5.6 times using longitudinal stretching rolls at a temperature of 140° C. to form a uniaxially oriented film.

Furthermore, the uniaxially oriented film was introduced into a tenter while holding both ends in the width direction with clips, and was stretched in the width direction at a temperature of 159° C. and a stretching ratio of 11 times. Next, a 12% relaxation treatment was performed in the width direction at a temperature of 158° C., and the material was gradually cooled to room temperature, and a corona discharge treatment was performed on the D side at a treatment intensity of 25 W·min/m ² . The ends of the resulting biaxially oriented polypropylene film held in the width direction by the clips were cut off and wound up using a winder to obtain an intermediate product roll having a length in the width direction of 6,500 mm. Next, the biaxially oriented polypropylene film was slit in parallel to the longitudinal direction using a slitter so that the length in the width direction was 600 mm, and the film was wound 30,000 m in the longitudinal direction around the core. Ten axially oriented polypropylene film rolls were obtained. Table 1 shows the physical properties and evaluation results of the obtained biaxially oriented polypropylene film. In addition, except for the items evaluated for intermediate product rolls, each evaluation regarding the film is based on the film roll closest to the center in the width direction of the intermediate product roll (the 5th or 6th film roll counting from one width direction end). The test was carried out by taking a film from one arbitrarily selected film roll. Table 1 shows the physical properties and evaluation results of the obtained biaxially oriented polypropylene film.

(Examples 2 to 7, Comparative Examples 1 to 7)
A biaxially oriented polypropylene film was obtained in the same manner as in Example 1, except that the type of polypropylene resin was as described in "(1) Resin" and the composition and preheating step before longitudinal stretching were as shown in Table 1. Ta. Table 1 shows the physical properties and evaluation results of the obtained biaxially oriented polypropylene film.

According to the present invention, a biaxially oriented polypropylene film having high processability and voltage resistance can be provided. By using the biaxially oriented polypropylene film of the present invention as a dielectric of a film capacitor, it is possible to uniformly control the amount of air between film layers and the distance between the layers during processing of the film capacitor. Therefore, when used as a film capacitor, it exhibits high safety even under high temperature and high voltage environments, and its lifespan is also improved.

Claims (8)

A biaxially oriented polypropylene film characterized in that at least one side is the A side, where the A side is the side in which the developed surface area ratio (Sdr) of the interface is 0.0001% or more and less than 0.0004%. The biaxially oriented polypropylene film according to claim 1, wherein the depth of the five-point valley region (S5v) of the A side is 30 nm or more and less than 70 nm. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the five-point peak region height (S5p) of the A side is 50 nm or more and less than 80 nm. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the film thickness (t) is 1.0 μm or more and 4.0 μm or less. When the maximum value, minimum value, and average value of BDV in a dielectric breakdown voltage (BDV) test conducted in accordance with JIS C 2330 (2014) at 23°C and 65% RH atmosphere are Vmax, Vmin, and Vave, respectively. The biaxially oriented polypropylene film according to claim 1 or 2, wherein (Vmax-Vmin)/Vave is 0.01 or more and 0.10 or less. Highly stereoregular polypropylene resin (A) is a highly stereoregular polypropylene resin, and high melt tension polypropylene resin (H) is a high melt tension polypropylene resin that has a high melt flow rate index (MFR) at 230°C. When a high melt tension polypropylene resin (I) is used, it contains a high stereoregular polypropylene resin (A) as a main component, and further contains a high melt tension polypropylene resin (H) and a high melt tension polypropylene resin (I). , The biaxially oriented polypropylene film according to claim 1 or 2. A metal film laminate film comprising the biaxially oriented polypropylene film according to claim 1 or 2. A film capacitor using the metal film laminate film according to claim 7.