Polypropylene film, metal layer-integrated polypropylene film, film capacitor, and film roll

Abstract

The present invention addresses the problem of providing a polypropylene film that makes it possible to achieve a film capacitor which has more excellent withstand voltage properties at high temperatures. The problem is solved by a polypropylene film which has a first surface and a second surface, and which is characterized in that, with respect to the surface property parameters as specified by ISO 25178, the Sku value of either the first surface or the second surface is 40 or less and / or the Spc value of either the first surface or the second surface is 16 (1 / mm) or less.

Description

Polypropylene film, metal layer integrated polypropylene film, film capacitor, and film roll

[0001] The present invention relates to a polypropylene film, a metal layer-integrated polypropylene film, a film capacitor, a film roll, etc.

[0002] Polypropylene films have excellent electrical properties, such as high voltage resistance and low dielectric loss, as well as high moisture resistance. Therefore, they are widely used in electronic and electrical devices. Specifically, they are used as films for high-voltage capacitors, various switching power supplies, filter capacitors (e.g., converters, inverters, etc.), smoothing capacitors, etc.

[0003] In particular, in recent years, polypropylene films have begun to be widely used as capacitors for inverter power supplies that control drive motors of electric vehicles, hybrid vehicles, etc. Capacitors for inverter power supplies used in automobiles, etc., are required to be small, lightweight, high-capacity, and highly reliable over a long period of time.

[0004] In Patent Document 1, the protrusion is 0.1 mm ２ Patent Document 1 discloses a biaxially oriented polypropylene film for capacitors, in which the number of particles per square meter and the 10-point average roughness satisfy a predetermined relationship. Patent Document 1 describes the effects of the biaxially oriented polypropylene film for capacitors having the above-mentioned configuration, such as excellent processability even for a thin film, and high voltage resistance even under a wide range of ambient temperature conditions from low (-40°C) to high (150°C).

[0005] International Publication No. 2013 / 146367

[0006] From the viewpoint of the long-term reliability of the capacitors described above, capacitors that are used under high temperatures, such as in automobiles, are required to have voltage resistance at high temperatures.

[0007] An object of the present invention is to provide a polypropylene film that can provide a film capacitor having excellent voltage resistance at high temperatures.

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that the above-mentioned problems can be solved by a polypropylene film having a first side and a second side, characterized in that, in terms of surface texture parameters defined by ISO 25178, either one of the first side or the second side has an Sku value of 40 or less and / or an Spc value of either one of the first side or the second side has an Spc value of 16 (1 / mm) or less. Based on this finding, the present inventors have conducted further research and have completed the present invention. That is, the present invention encompasses the following aspects.

[0009] Item 1. A polypropylene film having a first side and a second side, characterized in that, in surface texture parameters specified by ISO 25178, either one of the first side or the second side has an Sku value of 40 or less and / or an Spc value of either one of the first side or the second side has an Spc value of 16 (1 / mm) or less.

[0010] Item 2. The polypropylene film according to Item 1, wherein, when the side with a higher wet tension measured in accordance with JIS K6768:1999 is designated as the first side and the side with a lower wet tension is designated as the second side, the value obtained by dividing the Sku value of the second side by the Sku value of the first side is 1.0000 or less and / or the value obtained by dividing the Spc value of the second side by the Spc value of the first side is 1.0000 or less.

[0011] Item 3. The polypropylene film according to Item 1 or 2, wherein either one of the first side or the second side has an Sku value of 20 or less and / or an Spc value of either one of the first side or the second side has an Spc value of 13 (1 / mm) or less.

[0012] Item 4. The polypropylene film according to any one of Items 1 to 3, comprising: a linear polypropylene resin B having a molecular weight differential distribution curve in which the difference obtained by subtracting the differential distribution value when Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5 is less than 8.0% and a melt flow rate at 230°C of less than 4.0 g / 10 min; and a long-chain branched polypropylene resin C polymerized using a metallocene catalyst.

[0013] Item 5. The polypropylene film according to Item 4, further comprising a linear polypropylene resin A having, in a molecular weight differential distribution curve, a difference obtained by subtracting the differential distribution value when Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5 of less than 8.0% and a melt flow rate at 230°C of 4.0 g / 10 min or more.

[0014] Item 6. The polypropylene film according to any one of Items 1 to 5, which is a biaxially oriented polypropylene film.

[0015] Item 7. The polypropylene film according to any one of Items 1 to 6, having a thickness of 1.4 to 6.0 μm.

[0016] Item 8. The polypropylene film according to any one of Items 1 to 7, which is for use in a capacitor.

[0017] Item 9. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of items 1 to 8 and a metal layer laminated on a first surface or both surfaces of the polypropylene film.

[0018] Item 10. A film capacitor comprising the metal layer-integrated polypropylene film according to Item 9.

[0019] Item 11. A film roll obtained by winding the polypropylene film according to any one of items 1 to 8 into a roll.

[0020] According to the present invention, it is possible to provide a polypropylene film that can provide a film capacitor with excellent voltage resistance at high temperatures.

[0021] In this specification, the expressions "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0022] In this specification, the terms "element," "capacitor," "capacitor element," and "film capacitor" mean the same thing.

[0023] The polypropylene film of the present invention is not a microporous film and does not have a large number of pores.

[0024] The polypropylene film of the present invention may be composed of two or more layers, but is preferably composed of a single layer.

[0025] The polypropylene film of the present invention is a polypropylene film having a first side and a second side, characterized in that, in terms of surface texture parameters specified by ISO 25178, either one of the first side or the second side has an Sku value of 40 or less and / or an Spc value of either one of the first side or the second side has an Spc value of 16 (1 / mm) or less.

[0026] The Sku value of either the first surface or the second surface is preferably 30 or less, more preferably 20 or less, even more preferably 16 or less, still more preferably 14 or less, particularly preferably 12 or less, especially more preferably 10 or less, especially more preferably 9 or less, and especially still more preferably 8 or less. The lower limit of the Sku value is not particularly limited, and is, for example, 0.1, 0.5, 1, 2, or 3.

[0027] Sku refers to kurtosis, a measure of surface sharpness, and represents the sharpness of the height distribution. Therefore, an Sku value of 40 or less on either the first or second surface means that the number of steep peaks or valleys on one side of the film surface is less than a certain level, which means that the distance between the valleys on one side of the film and the valleys on the opposite side is relatively long, reducing leakage current and improving life performance (dielectric breakdown strength, capacitance change rate).

[0028] In one embodiment of the polypropylene film of the present invention, the surface opposite to the surface having an Sku value of 40 or less preferably has an Sku value of 500 or more, more preferably 1000 or more, and even more preferably 1500 or more. By disposing a metal layer on this surface, the metal film thickness in the shadows of steep peaks or steep valleys present on the surface becomes relatively thin, making it easier to blow fuses and to prevent short-circuit failures of the capacitor element. The upper limit of this value is not particularly limited, but is, for example, 10,000, 7,000, 5,000, or 4,000.

[0029] In one embodiment of the polypropylene film of the present invention, when the side having a higher wet tension as measured according to JIS K6768:1999 is designated as the first side and the side having a lower wet tension is designated as the second side, the value obtained by dividing the Sku value of the second side by the Sku value of the first side is 1.0000 or less. This value is more preferably 0.5000 or less, even more preferably 0.1000 or less, even more preferably 0.0500 or less, particularly preferably 0.0100 or less, and especially preferably 0.0050 or less. In this case, the Sku value of the second side is 40 or less.

[0030] The Spc value of either the first surface or the second surface is preferably 14 (1 / mm) or less, more preferably 13 (1 / mm) or less, even more preferably 12 (1 / mm) or less, still more preferably 11 (1 / mm) or less, and particularly preferably 10 (1 / mm) or less. The lower limit of the Spc value is not particularly limited, but is, for example, 0.1 (1 / mm), 0.5 (1 / mm), 1 (1 / mm), 2 (1 / mm), 4 (1 / mm), or 6 (1 / mm).

[0031] Spc represents the average principal curvature of the peaks on the surface. A small Spc value indicates that the point of contact with other objects is rounded, while a large Spc value indicates that the point of contact with other objects is sharp. Therefore, an Spc value of 16 (1 / mm) or less on either the first or second surface means that there are few steep peaks on one side of the film surface. Therefore, when the thickness measured by a micrometer, which is a mechanical thickness measurement method, is the same, the distance between the valleys on one side of the film and the valleys on the opposite side becomes relatively longer, reducing leakage current and leading to improved life performance (dielectric breakdown strength, capacitance change rate).

[0032] In one embodiment of the polypropylene film of the present invention, the surface opposite to the surface having an Spc value of 16 (1 / mm) or less has an Spc value of preferably 150 (1 / mm) or more, more preferably 200 (1 / mm) or more, and even more preferably 250 (1 / mm) or more. By disposing a metal layer on this surface, the metal film thickness in the shadows of steep peaks or steep valleys present on the surface becomes relatively thin, making it easier to blow fuses and prevent short-circuit failures of the capacitor element. The upper limit of this value is not particularly limited, but is, for example, 1500 (1 / mm), 1200 (1 / mm), 1000 (1 / mm), or 900 (1 / mm).

[0033] In one embodiment, the polypropylene film of the present invention preferably has an Spc value of the second side divided by the Spc value of the first side, where the side having a higher wet tension as measured according to JIS K6768:1999 is designated as the first side and the side having a lower wet tension is designated as the second side, of 1.0000 or less. This value is more preferably 0.5000 or less, even more preferably 0.2000 or less, even more preferably 0.1000 or less, particularly preferably 0.0500 or less, and especially preferably 0.0400 or less. In this case, the Spc value of the second side is 16 (1 / mm) or less.

[0034] In one embodiment, the polypropylene film of the present invention has a wetting tension of the first surface of, for example, 32 to 50 mN / m, 34 to 45 mN / m, or 35 to 40 mN / m.

[0035] In one embodiment, the polypropylene film of the present invention has a wetting tension of the second surface of, for example, 30 mN / m or less.

[0036] In one embodiment of the polypropylene film of the present invention, the difference between the wet tension value (mN / m) of the first surface and the wet tension value (mN / m) of the second surface is preferably 3 or more, more preferably 5 or more, and even more preferably 7 or more.

[0037] In one embodiment, the polypropylene film of the present invention has an Sa value of, for example, 0.0040 μm or more and 0.0600 μm or less, 0.0080 μm or more and 0.0300 μm or less, or 0.0100 μm or more and 0.0200 μm or less on the surface (e.g., the first surface) opposite to the surface having an Sku value of 40 or less.

[0038] In one embodiment, the polypropylene film of the present invention has an Sq value of, for example, 0.0080 μm or more and 0.1000 μm or less, 0.0150 μm or more and 0.0700 μm or less, or 0.0200 μm or more and 0.0400 μm or less on the surface (e.g., the first surface) opposite to the surface having an Sku value of 40 or less.

[0039] In one embodiment, the polypropylene film of the present invention has an Sa value of, for example, 0.0020 μm or more and 0.0600 μm or less, 0.0040 μm or more and 0.0300 μm or less, or 0.0060 μm or more and 0.0200 μm or less on the surface (e.g., the second surface) having an Sku value of 40 or less.

[0040] In one embodiment, the polypropylene film of the present invention has an Sq value of, for example, 0.0030 μm or more and 0.0800 μm or less, 0.0060 μm or more and 0.0500 μm or less, or 0.0090 μm or more and 0.0300 μm or less on the surface (e.g., the second surface) having an Sku value of 40 or less.

[0041] In one embodiment, the polypropylene film of the present invention has an Sa value of, for example, 0.0040 μm or more and 0.0600 μm or less, 0.0080 μm or more and 0.0300 μm or less, or 0.0100 μm or more and 0.0200 μm or less on the surface (e.g., the first surface) opposite to the surface having an Spc value of 16 (1 / mm) or less.

[0042] In one embodiment, the polypropylene film of the present invention has an Sq value of, for example, 0.0080 μm or more and 0.1000 μm or less, 0.0150 μm or more and 0.0700 μm or less, or 0.0200 μm or more and 0.0400 μm or less on the surface (e.g., the first surface) opposite to the surface having an Spc value of 16 (1 / mm) or less.

[0043] In one embodiment, the polypropylene film of the present invention has an Sa value of, for example, 0.0020 μm or more and 0.0600 μm or less, 0.0040 μm or more and 0.0300 μm or less, or 0.0060 μm or more and 0.0200 μm or less on the surface (e.g., the second surface) having an Spc value of 16 (1 / mm) or less.

[0044] In one embodiment, the polypropylene film of the present invention has an Sq value of, for example, 0.0030 μm or more and 0.0800 μm or less, 0.0060 μm or more and 0.0500 μm or less, or 0.0090 μm or more and 0.0300 μm or less on the surface (e.g., the second surface) having an Spc value of 16 (1 / mm) or less.

[0045] The Sku value, Spc value, Sa value, and Sq value are values ​​measured according to the methods of (4-4) in Test 1 and Test 2 described below.

[0046] The dielectric breakdown strength of the polypropylene film of the present invention at a direct current voltage of 120°C (DCES120°C) is preferably 500V ＤＣ / μm or more, and 550V ＤＣ / μm or more is preferable, and 580V ＤＣ / μm or more is more preferable, ＤＣ The higher the upper limit of the dielectric breakdown strength at a DC voltage at 120°C, the more preferable. ＤＣ / μm, 630V ＤＣ / μm, etc.

[0047] The dielectric breakdown strength is a value measured according to the method of (4-5) in the Examples described later.

[0048] The ash content of the polypropylene film of the present invention is preferably 6×10 ppm or less (60 ppm or less), more preferably 5×10 ppm or less (50 ppm or less), even more preferably 4×10 ppm or less (40 ppm or less), and particularly preferably 3.5×10 ppm or less (35 ppm or less). The ash content is preferably 0×10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1×10 ppm or more (10 ppm or more). When the ash content is within the above numerical range, the generation of polar low-molecular-weight components is suppressed, and the electrical properties as a capacitor are further improved.

[0049] The ash content is a value measured according to the method of (4-6) in the Examples described below.

[0050] The polypropylene film of the present invention preferably has a thickness of 9.5 μm or less, more preferably 6.0 μm or less, even more preferably 3.0 μm or less, even more preferably 2.9 μm or less, particularly preferably 2.8 μm or less, and particularly preferably 2.5 μm or less. The thickness of the polypropylene film of the present invention is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.4 μm or more, even more preferably 1.5 μm or more, and particularly preferably 1.8 μm or more. A thickness within the range of 1.4 to 6.0 μm, 1.5 to 3.0 μm, or 1.5 to 2.9 μm, etc., is particularly preferred because, despite being very thin, the polypropylene film exhibits excellent processability in the slitting process, suppression of blocking during the vapor deposition process, and processability for winding elements.

[0051] When the thickness is 9.5 μm or less, the capacitance can be increased, making it suitable for use in a capacitor. From the viewpoint of manufacturing, the thickness can be set to 0.8 μm or more.

[0052] The thickness is a value measured according to the method of (4-1) in the Examples described later.

[0053] The polypropylene film of the present invention preferably has a haze of 1.8 to 4.5, more preferably 1.8 to 4.0, and even more preferably 1.9 to 3.5.

[0054] The haze is a value measured according to the method of (4-2) in the Examples described later.

[0055] The polypropylene film of the present invention may be a biaxially stretched film, a uniaxially stretched film, or an unstretched film, but is preferably a biaxially stretched film from the viewpoint of easily adjusting the Sku value of either the first or second surface within a predetermined range and / or easily adjusting the Spc value of either the first or second surface within a predetermined range.

[0056] The polypropylene film and metal layer-integrated polypropylene film of the present invention are each wound into a roll, preferably in the form of a film roll. The film roll may or may not have a winding core. The film roll preferably has a winding core. The material of the winding core of the film roll is not particularly limited. Examples of the material include paper (paper tube), resin, fiber-reinforced plastic (FRP), metal, etc. Examples of the resin include polyvinyl chloride, polyethylene, polypropylene, phenolic resin, epoxy resin, acrylonitrile-butadiene-styrene copolymer, etc. Examples of plastics that constitute the fiber-reinforced plastic include polyester resin, epoxy resin, vinyl ester resin, phenolic resin, thermoplastic resin, etc. Examples of fibers that constitute the fiber-reinforced plastic include glass fiber, aramid fiber (Kevlar® fiber), carbon fiber, polyparaphenylenebenzoxazole fiber (Zylon® fiber), polyethylene fiber, boron fiber, etc. Examples of the metal include iron, aluminum, stainless steel, etc. The winding core of the film roll also includes a winding core formed by impregnating a paper tube with the resin. In this case, the material of the winding core is classified as a resin.

[0057] The polypropylene film of the present invention contains a polypropylene resin as a main component. In this specification, "containing a polypropylene resin as a main component" means that the polypropylene resin is contained in an amount of 50% by mass or more relative to the entire polypropylene film (when the entire polypropylene film is taken as 100% by mass). The content of the polypropylene resin relative to the entire polypropylene film is preferably 75% by mass or more, more preferably 90% by mass or more. The upper limit of the content of the polypropylene resin relative to the entire polypropylene film is, for example, 100% by mass, 98% by mass, etc.

[0058] The polypropylene resin is not particularly limited, and one type may be used alone, or two or more types may be used in combination. Among them, a polypropylene resin that forms β-type spherulites when made into a cast sheet is preferred.

[0059] Examples of the polypropylene resin include linear polypropylene resins. The linear polypropylene resins can be used alone or in combination of two or more. Among them, from the viewpoint of easily adjusting the Sku value of either the first surface or the second surface to an appropriate range and / or from the viewpoint of easily adjusting the Spc value of either the first surface or the second surface to an appropriate range, it is preferable to use the following linear polypropylene resin A and / or the following linear polypropylene resin B. In particular, it is preferable to use the following linear polypropylene resin B, and it is more preferable to use the following linear polypropylene resin A and the following linear polypropylene resin B in combination. The following linear polypropylene resin A and the following linear polypropylene resin B are preferably homopolypropylene resins. However, in the present invention, the polypropylene resin is not limited to the following resins.

[0060] <Linear Polypropylene Resin A> A linear polypropylene resin in which, in a molecular weight differential distribution curve, the difference obtained by subtracting the differential distribution value when Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5 is less than 8.0%, and the melt flow rate at 230°C is 4.0 g / 10 min or more.

[0061] <Linear Polypropylene Resin B> A linear polypropylene resin in which, in a molecular weight differential distribution curve, the difference obtained by subtracting the differential distribution value when Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5 is less than 8.0%, and the melt flow rate at 230°C is less than 4.0 g / 10 min.

[0062] The weight-average molecular weight Mw of the linear polypropylene resin A is preferably 250,000 or more. The weight-average molecular weight Mw of the linear polypropylene resin A is preferably 450,000 or less, more preferably 400,000 or less, even more preferably 350,000 or less, and particularly preferably 340,000 or less. When the weight-average molecular weight Mw of the linear polypropylene resin A is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, it is easy to control the thickness of the cast sheet, and it is easy to produce a thin stretched film. Furthermore, this is preferable because it makes it difficult for unevenness to occur in the thickness of the cast sheet and stretched film, and appropriate stretchability can be obtained.

[0063] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the linear polypropylene resin A is preferably 5.0 or more and 11.0 or less, more preferably 6.0 or more and 10.0 or less, even more preferably 6.5 or more and 9.0 or less, and particularly preferably 6.8 or more and 8.5 or less.

[0064] The molecular weight distribution [(z-average molecular weight Mz) / (number-average molecular weight Mn)] of the linear polypropylene resin A is preferably 12.0 or more and 60.0 or less, more preferably 16.0 or more and 50.0 or less, and even more preferably 20.0 or more and 40.0 or less.

[0065] When the molecular weight distribution of the linear polypropylene resin A is within the above-mentioned preferred range, unevenness in the thickness of the cast sheet and stretched film is unlikely to occur, and appropriate stretchability is preferably obtained.

[0066] The linear polypropylene resin A has a differential distribution value difference (the difference obtained by subtracting the differential distribution value when Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5 in a molecular weight differential distribution curve) of less than 8.0%, more preferably 7.0% or less, even more preferably 0% or more and 6.0% or less, and particularly preferably 2.0% or more and 5.5% or less.

[0067] The mesopentad fraction ([mmmm]) of the linear polypropylene resin A is preferably 99.8% or less, more preferably 99.5% or less, and even more preferably 99.0% or less. The mesopentad fraction is preferably 94.0% or more, more preferably 95.0% or more, even more preferably 96.0% or more, and particularly preferably 97.0% or more. When the mesopentad fraction is within the above numerical range, the moderately high stereoregularity leads to a moderate improvement in the crystallinity of the resin, thereby improving the voltage resistance at high temperatures. On the other hand, the solidification (crystallization) rate during cast sheet molding is moderate, resulting in moderate extensibility.

[0068] The heptane insoluble fraction (HI) of the linear polypropylene resin A is preferably 96.0% or more, more preferably 97.0% or more, and even more preferably 98.0% or more. The heptane insoluble fraction (HI) of the linear polypropylene resin A is preferably 99.5% or less, more preferably 99.0% or less. Here, the higher the heptane insoluble fraction, the higher the stereoregularity of the resin. When the heptane insoluble fraction (HI) is 96.0% or more and 99.5% or less, the moderately high stereoregularity improves the crystallinity of the resin and improves the voltage resistance at high temperatures. On the other hand, the solidification (crystallization) rate during cast sheet molding is moderate, resulting in moderate extensibility.

[0069] The ash content of the linear polypropylene resin A is preferably 6 x 10 ppm or less (60 ppm or less), more preferably 5 x 10 ppm or less (50 ppm or less), even more preferably 4 x 10 ppm or less (40 ppm or less), and particularly preferably 3 x 10 ppm or less (30 ppm or less). The ash content of the linear polypropylene resin A is preferably 0 x 10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1 x 10 ppm or more (10 ppm or more). When the ash content of the linear polypropylene resin A is within the above-mentioned preferred range, the electrical properties as a capacitor are further improved while suppressing the generation of polar low-molecular-weight components.

[0070] The linear polypropylene resin A has a melt flow rate (MFR) at 230°C of 4.0 g / 10 min or more, preferably 4.0 to 10.0 g / 10 min, and particularly preferably 4.0 to 6.0 g / 10 min. When the MFR at 230°C of polypropylene A is within the above range, it has excellent flow characteristics in a molten state, making it less likely to cause unstable flow such as melt fracture, and also suppresses breakage during stretching. Therefore, it has the advantage of having good film thickness uniformity, thereby suppressing the formation of thin-walled portions that are prone to dielectric breakdown.

[0071] The content of the linear polypropylene resin A is preferably 55% by mass or more, and more preferably 60% by mass or more, based on 100% by mass of the total polypropylene resin in the polypropylene film. The content of the linear polypropylene resin A is preferably 99.9% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less, based on 100% by mass of the total polypropylene resin in the polypropylene film.

[0072] The weight average molecular weight Mw of the linear polypropylene resin B is preferably 300,000 or more, more preferably 330,000 or more, even more preferably more than 340,000, still more preferably 350,000 or more, and particularly preferably more than 350,000. The weight average molecular weight Mw of the linear polypropylene resin B is preferably 400,000 or less, more preferably 380,000 or less.

[0073] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the linear polypropylene resin B is preferably 7.0 or more and 9.0 or less, more preferably 7.5 or more and 8.9 or less, and even more preferably 7.5 or more and 8.5 or less.

[0074] The molecular weight distribution [(z-average molecular weight Mz) / (number-average molecular weight Mn)] of the linear polypropylene resin B is preferably 20.0 or more and 70.0 or less, more preferably 25.0 or more and 60.0 or less, and even more preferably 25.0 or more and 50.0 or less.

[0075] When the molecular weight distribution of the linear polypropylene resin B is within the above-mentioned preferred range, unevenness in the thickness of the cast sheet and stretched film is unlikely to occur, and appropriate stretchability is obtained, which is preferable.

[0076] The differential distribution value difference of the linear polypropylene resin B is preferably less than 8.0%, more preferably −20.0% or more and less than 8.0%, even more preferably −10.0% or more and 7.9% or less, and particularly preferably −5.0% or more and 7.5% or less.

[0077] The mesopentad fraction ([mmmm]) of the linear polypropylene resin B is preferably less than 99.8%, more preferably 99.5% or less, and even more preferably 99.0% or less. The mesopentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and even more preferably 95.0% or more. When the mesopentad fraction is within the above range, the resin has a moderately high stereoregularity, which moderately improves the crystallinity of the resin and improves the voltage resistance at high temperatures. On the other hand, the solidification (crystallization) rate during cast sheet molding is moderate, resulting in moderate extensibility.

[0078] The heptane insoluble matter (HI) of the linear polypropylene resin B is, for example, 97% or more, preferably 97.5% or more, more preferably 98% or more, even more preferably more than 98.5%, and particularly preferably 98.6% or more. The heptane insoluble matter (HI) of the linear polypropylene resin B is preferably 99.5% or less, more preferably 99% or less.

[0079] The ash content of the linear polypropylene resin B is preferably 6 x 10 ppm or less (60 ppm or less), more preferably 5 x 10 ppm or less (50 ppm or less), even more preferably 4 x 10 ppm or less (40 ppm or less), and particularly preferably 3 x 10 ppm or less (30 ppm or less). The ash content of the linear polypropylene resin B is preferably 0 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1 x 10 ppm or more (10 ppm or more). When the ash content of the linear polypropylene resin B is within the above-mentioned preferred range, the electrical properties of the capacitor are further improved while suppressing the generation of polar low-molecular-weight components.

[0080] The linear polypropylene resin B has a melt flow rate (MFR) of less than 4.0 g / 10 min at 230° C. The linear polypropylene resin B has a melt flow rate (MFR) of preferably 0.1 g / 10 min or more, more preferably 1.0 g / 10 min or more, and even more preferably 1.5 g / 10 min or more at 230° C. The linear polypropylene resin B has a melt flow rate (MFR) of preferably 3.5 g / 10 min or less, more preferably 3.0 g / 10 min or less at 230° C.

[0081] When linear polypropylene resin B is used as the polypropylene resin, the content of linear polypropylene resin B is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to 100% by mass of the total polypropylene resin in the polypropylene film. Similarly, the content of linear polypropylene resin B is preferably 45% by mass or less, more preferably 40% by mass or less, relative to 100% by mass of the total polypropylene resin in the polypropylene film. In one embodiment (particularly when linear polypropylene resin B is not used in combination with linear polypropylene resin A), the content of linear polypropylene resin B is 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, relative to 100% by mass of the total polypropylene resin in the polypropylene film.

[0082] When the linear polypropylene resin A and the linear polypropylene resin B are used in combination as the polypropylene resin, the polypropylene resin preferably contains 55 to 90% by weight of the linear polypropylene resin A and 45 to 10% by weight of the linear polypropylene resin B, when the total polypropylene resin is taken as 100% by mass, more preferably contains 60 to 85% by weight of the linear polypropylene resin A and 40 to 15% by weight of the linear polypropylene resin B, and particularly preferably contains 60 to 80% by weight of the linear polypropylene resin A and 40 to 20% by weight of the linear polypropylene resin B.

[0083] When the polypropylene resin contains the linear polypropylene resin A and the linear polypropylene resin B, the polypropylene film is in a finely mixed state (phase-separated state) of the linear polypropylene resin A and the linear polypropylene resin B, thereby improving the voltage resistance at high temperatures.

[0084] The linear polypropylene resin can be produced by a generally known polymerization method. There are no particular limitations as long as a linear polypropylene resin that can be used for polypropylene films can be produced. Examples of such polymerization methods include gas phase polymerization, bulk polymerization, and slurry polymerization.

[0085] The polymerization may be a single-stage polymerization using one polymerization reactor, or a multi-stage polymerization using at least two polymerization reactors. Furthermore, hydrogen or a comonomer may be added to the reactor as a molecular weight modifier.

[0086] The catalyst used in the polymerization can be a commonly known Ziegler-Natta catalyst, and is not particularly limited as long as it can produce the linear polypropylene resin. The catalyst may contain a co-catalyst component or a donor. By adjusting the catalyst and polymerization conditions, it is possible to control the molecular weight, molecular weight distribution, stereoregularity, etc.

[0087] The molecular weight, molecular weight distribution, differential distribution value difference, etc. of the linear polypropylene resin can be adjusted by appropriately selecting, for example, (i) the polymerization method and the conditions such as temperature and pressure during polymerization, (ii) the shape of the reactor during polymerization, (iii) the presence or absence, type and amount of additives used, and (iv) the type and amount of catalyst used.

[0088] Specifically, the molecular weight, molecular weight distribution, differential distribution value difference D of the linear polypropylene resin Ｍ The above adjustments can be carried out, for example, by a multi-stage polymerization reaction. Examples of the multi-stage polymerization reaction include the following methods.

[0089] First, in the first polymerization step, propylene and a catalyst are supplied to a first polymerization reactor. Hydrogen, acting as a molecular weight regulator, is mixed with these components in an amount necessary to achieve the desired polymer molecular weight. For example, in the case of slurry polymerization, the reaction temperature is approximately 70 to 100°C, and the residence time is approximately 20 to 100 minutes. Multiple reactors can be used, for example, in series. In this case, the polymerization product of the first step is continuously sent to the next reactor together with additional propylene, catalyst, and molecular weight regulator, followed by a second polymerization in which the molecular weight is adjusted to a lower or higher molecular weight than in the first polymerization step. By adjusting the yields (production amounts) of the first and second reactors, it is possible to adjust the composition (configuration) of the high-molecular-weight and low-molecular-weight components.

[0090] The molecular weight, molecular weight distribution, differential distribution value difference, etc. of the linear polypropylene resin can also be adjusted by peroxidation decomposition, for example, by a peroxidation treatment using a decomposing agent such as hydrogen peroxide or an organic peroxide.

[0091] When peroxide is added to a degradable polymer such as polypropylene, a hydrogen abstraction reaction occurs from the polymer, and some of the resulting polymer radicals recombine and undergo crosslinking reactions, but most of the radicals undergo secondary decomposition (beta scission), splitting into two polymers with lower molecular weights. In other words, the higher the molecular weight component, the higher the probability of decomposition. This increases the amount of low molecular weight components, allowing the molecular weight distribution to be adjusted.

[0092] When adjusting the content of low molecular weight components by blending (resin mixing), it is preferable to dry mix or melt mix at least two or more resins with different molecular weights. Generally, a two-polypropylene blend system in which a main resin is mixed with an additive resin having a higher or lower average molecular weight in an amount of about 1 to 40% by mass is preferably used because it is easy to adjust the amount of low molecular weight components.

[0093] In this mixing adjustment, the melt flow rate (MFR) may be used as a guide for the average molecular weight. In this case, the difference in MFR between the main resin and the additive resin is preferably set to about 1 to 30 g / 10 min from the viewpoint of convenience during adjustment.

[0094] As the linear polypropylene resin, commercially available products can also be used.

[0095] The polypropylene resin preferably contains a long-chain branched polypropylene resin from the viewpoint of easily adjusting the Sku value of either the first or second surface within an appropriate range and / or from the viewpoint of easily adjusting the Spc value of either the first or second surface within an appropriate range. Among the long-chain branched polypropylene resins, long-chain branched polypropylene resin C (hereinafter also referred to as "long-chain branched polypropylene resin C") obtained by polymerizing propylene using a metallocene catalyst is preferred. Specifically, when the polypropylene resin contains long-chain branched polypropylene resin C, a large amount of β crystals is formed in the cast sheet. Furthermore, since the β crystals are transformed into α crystals by stretching a cast sheet containing β crystals, (approximately) arc-shaped irregularities are formed in the polypropylene film obtained by stretching due to the difference in density between the β crystals and the α crystals, which is preferable in that the surface can be suitably roughened.

[0096] Among these, it is more preferable that the polypropylene resin contains the linear polypropylene resin A and / or the linear polypropylene resin B and the long-chain branched polypropylene resin C, and it is even more preferable that the linear polypropylene resin B and the long-chain branched polypropylene resin C are contained.

[0097] Furthermore, it is particularly preferred that the polypropylene resin contains the linear polypropylene resin A and the linear polypropylene resin B, and also contains the long-chain branched polypropylene resin C. The linear polypropylene resin A and the linear polypropylene resin B differ in differential distribution value difference, heptane insoluble content (HI), and / or melt flow rate (MFR), and are in a finely mixed state (phase-separated state). Therefore, stretching such an unstretched polypropylene film complicates the arrangement of the resin components constituting the film. Therefore, by including the linear polypropylene resin A and the linear polypropylene resin B, which differ in differential distribution value difference, heptane insoluble content (HI), and / or melt flow rate (MFR), in addition to the long-chain branched polypropylene resin C, the arrangement of the resin components constituting the film is complicated, improving the voltage resistance of the stretched film. Furthermore, fine (approximately) arc-shaped irregularities are formed, enabling more suitable surface roughening to be achieved.

[0098] In addition, if a long-chain branched polypropylene resin obtained by crosslinking modification with a peroxide is used instead of the long-chain branched polypropylene resin C polymerized using a metallocene catalyst, the α-crystal nucleating effect of the long-chain branched polypropylene resin obtained by crosslinking modification with a peroxide will promote the formation of α-crystals in the cast sheet and significantly suppress the formation of β-crystals. Even if a cast sheet containing α-crystals is stretched, crystallite transition does not occur, so unevenness is unlikely to form. Therefore, in order to roughen the surface of a polypropylene film, long-chain branched polypropylene resin C polymerized using a metallocene catalyst is suitable.

[0099] The metallocene catalyst is generally a metallocene compound that forms a polymerization catalyst that produces an olefin macromer. A long-chain branched polypropylene resin C obtained by polymerizing propylene using a metallocene catalyst is preferred because the polypropylene has an appropriate branch chain length and branch chain spacing, resulting in excellent compatibility with linear polypropylene. It is also preferred because it provides a uniform composition and a uniform surface shape. In the production of the long-chain branched polypropylene resin C, other conditions besides the type and amount of catalyst used, such as (i) the polymerization method and the temperature and pressure during polymerization, (ii) the shape of the reactor during polymerization, and (iii) the presence or absence, type, and amount of additives, can be the same as those described in the section on the method for producing a linear polypropylene resin, taking into consideration the molecular weight, molecular weight distribution, differential distribution value difference, etc., of the long-chain branched polypropylene resin C to be produced.

[0100] The weight-average molecular weight Mw of the long-chain branched polypropylene resin C is preferably 150,000 or more and 600,000 or less, more preferably 200,000 or more and 500,000 or less, even more preferably 250,000 or more and 450,000 or less, and particularly preferably 350,000 or more and 420,000 or less. When the weight-average molecular weight Mw of the long-chain branched polypropylene resin C is 150,000 or more and 600,000 or less, the resin fluidity becomes appropriate. As a result, it is easy to control the thickness of the cast sheet, and it is easy to produce a thin stretched film. In addition, it is preferable because unevenness in the thickness of the cast sheet and stretched film is less likely to occur, and appropriate stretchability can be obtained.

[0101] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the long-chain branched polypropylene resin C is preferably 1.5 or more and 4.5 or less, more preferably 1.8 or more and 4.2 or less, even more preferably 2.0 or more and 4.0 or less, particularly preferably 2.1 or more and 3.9 or less, and particularly preferably 2.2 or more and 3.0 or less.

[0102] The long-chain branched polypropylene resin C preferably has a ratio of [(z-average molecular weight Mz) / (number-average molecular weight Mn)] of 4.0 to 9.0, more preferably 4.2 to 8.8, even more preferably 4.5 to 8.5, and particularly preferably 5.0 to 8.2.

[0103] The molecular weight, molecular weight distribution, differential distribution value difference, etc. of the long-chain branched polypropylene resin C can be controlled by adjusting the catalyst and polymerization conditions, as described above.

[0104] The long-chain branched polypropylene resin C preferably has a heptane insoluble fraction (HI) of 98.0% or more, more preferably 98.2% or more, and even more preferably 98.5% or more. The long-chain branched polypropylene resin C preferably has a heptane insoluble fraction (HI) of 99.5% or less, more preferably 99.0% or less. When the HI of the long-chain branched polypropylene resin C is within the above-mentioned preferred range, β crystals are more suitably formed in the cast sheet, and as a result, the surface of the polypropylene film can be suitably roughened.

[0105] The ash content of the long-chain branched polypropylene resin C is preferably 45×10 ppm or less (450 ppm or less), more preferably 40×10 ppm or less (400 ppm or less). The ash content of the long-chain branched polypropylene resin C is preferably 0 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, even more preferably 1×10 ppm or more (10 ppm or more), even more preferably 10×10 ppm or more (100 ppm or more), and particularly preferably 20×10 ppm or more (200 ppm or more). When the ash content of the long-chain branched polypropylene resin C is within the above-mentioned preferred range, β crystals are more suitably formed in the cast sheet, resulting in a suitably roughened surface of the polypropylene film.

[0106] The melt flow rate (MFR) of the long-chain branched polypropylene resin C at 230°C is preferably 0.1 to 12 g / 10 min, more preferably 0.5 to 5 g / 10 min, even more preferably 0.7 to 3.5 g / 10 min, and particularly preferably 1.0 to 2.2 g / 10 min. When the MFR of the long-chain branched polypropylene resin C at 230°C is within the above range, the resin has excellent flow properties in a molten state, making it less likely to experience unstable flow such as melt fracture, and also suppressing breakage during stretching. Therefore, the resin has good thickness uniformity, which has the advantage of suppressing the formation of thin-walled portions that are prone to dielectric breakdown.

[0107] The content of the long-chain branched polypropylene resin C is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and even more particularly preferably 2.5% by mass or more, based on 100% by mass of the total polypropylene resin in the polypropylene film. The content of the long-chain branched polypropylene resin C is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, particularly preferably 7% by mass or less, and even more particularly preferably 5% by mass or less, based on 100% by mass of the total polypropylene resin in the polypropylene film. The polypropylene film may contain one or more types of the long-chain branched polypropylene resin C.

[0108] Representative commercially available products of the long-chain branched polypropylene resin C include, for example, MFX3 and MFX6 manufactured by Japan Polypropylene Corporation, and MFX8 manufactured by Japan Polypropylene Corporation.

[0109] The methods for measuring the above-mentioned physical properties of the polypropylene resin are as follows. The average molecular weight and molecular weight distribution of the linear polypropylene resin are values ​​measured according to the method (2-1) of the Examples described later. The average molecular weight and molecular weight distribution of the branched polypropylene resin are values ​​measured according to the method (2-2) of the Examples described later. The differential distribution value difference is a value measured according to the method (2-3) of the Examples described later. The heptane insoluble matter is a value measured according to the method (2-4) of the Examples described later. The mesopentad fraction is a value measured according to the method (2-5) of the Examples described later. The melt flow rate is a value measured according to the method (2-6) of the Examples described later. The ash content is a value measured according to the method (2-7) of the Examples described later.

[0110] The polypropylene film may contain a resin other than polypropylene resin (hereinafter also referred to as "other resin"). The "other resin" refers to a resin other than polypropylene resin, which is generally considered to be the main component resin, and is not particularly limited as long as the desired polypropylene film can be obtained. Examples of other resins include polyolefins other than polypropylene, such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), and poly(1-methylpentene); copolymers of α-olefins, such as ethylene-propylene copolymers, propylene-butene copolymers, and ethylene-butene copolymers; random copolymers of vinyl monomers and diene monomers, such as styrene-butadiene random copolymers; and random copolymers of vinyl monomers, diene monomers, and vinyl monomers, such as styrene-butadiene-styrene block copolymers. The polypropylene film may contain an amount of other resin that does not adversely affect the desired polypropylene film. The polypropylene film may contain preferably 10 parts by mass or less, more preferably 5 parts by mass or less, of the other resin per 100 parts by mass of polypropylene resin. The polypropylene film may contain another resin in an amount of preferably 0.1 part by mass or more, more preferably 1 part by mass or more, per 100 parts by mass of the polypropylene resin.

[0111] In addition to the resin component, the polypropylene film may further contain at least one additive. The "additive" refers to an additive generally used in polypropylene, and is not particularly limited as long as the desired polypropylene film can be obtained. Examples of additives include nucleating agents (α-crystal nucleating agents, β-crystal nucleating agents), antioxidants, necessary stabilizers such as chlorine absorbers and UV absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers, organic fillers, etc. Examples of inorganic fillers include barium titanate, strontium titanate, and aluminum oxide. When using such additives, they can be included in an amount that does not adversely affect the desired polypropylene film.

[0112] The "nucleating agent" is not particularly limited as long as it is commonly used in polypropylene and can provide the desired polypropylene film.

[0113] Examples of the nucleating agent include an α-crystal nucleating agent that preferentially nucleates α-crystals and a β-crystal nucleating agent that preferentially nucleates β-crystals.

[0114] Among α-crystal nucleating agents, organic nucleating agents include dispersion-type nucleating agents and solution-type nucleating agents. Examples of dispersion-type nucleating agents include phosphate ester metal salt-based nucleating agents, carboxylate metal salt-based nucleating agents, and rosin metal salt-based nucleating agents. Examples of solution-type nucleating agents include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, and amide-based nucleating agents.

[0115] Examples of the β-crystal nucleating agent include amide-based nucleating agents, di- or polycarboxylic acid metal salt-based nucleating agents, quinacridone-based nucleating agents, aromatic sulfonic acid-based nucleating agents, phthalocyanine-based nucleating agents, and tetraoxaspiro compound-based nucleating agents.

[0116] The nucleating agent can be dry-blended or melt-blended with the polypropylene raw material and pelletized before use, or can be fed into an extruder together with the polypropylene pellets. The surface roughness of the film can be adjusted to a desired level by using a nucleating agent. A typical example of a commercially available nucleating agent is NJSTAR NU-100 manufactured by New Japan Chemical Co., Ltd., which is a β-crystal nucleating agent. When the polypropylene film contains a β-crystal nucleating agent, the content thereof is preferably 1 to 1000 ppm by mass, more preferably 50 to 600 ppm by mass, relative to the mass of the resin component (mass of the entire resin component).

[0117] The term "antioxidant" is generally used in polypropylene and is not particularly limited as long as it can produce the desired polypropylene film. Antioxidants are generally used for two purposes. One purpose is to suppress thermal and oxidative degradation in an extruder, and the other purpose is to contribute to suppressing degradation during long-term use as a capacitor film and improving capacitor performance. Antioxidants that suppress thermal and oxidative degradation in an extruder are also called "primary agents," and antioxidants that contribute to improving capacitor performance are also called "secondary agents."

[0118] Two types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for both purposes.

[0119] An example of a primary agent is 2,6-di-tertiary-butyl-para-cresol (general name: BHT). The primary agent can usually be added to the polypropylene resin composition during preparation, as described below in the polypropylene film manufacturing method, for the purpose of suppressing thermal and oxidative degradation in the extruder. Most of the antioxidant added to the polypropylene resin composition for this purpose is consumed during the molding process in the extruder, and almost none remains in the film after film formation. Therefore, when the polypropylene film contains a primary agent, the content thereof is usually less than 100 ppm by mass relative to the mass of the resin components (mass of the resin components as a whole).

[0120] The secondary agent may be a hindered phenol-based antioxidant having a carbonyl group.

[0121] The "hindered phenol antioxidant having a carbonyl group" is generally understood to be a hindered phenol antioxidant having a carbonyl group, and is not particularly limited as long as the desired polypropylene film can be obtained.

[0122] Examples of the hindered phenol antioxidant having a carbonyl group include triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] (trade name: Irganox 245), 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 259), pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1010), 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1011), Examples of suitable hydroxyl groups include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: Irganox 1035), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), and N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide) (trade name: Irganox 1098). Of these, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred because it has a high molecular weight, is highly compatible with polypropylene, and has low volatility and excellent heat resistance.

[0123] The polypropylene film may contain one or more types of hindered phenol-based antioxidants (secondary agents) having a carbonyl group for the purpose of suppressing deterioration that progresses over time during long-term use. When the polypropylene film contains one or more types of hindered phenol-based antioxidants having a carbonyl group, the content thereof is preferably 4000 ppm by mass or more and 6000 ppm by mass or less, more preferably 4500 ppm by mass or more and 6000 ppm by mass or less, relative to the mass of the resin component (mass of the resin component as a whole). From the viewpoint of achieving an appropriate effect, it is preferable that the content of the hindered phenol-based antioxidants having a carbonyl group in the film is 4000 ppm by mass or more and 6000 ppm by mass or less.

[0124] A polypropylene film containing an optimum specific range of amount of a hindered phenol-based antioxidant having a carbonyl group, which has good compatibility with polypropylene at the molecular level, is preferred because it improves long-term durability.

[0125] The term "chlorine absorbent" is generally used in polypropylene and is not particularly limited as long as it can be used to obtain the desired polypropylene film. Examples of chlorine absorbents include metal soaps such as calcium stearate. When such a chlorine absorbent is used, it can be contained in an amount that does not adversely affect the desired polypropylene film.

[0126] The polypropylene film of the present invention is preferably biaxially stretched. When the polypropylene film of the present invention is a biaxially stretched polypropylene film, the biaxially stretched polypropylene film can be produced by a commonly known method for producing a biaxially stretched polypropylene film. For example, the polypropylene film can be produced by producing a cast sheet from a polypropylene resin composition obtained by mixing a linear polypropylene resin A, a linear polypropylene resin B, and a long-chain branched polypropylene resin C, optionally together with other resins, additives, etc., and then biaxially stretching the cast sheet.

[0127] <Preparation of Polypropylene Resin Composition> The method for preparing the polypropylene resin composition is not particularly limited, and examples thereof include a method in which polymer powders or pellets of linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C are dry-blended, if necessary, together with other resins, additives, etc., using a mixer or the like; and a method in which polymer powders or pellets of linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C are supplied, if necessary, together with other resins, additives, etc., to a kneader and melt-kneaded to obtain a melt blend resin composition.

[0128] The mixer or kneader is not particularly limited. The kneader may be of a single screw type, a twin screw type, or a multi-screw type having two or more screws. In the case of a twin or more screw type, the kneader may be of either a co-rotating or counter-rotating type.

[0129] In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as good kneading can be achieved, but is preferably in the range of 170 to 320°C, more preferably in the range of 200 to 300°C, and even more preferably in the range of 230 to 270°C. In order to suppress deterioration during kneading and mixing of the resin, an inert gas such as nitrogen may be purged into the kneader. The melt-kneaded resin can be pelletized to an appropriate size using a commonly known granulator to obtain pellets of the melt blend resin composition.

[0130] When preparing the polypropylene resin composition, a primary agent as an antioxidant described in the section on additives above can be added for the purpose of suppressing thermal degradation and oxidative degradation in the extruder.

[0131] When the polypropylene resin composition contains a primary agent, the content thereof is preferably 1000 ppm by mass to 5000 ppm by mass relative to the mass of the resin components (mass of the resin components as a whole). Most of the antioxidant for this purpose is consumed in the molding process in the extruder, and almost no antioxidant remains in the film after film formation.

[0132] The hindered phenol antioxidant having a carbonyl group, which has been described above in the section on additives, can be added to the polypropylene resin composition as a secondary agent.

[0133] When the polypropylene resin composition contains a hindered phenol-based antioxidant having a carbonyl group, the content thereof is preferably 100 ppm by mass to 10,000 ppm by mass, more preferably 5,500 ppm by mass to 7,000 ppm by mass, relative to the mass of the resin components (mass of the resin components as a whole). A considerable amount of the hindered phenol-based antioxidant having a carbonyl group is also consumed in the extruder.

[0134] When the polypropylene resin composition does not contain a primary agent, a larger amount of the hindered phenol-based antioxidant having a carbonyl group can be used. This is because the consumption of the hindered phenol-based antioxidant having a carbonyl group increases in the extruder. When the polypropylene resin composition does not contain a primary agent but contains the hindered phenol-based antioxidant having a carbonyl group, the content thereof is 6,000 ppm by mass to 8,000 ppm by mass or less relative to the mass of the resin components (mass of the resin components as a whole).

[0135] <Preparation of Cast Sheet> A cast sheet can be obtained by feeding pre-prepared pellets of the dry blend resin composition and / or melt blend resin composition into an extruder, melting them, and filtering them. The pellets are then melt-extruded through a T-die by heating to a temperature of preferably 170°C to 320°C, more preferably 200°C to 300°C, and then cooled and solidified on at least one metal drum maintained at a temperature (casting temperature) of preferably 40°C to 140°C, more preferably 80°C to 140°C, even more preferably 90°C to 140°C, particularly preferably 90°C to 120°C, and even more particularly preferably 90°C to 105°C. The melt-extruded resin composition is preferably pressed against the metal drum with an air knife. The surface in contact with the metal drum is the first surface, and the opposite surface (the surface facing the air knife) is the second surface.

[0136] The thickness of the cast sheet is not particularly limited as long as the desired polypropylene film can be obtained, but is preferably 0.05 mm to 2 mm, more preferably 0.1 mm to 1 mm.

[0137] During the process of producing a cast sheet (particularly in an extruder), polypropylene undergoes considerable thermal degradation (oxidative degradation) and shear degradation. The degree of progression of such degradation, i.e., changes in molecular weight distribution and stereoregularity, can be suppressed by purging the extruder with nitrogen (oxidation suppression), the screw shape (shear force) in the extruder, the internal shape of the T-die (shear force) during casting, the amount of antioxidant added (oxidation suppression), the winding speed (extension force) during casting, etc.

[0138] <Stretching Treatment> The biaxially oriented polypropylene film can be produced by subjecting the cast sheet to a stretching treatment. Sequential biaxial stretching is preferred as the stretching method. In this sequential biaxial stretching method, the cast sheet is first maintained at a temperature of preferably 135 to 150°C, more preferably 140 to 146°C, passed through rolls with a speed differential, stretched 3 to 7 times in the machine direction, and immediately cooled to room temperature. By appropriately adjusting the temperature in this longitudinal stretching step, it becomes easier to adjust the Sku value of either the first or second side within an appropriate range and / or the Spc value of either the first or second side within an appropriate range. Subsequently, the stretched film is introduced into a tenter and transversely stretched 3 to 11 times in the width direction at a temperature of preferably 150°C or higher, more preferably 150 to 180°C, followed by relaxation, heat setting, and winding into a roll.

[0139] The film wound into a roll is subjected to an aging treatment in an atmosphere of about 20 to 45°C, and then, while being unwound (unwound), it is slit (cut) to the desired product width using a slitter or the like, and each piece is wound again.

[0140] Such a stretching step results in a biaxially stretched film having excellent mechanical strength and rigidity, and the surface irregularities are more clearly defined, resulting in a finely roughened film.

[0141] After the stretching and heat setting steps, the polypropylene film may be subjected to corona discharge treatment online or offline. Corona discharge treatment can improve adhesive properties in subsequent steps such as metal deposition processing. Corona discharge treatment can be performed using a known method. It is preferable to perform the treatment using air, carbon dioxide gas, nitrogen gas, or a mixture thereof as the atmospheric gas.

[0142] To process the polypropylene film into a capacitor, a metal layer may be laminated on one or both sides of the polypropylene film to form a metal layer-integrated polypropylene film. The metal layer functions as an electrode. Examples of metals that can be used for the metal layer include zinc, lead, silver, chromium, aluminum, copper, nickel, and other metals, as well as mixtures and alloys of these metals. However, considering environmental, economical, and capacitor performance considerations, zinc and aluminum are preferred.

[0143] Examples of methods for laminating a metal layer on the first surface or both surfaces of the polypropylene film include vacuum deposition and sputtering. Vacuum deposition is preferred from the viewpoints of productivity and economy. Examples of vacuum deposition methods include the crucible method and the wire method, but are not particularly limited, and an optimal method can be selected as appropriate.

[0144] The margin pattern used when laminating the metal layer by vapor deposition is not particularly limited, but in order to improve the safety and other properties of the capacitor, it is preferable to apply a pattern including a so-called special margin, such as a fishnet pattern or a T-margin pattern, to one side of the film. This is effective in terms of increasing safety and preventing capacitor damage and short circuits.

[0145] As a method for forming the margin, any generally known method such as a tape method or an oil method can be used without any limitation.

[0146] When forming a metal layer on the polypropylene film, the polypropylene film wound in a roll is unwound (unwound), a metal layer such as a vapor-deposited film is formed on one or both surfaces, and the film is then wound again.

[0147] The metal layer-integrated polypropylene film can be laminated in a plurality of layers by a conventionally known method, or can be wound around an element to form a film capacitor.

[0148] Specifically, a blade is used to slit the center of each margin of the metal layer-integrated polypropylene film, to prepare a take-up reel having a margin on one surface.

[0149] Next, using a winding reel with a left margin and a winding reel with a right margin, the two sheets are stacked and wound together so that the vapor-deposited area extends beyond the margin in the width direction (element winding process). Next, the core material is removed from the wound body and pressed. Next, external electrodes are formed on both end surfaces, and lead wires are attached to the external electrodes. This completes the wound film capacitor.

[0150] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0151] Test 1 was conducted to investigate the relationship between the Sku value and the problem of the present application, and Test 2 was conducted to investigate the relationship between the Spc value and the problem of the present application. In each test, the numbers of Examples and Comparative Examples are represented by consecutive numbers starting from 1.

[0152] <Test 1>

[0153] Test 1: (1) Preparation of Polypropylene Resins The polypropylene resins used to produce the polypropylene films of the Examples and Comparative Examples are shown in Table 1. Resin A1: manufactured by Prime Polymer Co., Ltd. Resin A2: HC300BF manufactured by Borealis Co., Ltd. Resin A3: manufactured by Prime Polymer Co., Ltd. Resin B1: S802M manufactured by Daehan Yuhka Industrial Co., Ltd. Resin B2: HPT-1 manufactured by Daehan Yuhka Industrial Co., Ltd. Resin B3: HP600J manufactured by HMC POLYMERS Co., Ltd. Resin C1: MFX6 manufactured by Japan Polypropylene Corporation Resin C2: WB135HMS manufactured by Borealis Co., Ltd.

[0154] Resin A1, Resin A2, and Resin A3 are linear polypropylene resins and correspond to or correspond to linear polypropylene resin A. Resin B1, Resin B2, and Resin B3 are linear polypropylene resins and correspond to linear polypropylene resin B. Resin A1, Resin A2, Resin A3, Resin B1, Resin B2, and Resin B3 are all homopolypropylene resins. Resin C1 is a branched polypropylene resin polymerized using a metallocene catalyst and corresponds to long-chain branched polypropylene resin C. Resin C2 is a branched polypropylene resin produced using a peroxide, but is not a branched polypropylene resin polymerized using a metallocene catalyst.

[0155] Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin. These values ​​are values ​​in the form of raw material resin pellets. The measurement methods are as follows.

[0156]

[0157] Test 1: (2) Measurement of physical properties of polypropylene resin Test 1: (2-1) Measurement of various average molecular weights and various molecular weight distributions of linear polypropylene resin Using SEC (size exclusion chromatography), various average molecular weights and various molecular weight distributions were measured under the following conditions. Apparatus: HLC-8321 GPC / HT (detector: differential refractometer (RI)) (manufactured by Tosoh Corporation) Column: TSKgel Guard column H ＨＲ (30) HT (7.5mm I.D. x 7.5cm) x 1 + TSKgel GMH ＨＲ-H(20)HT (7.8 mm ID x 30 cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (GPC grade, Fujifilm Wako Pure Chemical Industries, Ltd.) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0 mL / min Detection conditions: polarity = (-) Injection volume: 300 μL Column temperature: 140°C System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, and a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene added) was added and the mixture was dissolved by shaking at 140°C for 1 hour. The mixture was then heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solution revealed no undissolved matter. Calibration curve: A quintic approximation calibration curve was created using standard polystyrene (Tosoh Corporation). The molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0158] From the obtained calibration curve and SEC chromatogram, the number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) were obtained using analysis software for the measurement device. The Mw and Mn values ​​were used to obtain the molecular weight distribution (Mw / Mn). The Mz and Mn values ​​were also used to obtain the molecular weight distribution (Mz / Mn).

[0159] Test 1: (2-2) Measurement of Various Average Molecular Weights and Various Molecular Weight Distributions of Branched Polypropylene Resins Using SEC-MALS (size exclusion chromatography-multiangle light scattering detector), various average molecular weights and various molecular weight distributions were measured under the following conditions. This is a method of measuring the average molecular weight by fractionating according to molecular size using SEC and measuring the absolute molecular weight using MALS. Apparatus: HLC-8321GPC / HT (with built-in differential refractometer (RI)) (manufactured by Tosoh Corporation) Light scattering detector: DAWN HELEOS (manufactured by Wyatt Technology) MALS laser wavelength: 664 nm Column: TSKgel guard column H ＨＲ (30) HT (7.5mm I.D. x 7.5cm) x 1 + TSKgel GMH ＨＲ-H(20)HT (7.8 mm I.D. x 30 cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (GPC grade, Fujifilm Wako Pure Chemical Industries, Ltd.) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0 mL / min Injection volume: 300 μL Column temperature: 140°C System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene added) was added, and the mixture was dissolved by shaking at 140°C for 1 hour. The mixture was then heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solution revealed no insoluble matter.

[0160] Data processing was performed using analysis software Astra Ver. 5.3.4 manufactured by Wyatt Technology. The analysis was performed under the following conditions: Absolute molecular weight and radius of gyration were determined from the Zimm plot. The refractive index (1.501) of 1,2,4-trichlorobenzene at 140°C used in the calculation was determined by first approximation from the refractive index values ​​at 20°C and 135°C. The refractive index concentration increment (dn / dc) of the sample was determined from the literature value (-0.092 mL / g). Reference: K. Lederer and I. Mingozzi, Pure and Applied Chemistry, 69(5), 993-1006 (1997). - With GPC-MALS, there are regions where it is difficult to evaluate absolute molecular weight and radius of gyration for the following reasons, so these regions were excluded from the range of absolute molecular weight calculation and radius of gyration evaluation. - Low concentration (both high and low molecular weight sides): At the base of the peak in the chromatogram, the sample concentration is insufficient and sufficient sensitivity cannot be obtained. - Isotropic scattering (low molecular weight side only): When the molecular size is approximately 1 / 20 or less of the wavelength of the incident light, the scattered light does not exhibit anisotropy, and the radius of gyration cannot be obtained due to the measurement principle.

[0161] The above analysis yielded the radius of gyration (Rw), number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz). The Mw and Mn values ​​were used to obtain the molecular weight distribution (Mw / Mn). The Mz and Mn values ​​were also used to obtain the molecular weight distribution (Mz / Mn).

[0162] Test 1: (2-3) Differential distribution value difference (D Ｍ Measurement of differential distribution value difference (D Ｍ ) was obtained by the following method. A SEC chromatogram was obtained by the method described in (2-1) above. This chromatogram was converted into a differential molecular weight distribution curve using the analysis software built into the measurement device used. From this differential molecular weight distribution curve, the differential molecular weight distribution values ​​at Log(M) = 4.5 and Log(M) = 6.0 were read. The differential molecular weight distribution value difference (D Ｍ ) was calculated by subtracting the differential molecular weight distribution value when Log(M)=6.0 from the differential molecular weight distribution value when Log(M)=4.5.

[0163] Test 1: (2-4) Measurement of heptane insolubles [HI] A linear polypropylene resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample of approximately 3 g. Next, approximately 150 mL of heptane was added, and Soxhlet extraction was performed for 8 hours. The heptane insolubles were calculated from the sample mass before and after extraction.

[0164] Test 1: (2-5) Measurement of mesopentad fraction [mmmm] In order to analyze the stereoregularity of a polypropylene resin, the mesopentad fraction was measured by dissolving the resin in a solvent and using a nuclear magnetic resonance (NMR) analyzer equipped with a cryoprobe under the following conditions. Nuclear magnetic resonance (NMR) apparatus: AVANCE NEO 700 manufactured by Bruker Corporation Probe: 10 mmφ PABBO BB Observation nucleus: １３ C (176.07 MHz) Solvent: 1,1,2,2-tetrachloroethane-d ２ Concentration: approximately 250 mg / 2.5 mL Number of accumulations: 8,192 Temperature: 130°C Reference: 5-unit propylene chain (mmmm) = 21.86 ppm Pulse width: 5.3 μs Observation time: 0.8 s Waiting time: 2.2 s Measurement mode: power-gated decoupling (NOEs of all methyl carbons of the propylene unit were considered to be equal).

[0165] The pentad fraction, which represents the degree of stereoregularity, was calculated as a percentage (%) from the integrated intensity of each signal derived from a combination of five pentads (pentads) consisting of meso (m) tangles arranged in the same direction and racemo (r) tangles arranged in the opposite direction (e.g., mmmm, mrrm, etc.). The assignment of each signal derived from mmmm, mrrm, etc. was based on the spectral descriptions in, for example, T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988).

[0166] Test 1: (2-6) Measurement of Melt Flow Rate (MFR) The melt flow rate (MFR) of each resin in the form of raw resin pellets was measured using a melt indexer manufactured by Toyo Seiki Co., Ltd. in accordance with condition M of JIS K 7210. Specifically, a weighed 4 g sample was first inserted into a cylinder set to a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16 kg. The weight of the sample extruded from the bottom hole over 30 seconds was then measured, and the MFR (g / 10 min) was calculated. The above measurement was repeated three times, and the average value was used as the measured MFR.

[0167] Test 1: (2-7) Measurement of Ash Content The ash content of each resin was measured as follows. Approximately 200 g of the sample was weighed. Approximately 10 g of the sample was placed in a platinum dish and burned repeatedly until all of the weighed sample was burned, after which it was incinerated in an electric furnace at 800°C for 40 minutes. The ash content (ppm) was calculated from the resulting ash residue. This was performed twice, and the average value was taken as the ash content (ppm).

[0168] Test 1: (3) Preparation of Polypropylene Film Example 1 Resin A1, resin B1, and resin C1 were dry-blended. The mixing ratio by mass was (resin A1): (resin B1): (resin C1) = 63:34:3. The dry-blended resin was then melted at a resin temperature of 260 ° C, extruded using a T-die, and solidified by wrapping around a metal drum maintained at a surface temperature of 97 ° C to produce a cast sheet. At this time, the melt-extruded resin composition was pressed against the metal drum with an air knife to produce a cast sheet. The obtained unstretched cast sheet was kept at a temperature of 143 ° C, passed between rolls with a speed difference, stretched 4.6 times in the machine direction, and immediately cooled to room temperature. Subsequently, the cast sheet was stretched in the machine direction to produce a stretched film, which was introduced into a tenter and stretched 9.5 times in the width direction at a transverse stretching temperature of 155 ° C, followed by relaxation and heat setting. Subsequently, one side of the film was subjected to a corona treatment in an air atmosphere so that the wet tension was 37±1 mN / m, and then a biaxially oriented polypropylene film having a thickness of 2.3 μm was wound up. After the biaxially oriented polypropylene film was wound up, it was placed in an atmosphere of about 40° C. for 24 hours and subjected to an aging treatment, thereby obtaining the biaxially oriented polypropylene film according to Example 1.

[0169] Example 2 A biaxially oriented polypropylene film according to Example 2 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2, and the film was wrapped around a metal drum whose surface temperature was maintained at 92°C to solidify it, thereby producing a cast sheet.

[0170] Example 3 A biaxially oriented polypropylene film according to Example 3 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2.

[0171] Comparative Example 1 A biaxially oriented polypropylene film according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2, and a cast sheet was produced by winding the sheet around a metal drum whose surface temperature was maintained at 90°C and solidifying it, and the unstretched cast sheet was kept at a temperature of 145°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0172] Comparative Example 2 A biaxially oriented polypropylene film according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2, and a cast sheet was produced by winding the sheet around a metal drum whose surface temperature was maintained at 96°C and solidifying it, and the unstretched cast sheet was kept at a temperature of 147°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0173] Comparative Example 3 A biaxially oriented polypropylene film according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2, and the unstretched cast sheet was kept at a temperature of 145°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0174] Comparative Example 4 A biaxially oriented polypropylene film according to Comparative Example 4 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 2, the resin was melted at a resin temperature of 250°C, the resin was wrapped around a metal drum whose surface temperature was maintained at 93°C to solidify it, and a cast sheet was produced. The film was stretched in the width direction at a transverse stretching temperature of 158°C.

[0175]

[0176] Test 1: (4) Evaluation of physical properties of polypropylene film Test 1: (4-1) Measurement of thickness Measurement was performed using a paper thickness measuring instrument MEI-11 (measurement pressure 100 kPa, descending speed 3 mm / sec, measurement terminal φ=16 mm, measuring force 20.1 N) manufactured by Citizen Seimitsu Co., Ltd. in an environment of a temperature of 23±2°C and a humidity of 50±5% RH. The sample was cut from the roll with 10 or more sheets stacked, and handled so as not to wrinkle or trap air in the film during cutting. Five measurements were performed on a 10-sheet stack sample, and the thickness was calculated by dividing the average of the five measurements by 10.

[0177] Test 1: (4-2) Haze Measurement Haze was measured in accordance with JIS K 7136: 2000 using a haze meter ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.) A sample was cut out from the roll, and the size of the sample was 50 mm in the MD direction and 100 mm in the TD direction.

[0178] Test 1: (4-3) Measurement of Wet Tension The wet tension of the film surface was measured in accordance with JIS K6768:1999 under an environment of a temperature of 23±2° C. and a humidity of 50±5% RH.

[0179] Test 1: (4-4) Measurement of three-dimensional surface texture parameters The biaxially stretched polypropylene films of the examples and comparative examples were measured by the following methods, and the following three-dimensional surface texture parameters were calculated in accordance with ISO 25178-2 (2007 draft): Sa: arithmetic mean deviation Sq: root-mean-square deviation Sku: kurtosis The measurements were performed on both sides of the film using the following methods.

[0180] As an optical interference type non-contact surface shape measuring instrument, "VertScan 2.0 (model: R5500GML)" manufactured by Ryoka Systems Co., Ltd. was used in the following configuration. Manufacturer: Ryoka Systems Co., Ltd. Device name: VertScan 2.0 (R5500GML-A150-AC) Measurement software: VS-Measure Version 5.05.0014 CCD camera: SONY HR-50 1 / 3 Objective lens: 10x Lens barrel: 1xBODY Zoom lens: No Relay Wavelength filter: 530 white Measurement mode: WAVE Field of view size: 640 x 480 pixels Measurement area: 470.92 μm x 353.16 μm The sample was placed on an electrostatic adsorption plate (150 mm x 150 mm) with a porous plate fixed thereon and measured. In addition, measurements were made at 10 points at 1 cm intervals in the flow direction from the center in both the flow direction and width direction of the target sample (polypropylene film).

[0181] Next, the obtained measurement data was subjected to the following processes in order to calculate surface texture parameters: Analysis software: VS-Viewer Version 5.05.0013 1. Completion of invalid pixels using the command "Complete (Full)" 2. Noise removal using median (3 x 3) filtering 3. Waviness component removal using Gaussian filtering with a cutoff value of 30 μm 4. Calculation using the plug-in function "ISO parameters" (S-Filter: None) 5. The arithmetic mean value was calculated for each of the values ​​(Sa, Sq, Sku) obtained by measuring and analyzing the above 10 locations, and this value was used.

[0182] Test 1: (4-5) Measurement of dielectric breakdown strength The dielectric breakdown strength of the biaxially stretched film was measured in accordance with JIS C 2330:2010 6.2 b) and JIS C 2151:2006 17.2.2 (Dielectric breakdown strength, DC test, flat plate electrode method). However, the lower electrode used in the measurement was a metal flat plate (dimensions 150 mm × 150 mm, thickness 3 mm) with conductive rubber (manufactured by Seiwa Electric Co., Ltd., dimensions 100 mm × 200 mm, thickness 1 mm, model number E12S10) placed on top. This measurement was performed 44 times, and the highest and lowest six values ​​from the measurement results were discarded. The average of the remaining 32 results was divided by the film thickness to determine the dielectric breakdown strength (V ＤＣ The measurement conditions are as follows: Test piece: Approximately 150 mm x 150 mm Test piece conditioning: 30 minutes under atmospheric conditions Power source: Direct current Atmosphere: Air at 120°C Testing machine: DC withstand voltage / insulation resistance tester TOS9213AS manufactured by Kikusui Electronics Co., Ltd. Voltage rise rate: 100 V / s Current detection response speed: MID Upper limit reference value: 5 mA.

[0183] Test 1: (4-6) Measurement of Ash Content Approximately 200 g of a sample was weighed, transferred to a platinum dish, and incinerated for 40 minutes at 800° C. The ash content (ppm) was measured from the resulting ash residue.

[0184] Test 1: (5) Preparation of Metallized Film and Capacitor While unwinding a polypropylene film roll, an insulating margin and segmented electrode pattern were formed on the corona-treated surface using an ULVAC winding vacuum deposition device (EWE-060). Aluminum was vapor-deposited to form electrodes on the film, and zinc was vapor-deposited to form heavy edges (electrical introduction portions) on the film. This resulted in a metallized film roll with an electrode pattern, with an Al metal film resistance of 20 Ω / □ and a Zn metal film resistance of 5 Ω / □.

[0185] The electrical resistance (surface resistivity ρs) of the metal film was measured using an insulation resistance measuring instrument (Loresta GP-MCP-T610, manufactured by Mitsubishi Analytech Co., Ltd.) with a thin film measurement electrode (PSP probe MCP-TP06PRMH112) according to the following procedure: 1. A four-probe electrode, aligned in a substantially straight line, was placed in contact with the active electrode portion of the sample. 2. A constant current was passed between the two outer probes, and the potential difference generated between the two inner probes was measured to determine the film resistance value of the metal portion. 3. The sample size was not particularly limited, but because the distribution of electrical energy changes depending on the size of the sample being measured, the sample shape and size were entered into the instrument and multiplied by a resistivity correction coefficient (4.419) to obtain a numerical value.

[0186] The thickness of the metal film (effective electrode part) vapor-deposited on the polypropylene sheet is thin, at only a few tens of nanometers, making it difficult to measure. Therefore, the electrical resistance (surface resistivity ρs) of the metal film was measured and used as a substitute for the thickness.

[0187] The prepared metallized film roll was cut to a width of 30 mm using a slitter to produce small reels of metallized film for winding elements with an insulating margin width of 2.0 mm and a heavy edge width of 1.5 mm. Elements were wound onto the small reels using a fully automatic winding machine (3KAW-N2) manufactured by Kaito Seisakusho Co., Ltd., to a capacitance of approximately 50 μF, followed by pressing and flattening. Metallicon was sprayed onto the end surfaces of the flattened elements to form film electrode outlets, and the elements were then heat-treated at high temperatures in a vacuum to harden them. Leads were attached to the metallicon-sprayed portions, the elements were placed in a resin case, and the gaps were filled with epoxy resin. The resin was then cured to obtain metallized film capacitor elements for evaluation.

[0188] Test 1: (6) Characterization of Metallized Film and Capacitor Test 1: (6-1) Measurement of Capacitor Capacitance and Dielectric Dissipation Factor A four-terminal probe 9140 was attached to a Hioki E.E. Corporation LCR HiTester 3522-50. Two terminals (lead wires) of the capacitor were pinched with the four-terminal probe 9140, and a 0.1 V, 1 kHz AC voltage was applied from the built-in power supply of the LCR HiTester 3522-50. Once the displayed value had settled (e.g., approximately 30 seconds after application), the capacitance and tan δ values ​​were read. Note that measurement conditions other than those described here conformed to "4.2.2 Capacitance" and "4.2.3 Dielectric Dissipation Factor (tan δ)" of JIS C 5101-16:2009.

[0189] Test 1: (6-2) Capacitor life test (capacitance change rate and safety) A DC voltage of 750 V was continuously applied to the capacitor for 1,000 hours in a high-temperature chamber at 115°C. Based on the capacitance of the capacitor before and after the load, the capacity change rate before and after the voltage load was calculated using the following formula. The test was performed on two samples, and the average value was used for evaluation.

[0190] (Capacitance change rate)=[(capacitance after voltage load)−(initial capacitance)] / (initial capacitance)×100(%) It is preferable that the capacity change rate after 1000 hours is within −5%.

[0191] The insulation resistance was measured as follows: A shielding box SME-8350 was connected to a Hioki E.E. Corporation super insulation resistance meter DSM8104. A metallized film capacitor element was placed in the shielding box, and a DC voltage of 500 V was applied. The insulation resistance value was read after 1 minute. Measurement conditions other than those described here were in accordance with "4.2.4 Insulation Resistance" of JIS C 5101-16:2009.

[0192] In addition, when determining whether a short circuit occurred, an insulation resistance of less than 100 kΩ was determined to be a short circuit. Specifically, when the resistance was so low that it exceeded the lower measurement limit of the insulation resistance meter (when no value was displayed), it was determined to be a short circuit.

[0193] There are three main types of failure modes for capacitors, of which short circuit failures must be avoided because current continues to flow through a shorted capacitor, generating heat due to Joule heat, which can destroy the exterior and react with oxygen in the air, potentially causing a fire. 1. Open circuit failure: A failure in which the capacitance drops dramatically while the insulation resistance remains high. 2. Short circuit failure: A failure in which the insulation resistance drops dramatically. 3. Capacitance fluctuation: A failure in which the capacitor's characteristics, such as capacitance or loss, change beyond the specifications.

[0194] During the capacitor life test described above, if no short circuit failure occurred in either of the two capacitor elements tested, the safety was judged to be good, and if a short circuit failure occurred in either or both of the two capacitors, the safety was judged to be poor.

[0195] Test 1: (7) Characterization results

[0196]

[0197] <Test 2>

[0198] Test 2: (1) Preparation of Polypropylene Resins The polypropylene resins used to produce the polypropylene films of the Examples and Comparative Examples are shown in Table 4. Resin A1: manufactured by Prime Polymer Co., Ltd. Resin A2: HC300BF manufactured by Borealis Co., Ltd. Resin A3: manufactured by Prime Polymer Co., Ltd. Resin B1: S802M manufactured by Daehan Yuhka Industrial Co., Ltd. Resin B2: HPT-1 manufactured by Daehan Yuhka Industrial Co., Ltd. Resin B3: HP600J manufactured by HMC POLYMERS Co., Ltd. Resin C1: MFX6 manufactured by Japan Polypropylene Corporation Resin C2: WB135HMS manufactured by Borealis Co., Ltd.

[0199] Resin A1, Resin A2, and Resin A3 are linear polypropylene resins and correspond to or correspond to linear polypropylene resin A. Resin B1, Resin B2, and Resin B3 are linear polypropylene resins and correspond to linear polypropylene resin B. Resin A1, Resin A2, Resin A3, Resin B1, Resin B2, and Resin B3 are all homopolypropylene resins. Resin C1 is a branched polypropylene resin polymerized using a metallocene catalyst and corresponds to long-chain branched polypropylene resin C. Resin C2 is a branched polypropylene resin produced using a peroxide, but is not a branched polypropylene resin polymerized using a metallocene catalyst.

[0200] Table 4 shows the number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin. These values ​​are values ​​in the form of raw material resin pellets. The measurement methods are as follows.

[0201]

[0202] Test 2: (2) Measurement of physical properties of polypropylene resin Test 2: (2-1) Measurement of various average molecular weights and various molecular weight distributions of linear polypropylene resin Using SEC (size exclusion chromatography), various average molecular weights and various molecular weight distributions were measured under the following conditions. Apparatus: HLC-8321 GPC / HT (detector: differential refractometer (RI)) (manufactured by Tosoh Corporation) Column: TSKgel Guard column H ＨＲ(30) HT (7.5mm I.D. x 7.5cm) x 1 + TSKgel GMH ＨＲ -H(20)HT (7.8 mm ID x 30 cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (GPC grade, Fujifilm Wako Pure Chemical Industries, Ltd.) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0 mL / min Detection conditions: polarity = (-) Injection volume: 300 μL Column temperature: 140°C System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, and a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene added) was added and the mixture was dissolved by shaking at 140°C for 1 hour. The mixture was then heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solution revealed no undissolved matter. Calibration curve: A quintic approximation calibration curve was created using standard polystyrene (Tosoh Corporation). The molecular weight was converted to the molecular weight of polypropylene using the Q-factor.

[0203] From the obtained calibration curve and SEC chromatogram, the number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) were obtained using analysis software for the measurement device. The Mw and Mn values ​​were used to obtain the molecular weight distribution (Mw / Mn). The Mz and Mn values ​​were also used to obtain the molecular weight distribution (Mz / Mn).

[0204] Test 2: (2-2) Measurement of Various Average Molecular Weights and Various Molecular Weight Distributions of Branched Polypropylene Resins Using SEC-MALS (size exclusion chromatography-multiangle light scattering detector), various average molecular weights and various molecular weight distributions were measured under the following conditions. This is a method of measuring the average molecular weight by fractionating according to molecular size using SEC and measuring the absolute molecular weight using MALS. Apparatus: HLC-8321GPC / HT (with built-in differential refractometer (RI)) (manufactured by Tosoh Corporation) Light scattering detector: DAWN HELEOS (manufactured by Wyatt Technology) MALS laser wavelength: 664 nm Column: TSKgel guard column H ＨＲ (30) HT (7.5mm I.D. x 7.5cm) x 1 + TSKgel GMH ＨＲ-H(20)HT (7.8 mm I.D. x 30 cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene (GPC grade, Fujifilm Wako Pure Chemical Industries, Ltd.) + dibutylhydroxytoluene (0.05%) Flow rate: 1.0 mL / min Injection volume: 300 μL Column temperature: 140°C System temperature: 40°C Sample concentration: 1 mg / mL Pretreatment: The sample was weighed, a solvent (1,2,4-trichlorobenzene with 0.1% dibutylhydroxytoluene added) was added, and the mixture was dissolved by shaking at 140°C for 1 hour. The mixture was then heated and filtered through a 0.5 μm sintered filter. Visual observation of the sample solution revealed no insoluble matter.

[0205] Data processing was performed using analysis software Astra Ver. 5.3.4 manufactured by Wyatt Technology. The analysis was performed under the following conditions: Absolute molecular weight and radius of gyration were determined from the Zimm plot. The refractive index (1.501) of 1,2,4-trichlorobenzene at 140°C used in the calculation was determined by first approximation from the refractive index values ​​at 20°C and 135°C. The refractive index concentration increment (dn / dc) of the sample was determined from the literature value (-0.092 mL / g). Reference: K. Lederer and I. Mingozzi, Pure and Applied Chemistry, 69(5), 993-1006 (1997). - With GPC-MALS, there are regions where it is difficult to evaluate absolute molecular weight and radius of gyration for the following reasons, so these regions were excluded from the range of absolute molecular weight calculation and radius of gyration evaluation. - Low concentration (both high and low molecular weight sides): At the base of the peak in the chromatogram, the sample concentration is insufficient and sufficient sensitivity cannot be obtained. - Isotropic scattering (low molecular weight side only): When the molecular size is approximately 1 / 20 or less of the wavelength of the incident light, the scattered light does not exhibit anisotropy, and the radius of gyration cannot be obtained due to the measurement principle.

[0206] The above analysis yielded the radius of gyration (Rw), number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz). The Mw and Mn values ​​were used to obtain the molecular weight distribution (Mw / Mn). The Mz and Mn values ​​were also used to obtain the molecular weight distribution (Mz / Mn).

[0207] Test 2: (2-3) Differential distribution value difference (D Ｍ Measurement of differential distribution value difference (D Ｍ ) was obtained by the following method. A SEC chromatogram was obtained by the method described in (2-1) above. This chromatogram was converted into a differential molecular weight distribution curve using the analysis software built into the measurement device used. From this differential molecular weight distribution curve, the differential molecular weight distribution values ​​at Log(M) = 4.5 and Log(M) = 6.0 were read. The differential molecular weight distribution value difference (D Ｍ ) was calculated by subtracting the differential molecular weight distribution value when Log(M)=6.0 from the differential molecular weight distribution value when Log(M)=4.5.

[0208] Test 2: (2-4) Measurement of heptane insolubles [HI] A linear polypropylene resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample of approximately 3 g. Next, approximately 150 mL of heptane was added, and Soxhlet extraction was performed for 8 hours. The heptane insolubles were calculated from the sample mass before and after extraction.

[0209] Test 2: (2-5) Measurement of mesopentad fraction [mmmm] In order to analyze the stereoregularity of a polypropylene resin, the mesopentad fraction was measured by dissolving the resin in a solvent and using a nuclear magnetic resonance (NMR) analyzer equipped with a cryoprobe under the following conditions. Nuclear magnetic resonance (NMR) analyzer: AVANCE NEO 700 manufactured by Bruker Corporation Probe: 10 mmφ PABBO BB Observation nucleus: １３ C (176.07 MHz) Solvent: 1,1,2,2-tetrachloroethane-d ２ Concentration: approximately 250 mg / 2.5 mL Number of accumulations: 8,192 Temperature: 130°C Reference: 5-unit propylene chain (mmmm) = 21.86 ppm Pulse width: 5.3 μs Observation time: 0.8 s Waiting time: 2.2 s Measurement mode: power-gated decoupling (NOEs of all methyl carbons of the propylene unit were considered to be equal).

[0210] The pentad fraction, which represents the degree of stereoregularity, was calculated as a percentage (%) from the integrated intensity of each signal derived from a combination of five pentads (pentads) consisting of meso (m) tangles arranged in the same direction and racemo (r) tangles arranged in the opposite direction (e.g., mmmm, mrrm, etc.). The assignment of each signal derived from mmmm, mrrm, etc. was based on the spectral descriptions in, for example, T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988).

[0211] Test 2: (2-6) Measurement of Melt Flow Rate (MFR) The melt flow rate (MFR) of each resin in the form of raw resin pellets was measured using a melt indexer manufactured by Toyo Seiki Co., Ltd. in accordance with JIS K 7210, Condition M. Specifically, a weighed 4 g sample was first inserted into a cylinder set to a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16 kg. The weight of the sample extruded from the bottom hole over 30 seconds was then measured, and the MFR (g / 10 min) was calculated. The above measurement was repeated three times, and the average value was used as the measured MFR.

[0212] Test 2: (2-7) Measurement of Ash Content The ash content of each resin was measured as follows. Approximately 200 g of the sample was weighed. Approximately 10 g of the sample was placed in a platinum dish and burned repeatedly until all of the weighed sample was burned, after which it was incinerated in an electric furnace at 800°C for 40 minutes. The ash content (ppm) was calculated from the resulting ash residue. This was performed twice, and the average value was taken as the ash content (ppm).

[0213] Test 2: (3) Preparation of Polypropylene Film Example 1 Resin A1, resin B1, and resin C1 were dry-blended. The mixing ratio by mass was (resin A1): (resin B1): (resin C1) = 63:34:3. The dry-blended resin was then melted at a resin temperature of 260 ° C, extruded using a T-die, and solidified by wrapping around a metal drum maintained at a surface temperature of 97 ° C to produce a cast sheet. At this time, the melt-extruded resin composition was pressed against the metal drum with an air knife to produce a cast sheet. The obtained unstretched cast sheet was kept at a temperature of 143 ° C, passed between rolls with a speed difference, stretched 4.6 times in the machine direction, and immediately cooled to room temperature. Subsequently, the cast sheet was stretched in the machine direction to produce a stretched film, which was introduced into a tenter and stretched 9.5 times in the width direction at a transverse stretching temperature of 155 ° C, followed by relaxation and heat setting. Subsequently, one side of the film was subjected to a corona treatment in an air atmosphere so that the wet tension was 37±1 mN / m, and then a biaxially oriented polypropylene film having a thickness of 2.3 μm was wound up. After the biaxially oriented polypropylene film was wound up, it was placed in an atmosphere of about 40° C. for 24 hours and subjected to an aging treatment, thereby obtaining the biaxially oriented polypropylene film according to Example 1.

[0214] Example 2 A biaxially oriented polypropylene film according to Example 2 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 5, and the film was wrapped around a metal drum whose surface temperature was maintained at 92°C to solidify it, thereby producing a cast sheet.

[0215] Example 3 A biaxially oriented polypropylene film according to Example 3 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 5.

[0216] Comparative Example 1 A biaxially oriented polypropylene film according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 5, and a cast sheet was produced by winding the sheet around a metal drum whose surface temperature was maintained at 90°C and solidifying it, and the unstretched cast sheet was kept at a temperature of 145°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0217] Comparative Example 2 A biaxially oriented polypropylene film according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 5, and a cast sheet was produced by winding the sheet around a metal drum whose surface temperature was maintained at 96°C and solidifying it, and the unstretched cast sheet was kept at a temperature of 147°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0218] Comparative Example 3 A biaxially oriented polypropylene film according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw material resins during dry blending was changed as shown in Table 5, and the unstretched cast sheet was kept at a temperature of 145°C and stretched in the machine direction by passing it between rolls with a speed difference.

[0219] Comparative Example 4 A biaxially oriented polypropylene film according to Comparative Example 4 was obtained in the same manner as in Example 1, except that the mixing ratio of the raw resins during dry blending was changed as shown in Table 5, the resin was melted at a resin temperature of 250°C, the resin was wrapped around a metal drum whose surface temperature was maintained at 93°C to solidify it, and a cast sheet was produced. The film was stretched in the width direction at a transverse stretching temperature of 158°C.

[0220]

[0221] Test 2: (4) Evaluation of physical properties of polypropylene film Test 2: (4-1) Measurement of thickness Measurement was performed using a paper thickness measuring instrument MEI-11 (measurement pressure 100 kPa, descending speed 3 mm / sec, measurement terminal φ=16 mm, measuring force 20.1 N) manufactured by Citizen Seimitsu Co., Ltd. in an environment of a temperature of 23±2°C and a humidity of 50±5% RH. The sample was cut from the roll with 10 or more sheets stacked, and handled so as not to wrinkle or trap air in the film when cutting. Five measurements were performed on a 10-sheet stack sample, and the thickness was calculated by dividing the average of the five measurements by 10.

[0222] Test 2: (4-2) Haze Measurement Haze was measured in accordance with JIS K 7136: 2000 using a haze meter ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.) A sample was cut out from the roll, and the size of the sample was 50 mm in the MD direction and 100 mm in the TD direction.

[0223] Test 2: (4-3) Measurement of Wet Tension The wet tension of the film surface was measured in accordance with JIS K6768:1999 under an environment of a temperature of 23±2° C. and a humidity of 50±5% RH.

[0224] Test 2: (4-4) Measurement of three-dimensional surface texture parameters The biaxially stretched polypropylene films of the examples and comparative examples were measured by the following method, and the following three-dimensional surface texture parameters were calculated in accordance with ISO 25178-2 (2007 draft): Sa: arithmetic mean deviation Sq: root-mean-square deviation Spc: arithmetic mean peak curvature The measurements were performed on both sides of the film using the following method.

[0225] As an optical interference type non-contact surface shape measuring instrument, "VertScan 2.0 (model: R5500GML)" manufactured by Ryoka Systems Co., Ltd. was used in the following configuration. Manufacturer: Ryoka Systems Co., Ltd. Device name: VertScan 2.0 (R5500GML-A150-AC) Measurement software: VS-Measure Version 5.05.0014 CCD camera: SONY HR-50 1 / 3 Objective lens: 10x Lens barrel: 1xBODY Zoom lens: No Relay Wavelength filter: 530 white Measurement mode: WAVE Field of view size: 640 x 480 pixels Measurement area: 470.92 μm x 353.16 μm The sample was placed on an electrostatic adsorption plate (150 mm x 150 mm) with a porous plate fixed thereon and measured. In addition, measurements were made at 10 points at 1 cm intervals in the flow direction from the center in both the flow direction and width direction of the target sample (polypropylene film).

[0226] Next, the obtained measurement data was subjected to the following processes in order to calculate surface texture parameters. Analysis software: VS-Viewer Version 5.05.0013 1. Completion of invalid pixels using the command "Complete (Full)" 2. Noise removal using median (3 x 3) filtering 3. Removal of waviness components using Gaussian filtering with a cutoff value of 30 μm 4. Calculation using the plug-in function "ISO parameters" (S-Filter: None) 5. The arithmetic mean value was calculated for each of the values ​​(Sa, Sq, Spc) obtained by measuring and analyzing the above 10 locations, and this value was used. Note that since negative values ​​may be obtained for Spc due to the influence of the calculation definition in the analysis software, the arithmetic mean value of the absolute values ​​obtained was used as Spc.

[0227] Test 2: (4-5) Measurement of dielectric breakdown strength The dielectric breakdown strength of the biaxially stretched film was measured in accordance with JIS C 2330:2010 6.2 b) and JIS C 2151:2006 17.2.2 (Dielectric breakdown strength, DC test, flat plate electrode method). However, the lower electrode used in the measurement was a metal flat plate (dimensions 150 mm × 150 mm, thickness 3 mm) with conductive rubber (manufactured by Seiwa Electric Co., Ltd., dimensions 100 mm × 200 mm, thickness 1 mm, model number E12S10) placed on top. This measurement was performed 44 times, and the highest and lowest six values ​​from the measurement results were discarded. The average of the remaining 32 results was divided by the film thickness to determine the dielectric breakdown strength (V ＤＣ The measurement conditions are as follows: Test piece: Approximately 150 mm x 150 mm Test piece conditioning: 30 minutes under atmospheric conditions Power source: Direct current Atmosphere: Air at 120°C Testing machine: DC withstand voltage / insulation resistance tester TOS9213AS manufactured by Kikusui Electronics Co., Ltd. Voltage rise rate: 100 V / s Current detection response speed: MID Upper limit reference value: 5 mA.

[0228] Test 2: (4-6) Measurement of ash content Approximately 200 g of a sample was weighed, transferred to a platinum dish, and incinerated for 40 minutes at 800° C. The ash content (ppm) was measured from the resulting ash residue.

[0229] Test 2: (5) Preparation of Metallized Film and Capacitor While unwinding a polypropylene film roll, an insulating margin and segmented electrode pattern were formed on the corona-treated surface using an ULVAC winding vacuum deposition device (EWE-060). Aluminum was vapor-deposited to form electrodes on the film, and zinc was vapor-deposited to form heavy edges (electrical introduction portions) on the film. This resulted in a metallized film roll with an electrode pattern, with an Al metal film resistance of 20 Ω / □ and a Zn metal film resistance of 5 Ω / □.

[0230] The electrical resistance (surface resistivity ρs) of the metal film was measured using an insulation resistance measuring instrument (Loresta GP-MCP-T610, manufactured by Mitsubishi Analytech Co., Ltd.) with a thin film measurement electrode (PSP probe MCP-TP06PRMH112) according to the following procedure: 1. A four-probe electrode, aligned in a substantially straight line, was placed in contact with the active electrode portion of the sample. 2. A constant current was passed between the two outer probes, and the potential difference generated between the two inner probes was measured to determine the film resistance value of the metal portion. 3. The sample size was not particularly limited, but because the distribution of electrical energy changes depending on the size of the sample being measured, the sample shape and size were entered into the instrument and multiplied by a resistivity correction coefficient (4.419) to obtain a numerical value.

[0231] The thickness of the metal film (effective electrode part) vapor-deposited on the polypropylene sheet is thin, at only a few tens of nanometers, making it difficult to measure. Therefore, the electrical resistance (surface resistivity ρs) of the metal film was measured and used as a substitute for the thickness.

[0232] The prepared metallized film roll was cut to a width of 30 mm using a slitter to produce small reels of metallized film for winding elements with an insulating margin width of 2.0 mm and a heavy edge width of 1.5 mm. Elements were wound onto the small reels using a fully automatic winding machine (3KAW-N2) manufactured by Kaito Seisakusho Co., Ltd., to a capacitance of approximately 50 μF, followed by pressing and flattening. Metallicon was sprayed onto the end surfaces of the flattened elements to form film electrode outlets, and the elements were then heat-treated at high temperatures in a vacuum to harden them. Leads were attached to the metallicon-sprayed portions, the elements were placed in a resin case, and the gaps were filled with epoxy resin. The resin was then cured to obtain metallized film capacitor elements for evaluation.

[0233] Test 2: (6) Characterization of Metallized Film and Capacitor Test 2: (6-1) Measurement of Capacitor Capacitance and Dielectric Dissipation Factor A four-terminal probe 9140 was attached to a Hioki E.E. Corporation LCR HiTester 3522-50. Two terminals (lead wires) of the capacitor were pinched with the four-terminal probe 9140, and a 0.1 V, 1 kHz AC voltage was applied from the built-in power supply of the LCR HiTester 3522-50. Once the displayed value had settled (e.g., approximately 30 seconds after application), the capacitance and tan δ values ​​were read. Note that measurement conditions other than those described here conformed to "4.2.2 Capacitance" and "4.2.3 Dielectric Dissipation Factor (tan δ)" of JIS C 5101-16:2009.

[0234] Test 2: (6-2) Capacitor life test (capacitance change rate and safety) A DC voltage of 750 V was continuously applied to the capacitor for 1,000 hours in a high-temperature chamber at 115°C. Based on the capacitance of the capacitor before and after the load, the capacity change rate before and after the voltage load was calculated using the following formula. The test was performed on two samples, and the average value was used for evaluation.

[0235] (Capacitance change rate)=[(capacitance after voltage load)−(initial capacitance)] / (initial capacitance)×100(%) It is preferable that the capacity change rate after 1000 hours is within −5%.

[0236] The insulation resistance was measured as follows: A shielding box SME-8350 was connected to a Hioki E.E. Corporation super insulation resistance meter DSM8104. A metallized film capacitor element was placed in the shielding box, and a DC voltage of 500 V was applied. The insulation resistance value was read after 1 minute. Measurement conditions other than those described here were in accordance with "4.2.4 Insulation Resistance" of JIS C 5101-16:2009.

[0237] In addition, when determining whether a short circuit occurred, an insulation resistance of less than 100 kΩ was determined to be a short circuit. Specifically, when the resistance was so low that it exceeded the lower measurement limit of the insulation resistance meter (when no value was displayed), it was determined to be a short circuit.

[0238] There are three main types of failure modes for capacitors, of which short circuit failures must be avoided because current continues to flow through a shorted capacitor, generating heat due to Joule heat, which can destroy the exterior and react with oxygen in the air, potentially causing a fire. 1. Open circuit failure: A failure in which the capacitance drops dramatically while the insulation resistance remains high. 2. Short circuit failure: A failure in which the insulation resistance drops dramatically. 3. Capacitance fluctuation: A failure in which the capacitor's characteristics, such as capacitance or loss, change beyond the specifications.

[0239] During the capacitor life test described above, if no short circuit failure occurred in either of the two capacitor elements tested, the safety was judged to be good, and if a short circuit failure occurred in either or both of the two capacitors, the safety was judged to be poor.

[0240] Test 2: (7) Characterization results

[0241]

Claims

1. A polypropylene film having a first side and a second side, characterized in that, in terms of surface texture parameters defined by ISO 25178, either one of the first side or the second side has an Sku value of 40 or less and / or either one of the first side or the second side has an Spc value of 16 (1 / mm) or less.

2. A polypropylene film according to claim 1, wherein, when the side having a higher wet tension as measured in accordance with JIS K6768:1999 is designated as the first side and the side having a lower wet tension is designated as the second side, the value obtained by dividing the Sku value of the second side by the Sku value of the first side is 1.0000 or less and / or the value obtained by dividing the Spc value of the second side by the Spc value of the first side is 1.0000 or less.

3. The polypropylene film according to claim 1, wherein the Sku value of either the first side or the second side is 20 or less and / or the Spc value of either the first side or the second side is 13 (1 / mm) or less.

4. The polypropylene film according to claim 1, comprising: a linear polypropylene resin B, in which the difference in molecular weight differential distribution curve between the differential distribution value at logarithmic molecular weight Log(M)=4.5 and the differential distribution value at Log(M)=6.0 is less than 8.0% and the melt flow rate at 230°C is less than 4.0 g / 10 min; and a long-chain branched polypropylene resin C polymerized using a metallocene catalyst.

5. The polypropylene film according to claim 4, further comprising a linear polypropylene resin A having a molecular weight differential distribution curve in which the difference between the differential distribution value when the logarithmic molecular weight Log(M) is 4.5 and the differential distribution value when Log(M) is 6.0 is less than 8.0%, and the melt flow rate at 230°C is 4.0 g / 10 min or more.

6. The polypropylene film according to any one of claims 1 to 5, which is a biaxially oriented polypropylene film.

7. The polypropylene film according to any one of claims 1 to 5, having a thickness of 1.4 to 6.0 µm.

8. The polypropylene film according to any one of claims 1 to 5, which is for use in a capacitor.

9. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of claims 1 to 5 and a metal layer laminated on a first surface or both surfaces of the polypropylene film.

10. A film capacitor comprising the metal layer-integrated polypropylene film according to claim 9.

11. A film roll comprising the polypropylene film according to any one of claims 1 to 5 wound into a roll.

Images