Polypropylene film, metal layer integrated polypropylene film, and capacitors

Abstract

Provided is a polypropylene film with which it is possible not only to obtain a capacitor provided with a given level of processing suitability and a given level of capacitance stability with respect to long-term use, but also to obtain a capacitor that excels in insulation resistance stability when subjected to high temperature and high voltage. This propylene film has a first surface and a second surface, and is such that the arithmetic mean height Sa of the first surface is greater than the arithmetic mean height Sa of the second surface, the peak extreme height Sxp of the first surface is 0.04-0.12 μm, and the five-point peak height S5p of the first surface is 0.5-1.2 μm.

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film and the like. [Background technology]

[0002] Polypropylene film has excellent electrical properties, such as high voltage resistance and low dielectric loss, as well as high moisture resistance. Therefore, it is widely used in electronic and electrical devices. Specifically, it is used as a film 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 supply devices that control drive motors for electric vehicles, hybrid vehicles, etc. Capacitors for inverter power supply devices used in automobiles, etc., are required to be small, lightweight, high capacity, and highly reliable over a long period of time. Patent Document 1 describes a method for manufacturing capacitors with a 0.1 mm projection. 2 Patent Document 1 discloses a biaxially oriented polypropylene film for capacitors in which the number of defects 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 though it is a thin film, and high voltage resistance even under a wide range of ambient temperature conditions from low (-40°C) to high (150°C). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 146367 Summary of the Invention [Problem to be solved by the invention]

[0005] In particular, there is a growing need for thinner films for in-vehicle capacitors (e.g., for xEVs) due to demands for miniaturization and high efficiency. However, thin polypropylene films have poor processability, such as being prone to wrinkling and misalignment during the element winding process when manufacturing capacitors.

[0006] Furthermore, the inventors have recognized that, given the growing need for long-term reliability, not only capacitance stability over long-term use but also insulation resistance stability under high-temperature and high-voltage loads is particularly important. Here, capacitance / insulation resistance stability refers to the small change in capacitance / insulation resistance from the initial values ​​when the capacitor is used. If the insulation resistance drops significantly under high-temperature and high-voltage loads, leakage current increases sharply, causing thermal runaway and ultimately leading to short circuits and fires.

[0007] Therefore, an object of the present invention is to provide a polypropylene film that not only has a certain level of processability and capacitance stability over long-term use, but also can provide a capacitor with excellent insulation resistance stability under high temperature and high voltage loads. [Means for solving the problem]

[0008] In the course of intensive research aimed at solving the above-mentioned problems, the present inventors have discovered that the extreme point height Sxp and the five-point peak region height S5p are involved in the three characteristics described above. Furthermore, as a result of further intensive research, the present inventors have found that the above-mentioned problems can be solved by a polypropylene film having a first side and a second side, in which the arithmetic mean height Sa of the first side is greater than the arithmetic mean height Sa of the second side, the extreme point height Sxp of the first side is 0.04 to 0.12 μm, and the five-point peak region height S5p of the first side is 0.5 to 1.2 μm. Based on this finding, the present inventors have conducted further research and have completed the present invention. Specifically, the present invention encompasses the following aspects.

[0009] Item 1. A polypropylene film having a first surface and a second surface, the arithmetic mean height Sa of the first surface is greater than the arithmetic mean height Sa of the second surface; The pole height Sxp of the first surface is 0.04 to 0.12 μm, and The height S5p of the five-point mountain region of the first surface is 0.5 to 1.2 μm. Polypropylene film.

[0010] Item 2. The polypropylene film according to Item 1, wherein the root mean square slope Sdq of the first surface is 0.04 to 0.19.

[0011] Item 3. The polypropylene film according to Item 1 or 2, wherein the interfacial area development ratio Sdr of the first surface is 0.02 to 0.50%.

[0012] Item 4. The polypropylene film according to any one of Items 1 to 3, wherein the first surface has an arithmetic mean height Sa of 0.008 to 0.05 μm.

[0013] Item 5. The polypropylene film according to any one of Items 1 to 4, wherein the root mean square height Sq of the first surface is 0.02 to 0.12 μm.

[0014] Item 6. The polypropylene film according to any one of Items 1 to 5, having a haze value of 2.2 to 5.0%.

[0015] Item 7. The polypropylene film according to any one of Items 1 to 6, having a thickness of 0.8 to 9.5 μm.

[0016] Item 8. The polypropylene film according to any one of Items 1 to 7, which is a biaxially stretched film.

[0017] Item 9. The polypropylene film according to any one of Items 1 to 8, which is a monolayer film.

[0018] Item 10. The polypropylene film according to any one of Items 1 to 9, which is for use in a capacitor.

[0019] Item 11. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of items 1 to 10 and a metal layer laminated on one or both sides of the polypropylene film of the present invention.

[0020] Item 12. A capacitor comprising the metal layer-integrated polypropylene film according to Item 11. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a polypropylene film that can not only provide a capacitor that has a certain level of processability and a certain level of capacitance stability over long-term use, but also can provide a capacitor that has excellent insulation resistance stability under high temperature and high voltage loads. DETAILED DESCRIPTION OF THE INVENTION

[0022] In this specification, the expressions "contain" and "comprise" include the concepts of "contain", "include", "consist essentially of" and "consist only of".

[0023] In this specification, ranges in which the upper and / or lower limits are arbitrarily interchanged between multiple ranges based on the ranges consisting of the upper and / or lower limits stated for each parameter are also exemplified.

[0024] 1. Polypropylene film In one aspect, the present invention relates to a polypropylene film having a first side and a second side, wherein the arithmetic mean height Sa of the first side is greater than the arithmetic mean height Sa of the second side, the pole height Sxp of the first side is 0.04 to 0.12 μm, and the five-point peak region height S5p of the first side is 0.5 to 1.2 μm (also referred to as the "polypropylene film of the present invention" in this specification). This will be described below.

[0025] The polypropylene film of the present invention has a first surface and a second surface, and the arithmetic mean height Sa of the first surface is greater than the arithmetic mean height Sa of the second surface.

[0026] The arithmetic mean height Sa of the first surface is not particularly limited and is preferably 0.008 to 0.05 μm, more preferably 0.01 to 0.05 μm, even more preferably 0.01 to 0.04 μm, still more preferably 0.012 to 0.04 μm, and particularly preferably 0.012 to 0.035 μm.

[0027] The arithmetic mean height Sa of the second surface is not particularly limited and is preferably 0.005 to 0.030 μm, more preferably 0.007 to 0.025 μm, even more preferably 0.008 to 0.020 μm, and still more preferably 0.009 to 0.020 μm.

[0028] The ratio of the arithmetic mean height Sa of the first surface to the arithmetic mean height Sa of the second surface (arithmetic mean height Sa of the first surface / arithmetic mean height Sa of the second surface) is not particularly limited and is preferably 1.1 to 2.5, more preferably 1.2 to 2.2, and even more preferably 1.3 to 2.0.

[0029] The pole height Sxp of the first surface is 0.04 to 0.12 μm. By satisfying this range and also satisfying the predetermined range for the five-point peak region height S5p of the first surface described below, it is possible to exhibit a constant level of processability and capacitance stability over long-term use, and further to exhibit good insulation resistance stability under high-temperature, high-voltage loads. While not intended to be a restrictive interpretation, by adjusting the specific surface roughness parameters (pole height Sxp and five-point peak region height S5p) within the predetermined range, it is possible to exhibit a constant level of processability based on the surface roughness, while adjusting the gap and its shape between the metal layer and the first surface to achieve an appropriate level of self-healing action, which is thought to result in a constant level of capacitance stability over long-term use, and good insulation resistance stability under high-temperature, high-voltage loads. In view of these characteristics, in a particularly preferred embodiment of the present invention, the polar point height Sxp of the first surface is, for example, 0.04 to 0.09 μm, preferably 0.04 to 0.07 μm, more preferably 0.04 to 0.06 μm, even more preferably 0.045 to 0.06 μm, and still more preferably 0.05 to 0.06 μm.

[0030] The polar height Sxp of the second surface is not particularly limited and is preferably 0.01 to 0.08 μm, more preferably 0.02 to 0.07 μm, and even more preferably 0.025 to 0.06 μm.

[0031] The ratio of the polar point height Sxp of the first surface to the polar point height Sxp of the second surface (ratio of polar point height Sxp of the first surface / polar point height Sxp of the second surface) is not particularly limited and is preferably 1.1 to 2.5, more preferably 1.2 to 2.3, and even more preferably 1.3 to 2.1.

[0032] The five-point peak region height S5p of the first surface is 0.5 to 1.2 μm. By satisfying this range and the above-mentioned predetermined range for the pole height Sxp of the first surface, it is possible to exhibit a certain level of processability and capacitance stability over long-term use, and further to exhibit good insulation resistance stability under high temperature and high voltage loads. The mechanism behind this is not intended to be limited, but is thought to be as explained for the pole height Sxp above. From the perspective of these properties, the five-point peak region height S5p of the first surface is preferably 0.5 to 1.0 μm, more preferably 0.5 to 0.9 μm. In a particularly preferred embodiment of the present invention, the five-point peak region height S5p of the first surface is, for example, 0.55 to 0.9 μm, preferably 0.55 to 0.85 μm, more preferably 0.55 to 0.82 μm, even more preferably 0.6 to 0.80 μm, and even more preferably 0.7 to 0.80 μm.

[0033] The height S5p of the five-point mountain region on the second surface is not particularly limited and is preferably 0.05 to 0.8 μm, more preferably 0.1 to 0.6 μm, even more preferably 0.15 to 0.5 μm, and still more preferably 0.2 to 0.5 μm.

[0034] The ratio of the height S5p of the five-point mountain region on the first surface to the height S5p of the five-point mountain region on the second surface (ratio of the height S5p of the five-point mountain region on the first surface / the height S5p of the five-point mountain region on the second surface) is not particularly limited, and is preferably 1.1 to 4.5, more preferably 1.2 to 4.2, and even more preferably 1.3 to 4.1.

[0035] The root mean square slope Sdq of the first surface is not particularly limited and is preferably 0.04 to 0.19, more preferably 0.04 to 0.18, and even more preferably 0.05 to 0.17.

[0036] The root mean square slope Sdq of the second surface is not particularly limited and is preferably 0.002 to 0.08, more preferably 0.005 to 0.07, even more preferably 0.01 to 0.06, still more preferably 0.02 to 0.06, and particularly preferably 0.03 to 0.06.

[0037] The interface area development ratio Sdr of the first surface is not particularly limited and is preferably 0.02 to 0.50%, more preferably 0.06 to 0.45%, even more preferably 0.08 to 0.40%, and still more preferably 0.08 to 0.30%.

[0038] The area development ratio Sdr of the interface of the second surface is not particularly limited and is preferably 0.002 to 0.12%, more preferably 0.003 to 0.10%, even more preferably 0.004 to 0.09%, still more preferably 0.02 to 0.09%, and particularly preferably 0.05 to 0.09%.

[0039] The root mean square height Sq of the first surface is not particularly limited and is preferably 0.02 to 0.12 μm, more preferably 0.02 to 0.10 μm, even more preferably 0.03 to 0.10 μm, still more preferably 0.03 to 0.08 μm, and particularly preferably 0.03 to 0.07 μm.

[0040] The root mean square height Sq of the second surface is not particularly limited and is preferably 0.005 to 0.06 μm, more preferably 0.01 to 0.05 μm, even more preferably 0.01 to 0.04 μm, and still more preferably 0.02 to 0.04 μm.

[0041] The arithmetic mean height Sa, pole height Sxp, five-point peak region height S5p, root-mean-square slope Sdq, interfacial area development ratio Sdr, and root-mean-square height Sq are values ​​specified in ISO 25178 and are measured as follows. A non-contact optical interference surface profiler, the VertScan 2.0 (model: R5500GML) manufactured by Ryoka Systems Co., Ltd., is used. Using WAVE mode, a 530 white filter and a 1x BODY lens barrel are applied, and a x10 objective lens is used to measure 470.92 μm x 353.16 μm per field of view. This operation is performed at 10 locations, spaced 1 cm apart from the center in both the first direction and the second direction perpendicular to the first direction, of the target sample (polypropylene film). The data was then subjected to a median filter (3x3) to remove noise, followed by a Gaussian filter with a cutoff value of 30 μm to remove waviness. This allowed for accurate measurement of the roughened surface. Analysis was then performed using the "ISO Parameter" plug-in function of the "VS-Viewer" analysis software for "VertScan 2.0," to determine Sxp, S5p, Sdq, Sdr, Sa, and Sq for each surface. Finally, the average values ​​obtained at the 10 points (Sxp, S5p, Sdq, Sdr, Sa, and Sq for the first and second surfaces, respectively) were calculated. The "pole height" Sxp was calculated as the height difference specified on the load curve when the areal load ratios p = 2.5% and q = 50%, Sxp = Sdc(p) - Sdc(q).

[0042] The polypropylene film of the present invention has a certain haze value due to the polar height Sxp and the five-point peak region height S5p being within a certain range. The haze value is not particularly limited, but is, for example, 2.2 to 5.0%, preferably 2.3 to 4.5%, more preferably 2.5 to 4.5%, even more preferably 2.5 to 4.0%, and still more preferably 2.5 to 3.5%.

[0043] The haze value is measured as follows: Using a haze meter ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.), the measurement is performed in accordance with JIS K 7136:2000. The size of the sample is 50 mm x 100 mm.

[0044] 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 of 1.0 to 6.0 μm, 1.0 to 3.0 μm, or 1.0 to 2.9 μm is particularly preferred, since despite being very thin, the polypropylene film exhibits excellent processability in the slitting process, suppression of blocking during the vapor deposition process, and element winding processability. A thickness of 9.5 μm or less allows for increased capacitance, making the film suitable for use in capacitors. From a manufacturing standpoint, the thickness can be set to 0.8 μm or more.

[0045] Film thickness is measured in accordance with JIS-C2330, except that it is measured at 100±10 kPa using a Citizen Seimitsu paper thickness measuring instrument MEI-11.

[0046] The polypropylene film of the present invention may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film, and is preferably a biaxially stretched film.

[0047] The layer structure of the polypropylene film of the present invention is not particularly limited. The film of the present invention may be a single layer consisting of one layer, or may be multiple layers having the same or different compositions. The polypropylene film of the present invention is preferably a film consisting of one or multiple film-shaped molded layers, and more preferably a monolayer film (a film consisting of one film-shaped molded layer). 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.

[0048] 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, polypropylene resins that form β-type spherulites when made into a cast sheet are suitable.

[0049] A linear polypropylene resin is preferred, and a linear homopolypropylene resin is more preferred.

[0050] The lower the total ash content of the polypropylene resin, the better for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on the polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm. The lower the total ash content, the fewer impurities such as polymerization catalyst residues there are.

[0051] In the polypropylene film of the present embodiment, the polypropylene resin may contain, for example, only the first polypropylene resin described below, or may contain the first polypropylene resin and the second polypropylene resin described below.

[0052] The polypropylene resin may contain a first polypropylene resin. When the polypropylene resin contains the first polypropylene resin, the content of the first polypropylene resin is preferably 50% by weight or more, more preferably 55% by weight or more, and even more preferably 60% by weight or more, relative to 100% by weight of the polypropylene resin. The upper limit of the content of the first polypropylene resin may be, for example, 100% by weight or less, 99% by weight or less, 98% by weight or less, or 95% by weight or less, relative to 100% by weight of the polypropylene resin. The content is preferably 90% by weight or less, more preferably 85% by weight or less, and even more preferably 80% by weight or less, relative to 100% by weight of the polypropylene resin. Thus, the polypropylene film of this embodiment may contain the first polypropylene resin as a main component. An example of the first polypropylene resin is isotactic polypropylene.

[0053] The weight-average molecular weight Mw of the first polypropylene resin is preferably 250,000 or more and less than 400,000, more preferably 260,000 or more and less than 370,000, and even more preferably 270,000 or more and less than 350,000. When Mw is 250,000 or more and less than 400,000, it is easy to satisfy the Sxp, S5p, and other various specified parameters specified in ISO 25178 regarding the surface properties of polypropylene films. Furthermore, when Mw is 250,000 or more and less than 350,000, it is easy to control the thickness of the cast raw sheet, and thickness unevenness is less likely to occur.

[0054] The number average molecular weight Mn of the first polypropylene resin is preferably 30,000 or more and 52,000 or less, more preferably 32,000 or more and 50,000 or less, and even more preferably 34,000 or more and 48,000 or less. When the number average molecular weight Mn of the first polypropylene resin is 30,000 or more and 52,000 or less, it is easy to satisfy the Sxp, S5p, and other various predetermined parameters specified in ISO 25178 regarding the surface properties of polypropylene films.

[0055] The z-average molecular weight Mz of the first polypropylene resin is preferably 600,000 or more and 1,650,000 or less, more preferably 700,000 or more and 1,600,000 or less. When the z-average molecular weight Mz of the first polypropylene resin is 600,000 or more and 1,650,000 or less, it is easy to satisfy the Sxp, S5p, and other various predetermined parameters specified in ISO 25178 regarding the surface properties of polypropylene films.

[0056] The molecular weight distribution (Mw / Mn) of the first polypropylene resin is preferably 5.0 or more, more preferably 5.5 or more. The Mw / Mn of the first polypropylene resin is preferably 11.0 or less, more preferably 10.0 or less. When the Mw / Mn of the first polypropylene resin is 5.0 or more and 11.0 or less, it is easy to satisfy the Sxp, S5p, and other various predetermined parameters specified in ISO 25178 regarding the surface properties of polypropylene films. The molecular weight distribution Mw / Mn is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn.

[0057] The molecular weight distribution (Mz / Mn) of the first polypropylene resin is preferably 10 to 60, more preferably 12 to 50, and even more preferably 15 to 45. When the molecular weight distribution (Mz / Mn) of the polypropylene resin is 10 to 60, it is easy to satisfy the Sxp, S5p, and other predetermined parameters specified in ISO 25178 regarding the surface properties of polypropylene films. The molecular weight distribution Mz / Mn is the ratio of the z-average molecular weight Mz to the number-average molecular weight Mn.

[0058] In this specification, the weight-average molecular weight (Mw), number-average molecular weight (Mn), z-average molecular weight (Mz), and molecular weight distribution (Mw / Mn and Mz / Mn) of the polypropylene resin are values ​​measured using a gel permeation chromatograph (GPC) device. More specifically, these values ​​are measured using a high-temperature GPC analyzer with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, model HLC-8121GPC-HT (trade name). Three TSKgel GMHHR-H(20)HT columns manufactured by Tosoh Corporation were connected together and used as the GPC column. The column temperature was set to 140°C, and trichlorobenzene was used as the eluent at a flow rate of 1.0 ml / 10 min to obtain measured values ​​of Mw and Mn. A calibration curve for the molecular weight M was prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to polystyrene values ​​to obtain Mw, Mn, and Mz.

[0059] The melt flow rate (MFR) of the first polypropylene resin at 230°C is preferably 8.0 g / 10 min or less, more preferably 7.0 g / 10 min or less, and even more preferably 6.0 g / 10 min or less. The melt flow rate at 230°C is preferably 3.5 g / 10 min or more. The melt flow rate at 230°C is measured in accordance with JIS K 7210-1999 under a load of 2.16 kg at 230°C. The unit of the melt flow rate, g / 10 min, is also referred to as dg / min.

[0060] The heptane insoluble content of the first polypropylene resin is preferably 97.0% or more. The heptane insoluble content is preferably 98.5% or less. The higher the heptane insoluble content, the higher the stereoregularity of the resin. When the heptane insoluble content (HI) is 97.0% or more and 98.5% or less, the moderately high stereoregularity leads to a moderate improvement in the crystallinity of the polypropylene resin in the polypropylene film, improving the voltage resistance at high temperatures. Furthermore, the solidification (crystallization) rate during cast molding into a raw sheet is moderate, resulting in moderate stretchability. The heptane insoluble content (HI) is measured according to the method described in the Examples.

[0061] The lower the total ash content of the first polypropylene resin, the better for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on the first polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm.

[0062] The polypropylene resin may further contain a second polypropylene resin. The polypropylene film of the present embodiment preferably contains a second polypropylene resin in addition to the first polypropylene resin, and more preferably the resins constituting the polypropylene film are the first polypropylene resin and the second polypropylene resin.

[0063] When the polypropylene resin contains a second polypropylene resin, the content of the second polypropylene resin is preferably 50% by weight or less, more preferably 49% by weight or less, even more preferably 45% by weight or less, and particularly preferably 40% by weight or less, relative to 100% by weight of the polypropylene resin. Furthermore, when the polypropylene resin contains a second polypropylene resin, the lower limit of the content of the second polypropylene resin can be, for example, 1% by weight or more, 2% by weight or more, or 5% by weight or more, relative to 100% by weight of the polypropylene resin. The second polypropylene resin can be, for example, isotactic polypropylene.

[0064] The Mw of the second polypropylene resin is preferably 300,000 or more, more preferably 350,000 or more. The Mw of the second polypropylene resin is preferably 450,000 or less, more preferably 400,000 or less.

[0065] The Mn of the second polypropylene resin is preferably 40,000 or more and 54,000 or less, more preferably 42,000 or more and 50,000 or less, and even more preferably 44,000 or more and 48,000 or less.

[0066] The Mz of the second polypropylene resin is preferably more than 1,550,000 and not more than 2,000,000, and more preferably 1,580,000 or more and 1,700,000 or less.

[0067] In the second polypropylene resin, the ratio of Mw to Mn (Mw / Mn) is preferably 5.5 or more, more preferably 7.0 or more, and particularly preferably 7.5 or more. The upper limit of Mw / Mn in the second polypropylene resin is, for example, 11.0, 10.0, 9.0, or 8.5. By using a second polypropylene resin having Mw / Mn and Mw satisfying the above-mentioned ranges in combination with the first polypropylene resin, it becomes easier to satisfy the Sxp, S5p, and other various predetermined parameters specified in ISO 25178 regarding the surface properties of polypropylene films.

[0068] In the second polypropylene resin, the ratio of Mz to Mn (Mz / Mn) is preferably 30 or more and 40 or less, and more preferably 33 or more and 37 or less.

[0069] The melt flow rate of the second polypropylene resin at 230°C is preferably less than 4.0 g / 10 min, more preferably 3.9 g / 10 min or less, and even more preferably 3.8 g / 10 min or less. The melt flow rate at 230°C is preferably 1.0 g / 10 min or more, more preferably 1.5 g / 10 min or more, and even more preferably 2.0 g / 10 min or more.

[0070] The heptane insoluble content of the second polypropylene resin is preferably 97.5% or more, more preferably 98.0% or more, even more preferably more than 98.5%, particularly preferably 98.6% or more, and is preferably 99.5% or less, more preferably 99.0% or less.

[0071] The lower the total ash content of the second polypropylene resin, the better for electrical properties. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and even more preferably 30 ppm or less, based on the second polypropylene resin. The lower limit of the total ash content is, for example, 2 ppm or 5 ppm.

[0072] The total amount of the first polypropylene resin and the second polypropylene resin, when the total amount of the polypropylene resin is taken as 100% by weight, can be, for example, 90% by weight or more, or 95% by weight or more, or can be 100% by weight.

[0073] The polypropylene resin can be produced by a generally known polymerization method. There are no particular limitations as long as the polypropylene resin usable in the polypropylene film of the present embodiment can be produced by the polymerization method. Examples of such polymerization methods include gas phase polymerization, bulk polymerization, and slurry polymerization.

[0074] 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.

[0075] The catalyst used in the polymerization can be any commonly known Ziegler-Natta catalyst, and is not particularly limited as long as it can produce the polypropylene resin. The catalyst may contain a co-catalyst component or a donor. By adjusting the catalyst and polymerization conditions, the molecular weight, molecular weight distribution, etc. can be controlled.

[0076] The molecular weight, molecular weight distribution, etc. of the 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) whether or not an additive is used, and the type and amount used, and (iv) the type and amount used of the catalyst.

[0077] Specifically, the molecular weight, molecular weight distribution, etc. of the polypropylene resin can be adjusted, for example, by a multi-stage polymerization reaction. Examples of the multi-stage polymerization reaction include the following methods.

[0078] First, in the first polymerization step, propylene and a catalyst are supplied to a first polymerization reactor. Hydrogen, acting as a molecular weight modifier, 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 in series, for example. 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 modifier, 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, the composition (configuration) of the high-molecular-weight and low-molecular-weight components can be adjusted.

[0079] The molecular weight, molecular weight distribution, etc. of the 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.

[0080] 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 (β-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.

[0081] 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 mass % is preferably used because it is easy to adjust the amount of low molecular weight components.

[0082] 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 should be about 1 to 30 g / 10 min from the viewpoint of convenience during adjustment.

[0083] As the polypropylene resin, commercially available products can also be used.

[0084] The polypropylene film of the present invention may contain other resins (hereinafter also referred to as "other resins"). The "other resins" are resins other than polypropylene resin, which is generally considered to be the main component resin, and are 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 of the present invention may contain an amount of other resin that does not adversely affect the desired polypropylene film. The polypropylene film of the present invention 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 the polypropylene resin. The polypropylene film of the present invention may also contain other resins in an amount of preferably 0.1 part by mass or more, more preferably 1 part by mass or more, based on 100 parts by mass of the polypropylene resin.

[0085] The polypropylene film of the present invention may further contain at least one additive in addition to the resin component. 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 contained in an amount that does not adversely affect the desired polypropylene film.

[0086] The "nucleating agent" is not particularly limited as long as it is commonly used in polypropylene and can provide the desired polypropylene film.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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 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 of the present invention 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 resin component as a whole).

[0091] "Antioxidants" are generally referred to as antioxidants and are not particularly limited as long as they are used in polypropylene to obtain the desired polypropylene film. Antioxidants are generally used for two purposes. One purpose is to suppress thermal and oxidative degradation in the extruder, and the other purpose is to contribute to suppressing degradation over long-term use as a capacitor film and improving capacitor performance. Antioxidants that suppress thermal and oxidative degradation in the extruder are also called "primary agents," while antioxidants that contribute to improving capacitor performance are called "secondary agents."

[0092] Two types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for both purposes.

[0093] An example of a primary agent is 2,6-di-tertiary-butyl-para-cresol (general name: BHT). Primary agents can usually be added to the polypropylene resin composition during preparation, as described later in the polypropylene film production 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 of the present invention 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).

[0094] The secondary agent may be a hindered phenol-based antioxidant having a carbonyl group.

[0095] 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.

[0096] 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-hydroxyhydrocinnamamide) (trade name: Irganox 1098). Of these, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred due to its high molecular weight, excellent compatibility with polypropylene, low volatility, and excellent heat resistance.

[0097] The polypropylene film of the present invention may contain one or more hindered phenol 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 of the present invention contains one or more hindered phenol antioxidants having a carbonyl group, the content thereof is preferably 2000 ppm by mass or more and 6000 ppm by mass or less, more preferably 3000 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 antioxidants having a carbonyl group in the film is 2000 ppm by mass or more and 6000 ppm by mass or less.

[0098] 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.

[0099] 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.

[0100] 2. Polypropylene film manufacturing method The polypropylene film of the present invention is preferably biaxially stretched as described above. 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 first polypropylene resin and a second polypropylene resin, or the first polypropylene resin, optionally with other resins, additives, etc., and then biaxially stretching the cast sheet.

[0101] As will be described later, the polypropylene film of the present invention can be obtained by appropriately adjusting the heat-melting temperature in the production of a cast sheet, the cooling drum temperature in the production of a cast sheet, the longitudinal stretching temperature, and other stretching conditions. Also, the polypropylene film of the present invention can be effectively obtained by appropriately setting the heat-melting temperature in the production of a cast sheet to a relatively high temperature, and the cooling drum temperature or the longitudinal stretching temperature in the production of a cast sheet to a relatively high temperature.

[0102] 2-1. 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 the first polypropylene resin and the second polypropylene resin, or polymer powder or pellets of the first polypropylene resin, are dry-blended using a mixer or the like, together with other resins, additives, etc., as necessary; and a method in which the first polypropylene resin and the second polypropylene resin, or polymer powder or pellets of the first polypropylene resin, together with other resins, additives, etc., as necessary, are supplied to a kneader and melt-kneaded to obtain a melt blend resin composition.

[0103] The mixer and kneader are not particularly limited. The kneader may be 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 kneading type may be either a co-rotating or counter-rotating type.

[0104] 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.

[0105] 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 and oxidative degradation in the extruder.

[0106] 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.

[0107] 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.

[0108] 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 3,000 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.

[0109] When the polypropylene resin composition does not contain a primary additive, a larger amount of a 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 additive but contains a hindered phenol-based antioxidant having a carbonyl group, the content thereof is 4000 ppm by mass to 8000 ppm by mass or less relative to the mass of the resin components (mass of the resin components as a whole).

[0110] 2-2.Preparation of cast sheet A cast sheet can be obtained by feeding pre-prepared pellets of a dry-blend resin composition and / or a melt-blend resin composition into an extruder, melting them, filtering them, and then melt-extruding them through a T-die at a relatively high temperature, preferably 255°C to 320°C, more preferably 260°C to 300°C, and even more preferably 265°C to 280°C. The resulting extrusion is then cooled and solidified on at least one metal drum maintained at a relatively high temperature (casting temperature), preferably 96°C to 120°C, more preferably 96°C to 110°C, and even more preferably 96°C to 100°C. The 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.

[0111] 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.

[0112] During the process of producing a cast sheet (particularly in the extruder), polypropylene undergoes considerable thermal (oxidative) and shear degradation. The progression of this degradation, i.e., changes in molecular weight distribution and stereoregularity, can be controlled by purging the extruder with nitrogen (to suppress oxidation), adjusting the screw shape (shear force) in the extruder, the internal shape of the T-die (shear force) during casting, the amount of antioxidant added (to suppress oxidation), and the winding speed (extension force) during casting.

[0113] 2-3. Stretching process 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 the sequential biaxial stretching method, the cast sheet is first maintained at a relatively high temperature, preferably 142 to 180°C, more preferably 143 to 160°C (of which 144 to 160°C), and even more preferably 144 to 150°C (of which 145 to 150°C), and stretched between rolls with a speed difference in the machine direction by preferably 3 to 7 times, more preferably 4 to 6 times, and then immediately cooled to room temperature. The stretched film is then introduced into a tenter and transversely stretched by 3 to 11 times (preferably 8 to 11 times) in the width direction at a temperature of preferably 150 to 159°C, more preferably 150 to 158°C, and even more preferably 150 to 157°C, followed by relaxation, heat setting, and winding into a roll. The polypropylene film of the present invention can be obtained more effectively by adjusting the stretching temperature in the machine direction (longitudinal stretching temperature) and the stretching temperature in the width direction (transverse stretching temperature) within the above ranges.

[0114] The longitudinal stretching speed is preferably 60,000 to 70,000% / sec, more preferably 65,000 to 70,000% / sec, and the transverse stretching speed is preferably 300 to 400% / sec, more preferably 300 to 350% / sec.

[0115] 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 then wound again.

[0116] Such a stretching process results in a film with excellent mechanical strength and rigidity.

[0117] After the stretching and heat setting steps, the polypropylene film is preferably 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 carried out using a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixture thereof as the atmospheric gas.

[0118] 3. Polypropylene film with integrated metal layer In one aspect, the present invention relates to a metal layer-integrated polypropylene film (sometimes referred to as "metal layer-integrated polypropylene film of the present invention" in this specification) having the polypropylene film of the present invention and a metal layer laminated on one or both sides of the polypropylene film of the present invention. This will be described below.

[0119] The metal layer functions as an electrode when the metal layer-integrated polypropylene film of the present invention is used as a capacitor. The metal used for the metal layer can be, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, or nickel, or a mixture or alloy of two or more of these metals. However, considering the environment, economy, and capacitor performance, zinc and aluminum are preferred.

[0120] The thickness of the metal layer is preferably 0.1 to 50 nm, more preferably 10 to 50 nm. When the thickness of the metal layer is 0.1 to 50 nm, the thickness of the metal layer-integrated polypropylene film of the present invention and the thickness of the polypropylene film of the present invention show approximately the same values ​​when measured by the method described in this example.

[0121] The layer structure of the metal layer is not particularly limited, and may be a single layer consisting of one layer, or may be a plurality of layers having the same or different compositions.

[0122] The metal layer-integrated polypropylene film of the present invention can be obtained, for example, by a method including a step of laminating a metal layer on one or both sides of the polypropylene film of the present invention.

[0123] Examples of methods for laminating a metal layer on one or both sides of the polypropylene film of the present invention include vacuum deposition and sputtering. From the viewpoints of productivity and economy, vacuum deposition is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, but the method is not particularly limited and an optimal method can be selected as appropriate.

[0124] In the vacuum deposition method, the thickness of the metal layer is controlled by the film resistance. As a deposition condition in the vacuum deposition method, the film resistance may vary depending on the constituent metal of the metal layer, but in the case of an aluminum film, for example, it is, for example, 1 to 30 Ω / sq or 10 to 25 Ω / sq.

[0125] 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 characteristics 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.

[0126] 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.

[0127] After laminating a metal layer on one or both sides of the polypropylene film of the present invention, the film may be further subjected to a post-heat treatment, for example, by applying silicone oil heated to 120 to 130°C.

[0128] 4. Capacitor In one aspect, the present invention relates to a capacitor (sometimes referred to as "the capacitor of the present invention" in this specification) comprising the metal layer-integrated polypropylene film of the present invention. This will be described below.

[0129] The capacitor of the present invention not only has a constant level of capacitance stability over long-term use, but also has excellent insulation resistance stability under high temperature and high voltage load.

[0130] For example, the capacitance change rate of the capacitor of the present invention after 1000 hours of voltage load, as measured by the life test described in the Examples, is preferably −15% or more, more preferably −12% or more, and even more preferably −10% or more. The upper limit of the capacitance change rate is not particularly limited and may be, for example, 2%, 1%, 0.5%, 0.2%, or 0%.

[0131] For example, the capacitor of the present invention has an insulation resistance value after 1 minute measured by the high voltage application test described in the Examples of preferably 20 MΩ or more, more preferably 1000 MΩ or more, even more preferably 5000 MΩ or more, and still more preferably 10000 MΩ or more. The upper limit of the insulation resistance value is not particularly limited, and is, for example, 20000 MΩ, 30000 MΩ, or 50000 MΩ.

[0132] In one embodiment of the present invention, the process of producing a capacitor involves, for example, a film winding process. For example, two pairs of metal layer-integrated polypropylene films of the present invention are overlapped and wound so that the metal layers of the metal layer-integrated polypropylene film of the present invention and the polypropylene film of the present invention are alternately stacked and the insulating margins are on opposite sides. In this case, it is preferable to stack the two pairs of metal layer-integrated polypropylene films of the present invention with a 1 to 2 mm offset. The winding machine used is not particularly limited, and for example, an automatic winding machine 3KAW-N2 manufactured by Kaito Seisakusho Co., Ltd. can be used.

[0133] When producing a flat capacitor, after winding, the resulting wound product is usually pressed. Pressing promotes tightening of the capacitor and element formation. From the viewpoint of controlling and stabilizing the interlayer gap, the optimum pressure to be applied varies depending on the thickness of the film of the present invention, but is generally 2 to 20 kg / cm. 2 is.

[0134] Next, metal is sprayed onto both end surfaces of the wound body to provide metallikon electrodes, thereby producing a capacitor.

[0135] The capacitor is further subjected to a predetermined heat treatment. That is, the present invention includes a step of subjecting the capacitor to heat treatment (hereinafter, sometimes referred to as "thermal aging"). The heat treatment temperature is not particularly limited, but is, for example, 80 to 190°C. The method for subjecting the capacitor to heat treatment may be appropriately selected from known methods, including, for example, a method using a thermostatic bath in a vacuum atmosphere or a method using high-frequency induction heating. The heat treatment time is preferably 1 hour or more, more preferably 10 hours or more, from the viewpoint of obtaining mechanical and thermal stability, but more preferably 20 hours or less, from the viewpoint of preventing molding defects such as heat wrinkles and molding.

[0136] The heat treatment provides the effect of thermal aging. Specifically, the gaps between the films constituting the capacitor based on the metal layer-integrated polypropylene film of the present invention are reduced, corona discharge is suppressed, and the internal structure of the metal layer-integrated polypropylene film of the present invention is changed, promoting crystallization. As a result, it is believed that the voltage resistance is further improved.

[0137] Lead wires are usually welded to the metallikon electrodes of the heat-aged capacitor. To impart weather resistance, particularly to prevent humidity degradation, the capacitor is preferably encapsulated in a case and potted with epoxy resin.

[0138] The capacitor of the present invention, which uses the polypropylene film of the present invention, can be suitably used in high-temperature environments and can be small and have a high capacity (for example, a capacitance of 5 μF or more, preferably 10 μF or more, more preferably 20 μF or more, even more preferably 30 μF or more, and particularly preferably 40 μF or more. There is no particular upper limit to the capacitance, and it can be, for example, 100 μF, 80 μF, 70 μF, or 60 μF). Therefore, the capacitor of the present invention can be used as a high-voltage capacitor, a filter capacitor, a smoothing capacitor, etc. for various switching power supplies, converters, inverters, etc., which are used in electronic devices and electrical equipment. The capacitor of the present invention can also be suitably used as an inverter capacitor, a converter capacitor, etc., which control the drive motor of electric vehicles and hybrid vehicles, which have seen increasing demand in recent years. [Example]

[0139] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, parts and % represent "parts by mass" and "% by mass", respectively.

[0140] (1) Preparation of polypropylene resin The polypropylene resins used to produce the biaxially oriented polypropylene films of the Examples and Comparative Examples are shown in Table 1.

[0141] Resins A and B shown in Table 1 are products manufactured by Prime Polymer Co., Ltd. Resin C is S802M manufactured by Daehan Yuhwa Corporation. Resin D is HPT-1 manufactured by Daehan Yuhwa Corporation. Resin E is HC300BF manufactured by Borealis. Resins A, B, C, D, and E are all linear homopolypropylene resins. Resin F is long-chain branched polypropylene resin MFX6 manufactured by Japan Polypropylene Corporation.

[0142] Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), molecular weight distribution (Mz / Mn), melt flow rate (MFR), and heptane insoluble content (HI) of linear homopolypropylene resins A, B, C, D, and E. These values ​​are those in the form of raw resin pellets. The measurement methods are as follows.

[0143] (1-1) Measurement of 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 linear polypropylene resin The number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin were measured using GPC (gel permeation chromatography) under the following conditions.

[0144] Specifically, a Tosoh Corporation HLC-8121GPC-HT model high-temperature GPC system with a built-in differential refractometer (RI) was used. Three Tosoh Corporation TSKgel GMHHR-H(20)HT columns were connected together. Measurements were performed at a column temperature of 140°C using trichlorobenzene as the eluent at a flow rate of 1.0 ml / min. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to polypropylene molecular weights using the Q-factor to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). The molecular weight distribution (Mw / Mn) was calculated using the Mw and Mn values. The molecular weight distribution (Mz / Mn) was also calculated using the Mz and Mn values.

[0145] (1-2) Melt flow rate (MFR) measurement The melt flow rate (MFR) of each resin in the form of raw resin pellets was measured using a Toyo Seiki melt indexer in accordance with JIS K 7210, Condition M. Specifically, a 4-g sample was inserted into a cylinder heated to a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16 kg. The sample was then extruded through the bottom hole over a 30-second period, weighed, 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. The results are shown in Table 1.

[0146] (1-3) Measurement of heptane insolubles (HI) Each resin was press-molded to a size of 10 mm x 35 mm x 0.3 mm to prepare a measurement sample weighing approximately 3 g. Approximately 150 mL of heptane was then added, and Soxhlet extraction was performed for 8 hours. The heptane-insoluble fraction was calculated from the sample mass before and after extraction. The results are shown in Table 1.

[0147] (1-4) Physical properties of polypropylene resin

[0148] [Table 1]

[0149] (2) Preparation of biaxially oriented polypropylene film Using the above resins, biaxially stretched polypropylene films of Examples and Comparative Examples were produced by the following method.

[0150] Example 1 Resin A and Resin C were dry-blended. The mixing ratio was (Resin A):(Resin C) = 75:25 by mass. The dry-blended resin was then melted at a resin temperature of 270°C, extruded using a T-die, and solidified by wrapping around a metal drum maintained at a surface temperature of 98°C. This produced a cast sheet with a thickness of 115 μm. The melt-extruded resin composition was pressed against the metal drum with an air knife to produce the cast sheet. The resulting unstretched cast sheet was maintained at a temperature of 146°C and passed between rolls with a speed differential to be stretched 5 times in the machine direction at a stretching rate of 67,300% / sec. It was then immediately cooled to room temperature. The stretched film was then introduced into a tenter and stretched 10 times in the width direction at a temperature of 155°C and a stretching rate of 335% / sec, followed by relaxation and heat setting. The film surface (the side contacting the metal drum) was then stretched at 25 W·min / m 2 After that, the film was taken up and subjected to aging treatment in an atmosphere at about 30° C. This resulted in a biaxially oriented polypropylene film with a thickness of 2.3 μm.

[0151] Example 2 A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1, except that the temperature of the metal drum was set to 97°C.

[0152] Example 3 A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1, except that the temperature of the metal drum was set to 96°C.

[0153] Example 4 A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1, except that a resin obtained by dry blending Resin B and Resin D at a mass ratio of (Resin B):(Resin D) = 65:35 was used, and the temperature of the metal drum was set to 99°C.

[0154] Example 5 A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1, except that only resin E was used instead of the dry-blended resin, the temperature of the metal drum was set to 97°C, the unstretched cast sheet was kept at a temperature of 145°C, passed between rolls with a speed difference, and stretched 5 times in the machine direction, and the thickness of the cast sheet was set to 125 μm.

[0155] Example 6 A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 4, except that the temperature of the metal drum was set to 98°C.

[0156] Example 7 A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1, except that a resin obtained by dry-blending Resin B and Resin C in a mass ratio of (Resin B):(Resin D) = 65:35 was used, the temperature of the metal drum was set to 96°C, and the unstretched cast sheet was kept at a temperature of 145°C, passed between rolls with a speed difference, and stretched 5 times in the machine direction.

[0157] (Comparative Example 1) Resin A and Resin C were dry-blended. The mixing ratio was (Resin A):(Resin C) = 75:25 by mass. The dry-blended resin was then melted at 250°C, extruded using a T-die, and solidified by wrapping around a metal drum maintained at a surface temperature of 92°C. This produced a cast sheet with a thickness of 115 μm. The melt-extruded resin composition was pressed against the metal drum with an air knife to produce the cast sheet. The resulting unstretched cast sheet was maintained at 140°C and passed between rolls with a speed differential to be stretched 5 times in the machine direction at a stretching rate of 67,300% / sec. It was then immediately cooled to room temperature. The stretched film was then introduced into a tenter and stretched 10 times in the width direction at a temperature of 155°C and a stretching rate of 335% / sec. It was then relaxed and heat-set. The film surface (the side contacting the metal drum) was then stretched at 25 W·min / m 2After that, the film was taken up and subjected to aging treatment in an atmosphere at about 30° C. This resulted in a biaxially oriented polypropylene film with a thickness of 2.3 μm.

[0158] (Comparative Example 2) A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Comparative Example 1, except that the temperature of the metal drum was set to 91°C.

[0159] (Comparative Example 3) A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Comparative Example 1, except that a resin prepared by dry-blending Resin B and Resin D in a mass ratio of (Resin B):(Resin D) = 65:35 was used, an unstretched cast sheet was passed between rolls with a speed difference and stretched 5 times in the machine direction at a stretching speed of 57,600% / sec, the stretched film was introduced into a tenter and stretched 10 times in the width direction at a temperature of 165°C at a stretching speed of 305% / sec, and the thickness of the cast sheet was 125 μm.

[0160] Comparative Example 4 A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Comparative Example 1, except that the temperature of the metal drum was set to 95°C, the unstretched cast sheet was kept at a temperature of 130°C and passed between rolls with a speed difference to be stretched 4 times in the machine direction at a stretching speed of 46000% / sec, the stretched film was introduced into a tenter and stretched 10 times in the width direction at a temperature of 160°C and a stretching speed of 300% / sec, and the thickness of the cast sheet was set to 125 μm.

[0161] (Comparative Example 5) A biaxially oriented polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Comparative Example 1, except that a resin obtained by dry-blending Resin B, Resin C, and Resin F in a mass ratio of (Resin B):(Resin C):(Resin F) = 63:34:3 was used.

[0162] (3) Measurement of physical properties of biaxially oriented polypropylene film (3-1) Thickness measurement of biaxially oriented polypropylene film The thickness of the biaxially stretched polypropylene films of the examples and comparative examples was measured. Specifically, the measurements were performed in accordance with JIS-C2330, except that the measurements were performed using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu Co., Ltd. at 100±10 kPa. The results are shown in Table 2.

[0163] (3-2) Haze measurement of biaxially oriented polypropylene film The haze (unit: %) of the biaxially stretched polypropylene films of the Examples and Comparative Examples was measured in accordance with JIS K 7136:2000 using a haze meter ("NDH-5000" manufactured by Nippon Denshoku Industries Co., Ltd.). Samples were cut from the roll, and the size of the sample was 50 mm in the MD direction and 100 mm in the TD direction. The results are shown in Table 2.

[0164] (3-3) Measurement of various surface parameters specified in ISO25178 For the biaxially stretched polypropylene films of the Examples and Comparative Examples, the "pole height" Sxp, "quincunx region height" S5p, "root mean square slope" Sdq, "interfacial area development ratio" Sdr, "arithmetic mean height" Sa, and "root mean square height" Sq, all specified in ISO 25178, were measured using the following methods. Measurements were performed on both surfaces of the film, and hereinafter the surface with the larger Sa will be referred to as "Side A (roughened surface)" and the surface with the smaller Sa will be referred to as "Side B (non-roughened surface)."

[0165] The optical interference non-contact surface profiler used was the "VertScan 2.0 (Model: R5500GML)" manufactured by Ryoka Systems Co., Ltd. Using WAVE mode, a 530 white filter and a 1x body lens barrel were applied, and a x10 objective lens was used to measure 470.92 μm x 353.16 μm per field of view. This operation was performed at 10 locations, spaced 1 cm apart in the flow direction from the center in both the flow and width directions of the sample (polypropylene film).

[0166] Next, the obtained data was subjected to noise removal processing using a median filter (3 × 3), and then subjected to Gaussian filtering processing with a cutoff value of 30 μm to remove waviness components, thereby enabling the state of the roughened surface to be properly measured.

[0167] Next, an analysis was performed using the plug-in function "ISO parameters" of the analysis software "VS-Viewer" of "VertScan2.0", and Sxp, S5p, Sdq, Sdr, Sa, and Sq were calculated for each surface. Here, the respective values ​​for surface A and surface B are, for example, Sxp A , Sxp B Finally, the values ​​obtained at the above 10 points (Sxp A , Sxp B , S5p A , S5p B , Sdq A , Sdq B , Sdr A , Sdr B , Sa A , Sa B , Sq A , Sq B The average values ​​for each of the above were calculated. The results are shown in Table 2.

[0168] The "extreme point height" Sxp was calculated as the difference in height specified at areal load ratios p=2.5% and q=50% on the load curve, Sxp=Sdc(p)-Sdc(q).

[0169] The results are shown in Table 2.

[0170] (3-4) Physical properties of biaxially oriented polypropylene film

[0171] [Table 2]

[0172] (4) Evaluation (4-1) Yield evaluation of film rolls after cutting The film was unwound from the pre-cut film rolls obtained in the Examples and Comparative Examples and then cut widthwise using a slitter. The cut polypropylene film was wound around a fiber-reinforced plastic core with an outer diameter of 176 mm, and a winding device equipped with a contact pressure roll was used to apply surface pressure to the polypropylene film. The cutting conditions were a speed of 300 m / min, unwinding force of 40 N / m, winding tension of 50 N / m, and winding surface pressure of 400 N / m. The contact pressure roll was made of rubber with an outer diameter of 152 mm and a surface hardness of 40°. A biaxially oriented polypropylene roll (cut film roll) measuring 620 mm in width and 75,000 m in length was then produced.

[0173] In the production of cut film rolls, the film was visually inspected during winding, and any wrinkles were deemed to have occurred were rejected. Regarding winding misalignment, any misalignment of 2 mm or more observed from the end face of the cut roll was deemed to have failed. For all cut rolls, the percentage of cut film rolls that passed the above criteria was calculated as the cutting yield rate α, and the following criteria were applied for evaluation. The results are shown in Table 3.

[0174] A: α=100% B: 100% > α ≥ 80% C: 80%>α.

[0175] (4-2) Capacitor performance evaluation Capacitors were fabricated using the biaxially oriented polypropylene film rolls obtained in the Examples and Comparative Examples as follows. A special deposition pattern margin and insulating margin were formed on the biaxially oriented polypropylene film using a vacuum deposition machine manufactured by ULVAC Corporation to provide film capacitor safety. Aluminum deposition was then applied to the biaxially oriented polypropylene film to achieve a surface resistivity of 20 Ω / □, yielding a metallized film. The metallized film was then slit to the desired width, and two sheets of metallized film were combined and wound using a 3KAW-N2 automatic winder manufactured by Kaito Seisakusho, at a winding speed of 4 m / sec, a winding tension of 180 g, and a contact roller pressure of 260 g, with the number of turns set to achieve a capacitance of 50 μF. The wound element was then flattened by pressing, and zinc metal was sprayed onto the element end surfaces while the press load was still applied to form electrode leads. The element was then heat-cured at 120°C for 15 hours. After thermal curing, leads were soldered to the end faces of the elements and sealed with epoxy resin to obtain flat film capacitors. The capacitance of the completed capacitors was all 50μF (±3μF). The obtained capacitors were used in the following two tests.

[0176] (4-2-1) High voltage application test for capacitors The resulting capacitor was placed in a high-temperature chamber at 105°C and subjected to a DC voltage of 1200V for 10 minutes. A shielding box SME-8350 was connected to a Hioki E.E. Super Insulation Resistance Meter DSM8104. After 10 minutes, the capacitor element was placed in the shielding box, and a DC voltage of 500V was applied. The insulation resistance value (IR10) was read after 1 minute. The test was performed on two samples, and the average insulation resistance value (IR10) was evaluated according to the following criteria. The results are shown in Table 3. Measurement conditions other than those described here conformed to "4.2.4 Insulation Resistance" of JIS C 5101-16:2009.

[0177] A:IR10≧5000MΩ B: 5000MΩ > IR10 ≥ 20MΩ C: 20MΩ>IR10.

[0178] (4-2-2) Capacitor life test (rate of change in capacitance) The initial capacitance (C0) of the resulting capacitors before testing was measured using a Hioki E.E. Corporation LCR HiTester 3522-50. Next, a DC voltage of 325 V / μm was applied to the capacitors for 1,000 hours in a constant temperature bath at 115°C. The capacitance (C1000) of the capacitors after 1,000 hours was measured in the same manner, and the rate of capacitance change (ΔC) before and after voltage application was calculated using the following formula: ΔC = (C1000 - C0) / C0. The test was performed on two samples, and the average rate of capacitance change (ΔC) was evaluated according to the following criteria. The results are shown in Table 3.

[0179] A: ΔC≧-10% B: -10%>ΔC≧-15% C:-15%>ΔC.

[0180] [Table 3]

Claims

1. A polypropylene film having a first surface and a second surface, the arithmetic mean height Sa of the first surface is greater than the arithmetic mean height Sa of the second surface; The pole height Sxp of the first surface is 0.04 to 0.12 μm, The height S5p of the five-point mountain region of the first surface is 0.5 to 1.2 μm, The thickness is 0.8 to 9.5 μm, and It is a biaxially stretched film. Polypropylene film.

2. The polypropylene film according to claim 1, wherein the root mean square slope Sdq of the first surface is 0.04 to 0.

19.

3. The polypropylene film according to claim 1 or 2, wherein the interfacial area development ratio Sdr of the first surface is 0.02 to 0.50%.

4. The polypropylene film according to any one of claims 1 to 3, wherein the first surface has an arithmetic mean height Sa of 0.008 to 0.05 µm.

5. The polypropylene film according to any one of claims 1 to 4, wherein the root mean square height Sq of the first surface is 0.02 to 0.12 µm.

6. The polypropylene film according to any one of claims 1 to 5, having a haze value of 2.2 to 5.0%.

7. The polypropylene film according to any one of claims 1 to 6, having a thickness of 1.0 to 6.0 µm.

8. The polypropylene film according to any one of claims 1 to 7, which is a monolayer film.

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

10. A metal layer-integrated polypropylene film comprising the polypropylene film according to any one of claims 1 to 9 and a metal layer laminated on one or both sides of the polypropylene film of the present invention.

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

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