Biaxially oriented polypropylene film

Abstract

To provide a polypropylene film which has (A) more advanced element processability and (B) higher yield rates for products with higher withstand voltage properties (especially withstand voltage properties at high temperatures), and / or is capable of stably forming films over a longer period of time.SOLUTION: There is provided a biaxially oriented polypropylene film, wherein (a) the maximum amplitude in the range of wave numbers 0.002 to 0.02 m-1 obtained by fast Fourier transformation of the thickness of the film in the longitudinal direction using a non-contact thickness gauge is 4.0% or less of the average thickness, and / or (b) the maximum amplitude in the range of wave numbers 0.5 to 5 m-1 obtained by fast Fourier transformation of the thickness of the film in the longitudinal direction using a non-contact thickness gauge is 3.0% or less of the average thickness.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Polypropylene films have excellent electrical properties such as high voltage resistance and low dielectric loss, and also have high moisture resistance. Therefore, they are widely used in electronic devices and electrical equipment. Specifically, they are used as films for filter capacitors and smoothing capacitors in power conversion circuits such as high-voltage capacitors, converters, and inverters.

[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 of 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.

[0004] In Patent Document 1, the protrusion is 0.1 mm 2 The 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, is disclosed. Patent Document 1 describes that the biaxially oriented polypropylene film for capacitors having the above-mentioned configuration has the following effects: it has excellent processability even though it is a thin film, and exhibits high voltage resistance under a wide range of ambient temperature conditions from low temperature (-40°C) to high temperature (150°C). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 146367 Summary of the Invention [Problem to be solved by the invention]

[0006] Polypropylene films used as resin films for capacitors in electric vehicles, hybrid vehicles, etc., are required to be thinner and have larger electrode areas due to the recent trend toward smaller capacitors and higher capacitance. In addition, there has been a strong demand for further cost reductions in recent years, and a method of high-speed stretch molding of resin sheets has been considered as a method for producing films. In element production, there is a demand for capacitor elements that are excellent in processability and have high voltage resistance (especially high voltage resistance at high temperatures) and can be manufactured with high yield.

[0007] Therefore, the present invention provides (A) has better device processability, and (B) The yield rate of films having higher voltage resistance (particularly voltage resistance at high temperatures) is higher, and / or the films can be stably formed for a longer period of time. The objective is to provide a polypropylene film. [Means for solving the problem]

[0008] In view of the above problems, the present inventors have conducted intensive research and have found that (a) a non-contact thickness gauge is used to measure the thickness in the longitudinal direction by fast Fourier transform, and the wave number is 0.002 to 0.02 m -1 and / or (b) the maximum amplitude in the range of 0.5 to 5 m wavenumber obtained by fast Fourier transform of the longitudinal thickness using a non-contact thickness gauge is 4.0% or less of the average thickness. -1 It has been found that the above-mentioned problems can be solved by a biaxially oriented polypropylene film characterized in that the maximum amplitude in the range is 3.0% or less of the average thickness. That is, the present invention includes the following aspects.

[0009] Item 1. (a) The wave number obtained by fast Fourier transform of the longitudinal thickness using a non-contact thickness gauge is 0.002 to 0.02 m. -1 The maximum amplitude of the range is 4.0% or less of the average thickness, and / or (b) Wavenumbers of 0.5 to 5 m obtained by fast Fourier transform of the longitudinal thickness using a non-contact thickness gauge -1The maximum amplitude within the range is 3.0% or less of the average thickness, A biaxially stretched polypropylene film, characterized by the above.

[0010] Item 2. The biaxially stretched polypropylene film according to Item 1, wherein the change range of the slow axis angle is in the range of 0.3° or more and 2.8° or less.

[0011] Item 3. The biaxially stretched polypropylene film according to Item 1, wherein the change range of the crystallite size obtained by Scherrer's formula from the half-width of the α-crystal (040) plane reflection peak measured by wide-angle X-ray diffraction is 8.0 Å or less.

[0012] Item 4. The polypropylene resin constituting the biaxially stretched polypropylene film has a weight average molecular weight Mw of 250,000 or more and 450,000 or less, the ratio (Mw / Mn) of the weight average molecular weight Mw to the number average molecular weight Mn is 5.0 or more and 12.0 or less, the melt flow rate at 230 °C and a load of 2.16 kg is 7.0 g / 10 min or less, and the heptane insoluble content is 96.0% or more and 99.5% or less. The biaxially stretched polypropylene film according to Item 1.

[0013] Item 5. The biaxially stretched polypropylene film according to Item 1, having a thickness of 1.7 μm or more and 6.5 μm or less.

[0014] Item 6. The biaxially stretched polypropylene film according to Item 1, which is a single-layer film.

[0015] Item 7. The biaxially stretched polypropylene film according to any one of Items 1 to 6, for use in a capacitor.

[0016] Item 8. A metal layer integrated polypropylene film including the biaxially stretched polypropylene film according to any one of Items 1 to 7 and a metal layer disposed on one or both sides of the biaxially stretched polypropylene film.

[0017] Item 9. A capacitor including the metal layer integrated polypropylene film according to Item 8.

[0018] Item 10. A method for producing a biaxially stretched polypropylene film according to any one of Items 1 to 6, comprising obtaining a cast sheet using a casting drum having a microcrack surface in which when a virtual line having a length of 0.1 mm in the widthwise direction is provided at an arbitrary position on the surface at an arbitrary position, the virtual line intersects one or more and 15 or less grooves, and the groove width is 1 μm or more and 10 μm or less, and subjecting the cast sheet to a biaxial stretching treatment.

Advantages of the Invention

[0019] According to the present invention, (A) has better device processability, and further (B) has a higher yield rate of a product having higher breakdown voltage characteristics (particularly, breakdown voltage characteristics at high temperatures), and / or can form a film stably for a longer time. A polypropylene film can be provided.

Embodiments for Carrying Out the Invention

[0020] In this specification, the expressions "containing" and "comprising" include the concepts of "containing", "comprising", "consisting essentially of", and "consisting only of".

[0021] In this specification, based on the ranges consisting of the upper limit and / or the lower limit described for each parameter, ranges in which the upper limit and / or the lower limit are arbitrarily interchanged between a plurality of ranges are also exemplified.

[0022] 1. Biaxially oriented polypropylene film In one aspect of the present invention, (a) the maximum amplitude in the range of a wave number of 0.002 to 0.02 m obtained by performing fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge is 4.0% or less of the average thickness, and / or (b) the maximum amplitude in the range of a wave number of 0.5 to 5 m obtained by performing fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge -1 is -1The maximum amplitude in the range is 3.0% or less of the average thickness, which is a characteristic of a biaxially stretched polypropylene film (which may also be referred to as "the polypropylene film of the present invention" in this specification). This will be described below.

[0023] In one aspect, the polypropylene film of the present invention has a maximum amplitude in the range of wave numbers 0.002 to 0.02 m obtained by performing a fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge (a). -1 is 4.0% or less of the average thickness (Characteristic a).

[0024] The maximum amplitude in Characteristic a is 4.0% or less when the average thickness of the biaxially stretched polypropylene film is taken as 100%. From the viewpoint of element processability and / or the viewpoint of further improving the yield rate of those with higher withstand voltage properties, this value is preferably 3.5% or less, more preferably 3.0% or less, still more preferably 2.5% or less, even more preferably 2.0% or less, particularly preferably 1.5% or less, particularly more preferably 1.2% or less, and particularly still more preferably 1.0% or less. The lower limit of this value is not particularly limited and is, for example, 0%, 0.1%, or 0.2%.

[0025] The film length wound around the capacitor element is approximately 100 m to 300 m. If the thickness variation is large at the said film length, it is considered that wrinkles and buckling will occur in the capacitor element, resulting in a reduction in processability. In addition, variations occur in the gaps between the film layers inside the element, and the higher withstand voltage properties of the present invention cannot be obtained. The said wave number range in Characteristic a corresponds to a range of 50 to 500 m in terms of the film length and includes the film length wound around the capacitor element. For this reason, by setting the maximum amplitude within the range of the present invention in the said wave number range of Characteristic a, it is possible to obtain a polypropylene film that is more excellent in element processability and has a higher yield rate of those with even higher withstand voltage properties (particularly, withstand voltage properties at high temperatures).

[0026] In one aspect, the polypropylene film of the present invention has a maximum amplitude in the wave number range of 0.5 to 5 m obtained by performing fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge (Characteristic b). -1 is 3.0% or less of the average thickness.

[0027] The maximum amplitude in Characteristic b is 3.0% or less when the average thickness of the biaxially stretched polypropylene film is taken as 100%. From the viewpoint of element processability and / or film formation stability, this value is preferably 2.5% or less, more preferably 2.0% or less, still more preferably 1.5% or less, even more preferably 1.2% or less, and particularly preferably 1.0% or less. The lower limit of this value is not particularly limited and is, for example, 0%, 0.1%, or 0.2%.

[0028] The wave number range in Characteristic b corresponds to a range of 0.2 to 2 m in terms of the film length. If the thickness variation is large, it will cause a reduction in element processability as described above. Also, if the thickness variation is large, in the film production process, the thickness variation in the width direction becomes large, leading to film breakage and the like, and the process throughput tends to decrease. Therefore, by setting the maximum amplitude within the range of the present invention in the wave number range of Characteristic b, a polypropylene film with better element processability and capable of more stably forming a film for a longer time can be obtained.

[0029] The methods for measuring and calculating the average thickness, maximum amplitude, and the ratio of the maximum amplitude to 100% of the average thickness in Characteristics a and b are as follows.

[0030] In this specification, the thicknesses of characteristics a and b are measured specifically as follows. Using an X-ray online thickness measuring device (NSW-1450X manufactured by Yamabun Electric Co., Ltd.), measurements are taken. In advance, films with thicknesses of 1.5 μm, 1.8 μm, 2.0 μm, 2.3 μm, 2.5 μm, 3.0 μm, 4.0, 6.0 μm, and 8.0 μm that have been measured in accordance with JIS-C2330 using a micrometer (JIS-B7502) are measured with the X-ray online thickness measuring device to create a calibration curve. The thickness obtained by converting the measured value of the biaxially stretched polypropylene film of the sample measured with the X-ray online thickness measuring device using the calibration curve is used as data. In an environment of room temperature 23°C and humidity 60%, the biaxially stretched polypropylene film is set on a roll-to-roll unwinding and winding device, and the measuring part of the thickness measuring machine is placed at the center of the polypropylene film and run at a speed of 30 m / min. The thickness of characteristic a is measured at intervals of 3 seconds for a length of 6144 m in the longitudinal direction of the film, and the thickness of characteristic b is measured at intervals of 0.01 seconds for a length of 20.48 m in the longitudinal direction of the film, obtaining 4096 points of thickness data each. The obtained longitudinal thickness data is subjected to fast Fourier transform using data analysis software (Origin(R)6.1J manufactured by OriginLab Corporation) with the window method as a rectangle and the spectrum as the amplitude. For the data related to characteristic a, the maximum amplitude in the range of wave numbers 0.002 to 0.02 m-1 and for the data related to characteristic b, the maximum amplitude in the range of wave numbers 0.5 to 5 m-1 are each divided by the average thickness to calculate the ratio to the average thickness.

[0031] From the viewpoint of further improving the element processability, the yield rate of those with higher breakdown voltage resistance, and / or the film formation stability, the polypropylene film of the present invention preferably has a change width of the slow axis angle in the range of 0.3° or more and 2.8° or less. The change width is more preferably 0.3° or more and 2.0° or less, still more preferably 0.3° or more and 1.5° or less, and even more preferably 0.3° or more and 1.0° or less.

[0032] The slow axis angle of the biaxially stretched polypropylene film means the acute angle formed between the width direction of the biaxially stretched polypropylene film and the slow axis. The polypropylene film of the present invention is stretched biaxially in a first direction and a second direction orthogonal thereto. Since the polymer is oriented in the plane by the biaxial stretching, the biaxially stretched film has birefringence. In the plane of the film, the direction in which the refractive index is maximum is the direction in which the speed of light propagation is slow (the phase lags), and thus it is called the slow axis.

[0033] In the sequential biaxial stretching method, first, the cast base sheet is stretched in the flow direction (MD direction), and subsequently, the sheet is stretched in the transverse direction (TD direction). In this case, in the slow axis of the biaxially stretched polypropylene film, the refractive index in the transverse direction of the second direction tends to be larger than the refractive index in the flow direction of the first direction. Here, the transverse direction of the second direction becomes the slow axis.

[0034] In the stretching in the transverse direction (TD direction), when the stretching is completely performed in the transverse direction (when the stretching is completely performed in the direction orthogonal to the flow direction), the slow axis angle defined in this specification is 0°. However, in reality, shrinkage stress, mechanical external force, the thermoplasticity of the film, etc. act during stretching, and it is impossible to completely stretch in the transverse direction (TD direction), and the slow axis angle tends to be larger than 0°.

[0035] In a portion where the change width of the slow axis angle in the longitudinal direction is large, stretching is non-uniform, so distortion is likely to occur in the film. The non-uniformity of the above stretching practically causes a decrease in the withstand voltage performance of the capacitor and tends to significantly reduce the yield. This is presumably because when the stretching in the longitudinal direction is non-uniform, the dimensional change becomes non-uniform inside the capacitor exposed to high temperature, electric field concentration occurs due to local interlayer adhesion, and the film is damaged. By controlling the change width of the slow axis angle in the longitudinal direction within the range of 0.3° or more and 2.8° or less, it is considered that the above problems in the longitudinal direction are suppressed.

[0036] The method for measuring the change range of the slow axis angle and the average slow axis angle is as follows.

[0037] From the center of the biaxially oriented polypropylene film to be measured, measurement samples of 50 mm × 50 mm are cut out at 10 positions (at positions of 0 m, 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, and 90 m) every 10 m in the longitudinal direction. Next, with the width direction of the measurement sample set as 0°, the acute angle formed between the width direction of the measurement sample and the slow axis is measured as the slow axis angle. Among the 10 measurement samples, the difference between the maximum value and the minimum value of the slow axis angle is taken as the "change range", and the average value is taken as the "average slow axis angle". The measuring device and measurement conditions are as follows.

[0038] Measuring device: Retardation measuring device RE-100 manufactured by Otsuka Electronics Co., Ltd. Light source: Laser-emitting diode (LED) Band-pass filter: 550 nm (measurement wavelength) Measurement interval: 0.1 sec Integration times: 10 times Number of measurement points: 15 points Gain: 10 dB Measurement environment: Temperature 23°C, humidity 60%.

[0039] The average slow axis angle is preferably 0° or more and 20° or less, more preferably 0° or more and 15° or less, and still more preferably 0° or more and 13° or less, from the viewpoints such as the yield rate in film production.

[0040] From the viewpoint that the processability of the element, the yield rate of those having higher withstand voltage properties, and / or the film formation stability can be further improved, the polypropylene film of the present invention has a change width of the crystallite size obtained by Scherrer's formula from the half-value width of the α-crystal (040) plane reflection peak measured by the wide-angle X-ray diffraction method of 8.0 Å or less. The change width is more preferably 7.5 Å or less, still more preferably 7.0 Å or less, even more preferably 6.5 Å or less, particularly preferably 6.0 Å or less, particularly more preferably 5.5 Å or less, and particularly still more preferably 5.0 Å or less.

[0041] The smaller the change in the crystallite size, the more uniform the crystal structure inside the film is considered to be, and it becomes difficult for structural destruction due to Joule heat generation caused by local leakage current to occur. Thereby, it is considered that the heat resistance, the withstand voltage property, and the heat resistance and withstand voltage property over a long period are preferably improved.

[0042] The method for measuring the change width of the crystallite size and the crystallite size is as follows.

[0043] Measurement samples are cut out at a total of 10 locations (positions of 0 m, 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, and 90 m) at intervals of 10 m in the longitudinal direction from the center of each biaxially stretched polypropylene film to be measured. The measurement sample is measured by the following method.

[0044] To measure the diffraction reflection peak of the α-crystal (040) plane, a Rigaku D / MAX X-ray diffractometer MiniFlex300 (trade name) is used. Using X-rays generated at an output of 30 kV and 10 mA, the CuKα ray (wavelength 0.15418 nm) monochromatized by a receiving monochromator is collimated with a slit and irradiated onto the measurement film. The diffraction intensity is measured by performing 2θ / θ linked scanning using a scintillation counter and a goniometer. Using the integrated powder X-ray analysis software PDXL that comes standard with the device, the obtained data is utilized to determine the half-value width of the diffraction reflection peak of the α-crystal (040) plane. From the θ and half-value width of the obtained diffraction reflection peak by the above measurement, the crystallite size is determined using the aforementioned Scherrer's formula. Note that the shape factor constant K is 0.94 and λ is 0.15418 nm.

[0045] Of the 10 measurement samples, the difference between the maximum and minimum values of the crystallite size is determined as the "variation width".

[0046] From the viewpoint of further improving the element processability, the yield rate of those with higher breakdown voltage, and / or the film formation stability, the polypropylene film of the present invention has a DC voltage of 600 V per 1 μm of thickness applied using an insulation defect inspection device having a unwind-windup mechanism at 10 m 2 The number of insulation defects per meter is preferably 1.0 or less. More preferably, the number is 0 defects / 10 m 2 or more and 0.5 defects / 10 m 2 or less, more preferably 0 defects / 10 m 2 or more and 0.1 defects / 10 m 2 or less, particularly preferably 0 defects / 10 m 2 Although not wishing to be limited to this interpretation, a capacitor manufactured using such a film is less likely to have film breakage due to short circuit failure even when used for a long time in a high temperature environment, and high reliability can be obtained.

[0047] The method for measuring the number of insulation defects is as follows.

[0048] Using an insulation defect inspection device with a pay-off and take-up mechanism, measure the number of insulation defects (number / 10 m) of a biaxially stretched polypropylene film to be measured. 2 ) Run the polypropylene film to be measured through between a high-voltage electrode and a grounded metal roller, apply a DC voltage at that time, and measure the number of discharges occurring at the insulation defect part with a counter attached to the device. Divide the measured number by the measurement area to calculate the number of insulation defects (number / 10 m) of the film. The measurement conditions are as follows. 2 ) · Distance between the high-voltage electrode and the grounded metal roller: 50 μm · Wrapping angle where the film contacts the grounded metal roller: 120° · Shape of the high-voltage electrode: A metal plate with a thickness of 4 mm and the same width as the metal roller · Pay-off speed: 20 m / min · DC voltage: 600 V / μm · Measurement area: 472 m 2 · Test environment temperature: 20°C.

[0049] From the viewpoint of further improving the miniaturization and high capacitance of the capacitor when used in the capacitor, the upper limit of the thickness of the polypropylene film of the present invention is preferably 6.5 μm or less, more preferably 5.5 μm or less, still more preferably 3.5 μm or less, particularly preferably 3.0 μm or less, and most preferably 2.8 μm or less. Also, from the viewpoint of manufacturing, the lower limit is preferably 0.8 μm or more, more preferably 1.0 μm or more, still more preferably 1.7 μm or more, and particularly preferably 2.0 μm or more. Also, setting the thickness within the above range is also preferable from the viewpoints of element processability, yield rate of products with higher breakdown voltage resistance, film formation stability, etc. The method for measuring the thickness of the biaxially stretched polypropylene film in this specification is by the method described in the examples.

[0050] The layer structure of the polypropylene film of the present invention is not particularly limited. The polypropylene film of the present invention may be a single layer consisting of one layer, or may be a plurality of layers having the same or different compositions. The polypropylene film of the present invention is preferably a film composed of one or more film-shaped molding layers, and more preferably a single-layer film (a film composed of one film-shaped molding layer).

[0051] As long as the polypropylene film of the present invention contains a polypropylene resin, its constituent materials are not particularly limited. The polypropylene resin is not particularly limited, and examples thereof include propylene homopolymers such as isotactic polypropylene, copolymers of propylene and ethylene, long-chain branched polypropylene, ultra-high molecular weight polypropylene, and the like. Among these, isotactic polypropylene is preferably mentioned from the viewpoint of heat resistance.

[0052] The content of the polypropylene resin is preferably 90% by mass or more, more preferably 95% by mass or more, based on the entire polypropylene film of the present invention (when the entire polypropylene film is 100% by mass). The upper limit of the content of the polypropylene resin is, for example, 100% by mass, 98% by mass, etc., based on the entire polypropylene film of the present invention.

[0053] The polypropylene resin may be a single type alone, or may be a combination of two or more types.

[0054] Here, when there are two or more polypropylene resins contained in the polypropylene film of the present invention, the polypropylene resin with the higher content is referred to as the "main component polypropylene resin" in this specification. When there is one type of polypropylene resin contained in the polypropylene film of the present invention, the polypropylene resin is referred to as the "main component polypropylene resin" in this specification.

[0055] Hereinafter, in this specification, when "polypropylene resin" is mentioned without specifically stating whether it is the main component or not, unless otherwise specified, it means both the polypropylene resin as the main component and the polypropylene resin other than the main component. For example, when it is described that "the weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less", it means both that the weight average molecular weight Mw of the polypropylene resin as the main component is preferably 250,000 or more and 450,000 or less, and that the weight average molecular weight Mw of the polypropylene resin other than the main component is preferably 250,000 or more and 450,000 or less.

[0056] The weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less, more preferably 250,000 or more and 420,000 or less, still more preferably 250,000 or more and 400,000 or less, and even more preferably 260,000 or more and 390,000 or less, from the viewpoints of the thickness uniformity, mechanical properties, thermo-mechanical properties, etc. of the biaxially oriented polypropylene film. By using such a polypropylene resin, dielectric breakdown of the film is suppressed, and it becomes easy to obtain an extremely thin biaxially oriented polypropylene film suitable for a small and high-capacity capacitor. When two or more kinds of polypropylene resins are used, it is preferable to use in combination a polypropylene resin (preferably the polypropylene resin as the main component) having the above Mw of less than 250,000 and less than 330,000 (preferably 250,000 or more and 300,000 or less, more preferably 260,000 or more and 290,000 or less) and a polypropylene resin (preferably the polypropylene resin other than the main component) having the above Mw of 330,000 or more and 450,000 or less (preferably 350,000 or more and 420,000 or less, more preferably 370,000 or more and 400,000 or less, still more preferably 370,000 or more and 390,000 or less).

[0057] The ratio (Mw / Mn) of the weight-average molecular weight Mw to the number-average molecular weight Mn of the polypropylene resin is preferably 5.0 or more and 12.0 or less, more preferably 5.0 or more and 10.0 or less, and even more preferably 5.0 or more and 9.0 or less, from the viewpoint of obtaining appropriate resin fluidity during biaxial stretching and facilitating the production of an extremely thin biaxially stretched propylene film with no thickness unevenness. When using two or more polypropylene resins, it is preferable to use in combination a polypropylene resin (preferably the main component polypropylene resin) having a ratio of 5.0 or more and less than 7.0 (preferably 5.0 or more and 6.5 or less) and a polypropylene resin (preferably a polypropylene resin other than the main component) having a ratio of 7.0 or more and 12.0 or less (preferably 7.5 or more and 10.0 or less, more preferably 7.5 or more and 9.0 or less).

[0058] The measurement methods for the weight-average molecular weight Mw and the number-average molecular weight Mn of the polypropylene resin are those described in the examples.

[0059] The melt flow rate (MFR) of the polypropylene resin at 230 °C and a load of 2.16 kg is not particularly limited, but is preferably 7.0 g / 10 min or less from the viewpoint of stretchability and the like, and more preferably 0.5 g / 10 min or more and 6.0 g / 10 min or less from the viewpoint of improving the thickness accuracy of the polypropylene film of the present invention. When using two or more polypropylene resins, it is preferable to use in combination a polypropylene resin (preferably the main component polypropylene resin) having an MFR of 4.0 g / 10 min or more and less than 7.0 g / 10 min (preferably 4.5 g / 10 min or more and 6.5 g / 10 min or less, more preferably 5.0 g / 10 min or more and 6.0 g / 10 min or less) and a polypropylene resin (preferably a polypropylene resin other than the main component) having an MFR of 0.5 g / 10 min or more and less than 4.0 g / 10 min (preferably 1.0 g / 10 min or more and 3.5 g / 10 min or less, more preferably 1.5 g / 10 min or more and 3.0 g / 10 min or less). The measurement method for the melt flow rate of the polypropylene resin is the method described in the examples.

[0060] The heptane-insoluble content (HI) of the polypropylene resin is preferably 96.0% or more and 99.5% or less, more preferably 97.0% or more and 99.0% or less. Here, the higher the heptane-insoluble content, the higher the stereoregularity of the resin. By using such a polypropylene resin, the crystallinity is moderately improved, and the initial breakdown voltage resistance and the long-term breakdown voltage resistance are improved. The measurement method of the heptane-insoluble content (HI) is based on the method described in the examples.

[0061] The content of the polypropylene resin as the main component is preferably more than 50% by mass and 100% by mass or less, more preferably 55% by mass or more and 85% by mass or less, still more preferably 60% by mass or more and 75% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less, based on 100% by mass of the polypropylene resin.

[0062] The polypropylene resin can be produced using generally known polymerization methods. Examples of the polymerization method include gas-phase polymerization, bulk polymerization, and slurry polymerization.

[0063] The polymerization may be single-stage (one-stage) polymerization using one polymerization reactor, or multi-stage polymerization using two or more polymerization reactors. Also, the polymerization may be carried out by adding hydrogen or a comonomer as a molecular weight regulator into the reactor.

[0064] As the catalyst for polymerization, generally known Ziegler-Natta catalysts can be used, and it is not particularly limited as long as the polypropylene resin can be obtained. The catalyst may contain a cocatalyst component or a donor. By adjusting the catalyst and polymerization conditions, the molecular weight, molecular weight distribution, stereoregularity, etc. can be controlled.

[0065] The molecular weight distribution and the like of the polypropylene resin can be adjusted by resin mixing (blending). For example, a method of mixing two or more resins having different molecular weights and molecular weight distributions can be mentioned. Generally, a two-component polypropylene blend system in which a resin having a higher average molecular weight or a lower average molecular weight than the main resin is added to the main resin, and the main resin is 55% by mass or more and 90% by mass or less based on 100% by mass of the total resin, is preferable because it is easy to adjust the amount of low molecular weight components.

[0066] In addition, when adopting the above mixing and adjusting method, the melt flow rate (MFR) may be used as a measure of the average molecular weight. In this case, from the viewpoint of convenience during adjustment, the difference in MFR between the main resin and the additive resin is preferably about 1 to 30 g / 10 min.

[0067] The method of resin mixing is not particularly limited, but examples include a method of dry blending the polymerization powder or pellets of the main resin and the additive resin using a mixer or the like, and a method of supplying the polymerization powder or pellets of the main resin and the additive resin to a kneader and melt-kneading them to obtain a blended resin.

[0068] The mixer and the kneader are not particularly limited. The kneader may be of a single-screw type, a twin-screw type, or a multi-screw type with more than two screws. In the case of a twin-screw or multi-screw type, either a co-rotating or counter-rotating kneading type may be used.

[0069] In the case of blending by melt-kneading, the kneading temperature is not particularly limited as long as a good kneaded product can be obtained. Generally, it is in the range of 200°C to 300°C, and from the viewpoint of suppressing resin degradation, 230°C to 270°C is preferable. Also, in order to suppress degradation during the kneading and mixing of the resin, an inert gas such as nitrogen may be purged into the kneader. The melt-kneaded resin may generally be pelletized to an appropriate size using a known pelletizer. Thereby, a mixed polypropylene raw material resin pellet can be obtained.

[0070] By using the above-described polypropylene resin, it becomes easier to adjust the above-described film properties, and it is preferable from the viewpoints of element processability, yield rate of products with higher withstand voltage, film-forming stability, and the like.

[0071] The polypropylene film of the present invention may contain an additive. The "additive" is not particularly limited as long as it is generally an additive used in polypropylene resin.

[0072] Examples of the additive include an antioxidant, a light stabilizer, an ultraviolet absorber, a plasticizer, a lubricant, a crosslinking agent, a flame retardant, an antistatic agent, a heat resistance improver, a blocking inhibitor, inorganic particles, resin particles, and the like. The polypropylene resin may contain the additive in an amount that does not adversely affect the polypropylene film of the present invention (for example, 10% by mass or less, 5% by mass or less, 1% by mass or less, or 0.1% by mass or less based on 100% by mass of the polypropylene film of the present invention).

[0073] 2. Method for producing biaxially oriented polypropylene film The biaxially stretched polypropylene film can be produced by obtaining a cast sheet, which is a precursor for stretching, from resin pellets and then subjecting the cast sheet to a biaxial stretching treatment. As is clear from the results of the examples described below, by controlling the die lip opening, microcracks on the surface of the casting drum, the blowing air velocity of the air knife, the distance between the blowing outlet of the air knife and the cast sheet, the stretching nip roll temperature, the stretching nip roll hardness, etc., specifically, by manufacturing according to the following method, the biaxially stretched polypropylene film of the present invention can be obtained.

[0074] Among the above manufacturing conditions, the microcracks on the surface of the casting drum are important conditions. From this perspective, in one aspect of the present invention, when a virtual line with a length of 0.1 mm in the width direction is provided at an arbitrary position on the surface, the virtual line intersects with one or more and 15 or fewer grooves, and the groove width is 1 μm or more and 10 μm or less, and a cast sheet is obtained using a casting drum having a microcrack surface, and the cast sheet is biaxially stretched. The present invention relates to a method for manufacturing a biaxially stretched polypropylene film, which includes the above steps.

[0075] Hereinafter, the method for manufacturing the biaxially stretched polypropylene film of the present invention will be described in detail.

[0076] 2-1. Production of cast sheet The cast sheet can be formed using a known method. For example, polypropylene resin pellets, dry-mixed polypropylene resin pellets, or pre-melt-kneaded mixed polypropylene resin pellets are supplied to an extruder, heated and melted, foreign substances and modified polymers are removed through a filter, and then extruded in a sheet shape from a T-die and cooled and solidified with at least one metal drum (casting drum) to form a cast sheet.

[0077] In the extruder, the polypropylene resin is inevitably modified due to thermal degradation and oxidative degradation. From the perspective of suppressing such polymer modification, the resin temperature during melt extrusion is 170°C or higher and 320°C or lower, preferably 200°C or higher and 300°C or lower. In addition, it is possible to suppress degradation by nitrogen substitution in the extruder, screw shape, internal shape of the T-die during casting, addition amount of antioxidant, and the like.

[0078] The die lip opening of the T-die is preferably 0.3 mm or more and 0.6 mm or less. When the die lip opening within such a range is adopted, the speed of the resin discharged in a sheet form from the T-die increases, so it becomes difficult to be affected by the flow of surrounding air and air pressure, and the dimensions of the resin sheet are likely to be stable. As a result, the above-described film characteristics can be easily obtained.

[0079] The temperature of the casting drum is preferably 80°C or more and 140°C or less, and more preferably maintained at 90°C or more and 105°C or less. The β-crystal fraction of the cast sheet obtained within such a temperature range is about 5% or more and 20% or less by the X-ray method. Within the range of the β-crystal fraction, the roughness of the film surface is moderately improved, and both the capacitor characteristics and the element winding processability can be satisfied.

[0080] The surface of the casting drum is not particularly limited, but in terms of easily obtaining the desired physical properties of the present invention, a roll having an uneven surface such as a sandblasted roll or a ceramic roll, or a microcrack roll having a discharge path for the entrained air is preferred. The manufacturing methods of these rolls are known. For example, for the microcrack roll, it can be manufactured according to or in accordance with the method described in, for example, Japanese Patent No. 6974939. The microcracks are caused by the stress of the metal plating layer, and the shape and number can be controlled by the thickness of the metal plating layer, plating conditions, heat treatment, chemical treatment, multilayer formation, etc. For example, in the case of chrome plating, the plating thickness is preferably 100 μm to 400 μm, more preferably 120 μm to 350 μm, and still more preferably 150 μm to 300 μm. By setting it within this range, the control of the shape and number of the grooves becomes easier, and when the roll is heated, cracking is less likely to occur.

[0081] Regarding the microcrack roll, when a virtual line with a length of 0.1 mm in the width direction is provided at any position on the roll surface, it is preferable that the virtual line intersects with one or more and 15 or fewer grooves, more preferably two or more and 10 or fewer grooves, and even more preferably three or more and 8 or fewer grooves. Also, the groove width is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 9 μm or less, and even more preferably 3 μm or more and 8 μm or less. By using those within the range of the number of grooves and the groove width, the air that intrudes between the casting drum and the cast sheet is appropriately discharged, and even for a thinned cast sheet, close conveyance becomes easy, and it becomes easy to obtain an extremely thin biaxially stretched polypropylene film. Further, even when the forming speed of the thinned cast sheet is increased, a phenomenon in which the cast sheet thickness undulates, so-called draw resonance (surge) phenomenon, is less likely to occur, and an extremely thin biaxially stretched polypropylene film having a uniform thickness in the longitudinal direction can be easily obtained.

[0082] As a method of adhering to the casting drum, any method such as an air knife method, a touch roll method, an electrostatic printing method, a water-cooled casting method, etc. may be used, but the air knife method, which is easy to adjust regarding sheet adhesion and can be simply handled, is preferable.

[0083] When using an air knife, the wind speed of the blown air is preferably 70 m / s or more and 130 m / s or less, more preferably 80 m / s or more and 120 m / s or less, and even more preferably 90 m / s or more and 110 m / s or less. Also, the distance between the air outlet of the air knife and the cast sheet is preferably 2 mm or more and 5 mm or less, more preferably 2 mm or more and 4 mm or less. Using the air knife within such a range can appropriately adhere the thinned resin extruded in a sheet shape from the T-die to the casting drum, and can suppress the film vibration of the molten resin from the T-die outlet until it adheres to the casting drum. As a result, the above-described film characteristics can be easily obtained.

[0084] 2-2. Biaxial stretching treatment The biaxially oriented polypropylene film of the present invention is obtained by performing biaxial stretching in which the above-mentioned cast sheet is oriented biaxially in the longitudinal and transverse directions. Examples of the stretching method include simultaneous or sequential biaxial stretching methods. From the viewpoint of stably uniformizing the thickness and enhancing the mechanical strength of the film, the sequential biaxial stretching method is preferred.

[0085] As the sequential biaxial stretching method, first, the cast sheet is preheated through a conveying roll maintained at 70°C or higher and 135°C or lower, preferably 80°C or higher and 130°C or lower. Subsequently, it is preferably heated to 130°C or higher and 155°C or lower, preferably 140°C or higher and 150°C or lower, immediately before stretching in the longitudinal direction. By heating the cast sheet in this manner, excessive thermal expansion of the cast sheet is suppressed, the planarity of the sheet is easily maintained before stretching in the longitudinal direction described later, and the sheet is easily adhered to the conveying roll uniformly.

[0086] From the viewpoint of easily obtaining the biaxially oriented polypropylene film of the present invention, immediately before stretching in the longitudinal direction, a method of simultaneously heating both the front and back surfaces of the cast sheet is preferred. The method is not particularly limited, but from the viewpoint of suppressing the difference in the thermal history within the plane of the cast sheet, a method of heating the stretching nip roll or a method of heating with electromagnetic radiation is preferred. From the viewpoint of being able to simultaneously fix the cast sheet immediately before stretching and adjust the temperature of the sheet, the method of heating the stretching nip roll is more preferred.

[0087] When heating the stretching nip roll, from the viewpoint of suppressing the difference in the thermal history between the front and back surfaces of the cast sheet, the temperature of the stretching nip roll is preferably 95°C or higher and 170°C or lower, more preferably 100°C or higher and 150°C or lower.

[0088] When heating the stretching nip roll, the rubber hardness of the roll is preferably 40° or higher and 80° or lower, more preferably 50° or higher and 70° or lower, so that the shape of the roll surface follows the shape of the surface of the cast sheet.

[0089] Thereafter, it is stretched 3 to 7 times, preferably 4 to 6 times in the longitudinal direction, and immediately cooled to room temperature.

[0090] After stretching in the longitudinal direction, the stretched film is led to a tenter, both ends are gripped with clips heated to 80°C or higher and 140°C or lower, and after preheating at a temperature of 140°C or higher and 185°C or lower, preferably 150°C or higher and 175°C or lower, it is stretched 6 to 12 times, preferably 8 to 11 times in the width direction at a temperature of 140°C or higher and 170°C or lower, preferably 150°C or higher and 160°C or lower.

[0091] Thereafter, relaxation and heat setting are performed and it is wound up. The wound film can be cut to a desired product width after being subjected to an aging treatment in an atmosphere of 20°C or higher and 45°C or lower.

[0092] 3. Polypropylene film integrated with metal layer In one aspect of the present invention, there is also provided a metal layer integrated polypropylene film (which may also be referred to as "the metal layer integrated polypropylene film of the present invention" in this specification) including the biaxially stretched polypropylene film of the present invention and a metal layer disposed on one or both sides of the biaxially stretched polypropylene film. Hereinafter, the metal layer integrated polypropylene film of the present invention will be described in detail. A capacitor obtained by winding the metal layer integrated polypropylene film of the present invention is excellent in initial withstand voltage characteristics and long-term durability under high temperature and high voltage.

[0093] The polypropylene film of the present invention can be provided with electrodes on one or both sides for processing into a capacitor. Such electrodes are not particularly limited as long as the capacitor targeted by the present embodiment can be obtained, and electrodes usually used for manufacturing a capacitor can be used. Examples of the electrodes include metal foils, papers metallized on at least one side, and plastic films.

[0094] Since there is an increasing demand for smaller and lighter capacitors, it is preferable to form electrodes by directly metallizing one or both sides of the polypropylene film of the present invention. As the metal to be used, for example, simple metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of multiple types thereof, and alloys thereof can be used. However, considering the environment, economy, and capacitor performance, zinc and aluminum are preferable.

[0095] As methods for directly metallizing the surface of the polypropylene film, for example, vacuum evaporation method and sputtering method can be exemplified, and it is not particularly limited as long as the capacitor targeted by the present embodiment can be obtained. From the viewpoints of productivity and economy, the vacuum evaporation method is preferable. As the vacuum evaporation method, generally, the crucible method, the wire method, etc. can be exemplified, but it is not particularly limited as long as the capacitor targeted by the present embodiment can be obtained, and an appropriate optimal one can be selected as appropriate.

[0096] From the viewpoint of the electrical characteristics of the capacitor, the film resistance of the metal vapor deposition film is preferably 1 Ω / sq or more and 100 Ω / sq or less. Even within this range, it is desirable to be higher from the viewpoint of self-healing characteristics. Further, from the viewpoint of safety, the film resistance is more preferably 5 Ω / sq or more and 50 Ω / sq or less, and even more preferably 10 Ω / sq or more and 30 Ω / sq or less. The film resistance of the metal vapor deposition film can be measured during metal vapor deposition by, for example, the four-terminal method known to those skilled in the art. The film resistance of the metal vapor deposition film can be adjusted, for example, by adjusting the output of the evaporation source to adjust the evaporation amount.

[0097] When forming a metal vapor deposition film on one side of a film, an insulating margin is formed by not vapor-depositing a certain width from one end of the film so that a capacitor is formed when the film is wound. Further, in order to strengthen the bonding between the metal layer integrated polypropylene film of the present invention and the metallicon electrode, it is preferable to form a heavy edge structure at the end opposite to the insulating margin. The film resistance of the heavy edge is usually 1 Ω / sq or more and 8 Ω / sq or less, and preferably 1 Ω / sq or more and 5 Ω / sq or less. The thickness of the metal film is not particularly limited, but is preferably 1 nm or more and 200 nm or less.

[0098] There is no particular limitation on the margin pattern of the metal vapor deposition film to be formed. However, from the viewpoint of improving characteristics such as the safety of the capacitor, it is preferable to use a pattern including a so-called special margin such as a fishnet pattern or a T margin pattern. When the metal vapor deposition film is formed on one side of the polypropylene film with a pattern including a special margin, the safety of the obtained capacitor is improved, which is effective in terms of suppressing the destruction and short circuit of the capacitor, and is preferable.

[0099] As a method for forming the margin, known methods such as a tape method in which masking is performed with a tape during vapor deposition and an oil method in which masking is performed by applying oil can be used without any limitation.

[0100] The metal layer integrated polypropylene film of the present invention can be processed into the capacitor of the present invention described below through a winding process of winding along the long direction of the film. That is, two metal layer integrated polypropylene films of the present invention are used as a pair, and they are overlapped and wound so that the metal layer and the polypropylene film are alternately laminated. Then, a capacitor is obtained through a process of forming a pair of metallicon electrodes by metal spraying on both end faces to produce a film capacitor.

[0101] 4. Capacitor In one aspect of the present invention, a capacitor including the metal layer integrated polypropylene film of the present invention is provided (in this specification, it may also be referred to as "the capacitor of the present invention"). Hereinafter, the capacitor of the present invention will be described in detail.

[0102] In the process of manufacturing a capacitor, winding processing of the film is performed. For example, two pairs of the metal layer integrated polypropylene films of the present invention are overlapped and wound so that the metal layer and the polypropylene film in the metal layer integrated polypropylene film of the present invention are alternately laminated, and further, the insulating margin portion is on the reverse side. At this time, it is preferable to laminate the two pairs of the metal layer integrated polypropylene films of the present invention with a shift of 1 to 2 mm. The winding machine to be used is not particularly limited. For example, an automatic winder 3KAW-N2 type manufactured by Kaito Seisakusho Co., Ltd. can be used.

[0103] When manufacturing a flat capacitor, after winding, usually, pressing is performed on the obtained wound product. Pressing promotes winding and element forming of the capacitor. From the viewpoint of controlling and stabilizing the interlayer gap, the pressure to be applied varies depending on the thickness of the polypropylene film and the like, but is, for example, 2 to 20 kg / cm2.

[0104] Subsequently, a capacitor is manufactured by spraying metal on both end faces of the wound product to provide a metallized electrode. A predetermined heat treatment is further performed on the capacitor. That is, in the present embodiment, it includes a step of performing heat treatment on the capacitor under vacuum at a temperature of 80 to 125 ° C for 1 hour or more (hereinafter, may be referred to as "thermal aging").

[0105] In the above step of performing heat treatment on the capacitor, the temperature of the heat treatment is 80°C or higher and 130°C or lower, preferably 90°C or higher and 125°C or lower. By performing heat treatment at the above temperature, the effect of thermal aging can be obtained. Specifically, the voids 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 moreover, the internal structure of the metal layer integrated polypropylene film of the present invention changes and crystallization progresses. As a result, it is considered that the withstand voltage property is improved. When the temperature of the heat treatment is lower than the predetermined temperature, the above effects due to thermal aging cannot be sufficiently obtained. On the other hand, when the temperature of the heat treatment is higher than the predetermined temperature, thermal decomposition, oxidative degradation, etc. may occur in the polypropylene film.

[0106] As a method of performing heat treatment on the capacitor, for example, a known method including a method using a constant temperature bath or a method using high-frequency induction heating in a vacuum atmosphere may be appropriately selected. Specifically, it is preferable to adopt a method using a constant temperature bath.

[0107] The time for performing heat treatment is preferably 1 hour or longer, more preferably 10 hours or longer, from the viewpoint of obtaining mechanical and thermal stability, but more preferably 20 hours or shorter from the viewpoint of preventing molding defects such as heat wrinkles and shaping. Usually, a lead wire is welded to the metallicon electrode of the capacitor subjected to thermal aging. Further, in order to impart weather resistance and particularly prevent humidity degradation, it is preferable to enclose the capacitor in a case and potting it with an epoxy resin. The capacitor of the present invention is a small and large-capacity capacitor based on the metal layer integrated polypropylene film of the present invention, and has an initial withstand voltage property and long-term durability under high temperature and high voltage.

[0108] The capacitor of the present invention using the polypropylene film of the present invention is preferably used in a high-temperature environment, and can be made into a small-sized and high-capacity capacitor (for example, the capacitance is 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. The upper limit of the capacitance is not particularly limited, and is, 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 and a smoothing capacitor for various switching power supplies, converters and inverters, etc., which are used in electronic devices, electrical devices, etc. Further, the capacitor of the present invention can also be preferably used as a capacitor for an inverter, a capacitor for a converter, etc., which control drive motors of electric vehicles and hybrid vehicles, etc., the demand for which has been increasing in recent years.

Examples

[0109] The present invention will be described in detail below based on examples, but the present invention is not limited by these examples.

[0110] (1) Measurement of resin properties (1-1) Measurement of weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of polypropylene resin Using GPC (gel permeation chromatography), the weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the polypropylene resin used as a raw material in the examples and comparative examples were measured under the following conditions.

[0111] Specifically, an HLC-8121GPC-HT type, a differential refractometer (RI)-equipped high-temperature GPC apparatus manufactured by Tosoh Corporation, was used. As columns, three TSKgel GMHHR-H(20)HT columns manufactured by Tosoh Corporation were connected in series and used. At a column temperature of 140°C, trichlorobenzene was used as the eluent and flowed at a flow rate of 1.0 ml / min for measurement. A calibration curve was prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured molecular weight values were converted to polystyrene values to obtain the weight-average molecular weight (Mw) and the number-average molecular weight (Mn). Using these values of Mw and Mn, the molecular weight distribution (Mw / Mn) was obtained.

[0112] (1-2) Measurement of heptane insoluble content (HI) Regarding the polypropylene resins used as raw materials in the examples and comparative examples, they were press-molded into a size of 10 mm × 35 mm × 0.3 mm to prepare measurement samples of about 3 g. Next, about 150 mL of heptane was added, and Soxhlet extraction was performed for 8 hours. The heptane-insoluble content was calculated from the sample masses before and after extraction.

[0113] (1-3) Measurement of melt flow rate (MFR) Regarding the polypropylene resins used as raw materials in the examples and comparative examples, the melt flow rate (MFR) in the form of raw resin pellets was measured according to Condition M of JIS K 7210 using a melt indexer manufactured by Toyo Seiki Co., Ltd. Specifically, first, a sample weighed to 4 g was inserted into a cylinder set at a test temperature of 230°C and preheated under a load of 2.16 kg for 3.5 minutes. Then, the weight of the sample extruded from the bottom hole in 30 seconds was measured to obtain the MFR (g / 10 min). The above measurement was repeated three times, and the average value was taken as the measured value of MFR.

[0114] (2) Preparation of casting drum As the metal drums (casting drums) used when manufacturing the sheets (cast sheets) to be subjected to biaxial stretching treatment in the manufacturing process of biaxially stretched polypropylene films, casting drums A to E were prepared.

[0115] At any position on the surface of the casting drum, when a virtual line with a length of 0.1 mm in the width direction is provided at an arbitrary position, the number of grooves intersecting the virtual line and the average value of the groove widths were measured. Specifically, the measurement was carried out as follows. Twelve positions were observed in total, including four positions in the circumferential direction of the casting drum (0 degrees, 90 degrees, 180 degrees, 270 degrees on the clock) and three positions in the width direction (10 (one end), 50 (center), 90 (one end) with respect to a surface length of 100). A virtual line with a width of 0.1 mm was drawn at the center of the screen, and the number of intersecting grooves and the groove widths were measured, and the average values were calculated.

[0116] The number of grooves and the groove widths are shown in Table 1.

[0117]

Table 1

[0118] (3) Production of biaxially oriented polypropylene film A biaxially oriented polypropylene film was produced according to the production conditions in Table 2. The thickness of the biaxially oriented polypropylene film was measured in accordance with JIS-C2330 using a micrometer (JIS-B7502).

[0119] <Example 1> Polypropylene resin A (Mw = 270,000, Mw / Mn = 5.7, heptane-insoluble content = 97.8%, MFR = 5.6 g / 10 min, manufactured by Prime Polymer) and polypropylene resin B (Mw = 380,000, Mw / Mn = 8.3, heptane-insoluble content = 98.8%, MFR = 2.3 g / 10 min, manufactured by Korea Petrochemical) were supplied to an extruder at a mass ratio of A:B = 65:35 and melted at a resin temperature of 230°C. Then, after removing foreign substances and modified polymers with a filter installed in the middle of the polymer tube, extrusion was carried out using a T-die (die lip opening width 0.6 mm), and it was wound around a casting drum with a surface temperature maintained at 92°C and solidified to produce a cast sheet with a thickness of 0.1 mm at a speed of 60 m / min. Incidentally, the casting drum used was A in Table 1.

[0120] Also, as a method of adhering to the casting drum, an air knife was used, the wind speed of the blown air was 110 m / s, and the distance between the outlet of the air knife and the cast sheet was 3 mm.

[0121] The obtained cast sheet was preheated at a temperature of 130°C, sandwiched between a conveying roll heated to 145°C and a stretching nip roll with a rubber hardness of 70° heated to 110°C, stretched 5 times in the longitudinal direction, and immediately returned to room temperature.

[0122] Thereafter, the stretched film was guided to a tenter, both ends were gripped with clips at 110°C and preheated at 170°C, stretched 10 times in the width direction at a temperature of 155°C, and then relaxed and heat-fixed to wind up the biaxially stretched polypropylene film with a thickness of 2.3 μm in a roll shape.

[0123] <Example 2> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the distance between the outlet of the air knife and the sheet was set to 5 mm.

[0124] <Example 3> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 2, except that the wind speed of the blown air from the air knife was set to 70 m / s.

[0125] <Example 4> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the casting drum was set to B in Table 1.

[0126] <Example 5> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the casting drum was set to C in Table 1.

[0127] <Example 6> In the production of the cast sheet, except that the casting drum was E in Table 1, the blowing air velocity of the air knife was 130 m / s, the distance between the blowing outlet of the air knife and the sheet was 2 mm, and in the longitudinal stretching process, the temperature of the stretching nip roll was 130°C, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

[0128] <Example 7> A biaxially stretched polypropylene film was obtained in the same manner as in Example 6, except that the thickness of the finally wound biaxially stretched polypropylene film was 1.8 μm.

[0129] <Example 8> A biaxially stretched polypropylene film was obtained in the same manner as in Example 7, except that the die lip opening was 0.5 mm.

[0130] <Example 9> In the production of the cast sheet, except that the casting drum was D in Table 1, the blowing air velocity of the air knife was 70 m / s, and the distance between the blowing outlet of the air knife and the sheet was 5 mm, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

[0131] <Example 10> A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the die lip opening was 0.3 mm and the thickness of the finally wound biaxially stretched polypropylene film was 1.8 μm.

[0132] <Example 11> A biaxially stretched polypropylene film was obtained in the same manner as in Example 1, except that the thickness of the finally wound biaxially stretched polypropylene film was 6 μm.

[0133] <Example 12> In the production of the cast sheet, except that the resin supplied to the extruder was A, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

[0134] <Comparative Example 1> In the production of the cast sheet, the same procedure as in Example 1 was carried out except that the wind speed of the blowing air of the air knife was set to 140 m / s. In this case, since the air of the air knife entered between the resin extruded in a sheet form from the T-die and the casting drum, and the film vibration of the molten resin became remarkable until it adhered to the casting drum from the T-die outlet, it was not possible to produce a biaxially stretched film.

[0135] <Comparative Example 2> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 4 except that the wind speed of the blowing air of the air knife was 70 m / s and the distance between the blowing outlet of the air knife and the sheet was 5 mm.

[0136] <Comparative Example 3> In the production of the cast sheet, a biaxially stretched polypropylene film was obtained in the same manner as in Example 5 except that the wind speed of the blowing air of the air knife was 70 m / s and the distance between the blowing outlet of the air knife and the sheet was 5 mm.

[0137] <Comparative Example 4> In the stretching process in the longitudinal direction, a biaxially stretched polypropylene film was obtained in the same manner as in Example 6 except that the temperature of the stretching nip roll was 90°C.

[0138] <Comparative Example 5> A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the die lip opening was 0.7 mm and the thickness of the finally wound biaxially stretched polypropylene film was 1.8 μm.

[0139] <Comparative Example 6> A biaxially stretched polypropylene film was obtained in the same manner as in Example 1 except that the thickness of the finally wound biaxially stretched polypropylene film was 1.6 μm.

[0140] <Comparative Example 7> In the longitudinal stretching process, a biaxially stretched polypropylene film was obtained in the same manner as in Example 12, except that the temperature of the stretching nip roll was set at 90°C.

[0141] [Table 2]

[0142] (4) Measurement of properties of biaxially oriented polypropylene film (4-1) Measurement of maximum amplitude in a specific frequency range obtained by fast Fourier transform of the thickness in the longitudinal direction The thicknesses of properties a and b were specifically measured using an X-ray type on-line thickness measuring device (NSW-1450X manufactured by Yamabun Electric Co., Ltd.). In advance, films with thicknesses of 1.5 μm, 1.8 μm, 2.0 μm, 2.3 μm, 2.5 μm, 3.0 μm, 4.0, 6.0 μm, and 8.0 μm that were measured in accordance with JIS-C2330 using a micrometer (JIS-B7502) were measured with the X-ray type on-line thickness measuring device to create a calibration curve. The thickness obtained by converting the measured value of the biaxially stretched polypropylene film of the sample measured by the X-ray type on-line thickness measuring device using the calibration curve was used as data. In an environment of room temperature 23°C and humidity 60%, the biaxially stretched polypropylene film was set on a roll-to-roll unwinding / winding device, and the measuring part of the thickness measuring machine was placed at the center of the polypropylene film and run at a speed of 30 m / min. The thickness of property a was measured at intervals of 3 seconds for a length of 6144 m in the longitudinal direction of the film, and the thickness of property b was measured at intervals of 0.01 seconds for a length of 20.48 m in the longitudinal direction of the film, obtaining 4096 thickness data points each. The obtained longitudinal thickness data was subjected to fast Fourier transform using data analysis software (Origin(R)6.1J manufactured by OriginLab Corporation) with the window method as a rectangle and the spectrum as an amplitude. For the data related to property a, the maximum amplitude in the range of wave numbers 0.002 to 0.02 m-1 and for the data related to property b, the maximum amplitude in the range of wave numbers 0.5 to 5 m-1 were each divided by the average thickness to calculate the ratio to the average thickness.

[0143] (4-2) Measurement of slow axis angle and change width of slow axis angle From the center of each of the biaxially oriented polypropylene films of the examples and comparative examples, measurement samples of 50 mm × 50 mm were cut out at 10 locations (at positions of 0 m, 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, and 90 m) every 10 m in the longitudinal direction. Next, with the width direction of the measurement sample taken as 0°, the acute angle formed by the width direction of the measurement sample and the slow axis was measured as the slow axis angle. Among the 10 measurement samples, the difference between the maximum value and the minimum value of the slow axis angle was determined as the "change width". The measuring device and measurement conditions are as follows.

[0144] Measuring device: Retardation measuring device RE-100 manufactured by Otsuka Electronics Co., Ltd. Light source: Laser-emitting diode (LED) Band-pass filter: 550 nm (measurement wavelength) Measurement interval: 0.1 sec Integration times: 10 times Number of measurement points: 15 points Gain: 10 dB Measurement environment: Temperature 23°C, humidity 60%.

[0145] (4-3) Measurement of crystallite size and change width of crystallite size From the center of each of the biaxially oriented polypropylene films of the examples and comparative examples, measurement samples were cut out at 10 locations (at positions of 0 m, 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, 70 m, 80 m, and 90 m) every 10 m in the longitudinal direction. The measurement samples were measured by the following method.

[0146] To measure the diffraction reflection peak of the α-crystal (040) plane, a Rigaku D / STOP X-ray diffractometer MiniFlex300 (trade name) was used. Using X-rays generated at an output of 30 kV and 10 mA, CuKα rays (wavelength 0.15418 nm) monochromatized by a receiving monochromator were collimated with a slit and irradiated onto the measurement film. The diffraction intensity was measured by performing 2θ / θ linked scanning using a scintillation counter and a goniometer. Using the integrated powder X-ray analysis software PDXL, which is standardly attached to the device, the obtained data was used to determine the half-value width of the diffraction reflection peak of the α-crystal (040) plane. Using the θ and half-value width of the obtained diffraction reflection peak from the above measurement, the crystallite size was determined using the aforementioned Scherrer's equation. Note that the shape factor constant K was 0.94 and λ was 0.15418 nm.

[0147] Among the 10 measurement samples, the difference between the maximum and minimum values of the crystallite size was determined as the "variation width".

[0148] (4-4) Measurement of number of insulation defects Using an insulation defect inspection device having a unwind-windup mechanism, the number of insulation defects (number / 10 m 2 ) of the biaxially stretched polypropylene films of the examples and comparative examples was measured. The polypropylene film to be tested was run between a high-voltage electrode and a grounded metal roller, and a DC voltage was applied at that time, and the number of discharges occurring at the insulation defect portion was measured with a counter attached to the device. The measured count was divided by the measurement area to calculate the number of insulation defects (number / 10 m 2 ) of the film. The measurement conditions were as follows. · Distance between the high-voltage electrode and the grounded metal roller: 50 μm · Holding angle at which the film contacts the grounded metal roller: 120° · Shape of the high-voltage electrode: A metal plate with a thickness of 4 mm and the same width as the metal roller · Unwind speed: 20 m / min · DC voltage: 600 V / μm · Measurement area: 472 m 2 · Test environment temperature: 20°C.

[0149] (4-5) Measurement results The measurement results of the properties of the biaxially stretched polypropylene film are shown in Table 3.

[0150]

Table 3

[0151] (5) Evaluation of process passability The production of the biaxially stretched films of the examples and comparative examples was started, and from the time when the obtained film thickness reached the target thickness (Table 2) ±2%, the time until the film broke by stretching (the time during which continuous film formation was possible) was measured. Note that the time when the thickness reached the target thickness ±2% was measured and confirmed according to the thickness measurement method in (3) above. Based on the obtained time, the process passability was evaluated according to the following evaluation criteria. The results are shown in Table 4 described later. A++: Film formation was possible without breakage by stretching even after exceeding 48 hours. A+: Film formation was possible without breakage by stretching for more than 32 hours and less than 48 hours. A: Film formation was possible without breakage by stretching for more than 24 hours and less than 32 hours. B: Film formation was possible without breakage by stretching for more than 16 hours and less than 24 hours. C: Breakage by stretching occurred for more than 8 hours and less than 16 hours. D: Breakage by stretching occurred in less than 8 hours. E: Film formation was not possible.

[0152] (6) Evaluation of withstand voltage property and element processability Using the biaxially stretched films of the examples and comparative examples, capacitors were fabricated, and the withstand voltage property and element processability of the capacitors were evaluated.

[0153] (6-1) Fabrication of capacitor and evaluation of element processability Using a vacuum evaporator manufactured by ULVAC, Inc., an aluminum film was deposited on the measurement sample obtained in (4-1) above with a T margin deposition pattern at a deposition resistance of 20 Ω / sq to obtain a metallized film containing a metal film on one side of the biaxially stretched polypropylene film.

[0154] After slitting to a width of 50 mm, two metallized films were mated together, and using an automatic winder model 3KAW-N2 manufactured by Minato Seisakusho Co., Ltd., winding was performed at a winding tension of 210 g for 840 turns. The wound element was heat-treated at 120°C for 15 hours while being pressed, and then zinc metal was sprayed on the end face of the element to obtain a flat capacitor. Lead wires were soldered to the end faces of the flat capacitors, and then they were sealed with epoxy resin. Incidentally, the capacitance of the obtained capacitor was 50 μF.

[0155] All films with wrinkles visually observed during process conveyance and those with buckling after winding were regarded as non-conforming. Also, regarding winding deviation, when observed from the end face of the capacitor element, those with a deviation of 0.2 mm or more were regarded as non-conforming. 100 elements were fabricated, and the ratio of the number of qualified capacitor elements was calculated as the element yield rate and evaluated according to the following criteria. A++: 100% A+: 95% or more and less than 100% A: 90% or more and less than 95% B: 85% or more and less than 90% C: 80% or more and less than 85% D: 70% or more and less than 80% E: Less than 70%.

[0156] (6-2) Evaluation of initial withstand voltage property The initial capacitance (C0) of the capacitor before the test was measured using an LCR high tester 3522-50 manufactured by Hioki E.E. Corporation. Next, a DC voltage of 450 V / μm was applied to the capacitor for 10 seconds. The capacitance (C1) of the capacitor after voltage application was measured in the same manner, and the capacitance change rate before and after voltage application was calculated by the following formula.

[0157]

Equation

[0158] The above capacitance change rate ΔC was measured for 100 elements and evaluated according to the following criteria. The number of capacitors for each of A+ to C was calculated, and the ratio of capacitors of A+ and A (initial withstand voltage yield) was determined. An initial withstand voltage yield of 95% or more was considered a pass. A+: ΔC is less than -0.2%. A: ΔC is -0.5% or less and less than -1%. B: ΔC is -1% or less and less than -2%. C: ΔC is -2% or less.

[0159] (6-3) Evaluation of long-term withstand voltage property The initial capacitance (C0) of the capacitor before the test was measured using an LCR high tester 3522-50 manufactured by Hioki E.E. Corporation. Next, in a high-temperature bath at 115°C, a DC voltage of 320 V / μm was continuously applied to the capacitor for 1000 hours. The capacitance (C 1000 ) of the capacitor after 1000 hours was measured in the same manner, and the capacitance change rate (ΔC 1000 ) before and after the voltage application was calculated using the following formula.

[0160]

Equation

[0161] The above capacitance change rate ΔC 1000 was measured for 100 elements and evaluated according to the following criteria. The number of capacitors for each of A+ to C was calculated, and the ratio of capacitors of A+ and A (long-term withstand voltage yield) was determined. A long-term withstand voltage yield of 90% or more was considered a pass. A+: ΔC 1000 is less than 0.5%. A: ΔC 1000 is -0.5% or less and less than -5%. B: ΔC 1000 is -5% or less and less than -10%. C: ΔC 1000 is -10% or less.

[0162] (7) Evaluation results The evaluation results of process passability and withstand voltage are shown in Table 4.

[0163]

Table 4

Claims

1. The maximum amplitude in the range of wave numbers from 0.002 to 0.02 m obtained by performing fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge is 4.0% or less of the average thickness, and / or －１ [[ID (b) The maximum amplitude in the range of wave numbers from 0.5 to 5 m obtained by performing a fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge is 3.0% or less of the average thickness. －１ and that the maximum amplitude in the range of wave numbers from 0.5 to 5 m obtained by performing a fast Fourier transform on the longitudinal thickness using a non-contact thickness gauge is 3.0% or less of the average thickness. A biaxially stretched polypropylene film, characterized by

2. The biaxially stretched polypropylene film according to Claim 1, wherein the range of change in the slow axis angle is from 0.3° or more to 2.8° or less.

3. The biaxially stretched polypropylene film according to Claim 1, wherein the range of change in the crystallite size determined by the Scherrer's equation from the half-width of the α-crystal (040) plane reflection peak measured by the wide-angle X-ray diffraction method is 8.0 Å or less.

4. In the polypropylene resin constituting the biaxially stretched polypropylene film, the weight average molecular weight Mw is 250,000 or more and 450,000 or less, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 5.0 or more and 12.0 or less, the melt flow rate at 230 °C and a load of 2.16 kg is 7.0 g / 10 min or less, and the heptane-insoluble content is 96.0% or more and 99.5% or less. The biaxially stretched polypropylene film according to Claim 1.

5. The biaxially stretched polypropylene film according to Claim 1, having a thickness of 1.7 μm or more and 6.5 μm or less.

6. The biaxially stretched polypropylene film according to Claim 1, which is a single-layer film.

7. The biaxially stretched polypropylene film according to any one of Claims 1 to 6, for use in a capacitor.

8. A metal layer integrated polypropylene film, comprising the biaxially stretched polypropylene film according to any one of Claims 1 to 7 and a metal layer disposed on one or both sides of the biaxially stretched polypropylene film.

9. A capacitor, comprising the metal layer integrated polypropylene film according to Claim 8.

10. A method for manufacturing a biaxially stretched polypropylene film according to any one of Claims 1 to 6, comprising obtaining a cast sheet using a casting drum having a microcrack surface in which when a virtual line having a length of 0.1 mm in the widthwise direction is provided at an arbitrary position on the surface at an arbitrary position, the virtual line intersects one or more and 15 or less grooves and the groove width is 1 μm or more and 10 μm or less, and subjecting the cast sheet to a biaxial stretching treatment.

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