Polypropylene film, metal film laminated film using same, and film capacitor

Abstract

To provide a polypropylene film that is excellent in withstand voltage characteristics and reliability in a high-temperature environment when used for a high-voltage capacitor, has a structure suitable for a capacitor application or the like used under high temperature and high voltage, is excellent in stability to heat, does not cause crease in a transportation process including a vapor deposition process, and is excellent in workability.SOLUTION: A polypropylene film has: a crystal orientation degree of an α crystal (110) face of 0.73 or more when the polypropylene film after heated at 125°C for 60 minutes is measured by wide-angle X-ray diffraction; and a sum of stresses of a stress (F5MD) at 5% elongation in the longitudinal direction of the film when the film after heated at 150°C for 10 minutes is subjected to a tensile test at room temperature, and a stress (F5TD) at 5% elongation in the width direction of the film when the film after heated at 150°C for 10 minutes is subjected to a tensile test at room temperature of 150 MPa or larger.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film that is particularly suitable for use in capacitor applications. [Background technology]

[0002] Polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are therefore used in a variety of applications, including packaging, tape, cable wrapping, and electrical applications such as capacitors.

[0003] Among these, polypropylene films are particularly preferably used for capacitor applications, not only for DC but also for AC high voltage capacitors, due to their excellent voltage resistance and low loss characteristics.

[0004] Recently, various electrical devices have been converted to inverters, which has led to an even stronger demand for smaller capacitors with higher capacitance. In response to demands from such fields, particularly in automotive applications (including hybrid cars), solar power generation, and wind power generation, it has become essential for polypropylene films to be thinner, have higher breakdown voltages, and be highly reliable, able to maintain their properties over long periods of use in high-temperature environments.

[0005] Among polyolefin-based films, polypropylene film is considered to have high heat resistance and breakdown voltage. However, when applied to the aforementioned fields, it is important that it exhibits excellent dimensional stability at the ambient temperature and stable electrical performance, such as electrical resistance, even at temperatures 10 to 20°C higher than the ambient temperature. From the perspective of heat resistance, it is expected that the ambient temperature will become even higher in the future when considering power semiconductor applications using silicon carbide (SiC). Due to the demand for even higher heat resistance and high voltage resistance in capacitors, there is a need to improve the breakdown voltage of films in high-temperature environments exceeding 110°C. However, as described in Non-Patent Document 1, the upper limit of the operating temperature of polypropylene film is said to be approximately 110°C, and it has been extremely difficult to stably maintain breakdown voltage in such a temperature environment.

[0006] Furthermore, during the deposition process of the film, the film's orientation can be relaxed due to the thermal history caused by radiant heat, making it difficult for a film that is unstable to heat to fully utilize its inherent voltage resistance performance as a capacitor.

[0007] To date, methods for achieving excellent performance in high-temperature environments when polypropylene films are used as thin-film capacitors have been proposed, such as improving heat resistance and rigidity by controlling the raw material properties, such as the mesopentad fraction, and the planar orientation coefficient of the polypropylene resin that makes up the film (see, for example, Patent Document 1). Another proposal has been made for a film that improves rigidity by controlling the mesopentad fraction of the polypropylene resin, the orientation coefficient in the direction perpendicular to the film flow direction, and the planar orientation coefficient (see, for example, Patent Document 2). Furthermore, it has been proposed to improve voltage resistance in high-temperature environments by controlling the degree of crystal orientation and heat shrinkage (see, for example, Patent Document 3), and to improve heat resistance by increasing the raw material composition and the orientation of α-type crystals (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-141122 [Patent Document 2] Japanese Patent Application Publication No. 10-193451 [Patent Document 3] International Publication No. 2016 / 182003 Brochure [Patent Document 4] International Publication No. 2015 / 12324 Brochure [Non-patent literature]

[0009] [Non-Patent Document 1] Motonobu Kawai, "Film Capacitor Advances: From Automobiles to Energy," Nikkei Electronics, Nikkei BP, September 17, 2012, pp. 57-62 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the polypropylene film described in Patent Document 1 does not have sufficient projection height, which can lead to wrinkles, particularly during the vapor deposition process, and can result in reduced reliability when made into a capacitor. Furthermore, the polypropylene film described in Patent Document 2 is not intended for use in high-temperature environments, and the capacitor's withstand voltage and reliability can be impaired at temperatures above 110°C. Furthermore, the polypropylene film described in Patent Document 3 has sufficient breakdown voltage in a high-temperature environment of 110°C, but leaves room for improvement in terms of breakdown voltage and rigidity in high-temperature environments above 110°C. The polypropylene film described in Patent Document 4 is not intended for use in high-temperature environments, and the capacitor's withstand voltage and reliability can be impaired at temperatures above 110°C.

[0011] Therefore, the present invention aims to provide a polypropylene film that has excellent voltage resistance characteristics and reliability in high-temperature environments, has a structure with excellent heat stability suitable for applications such as capacitors used at high temperatures and high voltages, and has suitable processability, and also aims to provide a metal film laminated film and a film capacitor using the same. [Means for solving the problem]

[0012] The present inventors have conducted extensive research to solve the above problems and have arrived at the following invention: A polypropylene film in which, when the polypropylene film is heated at 125°C for 60 minutes and then measured by wide-angle X-ray diffraction, the degree of crystal orientation of the α-crystal (110) plane is 0.73 or more, and when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature, the sum of the stress at an elongation of 5% in the longitudinal direction of the film (F5MD) and the stress at an elongation of 5% in the width direction of the film (F5TD) is 150 MPa or more. [Effects of the Invention]

[0013] The present invention provides a polypropylene film that has excellent voltage resistance and reliability in high-temperature environments, is suitable for capacitor applications under high temperatures and high voltages, has excellent structural stability against heat, and has suitable processability with minimal wrinkling during transport processes including vapor deposition. Also provided are a metal film-laminated film and a film capacitor using the polypropylene film. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have conducted extensive research to solve the above-mentioned problems, and have concluded that the polypropylene films described in Patent Documents 1 to 4 above do not have sufficient breakdown voltage in a high-temperature environment, and that when used as a capacitor, they do not have sufficient voltage resistance, reliability, and processability in a high-temperature environment, as follows.

[0015] Specifically, the polypropylene film described in Patent Document 1 has a smooth surface, which may result in insufficient slipperiness. Furthermore, considering voltage resistance in high-temperature environments, the mesopentad fraction of the raw materials used is low, the heat treatment during transverse stretching during film formation is inappropriate, and the film is not slowly cooled at the heat treatment temperature after transverse stretching, resulting in the presence of a large amount of mobile amorphous components, which may result in low breakdown voltage at high temperatures. The polypropylene film described in Patent Document 2 is not designed for use in high-temperature environments, and the longitudinal and transverse stretching ratios during film formation are insufficient, which may lead to amorphous chain relaxation in high-temperature environments and a decrease in voltage resistance. The polypropylene film described in Patent Document 3 appears to have sufficient voltage resistance and reliability as a capacitor at 110°C. However, considering voltage resistance in even higher-temperature environments, the stretching ratio, heat treatment, molecular chain orientation, and structural fixation during film formation are not necessarily sufficient, resulting in the amorphous chains of the film relaxing in orientation at higher temperatures and a decrease in voltage resistance. Although Patent Document 4 enhances the orientation of molecular chains and improves heat resistance, the raw material composition does not take into consideration improvements in handleability and processability. In addition, the stretching ratio and heat treatment during film production, as well as the orientation of molecular chains and fixation of the structure, are not necessarily sufficient, resulting in poor handleability and device processability. Furthermore, the rigidity in high-temperature environments is insufficient, resulting in a corresponding decrease in voltage resistance.

[0016] Based on the above considerations, the inventors conducted further studies and found that the above problems can be solved by making the crystal orientation of the α-crystal (110) plane 0.73 or more when measured by wide-angle X-ray diffraction on a film after heating at 125°C for 60 minutes, and making the sum of the stress (F5MD) (MPa) at an elongation of 5% in the longitudinal direction of the film when a tensile test is performed at room temperature on a film after heating at 150°C for 10 minutes and the stress (F5TD) (MPa) at an elongation of 5% in the width direction of the film when a tensile test is performed at room temperature on a film after heating at 150°C for 10 minutes, 150 MPa or more.

[0017] That is, the present invention relates to a polypropylene film in which, when the polypropylene film is heated at 125°C for 60 minutes and then measured by wide-angle X-ray diffraction, the degree of crystal orientation of the α crystal (110) plane is 0.73 or more, and when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature, the sum of the stress at an elongation of 5% in the longitudinal direction of the film (F5MD) and the stress at an elongation of 5% in the width direction of the film (F5TD) is 150 MPa or more when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature.

[0018] The present invention will be described in detail below. In the present invention, "or higher" means the same as or higher than the indicated numerical value. "or lower" means the same as or lower than the indicated numerical value. "Room temperature" means 23°C.

[0019] In this specification, the polypropylene film may be simply referred to as a film. The polypropylene film of the present invention is not a microporous film and therefore does not have numerous pores. In other words, the polypropylene film of the present invention refers to a polypropylene film other than a microporous film. Here, a microporous film is defined as a film having a pore structure that penetrates both surfaces of the film and has an air permeability of 5,000 seconds / 100 ml or less, as measured at 23°C and 65% relative humidity using a JIS P 8117 (2009) Type B Gurley tester, in terms of the air permeation time of 100 ml of air.

[0020] The polypropylene film of the present invention has a crystal orientation degree of 0.73 or more in the α-crystal (110) plane when the film is heated at 125° C. for 60 minutes and then measured by wide-angle X-ray diffraction. By making this crystal orientation degree 0.73 or more, more preferably 0.75 or more, even more preferably 0.78 or more, and even more preferably 0.81 or more, the orientation order of the crystalline structure constituting the film is maintained at a high level, the occurrence of parts prone to dielectric breakdown is suppressed, and when used as a capacitor, a decrease in capacitance and short-circuit breakdown are suppressed even in high-temperature environments, a decrease in voltage resistance is suppressed, and high reliability can be achieved.

[0021] On the other hand, from the viewpoint of obtaining a stable film after biaxial stretching, the degree of crystal orientation of the α-crystal (110) plane is preferably 0.95 or less when the polypropylene film is heated at 125° C. for 60 minutes and then measured by wide-angle X-ray diffraction. There is no particular lower limit for the degree of crystal orientation of the α-crystal (110) plane, but from the viewpoint of reducing disorder in the orientation order of the crystalline structure constituting the film and suppressing the occurrence of parts prone to electrical breakdown, the lower limit is set to 0.60.

[0022] The crystal orientation of the α crystal (110) plane when the film after heating at 125°C for 60 minutes is measured by wide-angle X-ray diffraction as described above is, as will be described later, for example, when a raw material having a high mesopentad fraction and a cold xylene soluble fraction (CXS) of less than 3.0 mass% is used as polypropylene raw material A (sometimes referred to as polypropylene resin (A). The same applies to polypropylene raw material (B) and polypropylene raw material (C) described later), and a pre-stretching of 1.01 times or more and 1.10 times or less is performed before longitudinal stretching, and an areal stretching ratio of 60 is performed during biaxial stretching. The stretching ratio in the width direction is set to 11.0 times or more, and preferably 65 times or more, and the stretching ratio in the width direction is set to 11.0 times or more. In the heat setting and relaxation treatment steps after biaxial stretching, the film is first heat-treated at a temperature lower than the width-direction stretching temperature (first stage) while undergoing a relaxation treatment, and then, while maintaining tension in the width direction, the film is heat-treated at a temperature lower than the first-stage heat treatment temperature of 145°C or higher (second stage), and further heat-treated at 80°C or higher but lower than the second-stage heat treatment temperature (third stage). This multi-stage heat setting and relaxation treatment can be appropriately performed on the film to obtain the desired film.

[0023] The polypropylene film of the present invention has a sum of a stress at 5% elongation in the longitudinal direction of the film (F5MD) when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature, and a stress at 5% elongation in the transverse direction of the film (F5TD) when the film is heated under the same conditions and then subjected to a tensile test at room temperature, of 150 MPa or more. By making the sum of F5MD and F5TD 150 MPa or more, more preferably 170 MPa or more, even more preferably 180 MPa or more, and even more preferably 190 MPa or more, the film has rigidity in high-temperature environments and can achieve high reliability when used as a capacitor.

[0024] On the other hand, the sum of F5MD and F5TD is preferably 300 MPa or less. By setting the sum to 300 MPa or less, it is possible to prevent the film from breaking during the film-forming process and the film-formability from being reduced.

[0025] The sum of F5MD and F5TD in the above range can be obtained, as described below, by using a polypropylene raw material A having a high mesopentad fraction and a cold xylene solubles (CXS) content of less than 3.0% by mass, pre-stretching the film to between 1.01 and 1.10 times before stretching in the longitudinal direction, and biaxially stretching the film to an areal stretch ratio of 65 times or more and a widthwise stretch ratio of 11.0 times or more. In the heat setting and relaxation treatment steps after biaxial stretching, the film is first heat-treated at a temperature lower than the widthwise stretching temperature (first stage) while undergoing relaxation treatment, then heat-treated at a temperature lower than the first-stage heat treatment temperature of 145°C or higher (second stage) while maintaining tension in the width direction, and then heat-treated at a temperature higher than the first-stage heat treatment temperature of 80°C or higher but lower than the second-stage heat treatment temperature (third stage).

[0026] In the polypropylene film of the present invention, the "longitudinal direction" refers to the direction corresponding to the machine direction in the film production process (hereinafter sometimes referred to as "MD"), and the "transverse direction" refers to the direction perpendicular to the machine direction in the film production process (hereinafter sometimes referred to as "TD"). When a film sample is in the form of a reel or roll, the film winding direction can be considered the longitudinal direction. On the other hand, for films where it is unclear from the appearance which direction corresponds to the machine direction in the film production process, a slit-shaped film piece is sampled and its breaking strength is determined using a tensile tester. The direction giving the maximum breaking strength is considered to be the width direction and main orientation direction of the film, and the direction perpendicular to the width direction of the film is considered to be the longitudinal direction and the direction perpendicular to the main orientation direction. As will be described in detail later, when the sample width is less than 50 mm and breaking strength cannot be determined using a tensile tester, the crystal orientation of the α-crystal (110) plane is measured using wide-angle X-rays as follows, and the longitudinal and transverse directions of the film are determined based on the following criteria. Specifically, X-rays (CuKα rays) are incident perpendicular to the film surface, and the crystal peak at 2θ = approximately 14° (α crystal (110) plane) is scanned circumferentially. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution is defined as the film width direction and main orientation direction, and the direction perpendicular to this is defined as the longitudinal direction and the direction perpendicular to the main orientation direction.

[0027] The polypropylene film of the present invention preferably contains a linear polypropylene resin as a main component, where the main component refers to the component with the highest mass fraction (highest content) among the components constituting the polypropylene film.

[0028] Hereinafter, the polypropylene film may be simply referred to as the film.

[0029] Although polypropylene resins are primarily composed of propylene homopolymers, copolymerization components based on other unsaturated hydrocarbons may be used, or polymers other than propylene homopolymers may be blended, as long as the objectives of the present invention are not impaired. Examples of monomer components other than propylene that constitute such copolymerization components or blends include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, and 5-methyl-2-norbornene.

[0030] From the viewpoint of breakdown voltage and heat resistance, the copolymerization amount or blend amount of components other than the propylene component is preferably 1 mol% or less, and the blend amount is preferably 1 mass% or less of the total resin constituting the film as the amount of components other than propylene.

[0031] The polypropylene film of the present invention has a weight average molecular weight Mw and a z+1 average molecular weight M z+1 For M z+1 It is preferable that / Mw is 3 or more and 10 or less. z+1 By setting / Mw to 10 or less, more preferably 7.9 or less, even more preferably 6.9 or less, particularly preferably 6.5 or less, and most preferably 6.1 or less, the molecular weight distribution becomes narrow and the film structure becomes uniform with little local unevenness, thereby suppressing thermal shrinkage and achieving the effect of improving the breakdown voltage in high-temperature environments.

[0032] M z+1 As a means for controlling / Mw within the above range, polypropylene resin A may be prepared by using a polypropylene having a mesopentad fraction of 0.97 or more or a chip melting point of 160°C or more, a cold xylene soluble fraction (CXS) of less than 3 mass%, and a number average molecular weight (Mn) of 70,000 (7.0 x 10 4 ) below, Z+1 average molecular weight (M z+1 ) is 3 million (3.0 × 10 6) and appropriately blending polypropylene resin B and / or polypropylene resin C within the preferred range of the present application.

[0033] The polypropylene film of the present invention may contain various additives, such as organic particles, inorganic particles, crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, slipping agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors, as long as the additives do not impair the object of the present invention.

[0034] When an antioxidant is added, the type and amount of the antioxidant should be selected from the perspective of long-term heat resistance. Such antioxidants are preferably sterically hindered phenolic antioxidants, with at least one of them being a high-molecular-weight type with a molecular weight of 500 or more. Specific examples include various antioxidants, but it is preferable to use 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) in combination with 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (e.g., BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane (e.g., BASF's "Irganox"® 1010: molecular weight 1,177.7). The total content of these antioxidants is preferably 0.1% by mass or more and 1.0% by mass or less based on the total amount of polypropylene. By setting it to 0.1% by mass or more, more preferably 0.2% by mass or more, excellent long-term heat resistance is achieved. By setting it to 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.4% by mass or less, blocking at high temperatures due to bleed-out of the antioxidants can be suppressed, preventing adverse effects on the capacitor element.

[0035] The polypropylene film of the present invention may contain a resin other than polypropylene resin as long as it does not impair the object of the present invention. Examples of resins other than polypropylene resin include vinyl polymer resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, and polycarbonate resins, including various polyolefin resins. Particularly preferred examples include polymethylpentene, cycloolefin copolymers, cycloolefin polymers, and syndiotactic polystyrene. The content of resins other than polypropylene resin is preferably less than 30% by mass, more preferably 19% by mass or less, even more preferably 15% by mass or less, and most preferably 9% by mass or less, based on 100% by mass of the total resin components constituting the polypropylene film. If the content of resins other than polypropylene resin is 30% by mass or more, the influence of the domain interface becomes significant, which may result in a decrease in the breakdown voltage in high-temperature environments.

[0036] The polypropylene film of the present invention preferably has a melting peak temperature (Tm) of 170°C or higher, obtained when the film is heated from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC). By setting Tm to 170°C or higher, more preferably 171°C or higher, even more preferably 172°C or higher, even more preferably 173°C or higher, and even more preferably 174°C or higher, the breakdown voltage in a high-temperature environment can be effectively improved. On the other hand, Tm is preferably 200°C or lower, from the viewpoint of industrial production of polypropylene resin.

[0037] A Tm in the above range can be achieved, for example, by using as the polypropylene raw material A a raw material having a high mesopentad fraction and a cold xylene solubles (CXS) content of less than 3.0 mass %, as described below.

[0038] The polypropylene film of the present invention preferably has a difference (Tm - Tc) of 65°C or less between the melting peak temperature (Tm) of the film, obtained by heating the film from 30°C to 260°C at 20°C / min using a differential scanning calorimeter (DSC), and the crystallization peak temperature (Tc) obtained by cooling the film from 260°C to 30°C at 20°C / min. By keeping (Tm - Tc) at 65°C or less, more preferably 63°C or less, even more preferably 61°C or less, even more preferably 59°C or less, and even more preferably 57°C or less, the crystallization time during the resin cooling and solidification process can be shortened and the formation of coarse spherulites can be suppressed. Suppressing the formation of such coarse spherulites in a cast sheet can reduce the generation of internal voids during the stretching process and the reduction in reliability of capacitors due to the formation of coarse protrusions on the surface. Furthermore, the increased number of flat areas on the entire film surface can prevent the film's slipperiness from being reduced, which can lead to poor processability.

[0039] On the other hand, the difference between Tm and Tc (Tm-Tc) is preferably 40° C. or more. By setting the temperature at 40° C. or more, excellent film formation stability is achieved.

[0040] When the polypropylene film of the present invention is a film containing polypropylene and a thermoplastic resin that is immiscible with polypropylene, the melting peak temperature of the incompatible resin may be observed at a temperature different from that of the polypropylene, but in the present invention, the peak temperatures observed between 170°C and 200°C are defined as the melting peak temperature (Tm) and crystallization peak temperature (Tc) of the polypropylene film of the present invention. In this case, there may be cases where two or more peaks are observed within the above temperature range, or where the peak temperature is a peak temperature that can be observed on a multi-stage DSC chart called a shoulder (observed in a chart where two or more peaks overlap), but in the present invention, the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart is selected and defined as Tm and Tc, respectively.

[0041] The above-mentioned range of (Tm-Tc) can be achieved, for example, by using polypropylene raw material A and / or polypropylene raw material B having a high mesopentad fraction and a cold xylene solubles (CXS) of less than 3.0 mass % as polypropylene raw material A, by containing branched polypropylene raw material C, and by adjusting the ratio of these components.

[0042] The polypropylene film of the present invention exhibits a high breakdown voltage even in high-temperature environments. To ensure that a capacitor made from the film exhibits high voltage resistance and reliability even in high-temperature environments, the skewness (Ssk) of at least one surface of the film, as defined by ISO 25178, is preferably greater than -30 and less than 5. Here, Ssk is a parameter indicating the degree of unevenness of the surface. Ssk represents the cube mean of Z(x, y) on a reference plane that is dimensionless by the cube of the root-mean-square height Sq. This Ssk represents the skewness (width) and is a numerical value that indicates the symmetry of the peaks and valleys about the mean plane. Therefore, when Ssk is less than 0, the film is biased downward relative to the mean line, i.e., there are more concave valleys than convex peaks. On the other hand, when Ssk is greater than 0, the film is biased upward relative to the mean line, i.e., there are more convex peaks than concave valleys. A skewness Ssk of 0 indicates symmetry (normal distribution) relative to the mean line.

[0043] By setting the Ssk to a value exceeding -30, more preferably -28 or greater, and even more preferably -26 or greater, it is possible to prevent the film surface from being overly biased toward having recesses. This makes it difficult for the film's voltage resistance to be impaired even in high-temperature environments, particularly in high-voltage capacitor applications, and also makes the film more easily slippery and easier to process.

[0044] On the other hand, by making Ssk less than 5, more preferably 4 or less, and even more preferably 3 or less, the presence of excessive convex shapes on the film surface is suppressed, and when made into a capacitor, gaps are suppressed from occurring between the film layers, preventing a decrease in capacity in high-temperature environments and preventing the film's slipperiness from being impaired, which in turn prevents deterioration of voltage resistance and processability.

[0045] The Ssk of the polypropylene film of the present invention can be kept within the above range by, for example, using a polypropylene raw material B having the preferred properties described below, setting the areal stretching ratio during biaxial stretching to 60 times or more, preferably 65 times or more, and the widthwise stretching ratio to 11.0 times or more, and controlling the casting drum temperature, the film's melting peak temperature (Tm) and crystallization peak temperature (Tc) within preferred ranges.

[0046] In the polypropylene film of the present invention, it is preferable that the protruding peak heights SpkA and SpkB defined in ISO25178 of surface A on one side and surface B on the other side satisfy the following relationship: SpkA <SpkB 20nm≦SpkA≦100nm 80nm≦SpkB≦150nm where: SpkA: Height of the protruding peak on surface A SpkB: Height of the protruding peak on surface B.

[0047] Spk is a type of functional parameter defined in ISO25178, and indicates the average height of the part (protruding peak) that is higher than the intersection point between the equivalent line of the bearing curve of the height data and the line where the areal load ratio = 0%. Here, the bearing curve of the height data is calculated by accumulating the frequency at a certain height from the highest side and expressing it as a percentage with the total number of all height data being 100%, and the areal load ratio at a certain height C is given by Smr(C). Furthermore, the equivalent line is the line with the smallest slope where the difference in areal load ratio (Smr) is 40%.

[0048] In the polypropylene film of the present invention, SpkA is more preferably 30 nm or more, and even more preferably 40 nm or more, and more preferably 90 nm or less, and even more preferably 80 nm or less.

[0049] In the polypropylene film of the present invention, SpkB is more preferably 90 nm or more, and even more preferably 100 nm or more, and more preferably 140 nm or less, and even more preferably 130 nm or less.

[0050] When SpkA and SpkB satisfy the above ranges, the film has a moderately high surface protrusion height, resulting in sufficient slipperiness, excellent processability when producing capacitor elements, suppressing excessively high protrusions on the film surface and preventing a decrease in the withstand voltage of the capacitor.

[0051] Controlling SpkA and SpkB within the above-mentioned ranges is possible, for example, by using a polypropylene raw material B having the preferred properties described below, setting the areal stretching ratio during biaxial stretching to 60 times or more, preferably 65 times or more, and the width direction stretching ratio to 11 times or more, and controlling the casting drum temperature, the film's melting peak temperature (Tm), and the crystallization peak temperature (Tc) within preferred ranges.

[0052] The polypropylene film of the present invention has a total volume of valleys with a depth of 20 nm or more in an area of ​​0.561 mm x 0.561 mm measured by a scanning white light interference microscope on at least one surface of the film, of 50 μm 3 More than 5,000μm 3 It is preferable that the total volume is 50 μm or less. 3 More preferably, 100 μm 3 More preferably, 500 μm or more 3 By setting the thickness to above 5,000μm, the surface has a moderate unevenness, and the film has a moderate slipperiness, which improves handling, and the occurrence of wrinkles is reduced, improving device processability. In addition, even when used as a capacitor for a long time, the capacitance change due to the influence of wrinkles is suppressed, and even when the film is used as a laminated capacitor, there is a moderate gap between the films, which activates the self-healing function and improves the reliability of the capacitor. On the other hand, if the total volume of the valleys is 5,000μm, 3 Less than 4,000 μm, preferably 3Less than 3,500 μm, more preferably 3 Below 3,000 μm, particularly preferably 3 By setting the thickness to the range below 1000 ppm, it is possible to prevent localized thin portions from forming and causing dielectric breakdown, thereby improving the voltage resistance of the film and improving the voltage resistance and reliability in high-temperature environments even when used in high-voltage capacitor applications.

[0053] The total volume of valleys on the film surface can be adjusted to the preferred range described above, for example, by using polypropylene raw material B described below, setting the areal stretching ratio during biaxial stretching to 60 times or more, preferably 65 times or more, and the widthwise stretching ratio to 11.0 times or more, and controlling the casting drum temperature, the film's melting peak temperature (Tm), and the crystallization peak temperature (Tc) within the preferred ranges.

[0054] The polypropylene film of the present invention preferably has a widthwise heat shrinkage rate (HS125TD) of 1.0% or less after heat treatment for 15 minutes at 125° C. By setting this heat shrinkage rate to 1.0% or less, more preferably 0.8% or less, even more preferably 0.6% or less, and even more preferably 0.4% or less, it is possible to suppress film shrinkage due to heat during the capacitor manufacturing process and use process, and a decrease in voltage resistance due to poor contact with the metallicon at the element end, and to prevent a decrease in capacity due to tight winding of the element and a decrease in reliability due to short-circuit breakdown.

[0055] On the other hand, the thermal shrinkage in the width direction after heating at 125°C for 15 minutes is preferably 0.02% or more. By making it 0.02% or more, it is possible to prevent the wound state of the element from loosening due to heat during the capacitor manufacturing process and use process.

[0056] The heat shrinkage percentage in the width direction of the film after heat treatment at 125°C for 15 minutes within the above range can be achieved, for example, by using a polypropylene raw material A having a high mesopentad fraction and a cold xylene solubles (CXS) content of less than 3.0% by mass, pre-stretching the film to a ratio of 1.01 to 1.10 before longitudinal stretching, and biaxially stretching the film to an areal stretch ratio of 60 or more, preferably 65 or more, and a width direction stretch ratio of 11.0 or more. In the heat setting and relaxation treatment steps after biaxial stretching, the film is first heat-treated at a temperature lower than the width direction stretching temperature (first stage) while undergoing relaxation treatment, and then, while maintaining tension in the width direction, is heat-treated at a temperature lower than the first heat treatment temperature at 135°C or higher (second stage) and further heat-treated at 80°C or higher but lower than the second heat treatment temperature (third stage).

[0057] The polypropylene film of the present invention has a static friction coefficient (μ ) of at least one side when the same sides are overlapped with each other, from the viewpoint of imparting appropriate slipperiness and improving processability in the production of capacitor elements. s ) is preferably 0.2 or more and less than 0.8. s By making the coefficient of static friction μ 0.2 or more, more preferably 0.4 or more, it is possible to prevent the film from slipping too much during winding or element processing. s By making the value of [lambda] less than 0.8, more preferably 0.7 or less, and even more preferably 0.6 or less, an extreme decrease in the slipperiness of the film can be suppressed, thereby suppressing the occurrence of wrinkles and improving the handling properties and element processability.

[0058] The polypropylene film of the present invention preferably has a breakdown voltage of 350 V / μm or more at 130°C. By setting the breakdown voltage to 350 V / μm or more, more preferably 375 V / μm or more, even more preferably 400 V / μm or more, and even more preferably 420 V / μm or more, when used as a capacitor, short circuit breakdown is unlikely to occur, especially even when used for long periods of time in high-temperature environments, so that voltage resistance is maintained and high reliability can be obtained. The upper limit of the breakdown voltage at 130°C is not particularly limited, but is about 800 V / μm.

[0059] To control the film breakdown voltage at 130°C within the above range, for example, as described below, a polypropylene raw material A having a high mesopentad fraction and a cold xylene solubles (CXS) content of less than 3.0% by mass is used, the polypropylene raw material A is pre-stretched at a ratio of 1.01 to 1.10 before longitudinal stretching, and the area stretch ratio during biaxial stretching is set to 65 times or more and 11.0 times or more in the width direction. In the heat setting and relaxation treatment steps after biaxial stretching, the film is first heat-treated at a temperature lower than the width direction stretching temperature (first stage) while undergoing relaxation treatment, then heat-treated at a temperature lower than the first heat treatment temperature (second stage) at 135°C or higher while maintaining tension in the width direction, and then heat-treated at a temperature higher than the first heat treatment temperature (third stage) at 80°C or higher but lower than the second heat treatment temperature. This can be achieved by appropriately subjecting the film to a multi-stage heat setting and relaxation treatment.

[0060] The polypropylene film of the present invention preferably has a mesopentad fraction of 0.970 or more as measured by nuclear magnetic resonance (NMR). The mesopentad fraction is an index showing the stereoregularity of the crystalline phase of polypropylene, and by setting the mesopentad fraction to 0.970 or more, more preferably 0.975 or more, and even more preferably 0.981 or more, the degree of crystallinity is high, the melting point is high, and the breakdown voltage in high-temperature environments can be improved. There is no particular restriction on the upper limit of the mesopentad fraction.

[0061] In the present invention, the polypropylene resin with a high mesopentad fraction is preferably one produced using a Ziegler-Natta catalyst, and a method of appropriately selecting an electron donor component in the catalyst is preferably employed. The polypropylene resin produced in this manner can have a molecular weight distribution (Mw / Mn) of 3.0 or more and a <2,1> erythro moiety defect of 0.1 mol% or less, and it is preferable to use such a polypropylene resin.

[0062] The polypropylene film of the present invention preferably has a polypropylene component dissolved in xylene (CXS, also referred to as cold xylene solubles) of 3.0% by mass or less when completely dissolved in xylene and then precipitated at room temperature. Here, CXS is considered to be a component that is difficult to crystallize due to low stereoregularity, low molecular weight, or the like. By controlling the CXS content to 3.0% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.3% by mass or less, particularly preferably 1.1% by mass or less, and most preferably 0.9% by mass or less, the film's heat resistance, high-temperature voltage resistance, and breakdown voltage can be improved. Therefore, when used in capacitors, relaxation in high-temperature environments is suppressed, improving thermal dimensional stability and suppressing leakage current. While the lower limit of CXS is not particularly limited, a practical value is 0.1% by mass. Attempting to control the CXS content to less than 0.1% by mass can result in poor stretchability during film formation, potentially leading to tearing.

[0063] In order to adjust the CXS content to the above range, a method of increasing catalytic activity when obtaining the polypropylene resin to be used, a method of washing the obtained polypropylene resin with a solvent or propylene monomer itself, etc. can be used.

[0064] The polypropylene film of the present invention is preferably surface-treated. Polypropylene films usually have low surface energy, making it difficult to stably apply metal vapor deposition to them. Therefore, in order to improve adhesion to the metal film, it is preferable to perform a surface treatment before vapor deposition. Specific examples of surface treatments include corona discharge treatment, plasma treatment, glow discharge treatment, and flame treatment.

[0065] The surface wet tension of a normal polypropylene film is about 30 mN / m, but the polypropylene film of the present invention is preferably surface-treated to have a wet tension of about 37 to 75 mN / m, more preferably about 39 to 65 mN / m, and even more preferably about 41 to 55 mN / m, because this provides excellent adhesion to the metal film and improves the safety of the capacitor.

[0066] The polypropylene film of the present invention preferably has a film thickness of 0.5 μm or more and less than 25 μm. By setting the film thickness to 0.5 μm or more and less than 25 μm, more preferably 0.6 μm or more and 6 μm or less, even more preferably 0.8 μm or more and 4 μm or less, and even more preferably 1 μm or more and 2.5 μm or less, an excellent balance is achieved between voltage resistance characteristics in high-temperature environments and miniaturization of capacitor size due to thinning, and the film is particularly suitable for thin-film heat-resistant film capacitors required for automotive applications (including hybrid car applications) used in high-temperature environments.

[0067] The film thickness can be adjusted, for example, by adjusting the extrusion discharge rate, the rotation speed of the casting drum, the lip gap of the die, the stretch ratio, etc. More specifically, the film thickness can be reduced by reducing the extrusion discharge rate, increasing the rotation speed of the casting drum, narrowing the lip gap of the die, increasing the stretch ratio, etc. These methods can also be used in combination as appropriate.

[0068] The polypropylene film of the present invention is preferably in the form of a single layer film, but may also be in the form of a laminate film.

[0069] The polypropylene film of the present invention is preferably used as a dielectric film for capacitors, and can be used for various types of capacitors. Specifically, from the viewpoint of electrode configuration, it may be either a laminated wound capacitor of metal foil and film or a metal-vapor-deposited film capacitor. It is also preferably used in an oil-immersion type capacitor impregnated with insulating oil or a dry capacitor that does not use insulating oil at all. From the viewpoint of utilizing the properties of the film of the present invention, it is particularly preferably used as a metal-vapor-deposited film capacitor. The film shape in the capacitor may be a wound type or a laminated type.

[0070] The method for producing the polypropylene film of the present invention will now be described with reference to an example.

[0071] First, the raw materials preferably used for the polypropylene film of the present invention will be described. As described above, in order to obtain the polypropylene film of the present invention, it is preferable to use a plurality of types of polypropylene raw materials, particularly those having different number average molecular weights.

[0072] Polypropylene raw material A is a linear polypropylene having a number average molecular weight (Mn) smaller than that of polypropylene raw material B described later. From the viewpoint of biaxially stretching the film, the Mn of polypropylene raw material A is set to 30,000 (3.0 × 10 4 ) or more is preferable, and 40,000 (4.0 × 10 4 ) or more is preferable, and 50,000 (5.0 × 10 4 ) or more is more preferable. From the viewpoint of obtaining thermal stability in a high-temperature environment, the Mn of the polypropylene raw material A is 90,000 (9.0 × 10 4 ) or less is preferable, and 80,000 (8.0 × 10 4 ) or less is more preferable.

[0073] Z+1 average molecular weight (M z+1 ) is 1 million (1.0 × 10) from the viewpoint of biaxially stretching the film. 6 ) or more is preferable, and 1.5 million (1.5 × 10 6) or more is more preferable. z+1 From the viewpoint of obtaining thermal stability in a high-temperature environment, 6 ) or less is preferable, and 2 million (2.0 × 10 6 ) or less is more preferable.

[0074] The polypropylene raw material A preferably has a cold xylene solubles (hereinafter referred to as CXS) of 3% by mass or less. By setting the CXS to 3.0% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less, excellent film formation stability is achieved, and the strength, dimensional stability, and heat resistance of the film are improved. The lower the CXS, the better, but the lower limit is about 0.1% by mass.

[0075] In order to keep the CXS content within the above range, a method of increasing catalytic activity when obtaining the resin, or a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

[0076] The mesopentad fraction of polypropylene raw material A is preferably 0.970 or more. The mesopentad fraction is an index showing the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance (NMR). By making the mesopentad fraction 0.970 or more, more preferably 0.975 or more, even more preferably 0.980 or more, and even more preferably 0.983 or more, the crystallinity and melting point become high, making it suitable for use at high temperatures. There is no particular upper limit for the mesopentad fraction.

[0077] To obtain a polypropylene resin with a high mesopentad fraction, for example, a method of washing the obtained resin powder with a solvent such as n-heptane, or a method of appropriately selecting a catalyst and / or co-catalyst and a composition is preferably employed.

[0078] The melting point of the chips of polypropylene raw material A (meaning the melting point of the resin; the same applies hereinafter) is preferably 160° C. or higher. By making the melting point of the chips 160° C. or higher, more preferably 163° C. or higher, and even more preferably 166° C. or higher, it is possible to effectively obtain voltage resistance characteristics in high-temperature environments when made into a film.

[0079] The chip melting point is the melting peak temperature obtained when the chip is heated from 30°C to 260°C at a rate of 20°C / min using a differential scanning calorimeter (DSC). Two or more melting peak temperatures may be observed within the temperature range, or the melting point may be a peak temperature observable on a multi-stage DSC chart known as a shoulder (observed on a chart where two or more peaks overlap), but in the present invention, the chip melting point is the temperature of the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart.

[0080] The proportion of the polypropylene raw material A in the raw materials of the polyolefin film of the present invention is preferably such that the polypropylene raw material A is the main component, that is, the largest component, relative to the polyolefin film.

[0081] In order to effectively obtain voltage resistance characteristics in a high-temperature environment when made into a film, it is also preferable that the raw materials for the polyolefin film of the present invention contain, in addition to polypropylene raw material A, polypropylene raw material B having a number average molecular weight (Mn) larger than that of polypropylene raw material A.

[0082] The number average molecular weight (Mn) of polypropylene raw material B is set to 50,000 (5.0 × 10 4 ) or more is preferable, and 60,000 (6.0 × 10 4 ) or more is preferable, and 70,000 (7.0 × 10 4 On the other hand, from the viewpoint of obtaining thermal stability of the film in a high-temperature environment, Mn of the polypropylene raw material B is 120,000 (12.0 × 10 4 ) or less is preferable, and 110,000 (11.0 × 10 4 ) or less is more preferable, and 100,000 (10.0 × 10 4 ) The following is even more preferred.

[0083] The Mn of polypropylene raw material B is larger than that of polypropylene raw material A, and is 10,000 (1.0 × 10 4 ) or larger, and 20,000 (2.0 × 10 4 ) or more is more preferable.

[0084] Z+1 average molecular weight (M z+1 ) is 2.5 million (2.5 × 10) from the viewpoint of biaxially stretching the film. 6 ) or more is preferable, and 3.5 million (3.5 × 10 6 ) or more is more preferable, and 4 million (4.0 × 10 6 ) or more is more preferable, and 4.5 million (4.5 × 10 6 ) or more is more preferable. On the other hand, from the viewpoint of obtaining thermal stability of the film in a high-temperature environment, M of the polypropylene raw material B is z+1 is 8 million (8.0 × 10 6 ) or less is preferable, and 7 million (7.0 × 10 6 ) or less is more preferable.

[0085] Polypropylene raw material B M z+1 From the viewpoint of obtaining thermal stability of the film in a high-temperature environment, M of polypropylene raw material A is z+1 The average molecular weight is preferably greater than 500,000 (0.5 × 10 6 ) or more is more preferable, and 1 million (1.0 × 10 6 ) or more is more preferable, and 1.5 million (1.5 × 10 6 ) or more is more preferable.

[0086] The polypropylene raw material B preferably has a cold xylene solubles (CXS) content of 4.0% by mass or less. By setting the CXS content in the polypropylene raw material B to 4.0% by mass or less, more preferably 3.0% by mass or less, excellent film formation stability, improved film strength, dimensional stability, and heat resistance are achieved. The lower the CXS, the better, but the lower limit is about 0.1% by mass.

[0087] In order to keep the CXS content within the above range, a method of increasing catalytic activity when obtaining the resin, or a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

[0088] The mesopentad fraction of polypropylene raw material B is preferably 0.940 or more, more preferably 0.95 or more, and even more preferably 0.960 or more.

[0089] The melting point of the chips of polypropylene raw material B is preferably 160° C. or higher. By making the melting point of the chips 160° C. or higher, more preferably 162° C. or higher, and even more preferably 164° C. or higher, it is possible to effectively improve the voltage resistance characteristics in a high-temperature environment when the chips are made into a film.

[0090] The content of polypropylene resin B in the raw material of the polypropylene film of the present invention is preferably 1% by mass or more and 30% by mass or less, based on 100% by mass of the polypropylene film. The content of polypropylene raw material B is more preferably 2% by mass or more. The content of polypropylene raw material B is more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0091] Number average molecular weight (Mn) and Z+1 average molecular weight (M z+1), cold xylene solubles (CXS), mesopentad fraction, chip melting point, and content are set within the above-mentioned preferred ranges, and further, prior to stretching, the film is pre-stretched at 1.01 to 1.10 times in the machine direction, and during biaxial stretching, the areal stretching ratio is 65 times or more and the width direction stretching ratio is 11.0 times or more, and in the heat setting and relaxation treatment steps after biaxial stretching, first, relaxation treatment is performed while heat treatment (first stage) is performed at a temperature lower than the width direction stretching temperature, and then the film is tensioned in the width direction while the above-mentioned By appropriately subjecting the film to a multi-stage heat setting and relaxation process, which involves a second heat treatment at 135°C or higher, which is lower than the first heat treatment temperature, and a third heat treatment at 80°C or higher, which is lower than the second heat treatment temperature, the difference in viscosity with polypropylene raw material A causes appropriate protrusions to form on the surface.Furthermore, the number of tie molecules connecting crystals increases, which makes it easier to improve the orientation of the molecular chains when the stretching ratio is increased, and the binding force of the amorphous chains in a high-temperature environment can be increased.

[0092] The polyolefin film of the present invention may contain a branched chain polypropylene raw material C in addition to the polypropylene raw material A and the polypropylene raw material B.

[0093] There are several methods for producing polypropylene raw material C, such as Ziegler-Natta catalyst systems and metallocene catalyst systems. However, from the viewpoint of using it in combination with polypropylene raw material A or polypropylene raw material B, metallocene catalyst systems are more preferable because they have fewer low-molecular-weight and high-molecular-weight components and a narrow molecular weight distribution.

[0094] Specific examples of commercially available polypropylene raw material C include "Profax" (registered trademark) (PF-814, etc.) manufactured by Lyondell Basell, and examples of metallocene catalyst systems include "Daploy" (trademark) manufactured by Borealis (WB130HMS, WB135HMS, WB140HMS, etc.) and "WAYMAX" (registered trademark) manufactured by Japan Polypropylene Corporation (MFX8, MFX6, MFX3, etc.).

[0095] The polypropylene raw material C preferably has a CXS of 5.0% by mass or less, more preferably 3.0% by mass or less. The lower the CXS, the better, but the lower limit is about 0.1% by mass. To control the CXS within this range, methods can be used that increase the catalytic activity when obtaining the resin, or that wash the obtained resin with a solvent or the olefin monomer itself.

[0096] From the viewpoint of stretching uniformity, it is preferable that the melt tension of polypropylene raw material C at 230°C is 2 cN or more and 40 cN or less. The melt tension is more preferably 3 cN or more, and even more preferably 5 cN or more. Also, it is more preferably 30 cN or less, and even more preferably 20 cN or less. In order to set the melt tension of polypropylene raw material C within the above range, a method of controlling the average molecular weight, molecular weight distribution, or degree of branching in the polypropylene raw material can be adopted.

[0097] The content of polypropylene resin C in the raw materials for the polypropylene film of the present invention is preferably 0.10% by mass or more, based on 100% by mass of the polypropylene film. The content of polypropylene raw material C is more preferably 0.15% by mass or more, even more preferably 0.20% by mass or more, and even more preferably 0.50% by mass or more. The content of polypropylene raw material C is preferably 10% by mass or less, more preferably 4.5% by mass or less, and even more preferably 3.0% by mass or less. When the content of polypropylene resin C is within the above range, it is possible to prevent spherulite size from becoming too large when the molten polymer is formed into a sheet, and to maintain high-temperature withstand voltage.

[0098] The method for producing the polypropylene film of the present invention using the raw materials described above will be explained in more detail below, but the present invention should not be construed as being necessarily limited thereto.

[0099] The polypropylene resin as described above can be melt-extruded onto a support to form an unstretched polypropylene film.

[0100] The polypropylene raw material is melt-extruded from a single-screw extruder set at an extrusion temperature of preferably 220°C to 280°C, more preferably 230°C to 270°C, and then passed through a filtration filter. The extruded molten sheet is then extruded through a slit-shaped die at a temperature of preferably 200°C to 260°C, more preferably 210°C to 240°C. The molten sheet extruded from the slit-shaped die is solidified on a casting drum (cooling drum) controlled at a temperature of 30°C to 110°C, resulting in an unstretched polypropylene film. The molten sheet can be adhered to the casting drum using any of the following methods: electrostatic application, adhesion using the surface tension of water, air knife, press roll, underwater casting, and air chamber. The air knife method is preferred because it provides good flatness and allows control of surface roughness. It is also preferable to appropriately adjust the position of the air knife so that air flows downstream of the film production process to prevent vibration of the film. The temperature of the casting drum is more preferably 60°C or higher and 110°C or lower, and even more preferably 80°C or higher and 110°C or lower, from the viewpoint of improving element processability and voltage resistance by minimizing surface depressions and providing moderate slipperiness when formed into a film.

[0101] A biaxially oriented polypropylene film can be obtained by biaxially stretching an unstretched polypropylene film, heat treating it, and relaxing it.

[0102] The biaxial stretching method can be any of inflation simultaneous biaxial stretching, tenter simultaneous biaxial stretching, and tenter sequential biaxial stretching, but among these, sequential biaxial stretching using a tenter is preferred from the viewpoint of controlling the film formation stability, crystalline / amorphous structure, surface properties, and particularly the mechanical properties and thermal dimensional stability while increasing the stretch ratio in the width direction of the present invention. In sequential biaxial stretching, an unstretched polypropylene film is stretched in the longitudinal direction and then in the width direction.

[0103] In the longitudinal stretching process, multi-stage stretching, consisting of preliminary stretching and main stretching, is preferably performed. The unstretched polypropylene film is preheated by passing it between rolls maintained at a temperature of preferably 70°C to 150°C, more preferably 80°C to 145°C, and then pre-stretched in the longitudinal direction at a magnification of 1.01 to 1.10 times. This allows for moderate spherulite destruction in the unstretched sheet, pre-orienting the molecular chains, thereby further enhancing the crystallite size, crystalline orientation, and amorphous chain constraint of the stretched film obtained after the subsequent main stretching. This improves the film's withstand voltage and ensures a stable structure even in high-temperature environments.

[0104] Subsequently, the polypropylene film pre-stretched in the longitudinal direction is stretched between rolls maintained at a temperature of preferably 70°C or more and 150°C or less, more preferably 80°C or more and 145°C or less, preferably 2.0 times or more and 15.0 times or less, more preferably 4.5 times or more and 12.0 times or less, and even more preferably 5.5 times or more and 10.0 times or less, in the longitudinal direction, and then cooled to room temperature.

[0105] Next, the film is introduced into a tenter while both widthwise ends of the uniaxially stretched film are held with clips. In the present invention, the temperature in the preheating step immediately prior to widthwise stretching is preferably the widthwise stretching temperature +5 to +15°C, more preferably +5 to +12°C, and even more preferably +5 to +10°C. This is because the fibril structure highly oriented in the longitudinal direction by uniaxial stretching can be further strengthened and the change in breakdown voltage before and after film heating can be suppressed. Furthermore, the temperature conditions described above are also preferred from the viewpoint of improving thermal dimensional stability by stabilizing insufficiently oriented molecular chains after uniaxial stretching with high-temperature preheating. By setting the preheating temperature at the stretching temperature +5°C or higher, the change in breakdown voltage before and after film heating can be suppressed, effectively improving thermal dimensional stability. On the other hand, by setting the preheating temperature at the stretching temperature +15°C or lower, film tearing during the stretching step can be suppressed.

[0106] The film is then stretched in the width direction while the edges of the film are held with clips, at a temperature of preferably 150°C or higher and 170°C or lower, more preferably 155°C or higher and 165°C or lower.

[0107] From the viewpoint of suppressing the change in breakdown voltage before and after heating the film, the widthwise stretching ratio is preferably 11.0 times or more and 20.0 times or less. By setting the widthwise stretching ratio to 11.0 times or more, more preferably 11.5 times or more, and even more preferably 12.0 times or more, the contribution of the highly longitudinally oriented fibril structure obtained by uniaxial stretching is reduced, thereby effectively suppressing the change in breakdown voltage before and after heating the film. By increasing the widthwise stretching ratio, orientation is imparted in the widthwise direction while maintaining a high longitudinal orientation state, thereby increasing in-plane molecular chain tension and further improving structural stability against heat. Therefore, setting the widthwise stretching ratio as described above is preferable from the viewpoint of obtaining the effect of improving the heat shrinkage properties, which are a trade-off. On the other hand, setting the widthwise stretching ratio to 20.0 times or less, more preferably 19.0 times or less, and even more preferably 18.0 times or less can reduce film breakage during film formation.

[0108] In the production of the polypropylene film of the present invention, the areal stretching ratio is preferably 65 or more. The areal stretching ratio is the longitudinal stretching ratio multiplied by the widthwise stretching ratio. By setting the areal stretching ratio to 65 or more, more preferably 66 or more, even more preferably 68 or more, and even more preferably 72 or more, the change in breakdown voltage before and after heating the film can be suppressed, and when used as a capacitor, it can be made to have excellent reliability for long-term use in high-temperature environments.

[0109] In the production of the polypropylene film of the present invention, in the subsequent heat treatment and relaxation treatment steps, the film is heat-set (first-stage heat treatment) at a temperature of 145°C to 165°C, which is lower than the width-direction stretching temperature (first-stage heat treatment temperature), while being tension-held in the width direction with clips and relaxing by 2% to 20%. Thereafter, the film is again heat-set (second-stage heat treatment) at 135°C or higher, lower than the heat-setting temperature (first-stage heat treatment temperature), while being tension-held again with clips in the width direction, and then heat-set (third-stage heat treatment) at 80°C or higher, lower than the heat-setting temperature (second-stage heat treatment temperature), while being tension-held. This multi-stage heat treatment is preferred from the viewpoints of suppressing the change in breakdown voltage before and after heating the film, improving structural stability against heat, and obtaining high voltage resistance and reliability when made into a capacitor.

[0110] In the relaxation treatment, the relaxation rate is preferably 2% or more and 20% or less from the viewpoint of enhancing structural stability against heat. By setting the relaxation rate to 20% or less, more preferably 18% or less, and even more preferably 15% or less, it is possible to prevent excessive slack in the film inside the tenter, which can cause wrinkles in the product and lead to unevenness during vapor deposition. It is also possible to prevent a decrease in mechanical properties. On the other hand, by setting the relaxation rate to 2% or more, more preferably 5% or more, and even more preferably 8% or more, structural stability against heat is obtained, and when used as a capacitor, it is possible to prevent a decrease in capacity and short-circuit damage in high-temperature environments.

[0111] After undergoing a multistage heat treatment to lower the temperature, the film is led to the outside of the tenter, where the clips on both ends in the width direction of the film are released in a room temperature atmosphere, the film edges are slit in a winder process, and a film product roll with a film thickness of 0.5 μm or more and less than 10 μm is wound up. Here, before winding the film, it is preferable to perform a corona discharge treatment in air, nitrogen, carbon dioxide gas, or a mixture of these gases to improve the adhesion of the vapor-deposited metal to the surface to be vapor-deposited.

[0112] Specific examples of preferred production conditions to be focused on in order to obtain the polypropylene film of the present invention are as follows. The melt extrusion temperature should be lowered in multiple stages: before the filter, after the filter, and at the die. The mesopentad fraction of polypropylene resin A must be 0.970 or more. The CXS of polypropylene resin A is less than 3.0% by mass. -Preliminary stretching must be performed at a ratio of 1.01 to 1.10 before longitudinal stretching. The area stretching ratio is 65 times or more. The stretch ratio in the width direction is 11.0 times or more. The preheating temperature before stretching in the width direction must be +5 to +15°C higher than the stretching temperature in the width direction. The first heat treatment temperature is between 145°C and 165°C, and is lower than the width direction stretching temperature. The second heat treatment temperature must be 135°C or higher and lower than the first heat treatment temperature. The third heat treatment temperature must be at least 80°C and lower than the second heat treatment temperature. In the first heat treatment process, the fabric is relaxed by 2% to 20% in the width direction.

[0113] Next, a metal film laminated film using the polypropylene film of the present invention, a film capacitor using the same, and methods for producing them will be described.

[0114] The metal film-laminated film of the present invention has a metal film on at least one side of the polypropylene film of the present invention. This metal film-laminated film can be obtained by providing a metal film on at least one side of the polypropylene film of the present invention described above.

[0115] In the present invention, the method for applying the metal film is not particularly limited. For example, a preferred method is to deposit a metal film, such as a vapor-deposited film of aluminum or an aluminum-zinc alloy, on at least one side of the polypropylene film to form an internal electrode of the film capacitor. In this case, other metal components, such as nickel, copper, gold, silver, or chromium, can be deposited simultaneously with or sequentially to the aluminum. A protective layer, such as oil, can also be deposited on the vapor-deposited film. If the surface roughness of the polypropylene film differs between the front and back, it is preferable to deposit a metal film on the smoother surface to form a metal film-laminated film, from the viewpoint of improving voltage resistance.

[0116] In the present invention, if necessary, after forming the metal film, the metal film laminated film can be annealed at a specific temperature or heat treated. Furthermore, at least one side of the metal film laminated film can be coated with a resin such as polyphenylene oxide for insulation or other purposes.

[0117] The film capacitor of the present invention is formed using the metal film laminated film of the present invention, that is, the film capacitor of the present invention has the metal film laminated film of the present invention.

[0118] For example, the film capacitor of the present invention can be obtained by laminating or winding the metal film laminated film of the present invention by various methods. A preferred example of a method for producing a wound type film capacitor is as follows.

[0119] Aluminum is vapor-deposited under reduced pressure on one side of a polypropylene film. This is done in stripes with margins running longitudinally. Next, a blade is used to slit the center of each vapor-deposited area and the center of each margin on the surface, creating a tape-like take-up reel with a margin on one side of the surface. Two tape-like take-up reels with a left or right margin are stacked and wound together so that the vapor-deposited area extends beyond the margin in the width direction, producing a wound body.

[0120] When vapor deposition is performed on both sides, one side is vapor deposited in stripes with a margin running in the longitudinal direction, and the other side is vapor deposited in stripes so that the longitudinal margin is located in the center of the vapor deposition area on the back side. Next, a blade is cut into the center of the margin on each side to create a tape-like take-up reel with a margin on one side on each side (for example, if there is a margin on the right side of the front side, there will be a margin on the left side on the back side). One resulting reel and one unvaporized laminated film are overlapped and wound together so that the metallized film extends beyond the laminated film in the width direction, to obtain a wound body.

[0121] The core material is removed from the wound body prepared as described above and pressed, and metallikon is sprayed onto both end surfaces to form external electrodes. Lead wires are welded to the metallikon to obtain a wound film capacitor. Film capacitors have a wide range of uses, including railroad cars, automobiles (hybrid cars, electric cars), solar power generation, wind power generation, and general home appliances, and the film capacitor of the present invention can be suitably used for these applications. The polypropylene film of the present invention can also be used in a variety of applications, such as packaging film, release film, processing film, sanitary products, agricultural products, construction products, and medical products, and is particularly suitable for applications that involve a heating process in film processing. [Example]

[0122] The present invention will be described in more detail below with reference to examples.

[0123] [Measurement and evaluation method] The methods for measuring the characteristic values ​​and evaluating the effects in the present invention are as follows.

[0124] (1) Film thickness The thickness of ten randomly selected points on the polypropylene film was measured using a contact-type electronic micrometer (K-312A model) manufactured by Anritsu Corporation in an atmosphere of 23°C and 65% RH. The arithmetic mean value of the thicknesses at the ten points was taken as the film thickness of the polypropylene film.

[0125] (2) Crystal orientation of the (110) plane of the α crystal after heating The film was heat-treated at 125°C for 60 minutes using a 20mm-wide square metal frame with a thickness of 2mm, outer dimensions of 300mm x 300mm, and inner dimensions of 280mm x 280mm, cut out from the center. Double-sided tape (Nichiban "Nice Tack" (registered trademark) NW-H15 adhesive strength 02) was applied to all four sides of the frame, and the film was attached so that it covered the entire metal frame. The film was then sandwiched between metal frames of the same dimensions. The film was attached carefully to prevent wrinkles. Next, a sample was created by clamping the four sides of the frame in the metal frame / double-sided tape / film / metal frame configuration with clips, and the sample was placed in an oven heated to 125°C for 60 minutes. The sample was then removed and left at room temperature for 5 minutes. The film was then cut along the inner edge of the metal frame, and the film was heat-treated at 125°C. After heat treatment at 125°C, the film was cut into strips 4 cm long and 1 mm wide, and these were stacked to a thickness of 1 mm to prepare a sample. The film sample was placed between the X-ray source and detector so that the X-rays would penetrate the polypropylene film, and the X-rays were incident perpendicular to the film surface. The crystal peak at 2θ = approximately 14° (α crystal (110) plane) was scanned in the circumferential direction to obtain the half-width H (°) ​​of the orientation peak, and the following formula was used to calculate the orientation peak. Crystal orientation = (180°-H) / 180° The measurement equipment and conditions are shown below.

[0126] (Measuring equipment) X-ray diffractometer: Rigaku Corporation, Model 4036A2 X-ray source: CuKα ray (using Ni filter) Output: 40kV-30mA Goniometer: Rigaku Corporation, Model 2155D Slit: 2mmφ-1°-1° Detector: Scintillation counter Counting and recording device Rigaku Corporation RAD-C type (Measurement conditions) Circumferential scan (2θ=approx. 14°) Scanning method: Step scan Measurement range: 0~360° Step: 0.5° Accumulation time: 2 seconds.

[0127] (3) Stress of the heated film when elongated by 5% in the longitudinal direction (F5MD) and stress of the heated film when elongated by 5% in the transverse direction (F5TD) The film was heat-treated at 150°C for 10 minutes using a 20mm-wide square metal frame with a thickness of 2mm, outer dimensions of 300mm x 300mm, and inner dimensions of 280mm x 280mm. Double-sided tape (Nichiban "Nice Tack" (registered trademark) NW-H15 adhesive strength 02) was applied to all four sides of the frame, and the film was attached so that it covered the entire metal frame. The film was then sandwiched between metal frames of the same dimensions. The film was attached carefully to prevent wrinkles. Next, a sample was created by clamping the four sides of the metal frame / double-sided tape / film / metal frame combination with clips and placing it in an oven heated to 150°C for 10 minutes. The sample was then removed and left at room temperature for 5 minutes. The film was then cut along the inner edge of the metal frame to obtain the film after heat treatment at 150°C. The film after heat treatment at 150°C was cut into a rectangle measuring 50mm long and 10mm wide in the test direction to obtain a sample. Next, the film was placed in a tensile tester (Orientec Tensilon UCT-100) for rectangular samples with an initial chuck distance of 20 mm and subjected to a tensile test at a tension rate of 300 mm / min in a 23°C atmosphere. The load applied to the film when the sample was 5% elongated was read and divided by the cross-sectional area of ​​the sample before the test (film thickness x width (10 mm)) to calculate the stress at 5% elongation (F5 value, unit: MPa). Measurements were performed five times for each sample in the longitudinal and transverse directions, and the average values ​​were calculated to calculate F5MD and F5TD, respectively. The film thickness used to calculate the F5 value was the value measured in (1) above.

[0128] (4) Melting peak temperature (Tm) and crystallization peak temperature (Tc) of polypropylene resin and film Using a differential scanning calorimeter (Seiko Instruments EXSTAR DSC6220), 3 mg of polypropylene film was heated in a nitrogen atmosphere from 30°C to 260°C at a rate of 20°C / min. It was then held at 260°C for 5 minutes and then cooled to 30°C at a rate of 20°C / min. The endothermic peak temperature obtained during the heating process was defined as the melting peak temperature of the polypropylene film, and the exothermic peak temperature obtained during the cooling process was defined as the crystallization peak temperature of the polypropylene film. In this specification, Tm and Tc were calculated from the average values ​​obtained from three measurements. Two or more peak temperatures may be observed within the temperature range, or a peak temperature observable on a multi-stage DSC chart called a "shoulder" (observed when two or more peaks overlap) may occur. However, in the present invention, the temperatures of the peaks with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart were defined as Tm and Tc, respectively. The (Tm) and (Tc) of polypropylene resins were also measured in the same manner.

[0129] (5) Skewness (Ssk) of the surface protrusion shape Skewness (Ssk) is defined in ISO 25178. Measurements were taken using a VS1540 scanning white light interference microscope manufactured by Hitachi High-Tech Science Corporation. The attached analysis software was used to remove waviness components from the captured image using polynomial fourth-order approximation surface correction, and then processed with a median (3 x 3) filter. After that, interpolation processing was performed, i.e., pixels for which height data could not be obtained were supplemented with height data calculated from surrounding pixels. Measurements were taken at five randomly selected locations on one surface, and the average value was calculated. Measurements were taken on both sides of the film. The measurement conditions are as follows: Manufacturer: Ryoka Systems Co., Ltd. Distributor: Hitachi High-Tech Science Corporation Device name: Scanning white light interference microscope VS1540 Measurement conditions: 10x objective lens 1x telescope tube Zoom lens 1x Wavelength filter 530nm white Measurement mode: Wave Measurement software: VS-Measure Version 10.0.4.0 Analysis software: VS-Viewer Version 10.0.3.0 Measurement area: 0.561mm x 0.561mm.

[0130] (6) Cold xylene soluble portion of film (CXS) 0.5 g of the raw material polypropylene resin, or the film sample, was dissolved in 100 ml of xylene at 135°C and allowed to cool. After allowing to stand for 1 hour in a constant temperature water bath at 20°C to recrystallize, the polypropylene components dissolved in the filtrate were quantified using liquid chromatography. The amount of polypropylene components dissolved in the filtrate was determined by the following formula, where X (g) is the amount of polypropylene components dissolved in the filtrate and X0 (g) is the precise weight of 0.5 g of sample. CXS(mass%)=(X / X0)×100 was calculated from

[0131] (7) Height of protruding peaks on the film surface (SpkA), (SpkB) The protruding peak height (Spk) is defined in ISO 25178. Measurements were performed using a VS1540 scanning white light interference microscope manufactured by Hitachi High-Tech Science Corporation. The attached analysis software was used to remove waviness components from the captured image using a polynomial fourth-order approximation surface correction, and then processed with a median (3 x 3) filter, followed by interpolation (a process in which pixels for which height data could not be obtained are supplemented with height data calculated from surrounding pixels). Measurements were taken at five arbitrary points on one surface, and the average value was calculated. Both sides of the film were measured, and the value of the surface with the lowest value was designated SpkA, and that of the opposite surface was designated SpkB. The measurement conditions were the same as those for (5) above, Degree of bias of surface protrusion shape.

[0132] (8) The total volume of valleys with a depth of 20 nm or more on the film surface The measurements were carried out using a VS1540 scanning white light interference microscope manufactured by Hitachi High-Tech Science Corporation. The attached analysis software was used to remove waviness components from the image captured using a polynomial 4th order approximation surface correction, then processed with a median (3 x 3) filter, followed by interpolation, i.e., pixels for which height data could not be obtained were supplemented with height data calculated from surrounding pixels. Analysis was then carried out using the bearing function, an analysis tool in the analysis software. To specify valley-side voids with a depth of 20 nm or more, the valley-side height threshold was set to -20 nm in the height region specification. The volume value of the analyzed valleys that met this threshold was then read. Five 0.561 x 0.561 mm samples were randomly selected on one surface. 2 The measurement was carried out in the area, and the average value of the total volume in the area was taken as the total volume of valleys with a depth of 20 nm or more on the film surface.

[0133] Both sides of the film are measured, and the total volume of the valleys on one side is 50 to 5,000 μm 3 If the value falls within the range, the value of the surface that falls within the range. If both surfaces are within the range, the value of the surface with the smaller value. If neither surface is within the range, the total valley volume is 50 to 5,000 μm 3 The measurement conditions were the same as those for (5) Degree of bias of surface asperity shape above.

[0134] (9) Heat shrinkage in the width direction after heat treatment at 125°C for 15 minutes HS125TD Five samples, each 200 mm long and 10 mm wide, were cut out so that the long side was the width direction of the film. Marks were made 25 mm from both ends, and the distance between the marks was measured using a universal projector to determine the test length (L1). A 3 g load was then applied to one end (the bottom end) of the test piece in the longitudinal direction, and the piece was heated in a suspended state in an oven maintained at 125°C for 15 minutes. The test piece was then removed and cooled at room temperature. The distance between the previously marked marks (L2) was measured using a universal projector, and the heat shrinkage (HS125TD) of each sample was calculated using the following formula. The arithmetic average of the five samples was calculated as the heat shrinkage (HS125TD) in the measurement direction. HS125TD={(L1-L2) / L1}×100 Here, HS125TD: Heat shrinkage rate (%) in the width direction after heat treatment at 125°C for 15 minutes L1: Distance between gauge lines before heat treatment (150 mm) L2: The distance between the gauge lines after heat treatment.

[0135] (10) Static friction coefficient (μ s ) Measurements were made at 25°C and 65% RH using a slip tester manufactured by Toyo Seiki Co., Ltd. in accordance with JIS K 7125 (1999). The measurements were made in the longitudinal direction of the films, with different surfaces overlapping each other. The same measurement was made five times for each sample, and the average value of the obtained values ​​was calculated to determine the static friction coefficient (μ s ) was decided.

[0136] (11) Mesopentad fraction The raw material was polypropylene resin, and the film sample was freeze-pulverized to powder form, extracted with n-heptane at 60°C for 2 hours to remove impurities and additives in the polypropylene, and then dried under reduced pressure at 130°C for 2 hours or more to obtain the sample. The sample was dissolved in a solvent and 13 The mesopentad fraction (mmmm) was determined using C-NMR under the following conditions.

[0137] Measurement conditions Equipment: Bruker DRX-500 Measurement nuclei: 13 C nucleus (resonance frequency: 125.8MHz) ·Measurement concentration: 10% by mass Solvent: Benzene: deuterated orthodichlorobenzene = 1:3 mixed solution (volume ratio) ·Measurement temperature: 130℃ Spin speed: 12Hz NMR sample tube: 5mm tube Pulse width: 45° (4.5μs) Pulse repetition time: 10 seconds Data points: 64K Accumulation count: 10,000 times Measurement mode: complete decoupling.

[0138] The analysis was performed as follows. Fourier transformation was performed with LB (line broadening factor) set to 1, and the mmmm peak was set to 21.86 ppm. Peak splitting was performed using WINFIT software (Bruker). Peak splitting was performed as follows, starting from the peak on the high magnetic field side. Further automatic fitting was performed using the software to optimize the peak splitting, and the sum of the mmmm peak fractions was determined as the mesopentad fraction (mmmm). (1) mrrm (2), (3) rrrm (split into two peaks) (4)rrrr (5) mrmr (6)mrmm+rmrr (7) mmrr (8)rmmr (9) mmmr (10) mmmm The same measurement was carried out five times for the same sample, and the average value of the obtained mesopentad fractions was taken as the mesopentad fraction of the sample.

[0139] (12) Breakdown voltage at 130°C (V / μm) After heating the film for 1 minute in an oven maintained at 130°C, measurements were made in that atmosphere in accordance with JIS C2330(2014)6.2 and the JIS C2151(2019) 17.2 B method (plate electrode method) cited therein. However, for the lower electrode, a conductive rubber (E-100 manufactured by Togawa Rubber Co., Ltd.) of the same dimensions was placed on the aluminum foil described in JIS C2151(2019) 17.2.2 Figure 3-C. <65> The breakdown voltage test was performed 30 times, and the obtained value was divided by the film thickness (measured in (1) above) to convert it into units of V / μm. Of the 30 measured values ​​(calculated values), the five largest and five smallest values ​​were excluded, and the average of the remaining 20 values ​​was taken as the film breakdown voltage at 130°C.

[0140] (13) Molecular weight and molecular weight distribution of polypropylene resin and film Evaluation and calculation were performed using GPC (gel permeation chromatography) under the following equipment and measurement conditions. Sample pretreatment was performed under the following measurement conditions: the sample was weighed, a solvent (1,2,4-TCB with 0.1% BHT added) was added, and the sample was dissolved by shaking at 140°C for 1 hour. Next, the sample was heated and filtered using a sintered filter with a pore size of 0.5 μm, and fractionated by molecular size.

[0141] <Apparatus and measurement conditions> Instrument: HLC-8321GPC / HT (Detector: RT) Column: TSKgel guard column H HR (30)HT(7.5mmI.D.×7.5mm)×1 piece +TSKgel GMH HR -H(20)HT (7.8mm I.D. x 30cm) (Tosoh Corporation) x 3 Eluent: 1,2,4-trichlorobenzene (Fujifilm Wako Pure Chemical Industries, Ltd., GPC grade) + BHT (0.05%) ·Flow rate: 1.0mL / min. Detection condition: polarity=(-) ·Injection volume: 0.3mL Column temperature: 140℃ System temperature: 40°C Sample concentration: 1mg / mL 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 Z+1 average molecular weight (M z+1 ), weight average molecular weight (Mw) and number average molecular weight (Mn) were obtained. z+1 and the molecular weight distribution (M z+1 / Mw) was calculated.

[0142] (14) Evaluation of film capacitor characteristics (voltage resistance at 120°C, reliability, processability) Aluminum was vapor-deposited on one side of the film using a vacuum vapor deposition machine (ULVAC, Inc.), and a vapor deposition pattern with a film resistance of 10 Ω / sq and a margin section in the direction perpendicular to the longitudinal direction, known as a T-shaped margin (longitudinal pitch (period) of 17 mm, fuse width of 0.5 mm), was formed using masking oil. Note that when the wetting tension differed between the front and back sides, vapor deposition was performed on the side with the higher wetting tension.

[0143] The film on which the vapor deposition pattern was formed was slit to obtain a vapor deposition reel with a film width of 50 mm and an edge margin width of 2 mm.

[0144] Next, the capacitor element was wound using this reel on an element winding machine (KAW-4NHB manufactured by Kaito Seisakusho Co., Ltd.), and after applying metallicon, it was heat-treated at 128°C under reduced pressure for 12 hours, and lead wires were attached to complete the capacitor element.

[0145] Using 10 of the capacitor elements thus obtained, a so-called step-up test was conducted in which a voltage of 250 VDC was applied to the capacitor elements at a high temperature of 120°C, and after 10 minutes at that voltage, the applied voltage was gradually increased in steps of 50 VDC / minute, and this process was repeated.

[0146] <Voltage resistance evaluation> In the step-up test, the change in capacitance was measured and plotted on a graph. The voltage at which the capacitance reached 80% of the initial value was divided by the film thickness (above (1)) to determine the withstand voltage, which was then evaluated as follows: S: The withstand voltage is 400V / μm or more. A: The withstand voltage is 390V / μm or more and less than 400V / μm. B: The withstand voltage is 380 V / μm or more and less than 390 V / μm. C: The withstand voltage is less than 380 V / μm. S, A, and B are usable. C is inferior in practical performance.

[0147] <Reliability evaluation> After increasing the voltage until the capacitance was reduced to 15% or less of the initial value, the capacitor element was disassembled to check the state of breakdown, and the reliability was evaluated as follows. S: There is no change in the element shape, and no penetration damage is observed. A: There is no change in the element shape, but penetration damage is observed through 1 to 5 layers of film. B: There is no change in the element shape, and penetration damage is observed through 6 to 10 film layers. C: Changes in the element shape are observed, or breakage that penetrates more than 10 layers is observed, or the element shape changes significantly and breaks. S can be used without any problems, A and B can be used depending on the conditions, and C has poor practical performance.

[0148] <Processability evaluation> The evaluation was based on the following criteria: Capacitor elements were prepared in the same manner as above, and the shapes of the elements were visually confirmed. S: No misalignment, wrinkles, or deformation of the film on the end surface of the capacitor element, and no problems with subsequent processes A: The capacitor element is not deformed, and although there are slight wrinkles, it can still be used without any problems. B: The capacitor element is slightly deformed and wrinkled, but still usable. C: The capacitor element is severely deformed and wrinkled, causing problems in subsequent processes. S and A can be used without any problems, B can be used depending on the conditions, and C is difficult to put into practical use.

[0149] [Polypropylene raw material] The raw materials used in the production of the polypropylene films of the Examples and Comparative Examples were listed in Table 1 below. Four types of polypropylene raw material A (A1, A2, A3, A4), three types of polypropylene raw material B (B1, B2, B3), and two types of polypropylene raw material C (C1: Ziegler-Natta catalyst system, C2: metallocene catalyst system) were used.

[0150] [Example 1] The raw materials and film-forming conditions used in this example are as shown in Tables 1 and 2. First, 93 parts by mass of polypropylene raw material A1, 4 parts by mass of polypropylene raw material B1, and 3 parts by mass of polypropylene raw material C1 were dry-blended. The blended raw materials were fed into a single-screw extruder at 260°C, melted, passed through a filtration filter, passed through a pipe set at 255°C, and melt-extruded into a sheet from a T-slit die set at 250°C. This sheet was placed on a casting drum maintained at 99°C, adhered with an air knife, and cooled and solidified to obtain an unstretched polypropylene film. The unstretched polypropylene film was preheated to 143°C in stages using multiple rolls, passed between rolls with different peripheral speeds, pre-stretched 1.08 times at 130°C, and then stretched 6.1 times in the longitudinal direction at 143°C. The film was then introduced into a tenter, where it was preheated at 169°C (TD stretching temperature +7°C) while both widthwise ends of the film were held with clips, and then stretched 12.3 times in the width direction at a temperature of 163°C. The first heat treatment was then carried out at 159°C while providing 15% relaxation in the width direction, and the second heat treatment was carried out at 150°C while both widthwise ends of the film were held with clips in the width direction. The third heat treatment was carried out at 111°C, after which the film was introduced to the outside of the tenter, the clips on the film ends were released, and then a current of 25 W·min / m was applied to the film surface (the side that contacts the casting drum). 2 The polypropylene film was wound into a film roll with a film thickness of 2.3 μm. The evaluation results for each item are shown in Table 4.

[0151] [Examples 2 to 9, Comparative Examples 1 to 7] Polypropylene films having the thicknesses shown in Tables 2 and 3 were obtained in the same manner as in Example 1, except that the raw material compositions and film-forming conditions were as shown in Tables 2 and 3. The thickness was adjusted by increasing or decreasing the rotation speed of the single-screw extruder. The same applies to the other Examples and Comparative Examples below. The evaluation results for each item are shown in Tables 4 to 6.

[0152] [Table 1]

[0153]

Table 2

[0154]

Table 3

[0155]

Table 4

[0156]

Table 5

[0157]

Table 6

Claims

1. A polypropylene film in which, when the polypropylene film is heated at 125°C for 60 minutes, it has a crystal orientation of 0.73 or more in the α crystal (110) plane, as measured by wide-angle X-ray diffraction; and the sum of the stress at 5% elongation in the longitudinal direction of the film (F5MD) when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature, and the stress at 5% elongation in the width direction of the film (F5TD) when the film is heated at 150°C for 10 minutes and then subjected to a tensile test at room temperature, is 150 MPa or more.

2. 2. The polypropylene film according to claim 1, wherein the melting peak temperature (Tm) of the film obtained by heating the film from 30°C to 260°C at 20°C / min using a differential scanning calorimeter (DSC) and the crystallization peak temperature (Tc) obtained by cooling the film from 260°C to 30°C at 20°C / min satisfy the following relationship: Tm-Tc≦65(℃)

3. The polypropylene film according to claim 1 or 2, wherein the skewness (Ssk) defined by ISO 25178 on at least one surface of the film is greater than -30 and less than 5.

4. 4. The polypropylene film according to claim 1, wherein when the polypropylene film is completely dissolved in xylene and then precipitated at room temperature, the polypropylene component (CXS) dissolved in xylene is 3.0 mass% or less.

5. The polypropylene film according to any one of claims 1 to 4, wherein the protruding peak heights SpkA and SpkB defined in ISO 25178 of the surface A on one side and the surface B on the other side satisfy the following relationship. SpkA<SpkB 20 nm≦SpkA≦100 nm 80 nm≦SpkB≦150 nm where: SpkA: height of protruding peak on surface A SpkB: height of protruding peak on surface B

6. On at least one surface, the total volume of valleys with a depth of 20 nm or more in an area of ​​0.561 mm x 0.561 mm measured by a scanning white light interference microscope is 50 μm ３ 5,000 μm or more ３ The polypropylene film according to any one of claims 1 to 5, wherein:

7. The polypropylene film according to any one of claims 1 to 6, having a heat shrinkage rate in the width direction (HS125TD) after heating at 125°C for 15 minutes of 1.0% or less.

8. The polypropylene film according to any one of claims 1 to 7, wherein the static friction coefficient (μs) when the films are stacked is 0.2 or more and less than 0.

8.

9. A metal film laminated film having a metal film on at least one surface of the polypropylene film according to any one of claims 1 to 8.

10. A film capacitor comprising the metal film laminated film according to claim 9.

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