Polypropylene film

Abstract

The polypropylene film has a layer A when a layer containing a cyclic olefin resin and a polypropylene resin is denoted as the layer A and a cross-section X when the polypropylene film is cut along a plane parallel to the main orientation axis direction and the thickness direction is denoted as the cross-section X, and the orientation parameter I810 / I840 of the cross-section X measured by Raman spectroscopy is 2.2-20. The present application addresses the problem of providing a polypropylene film which has excellent processability in a high-temperature environment, has high withstand voltage characteristics regardless of the use temperature, and has excellent reliability when made into a thin-film capacitor.

Description

Technical Field

[0001] The present invention relates to polypropylene films which are particularly suitable for use in film capacitor applications. Background Art

[0002] In recent years, most of the various electrical equipment have been converted to inverters, and with this, the demand for miniaturization and high capacity of film capacitors has further increased. In particular, in the fields of automobiles (including electric vehicles and hybrid vehicles), electric aircraft, solar power generation and wind power generation, affected by this demand, in addition to the requirements for improving voltage resistance, productivity and maintaining processing adaptability in the production of film capacitor elements, further thinning and improving heat resistance are required for film used in film capacitors.

[0003] Among polyolefin films, polypropylene films have excellent heat resistance and voltage resistance. When applied to the above fields, it is important for the film to have excellent dimensional stability at the ambient temperature of use and stable electrical properties (voltage resistance, etc.) in a temperature range 10°C to 20°C higher than the ambient temperature of use. Here, from the perspective of heat resistance, when considering the use of power semiconductors using silicon carbide (SiC) in the future, it is believed that the ambient temperature of use will become higher.

[0004] Based on this background, film capacitors are required to have further improved heat resistance and withstand voltage, and films for film capacitors are required to have improved dielectric breakdown voltage in a high temperature environment exceeding 110° C. However, as described in Non-Patent Document 1, the upper limit of the operating temperature of polypropylene films is considered to be about 110° C., and it is extremely difficult for polypropylene films to stably maintain withstand voltage in such a temperature environment.

[0005] In order to miniaturize film capacitors and improve heat resistance, it is conceivable to use thinner films, films with higher relative dielectric constants, or films with glass transition temperatures exceeding the ambient temperature range for use of film capacitors.

[0006] For example, a laminated body has been proposed, which has a laminated structure formed by alternating two layers with different relative dielectric constants, one of which uses a cyclic olefin resin with a glass transition temperature exceeding 130°C, and the other uses a polypropylene layer, so that it has heat resistance and voltage resistance and can maintain a large electrostatic capacitance (for example, Patent Document 1). In addition, a film with improved processability by coextrusion and costretching when forming a laminated body of a cyclic olefin resin and polypropylene has been proposed (for example, Patent Documents 2 and 3). Furthermore, a film with improved thermal dimensional stability in a high temperature environment by blending a cyclic olefin resin with a polypropylene resin and performing film formation and biaxial stretching has been proposed (for example, Patent Document 4).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2015-012076

[0010] Patent Document 2: International Publication No. 2017 / 022706

[0011] Patent Document 3: Japanese Patent Application Publication No. 2018-034510

[0012] Patent Document 4: Japanese Patent Application No. 2020-521867

[0013] Non-patent literature

[0014] Non-patent document 1: Motobu Kawai, "Film capacitors leap forward from automobiles to energy", Nikkei Electronics, Nikkei BP, September 17, 2012, pp. 57-62 Summary of the invention

[0015] Problems to be solved by the invention

[0016] However, the film of patent document 1 is not a laminate based on co-extrusion, but a laminate with a cyclic olefin resin layer formed on a polypropylene film by a coating method. Therefore, the cyclic olefin resin layer is easy to peel off, and it is difficult to say that the processability under high temperature environment, the performance and reliability when made into a film capacitor are sufficient. The base layer of the laminated structure of the film of patent document 2 is also the cyclic olefin resin itself. Therefore, it is difficult to increase the area stretching ratio, the voltage resistance under high temperature environment is insufficient, etc., and it is difficult to say that the performance and reliability when made into a film capacitor are sufficient. The base layer of the laminated structure of the film of patent document 3 is also a cyclic olefin resin, and an elastomer is contained to improve the stretchability to increase the area stretching ratio, but the voltage resistance under high temperature environment is not satisfactory. It is difficult to say that the performance and reliability when made into a film capacitor are sufficient. The film of patent document 4 is a film formed by blending only cyclic olefin resin and polypropylene resin, so it is difficult to increase the area stretching ratio. Therefore, the voltage resistance under high temperature environment is insufficient, etc., and it is difficult to say that the performance and reliability when made into a film capacitor are sufficient. In addition, by increasing the preheating temperature and stretching temperature during width direction stretching, stretching can be performed at a high area stretching ratio. However, the withstand voltage of the film stretched at a high temperature decreases significantly when heated from room temperature to a high temperature, and there is also the problem of unstable characteristics when used as a thin film capacitor.

[0017] Therefore, an object of the present invention is to provide a polypropylene film which has excellent processability in a high temperature environment, has high withstand voltage characteristics regardless of the use temperature, and has excellent reliability when used as a film capacitor.

[0018] Means for solving problems

[0019] The present inventors have repeatedly conducted intensive studies to solve the above-mentioned problems and have invented a polypropylene film, wherein, when a layer containing a cyclic olefin resin and a polypropylene resin is referred to as an A layer and a cross section when the polypropylene film is cut along a plane parallel to the main orientation axis direction and the thickness direction is referred to as a cross section X, the film has the A layer, and the orientation parameter I810 / I840 of the cross section X measured by Raman spectroscopy is greater than or equal to 2.2 and less than or equal to 20.

[0020] Effects of the Invention

[0021] According to the present invention, it is possible to provide a polypropylene film which has excellent processability in a high temperature environment, has high withstand voltage characteristics regardless of the use temperature, and has excellent reliability when used as a film capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram shows a rectangle of 1 μm×2 μm in size defined so that a pair of short sides are parallel to the thickness direction in the cross section X of the polypropylene film of the present invention, and a structural domain of the cyclic olefin-based resin passing through a pair of sides of the rectangle parallel to the thickness direction.

[0023] Figure 2 The TEM observation images (magnification 20,000 times) of the A layer portion of the cross section X of the polypropylene film involved in one embodiment of the present invention (the polypropylene film of Example 5) are obtained by performing the treatment described up to ii) of (16) (left) and the image obtained by performing the treatment described up to v) of (16) (right). DETAILED DESCRIPTION

[0024] The present inventors have repeatedly conducted in-depth studies to solve the above-mentioned problems, and believe that the following are the reasons why the films described in the above-mentioned Patent Documents 1 to 4 have insufficient dielectric breakdown voltage in a high temperature environment, voltage resistance characteristics in a high temperature environment when made into film capacitors, reliability, and processability in a high temperature environment.

[0025] The film of Patent Document 1 is an unstretched film laminated by a coating method, so it is believed that there are the following problems: interlayer peeling occurs in a high temperature environment; the mechanical properties, especially the elongation at break, are insufficient, and it is easy to break during the processing of the film capacitor element; the withstand voltage in a high temperature environment is reduced. Regarding the films of Patent Documents 2 and 3, if the withstand voltage in a high temperature environment is assumed, it is believed that the ratio of longitudinal stretching in the film making is insufficient, and there are a large number of movable amorphous components in the film, so there is a problem of low insulation breakdown voltage at high temperature. For the film of Patent Document 4, if the withstand voltage in a high temperature environment is assumed, it is believed that it is difficult to fully increase the ratio of longitudinal stretching in the film making due to the insufficient mixing of cyclic olefin resin and polypropylene resin, and there is a problem of low insulation breakdown voltage at high temperature due to the presence of a large number of movable amorphous components in the film. In addition, by raising the preheating temperature and stretching temperature during the width direction stretching, it is possible to stretch at a high area stretching ratio, but it is believed that the film stretched at a high temperature has a large decrease in withstand voltage when heated from room temperature to high temperature, and there is a problem of unstable characteristics when used as a film capacitor.

[0026] Based on the above considerations, the present inventors have further conducted repeated studies and invented a polypropylene film that solves the above problems. The polypropylene film of the present invention has the above-mentioned A layer, when the layer containing the cyclic olefin resin and the polypropylene resin is referred to as the A layer, and the cross section when the polypropylene film is cut along a plane parallel to the main orientation axis direction and the thickness direction is referred to as the cross section X, and the orientation parameter I810 / I840 of the above-mentioned cross section X measured by Raman spectroscopy analysis is 2.2 or more and 20 or less.

[0027] Hereinafter, the polypropylene film of the present invention will be specifically described. It should be noted that, when the upper limit and the lower limit are recorded respectively for the preferred range below, the combination can be arbitrary. Herein, the polypropylene film refers to a sheet-like molded body with polypropylene resin as the main component, and the main component refers to a component containing more than 50% by mass and less than 100% by mass when all the components constituting the film are set to 100% by mass. It should be noted that, when a plurality of components equivalent to polypropylene resin are included in the film, even if each component is less than 50% by mass, as long as the total of these components exceeds 50% by mass, it is regarded as a film with polypropylene resin as the main component.

[0028] The polypropylene resin refers to a resin containing more than 50 mol % and 100 mol % or less of propylene units when all structural units constituting the resin are taken as 100 mol %, and does not belong to a cyclic olefin-based resin.

[0029] Cyclic olefin resin refers to a polyolefin resin containing 10 mol% or more and 100 mol% or less of cyclic olefin units when all structural units constituting the resin are set to 100 mol%. It should be noted that, for a resin containing multiple structural units equivalent to cyclic olefin units, even if the individual cyclic olefin units are less than 10 mol%, as long as the total of these structural units is 10 mol% or more, it is considered to belong to the cyclic olefin resin.

[0030] In addition, the polypropylene film is sometimes referred to as film below. It should be noted that the polypropylene film of the present invention is not a microporous film and therefore does not have a large number of pores. That is, the polypropylene film of the present invention refers to a polypropylene film other than a microporous film. Here, the microporous film is defined as a film having a pore structure that penetrates both surfaces of the film and having a permeability of 5000 seconds / 100 ml or less of 100 ml of air measured by a B-type Gray tester of JIS P 8117 (1998) at a temperature of 23°C and a relative humidity of 65%.

[0031] The main orientation axis direction in the polypropylene film of the present invention is described below. The main orientation axis direction refers to the direction in which the molecular chain orientation of the polypropylene resin is the largest in the film surface. When biaxial stretching is performed in the manufacture of the polypropylene film, it is usually stretched in the length direction and the width direction. Generally speaking, the direction with a large stretching ratio is the main orientation axis direction. The stretching direction (length direction and width direction) can be determined, but when the ratio is unknown, the maximum load until breakage is measured in each direction in the tensile test at 23°C described later, and the direction with a large measured value can be taken as the main orientation axis direction.

[0032] As described above, when there is a certain degree of difference in stretching ratio, the main orientation axis direction can be easily determined as long as the stretching direction and stretching ratio are known. However, in the case of films where these are unknown or films where the stretching ratios in both directions are approximately equal, the main orientation axis direction can be determined by the following method. Specifically, a rectangle of 50 mm in length and 10 mm in width is cut out as a sample. <1> , the sample <1> The direction of the long side is defined as 0°. Next, rectangular samples of the same size are collected in such a way that the long side direction becomes a direction rotated 15° to the right from the 0° direction. <2> , similarly, the rectangular sample is collected by rotating the long side of the rectangular sample by 15° each time. <3> ~ <12> . Next, each rectangular sample is placed in a tensile testing machine with an initial distance between clamps of 20 mm in a manner such that the long side direction is the tensile direction (measurement direction), and the tensile test is performed at a tensile speed of 300 mm / min at room temperature. At this time, the maximum load until the sample breaks is read, and it is divided by the cross-sectional area of ​​the sample before the test (film thickness × width), and the calculated value is used as the stress of the maximum point strength. The long side direction of the sample with the largest value is used as the main orientation axis direction of the polypropylene film, and the direction perpendicular to it in the film surface is used as the direction perpendicular to the main orientation axis of the polypropylene film.

[0033] In the case where the width of the sample is less than 50 mm and the above-mentioned tensile test cannot be performed, the crystal orientation of the α crystal (110) plane based on wide-angle X-rays can be measured as follows, and the main orientation axis direction can be determined based on the following judgment criteria. That is, X-rays (CuKα rays) can be incident in a direction perpendicular to the film surface, and the crystal peak of 2θ=about 14° (α crystal (110) plane) can be scanned in the circumferential direction. The direction with the highest diffraction intensity in the obtained diffraction intensity distribution is taken as the main orientation axis direction, and the direction perpendicular to it in the film surface is taken as the direction perpendicular to the main orientation axis direction.

[0034] In the polyolefin film of the present invention, the layer containing the cyclic olefin resin and the polypropylene resin is recorded as the A layer, and the cross section when the polypropylene film is cut along the plane parallel to the main orientation axis direction and the thickness direction is recorded as the cross section X, and the A layer is present, and the orientation parameter I810 / I840 of the cross section X measured by Raman spectroscopy is greater than 2.2 and less than 20. Here, the thickness direction refers to the direction perpendicular to the film surface. By making the orientation parameter I810 / I840 of the cross section X within this range, a polypropylene film with a small decrease in withstand voltage when heated from room temperature to high temperature can be obtained. It should be noted that the orientation parameter I810 / I840 of the polypropylene film is sometimes referred to as I810 / I840 below.

[0035] I810 / I840 is a parameter that reflects the tension state of the polypropylene chain in the polypropylene film. The higher it is, the more it can suppress the relaxation of the polypropylene chain in a high temperature environment and the resulting reduction in withstand voltage. When I810 / I840 is less than 2.2, the polypropylene chain in the polypropylene film relaxes by heating, resulting in a problem of reduced withstand voltage when the film capacitor is made in a high temperature environment. From the viewpoint of suppressing the reduction in withstand voltage of the polypropylene film when heated from room temperature to high temperature, I810 / I840 is preferably 2.8 or more, more preferably 3.5 or more, further preferably 4.2 or more, particularly preferably 4.7 or more, and most preferably 5.0 or more. On the other hand, as mentioned above, the higher I810 / I840, the better, but from the viewpoint of feasibility, I810 / I840 is 20 or less, preferably 15 or less, more preferably 10 or less, and further preferably 7.0 or less.

[0036] I810 / I840 can be measured by polarized light Raman measurement (measured using polarized light with a beam diameter of 1 μm and parallel to the main orientation axis) from the surface of the polypropylene film using Raman spectroscopy. It should be noted that the measurement position is the central position in the thickness direction of the polypropylene film, and the details of the measurement device, method, etc. will be described later.

[0037] As a method for making the I810 / I840 of the polypropylene film containing the cyclic olefin resin be 2.2 or more and 20 or less, there is no particular limitation. For example, it is effective to manufacture the polypropylene film by a sequential biaxial stretching method, make the stretching ratio in the width direction 8.5 times or more, and stretch the width direction by the following two-stage stretching method (I). In addition, it is also effective to use a polypropylene resin with high stereoregularity and melting point (for example, a polypropylene resin with a high meso pentad fraction and a high melting point). It should be noted that these methods can be used in combination as appropriate.

[0038] The two-stage stretching method (I) is a stretching method in which the second stage stretching is performed after the first stage stretching described below. That is, the two-stage stretching method (I) is a method in which a total of a×b times stretching is performed in the first stage stretching and the second stage stretching (both described below).

[0039] 2-stage stretching method (I):

[0040] First stage stretching: When the final stretching ratio in the width direction is represented by a×b times, stretching is performed in the width direction at a stretching ratio of a times at a temperature of 160°C to 185°C (the lower limit is preferably 170°C and the upper limit is preferably 180°C).

[0041] Second stage stretching: The film is further stretched in the width direction at a stretching ratio of b times at a temperature 1°C to 20°C lower than the temperature in the first stage stretching.

[0042] From the viewpoint of improving I810 / I840, the difference between the second stretching temperature and the first stretching temperature is more preferably 5°C or more, and from the viewpoint of improving film forming properties, it is more preferably 10°C or less. It should be noted that the "final stretch ratio in the width direction" refers to the stretch ratio immediately after the second stretching is completed (i.e., the ratio change caused by the relaxation treatment is not taken into account).

[0043] The polypropylene film of the present invention preferably has a length in the main orientation axis direction of the cyclic olefin resin domain in section X of 5.0 μm or more and 1 mm or less. By making the length in the main orientation axis direction of the cyclic olefin resin domain in section X to be 5.0 μm or more, the morphological stability of the film capacitor when used for a long time at high temperature can be improved. From the viewpoint of morphological stability when the film capacitor is used for a long time at high temperature, the length in the main orientation axis direction of the cyclic olefin resin domain in section X is as long as possible, and is 1 mm or less, preferably 30 μm or less, from the viewpoint of achievability. From the viewpoint of improving the morphological stability (reliability) of the film capacitor when used for a long time at high temperature and improving the life, the length in the main orientation axis direction of the cyclic olefin resin domain in section X is more preferably 7.0 μm or more, further preferably 10.0 μm or more, and particularly preferably 10.5 μm or more.

[0044] As a method for controlling the length of the main orientation axis direction of the structural domain of the cyclic olefin resin in the cross section X to be 5.0 μm or more and 1 mm or less, there is no particular limitation, and a method of stretching in a sequential biaxial stretching manner so that the stretching ratio in the width direction is 8.0 times or more, preferably 8.5 times or more is effective. Here, the above-mentioned structural domain length can be measured by an image of the cross section X obtained using a transmission electron microscope (TEM), and its details are described later.

[0045] The polypropylene film of the present invention preferably has a structure in which a cyclic olefin resin diffuses into a sea portion of the polypropylene resin in the A layer portion of the cross section X (hereinafter sometimes referred to as a diffusion structure). Such a diffusion structure is observed as a brightness intermediate between the cyclic olefin resin and the polypropylene resin when the A layer portion of the cross section X is observed using a TEM, the cyclic olefin resin being observed in black, and the polypropylene resin being observed in white. Here, having a "diffusion structure" in the A layer portion of the cross section X means that the proportion of the number of pixels with a brightness of 255 when the observed image of the A layer portion of the cross section X is binarized using the method described later is 0.01% or more of all pixels. It should be noted that, hereinafter, "pixels with a brightness of 255 when the observed image of the A layer portion of the cross section X is binarized using the method described later" is sometimes referred to as white pixels in the A layer portion after binarization.

[0046] When the polypropylene film of the present invention has such a diffusion structure, the relaxation of the molecular chain of the polypropylene resin generated when used for a long time in a high temperature and high voltage environment can be suppressed. Therefore, when such a polypropylene film is used as a dielectric of a thin film capacitor, the reduction in the reliability of the thin film capacitor can be easily reduced. From the above viewpoint, the proportion of white pixels in the A layer portion after binarization is preferably 5% or more of all pixels, and more preferably 15% or more. On the other hand, from the viewpoint of improving thermal stability and voltage resistance through domain structure and the viewpoint of feasibility, the proportion of white pixels in the A layer portion after binarization is preferably 50% or less.

[0047] The method for forming such a diffusion structure in the A layer portion of the polypropylene film of the present invention is not particularly limited, and the following method can be cited: after setting the ratio of the cyclic olefin resin to the polypropylene resin in the A layer to the range described below, stretching is performed by a sequential biaxial stretching method at an appropriate area stretching ratio described below, and stretching is performed in the width direction (transverse stretching) at a temperature 5° C. or higher than the glass transition temperature of the cyclic olefin resin used.

[0048] The dielectric loss tangent of the polypropylene film of the present invention is preferably 3×10 -6 Above and 1×10 -2 From the viewpoint of suppressing heat generation when using a polypropylene film as a dielectric of a film capacitor and improving the reliability of the film capacitor, the dielectric loss tangent is preferably 1×10 -2 Less than, more preferably 1×10 -3 Below, more preferably 5×10 -4 Below, particularly preferably 3×10 -4 On the other hand, from the above viewpoint, the lower the dielectric loss tangent, the better, but from the viewpoint of feasibility, it is preferably 3×10 -6 More preferably, 1×10 -5 The dielectric loss tangent of the polypropylene film can be measured in accordance with JIS C2138-2007, and the details thereof will be described later.

[0049] The dielectric loss tangent of the polypropylene film of the present invention is controlled to be 3×10 -6 Above and 1×10 -2 The following method is not particularly limited, and is effective for reducing the content of components other than polypropylene contained in the polypropylene film. In particular, when the mass of the entire film is set to 100 mass%, the content of the component is preferably 40 mass% or less, more preferably 30 mass% or less, further preferably 20 mass% or less, particularly preferably 9.5 mass% or less, and most preferably 9.0 mass% or less.

[0050] The polypropylene film of the present invention preferably has 2.0 or more and 1000 or less domains of the cyclic olefin resin passing through a pair of short sides in a rectangle of 1 μm×2 μm determined in the A layer portion of the cross section X so that the pair of short sides are parallel to the thickness direction. Hereinafter, a method for determining a rectangle of 1 μm×2 μm in the cross section X so that the pair of short sides are parallel to the thickness direction in the polypropylene film of the present invention and a method for determining the number of domains of the cyclic olefin resin passing through a pair of short sides of the rectangle will be described with reference to the accompanying drawings (details of observation conditions in TEM, etc. will be described later).

[0051] Figure 1 This is a schematic diagram showing a rectangle of 1 μm×2 μm in size defined so that a pair of sides are parallel to the thickness direction in the cross section X of the polypropylene film of the present invention, and a structural domain of a cyclic olefin-based resin passing through a pair of short sides of the rectangle. Figure 1 The reference numerals 1 to 5 in the figure respectively represent a part of the cross section X, a sea part, an island part (structural domain), a rectangle of 1 μm×2 μm determined in the cross section X with a pair of sides parallel to the thickness direction, and a pair of short sides of the rectangle. Figure 1 The left figure is a part of the cross section X, and the right figure is an enlarged view of a rectangle indicated by a dotted line of 1 μm×2 μm in cross section X, which is determined in such a way that a pair of short sides are parallel to the thickness direction. It should be noted that in the polypropylene film of the present invention, the sea portion is a polypropylene resin and the island portion is a cyclic olefin resin.

[0052] When a rectangle of 1 μm × 2 μm is defined in the cross section X so that a pair of short sides are parallel to the thickness direction, the bottom of the rectangle is set as the sea portion. If a domain is located on the side opposite to the bottom, it is considered that there is no domain and it is not counted as the number (in Figure 1 In the example above, no such domain exists).

[0053] Here, "the domain of the cyclic olefin resin passing through a pair of short sides parallel to the thickness direction" means the domain of the cyclic olefin resin passing through a pair of short sides parallel to the thickness direction at the same time. Figure 1 In the example (right figure), the 1st, 5th and 7th domains from the top belong to this structural domain, and the 2nd to 4th and 6th domains from the top do not belong to this structural domain. Therefore, there are 3 "structural domains of cyclic olefin-based resins through a pair of short sides parallel to the thickness direction" in this example.

[0054] By making the number of structural domains of such cyclic olefin resins more than 2.0, the cyclic olefin resins are micro-dispersed in a flatter shape in the plane. As a result, the polypropylene film can reflect the high thermal stability of the cyclic olefin resins and the high withstand voltage of the polypropylene resins, and the insulation breakdown voltage of the polypropylene film in a high temperature environment can be increased. Furthermore, when such a polypropylene film is used for a film capacitor, it is not easy to cause short-circuit damage even if used for a long time in a high temperature environment, and the withstand voltage of the film capacitor is maintained, and high reliability can be obtained.

[0055] The method for controlling the number of domains of such cyclic olefin resins within a suitable range is not particularly limited, for example, when the mass of the entire film is set to 100% by mass, on the basis of setting the content of cyclic olefin resins to 1.0% by mass or more and 30% by mass or less, in the process of extruding a resin composition comprising a polypropylene resin and a cyclic olefin resin, it is effective to set the temperature of the filter to be lower than the extrusion temperature and to perform biaxial stretching in a manner where the area stretching ratio reaches 40 times or more. The area stretching ratio is more preferably 45 times or more, more preferably 50 times or more, particularly preferably 54 times or more, and most preferably 60 times or more. In addition, it is also effective to pre-mix the polypropylene resin and the cyclic olefin resin before melting in the extruder to improve dispersibility. From the above viewpoints, in the polypropylene film of the present invention, the number of domains of such cyclic olefin resins is preferably 4.0 or more, more preferably 6.0 or more, and more preferably 7.0 or more. On the other hand, from the viewpoint of feasibility, the upper limit of the number of domains of the cyclic olefin resin is 1000, more preferably 20.

[0056] In the polypropylene film of the present invention, when the mass of the entire film is set to 100 mass%, the content of the cyclic olefin resin is preferably 1.0 mass% or more and 40 mass% or less. From the viewpoint of suppressing film cracking during stretching and improving productivity, and from the viewpoint of appropriately controlling the number of domains of the cyclic olefin resin passing through the pair of short sides, the content of the cyclic olefin resin in the polypropylene film is more preferably 30 mass% or less, further preferably 20 mass% or less, particularly preferably 9.5 mass% or less, and most preferably 9.0 mass% or less.

[0057] Generally, cyclic olefin resins are more expensive than polypropylene, so it is preferred in industry to obtain the prescribed effect with a lower content, especially 9.5% by mass or less. On the other hand, from the viewpoint of improving the heat resistance when used as a film capacitor, the content of cyclic olefin resin in the polypropylene film is more preferably 5.0% by mass or more. By controlling the content of cyclic olefin resin in the polypropylene film to be 1.0% by mass or more and 40% by mass or less or within the above preferred range, it is easy to obtain a polypropylene film that has high morphological stability when used for a long time at high temperature and high voltage, has high reliability when made into a film capacitor, and has excellent productivity.

[0058] From the viewpoint of improving the thermal dimensional stability at high temperature and improving the reliability of the film capacitor when used as the dielectric of the film capacitor, when all the constituent components of the A layer are set to 100% by mass, the content of the cyclic olefin resin in the A layer of the polypropylene film of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 4% by mass or more, and particularly preferably 7% by mass or more. On the other hand, from the viewpoint that the film cracking is not easy to occur when the area stretching ratio is increased during stretching, when all the constituent components of the A layer are set to 100% by mass, the content of the cyclic olefin resin in the A layer is preferably 38% by mass or less, more preferably 34% by mass or less, further preferably 25% by mass or less, particularly preferably 19.5% by mass or less, and most preferably 9.8% by mass or less. It should be noted that when the polypropylene film of the present invention is formed by stacking layers with different compositions of cyclic olefin resins, the layer with the largest content of cyclic olefin resins is the A layer.

[0059] From the viewpoint of suppressing film cracking when increasing the area stretch ratio, the polypropylene film of the present invention is preferably configured as a laminated structure in which a layer having a cyclic olefin resin content less than that of the A layer is laminated on at least one side of the outermost layer (hereinafter referred to as the B layer), and more preferably a structure in which the B layer is laminated on both sides. When the mass of the entire B layer is set to 100% by mass, the cyclic olefin resin content of the B layer is less than that of the A layer, preferably 3% by mass or less, more preferably 1% by mass or less, and most preferably the B layer does not contain a cyclic olefin resin. It should be noted that when the B layer is laminated on both sides, the composition of the B layer may be the same or different.

[0060] As the cyclic olefin resin contained in the polypropylene film of the present invention, cyclic olefin polymers and cyclic olefin copolymers can be preferably used. Among them, from the viewpoint of improving the compatibility with the polypropylene resin, it is more preferable to use a cyclic olefin copolymer obtained by copolymerizing a chain olefin monomer such as ethylene and propylene with a cyclic olefin such as norbornene, norbornadiene, tetracyclododecene and their derivatives.

[0061] The details of the cyclic olefin resin contained in the polypropylene film of the present invention are described below. Examples of cyclic olefin monomers that can be used to produce the cyclic olefin resin used in the polypropylene film of the present invention include monocyclic olefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, cyclopentadiene, and 1,3-cyclohexadiene; bicyclo[2,2,1]hept-2-ene, 5-methyl-bicyclo[2,2,1]hept-2-ene, 5,5-dimethyl-bicyclo[2,2,1]hept-2-ene, 5-ethyl-bicyclo[2,2,1]hept-2-ene, 5-butyl-bicyclo[2,2,1]hept-2-ene, 5-ethylidene-bicyclo[2,2,1]hept-2-ene, 5-hexyl-bicyclo[2,2,1]hept-2-ene, 5-octyl-bicyclo[2,2,1]hept-2-ene, 5-octadecyl-bicyclo[2,2,1]hept-2-ene, -bicyclo[2,2,1]hept-2-ene, 5-methylidene-bicyclo[2,2,1]hept-2-ene, 5-vinyl-bicyclo[2,2,1]hept-2-ene, 5-propenyl-bicyclo[2,2,1]hept-2-ene; tricyclo[4,3,0,12.5]dec-3,7-diene, tricyclo[4,3,0,12.5]dec-3-ene, tricyclo[4,3,0,12.5]undec-3,7-diene, tricyclo[4,3,0,12.5]undec-3,8-diene, tricyclo[4,3,0,12.5]undec-3-ene, 5-cyclopentyl-bicyclo[2,2,1]hept-2-ene, 5-cyclohexyl-bicyclo[2,2,1]hept-2-ene. tricyclic alkenes such as tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-methyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-ethyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-methylenetetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-ethylidenetetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-vinyltetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8- Tetracyclic olefins such as propenyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene and 8-cyclopentyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-cyclohexyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-cyclohexenyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, 8-phenyl-cyclopentyl-tetracyclo[4,4,0,12.5,17.10]dodec-3-ene, tetracyclo[7,4,13.6,01.9,02.7]tetradec-4,9,11,13-tetraene, tetracyclo[8,4,14.7,01.10,03.8] pentadeca-5,10,12,14-tetraene, pentacyclo[6,6,13.6,02.7,09.14]hexadec-4-ene, pentacyclo[6,5,1,13.6,02.7,09.13]pentadeca-4-ene, pentacyclo[7,4,0,02.7,13.6,110.13]pentadeca-4-ene, heptacyclo[8,7,0,12.9,14.7,111.17,03.8,012.16]eicos-5-ene, heptacyclo[8,7,0,12.9,03.8,14.7,012.17,113.16]eicos-14-ene, and polycyclic olefins such as tetramers such as cyclopentadiene. These cyclic olefin monomers can be used alone or in combination of two or more. .

[0062] As the cyclic olefin monomer, among the above, from the viewpoint of productivity and surface properties, it is preferred to use a tricyclic olefin having 10 carbon atoms such as bicyclo[2,2,1]hept-2-ene (hereinafter referred to as norbornene), a tricyclic olefin having 10 carbon atoms such as tricyclo[4,3,0,12.5]dec-3-ene (hereinafter referred to as tricyclodecene), a tetracyclic olefin having 12 carbon atoms such as tetracyclo[4,4,0,12.5,17.10]dodec-3-ene (hereinafter referred to as tetracyclododecene), cyclopentadiene, or 1,3-cyclohexadiene.

[0063] The cyclic olefin resin may be any of a resin obtained by polymerizing only the cyclic olefin monomer (hereinafter sometimes referred to as COP) and a resin obtained by copolymerizing the cyclic olefin monomer and a chain olefin monomer (hereinafter sometimes referred to as COC) as long as it satisfies the above definition.

[0064] Examples of methods for producing COP include known methods such as addition polymerization or ring-opening polymerization of cyclic olefin monomers, for example, methods of subjecting norbornene, tricyclodecene, tetracyclodecene and derivatives thereof to ring-opening metathesis polymerization followed by hydrogenation, methods of subjecting norbornene and derivatives thereof to addition polymerization, methods of subjecting cyclopentadiene and cyclohexadiene to 1,2 addition polymerization or 1,4 addition polymerization followed by hydrogenation, etc. Among these, methods of subjecting norbornene, tricyclodecene, tetracyclodecene and derivatives thereof to ring-opening metathesis polymerization followed by hydrogenation are more preferred from the viewpoint of productivity and moldability.

[0065] In the case of COC, preferred chain olefin monomers include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, etc. Among them, ethylene or both ethylene and propylene can be particularly preferably used from the viewpoint of productivity and cost. Examples of methods for producing a resin obtained by copolymerizing a cyclic olefin monomer and a chain olefin monomer include known methods such as addition polymerization of a cyclic olefin monomer and a chain olefin monomer. For example, examples include a method of addition polymerization of norbornene and its derivatives with ethylene.

[0066] Particularly from the viewpoint of productivity and moldability, a method of binary polymerization or ternary polymerization of norbornene, tetracyclododecene or their derivatives with ethylene and / or propylene can be used as a preferred method. That is, for example, a binary polymerization of a tetracyclododecene derivative with ethylene, and a ternary polymerization of norbornene with ethylene and propylene can be used as a preferred method.

[0067] The chain olefin monomer and the cyclic olefin monomer used to obtain the cyclic olefin copolymer may be one kind each, or one or both of them may be two or more kinds. Among them, from the viewpoint of improving the compatibility of the cyclic olefin resin and the polypropylene resin, it is particularly preferred to use a cyclic olefin copolymer having ethylene and propylene as structural units. As the cyclic olefin monomer, from the viewpoint of improving the heat resistance when making a capacitor, it is preferred to use a norbornene derivative, norbornadiene and its derivatives.

[0068] The crystallization temperature (Tmc) of the polypropylene film of the present invention during the cooling process measured by differential scanning calorimetry is preferably 110°C or more and 150°C or less, and Tmc is more preferably 112°C or more and 150°C or less. By making Tmc above 110°C, the film before stretching becomes a structure having a fine crystal structure, so that dense protrusions are formed on the surface of the polypropylene film after stretching, especially after biaxial stretching, and productivity is also improved. Through such protrusions, the polypropylene film has excellent withstand voltage at high temperatures. From the viewpoint of feasibility, the upper limit of Tmc is below 150°C. It should be noted that Tmc can be measured in accordance with JIS K7121-1987, and its details are described later.

[0069] The method for making Tmc be 110°C or higher is not particularly limited, and a method of making the polypropylene film contain a crystal nucleating agent that promotes the crystallization of the polypropylene resin can be cited. As the crystal nucleating agent that can be used in the polypropylene film of the present invention, sorbitol-based nucleating agents, 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonanol (nonitol)-based nucleating agents, amide-based nucleating agents, aromatic carboxylic acid metal salts, phosphoric acid metal salts, polypropylene resins having a crosslinked structure, branched polypropylene resins, etc. can be cited. From the viewpoint of suppressing film cracking during production caused by foreign matter, it is preferred to use branched polypropylene resins.

[0070] Here, the branched polypropylene resin refers to a polypropylene resin containing a polypropylene molecular chain having one or more side chains with a carbon number of 6 or more in the molecular chain. 13 C-NMR can confirm the presence of its branched structure. The branched polypropylene resin has a nucleating agent effect that accelerates crystallization when the molten polypropylene resin solidifies. Therefore, by containing a branched polypropylene resin, a more uniform crystallization of the film can be promoted, and it is easy to stretch at a high ratio while suppressing the formation of film cracks and voids during stretching.

[0071] From the viewpoint of obtaining the nucleating agent effect, the content of the branched polypropylene resin is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.3% by mass or more, based on the mass of the film being 100% by mass. On the other hand, from the viewpoint of reducing film cracking during extrusion that occurs with an increase in melt tension, the content of the branched polypropylene resin is preferably 50% by mass or less, more preferably 30% by mass or less, further preferably 10% by mass or less, and particularly preferably 7.0% by mass or less, based on the mass of the film being 100% by mass.

[0072] Examples of the branched polypropylene resin that can be used in the polypropylene film of the present invention include "Daploy" (registered trademark) WB135HMS manufactured by Borealis AG and "WAYMAX" (registered trademark) MFX6 manufactured by Nippon Polypro Corporation.

[0073] From the viewpoint of improving heat resistance and miniaturization of film capacitors, the thickness of the polypropylene film of the present invention is preferably 0.5 μm or more and 15 μm or less. From the above viewpoints, the thickness of the polypropylene film is more preferably 6.0 μm or less, further preferably 5.0 μm or less, particularly preferably 3.5 μm or less, and most preferably 3.0 μm or less. By making the thickness of the polypropylene film 15 μm or less, the effect of improving the heat resistance of the cyclic olefin resin can be increased, the withstand voltage under high temperature environment can be improved, and the size of the element when the film capacitor is made can be reduced. It should be noted that the thickness of the polypropylene film can be measured using a known electronic micrometer, and the details are described later.

[0074] From the viewpoint of improving processability, the tear strength in the direction perpendicular to the main orientation axis of the polypropylene film of the present invention / the tear strength in the direction of the main orientation axis (hereinafter sometimes referred to as the tear strength ratio) is preferably 0.10 or more and 10.0 or less. From the above viewpoint, the tear strength ratio is more preferably 0.40 or more, further preferably 0.50 or more, and particularly preferably 0.80 or more. By making the tear strength ratio 0.10 or more, it is easy to suppress the breakage when the polypropylene film is slit into a strip along the main orientation axis direction. The upper limit of the tear strength ratio is not particularly limited, but from the viewpoint of feasibility, it is preferably 10.0, more preferably 2.0.

[0075] The method for making the tear strength 0.10 or more is not particularly limited. When biaxial stretching is performed, it is effective to perform sequential stretching in a manner that the stretching ratio in the width direction is 3.0 times or less, preferably 2.0 times or less relative to the stretching ratio in the length direction, and to control the content of the cyclic olefin resin within the above-mentioned preferred range. It should be noted that the tear strength ratio can be measured according to JIS K 7128-2:1998 using a known tear tester, and the details are described later.

[0076] In the polypropylene film of the present invention, when the mass of the entire polypropylene film of the present invention is set to 100 mass%, the ash content is preferably 0.0ppm or more and 1000ppm or less. By controlling the ash content of the polypropylene film of the present invention within a suitable range, when used as a dielectric of a film capacitor, the reliability of the film capacitor can be improved. From the above viewpoint, the less ash content, the more preferred, more preferably 500ppm or less, further preferably 200ppm or less, particularly preferably 100ppm or less, and most preferably 55ppm or less. Theoretically, the ash content is 0.0ppm or more, and from the viewpoint of feasibility, it is preferably 10ppm or more.

[0077] The ash content can be measured according to JIS K7250-1: 2006, which will be described in detail later. The method for controlling the ash content to fall within the above-mentioned suitable range is not particularly limited, but it is effective to reduce the ash content of the polypropylene resin which is the main component for producing the polypropylene film of the present invention.

[0078] The polypropylene film of the present invention may contain various additives within the scope that does not impair the purpose of the present invention, such as organic particles, inorganic particles, crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, lubricants, antistatic agents, anti-blocking agents, fillers, viscosity modifiers, anti-coloring agents. It should be noted that these additives can be used alone or in combination, and in addition, when there are multiple layers, they can be added to any layer.

[0079] In the case where an antioxidant is contained in these additives, its type and addition amount are important from the viewpoint of long-term heat resistance of the polypropylene film. From the above viewpoint, as an antioxidant, it is preferred to use one or more sterically hindered phenolic antioxidants, preferably at least one of which is a high molecular weight antioxidant with a molecular weight of 500 or more. As a specific example, various examples can be cited, for example, preferably with 2,6-di-tert-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene (for example, BASF "Irganox" (registered trademark) 1330: molecular weight 775.2), or tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane (for example, BASF "Irganox" (registered trademark) 1010: molecular weight 1177.7) etc.

[0080] The total content of high molecular weight antioxidants with a molecular weight of 500 or more is preferably in the range of 0.1 to 1.0 parts by mass relative to the total amount of resin. When there is too little antioxidant, sometimes the long-term heat resistance is poor. When there is too much antioxidant, sometimes the film capacitor element is adversely affected by adhesion at high temperatures caused by the seepage of these antioxidants. From the above viewpoint, the more preferred content is 0.2 to 0.7 parts by mass relative to 100 parts by mass of the total mass of the resin, and more preferably 0.3 to 0.5 parts by mass. In the case where the polypropylene film is a stacked structure of more than two layers, from the viewpoint of suppressing defects such as fish eyes, improving quality, and withstand voltage performance, it is preferred that the high molecular weight antioxidant with a molecular weight of 500 or more in each layer is 0.3 to 0.5 parts by mass.

[0081] The polypropylene film of the present invention may include resins other than polypropylene resin and cyclic olefin resin within the scope of not damaging the purpose of the present invention. As specific resins, vinyl polymer resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, polycarbonate resins, etc., including various polyolefin resins, can be listed, and polymethylpentene, syndiotactic polystyrene, etc. are particularly preferably exemplified. When the resin component constituting the polypropylene film is set to 100% by mass as a whole, the content of these resins is preferably less than 3% by mass, more preferably less than 2% by mass, and further preferably less than 1% by mass. By controlling the content of the resin other than the polypropylene resin to less than 3% by mass, the influence of the domain interface can be suppressed, and the reduction of the insulation breakdown voltage under a high temperature environment can be reduced.

[0082] The polypropylene film of the present invention is preferably used as a dielectric for a film capacitor, but the type of film capacitor is not limited. Specifically, from the viewpoint of electrode composition, it can be any of a rolled film capacitor of metal foil and film and a metal vapor-deposited film capacitor. It is also preferably used for an oil-immersed film capacitor impregnated with insulating oil and a dry capacitor that does not use insulating oil at all. However, from the characteristics of the polypropylene film of the present invention, it is particularly preferably used as a metal vapor-deposited film capacitor. From the viewpoint of shape, it can be a winding type or a stacked type (the film capacitor of the present invention will be described later).

[0083] Polypropylene film generally has low surface energy and is difficult to stably deposit metal on. Therefore, in order to improve adhesion to the metal film, it is preferably subjected to surface treatment before deposition. Specific examples of surface treatment include corona discharge treatment, plasma treatment, glow treatment, and flame treatment.

[0084] The polypropylene film of the present invention can be obtained by using a resin composition containing a polypropylene resin as a main component and a cyclic olefin resin to obtain a polypropylene resin sheet, and then biaxially stretching, heat treating and relaxing the sheet. As a biaxial stretching method, the film can be obtained by any one of a simultaneous biaxial stretching method with an inflation machine, a simultaneous biaxial stretching method with a tenter machine, and a sequential biaxial stretching method with a tenter machine. Among them, the sequential biaxial stretching method with a tenter machine and the simultaneous biaxial stretching method with a tenter machine are preferably used in terms of improving the film forming stability, the crystallization / amorphous structure, the surface characteristics, and especially the stretching ratio of the present invention while controlling the mechanical characteristics and the thermal dimensional stability. From the viewpoint of making the I810 / I840 of the polypropylene film of the present invention fall within the above-mentioned preferred range, the sequential biaxial stretching method with a tenter machine is more preferably used.

[0085] Next, the preferred method for producing the polypropylene film of the present invention is described. The preferred method for producing the polypropylene film of the present invention comprises the following steps in sequence: a casting step of melt-extrude a resin composition containing a polypropylene resin and a cyclic olefin resin onto a support to prepare a polypropylene resin sheet; a stretching step of stretching the polypropylene resin sheet along the length direction and the width direction, and in the stretching step, the width direction is stretched by the following two-stage stretching method (I). It should be noted that having a casting step and a stretching step in sequence means that the casting step and the stretching step exist in sequence regardless of whether there are other steps upstream of the casting step, between the casting step and the stretching step, or downstream of the stretching step.

[0086] The manufacturing method comprises a casting step of melt-extrude a resin composition comprising a polypropylene resin and a cyclic olefin resin on a support to prepare a polypropylene resin sheet. The resin composition comprising a polypropylene resin and a cyclic olefin resin is not particularly limited as long as it is mainly composed of a polypropylene resin and contains a cyclic olefin resin. In order to improve the dispersibility of the cyclic olefin resin, it is preferred to use a mixed resin composition in which the cyclic olefin resin and the polypropylene resin are pre-mixed. The support is not particularly limited as long as it can cool and solidify the resin composition melt-extruded into a sheet to obtain a polypropylene resin sheet. For example, a cooling drum can be used.

[0087] In this production method, there is a stretching step of stretching the polypropylene resin sheet in the longitudinal direction and the width direction downstream of the casting step. "Stretching in the longitudinal direction and the width direction" includes any of a sequential biaxial stretching method in which stretching in the longitudinal direction is followed by stretching in the width direction, and a simultaneous biaxial stretching method in which stretching in the longitudinal direction and in the width direction is performed simultaneously. From the viewpoint of preferably controlling the temperature conditions in the stretching in the longitudinal direction and in the width direction, the sequential biaxial stretching method is preferred.

[0088] In the stretching step of the manufacturing method, the stretching in the width direction is performed by the following two-stage stretching method (I). By adopting such a stretching method, the orientation parameter I810 / I840 measured by Raman spectroscopy analysis of the cross section X can be easily controlled within a suitable range.

[0089] 2-stage stretching method (I):

[0090] First stage stretching: When the final stretching ratio in the width direction is represented by a×b times, stretching is performed in the width direction at a stretching ratio of a times at a temperature of 160°C to 185°C (the lower limit is preferably 170°C and the upper limit is preferably 180°C).

[0091] Second stage stretching: The film is further stretched in the width direction at a stretching ratio of b times at a temperature 1°C to 20°C lower than the temperature in the first stage stretching.

[0092] From the viewpoint of improving I810 / I840, the difference between the second stretching temperature and the first stretching temperature is more preferably 5°C or more, and from the viewpoint of improving film forming properties, it is more preferably 10°C or less. It should be noted that the "final stretch ratio in the width direction" refers to the stretch ratio immediately after the second stretching is completed (i.e., the ratio change caused by the relaxation treatment is not taken into account).

[0093] It should be noted that, when the two-stage stretching method (I) is adopted by simultaneous biaxial stretching, it is preferred to perform simultaneous biaxial stretching as the first stage stretching in a manner that the stretching in the width direction satisfies the conditions of the first stage stretching, and then perform stretching in the width direction as the second stage stretching in a manner that satisfies the conditions of the second stage stretching. Among them, the preferred temperature range for the first stage stretching by simultaneous biaxial stretching is 150° C. or more and 180° C. or less, and more preferably 165° C. or more and 180° C. or less.

[0094] In this production method, from the viewpoint of adjusting the number of domains of the cyclic olefin resin passing through a pair of short sides in a rectangle of 1 μm×2 μm defined in the A layer portion of the cross section X in a manner that the pair of short sides are parallel to the thickness direction to an appropriate range, the area stretching ratio is preferably 40 times or more. Here, the area stretching ratio refers to the stretching ratio in the length direction×the stretching ratio in the width direction.

[0095] Hereinafter, the method for producing the polypropylene film of the present invention will be described in more detail. However, the polypropylene film of the present invention is not limited to the polypropylene film obtained by the following method.

[0096] First, when producing the polypropylene film of the present invention, it is preferred to mix the cyclic olefin resin, the polypropylene resin and the antioxidant in advance from the viewpoint of improving the dispersion state of the cyclic olefin resin and the polypropylene resin and increasing the dielectric breakdown voltage of the obtained polypropylene film at high temperature.

[0097] The mixing can be performed using a single screw extruder, a twin screw extruder, etc., and from the viewpoint of achieving a good dispersion state, a twin screw extruder is particularly preferably used. From the viewpoint of making the dispersion state of the cyclic olefin resin and the polypropylene resin good and further improving the insulation breakdown voltage of the obtained polypropylene film at high temperature, the resin temperature during mixing is preferably controlled within the following temperature range. First, it is preferably 300°C or less, and more preferably 280°C or less. On the other hand, it is preferably 200°C or more, and more preferably 230°C or more.

[0098] When the entire mixed component is set to 100% by mass, the content of the cyclic olefin resin in the resin composition obtained by mixing is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 4% by mass or more, and particularly preferably 7% by mass or more. On the other hand, from the viewpoint of improving the dispersion state of the cyclic olefin resin, the content of the cyclic olefin resin in the mixed resin is preferably 49% by mass or less, more preferably 40% by mass or less.

[0099] When all the components in the resin raw material obtained by mixing are set to 100% by mass, the amount of the antioxidant is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.4% by mass or more. The upper limit is 1.0 parts by mass. In addition, by making the meso pentad fraction of the polypropylene resin 0.960 or more, the melting point of the obtained polypropylene film is high, which is suitable for use at high temperatures, and is therefore preferred.

[0100] Next, the polypropylene resin and the resin composition obtained by mixing are supplied to a single screw extruder after the amount of cyclic olefin resin is adjusted to the desired level, and extruded into a sheet from a slit-shaped die after passing through a filter. At this time, the temperature of the filter is preferably in the range of more than -40 ° C of extrusion temperature and less than the extrusion temperature, more preferably more than -40 ° C of extrusion temperature and less than -20 ° C of extrusion temperature. By controlling the temperature of the filter within this range, it is easy to control the number of domains of the cyclic olefin resin passing through a pair of short sides within a suitable range. Then, the molten sheet extruded from the slit-shaped die is solidified on a casting drum (cooling drum) that has been temperature controlled to obtain a polypropylene resin sheet.

[0101] As described above, from the viewpoint of increasing the area stretch ratio, the polypropylene film of the present invention is preferably a laminated structure. In this case, as a raw material for the A layer, a polypropylene resin is mixed with a resin composition obtained by mixing and supplied to a single screw extruder, and as a raw material for the B layer, a polypropylene resin is supplied to another single screw extruder. Then, the molten resin is laminated into a two-layer structure of A layer / B layer or a three-layer structure of B layer / A layer / B layer by a feed block method using melt co-extrusion, extruded from a slit-shaped die into a sheet, and solidified on a temperature-controlled cooling drum to obtain an unstretched polypropylene film.

[0102] Regardless of whether the structure is a single layer or a laminated structure, the temperature of the cooling drum is preferably 10° C. to 110° C., more preferably 10° C. to 95° C., from the viewpoint of appropriately controlling crystal growth and cooling and solidifying the molten resin.

[0103] As a method for making the molten sheet close to the cooling drum, any method among the electrostatic application method, the close bonding method using the surface tension of water, the air knife method, the pressure roller method, the underwater casting method, the air chamber method, etc. can be used. The air knife method with good planarity and controllable surface roughness is preferred. In addition, in order not to generate vibration of the film, it is preferred to appropriately adjust the position of the air knife in a manner that the air flows on the downstream side of the film. It should be noted that the air temperature of the air knife also depends on the temperature of the cooling drum, preferably above 5°C and below 130°C. From the viewpoint that the surface properties of the two sides of the obtained polypropylene film will not be greatly different, it is more preferred that the absolute value of the difference with the temperature of the cooling drum does not exceed 50°C.

[0104] Next, the polypropylene resin sheet is biaxially stretched to make it biaxially oriented. During stretching, the polypropylene resin sheet is brought into contact with a roller set to a predetermined longitudinal stretching temperature, and stretched at a predetermined ratio in the longitudinal direction. From the viewpoint of suppressing film cracking, the stretching temperature in the longitudinal direction is preferably above 100°C, more preferably above 120°C, and further preferably above 140°C. On the other hand, it is preferably below 170°C, more preferably below 165°C, and further preferably below 160°C. In addition, from the viewpoint of increasing the area stretching ratio and increasing the insulation breakdown voltage at high temperature, the stretching ratio in the longitudinal direction is preferably 3.5 times or more, more preferably 4.0 times or more, further preferably 5.0 times or more, and particularly preferably 5.2 times or more. On the other hand, from the viewpoint of suppressing film cracking, the stretching ratio in the longitudinal direction is preferably 10 times or less. After the polypropylene resin sheet is stretched in the longitudinal direction in this way, it is cooled to room temperature to obtain a uniaxially oriented polypropylene film.

[0105] The obtained uniaxially oriented polypropylene film is introduced into a tenter while holding both ends in the width direction with a clamp. Here, from the viewpoint of increasing the transverse stretching ratio, it is preferred that the tenter ambient temperature (preheating temperature in the width direction) of the preheating process for stretching in the width direction is set to the stretching temperature in the width direction + 5°C or more (the stretching temperature in the width direction mentioned here is set to the first stretching temperature in the case of adopting the two-stage stretching method (I) described later). On the other hand, from the viewpoint of suppressing the decrease in withstand voltage at high temperature, it is preferred that the preheating temperature in the width direction is set to the stretching temperature in the width direction + 15°C or less, more preferably + 12°C or less, and further preferably + 10°C or less. By controlling the temperature of the preheating process within the above range, the fibril structure highly oriented in the length direction by stretching in the length direction can be further strengthened, and the dielectric breakdown voltage of the obtained polypropylene film can be improved. In addition, from the viewpoint of being able to improve thermal dimensional stability, it is also preferred to stabilize the insufficiently oriented molecular chains by high-temperature preheating after uniaxial stretching.

[0106] Next, the preheated uniaxially oriented polypropylene film is stretched in the width direction while being held at both ends in the width direction by a clamp. From the viewpoint of uniformly stretching the cyclic olefin resin with a high glass transition temperature and improving the reliability of the film capacitor when used as a dielectric of the film capacitor, the tentering machine environment temperature (stretching temperature in the width direction) at this time is preferably above 150°C, more preferably above 155°C, and further preferably above 160°C. On the other hand, from the above viewpoint, the stretching temperature in the width direction is preferably below 190°C, more preferably below 185°C. It should be noted that when the two-stage stretching method (I) described later is adopted, it is preferred that the temperature conditions in the second stretching be set to the above range.

[0107] From the viewpoint of improving the dielectric breakdown voltage of the obtained polypropylene film, the stretching ratio in the width direction (the final stretching ratio when the width direction stretching is performed in multiple stages as in the case of the two-stage stretching method (I)) is preferably 8.5 times or more, more preferably 9.3 times or more, and further preferably 10.0 times or more. On the other hand, from the viewpoint of stably forming the film, the stretching ratio in the width direction is preferably 20.0 times or less, more preferably 17.0 times or less, and further preferably 15.0 times or less. By making the stretching ratio in the width direction 8.5 times or more, it is easy to make the length of the main orientation axis direction of the structural domain of the cyclic olefin resin be 5 μm or more.

[0108] It should be noted that the stretching in the width direction is preferably carried out at a temperature lower than the preheating temperature as described above, and is preferably carried out in a two-stage stretching mode (I) in which the first stage stretching and the second stage stretching are carried out in sequence. By adopting such a stretching mode, the orientation parameter I810 / I840 measured by Raman spectroscopy analysis of the cross section X can be easily controlled within a suitable range.

[0109] 2-stage stretching method (I):

[0110] First stage stretching: When the final stretching ratio in the width direction is represented by a×b times, stretching is performed in the width direction at a stretching ratio of a times at a temperature of 160°C to 185°C (the lower limit is preferably 170°C and the upper limit is preferably 180°C).

[0111] Second stage stretching: The film is further stretched in the width direction at a stretching ratio of b at a temperature 1°C to 20°C lower than the temperature in the first stage stretching.

[0112] From the viewpoint of improving I810 / I840, the difference between the second stretching temperature and the first stretching temperature is more preferably 5°C or more, and from the viewpoint of improving film forming properties, it is more preferably 10°C or less. It should be noted that the "final stretch ratio in the width direction" refers to the stretch ratio immediately after the second stretching is completed (i.e., the ratio change caused by the relaxation treatment is not taken into account).

[0113] From the viewpoint of stably forming the film, the stretching ratio a in the first stretching is preferably 1.8 times or more and 13.3 times or less, more preferably 1.8 times or more and 9.0 times or less. From the viewpoint of controlling I810 / I840 within a preferred range and suppressing the decrease in withstand voltage when used at high temperatures, the stretching ratio (b) in the second stretching is in the range of 1.1 times or more and 5.0 times or less, more preferably a>b.

[0114] Regarding the ratio of the stretching ratio in the width direction to the stretching ratio in the length direction, from the viewpoint of controlling I810 / I840 within the above range, the stretching ratio in the width direction is preferably 1.5 times or more relative to the stretching ratio in the length direction, and more preferably 1.7 times or more. On the other hand, sequential stretching in a manner in which the stretching ratio in the width direction is 3.0 times or less relative to the stretching ratio in the length direction is effective for further controlling the tear strength ratio within an appropriate range.

[0115] The area stretch ratio is preferably 40 times or more. By setting the area stretch ratio to 40 times or more, it is easy to control the number of domains of the cyclic olefin resin through a pair of short sides in the cross section X within a suitable range. As a result, the dielectric breakdown voltage of the obtained film, especially at high temperature, is high. In the present invention, the area stretch ratio refers to the value obtained by multiplying the stretch ratio in the length direction by the stretch ratio in the width direction. It should be noted that in the present invention, the stretch ratio in the width direction refers to the stretch ratio after the width direction is stretched and before the relaxation treatment is performed. From the above viewpoint, the area stretch ratio is more preferably 45 times or more, further preferably 50 times or more, particularly preferably 54 times or more, and most preferably 60 times or more. The upper limit of the area stretch ratio is not particularly limited, and from the viewpoint of feasibility, it is 90 times in the case of successive biaxial stretching and 150 times in the case of simultaneous biaxial stretching.

[0116] It is important for the polypropylene film of the present invention to improve I810 / I840 while containing a cyclic olefin resin. That is, in the production of the polypropylene film of the present invention, for example, the dispersibility of the cyclic olefin resin domain dispersed in the polypropylene resin is improved by pre-mixing, and by adopting the above-mentioned two-stage stretching method, a high area stretching ratio can be formed, thereby improving the withstand voltage at 135°C.

[0117] In the manufacture of the polypropylene film of the present invention, it is preferred to provide a heat treatment and relaxation treatment process after biaxial stretching. In this process, from the viewpoint of improving the reliability when the film capacitor is made, it is preferred to give 2 to 30% relaxation in the width direction while the width direction is tightly held by a clamp, and heat treatment is performed at a temperature of 150°C or more and 190°C or less at the ambient temperature of the tenter, more preferably 150°C or more and 164°C or less, and further preferably 150°C or more and 159°C or less. In addition, when the polypropylene film is made into a film capacitor for use, from the viewpoint of improving the reliability of the film capacitor, the relaxation treatment rate is preferably 5% or more, more preferably 7% or more, further preferably 9% or more, and particularly preferably 13% or more. On the other hand, from the viewpoint of improving the dielectric breakdown voltage of the polypropylene film, the relaxation treatment is more preferably 25% or less, and further preferably 18% or less.

[0118] After heat treatment and relaxation treatment, the polypropylene film is introduced to the outside of the tenter, and the clamps at both ends in the width direction are loosened at room temperature. Then, the edge of the film is slit in the winding process, and the polypropylene film is wound into a roll. Here, before the polypropylene film is wound, in order to improve the adhesion of the vapor-deposited metal, it is preferred to perform a surface treatment such as corona discharge treatment on at least one side in air, nitrogen, carbon dioxide gas, or a mixed gas thereof.

[0119] It should be noted that, in order to obtain the polypropylene film of the present invention, the manufacturing conditions of interest are specifically listed as examples as follows. It should be noted that it is preferred to satisfy all of these manufacturing conditions, but it is not necessary to have all of them, and they can be appropriately combined. For example, "In the sequential biaxial stretching, the preheating temperature before stretching in the width direction is the stretching temperature in the width direction + 5°C or more and + 15°C or less." Simultaneous biaxial stretching can also be used instead.

[0120] The meso pentad fraction of the polypropylene resin as the main component is 0.960 or more.

[0121] Contains a cross-linked polypropylene resin or a branched polypropylene resin.

[0122] · Pre-mix the cyclic olefin resin and the polypropylene resin.

[0123] · Make the extruder filter temperature lower than the extrusion temperature.

[0124] The content of the cyclic olefin-based resin is set to 1% by mass or more and 40% by mass or less.

[0125] The area stretching ratio of the biaxial stretching is set to 40 times or more.

[0126] The stretching ratio in the width direction is set to 8.5 times or more.

[0127] The stretching ratio in the width direction is 1.5 times or more and 3.0 times or less, preferably 1.7 times or more and 3.0 times or less, relative to the stretching ratio in the longitudinal direction.

[0128] In the sequential biaxial stretching, the preheating temperature before the stretching in the width direction is the stretching temperature in the width direction + 5°C to the stretching temperature in the width direction + 15°C.

[0129] Stretching in the width direction is performed by the above-mentioned two-stage stretching method (I).

[0130] After biaxial stretching, heat treatment and relaxation treatment are performed.

[0131] The heat treatment temperature after biaxial stretching is 150°C or higher.

[0132] Next, a metal film laminated film formed using the polypropylene film of the present invention, a thin film capacitor formed using the metal film laminated film, and methods for producing the metal film laminated film will be described.

[0133] 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. The 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.

[0134] In the present invention, the method of imparting the metal film is not particularly limited. For example, it is preferred to use a method in which aluminum, an alloy of aluminum and zinc, etc. are vapor-deposited on at least one side of a polypropylene film to form a metal film such as a vapor-deposited film that becomes an internal electrode of a film capacitor. In this case, other metal components such as nickel, copper, gold, silver, chromium, etc. may also be vapor-deposited simultaneously or sequentially with aluminum. In addition, a protective layer may also be provided on the vapor-deposited film using oil or the like. When the surface roughness of the polypropylene film is different on the front and back sides, it is preferred to provide a metal film on the surface side with a relatively small roughness to form a metal film laminated film from the viewpoint of improving the withstand voltage.

[0135] In the present invention, after forming the metal film, the metal film laminate can be annealed or heat treated at a specific temperature as needed. In addition, for insulation or other purposes, a resin such as polyphenylene ether can be coated on at least one side of the metal film laminate.

[0136] The thin film capacitor of the present invention is formed by using the metal film laminated film of the present invention. That is, the thin film capacitor of the present invention has the metal film laminated film of the present invention.

[0137] The capacitance density of the film capacitor of the present invention is preferably 1.1 μF / cm 3 Above and 18μF / cm 3 The higher the capacitance density of a film capacitor, the smaller the volume of a capacitor element with the same capacitance, and the more miniaturized it can be. Therefore, 1.5 μF / cm is more preferred.3 The higher the capacitance density of the film capacitor, the better. However, from the perspective of feasibility, 18 μF / cm is preferred. 3 Below, more preferably 10μF / cm 3 By using a film obtained by forming the polypropylene film of the present invention into a film having a thickness of 4.5 μm or less, it is easy to make the capacity density 1.1 μF / cm 3 As described above, by using a film formed so as to have a thickness of 3.5 μm or less, it is easy to make the capacity density of 1.5 μF / cm 3 above.

[0138] Capacitance density of film capacitors (μF / cm 3 ) can be calculated from the component capacitance (μF) and the component volume (cm 3 ) is calculated by the following calculation formula. The component capacitance can be measured at an ambient temperature of 23°C according to JIS C 4908:2007. The component volume refers to the volume of the part around which the vapor-deposited film is wound, excluding the external packaging materials, metal terminals, and reels, and can be measured by a known 3D scanning type three-dimensional measuring machine. In addition, the capacitance density (μF / cm 3 ) will be described in detail later.

[0139] Capacity density (μF / cm 3 ) = component capacitance (μF) / component volume (cm 3 ).

[0140] The withstand voltage of the film capacitor of the present invention at 135°C is preferably 0.60 kV or more, more preferably 0.75 kV or more, and further preferably 1.0 kV or more. The polypropylene film of the present invention has the above-mentioned characteristics and has a high withstand voltage at high temperatures. Therefore, by using it as a dielectric of a film capacitor, it is easy to make the withstand voltage of the obtained film capacitor at 135°C to be 0.60 kV or more. By using the polypropylene film of the preferred embodiment of the present invention, the withstand voltage at 135°C can be further increased.

[0141] 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 described above by various methods. The preferred method for producing a wound film capacitor is as follows.

[0142] Aluminum is vapor-deposited on one side of a polypropylene film under reduced pressure. At this time, the vapor deposition is performed in a stripe shape with blank portions extending in the length direction. Next, a blade is placed in the center of each vapor-deposited portion and the center of each blank portion on the surface for cutting, and a strip-shaped winding roll with blank portions on one side of the surface is produced. For the strip-shaped winding roll with blank portions on the left or right side, two sheets of the left blank roll and the right blank roll are overlapped and wound in such a way that the vapor-deposited portion extends from the blank portion in the width direction to obtain a wound body.

[0143] When vapor deposition is performed on both sides, vapor deposition is performed in a stripe shape with a blank portion extending in the length direction of one side, and vapor deposition is performed in a stripe shape on the other side in a manner such that the blank portion in the length direction is located in the center of the vapor deposition portion on the back side. Next, a blade is inserted into the center of each blank portion on the front and back sides for cutting, and a strip-shaped winding roll is produced with blanks on one side of each side (for example, if there is a blank on the right side of the front side, there is a blank on the left side of the back side). The obtained roll and the undeposited laminated film are overlapped and wound in such a manner that the metallized film extends from the laminated film in the width direction to obtain a wound body.

[0144] As a method for obtaining the film capacitor of the present invention from the metal layer laminated film of the present invention, for example, the following method can be cited: the core material is pulled out from the wound body prepared as above and pressed, metal terminals are sprayed on both end faces to form external electrodes, and leads are welded on the metal terminals to form a wound film capacitor. The uses of film capacitors involve many aspects such as power control units for electric vehicles, hybrid vehicles, fuel cell vehicles and other electric vehicles, electric aircraft such as drones, railway vehicle uses, solar power generation / wind power generation uses and general household appliances, and the film capacitor of the present invention can also be well used for these uses. In addition, the polypropylene film of the present invention can also be used for various uses such as packaging films, demoulding films, engineering films, sanitary products, agricultural products, construction products, medical products, etc., and can be particularly well used for uses that include a heating process in film processing.

[0145] The power control unit, electric vehicle, and electric aircraft of the present invention are described below. The power control unit of the present invention has the film capacitor of the present invention. The power control unit is a system for managing power in an electric vehicle, electric aircraft, etc. having a mechanism driven by electricity. By installing the film capacitor of the present invention in the power control unit, the power control unit itself can be miniaturized, heat-resistant, and efficient, and as a result, fuel economy is improved.

[0146] The electric vehicle of the present invention has the power control unit of the present invention. Here, the electric vehicle refers to a vehicle having a mechanism driven by electricity, such as an electric vehicle, a hybrid vehicle, and a fuel cell vehicle. As described above, the power control unit of the present invention is not only miniaturized, but also has excellent heat resistance and efficiency. Therefore, by providing the electric vehicle with the power control unit of the present invention, fuel efficiency can be improved.

[0147] The electric aircraft of the present invention has the power control unit of the present invention. Here, the electric aircraft refers to an aircraft having a mechanism driven by electricity, such as a manned electric aircraft and a drone. As described above, the power control unit of the present invention is not only miniaturized, but also has excellent heat resistance and efficiency. Therefore, by equipping the electric aircraft with the power control unit of the present invention, it is possible to achieve improved fuel economy, etc.

[0148] The packaging material of the present invention is characterized in that it is made of the polypropylene film of the present invention. The packaging material of the present invention has excellent structural stability against heat during vapor deposition, and particularly has good water vapor barrier properties and oxygen barrier properties when a transparent vapor-deposited layer is laminated, and is therefore suitable for packaging materials that are easily degraded by water vapor and oxygen.

[0149] Example

[0150] [Measurement and evaluation methods]

[0151] (1) Film thickness

[0152] The thickness of the polypropylene film was measured at 10 random locations using a contact-type electronic micrometer (K-312A model) manufactured by Anritsu Corporation at 23° C. and 65% RH. The arithmetic mean of the thickness at the 10 locations was defined as the film thickness (unit: μm) of the polypropylene film.

[0153] (2) The main orientation axis direction of the polypropylene film is perpendicular to the main orientation axis

[0154] In the Examples and Comparative Examples, the main orientation axis direction of the polypropylene film was determined by the following method (tensile test). It should be noted that in any of the Examples and Comparative Examples, the main orientation axis perpendicular direction of the polypropylene film was defined as a direction perpendicular to the main orientation axis direction in the film plane.

[0155] Examples 1 to 6, Comparative Examples 1 to 4, 7, and 8: The width direction is the main orientation axis direction of the polypropylene film.

[0156] Comparative Example 5: The length direction of the sample is the main orientation axis direction of the polypropylene film.

[0157] <Tensile test>

[0158] First, cut out a rectangle of 50 mm in length and 10 mm in width as a sample. <1> , the sample <1> The direction of the long side is defined as 0°. Next, rectangular samples of the same size are collected in such a way that the long side direction becomes a direction rotated 15° to the right from the 0° direction. <2> , the rectangular sample is rotated 15° in the same way as above, and the rectangular sample is collected. <3> ~ <12> . Next, each rectangular sample was placed in a tensile testing machine with an initial distance between the clamps of 20 mm in the manner of the long side direction being the tensile direction (measurement direction), and the tensile test was performed at a tensile speed of 300 mm / min at room temperature. At this time, the maximum load until the rectangular sample broke was read, and it was divided by the cross-sectional area of ​​the sample before the test (film thickness × width), and the calculated value was taken as the stress of the maximum point strength. The length direction of the sample with the largest value was taken as the main orientation axis direction of the polypropylene film.

[0159] (3) Crystallization temperature (Tmc) of polypropylene film during cooling process

[0160] The crystallization temperature (Tmc) during the cooling process of the polypropylene film is measured according to JIS K7121-1987. First, a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments) is used to raise the temperature of 3 mg of the film from 30°C to 260°C at 20°C / min in a nitrogen atmosphere. Then, after being kept at 260°C for 5 minutes, the film is cooled to 30°C at 20°C / min, and the peak temperature of the exothermic peak obtained during the cooling process is measured. The same measurement is performed 3 times, and the average value of the peak temperature obtained is used as the cooling crystallization temperature (Tmc) of the polypropylene film. It should be noted that when multiple exothermic peaks are found in one measurement, the peak temperature of the exothermic peak with the highest peak temperature is used as the peak temperature of the measurement.

[0161] (4) Glass transition temperature (Tg) of cyclic olefin resin

[0162] The measurement was performed in accordance with JIS K7121-1987. Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), 3 mg of the film or resin was heated from 30°C to 260°C at 20°C / min in a nitrogen atmosphere, then kept at 260°C for 5 minutes and then cooled to 30°C at 20°C / min. Furthermore, after being kept at 20°C for 5 minutes, the temperature was raised from 30°C to 260°C at 20°C / min as a re-heating. The glass transition temperature (Tg) was calculated by the following formula based on the DSC curve obtained during the re-heating process.

[0163] Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2.

[0164] (5)I810 / I840

[0165] Under the following apparatus and conditions, a section X was cut from the polypropylene film by a microtome method, and polarized light Raman measurement was performed on the center position in the thickness direction of the section X by micro-Raman spectroscopy (beam diameter 1 μm, measurement was performed using polarized light parallel to the main orientation axis direction). -1 and 840cm -1 The Raman band intensities are taken as I810 and I840 respectively, and I810 / I840 is calculated. It should be noted that the section X is cut out at 5 positions selected at a distance of more than 1 cm from the end of the polypropylene film and more than 1 cm from the center of the section measured once, and the average value of the measured values ​​obtained for each section is taken as the I810 / I840 of the polypropylene film. In addition, the polarized light Raman spectrum is obtained by incident linear polarized light on the polypropylene film and only detecting the components of the scattered light parallel to the incident light. However, in order to eliminate the anisotropy of the spectrometer, a λ / 4 plate is set after the analyzer and before the grating, and the grating is introduced in a state where the polarization state of the scattered light is eliminated.

[0166] <Measurement Device>

[0167] Measuring device: inVia (manufactured by RENISHAW)

[0168] <Measurement Conditions>

[0169] Measurement mode: Micro Raman

[0170] Objective lens: ×100

[0171] Beam diameter: 1μm

[0172] Light source: semiconductor laser / 532nm

[0173] Laser power: 300mW

[0174] Diffraction grating: Single-3000gr / mm

[0175] Slit: 65μm

[0176] Detector: CCD / RENISHAW 1024×256.

[0177] (6) The number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in a 1 μm×2 μm rectangle in layer A (number / 2 μm) 2 )

[0178] The polypropylene film was cut with a slicer method in a plane parallel to the main orientation axis direction and the thickness direction to produce a polypropylene film sheet having a cut surface. 4 After staining, the stained surface was cut to collect an ultrathin section having a cross section X. The collected ultrathin section was observed and photographed using a transmission electron microscope (TEM HT7700 manufactured by Hitachi, Ltd.) under the following observation conditions. It should be noted that at this time, the cyclic olefin resin was stained darker than the polypropylene resin.

[0179] <Observation conditions>

[0180] Accelerating voltage: 100 kV

[0181] Observation magnification: 2000 times

[0182] In the collected cross-sectional X-ray image, a 2 μm-thick film is drawn with a pair of sides of 1 μm in the thickness direction and 2 μm in the direction perpendicular to the thickness direction (the main orientation axis direction). 2 The number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in the rectangle is counted. The average value of the number of domains obtained by performing the same measurement 10 times with the position of the rectangle in the image changed is calculated as the number of domains of the cyclic olefin resin passing through a pair of sides parallel to the thickness direction in the A layer (number / 2 μm 2 ). It should be noted that, when a rectangle with a pair of sides of 1 μm in the thickness direction and 2 μm in the direction perpendicular to the thickness direction is determined in the section X, when the bottom side of the rectangle is set as the sea part and the structural domain is located on the side opposite to the bottom side, it is considered that there is no such structural domain and it is not counted as the number. In addition, the structural domain with a constricted neck is also treated as a connected structural domain.

[0183] (7) Length of the main orientation axis direction of the cyclic olefin-based resin domain in the cross section X

[0184] Under the conditions described in (6), TEM observation of section X is performed without moving the field of view. Five domains are first selected from the top in the order closest to the center of the field of view, and then five domains are selected from the bottom. The length of the selected domain in the direction of the main orientation axis is measured, and the average value is used as the length of the main orientation axis direction of the domain of the cyclic olefin resin in section X. It should be noted that when the selected domain has an end outside the field of view, the field of view is moved from one end toward the other end to obtain multiple images, and the length of the main orientation axis direction of the domain is calculated using the joined images. When 10 domains cannot be selected in one field of view, move to other fields of view and continue observing until the measurement of 10 domains is completed.

[0185] (8) Dielectric loss tangent

[0186] According to JIS C2138-2007, the dielectric loss tangent of the polypropylene film is measured. First, the film is cut into a square of 50mm×50mm, and the conductive paste is applied to one surface with Φ18mm and to the other surface with Φ28mm to form an electrode. After the electrode forming sample is stored for 90 hours under an environment of 22°C and 60%RH, the dielectric loss tangent is measured 5 times under the conditions of 22°C, 60%RH and a frequency of 10kHz using precision LCR meter HP-4284A (made by Agilent Technologies), and the average value of the obtained value is used as the dielectric loss tangent of the polypropylene film.

[0187] (9) Tear strength in the direction perpendicular to the main orientation axis / Tear strength in the direction of the main orientation axis

[0188] The measurement is performed in accordance with JIS K 7128-2:1998. Specifically, three rectangular test pieces of 63.5 mm × 50 mm are collected from the polypropylene film with the measurement direction as the long side. For each test piece, the tear force is measured using a light load tear tester manufactured by Toyo Seiki, and the tear strength is calculated by dividing it by the film thickness measured by the method described in (1). The average value of the tear strength of the three test pieces is taken as the tear strength in that direction. The measurement is performed in the direction of the main orientation axis and in the direction perpendicular to the main orientation axis, respectively, and the tear strength in the direction perpendicular to the main orientation axis of the film / the tear strength in the direction of the main orientation axis is calculated from the tear strength in each direction.

[0189] (10) Dielectric breakdown voltage of polypropylene film (V / μm)

[0190] After heating the polypropylene film for 1 minute in an oven kept at the measured temperature, a dielectric breakdown voltage test was performed in this environment according to JIS C2330 (2001) 7.4.11.2 B method (flat electrode method) to measure the dielectric breakdown voltage. As for the lower electrode, a conductive rubber E-100 made by Togawa Rubber Co., Ltd. of the same size was placed on a metal plate described in JIS C2330 (2001) 7.4.11.2 B method. <65> " electrode. The insulation breakdown voltage test was performed 30 times, and the obtained value was divided by the thickness of the polypropylene film (measured by the above (1)) to convert it into V / μm. From the total 30 measured values ​​(calculated values), 5 points from the maximum value in descending order and 5 points from the minimum value in ascending order were removed, and the average value of the obtained 20 points was taken as the insulation breakdown voltage of the polypropylene film at that temperature. The measurement temperatures were set to 23°C, 105°C, and 135°C. It should be noted that at 23°C, heating in the oven was not performed, and the ambient temperature of the room was maintained at 23°C for the insulation breakdown voltage test.

[0191] (11) Evaluation of film capacitor characteristics

[0192] The wetting tension of each surface of the polypropylene film was measured according to JIS K 6768-1995. Aluminum was vapor-deposited on the surface with high wetting tension using a vacuum vapor deposition machine manufactured by ULVAC Co., Ltd. so that the film resistance was 10Ω / sq. During the vapor deposition, a vapor-deposited film A was prepared in which a vapor deposition pattern with so-called T-shaped blanks (lengthwise pitch (period) of 17 mm and fuse width of 0.5 mm) was applied and a vapor-deposited film B was prepared in which a vapor deposition pattern with T-shaped blanks was not applied and blanks were provided in a direction perpendicular to the length direction using masking oil. The obtained vapor-deposited films A and B were cut into pieces to obtain vapor-deposited rolls A and B with a film width of 50 mm (blank width of 2 mm at the end). Next, the capacitor element is wound in a manner that the vapor deposition rolls A and B are alternately overlapped, using a component winding machine (KAW-4NHB) manufactured by Kaito Manufacturing Co., Ltd., so that the component capacity of the prepared capacitor element is 10μF. After the metal terminal treatment is implemented, the capacitor element is heat treated for 12 hours while reducing pressure in an environment of 135°C, and the lead is installed to make a capacitor element. Using 10 capacitor elements obtained in this way, a voltage of 150VDC is applied to the capacitor element at the evaluation temperature. After 10 minutes at this voltage, the applied voltage is gradually increased in a step-like manner at a rate of 50VDC / 1 minute. The above operation is repeated to perform the so-called boost test. In addition, the evaluation temperature is 23°C and 135°C, and the test is performed at each temperature.

[0193] <Withstand voltage evaluation>

[0194] In the voltage step-up test, the electrostatic capacitance is measured and plotted on a graph, and the voltage at which the capacitance reaches 75% of the initial value is divided by the thickness of the polypropylene film (the value measured in (1) above) to determine the withstand voltage at each temperature. The same measurement is performed on 10 capacitor elements, and the average of the obtained values ​​is calculated. The withstand voltage reduction rate caused by temperature changes and the withstand voltage at 135°C are evaluated according to the following criteria.

[0195] <Withstand voltage reduction rate caused by temperature change>

[0196] The withstand voltage at 23°C was denoted as B(23), and the withstand voltage at 135°C was denoted as (135), and the evaluation was performed according to the following evaluation criteria. The evaluation criteria "A" means that it can be used, "B" and "C" mean that it can be used depending on the conditions, and "D" means that the performance is poor in practice and it is difficult to use.

[0197] A: B(135) / B(23) is greater than 0.70.

[0198] B: B(135) / B(23) is greater than 0.60 and not more than 0.70.

[0199] C: B(135) / B(23) is greater than 0.50 and less than or equal to 0.60.

[0200] D: B(135) / B(23) is less than 0.5.

[0201] <Withstand voltage at 135°C>

[0202] The evaluation was performed based on B (135) according to the following evaluation criteria. It should be noted that "A" in the evaluation criteria means that it can be used, "B" and "C" mean that it can be used under specific conditions, and "D" means that the performance is poor in practice and it is difficult to use.

[0203] A: B(135) is greater than 410V / μm.

[0204] B: B(135) is greater than 360 V / μm and less than or equal to 410 V / μm.

[0205] C: B(135) is greater than 330 V / μm and less than or equal to 360 V / μm.

[0206] D: B (135) is 330 V / μm or less.

[0207] <Reliability Evaluation>

[0208] For 10 capacitor elements, the voltage was increased until the electrostatic capacitance decreased to less than 18% relative to the initial value, and the capacitor element with the highest withstand voltage increase was disassembled to investigate the state of damage and evaluate the reliability according to the following evaluation criteria. The evaluation criteria "S" means that it can be used, "A", "B", and "C" mean that it can be used under specific conditions, and "D" means that the performance is poor in practical use and difficult to use.

[0209] A: No change in element shape or through-breakage was observed.

[0210] B: There was no change in the element shape, and penetration-like damage was observed in one or more layers and five or less layers of the polypropylene film.

[0211] C: The device shape did not change, but penetration-like damage was observed in 6 or more layers and 10 or less layers of the polypropylene film.

[0212] D: Change in device shape was observed, or penetration-like damage was observed in 11 or more layers of the polypropylene film.

[0213] <Processability Evaluation>

[0214] When the slitting after the above-mentioned vapor deposition is performed, the processability is evaluated according to the frequency of the polypropylene film breaking according to the following evaluation criteria. In the evaluation criteria, "A" means that it can be used, "B" and "C" mean that it can be used under specific conditions, and "D" means that the performance is poor in practice and it is difficult to use.

[0215] A: The number of breaks is less than 1 per 20,000 m length cut.

[0216] B: The number of breaks occurring per 20,000 m cut is more than 1 and less than 3.

[0217] C: The number of breaks occurring per 20,000 m cut is more than 3 times and less than 10 times.

[0218] D: The number of breaks occurring for every 20,000 m cut is more than 10.

[0219] (12) Capacitance density of film capacitor elements

[0220] The capacitance of 10 capacitor elements was measured using the E4980A precision LCR meter manufactured by Keysight Technologies at a frequency of 1kHz and an ambient temperature of 23°C in accordance with JIS C 4908:2007 to determine the element capacitance of each element. Next, the volume of each element was measured using a VL-500 3D scanning three-dimensional measuring machine manufactured by KEYENCE as the element volume. Based on the obtained values, the capacitance density (μF / cm 3), and the average value of 10 capacitor elements was used as the measured value.

[0221] Capacity density (μF / cm 3 ) = component capacitance (μF) / component volume (cm 3 ).

[0222] (13) Withstand voltage of film capacitors at 135°C

[0223] Using 10 capacitor elements, a voltage of 150VDC was applied to the capacitor elements at a high temperature of 135°C. After 10 minutes at this voltage, the applied voltage was gradually increased in steps at a rate of 50VDC / 1 minute. The above operation was repeated to perform the so-called boost test. In the boost test, the change in electrostatic capacitance is measured and plotted on a graph, and the voltage when the capacitance becomes 75% of the initial value is recorded as the withstand voltage of the film capacitor at 135°C.

[0224] (14) Performance evaluation of film capacitors

[0225] <Lifespan Evaluation>

[0226] Use 10 capacitor elements, apply 750VDC voltage to the capacitor elements at a high temperature of 135°C, take them out every 100 hours, and measure the capacity. Find the time when the capacity becomes less than 90% of the initial value, calculate the average value of 10 capacitor elements, and use it as the lifespan, and evaluate according to the following criteria. A means it can be used well, and B means it is difficult to use.

[0227] A: The service life is more than 2000 hours.

[0228] B: Lifespan is less than 2000 hours.

[0229] <Component size evaluation (indicator for miniaturization)>

[0230] The average value of the volumes of 10 capacitor elements measured by the method of (12) was taken as the element volume, and the evaluation was performed according to the following criteria: A and B mean that the capacitor element can be miniaturized, and C means that it is difficult to miniaturize the capacitor element.

[0231] A: The component volume is 80cm 3 the following.

[0232] B: Component volume is greater than 80cm 3 And 160cm 3 the following.

[0233] C: Component volume greater than 160cm 3 .

[0234] (15) Ash content

[0235] The weighed resin or polypropylene film was burned in an electric furnace to evaluate the ash content according to JIS K 7250-1: 2006. The weighing was performed using an electronic balance XP26 manufactured by Mettler-Toledo and an electric furnace FO510 manufactured by Yamato Scientific, and the furnace was heated to 600° C. to perform the combustion.

[0236] (16) Diffusion structure of layer A in section X

[0237] TEM observation of the A layer portion of the cross section X of the polypropylene film was performed under the same conditions as described in (6) except that the observation magnification was set to 20,000 times, and the obtained image was processed as follows using Image J (version 1.53t) to determine the ratio of the number of pixels of the diffusion structure.

[0238] i) 250 pixels×250 pixels are cut out from the image obtained by TEM observation so that the center of gravity is located at the center of the A layer portion when viewed in the thickness direction.

[0239] ii) Convert to 8-bit grayscale image.

[0240] iii) Adjust the brightness by clicking Auto in the Brightness / Contrast function in the Adjust Tab in the Image Tab.

[0241] iv) Binarization is performed so that pixels with a brightness of 60 or more and 100 or less have a brightness of 255 and other pixels have a brightness of 0.

[0242] v) Perform mean filtering with a setting of 10 pixels.

[0243] vi) The number of pixels with a brightness of 255 is counted, divided by 62,500 pixels, which is the total number of pixels of the captured image, and multiplied by 100 to determine the ratio (%) of the number of pixels of the diffusion structure.

[0244] The same measurement was performed five times so as not to include the same pixel, and the average value of the obtained ratio of the number of pixels of the diffusion structure was taken as the ratio (%) of the number of pixels of the diffusion structure in the A layer portion of the cross section X of the polypropylene film.

[0245] [Resin, etc.]

[0246] The following resins and the like were used to produce the polypropylene films in the examples and comparative examples.

[0247] <Polypropylene resin>

[0248] Polypropylene resin 1: homopolypropylene (Borclean (registered trademark) HC300BF from Borealis AG) having a meso pentad fraction of 0.970, a melting point of 166° C., a melt flow rate (MFR) of 3.3 g / 10 min, and an ash content of 20 ppm.

[0249] Polypropylene resin 2: homopolypropylene having a meso pentad fraction of 0.982, a melting point of 168° C., a melt flow rate (MFR) of 2.2 g / 10 min, and an ash content of 15 ppm.

[0250] Branched polypropylene (B1): a branched polypropylene resin having a melt flow rate (MFR) of 2.4 g / 10 min ("Daploy" (registered trademark) WB135HMS manufactured by Borealis AG).

[0251] <Ingredients other than polypropylene resin>

[0252] Cyclic olefin resin (C1): Polyplastics "TOPAS" (registered trademark) 6013F-04 (resin obtained by copolymerization of ethylene and norbornene (COC), glass transition temperature of 138°C, amorphous)

[0253] Cyclic olefin resin (C2): Polyplastics "TOPAS" (registered trademark) 6017S-04 (resin obtained by copolymerization of ethylene and norbornene (COC), glass transition temperature of 178°C, amorphous)

[0254] Cyclic olefin resin (C3): APEL (registered trademark) 5014CL manufactured by Mitsui Chemicals (resin (COC) obtained by copolymerizing ethylene and a norbornadiene derivative, glass transition temperature of 136°C, amorphous)

[0255] Antioxidant: "IRGANOX" (registered trademark) 1010 manufactured by Ciba Specialty Chemicals.

[0256] <Cyclic olefin resin pre-mixed raw material>

[0257] Raw material (A1): 59.5 parts by mass of polypropylene resin 1, 40 parts by mass of cyclic olefin resin (C1) and 0.5 parts by mass of antioxidant were mixed, kneaded and extruded using a twin-screw extruder set at 260° C., and then the strands were water-cooled and pelletized.

[0258] Raw material (A2): 59.5 parts by mass of polypropylene resin 2, 40 parts by mass of cyclic olefin resin (C3) and 0.5 parts by mass of antioxidant were mixed, kneaded and extruded using a twin-screw extruder set at 260° C., and the strands were water-cooled and pelletized.

[0259] Raw material (A3): 59.5 parts by mass of polypropylene resin 2, 40 parts by mass of cyclic olefin resin (C2) and 0.5 parts by mass of antioxidant were mixed, kneaded and extruded using a twin-screw extruder set at 260°C, and then the strands were water-cooled and pelletized.

[0260] <Branched Polypropylene Pre-Mixed Raw Material>

[0261] Raw material (D1): 89.5 parts by mass of polypropylene resin 1, 10 parts by mass of branched polypropylene (B1) and 0.5 parts by mass of antioxidant were mixed, kneaded and extruded using a twin-screw extruder set at 260°C, and the strands were water-cooled and pelletized.

[0262] Raw material (D2): 89.5 parts by mass of polypropylene resin 2, 10 parts by mass of branched polypropylene (B1) and 0.5 parts by mass of antioxidant were mixed, kneaded and extruded using a twin-screw extruder set at 260°C, and the strands were water-cooled and pelletized.

[0263] (Example 1)

[0264] The resin composition obtained by mixing the components in a manner of 80.0 parts by mass of the raw material (A1), 19.7 parts by mass of the polypropylene resin 1, and 0.3 parts by mass of the antioxidant is supplied to a single screw extruder for the A layer. In the single screw extruder, the resin composition is melted at a temperature of 250°C, and after removing foreign matter with a sintered filter with a cutoff of 80 μm adjusted to a temperature of 250°C, the molten resin composition is discharged from the T-die in a sheet form. Then, an air knife (air temperature: 23°C) is used to make the molten sheet close to the casting drum whose surface temperature is maintained at 30°C and cool and solidify to obtain an unstretched polypropylene film. The unstretched polypropylene film is heated to a temperature of 155°C with a plurality of roller groups, and stretched 3.5 times in the length direction between rollers provided with a circumferential speed difference to obtain a uniaxially oriented polypropylene film. Next, the two ends in the width direction are gripped with a plurality of clamps, and the uniaxially oriented polypropylene film is introduced into a tenter and preheated at 185°C. Next, the uniaxially oriented polypropylene film was introduced into the transverse stretching chamber consisting of the first chamber and the second chamber, and after being stretched 3.2 times in the width direction at 180°C in the first chamber, it was stretched 3.7 times in the width direction at 175°C in the second chamber (a total of 11.8 times in the width direction in the two chambers). Furthermore, as a heat treatment and relaxation treatment, a 12% relaxation was given in the width direction while heat treatment was performed at 165°C, and the film was introduced to the outside of the tenter and the clamp was released. Furthermore, the film surface after heat treatment (casting drum contact side) was heated at 25 W·min / m in the atmosphere. 2 The polypropylene film was obtained by corona discharge treatment with a treatment intensity of . The evaluation results are shown in Table 1-1.

[0265] (Example 2)

[0266] The resin composition obtained by mixing each component in a manner of 48.0 parts by mass of raw material (A1), 51.7 parts by mass of polypropylene resin 1 and 0.3 parts by mass of antioxidant was supplied to a single screw extruder for layer A, and polypropylene resin 1 was supplied to a single screw extruder for layer B. In each single screw extruder, the resin composition and polypropylene resin 1 were melted at 260°C, and after removing foreign matter with a sintered filter with a cutoff of 80 μm adjusted to a temperature of 230°C, the resin composition (for layer A) and polypropylene resin 1 (for layer B) were stacked in a manner of 3 layers of layer B / layer A / layer B and a stacking thickness ratio of 1 / 10 / 1 using a feed module. The obtained molten laminate was discharged from the T die in a sheet form, and an air knife was used to make it close to the casting drum whose surface temperature was maintained at 30°C, and it was cooled and solidified to obtain an unstretched polypropylene film. Then, the film-making conditions were set to the conditions shown in Table 1-1, and a polypropylene film was obtained in the same manner as in Example 1 except that. The evaluation results are shown in Table 1-1.

[0267] (Examples 3 to 5, Comparative Examples 3, 4, and 6)

[0268] The raw material formula and film-making conditions are set as described in Table 1-1 and Table 1-2, and a polypropylene film is obtained in the same manner as in Example 2. The evaluation results are shown in Table 1-1 and Table 1-2. It should be noted that the adjustment of the film thickness is carried out by increasing or decreasing the discharge amount of the extruder, and the adjustment of the stacking ratio is carried out by the feed module. In Comparative Examples 3, 4, and 6, the lateral stretching chamber of the tenter is only the first chamber, and the stretching is also carried out in one stage (hereinafter, the same is true in the example of using a tenter in which the lateral stretching chamber is only the first chamber). It should be noted that Comparative Example 6 wanted to obtain a 5.5μm polypropylene film, but the film could not be produced due to film cracking (the polypropylene film could not be obtained, so the evaluation in Table 1-2 is indicated by a slash).

[0269] (Example 6, Comparative Examples 1, 5, 7, 9)

[0270] The raw material formula and film-forming conditions are as described in Table 1. Except for these, a polypropylene film was obtained in the same manner as in Example 1. The evaluation results are shown in Table 1-1 and Table 1-2. It should be noted that Comparative Example 5 is an unstretched film, and the processes after stretching are not performed. Comparative Example 9 was intended to obtain a 4.6 μm polypropylene film, but the film could not be produced due to film cracking (a polypropylene film could not be obtained, so the evaluation in Table 1-2 is indicated by diagonal lines).

[0271] (Comparative Example 2)

[0272] The components were mixed in a manner that the polypropylene resin 2 was 79.7 parts by mass, the cyclic olefin resin (C1) was 20 parts by mass, and the antioxidant was 0.3 parts by mass, and the components were supplied to a single screw extruder set at 260°C. After melting at a temperature of 260°C, foreign matter was removed with a sintered filter with a cut-off of 80 μm, and the molten monolayer polymer was discharged from the T die. It was made to fit closely on the casting drum maintained at 90°C by an air knife, and cooled and solidified to obtain an unstretched polypropylene film. For the obtained unstretched polypropylene film, the two ends in the width direction were gripped with multiple clamps and introduced into a simultaneous biaxial stretching machine. After preheating at 163°C while keeping the grip, it was simultaneously biaxially stretched at the same temperature at a ratio of 3.6 times in the length direction and 8.2 times in the width direction. Next, it was introduced to the outside of the simultaneous biaxial stretching machine without heat treatment and relaxation treatment, and after loosening the clamps at both ends in the width direction, corona discharge treatment was performed in the same manner as in Example 1 to obtain a polypropylene film. The evaluation results are shown in Table 1-2.

[0273] (Comparative Example 8)

[0274] The raw material formulation and film-forming conditions were as shown in Table 1-2, and the film thickness after stretching was 4.5 μm. A polypropylene film was obtained in the same manner as in Comparative Example 2. The evaluation results are shown in Table 1-2.

[0275] (Example C1)

[0276] Aluminum was deposited on the surface of the polypropylene film obtained in Example 5 subjected to corona discharge treatment using a vacuum vapor deposition machine manufactured by ULVAC Co., Ltd. at a film resistance of 20Ω / sq. During the vapor deposition, a vapor-deposited film C1A having a vapor deposition pattern with so-called T-shaped blanks (lengthwise pitch (period) of 17 mm, fuse width of 0.5 mm) and a vapor-deposited film C1B not having a vapor deposition pattern with T-shaped blanks were prepared, in which blanks were provided in a direction perpendicular to the longitudinal direction using masking oil. The vapor-deposited films C1A and C1B were cut to obtain vapor-deposited rolls C1A and C1B having a film width of 50 mm (end blank width of 2 mm). Next, the capacitor element was wound up using a component winding machine (KAW-4NHB) manufactured by Kaito Seisakusho Co., Ltd. in such a way that the vapor deposition coils C1A and C1B were alternately overlapped, so that the component capacity of the manufactured capacitor element was 10μF, and after metal terminal treatment, a heat treatment was performed for 12 hours in an environment of 135°C while reducing pressure, and a lead was installed to manufacture a capacitor element. The evaluation results of the obtained capacitor element are shown in Table 2.

[0277] (Example C2, Comparative Examples C1, C2)

[0278] The evaluation results are shown in Table 2.

[0279]

Table 1-1

[0280]

[0281] It should be noted that the polypropylene films described in the examples and Tables 1-2 are not microporous films.

[0282] [Table 1-2]

[0283]

[0284]

Table 2

[0285]

[0286] Industrial Applicability

[0287] The polypropylene film of the present invention can be widely used for industrial applications such as film capacitors, packaging, demolding, and tapes. In particular, it has excellent withstand voltage characteristics under high temperature environments and can be suitably used for film capacitors used under high temperature and high voltage.

[0288] Description of Reference Numerals

[0289] 1: Part of section X

[0290] 2: Sea part

[0291] 3: Island part (domain)

[0292] 4: A rectangle of 1 μm × 2 μm with one pair of sides parallel to the thickness direction in section X

[0293] 5: A pair of short sides of a 1μm×2μm rectangle in section X, which is parallel to the thickness direction

Claims

1. A polypropylene film, comprising: a layer containing a cyclic olefin resin and a polypropylene resin is referred to as layer A; a cross section when the polypropylene film is cut along a plane parallel to the main orientation axis direction and the thickness direction is referred to as cross section X; the film comprises the layer A; and an orientation parameter I810 / I840 of the cross section X measured by Raman spectroscopy is greater than or equal to 2.2 and less than or equal to 20. 2 . The polypropylene film according to claim 1 , wherein in the cross section X, a length of the domain of the cyclic olefin-based resin in the main orientation axis direction is 5.0 μm or more and 1 mm or less.

3. The polypropylene film according to claim 1 or 2, wherein the dielectric loss tangent is 3×10 －6 Above and 1×10 －2 the following.

4. The polypropylene film according to any one of claims 1 to 3, wherein in a rectangle of 1 μm×2 μm defined in the A layer portion of the cross section X so that a pair of short sides are parallel to the thickness direction, there are 2.0 or more and 1000 or less domains of the cyclic olefin-based resin passing through the pair of short sides. The polypropylene film according to any one of claims 1 to 4, wherein the content of the cyclic olefin-based resin is 1.0% by mass or more and 40% by mass or less, when the entire film mass is taken as 100% by mass. The polypropylene film according to any one of claims 1 to 5, wherein a crystallization temperature Tmc in a temperature drop process measured by differential scanning calorimetry is 110°C or more and 150°C or less. 7 . The polypropylene film according to claim 1 , wherein the thickness is 0.5 μm or more and 15 μm or less. The polypropylene film according to any one of claims 1 to 7, wherein the value of tear strength in a direction perpendicular to the main orientation axis / tear strength in the main orientation axis direction is 0.10 or more and 10.0 or less. 9 . The polypropylene film according to claim 1 , wherein the ash content is 0.0 ppm or more and 1000 ppm or less, when the entire mass of the polypropylene film is 100 mass %. 10 . The polypropylene film according to claim 1 , wherein the layer A portion of the cross section X has a structure in which a cyclic olefin-based resin is diffused in a sea portion of a polypropylene resin. 11 . A metal film laminated film comprising a metal film on at least one surface of the polypropylene film according to claim 1 . 12 . A thin film capacitor obtained by using the metal film laminate film according to claim 11 .

13. The film capacitor according to claim 12, wherein the capacitance density is 1.1 μF / cm 3 Above and 18μF / cm 3 the following. 14 . The film capacitor according to claim 12 , wherein the withstand voltage at 135° C. is 0.60 kV or more. 15 . A power control unit comprising the film capacitor according to claim 12 .

16. An electric vehicle comprising the power control unit according to claim 15.

17. An electric aircraft comprising the power control unit according to claim 15.

18. A packaging material obtained by using the polypropylene film according to any one of claims 1 to 10.

19. A method for producing a polypropylene film, which is a method for producing the polypropylene film according to any one of claims 1 to 18, the method comprising the following steps in order: A casting step of melt-extruding a resin composition containing a polypropylene resin and a cyclic olefin resin onto a support to prepare a polypropylene resin sheet; A stretching step of stretching the polypropylene resin sheet in a length direction and a width direction; In the stretching step, the stretching in the width direction is performed by the following two-stage stretching method (I), 2-stage stretching method (I): The first stretching step: when the final stretching ratio in the width direction is recorded as a×b times, stretching is performed in the width direction at a stretching ratio of a times at a temperature of 160°C to 185°C; Second stage stretching: further stretching in the width direction at a stretching ratio of b times at a temperature 1°C to 20°C lower than the temperature of the first stage stretching. 20 . The method for producing a polypropylene film according to claim 19 , wherein the area stretching ratio is 40 times or more. 21 . The method for producing a polypropylene film according to claim 19 or 20, wherein the stretching in the stretching step is performed by a sequential biaxial stretching method of first stretching in the longitudinal direction and then stretching in the width direction.

Images