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

Abstract

To provide a polypropylene film which is capable of suppressing blocking in a rolled polypropylene film.SOLUTION: Provided is a polypropylene film which has a first surface and a second surface, while containing a polypropylene resin as a main component, and which is configured such that: the Svk value (SvkA) of the first surface is from 0.005 μm to 0.030 μm (inclusive); the Spk value (SpkA) of the first surface is more than 0.035 μm and 0.080 μm or less; the Svk value (SvkB) of the second surface is from 0.005 μm to 0.030 μm (inclusive); and the Spk value (SpkB) of the second surface is from 0.015 μm to 0.035 μm (inclusive).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polypropylene film, a polypropylene film with an integrated metal layer, a film capacitor, and a film roll. [Background technology]

[0002] Polypropylene film possesses excellent electrical properties, such as high voltage resistance and low dielectric loss characteristics, as well as high moisture resistance. Therefore, it is widely used in electronic and electrical equipment. Specifically, it is used as a film in applications such as high-voltage capacitors, various switching power supplies, filter capacitors (e.g., converters, inverters, etc.), and smoothing capacitors.

[0003] In recent years, there has been an increasing demand for smaller and higher-capacitance capacitors. To improve capacitance without changing the volume of the capacitor, it is preferable to make the dielectric film thinner. Therefore, there is a need for thinner films.

[0004] However, thin polypropylene films have a problem in that they are prone to wrinkles and misalignment during the element winding process when manufacturing capacitors. Therefore, in order to improve the slipperiness during element winding and to facilitate the element winding process, fine irregularities are sometimes formed on the surface of the polypropylene film to roughen it.

[0005] Patent Document 1 describes a film with a thickness of 1 to 3 μm, where one surface is designated as surface A and the other as surface B, and the protrusions on surface A are 0.1 mm 2 Number per unit area (Pa), 0.1 mm of protrusions present on surface B 2 A biaxially oriented polypropylene film for capacitors is disclosed, in which the number of particles per unit area (Pb), the 10-point average roughness of side A (SRzA), and the 10-point average roughness of side B (SRzB) satisfy a predetermined relationship (see Claim 1). Patent Document 1 describes the effects of the biaxially oriented polypropylene film for capacitors with the above-described configuration, including excellent processability even in thin films, and high voltage resistance under a wide range of ambient temperature conditions from low temperatures (-40°C) to high temperatures (150°C) (see paragraph

[0023] ). Specifically regarding processability, it is described that the rate of wrinkles and misalignment is low when element winding is performed (see paragraphs

[0122] and

[0123] ).

[0006] Furthermore, Patent Document 2 describes a film having protrusions on both sides, where the height (PhZ) of the most numerous protrusion on each side is 100 nm or more and less than 400 nm on both sides, and each side is 0.1 mm 2 A biaxially oriented polypropylene film is disclosed, in which the number of protrusions per unit area (Pc) is 150 or more but less than 500 on both sides (see Claim 1). Patent Document 2 describes the effects of the biaxially oriented polypropylene film with the above-described configuration, stating that by having a surface with numerous low-height protrusions on both sides of the film, it has high voltage resistance, suitable device processability, and excellent noise characteristics, particularly in applications for AC voltage capacitors (see paragraph

[0025] ). Regarding device processability, it specifically states that the rate of wrinkles and misalignment is low when device winding is performed (see paragraphs

[0098] and

[0099] ). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2013 / 146367 [Patent Document 2] International Publication No. 2012 / 002123 [Overview of the project] [Problems that the invention aims to solve]

[0008] Polypropylene film for capacitors undergoes a process of being wound into a roll even before it is wound into elements to manufacture capacitors. Specifically, in the process of biaxial stretching an unstretched cast sheet, the biaxially stretched polypropylene film is first wound into a roll. Furthermore, the polypropylene film wound into a roll in the above process is then unwound (unwound), a metal layer such as a vapor-deposited film is formed on one side, and then it is wound again.

[0009] The inventors of the present invention have diligently studied polypropylene films for capacitors. As a result, they have found that even when using a polypropylene film with a roughened surface to improve slipperiness during element winding, when the film on which the above-mentioned metal layer is formed is unwound, the vapor-deposited surface and the non-vapor-deposited surface may block, causing wrinkles in the film in the direction of flow. In this specification, blocking refers to the adhesion between the upper polypropylene film and the lower polypropylene film that are wound and in contact with each other due to winding pressure, etc.

[0010] The present invention has been made in view of the above-mentioned problems, and its object is to provide a polypropylene film capable of suppressing blocking of a metal-layer integrated polypropylene film wound in a roll. The present invention also aims to provide a metal-layer integrated polypropylene film having the polypropylene film, a film capacitor having the metal-layer integrated polypropylene film, and a film roll in which the polypropylene film is wound in a roll. [Means for solving the problem]

[0011] The inventors of this invention conducted thorough research on the above findings. As a result, they discovered that blocking of polypropylene film wound in a roll can be suppressed by adopting the following configuration, and thus completed the present invention.

[0012] The polypropylene film according to the present invention is a polypropylene film having a first surface and a second surface, containing a polypropylene resin as a main component, where the Svk value (Svk A ) of the first surface is 0.005 μm or more and 0.030 μm or less, the Spk value (Spk A ) of the first surface exceeds 0.035 μm and is 0.080 μm or less, the Svk value (Svk B ) of the second surface is 0.005 μm or more and 0.030 μm or less, the Spk value (Spk B ) of the second surface is 0.015 μm or more and 0.035 μm or less.

[0013] Here, the Svk value and the Spk value are parameters defined by surface texture parameters (ISO 25178-2:2007). The Svk value refers to the average height of the protruding valleys under the curve obtained by removing the protruding peaks and protruding valleys from the bearing curve. The Spk value refers to the average height of the protruding peaks above the curve obtained by removing the protruding peaks and protruding valleys from the bearing curve.

[0014] A metal layer is formed on either one or both of the first surface and the second surface of the polypropylene film. When wound, the first surface and the second surface will contact with each other in the state where the metal layer is formed. According to the above configuration, the Spk value (Spk A ) of the first surface, the Spk value (Spk A ) of the first surface, the Svk value (Svk B ) of the second surface, and the Spk value (Spk BThe values ​​are within the aforementioned numerical range, and both sides of the polypropylene film are roughened. Furthermore, assuming that both sides are roughened, the degree of roughening is made different within the aforementioned numerical range. Consequently, the contact area between the first surface and the second surface when the polypropylene film is wound is reduced, and the gap between the first surface and the second surface is maintained by the appropriately large and small protrusions, resulting in excellent cushioning. As a result, as can be seen from the examples, blocking can be suppressed.

[0015] Furthermore, generally, polypropylene film is wound using multiple conveyor rolls to apply tension to the film, preventing wrinkles and meandering. Therefore, winding is performed with both sides of the film in contact with at least one of the conveyor rolls, rather than just one side. According to the above configuration, since both sides of the polypropylene film are roughened, when winding the biaxially stretched polypropylene film into a roll, the slipperiness against the conveying roll is suitable on both sides. As a result, good conveying performance is obtained, wrinkles and winding misalignment are suppressed, and the processability for winding elements is improved.

[0016] If only transportability is considered, it is preferable that the degree of roughening be the same for the first surface and the second surface. However, if the dielectric strength is considered, it is preferable that the degree of roughening be different for the first surface and the second surface. This point will be explained below. Generally, if there are irregularities on the surface of a film, the thickness is determined by the point where the peaks of the protrusions are located. In other words, if both the first and second surfaces have irregularities, the thickness of the film is the distance from the peak of a protrusion on the first surface to the peak of a protrusion on the second surface. Here, the thickness of the core is the thickness obtained by subtracting the height of the protrusions on the second surface from the height of the protrusions on the first surface. Therefore, if both sides are roughened polypropylene film, the thickness of the core becomes thinner, making it easier for leakage current to occur and reducing the dielectric strength. Therefore, in the present invention, (1) the Svk value of the first surface (Svk A ) and the Svk value of the second face (Svk B (2) The Spk value of the second surface (Spk B ) to the Spk value of the first face (Spk A The core thickness was secured by making it smaller than the specified size. As a result, the material maintains voltage resistance while also providing improved transportability through a roughened surface.

[0017] Thus, according to the present invention, blocking can be suppressed, and furthermore, both transportability and voltage resistance can be achieved.

[0018] The polypropylene film having the above configuration is preferably for use in capacitors.

[0019] Spk value of the first face (Spk A ), the Spk value of the first face (Spk A ), the Svk value of the second face (Svk B ), and the Spk value of the second face (Spk B Polypropylene films in which the above numerical range can suppress blocking and, furthermore, possess both transportability and voltage resistance, are suitable for use in capacitors.

[0020] The polypropylene film having the above configuration is preferably biaxially oriented.

[0021] When biaxially stretched, the Spk value of the first surface (Spk A ), the Spk value of the first face (Spk A ), the Svk value of the second face (Svk B ), and the Spk value of the second face (Spk B ) is more likely to be a polypropylene film within the aforementioned numerical range.

[0022] The polypropylene film having the above configuration has an Sq value (Sq) of the first surface.A ) and the Sq value of the second surface (Sq B ) ratio Sq B / Sq A It is preferable that the value is between 0.4 and 1.0.

[0023] Here, the Sq value is a parameter defined by the surface texture parameter (ISO 25178-2:2007), and is the root mean square value of the height data in the defined area.

[0024] The aforementioned ratio Sq B / Sq A A value of 0.4 to 1.0 is preferable because it maintains dielectric strength while suppressing blocking after metal layer formation. This leads to reduced wrinkling during the subsequent slitting process.

[0025] The polypropylene film having the above configuration has a Sa value (Sa) of the first surface. A ) and the Sa value of the second surface (Sa B ) Ratio Sa B / Sa A It is preferable that the value is between 0.6 and 1.0.

[0026] Here, the Sa value is a parameter defined by the surface texture parameter (ISO 25178-2:2007), and is the arithmetic mean of the absolute values ​​of the height data in the defined area.

[0027] The aforementioned ratio Sa B / Sa A When the ratio is between 0.6 and 1.0, the amount of accompanying air accompanying the film's movement becomes similar on both sides. As a result, meandering of the film is suppressed, which is preferable because it leads to the suppression of edge misalignment of small windings during the slitting process of metal-layer integrated films.

[0028] In the polypropylene film having the above configuration, The aforementioned polypropylene resin is In the molecular weight differential distribution curve, the difference obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 from the differential distribution value when Log(M) = 6.0 (the difference when the differential distribution value at Log(M) = 6.0 is set to 100% (reference), hereafter referred to as "differential distribution value difference D" M Linear polypropylene resin A, which contains 8.0% or more of (also known as) In the molecular weight differential distribution curve, the difference (differential distribution value difference D) is obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 from the differential distribution value when Log(M) = 4.5. M Linear polypropylene resin B, in which ) is less than 8.0%, It is preferable that the resin contains a long-chain branched polypropylene resin C polymerized using a metallocene catalyst.

[0029] The presence of linear polypropylene resins A and B, which have different differential distribution values, means that the film contains two types of linear polypropylene resins with different quantitative relationships between high and low molecular weight components. Therefore, an unstretched polypropylene film (cast sheet) containing linear polypropylene resins A and B is in a finely mixed state (phase-separated state). By stretching such an unstretched polypropylene film, the arrangement of the resin components constituting the film becomes more complex, which is thought to improve the dielectric strength at high temperatures compared to using a single type of linear polypropylene resin alone. Furthermore, the inventors discovered that when a long-chain branched polypropylene resin C polymerized using a metallocene catalyst is included, a large amount of β crystals are formed on the above-mentioned specific cast sheet. They then discovered that by stretching the cast sheet containing β crystals, the β crystals are transformed into α crystals, and due to the density difference between the β crystals and α crystals, arc-shaped irregularities are formed on the polypropylene film obtained by stretching, allowing for suitable surface roughening. Furthermore, by including linear polypropylene resins A and B, which have different differential distribution values, as well as long-chain branched polypropylene resin C polymerized using a metallocene catalyst, the arrangement of resin components constituting the film becomes more complex, improving the dielectric strength of the stretched film. In addition, finely detailed (omitted) arc-shaped irregularities are formed, making it possible to achieve a more suitable surface roughening. Thus, by incorporating linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C into the polypropylene film, it becomes possible to achieve a more suitable surface roughening while also improving the dielectric strength at high temperatures. Furthermore, if a long-chain branched polypropylene resin obtained by crosslinking modification with peroxides is used instead of the long-chain branched polypropylene resin C polymerized with a metallocene catalyst, the α-crystal nucleation effect of the long-chain branched polypropylene resin obtained by crosslinking modification with peroxides promotes the formation of α-crystals in the cast sheet and greatly suppresses the formation of β-crystals. Since crystallite transitions do not occur even when a cast sheet containing α-crystals is stretched, it is difficult to form irregularities. Therefore, for roughening the surface of a polypropylene film, the long-chain branched polypropylene resin C polymerized with a metallocene catalyst is preferable.

[0030] Furthermore, the metal layer integrated polypropylene film according to the present invention is The aforementioned polypropylene film, The polypropylene film is characterized by having a metal layer laminated on one or both sides of the polypropylene film.

[0031] According to the above configuration, since the polypropylene film has a metal layer laminated on one or both sides, it can be used in a film capacitor in which the polypropylene film is the dielectric and the metal layer is the electrode. Furthermore, since the polypropylene film has suppressed blocking and also possesses both transportability and voltage resistance, the metal-layer integrated polypropylene film having the polypropylene film can be suitably manufactured and possesses voltage resistance.

[0032] Furthermore, the film capacitor according to the present invention is characterized by having a wound metal layer-integrated polypropylene film, or having a configuration in which a plurality of metal layer-integrated polypropylene films are laminated.

[0033] Furthermore, the film roll according to the present invention is characterized in that the polypropylene film is wound in a roll shape. [Effects of the Invention]

[0034] According to the present invention, it is possible to provide a polypropylene film that can suppress blocking of a metal-layer integrated polypropylene film wound in a roll. Furthermore, it is possible to provide a metal-layer integrated polypropylene film having said polypropylene film, a film capacitor having said metal-layer integrated polypropylene film, and a film roll in which said polypropylene film is wound in a roll. [Brief explanation of the drawing]

[0035] [Figure 1] (a) is a schematic perspective view showing crater-like micro-irregularities, (b) is a cross-sectional view thereof, and (c) is a longitudinal cross-section of (b) along line I-I'. [Figure 2] This figure shows an example of a projected image obtained by projecting portions of the fine surface irregularities with a height of 0.02 μm or more onto a film surface using an optical interferometry non-contact surface shape measuring instrument. [Figure 3] (a) to (c) are schematic planar diagrams illustrating the method for determining the virtual ring. [Modes for carrying out the invention]

[0036] The embodiments of the present invention will be described below. However, the present invention is not limited to these embodiments.

[0037] In this specification, the expressions “contains” and “includes” include the concepts of “contains,” “includes,” “substantially consist of,” and “consist solely of.” In this specification, "element," "capacitor," "capacitor element," and "film capacitor" all mean the same thing.

[0038] The biaxially oriented polypropylene film of this embodiment is not a microporous film and therefore does not have a large number of pores. The biaxially oriented polypropylene film of this embodiment may be composed of two or more layers, but it is preferable that it be composed of a single layer.

[0039] The polypropylene film according to this embodiment is It contains polypropylene resin as its main component, The Svk value of the first surface (Svk A ) is 0.005 μm or more and 0.030 μm or less, The Spk value of the first surface (Spk A ) is greater than 0.035 μm and less than or equal to 0.080 μm, The Svk value of the second surface (Svk B ) is 0.005 μm or more and 0.030 μm or less, The Spk value of the second surface (Spk B The characteristic feature is that the particle size is between 0.015 μm and 0.035 μm.

[0040] The Svk value of the first surface (Svk A The particle size is preferably 0.007 μm or more and 0.025 μm or less, more preferably 0.008 μm or more and 0.020 μm or less, and even more preferably 0.009 μm or more and 0.015 μm or less. The Spk value of the first surface (Spk A The particle size is preferably 0.040 μm or more and 0.075 μm or less, more preferably 0.043 μm or more and 0.060 μm or less, and even more preferably 0.045 μm or more and 0.055 μm or less. The Svk value of the second surface (Svk BThe particle size is preferably 0.007 μm or more and 0.025 μm or less, more preferably 0.008 μm or more and 0.020 μm or less, and even more preferably 0.009 μm or more and 0.015 μm or less. The Spk value of the second surface (Spk B The particle size is preferably 0.017 μm or more and 0.033 μm or less, more preferably 0.018 μm or more and 0.030 μm or less, and even more preferably 0.020 μm or more and 0.025 μm or less.

[0041] The polypropylene film has a metal layer formed on either one or both of its first and second surfaces, and when wound, the first and second surfaces come into contact with each other with the metal layer formed on them. According to the polypropylene film, the Spk value of the first surface (Spk A ), the Spk value of the first face (Spk A ), the Svk value of the second face (Svk B ), and the Spk value of the second face (Spk B The values ​​are within the aforementioned numerical range, and both sides of the polypropylene film are roughened. Furthermore, assuming that both sides are roughened, the degree of roughening is made different within the aforementioned numerical range. Consequently, the contact area between the first surface and the second surface when the polypropylene film is wound is reduced, and the gap between the first surface and the second surface is maintained by the appropriately large and small protrusions, resulting in excellent cushioning. As a result, as can be seen from the examples, blocking can be suppressed.

[0042] Furthermore, generally, polypropylene film is wound using multiple conveyor rolls to apply tension to the film, preventing wrinkles and meandering. Therefore, winding is performed with both sides of the film in contact with at least one of the conveyor rolls, rather than just one side. According to the aforementioned polypropylene film, since both sides of the polypropylene film are roughened, when winding the biaxially stretched polypropylene film into a roll, the slipperiness against the conveying roll is suitable on both sides. As a result, good conveying performance is obtained, wrinkles and winding misalignment are suppressed, and the processability for winding elements is improved.

[0043] If only transportability is considered, it is preferable that the degree of roughening be the same for the first surface and the second surface. However, if the dielectric strength is considered, it is preferable that the degree of roughening be different for the first surface and the second surface. This point will be explained below. Generally, if there are irregularities on the surface of a film, the thickness is determined by the point where the peaks of the protrusions are located. In other words, if both the first and second surfaces have irregularities, the thickness of the film is the distance from the peak of a protrusion on the first surface to the peak of a protrusion on the second surface. Here, the thickness of the core is the thickness obtained by subtracting the height of the protrusions on the second surface from the height of the protrusions on the first surface. Therefore, if both sides are roughened polypropylene film, the thickness of the core becomes thinner, making it easier for leakage current to occur and reducing the dielectric strength. Therefore, in this embodiment, (1) the Svk value of the first surface (Svk A ) and the Svk value of the second face (Svk B (2) The Spk value of the second surface (Spk B ) to the Spk value of the first face (Spk A The core thickness was secured by making it smaller than the specified size. As a result, the material maintains voltage resistance while also providing improved transportability through a roughened surface.

[0044] Thus, the polypropylene film according to this embodiment makes it possible to suppress blocking and also combines transportability and voltage resistance.

[0045] The Svk value of the first surface (SvkA ), the Spk value of the first surface (Spk A ), the Svk value of the second surface (Svk B ), and the Spk value of the second surface (Spk B The surface roughness is determined by measuring the surface shape using a three-dimensional surface roughness evaluation method with an optical interferometry non-contact surface shape measuring instrument. The "three-dimensional surface roughness evaluation method" evaluates the height of the entire surface of the film, thus evaluating the shape of the film surface in three dimensions. Therefore, it is possible to grasp local minute changes and variations on the surface being measured, and to evaluate the surface roughness more accurately. By evaluating the film surface roughness using the average height of the three-dimensional protruding peaks and the average height of the protruding valleys, rather than just the height of protrusions (two-dimensional surface roughness evaluation using general centerline average roughness Ra, etc.), it is possible to suppress blocking. Furthermore, it is possible to create a configuration that combines good transportability and voltage resistance.

[0046] More specifically, the Svk value of the first surface (Svk A ), the Spk value of the first surface (Spk A ), the Svk value of the second surface (Svk B ), and the Spk value of the second surface (Spk B The values ​​shown are those measured using the "VertScan2.0 (Model: R5500GML)" manufactured by Ryoka Systems Co., Ltd., as an optical interferometry non-contact surface shape measuring instrument. The following describes the measurement method in detail. First, using WAVE mode, a 530 white filter and a 1×BODY microscope tube are applied, and a ×10 objective lens is used to measure an area of ​​470.92 μm × 353.16 μm per field of view. This procedure is performed at 10 locations on the target sample (polypropylene film) at 1 cm intervals in the flow direction, starting from the center in both the flow direction and width direction. Next, the obtained data is subjected to noise reduction using a median filter (3x3), followed by Gaussian filtering with a cutoff value of 30 μm to remove waviness components. This ensures that the roughened surface condition can be measured appropriately. Next, we perform the analysis using the "ISO parameters" feature in the "Bearing" plugin function of the "VS-Viewer" analysis software for "VertScan2.0". Finally, each of the values ​​obtained at the above 10 locations (Svk A , Spk A Svk B , Spk B Sq A Sq B Sa A Sa B , Sk A Sk B The average value is calculated for each of the following: A ), the Spk value of the first surface (Spk A ), the Svk value of the second surface (Svk B ), and the Spk value of the second surface (Spk B ) can be obtained. Also, Sq A Sq B Sa A Sa B Sk A Sk B It can be obtained in the same way. More specifically, see the method described in the examples.

[0047] The polypropylene film has an Sq value (Sq) of the first surface. A ) and the Sq value of the second surface (Sq B ) ratio Sq B / Sq A It is preferably 0.4 to 1.0, more preferably 0.45 to 0.8, and even more preferably 0.48 to 0.7. The aforementioned Sq A The particle size is preferably 0.020 μm to 0.080 μm, and more preferably 0.025 μm to 0.070 μm. The aforementioned Sq B The particle size is preferably 0.005 μm to 0.030 μm, and more preferably 0.010 μm to 0.025 μm.

[0048] The aforementioned ratio Sq B / Sq A When it is 0.4 to 1.0, blocking after the formation of the metal layer can be suppressed while maintaining the dielectric breakdown strength. As a result, it is preferable because it leads to suppression of wrinkles during feeding in the subsequent slit process. The Sq value (Sq A ) of the first surface, the Sq value (Sq B ) of the second surface, and the ratio Sq B / Sq A The detailed measurement method is according to the method described in the examples.

[0049] The polypropylene film preferably has a ratio Sa A / Sa B of the Sa value (Sa B ) of the first surface and the Sa value (Sa A ) of the second surface of 0.6 to 1.0, more preferably 0.65 to 0.9, and even more preferably 0.7 to 0.8. The Sa A is preferably 0.005 μm to 0.025 μm, and more preferably 0.009 μm to 0.020 μm. The Sa B is preferably 0.005 μm to 0.025 μm, and more preferably 0.007 μm to 0.015 μm.

[0050] When the ratio Sa B / Sa A is 0.6 to 1.0, the amount of accompanying air accompanying the running of the film becomes nearly the same on the front and back. As a result, the meandering of the film is suppressed, which is preferable because it leads to suppression of end face displacement in small winding in the slit process of the metal layer integrated film. The Sa value (Sa A ) of the first surface, the Sa value (Sa B ) of the second surface, and the ratio Sa B / Sa A The detailed measurement method is according to the method described in the examples.

[0051] The polypropylene film has a Sk value (Sk A) and the Sk value of the second surface (Sk B ) Ratio Sk B / Sk A It is preferably 0.6 to 1.0, more preferably 0.7 to 0.9, and even more preferably 0.75 to 0.85. Said Sk A The particle size is preferably 0.030 μm to 0.070 μm, and more preferably 0.035 to 0.060 μm. Said Sk B The particle size is preferably 0.010 μm to 0.050 μm, and more preferably 0.020 μm to 0.040 μm.

[0052] Here, the Sk value is a parameter defined in the surface texture parameter (ISO 25178-2:2007), and is the difference between the upper and lower levels of the curve obtained by removing the protruding peaks and protruding valleys from the bearing curve.

[0053] The ratio Sk B / Sk A A value of 0.6 to 1.0 is preferable because it maintains dielectric strength while suppressing blocking after metal layer formation. This leads to reduced wrinkling during the subsequent slitting process. The Sk value of the first surface (Sk A ), the Sk value of the second surface (Sk B ), the ratio Sk B / Sk A The detailed measurement method is as described in the examples.

[0054] The Svk value of the first surface (Svk A ), the Spk value of the first surface (Spk A ), the Svk value of the second surface (Svk B ), the Spk value of the second surface (Spk B ), the Sq value of the first surface (Sq A ), the Sq value of the second surface (Sq B ), the ratio Sq B / Sq A , the Sa value of the surface described above (Sa A), the Sa value of the second surface (Sa B ), the aforementioned ratio Sa B / Sa A , the Sk value of the first surface (Sk A ), the Sk value of the second surface (Sk B ), and the ratio Sk B / Sk A The method for setting the above numerical range is not particularly limited, but (i) the selection of the type of resin (raw material resin) constituting the polypropylene film, stereoregularity, molecular weight distribution, and differential distribution value difference D M (ii) the content of each resin relative to the entire polypropylene film, (iii) the stretching ratio in the longitudinal and transverse directions during stretching, and the stretching temperature, and (iv) the selection of the type of additive (especially the nucleating agent) and its content, etc., can be adjusted as appropriate.

[0055] The Svk value of the first surface (Svk A ) and the Svk value of the second surface (Svk B A method to make the Spk value of the first surface different from the Spk value of the first surface (Spk A ) and the Spk value of the second surface (Spk B A method to make the Sq value of the first surface different from the first surface (Sq A ) and the Sq value of the second surface (Sq B A method to make it different from the Sa value of the first surface (Sa A ) and the Sa value of the second surface (Sa B A method to make the first surface different from the Sk value (Sk A ) and the Sk value of the second surface (Sk B There are no particular limitations on the method of making it different from the first surface, but for example, a cast sheet can be made with the first surface facing the cast roll and the second surface facing the air knife, and this cast sheet can be adjusted by biaxial stretching.

[0056] The polypropylene film may have both sides roughened by crater-like micro-irregularities. Figure 1(a) is a schematic perspective view showing crater-like micro-irregularities, Figure 1(b) is a cross-sectional view thereof, and Figure 1(c) is a longitudinal cross-sectional view along line I-I' in (b). Note that Figures 1(a) to 1(c) are schematic diagrams for explaining the "ellipse" and do not represent the surface shape of the polypropylene film etc. according to the embodiments described later. Many of the crater-like micro-irregularities are observed, for example, with an optical microscope, as two pairs of arc shapes or roughly curved arc shapes (hereinafter, arc shapes and roughly curved arc shapes are collectively referred to as "(abbreviated) arc shapes") that are curved in opposite directions. When the observed pairs of (abbreviated) arc shapes are interpolated and connected, an ellipse shape or roughly ellipse shape (hereinafter, ellipse shapes and roughly ellipse shapes are collectively referred to as "(abbreviated) ellipse shape") is formed. These two (omitted) arc-shaped portions form protrusions and depressions between them (see Figure 1(a)). These protrusions and depressions form the crater-like fine irregularities described above (see Figures 1(b) and 1(c)). In addition, the two (omitted) arc shapes may combine to form a circle or a nearly circle (hereinafter, the circle and nearly circle shapes will be collectively referred to as "(omitted) circle") or an (omitted) ellipse. In this case, the cross-section of the protrusion will be annular or nearly annular (hereinafter, the annular and nearly annular shapes will be collectively referred to as "(omitted) annular") or elliptic annular or nearly elliptic annular (hereinafter, the elliptic annular and nearly elliptic annular shapes will be collectively referred to as "(omitted) elliptic annular"). Furthermore, they may be observed as single (omitted) arc shapes without forming a pair.

[0057] The polypropylene film has an elliptic density D of the first surface. A 85-120 pieces / mm 2 The elliptic density D of the second surface is B 1 to 12 pieces / mm 2 It is preferable that this be the case. The elliptic density D A The density is 85-110 pieces / mm 2 It is more preferable that the number be 90-105 pieces / mm 2It is even more preferable that this be the case. The elliptic density D B 3-11 pieces / mm 2 It is more preferable that the number be 4-10 pieces / mm 2 It is even more preferable that this be the case.

[0058] The aforementioned ellipse density refers to the total number of (X) and (Y) per unit area observed using a digital scope (for example, a digital microscope VHX-2000 manufactured by Keyence Corporation). Hereinafter, the shapes of (X) and (Y) below will be collectively referred to as "ellipses". Furthermore, when calculating the elliptic density, ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300, where L is the length of one axis and S is the length of the other axis, are considered "ellipses." Ellipses that do not satisfy these conditions are not considered when calculating the elliptic density (they are not counted as "ellipses" when calculating the elliptic density). (X) A circular or elliptical shape formed by the joining of two (omitted) arc-shaped protrusions as described above. (Y) An elliptical shape formed by interpolating and connecting the two (omitted) arc shapes described above.

[0059] The specific method for measuring the elliptic density is as described in the examples.

[0060] Elliptic density D of the first surface A 85-120 pieces / mm 2 The elliptic density D of the second surface is B 1 to 12 pieces / mm 2 This makes it possible to reduce the contact area between the first surface and the second surface when the polypropylene film is wound. Specifically, the elliptic density D of the first surface A 85-120 pieces / mm 2 In that case, the number of "ellipses" can be said to be relatively large. Therefore, the surface is roughened more significantly. On the other hand, the elliptic density D of the second surface B 1 to 12 pieces / mm 2Therefore, the number of "ellipses" is relatively small. Consequently, although there is some surface roughening, the degree of roughening is small. Thus, the elliptic density D of the first surface A 85-120 pieces / mm 2 In addition, the elliptic density D of the second surface B 1 to 12 pieces / mm 2 This prevents the film from meandering left and right during slitting, thus suppressing unevenness at the edges of the small rolls. As a result, as can be seen from the examples, the processability of the slitting process can be improved.

[0061] Furthermore, the elliptic density D of the first surface A 85-120 pieces / mm 2 The elliptic density D of the second surface is B 1 to 12 pieces / mm 2 As a result, both sides of the polypropylene film are more favorably roughened, and when the biaxially stretched polypropylene film is wound into a roll, the slipperiness against the conveying roll is more favorable on both sides. Consequently, better conveyance is obtained, and wrinkles and winding misalignment are further suppressed.

[0062] Here, considering only transportability, it is preferable that the degree of roughening be the same for the first and second surfaces. However, considering dielectric strength, it is preferable that the degree of roughening be different for the first and second surfaces. Generally, when the surface is roughened, the thin parts of the film (the recesses of the unevenness) become a source of leakage current. Therefore, the elliptic density D of the second surface B The elliptic density D of the first surface A By reducing it to less than this, the number of irregularities that can cause leakage current can be reduced. Specifically, the elliptic density D of the second surface B 1 to 12 pieces / mm 2 Therefore, the number of irregularities that could cause leakage current is small. As a result, the configuration better maintains voltage resistance while also better combining it with improved transportability due to the roughened surface.

[0063] The polypropylene film has an elliptic density D of the first surface.A The average major axis length L of the ellipse that makes up the ellipse A The elliptic density D of the second surface is 20-80 μm. B The average major axis length L of the ellipse that makes up the ellipse B It is preferable that the thickness is 30 to 100 μm. The average major axis length L A The particle size is more preferably 30-70 μm, and even more preferably 40-68 μm. The average major axis length L B The particle size is more preferably 35-90 μm, and even more preferably 40-80 μm.

[0064] The average major axis length L A The elliptic density D A This is the average value of the major axis of the "ellipse" observed in the measurement. The average major axis length L B The elliptic density D B This is the average value of the major axis of the "ellipse" observed in the measurement.

[0065] The average major axis length L A , and the average major axis length L B The specific measurement method is as described in the examples.

[0066] Elliptic density D of the first surface A The average major axis length L of the ellipse that makes up the ellipse A If the elliptic density D of the first surface is 20-80 μm, A This makes it easier to keep the value within the aforementioned numerical range. Also, the elliptic density D of the second surface B The average major axis length L of the ellipse that makes up the ellipse B If the elliptic density D of the second surface is 30-100 μm B This makes it easier to keep the value within the aforementioned range.

[0067] The polypropylene film has an elliptic density D of the first surface. A The elliptic perfection P of the constituent ellipses A The elliptic density D of the second surface is 30-70%. B The elliptic perfection P of the constituent ellipsesB Preferably, the percentage is between 15% and 50%. The ellipse completeness P A It is more preferable that the ratio be between 35% and 65%, and even more preferable that it be between 40% and 60%. The ellipse completeness P B It is more preferably 20-45%, and even more preferably 25-40%.

[0068] The elliptic perfection is a value obtained as follows. First, using a non-contact optical interferometry surface shape measuring instrument, the "VertScan2.0 (model R5500GML)" manufactured by Ryoka Systems Co., Ltd., a 530 white filter and a 1×BODY microscope tube were applied in WAVE mode, and surface shape data of 470.92 μm × 353.16 μm per field of view was obtained using a ×10 objective lens. This operation was performed at 10 locations on the target sample (polypropylene film) at 1 cm intervals in the flow direction, starting from the center in both the flow direction and width direction. Next, the obtained data is subjected to noise reduction using a median filter (3x3), and then Gaussian filtering with a cutoff value of 30 μm is performed to remove the undulation component. From the projection images of the 10 surface shape data obtained as described above (see Figure 2), three crater projection images consisting of pairs of circular arcs are extracted. Figure 2 shows an example of a projected image obtained by projecting portions of the fine irregularities with a height of 0.02 μm or more onto the film surface using an optical interferometry non-contact surface shape measuring instrument. Note that Figure 2 is shown to facilitate visual understanding of the "projected image" and is not a projected image of the polypropylene film, etc., described in the examples below. In extracting crater projection images, three crater projection images are selected where no overlap is observed between arcs based on different β-type spherulites. The method for selecting these three images is to extract ellipses that correspond to the quartiles (first quartile, second quartile (i.e., median), and third quartile) based on the area of ​​the ellipse as observed visually. For example, if N crater projection images are examined, the crater projection image with the largest area is extracted as the first quartile [(3+N) / 4], the second quartile as [(1+N) / 2], and the third quartile as [(1+3N) / 4]. If the first to third quartiles obtained by substituting N have decimal points, the decimal part is rounded so that the first to third quartiles become integers. Specifically, for example, if nine crater projection images are examined, the projection images of the 3rd, 5th, and 7th craters are extracted. Similarly, if twelve crater projection images are examined, the projection images of the 4th, 7th, and 9th craters are extracted. Next, for each of the three extracted crater projection images, the total length Lt of the paired arcs and the total circumference Lc of the virtual ring containing the paired arcs are measured, and the ratio (Lt / Lc) is calculated. Then, the average of the 30 obtained ratio values ​​is calculated to obtain the average value α of the ratio (Lt / Lc).

[0069] The virtual annulus is determined and Lt and Lc are measured using the "Edge Curve Length" plugin function of the "VS-Viewer" analysis software for the VertScan2.0 optical interferometry non-contact surface shape measuring instrument. The specific procedure is as follows. Figures 3(a) to 3(c) are schematic plan views illustrating the method for determining the virtual ring. (1) First, as shown in Figure 3(a), P1 and P2 are the two points furthest apart from each other on arc 30a and arc 30b, and the straight line connecting P1 and P2 (hereinafter referred to as the straight line (P1-P2)) is determined. (2) Next, as shown in Figure 3(b), an ellipse (E0) is derived by the least squares method from the shape (position data) of the arcs 30a and 30b located on one side of the straight line (P1-P2) (above the straight line (P1-P2) in Figure 3) such that the straight line (P1-P2) is the major axis. Then, the curve that constitutes this ellipse (E0) (part of the circumference of the ellipse (E0)) is used to interpolate the portion between the arcs 30a and 30b on the aforementioned one side to form the interpolation line 40a. Note that in Figure 3, the portion of the ellipse (E0) other than the part corresponding to the interpolation line 40a is not shown. (3) Next, as shown in Figure 3(c), an ellipse (E1) is derived by the least squares method from the shape (position data) of arcs 30a and 30b located on the other side of the straight line (P1-P2) (in Figure 3, below the straight line (P1-P2)). Then, the portion between arcs 30a and 30b on the other side is interpolated using the curve that constitutes this ellipse (E1) (part of the circumference of the ellipse (E1)) to form the interpolated line 40b. Note that in Figure 3, the portion of the ellipse (E1) other than the part corresponding to the interpolated line 40b is not shown. (4) The ring shown in Figure 3(c), which is connected by the interpolation lines 40a and 40b determined in this way and the arcs 30a and 30b, is the virtual ring. (5) Next, a height profile of the micro-irregularities 20 is drawn, showing the height of the micro-irregularities 20 at each position (distance from a point on the circumference) on the circumference of this virtual ring. From this height profile, Lt and Lc in the crater projection image G corresponding to the portion with a height of 0.02 μm or more are read. For the least squares method, 30 (n=30) positional data points will be used for each case.

[0070] The ellipse completeness P A The degree of elliptic perfection P is 40-60%. B A ratio of 25-35% is preferable because it maintains dielectric strength while suppressing blocking after metal layer formation. This is because it leads to reduced wrinkling during the subsequent slitting process.

[0071] The DC dielectric breakdown strength (ES) of the aforementioned polypropylene film at 100°C is 510V. DC It is preferable that the thickness is 1 / μm or more, and the V is 525V DC It is more preferable that the thickness be 1 / μm or greater, and 540V DC It is even more preferable that the thickness be greater than or equal to / μm. The DC dielectric breakdown strength ES of the polypropylene film at 100°C is preferable as long as it is high, for example, 600V. DC / μm or less, 570V DC / μm or less, 550V DC It is less than / μm.

[0072] The DC dielectric breakdown strength (ES) of the aforementioned polypropylene film at 120°C is 485V. DC Preferably, the thickness is 1 / μm or more, and the voltage is 490V. DC It is more preferable that the thickness be greater than or equal to / μm. The DC dielectric breakdown strength ES of the polypropylene film at 125°C is preferable as high as possible, for example, 600V DC / μm or less, 550V DC It is less than / μm.

[0073] The ash content of the polypropylene film is preferably 6 × 10 ppm or less (60 ppm or less), more preferably 5 × 10 ppm or less (50 ppm or less), even more preferably 4 × 10 ppm or less (40 ppm or less), and particularly preferably 3 × 10 ppm or less (30 ppm or less). The ash content is preferably 0 × 10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1 × 10 ppm or more (10 ppm or more). When the ash content is within the above numerical range, the electrical characteristics as a capacitor are further improved while suppressing the generation of polar low-molecular-weight components. The ash content refers to the value obtained by the method described in the examples.

[0074] The polypropylene film has a thickness of preferably 9.5 μm or less, more preferably 6.0 μm or less, even more preferably 3.0 μm or less, even more preferably 2.9 μm or less, particularly preferably 2.8 μm or less, and particularly most preferably 2.5 μm or less. Furthermore, the thickness of the polypropylene film is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.4 μm or more, even more preferably 1.5 μm or more, and particularly preferably 1.8 μm or more. In particular, when the thickness is within the range of 1.4 to 6.0 μm, 1.5 to 3.0 μm, 1.5 to 2.9 μm, etc., it is preferable because the polypropylene film is very thin yet exhibits excellent slitting process processability, blocking suppression during the vapor deposition process, and element winding processability.

[0075] A thickness of 9.5 μm or less allows for a larger capacitance, making it suitable for use as a capacitor. Furthermore, from a manufacturing standpoint, a thickness of 0.8 μm or more is also acceptable.

[0076] The thickness of the polypropylene film mentioned above refers to the value measured in accordance with JIS-C2330, except that it is measured at 100 ± 10 kPa using a paper thickness gauge MEI-11 manufactured by Citizen Seimitsu Co., Ltd.

[0077] The polypropylene film may be a biaxially oriented film, a uniaxially oriented film, or an unoriented film. In particular, the Spk value of the first surface (Spk A ), the Spk value of the first surface (Spk A ), the Svk value of the second surface (Svk B ), and the Spk value of the second surface (Spk B From the viewpoint of making it easier to keep the above numerical range, a biaxially oriented film is preferable.

[0078] The polypropylene film and the metal-layer integrated polypropylene film are each wound into a roll, preferably in the form of a film roll. The film roll may or may not have a winding core. It is preferable that the film roll has a winding core. The material of the winding core of the film roll is not particularly limited. Examples of materials include paper (paper tube), resin, fiber-reinforced plastic (FRP), and metal. Examples of resins include polyvinyl chloride, polyethylene, polypropylene, phenolic resin, epoxy resin, and acrylonitrile-butadiene-styrene copolymer. Examples of plastics constituting the fiber-reinforced plastic include polyester resin, epoxy resin, vinyl ester resin, phenolic resin, and thermoplastic resin. Examples of fibers constituting the fiber-reinforced plastic include glass fiber, aramid fiber (Kevlar® fiber), carbon fiber, poly(p-phenylenebenzoxazole) fiber (Zylon® fiber), polyethylene fiber, and boron fiber. Examples of metals include iron, aluminum, and stainless steel. The winding core of the film roll also includes a winding core formed by impregnating a paper tube with the resin. In this case, the material of the winding core is classified as resin.

[0079] As described above, the polypropylene film contains polypropylene resin as its main component. In this specification, "containing polypropylene resin as its main component" means that the polypropylene film contains 50% by mass or more of polypropylene resin relative to the entire polypropylene film (when the entire polypropylene film is considered to be 100% by mass). The content of the polypropylene resin relative to the entire polypropylene film is preferably 75% by mass or more, and more preferably 90% by mass or more. The upper limit of the polypropylene resin content is, for example, 100% by mass, 98% by mass, etc., relative to the entire polypropylene film.

[0080] The polypropylene resin is not particularly limited, and one type may be used alone, or two or more types may be used in combination. Among the polypropylene resins, those that form β-type spherulites when used as a cast sheet are preferred.

[0081] Examples of the polypropylene resins mentioned above include linear polypropylene resins. Linear polypropylene resins can be used alone or in mixtures of two or more types. In particular, it is preferable to use linear polypropylene resin A and / or linear polypropylene resin B described below. It is especially preferable to use linear polypropylene resin A and linear polypropylene resin B in combination. It is preferable that linear polypropylene resin A and linear polypropylene resin B described below are homopolypropylene resins. Suitable combinations of linear polypropylene resin A and linear polypropylene resin B described below include resin A-1 and resin B-1, resin A-2 and resin B-2, resin A-3 and resin B-3, and resin A-4 and resin B-4 described below. However, the present invention is not limited to the following resins as the polypropylene resins. <Linear polypropylene resin A> (Linear polypropylene resin A-1) A linear polypropylene resin in which, in the molecular weight differential distribution curve, the difference obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 from the differential distribution value when Log(M) = 6.0 is 8.0% or more, with the differential distribution value when Log(M) = 6.0 being set as 100% (reference). (Linear polypropylene resin A-2) A linear polypropylene resin with a heptane-insoluble content (HI) of 98.5% or less. (Linear polypropylene resin A-3) A linear polypropylene resin with a melt flow rate (MFR) of 4.0 to 10.0 g / 10 min at 230°C. (Linear polypropylene resin A-4) A linear polypropylene resin with a weight-average molecular weight (Mw) of 340,000 or less. <Linear polypropylene resin B> (Linear polypropylene resin B-1) A linear polypropylene resin in which, in the molecular weight differential distribution curve, the difference obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 4.5 from the differential distribution value when Log(M) = 6.0 is less than 8.0%, with the differential distribution value when Log(M) = 6.0 being set to 100% (reference). (Linear polypropylene resin B-2) A linear polypropylene resin with a heptane-insoluble content (HI) exceeding 98.5%. (Linear polypropylene resin B-3) Linear polypropylene resins having a melt flow rate (MFR) of less than 4.0 g / 10 min at 230°C (especially linear polypropylene resins with a MFR of 0.1 to 3.9 g / 10 min). (Linear polypropylene resin B-4) A linear polypropylene resin with a weight-average molecular weight (Mw) exceeding 340,000.

[0082] The weight-average molecular weight Mw of the linear polypropylene resin A is preferably 250,000 or more. Furthermore, the weight-average molecular weight Mw of the linear polypropylene resin A is preferably 450,000 or less, more preferably 400,000 or less, even more preferably 350,000 or less, and particularly preferably 340,000 or less. When the weight-average molecular weight Mw of the linear polypropylene resin A is between 250,000 and 450,000, the resin flowability is appropriate. As a result, the thickness of the cast sheet is easily controlled, and it becomes easy to produce a thin stretched film. In addition, unevenness in the thickness of the cast sheet and stretched film is less likely to occur, and appropriate stretchability is obtained, which is preferable.

[0083] The molecular weight distribution [(weight-average molecular weight Mw) / (number-average molecular weight Mn)] of the linear polypropylene resin A is preferably 5.5 or more and 12.0 or less, more preferably 7.0 or more and 12.0 or less, even more preferably 7.5 or more and 11.0 or less, particularly preferably 8.0 or more and 11.0 or less, and most particularly preferably 9.0 or more and 11.0 or less.

[0084] The molecular weight distribution of the linear polypropylene resin A [(z-average molecular weight Mz) / (number-average molecular weight Mn)] is preferably 15.0 to 70.0, more preferably 20.0 to 60.0, and even more preferably 25.0 to 50.0.

[0085] It is preferable that the molecular weight distribution of each component of the linear polypropylene resin A is within the preferred range, as this reduces the likelihood of unevenness in the thickness of the cast sheet and stretched film, and allows for appropriate stretchability.

[0086] In this specification, the weight-average molecular weight (Mw), number-average molecular weight (Mn), Z-average molecular weight, and molecular weight distribution (Mw / Mn and Mz / Mn) of linear polypropylene resin A and linear polypropylene resin B are values ​​measured using a gel permeation chromatograph (GPC) instrument. In this specification, the values ​​were measured using the HLC-8121GPC-HT (product name), a high-temperature GPC measuring instrument with a built-in differential refractometer (RI) manufactured by Tosoh Corporation. Three TSKgel GMHHR-H(20)HT columns manufactured by Tosoh Corporation were linked together and used as the GPC column. The column temperature was set to 140°C, and trichlorobenzene was flowed as the eluent at a flow rate of 1.0 ml / 10 min to obtain the measured values ​​of Mw and Mn. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to the molecular weight of polypropylene using the Q-factor to obtain Mw, Mn, and Mz. Furthermore, the logarithm of the base 10 of the molecular weight M is called the logarithmic molecular weight ("Log(M)").

[0087] Furthermore, the weight-average molecular weight (Mw), number-average molecular weight (Mn), Z-average molecular weight (Mz), and molecular weight distribution (Mw / Mn and Mz / Mn) of long-chain branched polypropylene C were measured using a gel permeation chromatography (GPC) instrument. More specifically, high-temperature GPC-MALS measurements were performed, i.e., using a high-temperature GPC instrument (HLC-8121GPC / HT; manufactured by Tosoh Corporation) equipped with a light scattering detector (DAWN EOS; manufactured by Wyatt Technology). As columns, TSKgel guardcolumnHHR(30) (7.8mm ID × 7.5cm) and three TSKgel GMH-HR-H(20)HT (7.8mm ID × 30cm), both manufactured by Tosoh Corporation, were used in conjunction. The column temperature was set to 140°C, and trichlorobenzene was flowed as the eluent at a flow rate of 1.0 ml / min to obtain the measured values ​​of Mw and Mn.

[0088] The linear polypropylene resin A has a differential distribution value difference D M Preferably, the differential distribution value difference D of the linear polypropylene resin A is 8.0% or more. M It is more preferably 8.0% to 18.0%, even more preferably 9.0% to 17.0%, and particularly preferably 10.0% to 16.0%.

[0089] The difference in differential distribution values ​​D of the linear polypropylene resin A. M The fact that it is between 8.0% and 18.0% means that when comparing the component with a logarithmic molecular weight of Log(M) = 4.5, which is a typical distribution value for the low molecular weight components (10,000 to 100,000 molecular weights, hereinafter also referred to as "low molecular weight components"), with the component with a logarithmic molecular weight of Log(M) = 6.0, which is a typical distribution value for the high molecular weight components (around 1,000,000 molecular weights, hereinafter also referred to as "high molecular weight components"), the low molecular weight components are more abundant, at a rate of 8.0% to 18.0%. In other words, for example, if the molecular weight distribution Mw / Mn is 7.0 to 12.0, saying that the molecular weight distribution Mw / Mn is 7.0 to 12.0 only indicates the breadth of the molecular weight distribution, and does not reveal the quantitative relationship between high molecular weight components and low molecular weight components within it. Therefore, the linear polypropylene resin A is designed to contain components with molecular weights of 10,000 to 100,000 in proportion to 8.0% to 18.0% of components with a molecular weight of 1,000,000.

[0090] The linear polypropylene resin A is the differential distribution value difference D M When the content is between 8.0% and 18.0%, the low molecular weight components are present in a proportion of 8.0% to 18.0% compared to the high molecular weight components. Therefore, it is easier to obtain the surface of the film in this embodiment, which is preferable.

[0091] The differential distribution value mentioned above was obtained using GPC as follows: A curve showing intensity over time (generally also called the "elution curve") obtained by the GPC differential refraction (RI) detector is used. By converting the time axis to the logarithmic molecular weight (Log(M)) using a calibration curve obtained using standard polystyrene, the elution curve is converted to a curve showing intensity against Log(M). Since the RI detection intensity is proportional to the component concentration, if the total area of ​​the intensity curve is set to 100%, an integral distribution curve against the logarithmic molecular weight Log(M) can be obtained. The differential distribution curve is obtained by differentiating this integral distribution curve with respect to Log(M). Therefore, "differential distribution" means the differential distribution of the concentration fraction with respect to molecular weight. From this curve, the differential distribution value for a specific Log(M) is read.

[0092] The mesopentad fraction ([mmmm]) of the linear polypropylene resin A is preferably 99.8% or less, more preferably 99.5% or less, and even more preferably 99.0% or less. Furthermore, the mesopentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and even more preferably 95.0% or more. When the mesopentad fraction is within the above numerical range, the crystallinity of the resin is moderately improved due to moderately high stereoregularity, and the dielectric strength at high temperatures is improved. On the other hand, the rate of solidification (crystallization) during cast sheet molding is moderate, and it has moderate stretchability.

[0093] The mesopentade fraction ([mmmm]) is an index of stereoregularity that can be obtained by high-temperature nuclear magnetic resonance (NMR) measurements. In this specification, the mesopentade fraction ([mmmm]) refers to the value measured using a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR), JNM-ECP500, manufactured by JEOL Ltd. The observed nuclei are: 13 The measurement frequency is C (125 MHz), the measurement temperature is 135°C, and the solvent used to dissolve the polypropylene resin is a mixed solvent of o-dichlorobenzene (ODCB: a mixture of ODCB and deuterated ODCB (mixing ratio = 4 / 1)). The measurement method by high-temperature NMR can be performed by referring to, for example, the method described in "New Edition Polymer Analysis Handbook, edited by the Japan Analytical Chemistry and Polymer Analysis Research Group, Kinokuniya Shoten, 1995, p. 610". A more detailed measurement method for the mesopentade fraction ([mmmm]) is provided by the method described in the examples.

[0094] The heptane-insoluble content (HI) of the linear polypropylene resin A is preferably 96.0% or more, more preferably 97.0% or more. Furthermore, the heptane-insoluble content (HI) of the linear polypropylene resin A is preferably 99.5% or less, more preferably 98.5% or less, and even more preferably 98.0% or less. Here, a higher heptane-insoluble content indicates higher stereoregularity of the resin. When the heptane-insoluble content (HI) is 96.0% or more and 99.5% or less, the moderately high stereoregularity moderately improves the crystallinity of the resin and improves the dielectric strength at high temperatures. On the other hand, the rate of solidification (crystallization) during cast sheet molding becomes moderate, and it has moderate stretchability. The method for measuring the heptane-insoluble content (HI) is as described in the examples.

[0095] The ash content of the linear polypropylene resin A is preferably 6 × 10 ppm or less (60 ppm or less), more preferably 5 × 10 ppm or less (50 ppm or less), even more preferably 4 × 10 ppm or less (40 ppm or less), and particularly preferably 3 × 10 ppm or less (30 ppm or less). Furthermore, the ash content of the linear polypropylene resin A is preferably 0 × 10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1 × 10 ppm or more (10 ppm or more). When the ash content of the linear polypropylene resin A is within the above preferred range, the electrical characteristics as a capacitor are further improved while suppressing the generation of polar low-molecular-weight components. The ash content refers to the value obtained by the method described in the examples.

[0096] The melt flow rate (MFR) of the linear polypropylene resin A at 230°C is preferably 1.0 to 15.0 g / 10 min, more preferably 2.0 to 10.0 g / 10 min, even more preferably 4.0 to 10.0 g / 10 min, and particularly preferably 4.3 to 6.0 g / 10 min. When the MFR of polypropylene A at 230°C is within the above range, it exhibits excellent flow characteristics in the molten state, making it less likely for unstable flow such as melt fracture to occur, and also suppressing breakage during stretching. Therefore, it has the advantage of good film thickness uniformity, which suppresses the formation of thin-walled sections where dielectric breakdown is likely to occur. The method for measuring the melt flow rate is as described in the examples.

[0097] The content of the linear polypropylene resin A is preferably 55% by mass or more, and more preferably 60% by mass or more, when the total amount of polypropylene resin in the polypropylene film is considered to be 100% by mass. The content of the linear polypropylene resin A is preferably 99.9% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less, when the total amount of polypropylene resin in the polypropylene film is considered to be 100% by mass.

[0098] The weight-average molecular weight Mw of linear polypropylene resin B is preferably 300,000 or more, more preferably 330,000 or more, even more preferably exceeding 340,000, even more preferably 350,000 or more, and particularly preferably exceeding 350,000. Furthermore, the weight-average molecular weight Mw of linear polypropylene resin B is preferably 400,000 or less, and more preferably 380,000 or less.

[0099] The molecular weight distribution [(weight-average molecular weight Mw) / (number-average molecular weight Mn)] of the linear polypropylene resin B is preferably 7.0 or more and 9.0 or less, more preferably 7.5 or more and 8.9 or less, and even more preferably 7.5 or more and 8.5 or less.

[0100] The molecular weight distribution of the linear polypropylene resin B [(z-average molecular weight Mz) / (number-average molecular weight Mn)] is preferably 20.0 to 70.0, more preferably 25.0 to 60.0, and even more preferably 25.0 to 50.0.

[0101] It is preferable that the molecular weight distribution of each component of the linear polypropylene resin B is within the preferred range described above, as this reduces the likelihood of unevenness in the thickness of the cast sheet and stretched film, and allows for appropriate stretchability.

[0102] The differential distribution difference D of the linear polypropylene resin B M It is preferably less than 8.0%, more preferably -20.0% or more and less than 8.0%, even more preferably -10.0% or more and 7.9%, and particularly preferably -5.0% or more and 7.5%.

[0103] The mesopentad fraction ([mmmm]) of the linear polypropylene resin B is preferably less than 99.8%, more preferably 99.5% or less, and even more preferably 99.0% or less. Furthermore, the mesopentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and even more preferably 95.0% or more. When the mesopentad fraction is within the above numerical range, the crystallinity of the resin is moderately improved due to moderately high stereoregularity, and the dielectric strength at high temperatures is improved. On the other hand, the rate of solidification (crystallization) during cast sheet molding is moderate, and it has moderate stretchability.

[0104] The heptane-insoluble content (HI) of the linear polypropylene resin B is preferably 97.5% or more, more preferably 98% or more, even more preferably over 98.5%, and particularly preferably 98.6% or more. Furthermore, the heptane-insoluble content (HI) of the linear polypropylene resin B is preferably 99.5% or less, more preferably 99% or less.

[0105] The ash content of the linear polypropylene resin B is preferably 6 × 10 ppm or less (60 ppm or less), more preferably 5 × 10 ppm or less (50 ppm or less), even more preferably 4 × 10 ppm or less (40 ppm or less), and particularly preferably 3 × 10 ppm or less (30 ppm or less). Furthermore, the ash content of the linear polypropylene resin B is preferably 0 × 10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, and particularly preferably 1 × 10 ppm or more (10 ppm or more). When the ash content of the linear polypropylene resin B is within the above preferred range, the electrical characteristics as a capacitor are further improved while suppressing the generation of polar low-molecular-weight components. The ash content refers to the value obtained by the method described in the examples.

[0106] The melt flow rate (MFR) of the linear polypropylene resin B at 230°C is preferably 0.1 g / 10 min or more. Furthermore, the melt flow rate (MFR) of the linear polypropylene resin B at 230°C is preferably 6.0 g / 10 min or less, more preferably 5.0 g / 10 min or less, even more preferably less than 4.0 g / 10 min, and particularly preferably 3.9 g / 10 min or less.

[0107] When the linear polypropylene resin B is used as the polypropylene resin, the content of the linear polypropylene resin B is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, when the total amount of polypropylene resin in the polypropylene film is considered to be 100% by mass. Similarly, the content of the linear polypropylene resin B is preferably 45% by mass or less, and more preferably 40% by mass or less, when the total amount of polypropylene resin in the polypropylene film is considered to be 100% by mass.

[0108] When the linear polypropylene resin A and the linear polypropylene resin B are used in combination as the polypropylene resin, it is preferable that the total polypropylene resin is 100% by mass, and that it contains 55-90% by weight of the linear polypropylene resin A and 45-10% by weight of the linear polypropylene resin B, more preferably 60-85% by weight of the linear polypropylene resin A and 40-15% by weight of the linear polypropylene resin B, and particularly preferably 60-80% by weight of the linear polypropylene resin A and 40-20% by weight of the linear polypropylene resin B.

[0109] When the polypropylene resin includes linear polypropylene resin A and linear polypropylene resin B, the polypropylene film is in a finely mixed state (phase-separated state) of linear polypropylene resin A and linear polypropylene resin B, thereby improving its dielectric strength at high temperatures.

[0110] The linear polypropylene resin can be produced using generally known polymerization methods. There are no particular limitations, as long as a linear polypropylene resin suitable for use in the polypropylene film of this embodiment can be produced. Examples of such polymerization methods include gas-phase polymerization, bulk polymerization, and slurry polymerization.

[0111] Polymerization may be a single-stage polymerization using one polymerization reactor, or it may be a multi-stage polymerization using at least two polymerization reactors. Furthermore, hydrogen or comonomers may be added to the reactor as molecular weight modifiers.

[0112] A generally known Ziegler-Natta catalyst can be used as the catalyst for polymerization, and is not particularly limited as long as it can produce the linear polypropylene resin. The catalyst may also contain co-catalyst components and donors. By adjusting the catalyst and polymerization conditions, the molecular weight, molecular weight distribution, stereoregularity, etc., can be controlled.

[0113] The molecular weight, molecular weight distribution, and differential distribution difference D of the aforementioned linear polypropylene resin.M These can be adjusted by appropriately selecting, for example, (i) the polymerization method and conditions such as temperature and pressure during polymerization, (ii) the form of the reactor during polymerization, (iii) whether or not additives are used, the type and amount used, and (iv) the type and amount of catalyst used.

[0114] Specifically, the molecular weight, molecular weight distribution, and differential distribution difference D of the linear polypropylene resin. M Such adjustments can be carried out, for example, by a multi-stage polymerization reaction. Examples of multi-stage polymerization reactions include the following methods.

[0115] First, in the first polymerization step, propylene and a catalyst are supplied to the first polymerization reactor. Along with these components, hydrogen, as a molecular weight modifier, is mixed in the amount necessary to reach the required molecular weight of the polymer. The reaction temperature is approximately 70-100°C, and the residence time is approximately 20-100 minutes, for example, in the case of slurry polymerization. Multiple reactors can be used, for example, in series. In this case, the polymerization product from the first step is continuously sent to the next reactor along with additional propylene, catalyst, and molecular weight modifier, and then a second polymerization is carried out, in which the molecular weight is adjusted to be lower or higher than that of the first polymerization step. By adjusting the yield (production amount) of the first and second reactors, it is possible to adjust the composition (constitution) of high molecular weight and low molecular weight components.

[0116] Furthermore, the molecular weight, molecular weight distribution, and differential distribution difference D of the linear polypropylene resin. M Such adjustments can also be carried out by peroxidative decomposition. For example, methods involving peroxidation treatment with decomposition agents such as hydrogen peroxide or organic peroxides can be cited. When peroxides are added to disintegrating polymers such as polypropylene, hydrogen abstraction reactions occur from the polymer. Some of the resulting polymer radicals recombine and undergo crosslinking reactions, but most radicals undergo secondary decomposition (β-cleavage), separating into two polymers with smaller molecular weights. In other words, the higher the molecular weight component, the higher the probability of decomposition. This increases the amount of low molecular weight components, allowing for adjustment of the molecular weight distribution.

[0117] When adjusting the content of low molecular weight components by blending (resin mixing), it is preferable to dry-mix or melt-mix at least two resins with different molecular weights. Generally, a two-polypropylene mixture system, in which a main resin is mixed with an additive resin having a higher or lower average molecular weight in an amount of about 1 to 40% by mass, is preferred because it makes it easier to adjust the amount of low molecular weight components.

[0118] Furthermore, in this mixing process, the melt flow rate (MFR) can be used as a guideline for the average molecular weight. In this case, it is preferable for convenience during the preparation process to keep the difference in MFR between the main resin and the additive resin to around 1-30 g / 10 min.

[0119] Commercially available products can also be used as the linear polypropylene resin.

[0120] The polypropylene resin preferably includes a long-chain branched polypropylene resin. Among the long-chain branched polypropylene resins, the long-chain branched polypropylene resin C obtained by polymerizing propylene using a metallocene catalyst (hereinafter also referred to as "long-chain branched polypropylene resin C") is preferred. Specifically, when the polypropylene resin contains the long-chain branched polypropylene resin C, a large amount of β crystals are formed in the cast sheet. When the cast sheet containing the β crystals is stretched, the β crystals are transformed into α crystals. Due to the difference in density between the β crystals and the α crystals, arc-shaped irregularities are formed in the polypropylene film obtained by stretching, which is preferable because it allows for suitable surface roughening. In particular, it is more preferable that the polypropylene resin contains the linear polypropylene resin A and the long-chain branched polypropylene resin C. Furthermore, it is more preferable that the polypropylene resin contains the linear polypropylene resin A and the linear polypropylene resin B, and also contains the long-chain branched polypropylene resin C. The difference in differential distribution value D between the linear polypropylene resin A and the linear polypropylene resin B is MBecause the heptane-insoluble portion (HI) and / or the melt flow rate (MFR) differ, and a finely mixed state (phase-separated state) is achieved, stretching such an unstretched polypropylene film complicates the arrangement of the resin components that make up the film. Therefore, the differential distribution value difference D M In addition to containing linear polypropylene resin A and linear polypropylene resin B, which have different heptane-insoluble content (HI) and / or melt flow rate (MFR), the inclusion of long-chain branched polypropylene resin C complicates the arrangement of the resin components constituting the film, thereby improving the dielectric strength of the stretched film, and also forming finely detailed (omitted) arc-shaped irregularities, making it possible to achieve a more suitable surface roughening. Furthermore, if a long-chain branched polypropylene resin obtained by crosslinking modification with peroxides is used instead of the long-chain branched polypropylene resin C polymerized with a metallocene catalyst, the α-crystal nucleation effect of the long-chain branched polypropylene resin obtained by crosslinking modification with peroxides promotes the formation of α-crystals in the cast sheet and greatly suppresses the formation of β-crystals. Since crystallite transitions do not occur even when a cast sheet containing α-crystals is stretched, it is difficult to form irregularities. Therefore, for roughening the surface of a polypropylene film, the long-chain branched polypropylene resin C polymerized with a metallocene catalyst is preferable.

[0121] Metallocene catalysts are generally metallocene compounds that form polymerization catalysts for generating olefin macromers. Long-chain branched polypropylene resin C obtained by polymerizing propylene using a metallocene catalyst is preferable because it has an appropriate branching chain length and spacing, resulting in excellent compatibility with linear polypropylene. It is also preferable because it provides a uniform composition and surface shape. In the production of long-chain branched polypropylene resin C, other conditions besides the type and amount of catalyst used, such as (i) polymerization method and conditions such as temperature and pressure during polymerization, (ii) reactor configuration during polymerization, and (iii) use of additives, type, and amount, affect the molecular weight, molecular weight distribution, and differential distribution difference D of the long-chain branched polypropylene resin C produced. MTaking these factors into consideration, the conditions can be the same as those described in the section on the method for producing linear polypropylene resin.

[0122] The weight-average molecular weight Mw of the long-chain branched polypropylene resin C is preferably 150,000 to 600,000, more preferably 200,000 to 500,000, even more preferably 250,000 to 450,000, and particularly preferably 350,000 to 420,000. When the weight-average molecular weight Mw of the long-chain branched polypropylene resin C is 150,000 to 600,000, the resin flowability is appropriate. As a result, the thickness of the cast sheet is easily controlled, and it is easy to produce a thin stretched film. Furthermore, unevenness in the thickness of the cast sheet and stretched film is less likely to occur, and appropriate stretchability is obtained, which is preferable.

[0123] The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the long-chain branched polypropylene resin C is preferably 1.5 or more and 4.5 or less, more preferably 1.8 or more and 4.2 or less, even more preferably 2.0 or more and 4.0 or less, particularly preferably 2.1 or more and 3.9 or less, and especially preferably 2.2 or more and 3.0 or less.

[0124] The [(z-average molecular weight Mz) / (number-average molecular weight Mn)] of the long-chain branched polypropylene resin C is preferably 4.0 or more and 9.0 or less, more preferably 4.2 or more and 8.8 or less, even more preferably 4.5 or more and 8.5 or less, and particularly preferably 5.0 or more and 8.2 or less.

[0125] Molecular weight, molecular weight distribution, and differential distribution difference D of the long-chain branched polypropylene resin C. M These can be controlled, as described above, by adjusting the catalyst and polymerization conditions.

[0126] The heptane-insoluble content (HI) of the long-chain branched polypropylene resin C is preferably 98.0% or more, more preferably 98.2% or more, and even more preferably 98.5% or more. Furthermore, the heptane-insoluble content (HI) of the long-chain branched polypropylene resin C is preferably 99.5% or less, and more preferably 99.0% or less. When the HI of the long-chain branched polypropylene resin C is within the above preferred range, β crystals are more preferably formed on the cast sheet, and as a result, the surface of the polypropylene film according to this embodiment can be preferably roughened.

[0127] The ash content of the long-chain branched polypropylene resin C is preferably 45 × 10 ppm or less (450 ppm or less), and more preferably 40 × 10 ppm or less (400 ppm or less). Furthermore, the ash content of the long-chain branched polypropylene resin C is preferably 0 × 10 ppm or more, more preferably 1 ppm or more, even more preferably 5 ppm or more, still more preferably 1 × 10 ppm or more (10 ppm or more), even more preferably 10 × 10 ppm or more (100 ppm or more), and particularly preferably 20 × 10 ppm or more (200 ppm or more). When the ash content of the long-chain branched polypropylene resin C is within the above preferred range, β crystals are more preferably formed on the cast sheet, and as a result, the surface of the polypropylene film according to this embodiment can be preferably roughened.

[0128] The melt flow rate (MFR) of the long-chain branched polypropylene resin C at 230°C is preferably 0.1 to 12 g / 10 min, more preferably 0.5 to 5 g / 10 min, even more preferably 0.7 to 3.5 g / 10 min, and particularly preferably 1.0 to 2.2 g / 10 min. When the MFR of the long-chain branched polypropylene resin C at 230°C is within the above range, it exhibits excellent flow characteristics in the molten state, making it less likely for unstable flow such as melt fracture to occur, and also suppressing breakage during stretching. Therefore, it has the advantage of good film thickness uniformity, which suppresses the formation of thin-walled sections where dielectric breakdown is likely to occur.

[0129] The content of the long-chain branched polypropylene resin C is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and most preferably 2.5% by mass or more, when the total polypropylene resin in the polypropylene film is considered to be 100% by mass. Furthermore, the content of the long-chain branched polypropylene resin C is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, particularly preferably 7% by mass or less, and most preferably 5% by mass or less, when the total polypropylene resin in the polypropylene film is considered to be 100% by mass. The polypropylene film may contain one or more types of the long-chain branched polypropylene resin C.

[0130] Examples of commercially available long-chain branched polypropylene resin C include MFX3, MFX6, and MFX8, all manufactured by Nippon Polypropylene Co., Ltd.

[0131] The polypropylene film may contain other resins other than polypropylene resin (hereinafter also referred to as "other resins"). "Other resins" generally refer to resins other than polypropylene resin, which is the main component resin, and are not particularly limited as long as the desired polypropylene film can be obtained. Examples of other resins include other polyolefins other than polypropylene, such as polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), and poly(1-methylpentene); copolymers of α-olefins such as ethylene-propylene copolymer, propylene-butene copolymer, and ethylene-butene copolymer; vinyl monomer-diene monomer random copolymers such as styrene-butadiene random copolymer; and vinyl monomer-diene monomer-vinyl monomer random copolymers such as styrene-butadiene-styrene block copolymer. The polypropylene film may contain other resins in an amount that does not adversely affect the desired polypropylene film. The polypropylene film may preferably contain 10 parts by mass or less, and more preferably 5 parts by mass or less, of the other resin per 100 parts by mass of polypropylene resin. Furthermore, the polypropylene film may preferably contain 0.1 parts by mass or more, and more preferably 1 part by mass or more, of another resin per 100 parts by mass of polypropylene resin.

[0132] The aforementioned polypropylene film may further contain at least one additive in addition to the resin component. "Additive" refers to any additive commonly used in polypropylene, and is not particularly limited as long as it allows for the acquisition of the desired polypropylene film. Examples of additives include nucleating agents (α-crystal nucleating agents, β-crystal nucleating agents), antioxidants, necessary stabilizers such as chlorine absorbers and UV absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers, and organic fillers. Examples of inorganic fillers include barium titanate, strontium titanate, and aluminum oxide. When using the aforementioned additive, it may be included in an amount that does not adversely affect the desired polypropylene film.

[0133] The "nucleating agent" is not particularly limited as long as it is commonly used with polypropylene and can be used to obtain the desired polypropylene film. Examples of nucleating agents include α-crystal nucleating agents that preferentially nucleate α-crystals and β-crystal nucleating agents that preferentially nucleate β-crystals. Among α-crystal nucleating agents, organic nucleating agents include dispersed nucleating agents and dissolving nucleating agents. Dispersed nucleating agents include phosphate ester metal salt nucleating agents, carboxylic acid metal salt nucleating agents, and rosin metal salt nucleating agents. Dissolving nucleating agents include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, and amide-based nucleating agents. Examples of β-crystal nucleating agents include amide-based nucleating agents, di- or polycarboxylate metal salt-based nucleating agents, quinacridone-based nucleating agents, aromatic sulfonic acid-based nucleating agents, phthalocyanine-based nucleating agents, and tetraoxaspiro compound-based nucleating agents. The nucleating agent can be dry-blended or melt-blended with the polypropylene raw material and used as pellets, or it can be fed into an extruder together with the polypropylene pellets. By using a nucleating agent, the surface roughness of the film can be adjusted to a desired roughness. A typical example of a commercially available nucleating agent is NJester NU-100 manufactured by Shin-Nippon Rika Co., Ltd., which is used as a β-crystal nucleating agent. When the polypropylene film contains a β-crystal nucleating agent, its content is preferably 1 to 1000 ppm by mass, more preferably 50 to 600 ppm by mass, relative to the mass of the resin component (by mass when the resin component is considered as the whole).

[0134] An "antioxidant" is generally referred to as an antioxidant and is used with polypropylene. There are no particular restrictions on the type of antioxidant used, as long as it can produce the desired polypropylene film. Antioxidants are generally used for two purposes. One purpose is to suppress thermal and oxidative degradation in the extruder, and the other purpose is to suppress degradation during long-term use as a film for capacitors and to contribute to improving capacitor performance. Antioxidants that suppress thermal and oxidative degradation in the extruder are also called "primary agents," and antioxidants that contribute to improving capacitor performance are also called "secondary agents."

[0135] Two types of antioxidants may be used for these two purposes, or one type of antioxidant may be used for both purposes.

[0136] Examples of primary agents include 2,6-di-tert-butyl-para-cresol (generic name: BHT). Primary agents can usually be added to the polypropylene resin composition during the preparation of the polypropylene resin composition, as described later in the method for manufacturing polypropylene films, in order to suppress thermal degradation and oxidative degradation in the extruder. Antioxidants added to the polypropylene resin composition for this purpose are almost entirely consumed during the molding process in the extruder, and almost none remain in the film after film formation. Therefore, when the polypropylene film contains a primary agent, its content is usually less than 100 ppm by mass relative to the mass of the resin component (by mass when the resin component is considered as the whole).

[0137] Examples of secondary agents include hindered phenol antioxidants having a carbonyl group.

[0138] "Hindered phenol antioxidant having a carbonyl group" usually refers to a hindered phenol antioxidant having a carbonyl group, and is not particularly limited as long as the desired polypropylene film can be obtained.

[0139] Examples of hindered phenol antioxidants having a carbonyl group include triethylene glycol-bis[3-(3-tertiary-butyl-5-methyl-4-hydroxyphenyl)propionate] (product name: Irganox 245), 1,6-hexanediol-bis[3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate] (product name: Irganox 259), pentaerythrultyl tetrakis[3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate] (product name: Irganox 1010), and 2,2-thio-diethylenebis[3-(3,5-di-tertiary- Examples include butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1035), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (trade name: Irganox 1076), and N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) (trade name: Irganox 1098). However, pentaerythrutyl tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is particularly preferred because it has a high molecular weight, excellent compatibility with polypropylene, low volatility, and excellent heat resistance.

[0140] The polypropylene film may contain one or more hindered phenol antioxidants (secondary agents) having carbonyl groups in order to suppress deterioration that progresses over time during long-term use. When the polypropylene film contains one or more hindered phenol antioxidants having carbonyl groups, the content thereof is preferably 4000 ppm by mass or more and 6000 ppm by mass or less, and more preferably 4500 ppm by mass or more and 6000 ppm by mass or less, relative to the mass of the resin component (by mass when the resin component is considered as the whole). From the viewpoint of achieving appropriate effects, it is preferable that the content of hindered phenol antioxidants having carbonyl groups in the film is 4000 ppm by mass or more and 6000 ppm by mass or less.

[0141] A polypropylene film containing a hindered phenol antioxidant having a carbonyl group that has good molecular compatibility with polypropylene, in an optimal range of amounts, is preferable because it improves long-term durability.

[0142] The term "chlorine absorbent" generally refers to a chlorine absorbent used with polypropylene, and is not particularly limited as long as it can be used to obtain the desired polypropylene film. Examples of chlorine absorbents include metal soaps such as calcium stearate. When using such a chlorine absorbent, it can be included in an amount that does not adversely affect the desired polypropylene film.

[0143] The polypropylene film is preferably biaxially oriented. When the polypropylene film is a biaxially oriented polypropylene film, it can be manufactured by a generally known method for manufacturing biaxially oriented polypropylene films. For example, it can be manufactured by preparing a cast sheet from a polypropylene resin composition obtained by mixing linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C together with other resins, additives, etc., as needed, and then biaxially oriented the cast sheet.

[0144] <Preparation of polypropylene resin composition> There are no particular limitations on the method for preparing the polypropylene resin composition, but examples include a method of dry blending polymerized powder or pellets of linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C together with other resins, additives, etc. as needed using a mixer, or a method of supplying polymerized powder or pellets of linear polypropylene resin A, linear polypropylene resin B, and long-chain branched polypropylene resin C together with other resins, additives, etc. as needed to a kneader and melt-kneading to obtain a melt-blended resin composition.

[0145] Mixers and kneaders are not particularly limited. Kneaders may be single-screw, twin-screw, or multi-screw types. In the case of twin-screw or multi-screw types, either co-rotating or staggered rotation kneading is acceptable.

[0146] In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as good kneading is achieved, but it is preferably in the range of 170 to 320°C, more preferably in the range of 200 to 300°C, and even more preferably in the range of 230 to 270°C. To suppress deterioration during the kneading of the resin, an inert gas such as nitrogen may be purged into the kneader. The melt-kneaded resin can be pelletized to an appropriate size using a generally known granulator to obtain pellets of the melt-blended resin composition.

[0147] When preparing a polypropylene resin composition, a primary agent as an antioxidant, as described in the section on additives above, may be added to suppress thermal degradation and oxidative degradation in the extruder. When the polypropylene resin composition contains a primary agent, its content is preferably 1,000 ppm to 5,000 ppm by mass relative to the mass of the resin component (by mass when the resin component is considered as the whole). This antioxidant is almost entirely consumed during the molding process in the extruder, and almost none remains in the film after film formation.

[0148] A hindered phenol antioxidant having a carbonyl group, as described in the section on additives above, can be added to the polypropylene resin composition as a secondary agent. When a polypropylene resin composition contains a hindered phenol antioxidant having a carbonyl group, its content is preferably 100 ppm to 10,000 ppm by mass, and more preferably 5,500 ppm to 7,000 ppm by mass, relative to the mass of the resin component (by mass when the resin component is considered as a whole). A considerable amount of the hindered phenol antioxidant having a carbonyl group is consumed in the extruder. When a polypropylene resin composition does not contain a primary agent, a larger amount of hindered phenol antioxidant containing a carbonyl group can be used. This is because the consumption of hindered phenol antioxidant containing a carbonyl group increases in the extruder. When a polypropylene resin composition does not contain a primary agent and contains a hindered phenol antioxidant containing a carbonyl group, its content is 6000 ppm to 8000 ppm by mass or less relative to the mass of the resin components (by mass when the resin components are considered as a whole).

[0149] <Cast sheet preparation> Cast sheets can be obtained by supplying pellets of a pre-made dry blend resin composition and / or melt blend resin composition to an extruder, heating and melting them, passing them through a filter, and then heating and melting them to preferably 170°C to 320°C, more preferably 200°C to 300°C, and extruding them from a T-die. The resulting material is then cooled and solidified in at least one metal drum held at a temperature (casting temperature) of preferably 40°C to 140°C, more preferably 80°C to 140°C, even more preferably 90°C to 140°C, particularly preferably 90°C to 120°C, and most preferably 90°C to 105°C. In this process, it is preferable to press the extruded resin composition against the metal drum with an air knife. The side in contact with the metal drum becomes the first surface, and the opposite side (the side with the air knife) becomes the second surface.

[0150] The thickness of the cast sheet is not particularly limited as long as the desired polypropylene film can be obtained, but is preferably 0.05 mm to 2 mm, more preferably 0.1 mm to 1 mm.

[0151] Furthermore, during the production process of cast sheets (especially inside the extruder), polypropylene inevitably undergoes some degree of thermal degradation (oxidative degradation) and shear degradation. The degree of such degradation, i.e., changes in molecular weight distribution and stereoregularity, can be suppressed by nitrogen purging inside the extruder (inhibition of oxidation), the screw shape inside the extruder (shear force), the internal shape of the T-die during casting (shear force), the amount of antioxidant added (inhibition of oxidation), and the winding speed during casting (extension force).

[0152] <Stretching process> The biaxially oriented polypropylene film can be manufactured by subjecting the cast sheet to a stretching treatment. A sequential biaxial stretching method is preferred as the stretching method. In the sequential biaxial stretching method, the cast sheet is first kept at a temperature of preferably 100 to 180°C, more preferably 140 to 160°C, passed between rolls with a speed difference and stretched 3 to 7 times in the flow direction, and immediately cooled to room temperature. By appropriately adjusting the temperature in this longitudinal stretching process, the β crystals melt and transform into α crystals, and the unevenness becomes apparent. Subsequently, the stretched film is guided to a tenter and transversely stretched 3 to 11 times in the width direction at a temperature of preferably 160°C or higher, more preferably 160 to 180°C, then relaxed and heat-set, and wound into a roll shape.

[0153] The film, wound in a roll, is subjected to an aging treatment in an atmosphere of approximately 20-45°C. After being unwound (or fed out), it is slit (cut) to the desired product width using a slitter or similar tool, and then each section is wound again.

[0154] This stretching process results in a film with excellent mechanical strength and rigidity, and also makes the surface irregularities more pronounced, resulting in a finely roughened biaxially oriented film.

[0155] The polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat setting processes are completed. Corona discharge treatment can improve the adhesive properties in subsequent processes such as metal vapor deposition. Corona discharge treatment can be carried out using known methods. It is preferable to use air, carbon dioxide, nitrogen gas, or mixtures thereof as the atmospheric gas.

[0156] To process the polypropylene film as a capacitor, a metal layer may be laminated on one or both sides to form a metal-layer integrated polypropylene film. The metal layer functions as an electrode. As the metal used for the metal layer, for example, individual metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of several of these, and alloys thereof can be used, but zinc and aluminum are preferred considering the environment, economy, and capacitor performance.

[0157] Examples of methods for laminating a metal layer onto one or both sides of the polypropylene film include vacuum deposition and sputtering. From the viewpoint of productivity and economic efficiency, vacuum deposition is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, but are not particularly limited, and the most suitable method can be selected as appropriate.

[0158] While there are no particular limitations on the margin pattern when laminating metal layers by vapor deposition, it is preferable to apply a pattern including so-called special margins, such as a fishnet pattern or T-margin pattern, to one side of the film in order to improve characteristics such as the safety of the capacitor. This enhances safety and is effective in preventing capacitor failure and short circuits.

[0159] Any method known to form a margin, such as the tape method or the oil method, can be used without any limitations.

[0160] When forming a metal layer on the polypropylene film, the polypropylene film wound in a roll is unwound (fed out), a metal layer such as a vapor deposition film is formed on one or both surfaces, and then it is wound again.

[0161] The metal layer integrated polypropylene film can be laminated in a plurality by a conventionally known method or can be wound into an element to form a film capacitor.

[0162] Specifically, a blade is inserted at the center of each margin portion of the metal layer integrated polypropylene film for slitting, and a winding reel having a margin on one surface of the surface is produced. Here, since the Spk value (Spk A ) of the first surface, the Spk value (Spk A ) of the first surface, the Svk value (Svk B ) of the second surface, and the Spk value (Spk B ) of the second surface of the polypropylene film are within a predetermined numerical range, blocking is suppressed. Therefore, during the above slitting process, it is possible to prevent the polypropylene film from blocking and wrinkles in the flow direction from occurring in the film. Next, using the winding reel of the left margin and the winding reel of the right margin, the two are overlapped and wound in the width direction so that the vapor deposition portion protrudes from the margin portion (element winding). Next, the core material is removed from the wound body and pressed. Next, external electrodes are formed on both end faces, and further, lead wires are provided on the external electrodes. Thus, a wound type film capacitor is obtained.

Example

[0163] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[0164] 〔Polypropylene resin〕 The polypropylene resins used to produce the polypropylene films of the examples and comparative examples are shown in Table 1. The resin A1 shown in Table 1 is a product of Prime Polymer Co., Ltd. The resin A2 is a product of Prime Polymer Co., Ltd. The resin B1 is S802M manufactured by Daehan Oil & Chemical Co., Ltd. The resin B2 is HPT-1 manufactured by Daehan Oil & Chemical Co., Ltd. The resin B3 is manufactured by Daehan Oil & Chemical Co., Ltd. The resin C1 is MFX6 manufactured by Nippon Polypropylene Co., Ltd. The resin X1 is WB135HMS (Daploy HMS-PP) manufactured by Borealis. Note that MFX6 is a long-chain branched polypropylene resin polymerized using a metallocene catalyst. WB135HMS is a long-chain branched polypropylene resin obtained by crosslinking modification with peroxides. Resins A1 and A2 correspond to linear polypropylene resin A. Resins B1, B2, and B3 correspond to linear polypropylene resin B. Resin C1 corresponds to long-chain branched polypropylene resin C. Resins A1, A2, B1, B2, and B3 are all homopolypropylene resins. Resin X2 is a product manufactured by Prime Polymer Co., Ltd. and is a linear homopolypropylene. Table 1 shows the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) for each resin. These values ​​are for the raw resin pellet form. The measurement method is as follows.

[0165] <Measurement of number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of linear polypropylene resin> Using GPC (gel permeation chromatography), the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of each resin were measured under the following conditions. Specifically, a high-temperature GPC instrument with a built-in differential refractometer (RI), the HLC-8121GPC-HT model, manufactured by Tosoh Corporation, was used. Three TSKgel GMHHR-H(20)HT columns, also manufactured by Tosoh Corporation, were used in conjunction. Measurements were taken at a column temperature of 140°C, with trichlorobenzene flowing as the eluent at a flow rate of 1.0 ml / min. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​were converted to the molecular weight of polypropylene using the Q-factor to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). The molecular weight distribution (Mw / Mn) was obtained using the Mw and Mn values. The molecular weight distribution (Mz / Mn) was also obtained using the Mz and Mn values.

[0166] <Measurement of number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of long-chain branched polypropylene> Using GPC (gel permeation chromatography), the number-average molecular weight (Mn), weight-average molecular weight (Mw), z-average molecular weight (Mz), molecular weight distribution (Mw / Mn), and molecular weight distribution (Mz / Mn) of polypropylene were measured under the following conditions. A Tosoh Corporation HLC-8121GPC-HT high-temperature GPC instrument with a built-in differential refractometer (RI) was used. Three Tosoh Corporation TSKgelGMHHR-H(20)HT columns were linked together, and one TSKgelguardcolumnHHR(30) column was also used. At a column temperature of 140°C, 0.05 wt% 2,6-di-tert-butyl-para-cresol (common name: BHT) was used as the eluent, and measurements were taken by flowing 1,2,4-trichlorobenzene at a flow rate of 1.0 ml / min to obtain the number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz). The molecular weight distribution (Mz / Mn) was obtained using the Mz and Mn values, and the molecular weight distribution (Mw / Mn) was obtained using the Mw and Mn values. The measurement conditions were as follows. GPC device: HLC-8121GPC / HT (manufactured by Tosoh) Light scattering detector: DAWN EOS (Wyatt Technology) Column: TSKgelguardcolumnHHR(30) (7.8mm ID x 7.5cm) x 1 + TSKgelGMHHR-H(20)HT (7.8mm ID x 30cm) x 3 (Tosoh Corporation) Eluent: 1,2,4-trichlorobenzene with 0.05 wt% BHT Flow rate: 1.0mL / min Sample concentration: 2 mg / mL Injection volume: 300μL Column temperature: 140℃ Temperature: 40°C Pretreatment: The sample was accurately weighed, the eluent was added, and it was dissolved by shaking at 140°C for 1 hour. The sample was then thermally filtered through a 0.5 μm sintered metal filter.

[0167] Differential distribution value when logarithmic molecular weight log(M) = 4.5, differential distribution value when logarithmic molecular weight log(M) = 6.0, and difference D in differential distribution values. M Measurement > For each resin, the differential distribution values ​​when the logarithmic molecular weight log(M) = 4.5 and when the logarithmic molecular weight log(M) = 6.0 were obtained using the following method. First, the time curve (elution curve) of the intensity distribution detected using an RI detector was converted into a distribution curve for the molecular weight M (Log(M)) of standard polystyrene using a calibration curve prepared using the standard polystyrene described above. Next, after obtaining the integral distribution curve for Log(M) with the total area of ​​the distribution curve set to 100%, the differential distribution curve for Log(M) was obtained by differentiating this integral distribution curve with respect to Log(M). From this differential distribution curve, the differential distribution values ​​for Log(M) = 4.5 and Log(M) = 6.0 were read. In addition, the difference between the differential distribution value for Log(M) = 4.5 and the differential distribution value for Log(M) = 6.0 was called the differential distribution value difference D. M The series of operations to obtain the differential distribution curve were performed using the analysis software built into the GPC measurement device used. The results are shown in Table 1.

[0168] <Measuring Melt Flow Rate (MFR)> For each resin, the melt flow rate (MFR) in the form of raw resin pellets was measured using a melt indexer from Toyo Seiki Co., Ltd., in accordance with condition M of JIS K 7210. Specifically, first, a 4g sample was placed in a cylinder heated to a test temperature of 230°C and preheated for 3.5 minutes under a load of 2.16kg. Then, the weight of the sample extruded from the bottom hole over 30 seconds was measured, and the MFR (g / 10min) was determined. The above measurement was repeated three times, and the average value was taken as the measured MFR. The results are shown in Table 1.

[0169] <Measurement of heptane insoluble matter (HI)> For each resin, a sample of approximately 3 g was prepared by press molding to 10 mm × 35 mm × 0.3 mm. Next, approximately 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane-insoluble portion was calculated from the sample mass before and after extraction. The results are shown in Table 1.

[0170] <Ash content measurement> The ash content of each resin was measured as follows: Approximately 200g of the sample was weighed, transferred to a platinum dish, and ashed at 800°C for 40 minutes. The ash content (ppm) was measured from the resulting ash residue. The results are shown in Table 1.

[0171] <Mesopentade fraction> Each resin was dissolved in a solvent and measured using a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR) under the following conditions. High-temperature nuclear magnetic resonance (NMR) spectrometer: JEOL Ltd., High-temperature Fourier transform nuclear magnetic resonance spectrometer (High-temperature FT-NMR), JNM-ECP500 Observed nucleus: 13C (125MHz) Measurement temperature: 135℃ Solvent: Ortho-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4 / 1)) Measurement mode: Single-pulse proton broadband decoupling Pulse width: 9.1 μsec (45° pulse) Pulse interval: 5.5 sec Number of integrations: 4,500 times Shift reference: CH3(mmmm) = 21.7 ppm The pentad fraction representing the stereoregularity degree was calculated in percentage (%) from the intensity integration values of the signals derived from the combinations (such as mmmm and mrrm) of five consecutive units (pentads) of the consecutive units in the same direction "meso (m)" and those in the opposite direction "racemo (r)". Regarding the assignment of each signal derived from mmmm, mrrm, etc., for example, the descriptions of spectra such as "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" were referred to.

[0172] [Table 1]

[0173] <氧 Using the above resin, polypropylene films of Examples and Comparative Examples were produced and their physical properties were evaluated.

[0174] <Production of Polypropylene Film>[ (Example 1) Resin A1, Resin B1 and Resin C1 were dry-blended. The mixing ratio was (Resin A1):(Resin B1):(Resin C1) = 63:34:3 by mass ratio. Then, using the dry-blended resin, it was melted at a resin temperature of 250 °C, and then extruded using a T-die, and wound around a metal drum maintained at a surface temperature of 95 °C and solidified to produce a cast sheet. At this time, the cast sheet was produced while pressing the melt-extruded resin composition against the metal drum with an air knife. The obtained unstretched cast sheet was kept at a temperature of 130 °C, passed through rolls with a speed difference, and stretched 4.5 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film was led to a tenter, stretched 8 times in the width direction at a temperature of 158 °C, then relaxed, heat-fixed, wound up, and subjected to an aging treatment in an atmosphere of about 40 °C to obtain the polypropylene film according to Example 1.

[0175] (Examples 2 to 5, Comparative Examples 1 to 6) Polypropylene films according to Examples 2 to 5 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1, except that the mixing ratio during the dry blending of the raw material resins was changed as shown in Table 2. However, in the case of Comparative Example 6, a smooth cast sheet could not be produced due to melt fracture during extrusion molding. As a result, fracture occurred when the cast sheet was stretched.

[0176] (Examples 6-8, Comparative Example 7, Comparative Example 8) Polypropylene films according to Examples 6 to 8, Comparative Example 7, and Comparative Example 8 were obtained in the same manner as in Example 1, except that the mixing ratio during the dry blending of the raw material resins was changed as shown in Table 2.

[0177] [Table 2]

[0178] <Measuring the thickness of polypropylene film> The thickness of the polypropylene films in the examples and comparative examples was measured. Specifically, the measurement was performed in accordance with JIS-C2330, except that it was measured at 100±10kPa using a Citizen Seimitsu MEI-11 paper thickness gauge. The results are shown in Table 3.

[0179] <Svk value of the first face (Svk A ), the Spk value of the first face (Spk A ), the Svk value of the second face (Svk B ), the Spk value of the second face (Spk B ), the Sq value of the first face (Sq A ), the Sq value of the second face (Sq B ), the Sa value of the first surface (Sa A ), the Sa value of the second surface (Sa B ), the Sk value of the first face (Sk A ), and the Sk value of the second face (Sk B ) measurement> Hereafter, the first surface may be referred to as "Surface A," and the second surface as "Surface B." The terms Surface A and Surface B may also be used in Table 3. We used the "VertScan2.0 (Model: R5500GML)" manufactured by Ryoka Systems Co., Ltd. as an optical interferometry non-contact surface shape measuring machine. First, using WAVE mode, a 530 white filter and a 1×BODY microscope tube were applied, and a ×10 objective lens was used to measure a field of view of 470.92 μm × 353.16 μm. This procedure was performed at 10 locations on the target sample (polypropylene film) at 1 cm intervals in the flow direction, starting from the center in both the flow direction and width direction. Next, the obtained data was subjected to noise reduction using a median filter (3x3), followed by Gaussian filtering with a cutoff value of 30 μm to remove the waviness component. This allowed for accurate measurement of the roughened surface condition. Next, we performed the analysis using the "ISO parameters" feature in the "Bearing" plugin function of the "VS-Viewer" analysis software for "VertScan2.0". Finally, each of the values ​​obtained at the above 10 locations (Svk A , Spk A Svk B , Spk B Sq A Sq B Sa A Sa B , Sk A , Sk B The average value was calculated for each of the following: ) A ), the Spk value of the first face (Spk A ), the Svk value of the second face (Svk B ), the Spk value of the second face (Spk B ), the Sq value of the first face (Sq A ), the Sq value of the second face (Sq B ), the Sa value of the first surface (Sa A ), the Sa value of the second surface (Sa B ), the Sk value of the first face (Sk A ), and the Sk value of the second face (Sk B The ratio Sq was determined. The results are shown in Table 3. Note that Table 3 shows the ratio Sq. B / Sq A, comparison with Sa B / Sa A , ratio Sk B / Sk A The value for [the other value] is also shown.

[0180] <Measurement of Elliptic Density> The elliptic density of the first surface (Surface A) and the second surface (Surface B) of the polypropylene films in the examples and comparative examples was measured. Specifically, using a digital scope (Keyence Corporation Digital Microscope VHX-2000), each surface of the polypropylene film was observed with a lens magnification of 100x, measurement method: reflectance measurement, and field of view: 3.4 mm × 2.6 mm. The number of "ellipses" observed within the field of view was measured, and then converted to a value per unit area. The results are shown in Table 3. Furthermore, when one axis length is Lμm and the other axis length is Sμm, ellipses that satisfy S ≤ L and 1 ≤ L ≤ 300 were considered "ellipses" for calculation of elliptic density. Those that do not satisfy these conditions were not considered (not counted as "ellipses" for calculation of elliptic density).

[0181] <Measurement of average major axis length> The average value of the major axis of the ellipse observed in the ellipse density measurement was calculated. The results are shown in Table 3.

[0182] <Measurement of Elliptic Perfection> First, using a non-contact optical interferometry surface shape measuring instrument, the "VertScan2.0 (model R5500GML)" manufactured by Ryoka Systems Co., Ltd., a 530 white filter and a 1×BODY microscope tube were applied in WAVE mode, and surface shape data of 470.92 μm × 353.16 μm per field of view was obtained using a ×10 objective lens. This operation was performed at 10 locations on the target sample (polypropylene film) at 1 cm intervals in the flow direction, starting from the center in both the flow direction and width direction. Next, the obtained data was subjected to noise reduction using a median filter (3x3), and then Gaussian filtering with a cutoff value of 30 μm was applied to remove the undulation component. From the projection images of the 10 surface shape data obtained as described above, three crater projection images consisting of paired arcs were extracted. The projection images were those of the fine irregularities with a height of 0.02 μm or more projected onto the film surface. In extracting the crater projection images, three crater projection images were selected for each type of spherulite where no overlap was observed between arcs based on different β-type spherulites. The method for selecting these three images was to extract ellipses whose areas, as visually determined, corresponded to the quartiles (first quartile, second quartile (i.e., median), and third quartile). Next, for each of the three extracted crater projection images, the total length Lt of the paired arcs and the total circumference Lc of the virtual ring containing the paired arcs were measured, and the ratio (Lt / Lc) was calculated. Then, the average of the 30 obtained ratio values ​​was calculated to obtain the average value α of the ratio (Lt / Lc). The virtual annulus was determined, and Lt and Lc were measured using the "Edge Curve Length" plugin function of the "VS-Viewer" analysis software for the VertScan2.0 optical interferometry non-contact surface shape measuring instrument. The specific procedure is as follows. (1) First, as shown in Figure 3(a), P1 and P2 are the two points furthest apart from each other on arc 30a and arc 30b, and the straight line connecting P1 and P2 (hereinafter referred to as the straight line (P1-P2)) is determined. (2) Next, as shown in Figure 3(b), an ellipse (E0) is derived by the least squares method from the shape (position data) of the arcs 30a and 30b located on one side of the straight line (P1-P2) (above the straight line (P1-P2) in Figure 3) such that the straight line (P1-P2) is the major axis. Then, the curve that constitutes this ellipse (E0) (part of the circumference of the ellipse (E0)) is used to interpolate the portion between the arcs 30a and 30b on the aforementioned one side to form the interpolation line 40a. Note that in Figure 3, the portion of the ellipse (E0) other than the part corresponding to the interpolation line 40a is not shown. (3) Next, as shown in Figure 3(c), an ellipse (E1) is derived by the least squares method from the shape (position data) of arcs 30a and 30b located on the other side of the straight line (P1-P2) (in Figure 3, below the straight line (P1-P2)). Then, the portion between arcs 30a and 30b on the other side is interpolated using the curve that constitutes this ellipse (E1) (part of the circumference of the ellipse (E1)) to form the interpolated line 40b. Note that in Figure 3, the portion of the ellipse (E1) other than the part corresponding to the interpolated line 40b is not shown. (4) The ring shown in Figure 3(c), which is connected by the interpolation lines 40a and 40b determined in this way and the arcs 30a and 30b, is the virtual ring. (5) Next, a height profile of the micro-irregularities 20 is drawn, showing the height of the micro-irregularities 20 at each position (distance from a point on the circumference) on the circumference of this virtual ring. From this height profile, Lt and Lc in the crater projection image G corresponding to the portion with a height of 0.02 μm or more are read. For the least squares method, 30 (n=30) positional data points will be used for each case.

[0183] <Measurement of dielectric breakdown strength of polypropylene film (voltage resistance evaluation)> In accordance with JIS C2330(2001)7.4.11.2 Method B (flat electrode method), the dielectric breakdown voltage of polypropylene film was measured 12 times at 100°C and 125°C using a DC power supply. Dielectric breakdown voltage V DC Divide this by the film thickness (μm), and take the average of the 8 results obtained by excluding the top 2 and bottom 2 from the 12 measurement results to determine the dielectric breakdown strength ES(V). DC The value was set to / μm. The results are shown in Table 3. In Comparative Examples 1 and 4, the dielectric breakdown strength at 120°C was 485V. DC The value is less than / μm, indicating poor dielectric strength.

[0184] <Evaluation of blocking in metal deposition rolls> A metal-layer integrated polypropylene film was obtained by depositing a T-margin deposition pattern onto a biaxially oriented polypropylene film using aluminum deposition at a deposition resistance of 15Ω / □. Pattern deposition was performed using a wire-type vacuum deposition method, and heavy-edge deposition was performed using a crucible-type vacuum deposition method. The film used for deposition had a width of 620 mm, and the length of the film after deposition was 50,000 m. A blade was inserted into the center of each margin of this 620 mm wide metal-layer integrated polypropylene film, and it was slit at a slitting speed of 350 m / min to produce small windings with a width of 30 mm and a length of 10,000 m. At that time, the evaluation was as follows: if no flow-direction wrinkles due to blocking between the deposited and non-deposited surfaces were observed at the metal-deposited winding unwinding section, it was evaluated as AA; if slight streaks that could not be called wrinkles were observed, it was evaluated as A; if flow-direction wrinkles were observed at the widthwise ends, it was evaluated as B; and if flow-direction wrinkles were observed even in the widthwise center, it was evaluated as C. The results are shown in Table 3.

[0185] <Ash content measurement> The polypropylene films of the examples and comparative examples were measured as follows. Approximately 200g of the sample was weighed, transferred to a platinum dish, and ashed at 800°C for 40 minutes. The ash content (ppm) was measured from the resulting ash residue. The results are shown in Table 3.

[0186] <Evaluation of machinability in the slitting process> A 620mm wide metal-deposited roll was slit at a slitting speed of 350m / min to divide it into 20 pieces with a width of 30mm and a length of 10,000m. The resulting 20 small rolls were evaluated as follows: A if the edge misalignment (the length of the misalignment when the film meanders left and right during winding, causing the edges of the small rolls to become uneven) of all 20 small rolls was within 0.5% of the slit width; B if the edge misalignment of all 20 small rolls was within 1.0% of the slit width and did not meet the A evaluation criteria; C if the edge misalignment of all 20 small rolls was within 2.0% of the slit width and did not meet either the A or B evaluation criteria; and D if one or more of the 20 small rolls had an edge misalignment exceeding 2.0% of the slit width. The results are shown in Table 3.

[0187] <Evaluation of element winding processability> From the small windings obtained through slit processability evaluation, a left-margin winding reel and a right-margin winding reel were used, and two pieces were overlapped and wound so that the vapor-deposited portion extended beyond the margin in the width direction (element winding process). Winding was performed using a 3KAW-N2 automatic winding machine manufactured by Kaito Seisakusho Co., Ltd., with a winding tension of 200g, for 1360 turns. During this process, the entire winding process was visually observed from start to finish, and any windings with wrinkles or misalignment were deemed unacceptable. The percentage of unacceptable windings relative to the total number manufactured was used as an indicator of processability (hereinafter referred to as element winding yield). A higher element winding yield is preferable. A yield of 95% or higher was evaluated as good ("○"), and a yield of less than 95% was evaluated as poor ("×"). The results are shown in Table 3.

[0188] [Table 3]

[0189] <Capacitor fabrication and capacitance> Capacitors were fabricated using the polypropylene film obtained in the example as follows. By depositing a T-margin deposition pattern onto the polypropylene film with aluminum at a deposition resistance of 15Ω / □, a metal-layer integrated polypropylene film containing a metal film on one side of the polypropylene film was obtained. After slitting to a width of 60 mm, two metal-layer integrated polypropylene films were joined together and wound 1076 turns using a 3KAW-N2 automatic winding machine manufactured by Kaito Seisakusho Co., Ltd., with a winding tension of 250 g. The wound elements were heat-treated at 120°C for 15 hours while being pressed, and then zinc metal was sprayed onto the end faces of the elements to obtain flat-type capacitors. Lead wires were soldered to the end faces of the flat-type capacitors, and then sealed with epoxy resin. The capacitance of the finished capacitors was 75 μF (±5 μF) in all cases.

Claims

1. A polypropylene film having a first surface and a second surface, It contains polypropylene resin as its main component, The Svk value of the first surface (Svk Ａ ) is 0.005 μm or more and 0.030 μm or less, The Spk value of the first surface (Spk Ａ ) is greater than 0.035 μm and less than or equal to 0.080 μm, The Svk value of the second surface (Svk Ｂ ) is 0.005 μm or more and 0.030 μm or less, The Spk value of the second surface (Spk Ｂ ) is 0.015 μm or more and 0.035 μm or less, The aforementioned polypropylene resin is In the molecular weight differential distribution curve, the difference (differential distribution value difference D) is obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) = 6.0 from the differential distribution value when Log(M) = 4.

5. Ｍ Linear polypropylene resin B, in which the content is less than 8.0%, It contains a long-chain branched polypropylene resin C polymerized using a metallocene catalyst, A polypropylene film characterized by being biaxially oriented.

2. The polypropylene film according to claim 1, characterized in that it is for use in capacitors.

3. The Sq value (Sq Ａ ) of the first surface and the Sq value (Sq Ｂ ) of the second surface, and the ratio Sq Ｂ / Sq Ａ is 0.4 to 1.0, and the polypropylene film according to claim 1 or 2, characterized in that.

4. The Sa value of the first surface (Sa Ａ ) and the Sa value of the second surface (Sa Ｂ ) Ratio Sa Ｂ / Sa Ａ A polypropylene film according to any one of claims 1 to 3, characterized in that the ratio is 0.6 to 1.

0.

5. A polypropylene film according to any one of claims 1 to 4, A metal-layer integrated polypropylene film characterized by having a metal layer laminated on one or both sides of the polypropylene film.

6. A film capacitor characterized by having a wound metal layer integrated polypropylene film according to claim 5, or having a configuration in which a plurality of metal layer integrated polypropylene films according to claim 5 are laminated.

7. A film roll characterized in that the polypropylene film according to any one of claims 1 to 4 is wound in a roll shape.

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