Polypropylene film roll and metallized polypropylene film roll

Abstract

To provide a polypropylene film roll where the metal vapor deposition of a polypropylene film wound out from a polypropylene film roll can be highly accurately performed while keeping high flatness, an obtained capacitor element is excellent in long term durability under high temperature and high voltage and the capacitor element can be produced with a high yield.SOLUTION: A polypropylene film wound around a core has a thickness of 20 μm or less and a width of 200 mm or more. The shortest distance ΔL from the intermediate point of a straight line connecting both ends of a peeling line peeling the polypropylene film from a polypropylene film roll to the peeling line is 20 mm or less. A ratio of difference between the maximum value and the minimum value of a circumferential length to the average value of the circumferential length is 0.2% or less when the circumferential length is measured at both end positions, a middle position and positions at 50 mm intervals toward both end positions from the middle position of the polypropylene film roll.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a roll of polypropylene film and a roll of metallized polypropylene film. [Background technology]

[0002] Conventionally, in electronic devices, electrical devices, etc., capacitors using resin films have been used as, for example, high-voltage capacitors, various switching power supplies, filter capacitors and smoothing capacitors for converters and inverters, etc. In such capacitors, the resin film is used as a dielectric film for a capacitor, for example, by (i) forming a so-called "metallized film" on the dielectric film by, for example, metal deposition or coating and drying of a metal-containing paste, or bonding of a metal foil or metal powder, or by (ii) laminating the dielectric film without a conductive layer such as a metal layer with another conductor such as a metal foil or a metallized film on which a metal layer is formed by the same method as (i), etc. The dielectric film for a capacitor is also used as a capacitor for inverter power supply devices that control the drive motors of electric vehicles and hybrid vehicles, which have been in high demand in recent years.

[0003] For example, polypropylene films used as resin films for capacitors in electric vehicles, hybrid vehicles, etc., have recently been required to be thinner and have larger electrode areas due to the miniaturization and high capacity of capacitors. In addition, the processing width of the film has become wider due to the demand for cost reduction, and there is a demand to provide polypropylene film rolls in which thin films are finished in a wide width.

[0004] However, polypropylene film is highly flexible, and therefore wrinkles and sagging easily occur when the film is transported thinly and wide. The decrease in the flatness of the film during transportation causes the thickness of the deposited film to become non-uniform in the deposition process.

[0005] As a technique for suppressing wrinkles in a polypropylene film during transport, for example, Patent Document 1 discloses a film roll having a polypropylene film wound around a core, in which the average hardness of the outermost layer of the roll is 84.0 to 94.0° and the hardness variation in the width direction of the outermost layer of the roll is within ±2.0°.

[0006] Furthermore, Patent Document 2 discloses a polypropylene film roll for capacitors, which is formed by winding a polypropylene film around a core, in which the difference R between the maximum and minimum roll diameters in the width direction and the difference H between the diameters at both ends of the roll are specified. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2018 / 034182 [Patent Document 2] JP 2015-195367 A Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Document 1 describes that by controlling the hardness of the polypropylene film roll to a predetermined value, problems such as misalignment of the film roll during the deposition process, vertical wrinkles, and meandering during transportation can be prevented.

[0009] However, although the hardness of a polypropylene film roll is one of the finishing qualities of the film roll, it is a composite characteristic of various components such as the thickness and hardness of the film itself, the material and thickness of the core, the amount of air between the films, internal stress, and friction between the film surfaces. As described above, there are many factors that determine the hardness of the roll, and it is very difficult to isolate the main factor that determines the hardness of the roll. Therefore, the hardness of the roll is merely a guideline for the finishing quality. Therefore, even if the average value, distribution, and variation of the hardness of the roll are controlled, wrinkles and sagging during processing cannot be sufficiently eliminated, and the obtained capacitor element does not necessarily have excellent electrical properties.

[0010] Patent Document 2 claims that problems such as the frequency of occurrence of winding misalignment can be prevented by controlling the difference R between the maximum and minimum diameters of the film roll in the width direction and the difference H between the diameters at both ends of the film roll to predetermined values. However, even if the R and H of the film roll are controlled, the film obtained from the film roll does not necessarily have excellent wrinkle and sagging suppression effects during processing, or excellent electrical properties under high temperature and high voltage as the obtained capacitor element.

[0011] Under such circumstances, the main object of the present invention is to provide a polypropylene film roll that can perform metal deposition processing with high precision while maintaining high flatness on a polypropylene film unwound from a polypropylene film roll, and the resulting capacitor element has excellent long-term durability under high temperature and high voltage, and also suppresses a decrease in yield caused by winding misalignment or cutting due to wrinkles or sagging of the film, thereby enabling capacitor elements to be manufactured with a high yield. Another object of the present invention is to provide a metallized polypropylene film roll using the capacitor film roll. [Means for solving the problem]

[0012] The present inventors have conducted extensive research to solve the above problems. As a result, in a polypropylene film roll having a polypropylene film with a thickness of 20 μm or less and a width of 200 mm or more wound around a core, (1) under specified conditions, the shortest distance ΔL from the midpoint of the straight line connecting both ends of the peel line, which is the boundary line where the polypropylene film is peeled from the polypropylene film roll, to the peel line is set to 20 mm or less, and (2) when the circumferential length is measured at both ends of the polypropylene film roll, the center position, and positions 50 mm apart from the center position toward both ends, the ratio ΔX of the difference (Xmax-Xmin) of the maximum circumferential length Xmax and the minimum circumferential length Xmin to the average circumferential length Xave is set to 0.2% or less. This makes it possible to perform metal deposition processing with high precision while maintaining high flatness on the polypropylene film unwound from the polypropylene film roll, and it was found that the obtained capacitor element has excellent long-term durability under high temperature and high voltage, and further, the decrease in yield due to winding misalignment and cutting due to wrinkles and sagging of the polypropylene film is suppressed, making it possible to manufacture capacitor elements with a high yield. The present invention was completed through further investigation based on these findings.

[0013] That is, the present invention includes the following. Item 1. A polypropylene film roll in which a polypropylene film is wound around a core, The polypropylene film has a thickness of 20 μm or less and a width of 200 mm or more, A polypropylene film roll satisfying the following physical properties (1) and (2). (1) In an environment of a temperature of 23°C and a humidity of 60%, when the polypropylene film is unwound from the polypropylene film roll at an unwinding force of 3 N / m and a speed of 2 m / min, the shortest distance ΔL from the midpoint of a line connecting both ends of a peel line, which is a boundary line where the polypropylene film is peeled from the polypropylene film roll, to the peel line is 20 mm or less. (2) When the circumferential length is measured at both ends, at the center, and at positions spaced 50 mm apart from the center toward both ends of the polypropylene film roll, the ratio ΔX of the difference (Xmax-Xmin) between the maximum circumferential length Xmax and the minimum circumferential length Xmin to the average circumferential length Xave is 0.2% or less. Item 2. The polypropylene film roll according to item 1, wherein, when hardness is measured at both end positions, a central position, and positions at 50 mm intervals from the central position toward both end positions of the polypropylene film roll, an average hardness value Mave is 88° or more and 96° or less, and a difference ΔM between a maximum hardness value Mmax and a minimum hardness value Mmin is less than 4°. Item 3. The polypropylene film roll according to item 1 or 2, wherein the polypropylene film has a longitudinal distortion rate (ε1), a transverse distortion rate (ε2), and a diagonal distortion rate (ε3) each in the range of 0.6% to 1.5% at a stress of 25 MPa. Item 4. The polypropylene film roll according to any one of Items 1 to 3, wherein the surface roughness of at least one surface of the polypropylene film is a center line average roughness (Ra) of 0.04 μm or more and 0.08 μm or less and a maximum height (Rz) of 0.3 μm or more and 0.9 μm or less. Item 5. The polypropylene film roll according to any one of Items 1 to 4, wherein the polypropylene film has a winding length of 10,000 m or more. Item 6. The polypropylene film roll according to any one of Items 1 to 5, which is used for producing a metallized polypropylene film for a capacitor by laminating a metal film on one or both sides of the polypropylene film. Item 7. A metallized polypropylene film roll comprising the polypropylene film roll according to any one of items 1 to 6, and a metal film laminated on one or both sides of the polypropylene film. Effect of the Invention

[0014] According to the present invention, a polypropylene film roll can be provided that can perform metal deposition processing with high precision while maintaining high flatness on a polypropylene film unwound from a polypropylene film roll, and the resulting capacitor element has excellent long-term durability under high temperature and high voltage, and also suppresses a decrease in yield due to winding misalignment or cutting caused by wrinkles or sagging of the film, making it possible to manufacture capacitor elements with a high yield.Furthermore, according to the present invention, a metallized polypropylene film roll can be provided using the capacitor film roll. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram for explaining a method for measuring the shortest distance ΔL from the midpoint of a straight line connecting both ends of a peel line, which is a boundary line where a polypropylene film is peeled off from a polypropylene film roll, to the peel line. [Diagram 2] FIG. 2 is a schematic diagram for explaining a method for producing a polypropylene film roll. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The polypropylene film roll according to this embodiment is formed by winding a polypropylene film having a thickness of 20 μm or less and a width of 200 mm or more around a core, and is characterized by satisfying the following physical properties (1) and (2). (1) In an environment of a temperature of 23°C and a humidity of 60%, when the polypropylene film is unwound from the polypropylene film roll at an unwinding force of 3 N / m and a speed of 2 m / min, the shortest distance ΔL from the midpoint of a line connecting both ends of a peel line, which is a boundary line where the polypropylene film is peeled from the polypropylene film roll, to the peel line is 20 mm or less. (2) When the circumference of a polypropylene film roll is measured at both ends, at the center, and at positions 50 mm apart from the center toward both ends, the ratio ΔX of the difference (Xmax-Xmin) between the maximum circumference Xmax and the minimum circumference Xmin to the average circumference Xave is 0.2% or less.

[0017] The polypropylene film roll according to this embodiment satisfies the above-mentioned thickness and width, and further satisfies the above-mentioned physical properties (1) and (2). As a result, the polypropylene film unwound from the polypropylene film roll can be subjected to metal deposition processing with high precision while maintaining high flatness, and the obtained capacitor element has excellent long-term durability under high temperature and high voltage. In addition, the decrease in yield due to winding misalignment and cutting caused by wrinkles and sagging of the film is suppressed, and capacitor elements can be manufactured with a high yield.

[0018] The polypropylene film roll according to the present embodiment, the metallized polypropylene film roll using the polypropylene film roll, and the capacitor element will be described in detail below. In this specification, the term "to" in the numerical range means "more than or equal to" and "less than or equal to". That is, the term "α to β" means "more than or equal to α and less than or equal to β", or "more than or equal to β and less than or equal to α", including α and β as the range. In this specification, the term "mass %" indicating the content of each component indicates the content ratio when the amorphous thermoplastic resin film is taken as 100 mass %, unless otherwise specified.

[0019] In addition, in this specification, the expression "capacitor" includes the concepts of "capacitor", "capacitor element" and "film capacitor". In addition, "polypropylene film" may be abbreviated to "film", "polypropylene film roll" to "film roll", "metallized polypropylene film" to "metallized film", and "metallized polypropylene film roll" to "metallized film roll". In addition, in the polypropylene film roll according to this embodiment, the polypropylene film is not a microporous film, so it does not have many pores. In addition, the polypropylene film may be composed of two or more layers, but is preferably composed of a single layer.

[0020] <1. Polypropylene film roll> The polypropylene film roll according to this embodiment is characterized in that a polypropylene film having a thickness of 20 μm or less and a width of 200 mm or more is wound around a core, and satisfies the physical properties (1) and (2) described above.

[0021] The physical property (1) is that the shortest distance ΔL from the midpoint of the straight line connecting both ends of the peeling line to the peeling line formed when the polypropylene film is unwound from the polypropylene film roll according to the present embodiment under predetermined conditions is 20 mm or less. As shown in the schematic diagram of FIG. 1, the peeling line S is the boundary line between the part where the polypropylene film 1 is peeled from the polypropylene film roll 10 and the part where it is not peeled. In general, when the polypropylene film is unwound from the polypropylene film roll, the peeling line is not linear in the width direction x, but is formed so as to draw an arc (the peeling line S is an arc toward the unwinding direction L) from one end to the other end of the width direction x of the polypropylene film (i.e., from one end x1 of the peeling line to the other end x2). The thinner and wider the polypropylene film roll is, the larger the shortest distance ΔL of the peeling line is. Note that when the polypropylene film roll is visually observed from above, the peeled part and the unpeeled part of the transparent polypropylene film roll look different on either side of the boundary line, so the peeling line can be visually recognized.

[0022] The shortest distance ΔL of the peel line of the polypropylene film roll can be measured by the method described in the Examples.

[0023] In the polypropylene film roll according to the present embodiment, the shortest distance ΔL of the peeling line is set to 20 mm or less, and the physical property (2) described below is also satisfied (the ratio ΔX of the circumference of the polypropylene film roll is set to 0.2% or less), so that the polypropylene film unwound from the polypropylene film roll can be subjected to metal deposition processing with high precision while maintaining high flatness, and the variation in the thickness of the metal film is suppressed. Furthermore, the capacitor element obtained from the polypropylene film has excellent long-term durability under high temperature and high voltage, and the decrease in yield due to winding misalignment and cutting caused by wrinkles and sagging of the film is also suppressed, so that the capacitor element can be manufactured with a high yield.

[0024] The polypropylene film unwound from the polypropylene film roll is subjected to highly accurate metal deposition processing while maintaining higher flatness, and the capacitor element has further improved long-term durability under high temperature and high voltage, and furthermore, the reduction in yield caused by winding deviation and cutting due to wrinkles and sagging of the polypropylene film is suppressed, so that the capacitor element is manufactured with a higher yield. In this respect, the shortest distance ΔL of the peel line in the polypropylene film roll according to this embodiment may be 20 mm or less, but is preferably 17 mm or less, more preferably 14 mm or less, and even more preferably 10 mm or less. The lower limit of the shortest distance ΔL of the peel line may be, for example, 0 mm or 2 mm.

[0025] The physical property (2) is that, when the circumferential length is measured at both ends of a polypropylene film roll, at the center, and at positions 50 mm apart from the center toward both ends, the ratio ΔX ((Xmax-Xmin) / Xave) of the difference (Xmax-Xmin) between the maximum circumferential length Xmax and the minimum circumferential length Xmin to the average circumferential length Xave is 0.2% or less.

[0026] In the polypropylene film roll according to the present embodiment, the circumferential length ratio ΔX may be 0.2% or less, but from the above viewpoint, it is preferably 0.19% or less, more preferably 0.18% or less, and further preferably 0.17% or less. The lower limit of the circumferential length ratio ΔX may be, for example, 0.00% or 0.01%.

[0027] The circumferential length ratio ΔX of the polypropylene film roll can be measured by the method described in the Examples.

[0028] From the above viewpoints, in the polypropylene film roll according to the present embodiment, when the hardness is measured at both end positions, the center position, and positions at 50 mm intervals from the center position toward both end positions of the polypropylene film roll, it is preferable that the average hardness Mave is 88 to 96°, and the difference ΔM between the maximum hardness Mmax and the minimum hardness Mmin is less than 4°. Mave is more preferably 96 to 86°, and even more preferably 94 to 88°, and ΔM is more preferably 3° or less, and even more preferably 2° or less. The lower limit of ΔM is, for example, 0°.

[0029] The average hardness value Mave of the polypropylene film roll and the difference ΔM between the maximum hardness value Mmax and the minimum hardness value Mmin can be measured by the method described in the Examples.

[0030] From the above viewpoints, in the polypropylene film roll according to the present embodiment, the polypropylene film preferably has a longitudinal direction (MD) distortion rate (ε1), transverse direction (TD) distortion rate (ε2), and diagonal direction (45°) distortion rate (ε3) in the range of 0.6 to 1.5%, more preferably 0.6 to 1.4%, and further preferably 0.6 to 1.3%, at a stress of 25 MPa.

[0031] The distortion rate of the polypropylene film is a value measured for the polypropylene film unwound from a polypropylene film roll, and specifically, it can be measured by the method described in the Examples.

[0032] From the above viewpoints, the ratio (ε2 / ε1) of the strain rate (ε1) to the strain rate (ε2), and the ratio (ε3 / ε1) of the strain rate (ε3) to the strain rate (ε1) are each preferably in the range of 0.5 to 1.0, more preferably in the range of 0.7 to 1.0, and even more preferably in the range of 0.8 to 0.9.

[0033] From the above viewpoints, in the polypropylene film roll according to the present embodiment, the surface roughness of at least one side of the polypropylene film is preferably a center line average roughness (Ra) of 0.04 to 0.08 μm and a maximum height (Rz) of 0.3 to 0.9 μm. The center line average roughness (Ra) is more preferably 0.05 to 0.08 μm, and even more preferably 0.05 to 0.07 μm. The maximum height (Rz) is more preferably 0.3 to 0.8 μm, and even more preferably 0.4 to 0.8 μm. The surface roughness of both sides of the polypropylene film may have the above values.

[0034] The surface roughness (center line average roughness (Ra) and maximum height (Rz)) of the polypropylene film is a value measured on the polypropylene film unwound from a polypropylene film roll, and specifically, can be measured by the method described in the examples.

[0035] In the polypropylene film roll according to the present embodiment, the difference between the maximum and minimum values ​​of the slow axis angle obtained by the following techniques (a) to (c) is preferably 5° or less. (a) When the total width of the polypropylene film is taken as 100%, nine measurement samples each measuring 50 mm x 50 mm are cut out, the centers of which are positioned 10% apart from both ends. (b) The width direction of the measurement sample is set to 0°, and the acute angle formed between the width direction of the measurement sample and the slow axis is measured as the slow axis angle. (c) Of the nine measurement samples, the difference between the maximum and minimum values ​​of the slow axis angle measured in (b) above is determined.

[0036] This physical property is related to the slow axis angle of the polypropylene film. Biaxially stretched polypropylene film is stretched in two axes, a first direction and a second direction perpendicular to the first direction. The polypropylene film has birefringence because the polypropylene is oriented in-plane by biaxial stretching. In the plane of the polypropylene film, the direction in which the refractive index is maximum is called the slow axis because it is the direction in which light travels slowly (the phase is delayed).

[0037] For example, in the sequential biaxial stretching method, a cast raw sheet is first stretched in the machine direction (MD direction), and then the sheet is stretched in the transverse direction (TD direction (width direction)). In this case, with respect to the slow axis of the biaxially stretched polypropylene film, the refractive index in the transverse direction of the second direction tends to be larger than the refractive index in the machine direction of the first direction. Here, the transverse direction of the second direction becomes the slow axis.

[0038] In the case of transverse (TD) stretching, when the film is completely stretched in the transverse direction (when the film is completely stretched in the direction perpendicular to the flow direction), the slow axis angle defined in this specification is 0°. However, in reality, Poisson shrinkage stress, external mechanical force, thermoplasticity of the film, etc. act during stretching, and the film cannot be completely stretched in the transverse direction (TD), so the slow axis angle tends to be larger than 0°. In addition, in the sequential biaxial stretching method, the slow axis angle tends to be larger at both ends of the biaxially stretched film.

[0039] In this embodiment, it can be said that the smaller the difference between the maximum and minimum values ​​of the slow axis angle, the smaller the deviation of the optical alignment axis with respect to the two orthogonal directions, the flow direction (MD) of the first direction and the transverse direction (TD) of the second direction. Therefore, when producing a metallized film, shrinkage in an oblique direction during heating is reduced, and it is easier to balance the thermal shrinkage in the first direction and the second direction. As a result, wrinkles and sagging during processing are suppressed, and the film can be used favorably.

[0040] The difference between the maximum and minimum values ​​of the slow axis angle according to this embodiment is not the anisotropy of the optical orientation strength indicated by birefringence, i.e., it is not the magnitude and direction of the orientation itself, but the angle between the second direction and the maximum and minimum values ​​of the slow axis, i.e., the fluctuation range in the width direction of the slow axis angle. In this embodiment, it is preferable to control the difference to be small in the roll width direction (processing width direction). The reason why it is preferable to control the difference to be small is that even if polypropylene, which is a flexible material, is given an orientation strength by biaxial stretching and a certain mechanical processing strength, the thermal dimensional change amount that occurs during metal deposition processing is not sufficiently reduced, and rather, suppressing the deviation and fluctuation of the orientation direction in the roll width direction works to balance the orientation of the in-plane shrinkage direction, and a metallized film with less deposition film unevenness can be obtained.

[0041] The capacitor element thus obtained has excellent long-term durability under high temperature and high voltage conditions. In addition, the winding misalignment caused by wrinkles and sagging during processing is significantly reduced, the yield of the capacitor element is excellent, and the polypropylene film roll can be used as a cost-effective roll.

[0042] In the polypropylene film roll according to the present embodiment, the difference between the maximum and minimum values ​​of the slow axis angle of the polypropylene film is set to less than 5°, and the physical property (2) described below is also satisfied (the ratio ΔX of the circumference length of the polypropylene film roll is set to 0.2% or less), so that the polypropylene film unwound from the polypropylene film roll can be subjected to metal deposition processing with high precision while maintaining high flatness, and the variation in the thickness of the metal film is suppressed. Furthermore, the capacitor element obtained from the polypropylene film has excellent initial voltage resistance and long-term durability under high temperature and high voltage, and also suppresses winding misalignment due to wrinkles and sagging of the film, allowing the capacitor element to be manufactured with a high yield.

[0043] From the viewpoint of manufacturing capacitor elements with a higher yield by subjecting the polypropylene film unwound from the polypropylene film roll to a highly accurate metal deposition process while maintaining a higher flatness, and further improving the initial voltage resistance and long-term durability under high temperature and high voltage conditions of the capacitor element, and further suppressing a decrease in yield due to winding deviation and cutting caused by wrinkles and sagging of the polypropylene film, the angle is preferably 4.5° or less, more preferably 4.0° or less, and even more preferably 3.0° or less. The lower limit of the difference between the maximum and minimum values ​​of the slow axis angle is 0°.

[0044] The difference between the maximum and minimum values ​​of the slow axis angle of the polypropylene film can be measured by the method described in the Examples.

[0045] In the polypropylene film roll according to the present embodiment, the thickness of the polypropylene film is, for example, 6.0 μm or less, and in the polypropylene film roll wound with the thin polypropylene film, from the viewpoint of suitably satisfying the physical properties (1) and (2) above, the thickness is preferably 4.0 μm or less, more preferably 3.0 μm or less, even more preferably 2.8 μm or less, and particularly preferably 2.5 μm or less. Also, from the viewpoint of suitably satisfying the physical properties (1) and (2) above, the thickness is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more.

[0046] In the polypropylene film roll according to the present embodiment, the width of the polypropylene film may be 200 mm or more. However, for a polypropylene film roll wound with a wide polypropylene film, from the viewpoint of suitably satisfying the physical properties (1) and (2) described above, the width is preferably 400 mm or more, more preferably 600 mm or more, and preferably within a range of 600 to 1200 mm, and even more preferably 600 to 1000 mm.

[0047] In the polypropylene film roll according to the present embodiment, the winding length of the polypropylene film is not particularly limited, but may be, for example, 10,000 m or more, or even 30,000 m or more. The upper limit of the winding length of the polypropylene film is, for example, 100,000 m.

[0048] The polypropylene film wound around the polypropylene film roll according to the present embodiment is preferably a biaxially stretched polypropylene film. From the viewpoint of suitably satisfying the physical properties (1) and (2) above, the preferred stretching ratios (longitudinal stretching ratio, transverse stretching ratio) of the biaxially stretched polypropylene film are as described in the section <2. Manufacturing method of polypropylene film roll> below.

[0049] As described later, the physical properties (1) and (2) are affected by the stretching conditions of the polypropylene film. The physical properties (1) and (2) can be adjusted by adjusting the stretching temperature and stretching ratio when stretching in the machine direction (hereinafter also referred to as "longitudinal stretching temperature" and "longitudinal stretching ratio", respectively), and the stretching temperature, stretching ratio and stretching angle when stretching in the width direction (hereinafter also referred to as "transverse stretching temperature", "transverse stretching ratio" and "transverse stretching angle", respectively). Examples of preferred stretching conditions in this embodiment will be described later in the section <2. Manufacturing method of polypropylene film roll>. In this specification, the "longitudinal direction" and the "machine direction" are synonymous, and the "transverse direction" and the "width direction" are synonymous.

[0050] The polypropylene film wound around the polypropylene film roll according to the present embodiment contains polypropylene resin as a resin. Preferably, the main component of the polypropylene film is polypropylene resin, and more preferably, the resin component constituting the film is polypropylene resin. The above-mentioned "main component" means that the main component resin is contained in the polypropylene film in an amount of 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, calculated as solid content. The polypropylene resin contained in the polypropylene film will be described in detail below.

[0051] <Polypropylene resin> The polypropylene resin is not particularly limited as long as a polypropylene film roll having the physical properties (1) and (2) can be obtained, and any polypropylene resin that can be used to form a polypropylene film can be widely used. Examples of polypropylene resins include propylene homopolymers such as isotactic polypropylene and syndiotactic polypropylene; copolymers of propylene and ethylene; long-chain branched polypropylene; and ultra-high molecular weight polypropylene. Among them, propylene homopolymers are preferred from the viewpoint of heat resistance, and isotactic polypropylene obtained by homopolymerizing polypropylene in the presence of an olefin polymerization catalyst is even more preferred. The polypropylene resin may be one type alone or two or more types in combination.

[0052] The weight average molecular weight (Mw) of the polypropylene resin is preferably 250,000 or more and 450,000 or less. When such a polypropylene resin is used, appropriate resin fluidity is obtained during biaxial stretching, and the thickness of the cast raw sheet is easily controlled. For example, this is preferable because it is easy to obtain an extremely thin biaxially stretched polypropylene film suitable for small and high-capacity capacitors. In addition, this is preferable because it is difficult for unevenness in the thickness of the cast raw sheet and the biaxially stretched polypropylene film to occur.

[0053] The molecular weight distribution (Mw / Mn) of the polypropylene resin, calculated as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 7 or more and 12 or less. The molecular weight distribution (Mw / Mn) is more preferably 7.1 or more, even more preferably 7.5 or more, and particularly preferably 8 or more. The molecular weight distribution (Mw / Mn) is more preferably 11 or less, and even more preferably 10 or less. When such a polypropylene resin is used, appropriate resin fluidity is obtained during biaxial stretching, and it is easy to obtain an extremely thin biaxially stretched propylene film without thickness unevenness, which is preferable. In addition, such a polypropylene resin is also preferable from the viewpoint of the voltage resistance of the biaxially stretched polypropylene film.

[0054] The weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the polypropylene resin can be measured using a gel permeation chromatograph (GPC). More specifically, for example, the measurement can be performed using a high-temperature GPC measuring instrument with built-in differential refractive index (RI) manufactured by Tosoh Corporation, HLC-8121GPC-HT (trade name). Mw and Mn are measured, for example, as follows. As the GPC column, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation are connected and used, the column temperature is set to 140°C, and trichlorobenzene is passed as an eluent at a flow rate of 1.0 ml / 10 min to obtain measured values ​​of Mw and Mn. A calibration curve for the molecular weight M is created using standard polystyrene manufactured by Tosoh Corporation, and the measured values ​​are converted to polystyrene values ​​to obtain Mw and Mn.

[0055] The melt flow rate (MFR) of the polypropylene resin at 230°C under a load of 2.16 kg is not particularly limited, but from the viewpoint of the stretchability of the obtained film, it is preferably 7 g / 10 min or less, more preferably 6 g / 10 min or less. Also, from the viewpoint of improving the accuracy of the thickness of the polypropylene film, it is preferably 0.3 g / 10 min or more, more preferably 0.5 g / 10 min or more. The MFR can be measured in accordance with JIS K 7210-1999.

[0056] The mesopentad fraction ([mmmm]) of the polypropylene resin is preferably 94% or more, more preferably 95% or more, and even more preferably more than 96%. The mesopentad fraction of the polypropylene resin is preferably 98.5% or less, more preferably 98.4% or less, and even more preferably 98% or less. The mesopentad fraction of the polypropylene resin is preferably 94% or more and 99% or less, and even more preferably 95% or more and 98.5% or less. By using such a polypropylene resin, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the initial voltage resistance and long-term voltage resistance are improved. On the other hand, the desired stretchability can be obtained by the moderate solidification (crystallization) speed when forming the cast raw sheet.

[0057] The mesopentad fraction ([mmmm]) is an index of stereoregularity that can be obtained by high-temperature nuclear magnetic resonance (NMR) measurement. Specifically, for example, it can be measured using a high-temperature Fourier transform nuclear magnetic resonance spectrometer (high-temperature FT-NMR), JNM-ECP500, manufactured by JEOL Ltd. The observation nucleus is 13C (125MHz), the measurement temperature is 135°C, and ortho-dichlorobenzene (ODCB: a mixed solvent of ODCB and deuterated ODCB (mixture ratio = 4 / 1) can be used as a solvent to dissolve polypropylene resin. The measurement method using high-temperature NMR can be performed by referring to the method described in, for example, "Japan Analytical Chemistry, Polymer Analysis Research Roundtable, edited by, New Edition Polymer Analysis Handbook, Kinokuniya Shoten, 1995, p. 610".

[0058] The measurement mode can be single pulse proton broadband decoupling, pulse width 9.1 μsec (45° pulse), pulse interval 5.5 sec, number of accumulations 4500, shift standard CH3(mmmm)=21.7 ppm. The pentad fraction, which indicates the degree of stereoregularity, is calculated as a percentage based on the integral value of the intensity of each signal derived from a combination of five pentads (pentads) of the same-direction pentads "meso (m)" and the opposite-direction pentads "racemo (r)" (mmmm, mrrm, etc.). Each signal derived from mmmm, mrrm, etc. can be assigned by referring to, for example, "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" or the like.

[0059] The polypropylene resin, which is the main component of the polypropylene film roll according to the present embodiment, may be a linear polypropylene resin. The linear polypropylene resin may be used alone or in a mixture of two or more. In particular, it is preferable to use the following linear polypropylene resin A and / or the following linear polypropylene resin B. In particular, it is preferable to use the following linear polypropylene resin A and the following linear polypropylene resin B in combination. The following linear polypropylene resin A and the following linear polypropylene resin B are preferably homopolypropylene resins. As the combined use of the following linear polypropylene resin A and the following linear polypropylene resin B, the following combinations of resin A-1 and resin B-1, resin A-2 and resin B-2, and resin A-3 and resin B-3 are preferable. However, the polypropylene resin in the present invention is not limited to the following resins.

[0060] <Linear polypropylene resin A> (Linear polypropylene resin A-1) 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-2) A linear polypropylene resin with a weight average molecular weight Mw of 340,000 or less. (Linear polypropylene resin A-3) A linear polypropylene resin with a molecular weight distribution Mw / Mn of 8.8 or more. A linear polypropylene resin.

[0061] <Linear polypropylene resin B> (Linear polypropylene resin B-1) A linear polypropylene resin with a melt flow rate (MFR) of less than 4.0 g / 10 min at 230°C. (Linear polypropylene resin B-2) A linear polypropylene resin with a weight average molecular weight Mw of more than 340,000. (Linear polypropylene resin B-3) A linear polypropylene resin having a molecular weight distribution Mw / Mn of less than 8.8.

[0062] When linear polypropylene resin A and linear polypropylene resin B are used in combination, the content ratio preferably includes 55 mass% or more of the linear polypropylene resin A and 45 mass% or less of the linear polypropylene resin B, more preferably includes 60 to 85 mass% of the linear polypropylene resin A and 40 to 15 mass% of the linear polypropylene resin B, and particularly preferably includes 60 to 80 mass% of the linear polypropylene resin A and 40 to 20 mass% of the linear polypropylene resin B.

[0063] (Additives) The polypropylene film may further contain additives. The "additives" are additives generally used in polypropylene resins, and are not particularly limited as long as the polypropylene film can be obtained. The additives include, for example, antioxidants, necessary stabilizers such as chlorine absorbers and ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, colorants, etc. The polypropylene resin for producing the polypropylene film may contain such additives in an amount that does not adversely affect the polypropylene film.

[0064] (core) The polypropylene film roll according to the present embodiment is formed by winding a polypropylene film around a core. The core is cylindrical or cylindrical, and the polypropylene film is wound around the core in the circumferential direction.

[0065] The material of the core is not particularly limited as long as the polypropylene film roll satisfies the physical properties (1) and (2) above, and examples thereof include plastics that are less prone to deformation, fiber-reinforced plastics, paper, metals (iron, SUS, aluminum, etc.), etc. Among these, fiber-reinforced plastics are preferred because they are lightweight and strong, and can easily satisfy the physical properties (1) and (2) above. Examples of fiber-reinforced plastic cores include those made by molding carbon fiber, glass fiber, etc. into a cylindrical shape and impregnating and curing a curable resin such as an unsaturated polyester resin.

[0066] The size of the core can be set according to the size of the intended polypropylene film roll. The outer diameter of the circular cross section of the core is, for example, about 50 to 500 mm, more preferably about 100 to 300 mm.

[0067] The polypropylene film wound around the polypropylene film roll according to the present embodiment has high initial voltage resistance and excellent long-term voltage resistance. Furthermore, it can be made very thin, so it is easy to achieve high capacitance. Therefore, it can be used very suitably for small-sized capacitors with a high capacitance of 5 μF or more, preferably 10 μF or more, and more preferably 20 μF or more.

[0068] The method for producing the polypropylene film roll according to the present embodiment is not particularly limited as long as the method can provide a film that satisfies the physical properties (1) and (2) described above. A preferred method for producing the polypropylene film roll according to the present embodiment is described in detail in the section <2. Method for producing the polypropylene film roll>.

[0069] <2. Manufacturing method of polypropylene film roll> The method for producing a polypropylene film roll is not limited to the following, but may be, for example, a production method including the following steps 1 to 5 in this order. (1) Step 1 of heating and melting a resin composition containing a polypropylene raw material resin (2) Step 2 of extruding the heat-molten resin composition (3) Step 3 of cooling and solidifying the extruded resin composition to obtain a cast raw sheet. (4) Step 4: Stretching the cast raw sheet in the machine direction and width direction to obtain a biaxially oriented polypropylene film (5) Step 5: The biaxially oriented polypropylene film is cut (slit) to a predetermined width and wound around a core to obtain a polypropylene film roll. The method for producing a polypropylene film roll will be described in detail below.

[0070] (Production of raw polypropylene resin) The polypropylene raw material resin that can be contained in the polypropylene film can be produced by a generally known polymerization method. The method for producing the polypropylene resin is not particularly limited as long as the produced polypropylene resin can be used to finally obtain a polypropylene film. Examples of such polymerization methods include gas phase polymerization, bulk polymerization, and slurry polymerization.

[0071] The total ash content resulting from polymerization catalyst residues and the like contained in the polypropylene raw material resin is preferably as low as possible in order to improve the electrical properties of the polypropylene film. The total ash content is preferably 50 ppm or less, more preferably 40 ppm or less, and particularly preferably 30 ppm or less, based on the polypropylene resin (100 parts by weight). The total ash content in the polypropylene film is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 5 ppm or more, based on the polypropylene resin.

[0072] (Steps 1 to 3: Manufacturing cast raw sheet) A "cast raw sheet", which is a sheet before stretching for producing a biaxially stretched polypropylene film, can be produced, for example, by using the polypropylene raw material resin produced as described above through steps 1 to 3 described above.

[0073] As the resin composition, polypropylene resin pellets, dry-mixed polypropylene resin pellets (and / or polymer powder), or mixed polypropylene resin pellets previously prepared by melt kneading, etc. are supplied to an extruder and heated and melted (step 1), passed through a filtration filter, and then heated and melted preferably to 170°C to 320°C, more preferably 200°C to 300°C, and melt extruded from a T-die (step 2), and cooled and solidified in at least one metal drum maintained at preferably 92°C to 105°C, even more preferably 93°C to 97°C, to form a cast raw sheet (step 3).

[0074] From the viewpoint of suitably imparting the physical properties (1) and (2) to the polypropylene film roll according to the present embodiment, the surface temperature of the metal drum when forming the cast raw sheet is preferably 92 to 97°C, more preferably 93 to 96°C, and even more preferably 94 to 95°C. When the surface temperature of the metal drum is in these preferred ranges, the β crystal fraction can be set in a preferred range, and fine roughness can be formed on the film surface. If the surface temperature is below 92°C, the film surface becomes smooth and has poor slippage, and wrinkles tend to occur on the roll of the processing machine. On the other hand, if the temperature exceeds 97°C, the film surface is excessively roughened, so that when the film is unwound from the film roll, winding slippage tends to occur, and the film tends to meander on the roll of the processing machine. The β crystal fraction is preferably 1% or more and 50% or less, more preferably 5% or more and 30% or less, and even more preferably 5% or more and 20% or less, as measured by the X-ray method. This value is the value when no β crystal nucleating agent is included. The above-mentioned range of the β crystal fraction is preferable because it is easy to satisfy both the physical properties of the capacitor and the processability of winding an element.

[0075] The β crystal fraction can be obtained by measuring the X-ray diffraction intensity and calculated by the method described in "A. Turner-Jonesetal., Makromol. Chem., Vol. 75, p. 134 (1964)", and is called the K value. In other words, the ratio of β crystals is expressed by the ratio of the sum of the heights of three diffraction peaks derived from α crystals to one diffraction peak derived from β crystals.

[0076] The thickness of the cast raw sheet is not particularly limited as long as a polypropylene film can be obtained, but is preferably 0.05 mm to 2 mm, and more preferably 0.1 mm to 1 mm.

[0077] (Step 4: Production of biaxially oriented polypropylene film) In step 4, the cast raw sheet is stretched in the machine direction and the width direction to produce the film. The stretching is performed by biaxial stretching in which the film is oriented in both the machine direction and the width direction. The stretching method may be a simultaneous or sequential biaxial stretching method, but a sequential biaxial stretching method is preferred.

[0078] In the sequential biaxial stretching method, for example, a cast raw sheet is first kept at a temperature of about 135 to 147°C (longitudinal stretching temperature), passed between rolls with a speed difference, stretched 4.00 to 4.95 times (longitudinal stretching ratio) in the machine direction, and immediately cooled to room temperature. The stretched film is then introduced into a tenter and stretched about 7 to 11 times (transverse stretching ratio) in the width direction at a temperature of 150°C or higher (transverse stretching temperature), and then relaxed and heat-set (heat-set temperature is about 158 ​​to 168°C) before being wound up. The wound up film can be aged in an atmosphere of about 20 to 45°C, and then cut to the desired product width.

[0079] In the above manufacturing process, the longitudinal stretching temperature, longitudinal stretching ratio, transverse stretching temperature, transverse stretching ratio, molecular weight distribution of polypropylene resin, resin temperature during melting, MFR of cast film, relaxation rate in the width direction after transverse stretching, relaxation temperature, heat setting temperature, etc. are parameters that affect the physical properties (1) and (2) described above, and these are appropriately adjusted. Among these parameters, the longitudinal stretching ratio is a parameter that has a large effect on the physical properties (1) and (2). An example of the adjustment range for some of these is shown below. However, in this embodiment, the above parameters are not limited to the following ranges.

[0080] <Longitudinal stretching temperature> From the viewpoint of easily imparting the desired physical properties in this embodiment, the longitudinal stretching temperature is preferably 135 to 147°C, more preferably 137 to 147°C, and further preferably 140 to 145°C.

[0081] <Longitudinal stretch ratio> From the viewpoint of easily providing the desired physical properties of the present embodiment, the longitudinal stretching ratio is preferably 4.00 to 4.95 times, more preferably 4.20 to 4.80 times. When the longitudinal stretching ratio is in the preferred range, film breakage is suppressed in the transverse stretching step during film production, resulting in excellent productivity. In addition, the obtained film has a moderately high mechanical strength and excellent processability. If the ratio is less than 4.00 times, the distortion rate (elongation change) when force is applied tends to be large, and wrinkles are likely to occur due to the tension of the processing machine. On the other hand, if the ratio exceeds 4.95 times, the distortion rate is small, so that the film does not easily follow the film roll during winding, and air tends to be unevenly entrained. Therefore, the film deforms at the portion where the air layer between the overlapping films is large, and wrinkles and sagging are likely to occur at specific portions during processing. <Transverse stretching temperature> From the viewpoint of easily providing the desired physical properties of the present embodiment, the transverse stretching temperature is preferably 150° C. or more, more preferably 155° C. or more and less than 165° C., even more preferably 155° C. or more and less than 160° C., and particularly preferably 155° C. or more and 159° C. or less. In order to set the transverse stretching temperature within the above range, the tenter temperature may be set within the above range. <Horizontal stretch ratio> From the viewpoint of easily imparting the desired physical properties in this embodiment, the transverse stretching ratio is preferably 7 to 11 times, more preferably 8 to 11 times, and further preferably 9 to 11 times.

[0082] A biaxially oriented polypropylene film can be produced by such a stretching process. It is preferable to impart a suitable surface roughness to the surface of the biaxially oriented polypropylene film so as to improve the winding suitability and also to improve the capacitor characteristics.

[0083] (Process 5: Slitting process and winding process onto a core) In step 5, the biaxially oriented polypropylene film obtained in step 4 is cut (slit) to a predetermined width. For example, as shown in the schematic diagram of FIG. 2, the biaxially oriented polypropylene film in step 4 is wound around a roll to prepare a pre-cut film roll. Next, the film is unwound from the pre-cut film roll, and while being cut in the unwound direction by a slitter (slit section), the cut polypropylene film is wound around a core to obtain a polypropylene film roll. In step 5, when winding the cut polypropylene film, a method can be adopted in which a winding device equipped with a contact pressure roll is used to apply a winding surface pressure to the polypropylene film while winding it. At this time, the winding tension and winding surface pressure during cutting, and further the rubber hardness of the contact pressure roll, are parameters that have a large effect on the physical properties (1) and (2) above, respectively.

[0084] From the viewpoint of suitably imparting the physical properties (1) and (2) to the polypropylene film roll of the present embodiment, the winding tension in step 5 is preferably 30 to 75 N / m, more preferably 40 to 70 N / m, even more preferably 50 to 65 N / m, and particularly preferably 50 to 60 N / m. The winding surface pressure in step 5 is preferably 200 to 440 N / m, more preferably 250 to 420 N / m, even more preferably 300 to 400 N / m, and extremely preferably 320 to 400 N / m.

[0085] The unwinding tension in step 5 is set in accordance with the winding tension, and is preferably 30 to 70 N / m, more preferably 30 to 65 N / m, and further preferably 35 to 60 N / m.

[0086] From the viewpoint of suitably imparting the physical properties (1) and (2) to the polypropylene film roll of this embodiment, the rubber hardness of the contact pressure roll used in step 5 is preferably 35° to 65°, more preferably 40° to 60°, and even more preferably 40° to 55°. When the rubber hardness is within the preferred range, the surface rubber is appropriately deformed to match the shape of the film roll, so that the surface pressure during winding is easily applied uniformly in the width direction. As a result, the air layer inside the obtained film roll is uniformed, so that the difference in the peeling position in the width direction when the film is unwound is small. When the rubber hardness is below 35°, the surface rubber is deformed to excessively follow the shape of the film roll, so that the air layer inside the obtained film roll is small and the film is wound tightly. Therefore, blocking is likely to occur between the overlapping wound films, and the difference in the peeling position in the width direction is large when the film is unwound. If the rubber hardness exceeds 65°, the surface rubber will have difficulty conforming to the shape of the film roll, the surface pressure during winding will be uneven in the width direction, and the film will tend to be wound tightly in some places. Inside the obtained film roll, the air layer will be uneven in the width direction, and when the film is unwound, the difference in the peeling position in the width direction will tend to become large.

[0087] <3. Metallized polypropylene film roll> In one aspect, the present embodiment provides a metallized polypropylene film roll having a metal film on one or both sides of a polypropylene film, and further a metallized polypropylene film unwound from the metallized polypropylene film roll. The metallized polypropylene film roll and the metallized polypropylene film of the present embodiment are described in detail below. The capacitor obtained by winding the metallized polypropylene film of the present embodiment has excellent long-term durability under high temperature and high voltage.

[0088] The polypropylene film can be provided with electrodes on one or both sides for processing into a capacitor. Such electrodes are not particularly limited as long as the capacitor targeted by this embodiment can be obtained, and electrodes that are usually used for manufacturing capacitors can be used. Examples of electrodes include metal foils, paper with at least one side metallized, and plastic films.

[0089] Since capacitors are increasingly required to be small and lightweight, it is preferable to form electrodes by directly metallizing one or both sides of the film of this embodiment. The metals used may be, for example, simple metals such as zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of multiple types of these, and alloys of these, but zinc and aluminum are preferred in consideration of the environment, economy, and capacitor performance.

[0090] Examples of methods for directly metallizing the surface of a polypropylene film include vacuum deposition and sputtering, and are not particularly limited as long as the capacitor of the present embodiment can be obtained. From the viewpoints of productivity and economy, the vacuum deposition method is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, but are not particularly limited as long as the capacitor of the present embodiment can be obtained, and the most suitable method can be selected as appropriate.

[0091] From the viewpoint of the electrical properties of the capacitor, the film resistance of the metal vapor deposition film is preferably about 1 to 100 Ω / □. Even within this range, it is desirable to have a higher film resistance from the viewpoint of self-healing properties, and the film resistance is more preferably 5 Ω / □ or more, and even more preferably 10 Ω / □ or more. From the viewpoint of safety as a capacitor, the film resistance is more preferably 50 Ω / □ or less, and even more preferably 30 Ω / □ or less. The film resistance of the metal vapor deposition film can be measured during metal vapor deposition, for example, by a four-terminal method known to those skilled in the art. The film resistance of the metal vapor deposition film can be adjusted, for example, by adjusting the output of the evaporation source to adjust the amount of evaporation.

[0092] When forming a metal deposition film on one side of the film, a certain width is not deposited from one end of the film to form an insulating margin so that the film will become a capacitor when rolled up. Furthermore, in order to strengthen the bond between the metallized polypropylene film and the metallikon electrode, it is preferable to form a heavy edge structure on the end opposite the insulating margin, and the film resistance of the heavy edge is usually about 1 to 8 Ω / □, and preferably about 1 to 5 Ω / □. The thickness of the metal film is not particularly limited, but is preferably 1 to 200 nm.

[0093] There are no particular limitations on the margin pattern of the metal vapor deposition film to be formed, but from the viewpoint of improving the characteristics of the capacitor, such as safety, it is preferable to use a pattern including a so-called special margin, such as a fishnet pattern, a T-margin pattern, etc. When a metal vapor deposition film is formed on one side of a polypropylene film in a pattern including a special margin, the safety of the resulting capacitor is improved, and it is also effective in preventing destruction and short circuits of the capacitor, and is therefore preferable.

[0094] The margin can be formed by any known method without any restriction, such as a tape method in which masking is performed with tape during deposition, or an oil method in which masking is performed by applying oil.

[0095] The metallized film of this embodiment can be processed into the capacitor of this embodiment described below by wrapping the film along its longitudinal direction. That is, two metallized films of this embodiment are stacked and wound together so that the metal deposition film and the polypropylene film are alternately laminated. The capacitor is then obtained by forming a pair of metallikon electrodes on both end faces by metal spraying to produce a film capacitor.

[0096] <4. Capacitor> In one aspect, the present invention provides a capacitor including the metallized polypropylene film of the present embodiment. The capacitor of the present embodiment will be described in detail below.

[0097] In the process of producing a capacitor, a film winding process is performed. For example, two metallized polypropylene films of the present embodiment are overlapped and wound so that the metal films and polypropylene films in the metallized polypropylene film of the present embodiment are alternately stacked and further so that the insulating margins are on opposite sides. In this case, it is preferable to stack the two metallized films of the present embodiment with a shift of 1 to 2 mm. There are no particular limitations on the winding machine used, and for example, an automatic winding machine 3KAW-N2 type manufactured by Kaito Seisakusho Co., Ltd. can be used.

[0098] When manufacturing flat capacitors, the resulting roll is usually pressed after winding. Pressing promotes tightening of the capacitor and element formation. From the viewpoint of controlling and stabilizing the interlayer gap, the optimum pressure to be applied varies depending on the thickness of the polypropylene film, etc., but is, for example, 2 to 20 kg / cm. 2 It is.

[0099] Next, metal is sprayed onto both end faces of the winding to provide metallikon electrodes, thereby completing a capacitor.

[0100] The capacitor is then subjected to a predetermined heat treatment, which in this embodiment includes a step of subjecting the capacitor to a heat treatment at a temperature of 80 to 125° C. for one hour or more in a vacuum (hereinafter, this may be referred to as “thermal aging”).

[0101] In the above process of subjecting the capacitor to heat treatment, the heat treatment temperature is usually 80°C or higher, preferably 90°C or higher. On the other hand, the heat treatment temperature is usually 130°C or lower, preferably 125°C or lower. By subjecting the heat treatment at the above temperature, the effect of thermal aging can be obtained. Specifically, the gap between the films constituting the capacitor based on the metallized film of this embodiment is reduced, corona discharge is suppressed, and the internal structure of the metallized film of this embodiment is changed and crystallization is promoted. As a result, it is considered that the voltage resistance is improved. If the heat treatment temperature is lower than a predetermined temperature, the above effect of thermal aging cannot be sufficiently obtained. On the other hand, if the heat treatment temperature is higher than a predetermined temperature, the polypropylene film may undergo thermal decomposition, oxidative deterioration, etc.

[0102] The method for subjecting the capacitor to heat treatment may be appropriately selected from known methods including, for example, a method using a thermostatic bath under a vacuum atmosphere, a method using high-frequency induction heating, etc. Specifically, it is preferable to employ a method using a thermostatic bath.

[0103] The time for the heat treatment is preferably 1 hour or more, and more preferably 10 hours or more, from the viewpoint of obtaining mechanical and thermal stability, but is more preferably 20 hours or less, from the viewpoint of preventing molding defects such as heat wrinkles and molding.

[0104] Lead wires are usually welded to the metallikon electrodes of the heat-aged capacitor. In order to impart weather resistance, particularly to prevent deterioration due to humidity, the capacitor is preferably encapsulated in a case and potted with epoxy resin.

[0105] The capacitor of the present embodiment is a small-sized, large-capacity capacitor based on the metallized film of the present embodiment, and has high voltage resistance at high temperatures and long-term durability at high temperatures and high voltages. EXAMPLES

[0106] The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples. In addition, unless otherwise specified, parts and % indicate "parts by mass" and "% by mass", respectively.

[0107] Example 1 [Example 1-1. Preparation of cast raw sheet] Polypropylene A1 (PP resin A1) and polypropylene B1 (PP resin B1) were fed to an extruder in a mass ratio of A1:B1 = 66:34, melted at a resin temperature of 230°C, extruded using a T-die, and solidified by wrapping around a metal drum whose surface temperature was kept at 95°C to produce a cast raw sheet (thickness 0.11 mm). PP resin A1 has Mw = 320,000, Mw / Mn = 9.3, difference (DM) = 11.2 ("difference (DM)" is 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 in the molecular weight differential distribution curve), mesopentad fraction [mmmm] = 95%, MFR = 4.9g / 10min, and is made by Prime Polymer. In addition, PP resin B1 has Mw=350,000, Mw / Mn=7.7, difference (DM)=7.2, mesopentad fraction [mmmm]=96.5%, MFR=3.8g / 10min, and is manufactured by Daehan Petrochemicals.

[0108] [Example 1-2. Preparation of biaxially oriented polypropylene film] The obtained cast raw sheet was kept at a temperature of 140°C, passed between rolls with a speed difference, stretched 4.5 times in the machine direction (longitudinal stretching), and immediately cooled to room temperature. Subsequently, the cast raw sheet was stretched in the machine direction to obtain a stretched film, which was introduced into a tenter and stretched 10 times in the width direction at a transverse stretching temperature of 158°C, then relaxed and heat-set at 166°C, wound up, and aged at 35°C to obtain a pre-cut film roll of 78,000 m of biaxially stretched polypropylene film with a width of 5,000 mm and a thickness of 2.5 μm.

[0109] [Example 1-3. Preparation of biaxially oriented polypropylene film roll after cutting] As shown in the schematic diagram of Figure 2, the film was unwound from the obtained pre-cut film roll and cut in the width direction using a slitter. When winding the cut polypropylene film, a fiber-reinforced plastic core with an outer diameter of 176 mm was used, and a winding device equipped with a contact pressure roll was used to wind the polypropylene film while applying surface pressure. The cutting conditions were a speed of 300 m / min, unwinding force of 40 N / m, winding tension of 50 N / m, and winding surface pressure of 400 N / m. A rubber contact pressure roll with an outer diameter of 152 mm and a surface hardness of 40° was used, and a biaxially oriented polypropylene roll (cut film roll) with a width of 620 mm and a length of 75,000 m was finished.

[0110] [Measurement of roll film properties] <The shortest distance ΔL from the midpoint of the line connecting both ends of the peeling line to the peeling line> As shown in the schematic diagram of FIG. 1, the obtained biaxially oriented polypropylene film roll was set in a roll-to-roll unwinding / winding device (NT-750 manufactured by NUINTEK) in an environment of room temperature 23° C. and humidity 60%, and unwinding of the polypropylene film was started under the conditions of unwinding force of 3 N / m and speed of 2 m / min. After 1 minute, while unwinding the film, the shortest distance ΔL from the midpoint P of the line connecting both ends of the peel line to the peel line S was measured. At this time, the shortest distance ΔL was indirectly measured by measuring the distance (distance in the unwinding direction L) between both ends (ends x1, x2) of the polypropylene film and the reference line U (present on the unwinding direction L side of the peel line S) provided along the width direction x of the polypropylene film as shown in the schematic diagram of FIG. 1, and the shortest distance from the center position of the reference line U in the width direction x to the peel line S. The results are shown in Table 2.

[0111] <Measurement of the circumference ratio ΔX> The circumference of the obtained biaxially oriented polypropylene film roll was measured at both ends, at the center, and at 50 mm intervals from the center toward both ends. A JIS Class 1 tape measure was used for the measurements. Next, the ratio ΔX ((Xmax-Xmin) / Xave), which is the difference (Xmax-Xmin) between the maximum circumference length Xmax and the minimum circumference length Xmin to the average circumference length Xave, was calculated. The results are shown in Table 2.

[0112] [Measurement of roll film properties] <Measurement of the difference between the maximum and minimum slow axis angles> For each of the biaxially stretched polypropylene films, the difference between the maximum and minimum values ​​of the slow axis angle was determined by the following methods (a) to (c). The results are shown in Table 2. (a) When the total width of the polypropylene film in the width direction is taken as 100%, nine measurement samples of 50 mm x 50 mm were cut out with the centers at positions every 10% from both ends. That is, in the case of a roll with a width of 620 mm, a total of nine measurement samples of 50 mm x 50 mm were cut out from one end of each roll with the centers at (620 / 9) mm, ([620 / 9] x 2) mm, ([620 / 9] x 3) mm, ([620 / 9] x 4) mm, ([620 / 9] x 5) mm, ([620 / 9] x 6) mm, ([620 / 9] x 7) mm, ([620 / 9] x 8) mm, and ([620 / 9] x 9) mm. (b) Next, the width direction of the measurement sample was set to 0°, and the acute angle between the width direction of the measurement sample and the slow axis was measured as the slow axis angle. The measurement device and measurement conditions were as follows. <Measurement equipment and conditions> Measurement equipment: Retardation measurement equipment RE-100 manufactured by Otsuka Electronics Co., Ltd. Light source: Laser light emitting diode (LED) Bandpass filter: 550 nm (measurement wavelength) Measurement interval: 0.1 sec Accumulation times: 10 times Number of measurement points: 15 points Gain: 10dB Measurement environment: temperature 23℃, humidity 60% (c) Of the nine measurement samples, the difference between the maximum and minimum values ​​of the slow axis angle measured in (b) above was determined.

[0113] <Measurement of roll hardness> The roll hardness (surface hardness) of the obtained biaxially stretched polypropylene film roll was measured at both ends, at the center, and at positions 50 mm apart from the center toward both ends using a rubber hardness tester conforming to JIS K6301. The results are shown in Table 2 for the average hardness value Mave, and the difference ΔM between the maximum hardness value Mmax and the minimum hardness value Mmin.

[0114] <Measurement of thickness of biaxially oriented polypropylene film> The thickness of the biaxially oriented polypropylene film unwound from the obtained biaxially oriented polypropylene film roll was measured using a micrometer (JIS-B7502) in accordance with JIS-C2330. The results are shown in Table 1.

[0115] <Ash content measurement of biaxially oriented polypropylene film> The ash content of the biaxially oriented polypropylene films obtained in Example 1 above and Examples 2 to 14 below was measured. Approximately 200 g of the film was weighed, transferred to a platinum dish, and incinerated at 800°C for 40 minutes. The ash content (ppm) was measured from the resulting ash residue. As a result, the ash content of the polypropylene films in all Examples was 20 ppm.

[0116] <Distortion rate at stress of 25 MPa> A tensile test was performed using a tension and compression testing machine (manufactured by Minebea Co., Ltd.) under test conditions (measurement temperature 23°C, test piece length 140 mm, test length 100 mm, test piece width 15 mm, tensile speed 100 mm / min). The tensile test was performed in three directions: MD, TD, and diagonal (45°). Next, the strain rates ε1 (MD), ε2 (TD), and ε3 (diagonal) at 25 MPa were calculated using data processing software built into the testing machine. The results are shown in Table 2.

[0117] <Surface roughness measurement> The center line average roughness (Ra) and Rz (Rmax defined in the old JIS) of the biaxially oriented polypropylene film were measured by the contact method in accordance with the method specified in JIS-B0601 using a three-dimensional surface roughness meter (Surfcom 1400D-3DF-12 type) manufactured by Tokyo Seimitsu Co., Ltd. Measurements were performed three times and the average value was calculated. Ra and Rz were measured by the contact method, but the reliability of the values ​​was confirmed by non-contact method values ​​as necessary. The results are shown in Table 2.

[0118] <Yield evaluation of film roll after cutting> In [Example 1-3. Preparation of biaxially oriented polypropylene film roll], the film was visually inspected during winding, and any film that had wrinkles was deemed to have failed. In addition, for winding misalignment, any film that had a misalignment of 2 mm or more when observed from the end face of the cutting roll was deemed to have failed. For all cutting rolls, the percentage of the number of film rolls that passed the above criteria after cutting was calculated as the cutting yield rate, and the following criteria were applied for evaluation. The results are shown in Table 2. A: 100% B: 80% or more, less than 100% C: Less than 80%

[0119] [Example 1-4. Preparation of a capacitor] Next, a capacitor was produced using the biaxially stretched polypropylene film roll obtained as follows. A biaxially stretched polypropylene film was subjected to aluminum deposition with a T-margin deposition pattern at a deposition resistance of 15Ω / □ using a vacuum deposition machine manufactured by ULVAC Co., Ltd., to obtain a metallized film containing a metal film on one side of the biaxially stretched polypropylene film. After slitting to a width of 60 mm, two sheets of the metallized film were put together and wound 1076 turns at a winding tension of 250g using an automatic winder 3KAW-N2 manufactured by Kaito Seisakusho Co., Ltd. The wound element was subjected to a heat treatment at 120°C for 15 hours while pressing, and then zinc metal was sprayed on the end surface of the element to obtain a flat capacitor. Lead wires were soldered to the end surface of the flat capacitor, and then it was sealed with epoxy resin.

[0120] [Evaluation of capacitor element processability] <Evaluation of deposition film unevenness> Regarding the pre-slit metallized film of the above [Example 1-4. Preparation of a capacitor], one full-width film for one revolution of the roll was peeled off from the pre-slit metallized film, and then a 100 mm square film piece was cut out from the center of the roll width direction of the peeled full-width film. The cut out film piece was divided into 100 10 mm square areas, and the color values ​​(L* value, a* value, b* value) were measured for the center of each of the 100 areas using a print density measuring instrument (X-Rite 938 model). The measurement diameter was 8 mm. For each of the L* value, a* value, and b* value, the variation was calculated using the following formula from the maximum value, minimum value, and average value of the 100 points. The largest variation among the L* value, a* value, and b* value was evaluated in three stages, A to C, as follows. The results are shown in Table 2. Variation in L* value (%) = (maximum L* value - minimum L* value) / average L* value of 100 points x 100 Variation of a* value (%) = (maximum a* value - minimum a* value) / average a* value of 100 points x 100 Variation of b* value (%) = (b* maximum value - b* minimum value) / average b* value of 100 points x 100 A: The largest variation among the L*, a*, and b* values ​​is less than 5%. B: The largest variation among the L*, a*, and b* values ​​is 5% or more and less than 10%. C: The largest variation among the L*, a*, and b* values ​​is 10% or more and less than 20%. D: The largest variation among L*, a*, and b* values ​​is 20% or more.

[0121] <Yield evaluation of capacitor element manufacturing> In the above [Example 1-4. Preparation of Capacitor], the film was visually inspected during the process, and any film with wrinkles was deemed to have failed. Regarding winding misalignment, any film with a misalignment of 0.2 mm or more was deemed to have failed when observed from the end face of the capacitor element. 100 elements were produced, and the percentage of the number of capacitor elements that passed was calculated as the element yield rate, and was evaluated according to the following criteria. The results are shown in Table 2. A: 100% B: 90% or more, less than 100% C: 80% or more, less than 90% D: Less than 80%

[0122] [Evaluation of long-term durability of capacitor elements] <Rate of change in capacitance ΔC> The initial capacitance (C0) of the capacitor element obtained in [Example 1-4. Preparation of Capacitor] before testing was measured using an LCR HiTester 3522-50 manufactured by Hioki E.E. Corporation. Next, a DC voltage of 300 V / μm per unit thickness was continuously applied to the capacitor for 500 hours in a high-temperature bath at 105°C. The capacitance (C 500 ) was measured using an LCR high tester, and the rate of change in capacity (ΔC) before and after the voltage load was calculated. Here, the rate of change in capacity was calculated using the following formula.

[0123]

number

[0124] The capacitance change rate was evaluated based on the average value of five capacitors according to the following criteria. The results are shown in Table 2. A+: -0.5% or more A: Less than -0.5%, -1% or more B: Less than -1%, -5% or more C: Less than -5%, -10% or more D: Less than -10%

[0125] Example 2 In the preparation of the biaxially oriented polypropylene film roll, the film roll was finished in the same manner as in Example 1, except that the surface hardness of the contact pressure roll was set to 55°, and a capacitor was prepared (Table 1). In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0126] Example 3 In the preparation of the biaxially oriented polypropylene film roll, except that the winding surface pressure was 350 N / m, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0127] Example 4 In the preparation of the biaxially oriented polypropylene film roll, the film roll was finished in the same manner as in Example 1, except that the surface hardness of the contact pressure roll was set to 55° and the winding surface pressure was set to 350 N / m, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0128] Example 5 In the preparation of the biaxially oriented polypropylene film roll, the film roll was finished in the same manner as in Example 1, except that the surface hardness of the contact pressure roll was 65° and the winding surface pressure was 320 N / m, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0129] Example 6 In the preparation of the biaxially oriented polypropylene film roll, except that the winding tension was set to 65 N / m, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0130] Example 7 In the preparation of the biaxially oriented polypropylene film, except that the film was stretched 4.00 times in the machine direction (longitudinal stretching), a film roll was finished and a capacitor was prepared in the same manner as in Example 1. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0131] Example 8 In the preparation of the biaxially oriented polypropylene film, except that the film was stretched 4.90 times in the machine direction (longitudinal stretching), a film roll was finished and a capacitor was prepared in the same manner as in Example 1. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0132] Example 9 In the preparation of the biaxially oriented polypropylene film, the film roll was finished in the same manner as in Example 1, except that the film was stretched 4.95 times in the machine direction (longitudinal stretching), the winding tension was set to 48 N / m, and the winding surface pressure was set to 390 N / m, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0133] Example 10 Except for changing the film thickness to 2.0 μm, a film roll was finished and a capacitor was produced in the same manner as in Example 1. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0134] Example 11 In the preparation of the biaxially oriented polypropylene film roll, except that the finished width of the roll was 820 mm, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0135] Example 12 In the preparation of the biaxially oriented polypropylene film, except that the surface temperature of the cast metal drum was set to 93° C., the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0136] (Example 13) In the preparation of the biaxially oriented polypropylene film, except that the surface temperature of the cast metal drum was set to 97° C., the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0137] Example 14 Except for setting the film thickness to 2.0 μm, the finish width of the roll to 820 m, and the tenter inlet speed ratio to a slightly lower value, the film roll was finished in the same manner as in Example 1, and a capacitor was produced. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0138] Comparative Example 1 In the preparation of the biaxially oriented polypropylene film roll, except that the surface hardness of the contact pressure roll was set to 65°, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0139] Comparative Example 2 In the preparation of the biaxially oriented polypropylene film roll, except that the surface hardness of the contact pressure roll was set to 70°, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0140] Comparative Example 3 In the preparation of the biaxially oriented polypropylene film roll, except that the surface hardness of the contact pressure roll was set to 75°, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0141] Comparative Example 4 In the preparation of the biaxially oriented polypropylene film roll, except that the winding tension was 80 N / m, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0142] Comparative Example 5 In the preparation of the biaxially oriented polypropylene film roll, except that the winding surface pressure was 450 N / m, the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0143] Comparative Example 6 In the preparation of the biaxially oriented polypropylene film, except that the film was stretched 3.90 times in the machine direction (longitudinal stretching), a film roll was finished and a capacitor was prepared in the same manner as in Example 1. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0144] Comparative Example 7 In the preparation of the biaxially oriented polypropylene film, except that the film was stretched 5.00 times in the machine direction (longitudinal stretching), a film roll was finished and a capacitor was prepared in the same manner as in Example 1. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0145] Comparative Example 8 In the preparation of the biaxially oriented polypropylene film, except that the surface temperature of the cast metal drum was set to 91° C., the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0146] Comparative Example 9 In the preparation of the biaxially oriented polypropylene film, except that the surface temperature of the cast metal drum was set to 98° C., the film roll was finished in the same manner as in Example 1, and a capacitor was prepared. In addition, the biaxially oriented polypropylene film and the capacitor element were each evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0147] [Table 1]

[0148] [Table 2]

[0149] The polypropylene film rolls of Examples 1 to 14 have a polypropylene film having a thickness of 20 μm or less and a width of 200 mm or more wound around a core, and (1) when the polypropylene film is unwound from the polypropylene film roll at an unwinding force of 3 N / m and a speed of 2 m / min in an environment of 23° C. and 60% humidity, the shortest distance ΔL from the midpoint of a line connecting both ends of a peel line, which is a boundary line where the polypropylene film is peeled from the polypropylene film roll, to the peel line is 20 mm or less, and (2) when the circumferential length is measured at both ends of the polypropylene film roll, at the center, and at positions 50 mm apart from the center toward both ends, the ratio ΔX of the difference (Xmax-Xmin) between the maximum circumferential length Xmax and the minimum circumferential length Xmin to the average circumferential length Xave is 0.2% or less. From the results shown in Table 2, it can be seen that the polypropylene film rolls of Examples 1 to 14 can be subjected to metal vapor deposition processing with high precision while maintaining high flatness on the polypropylene film unwound from the polypropylene film roll, the obtained capacitor elements have excellent long-term durability under high temperature and high voltage, and also suppresses reduction in yield due to winding misalignment and cutting caused by wrinkles and sagging of the film, making it possible to manufacture capacitor elements with a high yield.

[0150] Furthermore, as can be seen from the results of Examples 1 to 14 and Comparative Examples 1 to 9, the above physical properties (1) and (2) of the polypropylene film roll can be suitably set by adjusting the thickness and width of the polypropylene film, the surface temperature of the cast metal drum, the stretching ratio, the winding tension during cutting, the winding surface pressure, and the surface hardness of the contact pressure roll.

[0151] Specifically, for example, in Examples 1 to 4, the surface temperature of the cast metal drum is set to 94 to 95°C, and the longitudinal stretching ratio is set to 4.2 to 4.8 times, so that the film has a suitable surface roughness and mechanical strength, and is excellent in processability. In addition, the rubber hardness of the contact pressure roll is 40 to 55°, so that the surface rubber of the contact pressure roll easily follows the shape of the film roll, and the surface pressure during winding is easily applied uniformly in the width direction. Furthermore, the winding tension is 50 to 60 N / m, and the winding surface pressure is 320 to 400 N / m, so that the film roll does not have buckling, end surface misalignment, wrinkles, or other appearance defects. The film rolls of Examples 1 to 4 obtained in this manner satisfy the physical properties (1) and (2) described above, and a capacitor element having extremely excellent long-term durability could be manufactured. In addition, there was no wrinkle generation or vapor deposition unevenness during processing, and it could be used as a polypropylene film roll that is extremely suitable in terms of cost.

[0152] In Example 5, a contact pressure roll made of a relatively hard rubber with a rubber hardness of 65° was used. If the rubber hardness is high, it becomes difficult for the surface rubber to follow the shape of the film roll. Therefore, in Example 5, the surface pressure was lowered to 320 N / m and adjusted so as to contact the film roll uniformly in the width direction, thereby satisfying the physical properties (1) and (2) above. As in Examples 1 to 4, the capacitor element made from the film roll of Example 5 had extremely excellent long-term durability. In addition, there was no wrinkle or uneven deposition during processing, and it could be used as a polypropylene film roll that is extremely suitable in terms of cost.

[0153] On the other hand, Comparative Example 1 was the same as Example 1 except that the rubber hardness was changed to 65°. The surface rubber has difficulty in conforming to the shape of the film roll, and the surface pressure during winding tends to be uneven. The film roll obtained in this manner had a large shortest distance ΔL, and did not satisfy the physical property (1) above. In addition, the capacitor element made from the roll had poor long-term durability. Furthermore, the film could not maintain flatness even during processing, and wrinkles and sagging occurred, making it impossible to obtain satisfactory processability.

[0154] Comparative Example 2 was the same as Example 1, except that the rubber hardness was changed to 70°. Compared to Comparative Example 1, the surface rubber had further difficulty in conforming to the shape of the film roll, and the surface pressure during winding was more likely to become uneven. The film roll obtained in this way had a tendency to have a larger shortest distance ΔL, and the capacitor element made from the roll had poor long-term durability. In addition, the film could not maintain flatness during processing, and wrinkles and sagging occurred, making it impossible to obtain satisfactory processability.

[0155] Comparative Example 3 was the same as Example 1, except that the rubber hardness was changed to 75°. In Comparative Example 3, the surface pressure became even more uneven than in Comparative Examples 1 and 2, and the film tended to be wound tightly in the thicker parts. As a result, both the shortest distance ΔL and the circumferential length difference ΔX became large. The capacitor element made from such a roll had extremely poor long-term durability, and the film could not maintain its flatness even during processing, and wrinkles and sagging frequently occurred, making it impossible to obtain satisfactory processability.

[0156] In Example 6, the winding tension was set to 65 N / m, which was higher than that in Example 1. In Example 6, a slight difference in film thickness affected the air layer, and the circumferential length difference ΔX was larger than that in Example 1. However, the physical properties (1) and (2) above were satisfied, and a film roll that was excellent in long-term durability and suitable for processing could be obtained.

[0157] In Comparative Example 4, the winding tension was set to 80 N / m, which was even higher than that in Example 6. In Comparative Example 4, the excessive tension caused the circumferential length difference ΔX to be larger than that in Example 6, and the physical property (1) above was not satisfied, and both the long-term durability and the processability could not be satisfied.

[0158] In Comparative Example 5, the winding surface pressure was set to 450 N / m, which was higher than that in Example 1. When the winding surface pressure was too high, as in Comparative Example 5, the surface pressure during winding became uneven, and furthermore, the film tended to be wound tightly in some places (especially in the thick part of the film). The film roll obtained in this way had both a large shortest distance ΔL and a large circumferential length difference ΔX, and did not satisfy either of the physical properties (1) and (2) above. The capacitor element made from such a roll had extremely poor long-term durability. In addition, the film could not maintain flatness during processing, and wrinkles and sagging frequently occurred, and the processability was also unsatisfactory.

[0159] In Examples 7 and 8, the longitudinal stretching ratio was changed from 4.50 times in Example 1 to 4.00 times or 4.90 times. When the longitudinal stretching ratio was reduced, the distortion rate increased. Therefore, the film was easily stretched by the tension of the processing machine, and the shortest distance ΔL tended to increase. When the longitudinal stretching ratio was increased, the conformity to the film roll during winding decreased (distortion rate decreased), and the film was wound tightly in some parts (especially in the thick parts of the film), so the circumferential length difference ΔX increased. However, the film rolls of Examples 7 and 8 were able to satisfy both long-term durability and processability by satisfying the physical properties (1) and (2) above.

[0160] On the other hand, in Comparative Example 6, the longitudinal stretching ratio was 3.9 times, which was too small, and in Comparative Example 7, the longitudinal stretching ratio was 5.0 times, which was too large, so that the physical properties (1) or (2) above were not satisfied, and it was not possible to satisfy both long-term durability and processability.

[0161] In Example 9, the longitudinal stretching ratio was changed from 4.50 times in Example 1 to 4.95 times. When the longitudinal stretching ratio was increased, the conformity to the film roll during winding decreased (decreased distortion rate), and the film was wound tightly in some parts (especially in the thick parts of the film), so the circumferential length difference ΔX increased. However, the film roll of Example 9 was able to satisfy both long-term durability and processability by satisfying the physical properties (1) and (2) above.

[0162] In Example 10, the thickness of the film was changed from 2.5 mm in Example 1 to 2.0 μm. A pressure difference occurs between the upper and lower surfaces of the unwound film, and the film is subjected to forces in the upward and downward directions, which changes the peel position. The effect tends to be greater as the film thickness becomes thinner. Therefore, compared to Example 1, in Example 10, the shortest distance ΔL is larger, but by satisfying the physical properties (1) and (2) above, both long-term durability and processability were satisfied.

[0163] In Example 11, the roll width was changed from 620 mm in Example 1 to 820 mm. As the winding width was increased, the surface pressure applied to the film roll was easily made non-uniform, and the film roll tended to be wound tightly in some places. Therefore, the circumferential length difference ΔX tended to increase, but by satisfying the physical properties (1) and (2) above, it was possible to satisfy both long-term durability and processability.

[0164] In Examples 12 and 13, the surface temperature of the cast metal drum was changed from Example 1. At lower temperatures, the film surface was smoothed, and at higher temperatures, it was roughened. As the film became smoother, slippage tended to affect the shortest distance ΔL when unwound from the film roll, and as the film became rougher, the amount of air taken in during winding increased, and the circumferential length difference ΔX tended to increase. In Examples 12 and 13, by satisfying the physical properties (1) and (2) above, it was possible to satisfy both long-term durability and processability.

[0165] On the other hand, in Comparative Example 8, the surface temperature of the cast metal drum was lowered too much, so that the film roll did not satisfy the physical property (1) above, and was unable to satisfy both long-term durability and processability. In addition, the film roll had poor slipperiness and tended to wrinkle on the roll of the processing machine.

[0166] In Comparative Example 9, the surface temperature of the cast metal drum was too high, so the film roll did not satisfy the physical property (2) above, and both long-term durability and processability were not satisfied. In addition, when the film was unwound from the film roll, winding slippage occurred, and the film tended to meander on the roll of the processing machine. The capacitance of each of the capacitor elements of Examples 1 to 14 was measured and found to be 75 μF, indicating that the capacitor elements of Examples 1 to 14 are excellent in capacitance. [Explanation of symbols]

[0167] 1 Polypropylene film 2 cores 10 Polypropylene film rolls x1 One end of the peel line x2 The other end of the peel line L Unwinding direction M Circumferential direction ΔL The shortest distance from the midpoint of the line connecting both ends of the separation line to the separation line P Midpoint of the line connecting both ends of the peel line Q: The shortest point from the midpoint P to the peeling line S Peeling line T Straight line connecting both ends of the peeling line U reference line

Claims

1. A polypropylene film roll having a polypropylene film wound around a core, The polypropylene film has a thickness of 0.5 μm or more and 6.0 μm or less and a width of 200 mm or more and 1200 mm or less, A polypropylene film roll satisfying the following physical properties (1) and (2). (1) In an environment of a temperature of 23° C. and a humidity of 60%, when the polypropylene film is unwound from the polypropylene film roll at an unwinding force of 3 N / m and a speed of 2 m / min, the shortest distance ΔL from the midpoint of a line connecting both ends of a peel line, which is a boundary line at which the polypropylene film is peeled from the polypropylene film roll, to the peel line is 20 mm or less. (2) When the circumferential length of the polypropylene film roll is measured at both end positions, at the center position, and at positions spaced 50 mm apart from the center position toward both end positions, a ratio ΔX of the difference (Xmax-Xmin) between the maximum circumferential length Xmax and the minimum circumferential length Xmin to the average circumferential length Xave is 0.2% or less, The polypropylene film has a winding length of 10,000 m or more.

2. 2. The polypropylene film roll according to claim 1, wherein, when hardness is measured at both end positions, a central position, and positions spaced 50 mm apart from the central position toward both end positions of the polypropylene film roll, an average hardness value Mave is 88° or more and 96° or less, and a difference ΔM between a maximum hardness value Mmax and a minimum hardness value Mmin is less than 4°.

3. 3. The polypropylene film roll according to claim 1, wherein the polypropylene film has a longitudinal strain rate (ε1), a widthwise strain rate (ε2), and a diagonal strain rate (ε3) in the range of 0.6% or more and 1.5% or less at a stress of 25 MPa.

4. The polypropylene film roll according to any one of claims 1 to 3, wherein the surface roughness of at least one surface of the polypropylene film is a center line average roughness (Ra) of 0.04 μm or more and 0.08 μm or less and a maximum height (Rz) of 0.3 μm or more and 0.9 μm or less.

5. The polypropylene film roll according to any one of claims 1 to 4, wherein the polypropylene film has a winding length of 30,000 m or more.

6. The polypropylene film roll according to any one of claims 1 to 5, which is used for producing a metallized polypropylene film for a capacitor by laminating a metal film on one or both sides of the polypropylene film.

7. A metallized polypropylene film roll comprising the polypropylene film roll according to any one of claims 1 to 6, and a metal film laminated on one or both sides of the polypropylene film.

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