WO2020217930A1

WO2020217930A1 - Polypropylene film, polypropylene film with integrated metal layer, and film capacitor

Info

Publication number: WO2020217930A1
Application number: PCT/JP2020/015351
Authority: WO
Inventors: 道子末葭; 剛史冨永; 忠和石渡; 佳宗奥山
Original assignee: 王子ホールディングス株式会社
Priority date: 2019-04-22
Filing date: 2020-04-03
Publication date: 2020-10-29
Also published as: JP7192973B2; JPWO2020217930A1; CN113710734A

Abstract

A polypropylene film wherein the difference [(Δnyz) – (Δnxz)] between a birefringence value Δnxz and a birefringence value Δnyz is 0.009 or less, the ratio [(tensile modulus TD)/(tensile modulus MD)] of a machine-directional tensile modulus MD thereof at 25°C and a transverse-directional tensile modulus TD thereof at 25°C is 1.20 or less, the tensile modulus MD is 3.1 GPa or greater, and the thickness thereof is 0.8 μm to 5 μm, inclusive.

Description

Polypropylene film, metal layer integrated polypropylene film, and film capacitors

The present invention relates to a polypropylene film, a polypropylene film integrated with a metal layer, and a film capacitor.

Polypropylene film has excellent electrical characteristics such as high withstand voltage and low dielectric loss characteristics, and also has high moisture resistance. Therefore, it is widely used in electronic devices and electrical devices. Specifically, it is used as a film used for, for example, high-voltage capacitors, various switching power supplies, filter capacitors (for example, converters, inverters, etc.), smoothing capacitors, and the like.

In recent years, there has been a further demand for smaller capacitors and higher capacities. In order to improve the capacitance without changing the volume of the capacitor, it is preferable to make the film as a dielectric thin. Therefore, there is a demand for a film having a thinner thickness.

Conventionally, Patent Documents 1 to 4 have been disclosed as polypropylene films for capacitors.

Patent Document 1 describes a biaxially stretched polypropylene film for a capacitor having a refractive index Nz in the film thickness direction of 1.47 or more and 1.50 or less in the optical orientation measurement of the film (see, for example, claim 1). ).

In Patent Document 2, the plane orientation coefficient ΔPa calculated from the values of the birefringence values ΔNyz and ΔNxz in the thickness direction obtained by the optical birefringence measurement after the treatment at 105 ° C. for 200 hours (where ΔPa = (ΔNyz + ΔNxz)). ) / 2) is described as a birefringent polypropylene film having a value of 0.013 or more (see, for example, claim 1).

Patent Document 3 describes a biaxially stretched polypropylene film having a tensile strength in the longitudinal direction of 120 MPa to 250 MPa and a tensile strength in the width direction of 250 MPa to 400 MPa (see, for example, claim 1).

Patent Document 4 describes a biaxially stretched polypropylene film having a ratio of tensile elastic modulus in the TD direction to tensile elastic modulus in the MD direction M _TD / M _MD of 0.85 or more and 1.8 or less (for example, claim). 3). Further, there is a description that the lower limit value of the birefringence value ΔNxy is preferably 0.009 or more, and the upper limit value is preferably 0.014 or less (paragraph [0041]). Further, there is a description that the lower limit value of the birefringence value ΔNxz is preferably 0.015 or more, and the upper limit value is preferably 0.023 or less (paragraph [0042]).

JP-A-2010-254868 International Publication No. 2018/056404 Patent No. 5472461 International Publication No. 2018/124300

Conventionally, in the vapor deposition process of forming a metal layer on a polypropylene film, there is a problem that the thickness of the metal layer becomes non-uniform and shading occurs. Further, in recent years, the development of a thin polypropylene film capable of forming a more uniform thickness of a metal layer as compared with the conventional one has been desired. However, when the polypropylene films of Patent Documents 1 to 5 are used, it is not possible to obtain a polypropylene film integrated with a metal layer in which the thickness of the metal layer is uniformly controlled with high accuracy.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a polypropylene film capable of forming a metal layer with high accuracy and a uniform thickness. Another object of the present invention is to provide a metal layer integrated polypropylene film having the polypropylene film and a film capacitor having the metal layer integrated polypropylene film.

The present inventors diligently investigated the cause of the non-uniform thickness of the metal layer. As a result, in the thin polypropylene film, in the vapor deposition process of forming a metal layer on the polypropylene film, when the polypropylene film is unwound from the film roll, tension is applied in the MD direction (flow direction) of the film, and the polypropylene film shrinks due to Poisson shrinkage. It was found that the film contracted in the TD direction (width direction), resulting in wrinkles on the film. Then, it was found that when wrinkles occur, the metal deposition becomes non-uniform, the thickness of the metal layer becomes non-uniform, and shading occurs.

Furthermore, the present inventors have diligently studied a method for making the thickness of the metal layer uniform in the vapor deposition process of forming the metal layer on the polypropylene film. As a result, if the structure is isotropic at any temperature and has excellent mechanical properties, it is possible to suppress the occurrence of wrinkles in the film when the metal layer is formed. We have found that it is possible to make the thickness of the metal layer uniform, and have completed the present invention.

That is, the polypropylene film according to the present invention is
The difference [(Δnyz) − (Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz is 0.009 or less.
The ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] of the tensile elastic modulus MD at 25 ° C. in the MD direction and the tensile elastic modulus TD at 25 ° C. in the TD direction is 1.20 or less.
The tensile elastic modulus MD is 3.1 GPa or more, and the tensile elastic modulus MD is 3.1 GPa or more.
It is characterized in that the thickness is 0.8 μm or more and 5 μm or less.
(However, the double refractive index Δnxz is three-dimensional in the z-axis direction from the three-dimensional refractive index in the x-axis direction when the MD direction of the polypropylene film is the x-axis, the TD direction is the y-axis, and the thickness direction is the z-axis. It is a value obtained by subtracting the refractive index, and the double refractive index Δnyz is a value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the y-axis direction.)

According to the polypropylene film according to the present invention, since the difference [(Δnyz) − (Δnxz)] is 0.009 or less, it is isotropic with respect to the in-plane direction from the viewpoint of molecular orientation. The fact that the molecular orientation is isotropic means that it is isotropic at any temperature without depending on the temperature.
Further, since the ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] is 1.20 or less and the tensile elastic modulus MD is 3.1 GPa or more, the mechanical properties are in the in-plane direction. It is isotropic and has excellent mechanical properties in any direction in the plane.
That is, since the tensile elastic modulus MD is relatively large at 3.1 GPa or more, the contraction in the TD direction due to Poisson contraction can be reduced, and the tensile elastic modulus TD is also about the same as the tensile elastic modulus MD and is relatively large. Therefore, even if the polypropylene film is stretched in the MD direction, the shrinkage in the TD direction associated therewith can be reduced.
As described above, since there is no temperature dependence and the mechanical properties are isotropic at any temperature, wrinkles are suppressed in the polypropylene film in the vapor deposition process of forming the metal layer on the polypropylene film. This makes it possible to make the thickness of the metal layer more uniform.
Further, since the thickness is 5 μm or less, the capacitance per unit volume of a capacitor element can be increased, and it can be suitably used for a capacitor. Moreover, since the thickness is 0.8 μm or more, it is excellent from the viewpoint of film formation stability.

Note that Patent Document 1 does not describe the refractive index Nx and the refractive index Ny of the polypropylene film, and the difference between the birefringence value Δnxz and the birefringence value Δnyz [(Δnyz) − (Δnxz)] is unknown. is there.
Here, in Patent Document 1, a polypropylene film is produced by stretching a raw sheet, but the stretching treatment is sequentially biaxially stretched.
However, in the sequential biaxial stretching, the polypropylene film is isotropic in a temperature-independent manner and has a high area stretching ratio, that is, isotropic and thin in a temperature-independent manner. Polypropylene film cannot be obtained. In the sequential biaxial stretching, if the area stretching ratio is as low as 45 times or less, the polypropylene film having isotropic property can be produced without tearing the film during stretching. However, in the sequential biaxial stretching, an isotropic polypropylene film cannot be produced when the stretching ratio is as high as 46 times or more. Generally, in the case of sequential biaxial stretching, first stretching in the MD direction and then in the TD direction, but in the case of a high area stretching ratio, if the stretching ratio in the MD direction is increased, the stretching in the TD direction is performed. The film tears at the time. Therefore, in the case of sequential biaxial stretching, the stretching ratio in the MD direction must be about half as compared with the stretching ratio in the TD direction.
That is, the polypropylene film of Patent Document 1 produced by sequential biaxial stretching is isotropic in a temperature-independent manner as in the present invention, and a thin polypropylene film cannot be obtained. Specifically, a thin polypropylene film having a difference [(Δnyz)-(Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz of 0.009 or less and a thickness of 0.8 μm or more and 5 μm or less. Cannot be obtained.
Further, Patent Document 1 does not describe the tensile elastic modulus.
Therefore, the polypropylene film of Patent Document 1 is clearly different in composition from the present invention.

Further, Patent Document 2 describes that ΔPa = ((ΔNyz + ΔNxz) / 2) is 0.013 or more, but the difference between the birefringence value Δnxz and the birefringence value Δnyz [(Δnyz) − (Δnxz)] is not clear whether it is 0.009 or less.
Further, in Patent Document 2, a polypropylene film is produced by stretching a raw sheet, but the stretching treatment is sequentially biaxially stretched. As described above, the polypropylene film of Patent Document 2 produced by sequential biaxial stretching is isotropic in a temperature-independent manner and is thin as described above. I can't get it. Specifically, a thin polypropylene film having a difference [(Δnyz)-(Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz of 0.009 or less and a thickness of 0.8 μm or more and 5 μm or less. Cannot be obtained.
Further, Patent Document 2 does not describe the tensile elastic modulus.
Therefore, the polypropylene film of Patent Document 2 is clearly different in composition from the present invention.

Further, Patent Document 3 does not describe the birefringence value Δnxz or the birefringence value Δnyz, and it is unclear whether [(Δnyz) − (Δnxz)] is 0.009 or less.
Further, in Patent Document 3, a polypropylene film is produced by stretching a raw sheet, but the stretching treatment is sequentially biaxially stretched. As described above, the polypropylene film of Patent Document 3 produced by sequential biaxial stretching is isotropic in a temperature-independent manner and is thin as described above. I can't get it. Specifically, a thin polypropylene film having a difference [(Δnyz)-(Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz of 0.009 or less and a thickness of 0.8 μm or more and 5 μm or less. Cannot be obtained.
Further, Patent Document 3 does not describe the tensile elastic modulus.
Therefore, the polypropylene film of Patent Document 3 is clearly different in composition from the present invention.

Further, Patent Document 4 describes the birefringence value ΔNxy and the birefringence value ΔNxz, but does not describe the birefringence value Δnyz, and [(Δnyz) − (Δnxz)] is 0.009 or less. I don't know.
Further, in Patent Document 4, a polypropylene film is produced by stretching a raw sheet, but the stretching treatment is sequentially biaxially stretched. As described above, the polypropylene film of Patent Document 4 produced by sequential biaxial stretching is isotropic in a temperature-independent manner and is thin as described above. I can't get it. Specifically, a thin polypropylene film having a difference [(Δnyz)-(Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz of 0.009 or less and a thickness of 0.8 μm or more and 5 μm or less. Cannot be obtained.
In addition, Patent Document 4 describes the tensile elastic modulus at 23 ° C. For example, in Example 9, the ratio of the tensile elastic modulus at 23 ° C. [(tensile elastic modulus TD) / (tensile elastic modulus MD) ] Is 3.4 / 3.3 (about 1.03). However, as described above, since the polypropylene film of Patent Document 4 is manufactured by sequential biaxial stretching, it cannot be said that it is isotropic with respect to the in-plane direction from the viewpoint of molecular orientation. Therefore, even if the tensile elastic modulus is close to each other in the TD direction and the MD direction at 23 ° C., since the molecular orientation is not isotropic, the temperature other than 23 ° C. (particularly, such as in the vapor deposition step). At high temperatures), the tensile modulus is very likely to be significantly different in the TD and MD directions.
Therefore, the polypropylene film of Patent Document 4 is clearly different in composition from the present invention.

In the polypropylene film of the present invention, the number of fibrils when measuring 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per field using a light interference type non-contact surface shape measuring device is determined. It is preferable to have a surface having 20 or more and 50 or less and an area per number of the fibrils of 200 μm ² / piece or more and 1000 μm ² / piece or less. In the present invention, "VertScan2.0 (model: R5500GML)" manufactured by Ryoka System Co., Ltd. is used as the optical interference type non-contact surface shape measuring device.

According to the above configuration, since at least one surface of the polypropylene film is roughened by a large number of relatively small fibrils, the polypropylene film after biaxial stretching or the metal layer having the polypropylene film is one. When the body polypropylene film is wound in a roll shape, the slipperiness with respect to the transport roll is improved. As a result, suitable transportability is obtained, and wrinkles and unwinding are suppressed.

The polypropylene film having the above configuration is preferably for a capacitor.

The difference [(Δnyz) − (Δnxz)], the ratio [(tensile modulus TD) / (tensile modulus MD)], and the polypropylene film in which the tensile modulus MD is within the numerical range are temperature-dependent. Since it has no property and its mechanical properties are isotropic at any temperature, it is possible to suppress the occurrence of wrinkles on the polypropylene film in the vapor deposition process for forming the metal layer on the polypropylene film, and the metal layer can be suppressed. It becomes possible to make the thickness of the above uniform. Therefore, it can be suitably used for capacitors.

The polypropylene film having the above structure is preferably biaxially stretched at the same time.

When simultaneously biaxially stretched, the difference [(Δnyz) − (Δnxz)], the ratio [(tensile modulus TD) / (tensile modulus MD)], and the tensile modulus MD are in the numerical range. It is easy to obtain a polypropylene film having a thickness of 0.8 μm or more and 5 μm or less.

Further, the polypropylene film integrated with a metal layer according to the present invention is
With the polypropylene film
It is characterized by having a metal layer laminated on one side or both sides of the polypropylene film.

According to the above configuration, since it has a metal layer laminated on one side or both sides of the polypropylene film, it can be used for a film capacitor in which the polypropylene film is a dielectric and the metal layer is an electrode. Further, since the polypropylene film is not temperature-dependent and has isotropic mechanical properties at any temperature, wrinkles may occur in the polypropylene film in the vapor deposition process of forming a metal layer on the polypropylene film. Can be suppressed, and the thickness of the metal layer can be made more uniform. Therefore, in the polypropylene film integrated with the metal layer having the polypropylene film, the thickness of the metal layer is highly accurate and uniform.

Further, the film capacitor according to the present invention is characterized by having the wound metal layer integrated polypropylene film or having a structure in which a plurality of the metal layer integrated polypropylene films are laminated.

Further, the method for producing a polypropylene film according to the present invention is as follows.
The method for producing a polypropylene film according to the above.
It has a step A of simultaneously biaxially stretching a cast sheet, and has
In the step A, the ratio of the draw ratio MD in the MD direction to the draw ratio TD in the TD direction [(stretch ratio TD) / (stretch ratio MD)] is 1.0 or more and 1.7 or less.
The area stretch ratio, which is the product of the stretch ratio TD and the stretch ratio MD, is 46 times or more and 72 times or less.

In order to obtain a thin polypropylene film capable of increasing the capacitance per unit volume when used as a capacitor element, it is necessary to set a high area stretching ratio in the stretching step.
According to the above configuration, as can be seen from the examples, it is possible to obtain a thin polypropylene film having isotropic properties.
In addition, it is not possible to obtain a polypropylene film which is isotropic and has a high area draw ratio by sequential stretching. In the sequential stretching, if the area stretching ratio is as low as 45 times or less, the polypropylene film having isotropic property can be produced without tearing the film during stretching. However, in the sequential stretching, an isotropic polypropylene film cannot be produced when the area stretching ratio is 46 times or more. Generally, in the case of sequential stretching, the film is first stretched in the MD direction and then in the TD direction. However, in the case of a high area stretching ratio, if the stretching ratio in the MD direction is increased, the stretching in the TD direction occurs. The film tears. Therefore, in the case of sequential stretching, the stretching ratio in the MD direction must be about half as compared with the stretching ratio in the TD direction. That is, it is not possible to obtain a polypropylene film that is isotropic and has a high area draw ratio by sequential stretching.

According to the present invention, it is possible to provide a polypropylene film capable of forming a metal layer with high accuracy and a uniform thickness. Further, it is possible to provide a metal layer integrated polypropylene film having the polypropylene film and a film capacitor having the metal layer integrated polypropylene film.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments.

In the present specification, the expressions "contains" and "contains" include the concepts of "contains", "contains", "substantially consists", and "consists of only".
In the present specification, "element", "capacitor", "capacitor element", and "film capacitor" mean the same thing.

Since the polypropylene film of the present embodiment is not a microporous film, it does not have a large number of pores.
The polypropylene film of the present embodiment may be composed of a plurality of layers of two or more layers, but is preferably composed of a single layer.

The polypropylene film according to this embodiment is
The difference [(Δnyz) − (Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz is 0.009 or less.
The ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] of the tensile elastic modulus MD at 25 ° C. in the MD direction and the tensile elastic modulus TD at 25 ° C. in the TD direction is 1.20 or less.
The tensile elastic modulus MD is 3.1 GPa or more, and the tensile elastic modulus MD is 3.1 GPa or more.
It is characterized in that the thickness is 0.8 μm or more and 5 μm or less.
(However, the double refractive index Δnxz is three-dimensional in the z-axis direction from the three-dimensional refractive index in the x-axis direction when the MD direction of the polypropylene film is the x-axis, the TD direction is the y-axis, and the thickness direction is the z-axis. It is a value obtained by subtracting the refractive index, and the double refractive index Δnyz is a value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the y-axis direction.)

In the polypropylene film according to the present embodiment, the difference between the birefringence value Δnxz and the birefringence value Δnyz [(Δnyz) − (Δnxz)] is 0.009 or less, preferably 0.006 or less, preferably 0.003 or less. More preferred. The difference [(Δnyz) − (Δnxz)] is preferably −0.009 or more, more preferably −0.005 or more, and further preferably 0.000 or more. Since the difference [(Δnyz) − (Δnxz)] is 0.009 or less, it is isotropic with respect to the in-plane direction from the viewpoint of molecular orientation. The fact that the molecular orientation is isotropic means that it is isotropic at any temperature without depending on the temperature.

The birefringence value Δnxz is preferably 0.020 or less, more preferably 0.018 or less, and even more preferably 0.015 or less. When the birefringence value Δnxz is 0.02 or less, it is easy to balance the orientation in the in-plane direction in the stretch molding of the film, and it is easy to provide isotropic mechanical properties. As a result, the roll is miswound. It can be more suppressed. The birefringence value Δnxz is preferably 0.009 or more, more preferably 0.010 or more, and further preferably 0.012 or more. When the birefringence value Δnxz is 0.009 or more, the elastic modulus in the MD direction is maintained high, so that the dimensional change of the film is small due to the mechanical tension applied during the metal vapor deposition process, and the flatness of the film during the metal vapor deposition process is small. As a result, unevenness of the thin-film deposition film can be further suppressed.

The birefringence value Δnyz is preferably 0.020 or less, more preferably 0.018 or less, and even more preferably 0.016 or less. When the birefringence value Δnyz is 0.02 or less, it is easy to balance the orientation in the in-plane direction in the stretch molding of the film, and it is easy to provide isotropic mechanical properties. As a result, the roll is miswound. It can be more suppressed. The birefringence value Δnyz is preferably 0.090 or more, more preferably 0.011 or more, and even more preferably 0.013 or more. When the birefringence value Δnyz is 0.090 or more, the influence of Poisson deformation due to the mechanical tension applied during the metal vapor deposition process is small, and the flatness of the film during the metal vapor deposition process tends to be easily maintained.

The value P calculated from the birefringence value ΔNyz and the birefringence value ΔNxz by the following formula 1 is preferably 0.0141 or more, more preferably 0.0142 or more, still more preferably 0.0143 or more. The value P is preferably 0.020 or less, more preferably 0.018 or less, and even more preferably 0.015 or less.
(Equation 1) P = (ΔNyz + ΔNxz) / 2
When the value P is within the above preferable range, it is due to more preferable isotropic mechanical properties due to easy in-plane orientation balance in stretch molding of the film and little change in film size during metal vapor deposition processing. Since it has more preferable flatness, it is possible to further suppress the winding deviation of the roll and the unevenness of the vapor-deposited film as a result.

The birefringence value Δnxz is the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the x-axis direction when the MD direction of the polypropylene film is the x-axis, the TD direction is the y-axis, and the thickness direction is the z-axis. It is a value obtained by subtracting the birefringence value Δnyz, which is a value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the y-axis direction.
The specific measurement method of the birefringence value Δnxz and the birefringence value Δnyz is based on the method described in Examples.

The difference [(Δnyz) − (Δnxz)], the birefringence value Δnxz, and the birefringence value Δnyz depend on the film forming conditions (stretching magnification adjustment, etc.) and the characteristics of the polypropylene resin (molecular weight, degree of polymerization, molecular weight distribution, etc.). Can be controlled. When the difference [(Δnyz) − (Δnxz)] is controlled by the stretching ratio, the birefringence value Δnxz and the birefringence are required to reduce the difference [(Δnyz) − (Δnxz)] to 0.009 or less. A draw ratio may be adopted so that the value Δnyz is about the same. Specifically, the stretching ratio in the MD direction and the stretching ratio in the TD direction may be set to be about the same.

The polypropylene film has a ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] of the tensile elastic modulus MD at 25 ° C. in the MD direction and the tensile elastic modulus TD at 25 ° C. in the TD direction. It is 20 or less, preferably 1.19 or less, and more preferably 1.17 or less. The ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] is preferably 0.85 or more, more preferably 0.90 or more, and further preferably 0.95 or more. ..
The tensile elastic modulus MD is 3.1 GPa or more, preferably 3.2 GPa or more, and more preferably 3.3 GPa or more. The tensile elastic modulus MD is preferably 4.5 GPa or less, more preferably 4.4 GPa or less, and further preferably 4.2 GPa or less.
The tensile elastic modulus TD is preferably 3.1 GPa or more, more preferably 3.3 GPa or more, and further preferably 3.6 GPa or more. The tensile elastic modulus TD is preferably 4.5 GPa or less, more preferably 4.4 GPa or less, and further preferably 4.2 GPa or less.
Since the ratio [(tensile modulus TD) / (tensile modulus MD)] is 1.20 or less and the tensile modulus MD is 3.1 GPa or more, the mechanical properties are in the in-plane direction. It is isotropic and has excellent mechanical properties in any direction in the plane.
That is, since the tensile elastic modulus MD is relatively large at 3.1 GPa or more, the contraction in the TD direction due to Poisson contraction can be reduced, and the tensile elastic modulus TD is also about the same as the tensile elastic modulus MD. Since it is relatively large, even if the polypropylene film is stretched in the MD direction, the shrinkage in the TD direction associated therewith can be reduced.
The specific measurement method of the tensile elastic modulus MD and the tensile elastic modulus TD is based on the method described in Examples.

As described above, since the polypropylene film is not temperature-dependent and has isotropic mechanical properties at any temperature, wrinkles occur in the polypropylene film in the vapor deposition process for forming a metal layer on the polypropylene film. This can be suppressed and the thickness of the metal layer can be made more uniform.

The polypropylene film has a ratio [(breaking strength TD) / (breaking strength MD)] of the breaking strength MD at 25 ° C. in the MD direction and the breaking strength TD at 25 ° C. in the TD direction of 1.55 or less. It is preferably 1.40 or less, more preferably 1.25 or less. The ratio [(breaking strength TD) / (breaking strength MD)] is preferably 0.70 or more, more preferably 0.80 or more, and further preferably 0.90 or more.
The breaking strength MD is preferably 175 MPa or more, more preferably 177 MPa or more, and even more preferably 180 MPa or more. The breaking strength MD is preferably 280 MPa or less, more preferably 260 MPa or less, and even more preferably 240 MPa or less.
The breaking strength TD is preferably 165 MPa or more, more preferably 167 MPa or more, and further preferably 170 MPa or more. The breaking strength TD is preferably 280 MPa or less, more preferably 260 MPa or less, and even more preferably 240 MPa or less.

When the ratio [(breaking strength TD) / (breaking strength MD)] is 1.55 or less and the breaking strength MD is 175 MPa or more, the mechanical properties are more isotropic with respect to the in-plane direction. And the mechanical properties are better in any direction in the plane.
That is, if the breaking strength MD is relatively large at 175 MPa or more, the shrinkage in the TD direction due to Poisson shrinkage can be reduced, and the breaking strength TD is also about the same as the breaking strength MD and is relatively large. Even if the polypropylene film is stretched in the MD direction, the shrinkage in the TD direction associated therewith can be reduced.
The specific measurement method of the breaking strength MD and the breaking strength TD is based on the method described in Examples.

The polypropylene film has a ratio [(breaking elongation TD) / (breaking elongation MD)] of the breaking elongation MD at 25 ° C. in the MD direction and the breaking elongation TD at 25 ° C. in the TD direction. It is preferably 50 or less, more preferably 1.45 or less, and even more preferably 1.40 or less. The ratio [(breaking elongation TD) / (breaking elongation MD)] is preferably 0.55 or more, more preferably 0.60 or more, and further preferably 0.65 or more. ..
The elongation at break MD is preferably 30% or more, more preferably 34% or more, and further preferably 38% or more. The elongation at break MD is preferably 100% or less, more preferably 85% or less, and even more preferably 65% or less.
The elongation at break TD is preferably 20% or more, more preferably 24% or more, and even more preferably 28% or more. The elongation at break TD is preferably 100% or less, more preferably 85% or less, and even more preferably 65% or less.
The specific measuring method of the breaking elongation MD and the breaking elongation TD is based on the method described in Examples.

The ratio [(tensile elasticity TD) / (tensile elasticity MD)], the tensile elasticity MD, the tensile elasticity TD, the ratio [breaking strength TD) / (breaking strength MD)], the breaking strength MD, The method for keeping the breaking strength TD, the ratio [breaking elongation TD) / (breaking elongation MD)], the breaking elongation MD, and the breaking elongation TD within the numerical range is not particularly limited, but polypropylene. It can be controlled by the film forming conditions of the film (for example, stretching ratio, etc.) and the characteristics of the polypropylene resin (molecular weight, degree of polymerization, molecular weight distribution, etc.). When the ratio [(tensile modulus TD) / (tensile modulus MD)] is controlled by the draw ratio, the ratio [(tensile modulus TD) / (tensile modulus MD)] is set to 1.20 or less. The draw ratio may be such that the tensile elastic modulus MD and the tensile elastic modulus TD are about the same. Specifically, the stretching ratio in the MD direction and the stretching ratio in the TD direction may be set to be about the same.

The polypropylene film has 20 or more and 50 or less fibrils when measured at 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per field of view using a light interference type non-contact surface shape measuring device. It is preferable to have a surface in which the area per number of the fibrils is 200 μm ² / piece or more and 1000 μm ² / piece or less.
The number of fibrils is more preferably 24 or more, and even more preferably 28 or more. The number of fibrils is more preferably 48 or less, and even more preferably 46 or less.
The area per number of the fibrils is more preferably 210 .mu.m ² / number or more, and still more preferably 223μm ² / FOB. Area per number of the fibrils is more preferably 900 .mu.m ² / number less, still more preferably 850 .mu.m ² / number less.
Further, the fibril area when measuring 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per visual field is preferably 9000 μm ² or more, and more preferably 10000 μm ³ or more. The fibril area is preferably 30,000 μm ² or less, and more preferably 25,000 μm ³ or less.
If the number of the fibrils is 20 or more and 50 or less and the area per number of the fibrils is 200 μm ² / piece or more and 1000 μm ² / piece or less, at least one side of the polypropylene film is large. Since the surface is roughened by the fibrils having a relatively small area, the slipperiness to the transport roll becomes good when the polypropylene film after being biaxially stretched is wound into a roll shape. As a result, suitable transportability is obtained, and wrinkles and unwinding are suppressed.
The method for measuring the number of fibrils, the fibril area, and the area per number of fibrils is as follows.

<Measuring method of number of fibrils, area of fibrils, and area per number of fibrils>
As the optical interference type non-contact surface shape measuring device, "VertScan 2.0 (model: R5500GML)" manufactured by Ryoka System Co., Ltd. is used.
First, using the WAVE mode, a 530-white filter and a 1 × BODY lens barrel are applied, and a measurement of 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per field of view is performed using an × 10 objective lens. This operation is performed at 10 locations at 1 cm intervals in the flow direction from the central location in both the flow direction and the width direction of the target sample (polypropylene film).
Next, the obtained data is subjected to noise removal processing by a median filter (3 × 3), and then Gaussian filter treatment with a cutoff value of 30 μm is performed to remove undulation components.
For each surface shape data of the 10 locations obtained as described above, a region having a mountain side height of 0.05 μm or more is painted white, and a region having a mountain side height smaller than 0.05 μm is painted black to obtain binary values. A converted image (262 pixels × 194 pixels) is obtained.
Next, using the image analysis software Image Pro Plus 5.1J (manufactured by Nippon Rover), the number of objects having a brightness range of 128 or more and 255 or less in the binarized image obtained above and their areas are measured. When extracting objects, those on the lower boundary of the image and those on the left boundary are excluded. For the extracted objects, the number of objects having an area of 50 pixels or more is defined as the number of fibrils, and the sum of the areas of objects having an area of 50 pixels or more is defined as the fibril area. Objects with an area smaller than 50 pixels are removed as noise. Further, after calculating the sum of the areas of an object having an area of 50 pixels or more, the calculated sum divided by the number of fibrils is defined as the area (pixels / piece) per number of fibrils. Finally, with respect to the area per number of fibrils, the unit is converted to μm ² / piece.

The method for setting the number of fibrils, the fibril area, and the area per number of fibrils within the numerical range is not particularly limited, but the film forming conditions of the cast sheet (for example, cast cooling temperature, etc.) and polypropylene resin are not particularly limited. It can be controlled by the characteristics of (molecular weight, degree of polymerization, molecular weight distribution, etc.). The cast cooling temperature can be controlled by the resin temperature at the time of forming the cast sheet film, the air gap, the surface temperature of the metal drum, and the like.

DC breakdown strength ES in 100 ° C. of the polypropylene film is preferably at 510V _DC / [mu] m or more, more preferably 525V _DC / [mu] m or more, and still more preferably 540V _DC / [mu] m or more. DC breakdown strength ES in 100 ° C. of the polypropylene film is preferably as high, for example, 600V _DC / [mu] m or less, 570V _DC / [mu] m or less, or less 550V _DC / μm.

DC breakdown strength ES in 120 ° C. of the polypropylene film is preferably at 485V _DC / μm or more, and more preferably 490V _DC / [mu] m or more. The higher the DC dielectric breakdown strength ES of the polypropylene film at 125 ° C. is, the more preferable, but for example, it is 600 V _DC / μm or less and 550 V _DC / μm or less.

The ash content of the polypropylene film is preferably 6 × 10 ppm or less (60 ppm or less), more preferably 5 × 10 ppm or less (50 ppm or less), and 4 × 10 ppm or less (40 ppm or less) with respect to the polypropylene film. Is more preferable, and 3 × 10 ppm or less (30 ppm or less) is particularly preferable. The ash content is preferably 0 × 10 ppm or more, more preferably 1 ppm or more, further preferably 5 ppm or more, and particularly preferably 1 × 10 ppm or more (10 ppm or more). When the ash content is within the numerical range, the electrical characteristics of the capacitor are further improved while suppressing the formation of polar low molecular weight components. The ash content refers to a value obtained by the method described in Examples.

The polypropylene film has a thickness of 0.8 μm or more and 5 μm or less. The thickness of the polypropylene film is preferably 4.0 μm or less, more preferably 3.0 μm or less.
The thickness of the polypropylene film is preferably 1.5 μm or more, more preferably 2.0 μm or more. Since the thickness of the polypropylene film is 5 μm or less, the capacitance per unit volume of a capacitor element can be increased, and the polypropylene film can be suitably used for a capacitor. Further, since the thickness of the polypropylene film is 0.8 μm or more, it is excellent from the viewpoint of film formation stability.

The thickness of the polypropylene film refers to a value measured in accordance with JIS-C2330, except that it is measured at 100 ± 10 kPa using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu.

The polypropylene film is basically a simultaneous biaxially stretched film. When the polypropylene film is a simultaneous biaxially stretched film, the difference [(Δnyz) − (Δnxz)], the ratio [(tensile modulus TD) / (tensile modulus MD)], and the tensile modulus It is easy to obtain a polypropylene film having an MD within the numerical range and having a thin thickness (within the numerical range). However, the polypropylene film has the difference [(Δnyz) − (Δnxz)], the ratio [(tensile modulus TD) / (tensile modulus MD)], the tensile modulus MD, and the thickness of the polypropylene film. As long as it is within the above numerical range, it includes a case where it is a sequentially biaxially stretched film, a case where it is a uniaxially stretched film, and a case where it is a non-stretched film.

The polypropylene film and the polypropylene film integrated with a metal layer, which will be described later, are each wound in a roll shape, and are preferably in the form of a film roll. The film roll may or may not have a winding core. The film roll preferably has a winding core. The material of the winding core of the film roll is not particularly limited. Examples of the material include paper (paper tube), resin, fiber reinforced plastic (FRP), metal and the like. Examples of the resin include polyvinyl chloride, polyethylene, polypropylene, phenol resin, epoxy resin, acrylonitrile-butadiene-styrene copolymer and the like. Examples of the plastic constituting the fiber reinforced plastic include polyester resin, epoxy resin, vinyl ester resin, phenol resin, and thermoplastic resin. Examples of the fibers constituting the fiber-reinforced plastic include glass fibers, aramid fibers (Kevlar (registered trademark) fibers), carbon fibers, polyparaphenylene benzoxazole fibers (Zylon (registered trademark) fibers), polyethylene fibers, and boron fibers. Can be mentioned. Examples of the metal include iron, aluminum, stainless steel and the like. The winding core of the film roll also includes a winding core formed by impregnating a paper tube with the resin. In this case, the material of the winding core is classified as resin.

The polypropylene film contains a polypropylene resin as a main component. In the present specification, the inclusion of polypropylene resin as a main component means that the polypropylene resin is contained in an amount of 50% by mass or more with respect to the entire polypropylene film (when the entire polypropylene film is 100% by mass). The content of the polypropylene resin with respect to the entire polypropylene film is preferably 75% by mass or more, and more preferably 90% by mass or more. The upper limit of the content of the polypropylene resin is, for example, 100% by mass, 98% by mass, or the like with respect to the entire polypropylene film.

The polypropylene resin is not particularly limited, and one type may be used alone, or two or more types may be used in combination. Among the polypropylene resins, a polypropylene resin that forms β-type spherulites when used as a cast sheet is preferable.

The weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less, and more preferably 250,000 or more and 400,000 or less. When the weight average molecular weight Mw of the polypropylene resin is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, the thickness of the cast sheet can be easily controlled, and a thin stretched film can be easily produced. In addition, the cast sheet can be provided with appropriate stretchability. When two or more kinds of polypropylene resins are used, it is preferable to use the polypropylene resin having Mw of 250,000 or more and less than 330,000 and the polypropylene resin having Mw of 330,000 or more and 450,000 or less in combination.

The molecular weight distribution [(weight average molecular weight Mw) / (number average molecular weight Mn)] of the polypropylene resin is preferably 5 or more and 12 or less, more preferably 5 or more and 11 or less, and 5 or more and 10 or less. Is even more preferable. When two or more kinds of polypropylene resins are used, it is preferable to use the polypropylene resin having a molecular weight distribution of 5 or more and less than 8.5 and the polypropylene resin having a molecular weight distribution of 8.5 or more and 11 or less in combination.

In the present specification, the weight average molecular weight (Mw), the number average molecular weight (Mn), and the molecular weight distribution (Mw / Mn) of the polypropylene resin are values measured using a gel permeation chromatograph (GPC) apparatus. is there. More specifically, it is a value measured using HLC-8121GPC-HT (trade name) of a high temperature GPC measuring machine with a built-in differential refractometer (RI) manufactured by Tosoh Corporation. As a GPC column, three TSKgel GMHHR-H (20) HTs manufactured by Tosoh Corporation are connected and used. The column temperature is set to 140 ° C., and trichlorobenzene is flowed as an eluent at a flow rate of 1.0 ml / 10 minutes to obtain measured values of Mw and Mn. A calibration curve relating to the molecular weight M is prepared using standard polystyrene manufactured by Tosoh Corporation, and the measured values are converted into polystyrene values to obtain Mw and Mn. Here, the logarithm of the base 10 of the molecular weight M of standard polystyrene is referred to as a logarithmic molecular weight (“Log (M)”).

Differential distribution value difference _{D M} of the polypropylene resin, rather preferred that at most 5% to 14%, more preferably at most 12% -4% or more, that is 10% less than -4% More preferred. Here, the "differential distribution value difference _DM " is the differential distribution value when the logarithmic molecular weight Log (M) = 4.5 to the differential distribution value when Log (M) = 6.0 in the molecular weight differential distribution curve. Is the difference minus.
In addition, "differential distribution value difference _DM is -5% or more and 14% or less" means a component having a molecular weight of 10,000 to 100,000 on the low molecular weight side of the Mw value of the polypropylene resin (hereinafter, "low"). A component having a logarithmic molecular weight Log (M) = 4.5 as a typical distribution value of (also referred to as "molecular weight component") and a component having a molecular weight of about 1 million on the high molecular weight side (hereinafter, also referred to as "high molecular weight component"). When comparing the components with Log (M) = 6.0 as a typical distribution value, if the difference is positive, there are more low molecular weight components, and if the difference is negative, there are more high molecular weight components. It can be understood that there are many.

That is, even if the molecular weight distribution Mw / Mn is 5 to 12, it merely indicates the width of the molecular weight distribution, and the quantitative relationship between the high molecular weight component and the low molecular weight component in it is not known. Absent. Therefore, from the viewpoint of stable film forming property and thickness uniformity of cast raw sheet, polypropylene resin has a wide molecular weight distribution and at the same time has a molecular weight of 10,000 to 100,000 in order to appropriately contain low molecular weight components. It is preferable to use a polypropylene resin so that the difference in differential distribution value is -5% or more and 14% or less as compared with the component having a molecular weight of 1 million.

The differential distribution value is a value obtained as follows using GPC. A curve (commonly referred to as the "elution curve") indicating the intensity over time obtained by a GPC differential refractometer (RI) detector is used. Using a calibration curve obtained using standard polystyrene, the time axis is converted to a logarithmic molecular weight (Log (M)) to convert the elution curve into a curve showing the strength against Log (M). Since the RI detection intensity is proportional to the component concentration, an integral distribution curve with respect to the logarithmic molecular weight Log (M) can be obtained, assuming that the total area of the curve showing the intensity is 100%. The differential distribution curve is obtained by differentiating this integral distribution curve with Log (M). Therefore, the "differential distribution" means the differential distribution of the concentration fraction with respect to the molecular weight. From this curve, the differential distribution value at a specific Log (M) is read.

The heptane insoluble content (HI) of the polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. The heptane insoluble content (HI) of the polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, the larger the amount of heptane insoluble, the higher the stereoregularity of the resin. When the heptane insoluble content (HI) is 96.0% or more and 99.5% or less, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the withstand voltage at high temperature is improved. To do. On the other hand, the rate of solidification (crystallization) during molding of the cast sheet becomes appropriate, and the cast sheet has an appropriate stretchability. The method for measuring heptane insoluble matter (HI) is as described in Examples.

The melt flow rate (MFR) of the polypropylene resin is preferably 1.0 to 8.0 g / 10 min, more preferably 1.5 to 7.0 g / 10 min, and 2.0 to 6.0 g. It is more preferably / 10 min. The method for measuring the melt flow rate of the polypropylene resin is as described in Examples.

The mesopentad fraction ([mmmm]) of the polypropylene resin is preferably 99.8% or less, more preferably 99.5% or less, and further preferably 99.0% or less. The mesopentad fraction is preferably 94.0% or more, more preferably 94.5% or more, still more preferably 95.0% or more. When the mesopentad fraction is within the above numerical range, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the withstand voltage resistance at a high temperature is improved. On the other hand, the rate of solidification (crystallization) during molding of the cast sheet becomes appropriate, and the cast sheet has an appropriate stretchability.

The mesopentad fraction ([mm mm]) is an index of stereoregularity that can be obtained by high temperature nuclear magnetic resonance (NMR) measurements. In the present specification, the mesopentad fraction ([mm mm]) refers to a value measured using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR) manufactured by JEOL Ltd., JNM-ECP500. The observation nucleus is ¹³ C (125 MHz), the measurement temperature is 135 ° C., and the solvent for dissolving the polypropylene resin is o-dichlorobenzene (ODCB: ODCB and deuterated ODCB mixed solvent (mixing ratio = 4/1). )) Is used. The measurement method by high-temperature NMR can be performed by referring to the method described in, for example, "Japan Analytical Chemistry / Polymer Analysis Research Council, New Edition Polymer Analysis Handbook, Kinokuniya Bookstore, 1995, p. 610". it can. A more detailed method for measuring the mesopentad fraction ([mm mm]) is as described in Examples.

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

The polypropylene resin can be produced by using a generally known polymerization method. Examples of the polymerization method include a vapor phase polymerization method, a massive polymerization method and a slurry polymerization method.

The polymerization may be a single-stage (one-stage) polymerization using one polymerization reactor, or a multi-stage polymerization using two or more polymerization reactors. Further, the polymerization may be carried out by adding hydrogen or a comonomer as a molecular weight adjusting agent to the reactor.

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

The molecular weight distribution of the polypropylene resin can be adjusted by mixing (blending) the resins. For example, a method of mixing two or more kinds of resins having different molecular weights and molecular weight distributions from each other can be mentioned. Generally, when the main resin is a resin having a higher average molecular weight or a resin having a lower average molecular weight, and the total amount of the resin is 100% by mass, the main resin is a mixture of two types of polypropylene having 55% by mass or more and 90% by mass or less. The system is preferable because the amount of low molecular weight components can be easily adjusted.

When the above mixing adjustment method is adopted, the melt flow rate (MFR) may be used as a guideline for the average molecular weight. In this case, the difference in MFR between the main resin and the added resin is preferably about 1 to 30 g / 10 minutes from the viewpoint of convenience at the time of adjustment.

The method of mixing the resins is not particularly limited, but a method of dry-blending the polymer powder or pellets of the main resin and the additive resin using a mixer or the like, the polymer powder of the main resin and the additive resin, or pellets. Is supplied to a kneader and melt-kneaded to obtain a blended resin.

The mixer and the kneader are not particularly limited. The kneader may be a single-screw type, a double-screw type, or a multi-screw type or more. In the case of a screw type with two or more axes, either a kneading type that rotates in the same direction or in a different direction may be used.

In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as a good kneaded product is obtained. Generally, the temperature is in the range of 200 ° C. to 300 ° C., preferably 230 ° C. to 270 ° C. from the viewpoint of suppressing deterioration of the resin. Further, in order to suppress deterioration during kneading and mixing of the resin, the kneader may be purged with an inert gas such as nitrogen. The melt-kneaded resin may be pelletized to an appropriate size using a generally known granulator. As a result, mixed polypropylene raw material resin pellets can be obtained.

Hereinafter, each polypropylene resin when two or more kinds of polypropylene resins are used will be described.

When two or more kinds of polypropylene resins are used, the following polypropylene resin A-1 and the following polypropylene resin B-1, the following polypropylene resin A-2 and the following polypropylene resin B-2, or the following polypropylene resin A-3 and the following polypropylene resin The combination of B-3 is mentioned as a suitable one. In the present embodiment, the expression polypropylene resin A includes the concepts of polypropylene resin A-1, polypropylene resin A-2, and polypropylene resin A-3. The expression polypropylene resin B includes the concepts of polypropylene resin B-1, polypropylene resin B-2 and polypropylene resin B-3. The polypropylene resins A, A-1, A-2, A-3, polypropylene resins B, B-1, B-2, and B-3 are all preferably linear polypropylene resins.
<Polypropylene resin A>
(Polypropylene resin A-1)
A polypropylene resin having a differential distribution value difference _DM of 8.0% or more.
(Polypropylene resin A-2)
A polypropylene resin having a heptane insoluble content (HI) of 98.5% or less.
(Polypropylene resin A-3)
A polypropylene resin having a melt flow rate (MFR) of 4.0 to 10.0 g / 10 min at 230 ° C.
<Polypropylene resin B>
(Polypropylene resin B-1)
Polypropylene differential distribution value difference _{D M} is less than 8.0%.
(Polypropylene resin B-2)
Polypropylene resin with heptane insoluble content (HI) exceeding 98.5%.
(Polypropylene resin B-3)
A polypropylene resin having a melt flow rate (MFR) of 0.1 to 3.9 g / 10 min at 230 ° C.

The weight average molecular weight Mw of the polypropylene resin A is preferably 250,000 or more and 450,000 or less, more preferably 250,000 or more and 400,000 or less, and further preferably 250,000 or more and 340,000 or less. When the weight average molecular weight Mw of the polypropylene resin A is 250,000 or more and 450,000 or less, the resin fluidity becomes appropriate. As a result, the thickness of the cast raw sheet can be easily controlled, and a thin biaxially stretched polypropylene film can be easily produced. In addition, the thickness of the cast raw sheet and the biaxially stretched polypropylene film is less likely to be uneven, and appropriate stretchability can be obtained, which is preferable.

The molecular weight distribution Mw / Mn of the polypropylene resin A is preferably 8.5 or more and 12.0 or less, more preferably 8.5 or more and 11.0 or less, and 9.0 or more and 11.0 or less. Is even more preferable.

When the molecular weight distribution Mw / Mn of the polypropylene resin A is within the above-mentioned preferable range, unevenness is less likely to occur in the thickness of the cast raw sheet and the biaxially stretched polypropylene film, and appropriate stretchability can be obtained, which is preferable.

Polypropylene differential distribution value difference _{D M} of the resin A is preferably at least 8.0%, more preferably 8.0% or more and 18.0% or less, or less 17.0 percent 8.5% or more Is more preferable, and 9.0% or more and 16.0% or less are particularly preferable.

Differential distribution value difference _{D M} is, if 18.0% or less 8.0% or more, the low molecular weight component, rich in a ratio of when compared to high molecular weight components, 18.0% 8.0% inclusive. Therefore, it is preferable because the frequency of breakage in the stretching step can be reduced and the continuous film forming property is improved.

The heptane insoluble content (HI) of polypropylene resin A is preferably 96.0% or more, more preferably 97.0% or more. The heptane insoluble content (HI) of the polypropylene resin A is preferably 99.5% or less, more preferably 98.5% or less, still more preferably 98.0% or less.

The melt flow rate (MFR) of the polypropylene resin A at 230 ° C. is preferably 1.0 to 15.0 g / 10 min, more preferably 2.0 to 10.0 g / 10 min, and 4.0 to 10.0 to 10. It is more preferably 10.0 g / 10 min, and particularly preferably 4.3 to 6.0 g / 10 min. When the MFR of the polypropylene resin A at 230 ° C. is within the above range, the flow characteristics in the molten state are excellent, so that unstable flow such as melt fracture is unlikely to occur, and fracture during stretching is suppressed. Therefore, since the film thickness uniformity is good, there is an advantage that the formation of a thin-walled portion where dielectric breakdown is likely to occur is suppressed.

The content of the polypropylene resin A is preferably 55% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 85% by mass or less, and 60% by mass or more with respect to the entire biaxially stretched polypropylene film. It is more preferably 80% by mass or less.

The weight average molecular weight Mw of the polypropylene resin B is preferably 300,000 or more and 400,000 or less, more preferably 330,000 or more and 380,000 or less, and further preferably 350,000 or more and 380,000 or less.

The molecular weight distribution Mw / Mn of the polypropylene resin B is preferably 6.0 or more and less than 8.5, more preferably 6.5 or more and 8.4 or less, and 7.0 or more and 8.3 or less. Is even more preferable.

When the molecular weight distribution Mw / Mn of the polypropylene resin B is within the above preferable range, unevenness is less likely to occur in the thickness of the cast raw sheet and the biaxially stretched polypropylene film, and appropriate stretchability can be obtained, which is preferable.

Differential distribution value difference _{D M} of the polypropylene resin B is preferably less than 8.0%, more preferably less than 8.0% or more -20.0%, -10.0% over 7.9 % Or less is more preferable, and −5.0% or more and 7.5% or less is particularly preferable.

The heptane insoluble content (HI) of the polypropylene resin B is preferably 97.5% or more, more preferably 98% or more, still more preferably 98.5% or more, and particularly preferably 98.6%. That is all. The heptane insoluble content (HI) of the polypropylene resin B is preferably 99.5% or less, more preferably 99% or less.

The melt flow rate (MFR) of the polypropylene resin B at 230 ° C. is preferably 0.1 to 6.0 g / 10 min, more preferably 0.1 to 5.0 g / 10 min, and 0.1 to 6.0 g / 10 min. It is more preferably 3.9 g / 10 min.

When polypropylene resin B is used as the polypropylene resin, the content of polypropylene resin B is preferably 10% by mass or more and 45% by mass or less, preferably 15% by mass or more and 40% by mass or less, assuming that the polypropylene resin is 100% by mass. It is more preferable that it is 20% by mass or more and 40% by mass or less.

When polypropylene resin A and polypropylene resin B are used in combination as the polypropylene resin, 55 to 90% by weight of polypropylene resin A and 45 to 10% by weight of polypropylene resin B are contained, assuming that the total weight of the polypropylene resin is 100% by mass. More preferably, it contains 60 to 85% by weight of polypropylene resin A and 40 to 15% by weight of polypropylene resin B, and more preferably 60 to 80% by weight of polypropylene resin A and 40 to 20% by weight of polypropylene resin. It is particularly preferable to include B.

When the polypropylene resin contains polypropylene resin A and polypropylene resin B, the biaxially stretched polypropylene film is in a finely mixed state (phase-separated state) of polypropylene resin A and polypropylene resin B, so that it has withstand voltage at high temperatures. Is improved.

Above, each polypropylene resin when two or more kinds of polypropylene resins are used has been described.

The polypropylene film may contain a resin other than the polypropylene resin (hereinafter, also referred to as "other resin"). The "other resin" is generally a resin other than the polypropylene resin which is the main component resin, and is not particularly limited as long as the target polypropylene film can be obtained. Examples of other resins include polyolefins other than polypropylene such as polyethylene, poly (1-butene), polyisobutene, poly (1-pentene), and poly (1-methylpentene), ethylene-propylene copolymers, and propylene-. Butene copolymers, α-olefin copolymers such as ethylene-butene copolymers, vinyl monomer-diene monomer random copolymers such as styrene-butadiene random copolymers, styrene-butadiene-styrene Examples thereof include vinyl monomer-diene monomer-vinyl monomer random copolymer such as block copolymer. The polypropylene film can be contained in an amount that does not adversely affect the target polypropylene film. The polypropylene film may contain 10 parts by mass or less, and more preferably 5 parts by mass or less of another resin with respect to 100 parts by mass of the polypropylene resin. Further, the polypropylene film may contain 0.1 part by mass or more of another resin, more preferably 1 part by mass or more, based on 100 parts by mass of the polypropylene resin.

The polypropylene film may contain an additive. Examples of the additive include a nucleating agent (α crystal nucleating agent, β crystal nucleating agent), an antioxidant, a necessary stabilizer such as a chlorine absorber and an ultraviolet absorber, a lubricant, a plasticizer, and a flame retardant. Includes agents, antistatic agents, inorganic fillers, organic fillers and the like. Examples of the inorganic filler include barium titanate, strontium titanate, and aluminum oxide. When the additive is used, it can be contained in an amount that does not adversely affect the target polypropylene film.

<Manufacturing method of polypropylene film>
As a method for producing the polypropylene film, the difference [(Δnyz) − (Δnxz)], the ratio [(tensile modulus TD) / (tensile modulus MD)], and the tensile modulus MD are in the numerical range. As long as a polypropylene film having a thickness within the above numerical range can be obtained, it is not particularly limited, but can be suitably produced by simultaneous biaxial stretching. When the polypropylene film is a simultaneous biaxially stretched polypropylene film, it can be produced by preparing a cast sheet from a polypropylene resin composition and then simultaneously biaxially stretching the cast sheet.

<Preparation of polypropylene resin composition>
The method for preparing the polypropylene resin composition is not particularly limited, but a method of dry-blending the polymer powder or pellets of the polypropylene resin together with other resins, additives, etc., if necessary, using a mixer or the like. Alternatively, a method of supplying the polypropylene resin polymer powder or pellet together with other resins, additives and the like to a kneader, melt-kneading and melt-blending, and the like can be mentioned.

The mixer and kneader are not particularly limited. The kneader may be a single-screw type, a double-screw type, or a multi-screw type or more. In the case of a screw type with two or more axes, either a kneading type that rotates in the same direction or in a different direction may be used.

In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as good kneading can be obtained, but is preferably in the range of 170 to 320 ° C, more preferably in the range of 200 ° C to 300 ° C, and more preferably. Is in the range of 230 ° C to 270 ° C. In order to suppress deterioration during kneading and mixing of the resin, the kneader may be purged with an inert gas such as nitrogen. The melt-kneaded resin can be melt-blended to obtain pellets of the polypropylene resin composition by pelletizing the melt-kneaded resin to an appropriate size using a generally known granulator.

<Making a cast sheet>
In the cast sheet, first, pellets of a polypropylene resin composition (dry blend resin composition and / or melt blend resin composition) prepared in advance are supplied to an extruder and heated and melted. The resin temperature at the time of heating and melting is preferably 170 ° C. or higher, more preferably 175 ° C. or higher, and even more preferably 180 ° C. or higher. The resin temperature is preferably 300 ° C. or lower, more preferably 290 ° C. or lower, and even more preferably 285 ° C. or lower. By controlling the resin temperature within the numerical range, the cast cooling temperature described later can be adjusted within a suitable range.

Next, a cast sheet is obtained by melt-extruding the heat-melted resin composition from the T-die, winding it around a metal drum, and solidifying it. At this time, it is preferable to press the melt-extruded resin composition against the metal drum with an air knife.

The cast cooling rate at the time of producing the cast sheet is preferably 8 ° C./sec or higher, more preferably 8.5 ° C./sec or higher, and even more preferably 9.0 ° C./sec or higher. The cast cooling rate is preferably 16 ° C./sec or less, more preferably 15.6 ° C./sec or less, and even more preferably 15.4 ° C./sec or less. By setting the cast cooling rate within the numerical range, the number of the fibrils and the area per number of the fibrils can be easily set within the numerical range.
As used herein, the cast cooling rate means the rate at which the resin composition melt-extruded from the T-die is cooled until it becomes a cast sheet. Specifically, the cast cooling rate refers to a value obtained by the following method.

<Cast cooling rate>
The heat-melted resin composition is melt-extruded from a T-die and wound around a metal drum to be solidified, and the surface temperature of the central portion in the width direction is measured. The time when the cast sheet is in close contact with the metal drum is 0 seconds, and it is 0 seconds, 0.5 seconds, 1.5 seconds, 2.5 seconds, 3.5 seconds, 4.5 seconds, 5.5 seconds. The surface temperature of that point (measured as 0 seconds) after seconds is measured, and the average of [temperature decrease / time] between each measurement point is calculated as the "cast cooling rate".
More specifically, the value obtained by subtracting the temperature after 0.5 seconds from the temperature at 0 seconds is the temperature decrease amount A, and the value obtained by subtracting the temperature after 1.5 seconds from the temperature after 0.5 seconds is used. Temperature decrease amount B, the value obtained by subtracting the temperature after 2.5 seconds from the temperature after 1.5 seconds, and the value obtained by subtracting the temperature after 3.5 seconds from the temperature decrease amount C, the temperature after 2.5 seconds Temperature drop D, the value obtained by subtracting the temperature after 4.5 seconds from the temperature after 3.5 seconds, the temperature drop E, the value obtained by subtracting the temperature after 5.5 seconds from the temperature after 4.5 seconds If the temperature drop amount F,
[Temperature drop A / 0.5], [Temperature drop B / 1], [Temperature drop C / 1], [Temperature drop D / 1], [Temperature drop E / 1] and [Temperature drop] The arithmetic mean of the quantity F / 1] is calculated as the "cast cooling rate".
The cast cooling temperature can be controlled by adjusting the resin temperature at the time of heating and melting, the surface temperature of the metal drum, the air gap, and the like.

The surface temperature of the metal drum is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, and even more preferably 92 ° C. or higher. The surface temperature is preferably 140 ° C. or lower, more preferably 120 ° C. or lower, and even more preferably 105 ° C. or lower. By controlling the surface temperature within the numerical range, the cast cooling temperature can be adjusted within a suitable range.

The air gap at the time of producing the cast sheet is preferably 3.0 mm or more, more preferably 3.5 mm or more, and further preferably 4.0 mm or more. The air gap is preferably 10.0 mm or less, more preferably 8.0 mm or less, and even more preferably 6.0 mm or less. By controlling the air gap within the numerical range, the cast cooling temperature can be adjusted within a suitable range.
As used herein, the air gap refers to the distance between the discharge port of the T-die and the position on the metal drum where the resin composition discharged from the discharge port of the T-die first touches.

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

Note that polypropylene undergoes not a little thermal deterioration (oxidative deterioration) and shear deterioration during the casting sheet manufacturing process (particularly in the extruder). The degree of progress of such deterioration, that is, changes in molecular weight distribution and stereoregularity, are the nitrogen purge in the extruder (suppression of oxidation), the screw shape in the extruder (shearing force), and the internal shape of the T-die during casting ( It can be suppressed by (shearing force), the amount of antioxidant added (suppression of oxidation), the winding speed at the time of casting (extension force), and the like.

<Stretching treatment>
Next, the cast sheet is simultaneously biaxially stretched (step A). That is, the simultaneous biaxially stretched polypropylene film can be produced by simultaneously stretching the cast sheet in the MD direction and the TD direction.

As a simultaneous biaxial stretching method, for example, both ends of the cast sheet are gripped by a movable clip that moves on the rail, guided to a tenter, and stretched simultaneously in the MD direction and the TD direction.

The stretching temperature at the time of simultaneous stretching is preferably 160 ° C. or higher, more preferably 164 ° C. or higher, and even more preferably 168 ° C. or higher. The stretching temperature is preferably 180 ° C. or lower, more preferably 178 ° C. or lower, and even more preferably 175 ° C. or lower.

Simultaneous stretching is the ratio of the stretching ratio in the MD direction (hereinafter, also referred to as “MD stretching ratio”) to the stretching ratio in the TD direction (hereinafter, also referred to as “TD stretching ratio”) [(TD stretching ratio) / (MD stretching ratio) / (MD stretching ratio). Magnification)] is preferably in the range of 1.0 to 1.7, and the product of the TD stretching ratio and the MD stretching ratio (hereinafter, also referred to as “area stretching ratio”) is preferably 46 times or more.
The ratio [(TD stretching ratio) / (MD stretching ratio)] is preferably 1.0 or more, more preferably 1.1 or more, and even more preferably 1.2 or more. The ratio [(TD stretching ratio) / (MD stretching ratio)] is preferably 1.7 or less, more preferably 1.6 or less, and even more preferably 1.5 or less.
The area stretching ratio is preferably 46 times or more, more preferably 47 times or more, still more preferably 48 times or more. The area stretching ratio is preferably 72 times or less, more preferably 65 times or less, still more preferably 58 times or less.
By setting the ratio [(TD stretching ratio) / (MD stretching ratio)] and the area stretching ratio within the numerical range, it has isotropic properties at any temperature and is excellent in mechanical properties. A thin polypropylene film can be easily obtained. That is, the difference [(Δnyz) − (Δnxz)], the ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)], and the tensile elastic modulus MD are within the numerical range and the thickness. A polypropylene film having a thin thickness (within the above numerical range) can be easily obtained.

Further, by setting the cast cooling temperature within a predetermined range and setting the ratio [(TD stretching ratio) / (MD stretching ratio)] and the area stretching ratio within the numerical range, the number of the fibrils. , And the area per number of the fibrils can be easily set within the numerical range.
According to the present inventors, the number of the fibrils and the area per number of the fibrils could be relatively easily within the numerical range by sequentially biaxially stretching. However, in the case of simultaneous biaxial stretching, it is difficult to keep the number of the fibrils and the area per number of the fibrils within the numerical range.
However, as a result of diligent studies by the present inventors, the cast cooling temperature is within a predetermined range, and the ratio [(TD stretching ratio) / (MD stretching ratio)] and the area stretching ratio are within the numerical range. By setting the temperature to the inside, the number of the fibrils and the area per number of the fibrils can be easily set within the numerical range even in the case of simultaneous biaxial stretching.

The MD stretch ratio is preferably 5.0 times or more, more preferably 5.5 times or more, and further preferably 6.0 times or more. The MD stretching ratio is preferably 9.0 times or less, more preferably 8.0 times or less, and further preferably 7.0 times or less.
The TD stretching ratio is preferably 6.0 times or more, more preferably 7.0 times or more, and further preferably 8.0 times or more. The TD stretching ratio is preferably 10.0 times or less, more preferably 9.0 times or less, and further preferably 8.0 times or less.
By setting the MD stretching ratio and the TD stretching ratio within the numerical range, the ratio [(TD stretching ratio) / (MD stretching ratio)] and the area stretching ratio are within the numerical range. It becomes easy.

After simultaneous stretching, relax and heat-fix as necessary, and wind in a roll.

At least one surface of the polypropylene film is roughened by a large number of relatively small-area fibrils. Therefore, when the polypropylene film after being biaxially stretched is wound in a roll shape, the slipperiness with respect to the transport roll is improved. As a result, suitable transportability is obtained, and wrinkles and unwinding are suppressed.

The film wound in a roll shape is subjected to an aging treatment in an atmosphere of about 20 to 45 ° C., and then slit (cut) to a desired product width with a slitter or the like while being rewound (while being unwound). , Each is wound again.

The polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat fixing steps are completed. By performing the corona discharge treatment, the adhesive properties in the post-process such as the metal vapor deposition processing process can be improved. The corona discharge treatment can be performed by using a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as the atmospheric gas.

In order to process it as a capacitor, a metal layer may be laminated on one side or both sides of the polypropylene film to form a polypropylene film integrated with a metal layer. The metal layer functions as an electrode. As the metal used for the metal layer, for example, elemental metals such as zinc, lead, silver, chromium, aluminum, copper and nickel, a mixture of a plurality of kinds thereof, an alloy thereof and the like can be used, but the environment. Zinc and aluminum are preferable in consideration of economic efficiency and capacitor performance.

As a method of laminating a metal layer on one side or both sides of the polypropylene film, for example, a vacuum vapor deposition method or a sputtering method can be exemplified. The vacuum vapor deposition method is preferable from the viewpoint of productivity and economy. As the vacuum vapor deposition method, a crucible method, a wire method, or the like can be generally exemplified, but the method is not particularly limited, and the optimum method can be appropriately selected. When the metal layers are laminated by the vacuum deposition method or the sputtering method, the polypropylene film receives heat of about 130 to 140 ° C.
However, since the polypropylene film is not temperature-dependent and has isotropic mechanical properties at any temperature, the polypropylene film is wrinkled in the vapor deposition process and the sputtering process for forming a metal layer on the polypropylene film. It is possible to suppress the occurrence and make the thickness of the metal layer more uniform.

The margin pattern when laminating metal layers by vapor deposition or sputtering is not particularly limited, but includes so-called special margins such as a fishnet pattern or a T-margin pattern from the viewpoint of improving characteristics such as capacitor safety. It is preferable to apply the pattern on one side of the film. It is effective in terms of improving security, destroying capacitors, preventing short circuits, and so on.

As a method for forming a margin, a generally known method such as a tape method or an oil method can be used without any limitation.

When forming a metal layer on the polypropylene film, the polypropylene film wound in a roll shape is rewound (unwound), and a metal layer such as a thin-film deposition film is formed on one or both surfaces, and again. It is wound.

The metal layer integrated polypropylene film can be laminated by a conventionally known method, or can be element-wound (wound) to form a film capacitor.

Specifically, a blade is inserted in the center of each margin portion of the metal layer integrated polypropylene film and slit processing is performed to produce a take-up reel having a margin on one surface of the surface.
Next, using a take-up reel with a left margin and a take-up reel with a right margin, two reels are overlapped and wound so that the vapor-deposited portion protrudes from the margin portion in the width direction (element winding processing). Next, the core material is removed from the winding body and pressed. Next, external electrodes are formed on both end faces, and lead wires are further provided on the external electrodes. From the above, a winding type film capacitor can be obtained.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Polypropylene resin]
Table 1 shows the polypropylene resins used to produce the polypropylene films of Examples and Comparative Examples.
The resin A1 shown in Table 1 is a product manufactured by Prime Polymer Co., Ltd. Resin B1 is HPT-1 manufactured by Korea Yuka Co., Ltd. The resin C1 is HC300BF manufactured by Borealis.
Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of each resin. These values are values in the form of raw material resin pellets. The measurement method is as follows.

<Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of polypropylene resin>
Using GPC (gel permeation chromatography), the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of each resin were measured under the following conditions.
Specifically, an HLC-8121 GPC-HT type, which is a high temperature GPC device with a built-in differential refractometer (RI) manufactured by Tosoh Corporation, was used. As a column, three TSKgel GMHHR-H (20) HTs manufactured by Tosoh Corporation were connected and used. Trichlorobenzene was flowed as an eluent at a flow rate of 1.0 ml / min at a column temperature of 140 ° C. for measurement. A calibration curve for the molecular weight M was created using standard polystyrene manufactured by Tosoh Corporation, and the measured values were converted to the molecular weight of polypropylene using the Q-factor to convert the number average molecular weight (Mn) and the weight average molecular weight (Mn). Mw) was obtained. The molecular weight distribution (Mw / Mn) was obtained using the values of Mw and Mn.

<Differential distribution value when the log molecular weight log (M) = 4.5, the differential distribution value when the log molecular weight log (M) = 6.0, and the measurement of the differential distribution value difference _{D M>}
For each resin, the differential distribution value when the logarithmic molecular weight log (M) = 4.5 and the differential distribution value when the logarithmic molecular weight log (M) = 6.0 were obtained by the following methods. First, the time curve (elution curve) of the intensity distribution detected by the RI detector is used as the distribution curve for the molecular weight M (Log (M)) of the standard polystyrene using the calibration curve prepared using the standard polystyrene. Converted. Next, after obtaining an integral distribution curve for Log (M) when the total area of the distribution curve is 100%, the differential distribution for Log (M) is obtained by differentiating this integral distribution curve with Log (M). I got a curve. From this differential distribution curve, the differential distribution values when Log (M) = 4.5 and Log (M) = 6.0 were read. In addition, the Log (M) = 4.5 different differential distribution value difference _{D M} of the differential distribution value when the differential distribution value and Log (M) = 6.0 when the. A series of operations until the differential distribution curve was obtained was performed using the analysis software built in the GPC measuring device used. The results are shown in Table 1.

<Measurement of heptane insoluble matter (HI)>
Each resin was press-molded to 10 mm × 35 mm × 0.3 mm to prepare a measurement sample of about 3 g. Next, about 150 mL of heptane was added and Soxhlet extraction was performed for 8 hours. The heptane insoluble content was calculated from the sample mass before and after extraction. The results are shown in Table 1.

<Measurement of melt flow rate (MFR)>
For each resin, the melt flow rate (MFR) in the form of raw material resin pellets was measured using a melt indexer manufactured by Toyo Seiki Co., Ltd. according to the condition M of JIS K 7210. Specifically, first, a sample weighed to 4 g was inserted into a cylinder having a test temperature of 230 ° C., and preheated for 3.5 minutes under a load of 2.16 kg. Then, the weight of the sample extruded from the bottom hole was measured in 30 seconds to determine the MFR (g / 10 min). The above measurement was repeated 3 times, and the average value was taken as the measured value of MFR. The results are shown in Table 1.

<Mesopentad fraction>
Each resin was dissolved in a solvent and measured under the following conditions using a high-temperature Fourier transform nuclear magnetic resonance apparatus (high-temperature FT-NMR).
High Temperature Nuclear Magnetic Resonance (NMR) Device: JEOL Ltd., High Temperature Fourier Transform Nuclear Magnetic Resonance Device (High Temperature FT-NMR), JNM-ECP500
Observation nucleus: 13C (125MHz)
Measurement temperature: 135 ° C
Solvent: Ortho-dichlorobenzene (ODCB: mixed solvent of ODCB and deuterated ODCB (mixing ratio = 4/1))
Measurement mode: Single pulse Proton broadband decoupling Pulse width: 9.1 μsec (45 ° pulse)
Pulse interval: 5.5 sec
Number of integrations: 4,500 times Shift reference: CH3 (mmmm) = 21.7 ppm
The pentad fraction, which represents the degree of stereoregularity, is a combination (mmmm or mrrm) of the quintuplets (pentads) of the "meso (m)" aligned in the same direction and the "racemo (r)" aligned in different directions. Etc.), calculated as a percentage (%) from the integrated intensity of each signal. Regarding the attribution of each signal derived from mmmm, mrrm, etc., for example, the description of the spectrum such as "T. Hayashi et al., Polymer, Vol. 29, p. 138 (1988)" was referred to.

Using the above-mentioned resin, polypropylene films of Examples and Comparative Examples were prepared and their physical properties were evaluated.

<Making polypropylene film>
(Example 1)
Resin A1 and resin B1 are supplied to an extruder at a mass ratio of resin A1: resin B1 = 65:35, melted at a resin temperature of 230 ° C., and then extruded using a T-die to adjust the air gap to 4 mm. A cast sheet was prepared by winding it around a metal drum whose surface temperature was maintained at 95 ° C. and solidifying it.
The obtained unstretched cast sheet is gripped at both ends with a movable clip that moves on the rail, guided to a tenter, stretched 6 times in the MD direction (flow direction) at a temperature of 170 ° C., and at the same time, TD. After stretching 8 times in the direction (width direction), the film was relaxed in the flow direction and the width direction, heat-fixed and wound to obtain a biaxially stretched polypropylene film having a thickness of 2.8 μm according to Example 1.

(Example 2)
A biaxially stretched polypropylene film according to Example 2 was obtained in the same manner as in Example 1 except that the resin temperature was set to 180 ° C. in the preparation of the cast sheet.

(Example 3)
A biaxially stretched polypropylene film according to Example 3 was obtained in the same manner as in Example 2 except that the draw ratio in the flow direction was increased to 7 times in the preparation of the biaxially stretched polypropylene film.

(Example 4)
A biaxially stretched polypropylene film according to Example 4 was obtained in the same manner as in Example 1 except that resin C1 was used alone instead of using a mixture of resin A1 and resin B1 in the preparation of the cast sheet. ..

(Example 5)
Examples were the same as in Example 4 except that the resin temperature was set to 280 ° C. in the production of the cast sheet and the draw ratio in the flow direction was increased to 7 times in the production of the biaxially stretched polypropylene film. A biaxially stretched polypropylene film according to No. 5 was obtained.

(Example 6)
A biaxially stretched polypropylene film according to Example 6 was obtained in the same manner as in Example 5 except that the air gap was set to 6 mm in the production of the cast sheet.

(Example 7)
In the production of the biaxially stretched polypropylene film, the same as in Example 4 except that the draw ratio in the flow direction was set to 6.5 times and the thickness was set to 2.5 μm, according to Example 7. A shaft-stretched polypropylene film was obtained.

(Example 8)
In the production of the biaxially stretched polypropylene film, the same as in Example 4 except that the draw ratio in the flow direction was 6.5 times and the thickness was 2.0 μm, according to Example 8. A shaft-stretched polypropylene film was obtained.

(Comparative Example 1)
A biaxially stretched polypropylene film according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the stretch ratio in the flow direction was 4.5 times in the preparation of the biaxially stretched polypropylene film.

(Comparative Example 2)
In the production of the biaxially stretched polypropylene film, Comparative Example 2 was carried out in the same manner as in Example 1 except that the stretching ratio in the flow direction was 4.5 times and the stretching ratio in the width direction was 10 times. A biaxially stretched polypropylene film according to the above was obtained.

(Comparative Example 3)
Resin A1 and resin B1 are supplied to an extruder at a mass ratio of resin A1: resin B1 = 65:35, melted at a resin temperature of 250 ° C., and then extruded using a T-die to adjust the air gap to 5 mm. A cast sheet was prepared by winding it around a metal drum whose surface temperature was maintained at 95 ° C. and solidifying it.
The obtained unstretched cast sheet was kept at a temperature of 140 ° C., passed between rolls provided with a speed difference, stretched 4.5 times in the flow direction, and immediately cooled to room temperature. Subsequently, the stretched film was led to a tenter, stretched 10 times in the width direction at a temperature of 158 ° C., then relaxed, heat-fixed and wound, and aged in an atmosphere of about 30 ° C. to achieve a thickness of 2. An 8 μm biaxially stretched polypropylene film was obtained.

(Comparative Example 4)
A biaxially stretched polypropylene film according to Comparative Example 4 was obtained in the same manner as in Comparative Example 3 except that the thickness was 2.5 μm in the preparation of the biaxially stretched polypropylene film.

(Comparative Example 5)
According to Comparative Example 5 in the same manner as in Comparative Example 3 except that the resin temperature was set to 240 ° C. in the production of the cast sheet and the thickness was 2.3 μm in the production of the biaxially stretched polypropylene film. A biaxially stretched polypropylene film was obtained.

(Comparative Example 6)
A biaxially stretched polypropylene film according to Comparative Example 6 was obtained in the same manner as in Comparative Example 4 except that the resin C1 was used in the preparation of the cast sheet.

Table 2 summarizes the production conditions of the polypropylene films of Examples and Comparative Examples described above. In Table 2, the area stretching ratio means the product of the MD stretching ratio and the TD stretching ratio.
Here, the cast cooling rate, the thickness of the cast sheet, and the thickness of the polypropylene film are values obtained by the following methods.

<Calculation of cast cooling rate>
The surface temperature of the central portion in the width direction of the cast sheet extruded using a T-die and wound around a metal drum to be solidified was measured. The time when the cast sheet is in close contact with the metal drum is 0 seconds, and 0.5 seconds, 1.5 seconds, 2.5 seconds, 3.5 seconds, 4.5 seconds, and 5.5 seconds later. The surface temperature was measured, and the average of "temperature decrease amount ÷ time" between each measurement point was calculated as "cooling rate".

<Measurement of thickness of cast sheet and polypropylene film>
The thicknesses of the cast sheets of Examples and Comparative Examples and the polypropylene film were measured. Specifically, the measurement was performed in accordance with JIS-C2330 except that the measurement was performed at 100 ± 10 kPa using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu.

<Measurement of birefringence value Δnxz and birefringence value Δnyz, and calculation of difference [(Δnyz)-(Δnxz)]>
First, the retardation (phase difference) value of the biaxially stretched polypropylene film was measured by the inclination method as follows.
Measuring machine: Otsuka Electronics Co., Ltd. retardation measuring device RE-100
Light source: LED light source with a wavelength of 550 nm Measuring method: The MD direction of the polypropylene film is the x-axis, the TD direction is the y-axis, the thickness direction is the z-axis, and the x-axis is the tilt axis, and the z-axis is in the range of 0 ° to 50 °. Each retardation value when tilted by 10 ° was obtained.
Next, from the obtained retardation values, the method described in the non-patent document "Yu Awaya, Introduction to Birefringence Microscopes for Polymer Materials, pp. 105-120, 2001" was used with respect to the thickness direction (z-axis direction). The birefringence value ΔNyz in the y-axis direction was calculated.
First, for each inclination angle φ, the measured retardation value R was divided by the inclination-corrected thickness d to obtain R / d. For each R / d of φ = 10 °, 20 °, 30 °, 40 °, and 50 °, find the difference from the R / d of φ = 0 °, and divide them by sin2r (r: refraction angle). The birefringence ΔNyz at each φ was used, and the positive and negative signs were reversed to obtain the birefringence ΔNyz. The average value of the birefringence ΔNyz at φ = 20 °, 30 °, 40 °, and 50 ° was calculated and used as the birefringence value ΔNyz.
Next, the birefringence value ΔNxz was calculated by dividing the retardation value R measured at the inclination angle φ = 0 ° by the thickness d by dividing ΔNzy obtained above.
As the value of the refraction angle r at each inclination angle, the value described on page 109 of the above-mentioned document was used.
The results are shown in Table 3.

<Tensile modulus MD at 25 ° C. in the MD direction, tensile modulus TD at 25 ° C. in the TD direction, breaking strength MD at 25 ° C. in the MD direction, breaking strength TD at 25 ° C. in the TD direction, in the MD direction Measurement of breaking elongation MD at 25 ° C and breaking elongation TD at 25 ° C in the TD direction>
Tensile elastic modulus MD at 25 ° C. in the MD direction, tensile elastic modulus TD at 25 ° C. in the TD direction, breaking strength MD at 25 ° C. in the MD direction, and 25 ° C. in the TD direction of the polypropylene films of Examples and Comparative Examples. The breaking strength TD, the breaking elongation MD at 25 ° C. in the MD direction, and the breaking elongation TD at 25 ° C. in the TD direction were measured as follows.
The break point elongation was measured according to JIS K-7127 (1999). Specifically, a tensile compression tester (manufactured by Minebea Co., Ltd.) is used to perform a tensile test 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). went. Next, the elongation at break (%) and the tensile elastic modulus (GPa) were determined by automatic analysis using the data processing software built into the testing machine.
In addition, the ratio [(tensile modulus TD) / (tensile modulus MD)], ratio [(breaking strength TD) / (breaking strength MD)], ratio [(breaking elongation TD) / (breaking elongation MD)] Was calculated. The results are shown in Table 3.

<Measurement of ash>
The polypropylene films of Examples and Comparative Examples were measured as follows.
About 200 g of the sample was weighed, transferred to a platinum dish and incinerated at 800 ° C. for 40 minutes. The ratio of ash (ppm) was measured from the obtained ash residue. The results are shown in Table 3.

<Measurement of the number of fibrils, the area of fibrils, and the area per number of fibrils>
As a light interference type non-contact surface shape measuring device, "VertScan2.0 (model: R5500GML)" manufactured by Ryoka System Co., Ltd. was used.
First, using the WAVE mode, a 530-white filter and a 1 × BODY lens barrel were applied, and a measurement of 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per field of view was performed using an × 10 objective lens. .. This operation was performed at 10 locations at 1 cm intervals in the flow direction from the central location in both the flow direction and the width direction of the target sample (polypropylene film).
Next, the obtained data was subjected to noise removal processing by a median filter (3 × 3), and then Gaussian filter treatment with a cutoff value of 30 μm was performed to remove undulation components.
For each surface shape data of the 10 locations obtained as described above, a region having a mountain side height of 0.05 μm or more is painted white, and a region having a mountain side height smaller than 0.05 μm is painted black to obtain binary values. A converted image (262 × 194 pixels) was obtained.
Next, using the image analysis software Image Pro Plus 5.1J (manufactured by Nippon Rover), the number of objects having a brightness range of 128 or more and 255 or less in the binarized image obtained above and their areas were measured. When extracting the objects, those on the lower boundary of the image and those on the left boundary were excluded. For the extracted objects, the number of objects having an area of 50 pixels or more was defined as the number of fibrils, and the sum of the areas of objects having an area of 50 pixels or more was defined as the fibril area. Objects with an area smaller than 50 pixels were removed as noise. Further, after calculating the sum of the areas of an object having an area of 50 pixels or more, the calculated sum divided by the number of fibrils was defined as the area (pixels / piece) per number of fibrils. Finally, for the area per number of fibrils, the unit was converted to μm ² / piece. The results are shown in Table 4.
In the unit conversion method for the area per number of fibrils, the binarized image is 470.92 μm × 353.16 μm (262 × 194 pixels) per field, so 262 × 194 pixels = 470.92 ×. and using the equation of 1 pixel = 3.272μm ² obtained by calculating the 353.16μm ^2.

<Evaluation of film roll misalignment>
By applying a T-margin thin-film deposition pattern to the polypropylene films obtained in Examples 1 to 8 and Comparative Examples 1 to 6 with aluminum vapor deposition with a vapor deposition resistance of 15 Ω / □, a metal layer containing a metal film on one side of the polypropylene film. A body polypropylene film was obtained.
With respect to the obtained polypropylene film integrated with a metal layer, the winding deviation of the film roll was evaluated by the following method. That is, when the film roll is observed from the side, the lengths of the portion where the film roll width is maximized and the portion where the film roll width is minimized are measured, and from the difference between the maximum value and the minimum value, the winding deviation is A to A to the following. It was evaluated on a scale of C. The diameter of the winding core is 17.6 cm, and the length of the biaxially stretched polypropylene film wound around the winding core is 30,000 m.
A: The difference between the maximum and minimum values of the film roll width is less than 0.5 mm B: The difference between the maximum and minimum values of the film roll width is 0.5 mm or more and less than 1 mm C: The maximum and minimum values of the film roll width Difference is 1 mm or more

<Evaluation of thin film unevenness>
By applying a T-margin thin-film deposition pattern to the polypropylene films obtained in Examples 1 to 8 and Comparative Examples 1 to 6 with aluminum vapor deposition with a vapor deposition resistance of 15 Ω / □, a metal layer containing a metal film on one side of the polypropylene film. A body polypropylene film was obtained.
From the obtained polypropylene film integrated with a metal layer, one full-width film for one roll was peeled off from the center in the length direction of the roll, and then a 100 mm square film piece from the center in the roll width direction of the peeled full-width film. Was cut out. The cut-out film piece is divided into 100 areas of 10 mm square, and the color value (L *) is used for the central portion of each of the 100 areas using a print density measuring machine (Type 938 manufactured by X-Rite). Value, a * value, b * value) were measured. The measurement diameter used was 8 mm. For each of the L * value, a * value, and b * value, the variation was calculated from the maximum value and the minimum value at 100 points and the average value at 100 points using the following formula.
Variation of L * value (%) = [(L * maximum value-L * minimum value) / L * average value at 100 locations] x 100
Variation of a * value (%) = [(a * maximum value-a * minimum value) / a * average value at 100 locations] x 100
Variation of b * value (%) = [(b * maximum value-b * minimum value) / 100 b * average values] x 100
Among the variations of the L * value, the a * value, and the b * value, the one having the largest variation was evaluated on a scale of A to C as follows. The results are shown in Table 4.
A: The largest variation of L * value, a * value, and b * value is less than 10%. B: The largest variation of L * value, a * value, and b * value is 10% or more and 20%. Less than C: The largest variation of L * value, a * value, and b * value is 20% or more.

<Manufacturing of capacitors and capacitance>
Capacitors were produced as follows using the polypropylene films obtained in Examples 1 to 6 and Comparative Examples 1 to 3. By subjecting a polypropylene film to a T-margin thin-film deposition pattern with an aluminum vapor deposition with a vapor deposition resistance of 15 Ω / □, a metal layer-integrated polypropylene film containing a metal film on one side of the polypropylene film was obtained. After slitting to a width of 60 mm, two metal layer integrated polypropylene films are combined, and a winding machine 3KAW-N2 type manufactured by Minato Seisakusho Co., Ltd. is used to wind 1158 turns at a winding tension of 250 g. went. The element wound element was heat-treated at 120 ° C. for 15 hours while being pressed, and then zinc metal was sprayed on the element end face to obtain a flat capacitor. The lead wire was soldered to the end face of the flat capacitor, and then sealed with epoxy resin. From the above, the capacitors according to Examples 1 to 6 and Comparative Examples 1 to 3 were obtained.
The capacitors according to Example 7, Comparative Example 4, and Comparative Example 6 were obtained in the same manner as the capacitors of Example 1 except that the capacitors were wound for 1137 turns at a winding tension of 250 g.
A capacitor according to Example 8 was obtained in the same manner as the capacitor of Example 4 except that the capacitor was wound for 1137 turns at a winding tension of 250 g.
A capacitor according to Comparative Example 5 was obtained in the same manner as the capacitor of Example 1 except that the capacitor was wound for 1076 turns at a winding tension of 250 g.
The number of turns of the winding was changed in order to evaluate the capacitance under the same conditions because the thickness of the polypropylene film is different.
The capacitance of the completed capacitors was 75 μF (± 5 μF).

Claims

The difference [(Δnyz) − (Δnxz)] between the birefringence value Δnxz and the birefringence value Δnyz is 0.009 or less.
The ratio [(tensile elastic modulus TD) / (tensile elastic modulus MD)] of the tensile elastic modulus MD at 25 ° C. in the MD direction and the tensile elastic modulus TD at 25 ° C. in the TD direction is 1.20 or less.
The tensile elastic modulus MD is 3.1 GPa or more, and the tensile elastic modulus MD is 3.1 GPa or more.
A polypropylene film having a thickness of 0.8 μm or more and 5 μm or less.
(However, the double refractive index Δnxz is three-dimensional in the z-axis direction from the three-dimensional refractive index in the x-axis direction when the MD direction of the polypropylene film is the x-axis, the TD direction is the y-axis, and the thickness direction is the z-axis. It is a value obtained by subtracting the refractive index, and the double refractive index Δnyz is a value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the y-axis direction.)
The number of fibrils when measuring 470.92 μm × 353.16 μm (640 pixels × 480 pixels) per field using a light interference type non-contact surface shape measuring device is 20 or more and 50 or less, and the fibrils The polypropylene film according to claim 1, wherein the polypropylene film has a surface having an area of 200 μm 2 / piece or more and 1000 μm 2 / piece or less.
The polypropylene film according to claim 1 or 2, characterized in that it is for a capacitor.
The polypropylene film according to any one of claims 1 to 3, wherein the polypropylene film is biaxially stretched at the same time.
The polypropylene film according to any one of claims 1 to 4,
A polypropylene film integrated with a metal layer having a metal layer laminated on one side or both sides of the polypropylene film.
A film capacitor having a wound metal layer-integrated polypropylene film according to claim 5, or having a configuration in which a plurality of metal layer-integrated polypropylene films according to claim 5 are laminated.