JP7676746B2 - Metal layer-integrated polypropylene film, film capacitor, and method for producing metal layer-integrated polypropylene film - Google Patents

Description

The present invention relates to a metal layer-integrated polypropylene film, a film capacitor, and a method for producing a metal layer-integrated polypropylene film.

Polypropylene film has excellent electrical properties, such as high voltage resistance and low dielectric loss, and is also highly moisture resistant. For this reason, it is widely used in electronic and electrical equipment. Specifically, it is used as a film for high-voltage capacitors; filter capacitors and smoothing capacitors in power conversion circuits such as converters and inverters.

Japanese Patent Application Publication No. 11-273991 International Publication No. 2020/045482

In general, biaxially oriented polypropylene films have the property of shrinking when heated. For example, as in Patent Document 1, in order to reduce the heat shrinkage rate of the polypropylene film before laminating the metal layer, it is necessary to select a raw material resin that can produce a polypropylene film that does not shrink when heated. This creates a problem in that the range of choices for raw material resins is narrowed.

In addition, to obtain a polypropylene film with a small thermal shrinkage rate (polypropylene film before lamination of a metal layer), the manufacturing conditions, such as the manufacturing conditions for the cast sheet (e.g., melting temperature of the raw resin, casting temperature, etc.) and the stretching conditions when stretching the cast sheet to form the polypropylene film (e.g., temperature during stretching, stretch ratio, nip pressure, etc.), are very limited, and it may be difficult to balance this with other qualities (e.g., electrical properties such as dielectric breakdown strength). Also, the selection of raw resins to reduce the thermal shrinkage rate of the polypropylene film may sacrifice other properties (e.g., voltage resistance, etc.).

Patent Document 2 also discloses a technology that suppresses peeling of metallikon electrodes by setting the thermal shrinkage rate of the polypropylene film before laminating the metal layer and the thermal shrinkage rate of the metal layer-integrated polypropylene film after laminating the metal layer within a predetermined range.

In response to this, the inventors have found that, since polypropylene film is subjected to a considerable amount of heat history in the process of forming the metal layer, and in the subsequent winding, aging, and metallicon spraying processes during the process of manufacturing the capacitor, even if the thermal shrinkage rate of the polypropylene film is reduced, when a film capacitor is formed using the resulting metal layer-integrated polypropylene film and the film capacitor is exposed to a high-temperature atmosphere, the element shape changes, the gap between the winding layers changes, and the flat curved parts of the element are distorted and wrinkled, which makes it easy for the voltage resistance and insulation to decrease, and makes it easy for short circuits to occur when a high voltage is applied. The inventors have focused on the elongation rate of the metal layer-integrated polypropylene film at high temperatures and have attempted to obtain a film with stable thermo-mechanical properties by applying heat (thermal history) greater than that in the subsequent process (aging process) to the metallized film after the deposition process in advance.

In this situation, the main objective of the present invention is to provide a metal layer-integrated polypropylene film that can provide a film capacitor with the property of not shorting even when a high voltage is applied at a high temperature of 100°C or higher.

The present inventors conducted intensive research to solve the above problem. As a result, they found that in a metal layer-integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film, when a static load of 2 MPa is applied in the MD direction and the film is heated from 25°C at a temperature increase rate of 10°C/min, the elongation rates at 100°C, 120°C, and 130°C are set to specific ranges of 0% or more, respectively, to obtain a film capacitor having high voltage resistance and high insulation properties in a high-temperature atmosphere. That is, in the present invention, they found that the above problem can be solved by setting the elongation rate to a specific range of 0% or more (i.e., not thermally shrinking), rather than the thermal shrinkage described in Patent Document 2. The present invention was completed through further research based on such knowledge.

That is, the present invention includes the following.
Item 1. A metal layer-integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film,
The metal layer-integrated polypropylene film, when heated from 25°C at a temperature increase rate of 10°C/min under a static load of 2 MPa in the MD direction, has an elongation rate of 0% or more at 100°C and 1.8% or less, an elongation rate of 0% or more at 120°C and 2.3% or less, and an elongation rate of 0% or more at 130°C, assuming that the elongation rate at 25°C is 0%.
Item 2. The metal layer-integrated polypropylene film according to item 1, wherein when the metal layer-integrated polypropylene film is heated at a temperature increase rate of 10°C/min from 25°C under a static load of 2 MPa in the MD direction, the elongation gradient from 30°C to 100°C is 0.010%/°C or more and 0.030%/°C or less.
Item 3. The metal layer-integrated polypropylene film according to item 1 or 2, wherein the metal layer-integrated polypropylene film has an inflection point temperature of 130° C. or higher in a graph showing the relationship between temperature and elongation obtained by heating the film at a temperature increase rate of 10° C./min from 25° C. under a static load of 2 MPa in the MD direction.
Item 4. The metal layer-integrated polypropylene film according to any one of Items 1 to 3, having a thickness of 0.8 μm or more and 3.5 μm or less.
Item 5. The metal layer-integrated polypropylene film according to any one of Items 1 to 4, which is for use in a capacitor.
Item 6. A film capacitor having a configuration in which the metal layer-integrated polypropylene film according to any one of Items 1 to 5 is wound, or a plurality of the metal layer-integrated polypropylene films according to any one of Items 1 to 5 are laminated.
Item 7. A method for producing a metal layer-integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film, comprising:
a metal layer lamination step of laminating a metal layer on one or both sides of the polypropylene film to obtain a metal layer-integrated polypropylene film;
A heating step of heating the metal layer-integrated polypropylene film obtained in the metal layer lamination step at a temperature of 100° C. or more and 130° C. or less;
A method for producing a metal layer-integrated polypropylene film comprising the steps of:

According to the present invention, it is possible to provide a metal layer-integrated polypropylene film that can impart to a film capacitor the property of not shorting even when a high voltage is applied at a high temperature of 100°C or higher. In addition, according to the present invention, it is possible to provide a film capacitor that uses the metal layer-integrated polypropylene film, and a metal layer-integrated polypropylene film.

FIG. 2 is a schematic perspective view for explaining a metal layer-integrated polypropylene film.

The metal layer-integrated polypropylene film according to the present embodiment is a metal layer-integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film. The metal layer-integrated polypropylene film according to the present embodiment is characterized in that, when a static load of 2 MPa is applied in the MD (machine direction) direction (also called the flow direction or the longitudinal direction) and the film is heated from 25°C at a temperature increase rate of 10°C/min, the elongation rate at 100°C is 0% or more and 1.8% or less, the elongation rate at 120°C is 0% or more and 2.3% or less, and the elongation rate at 130°C is 0% or more and 2.7% or less, assuming that the elongation rate at 25°C is 0%. The metal layer-integrated polypropylene film according to the present embodiment has the above characteristics, and when a film capacitor is formed using the metal layer-integrated polypropylene film, the film capacitor can be given a property of not shorting even when a high voltage is applied at a high temperature of 100°C or more. The metal layer-integrated polypropylene film according to the present embodiment will be described in detail below.

In this specification, the term "to" in a numerical range means "greater than or equal to" or "less than or equal to." In other words, the expression "α to β" means "greater than or equal to α and less than or equal to β" or "greater than or equal to β and less than or equal to α," and includes α and β as a range.

In addition, in this specification, a metallikon electrode refers to an external electrode that is provided on the side where a metal layer-integrated polypropylene film is laminated and is electrically connected to the metal layer as an internal electrode.

As described above, when the metal layer-integrated polypropylene film according to this embodiment is heated from 25°C at a heating rate of 10°C/min under a static load of 2MPa in the MD direction, assuming that the elongation rate at 25°C is 0%, the elongation rate at 100°C is set to 0% or more and 1.8% or less, the elongation rate at 120°C is set to 0% or more and 2.3% or less, and the elongation rate at 130°C is set to 0% or more and 2.7% or less. In other words, in the metal layer-integrated polypropylene film according to this embodiment, the elongation rate in a high-temperature environment (100°C, 120°C, and 130°C) of the metal layer-integrated polypropylene film in which a metal layer is formed on a polypropylene film is set to a specific range of 0% or more, rather than the characteristics of the polypropylene film in a high-temperature environment before the metal layer is formed. Since the elongation rate is 0% or more, the metal layer-integrated polypropylene film according to this embodiment does not undergo heat shrinkage in a high-temperature environment. Film capacitors made from this metal layer-integrated polypropylene film are less likely to undergo thermal changes such as thermal expansion/contraction, especially in the winding direction of the capacitor (corresponding to the MD of the film), even when exposed to high-temperature environments. As a result, the gap between the winding layers changes, and in flat elements, there is no distortion or wrinkling in the flat curved parts, so the capacitor is less likely to short out even when a high voltage is applied in a high-temperature environment.

In order to provide the metal layer-integrated polypropylene film of this embodiment with the elongation rate at each of the temperatures described above, it is preferable to employ a method in which the metal layer-integrated polypropylene film is heat-treated under predetermined conditions, for example, as in the manufacturing method described below. The specific method of heat treatment will be described in detail in the section on the manufacturing method of the metal layer-integrated polypropylene film described below.

From the viewpoint of more optimally exerting the effects of the present invention, the elongation rate at 100°C is preferably 0 to 1.7%, more preferably 0 to 1.5%, and even more preferably 0 to 1%. The elongation rate at 120°C is preferably 0 to 2.2%, more preferably 0 to 2%, and even more preferably 0 to 1.9%. The elongation rate at 130°C is preferably 0 to 2.6%, more preferably 0 to 2.5%, and even more preferably 0 to 2.4%.

<Relationship between temperature and elongation rate of metal layer-integrated polypropylene film>
The expansion/contraction ratios at each temperature are values measured by using a thermo-mechanical measuring device (TMA) to heat the metal layer-integrated polypropylene film at a temperature increase rate of 10°C/min from 25°C under a static load of 2 MPa in the MD direction, and obtain a graph showing the relationship between temperature and expansion ratio. More specifically, the method described in the Examples is used.

In order to more effectively exert the effects of the present invention, the metal layer-integrated polypropylene film of this embodiment has an elongation gradient (i.e., average linear expansion coefficient) from 30°C to 100°C of preferably 0.010 to 0.030%/°C, more preferably 0.020 to 0.025, when heated from 25°C at a temperature increase rate of 10°C/min under a static load of 2 MPa in the MD direction. The elongation gradient can be determined based on a graph obtained by the method described in the above-mentioned <Relationship between Temperature and Elongation Rate of Metal Layer-Integrated Polypropylene Film>.

In addition, from the viewpoint of more suitably exerting the effects of the present invention, in a graph showing the relationship between temperature and elongation obtained by heating the metal layer-integrated polypropylene film of this embodiment at a temperature increase rate of 10°C/min from 25°C under a static load of 2 MPa, the temperature of the inflection point is preferably 130°C or higher, more preferably 140°C or higher. The temperature of the inflection point is, for example, 160°C or lower, 150°C or lower. The inflection point can be identified based on a graph obtained by the method described in the above-mentioned <Relationship between Temperature and Elongation of Metal Layer-Integrated Polypropylene Film>. Note that the inflection point refers to the inflection point that first appears in the graph at a temperature increase start temperature of 25°C. In other words, there is no inflection point on the lower temperature side than the inflection point.

In this embodiment, the thickness of the metal layer-integrated polypropylene film is preferably 0.8 μm or more, more preferably 1.2 μm or more, even more preferably 1.5 μm or more, even more preferably 1.6 μm or more, even more preferably 1.7 μm or more, and particularly preferably 1.8 μm or more. The thickness of the polypropylene film is preferably 3.5 μm or less, more preferably 3.0 μm or less, even more preferably 2.9 μm or less, and particularly preferably 2.8 μm or less.

The thickness of the metal layer-integrated polypropylene film is a value measured in accordance with JIS-C2330, except that it was measured at 100±10 kPa using a paper thickness measuring instrument MEI-11 manufactured by Citizen Seimitsu Co., Ltd. More specifically, it is measured according to the method described in the examples.

The following describes the polypropylene film that is included in the metal layer-integrated polypropylene film as a product after laminating the metal layer. In other words, hereinafter, without specifying whether it is before laminating the metal layer or after laminating the metal layer, when "polypropylene film" is mentioned, it is assumed to mean the polypropylene film after laminating the metal layer, unless otherwise specified.

The thickness of the polypropylene film is preferably 0.8 μm or more, more preferably 1.2 μm or more, even more preferably 1.5 μm or more, and particularly preferably 1.8 μm or more. The thickness of the polypropylene film is preferably 3.5 μm or less, more preferably 3.0 μm or less, even more preferably 2.9 μm or less, and particularly preferably 2.8 μm or less.

When the thickness of the polypropylene film is 3.0 μm or less, the capacitance per unit volume can be increased when the film is made into a capacitor element, so that the film can be suitably used for a capacitor. From the viewpoint of film formation stability and processability (handling property), the thickness of the polypropylene film can be 0.8 μm or more.
This point will be explained in detail below.

The thinner the polypropylene film, the greater the capacitance per unit volume. More specifically, the capacitance C is expressed as follows using the dielectric constant ε, the electrode area S, and the dielectric thickness d (thickness d of the polypropylene film):
C = εS/d
Here, in the case of a film capacitor, the thickness of the electrodes is three or more orders of magnitude thinner than the thickness of the polypropylene film (dielectric). Therefore, if the volume of the electrodes is ignored, the volume V of the capacitor can be expressed as follows:
V = Sd
Therefore, from the above two equations, the capacitance per unit volume, C/V, is expressed as follows:
C/V=ε/d ²
As can be seen from the above formula, the capacitance per unit volume (C/V) is inversely proportional to the square of the polypropylene film thickness. Also, the dielectric constant ε is determined by the material used. Therefore, unless the material is changed, it is not possible to improve the capacitance per unit volume (C/V) other than by reducing the thickness.
The electrode area does not affect the capacitance per unit volume (C/V), as will be described below.

Consider the case where a capacitor is made by winding a film of the same material and thickness. For example, suppose the number of turns is increased to make it 10 times longer (the electrode area is 10 times larger). In this case, the capacitance becomes 10 times larger, but the volume also becomes 10 times larger, so the capacitance per unit volume (C/V) does not change even if the electrode area changes.
The above description is idealized for ease of understanding. In reality, for example, there may be a small gap between the films, or there may be a fringe effect at the electrode ends, so the capacitance per unit volume (C/V) may vary slightly depending on the area. However, it can be understood that the capacitance per unit volume (C/V) is generally determined by the polypropylene film thickness.

In view of the above, it is preferable that the thickness of the polypropylene film is as thin as possible while ensuring the insulation property and/or voltage resistance. Therefore, the thickness of the polypropylene film is preferably 3.0 μm or less.
On the other hand, when the thickness of the polypropylene film is thin, the handling property becomes extremely poor, so that the film formation and the production of the capacitor become extremely difficult, and the processability tends to deteriorate. Furthermore, because of the thinness, breakage (fracture) and the like occur in the film formation process, and the film formation tends to become unstable. Therefore, the thickness of the polypropylene film is preferably 0.8 μm or more.

In the present invention and this specification, the thickness of the polypropylene film is defined as being obtained by subtracting the thickness of the metal layer (the thickness of the metal layer converted from the film resistance) from the thickness of the metal layer-integrated polypropylene film.
The thickness of the metal layer in the metal layer-integrated polypropylene film is preferably 0.1 to 10 nm. When the thickness of the metal layer is 0.1 to 10 nm, the thickness of the metal layer-integrated polypropylene film and the thickness of the polypropylene film are approximately the same when measured by the method described in this example.

The polypropylene film is a biaxially stretched film, and biaxial stretching can be simultaneous biaxial stretching, sequential biaxial stretching, or any other method. By biaxially stretching, the molecules of the polypropylene film are highly oriented, improving and/or stabilizing various physical properties such as mechanical properties, thermal properties, and electrical properties, making it suitable for industrial applications. However, when the biaxially stretched film is exposed to a certain level of heat (high temperature), the orientation relaxes and the film tends to return to a non-oriented state, resulting in so-called (thermal) shrinkage.

The polypropylene film preferably has a planar orientation coefficient ΔP of 0.010 to 0.016, more preferably 0.011 to 0.0155, and even more preferably 0.0115 to 0.015.

It is preferable that the plane orientation coefficient ΔP of the polypropylene film is within the above range, since this can further reduce dielectric breakdown at high temperatures and high voltages.

<Plane Orientation Coefficient ΔP>
In this specification, the "plane orientation coefficient ΔP" refers to the plane orientation coefficient ΔP (where ΔP = (ΔNyz + ΔNxz) / 2) calculated from the birefringence values ΔNyz and ΔNxz in the thickness direction of the polypropylene film obtained by optical birefringence measurement.
In this specification, the "birefringence value ΔNyz" in the thickness direction of a polypropylene film refers to the birefringence value ΔNyz in the thickness direction determined by optical birefringence measurement. More specifically, if the main axes in the in-plane direction of the film are the x-axis and y-axis, the thickness direction of the film (the normal direction to the in-plane direction) is the z-axis, and the slow axis in the in-plane direction with the higher refractive index is the x-axis, the birefringence value ΔNyz is the 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 addition, in this specification, the "birefringence value ΔNxz" in the thickness direction of a polypropylene film refers to the birefringence value ΔNxz in the thickness direction determined by optical birefringence measurement, and more specifically, the birefringence value ΔNxz is the value obtained by subtracting the three-dimensional refractive index in the z-axis direction from the three-dimensional refractive index in the x-axis (slow axis) direction.

In this embodiment, in order to measure the "birefringence value ΔNyz" in the thickness direction of the polypropylene film, specifically, a retardation measuring device RE-100 manufactured by Otsuka Electronics Co., Ltd. is used. The retardation (retardation) is measured using a tilt method. More specifically, the main axes in the in-plane direction of the film are the x-axis and y-axis, and the thickness direction of the film (normal direction to the in-plane direction) is the z-axis, and the slow axis in the in-plane direction with a higher refractive index is the x-axis. The retardation values are obtained when the x-axis is tilted by 10° increments relative to the z-axis in the range of 0° to 50° with the x-axis as the tilt axis. From the obtained retardation values, the birefringence ΔNyz in the y-axis direction relative to the thickness direction (z-axis direction) is calculated using the method described in the non-patent document "Awaya Yutaka, Introduction to Polarizing Microscopes of Polymer Materials, pp. 105-120, 2001". First, for each tilt angle φ, the measured retardation value R is divided by the tilt-corrected thickness d to obtain R/d. For each R/d of φ=10°, 20°, 30°, 40°, and 50°, the difference between R/d of φ=0° is obtained, and further divided by sin2r (r: refraction angle) to obtain the birefringence ΔNzy at each φ, and the positive and negative signs are reversed to obtain the birefringence value ΔNyz. The birefringence value ΔNyz is calculated as the average value of ΔNyz at φ=20°, 30°, 40°, and 50°. For example, in the sequential stretching method, when the stretching ratio in the TD direction (width direction) is higher than the stretching ratio in the MD direction (machine direction), the TD direction becomes the slow axis (x-axis) and the MD direction becomes the y-axis. In addition, when using polypropylene, the value of the refraction angle r at each inclination angle for polypropylene is that described on page 109 of the above-mentioned document.

In addition, in this embodiment, the "birefringence value ΔNxz" in the thickness direction of the polypropylene film is calculated by dividing the retardation value R measured at an inclination angle φ = 0° by the thickness d, and then dividing the ΔNzy obtained above to calculate the birefringence value ΔNxz.

The polypropylene film contains polypropylene resin, and there are no particular limitations on its constituent materials.

The content of the polypropylene resin is preferably 90% by mass or more, more preferably 95% by mass or more, based on the entire polypropylene film (when the entire polypropylene film is taken as 100% by mass). The upper limit of the content of the polypropylene resin is, for example, 100% by mass, 98% by mass, etc., based on the entire polypropylene film. The polypropylene resin may contain one type of polypropylene resin alone, or may contain two or more types of polypropylene resins. The polypropylene resin is preferably a homopolypropylene resin.

When the polypropylene film contains two or more types of polypropylene resin, the polypropylene resin with the greater content is referred to herein as the "main polypropylene resin." When the polypropylene film contains only one type of polypropylene resin, the polypropylene resin is referred to herein as the "main polypropylene resin."

Hereinafter, in this specification, when the term "polypropylene resin" is used without specifying whether it is the main component or not, it means both the polypropylene resin as the main component and the polypropylene resin other than the main component, unless otherwise specified. For example, if it is stated that "the weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less," it means that the weight average molecular weight Mw of the polypropylene resin as the main component is preferably 250,000 or more and 450,000 or less, and that the weight average molecular weight Mw of the polypropylene resin other than the main component is preferably 250,000 or more and 450,000 or less.

The weight average molecular weight Mw of the polypropylene resin is preferably 250,000 or more and 450,000 or less, 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 is moderate. As a result, it is easy to control the thickness of the cast raw sheet, and it is easy to prepare a thin stretched film with good thickness uniformity. In addition, from the viewpoint of the mechanical properties, thermo-mechanical properties, stretch moldability, etc. of the biaxially stretched polypropylene film, the weight average molecular weight Mw is preferably 250,000 or more and 450,000 or less. When two or more polypropylene resins are used, it is preferable to use a polypropylene resin having an Mw of 250,000 or more and less than 330,000 and a polypropylene resin having an Mw of 330,000 or more and 450,000 or less in combination.
The number average molecular weight Mn of the polypropylene resin is preferably 30,000 or more and 53,000 or less, and more preferably 33,000 or more and 52,000 or less.
The z-average molecular weight Mz of the polypropylene resin is preferably 500,000 or more and 2,100,000 or less, and more preferably 700,000 or more and 1,700,000 or less.

The molecular weight distribution of the polypropylene resin [(weight average molecular weight Mw)/(number average molecular weight Mn)] is preferably 5 or more and 12 or less, more preferably 5 or more and 11 or less, and even more preferably 5 or more and 10 or less. When the molecular weight distribution of the polypropylene resin [(weight average molecular weight Mw)/(number average molecular weight Mn)] is 5 or more and 12 or less, it is preferable because appropriate resin fluidity is obtained during biaxial stretching, and it is easy to obtain an extremely thin biaxially stretched propylene film without thickness unevenness.
The molecular weight distribution of the polypropylene resin [(z-average molecular weight Mz)/(number-average molecular weight Mn)] is preferably 10 or more and 70 or less, more preferably 15 or more and 60 or less, and even more preferably 15 or more and 50 or less.

In this specification, the weight average molecular weight (Mw), number average molecular weight (Mn), z-average molecular weight (Mz), and molecular weight distribution (Mw/Mn and Mz/Mn) of the polypropylene resin are values measured using a gel permeation chromatograph (GPC) device. More specifically, they are values measured using a high-temperature GPC measuring device with built-in differential refractometer (RI) HLC-8121GPC-HT (product name) manufactured by Tosoh Corporation. As the GPC column, three TSKgel GMHHR-H (20) HT manufactured by Tosoh Corporation are connected and used. The column temperature is set to 140°C, and trichlorobenzene is passed as the eluent at a flow rate of 1.0 ml/10 min to obtain measured values of Mw and Mn. A calibration curve for the molecular weight M is created using standard polystyrene manufactured by Tosoh Corporation, and the measured values are converted to polystyrene values to obtain Mw, Mn, and Mz. Here, the logarithm to the base 10 of the molecular weight M of standard polystyrene is called the logarithmic molecular weight ("Log(M)").

In the molecular weight differential distribution curve of the polypropylene resin, the difference obtained by subtracting the differential distribution value when the logarithmic molecular weight Log(M) is 6.0 from the differential distribution value when Log(M) is 4.5 (hereinafter also referred to as "differential distribution value difference D _M ") is preferably -5% or more and 14% or less, more preferably -4% or more and 12% or less, and even more preferably -4% or more and 10% or less.
Here, "the difference (differential distribution value difference D _M ) obtained by subtracting the differential distribution value when Log(M)=6.0 from the differential distribution value when Log(M)=4.5 is -5% or more and 14% or less" can be understood to mean that, when comparing a component with a logarithmic molecular weight Log(M)=4.5 as a representative distribution value of components with a molecular weight of 10,000 to 100,000 on the low molecular weight side (hereinafter also referred to as "low molecular weight components") with a component with a molecular weight of around 1,000,000 on the high molecular weight side (hereinafter also referred to as "high molecular weight components") as a representative distribution value, if the difference is positive, there is more low molecular weight components, and if the difference is negative, there is more high molecular weight components.

In other words, for example, if the molecular weight distribution Mw/Mn is 5 to 12, the fact that the molecular weight distribution Mw/Mn is 5 to 12 merely indicates the width of the molecular weight distribution, and does not reveal the quantitative relationship between the high molecular weight components and the low molecular weight components. Therefore, from the standpoint of resin fluidity, stretch moldability, and thickness uniformity, it is preferable to use a polypropylene resin such that the differential distribution value difference between the components with a molecular weight of 10,000 to 100,000 and the component with a molecular weight of 1,000,000 is -5% or more and 14% or less.

The differential distribution value is a value obtained using GPC as follows. A curve showing intensity versus time (generally called an "elution curve") obtained by a GPC differential refractive index (RI) detector is used. A calibration curve obtained using standard polystyrene is used to convert the time axis to logarithmic molecular weight (Log(M)), thereby converting the elution curve into a curve showing intensity versus Log(M). Since the RI detection intensity is proportional to the component concentration, if the total area of the curve showing intensity is taken as 100%, an integral distribution curve for the logarithmic molecular weight Log(M) can be obtained. The differential distribution curve is obtained by differentiating this integral distribution curve with Log(M). Therefore, "differential distribution" means the differential distribution of the concentration fraction versus the molecular weight. From this curve, the differential distribution value at a specific Log(M) is read.

The mesopentad fraction ([mmmm]) of the polypropylene resin is preferably less than 98.0%, more preferably 97.5% or less, even more preferably 97.4% or less, and particularly preferably 97.0% or less. The mesopentad fraction is preferably 94.0% or more, more preferably 94.5% or more, and even more preferably 95.0% or more. When the mesopentad fraction is within the above numerical range, the crystallinity of the resin is appropriately improved due to the moderately high stereoregularity, and the initial voltage resistance and long-term voltage resistance are improved, while the desired stretchability can be obtained due to the moderate solidification (crystallization) speed when forming the cast raw sheet.

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

The heptane insoluble fraction (HI) of the polypropylene resin is preferably 96.0% or more, more preferably 97.0% or more. The heptane insoluble fraction (HI) of the polypropylene resin is preferably 99.5% or less, more preferably 99.0% or less. Here, the higher the heptane insoluble fraction, the higher the stereoregularity of the resin. When the heptane insoluble fraction (HI) is 96.0% or more and 99.5% or less, the moderately high stereoregularity improves the crystallinity of the resin and improves the voltage resistance at high temperatures. On the other hand, the solidification (crystallization) speed during cast raw sheet molding becomes moderate, and the resin has moderate extensibility.

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 even more preferably 2.0 to 6.0 g/10 min.

When the polypropylene film contains two or more types of polypropylene resin, it is preferable that the main component polypropylene resin has at least a weight average molecular weight Mw of 250,000 or more and less than 345,000, and an MFR of 4 to 8 g/10 min. Also, when the polypropylene film contains two or more types of polypropylene resin, it is preferable that the polypropylene resin other than the main component has at least a weight average molecular weight Mw of 345,000 or more and 450,000 or less, and an MFR of 1 g/10 min or more and less than 4 g/10 min (more preferably 1 g/10 min or more and 3.9 g/10 min or less).

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

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

The catalyst used in the polymerization can be a generally known Ziegler-Natta catalyst, and is not particularly limited as long as the polypropylene resin can be obtained. The catalyst may contain a cocatalyst 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 resin mixing (blending). For example, two or more resins with different molecular weights or molecular weight distributions can be mixed. In general, a two-type polypropylene mixture in which the main resin is 55% by mass to 90% by mass, assuming that the total resin is 100% by mass, and a resin with a higher or lower average molecular weight than the main resin is mixed is preferred because it is easy to adjust the amount of low molecular weight components.

When using the above-mentioned mixing and adjustment method, the melt flow rate (MFR) may be used as a guide for the average molecular weight. In this case, it is preferable to set the difference in MFR between the main resin and the added resin to about 1 to 30 g/10 min from the viewpoint of convenience during adjustment.

There are no particular limitations on the method for mixing the resins, but examples include dry blending the polymer powder or pellets of the main resin and the additive resin using a mixer, or feeding the polymer powder or pellets of the main resin and the additive resin to a kneader and melt-kneading them to obtain a blended resin.

The mixer and the kneader are not particularly limited. The kneader may be a single screw type, a twin screw type, or a multi-screw type with more than one screw. In the case of a two or more screw type, the kneader may be either a co-rotating or counter-rotating type.

In the case of blending by melt kneading, the kneading temperature is not particularly limited as long as a good kneaded product is obtained. In general, it is in the range of 200°C to 300°C, and from the viewpoint of suppressing deterioration of the resin, 230°C to 270°C is preferable. In addition, in order to suppress deterioration during kneading and mixing of the resin, an inert gas such as nitrogen may be purged into the kneader. The melt kneaded resin may be pelletized to an appropriate size using a commonly known granulator. In this way, mixed polypropylene raw material resin pellets can be obtained.

The total ash content due to polymerization catalyst residues, etc. contained in the polypropylene raw material resin is preferably 50 ppm or less based on the polypropylene resin (100 parts by weight).

The total ash content (total ash content contained in the polypropylene raw material resin) is preferably 5 ppm or more and 35 ppm or less, more preferably 5 ppm or more and 30 ppm or less, and even more preferably 10 ppm or more and 25 ppm or less, in order to suppress the generation of polar low-molecular-weight components while improving the electrical properties of the capacitor.

The polypropylene film may contain an additive. The "additive" is an additive that is generally used in polypropylene resins, and is not particularly limited as long as it does not impair the effects of the present invention.

The additives include, for example, antioxidants, chlorine absorbers, ultraviolet absorbers, lubricants, plasticizers, flame retardants, antistatic agents, inorganic fillers, organic fillers, etc. Examples of the inorganic fillers include barium titanate, strontium titanate, aluminum oxide, etc. The polypropylene resin may contain the additives in an amount that does not adversely affect the polypropylene film.

The metal layer functions as an electrode when the metal layer-integrated polypropylene film is used as a capacitor. The metal used in the metal layer can be, for example, a single metal such as zinc, lead, silver, chromium, aluminum, copper, or nickel, a mixture of multiple metals, or an alloy of multiple metals. However, taking into consideration the environment, economy, and capacitor performance, zinc and aluminum are preferred.

Next, a method for producing the metal layer-integrated polypropylene film according to this embodiment will be described. Note that the metal layer-integrated polypropylene film according to this embodiment is preferably produced by the method for producing the metal layer-integrated polypropylene film described below, but it does not have to be produced by the method for producing the metal layer-integrated polypropylene film described below.

The method for producing the metal layer-integrated polypropylene film according to the present embodiment includes the steps of:
a metal layer lamination step of laminating a metal layer on one or both sides of the polypropylene film to obtain a metal layer-integrated polypropylene film;
A heating step of heating the metal layer-integrated polypropylene film obtained in the metal layer lamination step at a temperature of 100° C. or more and 130° C. or less;
Equipped with.

The cast raw sheet before stretching for producing the biaxially stretched polypropylene film can be produced as follows. However, the method for producing the cast raw sheet according to this embodiment is not limited to the method described below.

First, resin pellets, dry-mixed resin pellets, or resin pellets previously prepared by melt-kneading are fed into an extruder and heated to melt.
The melt-kneading temperature varies depending on the type of thermoplastic resin, but in the case of polypropylene resin, the extruder set temperature during heating and melting is preferably 220 to 280° C., more preferably 230 to 270° C. The resin temperature during heating and melting is preferably 220 to 280° C., more preferably 230 to 270° C. The resin temperature during heating and melting is a value measured by a thermometer inserted in the extruder.
The extruder temperature and resin temperature during heat melting are selected taking into consideration the physical properties of the resin used. By setting the resin temperature during heat melting within the above-mentioned range, deterioration of the resin can be suppressed.

Next, the molten resin is extruded into a sheet shape using a T-die, and is cooled and solidified on at least one metal drum to form an unstretched cast raw sheet.
The surface temperature of the metal drum (the temperature of the metal drum that first comes into contact after extrusion) is preferably 50 to 100° C., and more preferably 60 to 95° C. The surface temperature of the metal drum can be determined depending on the physical properties of the resin used, etc.

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

The polypropylene film according to this embodiment can be suitably produced as follows. However, the method for producing the polypropylene film according to this embodiment is not limited to the method described below.

The polypropylene film can be produced by subjecting the resin cast raw sheet to a stretching process. The stretching is preferably biaxial stretching, which orients the sheet biaxially in the longitudinal and transverse directions. The stretching method may be either simultaneous biaxial stretching or sequential biaxial stretching, but sequential biaxial stretching is preferred. In the sequential biaxial stretching method, for example, the cast raw sheet is first kept at a temperature of 100 to 170°C and passed between rolls with a speed difference to stretch the sheet 3 to 7 times in the MD direction (flow direction, longitudinal direction). The temperature during MD stretching is preferably 100 to 170°C, more preferably 120 to 160°C. The stretch ratio during MD stretching is preferably 3 to 7 times, more preferably 4 to 6 times. After stretching in the MD direction, the sheet is introduced into a tenter and stretched 3 to 11 times in the TD direction (transverse direction, width direction). The temperature during stretching in the TD direction is preferably 155 to 170°C. The film is then relaxed 2 to 10 times and heat-set. This results in a biaxially stretched polypropylene film.

The polypropylene film may be subjected to corona discharge treatment online or offline after the stretching and heat fixing processes in a post-process such as a metal layer lamination process, in order to enhance the adhesive properties. The corona discharge treatment can be performed using a known method. It is preferable to use air, carbon dioxide gas, nitrogen gas, or a mixture of these gases as the atmospheric gas.

In this way, polypropylene film can be obtained.

The metal layer lamination process for laminating a metal layer on one or both sides of the polypropylene film to obtain a metal layer-integrated polypropylene film will be described below. However, process B according to this embodiment is not limited to the process described below.

In the metal layer lamination process, a metal layer is laminated on one or both sides of the polypropylene film to obtain a polypropylene film integrated with a metal layer for processing into a capacitor.

Examples of methods for laminating a metal layer on one or both sides of the polypropylene film include vacuum deposition and sputtering. From the viewpoints of productivity and economy, vacuum deposition is preferred. Examples of vacuum deposition methods include the crucible method and the wire method, but there is no particular limitation, and the most suitable method can be selected as appropriate.

As deposition conditions in the vacuum deposition method, the temperature of the cooling roll is preferably -23°C to -19°C or less, more preferably -22°C to -19°C or less, and even more preferably -22°C to -18°C or less. By cooling the film with the cooling roll during deposition, heat damage (thermal deterioration, thermal deformation) due to the heat of deposition can be suppressed.

In the vacuum deposition method, the temperature of the evaporation source is controlled by the amount of electricity passed through. As a deposition condition in the vacuum deposition method, the amount of electricity passed through the evaporation source is preferably 650 A or more, more preferably 700 A or more, and even more preferably 800 A or more. Increasing the amount of electricity passed through (setting the temperature of the evaporation source higher) increases the temperature of the furnace and the amount of metal evaporated, allowing for more efficient deposition. From the viewpoint of preventing heat damage to the polypropylene film, the amount of electricity passed through is preferably 900 A or less, and more preferably 850 A or less.

In the vacuum deposition method, the thickness of the metal layer is controlled by the film resistance. As the deposition conditions in the vacuum deposition method, the film resistance is preferably 20 Ω/sq or less in the case of an aluminum film, and more preferably 17 Ω/sq or less. In the case of a zinc film, it is preferably 5 Ω/sq or less, and more preferably 4 Ω/sq or less. The film resistance being small means that the thickness of the metal layer is thick. From the viewpoint of self-recovery (self-healing property), the film resistance is preferably 1 Ω/sq or more in the case of an aluminum film, and more preferably 5 Ω/sq or more. In the case of a zinc film, it is preferably 1 Ω/sq or more, and more preferably 2 Ω/sq or more. Note that the self-recovery property refers to the fact that when a defective portion occurs in a polypropylene film, the metal of the deposition layer is instantly evaporated by the applied energy or the energy possessed by the capacitor itself, and the function of the capacitor is restored, and when the metal layer is thick, the self-healing property tends to be poor.
The thickness (film resistance) of the metal layer can be adjusted by the deposition line speed and the temperature of the evaporation source (amount of current flowing as described above).

The margin pattern used when laminating the metal layer by vapor deposition is not particularly limited, but in order to improve the safety and other characteristics of the capacitor, it is preferable to apply a pattern including a so-called special margin, such as a fishnet pattern or T-margin pattern, to one side of the film. This increases safety and is also effective in preventing capacitor destruction and short circuits.

The method for forming the margin can be any commonly known method, such as the tape method or oil method, without any restrictions.

Next, a heating (heat treatment) process is performed in which the metal layer integrated polypropylene film obtained in the metal layer lamination process is heated at a temperature of 100°C or higher and 130°C or lower. By performing this process, the heat history of the metal layer integrated polypropylene film is canceled, so that even if it is exposed to a high temperature environment after being formed into a film capacitor, it is difficult for the film capacitor to undergo thermal changes such as thermal expansion/contraction in the winding direction of the capacitor. As a result, the gap between the winding layers changes, and in the case of a flat element, the flat curve part is not distorted or wrinkled, so that even if a high voltage is applied in a high temperature environment, the capacitor is unlikely to be broken down by short circuiting, and the film capacitor can be given the characteristic of not being short-circuited even if a high voltage is applied at a high temperature of 100°C or higher. Preferred specific examples of the heating process are as follows. The heating (heat treatment) process may be either a batch type or a roll-to-roll type. From the viewpoint of work efficiency (time), it is preferable to heat (heat treat) the film capacitor by the roll-to-roll type. In the batch method, for example, a metal layer integrated polypropylene film roll (wound) cut to a desired width to form a capacitor or before cutting is placed in a thermostatic chamber set at a predetermined temperature and heat-treated for a predetermined time. The thermostatic chamber can be any type of thermostatic chamber, such as a general hot air (air blowing) type, an induction heating type, an infrared type, or the like, without any restrictions. There is no restriction on the heating time as long as the elongation rate according to the present invention can be achieved, but the larger the roll diameter (the longer the winding length), the longer the heating treatment time. Although it depends on the roll diameter, it is generally about 5 minutes to 6 hours, and from the viewpoint of work efficiency, it is preferable to keep it as short as possible, for example, about 1 hour or less. From the viewpoint of shortening the heat treatment time, a roll-to-roll method is preferably adopted. The film unwound from the roll is continuously introduced into a heating furnace (zone), and the film coming out of the furnace is wound up, thereby performing the heat treatment. The heating furnace (zone) may be any type of blowing type, infrared type, or the like. Also, instead of a heating furnace, a contact heating method using multiple heating rolls may be used. There is no limit to the processing speed as long as the elongation ratio according to the present invention can be achieved, and it also depends on the length of the heating zone. In general, it is effective to pass the unwound film through a part with multiple hot air heating zones, each several meters to several dozen meters long, for one to five minutes, and then wind it up to perform the heat treatment.

The metal layer-integrated polypropylene film of this embodiment can be laminated or rolled by conventional methods to form a film capacitor.

The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples. Unless otherwise specified, parts and percentages refer to "parts by mass" and "% by mass", respectively.

[Examples 1-5 and Comparative Examples 1-4]
<Production of metal layer-integrated polypropylene film>
A polypropylene resin (weight average molecular weight: 300,000, molecular weight distribution: 6, meso pend fraction: 96.5%) containing 5000 ppm of Irganox 1010 as an antioxidant was fed to an extruder, melted at a resin temperature of 250° C., extruded using a T-die, and solidified by wrapping around a metal drum whose surface temperature was kept at 92° C. to produce a cast raw sheet having a thickness of about 125 μm. The unstretched cast raw sheet was then stretched 5 times in the machine direction at a temperature of 140° C., immediately cooled to room temperature, and then stretched 10 times in the transverse direction at a temperature of 165° C. in a tenter to obtain a very thin biaxially stretched polypropylene film.

Next, an aluminum metal layer was formed on the biaxially oriented polypropylene film using a deposition device (ULVAC, product name: roll-type vacuum deposition device EWE-060) so that the surface resistivity of the metal film was 20 Ω/□, to obtain a polypropylene film with an integrated metal layer (before heat treatment). At this time, metal deposition was performed using the oil margin method so that after slitting, a metal electrode 3 as shown in Figure 1 was formed at one end of the film in the width direction, with an insulating margin 4 (insulating groove: 1 mm long in the width direction) that continued in the longitudinal direction of the film.

Next, the metal layer-integrated polypropylene film (before heat treatment) was slit and then heat-treated under the conditions (temperature, batch or roll-to-roll, time) described in Table 1 to obtain a metal layer-integrated polypropylene film (after heat treatment) with a total width of 60 mm. The thickness of the metal layer-integrated polypropylene film was measured by the method described below, and was as described in Table 1. In Comparative Example 1, the metal layer-integrated polypropylene film was not heat-treated. In Comparative Example 2, the biaxially oriented polypropylene film before the formation of the metal layer was heat-treated in a batch at 100°C for 10 minutes, but the metal layer-integrated polypropylene film was not heat-treated.

<Measurement of thickness of metal layer integrated polypropylene film>
A paper thickness measuring instrument MEI-11 (measurement pressure 100 kPa, drop speed 3 mm/sec, measurement terminal φ=16 mm, measurement force 20.1 N) manufactured by Citizen Seimitsu Co., Ltd. was used in an environment of temperature 23±2°C and humidity 50±5% RH. Five measurements were taken for a sample in which 10 metal layer-integrated polypropylene films were stacked while being careful not to allow wrinkles or air to enter, and the thickness was calculated by dividing the average value of the five measurements by 10.

<Manufacturing of film capacitors>
Two sheets of the obtained metal layer-integrated polypropylene film were used and laminated. The laminated metal layer-integrated polypropylene film was wound 1137 turns at a winding tension of 250 g, contact pressure of 880 g, and winding speed of 4 m/s using an automatic winding machine 3KAW-N2 manufactured by Kaito Seisakusho Co., Ltd. The wound element was heat-treated at 120°C for 15 hours while pressing with a load of 5.9 kg/ ^cm2 . Then, zinc metal was sprayed on the element end surface. The spraying conditions were a feed speed of 15 mm/s, a spraying voltage of 22 V, and a spraying pressure of 0.3 MPa, and the spraying was performed to a thickness of 0.7 mm. In this way, a flat film capacitor was obtained. Lead wires were soldered to the end surface of the flat film capacitor. The flat film capacitor was then sealed with epoxy resin. The epoxy resin was cured by heating at 90°C for 2.5 hours and then heating at 120°C for 2.5 hours. The resulting film capacitor had a capacitance of 75 μF.

<Relationship between temperature and elongation rate of metal layer-integrated polypropylene film>
Using a thermo-mechanical measuring device (TMA) manufactured by Seiko Instruments Co., Ltd., TMA/SS6000 type, a metal layer integrated polypropylene film sampled in a strip shape with a width of 4 mm and a length of 25 mm was heated at a heating rate of 10 ° C./min from 25 ° C. with a static load of 2 MPa applied in the MD direction, and a graph showing the relationship between temperature and expansion rate (TMA (%)) was obtained. In addition, for the obtained graph, the expansion rate (%) at 100 ° C., 120 ° C., and 130 ° C. (the expansion rate at 25 ° C. is set to 0%), the elongation gradient (average expansion rate) from 30 ° C. to 100 ° C., and the temperature of the inflection point (the inflection point that first appears from the start of the temperature rise) were read. The measurement conditions are summarized below.
Measurement device: Seiko Instruments Inc. TMA/SS6000 type Measurement probe: Quartz tensile probe Measurement mode: F mode (load control mode)
Static load: 2MPa
Initial chuck distance: 15 mm
Measurement temperature range: 25℃ to 165℃
Heating rate: 10° C./min
Data sampling time: 0.5 sec

<Evaluation of voltage resistance (whether or not a short circuit occurs) in a high-temperature environment>
The voltage resistance of the film capacitor in a high temperature environment was evaluated by the following procedure. The results are shown in Table 1. First, a voltage of 480 Vdc/μm (1200 V DC for a film capacitor with a thickness of 2.5 μm) was applied to the film capacitor for 10 minutes in a 150° C. environment. After static electricity was removed, the insulation resistance value of the film capacitor (value for 1 minute after application of 500 V DC) was measured at room temperature using a digital ultra-insulated microammeter DMS8104 manufactured by Hioki E.E.C. Corporation, and the voltage resistance (presence or absence of short circuit) was evaluated according to the following criteria. The results are shown in Table 1.
A: The resistance value was 0.05 MΩ (lower limit of measurement) or more (resistance value was not displayed), and it was determined that there was no short circuit.
C: The resistance value was below 0.05 MΩ (lower measurement limit) (resistance value was not displayed), and it was determined to be short-circuited.

<Evaluation of insulation properties in high temperature environments>
The insulation of the film capacitor in a high temperature environment was evaluated by the following procedure. The results are shown in Table 1. First, a voltage of 480 Vdc/μm (1200 V DC for a film capacitor with a thickness of 2.5 μm) was applied to the film capacitor for 10 minutes in a 150° C. environment (voltage resistance test). After neutralization, the insulation resistance value of the film capacitor (value for 1 minute after application of 500 V DC) was measured at room temperature using a digital ultra-insulated microammeter DMS8104 manufactured by Hioki E.E.C. Corporation, and the insulation was evaluated according to the following criteria. The results are shown in Table 1.
A: The resistance value was 1 GΩ or more.
C: The resistance value was below 1 GΩ.

REFERENCE SIGNS LIST 1 Metal layer integrated polypropylene film 2 Polypropylene film 3 Metal electrode 3a Metal layer 3b Electrode lead-out portion 4 Insulation margin

Claims (6)

A metal layer-integrated polypropylene film having a polypropylene film and a metal layer laminated on one or both sides of the polypropylene film,
The polypropylene film has a plane orientation coefficient ΔP of 0.010 to 0.016;
The total ash content in the resin constituting the polypropylene film is 50 ppm or less;
When the metal layer-integrated polypropylene film is heated from 25° C. at a temperature increase rate of 10° C./min under a static load of 2 MPa in the MD direction, the elongation at 100° C. is 0% or more and 1.8% or less, the elongation at 120° C. is 0% or more and 2.3% or less, and the elongation at 130° C. is 0% or more and 2.7% or less, assuming that the elongation at 25° C. is 0% .
A polypropylene film with an integrated metal layer for use in capacitors . The metal layer-integrated polypropylene film according to claim 1, wherein when the metal layer-integrated polypropylene film is heated from 25°C at a temperature increase rate of 10°C/min under a static load of 2 MPa in the MD direction, the elongation gradient from 30°C to 100°C is 0.010%/°C or more and 0.030%/°C or less. The metal layer-integrated polypropylene film according to claim 1 or 2, wherein the metal layer-integrated polypropylene film has an inflection point temperature of 130°C or higher in a graph showing the relationship between temperature and elongation obtained by heating the film at a temperature increase rate of 10°C/min from 25°C under a static load of 2 MPa in the MD direction. The metal layer-integrated polypropylene film according to any one of claims 1 to 3, having a thickness of 0.8 μm or more and 3.5 μm or less. A film capacitor having a wound metal layer-integrated polypropylene film according to any one of claims 1 to 4 , or having a configuration in which a plurality of metal layer-integrated polypropylene films according to any one of claims 1 to 4 are laminated. A method for producing a metal layer-integrated polypropylene film according to any one of claims 1 to 5 , comprising the steps of: a polypropylene film; and a metal layer laminated on one or both sides of the polypropylene film,
a metal layer lamination step of laminating a metal layer on one or both sides of the polypropylene film to obtain a metal layer-integrated polypropylene film;
A heating step of heating the metal layer-integrated polypropylene film obtained in the metal layer lamination step at a temperature of 100° C. or more and 130° C. or less;
A method for producing a metal layer-integrated polypropylene film comprising the steps of:

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