KR102494812B1 - Polypropylene film, polypropylene film with integrated metal layer, and film capacitor - Google Patents

Abstract

An object is to provide a polypropylene film that is excellent in dielectric breakdown strength at 120°C of direct current and also excellent in dielectric breakdown strength at 120°C of alternating current. The polypropylene film of the present disclosure is a polypropylene film that satisfies Formula I and has a thickness of 1.0 to 19 μm. 31.5 ≤ melting enthalpy/√crystal size ≤ 33.0 (I) In Formula I, the unit of fusion enthalpy is J/g, and the unit of crystallite size is nm. The crystallite size is obtained using Scherrer's formula from the half width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method.

Description

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

The present disclosure relates to a polypropylene film, a metal layer integral polypropylene film, and a film capacitor.

Polypropylene film can be used as a guide for capacitors. For example, it can be used as an inductor of a capacitor in an inverter constituting a power control unit of a hybrid or electric vehicle.

Japanese Unexamined Patent Publication No. 2010-280795 Japanese Patent No. 6238403 Japanese Patent No. 6089186 Japanese Patent No. 3689009

A capacitor using a polypropylene film as a capacitor inductor is compact, lightweight, and has a high capacity from the viewpoint of the above-mentioned use environment (for example, an environment in which the temperature rises in the engine room, self-heating of the capacitor, etc.) It is preferable to have excellent dielectric breakdown strength (dielectric breakdown strength) when a direct current voltage is applied under high temperature and dielectric breakdown strength when an alternating voltage is applied. That is, it is preferable that the thickness of the polypropylene film is as thin as less than 20 µm and that the dielectric breakdown strength is excellent.

In the polypropylene film described in Patent Document 1 described above, a low stereoregular resin is used, and when such a film is used as a capacitor element, excellent dielectric breakdown strength is not obtained under high temperature (eg, 120 ° C.) There is a problem that there are cases.

The present disclosure has been made in view of the above-mentioned problems, and its object is to provide a polypropylene film having excellent dielectric breakdown strength under high temperatures and consequently having good withstand voltage under high temperatures. More specifically, the objective is to have excellent dielectric breakdown strength (hereinafter, also referred to as dielectric breakdown strength at 120°C DC voltage, or V DC 120°C) measured by applying a DC voltage with a DC power supply in an environment of 120° _C . In addition, the dielectric breakdown strength measured by applying an AC voltage with an AC power supply in an environment of 120 ° C. (hereinafter referred to as dielectric breakdown strength at 120 ° C. AC voltage, or V AC 120 ° _C. ) is also excellent. Provide a polypropylene film is to do Another object of the present disclosure is to provide a metal layer-integrated polypropylene film having a polypropylene film, and a film capacitor having a metal layer-integrated polypropylene film.

The inventors of the present invention conducted an intensive examination of a polypropylene film. As a result, the present inventors have found that the dielectric breakdown strength at 120°C DC voltage and the dielectric breakdown strength at 120°C AC voltage tend to increase as the crystallite size of the polypropylene film decreases. In addition, it was found that the higher the enthalpy of fusion of the polypropylene film, the higher the dielectric breakdown strength at 120°C DC voltage and the higher the dielectric breakdown strength at 120°C AC voltage.

Based on these results, the present inventors intensively studied the relationship between the crystallite size and fusion enthalpy of the polypropylene film. As a result, it was found that the hole-fetch relationship, which is known mainly in the field of metal materials, is also applicable to the dielectric breakdown strength of polypropylene films. The relationship between hole and fetch is represented by σ _y = a + b/√d. σ _y is the yield stress (yield strength) of the polycrystal, a is the yield stress (or frictional stress for dislocation motion) in the case of a single crystal, a constant also expressed as σ _O , and b is the resistance to sliding of grain boundaries It is a constant also expressed as k as a constant, and d is an average grain size. It is known that the main cause of deformation of metal materials is sliding deformation caused by the movement of lattice defects called dislocations existing in the crystal. It is known to generate resistance. The present inventors determined the dielectric breakdown of the polypropylene film when a DC voltage or an AC voltage was applied to the polypropylene film capacitor as the deformation of the metal material, and the difference in yield stress value represented by σ _y -a was determined as the polypropylene film As an index of dielectric breakdown strength at 120 ° C., the relationship between b and d was examined. As a result, it was found that when b is the melting enthalpy of the polypropylene film and the d is the crystallite size of the polypropylene film, there is a correlation with the dielectric breakdown strength at 120 ° C. DC voltage and AC voltage. In addition, when the value of enthalpy of fusion / √ crystallite size is within a certain range (ie, when the polypropylene film satisfies Formula I), the dielectric breakdown strength at 120 ° C. DC voltage is excellent, and also at 120 ° C. AC voltage It was found that the dielectric breakdown strength in was excellent. The present inventors completed the polypropylene film of the present disclosure as described above.

The polypropylene film of the present disclosure satisfies Formula I and has a thickness of 1.0 μm to 19 μm.

31.5≤enthalpy of fusion/√crystallite size≤33.0 (I)

In Formula I, the unit of enthalpy of fusion is J/g, and the unit of crystallite size is nm. The crystallite size is obtained using Scherrer's formula from the half width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method.

The metal layer-integrated polypropylene film of the present disclosure includes the polypropylene film of the present disclosure and a metal layer laminated on one side or both sides of the polypropylene film.

The film capacitor of the present disclosure has the metal layer integrated polypropylene film of the present disclosure.

The polypropylene film of the present disclosure is excellent in electrical insulation resistance at 120°C. More specifically, according to the present disclosure, excellent dielectric breakdown strength in DC voltage under high temperature is obtained, and excellent dielectric breakdown strength in AC voltage under high temperature is obtained. As a result, it is possible to provide a polypropylene film having good withstand voltage under high temperature. In addition, the polypropylene film of the present disclosure is thin. For this reason, the polypropylene film of the present disclosure is suitable for use as a film capacitor.

Hereinafter, embodiments of the present disclosure will be described. However, this invention is not limited only to embodiment.

The polypropylene film of the embodiment in the present disclosure satisfies Formula I and has a thickness of 1.0 μm to 19 μm.

31.5≤enthalpy of fusion/√crystallite size≤33.0 (I)

In Formula I, the unit of enthalpy of fusion is J/g, and the unit of crystallite size is nm. The crystallite size is obtained using Scherrer's formula from the half width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method. In this specification, enthalpy of fusion/√crystal size is hereinafter also referred to as H _m /√S _c . H _m is the melting enthalpy (unit: J/g) of the polypropylene film, and S _c is the crystallite size (unit: nm) of the polypropylene film.

Since the polypropylene film of the embodiment in the present disclosure has an enthalpy of fusion/√crystal size of 31.5 or more and 33.0 or less, the polypropylene film is excellent in dielectric breakdown strength at 120°C DC voltage and also at 120°C alternating current. It is excellent in dielectric breakdown strength in voltage (in other words, it can also be said that it is excellent in electrical insulation resistance at 120°C). The reason why the electrical insulation resistance at 120 ° C. is excellent is that the quality (completeness) and quantity of crystallites that have an effective inhibitory effect on the propagation of leakage current in the polypropylene film and the size of the crystallites are properly controlled, as a result of which Joule It is estimated that structural destruction caused by heat generation is suppressed. When the enthalpy of fusion/√crystal size is significantly less than 31.5, the dielectric breakdown strength at 120°C DC voltage and/or the dielectric breakdown strength at 120°C AC voltage are poor. The reason for this is that the size of the crystallites in the polypropylene film is not refined, the number of crystallites is small, and/or the crystallites are not strong, so that leakage current propagation is likely to occur, resulting in a structure that occurs due to Joule heating. It is assumed that destruction is likely to occur. When the enthalpy of fusion/√crystal size significantly exceeds 33.0, the dielectric breakdown strength at 120°C DC voltage and/or the dielectric breakdown strength at 120°C AC voltage are poor. It is presumed that the reason for this is that since the size of the crystallites in the polypropylene film is too fine, the premise that current does not pass through the inside of the crystallites collapses, and as a result, propagation of leakage current tends to occur.

Since the thickness of the polypropylene film of the embodiment in the present disclosure is 1.0 μm to 19 μm, when the polypropylene film is used for a film capacitor, the capacitor can be reduced in size, reduced in weight, and increased in capacity. For this reason, it is preferably used for film capacitor applications required for applications such as electric vehicles and hybrid vehicles used in high-temperature environments. When it significantly exceeds 19 μm, miniaturization is difficult and high capacity is difficult. When it is significantly less than 1.0 µm, the variation in capacity as a film capacitor tends to increase.

In addition, the inventors of the present invention found that the electrical insulation resistance at 120 ° C. tends to increase as the melting point increases, and based on this finding and the theoretical expression for obtaining the equilibrium melting point T _m ° of the polymer crystal, formula II was devised. That is, it was found that even when the polypropylene film satisfies Formula II, the dielectric breakdown strength at 120°C DC voltage and the dielectric breakdown strength at 120°C AC voltage were excellent. T _m ° is the melting point when the thickness of the lamella is infinite. The theoretical formula for obtaining T _m ° is represented by T _m = T _m ° - (T _m ° × k) / l, and T _m is the melting point (more specifically, a polypropylene film obtained by performing DSC measurement on a polypropylene film melting point), k is a constant, and l is the thickness of the lamella.

The polypropylene film of the embodiment in the present disclosure preferably satisfies Formula II.

176≤melting point+50/crystallite size (II)

In Formula II, the unit of melting point is °C and the unit of crystallite size is nm. Formula II is derived as follows. First, substituting k = 2σe / Δhf for the above theoretical expression T _m = T _m ° - (T _m ° × k) / l, and T _m ° = T _m + (T _m ° × 2σe / Δhf) / l Derive (the derived expression is also referred to as expression α). Here, σe is the surface energy of the folded face of the lamella, and Δhf is the heat of fusion of the complete solid crystal structure. Next, T _m ° = 176, T _m ° × 2σe = 50, and Δhf × l = crystallite size (= S _c ) are substituted. Finally, when the right side of equation α (i.e., T _m +50/S _c ) is equal to or greater than the left side of equation α (i.e., the melting point T _m ° (= 176) when the lamella thickness is infinite), the above It becomes possible to derive formula II ("Polymer" Vol. 16 (1967) No. 6, pages 694-706 Fumiyuki Hamada).

When the melting point + 50 / crystallite size is 176 or more, it is assumed that the electrical insulation resistance at 120 ° C. is excellent because the crystallite size is difficult to propagate current and / or the integrity of the lamella is high.

It is preferable that the polypropylene film of embodiment in this indication is for capacitors.

The polypropylene film of the embodiment in the present disclosure contains the first polypropylene resin as a main component, the number average molecular weight Mn of the first polypropylene resin is 30000 or more and 54000 or less, and the weight average molecular weight of the first polypropylene resin is Mw is 250,000 or more and less than 350,000, and it is preferable that the ratio of Mw to Mn in the first polypropylene resin is 5.0 or more and 10.0 or less.

Further, it is preferable that the heptane insoluble content of the first polypropylene resin is 97.0% or more and 98.5% or less, and the melt flow rate of the first polypropylene resin is 4.0 g/10 min or more and 10.0 g/10 min or less.

The metal layer-integrated polypropylene film of the embodiment in the present disclosure has a polypropylene film and a metal layer laminated on one side or both sides of the polypropylene film.

A film capacitor of an embodiment in the present disclosure includes a wound metal layer integrated polypropylene film. The film capacitor may have a structure in which a plurality of metal layer-integrated polypropylene films are laminated.

In this specification, polypropylene is sometimes abbreviated as PP, and polypropylene resin is sometimes abbreviated as PP resin.

In this specification, the expressions "include" and "include" include the concepts of "contains", "includes", "consisting substantially" and "consisting only of".

In this specification, the expression "capacitor" includes the concepts of "capacitor", "capacitor element" and "film capacitor".

Since the polypropylene film of this embodiment is not a microporous film, it does not have many pores.

The polypropylene film of the embodiment in the present disclosure may be composed of a plurality of layers of two or more layers, but is preferably composed of a single layer.

Here, the directions described and used in the embodiments in the present disclosure will be described in detail. The longitudinal direction of the polypropylene film is sometimes referred to as the longitudinal direction. In the embodiment of the present disclosure, the vertical direction is the same direction as the Machine Direction (hereinafter referred to as “MD direction”). The MD direction is sometimes referred to as the forward direction. However, the present invention is not limited to a form in which the vertical direction points in the same direction as the MD direction. In contrast, the transverse direction of the polypropylene film is sometimes referred to as the width direction. In the embodiment of the present disclosure, the horizontal direction is the same direction as the Transverse Direction (hereinafter referred to as "TD direction"). However, the present invention is not limited to a form in which the horizontal direction points in the same direction as the TD direction.

Embodiment 1

Here, the present disclosure is described in terms of Embodiment 1.

Both surfaces of the polypropylene film in Embodiment 1 can be defined as a first surface and a second surface. The first surface may be a rough surface. If the first surface is a rough surface, wrinkles are less likely to occur on the element roll in capacitor production. The second surface may be a rough surface.

The center line average roughness Ra of the first surface of the polypropylene film is, for example, 0.03 μm or more and 0.08 μm or less. The maximum height Rz of the first surface of the polypropylene film is, for example, 0.3 μm or more and 0.8 μm or less. Both of Ra and Rz are obtained according to the method described in JIS-B0601: 2001 using a three-dimensional surface roughness meter SURFCOM 1400D-3DF-12 type manufactured by Tokyo Seiki Co., Ltd.

Ra of the 2nd surface in a polypropylene film is 0.03 micrometer or more and 0.08 micrometer or less, for example. Rz of the 2nd surface in a polypropylene film is 0.3 micrometer or more and 0.8 micrometer or less, for example.

The thickness of the polypropylene film in Embodiment 1 is 1.0 micrometer - 19 micrometers. Since it is 1.0 μm to 19 μm, in the case where the polypropylene film is used for a film capacitor, reduction in size, weight reduction, and high capacity of the capacitor can be achieved. For this reason, it is preferably used for film capacitor applications required for applications such as electric vehicles and hybrid vehicles used in high-temperature environments. The thickness of the polypropylene film is 19 μm or less, preferably 18 μm or less, more preferably 10 μm or less, still more preferably 6.0 μm or less, still more preferably 4.0 μm or less, and particularly preferably 3.0 μm or less. below When it significantly exceeds 19 μm, miniaturization is difficult and high capacity is difficult. Moreover, the thickness of the polypropylene film in Embodiment 1 is 1.0 micrometer or more, 1.5 micrometer or more is preferable, 1.8 micrometer or more is more preferable, and 2.0 micrometer or more is still more preferable. When it is significantly less than 1.0 µm, the variation in capacity as a film capacitor tends to increase. Thickness is measured based on JIS-C2330 using a micrometer (JIS-B7502).

The polypropylene film of Embodiment 1 satisfies Formula I.

31.5≤enthalpy of fusion/√crystallite size≤33.0 (I)

In Formula I, the unit of enthalpy of fusion is J/g, and the unit of crystallite size is nm. The polypropylene film of Embodiment 1 has excellent dielectric breakdown strength at 120°C DC voltage and excellent dielectric breakdown strength at 120°C AC voltage by satisfying Formula I. Therefore, the polypropylene film of Embodiment 1 can produce a film capacitor having excellent dielectric breakdown strength at 120°C DC voltage and excellent dielectric breakdown strength at 120°C AC voltage. Further, the polypropylene film of Embodiment 1 is excellent in dielectric breakdown strength at 120°C DC voltage and also excellent in dielectric breakdown strength at 120°C AC voltage, and at 100°C at 100°C AC voltage. It also has excellent dielectric breakdown strength. About this point, it is clear from the Example etc. in this specification. On the other hand, formula I is

31.5≤H _m ÷ (S _c ) ^0.5 ≤33.0 (I')

(H _m is the enthalpy of fusion of the polypropylene film (unit: J/g), and S _c is the crystallite size (unit: nm) of the polypropylene film). In addition, in this specification, fusion enthalpy/√crystal size is hereinafter also referred to as H _m /√S _c . H _m is the melting enthalpy (unit: J/g) of the polypropylene film, and S _c is the crystallite size (unit: nm) of the polypropylene film. The value of H _m /√S _c is preferably 31.6 or more, more preferably 31.7 or more, and still more preferably 31.8 or more. The value of H _m /√S _c is preferably 32.8 or less, more preferably 32.5 or less, still more preferably 32.3 or less, and particularly preferably 32.1 or less.

The enthalpy of fusion (H _m ) of the polypropylene film is, for example, 105 J/g or more, preferably 108 J/g or more. 105 J/g or more is preferable because crystallites are strong. The upper limit of enthalpy of fusion is, for example, 125 J/g, preferably 122 J/g. When the polypropylene film is a stretched film, the fusion enthalpy is not only influenced by the raw material, but also the conditions during stretching (eg, temperature during longitudinal stretching, stretching speed during longitudinal stretching, stretching ratio in vertical stretching, horizontal preheating temperature before stretching, temperature during transverse stretching, stretching speed during transverse stretching, and draw ratio in transverse stretching) and relaxation conditions after stretching. For example, the higher the temperature at the time of longitudinal stretching and transverse stretching, the higher the fusion enthalpy tends to be. The higher the preheating temperature before transverse stretching, the higher the fusion enthalpy tends to be. The degree of influence of the stretching speed on the melting enthalpy differs depending on the stretching temperature, but the melting enthalpy tends to increase as the speed during longitudinal stretching and transverse stretching decreases. Melting enthalpy tends to increase as the magnification of longitudinal stretching and transverse stretching decreases. The larger the relaxation rate defined by the following formula, the higher the enthalpy of fusion tends to be.

Relaxation rate (%) = {1-(transverse stretch magnification after relaxation/maximum transverse stretch magnification)} × 100

The enthalpy of fusion of a polypropylene film is a value obtained by first run of differential scanning calorimetry, and is a value specifically measured by the method described in Examples.

The crystallite size (S _c ) of the polypropylene film is preferably 14.5 nm or less, more preferably 14.2 nm or less, still more preferably 13.0 nm or less, particularly preferably 12.5 nm, from the viewpoint of dielectric breakdown strength. below When the crystallite size is 14.5 nm or less, the polypropylene film contains a crystallite interface with a large area, and leakage current tends to be difficult to propagate. The crystallite size is preferably 10.0 nm or larger, more preferably 10.5 nm or larger, still more preferably 11.0 nm or larger, and particularly preferably 11.5 nm or larger. The reason why 10.0 nm or more is preferable is that current does not pass through the inside of the crystallite and it is preferable in securing withstand voltage. When the polypropylene film is a stretched film, the crystallite size is not only affected by the compounding amount and molecular weight of the polypropylene resin, but also the conditions during stretching (eg, temperature during longitudinal stretching, speed during longitudinal stretching, horizontal preheating temperature before stretching, temperature during transverse stretching, speed during transverse stretching). For example, the lower the temperature during longitudinal stretching, the smaller the crystallite size tends to be. The slower the speed at the time of longitudinal stretching, the larger the crystallite size tends to be. The higher the preheating temperature before transverse stretching, the larger the crystallite size tends to be. The lower the temperature during transverse stretching, the smaller the crystallite size tends to be. The slower the speed at the time of transverse stretching, the larger the crystallite size tends to be. The crystallite size is calculated using Scherrer's formula from the half width of the reflection peak of the α crystal (040) plane measured by the wide-angle X-ray diffraction method (XRD method). Scherrer's equation is shown next as equation (1).

In Formula (1), D is the crystallite size (nm), K is a constant (shape factor), λ is the X-ray wavelength used (nm), β is the half width, and θ is the diffraction Bragg angle. Use 0.94 as K. 0.15418 nm is used as λ.

The polypropylene film of Embodiment 1 preferably satisfies Formula II.

176≤melting point+50/crystallite size (II)

In Formula II, the unit of melting point is °C and the unit of crystallite size is nm. Formula II is

176≤T _m +50÷S _c (II')

(T _m is the melting point (unit: ° C) of the polypropylene film, and S _c is the crystallite size (unit: nm) of the polypropylene film). As the lower limit of the melting point + 50/crystallite size, 176.05 and 176.1 are exemplified. As an upper limit of melting point + 50/crystallite size, 180, 179, and 178.4 are mentioned, for example.

The melting point of the polypropylene film is, for example, 170°C or higher, preferably 171°C or higher. If the melting point is 170°C or higher, the lamella integrity is high, and there is a tendency for current to propagate with difficulty. The upper limit of the melting point is, for example, 176°C, preferably 175°C. When the polypropylene film is a stretched film, the melting point is not only influenced by the raw material, but also the conditions during stretching (eg, temperature during longitudinal stretching, speed during longitudinal stretching, magnification of longitudinal stretching, and preheating temperature before horizontal stretching). , temperature during transverse stretching, speed during transverse stretching, magnification of transverse stretching) and relaxation conditions after stretching. For example, the higher the temperature at the time of longitudinal stretching and transverse stretching, the more difficult it is to progress in miniaturization of the lamella and the higher the melting point tends to be. The higher the preheating temperature before transverse stretching, the higher the melting point tends to be. The degree of influence of the stretching speed on the melting point differs depending on the stretching temperature, but the melting point tends to increase as the speed during longitudinal stretching and transverse stretching decreases. The lower the magnification of longitudinal stretching and transverse stretching, the higher the melting point tends to be. The larger the relaxation rate, the higher the melting point tends to be. The melting point of the polypropylene film is a value determined by the first run of differential scanning calorimetry, and is a value specifically measured by the method described in Examples.

The dielectric breakdown strength (V _DC120°C ) of the polypropylene film in Embodiment 1 at 120°C DC voltage is preferably 510 V/μm or more, more preferably 515 V/μm or more, still more preferably It is 530V/㎛ or more. The upper limit of the dielectric breakdown strength at 120°C DC voltage is preferably higher, but is, for example, 600 V/μm or 580 V/μm.

The polypropylene film according to Embodiment 1 has a dielectric breakdown strength (V _AC120°C ) at 120°C alternating voltage of preferably 230 V/μm or more, more preferably 232 V/μm or more, still more preferably 233 V/μm or more. more than μm. The upper limit of the dielectric breakdown strength at 120°C AC voltage is preferably higher, but is, for example, 300 V/μm or 270 V/μm.

The sum of the V _AC120°C and the V _DC120°C (V _AC120°C + V _DC120°C ) of the polypropylene film according to Embodiment 1 is preferably 750 V/μm or more, more preferably 760 V/μm or more, , more preferably 770 V/μm or more. The upper limit of the sum of the V _AC120°C and the V _DC120°C is preferably higher, but is, for example, 1000 V/μm, 900 V/μm, or 850 V/μm.

Since the polypropylene film of Embodiment 1 has enthalpy of fusion/√crystal size of 31.5 or more and 33.0 or less, it is excellent not only in electrical insulation resistance at 120°C but also in dielectric breakdown strength at 100°C alternating current. Therefore, the polypropylene film of Embodiment 1 can raise the capacitor|condenser rated voltage for rectifying the current containing an alternating-current component to a high voltage, and energy saving is possible. The alternating current 100°C dielectric breakdown strength (V _AC100°C ) of the polypropylene film in Embodiment 1 is preferably 243 V/μm or more. The upper limit of the dielectric breakdown strength at 100°C alternating current is preferably higher, but is, for example, 300 V/μm.

The polypropylene film of Embodiment 1 contains a polypropylene resin. The content of the polypropylene resin is preferably 90% by weight or more, more preferably 95% by weight or more with respect to the entire polypropylene film (when the entire polypropylene film is 100% by weight). The upper limit of content of polypropylene resin is 100 weight%, 98 weight%, etc. with respect to the whole polypropylene film, for example.

The smaller the total ash content of the polypropylene resin is, the better it is for electrical properties. The total ash is preferably 50 ppm or less, more preferably 40 ppm or less, still more preferably 30 ppm or less, based on the polypropylene resin. The lower limit of the total ash is, for example, 2 ppm, 5 ppm or the like. It means that there are few impurities, such as a polymerization catalyst residue, so that total ash content is small.

The polypropylene resin may contain one type of polypropylene resin alone, or may contain two or more types of polypropylene resins.

When the polypropylene resin contained in the polypropylene film of Embodiment 1 is 2 or more types, the polypropylene resin with the highest content is used as the main component in this specification, and is referred to as "the polypropylene resin of the main component" in this specification. In addition, when the polypropylene resin contained in the said polypropylene film is 1 type, the said polypropylene resin is also made into a main component in this specification, and is called "the polypropylene resin of a main component" in this specification.

The polypropylene film of Embodiment 1 may contain only the following 1st polypropylene resin, for example, and may also contain the following 2nd polypropylene resin together with the 1st polypropylene resin.

The polypropylene resin may include the first polypropylene resin. When the polypropylene resin contains the first polypropylene resin, the content of the first polypropylene resin is preferably 50% by weight or more, more preferably 55% by weight or more, and still more preferably 100% by weight of the polypropylene resin. It is preferably 60% by weight or more. Regarding the upper limit, the content of the first polypropylene resin is, for example, 100% by weight or less, 99% by weight or less, 98% by weight or less, 95% by weight or less with respect to 100% by weight of the polypropylene resin. , With respect to 100% by weight of the polypropylene resin, it is preferably 90% by weight or less, more preferably 85% by weight or less, still more preferably 80% by weight or less. Thus, the polypropylene film of Embodiment 1 can contain the 1st polypropylene resin as a main component. As the first polypropylene resin, isotactic polypropylene is exemplified.

The weight average molecular weight Mw of the first polypropylene resin is preferably 250,000 or more and less than 350,000, more preferably 250,000 or more and 345,000 or less, still more preferably 270,000 or more and 340,000 or less. When Mw is 250,000 or more and less than 350,000, it is easy to obtain a polypropylene film having the value of H _m /√S _c of 31.5 or more and 33.0 or less. Moreover, if Mw is 250,000 or more and less than 350,000, control of the thickness of a cast raw sheet|seat is easy, and thickness variation is hard to generate|occur|produce.

The number average molecular weight Mn of the first polypropylene resin is preferably 30000 or more and 54000 or less, more preferably 33000 or more and 52000 or less, still more preferably 33000 or more and 50000 or less. When the number average molecular weight Mn of the first polypropylene resin is 30000 or more and 54000 or less, it is easy to obtain a polypropylene film having the value of H _m /√S _c of 31.5 or more and 33.0 or less.

The z-average molecular weight Mz of the first polypropylene resin is preferably 700000 or more and 1550000 or less, more preferably 750000 or more and 1500000 or less. When the z-average molecular weight Mz of the first polypropylene resin is 700000 or more and 1550000 or less, it is easy to obtain a polypropylene film having the value of H _m /√S _c of 31.5 or more and 33.0 or less.

The molecular weight distribution (Mw/Mn) of the first polypropylene resin is preferably 5.0 or more, more preferably 5.5 or more. 10.0 or less are preferable and, as for said Mw/Mn of 1st polypropylene resin, 9.5 or less are more preferable. When Mw/Mn of the first polypropylene resin is 5.0 or more and 10.0 or less, it is easy to obtain a polypropylene film having the value of H _m /√S _c of 31.5 or more and 33.0 or less.

On the other hand, the molecular weight distribution Mw/Mn is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn.

The molecular weight distribution (Mz/Mn) of the first polypropylene resin is preferably 10 or more and 70 or less, more preferably 15 or more and 60 or less, still more preferably 15 or more and 50 or less. When the molecular weight distribution (Mz/Mn) of the polypropylene resin is 10 or more and 70 or less, it is easy to obtain a polypropylene film having the H _m /√S _c value of 31.5 or more and 33.0 or less. On the other hand, the molecular weight distribution Mz/Mn is the ratio of the z-average molecular weight Mz to the number-average molecular weight Mn.

In the present 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, gel permeation chromatograph ( It is a value measured using a GPC) device. More specifically, it is a value measured using HLC-8121GPC-HT (trade name), which is a built-in differential refractometer (RI) high-temperature GPC measuring instrument manufactured by Tosoh Corporation. As a GPC column, three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation were connected and used. The column temperature was set to 140 DEG C, and trichlorobenzene was 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 for 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, Mn, and Mz.

The melt flow rate (MFR) of the first polypropylene resin at 230°C is preferably 10.0 g/10 min or less, more preferably 7.0 g/10 min or less, still more preferably 6.0 g/10 min or less. . The melt flow rate at 230°C is preferably 4.0 g/10 minutes or more. The melt flow rate at 230°C is measured at 230°C under a load of 2.16 kg in accordance with JIS K 7210-1999. The unit g/10 min of the melt flow rate is also referred to as dg/min.

The heptane insoluble content of the first polypropylene resin is preferably 97.0% or more. The heptane insoluble content is preferably 98.5% or less. The larger the heptane-insoluble content, the higher the stereoregularity of the resin. When the heptane insoluble content (HI) is 97.0% or more and 98.5% or less, the crystallinity of the polypropylene resin in the polypropylene film is moderately improved due to moderately high stereoregularity, and the withstand voltage under high temperature is improved. In addition, the speed of solidification (crystallization) at the time of forming the cast raw sheet becomes appropriate, and it has appropriate stretchability. The method for measuring the heptane insoluble content (HI) was in accordance with the method described in Examples.

The smaller the total ash content of the first polypropylene resin is, the better the electrical properties are. The total ash is preferably 50 ppm or less, more preferably 40 ppm or less, still more preferably 30 ppm or less, based on the first polypropylene resin. The lower limit of the total ash is, for example, 2 ppm, 5 ppm or the like.

The polypropylene resin may further include a second polypropylene resin. The polypropylene film of the present embodiment preferably contains a second polypropylene resin in addition to the first polypropylene resin, and the resin constituting the polypropylene film is the first polypropylene resin and the second polypropylene resin. more preferable

When the polypropylene resin contains the second polypropylene resin, the content of the second polypropylene resin is preferably 50% by weight or less, more preferably 49% by weight or less, and 45% by weight with respect to 100% by weight of the polypropylene resin. % or less is more preferable, and 40 weight% or less is especially preferable. In addition, when the polypropylene resin contains the second polypropylene resin, the lower limit of the content of the second polypropylene resin is, for example, 1% by weight or more and 2% by weight with respect to 100% by weight of the polypropylene resin. above, 5% by weight or more, and the like, preferably 10% by weight or more, more preferably 15% by weight or more, still more preferably 20% by weight or more with respect to 100% by weight of the polypropylene resin. As the second polypropylene resin, isotactic polypropylene is exemplified. The second polypropylene resin preferably has at least a Mw of 350,000 or more and 550,000 or less, a Mw/Mn of 3.0 or more and 11.0 or less, and a melt flow rate at 230°C of less than 4.0 g/10 minutes.

The Mw of the second polypropylene resin is preferably 350,000 or more. The Mw of the second polypropylene resin is preferably 550,000 or less, more preferably 450,000 or less, still more preferably 380,000 or less.

The Mn of the second polypropylene resin is preferably 40000 or more and 54000 or less, more preferably 42000 or more and 50000 or less, still more preferably 44000 or more and 48000 or less.

The Mz of the second polypropylene resin is preferably more than 1550000 and 2000000 or less, more preferably 1580000 or more and 1700000 or less.

In the second polypropylene resin, the ratio of Mw to Mn (Mw/Mn) is preferably 3.0 or more, more preferably 4.5 or more, still more preferably 5.0 or more, still more preferably 5.5 or more, still more preferably. It is preferably 7.0 or more, particularly preferably 7.5 or more. The upper limit of Mw/Mn in the second polypropylene resin is, for example, 11.0, 10.0, 9.0, 8.5 or the like. By using together with the first polypropylene resin the second polypropylene resin whose Mw/Mn and Mw satisfy the above-mentioned respective ranges, it is possible to easily reduce the crystallite size.

The ratio of Mz to Mn (Mz/Mn) in the second polypropylene resin is preferably 30 or more and 40 or less, more preferably 33 or more and 36 or less.

The melt flow rate at 230°C of the second polypropylene resin is preferably less than 4.0 g/10 min, more preferably 3.9 g/10 min or less, still more preferably 3.8 g/10 min or less. The melt flow rate at 230°C is preferably 1.0 g/10 min or more, more preferably 1.5 g/10 min or more, and even more preferably 2.0 g/10 min or more.

The heptane insoluble content of the second polypropylene resin is preferably 97.5% or more, more preferably 98.0% or more, even more preferably more than 98.5%, and particularly preferably 98.6% or more. In addition, the heptane insoluble content is preferably 99.5% or less, more preferably 99.0% or less.

The smaller the total ash content of the second polypropylene resin is, the better the electrical properties are. The total ash is preferably 50 ppm or less, more preferably 40 ppm or less, still more preferably 30 ppm or less based on the second polypropylene resin. The lower limit of the total ash is, for example, 2 ppm, 5 ppm or the like.

The total amount of the first polypropylene resin and the second polypropylene resin may be, for example, 90% by weight or more, 95% by weight or more, or 100% by weight, when the total amount of the polypropylene resin is 100% by weight. .

The polypropylene film of Embodiment 1 may further contain a resin other than the polypropylene resin. Examples of such resins include polyethylene, poly(1-butene), polyisobutene, poly(1-pentene), poly(1-methylpentene), ethylene-propylene copolymer, propylene-butene copolymer, and ethylene-butene. A copolymer, a styrene-butadiene random copolymer, a styrene-butadiene-styrene block copolymer, etc. are mentioned.

The polypropylene film of Embodiment 1 may further contain an additive. As an additive, antioxidant, a chlorine absorber, a ultraviolet absorber, a lubricant, a plasticizer, a flame retardant, an antistatic agent, a coloring agent etc. are mentioned, for example.

The polypropylene film of Embodiment 1 may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film, but is preferably a biaxially stretched film.

Next, the manufacturing method of the polypropylene film of this Embodiment 1 is demonstrated. However, the manufacturing method of the polypropylene film of this Embodiment 1 is not limited to the following description.

The polypropylene film of Embodiment 1 can be produced, for example, by preparing a cast raw sheet and biaxially stretching the cast raw sheet. A cast raw sheet can be produced, for example, by supplying resin and, if necessary, additives to an extruder, followed by melting and extruding from a T die to solidify. The biaxial stretching of the cast raw sheet is preferably sequential biaxial stretching. In sequential biaxial stretching, for example, a cast raw sheet is guided between rolls having a speed difference and stretched in the forward direction (hereinafter sometimes referred to as "longitudinal stretching"), cooled as necessary, guided by a tenter, and then stretched in the width direction. It is stretched (hereinafter, sometimes referred to as “transverse stretching”), relaxed, heat-set, and wound up. Therefore, aging treatment is performed in an atmosphere of about 20° C. to 45° C. as necessary, and the product is cut into a desired product width. Corona discharge treatment is performed on one side or both sides of the polypropylene film obtained in this way as necessary.

Extrusion for forming a cast raw sheet is preferably performed at an extrusion temperature of 220°C to 270°C.

The casting temperature, that is, the surface temperature of the metal drum is preferably 40°C to 100°C, and more preferably 45°C to 95°C. If the casting temperature is significantly lower than 40°C, the H _m /√S _c may fall below 31.5, resulting in poor electrical insulation resistance at 120°C. The higher the casting temperature, the higher the enthalpy of fusion/√crystallite size, that is, the value of H _m /√S _c tends to increase. In addition, the lower the casting temperature, the smaller the value of H _m /√S _c tends to be.

The thickness of the cast raw sheet may be, for example, 0.05 mm or more, and may be 0.1 mm or more. 2 mm, 1 mm, etc. are mentioned as an upper limit of the thickness in a cast raw sheet|seat.

Regarding the biaxial stretching of the cast raw sheet, it is preferable to preheat at 125°C to 165°C before longitudinally stretching the cast raw sheet. Hereinafter, the preheating temperature before longitudinal stretching may be referred to as preheating temperature before longitudinal stretching.

The temperature at the time of longitudinal stretching (longitudinal stretching temperature) is preferably 125°C to 165°C. When the temperature during longitudinal stretching significantly exceeds 165°C, the H _m /√S _c may fall below 31.5, resulting in poor electrical insulation resistance at 120°C. The higher the longitudinal stretching temperature, the smaller the value of H _m /√S _c tends to be. The lower the longitudinal stretching temperature, the higher the value of H _m /√S _c tends to be.

400%/sec or more is preferable, and, as for the extending|stretching speed at the time of longitudinal stretching (it may be hereafter referred to as "longitudinal stretching speed"), 500%/sec - 60000%/sec are more preferable.

The stretch magnification (longitudinal stretch magnification) of the longitudinal stretch is preferably 3.5 to 5.5 times, more preferably 4.0 to 5.4 times, still more preferably 4.0 to 5.0 times. If it significantly exceeds 5.5 times, the value of H _m /√S _c exceeds 33, and there is a fear that the electrical insulation resistance at 120 ° C. becomes poor. As the longitudinal stretch ratio increases, the value of H _m /√S _c tends to increase. In addition, the value of H _m /√S _c tends to decrease as the longitudinal stretch ratio decreases.

It is preferable to preheat the film after longitudinal stretching to 155°C to 172°C before transverse stretching. If the temperature significantly exceeds 172°C, the value of H _m /√S _c may fall below 31.5, resulting in poor electrical insulation resistance at 120°C. The value of H _m /√S _c tends to decrease as the temperature of preheating performed before transverse stretching (hereinafter sometimes referred to as “preheating temperature before transverse stretching”) is increased. The lower the preheating temperature before transverse stretching, the higher the value of H _m /√S _c tends to be.

It is preferable to transversely stretch the film after preheating before transverse stretching at 150°C to 165°C. The temperature at the time of this transverse stretching (hereinafter sometimes referred to as "transverse stretching temperature") is preferably 155°C to 165°C, more preferably 160°C to 165°C. However, when the temperature significantly exceeds 165°C, the value of H _m /√S _c is less than 31.5, and the electrical insulation resistance at 120°C may deteriorate. The higher the transverse stretching temperature, the smaller the value of H _m /√S _c tends to be. The lower the transverse stretching temperature, the higher the value of H _m /√S _c tends to be.

The stretching speed at the time of transverse stretching (hereinafter sometimes referred to as "transverse stretching speed") is preferably 280%/sec to 350%/sec. If the transverse stretching rate is significantly less than 280%/sec, the value of H _m /√S _c may be less than 31.5, and the electrical insulation resistance at 120°C may deteriorate. In addition, when the transverse stretching speed significantly exceeds 350%/sec, the value of H _m /√S _c exceeds 33, or the film may break during transverse stretching.

The lower the transverse stretching speed, the smaller the H _m /√S _c tends to be. In addition, the higher the transverse stretching speed, the higher the H _m /√S _c tends to be.

The draw ratio of transverse stretch (hereinafter sometimes referred to as “transverse stretch ratio”) is preferably 9 to 11 times, and more preferably 9.2 to 10.7 times. If it is significantly less than 9 times, the value of H _m /√S _c is less than 31.5, and as a result, there is a possibility that the electrical insulation resistance at 120 ° C. becomes poor. On the other hand, when it is significantly higher than 11 times, the value of H _m /√S _c exceeds 33.0, or there is a concern that the film may break during transverse stretching.

It is preferable to relax|relax the film after transverse stretching at 157 degreeC - 170 degreeC. Hereinafter, the temperature at the time of relaxation may be referred to as relaxation temperature.

The time required for relaxation, that is, the time required for heat setting, is preferably within 10 seconds, more preferably from 1 second to 9 seconds.

It is preferable to relax the relaxation rate [{1-(transverse stretch ratio after relaxation/maximum transverse stretch ratio)}×100] to 1% to 15%.

On the other hand, enthalpy of fusion and crystallite size are affected by conditions during stretching. For example, when the transverse stretching speed is changed, the values of both fusion enthalpy and crystallite size are changed. For this reason, it is difficult to change the other after fixing either the fusion enthalpy or the crystallite size. On the other hand, in Embodiment 1, H _m /√S _c incorporating both enthalpy of fusion and crystallite size satisfies a certain range, that is, 31.5 or more and 33.0 or less. That is, the enthalpy of fusion and the crystallite size are not individually controlled, but H _m /√S _c incorporating both is controlled.

The polypropylene film of Embodiment 1 thus obtained can be used as a dielectric for a capacitor. Preferably, it can be used as a derivative of a capacitor constituting an inverter in a hybrid vehicle/electric vehicle.

In order to process into a capacitor, a metal layer may be laminated on one side or both sides of the polypropylene film in the first embodiment to obtain a metal layer integrated polypropylene film. The metal layer functions as an electrode. As the metal used for the metal layer, for example, a simple metal such as zinc, lead, silver, chromium, aluminum, copper, nickel, a mixture of a plurality of these, an alloy thereof, etc. can be used, but environmental, economical and Considering capacitor performance and the like, zinc and aluminum are preferable.

As a method of laminating a metal layer on one side or both sides of a polypropylene film, a vacuum deposition method or a sputtering method can be exemplified. From the viewpoints of productivity and economy, the vacuum deposition method is preferred. Although a crucible method, a wire method, etc. can be exemplified in general as a vacuum deposition method, it is not specifically limited, An optimal thing can be selected suitably.

The margin pattern when the metal layers are laminated by vapor deposition is not particularly limited, but a pattern including so-called special margins such as a fishnet pattern or a T-margin pattern is a polypropylene pattern from the viewpoint of improving characteristics such as security of a capacitor. It is preferably carried out on one side of the film. Security is enhanced, and it is also effective from points such as prevention of destruction of capacitors and short circuits.

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

The metal layer-integrated polypropylene film of Embodiment 1 can be laminated or wound by a conventionally known method to form a film capacitor.

The film capacitor of Embodiment 1 may have a configuration in which a plurality of metal layer-integrated polypropylene films are laminated, or may have a wound metal layer-integrated polypropylene film. Such film capacitors can be suitably used for capacitors for inverter power supply devices that control drive motors of electric vehicles, hybrid vehicles, and the like. In addition, it can also be suitably used for railway vehicles, wind power generation, solar power generation, and general home appliances.

Example

Here, an embodiment of the present disclosure is described. However, this invention is not limited to the aspect of an Example.

Table 1 shows the physical properties of the polypropylene resin used to prepare the biaxially stretched polypropylene film. Polypropylene resin B shown in Table 1 is HPT-1 manufactured by Korea Petrochemical Corporation, and polypropylene resin C is S802M manufactured by Korea Petrochemical Corporation. Polypropylene resin D is HC300-BF by Borealis, polypropylene resin G is HB311-BF by Borealis, and polypropylene resin J is HC318-BF by Borealis. Polypropylene resin A, polypropylene resin E, polypropylene resin F, and polypropylene resin H are products manufactured by Prime Polymer Co., Ltd.

Measurement of weight average molecular weight (Mw), number average molecular weight (Mn), z average molecular weight (Mz), molecular weight distribution (Mw/Mn), molecular weight distribution (Mz/Mn)

The weight average molecular weight (Mw), number average molecular weight (Mn), and z average molecular weight (Mz) were measured under the following conditions using GPC (gel permeation chromatography). For preparation of the calibration curve, standard polystyrene manufactured by Tosoh Corporation was used, and measurement results were obtained by polystyrene conversion. In conversion to the molecular weight of polypropylene, the Q-factor was used.

Measuring instrument: High-temperature GPC device with built-in differential refractometer (RI) manufactured by Tosoh Corporation, HLC-8121GPC-HT type

Column: Three TSKgel GMHHR-H(20)HT manufactured by Tosoh Corporation are connected.

Column temperature: 140°C

Eluent: Trichlorobenzene

Flow rate: 1.0mL/min

Measurement of Melt Flow Rate (MFR)

Based on JIS K 7210-1999, it measured at 230 degreeC under the load of 2.16 kg.

Measurement of heptane insoluble content (HI)

A sample of about 3 g of 10 mm x 35 mm x 0.3 mm was prepared by press molding, to which about 150 mL of heptane was added, and Soxhlet extraction was performed for 8 hours. Heptane insoluble content was calculated from the sample mass before and after extraction.

Preparation of biaxially oriented polypropylene film in Example 1

According to Table 2, a dry blend resin composition by weighing polypropylene resins (PP resin A and PP resin B) and mixing PP resin A and PP resin B at a ratio of PP resin A:PP resin B = 65:35 (weight ratio) got Then, the dry blended resin composition was supplied to an extruder, melted at 230°C, extruded with a T die, and wound on a metal drum with a surface temperature (casting temperature) maintained at 45°C to solidify. In this way, a cast raw sheet having a thickness of 900 µm was obtained. Subsequently, the cast original sheet was preheated at 165° C. using a batch type biaxial stretching machine KARO IV manufactured by Bruckner, and then stretched 5.0 times in the longitudinal direction at a longitudinal stretching temperature of 165° C. at a stretching rate of 600%/sec, followed by transverse stretching. After preheating at 165°C before directional stretching, it was stretched 10.5 times in the transverse direction at a stretching rate of 300%/sec at a transverse stretching temperature of 165°C, and then relaxed 10 times. In this way, a biaxially stretched polypropylene film having a thickness of 18 μm was obtained. On the other hand, operation was performed at 165°C in any of the steps of preheating before longitudinal stretching, longitudinal stretching, preheating before longitudinal stretching, transverse stretching, and relaxation. In the preheating step, the air volume was increased by means of a diffuser. The temperature of the relaxation was 165°C, and the time of the relaxation was 5 seconds. The relaxation rate was 4.8% [= {1-(10/10.5)} x 100].

Preparation of biaxially oriented polypropylene film in Example 2

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin C = 65:35 (weight ratio) was used. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Example 3

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin D=65:35 (weight ratio) was used. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Example 4

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin B=65:35 (weight ratio) was used. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Example 5

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin H=65:35 (weight ratio) was used. In addition, the operation was performed at 160°C with respect to the temperature of any of the preheating before longitudinal stretching, longitudinal stretching, preheating before transverse stretching, transverse stretching, and relaxation. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Example 6

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin B=65:35 (weight ratio) was used. In addition, the stretching speed in the transverse direction was set to 320%/sec instead of 300%/sec. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Example 7

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin B=65:35 (weight ratio) was used. In addition, the stretching speed in the transverse direction was set to 280%/sec instead of 300%/sec. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Comparative Example 1

As the polypropylene resin, PP resin E was used. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially oriented polypropylene film in Comparative Example 2

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin F:PP resin G=65:35 (weight ratio) was used. In addition, the operation was performed at 166°C with respect to the temperature of any of the preheating before longitudinal stretching, longitudinal stretching, preheating before transverse stretching, transverse stretching, and relaxation. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially stretched polypropylene film in Comparative Example 3

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin H=65:35 (weight ratio) was used. In addition, the operation was performed at 166°C with respect to the temperature of any of the preheating before longitudinal stretching, longitudinal stretching, preheating before transverse stretching, transverse stretching, and relaxation. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially stretched polypropylene film in Comparative Example 4

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin J:PP resin H=65:35 (weight ratio) was used. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially stretched polypropylene film in Comparative Example 5

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin B=65:35 (weight ratio) was used. In addition, the stretching speed in the transverse direction was set to 250%/sec instead of 300%/sec. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially stretched polypropylene film in Comparative Example 6

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin C:PP resin A = 90:10 (weight ratio) was used. In addition, the operation was performed at 163°C with respect to the temperature of any of the preheating before longitudinal stretching, longitudinal stretching, preheating before transverse stretching, transverse stretching, and relaxation. Otherwise, a biaxially stretched polypropylene film was obtained in the same manner as in Example 1.

Preparation of biaxially stretched polypropylene film in Comparative Example 7

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin B=65:35 (weight ratio) was used. In addition, the stretching speed in the transverse direction was set to 700%/sec instead of 300%/sec. Other than that, in the same manner as in Example 1, an attempt was made to obtain a biaxially stretched polypropylene film having a thickness of 18 μm, and the film thickness variation was so large that it could not be used as a film capacitor element.

Measurement of melting point and enthalpy of fusion

A 5 mg sample was cut out from the biaxially stretched polypropylene film, sealed in an aluminum plate, and input-compensated differential scanning calorimetry was performed with a differential scanning calorimeter (Diamond DSC manufactured by Perkin Elmer). In the measurement, the temperature was raised (first run) from 30°C to 280°C at 20°C/min in a nitrogen atmosphere. From the results of the first run, the melting point and melting enthalpy were determined.

Measurement of crystallite size

The crystallite size of the biaxially stretched polypropylene film was measured with an XRD (wide-angle X-ray diffraction) apparatus according to the following.

Measuring device: Desktop X-ray diffractometer "MiniFlex300" manufactured by Rigaku Co., Ltd.

X-ray generation output: 30 kV, 10 mA

Irradiation X-rays: monochromator monochromatic CuKα rays (wavelength 0.15418 nm)

Detector: Scintillation Counter

Goniometer scanning: 2θ/θ interlocking scanning

From the obtained data, the full width at half maximum of the diffraction/reflection peak of the α-crystal (040) plane was calculated using an analysis computer and integrated powder X-ray analysis software PDXL included in the apparatus standard. From the half-value width, the crystallite size was determined using Scherrer's equation represented as equation (1).

In Formula (1), D is the crystallite size (nm), K is a constant (shape factor), λ is the wavelength of the X-ray used (nm), β is the half width obtained, and θ is the diffraction Bragg angle. 0.94 was used as K.

Measurement of Dielectric Breakdown Strength

In accordance with JIS C2330 (2001) 7.4.11.2 B method (plate electrode method), the dielectric breakdown voltage is measured 12 times, these dielectric breakdown voltages are divided by the thickness (μm) of the biaxially stretched polypropylene film, and the upper two and lower The average value of 8 times excluding the value of 2 times was calculated|required, and this was made into dielectric breakdown strength. In the test using an AC power supply, the breakdown voltage was measured at ambient temperatures of 100°C and 120°C. In the test using a DC power supply, the breakdown voltage was measured at an ambient temperature of 120°C.

The "melting point + 50/crystallite size" of the biaxially stretched polypropylene film was 177.2 in Example 1, 178.4 in Example 2, 177.5 in Example 3, 178.4 in Example 4, 177.4 in Example 5, and 178.3 in Example 6. , 178.5 in Example 7, 175.9 in Comparative Example 1, 174.1 in Comparative Example 2, 178.0 in Comparative Example 3, 174.8 in Comparative Example 4, 178.7 in Comparative Example 5, and 178.5 in Comparative Example 6.

The biaxially stretched polypropylene films of Examples 1 to 7 were excellent in dielectric breakdown strength at 120°C of direct current and also excellent in dielectric breakdown strength at 120°C of alternating current. Further, the biaxially stretched polypropylene films of Examples 1 to 7 were also excellent in dielectric breakdown strength at 100°C alternating current. In the dielectric breakdown strength test of an AC power supply, heat generation or deterioration (decomposition, etc.) of the film due to corona discharge occurs, or leakage current occurs due to alternating polarity, and the Joule heating value in the leakage current It differs from the dielectric breakdown strength test in DC power supply in that it occurs. As described above, the biaxially stretched polypropylene films of Examples 1 to 7 had excellent dielectric breakdown strength even when both DC voltage and AC voltage were applied at 120°C.

Preparation of biaxially oriented polypropylene film in Example 8

According to Table 3, polypropylene resins (PP resin F and PP resin B) are weighed, and PP resin F and PP resin B are mixed at a ratio of PP resin A: PP resin B = 60: 40 (weight ratio) to dry blend resin composition got Subsequently, the dry blend resin composition was supplied to an extruder, melted at 250°C, extruded through a T die, and wound on a metal drum with a surface temperature (cast temperature) maintained at 95°C to solidify. In this way, an unstretched cast raw sheet having a thickness of 100 µm was obtained. The obtained unstretched cast raw sheet was preheated to 130 ° C. before longitudinal stretching, maintained at a temperature of 130 ° C. so that the longitudinal stretching temperature reached 130 ° C., passed between rolls having a speed difference, and stretched 4.0 times in the longitudinal direction, Cool immediately to room temperature. Next, the uniaxially stretched film was guided to a tenter, preheated at 171°C before transverse stretching, and then stretched 10.0 times in the transverse direction at a transverse stretching temperature of 160°C at a stretching rate of 300%/sec. Thereafter, the biaxially stretched film was relaxed 9 times in the transverse direction, heat-set, rolled up, and aged in an atmosphere of about 30°C. In this way, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained. The temperature of the relaxation (heat setting) was 160° C., and the relaxation time was 4 seconds. The relaxation rate was 10% [= {1-(9/10)} x 100].

Preparation of biaxially oriented polypropylene film in Example 9

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin D:PP resin C = 80:20 (weight ratio) was used. In addition, the preheating temperature before transverse stretching (preheating temperature before transverse stretching) was set to 172°C instead of 171°C. Otherwise, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 8.

Preparation of biaxially oriented polypropylene film in Example 10

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin C = 75:25 (weight ratio) was used. In addition, by adjusting the amount of extrusion of the dry blend resin composition, the thickness of the unstretched cast raw sheet was set to 90 µm instead of 100 µm. In addition, the preheating temperature before transverse stretching (preheating temperature before transverse stretching) was set to 172°C instead of 171°C. Otherwise, a biaxially stretched polypropylene film having a thickness of 2.3 µm was obtained in the same manner as in Example 8.

Preparation of biaxially oriented polypropylene film in Example 11

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin F:PP resin C = 65:35 (weight ratio) was used. In addition, by adjusting the amount of extrusion of the dry blend resin composition, the thickness of the unstretched cast raw sheet was set to 90 µm instead of 100 µm. In addition, the preheating temperature before transverse stretching (preheating temperature before transverse stretching) was set to 172°C instead of 171°C. Otherwise, a biaxially stretched polypropylene film having a thickness of 2.3 µm was obtained in the same manner as in Example 8.

Preparation of biaxially stretched polypropylene film in Comparative Example 8

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin F:PP resin B = 60:40 (weight ratio) was used. In addition, the preheating temperature before transverse stretching (preheating temperature before transverse stretching) was set to 173°C instead of 171°C. Otherwise, a biaxially stretched polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 8.

Preparation of biaxially stretched polypropylene film in Comparative Example 9

As the polypropylene resin, a dry blend resin composition mixed in a ratio of PP resin A:PP resin C = 75:25 (weight ratio) was used. In addition, by adjusting the amount of extrusion of the dry blend resin composition, the thickness of the unstretched cast raw sheet was set to 90 µm instead of 100 µm. In addition, the preheating temperature before transverse stretching (preheating temperature before transverse stretching) was set to 173°C instead of 171°C. Otherwise, a biaxially stretched polypropylene film having a thickness of 2.3 µm was obtained in the same manner as in Example 8.

The melting point, melting enthalpy, crystallite size, and dielectric breakdown strength of the biaxially stretched polypropylene film were measured by the methods described above.

The "melting point + 50/crystallite size" of the biaxially stretched polypropylene film was 176.1 in Example 8, 177.8 in Example 9, 176.8 in Example 10, 176.7 in Example 11, 177.2 in Comparative Example 8, and 177.3 in Comparative Example 9. was

The biaxially stretched polypropylene films of Examples 8 to 11 were excellent in dielectric breakdown strength at 120°C of direct current and also excellent in dielectric breakdown strength at 120°C of alternating current. Further, the biaxially stretched polypropylene films of Examples 8 to 11 were also excellent in dielectric breakdown strength at 100°C alternating current.

Claims (7)

Satisfy Expression I,
Dielectric breakdown strength (V DC 120 ° _C ) at 120 ° C DC voltage is 510 V / μm or more and 600 V / μm or less,
The crystallite size is 12.5 nm or less,
It has a thickness of 1 to 3 μm,
A polypropylene film having a melting enthalpy of 105 to 122 J/g,
The above formula I,
31.5≤enthalpy of fusion/√crystallite size≤33.0
is,
In the above formula I, the unit of the fusion enthalpy is J / g, the unit of the crystallite size is nm,
The crystallite size is obtained using Scherrer's formula from the half width of the reflection peak of the α crystal (040) plane measured by wide-angle X-ray diffraction. According to claim 1,
further satisfies Equation II,
Equation II above is
176 ≤ melting point + 50 / crystallite size
is,
In Formula II, the unit of the melting point is ° C, and the unit of the crystallite size is nm. According to claim 1,
Polypropylene film for capacitors. According to claim 1,
Containing a first polypropylene resin as a main component,
The number average molecular weight Mn of the first polypropylene resin is 30000 or more and 54000 or less,
The weight average molecular weight Mw of the first polypropylene resin is 250,000 or more and less than 350,000,
The polypropylene film whose ratio of Mw to Mn in the said 1st polypropylene resin is 5.0 or more and 10.0 or less. According to claim 4,
The heptane insoluble content of the first polypropylene resin is 97.0% or more and 98.5% or less,
A polypropylene film having a melt flow rate of the first polypropylene resin of 4.0 g/10 min or more and 10.0 g/10 min or less. The polypropylene film of claim 1,
A metal layer-integrated polypropylene film having a metal layer laminated on one side or both sides of the polypropylene film. A film capacitor having the wound metal layer-integrated polypropylene film of claim 6 or having a configuration in which a plurality of metal layer-integrated polypropylene films of claim 6 are laminated.