JP7247918B2 - Polypropylene film, metal film laminated film using the same, film capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polypropylene film that is particularly suitable for use in capacitors.

Polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are used in various applications such as packaging, tape, cable wrapping, and electrical applications such as capacitors.

Among these, in the use of capacitors, polypropylene films are particularly preferably used for high voltage capacitors, not only for direct current and alternating current, because of their excellent voltage resistance and low loss characteristics.

In recent years, various electric devices have been converted to inverters, and along with this, the demand for smaller size capacitors and larger capacity capacitors has become stronger. In response to demands from such fields, particularly automobile applications (including hybrid car applications), solar power generation, and wind power generation applications, polypropylene film can be made thinner and have improved dielectric breakdown voltage, and properties that can be used for a long time in a high temperature environment. It has become a situation where excellent reliability that can maintain high reliability is essential.

Polypropylene films are considered to have high heat resistance and dielectric breakdown voltage among polyolefin films. On the other hand, when applying to the above fields, it is important to exhibit excellent dimensional stability at the operating environment temperature and to exhibit stable electrical performance such as electrical resistance even in a region 10 to 20 ° C higher than the operating environment temperature. is. From the viewpoint of heat resistance, it is said that in the future, when power semiconductor applications using silicon carbide (SiC) are considered, the operating environment temperature will be higher. Due to the demand for higher heat resistance and higher voltage resistance for capacitors, there is a demand for an improvement in dielectric breakdown voltage of the film in a high temperature environment exceeding 110°C. However, as described in Non-Patent Document 1, the upper temperature limit of polypropylene film is said to be about 110° C., and it has been extremely difficult to maintain a stable dielectric breakdown voltage under such a temperature environment. . In addition, it is thought that the heat history of the film itself in the process of vapor deposition processing reaches up to around 150°C. It was difficult to fully demonstrate as

Until now, as a method for obtaining excellent performance in a high-temperature environment when a polypropylene film is made into a thin film and made into a capacitor, for example, the relaxation time of the amorphous component of polypropylene and the relaxation time of the intermediate component in a 70 ° C atmosphere are controlled. There have been proposals for a film with improved dielectric breakdown voltage (for example, Patent Document 1) and a film in which the dielectric breakdown voltage is improved by controlling the storage elastic modulus at 125 ° C. so that the change in storage elastic modulus at 125 ° C. is smaller than the storage elastic modulus at room temperature. (For example, Patent Document 2). Furthermore, a polypropylene film has a high stereoregularity polypropylene raw material having a high elastic modulus at high temperature and is rapidly cooled after melt extrusion, and then a proposal of a sheet formed by heat treatment (for example, Patent Document 3), molecular weight distribution of polypropylene raw material, stereo A biaxially stretched film having an improved high-temperature dielectric breakdown voltage at 100° C. by controlling regularity has been proposed (for example, Patent Document 4).

Japanese Patent Application Laid-Open No. 2002-248681 International Publication No. 2015/146894 pamphlet WO 2009/008340 Pamphlet WO 2009/060944 Pamphlet

Motonobu Kawai, "Leap Forward from Film Capacitors, From Cars to Energy," Nikkei Electronics, Nikkei Business Publications, September 17, 2012, p.57-62

However, none of the polypropylene films described in Patent Documents 1 to 4 has sufficient improvement in dielectric breakdown voltage in a high temperature environment exceeding 110 ° C., and furthermore reliability in long-term use in a high temperature environment when used as a capacitor. Even so, it was not enough.

Therefore, the present invention aims to provide a polypropylene film that has excellent structural stability against heat, which is excellent in long-term use reliability in a high-temperature environment and suitable for capacitors used under high temperature and high voltage. Another object of the present invention is to provide a metal film laminated film and a film capacitor using the same.

In order to solve the above problems, the present inventors have made intensive studies and arrived at the following invention.

Regarding the relaxation time T2 of the amorphous component obtained by the pulse NMR method, the relationship between the relaxation time (T2A) (μs) after heat treatment at 150° C. for 1 minute and the relaxation time (T2B) (μs) before heat treatment is , a polypropylene film that satisfies the following formula:
(T2B)/(T2A)≧0.90.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a polypropylene film which is excellent in long-term use reliability in a high-temperature environment, suitable for use in capacitors used under high temperature and high voltage, and excellent in structural stability against heat. Also provided are a metal film laminated film and a film capacitor using the same.

The present inventors have made intensive studies to solve the above-mentioned problems, and have found that the polypropylene films described in Patent Documents 1 to 4 have a dielectric breakdown voltage in a high temperature environment, and a long time in a high temperature environment when used as a capacitor. The reason why the use reliability is not sufficient is considered as follows.

That is, in the polypropylene film described in Patent Document 1, a propylene-based random copolymer is added to the polypropylene resin for the purpose of imparting high rigidity and antistatic properties for packaging. We thought that the combined heat resistance was insufficient and it was not suitable for capacitors. In addition, the polypropylene film described in Patent Document 2 can be said to have sufficient voltage resistance and reliability as a capacitor in a 105°C environment. Preheating and heat treatment at the time of stretching are not necessarily sufficient, and since there are many cold xylene soluble parts (CXS) contained in the raw material, it is difficult to increase the degree of crystallinity, and the amorphous component of the film is relaxed at high temperatures. I thought there was a problem with the decrease in time. The polypropylene film of Patent Document 3 is an unstretched sheet, and there is no technical idea of biaxially stretching the sheet having excellent rigidity to develop withstand voltage performance. I thought it was because it was lower. Since the polypropylene film described in Patent Document 4 uses polypropylene resin with high stereoregularity, it has voltage resistance and reliability in a 100 ° C. environment, but further assume voltage resistance in a high temperature environment. Therefore, preheating and heat treatment during lateral stretching in film formation are not always sufficient, there are many movable amorphous components in the film, the preheating temperature before lateral stretching is low, and slow cooling is performed at the heat treatment temperature after lateral stretching. The reason for this is thought to be that the stabilization of the molecular chain orientation structure is insufficient and the relaxation time of the amorphous component at high temperatures is shortened.

Based on the above considerations, the present inventors have further studied, and the relationship between the relaxation time of the amorphous component before and after the heat treatment of the polypropylene film at 150 ° C. for 1 minute is a value of more than a certain value. We have found that the above problems can be solved.

That is, in the present invention, the relationship between the relaxation time T2 of the amorphous component obtained by the pulse NMR method after heat treatment at 150 ° C. for 1 minute (T2A) and before heat treatment (T2B) satisfies the following formula. film.
(T2B)/(T2A)≧0.90.

In this specification, the polypropylene film may be simply referred to as a film hereinafter. Note that the polypropylene film of the present invention is not a microporous film and therefore does not have many pores. That is, the polypropylene film of the present invention means a polypropylene film other than a microporous film. Here, the term “microporous film” refers to a film that penetrates both surfaces and is subjected to penetration time of 100 ml of air at 23 ° C. and 65% relative humidity using a B-type Gurley tester of JIS P 8117 (1998). ,000 sec/100 ml or less.

In the polypropylene film of the present invention, the relaxation time T2 of the amorphous component obtained by the pulse NMR method is the relaxation time (T2A) (μs) after heat treatment of the film at 150 ° C. for 1 minute and the relaxation time before heat treatment ( T2B) (μs) must satisfy the following equation.
(T2B)/(T2A)≧0.90.

The value of (T2B)/(T2A) is preferably 0.92 or greater, more preferably 0.95 or greater, and most preferably 0.97 or greater. The higher this value is, the higher the dielectric breakdown voltage is exhibited even at high temperature, and the capacitor can exhibit long-term reliability in a high-temperature environment.

In other words, the present inventors have made intensive studies to obtain a polypropylene film that exhibits long-term reliability in a high-temperature environment for use in capacitors. It was found that there is a high correlation between the parameter (T2B)/(T2A) and the long-term reliability of the capacitor at high temperatures. In other words, in the case of a polypropylene film that can exhibit long-term reliability in a high-temperature environment in a capacitor application, the relaxation time T2 of the amorphous component obtained by the pulse NMR method before and after heating the film at a temperature higher than the operating environment temperature is It is the present invention that it has been found that controlling the change to be small is particularly important for long-term capacitor long-term reliability. Here, satisfying the relationship of (T2B)/(T2A) ≥ 0.90 means that even if the film is heated, the structural change due to amorphous relaxation is small. This means that the film is restrained from loosening and has a very stable structure against heat.

In order for the polypropylene film of the present invention to satisfy the relationship of the above formula ((T2B) / (T2A) ≥ 0.90), the area draw ratio is increased in the stretching process during film formation, particularly by the sequential biaxial stretching method. It is effective to increase the draw ratio in the width direction. On the other hand, it was found that the thermal shrinkage rate tends to increase due to the orientation caused by stretching, and the thermal shrinkage stress tends to increase. By using a polypropylene raw material with a small amount of fusible part (CXS), conventionally, deterioration of heat shrinkage characteristics in the width direction occurs when stretching in the width direction at a high magnification, but it has an unexpected effect of suppressing this. . Furthermore, it was found that the preheating temperature during lateral stretching is set to a temperature higher than the lateral stretching temperature, and the heat treatment after lateral stretching is performed by multi-stage heat setting treatment and relaxation treatment, whereby the effect can be obtained more remarkably.

That is, using a polypropylene raw material having a mesopentad fraction of 0.970 or more and a cold xylene soluble part (CXS) of less than 1.5% by mass, the melt extrusion temperature before the filter, after the filter, and at the die is reduced in multiple stages ( Here, the multistage low temperature means that the temperature is lowered in each stage before and after the filter and in the die stage, as described later. Sometimes the area draw ratio is 60 times or more and the width direction draw ratio is 10.5 times or more, and the preheating temperature after uniaxial stretching in the longitudinal direction and immediately before biaxial stretching in the width direction is the stretching temperature in the width direction. +5 to +15 ° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first, relaxation treatment is performed while performing heat treatment (first stage) at a temperature lower than the stretching temperature in the width direction, and then the film is stretched in the width direction. Heat treatment at 135 ° C. or higher at a temperature lower than the heat treatment temperature in the first step (second step) while maintaining tension, and further heat treatment at a temperature of 80 ° C. or higher and lower than the heat treatment temperature in the second step (third step). A polypropylene film having (T2B)/(T2A)≧0.90 can be easily obtained by appropriately subjecting the film to multistage heat setting treatment and relaxation treatment.

On the other hand, when the value of (T2B)/(T2A) is less than 0.90, when used as a capacitor in a high-temperature environment where high voltage is applied, especially when placed in a high-temperature state for a long time, Molecular chain relaxation of the film progresses, lowering the withstand voltage, causing a decrease in capacitor capacity and short-circuit breakdown, resulting in an unreliable capacitor. Although the upper limit of the above relational expression ((T2B)/(T2A)≧0.90) is not particularly limited, it is practically 0.99 or less. If (T2B)/(T2A) is to be greater than 0.99, the draw ratio must be increased during film formation, which may cause tearing.

The polypropylene film of the present invention preferably has a heat shrinkage stress value (SF130TD) (MPa) of 2.0 MPa or less, more preferably 1.5 MPa, obtained using a thermomechanical analyzer at 130 ° C. in the width direction of the film. Below, more preferably 1.1 MPa or less, most preferably 0.9 MPa or less.

Here, in the polypropylene film of the present invention, the "longitudinal direction" is the direction corresponding to the flow direction in the film manufacturing process (hereinafter sometimes referred to as "MD"), and the "width direction" is the film It is a direction perpendicular to the flow direction in the manufacturing process (hereinafter sometimes referred to as "TD"). When the film sample is in the form of a reel, roll, or the like, the winding direction of the film can be said to be the longitudinal direction. On the other hand, in the case of a film in which it is unclear from the appearance of the film which direction corresponds to the flow direction in the film manufacturing process, for example, lines are drawn at 15° increments based on an arbitrary straight line on the film plane. Pull, sample a slit-shaped film piece parallel to each line, determine the breaking strength with a tensile tester, consider the direction that gives the maximum breaking strength as the width direction of the film, and the direction perpendicular to the width direction of the film. is taken as the longitudinal direction. Details will be described later, but if the sample width is less than 50 mm and the breaking strength cannot be obtained with a tensile tester, the crystal orientation of the α crystal (110) plane of the polypropylene film by wide-angle X-rays is measured as follows. , the longitudinal direction and the width direction of the film based on the following criteria. That is, X-rays (CuKα rays) are incident in the direction perpendicular to the film surface, and the crystal peak at 2θ = about 14 ° (α crystal (110) plane) is scanned in the circumferential direction, and the obtained diffraction intensity distribution The direction in which the diffraction intensity is the highest is defined as the width direction of the film, and the direction perpendicular thereto is defined as the longitudinal direction.

When the polypropylene film of the present invention has a thermal shrinkage stress value (SF130TD) (MPa) of 2.0 MPa or less obtained using a thermomechanical analyzer at 130 ° C. in the film width direction, after metallikon thermal spraying in the capacitor manufacturing process Prevents poor contact between vapor-deposited film electrodes and metallikon electrodes during aging treatment, enabling capacitor elements to meet design capacity. be able to. The lower limit of the thermal shrinkage stress value (SF130TD) (MPa) obtained using a thermomechanical analyzer at 130° C. in the film width direction is not particularly limited, but it is practical to set it to about 0.1 MPa. If the thermal shrinkage stress is lower than 0.1 MPa, the shrinkage of the film itself becomes insufficient due to the heat of the capacitor manufacturing process and the use process, and there is a possibility that sufficient capacity relative to the designed capacity will not be developed.

In order to control the heat shrinkage stress value (SF130TD) (MPa) obtained using a thermomechanical analyzer in the film width direction at 130 ° C. within a preferable range, for example, a high mesopentad fraction and a cold xylene soluble part (CXS ) is less than 1.5% by mass, the areal stretch ratio is 60 times or more during biaxial stretching, and the stretch ratio in the width direction is 10.5 times or more, and the width after uniaxial stretching in the longitudinal direction The preheating temperature immediately before biaxial stretching in the direction can be obtained by setting the stretching temperature in the width direction to +5 to +15°C. In addition, the detailed measuring method of the thermal shrinkage stress value obtained using a thermomechanical analyzer at 130° C. is as described below.

The polypropylene film of the present invention is the sum of the storage elastic moduli (E'135 (MD + TD)) obtained by fixed viscoelasticity measurement at 135 ° C. in the longitudinal direction and the width direction of the film, and at 125 ° C. in the longitudinal direction and the width direction It is preferable that the relationship of the sum of storage elastic moduli (E'125 (MD+TD)) obtained by fixed viscoelasticity measurement satisfies the following equation.
(E'135(MD+TD))/(E'125(MD+TD))>0.80.

The value of (E'135(MD+TD))/(E'125(MD+TD)) is more preferably 0.83 or more, still more preferably 0.86 or more, and most preferably 0.89 or more. The fact that the ratio of the sum of the storage elastic moduli at 135° C. and 125° C. satisfies the above relationship ((E′135 (MD+TD))/(E′125 (MD+TD))>0.80) means that the storage elastic modulus It means that the temperature dependence at high temperature is small, especially in a high temperature environment, the movement and loosening of the film molecular chain is suppressed, and it means that the film has a very stable structure against heat. . That is, it exhibits a high dielectric breakdown voltage even at high temperatures, and can exhibit long-term reliability in a high-temperature environment when used as a capacitor. Although the upper limit of the above relational expression is not particularly limited, it is practically 0.99 or less.

The ratio of the sum of the storage elastic moduli at 135° C. and 125° C. satisfies the above relationship ((E′135 (MD+TD))/(E′125 (MD+TD))>0.80), as described later, For example, using a polypropylene raw material with a high mesopentad fraction and a cold xylene soluble portion (CXS) of less than 1.5% by mass, the area draw ratio is 60 times or more during biaxial stretching, and the width direction draw ratio is 10. .5 times or more, the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction is the stretching temperature in the width direction +5 to +15 ° C., heat setting treatment and relaxation treatment after biaxial stretching. In the process, first, a relaxation treatment is performed while performing a heat treatment (first stage) at a temperature lower than the stretching temperature in the width direction, and then the film is stretched at a temperature lower than the heat treatment temperature in the first stage while maintaining tension in the width direction. ° C. or higher (second stage), and further heat treatment (third stage) under conditions of 80 ° C. or higher and less than the heat treatment temperature of the second stage. It is preferable that the polypropylene film of the present invention has a film dielectric breakdown voltage at 130° C. of 350 V/μm or more. It is more preferably 375 V/μm or more, still more preferably 400 V/μm or more, particularly preferably 420 V/μm or more, and most preferably 440 V/μm or more. Although the upper limit is not particularly limited, it is about 800 V/μm. When the dielectric breakdown voltage of the film at 130°C is 350 V/μm or higher, when the capacitor is used for a long period of time in a high-temperature environment, it is difficult to cause short-circuit breakdown, the withstand voltage is maintained, and high reliability is achieved. Obtainable. In order to control the dielectric breakdown voltage of the film at 130° C. within the above range (350 V/μm or more), for example, a high mesopentad fraction and a cold xylene soluble portion (CXS) of 1.5% by mass are used as described later. Using a polypropylene raw material of less than 100%, the melt extrusion temperature at the die before and after the filter is reduced in multiple stages, and the area draw ratio is 60 times or more and the width direction draw ratio is 10.5 times or more during biaxial stretching. It is possible to obtain by

The polypropylene film of the present invention has few dents on the surface and has moderate slipperiness, so from the viewpoint of improving element processability and improving voltage resistance, at least one surface of the film has a thickness of 1,252 μm × It is preferable that the total valley side volume, which is the sum of the volumes of valleys having a depth of 20 nm or more in the 939 μm region, is 1 to 12,000 μm ³ . From the viewpoint of the lower limit, the total valley side volume is more preferably 300 μm ³ or more, and more preferably 600 μm ³ or more. From the viewpoint of the upper limit, the total valley side volume is more preferably 5,000 μm ³ or less, even more preferably 2,500 μm ³ or less, and particularly preferably 1,000 μm ³ or less.

If the total valley side volume is less than 1 μm ³ , the surface tends to be flat without unevenness. may be affected. In addition, when the capacitor is used for a long time, the change in capacity becomes large due to the effects of wrinkles, etc., and in the case of a capacitor with laminated films, there is no appropriate gap between the films, so it has a self-recovery function (self-recovery function). Healing) is difficult to operate, and the reliability of the capacitor may decrease. On the other hand, if the thickness exceeds 12,000 μm ³ , there are many locally thin portions, and there is a risk that dielectric breakdown will occur from these portions, and the voltage resistance of the film will decrease. voltage resistance and reliability in high temperature environments may be compromised.

By setting the total valley side volume to the above-mentioned preferred range (the total valley side volume is 1 μm ³ or more and 12,000 μm ³ or less), there are few surface dents, the risk of dielectric breakdown occurring at low voltage is reduced, and the withstand voltage of the film is reduced. In particular, when used in high-voltage capacitor applications, it improves voltage resistance and reliability in high-temperature environments, and can suppress changes in capacitance when used as a capacitor for a long period of time. Also, in the case of a capacitor in which films are laminated, a proper gap can be formed between the films, so that a self-healing function can operate and the reliability of the capacitor can be improved.

As a method for controlling the total valley side volume, for example, a polypropylene raw material having a high mesopentad fraction and a cold xylene soluble portion (CXS) of less than 1.5% by mass is used, and the stretching temperature in the longitudinal direction is adjusted within a preferred range. It can be obtained by controlling the area draw ratio to 60 times or more and the width direction draw ratio to 10.5 times or more at the time of biaxial stretching.

In the polypropylene film of the present invention, the polypropylene component dissolved in xylene (CXS, also referred to as cold xylene solubles) is 1.1. It is preferably less than 5% by mass. Here, the cold xylene soluble portion (CXS) is considered to be a component that is difficult to crystallize due to low stereoregularity, low molecular weight, or the like. By reducing the CXS to less than 1.5% by mass, the absolute value of the storage elastic modulus of the film at high temperatures is increased, and the temperature dependence is improved, the dielectric breakdown voltage is increased, and the thermal dimensional stability is improved. can be done. On the other hand, when the CXS is 1.5% by mass or more, the temperature dependence of the storage elastic modulus of the film at high temperatures is inferior, the absolute value of the storage elastic modulus at high temperatures is low, and the dielectric breakdown voltage is lowered. In addition, problems such as deterioration in thermal dimensional stability and increased leakage current may occur. Therefore, CXS is preferably 1.3 wt% or less, more preferably 1.1 wt% or less, even more preferably less than 1.0 wt%, and most preferably less than 0.9 wt%.

In order to achieve such a CXS content (less than 1.5% by mass of CXS), a method of increasing the catalytic activity when obtaining the polypropylene resin to be used, a method of washing the obtained polypropylene resin with a solvent or propylene monomer itself etc. can be used. Although the lower limit of CXS is not particularly limited, it is practically 0.1% by mass. Attempting to make the CXS less than 0.1% by mass may deteriorate the stretchability during film formation and cause tearing.

The polypropylene used for the polypropylene film of the present invention preferably has a melt flow rate (MFR) of 1 to 10 g/10 minutes (230° C., 21.18 N load), more preferably 2 to 5 g/ 10 minutes (230° C., 21.18 N load). In order to set the melt flow rate (MFR) to the above value, a method of controlling the average molecular weight and molecular weight distribution is adopted.

The polypropylene used in the polypropylene film of the present invention is mainly composed of a homopolymer of propylene. Polymers that are not homopolymers may be blended. Examples of monomer components other than propylene constituting such copolymer components and blends include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4- methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene and the like.

The amount of copolymerization or blending other than the propylene component is preferably less than 1 mol % in terms of dielectric breakdown voltage and heat resistance, and the blending amount constitutes the film as the amount of components other than propylene. It is preferably less than 1% by mass of the total resin.

The polypropylene film of the present invention may contain a branched chain polypropylene resin. Specifically, "Profax" (registered trademark) (PF-814, etc.) manufactured by Lyondell Basell, "Daploy" manufactured by Borealis (WB130HMS, WB135HMS, etc.), "WAYMAX" (MFX8, MFX6, MFX3, etc.) can be appropriately selected and used.

Several types of branched chain polypropylene resins, such as Ziegler-Natta catalysts and metallocene catalysts, are commercially available. It is more preferable from the viewpoint of improving capacitor characteristics. The melt tension of the branched polypropylene resin is preferably 2 cN or more and 40 cN or less from the viewpoint of stretching uniformity. The lower limit of the melt tension is more preferably 3 cN or more, more preferably 5 cN or more. The upper limit is more preferably 30 cN or less, and even more preferably 20 cN or less. In order to set the melt tension to the above value, a method of controlling the average molecular weight, molecular weight distribution, and the degree of branching in the polypropylene resin is adopted.

The content of the branched chain polypropylene resin is preferably 0.1 to 10% by mass in the entire film. The lower limit of the branched-chain polypropylene resin content is more preferably 0.15% by mass, and even more preferably 0.2% by mass. On the other hand, the upper limit is more preferably 9% by mass, more preferably 8% by mass. By setting the content of the branched-chain polypropylene resin within the above range, it is possible to easily control the size of the spherulites formed during the cooling process of the melt-extruded resin sheet to be small, and to suppress the formation of insulation defects formed during the stretching process. , a polypropylene film having excellent high-temperature withstand voltage can be obtained.

The polypropylene resin used in the polypropylene film of the present invention contains various additives such as organic particles, inorganic particles, crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, slip agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and anticoloring agents.

When an antioxidant is included among these, the selection of the type and amount of the antioxidant to be added is important from the viewpoint of long-term heat resistance. That is, such antioxidants are preferably phenolic antioxidants having steric hindrance, at least one of which is of a high molecular weight type having a molecular weight of 500 or more. Various specific examples thereof include 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4) and 1,3,5-trimethyl-2,4,6- Tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (for example, BASF Irganox® 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di-t -Butyl-4-hydroxyphenyl)propionate]methane (for example, Irganox (registered trademark) 1010 manufactured by BASF; molecular weight 1,177.7) is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.1 to 1.0% by mass based on the total amount of polypropylene. If the amount of antioxidant is too small, the long-term heat resistance may be poor. If the amount of antioxidant is too large, blocking at high temperature due to bleeding out of these antioxidants may adversely affect the capacitor element. A more preferable total content is 0.2 to 0.7% by weight, particularly preferably 0.2 to 0.4% by weight, based on the total weight of the resin.

The polypropylene film of the present invention preferably has a mesopentad fraction of 0.970 or more. The mesopentad fraction is more preferably 0.975 or more, still more preferably 0.980 or more, and most preferably 0.983 or more.

The mesopentad fraction is an index indicating the stereoregularity of the crystalline phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). It is preferable because it has the effect of increasing the high-temperature storage elastic modulus and can improve the dielectric breakdown voltage in a high-temperature environment. The upper limit of the mesopentad fraction is not particularly specified. In the present invention, the polypropylene resin having a high mesopentad fraction is particularly preferably produced by a so-called Ziegler-Natta catalyst, and a method of appropriately selecting an electron-donating component in the catalyst is preferably employed. has a molecular weight distribution (Mw/Mn) of 3.0 or more and a <2,1> erythro site deficiency of 0.1 mol % or less, and it is preferable to use such a polypropylene resin.

The melting point of the polypropylene resin used in the polypropylene film of the present invention is preferably 164° C. or higher, more preferably 166° C. or higher, still more preferably 167° C. or higher, and most preferably 168° C. or higher. If the melting point of the polypropylene resin is less than 164°C, the crystallinity is low, so the storage elastic modulus at high temperatures is low, and the dielectric breakdown voltage and thermal dimensional stability of the film are lowered in high-temperature environments. In the process of forming a metal film by vapor deposition or in the process of winding a capacitor element, the film may break during transport.

The polypropylene film of the present invention is a melting peak temperature (Tmβ) (°C) observed by DSC measurement at a heating rate β (°C/min) for each of the film heat-treated at 150°C for 1 minute and the untreated film. is the Y axis, and the value obtained by multiplying the temperature increase rate β ⁽ ° C./min) to the power of 0.5 (β ^0.5 ) is the X axis. , the relationship between the y-intercept (H1y) (°C) of the film heat-treated at 150°C for 1 minute and the y-intercept (H0y) (°C) of the untreated film preferably satisfies the following relationship.
(H1y)/(H0y)≧0.90.

The value of (H1y)/(H0y) is preferably 0.92 or greater, more preferably 0.94 or greater, and most preferably 0.96 or greater. The higher this value, the higher the dielectric breakdown voltage even at high temperatures, and the longer the reliability in a high-temperature environment when used as a capacitor. In order to control the value of (H1y)/(H0y) in a preferable range (0.90 or more), for example, a high mesopentad fraction and a cold xylene soluble portion (CXS) of 1.5% by mass are used, as described later. Using a polypropylene raw material of less than 100%, the melt extrusion temperature at the die before and after the filter is reduced in multiple stages, and the area draw ratio is 60 times or more and the width direction draw ratio is 10.5 times or more during biaxial stretching. And, the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction is set to the stretching temperature in the width direction +5 to +15 ° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first , Relaxing treatment is performed while performing heat treatment (first stage) at a temperature lower than the stretching temperature in the width direction, and then heat treatment at 135 ° C. or higher at a temperature lower than the heat treatment temperature in the first stage while maintaining tension in the width direction. (Second stage), and further heat treatment (third stage) under conditions of 80 ° C. or higher and less than the heat treatment temperature of the second stage. is.

It is preferable that the polypropylene film of the present invention has a y-intercept (H1y) (°C) of 155°C or higher after heat treatment at 150°C for 1 minute. A high y-intercept (H1y) (°C) means that the film has a high melting temperature and high heat resistance. Voltage resistance is maintained and high reliability can be obtained. The y-intercept (H1y) (°C) is more preferably 157°C or higher, still more preferably 159°C or higher, and particularly preferably 161°C or higher.

The polypropylene film of the present invention preferably has a sum of F5 values of 15 MPa or more at 130° C. in the longitudinal direction and the width direction of the film. If the sum of the F5 values at 130° C. is 15 MPa or more, it means that sufficient film strength is maintained even at high temperatures. performance is maintained and high reliability can be obtained. The sum of F5 values at 130° C. is more preferably 17 MPa or higher, still more preferably 19 MPa or higher, and particularly preferably 21 MPa or higher.

In order to make the sum of the F5 values at 130° C. 15 MPa or more, as described later, for example, a polypropylene raw material having a high mesopentad fraction and a cold xylene soluble part (CXS) of less than 1.5% by mass is used, At the time of biaxial stretching, the area stretching ratio is 60 times or more, and the stretching ratio in the width direction is 10.5 times or more, and the preheating temperature immediately before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction is The stretching temperature is set to +5 to +15° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first, the relaxation treatment is performed while heat treatment (first stage) is performed at a temperature lower than the stretching temperature in the width direction, and then the relaxation treatment is performed. Heat treatment at 135 ° C. or higher at a temperature lower than the heat treatment temperature in the first stage while maintaining tension in the width direction of the film (second stage), and further heat treatment at 80 ° C. or higher and lower than the heat treatment temperature in the second stage (3 It can be obtained by appropriately subjecting the film to multi-stage heat setting treatment and relaxation treatment.

In a dielectric breakdown test at 130 ° C., the polypropylene film of the present invention has a dielectric breakdown voltage (B150) when heat treated at 150 ° C. for 1 minute and a dielectric breakdown voltage (B0) when no heat treatment is performed. It is preferable to satisfy the relationship.
(B150)/(B0)≧0.80.

The value of (B150)/(B0) is preferably 0.83 or more, more preferably 0.86 or more, even more preferably 0.89 or more, and most preferably 0.94 or more. The higher this value is, the higher the dielectric breakdown voltage is exhibited even at high temperature, and the capacitor can exhibit long-term reliability in a high-temperature environment. In order to satisfy (B150) / (B0) ≥ 0.80, as described later, for example, using a polypropylene raw material having a high mesopentad fraction and a cold xylene soluble part (CXS) of less than 1.5% by mass, Before the filter, after the filter, the melt extrusion temperature in the die is lowered in a multistage manner, the area draw ratio is set to 60 times or more in the biaxial drawing, the draw ratio in the width direction is set to 10.5 times or more, and after uniaxial drawing in the longitudinal direction The preheating temperature immediately before biaxial stretching in the width direction is set to the stretching temperature in the width direction +5 to +15 ° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first, the temperature is lower than the stretching temperature in the width direction. Then, while maintaining tension in the width direction of the film, heat treatment is performed at 135 ° C. or higher at a temperature lower than the heat treatment temperature of the first step (second step), and further at 80 The film can be obtained by appropriately subjecting the film to a multistage heat setting treatment and relaxation treatment in which heat treatment (third stage) is performed at a temperature of 0° C. or more and less than the heat treatment temperature of the second stage.

The polypropylene film of the present invention preferably has a heat shrinkage stress value (SF130MD) (MPa) of 2.0 MPa or less, more preferably 1.7 MPa, obtained using a thermomechanical analyzer at 130 ° C. in the longitudinal direction of the film. Below, more preferably 1.3 MPa or less, most preferably less than 1.0 MPa. When the thermal shrinkage stress value (SF130MD) (MPa) obtained using a thermomechanical analyzer at 130°C in the longitudinal direction of the film is 2.0 MPa or less, the shrinkage of the film itself is suppressed by the heat of the capacitor manufacturing process and usage process. Since the element is not tightly wound, the self-healing function operates by maintaining an appropriate gap between the film layers, suppressing the breakthrough short circuit that accompanies a rapid decrease in capacitance, and improving the reliability of the capacitor. can be enhanced. The lower limit of the thermal shrinkage stress value (SF130MD) (MPa) obtained using a thermomechanical analyzer at 130° C. in the longitudinal direction of the film is not particularly limited, but it is practical to set it to about 0.1 MPa. If the shrinkage stress is lower than 0.1 MPa, the shrinkage of the film itself becomes insufficient due to the heat in the capacitor manufacturing process and use process, and there is a possibility that a sufficient capacity relative to the designed capacity will not be developed.

In order to control the thermal shrinkage stress value obtained using a thermomechanical analyzer in the longitudinal direction of the film at 130 ° C. within a preferable range, for example, a high mesopentad fraction and a cold xylene soluble part (CXS) of 1.5 mass %, the stretch ratio in the width direction is 10.5 times or more during biaxial stretching, and the preheating temperature just before biaxial stretching in the width direction after uniaxial stretching in the longitudinal direction is set to the stretching in the width direction. The temperature is set to +5 to +15 ° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first, the relaxation treatment is performed while performing heat treatment (first stage) at a temperature lower than the stretching temperature in the width direction, and then the film. Heat treatment at 135 ° C. or higher at a temperature lower than the heat treatment temperature of the first stage while maintaining tension in the width direction (second stage), and further heat treatment at a temperature of 80 ° C. or higher and less than the heat treatment temperature of the second stage (3 stages It is possible to obtain the film by appropriately subjecting the film to multistage heat setting treatment and relaxation treatment.

In the polypropylene film of the present invention, the ratio of heat shrinkage stress values (SF130MD)/(SF130TD) obtained using a thermomechanical analyzer at 130 ° C. in the longitudinal direction and the width direction of the film is 0.5 or more and 1.7. The following are preferable. When the ratio of heat shrinkage stress values (SF130MD)/(SF130TD) is in this range, that is, 0.5 or more and 1.7 or less, the balance of heat shrinkage stress is good in the film plane, and the film interlayer when it is made into a capacitor. The uniformity of the gap is improved, and the life and reliability of the capacitor are improved. The lower limit of the value of the ratio (SF130MD)/(SF130TD) of the thermal shrinkage stress values is more preferably 0.8 or more, still more preferably 1.0 or more, and most preferably 1.2 or more. On the other hand, the upper limit of the ratio of the thermal shrinkage stress values (SF130MD)/(SF130TD) is more preferably 1.5 or less, still more preferably 1.4 or less, and most preferably 1.3 or less.

In order to control the ratio of heat shrinkage stress values (SF130MD)/(SF130TD) within a preferable range, that is, 0.5 or more and 1.7 or less, as described later, for example, a high mesopentad fraction and a cold xylene soluble part (CXS) using a polypropylene raw material of less than 1.5% by mass, the areal stretch ratio is 60 times or more during biaxial stretching, and the stretch ratio in the width direction is 10.5 times or more, and after uniaxial stretching in the longitudinal direction The preheating temperature immediately before biaxial stretching in the width direction is set to the stretching temperature in the width direction +5 to +15 ° C., and in the heat setting treatment and relaxation treatment steps after biaxial stretching, first, the temperature is lower than the stretching temperature in the width direction. The relaxation treatment is performed by 2 to 20% while performing heat treatment (first stage) at , and then heat treatment at 135 ° C. or higher at a temperature lower than the heat treatment temperature of the first stage while maintaining tension in the width direction of the film (second stage 3), and further heat treatment (third stage) at 80° C. or higher and below the heat treatment temperature in the second stage.

In the polypropylene film of the present invention, the relationship between the F5 value (F5MD) (MPa) in the longitudinal direction and the F5 value (F5TD) (MPa) in the width direction at room temperature preferably satisfies the following formula.
(F5TD)/(F5MD)≧1.5.

The value of (F5TD)/(F5MD) is more preferably 1.7 or more, still more preferably 1.9 or more, and most preferably 2.1 or more. A polypropylene film with a higher value has a higher degree of orientation in the TD and can exhibit a higher dielectric breakdown voltage even at high temperatures. In order to satisfy (F5TD) / (F5MD) ≥ 1.5, as described later, the area draw ratio is 60 times or more and the width direction draw ratio is 10.5 times or more during biaxial stretching. It is possible to obtain The upper limit of the value of (F5TD)/(F5MD) is not particularly limited as long as it is 1.5 or more, but a practically achievable value is considered to be about 4.0.

The polypropylene film of the present invention has a film thickness of 0.5 μm or more and less than 10 μm from the viewpoint that it is suitable for a thin heat-resistant film capacitor required for automobile applications (including hybrid car applications) that are used in a high-temperature environment. Preferably. It is more preferably 0.6 μm or more and 8 μm or less, still more preferably 0.8 μm or more and 6 μm or less, and is most preferably 0.8 μm or more and 4 μm or less from the viewpoint of balance between characteristics and capacitor size due to thinning for the heat-resistant film capacitor.

The polypropylene film of the present invention is preferably in the form of a single-layer film, but may be in the form of a laminated film.

The polypropylene film of the present invention is preferably used as a dielectric film for capacitors, but the type of capacitor is not limited. Specifically, from the viewpoint of the electrode configuration, it may be either a laminated winding capacitor of metal foil and film, a metal deposition film capacitor, an oil immersion type capacitor impregnated with insulating oil, or a capacitor that does not use insulating oil at all. It is also preferably used for dry capacitors. However, due to the characteristics of the film of the present invention, it is preferably used as a metal-deposited film capacitor. From the viewpoint of the shape, it may be of a wound type or a laminated type.

A polypropylene film usually has a low surface energy, and it is difficult to stably perform metal vapor deposition. Therefore, it is preferable to perform a surface treatment before vapor deposition for the purpose of improving adhesion to a metal film. The surface treatment is specifically exemplified by corona discharge treatment, plasma treatment, glow treatment, flame treatment and the like. Normally, the surface wetting tension of a polypropylene film is about 30 mN/m. It is preferable to set the thickness to about 100 to 100% because the adhesiveness to the metal film is excellent and the security is also improved.

The polypropylene film of the present invention can be obtained by biaxially stretching, heat-treating and relaxing using a raw material capable of imparting the properties described above. As the biaxial stretching method, it can be obtained by any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method. It is preferable to adopt the tenter sequential biaxial stretching method from the viewpoint of controlling the mechanical properties and thermal dimensional stability while increasing the stretch ratio in the width direction of the present invention, in particular the structure and surface properties.

Next, the method for producing the polypropylene film of the present invention will be described as an example. First, a polypropylene resin is melt extruded onto a support to form an unstretched polypropylene film. This unstretched polypropylene film is stretched in the longitudinal direction, then stretched in the width direction, and biaxially stretched successively. Thereafter, heat treatment and relaxation treatment are performed to produce a biaxially oriented polypropylene film. Although more specific description will be given below, the present invention is not necessarily interpreted as being limited to this.

First, the CXS is less than 1.5% by mass from the viewpoint of suppressing the change in the relaxation time T2 of the amorphous component before and after the film is heated, and reducing the dielectric breakdown voltage at high temperatures, the structural stability against heat, and the leakage current. The polypropylene resin is extruded at an extrusion temperature of 220 to 280° C., preferably 230 to 270° C., through a single-screw extruder and passed through a melt-extrusion filtration filter, and then slit-shaped at a temperature of 210 to 240° C. Push out from the mouthpiece. Here, during melt extrusion, the resin is sufficiently melted and the molecular chain length is prevented from being cut due to shearing caused by screw rotation, so that the film structure does not relax even at high temperatures and is stabilized. is set to a low temperature, and the nozzle temperature immediately before ejection is preferably set to a temperature setting that can achieve further low temperature multistage low temperature. The molten sheet extruded from the slit-shaped die is solidified on a casting drum (cooling drum) controlled at a temperature of 40 to 110°C to obtain an unstretched polypropylene film. As a method of contacting the molten sheet to the casting drum, any of the electrostatic application method, the contact method using the surface tension of water, the air knife method, the press roll method, the underwater casting method, and the air chamber method can be used. However, the air-knife method is preferable because it provides good flatness and allows control of surface roughness. Moreover, it is preferable to appropriately adjust the position of the air knife so that the air flows downstream of the film formation so as not to cause vibration of the film. The temperature of the casting drum is preferably 60 to 110° C., more preferably 80 to 110° C., from the viewpoint of improving element workability and voltage resistance by having less dents on the surface and having moderate slipperiness. °C.

Next, the unstretched polypropylene film is biaxially stretched and biaxially oriented. An unstretched polypropylene film is preferably passed between rolls maintained at 70 to 150° C., more preferably 80 to 145° C., and preheated. The film is stretched in the longitudinal direction preferably 2 to 15 times, more preferably 4.5 to 12 times, still more preferably 5.5 to 10 times, while being kept at a temperature of ~145°C, and then cooled to room temperature.

Then, the film uniaxially stretched in the longitudinal direction is guided to a tenter while holding the ends with clips. Here, in the present invention, the temperature in the preheating step immediately before stretching in the width direction is a stretching temperature in the width direction +5 to +15°C, preferably +5 to +12°C, more preferably +5 to +10°C in uniaxial stretching. The fibril structure highly oriented in the direction can be further strengthened, and the change in the relaxation time T2 of the amorphous component before and after the film heating can be suppressed. In addition, it is preferable from the viewpoint that the thermal dimensional stability can be improved by stabilizing the insufficiently oriented molecular chains by preheating at a high temperature after the uniaxial stretching. If the preheating temperature is less than the stretching temperature + 5 ° C., the change in the relaxation time T2 of the amorphous component before and after the film heating cannot be suppressed, and the thermal dimensional stability may not be improved. is higher than the stretching temperature +15°C, the film may be torn during the stretching process.

Next, the temperature at which the film is stretched in the width direction while the edges of the film are held by clips (the temperature for stretching in the width direction) is 150 to 170°C, preferably 155 to 165°C.

From the viewpoint of suppressing and reducing the change in the relaxation time T2 of the amorphous component before and after the film is heated, the stretch ratio in the width direction is 10.5 to 20 times, more preferably 11 to 19 times, and most preferably 11.5 to 18 times. Double. When the stretch ratio in the width direction is less than 10.5 times, the orientation contribution of the fibril structure highly oriented in the longitudinal direction by uniaxial stretching remains largely, so that the change in the relaxation time T2 of the amorphous component before and after the film is heated can be suppressed. It becomes a film that does not exist. Increasing the stretch ratio in the width direction gives the orientation in the width direction while maintaining a high orientation state in the longitudinal direction, so the in-plane molecular chain tension increases and the structural stability against heat can be improved, so there is a trade-off. It is preferable from the viewpoint of considering that the effect of improving the heat shrinkage characteristics can be obtained. On the other hand, if the stretch ratio in the width direction exceeds 20 times, the film tends to tear during film formation, and the productivity may be inferior.

Here, when the area draw ratio is 60 times or more, the change in the relaxation time T2 of the amorphous component before and after the film is heated is suppressed, and when the film is made into a capacitor, it has excellent long-term use reliability in a high-temperature environment. It is preferable from the point of view. In the present invention, the area draw ratio is obtained by multiplying the draw ratio in the longitudinal direction by the draw ratio in the width direction. The area draw ratio is more preferably 64 times or more, still more preferably 68 times or more, and most preferably 72 times or more.

In the production of the polypropylene film of the present invention, in the subsequent heat treatment and relaxation treatment steps, while the width direction is tensely held by the clip and the width direction is relaxed by 2 to 20%, the temperature is 145 ° C. or higher and 165 ° C. or lower, and the width direction After heat-setting (first-stage heat treatment) at a temperature lower than the stretching temperature (first-stage heat treatment temperature), the film is again held with tension in the width direction by a clip at 135°C or higher to the heat-setting temperature (first-stage heat treatment temperature). Heat treatment is performed under conditions below (second heat treatment), and further heat setting (third heat treatment) is performed under conditions of 80 ° C. or higher and less than the above heat setting temperature (second heat treatment temperature) while being tension-held. From the viewpoint of suppressing the change in the relaxation time T2 of the amorphous component before and after the film is heated, improving the structural stability against heat, and obtaining the voltage resistance and reliability of the capacitor. preferable.

In the relaxation treatment, the relaxation rate is preferably 2 to 20%, more preferably 5 to 18%, even more preferably 8 to 15%, from the viewpoint of enhancing structural stability against heat. If it exceeds 20%, the film may become too slack inside the tenter, causing wrinkles in the product, which may cause unevenness during vapor deposition, or cause deterioration in mechanical properties. Structural stability against heat cannot be obtained, and when a capacitor is used in a high-temperature environment, it may cause a decrease in capacity or short-circuit destruction.

After undergoing multi-stage low temperature heat treatment, the film is guided to the outside of the tenter, the clip of the film edge is released at room temperature, the film edge is slit in the winder process, and the film thickness is 0.5 μm or more and less than 10 μm. Rewind product roll. In order to improve the adhesiveness of the vapor-deposited metal to the vapor-deposited surface before winding the film, it is preferable to carry out corona discharge treatment in air, nitrogen, carbon dioxide, or a mixture of these gases.

In order to obtain the polypropylene film of the present invention, specific examples of production conditions to be focused on are as follows.
・Melt extrusion temperature should be lowered in multiple stages, including before the filter, after the filter, and at the nozzle.
- The mesopentat fraction of the polypropylene resin is 0.970 or more. - The CXS of the polypropylene resin is less than 1.5% by mass.
・The area draw ratio of the drawing is 60 times or more.
- The stretch ratio in the width direction is 10.5 times or more.
- The preheating temperature before stretching in the width direction is the stretching temperature in the width direction +5 to +15°C.
- The heat treatment temperature in the first stage is 145°C or higher and 165°C or lower, and is lower than the stretching temperature in the width direction.
・The heat treatment temperature in the second stage must be 135°C or higher and less than the heat treatment temperature in the first stage.
・The temperature of the heat treatment in the third stage should be 80°C or more and less than the temperature of the heat treatment in the second stage.
・2 to 20% relaxation treatment is applied in the width direction in the first stage heat treatment process.

Next, a metal film laminated film using the polypropylene film of the present invention, a film capacitor using the same, and methods for producing them will be described.

The metal film laminated film of the present invention has a metal film on at least one surface of the polypropylene film of the present invention. This metal film laminated film can be obtained by providing a metal film on at least one side of the polypropylene film according to the present invention.

In the present invention, the method of applying a metal film is not particularly limited, but for example, metal such as a vapor deposition film that becomes an internal electrode of a film capacitor by vapor-depositing aluminum or an alloy of aluminum and zinc on at least one side of a polypropylene film A method of providing a membrane is preferably used. At this time, other metal components such as nickel, copper, gold, silver, chromium, etc. can be vapor-deposited simultaneously or sequentially with aluminum. Also, a protective layer can be provided on the deposited film with oil or the like. When the surface roughness of the polypropylene film is different between the front and back surfaces, it is preferable to form a metal film laminated film by providing a metal film on the smooth surface side from the viewpoint of increasing the voltage resistance.

In the present invention, if necessary, after forming the metal film, the metal film laminated film can be annealed at a specific temperature or heat-treated. Also, for insulation or other purposes, at least one surface of the metal film laminated film can be coated with a resin such as polyphenylene oxide.

The film capacitor of the present invention uses the metal film laminated film of the present invention. That is, the film capacitor of the present invention has the metal film laminated film of the present invention.

For example, the film capacitor of the present invention can be obtained by laminating or winding the above metal film laminated film of the present invention by various methods. A preferred method for manufacturing a wound film capacitor is as follows.

Aluminum is vapor-deposited on one side of a polypropylene film under reduced pressure. At that time, vapor deposition is performed in stripes having margins running in the longitudinal direction. Next, a blade is inserted into the center of each vapor-deposited portion and the center of each margin portion on the surface to form a slit, thereby forming a tape-shaped take-up reel having a margin on one side of the surface. A tape-shaped take-up reel having a margin on the left or right is wound by stacking two reels each of the left margin and the right margin so that the vapor-deposited portion protrudes from the margin in the width direction, and a wound body is obtained. get

When vapor deposition is performed on both sides, vapor deposition is performed in stripes having a margin running in the longitudinal direction on one surface, and stripes are deposited on the other surface so that the margin in the longitudinal direction is positioned in the center of the vapor deposition on the back side. evaporate in a shape. Next, a blade is inserted in the center of the margins on the front and back sides to form a slit to produce a tape-shaped take-up reel having margins on one side on both sides (for example, if there is a margin on the right side on the front side, a margin on the left side on the back side). Two sheets of the obtained reel and one undeposited laminated film are superimposed and wound so that the metallized film protrudes from the laminated film in the width direction to obtain a wound body.

A wound film capacitor can be obtained by removing the core material from the wound body prepared as described above, pressing it, thermally spraying metallikon on both end surfaces to form external electrodes, and welding lead wires to the metallikon. Film capacitors are used in a wide variety of applications, including railway vehicles, automobiles (hybrid cars and electric vehicles), solar power generation, wind power generation, and general household appliances, and the film capacitor of the present invention is suitable for these applications. can be used. In addition, it can be used for various purposes such as packaging films, release films, process films, sanitary goods, agricultural goods, construction goods, and medical goods.

The method for measuring characteristic values and the method for evaluating effects in the present invention are as follows.

(1) Film Thickness The thickness of the polypropylene film at 10 arbitrary points was measured in an atmosphere of 23° C. and 65% RH using a contact electronic micrometer (K-312A type) manufactured by Anritsu Corporation. The arithmetic mean value of the thicknesses at the 10 locations was taken as the film thickness (unit: μm) of the polypropylene film.

(2) NMR relaxation times (T2B) (μs) and (T2A) (μs) and their ratio (T2B)/(T2A)
The method of heat-treating the film at 150°C for 1 minute uses a square metal frame with a thickness of 2 mm, an outer dimension of 300 mm x 300 mm and an inner dimension of 280 mm x 280 mm and a width of 20 mm. A tape ("Nice Tac" NW-H15 adhesive strength 02, manufactured by Nichiban Co., Ltd.) is attached, a film is attached so that the film covers the entire surface of the metal frame, and the film is sandwiched between metal frames of the same size. At this time, the film is attached so as not to cause wrinkles. Next, a sample was prepared by fixing four sides of the frame with clips in a state of metal frame/double-sided tape/film/metal frame, and left in an oven heated to 150° C. for 1 minute. After 1 minute, the sample was taken out and allowed to stand at room temperature for 5 minutes, and then the film was cut out along the inner frame of the metal frame to obtain a film after heat treatment at 150°C for 1 minute. When a film with dimensions of 300 mm x 300 mm was not obtained, a metal frame with dimensions that could be attached was used.

Next, the relaxation time (T2B) (μs) of the amorphous component of the polypropylene film by the pulse NMR method before the heat treatment at 150° C. for 1 minute, and the relaxation time (T2A) of the amorphous component of the polypropylene film by the pulse NMR method after the treatment. (μs) was obtained using the following equipment and conditions, and the ratio (T2B)/(T2A) was calculated.
Apparatus: mq20 manufactured by Bruker Biospin
Temperature: 40°C
Observation frequency: 20MHz
90° pulse width: 2.74 μs
Pulse repetition time: 2.0s
Pulse mode: Solido Echo method For the measurement, the film before heat treatment and the film after heat treatment were cut and packed into a glass tube with an outer diameter of 10 mm to a height of 1 cm. , the spin-spin relaxation time T2 of ¹ H nucleus was determined for the amorphous component of the polypropylene film. The measurement was started after the film was placed in the apparatus and kept warm for 15 minutes, and the attenuation curve obtained was separated into a short Gaussian function component of T2 and a long exponential function component of T2 by the method of least squares. The short-time component corresponds to the crystalline component, and the long-term component corresponds to the amorphous component.

(3) Ratio of the sum of storage elastic moduli ((E'135 (MD + TD)) / (E'125 (MD + TD)))
Using the following equipment and conditions, a rectangular polypropylene film (width (short side) 10 mm x length (long side) 50 mm) cut out with the film trial length direction (longitudinal direction or width direction) as the long side direction is cut into 23 C. atmosphere, and the temperature was raised from 23.degree. C. to 260.degree. A viscoelasticity-temperature curve was drawn by the dynamic viscoelasticity method, and the storage modulus (E'125) (GPa) at 125°C and the storage modulus (E'135) (GPa) at 135°C were read. The number of measurement tests was n = 5, and the average value of the remaining n = 3 excluding the maximum and minimum values was taken as the storage elastic modulus in that direction, and each direction in the longitudinal direction and width direction of the film. measured in From the obtained results, the sum of the storage moduli in the longitudinal direction and the width direction at 125 ° C. (E'125 (MD + TD)) (GPa), and the sum of the storage modulus in the longitudinal direction and the width direction at 135 ° C. (E '135 (MD+TD)) (GPa) was calculated, and ((E'135 (MD+TD))/(E'125 (MD+TD))) was calculated.

Apparatus: EXSTAR DMS6100 (manufactured by Seiko Instruments Inc.)
Test mode: Tensile mode Distance between chucks: 20mm
Frequency: 1Hz
Strain amplitude: 10.0 μm
Gain: 1.5
Force amplitude initial value: 400mN
Temperature range: 23-260°C
Heating rate: 2°C/min Measurement atmosphere: Nitrogen Measurement thickness: The film thickness was obtained by the method (1) above.

(4) Heat shrinkage stress (SF130MD) (MPa) and (SF130TD) (MPa) at 130°C in the longitudinal and width directions of the film, ratio of heat shrinkage stress at 130°C ((SF130MD)/(SF130TD))
A polypropylene film was cut into a rectangular sample having a width of 4 mm and a length of 50 mm with the long side in the measurement direction (longitudinal direction and width direction) of the film, and the film was sandwiched between metal chucks so as to have a sample length of 20 mm. The sample sandwiched between the chucks was set in the apparatus described below, and stress curves in the longitudinal direction and the width direction of the film whose test length was kept constant under the temperature program described below were obtained. From the obtained stress curve, the shrinkage stress (SF130MD) (MPa) and (SF130TD) (MPa) of the film at 130° C. were read. The 130° C. heat shrinkage stress ratio ((SF130MD)/(SF130TD)) was calculated from the ratio of the longitudinal direction (SF130MD) (MPa) and the width direction (SF130TD) (MPa).

Apparatus: Thermomechanical analyzer TMA/SS6000 (manufactured by Seiko Instruments Inc.)
Test mode: L control mode Test length: 20 mm
Temperature range: 23-200°C
Heating rate: 10° C./min SS program: 0.1 μm/min Measurement atmosphere: Nitrogen Measured thickness: The film thickness of (1) above was used.

(5) Film dielectric breakdown voltage (V/μm) at 130°C
After heating the film for 1 minute in an oven maintained at 130° C., the film was measured in that atmosphere according to JIS C2330 (2001) 7.4.11.2 B method (plate electrode method). However, for the lower electrode, on top of the metal plate described in JIS C2330 (2001) 7.4.11.2 B method, "Conductive rubber E-100 <65>" made by Sogawa Rubber Co., Ltd. with the same dimensions is placed. was used as an electrode. The dielectric breakdown voltage test was performed 30 times, and the obtained value was divided by the film thickness (measured in (1) above), converted to (V / μm), and measured values (calculated values) at a total of 30 points. The average value of 20 points obtained by excluding 5 points in descending order from the maximum value and 5 points in ascending order from the minimum value was taken as the dielectric breakdown voltage of the film at 130°C.

(6) Total volume of valleys with a depth of 20 nm or more on the film surface (total valley side volume)
VertScan 2.0 R5300GL-Lite-AC manufactured by Ryoka Systems Co., Ltd. was used for the measurement, and analysis was performed using the bearing function, which is an analysis tool of the attached analysis software. In order to specify valley-side gaps with a depth of 20 nm or more, the valley-side height threshold was set to −20 nm in the height region specification. The value of the analyzed valley side void volume was then read and rounded to two significant figures.

In addition, when both sides of the film are measured and the total valley side volume is within the range of 1 to 12,000 μm ³ , the value of the side that is within the range (when both sides are within the range , the value of the side with the smaller value), and when both sides did not fall within the range, the value of the side whose total valley side volume was close to the range of 1 to 12,000 μm ³ was noted.

The measurement conditions are as follows.
Manufacturer: Ryoka System Co., Ltd. Device name: VertScan2.0 R5300GL-Lite-AC
Measurement conditions: CCD camera SONY HR-57 1/2 inch (1.27 cm)
objective lens 10x
Intermediate lens 0.5x
Wavelength filter 520nm white
Measurement mode: Phase
Measurement software: VS-Measure Version 5.5.1
Analysis software: VS-Viewer Version 5.5.1
Measurement area: 1.252 x 0.939 ^mm2 .

(7) Cold xylene soluble portion of film (CXS)
0.5 g of a polypropylene resin in the case of a raw material and a film sample in the case of a film were dissolved in 100 ml of xylene at 135°C, left to cool, recrystallized in a constant temperature water bath at 20°C for 1 hour, and then dissolved in the filtrate. The polypropylene component contained in the sample was quantified by liquid chromatography. The following formula CXS (%) = (X / X0) × 100, where X (g) is the amount of the polypropylene-based component dissolved in the filtrate and X0 (g) is the precision value of 0.5 g of the sample.
calculated from

(8) Mesopentad fraction In the case of the raw material, the polypropylene resin, and in the case of the film, the film sample was powdered by freeze-pulverization and extracted with n-heptane at 60°C for 2 hours to remove impurities and additives in the polypropylene. After that, dried under reduced pressure at 130° C. for 2 hours or more was used as a sample. The sample was dissolved in a solvent, and mesopentad fraction (mmmm) was determined using ¹³ C-NMR under the following conditions.

Measurement conditions/apparatus: Bruker DRX-500
・Measurement nucleus: ^13C nucleus (resonance frequency: 125.8MHz)
・Measured concentration: 10% by mass
・ Solvent: benzene: heavy orthodichlorobenzene = 1:3 mixed solution (volume ratio)
・Measurement temperature: 130°C
・Spin speed: 12Hz
・ NMR sample tube: 5 mm tube ・ Pulse width: 45 ° (4.5 μs)
・Pulse repetition time: 10 seconds ・Data points: 64K
・Number of times of accumulation: 10,000 times ・Measurement mode: complete decoupling
Analysis conditions Fourier transform was performed with LB (line broadening factor) set to 1, and the mmmm peak was set to 21.86 ppm. Peak splitting was performed using WINFIT software (manufactured by Bruker). At that time, peak division is performed from the peak on the high magnetic field side as follows, automatic fitting of software is performed, and the peak division is optimized, and the sum of the mmmm peak fractions is the mesopentad fraction (mmmm).
(1) Mrrm
(2)(3)rrrm (split as two peaks)
(4) rrrr
(5) mrmr
(6) mrmm + rmrr
(7) mmrr
(8) rmmr
(9) mmmr
(10)mmmm
The same measurement was performed 5 times for the same sample, and the average value of the obtained mesopentad fractions was taken as the mesopentad fraction of the sample.

(9) Melting Point of Polypropylene Resin Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), a 3 mg polypropylene chip is heated from 30° C. to 260° C. at 20° C./min in a nitrogen atmosphere. Then, after holding at 260° C. for 5 minutes, the temperature is lowered to 30° C. at 20° C./min. Further, after holding at 30° C. for 5 minutes, the temperature is raised from 30° C. to 260° C. at 20° C./min. The peak temperature of the endothermic curve obtained during this temperature rise was taken as the melting point of the polypropylene resin. When multiple peak temperatures were observed, the highest temperature was taken as the melting point (unit: °C) of the polypropylene resin.

(10) F5 value ratio (F5TD)/(F5MD)
A rectangular polypropylene film (width (short side) 10 mm×length (long side) 150 mm) cut out with the longitudinal direction (longitudinal direction or width direction) as the long side direction was used as a measurement sample. Next, the sample tensile tester (Tensilon UCT-100 manufactured by Orientec) was set at an initial chuck distance of 20 mm, and a tensile test was performed on the film at a tensile speed of 300 mm/min under room temperature. At this time, the position of the sample in the longitudinal direction was adjusted so that the center of the sample was located near the center between the chucks. The load applied to the film when the sample elongation is 5% is read, and the value obtained by dividing the cross-sectional area of the sample before the test (film thickness x width (10 mm)) is the stress when the elongation is 5% (F5 value, unit: MPa). The measurement is performed five times each for the sample for measurement in the longitudinal direction and the width direction, and as the arithmetic average value, the F5 value (F5MD) (MPa) and (F5TD) (MPa) in the longitudinal direction and the width direction are obtained. A ratio of F5TD)/(F5MD) was determined.

For the film thickness used for calculating the F5 value, the value measured in (1) above was used.

(11) Evaluation of film capacitor characteristics (reliability at 120°C)
On one side of the film (if the wetting tension is different on the front and back sides, the side with the higher wetting tension) is coated with aluminum using a vacuum deposition machine manufactured by ULVAC, Inc. perpendicularly to the longitudinal direction with a film resistance of 10 Ω / sq. Vapor deposition is performed with a deposition pattern having a so-called T-shaped margin (longitudinal pitch (cycle) of 17 mm due to masking oil, fuse width of 0.5 mm), and after slitting, a film width of 50 mm (edge A deposition reel with a margin width of 2 mm was obtained.

Then, using this reel, the capacitor element was wound by an element winding machine (KAW-4NHB) manufactured by Kaito Seisakusho Co., Ltd. After applying metallikon, it was subjected to heat treatment at a temperature of 130° C. for 8 hours under reduced pressure. A lead wire was attached to complete the capacitor element.

Using ten capacitor elements thus obtained, a voltage of 250 VDC is applied to the capacitor elements at a high temperature of 120° C., and after 10 minutes at this voltage, the applied voltage is gradually increased stepwise at 50 VDC/1 minute. A so-called step-up test was performed by repeating the above.

<Reliability>
After increasing the voltage until the capacitance decreased to 12% or less of the initial value, the capacitor element was disassembled and the state of destruction was examined to evaluate the reliability as follows.
⊚: No change in the shape of the element, and no penetrating breakage was observed.
◯: No change in element shape, and penetrating breakage within 5 layers of the film is observed.
F: There is no change in the element shape, and penetration-like destruction is observed in 6 to 10 layers of the film.
Δ: A change in the element shape is observed, or a penetrating breakdown of more than 10 layers is observed.
x: The device shape is greatly changed and destroyed. Δ and x are inferior in practical performance.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

(Example 1)
Manufactured by Prime Polymer Co., Ltd., which has a mesopentad fraction of 0.984, a melting point of 168° C., a melt flow rate (MFR) of 2.5 g/10 min, and a cold xylene soluble portion (CXS) of 0.8% by mass. A polypropylene resin is supplied to an extruder at a temperature of 255 ° C. and melted, passed through a pipe set at 250 ° C. after passing through a filtration filter, melted and extruded into a sheet from a T-type slit die set at 245 ° C., and the melted sheet. were brought into close contact with each other by an air knife on a casting drum maintained at 77° C. and solidified by cooling to obtain an unstretched polypropylene film. The unstretched polypropylene film was preheated step by step to 142° C. by a plurality of roll groups, passed as it was between rolls provided with a difference in peripheral speed, and stretched 6.3 times in the longitudinal direction. Subsequently, the film was guided to a tenter, preheated at a temperature of 169 ° C. (TD stretching temperature + 8 ° C.) while holding both ends of the film width with clips, and then stretched 12.3 times in the width direction at a temperature of 161 ° C. . Further, as the first heat treatment and relaxation treatment, heat treatment was performed at 158° C. while giving 11% relaxation in the width direction, and further heat treatment was performed at 143° C. as the second heat treatment while being held by clips in the width direction. Finally, as the third stage of heat treatment, the film is guided to the outside of the tenter through heat treatment at 114°C, the clips at the ends of the film are released, and then the film surface (the casting drum contact surface side) is applied to the film surface (the casting drum contact surface side) at a treatment intensity of 25 W min/m ² in the atmosphere. A corona discharge treatment was performed in the inside, and a film having a thickness of 2.2 μm was wound up as a film roll. The properties and capacitor properties of the polypropylene film of this example are shown in the table. The quality was also excellent.

(Examples 2 and 3)
Manufactured by Prime Polymer Co., Ltd., which has a mesopentad fraction of 0.981, a melting point of 166° C., a melt flow rate (MFR) of 3.0 g/10 min, and a cold xylene soluble portion (CXS) of 1.4% by mass. Example 1 was performed in the same manner as in Example 1 except that a polypropylene resin was used and the temperature of the casting drum for cooling the melt extruded sheet, the draw ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions were set to the conditions shown in the table. No. 2 obtained a polypropylene film having a thickness of 2.1 μm, and Example 3 obtained a polypropylene film having a thickness of 2.2 μm. The properties and capacitor properties of the polypropylene films of Examples 2 and 3 are as shown in the table. It was at a level where there was no problem with reliability.

(Example 4)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.982, a melting point of 167° C., a melt flow rate (MFR) of 3.0 g/10 min, and a cold xylene soluble portion (CXS) of 0.8% by mass. Example 1 was performed in the same manner as in Example 1 except that a polypropylene resin was used and the temperature of the casting drum for cooling the melt extruded sheet, the draw ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions were set to the conditions shown in the table. 4 obtained a polypropylene film having a thickness of 2.1 μm. The properties and capacitor properties of the polypropylene film of this example are shown in the table. It was at a level where there was no problem with the above reliability.

(Example 5)
Manufactured by Prime Polymer Co., Ltd., which has a mesopentad fraction of 0.981, a melting point of 166° C., a melt flow rate (MFR) of 3.0 g/10 min, and a cold xylene soluble portion (CXS) of 1.4% by mass. The polypropylene resin was blended with 1.0% by mass of a branched polypropylene resin (high melt tension polypropylene Profax PF-814) manufactured by Basell, and supplied to an extruder at a temperature of 260° C. to obtain a melt extruded sheet. The temperature of the casting drum to be cooled, the stretch ratio during biaxial stretching, the TD preheating, the TD stretching, and the heat treatment conditions were set to the conditions shown in the table in the same manner as in Example 2. Example 3 obtained a polypropylene film with a thickness of 2.2 μm. The properties and capacitor properties of the polypropylene film of Example 5 are shown in the table. The relationship of the relaxation time ratio (T2B)/(T2A) and the relationship of the film melting point y-intercept ratio (H1y)/(H0y) were good, and the reliability of the capacitor in practical use was at a satisfactory level.

(Example 6)
The temperature of the casting drum for cooling the melt extruded sheet was set to 50 ° C., and the stretch ratio during biaxial stretching, TD stretching, and heat treatment conditions were set to the conditions shown in the table. A 0.3 μm polypropylene film was obtained. As shown in the table, the properties of the polypropylene film of this example and the capacitor properties show that the ratio of the NMR relaxation times (T2B)/(T2A) before and after heating at 150°C for 1 minute is good, and the capacitor is reliable in practical use. It was a level that did not cause any problems.

(Example 7)
Manufactured by Prime Polymer Co., Ltd., which has a mesopentad fraction of 0.984, a melting point of 168° C., a melt flow rate (MFR) of 2.5 g/10 min, and a cold xylene soluble portion (CXS) of 0.8% by mass. 3.0% by mass of branched chain polypropylene resin (“WAYMAX” MFX3) manufactured by Japan Polypropylene Co., Ltd. is blended with polypropylene resin, supplied to an extruder at 255 ° C. and melted, and a pipe set at 250 ° C. after passing through a filtration filter. A melt-extruded sheet was obtained in the form of a sheet from a T-shaped slit die set at 245°C. The temperature of the casting drum for cooling the melt extruded sheet, the stretch ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions were the same as in Example 1, and in Example 9 a polypropylene film with a thickness of 2.2 μm was obtained. . The characteristics and capacitor characteristics of the polypropylene film of this example are as shown in the table. B150)/(B0) relationship, relationship of NMR relaxation time ratio (T2B)/(T2A) before and after heating at 150°C for 1 minute, relationship of film melting point y-intercept ratio (H1y)/(H0y) are very good. And the reliability as a capacitor was also excellent.

(Comparative example 1)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.981, a melting point of 166° C., a melt flow rate (MFR) of 4.0 g/10 min, and a cold xylene soluble portion (CXS) of 1.8% by mass. A polypropylene resin is supplied to an extruder at a temperature of 255°C, melted, and melt-extruded into a sheet from a T-shaped slit die with the resin temperature set to 255°C after passing through a filtration filter, and the melt-extruded sheet is cooled. In Comparative Example 1, a polypropylene film with a thickness of 2.2 μm was obtained in the same manner as in Example 1 except that the temperature of the casting drum, the draw ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions were set to the conditions shown in the table. . The properties and capacitor properties of the polypropylene film of Comparative Example 1 are shown in the table.

The polypropylene film of Comparative Example 1 has no gradient in the extrusion temperature, contains a large amount of CXS as a raw material, and has a low areal draw ratio. As for the reliability of the capacitor, the change in the shape of the element was observed and the capacitor was destroyed, which was at a level that would pose a problem in actual use.

(Comparative Examples 2, 3, 4)
Comparative Examples 2, 3, and 4 were prepared in the same manner as in Example 1, except that the temperature of the casting drum for cooling the melt-extruded sheet, the stretch ratio during biaxial stretching, the TD preheating, the TD stretching, and the heat treatment conditions were set to the conditions shown in the table. A polypropylene film having a thickness of 2.3 μm was obtained.

As shown in the table, the polypropylene film of Comparative Example 2 had the same TD preheating temperature and TD stretching temperature, and was not subjected to multistage heat treatment. The relationship of the NMR relaxation time ratio (T2B)/(T2A) before and after heating at 150°C for 1 minute was insufficient, and changes in the element shape were observed in the reliability of the capacitor. rice field.

In addition, the polypropylene film of Comparative Example 3 has a high MD draw ratio and a low TD draw ratio, so the F5 value ratio is small, and the MD film heat shrinkage stress is high, and the storage elastic modulus of 135 ° C. and 125 ° C. The ratio (T2B)/(T2A) of the NMR relaxation time before and after heating at 150°C for 1 minute is insufficient, and the reliability of the capacitor varies depending on the element shape. It was damaged and destroyed, and it was a level that became a problem in actual use.

Furthermore, the polypropylene film of Comparative Example 4 has a low preheating temperature for TD stretching, and the heat treatment condition is a two-step heat treatment of low temperature 130 ° C./high temperature 140 ° C., so the film heat shrinkage stress is high in both MD and TD, and 135 ° C. The ratio of the storage modulus at 125 ° C. and the dielectric breakdown voltage at 130 ° C. are insufficient, the thermal stability is poor, and the relationship between the NMR relaxation time ratio (T2B) / (T2A) before and after heating at 150 ° C. for 1 minute is inadequate. Since it was sufficient, the reliability of the capacitor was broken due to a change in the element shape, which was at a level that poses a problem in actual use.

(Comparative Example 5)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.972, a melting point of 165°C, a melt flow rate (MFR) of 4.0 g/10 min, and a cold xylene soluble portion (CXS) of 2.4% by mass. A comparative example was prepared in the same manner as in Example 1 except that a polypropylene resin was used and the temperature of the casting drum for cooling the melt extruded sheet, the draw ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions were set to the conditions shown in the table. 5, a polypropylene film having a thickness of 2.2 μm was obtained. The properties and capacitor properties of the polypropylene film of this comparative example are shown in the table. was high, and the relationship of the NMR relaxation time ratio (T2B)/(T2A) before and after heating at 150°C for 1 minute was insufficient. was at a problematic level.

(Comparative Example 6)
Manufactured by Prime Polymer Co., Ltd., which has a mesopentad fraction of 0.979, a melting point of 167° C., a melt flow rate (MFR) of 2.6 g/10 min, and a cold xylene soluble portion (CXS) of 1.8% by mass. Using a polypropylene resin, the temperature of the casting drum for cooling the melt extruded sheet, the stretch ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions are the conditions shown in the table, and the first stage heat treatment and relaxation treatment are performed in the width direction. A polypropylene film having a thickness of 2.3 μm was obtained in Comparative Example 6 in the same manner as in Example 1, except that 25% relaxation was applied. As shown in the table, the properties and capacitor properties of the polypropylene film of this comparative example are as follows: the cold xylene soluble portion (CXS) of the film is large; Therefore, the ratio of the storage elastic modulus at 135°C and 125°C and the dielectric breakdown voltage at 130°C were insufficient, and the thermal stability was poor. ) was insufficient, the reliability of the capacitor was destroyed due to changes in the element shape.

(Comparative Example 7)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.975, a melting point of 165° C., a melt flow rate (MFR) of 4.6 g/10 min, and a cold xylene soluble portion (CXS) of 1.4% by mass. 80% by mass of polypropylene resin, a mesopentad fraction of 0.970, a melting point of 164° C., a melt flow rate (MFR) of 0.4 g/10 min, and a cold xylene soluble part (CXS) of 1.4% by mass Using 20% by mass of polypropylene resin manufactured by Japan Polypropylene Corporation, the temperature of the casting drum for cooling the melt extruded sheet, the stretch ratio during biaxial stretching, the TD preheating, the TD stretching and the heat treatment conditions are the conditions shown in the table. A polypropylene film having a thickness of 2.2 μm was obtained. As shown in the table, the properties and capacitor properties of the polypropylene film of this comparative example were as follows: the TD preheating temperature and the TD stretching temperature were the same, the area stretch ratio was low, and heat treatment was not performed. and the dielectric breakdown voltage at 130 ° C. were insufficient, the thermal stability was poor, and the relationship of the NMR relaxation time ratio (T2B) / (T2A) before and after heating at 150 ° C. for 1 minute was insufficient. As for reliability, a change in the element shape was observed and the element was destroyed, which was at a level that poses a problem in actual use.

(Comparative Example 8)
The temperature of the casting drum for cooling the melt extruded sheet was set to 25° C., and the stretch ratio during biaxial stretching, TD stretching, and heat treatment conditions were set to the conditions shown in the table. A 0.3 μm polypropylene film was obtained. As shown in the table, the properties and capacitor properties of the polypropylene film of this comparative example are as follows: the temperature of the casting drum is as low as 25°C; Due to the two-stage heat treatment, the relationship of the ratio (T2B)/(T2A) of the NMR relaxation time before and after heating at 150°C for 1 minute is insufficient, and the reliability of the capacitor has been recognized to change depending on the element shape. , was at a level that poses a problem in actual use.

Claims (9)

Regarding the relaxation time T2 of the amorphous component obtained by the pulse NMR method, the relationship between the relaxation time (T2A) (μs) after heat treatment at 150° C. for 1 minute and the relaxation time (T2B) (μs) before heat treatment is , a polypropylene film that satisfies the following formula:
(T2B)/(T2A) ≥ 0.90 The polypropylene film according to claim 1, wherein the heat shrinkage stress value (SF130TD) (MPa) at 130°C in the width direction determined using a thermomechanical analyzer is 2.0 MPa or less. Sum of storage elastic modulus (E'135 (MD + TD)) determined by fixed viscoelasticity measurement at 135 ° C in the longitudinal direction and the width direction, and determined by fixed viscoelasticity measurement at 125 ° C in the longitudinal direction and the width direction 3. The polypropylene film according to claim 1, wherein the relationship of the sum of storage elastic moduli (E'125(MD+TD)) satisfies the following formula.
(E'135 (MD+TD))/(E'125 (MD+TD))>0.80 The polypropylene film according to any one of claims 1 to 3, which has a dielectric breakdown voltage of 350 V/μm or more at 130°C. 5. The method according to any one of claims 1 to 4, wherein, on at least one surface, the total valley side volume, which is the sum of the volumes of valleys with a depth of 20 nm or more in an area of 1,252 µm × 939 µm, is 1 to 12,000 µm ³ . polypropylene film. The polypropylene according to any one of claims 1 to 5, wherein the polypropylene component (CXS) dissolved in xylene is less than 1.5% by weight when precipitated at room temperature after complete dissolution in xylene. the film. The polypropylene film according to any one of claims 1 to 6, wherein the relationship between the F5 value (F5MD) (MPa) in the longitudinal direction and the F5 value (F5TD) (MPa) in the transverse direction at room temperature satisfies the following formula.
(F5TD)/(F5MD)≧1.5 A metal film laminated film comprising a metal film on at least one surface of the polypropylene film according to any one of claims 1 to 7. A film capacitor comprising the metal film laminated film according to claim 8 .