JP7318187B2 - Polypropylene film, metal film laminated film and film capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polypropylene film, a metal film laminated film and a film capacitor.

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 capacitor applications, polypropylene is particularly preferably used for high-voltage capacitors, not only for direct current and alternating current applications, because of its excellent voltage resistance and low loss characteristics.

In recent years, various electrical equipment is being converted to inverters, and along with this, the demand for smaller size capacitors and larger capacity capacitors is becoming stronger. In response to the demand from such markets, especially for automobile applications (including hybrid car applications), solar power generation, and wind power generation, we have improved the dielectric breakdown voltage of polypropylene film, and made it even thinner while maintaining productivity and workability. It has become a situation where it is essential to change

It is particularly important for such a polypropylene film to improve the crystallinity of the film from the viewpoints of improvement in dielectric breakdown voltage, productivity, workability and heat resistance, and at the same time to have excellent dimensional stability at the temperature of the environment in which it is used. From the viewpoint of heat resistance, it is said that the temperature of the environment in which SiC is used will become even higher when power semiconductor applications using SiC are considered in the future. Due to the demand for further heat resistance and 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, it is said that the upper limit of the operating temperature of the polypropylene film is about 110° C., and it is extremely difficult to stably maintain the dielectric breakdown voltage under such a temperature environment.

Until now, as a method for obtaining thin film and performance in a high temperature environment in polypropylene film, for example, a polypropylene resin composition containing polypropylene resin as a main component contains polymethylpentene to form fine unevenness on the surface. Techniques have been proposed (for example, Patent Documents 1 and 2). In addition, for release applications, polymethylpentene has a low surface free energy, and a biaxially oriented polypropylene film with excellent releasability and smoothness has been developed. (For example, Patent Literatures 3 and 4) In Patent Literature 5, a phenolic antioxidant having a melting point of 140° C. or less and polymethylpentene are added and corona treatment is performed to reduce the occurrence of blocking during processing, and the element after winding is reduced. proposed a film for capacitors with high adhesion strength. However, none of the polypropylene films described in Patent Documents 1 to 5 has a sufficient improvement in dielectric breakdown voltage in an environment of 115 ° C., and furthermore, when used as a capacitor, it has high voltage resistance and reliability in a high temperature environment. Also, it was difficult to say that it was sufficient.

JP 2016-191059 A JP 2014-114419 A JP 2014-030974 A JP 2008-189795 A JP-A-09-270361

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

Therefore, the present invention provides a polypropylene film that exhibits a higher dielectric breakdown voltage even in a high-temperature environment and can exhibit voltage resistance and reliability even in a high-temperature environment when made into a capacitor, a metal film laminated film and a film capacitor using the same. intended to provide

The present inventors have made intensive studies to solve the above problems, and have found that the dielectric breakdown voltage of the polypropylene films described in Patent Documents 1 to 5 in a high-temperature environment, and the voltage resistance and reliability when used as a capacitor. The reason why is not sufficient is considered as follows.

That is, the polypropylene films of Patent Documents 1, 2 and 5 have low crystallinity because the stereoregularity of the polypropylene resin is not sufficiently high, and the polypropylene films described in Patent Documents 3 and 4 contain polymethylpentene. In addition, the polypropylene film described in Patent Document 5 has a single-layer structure, so it is difficult to obtain a film with excellent slipperiness. of polymethylpentene, the dielectric breakdown strength of the film is lowered, and the film surface becomes too rough.

Based on the above considerations, the present inventors have further studied, and found that the heat of fusion indicating the melting point and crystal content of the polypropylene resin is above a certain level, and the arithmetic mean height (Sa) of at least one surface of the film , and that the maximum height (Sz) is within a predetermined range, the above problems can be solved. Therefore, in the configuration of the present invention, the film contains 0.1% by mass or more and 4% by mass or less of polymethylpentene as a thermoplastic resin incompatible with polypropylene, and the film is a laminated film having three or more layers. The content of polymethylpentene , which is incompatible with polypropylene in the surface layer (layer A , the thickness from the minimum to 30% from the surface side when the thickness of the film is 100%) is the inner layer ( B layer), when the film is completely dissolved in xylene and then precipitated at room temperature, the polypropylene component (CXS) dissolved in xylene is less than 1.5% by mass relative to the total mass of the film The mesopentad fraction of the film is 0.970 or more, and the film is heated from 30° C. to 260° C. at a rate of 20° C./min with a differential scanning calorimeter (DSC), and then from 260° C. to 30° C. at 20° C. The melting peak temperature (T _m2 ) is 164° C. or higher when the temperature is lowered at a rate of 20° C./min and then reheated from 30° C. to 260° C. at a rate of 20° C./min. The sum of the heat of fusion in the 100° C. to 180° C. region of the DSC curve is 105 J/g or more, the arithmetic mean height Sa of at least one surface of the film is 5 to 20 nm, and the maximum height Sz is 100 to 500 nm. A polypropylene film.

The present invention provides a polypropylene film that exhibits a high dielectric breakdown voltage even in a high-temperature environment and can exhibit voltage resistance and reliability even in a high-temperature environment when used as a capacitor, a metal film laminate film using the same, and a film capacitor. be able to.

The polypropylene film of the present invention is obtained by heating the film from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter (DSC), then decreasing the temperature from 260 ° C. to 30 ° C. at 20 ° C./min, and further 30 ° C. The melting peak temperature (T _m2 ) is 164°C or more when reheated from to 260°C at 20°C/min, and the total heat of fusion in the 100°C to 180°C region of the DSC curve is 105 J/g or more. A polypropylene film having an arithmetic mean height Sa of at least one surface of the film of 5 to 20 nm and a maximum height Sz of 100 to 500 nm. In addition, in this invention, a polypropylene film may be called a film. Moreover, since the polypropylene film of the present invention is not a microporous film, it does not have many pores.

Here, the melting peak temperature (T _m2 ) obtained when the film is heated and melted by a differential scanning calorimeter (DSC), then cooled, and then heated again is generally referred to as the "melting peak temperature of 2nd RUN". call. Further, the melting peak temperature (T _m1 ) obtained when the film is first heated with a differential scanning calorimeter (DSC) is called the "1stRUN melting peak temperature".

The polypropylene film of the present invention exhibits a high dielectric breakdown voltage even in a high-temperature environment. C. to 260.degree. C. at 20.degree. C./min, then from 260.degree. The melting peak temperature (T _m2 ) at warm temperature is preferably 164° C. or higher. It is more preferably 165° C. or higher, still more preferably 166° C. or higher. Although the upper limit is not particularly limited, it is preferably 175°C. If T _m2 is less than 164°C, the stability of the crystal structure is considered to be insufficient, and partial dielectric breakdown is likely to occur, lowering the dielectric breakdown voltage of the film, or reducing the capacity of the capacitor in a high temperature environment. or short circuit destruction. Here, when the polypropylene film of the present invention is a film containing polypropylene and a thermoplastic resin incompatible with polypropylene, which will be described later, the melting peak temperature of the incompatible resin is the melting peak temperature of the 2nd RUN of polypropylene ( Although it may be observed at a temperature different from T _m2 ), in the present invention, the peak observed at 164 ° C. or higher and 200 ° C. or lower is defined as the melting peak temperature (T _m2 ) of the polypropylene film of the present invention. is. At this time, when two or more melting peak temperatures are observed in the temperature range, or peak temperatures observable on a multistage DSC chart called a shoulder (observed in a chart in which two or more peaks overlap) However, in the present invention, the temperature of the peak with the largest absolute value of the vertical axis heat flow (unit: mW) of the DSC chart is defined as the melting peak temperature (T _m2 ) of the polypropylene film of the present invention. It is.

Furthermore, in the polypropylene film of the present invention, the temperature is raised from 30 ° C. to 260 ° C. at 20 ° C./min, then from 260 ° C. to 30 ° C. at 20 ° C./min, and further from 30 ° C. to 260 ° C. at 20 ° C./min. The sum of the heat of fusion in the 100°C to 180°C region of the DSC curve at the time of reheating (2nd RUN) is preferably 105 J/g or more, more preferably 108 J/g or more, and still more preferably. is 110 J/g or more. Although the upper limit is not particularly limited, it is 130 J/g. If the heat of fusion is less than 10 J / g, it means that there are many crystals and amorphous components constituting the film, and the dielectric breakdown voltage of the film is lowered, and when it is used as a capacitor. In high temperature environments, it may cause capacity reduction or short circuit destruction. Here, the total heat of fusion is indicated by the heat of fusion of the entire film containing the incompatible thermoplastic resin and other additive compounds. This is because the amounts of incompatible thermoplastic resins and other additive compounds are small and have little effect on the heat of fusion derived from the high crystallinity of the polypropylene of the present invention.

In order to control the DSC melting peak temperature of the polypropylene film of the present invention described above and the heat of fusion of the 2nd RUN in the 100 ° C. to 180 ° C. region of the DSC curve, respectively, within the above preferable ranges, for example, a high mesopentad fraction and a low CXS, which will be described later. (high mesopentad fraction, low CXS will be described later).

In addition, the polypropylene film of the present invention has a moderately roughened surface, from the viewpoint of obtaining uniformity of the film interlayer gap, ease of slipping between films or between transport rolls, workability when producing a capacitor element, and reliability as a capacitor, The arithmetic mean height Sa of at least one surface is preferably 5 to 20 nm, more preferably 7 to 18 nm, still more preferably 9 to 15 nm. If the Sa on at least one surface is less than 5 nm, the slippage of the film is extremely reduced, resulting in poor handleability and poor device workability such as wrinkles. In addition, when used continuously as a capacitor, the change in capacitance 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 film layers, making it difficult for the self-healing function to operate. may reduce the reliability of On the other hand, when the Sa of at least one surface exceeds 20 nm, the surface roughness increases, so that locally thin portions tend to occur, which may affect the decrease in withstand voltage.

In addition, the polypropylene film of the present invention has a moderately roughened surface from the viewpoint of obtaining uniformity of the film interlayer gap, ease of slipping between films or between transport rolls, workability when producing a capacitor element, and reliability as a capacitor. , the maximum height Sz of at least one surface is preferably 100 to 500 nm, more preferably 100 to 350 nm, even more preferably 100 to 200 nm. When the Sz of at least one surface is less than 100 nm, the slippage of the film is extremely reduced, resulting in poor handleability and poor device workability such as wrinkles. In addition, when used continuously as a capacitor, the change in capacitance 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 film layers, making it difficult for the self-healing function to operate. Capacitor reliability may decrease. On the other hand, when the Sz of at least one surface exceeds 500 nm, it affects as coarse projections, it is difficult to obtain a decrease in withstand voltage and thickness uniformity, and the capacity change becomes large due to the influence of wrinkles during continuous use as a capacitor. sometimes.

Here, in order to control Sa and Sz of the film of the present invention within the above-described preferred ranges, for example, conditions such as the cooling temperature during cooling and solidification of the molten sheet during film formation described later and the preheating temperature before stretching in the width direction are adjusted. It can be achieved by controlling within a preferable range, and by configuring the surface of a film containing a resin in which polypropylene and polypropylene are blended with an incompatible thermoplastic resin, and controlling the blend ratio within a preferable range. is.

The polypropylene film of the present invention preferably contains 0.1% by mass or more and 4% by mass or less of a thermoplastic resin incompatible with polypropylene relative to the mass of the film. The proportion of the incompatible thermoplastic resin contained in the film is more preferably 0.5 to 3.5% by mass, still more preferably 1 to 3% by mass. If the content of the thermoplastic resin is less than 0.1% by mass, unevenness is not formed efficiently on the film surface, resulting in poor slidability and poor capacitor element processing. On the other hand, if the content of the thermoplastic resin exceeds 4% by mass, the interfacial adhesion between resins is poor due to low compatibility with polypropylene, voids are generated during stretching, and the dielectric breakdown strength of the film is reduced. , may lead to a drop in breakdown voltage when used as a capacitor.
A case where the polypropylene film is a film in which a plurality of layers are laminated will be described below. A plurality of layers may consist of two layers or three or more layers. In the present invention, all of the layers are laminated film layers containing polypropylene as a main component. When it consists of two layers, one is called the A layer and the other is called the B layer, and the surface opposite to the laminated surface of the A layer and the B layer is the exposed surface. A film in such a laminated state is denoted as A/B. In the case of three layers, the surface layer is A layer and the inner layer is B layer. A film in such a laminated state is expressed as A/B/A. Furthermore, when the number of layers is four or more, the B layers are two or more inner layers, and the A layer is the outermost layer. A film in such a laminated state is expressed as A/B/B/A. Here, at least the surface layer (A layer) of the film, a laminated film containing a thermoplastic resin incompatible with polypropylene in an amount of 0.1% by mass or more and 4% by mass or less with respect to the polypropylene resin, has the Sa of the above film. and Sz can be controlled within a preferred range. This means that the surface roughness of the film depends on the surface layer (A layer), and the layer made of polypropylene in the inner layer (B layer) is the incompatible An inner layer (B layer) containing no thermoplastic resin may be used, or an inner layer (B layer) containing 0.1% by mass or more and 4% by mass or less of an incompatible thermoplastic resin as in the surface layer may be used. From the viewpoint of efficiently forming irregularities on the surface, it is preferable that the content of the incompatible thermoplastic resin in the surface layer A layer is larger than that in the inner layer B layer. In addition, it is preferably 0.1% by mass or more and 4% by mass or less, more preferably 0.5 to 3%, based on the mass of the constituent layer (A layer) containing a thermoplastic resin incompatible with the polypropylene. .5 mass %, more preferably 1 to 3 mass %. When there are multiple A layers such as A layer / B layer / A layer, the content of the thermoplastic resin incompatible with the polypropylene of each A layer is 0.1% by mass or more and 4% by mass or less is preferably

Examples of lamination methods include a method of laminating films together, a feed block method and a multi-manifold method using co-extrusion, and a coating method. Among these lamination methods, the lamination method by melt co-extrusion and the lamination method by coating are preferable from the viewpoint of production efficiency and cost. Moreover, it is preferable that the laminated structure is formed by laminating two or more layers, more preferably three or more layers in the thickness direction of the film. Specifically, it is a structure of two or more layers with at least one surface being an A layer, for example, a two-layer structure of A layer / B layer, more preferably a three-layer structure of A layer / B layer / A layer and A layer are the outermost layers on both surfaces of the film.
Next, as a general method for roughening the surface of a polypropylene film, a technique utilizing crystal transformation can be preferably used. In the film manufacturing process, the solidification temperature on the casting (cooling) drum after melt extrusion is raised to a high temperature of 60 ° C. or higher to form β crystal system spherulites, and in the stretching process, thermally unstable β crystals are formed. Crystal transformation into α crystals forms irregularities on the film surface, but voids formed during the crystal transformation process may become insulation defects and reduce the withstand voltage. On the other hand, in the polypropylene film of the present invention, the layer A is composed of a resin blended with polypropylene and a thermoplastic resin incompatible with polypropylene, and the temperature for solidifying on the cooling drum after melt extrusion in the film manufacturing process is set to By setting the temperature to less than 60° C., preferably less than 40° C., more preferably less than 30° C., it is preferable to preferentially form fine α crystal system spherulites or mesophases. For this reason, the polypropylene film of the present invention does not form voids due to crystal transformation in the stretching process, does not substantially generate insulation defects, is excellent in capacitor element processing aptitude even when it is a thin film, and is highly suitable even in a high temperature environment. It can exhibit voltage resistance. Here, the mesophase indicates an ordered state between crystal and amorphous, and is also called smectic crystal or smectic crystal, and it is known that the mesophase occurs when solidified at a very high cooling rate from a molten state. there is Since the mesophase is an intermediate phase, it forms a uniform structure in the stretching process, and is therefore a preferable structure for reducing insulation defects. In addition, in the composition layer made of a resin blended with polypropylene and a thermoplastic resin incompatible with the polypropylene, since it is possible to impart surface unevenness using the domain structure, it is accompanied by crystal transformation during the stretching process. Without causing insulation defects such as void formation, even a thin film is excellent in processing suitability for capacitor elements, and can exhibit high withstand voltage even in a high-temperature environment. As a thermoplastic resin that is incompatible with polypropylene, for example, a polymethylpentene-based resin can be preferably used, and by controlling its content to the resin content described above, high voltage resistance is maintained. Appropriate unevenness can be imparted to the surface.
Here, the film of the present invention is formed by stretching the polypropylene resin after forming a mesophase structure in a component layer made of a resin blended with a polypropylene and a thermoplastic resin incompatible with the polypropylene, which is accompanied by stretching. Since the polypropylene and the polypropylene can suppress peeling at the resin interface with the incompatible thermoplastic resin, there is no void formation, and insulation defects are not substantially generated, even if the film is thin. , surface unevenness that is excellent in capacitor element processability, and exhibits high voltage resistance even in high temperature environments.

Here, when the polypropylene film of the present invention has a structure in which two or more layers are laminated in the thickness direction, the ratio of the thickness of the A layer to the total thickness of the film (when both surfaces are A layers, the ratio of the combined thickness) is preferably 1% to 60%, more preferably 5% to 40%, and most preferably 5% to 25%, from the viewpoint of controlling film formability and surface shape. If the ratio of the A layer is too large, the voltage resistance in a high-temperature environment is lowered due to voids. Processing aptitude may not be obtained. Here, the thickness of the A layer is determined, for example, by preparing a cross section of the film and observing the cross section using a scanning electron microscope (SEM) or the like. By cross-sectional observation, it is possible to determine the resin interface between the A layer or the A layer and the B layer of the constituent layer made of a resin blended with polypropylene and a thermoplastic resin incompatible with the polypropylene, and from the cross-sectional image. Measure the thickness of the A layer.

When the polypropylene film of the present invention has a laminated structure, the inner layer (B layer) is composed of polypropylene, and the polypropylene in the inner layer is incompatible with respect to 100% by mass of the total film mass constituting the B layer. It is preferable that the content of the thermoplastic resin is 0 to 4% by mass or less. More preferably 0 to 3 mass %, still more preferably 0 to 2 mass %. From the viewpoint of reducing costs and efficiently forming unevenness on the surface, the content of the thermoplastic resin in the inner layer B is preferably as low as possible. On the other hand, if the content of the thermoplastic resin in the inner layer exceeds 4% by mass, the interfacial adhesion between the resins is poor due to low compatibility with polypropylene, and voids occur during stretching, resulting in a decrease in dielectric breakdown strength of the film. , may lead to a drop in breakdown voltage when used as a capacitor.

The polypropylene used in the polypropylene film of the present invention is mainly composed of a propylene homopolymer, but may contain other unsaturated hydrocarbon copolymer components within a range that does not impair the object of the present invention. may be blended. Examples of monomer components constituting such copolymer components and blends include ethylene, propylene (in the case of copolymerized blends), 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- and norbornene. The copolymerization amount or blend amount is preferably less than 1 mol % in terms of dielectric breakdown voltage and heat resistance, and preferably less than 10% by mass in terms of blend amount.

The polypropylene film of the present invention can have unevenness on at least one surface by utilizing a sea-island structure formed by blending polypropylene and a thermoplastic resin incompatible with polypropylene. As the thermoplastic resin that is incompatible with polypropylene, resins other than the above-mentioned polypropylene can be used. based resins are preferred. The melting point of the polymethylpentene-based resin is preferably 205 to 240° C., although it is incompatible with polypropylene, but from the viewpoint of extrusion stability when blended and surface unevenness using the domain sea-island structure. , More preferably 220 to 240 ° C., "TPX" (registered trademark) MX sold as "TPX" (registered trademark) series by Mitsui Chemicals, Inc., which is a polymer composed of 4-methylpentene-1 The DX series of the same series can be preferably used.

The polypropylene film of the present invention preferably has a glossiness of at least one surface of 130% or more and less than 150%, more preferably 132% or more and less than 148%, still more preferably 135% or more and less than 146%. If the glossiness is less than 130%, the light scattering density on the film surface is high, which means that the surface is excessively roughened, which may reduce the dielectric breakdown voltage of the film. On the other hand, when the glossiness is 150% or more, it means that the surface is smoothed, and the slippage of the film tends to be extremely reduced. As a result, handleability is deteriorated, wrinkles are likely to occur, and element workability may be deteriorated.

The polypropylene film of the present invention preferably has a static friction coefficient (μs) of 0.3 or more and less than 0.95 when the films are laminated, from the viewpoint of improving the withstand voltage characteristics and having device processability. If μs is less than 0.3, the film may be too slippery to cause winding misalignment during winding during film formation or element processing. If μs exceeds 0.95, the slippage of the film is extremely reduced, which may result in poor handling, wrinkles, and poor device workability. μs is more preferably 0.4 or more and 0.85 or less, still more preferably 0.5 or more and 0.75 or less.

The polypropylene film of the present invention preferably has a melting peak temperature (T _m1 ) of 174° C. or higher in 1st RUN when the temperature is raised from 30° C. to 260° C. at a rate of 20° C./min by DSC. It is more preferably 176° C. or higher, still more preferably 178° C. or higher. The upper limit of the peak temperature is 200°C. A higher _Tm1 means a higher degree of crystallinity of the film, which is preferable from the viewpoint of improving the dielectric breakdown voltage in a high-temperature environment. Here, when the polypropylene film of the present invention is a film containing polypropylene and a thermoplastic resin incompatible with polypropylene, the melting peak temperature of the incompatible resin is observed at a temperature different from the peak temperature of polypropylene. In the present invention, the peak observed at 174° C. or higher and 200° C. or lower is defined as the 1stRUN melting peak temperature (T _m1 ) of the polypropylene film of the present invention. At this time, when two or more melting peak temperatures are observed in the temperature range, or peak temperatures observable on a multistage DSC chart called a shoulder (observed in a chart in which two or more peaks overlap) However, in the present invention, the temperature of the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart is defined as _Tm1 . Here, the relationship between the DSC 1stRUN melting peak temperature (T _m1 ) and the 2ndRUN melting peak temperature (T _m2 ) of the polypropylene film of the present invention is such that (T _m1 ) is higher than (T _m2 ) ((T _m1 )>(T _m2 ) show). The increase in (T _m1 ) is due to the increase in the melting peak temperature due to the increase in molecular chain orientation and crystal size due to the influence of the stretching and heat treatment steps during the production of the polypropylene film.

The polypropylene film of the present invention preferably has a mesopentad fraction of 0.970 or more. It is more preferably 0.975 or more, still more preferably 0.980 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystalline phase of polypropylene measured by nuclear magnetic resonance ( _NMR ). is increased, and the dielectric breakdown voltage can be improved 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 obtained by using a so-called Ziegler-Natta catalyst, and a method of properly selecting an electron-donating component is preferably employed. Mn) can be 3.0 or more, <2,1> erythro site deficiency can be 0.1 mol % or less, and it is preferable to use such a polypropylene resin. If the mesopentad fraction of the polypropylene resin is less than 0.970, the regularity of the polypropylene is low, which may lead to a decrease in the strength and dielectric breakdown voltage of the film in a high-temperature environment. In the element winding process, the membrane may break during transport of the film.

When the polypropylene film of the present invention was completely dissolved in xylene and allowed to precipitate at room temperature, the polypropylene component dissolved in xylene (represented as CXS, also referred to as the cold xylene soluble portion) dissolved in the entire film. It is preferably less than 1.5% by mass. Here, the cold xylene soluble portion (CXS) is considered to correspond to a component that is difficult to crystallize due to low stereoregularity, low molecular weight, and the like. If the CXS exceeds 1.5% by mass, problems such as a decrease in dielectric breakdown voltage of the film, a decrease in thermal dimensional stability, and an increase in leakage current may occur. Therefore, CXS is more preferably 1.3% by mass or less, still more preferably 1.1% by mass or less. In order to obtain such a CXS content, methods such as a method of increasing the catalytic activity when obtaining the polypropylene resin to be used, and a method of washing the obtained polypropylene resin with a solvent or the propylene monomer itself can be used.

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) is preferable from the viewpoint of film formability. 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 may contain various additives, such as crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, slip agents, antistatic agents, blocking agents, as long as the objects of the present invention are not impaired. It may contain inhibitors, fillers, viscosity modifiers, and anti-coloring agents. Among these, the selection of the type and amount of 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" (registered trademark) 1330: molecular weight 775.2) or tetrakis[methylene-3(3,5-di It is preferable to use t-butyl-4-hydroxyphenyl)propionate]methane (for example, "Irganox" (registered trademark) 1010 manufactured by BASF, molecular weight 1177.7) 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 mass, and particularly preferably 0.2 to 0.4% by mass.

The polypropylene film of the present invention has a film thickness of 0.5 μm or more and 10 μm or less 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 the balance between characteristics and capacitor size due to thinning for the heat-resistant film capacitor.
According to one embodiment described above, the polypropylene film of the present invention has a film dielectric breakdown voltage at 130° C. of 420 V/μm or more. In order to effectively obtain a high film dielectric breakdown voltage even in a high-temperature environment, for example, a polypropylene raw material with high stereoregularity or a CXS content of less than 1.5% by mass is used. When a compatible thermoplastic resin is blended, 0.1% by mass or more and 4% by mass or less of a thermoplastic resin that is incompatible with polypropylene is added, and the casting drum temperature is controlled within a preferable range. A preferable method is the condition of the film forming process (the film forming method will be described later).

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 electrode configuration, it may be either a double-wound capacitor of metal foil and film, or a metal-deposited film capacitor, or an oil-immersed capacitor impregnated with insulating oil, or one 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 winding type or a laminated type.

The polypropylene film of the present invention is preferably obtained by using a raw material capable of imparting the properties described above and subjecting it to biaxial orientation, heat treatment and relaxation treatment. 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 preferred to employ the tenter sequential biaxial stretching method in terms of controlling structure, surface properties, mechanical properties and thermal dimensional stability.

Next, the method for producing the polypropylene film of the present invention will be explained. First, polypropylene 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. A more specific description will be given below, but the present invention is not necessarily limited to this.

First, a polypropylene resin is melt-extruded from a single-screw extruder, passed through a filtration filter, and then extruded from a slit-shaped die at a temperature of 230 to 280°C, more preferably 230 to 260°C. In the case of a laminated structure, raw material A obtained by pre-compounding polypropylene resin with a resin incompatible with polypropylene resin is supplied to a single screw extruder for A layer, and polypropylene resin raw material B is single screw extruded for B layer. The resin is fed into a machine and melted at 200 to 280° C., more preferably 200 to 260° C., by a feed block method by melt co-extrusion. A sheet is extruded and solidified on a cooling drum controlled at a temperature of 10 to 110° C. to obtain an unstretched polypropylene film.

The unstretched polypropylene film more preferably has a mesophase structure, and the mesophase fraction is preferably 20% or more, more preferably 40% or more, still more preferably 70% or more, most preferably 80% or more, More preferably, it is 90% or more. To calculate the mesophase fraction of the unstretched polypropylene film, the unstretched polypropylene film is measured by wide-angle X-ray diffraction, and the X-ray diffraction profile is used for calculation. The obtained X-ray diffraction profile is processed with peak separation software to separate the mesophase, α-crystalline and amorphous profiles, and the mesophase fraction is calculated. In the present invention, forming a mesophase or having a mesophase structure means that the mesophase fraction is 20% or more. The diffraction profile derived from the α crystal is observed in wide-angle X-ray diffraction measurement with a diffraction angle (2θ) in the range of 10 to 30 degrees, near 14.1 degrees, near 16.9 degrees, and 18.6 degrees. It consists of five peaks near, around 21.6 degrees and around 21.9 degrees. The diffraction profile derived from the mesophase consists of two broad peaks near 15 degrees and 21 degrees. The diffraction profile derived from amorphous is a broad peak with a diffraction angle of around 16.2 degrees, which is obtained by measuring the polypropylene resin in a molten state by wide-angle X-ray diffraction.

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.

From the viewpoint of improving the mechanical properties of the biaxially stretched film, improving the electrical properties, controlling the surface roughness, and increasing the glossiness of the surface, the temperature of the casting drum is more preferably 10 to 90 ° C. , more preferably 10 to 60°C, most preferably 10 to 30°C. In particular, by setting the temperature of the casting drum to 10 to 30° C., the mesophase fraction of the unstretched polypropylene film can be increased so that the unstretched polypropylene film has a mesophase structure.

Next, the unstretched polypropylene film is biaxially stretched and biaxially oriented. Here, in the polypropylene film of the present invention, from the viewpoint of improving the withstand voltage of the film, it is preferable to have a step of stretching an unstretched polypropylene film having a mesophase structure in at least one direction by a factor of 2 or more. When the unstretched polypropylene film has a mesophase fraction of 20% or more, it is passed between rolls maintained at 80 to 130° C., preferably 90 to 120° C., and preheated. ° C., preferably 90 to 120 ° C. and stretched in the longitudinal direction 2 to 15 times, preferably 4.6 to 12 times, more preferably 5.0 to 11 times, most preferably 5.6 to 10 times Then cool 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 set to the stretching temperature in the width direction +1 to +15 ° C., preferably +3 to +14 ° C., more preferably +5 to +13 ° C. It is high in the longitudinal direction. The oriented fibril structure is further strengthened, and the degree of crystallinity is improved. In addition, from the viewpoint of improving the thermal dimensional stability by relaxing excess tension by previously relaxing molecular chains whose orientation is insufficient in the process of stretching in the longitudinal direction, furthermore, the film surface fibrils oriented by stretching in the longitudinal direction. It is preferable from the viewpoint that the convex shape can be made conspicuous and the film surface unevenness can be formed after biaxial stretching. If the preheating temperature is less than the stretching temperature + 5 ° C., the crystallinity and thermal dimensional stability cannot be improved, or the surface unevenness is not formed. The film may tear during the process.

Then, the temperature at which the film is stretched in the width direction while the ends of the film are held with clips (stretching temperature in the width direction) is 140 to 170 ° C., preferably 145 to 160 ° C., and the width is 7 to 15 times, more preferably 9 to 15 times. It is stretched 12 times, most preferably 9.2 to 11.5 times.

Here, the area magnification is preferably 50 times or more from the viewpoint of improving the withstand voltage. In the present invention, the area ratio is obtained by multiplying the draw ratio in the longitudinal direction by the draw ratio in the width direction. The area magnification is more preferably 55 times or more, and particularly preferably 60 times or more.

In the present invention, in the subsequent heat treatment and relaxation treatment steps, the clip is held with tension in the width direction and relaxed by 2 to 20% in the width direction at a temperature of 145 ° C. or higher and 165 ° C. or lower (first heat treatment temperature). After heat setting (first heat treatment), heat treatment is performed under conditions of 130 ° C. or more and less than the heat setting temperature (first heat treatment temperature) while the width direction is held tightly with a clip (second heat treatment). Furthermore, a multi-stage heat treatment that performs heat setting (third-stage heat treatment) under the conditions of 80 ° C. or more and less than the heat setting temperature (second-stage heat treatment temperature) while being held tightly is effective for uniformity of film thickness. By sufficiently fixing and stabilizing the molecular chain orientation advanced by stretching and improving the crystallinity, the DSC1stRUN melting peak temperature (T _m1 ) is increased, the thermal dimensional stability is improved, and the resistance when used as a capacitor is improved. It is preferable from the viewpoint of voltage resistance and reliability.

In the relaxation treatment, the relaxation rate is preferably 2 to 20%, more preferably 5 to 18%, and even more preferably 8 to 15%, from the viewpoint of improving thermal dimensional stability. 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. Thermal dimensional stability cannot be obtained, and when used as a capacitor, it may cause a decrease in capacity or short circuit breakdown in a high temperature environment.

After undergoing multi-stage heat treatment, it 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 a film product roll with a film thickness of 0.5 μm or more and 10 μm or less is produced. take up. 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.

A specific example of the manufacturing conditions for obtaining the polypropylene film of the present invention is as follows.
・A resin incompatible with polypropylene must be blended on at least one surface or all layers.
- The CXS content of the polypropylene resin is less than 1.5% by mass.
- An unstretched polypropylene film having a mesophase structure must be stretched twice or more in at least one direction.
- The area draw ratio is 50 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 temperature of the heat treatment in the first stage must be 145°C or higher and 165°C or lower.
・The second heat treatment temperature must be 130°C or higher and less than the first heat treatment temperature.
・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.
- The thickness of the film should be 0.5 μm or more and 10 μm or less.

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

The metal film laminated film of the present invention is obtained by providing a metal film on at least one surface of the polypropylene film of the present invention.

In addition, the method for producing a metal film laminated film of the present invention has a step of providing a metal film on at least one side of the polypropylene film obtained by the above method for producing a polypropylene film.

In the present invention, the method of the step of providing a metal film to form a metal film laminated film by providing a metal film on at least one side of the polypropylene film is not particularly limited. A method of providing a metal film such as a vapor-deposited film that becomes an internal electrode of a film capacitor by vapor-depositing an alloy with 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 polyphenylene oxide or the like.

The film capacitor of the present invention uses the metal film laminated film of the present invention. Further, the method for manufacturing a film capacitor of the present invention uses 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 to form 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 overlapping two reels, one each for 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 margins running in the longitudinal direction on one surface, and stripes are deposited on the other surface so that the margins in the longitudinal direction are 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 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 average value of the thicknesses of the ten locations was taken as the film thickness of the polypropylene film.

(2) Melting peak temperature and heat of fusion of film (DSC2ndRUN melting peak temperature _Tm2 and melting heat in the region of 100°C to 180°C in DSC2ndRUN)
Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), 3 mg of a polypropylene film is heated from 30° C. to 260° C. at a rate of 20° C./min in a nitrogen atmosphere. Then, after holding at 260° C. for 5 minutes, the temperature is lowered to 30° C. at a rate of 20° C./min. Furthermore, after holding at 30° C. for 5 minutes, the temperature is raised again from 30° C. to 260° C. at a rate of 20° C./min. The peak temperature of the endothermic curve obtained during this reheating was taken as the DSC2ndRUN melting peak temperature (T _m2 ). At this time, when two or more melting peak temperatures are observed in the temperature range, or peak temperatures observable on a multistage DSC chart called a shoulder (observed in a chart in which two or more peaks overlap) However, in the present invention, the temperature of the peak with the largest absolute value of the heat flow (unit: mW) on the vertical axis of the DSC chart is the DSC melting peak temperature (T _m2 ) of the polypropylene film of the present invention. . Further, in the DSC curve obtained by the above measurement, the heat of fusion in the region of 100°C to 180°C was calculated as the heat of fusion in the region of 100°C to 180°C in DSC 2ndRUN. In addition, the number of measurements n was performed three times, and the average value was used for (T _m2 ) and the heat of fusion.

(3) Film melting peak temperature (DSC1stRUN melting peak temperature T _m1 )
Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), 3 mg of a polypropylene film is heated from 30° C. to 260° C. at a rate of 20° C./min in a nitrogen atmosphere. The peak temperature of the endothermic curve obtained during this temperature rise was taken as the DSC1stRUN melting peak temperature (T _m1 ). At this time, when two or more melting peak temperatures are observed in the temperature range, or peak temperatures observable on a multistage DSC chart called a shoulder (observed in a chart in which two or more peaks overlap) ), but in the present invention, the temperature of the peak with the largest absolute value of the vertical axis heat flow (unit: mW) of the DSC chart is the DSC melting peak temperature (T _m1 ) of the polypropylene film of the present invention. . In addition, the number of measurements n was performed three times, and the average value was used for (T _m1 ).

(4) Arithmetic mean height (Sa), maximum height (Sz),
VertScan2.0 R5300GL-Lite-AC manufactured by Ryoka Systems Co., Ltd. was used for the measurement. A process of supplementing pixels for which height data could not be obtained with height data calculated from surrounding pixels) was performed. Sa and Sz were obtained based on ISO25178, and the average value of measurements at five arbitrary points in one plane was calculated.
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 .

(5) Glossiness of film According to JIS K-7105 (1981), using a digital variable angle gloss meter UGV-5D manufactured by Suga Test Instruments Co., Ltd., the casting drum contact surface side under the condition of an incident angle of 60° and a light receiving angle of 60°. The glossiness (%) was defined as the average value of the five points of data obtained by measuring the surface of .

(6) Static friction coefficient (μs)
Using a slip tester manufactured by Toyo Seiki Co., Ltd., it was measured at 25° C. and 65% RH according to JIS K 7125 (1999). In addition, the measurement was carried out by aligning the film longitudinal directions of the two films and overlapping one surface and the opposite surface of the films. The same measurement was performed 5 times for each sample, and the average value of the obtained values was calculated as the static friction coefficient (μs) of the sample.

(7) 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 ((1) above), converted to (V / μm), and the maximum value among the measured values (calculated values) at a total of 30 points. The film dielectric breakdown voltage at 130° C. was determined by excluding 5 points in descending order and 5 points in ascending order from the minimum value, and the average value of 20 points.

(8) % by mass of cold xylene solubles (CXS)
In the case of a raw material, 0.5 g of a polypropylene resin, and in the case of a film, a film sample was dissolved in 100 ml of xylene at 135° C., allowed to cool, and then recrystallized in a constant temperature water bath at 20° C. for 1 hour. Thereafter, the recrystallized polypropylene is removed by filtration, and the polypropylene-based component dissolved in xylene in the filtrate is quantified by liquid chromatography (X(g)). Using the precision value (X0 (g)) of 0.5 g of the sampled sample, the following formula CXS (mass%) = (X / X0) × 100
calculated from

(9) 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 is 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 integration: 10000 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 division is 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.

(10) Mesophase fraction of unstretched polypropylene film (wide-angle X-ray diffraction)
After the casting step, the unstretched polypropylene film was cut into a width of 10 mm and a length of 20 mm. Using this sample, measurements were performed at room temperature with diffraction angles (2θ) in the range of 5 to 30 degrees. Detailed measurement conditions are described below.
・Equipment: nano viewer (manufactured by Rigaku Co., Ltd.)
・Wavelength: 0.15418 nm
・X-ray incident direction: Through direction (perpendicular to the film surface)
- Measurement time: 300 seconds Next, the obtained diffraction profile is processed with peak separation software to separate into three components of the mesophase, α crystal, and amorphous profiles. IGOR Pro (Ver. 6) software manufactured by WaveMetrics, Inc. was used as analysis software. In conducting the analysis, the following assumptions were made.
・Peak shape function: Lorentz function ・Peak position: amorphous = 16.2 degrees, meso phase = 15.0 degrees, 21.0 degrees α crystal = 14.1 degrees, 16.9 degrees, 18.6 degrees, 21 degrees .6 degrees, 21.9 degrees Peak half width: amorphous = 8.0, mesophase (15.0 degrees) = 3.5, mesophase (21.0 degrees) = 2.7
The half-value widths of amorphous and mesophases are fixed at the above values, but α-crystals are not fixed.

For the obtained peak separation results, the areas (m ₁₅ and m ₂₁ ) of the diffraction profile having peaks at 15 degrees and 21 degrees derived from the mesophase were calculated, and 14.1 degrees and 16 degrees derived from the α crystal were calculated. The areas of the diffraction profiles with peaks at .9 degrees, 18.6 degrees, 21.6 degrees and 21.9 degrees (α _14.1 and α _16.9 and α _18.6 and α 21.6 and α _21.6 and _{.alpha. 9} ) is calculated by the following formula (Formula) mesophase fraction (%) = 100 × (m ₁₅ + m ₂₁ ) / (m ₁₅ + m ₂₁ + α _14.1 + α _16.9 + α _18.6 + α _21.6 + α _21.9 )
By calculating as follows, the ratio of the area of the profile derived from the mesophase was obtained, and this was defined as the mesophase fraction.

(12) Evaluation of film capacitor characteristics (withstanding voltage and reliability at 115°C)
On the film surface (if the film-treated surface is unknown, the film surface with the higher wetting tension among both sides of the film) of the film obtained in each example and comparative example described later was subjected to corona discharge treatment. Aluminum was vapor-deposited with a vacuum vapor deposition machine manufactured by ULVAC in a vapor deposition pattern having a film resistance of 8 Ω/sq and a so-called T-shaped margin pattern in which margins were provided in the direction perpendicular to the longitudinal direction to obtain a vapor deposition reel with a width of 50 mm.

Next, 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 128 ° C. for 10 hours under reduced pressure, A lead wire was attached to complete the capacitor element.

Using 10 capacitor elements thus obtained, a voltage of 250 VDC is applied to the capacitor elements at a high temperature of 115° 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.

<Element workability>
Judgment was made according to the following criteria. A capacitor element was produced in the same manner as described above, and the shape of the element was visually confirmed.
◎: No deviation, wrinkles, or deformation of the end face film of the capacitor element, and there is no problem in the subsequent processes. , wrinkles, and edge misalignment, which interferes with subsequent processes. Practical use is difficult with ×.

<Withstand voltage>
The capacitance change at this time was measured and plotted on a graph, and the voltage at which the capacitance became 70% of the initial value was divided by the film thickness ((1) above) to obtain a withstand voltage evaluation. rated the street.
◎: 400 V/μm or more ○: 380 V/μm or more and less than 400 V/μm △: 360 V/μm or more and less than 380 V/μm ×: less than 360 V/μm ◎, ○ can be used. Δ and x are inferior in practical performance.

<Reliability>
After increasing the voltage until the capacitance decreased to 8% or less of the initial value, the capacitor element was disassembled and the state of breakdown was examined to evaluate the reliability as follows.
⊚: There is no change in the element shape and no penetrating breakage is observed.
◯: Penetration-like fracture within 10 layers of the film is observed without change in element shape.
Δ: A change in the element shape is observed, or a penetrating breakdown of more than 10 layers is observed.
x: The element shape is destroyed.
⊚ can be used without problems, and ○ can be used depending on the conditions. Δ and x are inferior in practical performance.

The effects of the present invention will be further described below with reference to examples.

(Example 1)
In a laminated film including a surface layer (A layer) and an inner layer (B layer), the A raw material was used for the A layer, and the B raw material was used for the B layer. The resin for layer A has a mesopentad fraction of 0.984, a melting point of 168° C., a melt flow rate (MFR) of 2.2 g/10 min, and a cold xylene soluble part (CXS) of 0.8% by mass. 98% by weight of a polypropylene resin manufactured by Prime Polymer Co., Ltd. and 2% by weight of "TPX" (registered trademark) (MX002, melting point of 224° C.) manufactured by Mitsui Chemicals, Inc. as a polymethylpentene-based resin were blended and heated at 260° C. The mixture was kneaded and extruded by an extruder set to 200°C, and the strand was water-cooled and chipped to obtain a polypropylene resin raw material (A1). The resin for the inner layer (layer B) does not contain an incompatible thermoplastic resin, has a mesopentad fraction of 0.984, a melting point of 168° C., a melt flow rate (MFR) of 2.2 g/10 minutes, 100% by weight of polypropylene resin manufactured by Prime Polymer Co., Ltd. having a cold xylene soluble portion (CXS) of 0.8% by mass. The raw material (A1) for the surface layer (A layer) and the raw material for the inner layer (B layer) are each supplied to a single screw extruder, melted at a resin temperature of 260 ° C., and after removing foreign matter with a sintered filter cut to 80 μm, Using a feed block, the extrusion rate is adjusted so that the thickness ratio of the three layers of A/B/A is 1/8/1 (the ratio of the surface layer A layer to the total thickness of the film is 20%), and the melt The laminated polymer was discharged from a T-die, and the molten sheet was brought into close contact with a casting drum maintained at 25° C. with an air knife and solidified by cooling to obtain an unstretched polypropylene film. The unstretched polypropylene film was preheated step by step to 84° C. with a group of rolls, then passed between rolls maintained at 125° C. with different circumferential speeds, and stretched 6.2 times in the longitudinal direction. Subsequently, the film was guided to a tenter, and while both ends of the width of the film were held with clips, it was preheated at a TD preheating temperature of 167°C (+8°C higher than the TD stretching temperature), and then stretched in the width direction at a temperature of 159°C. Stretched 0 times. Furthermore, as the first heat treatment and relaxation treatment, heat treatment was performed at 155° C. while giving 8% relaxation in the width direction, and as the second heat treatment, heat treatment was performed at 140° C. while being held by clips in the width direction. Finally, as the third-stage heat treatment, the film is guided to the outside of the tenter through a heat treatment at 120°C, the clips at the ends of the film are released, and then the film surface (the casting drum contact surface side) is subjected to 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 2.4 μm was wound up as a film roll. The properties and capacitor properties of the polypropylene film of this example are as shown in Table 1. The film was excellent in capacitor element workability, reliability as a capacitor, and withstand voltage.

( Reference example 1 )
The polypropylene resin (A1) of Reference Example 1 was supplied to a single-screw melt extruder and melted at a resin temperature of 260°C. The melted sheet was brought into close contact with a casting drum maintained at 25° C. with an air knife and solidified by cooling to obtain an unstretched polypropylene film having a substantially single-layer structure. A polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1 with respect to the stretching ratio, TD preheating temperature, TD stretching temperature and heat treatment conditions during biaxial stretching of the unstretched polypropylene film. The polypropylene film of this example was excellent in properties and processability as a capacitor element, and was excellent in withstand voltage as a capacitor, but the reliability was usable depending on the conditions.

(Example 3)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.973, a melting point of 165°C, a melt flow rate (MFR) of 3.0 g/10 min, and a cold xylene soluble portion (CXS) of 1.3% by mass. 98% by weight of polypropylene resin and 2% by weight of "TPX" (registered trademark: MX002, melting point: 224°C) manufactured by Mitsui Chemicals, Inc. as a polymethylpentene-based resin are blended, and the mixture is kneaded and extruded by an extruder set at 260°C. , the strand was water-cooled and chipped to obtain a polypropylene resin raw material (A2). The polypropylene resin (A2) for layer A was used, and the polypropylene resin for layer B had a mesopentad fraction of 0.973, a melting point of 165°C, a melt flow rate (MFR) of 3.0 g/10 minutes, and a Using 100% by mass of polypropylene resin manufactured by Prime Polymer Co., Ltd. with a xylene soluble portion (CXS) of 1.3% by mass, the temperature of the casting drum, the stretching ratio during biaxial stretching, the TD preheating temperature, the TD stretching temperature and A polypropylene film having a thickness of 2.4 μm was obtained in the same manner as in Example 1, except that the heat treatment conditions were changed to those shown in Table 1. The characteristics and capacitor characteristics of the polypropylene film of this example are as shown in Table 1. The capacitor element workability was excellent, and although the withstand voltage and reliability as a capacitor were slightly inferior, there was no problem in practical use.

(Example 4)
The polymethylpentene-based resin for the layer A was blended to 4% by weight, kneaded and extruded with an extruder set at 260° C., the strand was water-cooled and chipped to obtain a polypropylene resin raw material (A3). Next, the polymethylpentene-based resin for the layer B was blended to 2% by weight, kneaded and extruded with an extruder set at 260° C., the strand was water-cooled and chipped to obtain a polypropylene resin raw material (B1). A polypropylene film having a thickness of 2.4 μm was obtained in the same manner as in Example 1 except that the polypropylene resin raw materials (A3) and (B1) described above were used for the A layer and the B layer, respectively. The polypropylene film of this example was excellent in properties and processability as a capacitor element, and was excellent in withstand voltage as a capacitor, but the reliability was usable depending on the conditions.

(Example 5)
A polypropylene film was obtained in the same manner as in Example 1, except that the film thickness was 6.0 μm, and the MD draw ratio, TD preheating temperature, TD drawing temperature, and heat setting temperature were changed to the conditions shown in Table 1. The properties and capacitor properties of the polypropylene film of this example are shown in Table 1. It was excellent in capacitor element workability and withstand voltage, and although it was slightly inferior in reliability, it was at a level that poses no problems in practical use.

(Comparative example 1)
The polypropylene raw material to be used and the blend ratio of polymethylpentene are the same as in Example 1, the temperature of the casting drum for cooling the melt extruded sheet is 95 ° C., and the temperature for preheating the unstretched polypropylene film with a plurality of roll groups is set. 120 ° C., the temperature for stretching between rolls with a peripheral speed difference was 140 ° C., the TD preheating temperature and the TD stretching temperature were the same temperature, the area stretching ratio was 48 times, and the heat setting temperature was only 1 stage. A polypropylene film having a thickness of 2.4 μm was obtained in the same manner as in Example 1. 1 shows the properties and capacitor properties of the polypropylene film of Comparative Example 1. Regarding the characteristics of the capacitor element, while it has excellent workability, the withstand voltage as a capacitor is insufficient and cannot be practically withstood. .

(Comparative Example 2 and Comparative Example 3)
Comparative Example 2 is a prime polymer having a mesopentad fraction of 0.984, a melting point of 168° C., a melt flow rate (MFR) of 2.2 g/10 min, and a cold xylene soluble portion (CXS) of 0.8% by mass. 95% by weight of polypropylene resin manufactured by Co., Ltd. and 5% by weight of "TPX" (registered trademark: MX002, melting point: 224 ° C.) manufactured by Mitsui Chemicals, Inc. as a polymethylpentene-based resin incompatible with polypropylene. The mixture was kneaded and extruded by an extruder set at 260° C., and the strand was cooled with water and chipped to obtain a polypropylene resin raw material (A4). In the same manner as in Example 1, except that the polypropylene resin (A4) had a single layer structure, the heat treatment process was a two-stage treatment, and the casting drum temperature and the film forming conditions such as MD and TD stretching were used. A polypropylene film was obtained. In Comparative Example 3, the content of the thermoplastic resin incompatible with polypropylene was set to 0% by weight for both the A layer and the B layer, and the casting drum temperature and the film forming conditions such as MD and TD stretching were the same as in Example 1. Then, a polypropylene film having a thickness of 2.4 µm was obtained. The properties and capacitor properties of the polypropylene film of Comparative Example 2 are as shown in Table 1. The capacitor element had good workability, but had poor withstand voltage and reliability at a level causing problems in actual use. The properties of the film of Comparative Example 3 and the properties of the capacitor are shown in Table 1. The workability of the capacitor element was such that deformation, wrinkles, and edge misalignment could occur, which could interfere with subsequent steps. In addition, the withstand voltage as a capacitor was low, and a change in element shape was observed in the reliability evaluation, which was at a level that could not withstand actual use.

(Comparative Example 4)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.967, a melting point of 164° C., a melt flow rate (MFR) of 3.1 g/10 min, and a cold xylene soluble portion (CXS) of 0.8% by mass. 98% by weight of polypropylene resin and 2% by weight of "TPX" (registered trademark: MX002, melting point: 224°C) manufactured by Mitsui Chemicals, Inc. as a polymethylpentene-based resin are blended, and the mixture is kneaded and extruded by an extruder set at 260°C. , the strand was water-cooled and chipped to obtain a polypropylene resin raw material (A5). The polypropylene resin for the A layer uses (A5), and the polypropylene resin for the B layer has the above 0.967, a melting point of 164 ° C., a melt flow rate (MFR) of 3.1 g / 10 minutes, and is soluble in cold xylene. Using 100% by weight of polypropylene resin manufactured by Prime Polymer Co., Ltd. with a part (CXS) of 0.8% by weight, the temperature of the casting drum for cooling the melt extruded sheet, the stretch ratio during biaxial stretching, TD preheating temperature, TD A polypropylene film having a thickness of 2.4 μm was obtained in the same manner as in Example 1, except that the stretching temperature, heat treatment conditions, etc. were the conditions shown in Table 1. The properties and capacitor properties of the polypropylene film of this comparative example are shown in Table 1. Although the processability of the capacitor element was excellent, the withstand voltage as a capacitor was low, and a change in the element shape was observed in the reliability evaluation. It was of a level that could not withstand actual use.

(Comparative Example 5)
Manufactured by Prime Polymer Co., Ltd., having a mesopentad fraction of 0.965, a melting point of 163° C., a melt flow rate (MFR) of 3.5 g/10 min, and a cold xylene soluble portion (CXS) of 1.8% by mass. 98% by weight of polypropylene resin and 2% by weight of "TPX" (registered trademark: MX002, melting point: 224°C) manufactured by Mitsui Chemicals, Inc. as a polymethylpentene-based resin are blended, and the mixture is kneaded and extruded by an extruder set at 260°C. , the strand was water-cooled and chipped to obtain a polypropylene resin raw material (A6). (A6) is used as the polypropylene resin for layer A, and the polypropylene resin for layer B is the above 0.967, has a melting point of 164 ° C., a melt flow rate (MFR) of 3.1 g / 10 minutes, and is soluble in cold xylene. Using 100% by weight of polypropylene resin manufactured by Prime Polymer Co., Ltd. with a part (CXS) of 0.8% by weight, the temperature of the casting drum for cooling the melt extruded sheet, the stretch ratio during biaxial stretching, TD preheating temperature, TD A polypropylene film having a thickness of 2.3 μm was obtained in the same manner as in Example 1, except that the stretching temperature, heat treatment conditions, etc. were the conditions shown in Table 1. The characteristics of the polypropylene film of this comparative example and the capacitor characteristics are shown in Table 1. Regarding the characteristics of the capacitor element, while the workability is excellent, the withstand voltage as a capacitor is insufficient and cannot be practically withstood. In the reliability evaluation, a penetrating fracture exceeding 10 layers was observed.

Claims (6)

The film contains 0.1% by mass or more and 4% by mass or less of polymethylpentene as a thermoplastic resin incompatible with polypropylene, and the film is a laminated film having three or more layers, and the surface layer (A layer , When the thickness of the film is 100%, the content of polypropylene and incompatible polymethylpentene in the thickness from the surface side of 0.5% to 30% is greater than the inner layer (B layer), and the film is The polypropylene component (CXS) dissolved in xylene is less than 1.5% by mass relative to the total mass of the film when precipitated at room temperature after being completely dissolved in xylene, and the mesopentad fraction of the film is is 0.970 or more, and the film is heated from 30° C. to 260° C. at a rate of 20° C./min using a differential scanning calorimeter (DSC), then cooled from 260° C. to 30° C. at a rate of 20° C./min. The melting peak temperature (T _m2 ) is 164°C or higher when the temperature is reheated from °C to 260°C at 20°C/min, and the heat of fusion in the 100°C to 180°C region of the DSC curve is 105 J/g or more. A polypropylene film having an arithmetic mean height Sa of at least one surface of the film of 5 to 20 nm and a maximum height Sz of 100 to 500 nm. The polypropylene film according to claim 1 , wherein the glossiness of at least one surface of the film is 130% or more and less than 150%. The polypropylene film according to claim 1 or 2 , wherein the film has a peak melting temperature (T _m1 ) of 174°C or higher when the temperature is raised from 30°C to 260°C at a rate of 20°C/min by DSC. The polypropylene film according to any one of claims 1 to 3 , which has a thickness of 0.5 µm or more and 10 µm or less. A metal film laminated film comprising the polypropylene film according to any one of claims 1 to 4 and a metal film provided on at least one side thereof. A film capacitor using the metal film laminated film according to claim 5 .