JP6992919B2 - Polypropylene film, metal film laminated film and film capacitors - Google Patents

Description

The present invention relates to a polypropylene film particularly preferably used for capacitor applications.

Since polypropylene film is excellent in transparency, mechanical properties, electrical properties, etc., it is used in various applications such as packaging applications, tape applications, cable wrapping, and electrical applications such as capacitors.

Among these, polypropylene films are particularly preferably used for high-voltage capacitors, not limited to direct current and alternating current, because of their excellent withstand voltage resistance and low loss characteristics in capacitor applications.

Recently, various electric devices are becoming inverters, and along with this, there is an increasing demand for smaller capacitors and larger capacities. In response to demands from such fields, especially automobile applications (including hybrid car applications), solar power generation, and wind power generation applications, polypropylene films are also thinned and have improved breakdown voltage, and have characteristics for long-term use in high-temperature environments. It is becoming an essential situation to have excellent reliability that can maintain the power generation.

Polypropylene film is said to have high heat resistance and dielectric breakdown voltage among polyolefin films. On the other hand, when applied to the above fields, it is required to exhibit excellent dimensional stability at the operating environment temperature and stable electrical performance such as electric resistance even in a region 10 to 20 ° C higher than the operating environment temperature. Has been done. Here, from the viewpoint of heat resistance, it is said that the operating environment temperature will be higher when considering power semiconductor applications using silicon carbide (SiC) in the future. Due to the demand for higher heat resistance and higher withstand voltage as a capacitor, it is required to improve the dielectric breakdown voltage of a 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 in such a temperature environment. ..

Also, even in the process of vapor deposition of a film, the orientation of the film may be relaxed due to the heat history due to radiant heat, so a film that is unstable to heat should fully demonstrate the withstand voltage performance that the film originally has as a capacitor. Was difficult.

As a method for obtaining excellent performance in a high temperature environment when a polypropylene film is a thin film and used as a capacitor, for example, the crystallite size of the α (040) plane obtained by wide-angle X-ray diffraction and optical Proposal of a film that can be used for a long time at high temperature as a capacitor by controlling the total volume of compound refraction and surface protrusions of a certain height (for example, Patent Document 1), and polypropylene resins having different viscosities are blended and rapidly cooled after melt extrusion. As a result, a film has been proposed that reduces the recessed portion of the protrusion on the film surface by forming a meso phase on the cast sheet and exhibits a high insulation breakdown voltage even in a high temperature environment due to the smooth surface (for example, Patent Document 2). Further, it has been proposed to improve the dielectric breakdown strength by using a polypropylene raw material whose strain curability parameter is within a certain range (for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2014-231584 Japanese Unexamined Patent Publication No. 2019-179221 International Publication No. 2017/22 1985

Motonobu Kawai, "Film Capacitor Breakthrough, From Car to Energy", Nikkei Electronics (Japan), Nikkei BP, September 17, 2012, p.57-62

However, the polypropylene film described in Patent Document 1 does not sufficiently improve the dielectric breakdown voltage in a high temperature environment exceeding 110 ° C., and also has sufficient withstand voltage when converted into a capacitor and reliability in a high temperature environment. It was hard to say.

Further, the polypropylene film described in Patent Document 2 has a high dielectric breakdown voltage at a high temperature of 115 ° C., but the protrusion height of the film is not sufficient, wrinkles occur in the vapor deposition processing process, and in a high temperature environment exceeding 115 ° C. In some cases, reliability deteriorated when the film was made into a capacitor.

Further, the polypropylene film described in Patent Document 3 is not supposed to be used in a high temperature environment, and the withstand voltage and reliability of the capacitor may be impaired in a temperature range exceeding 110 ° C.

Therefore, the present invention has a structure having excellent withstand voltage characteristics and reliability in a high temperature environment, suitable for capacitors used under high temperature and high voltage, and having excellent heat stability, and is suitable for processing. It is an object of the present invention to provide a polypropylene film having a property, and an object of the present invention is to provide a metal film laminated film and a film capacitor using the polypropylene film.

The present inventors have made extensive studies to solve the above-mentioned problems, and the polypropylene films described in Patent Documents 1 to 3 have an dielectric breakdown voltage in a high-temperature environment and a withstand voltage in a high-temperature environment when used as a capacitor. The reasons why the characteristics, reliability, and workability are not sufficient are considered as follows.

That is, the polypropylene film described in Patent Document 1 can be said to have sufficient withstand voltage and reliability in a 110 ° C. environment as a capacitor, but when further assuming the withstand voltage in a high temperature environment, film formation It was considered that there was a problem that the draw ratio and heat treatment, the orientation of the molecular chains and the fixation of the structure were not always sufficient, and the aspherical chains of the film were relaxed at higher temperatures and the withstand voltage was lowered. The polypropylene film described in Patent Document 2 may not have sufficient slipperiness because the film surface is smooth, and gel is generated by blending a polypropylene raw material having a low melt flow rate (MFR) to withstand it. It was considered that the problem was that the voltage may drop or the film may be torn during film formation due to the gel as the starting point. The polypropylene film of Patent Document 3 contains a polypropylene raw material having strain curability within a certain range, but there is no idea of controlling the structure of the film by optimizing the stretching conditions at the time of film formation. It was considered that the problem was that the orientation of the molecular chains and the fixation of the structure were not always sufficient, and the orientation of the amorphous chains was relaxed and the withstand voltage was lowered in a high temperature environment.

Based on the above considerations, the present inventors further study and obtain the crystallite size and main orientation (of Through-TD) obtained by scanning in the main orientation direction of the α crystal (110) plane of wide-angle X-ray diffraction. The difference in crystallite size from (Through-MD) obtained by scanning in the direction orthogonal to the direction is less than a certain value, and the shrinkage stress in the longitudinal direction at 135 ° C. in thermomechanical analysis (TMA) is It has been found that the above problem can be solved by using a film having a value of a certain value or less.

That is, the present invention has a crystallite size obtained by scanning the α crystal (110) plane measured by wide-angle X-ray diffraction in the main orientation direction and a crystallite size obtained by scanning in a direction orthogonal to the main orientation direction. The absolute value of the difference from the above is 3.0 nm or less, and the longitudinal shrinkage stress (SF135MD) at 135 ° C. is 2.0 MPa in the heating process at a heating rate of 10 ° C./min in thermomechanical analysis (TMA). The following is a polypropylene film.

Further, the present invention is a metal film laminated film having a metal film on at least one side of the polypropylene film of the present invention.

Further, the present invention is a film capacitor using the metal film laminated film of the present invention.

According to the present invention, it has excellent withstand voltage characteristics and reliability in a high temperature environment, is suitable for capacitors used under high temperature and high voltage, has excellent structural stability against heat, and is used in a transfer process including a vapor deposition process. Provided is a polypropylene film capable of obtaining appropriate processability with less wrinkles. Further, a metal film laminated film and a film capacitor using the same are provided.

Hereinafter, the present invention will be described in detail. In the present invention, "greater than or equal to" means the same as or larger than the numerical value shown therein. Further, "less than or equal to" means the same as or smaller than the numerical value shown therein. Further, "room temperature" means 23 ° C.

The polypropylene film of the present invention preferably contains a linear polypropylene resin as a main component. Here, the main component means a component having the highest mass fraction (high content) among the components constituting the polypropylene film.

Hereinafter, the polypropylene film may be simply referred to as a film.

The polypropylene resin is mainly composed of a homopolymer of propylene, but a copolymerization component using other unsaturated hydrocarbons may be used as long as the object of the present invention is not impaired, or a polymer that is not a homopolymer of propylene. May be blended. Examples of monomer components other than propylene constituting such copolymerization components and blends include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, and 4-methyl. Examples thereof include pentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene and the like.

The copolymerization amount or blend amount other than the propylene component is preferably 1 mol% or less as the copolymerization amount from the viewpoint of insulation breakdown voltage and heat resistance, and the blend amount constitutes the film as the amount of the component other than propylene. It is preferably 1% by mass or less of the total resin.

The polypropylene film of the present invention preferably has M _{z + 1} / Mw of 3 or more and 10 or less with respect to its weight average molecular weight Mw and z + 1 average molecular weight M _{z + 1} . By setting M _{z + 1} / Mw to 10 or less, more preferably 7.9 or less, further preferably 6.9 or less, particularly preferably 6.5 or less, and most preferably 6.1 or less, the molecular weight distribution is narrow and the film has a narrow molecular weight distribution. As for the structure, it becomes a uniform structure with little local unevenness, heat shrinkage can be suppressed, and the effect of improving the dielectric breakdown voltage in a high temperature environment can be obtained.

As a means for controlling M _{z + 1} / Mw to the above range, the polypropylene resin A has a mesopentad molecular weight of 0.97 or more, a chip melting point of 160 ° C. or more, and a cold xylene soluble part (CXS) of less than 3% by mass. Using raw materials with a number average molecular weight (Mn) of 70,000 (7.0 × 10 ⁴ ) or less and a Z + 1 average molecular weight (M _{z + 1} ) of less than 3 million (3.0 × ¹⁰⁶ ), polypropylene resin B and / or This can be achieved by appropriately blending the polypropylene resin C within the preferable range of the present application.

The polypropylene film of the present invention has various additives such as organic particles, inorganic particles, crystal nucleating agents, antioxidants, heat stabilizers, chlorine scavengers, slip agents, and antistatic agents as long as the object of the present invention is not impaired. , Anti-blocking agent, filler, viscosity modifier, anti-coloring agent.

When an antioxidant is contained, it is preferable that the type and amount of the antioxidant are selected from the viewpoint of long-term heat resistance. The antioxidant is a phenolic agent having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various examples, such as 1,3,5-trimethyl-2,4,6-with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4). Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (eg, BASF's "Irganox"® 1330: molecular weight 775.2) or tetrakis [methylene-3 (3,5-di) -T-Butyl-4-hydroxyphenyl) propionate] It is preferable to use methane (for example, "Irganox" (registered trademark) 1010: molecular weight 1,177.7) manufactured by BASF Corporation in combination. The total content of these antioxidants is preferably 0.1% by mass or more and 1.0% by mass or less with respect to the total amount of polypropylene. By setting the content to 0.1% by mass or more, more preferably 0.2% by mass or more, the long-term heat resistance is excellent. By setting the content to 1.0% by mass or less, more preferably 0.7% by mass or less, still more preferably 0.4% by mass or less, blocking at high temperatures due to bleed-out of the antioxidant can be suppressed, and the capacitor element can be used. You can prevent adverse effects.

The polypropylene film of the present invention may contain a resin other than the polypropylene resin as long as the object of the present invention is not impaired. Examples of the resin other than the polypropylene resin include vinyl polymer resins including various polyolefin resins, polyester resins, polyamide resins, polyphenylene sulfide resins, polyimide resins, polycarbonate resins, and the like, and in particular, polymethylpentene and cyclo. Olefin copolymas, cycloolefin polymers, syndiotactic polystyrene and the like are preferably exemplified. The content of the resin other than the polypropylene resin is preferably less than 30% by mass, more preferably 19% by mass or less, still more preferably 15% by mass or less, most preferably, when the total resin component constituting the polypropylene film is 100% by mass. It is preferably 9% by mass or less. If the content of the resin other than the polypropylene resin is 30% by mass or more, the influence of the domain interface becomes large, so that the dielectric breakdown voltage in a high temperature environment may be lowered.

The polypropylene film of the present invention is a crystal obtained by scanning the α crystal (110) plane measured by wide-angle X-ray diffraction in the crystallite size obtained by scanning in the main orientation direction and in the direction orthogonal to the main orientation direction. The absolute value of the difference from the child size (hereinafter, also referred to as "difference in crystallite size depending on the orientation direction of the α crystal (110) plane") is 3.0 nm or less, and the temperature rise in thermomechanical analysis (TMA). It is important that the longitudinal shrinkage stress (SF135MD) at 135 ° C. is 2.0 MPa or less in the heating process at a rate of 10 ° C./min.

The polypropylene film of the present invention is not a microporous film. Here, the microporous film penetrates both surfaces of the film and uses a JIS P 8117 (2009) B-type Garley tester at 23 ° C. and a relative humidity of 65%, and the permeation time of 100 mL of air is 5 It is defined as a film having a pore structure with air permeability of 1,000 seconds / 100 mL or less.

In the polypropylene film of the present invention, it is important that the difference in crystallite size depending on the orientation direction of the α crystal (110) plane is 3.0 nm or less and the shrinkage stress SF135MD is 2.0 MPa or less.

In the polypropylene film of the present invention, the difference in crystallite size depending on the orientation direction of the α crystal (110) plane has a high correlation with the withstand voltage characteristics and reliability of the capacitor in a high temperature environment, and further, the thermal shrinkage stress. SF135MD affects workability and withstand voltage characteristics when used as a capacitor. In order to obtain a polypropylene film with high reliability even when used for a long time in a high temperature environment in capacitor applications, the difference in crystallite size depending on the orientation direction of the α crystal (110) plane and the thermal shrinkage stress SF135MD are below a certain value. It is especially important to control the capacitor in a high temperature environment in terms of withstand voltage characteristics, long-term reliability, and workability.

The difference in crystallite size depending on the orientation direction of the α crystal (110) plane of the polypropylene film is 3.0 nm or less, which means that the difference in width of the crystal lamellas constituting the film is small in the longitudinal direction and the width direction, and is more uniform. It is suggested that the structure is similar. The difference in crystallite size depending on the orientation direction of the α crystal (110) plane is 3.0 nm or less, preferably 2.5 nm or less, more preferably 2.1 or less, still more preferably 1.9 nm or less, still more preferably 1.7 nm. By doing the following, the structural difference is small, the structure becomes more uniform, the degree of crystal orientation is likely to increase, and the structural change can be suppressed to be small even when the film is heated. As a result, the film has a very stable structure especially in a high temperature environment and exhibits a high dielectric breakdown voltage even at a high temperature, so that the leakage current becomes small when it is used as a capacitor, and excellent reliability can be exhibited in a high temperature environment. When the difference in crystallite size depending on the orientation direction of the α crystal (110) plane is larger than 3.0 nm, it is placed in a high temperature state for a long time, especially when it is used as a capacitor in a high temperature environment where a high voltage is applied. At that time, the crystal denseness of the film is low, and the molecular chain relaxation of the amorphous portion connecting the adjacent crystal lamellas and the crystal lamellas progresses, and the withstand voltage is lowered. Therefore, the capacity of the capacitor is reduced, short circuit is broken, and the capacitor becomes inferior in reliability. Further, the difference in crystallite size depending on the orientation direction of the α crystal (110) plane is 0.5 nm or more from the viewpoint that the structural difference of the entire film is small, the structure is more uniform, and a stable film can be obtained even when biaxially stretched. Is preferable.

The difference in crystallite size can be reduced by stretching the unstretched sheet in which the β-spherulite size is controlled to be small at a high area magnification in the stretching step, and particularly by stretching at a high magnification in the width direction. As will be described later, for example, polypropylene raw material A (sometimes referred to as polypropylene resin (A); the same applies to polypropylene raw material (B) and polypropylene raw material (C) described later) has a high mesopentad fraction and cold xylene is acceptable. Use of polypropylene raw material A and / or polypropylene raw material B having a melted portion (CXS) of less than 3.0% by mass, containing a branched polypropylene raw material C, and setting the temperature of the casting drum within a preferable range described later. Preliminary stretching of 1.01 times or more and 1.10 times or less is performed before stretching in the longitudinal direction, and the area stretching ratio is 60 times or more, preferably 65 times or more, and the stretching ratio in the width direction is 11. In the heat fixing treatment and relaxation treatment step 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 is stretched in the width direction. While maintaining tension, heat treatment is performed at a temperature lower than the heat treatment temperature of the first stage at 135 ° C. or higher (second stage), and further at 80 ° C. or higher under the condition of being lower than the heat treatment temperature of the second stage (third stage). By appropriately performing a multi-stage heat fixing treatment and relaxation treatment on the film, a polypropylene film having a small difference in crystallite size depending on the orientation direction of the α crystal (110) plane can be preferably obtained as described above.

The polypropylene film of the present invention needs to have a longitudinal contraction stress (SF135MD) at 135 ° C. of 2.0 MPa or less in the heating process of thermomechanical analysis (TMA). By setting SF135MD to 2.0 MPa or less, preferably 1.8 MPa or less, more preferably 1.5 MPa or less, and further preferably 1.3 MPa or less, shrinkage of the film itself can be suppressed by heat in the capacitor manufacturing process and the use process. .. Therefore, when the capacitor is used, the element does not wind tightly, so the self-healing function operates by maintaining an appropriate gap between the film layers, and the penetration short-circuit fracture accompanied by a rapid capacity decrease is suppressed, and the capacitor. The reliability as a product is increased. When SF135MD is larger than 2.0 MPa, the molecular chain relaxation of the film progresses when it is used as a capacitor in a high temperature environment where a high voltage is applied, especially when it is placed in a high temperature state for a long time. The withstand voltage decreases. Therefore, the capacity of the capacitor is reduced, short circuit is broken, and the capacitor becomes inferior in reliability.

On the other hand, SF135MD is preferably 0.1 MPa or more. When the value is 0.1 MPa or more, the film itself shrinks sufficiently due to the heat of the capacitor manufacturing process and the usage process, and the capacity according to the design can be obtained.

As will be described later, the SF135MD within the preferable range as described above uses, for example, a raw material having a high mesopentad fraction and a cold xylene-soluble portion (CXS) of less than 3% by mass as the polypropylene raw material A, and is stretched in the longitudinal direction. Preliminary stretching of 1.01 times or more and 1.10 times or less was performed before, and the area stretching ratio was 65 times or more at the time of biaxial stretching, and the stretching ratio in the width direction was 11.0 times or more. In the heat fixing treatment and the relaxation treatment step, first, the relaxation treatment is performed while performing the heat treatment (first step) at a temperature lower than the stretching temperature in the width direction, and then the first step is performed while maintaining the tension in the width direction of the film. A multi-stage heat fixing treatment and relaxation treatment in which heat treatment at 135 ° C. or higher (second stage) at a temperature lower than the heat treatment temperature and then heat treatment (third stage) at 80 ° C. or higher under conditions lower than the heat treatment temperature of the second stage are performed. It can be obtained by appropriately applying it to a film.

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, may be referred to as "MD"), and the "width direction" is the above-mentioned film. It is a direction orthogonal to the flow direction in the manufacturing process (hereinafter, may be referred to as "TD"). When the film sample has a shape such as a reel or a roll, it can be said that the film winding direction is the longitudinal direction. On the other hand, in the case of a film whose direction corresponds to the flow direction in the film manufacturing process from the appearance of the film, a slit-shaped film piece is sampled and the breaking strength is determined by a tensile tester. , The direction giving the maximum breaking strength is regarded as the film width direction and the main orientation direction, and the direction orthogonal to the film width direction is regarded as the direction orthogonal to the longitudinal direction and the main orientation direction. Details will be described later, but if the sample width is less than 50 mm and the breaking strength cannot be determined with a tensile tester, the crystal orientation of the α crystal (110) plane by wide-angle X-rays is measured as follows, and the following is performed. The film length and width directions are set based on the judgment 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 is obtained. The direction in which the diffraction intensity is highest is defined as the film width direction and the main orientation direction, and the directions orthogonal to the film width direction and the main orientation direction are defined as the longitudinal direction and the direction orthogonal to the main orientation direction.

The polypropylene film of the present invention has a crystallite size (of Through-MD) of 10.0 nm or less obtained by scanning in a direction orthogonal to the main orientation direction of the α crystal (110) plane, which is measured by wide-angle X-ray diffraction. It is preferable to have. By setting the crystallite size to 10.0 nm or less, more preferably 8.0 nm or less, further preferably 6.9 nm or less, particularly preferably 6.6 nm or less, and most preferably 6.4 nm or less, the crystal becomes fine. The degree of crystal orientation is also high, and it shows a high breakdown voltage even at high temperatures. Therefore, when it is used as a capacitor, the leakage current becomes small, and excellent reliability can be exhibited in a high temperature environment. The lower limit of the crystallite size obtained by scanning in the direction orthogonal to the main orientation direction of the α crystal (110) plane has a small structural difference in the entire film, has a more uniform structure, and is stable even when biaxially stretched. It is substantially 3.0 nm from the viewpoint of obtaining.

Further, the polypropylene film of the present invention has a crystallite size (Through-TD) of 10.0 nm or less obtained by scanning in the main orientation direction of the α crystal (110) plane as measured by wide-angle X-ray diffraction. Is preferable. By setting the crystallite size to 10.0 nm or less, more preferably 9.0 nm or less, further preferably 8.9 or less, particularly preferably 8.7 nm or less, and most preferably 8.5 nm or less, the crystals become fine. The degree of crystal orientation is also high, and it shows a high breakdown voltage even at high temperatures. Therefore, when it is used as a capacitor, the leakage current becomes small, and excellent reliability can be exhibited in a high temperature environment. The lower limit of the crystallite size obtained by scanning in the main orientation direction of the α crystal (110) plane has a small structural difference in the entire film, and by making the structure more uniform, the film can be stably stretched even if it is biaxially stretched. From the viewpoint of obtaining, it is substantially 5.0 nm.

The polypropylene film of the present invention preferably has a crystal orientation of the α crystal (110) plane measured by wide-angle X-ray diffraction of 0.77 or more. By setting the degree of crystal orientation to 0.77 or more, more preferably 0.78 or more, further preferably 0.80 or more, still more preferably 0.82 or more, the orientation order of the crystal structure constituting the film is disturbed. It is possible to reduce the number of parts and prevent the occurrence of a part where dielectric breakdown is likely to occur. Therefore, when a capacitor is used, capacity reduction and short-circuit fracture are suppressed even in a high temperature environment, and withstand voltage is maintained, so that high reliability can be obtained. On the other hand, the crystal orientation of the α crystal (110) plane measured by wide-angle X-ray diffraction is preferably 0.95 or less from the viewpoint of stably obtaining a film after biaxial stretching.

The crystal orientation of the α crystal (110) plane as described above is, for example, polypropylene raw material A and / or polypropylene having a high mesopentad fraction as polypropylene raw material A and a cold xylene soluble portion (CXS) of less than 3.0% by mass. Use of raw material B, inclusion of branched polypropylene raw material C, pre-stretching of 1.01 times or more and 1.10 times or less before stretching in the longitudinal direction, and area stretching ratio of 60 times or more during biaxial stretching. It can be achieved by preferably 65 times or more and the stretching ratio in the width direction is 11.0 times or more.

The polypropylene film of the present invention preferably has a crystal orientation of 0.73 or more on the α crystal (110) plane when the film after heating at 125 ° C. for 60 minutes is measured by wide-angle X-ray diffraction. By setting the degree of crystal orientation to 0.73 or more, more preferably 0.75 or more, further preferably 0.78 or more, still more preferably 0.81 or more, the orientation order of the crystal structure constituting the film is high. It is maintained and suppresses the occurrence of parts that are prone to dielectric breakdown, and when used as a capacitor, it suppresses capacity reduction and short-circuit breakdown even in a high temperature environment, suppresses deterioration of withstand voltage, and obtains high reliability. Can be done.

On the other hand, from the viewpoint of obtaining a stable film after biaxial stretching, the crystal orientation of the α crystal (110) plane when the polypropylene film after heating at 125 ° C. for 60 minutes is measured by wide-angle X-ray diffraction is 0.95 or less. Is preferable. Further, the lower limit of the crystal orientation of the α crystal (110) plane is not particularly limited, but the disorder of the orientation order of the crystal structure constituting the film is reduced, and the occurrence of a portion where dielectric breakdown is likely to occur is suppressed. From the viewpoint, it is 0.60.

As described later, the degree of crystal orientation of the α crystal (110) plane when the film after heating at 125 ° C. for 60 minutes is measured by wide-angle X-ray diffraction has a high mesopentad fraction as, for example, polypropylene raw material A. In addition, using a raw material having a cold xylene soluble part (CXS) of less than 3.0% by mass, pre-stretching of 1.01 times or more and 1.10 times or less was performed before stretching in the longitudinal direction, and the area was subjected to biaxial stretching. The stretching ratio is 60 times or more, preferably 65 times or more, and the stretching ratio in the width direction is 11.0 times or more. The relaxation treatment is performed while performing the heat treatment at a low temperature (first stage), and then the heat treatment at 145 ° C. or higher (second stage) at a temperature lower than the heat treatment temperature of the first stage while maintaining the tension in the width direction of the film is further performed. It can be obtained by appropriately applying a multi-stage heat fixing treatment and relaxation treatment of heat treatment (third stage) at 80 ° C. or higher and lower than the heat treatment temperature of the second stage.

In the polypropylene film of the present invention, the stress (F5MD) at 5% elongation in the longitudinal direction of the film when the film after heating at 150 ° C. for 10 minutes was subjected to a tensile test at room temperature and the film after heating under the same conditions at room temperature. It is preferable that the sum of the stress (F5TD) at 5% elongation in the film width direction in the tensile test is 150 MPa or more. By setting the sum of F5MD and F5TD to 150 MPa or more, more preferably 170 MPa or more, further preferably 180 MPa or more, still more preferably 190 MPa or more, it has rigidity in a high temperature environment and high reliability when used as a capacitor. Can be obtained.

On the other hand, the sum of F5MD and F5TD is preferably 300 MPa or less. By setting the pressure to 300 MPa or less, it is possible to prevent the film from breaking in the film forming process and deteriorating the film forming property.

As described later, for the sum of F5MD and F5TD in the above range, for example, a raw material having a high mesopentad fraction and a cold xylene soluble portion (CXS) of less than 3.0% by mass is used as the polypropylene raw material A. Preliminary stretching of 1.01 times or more and 1.10 times or less was performed before stretching in the longitudinal direction, and the area stretching ratio was 65 times or more and the stretching ratio in the width direction was 11.0 times or more during biaxial stretching. In the heat fixing treatment and relaxation treatment step 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 is kept tense in the width direction. A multi-stage heat treatment method in which heat treatment is performed at a temperature lower than the heat treatment temperature of the first stage at 145 ° C. or higher (second stage), and further at 80 ° C. or higher at a temperature lower than the heat treatment temperature of the second stage (third stage). It can be obtained by appropriately applying a treatment and a relaxation treatment to the film.

The polypropylene film of the present invention preferably has a heat shrinkage rate (HS125TD) in the width direction after heat treatment at 125 ° C. for 15 minutes at 1.0% or less. By setting the heat shrinkage rate to 1.0% or less, more preferably 0.8% or less, further preferably 0.6% or less, still more preferably 0.4% or less, the heat of the capacitor manufacturing process and the use process is set. It is possible to suppress the shrinkage of the film due to the shrinkage of the film and the deterioration of the withstand voltage due to the poor contact with the metallikon at the end of the element, and it is possible to prevent the reliability from being deteriorated due to the capacity decrease due to the winding of the element and the short circuit breakage.

On the other hand, the heat shrinkage in the width direction after heating at 125 ° C. for 15 minutes is preferably 0.02% or more. By setting it to 0.02% or more, it is possible to prevent the winding state of the element from loosening due to the heat of the capacitor manufacturing process and the usage process.

As for the heat shrinkage in the heat treatment at 125 ° C. for 15 minutes in the film width direction in the above range, for example, as described later, the polypropylene raw material A has a high mesopentad fraction and the cold xylene soluble portion (CXS) is 3. Using a raw material of less than 0% by mass, pre-stretching 1.01 times or more and 1.10 times or less is performed before stretching in the longitudinal direction, and the area stretching ratio is 60 times or more, preferably 65 times or more during biaxial stretching. In addition, the stretching ratio in the width direction is set to 11.0 times or more, and in the heat fixing treatment and the relaxation treatment step after the biaxial stretching, first, the heat treatment (first step) at a temperature lower than the stretching temperature in the width direction is performed for relaxation. After the treatment, the film is heat-treated at a temperature of 135 ° C. or higher (second stage) at a temperature lower than the heat treatment temperature of the first stage while maintaining tension in the width direction (second stage), and further at 80 ° C. or higher and lower than the heat treatment temperature of the second stage. This can be achieved by appropriately performing a multi-stage heat fixing treatment and relaxation treatment in which heat treatment (third stage) is performed under the conditions.

The polypropylene film of the present invention preferably has a melting peak temperature (Tm) of 170 ° C. or higher obtained when the film is heated from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC. .. By setting the Tm to 170 ° C. or higher, more preferably 171 ° C. or higher, further preferably 172 ° C. or higher, further preferably 173 ° C. or higher, still more preferably 174 ° C. or higher, the dielectric breakdown voltage in a high temperature environment can be effectively reduced. Can be improved. On the other hand, Tm is preferably 200 ° C. or lower from the viewpoint that polypropylene resin can be industrially produced.

Tm in the above range can be achieved, for example, by using a raw material having a high mesopentad fraction and a cold xylene-soluble portion (CXS) of less than 3.0% by mass as the polypropylene raw material A, as described later. be.

The polypropylene film of the present invention has a melting peak temperature (Tm) of the film obtained by heating the film from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC, and 260 ° C. to 30 ° C. after the temperature rise. It is preferable that the difference (Tm-Tc) from the crystallization peak temperature (Tc) obtained when the temperature is lowered to 20 ° C./min is 65 ° C. or less. By setting (Tm-Tc) to 65 ° C. or lower, more preferably 63 ° C. or lower, still more preferably 61 ° C. or lower, still more preferably 59 ° C. or lower, still more preferably 57 ° C. or lower, crystallization in the cooling solidification process of the resin is performed. The time can be shortened and the formation of coarse spherulites can be suppressed. By suppressing the formation of such coarse spherulites in the cast sheet, it is possible to reduce the generation of internal voids in the stretching step and the decrease in reliability of the capacitor due to the formation of coarse protrusions on the surface. Further, it is possible to prevent the film from deteriorating the slipperiness of the film and the processability from deteriorating due to the increase in the number of flat portions on the entire surface of the film.

On the other hand, the difference between Tm and Tc (Tm-Tc) is preferably 40 ° C. or higher. When the temperature is 40 ° C. or higher, the film forming stability is excellent.

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 different from the melting peak temperature of polypropylene. In the present invention, the peak temperature observed at 170 ° C. or higher and 200 ° C. or lower is defined as the melting peak temperature (Tm) and the crystallization peak temperature (Tc) of the polypropylene film of the present invention. At this time, it is observed when two or more peaks are observed in the temperature range, or when the peak temperature can be observed on a multi-stage DSC chart called a shoulder (when two or more peaks overlap each other). ), But in the present invention, the peak having the largest absolute value of the vertical axis heat flow (unit: mW) of the DSC chart is selected and used as Tm and Tc, respectively.

The (Tm-Tc) in the above range is, for example, a polypropylene raw material A and / or a polypropylene raw material B having a high mesopentad fraction and a cold xylene soluble portion (CXS) of less than 3.0% by mass as the polypropylene raw material A. It can be achieved by using, containing a branched polypropylene raw material C, and adjusting the ratio of these components.

The polypropylene film of the present invention exhibits a high breakdown voltage even in a high temperature environment, and is defined by ISO25178 on at least one surface of the film in order to exhibit withstand voltage and reliability even in a high temperature environment when used as a capacitor. The skewness (Ssk) is preferably more than -30 and less than 5. Here, Sk is a parameter indicating the degree of deviation of the unevenness of the surface. This Sk represents the mean square of Z (x, y) on the reference plane dimensionless by the cube of the root mean square root height Sq, and means the skewness (waido), which is the average plane. It is a numerical value showing the symmetry of the mountain part and the valley part centered on. Therefore, when Sk is smaller than 0, it means that the Sk is biased downward with respect to the average line, that is, there are more concave valleys than convex peaks. On the other hand, when Sk is larger than 0, it means that the sk is biased upward with respect to the average line, that is, there are more convex peaks than concave valleys. When the degree of deviation Sk is 0, it means a state symmetric (normally distributed) with respect to the average line.

By setting the Sk to more than -30, more preferably -28 or more, still more preferably -26 or more, it is possible to prevent the film surface from having many dented shapes and being overly biased, and especially in high voltage capacitor applications. Even in an environment, the withstand voltage is less likely to be impaired, the slipperiness of the film can be obtained, and good processability can be obtained.

On the other hand, by setting the Sk to less than 5, more preferably 4 or less, still more preferably 3 or less, it is possible to suppress the excessive presence of the shape of the convex portion on the film surface, and when the capacitor is used, the layer between the films. It is possible to prevent a gap from being generated in the film, prevent a decrease in capacity in a high temperature environment, and prevent the film from being impaired in slipperiness and deterioration in withstand voltage and workability.

For Sk in the polypropylene film of the present invention, for example, polypropylene raw material B having preferable properties described later is used, the area stretching ratio is 60 times or more, preferably 65 times or more during biaxial stretching, and the stretching ratio in the width direction is By setting the temperature to 11.0 times or more and controlling the casting drum temperature, the melting peak temperature (Tm) and the crystallization peak temperature (Tc) of the film within a preferable range, it is possible to keep the temperature within the above range.

In the polypropylene film of the present invention, the protruding peak heights SpkA and SpkB defined in ISO25178 of the surface A of one side surface and the surface B of the other side surface satisfy the following relationship, respectively. preferable.
SpkA <SpkB
20nm ≤ SpkA ≤ 100nm
80nm ≤ SpkB ≤ 150nm
here,
SpkA: Height of the protruding ridge of the surface A SpkB: Height of the protruding ridge of the surface B.

Spk is a kind of functional parameter defined by ISO25178, and indicates the average height of a portion (protruding mountain portion) higher than the intersection of the equivalent straight line of the bearing curve of the height data and the straight line of the load area ratio = 0%. Here, the bearing curve of the height data is expressed as a percentage by accumulating the frequency at a certain height from the higher side and assuming that the total number of the total height data is 100%, and the load area ratio at a certain height C is Smr. Given in (C). Further, the equivalent straight line has the smallest slope among the straight lines in which the difference in load area ratio (Smr) is 40%.

In the polypropylene film of the present invention, SpkA is more preferably 30 nm or more, further preferably 40 nm or more. Further, SpkA is more preferably 90 nm or less, and further preferably 80 nm or less.

In the polypropylene film of the present invention, SpkB is more preferably 90 nm or more, further preferably 100 nm or more. Further, SpkB is more preferably 140 nm or less, and further preferably 130 nm or less.

When SpkA and SpkB satisfy the above range, the height of the surface protrusions of the film is moderately high, so that sufficient slipperiness can be obtained, excellent workability at the time of making a capacitor element, and excessively high protrusions on the film surface. It can be suppressed and the withstand voltage of the capacitor can be prevented from decreasing.

To control SpkA and SpkB within the above range, for example, using a polypropylene raw material B having preferable properties described later, an area stretching ratio of 60 times or more, preferably 65 times or more, and a width at the time of biaxial stretching. It is possible by setting the draw ratio in the direction to 11 times or more and controlling the casting drum temperature, the melting peak temperature (Tm) and the crystallization peak temperature (Tc) of the film within a preferable range.

The polypropylene film of the present invention preferably has an arithmetic mean height (Sa) of 35 nm or more and 100 nm or less as defined by ISO25178 on at least one surface of the film. By setting Sa to 35 nm or more, more preferably 40 nm or more, the slip of the film is kept moderate, the handling property is excellent, the generation of wrinkles is suppressed, and the element processability is excellent. On the other hand, by setting Sa to 100 nm or less, more preferably 75 nm or less, still more preferably 60 nm or less, a high withstand voltage can be effectively obtained. From the above viewpoint, it is preferable that Sa is 35 nm or more and 100 nm or less, or in the above-mentioned preferable range, on the surface of both sides where Sa is smaller.

In order to control the Sa of the polypropylene film of the present invention within the above-mentioned preferable range, for example, the polypropylene raw material B and / or the polypropylene raw material C should be used as the polypropylene raw material A having the preferable properties described later, and the area may be stretched during biaxial stretching. The magnification is 60 times or more, preferably 65 times or more, and the stretching ratio in the width direction is 11.0 times or more, and the casting drum temperature, the melting peak temperature (Tm) and the crystallization peak temperature (Tc) of the film are in a preferable range. It is possible by controlling to.

The polypropylene film of the present invention has a total volume of 50 μm ³ or more, which is the total volume of valleys having a depth of 20 nm or more in a region of 0.561 mm × 0.561 mm measured by a scanning white interference microscope on at least one surface. It is preferably 5,000 μm ³ or less. By setting the total volume to 50 μm ³ or more, more preferably 100 μm ³ or more, still more preferably 500 μm ³ or more, the surface is appropriately uneven, the handling property is improved by the appropriate slip of the film, and wrinkles are formed. Occurrence is reduced and element workability is improved. In addition, even when used as a capacitor for a long time, it suppresses large changes in capacitance due to the effects of wrinkles, etc., and even when a capacitor with laminated films is used, it self-recovers because there is an appropriate gap between the films. The function (self-healing) works and the reliability of the capacitor is improved. On the other hand, the total volume of the valley is 5,000 μm ³ or less, preferably 4,000 μm ³ or less, more preferably 3,500 μm ³ or less, and particularly preferably 3,000 μm ³ or less, so that the thickness is locally thin. It is possible to suppress the occurrence of dielectric breakdown. Therefore, the withstand voltage of the film is improved, and the withstand voltage and reliability in a high temperature environment can be improved even when used for a high voltage capacitor application.

To set the total volume of the valleys on the film surface in the above-mentioned preferable range, for example, the polypropylene raw material B described later is used, the area stretching ratio is 60 times or more, preferably 65 times or more in the biaxial stretching, and in the width direction. It is possible by setting the draw ratio to 11.0 times or more and controlling the casting drum temperature, the melting peak temperature (Tm) and the crystallization peak temperature (Tc) of the film within a preferable range.

The polypropylene film of the present invention has a coefficient of static friction (μ) when the surfaces on at least one side are overlapped with each other on the same side, from the viewpoint of imparting appropriate slipperiness and improving workability at the time of manufacturing a capacitor element. It is preferable that _s ) is 0.3 or more and 1.5 or less. By setting the static friction coefficient μ _s to 0.3 or more, more preferably 0.4 or more, and further preferably 0.5 or more, the film slips too much and unwinding occurs during film forming or element processing. You can prevent it from happening. On the other hand, by setting the static friction coefficient μ _s to 1.5 or less, more preferably 1.0 or less, and further preferably 0.8 or less, an extreme decrease in the slipperiness of the film can be suppressed, so that the occurrence of wrinkles can be suppressed. Further, the handling property and the element processability can be improved.

The polypropylene film of the present invention preferably has a mesopentad fraction of 0.970 or more as measured by a nuclear magnetic resonance method (NMR method). The mesopentad fraction is an index showing the stereoregularity of the crystal phase of polypropylene, and the crystallinity is set by setting the mesopentad fraction to 0.970 or more, more preferably 0.975 or more, and further preferably 0.981 or more. The temperature is high, the melting point is high, and the breakdown voltage in a high temperature environment can be improved. The upper limit of the mesopentad fraction is not specified.

In the present invention, the polypropylene resin having a high mesopentad fraction is preferably prepared by a Ziegler-Natta catalyst, and a method of appropriately selecting an electron donating component in the catalyst is preferably adopted. As a result, the polypropylene resin can have a molecular weight distribution (Mw / Mn) of 3.0 or more and a <2,1> erythro site defect of 0.1 mol% or less, and it is preferable to use such a polypropylene resin.

In the polypropylene film of the present invention, the polypropylene component (CXS, also referred to as a cold xylene-soluble portion) dissolved in xylene is contained in the polypropylene film when the polypropylene film is completely dissolved with xylene and then precipitated at room temperature. It is preferably 0% by mass or less. Here, it is considered that CXS corresponds to a component that is difficult to crystallize due to reasons such as low stereoregularity and low molecular weight. CXS is 3.0% by mass or less, more preferably 1.5% by mass or less, further preferably 1.3% by mass or less, particularly preferably 1.1% by mass or less, and most preferably 0.9% by mass or less. This makes it possible to increase the heat resistance of the film, the withstand voltage at high temperatures, or the dielectric breakdown voltage. Therefore, when it is used for a capacitor, relaxation in a high temperature environment is suppressed, thermal dimensional stability is improved, and leakage current can be suppressed. Further, the lower limit of CXS is not particularly limited, but it is practical that it is 0.1% by mass. If the CXS is set to less than 0.1% by mass, the stretchability during film formation may deteriorate and tearing may occur.

In order to keep the CXS content in the above range, 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 the propylene monomer itself, or the like can be used.

The polypropylene film of the present invention preferably has a breakdown voltage of 350 V / μm or more at 130 ° C. By setting the breakdown voltage to 350 V / μm or more, more preferably 375 V / μm or more, further preferably 400 V / μ m or more, still more preferably 420 V / μ m or more, the capacitor can be used for a long time especially in a high temperature environment. Since it is difficult to cause short circuit breakdown even in use, withstand voltage resistance can be maintained and high reliability can be obtained. The upper limit of the dielectric breakdown voltage at 130 ° C. is not particularly limited, but is about 800 V / μm.

In order to control the film insulation breakdown voltage at 130 ° C. within the above range, for example, as will be described later, the polypropylene raw material A has a high mesopentad fraction and the cold xylene soluble part (CXS) is less than 3.0% by mass. Using raw materials, pre-stretching 1.01 to 1.10 times is performed before stretching in the longitudinal direction, the area stretching ratio is 65 times or more during biaxial stretching, and the stretching ratio in the width direction is 11.0 times or more. In the heat fixing treatment and relaxation treatment step 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 is kept tense in the width direction. A multi-stage method in which heat treatment is performed at a temperature lower than the heat treatment temperature of the first stage at 135 ° C. or higher (second stage), and further at 80 ° C. or higher under conditions lower than the heat treatment temperature of the second stage (third stage). This can be achieved by appropriately applying heat treatment and relaxation treatment to the film.

The polypropylene film of the present invention is preferably surface-treated. Polypropylene film usually has a low surface energy, and it is difficult to stably apply metal vapor deposition. Therefore, it is preferable to perform surface treatment before vapor deposition for the purpose of improving the adhesiveness with the metal film. Specific examples of the surface treatment include 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, but the polypropylene film of the present invention has a wetting tension of preferably 37 to 75 mN / m, more preferably 39 to 65 mN / m, and further, by these surface treatments. It is preferable that the temperature is about 41 to 55 mN / m because the adhesiveness to the metal film is excellent and the safety as a capacitor is also good.

The polypropylene film of the present invention preferably has a film thickness of 0.5 μm or more and less than 25 μm. By setting the film thickness to 0.5 μm or more and less than 25 μm, more preferably 0.6 μm or more and 6 μm or less, further preferably 0.8 μm or more and 4 μm or less, and further preferably 1 μm or more and 2.5 μm or less, the film resistance in a high temperature environment. It has an excellent balance between voltage characteristics and miniaturization of the capacitor size due to thinning, and is particularly suitable for thin-film heat-resistant film capacitors required for automobile applications (including hybrid car applications) used in high-temperature environments.

The film thickness can be adjusted by, for example, adjusting the extrusion discharge amount, the rotation speed of the casting drum, the lip gap of the base, the stretching ratio, and the like. More specifically, it can be reduced by reducing the extrusion discharge amount, increasing the rotation speed of the casting drum, narrowing the lip gap of the base, increasing the stretching ratio, and the like. In addition, these methods can be used together as appropriate.

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 a capacitor, but various types of capacitors can be used. Specifically, from the viewpoint of the electrode configuration, it may be either a combined winding capacitor of a metal foil and a film or a metal vapor-deposited film capacitor, and an oil-immersed type capacitor impregnated with insulating oil or insulating oil is completely used. It is also preferably used for dry capacitors that do not. From the viewpoint of utilizing the characteristics of the film of the present invention, it is particularly preferably used as a metal-deposited film capacitor. The shape of the film in the capacitor may be a winding type or a laminated type.

The method for producing the polypropylene film of the present invention will be described with reference to an example.

First, a raw material preferable to be used for the polypropylene film of the present invention will be described. As described above, in order to obtain the polypropylene film of the present invention, it is preferable to use a plurality of types of polypropylene raw materials having different number average molecular weights.

The polypropylene raw material A refers to linear polypropylene having a smaller number average molecular weight (Mn) than the polypropylene raw material B described later. The Mn of the polypropylene raw material A is preferably 30,000 (3.0 × 10 ⁴ ) or more, more preferably 40,000 (4.0 × 10 ⁴ ) or more, and 50,000 (5. 0 × 10 ⁴ ) or more is more preferable. The Mn of the polypropylene raw material A is preferably 90,000 (9.0 × 10 ⁴ ) or less, more preferably 80,000 (8.0 × 10 ⁴ ) or less, from the viewpoint of obtaining thermal stability in a high temperature environment.

The Z + 1 average molecular weight (M _{z + 1} ) of the polypropylene raw material A is preferably 1 million (1.0 × ¹⁰⁶ ) or more, and more preferably 1.5 million (1.5 × ¹⁰⁶ ) or more from the viewpoint of biaxially stretching the film. .. Further, the _{Mz + 1} of the polypropylene raw material A is preferably 2.5 million (2.5 × ¹⁰⁶ ) or less, more preferably 2 million (2.0 × ¹⁰⁶ ) or less, from the viewpoint of obtaining thermal stability in a high temperature environment. ..

The polypropylene raw material A preferably has a cold xylene-soluble portion (hereinafter, CXS) of 3% by mass or less. By setting the CXS to 3.0% by mass or less, more preferably 2.0% by mass or less, further preferably 1.5% by mass or less, still more preferably 1.0% by mass or less, the film forming stability is excellent. Improves film strength, dimensional stability, and heat resistance. The lower the CXS, the more preferable, but the lower limit is about 0.1% by mass.

In order to keep the CXS content within the above range, a method of increasing the catalytic activity when obtaining the resin and a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

The mesopentad fraction of the polypropylene raw material A is preferably 0.970 or more. The mesopentad fraction is an index showing the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method), and the mesopentad fraction is 0.970 or more, more preferably 0.975 or more, still more preferably. When it is 0.980 or more, more preferably 0.983 or more, the crystallinity and the melting point become high, and it is suitable for use at a high temperature. The upper limit of the mesopentad fraction is not specified.

In order to obtain a polypropylene resin having a high mesopentad fraction, for example, a method of washing the resin powder obtained with a solvent such as n-heptane, a method of appropriately selecting a catalyst and / or a co-catalyst, and a method of appropriately selecting a composition are preferable. Will be adopted.

The melting point of the chip of the polypropylene raw material A (meaning the melting point of the resin; the same applies hereinafter) is preferably 160 ° C. or higher. By setting the melting point of the chip to 160 ° C. or higher, more preferably 163 ° C. or higher, still more preferably 166 ° C. or higher, it is possible to effectively obtain withstand voltage characteristics in a high temperature environment when the film is formed.

The melting point of the chip is the melting peak temperature obtained when the chip is heated from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC. When two or more melting peak temperatures are observed within the above temperature range, or when the peak temperature can be observed on a multi-stage DSC chart called a shoulder (observed when two or more peaks overlap). However, in the present invention, the temperature of the peak having the largest absolute value of the vertical axis heat flow (unit: mW) of the DSC chart is defined as the chip melting point.

As for the ratio of the polypropylene raw material A in the raw material of the polyolefin film of the present invention, it is preferable that the polypropylene raw material A is the main component, that is, the largest amount with respect to the polyolefin film.

The raw material for the polyolefin film of the present invention has a number average molecular weight (Mn) higher than that of the polypropylene raw material A in addition to the polypropylene raw material A from the viewpoint of effectively obtaining withstand voltage characteristics in a high temperature environment when the film is made. It is also preferable to include a large polypropylene raw material B.

The number average molecular weight (Mn) of the polypropylene raw material B is preferably 50,000 (5.0 × 10 ⁴ ) or more, more preferably 60,000 (6.0 × 10 ⁴ ) or more, from the viewpoint of biaxially stretching the film. More preferably 70,000 (7.0 × ¹⁰⁴ ) or more. On the other hand, from the viewpoint of obtaining thermal stability of the film in a high temperature environment, the Mn of the polypropylene raw material B is preferably 120,000 (12.0 × 10 ⁴ ) or less, more preferably 110,000 (11.0 × 10 ⁴ ) or less. More preferably, it is 100,000 ⁽ 10.0 × 104) or less.

The Mn of the polypropylene raw material B is larger than the Mn of the polypropylene raw material A, preferably 10,000 (1.0 × 10 ⁴ ) or more, and more preferably 20,000 (2.0 × 10 ⁴ ) or more.

The Z + 1 average molecular weight (M _{z + 1} ) of the polypropylene raw material B is preferably 2.5 million (2.5 × ¹⁰⁶ ) or more, and more preferably 3.5 million (3.5 × ¹⁰⁶ ) or more from the viewpoint of biaxially stretching the film. , 4 million (4.0 × ¹⁰⁶ ) or more is more preferable, and 4.5 million (4.5 × ¹⁰⁶ ) or more is further preferable. On the other hand, from the viewpoint of obtaining thermal stability of the film in a high temperature environment, the _{Mz + 1} of the polypropylene raw material B is preferably 8 million (8.0 × ¹⁰⁶ ) or less, and 7 million (7.0 × ¹⁰⁶ ) or less. More preferred.

The M _{z + 1} of the polypropylene raw material B is preferably larger than the M _{z + 1} average molecular weight of the polypropylene raw material A from the viewpoint of obtaining the thermal stability of the film in a high temperature environment, and is larger than 500,000 (0.5 × ¹⁰⁶ ). Is more preferable, and it is more preferable that it is larger by 1 million (1.0 × ¹⁰⁶ ) or more, and it is further preferable that it is larger by 1.5 million (1.5 × ¹⁰⁶ ) or more.

The polypropylene raw material B preferably has a cold xylene soluble portion (CXS) content of 4.0% by mass or less. By setting the CXS content in the polypropylene raw material B to 4.0% by mass or less, more preferably 3.0% by mass or less, the film forming stability is excellent, the strength of the film is improved, and the dimensional stability and heat resistance are improved. Also improves. The lower the CXS, the more preferable, but the lower limit is about 0.1% by mass.

In order to keep the CXS content within the above range, a method of increasing the catalytic activity when obtaining the resin and a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

The mesopentad fraction of the polypropylene raw material B is preferably 0.940 or more, more preferably 0.95 or more, still more preferably 0.960 or more.

The melting point of the chip of the polypropylene raw material B is preferably 160 ° C. or higher. By setting the melting point of the chip to 160 ° C. or higher, more preferably 162 ° C. or higher, still more preferably 164 ° C. or higher, the withstand voltage characteristics in a high temperature environment can be effectively enhanced when the film is formed.

The content of the polypropylene resin B in the raw material of the polypropylene film of the present invention is preferably 1% by mass or more and 30% by mass or less in 100% by mass of the polypropylene film. The content of the polypropylene raw material B is more preferably 2% by mass or more. Further, the content of the polypropylene raw material B is more preferably 25% by mass or less, further preferably 20% by mass or less.

The number average molecular weight (Mn), Z + 1 average molecular weight (M _{z + 1} ), cold xylene soluble component (CXS), mesopentad fraction, chip melting point, and content of the polypropylene raw material B were set in the above-mentioned preferable ranges, and were further lengthened before stretching. Preliminary stretching of 1.01 to 1.10 times is applied in the direction, the area stretching ratio is 65 times or more at the time of biaxial stretching, and the stretching ratio in the width direction is 11.0 times or more. In the treatment and relaxation treatment steps, first, the relaxation treatment is performed while performing the heat treatment (first stage) at a temperature lower than the stretching temperature in the width direction, and then the heat treatment temperature of the first stage while maintaining the tension in the width direction of the film. The film is subjected to a multi-stage heat fixing treatment and relaxation treatment in which heat treatment at a lower temperature of 135 ° C. or higher (second stage) and heat treatment at 80 ° C. or higher below the heat treatment temperature of the second stage (third stage) are performed. When appropriately applied, appropriate protrusions are formed on the surface due to the difference in viscosity from the polypropylene raw material A, and the number of tie molecules connecting the crystals increases, so that the orientation of the molecular chains increases when the draw ratio is increased. It becomes easier and the binding force of the amorphous chain in a high temperature environment can be enhanced.

The polyolefin film of the present invention may contain a branched polypropylene raw material C in addition to the polypropylene raw material A and the polypropylene raw material B.

The polypropylene raw material C has a plurality of manufacturing methods such as a Ziegler-Natta catalyst system and a metallocene catalyst system, but from the viewpoint of being used in combination with the polypropylene raw material A and the polypropylene raw material B, there are few low molecular weight components and high molecular weight components. A metallocene catalyst system having a narrow molecular weight distribution is more preferable.

As a commercially available product of polypropylene raw material C, specifically, for example, "Protax" (registered trademark) (PF-814, etc.) manufactured by Lyondell Basell, and as a metallocene catalyst system, "Daplay" (trademark) (WB130HMS) manufactured by Borearis. WB135HMS, WB140HMS, etc.) and "WAYMAX" (registered trademark) (MFX8, MFX6, MFX3, etc.) manufactured by Japan Polypropylene Corporation can be appropriately selected and used.

The polypropylene raw material C preferably has a CXS of 5.0% by mass or less, more preferably 3.0% by mass or less. The lower the CXS, the more preferable, but the lower limit is about 0.1% by mass. In order to control CXS in such a range, a method of increasing the catalytic activity when obtaining the resin and a method of washing the obtained resin with a solvent or the olefin monomer itself can be used.

The polypropylene raw material C preferably has a melt tension of 2 cN or more and 40 cN or less at 230 ° C. from the viewpoint of stretching uniformity. The melting tension is more preferably 3 cN or more, further preferably 5 cN or more. Further, 30 cN or less is more preferable, and 20 cN or less is further preferable. In order to keep the melt tension of the polypropylene raw material C within the above range, a method of controlling the average molecular weight, the molecular weight distribution, the degree of branching in the polypropylene raw material, or the like can be adopted.

The content of the polypropylene resin C in the raw material of the polypropylene film of the present invention is preferably 0.10% by mass or more in 100% by mass of the polypropylene film. The content of the polypropylene raw material C is more preferably 0.15% by mass or more, further preferably 0.20% by mass or more, still more preferably 0.50% by mass or more. The content of the polypropylene raw material C is preferably 10% by mass or less, more preferably 4.5% by mass or less, still more preferably 3.0% by mass or less. When the content of the polypropylene resin C is within the above range, it is possible to prevent the spherulite size from becoming too large when the molten polymer is formed into a sheet, and to maintain a high temperature withstand voltage.

Hereinafter, the method for producing the polypropylene film of the present invention using the above-mentioned raw materials will be described more specifically, but the present invention is not necessarily limited to this.

The polypropylene resin as described above can be melt-extruded onto the support to obtain an unstretched polypropylene film.

After passing through a melt extrusion filtration filter from a single-screw extruder in which the polypropylene raw material is preferably set to an extrusion temperature of 220 ° C. or higher and 280 ° C. or lower, more preferably 230 ° C. or higher and 270 ° C. or lower, the temperature is preferably 200 ° C. or higher and 260 ° C. or lower. More preferably, it is extruded from the slit-shaped mouthpiece at a temperature of 210 ° C. or higher and 240 ° C. or lower. The molten sheet extruded from the slit-shaped mouthpiece is solidified on a casting drum (cooling drum) controlled to a temperature of 30 ° C. or higher and 110 ° C. or lower to become an unstretched polypropylene film. As a method of adhering the molten sheet to the casting drum, any of the electrostatic application method, the adhesion method using the surface tension of water, the air knife method, the press roll method, the underwater casting method, the air chamber method, etc. is used. However, the air knife method having good flatness and control of surface roughness is preferable. Further, it is preferable to appropriately adjust the position of the air knife so that air flows to the downstream side of the film formation so as not to cause vibration of the film. The temperature of the casting drum is more preferably 60 ° C or higher and 110 ° C from the viewpoint of improving element workability and withstand voltage by having less dents on the surface when made into a film and having appropriate slipperiness. Below, it is more preferably 80 ° C. or higher and 110 ° C. or lower.

A biaxially oriented polypropylene film can be obtained by biaxially stretching, heat treating and relaxing the unstretched polypropylene film.

As a method of biaxial stretching, any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method can be obtained. Among them, the film formation stability and crystal / amorphous of the film are obtained. It is preferable to adopt the sequential biaxial stretching method using a tenter in terms of controlling the mechanical properties and thermal dimensional stability while increasing the structure and surface characteristics, particularly the stretching ratio in the width direction of the present invention. In the sequential biaxial stretching, the unstretched polypropylene film is stretched in the longitudinal direction and then in the width direction.

In the longitudinal stretching step, it is preferable to perform pre-stretching and multi-step stretching of the main stretching. The unstretched polypropylene film is preheated by passing it between rolls kept at preferably 70 ° C. or higher and 150 ° C. or lower, more preferably 80 ° C. or higher and 145 ° C. or lower, and reserves 1.01 times or more and 1.10 times or less in the longitudinal direction. Perform stretching. As a result, the spherulite fracture of the unstretched sheet proceeds appropriately and the molecular chains are pre-oriented, so that the crystallite size, crystal orientation and amorphous chain restraint of the stretched film obtained after the subsequent main stretching are further enhanced. Therefore, the withstand voltage of the film can be improved and a stable structure can be obtained even in a high temperature environment.

The polypropylene film pre-stretched in the longitudinal direction is preferably kept at a temperature of 70 ° C. or higher and 150 ° C. or lower, more preferably 80 ° C. or higher and 145 ° C. or lower, preferably 2.0 times or more in the longitudinal direction. After main stretching to 15.0 times or less, more preferably 4.5 times or more and 12.0 times or less, still more preferably 5.5 times or more and 10.0 times or less, the mixture is cooled to room temperature.

Next, the film is guided to the tenter while gripping both ends in the width direction of the film stretched uniaxially in the longitudinal direction with clips. Here, in the present invention, the temperature of the preheating step immediately before stretching in the width direction is preferably set to a stretching temperature of +5 to + 15 ° C., more preferably +5 to + 12 ° C., still more preferably +5 to + 10 ° C. in the width direction. .. This is because the fibril structure highly oriented in the longitudinal direction can be further strengthened by uniaxial stretching, and the change in the dielectric breakdown voltage before and after the film heating can be suppressed. Further, it is preferable that the temperature conditions are as described above from the viewpoint that the thermal dimensional stability can be improved by stabilizing the molecular chain having insufficient orientation by high temperature preheating after uniaxial stretching. By setting the preheating temperature to the stretching temperature + 5 ° C. or higher, the change in the dielectric breakdown voltage before and after the film heating can be suppressed, and the thermal dimensional stability can be effectively improved. On the other hand, by setting the preheating temperature to the stretching temperature + 15 ° C. or lower, it is possible to suppress the film from being torn in the stretching step.

Then, the end of the film is stretched in the width direction while being gripped by the clip. The temperature at that time (stretching temperature in the width direction) is preferably 150 ° C. or higher and 170 ° C. or lower, more preferably 155 ° C. or higher and 165 ° C. or lower.

From the viewpoint of suppressing changes in the dielectric breakdown voltage before and after heating the film, the draw ratio in the width direction is preferably 11.0 times or more and 20.0 times or less. By setting the stretching ratio in the width direction to 11.0 times or more, more preferably 11.5 times or more, still more preferably 12.0 times or more, the orientation contribution of the highly oriented fibril structure in the longitudinal direction by uniaxial stretching is reduced. However, changes in the dielectric breakdown voltage before and after heating the film can be effectively suppressed. By increasing the stretching ratio in the width direction, the orientation in the width direction is imparted while maintaining a high orientation state in the longitudinal direction, so that the molecular chain tension in the plane is increased and the structural stability with respect to heat can be improved. Therefore, it is preferable to set the draw ratio in the width direction as described above from the viewpoint of considering that the effect of improving the heat shrinkage characteristics, which is a trade-off, can be obtained. On the other hand, by setting the draw ratio in the width direction to 20.0 times or less, more preferably 19.0 times or less, still more preferably 18.0 times or less, film tearing during film formation can be reduced.

In the production of the polypropylene film of the present invention, the area stretch ratio is preferably 65 times or more. The area stretch ratio is obtained by multiplying the stretch ratio in the longitudinal direction by the stretch ratio in the width direction. By setting the area stretch ratio to 65 times or more, more preferably 66 times or more, further preferably 68 times or more, still more preferably 72 times or more, the change in the dielectric breakdown voltage before and after film heating is suppressed, and a capacitor is used. When used in a high temperature environment for a long time, it can be used with excellent reliability.

In the production of the polypropylene film of the present invention, in the subsequent heat treatment and relaxation treatment steps, the width is 145 ° C. or higher and 165 ° C. or lower and the width is increased while giving relaxation of 2% or more and 20% or less in the width direction while tension-grasping the width direction with a clip. After heat-fixing (first-stage heat treatment) at a temperature lower than the stretching temperature in the direction (first-stage heat treatment), the heat-fixing temperature (first-stage heat treatment) is 135 ° C. or higher while the width direction is tightly gripped with the clip again. Heat treatment is performed under the condition of less than (temperature) (second stage heat treatment), and further heat treatment (third stage heat treatment) is performed under the condition of 80 ° C. or higher and less than the heat fixing temperature (second stage heat treatment temperature) while holding the tension. It is preferable to perform the multi-stage heat treatment from the viewpoint of suppressing the change in the insulation breakdown voltage before and after heating the film, improving the structural stability against heat, and obtaining the withstand voltage and reliability when the capacitor is used.

In the relaxation treatment, the relaxation rate is preferably 2% or more and 20% or less from the viewpoint of enhancing the structural stability against heat. By setting the relaxation rate to 20% or less, more preferably 18% or less, still more preferably 15% or less, it is possible to prevent the film from loosening too much inside the tenter, causing wrinkles in the product and causing unevenness during vapor deposition. can. In addition, it is possible to prevent deterioration of mechanical characteristics. On the other hand, by setting the relaxation rate to 2% or more, more preferably 5% or more, still more preferably 8% or more, structural stability with respect to heat can be obtained, and when a capacitor is used, the capacity can be reduced in a high temperature environment. It is possible to prevent short-circuit destruction.

After undergoing a multi-stage low temperature heat treatment, the film is guided to the outside of the tenter, the clips at both ends in the film width direction are released in a room temperature atmosphere, the film edges are slit in the winder process, and the film thickness is 0.5 μm or more and 10 μm. Take up less than a roll of film product. Here, it is preferable to perform the corona discharge treatment in air, nitrogen, carbon dioxide gas, or a mixed gas thereof in order to improve the adhesiveness of the vapor-deposited metal on the surface to be vapor-deposited before winding the film.

Specific examples of preferable production conditions to be focused on in order to obtain the polypropylene film of the present invention are as follows.
-The melt extrusion temperature should be lowered in multiple stages with the mouthpiece before and after the filter.
-The polypropylene resin A has a mesopentad fraction of 0.970 or more.
-The CXS of polypropylene resin A is less than 3.0% by mass.
-Before longitudinal stretching, perform preliminary stretching of 1.01 times or more and 1.10 times or less.
-Area of stretching The stretching ratio is 65 times or more.
-The draw ratio in the width direction is 11.0 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 of 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 of the second stage is 135 ° C or higher and lower than the heat treatment temperature of the first stage.
-The heat treatment temperature of the third stage is 80 ° C. or higher and lower than the heat treatment temperature of the second stage.
-In the first stage heat treatment step, a relaxation treatment of 2% or more and 20% or less in the width direction is performed.

Subsequently, a metal film laminated film made of the polypropylene film of the present invention, a film capacitor made of the same, and a method for manufacturing them will be described.

The metal film laminated film of the present invention has a metal film on at least one side 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 for applying the metal film is not particularly limited, but for example, a metal such as a vapor-deposited film which is an internal electrode of a film capacitor by depositing aluminum or an alloy of aluminum and zinc on at least one surface of a polypropylene film. A method of providing a film is preferably used. At this time, other metal components such as nickel, copper, gold, silver, and chromium can be vapor-deposited simultaneously or sequentially with aluminum. Further, a protective layer may be provided on the vapor-filmed film with oil or the like. When the roughness of the polypropylene film surface is different on the front and back, it is preferable to provide a metal film on the surface side having a smooth roughness to form a metal film laminated film from the viewpoint of enhancing the withstand voltage.

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. Further, for insulation or other purposes, at least one surface of the metal film laminated film may be coated with a resin such as polyphenylene sulfide.

The film capacitor of the present invention is made by using 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-mentioned metal film laminated film of the present invention by various methods. An example of 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, the film is deposited in a striped shape having a margin portion running in the longitudinal direction. Next, a blade is inserted into the center of each vapor deposition portion and the center of each margin portion on the surface to slit the reel, and a tape-shaped take-up reel having a margin on one side of the surface is created. Two tape-shaped take-up reels with a left or right margin, one each for the left margin and one for the right margin, are stacked and wound so that the vapor-filmed portion protrudes from the margin portion in the width direction. To get.

When vapor deposition is performed on both sides, vapor deposition is performed in a striped shape having a margin portion running in the longitudinal direction of one surface, and the other surface is striped so that the margin portion in the longitudinal direction is located in the center of the vapor deposition portion on the back surface side. Deposit in the form. Next, a blade is inserted in the center of each of the front and back margins to make a slit, and a tape-shaped take-up reel having a margin on one side of both sides (for example, if there is a margin on the right side of the front surface, a margin on the left side on the back surface) is produced. Two of the obtained reels and one undeposited laminated film are laminated 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 the core material, spraying metallicon on both end surfaces to form an external electrode, and welding a lead wire to the metallicon. The applications of the film capacitor are wide-ranging, such as for railway vehicles, automobiles (hybrid cars, electric vehicles), solar power generation / wind power generation, and general household appliances, and the film capacitor of the present invention is also suitable for these applications. Can be used. In addition, the polypropylene film of the present invention can be used in various applications such as packaging films, mold release films, process films, sanitary products, agricultural products, building products, medical products, etc., and in particular, applications including a heating process in film processing. Can be preferably used for.

Hereinafter, the present invention will be described in more detail with reference to examples.

[Measurement / evaluation method]
The method for measuring the characteristic value and the method for evaluating the effect in the present invention are as follows.

(1) Film thickness The thickness of 10 randomly sampled polypropylene films was measured using a contact-type electronic micrometer manufactured by Anritsu Co., Ltd. (K-312A type) in an atmosphere of 23 ° C. and 65% RH. .. The arithmetic mean value of the thicknesses at the 10 points was taken as the film thickness of the polypropylene film.

(2) Difference in crystallite size depending on the orientation direction of the α crystal (110) plane The polypropylene film was cut into strips having a length of 4 cm and a width of 1 mm, and the samples were stacked so as to have a thickness of 1 mm. A sample is placed between the X-ray source and the detector so that X-rays can pass through this sample, and the angle (2θ / θ) between the X-ray source and the detector is scanned symmetrically with respect to the film surface. The line diffraction was measured. From the half-value width βe of the crystal peak at 2θ = about 14 ° (α crystal (110) plane) in each scanning direction of the main orientation and its orthogonal direction, the main orientation is used using the following equations (1) and (2). The crystallite size (nm) obtained by scanning in (Through-MD) and the crystallite size (nm) obtained by scanning in the direction orthogonal to the main orientation direction are obtained. The absolute value of the difference was defined as the difference in crystallite size (nm) depending on the orientation direction of the α crystal (110) plane.
Crystallite size = Kλ / (βcosθ)… Equation (1)
β = (βe ² + βo ² ) ^1/2 ... Equation (2)
here,
λ: X-ray wavelength (0.15418 nm),
βe: half width of diffraction peak,
βo: Half width correction value (0.6),
K: Scherrer constant (1.0)
Is.

(measuring device)
・ X-ray diffractometer 4036A2 type X-ray source manufactured by Rigaku Denki Co., Ltd .: CuKα ray (using Ni filter)
Output: 40kV-30mA
・ Goniometer 2155D type slit manufactured by Rigaku Denki Co., Ltd .: 2 mm φ-1 ° -1 °
Detector: Scintillation counter / counting / recording device RAD-C type manufactured by Rigaku Denki Co., Ltd.

(Measurement condition)
-Through-TD scan, Throw-MD scan Scan method: Step scan Measurement range: 2θ = 5 to 60 °
Step: 0.05 °
Accumulated time: 2 seconds.

(3) Degree of Crystal Orientation of α Crystal (110) Plane A polypropylene film was cut into strips having a length of 4 cm and a width of 1 mm, and the samples were prepared by stacking them so as to have a thickness of 1 mm. A film sample is placed between the X-ray source and the detector so that X-rays can pass through the polypropylene film, and X-rays are incident in the direction perpendicular to the film surface, and 2θ = about 14 ° (α crystal). It was calculated by the following formula from the half-value width H (°) of the orientation peak obtained by scanning the crystal peak on the (110) plane in the circumferential direction.
Crystal orientation = (180 ° -H) / 180 °
The measuring device and conditions are shown below.

(measuring device)
-The same equipment as in (2) above was used.

(Measurement condition)
・ Circumferential scan (2θ = approx. 14 °)
Scan method: Step scan Measurement range: 0 to 360 °
Step: 0.5 °
Accumulated time: 2 seconds.

(4) Longitudinal shrinkage stress at 135 ° C (SF135MD)
The polypropylene film was cut into a rectangular sample having a width of 4 mm and a length of 50 mm with the measurement direction (longitudinal direction) of the film as the long side, and the film was sandwiched between metal chucks so as to have a trial length of 20 mm. The sample sandwiched between the chucks was set in the following device, and the stress curve in the longitudinal direction of the film in which the test length was kept constant was obtained by the following temperature program. From the obtained stress curve, the value of the contraction stress at 135 ° C. (SF135MD) was read, and the average value obtained by measuring n = 3 was taken as the longitudinal contraction stress (unit: MPa) at 135 ° C.
Equipment: Thermomechanical analyzer TMA / SS6000 (manufactured by Seiko Instruments Inc.)
Test mode: L control mode Test length: 20 mm
Temperature range: 23-200 ° C
Temperature rise rate: 10 ° C / min Start displacement: 0 μm
SS program: 0.1 μm / min Measurement atmosphere: Measured thickness in nitrogen: The film thickness measured in (1) above was used.

(5) Degree of deviation of the protrusion shape on the surface Skewness (Ssk)
Skewness (Ssk) is as defined by ISO25178. The measurement was performed using the scanning white interference microscope VS1540 of Hitachi High-Tech Science Co., Ltd., and the undulation component was removed from the imaged screen by polynomial fourth-order approximate plane correction using the attached analysis software, and then the median (3 × 3). After the processing with the filter, the interpolation processing, that is, the processing of supplementing the pixels for which the height data could not be acquired with the height data calculated from the surrounding pixels was performed. The average value measured at 5 randomly sampled points in one plane was calculated. Measurements were made on both sides of the film.
The measurement conditions are as follows.
Manufacturer: Ryoka System Co., Ltd. Distributor: Hitachi High-Tech Science Co., Ltd. Device name: Scanning white interference microscope VS1540
Measurement conditions: Objective lens 10 ×
Lens barrel 1 ×
Zoom lens 1x
Wavelength filter 530nm white
Measurement mode: Wave
Measurement software: VS-Measure Version 10.0.4.0
Analysis software: VS-Viewer Version 10.0.3.0
Measurement area: 0.561 mm x 0.561 mm.

(6) Mesopentad fraction In the case of raw material, polypropylene resin was used, and in the case of film, the film sample was frozen and crushed into a powder, and extracted with n-heptane at 60 ° C. for 2 hours to remove impurities and additives in polypropylene. Then, a sample dried at 130 ° C. for 2 hours or more under reduced pressure was used as a sample. The sample was dissolved in a solvent, and the mesopentad fraction (mm mm) was determined under the following conditions using ¹³ C-NMR.

Measurement conditions / equipment: Bruker DRX-500
・ Measurement nucleus: ¹³ C nucleus (resonance frequency: 125.8 MHz)
-Measured concentration: 10% by mass
-Solvent: Benzene: Heavy orthodichlorobenzene = 1: 3 mixed solution (volume ratio)
・ Measurement temperature: 130 ℃
・ Spin rotation speed: 12Hz
・ NMR sample tube: 5 mm tube ・ Pulse width: 45 ° (4.5 μs)
・ Pulse repetition time: 10 seconds ・ Data point: 64K
-Number of integrations: 10,000 times-Measurement mode: complete decoupling.

The analysis was performed as follows. The Fourier transform was performed with LB (line broadening factor) as 1, and the mmmm peak was set to 21.86 ppm. Peak splitting was performed using WINFIT software (manufactured by Bruker). At that time, the peak is divided from the peak on the high magnetic field side as follows, and the software is automatically fitted to optimize the peak division. mmmm).
(1) mrrm
(2), (3) rrrm (divided as two peaks)
(4) rrrrr
(5) mrmr
(6) mrmm + rmrr
(7) mmrr
(8) rmmr
(9) mmml
(10) mmmm
The same measurement was performed 5 times for the same sample, and the average value of the obtained mesopentad fraction was taken as the mesopentad fraction of the sample.

(7) Melting peak temperature (Tm) and crystallization peak temperature (Tc) of polypropylene resin and film
Using a differential scanning calorimeter (EXSTAR DSC6220 manufactured by Seiko Instruments Inc.), heat the 3 mg polypropylene film from 30 ° C to 260 ° C at 20 ° C / min in a nitrogen atmosphere, and then hold it at 260 ° C for 5 minutes. After that, the temperature is lowered to 30 ° C. under the condition of 20 ° C./min. The heat absorption peak temperature obtained in the temperature raising process was defined as the melting peak temperature of the polypropylene film, and the exothermic peak temperature obtained in the temperature lowering process was defined as the crystallization peak temperature of the polypropylene film. In the present specification, Tm and Tc are calculated from the average value obtained by measuring n = 3. When two or more peak temperatures are observed within the temperature range, or when the peak temperature that can be observed on a multi-stage DSC chart called a shoulder (observed when two or more peaks overlap) However, in the present invention, the temperature of the peak having the largest absolute value of the vertical axis heat flow (unit: mW) of the DSC chart is Tm and Tc, respectively. The polypropylene resin (Tm) and (Tc) were also measured in the same manner.

(8) Arithmetic mean height (Sa) on the surface of the film
The arithmetic mean height (Sa) is as defined by ISO25178. The measurement was performed using the scanning white interference microscope VS1540 of Hitachi High-Tech Science Co., Ltd., and the undulation component was removed from the imaged screen by polynomial fourth-order approximate plane correction using the attached analysis software, and then the median (3 × 3). ) After processing with a filter, interpolation processing, that is, processing of supplementing pixels for which height data could not be obtained with height data calculated from surrounding pixels was performed. Sa was measured on both sides of the polypropylene film surface, and the values on the polypropylene film surface from which small values were obtained are shown in the table. The measurement conditions were the same as in (5) the degree of bias of the surface protrusions.

(9) Projection peak height (SpkA), (SpkB) on the film surface
The protruding mountain height (Spk) is as defined by ISO25178. The measurement was performed using the scanning white interference microscope VS1540 of Hitachi High-Tech Science Co., Ltd., and the undulation component was removed from the imaged screen by polynomial fourth-order approximate plane correction using the attached analysis software, and then the median (3 × 3). After processing with a filter, interpolation processing (processing of supplementing pixels for which height data could not be acquired with height data calculated from surrounding pixels) was performed. The average value obtained by measuring at any 5 points in one plane was calculated. Both sides of the film were measured, and the value of the low value surface was designated as SpkA, and the value of the opposite surface was defined as SpkB. The measurement conditions were the same as in (5) the degree of bias of the surface protrusions.

(10) Dielectric breakdown voltage (V / μm) at 130 ° C.
After heating the film for 1 minute in an oven kept at 130 ° C., in the atmosphere, JIS C2330 (2014) 6.2 and JIS C2151 (2019) 17.2 B method (plate electrode method) cited therein are applied. It was measured according to the above. However, for the lower electrode, a conductive rubber of the same dimensions (E-100 <65> manufactured by Togawa Rubber Co., Ltd.) is placed on the aluminum foil shown in FIG. 3-C of JIS C2151 (2019) 17.2.2. 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) and converted into V / μm units, and out of a total of 30 measured values (calculated values). The average value of 20 points excluding 5 points in descending order from the maximum value and 5 points in ascending order from the minimum value was taken as the film dielectric breakdown voltage at 130 ° C.

(11) Cold xylene-soluble portion (CXS) of the film
For polypropylene resin in the case of raw materials and film samples in the case of films, 0.5 g is dissolved in 100 ml of xylene at 135 ° C., allowed to cool, allowed to stand in a constant temperature water bath at 20 ° C. for 1 hour to recrystallize, and then filtered. The polypropylene-based components dissolved in the liquid were quantified by the liquid chromatograph method. The following formula CXS (mass%) = (X / X ₀ ) × 100, where the amount of the polypropylene-based component dissolved in the filtrate is X (g) and the precision value of 0.5 g of the sample is X ₀ (g).
Calculated from.

(12) Crystal Orientation Degree of Crystal Orientation of α Crystal (110) Surface After Heating The method of heat-treating the film at 125 ° C. for 60 minutes has a thickness of 2 mm, an outer dimension of 300 mm × 300 mm, and an inner dimension of 280 mm × 280 mm with a width of 20 mm. Using a square metal frame, attach double-sided tape (Nichiban "Nystack" (registered trademark) NW-H15 adhesive strength 02) to the four sides of the frame surface, and cover the entire surface of the metal frame with the film. Attach it, and then sandwich the film with a metal frame of the same size. At this time, attach the film so that it does not wrinkle. Next, in the state of a metal frame / double-sided tape / film / metal frame, a sample was prepared by sandwiching the four sides of the frame with clips and fixed, and left in an oven heated to 125 ° C. for 60 minutes. Then, the sample was taken out and left at room temperature for 5 minutes, and then a film was cut out along the inner frame of the metal frame to obtain a film after heat treatment at 125 ° C. The film after heat treatment at 125 ° C. was cut into strips having a length of 4 cm and a width of 1 mm, and the samples were prepared by stacking them so as to have a thickness of 1 mm. A film sample is placed between the X-ray source and the detector so that X-rays can pass through the polypropylene film, and X-rays are incident in the direction perpendicular to the film surface, and 2θ = about 14 ° (α crystal). It was calculated by the following formula from the half-value width H (°) of the orientation peak obtained by scanning the crystal peak on the (110) plane in the circumferential direction.
Crystal orientation = (180 ° -H) / 180 °
The measuring device and conditions are shown below.

(measuring device)
・ X-ray diffractometer 4036A2 type X-ray source manufactured by Rigaku Denki Co., Ltd .: CuKα ray (using Ni filter)
Output: 40kV-30mA
・ Goniometer 2155D type slit manufactured by Rigaku Denki Co., Ltd .: 2 mm φ-1 ° -1 °
Detector: Scintillation counter / counting / recording device RAD-C type manufactured by Rigaku Denki Co., Ltd. (measurement conditions)
・ Circumferential scan (2θ = approx. 14 °)
Scan method: Step scan Measurement range: 0 to 360 °
Step: 0.5 °
Accumulated time: 2 seconds.

(13) Stress at 5% elongation in the film longitudinal direction of the film after heating (F5MD) and stress at 5% elongation in the film width direction (F5TD).
The method of heat-treating the film at 150 ° C. for 10 minutes uses a square metal frame with a thickness of 2 mm, an outer dimension of 300 mm × 300 mm, and an inner dimension of 280 mm × 280 mm with a width of 20 mm, and double-sided tape (double-sided tape) on the four sides of the frame surface. Nichiban's "Nystack" (registered trademark) NW-H15 adhesive strength 02) is applied, the film is attached so that the film covers the entire surface of the metal frame, and the film is further sandwiched between metal frames of the same size. At this time, attach the film so that it does not wrinkle. Next, in the state of a metal frame / double-sided tape / film / metal frame, a sample was prepared by sandwiching the four sides of the frame with clips and fixed, and left in an oven heated to 150 ° C. for 10 minutes. Then, the sample was taken out and left 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. The film after heat treatment at 150 ° C. was cut into a rectangle having a length of 50 mm and a width of 10 mm in the test direction and used as a sample. Next, a tensile tester for a rectangular sample (Tencilon UCT-100 manufactured by Orientec) was set at an initial chuck distance of 20 mm, and a tensile test was performed on the film under an atmosphere of 23 ° C. at a tensile speed of 300 mm / min. .. The load applied to the film when the sample elongation was 5% was read, and the value divided by the cross-sectional area (film thickness x width (10 mm)) of the sample before the test was divided by the stress (F5 value, unit: MPa) when the elongation was 5%. ), The measurement was performed 5 times for each sample in the longitudinal direction and the width direction, the average value was calculated, and F5MD and F5TD were calculated, respectively. As the film thickness used for calculating the F5 value, the value measured in (1) above was used.

(14) The total volume of valleys with a depth of 20 nm or more on the film surface is measured using the scanning white interference microscope VS1540 of Hitachi High-Tech Science Co., Ltd., and the imaged screen is corrected by the attached analysis software. After removing the waviness component with, then processing with a median (3 × 3) filter, and then interpolation processing, that is, the height data calculated from the surrounding pixels is used to supplement the pixels for which height data could not be obtained. Processing was performed. Next, the analysis was performed using the bearing function, which is an analysis tool of the analysis software. In order to specify a valley-side void having a depth of 20 nm or more, the valley-side height threshold was set to −20 nm in the height region designation. Then, the value of the volume of the valley that satisfied the threshold value and was analyzed was read. Measurements were made in five randomly sampled 0.561 × 0.561 mm ² regions on one surface, and the average value of the total volume in the regions was taken as the total volume of valleys with a depth of 20 nm or more on the film surface. ..

When both sides of the film are measured and the total volume of the valley on one side is within the range of 50 to 5,000 μm ³ , the value of the side surface that is within the range and both sides are within the range. When it became, the value of the surface having a small value was described, and when both sides were not within the range, the value of the surface on the side where the total valley side volume was close to the range of 50 to 5,000 μm ³ was described. The measurement conditions were the same as in (5) the degree of bias of the surface protrusions.

(15) Heat shrinkage rate in the width direction after heat treatment at 125 ° C. for 15 minutes HS125TD
Cut out five samples with a length of 200 mm and a width of 10 mm so that the width direction of the film is the long side, mark them as marked lines at positions 25 mm from both ends, and measure the distance between the marked lines with a universal projector. The test length (L1) is used. Next, a load of 3 g was applied to one end (the lower end) in the length direction of the test piece, and the test piece was heated in an oven kept at 125 ° C. for 15 minutes while suspended, and the test piece was taken out and kept at room temperature. After cooling with, measure the dimension (L2) between the marked lines attached earlier with a universal projector, obtain the heat shrinkage rate HS125TD of each sample by the following formula, and use the arithmetic average value of 5 lines as the heat in the measurement direction. It was calculated as a shrinkage rate HS125TD.
HS125TD = {(L1-L2) / L1} x 100
Here,
HS125TD: Thermal shrinkage rate (%) in the width direction after heat treatment at 125 ° C. for 15 minutes.
L1: Distance between marked lines before heat treatment (150 mm)
L2: Distance between marked lines after heat treatment.

(16) Static friction coefficient (μ _s )
The measurement was carried out at 25 ° C. and 65% RH according to JIS K 7125 (1999) using a slip tester manufactured by Toyo Seiki Co., Ltd. The measurement was performed in the longitudinal direction of the film and with different surfaces overlapped with each other. The same measurement was performed 5 times for each sample, and the average value of the obtained values was calculated and used as the static friction coefficient (μ _s ) of the sample.

(17) Molecular weight and molecular weight distribution of polypropylene resin and film GPC (Gel Permeation Chromatography) was used for evaluation and calculation under the following equipment and measurement conditions. The sample was weighed as a sample pretreatment under the following measurement conditions, a solvent (1,2,4-TCB to which 0.1% BHT was added) was added, and the mixture was dissolved by shaking at 140 ° C. for 1 hour. Next, heat filtration was performed with a sintered filter having a pore size of 0.5 μm, and fractionation was performed according to the molecular size.

<Device and measurement conditions>
-Device: HLC-8321GPC / HT (detector: RT)
・ Column:
TSKgel guardcolumnH _HR (30) HT (7.5 mm I.D. x 7.5 mm) x 1 + TSKgel GMH _HR -H (20) HT (7.8 mm I.D. x 30 cm) (manufactured by Tosoh Corporation) x 3 Eluent: 1,2,4-trichlorobenzene (for GPC manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) + BHT (0.05%)
-Flow rate: 1.0 mL / min.
-Detection condition: polarity = (-)
・ Injection amount: 0.3 mL
-Column temperature: 140 ° C
・ System temperature: 40 ℃
-Sample concentration: 1 mg / mL
A calibration curve is prepared using standard polystyrene (manufactured by Tosoh Corporation), and the measured molecular weight values are converted into polystyrene values to achieve Z + 1 average molecular weight (M _{z + 1} ), weight average molecular weight (Mw), and number average molecular weight. (Mn) was obtained. Then, the molecular weight distribution (M _{z + 1} / Mw) using the values of M _{z + 1} and M w was calculated.

(18) Evaluation of film capacitor characteristics (withstand voltage at 120 ° C, reliability, workability)
Aluminum is vapor-deposited on one surface of the film with a vacuum vapor deposition machine (manufactured by ULVAC, Inc.), and a so-called T-shaped margin is provided with a masking oil having a film resistance of 10 Ω / sq in the direction perpendicular to the longitudinal direction. A thin-film deposition pattern having a longitudinal pitch (period) of 17 mm and a fuse width of 0.5 mm was formed. When the wet tension was different on both the front and back sides, the surface having the higher wet tension was vapor-deposited.

The film on which the vapor deposition pattern was formed was slit to obtain a vapor deposition reel having a film width of 50 mm and an end margin width of 2 mm.

Next, using this reel, the capacitor element was wound up by an element winder (KAW-4NHB manufactured by Minato Seisakusho Co., Ltd.), subjected to metallicon, and then heat-treated at a temperature of 128 ° C. for 12 hours under reduced pressure. The lead wire was attached and finished as a capacitor element.

Using the 10 capacitor elements thus obtained, a voltage of 250 VDC is applied to the capacitor element at a high temperature of 120 ° C., and after 10 minutes have passed at the voltage, the applied voltage is gradually increased at 50 VDC / min. A so-called step-up test was performed in which the above steps were repeated.

<Withstand voltage evaluation>
In the step-up test, the change in capacitance at this time is measured and plotted on a graph, and the voltage at the time when the capacitance reaches 80% of the initial value is divided by the film thickness ((1) above). The withstand voltage was evaluated as follows.
S: The withstand voltage is 400 V / μm or more.
A: The withstand voltage is 390 V / μm or more and less than 400 V / μm.
B: The withstand voltage is 380 V / μm or more and less than 390 V / μm.
C: Withstand voltage is less than 380 V / μm.
S, A and B can be used. C is inferior in practical performance.

<Reliability evaluation>
After increasing the voltage until the capacitance decreased to 15% or less of the initial value, the capacitor element was disassembled and the state of failure was investigated, and the reliability was evaluated as follows.
S: There is no change in the element shape, and no penetrating fracture is observed.
A: There is no change in the element shape, and penetration-like fracture within 1 to 5 layers of the film is observed.
B: There is no change in the element shape, and penetration-like fracture within 6 to 10 layers of the film is observed.
C: Change in the element shape is observed, penetration-like fracture exceeding 10 layers is observed, or S, in which the element shape changes significantly and breaks, can be used without problems, and A and B can be used depending on the conditions. be. C is inferior in practical performance.

<Evaluation of workability>
Judgment was made based on the following criteria. A capacitor element was created in the same manner as above, and the shape of the element was visually confirmed.
S: There is no deviation, wrinkles, or deformation of the end face film of the capacitor element, and there is no problem in the subsequent process. Level A: There is no deformation of the capacitor element, and there are slight wrinkles, but it can be used without problems. Level B: Capacitor Level C that can be used although there is slight deformation of the element and wrinkles: Levels S and A that are severely deformed and wrinkled in the capacitor element and interfere with the subsequent process can be used without problems, and B is a condition. It can be used depending on the situation, and it is difficult to put it to practical use in C.

[Polypropylene raw material]
The raw materials shown in Table 1 below were used for producing the polypropylene films of Examples and Comparative Examples. 4 types of polypropylene raw material A (A1, A2, A3, A4), 3 types of polypropylene raw material B (B1, B2, B3), 2 types of polypropylene raw material C (C1: Ziegler-Natta catalyst system, C2: metallocene catalyst system) ) Raw material was used.

[Example 1]
The raw materials and film forming conditions used in this example are as shown in Tables 1 and 2. First, the polypropylene raw material A1 was dry-blended by 92 parts by mass, the polypropylene raw material B1 by 5 parts by mass, and the polypropylene raw material C1 by 3 parts by mass. The blended raw material is supplied to a single-screw extruder having a temperature of 260 ° C., melted, passed through a pipe whose temperature is set to 255 ° C. after passing through a filtration filter, and formed into a sheet from a T-shaped slit die set to 250 ° C. Melt extruded. This sheet-like material was brought into close contact with an air knife on a casting drum kept at 98 ° C. and cooled and solidified to obtain an unstretched polypropylene film. The unstretched polypropylene film was preheated stepwise to 143 ° C. in a plurality of roll groups, passed directly between rolls provided with a peripheral speed difference, pre-stretched at 130 ° C. by 1.08 times, and then 143. It was stretched 6.1 times in the longitudinal direction at ° C. Continue to guide the film to the tenter, preheat it at a temperature of 169 ° C (TD stretching temperature + 7 ° C) while holding both ends of the film width with clips, and then stretch it 12.3 times in the width direction at a temperature of 162 ° C. did. Further, as the first stage heat treatment, heat treatment is performed at 159 ° C while giving 15% relaxation in the width direction, and as the second stage heat treatment, heat treatment is performed at 150 ° C while holding both ends of the film width with clips in the width direction. went. As the third stage heat treatment, the film is guided to the outside of the tenter through a heat treatment at 110 ° C., the clip at the end of the film is released, and then the film surface (casting drum contact surface side) is exposed to the film surface (casting drum contact surface side) at a processing strength of 25 W / min / m ² in the air. A corona discharge treatment was performed, and a polypropylene film having a film thickness of 2.3 μm was wound up as a film roll. Table 4 shows the evaluation results of each item.

[Examples 2 to 9, Comparative Examples 1 to 6]
Polypropylene films having the thicknesses shown in Tables 2 and 3 were obtained in the same manner as in Example 1 except that the raw material composition and the film forming conditions were as shown in Tables 2 and 3. The thickness was adjusted by increasing or decreasing the rotation speed of the single-screw extruder. Hereinafter, the same applies to the other examples and comparative examples. The evaluation results of each item are shown in Tables 4 to 6.

Claims (16)

Absolute difference between the crystallite size obtained by scanning in the main orientation direction of the α crystal (110) plane measured by wide-angle X-ray diffraction and the crystallite size obtained by scanning in the direction orthogonal to the main orientation direction. A polypropylene film having a value of 3.0 nm or less and a longitudinal shrinkage stress (SF135MD) at 135 ° C. of 2.0 MPa or less in the heating process at a heating rate of 10 ° C./min in thermomechanical analysis (TMA). .. The polypropylene film according to claim 1, wherein the polypropylene film having a crystallite size of 10.0 nm or less obtained by scanning in a direction orthogonal to the main orientation direction of the α crystal (110) plane as measured by wide-angle X-ray diffraction. The polypropylene film according to claim 1 or 2, wherein the crystallite size obtained by scanning in the main orientation direction of the α crystal (110) plane as measured by wide-angle X-ray diffraction is 10.0 nm or less. The polypropylene film according to any one of claims 1 to 3, wherein the degree of crystal orientation of the α crystal (110) plane measured by wide-angle X-ray diffraction is 0.77 or more. The invention according to any one of claims 1 to 4, wherein the melting peak temperature (Tm) of the film obtained by heating the film from 30 ° C. to 260 ° C. with a differential scanning calorimeter DSC at 20 ° C./min is 170 ° C. or higher. Polypropylene film. The melting peak temperature (Tm) of the film obtained by raising the temperature of the film from 30 ° C. to 260 ° C. at 20 ° C./min with a differential scanning calorimeter DSC, and lowering the temperature from 260 ° C. to 30 ° C. at 20 ° C./min after the temperature rise. The polypropylene film according to any one of claims 1 to 5, wherein the crystallization peak temperature (Tc) obtained at the same time satisfies the following relationship.
Tm-Tc ≦ 65 (° C) The polypropylene film according to any one of claims 1 to 6, wherein the skewness (Ssk) defined by ISO25178 on at least one surface of the film is more than -30 and less than 5. One of claims 1 to 7, wherein the protruding peak heights SpkA and SpkB defined in ISO25178 of the surface A of one side surface and the surface B of the other side surface satisfy the following relationship, respectively. The polypropylene film described.
SpkA <SpkB
20nm ≤ SpkA ≤ 100nm
80nm ≤ SpkB ≤ 150nm
here,
SpkA: Height of protruding peak of surface A SpkB: Height of protruding peak of surface B The polypropylene film according to any one of claims 1 to 8, wherein the arithmetic mean height (Sa) defined by ISO25178 on at least one surface of the film is 35 nm or more and 100 nm or less. The polypropylene film according to any one of claims 1 to 9, wherein the polypropylene film heated at 125 ° C. for 60 minutes has a crystal orientation of 0.73 or more on the α crystal (110) plane when measured by wide-angle X-ray diffraction. .. Stress (F5MD) at 5% elongation in the longitudinal direction of the film when the film heated at 150 ° C. for 10 minutes was subjected to a tensile test at room temperature, and when the film heated at 150 ° C. for 10 minutes was subjected to a tensile test at room temperature. The polypropylene film according to any one of claims 1 to 10, wherein the sum of the stress (F5TD) at an elongation of 5% in the film width direction is 150 MPa or more. One of claims 1 to 11 in which the polypropylene component (CXS) dissolved in xylene is 3.0% by mass or less when the polypropylene film is completely dissolved with xylene and then precipitated at room temperature. The polypropylene film described. On at least one surface, the total volume of valleys with a depth of 20 nm or more in a region of 0.561 mm × 0.561 mm measured by a scanning white interference microscope is 50 μm ³ or more and 5,000 μm ³ or less. , The polypropylene film according to any one of claims 1 to 12. The polypropylene film according to claim 1 to 13, wherein the heat shrinkage rate (HS125TD) in the width direction after heating at 125 ° C. for 15 minutes is 1.0% or less. A metal film laminated film having a metal film on at least one side of the polypropylene film according to any one of claims 1 to 14. A film capacitor using the metal film laminated film according to claim 15.