JP2016187959A - Biaxially oriented polypropylene film, metal film laminated film, and film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene film which has small unevenness of thickness of the film in a longitudinal direction and a width direction and is excellent in withstanding voltage characteristics and workability, and is also excellent in withstanding voltage characteristics even at high temperature because of having a stable high-temperature melting peak, when used as a dielectric for capacitor.SOLUTION: There is provided a biaxially oriented polypropylene film containing a polypropylene resin as a main component, where unevenness of thickness of the film in a longitudinal direction is 0-10% and unevenness of thickness of the film in a width direction is 0-10%, and the film has two or more melting peaks in a range of 158-180°C in DSC measurement.SELECTED DRAWING: None

Description

  The present invention relates to a biaxially oriented polypropylene film that, when used as a dielectric for a film capacitor, has a small thickness variation and thus has excellent transportability during processing and excellent voltage resistance characteristics. Specifically, a film with a small thickness unevenness can be produced with a good film forming property, and not only has excellent workability and withstand voltage characteristics, but also a film that can be thinned to a film thickness that has been difficult to form conventionally. The present invention relates to a biaxially oriented polypropylene film that can be suitably used for a capacitor dielectric.

  Biaxially oriented polypropylene films are excellent in transparency, mechanical properties, electrical properties, etc., and are therefore used in various applications such as packaging, tapes, cable wrapping, and electrical applications including capacitors.

  Among these, the capacitor application is particularly preferably used for high voltage capacitors because of its excellent withstand voltage characteristics and low loss characteristics, not limited to DC applications and AC applications. Recently, various types of electrical equipment are being converted to inverters, and accordingly, there is an increasing demand for miniaturization and large capacity of capacitors. In response to the demands of such markets, especially automobile applications (including hybrid car applications), solar power generation and wind power generation applications, while improving the voltage resistance of biaxially oriented polypropylene film, maintaining productivity and processability, It has become an essential situation to reduce the film thickness.

  As a means for improving the withstand voltage characteristics and workability, it is considered effective to suppress the uneven thickness of the biaxially oriented polypropylene film. Moreover, it can be said that suppressing the thickness unevenness by making the stretchability at the time of film formation uniform can suppress the film breakage at the time of stretching, and is effective for productivity and thinning.

  As described above, various studies have been made on the method for making the stretchability of the biaxially oriented polypropylene film uniform. For example, a method for improving stretchability by mixing polypropylenes having different molecular weight distributions and controlling the molecular weight distribution has been proposed (for example, see Patent Document 1). However, since the melting point of the low molecular weight distribution polypropylene to be mixed is as low as about 80 ° C., the withstand voltage characteristics at high temperatures exceeding 100 ° C. are particularly inferior.

  In addition, a method has been proposed in which stretchability is improved while adding high melt tension polypropylene having a branched structure to high stereoregular polypropylene, thereby improving stretchability and improving thickness uniformity (for example, Patent Documents). 2 and 3). However, although the improvement of the high melt tension polypropylene non-added product, the thickness unevenness and the withstand voltage characteristics are improved, the effects are limited, and the characteristics required for the current capacitor are not satisfied. Furthermore, the addition of the second component leads to an increase in cost from the viewpoint of an increase in the number of steps and raw material costs, so that it is ideal to improve by modifying the base polypropylene or film forming conditions. In addition, a method of adding polybutene-1 for the purpose of improving stretching uniformity has been proposed (for example, Patent Document 4). However, when compared with a polybutene-1 non-added product, the stretchability and withstand voltage characteristics are improved, but the effects are limited, and the characteristics required for current capacitors are not satisfied.

JP 2014-205799 A JP 2006-63186 A JP 2007-84813 A JP 2007-169595 A

  An object of the present invention is to solve the above-described problems. That is, for example, even if the second component is not added as a stretching aid, the stretching uniformity is excellent, the thickness unevenness is small, the processability and the withstand voltage characteristics are not only excellent, but the film thickness that has been difficult to form conventionally is thin. It is to provide a biaxially oriented polypropylene film that can be suitably used for various film capacitors.

  The above-described problem is a biaxially oriented polypropylene film containing a polypropylene resin as a main component, the thickness variation in the longitudinal direction is 0 to 10%, the thickness variation in the width direction is 0 to 10%, and DSC measurement Can be achieved by a biaxially oriented polypropylene film having two or more melting peaks in the range of 158 to 180 ° C.

  When the biaxially oriented polypropylene film of the present invention is used as a dielectric for a capacitor, it is excellent in processability and withstand voltage characteristics during the production of the capacitor, and can be suitably used as a dielectric for a capacitor.

  Hereinafter, the biaxially oriented polypropylene film, metal film laminated film and film capacitor of the present invention will be described in more detail.

  The biaxially oriented polypropylene film of the present invention contains a polypropylene resin as a main component. The “main component” means that the proportion of a specific component in all components is 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably. It is 95 mass% or more.

  Such a polypropylene resin is mainly composed of a homopolymer of propylene, but may contain other unsaturated hydrocarbon copolymerization components or the like within a range not impairing the object of the present invention. The coalescence may be blended. Examples of the monomer component constituting such a copolymer component or blend include, for example, ethylene, propylene (in the case of a copolymer blend), 1-butene, 1-pentene, 3-methylpentene-1, 3 -Methylbutene-1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene 1-eicosene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene, and the like. The copolymerization amount or blend amount is preferably less than 1 mol% from the viewpoint of voltage endurance characteristics and dimensional stability.

  It is preferable that the cold xylene soluble part (henceforth CXS) of the said polypropylene resin which comprises the biaxially oriented polypropylene film of this invention is 4 mass% or less. Here, CXS refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene at 135 ° C. and then precipitated at 20 ° C., and has low stereoregularity and low molecular weight. This is considered to correspond to a component that is difficult to crystallize. The CXS of the polypropylene resin is more preferably 3% by mass or less, further preferably 2% by mass or less, and particularly preferably 1% by mass or less. When CXS exceeds 4 mass%, the withstand voltage characteristic and dimensional stability of a biaxially oriented polypropylene film may be inferior. In order to bring the polypropylene resin CXS within the above range, there are a method for increasing the catalytic activity in obtaining the resin, a method for washing the obtained resin with a solvent or the propylene monomer itself, and the like.

  The biaxially oriented polypropylene film of the present invention and the mesopentad fraction (mmmm) of the polypropylene resin constituting the film are as described below in terms of obtaining a film having a stable crystal form after biaxial stretching, that is, a melting peak of 2 From the viewpoint of making it more than one, it is preferably within the range of 0.980 to 0.995, more preferably 0.983 to 0.995, still more preferably 0.986 to 0.995, and Particularly preferred is 990 to 0.995. The mesopentad fraction is an index indicating the stereoregularity of the crystalline phase of polypropylene measured by a nuclear magnetic resonance method (so-called NMR method). The higher the numerical value, the higher the crystallinity and the melting point, and the higher the temperature. However, it is preferable because of its excellent withstand voltage characteristics. When the mesopentad fraction of the polypropylene resin and the biaxially oriented polypropylene film is less than 0.980, the withstand voltage characteristics and dimensional stability may be inferior. On the other hand, when the mesopentad fraction of the polypropylene resin and the biaxially oriented polypropylene film exceeds 0.995, the biaxially oriented polypropylene film may not be obtained stably due to poor film formation. In order to set the mesopentad fraction of the polypropylene resin and the biaxially oriented polypropylene film within the above range, a method of washing the resin powder obtained with a solvent such as n-heptane, and selection of a catalyst and / or a cocatalyst are selected. A method of appropriately selecting the composition is preferably employed.

  In the case where the melt flow rate (hereinafter referred to as MFR) of the polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is measured in accordance with the condition M (230 ° C., 2.16 kg) of JIS K 7210 (1995). 0.5 to 10 g / 10 minutes, preferably 1 to 8 g / 10 minutes, more preferably 1.5 to 5 g / 10 minutes, and 2 to 5 g / 10 minutes. Particularly preferred. When the MFR of the polypropylene resin is less than 0.5 g / 10 minutes, the biaxially oriented polypropylene film may not be obtained stably due to poor film forming properties. On the other hand, when the MFR of the polypropylene resin exceeds 10 g / 10 minutes, the withstand voltage characteristics may be inferior. In order to set the MFR of the polypropylene resin within the above range, a method of controlling the average molecular weight or the molecular weight distribution is preferably employed.

  The biaxially oriented polypropylene film of the present invention has a thickness variation of 0 to 10% in the longitudinal direction (the direction in which the film flows during film formation). The thickness unevenness in the longitudinal direction is more preferably 0 to 8%, further preferably 0 to 6%, and particularly preferably 0 to 4% or less. When the thickness unevenness in the longitudinal direction exceeds 10%, tension fluctuation occurs in film transport and winding processes during film formation and processing, and the roll shape of the film roll is lowered, or the film may be broken in some cases. There is. Furthermore, in the withstand voltage characteristic evaluation, there are cases where the voltage is locally concentrated at a thin film thickness and the withstand voltage is significantly reduced. In order to make the thickness unevenness in the longitudinal direction within the above range, using the above-described polypropylene resin, as described later, the extrusion process, the casting process, the longitudinal stretching process, and the heat treatment process at the time of film formation have specific conditions. This can be achieved for the first time.

  The biaxially oriented polypropylene film of the present invention has a thickness variation of 0 to 10% in the width direction (the direction perpendicular to the longitudinal direction on the film plane). The thickness variation in the width direction is more preferably 0 to 8%, further preferably 0 to 6%, and particularly preferably 0 to 4% or less. If the thickness unevenness in the width direction exceeds 10%, conveyance wrinkles are likely to occur in the film conveyance process during film formation and processing, and the roll shape of the film roll may be lowered, or the film may be broken in some cases. . Furthermore, in the withstand voltage characteristic evaluation, there are cases where the voltage is locally concentrated at a thin film thickness and the withstand voltage is significantly reduced. In order to set the thickness variation in the width direction within the above range, by using the above-described polypropylene resin, as described later, the extrusion process, the lateral stretching process, and the heat treatment process are performed under specific conditions as described later. Can be achieved for the first time.

  The biaxially oriented polypropylene film of the present invention is characterized by having two or more melting peaks in the range of 158 to 180 ° C. when the film is subjected to DSC measurement. The plurality of melting peaks are peaks due to the α crystal of polypropylene, and the peak on the high temperature side is considered to originate from the crystal transition of the α crystal to a stable form. That is, when the α-crystal melting peak is present on the high temperature side, this means that the biaxially oriented polypropylene film has excellent heat resistance, and as a result, the present invention has a tendency to have excellent withstand voltage characteristics at high temperatures. So what we found. The reason why the melting peak of α crystal becomes two or more is to use the above-described polypropylene resin in an environment under a certain condition, and as described later, an extrusion process, a longitudinal stretching process, a lateral stretching process during film formation It is considered that α crystals are more stable than before in a biaxially oriented polypropylene film by setting the above to a specific condition, and it was found by the present invention that the first manifestation occurs when the above condition is taken. When only one melting peak exists in the range of 158 to 180 ° C., it means that the film is composed of only normal α crystals, and the withstand voltage characteristics at high temperatures may be inferior. In addition, when there is a second or more melting peak below 158 ° C., it is considered that the peak is not attributable to the α crystal, and it is estimated that the withstand voltage characteristics at high temperatures required by the present invention cannot be achieved. The

The biaxially oriented polypropylene film of the present invention preferably has a Young's modulus E _{MD in} the longitudinal direction and a Young's modulus E _{TD in the} width direction of 2.5 GPa or more. The Young's modulus in the longitudinal direction and the width direction are both preferably 2.8 GPa or more, more preferably 3.0 GPa or more, and particularly preferably both 3.3 GPa or more. When the Young's modulus in either the longitudinal direction or the width direction is less than 2.5 GPa, wrinkles are likely to occur in the film conveying process during film formation and processing, and the roll shape of the film roll is deteriorated, or in some cases the film is It may break. Furthermore, the withstand voltage characteristics may be inferior. The upper limit of the Young's modulus of the biaxially oriented polypropylene film of the present invention is substantially 5.0 GPa in any direction. In order to make the Young's modulus in the longitudinal direction and the width direction both in the above range, using the above-described polypropylene resin, the longitudinal stretching process, the lateral stretching process, and the heat treatment process during film formation are performed under specific conditions as described later. This can be achieved.

In the biaxially oriented polypropylene film of the present invention, the relationship between the Young's modulus E _{MD in} the longitudinal direction and the Young's modulus E _{TD in} the width direction preferably satisfies the following formula (1).

0.5 ≦ E _MD / E _TD ≦ 1.2 (1)
The ratio value E _MD / E _TD of Young's modulus E _{MD in the} longitudinal direction and Young's modulus E _{TD in} the width direction is more preferably in the range of 0.6 to 1.2, and in the range of 0.7 to 1.1. Is more preferable, and is particularly preferably in the range of 0.8 to 1.1. If the value E _MD / E _TD of the Young's modulus E _{MD in the} longitudinal direction and the Young's modulus E _{TD in} the width direction is less than 0.5, the orientation in the width direction is too high relative to the orientation in the longitudinal direction. The film may be broken in the transverse stretching step in stretching. On the other hand, when the value E _MD / E _TD of the Young's modulus E _MD in the longitudinal direction and the Young's modulus E _{TD in} the width direction exceeds 1.2, the orientation in the width direction is too low relative to the orientation in the longitudinal direction. The thickness unevenness in the width direction may increase. In order to make the relationship between the Young's modulus E _{MD in the} longitudinal direction and the Young's modulus E _{TD in} the width direction within the range of the formula (1), the longitudinal stretching step and the lateral stretching step during film formation are specified conditions as described later. This can be achieved.

  The biaxially oriented polypropylene film of the present invention preferably has a thermal shrinkage of −1 to 5% in both the longitudinal direction and the width direction under the processing conditions of 120 ° C. for 15 minutes. The thermal shrinkage rates in the longitudinal direction and the width direction under the treatment conditions of 120 ° C. for 15 minutes are more preferably both −0.5 to 4.5%, more preferably 0 to 4%, and both 0 to Particularly preferred is 3.5%. When the thermal shrinkage rate in either the longitudinal direction or the width direction at 120 ° C. for 15 minutes is less than −1% (that is, when the thermal expansion coefficient exceeds 1%), it is greatly increased on the cooling can during metal deposition processing. Since the film is thermally expanded, wrinkles are generated, which may cause vapor deposition spots. Moreover, it may be inferior to the withstand voltage characteristic under high temperature. On the other hand, if the thermal shrinkage rate in either the longitudinal direction or the width direction under the processing conditions at 120 ° C. for 15 minutes exceeds 5%, the film is thermally shrunk on the cooling can during metal vapor deposition processing in the same manner as described above. Wrinkles can occur, which can cause deposition spots. Moreover, it may be inferior to the withstand voltage characteristic under high temperature. In order to make both the heat shrinkage in the longitudinal direction and the width direction in the processing conditions at 120 ° C. for 15 minutes within the above range, the above-described polypropylene resin is used, and as described later, the longitudinal stretching step during film formation It can be achieved by setting the transverse stretching step and the heat treatment step to specific conditions.

  The biaxially oriented polypropylene film of the present invention preferably has a thermal shrinkage rate of −1 to 10% in both the longitudinal direction and the width direction at 140 ° C. for 15 minutes. The thermal shrinkage in the longitudinal direction and the width direction under the treatment conditions at 140 ° C. for 15 minutes is more preferably 0 to 8%, more preferably 0 to 7%, and both 0 to 6%. Particularly preferred. When the thermal shrinkage rate in either the longitudinal direction or the width direction at 140 ° C. for 15 minutes is less than −1% (that is, when the thermal expansion coefficient exceeds 1%), it is greatly increased on the cooling can during metal deposition processing. Since the film is thermally expanded, wrinkles are generated, which may cause vapor deposition spots. Moreover, it may be inferior to the withstand voltage characteristic under high temperature. On the other hand, if the thermal shrinkage rate in either the longitudinal direction or the width direction under the processing conditions at 140 ° C. for 15 minutes exceeds 10%, the film is thermally shrunk on the cooling can during metal vapor deposition processing as described above, so that it is conveyed Wrinkles can occur, which can cause deposition spots. Moreover, it may be inferior to the withstand voltage characteristic under high temperature. In order to make the thermal shrinkage rate in the longitudinal direction and the width direction both within the above-mentioned range at 140 ° C. for 15 minutes, using the above-described polypropylene resin, as described later, a longitudinal stretching step during film formation It can be achieved by setting the transverse stretching step and the heat treatment step to specific conditions.

  In the biaxially oriented polypropylene film of the present invention, the coefficient of dynamic friction μd between one surface and the other surface (one surface and the other surface) of the film is preferably 0.5 to 1.2. The dynamic friction coefficient μd is more preferably 0.6 to 1.1, further preferably 0.7 to 1.0, and particularly preferably 0.8 to 1.0. When the dynamic friction coefficient μd is less than 0.5, the slipperiness is too good, and the running film may meander in the film transport process during film formation and processing, which may deteriorate the roll form of the roll. On the other hand, when the dynamic friction coefficient μd exceeds 1.2, since the slipperiness is poor, the film is easily wrinkled in the film transport process during film formation and processing, and the roll shape of the film roll is deteriorated. It may break. In order to set the dynamic friction coefficient μd within the above range, it can be achieved by using the above-described polypropylene resin and setting the casting process and the longitudinal stretching process during film formation to specific conditions as described later. . Moreover, it is also preferable to contain easy-slip particles within a range that does not deteriorate the withstand voltage characteristics.

  The biaxially oriented polypropylene film of the present invention preferably has a glossiness of 120 to 150% on both sides. The glossiness is more preferably 123 to 145% on both sides, more preferably 125 to 140% on both sides, and particularly preferably 128 to 138% on both sides. If the glossiness of at least one side is less than 120%, it means that the density of light scattering on the film surface increases, that is, there are many irregularities on the film surface, and the withstand voltage characteristic can be reduced due to the irregularities. is there. On the other hand, if the glossiness of at least one side exceeds 150%, the film surface has less unevenness, so it is inferior in slipperiness and easily causes wrinkles in the film transport process during film formation and processing, and deteriorates the roll shape of the film roll. In some cases, the film may break. In order to make the glossiness of the film within the above range on both sides, it can be achieved by using the above-mentioned polypropylene resin and setting the casting process and the longitudinal stretching process during film formation to specific conditions as described later. can do.

  The biaxially oriented polypropylene film of the present invention preferably has a film thickness of 0.5 to 3 μm. The film thickness is more preferably 0.8 to 2.8 μm, further preferably 1.0 to 2.5 μm, and particularly preferably 1.2 to 2.5 μm. When the film thickness is less than 0.5 μm, the mechanical strength and withstand voltage characteristics may be inferior, or film breakage may occur during film formation and processing. On the other hand, when the film thickness exceeds 3 μm, the capacity per volume may be small when used as a capacitor dielectric. In order to make the film thickness within the above range, it can be appropriately set by adjusting the discharge amount of the resin or adjusting the draft ratio when forming the sheet, but as the film thickness becomes thinner Since film breakage during film formation is likely to occur, by using the polypropylene resin described above, the extrusion process, film casting process, longitudinal stretching process, and lateral stretching process during film formation are made specific conditions as described later. It becomes possible to form a film stably.

The biaxially oriented polypropylene film of the present invention may contain a branched polypropylene for the purpose of improving the film forming property or controlling the film surface shape. In this case, in the branched polypropylene, the melt tension (MS) and the melt flow rate (MFR) measured at 230 ° C. satisfy the relational expression log (MS)> − 0.56 log (MFR) +0.74. A branched polypropylene is preferred. To obtain a branched polypropylene satisfying the relational expression that the melt tension (MS) and the melt flow rate (MFR) measured at 230 ° C. are log (MS)> − 0.56 log (MFR) +0.74. A method of blending a polypropylene containing a large amount of high molecular weight components, a method of blending an oligomer or polymer having a branched structure, and introducing a long chain branched structure into a polypropylene molecule as described in JP-A-62-1121704 A method or a method described in Japanese Patent No. 2869606 is preferably used. Specific examples include “Profax PF-814” manufactured by Basell and “Daploy HMS-PP” (WB130HMS, WB135HMS, etc.) manufactured by Borealis, among which resins obtained by the electron beam cross-linking method are included in the resin. It is preferably used because of its low gel component. The branched polypropylene referred to here is a polypropylene having 5 or less internal trisubstituted olefins per 10,000 carbon atoms, and the presence of these internal trisubstituted olefins is determined by ¹ H-NMR spectrum. This can be confirmed by the proton ratio. The branched polypropylene can act as an α crystal nucleating agent, and can form a rough surface by a crystal form as long as the amount is within a certain range. Specifically, the spherulite size of the polypropylene produced in the cooling process of the melt-extruded resin sheet can be controlled to be small, the occurrence of insulation defects produced in the stretching process is suppressed, and a biaxially oriented polypropylene film having excellent withstand voltage characteristics is obtained. be able to.

  When the branched polypropylene is included in the biaxially oriented polypropylene film of the present invention, the content is preferably 0.05 to 3% by mass, more preferably 0.1 to 2% by mass, and 0.3 It is more preferable in it being -1.5 mass%, and it is especially preferable in it being 0.5-1 mass%. When the content of the branched polypropylene is less than 0.05% by mass, the above effect may not be obtained. On the other hand, when the content of the branched polypropylene exceeds 3% by mass, the stereoregularity as a biaxially oriented polypropylene film is lowered, and the withstand voltage characteristic may be inferior.

  In the polypropylene resin constituting the biaxially oriented polypropylene of the present invention, various additives such as a crystal nucleating agent, an antioxidant, a thermal stabilizer, a lubricant, an antistatic agent, as long as the object of the present invention is not impaired. It is also preferable to contain an anti-blocking agent, a filler, a viscosity modifier, an anti-coloring agent and the like.

  Among the above-mentioned additives, the type of antioxidant and the selection of the addition amount are important from the viewpoint of long-term heat resistance. That is, the antioxidant is a phenolic compound having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specifically, for example, 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4), 1,3,5-trimethyl-2,4,6-tris (3,5-di- -T-butyl-4-hydroxybenzyl) benzene (for example, Irganox (registered trademark) 1330 manufactured by BASF: molecular weight 775.2), tetrakis [methylene-3 (3,5-di-t-butyl-4-hydroxyphenyl) ) Propionate] Methane (for example, Irganox 1010 manufactured by BASF: molecular weight 1177.7) is preferably used alone or in combination. The total content of these antioxidants is preferably 0.03 to 1.0% by mass, more preferably 0.1 to 0.9% by mass, and 0.15 to 0% with respect to the total amount of the polypropylene resin. More preferably, it is 0.8 mass%, and it is especially preferable in it being 0.15-0.6 mass%. When the content of the antioxidant in the polypropylene resin is less than 0.03% by mass, the antioxidant effect is difficult to obtain and the long-term heat resistance may be poor. On the other hand, when the antioxidant content in the polypropylene resin exceeds 1.0% by mass, the withstand voltage characteristics at high temperatures may be inferior.

  The biaxially oriented polypropylene film of the present invention preferably has an ash content of 50 ppm (mass basis, hereinafter the same) or less, more preferably 40 ppm or less, further preferably 30 ppm or less, and particularly preferably 20 ppm or less. . When the ash content exceeds 50 ppm, the withstand voltage characteristics of the biaxially oriented polypropylene film may be inferior. In order to make the ash content in the above range, it is important to use a raw material with a small amount of catalyst residue, but a method for reducing contamination from the extrusion system as much as possible, such as undegraded before starting film formation. A method of sufficiently washing the flow path of the polymer with the polypropylene resin can be preferably employed.

  The biaxially oriented polypropylene film of the present invention preferably has a surface wetting tension of at least one surface of 37 to 50 mN / m, more preferably 38 to 49 mN / m, still more preferably 39 to 48 mN / m, It is especially preferable that it is 40-47 mN / m. When the surface wetting tension is less than 37 mN / m, adhesion to the metal may be insufficient during metal deposition. On the other hand, when the surface wetting tension exceeds 50 mN / m, the withstand voltage characteristics may be inferior. A polypropylene film usually has a low surface energy and a surface wetting tension of about 30 mN / m. In order to make the surface wetting tension within the above range, a method of performing surface treatment after biaxial stretching is preferably employed during film formation. Specifically, corona discharge treatment, plasma treatment, glow treatment, flame treatment, and the like can be employed.

  The biaxially oriented polypropylene film of the present invention is preferably obtained by preparing a sheet mainly composed of the above-described polypropylene resin and biaxially stretching. The biaxial stretching method can be obtained by any of the inflation simultaneous biaxial stretching method, the tenter simultaneous biaxial stretching method, and the tenter sequential biaxial stretching method, but from the viewpoint of film formation stability and thickness uniformity, It is preferable to employ an axial stretching method. In particular, it is preferable to stretch in the width direction after stretching in the longitudinal direction.

  In the biaxially oriented polypropylene film of the present invention, a functional layer may be laminated on at least one side for the purpose of imparting various effects. The laminated structure may be a two-layered structure, a three-layered structure, or a larger number of stacked layers. As a lamination method, for example, a feed block method or a multi-manifold method by co-extrusion or a method of laminating polypropylene films by lamination may be used. In particular, for the purpose of improving the workability of a biaxially oriented polypropylene film, for example, it is preferable to laminate an easy-sliding layer in which fine particles are uniformly arranged in a range that does not deteriorate the withstand voltage characteristics.

  Next, although the manufacturing method of the biaxially oriented polypropylene film of this invention is demonstrated below, it is not necessarily limited to this.

First, the preferable polypropylene resin mentioned above is supplied to a single screw melt extruder, and melt extrusion is performed at 220 to 250 ° C. Next, after removing foreign substances, modified polymers, and the like with a filter installed in the middle of the polymer tube, the filter is discharged from a T-die onto a cast drum to obtain an unstretched sheet. In addition, at the time of extrusion, the film which has a stable crystal form after biaxial stretching is obtained from the viewpoint of reducing the thickness variation in the longitudinal direction and the width direction by setting the shear rate at the T die to 100 to 1,500 sec ^−1. This is preferable. More preferably, it is 150-1,000 sec < ^-1 >, More preferably, it is 200-800 sec < ^-1 >, Most preferably, it is 300-600 sec < ^-1 >. The shear rate at the T-die is expressed by equation (2). When the shear rate at the T-die is less than 100 sec ⁻¹ , shearing is not sufficiently performed and the crystal arrangement in the unstretched sheet becomes insufficient, so that uniform stretching becomes difficult in the subsequent stretching step, and thickness unevenness is excellent. A biaxially oriented polypropylene film cannot be obtained. On the other hand, when the shear rate at the T-die exceeds 1,500 sec ⁻¹ , excessive shearing occurs, and film breakage tends to occur when an unstretched sheet that is strongly oriented in the longitudinal direction is stretched.

Shear rate (sec ⁻¹ ) = 6Q / ρWt ² (2)
Q: Flow rate (kg / sec)
ρ: specific gravity (kg / cm ³ )
W: Groove width (cm)
t: Groove gap (cm)
The polymer flow rate, the T-die groove width, and the groove gap are appropriately adjusted so that the shear rate of the T-die is in the above-described range. The flow rate of the polymer is preferably in the range of 150 to 500 kg / hr from the viewpoint of extrusion stability. The groove width of the T die is preferably in the range of 500 to 1,000 mm from the viewpoint of productivity. The groove width of the T die is preferably in the range of 0.8 to 2 mm from the viewpoint of internal pressure in the extrusion system and casting accuracy.

  The cast drum preferably has a surface temperature of 60 to 120 ° C. from the viewpoint of reducing thickness unevenness in the longitudinal direction and from the viewpoint of controlling the dynamic friction coefficient and the glossiness within an appropriate range. More preferably, it is 70-110 degreeC, It is further more preferable that it is 80-100 degreeC, It is especially preferable that it is 90-100 degreeC. The time for the molten sheet discharged from the T die to land on the cast drum and adhere to the cast drum is 1 second from the viewpoint of solidifying the molten sheet and promoting crystal growth, that is, not causing longitudinal thickness unevenness. Preferably, it is 1.5 seconds or more, more preferably 2 seconds or more, and particularly preferably 2.5 seconds or more.

  As a method for bringing the sheet into close contact with the cast drum, methods such as an electrostatic application method, an air knife method, a nip roll method, and an underwater casting method can be adopted. The air knife method is preferable from the viewpoint of conversion. The distance between the air knife and the seat landing point is preferably 1 to 10 mm, more preferably 1 to 8 mm, further preferably 2 to 8 mm, and 2 to 5 mm from the viewpoint of thickness unevenness in the longitudinal direction. Particularly preferred. When the distance between the air knife and the sheet landing point exceeds 10 mm, the molten sheet discharged from the T-die is likely to vibrate due to the air of the air knife, and in particular, the thickness unevenness in the longitudinal direction may be deteriorated. The air temperature of the air knife is preferably 60 to 80 ° C. from the viewpoint of reducing thickness unevenness in the longitudinal direction and the width direction, from the viewpoint of film forming properties, more preferably 60 to 75 ° C., and 60 to 70 ° C. Is more preferable, and is particularly preferably 62 to 68 ° C. When the air temperature of the air knife is less than 60 ° C., the crystal formation of the molten sheet is insufficient and not only the thickness unevenness in the longitudinal direction and the width direction is deteriorated, but also the film may be easily broken in the stretching process. On the other hand, when the air temperature of the air knife exceeds 80 ° C., crystallization of the molten sheet proceeds excessively, and film breakage may easily occur in the subsequent stretching step. By controlling the air temperature of the air knife within the above range, the molten sheet discharged from the T-die can be prevented from being excessively crystallized by air, and an unstretched sheet having a uniform structure can be obtained. it can.

  Since the unstretched sheet can be uniformly stretched in a stretching process described later, it is possible to suppress occurrence of thickness unevenness in the longitudinal direction and the width direction, and to suppress film breakage in the stretching process. The blowing air speed of the air knife is preferably 80 to 120 m / s. If the blown air speed is less than 80 m / s, the sheet adhesion may be insufficient and an unstretched sheet having a uniform structure may not be obtained. On the other hand, when the blown air speed exceeds 120 m / s, the molten sheet discharged from the T die is likely to vibrate by the air of the air knife, and the thickness unevenness in the longitudinal direction may be deteriorated. When the sheet is brought into close contact with the cast drum, in particular, the forming of the end portion of the sheet affects the subsequent stretchability. Therefore, it is preferable that the end portion is sprayed with spot air to be brought into close contact with the cast drum.

  Next, the obtained unstretched sheet is biaxially stretched and biaxially oriented. As specific stretching conditions, first, the temperature at which the unstretched sheet is stretched in the longitudinal direction is controlled. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. As a film temperature at the time of extending | stretching to a longitudinal direction, it is preferable in it to be 100-150 degreeC from a viewpoint of reducing the thickness spot of a longitudinal direction, More preferably, it is 110-145 degreeC, More preferably, it is 120-145 degreeC, Especially preferably, 130-145 ° C. The stretch ratio is 4 to 4 in terms of reducing the thickness unevenness in the longitudinal direction and the width direction, obtaining a film having a stable crystal form after biaxial stretching, Young's modulus, and heat shrinkage rate within an appropriate range. It is preferably 6.5 times, more preferably 4.5 to 6 times, still more preferably 5 to 6 times, and particularly preferably 5.5 to 6 times. As the draw ratio is increased, the thickness unevenness in the longitudinal direction is improved, and the withstand voltage characteristics are also improved. However, if the film is stretched over 6.5 times, the film is broken in the longitudinal stretching process or in the next transverse stretching process. It may be easy to get up.

  In order to achieve the above-mentioned high-magnification stretching without film breakage, it is preferable to introduce a mechanism for assisting stretching by giving a heat amount to the film in the stretched part immediately before stretching or by a radiation heater. Especially when stretching at a high magnification, since the orientation is strongly applied, the above-mentioned high-strength stretching is achieved from the viewpoint of improving the stretchability of the film by applying heat to the film of the above-mentioned radiation heater immediately before stretching or from the both sides of the stretched portion. This is more preferable. From the viewpoint of reducing the thickness unevenness in the longitudinal direction and the width direction, obtaining a film having a stable crystal form after biaxial stretching, the Young's modulus, and the heat shrinkage rate can be controlled within appropriate ranges. It is preferably 1,000,000-3,500,000% / min, more preferably 1,000,000-3,000,000% / min, 1,500,000-3,000, More preferably, it is 000% / min, and particularly preferably 2,000,000 to 3,000,000% / min. When the film is stretched in the longitudinal direction, a so-called neck-down phenomenon in which the film width decreases is observed, but in order to reduce thickness unevenness in the longitudinal direction and the width direction, the neck-down rate (after stretching) The film width / film width before stretching × 100) is preferably 90 to 99%.

  Next, the end of the film is gripped and introduced into a tenter type stretching machine. And, preferably from 140 to 165 ° C, more preferably from 142 to 163 ° C, still more preferably from 144 to 160 ° C in terms of obtaining a film having a stable crystal form after biaxial stretching, from the viewpoint of reducing thickness unevenness in the width direction. Particularly preferably, the film is heated to 145 to 155 ° C. and stretched in the width direction by 8 to 15 times, more preferably 9 to 14 times, still more preferably 10 to 13 times, and particularly preferably 10 to 12 times. In addition, as the transverse stretching speed at this time, from the viewpoint of reducing thickness unevenness in the width direction, the point of obtaining a film having a stable crystal form after biaxial stretching, the viewpoint of controlling Young's modulus and heat shrinkage within an appropriate range Is preferably 15,000 to 30,000% / min, more preferably 18,000 to 28,000% / min, even more preferably 20,000 to 28,000% / min, 20 5,000 to 25,000% / min is particularly preferable.

  Next, heat treatment may be performed in the tenter as it is, but from the viewpoint of reducing thickness unevenness in the longitudinal direction and width direction, from the viewpoint of controlling Young's modulus and heat shrinkage within an appropriate range, from the viewpoint of withstand voltage characteristics at high temperatures The temperature is preferably 147 to 167 ° C, more preferably 150 to 165 ° C, further preferably 152 to 163 ° C, and particularly preferably 155 to 160 ° C. Furthermore, the heat treatment may be performed while relaxing in the longitudinal direction and / or the width direction of the film, and in particular, the relaxation rate in the width direction is 5 to 15%, more preferably 8 to 13%, and still more preferably 9 to 12%. Particularly preferably, the content is 10 to 12% from the viewpoint of reducing thickness unevenness in the width direction and thermal dimensional stability.

  Finally, from the viewpoint of improving the adhesion of the deposited metal to the surface to be deposited, the biaxially stretched polypropylene film is subjected to corona discharge treatment in air, nitrogen, carbon dioxide, or a mixed gas thereof. An inventive biaxially oriented polypropylene film is obtained.

  The biaxially oriented polypropylene film of the present invention is preferably used as a dielectric for a capacitor, but is not limited to the type of capacitor. Specifically, from the viewpoint of electrode configuration, either a foil-wound capacitor or a metal-deposited film capacitor may be used, and it is also preferable for an oil-immersion type capacitor containing insulating oil or a dry-type capacitor not using insulating oil at all. Used. Further, from the viewpoint of shape, it may be a winding type or a laminated type. In view of the characteristics of the biaxially oriented polypropylene film of the present invention, it is particularly preferably used as a metal vapor deposition film capacitor.

  In the present invention, it is preferable to provide a metal film laminated film by providing a metal film on the surface of the biaxially oriented polypropylene film. Although the method is not particularly limited, for example, a method in which aluminum is vapor-deposited on at least one surface of the film to provide a metal film such as an aluminum vapor-deposited film that serves as an internal electrode of the film capacitor is preferably used. At this time, other metal components such as nickel, copper, gold, silver, chromium, and zinc can be deposited simultaneously or sequentially with aluminum. In addition, a protective layer can be provided on the deposited film with oil or the like.

  The thickness of the metal film of the metal film laminated film is preferably 20 to 100 nm from the viewpoint of the electrical characteristics and self-heeling property of the film capacitor. For the same reason, the surface resistance value of the metal film is preferably 1 to 20Ω / □. The surface resistance value can be controlled by the type of metal used and the film thickness.

  In the present invention, the metal film laminated film can be subjected to aging treatment or heat treatment at a specific temperature after forming a metal film as necessary. In addition, for insulation or other purposes, a coating of polyphenylene oxide or the like can be applied to at least one surface of the metal film laminated film.

  The metal film laminated film thus obtained can be laminated or wound by various methods to obtain a film capacitor. A preferred method for manufacturing a wound capacitor will be described below, but is not necessarily limited thereto.

  Aluminum is vacuum-deposited on one side of the biaxially oriented polypropylene film of the present invention. In that case, it vapor-deposits in the stripe form which has the margin part which runs in the longitudinal direction of a film. Next, a tape-shaped take-up reel having a margin on one side is prepared by inserting a blade into the center of each vapor deposition section on the surface and the center of each margin section. Two tape-shaped take-up reels with margins on the left or right are wound on the left margin and one on the right margin, overlapping each other so that the vapor deposition part protrudes from the margin part in the width direction. Get the body. The core material was removed from the wound body and pressed, and metallicon was sprayed on both ends to form external electrodes. Then, a wound film capacitor can be obtained by welding a lead wire to the metallicon. Film capacitors are used for various purposes such as for vehicles, home appliances (TVs, refrigerators, etc.), general noise prevention, automobiles (hybrid cars, power windows, wipers, etc.), and power supplies. Capacitors can also be suitably used for these applications.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Xylene soluble part (CXS)
After dissolving 0.5 g of a polypropylene resin sample in 100 ml of xylene at 135 ° C. and allowing to cool, recrystallizing in a constant temperature water bath at 20 ° C. for 1 hour, and then dissolving the polypropylene component dissolved in the filtrate by liquid chromatography. Quantify (X (g)). It calculated from the following formula using the precision value (X ₀ (g)) of 0.5 g of the sample.

CXS (%) = (X / X ₀ ) × 100
(2) Mesopentad fraction (mmmm)
A polypropylene resin or a biaxially oriented polypropylene film was dissolved in a solvent, and ¹³ C-NMR was used to determine the mesopentad fraction (mmmm) under the following conditions (Reference: New Edition Polymer Analysis Handbook) Japan Analytical Chemical Society / Polymer Analysis Research Roundtable, 1995, P609-611).

A. Measurement conditions Apparatus: DRX-500 manufactured by Bruker
Measurement nucleus: ¹³ C nucleus (resonance frequency: 125.8 MHz)
Measurement concentration: 10 wt%
Solvent: benzene / heavy orthodichlorobenzene = mass ratio 1: 3 mixed solution Measurement temperature: 130 ° C.
Spin rotation speed: 12Hz
NMR sample tube: 5 mm tube Pulse width: 45 ° (4.5 μs)
Pulse repetition time: 10 seconds Data point: 64K
Conversion count: 10,000 times Measurement mode: complete decoupling
B. Analysis condition LB (line broadening factor) was set to 1.0, and Fourier transform was performed to set the mmmm peak to 21.86 ppm. Peak splitting is performed using WINFIT software (manufactured by Bruker). At that time, the peak was divided from the peak on the high magnetic field side as follows, and the attached software was automatically fitted. After optimizing the peak division, the total of the mmmm peak fractions was determined. In addition, the said measurement was performed 5 times and the average value was made into the mesopentad fraction (mmmm) of this sample.

Peak (a) mrrm
(B) (c) rrrrm (divided as two peaks)
(D) rrrr
(E) mrmr
(F) mrmm + rmrr
(G) mmrr
(H) rmmr
(I) mmmr
(J) mmmm
(3) Melt flow rate (MFR)
It measured based on the conditions M (230 degreeC, 2.16 kg) of JISK7210 (1995).

(4) Melt tension (MS)
It measured according to the apparatus for MFR measurement shown by JISK7210 (1999). Using a melt tension tester manufactured by Toyo Seiki Co., Ltd., the resin sample was heated to 230 ° C., and the molten polymer was discharged at an extrusion speed of 15 mm / min to form a strand. The tension at the time of drawing this strand at a speed of 6.5 m / min was measured to determine the melt tension.

(5) Longitudinal and width-direction thickness variation A biaxially oriented polypropylene film cut out from any place to form a square of 102 mm in the longitudinal direction and 102 mm in the width direction, and a contact type film thickness meter made by Mitutoyo Co., Ltd. Lightmatic Measured with a VL-50A (10.5 mmφ super hard sphere probe, measuring load 0.06 N). Thickness measurement positions were set at 100 locations at 1 mm intervals in the central portion in the width direction of the sample in the longitudinal direction, and similarly at 100 locations at 1 mm intervals in the central portion in the longitudinal direction of the sample in the width direction. From the maximum value, the minimum value, and the average value at 100 locations in each of the longitudinal and width directions, thickness spots were obtained from the following formula.

Thickness unevenness (%) = ((maximum thickness−minimum thickness) / average thickness at 100 locations) × 100
(6) Melting peak temperature, number of melting peaks (158 to 180 ° C.)
A biaxially oriented polypropylene film (5 mg) was sealed in an aluminum pan as a sample, and measured using a differential scanning calorimeter (DSC) (RDC220 manufactured by Seiko Denshi Kogyo Co., Ltd.). Under a nitrogen atmosphere, the temperature was raised from room temperature to 280 ° C. at 20 ° C./min (first run), held for 5 minutes, and then cooled to 30 ° C. at 20 ° C./min. The melting peak temperature observed in the first run and the number of melting peaks present in the range of 158 to 180 ° C. were determined. In addition, this measurement was performed 3 times and let the average value of three data about each melting peak be the melting peak temperature of the biaxially oriented polypropylene film of this invention.

(7) Young's modulus About the longitudinal direction or the width direction of the biaxially oriented polypropylene film, cut out 5 samples so that the measurement direction is 200 mm and the direction perpendicular to the measurement direction is 10 mm, and mark the positions at 50 mm from both ends. The length was 100 mm. Using a film strong elongation measuring apparatus (AMF / RTA-100) manufactured by Orientec Co., Ltd., measurement was performed at 23 ° C. and 65% RH at a tensile rate of 300 mm / min. The average value of five samples in each of the longitudinal direction and the width direction was taken as the Young's modulus of the biaxially oriented polypropylene film of the present invention.

(8) 120 ° C., 140 ° C. heat shrinkage ratio For the longitudinal direction or width direction of the biaxially oriented polypropylene film, 5 samples were cut out so that the measurement direction was 200 mm and the direction perpendicular to the measurement direction was 10 mm, and the position was 50 mm from both ends. Was marked with a test length of 100 mm. Next, it is hung in an oven kept at 120 ° C. or 140 ° C. with a load of 3 g, taken out after heating for 15 minutes, cooled at room temperature, measured for dimensions (l ₁ ), and obtained by the following formula: The average value of 5 pieces in each of the longitudinal direction and the width direction was taken as the heat shrinkage rate of the biaxially oriented polypropylene film of the present invention.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
(9) Dynamic friction coefficient μd
Based on JIS K7125 (1999), it measured using the slip tester (200G-15C) by Toray Industries, Inc. A biaxially oriented polypropylene film was sampled so as to have a strip shape with a longitudinal direction of 100 mm and a width direction of 75 mm, and two similar samples were prepared. The two samples were then conditioned for 24 hours in an atmosphere of 23 ° C. and 65% RH. Two samples after humidity conditioning are overlapped and different loads are applied, and a load (mass 200 g, bottom area 50 mm × 50 mm square) is placed on one sample. I picked it up. The frictional force is classified into a static frictional force observed at the critical point at which the sample starts to slide and a dynamic frictional force in the stable region after the specimen starts to slide. In this evaluation, the dynamic frictional force R (g) is read from the chart, and the dynamic friction coefficient μd = R (g) / 200 (g). In addition, this measurement was performed 3 times and the average value was made into the dynamic friction coefficient of the biaxially oriented polypropylene film of this invention.

(10) Glossiness According to JIS K7105 (1981), the gloss was measured under the conditions of an incident angle of 60 ° and a light receiving angle of 60 ° using a digital variable angle glossmeter UGV-5D manufactured by Suga Test Instruments Co., Ltd. In addition, this measurement was performed 5 times and the average value was made into the glossiness of the biaxially oriented polypropylene film of this invention.

(11) Film thickness The thickness of the micrometer method was measured according to 7.4.1.1 of JIS C2330 (2001).

(12) Ash content In accordance with JIS C2330 (1995), a biaxially oriented polypropylene film having an initial mass of W ₀ is put in a platinum crucible, and first burned sufficiently with a gas burner, and then treated in an electric furnace at 750 to 800 ° C. for 1 hour. The ash mass W1 of the obtained ash was measured and calculated from the following formula.

Ash content = (W ₁ / W ₀ ) × 1,000,000 (ppm)
(13) Surface wetting tension The surface wetting tension was measured based on a measurement method defined in JIS K6768 (1999) using a mixed solution of formaldehyde and ethylene glycol monoethyl ether.

(14) Surface resistance of metal film The resistance of a metal film between 30 mm in the width direction was measured by a four-terminal method using a sample obtained by sampling a metal film laminated film in a strip shape of 10 mm in the longitudinal direction and 50 mm in the width direction. The surface resistance value per 10 mm × 10 mm was calculated by multiplying the obtained measurement value by the sample width (10 mm) and dividing the distance between electrodes (30 mm). The unit of the surface resistance value is Ω / □.

(15) Element workability in capacitor production On one side of the biaxially oriented polypropylene film obtained in each of Examples and Comparative Examples described later, aluminum is vacuumed to 8 Ω / □ with a vacuum vapor deposition machine manufactured by ULVAC. Vapor deposited. At that time, vapor deposition was performed in a stripe shape having a margin portion running in the longitudinal direction (repetition of a vapor deposition portion width of 39.0 mm and a margin portion width of 1.0 mm). Next, a tape-shaped take-up reel having a full width of 20 mm having a 0.5 mm margin at either the left or right end was slit by inserting a blade into the center of each vapor deposition section and the center of each margin section. Two reels, each having a left margin and a right margin, were wound and overlapped in the width direction so that the vapor deposition portion protruded 0.5 mm from the margin portion, and a wound body having a capacitance of 10 μF. Got. KAW-4NHB manufactured by Minato Co., Ltd. was used for element winding.

  When the capacitor was manufactured, from the start to the end of winding was visually observed. Wrinkles and misalignments were rejected, and the device workability was evaluated based on the number of rejects. In addition, 50 capacitor elements were produced and evaluated according to the following criteria.

○: No defective product △: 1-2 defective products ×: 3 or more defective products (16) High-temperature withstand voltage characteristics In accordance with JIS C2330 (2001), an electrode was installed in a hot air oven adjusted to 125 ° C. The dielectric breakdown voltage of the biaxially oriented polypropylene film was measured. In addition, this measurement was performed 5 times, the average value was calculated | required, and it divided | segmented by the film thickness calculated | required by said (11) term, and calculated | required the high temperature dielectric breakdown voltage (V / micrometer) per micrometer. For the high temperature withstand voltage characteristics, the high temperature breakdown voltage was evaluated according to the following criteria.

○: 450 V / μm or more Δ: 400 V / μm or more, less than 450 V / μm ×: less than 400 V / μm (Example 1)
100% by mass of polypropylene resin (manufactured by Prime Polymer Co., Ltd., melting point: 166 ° C., MFR: 2.5 g / 10 min, mmmm: 0.991) is supplied to a single-screw melt extruder, and melt extrusion is performed at 230 ° C. Foreign matter was removed with a sintered filter of 25 μm cut. The shear rate applied by the T die during extrusion was 600 sec ⁻¹ . The molten sheet discharged from the T-die was brought into intimate contact with a cast drum whose surface temperature was controlled at 90 ° C., and was cast so as to be indirectly on the cast drum for 4 seconds to obtain an unstretched sheet. An air knife and end spot air were used to bring the molten sheet into close contact with the cast drum. The distance between the air knife and the seat landing point was set to 2 mm, and air adjusted to 62 ° C. was blown at a blowing speed of 100 m / s. Subsequently, it preheated using the ceramic roll heated at 130 degreeC, and stretched 5.8 times in the longitudinal direction of the film. At this time, the stretching speed in the longitudinal direction was 2,500,000% / min, and the neck-down rate was 98%. Further, for the purpose of improving the stretchability of the film, heat was applied from both sides of the film stretching portion with a radiation heater, so that the film was not broken in the longitudinal stretching and the film forming property was excellent. Next, the edge part was hold | gripped with the clip, and it extended | stretched 10 time at the extending | stretching speed of 22,000% / min at 145 degreeC in the width direction. Further, heat treatment was performed at 155 ° C. for 7 seconds, and 10% relaxation was performed in the width direction. Thereafter, after cooling to room temperature, one side of the film was subjected to corona discharge treatment at a treatment strength of 25 W · min / m ² , and the film ears held by the clips were cut and removed. It should be noted that the surface treated surface is referred to as A surface, and the untreated surface is referred to as B surface. The film from which the end portion was removed was wound up by a winder to obtain a biaxially oriented polypropylene film having a thickness of 2.5 μm. Table 1 shows the physical properties of the obtained film.

(Example 2)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the shear rate applied by a T die during extrusion was 150 sec ⁻¹ . Table 1 shows the physical properties of the obtained film.

Example 3
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the mesopentad fraction (mmmm) of the polypropylene resin was changed to 0.980. Table 1 shows the physical properties of the obtained film.

Example 4
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the shear rate applied by a T-die during extrusion was 200 sec ⁻¹ . Table 1 shows the physical properties of the obtained film.

(Example 5)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the shear rate applied by a T-die during extrusion was set to 100 sec ⁻¹ . Table 1 shows the physical properties of the obtained film.

(Example 6)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the distance between the air knife and the sheet landing point was 5 mm. Table 1 shows the physical properties of the obtained film.

(Example 7)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the distance between the air knife and the sheet landing point was 6 mm. Table 1 shows the physical properties of the obtained film.

(Example 8)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the distance between the air knife and the sheet landing point was 10 mm. Table 1 shows the physical properties of the obtained film.

Example 9
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the time during which the molten sheet discharged from the T die was in close contact with the cast drum was 2 seconds. Table 1 shows the physical properties of the obtained film.

(Example 10)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the time during which the molten sheet discharged from the T die was in close contact with the cast drum was 1.5 seconds. Table 1 shows the physical properties of the obtained film.

(Example 11)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the time during which the molten sheet discharged from the T die was in close contact with the cast drum was 1 second. Table 1 shows the physical properties of the obtained film.

(Example 12)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the air temperature of the air knife in the casting step was 60 ° C. Table 1 shows the physical properties of the obtained film.

(Example 13)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the stretching speed in the longitudinal direction was changed to 1,500,000% / min. Table 2 shows the physical properties of the obtained film.

(Example 14)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the stretching speed in the longitudinal direction was changed to 1,000,000% / min. Table 2 shows the physical properties of the obtained film.

(Example 15)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the stretching speed in the width direction was changed to 18,000% / min. Table 2 shows the physical properties of the obtained film.

(Example 16)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the stretching speed in the width direction was changed to 15,000% / min. Table 2 shows the physical properties of the obtained film.

(Comparative Example 1)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the shear rate applied by a T-die during extrusion was 90 sec ⁻¹ . Table 2 shows the physical properties of the obtained film.

(Comparative Example 2)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the mesopentad fraction (mmmm) of the polypropylene resin was changed to 0.978. Table 2 shows the physical properties of the obtained film.

(Comparative Example 3)
It was produced in the same manner as in Example 1 except that the air temperature of the air knife in the casting process was 90 ° C. As a result, film breakage occurred in the longitudinal stretching step, and a biaxially oriented polypropylene film could not be obtained.

(Comparative Example 4)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the air temperature of the air knife in the casting step was 50 ° C. Table 2 shows the physical properties of the obtained film.

(Comparative Example 5)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the air blowing speed of the air knife in the casting step was 130 m / s. Table 2 shows the physical properties of the obtained film.

(Comparative Example 6)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal direction was 3.8 times. Table 2 shows the physical properties of the obtained film.

(Comparative Example 7)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the stretching ratio in the width direction was 7 times. Table 2 shows the physical properties of the obtained film.

(Comparative Example 8)
A biaxially oriented polypropylene film having a thickness of 2.5 μm was obtained in the same manner as in Example 1 except that the surface temperature of the cast drum was 121 ° C. Table 2 shows the physical properties of the obtained film.

  When used as a capacitor dielectric, the biaxially oriented polypropylene film of the present invention provides a biaxially oriented polypropylene film having excellent withstand voltage characteristics and excellent workability due to small thickness unevenness in the longitudinal and width directions. be able to.

Claims (11)

A biaxially oriented polypropylene film containing a polypropylene resin as a main component, the thickness variation in the longitudinal direction is 0 to 10%, the thickness variation in the width direction is 0 to 10%, and 158 to 180 ° C. in DSC measurement. Biaxially oriented polypropylene film having two or more melting peaks in the range of. Is the longitudinal direction of the Young's modulus _{E MD} and the width direction of the Young's modulus _{E TD} are both 2.5GPa or more, the biaxially oriented polypropylene film according to claim 1. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the relationship between the Young's modulus E _{MD in the} longitudinal direction and the Young's modulus E _{TD in} the width direction satisfies the following formula (1).
0.5 ≦ E _MD / E _TD ≦ 1.2 (1) The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the heat shrinkage ratio in the longitudinal direction and the width direction under the treatment conditions at 120 ° C for 15 minutes is -1 to 5%. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein the heat shrinkage ratio in the longitudinal direction and the width direction under treatment conditions of 140 ° C for 15 minutes is -1 to 10%. The biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein a coefficient of dynamic friction μd between one surface and the other surface is 0.5 to 1.2. The biaxially oriented polypropylene film according to any one of claims 1 to 6, wherein the glossiness is 120 to 150% on both sides. The biaxially oriented polypropylene film according to any one of claims 1 to 7, wherein the film thickness is 0.5 to 3 µm. The biaxially oriented polypropylene film according to any one of claims 1 to 8, which is used as a dielectric for a capacitor. A metal film laminated film formed by forming a metal layer on at least one surface of the biaxially oriented polypropylene film according to claim 9. A film capacitor formed by winding the metal film laminated film according to claim 10.