JPWO2015129851A1 - Biaxially oriented polypropylene film - Google Patents

Abstract

It is an object to provide a biaxially oriented polypropylene film that has high strength, low heat yield, excellent transparency, and can be suitably used as a film for a manufacturing process such as a flat panel display film or a display or a film for a capacitor. To do. The sum EMD + TD of the tensile modulus EMD in the longitudinal direction of the film and the tensile modulus ETD in the width direction is 4.5 GPa or more, the total haze is 1% or less, and the thermal shrinkage after treatment at 85 ° C. for 100 hours is The biaxially oriented polypropylene film is 1.0% or less in both the longitudinal direction and the width direction of the film.

Description

  The present invention relates to a biaxially oriented polypropylene film that has high strength and low heat yield, is excellent in transparency, and can be suitably used as a film for a manufacturing process such as a flat panel display film or a display or a film for a capacitor.

  Biaxially oriented polypropylene film is excellent in transparency, mechanical properties, electrical properties, etc., so it is used in various applications such as packaging, mold release, tape, cable wrapping and electrical applications including capacitors. .

  Further, in recent years, studies have been carried out to develop a film for a flat panel display such as a polarizer protective film and a retardation film, taking advantage of the optical properties and productivity of the polypropylene film (for example, Patent Documents 1 and 2). However, the polypropylene film has a rough film surface due to the β crystal of polypropylene produced at the time of melt extrusion, the haze of the film may increase, and the visibility may decrease when used in display applications. . In particular, in the biaxially stretched film, fibrils due to β crystals are generated in the stretching process in the width direction, and the haze may be increased. To improve the transparency of polypropylene film, use polypropylene with low stereoregularity as raw material, increase the content of polyethylene component, add petroleum resin, etc. to lower the crystallinity of polypropylene Although the method can be considered, since the above components are generally soft components or have low heat resistance, there are cases where the strength and heat resistance of the film are lowered when the amount added is large. In addition, in the production method, in order to prevent a decrease in transparency, a method of unstretching or longitudinal uniaxial stretching can be considered, but the strength of the film may be lowered. For example, Patent Document 3 uses syndiotactic polypropylene as a raw material, lowers the temperature of a cooling roll after extrusion, suppresses crystal formation of an unstretched sheet, and uniaxially stretches in the range of 1 to 4 times in the longitudinal direction. Thus, an example of improving the transparency of a polypropylene film is described. Since these polypropylene films use syndiotactic polypropylene having low crystallinity as a raw material and have a low draw ratio and are further uniaxially stretched, the film strength may be insufficient. When the film strength is insufficient, in a flat panel display film, for example, when the polarizer and the film of the present invention are bonded together, the film is deformed by the tension of the apparatus, the phase difference changes, and the color tone of the display changes. There was a case where it shifted. In addition, the withstand voltage may be reduced in capacitor applications.

  Patent Documents 4 and 5 describe examples in which the strength and transparency of a polypropylene film are compatible. However, both strength and transparency are insufficient for use in flat panel displays.

JP2013-152455A JP 2010-164733 A JP 2010-195993 A JP 2003-170485 A JP 2009-012225 A

  An object of the present invention is to solve the above-described problems. That is, to provide a biaxially oriented polypropylene film that has high strength, low heat yield, excellent transparency, and can be suitably used as a film for a manufacturing process such as a flat panel display film or a display or a film for a capacitor. is there. In the present invention, strength refers to the strength of a property that is difficult to deform, and tensile modulus is used as an index thereof. That is, in this specification, “high strength” indicates that the tensile elastic modulus is high.

In order to solve the above-described problems and achieve the object, the biaxially oriented polypropylene film of the present invention has a value of the sum E _{MD + TD} of the tensile elastic modulus E _MD in the longitudinal direction of the film and the tensile elastic modulus E _TD in the width direction. 4.5 GPa or more, total haze is 1% or less, and heat shrinkage ratio after treatment at 85 ° C. for 100 hours is 1.0% or less in both the longitudinal direction and the width direction of the film. .

  Since the biaxially oriented polypropylene film of the present invention has high strength, low heat gain, and excellent transparency, it can be suitably used as a film for manufacturing processes such as a flat panel display film and a display, and a film for a capacitor. it can.

In the biaxially oriented polypropylene film of the present invention, the sum E _{MD + TD} of the tensile elastic modulus E _MD in the longitudinal direction of the film and the tensile elastic modulus E _TD in the width direction is 4.5 GPa or more. When the value of E _{MD + TD} is less than 4.5 GPa, when used as a film for a flat panel display, for example, when the polarizer and the film of the present invention are bonded, the film is deformed by the tension of the apparatus, and the phase difference changes. As a result, the color tone of the display may shift. In addition, the withstand voltage may decrease in the capacitor application. The value of E _{MD + TD} is more preferably 5.0 GPa or more, still more preferably 5.5 GPa or more, and most preferably 6.0 GPa or more. The higher the value of E _{MD + TD} , the better, but about 20 GPa is the upper limit, more preferably 10 GPa or less, and even more preferably 7 GPa or less. _Further, values of and _{E TD} of _{E MD} is preferably both 2GPa or more. Even if the value of E _{MD + TD} is 4.5 GPa or more, if there is a certain difference in tensile elastic modulus between the longitudinal direction and the width direction, handling properties may be deteriorated, such as film tearing. In order to set the value of E _{MD + TD in} the above range, the raw material composition of the film is set in the range described later, and a highly transparent film is obtained while reducing flexible components such as low stereoregular polypropylene, and the film forming conditions are described later. It is preferable to obtain a biaxially oriented polypropylene film by stretching the film at a high magnification.

The biaxially oriented polypropylene film of the present invention preferably has an E _MD / E _TD value of 0.5 or more and 2.0 or less. If the value of E _MD / E _TD is out of the above range, the orientation balance of the biaxially oriented polypropylene film is deteriorated, and the film may be easily torn during handling. The value of E _MD / E _TD is more preferably 0.55 or more and 1.5 or less, and further preferably 0.57 or more and 1.2 or less. In order to make the value of E _MD / E _TD within the above range, it is preferable to obtain a biaxially oriented polypropylene film with the MD and TD stretching conditions and heat setting conditions as described later.

  In the present application, a direction parallel to the film forming direction is referred to as a film forming direction, a longitudinal direction, or an MD direction, and a direction perpendicular to the film forming direction in the film plane is referred to as a width direction or a TD direction.

  The biaxially oriented polypropylene film of the present invention has a total haze of 1% or less. If the total haze exceeds 1%, the visibility of the display may be lowered when used as a film for a flat panel display. In capacitor applications, particularly when a thin film having a thickness of 2 μm or less is used, film breakage may occur during deposition of a metal layer. This is presumably because the fine voids inside the film caused by the β crystals of polypropylene cause the film to break. The total haze is more preferably 0.8% or less, still more preferably 0.5% or less. The total haze is preferably as low as possible from the viewpoint of transparency, but the lower limit is substantially about 0.05%.

  In order to make the total haze within the above range, it is preferable that the raw material composition of the film is within the range described below, and that the casting conditions and the longitudinal stretching conditions are within the range described below, and β crystals of the cast sheet are reduced.

  The biaxially oriented polypropylene film of the present invention has a heat shrinkage ratio after treatment at 85 ° C. for 100 hours of 1.0% or less in both the longitudinal direction and the width direction of the film. When the thermal shrinkage rate exceeds 1.0%, when a flat panel display is used at a high temperature, the film peels off due to the shrinkage stress of the film, and the visibility is lowered, or the phase difference changes due to the shrinkage stress of the film. May change. In capacitor applications, the film itself contracts due to heat in the capacitor manufacturing process and use process, and the withstand voltage may decrease due to poor contact with the element end metallicon. The thermal contraction rate is more preferably 0.5% or less, still more preferably 0.3% or less, and most preferably 0.1% or less. Although a minimum is not specifically limited, A film may expand | swell too much, and about -1.0% is a minimum substantially. In order to make the heat shrinkage rate within the above range, the raw material composition is within the range described later, and the addition amount of the low melting point component is reduced as much as possible while maintaining the transparency, and the longitudinal stretching condition, the transverse stretching condition, the heat It is preferable that the fixing condition and the relaxing condition are within the ranges described later, and the heat yield is reduced while maintaining the strength.

  The biaxially oriented polypropylene film of the present invention preferably has a ten-point average roughness SRz of at least one surface of 500 nm or less. When the SRz on at least one side is 500 nm or less, the visibility of the display can be further enhanced when used as a flat panel display film. SRz on at least one side is more preferably 200 nm or less, still more preferably 150 nm or less, and most preferably 100 nm or less. Although the SRz on at least one side is preferably as low as possible, the lower limit is substantially about 1 nm. In order to set SRz in the above range, it is preferable to set the raw material composition of the film to a range described later, and to set the casting conditions and longitudinal stretching conditions in the ranges described later, and to reduce the β crystal of the cast sheet.

  The biaxially oriented polypropylene film of the present invention preferably has a center average surface roughness SRa of at least one surface of 50 nm or less. When the SRa on at least one side is 50 nm or less, the visibility of the display can be further enhanced when used as a flat panel display film. The SRa on at least one side is more preferably 20 nm or less, and further preferably 15 nm or less. The lower the SRa of at least one side, the better. However, the lower limit is substantially about 1 nm. In order to make SRa within the above range, it is preferable that the raw material composition of the film is within the range described later, and that the casting conditions and longitudinal stretching conditions are within the ranges described below, and that β crystals of the cast sheet are reduced.

  The biaxially oriented polypropylene film of the present invention preferably has an in-plane retardation Ret of 0.1 to 500 nm. For flat panel display films, the required retardation of the film differs depending on the site used, and for optically isotropic films such as polarizer protective films, the retardation is about 0.1 to 100 nm, such as 1 / 4λ retardation film. In the case of a film, the thickness is preferably about 50 to 500 nm. If the phase difference exceeds 500 nm, the color tone of the display may change. For capacitor applications, the higher the phase difference, the higher the orientation of the film and the better the withstand voltage. In order to set the value of Ret within the above range, it is preferable that the raw material composition, the longitudinal stretching condition, the lateral stretching condition, the heat setting condition, and the relaxing condition are within the ranges described later.

  The biaxially oriented polypropylene film of the present invention preferably has a ratio value Rth / Ret of 1 or less with respect to the above Ret, where Rth is the retardation in the thickness direction of the film. In the flat panel display film, when the value of Rth / Ret is 1 or less, the viewing angle characteristics are improved. The value of Rth / Ret is more preferably 0.8 or less, and still more preferably 0.5 or less. The target value of Rth / Ret is appropriately set depending on the configuration of the display used, but about 0.1 is a controllable lower limit value. In order to make the value of Rth / Ret within the above range, it is preferable that the raw material composition, the longitudinal stretching condition, the transverse stretching condition, the heat setting condition, and the relaxing condition are within the ranges described later.

  In the biaxially oriented polypropylene film of the present invention, the static friction coefficient μs between one surface of the film and its back surface is preferably 0.5 or less. When the static friction coefficient μs exceeds 0.5, the film is not slidable and difficult to handle, and wrinkles may occur during film formation and post-processing, or the roll shape of the product roll may deteriorate. The static friction coefficient μs is more preferably 0.45 or less, and still more preferably 0.4 or less. The static friction coefficient μs is preferably low from the viewpoint of handling properties. However, in order to reduce the static friction coefficient μs, it is necessary to roughen the surface, haze increases, and transparency deteriorates. About 1 is the lower limit. In order to set the static friction coefficient μs in the above range, it is preferable that the raw material composition, the laminated structure of the film, the longitudinal stretching conditions, and the lateral stretching conditions are within the ranges described below.

  The biaxially oriented polypropylene film of the present invention preferably has a melting point Tm of 158 ° C. or higher. When the melting point Tm is less than 158 ° C., the heat resistance may be insufficient and the heat shrinkage rate may be increased, or because the content of the ethylene component is large, the tensile rigidity may be reduced or fish eyes may be easily generated. . Melting | fusing point Tm becomes like this. More preferably, it is 160 degreeC or more, More preferably, it is 163 degreeC or more. From the viewpoint of reducing the heat shrinkage rate, the higher the melting point Tm of the biaxially oriented polypropylene film, the better. However, practically, the upper limit is about 180 ° C. In order to make the melting point Tm within the above range, the raw material composition is within the range described later, and in particular, the content of the ethylene component having low heat resistance is lowered, the longitudinal stretching condition, the lateral stretching condition, the heat setting condition, the relaxation. It is preferable that the conditions are within a range described later. In the measurement with a differential scanning calorimeter, when two or more melting peak temperatures of the film are observed, the lowest peak temperature is taken as the melting point Tm of the biaxially oriented polypropylene film.

  The thickness of the biaxially oriented polypropylene film of the present invention is appropriately adjusted depending on the application and is not particularly limited, but is preferably 0.5 μm or more and 100 μm or less. When the thickness is less than 0.5 μm, handling may be difficult. When the thickness exceeds 100 μm, the thickness of the unstretched sheet becomes thick, so the cooling rate with the cooling roll during extrusion becomes slow, and β crystal May be easily formed and the haze of the film may be increased. The thickness is more preferably 5 to 60 μm and even more preferably 5 to 30 μm for flat panel display applications. For capacitor use, it is preferably 0.5 to 10 μm, and more preferably 1 to 3 μm. The thickness can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties.

  Next, a preferable polypropylene raw material when used for a biaxially oriented polypropylene film will be described.

  In the biaxially oriented polypropylene film of the present invention, it is preferable to use at least two types of polypropylene raw materials (polypropylene raw material A and polypropylene raw material B). As the polypropylene raw material A, it is preferable to use a polypropylene raw material having high crystallinity in order to improve the strength of the film, and as the polypropylene raw material B, a polypropylene raw material having low stereoregularity is used to improve the transparency of the film. Is preferred.

  The polypropylene raw material A is preferably a polypropylene having a cold xylene soluble part (hereinafter referred to as CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these conditions are not satisfied, film-forming stability may be inferior, film strength may be reduced, and dimensional stability and voltage resistance may be greatly reduced.

  Here, the cold xylene-soluble part (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then deposited at room temperature, and has low stereoregularity. It is considered that it corresponds to a component that is difficult to crystallize due to low molecular weight. If many such components are contained in the resin, problems such as inferior thermal dimensional stability of the film and reduction in dielectric breakdown voltage at high temperatures may occur. Therefore, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. CXS is preferably as low as possible, but about 0.1% by mass is the lower limit. In order to obtain such polypropylene having CXS, methods such as a method for increasing the catalytic activity in obtaining a resin and a method for washing the obtained resin with a solvent or propylene monomer itself can be used.

  From the same viewpoint, the mesopentad fraction of the polypropylene raw material A is preferably 0.95 or more, more preferably 0.97 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). The higher the numerical value, the higher the crystallinity, the higher the melting point, and the higher the temperature. This is preferable because the dielectric breakdown voltage is increased. The upper limit of the mesopentad fraction is not particularly specified. In order to obtain a resin with high stereoregularity in this way, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and / or promoter, and a composition as appropriate. Preferably employed.

  Further, as the polypropylene raw material A, the melt flow rate (MFR) is more preferably 1 to 10 g / 10 min (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 min (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of film forming properties and film strength. In order to set the melt flow rate (MFR) to the above value, a method of controlling the average molecular weight or the molecular weight distribution is employed.

  The polypropylene raw material A is mainly composed of a propylene homopolymer, 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. For example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene as monomer components constituting such a copolymer component or blend. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Examples include norbornene. From the viewpoint of dielectric breakdown resistance and dimensional stability, the copolymerization amount or blend amount is preferably less than 1 mol% in copolymerization amount and less than 10 mass% in blend amount.

  Next, the polypropylene raw material B will be described.

  The polypropylene raw material B is preferably a polypropylene raw material having good compatibility with the above-described polypropylene raw material A and low crystallinity and stereoregularity in order to obtain high transparency. As such a polypropylene raw material B, amorphous polypropylene, low stereoregular polypropylene, syndiotactic polypropylene, α-olefin copolymer and the like can be used, but excellent transparency can be obtained with a small addition amount. Therefore, amorphous polypropylene and low stereoregular polypropylene are particularly preferable.

  As the polypropylene raw material B, the amorphous polypropylene preferably used is preferably mainly composed of a polypropylene polymer having mainly atactic stereoregularity, specifically, a homopolymer or a copolymer with an α-olefin. Can be mentioned. In particular, the latter, that is, an amorphous polypropylene-α-olefin copolymer is preferred. In the present application, the term “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, most preferably Preferably it is 95 mass% or more.

  The amorphous polypropylene can be produced as a by-product of isotactic polypropylene during homopolypropylene polymerization. Since the glass transition temperature is lower than that of general polypropylene, it can be extracted as a boiling n-heptane (or xylene) soluble component of homopolypropylene. Alternatively, it is possible to polymerize amorphous polypropylene independently by changing the catalyst and polymerization conditions applied during the production of crystalline polypropylene. The amorphous polypropylene preferably used in the present invention can be used without particular limitation as long as it is produced by a conventionally known production method. Commercially available products such as “Tufselen” manufactured by Sumitomo Chemical Co., Ltd. can be appropriately selected and used as the amorphous polypropylene having the above characteristics.

  When an amorphous polypropylene-α-olefin copolymer is used as the amorphous polypropylene in the present invention, examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene. 4-methyl 1-pentene or propylene-ethylene-1-butene is desirable.

  Examples of amorphous polypropylene-α-olefin copolymers using such α-olefins include propylene / ethylene copolymers, propylene / ethylene / 1-butene copolymers, and propylene-1-butene copolymers. , Propylene / ethylene / cyclic olefin copolymer, propylene / ethylene / butadiene copolymer, and the like.

  The low stereoregular polypropylene preferably used as the polypropylene raw material B is preferably a homopolymer of propylene and produced using a metallocene catalyst as a polymerization catalyst. The melting point of the low stereoregular polypropylene is 100 ° C. or less, more preferably 60 to 90 ° C., and particularly preferably 65 to 85 ° C. The weight average molecular weight is preferably 40,000 to 200,000, and the molecular weight distribution Mw / Mn is preferably 1 to 3 (Mw: weight average molecular weight, Mn: number average molecular weight). As the low stereoregularity polypropylene having the above-described characteristics, a commercially available product such as “El Modu” manufactured by Idemitsu Kosan Co., Ltd. can be appropriately selected and used.

  Moreover, the biaxially oriented polypropylene film of the present invention may contain a branched polypropylene H in addition to the polypropylene raw material A and the polypropylene raw material B described above from the viewpoint of improving the strength and improving the withstand voltage. When adding, 0.05-10 mass% is preferable, More preferably, it is 0.5-8 mass%, More preferably, it is preferable to make it contain 1-5 mass%. By containing the branched polypropylene H, the size of the spherulite produced in the cooling step of the melt-extruded resin sheet can be controlled to be small, and a polypropylene film excellent in transparency and strength can be obtained.

As the above-mentioned branched polypropylene H, the melt flow rate (MFR) is preferably in the range of 1 to 20 g / 10 minutes, and more preferably in the range of 1 to 10 g / 10 minutes, from the viewpoint of film formability. preferable. Moreover, about melt tension, what exists in the range of 1-30 cN is preferable, and what exists in the range of 2-20 cN is more preferable. Moreover, the branched polypropylene H here is a polypropylene having 5 or less internal 3-substituted olefins per 10,000 carbon atoms. The presence of this internal tri-substituted olefin can be confirmed by the proton ratio in the ¹ H-NMR spectrum.

  In the biaxially oriented polypropylene film of the present invention, the content of the ethylene component contained in the polymer constituting the film is preferably 10% by mass or less. More preferably, it is 5 mass% or less, More preferably, it is 3 mass% or less. As the content of the ethylene component increases, the crystallinity decreases and the transparency is easily improved. However, if the content of the ethylene component exceeds 10% by mass, the strength decreases or the heat resistance decreases and heat increases. The shrinkage rate may deteriorate.

  In the biaxially oriented polypropylene film of the present invention, the content of petroleum resin contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that petroleum resin is not included. Transparency and strength can be improved by adding petroleum resin. However, if the content of petroleum resin exceeds 5% by mass, the heat shrinkage decreases and the thermal shrinkage rate deteriorates. May be higher.

  In the biaxially oriented polypropylene film of the present invention, the content of the cycloolefin polymer contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that a cycloolefin polymer is not included. Heat resistance and strength can be improved by adding a cycloolefin polymer. However, if the content of the cycloolefin polymer exceeds 5% by mass, the transparency is lowered due to a compatibility problem with polypropylene and haze is reduced. It may worsen or the raw material cost may increase.

  In the biaxially oriented polypropylene film of the present invention, the content of the polypropylene polymer contained in the polymer constituting the film is preferably 95% by mass or more from the viewpoints of transparency, heat resistance and strength. More preferably, it is 96 mass% or more, More preferably, it is 97 mass% or more, Most preferably, it is 98 mass% or more.

  In the polypropylene raw material of the present invention, various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slip agent, an antistatic agent, an antiblocking agent, a filler, a viscosity are included within the range not impairing the object of the present invention. An adjusting agent, an anti-coloring agent, etc. can also be included.

  Among these, the selection of the type and amount of antioxidant is 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. Specific examples thereof include various ones. For example, 1,3,5-trimethyl-2,4,6-, together with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4). Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, Irganox (registered trademark) 1330: molecular weight 775.2 manufactured by BASF) or tetrakis [methylene-3 (3,5-di-t- Butyl-4-hydroxyphenyl) propionate] methane (for example, Irganox (registered trademark) 1010: molecular weight 1177.7 manufactured by BASF) is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0 mass% with respect to the total amount of polypropylene. When there are too few antioxidants, a polymer may deteriorate in an extrusion process and a film may color, or it may be inferior to long-term heat resistance. When there are too many antioxidants, transparency may fall by the bleeding out of these antioxidants. The more preferable content is 0.1 to 0.9% by mass, and particularly preferably 0.2 to 0.8% by mass.

  A crystal nucleating agent can be added to the polypropylene raw material of the present invention as long as it does not contradict the purpose of the present invention. As described above, the branched polypropylene (H) has an α-crystal or β-crystal nucleating agent effect itself, but other α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.) ), Β crystal nucleating agents (amide compounds such as potassium 1,2-hydroxystearate, magnesium benzoate, N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compounds, etc.) and the like. . However, since excessive addition of the above-mentioned different kind of nucleating agent may cause a decrease in stretchability or a decrease in transparency and strength due to void formation, the addition amount is usually 0.5% by mass or less, preferably 0.1%. It is preferable to set it as mass% or less, More preferably, it is 0.05 mass% or less, It is most preferable not to add.

  The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching using the raw materials described above. The biaxial stretching method can be obtained by any of the inflation simultaneous biaxial stretching method, the stenter simultaneous biaxial stretching method, and the stenter sequential biaxial stretching method. Among them, the film forming stability, the thickness uniformity, In terms of controlling high rigidity and dimensional stability, it is preferable to employ a stenter sequential biaxial stretching method.

  Next, the structure of the film using the said polypropylene raw material is demonstrated.

  The biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers in order to satisfy high strength, high transparency and low heat yield at the same time.

  In the biaxially oriented polypropylene film of the present invention, at least one layer (hereinafter referred to as I layer) of the laminated structure preferably contains 96% by mass or more of polypropylene raw material A from the viewpoint of high strength and low heat yield. The content of the polypropylene raw material A in the I layer is more preferably 97% by mass or more, and still more preferably 98% by mass or more. When the content of the polypropylene raw material A in the I layer is less than 96% by mass, the orientation of the film is lowered and the strength is lowered, and when there are many additive components having low heat resistance, the heat yield is increased. There is a case.

  In addition, the biaxially oriented polypropylene film of the present invention has at least one layer (hereinafter referred to as “II layer”) in the laminated structure, and the mixing ratio of the polypropylene raw material A and the polypropylene raw material B is from the viewpoint of transparency and low heat yield. It is preferably 50:50 to 95: 5 (mass ratio; the same applies hereinafter). More preferably, it is 60: 40-95: 5, More preferably, it is 70: 30-93: 7. When the mixing ratio of the polypropylene raw material B in the II layer exceeds 50, strength and heat resistance may be lowered. If it is less than 5, the stereoregularity of the unstretched film becomes too high, and the transparency may be lowered during stretching.

  The biaxially oriented polypropylene film of the present invention has a laminate structure of at least two layers, and preferably includes at least one I layer and II layer described above. The lamination thickness ratio of the I layer in the thickness direction of the film is preferably 0.5% or more, more preferably 1% or more, still more preferably 1.5% or more, and most preferably 2% or more. The layer thickness ratio of the II layer is preferably 1% or more, more preferably 10% or more, still more preferably 15% or more, and most preferably 20% or more.

  In addition, the biaxially oriented polypropylene film of the present invention preferably contains particles (hereinafter referred to as easy-slip particles) on at least one surface layer of the above-described laminated structure from the viewpoint of reducing the friction coefficient. The easy-slip particles are not particularly limited as long as they do not impair the effects of the present invention, and inorganic particles include organic particles such as silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, zeolite particles, etc. As acrylic resin particles, styrene resin particles, polyester resin particles, polyurethane resin particles, polycarbonate resin particles, polyamide resin particles, silicone resin particles, fluorine resin particles, or used for the synthesis of the above resins Examples thereof include copolymer resin particles of two or more monomers obtained. However, since the polypropylene resin has low surface energy, when the particles are added and stretched, the particle interface peels off during stretching, voids are generated, haze increases, and transparency may decrease. From the viewpoint of improving transparency, it is preferable to use the above inorganic particles or organic particles having a silane coupling treatment on the surface, and particularly preferred are silica particles having a silane coupling treatment.

  The average particle diameter of the easy-slip particles is preferably 0.1 μm or more and less than 1.0 μm. If the average particle size is less than 0.1 μm, the particles may aggregate to form coarse particles, which may reduce transparency. When the average particle size is 1.0 μm or more, voids are likely to be generated at the particle interface during stretching, and transparency may be lowered. In addition, particles added to the surface layer may fall off during film formation, resulting in increased surface roughness or increased haze. The average particle size is more preferably 0.1 μm or more and less than 0.9 μm, and still more preferably 0.1 μm or more and less than 0.8 μm. Moreover, you may use together two or more types of particle | grains from which an average particle diameter differs from a viewpoint of handling property improvement.

  The biaxially oriented polypropylene film of the present invention preferably has a laminate structure of at least two layers and includes easy-slip particles on at least one surface layer. At this time, the thickness of the layer containing easy-slip particles is preferably 0.05 to 2.0 μm. If it is less than 0.05 μm, the slippery particles may fall off during film formation. If it exceeds 2.0 μm, the haze may increase and the transparency may decrease. The thickness of the layer containing easy-slip particles is more preferably 0.1 to 1.0 μm, and still more preferably 0.2 to 0.8 μm.

  The content of the easy-slip particles in the raw material of the layer containing the easy-slip particles is preferably 0.01% by mass or more and less than 1.0% by mass. If the content is less than 0.01% by mass, the effect of reducing the friction coefficient may not be obtained. If the content is 1.0% by mass or more, haze may increase and transparency may decrease. The content is more preferably 0.05% by mass or more and less than 0.9% by mass, and still more preferably 0.1% by mass or more and less than 0.8% by mass.

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

  First, the polypropylene raw material A is supplied to the single screw extruder for the A layer, and the raw material obtained by dry blending the polypropylene raw material A and the polypropylene raw material B at 90:10 (mass ratio) is supplied to the single screw extruder for the B layer. And melt extrusion at 200 to 260 ° C. After removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, a multilayer thickness ratio of 1/4 to 1/200 is obtained with a multi-manifold type A layer / B layer composite T die. And discharged onto a cast drum to obtain a laminated unstretched sheet having a layer configuration of A layer / B layer. Here, the laminated structure may be a three-layer laminated structure of A layer / B layer / A layer, and the lamination thickness ratio (ratio of individual A layer and B layer) at that time is also 1/4 to 1/200. Is preferred. At this time, the surface temperature of the cast drum is preferably 10 to 40 ° C. from the viewpoint of transparency. In addition, it is preferable from the viewpoint of transparency that the layer A is a surface in contact with the drum. Moreover, it does not matter as a 3 layer laminated structure of A layer / B layer / A layer. As an adhesion method to the casting drum, any method of an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. may be used. The air knife method is preferable because it is good and the surface roughness can be controlled. The air temperature of the air knife is 0 to 50 ° C., preferably 0 to 30 ° C., the blowing air speed is preferably 130 to 150 m / s, and a double tube structure is used to improve the uniformity in the width direction. Is preferred. Further, it is preferable to appropriately adjust the position of the air knife so that air flows downstream of the film formation so as not to cause vibration of the film.

  In addition, after the film is brought into close contact with the casting drum, the non-casting drum surface of the film is further forcibly cooled, so that β crystal formation on the non-casting drum surface can be suppressed, and the haze of the film is reduced or smoothness is reduced. Can be improved. Especially when the film is thick, even if the temperature of the casting drum surface is set low and the β crystal on the casting drum surface of the film is reduced, the temperature of the non-casting drum surface does not decrease rapidly, May be generated, leading to deterioration of haze and flatness. Since the temperature at which β crystals are likely to be generated is 80 to 120 ° C., it is preferable that the non-casting drum surface of the film is forcibly cooled to 80 ° C. or less after being in close contact with the casting drum. The time for lowering to 80 ° C. or lower is preferably within 5 seconds after casting, and more preferably within 4 seconds. The cooling method for the non-casting drum surface may be any of the air knife method, press roll method, underwater casting method, etc., but it is simple as equipment, easy to control the surface roughness, and smooth. A good air knife method is preferred.

  The obtained unstretched sheet is allowed to cool in air and then introduced into the longitudinal stretching step. In the longitudinal stretching step, first, an unstretched sheet is brought into contact with a plurality of metal rolls maintained at 120 ° C. or more and less than 150 ° C. to preheat and raise the temperature to the stretching temperature. It is preferable to make it contact the metal roll kept at -170 degreeC from a viewpoint of transparency improvement. Specifically, for example, when there are 6 preheating rolls, the first roll is set to 100 ° C., the second roll is set to 140 ° C., the temperature is gradually raised, the third roll and the fourth roll are set to 155 ° C., and unstretched Examples of the conditions include that both surfaces of the sheet are sequentially brought into contact with a roll, the fifth and sixth are set at 140 ° C., and preheated to the stretching temperature. The reason why the transparency is improved by the above-described method is considered as follows. The surface of the unstretched sheet after casting is allowed to cool in the air, and then there are fine β crystal crystals. In the subsequent longitudinal and transverse stretching steps, the β crystals are cleaved to form fibrils and form haze. This may cause a decrease in the transparency of the film. By bringing the surface of the unstretched film into contact with a metal roll of 150 to 170 ° C. once in the preheating step of the longitudinal stretching, the β crystal on the surface of the unstretched film can be transformed into the α crystal, and the resulting biaxial It is considered that the transparency of the oriented polypropylene film is improved. Once contacted with a metal roll at 150 to 170 ° C., it is preheated to the stretching temperature by a roll kept at 120 ° C. or more and less than 150 ° C., stretched 3 to 8 times in the longitudinal direction, and then cooled to room temperature. . When the stretching temperature is 150 ° C. or higher, the orientation of the film becomes weak, and the strength may decrease. On the other hand, if the draw ratio is less than 3, the orientation of the film becomes weak and the strength may be lowered.

  Next, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is held by a clip, and the transverse stretching is stretched 7 to 13 times in the width direction at a temperature of 140 to 165 ° C. If the stretching temperature is low, the film may be broken or the transparency may be lowered. If the stretching temperature is too high, the orientation of the film is weak and the strength may be lowered. Further, when the magnification is high, the film may be broken, and when the magnification is low, the orientation of the film is weak and the strength may be lowered.

  In the present invention, in the subsequent heat treatment and relaxation treatment step, heat-fixing is performed at a temperature of 100 ° C. or more and less than 140 ° C. while giving relaxation at a relaxation rate of 2 to 20% in the width direction while holding the tension in the width direction with a clip. (Stage)), and then heat-treating in a multi-stage manner so as to perform heat setting under the condition of exceeding the heat setting temperature and less than the transverse stretching temperature (second stage) while holding the tension in the width direction with a clip, It is preferable from the viewpoint of achieving both high strength and low heat yield.

  From the viewpoint of obtaining thermal dimensional stability, the relaxation rate is more preferably 5 to 18%, and further preferably 8 to 15%. If it exceeds 20%, the film may be too slack inside the tenter, and the product may be wrinkled. If the relaxation rate is less than 2%, thermal dimensional stability may not be obtained.

  The first stage heat treatment / relaxation temperature is more preferably 100 ° C. or more and less than 130 ° C., and further preferably 110 ° C. or more and less than 130 ° C. When the heat treatment temperature is less than 100 ° C., the film does not relax sufficiently, heat shrinkage may increase, or the film may flutter and wrinkle. On the other hand, in the case of heat treatment at 130 ° C. or higher, molecular chain orientation relaxation proceeds, so that the strength of the film may be lowered.

  The second-stage heat treatment temperature exceeds the first-stage heat treatment temperature and the first-stage heat treatment temperature is 30 ° C. or less, thereby relaxing amorphous molecular chains with high mobility that are insufficiently relaxed in the first-stage heat treatment process. It is possible to achieve both high strength and low heat yield. From this viewpoint, the second-stage heat treatment temperature is more preferably the first-stage heat treatment temperature + 5 ° C. or more, the first-stage heat treatment temperature + 25 ° C. or less, and the first-stage heat treatment temperature + 8 ° C. or more. More preferably, it is not higher than ° C.

  After undergoing multi-stage heat treatment, with the clip held tightly in the width direction, it is guided to the outside of the tenter through a cooling process at 80-100 ° C, the clip at the end of the film is released, and the film edge is slit in the winder process And roll up the film product roll.

  The biaxially oriented polypropylene film of the present invention obtained as described above can be used in various applications such as packaging films, release films, process films, sanitary products, agricultural products, building products, and medical products. However, because of its high strength, low heat yield, and excellent transparency, it is preferred as a film for flat panel display films such as retardation films and polarizer protective films, films for manufacturing processes such as displays, and elements for film capacitors. Can be used.

  When the biaxially oriented polypropylene film of the present invention is used as a film for a flat panel display, the biaxially oriented polypropylene film of the present invention can be bonded to at least one surface of a polarizer and used as a polarizing plate. Moreover, when using as a phase difference film, it can be used by installing the biaxially oriented polypropylene film of this invention in a predetermined angle between a liquid crystal cell and a polarizing plate, or the outer side of a polarizing plate. For example, it can be used as a liquid crystal display by disposing the above-described retardation film or polarizing plate on both surfaces of the liquid crystal panel and applying a light source from the back.

  When the biaxially oriented polypropylene film of the present invention is used as a capacitor film, a metal film is first provided on the surface. The method of providing the metal film to form the metal film laminated film is not particularly limited. 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.

  In the present invention, if necessary, after the metal film is formed, the metal film laminated film can be annealed at a specific temperature or heat-treated. 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. An example of a preferred method for producing a wound film capacitor is as follows.

  Aluminum is vapor-deposited on one side of the polypropylene film under reduced pressure. In that case, it vapor-deposits in the stripe form which has the margin part which runs in a film longitudinal direction. 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 each other so that the vapor deposition part protrudes from the margin part in the width direction. Get.

  When vapor deposition is performed on both sides, the vapor deposition is performed in a stripe shape having a margin portion that runs in the longitudinal direction of one surface, and the other surface is striped so that the longitudinal margin portion is located at the center of the vapor deposition portion on the back side. Vapor deposition. Next, a tape-like take-up reel having a margin on one side (for example, a margin on the right side of the front surface and a margin on the left side of the back surface) is prepared on both sides of the front and back margins with a blade. Two each of the obtained reel and undeposited laminated film are overlapped and wound so that the metallized film protrudes from the laminated film in the width direction, and a wound body is obtained.

  The core material is removed from the wound body produced as described above and pressed, and the metallicon is sprayed on both end faces to form external electrodes, and a lead wire is welded to the metallicon to obtain a wound film capacitor. There are many uses for film capacitors such as those for railway vehicles, automobiles (hybrid cars, electric vehicles), solar power generation / wind power generation, and general household appliances. The film capacitor of the present invention is also suitable for these applications. Can be used.

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

(1) Film thickness Five points were measured using a micro thickness gauge (manufactured by Anritsu), and an average value was obtained.

(2) Tensile elastic modulus in the longitudinal direction and width direction (E _MD , E _TD )
A biaxially oriented polypropylene film was cut into a rectangular shape having a length of 150 mm in the test direction and a width of 10 mm as a sample. Using a tensile tester (Tensilon AMF / RTA-100, manufactured by Orientec Co., Ltd.), in accordance with the method defined in JIS K 7127: 1999, measurement is performed 5 times in an atmosphere of 25 ° C. and 65% RH, and an average value is obtained. It was. However, the distance between the initial chucks was set to 50 mm, the tensile speed was set to 300 mm / min, and the point where the load passed 1 N after the start of the test was used as the origin of elongation.

(3) Total haze of film Using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.), the haze value at 23 ° C. of the biaxially oriented polypropylene film of the present invention was measured according to JIS K 7136: 2000 ( %) Was measured three times and the average value was used.

(4) Film surface roughness (SRa, SRz)
A biaxially oriented polypropylene film was measured under the following measurement conditions based on JIS B 0601: 2001 using a surface roughness meter (SURFCORDER ET4000A: manufactured by Kosaka Laboratory Ltd.), and the center average surface roughness SRa ( nm) and ten-point average roughness SRz (nm). However, the measurement was carried out at three points on the surface that was in contact with the cast drum during extrusion, and the average value was taken.

<Measurement conditions>
Measurement speed: 0.1 mm / S
Measurement range: 1000 μm in the longitudinal direction, 400 μm in the width direction
Measurement pitch: 1 μm in the longitudinal direction, 5 μm in the width direction
Cut-off value λc: 0.2 mm
Stitch tip radius: 0.5 μm
(5) In-plane retardation of film and thickness direction retardation (Ret, Rth)
Using an automatic birefringence meter (KOBRA-21ADH) manufactured by Oji Scientific Co., Ltd., an in-plane retardation and a thickness direction retardation for a light beam having a wavelength of 548.3 nm were measured.

(6) Thermal shrinkage after treatment at 85 ° C. for 100 hours in the longitudinal direction and the width direction For each of the longitudinal direction and the width direction of the film, 5 samples having a width of 10 mm and a length of 200 mm (measurement direction) were cut out and 25 mm from both ends. Is marked as a marked line, and the distance between marked lines is measured with a universal projector as the test length (l ₀ ). Next, the test piece was sandwiched between papers, taken out after heating for 100 hours in an oven kept at 85 ° C. with zero load, cooled at room temperature, and the dimension (l ₁ ) was measured with a universal projector. It calculated | required by the type | formula and made the average value of 5 the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
(7) Coefficient of static friction μs
Initial rise resistance when the MD direction is rubbed with one side of the film in contact with the back side according to ASTM-D1894 (1999) using a friction measuring instrument manufactured by Toyo Tester Industries The value was measured, and the maximum value was defined as the static friction coefficient μs. However, when the initial rise was large and the measurement value upper limit (5.0) was exceeded, measurement was impossible. Samples were rectangular with a width of 80 mm and a length of 200 mm, and 5 sets (10 sheets) were cut out. Measurement was performed 5 times, and an average value was obtained.

(8) Melting point Tm of film
A biaxially oriented polypropylene film (5 mg) was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 260 ° C. at a rate of 10 ° C./minute (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 20 ° C. at a rate of 10 ° C./minute. The melting peak temperature observed when the temperature was raised again (second run) at 10 ° C./min after holding for 5 minutes was defined as the melting point Tm of the film.

Example 1
Crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, intrinsic viscosity [η]: 1.8 dl / g, MFR: 2.9 g / 10 min, isotactic) as a polypropylene raw material for the surface layer (A) (Index: 96%) is supplied to a monoaxial melt extruder for the A layer, and 90 parts by mass of the crystalline PP (a) and the low stereoregular PP (b) are used as the polypropylene raw material for the core layer (B). ) (Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 minutes, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) 10 parts by mass dry blended and uniaxial melt extrusion for B layer And then extrude at 240 ° C, remove foreign matter with a 60μm cut sintered filter, and laminate with a feed block type A / B / A composite T die at a thickness ratio of 1/8/1. , CAS with surface temperature controlled to 30 ° C A cast sheet was obtained by discharging to the drum. Next, preheating was performed to 140 ° C. using seven ceramic rolls (however, the roll temperature was set to 100 ° C. for the first, 125 ° C. for the second, and 140 ° C. for the third to seventh). The film was stretched 6 times. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment step, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction as the first step heat treatment and relaxation treatment, and further at 140 ° C. for 3 seconds while being held in the width direction by the clip as the second step heat treatment. Heat treatment was performed. Then, the film was guided to the outside of the tenter through a cooling process at 100 ° C., the clip at the end of the film was released, and the film was wound around a core to obtain a biaxially oriented polypropylene film having a thickness of 12 μm. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 2)
In the longitudinal stretching step of Example 1, biaxially oriented polypropylene films were obtained in the same manner as in Example 1 except that the temperature of the fourth and fifth of the seven ceramic rolls was 155 ° C. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 3)
A biaxially oriented polypropylene film was obtained in the same manner as in Example 1 except that the relaxation rate was 15% in the heat treatment step of Example 1. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

Example 4
Crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, intrinsic viscosity [η]: 1.8 dl / g, MFR: 2.9 g / 10 min, isotactic) as a polypropylene raw material for the surface layer (A) Index: 96%) is supplied to a uniaxial melt extruder for the A layer, and as a polypropylene raw material for the core layer (B), 85 parts by mass of the crystalline PP (a) and a low stereoregular PP (b ) (Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 min, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) The melt is extruded at 240 ° C., and foreign matter is removed with a 60 μm-cut sintered filter, which is then laminated with a feed block type A / B / A composite T die at a thickness ratio of 1/10/1. The surface temperature is controlled at 30 ° C. The cast sheet was obtained by discharging to a stock drum. Next, preheating was performed to 140 ° C. using seven ceramic rolls (however, the roll temperature was set to 100 ° C. for the first, 125 ° C. for the second, and 140 ° C. for the third to seventh). The film was stretched 6 times. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment step, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction as the first step heat treatment and relaxation treatment, and further at 140 ° C. for 3 seconds while being held in the width direction by the clip as the second step heat treatment. Heat treatment was performed. Then, the film was guided to the outside of the tenter through a cooling process at 100 ° C., the clip at the end of the film was released, and the film was wound around a core to obtain a biaxially oriented polypropylene film having a thickness of 12 μm. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 5)
First, 99.3 parts by mass of crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, MFR: 2.9 g / 10 min) and surface silane coupling treatment silica particles (manufactured by Denki Kagaku Kogyo Co., Ltd., SFP) -20MHE, average particle size 0.3 μm) 0.5 parts by weight, and further, 0.1 parts by weight of IRGANOX 1010 and IRGAFOS 168 manufactured by Ciba Specialty Chemicals, which are antioxidants, are mixed at this ratio. The raw material is supplied from the hopper to the twin screw extruder, melt kneaded at 260 ° C., discharged from the die in a strand shape, cooled and solidified in a 25 ° C. water tank, cut into a chip shape, and the polypropylene raw material for the A layer (1) was obtained.

  The polypropylene raw material (1) as a polypropylene raw material for the surface layer (A) is supplied to a uniaxial melt extruder for the A layer, and the crystalline PP (a) 90 mass as a polypropylene raw material for the core layer (B). Part and 10 parts by mass of low stereoregularity PP (b) (manufactured by Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 min, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) The B-layer is supplied to a single-screw melt extruder, melt extruded at 240 ° C., removed foreign matter with a 60 μm cut sintered filter, and then fed into a feed block type A / B / A composite T die. A cast sheet was obtained by laminating at a thickness ratio of / 15/1 and discharging onto a cast drum whose surface temperature was controlled at 30 ° C. Next, preheating was performed to 140 ° C. using seven ceramic rolls (however, the roll temperature was set to 100 ° C. for the first, 125 ° C. for the second, and 140 ° C. for the third to seventh). The film was stretched 6 times. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment step, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction as the first step heat treatment and relaxation treatment, and further at 140 ° C. for 3 seconds while being held in the width direction by the clip as the second step heat treatment. Heat treatment was performed. Then, the film was guided to the outside of the tenter through a cooling process at 100 ° C., the clip at the end of the film was released, and the film was wound around a core to obtain a biaxially oriented polypropylene film having a thickness of 12 μm. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 6)
The polypropylene raw material (1) as a polypropylene raw material for the surface layer (A) is supplied to a uniaxial melt extruder for the A layer, and the crystalline PP (a) is used as a polypropylene raw material for the core layer (B). Supplied to a single-screw melt extruder for the layer, melt-extruded at 240 ° C., removed foreign matter with a 60 μm cut sintered filter, and then fed with a feed block type A / B / A composite T-die. / 1 thickness ratio, discharged onto a cast drum whose surface temperature was controlled at 30 ° C. to form a cast sheet, and after casting, a non-cooled drum surface of the cast sheet was heated at a temperature of 30 ° C. and a pressure of 0.3 MPa. A cast sheet was obtained by cooling with compressed air. The temperature of the non-casting drum surface 4 seconds after casting was 75 ° C. Next, preheating was performed to 140 ° C. using seven ceramic rolls (however, the roll temperature was set to 100 ° C. for the first, 125 ° C. for the second, and 140 ° C. for the third to seventh). The film was stretched 6 times. Next, the end portion was introduced into a tenter type stretching machine by holding it with a clip, preheated at 170 ° C. for 3 seconds, and then stretched 8.0 times at 165 ° C. In the subsequent heat treatment step, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction as the first step heat treatment and relaxation treatment, and further at 140 ° C. for 3 seconds while being held in the width direction by the clip as the second step heat treatment. Heat treatment was performed. Thereafter, the film was guided to the outside of the tenter through a cooling step at 100 ° C., the clip at the end of the film was released, and the film was wound around a core to obtain a biaxially oriented polypropylene film having a thickness of 25 μm. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 1)
In Example 1, crystalline PP (a) is used as the polypropylene raw material for the core layer (B) (the same raw material is used for the surface layer and the core layer), and other than that, biaxial orientation is performed in the same manner as in Example 1. A polypropylene film was obtained. The crystallinity of the raw material was high and the transparency was deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 2)
In Example 1, 50 parts by mass of crystalline PP (a) as a polypropylene raw material for the core layer (B), syndiotactic PP (c) (syndiotactic pentad fraction: 0.92, MFR: 3. 5 g / 10 min) and 50 parts by mass were dry blended and supplied to a uniaxial melt extruder for the B layer. Otherwise, a biaxially oriented polypropylene film was obtained in the same manner as in Example 1. Although the crystallinity and heat resistance of the raw material were low and the transparency was improved, the strength and heat yield were deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 3)
In the heat treatment step of Example 4, heat treatment was performed at 145 ° C. while giving 10% relaxation in the width direction as the first-stage heat treatment and relaxation treatment. Otherwise, the biaxially oriented polypropylene film was processed in the same manner as in Example 4. Got. Since the relaxation temperature was high, the relaxation of the orientation progressed and the strength of the film deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 4)
In the transverse stretching step of Example 4, a biaxially oriented polypropylene film was obtained in the same manner as in Example 4 except that the transverse stretching ratio was 5.5 times. The thickness of the obtained film was 17 μm. Since the draw ratio was low, the orientation was weak and the strength of the film deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 5)
In Example 6, after casting, a biaxially oriented polypropylene film was obtained in the same manner as in Example 6 except that cooling with air was not performed. The thickness of the obtained film was 25 μm. Since cooling was not performed, the haze and flatness of the film deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 6)
In Example 6, the same polypropylene raw material (1) as the polypropylene raw material for the surface layer (A) was used for the polypropylene raw material for the core layer (B), and the other biaxially in the same manner as in Example 6. An oriented polypropylene film was obtained. The thickness of the obtained film was 25 μm. Since particles contained in all layers, the haze of the film was deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 7)
In Example 5, 1.25 parts by mass of silica particle SILTON AMT-20S (particle size 1.7 μm, no surface treatment) manufactured by Mizusawa Chemical Co., Ltd. was used instead of silica particle SFP-20MHE manufactured by Denki Kagaku Kogyo Co., Ltd. Otherwise, a biaxially oriented polypropylene film was obtained in the same manner as in Example 5. The thickness of the obtained film was 12 μm. During stretching, voids were generated at the interface between the particles and the polypropylene, and the haze of the film deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

Claims (11)

The value of the sum _{E MD + TD} tensile modulus _{E TD} in the tensile elastic modulus _{E MD} and the width direction in the longitudinal direction of the film is not less than 4.5 GPa, the total haze is not more than 1%, 85 ℃ 100 hours after the heat A biaxially oriented polypropylene film having a shrinkage ratio of 1.0% or less in both the longitudinal direction and the width direction of the film. The biaxially oriented polypropylene film according to claim 1, wherein the ten-point average roughness SRz of at least one surface is 500 nm or less. The biaxially oriented polypropylene film according to claim 1 or 2, wherein at least one surface has a center average surface roughness SRa of 50 nm or less. The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the in-plane retardation Ret of the film is 0.1 to 500 nm. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein a value Rth / Ret of a ratio of a retardation Rth in the thickness direction of the film and an in-plane retardation Ret of the film is 1 or less. The biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein a coefficient of static friction μs between one surface of the biaxially oriented polypropylene film and the back surface thereof is 0.5 or less. The biaxially oriented polypropylene film according to any one of claims 1 to 6, wherein the biaxially oriented polypropylene film has a melting point Tm of 158 ° C or higher. The biaxially oriented polypropylene film according to any one of claims 1 to 7, which is used as a film for a flat panel display. A flat panel display using the biaxially oriented polypropylene film according to claim 8. The biaxially oriented polypropylene film according to any one of claims 1 to 7, which is used as an element for a film capacitor. A film capacitor using the biaxially oriented polypropylene film according to claim 10.