Biaxially oriented polypropylene film

Abstract

To provide a biaxially oriented laminated polypropylene film having higher heat resistance and rigidity. The polypropylene resin constituting the film, which is a completely homopolypropylene resin containing no copolymerization component and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms, satisfies the following conditions 1) to 4), and The lower limit of the film's plane orientation coefficient is 0.0125. The tensile modulus of the film in the transverse direction is 5.1 A biaxially oriented stretched polypropylene film characterized by a strength of 100 GPa or more. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%. 3) The mass average molecular weight (Mw) / number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.5 g / 10 min or more and 9.0 g / 10 min or less.

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented laminated polypropylene film, and more particularly to a biaxially oriented polypropylene film having excellent heat resistance and mechanical properties. [Background technology]

[0002] Traditionally, oriented polypropylene films have been widely used for a wide range of applications, including packaging for food and various other products, electrical insulation, and surface protection films. However, conventional polypropylene films have a shrinkage rate of several tens of percent at 150°C, and compared to polyethylene terephthalate (PET) films, they have lower heat resistance and lower rigidity, limiting their applications.

[0003] Various techniques have been proposed to improve the physical properties of polypropylene film. For example, one technique is known in which a film is made using polypropylene that contains approximately equal amounts of high-molecular-weight and low-molecular-weight components (or a small amount of low-molecular-weight components), has a wide molecular weight distribution, and has a low decalin-soluble content, thereby achieving a balance between rigidity and processability (Patent Document 1). However, this technique still does not provide sufficient heat resistance at high temperatures exceeding 150°C, and no polypropylene film with high heat resistance, impact resistance, and transparency has been known.

[0004] As a result of extensive research based on the above-mentioned prior art, the applicant of the present application succeeded in providing a stretched polypropylene film with high rigidity and high heat resistance by using a polypropylene polymer with a mesopentad fraction of 96% or more (Patent Document 2). However, there was room for improvement in the heat resistance of this film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2008-540815 [Patent Document 2] WO2015 / 012324 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a biaxially oriented laminated polypropylene film having higher heat resistance and rigidity. [Means for solving the problem]

[0007] The present invention, which has solved the above problems, is a biaxially oriented polypropylene film characterized in that the polypropylene resin constituting the film satisfies the following conditions 1) to 4) and the lower limit of the film's planar orientation coefficient is 0.0125. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.2 g / 10 min or more and 9.0 g / 10 min or less.

[0008] The second invention, which has solved the above-mentioned problems, is a biaxially oriented polypropylene film having a base layer (A) mainly composed of a polypropylene-based resin and a surface layer (B) mainly composed of a polypropylene-based resin on at least one surface of the base layer (A), wherein the polypropylene resin constituting the base layer (A) satisfies the following conditions 1) to 4), and the lower limit of the plane orientation coefficient of the film is 0.0125. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.2 g / 10 min or more and 9.0 g / 10 min or less.

[0009] In this case, it is preferable that the heat shrinkage rate of the film at 150°C in both the longitudinal and transverse directions is 8% or less.

[0010] In this case, it is preferable that the tensile modulus of the film in the machine direction is 2.0 GPa or more, and the tensile modulus of the film in the transverse direction is 4.5 GPa or more.

[0011] In this case, it is preferable that the haze value of the film is 5% or less. [Effects of the Invention]

[0012] The biaxially oriented polypropylene film of the present invention has a narrow molecular weight distribution and little entanglement of molecular chains, resulting in stronger orientation, higher thermal dimensional stability and rigidity in the lateral direction, less wrinkles caused by heat, and less breakage, making it easier to process. Very excellent. DETAILED DESCRIPTION OF THE INVENTION

[0013] The biaxially oriented polypropylene film of the first invention is characterized in that the polypropylene resin constituting the film satisfies the following conditions 1) to 4), and the lower limit of the plane orientation coefficient of the film is 0.0125. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.2 g / 10 min or more and 9.0 g / 10 min or less. The biaxially oriented polypropylene film of the second invention has a base layer (A) mainly composed of a polypropylene-based resin and a surface layer (B) mainly composed of a polypropylene-based resin on at least one surface of the base layer (A), and is characterized in that the polypropylene resin constituting the base layer (A) satisfies the following conditions 1) to 4), and the lower limit of the plane orientation coefficient of the film is 0.0125. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol%. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 5.4 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is 6.2 g / 10 min or more and 9.0 g / 10 min or less. Further details are provided below.

[0014] (1) The polypropylene resin used in the first invention may be a polypropylene resin copolymerized with 0.5 mol% or less of ethylene and / or an α-olefin having 4 or more carbon atoms. Such copolymerized polypropylene resins are also included in the polypropylene resin of the present invention (hereinafter referred to as polypropylene resin). The copolymerization component is preferably 0.3 mol% or less, more preferably 0.1 mol% or less, and a completely homopolypropylene resin containing no copolymerization component is most preferred. When ethylene and / or an α-olefin having 4 or more carbon atoms is copolymerized in an amount exceeding 0.5 mol %, the crystallinity and rigidity may be reduced too much, resulting in a large heat shrinkage rate at high temperatures. Such resins may be blended and used.

[0015] The mesopentad fraction ([mmmm]%), which is an index of the stereoregularity of polypropylene resins, measured by 13C-NMR is preferably 96 to 99.5%, more preferably 97% or more, and even more preferably 98% or more. If the mesopentad fraction of the polypropylene of the base layer (A) is low, the elastic modulus may be low and the heat resistance may be insufficient. 99.5% is the practical upper limit.

[0016] Furthermore, the Mw / Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 for polypropylene resin, more preferably 3.0 to 5.0, even more preferably 3.2 to 4.5, and particularly preferably 3.3 to 4.0. When the Mw / Mn of the entire polypropylene resin constituting the biaxially oriented polypropylene film of the present invention exceeds 5.4, the amount of high molecular weight components increases, which can increase the heat shrinkage rate and decrease the tensile modulus of elasticity (Young's modulus) in the transverse direction (TD). The presence of high molecular weight components can promote the crystallization of low molecular weight components, but the molecules also become more entangled, which can increase the heat shrinkage rate even if the crystallinity is high. If the Mw / Mn of the entire polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is less than 3.0, film formation becomes difficult. Mw means the weight average molecular weight, and Mn means the number average molecular weight.

[0017] The mass average molecular weight (Mw) of the polypropylene resin is preferably 180,000 to 500,000. The lower limit of Mw is more preferably 190,000, still more preferably 200,000, and the upper limit of Mw is more preferably 320,000, still more preferably 300,000, and particularly preferably 250,000.

[0018] The number average molecular weight (Mn) of the polypropylene resin is preferably 20,000 to 200,000. The lower limit of Mn is more preferably 30,000, even more preferably 40,000, and particularly preferably 50,000, and the upper limit of Mn is more preferably 80,000, even more preferably 70,000, and particularly preferably 60,000.

[0019] When measuring the gel permeation chromatography (GPC) cumulative curve of the entire polypropylene resin constituting the biaxially oriented polypropylene film of the first invention, the lower limit of the amount of components having a molecular weight of 100,000 or less is preferably 35 mass%, more preferably 38 mass%, even more preferably 40 mass%, particularly preferably 41 mass%, and most preferably 42 mass%. On the other hand, the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, even more preferably 58% by mass, particularly preferably 56% by mass, and most preferably 55% by mass. Within this range, stretching becomes easier, thickness unevenness is reduced, and the stretching temperature and heat setting temperature can be easily increased, thereby further reducing the heat shrinkage rate.

[0020] At this time, the melt flow rate (MFR; 230°C, 2.16 kgf) of the polypropylene resin is preferably 6.2 g / 10 min to 10.0 g / 10 min. The lower limit of the MFR of the polypropylene resin is more preferably 6.5 g / 10 min, even more preferably 7 g / 10 min, and particularly preferably 7.5 g / 10 min. The upper limit of the MFR of the polypropylene resin is more preferably 9 g / 10 min, even more preferably 8.5 g / 10 min, and particularly preferably 8.2 g / 10 min. A melt flow rate (MFR; 230°C, 2.16 kgf) of 6.2 g / 10 min or more can reduce the heat shrinkage rate at high temperatures. Furthermore, the degree of orientation of the film caused by stretching is increased, resulting in a higher film rigidity, particularly a higher tensile modulus of elasticity (Young's modulus) in the transverse (TD) direction. Furthermore, a melt flow rate (MFR; 230°C, 2.16 kgf) of 9.0 g / 10 min or less facilitates film formation without breakage. The molecular weight distribution of polypropylene resin can be adjusted by polymerizing components of different molecular weights in multiple stages in a series of plants, blending components of different molecular weights offline using a kneader, blending catalysts with different performances and polymerizing them, or using a catalyst that can achieve the desired molecular weight distribution.

[0021] The polypropylene resin used in the present invention is obtained by polymerizing the raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among these, it is preferable to use a Ziegler-Natta catalyst, which is capable of polymerization with high stereoregularity, in order to eliminate heterogeneous bonds. As a method for polymerizing propylene, any known method may be employed, and examples thereof include a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of adding a catalyst to a gaseous monomer and polymerizing in a gas phase, or a method of polymerizing using a combination of these.

[0022] The polypropylene resin may contain additives or other resins. Examples of additives include antioxidants, UV absorbers, nucleating agents, adhesives, anti-fogging agents, flame retardants, inorganic or organic fillers, etc. Examples of other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene with ethylene and / or α-olefins having 4 or more carbon atoms, and various elastomers. These may be sequentially polymerized using a multi-stage reactor, blended with polypropylene resin using a Henschel mixer, master pellets prepared in advance using a melt kneader may be diluted with polypropylene to a predetermined concentration, or the entire amount may be melt kneaded in advance before use.

[0023] (2) The polypropylene resin used in the base layer (A) of the second invention is ethylene and / or a polypropylene having 4 or more carbon atoms. Polypropylene resins copolymerized with 0.5 mol % or less of the above α-olefins can also be used. Such copolymerized polypropylene resins are also included in the polypropylene resin of the present invention (hereinafter referred to as polypropylene resin). The copolymerization component is preferably 0.3 mol % or less, more preferably 0.1 mol % or less, and a completely homopolypropylene resin containing no copolymerization component is most preferred. When ethylene and / or an α-olefin having 4 or more carbon atoms is copolymerized in an amount exceeding 0.5 mol %, the crystallinity and rigidity may be reduced too much, resulting in a large heat shrinkage rate at high temperatures. Such resins may be blended and used.

[0024] The mesopentad fraction ([mmmm]%), which is an index of the stereoregularity of polypropylene resins, measured by 13C-NMR is preferably 96 to 99.5%, more preferably 97% or more, and even more preferably 98% or more. If the mesopentad fraction of the polypropylene of the base layer (A) is low, the elastic modulus may be low and the heat resistance may be insufficient. 99.5% is the practical upper limit.

[0025] Furthermore, the Mw / Mn, which is an index of molecular weight distribution, is preferably 3.0 to 5.4 for polypropylene resin, more preferably 3.0 to 5.0, even more preferably 3.2 to 4.5, and particularly preferably 3.3 to 4.0. If the Mw / Mn of the entire polypropylene resin constituting the base layer (A) exceeds 5.4, the amount of high molecular weight components increases when the Mw / Mn is too large, which may result in an increase in the heat shrinkage rate or a decrease in the tensile modulus of elasticity (Young's modulus) in the transverse direction (TD). When high molecular weight components are present, the high molecular weight components tend to promote the crystallization of the low molecular weight components, but this also increases the entanglement between the molecules, which tends to increase the heat shrinkage rate even if the crystallinity is high. When the Mw / Mn of the entire polypropylene resin constituting the biaxially oriented polypropylene film of the present invention is less than 3.0, film formation becomes difficult. Mw means mass average molecular weight, and Mn means number average molecular weight.

[0026] The mass average molecular weight (Mw) of the polypropylene resin is preferably 180,000 to 500,000. The lower limit of Mw is more preferably 190,000, still more preferably 200,000, and the upper limit of Mw is more preferably 320,000, still more preferably 300,000, and particularly preferably 250,000.

[0027] The number average molecular weight (Mn) of the polypropylene resin is preferably 20,000 to 200,000. The lower limit of Mn is more preferably 30,000, even more preferably 40,000, and particularly preferably 50,000, and the upper limit of Mn is more preferably 80,000, even more preferably 70,000, and particularly preferably 60,000.

[0028] When measuring the gel permeation chromatography (GPC) cumulative curve of the entire polypropylene resin constituting the base layer (A), the lower limit of the amount of components having a molecular weight of 100,000 or less is preferably 35 mass%, more preferably 38 mass%, even more preferably 40 mass%, particularly preferably 41 mass%, and most preferably 42 mass%. On the other hand, the upper limit of the amount of components having a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, even more preferably 58% by mass, particularly preferably 56% by mass, and most preferably 55% by mass. Within this range, stretching becomes easier, thickness unevenness is reduced, and the stretching temperature and heat setting temperature can be easily increased, thereby further reducing the heat shrinkage rate.

[0029] At this time, the melt flow rate (MFR; 230°C, 2.16 kgf) of the polypropylene resin is preferably 6.2 g / 10 min to 10.0 g / 10 min. The lower limit of the MFR of the polypropylene resin is more preferably 6.5 g / 10 min, even more preferably 7 g / 10 min, and particularly preferably 7.5 g / 10 min. The upper limit of the MFR of the polypropylene resin is more preferably 9 g / 10 min, even more preferably 8.5 g / 10 min, and particularly preferably 8.2 g / 10 min. A melt flow rate (MFR; 230°C, 2.16 kgf) of 6.2 g / 10 min or more can reduce the heat shrinkage rate at high temperatures. Furthermore, the degree of orientation of the film caused by stretching is increased, resulting in a higher film rigidity, particularly a higher tensile modulus of elasticity (Young's modulus) in the transverse (TD) direction. Furthermore, a melt flow rate (MFR; 230°C, 2.16 kgf) of 9.0 g / 10 min or less facilitates film formation without breakage. The molecular weight distribution of polypropylene resin can be adjusted by polymerizing components of different molecular weights in multiple stages in a series of plants, blending components of different molecular weights offline in a kneader, blending catalysts with different performances and polymerizing them, or using a catalyst that can achieve the desired molecular weight distribution.

[0030] The polypropylene resin used in the base layer (A) is obtained by polymerizing the raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among these, it is preferable to use a Ziegler-Natta catalyst to eliminate heterogeneous bonds and to use a catalyst that can polymerize with high stereoregularity. As a method for polymerizing propylene, any known method may be employed, and examples thereof include a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of adding a catalyst to a gaseous monomer and polymerizing in a gas phase, or a method of polymerizing using a combination of these.

[0031] The polypropylene resin may contain additives or other resins. Examples of additives include antioxidants, UV absorbers, nucleating agents, adhesives, anti-fogging agents, flame retardants, inorganic or organic fillers, etc. Examples of other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene with ethylene and / or α-olefins having 4 or more carbon atoms, and various elastomers. These may be sequentially polymerized using a multi-stage reactor, blended with polypropylene resin using a Henschel mixer, master pellets prepared in advance using a melt kneader may be diluted with polypropylene to a predetermined concentration, or the entire amount may be melt kneaded in advance before use.

[0032] (3) The surface roughness of the surface layer (B) of the second invention is preferably 0.027 μm or more and 0.40 μm or less. If it is less than 0.027 μm, adhesion to printing ink and adhesives used for laminating with other film components will be insufficient, and if it exceeds 0.40 μm, problems such as color development and color fading will occur. To achieve a surface roughness of 0.027 μm or more and 0.40 μm or less for the surface layer (B), it is preferable to use a mixture of two or more polypropylene resins with different melt flow rates (MFR) as the polypropylene resin composition forming the surface layer (B). In this case, the difference in MFR is preferably 3 g / 10 min or more, more preferably 3.5 g / 10 min or more. It is presumed that the use of such a mixture results in the surface roughness of the surface layer (B) being 0.027 μm or more due to the difference in crystallization rate. Polypropylene resins with a higher MFR can also be copolymerized with ethylene and / or α-olefins with four or more carbon atoms. Examples of α-olefins with four or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. In addition, polypropylene copolymerized with ethylene and / or an α-olefin having four or more carbon atoms can also be used as a polypropylene-based resin with a smaller MFR. Examples of α-olefins having four or more carbon atoms include 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Furthermore, maleic acid or the like having polarity may be used as another copolymerization component. The total amount of ethylene, α-olefins having 4 or more carbon atoms, and other copolymerization components is preferably 8.0 mol% or less. If copolymerization exceeds 8.0 mol%, the film may whiten, resulting in poor appearance, or may become sticky, making film formation difficult. Two or more of these resins may be blended for use. When blended, each resin may be copolymerized in an amount exceeding 8.0 mol%, but the blend preferably contains 8.0 mol% or less of monomers other than propylene on a monomer unit basis.

[0033] Furthermore, the polypropylene resin composition of the surface layer (B) preferably has an MFR of 1.0 g / 10 min to 8 g / 10 min. The lower limit of the MFR of the polypropylene resin composition of the surface layer (B) is more preferably 2 g / 10 min, and even more preferably 3 g / 10 min. The upper limit of the MFR of the polypropylene resin composition of the surface layer (B) is more preferably 7 g / 10 min, and even more preferably 6.0 g / 10 min. Within this range, the film formability is good and the heat shrinkage rate at high temperatures can be kept low. If the MFR of the polypropylene resin composition of the surface layer (B) is less than 1.0 g / 10 min, when the MFR of the polypropylene in the base layer (A) is high, the viscosity difference between the base layer (A) and the surface layer (B) becomes large, making unevenness (unevenness in the original web) more likely to occur during film formation. If the MFR of the polypropylene resin composition of the surface layer (B) exceeds 8 g / 10 min, the adhesion to the cooling roll will be poor, air will be entrapped, the smoothness will be poor, and there is a risk that defects will occur as a result.

[0034] The polypropylene resin used in the surface layer (B) is obtained by polymerizing the raw material propylene using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst. Among these, it is preferable to use a Ziegler-Natta catalyst to eliminate heterogeneous bonds and to use a catalyst that can polymerize with high stereoregularity. As a method for polymerizing propylene, any known method may be employed, and examples thereof include a method of polymerizing in an inert solvent such as hexane, heptane, toluene, or xylene, a method of polymerizing in a liquid monomer, a method of adding a catalyst to a gaseous monomer and polymerizing in a gas phase, or a method of polymerizing using a combination of these.

[0035] The surface layer (B) may contain additives and other resins. Examples of additives include antioxidants, ultraviolet absorbers, nucleating agents, adhesives, anti-fogging agents, flame retardants, inorganic or organic fillers, etc. Examples of other resins include polypropylene resins other than the polypropylene resin used in the present invention, random copolymers of propylene with ethylene and / or α-olefins having 4 or more carbon atoms, and various elastomers. These may be sequentially polymerized using a multi-stage reactor, blended with polypropylene resin using a Henschel mixer, master pellets prepared in advance using a melt kneader may be diluted with polypropylene to a predetermined concentration, or the entire amount may be melt kneaded in advance before use.

[0036] The surface layer (B) preferably has a surface wetting tension of 38 mN / m or more. If the wetting tension is 38 mN / m or more, the adhesion to printing inks and adhesives is improved. The wet tension is more preferably 16 Log Ω or more. To achieve a wet tension of 38 mN / m or more, additives such as antistatic agents and surfactants are usually used, but surface treatments such as corona treatment and flame treatment can also be used, as these have the effect of reducing surface resistivity. For example, in the case of corona treatment, it is preferable to use a preheating roll and a treatment roll and carry out the treatment in the air.

[0037] The biaxially oriented polypropylene film of the present invention preferably has a surface layer (B) of which the sum of the central surface peak height SR) and the central surface valley depth SRv is 1.0 μm or more and 2.0 μm or less. Here, the surface roughness central peak height SRp and central valley depth SRv of the surface of the surface layer (B) are determined in accordance with the definition of arithmetic mean roughness described in JIS B0601 (1994) by measuring using a three-dimensional roughness meter with a stylus pressure of 20 mg, a measurement length of 1 mm in the X direction, a feed pitch of 2 μm in the Y direction, 99 recorded lines, a height direction magnification of 20,000 times, and a cutoff of 80 μm.

[0038] The central surface peak height SRp+central surface valley depth SRv of the surface layer (B) is an index of the state of the large uneven areas formed by the lubricant, and is related to the slipperiness when in contact with the base layer (A) in the form of a roll film. When the central surface peak height SRp+central surface valley depth SRv of the surface layer (B) is 1.0 μm or more, the unwinding property from the roll film is improved, and when it is 2.0 μm or less, transparency is maintained. The sum of the central plane peak height SRp and the central plane valley depth SRv of the surface of the surface layer (B) is preferably 1.0 μm or more to 1.1 μm or more, more preferably 1.2 μm or more, and particularly preferably 1.3 μm or more.

[0039] In order to make the sum of the central plane peak height SRp and the central plane valley depth SRv of the surface of the surface layer (B) 1.0 μm or more and 2.0 μm or less, it is preferable to incorporate an antiblocking agent into the polypropylene resin composition forming the surface layer (B). The antiblocking agent can be appropriately selected from inorganic antiblocking agents such as silica, calcium carbonate, kaolin, zeolite, etc., and organic antiblocking agents such as acrylic, polymethacrylic, polystyrene, etc. Among these, silica is particularly preferred. The average particle size of the antiblocking agent is preferably 1.0 to 2.0 μm, and more preferably 1.0 to 1.5 μm. The antiblocking agent is preferably contained in an amount of 3000 ppm by mass in the polypropylene resin composition. The average particle size herein is measured by taking a photograph with a scanning electron microscope, measuring the Feret's diameter in the horizontal direction using an image analyzer, and expressing the average value.

[0040] (4) Biaxially oriented polypropylene film The total thickness of the biaxially oriented polypropylene film of the present invention is preferably 9 to 200 μm, more preferably 10 to 150 μm, even more preferably 12 to 100 μm, and particularly preferably 12 to 80 μm.

[0041] In the biaxially oriented polypropylene film of the second invention, the ratio of the thickness of the surface layer (B) to the thickness of the base layer (A) is preferably 0.01 to 0.5, more preferably 0.03 to 0.4, and even more preferably 0.05 to 0.3, i.e., total surface layers (B) / total base layers (A). When the ratio of total surface layers (B) / total base layers (A) exceeds 0.5, the shrinkage rate tends to increase. Furthermore, the thickness of all base layers (A) relative to the total thickness of the film is preferably 50 to 99%, more preferably 60 to 97%, and particularly preferably 70 to 95%. The remainder is the surface layer (B) or the surface layer (B) and other layers (e.g., layer C). The effective thickness of all surface layers (B) is preferably 0.5 to 4 μm, more preferably 1 to 3.5 μm, and even more preferably 1.5 to 3 μm.

[0042] The ratio of the thickness of the surface layer (B) to the base layer (A) in the biaxially oriented polypropylene film of the second invention is preferably 0.01 to 0.5, more preferably 0.03 to 0.4, and even more preferably 0.05 to 0.3, i.e., total surface layers (B) / total base layers (A). If the ratio exceeds 0.5, the shrinkage rate tends to increase. The thickness of all base layers (A) relative to the total thickness of the film is preferably 50 to 99%, more preferably 60 to 97%, and particularly preferably 70 to 95%. The remainder is the surface layer (B) or the surface layer (B) and other layers (e.g., Layer C). The substantial thickness of the entire surface layer (B) is preferably from 0.5 to 4 μm, more preferably from 1 to 3.5 μm, and even more preferably from 1.5 to 3 μm. The biaxially oriented polypropylene film of the second invention may be a two-layer film having one base layer (A) and one surface layer (B), but may also be a film having three or more layers. A two-layer structure of base layer (A) / surface layer (B) is preferred. It may also have a three-layer structure of surface layer (B) / layer A / surface layer (B), or / base layer (A) / intermediate layer (C) / surface layer (B), or a multilayer structure with more than one layer. When there are a plurality of substrate layers (A) or surface layers (B), the compositions of the layers may be different as long as they satisfy the required properties.

[0043] (5) Film characteristics The heat shrinkage rate of the biaxially oriented polypropylene film of the present invention in both the longitudinal and transverse directions at 150°C is preferably 8% or less, more preferably 7% or less, and particularly preferably 8% or less. By keeping the heat shrinkage rate at 8% or less, it is possible to reduce heat-induced wrinkles during processing.

[0044] In the biaxially oriented polypropylene film of the present invention, the heat shrinkage in the longitudinal direction at 150°C is preferably 0.2 to 8%, more preferably 0.3 to 7%. If the heat shrinkage is within the above range, the film can be said to have excellent heat resistance and can be used in applications where it may be exposed to high temperatures. Note that the heat shrinkage at 150°C can be reduced to about 1.5%, for example, by increasing the amount of low molecular weight components or adjusting the stretching conditions and heat setting conditions, but to reduce it below that level, offline annealing treatment is preferred.

[0045] In the biaxially oriented polypropylene film of the present invention, the heat shrinkage in the transverse direction at 150°C is preferably 0.2 to 8%, more preferably 0.3 to 7%, even more preferably 0.4 to 6%, and particularly preferably 0.5 to 5%. If the heat shrinkage is within the above range, the film can be said to have particularly excellent heat resistance and can be used in applications where it may be exposed to high temperatures. Note that the heat shrinkage at 150°C can be reduced to about 1.5%, for example, by increasing the amount of low-molecular-weight components or adjusting the stretching conditions and heat setting conditions, but to reduce it below that level, offline annealing or the like is preferred.

[0046] The tensile modulus in the machine direction of the biaxially oriented polypropylene film of the present invention is preferably 1.8 to 4 GPa, more preferably 2.1 to 3.7 GPa, even more preferably 2.2 to 3.5 GPa, and particularly preferably 2.3 to 3.4 GPa. The measuring method will be described later.

[0047] The tensile modulus in the transverse direction of the biaxially oriented polypropylene film of the present invention is preferably 4.5 to 8 GPa, more preferably 4.6 to 7.5 GPa, even more preferably 4.7 to 7 GPa, and particularly preferably 4.8 to 6.5 GPa. If the tensile modulus in the transverse direction is within the above range, it becomes possible to produce a film that is less likely to break.

[0048] The break resistance of the biaxially oriented polypropylene film of the present invention was evaluated by measuring the ring crush force by compressing the film in a ring shape and detecting the resistance with a load cell. The measurement method will be described later.

[0049] The haze of the biaxially oriented polypropylene film of the present invention is preferably 5% or less, more preferably 0.2 to 5%, even more preferably 0.3 to 4.5%, and particularly preferably 0.4 to 4%. A haze within the above range may facilitate use in applications requiring transparency. Haze tends to deteriorate, for example, when the stretching temperature or heat setting temperature is too high, the cooling roll (CR) temperature is high and the cooling rate of the stretched raw sheet is slow, or the low-molecular-weight component content is too high. By adjusting these factors, the haze can be kept within the above range. The method for measuring haze will be described later.

[0050] The lower limit of the impact resistance (23° C.) of the stretched polypropylene film of the present invention is preferably 0.6 J, more preferably 0.7 J. Within this range, the film has sufficient toughness and will not break during handling. From a practical standpoint, the upper limit of impact resistance is preferably 3 J, more preferably 2.5 J, even more preferably 2.2 J, and particularly preferably 2 J. Impact resistance tends to decrease, for example, when there is a large amount of low molecular weight components and the overall molecular weight is low, or when there is a small amount of high molecular weight components or when the molecular weight of the high molecular weight components is low. Therefore, these components can be adjusted to suit the application to fall within the range.

[0051] The lower limit of the plane orientation coefficient of the biaxially oriented laminated polypropylene film of the present invention is preferably 0.011, more preferably 0.012, and even more preferably 0.013. Within this range, the heat resistance and rigidity of the film tend to be increased. Stretched laminated polypropylene films generally have crystalline orientation, and the direction and degree of this orientation have a significant effect on the film's physical properties. The degree of crystalline orientation tends to vary depending on the molecular structure of the polypropylene used and the process and conditions in film production, and can be adjusted to fall within the above range. The measurement method will be described later.

[0052] The ink adhesion of the biaxially oriented polypropylene film of the present invention was evaluated by conducting a peeling test of gravure-printed printing ink and counting the number of peeled areas out of a total of 25 locations. The number of peeled areas is preferably 15 or less, more preferably 5 or less, and most preferably 0. If the number is 15 or more, the extent of ink peeling becomes significant, which is problematic. The method for evaluating ink adhesion will be described later.

[0053] The laminate strength in the machine direction after lamination to the biaxially oriented polypropylene film of the present invention is preferably 1.2 to 2.5 N / 15 mm, more preferably 1.3 to 2.5 N / mm, and even more preferably 1.4 to 2.5 N / mm. The method for measuring the laminate strength will be described later.

[0054] The dynamic friction coefficient of the biaxially oriented polypropylene film of the present invention is preferably 0.5 or less, more preferably 0.48 or less, and particularly preferably 0.45 or less. When the dynamic friction coefficient is 0.5 or less, the film can be smoothly unwound from the roll film, facilitating printing processing. The method for measuring the dynamic friction coefficient will be described later.

[0055] (4) Manufacturing method The biaxially oriented laminated polypropylene film of the present invention can be obtained by melt-extruding a polypropylene resin using an extruder to form an unstretched sheet, and then stretching and heat-treating the unstretched sheet by a predetermined method. In the case of the second invention, the polypropylene raw material for the base layer (A) (polypropylene-based resin composition for the base layer (A)) and the polypropylene raw material for the surface layer (B) (polypropylene-based resin composition for the surface layer (B)) are melt-extruded in separate extruders to form a laminated unstretched sheet, and the unstretched sheet is stretched and heat-treated by a predetermined method, thereby obtaining the laminated polypropylene raw material. The unstretched sheet can be obtained by using a plurality of extruders, feed blocks, multi-manifolds, etc. The melt extrusion temperature is preferably about 200 to 280°C. In the second invention, to obtain a laminated film with good appearance without disrupting the layers within this temperature range, it is preferable that the viscosity difference (MFR difference) between the polypropylene raw material for the base layer (A) and the polypropylene raw material for the surface layer (B) is 6 g / 10 min or less. If the viscosity difference is more than 6 g / 10 min, the layers will be disrupted and the appearance will be poor. A viscosity difference of 5.5 g / 10 min or less is more preferable, and 5 g / 10 min or less is even more preferable.

[0056] The surface temperature of the chill roll is preferably 25 to 35°C, more preferably 27 to 33°C. Next, the film is stretched 3 to 8 times, preferably 3 to 7 times, in the machine direction (MD) using a stretching roll at 120 to 165°C, and subsequently stretched 4 to 20 times, preferably 6 to 12 times, in the transverse direction at 155 to 175°C, more preferably 160 to 163°C. The film is then heat-set at 165 to 176°C, more preferably 170 to 176°C, and even more preferably 172 to 175°C, while relaxing by 2 to 10%. The biaxially oriented laminated polypropylene film thus obtained can be subjected to corona discharge, plasma treatment, flame treatment, etc., as needed, and then wound up on a winder to obtain a film roll.

[0057] The lower limit of the MD stretching ratio is preferably 3 times, more preferably 3.5 times. If it is less than this, film thickness unevenness may occur. The upper limit of the MD stretching ratio is preferably 8 times, more preferably 7 times. If it exceeds this, subsequent TD stretching may become difficult. The lower limit of the MD stretching temperature is preferably 120°C, more preferably 125°C, and even more preferably 130°C. If it is less than this, mechanical load may increase, thickness unevenness may increase, or surface roughness of the film may occur. The upper limit of the MD stretching temperature is preferably 160°C, more preferably 155°C, and even more preferably 150°C. A higher temperature is preferable for reducing heat shrinkage, but it may cause adhesion to the roll, making stretching impossible, or surface roughness may occur.

[0058] The lower limit of the TD stretching ratio is preferably 4 times, more preferably 5 times, and even more preferably 6 times. A stretch ratio less than this may result in thickness unevenness. The upper limit of the TD stretching ratio is preferably 20 times, more preferably 17 times, even more preferably 15 times, and particularly preferably 12 times. A stretch ratio greater than this may result in high heat shrinkage or breakage during stretching. The preheating temperature for TD stretching is preferably set 5 to 15°C higher than the stretching temperature in order to quickly raise the film temperature to near the stretching temperature. TD stretching is performed at a temperature higher than that of conventional biaxially oriented polypropylene films. The lower limit of the TD stretching temperature is preferably 155°C, more preferably 157°C, even more preferably 158°C, and particularly preferably 160°C. A stretch ratio less than this may result in insufficient softening and breakage, or a high heat shrinkage. The upper limit of the TD stretching temperature is preferably 170°C, more preferably 168°C, and even more preferably 163°C. A higher temperature is preferred to reduce the heat shrinkage rate, but if the temperature exceeds the above range, the low molecular weight components will melt and recrystallize, resulting in a decrease in orientation and possibly causing surface roughness and whitening of the film.

[0059] The stretched film is heat-set. Heat-setting can be carried out at a higher temperature than conventional biaxially oriented polypropylene films. The lower limit of the heat-setting temperature is preferably 165°C, more preferably 166°C. If the temperature is lower than this, the heat shrinkage rate may be high. Furthermore, a long treatment time may be required to reduce the heat shrinkage rate, which may result in poor productivity. The upper limit of the heat-setting temperature is preferably 176°C, more preferably 175°C. If the temperature exceeds this range, low-molecular-weight components may melt and recrystallize, causing surface roughness and whitening of the film.

[0060] It is preferable to relax (relax) the film during heat setting. The lower limit of the relaxation is preferably 2%, more preferably 3%. If it is less than this, the thermal shrinkage rate may become high. The upper limit of the relaxation is preferably 10%, more preferably 8%. If it exceeds this, thickness unevenness may become large.

[0061] Furthermore, in order to reduce the thermal shrinkage rate, the film produced by the above process can be wound into a roll and then annealed offline. The lower limit of the offline annealing temperature is preferably 160°C, more preferably 162°C, and even more preferably 163°C. If the temperature is lower than the above, the annealing effect may not be obtained. The upper limit of the offline annealing temperature is preferably 175°C, more preferably 174°C, and even more preferably 173°C. If the temperature exceeds the above, transparency may decrease and thickness unevenness may increase.

[0062] The lower limit of the offline annealing time is preferably 0.1 minutes, more preferably 0.5 minutes, and even more preferably 1 minute. If the time is less than the above, the annealing effect may not be obtained. The upper limit of the offline annealing time is preferably 30 minutes, more preferably 25 minutes, and even more preferably 20 minutes. If the time exceeds the above, productivity may decrease. [Example]

[0063] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the present invention, and any modifications or variations that do not depart from the spirit of the present invention are included in the present invention. The physical properties of the films obtained in the examples and comparative examples were measured as follows.

[0064] 1) Stereoregularity The mesopentad fraction ([mmmm]%) was measured using C-NMR. The mesopentad fraction was calculated according to the method described in "Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973)." C-NMR measurements were performed using a BRUKER AVANCE500 at 110°C after dissolving 200 mg of a sample in a 8:2 (volume ratio) mixture of o-dichlorobenzene and deuterated benzene at 135°C.

[0065] 2) Melt flow rate (MFR; g / 10 min) Measurement was carried out in accordance with JIS K7210 at a temperature of 230°C and a load of 2.16 kgf. The required amount of resin pellets (powder) was measured and used as is. The required amount of film was cut out and then cut into approximately 5 mm square samples.

[0066] 3) Molecular weight and molecular weight distribution The molecular weight and molecular weight distribution were determined using gel permeation chromatography (GPC) with monodisperse polystyrene as the standard and converted to polypropylene values. Measurement conditions such as the column and solvent used in the GPC measurement were as follows: The matters are as follows: Solvent: 1,2,4-trichlorobenzene Column: TSKgel GMHHR-H(20)HT x 3 Flow rate: 1.0ml / min Detector: RI Measurement temperature: 140℃

[0067] The number average molecular weight (Mn), mass average molecular weight (Mw), and molecular weight distribution are each defined by the number of molecules (Ni) at each elution position of the molecular weight (Mi) on the GPC curve obtained via the molecular weight calibration curve, as follows: Number average molecular weight: Mn=Σ(Ni·Mi) / ΣNi Mass average molecular weight: Mw=Σ(Ni·Mi 2 ) / Σ(Ni·Mi) Molecular weight distribution: Mw / Mn When the baseline was unclear, it was set in the range up to the lowest point of the high molecular weight side base of the elution peak on the high molecular weight side closest to the elution peak of the standard substance.

[0068] 4) Thickness The thickness of each of the base layer (A) and surface layer (B) was measured by cutting a cross section of a biaxially oriented laminated polypropylene film solidified with a modified urethane resin using a microtome and observing it with a differential interference microscope.

[0069] 5) Heat shrinkage rate (%) Measurement was carried out in accordance with JIS Z1712 using the following method: The film was cut into a width of 20 mm and a length of 200 mm in both the MD and TD directions, and then hung in a hot air oven at 150°C and heated for 5 minutes. The length after heating was measured, and the heat shrinkage rate was calculated as the ratio of the shrunken length to the original length.

[0070] 6) Tensile modulus (Young's modulus (unit: GPa)) The Young's modulus of the film in the MD and TD directions was measured at 23°C in accordance with JIS K7127. 7) Ring Crush (g) A film sample of 12.7 mm x 152 mm was prepared in a digital ring crush tester (manufactured by Tester Sangyo Co., Ltd.), and an attachment spacer was set on the sample table to match the thickness of the film sample. The film sample was inserted along the circumference in both the MD and TD directions. The maximum load when the compression plate was compressed at a descending speed of 12 mm / min at 23°C was taken as the ring crush measurement value.

[0071] 8) Haze (unit: %) Measurement was carried out in accordance with JIS K7105.

[0072] 9) Coefficient of dynamic friction According to JIS K7125, the corona-treated surfaces of the films were placed together and the measurement was carried out at 23°C. 10) Impact resistance Measurement was carried out at 23°C using a film impact tester manufactured by Toyo Seiki.

[0073] 11) Refractive index, plane orientation coefficient Measurements were made using an Atago Abbe refractometer according to JIS K7142-1996 5.1 (Method A). The refractive indices along the MD and TD directions were designated Nx and Ny, respectively, and the refractive index in the thickness direction was designated Nz. The plane orientation coefficient (ΔP) was calculated as (Nx + Ny) / 2 - Nz.

[0074] 12) Surface roughness The surface roughness of the obtained film was evaluated using a three-dimensional roughness meter (manufactured by Kosaka Laboratory, model number ET-30HK) with a stylus pressure of 20 mg, a measurement length in the X direction of 1 mm, a feed speed of 100 μm / sec, a feed pitch in the Y direction of 2 μm, 99 recorded lines, a height direction magnification of 20,000 times, and a cutoff of 80 μm. Three-dimensional roughness measurements were performed three times, and the arithmetic mean roughness (SRa), central surface peak height (SRp), and central surface valley depth (SRv) were evaluated using the average values.

[0075] 13) Surface resistivity (LogΩ) According to JIS K6911, the film was aged at 23°C for 24 hours, and then the corona-treated surface of the film was measured.

[0076] 14) Wetting tension (mN / m) In accordance with JIS K6768:1999, the film was aged at 23°C and a relative humidity of 50% for 24 hours, and then the corona-treated surface of the film was measured using the following procedure. 1) Measurements are carried out in a standard laboratory atmosphere (see JIS K7100) at a temperature of 23°C and a relative humidity of 50%. 2) Place the test piece on the substrate of the hand coater (4.1), drop a few drops of the test mixture onto the test piece, and immediately pull the wire bar to spread it out. If a cotton swab or brush is used to spread the test mixture, the liquid should be at least 6 cm 2 Spread the liquid quickly over the above area. The amount of liquid should be enough to form a thin layer without creating any puddles. The wetting tension is determined by observing the liquid film of the test mixture in a bright place and checking the state of the liquid film after 3 seconds. If the liquid film does not break and remains in the same state as when it was applied for 3 seconds or more, it is considered to be wet. If the wetness remains for 3 seconds or more, proceed to the mixture with the next higher surface tension, and conversely, if the liquid film breaks in 3 seconds or less, proceed to the mixture with the next lower surface tension. Repeat this process to select a mixture that can accurately wet the surface of the test piece in 3 seconds. 3) Use a new cotton swab for each test. Brushes or wire burrs should be cleaned with methanol and dried after each use, as residual liquid will change composition and surface tension with evaporation. 4) Repeat this procedure at least three times to select the mixture that can wet the surface of the test piece in 3 seconds. The surface tension of the mixture selected in this way is reported as the wetting tension of the film.

[0077] 15) Ink adhesion The entire surface of the film was gravure printed at a speed of 50 m / min using a gravure printing machine (Mitani Iron Works Co., Ltd.) (printing ink amount: 2 g / m 2 ) was carried out. The ink used here was a water-based ink (manufactured by Dainippon Ink and Chemicals, Inc.: trade name Ecofine 709 White). Using this print sample, an evaluation was carried out (in more detail) by grid peeling (25 x 2 mm squares, 90° peeling method using 18 mm wide Cellotape (registered trademark) manufactured by Nichiban Co., Ltd.), and the following ranking was carried out based on practicality. Grid pattern peeling area: 0 pieces ◎: Excellent printing ink adhesion. Same as above: 1 to 5 points: ○: Good printing ink adhesion. Same as above: 6 to 15 pieces...△: Poor printing ink adhesion. Same as above: 1 or more...×: No printing ink adhesion.

[0078] 16) Laminate strength The laminate strength was measured by the following procedure. 1) Creating a laminate film with a sealant film The lamination was carried out using a continuous dry laminating machine as follows. The adhesive was applied to the corona surface of the biaxially oriented polypropylene film obtained in the Examples and Comparative Examples in an amount of 3.0 g / m2 when dried. 2 After gravure coating, the film was introduced into a drying zone and dried at 80°C for 5 seconds. The film was then laminated with a sealant film between rolls located downstream (roll pressure: 0.2 MPa, roll temperature: 60°C). The resulting laminated film was then aged at 40°C for 3 days in a rolled state. The adhesive used was an ether-based adhesive obtained by mixing 17.9% by mass of a base agent (TM329, manufactured by Toyo Morton Co., Ltd.), 17.9% by mass of a curing agent (CAT8B, manufactured by Toyo Morton Co., Ltd.), and 64.2% by mass of ethyl acetate, and the sealant film used was a non-biaxially oriented polypropylene film (Pylen (registered trademark) CT P1128, thickness 30 μm) manufactured by Toyobo Co., Ltd. 2) Measurement of laminate strength The laminate film obtained above was cut into strips (200 mm long, 15 mm wide) with the long side in the machine direction of the biaxially oriented polypropylene film, and the peel strength (N / 15 mm) was measured using a tensile tester (Tensilon, manufactured by Orientec Co., Ltd.) when T-peeling at a tensile speed of 200 mm / min in an environment of 23°C. The measurement was performed three times, and the average value was taken as the laminate strength.

[0079] (Comparative Example 7) A mixture of 99% by weight of polypropylene homopolymer PP-1 shown in Table 1 and 1% by weight of an antistatic agent (stearyldiethanolamine stearate (KYM-4K, manufactured by Matsumoto Yushi Co., Ltd.)) was used. This mixture was melted at 250°C using a 60mm extruder, co-extruded from a T-die into a sheet, cooled and solidified on a 30°C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 135°C. Next, in a tenter, both ends of the film width were clamped with clips, preheated to 175°C, stretched 8.2 times in the transverse direction (TD) at 160°C, and heat-set at 170°C while relaxing by 6.7% in the transverse direction (TD). The film-forming conditions at this time are referred to as film-forming condition a and are shown in Table 2. One surface of the obtained biaxially oriented polypropylene film was subjected to a corona treatment using a corona treater manufactured by Softal Corona & Plasma GmbH at an applied current of 0.75 A, and then the film was wound up on a winder to obtain the biaxially oriented monolayer polypropylene film of the present invention. The physical properties of the obtained film are shown in Table 3.

[0080] Example 2 The polypropylene homopolymer PP-1 shown in Table 1 was replaced with polypropylene resin PP-2. Using a 60 mm extruder, the mixed raw materials were melted at 250°C and co-extruded into a sheet from a T-die. The resulting sheet was cooled and solidified using a 30°C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 125°C. The film was then clamped at both widthwise ends with clips in a tenter, preheated to 170°C, stretched 8.2 times in the transverse direction (TD) at 158°C, and heat-set at 165°C while relaxing by 6.7% in the transverse direction (TD). A biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7. The film-forming conditions used here are designated film-forming conditions b and are shown in Table 2. The physical properties of the resulting film are shown in Table 3.

[0081] (Comparative Example 8) The base layer (A) was a mixture of 99% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 1% by weight of an antistatic agent (stearyl diethanolamine stearate (KYM-4K, Matsumoto Oil & Fats Co., Ltd.)). The surface layer (B) was a mixture of 99.7% by weight of the polypropylene homopolymer PP-1 shown in Table 1 and 0.3% by mass of an antiblocking agent (commercially available silica particles (average particle diameter: 1.3 μm)). The mixed raw materials used for the base layer (A) were extruded using a 60 mm extruder, and the mixed raw materials used for the surface layer (B) were extruded using a 65 mm extruder. The raw material resins were melted at 250 ° C and co-extruded into a sheet from a T-die. The material was cooled and solidified on a 30 ° C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 135 ° C. Next, in a tenter, both ends of the film width direction were clamped with clips, preheated to 175 ° C, stretched 8.2 times in the transverse direction (TD) at 160 ° C, and heat-set at 170 ° C while relaxing 6.7% in the transverse direction (TD). The film was produced under the film-forming conditions a shown in Table 2 and wound on a winder to obtain a biaxially oriented laminated polypropylene film of the present invention, in which one base layer (A) and one surface layer (B) were laminated. The surface side of the surface layer (B) of the obtained biaxially oriented polypropylene film was subjected to corona treatment using a corona treater manufactured by Softal Corona & Plasma GmbH at an applied current of 0.75 A, and then the film was wound up on a winder to obtain the biaxially oriented monolayer polypropylene film of the present invention. The physical properties of the obtained film are shown in Table 3.

[0082] Example 4 A biaxially oriented laminated polypropylene film was obtained in the same manner as in Comparative Example 8, except that the raw materials used for the base layer (A) did not contain an antistatic agent. The physical properties of the obtained film are shown in Table 3.

[0083] (Comparative Example 9) The base layer (A) was a mixture of 99% by mass of polypropylene homopolymer PP-1 shown in Table 1 and 1% by mass of stearyl diethanolamine stearate (KYM-4K, Matsumoto Oil & Fats Co., Ltd.) as an antistatic agent. The surface layer (B) was a mixture of 48.7% by mass of polypropylene homopolymer PP-6 shown in Table 1, 51% by mass of ethylene copolymerized polypropylene polymer PP-7 shown in Table 1, and 0.3% by mass of commercially available silica particles (average particle size: 1.3 μm) as an antiblocking agent. A biaxially oriented laminated polypropylene film was obtained in the same manner as in Comparative Example 8, except that the surface layer (B) was a mixture of 48.7% by mass of polypropylene homopolymer PP-6 shown in Table 1, 51% by mass of ethylene copolymerized polypropylene polymer PP-7 shown in Table 1, and 0.3% by mass of commercially available silica particles (average particle size: 1.3 μm) as an antiblocking agent.

[0084] Example 6 Except for changing the film thickness to 30 μm, a biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7. The physical properties of the obtained film are shown in Table 3.

[0085] Example 7 Except for changing the film thickness to 40 μm, a biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7. The physical properties of the obtained film are shown in Table 3.

[0086] (Comparative Example 1) A biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7, except that the polypropylene resin PP-1 shown in Table 1 was changed to the polypropylene resin PP-3 shown in Table 1. The physical properties of the obtained film are as shown in Table 4.

[0087] (Comparative Example 2) A biaxially oriented monolayer polypropylene film was produced in the same manner as in Comparative Example 7, except that the polypropylene resin PP-1 shown in Table 1 was changed to the polypropylene resin PP-4 shown in Table 1. However, the film broke during stretching, and no film could be obtained.

[0088] (Comparative Example 3) A biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7, except that the polypropylene resin PP-1 shown in Table 1 was changed to the polypropylene resin PP-5 shown in Table 1. The physical properties of the obtained film are as shown in Table 4.

[0089] Comparative Example 4 The polypropylene resin PP-1 shown in Table 1 was replaced with the polypropylene resin PP-6 shown in Table 1. Using a 60 mm extruder, the raw resins were melted at 250°C and co-extruded into a sheet from a T-die. The extruded sheet was cooled and solidified on a 30°C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 125°C. The film was then clamped at both widthwise ends with clips in a tenter, preheated to 170°C, stretched 8.2 times in the transverse direction (TD) at 158°C, and heat-set at 165°C while relaxing by 6.7% in the transverse direction (TD). A biaxially oriented monolayer polypropylene film was obtained in the same manner as in Comparative Example 7. The physical properties of the resulting film are shown in Table 4.

[0090] (Comparative Example 5) The polypropylene resin PP-1 shown in Table 1 was replaced with the polypropylene resin PP-8 shown in Table 1. Using a 60 mm extruder, the raw resins were melted at 250°C and co-extruded through a T-die into a sheet. The resulting film was cooled and solidified using a 30°C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 140°C. The film was then clamped at both widthwise ends with clips in a tenter, preheated to 170°C, stretched 8.2 times in the transverse direction (TD) at 160°C, and heat-set at 168°C while relaxing by 6.7% in the transverse direction (TD). A biaxially stretched monolayer polypropylene film was obtained in the same manner as in Comparative Example 7, except that the film formation conditions were designated as film formation conditions c and are shown in Table 2. The physical properties of the resulting film are shown in Table 4.

[0091] (Comparative Example 6) The polypropylene resin PP-1 shown in Table 1 was replaced with the polypropylene resin PP-9 shown in Table 1. Using a 60 mm extruder, the raw resins were melted at 250°C and co-extruded through a T-die into a sheet. The extruded sheet was cooled and solidified on a 30°C cooling roll, and then stretched 4.5 times in the machine direction (MD) at 135°C. The film was then clamped at both widthwise ends with clips in a tenter, preheated to 170°C, stretched 8.2 times in the transverse direction (TD) at 160°C, and heat-set at 168°C while relaxing by 6.7% in the transverse direction (TD). A biaxially oriented monolayer polypropylene film was obtained in the same manner as in Comparative Example 7, except that the film formation conditions were designated as film formation conditions d and are shown in Table 2. The physical properties of the resulting film are shown in Table 4.

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] [Table 4]

[0096] The biaxially oriented polypropylene films obtained in Examples 2, 4, 6, and 7 had small heat shrinkage and large Young's modulus. Among them, the laminated film obtained in Example 4 was a film with even better lamination strength and ink adhesion. In contrast, the film obtained in Comparative Example 1 had a large heat shrinkage rate in the transverse direction (TD). The film obtained in Comparative Example 3 had a large heat shrinkage rate in the transverse direction (TD) and a small Young's modulus in the transverse direction (TD). The film obtained in Comparative Example 4 had a large heat shrinkage rate and a small Young's modulus in both the transverse direction (TD) and the machine direction (MD). The film obtained in Comparative Example 5 had a small Young's modulus in the transverse direction (TD), and the film obtained in Comparative Example 6 had a large heat shrinkage rate in the transverse direction (TD). [Industrial Applicability]

[0097] The biaxially oriented laminated polypropylene film of the present invention has higher heat resistance and rigidity, and exhibits less wrinkles due to heat and is less likely to break, and therefore has excellent processability. The biaxially oriented polypropylene film of the present invention can be used not only for food packaging such as stand-up pouches, but also for label applications.

Claims

1. The polypropylene resin constituting the film, which is a completely homopolypropylene resin containing no copolymerization component and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms, satisfies the following conditions 1) to 4): The lower limit of the film's plane orientation coefficient is 0.0125; A biaxially oriented polypropylene film characterized in that the tensile modulus of the film in the transverse direction is 5.1 GPa or more. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 3.9 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is more than 7.0 g / 10 min and 9.0 g / 10 min or less.

2. The present invention has a base layer (A) mainly composed of a polypropylene resin made of a completely homogeneous polypropylene resin containing no copolymerizable components and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms, and a surface layer (B) on at least one surface of the base layer (A) mainly composed of a polypropylene-based resin made of a completely homogeneous polypropylene resin containing no copolymerizable components and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms, wherein the polypropylene resin constituting the base layer (A) made of a completely homogeneous polypropylene resin containing no copolymerizable components and / or a polypropylene resin copolymerized with ethylene and / or an α-olefin having 4 or more carbon atoms satisfies the following conditions 1) to 4): The lower limit of the film's plane orientation coefficient is 0.0125; A biaxially oriented polypropylene film characterized in that the tensile modulus of the film in the transverse direction is 4.8 GPa or more. 1) The lower limit of the mesopentad fraction is 96%. 2) The upper limit of the amount of copolymerizable monomers other than propylene is 0.1 mol %. 3) The ratio of mass average molecular weight (Mw) to number average molecular weight (Mn) is 3.0 or more and 3.9 or less. 4) The melt flow rate (MFR) measured at 230°C and 2.16 kgf is more than 7.0 g / 10 min and 9.0 g / 10 min or less.

3. 3. The biaxially oriented polypropylene film according to claim 1, wherein the heat shrinkage of the film in both the longitudinal and transverse directions at 150°C is 8% or less.

4. 4. The biaxially oriented polypropylene film according to claim 1, wherein the tensile modulus of the film in the machine direction is 2.0 GPa or more and the tensile modulus of the film in the transverse direction is 4.5 GPa or more.

5. 5. The biaxially oriented polypropylene film according to claim 1, wherein the haze value of the film is 5% or less.

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