Biaxially oriented polypropylene film

Abstract

To provide a biaxially oriented polypropylene film that is highly rigid, has excellent heat resistance at temperatures as high as 150°C, easily maintains the shape of a packaging bag, minimizes pitch misalignment during printing and wrinkles in the sealed area when heat-sealed, and exhibits superior lamination strength. [Solution] A biaxially oriented polypropylene film in which the stress (F5) at 5% elongation is 40 MPa or more in the longitudinal direction and 160 MPa or more in the width direction at 23°C, the thermal shrinkage rate at 150°C is 10% or less in the longitudinal direction and 30% or less in the width direction, and the laminate strength (90° peel) in the width direction is 1.0 N / 15 mm or more.

Description

[Technical Field]

[0001] This invention relates to a biaxially oriented polypropylene film that is excellent in rigidity and heat resistance. More specifically, it relates to a biaxially oriented polypropylene film that is suitable for use in packaging bags because it easily maintains the shape of the bag when used as a packaging bag, produces fewer wrinkles at the sealed area when heat-sealed, and has excellent lamination strength. [Background technology]

[0002] Biaxially oriented polypropylene films are used in packaging and industrial applications because they possess moisture resistance, as well as the necessary rigidity and heat resistance. In recent years, as their applications have expanded, there has been a demand for higher performance, particularly improved rigidity. Furthermore, due to environmental considerations, it is necessary to maintain strength even when reducing volume (making the film thinner), and to achieve this, significantly improving rigidity is essential. As a means of improving rigidity, it is known that the crystallinity and melting point of the polypropylene resin can be improved by improving the catalyst and process technology during polymerization of the polypropylene resin. However, despite such improvements, there has been no biaxially oriented polypropylene film with sufficient rigidity until now.

[0003] In the manufacturing process of biaxially oriented polypropylene films, methods have been proposed in which, after stretching in the width direction, a first-stage heat treatment is performed while relaxing the film at a temperature below that of the width-direction stretching, and a second-stage heat treatment is performed at a temperature between the first-stage temperature and the width-direction stretching temperature (see, for example, Reference 1). Alternatively, a method has been proposed in which the film is stretched in the width direction and then further stretched in the longitudinal direction (see, for example, Reference 2). However, although the film described in Patent Document 2 has excellent rigidity, it is prone to wrinkles in the sealed area after heat sealing and has poor heat resistance. Furthermore, the orientation of the film described in Patent Document 1 is low and its rigidity is insufficient. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Gazette WO2016 / 182003 [Patent Document 2] Japanese Patent Publication No. 2013-177645 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to solve the above-mentioned problems. Specifically, it relates to a biaxially oriented polypropylene film that is excellent in rigidity and heat resistance at high temperatures of 150°C. More specifically, it is to provide a biaxially oriented polypropylene film that easily maintains the shape of a packaging bag, has fewer wrinkles in and around the sealed area when heat-sealed, and also has excellent lamination strength. [Means for solving the problem]

[0006] As a result of diligent research conducted by the present inventors to achieve the above objective, they have found that by using a biaxially oriented polypropylene film in which the stress (F5) at 5% elongation is 40 MPa or more in the longitudinal direction and 160 MPa or more in the width direction at 23°C, the thermal shrinkage rate at 150°C is 10% or less in the longitudinal direction and 30% or less in the width direction, and the laminate strength (90° peel), expressed as the peel strength when the laminate film obtained by laminating with a sealant film is peeled at 90° (T-shape) in the width direction, is 1.0 N / 15 mm or more, a biaxially oriented polypropylene film with excellent rigidity, heat resistance at high temperatures of 150°C, and excellent laminate strength can be obtained.

[0007] In this case, it is preferable that the heat shrinkage rate of the biaxially oriented polypropylene film at 120°C is 2.0% or less in the longitudinal direction and 5.0% or less in the width direction, and that the heat shrinkage rate at 120°C in the longitudinal direction is smaller than the heat shrinkage rate at 120°C in the width direction.

[0008] Also, in this case, it is preferable that the refractive index Ny in the longitudinal direction of the biaxially oriented polypropylene film is 1.5230 or more and △Ny is 0.0220 or more.

[0009] Furthermore, in this case, it is preferable that the haze of the biaxially oriented polypropylene film is 5.0% or less.

[0010] Furthermore, in this case, it is preferable that the biaxially oriented polypropylene film has a structure including a base material layer (A), an intermediate layer (B), and a surface layer (C).

[0011] Furthermore, in this case, it is preferable that the mesopentad fraction of the main polypropylene resin constituting the base material layer (A) is 97.0% or more.

[0012] Furthermore, in this case, it is preferable that the crystallization temperature of the main polypropylene resin constituting the base material layer (A) is 105°C or more and the melting point is 161°C or more.

[0013] Furthermore, in this case, it is preferable that the melt flow rate of the main polypropylene resin constituting the base material layer (A) is 4.0 g / 10 min or more.

[0014] Furthermore, in this case, it is preferable that the component amount of the main polypropylene resin constituting the base material layer (A) having a molecular weight of 100,000 or less is 35% by mass or more.

Advantages of the Invention

[0015] The biaxially oriented polypropylene film of the present invention has high rigidity and excellent heat resistance at a high temperature of 150°C. Therefore, it is easy to maintain the bag shape when used as a packaging bag, and there are few wrinkles in the seal part when heat-sealed. Furthermore, since the laminating strength is excellent, a biaxially oriented polypropylene film that can be suitably used for a packaging bag can be obtained. In addition, since the biaxially oriented polypropylene film is also excellent in rigidity, the strength can be maintained even when the film thickness is reduced, and it can be suitably used for applications that require higher rigidity.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the biaxially oriented polypropylene film of the present invention will be described in more detail. The biaxially oriented polypropylene film of the present invention preferably has a structure including a base material layer (A), an intermediate layer (B), and a surface layer (C), and the base material layer (A), the intermediate layer (B), and the surface layer (C) are preferably adjacent in this order.

[0017] Hereinafter, each of the base material layer (A), the intermediate layer (B), and the surface layer (C) will be described in detail.

[0018] (Base material layer (A)) The base material layer (A) of the biaxially oriented polypropylene film of the present invention is made of a polypropylene resin composition mainly composed of the following polypropylene homopolymer.

[0019] (Polypropylene homopolymer) The polypropylene homopolymer used for the base material layer (A) is preferably a polypropylene polymer that does not substantially contain ethylene and / or an α-olefin having 4 or more carbon atoms. Even when it contains an ethylene and / or an α-olefin component having 4 or more carbon atoms, the amount of the ethylene and / or an α-olefin component having 4 or more carbon atoms is preferably 0.3 mol% or less, more preferably 0.2 mol or less, and still more preferably 0.1 mol or less. When it is within the above range, the crystallinity is likely to be improved. Examples of α-olefin components with 4 or more carbon atoms that constitute such copolymers include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. Polypropylene homopolymers can be made from two or more different types of polypropylene homopolymers.

[0020] (stereoregularity) The mesopentad fraction ([mmmm]%), which is an indicator of the stereoregularity of the polypropylene homopolymer used in the present invention, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, and in the range of 98.0 to 99.5%. More preferably, and especially preferably within the range of 98.5 to 99.3%. A mesopentad fraction of 97.0% or higher enhances the crystallinity of the polypropylene resin, improving the melting point, crystallinity, and crystal orientation of the crystals in the film, resulting in improved rigidity and heat resistance at high temperatures. A fraction of 99.9% or lower helps to reduce costs in polypropylene manufacturing and makes the film less prone to breakage during formation. The mesopentad fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. In order to keep the mesopentade fraction of the polypropylene homopolymer within the above-mentioned range, methods such as washing the obtained polypropylene resin powder with a solvent such as n-heptane, selecting a catalyst and / or co-catalyst, and appropriately selecting the components of the polypropylene resin composition are preferably employed.

[0021] (Melting temperature) The lower limit of the melting temperature (Tm) of the polypropylene homopolymer constituting the biaxially oriented polypropylene film of the present invention is preferably 160°C, more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and still more preferably 164°C. When Tm is 160°C or higher, rigidity and heat resistance at high temperatures are easily obtained. The upper limit of Tm is preferably 170°C, more preferably 169°C, even more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. When Tm is 170°C or lower, it is easier to suppress cost increases in terms of polypropylene production, and the film is less likely to break during film formation. The melting temperature can be further increased by blending a crystal nucleating agent into the aforementioned polypropylene resin. Tm is measured using a differential scanning calorimeter (DSC). A 1-10 mg sample is placed in an aluminum pan, melted at 230°C for 5 minutes under a nitrogen atmosphere, cooled to 30°C at a scanning rate of -10°C / min, held for 5 minutes, and then heated again at a scanning rate of 10°C / min. Tm is the main peak temperature of the endothermic peak observed during melting.

[0022] (crystallization temperature) The lower limit of the crystallization temperature (Tc) of the polypropylene homopolymer constituting the biaxially oriented polypropylene film of the present invention, as measured by DSC, is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105°C or higher, crystallization proceeds easily during the widthwise stretching and subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. When Tc is 135°C or lower, it is easier to suppress cost increases in terms of polypropylene production, and the film is less likely to break during film formation. The crystallization temperature can be further increased by blending a crystal nucleating agent into the aforementioned polypropylene resin. Tc is measured using DSC. A 1-10 mg sample is placed in an aluminum pan, melted at 230°C for 5 minutes under a nitrogen atmosphere, and then cooled to 30°C at a scanning rate of -10°C / min. Tc is the main peak temperature of the exothermic peak observed during this process.

[0023] (Melt flow rate) The melt flow rate (MFR) of the polypropylene homopolymer constituting the biaxially oriented polypropylene film of the present invention is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, even more preferably 4.8 to 22 g / 10 min, particularly preferably 5.0 to 20 g / 10 min, and most preferably 6.0 to 20 g / 10 min, when measured in accordance with the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995). When the MFR of the polypropylene homopolymer is 4.0 g / 10 min or higher, it is easier to obtain a biaxially oriented polypropylene film with low thermal shrinkage. Furthermore, if the MFR of the polypropylene homopolymer is 30 g / 10 min or less, it is easier to maintain film-forming properties.

[0024] From the viewpoint of film properties, it is preferable to set the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene homopolymer constituting the film to preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min. When the MFR of the polypropylene resin is 5.0 g / 10 min or higher, the amount of low molecular weight components in the polypropylene resin constituting the film increases. Therefore, by employing the widthwise stretching process in the film manufacturing process described later, the orientation and crystallization of the polypropylene resin are further promoted, and the degree of crystallinity in the film tends to increase. In addition, the entanglement between polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. In order to keep the MFR of the polypropylene homopolymer within the above range, it is preferable to employ methods to control the average molecular weight and molecular weight distribution of the polypropylene homopolymer.

[0025] In other words, the lower limit of the amount of components with a molecular weight of 100,000 or less in the integrated gel permeation chromatography (GPC) curve of the polypropylene homopolymer constituting the film of the present invention is 35% by mass, preferably 38% by mass, more preferably 40% by mass, even more preferably 41% by mass, and particularly preferably 42% by mass. The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease. In this case, including high molecular weight components or long-chain branched components with long relaxation times makes it easier to adjust the amount of components with a molecular weight of 100,000 or less in the polypropylene resin without significantly changing the overall viscosity, thus improving film-forming properties without significantly affecting rigidity or thermal shrinkage.

[0026] (molecular weight distribution) The lower limit of the mass-average molecular weight (Mw) / number-average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution of the polypropylene homopolymer used in the present invention, is preferably 3.5, more preferably 4.0, even more preferably 4.5, and particularly preferably 5.0. The upper limit of Mw / Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. Mw / Mn can be obtained using GPC. When Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight of 100,000 or less.

[0027] Furthermore, the molecular weight distribution of polypropylene homopolymers can be adjusted by polymerizing components of different molecular weights in a multi-step process in a series of plants, blending components of different molecular weights offline in a kneader, polymerizing with a blend of catalysts having different properties, or using a catalyst capable of achieving the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC can be a smooth molecular weight distribution with a single peak in a GPC chart with the logarithm of molecular weight (M) (logM) on the x-axis and the differential distribution value (weight fraction per logM) on the y-axis, or it can be a molecular weight distribution with multiple peaks or shoulders.

[0028] (Propylene resin composition) When a copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, with an ethylene and / or α-olefin component content exceeding 0.3%, is used in the propylene resin composition constituting the base layer (A), it is preferable that the content of the copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, with an ethylene and / or α-olefin component content exceeding 0.3%, relative to the total polypropylene resin used in the base layer (A), be 5% by weight or less, more preferably 3% by weight or less, even more preferably 1% by weight or less, and particularly preferably 0% by weight.

[0029] (Antistatic agent) By using a specific ratio of a specific diethanolamine fatty acid ester compound, a specific amine compound, and a specific glycerin mono fatty acid ester compound in the propylene resin composition constituting the base layer (A), it is possible to produce a biaxially oriented polypropylene resin film that has sufficient initial antistatic properties, maintains excellent antistatic properties over a long period of time, and exhibits almost no decrease in initial transparency even when exposed to high temperatures, and is non-sticky.

[0030] For example, 0.3 to 0.2 parts by weight of a polyoxyethylene alkylamine monofatty acid ester compound (A) is added to 1 mole of amine represented by formula (1) with 2 moles or more of ethylene oxide per 1 mole of amine, per 100 parts by weight of the polypropylene resin composition constituting the base layer (A). [ka] In the formula, R1 and R2 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0031] 0.03 to 0.2 parts by weight of the glycerol monofatty acid ester compound (B) represented by formula (2), [ka] In the formula, R3 is an alkyl group having 7 to 21 carbon atoms.

[0032] 0 to 0.2 parts by weight of a polyoxyethylene alkylamine difatty acid ester compound (C) obtained by adding 2 moles or more of ethylene oxide to 1 mole of amine represented by formula (3), [ka] In the formula, R4, R5, and R6 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0033] 0 to 0.2 parts by weight of a polyoxyethylene alkenylamine compound (D) obtained by adding 2 moles or more of ethylene oxide to 1 mole of amine represented by formula (4), [ka] In the formula, R7 is an alkenyl group having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30. It is preferable that it contains this.

[0034] The polyoxyethylene amine monoester compound (A) used in the present invention, obtained by adding 2 moles of ethylene oxide to 1 mole of amine, is a nonionic antistatic agent represented by formula (1), and is preferably contained in a ratio of 0.3 to 1.2 parts by weight, and particularly preferably 0.3 to 1.1 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the base layer (A). When the content of compound (A) is 0.3 parts by weight or more, an antistatic effect is obtained over a long period of time, and when the content is 1.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0035] The glycerin monofatty acid ester compound (B) used in the present invention is a nonionic antistatic agent represented by formula (2), where R3 is a linear or branched alkyl group, preferably an alkyl group having 10 to 21 carbon atoms, and particularly preferably an alkyl group having 14 to 20 carbon atoms, and is contained in a ratio of preferably 0.03 to 0.3 parts by weight, and particularly preferably 0.03 to 0.2 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the base layer (A). When the content of compound (E) is 0.03 parts by weight or more, the antistatic effect is obtained quickly, and when the content is 0.3 parts by weight or less, the amount of bleeding is small, tackiness on the film surface is less likely to occur, and the decrease in transparency due to whitening is small.

[0036] The polyoxyethylene alkyldiethanolamine compound (C) used in the present invention, obtained by adding 2 moles or more of ethylene oxide to 1 mole of amine, is a nonionic antistatic agent represented by formula (3), and is contained in a ratio of preferably 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the base layer (A). When the content of compound (C) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0037] The polyoxyethylene alkenyl diethanolamine compound (D), represented by formula (4), is a nonionic antistatic agent obtained by adding 2 moles or more of ethylene oxide to 1 mole of amine used in the present invention. It is preferably contained in a ratio of 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the base layer (A). When the content of compound (C) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0038] In equations (1) to (4), X and Y are integers from 1 to 29, and X + Y is an integer from 2 to 30, preferably from 2 to 4. R1 to R6 are linear or branched alkyl groups, particularly preferably alkyl groups having 13 to 25 carbon atoms, and especially preferably alkyl groups having 13 to 18 carbon atoms.

[0039] Examples of alkyl groups R1 to R6 in formulas (1) to (3) include methyl, ethyl, propyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, nonyl, decyl, undecyl, lauryl, trilauryl, myristyl, pentadecyl, palmityl, heptadecyl, stearyl, nonadecyl, and eicosyl groups.

[0040] In formula (4), the alkenyl group R7 is preferably at least one selected from higher unsaturated aliphatic groups having 12 to 21 carbon atoms.

[0041] Furthermore, within the limits that do not impair the effects of the present invention, the polypropylene resin composition constituting the base layer (A) may also contain various additives for improving quality such as slipperiness, for example, lubricants such as waxes and metal soaps, plasticizers, processing aids, and known heat stabilizers, antioxidants, and ultraviolet absorbers that are commonly added to polypropylene films, in order to improve productivity.

[0042] (Middle layer (B)) (Polypropylene resin) When using a polypropylene resin composition for the intermediate layer (B) of the biaxially oriented polypropylene film of the present invention, a copolymer of the polypropylene homopolymer described below and propylene with ethylene and / or α-olefins having 4 or more carbon atoms is used, which makes it easier to improve the laminate strength while maintaining rigidity.

[0043] (Polypropylene monopolymer) The polypropylene homopolymer used in the intermediate layer (B) is preferably a polypropylene polymer that is substantially free of ethylene and / or α-olefins having 4 or more carbon atoms. Even if it contains ethylene and / or α-olefin components having 4 or more carbon atoms, the amount of ethylene and / or α-olefin components is preferably 0.3 mol% or less, more preferably 0.2 mol% or less, and even more preferably 0.1 mol or less. Crystallinity tends to improve within the above range. Examples of α-olefin components with 4 or more carbon atoms that constitute such copolymers include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. Polypropylene homopolymers can be made from two or more different types of polypropylene homopolymers.

[0044] The polypropylene homopolymer content is preferably 55% by weight or more, more preferably 55% by weight or more and 95% by weight or less, even more preferably 60% by weight or more and 92% by weight or less, and particularly preferably 65% ​​by weight or more and 92% by weight or less, relative to the total polypropylene resin used in the intermediate layer (B).

[0045] (stereoregularity) The mesopentade fraction ([mmmm]%), which is an indicator of the stereoregularity of polypropylene homopolymers, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, and within the range of 98.0 to 99.5%. More preferably, and especially preferably within the range of 98.5 to 99.3%. A mesopentad fraction of 97.0% or higher increases the crystallinity of the polypropylene homopolymer, improving the melting point, crystallinity, and crystal orientation of the crystals in the film, and making it easier to obtain rigidity and heat resistance at high temperatures. A mesopentad fraction of 99.9% or lower makes it easier to reduce costs in polypropylene manufacturing and makes the film less prone to breakage during formation. The mesopentad fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. A concentration of 99.5% or less is more preferable. The mesopentade fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. In order to keep the mesopentade fraction of the polypropylene homopolymer within the above-mentioned range, methods such as washing the obtained polypropylene homopolymer powder with a solvent such as n-heptane, selecting a catalyst and / or co-catalyst, and selecting components of the polypropylene resin composition are preferably employed.

[0046] (Melting temperature) The lower limit of the melting temperature (Tm) of the above polypropylene homopolymer, as measured by DSC, is preferably 160°C, more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and still more preferably 164°C. A Tm of 160°C or higher makes it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tm is preferably 170°C, more preferably 169°C, even more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. A Tm of 170°C or lower makes it easier to suppress cost increases in polypropylene manufacturing and makes it less prone to rupture during film formation. The melting temperature can also be further increased by blending a crystal nucleating agent into the aforementioned polypropylene homopolymer. Tm is measured using a differential scanning calorimeter (DSC). A 1-10 mg sample is placed in an aluminum pan and set in the DSC. Under a nitrogen atmosphere, it is melted at 230°C for 5 minutes, cooled to 30°C at a scanning rate of -10°C / min, held for 5 minutes, and then heated again at a scanning rate of 10°C / min. Tm is the main peak temperature of the endothermic peak observed during melting.

[0047] (crystallization temperature) The lower limit of the crystallization temperature (Tc) of polypropylene homopolymers, as measured by DSC, is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105°C or higher, crystallization proceeds easily during the widthwise stretching and subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. When Tc is 135°C or lower, it is less likely to increase the cost of polypropylene production and the film is less prone to rupture during film formation. The crystallization temperature can also be further increased by incorporating a crystal nucleating agent into the aforementioned polypropylene homopolymer. Tc is measured using a differential scanning calorimeter (DSC). A 1-10 mg sample is placed in an aluminum pan, set in the DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and then cooled to 30°C at a scanning rate of -10°C / min. Tc is the main peak temperature of the exothermic peak observed during this process.

[0048] (Melt flow rate) The melt flow rate (MFR) of polypropylene homopolymer, when measured according to the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995), is preferably 4.0 to 30 g / 10 min, more preferably 5.0 to 25 g / 10 min, even more preferably 6.0 to 22 g / 10 min, particularly preferably 7.0 to 20 g / 10 min, and most preferably 8.0 to 20 g / 10 min. When the melt flow rate (MFR) of the polypropylene homopolymer is 4.0 g / 10 min or higher, it is easier to obtain a biaxially oriented polypropylene film with low thermal shrinkage. Furthermore, if the melt flow rate (MFR) of the polypropylene homopolymer is 30 g / 10 min or less, it is easier to maintain the film-forming properties.

[0049] From the viewpoint of film properties, the lower limit of the melt flow rate (MFR) (230°C, 2.16 kgf) of the polypropylene homopolymer is preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min. When the melt flow rate (MFR) of the polypropylene homopolymer lipid is 5.0 g / 10 min or higher, the amount of low molecular weight components in the polypropylene homopolymer lipid constituting the film increases. Therefore, by employing the widthwise stretching process in the film manufacturing process described later, the oriented crystallization of the polypropylene homopolymer is further promoted, and the degree of crystallinity in the film tends to increase. In addition, the entanglement between polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. In order to keep the melt flow rate (MFR) of the polypropylene homopolymer within the above range, it is preferable to employ methods to control the average molecular weight and molecular weight distribution of the polypropylene resin.

[0050] In other words, the lower limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve of the polypropylene homopolymer is 35% by mass, preferably 38% by mass, more preferably 40% by mass, even more preferably 41% by mass, and particularly preferably 42% by mass. The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease. In this case, including high molecular weight components or long-chain branched components with long relaxation times makes it easier to adjust the amount of components with a molecular weight of 100,000 or less in the polypropylene homopolymer without significantly changing the overall viscosity. This makes it easier to improve film-forming properties without significantly affecting rigidity or thermal shrinkage.

[0051] (molecular weight distribution) The lower limit of the mass-average molecular weight (Mw) / number-average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4, even more preferably 4.5, and particularly preferably 5. The upper limit of Mw / Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. Mw / Mn can be obtained using gel permeation chromatography (GPC). When Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight of 100,000 or less.

[0052] Furthermore, the molecular weight distribution of polypropylene homopolymers can be adjusted by polymerizing components of different molecular weights in a multi-step process in a series of plants, blending components of different molecular weights offline in a kneader, polymerizing by blending catalysts with different properties, or using a catalyst capable of achieving the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC can be a smooth molecular weight distribution with a single peak in a GPC chart where the horizontal axis is the logarithm of molecular weight (logM) and the vertical axis is the differential distribution value (weight fraction per logM), or it can be a molecular weight distribution with multiple peaks or shoulders.

[0053] (A copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms) The copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms used in the intermediate layer (B) is preferably a copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms in an amount of ethylene and / or α-olefins having 4 or more carbon atoms exceeding 0.3 mol%. Copolymers of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, with an ethylene and / or α-olefin component content exceeding 0.3 mol%, are preferably low in crystallinity. Examples of other α-olefins include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. The amount of ethylene and / or α-olefin components having 4 or more carbon atoms is preferably 0.4 mol% or more, and more preferably 0.6 mol% or more. Crystallinity tends to decrease when the amount is within the above range. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing propylene with one or more of the α-olefins exemplified above, and is preferably a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, or a propylene-pentene-1 copolymer. It is preferable that the copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms has a peak melting point temperature of 150°C or higher and 160°C or lower, which has the lowest DSC melting point.

[0054] The content of the copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms in an amount of ethylene and / or α-olefins having 4 or more carbon atoms exceeding 0.3 mol% is preferably 45% by weight or less, more preferably 5% by weight or more and 45% by weight or less, even more preferably 8% by weight or more and 40% by weight or less, and particularly preferably 8% by weight or more and 35% by weight or less, relative to the total polypropylene resin material used in the intermediate layer (B).

[0055] (Polypropylene resin composition) The proportion of α-olefin monomer-derived components to the total amount of propylene monomer-derived components and α-olefin monomer-derived components in the polypropylene resin composition used in the intermediate layer (B) is preferably 0.03 mol% or more and 0.4 mol% or less, more preferably 0.04 mol% or more and 0.3 mol% or less, and even more preferably 0.05 mol% or more and 0.2 mol% or less.

[0056] From the viewpoint of rigidity, the isotactic mesopentad fraction of the entire polypropylene resin composition constituting the intermediate layer (B) is preferably 95% or more. From the viewpoint of film-forming properties, it is preferably 99.5% or less.

[0057] Furthermore, the melt flow rate (MFR) of the polypropylene resin composition used in the intermediate layer (B) is preferably 5.0 g / 10 min or higher from the viewpoint of heat sealing properties. This allows for a higher level of balance between rigidity and heat resistance at high temperatures. It is more preferable to have a MFR of 6.0 g / 10 min or higher, particularly preferable to have a MFR of 7.0 g / 10 min or higher, and most preferably to have a MFR of 8.0 g / 10 min or higher.

[0058] (Antistatic agent) By using a specific amine ester compound, a specific amine compound, and a specific glycerin monofatty acid ester compound in specific proportions in the propylene resin composition constituting the intermediate layer (B), the antistatic properties can be further improved.

[0059] For example, to 100 parts by weight of the polypropylene resin composition constituting the intermediate layer (B), 0.3 to 1.2 parts by weight of a polyoxyethylene alkylamine monofatty acid ester compound (A) obtained by adding 2 moles or more of ethylene oxate to 1 mole of amine represented by general formula (1) is added. [ka] In the formula, R1 and R2 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0060] 0.03 to 1.2 parts by weight of glycerol monofatty acid ester compound (B) represented by general formula (2), [ka] In the formula, R3 is an alkyl group having 7 to 21 carbon atoms.

[0061] 0 to 0.2 parts by weight of a polyoxyethylene alkylamine difatty acid ester compound (C) obtained by adding 2 moles or more of ethylene oxate to 1 mole of an amine represented by general formula (3), [ka] In the formula, R4, R5, and R6 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0062] 0 to 0.2 parts by weight of a polyoxyethylene alkenylamine compound (D) obtained by adding 2 moles or more of ethylene oxate to 1 mole of an amine represented by general formula (4), [ka] In the formula, R7 is an alkenyl group having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30. It is preferable that it contains this.

[0063] The polyoxyethylene amine monoester compound (A) used in the present invention, obtained by adding 2 moles of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (1), and is preferably contained in a ratio of 0.3 to 1.2 parts by weight, and particularly preferably 0.3 to 1.1 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the intermediate layer (B). When the content of compound (A) is 0.3 parts by weight or more, an antistatic effect is obtained over a long period of time, and when the content is 1.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0064] The glycerin monofatty acid ester compound (B) used in the present invention is a nonionic antistatic agent represented by formula (2), where R3 is a linear or branched alkyl group, preferably an alkyl group having 10 to 21 carbon atoms, and particularly preferably an alkyl group having 14 to 20 carbon atoms, and is contained in a ratio of preferably 0.03 to 0.3 parts by weight, and particularly preferably 0.03 to 0.2 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the intermediate layer (B). When the content of compound (E) is 0.03 parts by weight or more, the antistatic effect is obtained quickly, and when the content is 1.2 parts by weight or less, the amount of bleeding is small, tackiness on the film surface is less likely to occur, and the reduction in transparency due to whitening is small.

[0065] The polyoxyethylene alkyldiethanolamine compound (C) used in the present invention, obtained by adding 2 moles or more of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (3), and is contained in a ratio of preferably 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the intermediate layer (B). When the content of compound (C) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0066] The polyoxyethylene alkenyl diethanolamine compound (D) used in the present invention, obtained by adding 2 moles or more of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (4), and is contained in a ratio of preferably 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the intermediate layer (B). When the content of compound (C) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0067] In formulas (1) to (4), X and Y are integers from 1 to 29, and X + Y is an integer from 2 to 30, preferably from 2 to 4. R1 is a linear or branched alkyl group, particularly preferably an alkyl group having 13 to 25 carbon atoms, and especially preferably an alkyl group having 13 to 18 carbon atoms.

[0068] Examples of alkyl groups R1 to R6 in formulas (1) to (3) include methyl, ethyl, propyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, nonyl, decyl, undecyl, lauryl, trilauryl, myristyl, pentadecyl, palmityl, heptadecyl, stearyl, nonadecyl, and eicosyl groups.

[0069] In formula (4), the alkenyl group R7 is preferably at least one selected from higher unsaturated aliphatic groups having 12 to 21 carbon atoms.

[0070] Furthermore, within the limits that do not impair the effects of the present invention, the polypropylene resin composition constituting the intermediate layer (B) may also contain various additives for improving quality such as slipperiness, for example, lubricants such as waxes and metal soaps for improving productivity, plasticizers, processing aids, and known heat stabilizers, antioxidants, and ultraviolet absorbers that are commonly added to polypropylene films.

[0071] (Surface layer (C)) (Polypropylene resin) When using a polypropylene resin composition for the surface layer (C) of the biaxially oriented polypropylene film of the present invention, a copolymer of the polypropylene homopolymer described below and propylene with ethylene and / or α-olefins having 4 or more carbon atoms is used, which makes it easier to improve the laminate strength while maintaining rigidity.

[0072] (Polypropylene monopolymer) The polypropylene homopolymer used for the surface layer (C) is preferably a polypropylene polymer that is substantially free of ethylene and / or α-olefins having 4 or more carbon atoms. Even if it contains ethylene and / or α-olefin components having 4 or more carbon atoms, the amount of ethylene and / or α-olefin components is preferably 0.3 mol% or less, more preferably 0.2 mol% or less, and even more preferably 0.1 mol or less. Crystallinity tends to improve within the above range. Examples of α-olefin components with 4 or more carbon atoms that constitute such copolymers include 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. Polypropylene homopolymers can be made from two or more different types of polypropylene homopolymers.

[0073] The polypropylene homopolymer content is preferably 90% by weight or less, more preferably 40% by weight or more and 90% by weight or less, even more preferably 50% by weight or more and 80% by weight or less, and particularly preferably 60% by weight or more and 70% by weight or less, relative to the total polypropylene resin used in the surface layer (C).

[0074] (stereoregularity) The mesopentade fraction ([mmmm]%), which is an indicator of the stereoregularity of polypropylene homopolymers, is preferably in the range of 97.0 to 99.9%, more preferably in the range of 97.5 to 99.7%, and within the range of 98.0 to 99.5%. More preferably, and especially preferably within the range of 98.5 to 99.3%. A mesopentad fraction of 97.0% or higher enhances the crystallinity of the polypropylene resin, improving the melting point, crystallinity, and crystal orientation of the crystals in the film, resulting in improved rigidity and heat resistance at high temperatures. A fraction of 99.9% or lower helps to reduce costs in polypropylene manufacturing and makes the film less prone to breakage during formation. The mesopentad fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. A concentration of 99.5% or less is more preferable. The mesopentade fraction is measured by nuclear magnetic resonance (NMR) spectroscopy. In order to keep the mesopentade fraction of the polypropylene homopolymer within the above-mentioned range, methods such as washing the obtained polypropylene homopolymer powder with a solvent such as n-heptane, selecting a catalyst and / or co-catalyst, and selecting components of the polypropylene resin composition are preferably employed.

[0075] (Melting temperature) The lower limit of the melting temperature (Tm) of the above polypropylene homopolymer, as measured by DSC, is preferably 160°C, more preferably 161°C, even more preferably 162°C, even more preferably 163°C, and still more preferably 164°C. A Tm of 160°C or higher makes it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tm is preferably 170°C, more preferably 169°C, even more preferably 168°C, even more preferably 167°C, and particularly preferably 166°C. A Tm of 170°C or lower makes it easier to suppress cost increases in polypropylene manufacturing and makes it less prone to rupture during film formation. The melting temperature can also be further increased by blending a crystal nucleating agent into the aforementioned polypropylene homopolymer. Tm is measured using a differential scanning calorimeter (DSC). A 1-10 mg sample is placed in an aluminum pan and set in the DSC. Under a nitrogen atmosphere, it is melted at 230°C for 5 minutes, cooled to 30°C at a scanning rate of -10°C / min, held for 5 minutes, and then heated again at a scanning rate of 10°C / min. Tm is the main peak temperature of the endothermic peak observed during melting.

[0076] (crystallization temperature) The lower limit of the crystallization temperature (Tc) of polypropylene homopolymer is 105°C, preferably 108°C, and more preferably 110°C. When Tc is 105°C or higher, crystallization proceeds easily during the widthwise stretching and subsequent cooling process, making it easier to obtain rigidity and heat resistance at high temperatures. The upper limit of Tc is preferably 135°C, more preferably 133°C, even more preferably 132°C, even more preferably 130°C, particularly preferably 128°C, and most preferably 127°C. When Tc is 135°C or lower, it is less likely to increase the cost of polypropylene production and the film is less likely to break during film formation. The crystallization temperature can also be further increased by incorporating a crystal nucleating agent into the aforementioned polypropylene homopolymer. Tc is measured using a differential scanning calorimeter (DSC). A 1-10 mg sample is placed in an aluminum pan, set in the DSC, melted at 230°C for 5 minutes under a nitrogen atmosphere, and then cooled to 30°C at a scanning rate of -10°C / min. Tc is the main peak temperature of the exothermic peak observed during this process.

[0077] (Melt flow rate) The MFR of polypropylene homopolymer, when measured according to the conditions M (230°C, 2.16 kgf) of JIS K 7210 (1995), is preferably 4.0 to 30 g / 10 min, more preferably 4.5 to 25 g / 10 min, even more preferably 4.8 to 22 g / 10 min, particularly preferably 5.0 to 20 g / 10 min, and most preferably 6.0 to 20 g / 10 min. When the MFR of the polypropylene homopolymer is 4.0 g / 10 min or higher, it is easier to obtain a biaxially oriented polypropylene film with low thermal shrinkage. Furthermore, if the MFR of the polypropylene homopolymer is 30 g / 10 min or less, it is easier to maintain film-forming properties.

[0078] From the viewpoint of film properties, the lower limit of the MFR (230°C, 2.16 kgf) of the polypropylene homopolymer is preferably 5.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 6.0 g / 10 min, particularly preferably 6.3 g / 10 min, and most preferably 6.5 g / 10 min. When the MFR of the polypropylene homopolymer is 5.0 g / 10 min or higher, the amount of low molecular weight components in the polypropylene homopolymer constituting the film increases. Therefore, by employing the widthwise stretching process in the film manufacturing process described later, the orientation and crystallization of the polypropylene resin are further promoted, and the degree of crystallinity in the film tends to increase. In addition, the entanglement between polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. In order to keep the MFR of the polypropylene homopolymer within the above range, it is preferable to employ methods to control the average molecular weight and molecular weight distribution of the polypropylene resin.

[0079] In other words, the lower limit of the amount of components with a molecular weight of 100,000 or less in the gel permuration chromatography (GPC) integrated curve of the polypropylene homopolymer is 35% by mass, preferably 38% by mass, more preferably 40% by mass, even more preferably 41% by mass, and particularly preferably 42% by mass. The upper limit of the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is preferably 65% ​​by mass, more preferably 60% by mass, and even more preferably 58% by mass. When the amount of components with a molecular weight of 100,000 or less in the GPC integrated curve is 65% by mass or less, the film strength is less likely to decrease. In this case, including high molecular weight components or long-chain branched components with long relaxation times makes it easier to adjust the amount of components with a molecular weight of 100,000 or less in the polypropylene homopolymer without significantly changing the overall viscosity. This makes it easier to improve film-forming properties without significantly affecting rigidity or thermal shrinkage.

[0080] (molecular weight distribution) The lower limit of the mass-average molecular weight (Mw) / number-average molecular weight (Mn), which is an indicator of the breadth of the molecular weight distribution, is preferably 3.5, more preferably 4, even more preferably 4.5, and particularly preferably 5. The upper limit of Mw / Mn is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. Mw / Mn can be obtained using gel permeation chromatography (GPC). When Mw / Mn is within the above range, it is easy to increase the amount of components with a molecular weight of 100,000 or less.

[0081] Furthermore, the molecular weight distribution of polypropylene homopolymers can be adjusted by polymerizing components of different molecular weights in a multi-step process in a series of plants, blending components of different molecular weights offline in a kneader, polymerizing by blending catalysts with different properties, or using a catalyst capable of achieving the desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC can be a smooth molecular weight distribution with a single peak in a GPC chart where the horizontal axis is the logarithm of molecular weight (logM) and the vertical axis is the differential distribution value (weight fraction per logM), or it can be a molecular weight distribution with multiple peaks or shoulders.

[0082] (A copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms) The copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms used in the surface layer (C) is preferably a copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms with an ethylene and / or α-olefin component amount exceeding 0.3 moles. Copolymers of propylene and ethylene and / or α-olefins having 4 or more carbon atoms, with an ethylene and / or α-olefin component content exceeding 0.3 moles, are preferably low in crystallinity. Examples of other α-olefins include ethylene, 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. The amount of ethylene and / or α-olefin components having 4 or more carbon atoms is preferably 0.4 mol% or more, and more preferably 0.5 mol% or more. Crystallinity tends to decrease within the above range. Here, the copolymer is preferably a random or block copolymer obtained by polymerizing propylene with one or more of the α-olefins exemplified above, and is preferably a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, or a propylene-pentene-1 copolymer.

[0083] It is preferable that the copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms has a peak melting point temperature of 150°C or higher and 160°C or lower, which has the lowest DSC melting point.

[0084] The content of the copolymer of propylene and ethylene and / or α-olefins having 4 or more carbon atoms in an amount exceeding 0.3 moles is more preferably 10% by weight or more, more preferably 10% by weight or more and 60% by weight or less, even more preferably 20% by weight or more and 50% by weight or less, and particularly preferably 30% by weight or more and 50% by weight or less, relative to the total polypropylene resin used in the surface layer (C).

[0085] (Polypropylene resin composition) The proportion of α-olefin monomer-derived components to the total amount of propylene monomer-derived components and α-olefin monomer-derived components in the polypropylene resin composition used in the surface layer (C) is preferably 0.10 mol% or more and 0.4 mol% or less, more preferably 0.15 mol% or more and 0.2 mol% or less, and even more preferably 0.2 mol% or more and 0.25 mol% or less.

[0086] From the viewpoint of rigidity, the isotactic mesopentad fraction of the entire polypropylene resin composition constituting the surface layer (C) is preferably 95% or more. From the viewpoint of film-forming properties, it is preferably 99.5% or less.

[0087] Furthermore, the melt flow rate (MFR) of the polypropylene resin composition used in the surface layer (C) is preferably 5.0 g / 10 min or higher from the viewpoint of heat sealing properties. This allows for a higher level of balance between rigidity and heat resistance at high temperatures. It is more preferable to have a MFR of 6.0 g / 10 min or higher, particularly preferable to have a MFR of 7.0 g / 10 min or higher, and most preferably to have a MFR of 8.0 g / 10 min or higher.

[0088] (Antistatic agent) By using a specific amine ester compound, a specific amine compound, and a specific glycerin monofatty acid ester compound in a specific ratio in the propylene resin composition constituting the surface layer (C), the antistatic properties can be further improved.

[0089] For example, 0.3 to 1.2 parts by weight of a polyoxyethylene alkylamine monofatty acid ester compound (A) is added to 1 mole of ethylene oxate per mole of amine represented by general formula (1) for 100 parts by weight of the polypropylene resin composition constituting the surface layer (C). [ka] In the formula, R1 and R2 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0090] 0.03 to 1.2 parts by weight of a glycerol monofatty acid ester compound (B) represented by the following formula (2), [ka] In the formula, R3 is an alkyl group having 7 to 21 carbon atoms.

[0091] 0 to 0.2 parts by weight of a polyoxyethylene alkylamine difatty acid ester compound (C) obtained by adding 2 moles or more of ethylene oxate to 1 mole of an amine represented by the following formula (3), [ka] In the formula, R4, R5, and R6 are alkyl groups having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30.

[0092] 0 to 0.2 parts by weight of a polyoxyethylene alkenylamine compound (D) obtained by adding 2 moles or more of ethylene oxate to 1 mole of an amine represented by the following formula (4), [ka] In the formula, R7 is an alkenyl group having 7 to 21 carbon atoms, X and Y are integers from 1 to 29, and X+Y is an integer from 2 to 30. It is preferable that it contains this.

[0093] The polyoxyethylene alkylamine monofatty acid ester compound (A) used in the present invention, obtained by adding 2 moles of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (1), and is preferably contained in a ratio of 0.3 to 1.2 parts by weight, and particularly preferably 0.3 to 1.1 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the surface layer (C). When the content of compound (A) is 0.3 parts by weight or more, an antistatic effect is obtained over a long period of time, and when the content is 1.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0094] The glycerin monofatty acid ester compound (B) used in the present invention is a nonionic antistatic agent represented by formula (2), where R3 is a linear or branched alkyl group, preferably an alkyl group having 10 to 21 carbon atoms, and particularly preferably an alkyl group having 14 to 20 carbon atoms, and is contained in a ratio of preferably 0.03 to 0.3 parts by weight, and particularly preferably 0.03 to 0.2 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the surface layer (C). When the content of compound (E) is 0.03 parts by weight or more, the antistatic effect is obtained quickly, and when the content is 1.2 parts by weight or less, the amount of bleeding is small, stickiness on the film surface is less likely to occur, and the reduction in transparency due to whitening is small.

[0095] The polyoxyethylene alkylamine difatty acid ester compound (C) used in the present invention, obtained by adding 2 moles or more of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (3), and is preferably contained in a ratio of 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the surface layer (C). When the content of compound (C) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0096] The polyoxyethylene alkenylamine compound (D) used in the present invention, obtained by adding 2 moles or more of ethylene oxate to 1 mole of amine, is a nonionic antistatic agent represented by formula (4), and is contained in a ratio of preferably 0 to 0.2 parts by weight, and particularly preferably 0.002 to 0.15 parts by weight, per 100 parts by weight of the polypropylene resin composition constituting the surface layer (C). When the content of compound (D) is 0.2 parts by weight or less, the amount of bleeding is small and the decrease in transparency due to whitening is small.

[0097] In formulas (1) to (4), X and Y are integers from 1 to 29, and X + Y is an integer from 2 to 30, preferably from 2 to 4. R1 is a linear or branched alkyl group, particularly preferably an alkyl group having 13 to 25 carbon atoms, and especially preferably an alkyl group having 13 to 18 carbon atoms.

[0098] Examples of alkyl groups R1 to R6 in formulas (1) to (3) include methyl, ethyl, propyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, nonyl, decyl, undecyl, lauryl, trilauryl, myristyl, pentadecyl, palmityl, heptadecyl, stearyl, nonadecyl, and eicosyl groups.

[0099] In formula (4), the alkenyl group R7 is preferably at least one selected from higher unsaturated aliphatic groups having 12 to 21 carbon atoms.

[0100] Furthermore, within the limits that do not impair the effects of the present invention, the polypropylene resin composition constituting the surface layer (C) may also contain various additives for improving quality such as slipperiness, for example, lubricants such as waxes and metal soaps for improving productivity, plasticizers, processing aids, and known heat stabilizers, antioxidants, ultraviolet absorbers, and inorganic or organic fine particles that are commonly added to polypropylene films.

[0101] Examples of inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite. These particles can be spherical, elliptical, conical, or amorphous, and their particle size can be customized to suit the film's intended use and application. Furthermore, as organic fine particles, cross-linked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and in terms of shape and size, a wide variety of options are available, similar to inorganic fine particles. In addition, various surface treatments can be applied to the surface of these inorganic or organic fine particles, and these can be used individually or in combination of two or more. The above also applies to the surface layer (B) described later.

[0102] (Film layer composition) The biaxially oriented polypropylene film of the present invention may have a three-layer structure of base layer (A) / intermediate layer (B) / surface layer (C), a four-layer structure of surface layer (C) / base layer (A) / intermediate layer (B) / surface layer (C), or a six-layer structure of surface layer (C) / intermediate layer (B) / base layer (A) / intermediate layer (B) / surface layer (C).

[0103] (Film thickness) The total thickness of the biaxially oriented polypropylene resin film of the present invention varies depending on its application and method of use, but is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, from the viewpoint of film strength, sealing properties, or water vapor barrier properties. Furthermore, in terms of high-speed packaging processability or visibility, a particle size of 60 μm or less is preferred, 50 μm or less is more preferred, 45 μm or less is particularly preferred, and 40 μm or less is most preferred.

[0104] The thickness of the substrate layer (A) varies depending on its application and method of use, but is preferably 10 μm or more in terms of film rigidity and water vapor barrier properties. In terms of transparency and environmental impact, it is preferably 50 μm or less, more preferably 45 μm or less, even more preferably 40 μm or less, and particularly preferably 37 μm or less. The thickness of the intermediate layer (B) varies depending on its application and usage, but in terms of film lamination strength and antistatic properties, it is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 4 μm or more.

[0105] The thickness of the intermediate layer (B) varies depending on its application and usage, but in terms of film rigidity and heat resistance at high temperatures, it is preferably 8 μm or less, and more preferably 6 μm or less. The ratio of the thickness of the intermediate layer (B) to the total thickness of the biaxially oriented polypropylene resin film is preferably 5% or more from the viewpoint of rigidity and heat resistance at high temperatures, more preferably 10% or more, and even more preferably 15% or more.

[0106] The ratio of the thickness of the intermediate layer (B) to the total thickness of the biaxially oriented polypropylene resin film is preferably 30% or less from the viewpoint of rigidity and heat resistance at high temperatures, and more preferably 25% or less. The thickness of the surface layer (C) varies depending on its application and usage, but in terms of film lamination strength and antistatic properties, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.8 μm or more. The thickness of the surface layer (C) varies depending on its application and usage, but it is preferably 4 μm or less, and more preferably 3 μm or less, in terms of film rigidity and heat resistance at high temperatures.

[0107] The ratio of the thickness of the surface layer (C) to the total thickness of the biaxially oriented polypropylene resin film is preferably 2% or more from the viewpoint of rigidity and heat resistance at high temperatures, more preferably 3% or more, and even more preferably 4% or more. The ratio of the thickness of the surface layer (C) to the total thickness of the biaxially oriented polypropylene resin film is preferably 20% or less from the viewpoint of rigidity and heat resistance at high temperatures, and more preferably 15% or less.

[0108] (Method for producing biaxially oriented polypropylene film) The biaxially oriented polypropylene film of the present invention is preferably obtained by preparing an unstretched sheet made from a polypropylene resin composition mainly composed of the polypropylene resin described above, and then biaxially stretching it. The biaxial stretching can be performed by any of the following methods: simultaneous inflation biaxial stretching, simultaneous tenter biaxial stretching, or sequential tenter biaxial stretching. However, sequential tenter biaxial stretching is preferred from the viewpoint of film formation stability and thickness uniformity. In particular, it is preferable to stretch in the longitudinal direction first, followed by stretching in the width direction, but a method of stretching in the width direction first, followed by stretching in the longitudinal direction is also acceptable.

[0109] Next, the method for producing the biaxially oriented polypropylene film of the present invention will be described below, but is not necessarily limited thereto. The following describes an example of a surface layer (C) / intermediate layer (B) / base layer (A) / intermediate layer (B) / surface layer (C) when using the tenter sequential biaxial stretching method. First, a multilayer sheet of molten polypropylene resin composition consisting of a surface layer (C) / intermediate layer (B) / base layer (A) / intermediate layer (B) / surface layer (C) is extruded from a T-die. One possible method is to use three or more extruders to co-extrude thermoplastic resins fed from different flow paths, while simultaneously laminating them in multiple layers using a multilayer feed block, static mixer, multilayer multi-manifold die, etc. Furthermore, it is possible to introduce the aforementioned multilayering device into the melt line from the extruder to the T-type die using only one extruder. From the viewpoint of stabilizing back pressure and suppressing thickness fluctuations, a method of installing a gear pump in the polymer flow path is preferred. The molten sheet, co-extruded from a T-die into a sheet, is placed on a metal cooling roll for cooling and solidification. To accelerate solidification, it is preferable to further cool the sheet cooled on the cooling roll by immersing it in a water tank or similar method.

[0110] Next, the sheet is stretched longitudinally by increasing the rotation speed of the rear stretching roll using two heated stretching rolls, thereby obtaining a uniaxially oriented film.

[0111] Next, after preheating the uniaxially oriented film, the film is stretched in the width direction at a specific temperature using a tenter-type stretcher while gripping the film edges, thereby obtaining a biaxially oriented film. This width-direction stretching process will be described in detail later.

[0112] After the widthwise stretching process is completed, the biaxially oriented film is heat-treated at a specific temperature to obtain a biaxially oriented film. During the heat treatment process, the film may be relaxed in the widthwise direction.

[0113] The biaxially oriented polypropylene film thus obtained can be subjected to corona discharge treatment on, for example, at least one side, as needed, and then wound up with a winder to obtain a film roll.

[0114] The following sections will explain each step in detail. (Extrusion process) The temperature of the cooling roll, or the temperature of the cooling roll and water bath, is preferably in the range of 10°C to Tc. If you want to increase the transparency of the film, it is preferable to cool and solidify it with a cooling roll at a temperature in the range of 10 to 50°C. Lowering the cooling temperature to 50°C or below tends to increase the transparency of the unstretched sheet, so it is preferably 40°C or below, and more preferably 30°C or below. In order to increase the degree of crystal orientation after sequential biaxial stretching, it may be preferable to set the cooling temperature to 40°C or below when using a propylene homopolymer with a mesopentat fraction of 97.0% or more, as described above, in order to facilitate the stretching in the next step and reduce thickness variations, it is preferable to set the cooling temperature to 40°C or below, and more preferably 30°C or below. The thickness of the unstretched sheet is preferably 3500 μm or less for optimal cooling efficiency, and more preferably 3000 μm or less. This can be adjusted as appropriate depending on the film thickness after sequential biaxial stretching. The thickness of the unstretched sheet can be controlled by the extrusion speed of the polypropylene resin composition and the lip width of the T-die, etc.

[0115] (Longitudinal stretching process) The lower limit of the longitudinal stretching ratio is preferably 3 times, more preferably 3.5 times, and particularly preferably 3.8 times. Within this range, it is easier to increase strength and reduce film thickness unevenness. The upper limit of the longitudinal stretching ratio is preferably 8 times, more preferably 7.5 times, and particularly preferably 7 times. Within this range, it is easier to perform the widthwise stretching process, and productivity is improved. The lower limit of the longitudinal stretching temperature is preferably Tm-40°C, more preferably Tm-37°C, and even more preferably Tm-35°C. Within this range, subsequent widthwise stretching is facilitated and thickness unevenness is reduced. The upper limit of the longitudinal stretching temperature is preferably Tm-7°C, more preferably Tm-10°C, and even more preferably Tm-12°C. Within this range, the thermal shrinkage rate is easily reduced, making it less difficult to stretch the material by attaching it to the stretching rolls, and reducing the quality by increasing surface roughness. Furthermore, longitudinal stretching may be performed in two or more stages using three or more stretching rolls.

[0116] (Preheating process) Before the widthwise stretching process, the uniaxially oriented film after longitudinal stretching must be heated to a temperature range of Tm to Tm+25°C to soften the polypropylene resin composition. Tm is the melting point of the polypropylene homopolymer constituting the base layer. Setting the temperature above Tm promotes softening and facilitates widthwise stretching. Setting the temperature below Tm+25°C promotes orientation during transverse stretching and facilitates the development of rigidity. More preferably, the temperature is Tm+2 to Tm+22°C, and particularly preferably Tm+3 to Tm+20°C. Here, the highest temperature reached during the preheating process is defined as the preheating temperature.

[0117] (Width direction stretching process) In the widthwise stretching process after the preheating process, the preferred method is as follows:

[0118] In the widthwise stretching process, a section (early section) is provided in which stretching is performed at a temperature of Tm -10°C or higher and below the preheating temperature. At this time, the start of the early section may be when the preheating temperature is reached, or it may be when the temperature is lowered after reaching the preheating temperature and reaches a temperature lower than the preheating temperature. The lower limit of the temperature in the initial stage of the widthwise stretching process is preferably Tm°C, more preferably Tm+1°C, and even more preferably Tm+3°C. When the stretching temperature in the initial stage is within this range, shrinkage at high temperatures is easily reduced, the surface orientation coefficient does not become too high, and the laminate strength is easily improved. Following the initial section, a section (later section) may be added where the temperature is lower than that of the initial section, but between Tm-70°C and Tm-5°C. Alternatively, the lateral extension may continue at the same temperature as the initial section. The upper limit of the stretching temperature in the later stage is preferably Tm-8°C, and more preferably Tm-10°C. Stiffness is more easily developed when the stretching temperature in the later stage is within this range. The lower limit of the stretching temperature in the later stage is preferably Tm-65°C, more preferably Tm-60°C, and even more preferably Tm-55°C. Film formation is more stable when the stretching temperature in the later stage is within this range.

[0119] It is preferable to cool the film at the end of the later stage, or immediately after continuing to stretch it laterally at the temperature from the earlier stage and reaching the final stretch ratio in the width direction. The cooling temperature at this time is preferably below the temperature of the later stage, and preferably between Tm-80°C and Tm-15°C, more preferably between Tm-80°C and Tm-20°C, even more preferably between Tm-80°C and Tm-30°C, and particularly preferably between Tm-70°C and Tm-40°C. The temperatures in the initial and later stages can be gradually decreased, but they can also be decreased in stages or in a single step, and they may remain constant. Gradually decreasing the temperature makes it less likely for the film to break and also helps to minimize variations in film thickness. It is also preferable because it helps to reduce the thermal shrinkage rate and minimizes film whitening. In the widthwise stretching process, the temperature from the end of the initial stage to the start of the later stage can be gradually decreased, but it can also be decreased in stages or in a single step.

[0120] If a later section is provided, the lower limit of the stretching ratio at the end of the earlier section of the widthwise stretching process is preferably 5 times, more preferably 6 times, and even more preferably 7 times. The upper limit of the stretching ratio at the end of the earlier section is preferably 15 times, more preferably 14 times, and even more preferably 13 times.

[0121] If a later stage is included, the lower limit of the final widthwise stretching ratio in the widthwise stretching process is preferably 7 times, more preferably 8 times, even more preferably 9 times, and particularly preferably 10 times. A ratio of 7 times or higher makes it easier to increase rigidity and reduce unevenness in film thickness. The upper limit of the widthwise stretching ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. A ratio of 20 times or lower makes it easier to reduce the thermal shrinkage rate and makes it less likely to break during stretching.

[0122] If the lateral stretching is continued at the temperature of the initial stage without a later stage, the lower limit of the final widthwise stretching ratio in the widthwise stretching process is preferably 10 times, more preferably 11 times. A ratio of 10 times or more makes it easier to increase rigidity and reduce unevenness in film thickness. The upper limit of the widthwise stretching ratio is preferably 20 times, more preferably 17 times, and even more preferably 15 times. A ratio of 20 times or less makes it easier to reduce the thermal shrinkage rate and makes it less likely to break during stretching.

[0123] Thus, by using a highly crystalline polypropylene resin with high stereoregularity and a high melting point, and employing the widthwise stretching process described above, the molecules of the polypropylene resin align to a high degree in the principal orientation direction (the widthwise direction in the widthwise stretching process described above) even without extremely high stretching ratios. As a result, the resulting biaxially oriented film has very strong crystal orientation, and crystals with high melting points are easily formed. Furthermore, the orientation of the amorphous regions between crystals increases in the main orientation direction (which corresponds to the width direction in the width direction stretching process described above). Because there are many crystals with high melting points around the amorphous regions, the elongated polypropylene molecules in the amorphous regions do not easily relax at temperatures below the melting point of the crystals, and tend to maintain their tensioned state. Therefore, the entire biaxially oriented film can maintain high rigidity even at high temperatures. Furthermore, it is noteworthy that employing this widthwise stretching process also tends to reduce the thermal shrinkage rate at high temperatures of 150°C. The reason for this is that there are many crystals with high melting points surrounding the amorphous region, so at temperatures lower than the melting point of the crystals, the stretched polypropylene resin molecules in the amorphous region do not relax easily, and there is less entanglement between the molecules.

[0124] Furthermore, it is noteworthy that increasing the low molecular weight components of the polypropylene resin makes it easier to achieve a higher degree of crystallinity in the film, and also reduces the entanglement of polypropylene resin molecular chains in the amorphous portion, thereby weakening the thermal shrinkage stress and further lowering the thermal shrinkage rate. Considering that conventionally, improving either strength or thermal shrinkage rate tends to decrease the other property, this can be considered a groundbreaking development.

[0125] (Heat treatment process) Biaxially oriented films can be heat-treated as needed to further reduce their thermal shrinkage. The upper limit of the heat treatment temperature is preferably Tm+10°C, and more preferably Tm+7°C. Lowering the temperature to Tm+10°C or below facilitates the development of rigidity, prevents excessive roughness on the film surface, and reduces the likelihood of film whitening. The lower limit of the heat treatment temperature is preferably Tm-10°C, and more preferably Tm-7°C. Lowering the temperature to Tm-10°C may result in a higher thermal shrinkage. By employing the widthwise stretching process described above, even when heat treatment is performed at temperatures between Tm-10°C and Tm+10°C, the highly oriented crystals generated in the stretching process are less likely to melt, and the thermal shrinkage rate can be reduced without decreasing the rigidity of the resulting film. To adjust the thermal shrinkage rate, the film may be relaxed (relaxed) in the widthwise direction during heat treatment. The upper limit of the relaxation rate is preferably 10%. Within this range, the film strength is less likely to decrease, and the variation in film thickness tends to be small. More preferably 8%, even more preferably 7%, even more preferably 3%, particularly preferably 2%, and most preferably 0%.

[0126] (Film thickness) The thickness of the biaxially oriented polypropylene film of the present invention is set according to each application, but in order to obtain the strength of the film, the lower limit of the film thickness is preferably 10 μm, more preferably 12 μm, even more preferably 14 μm, and particularly preferably 16 μm. When the film thickness is 2 μm or more, it is easier to obtain the rigidity of the film. The upper limit of the film thickness is preferably 100 μm, more preferably 70 μm, even more preferably 50 μm, particularly preferably 40 μm, and most preferably 30 μm. When the film thickness is 100 μm or less, the cooling rate of the unstretched sheet during the extrusion process does not tend to decrease. The biaxially oriented polypropylene film of the present invention is typically manufactured as a roll with a width of 2,000 to 12,000 mm and a length of 1,000 to 50,000 m, and then wound into a film roll. Furthermore, it is slit according to various applications and supplied as slit rolls with a width of 300 to 2,000 mm and a length of 500 to 5,000 m. The biaxially oriented polypropylene film of the present invention makes it possible to obtain longer film rolls.

[0127] The antistatic biaxially oriented polypropylene resin film used in the present invention may be subjected to surface treatment by conventionally known methods such as corona discharge treatment, plasma treatment, ozone treatment, or chemical treatment, or anchor treatment using known anchoring agents, depending on the purpose. In particular, antistatic properties can be improved by performing corona discharge treatment, plasma treatment, and ozone treatment. For example, it is preferable to perform corona treatment on the film surface of the obtained biaxially oriented polypropylene film that is in contact with the cooling roll using a corona treatment machine such as one manufactured by Softal Corona and Plasma GmbH, under the condition that the applied current value is 0.30 to 2.0 A, more preferably 0.50 to 2.0 A, even more preferably 0.80 to 2.0 A, and particularly preferably 1.5 to 2.0 A.

[0128] (Uniformity of thickness) The lower limit of the thickness uniformity of the biaxially oriented polypropylene film of the present invention is preferably 0%, more preferably 0.1%, even more preferably 0.5%, and particularly preferably 1%. The upper limit of the thickness uniformity is preferably 20%, more preferably 17%, even more preferably 15%, particularly preferably 12%, and most preferably 10%. Within the above range, defects are less likely to occur during post-processing such as coating and printing, making it easy to use in applications requiring precision. The measurement method was as follows: A 40 mm wide test piece was cut from the steady-state region where the film properties were stable in the length direction of the film. The film thickness was continuously measured over 20,000 mm using a film feeding device manufactured by Micron Measuring Instruments Co., Ltd. (product number: A90172) and a continuous film thickness measuring instrument manufactured by Anritsu Corporation (product name: K-313A wide-range high-sensitivity electronic micrometer), and the thickness uniformity was calculated from the following formula. Thickness uniformity (%) = [(Maximum thickness - Minimum thickness) / Average thickness] × 100

[0129] (Film characteristics) The biaxially oriented polypropylene film of the present invention is characterized by the following properties. Here, the "longitudinal direction" in the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film manufacturing process, and the "width direction" refers to the direction perpendicular to the flow direction in the film manufacturing process. For polypropylene films in which the flow direction in the film manufacturing process is unknown, wide-angle X-rays are incident perpendicular to the film surface, and the scattering peaks originating from the (110) plane of the α-type crystal are scanned in the circumferential direction. The direction with the largest diffraction intensity in the obtained diffraction intensity distribution is defined as the "width direction," and the direction perpendicular to it is defined as the "longitudinal direction."

[0130] (Stress at 23°C and 5% elongation) The lower limit of the stress (F5) of the biaxially oriented polypropylene film of the present invention at 23°C with 5% elongation in the longitudinal direction is 40 MPa, preferably 42 MPa, more preferably 43 MPa, even more preferably 44 MPa, and particularly preferably 45 MPa. Above 40 MPa, the rigidity is high, making it easier to maintain the shape of the bag when used as a packaging bag, and preventing deformation of the film during processing such as printing. The upper limit of F5 in the longitudinal direction is preferably 70 MPa, more preferably 65 MPa, even more preferably 62 MPa, particularly preferably 61 MPa, and most preferably 60 MPa. Below 70 MPa, practical manufacturing is easier, and the balance of the vertical width is easier to achieve.

[0131] The lower limit of F5 in the width direction at 23°C for the biaxially oriented polypropylene film of the present invention is 160 MPa, preferably 165 MPa, more preferably 168 MPa, and even more preferably 170 MPa. Above 160 MPa, the rigidity is high, making it easier to maintain the shape of the bag when used as a packaging bag, and preventing deformation of the film during processing such as printing. The upper limit of F5 in the width direction is preferably 250 MPa, more preferably 245 MPa, and even more preferably 240 MPa. Below 250 MPa, practical manufacturing is easier, and the vertical-to-width balance is easier to achieve. F5 can be brought within the range by adjusting the stretching ratio, relaxation rate, and temperature during film formation.

[0132] (Heat shrinkage rate at 150°C) The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 150°C is 10%, preferably 7.0%, more preferably 6.0%, particularly preferably 4.5%, and most preferably 3.0%. The upper limit of the widthwise heat shrinkage rate at 150°C is 30%, preferably 16%, more preferably 15%, particularly preferably 12%, and most preferably 10%. When the longitudinal heat shrinkage rate is 10% or less and the widthwise heat shrinkage rate is 30% or less, wrinkles are less likely to occur during heat sealing. In particular, when the longitudinal heat shrinkage rate at 150°C is 8.0% or less and the widthwise heat shrinkage rate at 150°C is 15% or less, the distortion when fusing the chuck portion to the opening portion is extremely small, which is preferable. To reduce the heat shrinkage rate at 150°C, it is effective to set the lower limit of the amount of components with a molecular weight of 100,000 or less, when the gel permeation chromatography (GPC) integrated curve of the polypropylene resin constituting the film is measured, to 35% by mass.

[0133] (Lamination strength) The lower limit of the longitudinal lamination strength of the biaxially oriented polypropylene film of the present invention is preferably 1.2 N / 15 mm, more preferably 1.3 N / 15 mm, even more preferably 1.4 N / 15 mm, even more preferably 1.5 N / 15 mm, and particularly preferably 1.6 N / 15 mm. A strength of 1.2 N / 15 mm or higher tends to reduce the likelihood of packaging bags tearing. The upper limit of the longitudinal lamination strength is preferably 2.7 N / 15 mm as a practical value, and more preferably 2.5 N / 15 mm.

[0134] The lower limit of the lamination strength in the width direction of the biaxially oriented polypropylene film of the present invention is 1.0 N / 15 mm, preferably 1.1 N / 15 mm, more preferably 1.2 N / 15 mm, even more preferably 1.3 N / 15 mm, particularly preferably 1.4 N / 15 mm, and most preferably 1.5 N / 15 mm. A strength of 1.0 N / 15 mm or higher tends to reduce the likelihood of packaging bags tearing. The upper limit of the lamination strength in the width direction is preferably 2.5 N / 15 mm as a practical value, and more preferably 2.2 N / 15 mm.

[0135] The biaxially oriented polypropylene film of the present invention is preferable if it has the following properties and structure.

[0136] (Heat shrinkage rate at 120°C) The upper limit of the longitudinal heat shrinkage rate of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.0%, more preferably 1.7%, even more preferably 1.5%, and particularly preferably 1.0%. If it is 2.0% or less, misalignment of the printing pitch when transferring printing ink becomes less likely. The upper limit of the widthwise heat shrinkage rate at 120°C is 5.0%, preferably 4.0%, more preferably 3.0%, even more preferably 2.0%, and particularly preferably 1.5%. If it is 5.0% or less, wrinkles are less likely to occur during heat sealing. If the longitudinal heat shrinkage rate at 120°C is smaller than the widthwise heat shrinkage rate at 120°C, misalignment of the print pitch during ink transfer becomes less likely. The balance between the longitudinal and widthwise heat shrinkage rates at 120°C can be kept within a certain range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0137] (Refractive index) The lower limit of the longitudinal refractive index (Nx) of the biaxially oriented polypropylene film of the present invention is preferably 1.4970, more preferably 1.4990, even more preferably 1.5000, and particularly preferably 1.5020. A value of 1.4970 or higher tends to increase the rigidity of the film. The upper limit of the longitudinal refractive index (Nx) is preferably 1.5100, more preferably 15070, and even more preferably 1.5050. A value of 1.5100 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0138] The lower limit of the refractive index (Ny) in the width direction of the biaxially oriented polypropylene film of the present invention is 1.5230, preferably 1.5240, and more preferably 1.5250. A refractive index of 1.5230 or higher tends to increase the rigidity of the film. The upper limit of the refractive index (Ny) in the width direction is preferably 1.5280, more preferably 1.5275, and even more preferably 1.5270. A refractive index of 1.5280 or lower tends to provide a good balance of longitudinal-width properties of the film.

[0139] The lower limit of the refractive index (Nz) in the thickness direction of the biaxially oriented polypropylene film of the present invention is preferably 1.4960, more preferably 14970, even more preferably 1.4990, and particularly preferably 1.5000. A refractive index of 1.4960 or higher makes it easier to increase the rigidity of the film. The upper limit of the refractive index (Nz) in the thickness direction is preferably 1.5020, more preferably 1.5015, and even more preferably 1.5010. A refractive index of 1.5020 or lower makes it easier to increase the heat resistance of the film. The refractive index can be kept within a specified range by adjusting the stretching ratio, stretching temperature, and heat-fixing temperature.

[0140] (△Ny) The lower limit of △Ny, which is the degree of orientation in the width direction of the biaxially oriented polypropylene film of the present invention, is 0.0220, preferably 0.0230, more preferably 0.0235, and still more preferably 0.0240. If it is 0.0220 or higher, the rigidity of the film tends to be high. The upper limit of △Ny is preferably 0.0270 as a practical value, more preferably 0.0265, still more preferably 0.0262, and particularly preferably 0.0260. If it is 0.0270 or lower, thickness uniformity tends to be good. △Ny can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature of the film. △Ny is calculated using the following formula, where Nx, Ny, and Nz are the refractive indices along the longitudinal, width, and thickness directions of the film, respectively. It represents the degree of orientation in the width direction within the overall orientation of the film in the longitudinal, width, and thickness directions. △Ny=Ny-[(Nx+Nz) / 2]

[0141] (Coefficient of surface orientation) The lower limit of the plane orientation coefficient (ΔP) of the biaxially oriented polypropylene film of the present invention is preferably 0.0135, more preferably 0.0138, and even more preferably 0.0140. A value of 0.0135 or higher indicates good balance in the plane direction of the film and good thickness uniformity. The upper limit of the plane orientation coefficient (ΔP) is preferably 0.0155, more preferably 0.0152, and even more preferably 0.0150 as a practical value. A value of 0.0155 or lower tends to result in excellent heat resistance at high temperatures. The plane orientation coefficient (ΔP) can be brought within the range by adjusting the stretching ratio, stretching temperature, and heat setting temperature. Furthermore, the surface orientation coefficient (ΔP) was calculated using the formula [(Nx+Ny) / 2]-Nz.

[0142] (Hayes) The upper limit of the haze of the biaxially oriented polypropylene film of the present invention is preferably 5.0%, more preferably 4.5%, even more preferably 4.0%, particularly preferably 3.5%, and most preferably 3.0%. A haze of 5.0% or less makes it easy to use in applications where transparency is required. The lower limit of the haze is preferably 0.1%, more preferably 0.2%, even more preferably 0.3%, and particularly preferably 0.4% as a practical value. A haze of 0.1% or more makes it easy to manufacture. The haze can be kept within the range by adjusting the cooling roll (CR) temperature, the widthwise stretching temperature, the tenter preheating temperature before widthwise stretching, the widthwise stretching temperature, or the heat setting temperature, or the amount of components with a molecular weight of 100,000 or less in the polypropylene resin, but it may increase with the addition of anti-blocking agents or the application of a sealing layer.

[0143] (Practical characteristics of the film) The practical properties of the biaxially oriented polypropylene film of the present invention will be described below. (Tensile breaking strength) The lower limit of the longitudinal tensile breaking strength of the biaxially oriented polypropylene film of the present invention is preferably 90 MPa, more preferably 95 MPa, and even more preferably 100 MPa. A tensile breaking strength of 90 MPa or higher reduces the likelihood of misalignment of the printing pitch when transferring printing ink, and also improves the durability of the packaging bag. The upper limit of the longitudinal tensile breaking strength is preferably 200 MPa, more preferably 190 MPa, and even more preferably 180 MPa as a practical value. A tensile breaking of 200 MPa or lower tends to reduce film breakage and packaging bag rupture.

[0144] The lower limit of the tensile breaking strength in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 320 MPa, more preferably 340 MPa, and even more preferably 350 MPa. A strength of 320 MPa or higher reduces the likelihood of misalignment of the printing pitch when transferring printing ink, and also improves the durability of the packaging bag. The upper limit of the tensile breaking strength in the width direction is preferably 500 MPa, more preferably 480 MPa, and even more preferably 470 MPa as a practical value. A strength of 500 MPa or lower tends to reduce film breakage and packaging bag tearing. The tensile breaking strength can be kept within a specified range by adjusting the elongation ratio, elongation temperature, and heat-fixing temperature.

[0145] (Tensile elongation at fracture) The lower limit of the longitudinal tensile elongation at break of the biaxially oriented polypropylene film of the present invention is preferably 50%, more preferably 55%, and even more preferably 60%. If it is 50% or higher, film breakage and packaging bag tearing tend to be less likely. The upper limit of the longitudinal tensile elongation at break is preferably 230%, more preferably 220%, and even more preferably 210% as a practical value. If it is 230% or lower, printing pitch misalignment when transferring printing ink is less likely to occur, and the durability of the packaging bag tends to be excellent.

[0146] The lower limit of the tensile elongation at break in the width direction of the biaxially oriented polypropylene film of the present invention is preferably 10%, more preferably 15%, and even more preferably 17%. If it is 10% or higher, film breakage and packaging bag tearing tend to be less likely. The upper limit of the tensile elongation at break in the width direction is preferably 60%, more preferably 55%, and even more preferably 50%. If it is 60% or lower, printing pitch misalignment when transferring printing ink is less likely to occur, and the durability of the packaging bag tends to be excellent. The tensile elongation at break can be kept within a specified range by adjusting the stretch ratio, stretching temperature, and heat-fixing temperature.

[0147] (Loop stiffness stress) The lower limit of the longitudinal loop stiffness stress S (mN) at 23°C of the biaxially oriented polypropylene film of the present invention is preferably 0.00020 × t, where t (μm) is the thickness of the biaxially oriented polypropylene film. , , 3 , 3 , 3 , 3 , 3 , 3 , 3 ,

[0148] , , 3 , 3 , 3 , 3 , 3 , 3 , 3 More preferably, it is 0.00025 × t. 3 Even more preferably, it is 0.00030 × t. 3 Particularly preferably, it is 0.00035 × t. 3 That is. 0.00020 × t 3 If it is above this value, it is easy to maintain the shape of the package. The upper limit of the longitudinal loop stiffness stress S (mN) at 23°C is preferably 0.00080 × t. 3 More preferably, it is 0.00075 × t. 3 Even more preferably, it is 0.00072 × t. 3 Particularly preferably, it is 0.00070 × t. 3 That is. 0.00080 × t 3 If it is below this value, it is realistically easy to manufacture. The lower limit of the widthwise loop stiffness stress S (mN) at 23°C of the biaxially oriented polypropylene film of the present invention is preferably 0.0010 × t, where t (μm) is the thickness of the biaxially oriented polypropylene film. 3 More preferably, it is 0.0011 × t. 3 Even more preferably, it is 0.0012 × t. 3 Particularly preferably, it is 0.0013 × t. 3 That is. 0.0010 × t 3 If it is above this value, it is easy to maintain the shape of the package. The upper limit of the widthwise loop stiffness stress S (mN) at 23°C is preferably 0.0020 × t. 3 More preferably, it is 0.0019 × t. 3 Even more preferably, it is 0.0018 × t. 3 Particularly preferably, it is 0.0017 × t. 3 That is. 0.0020 × t 3 If it is below this value, it is realistically easy to manufacture.

[0148] Loop stiffness stress is an indicator of the stiffness of a film, but it also depends on the thickness of the film. The measurement method is as follows: Two strips measuring 110 mm x 25.4 mm were cut out, with the longitudinal direction of the film as the major axis of the strip (loop direction), or the width direction of the film as the major axis of the strip (loop direction). These were clipped together to create measurement loops, one where one side of the film is the inner surface of the loop, and the other where the opposite side is the inner surface of the loop, for both the longitudinal and width directions of the strip. The measurement loop with the major axis of the strip being the longitudinal direction of the film was set in the chuck of a Loop Stiffness Tester DA manufactured by Toyo Seiki Co., Ltd. with the width direction perpendicular, the clip was removed, and the loop stiffness stress was measured with a chuck spacing of 50 mm, a compression depth of 15 mm, and a compression speed of 3.3 mm / second. The measurements involved measuring the loop stiffness stress and thickness five times with one side of the film facing the inner surface of the loop, and then measuring five more times with the other side facing the inner surface of the loop. Using this total of 10 sets of data, the cube of the thickness (μm) of each test specimen was plotted on the x-axis, and its loop stiffness stress (mN) was plotted on the y-axis. The slope a was determined by approximating the plot with a straight line having an intercept of 0. Slope a represents a characteristic value inherent to the film that does not depend on the thickness determining the stiffness. Slope a was used as the evaluation value for stiffness. Measurement loops with the long axis of the strip oriented in the width direction of the film were measured in the same manner.

[0149] (Wrinkles from heat sealing) To form food packaging bags, the contents are filled into pre-made bags, and the film is heated to melt and fuse together for sealing. This process is often carried out similarly when filling bags while they are being made. Typically, a sealant film made of polyethylene or polypropylene is laminated onto a base film, and these sealant film surfaces are fused together. The heating method involves applying pressure from a heating plate on the base film side to press and seal the film, with a seal width of approximately 10 mm being common. During this process, the base film is also heated, causing shrinkage and resulting wrinkles. Fewer wrinkles are desirable for bag durability and to increase purchasing intent. While the sealing temperature may be around 120°C, higher temperatures are required to increase the bag-making speed, and even then, smaller shrinkage is preferable. When a zipper is fused to the opening of the bag, an even higher sealing temperature is required.

[0150] (Surface resistivity test) The surface resistivity of the biaxially oriented polypropylene film of the present invention is preferably 15 Ω / □ or less, more preferably 14.5 Ω / □ or less, even more preferably 14.0 Ω / □ or less, and particularly preferably 13.5 Ω / □ or less. When it is 15 Ω / □ or less, the film roll and the film during processing are less charged, making bag making easier and resulting in fewer defects in the resulting bags. The lower limit of the surface resistivity length is preferably 10 N / 15 mm as a practical value, and more preferably 11 N / 15 mm.

[0151] (Print pitch misalignment) Packaging films typically consist of a laminated film made of a printed base film and a sealant film. Bags are manufactured using bag-making machines, and various types of bags are used, including three-side seal bags, standing bags, and gusseted bags. Print pitch misalignment is thought to occur because the film's base material expands and contracts due to tension and heat applied during the printing process. Eliminating defective products due to print pitch misalignment is important for the efficient use of resources and for increasing consumer purchasing intent.

[0152] (Film processing) The biaxially oriented polypropylene film of the present invention can be printed using letterpress printing, lithographic printing, intaglio printing, stencil printing, or transfer printing methods, depending on the application. Furthermore, unstretched sheets, uniaxially oriented films, and biaxially oriented films made of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, polypropylene, and polyester can be laminated together as a sealant film to provide heat-sealing properties. To further enhance gas barrier properties and heat resistance, unstretched sheets, uniaxially oriented films, and biaxially oriented films made of aluminum foil, polyvinylidene chloride, nylon, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol can be provided as intermediate layers between the biaxially oriented polypropylene film and the sealant film. Adhesives applied by dry lamination or hot-melt lamination can be used to laminate the sealant films. To enhance gas barrier properties, aluminum or inorganic oxides can be deposited onto biaxially oriented polypropylene films, intermediate films, or sealant films. Vacuum deposition, sputtering, and ion plating can be used as deposition methods, but vacuum deposition of silica, aluminum, or mixtures thereof is particularly preferred.

[0153] The biaxially oriented polypropylene film of the present invention can be made suitable for packaging fresh produce such as vegetables, fruits, and flowers, which require high freshness, by adjusting the amount of antifogging agents in the film, such as polyhydric alcohol fatty acid esters, higher fatty acid amines, higher fatty acid amides, and ethylene oxide adducts of higher fatty acid amines and amides, to a range of 0.2 to 5% by mass.

[0154] Furthermore, within limits that do not impair the effects of the present invention, various additives for improving quality such as lubricity and antistatic properties may be incorporated, such as waxes, lubricants such as metal soaps, plasticizers, processing aids, heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers to improve productivity.

[0155] (Industrial applicability) Because the biaxially oriented polypropylene film of the present invention has the above-mentioned superior properties not found in conventional films, it can be preferably used in packaging bags, and it is also possible to make the film thinner than conventional films.

[0156] Furthermore, it is suitable for applications that use high temperatures, such as insulating films for capacitors and motors, backsheets for solar cells, barrier films for inorganic oxides, and base films for transparent conductive films such as ITO, as well as applications that require rigidity, such as separator films. In addition, it enables coating and printing processes at high temperatures using coating agents, inks, and laminating adhesives that were previously difficult to use, which is expected to improve production efficiency. [Examples]

[0157] The present invention will be described in detail below with reference to examples. The characteristics were measured and evaluated by the following methods. (1) Melt flow rate The melt flow rate (MFR) was measured in accordance with JIS K7210, at a temperature of 230°C and a load of 2.16 kgf.

[0158] (2) Mesopentat fraction The measurement of the mesopentad fraction ([mmmm]%) of polypropylene resin is performed as follows: 13 The analysis was performed using 1C-NMR. The mesopentade fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 ¹

[0159] (3) Number average molecular weight, weight average molecular weight, amount of components with a molecular weight of 100,000 or less, and molecular weight distribution of polypropylene resin Gel permeation chromatography (GPC) was used to determine the molecular weight in terms of PP equivalent, based on monodisperse polystyrene. When the baseline was not clear, the baseline was set within the range from the lowest point of the high molecular weight tail of the elution peak closest to the elution peak of the standard substance. The GPC measurement conditions are as follows: Equipment: HLC-8321PC / HT (manufactured by Tosoh Corporation) Detector: RI Solvent: 1,2,4-Trichlorobenzene + Dibutylhydroxytoluene (0.05%) Column: TSKgelguardcolumnHHR(30)HT (7.5mm I.D. × 7.5cm) × 1 + TSKgelGMHHR-H(20)HT (7.8mm I.D. × 30cm) × 3 Flow rate: 1.0mL / min Injection volume: 0.3mL Measurement temperature: 140℃ The number-average molecular weight (Mn) and mass-average molecular weight (Mw) are obtained by analyzing the number of molecules (N) of molecular weight (Mi) at each elution position of the GPC curve obtained via the molecular weight calibration curve. i It is defined by the following equation. Number average molecular weight: Mn=Σ(N i ·M i ) / ΣNi Mass average molecular weight: Mw=Σ(N i ·M i 2 ) / Σ(N i ·M i ) Here, the molecular weight distribution can be obtained as Mw / Mn. Furthermore, the proportion of components with a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight distribution obtained by GPC.

[0160] (4) Crystallization temperature (Tc), melting temperature (Tm) Thermal measurements were performed under a nitrogen atmosphere using a Q1000 differential scanning calorimeter manufactured by T.A. Instruments. Approximately 5 mg was cut from a polypropylene resin pellet and sealed in an aluminum pan for measurement. The temperature was raised to 230°C and held for 5 minutes, then cooled to 30°C at a rate of -10°C / min, and the exothermic peak temperature was defined as the crystallization temperature (Tc). The heat of crystallization (ΔHc) was determined by setting a baseline so that the area of ​​the exothermic peak was smoothly connected from the start to the end of the peak. The temperature was then held at 30°C for 5 minutes, and the temperature was raised to 230°C at a rate of 10°C / min, and the main endothermic peak temperature was defined as the melting temperature (Tm).

[0161] (5) Film thickness The film thickness was measured using a Seiko EM Miltron 1202D.

[0162] (6) Hayes Measurements were taken using an NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. at 23°C in accordance with JIS K7105.

[0163] (7) Tensile test The tensile strength in the longitudinal and widthwise directions of the film was measured at 23°C in accordance with JIS K7127. Samples were cut from the film to a size of 15 mm x 200 mm, and the chuck width was 100 mm. The samples were then set on a tensile testing machine (Instron 5965, a dual-column benchtop testing machine manufactured by Instron Japan Company Limited). Tensile tests were performed at a tensile speed of 200 mm / min. From the obtained strain-stress curve, the stress at 5% elongation was defined as F5. The tensile breaking strength and tensile breaking elongation were defined as the strength and elongation at the time the sample broke, respectively.

[0164] (8) Thermal shrinkage The following method was used in accordance with JIS Z 1712: The film was cut to a length of 20 mm in width and 200 mm in length, and then suspended in a hot air oven at 120°C or 150°C for 5 minutes. The length after heating was measured, and the thermal shrinkage rate was determined as the ratio of the length shrunk to the original length.

[0165] (9) Refractive index, ΔNy, surface orientation coefficient Measurements were taken using an Abbe refractometer manufactured by Atago Corporation at a wavelength of 589.3 nm and a temperature of 23°C. The refractive indices along the longitudinal and width directions of the film were denoted as Nx and Ny, respectively, and the refractive index along the thickness direction was denoted as Nz. The degree of orientation in the width direction, ΔNy, was calculated using Nx, Ny, and Nz with the formula ΔNy = Ny - [(Nx + Nz) / 2]. The surface orientation coefficient (ΔP) was calculated using the formula ΔP = [(Nx + Ny) / 2] - Nz.

[0166] (12) Loop stiffness stress Ten strip-shaped test pieces measuring 110 mm x 25.4 mm were cut out, with the longitudinal direction of the film as the major axis of the strip (loop direction), or the width direction of the film as the major axis of the strip (loop direction). These were clipped together to create measurement loops, one where one side of the film was the inner surface of the loop, and the other where the opposite side was the inner surface of the loop, for both cases where the major axis of the strip was the longitudinal direction of the film and the other where it was the width direction. The measurement loops where the major axis of the strip was the longitudinal direction of the film were set in the chuck of a Loop Stiffness Tester DA manufactured by Toyo Seiki Seisakusho Co., Ltd. with the width direction perpendicular, the clips were removed, and the loop stiffness stress was measured with a chuck spacing of 50 mm, a compression depth of 15 mm, and a compression speed of 3.3 mm / second. The measurements involved first measuring the loop stiffness stress and thickness five times with one side of the film facing the inner surface of the loop, and then measuring five more times with the other side facing the inner surface of the loop. Using this total of 10 sets of data, the cube of the thickness (μm) of each test specimen was plotted on the x-axis and its loop stiffness stress (mN) on the y-axis. The plot was approximated by a straight line with an intercept of 0, and its slope 'a' was determined. Slope 'a' was used as the evaluation value for stiffness. Measurement loops with the long axis of the strip aligned with the width direction of the film were measured in the same manner.

[0167] (13) Lamination strength The laminate strength was measured using the following procedure. 1) Preparation of a laminate film with sealant film The following procedure was performed using a continuous dry laminating machine. First, adhesive was applied to the corona surface of the biaxially oriented polypropylene films obtained in the examples and comparative examples, with a drying amount of 3.0 g / m². 2 After gravure coating, the film was guided to a drying zone and dried at 80°C for 5 seconds. Subsequently, it was bonded to a sealant film between rolls located downstream (roll pressure 0.2 MPa, roll temperature: 60°C). The resulting laminate film was then subjected to an aging treatment at 40°C for 3 days while wound up. The adhesive used was an ether-based adhesive obtained by mixing 17.9% by mass of the main component (TM329, manufactured by Toyo Morton Co., Ltd.), 17.9% by mass of the curing agent (CAT8B, manufactured by Toyo Morton Co., Ltd.), and 64.2% by mass of ethyl acetate. The sealant film used was a nonaxially oriented polypropylene film (Pyrene® CT P1128, 30 μm thick) manufactured by Toyobo Co., Ltd. The laminate film obtained above was cut into strips (200 mm long, 15 mm wide) with the longer side in the longitudinal and width directions of the biaxially oriented polypropylene film. The peel strength (N / 15 mm) was measured using a tensile testing machine (Tensilon, manufactured by Orientec Co., Ltd.) at a tensile speed of 200 mm / min in an environment of 23°C when peeled at 90° (T-shape). Three measurements were taken, and the average values ​​were taken as the laminate strength in the longitudinal and width directions.

[0168] (14) Surface resistivity test The surface resistivity (Ω / □) of the biaxially oriented polypropylene films obtained in the examples and comparative examples was measured on the corona surface in accordance with ASTM D257. The measurement temperature and humidity were 23°C × 65%RH.

[0169] (Example 1) [Base material layer (A)] As a polypropylene resin, 100 parts by weight of a blend of 80 parts by weight of PP-1 (FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.), a propylene homopolymer with MFR=7.5g / 10 min, [mmmm]=98.9%, Tc=116.2℃, and Tm=162.5℃, and 20 parts by weight of PP-2 (EL80F5, manufactured by Sumitomo Chemical Co., Ltd.), a propylene homopolymer with MFR=11g / 10 min, [mmmm]=98.8%, Tc=116.5℃, and Tm=161.5℃, is added. Compound (A) is 0.9912 parts by weight of stearylamine monostearate (Anstex SA321, manufactured by Toho Chemical Industry Co., Ltd.), an anti-fogging agent, and compound (B) is glycerin monostearate (Anstex SA321, manufactured by Toho Chemical Industry Co., Ltd.). 0.156 parts by weight of MG100) were added and mixed, then melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as a polypropylene resin composition for the base layer (A). [Middle layer (B)] As polypropylene resin, parts by weight of 70 propylene homopolymer PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) has an MFR of 7.5 g / 10 min, [mmmm] of 98.9%, Tc of 116.2°C, and Tm of 162.5°C, and PP-2 propylene homopolymer (manufactured by Sumitomo Chemical Co., Ltd., EL) has an MFR of 11 g / 10 min, [mmmm] of 98.8%, Tc of 116.5°C, and Tm of 161.5°C. 100 parts by weight of a blend of 20 parts by weight of 80F5) and 10 parts by weight of propylene-ethylene copolymer PP-3 (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.) containing 0.6 mol% of ethylene monomer-derived components with MFR=7.5 g / 10 min, Tc=111.7℃, and Tm=158℃, and compound (A) is stearylamine monostearate ester (Anstex, manufactured by Toho Chemical Industry Co., Ltd.). 1,000 parts by weight of SA321, 0.155 parts by weight of glycerin monostearate (manufactured by Toho Chemical Industry Co., Ltd.: Anstex MG100), an antifogging agent, as compound (B), and 0.0400 parts by weight of stearyldiethanolamine (manufactured by Toho Chemical Industry Co., Ltd.: Anstex SA20), an antifogging agent, as compound (C) were mixed and then melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as a polypropylene resin composition for the intermediate layer (B). [Surface layer (C)] As a polypropylene resin, 64 parts by weight of PP-1 (FLX80E4, manufactured by Sumitomo Chemical Co., Ltd.), a propylene homopolymer with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, and 36 parts by weight of PP-3 (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.), a propylene-ethylene copolymer with MFR = 7.5 g / 10 min, Tc = 111.7°C, and Tm = 158°C, containing 0.6 mol% of ethylene monomer-derived components, were blended and melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as a polypropylene resin composition for the surface layer (C). First, the polypropylene resin compositions constituting the surface layer (C), base layer (A), intermediate layer (B), and surface layer (C) were heated and melted in an extruder using a multilayer feed block at 250°C, 250°C, and 250°C respectively. The molten polypropylene resin compositions were then co-extruded into a sheet form from a T-die at 250°C while being laminated. The surface layer (C) on the base layer (A) side of the molten sheet was brought into contact with a cooling roll at 20°C and then placed in a 20°C water bath. After preheating to 137°C, it was stretched 4.5 times in the longitudinal direction using two pairs of rolls at 142°C. Then, both ends were clipped, and it was introduced into a hot air oven. After preheating to 170°C, it was stretched 7 times in the width direction as the first stage at 168°C, and then stretched 1.43 times as the second stage at 145°C, for a total of 10 times stretching. Immediately after the width direction stretching, it was cooled at 100°C while still held by the clips, and then heat-set at 165°C while relaxing by 3% in the width direction. The obtained biaxially oriented polypropylene film was subjected to corona treatment on the film surface in contact with the cooling roll using a corona treatment machine manufactured by Softal Corona and Plasma GmbH, under the condition of an applied current of 0.75 A. After this, the film was wound up with a winder to obtain the biaxially oriented single-layer polypropylene film of the present invention. The thickness of the obtained film was 20 μm. The thickness of the resulting film was surface layer (C) / substrate layer (A) / intermediate layer (B) / surface layer (C) = 1 / 16 / 2 / 1 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0170] (Example 2) The procedure was the same as in Example 1, except that an antistatic agent was not included in the intermediate layer (B). Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, a film was obtained with high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0171] (Example 3) Without adding an antistatic agent to the intermediate layer (B), As a polypropylene resin, 64 parts by weight of PP-1 (Sumitomo Chemical Co., Ltd., FLX80E4), a propylene homopolymer with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, and 36 parts by weight of PP-3 (Sumitomo Chemical Co., Ltd., WF836DG3), a propylene-ethylene copolymer with MFR = 7.5 g / 10 min, Tc = 111.7°C, and Tm = 158°C, containing 0.6 mol% of ethylene monomer-derived components, were blended into 100 parts by weight of this mixture. Then, 1.0752 parts by weight of stearylamine monostearate (Toho Chemical Industry Co., Ltd.: Anstex SA321) was added as compound (A) and mixed. After mixing, the mixture was melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as a polypropylene resin composition for the surface layer (C). The procedure was the same as in Example 1. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film exhibited high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0172] (Example 4) The procedure was the same as in Example 1, except that no antistatic agent was added to the base layer (A), and the intermediate layer (B) contained 1.2974 parts by weight of stearylamine monostearate (manufactured by Toho Chemical Industry Co., Ltd.: Anstex SA321) as compound (A), 0.155 parts by weight of glycerin monostearate (manufactured by Toho Chemical Industry Co., Ltd.: Anstex MG100) as compound (B), and 0.0400 parts by weight of stearyldiethanolamine (manufactured by Toho Chemical Industry Co., Ltd.: Anstex SA20) as compound (C). Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, a film was obtained with high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0173] (Example 5) The procedure was the same as in Example 1, except that the film thickness was set to surface layer (C) / substrate layer (A) / intermediate layer (B) / surface layer (C) = 3 / 16 / 2 / 3 μm. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film formation conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0174] (Example 6) The film thickness was set to surface layer (C) / substrate layer (A) / intermediate layer (B) / surface layer (C) = 1 / 14 / 4 / 1 μm. The procedure was the same as in Example 1, except that the first layer was stretched at 164°C in the width direction and the heat-fixing temperature was set to 168°C. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0175] (Example 7) The film thickness was set to surface layer (C) / substrate layer (A) / intermediate layer (B) / surface layer (C) = 1 / 12 / 6 / 1 μm. The procedure was the same as in Example 1, except that the first layer was stretched at 164°C in the width direction and the heat-fixing temperature was set to 168°C. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0176] (Example 8) The procedure was the same as in Example 1, except that the first layer was stretched at 166°C in the width direction, followed by a second layer of double stretching at 162°C. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0177] (Example 9) The procedure was carried out in the same manner as in Example 1, except that 100 parts by weight of propylene-ethylene copolymer PP-3 (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.), which contains 0.6 mol% of ethylene monomer-derived components with an MFR of 7.5 g / 10 min, Tc of 111.7 °C, and Tm of 158 °C, was used as the polypropylene resin composition for the surface layer (C). Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, a film was obtained with high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0178] (Example 10) As a polypropylene resin, 100 parts by weight of a blend of 80 parts by weight of PP-1 (Sumitomo Chemical Co., Ltd., FLX80E4), a propylene homopolymer with MFR=7.5g / 10 min, [mmmm]=98.9%, Tc=116.2℃, and Tm=162.5℃, and 20 parts by weight of PP-2 (Sumitomo Chemical Co., Ltd., EL80F5), a propylene homopolymer with MFR=11g / 10 min, [mmmm]=98.8%, Tc=116.5℃, and Tm=161.5℃, is added. Compound (A) is 0.9912 parts by weight of stearylamine monostearate (Toho Chemical Industry Co., Ltd.: Anstex SA321), and compound (B) is glycerin monostearate (Toho Chemical Industry Co., Ltd.: Anstex) The procedure was the same as in Example 1, except that 0.156 parts by weight of MG100 was added and mixed, then melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as the polypropylene resin composition for the intermediate layer (B). Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity, low thermal shrinkage at high temperatures, and high laminate strength.

[0179] (Comparative Example 1) As polypropylene resin, 30 parts by weight of PP-1 (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4) has an MFR of 7.5 g / 10 min, [mmmm] of 98.9%, Tc of 116.2°C, and Tm of 162.5°C, and 30 parts by weight of PP-2 (manufactured by Sumitomo Chemical Co., Ltd., EL) has an MFR of 11 g / 10 min, [mmmm] of 98.8%, Tc of 116.5°C, and Tm of 161.5°C. 100 parts by weight of a blend of 20 parts by weight of 80F5) and 50 parts by weight of propylene-ethylene copolymer PP-3 (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.) containing 0.6 mol% of ethylene monomer-derived components with MFR=7.5 g / 10 min, Tc=111.7℃, and Tm=158℃, and compound (A) is stearylamine monostearate ester (Anstex, manufactured by Toho Chemical Industry Co., Ltd.). The procedure was carried out in the same manner as in Example 1, except that 0.9554 parts by weight of SA321) was mixed with 0.153 parts by weight of glycerin monostearate (manufactured by Toho Chemical Industry Co., Ltd.: Anstex MG100) as compound (B) and 0.120 parts by weight of stearyldiethanolamine (manufactured by Toho Chemical Industry Co., Ltd.: Anstex SA20) as compound (C), and after mixing, the mixture was melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as the polypropylene resin composition for the intermediate layer (B). Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, a film with low rigidity and low lamination strength was obtained.

[0180] (Comparative Example 2) As a polypropylene resin, 100 parts by weight of propylene-ethylene copolymer PP-3 (WF836DG3, manufactured by Sumitomo Chemical Co., Ltd.) with an ethylene monomer-derived component of 0.6 mol%, MFR = 7.5 g / 10 min, Tc = 111.7 °C, and Tm = 158 °C was used. To this, 0.800 parts by weight of stearylamine monostearate (Anstex SA321, manufactured by Toho Chemical Industry Co., Ltd.) was used as compound (A), 0.157 parts by weight of glycerin monostearate (Anstex MG100, manufactured by Toho Chemical Industry Co., Ltd.) was used as compound (B), and 0.200 parts by weight of stearyldiethanolamine (Anstex SA20, manufactured by Toho Chemical Industry Co., Ltd.) was used as compound (C). After mixing, the mixture was melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which were used as the polypropylene resin composition for the intermediate layer (B). The procedure was carried out in the same manner as in Example 1. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had low rigidity and low laminate strength.

[0181] (Comparative Example 3) As a polypropylene resin, 80 parts by weight of PP-1 (Sumitomo Chemical Co., Ltd., FLX80E4), a propylene homopolymer with MFR=7.5g / 10 min, [mmmm]=98.9%, Tc=116.2℃, and Tm=162.5℃, and 20 parts by weight of PP-2 (Sumitomo Chemical Co., Ltd., EL80F5), a propylene homopolymer with MFR=11g / 10 min, [mmmm]=98.8%, Tc=116.5℃, and Tm=161.5℃, are blended into 100 parts by weight of this mixture. Compound (A) is stearylamine monostearate (Toho Chemical Industry Co., Ltd.: Anstex A321), and compound (B) is glycerin monostearate (Toho Chemical Industry Co., Ltd.: Anstex After mixing 0.156 parts by weight of MG100), the mixture is melt-kneaded and granulated using an extruder with a pelletizer to obtain polypropylene composition pellets, which are used as the polypropylene resin composition for the intermediate layer (B). The procedure was carried out in the same manner as in Example 1, except that the polypropylene resin composition for the surface layer (C) was a blend of 94 parts by weight of propylene homopolymer PP-1 (Sumitomo Chemical Co., Ltd., FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, and 6 parts by weight of propylene-ethylene copolymer PP-3 (Sumitomo Chemical Co., Ltd., WF836DG3) with MFR = 7.5 g / 10 min, Tc = 111.7°C, and Tm = 158°C, containing 0.6 mol% of ethylene monomer-derived components. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity and low thermal shrinkage at high temperatures, but low laminate strength.

[0182] (Comparative Example 4) The procedure was carried out in the same manner as in Example 1, except that the polypropylene resin composition for the surface layer (C) was a blend of 94 parts by weight of propylene homopolymer PP-1 (Sumitomo Chemical Co., Ltd., FLX80E4) with MFR = 7.5 g / 10 min, [mmmm] = 98.9%, Tc = 116.2°C, and Tm = 162.5°C, and 6 parts by weight of propylene-ethylene copolymer PP-3 (Sumitomo Chemical Co., Ltd., WF836DG3) with MFR = 7.5 g / 10 min, Tc = 111.7°C, and Tm = 158°C, containing 0.6 mol% of ethylene monomer-derived components. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film-forming conditions. As shown in Table 4, the resulting film had high rigidity and low thermal shrinkage at high temperatures, but low laminate strength.

[0183] (Comparative Example 5) The procedure was the same as in Example 1, except that the first layer was stretched at 162°C in the width direction. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film formation conditions. As shown in Table 4, the resulting film had high rigidity but a high thermal shrinkage rate at high temperatures.

[0184] (Comparative Example 6) It was stretched at 162°C in the width direction, the heat setting temperature was 168°C, and it was carried out in the same manner as in Example 1 except that it was relaxed by 5% in the width direction. Table 1 shows the structure of the polypropylene resin, Table 2 shows the raw materials for each layer, and Table 3 shows the film forming conditions. As shown in Table 4, a film with low rigidity was obtained.

[0185]

Table 1

[0186]

Table 2

[0187]

Table 3

[0188]

Table 4

Claims

1. A biaxially oriented polypropylene film having a stress (F5) of 40 MPa or more in the longitudinal direction and 162 MPa or more in the width direction at 23°C when elongated by 5%, a thermal shrinkage rate of 4.5% or less in the longitudinal direction and 15% or less in the width direction at 150°C, and a laminate strength (90° peel) of 1.0 N / 15 mm or more, which is expressed as the peel strength when the laminate film obtained by laminating with a sealant film is peeled at 90° (T-shape) in the width direction.

2. The biaxially oriented polypropylene film according to claim 1, wherein the heat shrinkage rate at 120°C of the biaxially oriented polypropylene film is 2.0% or less in the longitudinal direction and 5.0% or less in the width direction, and the heat shrinkage rate at 120°C in the longitudinal direction is smaller than the heat shrinkage rate at 120°C in the width direction.

3. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the refractive index Ny in the width direction of the biaxially oriented polypropylene film is 1.5230 or more, and ΔNy is 0.0220 or more.

4. The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the haze of the biaxially oriented polypropylene film is 5.0% or less.

5. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein the biaxially oriented polypropylene film comprises a base layer (A), an intermediate layer (B), and a surface layer (C).

6. The biaxially oriented polypropylene film according to any one of claims 1 to 5, wherein the mesopentad fraction of the main polypropylene resin constituting the base layer (A) is 97.0% or more.

7. The biaxially oriented polypropylene film according to any one of claims 1 to 6, wherein the crystallization temperature of the main polypropylene resin constituting the base layer (A) is 105°C or higher, and the melting point is 160°C or higher.

8. The biaxially oriented polypropylene film according to any one of claims 1 to 7, wherein the melt flow rate of the main polypropylene resin constituting the base layer (A) is 4.0 g / 10 min or more.

9. The biaxially oriented polypropylene film according to any one of claims 1 to 8, wherein the amount of the main polypropylene resin constituting the base layer (A) with a molecular weight of 100,000 or less is 35% by mass or more.

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