Biaxially oriented polypropylene film

Abstract

The purpose of the present invention is to provide a biaxially oriented polypropylene film having a great clarity, a high storage modulus at high temperature, and a low heat shrinkage rate at high temperature. A biaxially oriented polypropylene film according to the present invention is characterized by: having a base material layer A made of a polypropylene-based resin composition and a seal layer B made of a polypropylene-based resin composition; and satisfying the following (1)-(4).　(1) The seal layer B is provided on at least one of the outermost surfaces.　(2) The clarity is 90-100%.　(3) The storage modulus at 140°C in the width direction is 0.7-5.0 GPa.　(4) The 150°C heat shrinkage rate in the width direction is at most 10%.

Description

Biaxially oriented polypropylene film

[0001] The present invention relates to a biaxially oriented polypropylene film.

[0002] Polypropylene-based resin films have been widely used as heat-sealable films for packaging. Examples of heat-sealable polypropylene-based resin films include laminated polypropylene-based resin films obtained by laminating an unstretched polyethylene-based resin film or an unstretched polypropylene-based resin film with an oriented polypropylene-based resin film. Although the laminated polypropylene-based resin film has sufficient sealing strength, it requires a lamination process using organic solvents, which is undesirable in terms of both cost and environmental impact.

[0003] Another example is a laminated polypropylene resin film obtained by stretching a sheet in which a layer made of a high-melting-point polypropylene resin and a layer made of a low-melting-point polyolefin resin are co-extruded together. For example, Patent Documents 1 and 2 disclose biaxially oriented polypropylene resin films having excellent rigidity, transparency, and heat sealability.

[0004] International Publication No. 2021 / 5893 Pamphlet International Publication No. 2019 / 244708 Pamphlet

[0005] However, the films of Patent Documents 1 and 2 have the problem of poor processability, and there is also a demand for improved transparency.

[0006] An object of the present invention is to provide a biaxially oriented polypropylene film having high clarity, a high storage modulus at high temperatures, and a small heat shrinkage rate at high temperatures.

[0007] As a result of extensive research to achieve this object, the inventors have developed a biaxially oriented polypropylene film having high clarity, a high storage modulus at high temperatures, and a small heat shrinkage rate at high temperatures, thereby completing the present invention. That is, the present invention includes the following inventions. [1] A biaxially oriented polypropylene film having a base layer A made of a polypropylene-based resin composition and a seal layer B made of a polypropylene-based resin composition, characterized in that the film satisfies the following (1) to (4): (1) The film has seal layer B on at least one outermost surface. (2) The film has a clarity of 90% or more and 100% or less. (3) The film has a storage modulus at 140°C in the width direction of 0.7 GPa or more and 5.0 GPa or less. (4) The film has a heat shrinkage rate at 150°C in the width direction of 10% or less. [2] The biaxially oriented polypropylene film according to [1], wherein, in thermomechanical analysis, when heated from 30°C to 160°C at a heating rate of 10°C / min, the temperature at which the widthwise length is 0.9950 × X0 or less relative to the widthwise length X0 at 30°C is 129°C or higher, and the storage modulus in the longitudinal direction at 23°C is 2.0 GPa or higher and the storage modulus in the widthwise direction at 23°C is 7.0 GPa or higher. [3] The biaxially oriented polypropylene film according to [1] or [2], wherein the storage modulus in the longitudinal direction at 120°C is 0.5 GPa or higher and the storage modulus in the widthwise direction at 120°C is 1.5 GPa or higher. [4] The biaxially oriented polypropylene film according to any one of [1] to [3], wherein the heat shrinkage in the longitudinal direction at 120°C is 2.5% or lower and the heat shrinkage in the widthwise direction at 120°C is 1.1% or lower. [5] The biaxially oriented polypropylene film according to any one of [1] to [4], wherein the stress at 5% elongation in the width direction at 23°C is 120 MPa or more. [6] The biaxially oriented polypropylene film according to any one of [1] to [5], wherein the haze is 7.0% or less. [7] The biaxially oriented polypropylene film according to any one of [1] to [6], wherein the base layer A contains 0.2% by mass or more and 2.0% by mass or less of an anti-fogging agent. [8] The biaxially oriented polypropylene film according to any one of [1] to [7], wherein the base layer A contains 90% by mass or more of a polypropylene resin having a mesopentad fraction of 97.0% or more.[9] The biaxially oriented polypropylene film according to any one of [1] to [8], wherein the seal layer B contains 70% by mass or more of a polypropylene copolymer, and the polypropylene copolymer contains 4% by mol or more of an α-olefin other than propylene.

[10] The biaxially oriented polypropylene film according to any one of [1] to [9], wherein an intermediate layer C made of a polypropylene-based resin composition is between the base layer A and the seal layer B, and the melting point of the polypropylene-based resin composition constituting the intermediate layer C is higher than the melting point of the polypropylene-based resin composition constituting the seal layer B.

[11] The biaxially oriented polypropylene film according to any one of [1] to

[10] , wherein the thickness is 10 μm or more and 100 μm or less.

[0008] The polypropylene film of the present invention is a film with excellent rigidity and heat resistance and heat-sealability, so that it easily maintains its bag shape when made into a packaging bag. Furthermore, it can be suitably used for applications requiring high rigidity without laminating a sealant film, and can maintain its strength even when the film is thin. Furthermore, because of its excellent heat resistance, there are fewer wrinkles in the sealed area when heat-sealed, and the appearance of the bag when made into a bag is excellent.

[0009] Fig. 1 is a diagram showing the relationship between temperature and the length in the width direction of the film in Example 1 according to the present invention, Comparative Example 1, and Comparative Example 4. Fig. 2 is a diagram showing the relationship between temperature and loss modulus in Example 1 according to the present invention and Comparative Example 1. Fig. 3 is a diagram showing the relationship between temperature and storage modulus in Example 1 according to the present invention and Comparative Example 1.

[0010] The biaxially oriented polypropylene film of the present invention will be described below.

[0011] Layer structure of biaxially oriented polypropylene film The biaxially oriented polypropylene film of the present invention has a base layer A made of a polypropylene-based resin composition, and a seal layer B made of a polypropylene-based resin composition. The biaxially oriented polypropylene film of the present invention may have an intermediate layer C made of a polypropylene-based resin composition between the base layer A and the seal layer B. Furthermore, the biaxially oriented polypropylene film of the present invention may have a functional layer D. The base layer A, seal layer B, intermediate layer C, and functional layer D will be described in detail below.

[0012] 1. Substrate Layer A The substrate layer A made of a polypropylene-based resin composition is preferably made of a polypropylene-based resin composition containing a polypropylene homopolymer as a main component. The term "main component" means that 80% by mass or more of the entire substrate layer A is polypropylene homopolymer, more preferably 90% by mass or more of the entire substrate layer A is polypropylene homopolymer, even more preferably 95% by mass or more of the entire substrate layer A is polypropylene homopolymer, particularly preferably 97% by mass or more of the entire substrate layer A is polypropylene homopolymer, and most preferably 99% by mass or more of the entire substrate layer A is polypropylene homopolymer. The upper limit of this proportion is not particularly limited, but 100% by mass or less of the entire substrate layer A may be polypropylene homopolymer.

[0013] 1-1. Polypropylene Homopolymer The polypropylene homopolymer used in the base layer A is a polypropylene polymer that is substantially free of α-olefin components other than propylene. Specifically, it is a 100 mol% propylene homopolymer or a polypropylene copolymer having structural units of more than 0 mol% and 1 mol% or less of α-olefin components other than propylene and 99 mol% or more but less than 100 mol% of propylene (total 100 mol%). α-olefin components other than propylene refer to ethylene and α-olefins having 4 or more carbon atoms. Even when α-olefin components other than propylene are contained, the content of α-olefin components other than propylene is 1 mol% or less, as described above, preferably 0.3 mol% or less, more preferably 0.2 mol% or less, and even more preferably 0.1 mol% or less. Within the above range, crystallinity is likely to be improved.

[0014] Examples of the α-olefin component having 4 or more carbon atoms include 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene.

[0015] The polypropylene homopolymer may be two or more different polypropylene homopolymers, and in that case, it is preferable that the total content is within the above range. Note that the polypropylene homopolymer used in the base layer A includes not only polypropylene homopolymers containing no α-olefin components other than propylene, but also polypropylene copolymers having as constituent units more than 0 mol % and 1 mol % or less of α-olefin components other than propylene and 99 mol % or more but less than 100 mol % of propylene.

[0016] Various suitable physical properties of the polypropylene homopolymer are described below. When two or more different polypropylene homopolymers are used, the physical property values ​​are mass average values ​​of the physical properties of the individual polypropylene homopolymers.

[0017] Melting point Tm of polypropylene homopolymer used in base layer A a The Tm is preferably 160°C or higher and 170°C or lower. a If Tm is 160°C or higher, rigidity and heat resistance at high temperatures are likely to be obtained. a When the Tm is 170°C or less, it is easy to suppress an increase in the cost of producing polypropylene, and the film is less likely to break during film formation. a The Tm is more preferably 161°C or higher, even more preferably 162°C or higher, more preferably 169°C or lower, even more preferably 168°C or lower, particularly preferably 167°C or lower, and most preferably 166°C or lower. a The melting point of the resin is the main peak temperature of the endothermic peak accompanying melting, which is observed when 5 mg of polypropylene homopolymer is packed into an aluminum pan, set in a differential scanning calorimeter (DSC), heated from 30°C to 230°C at a heating rate of 20°C / min under a nitrogen atmosphere, and held at 230°C for 5 minutes to melt the polypropylene homopolymer, then cooled to 30°C at a heating rate of -10°C / min, held at 30°C for 5 minutes, and then heated at a heating rate of 10°C / min.

[0018] The polypropylene homopolymer used in the base layer A preferably has a mesopentad fraction ([mmmm]%), which is an index of stereoregularity, of 97.0% or more and 99.9% or less. When the mesopentad fraction is 97.0% or more, the crystallinity of the polypropylene resin is increased, and the melting point Tm of the crystal in the base layer A is a, crystallinity, and crystalline orientation are improved, and rigidity and heat resistance at high temperatures are likely to be obtained. When the mesopentad fraction is 99.9% or less, costs in polypropylene production are easily reduced and the polypropylene is less likely to break during film formation. The mesopentad fraction is more preferably 97.5% or more, even more preferably 98.0% or more, and more preferably 99.7% or less, even more preferably 99.5% or less. The mesopentad fraction is measured by nuclear magnetic resonance spectroscopy (the so-called NMR method). To achieve a mesopentad fraction of the polypropylene homopolymer within the above range, methods such as washing the obtained polypropylene polymer powder with a solvent such as n-heptane, appropriately selecting a catalyst and / or co-catalyst, and appropriately selecting the components of the polypropylene resin composition are preferably employed.

[0019] The melt flow rate (MFR) of the polypropylene homopolymer used in the base layer A is preferably 5.0 g / 10 min or more and 30 g / 10 min or less, as measured at 230°C and a load of 2.16 kgf according to condition M of JIS K 7210 (1995). When the MFR of the polypropylene resin is 5.0 g / 10 min or more, the polypropylene resin constituting the base layer A contains a large amount of low-molecular-weight components. Therefore, by employing a width direction stretching step in the film formation process described below, the oriented crystallization of the polypropylene resin is further promoted, the crystallinity of the base layer A is more likely to be increased, and the entanglement of polypropylene molecular chains in the amorphous portion is reduced, making it easier to improve heat resistance. Furthermore, when the MFR of the polypropylene resin is 30 g / 10 min or less, the film formability of the film is easily maintained. The MFR is more preferably 5.5 g / 10 min or more, even more preferably 6.0 g / 10 min or more, particularly preferably 6.3 g / 10 min or more, and most preferably 6.5 g / 10 min or more, and is more preferably 25 g / 10 min or less, even more preferably 22 g / 10 min or less, particularly preferably 20 g / 10 min or less, and most preferably 10 g / 10 min or less. In order to set the MFR of the polypropylene homopolymer within the above range, it is preferable to employ a method of controlling the molecular weight or molecular weight distribution of the polypropylene homopolymer.

[0020] The polypropylene homopolymer used in the base layer A has an M w / M n The lower limit of M is preferably 3.5, more preferably 4.0, even more preferably 4.5, and particularly preferably 5.0. w / M n The upper limit of M is preferably 30, more preferably 25, even more preferably 23, particularly preferably 21, and most preferably 20. w / M n When M is within the above range, it is easy to increase the amount of components having a molecular weight of 100,000 or less. w / M n can be obtained using gel permeation chromatography (GPC).

[0021] The molecular weight distribution of the polypropylene polymer can be adjusted by polymerizing components of different molecular weights in a series of plants in multiple stages, blending components of different molecular weights offline in a kneader, polymerizing by blending catalysts with different performances, or using a catalyst that can achieve a desired molecular weight distribution. The shape of the molecular weight distribution obtained by GPC may be a gentle molecular weight distribution with a single peak in a GPC chart with the logarithm (log M) of the molecular weight (M) on the horizontal axis and the differential distribution value (mass fraction per log M) on the vertical axis, or may be a molecular weight distribution with multiple peaks or shoulders.

[0022] The amount of components with a molecular weight of 100,000 or less in the GPC cumulative curve of the propylene-based resin composition constituting the base layer A is preferably 38% by mass or more, more preferably 38% by mass or more and 65% by mass or less. By setting the amount of components with a molecular weight of 100,000 or less to 38% by mass or more, heat resistance is easily improved. When the amount of components with a molecular weight of 100,000 or less is 65% by mass or less, film strength is less likely to decrease. In this case, if a high-molecular-weight component with a long relaxation time or a long-chain branched component is included, it is easy to adjust the amount of components with a molecular weight of 100,000 or less contained in the polypropylene resin without significantly changing the overall viscosity, which makes it easy to improve film formability without significantly affecting rigidity or heat resistance. The amount is more preferably 40% by mass or more, particularly preferably 41% by mass or more, most preferably 42% by mass or more, even more preferably 60% by mass or less, particularly preferably 55% by mass or less, and most preferably 50% by mass or less.

[0023] 1-2. Anti-Fog Agent It is preferable to blend an anti-fogging agent into the polypropylene resin composition constituting the base layer A. The biaxially oriented polypropylene film of the present invention can be processed into packaging bags, and when fruits and vegetables are placed in the packaging bags, the addition of an anti-fogging agent can prevent fogging of the packaging bags, since the physiological functions of the fruits and vegetables continue even after harvest.

[0024] Examples of antifogging agents that can be used include known antifogging agents such as ethylene oxide adducts of aliphatic amines, ethylene oxide adducts of aliphatic amides, esters of ethylene oxide adducts of aliphatic amines and fatty acids, fatty acid esters of polyhydric alcohols, fatty acid amines, and fatty acid amides. Among these, it is preferable to use at least one selected from the group consisting of ethylene oxide adducts of aliphatic amines and esters of ethylene oxide adducts of aliphatic amines and fatty acids, and it is more preferable to use an ethylene oxide adduct of aliphatic amines and esters of ethylene oxide adducts of aliphatic amines and fatty acids. The esters of ethylene oxide adducts of aliphatic amines and fatty acids preferably include at least one selected from the group consisting of stearyl diethanolamine monoesters and stearyl diethanolamine diesters. In addition, packaging bags are often stored at room temperature rather than frozen, and in order to maintain excellent anti-fogging properties over the long term during distribution, it is preferable to use an anti-fogging agent that continues to exhibit anti-fogging properties over the course of repeated temperature changes between 5° C. and 30° C., taking into consideration changes in temperature during storage or distribution, but is not limited to the above-mentioned preferred embodiments and may be selected appropriately depending on the application. Only one type of anti-fogging agent may be used, or two or more types may be used in combination.

[0025] Examples of stearyl diethanolamine monoesters include stearyl diethanolamine monolaurate, stearyl diethanolamine monomyristate, stearyl diethanolamine monopalmitate, stearyl diethanolamine monostearate, and stearyl diethanolamine monooleate, with stearyl diethanolamine monostearate being preferred. Examples of stearyl diethanolamine diesters include stearyl diethanolamine dilaurate, stearyl diethanolamine dimyristate, stearyl diethanolamine dipalmitate, stearyl diethanolamine distearate, and stearyl diethanolamine dioleate, with stearyl diethanolamine distearate being preferred. Examples of ethylene oxide adducts of aliphatic amines include lauryl diethanolamine, myristyl diethanolamine, palmityl diethanolamine, and stearyl diethanolamine, with stearyl diethanolamine being preferred. The ethylene oxide adducts of aliphatic amines may be used alone or in combination of two or more.

[0026] The amount of the antifogging agent in the propylene-based resin composition constituting the base layer A is preferably 0.2% by mass or more and 2.0% by mass or less. The amount is more preferably 0.3% by mass or more, even more preferably 0.35% by mass or more, and more preferably 1.8% by mass or less, even more preferably 1.6% by mass or less. However, as described below, the antifogging agent may migrate from the base layer A to other layers such as the intermediate layer C during the film formation process.

[0027] 1-3. Others The polypropylene resin composition constituting the base layer A may contain resins other than polypropylene homopolymers, as well as additives such as known heat stabilizers, antioxidants, UV absorbers, nucleating agents, adhesives, flame retardants, and inorganic or organic fillers, as long as the effects of the present invention are not impaired. However, these additives are preferably added in small amounts, and the amount of resins other than polypropylene homopolymers in the polypropylene resin composition constituting the base layer A is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 2% by mass or less, and most preferably 1% by mass or less. Furthermore, the amount of additives other than resins in the polypropylene resin composition constituting the base layer A is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. These resins other than polypropylene homopolymers and / or additives other than resins do not need to be incorporated into the base layer A. That is, the amount of resins other than polypropylene homopolymers and / or additives other than resins in the base layer A is 0% by mass or more. Examples of resins other than polypropylene homopolymers include polyolefin resins other than the polypropylene homopolymer used in the base layer A, various elastomers, etc. These may be used by sequential polymerization using a multi-stage reactor, blending with polypropylene resin in a Henschel mixer, diluting master pellets prepared in advance using a melt kneader with polypropylene to a predetermined concentration, or melt-kneading the entire amount in advance. If the surface resistance of the polypropylene homopolymer used in the base layer A is too high, a surfactant may be added to reduce the surface resistance.

[0028] 2. Seal Layer B 2-1. Polypropylene Resin Composition The seal layer B, which is made of a polypropylene resin composition, preferably contains a polypropylene copolymer containing an α-olefin other than propylene. That is, the polypropylene resin composition constituting the seal layer B preferably contains a polypropylene copolymer containing an α-olefin other than propylene. In the description of the seal layer B, even if the term "polypropylene copolymer (contained in seal layer B)" is simply used, it refers to a polypropylene copolymer containing propylene and an α-olefin other than propylene. The seal layer B preferably contains 70% by mass or more of the polypropylene copolymer. By containing 70% by mass or more of the polypropylene copolymer, it is easy to improve the interlayer adhesion between the seal layer B and the intermediate layer C, and the heat seal strength of the biaxially oriented polypropylene film can be further increased. The proportion is more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. In addition, two or more different polypropylene copolymers can be used as the polypropylene copolymer contained in the seal layer B, and it is preferable that the total content is within the above range. The upper limit of this proportion is not particularly limited, but the polypropylene copolymer may account for 100 mass% or less of the entire seal layer B. The content of α-olefin components other than propylene in the polypropylene copolymer contained in the seal layer B is preferably 4.0 mol% or more. In this case, the propylene content in the polypropylene copolymer is 96 mol% or less, and the sum of the propylene content and the content of α-olefin components other than propylene is 100 mol%. The content of the α-olefin components is the total amount of ethylene and α-olefins having 4 or more carbon atoms. The content of the α-olefin components other than propylene is more preferably 5.0 mol% or more, even more preferably 6.0 mol% or more, particularly preferably 7.0 mol% or more, and more preferably 15 mol% or less, even more preferably 12 mol% or less, and particularly preferably 10 mol% or less.Examples of the α-olefin component having 4 or more carbon atoms include 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, etc. The α-olefin component other than propylene is preferably an α-olefin component other than propylene having 2 to 20 carbon atoms, more preferably an α-olefin component other than propylene having 2 to 10 carbon atoms, even more preferably an α-olefin component other than propylene having 2 to 6 carbon atoms, and particularly preferably an α-olefin component other than propylene having 2 to 4 carbon atoms.

[0029] Melting point Tm of the polypropylene resin composition constituting the seal layer B b The Tm is preferably 150°C or less, more preferably 145°C or less, even more preferably 140°C or less, particularly preferably 135°C or less, and most preferably 130°C or less. b By setting the melting point Tm of the polypropylene resin composition constituting the seal layer B within the above range, it is possible to easily lower the heat seal rising temperature and also to increase the heat seal strength. b The lower limit of the melting point Tm of the polypropylene resin composition constituting the seal layer B is not particularly limited, and is, for example, 110° C. or more. b is the melting point Tm of the polypropylene resin composition constituting the intermediate layer C c Lower is preferable.

[0030] The melt flow rate (MFR) of the polypropylene resin composition constituting the seal layer (B), measured at a temperature of 230°C and a load of 2.16 kgf, is preferably 5.0 g / 10 min or more and 8.0 g / 10 min or less. The MFR is more preferably 5.5 g / 10 min or more, even more preferably 6.0 g / 10 min or more, particularly preferably 6.3 g / 10 min or more, and more preferably 7.5 g / 10 min or less, even more preferably 7.0 g / 10 min or less, particularly preferably 6.8 g / 10 min or less. From the viewpoint of increasing the heat seal strength, the melt flow rate of the polypropylene resin composition constituting the seal layer (B) is preferably higher than the melt flow rate of the polypropylene resin composition constituting the intermediate layer (C).

[0031] The polypropylene copolymer contained in the seal layer B preferably contains at least one selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer, and more preferably contains a propylene-butene copolymer.

[0032] 2-2. Propylene-Ethylene-Butene Copolymer The content of α-olefin components other than propylene in the propylene-ethylene-butene copolymer is preferably 4 mol% or more. When the content of α-olefin components other than propylene is 4 mol% or more, the interlayer adhesion between the intermediate layer C and the seal layer B is likely to be improved, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The content of α-olefin components other than propylene is more preferably 5 mol% or more, and even more preferably 6 mol% or more. The upper limit of the content of α-olefin components other than propylene is not particularly limited, and is, for example, 25 mol% or less. Note that when there are two or more α-olefin components other than propylene, the total amount is the content of the α-olefin components other than propylene. The ethylene content is preferably 1 mol% or more, and more preferably 2 mol% or more. The upper limit of the ethylene content is not particularly limited, but since an ethylene content that is too high may cause the film surface to become sticky and may reduce slipperiness and blocking resistance, it is, for example, 12 mol% or less. The butene content is preferably 1 mol% or more, more preferably 2 mol% or more. There is no particular upper limit to the butene content, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so for example, it is 16 mol% or less. As the propylene-ethylene-butene copolymer having a total content of α-olefin components other than propylene of 4 mol% or more, a commercially available product may be used, such as FSX66E8 manufactured by Sumitomo Chemical Co., Ltd.

[0033] 2-3. Propylene-Butene Copolymer The butene content in the propylene-butene copolymer is preferably 4 mol% or more. A butene content of 4 mol% or more tends to improve the interlayer adhesion between the intermediate layer C and the seal layer B, and as a result, tends to improve heat seal strength and hermetic sealability. The butene content is more preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the butene content, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so for example, it is 16 mol% or less, preferably 12 mol% or less. As a propylene-butene copolymer having a butene content of 4 mol% or more, commercially available products may be used, such as SP7843 manufactured by Sumitomo Chemical Co., Ltd., SPX78J1 manufactured by Sumitomo Chemical Co., Ltd., and XR110H manufactured by Mitsui Chemicals, Inc.

[0034] 2-4. Propylene-Ethylene Copolymer The ethylene content of the propylene-ethylene copolymer is preferably 4 mol% or more. When the ethylene content is 4 mol% or more, the interlayer adhesion between the intermediate layer C and the seal layer B is likely to be improved, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The ethylene content is more preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the ethylene content, but if the ethylene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may be reduced, so for example, it is 12 mol% or less. As a propylene-ethylene copolymer having an ethylene content of 4 mol% or more, commercially available products may be used, such as PC540R manufactured by SunAllomer Co., Ltd. and VM3588FL manufactured by Mitsui Chemicals, Inc.

[0035] 2-5. Anti-Fog Agent The polypropylene resin composition constituting the seal layer B may or may not contain an anti-fogging agent. The anti-fogging agents described in the description of the substrate layer A can be used as the anti-fogging agent. Even if the polypropylene resin composition constituting the seal layer B does not contain an anti-fogging agent, the anti-fogging agent may migrate from the substrate layer A to the seal layer B during the film-forming process, and the resulting biaxially oriented polypropylene film may contain the anti-fogging agent in the seal layer B. Furthermore, as long as the effects of the present invention are not impaired, the polypropylene resin composition constituting the seal layer B may contain additives such as resins other than polypropylene copolymers, the anti-fogging agents described above, known heat stabilizers, antioxidants, UV absorbers, nucleating agents, adhesives, flame retardants, inorganic or organic fillers, etc. Examples of resins other than polypropylene copolymers include polyolefin resins other than the polypropylene copolymers used in the seal layer B, and various elastomers. However, it is preferable that these are added in small amounts, and the amount of resins other than polypropylene copolymers in the polypropylene resin composition constituting seal layer B is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 2% by mass or less, and may be 0% by mass or more. Also, the amount of additives other than resins in the polypropylene resin composition constituting seal layer B is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, particularly preferably 1% by mass or less, and may be 0% by mass or more.

[0036] 3. Intermediate Layer C 3-1. Polypropylene Resin Composition The intermediate layer C made of a polypropylene resin composition preferably contains a polypropylene copolymer containing an α-olefin other than propylene. That is, the polypropylene resin composition constituting the intermediate layer C preferably contains a polypropylene copolymer containing an α-olefin other than propylene. The provision of the intermediate layer C can improve heat seal strength. In the description of the intermediate layer C, even when the term "polypropylene copolymer" is simply used, it refers to a polypropylene copolymer containing an α-olefin other than propylene. The intermediate layer C preferably contains 70% by mass or more of the polypropylene copolymer. By including 70% by mass or more of the polypropylene copolymer, it is easy to improve the interlayer adhesion between the intermediate layer C and the seal layer B and between the base layer A and the intermediate layer C, thereby further increasing the heat seal strength of the biaxially oriented polypropylene film. The proportion of the polypropylene copolymer in the intermediate layer C is more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may even be 100% by mass or more. The polypropylene copolymer contained in the intermediate layer C may be two or more different polypropylene copolymers, and it is preferable that the total content is within the above range. The content of α-olefin components other than propylene in the polypropylene copolymer contained in the intermediate layer C, i.e., the total amount of ethylene and α-olefins having 4 or more carbon atoms, is preferably 4.0 mol% or more. In this case, the propylene content in the polypropylene copolymer is 96 mol% or less, and the sum of the propylene content and the content of α-olefin components other than propylene is 100 mol%. The amount is more preferably 4.0 mol% or more, even more preferably 5.0 mol% or more, particularly preferably 6.0 mol% or more, more preferably 12 mol% or less, even more preferably 11 mol% or less, and particularly preferably 10 mol% or less.Examples of the α-olefin component having 4 or more carbon atoms include 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, etc. The α-olefin component other than propylene is preferably an α-olefin component other than propylene having 2 to 20 carbon atoms, more preferably an α-olefin component other than propylene having 2 to 10 carbon atoms, even more preferably an α-olefin component other than propylene having 2 to 6 carbon atoms, and particularly preferably an α-olefin component other than propylene having 2 to 4 carbon atoms.

[0037] Various suitable physical properties of the polypropylene resin composition are described below. When two or more different polypropylene copolymers are used, the physical property values ​​are the mass average values ​​of the physical properties of each polypropylene copolymer. The same applies to the sealing layer B described above and the functional layer D described below.

[0038] Melting point Tm of the polypropylene resin composition constituting the intermediate layer C c is preferably 150°C or less, more preferably 145°C or less, and even more preferably 140°C or less. c By setting the melting point Tm of the polypropylene resin composition constituting the intermediate layer C within the above range, the heat seal strength can be increased. c The lower limit of the melting point Tm of the polypropylene resin composition constituting the intermediate layer C is not particularly limited, and is, for example, 120° C. or more. c is the melting point Tm of the polypropylene resin composition constituting the seal layer B b Higher is preferable.

[0039] The melt flow rate (MFR) of the polypropylene resin composition constituting the intermediate layer C, measured at a temperature of 230°C and a load of 2.16 kgf, is preferably 3.0 g / 10 min or more and 6.0 g / 10 min or less. The melt flow rate value is more preferably 3.5 g / 10 min or more, even more preferably 4.0 g / 10 min or more, particularly preferably 4.3 g / 10 min or more, and more preferably 5.5 g / 10 min or less, even more preferably 5.0 g / 10 min or less, particularly preferably 4.8 g / 10 min or less. Furthermore, from the viewpoint of increasing the heat seal strength, the melt flow rate of the polypropylene resin composition constituting the intermediate layer C is preferably smaller than the melt flow rate of the polypropylene resin composition constituting the seal layer B.

[0040] The polypropylene copolymer contained in the intermediate layer C is preferably at least one selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer, and more preferably a propylene-ethylene-butene copolymer.

[0041] 3-2. Propylene-Ethylene-Butene Copolymer The content of the α-olefin component other than propylene in the propylene-ethylene-butene copolymer in the intermediate layer C is preferably 4 mol% or more. When the content of the α-olefin component other than propylene is 4 mol% or more, the interlayer adhesion between the intermediate layer C and the seal layer B is likely to be improved, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The content of the α-olefin component other than propylene is more preferably 5 mol% or more, and even more preferably 6 mol% or more. The upper limit of the content of the α-olefin component other than propylene is not particularly limited, and is, for example, 25 mol% or less. Note that when there are two or more α-olefin components other than propylene, the total amount is the content of the α-olefin components other than propylene. The ethylene content is preferably 1 mol% or more, and more preferably 2 mol% or more. The upper limit of the ethylene content is not particularly limited, but if the ethylene content is too high, crystallization is too suppressed, resulting in lower crystallinity compared to a propylene homopolymer, which may result in a decrease in the stiffness of the film; therefore, it is, for example, 10 mol% or less. The butene content is preferably 1 mol% or more, more preferably 2 mol% or more. There are no particular limitations on the upper limit of the butene content, but if the butene content is too high, crystallization is too suppressed, resulting in lower crystallinity compared to a propylene homopolymer, and as a result, there is a risk of reducing the stiffness of the film, so the upper limit is, for example, 16 mol% or less. As a propylene-ethylene-butene copolymer having a total content of α-olefin components other than propylene of 4 mol% or more, a commercially available product may be used, such as FSX66E8 manufactured by Sumitomo Chemical Co., Ltd.

[0042] 3-3. Propylene-Butene Copolymer The butene content in the propylene-butene copolymer is preferably 4 mol% or more. A butene content of 4 mol% or more tends to improve the interlayer adhesion between the intermediate layer C and the seal layer B, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The butene content is preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the butene content, but if the butene content is too high, crystallization is too suppressed, resulting in lower crystallinity compared to propylene homopolymer, which may result in a decrease in the stiffness of the film. Therefore, for example, the upper limit is 16 mol% or less, and preferably 12 mol% or less. As a propylene-butene copolymer having a butene content of 4 mol% or more, commercially available products may be used, such as SP7843 manufactured by Sumitomo Chemical Co., Ltd., SPX78J1 manufactured by Sumitomo Chemical Co., Ltd., and XR110H manufactured by Mitsui Chemicals, Inc.

[0043] 3-4. Propylene-Ethylene Copolymer The ethylene content of the propylene-ethylene copolymer is preferably 4 mol% or more. An ethylene content of 4 mol% or more tends to improve the interlayer adhesion between the intermediate layer C and the seal layer B, and as a result, tends to improve heat seal strength and hermetic sealability. The ethylene content is more preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the ethylene content, but if the ethylene content is too high, crystallization is too suppressed, resulting in lower crystallinity compared to propylene homopolymer, which may result in a decrease in the stiffness of the film. Therefore, for example, the upper limit is 12 mol% or less. As a propylene-ethylene copolymer having an ethylene content of 4 mol% or more, commercially available products may be used, such as PC540R manufactured by SunAllomer Co., Ltd. and VM3588FL manufactured by Mitsui Chemicals, Inc.

[0044] 3-5. Anti-Fog Agent The polypropylene resin composition constituting the intermediate layer C may or may not contain an anti-fogging agent. The anti-fogging agents described in the description of the substrate layer A can be used as the anti-fogging agent. Even if the polypropylene resin composition constituting the intermediate layer C does not contain an anti-fogging agent, the anti-fogging agent may migrate from the substrate layer A to the intermediate layer C during the film formation process, and the resulting biaxially oriented polypropylene film may contain an anti-fogging agent in the intermediate layer C. Furthermore, as long as the effects of the present invention are not impaired, the polypropylene resin composition constituting the intermediate layer C may contain additives such as resins other than polypropylene copolymers, the anti-fogging agents described above, known heat stabilizers, antioxidants, UV absorbers, nucleating agents, adhesives, flame retardants, inorganic or organic fillers, etc. Examples of resins other than polypropylene copolymers include polyolefin resins other than the polypropylene copolymers used in the intermediate layer B, and various elastomers. However, the amount of these additives is preferably small, and the amount of resins other than polypropylene copolymers in the polypropylene resin composition constituting the intermediate layer C is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 2% by mass or less, and may be 0% by mass or more. Furthermore, the amount of additives other than resins in the polypropylene resin composition constituting the intermediate layer C is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, particularly preferably 1% by mass or less, and may be 0% by mass or more.

[0045] 4. Functional Layer D The functional layer D is preferably provided on the surface of the base layer A on which the seal layer B is not provided. The functional layer D is not particularly limited and may be a layer of the same composition as the intermediate layer C. In order to impart functions such as easy lubricity between films or between the film and processing tools, or antistatic properties to the functional layer D, an antiblocking agent, a lubricant such as wax or metal soap, a plasticizer, a processing aid, an antistatic agent, etc. may be blended into the polypropylene resin composition constituting the functional layer D.

[0046] 4-1. Polypropylene Resin Composition The functional layer D is preferably a layer made of a polypropylene resin composition, and more preferably contains a polypropylene copolymer containing an α-olefin other than propylene. That is, the polypropylene resin composition constituting the functional layer D more preferably contains a polypropylene copolymer containing an α-olefin other than propylene. In the description of the functional layer D, even when the term "polypropylene copolymer" is simply used, it refers to a polypropylene copolymer containing an α-olefin other than propylene. The functional layer D preferably contains 70% by mass or more of the polypropylene copolymer, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. This proportion may be 100% by mass or less. The polypropylene copolymer contained in the functional layer D can also be two or more different polypropylene copolymers, with the total content preferably being within the above range. By containing the polypropylene copolymer in an amount of 70% by mass or more and 100% by mass or less, it is easy to improve the interlayer adhesion between the functional layer D and the layer adjacent to the functional layer D, thereby further increasing the heat seal strength of the biaxially oriented polypropylene film. The content of α-olefin components other than propylene in the polypropylene copolymer contained in the functional layer D, i.e., the total amount of ethylene and α-olefins having 4 or more carbon atoms, is preferably 4.0 mol% or more. In this case, the propylene content in the polypropylene copolymer is 96 mol% or less, and the sum of the propylene content and the content of α-olefin components other than propylene is 100 mol%. The amount is more preferably 4.0 mol% or more, even more preferably 5.0 mol% or more, particularly preferably 6.0 mol% or more, more preferably 12 mol% or less, even more preferably 11 mol% or less, and particularly preferably 10 mol% or less.Examples of the α-olefin component having 4 or more carbon atoms include 1-butene, 1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 5-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-eicosene, etc. The α-olefin component other than propylene is preferably an α-olefin component other than propylene having 2 to 20 carbon atoms, more preferably an α-olefin component other than propylene having 2 to 10 carbon atoms, even more preferably an α-olefin component other than propylene having 2 to 6 carbon atoms, and particularly preferably an α-olefin component other than propylene having 2 to 4 carbon atoms.

[0047] Melting point Tm of the polypropylene resin composition constituting the functional layer D d is preferably 150°C or less, more preferably 145°C or less, and even more preferably 140°C or less. d By setting the melting point Tm of the polypropylene resin composition constituting the functional layer D within the above range, the heat seal strength can be increased. d The lower limit is not particularly limited, and is, for example, 120°C or higher.

[0048] The polypropylene resin composition constituting the functional layer D preferably has a melt flow rate (MFR) of 3.0 g / 10 min or more and 6.0 g / 10 min or less, as measured at a temperature of 230° C. and a load of 2.16 kgf. The melt flow rate is more preferably 3.5 g / 10 min or more, even more preferably 4.0 g / 10 min or more, and particularly preferably 4.3 g / 10 min or more, and is more preferably 5.5 g / 10 min or less, even more preferably 5.0 g / 10 min or less, and particularly preferably 4.8 g / 10 min or less.

[0049] The polypropylene copolymer contained in the functional layer D preferably contains at least one selected from the group consisting of a propylene-butene copolymer, a propylene-ethylene-butene copolymer, and a propylene-ethylene copolymer, and more preferably contains a propylene-ethylene-butene copolymer.

[0050] 4-2. Propylene-Ethylene-Butene Copolymer The content of the α-olefin component other than propylene in the propylene-ethylene-butene copolymer is preferably 4 mol% or more. When the content of the α-olefin component other than propylene is 4 mol% or more, the interlayer adhesion between the functional layer D and the layer adjacent to the functional layer D is likely to be improved, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The content of the α-olefin component other than propylene is more preferably 5 mol% or more, and even more preferably 6 mol% or more. The upper limit of the content of the α-olefin component other than propylene is not particularly limited, and is, for example, 25 mol% or less. Note that when there are two or more α-olefin components other than propylene, the total amount is the content of the α-olefin components other than propylene. The ethylene content is preferably 1 mol% or more, and more preferably 2 mol% or more. The upper limit of the ethylene content is not particularly limited, but since an ethylene content that is too high may cause the film surface to become sticky and may reduce slipperiness and blocking resistance, it is, for example, 10 mol% or less. The butene content is preferably 1 mol% or more, more preferably 2 mol% or more. There is no particular upper limit to the butene content, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease, so for example, it is 16 mol% or less. As the propylene-ethylene-butene copolymer having a total content of α-olefin components other than propylene of 4 mol% or more, a commercially available product may be used, such as FSX66E8 manufactured by Sumitomo Chemical Co., Ltd.

[0051] 4-3. Propylene-Butene Copolymer The butene content in the propylene-butene copolymer is preferably 4 mol% or more. A butene content of 4 mol% or more tends to improve the interlayer adhesion between the functional layer D and the layer adjacent to the functional layer D, and as a result, tends to improve heat seal strength and hermetic sealability. The butene content is more preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the butene content, but if the butene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may decrease. Therefore, for example, it is 16 mol% or less, preferably 12 mol% or less. As a propylene-butene copolymer having a butene content of 4 mol% or more, commercially available products may be used, such as SP7843 manufactured by Sumitomo Chemical Co., Ltd., SPX78J1 manufactured by Sumitomo Chemical Co., Ltd., and XR110H manufactured by Mitsui Chemicals, Inc.

[0052] 4-4. Propylene-Ethylene Copolymer The ethylene content of the propylene-ethylene copolymer is preferably 4 mol% or more. When the ethylene content is 4 mol% or more, the interlayer adhesion between the functional layer D and the layer adjacent to the functional layer D is likely to be improved, and as a result, the heat seal strength and hermetic sealability are likely to be improved. The ethylene content is more preferably 5 mol% or more, and even more preferably 6 mol% or more. There is no particular upper limit for the ethylene content, but if the ethylene content is too high, the film surface may become sticky and the slipperiness and blocking resistance may be reduced, so for example, it is 12 mol% or less. As a propylene-ethylene copolymer having an ethylene content of 4 mol% or more, commercially available products may be used, such as PC540R manufactured by SunAllomer Co., Ltd. and VM3588FL manufactured by Mitsui Chemicals, Inc.

[0053] 4-5. Anti-Fog Agent The polypropylene resin composition constituting the functional layer D may or may not contain an anti-fogging agent. The anti-fogging agents described in the description of the substrate layer A can be used as the anti-fogging agent. Even if the polypropylene resin composition constituting the functional layer D does not contain an anti-fogging agent, the anti-fogging agent may migrate from the substrate layer A to the functional layer D during the film formation process, and the resulting biaxially oriented polypropylene film may contain the anti-fogging agent in the functional layer D. Furthermore, as long as the effects of the present invention are not impaired, the polypropylene resin composition constituting the functional layer D may contain additives such as resins other than polypropylene copolymers, the anti-fogging agents described above, known heat stabilizers, antioxidants, UV absorbers, nucleating agents, adhesives, flame retardants, inorganic or organic fillers, etc. Examples of resins other than polypropylene copolymers include polyolefin resins other than the polypropylene copolymers used in the functional layer D, and various elastomers. However, it is preferable that these are added in small amounts, and the amount of resins other than polypropylene copolymers in the polypropylene resin composition constituting the functional layer D is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, particularly preferably 2% by mass or less, and can be 0% by mass or more. Also, the amount of additives other than resins in the polypropylene resin composition constituting the functional layer D is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, particularly preferably 1% by mass or less, and can be 0% by mass or more.

[0054] 5. Content of Anti-Fog Agent in Film The content of the anti-fogging agent in the biaxially oriented polypropylene film of the present invention is preferably 0.1% by mass or more and 10% by mass or less. The content is more preferably 0.15% by mass or more, even more preferably 0.2% by mass or more, particularly preferably 0.25% by mass or more, most preferably 0.3% by mass or more, more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, particularly preferably 2.0% by mass or less, and most preferably 1.5% by mass or less. Even if the anti-fogging agent is added only to the polypropylene resin composition constituting the base layer A, the anti-fogging agent may migrate from the base layer A to other layers during film formation and storage after film formation, and the anti-fogging agent may migrate to the outermost seal layer B, causing the anti-fogging agent to be present on the surface of the seal layer B, thereby providing anti-fogging properties.

[0055] 6. Layer structure and thickness structure of biaxially oriented polypropylene film The biaxially oriented polypropylene film of the present invention has a base layer A and a seal layer B. An intermediate layer C may be present between the base layer A and the seal layer B. The layer structure of the biaxially oriented polypropylene film of the present invention has the base layer A and the seal layer B, and as long as the seal layer B is present on at least one outermost surface, the intermediate layer C may be present between the base layer A and the seal layer B, or another layer may be present between the base layer A and the intermediate layer C, or the intermediate layer C may be laminated directly on the base layer A. Furthermore, another layer may be present between the intermediate layer C and the seal layer B, or the seal layer B may be laminated directly on the intermediate layer C. Examples of the biaxially oriented polypropylene film of the present invention include a two-layer structure of base layer A / seal layer B, a three-layer structure of base layer A / intermediate layer C / seal layer B, a three-layer structure of seal layer B1 / base layer A / seal layer B2, a four-layer structure of seal layer B1 / base layer A / intermediate layer C / seal layer B2, a five-layer structure of seal layer B1 / intermediate layer C1 / base layer A / intermediate layer C2 / seal layer B2, and a six-layer structure of seal layer B1 / base layer A1 / intermediate layer C1 / base layer A2 / intermediate layer C2 / seal layer B2. In this case, the base layer A1 and the base layer A2 may be made of different polypropylene-based resin compositions or may be the same, the intermediate layers C1 and C2 may be made of different polypropylene-based resin compositions or may be the same, and the seal layer B1 and the seal layer B2 may be made of different polypropylene-based resin compositions or may be the same.

[0056] When the biaxially oriented polypropylene film of the present invention has a functional layer D, the functional layer D may be laminated directly on the surface of the base layer A, or an intermediate layer C may be interposed between the base layer A and the functional layer D. The functional layer D may also be located between the base layer A and the intermediate layer C, or between the intermediate layer C and the seal layer B. When the biaxially oriented polypropylene film of the present invention has a functional layer D, the structure is not particularly limited as long as the base layer A, intermediate layer C, and seal layer B are arranged in this order and the seal layer B is located on at least one outermost surface. Examples of the structure include a four-layer structure of functional layer D / base layer A / intermediate layer C / seal layer B, in which the base layer A / intermediate layer C / seal layer B further has a functional layer D, and a five-layer structure of functional layer D / intermediate layer C / base layer A / intermediate layer C / seal layer B, in which the intermediate layer C / base layer A / intermediate layer C / seal layer B further has a functional layer D.

[0057] The overall thickness of the biaxially oriented polypropylene film of the present invention varies depending on its application and method of use, but from the viewpoints of film strength, sealing ability, and water vapor barrier property, it is preferably 5 μm or more and 100 μm or less. The thickness is more preferably 10 μm or more, even more preferably 18 μm or more, and more preferably 80 μm or less, and even more preferably 50 μm or less. When the biaxially oriented polypropylene film of the present invention is used as a freshness-preserving packaging material, the thickness is preferably 33 μm or less, more preferably 28 μm or less, even more preferably 23 μm or less, and particularly preferably 18 μm or less.

[0058] The thickness of the base layer A varies depending on the application and method of use, but is preferably 5 μm or more and 90 μm or less. A thickness of 5 μm or more can improve film strength, sealing property, or water vapor barrier property. Furthermore, a thickness of 90 μm or less can reduce the environmental load by reducing the volume. The thickness of the base layer A is more preferably 10 μm or more, even more preferably 15 μm or more, and more preferably 50 μm or less, and even more preferably 30 μm or less.

[0059] The thickness of the intermediate layer C varies depending on the application and method of use, but is preferably 0.5 μm or more and 4 μm or less. By making the thickness 0.5 μm or more, the adhesion between the base layer A and the seal layer B can be increased, thereby increasing the seal strength. Furthermore, by making the thickness 4 μm or less, the environmental load can be reduced by reducing the volume. The thickness of the intermediate layer C is more preferably 1 μm or more and 3 μm or less.

[0060] The thickness of the sealing layer B varies depending on the application and method of use, but is preferably 0.3 μm or more and 2 μm or less. A thickness of 0.3 μm or more can increase the heat seal strength. Furthermore, a thickness of 2 μm or less can reduce the environmental load by reducing the volume. The thickness of the sealing layer B is more preferably 0.5 μm or more and 1.5 μm or less.

[0061] The thickness of the functional layer D varies depending on the application and method of use, but is preferably 0.3 μm or more and 2 μm or less. A thickness of 0.3 μm or more can increase heat seal strength. Furthermore, a thickness of 2 μm or less can reduce the environmental load by reducing the volume. The thickness of the functional layer D is more preferably 0.5 μm or more and 1.5 μm or less.

[0062] 7. Method for Producing Biaxially Oriented Polypropylene Film The method for producing the biaxially oriented polypropylene film of the present invention is not particularly limited, but examples thereof include a method in which melt lamination is performed by a T-die method, inflation method, or the like using an extruder suitable for the number of layers, followed by cooling by a cooling roll method, water cooling method, or air cooling method to obtain an unstretched laminated film, and then stretching the obtained film by a sequential biaxial stretching method, simultaneous biaxial stretching method, tube stretching method, or the like.

[0063] Below, an example is given of a method for producing a biaxially oriented polypropylene film having a structure of functional layer D / substrate layer A / intermediate layer C / sealing layer B by a sequential biaxial stretching method. Note that the following example can be modified as appropriate depending on the layer structure, etc. The polypropylene resin compositions constituting each of the substrate layer A, intermediate layer C, sealing layer B, and functional layer D are as described above. Furthermore, it is preferable to adjust the amount of anti-fogging agent added to the substrate layer A, intermediate layer C, and sealing layer B taking into consideration that the anti-fogging agent will evaporate into the atmosphere when exposed to high temperatures during the film production process.

[0064] The polypropylene resin compositions constituting the functional layer D, substrate layer A, intermediate layer C, and seal layer B are melt-extruded using one or more extruders, and the extruded multilayer sheet is cooled with a cooling roll to form an unstretched sheet. The resulting unstretched sheet is then stretched in the longitudinal direction (MD). The stretched sheet is then preheated, stretched in the transverse direction (TD), and finally heat-set to obtain the biaxially oriented polypropylene film of the present invention. If necessary, the biaxially oriented polypropylene film can be surface-treated on at least one side and then wound up on a winder to obtain a film roll.

[0065] 7-1. Extrusion Process The polypropylene resin compositions constituting the functional layer D, base layer A, intermediate layer C, and seal layer B are each melted at, for example, 200°C or higher and 260°C or lower, and the molten polypropylene resin compositions are delivered from different flow paths using four extruders. The delivered polypropylene resin compositions are laminated in multiple layers using a multi-layer feed block, static mixer, multi-layer multi-manifold die, or the like, and a multi-layer sheet laminated in the order of functional layer D / base layer A / intermediate layer C / seal layer B is extruded from a T-die. It is also possible to obtain a multi-layer sheet using only one extruder by introducing a multi-layering device into the melt line from the extruder to the T-die. Furthermore, from the viewpoints of stabilizing back pressure and suppressing thickness fluctuations, it is preferable to install a gear pump in the polymer flow path.

[0066] The thickness of the unstretched multilayer sheet is preferably 3500 μm or less from the viewpoint of improving cooling efficiency, and more preferably 3000 μm or less, but can be appropriately adjusted depending on the film thickness after sequential biaxial stretching. The thickness of the unstretched multilayer sheet can be adjusted by the extrusion speed of the polypropylene resin composition and the lip width of the T-die, etc. The lower limit of the thickness of the unstretched multilayer sheet is not particularly limited, but can be, for example, 500 μm.

[0067] 7-2. Cooling Step The unstretched multilayer sheet co-extruded into a sheet form from a T-die is brought into contact with a metal cooling roll and cooled and solidified. At this time, it is preferable to ground the seal layer B side on the cooling roll. Furthermore, in order to accelerate solidification, it is preferable to further cool the unstretched multilayer sheet cooled on the cooling roll by, for example, immersing it in a water bath. The temperature of the cooling roll is preferably 10°C or higher and lower than the crystallization temperature of the polypropylene resin composition. When increasing the transparency of the film, it is preferable to cool and solidify using a cooling roll at 10°C or higher and 50°C or lower. A cooling roll temperature of 50°C or lower tends to increase the transparency of the unstretched multilayer sheet, and is more preferably 40°C or lower, and even more preferably 30°C or lower. In order to increase the degree of crystal orientation after successive biaxial stretching, it is sometimes preferable to set the cooling temperature to 40° C. or higher, but when a propylene homopolymer having a mesopentad fraction of 97.0% or higher is used as described above, the temperature of the cooling roll is preferably 40° C. or lower, more preferably 30° C. or lower, from the viewpoint of facilitating the stretching in the next step and reducing thickness unevenness. When a water bath is used, the temperature of the water bath is also preferably 10° C. or higher and 50° C. or lower, more preferably 40° C. or lower, and even more preferably 30° C. or lower, for the same reasons as above.

[0068] 7-3. Longitudinal Stretching Process The longitudinal stretching temperature is preferably Tm-30°C or higher and Tm-7°C or lower. A temperature of Tm-30°C or higher facilitates subsequent widthwise stretching and reduces film thickness unevenness. Furthermore, a temperature of Tm-7°C or lower facilitates a reduction in heat shrinkage, and also reduces the risk of difficulty in stretching by applying stretching rolls or deterioration in quality due to increased surface roughness. The temperature is more preferably Tm-27°C or higher, even more preferably Tm-25°C or higher, and even more preferably Tm-12°C or lower, and even more preferably Tm-10°C or lower. Here, Tm refers to the Tm of the resin forming the thickest layer. The longitudinal stretching ratio is preferably 3.5 times or higher and 8.0 times or lower. A stretching ratio of 3.5 times or higher facilitates increased strength and reduced film thickness unevenness. Furthermore, when the stretching ratio is 8.0 times or less, the width direction stretching in the width direction stretching step is easy, and productivity is easily improved. The stretching ratio is more preferably 3.8 times or more, even more preferably 4.2 times or more, and more preferably 7.0 times or less, and even more preferably 6.0 times or less. Note that the longitudinal stretching may be performed in two or more stages using three or more pairs of stretching rolls, but it is preferable to perform stretching in one stage using two pairs of stretching rolls. When stretching in multiple stages, it is preferable that the highest stretching temperature is within the above range.

[0069] 7-4. Preheating Step It is preferable to heat the uniaxially stretched film after longitudinal stretching in a preheating step to sufficiently soften the polypropylene resin composition before the widthwise stretching step. The heating temperature in the preheating step is preferably Tm or higher and Tm + 25°C or lower. By setting the heating temperature in the preheating step to the melting point or higher, softening proceeds, facilitating widthwise stretching. Furthermore, by setting the heating temperature in the preheating step to Tm + 25°C or lower, orientation proceeds during widthwise stretching, making it easier to develop rigidity. The heating temperature is more preferably Tm + 2°C or higher, even more preferably Tm + 3°C or higher, more preferably Tm + 20°C or lower, and even more preferably Tm + 15°C or lower. Note that if the preheating step consists of multiple zones, the temperature of the hottest zone among them is taken as the preheating temperature. Note that Tm here refers to the Tm of the resin forming the thickest layer.

[0070] 7-5. Width Direction Stretching Process The width direction stretching temperature is preferably Tm-10°C or higher and the heating temperature in the preheating process or lower. When the temperature is Tm-10°C or higher, the rigidity of the resulting film is easily improved, and when the temperature is lower than the heating temperature in the preheating process, stretching unevenness is less likely to occur. The temperature is more preferably Tm-9°C or higher, even more preferably Tm-7°C or higher, particularly preferably Tm-5°C or higher, and more preferably Tm+10°C or lower, even more preferably Tm+7°C or lower, and particularly preferably Tm+5°C or lower. Note that Tm here refers to the Tm of the resin forming the thickest layer. In the width direction stretching process, a width direction stretching process in the above temperature range (hereinafter sometimes referred to as the "early stretching process") is preferably followed by a later stretching process in which stretching is performed at a lower temperature. The later stretching process facilitates increasing the rigidity of the film. The width direction stretching ratio is preferably 10 times or higher and 20 times or lower. When the stretching ratio is 10 times or more, rigidity is easily increased and thickness unevenness is easily reduced. When the stretching ratio is 20 times or less, the heat shrinkage rate is easily reduced and the film is less likely to break during stretching. The stretching ratio is more preferably 11 times or more, even more preferably 12 times or more, particularly preferably 12.5 times or more, and more preferably 17 times or less, and even more preferably 15 times or less. When a later stretching step is added, it is preferable that the total stretching ratio be within the above range.

[0071] 7-6. Heat Treatment Step It is preferable to perform heat treatment after the width direction stretching step. Specific means for heat treatment include providing a zone with a higher temperature than the stretching zone after the width direction stretching is completed, or increasing the zone temperature in the latter half of stretching and passing the film through a zone at the same temperature after the stretching is completed to increase the film temperature. Examples of heating methods include blowing hot air or heating with an infrared heater, but there are no particular limitations as long as the method increases the film temperature from the temperature at the end of the width direction stretching step.

[0072] The heat treatment step is preferably carried out immediately after the end of the width direction stretching step, i.e., immediately after the width direction stretching reaches the final stretch ratio. The temperature in the heat treatment step is preferably higher than that at the end of the width direction stretching step, specifically, preferably the width direction stretching temperature + 1°C or more. Furthermore, the heat treatment step is preferably carried out in two stages, and it is preferable that the heat treatment is carried out at a temperature higher than that at the end of the width direction stretching step in the early heat treatment step, and then at a temperature lower than that in the early heat treatment step in the late heat treatment step. The early heat treatment step and the late heat treatment step will be described below.

[0073] 7-6-1. Preliminary Heat Treatment Step The heating temperature in the preliminary heat treatment step is preferably Tm or higher and Tm + 20°C or lower. Heating at a temperature above Tm promotes relaxation, reducing tension in the molecular chains and allowing crystallization to proceed more reliably. On the other hand, heating at a temperature below Tm + 20°C suppresses melting while suppressing relaxation of the oriented molecular chains, thereby more reliably preventing a decrease in rigidity. The heating temperature is more preferably Tm + 3°C or higher, even more preferably Tm + 4°C or higher, particularly preferably Tm + 5°C or higher, more preferably Tm + 18°C ​​or lower, even more preferably Tm + 14°C or lower, and particularly preferably Tm + 10°C or lower. Heating in the heat treatment step after the stretching step relaxes the molecular chain orientation formed during stretching, making crystallization more likely to occur in the final heat treatment step. The temperature can be gradually increased from the temperature at the end of width direction stretching to the temperature during heating, or it can be increased in stages or in a single step. Raising the temperature stepwise or in one step is preferred because it is easier to control the orientation of molecular chains in the film. Here, Tm refers to the Tm of the resin forming the thickest layer. In the heat treatment step, the film may or may not be relaxed in the width direction. Specifically, a relaxation rate of 0% or more and 3% or less is preferred. If the relaxation rate is within this range, the rigidity is less likely to decrease and film thickness fluctuations tend to be small. The relaxation rate is more preferably 0% or more and 1% or less, and even more preferably 0%, i.e., no relaxation. If it is desired to further increase the rigidity, relaxation is not necessary. Furthermore, the film may be slightly expanded to suppress sagging, etc., as long as it does not impair the effects of the present invention.

[0074] 7-6-2. Later Heat Treatment Step The heating temperature in the later heat treatment step is preferably Tm-70°C or higher and Tm or lower. If the heating temperature is Tm-70°C or higher, lamellar thickening proceeds, and the melting point of the film is likely to increase. In other words, heat resistance at high temperatures is obtained. On the other hand, if the heating temperature is Tm or lower, crystallization proceeds and the heat shrinkage rate is likely to decrease. The heating temperature is more preferably Tm-50°C or higher, even more preferably Tm-40°C or higher, particularly preferably Tm-30°C or higher, more preferably Tm-1°C or lower, even more preferably Tm-2°C or lower, and particularly preferably Tm-3°C or lower. Note that Tm here refers to the Tm of the resin forming the thickest layer. In the later heat treatment step, the film may be relaxed in the width direction to adjust the heat shrinkage rate. When relaxed, the relaxation rate is preferably 1% or higher and 8% or lower. If the relaxation rate is within this range, rigidity is less likely to decrease and film thickness fluctuations are likely to be small. The relaxation rate is more preferably 2% or more, even more preferably 3% or more, and more preferably 6% or less, even more preferably 5% or less. However, if it is desired to further increase the rigidity, relaxation may not be required.

[0075] During the widthwise stretching process, molecular chains are oriented by stretching, but remain strongly entangled, resulting in an excessively constrained state of the molecular chains. If a heat treatment process is performed in this state, the excessively constrained molecular chains due to entanglement make it difficult to increase the crystallinity, and the lamellae in the crystalline region do not increase in thickness. This leads to the formation of crystalline regions that melt at lower temperatures, resulting in insufficient heat resistance at high temperatures. Therefore, in conventional film-forming processes, in order to eliminate the entanglement of molecular chains after widthwise stretching, the film is relaxed by several percent to several tens of percent during the heat treatment process to promote crystallization. However, relaxation reduces the molecular chain orientation generated during the widthwise stretching process, resulting in a decrease in the rigidity of the film. Therefore, it is difficult to achieve both heat resistance and rigidity in conventional film-forming processes. Furthermore, heat treatment at high temperatures can cause excessive melting, resulting in the whitening of the film. To solve this problem, it is preferable to perform heat treatment immediately after the end of the width direction stretching step at a temperature higher than that used for width direction stretching, for example, at a relaxation rate of 1% to 5%, preferably 3% or less, to relieve the constraint of the molecular chains due to excessive entanglement while maintaining the molecular chain orientation. By performing this heat treatment step, the presence of constrained molecular chains due to entanglement is reduced, which increases the crystallinity and makes it easier to increase the thickness of the lamellae in the crystalline portion, thereby enabling the film to exhibit sufficient heat resistance even at high temperatures.

[0076] Furthermore, increasing the amount of low molecular weight polypropylene components in the polypropylene resin composition constituting the biaxially oriented polypropylene film can reduce the entanglement of molecular chains, thereby weakening the heat shrinkage stress in parts other than the lamellae of the crystalline portion and further reducing the heat shrinkage rate, which is preferable.

[0077] 7-7. Cooling Step It is preferable to cool the film immediately after the heat treatment step. The cooling temperature is preferably 10°C or higher and 140°C or lower. The cooling temperature is more preferably 15°C or higher, even more preferably 20°C or higher, more preferably 135°C or lower, even more preferably 130°C or lower, particularly preferably 80°C or lower, and most preferably 50°C or lower. By providing a cooling step, the state of molecular orientation within the film can be fixed.

[0078] 7-8. Surface Treatment Step In order to improve printability and lamination properties, the biaxially oriented polypropylene film of the present invention is preferably surface-treated on at least one of the seal layer B and the surface layer opposite to the seal layer B, and it is more preferable to surface-treat the seal layer B from the viewpoint of increasing the surface tension of the seal layer B. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, and acid treatment, and there are no particular restrictions on the method. However, from the viewpoints that continuous treatment is possible and that it can be easily carried out before the winding step in the film production process, it is preferable to carry out corona discharge treatment, plasma treatment, or flame treatment, and from the viewpoint of improving anti-fogging properties, it is more preferable to carry out corona discharge treatment.

[0079] 8. Various Properties of the Biaxially Oriented Polypropylene Film of the Present Invention The biaxially oriented polypropylene film of the present invention preferably has the following properties. Here, the "longitudinal direction (MD direction)" of the biaxially oriented polypropylene film of the present invention refers to the direction corresponding to the flow direction in the film production process, and the "width direction (TD direction)" refers to the direction perpendicular to the flow direction in the film production process, and the same applies hereinafter. For polypropylene films whose flow direction in the film production process is unknown, wide-angle X-rays are incident perpendicular to the film surface, and scattering peaks derived from the (110) plane of the α-crystals are scanned in the circumferential direction. The direction with the greatest diffraction intensity in the obtained diffraction intensity distribution is defined as the "longitudinal direction," and the direction perpendicular to that is defined as the "width direction."

[0080] 8-1. Width-Direction Length In thermomechanical analysis, when the temperature of the biaxially oriented polypropylene film of the present invention is increased from 30°C to 130°C at a heating rate of 10°C / min, where X0 is the width-direction length at 30°C, X1 is the maximum width-direction length during the heating period, and X2 is the minimum width-direction length during the heating period, the percentage of (X1-X0) / X0 is preferably 0.50% or less. When this percentage is 0.50% or less, film deformation can be suppressed even after heating at high temperatures, such as during heat processing with a roll, printing, or heat sealing. This reduces the deterioration of film flatness and improves film processability. Furthermore, high-temperature printing ink is transferred during printing, reducing the risk of printing pitch deviation. The percentage is more preferably 0.45% or less, even more preferably 0.40% or less, particularly preferably 0.35% or less, and most preferably 0.30% or less. The smaller the percentage of (X1-X0) / X0, the better. While the lower limit is not particularly limited, considering technical difficulties, it is, for example, 0.01% or more, preferably 0.02% or more. The percentage of (X2-X0) / X0 of the biaxially oriented polypropylene film of the present invention is preferably -0.50% or more. When this percentage is -0.50% or more, film deformation can be suppressed even after heating at high temperatures, such as during heat processing with a roll, printing, or heat sealing. This prevents deterioration of the film's flatness and improves the film's processability. The percentage is more preferably -0.45% or more, even more preferably -0.40% or more, particularly preferably -0.35% or more, and most preferably -0.30% or more. The larger the percentage of (X2-X0) / X0, the better. Although the upper limit is not particularly limited, considering technical difficulties, it is, for example, 0.01% or less, preferably 0.00% or less.

[0081] In thermomechanical analysis, when the biaxially oriented polypropylene film of the present invention is heated from 30°C to 160°C at a heating rate of 10°C / min, the temperature at which the width direction length is 0.9950 x X0 or less, i.e., the temperature at which the film shrinks by 0.5%, is preferably 129°C or higher, more preferably 130°C or higher, even more preferably 131°C or higher, particularly preferably 132°C or higher, and most preferably 133°C or higher. The "temperature at which the width direction length is 0.9950 x X0 or less" refers to the lowest temperature at which the width direction length is 0.9950 x X0 or less when the film is heated from 30°C to 160°C at a heating rate of 10°C / min. When the temperature at which the width direction length is 0.9950 x X0 or less is 129°C or higher, deformation of the film can be suppressed even after heating at high temperatures, such as during heat processing with a roll, printing, or heat sealing. This prevents deterioration of the film's flatness and improves the film's processability. The temperature at which the temperature becomes 0.9950 × X0 or less is preferably higher, and the upper limit is not particularly limited, but is, for example, 160° C. or less, preferably 156° C. or less. When the temperature is 160° C. or less, practical production is easy and transparency is easily maintained.

[0082] 8-2. Loss Modulus The loss modulus is determined by dynamic viscoelasticity measurement. Specifically, the temperature is raised from -60°C to 160°C at a rate of 5°C / min under a nitrogen atmosphere with a measurement load of 10 g and a frequency of 10 Hz, and the loss modulus is measured at each temperature during the temperature rise. The inventors have found that while increasing the rigidity and heat resistance alone may not be enough to maintain the flatness of the film after heating, controlling the loss modulus in a predetermined temperature range to fall within a predetermined range makes it possible to maintain the flatness of the film even after heating.

[0083] Hereinafter, five parameters related to the loss modulus will be described: the maximum value E"(A) of the loss modulus between -25°C and 25°C, the minimum value E"(B) of the loss modulus between 25°C and 75°C, the maximum value E"(C) of the loss modulus between 100°C and 160°C, E"(C) / E"(A), and E"(B) / E"(C). In this specification, even when simply referring to "loss modulus," it always refers to the loss modulus in the width direction.

[0084] 8-2-1. Maximum value of loss modulus E" (A) from -25°C to 25°C Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers," Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that relaxation (primary dispersion) due to micro-Brownian motion of the main chain occurs in polypropylene films at temperatures from -25°C to 25°C, and also describes that the loss modulus from -25°C to 25°C increases as the degree of orientation by stretching increases. The present inventors have found that by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process, it is possible to increase the orientation in the film, i.e., to increase the value of the loss modulus from -25°C to 25°C.

[0085] The E"(A) of the biaxially oriented polypropylene film of the present invention is preferably 0.40 GPa or more. When E"(A) is 0.40 GPa or more, the rigidity tends to be high. E"(A) is more preferably 0.42 GPa or more, even more preferably 0.44 GPa or more, particularly preferably 0.46 GPa or more, and most preferably 0.48 GPa or more. There is no particular upper limit for E"(A), but a realistic value is, for example, 0.70 GPa or less, and preferably 0.60 GPa or less.

[0086] 8-2-2. Minimum value E"(B) of loss modulus between 25°C and 75°C. Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers," Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that increasing the crystallinity in a film, which contributes greatly to heat resistance, and reducing the amount of crystals that melt in a relatively low temperature range above the glass transition temperature of polypropylene resin (hereinafter referred to as the low temperature range) makes it difficult for relaxation due to melting to occur, which in turn suppresses relaxation of the amorphous portion. In other words, even when treated at high temperatures, the mobility of the amorphous portion is reduced, resulting in good heat resistance. The present inventors have found that by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process, it is possible to reduce the amount of crystals that melt in the low temperature range and thereby reduce the change in loss modulus from the glass transition temperature to 75°C.

[0087] The E"(B) of the biaxially oriented polypropylene film of the present invention is preferably 0.16 GPa or more. If E"(B) is 0.16 GPa or more, the heat shrinkage rate is likely to decrease. Furthermore, if E"(B) is 0.16 GPa or more, fewer crystals will melt in the low temperature range, thereby improving the flatness. E"(B) is more preferably 0.17 GPa or more, even more preferably 0.18 GPa or more, particularly preferably 0.19 GPa or more, and most preferably 0.20 GPa or more. There is no particular upper limit for E"(B), but a realistic value is, for example, 0.60 GPa or less, and preferably 0.50 GPa or less.

[0088] 8-2-3. Maximum value of loss modulus E" (C) from 100°C to 160°C Takayanagi Motoo, "Temperature Dispersion of Crystalline Polymers," Polymer, Society of Polymer Science, 1961, Vol. 10, No. 3, pp. 289-295, describes that when a stretched polypropylene film is heated and the loss modulus is measured at each temperature, a peak due to crystal dispersion appears at temperatures above 100°C. This crystal dispersion peak is thought to be due to an increase in frictional viscosity between the planes of the crystalline structure, and increases when the film is stretched at an optimal temperature during film formation. An increase in frictional viscosity indicates strong stress transmission within the crystalline phase, and is thought to correlate with increased rigidity. From the above, the present inventors have found that the maximum value of the loss modulus at 100°C or above can be increased by using highly stereoregular polypropylene and employing the above-mentioned width direction stretching process.

[0089] The E"(C) of the biaxially oriented polypropylene film of the present invention is preferably 0.28 GPa or more and 0.80 GPa or less. When E"(C) is 0.28 GPa or more, the rigidity is high, so that the bag shape when made into a packaging bag is easily maintained and the film is less likely to deform during processing such as printing. When E"(C) is 0.80 GPa or less, practical production is easier and the film is less likely to tear in the width direction. E"(C) is more preferably 0.29 GPa or more, even more preferably 0.30 GPa or more, particularly preferably 0.31 GPa or more, and most preferably 0.32 GPa or more. It is more preferably 0.75 GPa or less, even more preferably 0.70 GPa or less, particularly preferably 0.65 GPa or less, and most preferably 0.60 GPa or less.

[0090] The E"(C) / E"(A) ratio of the biaxially oriented polypropylene film of the present invention is preferably 0.55 or more, more preferably 0.55 or more and 1.30 or less. When E"(C) / E"(A) is 0.55 or more, the film has high rigidity, and the shape of the bag is easily maintained when made into a packaging bag, and the film is less likely to deform during processing such as printing. When E"(C) / E"(A) is 1.30 or less, practical production is easier and the film is less likely to tear in the width direction. E"(C) / E"(A) is more preferably 0.60 or more or 0.62 or more, particularly preferably 0.64 or more, and most preferably 0.66 or more. It is even more preferably 1.20 or less or 1.10 or less, particularly preferably 1.00 or less, and most preferably 0.90 or less.

[0091] The E"(B) / E"(C) ratio of the biaxially oriented polypropylene film of the present invention is preferably 0.55 or more, more preferably 0.55 or more and 1.30 or less. When E"(B) / E"(C) is 0.55 or more, there is little crystallization in the low temperature region, so that relaxation associated with melting is less likely to occur, and as a result, relaxation of the amorphous portion is also suppressed. As a result, even when treated at high temperatures, the mobility of the amorphous portion is low, and flatness and heat resistance can be improved. When E"(B) / E"(C) is 1.30 or less, rigidity is less likely to decrease and thickness fluctuation of the film is likely to be small. E"(B) / E"(C) is more preferably 0.60 or more or 0.61 or more, particularly preferably 0.62 or more, and most preferably 0.63 or more. It is even more preferably 1.25 or less or 1.20 or less, particularly preferably 1.15 or less, and most preferably 1.10 or less.

[0092] The storage modulus is determined by dynamic viscoelasticity measurement. Specifically, the temperature is increased from -60°C to 160°C at a rate of 5°C / min under a nitrogen atmosphere with a measurement load of 10 g and a frequency of 10 Hz, and the storage modulus is measured at each temperature during the temperature increase.

[0093] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 2.0 GPa or more and 5.0 GPa or less. The storage modulus is more preferably 2.3 GPa or more, even more preferably 2.5 GPa or more, particularly preferably 2.9 GPa or more, most preferably 3.0 GPa or more, more preferably 4.5 GPa or less, even more preferably 4.3 GPa or less, particularly preferably 4.2 GPa or less, and most preferably 4.0 GPa or less. The storage modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 7.0 GPa or more and 15.0 GPa or less. The storage modulus is more preferably 7.3 GPa or more, even more preferably 7.6 GPa or more, particularly preferably 8.0 GPa or more, and more preferably 14.0 GPa or less, even more preferably 13.5 GPa or less, and particularly preferably 13.0 GPa or less. When the storage modulus at 23°C in the longitudinal and transverse directions is within the above range, the strength of the biaxially oriented polypropylene film is significantly increased, and even if the film is thin, it can maintain its stiffness and strength, which greatly contributes to reducing the volume of the film.

[0094] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 0.5 GPa or more and 2.5 GPa or less. The storage modulus is more preferably 0.6 GPa or more, even more preferably 0.7 GPa or more, particularly preferably 0.8 GPa or more, and more preferably 2.3 GPa or less, even more preferably 2.1 GPa or less, particularly preferably 2.0 GPa or less. When the storage modulus in the longitudinal direction at 120°C is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when hot printing ink is transferred during printing.

[0095] The storage modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 1.5 GPa or more and 8.0 GPa or less. The storage modulus is more preferably 1.8 GPa or more, even more preferably 2.0 GPa or more, particularly preferably 2.1 GPa or more, and more preferably 7.8 GPa or less, even more preferably 7.6 GPa or less, particularly preferably 7.4 GPa or less. When the storage modulus in the width direction at 120°C is within the above range, strength at high temperatures tends to be increased, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. Furthermore, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0096] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 140°C is preferably 0.3 GPa or more and 1.5 GPa or less. The storage modulus is more preferably 0.35 GPa or more, even more preferably 0.4 GPa or more, particularly preferably 0.45 GPa or more, and more preferably 1.45 GPa or less, even more preferably 1.4 GPa or less, and particularly preferably 1.35 GPa or less. The storage modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 140°C is preferably 0.9 GPa or more and 5.0 GPa or less. The storage modulus is more preferably 1.0 GPa or more, even more preferably 1.2 GPa or more, particularly preferably 1.3 GPa or more, and more preferably 4.5 GPa or less, even more preferably 4.0 GPa or less, and particularly preferably 3.5 GPa or less. When the storage modulus at 140°C in the longitudinal and transverse directions is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. In addition, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0097] The storage modulus in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 0.1 GPa or more and 1.0 GPa or less. The storage modulus is more preferably 0.15 GPa or more, even more preferably 0.2 GPa or more, particularly preferably 0.25 GPa or more, and more preferably 0.9 GPa or less, even more preferably 0.8 GPa or less, and particularly preferably 0.7 GPa or less. The storage modulus in the width direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 0.85 GPa or more and 2.5 GPa or less. The storage modulus is more preferably 0.9 GPa or more, even more preferably 0.95 GPa or more, particularly preferably 1.0 GPa or more, and more preferably 2.4 GPa or less, even more preferably 2.3 GPa or less, and particularly preferably 2.2 GPa or less. When the storage modulus at 150°C in the longitudinal and transverse directions is within the above range, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. In addition, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0098] The sum of the longitudinal storage modulus at 23°C and the longitudinal storage modulus at 140°C of the biaxially oriented polypropylene film of the present invention is preferably 2.8 GPa or more and 8.0 GPa or less. The sum of these storage moduli is more preferably 3.0 GPa or more, even more preferably 3.1 GPa or more, particularly preferably 3.2 GPa or more, and more preferably 7.5 GPa or less, even more preferably 7.0 GPa or less, particularly preferably 6.5 GPa or less. The sum of the width direction storage modulus at 23°C and the width direction storage modulus at 140°C of the biaxially oriented polypropylene film of the present invention is preferably 8.5 GPa or more and 19.0 GPa or less. The sum of these storage moduli is more preferably 8.8 GPa or more, even more preferably 9.1 GPa or more, particularly preferably 9.5 GPa or more, and more preferably 18.0 GPa or less, even more preferably 17.0 GPa or less, particularly preferably 16.0 GPa or less. When the sum is within the above ranges, the strength at high temperatures tends to be high, and printing pitch deviation is less likely to occur when transferring high-temperature printing ink during printing. Furthermore, the flatness of the film is less likely to deteriorate and the processability of the film can be improved.

[0099] 8-4. Physical Properties Other than Loss Modulus and Storage Modulus 8-4-1. Stress at 5% Elongation (F5) The stress at 5% elongation (F5) in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 40 MPa or more and 70 MPa or less. If the F5 is 40 MPa or more, the film has high rigidity, making it easier to maintain the shape of the bag when made into a packaging bag, and the film is less likely to deform during processing such as printing. If the F5 is 70 MPa or less, practical manufacturing becomes easier and the balance between the longitudinal and transverse directions tends to be improved. The F5 is more preferably 42 MPa or more, even more preferably 46 MPa or more, particularly preferably 48 MPa or more, more preferably 65 MPa or less, even more preferably 62 MPa or less, and particularly preferably 60 MPa or less. The F5 in the longitudinal direction can be adjusted within the above range by adjusting the stretch ratio or relaxation rate or the temperature during film formation.

[0100] The stress at 5% elongation in the width direction (F5) of the biaxially oriented polypropylene film of the present invention at 23°C is preferably 90 MPa or more and 280 MPa or less. When the F5 is 90 MPa or more, the film has high rigidity, making it easier to maintain the shape of the bag when made into a packaging bag, and the film is less likely to deform during processing such as printing. Furthermore, when the F5 is 90 MPa or more, flatness can be improved. When the F5 is 280 MPa or less, practical manufacturing is easier and the film is less likely to tear in the width direction. The F5 is preferably 110 MPa or more or 120 MPa or more, more preferably 130 MPa or more, particularly preferably 150 MPa or more, most preferably 156 MPa or more, more preferably 250 MPa or less, even more preferably 230 MPa or less, particularly preferably 210 MPa or less, and most preferably 200 MPa or less. The F5 in the width direction can be adjusted within the above range by adjusting the stretch ratio or relaxation rate or the temperature during film formation.

[0101] 8-4-2. Heat Shrinkage at 120°C The heat shrinkage in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 2.5% or less. If the heat shrinkage is 2.5% or less, printing pitch deviation is less likely to occur when transferring printing ink. The heat shrinkage is more preferably 2.0% or less, even more preferably 1.7% or less, and particularly preferably 1.5% or less. The lower the heat shrinkage in the longitudinal direction at 120°C, the more preferable it is. Although there is no particular lower limit, in view of technical difficulties, it is, for example, 0.1% or more, preferably 0.3% or more. The heat shrinkage in the longitudinal direction at 120°C can be adjusted to fall within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0102] The heat shrinkage rate in the width direction of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 1.1% or less. When the heat shrinkage rate is 1.1% or less, wrinkles are less likely to occur during heat sealing. The heat shrinkage rate is more preferably 1.0% or less, even more preferably 0.7% or less, particularly preferably 0.5% or less, and most preferably 0.3% or less. The lower limit of the heat shrinkage rate in the width direction at 120°C is not particularly limited, but is, for example, -0.2%. The heat shrinkage rate in the width direction at 120°C can be kept within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0103] The sum of the heat shrinkage rates in the longitudinal and width directions of the biaxially oriented polypropylene film of the present invention at 120°C is preferably 3.5% or less. When this sum is 3.5% or less, flatness is easily improved and printing pitch deviation when transferring printing ink is more unlikely to occur. This sum is more preferably 3.0% or less, even more preferably 2.5% or less, particularly preferably 2.0% or less, and most preferably 1.7% or less. A lower sum is preferable, and although there is no particular lower limit, considering technical difficulties, it is, for example, 1.0% or more, preferably 1.3% or more. The sum of the heat shrinkage rates in the longitudinal and width directions at 120°C can be adjusted within the above range by adjusting the stretching ratio, stretching temperature, and heat treatment temperature.

[0104] 8-4-3. Heat Shrinkage at 150°C The heat shrinkage in the longitudinal direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 10% or less. If the heat shrinkage is 10% or less, printing pitch deviation is less likely to occur when transferring printing ink. The heat shrinkage is more preferably 7.0% or less, even more preferably 6.0% or less, particularly preferably 5.0% or less, and most preferably 4.0% or less. The lower the heat shrinkage in the longitudinal direction at 150°C, the more preferable it is. Although there is no particular lower limit, considering technical difficulties, it is, for example, 0.1% or more, preferably 0.5% or more. The heat shrinkage in the longitudinal direction at 150°C can be adjusted to fall within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0105] The heat shrinkage rate in the width direction of the biaxially oriented polypropylene film of the present invention at 150°C is preferably 20% or less. When the heat shrinkage rate is 20% or less, wrinkles are less likely to occur during heat sealing. The heat shrinkage rate is more preferably 15% or less, even more preferably 12% or less, and particularly preferably 10% or less. The lower limit of the heat shrinkage rate in the width direction at 150°C is not particularly limited, but is, for example, 0% or more, preferably 1% or more. The heat shrinkage rate in the width direction at 150°C can be adjusted to fall within the above range by adjusting the stretch ratio, stretching temperature, and heat treatment temperature.

[0106] If the heat shrinkage rate in the longitudinal direction at 150°C is 10% or less and the heat shrinkage rate in the width direction is 20% or less, wrinkles are less likely to occur during heat sealing, and it is particularly preferable that the heat shrinkage rate in the longitudinal direction at 150°C is 8.0% or less and the heat shrinkage rate in the width direction at 150°C is 15% or less, since this reduces distortion when the zipper part is fused to the opening. In order to reduce the heat shrinkage rate at 150°C, it is effective to set the amount of components with a molecular weight of 100,000 or less to 35% by mass or more when measuring the gel permeation chromatography (GPC) integrated curve of the polypropylene resin composition constituting the film.

[0107] 8-4-4. Thickness Uniformity 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 or printing, making the film suitable for applications requiring precision. The thickness uniformity was measured as follows. A 40 mm test piece was cut out from a steady region of the film where the film properties were stable in the longitudinal direction. The film thickness was measured continuously over 20,000 mm using a film feeder manufactured by Micron Measurement Instruments (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 using the following formula. Thickness uniformity (%) = [(maximum thickness - minimum thickness) / average thickness] x 100

[0108] 8-4-5. Haze The upper limit of the haze of the biaxially oriented polypropylene film of the present invention is preferably 7.0%. A haze of 7.0% or less makes it easy to use in applications requiring transparency. The haze is more preferably 5.0% or less, even more preferably 4.0% or less, particularly preferably 3.5% or less, and most preferably 3.0% or less. The lower limit of the haze is preferably 0%, with 0.1% being a practical value. The haze can be adjusted within the above range by adjusting the cooling roll temperature, the longitudinal stretching temperature, the tenter preheating temperature before widthwise stretching, the widthwise stretching temperature, the heat setting temperature, or the amount of polypropylene polymer components with a molecular weight of 100,000 or less. The haze may increase depending on the addition of an antiblocking agent or the composition of the sealing layer B.

[0109] 8-4-6. Image clarity The lower limit of the image clarity of the biaxially oriented polypropylene film of the present invention is preferably 55%. An image clarity of 55% or higher is easy to use in applications requiring transparency. The image clarity is more preferably 57% or higher, even more preferably 59% or higher, particularly preferably 61% or higher, and most preferably 65% ​​or higher. The upper limit of the image clarity is preferably 100%, with 95% being a realistic value. The image clarity can be kept within the range by adjusting the chill roll temperature, longitudinal stretching temperature, tenter preheating temperature before widthwise stretching, widthwise stretching temperature, heat setting temperature, or the amount of polypropylene polymer components with a molecular weight of 100,000 or less. The image clarity may be increased by adding an antiblocking agent or by adjusting the composition of the sealing layer B.

[0110] 8-4-7. Clarity The lower limit of the clarity of the biaxially oriented polypropylene film of the present invention is preferably 90%. A clarity of 90% or higher makes it easy to use in applications requiring transparency. The clarity is more preferably 92% or higher, even more preferably 93% or higher, particularly preferably 94% or higher, and most preferably 95% or higher. The upper limit of the clarity is preferably 100%, with 99% being a realistic value. The clarity can be adjusted within the above range by adjusting the cooling roll temperature, longitudinal stretching temperature, tenter preheating temperature before widthwise stretching, widthwise stretching temperature, heat setting temperature, or the amount of polypropylene polymer components with a molecular weight of 100,000 or less. The clarity may be increased by adding an antiblocking agent or by adjusting the composition of the sealing layer B.

[0111] 9. Applications The biaxially oriented polypropylene film of the present invention exhibits minimal dimensional change over the entire temperature range from room temperature to 130°C. Therefore, deformation of the film can be suppressed even after heating at high temperatures, such as during heat processing with a roll, printing, or heat sealing. This prevents deterioration of the film's flatness and improves its processability. Furthermore, thinner films are possible, contributing to the reduction of packaging material volume. For these reasons, when the biaxially oriented polypropylene film of the present invention is used, the film easily maintains its shape when made into a packaging bag, is less likely to deform during processing such as heat sealing at high temperatures, and is less likely to cause printing pitch deviation during printing, making it suitable for packaging applications. Furthermore, the film is less likely to lose flatness even after being coated with a silicone release agent and heated and dried, making it suitable as a release film for optical applications and other applications requiring high flatness.

[0112] To form a bag for packaging food, the contents are filled into a pre-made bag, and the film is heated to melt and fuse, sealing it. This process is often repeated when making a bag while filling it with food. Typically, a sealant film made of polyethylene resin, polypropylene resin, or the like is laminated onto the biaxially oriented polypropylene film of the present invention as a base film, and the sealant film surfaces are fused together. The heating method involves applying pressure from a heating plate from the base film side to hold down the film and seal it, with a seal width of approximately 10 mm being common. Since the base film is also heated during this process, the resulting expansion and contraction causes wrinkles. Fewer wrinkles are desirable for bag durability and to increase consumer appetite. While the sealing temperature may be around 120°C, a higher temperature is required to increase the bag-making processing speed, and even in this case, minimal expansion and contraction is preferable. Furthermore, if a zipper is to be fused to the opening of the bag, sealing at an even higher temperature is required.

[0113] 10. Heat Seal Strength In order to prevent the contents from falling out, the biaxially oriented polypropylene film of the present invention preferably has a heat seal strength at 130°C on the seal layer B side, measured by the measurement method described below, of 4.8 N / 15 mm or more, more preferably 5.0 N / 15 mm or more, even more preferably 5.5 N / 15 mm or more, and particularly preferably 6.0 N / 15 mm or more. The upper limit is about 8.0 N / 15 mm. There is little need for a strength greater than this, and if it is too great, the bag may be difficult to open. Furthermore, when one surface of the biaxially oriented polypropylene film of the present invention is a sealing layer B and the other surface is a functional layer D, in order to maintain the packaging form, for example, as in Z-packaging, the heat-sealed portion after bag-making processing is folded to bond the functional layers D together.However, so that the bag can be easily opened by hand, it is preferable that the heat seal strength at 130°C on the functional layer D side is lower than the heat seal strength at 130°C on the sealing layer B side, for example, 3.5 N / 15 mm or less, preferably 2.0 N / 15 mm or less, and more preferably 1.0 N / 15 mm or less.

[0114] 11. Heat-sealing Rise Temperature The heat-sealing rise temperature of the seal layer B of the biaxially oriented polypropylene film of the present invention is preferably 90°C or higher and 130°C or lower. When the heat-sealing rise temperature of the seal layer B is 130°C or lower, high heat-sealing strength can be achieved at a relatively low temperature of around 130°C, allowing the temperature of the processing equipment during heat-sealing to be relatively low, enabling high-speed operation during automatic packaging. Furthermore, because heat-sealing can be performed at a relatively low temperature, the entire film is less likely to shrink and wrinkles are less likely to form in the sealed portion. By setting the heat-sealing rise temperature of the seal layer B to 90°C or higher, the film is less likely to fuse to the film-forming equipment. The above temperature is more preferably 100°C or higher, even more preferably 110°C or higher, and more preferably 125°C or lower, and even more preferably 120°C or lower. The heat-sealing rise temperature can be kept within the above range by adjusting the raw material composition of each layer described above, particularly the raw material composition of the base layer A, the stretch ratio and relaxation rate during film formation, the temperature of each film-forming step, etc.

[0115] 12. Coefficient of Dynamic Friction The coefficient of dynamic friction of the biaxially oriented polypropylene film of the present invention is preferably 0.50 or less on both sides, i.e., on both the seal layer B and the surface layer opposite to the seal layer B. If the coefficient of dynamic friction is 0.50 or less on both sides, the film can be smoothly unwound from the roll film, facilitating printing processing. The coefficient of dynamic friction is more preferably 0.48 or less, and even more preferably 0.45 or less. There is no particular restriction on the lower limit of the coefficient of dynamic friction, but it is, for example, 0.10 or more.

[0116] 13. Wet Tension The wet tension of the surface of the seal layer B of the biaxially oriented polypropylene film of the present invention is preferably 35 mN / m or more. A wet tension of 35 mN / m or more can improve adhesion to the surface layer opposite the seal layer B. Furthermore, a wet tension of 35 mN / m or more can improve the anti-fogging properties of the film. To achieve a wet tension of 35 mN / m or more, it is preferable to perform a physicochemical surface treatment such as corona treatment or flame treatment. In corona treatment, it is preferable to use a preheating roll and a treatment roll and perform discharge in the air. The wet tension is more preferably 37 mN / m or more. If the wet tension is too high, the effect will saturate, so it is preferably 43 mN / m or less.

[0117] 14. Anti-Fog Property The anti-fogging property of the surface of the seal layer B of the biaxially oriented polypropylene film of the present invention is preferably grade 1 to 3, more preferably grade 1 or 2, and even more preferably grade 1, as determined by the evaluation method described below.

[0118] 15. Packaging Materials When the biaxially oriented polypropylene film of the present invention is used as a packaging material, it may be used alone or with a printed layer. Packaging materials using the biaxially oriented polypropylene film of the present invention can be used to produce three-sided seal type, pillow type, and gusset type packaging bags with good seal strength and seal appearance. The biaxially oriented polypropylene film of the present invention can be used for letterpress printing, lithographic printing, intaglio printing, stencil printing, and transfer printing, depending on the application.

[0119] This application claims the benefit of priority based on Japanese Patent Application No. 2024-14405, filed February 1, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-14405, filed February 1, 2024, are incorporated herein by reference.

[0120] The present invention will be described below using examples, but the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are as follows. Furthermore, the "surface layer opposite to the sealing layer B" refers to the base layer A in Examples 3 and 4, and to the functional layer D in Examples 1 and 2 and Comparative Examples 1 to 4.

[0121] (1) Melt Flow Rate of Polypropylene Resin 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.

[0122] (2) Mesopentad fraction of polypropylene resin The mesopentad fraction ([mmmm]%) of polypropylene resin is measured by 13 The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 C-NMR measurement was performed using an "AVANCE 500" manufactured by BRUKER, by dissolving 200 mg of a sample in a 8:2 mixture of o-dichlorobenzene and deuterated benzene at 135°C and at 110°C.

[0123] (3) Amount of components with a molecular weight of 100,000 or less: Using gel permeation chromatography (GPC), an integral curve of the polypropylene-equivalent molecular weight was obtained using monodisperse polystyrene as a standard. When the baseline was unclear, the baseline was set in the range from the lowest point of the high molecular weight side of the elution peak closest to the elution peak of the standard substance. The GPC measurement conditions were as follows: Apparatus: "HLC-8321PC / HT" manufactured by Tosoh Corporation Detector: RI Solvent: 1,2,4-trichlorobenzene + dibutylhydroxytoluene (0.05%) Column: TSK gelguard column HHR (30) HT (7.5 mm I.D. × 7.5 cm) × 1 + TSK gel GMHHR-H (20) HT (7.8 mm I.D. × 30 cm) × 3 Flow rate: 1.0 mL / min Injection amount: 0.3 mL Measurement temperature: 140°C The mass proportion of components having a molecular weight of 100,000 or less was determined from the integral curve of the molecular weight obtained by GPC.

[0124] (4) Melting point and crystallization temperature Thermal measurements were performed using a differential scanning calorimeter ("Q1000" manufactured by TA Instruments). Approximately 5 mg was cut out from the pellet, placed in an aluminum pan for measurement, and set in a differential scanning calorimeter. Under a nitrogen atmosphere, the resin was melted by heating from 30 ° C. to 230 ° C. at a heating rate of 20 ° C. / min and holding at 230 ° C. for 5 minutes, and then cooled to 30 ° C. at a heating rate of -10 ° C. / min and held at 30 ° C. for 5 minutes. The temperature was then increased to 230 ° C. at a heating rate of 10 ° C. / min. The melting point was the main peak temperature of the endothermic peak associated with melting observed during the second heating. The crystallization temperature was the main peak temperature of the exothermic peak observed when the temperature was lowered from 230 ° C. to 30 ° C.

[0125] (5) Film Thickness The thickness of the film was measured using a stylus film thickness meter ("Militron 1202D" manufactured by Seiko EM Corporation).

[0126] (6) Thermomechanical Analysis (TMA) Measurement (Measurement of Film Width from 30°C to 130°C) A film was cut so that the width of the film was 40 mm and the length of the film was 4 mm, and the film was set in a thermomechanical analyzer ("TMA-60", manufactured by Shimadzu Corporation) so that the chuck width was 10 mm. The sample was heated from 30°C to 130°C at a heating rate of 10°C / min with a measuring load of 0.5 g, and the length X of the sample in the width direction during the heating was continuously measured. The maximum value of the length between the chucks during the heating period was designated X1 (mm), and the minimum value of the length between the chucks during the heating period was designated X2 (mm). The percentages of (X1-10) / 10 and (X2-10) / 10 were calculated.

[0127] (7) Thermomechanical analysis (TMA) measurement (temperature measurement at 0.5% shrinkage) A film was cut so that the width direction of the film was 40 mm and the length direction of the film was 4 mm, and the film was set in a thermomechanical analyzer ("TMA-60", manufactured by Shimadzu Corporation) so that the chuck width was 10 mm. The temperature was increased from 30°C to 160°C at a heating rate of 10°C / min with a measurement load of 0.5 g, and the width direction length of the sample was continuously measured during the temperature increase. From the measurement results, the lowest temperature at which the width direction length of the sample was 9.95 mm or less was determined as the temperature at 0.5% shrinkage.

[0128] (8) Loss modulus by dynamic mechanical analysis (DMA) A film was cut to a width of 40 mm and a length of 4 mm, and set in a solid viscoelastic analyzer (RSA-G2, manufactured by TA Instruments Japan) with a chuck width of 10 mm. The film was heated from -60°C to 160°C at a heating rate of 5°C / min under a nitrogen atmosphere with a measuring load of 10 g and a frequency of 10 Hz, and the loss modulus of the film was measured during the heating in the width direction. A graph was drawn with temperature on the horizontal axis and loss modulus on the vertical axis, and the maximum loss modulus E"(A) from -25°C to 25°C, the minimum loss modulus E"(B) from 25°C to 75°C, and the maximum loss modulus E"(C) at 100°C or higher were calculated. The values ​​of E"(C) / E"(A) and E"(B) / E"(C) were also calculated.

[0129] (9) Storage modulus by dynamic mechanical analysis (DMA) The storage modulus in the longitudinal and transverse directions of the film was measured by the following method. A film was cut so that the measurement direction was 40 mm and the direction perpendicular thereto was 4 mm, and the film was set in a solid viscoelasticity analyzer ("RSA-G2" manufactured by TA Instruments Japan) so that the chuck width was 10 mm. The temperature was raised from -60 ° C to 160 ° C at a heating rate of 5 ° C / min under a nitrogen atmosphere with a measurement load of 10 g and a frequency of 10 Hz, and the storage moduli at 23 ° C, 120 ° C, 140 ° C, and 150 ° C were determined. Furthermore, the sum of the storage moduli at 23 ° C and 140 ° C in the longitudinal direction and the sum of the storage moduli at 23 ° C and 140 ° C in the transverse direction were calculated from the obtained values.

[0130] (10) Haze: Measured at 23° C. in accordance with JIS K7105 using a turbidity meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0131] (11) Image clarity Using an image clarity measuring instrument ("ICM-1T" manufactured by Suga Test Instruments Co., Ltd.), image clarity was measured in accordance with the transmission method of JIS K7374: 2007, with the slit width of the optical comb set to 0.5 mm. During measurement, the sample was set so that the width direction was perpendicular to the optical comb of the measuring instrument.

[0132] (12) Clarity Clarity was measured using a transparency measuring instrument ("Hazeguard i" manufactured by BYK). The light transmitted through the film during measurement includes straight light that travels straight along the optical axis of the incident parallel light and narrow-angle scattered light that has an angle of ±2.5° or less with respect to the optical axis of the parallel light. The amount of straight light is expressed as I c , the amount of narrow-angle scattered light within ±2.5° is I s When the clarity is calculated, the clarity is calculated by the following formula: Clarity (%) = (I c -I s ) / (I c +I s ) x 100

[0133] (13) Stress at 5% Elongation (F5), Tensile Modulus, Tensile Breaking Strength, and Tensile Breaking Elongation Various physical properties were measured at 23°C during tensile testing of the film in the longitudinal and transverse directions in accordance with JIS K7127. The film was cut so that the measurement direction was 200 mm and the direction perpendicular thereto was 15 mm, and the chuck width was 100 mm. The film was set in a tensile testing machine ("Dual Column Tabletop Tester Instron 5965" manufactured by Instron Japan Co., Ltd.). The tensile test was performed at a pulling rate of 200 mm / min. From the obtained strain-stress curve, the tensile modulus was calculated from the slope of the linear portion at the beginning of elongation, and the stress at 5% elongation was designated as F5. The tensile breaking strength and tensile breaking elongation were defined as the strength and elongation, respectively, at the time the sample broke.

[0134] (14) Heat Shrinkage Ratio The heat shrinkage ratios of the film in the longitudinal and transverse directions were measured according to JIS Z1712 by the following method. A film was cut so that the measurement direction was 200 mm and the direction perpendicular to this was 20 mm, and the film was hung in a hot air oven at 120°C and heated for 5 minutes. The length after heating was measured, and the heat shrinkage ratio was calculated as the ratio of the shrunken length to the original length.

[0135] (15) Dynamic friction coefficient A sample measuring 400 mm in the longitudinal direction and 100 mm in the width direction was cut out from the film. This was aged for 12 hours in an atmosphere of 23°C and 65% RH, and the sample was divided into a test table sample measuring 300 mm in the longitudinal direction x 100 mm in the width direction and a sliding piece sample measuring 100 mm in the longitudinal direction x 100 mm in the width direction. The test table sample was set on the test table, and the sliding piece sample was measured by measuring the bottom surface (area 39.7 mm) of a metal sliding piece with a load of 1.5 kg. 2 The test pieces were attached to two square plates (each of which has a diameter of 1 / 4" x 1 / 4") so that the seal layers B were in contact with each other. In accordance with JIS K-7125, a tensile tester ("Tensilon RTG-1210" manufactured by A&D) was used to measure the dynamic friction coefficient of the seal layer B surface under conditions of a sliding speed of 200 mm / min, 23°C, and 65% RH, and the average of three measurements was used. The dynamic friction coefficient of the surface opposite the seal layer B was also determined in the same manner as above, except that the surfaces opposite the seal layer B were attached so that they were in contact with each other.

[0136] (16) Wet tension (mN / m) The film was cut into a size of 297 mm in the longitudinal direction and 210 mm in the transverse direction, and after aging for 24 hours at a temperature of 23°C and a relative humidity of 50%, the wet tension of the surface on the seal layer B side of the sample was measured by the following procedure in accordance with JIS K 6768. The wet tension was measured in a laboratory atmosphere in accordance with JIS K7100 at a temperature of 23°C and a relative humidity of 50%. The sample was placed on a flat substrate, and several drops of a wet tension standard liquid (a test mixture liquid described in JIS K 6768) were dropped on the seal layer B of the sample, and the wet tension standard liquid was applied to the surface of the seal layer B by a cotton swab to a depth of 6 cm. 2 The liquid film was spread to an area of ​​at least 100 mm or more, and the state of the liquid film was visually observed in a bright place 3 seconds after application. If the liquid film did not break and maintained its initial state 3 seconds after application, it was considered wet. Therefore, a liquid film was formed using a wetting tension standard solution with a surface tension one level higher than that of the wetting tension standard solution used to form the liquid film. On the other hand, if the liquid film broke in less than 3 seconds, a liquid film was formed using a wetting tension standard solution with a surface tension one level lower than that of the wetting tension standard solution used to form the liquid film. A new cotton swab was used for each liquid film formation. The liquid film formation was repeated, and the value of the wetting tension standard solution with the highest value that could wet the surface of sealing layer B in 3 seconds was taken as the wetting tension. Liquid films were formed three times using the wetting tension standard solution with the highest value, and it was confirmed that the initial state was maintained 3 seconds after application. The wetting tension of the surface layer opposite sealing layer B was also measured using the same measurement and calculation methods as above.

[0137] (17) Anti-Fog Properties Using a film, the anti-fogging properties of the film surface on the seal layer B side and the film surface on the opposite side to the seal layer B were evaluated according to the following procedure. 1) 300 mL of 50°C hot water was poured into a 500 mL open-top container. 2) The film surface on the side where the anti-fogging properties of the film were to be measured was facing inward, and the opening of the container was sealed with the film. 3) The film was left in a 5°C cold room for 30 minutes, and then the state of dew adhesion on the film surface on the side where the anti-fogging properties were to be measured was evaluated on the following 5-point scale. Grade 1: No dew on the entire surface (0 area) Grade 2: Dew on a small part of the surface (more than 0 to 1 / 4 area) Grade 3: Dew on just under half of the surface (more than 1 / 4 to 2 / 4 area) Grade 4: Dew on most of the surface (more than 2 / 4 to 3 / 4 area) Grade 5: Dew on almost the entire surface (more than 3 / 4 area)

[0138] (18) Heat-sealing rise temperature Two samples measuring 20 cm in the longitudinal direction and 5 cm in the width direction were cut out from the film. The seal layers B of the two cut-out samples were placed face to face and then heat-sealed using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). Five rectangular heat-sealed surfaces were placed in a row in the center of the width direction of the sample, parallel to the longitudinal direction of the sample. The heat-sealed surfaces were placed 1 cm in the longitudinal direction of the sample and 3 cm in the width direction of the sample, with a distance of 1.5 cm between adjacent heat-sealed surfaces. The heat-sealing temperatures were different for each heat-sealed surface, and were 80°C, 85°C, 90°C, 95°C, and 100°C. The heat-sealing pressure was 1 kg / cm. 2The time was 1 second. Then, a 19 cm length and a 1.5 cm widthwise central portion of the sample were cut to include five heat-sealed surfaces. The sample was cut longitudinally so that the longitudinal direction of the sample and the longitudinal direction of the cut sample were parallel, with the heat-sealed surface heat-sealed at 90°C positioned at the longitudinal center. The cut samples were attached to the upper and lower chucks of a tensile tester (Instron Corporation's "5965 Dual Column Tabletop Tester"), and the heat-seal strength was measured for each heat-sealed surface when pulled at a tensile speed of 200 mm / min (unit: N / 15 mm). Two new cut-out samples were prepared, and five measurement samples were prepared in the same manner as above, except that they were heat-sealed at 105°C, 110°C, 115°C, 120°C, and 125°C. The heat-seal strength was measured. A linear graph was drawn with the horizontal axis representing temperature and the vertical axis representing heat seal strength, and the temperature at which the heat seal strength reached 1 N / 15 mm was taken as the heat seal initiation temperature. Another sample was prepared and the heat seal strength was measured two more times at 80 to 125°C to determine the heat seal initiation temperature, and the average of the three calculated values ​​was taken as the heat seal initiation temperature of the film. The heat seal initiation temperature of the surface layer opposite seal layer B was also determined using the same measurement and calculation methods as above, except that the surface layers opposite seal layer B were overlapped facing each other.

[0139] (19) Heat Seal Strength Two samples measuring 29.7 cm in the longitudinal direction and 21.0 cm in the width direction were cut out from the film. The seal layers B of the two cut out samples were placed face to face, and then heat sealed at 130 ° C. using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). A rectangular heat seal surface was placed in the center of the width direction of the sample so that it was parallel to the longitudinal direction of the sample. The heat seal surface was placed so that it was 1.5 cm in the longitudinal direction of the sample and 3 cm in the width direction of the sample. Then, the sample was cut to a length of 9.5 cm in the longitudinal direction and 1.5 cm in the central part of the width direction. In the longitudinal direction, the sample was cut so that the longitudinal direction of the sample and the longitudinal direction of the cut sample were parallel, and the heat seal surface was located in the center of the longitudinal direction. The cut sample was attached to the upper and lower chucks of a tensile tester (Instron "5965 Dual Column Tabletop Tester") and the heat seal strength (unit: N / 15 mm) was measured when pulled at a tensile speed of 200 mm / min. Two other samples were prepared and their heat seal strengths were measured, and the average of the three calculated values ​​was used as the heat seal strength of the film. The heat seal strength of the film was determined using the same measurement and calculation methods as above, except that the surface layers opposite the seal layer B of the two cut samples were placed face to face. Furthermore, the heat seal strength of the seal layer B and the heat seal strength of the surface layer opposite the seal layer B were determined using the same measurement and calculation methods as above, except that the heat seal temperature was 140°C.

[0140] (20) Appearance Evaluation of Heat-Sealed Portions The obtained film was heat-sealed with a heat sealer to form a three-sided sealed bag measuring 130 mm x 180 mm, by heat-sealing the sealant films of the laminate together. The seal bar width was 10 mm and the heat-sealing temperature was 150°C at a pressure of 0.2 MPa for 1 second. The appearance of wrinkles in the heat-sealed portions was visually evaluated. A: No wrinkles were observed in the heat-sealed portions in either the width or length direction of the film. B: Wrinkles were observed in the heat-sealed portions in only one of the width or length directions of the film. C: Wrinkles were observed in the heat-sealed portions in both the width and length directions of the film.

[0141] (21) Flatness Evaluation (Flatness after Treatment at 130°C) A sample was cut out from the film so that both the width and length directions were 200 mm, and used as a sample for evaluation. The sample was hung in a hot air oven at 130°C and heated for 5 minutes. After cooling to room temperature, the film was placed on a black mount, and the film surface was observed at a 45-degree angle under a fluorescent lamp. A: No heat wrinkles or large waviness of 5 mm or more were present. B: No heat wrinkles were observed, but large waviness of 5 mm or more was observed. C: Heat wrinkles were observed.

[0142] Raw Materials Used The polypropylene resins constituting the layers of the films in the following Examples and Comparative Examples are as follows. PP-1: Propylene homopolymer ("FLX80H5" manufactured by Sumitomo Chemical Co., Ltd., mesopentad fraction: 98.9%, melting point: 163°C, MFR: 7.5g / 10min, amount of components with a molecular weight of 10,000 or less: 4.0% by mass, amount of components with a molecular weight of 100,000 or less: 40.5% by mass) PP-2: Propylene homopolymer ("EL80F5" manufactured by Sumitomo Chemical Co., Ltd., mesopentad fraction: 98.8%, melting point: 162°C, MFR: 11g / 10min, amount of components with a molecular weight of 10,000 or less: 6.9% by mass, amount of components with a molecular weight of 100,000 or less: 53.1% by mass) PP-3: A composition comprising PP-1 plus 1.7% by mass of stearyl diethanolamine monostearate, stearyl diethanolamine distearate, and stearyl diethanolamine as anti-fogging agents, and 0.25% by mass of glycerin monostearate PP-4: Propylene homopolymer ("FY6H" manufactured by Japan Polypropylene Corporation, MFR: 1.9 g / 10 min, melting point: 163°C, mesopentad fraction: 98.9%) PP-5: Propylene homopolymer ("FL203D" manufactured by Japan Polypropylene Corporation, mesopentad fraction: 94.8%, melting point: 161°C, MFR: 3 g / 10 min, amount of components with a molecular weight of 10,000 or less: 3.0% by mass, amount of components with a molecular weight of 100,000 or less: 37.1% by mass), and a composition containing 1.7% by mass of stearyl diethanolamine monostearate and 0.25% by mass of glycerin monostearate as anti-fogging agents. PP-6: Propylene-ethylene-butene copolymer ("FSX66M4" manufactured by Sumitomo Chemical Co., Ltd., melting point: 138°C, MFR: 4.5 g / 10 min, ethylene content: 3.3 mol%, butene content: 2.9 mol%, glycerin monostearate content: 0.45 mass%) PP-7: Propylene-butene copolymer ("SP7843" manufactured by Sumitomo Chemical Co., Ltd., melting point: 128°C, MFR: 6.5 g / 10 min, butene content: 8.2 mol%)

[0143] Example 1 (1) Preparation of Base Material for Base Layer A A polypropylene-based resin composition containing 20% ​​by mass of propylene homopolymer PP-1, 20% by mass of propylene homopolymer PP-2, and 60% by mass of propylene homopolymer PP-3 was used as the base material. When the physical properties of each polypropylene homopolymer were averaged by mass, the polypropylene-based resin composition constituting base layer A had a mesopentad fraction of 98.88%, a melting point of 162.8°C, an MFR of 8.2 g / 10 min, a molecular weight of 10,000 or less of 4.58% by mass, and a molecular weight of 100,000 or less of 43.02% by mass. (2) Raw Material for Sealing Layer B Propylene-butene copolymer PP-7 was used as the raw material. (3) Raw Material for Functional Layer D Propylene-ethylene-butene copolymer PP-6 was used as the raw material. (4) Film Preparation First, the polypropylene resin compositions constituting each of the functional layer D, base layer A, and seal layer B were heated and melted in an extruder using a multi-layer feed block at 250 ° C, 250 ° C, and 210 ° C, respectively. The molten polypropylene resin composition was laminated from a T-die at 250 ° C to form a 1.8 mm thick laminated molten sheet, with the thickness ratio of functional layer D, base layer A, and seal layer B being 1 / 14 / 1. The functional layer D side of the molten sheet was contacted with a cooling roll at 20 ° C and then placed in a water bath at 20 ° C. Thereafter, the sheet was stretched 4.5 times in the longitudinal direction with two pairs of rolls at 142 ° C, and then both ends were clamped and introduced into a hot air oven, preheated at 172 ° C, and then stretched 12.7 times in the width direction at 162 ° C. Immediately after widthwise stretching, the film was heat-treated at 170°C without relaxation while held by the clips, and then heat-treated at 140°C to achieve a relaxation rate of 3% in the widthwise direction. Finally, the film was cooled to room temperature. The surface of the resulting biaxially oriented polypropylene film on the seal layer B side was corona-treated using a corona treater (manufactured by Softal Corona & Plasma GmbH) at an applied current of 0.75A and an applied voltage of 1.8kW, and then wound up on a winder to form the biaxially oriented polypropylene film of the present invention. The thickness of the resulting film was 16 μm. The thicknesses of the functional layer D, substrate layer A, and seal layer B of the resulting film were 1 μm, 14 μm, and 1 μm. The raw material composition of each layer and the film-forming conditions are shown in Table 1, and the various physical properties of the film are shown in Table 2.In the table, "%" indicates % by mass. The biaxially oriented polypropylene film had high rigidity, but low heat shrinkage at high temperatures, high seal strength, and excellent anti-fogging properties. It also had excellent flatness after treatment at 130°C. The three-side sealed bag produced using the film of Example 1 had a good heat-sealed appearance and excellent handleability due to the excellent stiffness of the bag product.

[0144] Examples 2 to 4 In Examples 2 to 4, films were produced using the same production method as in Example 1, except that the film production conditions were changed to those shown in Table 1. Various physical properties of the films are shown in Table 2. The biaxially oriented polypropylene films of Examples 2 to 4 had high rigidity like that of Example 1, but also had low heat shrinkage at high temperatures, high seal strength, and excellent anti-fogging properties.

[0145] Examples 5 and 6: The same materials as in Examples 1 to 4 were used for the base layer A and the seal layer B, and propylene-ethylene-butene copolymer PP-6 was used for the intermediate layer C. First, the polypropylene-based resin compositions constituting the base layer A, intermediate layer C, and seal layer B were heated and melted in an extruder using a multilayer feedblock at 250°C, 250°C, and 210°C, respectively. The molten polypropylene-based resin compositions were then laminated at 250°C through a T-die to produce a 1.8 mm-thick laminated molten sheet, co-extruded so that the thickness ratio of the base layer A, intermediate layer C, and seal layer B was 13 / 2 / 1. A molten sheet was obtained in the same manner as in Example 1 and stretched in the longitudinal and width directions. Immediately after stretching in the width direction, the sheet was heat-treated at 170°C while held by the clips without relaxation, then heat-treated at 140°C to relax the sheet in the width direction by 3%, and finally cooled to room temperature. The surface of the obtained biaxially oriented polypropylene film on the seal layer B side was subjected to a corona treatment, and the film was wound up on a winder to obtain a biaxially oriented polypropylene film of the present invention. The thickness of the obtained film was 16 μm. In the obtained film, the thicknesses of the base layer A, intermediate layer C, and seal layer B were 13 μm, 2 μm, and 1 μm. The raw material composition of each layer and the film production conditions are shown in Table 1, and various physical properties of the film are shown in Table 2. The biaxially oriented polypropylene films of Examples 5 and 6 had low heat shrinkage at high temperatures, high seal strength, and excellent anti-fogging properties, despite their high rigidity.

[0146] Example 7 The same raw materials as in Examples 1 to 4 were used as the raw materials for the base layer A, seal layer B, and functional layer D, and propylene-ethylene-butene copolymer PP-6 was used as the raw material for the intermediate layer C. First, the polypropylene resin compositions constituting each of the functional layer D, base layer A, intermediate layer C, and seal layer B were heated and melted in an extruder using a multi-layer feed block at 250 ° C, 250 ° C, 250 ° C, and 210 ° C, respectively, and the molten polypropylene resin composition was laminated from a T-die at 250 ° C to produce a 1.8 mm thick laminated molten sheet so that the thickness ratio of the functional layer D, base layer A, intermediate layer C, and seal layer B was 1 / 16 / 2 / 1. A molten sheet was obtained in the same manner as in Example 1 and stretched in the longitudinal and width directions. Immediately after stretching in the width direction, it was heat-treated at 170 ° C while held by the clip without relaxation, then heat-treated at 140 ° C to relax the sheet to a relaxation rate of 3% in the width direction, and finally cooled to room temperature. The surface of the obtained biaxially oriented polypropylene film on the seal layer B side was subjected to a corona treatment, and the film was then wound up on a winder to form a biaxially oriented polypropylene film of the present invention. The thickness of the obtained film was 20 μm. In the obtained film, the thicknesses of the functional layer D / substrate layer A / intermediate layer C / seal layer B were 1 μm / 16 μm / 2 μm / 1 μm. The raw material composition of each layer and the film production conditions are shown in Table 1, and various physical properties of the film are shown in Table 2. The biaxially oriented polypropylene film of Example 7 had low heat shrinkage at high temperatures, high seal strength, and excellent anti-fogging properties, despite its high rigidity.

[0147] Comparative Examples 1 to 6 In Comparative Examples 1 to 6, the same raw materials as in Example 7 were used to form a layer structure of functional layer D / substrate layer A / intermediate layer C / sealing layer B, and except for Comparative Example 3, the thickness structure was also the same as in Example 7, with a total thickness of 20 μm, being 1 μm / 16 μm / 2 μm / 1 μm. In Comparative Example 3, the thicknesses of the layers were 1 μm / 31 μm / 2 μm / 1 μm, and the total thickness was 35 μm. The film formation conditions for Comparative Examples 1 to 6 are shown in Table 3, and the various physical properties of the films are shown in Table 4.

[0148] Comparative Example 7 In Comparative Example 7, the layer structure was the same as in Example 7, that is, functional layer D / base layer A / intermediate layer C / sealing layer B, and the thickness structure was also the same as in Example 7, that is, 1 μm / 16 μm / 2 μm / 1 μm, for a total thickness of 20 μm. The base layer A was made from a polypropylene resin composition containing 43% by mass of PP-6 ("FY6H" manufactured by Japan Polypropylene Corporation, MFR: 1.9 g / 10 min, melting point: 163°C, mesopentad fraction: 98.9%), a propylene homopolymer, and 57% by mass of PP-7 (a composition obtained by adding 0.16% by mass of glycerin monostearate (TB-123 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), 0.2% by mass of polyoxyethylene (2) stearylamine (TB-12 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), and 0.6% by mass of polyoxyethylene (2) stearylamine monostearate (Elex 334 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) to 100% by mass of the above PP-1). The film formation conditions are shown in Table 3, and the physical properties of the film are shown in Table 4.

[0149]

[0150]

[0151]

[0152]

[0153] As shown in Table 4, in Comparative Examples 1 to 7, at least one of the percentages of (X1-X0) / X0 or (X2-X0) / X0 (X0: 10 mm, X1: maximum value of the gap between chucks during heating (mm), X2: minimum value of the gap between chucks during heating (mm)) was outside the specified range, and therefore, the films of Comparative Examples 1 to 7 developed wrinkles in the heat-sealed area at 150°C. Furthermore, the flatness of the films after treatment at 130°C was poor. On the other hand, as shown in Table 3, when the percentages of (X1-X0) / X0 and (X2-X0) / X0 were the specified values, the change in the length of the film, particularly the width direction, was small even during and after heating, suppressing the development of wrinkles and providing excellent flatness.

[0154] 1 is a graph showing the relationship between temperature and the length in the width direction of the film in Example 1, Comparative Example 1, and Comparative Example 4, and more precisely, the relationship between temperature and the percentage of (X1-X0) / X0. Also, FIG. 2 is a graph showing the relationship between temperature and loss modulus in Example 1 and Comparative Example 1, and FIG. 3 is a graph showing the relationship between temperature and storage modulus in Example 1 and Comparative Example 1.

[0155] The biaxially oriented polypropylene film of the present invention has excellent rigidity and heat resistance, and therefore has excellent bag-making processability and easily maintains the shape of the bag when made into a packaging bag. Therefore, the biaxially oriented polypropylene film of the present invention can be used for packaging bags, and packaging bags containing an anti-fogging agent are particularly suitable for packaging fruits and vegetables. Furthermore, the biaxially oriented polypropylene film of the present invention can be suitably used for applications requiring high rigidity even without laminating a sealant film, and can maintain its strength even when the film is thin, thereby reducing the burden on the environment.

Claims

1. A biaxially oriented polypropylene film having a base layer A made of a polypropylene-based resin composition and a seal layer B made of a polypropylene-based resin composition, and satisfying the following (1) to (4): (1) The seal layer B is on at least one outermost surface. (2) The clarity is 90% or more and 100% or less. (3) The storage modulus at 140°C in the width direction is 0.7 GPa or more and 5.0 GPa or less. (4) The heat shrinkage at 150°C in the width direction is 10% or less.

2. A biaxially oriented polypropylene film according to claim 1, which, in thermomechanical analysis, when heated from 30°C to 160°C at a heating rate of 10°C / min, has a temperature of 129°C or higher at which the widthwise length becomes 0.9950 x X0 or less relative to the widthwise length X0 at 30°C, and has a longitudinal storage modulus of 2.0 GPa or more at 23°C and a widthwise storage modulus of 7.0 GPa or more at 23°C.

3. A biaxially oriented polypropylene film according to claim 1 or 2, having a longitudinal storage modulus of 0.5 GPa or more at 120°C and a transverse storage modulus of 1.5 GPa or more at 120°C.

4. A biaxially oriented polypropylene film according to claim 1 or 2, having a longitudinal heat shrinkage rate of 2.5% or less at 120°C and a transverse heat shrinkage rate of 1.1% or less at 120°C.

5. A biaxially oriented polypropylene film according to claim 1 or 2, which has a stress of 120 MPa or more at 5% elongation in the width direction at 23°C.

6. The biaxially oriented polypropylene film according to claim 1 or 2, having a haze of 7.0% or less.

7. A biaxially oriented polypropylene film according to claim 1 or 2, containing an anti-fogging agent in an amount of 0.2% by mass or more and 2.0% by mass or less.

8. A biaxially oriented polypropylene film according to claim 1 or 2, wherein the base layer A contains 90% by mass or more of a polypropylene resin having a mesopentad fraction of 97.0% or more.

9. The biaxially oriented polypropylene film according to claim 1 or 2, wherein the sealing layer B contains 70% by mass or more of a polypropylene copolymer, and the polypropylene copolymer contains 4% by mole or more of an α-olefin other than propylene.

10. A biaxially oriented polypropylene film as described in claim 1 or 2, which has an intermediate layer C consisting of a polypropylene-based resin composition between the base layer A and the sealing layer B, and the melting point of the polypropylene-based resin composition constituting the intermediate layer C is higher than the melting point of the polypropylene-based resin composition constituting the sealing layer B.

11. The biaxially oriented polypropylene film according to claim 1 or 2, having a thickness of 10 μm or more and 100 μm or less.

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