Biaxially oriented polypropylene film

Abstract

To provide a biaxially oriented polypropylene film that hardly tears during production, has good heat resistance, and can reduce the environmental load.SOLUTION: A biaxially oriented polypropylene film comprises at least a base layer B comprising: at least 50.0 mass% and less than 99.0 mass% of a polypropylene resin (B1) having a melting point greater than or equal to 150°C and less than or equal to 170°C; and at least 1.0 mass% and less than 50 mass% of a plant-derived ethylene-α-olefin copolymer (B2) with a density greater than or equal to 0.936 g / cm3 and less than or equal to 0.970 g / cm3 and an MFR greater than or equal to 0.01 g / 10 min and less than 1.0 g / 10 min.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polypropylene-based film. [Background technology]

[0002] Biaxially oriented polypropylene films (hereinafter also referred to as OPP films) are excellent in transparency, rigidity, surface hardness, impact resistance, moisture resistance, etc., and are widely used as packaging bags for food, daily necessities, miscellaneous goods, etc. The main raw material for biaxially oriented polypropylene films is polypropylene resin, but films using raw materials that are a blend of polypropylene resin and polyethylene resin are also known as semi-transparent or low-gloss films.

[0003] For example, Patent Document 1 discloses an invention relating to a decorative sheet that includes, as a constituent layer, a polyolefin film made of a composition of 100 parts by weight of polypropylene and 1 to 50 parts by weight of high-density polyethylene, and describes that it is possible to provide a decorative sheet that has excellent secondary processability and is imparted with a matte finish to give it a luxurious feel.

[0004] Patent Document 2 discloses an invention relating to a matte finish in-mold label film having a matte finish surface layer portion that contains 45 to 80% by weight of polypropylene resin, 15 to 35% by weight of high-density polyethylene resin, and 5 to 20% by weight of low-density polyethylene resin. It also describes that it is possible to provide an in-mold label film in which a moderately matte finish uneven surface is formed on the film surface.

[0005] Meanwhile, in recent years, plant-derived polyethylene resins have been developed, and from the viewpoint of reducing the environmental load, the incorporation of plant-derived polyethylene resins in place of petroleum-derived polyethylene resins has been considered.

[0006] In Patent Document 3, a polypropylene resin having a melt flow rate of 1.5 g / 10 min or more and 15 g / 10 min or less at 190° C. and a density of 0.910 g / cm3 for 100 parts by mass of polypropylene is described. 3 More than 0.935g / cm 3 The invention discloses an oriented polypropylene film having a base layer containing 1 to 23 parts by mass of the following polyethylene, and having an image clarity of 65% or more and a haze value of 8% or less. It also discloses that plant-derived polyethylene can be used as the polyethylene.

[0007] Patent Document 4 describes a biaxially oriented polypropylene film having excellent transparency, visibility, glossiness, and heat-sealing strength, which is composed of at least three layers, an outer surface layer, an intermediate layer, and an inner surface layer, and the intermediate layer contains 85 to 95% by weight of a propylene-based polymer and 2 to 15% by weight of an ethylene-based polymer (E). The ethylene-based polymer (E) is a biomass-derived ethylene polymer, and the density of the ethylene-based polymer (E) is 0.904 to 0.945 g / cm. 3 It is also described that the melt flow rate (MFR: 190°C) is 1.0 to 8.0 g / 10 min. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-235818 [Patent Document 2] JP 2015-139893 A [Patent Document 3] JP 2018-65267 A [Patent Document 4] JP 2021-133509 A Summary of the Invention [Problem to be solved by the invention]

[0009] The films described in Patent Documents 1 and 2 use petroleum-derived polyethylene resins that are commonly used as polyethylene resins, and there is no mention of using plant-derived polyethylene resins in particular. Therefore, the films described in Patent Documents 1 and 2 have room for improvement from the perspective of reducing the environmental load. On the other hand, Patent Documents 3 and 4 state that a plant-derived polyethylene resin is used, which has a certain effect of reducing the environmental load. However, the film described in Patent Document 3 tends to have a large thermal shrinkage rate, etc., and there is room for improvement in terms of heat resistance. In addition, the film described in Patent Document 4 tends to be easily torn during film production.

[0010] Therefore, an object of the present invention is to provide a biaxially oriented polypropylene film which is less prone to film tearing during production, has good heat resistance, and can reduce the environmental impact. [Means for solving the problem]

[0011] Means for Solving the Problems The inventors of the present invention have conducted intensive research to achieve the above-mentioned object, and as a result have found that the above-mentioned problems can be solved by a biaxially oriented polypropylene-based film having a base layer containing a polypropylene-based resin having a specific melting point and a plant-derived ethylene-α-olefin copolymer having a specific density and melt flow rate (MFR) in specific ranges, respectively, and have thus completed the present invention.

[0012] The gist of the present invention is the following [1] to [7]. [1] Polypropylene resin (B1) having a melting point of 150°C or more and 170°C or less, 50.0% by mass or more and less than 99.0% by mass, and a density of 0.936 g / cm 3 More than 0.970g / cm 3 The biaxially oriented polypropylene film has at least a base layer B containing 1.0% by mass or more and less than 50.0% by mass of a plant-derived ethylene-α-olefin copolymer (B2) having an MFR of 0.01 g / 10 min or more and less than 1.0 g / 10 min. [2] Further, a polypropylene-based resin layer A is provided as an outermost layer, and the polypropylene-based resin layer A is (i) a layer containing at least 80% by mass of a polypropylene-based resin having a melting point of 150° C. or more and 170° C. or less; (ii) a layer containing a polyethylene-based resin in an amount of 1 part by mass or more and 100 parts by mass or less relative to 100 parts by mass of a polypropylene-based resin; and (iii) A layer containing at least a propylene-α-olefin copolymer having a melting point of 70° C. or more and less than 150° C. The biaxially oriented polypropylene film according to the above item [1], [3] The biaxially oriented polypropylene-based film according to the above [2], further comprising a polypropylene-based resin layer C as an outermost layer on the opposite side to the polypropylene-based resin layer A, the polypropylene-based resin layer C being any layer selected from the group consisting of the layers (i) to (iii). [4] The biaxially oriented polypropylene film according to [2] above, wherein the polypropylene-based resin layer A has a thickness of 0.5 μm or more and 8.0 μm or less, the base layer B has a thickness of 9.0 μm or more and 60.0 μm or less, and the polypropylene-based resin layer A and the base layer B are laminated by a coextrusion method. [5] The biaxially stretched polypropylene film according to any one of the above [1] to [4], having a longitudinal tensile modulus of 1000 MPa or more and 2500 MPa or less, a transverse tensile modulus of 1500 MPa or more and 4000 MPa or less, a longitudinal heat shrinkage rate of -1.0% or more and 3.0% or less, and a transverse heat shrinkage rate of -1.0% or more and 2.5% or less. [6] The biaxially oriented polypropylene film according to any one of claims [2] to [5], wherein in the case where the outermost layer contains a polyethylene resin, the polyethylene resin contains polyethylene derived from plants. [7] A rice ball packaging bag comprising the biaxially oriented polypropylene film according to any one of [1] to [6] above. Effect of the Invention

[0013] According to the present invention, it is possible to provide a biaxially oriented polypropylene film which is less prone to film tearing during production, has good heat resistance, and can reduce the environmental impact. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view illustrating a biaxially oriented polypropylene film according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view illustrating a biaxially oriented polypropylene film according to another embodiment of the present invention. [Diagram 3] FIG. 1 is a cross-sectional view showing a schematic diagram of another embodiment of the biaxially oriented polypropylene film of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Biaxially oriented polypropylene film] The biaxially stretched polypropylene film of the present invention comprises 50.0% by mass or more and less than 99.0% by mass of a polypropylene resin (B1) having a melting point of 150° C. or more and 170° C. or less, and a density of 0.936 g / cm 3 More than 0.970g / cm 3 or less and containing 1.0 mass % or more and less than 50.0 mass % of a plant-derived ethylene-α-olefin copolymer (B2) having an MFR of 0.01 g / 10 min or more and less than 1.0 g / 10 min.

[0016] In the present invention, the biaxially stretched polypropylene film means a polypropylene film stretched in both MD (machine direction) and TD (transverse direction). In the present specification, the MD may be referred to as the machine direction, and the TD may be referred to as the transverse direction. Hereinafter, biaxially oriented polypropylene film may be referred to as "OPP film."

[0017] The structure of the OPP film of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the contents of the drawings. An OPP film 10 according to one embodiment of the present invention is a single-layer OPP film made of a base layer B as shown in FIG. The base layer B is a polypropylene resin (B1) having a melting point of 150°C or more and 170°C or less and a density of 0.936 g / cm 3 More than 0.970g / cm 3 By including the plant-derived ethylene-α-olefin copolymer (B2) having a MFR of 0.01 g / 10 min or more and less than 1.0 g / 10 min in specific amounts, the heat resistance of the OPP film is high, film breakage during film production is suppressed, and the environmental impact is also reduced. The reason for this is unclear, but is presumed to be as follows.

[0018] In the above-mentioned base layer B, the melting point of the polypropylene resin (B1) is relatively high, and the ethylene-α-olefin copolymer also has a high density. Therefore, the OPP film of the present invention has high heat resistance. The ethylene-α-olefin copolymer (B2) has a density of 0.936 g / cm 3 More than 0.970g / cm 3It has a relatively high density, with an MFR of 0.01 g / 10 min or more and less than 1.0 g / 10 min, and a relatively low MFR. The ethylene-α-olefin copolymer (B2) is considered to be dispersed in the polypropylene resin (B1) which is the matrix, and since the ethylene-α-olefin copolymer (B2) has a relatively low MFR as described above, it is presumed that it forms an appropriate phase separation structure in which film breakage is unlikely to occur, thereby suppressing film breakage. Specifically, it is considered that it forms a sea-island structure in which the ethylene-α-olefin copolymer (B2) is dispersed in the polypropylene resin (B1) which is the matrix. Since the melting point and density of the polypropylene resin (B1) and the ethylene-α-olefin copolymer (B2) are in the above ranges, the interfacial strength between the sea [(B1) component] and the islands [(B2) component] is high, and since the MFR of the (B2) component is in a specific range, the distance between the islands is not too close, and therefore film breakage is considered to be suppressed. Furthermore, the ethylene-α-olefin copolymer (B2) is a plant-derived ethylene-α-olefin copolymer, and therefore the environmental impact can be reduced.

[0019] The OPP film of the present invention may be an OPP film 10 comprising a base layer B and a polypropylene resin layer A provided on one surface of the base layer B, as shown in FIG. 3, the OPP film of the present invention may further include a polypropylene-based resin layer C as the outermost layer opposite the polypropylene-based resin layer A. In other words, the OPP film of the present invention may be an OPP film 10 in which the polypropylene-based resin layer A, the base layer B, and the polypropylene-based resin layer C are laminated in this order. By providing the outermost layer of polypropylene-based resin layer A and / or polypropylene-based resin layer C in this manner, the OPP film has high heat resistance, is less likely to break during film production, and has a reduced environmental impact, and can also be endowed with functions according to the composition of the outermost layer.

[0020] [Base material layer B] The OPP film of the present invention comprises at least a base layer B containing a specific polypropylene resin (B1) and a specific plant-derived ethylene-α-olefin copolymer (B2) each in an amount within a specific range.

[0021] <Polypropylene resin (B1)> The base layer B contains a polypropylene-based resin (B1). The polypropylene-based resin (B1) is a polymer containing propylene monomer as a main monomer, and is preferably a polymer containing 80 mol % or more, more preferably 90 mol % or more of propylene monomer.

[0022] The type of polypropylene resin (B1) is not particularly limited, but is preferably at least one selected from the group consisting of propylene homocopolymer, propylene-ethylene copolymer, propylene-butene-1 copolymer, and propylene-ethylene-butene-1 copolymer. The copolymer may be a random copolymer or a block copolymer. For example, the propylene-ethylene copolymer may be a propylene-ethylene random copolymer (random PP) or a propylene-ethylene block copolymer (block PP). The polypropylene resin (B1) may be used alone or in combination of two or more kinds. Among these, from the viewpoint of improving the heat resistance and mechanical strength of the base layer B, the polypropylene-based resin (B1) is more preferably at least one selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers, and even more preferably a propylene-ethylene copolymer. The propylene-ethylene copolymer has an ethylene content of preferably 0.05% by mass or more and 2% by mass or less, more preferably 0.1% by mass or more and 1% by mass or less. By using a propylene-ethylene copolymer with a low ethylene content in this way, it is possible to impart a physical property that makes the base layer relatively easy to stretch while maintaining the heat resistance of the base layer B. As a result, it is easy to suppress film breakage during production.

[0023] From the viewpoint of reducing the environmental load, the polypropylene-based resin (B1) may contain a polypropylene-based resin that employs a mass balance method certified by ISCC PLUS certification or the like, or may contain a plant-derived polypropylene-based resin. The plant-derived polypropylene resin is not particularly limited as long as it is polypropylene produced using plant-derived propylene (monomer) as a raw material, and examples thereof include homopolymers of plant-derived propylene and plant-derived propylene copolymers obtained by copolymerizing plant-derived propylene with other monomers. Here, examples of the other monomers include α-olefins other than propylene having 2 to 20 carbon atoms, and examples of other monomers that are preferably used include ethylene and butene-1. The other monomers may be petroleum-derived monomers or plant-derived monomers. In addition, the other monomers may be one type or two or more types in combination. Examples of suitable plant-derived propylene copolymers include propylene-ethylene copolymers, propylene-butene-1 copolymers, and propylene-ethylene-butene-1 copolymers. The copolymers may be random copolymers or block copolymers. For example, the propylene-ethylene copolymers may be propylene-ethylene random copolymers (random PP) or propylene-ethylene block copolymers (block PP).

[0024] Plant-derived propylene, which is the raw material for plant-derived polypropylene resins, can be produced by known methods, such as a method of thermally cracking vegetable oils (see JP 2018-522087 A), a method of metathesis reacting ethylene obtained from ethanol derived from biomass such as corn or sugar cane with n-butene (see WO 2007 / 055361 A), and a method of dehydrating 1,3-propylene glycol obtained by fermenting biomass (JP 2013-76192 A). The plant-derived propylene obtained as described above can be homopolymerized or copolymerized with other monomers by a known method to obtain a plant-derived polypropylene-based resin.

[0025] The melting point of the polypropylene resin (B1) is 150°C or more and 170°C or less. When the melting point of the polypropylene resin (B1) is in this range, the heat resistance is good and the mechanical strength of the film is also improved. The melting point of the polypropylene resin (B1) is preferably 153°C or more and 168°C or less, more preferably 155°C or more and 165°C or less.

[0026] The melt flow rate (MFR) of the polypropylene resin (B1) at 230°C is not particularly limited, but is preferably 1 g / 10 min or more and 5 g / 10 min or less, more preferably 1.5 g / 10 min or more and 4.5 g / 10 min or less, and even more preferably 2.0 g / 10 min or more and 4.0 g / 10 min or less. By setting the MFR of the polypropylene resin (B1) within the above range and the MFR of the plant-derived ethylene-α-olefin copolymer (B2) within the specific range described below, film breakage can be effectively suppressed.

[0027] The content of the polypropylene-based resin (B1) in the base layer B is 50.0% by mass or more and less than 99.0% by mass. By making the content of the polypropylene-based resin (B1) 50.0% by mass or more, it is possible to impart a certain level of heat resistance and mechanical strength to the base layer B. By making the content of the polypropylene-based resin (B1) less than 99.0% by mass, it is possible to blend in a certain amount or more of the plant-derived ethylene-α-olefin copolymer (B2) described later, thereby reducing the environmental impact. The content of the polypropylene resin (B1) in the base layer B is preferably from 55.0% by mass to 98.0% by mass, and more preferably from 60.0% by mass to 97.0% by mass.

[0028] <Plant-derived ethylene-α-olefin copolymer (B2)> The substrate layer B contains a plant-derived ethylene-α-olefin copolymer (B2). The plant-derived ethylene-α-olefin copolymer (B2) is a copolymer of ethylene and an α-olefin, and is a copolymer containing ethylene as a main monomer. More specifically, the plant-derived ethylene-α-olefin copolymer (B2) is a copolymer containing preferably 80 mol% or more, more preferably 90 mol% or more, of ethylene. At least one of the raw materials, ethylene monomer and α-olefin monomer, contains a plant-derived monomer.

[0029] In the ethylene-α-olefin copolymer (B2), the α-olefin is preferably an α-olefin having a carbon number of 3 to 12, more preferably an α-olefin having a carbon number of 4 to 8. The α-olefin is preferably an α-olefin such as propylene, butene-1, hexene-1, octene-1, or 4-methyl-1-pentene. Among the above-mentioned ethylene-α-olefin copolymers (B2), ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers, etc. are preferred, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers are more preferred, and ethylene-butene-1 copolymers are even more preferred. The ethylene-α-olefin copolymers (B2) may be used alone or in combination of two or more kinds.

[0030] The amount of α-olefin in the ethylene-α-olefin copolymer (B2) is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 1% by mass or less. When the amount of α-olefin in the ethylene-α-olefin copolymer (B2) is within the above range, it becomes easy to adjust the density described below to a desired range, and it becomes easy to improve the heat resistance of the film.

[0031] The density of the plant-derived ethylene-α-olefin copolymer (B2) is 0.936 g / cm 3 More than 0.970g / cm 3By adjusting the density to such a range, the heat resistance of the film can be improved. The density of the plant-derived ethylene-α-olefin copolymer (B2) is preferably 0.940 g / cm or less. 3 More than 0.965g / cm 3 More preferably, it is 0.950 g / cm or less. 3 More than 0.960g / cm 3 The following is the result.

[0032] The melt flow rate (MFR) of the plant-derived ethylene-α-olefin copolymer (B2) is 0.01 g / 10 min or more and less than 1.0 g / 10 min. By setting the MFR in such a range, film breakage during film formation can be easily suppressed. From this viewpoint, the MFR of the plant-derived ethylene-α-olefin copolymer (B2) is preferably 0.05 g / 10 min or more and 0.5 g / 10 min or less, more preferably 0.1 g / 10 min or more and 0.3 g / 10 min or less. The MFR of the plant-derived ethylene-α-olefin copolymer (B2) is the MFR at 190°C.

[0033] The plant-derived ethylene-α-olefin copolymer of the present invention is a copolymer polymerized using a plant-derived monomer as at least a part of the monomers used to produce the copolymer. The plant-derived ethylene-α-olefin copolymer has the same physical properties as the petroleum-derived ethylene-α-olefin copolymer, but reduces petroleum consumption and CO2 emissions, thereby suppressing the environmental load. From the viewpoint of reducing the environmental load, the biomass degree of the plant-derived ethylene-α-olefin copolymer (B2) is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, even more preferably 70% or more, even more preferably 90% or more, and is 100% or less. The biomass ratio can be determined by measuring the concentration of C14 in a sample by accelerator mass spectrometry. Resins such as the plant-derived ethylene-α-olefin copolymers described above contain a certain concentration of C14 because the atmosphere contains a certain concentration of C14. On the other hand, there is almost no C14 in petroleum trapped underground. Therefore, the content ratio of plant-derived raw materials in a sample (biomass ratio) can be determined by measuring the concentration of C14 by accelerator mass spectrometry.

[0034] For example, the concentration of C14 in a sample can be measured as follows. That is, the sample to be measured is burned to generate carbon dioxide, and the carbon dioxide refined in a vacuum line is reduced with hydrogen using iron as a catalyst to refine graphite. This graphite is then attached to a dedicated C14-AMS device (manufactured by NEC) based on a tandem accelerator to measure the C14 count, C13 concentration (C13 / C12), and C14 concentration (C14 / C12), and the ratio of the C14 concentration of the sample carbon to standard modern carbon is calculated from these measurements. Oxalic acid (HOXII) provided by the National Bureau of Standards (NIST) is used as the standard sample.

[0035] The content of the plant-derived ethylene-α-olefin copolymer (B) in the base layer B is 1.0% by mass or more and less than 50.0% by mass. By making the content of the plant-derived ethylene-α-olefin copolymer (B) 1.0% by mass or more, it becomes easier to reduce the environmental load. By making the content of the plant-derived ethylene-α-olefin copolymer (B) less than 50.0% by mass, it becomes easier to suppress film breakage. The content of the plant-derived ethylene-α-olefin copolymer (B) in the base layer B is preferably 3.0% by mass or more and 45.0% by mass or less, and more preferably 5.0% by mass or more and 35.0% by mass or less.

[0036] The base layer B may contain other resins other than the polypropylene-based resin (B1) and the plant-derived ethylene-α-olefin copolymer (B2) as long as the effect of the present invention is not hindered. The other resins are not particularly limited, but examples thereof include polyethylene-based resins other than the plant-derived ethylene-α-olefin copolymers described above (e.g., petroleum-derived ethylene-α-olefin copolymers, ethylene homopolymers, etc.), aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, aliphatic polyesters such as polylactic acid, polybutylene succinate-based resins, polycaprolactone-based resins, polyamides, polystyrene, ethylene-vinyl acetate copolymers, and petroleum resins. The polyesters and polyamides described above may be derived from biomass from the viewpoint of reducing the environmental load. The amount of other resins is preferably a certain amount or less, and other resins may not be used. That is, the total amount of the polypropylene-based resin (B1) and the plant-derived ethylene-α-olefin copolymer (B2) in the base layer B is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

[0037] The thickness of the base layer is not particularly limited, but from the viewpoint of ensuring a certain level of mechanical strength of the film, it is preferably 9.0 μm or more and 60 μm or less, and from the viewpoint of improving the mechanical strength and suppressing film tearing, it is more preferably 15 μm or more and 50 μm or less.

[0038] [Polypropylene resin layer A] The OPP film of the present invention may include the above-mentioned base layer B and a polypropylene-based resin layer A. The polypropylene-based resin layer A is the outermost layer of the OPP film, in other words, the surface layer (skin layer) of the OPP film. By providing the OPP film with the polypropylene-based resin layer A, various functions can be imparted depending on the type of resin that constitutes the polypropylene-based resin layer A.

[0039] The polypropylene resin layer A is preferably any layer selected from the group consisting of the following (i) to (iii). (i) A layer containing at least 80% by mass of a polypropylene-based resin having a melting point of 150° C. or higher and 170° C. or lower. (ii) A layer containing a polyethylene-based resin in an amount of 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of a polypropylene-based resin. (iii) A layer containing at least a propylene-α-olefin copolymer having a melting point of 70° C. or higher and lower than 150° C.

[0040] <(i) Layer> The layer containing at least 80% by mass of a polypropylene resin having a melting point of 150° C. or more and 170° C. or less (hereinafter also referred to as layer (i)) will be described. Since layer (i) contains as a main component a polypropylene-based resin having a relatively high melting point, it becomes a layer having excellent heat resistance and transparency. The polypropylene resin used in the layer (i) may be any of the resins described above in the polypropylene resin (B1) without any particular limitation. Among them, the polypropylene resin used in the layer (i) is preferably at least one selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers. The polypropylene resin used in the layer (i) may be one type alone or two or more types in combination. As described above, the propylene-ethylene copolymer preferably has an ethylene content of 0.05 to 2% by mass, more preferably 0.1 to 1% by mass. The preferred melting point and preferred MFR of the polypropylene resin used in the layer (i) are the same as those described for the polypropylene resin (B1).

[0041] Layer (i) may contain other resins than the polypropylene resin having a melting point of 150° C. or more and 170° C. or less, but it is preferable to keep the amount of other resins below a certain amount, and other resins may not be used. That is, in layer (i), the content of the polypropylene resin having a melting point of 150° C. or more and 170° C. or less is 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0042] <(ii) layer> The layer containing 1 part by mass or more and 100 parts by mass or less of a polyethylene-based resin with respect to 100 parts by mass of a polypropylene-based resin (hereinafter also referred to as layer (ii)) will be described. The (ii) layer is a layer containing both a polypropylene-based resin and a polyethylene-based resin, and constitutes a matte layer. The matte layer is a layer that can reduce the gloss of the matte layer side of the OPP film by forming the matte layer. When the matte layer is formed, the gloss of the matte layer side is, for example, 30% or less, more preferably 20% or less. The gloss can be measured in accordance with JIS K 7105.

[0043] The polypropylene-based resin used in the (ii) layer is preferably at least one selected from a propylene homopolymer, a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. The copolymer may be a random copolymer or a block copolymer. For example, the propylene-ethylene copolymer may be a propylene-ethylene random copolymer (random PP) or a propylene-ethylene block copolymer (block PP). From the viewpoint of imparting heat sealability to the (ii) layer, the polypropylene-based resin used in the (ii) layer is preferably at least one selected from a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. The polypropylene-based resin used in the (ii) layer may be one type alone or two or more types in combination. The melting point of the polypropylene resin used in the layer (ii) is preferably 70°C or more and 140°C or less, and more preferably 100°C or more and 135°C or less. When layer (ii) contains two or more polypropylene resins, the polypropylene resins preferably contain at least a polypropylene resin having a melting point of 70° C. to 90° C. and a polypropylene resin having a melting point of 110° C. to 140° C. By using such polypropylene resins in layer (ii), a matte layer that can be heat-sealed at low temperatures can be obtained. In this case, the content of the polypropylene resin having a melting point of 70° C. to 90° C. is preferably 5 to 100 parts by mass, more preferably 20 to 40 parts by mass, per 100 parts by mass of the polypropylene resin having a melting point of 110° C. to 140° C.

[0044] The content of the polypropylene resin in layer (ii) is preferably from 50 to 95% by mass, more preferably from 60 to 90% by mass, and further preferably from 70 to 85% by mass.

[0045] The polyethylene resin in the layer (ii) may be any one of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and a polyethylene elastomer. Among these, it is preferable to contain linear low-density polyethylene. The linear low density polyethylene is an ethylene-α-olefin copolymer, and the α-olefin is preferably an α-olefin having 3 to 12 carbon atoms, more preferably 4 to 8 carbon atoms. Preferred α-olefins include butene-1, hexene-1, octene-1, and 4-methyl-1-pentene. The density of the linear low density polyethylene is not particularly limited, but is, for example, 0.910 g / cm. 3 More than 0.960g / cm 3 or less, preferably 0.940 g / cm 3 More than 0.960g / cm 3 The following is the result. The polyethylene elastomer is an ethylene-α-olefin copolymer, and the α-olefin is preferably an α-olefin having 3 to 12 carbon atoms, more preferably 4 to 8 carbon atoms. As the α-olefin, butene-1, hexene-1, octene-1, 4-methyl-1-pentene, etc. are preferable. The density of the polyethylene elastomer is not particularly limited, but is, for example, 0.880 g / cm. 3 More than 0.910g / cm 3 is less than. The polyethylene resin used in the layer (ii) may be used alone or in combination of two or more kinds.

[0046] The content of the polyethylene resin in layer (ii) is preferably from 3 to 50% by mass, more preferably from 5 to 30% by mass, and further preferably from 15 to 25% by mass.

[0047] The content of the polyethylene resin in the layer (ii) is 1 to 100 parts by mass, preferably 5 to 50 parts by mass, more preferably 10 to 30 parts by mass, and further preferably 15 to 25 parts by mass, relative to 100 parts by mass of the polypropylene resin. By setting the content of the polyethylene resin in the layer (ii) within such a range, the layer (ii) can be made into a matte layer, and the adhesion to the base layer B is also improved.

[0048] Layer (ii) may contain other resins besides the polypropylene-based resin and polyethylene-based resin described above, but the amount of other resins is preferably less than a certain amount, and other resins may not be used. That is, the total amount of polypropylene-based resin and polyethylene-based resin in layer (ii) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

[0049] <(iii) layer> The layer containing at least a propylene-α-olefin copolymer having a melting point of 70° C. or more and less than 150° C. (hereinafter also referred to as layer (iii)) will be described. Since the layer (iii) contains the propylene-α-olefin copolymer having a low melting point as described above, it can be used as a heat seal layer. The heat seal layer is a layer that enables heat sealing when the OPP film is used as a packaging bag, and is a layer that melts or softens with heat. More specifically, when the OPP film is used as a packaging bag, it is a layer that enables the bag to be sealed by heat compression after the contents are placed in the bag. Therefore, it is preferable that the heat seal layer contains a propylene-α-olefin copolymer with a relatively low melting point. The melting point of the propylene-α-olefin copolymer is 70°C or higher and lower than 150°C, preferably 70°C or higher and 140°C or lower, and more preferably 100°C or higher and 135°C or lower.

[0050] The propylene-α-olefin copolymer contained in the (iii) layer is preferably at least one selected from a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer. The propylene-α-olefin copolymer may be used alone or in combination of two or more. The amount of comonomer (α-olefin amount) of the propylene-α-olefin copolymer is preferably 1 to 15% by mass, more preferably 2 to 8% by mass, from the viewpoint of adjusting the melting point to the above-mentioned range and imparting the desired heat sealability.

[0051] The (iii) layer may contain other resins than the propylene-α-olefin copolymer, but the amount of the other resins is preferably small, and other resins may not be used. That is, the content of the propylene-α-olefin copolymer in the (iii) layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

[0052] The thickness of the polypropylene-based resin layer A is not particularly limited, but is preferably 0.5 μm to 8.0 μm, more preferably 0.8 μm to 6.0 μm, and even more preferably 1.0 μm to 5.0 μm. By adjusting the thickness of the polypropylene-based resin layer A as described above, film breakage can be easily suppressed and film formation stability can be improved.

[0053] [Polypropylene resin layer C] The OPP film of the present invention may further include a polypropylene-based resin layer C as the outermost layer opposite to the polypropylene-based resin layer A. In this case, the OPP film is a multilayer film in which the polypropylene-based resin layer A, the base layer B, and the polypropylene-based resin layer C are laminated in this order.

[0054] The polypropylene resin layer C is preferably any layer selected from the group consisting of the above-mentioned (i) to (iii). The type of the polypropylene-based resin layer C may be the same as or different from the type of the polypropylene-based resin layer A, but is preferably the same. For example, when the polypropylene-based resin layer A is made of the above-mentioned (iii) layer (heat seal layer), the polypropylene-based resin layer C is preferably made of the above-mentioned (iii) layer (heat seal layer). Of course, even when the polypropylene-based resin layer A is made of the above-mentioned (iii) layer (heat seal layer), the polypropylene-based resin layer C may be made of the (i) layer or the (ii) layer. The details of the layers (i), (ii) and (iii) are as described above, and therefore will not be described here.

[0055] The thickness of the polypropylene-based resin layer C is not particularly limited, but is preferably 0.5 μm to 8.0 μm, more preferably 0.8 μm to 6.0 μm, and even more preferably 1.0 μm to 5.0 μm. By adjusting the thickness of the polypropylene-based resin layer C as described above, film breakage can be easily suppressed and film formation stability can be improved.

[0056] When the outermost polypropylene-based resin layer A or polypropylene-based resin layer C contains a polyethylene-based resin, it is preferable that the polyethylene-based resin contains plant-derived polyethylene. By containing plant-derived polyethylene, the environmental load can be suppressed in order to reduce the petroleum consumption and CO2 emissions.

[0057] (Additive) The OPP film of the present invention may contain, as an additive, an additive that functions as an anti-fogging agent and an antistatic agent. The additive may be contained in at least one of the base layer and the outermost layer, but is preferably contained in the base layer. The content of the additive that functions as an anti-fogging agent and an antistatic agent is preferably 0.4 to 1.0% by mass, more preferably 0.6 to 0.8% by mass, in the layer (base layer or outermost layer) containing the additive.

[0058] The type of the additive that functions as an anti-fogging agent and an antistatic agent is not particularly limited as long as it is used in a general polyolefin film. For example, esters of polyhydric alcohols such as glycerin, polyethylene glycol, pentaerythritol, sorbitol, polypropylene glycol and higher fatty acids such as lauric acid, stearic acid, oleic acid, ethylene oxide adducts of higher aliphatic amines, higher aliphatic alkanolamides, higher alcohol phosphate esters, and mixtures thereof can be mentioned.

[0059] The OPP film of the present invention may contain other additives other than the additives that function as the above-mentioned anti-fogging agent and antistatic agent. Examples of the other additives include a crystallization nucleating agent, an antioxidant, a lubricant, an anti-blocking agent, a chlorine scavenger, cellulose nanofibers, inorganic fine particles, starch, etc. Examples of the inorganic fine particles include calcium carbonate, an adsorbent, an antibacterial agent, etc. The other additives may be contained in the base layer, may be contained in the outermost layer, or may be contained in both the base layer and the outermost layer.

[0060] <OPP film physical property: Tensile modulus of elasticity> The tensile elastic modulus of the OPP film of the present invention in the machine direction (MD) is preferably 1000 MPa or more and 2500 MPa or less, more preferably 1200 MPa or more and 2000 MPa or less. Further, the tensile elastic modulus of the OPP film of the present invention in the transverse direction (TD) is preferably 1500 MPa or more and 4000 MPa or less, more preferably 2000 MPa or more and 3500 MPa or less. By setting the tensile elastic modulus within the above range, the packaging machine characteristics of the OPP film are improved.

[0061] <OPP film physical properties: Heat shrinkage rate> The heat shrinkage rate of the OPP film of the present invention in the machine direction (MD) is preferably -1.0% or more and 3.0% or less, more preferably -0.5% or more and 2.5% or less. Further, the heat shrinkage rate of the OPP film of the present invention in the transverse direction (TD) is preferably -1.0% or more and 2.5% or less, more preferably -0.5% or more and 2.5% or less. When the heat shrinkage rate is within the above range, it has good heat resistance, so when processing at a high temperature such as heat sealing, it is easier to maintain the appearance and physical properties of the film well.

[0062] <OPP film physical properties: Biomass content> The biomass content of the OPP film of the present invention is preferably 1% or more, more preferably 3% or more, and even more preferably 10% or more. Ideally, the biomass content is 100%, but in practice, it can be appropriately determined considering the cost. The larger the biomass content, the more the environmental load can be reduced. The biomass content of the OPP film can be adjusted by the content of the plant-derived raw material used in the base material layer B and / or the outermost layer. The biomass content is the content ratio of the plant-derived raw material in the OPP film, and is determined by measuring the concentration of C14 by accelerator mass spectrometry based on ISO 16620-2:2015. Further, when using a raw material with a known biomass content, it can also be obtained by calculation from the mixing ratio with the petroleum-derived raw material.

[0063] [Manufacturing method of biaxially oriented polypropylene film (OPP film)] The method for producing the OPP film of the present invention is not particularly limited, and the film can be produced by applying an extrusion method, an in-line lamination method, a co-extrusion method, or the like.

[0064] In the extrusion method, the resin composition that is the raw material of the base layer is extruded through a T-die to form an unstretched sheet. Here, the resin composition that is the raw material of the base layer is a resin composition that contains a polypropylene resin (B1) and a plant-derived ethylene-α-olefin copolymer (B2). Next, the unstretched sheet is stretched with MD rolls by using a speed difference between the rolls to obtain an MD stretched sheet. Next, the MD-stretched sheet is introduced into a tenter, both ends of the MD-stretched sheet are held with clips, and the MD-stretched sheet is subjected to TD stretching to a predetermined width in a tenter oven to obtain an OPP film. The extrusion process results in a single layer OPP film.

[0065] In the in-line lamination method, first, the resin composition that is the raw material for the base layer is extruded through a T-die to form an unstretched sheet. Next, the unstretched sheet is MD roll stretched by the roll speed difference to obtain an MD stretched sheet. Next, a resin composition as a raw material for the outermost layer is extruded from a T-die using a separately installed extruder, and melt-laminated on one or both sides of the MD stretched sheet to obtain a laminated MD stretched sheet with the outermost layer laminated thereon. The resin composition as a raw material for the outermost layer is preferably a resin composition for forming the above-mentioned (i), (ii), or (iii) layer. Next, the laminated MD stretched sheet is introduced into a tenter, both ends of the laminated MD stretched sheet are held with clips, and the laminated MD stretched sheet is subjected to TD stretching to a predetermined width in a tenter oven, thereby obtaining the OPP film of the present invention.

[0066] In the co-extrusion method, the resin composition as the raw material of the base layer and the resin composition as the raw material of the outermost layer are co-extruded from a co-extrusion die, respectively, to form a laminated unstretched sheet. Next, the laminated unstretched sheet is MD roll stretched by the speed difference of the rolls to obtain a laminated MD stretched sheet. Next, the laminated MD stretched sheet is introduced into a tenter, both ends of the laminated MD stretched sheet are held with clips, and TD stretching is performed to a predetermined width in a tenter oven to obtain an OPP film. In this way, an OPP film in which the above-mentioned polypropylene-based resin layer A and base layer B are laminated by the co-extrusion method, or an OPP film in which the polypropylene-based resin layer A, base layer B, and polypropylene-based resin layer C are laminated by the co-extrusion method is obtained.

[0067] The OPP film produced by the above-mentioned extrusion method, in-line lamination method, co-extrusion method, etc. may be used as it is, or the OPP film may be used after secondary processing. Examples of secondary processing include surface processing by printing, coating, vapor deposition, etc., or lamination with other films. The secondary processing may be performed on one side or both sides of the OPP film.

[0068] [Application] The biaxially oriented polypropylene film of the present invention is not particularly limited in its use, but can be used, for example, as packaging for food, daily necessities, miscellaneous goods, etc. In particular, since the biaxially oriented polypropylene film of the present invention has high mechanical strength, excellent packaging machine properties, and excellent heat resistance, it is preferably used as a packaging for sandwiches, rice balls, etc., and is particularly preferably used as a rice ball packaging material made of a biaxially oriented polypropylene film. EXAMPLES

[0069] The present invention will now be described in more detail, but it should be understood that the present invention is not limited to these examples.

[0070] [Raw material evaluation] <Melting point> Approximately 4 mg of the resin sample was weighed out and sealed in an aluminum pan. This was then attached to a differential scanning calorimeter (PerkinElmer, Inc., model "DSC8500AS") and heated to 230°C in a nitrogen gas flow of 20 mL / min. The sample was then held at this temperature for 5 minutes, after which it was cooled to -10°C at a rate of 10°C / min. The sample was then heated to 230°C at a rate of 10°C / min. The peak temperature showing the maximum endothermic heat in the endothermic curve obtained was taken as the melting point.

[0071] <Melt flow rate (MFR)> Measurements were performed under a load of 2.16 kg in accordance with JIS K 7210. The measurement temperatures were 230°C for polypropylene-based resins and 190°C for polyethylene-based resins.

[0072] <Raw materials> Details of the raw materials used in each of the examples and comparative examples are shown in Table 1 below.

[0073] [Table 1]

[0074] [Example 1] Using the raw materials listed in Table 1, an OPP film consisting of a single layer of base material layer B was produced. Specifically, a composition for base layer B consisting of 65% by mass of PP1 and 35% by mass of PE1 was melt-kneaded and extruded at 250°C by a first extruder to obtain a single-layer sheet. The obtained sheet was heated to 130°C by a longitudinal stretching machine and then stretched 5 times in the longitudinal direction (MD). Subsequently, the sheet was heated to 190°C by a transverse stretching machine and then stretched 10 times in the transverse direction (TD) to obtain an OPP film. The film-forming speed during the production of the OPP film was 25 m / min.

[0075] <Evaluation of film tear> The above-mentioned OPP film was continuously produced, and it was confirmed whether or not the film was torn within a certain period of time from the start of production. (evaluation) 〇: No film tear occurred within 2 hours of starting production ×: Film breakage occurred within 2 hours of starting production.

[0076] <Evaluation of environmental friendliness> The evaluation was based on the following criteria. 〇: Contains plant-derived resin, reducing environmental impact ×: Does not contain plant-derived resin and does not reduce environmental impact

[0077] <Evaluation of tensile modulus> In accordance with JIS K7127, the tensile modulus of elasticity in the machine direction (MD) and transverse direction (TD) was measured for type 2 test pieces using a tensile testing machine (AG-Xplus, manufactured by Shimadzu Corporation) at a tensile speed of 50 mm / min.

[0078] <Evaluation of heat shrinkage rate> After cutting the film to a width of 15 mm and a length of 600 mm, the film was marked at a length of 500 mm and left in an oven at 120°C for 15 minutes without a load. It was then allowed to cool at room temperature for 15 minutes and the length of the mark was measured. The thermal shrinkage was calculated as follows: Heat shrinkage rate (%) = (500 - length between marks after shrinkage (mm)) x 100 / 500

[0079] [Examples 2 to 5, Comparative Examples 1 to 7] Except for changing the types and amounts of raw materials used in the base layer B as shown in Tables 2 and 3, OPP films were produced in the same manner as in Example 1, and each evaluation was performed. The numerical values ​​of each resin shown in Tables 2 and 3 indicate the content (mass %) in each layer.

[0080] [Example 6] (Materials for forming each layer) First, the following compositions having the formulations shown in Table 2 were prepared. Composition for polypropylene-based resin layer A: A composition consisting of 100% by mass of PP1. Composition for base layer B: A composition consisting of 65% by mass of PP2 and 35% by mass of PE2. (OPP film manufacturing) Next, each composition was introduced into a separate extruder (a total of two extruders), and in each extruder, melt-kneaded and extruded at 250°C, laminated in a T-die, and two layers were co-extruded onto a metal roll at 30°C to obtain a laminated sheet. The obtained laminated sheet was heated to 130°C in a longitudinal stretching machine, and then stretched 5 times in the longitudinal direction (MD). Subsequently, it was heated to 190°C in a transverse stretching machine, and then stretched 10 times in the transverse direction (TD) to obtain an OPP film. The film-forming speed during the production of the OPP film was 25 m / min. In the manner described above, an OPP film of the present invention having the outermost layer (polypropylene-based resin layer A) and the base layer B laminated in this order was produced, and each evaluation was carried out.

[0081] [Examples 7 to 8] An OPP film was produced in the same manner as in Example 6, except that the formulation of the composition for forming each layer was changed as shown in Table 2, and each evaluation was performed.

[0082] [Example 9] (Materials for forming each layer) First, the following compositions having the formulations shown in Table 2 were prepared. Composition for polypropylene-based resin layer A: A composition consisting of 100% by mass of PP1. Composition for base layer B: A composition consisting of 90% by mass of PP2 and 10% by mass of PE2. Composition for polypropylene-based resin layer C: A composition consisting of 100% by mass of PP1. (OPP film manufacturing) Next, each composition was introduced into a separate extruder (a total of three extruders), and in each extruder, melt-kneaded and extruded at 250°C, laminated in a T-die, and the three layers were co-extruded onto a metal roll at 30°C to obtain a laminated sheet. The obtained laminated sheet was heated to 130°C in a longitudinal stretching machine, and then stretched 5 times in the longitudinal direction (MD). Subsequently, it was heated to 190°C in a transverse stretching machine, and then stretched 10 times in the transverse direction (TD) to obtain an OPP film. The film-forming speed during the production of the OPP film was 25 m / min. In the manner described above, an OPP film of the present invention having the outermost layer (polypropylene-based resin layer A), the base layer B, and the outermost layer (polypropylene-based resin layer C) laminated in this order was produced, and each evaluation was carried out.

[0083] [Examples 10 to 18, Comparative Example 8] Except for changing the formulation of the composition for forming each layer as shown in Tables 2 and 3, an OPP film was produced in the same manner as in Example 9, and each evaluation was carried out.

[0084] [Table 2]

[0085] [Table 3]

[0086] The OPP films of the respective Examples that satisfied the requirements of the present invention were films with reduced environmental impact, were suppressed from breaking during production, and had excellent heat resistance. In contrast, the OPP films of Comparative Examples 1 and 2 do not contain the plant-derived ethylene-α-olefin copolymer (B2), and the environmental load is not reduced. In the OPP films of Comparative Examples 3 and 4, the MFR of the plant-derived ethylene-α-olefin copolymer (B2) was high, and as a result, the film was prone to tearing during production. The OPP films of Comparative Examples 5 and 6 had a high heat shrinkage rate and poor heat resistance because the density of the plant-derived ethylene-α-olefin copolymer (B2) was low. The OPP films of Comparative Examples 7 and 8 had a high content of the plant-derived ethylene-α-olefin copolymer (B2), and as a result, the films were prone to tearing during production. [Explanation of symbols]

[0087] 10 OPP film A Polypropylene resin layer A B Base material layer B C Polypropylene resin layer C

Claims

1. 50.0% by mass or more and less than 99.0% by mass of a polypropylene-based resin (B1) having a melting point of 150°C or more and 170°C or less, Density is 0.936 g / cm ３ 0.970g / cm or more ３ and 1.0% by mass or more and less than 50.0% by mass of a plant-derived ethylene-α-olefin copolymer (B2) having an MFR of 0.01 g / 10 min or more and less than 1.0 g / 10 min. and a biaxially oriented polypropylene-based film for packaging, comprising at least a base layer B having a thickness of 9.0 μm or more and 60.0 μm or less.

2. Further, a polypropylene-based resin layer A is provided as an outermost layer, and the polypropylene-based resin layer A is (i) a layer containing at least 80% by mass of a polypropylene-based resin having a melting point of 150°C or higher and 170°C or lower; (ii) a layer containing a polyethylene-based resin in an amount of 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of a polypropylene-based resin; and (iii) A layer containing at least a propylene-α-olefin copolymer having a melting point of 70°C or higher and lower than 150°C. The biaxially oriented polypropylene film for packaging according to claim 1, wherein the biaxially oriented polypropylene film is any layer selected from the group consisting of:

3. 3. The biaxially oriented polypropylene-based packaging film according to claim 2, further comprising a polypropylene-based resin layer C as an outermost layer on the side opposite to the polypropylene-based resin layer A, wherein the polypropylene-based resin layer C is any layer selected from the group consisting of (i) to (iii).

4. the thickness of the polypropylene-based resin layer A is 0.5 μm or more and 8.0 μm or less; 3. The biaxially oriented polypropylene film for packaging according to claim 2, wherein the polypropylene resin layer A and the base material layer B are laminated by a coextrusion method.

5. A longitudinal tensile modulus of elasticity of 1000 MPa or more and 2500 MPa or less, a tensile modulus in the transverse direction of 1500 MPa or more and 4000 MPa or less; The thermal shrinkage rate in the longitudinal direction is -1.0% or more and 3.0% or less, The biaxially oriented polypropylene film for packaging according to any one of claims 1 to 4, wherein the heat shrinkage rate in the transverse direction is -1.0% or more and 2.5% or less.

6. 5. The biaxially oriented polypropylene film for packaging according to claim 2, wherein the outermost layer comprises a polyethylene resin, and the polyethylene resin comprises plant-derived polyethylene.

7. A rice ball packaging bag made of the biaxially oriented polypropylene film for packaging according to any one of claims 1 to 4.

8. A rice ball packaging bag made of the biaxially oriented polypropylene film for packaging according to claim 5.

9. A rice ball packaging bag made of the biaxially oriented polypropylene film for packaging according to claim 6.

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