Biaxially stretched polypropylene-based heat seal film

Abstract

To provide a biaxially stretched polypropylene-based heat seal film that offers high heat seal strength, an extended heat-sealable temperature range, and high peel energy.SOLUTION: A biaxially stretched polypropylene-based heat seal film comprises at least a substrate layer (A) and a seal layer (B) laminated on the substrate layer (A). The substrate layer (A) contains 60 to 90 mass% of a polypropylene-based resin (a-1) and 10 to 40 mass% of a propylene-α olefin copolymer (a-2). The polypropylene-based resin (a-1) has a melting point of 150 to 160°C and an MFR (230°C) of 1.0 to 4.0 g / 10 min, and the propylene-α olefin copolymer (a-2) has a melting point of 125 to 140°C and an MFR (230°C) of 1.0-10.0 g / 10 min. The seal layer (B) includes 70 to 85 mass% of a propylene-α-olefin random copolymer (b-1) and 15 to 30 mass% of an ethylene-α-olefin copolymer (b-2). The propylene-α-olefin random copolymer (b-1) has an MFR (230°C) of 1.0 to 5.5 g / 10 min, a molecular weight distribution (Mw / Mn) of 4.0 or more, and a melting point of 125 to 140°C, and the ethylene-α-olefin copolymer (b-2) has an MFR (190°C) of 1.0 to 4.0 g / 10 min, and a melting point of 50 to 75°C.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Biaxially oriented polypropylene film (OPP film) has excellent transparency, rigidity, surface hardness, impact resistance, and moisture resistance, and is widely used as packaging bags for food, daily necessities, and miscellaneous goods. Generally, packaging bags are formed by a method called heat sealing, in which films are fused together by heat. To maintain the functionality of the packaging bag, the heat seal strength is required to prevent the heat-sealed portion from peeling off.

[0003] OPP film generally has low heat-sealing strength and poor heat-sealing properties. To achieve higher heat-sealing strength, it was necessary to laminate a non-oriented polypropylene film (CPP film) with excellent heat-sealing properties to the OPP film. This process involves laminating the CPP film to the OPP film using an adhesive, which requires many manufacturing steps, leaving room for simplification of the manufacturing process and improvement in terms of cost. If it were possible to develop an OPP film with high heat seal strength by itself, eliminating the lamination process with CPP film, the need for dry lamination would be reduced, resulting in a reduction in CO2 and VOC (volatile organic compound) emissions.

[0004] Patent Document 1 discloses a packaging film with excellent heat seal strength in a low-temperature atmosphere, which comprises a base layer (A) made of crystalline polypropylene, and a heat seal layer (B) made of a mixture containing, in a specific weight range, a propylene-ethylene random copolymer or a propylene-ethylene-butene ternary random copolymer, and a linear low-density polyethylene having a density of 0.89 or less obtained by copolymerizing ethylene with an olefin having 8 or more carbon atoms in the presence of a metallocene catalyst. The examples in Patent Document 1 describe an embodiment of a biaxially oriented polypropylene film, and the film is characterized by a heat seal strength of 140°C and 2 kg / cm. 2 It is described that after heat sealing under the condition of (23°C) and leaving it in a 23°C atmosphere for 24 hours, the heat seal strength in a 23°C atmosphere is 1000 to 1350 g / 15 mm (i.e., 10 to 13 N / 15 mm). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3795264 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for OPP films with higher heat seal strength than before, and from the standpoint of workability during heat sealing, there is also a demand for OPP films with a wide heat sealable temperature range. Although the OPP film disclosed in Patent Document 1 has a certain heat seal strength, it does not disclose any detailed knowledge about the composition of each layer from the viewpoint of obtaining a higher heat seal or widening the heat sealable temperature range. Furthermore, conventional OPP films tend to be easily broken and vulnerable to impacts because the peel energy at the heat-sealed parts is small.

[0007] Therefore, an object of the present invention is to provide a biaxially oriented polypropylene-based heat seal film that has high heat seal strength, a wide heat sealable temperature range, high peel energy, and a certain level of mechanical strength or higher. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above object, the present inventors have found that the above problem can be solved by providing at least a base layer (A) and a seal layer (B), and by making the base layer (A) and the seal layer (B) have specific resin compositions, and have thus completed the present invention.

[0009] The gist of the present invention is the following [1] to [4]. [1] At least a substrate layer (A) and a seal layer (B) laminated on the substrate layer (A), the base layer (A) contains 60 to 90 mass% of a polypropylene-based resin (a-1) and 10 to 40 mass% of a propylene-α-olefin copolymer (a-2), The polypropylene resin (a-1) has a melting point of 150 to 160°C and an MFR (230°C) of 1.0 to 4.0 g / 10 min, The propylene-α-olefin copolymer (a-2) has a melting point of 125 to 140°C and an MFR (230°C) of 1.0 to 10.0 g / 10 min, the sealing layer (B) contains 70 to 85 mass% of a propylene-α-olefin random copolymer (b-1) and 15 to 30 mass% of an ethylene-α-olefin copolymer (b-2); The propylene-α-olefin random copolymer (b-1) has an MFR (230°C) of 1.0 to 5.5 g / 10 min, a molecular weight distribution (Mw / Mn) of 4.0 or more, and a melting point of 125 to 140°C, The ethylene-α-olefin copolymer (b-2) is a biaxially oriented polypropylene-based heat seal film having an MFR (190°C) of 1.0 to 4.0 g / 10 min and a melting point of 50 to 75°C. [2] The biaxially oriented polypropylene-based heat seal film according to the above [1], which satisfies the following (1) to (5): (1) Film thickness: 20 to 60 μm (2) MD tensile modulus of elasticity is 1200 MPa or more, TD tensile modulus is 2400 MPa or more (3) The thickness of the sealing layer (B) is 3.5 μm or more. (4) The maximum heat seal strength in at least one of the MD and TD directions is 15N / 15mm or more, and the maximum peel energy is 100mJ / 15mm or more. (5) At least one of the following is satisfied: (a) the temperature range in which the heat seal strength in the MD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher; and (b) the temperature range in which the heat seal strength in the TD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher. [3] A surface layer (C) is provided on the surface of the base material layer (A) opposite to the surface on which the sealing layer (B) is provided, and the surface layer (C) 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 175°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 but lower than 150°C. The biaxially oriented polypropylene-based heat seal film according to [1] or [2] above, wherein the biaxially oriented polypropylene-based heat seal film is any layer selected from the group consisting of: [4] A packaging bag using the biaxially oriented polypropylene-based heat seal film according to any one of [1] to [3] above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a biaxially oriented polypropylene-based heat seal film that has high heat seal strength, a wide heat sealable temperature range, high peel energy, and a certain level of mechanical strength or more. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Biaxially oriented polypropylene heat seal film] The biaxially oriented polypropylene-based heat seal film of the present invention comprises at least a base layer (A) and a seal layer (B) laminated on one side of the base layer (A). The base layer (A) contains 60 to 90% by mass of a polypropylene resin (a-1) and 10 to 40% by mass of a propylene-α-olefin copolymer (a-2). The polypropylene resin (a-1) has a melting point of 150 to 160°C and an MFR (230°C) of 1.0 to 4.0 g / 10 min, and the propylene-α-olefin copolymer (a-2) has a melting point of 125 to 140°C and an MFR (230°C) of 1.0 to 10.0 g / 10 min. The sealing layer (B) contains 70 to 85% by mass of a propylene-α-olefin random copolymer (b-1) and 15 to 30% by mass of an ethylene-α-olefin copolymer (b-2). The propylene-α-olefin random copolymer (b-1) has an MFR (230°C) of 1.0 to 5.5 g / 10 min, a molecular weight distribution (Mw / Mn) of 4.0 or more, and a melting point of 125 to 140°C, and the ethylene-α-olefin copolymer (b-2) has an MFR (190°C) of 1.0 to 4.0 g / 10 min, and a melting point of 50 to 75°C.

[0012] In the present invention, the biaxially oriented polypropylene heat seal film is a polypropylene heat seal film stretched in both the MD (machine direction) and TD (transverse direction). The heat seal film is a film used for heat sealing. Heat sealing is a method of joining two films by applying pressure and heat to the two films to melt their surfaces. Hereinafter, biaxially oriented polypropylene heat seal film may be referred to simply as "OPP film."

[0013] <Base material layer (A)> The substrate layer (A) contains a polypropylene resin (a-1) and a propylene-α-olefin copolymer (a-2).

[0014] (Polypropylene resin (a-1)) The polypropylene resin (a-1) is a polymer containing propylene monomer as the main monomer, and is a polymer containing preferably 80 mol % or more, more preferably 90 mol % or more of propylene monomer.

[0015] The melting point of the polypropylene resin (a-1) contained in the base layer (A) is 150 to 160°C. When the polypropylene resin (a-1) has a melting point of 150°C or higher, the heat resistance and mechanical strength of the OPP film tend to be improved. Furthermore, when the polypropylene resin (a-1) has a melting point of 160°C or lower, the heat seal strength tends to be improved. This is thought to be because when the polypropylene resin (a-1) has a melting point of more than 160°C, the interfacial strength between the base layer (A) and the seal layer (B) decreases. From the viewpoint of increasing the interfacial strength with the seal layer and increasing the heat sealing temperature, the melting point of the polypropylene resin in the base layer (A) is preferably 153 to 159°C, more preferably 155 to 158°C.

[0016] The type of polypropylene resin (a-1) contained in the base layer (A) 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). One type of polypropylene resin may be used alone, or two or more types may be used in combination. Among these, the polypropylene-based resin having a melting point of 150 to 160°C is more preferably at least one selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers, even more preferably propylene-ethylene copolymers, and even more preferably propylene-ethylene random copolymers.

[0017] The propylene-ethylene copolymer preferably has an ethylene content of 0.05 to 2% by mass, more preferably 0.1 to 1% by mass. By using a propylene-ethylene copolymer with such an ethylene content, it is possible to increase the heat seal strength. Although the reason for this is unclear, it is presumed that the use of a propylene-ethylene copolymer with an ethylene content within the above range as the substrate increases the interfacial strength between the substrate layer (A) and the seal layer (B).

[0018] The content of the polypropylene resin (a-1) in the base layer (A) is 60 to 90% by mass, and preferably 75 to 85% by mass.

[0019] (Propylene-α-olefin copolymer (a-2)) The base layer (A) contains a propylene-α-olefin copolymer (a-2) having a melting point of 125 to 140°C and an MFR (230°C) of 1.0 to 10.0 g / 10 min. The inclusion of the propylene-α-olefin copolymer (a-2) increases the peel energy at the heat-sealed site, making it less susceptible to breakage and improving impact resistance.

[0020] The MFR (230°C) of the propylene-α-olefin copolymer (a-2) is 1.0 to 10.0 g / 10 min, preferably 1.5 to 8.0 g / 10 min, and more preferably 2.0 to 5.0 g / 10 min. The MFR (230°C) means the melt flow rate measured at 230°C, and is measured by the method described in the Examples.

[0021] The propylene-α-olefin random copolymer (a-2) has a melting point of 125 to 140°C, preferably 127 to 137°C, and more preferably 130 to 135°C. By adjusting the MFR and melting point of the propylene-α-olefin random copolymer (a-2) to fall within the desired ranges described above, the peel energy tends to increase.

[0022] The propylene-α-olefin random copolymer (a-2) is a random polymer of propylene and α-olefin, with propylene monomer as the main monomer, and is, for example, a copolymer containing 60 mol % or more, more preferably 80 mol % or more, of propylene monomer. Here, examples of the α-olefin include α-olefins having 2 to 8 carbon atoms other than propylene, such as ethylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, and 4-methyl-pentene-1, and preferably ethylene and butene-1. Only one type of α-olefin may be used, or two or more types may be used. The propylene-α-olefin random copolymer (a-2) is preferably at least one selected from a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer, and among these, a propylene-ethylene copolymer is more preferred.

[0023] The content of the propylene-α-olefin random copolymer (a-2) in the base layer (A) is 10 to 40% by mass, preferably 15 to 35% by mass, from the viewpoint of improving peel energy. Furthermore, if the content of the propylene-α-olefin random copolymer (a-2) in the base layer (A) exceeds 40% by mass, the tensile modulus decreases, and the mechanical strength of the OPP film decreases.

[0024] The base layer (A) may contain other resins in addition to the polypropylene-based resin (a-1) and the propylene-α-olefin random copolymer (a-2), but the proportion of the other resins is preferably 5 mass% or less, more preferably 3 mass% or less, and even more preferably 0 mass%, based on the total amount of resins contained in the base layer (A).

[0025] The base layer (A) may contain additives, but the main component is a resin, and the content of the resin in the total amount of the base layer (A) is, for example, 98 mass % or more, and preferably 99 mass % or more.

[0026] The thickness of the substrate layer (A) is not particularly limited, but is preferably 15 to 60 μm, more preferably 20 to 55 μm, from the viewpoint of ensuring a certain level of mechanical strength of the film.

[0027] <Sealing layer (B)> The OPP film of the present invention has a sealing layer (B). By providing the sealing layer (B), the OPP film can be heat-sealed, and can be formed into packaging bags and the like. The sealing layer (B) contains 70 to 85 mass% of a propylene-α-olefin random copolymer (b-1) having an MFR (230°C) of 1.0 to 5.5 g / 10 min, a molecular weight distribution (Mw / Mn) of 4 or more, and a melting point of 125 to 140°C, and 15 to 30 mass% of an ethylene-α-olefin copolymer (b-2) having an MFR (190°C) of 1.0 to 4.0 g / 10 min and a melting point of 50 to 75°C. By having a seal layer (B) with such a specific composition, the heat seal strength of the OPP film can be increased and the heat sealable temperature range can be widened. The reason for this is not clear, but is presumed to be as follows. That is, the seal layer (B) is thought to form a phase-separated structure, such as an island-sea structure, in which ethylene-α-olefin copolymers are dispersed in a matrix of propylene-α-olefin random copolymer. The propylene-α-olefin random copolymer and ethylene-α-olefin copolymer are presumably provided with the specific structures described above, resulting in the seal layer (B) forming an appropriate phase-separated structure that is easily stretched under stress. Such a characteristic seal layer (B) is thought to have high heat seal strength over a relatively wide heat seal temperature range.

[0028] (Propylene-α-olefin copolymer (b-1)) The propylene-α-olefin random copolymer (b-1) has a specific range of MFR (230°C), molecular weight distribution (Mw / Mn), and melting point as described below, which increases the heat seal strength of the OPP film of the present invention and widens the heat sealable temperature range.

[0029] The propylene-α-olefin random copolymer (b-1) has an MFR (230° C.) of 1.0 to 5.5 g / 10 min, preferably 1.2 to 5.3 g / 10 min, and more preferably 1.5 to 5.0 g / 10 min.

[0030] The propylene-α-olefin random copolymer (b-1) has a molecular weight distribution (Mw / Mn) of 4.0 or more, preferably 4.0 to 6.0, more preferably 4.1 to 5.8, and even more preferably 4.2 to 5.5. The molecular weight distribution (Mw / Mn) is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (GPC). The number average molecular weight (Mn) and weight average molecular weight (Mw) are values ​​converted into polystyrene equivalents.

[0031] The propylene-α-olefin random copolymer (b-1) has a melting point of 125 to 140° C., preferably 127 to 137° C., and more preferably 130 to 135° C. By adjusting the melting point of the propylene-α-olefin random copolymer to fall within this range, the seal layer (B) becomes more easily melted at an appropriate heat sealing temperature, and the heat sealing strength can be increased. From the viewpoint of increasing the heat seal strength, the crystallization temperature of the propylene-α-olefin random copolymer is preferably 86° C. or higher, more preferably 88 to 110° C., and even more preferably 90 to 105° C. The melting point and crystallization temperature are measured by the method described in the Examples.

[0032] The propylene-α-olefin random copolymer (b-1) contained in the sealing layer (B) is a random polymer of propylene and α-olefin, with propylene monomer as the main monomer, and is, for example, a copolymer containing 60 mol% or more, more preferably 80 mol% or more, of propylene monomer. Here, examples of the α-olefin include α-olefins having 2 to 8 carbon atoms other than propylene, such as ethylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, and 4-methyl-pentene-1, and preferably ethylene and butene-1. Only one type of α-olefin may be used, or two or more types may be used. The propylene-α-olefin random copolymer (b-1) contained in the sealing layer (B) is preferably at least one selected from a propylene-ethylene copolymer, a propylene-butene-1 copolymer, and a propylene-ethylene-butene-1 copolymer.

[0033] The content of the propylene-α-olefin random copolymer (b-1) in the sealing layer (B) is 70 to 85% by mass, and preferably 75 to 85% by mass.

[0034] (Ethylene-α-olefin copolymer (b-2)) The seal layer (B) contains an ethylene-α-olefin copolymer (b-2), which has the following MFR (190°C) and melting point, thereby increasing the heat seal strength of the OPP film of the present invention and widening the heat sealable temperature range.

[0035] The MFR (190°C) of the ethylene-α-olefin copolymer (b-2) is 1.0 to 4.0 g / 10 min, preferably 2.0 to 4.0 g / 10 min, and more preferably 3.0 to 4.0 g / 10 min. By adjusting the MFR of the ethylene-α-olefin copolymer to fall within this range and the MFR of the propylene-α-olefin random copolymer to fall within the above range, the heat seal strength tends to be increased. It should be noted that MFR (190°C) means the melt flow rate measured at 190°C, and is measured by the method described in the examples.

[0036] The melting point of the ethylene-α-olefin copolymer is 50 to 75° C. When the ethylene-α-olefin copolymer has a melting point in this range, the seal layer (B) begins to melt at a relatively low temperature, and the heat-sealable temperature range tends to be wide. The melting point of the ethylene-α-olefin copolymer is preferably 51 to 69°C, more preferably 53 to 68°C.

[0037] The ethylene-α-olefin copolymer is a copolymer of ethylene and an α-olefin, with ethylene being the main monomer, and is, for example, a copolymer containing 60 mol % or more, preferably 80 mol % or more, of ethylene monomer. The type of α-olefin in the ethylene-α-olefin copolymer is not particularly limited, but examples include α-olefins having 3 to 8 carbon atoms. Examples of α-olefins include propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, and 4-methyl-pentene-1, and preferred are propylene, butene-1, hexene-1, and octene-1. Only one type of α-olefin may be used, or two or more types may be used.

[0038] The ethylene-α-olefin copolymer (b-2) contained in the sealing layer (B) is preferably at least one selected from the group consisting of ethylene-butene-1 copolymer, ethylene-octene-1 copolymer, and ethylene-propylene-hexene-1 copolymer.

[0039] The content of the ethylene-α-olefin copolymer (b-2) in the sealing layer (B) is 15 to 30% by mass, and preferably 15 to 25% by mass.

[0040] The sealing layer (B) may contain other resins in addition to the propylene-α-olefin copolymer (b-1) and the ethylene-α-olefin copolymer (b-2), but the proportion of the other resins is preferably 5 mass% or less, more preferably 3 mass% or less, and even more preferably 0 mass%, based on the total amount of resins contained in the sealing layer (B).

[0041] The sealing layer (B) may contain additives, but the main component is resin, and the resin content in the total amount of the sealing layer (B) is, for example, 98 mass % or more, preferably 99 mass % or more.

[0042] The thickness of the sealing layer (B) is preferably 3 μm or more from the viewpoint of increasing the heat seal strength, more preferably 3.5 μm or more, even more preferably 4 μm or more, and usually 10 μm or less.

[0043] <Surface layer (C)> The OPP film of the present invention may also have a surface layer (C) provided on the surface of the base layer (A) opposite to the surface on which the seal layer (B) is provided. That is, the OPP film of the present invention may have the seal layer (B), base layer (A), and surface layer (C) laminated in this order.

[0044] The surface layer (C) 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 175°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.

[0045] <(i) layer> The layer containing at least 80% by mass of a polypropylene resin having a melting point of 150° C. or higher and 170° C. or lower (hereinafter also referred to as layer (i)) will be described. Layer (i) contains a polypropylene-based resin having a relatively high melting point as a main component, and therefore is a layer having excellent heat resistance and transparency. The polypropylene resin used in layer (i) can be any of the resins described above in connection with polypropylene resin (a-1) without any particular limitations. Among these, the polypropylene resin used in layer (i) is preferably at least one selected from the group consisting of propylene homopolymers and propylene-ethylene copolymers. The polypropylene resin used in layer (i) may be used singly or in combination of two or more. 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 (a-1).

[0046] Layer (i) may contain resins other than the polypropylene-based resin having a melting point of 150° C. or higher and 170° C. or lower, but the amount of other resins is preferably kept below a certain amount, and other resins may not be used at all. That is, the content of polypropylene-based resins having a melting point of 150° C. or higher and 170° C. or lower in Layer (i) is 80% by mass or higher, preferably 90% by mass or higher, more preferably 95% by mass or higher, and even more preferably 100% by mass.

[0047] <(ii) layer> The layer containing 1 part by mass or more and 100 parts by mass or less of polyethylene-based resin per 100 parts by mass of 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.

[0048] The polypropylene resin used in layer (ii) 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-sealing properties to layer (ii), the polypropylene-based resin used in layer (ii) 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 layer (ii) may be used singly or in combination of two or more. The melting point of the polypropylene resin used in the layer (ii) is preferably 70°C or higher and 140°C or lower, more preferably 100°C or higher and 135°C or lower. When layer (ii) contains two or more polypropylene resins, the polypropylene resins preferably contain at least one polypropylene resin having a melting point of 70°C or higher and 90°C or lower and another polypropylene resin having a melting point of 110°C or higher and 140°C or lower. The combined use of such polypropylene resins in layer (ii) makes it possible to obtain a matte layer that can be heat-sealed at low temperatures. In this case, the content of the polypropylene resin having a melting point of 70°C or higher and 90°C or lower 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 or higher and 140°C or lower.

[0049] The content of the polypropylene resin in the layer (ii) is preferably 50 to 95% by mass, more preferably 60 to 90% by mass, and even more preferably 70 to 85% by mass.

[0050] The polyethylene resin in the layer (ii) may be any of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and polyethylene elastomers. Among these, linear low-density polyethylene is preferred. The linear low-density polyethylene is an ethylene-α-olefin copolymer, and the α-olefin preferably has 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 may be, 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 preferably has 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 polyethylene elastomer is not particularly limited, but may be, 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.

[0051] The content of the polyethylene resin in the layer (ii) is preferably 3 to 50% by mass, more preferably 5 to 30% by mass, and even more preferably 15 to 25% by mass.

[0052] The content of the polyethylene resin in 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 even more 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 Layer (ii) within this range, Layer (ii) can be made into a matte layer, and adhesion to the base layer is also improved.

[0053] Layer (ii) may contain resins other than the polypropylene-based resin and polyethylene-based resin described above, but the amount of the other resins is preferably kept below a certain amount, and other resins may not be used at all. That is, the total amount of the 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.

[0054] <(iii) layer> The layer containing at least a propylene-α-olefin copolymer having a melting point of 70° C. or higher and lower than 150° C. (hereinafter also referred to as layer (iii)) will be described. Layer (iii) can be a heat-sealable layer since it contains the propylene-α-olefin copolymer having a low melting point as described above. The heat-sealing 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 when heated. 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-pressing after the contents are placed inside. Therefore, the heat-sealing layer preferably 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.

[0055] The propylene-α-olefin copolymer contained in layer (iii) 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) in 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.

[0056] Layer (iii) may contain resins other than the propylene-α-olefin copolymer, but the amount of other resins is preferably small, and other resins may not be used at all. That is, the content of the propylene-α-olefin copolymer in layer (iii) 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.

[0057] When a surface layer (C) is provided, the OPP film of the present invention becomes a multilayer film in which the seal layer (B), base layer (A), and surface layer (C) are laminated in this order, and the interface between each layer can be confirmed, for example, using an electron microscope such as a scanning electron microscope.

[0058] The thickness of the surface layer (C) is not particularly limited, but is preferably 0.5 μm or more and 8.0 μm or less, more preferably 0.8 μm or more and 6.0 μm or less, and even more preferably 1.0 μm or more and 5.0 μm or less.

[0059] (Plant-derived polyolefin resin) The resin used in the base layer and / or skin layer of the OPP film of the present invention may contain a plant-derived polyolefin resin to reduce environmental impact. Examples of plant-derived polyolefin resins include polypropylene-based resins and polyethylene-based resins. Polyolefins may be composed of a single olefin monomer (homopolymer), or may be copolymerized with multiple olefin monomers. When multiple olefin monomers are copolymerized, the type, combination, and copolymerization ratio of the monomers are not important. Examples of copolymers include, but are not limited to, propylene-ethylene copolymer, propylene-ethylene-butene copolymer, propylene-butene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-propylene-hexene copolymer, and ethylene-1-methylpentene. The copolymer may be a random copolymer or a block copolymer. Depending on the desired content of plant-derived raw materials, the monomers constituting the polyolefin may be polymerized solely from plant-derived monomers, or may be copolymerized with plant-derived monomers and petroleum-derived monomers. Plant-derived polyolefin resins have the same physical properties as petroleum-derived polyolefin resins, but they reduce petroleum consumption and CO2 emissions, thereby reducing the environmental impact.

[0060] Plant-derived polyolefin resins contain a certain concentration of C14 because the atmosphere contains a certain concentration of C14. However, there is almost no C14 in petroleum trapped underground. Therefore, measuring the C14 concentration using accelerator mass spectrometry can be used as an indicator of the proportion of plant-derived raw materials. For example, the concentration of C14 in a resin film can be measured as follows: The sample is burned to generate carbon dioxide, which is then purified in a vacuum line. This carbon dioxide is then reduced with hydrogen using iron as a catalyst to produce graphite. This graphite is then loaded into a dedicated C14-AMS instrument (manufactured by NEC) based on a tandem accelerator to measure C14 counts, the C13 concentration (C13 / C12), and the C14 concentration (C14 / C12). From these measurements, the ratio of the C14 concentration of the sample carbon to that of a standard modern carbon is calculated. Oxalic acid (HOXII), provided by the National Institute of Standards (NIST), is used as the standard sample.

[0061] Plant-derived polyolefin resins include polyolefin resins manufactured using a mass balance method certified by ISCC PLUS certification, etc. Polyolefin resin products classified as biomass products using the mass balance method may not contain C14, but they contribute to reducing the environmental impact when considering the entire production, use, and disposal of various products in the petrochemical industry, and can be used in accordance with the plant-derived polyolefin resin of the present invention. Plant-derived polyolefin resins are commercially available from Braskem, Dow Chemical, Lyondell Basell, SABIC, Borealis, Mitsui Chemicals, and others.

[0062] (additives) The OPP film of the present invention may contain an additive that functions as an antifogging agent and an antistatic agent. The additive may be contained in at least one of the base layer, the seal layer, and the surface layer, but is preferably contained in the base layer. The content of the additives that function as antifogging agents and antistatic agents in the layer containing the additives (substrate layer or seal layer) is preferably 0.4 to 1.0 mass %, more preferably 0.6 to 0.8 mass %.

[0063] The type of additive that functions as an anti-fogging agent and an anti-static agent is not particularly limited as long as it is one that is commonly used in polyolefin films, and examples include esters of polyhydric alcohols such as glycerin, polyethylene glycol, pentaerythritol, sorbitol, and polypropylene glycol with higher fatty acids such as lauric acid, stearic acid, and oleic acid, ethylene oxide adducts of higher aliphatic amines, higher aliphatic alkanolamides, higher alcohol phosphate ester salts, and mixtures thereof.

[0064] The OPP film of the present invention may contain additives other than the additives that function as the antifogging agent and antistatic agent described above. Examples of such additives include crystallization nucleating agents, antioxidants, lubricants, antiblocking agents, chlorine scavengers, cellulose nanofibers, inorganic fine particles, and starch. Examples of such inorganic fine particles include calcium carbonate, adsorbents, and antibacterial agents. The additives may be contained in at least one of the substrate layer, seal layer, and surface layer, or in two or more layers.

[0065] [Packaging bag] The OPP film of the present invention can be formed into a packaging bag by heat sealing. A heat-sealed packaging bag can be obtained by processing the OPP film of the present invention into a bag shape with an opening, with the sealing layer (B) facing inward. Specifically, the packaging bag can be obtained by folding the OPP film to an appropriate size with the sealing layer (B) facing inward, and heat-sealing the edges to form a bag shape. The heat-sealing temperature is preferably a temperature at which the sealing layers (B) can be thermocompression-bonded together, and can be, for example, 120 to 150°C. The heat-sealing pressure can be, for example, about 0.1 to 0.5 MPa, and the heat-sealing time can be, for example, 0.1 to 2 seconds. After placing the contents in the resulting packaging bag, the opening can be heat-sealed to seal it. The uses of the OPP film of the present invention are not particularly limited, and it can be used, for example, as packaging bags for food, daily necessities, miscellaneous goods, and the like.

[0066] <Various physical properties> The OPP film of the present invention preferably satisfies the following requirements (1) to (5). (1) Film thickness: 20 to 60 μm (2) MD tensile modulus of elasticity is 1200 MPa or more, TD tensile modulus is 2400 MPa or more (3) The thickness of the sealing layer (B) is 3.5 μm or more. (4) The maximum heat seal strength in at least one of the MD and TD directions is 15N / 15mm or more, and the maximum peel energy is 100mJ / 15mm or more. (5) At least one of the following is satisfied: (a) the temperature range in which the heat seal strength in the MD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher; and (b) the temperature range in which the heat seal strength in the TD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher.

[0067] <(1) Film Thickness> The thickness of the OPP film of the present invention is not particularly limited and may be adjusted appropriately depending on the application, but is preferably 20 to 60 μm, more preferably 25 to 50 μm, and even more preferably 30 to 40 μm.

[0068] (2) Tensile modulus The tensile modulus of elasticity in the MD direction of the OPP film of the present invention is preferably 1200 MPa or more, more preferably 1300 MPa or more, and usually 1400 MPa or less. The tensile modulus of elasticity in the TD direction of the OPP film of the present invention is preferably 2400 MPa or more, more preferably 2500 MPa or more, and usually 2600 MPa or less. By providing the OPP film with the above-mentioned tensile modulus, the film can have good mechanical strength, and the packaging machine properties and the like are improved.

[0069] <(3) Thickness of sealing layer (B)> The thickness of the sealing layer (B) is preferably 3.5 μm or more from the viewpoint of increasing the heat seal strength, and is preferably 4 μm or more, and usually 10 μm or less.

[0070] <(4) Highest heat seal strength and maximum peel energy> The OPP film of the present invention preferably has a maximum heat seal strength of 15 N / 15 mm or more in at least one of the MD and TD directions and a maximum peel energy of 100 mJ / 15 mm or more.Furthermore, the OPP film of the present invention preferably has a maximum heat seal strength of 15 N / 15 mm or more in both the MD and TD directions and a maximum peel energy of 100 mJ / 15 mm or more. The maximum heat seal strength is more preferably 17 N / 15 mm or more. The maximum peel energy is more preferably 110 mJ / 15 mm or more. When the maximum heat seal strength is high, the sealed portion is less likely to peel, improving the reliability of the product. Furthermore, since the heat seal strength is high, even without laminating a CPP film on an OPP film as in the past, the manufacturing process can be simplified and manufacturing costs can be reduced. Furthermore, when the maximum peel energy is high, the sealed portion is less likely to break, and the impact resistance is excellent. The higher the maximum heat seal strength in the MD and TD directions, the better, but in practice it is 25 N / 15 mm or less. The higher the maximum peel energy in the MD and TD directions, the better, but in practice it is 140 mJ / 15 mm or less.

[0071] The maximum heat seal strength refers to the highest heat seal strength measured when multiple test pieces are heat-sealed at different temperatures (e.g., 1°C intervals) between 125°C and 145°C. Heat sealing is performed at each temperature with a sealing time of 1 second and a heat seal pressure of 0.1 MPa. The heat seal strength is measured as the peel strength when the heat-sealed test pieces are subjected to a tensile test with a chuck distance of 40 mm and a tensile speed of 100 mm / min. The peel energy is determined from the area of ​​the curve showing the relationship between stress and peel distance in the tensile test. The maximum value of the peel energies obtained at each temperature is defined as the maximum peel energy.

[0072] More specifically, the methods for measuring the heat seal strength, maximum heat seal strength, peel energy, and maximum peel energy in the MD direction of an OPP film are as follows (i) to (ii). The "methods for measuring the heat seal strength, maximum heat seal strength, peel energy, and maximum peel energy in the MD direction" are explained below.

[0073] (i) Two 15 mm wide films were prepared with the MD of the film as the longitudinal direction. The seal layers (B) were heat-sealed together in the width direction to form a 5 mm seal width under the following conditions: upper metal heat seal bar temperature 125°C to 145°C, lower Teflon® rubber temperature 90°C, sealing time 1 second, and sheet sealing pressure 0.1 MPa. A tensile test was then conducted at a chuck distance of 40 mm and a pulling speed of 100 mm / min to determine the peel strength, which was defined as the heat seal strength at the heat seal temperature. The area under the curve showing the stress-peel distance relationship in the tensile test was defined as the peel energy. The 15 mm wide film may be cut into a strip shape, for example, 15 mm wide and 150 mm long. Heat sealing can be performed using a heat sealing machine. The heat sealing temperature can be adjusted by adjusting the temperature of the metal heat sealing bar of the heat sealing machine. The tensile test was carried out using a tensile tester by moving the ends of two films in opposite directions, and the peel strength was the maximum strength (unit: N / 15 mm) at which the heat-sealed portion peeled or broke. The peel energy can be calculated from the area of ​​the stress-peel distance curve obtained in the tensile test, which is enclosed by a line passing through the end point of the stress-peel distance curve (the point where peeling ends) and parallel to the y-axis, the x-axis, and the stress-peel distance curve. The stress-peel distance curve is assumed to be at the origin (x = 0, y = 0) at the start of measurement, with the horizontal x-axis representing the peel distance (mm) and the vertical y-axis representing the stress (N). (ii) The heat-sealing temperature was changed to several different temperatures between 125°C and 145°C, and for several test pieces prepared by heat-sealing, the heat-sealing strength and peel energy were measured at each temperature in the same manner as in (i) above, and the maximum value among the obtained heat-sealing strengths was defined as the maximum heat-sealing strength in the MD. Also, the maximum value among the obtained peel energies at each temperature was defined as the maximum peel energy in the MD. Regarding (ii), the "multiple test pieces produced by heat-sealing after changing the heat-sealing temperature to a plurality of different temperatures from 125°C to 145°C" preferably means multiple test pieces produced by changing the heat-sealing temperature at intervals of 1°C within the range of 125 to 145°C.

[0074] The measurement methods for the heat-sealing strength, maximum heat-sealing strength, peel energy, and maximum peel energy in the TD direction of the OPP film can be carried out in accordance with the measurement methods in the MD direction described above. That is, in the "measurement methods for the heat-sealing strength, maximum heat-sealing strength, peel energy, and maximum peel energy in the MD direction" described above, MD can be read as TD.

[0075] <(4) Heat-sealable temperature range, peel energy temperature range> The OPP film of the present invention preferably satisfies at least one of the following: (a) the temperature range (heat-sealing temperature range) in which the heat-sealing strength in the MD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or more, and (b) the temperature range (heat-sealing temperature range) in which the heat-sealing strength in the TD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or more. Furthermore, it is preferable that the OPP film of the present invention satisfies both the requirements of (a) and (b) above. An OPP film that satisfies such requirements has a wide heat-sealable temperature range and can be heat-sealed at various temperatures. Furthermore, the peel energy is high within a wide range of heat-sealing temperature ranges, and the impact resistance of the seal part is excellent.

[0076] <Manufacturing method of OPP film> The manufacturing method of the OPP film of the present invention is not particularly limited, and it can be manufactured by applying an in-line lamination method, a co-extrusion method, or the like.

[0077] In the in-line lamination method, first, the resin composition for forming the above-mentioned base layer (A) 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, using a separately installed extruder, a resin composition for forming the seal layer (B) is extruded from a T-die and melt-laminated on one or both sides of the MD stretched sheet 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 gripped with clips, and TD stretching to a predetermined width is performed in a tenter oven to obtain the OPP film of the present invention.

[0078] In the coextrusion method, the resin composition for forming the base layer (A) and the resin composition for forming the seal layer (B) are coextruded through a coextrusion die to form a laminated unstretched sheet. The laminated unstretched sheet is then MD roll stretched using a roll speed differential to obtain a laminated MD stretched sheet. The laminated MD stretched sheet is then introduced into a tenter, both ends of the laminated MD stretched sheet are gripped with clips, and TD stretched to a predetermined width in a tenter oven to obtain an OPP film. In this way, an OPP film is obtained in which the base layer (A) and the seal layer (B) are laminated by the coextrusion method. When producing an OPP film further having a surface layer (C), the film can be produced by co-extruding a resin composition for forming the base layer (A), a resin composition for forming the seal layer (B), and a resin composition for forming the surface layer (C). Each of these resin compositions can be prepared by mixing the above-mentioned resins constituting each layer with additives that are blended as needed.

[0079] The OPP film produced by the above-mentioned inline lamination method, coextrusion method, or the like may be used as is, or may be subjected to secondary processing. Examples of secondary processing include surface processing by methods such as printing, coating, and vapor deposition, or lamination with other films. The secondary processing may be performed on one side or both sides of the OPP film.

[0080] [Application] The uses of the OPP film of the present invention are not particularly limited, but it can be used, for example, as packaging bags for food, daily necessities, miscellaneous goods, and the like. Furthermore, because the OPP film of the present invention has high heat seal strength as described above, it can be used in place of the conventional laminate of OPP film and CPP film. Furthermore, because the peel energy of the sealed portion is high, it is difficult to break, resulting in high product reliability. [Example]

[0081] The present invention will be explained in more detail below, but the present invention is not limited to these examples.

[0082] [evaluation] <Melting point, crystallization temperature> Approximately 4 mg of the sample was weighed accurately and sealed in an aluminum pan, which was then attached to a differential scanning calorimeter (manufactured by PerkinElmer, Inc., model "DSC8500AS") and heated to 230°C in a nitrogen stream of 20 mL / min, held at this temperature for 5 minutes, and then cooled to -10°C at a rate of 10°C / min. The peak temperature showing the maximum heat generation in the exothermic curve obtained during the cooling was taken as the crystallization temperature. After cooling to -10°C, the sample was heated to 230°C at a rate of 10°C / min. The peak temperature showing the maximum endothermic heat in the endothermic curve was taken as the melting point.

[0083] <Melt flow rate (MFR)> Measurements were carried out 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. The polypropylene-based resins include the propylene-α-olefin random copolymer (b-1) contained in the sealing layer (B), and the polypropylene-based resin (a-1) and propylene-α-olefin copolymer (a-2) contained in the base layer (A). The polyethylene resin is the ethylene-α-olefin copolymer (b-2) contained in the sealing layer (B).

[0084] <Evaluation of tensile modulus> In accordance with JIS K7127, the tensile modulus of elasticity in the MD and TD directions was measured for type 2 test pieces using a tensile tester (AG-Xplus manufactured by Shimadzu Corporation) at a tension speed of 50 mm / min.

[0085] <Heat seal strength, maximum heat seal strength, peel energy, maximum peel energy> The heat seal strength in the MD and TD directions, the maximum heat seal strength, the peel energy, and the maximum peel energy were measured according to the methods described in the specification. The heat sealer used was a "No. 3 YSS TYPE HEAT SEALER" manufactured by Yasuda Seiki Seisakusho Co., Ltd. The tensile tester used was an "AG-Xplus" manufactured by Shimadzu Corporation. (Evaluation criteria for heat seal strength) A maximum heat seal strength of 15 N / 15 mm or more was evaluated as "good", and a maximum heat seal strength of less than 15 N / 15 mm was evaluated as "poor". (Evaluation criteria for heat sealable temperature range) If the temperature range for a heat seal strength of 15 N / 15 mm or more was 10°C or higher, the heat sealable temperature range was evaluated as "Good", as the heat sealable temperature range was wide; if the temperature range for a heat seal strength of 15 N / 15 mm or more was less than 10°C, the heat sealable temperature range was evaluated as "Poor". (Evaluation criteria for peeling energy) The maximum peel energy of 100 mJ / 15 mm or more was marked "Good", and the maximum peel energy of less than 100 mJ / 15 mm was marked "Poor". (peeling energy temperature range) If the temperature range for peel energy of 100 mJ / 15 mm or more was 10°C or more, the peel energy temperature range was evaluated as wide and given a "Good" rating. If the temperature range for peel energy of 100 mJ / 15 mm or more was less than 10°C, the peel energy temperature range was evaluated as narrow and given a "Poor" rating.

[0086] [Example 1] The resin composition for forming the base layer (A) [80% by weight of PE copolymer (ethylene content 0.4% by weight), 20% by weight of PE copolymer] and the resin composition for forming the seal layer (B) [80% by weight of PE copolymer, 20% by weight of EB copolymer] were introduced into separate extruders (two extruders in total), laminated in a T-die, and the two layers were co-extruded onto a metal roll at 30°C to obtain a laminated sheet. The resulting laminated sheet was heated to 130°C in a longitudinal stretching machine and stretched 5 times in the machine direction (MD). Subsequently, it was heated to 190°C in a transverse stretching machine and stretched 10 times in the transverse direction (TD) to obtain a 35 μm-thick OPP film. In this manner, an OPP film was obtained comprising a base layer (A) and a seal layer (B) laminated on one side of the base layer (A). The compositions of the base layer (A) and the seal layer (B) are as shown in Table 1. The obtained OPP film was subjected to various evaluations.

[0087] [Examples 2 to 9, Comparative Examples 1 to 9] An OPP film was obtained in the same manner as in Example 1, except that the compositions of the base layer (A) and the seal layer (B) were changed as shown in Tables 1 and 2. The obtained OPP film was subjected to various evaluations.

[0088] In the explanations of the above examples and comparative examples and the notation in Table 1, in "PE copolymer," "PEB copolymer," "P homocopolymer," and "EB copolymer," "E" represents "ethylene," "P" represents "propylene," and "B" represents "butene."

[0089] [Table 1]

[0090] [Table 2]

[0091] The OPP films of the Examples that satisfied the requirements of the present invention had high maximum heat seal strength and a wide heat sealable temperature range. In addition, the OPP films of the Examples also had high maximum peel energy and a wide peel energy temperature range. In contrast, Comparative Examples 1 to 2, in which the resin constituting the sealing layer (B) did not satisfy the requirements of the present invention, and Comparative Examples 3 to 8, in which the resin constituting the base layer (A) did not satisfy the requirements of the present invention, were inferior to the Examples at least in terms of maximum peel energy and peel energy temperature range.

Claims

1. The film includes at least a substrate layer (A) and a seal layer (B) laminated on the substrate layer (A), the base layer (A) contains 60 to 90 mass% of a polypropylene-based resin (a-1) and 10 to 40 mass% of a propylene-α-olefin copolymer (a-2), The polypropylene resin (a-1) has a melting point of 150 to 160°C and an MFR (230°C) of 1.0 to 4.0 g / 10 min, The propylene-α-olefin copolymer (a-2) has a melting point of 125 to 140°C and an MFR (230°C) of 1.0 to 10.0 g / 10 min, The sealing layer (B) contains 70 to 85% by mass of a propylene-α-olefin random copolymer (b-1) and 15 to 30% by mass of an ethylene-α-olefin copolymer (b-2), The propylene-α-olefin random copolymer (b-1) has an MFR (230°C) of 1.0 to 5.5 g / 10 min, a molecular weight distribution (Mw / Mn) of 4.0 or more, and a melting point of 125 to 140°C, The ethylene-α-olefin copolymer (b-2) is a biaxially oriented polypropylene-based heat seal film having an MFR (190°C) of 1.0 to 4.0 g / 10 min and a melting point of 50 to 75°C.

2. The biaxially oriented polypropylene-based heat seal film according to claim 1, which satisfies the following (1) to (5): (1) Film thickness: 20 to 60 μm (2) MD tensile modulus of elasticity is 1200 MPa or more, TD tensile modulus of elasticity is 2400 MPa or more (3) The thickness of the sealing layer (B) is 3.5 μm or more. (4) The maximum heat seal strength in at least one of the MD and TD directions is 15 N / 15 mm or more, and the maximum peel energy is 100 mJ / 15 mm or more. (5) At least one of the following is satisfied: (a) the temperature range in which the heat seal strength in the MD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher; and (b) the temperature range in which the heat seal strength in the TD direction is 15 N / 15 mm or more and the peel energy is 100 mJ / 15 mm or more is 10°C or higher.

3. The adhesive tape further comprises a surface layer (C) provided on the surface of the base material layer (A) opposite to the surface on which the sealing layer (B) is provided, and the surface layer (C) 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 175°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-based heat seal film according to claim 1 or 2, wherein the biaxially oriented polypropylene-based heat seal film is any layer selected from the group consisting of:

4. A packaging bag using the biaxially oriented polypropylene heat seal film according to claim 1 or 2.

5. A packaging bag using the biaxially oriented polypropylene heat seal film according to claim 3.

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