Biaxially stretched polyethylene film, packaging material, and package

Abstract

A biaxially stretched polyethylene film (100) is provided with a biaxially stretched film layer (101) containing an ethylene-based polymer (A). When the biaxially stretched polyethylene film (100) is measured through a dynamic mechanical analysis (DMA) under conditions at a frequency of 1 Hz, at a temperature increase rate of 5°C / min, with a strain of 0.1%, in a tensile mode, with an inter-chuck distance of 20 mm, and with a sample width of 5 mm, the biaxially stretched polyethylene film has a storage modulus E'MD of 50 MPa or more in the MD direction at 100°C, and has a storage modulus E'TD of 100 MPa or more in the TD direction at 100°C.

Description

Biaxially oriented polyethylene film, packaging material and packaging body

[0001] The present invention relates to a biaxially oriented polyethylene film, a packaging material, and a package.

[0002] Biaxially oriented polyethylene films are used, for example, as packaging films.

[0003] Patent Document 1 describes a polyethylene laminate for packaging material, which includes at least a stretched polyethylene film, an adhesive layer, and a heat-sealable polyethylene layer, wherein the adhesive layer contains a solventless adhesive. Patent Document 1 also describes that it is possible to provide a polyethylene laminate for packaging material that can significantly reduce the burden on the environment and has high printability and strength.

[0004] Patent Document 2 describes a stretched polyethylene film that is a uniaxially or biaxially stretched film made of a polyethylene resin composition containing polyethylene and a petroleum resin, and that has an areal stretching ratio of 3 or more. Patent Document 2 also describes that it is possible to provide a stretched polyethylene film that does not break even at a high stretching ratio and has high strength.

[0005] JP 2022-079510 A JP 2023-031061 A

[0006] A first embodiment of the present invention provides a biaxially oriented polyethylene film with improved thermal dimensional stability.

[0007] The second embodiment of the present invention provides a biaxially oriented polyethylene film having improved heat fusion resistance.

[0008] A third embodiment of the present invention provides a biaxially oriented polyethylene film with improved thermal dimensional stability.

[0009] The fourth embodiment of the present invention provides a biaxially oriented polyethylene film having an improved balance of film-forming properties and thermal dimensional stability.

[0010] The present inventors have conducted extensive research to solve the problems of the first embodiment of the present invention. As a result, the storage modulus E' in the MD direction obtained by dynamic viscoelasticity measurement ＭＤ and storage modulus E' in the TD direction ＴＤ It has been found that the thermal dimensional stability can be improved by setting the thickness within a predetermined range.

[0011] That is, according to a first embodiment of the present invention, there are provided the following biaxially oriented polyethylene film, packaging material, and packaging body.

[0012] [1A] A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene polymer (A), wherein the storage modulus E' in the MD direction at 100°C is measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a heating rate of 5°C / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ The storage modulus E' in the TD direction at 100°C is 50 MPa or more. ＴＤ [2A] The biaxially oriented polyethylene film according to [1A], wherein the loss tangent (tanδ) in the TD direction at 100°C is 0.25 or more, as measured by dynamic mechanical analysis (DMA) under conditions of a frequency of 1 Hz, a heating rate of 5°C / min, a strain of 0.1%, a tensile mode, a chuck distance of 20 mm, and a sample width of 5 mm. [3A] The biaxially oriented polyethylene film according to [1A] or [2A], wherein the ethylene polymer (A) contains high-density polyethylene, and the content of the high-density polyethylene in the biaxially oriented film layer is 60% by mass or more, when the entire biaxially oriented film layer is taken as 100% by mass. [4A] The tensile modulus in the MD direction, T, measured according to JIS K7127:1999 using a tensile tester under conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２The biaxially oriented polyethylene film according to any one of [1A] to [3A], wherein the total value of (a) and (b) is 2500 MPa or more and 9000 MPa or less. [5A] The biaxially oriented polyethylene film according to any one of [1A] to [4A], wherein the heat shrinkage in the MD direction is 4.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [6A] The biaxially oriented polyethylene film according to any one of [1A] to [5A], wherein the heat shrinkage in the TD direction is 7.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [7A] The biaxially oriented polyethylene film according to any one of [1A] to [6A], wherein the heat shrinkage in the MD direction is 9.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [8A] The biaxially oriented polyethylene film according to any one of [1A] to [7A], which has a heat shrinkage rate in the TD direction of 30.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [9A] The biaxially oriented polyethylene film according to any one of [1A] to [7A], which has a moisture permeability of 12.0 g / (m2), as measured in accordance with JIS Z 0208:1976. ２The biaxially stretched polyethylene film according to any one of [1A] to [8A], wherein the total stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [10A] The biaxially stretched polyethylene film according to any one of [1A] to [9A], wherein the sum of the stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [11A] The biaxially stretched polyethylene film according to any one of [1A] to [10A], further comprising a surface resin layer on at least one side of the biaxially stretched film layer. [12A] The biaxially stretched polyethylene film according to [11A], wherein the surface resin layer contains an ethylene-based polymer. [13A] The biaxially stretched polyethylene film according to [12A], wherein the content of the ethylene-based polymer in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is taken as 100% by mass. [14A] The biaxially oriented polyethylene film according to any one of [11A] to [13A], wherein the thickness of the surface resin layer is from 0.1 μm to 10 μm. [15A] The biaxially oriented polyethylene film according to any one of [1A] to [14A], wherein the thickness of the biaxially oriented film layer is from 5 μm to 100 μm. [16A] The biaxially oriented polyethylene film according to any one of [1A] to [15A], wherein the ratio of the thickness of the biaxially oriented film layer to the total thickness of the biaxially oriented polyethylene film is from 50% to 100%. [17A] The biaxially oriented polyethylene film according to any one of [1A] to [16A], wherein the biaxially oriented polyethylene film is a packaging film. [18A] A packaging material comprising the biaxially oriented polyethylene film according to any one of [1A] to [17A]. [19A] The packaging material according to [18A], further comprising one or more layers selected from the group consisting of an inorganic layer and a coating layer on at least one surface of the biaxially oriented polyethylene film. [20A] A package comprising the packaging material according to [18A] or [19A] and an article inside the packaging material.

[0013] Furthermore, the present inventors have conducted extensive research to solve the problems of the second embodiment of the present invention, and have found that heat fusion resistance can be improved by setting the average linear expansion coefficient in the MD direction measured by thermomechanical analysis to a predetermined value or less.

[0014] That is, according to a second embodiment of the present invention, there are provided the following biaxially oriented polyethylene film, packaging material, and packaging body.

[0015] [1B] A biaxially oriented polyethylene film comprising a biaxially oriented film layer containing an ethylene polymer (A), wherein the average linear expansion coefficient (α) in the MD direction is 4.5×10 when measured by thermomechanical analysis (TMA) according to JIS K 7197:2012 under the conditions of a heating rate of 10°C / min, a tensile mode, a load of 10 g / 4 mm, an initial chuck distance of 8 mm, and a test piece width of 4 mm, as calculated from the following formula (1) in the measurement temperature range from 20°C to 100°C: －４ The average linear expansion coefficient (α) of a biaxially stretched polyethylene film is expressed by the formula (1): α = 1 / L (1 / °C) or less. ０ ・[{L(t ２ ) - L(t １ ) / (t ２ -t １ )] In formula (1), L ０、 T １ , T ２ , L(t １ ) and L(t ２ ) is expressed as follows: L ０ : Initial chuck distance 8 mm t １ : 20 ° C. ２ : 100 ° C. L (t １ ): temperature t １ Distance between chucks (mm) L (t ２ ): temperature t ２[2B] The biaxially oriented polyethylene film according to [1B], which has an MD elongation of 3.5% or less when measured by thermomechanical analysis (TMA) according to JIS K 7197:2012 under the conditions of a temperature range of 20°C to 100°C, a heating rate of 10°C / min, a tensile mode, a load of 10 g / 4 mm, an initial chuck distance of 8 mm, and a test piece width of 4 mm. [3B] The biaxially oriented polyethylene film according to [1B] or [2B], which has a heat-fusion strength of 1.0 N / 15 mm or less at 130°C, as measured in accordance with the <Heat-fusion strength> below. <Heat-fusion strength> Two sheets of the biaxially oriented polyethylene film cut to a width of 15 mm are bonded together, sandwiched between 12 μm-thick biaxially oriented polyethylene terephthalate films, and tested using a heat-seal tester at a temperature of 130°C and a pressure of 2.0 kgf / cm. ２ The biaxially oriented polyethylene film is heat-sealed under conditions of 90° peeling, a peeling speed of 300 mm / min, and a sealing time of 1.0 second to obtain a laminated film, and then the two biaxially oriented polyethylene films are peeled at a 90° peeling angle, a peeling speed of 300 mm / min, and tension in the MD direction, and the peel strength at this time is defined as the heat-sealing strength (N / 15 mm). [4B] The biaxially oriented polyethylene film according to any one of [1B] to [3B], wherein the ethylene polymer (A) contains high-density polyethylene, and the content of the high-density polyethylene in the biaxially oriented film layer is 60% by mass or more, when the entire biaxially oriented film layer is taken as 100% by mass. [5B] The tensile modulus T in the MD direction, measured using a tensile tester in accordance with JIS K7127:1999, is defined as the tensile modulus T １ and the tensile modulus in the TD direction T ２The biaxially oriented polyethylene film according to any one of [1B] to [4B], wherein the total value of (a) and (b) is 2500 MPa or more and 9000 MPa or less. [6B] The biaxially oriented polyethylene film according to any one of [1B] to [5B], wherein the heat shrinkage in the MD direction is 4.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [7B] The biaxially oriented polyethylene film according to any one of [1B] to [6B], wherein the heat shrinkage in the TD direction is 7.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [8B] The biaxially oriented polyethylene film according to any one of [1B] to [7B], wherein the heat shrinkage in the MD direction is 9.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [9B] The biaxially oriented polyethylene film according to any one of [1B] to [8B], which has a heat shrinkage rate in the TD direction of 30.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [10B] The biaxially oriented polyethylene film according to any one of [1B] to [8B], which has a moisture permeability of 12.0 g / (m2), as measured in accordance with JIS Z 0208:1976. ２The biaxially oriented polyethylene film according to any one of [1B] to [9B], wherein the total stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [11B] The biaxially oriented polyethylene film according to any one of [1B] to [10B], wherein the sum of the stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [12B] The biaxially oriented polyethylene film according to any one of [1B] to [11B], further comprising a surface resin layer on at least one side of the biaxially oriented film layer. [13B] The biaxially oriented polyethylene film according to [12B], wherein the surface resin layer contains an ethylene-based polymer. [14B] The biaxially oriented polyethylene film according to [13B], wherein the content of the ethylene-based polymer in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is taken as 100% by mass. [15B] The biaxially oriented polyethylene film according to any one of [12B] to [14B], wherein the thickness of the surface resin layer is from 0.1 μm to 10 μm. [16B] The biaxially oriented polyethylene film according to any one of [1B] to [15B], wherein the thickness of the biaxially oriented film layer is from 5 μm to 100 μm. [17B] The biaxially oriented polyethylene film according to any one of [1B] to [16B], wherein the ratio of the thickness of the biaxially oriented film layer to the total thickness of the biaxially oriented polyethylene film is from 50% to 100%. [18B] The biaxially oriented polyethylene film according to any one of [1B] to [17B], which is a packaging film. [19B] A packaging material comprising the biaxially oriented polyethylene film according to any one of [1B] to [18B]. [20B] The packaging material according to [19B], further comprising one or more layers selected from the group consisting of an inorganic layer and a coating layer on at least one surface of the biaxially oriented polyethylene film. [21B] A package comprising the packaging material according to [19B] or [20B] and an article inside the packaging material.

[0016] The present inventors have also conducted extensive research to solve the problems of the third embodiment of the present invention, and have found that the thermal dimensional stability of a biaxially oriented polyethylene film can be improved by adjusting the heat of fusion (ΔH) of the biaxially oriented polyethylene film obtained by differential scanning calorimetry to fall within a predetermined range.

[0017] That is, according to a third embodiment of the present invention, there are provided the following biaxially oriented polyethylene film, packaging material, and packaging body.

[0018] [1C] A biaxially oriented polyethylene film comprising a biaxially oriented film layer containing an ethylene polymer (A), wherein when the following steps are successively performed using a differential scanning calorimeter (DSC): a first differential scanning calorimetry (1st Run) consisting of a process of increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 200°C for 5 minutes, and a process of decreasing the temperature from 200°C to -50°C at a heating rate of 10°C / min; and a second differential scanning calorimetry (2nd Run) consisting of a process of maintaining the temperature at -50°C for 5 minutes and increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min, [2C] A biaxially stretched polyethylene film in which an endothermic peak A is observed in the range of 20°C to 150°C in the DSC curve 2 obtained by the second differential scanning calorimetry, and the heat of fusion (ΔH) of the endothermic peak A is 175 J / g to 250 J / g. １ ) from the melting point (Tm ２ ) minus (Tm １ -Tm ２ [3C] The biaxially stretched polyethylene film according to [1C], wherein the exothermic peak observed in the DSC curve 1 obtained in the first cooling step is the crystallization peak, and the temperature at the peak of the crystallization peak is the crystallization temperature (Tc), (Tm ２ [4C] The biaxially stretched polyethylene film according to [1C] or [2C], wherein the melting point (Tm −Tc) obtained by the second differential scanning calorimetry is 12.1°C or higher. ２[5C] The biaxially oriented polyethylene film according to any one of [1C] to [3C], wherein the ethylene polymer (A) contains high-density polyethylene, and the content of the high-density polyethylene in the biaxially oriented film layer is 60% by mass or more when the entire biaxially oriented film layer is taken as 100% by mass. [6C] The tensile modulus in the machine direction T １ and the tensile modulus in the TD direction T ２ The biaxially oriented polyethylene film according to any one of [1C] to [5C], wherein the total value of (a) and (b) is 2500 MPa or more and 9000 MPa or less. [7C] The biaxially oriented polyethylene film according to any one of [1C] to [6C], wherein the heat shrinkage in the MD direction is 4.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [8C] The biaxially oriented polyethylene film according to any one of [1C] to [7C], wherein the heat shrinkage in the TD direction is 7.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [9C] The biaxially oriented polyethylene film according to any one of [1C] to [8C], wherein the heat shrinkage in the MD direction is 9.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [10C] The biaxially oriented polyethylene film according to any one of [1C] to [9C], which has a heat shrinkage rate in the TD direction of 30.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [11C] The biaxially oriented polyethylene film according to any one of [1C] to [9C], which has a moisture permeability of 12.0 g / (m2), as measured in accordance with JIS Z 0208:1976. ２The biaxially oriented polyethylene film according to any one of [1C] to [10C], wherein the total stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [12C] The biaxially oriented polyethylene film according to any one of [1C] to [11C], wherein the sum of the stress at break in the TD direction and the stress at break in the MD direction measured in accordance with JIS K7127:1999 is 210 MPa or more. [13C] The biaxially oriented polyethylene film according to any one of [1C] to [12C], further comprising a surface resin layer on at least one side of the biaxially oriented film layer. [14C] The biaxially oriented polyethylene film according to [13C], wherein the surface resin layer contains an ethylene-based polymer. [15C] The biaxially oriented polyethylene film according to [14C], wherein the content of the ethylene-based polymer in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is taken as 100% by mass. [16C] The biaxially oriented polyethylene film according to any one of [13C] to [15C], wherein the thickness of the surface resin layer is from 0.1 μm to 10 μm. [17C] The biaxially oriented polyethylene film according to any one of [1C] to [16C], wherein the thickness of the biaxially oriented film layer is from 5 μm to 100 μm. [18C] The biaxially oriented polyethylene film according to any one of [1C] to [17C], wherein the ratio of the thickness of the biaxially oriented film layer to the total thickness of the biaxially oriented polyethylene film is from 50% to 100%. [19C] The biaxially oriented polyethylene film according to any one of [1C] to [18C], which is a packaging film. [20C] A packaging material comprising the biaxially oriented polyethylene film according to any one of [1C] to [19C]. [21C] The packaging material according to [20C], further comprising one or more layers selected from the group consisting of an inorganic layer and a coating layer on at least one surface of the biaxially oriented polyethylene film. [22C] A package comprising the packaging material according to [20C] or [21C] and an article inside the packaging material.

[0019] The present inventors have also conducted extensive research to solve the problems of the fourth embodiment of the present invention, and have found that the performance balance between film-forming ability and thermal dimensional stability can be improved by adjusting the z-average molecular weight (Mz) of the ethylene polymer contained in the biaxially oriented polyethylene film to a predetermined range.

[0020] That is, according to a fourth embodiment of the present invention, there are provided the following biaxially oriented polyethylene film, packaging material, and packaging body.

[0021] [1D] A biaxially stretched polyethylene film comprising a biaxially stretched film layer containing an ethylene polymer (A), wherein the ethylene polymer (A) has a z-average molecular weight (Mz) of 800,000 or more and 4,000,000 or less, measured by gel permeation chromatography (GPC) in terms of polystyrene. [2D] The biaxially stretched polyethylene film according to [1D], wherein the ethylene polymer (A) has a weight-average molecular weight (Mw) of 130,000 or more and 1,000,000 or less, measured by gel permeation chromatography (GPC). [3D] The biaxially stretched polyethylene film according to [1D] or [2D], wherein the ethylene polymer (A) has a number-average molecular weight (Mn) of 5,000 or more and 200,000 or less, measured by gel permeation chromatography (GPC) in terms of polystyrene. [4D] The biaxially stretched polyethylene film according to any one of [1D] to [3D], wherein the ethylene polymer (A) has a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene, as measured by gel permeation chromatography (GPC), of 30.0 or less. [5D] The density of the ethylene polymer (A) measured in accordance with JIS K 7112:1999 is 0.937 g / cm ３ 0.970g / cm or more ３The biaxially oriented polyethylene film according to any one of [1D] to [4D], wherein the ethylene polymer (A) has a melt mass-flow rate (MFR) of 0.1 g / 10 min or more and 5.0 g / 10 min or less, as measured in accordance with JIS K 7210:1999 at 190°C under a load of 2160 g. [7D] The biaxially oriented polyethylene film according to any one of [1D] to [6D], wherein the ethylene polymer (A) contains high-density polyethylene, and wherein the content of the high-density polyethylene in the biaxially oriented film layer is 60% by mass or more, when the entire biaxially oriented film layer is taken as 100% by mass. [8D] The biaxially oriented polyethylene film according to any one of [1D] to [7D], wherein the sum of the tensile modulus in the MD direction (T1) and the tensile modulus in the TD direction (T2) is 2500 MPa or more and 9000 MPa or less, as measured in accordance with JIS K7127:1999 using a tensile tester at a temperature of 23±2°C, 50±5% RH, and a pulling rate of 5 mm / min. [9D] The biaxially oriented polyethylene film according to any one of [1D] to [8D], wherein the heat shrinkage in the MD direction is 4.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [10D] The biaxially oriented polyethylene film according to any one of [1D] to [9D], wherein the heat shrinkage in the TD direction is 7.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019. [11D] The biaxially oriented polyethylene film according to any one of [1D] to [10D], having a heat shrinkage rate in the MD direction of 9.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [12D] The biaxially oriented polyethylene film according to any one of [1D] to [11D], having a heat shrinkage rate in the TD direction of 30.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019. [13D] The biaxially oriented polyethylene film according to any one of [1D] to [12D], having a moisture permeability of 12.0 g / (m2·day) or less, as measured in accordance with JIS Z 0208:1976.[14D] The biaxially oriented polyethylene film according to any one of [1D] to [13D], wherein the sum of the stress at break in the TD direction and the stress at break in the MD direction, measured in accordance with JIS K7127:1999, is 210 MPa or more. [15D] The biaxially oriented polyethylene film according to any one of [1D] to [14D], wherein the sum of the elongation at break in the TD direction and the elongation at break in the MD direction, measured in accordance with JIS K7127:1999, is 200% or less. [16D] The biaxially oriented polyethylene film according to any one of [1D] to [15D], further comprising a surface resin layer on at least one side of the biaxially oriented film layer. [17D] The biaxially oriented polyethylene film according to [16D], wherein the surface resin layer contains an ethylene-based polymer. [18D] The biaxially oriented polyethylene film according to [17D], wherein the content of the ethylene polymer in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is taken as 100% by mass. [19D] The biaxially oriented polyethylene film according to any of [16D] to [18D], wherein the thickness of the surface resin layer is 0.1 μm or more and 10 μm or less. [20D] The biaxially oriented polyethylene film according to any of [1D] to [19D], wherein the thickness of the biaxially oriented film layer is 5 μm or more and 100 μm or less. [21D] The biaxially oriented polyethylene film according to any of [1D] to [20D], wherein the ratio of the thickness of the biaxially oriented film layer to the total thickness of the biaxially oriented polyethylene film is 50% or more and 100% or less. [22D] The biaxially oriented polyethylene film according to any of [1D] to [21D], wherein the biaxially oriented polyethylene film is a packaging film. [23D] A packaging material comprising the biaxially oriented polyethylene film according to any one of [1D] to [22D]. [24D] The packaging material according to [23D], further comprising one or more layers selected from the group consisting of an inorganic layer and a coating layer on at least one surface of the biaxially oriented polyethylene film. [25D] A package comprising the packaging material according to [23D] or [24D], and an article placed inside the packaging material.

[0022] According to the first embodiment of the present invention, a biaxially oriented polyethylene film having improved thermal dimensional stability can be provided.

[0023] Furthermore, according to the second embodiment of the present invention, it is possible to provide a biaxially oriented polyethylene film having improved heat fusion resistance.

[0024] Furthermore, according to the third embodiment of the present invention, it is possible to provide a biaxially oriented polyethylene film having improved thermal dimensional stability.

[0025] Furthermore, according to the fourth embodiment of the present invention, it is possible to provide a biaxially oriented polyethylene film having an improved balance of film-forming properties and thermal dimensional stability.

[0026] Fig. 1 is a cross-sectional view schematically showing an example of the structure of a biaxially oriented polyethylene film according to each embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing an example of the structure of a biaxially oriented polyethylene film according to each embodiment of the present invention. Fig. 3 is a cross-sectional view schematically showing an example of the structure of a biaxially oriented polyethylene film according to each embodiment of the present invention.

[0027] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic diagrams and do not correspond to actual dimensional proportions. In this specification, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0028] <<First Embodiment>> Hereinafter, a biaxially oriented polyethylene film, a packaging material, and a package according to a first embodiment of the present invention will be described.

[0029] <Biaxially Stretched Polyethylene Film> The biaxially oriented polyethylene film 100 of the first embodiment includes a biaxially oriented film layer 101 containing an ethylene polymer (A), and has a storage modulus E′ in the machine direction at 100° C., measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a heating rate of 5° C. / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ The storage modulus E' in the TD direction at 100°C is 50 MPa or more. ＴＤ is 100 MPa or more.

[0030] The inventors of the present invention measured the storage modulus E' of the biaxially stretched polyethylene film 100 in the MD direction at 100°C using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a temperature rise rate of 5°C / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ and storage modulus E' in the TD direction at 100°C ＴＤ It has been found that by making the hardness of the film to be a predetermined value or more, the film becomes suitably hard, the coating suitability during processing is improved, and the thermal dimensional stability of the biaxially oriented polyethylene film 100 can be improved.

[0031] In the biaxially stretched polyethylene film 100 of the first embodiment, the storage modulus E′ in the MD direction at 100° C. is measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a temperature rise rate of 5° C. / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ From the viewpoint of improving thermal dimensional stability, is 50 MPa or more, preferably 70 MPa or more, more preferably 100 MPa or more, even more preferably 130 MPa or more, even more preferably 150 MPa or more, even more preferably 180 MPa or more, even more preferably 200 MPa or more, even more preferably 220 MPa or more, even more preferably 250 MPa or more, and is preferably 600 MPa or less, more preferably 550 MPa or less, even more preferably 500 MPa or less, even more preferably 450 MPa or less.

[0032] The storage modulus E' of the biaxially stretched polyethylene film 100 in the TD direction at 100°C is measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a temperature rise rate of 5°C / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＴＤFrom the viewpoint of improving thermal dimensional stability, is 100 MPa or more, preferably 120 MPa or more, more preferably 150 MPa or more, even more preferably 180 MPa or more, even more preferably 200 MPa or more, even more preferably 220 MPa or more, even more preferably 250 MPa or more, even more preferably 300 MPa or more, even more preferably 320 MPa or more, even more preferably 350 MPa or more, and is preferably 700 MPa or less, more preferably 680 MPa or less, even more preferably 650 MPa or less, even more preferably 630 MPa or less, even more preferably 600 MPa or less, even more preferably 580 MPa or less.

[0033] The biaxially stretched polyethylene film 100 has a loss tangent (tanδ) in the TD direction at 100°C, measured using dynamic mechanical analysis (DMA) under conditions of a frequency of 1 Hz, a heating rate of 5°C / min, a strain of 0.1%, a tensile mode, a chuck distance of 20 mm, and a sample width of 5 mm. From the viewpoint of further improving thermal dimensional stability, the loss tangent (tanδ) is preferably 0.25 or more, more preferably 0.28 or more, even more preferably 0.30 or more, and still more preferably 0.33 or more, and is preferably 0.60 or less, more preferably 0.55 or less, even more preferably 0.50 or less, even more preferably 0.48 or less, even more preferably 0.45 or less, even more preferably 0.40 or less, and still more preferably 0.38 or less.

[0034] The loss modulus E'' of the biaxially stretched polyethylene film 100 in the MD direction at 100°C was measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a temperature rise rate of 5°C / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ From the viewpoint of further improving the thermal dimensional stability, is preferably 10 MPa or more, more preferably 20 MPa or more, even more preferably 30 MPa or more, even more preferably 40 MPa or more, even more preferably 50 MPa or more, even more preferably 60 MPa or more, even more preferably 65 MPa or more, and is preferably 150 MPa or less, more preferably 130 MPa or less, even more preferably 110 MPa or less.

[0035] The loss modulus E'' of the biaxially stretched polyethylene film 100 in the TD direction at 100°C was measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a temperature rise rate of 5°C / min, a strain of 0.1%, a tension mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＴＤ From the viewpoint of further improving the thermal dimensional stability, the compressive strength is preferably 30 MPa or more, more preferably 50 MPa or more, even more preferably 70 MPa or more, even more preferably 100 MPa or more, even more preferably 120 MPa or more, and is preferably 250 MPa or less, more preferably 230 MPa or less, even more preferably 200 MPa or less.

[0036] In the biaxially stretched polyethylene film 100, the storage modulus E' ＭＤ , loss modulus E'' ＭＤ , storage modulus E' ＴＤ , loss modulus E'' ＴＤ The storage modulus E' of a biaxially stretched polyethylene film 100 in the MD direction at 100° C. was measured under the following conditions: ＭＤ , loss modulus E'' ＭＤ Measure E' ＭＤ and E'' ＭＤ From the ratio, the loss tangent (tanδ ＭＤ [Measurement conditions] Apparatus: Dynamic viscoelasticity measuring apparatus Measurement temperature range: 30 to 130°C Heating rate: 5°C / min Strain: 0.1% Measurement mode: Tensile Frequency: 1 Hz Sample width: 5 mm Distance between chucks: 20 mm Measurement direction: MD direction Also, the storage modulus E' at 100°C in the TD direction was calculated under the same conditions as above, except that the measurement direction was changed to the TD direction. ＴＤ , loss modulus E'' ＴＤ , and E' ＴＤ and E'' ＴＤ From the ratio, the loss tangent (tanδ ＴＤ ) is calculated.

[0037] The density of the biaxially oriented polyethylene film 100, measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming property, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ The following is the result.

[0038] The melting point of the biaxially oriented polyethylene film 100, as measured by a differential scanning calorimeter (DSC), is preferably 70°C or higher, more preferably 75°C or higher, even more preferably 90°C or higher, even more preferably 95°C or higher, even more preferably 100°C or higher, even more preferably 110°C or higher, even more preferably 120°C or higher, even more preferably 125°C or higher, and is preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, even more preferably 134°C or lower, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability.

[0039] JIS K The melt mass flow rate (MFR) of the biaxially oriented polyethylene film 100, measured in accordance with J.P. 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less.

[0040] From the viewpoint of further improving the balance of performance factors such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented polyethylene film 100 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0041] The physical properties of the biaxially oriented polyethylene film 100 will be described below.

[0042] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction is measured using a tensile tester in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２) is preferably 2500 MPa or more, more preferably 3000 MPa or more, even more preferably 3500 MPa or more, even more preferably 4000 MPa or more, even more preferably 4500 MPa or more, and is preferably 9000 MPa or less, more preferably 8000 MPa or less, even more preferably 7000 MPa or less, even more preferably 6500 MPa or less, even more preferably 6000 MPa or less. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ When the tensile modulus T in the MD direction of the biaxially oriented polyethylene film 100 is equal to or greater than the lower limit, the biaxially oriented polyethylene film 100 can have a better balance of properties such as thermal dimensional stability, film-forming properties, water vapor barrier properties, mechanical properties, transparency, bag-forming properties, and handling properties, and the stiffness of the biaxially oriented polyethylene film 100 can be improved. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ ) is not more than the above upper limit, problems such as breakage are less likely to occur during the formation of the biaxially oriented polyethylene film 100, continuous stretching of the film becomes easier, and industrial continuous productivity can be further improved. Such tensile modulus is a substitute value for quantitatively measuring the stiffness of the film, and can be adjusted, for example, by adjusting the type and content ratio of the ethylene polymer (A) contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0043] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction １is preferably 800 MPa or more, more preferably 1000 MPa or more, even more preferably 1100 MPa or more, even more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, and even more preferably 2000 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, film-formability, water vapor barrier property, mechanical properties, transparency, bag-formability, handleability, and packaging suitability; and is preferably 4000 MPa or less, more preferably 3500 MPa or less, even more preferably 3000 MPa or less, even more preferably 2500 MPa or less, and even more preferably 2300 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic property, bag-formability, and packaging suitability.

[0044] In addition, the tensile modulus T of the biaxially stretched polyethylene film 100 in the TD direction ２ is preferably 1000 MPa or more, more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, even more preferably 2000 MPa or more, even more preferably 2500 MPa or more, and even more preferably 2800 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability; and is preferably 5000 MPa or less, more preferably 4500 MPa or less, even more preferably 4000 MPa or less, and even more preferably 3500 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability.

[0045] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１００From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, the shrinkage ratio is preferably 4.0% or less, more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, and even more preferably 2.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. Generally, a roll of biaxially oriented polyethylene film 100 is unwound in the MD direction, and bag-making, coating, vapor deposition, and the like are carried out while applying tension. That is, because tension is applied in the MD direction, if the film has low heat resistance, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage ratio in the MD direction when heated at 100°C for 15 minutes is within the above range, thermal elongation in the MD direction can be further suppressed when the biaxially oriented polyethylene film is heated.

[0046] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１００ From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 7.0% or less, more preferably 6.0% or less, even more preferably 5.0% or less, even more preferably 4.5% or less, even more preferably 4.0% or less, even more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less, and may be 0.01% or more, 0.02% or more, 0.05% or more, or 0.1% or more.

[0047] In addition, the heat shrinkage rate X of the biaxially stretched polyethylene film 100 when heated at 100° C. for 15 minutes is ＭＤ１００ [%] and X ＴＤ１００[%] is calculated by the following method: First, a test piece of 10 cm x 10 cm is cut out from a biaxially stretched polyethylene film 100, and this test piece is heat-treated at 100°C for 15 minutes. Then, the length in the MD direction of the test piece after the heat treatment is １００ The length of the test piece in the TD direction after heat treatment is defined as TD [cm]. １００ When [cm], X ＭＤ１００ [%] is 100 x (10-MD １００ ) / 10, and X ＴＤ１００ [%] is 100 × (10-TD １００ ) / 10.

[0048] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, it is preferably 9.0% or less, more preferably 8.5% or less, even more preferably 8.0% or less, even more preferably 7.5% or less, and even more preferably 7.0% or less, and may be 0.1% or more, 0.5% or more, 1.0% or more, or 3.0% or more.

[0049] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heat-treated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, the heat shrinkage ratio X of the biaxially oriented polyethylene film 100 when heated at 120° C. for 15 minutes is preferably 30.0% or less, more preferably 25.0% or less, even more preferably 20.0% or less, even more preferably 15.0% or less, even more preferably 13.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 5.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. ＭＤ１２０ [%] and X ＴＤ１２０ [%] is the heat shrinkage rate X of the biaxially oriented polyethylene film 100 when it is heated at 100° C. for 15 minutes. ＭＤ１００[%] and X ＴＤ１００ The measurement of [%] can be carried out in the same manner except that the heating temperature is 120° C. Specific details will be described in the Examples section.

[0050] The moisture permeability of the biaxially oriented polyethylene film 100 measured in accordance with JIS Z 0208:1976 is preferably 12.0 g / (m ２ ·day) or less, more preferably 11.5 g / (m ２ ·day) or less, more preferably 11.0 g / (m ２ ·day) or less, more preferably 10.5 g / (m ２ ·day) or less, more preferably 10.0 g / (m ２ ·day) or less, more preferably 9.0 g / (m ２ ·day) or less, more preferably 7.5 g / (m ２ ·day) or less, more preferably 7.0 g / (m ２ ·day) or less, more preferably 6.5 g / (m ２ ·day) or less, more preferably 6.0 g / (m ２ ·day) or less, and 0.01 g / (m ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ ・day) or more.

[0051] The sum of the stress at break in the TD direction and the stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 210 MPa or more, more preferably 220 MPa or more, even more preferably 230 MPa or more, even more preferably 250 MPa or more, even more preferably 280 MPa or more, and even more preferably 300 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 600 MPa or less, 500 MPa or less, or 450 MPa or less.

[0052] The stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 50 MPa or more, more preferably 60 MPa or more, even more preferably 70 MPa or more, even more preferably 80 MPa or more, and even more preferably 90 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 300 MPa or less, 200 MPa or less, or 150 MPa or less.

[0053] The stress at break in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 70 MPa or more, more preferably 90 MPa or more, even more preferably 100 MPa or more, even more preferably 120 MPa or more, even more preferably 150 MPa or more, and even more preferably 180 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 500 MPa or less, 400 MPa or less, 350 MPa or less, or 330 MPa or less.

[0054] Each layer constituting the biaxially oriented polyethylene film 100 will be described below.

[0055] [Biaxially Stretched Film Layer] The biaxially stretched film layer 101 contains an ethylene-based polymer. The biaxially stretched film layer 101 is formed by biaxially stretching a film constituted of an ethylene-based polymer composition containing the ethylene-based polymer (A).

[0056] (Ethylene-Based Polymer (A)) The content of the ethylene-based polymer (A) in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 97% by mass or more, and still more preferably 99% by mass or more, from the viewpoint of further improving the balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, rigidity, and transparency, and is preferably 100% by mass or less, from the viewpoint of further improving the balance of performances such as processability and continuous productivity.

[0057] The ethylene polymer (A) of the first embodiment preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). From the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, water vapor barrier property, mechanical properties, and rigidity, the ethylene polymer (A) more preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and even more preferably contains high-density polyethylene (HDPE). Here, the low-density polyethylene (LDPE) is defined as a polyethylene having a viscosity of 0.910 g / cm or less. ３ 0.930g / cm or more ３ and medium density polyethylene (MDPE) refers to polyethylene having a density of less than 0.930 g / cm ３ 0.942g / cm or more ３ High density polyethylene (HDPE) refers to polyethylene having a density of less than 0.942 g / cm ３ Low-density polyethylene with little branching structure is referred to as linear low-density polyethylene (LLDPE).

[0058] The content of high-density polyethylene in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, and rigidity, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is taken as 100% by mass. Also, from the viewpoint of further improving the performance balance of processability and continuous productivity, the content is preferably 100% by mass or less, more preferably 95% by mass or less.

[0059] The density of the ethylene polymer (A), measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ When two or more types of polymers are used as the ethylene polymer, the density of a mixture obtained by melt blending two or more types of ethylene polymers by a known method can be adopted.

[0060] The melt mass flow rate (MFR) of the ethylene polymer (A), measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less. When two or more types of polymers are used as the ethylene polymer (A), the MFR of a mixture obtained by melt-blending two or more types of polymers by a known method can be used.

[0061] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, the melting point of the ethylene polymer (A) measured by differential scanning calorimetry (DSC) is preferably 70° C. or higher, more preferably 75° C. or higher, even more preferably 90° C. or higher, even more preferably 95° C. or higher, even more preferably 100° C. or higher, even more preferably 110° C. or higher, even more preferably 120° C. or higher, and even more preferably 125° C. or higher, and is preferably 150° C. or lower, more preferably 140° C. or lower, even more preferably 135° C. or lower, and even more preferably 134° C. or lower. When two or more types of polymers are used as the ethylene polymer, the melting point of the ethylene polymer (A) is the peak temperature of the largest endothermic peak.

[0062] Furthermore, the ethylene polymer (A) of the first embodiment may further contain, in addition to the polyethylene described above, one or more selected from the group consisting of α-olefin copolymers (excluding ethylene-α-olefin copolymers) and ethylene-α-olefin copolymers, and more preferably contains an ethylene-α-olefin copolymer. From the viewpoint of further improving the balance of thermal dimensional stability, film-forming ability, and flexibility, the ethylene-α-olefin copolymer preferably contains one or more selected from the group consisting of ethylene-1-butene random copolymers and ethylene-propylene random copolymers, and more preferably contains an ethylene-1-butene random copolymer. The α-olefin copolymer contains one or more selected from the group consisting of propylene-ethylene random copolymers and 1-butene-propylene random copolymers.

[0063] The density of the ethylene-α-olefin copolymer measured in accordance with JIS K 7112:1999 is preferably 0.860 g / cm from the viewpoint of further improving the performance balance of thermal dimensional stability, film-forming property, and flexibility. ３ More preferably, 0.870 g / cm ３ More preferably, 0.880 g / cm ３ More preferably, 0.890 g / cm ３ or more, and preferably 0.920 g / cm ３ or less, more preferably 0.910 g / cm ３ More preferably, 0.900 g / cm ３ The following is the result.

[0064] The melt mass flow rate (MFR) of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 1.0 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less, from the viewpoint of further improving the performance balance of film-formability and thermal dimensional stability while improving the stiffness of the biaxially oriented polyethylene film 100.

[0065] The melting point of the ethylene-α-olefin copolymer measured by differential scanning calorimetry (DSC) is preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and still more preferably 70° C. or higher, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, and is preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 100° C. or lower, even more preferably 90° C. or lower, and still more preferably 80° C. or lower.

[0066] The content of the ethylene-α-olefin copolymer in the biaxially stretched film layer 101 is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[0067] (Other Components) If necessary, various additives such as a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slipping agent, a nucleating agent, an antiblocking agent, an antistatic agent, an antifogging agent, a pigment, a dye, and an inorganic or organic filler may be added to the ethylene polymer composition constituting the biaxially stretched film layer 101, within a range that does not impair the object of the first embodiment.

[0068] (Method for preparing ethylene-based polymer composition) The ethylene-based polymer composition can be prepared, for example, by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0069] The biaxially stretched film layer 101 may be a single layer or may have a structure in which a plurality of layers made of an ethylene-based polymer composition are laminated, but it is necessary that it is biaxially stretched.

[0070] From the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented film layer 101 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0071] In the biaxially oriented polyethylene film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the biaxially oriented polyethylene film 100 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and is preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0072] [Surface Resin Layer] The biaxially oriented polyethylene film 100 preferably further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101, from the viewpoint of imparting functions such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties to the film surface depending on the purpose. The surface resin layer 103 may be provided on both sides of the biaxially oriented film layer 101. By providing the surface resin layer 103 on both sides of the biaxially oriented film layer 101, different functions can be imparted to each surface of the film. When the surface resin layer 103 is provided on both sides of the biaxially oriented film layer 101, the surface resin layer 103 on one side preferably has heat sealing properties. The biaxially oriented polyethylene film 100 can be folded with this surface facing inward and the edges heat-sealed to form a bag shape. The surface resin layer 103 on the other side preferably has blocking resistance, antistatic properties, printability, and the like. In addition, the surface resin layer 103 is preferably provided as the outermost layer of the biaxially oriented polyethylene film 100, from the viewpoint of further improving the functions of the biaxially oriented polyethylene film 100, such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties, depending on the purpose.

[0073] The surface resin layer 103 is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the biaxially oriented polyethylene film 100.

[0074] In the biaxially oriented polyethylene film 100, the thickness of the surface resin layer 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight. Here, the thickness of the surface resin layer 103 refers to the thickness of the surface resin layer 103 provided on one side of the biaxially oriented film layer 101. That is, in the first embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the surface resin layer 103 indicates the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101.

[0075] In the biaxially oriented polyethylene film 100, the surface resin layer 103 is preferably a single layer, which can further simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0076] The surface resin layer 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the biaxially stretched polyethylene film 100 to be produced by a molding method such as co-extrusion, i.e., using a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the biaxially stretched polyethylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0077] The surface resin layer 103 may be subjected to a surface treatment in order to further improve the balance between printability and blocking resistance of the biaxially oriented polyethylene film 100. Specifically, the surface may be subjected to a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, or ozone treatment.

[0078] The surface resin layer 103 is composed of, for example, a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface resin layer 103 includes, for example, one or more selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, an ethylene-based polymer is preferred as the polyolefin constituting the surface resin layer 103 from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100 in terms of film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-forming ability, and flowability. Here, preferred embodiments of the ethylene-based polymer constituting the surface resin layer 103 are the same as those of the ethylene-based polymer described above. That is, the ethylene-based polymer constituting the surface resin layer 103 preferably contains the above-mentioned ethylene-based polymer (A). When the surface resin layers 103 are provided on both sides of the biaxially stretched film, the polyolefin-based resin compositions constituting the respective surface resin layers 103 may be the same or different.

[0079] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of polyolefin in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0080] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of the ethylene polymer in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0081] (Other Components) Various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition constituting the surface resin layer 103, as needed, within the scope that does not impair the object of the first embodiment.

[0082] (Method for preparing polyolefin-based resin composition) The polyolefin-based resin composition can be prepared, for example, by mixing or melting and kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0083] <Method for producing biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 can be obtained, for example, by co-extrusion molding an ethylene polymer composition for forming the biaxially oriented film layer 101 into a film, and then biaxially stretching the resulting film using a known biaxially oriented film production method such as simultaneous biaxial stretching, sequential biaxial stretching, or inflation biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be used. Examples of molding apparatus that can be used include a T-die extruder, a multilayer T-die extruder, an inflation molding machine, and a multilayer inflation molding machine. The biaxial stretching conditions can be, for example, those used for producing polyethylene films. For example, in the sequential biaxial stretching method, the stretching temperature in the MD direction is preferably in the range of 100°C to 145°C, more preferably 110°C to 140°C, and even more preferably 120°C to 135°C, and the stretching temperature in the TD direction is preferably in the range of 110°C to 190°C, more preferably 120°C to 170°C. The stretching ratio in the MD direction is preferably in the range of 4.5 to 7 times, and the stretching ratio in the TD direction is preferably in the range of 9 to 11 times. Specifically, the stretching temperature must be set at three stages: preheating temperature (the temperature at which the raw film is heated before stretching), stretching temperature (the temperature at which the stretching is performed), and heat setting temperature (the temperature at which the heat setting (annealing) is performed after stretching). The temperatures from preheating to heat setting can be within the above range. That is, the temperature can be set to the same level as that for stretching and heat setting from the preheating stage. Since the biaxially oriented polyethylene film 100 of the first embodiment contains the ethylene polymer (A), it can be processed at higher temperatures, which can further improve the heat resistance and therefore the thermal dimensional stability of the obtained biaxially oriented polyethylene film 100. The biaxially oriented polyethylene film 100 can also be obtained by separately molding the biaxially oriented film layer 101 and, if necessary, the surface resin layer 103, laminating them together, and hot molding them.

[0084] <Uses of Biaxially Stretched Polyethylene Film / Packaging Material / Packaging Body> The biaxially oriented polyethylene film 100 of the first embodiment can be suitably used, specifically, as a packaging film. The biaxially oriented polyethylene film 100 of the first embodiment can also be suitably used as a packaging material. When used as a packaging material, the stretched polyethylene film 100 of the first embodiment may be used alone, or other layers may be laminated thereon. The other layers preferably further include one or more selected from the group consisting of an inorganic layer, a substrate layer, a coating layer, an adhesive layer, and a heat-seal layer, and more preferably, one or more selected from the group consisting of an inorganic layer and a coating layer. From the perspective of ease of recycling, when these layers are laminated, they are preferably formed from a polyethylene-based resin. The packaging material of the first embodiment can also be suitably used as a packaging body. The packaging body is used, for example, for the purpose of packaging an item, and specifically includes the packaging material of the first embodiment and the item inside the packaging material. In particular, the packaging body of the first embodiment can be suitably used as a food packaging body and is used for the purpose of packaging food, specifically including the packaging material of the first embodiment and the food inside the packaging material. The food packaged in the food packaging body is not limited, but examples thereof include baked goods, rice crackers, snacks, sprinkles, grain powder, etc. Depending on the application, only a portion of the packaging body may be made of the packaging material of the first embodiment, or substantially the entire packaging body may be made of the packaging material of the first embodiment.

[0085] There are no particular limitations on the method for producing a package from the biaxially oriented polyethylene film 100 or the packaging material. Any method known in the field of packaging materials / packages, such as heat sealing or fusing, can be used as appropriate.

[0086] The biaxially oriented polyethylene film 100 according to the first embodiment is preferably used for packaging that requires good film-forming properties and thermal dimensional stability. The form of the packaging can be, for example, a two-sided bag or a standing pouch (pouch packaging).

[0087] Furthermore, when a package (such as a food packaging bag) is constructed using the biaxially oriented polyethylene film 100 of the first embodiment or a packaging material, it is preferable that the corona-treated surface be the inner surface and the non-corona-treated surface be the outer surface. Furthermore, as described above, when another layer is laminated on the biaxially oriented polyethylene film 100, it is preferable that the layer be laminated on the corona-treated surface. That is, when a laminate using the biaxially oriented polyethylene film 100 of the first embodiment is used for a package (such as a food packaging bag), it is preferable that the biaxially oriented polyethylene film 100 of the first embodiment be the outermost layer of the package.

[0088] Although the first embodiment of the present invention has been described above, these are merely examples of the first embodiment of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the first embodiment described above, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0089] <<Second Embodiment>> Hereinafter, a biaxially oriented polyethylene film, a packaging material, and a package according to a second embodiment of the present invention will be described.

[0090] <Biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 of the second embodiment includes a biaxially oriented film layer 101 containing an ethylene-based polymer (A). When measured by thermomechanical analysis (TMA) with reference to JIS K 7197:2012 under conditions of a heating rate of 10°C / min, a tensile mode, a load of 10 g / 4 mm, an initial chuck distance of 8 mm, and a test piece width of 4 mm, the biaxially oriented polyethylene film 100 has an average linear expansion coefficient (α) in the MD direction calculated from the following formula (1) in a measurement temperature range of 20°C to 100°C of 4.5 x 10 －４ (1 / °C) or less. Equation (1): Average linear expansion coefficient (α) = 1 / L ０ ・[{L(t ２ ) - L(t １ ) / (t ２ -t １ )] In formula (1), L ０、 T １ , T ２ , L(t １ ) and L(t ２ ) is expressed as follows: L ０: Initial chuck distance 8 mm t １ : 20 ° C. ２ : 100 ° C. L (t １ ): temperature t １ Distance between chucks (mm) L (t ２ ): temperature t ２ Distance between chucks (mm)

[0091] The inventors have discovered that by setting the average linear expansion coefficient in the MD direction of the biaxially oriented polyethylene film 100, as measured by thermomechanical analysis, to a predetermined value or less, the biaxially oriented polyethylene film 100 becomes less likely to stretch, thereby improving its heat-sealing resistance.

[0092] The biaxially stretched polyethylene film 100 of the second embodiment was measured by thermomechanical analysis (TMA) with reference to JIS K 7197:2012 under the conditions of a heating rate of 10°C / min, a tensile mode, a load of 10 g / 4 mm, an initial chuck distance of 8 mm, and a test piece width of 4 mm. The average linear expansion coefficient (α) in the MD direction measured in the measurement temperature range from 20°C to 100°C was 4.5 x 10 －４ (1 / °C) or less, preferably 4.0 x 10 －４ (1 / °C) or less, more preferably 3.5 x 10 －４ (1 / °C) or less, more preferably 3.0 x 10 －４ (1 / °C) or less, more preferably 2.5 x 10 －４ (1 / °C) or less, more preferably 2.0 x 10 －４ (1 / °C) or less, more preferably 1.8 x 10 －４ (1 / °C) or less, more preferably 1.7 x 10 －４ (1 / °C) or less, more preferably 1.5 x 10 －４ (1 / °C) or less, and preferably 5.0 x 10 －５ (1 / °C) or more, more preferably 7.0 x 10 －５ (1 / °C) or more, more preferably 8.5.0 x 10 －５ (1 / °C) or more, more preferably 1.0 x 10 －４ (1 / °C) or more, more preferably 1.1 x 10 －４ (1 / °C) or more, more preferably 1.2 × 10 －４(1 / °C) or more. When the average linear expansion coefficient (α) in the MD direction of the biaxially oriented polyethylene film 100 is the above upper limit or less, the biaxially oriented polyethylene film 100 is less likely to stretch, thereby improving heat-sealing resistance. Furthermore, stretching in the MD direction during processing such as printing is suppressed, thereby improving processing suitability such as printability, coating suitability, and vapor deposition suitability. Furthermore, when the average linear expansion coefficient (α) in the MD direction of the biaxially oriented polyethylene film 100 is the above lower limit or more, the flexibility of the biaxially oriented polyethylene film 100 can be further improved.

[0093] The biaxially oriented polyethylene film 100 has an MD elongation at 100°C measured by thermomechanical analysis (TMA) according to JIS K 7197:2012 under conditions of a temperature range of 20°C to 100°C, a heating rate of 10°C / min, a tensile mode, a load of 10 g / 4 mm, an initial chuck distance of 8 mm, and a test piece width of 4 mm. From the viewpoints of further improving heat fusion resistance, further suppressing elongation in the MD during printing or coating processing, and further improving processability, the elongation is preferably 3.5% or less, more preferably 3.3% or less, even more preferably 3.0% or less, still more preferably 2.8% or less, still more preferably 2.5% or less, still more preferably 2.3% or less, still more preferably 2.0% or less, still more preferably 1.8% or less, and still more preferably 1.5% or less, and may be 0.1% or more, 0.3% or more, 0.5% or more, or 0.8% or more.

[0094] The average coefficient of linear expansion (α) of the biaxially oriented polyethylene film 100 in the MD direction at 100°C and the elongation (%) of the biaxially oriented polyethylene film 100 in the MD direction at 100°C are measured by thermomechanical analysis (TMA) in accordance with the following measurement conditions, with reference to JIS K 7197:2012. [Measurement Conditions] Measuring device: TMA Q400 (manufactured by TA Instruments) Measurement mode: Tensile mode Test piece width: 4 mm Initial chuck distance: 8 mm Measurement direction: MD direction Load: 10 g / 4 mm Heating rate: 10°C / min Measurement temperature range: 20 to 100°C The average coefficient of linear expansion (α) is calculated by the following formula (1): Formula (1): Average coefficient of linear expansion (α) = 1 / L ０ ・[{L(t ２ ) - L(t １ ) / (t ２ -t １ )] In formula (1), L ０、 T １ , T ２ , L(t １ ) and L(t ２ ) is expressed as follows: L ０ : Initial chuck distance 8 mm t １ : 20 ° C. ２ : 100 ° C. L (t １ ): temperature t １ Distance between chucks (mm) L (t ２ ): temperature t ２ The MD elongation at 100°C is calculated using the following formula (2): Formula (2): MD elongation at 100°C (%) = 100 × (chuck distance at 100°C - initial chuck distance) / initial chuck distance

[0095] The density of the biaxially oriented polyethylene film 100, measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming property, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ The following is the result.

[0096] The melting point of the biaxially oriented polyethylene film 100, as measured by a differential scanning calorimeter (DSC), is preferably 70°C or higher, more preferably 75°C or higher, even more preferably 90°C or higher, even more preferably 95°C or higher, even more preferably 100°C or higher, even more preferably 110°C or higher, even more preferably 120°C or higher, even more preferably 125°C or higher, and is preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, even more preferably 134°C or lower, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability.

[0097] JIS K The melt mass flow rate (MFR) of the biaxially oriented polyethylene film 100, measured in accordance with J.P. 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less.

[0098] From the viewpoint of further improving the balance of performance factors such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented polyethylene film 100 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0099] The physical properties of the biaxially oriented polyethylene film 100 will be described below.

[0100] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction is measured using a tensile tester in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ ) is preferably 2500 MPa or more, more preferably 3000 MPa or more, even more preferably 3500 MPa or more, even more preferably 4000 MPa or more, even more preferably 4500 MPa or more, and is preferably 9000 MPa or less, more preferably 8000 MPa or less, even more preferably 7000 MPa or less, even more preferably 6500 MPa or less, even more preferably 6000 MPa or less. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ When the tensile modulus T in the MD direction of the biaxially oriented polyethylene film 100 is equal to or greater than the lower limit, the biaxially oriented polyethylene film 100 can have a better balance of properties such as thermal dimensional stability, film-forming properties, water vapor barrier properties, mechanical properties, transparency, bag-forming properties, and handling properties, and the stiffness of the biaxially oriented polyethylene film 100 can be improved. １ and the tensile modulus in the TD direction T２ The sum of (T １ +T ２ ) is not more than the above upper limit, problems such as breakage are less likely to occur during the formation of the biaxially oriented polyethylene film 100, continuous stretching of the film becomes easier, and industrial continuous productivity can be further improved. Such tensile modulus is a substitute value for quantitatively measuring the stiffness of the film, and can be adjusted, for example, by adjusting the type and content ratio of the ethylene polymer (A) contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0101] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction １ is preferably 800 MPa or more, more preferably 1000 MPa or more, even more preferably 1100 MPa or more, even more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, and even more preferably 2000 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, film-formability, water vapor barrier property, mechanical properties, transparency, bag-formability, handleability, and packaging suitability; and is preferably 4000 MPa or less, more preferably 3500 MPa or less, even more preferably 3000 MPa or less, even more preferably 2500 MPa or less, and even more preferably 2300 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic property, bag-formability, and packaging suitability.

[0102] In addition, the tensile modulus T of the biaxially stretched polyethylene film 100 in the TD direction ２is preferably 1000 MPa or more, more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, even more preferably 2000 MPa or more, even more preferably 2500 MPa or more, and even more preferably 2800 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability; and is preferably 5000 MPa or less, more preferably 4500 MPa or less, even more preferably 4000 MPa or less, and even more preferably 3500 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability.

[0103] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１００ From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, the shrinkage ratio is preferably 4.0% or less, more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, and even more preferably 2.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. Generally, a roll of biaxially oriented polyethylene film 100 is unwound in the MD direction, and bag-making, coating, vapor deposition, and the like are carried out while applying tension. That is, because tension is applied in the MD direction, if the film has low heat resistance, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage ratio in the MD direction when heated at 100°C for 15 minutes is within the above range, thermal elongation in the MD direction can be further suppressed when the biaxially oriented polyethylene film is heated.

[0104] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１００From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 7.0% or less, more preferably 6.0% or less, even more preferably 5.0% or less, even more preferably 4.5% or less, even more preferably 4.0% or less, even more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less, and may be 0.01% or more, 0.02% or more, 0.05% or more, or 0.1% or more.

[0105] In addition, the heat shrinkage rate X of the biaxially stretched polyethylene film 100 when heated at 100° C. for 15 minutes is ＭＤ１００ [%] and X ＴＤ１００ [%] is calculated by the following method: First, a test piece of 10 cm x 10 cm is cut out from a biaxially stretched polyethylene film 100, and this test piece is heat-treated at 100°C for 15 minutes. Then, the length in the MD direction of the test piece after the heat treatment is １００ The length of the test piece in the TD direction after heat treatment is defined as TD [cm]. １００ When [cm], X ＭＤ１００ [%] is 100 x (10-MD １００ ) / 10, and X ＴＤ１００ [%] is 100 × (10-TD １００ ) / 10.

[0106] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, it is preferably 9.0% or less, more preferably 8.5% or less, even more preferably 8.0% or less, even more preferably 7.5% or less, and even more preferably 7.0% or less, and may be 0.1% or more, 0.5% or more, 1.0% or more, or 3.0% or more.

[0107] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heat-treated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, the heat shrinkage ratio X of the biaxially oriented polyethylene film 100 when heated at 120° C. for 15 minutes is preferably 30.0% or less, more preferably 25.0% or less, even more preferably 20.0% or less, even more preferably 15.0% or less, even more preferably 13.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 5.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. ＭＤ１２０ [%] and X ＴＤ１２０ [%] is the heat shrinkage rate X of the biaxially oriented polyethylene film 100 when it is heated at 100° C. for 15 minutes. ＭＤ１００ [%] and X ＴＤ１００ The measurement of [%] can be carried out in the same manner except that the heating temperature is 120° C. Specific details will be described in the Examples section.

[0108] The moisture permeability of the biaxially oriented polyethylene film 100 measured in accordance with JIS Z 0208:1976 is preferably 12.0 g / (m ２ ·day) or less, more preferably 11.5 g / (m ２ ·day) or less, more preferably 11.0 g / (m ２ ·day) or less, more preferably 10.5 g / (m ２ ·day) or less, more preferably 10.0 g / (m ２ ·day) or less, more preferably 9.0 g / (m ２ ·day) or less, more preferably 7.5 g / (m ２ ·day) or less, more preferably 7.0 g / (m ２ ·day) or less, more preferably 6.5 g / (m ２ ·day) or less, more preferably 6.0 g / (m ２ ·day) or less, and 0.01 g / (m ２· day) or more, and ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ ・day) or more.

[0109] The sum of the stress at break in the TD direction and the stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 210 MPa or more, more preferably 220 MPa or more, even more preferably 230 MPa or more, even more preferably 250 MPa or more, even more preferably 280 MPa or more, and even more preferably 300 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 600 MPa or less, 500 MPa or less, or 450 MPa or less.

[0110] The stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 50 MPa or more, more preferably 60 MPa or more, even more preferably 70 MPa or more, even more preferably 80 MPa or more, and even more preferably 90 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 300 MPa or less, 200 MPa or less, or 150 MPa or less.

[0111] The stress at break in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 70 MPa or more, more preferably 90 MPa or more, even more preferably 100 MPa or more, even more preferably 120 MPa or more, even more preferably 150 MPa or more, and even more preferably 180 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 500 MPa or less, 400 MPa or less, 350 MPa or less, or 330 MPa or less.

[0112] In the biaxially oriented polyethylene film 100, the heat-seal strength at 130°C is preferably 1.0 N / 15 mm or less, more preferably 0.8 N / 15 mm or less, even more preferably 0.5 N / 15 mm or less, even more preferably 0.4 N / 15 mm or less, and even more preferably 0.3 N / 15 mm or less, and may be, for example, 0.0 N / 15 mm or more, preferably 0.0 N / 15 mm. When the biaxially oriented polyethylene film 100 has a heat-seal strength at 130°C of not more than the above upper limit, the heat resistance is further improved, and the crystallinity of the film is further improved, thereby further improving the water vapor barrier property.

[0113] The biaxially oriented polyethylene film 100 has a heat-seal strength at 135°C of preferably 1.5 N / 15 mm or less, more preferably 1.3 N / 15 mm or less, even more preferably 1.0 N / 15 mm or less, even more preferably 0.8 N / 15 mm or less, even more preferably 0.5 N / 15 mm or less, and even more preferably 0.3 N / 15 mm or less, and may be, for example, 0.0 N / 15 mm or more, preferably 0.0 N / 15 mm. When the biaxially oriented polyethylene film 100 has a heat-seal strength at 135°C of not more than the above upper limit, the heat resistance is further improved, and the crystallinity of the film is further improved, thereby further improving the water vapor barrier property.

[0114] The biaxially oriented polyethylene film 100 has a heat-seal strength at 140°C of preferably 5.5 N / 15 mm or less, more preferably 5.3 N / 15 mm or less, even more preferably 5.0 N / 15 mm or less, even more preferably 4.5 N / 15 mm or less, even more preferably 4.0 N / 15 mm or less, even more preferably 3.0 N / 15 mm or less, even more preferably 2.0 N / 15 mm or less, even more preferably 1.0 N / 15 mm or less, even more preferably 0.8 N / 15 mm or less, even more preferably 0.5 N / 15 mm or less, even more preferably 0.3 N / 15 mm or less, and may be, for example, 0.0 N / 15 mm or more. When the biaxially oriented polyethylene film 100 has a heat-seal strength at 140°C of not more than the above upper limit, the heat resistance is further improved, and the crystallinity of the film is further improved, thereby further improving the water vapor barrier property.

[0115] In the biaxially oriented polyethylene film 100 of the second embodiment, the heat-seal strength is measured as follows: Two biaxially oriented polyethylene films cut to a width of 15 mm are laminated together, sandwiched between 12 μm-thick biaxially oriented polyethylene terephthalate films, and measured using a heat seal tester at temperatures of 110° C., 120° C., 125° C., 130° C., 135° C., 140° C., and 150° C. under a pressure of 2.0 kgf / cm. ２ After each laminated film was obtained by heat sealing under the conditions of 1.0 second, 1.0 second sealing time, the two biaxially oriented polyethylene films were each peeled off under the conditions of 90° peeling, a peeling speed of 300 mm / min and pulling in the MD direction, and the peel strength at this time was taken as the heat sealing strength (N / 15 mm).

[0116] Each layer constituting the biaxially oriented polyethylene film 100 will be described below.

[0117] [Biaxially Stretched Film Layer] The biaxially stretched film layer 101 contains an ethylene-based polymer. The biaxially stretched film layer 101 is formed by biaxially stretching a film constituted of an ethylene-based polymer composition containing the ethylene-based polymer (A).

[0118] (Ethylene-Based Polymer (A)) The content of the ethylene-based polymer (A) in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 97% by mass or more, and still more preferably 99% by mass or more, from the viewpoint of further improving the balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, rigidity, and transparency, and is preferably 100% by mass or less, from the viewpoint of further improving the balance of performances such as processability and continuous productivity.

[0119] The ethylene polymer (A) of the second embodiment preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). From the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, water vapor barrier property, mechanical properties, and rigidity, the ethylene polymer (A) more preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and even more preferably contains high-density polyethylene (HDPE). Here, the low-density polyethylene (LDPE) is a polyethylene having a viscosity of 0.910 g / cm or less. ３ 0.930g / cm or more ３ and medium density polyethylene (MDPE) refers to polyethylene having a density of less than 0.930 g / cm ３ 0.942g / cm or more ３ High density polyethylene (HDPE) refers to polyethylene having a density of less than 0.942 g / cm ３ Low-density polyethylene with little branching structure is referred to as linear low-density polyethylene (LLDPE).

[0120] The content of high-density polyethylene in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, and rigidity, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is taken as 100% by mass. Also, from the viewpoint of further improving the performance balance of processability and continuous productivity, the content is preferably 100% by mass or less, more preferably 95% by mass or less.

[0121] The density of the ethylene polymer (A), measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ When two or more types of polymers are used as the ethylene polymer, the density of a mixture obtained by melt blending two or more types of ethylene polymers by a known method can be adopted.

[0122] The melt mass flow rate (MFR) of the ethylene polymer (A), measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less. When two or more types of polymers are used as the ethylene polymer (A), the MFR of a mixture obtained by melt-blending two or more types of polymers by a known method can be used.

[0123] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, the melting point of the ethylene polymer (A) measured by differential scanning calorimetry (DSC) is preferably 70° C. or higher, more preferably 75° C. or higher, even more preferably 90° C. or higher, even more preferably 95° C. or higher, even more preferably 100° C. or higher, even more preferably 110° C. or higher, even more preferably 120° C. or higher, and even more preferably 125° C. or higher, and is preferably 150° C. or lower, more preferably 140° C. or lower, even more preferably 135° C. or lower, and even more preferably 134° C. or lower. When two or more types of polymers are used as the ethylene polymer, the melting point of the ethylene polymer (A) is the peak temperature of the largest endothermic peak.

[0124] Furthermore, the ethylene polymer (A) of the second embodiment may further contain, in addition to the polyethylene described above, one or more selected from the group consisting of α-olefin copolymers (excluding ethylene-α-olefin copolymers) and ethylene-α-olefin copolymers, and more preferably contains an ethylene-α-olefin copolymer. From the viewpoint of further improving the balance of thermal dimensional stability, film-forming ability, and flexibility, the ethylene-α-olefin copolymer preferably contains one or more selected from the group consisting of ethylene-1-butene random copolymers and ethylene-propylene random copolymers, and more preferably contains an ethylene-1-butene random copolymer. The α-olefin copolymer contains one or more selected from the group consisting of propylene-ethylene random copolymers and 1-butene-propylene random copolymers.

[0125] The density of the ethylene-α-olefin copolymer measured in accordance with JIS K 7112:1999 is preferably 0.860 g / cm from the viewpoint of further improving the performance balance of thermal dimensional stability, film-forming property, and flexibility. ３ More preferably, 0.870 g / cm ３ More preferably, 0.880 g / cm ３ More preferably, 0.890 g / cm ３ or more, and preferably 0.920 g / cm ３ or less, more preferably 0.910 g / cm ３ More preferably, 0.900 g / cm ３ The following is the result.

[0126] The melt mass flow rate (MFR) of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 1.0 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less, from the viewpoint of further improving the performance balance of film-formability and thermal dimensional stability while improving the stiffness of the biaxially oriented polyethylene film 100.

[0127] The melting point of the ethylene-α-olefin copolymer measured by differential scanning calorimetry (DSC) is preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and still more preferably 70° C. or higher, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, and is preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 100° C. or lower, even more preferably 90° C. or lower, and still more preferably 80° C. or lower.

[0128] The content of the ethylene-α-olefin copolymer in the biaxially stretched film layer 101 is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[0129] (Other Components) Various additives such as a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slipping agent, a nucleating agent, an antiblocking agent, an antistatic agent, an antifogging agent, a pigment, a dye, and an inorganic or organic filler may be added to the ethylene polymer composition constituting the biaxially stretched film layer 101, as needed, within a range that does not impair the object of the second embodiment.

[0130] (Method for preparing ethylene-based polymer composition) The ethylene-based polymer composition can be prepared, for example, by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0131] The biaxially stretched film layer 101 may be a single layer or may have a structure in which a plurality of layers made of an ethylene-based polymer composition are laminated, but it is necessary that it is biaxially stretched.

[0132] From the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented film layer 101 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0133] In the biaxially oriented polyethylene film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the biaxially oriented polyethylene film 100 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and is preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0134] [Surface Resin Layer] The biaxially oriented polyethylene film 100 preferably further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101, from the viewpoint of imparting functions such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties to the film surface depending on the purpose. The surface resin layer 103 may be provided on both sides of the biaxially oriented film layer 101. By providing the surface resin layer 103 on both sides of the biaxially oriented film layer 101, different functions can be imparted to each surface of the film. When the surface resin layer 103 is provided on both sides of the biaxially oriented film layer 101, the surface resin layer 103 on one side preferably has heat sealing properties. The biaxially oriented polyethylene film 100 can be folded with this surface facing inward and the edges heat-sealed to form a bag shape. The surface resin layer 103 on the other side preferably has blocking resistance, antistatic properties, printability, and the like. In addition, the surface resin layer 103 is preferably provided as the outermost layer of the biaxially oriented polyethylene film 100, from the viewpoint of further improving the functions of the biaxially oriented polyethylene film 100, such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties, depending on the purpose.

[0135] The surface resin layer 103 is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the biaxially oriented polyethylene film 100.

[0136] In the biaxially oriented polyethylene film 100, the thickness of the surface resin layer 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight. Here, the thickness of the surface resin layer 103 refers to the thickness of the surface resin layer 103 provided on one side of the biaxially oriented film layer 101. That is, in the second embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the surface resin layer 103 indicates the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101.

[0137] In the biaxially oriented polyethylene film 100, the surface resin layer 103 is preferably a single layer, which can further simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0138] The surface resin layer 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the biaxially stretched polyethylene film 100 to be produced by a molding method such as co-extrusion, i.e., using a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the biaxially stretched polyethylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0139] The surface resin layer 103 may be subjected to a surface treatment in order to further improve the balance between printability and blocking resistance of the biaxially oriented polyethylene film 100. Specifically, the surface may be subjected to a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, or ozone treatment.

[0140] The surface resin layer 103 is composed of, for example, a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface resin layer 103 includes, for example, one or more selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, an ethylene-based polymer is preferred as the polyolefin constituting the surface resin layer 103 from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100 in terms of film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-forming ability, and flowability. Here, preferred embodiments of the ethylene-based polymer constituting the surface resin layer 103 are the same as those of the ethylene-based polymer described above. That is, the ethylene-based polymer constituting the surface resin layer 103 preferably contains the above-mentioned ethylene-based polymer (A). When the surface resin layers 103 are provided on both sides of the biaxially stretched film, the polyolefin-based resin compositions constituting the respective surface resin layers 103 may be the same or different.

[0141] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of polyolefin in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0142] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of the ethylene polymer in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0143] (Other Components) Various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition constituting the surface resin layer 103, as needed, within a range that does not impair the object of the second embodiment.

[0144] (Method for preparing polyolefin-based resin composition) The polyolefin-based resin composition can be prepared, for example, by mixing or melting and kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0145] <Method for producing biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 can be obtained, for example, by co-extrusion molding an ethylene polymer composition for forming the biaxially oriented film layer 101 into a film, and then biaxially stretching the resulting film using a known biaxially oriented film production method such as simultaneous biaxial stretching, sequential biaxial stretching, or inflation biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be used. Examples of molding apparatus that can be used include a T-die extruder, a multilayer T-die extruder, an inflation molding machine, and a multilayer inflation molding machine. The biaxial stretching conditions can be, for example, those used for producing polyethylene films. For example, in the sequential biaxial stretching method, the stretching temperature in the MD direction is preferably in the range of 100°C to 145°C, more preferably 110°C to 140°C, and even more preferably 120°C to 135°C, and the stretching temperature in the TD direction is preferably in the range of 110°C to 190°C, more preferably 120°C to 170°C. The stretching ratio in the MD direction is preferably in the range of 4.5 to 7 times, and the stretching ratio in the TD direction is preferably in the range of 9 to 11 times. Specifically, the stretching temperature must be set at three stages: preheating temperature (the temperature at which the raw film is heated before stretching), stretching temperature (the temperature at which the stretching is performed), and heat setting temperature (the temperature at which the heat setting (annealing) is performed after stretching). The temperatures from preheating to heat setting can be within the above range. That is, the temperature can be set to the same level as that for stretching and heat setting from the preheating stage. Since the biaxially oriented polyethylene film 100 of the second embodiment contains the ethylene polymer (A), it can be processed at higher temperatures, which can further improve the heat resistance and therefore the thermal dimensional stability of the obtained biaxially oriented polyethylene film 100. The biaxially oriented polyethylene film 100 can also be obtained by separately molding the biaxially oriented film layer 101 and, if necessary, the surface resin layer 103, and laminating and molding these together.

[0146] <Uses of Biaxially Stretched Polyethylene Film / Packaging Material / Packaging Body> The biaxially oriented polyethylene film 100 of the second embodiment can be suitably used, specifically, as a packaging film. The biaxially oriented polyethylene film 100 of the second embodiment can also be suitably used as a packaging material. When used as a packaging material, the stretched polyethylene film 100 of the second embodiment may be used alone, or other layers may be laminated thereon. The other layers preferably further include one or more selected from the group consisting of an inorganic layer, a substrate layer, a coating layer, an adhesive layer, and a heat-seal layer, and more preferably, one or more selected from the group consisting of an inorganic layer and a coating layer. From the perspective of ease of recycling, when these layers are laminated, they are preferably formed from a polyethylene-based resin. The packaging material of the second embodiment can also be suitably used as a packaging body. The packaging body is used, for example, for the purpose of packaging an item, and specifically includes the packaging material of the second embodiment and the item inside the packaging material. In particular, the packaging body of the second embodiment can be suitably used as a food packaging body and is used for the purpose of packaging food, specifically including the packaging material of the second embodiment and the food inside the packaging material. The food packaged in the food packaging body is not limited, but examples thereof include baked goods, rice crackers, snacks, sprinkles, grain powder, etc. Depending on the application, only a portion of the packaging body may be made of the packaging material of the second embodiment, or substantially the entire packaging body may be made of the packaging material of the second embodiment.

[0147] There are no particular limitations on the method for producing a package from the biaxially oriented polyethylene film 100 or the packaging material. Any method known in the field of packaging materials / packages, such as heat sealing or fusing, can be used as appropriate.

[0148] The biaxially oriented polyethylene film 100 according to the second embodiment is preferably used for packaging that requires good film-forming properties and thermal dimensional stability. The packaging may be in the form of, for example, a two-sided bag or a standing pouch (pouch packaging).

[0149] Furthermore, when a package (such as a food packaging bag) is constructed using the biaxially oriented polyethylene film 100 of the second embodiment or a packaging material, it is preferable that the corona-treated surface be the inner surface and the non-corona-treated surface be the outer surface. Furthermore, as described above, when another layer is laminated on the biaxially oriented polyethylene film 100, it is preferable that the layer be laminated on the corona-treated surface. That is, when a laminate using the biaxially oriented polyethylene film 100 of the second embodiment is used for a package (such as a food packaging bag), it is preferable that the biaxially oriented polyethylene film 100 of the second embodiment be the outermost layer of the package.

[0150] While the second embodiment of the present invention has been described above, these are merely examples of the second embodiment of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the second embodiment described above, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0151] <<Third Embodiment>> Hereinafter, a biaxially oriented polyethylene film, a packaging material, and a package according to a third embodiment of the present invention will be described.

[0152] <Biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 of the third embodiment includes a biaxially oriented film layer 101 containing an ethylene polymer (A). The biaxially oriented polyethylene film 100 is subjected to a first differential scanning calorimetry (1st Run) using a differential scanning calorimeter (DSC) that includes a process of increasing the temperature from −50° C. to 200° C. at a temperature increasing rate of 10° C. / min, an isothermal process of maintaining the temperature at 200° C. for 5 minutes, and a process of decreasing the temperature from 200° C. to −50° C. at a temperature decreasing rate of 10° C. / min. When a second differential scanning calorimetry (2nd Run) consisting of a step of holding at -50°C for 5 minutes and a step of heating from -50°C to 200°C at a heating rate of 10°C / min is performed in succession, an endothermic peak A is observed in the range of 20°C or higher and 150°C or lower in DSC curve 2 obtained by the second differential scanning calorimetry, and the heat of fusion (ΔH) of endothermic peak A is 175 J / g or higher and 250 J / g or lower.

[0153] The inventors have discovered that the thermal dimensional stability of the biaxially oriented polyethylene film 100 can be improved by setting the heat of fusion (ΔH) obtained by differential scanning calorimetry of the biaxially oriented polyethylene film 100 within a predetermined range.

[0154] In the biaxially oriented polyethylene film 100 of the third embodiment, from the viewpoint of improving thermal dimensional stability, the heat of fusion (ΔH) obtained by differential scanning calorimetry is 175 J / g or more, preferably 178 J / g or more, more preferably 180 J / g or more, even more preferably 185 J / g or more, even more preferably 190 J / g or more, even more preferably 200 J / g or more, even more preferably 210 J / g or more, and is 250 J / g or less, preferably 240 J / g or less, more preferably 235 J / g or less, even more preferably 230 J / g or less.

[0155] The melting point (Tm １ ) to the melting point (Tm ２ ) minus (Tm １ -Tm ２ From the viewpoint of further improving the thermal dimensional stability, the temperature is preferably 0.0°C or higher, more preferably 0.5°C or higher, even more preferably 1.0°C or higher, even more preferably 1.5°C or higher, even more preferably 2.0°C or higher, and even more preferably 2.3°C or higher, and is preferably 5.0°C or lower, more preferably 4.5°C or lower, even more preferably 4.0°C or lower, even more preferably 3.5°C or lower, even more preferably 3.3°C or lower, even more preferably 3.1°C or lower, and even more preferably 3.0°C or lower.

[0156] In the biaxially stretched polyethylene film 100, when the exothermic peak observed in the DSC curve 1 obtained in the first cooling step is defined as the crystallization peak, and the temperature at the peak of the crystallization peak is defined as the crystallization temperature (Tc), Tm ２From the viewpoint of further improving the thermal dimensional stability and further improving the stretch processability, -Tc is preferably 12.1°C or higher, more preferably 12.3°C or higher, even more preferably 12.5°C or higher, even more preferably 12.8°C or higher, even more preferably 13.0°C or higher, and even more preferably 13.3°C or higher; from the viewpoint of further improving the crystallinity and thus the thermal dimensional stability, -Tc is preferably 17.0°C or lower, more preferably 16.5°C or lower, even more preferably 16.0°C or lower, even more preferably 15.5°C or lower, even more preferably 15.0°C or lower, and even more preferably 14.5°C or lower.

[0157] The melting point (Tm ２ From the viewpoint of further improving the thermal dimensional stability, the temperature is preferably 130°C or higher, more preferably 131°C or higher, even more preferably 132°C or higher, and even more preferably 133°C or higher, and is preferably 137°C or lower, more preferably 136°C or lower, even more preferably 135°C or lower, and even more preferably 134°C or lower.

[0158] In the biaxially stretched polyethylene film 100, ΔH, Tm １ , Tm ２ , Tc, Tm １ -Tm ２ and Tm ２ -Tc is measured as follows. A biaxially stretched polyethylene film 100 is subjected to a first differential scanning calorimetry (1st Run) using a differential scanning calorimeter, which consists of a process of increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 200°C for 5 minutes, and a process of decreasing the temperature from 200°C to -50°C at a heating rate of 10°C / min. A second differential scanning calorimetry (2nd Run) consists of a process of maintaining the temperature at -50°C for 5 minutes and a process of increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min. The peak temperature of the maximum endothermic peak of the DSC curve 1 in the 1st Run is defined as Tm １ (°C), and the peak temperature of the maximum endothermic peak of DSC curve 2 in the 2nd run is Tm ２(°C). The maximum exothermic peak observed in DSC curve 1 during the temperature-lowering step of the 1st run is taken as the crystallization peak, and the temperature at the apex of the crystallization peak is taken as the crystallization temperature Tc (°C). In DSC curve 2 during the 2nd run, an endothermic peak A is observed in the range of 20°C to 150°C, and the heat of fusion of endothermic peak A is taken as ΔH (J / g). When multiple endothermic peaks A are observed in the range of 20°C to 150°C during the 2nd run, the total heat of fusion of the multiple endothermic peaks A is taken as ΔH (J / g). The obtained Tm １ , Tm ２ and Tc, (Tm １ -Tm ２ ) (°C) and (Tm ２ -Tc) (°C) is calculated for each.

[0159] The density of the biaxially oriented polyethylene film 100, measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming property, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ The following is the result.

[0160] JIS K The melt mass flow rate (MFR) of the biaxially oriented polyethylene film 100, measured in accordance with J.P. 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less.

[0161] From the viewpoint of further improving the balance of performance factors such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented polyethylene film 100 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0162] The physical properties of the biaxially oriented polyethylene film 100 will be described below.

[0163] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction is measured using a tensile tester in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２) is preferably 2500 MPa or more, more preferably 3000 MPa or more, even more preferably 3500 MPa or more, even more preferably 4000 MPa or more, even more preferably 4500 MPa or more, and is preferably 9000 MPa or less, more preferably 8000 MPa or less, even more preferably 7000 MPa or less, even more preferably 6500 MPa or less, even more preferably 6000 MPa or less. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ When the tensile modulus T in the MD direction of the biaxially oriented polyethylene film 100 is equal to or greater than the lower limit, the biaxially oriented polyethylene film 100 can have a better balance of properties such as thermal dimensional stability, film-forming properties, water vapor barrier properties, mechanical properties, transparency, bag-forming properties, and handling properties, and the stiffness of the biaxially oriented polyethylene film 100 can be improved. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ ) is not more than the above upper limit, problems such as breakage are less likely to occur during the formation of the biaxially oriented polyethylene film 100, continuous stretching of the film becomes easier, and industrial continuous productivity can be further improved. Such tensile modulus is a substitute value for quantitatively measuring the stiffness of the film, and can be adjusted, for example, by adjusting the type and content ratio of the ethylene polymer (A) contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0164] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction １is preferably 800 MPa or more, more preferably 1000 MPa or more, even more preferably 1100 MPa or more, even more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, and even more preferably 2000 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, film-formability, water vapor barrier property, mechanical properties, transparency, bag-formability, handleability, and packaging suitability; and is preferably 4000 MPa or less, more preferably 3500 MPa or less, even more preferably 3000 MPa or less, even more preferably 2500 MPa or less, and even more preferably 2300 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic property, bag-formability, and packaging suitability.

[0165] In addition, the tensile modulus T of the biaxially stretched polyethylene film 100 in the TD direction ２ is preferably 1000 MPa or more, more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, even more preferably 2000 MPa or more, even more preferably 2500 MPa or more, and even more preferably 2800 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability; and is preferably 5000 MPa or less, more preferably 4500 MPa or less, even more preferably 4000 MPa or less, and even more preferably 3500 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability.

[0166] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１００From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, the shrinkage ratio is preferably 4.0% or less, more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, and even more preferably 2.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. Generally, a roll of biaxially oriented polyethylene film 100 is unwound in the MD direction, and bag-making, coating, vapor deposition, and the like are carried out while applying tension. That is, because tension is applied in the MD direction, if the film has low heat resistance, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage ratio in the MD direction when heated at 100°C for 15 minutes is within the above range, thermal elongation in the MD direction can be further suppressed when the biaxially oriented polyethylene film is heated.

[0167] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１００ From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 7.0% or less, more preferably 6.0% or less, even more preferably 5.0% or less, even more preferably 4.5% or less, even more preferably 4.0% or less, even more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less, and may be 0.01% or more, 0.02% or more, 0.05% or more, or 0.1% or more.

[0168] In addition, the heat shrinkage rate X of the biaxially stretched polyethylene film 100 when heated at 100° C. for 15 minutes is ＭＤ１００ [%] and X ＴＤ１００[%] is calculated by the following method: First, a test piece of 10 cm x 10 cm is cut out from a biaxially stretched polyethylene film 100, and this test piece is heat-treated at 100°C for 15 minutes. Then, the length in the MD direction of the test piece after the heat treatment is １００ The length of the test piece in the TD direction after heat treatment is defined as TD [cm]. １００ When [cm], X ＭＤ１００ [%] is 100 x (10-MD １００ ) / 10, and X ＴＤ１００ [%] is 100 × (10-TD １００ ) / 10.

[0169] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, it is preferably 9.0% or less, more preferably 8.5% or less, even more preferably 8.0% or less, even more preferably 7.5% or less, and even more preferably 7.0% or less, and may be 0.1% or more, 0.5% or more, 1.0% or more, or 3.0% or more.

[0170] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heat-treated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, the heat shrinkage ratio X of the biaxially oriented polyethylene film 100 when heated at 120° C. for 15 minutes is preferably 30.0% or less, more preferably 25.0% or less, even more preferably 20.0% or less, even more preferably 15.0% or less, even more preferably 13.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 5.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. ＭＤ１２０ [%] and X ＴＤ１２０ [%] is the heat shrinkage rate X of the biaxially oriented polyethylene film 100 when it is heated at 100° C. for 15 minutes. ＭＤ１００[%] and X ＴＤ１００ The measurement of [%] can be carried out in the same manner except that the heating temperature is 120° C. Specific details will be described in the Examples section.

[0171] The moisture permeability of the biaxially oriented polyethylene film 100 measured in accordance with JIS Z 0208:1976 is preferably 12.0 g / (m ２ ·day) or less, more preferably 11.5 g / (m ２ ·day) or less, more preferably 11.0 g / (m ２ ·day) or less, more preferably 10.5 g / (m ２ ·day) or less, more preferably 10.0 g / (m ２ ·day) or less, more preferably 9.0 g / (m ２ ·day) or less, more preferably 7.5 g / (m ２ ·day) or less, more preferably 7.0 g / (m ２ ·day) or less, more preferably 6.5 g / (m ２ ·day) or less, more preferably 6.0 g / (m ２ ·day) or less, and 0.01 g / (m ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ ・day) or more.

[0172] The sum of the stress at break in the TD direction and the stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 210 MPa or more, more preferably 220 MPa or more, even more preferably 230 MPa or more, even more preferably 250 MPa or more, even more preferably 280 MPa or more, and even more preferably 300 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 600 MPa or less, 500 MPa or less, or 450 MPa or less.

[0173] The stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 50 MPa or more, more preferably 60 MPa or more, even more preferably 70 MPa or more, even more preferably 80 MPa or more, and even more preferably 90 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 300 MPa or less, 200 MPa or less, or 150 MPa or less.

[0174] The stress at break in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 70 MPa or more, more preferably 90 MPa or more, even more preferably 100 MPa or more, even more preferably 120 MPa or more, even more preferably 150 MPa or more, and even more preferably 180 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 500 MPa or less, 400 MPa or less, 350 MPa or less, or 330 MPa or less.

[0175] Each layer constituting the biaxially oriented polyethylene film 100 will be described below.

[0176] [Biaxially Stretched Film Layer] The biaxially stretched film layer 101 contains an ethylene-based polymer. The biaxially stretched film layer 101 is formed by biaxially stretching a film constituted of an ethylene-based polymer composition containing the ethylene-based polymer (A).

[0177] (Ethylene-Based Polymer (A)) The content of the ethylene-based polymer (A) in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 97% by mass or more, and still more preferably 99% by mass or more, from the viewpoint of further improving the balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, rigidity, and transparency, and is preferably 100% by mass or less, from the viewpoint of further improving the balance of performances such as processability and continuous productivity.

[0178] The ethylene polymer (A) of the third embodiment preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). From the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, water vapor barrier property, mechanical properties, and rigidity, the ethylene polymer (A) more preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and even more preferably contains high-density polyethylene (HDPE). Here, the low-density polyethylene (LDPE) is a polyethylene having a viscosity of 0.910 g / cm or less. ３ 0.930g / cm or more ３ and medium density polyethylene (MDPE) refers to polyethylene having a density of less than 0.930 g / cm ３ 0.942g / cm or more ３ High density polyethylene (HDPE) refers to polyethylene having a density of less than 0.942 g / cm ３ Low-density polyethylene with little branching structure is referred to as linear low-density polyethylene (LLDPE).

[0179] The content of high-density polyethylene in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, and rigidity, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is taken as 100% by mass. Also, from the viewpoint of further improving the performance balance of processability and continuous productivity, the content is preferably 100% by mass or less, more preferably 95% by mass or less.

[0180] The density of the ethylene polymer (A), measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ When two or more types of polymers are used as the ethylene polymer, the density of a mixture obtained by melt blending two or more types of ethylene polymers by a known method can be adopted.

[0181] The melt mass flow rate (MFR) of the ethylene polymer (A), measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less. When two or more types of polymers are used as the ethylene polymer (A), the MFR of a mixture obtained by melt-blending two or more types of polymers by a known method can be used.

[0182] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, the melting point of the ethylene polymer (A) measured by differential scanning calorimetry (DSC) is preferably 70° C. or higher, more preferably 75° C. or higher, even more preferably 90° C. or higher, even more preferably 95° C. or higher, even more preferably 100° C. or higher, even more preferably 110° C. or higher, even more preferably 120° C. or higher, and even more preferably 125° C. or higher, and is preferably 150° C. or lower, more preferably 140° C. or lower, even more preferably 135° C. or lower, and even more preferably 134° C. or lower. When two or more types of polymers are used as the ethylene polymer, the melting point of the ethylene polymer (A) is the peak temperature of the largest endothermic peak.

[0183] Furthermore, the ethylene polymer (A) of the third embodiment may further contain, in addition to the polyethylene described above, one or more selected from the group consisting of α-olefin copolymers (excluding ethylene-α-olefin copolymers) and ethylene-α-olefin copolymers, and more preferably contains an ethylene-α-olefin copolymer. From the viewpoint of further improving the balance of thermal dimensional stability, film-forming ability, and flexibility, the ethylene-α-olefin copolymer preferably contains one or more selected from the group consisting of ethylene-1-butene random copolymers and ethylene-propylene random copolymers, and more preferably contains an ethylene-1-butene random copolymer. The α-olefin copolymer contains one or more selected from the group consisting of propylene-ethylene random copolymers and 1-butene-propylene random copolymers.

[0184] The density of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7112:1999, is preferably 0.860 g / cm from the viewpoint of further improving the performance balance of thermal dimensional stability, film-forming property, and flexibility. ３ More preferably, 0.870 g / cm ３ More preferably, 0.880 g / cm ３ More preferably, 0.890 g / cm ３ or more, and preferably 0.920 g / cm ３ or less, more preferably 0.910 g / cm ３ More preferably, 0.900 g / cm ３ The following is the result.

[0185] The melt mass flow rate (MFR) of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 1.0 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less, from the viewpoint of further improving the performance balance of film-formability and thermal dimensional stability while improving the stiffness of the biaxially oriented polyethylene film 100.

[0186] The melting point of the ethylene-α-olefin copolymer measured by differential scanning calorimetry (DSC) is preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and still more preferably 70° C. or higher, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, and is preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 100° C. or lower, even more preferably 90° C. or lower, and still more preferably 80° C. or lower.

[0187] The content of the ethylene-α-olefin copolymer in the biaxially stretched film layer 101 is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[0188] (Other Components) Various additives such as a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slipping agent, a nucleating agent, an antiblocking agent, an antistatic agent, an antifogging agent, a pigment, a dye, and an inorganic or organic filler may be added to the ethylene polymer composition constituting the biaxially stretched film layer 101, as needed, within a range that does not impair the object of the third embodiment.

[0189] (Method for preparing ethylene-based polymer composition) The ethylene-based polymer composition can be prepared, for example, by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0190] The biaxially stretched film layer 101 may be a single layer or may have a structure in which a plurality of layers made of an ethylene-based polymer composition are laminated, but it is necessary that it is biaxially stretched.

[0191] From the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented film layer 101 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0192] In the biaxially oriented polyethylene film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the biaxially oriented polyethylene film 100 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and is preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0193] [Surface Resin Layer] The biaxially oriented polyethylene film 100 preferably further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101, from the viewpoint of imparting functions such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties to the film surface depending on the purpose. The surface resin layer 103 may be provided on both sides of the biaxially oriented film layer 101. By providing the surface resin layer 103 on both sides of the biaxially oriented film layer 101, different functions can be imparted to each surface of the film. When the surface resin layer 103 is provided on both sides of the biaxially oriented film layer 101, the surface resin layer 103 on one side preferably has heat sealing properties. The biaxially oriented polyethylene film 100 can be folded with this surface facing inward and the edges heat-sealed to form a bag shape. The surface resin layer 103 on the other side preferably has blocking resistance, antistatic properties, printability, and the like. In addition, the surface resin layer 103 is preferably provided as the outermost layer of the biaxially oriented polyethylene film 100, from the viewpoint of further improving the functions of the biaxially oriented polyethylene film 100, such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties, depending on the purpose.

[0194] The surface resin layer 103 is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the biaxially oriented polyethylene film 100.

[0195] In the biaxially oriented polyethylene film 100, the thickness of the surface resin layer 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight. Here, the thickness of the surface resin layer 103 refers to the thickness of the surface resin layer 103 provided on one side of the biaxially oriented film layer 101. That is, in the third embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the surface resin layer 103 indicates the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101.

[0196] In the biaxially oriented polyethylene film 100, the surface resin layer 103 is preferably a single layer, which can further simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0197] The surface resin layer 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the biaxially stretched polyethylene film 100 to be produced by a molding method such as co-extrusion, i.e., using a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the biaxially stretched polyethylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0198] The surface resin layer 103 may be subjected to a surface treatment in order to further improve the balance between printability and blocking resistance of the biaxially oriented polyethylene film 100. Specifically, the surface may be subjected to a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, or ozone treatment.

[0199] The surface resin layer 103 is composed of, for example, a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface resin layer 103 includes, for example, one or more selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, an ethylene-based polymer is preferred as the polyolefin constituting the surface resin layer 103 from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100 in terms of film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-forming ability, and flowability. Here, preferred embodiments of the ethylene-based polymer constituting the surface resin layer 103 are the same as those of the ethylene-based polymer described above. That is, the ethylene-based polymer constituting the surface resin layer 103 preferably contains the above-mentioned ethylene-based polymer (A). When the surface resin layers 103 are provided on both sides of the biaxially stretched film, the polyolefin-based resin compositions constituting the respective surface resin layers 103 may be the same or different.

[0200] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of polyolefin in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0201] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of the ethylene polymer in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0202] (Other Components) Various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition constituting the surface resin layer 103, as needed, within a range that does not impair the object of the third embodiment.

[0203] (Method for preparing polyolefin-based resin composition) The polyolefin-based resin composition can be prepared, for example, by mixing or melting and kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0204] <Method for producing biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 can be obtained, for example, by co-extrusion molding an ethylene polymer composition for forming the biaxially oriented film layer 101 into a film, and then biaxially stretching the resulting film using a known biaxially oriented film production method such as simultaneous biaxial stretching, sequential biaxial stretching, or inflation biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be used. Examples of molding apparatus that can be used include a T-die extruder, a multilayer T-die extruder, an inflation molding machine, and a multilayer inflation molding machine. The biaxial stretching conditions can be, for example, those used for producing polyethylene films. For example, in the sequential biaxial stretching method, the stretching temperature in the MD direction is preferably in the range of 100°C to 145°C, more preferably 110°C to 140°C, and even more preferably 120°C to 135°C, and the stretching temperature in the TD direction is preferably in the range of 110°C to 190°C, more preferably 120°C to 170°C. The stretching ratio in the MD direction is preferably in the range of 4.5 to 7 times, and the stretching ratio in the TD direction is preferably in the range of 9 to 11 times. Specifically, the stretching temperature must be set at three stages: preheating temperature (the temperature at which the raw film is heated before stretching), stretching temperature (the temperature at which the stretching is performed), and heat setting temperature (the temperature at which the heat setting (annealing) is performed after stretching). The temperatures from preheating to heat setting can be within the above range. That is, the temperature can be set to the same level as that for stretching and heat setting from the preheating stage. The biaxially oriented polyethylene film 100 of the third embodiment contains the ethylene polymer (A), and therefore can be processed at higher temperatures, thereby further improving the heat resistance and therefore the thermal dimensional stability of the obtained biaxially oriented polyethylene film 100. The biaxially oriented polyethylene film 100 can also be obtained by separately molding the biaxially oriented film layer 101 and, if necessary, the surface resin layer 103, and laminating and molding these together.

[0205] <Uses of Biaxially Stretched Polyethylene Film / Packaging Material / Packaging Body> The biaxially oriented polyethylene film 100 of the third embodiment can be suitably used, specifically, as a packaging film. The biaxially oriented polyethylene film 100 of the third embodiment can also be suitably used as a packaging material. When used as a packaging material, the stretched polyethylene film 100 of the third embodiment may be used alone, or other layers may be laminated thereon. The other layers preferably further include one or more selected from the group consisting of an inorganic layer, a substrate layer, a coating layer, an adhesive layer, and a heat-seal layer, and more preferably, one or more selected from the group consisting of an inorganic layer and a coating layer. From the perspective of ease of recycling, when these layers are laminated, they are preferably formed from a polyethylene-based resin. The packaging material of the third embodiment can also be suitably used as a packaging body. The packaging body is used, for example, for packaging an item, and specifically includes the packaging material of the third embodiment and the item inside the packaging material. In particular, the packaging body of the third embodiment can be suitably used as a food packaging body and is used for the purpose of packaging food, specifically including the packaging material of the third embodiment and the food inside the packaging material. The food packaged in the food packaging body is not limited, but examples thereof include baked goods, rice crackers, snacks, sprinkles, grain powder, etc. Depending on the application, only a portion of the packaging body may be made of the packaging material of the third embodiment, or substantially the entire packaging body may be made of the packaging material of the third embodiment.

[0206] There are no particular limitations on the method for producing a package from the biaxially oriented polyethylene film 100 or the packaging material. Any method known in the field of packaging materials / packages, such as heat sealing or fusing, can be used as appropriate.

[0207] The biaxially oriented polyethylene film 100 according to the third embodiment is preferably used for packaging that requires good film-forming properties and thermal dimensional stability. The form of the packaging can be, for example, a two-sided bag or a standing pouch (pouch packaging).

[0208] Furthermore, when a package (such as a food packaging bag) is constructed using the biaxially oriented polyethylene film 100 of the third embodiment or a packaging material, it is preferable that the corona-treated surface be the inner surface and the non-corona-treated surface be the outer surface. Furthermore, as described above, when another layer is laminated on the biaxially oriented polyethylene film 100, it is preferable that the layer be laminated on the corona-treated surface. That is, when a laminate using the biaxially oriented polyethylene film 100 of the third embodiment is used for a package (such as a food packaging bag), it is preferable that the biaxially oriented polyethylene film 100 of the third embodiment be the outermost layer of the package.

[0209] Although the third embodiment of the present invention has been described above, these are merely examples of the third embodiment of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the third embodiment described above, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0210] <<Fourth Embodiment>> Hereinafter, a biaxially oriented polyethylene film, a packaging material, and a package according to a fourth embodiment of the present invention will be described.

[0211] <Biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 of the fourth embodiment includes a biaxially oriented film layer 101 containing an ethylene polymer (A), and the ethylene polymer (A) has a polystyrene-equivalent z-average molecular weight (Mz) of 800,000 or more and 4,000,000 or less, measured by gel permeation chromatography (GPC).

[0212] The present inventors have found that the performance balance between film-forming properties and thermal dimensional stability of the biaxially oriented polyethylene film 100 can be improved by adjusting the polystyrene-equivalent z-average molecular weight (Mz) of the ethylene polymer (A) in the biaxially oriented film layer 101 of the biaxially oriented polyethylene film 100, as measured by gel permeation chromatography (GPC), to a predetermined range.

[0213] The density of the biaxially oriented polyethylene film 100, measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming property, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ The following is the result.

[0214] JIS K The melt mass flow rate (MFR) of the biaxially oriented polyethylene film 100, measured in accordance with J.P. 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less.

[0215] The melting point of the biaxially oriented polyethylene film 100, as measured by a differential scanning calorimeter (DSC), is preferably 70°C or higher, more preferably 75°C or higher, even more preferably 90°C or higher, even more preferably 95°C or higher, even more preferably 100°C or higher, even more preferably 110°C or higher, even more preferably 120°C or higher, even more preferably 125°C or higher, and is preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, even more preferably 134°C or lower, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability.

[0216] From the viewpoint of further improving the balance of performance factors such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented polyethylene film 100 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0217] The physical properties of the biaxially oriented polyethylene film 100 will be described below.

[0218] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction is measured using a tensile tester in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２) is preferably 2500 MPa or more, more preferably 3000 MPa or more, even more preferably 3500 MPa or more, even more preferably 4000 MPa or more, even more preferably 4500 MPa or more, and is preferably 9000 MPa or less, more preferably 8000 MPa or less, even more preferably 7000 MPa or less, even more preferably 6500 MPa or less, even more preferably 6000 MPa or less. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ When the tensile modulus T in the MD direction of the biaxially oriented polyethylene film 100 is equal to or greater than the lower limit, the biaxially oriented polyethylene film 100 can have a better balance of properties such as thermal dimensional stability, film-forming properties, water vapor barrier properties, mechanical properties, transparency, bag-forming properties, and handling properties, and the stiffness of the biaxially oriented polyethylene film 100 can be improved. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ ) is not more than the above upper limit, problems such as breakage are less likely to occur during the formation of the biaxially oriented polyethylene film 100, continuous stretching of the film becomes easier, and industrial continuous productivity can be further improved. Such tensile modulus is a substitute value for quantitatively measuring the stiffness of the film, and can be adjusted, for example, by adjusting the type and content ratio of the ethylene polymer (A) contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0219] The tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction １is preferably 800 MPa or more, more preferably 1000 MPa or more, even more preferably 1100 MPa or more, even more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, and even more preferably 2000 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, film-formability, water vapor barrier property, mechanical properties, transparency, bag-formability, handleability, and packaging suitability; and is preferably 4000 MPa or less, more preferably 3500 MPa or less, even more preferably 3000 MPa or less, even more preferably 2500 MPa or less, and even more preferably 2300 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic property, bag-formability, and packaging suitability.

[0220] In addition, the tensile modulus T of the biaxially stretched polyethylene film 100 in the TD direction ２ is preferably 1000 MPa or more, more preferably 1300 MPa or more, even more preferably 1500 MPa or more, even more preferably 1800 MPa or more, even more preferably 2000 MPa or more, even more preferably 2500 MPa or more, and even more preferably 2800 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability; and is preferably 5000 MPa or less, more preferably 4500 MPa or less, even more preferably 4000 MPa or less, and even more preferably 3500 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability.

[0221] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１００From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, the shrinkage ratio is preferably 4.0% or less, more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, and even more preferably 2.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. Generally, a roll of biaxially oriented polyethylene film 100 is unwound in the MD direction, and bag-making, coating, vapor deposition, and the like are carried out while applying tension. That is, because tension is applied in the MD direction, if the film has low heat resistance, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage ratio in the MD direction when heated at 100°C for 15 minutes is within the above range, thermal elongation in the MD direction can be further suppressed when the biaxially oriented polyethylene film is heated.

[0222] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１００ From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 7.0% or less, more preferably 6.0% or less, even more preferably 5.0% or less, even more preferably 4.5% or less, even more preferably 4.0% or less, even more preferably 3.8% or less, even more preferably 3.5% or less, even more preferably 3.0% or less, even more preferably 2.8% or less, even more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less, and may be 0.01% or more, 0.02% or more, 0.05% or more, or 0.1% or more.

[0223] In addition, the heat shrinkage rate X of the biaxially stretched polyethylene film 100 when heated at 100° C. for 15 minutes is ＭＤ１００ [%] and X ＴＤ１００[%] is calculated by the following method: First, a test piece of 10 cm x 10 cm is cut out from a biaxially stretched polyethylene film 100, and this test piece is heat-treated at 100°C for 15 minutes. Then, the length in the MD direction of the test piece after the heat treatment is １００ The length of the test piece in the TD direction after heat treatment is defined as TD [cm]. １００ When [cm], X ＭＤ１００ [%] is 100 x (10-MD １００ ) / 10, and X ＴＤ１００ [%] is 100 × (10-TD １００ ) / 10.

[0224] The heat shrinkage rate X in the MD direction of the biaxially oriented polyethylene film 100 when heated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＭＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, it is preferably 9.0% or less, more preferably 8.5% or less, even more preferably 8.0% or less, even more preferably 7.5% or less, and even more preferably 7.0% or less, and may be 0.1% or more, 0.5% or more, 1.0% or more, or 3.0% or more.

[0225] The heat shrinkage rate X in the TD direction of the biaxially oriented polyethylene film 100 when heat-treated at 120°C for 15 minutes, measured in accordance with JIS C2151:2019 ＴＤ１２０ From the viewpoint of further improving the thermal dimensional stability and bag formability, the heat shrinkage ratio X of the biaxially oriented polyethylene film 100 when heated at 120° C. for 15 minutes is preferably 30.0% or less, more preferably 25.0% or less, even more preferably 20.0% or less, even more preferably 15.0% or less, even more preferably 13.0% or less, even more preferably 10.0% or less, even more preferably 8.0% or less, and even more preferably 5.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. ＭＤ１２０ [%] and X ＴＤ１２０ [%] is the heat shrinkage rate X of the biaxially oriented polyethylene film 100 when it is heated at 100° C. for 15 minutes. ＭＤ１００[%] and X ＴＤ１００ The measurement of [%] can be carried out in the same manner except that the heating temperature is 120° C. Specific details will be described in the Examples section.

[0226] The moisture permeability of the biaxially oriented polyethylene film 100 measured in accordance with JIS Z 0208:1976 is preferably 12.0 g / (m ２ ·day) or less, more preferably 11.5 g / (m ２ ·day) or less, more preferably 11.0 g / (m ２ ·day) or less, more preferably 10.5 g / (m ２ ·day) or less, more preferably 10.0 g / (m ２ ·day) or less, more preferably 9.0 g / (m ２ ·day) or less, more preferably 7.5 g / (m ２ ·day) or less, more preferably 7.0 g / (m ２ ·day) or less, more preferably 6.5 g / (m ２ ·day) or less, more preferably 6.0 g / (m ２ ·day) or less, and 0.01 g / (m ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ · day) or more, and ２ ・day) or more.

[0227] The sum of the stress at break in the TD direction and the stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 210 MPa or more, more preferably 220 MPa or more, even more preferably 230 MPa or more, even more preferably 250 MPa or more, even more preferably 280 MPa or more, and even more preferably 300 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 600 MPa or less, 500 MPa or less, or 450 MPa or less.

[0228] The stress at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 50 MPa or more, more preferably 60 MPa or more, even more preferably 70 MPa or more, even more preferably 80 MPa or more, and even more preferably 90 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 300 MPa or less, 200 MPa or less, or 150 MPa or less.

[0229] The stress at break in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 70 MPa or more, more preferably 90 MPa or more, even more preferably 100 MPa or more, even more preferably 120 MPa or more, even more preferably 150 MPa or more, and even more preferably 180 MPa or more, from the viewpoint of further improving mechanical strength such as toughness, and may be 500 MPa or less, 400 MPa or less, 350 MPa or less, or 330 MPa or less.

[0230] The sum of the elongation at break in the TD direction and the elongation at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 200% or less, more preferably 190% or less, even more preferably 180% or less, even more preferably 170% or less, even more preferably 160% or less, and even more preferably 155% or less, from the viewpoint of further improving the balance of mechanical strength and heat resistance, and is preferably 50% or more, more preferably 80% or more, and even more preferably 100% or more, from the viewpoint of further improving flexibility.

[0231] The elongation at break in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 180% or less, more preferably 170% or less, even more preferably 160% or less, and even more preferably 155% or less, from the viewpoint of further improving the balance of mechanical strength and heat resistance, and is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 100% or more, from the viewpoint of further improving flexibility.

[0232] The elongation at break in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is preferably 60% or less, more preferably 50% or less, even more preferably 45% or less, and even more preferably 40% or less, from the viewpoint of further improving the balance of mechanical strength and heat resistance, and is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more, from the viewpoint of further improving flexibility.

[0233] Each layer constituting the biaxially oriented polyethylene film 100 will be described below.

[0234] [Biaxially Stretched Film Layer] The biaxially stretched film layer 101 contains an ethylene-based polymer. The biaxially stretched film layer 101 is formed by biaxially stretching a film constituted of an ethylene-based polymer composition containing the ethylene-based polymer (A).

[0235] (Ethylene-Based Polymer (A)) In the ethylene-based polymer (A) of the fourth embodiment, the z-average molecular weight (Mz) in terms of polystyrene, measured by gel permeation chromatography (GPC), from the viewpoint of improving the performance balance between film-forming ability and thermal dimensional stability, is 800,000 or more, preferably 850,000 or more, more preferably 900,000 or more, even more preferably 950,000 or more, still more preferably 1,000,000 or more, still more preferably 1,050,000 or more, and is 4,000,000 or less, preferably 3,500,000 or less, more preferably 3,000,000 or less, still more preferably 2,500,000 or less, still more preferably 2,000,000 or less, still more preferably 1,500,000 or less, and still more preferably 1,300,000 or less.

[0236] From the viewpoint of further improving the balance of film-forming ability and thermal dimensional stability, the ethylene polymer (A) has a polystyrene-equivalent weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of preferably 130,000 or more, more preferably 135,000 or more, even more preferably 140,000 or more, even more preferably 145,000 or more, even more preferably 150,000 or more, and still more preferably 155,000 or more, and is preferably 1,000,000 or less, more preferably 800,000 or less, even more preferably 600,000 or less, even more preferably 500,000 or less, even more preferably 400,000 or less, even more preferably 300,000 or less, and still more preferably 200,000 or less.

[0237] The polystyrene-equivalent number average molecular weight (Mn) of the ethylene polymer, measured by gel permeation chromatography (GPC), is preferably 5,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, even more preferably 10,000 or more, even more preferably 13,000 or more, even more preferably 15,000 or more, even more preferably 18,000 or more, and even more preferably 20,000 or more, and is preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less, even more preferably 80,000 or less, even more preferably 60,000 or less, even more preferably 50,000 or less, even more preferably 40,000 or less, even more preferably 30,000 or less, and even more preferably 28,000 or less, from the viewpoints of further improving the balance of film-forming ability and thermal dimensional stability and setting the degree of polymerization of the ethylene polymer (A) in a more appropriate range.

[0238] From the viewpoint of further improving thermal dimensional stability, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of polystyrene of the ethylene polymer (A) measured by gel permeation chromatography (GPC) is preferably 30.0 or less, more preferably 28.0 or less, even more preferably 25.0 or less, even more preferably 20.0 or less, even more preferably 15.0 or less, even more preferably 13.0 or less, even more preferably 10.0 or less, even more preferably 8.0 or less, and is preferably 2.0 or more, more preferably 3.0 or more, even more preferably 4.0 or more, even more preferably 5.0 or more, even more preferably 6.0 or more, even more preferably 6.5 or more, even more preferably 7.0 or more.

[0239] The ethylene polymer (A) has a polystyrene-equivalent z+1 average molecular weight (Mz+1) measured by gel permeation chromatography (GPC) of preferably 10,000,000 or less, more preferably 8,000,000 or less, even more preferably 5,000,000 or less, even more preferably 4,000,000 or less, and even more preferably 3,500,000 or less from the viewpoint of further improving film-forming ability; and from the viewpoint of further improving thermal dimensional stability, it is preferably 1,000,000 or more, more preferably 1,500,000 or more, even more preferably 1,800,000 or more, even more preferably 2,000,000 or more, even more preferably 2,200,000 or more, even more preferably 2,300,000 or more, and even more preferably 2,500,000 or more.

[0240] When two or more types of polymers are used as the ethylene polymer (A), the z-average molecular weight (Mz), weight-average molecular weight (Mw), number-average molecular weight (Mn), and z+1-average molecular weight (Mz+1) of the ethylene polymer (A) can be determined by the method described in the Examples.

[0241] The content of the ethylene polymer (A) in the ethylene polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 97% by mass or more, and still more preferably 99% by mass or more, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film formability, heat resistance, mechanical properties, rigidity, and transparency, when the entire ethylene polymer composition, i.e., the entire biaxially stretched film layer 101, is taken as 100% by mass, and from the viewpoint of further improving the performance balance of processability and continuous productivity, the content is preferably 100% by mass or less.

[0242] The ethylene polymer (A) of the fourth embodiment preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). From the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, water vapor barrier property, mechanical properties, and rigidity, the ethylene polymer (A) more preferably contains one or more polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and even more preferably contains high-density polyethylene (HDPE). Here, the low-density polyethylene (LDPE) is defined as a polyethylene having a viscosity of 0.910 g / cm or more. ３ 0.930g / cm or more ３ and medium density polyethylene (MDPE) refers to polyethylene having a density of less than 0.930 g / cm ３ 0.942g / cm or more ３ High density polyethylene (HDPE) refers to polyethylene having a density of less than 0.942 g / cm ３ Low-density polyethylene with little branching structure is referred to as linear low-density polyethylene (LLDPE).

[0243] The content of high-density polyethylene in the ethylene-based polymer composition, i.e., the biaxially stretched film layer 101, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film-formability, heat resistance, mechanical properties, and rigidity, when the entire ethylene-based polymer composition, i.e., the entire biaxially stretched film layer 101, is taken as 100% by mass. Also, from the viewpoint of further improving the performance balance of processability and continuous productivity, the content is preferably 100% by mass or less, more preferably 95% by mass or less.

[0244] High-density polyethylene has a problem in that it has low processability and is difficult to biaxially stretch into a film. The present inventors have found that by adjusting the z-average molecular weight of the ethylene polymer (A) containing high-density polyethylene to fall within a predetermined range, it is possible to improve both the film-forming ability and the thermal dimensional stability.

[0245] The density of the ethylene polymer (A), measured in accordance with JIS K 7112:1999, is preferably 0.937 g / cm from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-forming ability, heat resistance, mechanical properties, and rigidity. ３ More preferably, 0.940 g / cm ３ More preferably, 0.943 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.948 g / cm ３ More preferably, 0.950 g / cm ３ From the viewpoint of further improving film-forming properties, it is preferably 0.970 g / cm ３ or less, more preferably 0.965 g / cm ３ More preferably, 0.963 g / cm or less ３ More preferably, 0.960 g / cm ３ When two or more types of polymers are used as the ethylene polymer, the density of a mixture obtained by melt blending two or more types of ethylene polymers by a known method can be adopted.

[0246] The melt mass flow rate (MFR) of the ethylene polymer (A), measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and still more preferably 0.8 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and from the viewpoint of improving the stiffness of the biaxially oriented polyethylene film 100 while further improving the performance balance of film-formability and thermal dimensional stability, is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, even more preferably 4.0 g / 10 min or less, even more preferably 3.5 g / 10 min or less, even more preferably 3.0 g / 10 min or less, even more preferably 2.5 g / 10 min or less, and still more preferably 2.0 g / 10 min or less. When two or more types of polymers are used as the ethylene polymer (A), the MFR of a mixture obtained by melt-blending two or more types of polymers by a known method can be used.

[0247] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, the melting point of the ethylene polymer (A) measured by differential scanning calorimetry (DSC) is preferably 70° C. or higher, more preferably 75° C. or higher, even more preferably 90° C. or higher, even more preferably 95° C. or higher, even more preferably 100° C. or higher, even more preferably 110° C. or higher, even more preferably 120° C. or higher, and even more preferably 125° C. or higher, and is preferably 150° C. or lower, more preferably 140° C. or lower, even more preferably 135° C. or lower, and even more preferably 134° C. or lower. When two or more types of polymers are used as the ethylene polymer, the melting point of the ethylene polymer (A) is the peak temperature of the largest endothermic peak.

[0248] Furthermore, the ethylene polymer (A) of the fourth embodiment may further contain, in addition to the polyethylene described above, one or more selected from the group consisting of α-olefin copolymers (excluding ethylene-α-olefin copolymers) and ethylene-α-olefin copolymers, and more preferably contains an ethylene-α-olefin copolymer. From the viewpoint of further improving the balance of thermal dimensional stability, film-forming ability, and flexibility, the ethylene-α-olefin copolymer preferably contains one or more selected from the group consisting of ethylene-1-butene random copolymers and ethylene-propylene random copolymers, and more preferably contains an ethylene-1-butene random copolymer. The α-olefin copolymer contains one or more selected from the group consisting of propylene-ethylene random copolymers and 1-butene-propylene random copolymers.

[0249] The density of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7112:1999, is preferably 0.860 g / cm from the viewpoint of further improving the performance balance of thermal dimensional stability, film-forming property, and flexibility. ３ More preferably, 0.870 g / cm ３ More preferably, 0.880 g / cm ３ More preferably, 0.890 g / cm ３ or more, and preferably 0.920 g / cm ３ or less, more preferably 0.910 g / cm ３ More preferably, 0.900 g / cm ３ The following is the result.

[0250] The melt mass flow rate (MFR) of the ethylene-α-olefin copolymer, measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g, is preferably 0.1 g / 10 min or more, more preferably 0.2 g / 10 min or more, even more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and still more preferably 1.0 g / 10 min or more, from the viewpoint of further improving the performance balance of fluidity, film-formability, and thermal dimensional stability; and is preferably 5.0 g / 10 min or less, more preferably 4.5 g / 10 min or less, and even more preferably 4.0 g / 10 min or less, from the viewpoint of further improving the performance balance of film-formability and thermal dimensional stability while improving the stiffness of the biaxially oriented polyethylene film 100.

[0251] The melting point of the ethylene-α-olefin copolymer measured by differential scanning calorimetry (DSC) is preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and still more preferably 70° C. or higher, from the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-forming ability, and flowability, and is preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 100° C. or lower, even more preferably 90° C. or lower, and still more preferably 80° C. or lower.

[0252] The content of the ethylene-α-olefin copolymer in the biaxially stretched film layer 101 is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[0253] (Other Components) Various additives such as a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slipping agent, a nucleating agent, an antiblocking agent, an antistatic agent, an antifogging agent, a pigment, a dye, and an inorganic or organic filler may be added to the ethylene polymer composition constituting the biaxially stretched film layer 101, as needed, within a range that does not impair the object of the fourth embodiment.

[0254] (Method for preparing ethylene-based polymer composition) The ethylene-based polymer composition can be prepared, for example, by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0255] The biaxially stretched film layer 101 may be a single layer or may have a structure in which a plurality of layers made of an ethylene-based polymer composition are laminated, but it is necessary that it is biaxially stretched.

[0256] From the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and lightness, the thickness of the biaxially oriented film layer 101 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and still more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and still more preferably 25 μm or less.

[0257] In the biaxially oriented polyethylene film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the biaxially oriented polyethylene film 100 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and is preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0258] [Surface Resin Layer] The biaxially oriented polyethylene film 100 preferably further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101, from the viewpoint of imparting functions such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties to the film surface depending on the purpose. The surface resin layer 103 may be provided on both sides of the biaxially oriented film layer 101. By providing the surface resin layer 103 on both sides of the biaxially oriented film layer 101, different functions can be imparted to each surface of the film. When the surface resin layer 103 is provided on both sides of the biaxially oriented film layer 101, the surface resin layer 103 on one side preferably has heat sealing properties. The biaxially oriented polyethylene film 100 can be folded with this surface facing inward and the edges heat-sealed to form a bag shape. The surface resin layer 103 on the other side preferably has blocking resistance, antistatic properties, printability, and the like. In addition, the surface resin layer 103 is preferably provided as the outermost layer of the biaxially oriented polyethylene film 100, from the viewpoint of further improving the functions of the biaxially oriented polyethylene film 100, such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, and slip properties, depending on the purpose.

[0259] The surface resin layer 103 is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the biaxially oriented polyethylene film 100.

[0260] In the biaxially oriented polyethylene film 100, the thickness of the surface resin layer 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight, and is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, and even more preferably 3 μm or less, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, including film-formability, thermal dimensional stability, water vapor barrier property, mechanical properties, bag-formability, handleability, packaging suitability, cost, environmental compatibility, and light weight. Here, the thickness of the surface resin layer 103 refers to the thickness of the surface resin layer 103 provided on one side of the biaxially oriented film layer 101. That is, in the fourth embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the surface resin layer 103 indicates the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101.

[0261] In the biaxially oriented polyethylene film 100, the surface resin layer 103 is preferably a single layer, which can further simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0262] The surface resin layer 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the biaxially stretched polyethylene film 100 to be produced by a molding method such as co-extrusion, i.e., using a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the biaxially stretched polyethylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0263] The surface resin layer 103 may be subjected to a surface treatment in order to further improve the balance between printability and blocking resistance of the biaxially oriented polyethylene film 100. Specifically, the surface may be subjected to a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, or ozone treatment.

[0264] The surface resin layer 103 is composed of, for example, a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface resin layer 103 includes, for example, one or more selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, an ethylene-based polymer is preferred as the polyolefin constituting the surface resin layer 103 from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100 in terms of film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-forming ability, and flowability. Here, preferred embodiments of the ethylene-based polymer constituting the surface resin layer 103 are the same as those of the ethylene-based polymer described above. That is, the ethylene-based polymer constituting the surface resin layer 103 preferably contains the above-mentioned ethylene-based polymer (A). When the surface resin layers 103 are provided on both sides of the biaxially stretched film, the polyolefin-based resin compositions constituting the respective surface resin layers 103 may be the same or different.

[0265] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of polyolefin in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0266] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and flowability of the biaxially oriented polyethylene film 100, the content of the ethylene polymer in the polyolefin resin composition, i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition, i.e., the entire surface resin layer 103, is taken as 100% by mass.

[0267] (Other Components) Various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition constituting the surface resin layer 103, as needed, within a range that does not impair the object of the fourth embodiment.

[0268] (Method for preparing polyolefin-based resin composition) The polyolefin-based resin composition can be prepared, for example, by mixing or melting and kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0269] <Method for producing biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 can be obtained, for example, by co-extrusion molding an ethylene polymer composition for forming the biaxially oriented film layer 101 into a film, and then biaxially stretching the resulting film using a known biaxially oriented film production method such as simultaneous biaxial stretching, sequential biaxial stretching, or inflation biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be used. Examples of molding apparatus that can be used include a T-die extruder, a multilayer T-die extruder, an inflation molding machine, and a multilayer inflation molding machine. The biaxial stretching conditions can be, for example, those used for producing polyethylene films. For example, in the sequential biaxial stretching method, the stretching temperature in the MD direction is preferably in the range of 100°C to 145°C, more preferably 110°C to 140°C, and even more preferably 120°C to 135°C, and the stretching temperature in the TD direction is preferably in the range of 110°C to 190°C, more preferably 120°C to 170°C. The stretching ratio in the MD direction is preferably in the range of 4.5 to 7 times, and the stretching ratio in the TD direction is preferably in the range of 9 to 11 times. Specifically, the stretching temperature must be set at three stages: preheating temperature (the temperature at which the raw film is heated before stretching), stretching temperature (the temperature at which the stretching is performed), and heat setting temperature (the temperature at which the heat setting (annealing) is performed after stretching). The temperatures from preheating to heat setting can be within the above range. That is, the temperature can be set to the same level as that for stretching and heat setting from the preheating stage. The biaxially oriented polyethylene film 100 of the fourth embodiment contains the ethylene polymer (A), and therefore can be processed at higher temperatures, thereby further improving the heat resistance and therefore the thermal dimensional stability of the obtained biaxially oriented polyethylene film 100. The biaxially oriented polyethylene film 100 can also be obtained by separately molding the biaxially oriented film layer 101 and, if necessary, the surface resin layer 103, and laminating and molding these together.

[0270] <Uses of Biaxially Stretched Polyethylene Film / Packaging Material / Packaging Body> The biaxially oriented polyethylene film 100 of the fourth embodiment can be suitably used, specifically, as a packaging film. The biaxially oriented polyethylene film 100 of the fourth embodiment can also be suitably used as a packaging material. When used as a packaging material, the stretched polyethylene film 100 of the fourth embodiment may be used alone, or other layers may be laminated thereon. The other layers preferably further include one or more selected from the group consisting of an inorganic layer, a substrate layer, a coating layer, an adhesive layer, and a heat-seal layer, and more preferably, one or more selected from the group consisting of an inorganic layer and a coating layer. From the perspective of ease of recycling, when these layers are laminated, they are preferably formed from a polyethylene-based resin. The packaging material of the fourth embodiment can also be suitably used as a packaging body. The packaging body is used, for example, for packaging an item, and specifically includes the packaging material of the fourth embodiment and the item inside the packaging material. In particular, the packaging body of the fourth embodiment can be suitably used as a food packaging body and is used for the purpose of packaging food, and specifically includes the packaging material of the fourth embodiment and the food inside the packaging material. The food packaged in the food packaging body is not limited, but examples thereof include baked goods, rice crackers, snacks, sprinkles, grain powder, etc. Depending on the application, only a portion of the packaging body may be made of the packaging material of the fourth embodiment, or substantially the entire packaging body may be made of the packaging material of the fourth embodiment.

[0271] There are no particular limitations on the method for producing a package from the biaxially oriented polyethylene film 100 or the packaging material. Any method known in the field of packaging materials / packages, such as heat sealing or fusing, can be used.

[0272] The biaxially oriented polyethylene film 100 according to the fourth embodiment is preferably used for packaging that requires good film-forming properties and thermal dimensional stability. The form of the packaging can be, for example, a two-sided bag or a standing pouch (pouch packaging).

[0273] Furthermore, when a package (such as a food packaging bag) is constructed using the biaxially oriented polyethylene film 100 of the fourth embodiment or a packaging material, it is preferable that the corona-treated surface be the inner surface and the non-corona-treated surface be the outer surface. Furthermore, as described above, when another layer is laminated on the biaxially oriented polyethylene film 100, it is preferable that the layer be laminated on the corona-treated surface. That is, when a laminate using the biaxially oriented polyethylene film 100 of the fourth embodiment is used for a package (such as a food packaging bag), it is preferable that the biaxially oriented polyethylene film 100 of the fourth embodiment be the outermost layer of the package.

[0274] Although the fourth embodiment of the present invention has been described above, these are merely examples of the fourth embodiment of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the fourth embodiment described above, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0275] While the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention.

[0276] Additionally, the present invention also includes configurations that combine the configurations of the above-described embodiments.

[0277] Hereinafter, each embodiment of the present invention will be described in detail with reference to examples and comparative examples. However, each embodiment of the present invention is not limited to the description of these examples.

[0278] <<Examples 1A to 8A and Comparative Examples 1A to 4A>> The first embodiment will be described in detail below with reference to Examples 1A to 8A and Comparative Examples 1A to 4A. Note that the first embodiment is not limited to the descriptions of these examples.

[0279] <Raw Materials> The raw materials used in Examples 1A to 8A and Comparative Examples 1A to 4A are listed below. The density was measured in accordance with JIS K 7112:1999. The MFR was measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g. The melting point was measured using a differential scanning calorimeter (DSC). Specifically, using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments), a first differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min and a process of decreasing the temperature from 230°C to -50°C at a heating rate of 10°C / min was performed in a nitrogen stream. A second differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min was also performed. The peak temperature of the maximum endothermic peak in the second DSC curve was taken as the melting point (°C).

[0280] Linear low density polyethylene 1 (LLDPE1), density: 0.928 g / cm ３ , MFR: 1.9 g / 10 min, melting point: 126 ° C. Linear low density polyethylene 2 (LLDPE2), density: 0.937 g / cm ３ , MFR: 1.8 g / 10 min, melting point: 127 ° C. Linear low density polyethylene 3 (LLDPE3), density: 0.903 g / cm ３ , MFR: 3.8 g / 10 min, melting point: 98 ° C. High density polyethylene 1 (HDPE1), density: 0.964 g / cm ３ , MFR: 5.2 g / 10 min, melting point: 135 ° C. High density polyethylene 2 (HDPE2), density: 0.958 g / cm ３ , MFR: 1.0 g / 10 min, melting point: 133 ° C. High density polyethylene 3 (HDPE3), density: 0.955 g / cm ３ , MFR: 0.36 g / 10 min, melting point: 130 ° C. Ethylene / 1-butene random copolymer 1 (EBR1), density: 0.893 g / cm ３ , MFR: 3.6 g / 10 min, melting point: 77°C

[0281] <Production of Biaxially Stretched Polyethylene Film> For Examples 1A to 8A and Comparative Examples 1A to 4A, polyethylene films were extruded to the compositions shown in Table 1, and then biaxially stretched to produce biaxially oriented polyethylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. Corona treatment was also performed on the surface of the surface resin layer 2 shown in Table 1. Extruder: 60 mmφ multilayer T-die extruder (screw: L / D = 27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230 to 250°C, Processing speed: 15 m / min (take-up speed) MD stretching temperature [°C]: shown in Table 1 MD stretch ratio [times]: shown in Table 1 TD stretching temperature [°C]: shown in Table 1 TD stretch ratio [times]: shown in Table 1 Relaxation rate [%]: shown in Table 1 Here, the relaxation rate refers to the maximum stretch ratio width in the device settings divided by the tenter exit width. In Table 1, the notation "A / B / C" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature (temperature during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." In Table 1, the notation "A / B / C / D" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature 1 (temperature 1 during stretching) / stretching temperature 2 (temperature 2 during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." The MFR of the entire biaxially oriented polyethylene film obtained in each example was measured. In addition, in each example, the density of the resin before being made into a film was measured. The following evaluations were also performed. The obtained results are shown in Table 1. In Comparative Example 4A, the film broke during stretching, so a biaxially oriented polyethylene film could not be obtained.

[0282] <Dynamic Viscoelasticity Measurement (DMA)> Dynamic viscoelasticity measurement (DMA) was carried out on the biaxially stretched polyethylene film of each example as follows. The storage modulus E' in the MD direction at 100°C was measured on the biaxially stretched polyethylene film of each example using a dynamic viscoelasticity measuring device under the following measurement conditions. ＭＤ , loss modulus E'' ＭＤ , and E' ＭＤ and E''ＭＤ From the ratio, the loss tangent (tanδ ＭＤ [Measurement conditions] Apparatus: Dynamic viscoelasticity measuring apparatus RSA-G2, manufactured by TA Instruments Measurement temperature range: 30 to 130°C Heating rate: 5°C / min Strain: 0.1% Measurement mode: Tensile Frequency: 1 Hz Sample width: 5 mm Chuck distance: 20 mm Measurement direction: MD direction Also, under the same conditions as above except that the measurement direction was changed to TD direction, the storage modulus E' in the TD direction at 100°C was calculated. ＴＤ , loss modulus E'' ＴＤ , and E' ＴＤ and E'' ＴＤ From the ratio, the loss tangent (tanδ ＴＤ ) was calculated.

[0283] <Tensile modulus> A test piece of 15 mm x 15 cm was cut out from the biaxially stretched polyethylene film of each example. Then, the tensile modulus T of the test piece in the MD direction was measured using a tensile tester manufactured by Orientec Co., Ltd. in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min. １ and tensile modulus in the TD direction T ２ From the obtained values, T １ and T ２ The total value was calculated.

[0284] <Moisture permeability> The moisture permeability (g / (m ２ The elapsed time (day) was measured in accordance with JIS Z 0208:1976.

[0285] <Stress at Break> The stress at break (MPa) in each MD and TD direction of the biaxially oriented polyethylene film of each example was measured using a tensile tester in accordance with JIS K7127:1999. Each biaxially oriented polyethylene film of each example was cut into a dumbbell-shaped test piece in accordance with the JIS standard. The stress at break (MPa) in each MD and TD direction was measured by pulling the film in each direction under the following conditions: a chuck distance of 50 mm, a pulling speed of 300 mm / min, 23°C, and a relative humidity of 50% RH. The stress at break was calculated by dividing the tensile force at the break point in the tensile test by the initial cross-sectional area of ​​the test piece. The sum of the stress at break in the MD and TD directions was calculated from the obtained value.

[0286] <Heat shrinkage of biaxially oriented polyethylene film at 100°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 100°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 100°C for 15 minutes. At this time, the test piece was heated in a hot air circulation thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １００ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１００ [%] is multiplied by 100 (10-MD １００ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １００ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１００ [%] = 100 x (10 - TD １００ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 100°C.

[0287] <Heat shrinkage of biaxially oriented polyethylene film at 120°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 120°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 120°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １２０ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１２０ [%] is multiplied by 100 (10-MD １２０ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １２０ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１２０ [%] = 100 x (10 - TD １２０ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 120°C.

[0288]

[0289] <<Examples 1B to 8B and Comparative Examples 1B to 4B>> The second embodiment will be described in detail below with reference to Examples 1B to 8B and Comparative Examples 1B to 4B. Note that the second embodiment is not limited to the descriptions of these examples.

[0290] <Raw Materials> The raw materials used in Examples 1B to 8B and Comparative Examples 1B to 4B are listed below. Density was measured in accordance with JIS K 7112:1999. MFR was measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g. Melting point was measured using a differential scanning calorimeter (DSC). Specifically, using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments), a first differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min and a process of decreasing the temperature from 230°C to -50°C at a heating rate of 10°C / min was performed in a nitrogen stream. The second differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min was also performed. The peak temperature of the maximum endothermic peak in the second DSC curve was taken as the melting point (°C).

[0291] Linear low density polyethylene 1 (LLDPE1), density: 0.928 g / cm ３ , MFR: 1.9 g / 10 min, melting point: 126 ° C. Linear low density polyethylene 2 (LLDPE2), density: 0.937 g / cm ３ , MFR: 1.8 g / 10 min, melting point: 127 ° C. Linear low density polyethylene 3 (LLDPE3), density: 0.903 g / cm ３ , MFR: 3.8 g / 10 min, melting point: 98 ° C. High density polyethylene 1 (HDPE1), density: 0.964 g / cm ３ , MFR: 5.2 g / 10 min, melting point: 135 ° C. High density polyethylene 2 (HDPE2), density: 0.958 g / cm ３ , MFR: 1.0 g / 10 min, melting point: 133 ° C. High density polyethylene 3 (HDPE3), density: 0.955 g / cm ３ , MFR: 0.36 g / 10 min, melting point: 130 ° C. Ethylene / 1-butene random copolymer 1 (EBR1), density: 0.893 g / cm ３ , MFR: 3.6 g / 10 min, melting point: 77°C

[0292] <Production of biaxially oriented polyethylene film> For Examples 1B to 8B and Comparative Examples 1B to 4B, polyethylene films were extruded to the compositions shown in Table 2, and then biaxially stretched to produce biaxially oriented polyethylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. In addition, a corona treatment was performed on the surface on the surface resin layer 2 side in Table 2. The corona treatment was performed by adjusting the discharge power to a discharge amount of 20 W min / m. ２ The settings were as follows: Extruder: 60 mmφ multilayer T-die extruder (screw: L / D = 27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230 to 250°C, Processing speed: 15 m / min (take-up speed) MD direction stretching temperature [°C]: shown in Table 2 MD direction stretching ratio [times]: shown in Table 2 TD direction stretching temperature [°C]: shown in Table 2 TD direction stretching ratio [times]: shown in Table 2 Relaxation rate [%]: shown in Table 2 Here, the relaxation rate refers to the maximum stretching ratio width in the device settings divided by the tenter outlet width. In addition, the notation "A / B / C" for the stretching temperature in Table 2 means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature (temperature during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." Furthermore, the notation "A / B / C / D" for the stretching temperatures in Table 2 means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature 1 (temperature 1 during stretching) / stretching temperature 2 (temperature 2 during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." The MFR of the entire biaxially oriented polyethylene film obtained in each example was measured. Furthermore, in each example, the density of the resin before being made into a film was measured. The following evaluations were also carried out. The obtained results are shown in Table 2. In Comparative Example 4B, the film broke during stretching, and therefore a biaxially oriented polyethylene film could not be obtained.

[0293] <Thermomechanical analysis (TMA)> For each biaxially stretched polyethylene film, the average coefficient of linear expansion (α) in the machine direction at 100°C and the elongation (%) in the machine direction at 100°C were measured as follows, with reference to JIS K 7197:2012. [Measurement conditions] Measurement device: TMA Q400 (manufactured by TA Instruments) Measurement mode: Tensile mode Test piece width: 4 mm Initial chuck distance: 8 mm Measurement direction: Machine direction Load: 10 g / 4 mm Heating rate: 10°C / min Measurement temperature range: 20 to 100°C The average coefficient of linear expansion (α) was calculated using the following formula (1): Formula (1): Average coefficient of linear expansion (α) = 1 / L ０ ・[{L(t ２ ) - L(t １ ) / (t ２ -t １ )] In formula (1), L ０、 T １ , T ２ , L(t １ ) and L(t ２ ) is expressed as follows: L ０ : Initial chuck distance 8 mm t １ : 20 ° C. ２ : 100 ° C. L (t １ ): temperature t １ Distance between chucks (mm) L (t ２ ): temperature t ２ The MD elongation at 100°C was calculated using the following formula (2): Formula (2): MD elongation at 100°C (%) = 100 × (chuck distance at 100°C - initial chuck distance) / initial chuck distance

[0294] <Tensile modulus> A test piece of 15 mm x 15 cm was cut out from the biaxially stretched polyethylene film of each example. Then, the tensile modulus T of the test piece in the MD direction was measured using a tensile tester manufactured by Orientec Co., Ltd. in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min. １ and tensile modulus in the TD direction T ２ From the obtained values, T １ and T ２The total value was calculated.

[0295] <Moisture permeability> The moisture permeability (g / (m ２ The elapsed time (day) was measured in accordance with JIS Z 0208:1976.

[0296] <Stress at Break> The stress at break (MPa) in each MD and TD direction of the biaxially oriented polyethylene film of each example was measured using a tensile tester in accordance with JIS K7127:1999. Each biaxially oriented polyethylene film of each example was cut into a dumbbell-shaped test piece in accordance with the JIS standard. The stress at break (MPa) in each MD and TD direction was measured by pulling the film in each direction under the following conditions: a chuck distance of 50 mm, a pulling speed of 300 mm / min, 23°C, and a relative humidity of 50% RH. The stress at break was calculated by dividing the tensile force at the break point in the tensile test by the initial cross-sectional area of ​​the test piece. The sum of the stress at break in the MD and TD directions was calculated from the obtained value.

[0297] <Heat shrinkage of biaxially oriented polyethylene film at 100°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 100°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 100°C for 15 minutes. At this time, the test piece was heated in a hot air circulation thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １００ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１００ [%] is multiplied by 100 (10-MD １００ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １００ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１００ [%] = 100 x (10 - TD １００The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 100°C.

[0298] <Heat shrinkage of biaxially oriented polyethylene film at 120°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 120°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 120°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １２０ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１２０ [%] is multiplied by 100 (10-MD １２０ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １２０ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１２０ [%] = 100 x (10 - TD １２０ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 120°C.

[0299] <Heat-sealing strength> Two biaxially oriented polyethylene films of each example cut to a width of 15 mm were laminated together so that the surface resin layer 1 sides overlapped each other, and the laminate was sandwiched between 12 μm-thick biaxially oriented polyethylene terephthalate films. Using a heat-sealing tester (TP-701-B, manufactured by Tester Sangyo Co., Ltd.), the heat-sealing strength was measured at temperatures of 110°C, 120°C, 125°C, 130°C, 135°C, 140°C, and 150°C under a pressure of 2.0 kgf / cm. ２ After each laminated film was obtained by heat sealing under the conditions of 1.0 second, 1.0 second sealing time, the two biaxially oriented polyethylene films were each peeled under the conditions of 90° peeling, a peeling speed of 300 mm / min, and tension in the MD direction, and the peel strength at this time was recorded as the heat sealing strength (N / 15 mm).

[0300]

[0301] <<Examples 1C to 8C and Comparative Examples 1C to 3C>> The third embodiment will be described in detail below with reference to Examples 1C to 8C and Comparative Examples 1C to 3C. Note that the third embodiment is not limited to the descriptions of these examples.

[0302] <Raw Materials> The raw materials used in Examples 1C to 8C and Comparative Examples 1C to 3C are listed below. The density was measured in accordance with JIS K 7112:1999. The MFR was measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g. The melting point was measured using a differential scanning calorimeter (DSC). Specifically, using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments), a first differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min and a process of decreasing the temperature from 230°C to -50°C at a heating rate of 10°C / min was performed in a nitrogen stream. A second differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min was also performed. The peak temperature of the maximum endothermic peak in the second DSC curve was taken as the melting point (°C).

[0303] Linear low density polyethylene 1 (LLDPE1), density: 0.928 g / cm ３ , MFR: 1.9 g / 10 min, melting point: 126 ° C. Linear low density polyethylene 2 (LLDPE2), density: 0.937 g / cm ３ , MFR: 1.8 g / 10 min, melting point: 127 ° C. Linear low density polyethylene 3 (LLDPE3), density: 0.903 g / cm ３ , MFR: 3.8 g / 10 min, melting point: 98 ° C. High density polyethylene 1 (HDPE1), density: 0.964 g / cm ３ , MFR: 5.2 g / 10 min, melting point: 135 ° C. High density polyethylene 2 (HDPE2), density: 0.958 g / cm ３ , MFR: 1.0 g / 10 min, melting point: 133 ° C. High density polyethylene 3 (HDPE3), density: 0.955 g / cm ３, MFR: 0.36 g / 10 min, melting point: 130 ° C. Ethylene / 1-butene random copolymer 1 (EBR1), density: 0.893 g / cm ３ , MFR: 3.6 g / 10 min, melting point: 77°C

[0304] <Production of Biaxially Stretched Polyethylene Film> For Examples 1C to 8C and Comparative Examples 1C to 3C, polyethylene films were extruded to the compositions shown in Table 3, and then biaxially stretched to produce biaxially oriented polyethylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. Corona treatment was also performed on the surface of the surface resin layer 2 side shown in Table 3. Extruder: 60 mmφ multilayer T-die extruder (screw: L / D = 27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230 to 250°C, Processing speed: 15 m / min (take-up speed) MD stretching temperature [°C]: shown in Table 3 MD stretch ratio [times]: shown in Table 3 TD stretching temperature [°C]: shown in Table 3 TD stretch ratio [times]: shown in Table 3 Relaxation rate [%]: shown in Table 3 Here, the relaxation rate refers to the maximum stretch ratio width in the device settings divided by the tenter exit width. In Table 3, the notation "A / B / C" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature (temperature during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." In Table 3, the notation "A / B / C / D" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature 1 (temperature 1 during stretching) / stretching temperature 2 (temperature 2 during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." The MFR of the entire biaxially oriented polyethylene film obtained in each example was measured. In addition, in each example, the density of the resin before being made into a film was measured. The following evaluations were also performed. The obtained results are shown in Table 3. In Comparative Example 3C, the film broke during stretching, so a biaxially oriented polyethylene film could not be obtained.

[0305] <Differential Scanning Calorimetry (DSC)> Differential scanning calorimetry (DSC) was performed on the biaxially oriented polyethylene film of each example as follows. Using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments), the biaxially oriented polyethylene film of each example was subjected to the following consecutive differential scanning calorimetry runs in a nitrogen atmosphere: a first run (1st Run) consisting of a process of increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 200°C for 5 minutes, and a process of decreasing the temperature from 200°C to -50°C at a heating rate of 10°C / min; and a second run (2nd Run) consisting of a process of maintaining the temperature at -50°C for 5 minutes (cooling) and a process of increasing the temperature from -50°C to 200°C at a heating rate of 10°C / min. The peak temperature of the maximum endothermic peak of DSC curve 1 in the 1st run is Tm １ (°C), and the peak temperature of the maximum endothermic peak of DSC curve 2 in the 2nd run is Tm ２ The maximum exothermic peak observed in DSC curve 1 during the cooling process of the first run was taken as the crystallization peak, and the temperature at the apex of the crystallization peak was taken as the crystallization temperature Tc (°C). In DSC curve 2 during the second run, an endothermic peak A was observed in the range of 20°C to 150°C, and the heat of fusion of endothermic peak A was taken as ΔH (J / g). The obtained Tm １ , Tm ２ and Tc, (Tm １ -Tm ２ ) (°C) and (Tm ２ -Tc) (°C) was calculated for each.

[0306] <Tensile modulus> A test piece of 15 mm x 15 cm was cut out from the biaxially stretched polyethylene film of each example. Then, the tensile modulus T of the test piece in the MD direction was measured using a tensile tester manufactured by Orientec Co., Ltd. in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min. １ and tensile modulus in the TD direction T ２ From the obtained values, T １ and T ２ The total value was calculated.

[0307] <Moisture permeability> The moisture permeability (g / (m ２ The elapsed time (day) was measured in accordance with JIS Z 0208:1976.

[0308] <Stress at Break> The stress at break (MPa) in each MD and TD direction of the biaxially oriented polyethylene film of each example was measured using a tensile tester in accordance with JIS K7127:1999. Each biaxially oriented polyethylene film of each example was cut into a dumbbell-shaped test piece in accordance with the JIS standard. The stress at break (MPa) in each MD and TD direction was measured by pulling the film in each direction under the following conditions: a chuck distance of 50 mm, a pulling speed of 300 mm / min, 23°C, and a relative humidity of 50% RH. The stress at break was calculated by dividing the tensile force at the break point in the tensile test by the initial cross-sectional area of ​​the test piece. The sum of the stress at break in the MD and TD directions was calculated from the obtained value.

[0309] <Heat shrinkage of biaxially oriented polyethylene film at 100°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 100°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 100°C for 15 minutes. At this time, the test piece was heated in a hot air circulation thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １００ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１００ [%] is multiplied by 100 (10-MD １００ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １００ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１００ [%] = 100 x (10 - TD １００ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 100°C.

[0310] <Heat shrinkage of biaxially oriented polyethylene film at 120°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 120°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 120°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １２０ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１２０ [%] is multiplied by 100 (10-MD １２０ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １２０ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１２０ [%] = 100 x (10 - TD １２０ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 120°C.

[0311]

[0312] <<Examples 1D to 8D and Comparative Examples 1D to 4D>> The fourth embodiment will be described in detail below with reference to Examples 1D to 8D and Comparative Examples 1D to 4D. Note that the fourth embodiment is not limited to the descriptions of these examples.

[0313] <Raw Materials> The raw materials used in Examples 1D to 8D and Comparative Examples 1D to 4D are listed below. The density was measured in accordance with JIS K 7112:1999. The MFR was measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2160 g. The melting point was measured using a differential scanning calorimeter (DSC). Specifically, using a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments), a first differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min and a process of decreasing the temperature from 230°C to -50°C at a heating rate of 10°C / min was performed in a nitrogen stream, and a second differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a heating rate of 10°C / min was performed in succession. The peak temperature of the maximum endothermic peak in the second DSC curve was taken as the melting point (°C).

[0314] Linear low density polyethylene 1 (LLDPE1), density: 0.928 g / cm ３ , MFR: 1.9 g / 10 min, melting point: 126 ° C. Linear low density polyethylene 2 (LLDPE2), density: 0.937 g / cm ３ , MFR: 1.8 g / 10 min, melting point: 127 ° C. Linear low density polyethylene 3 (LLDPE3), density: 0.903 g / cm ３ , MFR: 3.8 g / 10 min, melting point: 98 ° C. High density polyethylene 1 (HDPE1), density: 0.964 g / cm ３ , MFR: 5.2 g / 10 min, melting point: 135 ° C. High density polyethylene 2 (HDPE2), density: 0.958 g / cm ３ , MFR: 1.0 g / 10 min, melting point: 133 ° C. High density polyethylene 3 (HDPE3), density: 0.955 g / cm ３ , MFR: 0.36 g / 10 min, melting point: 130 ° C. Ethylene / 1-butene random copolymer 1 (EBR1), density: 0.893 g / cm ３ , MFR: 3.6 g / 10 min, melting point: 77°C

[0315] <Production of Biaxially Stretched Polyethylene Film> For Examples 1D to 8D and Comparative Examples 1D to 4D, polyethylene films were extruded to the compositions shown in Table 4, and then biaxially stretched to produce biaxially oriented polyethylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. Corona treatment was also performed on the surface of the surface resin layer 2 side shown in Table 4. Extruder: 60 mmφ multilayer T-die extruder (screw: L / D = 27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230 to 250°C, Processing speed: 15 m / min (take-up speed) MD stretching temperature [°C]: shown in Table 4 MD stretch ratio [times]: shown in Table 4 TD stretching temperature [°C]: shown in Table 4 TD stretch ratio [times]: shown in Table 4 Relaxation rate [%]: shown in Table 4 Here, the relaxation rate refers to the maximum stretch ratio width in the device settings divided by the tenter exit width. In Table 4, the notation "A / B / C" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature (temperature during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." In Table 4, the notation "A / B / C / D" for the stretching temperature means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature 1 (temperature 1 during stretching) / stretching temperature 2 (temperature 2 during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." The MFR of the entire biaxially oriented polyethylene film obtained in each example was measured. In addition, in each example, the density of the resin before being made into a film was measured. The following evaluations were also performed. The obtained results are shown in Table 4. In Comparative Example 4D, the film broke during stretching, so a biaxially oriented polyethylene film could not be obtained.

[0316] [Z-average molecular weight (Mz), weight-average molecular weight (Mw), number-average molecular weight (Mn), and z+1-average molecular weight (Mz+1) of ethylene-based polymers constituting biaxially stretched polyethylene films] The z-average molecular weight (Mz), weight-average molecular weight (Mw), number-average molecular weight (Mn), and z+1-average molecular weight (Mz+1) of ethylene-based polymers constituting biaxially stretched polyethylene films were measured by gel permeation chromatography (GPC). The biaxially stretched polyethylene film obtained in each example was cut into pieces of approximately 5.0 mm x 5.0 mm, added to a mobile phase for GPC measurement, heated at 145°C, stirred, and dissolved, and the volume was adjusted to the following concentration to obtain a sample. The GPC method was performed using a gel permeation chromatograph (Tosoh Corporation, HLC-8321 GPC / HT type) as follows: The separation columns consisted of two TSKgel GNH6-HT columns and two TSKgel GNH6-HTL columns, each with a diameter of 7.5 mm and a length of 300 mm. The column temperature was 140°C, the mobile phase consisted of o-dichlorobenzene and 0.025% by mass of BHT as an antioxidant, and the flow rate was 1.0 mL / min. The sample concentration was 0.1% (w / v), the sample injection volume was 400 μL, and a differential refractometer was used as the detector. The molecular weight was calculated as polyethylene equivalent molecular weight using monodisperse polystyrene as the standard. From the obtained values, Mz, Mw, Mn, Mz+1, and Mw / Mn were calculated.

[0317] <Tensile modulus> A test piece of 15 mm x 15 cm was cut out from the biaxially stretched polyethylene film of each example. Then, the tensile modulus T of the test piece in the MD direction was measured using a tensile tester manufactured by Orientec Co., Ltd. in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min. １ and tensile modulus in the TD direction T ２ From the obtained values, T １ and T ２ The total value was calculated.

[0318] <Moisture permeability> The moisture permeability (g / (m ２ The elapsed time (day) was measured in accordance with JIS Z 0208:1976.

[0319] <Stress at Break and Elongation at Break> For each biaxially oriented polyethylene film, the stress at break (MPa) and elongation at break (%) in the MD and TD directions were measured using a tensile tester in accordance with JIS K7127:1999. Each biaxially oriented polyethylene film was cut into a dumbbell-shaped test piece in accordance with the JIS standard, and the test piece was stretched in the MD and TD directions under the following conditions: a chuck distance of 50 mm, a pulling speed of 300 mm / min, 23°C, and a relative humidity of 50% RH. The elongation at break represents the elongation of the test piece just before break between designated gauge points in the tensile test. The stress at break is the tensile force at the break point during the tensile test divided by the initial cross-sectional area of ​​the test piece. From the obtained values, the sum of the stress at break in the MD and TD directions and the sum of the elongation at break in the MD and TD directions were calculated.

[0320] <Heat shrinkage of biaxially oriented polyethylene film at 100°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 100°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 100°C for 15 minutes. At this time, the test piece was heated in a hot air circulation thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １００ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１００ [%] is multiplied by 100 (10-MD １００ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １００ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１００ [%] = 100 x (10 - TD １００ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 100°C.

[0321] <Heat shrinkage of biaxially oriented polyethylene film at 120°C> The heat shrinkage of the biaxially oriented polyethylene film in the MD and TD directions at 120°C was measured in accordance with JIS C2151:2019. A 10 cm x 10 cm test piece was cut out from the biaxially oriented polyethylene film of each example. The test piece was then heat-treated at 120°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length in the MD direction of the test piece after heat treatment was determined as the MD length. １２０ [cm], and the thermal shrinkage rate X in the MD direction ＭＤ１２０ [%] is multiplied by 100 (10-MD １２０ The length of the test piece in the TD direction after the heat treatment was calculated by the following formula: １２０ [cm], and the thermal shrinkage rate X in the TD direction ＴＤ１２０ [%] = 100 x (10 - TD １２０ The above measurements were each carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially stretched polyethylene film at 120°C.

[0322] <Evaluation of processability> The biaxially oriented polyethylene film of each example was continuously stretched for 30 minutes in the above-mentioned <Production of biaxially oriented polyethylene film>, and the presence or absence of breakage of the film was evaluated according to the following criteria. (Criteria) A (best): The film did not break. B (good): The film broke once. C (poor): The film broke two or more times.

[0323]

[0324] This application claims priority based on Japanese Patent Application Nos. 2023-198983, 2023-199019, 2023-198975, and 2023-198966, all filed on November 24, 2023, the disclosures of which are incorporated herein in their entireties.

[0325] 100 Biaxially stretched polyethylene film 101 Biaxially stretched film layer 103 Surface resin layer

Claims

1. A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene polymer (A), which has a storage modulus E' in the MD direction at 100°C, measured using a dynamic mechanical analyzer (DMA) under the conditions of a frequency of 1 Hz, a heating rate of 5°C / min, a strain of 0.1%, a tensile mode, a chuck distance of 20 mm, and a sample width of 5 mm. ＭＤ is 50 MPa or more, and the storage modulus E' in the TD direction at 100°C is ＴＤ A biaxially oriented polyethylene film having a modulus of 100 MPa or more.

2. The biaxially oriented polyethylene film according to claim 1, which has a loss tangent (tan δ) of 0.25 or more in the TD direction at 100°C, measured using dynamic mechanical analysis (DMA) under the conditions of a frequency of 1 Hz, a heating rate of 5°C / min, a strain of 0.1%, a tensile mode, a chuck distance of 20 mm, and a sample width of 5 mm.

3. A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene-based polymer (A), wherein the average linear expansion coefficient (α) in the MD direction is 4.5×10 or less when measured by thermomechanical analysis (TMA) according to JIS K 7197:2012 under the conditions of a heating rate of 10°C / min, a tensile mode, a load of 10g / 4mm, an initial chuck distance of 8mm, and a test piece width of 4mm in a measurement temperature range of 20°C to 100°C, as calculated by the following formula (1): －４ (1 / °C) or less. ０ ・[{L(t ２ ) -L(t １ )} / (t ２ -t １ )] In formula (1), L ０、 T １ , T ２ , L(t １ ) and L(t ２ ) is expressed as follows: L ０ : Initial chuck distance 8 mm t １ :20℃ t ２ : 100 ° C. L (t １ ): temperature t １ Distance between chucks (mm) L (t ２ ): temperature t ２ Distance between chucks (mm) 4. The biaxially oriented polyethylene film according to claim 3, wherein the elongation in the MD direction at 100°C is 3.5% or less when measured by thermomechanical analysis (TMA) according to JIS K 7197:2012 under the conditions of a temperature range of 20°C to 100°C, a heating rate of 10°C / min, a tensile mode, a load of 10g / 4mm, an initial chuck distance of 8mm, and a test piece width of 4mm.

5. The biaxially oriented polyethylene film according to claim 3 or 4, which has a heat fusion strength of 1.0 N / 15 mm or less at 130°C, as measured in accordance with the following <Heat fusion strength>. <Heat fusion strength> Two pieces of the biaxially oriented polyethylene film cut to a width of 15 mm are laminated together, sandwiched between a biaxially oriented polyethylene terephthalate film having a thickness of 12 μm, and measured at a temperature of 130°C and a pressure of 2.0 kgf / cm using a heat seal tester. ２ After obtaining a laminated film by heat sealing under conditions of 1.0 second and a sealing time of 1.0 second, the two biaxially oriented polyethylene films were peeled off under conditions of 90° peeling, a peeling speed of 300 mm / min and pulling in the MD direction, and the peel strength at this time was recorded as the heat sealing strength (N / 15 mm).

6. A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene polymer (A), which, when the following steps are successively performed using a differential scanning calorimeter (DSC): a first differential scanning calorimeter measurement (1st Run) consisting of a process of heating from -50°C to 200°C at a heating rate of 10°C / min, an isothermal process of maintaining at 200°C for 5 minutes, and a process of cooling from 200°C to -50°C at a heating rate of 10°C / min; a process of maintaining at -50°C for 5 minutes; and a second differential scanning calorimeter measurement (2nd Run) consisting of a process of heating from -50°C to 200°C at a heating rate of 10°C / min, In a DSC curve 2 obtained by the second differential scanning calorimetry, an endothermic peak A is observed in the range of 20°C or more and 150°C or less, and the heat of fusion (ΔH) of the endothermic peak A is 175 J / g or more and 250 J / g or less.

7. The melting point (Tm １ ) from the melting point (Tm ２ ) minus (Tm １ -Tm ２ 7. The biaxially oriented polyethylene film according to claim 6, wherein the temperature difference (Tc) is 0.0° C. or higher.

8. When the exothermic peak observed in the DSC curve 1 obtained in the first cooling step is defined as the crystallization peak, and the temperature at the top of the crystallization peak is defined as the crystallization temperature (Tc), (Tm ２ The biaxially oriented polyethylene film according to claim 6 or 7, wherein Tc) is 12.1 ° C. or more.

9. The melting point (Tm ２ 9. The biaxially oriented polyethylene film according to any one of claims 6 to 8, wherein the temperature (T) of the biaxially oriented polyethylene film is 130°C or higher.

10. A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene-based polymer (A), wherein the ethylene-based polymer (A) has a z-average molecular weight (Mz) of 800,000 or more and 4,000,000 or less in terms of polystyrene, as measured by gel permeation chromatography (GPC).

11. The biaxially oriented polyethylene film according to claim 10, wherein the ethylene polymer (A) has a weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) of 130,000 or more and 1,000,000 or less.

12. The biaxially oriented polyethylene film according to claim 10 or 11, wherein the ethylene polymer (A) has a number average molecular weight (Mn) of 5,000 or more and 200,000 or less in terms of polystyrene as measured by gel permeation chromatography (GPC).

13. The biaxially oriented polyethylene film according to any one of claims 10 to 12, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the ethylene polymer (A) in terms of polystyrene, as measured by gel permeation chromatography (GPC), is 30.0 or less.

14. The density of the ethylene polymer (A) measured in accordance with JIS K 7112:1999 is 0.937 g / cm ３ 0.970g / cm or more ３ The biaxially oriented polyethylene film according to any one of claims 10 to 13, wherein:

15. The biaxially oriented polyethylene film according to any one of claims 10 to 14, wherein the melt mass flow rate (MFR) of the ethylene polymer (A), measured in accordance with JIS K 7210:1999 under conditions of 190°C and a load of 2,160 g, is 0.1 g / 10 min or more and 5.0 g / 10 min or less.

16. The biaxially oriented polyethylene film according to any one of claims 10 to 15, wherein the sum of the elongation at break in the TD direction and the elongation at break in the MD direction, measured in accordance with JIS K7127:1999, is 200% or less.

17. A biaxially oriented polyethylene film according to any one of claims 1 to 16, wherein the ethylene-based polymer (A) contains high-density polyethylene, and when the entire biaxially oriented film layer is taken as 100% by mass, the content of the high-density polyethylene in the biaxially oriented film layer is 60% by mass or more.

18. The tensile modulus T in the MD direction is measured using a tensile tester in accordance with JIS K7127:1999 under the conditions of a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. １ and the tensile modulus in the TD direction T ２ The biaxially oriented polyethylene film according to any one of claims 1 to 17, wherein the total value of is 2500 MPa or more and 9000 MPa or less.

19. A biaxially oriented polyethylene film according to any one of claims 1 to 18, which has a heat shrinkage rate in the MD direction of 4.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019.

20. A biaxially oriented polyethylene film according to any one of claims 1 to 19, which has a thermal shrinkage rate in the TD direction of 7.0% or less when heated at 100°C for 15 minutes, as measured in accordance with JIS C2151:2019.

21. A biaxially oriented polyethylene film according to any one of claims 1 to 20, which has a heat shrinkage rate in the MD direction of 9.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019.

22. A biaxially oriented polyethylene film according to any one of claims 1 to 21, which has a heat shrinkage rate in the TD direction of 30.0% or less when heated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019.

23. The moisture permeability measured in accordance with JIS Z 0208:1976 is 12.0 g / (m ２ The biaxially oriented polyethylene film according to any one of claims 1 to 22, wherein the stretching time is 100 min-100 min.

24. A biaxially oriented polyethylene film according to any one of claims 1 to 23, in which the sum of the stress at break in the TD direction and the stress at break in the MD direction, measured in accordance with JIS K7127:1999, is 210 MPa or more.

25. The biaxially oriented polyethylene film according to any one of claims 1 to 24, further comprising a surface resin layer on at least one side of the biaxially oriented film layer.

26. The biaxially oriented polyethylene film according to claim 25, wherein the surface resin layer comprises an ethylene-based polymer.

27. A biaxially oriented polyethylene film as described in claim 26, wherein the content of the ethylene polymer in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is taken as 100% by mass.

28. The biaxially oriented polyethylene film according to any one of claims 25 to 27, wherein the thickness of the surface resin layer is from 0.1 μm to 10 μm.

29. The biaxially oriented polyethylene film according to any one of claims 1 to 28, wherein the thickness of the biaxially oriented film layer is 5 µm or more and 100 µm or less.

30. A biaxially oriented polyethylene film according to any one of claims 1 to 29, in which the ratio of the thickness of the biaxially oriented film layer to the total thickness of the biaxially oriented polyethylene film is 50% or more and 100% or less.

31. The biaxially oriented polyethylene film according to any one of claims 1 to 30, which is a packaging film.

32. A packaging material comprising the biaxially oriented polyethylene film according to any one of claims 1 to 31.

33. The packaging material according to claim 32, further comprising one or more layers selected from the group consisting of an inorganic layer and a coating layer on at least one surface of the biaxially oriented polyethylene film.

34. A package comprising the packaging material according to claim 32 or 33 and an article within said packaging material.

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