Biaxially stretched polyethylene film, packaging material and package

Abstract

To provide a biaxially stretched polyethylene film having improved performance balance between film-forming property and thermal dimensional stability.SOLUTION: A biaxially stretched polyethylene film (100) includes a biaxially stretched film layer (101) containing an ethylenic polymer (A), wherein a z average molecular weight (Mz) in terms of polystyrene measured by gel permeation chromatography (GPC) of the ethylenic polymer (A) is 800,000 or more and 4,000,000 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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, and is characterized in that 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 made of a polyethylene resin composition containing polyethylene and a petroleum resin, is a uniaxially stretched film or a biaxially stretched film, and has an areal stretch 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 stretch ratio and has high strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-079510 [Patent Document 2] JP 2023-031061 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a biaxially oriented polyethylene film having an improved balance of film-formability and thermal dimensional stability. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and have found that the performance balance between film-forming properties and thermal dimensional stability can be improved by controlling the z-average molecular weight (Mz) of the ethylene polymer contained in the biaxially oriented polyethylene film to fall within a predetermined range.

[0008] That is, according to the present invention, there are provided the following biaxially oriented polyethylene film, packaging material, and packaging article.

[0009] [1] A biaxially oriented polyethylene film having a biaxially oriented film layer containing an ethylene polymer (A), The biaxially oriented polyethylene film, wherein the ethylene polymer (A) has a z-average molecular weight (Mz) in terms of polystyrene measured by gel permeation chromatography (GPC) of 800,000 or more and 4,000,000 or less. [2] The biaxially oriented polyethylene film according to [1], 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. [3] The biaxially oriented polyethylene film according to [1] or [2], 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 measured by gel permeation chromatography (GPC). [4] The biaxially oriented polyethylene film according to any one of [1] to [3], 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. [5] The density of the ethylene polymer (A) measured in accordance with JIS K 7112:1999 is 0.937 g / cm 3 More than 0.970g / cm 3 The biaxially stretched polyethylene film according to any one of [1] to [4] below. [6] The biaxially stretched polyethylene film according to any one of [1] to [5], 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 under conditions of 190°C and a load of 2160 g. [7] The ethylene polymer (A) contains high-density polyethylene, The biaxially oriented polyethylene film according to any one of [1] to [6], 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. [8] The tensile modulus in the MD direction, T, is measured using a tensile tester at a temperature of 23±2°C, 50±5% RH, and a tensile speed of 5mm / min. 1 and tensile modulus in the TD direction T 2 The biaxially stretched polyethylene film according to any one of [1] to [7], wherein the total value of is 2500 MPa or more and 9000 MPa or less. [9] The biaxially oriented polyethylene film according to any one of [1] to [8], 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.

[10] The biaxially oriented polyethylene film according to any one of [1] to [9], which has a heat 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.

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

[10] , which has a heat shrinkage rate in the MD direction of 9.0% or less when heat-treated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019.

[12] The biaxially oriented polyethylene film according to any one of [1] to

[11] , which has a heat shrinkage rate in the TD direction of 30.0% or less when heat-treated at 120°C for 15 minutes, as measured in accordance with JIS C2151:2019.

[13] The moisture permeability measured according to JIS Z 0208:1976 is 12.0g / (m 2 The biaxially stretched polyethylene film according to any one of [1] to

[12] , wherein the duration is 1.0 days or less.

[14] The biaxially oriented polyethylene film according to any one of [1] to

[13] , wherein the sum of the stress at break in the TD direction and the stress at break in the MD direction, as measured in accordance with JIS K7127:1999, is 210 MPa or more.

[15] The biaxially oriented polyethylene film according to any one of [1] to

[14] , wherein the sum of the elongation at break in the TD direction and the elongation at break in the MD direction, as measured in accordance with JIS K7127:1999, is 200% or less.

[16] The biaxially oriented polyethylene film according to any one of [1] to

[15] , further comprising a surface resin layer on at least one surface of the biaxially oriented film layer.

[17] The biaxially oriented polyethylene film according to

[16] , wherein the surface resin layer contains an ethylene-based polymer.

[18] The biaxially oriented polyethylene film according to

[17] , 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.

[19] The biaxially oriented polyethylene film according to any one of

[16] to

[18] , wherein the surface resin layer has a thickness of 0.1 μm or more and 10 μm or less.

[20] The biaxially oriented polyethylene film according to any one of [1] to

[19] , wherein the biaxially oriented film layer has a thickness of 5 μm or more and 100 μm or less. [twenty one] The biaxially oriented polyethylene film according to any one of [1] to

[20] , 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. [twenty two] The biaxially oriented polyethylene film according to any one of [1] to

[21] , which is a packaging film. [twenty three] A packaging material comprising the biaxially oriented polyethylene film according to any one of [1] to

[22] . [twenty four] The packaging material described in

[23] , 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. [twenty five]

[23] or

[24] , and an item within the packaging material. Effect of the Invention

[0010] According to 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. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polyethylene film according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polyethylene film according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polyethylene film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an 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 the actual dimensional ratio. Note that in this specification, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0013] <Biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 of this embodiment has a biaxially oriented film layer 101 containing an ethylene-based polymer (A), and the ethylene-based 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).

[0014] The inventors have found that the performance balance between the 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 in the biaxially oriented polyethylene film 100 to a predetermined range, as measured by gel permeation chromatography (GPC).

[0015] 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 performances such as thermal dimensional stability, film formability, 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 the film-forming property, it is preferably 0.970 g / cm 3 Less than or equal to 0.965 g / cm 3 More preferably, 0.963 g / cm 3More preferably, 0.960 g / cm 3 The following is the result.

[0016] The melt mass flow rate (MFR) of the biaxially oriented polyethylene film 100, 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 even 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 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 even more preferably 2.0 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.

[0017] The melting point of the biaxially oriented polyethylene film 100 measured by a differential scanning calorimeter (DSC) is, 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 fluidity, 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 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.

[0018] From the viewpoint of further improving the balance of performance such as thermal dimensional stability, film-forming properties, water vapor barrier properties, cost, mechanical properties, transparency, bag-forming properties, handleability, appearance, and light weight, 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 even 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 even more preferably 25 μm or less.

[0019] The physical properties of the biaxially oriented polyethylene film 100 will be described below.

[0020] The tensile modulus T in the MD direction of biaxially oriented polyethylene film 100 measured using a tensile tester at a temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min. 1 and 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. Tensile modulus T in the MD direction of biaxially oriented polyethylene film 100 1 and tensile modulus in the TD direction T 2 The sum of (T 1 +T 2 ) is equal to or greater than the above lower limit, the biaxially oriented polyethylene film 100 can have a better balance of performance such as thermal dimensional stability, film-forming properties, water vapor barrier properties, mechanical properties, transparency, bag-forming properties, and handleability, and the stiffness of the biaxially oriented polyethylene film 100 can be improved. In addition, the tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction 1and tensile modulus in the TD direction T 2 The sum of (T 1 +T 2 ) is equal to or less than the upper limit above, problems such as breakage during film formation of the biaxially oriented polyethylene film 100 are less likely to occur, continuous stretch molding of the film becomes easier, and industrial continuous productivity can be further improved. Such a tensile modulus is a substitute value for quantitatively measuring the stiffness of a 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.

[0021] In addition, the tensile modulus T of the biaxially oriented polyethylene film 100 in the MD direction 1 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, 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, and 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, 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.

[0022] The tensile modulus T of the biaxially oriented polyethylene film 100 in the TD direction 2from 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, 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, and 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, 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.

[0023] The heat shrinkage ratio X in the MD direction of 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, it 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 the biaxially oriented polyethylene film 100 is unwound in the MD direction, and bag making, coating, deposition, etc. are performed while tension is applied. That is, since tension is applied in the MD direction, if the heat resistance of the film is low, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage rate in the MD direction when heated at 100°C for 15 minutes is within the above range, it is possible to further suppress the thermal elongation in the MD direction when the biaxially oriented polyethylene film is heated.

[0024] The thermal shrinkage ratio X in the TD direction of biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes, measured in accordance with JIS C2151:2019TD100 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.

[0025] In addition, the heat shrinkage rate X of biaxially oriented polyethylene film 100 when heated at 100°C for 15 minutes is MD100 [%] and X TD100 [%] is calculated as follows: First, a test piece of 10 cm x 10 cm is cut out from a biaxially oriented polyethylene film 100, and the test piece is heat-treated at 100°C for 15 minutes. Then, the length of the test piece in the MD direction after the heat treatment is 100 [cm], and the length of the test piece in the TD direction after heat treatment is TD 100 When expressed in [cm], X MD100 [%] is 100 × (10-MD 100 ) / 10, and X TD100 [%] is 100×(10-TD 100 ) / 10.

[0026] The heat shrinkage ratio X in the MD direction of 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.

[0027] The thermal shrinkage ratio X in the TD direction of biaxially oriented polyethylene film 100 when heated 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, 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, even more preferably 5.0% or less, and may be 0.1% or more, 0.5% or more, or 1.0% or more. In addition, the heat shrinkage rate X of biaxially oriented polyethylene film 100 when heated at 120°C for 15 minutes was 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 performed in the same manner, except that the heating temperature is 120° C. Specific details are described in the Examples section.

[0028] The moisture permeability of the biaxially oriented polyethylene film 100 measured in accordance with JIS Z 0208:1976 is preferably 12.0 g / (m2) from the viewpoint of further improving the water vapor barrier property. 2 ·day) or less, more preferably 11.5g / (m 2 ·day) or less, and more preferably 11.0 g / (m 2 ·day) or less, and more preferably 10.5 g / (m 2 ·day), and more preferably 10.0 g / (m 2 ·day) or less, and more preferably 9.0 g / (m 2 ·day) or less, and more preferably 7.5 g / (m 2 ·day) or less, and more preferably 7.0 g / (m 2 ·day) or less, and more preferably 6.5g / (m 2 ·day) or less, and more preferably 6.0 g / (m 2·day) or less, and 0.01g / (m 2 ·day) or more, and may be 0.1g / (m 2 ·day) or more, and may be 0.5g / (m 2 ·day) or more, and may be 1.0 g / (m 2 ·day) or more, and may be 3.0 g / (m 2 10 days) or more.

[0029] 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, from the viewpoint of further improving mechanical strength such as toughness, 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, and may be 600 MPa or less, 500 MPa or less, or 450 MPa or less.

[0030] The breaking stress in the MD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is, from the viewpoint of further improving mechanical strength such as toughness, 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, and may be 300 MPa or less, 200 MPa or less, or 150 MPa or less.

[0031] The breaking stress in the TD direction of the biaxially oriented polyethylene film 100, measured in accordance with JIS K7127:1999, is, from the viewpoint of further improving mechanical strength such as toughness, 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, and may be 500 MPa or less, 400 MPa or less, 350 MPa or less, or 330 MPa or less.

[0032] 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 performance balance between 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.

[0033] 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.

[0034] 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.

[0035] Each layer constituting the biaxially oriented polyethylene film 100 will now be described.

[0036] [Biaxially oriented film layer] The biaxially oriented film layer 101 contains an ethylene-based polymer. The biaxially stretched film layer 101 is formed by biaxially stretching a film made of an ethylene-based polymer composition containing an ethylene-based polymer (A).

[0037] (Ethylene-based polymer (A)) In the ethylene polymer (A) of the present embodiment, the z-average molecular weight (Mz) in terms of polystyrene as measured by gel permeation chromatography (GPC) is 800,000 or more, preferably 850,000 or more, more preferably 900,000 or more, even more preferably 950,000 or more, even more preferably 1,000,000 or more, even 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, even more preferably 2,500,000 or less, even more preferably 2,000,000 or less, even more preferably 1,500,000 or less, and even more preferably 1,300,000 or less, from the viewpoint of improving the performance balance of film-forming property and thermal dimensional stability.

[0038] The weight average molecular weight (Mw) of the ethylene polymer (A) in terms of polystyrene as measured by gel permeation chromatography (GPC) is 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 even 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 even more preferably 200,000 or less, from the viewpoint of further improving the performance balance of film-forming ability and thermal dimensional stability.

[0039] The number average molecular weight (Mn) of the ethylene polymer, measured by gel permeation chromatography (GPC) in terms of polystyrene, 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, 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, even more preferably 28,000 or less, from the viewpoint of further improving the performance balance of film-forming property and thermal dimensional stability and setting the polymerization degree of the ethylene polymer (A) in a more appropriate range.

[0040] The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the ethylene polymer (A) in terms of polystyrene, measured by gel permeation chromatography (GPC), is, from the viewpoint of further improving the thermal dimensional stability, 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, and even more preferably 7.0 or more.

[0041] The polystyrene-equivalent z+1 average molecular weight (Mz+1) of the ethylene polymer (A) measured by gel permeation chromatography (GPC) is 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 the film-forming property, and 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, from the viewpoint of further improving the thermal dimensional stability.

[0042] 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 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 a mixture obtained by melt blending two or more types of polymers by a known method. 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 measured by the method described in the Examples.

[0043] 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 taken as 100 mass%, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film formability, heat resistance, mechanical properties, rigidity, transparency, etc., is preferably 80 mass% or more, more preferably 85 mass% or more, even more preferably 90 mass% or more, even more preferably 95 mass% or more, even more preferably 97 mass% or more, and even more preferably 99 mass% or more, and from the viewpoint of further improving the performance balance of processability and continuous productivity, it is preferably 100 mass% or less.

[0044] The ethylene polymer (A) of the present embodiment preferably contains one or more selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE), and from the viewpoint of achieving a better balance of various properties such as thermal dimensional stability, film-formability, heat resistance, water vapor barrier property, mechanical properties, rigidity, etc., it more preferably contains one or more selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE), and further preferably contains high-density polyethylene (HDPE). Here, low density polyethylene (LDPE) is 0.910 g / cm 3 More than 0.930g / cm 3 Medium density polyethylene (MDPE) refers to polyethylene having a density less than 0.930 g / cm 3 More than 0.942g / cm 3 High density polyethylene (HDPE) refers to polyethylene having a density less than 0.942 g / cm 3 It refers to polyethylene having a density of 100 or more. In addition, low-density polyethylene with little branching structure is called linear low-density polyethylene (LLDPE).

[0045] 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 taken as 100% by mass, from the viewpoint of achieving a better balance of various performances such as thermal dimensional stability, film formability, heat resistance, mechanical properties, and rigidity, 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, and 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.

[0046] High density polyethylene has a problem 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 a predetermined range, it is possible to improve the film formability and thermal dimensional stability.

[0047] 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 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 the film-forming property, it is preferably 0.970 g / cm 3 Less than or equal to 0.965 g / cm 3 More preferably, 0.963 g / cm 3 More preferably, 0.960 g / cm 3 The following is the result. 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.

[0048] 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, even more preferably 0.5 g / 10 min or more, and even 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 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 even more preferably 2.0 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. 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 adopted.

[0049] From the viewpoint of further improving the balance of performance such as film-formability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-formability, and flowability, the melting point of the ethylene polymer (A) 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, 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 maximum endothermic peak.

[0050] In addition to the polyethylene described above, the ethylene-based polymer (A) of the present embodiment may further contain 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 performance balance of thermal dimensional stability, film-forming property, 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.

[0051] 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 balance of performance among 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 Less than or equal to 0.910 g / cm 3 or less, more preferably 0.900 g / cm 3 The following is the result.

[0052] 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 even 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.

[0053] The melting point of the ethylene-α-olefin copolymer measured by differential scanning calorimetry (DSC) is, from the viewpoint of further improving the balance of performance such as film-formability, thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag-formability, and fluidity, preferably 40° C. or higher, more preferably 50° C. or higher, even more preferably 60° C. or higher, and even more preferably 70° C. or higher, 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 even more preferably 80° C. or lower.

[0054] The content of ethylene-α-olefin copolymer in the biaxially oriented film layer 101, when the entire biaxially oriented film layer is taken as 100% by mass, 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.

[0055] (Other Ingredients) If necessary, various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers 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 this embodiment.

[0056] (Method for preparing ethylene polymer composition) The ethylene 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.

[0057] 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.

[0058] From the viewpoint of further improving the balance of performance 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 light weight, 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 even 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 even more preferably 25 μm or less.

[0059] 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 preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0060] [Surface resin layer] It is preferable that the biaxially oriented polyethylene film 100 further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101 in order to impart functions such as heat resistance, heat sealability, 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 stretched film layer 101. By providing the surface resin layer 103 on both sides of the biaxially stretched 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, it is preferable that the surface resin layer 103 on one side has heat sealability. The biaxially oriented polyethylene film 100 can be folded with this side facing inward and the ends heat sealed to form a bag. It is preferable that the surface resin layer 103 on the other side has blocking resistance, antistatic properties, printability, etc. In addition, the surface resin layer 103 is preferably provided on the outermost layer of the biaxially oriented polyethylene film 100 in order to further improve the functions of the biaxially oriented polyethylene film 100, such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, slip properties, etc., depending on the purpose.

[0061] 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 makes it possible to simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0062] 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, such as 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. 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 stretched film layer 101. That is, in this embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above-mentioned 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.

[0063] In the biaxially oriented polyethylene film 100, the surface resin layer 103 is preferably a single layer. This makes it possible to further simplify the manufacturing process of the biaxially oriented polyethylene film 100.

[0064] 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 coextrusion molding, i.e., by using a laminated film produced in a single molding operation, thereby further simplifying the manufacturing process of the biaxially stretched polyethylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0065] The surface resin layer 103 may be subjected to a surface treatment from the viewpoint of further improving the balance of printability and blocking resistance of the biaxially oriented polyethylene film 100. Specifically, a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coat treatment, or ozone treatment may be performed.

[0066] The surface resin layer 103 is made of, for example, a polyolefin-based resin composition containing polyolefin. The polyolefin constituting the surface resin layer 103 includes 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, 1-octene, etc.; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, the polyolefin constituting the surface resin layer 103 is preferably an ethylene-based polymer from the viewpoint of further improving the balance of performance among film-forming property, thermal dimensional stability, heat-resistant adhesion property, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming property and flowability of the biaxially oriented polyethylene film 100. Here, the preferred embodiment of the ethylene-based polymer constituting the surface resin layer 103 is the same as the above-mentioned ethylene-based polymer. 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 layer 103 is provided on both sides of the biaxially stretched film, the polyolefin resin composition constituting each surface resin layer 103 may be the same or different.

[0067] 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, from the viewpoint of further improving the performance balance of the biaxially oriented polyethylene film 100, such as film-forming ability, thermal dimensional stability, heat resistance, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-forming ability, and fluidity.

[0068] From the viewpoint of further improving the balance of performance such as film-forming ability, thermal dimensional stability, heat resistance, heat fusion resistance, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag-formability and fluidity 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.

[0069] (Other Ingredients) If necessary, various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, inorganic or organic fillers, etc. may be added to the polyolefin resin composition constituting the surface resin layer 103, within the scope that does not impair the purpose of this embodiment.

[0070] (Method for preparing polyolefin-based resin composition) The polyolefin resin 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.

[0071] <Method of manufacturing biaxially oriented polyethylene film> The biaxially oriented polyethylene film 100 can be obtained, for example, by co-extrusion molding an ethylene-based polymer composition for forming the biaxially oriented film layer 101 into a film, and then biaxially stretching the film obtained by the co-extrusion molding using a known biaxially oriented film production method such as a simultaneous biaxial stretching method, a sequential biaxial stretching method, or an inflation biaxial stretching method. The molding device and molding conditions are not particularly limited, and conventionally known molding devices and molding conditions can be adopted. As the molding device, a T-die extruder, a multi-layer T-die extruder, an inflation molding machine, a multi-layer inflation molding machine, or the like can be used. As the biaxial stretching conditions, for example, known polyethylene film manufacturing conditions can be adopted. For example, in the sequential biaxial stretching method, the stretching temperature in the MD direction may be 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 may be preferably in the range of 110°C to 190°C, more preferably 120°C to 170°C. In addition, the stretching ratio in the MD direction may be in the range of 4.5 to 7 times, and the stretching ratio in the TD direction may be in the range of 9 to 11 times. Here, the stretching temperature must be set at three stages, specifically, the preheating temperature (temperature at which the raw film before stretching is heated), the stretching temperature (temperature during stretching), and the heat setting temperature (temperature during heat setting (annealing) after stretching), and the temperature can be set within the above range from preheating to heat setting. That is, the temperature can be set to about the same as that for stretching and heat setting from the preheating stage. Since the biaxially stretched polyethylene film 100 of this embodiment contains an ethylene polymer (A), it can be processed at a higher temperature, and the heat resistance of the obtained biaxially stretched polyethylene film 100 can be further improved, and thus the thermal dimensional stability can be further improved. 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 these together and molding them under heat.

[0072] <Applications of biaxially oriented polyethylene film / packaging materials / packaging bodies> Specifically, the biaxially oriented polyethylene film 100 of the present embodiment can be suitably used as a packaging film. Moreover, the biaxially oriented polyethylene film 100 of the present embodiment can be suitably used as a packaging material. When used as a packaging material, the stretched polyethylene film 100 of this embodiment may be used alone, or may be laminated with other layers to form a packaging material. The other layers preferably further include one or more selected from the group consisting of an inorganic layer, a base layer, a coating layer, an adhesive layer, and a heat seal layer, and more preferably further include one or more selected from the group consisting of an inorganic layer and a coating layer. From the viewpoint of ease of recycling, when these layers are laminated, they are preferably formed of a polyethylene-based resin. The packaging material of the present embodiment can be suitably used as a package. The package is used, for example, for packaging an item, and specifically includes the packaging material of the present embodiment and an item inside the packaging material. In particular, the packaging material of the present embodiment can be suitably used as a food package, and is used for packaging food, and specifically includes the packaging material of the present embodiment and food inside the packaging material. There is no limitation on the food to be packaged in the food package, but examples include baked goods, rice confectioneries, snacks, sprinkles, grain powders, and the like. Depending on the application, only a portion of the package may be made of the packaging material of this embodiment, or substantially the entire package may be made of the packaging material of this embodiment.

[0073] There is no particular limitation on the method for producing a package from the biaxially oriented polyethylene film 100 or the packaging material, and any method known in the field of packaging materials / packages, such as heat sealing or melt cutting, can be used as appropriate.

[0074] The biaxially oriented polyethylene film 100 according to this 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).

[0075] Furthermore, when a package (such as a food packaging bag) is made using the biaxially oriented polyethylene film 100 of this embodiment or a packaging material, it is preferable that the corona-treated surface is the inner surface and the non-corona-treated surface is the outer surface. As described above, when another layer is laminated on the biaxially oriented polyethylene film 100, it is preferable to laminate it on the corona-treated surface side. That is, when a laminate using the biaxially oriented polyethylene film 100 of this embodiment is used for a package (such as a food packaging bag), it is preferable that the biaxially oriented polyethylene film 100 of this embodiment side is the outermost layer of the package.

[0076] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of the present invention are included in the present invention. EXAMPLES

[0077] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0078] <Raw materials> The raw materials used in the examples and comparative examples are shown 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 temperature increase rate of 10°C / min and a process of decreasing the temperature from 230°C to -50°C at a temperature decrease rate of 10°C / min under a nitrogen gas flow, and a second differential scanning calorimeter measurement consisting of a process of increasing the temperature from -50°C to 230°C at a temperature increase rate of 10°C / min were successively performed. The peak temperature of the maximum endothermic peak in the second DSC curve was taken as the melting point (°C).

[0079] Linear low density polyethylene 1 (LLDPE1), density: 0.928g / cm 3 , MFR: 1.9g / 10min, Melting point: 126℃ Linear low density polyethylene 2 (LLDPE2), density: 0.937g / cm 3 , MFR: 1.8g / 10min, Melting point: 127℃ Linear low density polyethylene 3 (LLDPE3), density: 0.903g / cm 3 , MFR: 3.8g / 10min, Melting point: 98℃ High density polyethylene 1 (HDPE1), density: 0.964g / cm 3 , MFR: 5.2g / 10min, Melting point: 135℃ High density polyethylene 2 (HDPE2), density: 0.958g / cm 3 , MFR: 1.0g / 10min, Melting point: 133℃ High density polyethylene 3 (HDPE3), density: 0.955g / cm 3 , MFR: 0.36g / 10min, Melting point: 130℃ Ethylene-1-butene random copolymer 1 (EBR1), density: 0.893 g / cm 3 , MFR: 3.6g / 10min, Melting point: 77℃

[0080] <Production of biaxially oriented polyethylene film> For Examples 1 to 8 and Comparative Examples 1 to 4, polyethylene films were extruded with the compositions shown in Table 1, and then biaxially stretched to produce biaxially stretched polyethylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. In addition, the surface on the side of the surface resin layer 2 in Table 1 was subjected to a corona treatment. Extrusion molding machine: 60mmφ multi-layer T-die extrusion molding machine (screw: L / D=27, manufactured by Screw Seiki Co., Ltd.) Extrusion temperature setting: 230-250℃, Processing speed: 15m / min (winding speed) Stretching temperature in MD direction [℃]: See Table 1 Stretching ratio in MD direction [times]: See Table 1 Stretching temperature in TD direction [℃]: See Table 1 Stretching ratio in TD direction [times]: See Table 1 Relaxation rate [%]: See Table 1 The relaxation rate herein means the maximum stretching width in the device settings divided by the tenter outlet width. In addition, the notation "A / B / C" of the stretching temperature in Table 1 means "preheating temperature (temperature for heating the original film before stretching) / stretching temperature (temperature during stretching) / heat setting temperature (temperature during heat setting (annealing) after stretching)." In addition, the notation "A / B / C / D" of the stretching temperature in Table 1 means "preheating temperature (temperature for heating the original film 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, the density of the resin before being made into a film was measured in each example. The following evaluations were also performed. The results are shown in Table 1. In Comparative Example 4, the film was broken during stretching, and therefore a biaxially stretched polyethylene film could not be obtained.

[0081] [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 constituting the biaxially oriented polyethylene film] 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 constituting the biaxially oriented polyethylene film were measured by gel permeation chromatography (GPC). The biaxially oriented polyethylene film obtained in each example was cut to approximately 5.0 mm x 5.0 mm, added to the mobile phase for GPC measurement, heated at 145°C, stirred and dissolved, and the volume was adjusted to the following concentration to prepare a sample. The GPC method was performed using a gel permeation chromatograph (Tosoh Corporation, HLC-8321 GPC / HT type) as follows. The separation columns were two TSKgel GNH6-HT and two TSKgel GNH6-HTL, each with a diameter of 7.5 mm and a length of 300 mm, the column temperature was 140°C, the mobile phase was o-dichlorobenzene and 0.025 mass% BHT as an antioxidant, and the flow rate was 1.0 mL / min, the sample concentration was 0.1% (w / v), the sample injection amount 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.

[0082] <Tensile modulus> A test piece of 15 mm x 15 cm was cut out from each biaxially stretched polyethylene film. Then, the tensile modulus T in the MD direction of the test piece 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 tensile 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.

[0083] <Moisture permeability> The moisture permeability (g / (m 2 ·day) was measured in accordance with JIS Z 0208:1976.

[0084] <Stress at break and elongation at break> The stress at break (MPa) and elongation at break (%) in the MD and TD directions of each biaxially oriented polyethylene film were measured using a tensile tester in accordance with JIS K7127:1999. The biaxially oriented polyethylene film of each example was cut into a dumbbell shape in accordance with the above JIS standard to prepare a test piece, and the test piece was pulled in the MD and TD directions under the conditions of 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 the designated gauge points in the tensile test. The stress at break is the value obtained by dividing the tensile force at the break point at the time of break in the tensile test by the initial cross-sectional area of ​​the test piece. From the obtained values, the total stress at break in the MD and TD directions and the total elongation at break in the MD and TD directions were calculated.

[0085] <Heat shrinkage rate of biaxially oriented polyethylene film at 100℃> The heat shrinkage in the MD and TD directions of the biaxially oriented polyethylene film at 100°C was measured in accordance with JIS C2151:2019. A test piece measuring 10 cm x 10 cm 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 while hanging without applying force in a hot air circulation type thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE). The test piece was then cooled to room temperature, and the length of the test piece was measured. The length of the test piece in the MD direction after heat treatment was measured as the MD 100 [cm], and the thermal shrinkage rate in the MD direction X MD100 [%] = 100 × (10-MD 100 The length of the test piece in the TD direction after heat treatment was calculated as TD 100 [cm], and the thermal shrinkage rate in the TD direction X TD100 [%] = 100 × (10-TD 100The above measurements were each carried out three times, and the average of the measured values ​​was used as the heat shrinkage rate of the biaxially oriented polyethylene film at 100°C.

[0086] <Heat shrinkage rate of biaxially oriented polyethylene film at 120℃> The heat shrinkage ratios in the MD and TD directions of the biaxially oriented polyethylene films at 120°C were measured in accordance with JIS C2151:2019. A test piece measuring 10 cm x 10 cm 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 while hanging without applying force in a hot air circulation type thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE). The test piece was then cooled to room temperature, and the length of the test piece was measured. The length of the test piece in the MD direction after heat treatment was measured as the MD 120 [cm], and the thermal shrinkage rate in the MD direction X MD120 [%] = 100 × (10-MD 120 The length of the test piece in the TD direction after heat treatment was calculated as TD 120 [cm], and the thermal shrinkage rate in the TD direction X TD120 [%] = 100 × (10-TD 120 The above measurements were each carried out three times, and the average of the measured values ​​was used as the heat shrinkage rate of the biaxially oriented polyethylene film at 120°C.

[0087] <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. (standard) A (best): The film did not break. B (Good): The film was cut once. C (poor): The film was cut two or more times.

[0088] [Table 1] [Explanation of symbols]

[0089] 100 Biaxially oriented polyethylene film 101 Biaxially oriented film layer 103 Surface resin layer

Claims

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

2. 2. The biaxially oriented polyethylene film according to claim 1, 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.

3. 3. The biaxially oriented polyethylene film according to claim 1, 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).

4. The biaxially stretched polyethylene film according to any one of claims 1 to 3, wherein the ethylene polymer (A) has a ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) in terms of polystyrene, as measured by gel permeation chromatography (GPC), of 30.0 or less.

5. 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 1 to 4, wherein:

6. The biaxially stretched polyethylene film according to any one of claims 1 to 5, 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 under conditions of 190°C and a load of 2160 g.

7. The ethylene polymer (A) contains high-density polyethylene, The biaxially oriented polyethylene film according to any one of claims 1 to 6, 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.

8. 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 7, wherein the total value of is 2500 MPa or more and 9000 MPa or less.

9. The biaxially oriented polyethylene film according to any one of claims 1 to 8, having 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.

10. The biaxially oriented polyethylene film according to any one of claims 1 to 9, having a heat 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.

11. The biaxially oriented polyethylene film according to any one of claims 1 to 10, 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.

12. The biaxially stretched polyethylene film according to any one of claims 1 to 11, 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.

13. 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 12, wherein the stretching time is 100 min-100 min.

14. The biaxially oriented polyethylene film according to any one of claims 1 to 13, 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.

15. The biaxially oriented polyethylene film according to any one of claims 1 to 14, 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.

16. The biaxially oriented polyethylene film according to any one of claims 1 to 15, further comprising a surface resin layer on at least one surface of the biaxially oriented film layer.

17. The biaxially oriented polyethylene film according to claim 16, wherein the surface resin layer comprises an ethylene-based polymer.

18. 18. The biaxially oriented polyethylene film according to claim 17, 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.

19. The biaxially oriented polyethylene film according to any one of claims 16 to 18, wherein the thickness of the surface resin layer is 0.1 µm or more and 10 µm or less.

20. The biaxially oriented polyethylene film according to any one of claims 1 to 19, wherein the biaxially oriented film layer has a thickness of 5 µm or more and 100 µm or less.

21. The biaxially oriented polyethylene film according to any one of claims 1 to 20, 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.

22. The biaxially oriented polyethylene film according to any one of claims 1 to 21, which is a packaging film.

23. A packaging material comprising the biaxially oriented polyethylene film according to any one of claims 1 to 22.

24. The packaging material according to claim 23, 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.

25. A packaging material according to claim 23 or 24, and an item within the packaging material.

Images